Decoding the Regulatory Mechanism of Astaxanthin on Autophagy: Insights for Anti-Inflammatory Intervention

Inflammation is a highly complex physiological and pathological process initiated by the body’s response to endogenous or exogenous damaging stimuli [1]. At its core, it is a defensive reaction aimed at isolating and eliminating harmful stimuli while initiating tissue repair and regeneration. This process involves intricate changes in microcirculation, the immune system, and cellular behavior, characterized by the classic signs of redness, swelling, heat, pain, and loss of function [2]. The triggers of inflammation are remarkably diverse, encompassing physical injuries, chemical exposure, and various biological infections, including viral, bacterial, fungal, and protozoan pathogens [3,4]. During the acute phase, immune cells migrate to the injury or infection site through a meticulously orchestrated sequence of events, facilitated by soluble mediators like cytokines and chemokines. However, if the condition persists due to prolonged stimulus exposure or aberrant reactions to self-molecules, inflammation may progress into a chronic stage [5]. Extensive research has confirmed that chronic inflammation is a common underlying factor in many major chronic diseases, including atherosclerosis, metabolic syndrome, neurodegenerative disorders, autoimmune diseases, and various cancers [3,6]. Notably, the initiation, progression, and resolution of inflammation are profoundly influenced by intracellular regulatory mechanisms, among which autophagy plays a particularly critical dual role. While appropriate autophagy helps remove inflammatory triggers and resolve inflammation, dysregulated autophagy can itself act as an inflammatory trigger, contributing to both the initiation of acute inflammation and the sustained activation of immune cells and pro-inflammatory signaling that drives chronic inflammation [7].

Autophagy is a highly conserved intracellular degradation and recycling system in eukaryotic cells, playing a critical role as a “cleaner” and “recycling center” in maintaining cellular homeostasis. Its primary functions include clearing misfolded or aggregated proteins, degrading dysfunctional or excess organelles (such as mitochondria and endoplasmic reticulum), and eliminating intracellular pathogens, thereby providing nutrients and maintaining internal stability. Depending on how substrates are delivered to the lysosome, autophagy is classified into three main types: microautophagy, macroautophagy, and chaperone-mediated autophagy. Among these, macroautophagy is the most extensively studied and has the broadest physiological significance [8]. The initiation and execution of autophagy are precisely regulated processes. Under stress signals such as oxidative stress, the mammalian target of rapamycin (mTOR) kinase activity is suppressed, while the AMP-activated protein kinase (AMPK) pathway is activated, both of which act on the UNC-51-like kinase 1(ULK1)/2-ATG13-FIP200 complex to initiate autophagy [9,10]. Subsequently, c-Jun N-terminal kinase 1 (JNK1) phosphorylates endoplasmic reticulum-localized BCL-2 at residues T69, S70, and S87, leading to the dissociation of BCL2 interacting protein (Beclin1) [11]. Liberated Beclin1 then activates the Beclin-1-Vps34 (class III phosphatidylinositol 3-kinase, PI3K) complex, promoting the production of phosphatidylinositol 3-phosphate (PI3P). PI3P recruits effector proteins such as WIPI2, thereby facilitating the recruitment of the ATG12-ATG5-ATG16L1 complex and the lipidation of Microtubule-associated Protein 1 Light Chain 3(LC3), driving phagophore elongation [12]. Thereafter, two ubiquitin-like conjugation systems—the ATG12-ATG5-ATG16L1 complex and the lipidation system converting LC3-I to phosphatidylethanolamine-conjugated LC3-II—cooperate to drive the extension and closure of the phagophore, ultimately forming an autophagosome that sequesters cytoplasmic contents [13]. Mature autophagosomes fuse with lysosomes through membrane fusion proteins including syntaxin-17 (STX17), synaptosomal-associated protein 29 (SNAP29), and vesicle-associated membrane protein 8 (VAMP8), forming autolysosomes in which the contents are thoroughly degraded by various hydrolytic enzymes, and the degradation products are recycled back into the cytoplasm [14]. Autophagy serves as a bridge that links cellular homeostasis with systemic immune responses. By directly eliminating pathogens, processing antigens, suppressing excessive inflammation, and supporting immune cell survival, it fine-tunes both the intensity and the tolerance of the immune system. While the immune system defends the body by initiating inflammation—a vital mechanism for pathogen clearance and tissue repair—autophagy and inflammation engage in a complex and bidirectional regulatory interaction [15,16]. On one hand, at baseline, autophagy in alveolar macrophages effectively suppresses spontaneous pulmonary inflammation [17]. On the other hand, uncontrolled autophagy—whether due to insufficient function or excessive activation—can promote cell death (such as apoptosis and necroptosis) and release damage-associated molecular patterns, thereby exacerbating the inflammatory response and creating a vicious cycle [18]. This ‘double-edged sword’ property highlights the precise regulation of autophagy as a promising mechanistic target for intervening in inflammation-related diseases.

