Role of oxidative stress in sepsis: Mechanisms, pathways, and therapeutic strategies

Abstract

Sepsis, a life-threatening condition caused by dysregulated host response to infection, leads to high morbidity and mortality, primarily due to sepsis-induced organ dysfunction. Oxidative stress, driven by excessive reactive oxygen species (ROS), plays a central role in sepsis pathophysiology, exacerbating inflammation, mitochondrial dysfunction, and cellular damage in multiple organs, including the heart, kidneys, liver, lungs, brain, and skeletal muscles. This review provides a comprehensive analysis of mechanisms by which oxidative stress contributes to sepsis-induced organ injury. Most current research examining the interplay between ROS, inflammation, mitochondrial dysfunction, and cell death pathways such as apoptosis, ferroptosis, and pyroptosis, are animal- or cell-based. Key signaling pathways, including nuclear factor κB (NF-κB), NLR family pyrin domain-containing 3 inflammasome (NLRP3), nuclear factor erythroid 2-related factor 2 (Nrf-2)/heme oxygenase-1 (HO-1), and phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt), are explored as potential therapeutic targets. This review also highlights the roles of mitochondrial quality control (MQC), autophagy, and noncoding RNAs in mitigating oxidative damage.

Graphical abstract

Highlights

• •Sepsis is a life-threatening condition characterized by dysregulated host responses to infection.
• •Oxidative stress plays a central role in sepsis pathophysiology
• •Mechanisms underlying sepsis-induced organ injury are comprehensively analyzed.
• •Targeting oxidative stress and enhancing antioxidant defenses may help prevent organ damage.

1. Introduction

Sepsis is a life-threatening organ dysfunction caused by a dysregulated host response to infection [1]. According to the Surviving Sepsis Campaign: International Guidelines for Management of Sepsis and Septic Shock 2021, the current management recommendations for sepsis consist mainly of screening, treatment, immediate resuscitation, immediate administration of antimicrobials, hemodynamic management, ventilation, additional therapies, long-term outcomes, and goals of care [2]. Despite the availability of guidelines for treating sepsis, mortality rates remain high. In 2017, approximately 48.9 million cases of sepsis were recorded globally, with 11 million deaths due to sepsis, accounting for 19.7% of global deaths [3]. Among its most severe complications, sepsis-induced organ dysfunction is a key contributor to the high morbidity and mortality associated with sepsis. Understanding the pathogenesis of sepsis-induced organ dysfunction at the molecular level is critical for developing targeted therapies to improve patient survival and prognosis.

Oxidative stress plays a central role in sepsis pathophysiology. Oxidative metabolites, including superoxide anion radicals, hydrogen peroxide, hydroxyl radicals, singlet oxygen, nitric oxide (NO) radicals, and peroxynitrite (ONOO⁻), contribute to cellular damage. Although reactive oxygen species (ROS) are commonly used as a broad term for oxidative stress products, this classification is not entirely precise [4]. In sepsis, excessive ROS exacerbates inflammation, disrupts mitochondrial function, induces programmed cell death, and inhibits autophagy, leading to disturbances in intracellular homeostasis and subsequent organ dysfunction. Sepsis-induced organ failure, including myocardial depression, acute kidney injury (AKI), acute liver injury, encephalopathy, and acute respiratory distress syndrome (ARDS), result from the complex interplay between oxidative stress, immunosuppression, and inflammation, all of which contribute to mitochondrial dysfunction and cellular damage [5].

Although numerous studies have explored the role of ROS in diseases, such as cancer and aging, mounting evidence indicates that ROS also play a crucial role in sepsis progression. However, most existing reviews have focused on oxidative stress in single-organ dysfunction and lack a comprehensive analysis of its systemic impact. This review provides an integrated perspective on the role of oxidative stress in sepsis-induced organ dysfunction with ROS as the central focus. However, most current studies, including those reviewed in this article, are based on animal or cell models, with limited clinical research available. Furthermore, some cited studies employ lipopolysaccharide (LPS)-induced endotoxemia as a surrogate model for sepsis. Although LPS challenge reproduces certain inflammatory and pathophysiological features observed in sepsis, it does not fully recapitulate the complex syndrome induced by infection as defined by the Third International Consensus Definitions for Sepsis and Septic Shock (Sepsis-3) [1]. Therefore, in our descriptions of these studies, we refer to them as LPS-induced endotoxemia models rather than sepsis models to avoid misinterpretation of the two conditions. By offering a comprehensive overview, we aimed to enhance an understanding of oxidative stress in sepsis and explore potential therapeutic strategies for mitigating organ dysfunction and improving patient outcomes.

2. Mechanisms of oxidative stress in sepsis

Oxidative stress is a core mechanism underlying the pathophysiology of sepsis (Fig. 1). In patients with sepsis, excessive ROS production directly damages cells and tissues and significantly affects the onset and progression of sepsis through the modulation of inflammation, ferroptosis, pyroptosis, autophagy, and mitochondrial function.

Fig. 1.

Mechanisms of oxidative stress in sepsis. Oxidative stress, the central driver of sepsis-induced organ injury, amplifies the inflammatory response and exacerbates mitochondrial dysfunction, triggering cell death (pyroptosis and ferroptosis). Collectively, these interconnected mechanisms exacerbate organ damage and increase mortality in patients with sepsis. Conversely, the activation of antioxidant pathways (e.g., nuclear factor erythroid 2-related factor 2 (Nrf-2)/heme oxygenase 1 (HO-1) axis), autophagy, and mitophagy confer cytoprotective effects, and sirtuins (SIRTs) have emerged as critical regulators of oxidative stress dynamics during sepsis progression. AMPK: adenosine monophosphate (AMP)-activated protein kinase; PI3K: phosphoinositide 3-kinase; Akt: protein kinase B; PINK1: PTEN-induced putative kinase 1; ROS: reactive oxygen species; NLRP3: NLR family pyrin domain-containing 3; MAPK: mitogen-activated protein kinase; NF-κB: nuclear factor κB; GPX4: glutathione peroxidase 4.

2.1. Oxidative stress and inflammation in sepsis

Oxidative stress regulates inflammation through multiple signaling pathways, with nuclear factor κB (NF-κB) playing a central role. The activation of NF-κB promotes the secretion of pro-inflammatory cytokines and enhances immune cell activation and infiltration, thus exacerbating the systemic inflammatory response. Oxidative stress activates the NF-κB pathway, promoting M1 macrophage polarization and exacerbating sepsis-induced inflammation. In septic mice, overexpression of MALT1 enhances NF-κB activation, shifts T cell balance (decreasing type 1 T helper (Th1)/Th2 and increasing Th17/regulatory T (Treg) ratios), and elevates pro-inflammatory cytokines such as tumor necrosis factor α (TNF-α) and interleukin-1β (IL-1β), thereby intensifying oxidative stress [6]. Moreover, several studies have shown that NF-κB activation is accompanied by the activation of the mitogen-activated protein kinase (MAPK) pathway, where the phosphorylation of MAPK further aggravates inflammation and oxidative stress caused by sepsis [7].

In sepsis, the ROS-induced increase in oxidative stress promotes activation of the NLR family pyrin domain-containing 3 (NLRP3) inflammasome, which in turn activates caspase-1/gasdermin D (GSDMD), leading to pyroptosis. Activated caspase-1 further cleaves pro-inflammatory cytokines such as IL-1β and IL-18 into their active forms, amplifying the inflammatory response and resulting in widespread organ damage [8]. Thioredoxin-interacting protein (TXNIP) functions as a critical upstream activator of the NLRP3 inflammasome, aggravating oxidative stress, neuroinflammation, and pyroptosis via the TXNIP/NLRP3/caspase-1/GSDMD pathway [9]. ROS play a key role in this process by acting as a crucial bridge between inflammation and cell death. Therefore, inhibition of ROS-driven NLRP3 inflammasome activation is an important therapeutic target for the treatment of sepsis-related organ injury.

2.2. Major antioxidant pathways in sepsis

Under oxidative stress, several antioxidant pathways are activated, including the nuclear factor erythroid 2-related factor 2 (Nrf-2)/heme oxygenase-1 (HO-1), adenosine monophosphate (AMP)-activated protein kinase (AMPK), and phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt) pathways, which promote the expression of downstream antioxidant factors and mitigate organ oxidative damage caused by sepsis.

Under normal conditions, Nrf-2 is rapidly degraded because of its binding to Kelch-like ECH-associated protein 1 (KEAP1) and the E3 ubiquitin ligase CUL3. However, during sepsis, high ROS levels disrupt this interaction, leading to Nrf-2 dissociation from KEAP1 and its subsequent nuclear translocation. This enhances the expression of antioxidant enzymes [10]. Numerous pharmacological studies have demonstrated that the dual effect of inhibiting the NF-κB pathway and activating the Nrf-2 pathway is central to the mechanisms of the treatment of endotoxemia [11]. Additionally, malvidin mitigates LPS-induced endotoxemia by regulating the Nrf-2/NLRP3 pathway [12]. The AMPK pathway also plays an important role in anti-inflammatory and antioxidant responses. AMPK can promote Nrf-2 activation for antioxidant effects while simultaneously inhibiting NF-κB activation to exert dual protective effects [13]. In addition, the PI3K/Akt pathway has received increasing attention in sepsis as research suggests that it plays a key role in inhibiting oxidative damage, improving cellular inflammation, and preventing cell death. Activation of Akt promotes Nrf-2 nuclear translocation by phosphorylating and inactivating glycogen synthase kinase 3 β (GSK3β), thereby relieving its inhibitory effect on Nrf-2. This suppresses ferroptosis, driven by inflammation and oxidative stress [14]. Other antioxidant pathways are activated in different organ injuries and are described in detail in the following review.

