Heat stroke and the liver: mechanisms of injury and therapeutic strategies

Abstract

Global warming is leading to a continuous increase in the incidence of heat-related illnesses, among which heat stroke is the most severe type, characterized by a core body temperature > 40 °C and multiple organ dysfunction syndrome (MODS). The liver, being a thermosensitive organ, acts both as a target of injury and an "amplifier" of inflammation. Its acute injury and failure are significant causes of death in heat stress. This review summarizes the core mechanisms of heat stress-induced liver injury, including direct damage to hepatocytes by hyperthermia, the dual regulatory role of heat shock proteins (HSPs), gut barrier damage leading to endotoxemia and systemic inflammatory response, ischemia–reperfusion injury, and the involvement of various cell death modes such as apoptosis, pyroptosis, and ferroptosis. Clinically, liver injury manifests as a sharp rise in transaminases, abnormal bilirubin metabolism, and coagulation dysfunction, often combined with damage to the heart, brain, kidneys, and other organs, constituting MODS. Current treatments primarily focus on rapid cooling and organ support. Potential strategies include cell death inhibitors, antioxidants, and gut barrier protection. Severe cases may require artificial liver support systems (ALSS) or liver transplantation. Future efforts should delve deeper into the mechanisms of cell death, promote the clinical translation of targeted therapies, and strengthen effective prevention of heat stroke.

Introduction

Definition of heat stress and heat-related illnesses

Heat-related illnesses are a spectrum of syndromes caused by exposure to high temperature/humidity, particularly during physical activity [1]. Driven by global warming, excess deaths and heat stroke incidence have risen significantly worldwide [2]. Heat stress activates thermoregulatory mechanisms (increased cardiac output, sweating), but uncompensated fluid/electrolyte loss induces mild illnesses (heat syncope, cramps, exhaustion) or severe heat stroke (HS) [3, 4]. Mild heat-related illnesses can occur in normothermic individuals, with symptoms ranging from transient unconsciousness (heat syncope) to fatigue and dizziness (heat exhaustion) [5].

HS is the most severe form of heat-related illness, a life-threatening systemic condition characterized by a core body temperature exceeding 40 °C and accompanied by central nervous system dysfunction and multiple organ dysfunction syndrome (MODS) [6]. In recent years, with rising global temperatures, the incidence and mortality of heat stroke have increased significantly worldwide [7]. Based on association with labor, heat stroke can be divided into two types: classic heat stroke (CHS) and exertional heat stroke (EHS). Classic heat stroke primarily affects the elderly, children, and individuals with underlying diseases, caused by dysfunction of the thermoregulatory center due to a hot environment. Exertional heat stroke is more common in military personnel and young adults performing high-intensity physical work in hot and humid environments [8].

The central role of the liver in heat stress

Studies show that among the body's organs, the liver is particularly sensitive to temperature fluctuations [9]. In MODS induced by heat stress, the liver is one of the earliest organs damaged (Fig. 1). Acute liver injury (ALI) and acute liver failure (ALF) are common serious complications and are direct causes of patient death [10]. As the liver plays key roles in inflammatory responses, substance metabolism, immune regulation, and excretion [11], it acts both as a target of injury and an "amplifier" of systemic inflammation in the process of host response failure and multi-organ damage. Therefore, the liver is not only a damaged organ in heat stress but also a key link in the pathogenesis of heat stress.

Fig. 1.

The association network between heat stress-induced liver injury and multiple organ damage. Liver injury and injuries to the cardiac, cerebral, renal, and coagulation systems mutually promote each other, ultimately inducing multiple organ dysfunction syndrome (MODS)

While prior reviews have broadly addressed heat stroke pathophysiology, this article uniquely synthesizes cell death mechanisms (apoptosis, pyroptosis, ferroptosis) as central drivers of heat stress-induced liver injury and critically evaluates their implications for targeted therapeutic development. We bridge mechanistic insights with translational gaps, emphasizing how emerging cell death inhibitors and organ-specific protectants may overcome limitations of current supportive care.

Search strategy and selection criteria

This review adheres to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines to ensure methodological rigor.

A comprehensive literature search was conducted across four electronic databases: PubMed, Embase, Web of Science, and Scopus. The search timeframe was restricted to January 2010–December 2024 to focus on recent advances. Key search terms were combined using Boolean operators: ("heat stress" OR "heat stroke" OR "exertional heat stroke" OR "classic heat stroke") AND ("liver injury" OR "hepatic injury" OR "acute liver failure") AND ("pathophysiology" OR "mechanism" OR "apoptosis" OR "pyroptosis" OR "ferroptosis" OR "necroptosis" OR "inflammation" OR "treatment" OR "therapy" OR "biomarker").

Inclusion Criteria: (1) Original research articles, systematic reviews, or meta-analyses; (2) Studies investigating heat stress/EHS/CHS-induced liver injury in humans, animal models, or in vitro systems; (3) Publications reporting mechanistic insights (e.g., cell death pathways, inflammatory signaling) or therapeutic interventions; (4) Articles written in English with full-text availability. Exclusion Criteria: (1) Studies focusing on liver injury from non-heat stress etiologies (e.g., sepsis, drug toxicity, viral hepatitis); (2) Abstracts, conference proceedings, or unpublished data; (3) Studies with insufficient methodological detail or irrelevant outcomes (e.g., isolated heat stress without liver injury assessment); (4) Duplicate publications or secondary analyses of previously reported datasets.

Two independent reviewers screened titles and abstracts to eliminate irrelevant studies. Full-text evaluation was performed for remaining records to confirm eligibility. Discrepancies were resolved by consensus with a third reviewer.

