The research progress of α-ketoglutarate in osteoarthritis

Abstract

α-Ketoglutarate (AKG) is a key intermediate in the tricarboxylic acid, (TCA) cycle. AKG is not only involved in cellular energy metabolism but also plays important roles in a variety of physiological and pathological processes such as antioxidant activity, anti-inflammatory effects, immune regulation, and maintenance of mitochondrial function, which have garnered widespread attention. Many experiments have shown that there is a certain correlation between AKG and OA. The purpose of this paper is to comprehensively review the literature to elucidate the mechanisms of AKG in alleviating osteoarthritis (OA), such as autophagy, gut microbiota, cellular senescence, and ferroptosis. We aim to provide theoretical references and evidence for the use of AKG in the prevention and treatment of OA.

Highlights

• •AKG shows therapeutic promise by targeting multiple pathological processes, offering a potential OA treatment avenue.

1. Introduction

α-Ketoglutarate (AKG), also known as 2-oxoglutarate, is a key intermediate in the tricarboxylic acid (TCA) cycle, participating in or regulating a variety of physiological and pathological processes [1,2]. Studies have shown that AKG plays a significant role in anti-inflammation, oxidative stress regulation, and protein synthesis as well as in energy metabolism [1]. Moreover, AKG is essential for maintaining cellular metabolism and homeostasis and also participates in regulating complex biological processes such as epigenetic modifications, apoptosis, and immune responses [2]. Therefore, AKG may serve as a promising metabolic regulatory factor and offer new therapeutic insights for age-related metabolic diseases.

Osteoarthritis (OA) is a disease closely related to aging and metabolism, primarily characterized by joint pain, stiffness, deformities, and limited mobility. As OA progresses, the frequency and severity of pain symptoms significantly increase, severely affecting the quality of patients' life [3]. OA is a leading cause of global disability, affecting more than 7% of the global population (approximately 528 million people) [4]. Currently, no effective treatments are available to inhibit OA progression, and existing therapies provide only limited symptomatic relief [5]. Therefore, it is crucial to identify effective therapeutic targets for OA to control its progression.

Recently, studies have suggested that AKG plays an important role in bone metabolism and joint cartilage health [6,7]. This review aims to summarize the research on the role of AKG in regulating inflammation, oxidative stress, mitochondrial function, apoptosis, autophagy, gut microbiota composition, cellular senescence, ferroptosis, and HIF-1α. The study aims to provide new insights into how AKG alleviates OA through these mechanisms and offer novel perspectives and ideas for future research.

2. Overview of AKG

AKG exerts diverse biological effects through multiple pathways, including acting as a co-substrate for dioxygenases involved in DNA and histone demethylation, which are essential for epigenetic regulation and maintenance of cellular pluripotency [8,9]. Studies have shown that AKG maintains embryonic stem cell pluripotency by influencing the cellular AKG/succinate ratio, which in turn regulates chromatin-modifying enzymes such as ten-eleven translocation (TET) DNA hydroxylases and Jumonji-C domain-containing histone demethylases [9]. AKG is also involved in antioxidative processes. It scavenges reactive oxygen species (ROS) and reactive nitrogen species and supports the activity of endogenous antioxidant enzymes (superoxide dismutase (SOD) and catalase), thereby protecting cells from oxidative stress-induced damage [10,11]. Furthermore, AKG has shown potential in modulating inflammation, regulating collagen synthesis, supporting skeletal health, and delaying the progression of aging through its effects on various signaling pathways [[12], [13], [14]]. Moreover, AKG maintains mitochondrial function by promoting mitophagy, facilitating the removal of damaged mitochondria, and reducing ROS production [6]. In aging mouse models, dietary supplementation with a calcium salt of AKG shows significant effects in extending median lifespan and compressing morbidity, as evidenced by delayed onset and reduced severity of multiple age-related phenotypes, including improved frailty index scores [13]. AKG also participates in the regulation of systemic immune responses, as well as muscle and tissue metabolism. In cancer-induced cachexia models, AKG could attenuate muscle wasting by downregulating the expression of pro-inflammatory genes such as FN14, thus alleviating systemic inflammation and preserving muscle mass [15].