2.3. Oxidative stress exacerbates ferroptosis in sepsis

Ferroptosis is an iron-dependent, ROS-driven programmed cell death pathway. During sepsis, accumulation of iron and ROS promotes ferroptosis. A core feature of ferroptosis is accumulation of lipid peroxides. Owing to their high susceptibility to ROS attack, polyunsaturated fatty acids (PUFAs) in cell membranes undergo peroxidation to form lipid peroxides. The accumulation of lipid peroxides directly damages cell membranes, and generates more ROS, creating a positive feedback loop that exacerbates oxidative stress [15]. Glutathione peroxidase 4 (GPX4) is a crucial cellular antioxidant enzyme that reduces lipid peroxides to non-toxic lipid alcohols, thereby inhibiting lipid peroxidation. Although the exact mechanism by which lipid peroxidation induces ferroptosis remains unclear, evidence suggests that the activation of the Nrf-2 pathway restores GPX4 expression, inhibits ferroptosis, and protects against LPS-induced organ damage [16]. Further research has proved that the activation of Sestrin2 can suppress ferroptosis of dendritic cells in sepsis by downregulating the activating transcription factor (ATF4)-C/EBP homologous protein (CHOP)-cation transport regulator homolog 1 (CHAC1) signaling pathway [17].

2.4. Mitochondrial dysfunction and mitochondrial quality control (MQC) regulate oxidative stress in sepsis

Mitochondria are a major source of oxidative stress and are severely impaired during sepsis, resulting in metabolic dysfunction and cell death. MQC is maintained by mechanisms such as fission, fusion, biogenesis, unfolded protein response (UPR), and mitophagy to preserve mitochondrial homeostasis [18]. For example, calcium/calmodulin-dependent protein kinase IV (CaMKIV) activates dynamin-related protein 1 (Drp1) while inhibiting Mfn1 and OPA1 expression, promoting mitochondrial fission. It also upregulates autophagy-related proteins such as PTEN-induced kinase 1 (PINK1) and parkin (PRKN), thereby restoring mitochondrial function and reducing renal oxidative stress in septic mice [19]. Moreover, melatonin enhances mitochondrial biogenesis (peroxisome proliferator-activated receptor (PPAR) gamma coactivator 1α (PGC-1α), mitochondrial transcription factor A (TFAM), and Nrf1, mitophagy (PINK1, PRKN, and microtubule-associated protein 1 light chain 3-II (LC3-II)), and fission-fusion dynamics across multiple organs [[20], [21], [22]]. These studies provide new directions for the development of antioxidant therapies against sepsis.

2.5. Autophagy and mitophagy in sepsis-induced oxidative damage

Autophagy is a cellular self-digestion process characterized by the expression of autophagy-associated markers such as LC3 and activation of mammalian target of rapamycin (mTOR) [23]. In the early stages of sepsis, moderating autophagy helps mitigate inflammation by inhibiting NLRP3 inflammasome activation and reducing the release of pro-inflammatory cytokines such as IL-1β and TNF-α, thereby alleviating excessive systemic inflammation [24]. However, in the later stages of sepsis, excessive autophagy can lead to autophagic cell death, exacerbating immune suppression and contributing to multi-organ failure [25].

Mitophagy, a specialized form of autophagy, selectively removes damaged or dysfunctional mitochondria to maintain the cellular energy balance and prevent oxidative damage. Dysfunctional mitochondria fail to generate ATP efficiently and release excessive ROS, which exacerbates oxidative stress and cellular injury. Mitophagy plays a crucial role in limiting ROS accumulation and mitigating oxidative stress, by eliminating damaged mitochondria [26].

2.6. Role of non-coding RNAs (ncRNA) in regulating oxidative stress in sepsis

The role of ncRNAs, such as microRNAs (miRNAs), long ncRNA (lncRNAs), and circular RNAs (circRNAs), in regulating oxidative stress in sepsis has been increasingly recognized. These ncRNAs modulate multiple signaling pathways, including those involved in inflammation, cell apoptosis, and oxidative stress responses. Table S1 summarizes the ncRNAs associated with regulating oxidative stress and their roles in sepsis.

3. Sepsis-induced myocardial dysfunction (SIMD) and oxidative stress

SIMD, a key complication of sepsis, is characterized by impaired myocardial contractility, diastolic dysfunction, and overall cardiac dysfunction (Fig. 2). The prevalence of sepsis-induced cardiomyopathy in patients with sepsis ranges from 10% to 70% [27]. Numerous studies have demonstrated a significant increase in oxidative stress levels in myocardial cells during LPS-induced myocardial dysfunction [28]. Given the role of oxidative stress in SIMD pathophysiology, targeted modulation of oxidative stress, inflammation, and mitochondrial dysfunction is critical for reducing mortality and improving patient outcomes.

Fig. 2.

Role of oxidative stress in sepsis-induced myocardial dysfunction (SIMD). Sepsis induces excessive reactive oxygen species (ROS) production, activation of the NOD-like receptor family pyrin domain-containing 3 (NLRP3) inflammasome, and release of pro-inflammatory cytokines. Peroxynitrite (ONOO⁻) formation and lipid peroxidation lead to oxidative stress, ferroptosis, and mitochondrial injury. Mitochondrial quality control (MQC), including biogenesis, mitophagy, and the mitochondrial unfolded protein response (UPR), helps maintain mitochondrial homeostasis. Protective pathways involving sirtuin 1 (SIRT1), SIRT3, dual-specificity phosphatase 1 (DUSP1), thioredoxin 1 (Trx-1), and acetaldehyde dehydrogenase 2 (ALDH2) mitigate myocardial damage. PINK1: PTEN-induced kinase 1; Pgam5: phosphoglycerate mutase 5; PARP1: poly(adenosine diphosphate (ADP)-ribose) polymerase 1; Nrf-2: nuclear factor erythroid 2-related factor 2; HO-1: heme oxygenase-1; GAS6: growth arrest-specific 6; LXRα: liver X receptor α; AXL: AXL receptor tyrosine kinase; BMAL1: brain and muscle ARNT-like protein 1.

3.1. NLRP3 inflammasome and Nrf-2 antagonize each other to co-regulate SIMD

In sepsis, ROS accumulation activates the NLRP3 inflammasome, which promotes the release of pro-inflammatory cytokines such as IL-1β, IL-18, and high-mobility group box 1 (HMGB1). These cytokines, in turn, exacerbate oxidative stress and establish a vicious cycle that worsens myocardial injury [29]. The inhibition of NLRP3 inflammasome activation mitigates oxidative stress, suppress pyroptosis, and improve cardiac function in SIMD. For example, overexpression of growth arrest-specific 6 (GAS6) attenuates LPS-induced inflammation, oxidative stress, mitochondrial dysfunction, and apoptosis by activating the GAS6/AXL signaling pathway, thereby inhibiting NLRP3 inflammasome activation [30]. Similarly, liver X receptor α (LXRα) activation alleviates septic myocarditis by binding to NLRP3 inflammasome and repressing its transcription [31].

To counter oxidative stress, cells activate various antioxidant pathways, among which the Nrf-2 pathway is one of the most crucial. Activation of the sigma-1 receptor (S1R) stimulates the Nrf-2/HO-1 signaling pathway, reducing mitochondrial oxidative stress, and providing cardioprotection [32].

In summary, ROS accumulation in SIMD activates the NLRP3 inflammasome, triggering pro-inflammatory cytokine release, and exacerbating oxidative stress. The inhibition of NLRP3 activation reduces inflammation and oxidative damage, thereby improving cardiac function. Antioxidant pathways, particularly Nrf-2 pathway, confer cardioprotection by alleviating mitochondrial oxidative stress.

3.2. NO-mediated mitochondrial toxicity and intervention strategies

NO is synthesized by NO synthase (NOS). At low concentrations, NO may ameliorate myocardial ischemia-reperfusion (IR) injury by inhibiting nicotinamide adenine dinucleotide (NAD) phosphate (NADPH) oxidase (NOX) activity and mitochondrial ROS production [33]. However, during sepsis, high NO levels impair mitochondrial respiratory chain function and compromise cardiac contractility. The surplus NO reacts with superoxide anions to form ONOO⁻. Inhibition of NOS, particularly NOS2, reduces oxidative damage and improves cardiac performance in endotoxemia. Agents like cyclosporine A (CsA) alleviate NO-mediated injury by stabilizing mitochondrial permeability transition pore (mPTP) and reducing protein nitration [34]. Additionally, ONOO⁻-induced overactivation of poly (adenosine diphosphate (ADP)-ribose) polymerase (PARP) leads to the depletion of NAD⁺ and adenosine triphosphate (ATP), resulting in cellular dysfunction, necrosis, or apoptosis, ultimately causing myocardial injury and impaired myocardial contractile function [35]. In vitro experiments have shown that inhibiting the PARP1/NLRP3 signaling pathway suppresses M1 polarization in macrophages, effectively improving oxidative stress and apoptosis in myocardial cells [36]. These findings highlight the crucial role of NO in regulating oxidative stress, and suggest that targeting NO synthesis may serve as a promising therapeutic approach for treating SIMD by mitigating mitochondrial dysfunction.