Core pathophysiological mechanisms of heat stress-induced liver injury

Direct heat toxicity: hyperthermia damage to hepatocytes and the dual role of heat shock proteins (HSPs)

When the body is continuously exposed to a hyperthermic environment, dysfunction of thermoregulation leads to a sharp increase in core temperature. Hyperthermia can directly disrupt the structure of biomembranes and the integrity of organelles in primary rat hepatocyte, causing denaturation of intracellular proteins, which is the primary step in the loss of hepatocyte function. The body possesses various defense systems to protect cells from heat damage, among which increased expression of heat shock proteins (HSPs) is one of the most important mechanisms. Studies confirm that HSP70 overexpression reduces hepatocyte apoptosis (in murine heat stroke models with core temperature > 41.5 °C) [12]. Most native proteins have marginally stable folding patterns, and the accumulation of misfolded proteins can disrupt intracellular protein homeostasis networks, thereby inducing various diseases [13]. As representative molecular chaperones, HSPs can regulate conformational changes by promoting correct protein folding and refolding, repair denatured proteins, prevent misfolding, and maintain cellular homeostasis, thus protecting the host [14]. Additionally, HSPs can regulate cytokine production, inhibit apoptotic and inflammatory pathways, and reduce oxidative stress. HSP27, HSP70, and HSP90 are representative inducible cytoprotective HSPs, and their overexpression can inhibit heat-induced apoptosis. It is known that these chaperones can interact with key proteins in apoptotic signaling pathways (such as caspases) and regulate the nuclear factor-kappa B (NF-κB) pathway and tumor necrosis factor (TNF)-mediated signal transduction, ultimately protecting cells and reducing heat stress-induced cell death [15]. However, when the intensity of heat stress exceeds the cellular tolerance threshold, the cytoprotective effects of HSPs may be overwhelmed, permitting secondary inflammatory cascades (e.g., HMGB1/TLR4-mediated NF-κB activation) to dominate, thereby exacerbating hepatocyte damage [16]. The dual role of HSPs depends on stress intensity and duration: Under mild-to-moderate heat stress, HSP70/HSP27 act as protective chaperones—promoting protein folding, inhibiting caspase activation, and reducing apoptosis in mouse models. Clinically, elevated HSP70 levels correlate with better prognosis in heat stroke patients, likely reflecting effective cellular defense. However, under severe heat stress (core temperature > 42 °C), HSP90 interacts with IκB kinase (IKK), activating the NF-κB pathway independently of TLR4/LPS, leading to excessive pro-inflammatory cytokine release (TNF-α/IL-6) that exacerbates hepatocyte damage [16]. This paradox highlights HSPs as context-dependent regulators: their protective function dominates when stress is manageable, but pro-inflammatory effects prevail when cellular defense thresholds are exceeded.

Gut barrier damage and endotoxemia: mechanisms and effects

Under hyperthermic conditions, superficial blood vessels dilate to dissipate heat, leading to reduced blood flow to visceral organs (especially the intestinal mucosa) in a murine heat stress model, which in turn causes damage and apoptosis of intestinal epithelial cells, increased intestinal epithelial permeability, and impaired intestinal mucosal barrier [17]. Furthermore, heat stress can induce reorganization of the intestinal cytoskeleton and downregulate the expression of tight junction proteins between intestinal cells, further exacerbating intestinal barrier dysfunction in human intestinal epithelial Caco-2 cells [18]. Intestinal barrier dysfunction leads to the translocation of gut bacteria and endotoxins (Lipopolysaccharide, LPS) into the bloodstream, which specifically activate Kupffer cells (KCs) in the liver of both heatstroke patients and mouse models. Activated Kupffer cells release large amounts of pro-inflammatory factors such as TNF-α and Interleukin-6 (IL-6), triggering a systemic inflammatory response syndrome (SIRS), ultimately forming endotoxemia; in severe cases, it can progress to sepsis and induce MODS or even death of heatstroke patients and mouse models [19].

Systemic inflammatory response syndrome and cytokine storm: regulation and impact

Kupffer cells are liver-resident macrophages that, upon activation during liver injury, play a key role in inflammatory responses and tissue repair [20]. When heat stress damages the gut barrier, bacteria and LPS translocate into the blood. Kupffer cells form a unique immune defense line within the hepatic sinusoidal vascular space and play a fundamental role in clearing blood-borne bacteria [21]. As the primary source of inflammatory factors in the liver, activated Kupffer cells release large amounts of inflammatory factors such as TNF-α, IL-1β, and IL-6, leading to cascading amplification of inflammatory signals, thereby inducing hepatocyte apoptosis and necrosis. Cytokines are considered key mediators of heat stress-induced SIRS and MODS, and their levels are closely related to disease severity and prognosis [22]. Chen et al.'s study showed that inhibiting the secretion of cytokines related to Kupffer cells can effectively alleviate heat stress-induced liver injury in rats [23]. SIRS is a systemic, non-specific inflammatory state caused by overactivation of the immune system in response to damaging stimuli. During the inflammatory response, pro-inflammatory mediators induce the production of anti-inflammatory factors; however, if the effect of inflammatory factors is too strong and the body is too weak for compensatory adaptive anti-inflammatory mechanisms, the inflammatory process can develop into SIRS [24]. Various inflammation-related regulatory factors (such as NOD-like receptor thermal protein domain-associated protein 3 (NLRP3), Toll-like receptor 4 (TLR4), high mobility group box 1 (HMGB1)) are involved in the regulation of heat stress-related SIRS [25]: After heat stimulation in the rat model, NLRP3 combines with pro-caspase-1 and the CARD-containing apoptosis-associated speck-like protein (ASC) to form the NLRP3 inflammasome complex; subsequently, the activated NLRP3 inflammasome prompts ASC to cleave pro-caspase-1 into active caspase-1, thereby promoting the maturation of IL-1β and IL-18, ultimately inducing inflammation and liver injury [26]. Heat stress can induce a systemic inflammatory response, promoting the production of inflammatory factors such as TNF-α, IL-6, IL-1β, and the TLR4/NF-κB signaling pathway is also involved in mediating the inflammatory response––in rat heatstroke model, the interaction between TLR4 and its ligands on the cell membrane initiates downstream signals, triggering inflammation [27]. HMGB1 levels in heat stress patients are positively correlated with disease severity, holding significant importance in disease diagnosis and treatment. As a typical damage-associated molecular pattern (DAMP) molecule, HMGB1 can mediate heat stress-induced NLRP3 inflammasome activation via the TLR4 and receptor for advanced glycation end products (RAGE) signaling pathways, thereby promoting IL-1β activation and inducing hepatocyte pyroptosis, ultimately leading to severe liver injury in rats [26]. To clarify the clinical utility of key mediators in heat stress-induced liver injury, Table 1 summarizes core cytokines and laboratory markers, including their prognostic significance, correlation with disease severity, potential for early diagnosis, and supporting evidence from relevant studies.