Collectively, AKG, a key metabolic and signaling molecule with broad biological activity, plays essential roles in cellular metabolism, antioxidative defense, epigenetic regulation, immune modulation, and tissue homeostasis, providing potential therapeutic value for aging, metabolic disorders, cancer-associated cachexia, and skeletal disease.

3. The Association between AKG and OA

Growing evidence has demonstrated a significant correlation between AKG and OA. In a three-dimensional cryogel matrix culture model, AKG supplementation could significantly enhance chondrocyte proliferation and extracellular matrix (ECM) accumulation, indicating its potential to support cartilage regeneration relevant to OA pathology [16]. AKG could also reduce oxidative damage and increase ECM production in a chondrocyte model treated with interleukin-1β (IL-1β) [6,7].

Moreover, He et al. found that in an OA mouse model, intra-articular injection of AKG could notably reduce cartilage degradation and improve histological scores, highlighting its protective effects on joint integrity [7]. Furthermore, in a murine model of temporomandibular joint OA, AKG supplementation improves both age-related and post-traumatic cartilage damage [17]. In an intervertebral disc degeneration rat model, long-term AKG administration reduces inflammatory cytokine expression and mitigates ECM degradation through inhibition of the IL-6/JAK2/STAT3 signaling pathway [18]. Additionally, the use of AKG-loaded hyaluronic acid nanoparticles in OA rat models shows sustained cartilage protection, with notable improvements in matrix production and a reduction in chondrocyte apoptosis [19]. Further evidence from an OA model treated with AKG indicates improvements in cartilage structure and a reduction in oxidative stress levels, reinforcing its potential to mitigate OA-related damage [6]. Another study involving female rats undergoing gastrectomy demonstrates that dietary AKG reduces cartilage thinning and growth plate disruption [20].

In summary, these findings provide robust experimental evidence for the correlation between AKG and OA. Across diverse species and disease models, AKG and its analogs consistently demonstrate a beneficial impact on cartilage preservation and structural integrity, laying a foundation for their potential therapeutic application in OA management.

4. Mechanisms by which AKG alleviates OA

4.1. AKG alleviates OA by regulating inflammation and oxidative stress

Research have shown that both inflammation and oxidative stress are crucial in the pathogenesis of OA [21,22]. Chronic inflammation not only triggers inflammatory response through the secretion of pro-inflammatory cytokines such as IL-1β and tumor necrosis factor-α (TNF-α) in synovial and chondrocyte cells but also induces the secretion of matrix metalloproteinases (MMP), thereby promoting the degradation of the ECM [22,23]. Oxidative stress, defined as an imbalance between the production of ROS and the capacity of antioxidant defense systems to neutralize them, plays a critical role in cellular dysfunction [24]. This redox imbalance triggers a cascade of pathological events, including the activation of inflammatory and apoptotic pathways, the disruption of organelle function, and the disturbance of cellular homeostasis. However, under oxidative stress, intracellular ROS levels rise significantly, and excessive ROS accumulation promotes chondrocyte apoptosis and cartilage degradation [25,26]. Therefore, modulating inflammation and oxidative stress may be an effective therapeutic target for OA.

AKG has been demonstrated to exhibit anti-inflammatory and antioxidant properties [27,28]. AKG reduces inflammation and oxidative damage and restores mitochondrial function through the AMPK-PGC-1α/Nrf2 pathway, thereby alleviating fatty liver induced by a high-fat diet [29]. Studies have also shown that AKG supplementation significantly reduced the levels of pro-inflammatory cytokines secreted by synovial macrophages, further reinforcing its anti-inflammatory effects [28,29]. In addition, in vitro cultured chondrocytes, it has been found that AKG can inhibit the expression of pro-inflammatory factors (such as IL-6 and TNF-α) and the activity of MMP-13 and MMP5 induced by IL-1β through downregulation of the NF-κB signaling pathway [22,23,30].