3.3. Lipid peroxidation mediated ferroptosis and antioxidant defense in SIMD aldehydes

Previous studies have shown that the active aldehydes produced during lipid peroxidation led to ferroptosis in cardiomyocytes [37]. Overexpression of acetaldehyde dehydrogenase 2 (ALDH2) blocks the inflammatory response driven by cyclic guanosine monophosphate-AMP (GMP-AMP) synthase (cGAS)/stimulator of the interferon gene (STING) pathway, thereby reducing LPS-induced myocardial ROS accumulation [38]. Moreover, annexin A1 short peptide (ANXA1sp) also protects against SIMD by attenuating ferroptosis through sirtuin 3 (SIRT3)-mediated p53 deacetylation [39]. Notably, prolonged exposure to artificial light can disrupt the circadian rhythm, leading to altered ROS production in cardiomyocytes [40]. Suppression of BMAL1, a core clock gene, impairs antioxidant signaling and promotes ferroptosis, highlighting the relevance of circadian regulation in maintaining cardiac mitochondrial homeostasis [41].

3.4. Mitochondrial dysfunction and protective pathways in SIMD

Mitochondrial dysfunction is a core pathological feature of SIMD and its repair relies on the dynamic balance of the MQC system.

In animal and cell models of LPS-induced endoxemia, overexpression of dual-specificity phosphatase 1 (DUSP1) enhances its interaction with valosin-containing protein (VCP), preventing LPS-induced phosphorylation of VCP at Ser784. This interaction helps maintain MQC b62y normalizing mitochondrial dynamics, improving mitophagy, enhancing biogenesis, and attenuating mitochondrial UPR [42]. Additionally, in LPS-treated cardiomyocytes, deletion of phosphoglycerate mutase 5 (Pgam5) promotes prohibitin 2 (PHB2) phosphorylation and mitochondrial localization, which contributes to mitochondrial UPR and mitophagy and thus maintains mitochondrial metabolism, prevents oxidative stress injury, and enhances cardiomyocyte viability [43].

MQC is tightly regulated by SIRT1/3. Activation of SIRT1 and SIRT3 promotes mitochondrial biogenesis, mitophagy, and energy metabolism [44,45]. Similarly, the redox protein thioredoxin 1 (Trx-1), a small multifunctional redox-active protein, enhances mitochondrial biogenesis and mitophagy and reduces oxidative stress, thereby alleviating cardiac injury in sepsis [46].

In conclusion, MQC plays crucial roles in maintaining mitochondrial function and preventing oxidative stress during myocardial injury. Additionally, the SIRT1/3 axis is critical for regulating mitochondrial biosynthesis and dynamics, highlighting the importance of mitochondrial maintenance in mitigating myocardial damage under conditions such as SIMD.

3.5. Bidirectional role of autophagy in SIMD

Autophagy is involved in the protective effects against LPS-induced myocardial dysfunction. For example, elabela, an endogenous ligand of apelin receptor (Aplnr), promotes autophagic clearance of the NLRP3 inflammasome, reducing pyroptosis [47]. In addition, mitophagy, together with the UPR, can jointly maintain mitochondrial homeostasis and alleviate myocardial inflammation [48]. However, excessive mitophagy can be harmful, i.e., ALDH2 prevents overactivation of the PINK1/PRKN pathway, thereby protecting cardiac function [49]. These findings underscore the intricate balance between autophagy regulation and myocardial injury in SIMD and offer insights into potential therapeutic strategies targeting autophagy-related pathways.

Therefore, oxidative stress plays a crucial role in SIMD development. Excessive accumulation of ROS induced by sepsis activates the NLRP3 inflammasome and promotes the release of pro-inflammatory cytokines, exacerbating myocardial injury. Additionally, ROS induces lipid peroxidation and ferroptosis, leading to mitochondrial dysfunction. NO also contributes to myocardial dysfunction, as high levels of NO damage the mitochondria and worsen cardiac function. In summary, oxidative stress affects SIMD via multiple mechanisms and provides potential therapeutic targets.

4. Sepsis-associated AKI (SA-AKI) and oxidative stress

SA-AKI is mainly caused by renal IR injury and subsequent acute tubular necrosis, a syndrome characterized by acute functional impairment and organ damage [50] (Fig. 3). Sepsis-induced systemic oxidative stress generates free radicals and ROS that contribute to kidney injury. The mechanisms underlying oxidative stress-induced kidney damage are complex and multifaceted.

Fig. 3.

Role of oxidative stress in sepsis-associated acute kidney injury (SA-AKI). This figure illustrates the key pathways and molecular mechanisms contributing to oxidative stress and kidney injury in SA-AKI. Mitochondrial dysfunction induces excessive reactive oxygen species (ROS) production, leading to the activation of the NLR family pyrin domain containing 3 (NLRP3) inflammasome, which exacerbates renal inflammation and contributes to apoptosis, pyroptosis, and ferroptosis in renal epithelial cells. Promoting autophagy may facilitate the clearance of damaged organelles and toxic metabolites, thereby alleviating cellular injury. LPS: lipopolysaccharide; TLR4: Toll-like receptor 4; SIRT3: sirtuin 3; AMPK: adenosine monophosphate (AMP)-activated protein kinase; Akt: protein kinase B; mTOR: mammalian target of rapamycin; PI3K: phosphoinositide 3-kinase; NF-κB: nuclear factor κB; PGC-1α: peroxisome proliferator-activated receptor (PPAR) gamma coactivator 1α; Nrf-2: nuclear factor erythroid 2-related factor 2; USF2: upstream stimulatory factor 2; THBS1: thrombospondin 1; TGF-β: transforming growth factor β; Smad3: SMAD family member 3; CO: carbon monoxide; HIF-1α: hypoxia-inducible factor 1α; NDUFS3: nicotinamide adenine dinucleotide, reduced form (NADH):ubiquinone oxidoreductase core subunit S3; UCP2: uncoupling protein 2; ATP: adenosine triphosphate; IR: ischemia-reperfusion.

4.1. Activation of the NLRP3 inflammasome in SA-AKI

Renal tubular epithelial cells play a critical role in oxidative stress-induced damage during sepsis. ROS activates the NLRP3 inflammasome, which leads to renal tubular epithelial cell injury. Previous studies have indicated that inhibiting the NF-κB signaling pathway can reduce NLRP3 activation, thereby alleviating oxidative stress, inflammatory response, and NLRP3-mediated pyroptosis. For example, Yang et al. [51] utilized network pharmacology combined with cellular and animal experiments to identify that Polygonum cuspidatum mitigates oxidative stress by inhibiting NF-κB, significantly reducing the expression levels of pyroptosis related proteins, including NLRP3. Moreover, exogenous carbon monoxide (CO) reduces oxidative damage by inhibiting NO-mediated NLRP3 inflammasome activation in septic rat models of SA-AKI [52]. Moreover, treatment with cichoric acid in LPS-induced mice can impede the activation of NLRP3 inflammasome by inhibiting ROS/hypoxia-inducible factor 1α (HIF-1α) pathway, while the inactivation of HIF-1α prevents macrophage M1 polarization induced by increased glycolysis, thereby protecting renal function [53]. In addition, in patients with sepsis, thrombospondin-1 (THBS1) and upstream stimulatory factor 2 (USF2) levels are elevated in the blood. Inhibiting the USF2 suppresses the transcription of THBS1, which mediates the suppression of the transforming growth factor β (TGF-β)/SMAD family member 3 (Smad3)/NLRP3 signaling pathway, reducing pyroptosis and further ameliorating sepsis-induced AKI [54].

To sum up, inhibiting NLRP3 inflammasome activation through various signaling pathways has shown potential in reducing oxidative stress, inflammation, and pyroptosis in SA-AKI. Studies on compounds such as Polygonum cuspidatum, CO, and cichoric acid have underscored their protective effects on renal function by targeting these pathways. These findings suggest that the inhibition of the NLRP3 inflammasome is a promising therapeutic strategy for SA-AKI.

4.2. Mitochondrial dysfunction in SA-AKI

Sepsis-induced oxidative stress causes mitochondrial dysfunction in renal tubular epithelial cells, leading to energy metabolism disturbances, impaired mitophagy, and reduced mitochondrial biogenesis. These dysfunctions result in excessive ROS production, exacerbating kidney inflammation and IR injury.

Overexpression of uncoupling protein 2 (UCP2) significantly alleviates mitochondrial ultrastructural damage, inhibits ROS production, and increases ATP levels and mitochondrial DNA content under septic conditions, ultimately reducing oxidative stress in sepsis [55]. Several mitochondria-targeted antioxidants have demonstrated significant renal-protective effects by preserving mitochondrial membrane potential and mitochondrial respiratory chain function [56,57]. In addition, the PGC-1α/Nrf-2 axis forms a positive feedback loop that enhances mitochondrial biogenesis. Activation of this pathway both improves mitochondrial function and inhibits NLRP3 inflammasome activation in the kidney, thereby providing protection against SA-AKI [58].