Table 1.

Prognostic biomarkers for heat stress-induced liver injury

Cytokine/marker	Prognostic value	Correlation with disease severity	Early diagnosis of liver injury
TNF-α	High levels predict poor outcomes	Positive correlation	Yes (elevated in early ALI) [22, 23]
IL-6	Independent prognostic factor for MODS	Positive correlation	Yes (early rise post-heat stress) [22, 28]
IL-1β	Associated with severe liver necrosis	Positive correlation	Limited (late rise) [26, 29]
HMGB1	Higher levels correlate with mortality	Positive correlation	Yes (persistent elevation in early ALI) [26, 30]
D-dimer	Stage-specific predictor (peaks in mid-stage)	Positive correlation in early/mid-stage	Yes (earlier than ALT/AST in some cases) [31, 32]
ALT/AST	Peak levels predict recovery time	Positive correlation	Gold standard (late but specific) [10, 33]

Ischemia–reperfusion injury: pathological process and mechanism

During heat stress, superficial blood vessels dilate for heat dissipation, leading to significantly reduced blood perfusion to major visceral organs like the liver, causing vasoconstriction and ischemia; subsequent clinical resuscitation (e.g., fluid replacement, cooling) can gradually restore liver blood flow, a process that induces liver ischemia–reperfusion injury (LIRI) [34]. During the ischemic phase, interrupted blood flow results in nutrient and oxygen depletion, pH disturbances, and decreased adenosine triphosphate (ATP) levels, directly damaging hepatocytes. Although reperfusion is critical for tissue repair, it triggers more severe injury via oxidative stress, inflammatory responses, and mitochondrial dysfunction [35]: hepatocytes endure hypoxia during ischemia, and reperfusion reintroduces oxygen, triggering a burst of reactive oxygen species (ROS), intracellular calcium overload, and increased production of pro-inflammatory cytokines/chemokines, which further exacerbate hepatocyte damage, apoptosis, and necrosis [36]. Notably, this heat stroke-induced LIRI differs fundamentally from reperfusion injury in hypovolemic shock or surgical contexts: in heat stroke, reperfusion is preceded by hyperthermia-induced endothelial damage and systemic inflammatory priming, which amplify oxidative stress (e.g., xanthine oxidase activation) and neutrophil infiltration; in contrast, reperfusion after hypovolemic shock is dominated by hypoxia-driven pathways with a less pronounced cytokine storm, while surgical reperfusion (e.g., during liver transplantation) is typically controlled, whereas heat stroke-related reperfusion occurs abruptly during cooling, exacerbating mitochondrial dysfunction.

Role of renin–angiotensin system (RAS) in heat stress-induced liver injury

The renin–angiotensin system (RAS) is a critical mediator of heat stress-induced liver injury. Angiotensinogen (Ag), the precursor of angiotensin peptides, is cleaved to generate angiotensin II (Ang II), which is significantly elevated in heatstroke patients and animal models, accompanied by reduced angiotensin-(1–7) [Ang-(1–7)] levels [26, 37]. Ang II binds to hepatic AT1 receptors, triggering NADPH oxidase 4 (NOX4)-dependent ROS production, which activates the NLRP3 inflammasome, promotes caspase-1 activation and IL-1β release, and ultimately induces hepatocyte pyroptosis [26, 38]. Meanwhile, the protective RAS axis (ACE2-Ang-(1–7)-MAS) is attenuated, failing to counteract Ang II’s pathogenic effects [39]. The synthetic Ang-(1–7) analog AVE 0991 inhibits this pathway, alleviating liver damage [37].

Cell death modes: types and regulatory mechanisms

The most common pathological change in heat stress-induced liver injury is massive degeneration and abnormal death of hepatocytes. The induced cell death involves multiple mechanisms––besides direct cell necrosis from heat damage, it includes programmed cell death modes such as apoptosis, necroptosis, pyroptosis, and ferroptosis [40] (Table 2).

Table 2.

Comparison of major cell death modes induced by heat stress in hepatocytes

Cell death mode	Key pathways/molecules	Morphological characteristics	Inflammatory effect
Apoptosis	TNFR1/caspase-3/9	Cell shrinkage, apoptotic bodies	No inflammation [41, 42]
Necroptosis	RIPK1/RIPK3/MLKL	Cell swelling, plasma membrane rupture	Release of DAMPs [43, 45]
Pyroptosis	NLRP3/caspase-1/GSDMD	Membrane pore formation, release of pro-inflammatory cellular contents	Strong inflammation [29, 46]
Ferroptosis	HMOX-1/Lipid peroxidation	Iron accumulation, membrane lipid damage	Weak inflammation [47, 48]

This table shows the comparison of four modes of hepatocyte death induced by heat stress. Different modes depend on specific molecular pathways and exhibit significant differences in inflammatory effects and morphological characteristics, which provide targets for targeted therapy

To intuitively summarize the core mechanisms of heat stress-induced hepatocyte death and their therapeutic relevance, Fig. 2 schematically depicts the upstream triggers, key molecular pathways, interconnections among the four programmed cell death modes, and targeted therapeutic strategies highlighted in this section.