Astaxanthin (AST) is a naturally occurring lipid-soluble red-orange pigment (chemical name: 3, 3′-dihydroxy-β, β′-carotene-4,4′-dione) belonging to the xanthophyll carotenoid family [4,19], widely used in dietary supplements for health or nutritional support [20]. It is mainly synthesized by microalgae, such as Haematococcus pluvialis, in marine environments and accumulates in marine organisms like shrimp, crabs, and salmon through the food chain [21]. Its unique molecular structure—characterized by two ends containing a hydroxyl and keto group and a polyene long chain composed of 13 conjugated double bonds—forms the chemical basis for its exceptional biological activities [22,23]. Compared to natural compounds such as vitamin D3, trehalose, and spermine, AST provides broader membrane protection, stronger antioxidant activity, enhanced stability, and more precise bidirectional regulation of autophagy. Additionally, it holds FDA GRAS (Generally Recognized as Safe) certification, attributed to its unique molecular structure [24,25,26,27,28]. Recent cutting-edge research has further revealed that AST can profoundly influence the process of cellular autophagy. Rather than merely activating or inhibiting autophagy, it acts as a “regulator,” finely tuning autophagy in response to the cellular microenvironment or immune system status. For instance, under oxidative stress conditions, AST can restore impaired autophagy by inducing mitophagy [29] or directly regulating the expression and function of key autophagic proteins such as Beclin-1, LC3-II, and Sequestosome-1 (SQSTM1/p62), thus providing cellular protection [30]. Notably, AST regulates autophagy and activity to influence inflammatory responses, thereby alleviating disease progression and reducing organ damage. Examples include enhancing podocyte autophagy and inhibiting mesangial cell pathological crosstalk to alleviate diabetic kidney injury [31], or alleviating NLRP3-mediated inflammation to improve Age-Related Macular Degeneration (AMD) [32]. At both cellular and organ levels, AST can ameliorate inflammatory damage induced by autophagy.

Given these finding, elucidating the regulatory role of AST in the complex interplay between autophagy and inflammation is critical not only for understanding the biological activity of this natural compound, but also for developing novel intervention strategies for inflammatory diseases. Although previous reviews have summarized the anti-inflammatory properties of AST, the specific mechanisms by which it modulates autophagy to influence inflammatory outcomes remain to be systematically synthesized. This review provides a conceptual framework that integrates current preclinical evidence, critically evaluates how AST regulates autophagy across different organ systems in animal and cellular models of inflammation, and assesses the translational gap between these promising preclinical findings and the requirement for future clinical validation. By delineating this research landscape, we aim to offer a forward-looking roadmap that identifies key unanswered questions and guides future research directions in this field.

We conducted a systematic review to comprehensively analyze and summarize studies exploring the regulatory mechanism of AST on autophagy in the context of anti-inflammatory intervention. The following academic databases comprising a broad, authoritative literature base, including PubMed, EMBASE, and Web of Science have been explored. The search terms were meticulously formulated as “astaxanthin” and its synonyms “AST” and “3,3′-dihydroxy-β,β-carotene-4,4′-dione”. The related terms regarding autophagy were formulated as “autophagy”, “autophagic”, “macroautophagy”, “mitophagy”, and “autophagosome”, while inflammatory-related terms included “anti-inflammatory”, “inflammation”, “inflammatory”, and “cytokines”. To select the relevant studies, the final search formula was created as follows: (“astaxanthin” OR “AST” OR “3,3′-dihydroxy-β,β-carotene-4,4′-dione”) AND (“autophagy” OR “autophagic” OR “macroautophagy” OR “mitophagy” OR “autophagosome”) AND (“anti-inflammatory” OR “inflammation” OR “inflammatory” OR “cytokines”).