Notably, NAD⁺/NADPH is crucial for driving redox reactions and protecting kidneys from ROS-induced damage [59]. SIRTs, by coupling NAD⁺ consumption and deacetylating key lysine residues in metabolic proteins, help mitigate SA-AKI. For example, SIRT3 protects against mitochondrial damage in the kidney by attenuating ROS production, inhibiting the NLRP3 inflammasome [60]. Additionally, upregulating the SIRT1/PGC-1α pathway reduces mitochondrial dynamics in AKI [61]. He et al. [62] demonstrated that pretreatment of LPS-exposed mice with nicotinamide mononucleotide restored NAD⁺ levels while significantly suppressing elevated mitochondrial ROS and inducible NOS (iNOS) expression. NAD⁺ activates the SIRT1-dependent GSK-3β/Nrf-2 signaling pathway, protecting mitochondria from oxidative damage, improving mitochondrial morphology, and ultimately reducing SA-AKI.

In summary, recent studies highlight that oxidative stress plays a key role in AKI by damaging mitochondria, increasing ROS, and impairing ATP production. Protective strategies, such as UCP2 overexpression, NAD⁺/SIRTs activation, and PGC-1α/Nrf-2 signaling, mitigate oxidative stress, restore mitochondrial function, and reduce kidney damage. Targeting these pathways offers potential therapeutic approaches for AKI.

4.3. Autophagy and mitophagy in oxidative stress mitigation in SA-AKI

In SA-AKI, oxidative stress and apoptosis are important factors leading to AKI. Enhanced autophagy can effectively remove the products of oxidative damage and reduce oxidative stress. For instance, dexmedetomidine ameliorates LPS-induced AKI by reducing oxidative stress and apoptosis, and upregulates autophagy by inhibiting PI3K/Akt/mTOR pathway [63]. SIRT3 upregulation promotes autophagy by upregulating p-AMPK and downregulating p-mTOR in cecal ligation and puncture (CLP) mice [64].

Additionally, mitophagy is a key process for the selective removal of damaged mitochondria. Both in vitro and in vivo studies have shown that promoting SIRT3-mediated deacetylation of TFAM enhances mitophagy and alleviating SA-AKI [21]. However, mitophagy is impaired in later stages of kidney sepsis. This dysfunction may be due to activation of the NLRP3 inflammasome, which promotes PRKN cleavage, thereby inhibiting mitophagy [65].

In summary, oxidative stress plays a crucial role in the pathogenesis of SA-AKI and contributes to kidney injury via mitochondrial dysfunction and apoptosis. Enhancing autophagy, particularly mitophagy, is a promising strategy for mitigating oxidative damage. However, impairment of mitophagy due to NLRP3 inflammasome activation in sepsis poses significant challenges.

4.4. Inhibiting ferroptosis to ameliorate oxidative damage in SA-AKI

Ferroptosis is increasingly being recognized as a key contributor to the development of SA-AKI. Mitochondrial damage leads to impaired oxidative phosphorylation, increased ROS production, and ferroptosis, with key mitochondria-related proteins such as nicotinamide adenine dinucleotide, reduced form (NADH):ubiquinone oxidoreductase core subunit S3 (NDUFS3), showing protective effects when overexpressed in septic models by activating AMPK [66]. Many compounds protect the kidneys by inhibiting oxidative stress and reducing ferroptosis. For example, the endogenous hydrogen sulfide (H₂S) pathway is a potential therapeutic target for attenuating mitochondrial oxidative stress and ferroptosis in SA-AKI [67]. Furthermore, prostaglandin E2 (PGE2) promotes ferroptosis by upregulating cyclooxygenase enzymes and increasing lipid peroxide accumulation in renal tubular cells. This process is exacerbated under oxidative stress conditions, and the inhibition of the PGE2 pathway attenuates ferroptosis and preserves kidney function [68].

Collectively, SA-AKI is a multifactorial condition driven by oxidative stress, mitochondrial dysfunction, and inflammatory pathways such as NLRP3 inflammasome activation. The key mechanisms include renal IR injury, acute tubular necrosis, and excessive ROS production, which exacerbate kidney damage. Therapeutic strategies targeting oxidative stress and mitochondrial dysfunction, such as the modulation of UCP2 and SIRT1/3, have shown promise in mitigating SA-AKI. Enhancing mitophagy and inhibiting ferroptosis offer potential avenues for reducing oxidative damage and improving renal outcomes. However, challenges remain, particularly in addressing the impairment of mitophagy and ferroptosis in later stages of sepsis. These findings highlight the importance of integrating molecular and cellular approaches for the development of effective therapies for SA-AKI.

5. Sepsis-induced acute liver injury (SALI) and oxidative stress

The liver is an important metabolic detoxification organ that helps remove pathogenic substances and other toxins from the body of patients in septic shock (Fig. 4). However, the imbalance between oxidation and antioxidant defenses, along with increased oxidative and nitration stress, leads to the excessive production of ROS. This results in morphological changes in the liver, such as steatosis and watery degeneration, which exacerbate inflammation and cell apoptosis [69]. Elevated serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels indicate liver damage. Severe acute liver injury can lead to liver failure and increased mortality. Therefore, oxidative stress is the central mechanism that drives SALI.

Fig. 4.

Role of oxidative stress in sepsis-induced acute liver injury (SALI). Oxidative damage plays a central role in the pathogenesis of SALI. Reactive oxygen species (ROS) activate the nuclear factor κB (NF-κB) pathway, leading to inflammatory cytokine production. Nuclear factor erythroid 2-related factor 2 (Nrf-2) dissociates from Kelch-like ECH-associated protein 1 (KEAP1) and translocate to the nucleus to activate antioxidant genes. Mitochondrial dysfunction, particularly damage to the electron transport chain, increases ROS production, leading to liver injury. The inhibition of autophagic flow due to oxidative stress exacerbates liver injury. Cytochrome P450 (CYP) enzymes contribute to ROS production and inflammation in the liver. I–IV: mitochondrial electron transport chain complexes I–IV, namely NADH:ubiquinone oxidoreductase, succinate dehydrogenase, ubiquinol:cytochrome c (Cyt c) oxidoreductase, and Cyt c oxidase, respectively. AST: aspartate aminotransferase; ALT: alanine aminotransferase; HMGB1: high-mobility group box 1; TNF-α: tumor necrosis factor α; IL-6/1β: interleukin-6/1β; MAPK: mitogen-activated protein kinase; NLRP3: NLR family pyrin domain-containing 3; CUL3: cullin 3; PI3K: phosphoinositide 3-kinase; Akt: protein kinase B; PPAR: peroxisome proliferator-activated receptor; ARE: antioxidant response element; GCLM: glutamate-cysteine ligase regulatory subunit; NQO-1: NAD(P)H:quinone oxidoreductase-1; SIRT: sirtuin; FOXO1: forkhead box O1; Ac: acetylation; SOD2: superoxide dismutase 2; AMPK: adenosine monophosphate (AMP)-activated protein kinase; mTOR: mammalian target of rapamycin; NADPH: nicotinamide adenine dinucleotide (NAD) phosphate (reduced form); Gln: glutamine; HSP: heat shock protein; ADP: adenosine diphosphate; ATP: adenosine triphosphate.

5.1. Inflammatory and antioxidant pathways co-regulate SALI

In sepsis, the interplay between oxidative stress and inflammation exacerbates liver damage, creating a vicious cycle. This section explores the synergistic interaction between inflammation and oxidative stress, focusing on the NF-κB and Nrf-2 pathways as key examples.

Many bioactive substances alleviate inflammation and oxidative stress in SALI by blocking the Toll-like receptor 4 (TLR4)/NF-κB pathway. For example, treatment with ulinastatin and thrombomodulin mitigates LPS-induced liver injury by suppressing the HMGB1/TLR4/NF-κB pathway [70]. Additionally, network pharmacology and in vivo experiments have demonstrated that LPS-induced acute liver injury significantly increases the phosphorylation of MAPK (e.g., c-Jun N-terminal kinase (JNK), extracellular signal-regulated kinase (ERK), and P38) and NF-κB [71].

The Nrf-2 pathway serves as the central antioxidant defense in SALI. By regulating downstream targets such as glutamate-cysteine ligase regulatory subunit (GCLM) and NAD(P)H:quinone oxidoreductase-1 (NQO-1), Nrf-2 reduces oxidative stress and improves liver function [72]. Furthermore, liver IR injury is a critical mechanism in SALI, contributing to oxidative damage and inflammation. Some agents exert dual effects by modulating both the Akt/Nrf2 axis and suppressing the TLR4/NF-κB/NLRP3 pathway, thereby reducing hepatocellular injury [73].

Severe impairments of energy homeostasis, inflammation, and redox balance are closely linked to liver steatosis progression. PPARs, particularly PPARα, PPARβ/δ, and PPARγ, are key regulators of hepatic lipid homeostasis [74]. The activation of PPARα and PPARγ reduces lipid accumulation in the liver of CLP mice and attenuates lipid peroxidation by activating Nrf-2 to inhibit ROS-mediated NLRP3 signaling pathway, thereby reducing hepatocyte pyroptosis and inflammatory responses [75].