Although AKG exhibits radical scavenging capacity, its direct role in neutralizing free radicals is relatively limited [31,32]. Studies demonstrate that, at neutral pH, AKG can scavenge ROS, such as hydrogen peroxide (H₂O₂), through a non-enzymatic oxidative decarboxylation process, generating succinate, carbon dioxide, and water, without compromising the primary immune system [33,34]. Experimental studies demonstrate the capacity of AKG to prevent peroxynitrite-induced protein nitration, particularly at tyrosine residues, in cellular models. The peroxynitrite-scavenging ability of AKG is demonstrated by its inhibition of protein nitration, including that of bovine serum albumin [32,33,35]. This protective mechanism is critical in preventing oxidative modifications commonly observed in pathological conditions such as inflammation, neurodegeneration, and cancer, where elevated levels of peroxynitrite are frequently reported [31,33]. Moreover, the antioxidative effects of AKG extend beyond scavenging peroxides and peroxynitrite to include the enhancement of cellular redox balance by upregulating endogenous antioxidant enzymes, such as SOD, catalase, and glutathione peroxidase [33]. These enzymes play a critical role in neutralizing ROS, thereby reducing oxidative damage and inflammation in tissues affected by conditions such as OA and hyperlipidemia [[31], [32], [33], [34]]. AKG upregulates these antioxidant pathways, thereby providing cellular protection against oxidative stress-induced damage and supporting the maintenance of mitochondrial function and overall cellular integrity. Studies have also shown that AKG activates the nuclear factor erythroid 2-related factor 2 (Nrf2) signaling pathway, enhancing the expression of antioxidant enzymes (such as superoxide dismutase and glutathione peroxidase), decreasing ROS production, and restoring redox balance in chondrocytes [21,28]. Animal studies have further shown that AKG suppresses synovial inflammation and reduces ROS levels in an OA mouse model, resulting in decreased expression of MMP-13 and improved cartilage wear and degeneration [6,23]. These studies indicated that AKG, through its multi-pathway and multi-target mechanisms, effectively alleviates inflammation and oxidative stress associated with OA, underscoring its significant therapeutic potential in preventing disease progression and improving joint function.

4.2. AKG alleviates OA by regulating mitochondrial function

A growing body of research have indicated that mitochondrial dysfunction is closely associated with the pathogenesis of OA. Mitochondria, as the energy metabolism center, not only supply energy but also regulate cellular redox homeostasis, apoptosis, autophagy, and other essential processes that maintain the normal metabolic functions of articular cartilage tissue [36]. However, when mitochondrial dysfunction occurs, it often results in excessive generation of ROS, which further induces cell apoptosis, dysregulation of autophagy, and chondrocyte senescence, thereby accelerating the progression of OA [36,37].

AKG could significantly improve mitochondrial function and upregulate the expression of antioxidant-related proteins by activating the AMPK-PGC-1α/Nrf2 pathway in a fatty liver animal model [6,29]. Furthermore, AKG improves OA-related mitochondrial dysfunction through several mechanisms. Liu et al. found that in an IL-1β-induced chondrocyte OA model, AKG could significantly reduce mitochondrial ROS production and enhance mitochondrial autophagy, thereby alleviating oxidative stress-induced damage to chondrocytes and mitigating OA progression [6]. Jiang et al. revealed that AKG could restore mitochondrial morphological abnormalities caused by mechanical stress (such as the structural integrity of mitochondrial cristae) while regulating the expression of mitochondrial fission protein DRP1 and fusion protein OPA1, thus maintaining mitochondrial structural and functional stability and reducing cartilage degeneration [36]. Dalmao-Fernández et al. reported that AKG significantly mitigates mitochondrial dysfunction in chondrocytes, inhibits chondrocyte apoptosis, and reduces the detrimental effects of inflammation on chondrocytes [37]. Overall, these studies indicated that AKG plays a crucial role in protecting and maintaining chondrocyte homeostasis by alleviating mitochondrial dysfunction. These studies provide a theoretical foundation and potential direction for developing OA treatment strategies based on mitochondrial modulation.