Our initial search yielded 988 publications, including 255 from PubMed, 407 from EMBASE, and 326 from Web of Science. Subsequently, 736 duplicate articles and those whose titles were considered irrelevant to our topic were eliminated following meticulous screening of titles and abstracts. The remaining 252 articles were thoroughly evaluated, and 236 studies were ultimately excluded due to the following criteria: (i) reviews, commentaries, or conference abstracts without original experimental data; (ii) studies not focusing on AST as the primary intervention; (iii) articles lacking clear investigation of autophagy-related mechanisms; (iv) studies without anti-inflammatory endpoints or relevant inflammatory biomarkers; and (v) insufficient methodological details or lack of proper controls. Finally, 16 studies were included based on their relevance to AST-mediated autophagy regulation in anti-inflammatory intervention and the scientific rigor of their designs (Figure 1).

Autophagy is a key process to maintain cell homeostasis, and its regulation involves the precise integration of multiple signaling pathways. Studies have shown that moderate autophagy activation has a protective effect on cells; however its imbalance is closely related to the pathogenesis of many diseases. Notably, we found that AST can regulate the autophagy process through multiple pathways, including Reactive Oxygen Species (ROS)/Mitogen-activated Protein Kinase (MAPK), AMPK-mTOR-ULK1, protein kinase B (PKB/Akt)/mTOR, nuclear factor erythroid 2-related factor 2 (Nrf2), as well as via the NLRP3 inflammasome (Figure 2).

The schematic illustrates that AST modulates cellular autophagy through multiple signaling pathways. Under stress stimulation, AST reduces ROS generation, thereby inhibiting the phosphorylation levels of MAPK family members (p38 MAPK, JNK, and ERK) and ultimately suppressing autophagy. Additionally, AST promotes autophagosome formation by activating AMPK to directly inhibit mTOR complex assembly; it further enhances autophagy by alleviating the inhibitory effect of mTOR on the ULK1 complex. Notably, in the Akt/mTOR signaling pathway, Jia et al. demonstrated that AST promotes hepatic autophagy by inhibiting Akt/mTOR, whereas Yan et al. reported that AST suppresses mitophagy through activation of Akt/mTOR, illustrating the bidirectional regulatory effect of AST on autophagy. In this figure, red “┬” arrows denote reduced levels of autophagy-related markers (e.g., LC3-II, Beclin1) or increased p62 accumulation, indicating inhibition of autophagic activity. Green “↑” arrows denote elevated levels of such markers or decreased p62 accumulation, indicating promotion of autophagic activity. The ROS/MAPK signaling pathway is adapted from Li et al. [33]. and the process of autophagosome formation and maturation is adapted from Yu et al. [19]. The remaining content is original.

Autophagy is a critical cellular homeostasis mechanism, and its dysregulation is closely associated with the pathogenesis of various inflammatory diseases [48]. As discussed in the preceding section, AST is a multifaceted natural compound that fine-tunes autophagic activity by modulating key signaling pathways, including AMPK/ULK1/mTOR, ROS/MAPK, Akt/mTOR, Nrf2, and the NLRP3 inflammasome. This dual regulatory capability forms the foundation of its potent antioxidant and anti-inflammatory effects at both cellular and molecular levels. Building on these insights, this chapter delves into the protective effects of AST in organ systems commonly affected by inflammatory pathologies. Particular attention is given to its roles in the joints, eyes, brain, liver, digestive tract, and urinary system, with a focus on synthesizing recent research advances that shed light on AST’s ability to modulate autophagy and influence disease progression (Figure 3). Additionally, we discuss its potential as a nutritional strategy and its possible adjunctive role in supportive care, aiming to inform and guide future research directions.

This schematic illustrates how AST regulates autophagy to mitigate inflammation across key human organs. In the eye, AST enhances autophagy via SLC7A11/GPX4 activation to alleviate dry eye disease (DED) and inhibits NLRP3/LC3 to attenuate age-related macular degeneration (AMD). For liver diseases, AST enhances autophagy (e.g., liver injury) or attenuates excessive autophagy (e.g., liver fibrosis, hepatic ischemia–reperfusion (IR)) by modulating Nrf2, ROS/MAPK, NF-κB, and JNK pathways. In kidney diseases such as diabetic nephropathy and renal IR, AST enhances autophagy by upregulating LC3-II/I and Beclin-1 while downregulating p62. For bone and joint diseases like osteoarthritis, AST enhances autophagy by suppressing ROS/NLRP3 upregulation. In brain diseases including Alzheimer’s disease (AD) and subarachnoid hemorrhage, AST enhances autophagy via AMPK-ULK1 activation and AKT-mTOR inhibition. In gastric diseases such as H. pylori infection, AST enhances autophagy by AMPK activation and Akt/mTOR inhibition. For pancreatic diseases like cerulein- or caerulein-induced acute pancreatitis (AP), AST enhances or attenuates autophagy by modulating Nrf2 and JAK/STAT3 pathways. This figure is original and was created by the authors.