Therefore, oxidative stress and inflammation play central roles in the pathogenesis of SALI by creating a detrimental feedback loop that exacerbates liver damage. Key signaling pathways, including the TLR4/NF-κB and Nrf-2 pathways, mediate the crosstalk between oxidative stress and inflammation. Additionally, PPARs and their interaction with Nrf-2 provide further insights into the regulation of hepatic lipid metabolism. Targeting these pathways offers novel strategies for treating SALI and other liver disorders driven by oxidative stress and inflammation.

5.2. Damage to the electron transport chain in SALI

Mitochondria, the primary energy suppliers in cells experience reduced ATP synthesis and decreased oxidative phosphorylation efficiency when their function is impaired. This dysfunction is associated with reduced cytochrome C (Cyt c) levels. However, one study also found no significant change in the mitochondrial oxidative phosphorylation rate during the early stages of sepsis. This suggests that liver mitochondria adjust their oxidative phosphorylation efficiency in response to the reduced oxidative activity induced by CLP [76]. Generally, damage to mitochondrial complex I disrupts the electron transport chain, increases ROS production, and contributes to liver injury [77]. In mice with endotoxemia induced by LPS, treatment with Rho-associated protein kinase (ROCK) inhibitors or the mitochondrial antioxidant Mito-TEMPO significantly alleviated liver damage compared to controls, as evidenced by the increased activity of complexes I and IV, enhanced manganese superoxide dismutase (MnSOD) activity, and upregulated expression of mitochondrial DNA (mtDNA)-encoded genes [78]. Moreover, SIRT1 deacetylates forkhead box O1 (FOXO1), enhances its nuclear retention and DNA-binding activity, and regulates the expression of antioxidant enzyme genes such as superoxide dismutase 2 (SOD2). This in turn facilitates the clearance of mitochondrial ROS, restores mitochondrial membrane potential loss, and increases the levels of ATP and the enzyme activity of complexes I and III [79].

Additionally, increasing ROS levels leads to the accumulation of misfolded proteins in the mitochondria, which leads to the activation of UPR. The mitochondrial heat shock protein 60 (HSP60) and HSP10 to multi-ubiquitinated protein ratio could be used as an indicator of UPR failure in the septic liver and are associated with elevated hepatic dysfunction in patients with sepsis [80]. Yang et al. [81] demonstrates that glutamine (Gln) could activate NAD⁺-dependent SIRT4, promote HSP60 deacetylation, and enhance the assembly of the HSP60-HSP10 complex. The HSP60-HSP10-dependent UPR maintains the activity of complexes II and III, ultimately promoting ATP generation in hepatocytes and alleviating liver injury in burn-induced sepsis.

In summary, mitochondrial dysfunction and oxidative stress play crucial roles in SALI progression. Impaired mitochondrial function, particularly damage to the electron transport chain, results in reduced ATP synthesis, increased production of ROS, and compromised mitochondrial integrity. Furthermore, the accumulation of misfolded proteins in the mitochondria triggers the UPR, exacerbating liver dysfunction. Targeting these pathways may preserve mitochondrial integrity and attenuate oxidative injury, providing promising therapeutic approaches for SALI.

5.3. Autophagy and oxidative stress in SALI

Autophagy, a protective mechanism against SALI, protects the liver from sepsis-induced injury. This process is essential for recycling cellular components and removing damaged organelles, thereby mitigating oxidative stress and cellular damage. Overexpression of homeodomain-interacting protein kinase 2 (HIPK2) inhibits LPS-induced apoptosis in primary hepatocytes and increases autophagic flux. Mechanistically, HIPK2 may dissociate from calpain 1 under sepsis, bind to calmodulin, lower intracellular Ca²⁺ levels, and promote autophagy [82]. In addition, activating AMPK increases autophagy in mitochondria and thus attenuating mitochondrial dysfunction [83].

5.4. Cytochrome P450 (CYP) enzymes and their roles in ROS production and liver inflammation

In addition to the mitochondria, hepatic CYP enzymes are a major intracellular source of ROS. These enzymes catalyze substrate oxidation, generating free radicals that exacerbate liver inflammation and oxidative stress. In LPS-induced ALI, hepatic CYP isoforms such as CYP3A4 are upregulated, directly inducing ROS production and oxidative stress, which exacerbates liver injury [84]. Additionally, inhibition or genetic knockout of CYP2E1 suppresses the expression of pro-inflammatory mediators such as NLRP3 in hepatocytes. This reduction in inflammatory signaling alleviates oxidative stress and attenuates liver fibrosis progression [85]. Thus, CYP enzymes are critical contributors to ROS-driven inflammation and liver damage in SALI patients.

In conclusion, oxidative stress plays a critical role in the pathogenesis of SALI by triggering inflammatory responses and mitochondrial dysfunction, which exacerbate liver damage. The interplay between oxidative stress and inflammation underscore the complexity of liver injury mechanisms. Targeting these pathways has shown a promising therapeutic potential, with various bioactive substances and pharmacological agents demonstrating the ability to alleviate oxidative stress, inflammation, and mitochondrial damage. Moreover, the roles of autophagy and CYP enzymes in mitigating oxidative damage offer additional therapeutic avenues. However, the mechanisms underlying the intricate relationship among oxidative stress, inflammation, and cellular dysfunction in SALI remain an active area of research. A deeper understanding of these pathways is essential to develop more effective treatments for sepsis-induced liver injury and ultimately improve patient outcomes in clinical settings.

6. Role of oxidative stress in sepsis-associated acute lung injury (SA-ALI)

Among organs affected by sepsis, the lungs are particularly vulnerable (Fig. 5). ARDS is an independent risk factor for in-hospital mortality, contributing up to 37% of the deaths in patients. Despite advances in corticosteroids and mechanical ventilation, the annual mortality rate of ALI remains at approximately 40% [86]. Therefore, exploring and targeting the mechanisms underlying sepsis-induced lung injury is crucial, and oxidative stress has been identified as a key driver of SA-ALI.

Fig. 5.

Role of oxidative stress in sepsis-associated acute lung injury (SA-ALI). In response to sepsis, oxidative stress triggers mitochondrial dysfunction and endoplasmic reticulum (ER) stress. Additionally, oxidative stress triggers ferroptosis and pyroptosis, which further exacerbates lung injury. These mechanisms collectively contribute to endothelial damage and increased alveolar permeability. The worsening of acute lung injury contributes to impaired gas exchange and further progression of acute lung injury. ROS: reactive oxygen species; mtDNA: mitochondrial DNA; NETs: neutrophil extracellular traps.

6.1. Oxidative stress activates inflammation pathway in SA-ALI

ROS generated by oxidative stress activate multiple inflammatory pathways, including NF-κB, NLRP3, and HMGB1, which exacerbate lung endothelial permeability and inflammation. For example, calycosin inhibits the HMGB1/myeloid differentiation primary response 88 (MyD88)/NF-κB pathway, suppresses inflammation and oxidative stress in vitro and in vivo, and significantly alleviates pathological lung damage, pulmonary edema, and apoptosis in rats [87]. As mentioned previously, in septic mouse models, activation of the MAPK pathway significantly increases NF-κB P65 phosphorylation, but paeoniflorin combined with luteolin alleviates LPS-induced ALI by regulating NF-κB and MAPK signaling pathways [88]. Genetic deletion of RNA-binding motif protein 3 (RBM3) significantly increases NF-κB and NLRP3 expression, aggravating SA-ALI [89].

Lung macrophages play an indispensable role in initiating the inflammatory response. In LPS-induced mouse macrophage cell line (RAW246.7 cells), phosphorylation of epidermal growth factor receptor (EGFR) is elevated, promoting macrophage M1 polarization. Overexpression of quiescin Q6 sulfhydryl oxidase 1 (QSOX1) significantly reduces EGFR phosphorylation, exerting anti-inflammatory and antioxidant effects, and attenuating lung injury [90]. Previous studies show that the NF-κB/HIF-1α cascade promotes ROS production, facilitates M1 polarization of macrophages, and exacerbates inflammation [91].

Moreover, LPS-induced platelet activation triggers the release of neutrophil extracellular traps (NETs) [92]. NETs stimulate macrophages to produce excessive ROS, leading to deubiquitination and assembly of the NLRP3 inflammasome, inducing pyroptosis in alveolar macrophages and exacerbating lung injury [93]. Recent studies have shown that, in CLP-induced mouse lung epithelial cells, an increase in NETs is accompanied by enhanced ferroptosis. NETs activate the TLR9/MyD88/NF-κB pathway, leading to the upregulation of methyltransferase 3 (METTL3), which in turn promotes METTL3-mediated N⁶-methyladenosine (m⁶A) modification and subsequent ferroptosis [94]. Moreover, suppressing PI3K/Akt pathway inhibits mTOR and thus promoting autophagy and attenuates ferroptosis in septic ALI mice [95,96].

These studies highlight the potential of targeting multiple signaling pathways to alleviate ALI, particularly by inhibiting NETs-induced pyroptosis and ferroptosis, and other inflammatory pathways. Although these therapies have shown promise in experimental models, further clinical validation and evaluation of their potential side effects are necessary to translate these findings into effective treatments for sepsis-induced ALI.