4.3. AKG improves OA through epigenetic mechanisms

AKG is an essential cofactor for enzymes involved in epigenetic modifications, playing a critical role in the regulation of gene expression and cellular functions. In OA, AKG affects the epigenetic state by modulating DNA demethylation and histone modifications, potentially playing a role in the disease's pathology [38]. Specifically, AKG is required by 2-oxoglutarate-dependent dioxygenases, which are responsible for DNA and histone demethylation. These enzymes, including the TET and Jumonji C domain-containing protein family, catalyze the demethylation of 5-methylcytosine in DNA and methylated lysine residues on histones [2,[38], [39], [40]].

During OA progression, alterations in epigenetic regulation often disrupt cartilage gene expression. For instance, reduced TET enzyme activity results in the diminished expression of genes critical for cartilage matrix synthesis. However, AKG supplementation could activate TET enzymes, promote DNA demethylation, and enhance the expression of genes such as COL2A1 and ACAN, which are essential for cartilage matrix synthesis [[2], [40], [41]]. Thus, the activation of TET enzymes may help restore normal chondrocyte function in OA [40,41]. Furthermore, AKG stimulates Jumonji C family histone demethylases, which modify the gene expression profiles of chondrocytes and synoviocytes. Jumonji C family histone demethylases also could regulate histone modifications that influence the expression of genes involved in inflammation, such as TNF-α and iNOS, thereby helping to reduce inflammation [2]. Overall, these findings indicated that AKG, as a critical regulator of epigenetic enzymes, modifies gene expression in OA through DNA demethylation and histone modification.

4.4. AKG improves OA by regulating apoptosis and autophagy

Chondrocyte apoptosis and autophagy imbalance are important pathological features in the pathogenesis of OA. AKG could regulate apoptosis and autophagy, showing the therapeutic potential of AKG in alleviating OA. Research indicates that under oxidative stress conditions, AKG induces mitophagy to remove damaged mitochondria, thereby reducing ROS accumulation, attenuating apoptosis, and preserving cellular homeostasis [6]. Lee et al. have reported that AKG regulates autophagy-related pathways by blocking the activation of the NLRP3 inflammasome, which reduces the release of pyroptosis-related pro-inflammatory factors [42]. Moreover, by regulating the AMP-activated Protein Kinase (AMPK) signaling pathway, AKG could protect chondrocyte function by promoting autophagy. Activation of the AMPK signaling pathway then improved mitochondrial autophagy and enhanced cellular response to stress by inhibiting mammalian target of rapamycin (mTOR) signaling pathway [43]. In a medial meniscectomy-induced OA mouse model, AKG significantly inhibited matrix degradation and cartilage degeneration by reducing MMP expression and improving chondrocyte activity [44].

Additionally, AKG also has a significant role in regulating apoptosis. AKG could significantly reduce p53-dependent apoptosis in chondrocytes by inhibiting oxidative stress and pro-inflammatory signaling pathways [44,45]. By downregulating pro-inflammatory mediators, including IL-1β and TNF-α, AKG could contribute to the preservation of chondrocyte viability and function within an inflammatory microenvironment induced by apoptosis [42,46]. It suggested that AKG exhibits significant potential value in alleviating the pathological process of OA by regulating apoptosis and autophagy.