AST has emerged as a compound of interest for its role in modulating autophagy, a process implicated in the pathogenesis of various chronic diseases. However, its development as a reliable therapeutic agent faces several critical challenges, underscoring the need for systematic advancements in future research. First, while current studies provide evidence of AST’s potential, they largely remain focused on phenotypic associations. The direct upstream molecular targets of AST—such as specific membrane receptors or intracellular sensor proteins—have yet to be clearly identified. To enhance the translational rigor of this field, future studies must prioritize the methodological diversification of experimental models. Notably, as a significant portion of current in vitro evidence is derived from single cell lines, it is imperative that forthcoming research validates these findings across multiple relevant cell types or primary cell lines. Such cross-model validation is essential to account for cellular heterogeneity and to confirm the reproducibility of AST’s observed biological effects. Furthermore, by integrating advanced techniques in chemical biology and proteomics, researchers can more robustly pinpoint the primary molecular switches—such as the orchestrated modulation of AMPK, mTOR, and Nrf2—that drive AST’s synergistic protection across diverse biological contexts. This will not only deepen our understanding of AST as a “multi-pathway network modulator” but also provide a foundation for structure-based drug optimization. Moreover, there remains a substantial translational gap between preclinical findings and human applications. Current evidence is predominantly derived from cell and animal models, where the doses, routes of administration, and physiological contexts differ significantly from those in humans. To bridge this gap, systematic pharmacokinetic studies are essential to elucidate the absorption, distribution, metabolism, and excretion (ADME) profiles of various AST formulations, including esterified derivatives and nano-formulations, in humans. Identifying optimal dose–response relationships and therapeutic windows for specific diseases—such as neurodegenerative diseases—while rigorously evaluating the long-term safety of AST use, will be critical for its clinical translation.

Addressing AST’s inherent limitations in bioavailability and stability is another key priority. Its low solubility and instability hinder effective accumulation at disease sites. Future research should move beyond conventional encapsulation methods and focus on developing advanced, intelligent delivery systems. For instance, nanocarriers responsive to pathological cues such as elevated reactive ROS or disease-specific enzymes could enable targeted delivery to inflammation sites, atherosclerotic plaques, or tumor microenvironments. Overcoming barriers like the blood–brain barrier and the retinal barrier will require bioinspired or functionalized delivery platforms to ensure efficient transport to the central nervous system and the eye. Additionally, co-delivery strategies that combine AST with other autophagy modulators, such as rapamycin, could enhance therapeutic synergy.

Prospectively, translating preclinical findings on AST into clinical applications will require a comprehensive and interdisciplinary approach that bridges basic and clinical research. This includes uncovering its molecular targets, developing innovative delivery systems, and designing well-controlled clinical trials to evaluate its efficacy and safety. By integrating these efforts, AST may ultimately be positioned as an evidence-based nutritional strategy for supporting health and managing disease risk through autophagy modulation.

AST is a natural compound that regulates autophagy through multiple signaling pathways, including AMPK-mTOR-ULK1, MAPK, Akt/mTOR, and Nrf2. By fine-tuning autophagic activity, AST helps maintain cellular balance and reduces inflammation in various diseases, such as osteoarthritis, liver injury, kidney damage, and neuroinflammation. Notably, AST does not simply activate or inhibit autophagy; rather, its regulatory direction is context-dependent, balancing protective and excessive autophagic responses across different diseases. Therefore, we propose that AST is a natural compound capable of bidirectionally regulating autophagy to influence inflammatory responses and maintain homeostasis, with the potential for multi-target and multi-organ clinical applications. Nevertheless, the path to clinical application is hindered by unresolved issues—limited bioavailability, unidentified direct targets, and an absence of rigorous clinical trials—that must be addressed in future research. Future research should focus on identifying how AST directly binds to cellular targets, developing better delivery systems, and conducting well-designed clinical studies to confirm its therapeutic value.