6.2. MQC in SA-ALI

Persistent mitochondrial damage and dysfunction contribute significantly to lung injury in patients with sepsis. This process can be reversed by activating mitophagy and maintaining mitochondrial homeostasis. For example, activating the calcium/calmodulin-dependent protein kinase kinase II (CaMKKII)/AMPK pathway improves mitochondrial dynamics and mitophagy and protects against sepsis-induced lung inflammation and oxidative damage [97]. Moreover, hydrogen therapy alleviates cell damage and ALI in sepsis by regulating mitochondrial dynamics via PINK1/PRKN-mediated mitophagy [98]. In lipoteichoic acid (LTA)-induced SA-ALI mouse models, Nrf-2 directly binds to the promoter of PHB2, a key mitophagy receptor, on the inner mitochondrial membrane, thereby enhancing its expression. This promotes mitophagy and reduces oxidative stress and mitochondrial fragmentation, thereby alleviates SA-ALI [99].

In addition to mitophagy, regulation of mitochondrial fusion and fission is an essential part of MQC. Dexmedetomidine protects the lung from endotoxemia by activating the HIF-1α/HO-1 and protein kinase C-α (PKC-α)/HO-1 pathways. This leads to the upregulation of the mitochondrial fusion proteins Mfn1, Mfn2, and OPA1 while downregulating mitochondrial fission-related Drp1 and fission protein 1 (Fis1) [100,101]. mtDNA released from damaged mitochondria promotes inflammation and tissue injury. In LPS-treated mice, mtDNA recognizes and activates TLR9, causing systemic inflammation and ALI [102]. Li et al. [103] further demonstrated that mtDNA activates the cGAS/STING/NLRP3 axis, inducing pyroptosis and exacerbating lung injury in LPS-induced ALI, although it does not affect STING expression.

Collectively, these findings highlight the interconnected role of MQC in alleviating mitochondrial damage and oxidative stress in sepsis. Maintaining mitochondrial health via these pathways offers promising therapeutic avenues for mitigating ALI and other organ dysfunctions associated with sepsis.

6.3. Deacetylases in regulating oxidative stress in SA-ALI

Deacetylase is an important post-translational modification regulatory protein, and its protective effect on SA-ALI cannot be ignored. Activating the SIRT1/AMPK pathway reduces LPS-induced ER stress and mitochondrial dysfunction [104]. SIRT1 and SIRT3 upregulate the expression of Nrf-2, protecting lung epithelial MQC and helping clear ROS and alleviate ALI [105,106]. Similarly, overexpression of SIRT3, which regulates FOXO3a deacetylation, can alleviate oxidative stress and the expression of pyroptosis-related proteins, such as GSDMD [107]. Furthermore, menaquinone-4 (MK-4), a major component of vitamin K, inhibits the p53/solute carrier family 7 member 11 (SLC7A11) signaling pathway in ferroptosis by activating SIRT3-mediated deacetylation of P53 [108].

In addition, targeted inhibition of histone deacetylase 3 (HDAC3) increases FOXO1 acetylation levels, suppressing ROCK1-dependent damage to the pulmonary epithelial barrier and preventing MQC dysfunction, including disruptions in mitochondrial dynamics, mitochondrial number and size, and mitophagy [109]. Liu et al. [110] found that inhibiting HDAC3-mediated H3K27 deacetylation promotes autophagy via autophagy related 5 and alleviates macrophage pyroptosis in septic mice.

In summary, deacetylases, particularly SIRT1 and SIRT3, play vital roles in mitigating oxidative stress in SA-ALI via mechanisms involving autophagy, MQC, pyroptosis, and ferroptosis. These findings underscore the therapeutic potential of targeting deacetylases to alleviate oxidative stress and improve outcomes of SA-ALI.

Oxidative stress plays a central role in the pathogenesis of SA-ALI by driving inflammation, mitochondrial dysfunction, and cell death via pyroptosis, ferroptosis, and impaired MQC. Deacetylases, particularly SIRT1 and SIRT3, further contribute to oxidative stress regulation by enhancing antioxidant defenses and modulating cellular process. Therapeutic strategies targeting these pathways are promising in preclinical models. However, further clinical validation is required to translate these findings into effective treatments for SA-ALI. These insights highlight the complex interplay between oxidative stress, inflammation, and mitochondrial dysfunction in SA-ALI and underscore the potential of targeted therapies to improve outcomes in sepsis-induced lung injury.

7. Role of oxidative stress in sepsis associated encephalopathy

SAE, a common neurological complication of sepsis, is characterized by acute disturbances of consciousness, cognitive decline, and changes in mental status (Fig. 6). Survivors of sepsis often suffer from long-term cognitive impairment due to cortical damage and may even be predisposed to neurodegenerative diseases such as Alzheimer's disease and Parkinson's disease [111]. The pathogenesis of SAE is highly complex, and oxidative stress plays a crucial role in the development of sepsis-induced encephalopathy. Excessive accumulation of ROS not only causes direct damage to brain cells, but may also contribute to the onset and progression of SAE through mechanisms such as neuroinflammatory induction, disruption of the blood-brain barrier (BBB), and alteration of neuronal function [112].

Fig. 6.

Role of oxidative stress in sepsis-associated encephalopathy (SAE). SAE can cause cognitive impairment in patients. Oxidative stress activates neuroinflammatory pathways, including NLR family pyrin domain-containing 3 (NLRP3) inflammasome, mitogen-activated protein kinase (MAPK), and nuclear factor κB (NF-κB), leading to the release of pro-inflammatory cytokines. Reactive oxygen species (ROS) also impair mitochondrial function by affecting mitochondrial dynamics and mitochondrial permeability transition pore (mPTP). Various agents activate nuclear factor erythroid 2-related factor 2 (Nrf-2)/heme oxygenase 1 (HO-1) pathway exerting neuroprotective effects. BBB: blood-brain barrier; Cyp D: cyclophilin D; ATP: adenosine triphosphate; Drp1: dynamin-related protein 1; PGC-1α: peroxisome proliferator-activated receptor (PPAR) gamma coactivator 1α; SIRT1: sirtuin 1; MMPs: matrix metalloproteinases; RAGE: receptor for advanced glycation end products; S100B: S100 calcium-binding protein B; AMPK: adenosine monophosphate (AMP)-activated protein kinase.

7.1. Oxidative stress and inflammatory pathways in SAE

Oxidative stress promotes the development of septic encephalopathy by activating immune cells in the brain, such as microglia, and inflammatory responses in neurons. The receptor for advanced glycation end products (RAGE) is a multi-ligand pattern recognition receptor that can recognize various damage-associated molecular patterns (DAMPs) and pathogen-associated molecular patterns (PAMPs) [113]. In septic mice, high concentrations of S100 calcium-binding protein B (S100B) usually interact with RAGE to induce ROS production, activate the MAPK and NF-κB signaling pathways, and lead to abnormal mitochondrial dynamics and ceramide accumulation in vitro and in vivo. Morris water maze (MWM) tests revealed cognitive dysfunction in CLP-induced mice [114]. Furthermore, Song and Zhou [115] confirms that AMPK may suppress NF-κB expression by upregulating SIRT1 levels, thereby reducing brain injury, oxidative stress, and inflammation in septic mouse models.

Notably, activation of the NLRP3 inflammasome significantly exacerbates neuroinflammation and memory impairment following sepsis. Elevated NLRP3 levels are associated with microglial activation, leading to increased levels of inflammatory factors in the prefrontal cortex and hippocampus. Recent studies have shown that hydrogen is an effective treatment for SAE, as it inhibits NLRP3 inflammasome activation and reduces oxidative stress and inflammatory factor release, thus improving sepsis-associated brain injury and cognitive dysfunction [116,117].

In summary, oxidative stress plays a crucial role in the pathogenesis of SAE by triggering neuroinflammation and neuronal dysfunction. Key signaling pathways such as NLRP3 inflammasome, MAPK, and NF-κB are activated by excessive ROS production, leading to the release of pro-inflammatory cytokines and exacerbating neuronal damage. Therapeutic strategies targeting these pathways show promise for mitigating oxidative stress and inflammation in SAE models.

7.2. Neuroprotective pathway in SAE

The antioxidant effects of the Nrf-2/HO-1 pathway are well established in the hippocampus, preventing neuronal apoptosis and ultimately improving sepsis prognosis and cognitive dysfunction [118]. For example, GYY4137, a novel synthetic H₂S compound, reduces BBB permeability by inhibiting matrix metalloproteinases (MMPs) and preventing tight junction protein degradation via activating the Nrf-2/antioxidant response element (ARE)/HO-1 pathway, thereby maintaining BBB integrity. Its mechanism involves the modification of KEAP1 by GYY4137 through sulfhydryl groups [119]. Angiotensin-converting enzyme 2 (ACE2) has gained attention because of its role in neurological diseases. Overexpression of ACE2 increases the level of angiotensin (1–7) in the SAE mouse model, leading to activation of the Nrf-2 pathway and upregulation of downstream antioxidant proteins, such as Sestrin2, which alleviates SAE-induced damage [120].

Moreover, lipid peroxidation-induced ferroptosis contributes to SAE. A clinical experiment showed that the levels of S100B, glial fibrillary acidic protein, and malondialdehyde (MDA) in the serum fluctuates significantly at 72 h. Meanwhile, the mRNA and protein expression levels of 15-lipoxygenase (15-LOX) and acyl-CoA synthetase long-chain family member 4 (ACSL4) in the peripheral blood were significantly higher than those in the control group, whereas the mRNA and protein expression levels of GPX4 and cystine/glutamate transporter xCT were significantly lower than those in the control group. Inhibition of ferroptosis alleviates SAE mitochondrial damage and neuroinflammation by downregulating phosphatidylethanolamine-binding protein 1 (PEBP-1) and 15-LOX, while restoring GPX4 activity [121].