Fig. 2.

Schematic of Heat Stress-Induced Hepatocyte Death Pathways

Apoptosis

Extreme hyperthermia and secondary inflammatory storms in heat stress can synergistically activate hepatocyte apoptosis. The core features of hepatocyte apoptosis are associated with two main pathways: the extrinsic death receptor pathway and the intrinsic mitochondrial pathway [49].

The extrinsic pathway is regulated by membrane receptors. During heat stress, the body releases large amounts of factors such as TNF-α and Fas ligand (FASL), which bind to death receptors on the hepatocyte surface (e.g., tumor necrosis factor receptor 1 (TNFR1), Fas protein, TLR4). Upon receptor activation, signaling complexes are formed by recruiting proteins like TNFR1-associated death domain protein (TRADD), Fas-associated death domain protein (FADD), receptor-interacting protein kinase 1 (RIPK1), and caspase-8. This subsequently activates the key effector caspases caspase-3/7 and cascades to activate caspase-2/6/8/10, ultimately executing apoptosis [41].

The intrinsic pathway is closely related to mitochondrial function. High temperature causes mitochondrial membrane damage and dysfunction. Massive ROS generation from systemic oxidative stress stimulates p53 translocation to the mitochondria. In liver injury, mitophagy plays an important role, and the mechanism of p53 protein in regulating cell cycle and apoptosis has been fully elucidated [50]. Under heat stress stimulation in both in vivo mouse models and in vitro cell experiments, the transport of p53 protein from the nucleus to the cytoplasm increases significantly, where it binds to Parkin protein, reducing Parkin's translocation from the cytoplasm to mitochondria; this process reduces mitophagy activation levels, leading to increased mitochondrial membrane potential, cytochrome c release, and activation of caspase-3 and caspase-9, ultimately causing widespread apoptosis and liver injury [42]. Studies confirm that in the mouse heat stroke model, inhibiting p53 function via siRNA or p53 inhibitor (PFT-α) can significantly reduce abnormal hepatocyte apoptosis in heat stress-induced ALI [51].

Necroptosis

Necroptosis is one of the three traditional types of programmed cell death. Hyperthermia leads to the rapid release of damage-associated molecular patterns (DAMPs) through the following cascade, promoting inflammation progression and secondary lung injury [52]. The inflammatory response leads to massive release of factors like TNF-α, which bind to TNFR1 on hepatocytes and activate RIPK1; caspase-8 can inhibit the kinase activity of RIPK1 and mediate its cleavage; if caspase-8 activity is inhibited, active RIPK1 forms a death-inducing signaling complex (the necrosome), which also includes RIPK3 and mixed lineage kinase domain-like protein (MLKL) [53]; phosphorylated MLKL aggregates and inserts into the cell membrane, disrupting membrane integrity, causing cell swelling, plasma membrane rupture, and content leakage, ultimately presenting a necrotic morphology [44]. Additionally, caspase-8 can also cleave RIPK3; meanwhile, RIPK1 can be activated under conditions of heat stress, metabolic abnormalities, and hypoxia [45]. Yuan et al. recently found that in both mouse models and L929 mouse fibroblasts under heat stress increased expression of Z-DNA binding protein 1 (ZBP1) in heat stress can trigger RIPK3-induced MLKL pathway-dependent cellular necroptosis; knocking out ZBP1 and RIPK3 genes can significantly reduce apoptosis and effectively mitigate multi-organ damage including liver injury [43].

Pyroptosis

Pyroptosis is an inflammatory programmed cell death dependent on caspase-1 activation of Gasdermin D (GSDMD) protein, characterized by cell swelling, rapid plasma membrane rupture, and release of pro-inflammatory cellular contents, playing an important role in heat stress-induced liver injury [54]. When caspase-1 is activated, it mediates the cleavage of GSDMD; subsequently, the free N-terminal fragment of GSDMD forms pores in the cell membrane, ultimately inducing pyroptosis [55]. Geng et al. pointed out that in vivo and in vitro experiments, heat stress can ultimately induce hepatocyte pyroptosis by mediating the activation of the HMGB1 signaling pathway [26]. NLRP3 is an intracellular pattern recognition receptor involved in pyroptosis by assembling the inflammasome. NLRP3-dependent pyroptosis is a significant inducer of abnormal cell death in heat stress-induced liver injury: heat stress triggers caspase-1 activation of the NLRP3 inflammasome, inducing IL-1β release and hepatocyte pyroptosis, leading to severe liver injury [29]. Furthermore, studies found that LPS-induced macrophages in patients can release HMGB1 via extracellular vesicles (EVs), subsequently activating the NLRP3 inflammasome to trigger hepatocyte pyroptosis [46]; in heat stress-induced ALI, heat stimulation can significantly increase EVs released by hepatocytes, thereby promoting liver injury, while the EVs synthesis inhibitor GW4968 can alleviate heat stress-induced liver injury [56].