4.5. AKG alleviates OA by regulating gut microbiota

The gut microbiota plays a crucial role in regulating inflammation and metabolic functions. Dysbiosis of the gut microbiota is considered a key factor in promoting an inflammatory state and may contribute to the progression of OA through systemic inflammation [46,47]. Studies have demonstrated that gut microbiota metabolites, such as short-chain fatty acids, could regulate the host immune response, thus alleviating symptoms related to OA [48]. AKG, owing to its anti-inflammatory and antioxidant properties, profoundly influences the gut microbiota and its associated metabolic pathways. Research indicates that AKG supplementation could notably enhance the gut microbiota composition, such as an increase in the abundance of Bacteroidetes and optimizing the Firmicutes ratio [46,49]. These modifications likely contribute to mitigating inflammation and oxidative stress [49]. AKG also positively influences the host's metabolic and immune balance through the regulation of gut microbiota metabolism [50]. AKG ameliorates gut microbiota dysfunction, including the diversity of the ileal microbiota, the relative abundance of Actinobacillus, Turicibacter, and Acetivibrio ethanolgignens, which results in the enhancement of IL-1β and IL-10 mRNA expression in the ileum with the reduced inflammatory responses or pathways such as NF-κB and MyD88, and improves growth performance and modulates immunity in enterotoxigenic Escherichia coli (ETEC)-infected piglets [51]. It is indicated that AKG could alleviate OA by modulating gut microbiota.

4.6. AKG improves OA by regulating cellular senescence

The senescence-associated secretory phenotype (SASP) is a key feature of cellular senescence, which includes a variety of bioactive molecules secreted by senescent cells. These molecules include pro-inflammatory cytokines, chemokines, matrix metalloproteinases, growth factors, and bioactive lipids. The release of SASP factors aggravates local inflammation, causing chromatin remodeling and changes in gene expression. Furthermore, SASP influences adjacent cells and tissues via paracrine signaling, deteriorating the microenvironment and accelerating the progression of aging-related diseases such as OA [52].

AKG plays a key role in oxidative phosphorylation and serves as a substrate for DNA and histone demethylases, directly affecting gene expression and cellular epigenetic regulation [14].AKG could mitigate pathological and physiological alterations associated with aging or cellular senescence by modulating metabolic pathways and key intracellular regulatory factors, suggesting its potential therapeutic value in OA [52]. AKG could also suppress the formation and release of SASP by regulating the mTOR signaling pathway, thereby reducing the cellular stress response and alleviating local inflammation to inhibit chondrocyte senescence [53]. Moreover, AKG could significantly reduce cellular senescence and preserve the physiological function of chondrocytes by reducing ROS production and enhancing mitochondrial function [52]. This effect bolsters the metabolic stability of the cartilage matrix while potentially reducing joint inflammation and alleviating joint damage [27]. AKG supplementation is found in vivo animal experiments to potentially reduce chronic inflammation levels and improve nutrient-sensing capacity, significantly decelerate aging-related phenotypes, and improve joint function [54]. These findings suggested that AKG is involved in the onset and progression of OA by regulating cellular senescence; however, its specific therapeutic mechanisms and effects require further validation through clinical trials.

4.7. AKG improves OA by regulating ferroptosis

Ferroptosis is an iron-catalyzed form of necrotic cell death characterized by lipid peroxidation and mitochondrial dysfunction. It is closely associated with chondrocyte degeneration and the progression of OA [[55], [56], [57]]. During the pathological process of OA, excessive iron accumulation triggers increased ROS levels and lipid peroxidation, leading to mitochondrial dysfunction and chondrocyte death [7,57].

Studies have shown that AKG reduces the accumulation of lipid peroxidation products, such as malondialdehyde, enhances antioxidant capacity, and modulates ferroptosis to mitigate the onset and progression of OA [7,58]. Studies have also shown that AKG could modulate ferroptosis through the activation of the ETV4/SLC7A11/GPX4 signaling pathway [7]. Moreover, SLC7A11 and GPX4 expression is significantly upregulated by AKG, which reduces lipid peroxides and divalent iron ion levels and maintains mitochondrial membrane potential, thereby reducing chondrocyte damage [7]. Furthermore, animal studies have demonstrated that AKG could markedly reduce the expression of ferroptosis-related markers, alleviating ECM degradation in cartilage and improving joint function [7,58]. Moreover, it is reported that AKG could also elevate NAD⁺ levels and activate the SIRT1 pathway, then promoting mitochondrial autophagy and clearing damaged mitochondria, thus preventing ferroptosis and protecting chondrocytes [58]. These findings suggested that AKG may improve OA by regulating ferroptosis. This research offers novel insights into the role of AKG in OA pathology and establishes a foundation for developing ferroptosis-targeted therapeutic strategies for OA.