Certain anesthetics, including esketamine, propofol, and remimazolam, activate the Nrf-2/HO-1 pathway to alleviate hippocampal neuroinflammation, oxidative stress, and neuronal apoptosis, thereby improving SAE outcomes [[122], [123], [124]]. Remimazolam achieves this via α7-nicotinic acetylcholine receptors on the vagus nerve, suppressing M1 microglial activation and systemic inflammation while enhancing cognitive function [124]. Additionally, propofol reduces MDA levels and iron accumulation, and restores GSH and GPX4, thereby inhibiting ferroptosis-related neuronal injury [123].

In conclusion, the neuroprotective role of the Nrf-2/HO-1 pathway in alleviating SAE has been increasingly recognized. Various bioactive substances and anesthetics exert their effects through this pathway, reducing neuroinflammation, oxidative stress, and cell death, thereby offering new insights and potential therapeutic targets for the treatment of SAE.

7.3. Role of mitochondrial dysfunction in SAE

Mitochondrial dysfunction leads to excessive ROS production, which triggers oxidative stress and damages neuronal cells and BBB integrity. In an SAE mouse model, Drp1 phosphorylation was significantly increased. However, inhibiting the interaction between Drp1 and Fis reduced the release of mitochondrial Cyt c and decreased levels of neuroinflammatory markers such as TNF-α and IL-1β [125]. Similarly, Gardner-Rasheed feline sarcoma viral oncogene homolog (Fgr), a member of the Src family of tyrosine kinases, can phosphorylate SIRT1, leading to reduced expression of PGC-1α, while simultaneously increasing Drp1 expression. These changes lead to alterations in mitochondrial morphology in the hippocampus of septic mice, resulting in decreased ATP production and a significant reduction in the activity of mitochondrial respiratory chain complexes I/II/IV and V [126]. Additionally, Xie et al. [117] demonstrated that hydrogen-rich saline alleviated brain mitochondrial dysfunction by increasing mitochondrial membrane potential, respiratory control ratio, and ATP release, while alleviating ROS production through the activation of Nrf-2 to suppress the NLRP3 pathway.

In addition, the accumulation of ROS can open the mPTP, causing abnormal small-molecule solutes to penetrate the inner mitochondrial membrane, which in turn leads to apoptosis [127]. Kobayashi et al. [128] constructed cyclophilin D (Cyp D) knockout mice and found that after CLP, compared to the control group, the knockout mice had reduced ROS and free radical production, as well as decreased Cyt c release and reduced apoptosis.

In summary, mitochondrial dysfunction plays a key role in SAE, leading to excessive ROS production, which triggers oxidative stress and damages neuronal cells and BBB. Changes in mitochondrial dynamics such as fission/fusion and mitophagy are crucial mechanisms in this process. Drp1 phosphorylation, Fgr activation, and mPTP opening are significant factors regulating mitochondrial function. Interventions aimed at inhibiting these pathways or promoting mitochondrial repair can reduce neuroinflammation and improve the cognitive function in patients with sepsis.

7.4. Antioxidant therapies in SAE

Given the important role of oxidative stress in septic encephalopathy, therapeutic strategies targeting oxidative stress have received considerable attention. Most therapeutic drugs, such as atorvastatin [129], exert a dual effect by inhibiting neuroinflammation and oxidative stress, thereby improving neuronal injury and cognitive dysfunction. Antioxidants, such as vitamin C, help reduce oxidative stress, limit neutrophil infiltration, improve mitochondrial function, and enhance survival rates in animal models of sepsis through activation of the Nrf-2/HO-1 pathway [130].

Several anti-inflammatory and antioxidant therapies including dietary and physical treatments have been explored. For instance, fish oil (FO), an anti-inflammatory compound, and lipoic acid (LA), a general antioxidant, when used in combination, significantly reduce pro-inflammatory factors and myeloperoxidase (MPO) activity. They also enhance SOD activity in the hippocampus and increase brain-derived neurotrophic factor (BDNF) levels, effectively preventing cognitive dysfunction [131]. Furthermore, hypothermic therapy has shown promise as a treatment for acute neuroinjury. Fu et al. [132] used the A1 adenosine receptor (A1AR) agonist, N⁶-cyclohexyladenosine (CHA) to induce a hibernation-like state. Their experimental data suggest that this hypothermic state effectively alleviates neuroinflammation and preserves the integrity of the BBB, thus limiting the infiltration of inflammatory factors into the central nervous system. The protective effects of hypothermia are attributed to the suppression of macrophage proinflammatory responses and reduced endothelial cell oxidative stress under systemic hypothermic conditions.

In summary, oxidative stress plays a critical role in SAE onset and progression. Therapeutic strategies targeting oxidative stress have become a major research focus, with many drugs exerting dual effects by inhibiting neuroinflammation and oxidative stress, thereby effectively improving neuronal injury and cognitive dysfunction. Antioxidants, anti-inflammatory therapies, and temperature-modulation treatments offer new avenues for the clinical management of SAE. Further exploration of the underlying mechanisms of these therapies and optimization of their clinical application is essential to improving treatment outcomes and patient prognosis of SAE.

In conclusion, oxidative stress plays a central role in the development and progression of SAE, triggering a cascade of neuroinflammatory and mitochondrial dysfunctional processes leading to neuronal damage and cognitive impairment. However, further clinical validation is required to translate these findings into effective treatments for SAE. These findings highlight the importance of addressing oxidative stress and mitochondrial dysfunction in the development of novel therapies for sepsis-induced neurological complications.

8. Role of oxidative stress in sepsis-associated endothelium and microvascular injury

Sepsis-induced endothelial dysfunction is a hallmark of multiorgan failure, with oxidative stress acting as a central mediator (Fig. 7). Pulmonary endothelial dysfunction can lead to pulmonary edema, whereas inflammatory cell infiltration can cause ALI [133]. Endothelial injury in the renal microvessels results in reduced renal IR, leading to acute kidney failure [134]. Furthermore, sepsis may act as a “second hit” in older adult patients causing more severe microvascular complications [135]. Under physiological conditions, endothelial cells regulate vascular tone, permeability, and immune responses. However, in sepsis, excessive ROS production overwhelms the antioxidant system, leading to endothelial activation, microvascular leakage, and tissue hypoperfusion. We explored the interplay between oxidative stress, inflammation, and endothelial injury, focusing on molecular mechanisms and therapeutic implications.

Fig. 7.

Role of oxidative stress in sepsis-associated endothelium and microvascular injury. Reactive oxygen species (ROS), combined with nitric oxide (NO), forms peroxynitrite (ONOO⁻), disrupting endothelial function, promoting apoptosis, and exacerbating vascular injury. Extracellular histones released during neutrophil extracellular trap (NET) formation (NETosis) further enhances oxidative stress and inflammation, thereby increasing endothelial adhesion and vascular inflammation. Modulation of oxidative stress pathways, including activation of nuclear factor erythroid 2-related factor 2 (Nrf-2), may promote endothelial repair. IL-6: interleukin-6; HIF-1α: hypoxia-inducible factor 1α; VEGF: vascular endothelial growth factor; TLR4: Toll-like receptor 4; NF-κB: nuclear factor κB; NLRP3: NLR family pyrin domain-containing 3; ICAM: intercellular adhesion molecule; VCAM: vascular cell adhesion molecule.

8.1. Molecular mechanisms of oxidative stress in endothelial injury

In sepsis, endothelial cell damage causes increased vascular permeability, promoting tissue edema and leakage of inflammatory factors, leading to multi-organ dysfunction and increased mortality [136]. Under normal physiological conditions, NO plays a protective role by maintaining the endothelial cell function, promoting vasodilation, and inhibiting platelet aggregation. However, under the stress conditions of sepsis, an excess of ROS and reactive nitrogen species (RNS) are produced, and excessive NO combines with ROS to form ONOO⁻. ONOO⁻ is a potent oxidant that can disrupt the structure and function of endothelial cells, increase vascular permeability, and promote endothelial cell apoptosis and necrosis [137].

Extracellular histones play a crucial role in inducing oxidative stress and activating inflammatory responses. When pathogens invade the neutrophils, the enhanced interaction between iNOS and Ras-related C3 botulinum toxin substrate 2 (Rac2) is accompanied by increased levels of superoxide (O₂⁻), NO, and ONOO⁻ [138]. Subsequently, neutrophil extracellular trap formation (NETosis) is activated, releasing NETs, and leading to elevated extracellular histone levels. Native extracellular histones promote cyclooxygenase-dependent ROS release and increase endothelial cell adhesion by upregulating the expression of intercellular adhesion molecules (ICAMs) and vascular cell adhesion molecules (VCAMs) expression, thereby enhancing vascular inflammation and exacerbating endothelial damage. In contrast, citrullinated histones do not affect the expression of antioxidant enzymes, exerting a protective effect on the endothelium by regulating inflammation [139]. Pérez-Cremades et al. [140] further demonstrated that in human umbilical vein endothelial cells treated with exogenous histones, extracellular histones exacerbated endothelial inflammation by activating the TLR4/NF-κB pathway. Additionally, extracellular histones induce NLRP3 activation and pyroptosis. Enhancing autophagy effectively inhibits NLRP3 activation, providing protection to endothelial cells [141].