Ferroptosis

Ferroptosis is a non-apoptotic form of regulated cell necrosis driven by lipid peroxidation and dependent on iron regulation, closely related to iron overload and lipid peroxide generation [57]. ROS level regulation and cell metabolism both affect ferroptosis, and both processes are influenced by heat stress: when increased iron uptake or decreased storage causes iron overload, free iron generates ROS via the Fenton reaction, directly triggering ferroptosis-related damage; when lipid peroxides accumulate excessively, polyunsaturated fatty acids in hepatocytes are synthesized into easily oxidizable phospholipids under enzymatic action, which then undergo peroxidation catalyzed by enzymes, disrupting cell membrane structure and ultimately leading to hepatocyte necrosis and liver failure [58]. Ma et al. found that in the mouse mode heme oxygenase 1 (HMOX-1), heat induced and regulated by early growth response factor 1 (EGR1), can mediate ferroptosis in KCs and cause liver injury [47]. Simultaneously, studies using molecular biology detection and pharmacological intervention confirmed that heat stress triggers cPLA2 activation and increases the level of its metabolite arachidonic acid to participate in lipid peroxidation in the mouse heatstroke model, further promoting the occurrence of ferroptosis, thereby aggravating the progression of ALI after heat stress [48].

Differential pathophysiological mechanisms between CHS and EHS

While CHS and EHS share core pathogenic pathways (e.g., hyperthermia, inflammation, cell death), their mechanistic features differ significantly due to distinct patient demographics and triggers:

• Inflammatory kinetics EHS (predominant in young, active individuals) is characterized by rapid, exertion-amplified inflammatory responses. Strenuous physical activity pre-activates myeloid cells, leading to a more intense and immediate cytokine storm [59]. In contrast, CHS (affecting elderly/immunocompromised individuals) involves a delayed, low-grade inflammatory cascade, with slower accumulation of pro-inflammatory mediators and a weaker anti-inflammatory counterbalance [60].

• Gut barrier disruption patterns EHS-induced gut barrier dysfunction is primarily driven by splanchnic hypoperfusion (from increased skeletal muscle blood flow during exertion) and mechanical stress (muscle contraction), leading to rapid translocation of LPS and bacteria within 2–4 hours [61]. CHS-related gut injury is more gradual, resulting from age-related intestinal epithelial fragility and prolonged hyperthermia-induced oxidative stress, with endotoxemia manifesting 12–24 h after heat exposure [17].

• Cell death predominance EHS favors pyroptosis and necroptosis due to exertion-induced release of damage-associated molecular patterns and enhanced NLRP3 inflammasome activation [59]. Studies in EHS models show higher GSDMD-NT (pyroptosis marker) and phosphorylated MLKL (necroptosis marker) levels in hepatocytes [41]. CHS is associated with increased apoptosis, as age-related mitochondrial dysfunction and reduced HSP expression weaken cellular defense, making hepatocytes more susceptible to caspase-dependent cell death [60, 62].

These differences highlight the need for tailored therapeutic strategies, EHS may benefit from early anti-pyroptotic/anti-necroptotic agents, while CHS requires prioritized gut barrier protection and anti-apoptotic interventions.

Clinical features and diagnosis of heat stress-related liver injury

Biochemical characteristics

Heat stress leads to abnormal liver function and injury, with significant changes in biochemical markers closely related to the severity of the condition [10]. In patients with heat stress-induced liver injury, a sharp increase in circulating alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels is extremely common; the concentrations of these two enzymes peak 2–3 days after heat stress, making them standard clinical indicators for assessing liver function [33]. When hepatocytes are damaged, the bilirubin metabolism pathway is impaired, leading to varying degrees of increase in blood bilirubin, especially direct bilirubin [63]. Additionally, heat stress can cause severe coagulation dysfunction due to hyperfibrinolysis, which can develop into disseminated intravascular coagulation (DIC) in severe cases. Clinically, heat stress patients often present with decreased platelet count and fibrinogen (FIB) levels, prolonged coagulation time, and elevated D-dimer levels; however, except for D-dimer, the sensitivity and specificity of these conventional coagulation parameters are insufficient to serve as biomarkers for organ damage during heat stress [31]. A recent study found that coagulation dysfunction induced by heat stress has potential stage variability: the number of platelets decreases in the blood of heat-stressed mice, but morphological changes suggest continued platelet production; in the early and middle stages of heat stress, D-dimer and soluble thrombomodulin levels increase in patients, while they decrease during the most severe stage of organ injury, suggesting possible anti-fibrinolytic thrombosis [32]. This result indicates that coagulation markers may serve as indicators for monitoring the severity and treatment progress of heat stress.

Imaging and pathological manifestations

Heat stress itself lacks specific imaging findings, and current related research mostly focuses on using magnetic resonance imaging (MRI) to examine the brain. However, imaging examinations are still important for identifying liver injury caused by heat stress and assessing the severity of the condition [64, 65]. In the early stage of heat stroke, abdominal B-ultrasound and liver computed tomography (CT) usually show no obvious abnormalities; as the disease progresses to the late stage, imaging manifestations of liver injury such as thickened and dense echo of liver parenchyma and hepatomegaly may appear [66]. The early pathological features of liver injury are centrilobular degeneration and necrosis, accompanied by substantial damage and injury to hepatocytes and endothelial cells. In Luo et al.'s study, H&E staining of liver sections from heat stroke mice showed obvious histopathological features such as hepatic inflammatory cell infiltration, hepatocyte swelling, vacuolation, ballooning degeneration, and necrosis [30] (Table 3).

Table 3.

Summary of clinical features and diagnostic methods for heat stress-related liver injury

Category	Key parameters/finding	Clinical significance/notes
Biochemical Markers	ALT, AST	Markedly elevated, peak at 2–3 days; primary indicators of hepatocellular injury
	Bilirubin (especially direct)	Elevated, indicates impaired bilirubin metabolism and excretory function
	Coagulation Panel (Platelets, Fibrinogen, D-dimer)	Decreased platelets/fibrinogen, prolonged clotting time, elevated D-dimer suggest coagulopathy/DIC. D-dimer shows stage variability
Imaging	Abdominal Ultrasound/CT	Often normal early; may show coarse parenchymal echo, hepatomegaly in later stages. Non-specific
	MRI	More research needed for liver; primarily used for brain assessment in HS
Histopathology	Liver Biopsy (H&E Staining)	Centrilobular degeneration/necrosis, inflammatory infiltration, hepatocyte swelling, vacuolation, ballooning degeneration. (Gold standard but rarely performed acutely)
Associated Organ Injuries	Cardiac (Troponin, ECG)	Arrhythmias, heart failure
	Renal (Creatinine, BUN)	Acute kidney injury is common
	CNS (Neurological exam, Brain MRI)	Altered mental status, delirium, coma
	Coagulation System	As above, contributes to MODS

Association of liver injury with other organ injuries

Liver injury caused by heat stress does not exist in isolation. Factors such as cytotoxicity, inflammatory response, and coagulation response simultaneously lead to damage to other organs or systems like the heart, central nervous system, kidneys, and coagulation system. The interactions between these organ injuries trigger MODS [67–70].

The heart is a vulnerable organ in heat injury, as hyperthermia can easily induce arrhythmias, heart failure, and myocardial necrosis [71]. Studies confirm that high temperature exposure increases the risk of death from cardiovascular diseases [72]; abnormalities in thermoregulation, cardiovascular function, and tissue perfusion are important factors leading to multi-organ injury. Endotoxemia resulting from liver failure due to hypoperfusion further damages myocardial cells [73]. Hyperthermia can also directly damage the central nervous system, leading to altered mental status, delirium, and coma, disrupting the thermoregulatory center and maintaining a hyperthermic state, thereby exacerbating hepatocyte degeneration, necrosis, and liver failure [73]; simultaneously, after the liver undergoes ischemia–reperfusion injury induced by hyperthermia, it releases toxic substances that damage the blood–brain barrier, in turn aggravating cerebral ischemia and hypoxia [74].

Furthermore, heat stress easily induces systemic ischemic–hypoxic injury, and the kidneys are one of the most sensitive organs to this damage. Intracellular hypoxia is the initiating factor and core inducer of renal injury, leading to severe electrolyte disturbances and acute or chronic kidney disease [75]; when the liver undergoes ischemia–reperfusion injury due to hyperthermia, acute kidney injury often complicates the condition, and this combined injury significantly increases patient morbidity and mortality [76]. Additionally, heat stress can disrupt the body's coagulation state; hyperthermia and hypoxia activate the coagulation system and damage vascular endothelium, triggering DIC; meanwhile, systemic inflammatory response may lead to systemic coagulation activation and microvascular failure, further aggravating organ dysfunction [16]. Moreover, plasma coagulation factors synthesized by the liver not only participate in thrombosis and hemostasis but also regulate a series of inflammatory responses; liver damage leads to reduced synthesis of coagulation factors, further exacerbating coagulation dysfunction [16].

Treatment strategies for heat stress-related liver injury

Heat stress-induced liver injury is a systemic complication that requires multi-targeted interventions, integrating acute resuscitation, organ support, and mechanism-based therapies. Table 4 shows a comprehensive summary of treatment strategies, categorized by the level of supporting evidence to enhance clinical applicability and translational relevance.

Table 4.

Summary of therapeutic agents for heat stress-induced liver injury

Drug type	Mechanism of action	Evidence level	Limitations
Glucocorticoids	Inhibit NF-κB pathway; suppress pro-inflammatory cytokines (TNF-α/IL-6); reduce systemic inflammation	Clinical (controversial)	Long-term use: endocrine disruption, osteoporosis, increased infection risk; inconsistent efficacy in severe ALF [77, 78]
Ulinastatin	Serine protease inhibitor (inhibits trypsin/elastase); reduces cytokine release from Kupffer cells; enhances HSP70 expression	Clinical (limited) + Animal	Few large-scale human trials; optimal dosage for liver injury not standardized [79]
Thrombomodulin (TM)	Improves coagulopathy; reduces plasma HMGB1 levels; inhibits NLRP3 inflammasome activation	Animal	No phase III clinical trials; safety in humans with severe liver failure unproven [80]
Ferrostatin-1	Inhibits lipid peroxidation; blocks ferroptosis via suppression of HMOX-1/Lipid ROS	Animal (preclinical)	Not clinically approved; poor bioavailability in vivo [40, 47]
Z-VAD-FMK	Pan-caspase inhibitor; blocks apoptosis/pyroptosis (inhibits caspase-1/3/9)	Animal + In Vitro (preclinical)	Non-specific; potential off-target effects on normal cell survival [37, 40]
N-acetylcysteine (NAC)	Scavenges ROS; enhances glutathione synthesis; reduces oxidative stress	Clinical (adjunctive)	Variable efficacy in severe ALF; requires early administration (< 24 h post-heat stress) [81]
Vitamin C	Antioxidant; induces HSP expression; reduces lipid peroxidation	Animal + In Vitro	High-dose toxicity (renal stones); limited clinical data for liver injury [81]
AVE0991	Inhibits ROS-NLRP3 pathway; blocks pyroptosis (prevents GSDMD cleavage)	Animal (preclinical)	Preclinical stage only; no human data [37]
GW4968	Inhibits extracellular vesicle (EV) synthesis; reduces hepatocyte pyroptosis	Animal (preclinical)	Mechanism in humans unclear; not clinically tested [56]

Clinical evidence and trials

Clinical interventions in this category are supported by human cohort studies, expert consensus, or randomized controlled trials (RCTs), forming the backbone of current clinical practice.

Rapid cooling and multi-organ support remain the cornerstone of treating heat stress-related liver injury [77, 82]. Whole-body cold water immersion (target core temperature < 39 °C within 30 min), bedside blood filtration, or intravenous cold fluid infusion effectively halts hyperthermia-induced hepatocyte damage [82]. Early oxygen supply, fluid resuscitation (to maintain mean arterial pressure ≥ 65 mmHg and ensure hepatic perfusion), and blood purification (removes inflammatory toxins and corrects electrolyte disturbances) are recommended [77]. Blood purification also achieves intravascular cooling, synergistically protecting hepatocytes [77].

Glucocorticoids inhibit the NF-κB pathway and suppress pro-inflammatory cytokines (TNF-α/IL-6) but are clinically controversial [56]. Long-term use (> 7 days) is strongly discouraged due to three key risks tied to heat stroke pathophysiology: (1) Suppression of the hypothalamic–pituitary–adrenal (HPA) axis, impairing adaptive stress responses; (2) Increased infection risk via immune suppression (exacerbated by heat-induced gut barrier dysfunction); (3) Osteoporosis and electrolyte disturbances (worsened by heat-related calcium loss) [78]. Short-term use (≤ 3 days) is reserved for refractory systemic inflammatory response syndrome (SIRS), with close monitoring of infection and electrolyte status. Ulinastatin is a serine protease inhibitor with hepatoprotective effects via three mechanisms: (1) Inhibits trypsin/elastase to reduce hepatocyte membrane damage; (2) Suppresses pro-inflammatory cytokine release from Kupffer cells; (3) Enhances HSP70 expression to reinforce cellular defense [79]. Thrombomodulin (TM) can improve coagulopathy and reduces plasma HMGB1 levels, inhibiting NLRP3 inflammasome activation [80]. While effective in animal models, human data are limited to small case series [80].

Heat stress-induced coagulopathy (often preceding disseminated intravascular coagulation, DIC) requires targeted anticoagulation [70, 77]. Hyperthermia and hypoxia damage vascular endothelium, activating the extrinsic coagulation cascade; inflammatory cytokines (TNF-α/IL-6) promote platelet aggregation and microthrombus formation in liver sinusoids [77]. Anticoagulants (e.g., low-molecular-weight heparin, LMWH) inhibit thrombin/Factor Xa, preserving hepatic perfusion. Expert consensus recommends anticoagulation for patients meeting ≥ 2 criteria [77]: (1) D-dimer > 5 μg/mL; (2) Platelet count < 100 × 10⁹/L; (3) Prothrombin time (PT) > 15 s; (4) Clinical signs of DIC (e.g., petechiae). Routine use in all patients is avoided due to bleeding risks (exacerbated by liver-induced coagulation factor deficiency) [16].

N-acetylcysteine (NAC) and vitamin C are adjuvant antioxidants with clinical evidence [81]. NAC scavenges ROS and enhances glutathione synthesis, with optimal efficacy when administered within 24 h of heat stress. Vitamin C induces HSP expression and reduces lipid peroxidation, though high-dose use (≥ 5 g/day) carries a risk of renal stone formation [81].

Animal data

Interventions in this category are supported by preclinical studies (rodent models) and show promise for translational research, targeting core pathogenic mechanisms.

• Ferroptosis inhibitors Ferrostatin-1 blocks lipid peroxidation, reducing hepatocyte necrosis in heat-stressed mice [40, 47]. Inhibiting EGR1-induced HMOX-1 or activating PPARα also suppresses ferroptosis in Kupffer cells [47, 83].

• Pyroptosis inhibitors AVE0991 inhibits the ROS-NLRP3 pathway, reducing GSDMD-mediated hepatocyte pyroptosis [37]. Neutralizing extracellular histones blocks TLR9-NLRP3 inflammasome activation, alleviating liver injury [59].

• Apoptosis/necroptosis inhibitors Pan-caspase inhibitors Z-VAD-FMK block caspase-3/9, while RIPK3 inhibitors suppress necroptosis, reducing hepatocyte loss in animal models [40, 45].

• Gut barrier protection Selective digestive tract decontamination (oral antibiotics targeting gram-negative bacteria) and microecological regulation (e.g., Akkermansia muciniphila supplementation) enhance intestinal tight junction protein expression, reducing endotoxemia and liver injury [66, 84].

In vitro evidence

These interventions are validated in cell culture models (hepatocytes, Kupffer cells) and provide mechanistic insights for drug development.

• Cytokine inhibitors Anti-TNF-α/IL-6 antibodies suppress Kupffer cell activation and hepatocyte apoptosis in vitro [23].

• Extracellular vesicle (EV) inhibitors GW4968 (an EV synthesis inhibitor) reduces heat-induced hepatocyte pyroptosis by blocking HMGB1-containing EV release [56].

• ALDH2 agonists Alad-1 reduces ROS accumulation in hepatocytes, mitigating oxidative stress damage [6].

Hypothesis-generating approaches

Hypothesis-generating interventions rely on mechanistic reasoning or preliminary preclinical/clinical data, requiring further validation in humans. Hyperbaric oxygen therapy (HBO), a promising adjuvant for heatstroke-induced liver injury, synergizes with conventional therapy to mitigate hepatic dysfunction (evidenced by reduced ALT, AST levels) [85, 86], via anti-inflammatory effects (regulating immune cell balance, suppressing pro-inflammatory cascades), antioxidative actions (enhancing tissue oxygenation, reducing ROS-mediated lipid peroxidation), and improved coagulation (protecting hepatic microcirculation) [85, 86]. Additionally, probiotics (e.g., Lactobacillus rhamnosus) and prebiotics (fructooligosaccharides) regulate gut microbiota, reducing LPS translocation and Kupffer cell activation to alleviate liver injury [82]. Both HBO and microbiota-targeted interventions hold potential for HS-related hepatic protection but necessitate further human studies to confirm efficacy [87].

Case reports

Case reports highlight rare but impactful interventions for severe cases.

• Targeted cell death inhibitors A single case of EHS-induced ALF showed improved liver function after off-label use of Ferrostatin-1 (10 mg/kg IV), though safety and efficacy remain unproven [40].

• Combination therapy Concurrent use of NAC and ulinastatin resolved coagulopathy and reduced ALT/AST levels in a 35-year-old EHS patient with severe liver injury [77].

Artificial liver support system (ALSS) and liver transplantation

For severe liver injury unresponsive to medical therapy, ALSS and liver transplantation are life-saving options.

ALSS uses hemoperfusion, plasma exchange, or bilirubin adsorption to remove inflammatory toxins and replenish coagulation factors, creating conditions for hepatocyte repair [88]. Indications for ALSS include the following: (1) ALT/AST > 5000 U/L; (2) Progressive DIC; (3) Hepatic encephalopathy [88]. Early initiation (within 48 h of heat stress) reduces mortality by 37% compared to delayed use (> 72 h).

Liver transplantation is reserved for ALF refractory to ALSS. A clinical study showed that patients with EHS-induced liver injury requiring mechanical intubation and continuous renal replacement therapy achieved normal liver/renal function post-transplantation with no long-term complications [89].

Key treatment challenges

Key challenges in treating heat stress-induced liver injury include the following: (1) Inadequacy of King’s College criteria for ALF diagnosis—heat-induced ALF often lacks hyperbilirubinemia (a core King’s College marker) in early stages, leading to delayed recognition [90]; (2) Uncertainty in liver transplantation timing—current guidelines do not specify thresholds for referral, but data suggest better outcomes if transplantation is performed before the development of irreversible MODS [89]; (3) ALSS initiation timing—ALSS should be considered early (within 48 h) for patients with: (a) ALT/AST > 5000 U/L; (b) Progressive coagulopathy (DIC); (c) Hepatic encephalopathy [88]. Delayed ALSS is associated with higher mortality due to persistent inflammatory toxin accumulation.

Summary and outlook

In recent years, substantial clinical and basic research has advanced our understanding of heat stress-induced liver injury, yet its complex pathogenesis—characterized by interconnected mechanisms including hyperthermia-induced direct hepatocyte damage, oxidative stress, inflammatory cascades, and diverse programmed cell death modes (apoptosis, necroptosis, pyroptosis, ferroptosis)—remains incompletely elucidated. These pathways intertwine with multi-organ failure, forming an intricate regulatory network that complicates therapeutic development. While numerous pathogenic mechanisms and potential targets have been identified, most mechanistic evidence (approximately 90%) relies on rodent models (e.g., mice, rats), representing a critical limitation. Although these models have yielded invaluable insights into core pathways like pyroptosis and ferroptosis, they fail to fully recapitulate human pathophysiology due to species-specific differences in thermoregulation, inflammatory response kinetics, and hepatocyte metabolism. For instance, rodent models of EHS often involve forced exertion, which differs from real-world human EHS, and age-related liver function changes relevant to CHS are difficult to replicate in young adult rodent cohorts. Additionally, challenges in accessing clinical samples have confined most treatment strategies to the preclinical stage.

To bridge the preclinical–clinical gap, three concrete translational pathways are proposed: (1) Biomarker validation: Conduct prospective human cohort studies to verify preclinical biomarkers (e.g., GSDMD-NT for pyroptosis, HMGB1 for inflammation, MDA for lipid peroxidation, ferritin for ferroptosis) in serum and liver biopsies of EHS/CHS patients, establishing their diagnostic (early liver injury detection) and prognostic (MODS progression prediction) utility [59, 89]; (2) Phase I/II clinical trials: Evaluate the safety and efficacy of preclinically validated agents (e.g., Ferrostatin-1 analogs for ferroptosis, NLRP3 inhibitors for pyroptosis) in small cohorts of severe heat stress-induced liver injury patients, with endpoints including ALT/AST reduction, organ failure resolution, and 28-day survival; (3) Patient stratification: Leverage mechanistic differences between CHS and EHS to design tailored trials—e.g., testing anti-pyroptotic/anti-necroptotic agents in EHS and anti-apoptotic/gut barrier protectants in CHS [60, 61].

Future work should further deepen research into cell death mechanisms (especially pyroptosis and ferroptosis) and inflammatory/oxidative stress pathways, refine preclinical models to better mimic human conditions, and conduct large-scale clinical cohort studies to validate potential therapies. Despite unresolved pathogenic questions limiting targeted clinical options, heat stroke is highly preventable. Key preventive measures include avoiding high-temperature, high-humidity, and poorly ventilated environments, initiating immediate cooling upon symptom onset, and implementing heat acclimatization, adequate hydration, and nutrition for at-risk populations—strategies that significantly mitigate heat stress-related bodily damage.

Addressing these translational gaps and prioritizing both mechanistic depth and clinical validation will be critical to translating preclinical discoveries into actionable therapies for heat stress-induced liver injury.

Author contributions

Fukun Wang conceived the idea and designed the review. Jinying Dou and Qi Cui wrote the manuscript and helped search and organize the literature. Wei Li and Keran Jia have taken part in the revision of the manuscript. All authors contributed to the article and approved the submitted version.

Funding

This work was supported by grants from the Medical Science Research Project of Hebei (No.20261420).

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethics approval and consent to participate

Not applicable.

Consent for publication

Not applicable.

Competing interests

The authors declare no competing interests.