4.8. Role of AKG in regulating Hypoxia-inducible factor 1-alpha (HIF-1α) for OA

HIF-1α, a crucial transcriptional regulator that mediates cellular responses to hypoxic conditions, plays a significant role in the pathophysiology of OA and is precisely regulated by prolyl hydroxylases (PHDs), which require AKG, ferrous iron (Fe²⁺), molecular oxygen (O₂), and vitamin C (VC) as essential cofactors for their catalytic activity [59,60]. Studies have shown that in OA, stabilizing HIF-1α enhances chondrocyte differentiation, ECM synthesis, and protection against apoptosis under hypoxic conditions [[61], [62], [63]]. Furthermore, modulating HIF-1α influences the inflammatory responses in the synovium by regulating macrophage polarization towards the M2 phenotype, which could alleviate synovitis and reduce pain [61,62]. AKG serves as a cofactor for PHDs, facilitating the hydroxylation of specific proline residues on HIF-1α, thereby targeting it for proteasomal degradation under normoxic conditions [59,64]. The presence of Fe²⁺ is indispensable for the catalytic activity of PHDs, as it coordinates with the active site of PHD2 to facilitate the incorporation of one oxygen atom into the proline residue of HIF-1α and the other into α-ketoglutarate, thus generating succinate and carbon dioxide [65,66]. Studies have shown that intra-articular administration of VC could significantly enhance the expression of HIF-1α in cartilage when combined with magnesium ions [63]. This additive effect of VC is likely attributed to its ability to eliminate oxidative stress, which otherwise compromises HIF-1α expression, thereby restoring its downstream anabolic signaling, including upregulation of SRY-box transcription factor 9 (SOX-9) and collagen type 2A1 (COL2A1) [63]. These results indicate that VC acts as a crucial regulatory element that preserves and enhances HIF-1α-mediated matrix synthesis by neutralizing oxidative stress in osteoarthritic cartilage [63]. Furthermore, VC maintains iron in its reduced Fe²⁺ state, thereby preserving the catalytic activity of PHDs under oxidative stress [67,68]. O₂ acts as the terminal electron acceptor in the hydroxylation reaction. Consequently, limited oxygen availability impairs PHD activity, resulting in the stabilization of HIF-1α [59,69].

In summary, the synergistic interaction among AKG, VC, and iron in regulating HIF-1α stability offers a promising therapeutic strategy for managing OA by enhancing cartilage repair and reducing inflammation through the modulation of key anabolic and anti-inflammatory pathways.

5. On the formulation and dosage of AKG in OA treatment

It is well established that AKG is a weak dicarboxylic acid with limited membrane permeability. When administered orally, approximately 80% of dietary AKG is rapidly cleared from the bloodstream in rats and converted into amino acids such as proline and leucine, leading to only minimal increases in circulating AKG levels [[70], [71], [72]]. To overcome this bioavailability limitation, several in vivo and in vitro studies investigating the role of AKG in OA have employed dimethyl-AKG (DM-AKG), which exhibits better absorption and readily diffuses into cells [73]. To evaluate the protective effect of DM-AKG against OA-related ferroptosis, He et al. administered a weekly intra-articular injection of 100 μL DM-AKG (0.32 mM) following destabilization of the medial meniscus (DMM) surgery in mice, which demonstrated significant attenuation of cartilage degeneration and inhibition of lipid peroxidation via the ETV4/SLC7A11/GPX4 axis [74]. In another study, 2% DM-AKG, dissolved in drinking water, was orally administered for 8 weeks to OA rats induced by anterior cruciate ligament transection. This treatment enhanced chondrocyte survival, reduced apoptosis, increased extracellular matrix synthesis, promoted mitophagy, and suppressed ROS accumulation [73].

Overall, although recent studies suggest that DM-AKG possesses therapeutic potential in animal models of OA, including the attenuation of cartilage degeneration, suppression of lipid peroxidation, promotion of autophagy, and enhancement of cell survival, the majority of these findings are derived from in vitro experiments or animal studies. There is a clear absence of systematic clinical research on the use of AKG or its derivatives for the treatment of OA. Therefore, to evaluate its safety and efficacy in humans, further high-quality clinical trials are needed.

6. Summary and outlook

OA is a degenerative disorder closely associated with aging and metabolic dysfunction, characterized by multiple pathological features, including cartilage degradation, inflammatory responses, cellular senescence, mitochondrial dysfunction, and ferroptosis. Recently, AKG has emerged as a promising therapeutic approach for OA. AKG exhibits considerable potential for the prevention and treatment of OA by modulating inflammation, oxidative stress, mitochondrial function, apoptosis, autophagy, gut microbiota composition, cellular senescence, and ferroptosis (Fig. 1).

Fig. 1.

Mechanism of AKG in alleviating OA. AKG could alleviate OA by regulating inflammation, oxidative stress, HIF-α stability, mitochondrial function, epigenetic mechanisms, apoptosis, autophagy, gut microbiota composition, cellular senescence, and ferroptosis. (By Figdraw).

Nevertheless, despite the promising physiological roles of AKG, current evidence indicates several limitations that constrain its therapeutic applications [75]. In vivo studies using Hyaluronic Acid–AKG (HA-AKG) nanoparticles in OA murine models demonstrate substantial chondroprotective effects, yet the therapeutic outcomes vary depending on disease stage and administration frequency, suggesting limited long-term stability and efficacy in progressive OA conditions [75]. Furthermore, although AKG exhibits antioxidative activity by directly scavenging ROS, its short half-life in vivo and rapid metabolism reduce its bioavailability, making sustained delivery systems essential for clinical effectiveness [24]. Studies have also shown that AKG's non-enzymatic decarboxylation reaction with H₂O₂ generates succinate and carbon dioxide, which, although detoxifying, lacks tissue specificity and may inadvertently disturb metabolic balance under systemic administration [24]. Additionally, the antioxidative function of AKG appears to be dose-dependent and may not suffice in conditions with excessive oxidative stress, where its scavenging capacity is quickly saturated [24].

Evidence from long-term supplementation trials suggests that although AKG could beneficially modulate age-related molecular pathways such as mTOR and AMPK, its biological effects vary considerably among species and individuals, reflecting limited universality and potential interspecies translational gaps [76,77]. Moreover, AKG does not directly activate these pathways but rather alters metabolic states that indirectly influence their activity, suggesting its regulatory role may be secondary or context-dependent [76,77]. Preclinical studies in rodents and invertebrates have reported lifespan extension and improved physiological resilience, but human trials remain limited in both size and duration, thereby restricting conclusions regarding its long-term safety and efficacy in clinical settings [76].

In conclusion, while AKG exerts multifaceted physiological functions through metabolic, antioxidative, and regulatory pathways, its therapeutic potential is constrained by factors including low bioavailability, disease stage sensitivity, interspecies variability, and dependence on delivery modalities. These limitations underscore the need for further large-scale clinical investigations and the development of advanced delivery technologies to optimize its translational applications in OA and other age-related conditions.

CRediT authorship contribution statement

Fanghao Long: Writing – review & editing, Writing – original draft, Resources, Conceptualization. Junlin Xiang: Writing – review & editing, Writing – original draft. Yangfan Tan: Writing – review & editing, Validation, Supervision. Jun Zhao: Writing – review & editing, Validation, Supervision. Chi Ma: Writing – review & editing, Writing – original draft, Validation, Supervision, Methodology, Conceptualization.

Declaration of competing interest

The authors declare no competing interests.

Data availability

No data was used for the research described in the article.