8.2. Antioxidant pathways in endothelial injury

Nrf-2 remains the most important pathway of protection against endothelial injury. Betulinic acid activates Nrf-2 and reduces LPS-induced aortic contractions in rats in a dose-dependent manner, thereby promoting vasodilation [142]. Moreover, dexpanthenol exerts anti-inflammatory and antioxidant effects by inhibiting the IL-6/HIF1α/vascular endothelial growth factor (VEGF) pathway, thereby reducing LPS-induced cardiovascular toxicity [143].

The role of oxidative stress in endothelial injury is multifaceted and involves excessive production of ROS and RNS, which disrupt endothelial cell function. Activation of the Nrf-2 pathway and the upregulation of antioxidant enzymes may provide potential protective mechanisms. These findings suggest that endothelial injury can be mitigated by modulating oxidative stress-related pathways, offering new targets and strategies for treating sepsis and other related organ injuries.

9. Role of oxidative stress in sepsis-associated skeletal muscle damage

Muscle damage, a common complication of sepsis, often manifests as muscle atrophy affecting the ventilator and limb muscles. Muscle atrophy can result in prolonged mechanical ventilation and seriously affect patient prognosis and quality of life [144]. Excessive release of proinflammatory factors contributes to skeletal muscle injury. Hou et al. [145] injected L-Gln and/or L-leucine (Leu) into CLP-induced septic mice and found that Gln promotes the conversion of macrophages in muscle to the M2 phenotype, exerting an anti-inflammatory effect, while Leu increases the expression of PGC-1α. However, no synergistic effects were observed when Gln and Leu were administered simultaneously. In addition, sepsis-induced skeletal muscle injury is closely associated with mitochondrial dysfunction primarily driven by oxidative stress [146].

Despite profound muscle injury during sepsis, muscle regeneration can occur if the regulatory mechanisms governing muscle satellite cells (MuSCs) remain intact. However, sepsis-induced oxidative stress leads to mitochondrial dysfunction in MuSCs, which impairs their ability to proliferate, differentiate, and prevents effective muscle regeneration [147].

In summary, oxidative stress plays a central role in sepsis-induced skeletal muscle injury by disrupting the mitochondrial function and activating inflammatory pathways. These mechanisms contribute to muscle wasting and impaired regeneration in sepsis survivors. Understanding the interplay among oxidative stress, inflammation, and muscle regeneration is crucial for developing effective therapeutic strategies to prevent or mitigate muscle dysfunction in sepsis. Targeting oxidative stress pathways, including antioxidants and metabolic modulators, holds promise for improving the outcomes of patients with sepsis and enhancing their recovery.

10. Clinical therapeutic agents targeting oxidative stress

We summarized the drugs or dietary supplements discussed in this review that have progressed to phases II/III clinical trial and received the U.S. Food and Drug Administration (FDA) approval (Table 1 [[20], [21], [22],34,61,63,100,101,[122], [123], [124],129,130]). A single-center, phase II, double-blind, randomized, placebo-controlled trial investigated the effects of intravenous infusion of melatonin in intensive care unit (ICU) patients with sepsis. Compared to the placebo group, melatonin exhibited potent antioxidative and anti-inflammatory effects by directly scavenging free radicals independent of the enzymatic antioxidant system. These effects were shown without associated adverse reactions and ultimately contributed to reduced mortality and shorter hospital stay [148]. Furthermore, patients in septic shock sedated with dexmedetomidine required less norepinephrine to maintain vascular tone and hemodynamic stability than those sedated with propofol, and demonstrated higher regional cerebral oxygen saturation levels [149]. Although animal studies have demonstrated the anti-inflammatory and antioxidant properties of atorvastatin and vitamin C, current clinical data do not support their routine use for alleviating inflammation or improving outcomes in critically ill patients with sepsis, warranting further investigation [150]. These discrepancies in study results may be attributed to heterogeneity in study design, patient population, timing, and dosing strategies. Despite encouraging preclinical data, translation of antioxidants into effective clinical therapies remains limited. Thus, future large-scale, multicenter, and rigorously designed trials are essential to validate their efficacy and define optimal treatment protocols.

Table 1.

Clinical therapeutic agents targeting oxidative stress.

Therapeutic agents	Organ dysfunction	Mechanism	Refs.
Melatonin	SIMD, SA-ALI, and SA-AKI	Improving MQC	[[20], [21], [22]]
Cyclosporine A	SIMD	Inhibiting NOS2, reducing myocardial protein nitrosylation, and restoring mitochondrial permeability transition	[34]
Dexmedetomidine	SA-AKI and SA-ALI	Enhancing autophagy/mitophagy by inhibiting the PI3K/Akt/mTOR pathway, upregulating the SIRT1/PGC-1α pathway to protect mitochondrial structure and function, alleviating oxidative stress and apoptosis in SA-AKI, and improving mitochondrial dynamics by activating HO-1, thereby mitigating SA-ALI	[61,63,100,101]
Esketamine	SAE	Activating the Nrf-2/HO-1 signaling pathway, reducing neuroinflammation and oxidative damage	[122]
Propofol	SAE	Activating the Nrf-2/HO-1 pathway, inhibiting MDA and iron accumulation, reducing mitochondrial permeability transition, and inhibiting nervous system dysfunction	[123]
Remimazolam	SAE	Activating the Nrf-2/HO-1 pathway and improving neural function and cognitive impairment via α-7 nicotinic acetylcholine receptor	[124]
Atorvastatin	SAE	Improving neural function and lipid-related membrane damage through antioxidant and anti-inflammatory effects	[129]
Vitamin C (ascorbic acid)	SAE	Antioxidant effects, reducing oxidative stress and inflammation, and improving cellular function	[130]

SIMD: sepsis-induced myocardial dysfunction; SA-ALI: sepsis-associated acute lung injury; SA-AKI: sepsis-associated acute kidney injury; MQC: mitochondrial quality control; NOS2: nitric oxide (NO) synthase 2; PI3K: phosphoinositide 3-kinase; Akt: protein kinase B; mTOR: mammalian target of rapamycin; SIRT1: sirtuin 1; PGC-1α: peroxisome proliferator-activated receptor (PPAR) gamma coactivator 1α; HO-1: heme oxygenase-1; SAE: sepsis-associated encephalopathy; Nrf-2: nuclear factor erythroid 2-related factor 2; MDA: malondialdehyde.

Besides the agents discussed above, other drugs have undergone preliminary clinical evaluations; however, their therapeutic potential in sepsis remains largely underexplored, representing a significant area for future research.

11. Further direction

This review not only focuses on the oxidative stress mechanisms of a single organ but also provides a comprehensive overview of oxidative stress mechanisms in multiple organs affected by sepsis. It offers a broader perspective, particularly regarding the mechanisms of injury to the myocardium, kidneys, liver, lungs, brain, skeletal muscles, and endothelial cells. By exploring the interactions among oxidative stress, inflammation, mitochondrial dysfunction, apoptosis, ferroptosis, and pyroptosis, this review integrates research findings from molecular biology, immunology, pharmacology, and other disciplines, revealing the complex role of oxidative stress in sepsis and providing a reference for interdisciplinary research.

Despite this comprehensive review of oxidative stress in sepsis, this study has some limitations.

• i)Complexity of mechanisms: the pathological mechanisms of sepsis are highly complex and involve various cell types, signaling pathways, and molecular mechanisms. Although this review extensively discusses the interactions among oxidative stress, inflammation, mitochondrial dysfunction, and other factors, many unknown mechanisms require further investigation.
• ii)Differences between animal models and clinical studies: most studies referenced in this review were based on animal models or in vitro cell experiments. However, it remains uncertain whether these findings can be directly applied in clinical settings.
• iii)Limitations of research data: although current studies provide valuable insights into the mechanisms of oxidative stress in sepsis, the differences between animal models and clinical studies may limit the translatability of these results.
• iv)Lack of clinical validation: the studies cited in this review primarily focused on animal experiments and cell culture models with insufficient clinical validation to directly confirm the applicability of the results.

12. Conclusion

Oxidative stress plays a central role in sepsis and associated organ dysfunction. By modulating oxidative stress-related signaling pathways, such as the Nrf-2/HO-1 pathway and NLRP3 inflammasome, inflammation can be alleviated, mitochondrial function is protected, and ultimately, the prognosis of patients with sepsis improves. However, the pathological mechanisms underlying sepsis are complex, and the clinical application of antioxidant therapies still faces numerous challenges. Future studies should explore the intricate mechanisms underlying oxidative stress and develop more effective and personalized treatment strategies to improve the prognosis of patients with sepsis.

CRediT authorship contribution statement

Xin-Ru Yang: Writing – review & editing, Writing – original draft, Methodology. Ri Wen: Writing – review & editing, Writing – original draft, Methodology. Ni Yang: Writing – review & editing, Writing – original draft, Methodology. Yang Gao: Writing – review & editing, Validation, Supervision, Methodology, Investigation, Conceptualization. Tie-Ning Zhang: Writing – review & editing, Visualization, Validation, Supervision, Investigation, Conceptualization.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Appendix A. Supplementary data

The following is the supplementary data to this article: