Four-octyl itaconate improves osteoarthritis by enhancing autophagy in chondrocytes via PI3K/AKT/mTOR signalling pathway inhibition

Insights into the itaconate family: Immunomodulatory mechanisms and therapeutic potentials

The itaconate family, comprising itaconate derivatives, endogenous isomers, and other related compounds, has demonstrated substantial immunoregulatory properties. These compounds exhibit significant therapeutic potential in various disease models by modulating metabolic pathways, signal transduction cascades, and post-translational modifications. In this review, we delineate the structural characteristics and biological functions of the members of the itaconate family and elucidate their immunomodulatory mechanisms. Additionally, we summarize the immunomodulatory effects of the itaconate family across various disease categories, including cardiovascular, liver, respiratory, bone and cartilage, neurological, and autoimmune diseases. This review aims to deepen our understanding of the itaconate family and its potential applications, providing new perspectives and therapeutic strategies for inflammatory disorders and autoimmune diseases.

Itaconate: A Potential Therapeutic Strategy for Autoimmune Disease

Itaconate is a metabolite of the Krebs cycle, and endogenous itaconate is driven by a variety of innate signals that inhibit the production of inflammatory cytokines. The key mechanism of action of itaconate was initially found to be the competitive inhibition of succinate dehydrogenase (SDH), which inhibits the production of inflammatory factors, as well as its antioxidant effects. With increasing research, it was discovered that it modifies cysteine residues of related proteins through the Michael addition, such as modifying the Kelch-like ECH-associated protein 1 (KEAP1) protein and activating the nuclear factor erythroid 2-related factor 2 (NRF2) signalling pathway, as well as glycolytic enzymes and cellular pathway-associated factors that attenuate inflammatory responses and oxidative stress. It also acts on a variety of immune cells, affecting their function and activity, and has been increasingly shown to play a therapeutic role in a variety of inflammatory and autoimmune diseases through a combination of these mechanisms. In conclusion, there has been a great breakthrough in the research of itaconate, from the initial industrial application to the redefinition of the biological functions of itaconate. However, with the deepening of the research, we also found that there are more questions: the mechanism of action of itaconate, more functions of itaconate, clinical application of itaconate, and the use of itaconate still needs to be solved.

Metabolic Reprogramming in Stromal and Immune Cells in Rheumatoid Arthritis and Osteoarthritis: Therapeutic Possibilities

Metabolic reprogramming of stromal cells, including fibroblast-like synoviocytes (FLS) and chondrocytes, as well as osteoclasts (OCs), are involved in the inflammatory and degenerative processes underlying rheumatoid arthritis (RA) and osteoarthritis (OA). In RA, FLS exhibit mTOR activation, enhanced glycolysis and reduced oxidative phosphorylation, fuelling inflammation, angiogenesis, and cartilage degradation. In OA, chondrocytes undergo metabolic rewiring, characterised by mTOR and NF-κB activation, mitochondrial dysfunction, and increased glycolysis, which promotes matrix metalloproteinase production, extracellular matrix (ECM) degradation, and angiogenesis. Macrophage-derived immunometabolites, including succinate and itaconate further modulate stromal cell function, acting as signalling molecules that modulate inflammatory and catabolic processes. Succinate promotes inflammation whilst itaconate is anti-inflammatory, suppressing inflammatory joint disease in models. Itaconate deficiency also correlates inversely with disease severity in RA in humans. Emerging evidence highlights the potential of targeting metabolic processes as promising therapeutic strategies for connective tissue disorders.

Activation of Nrf2 pathway by 4-Octyl itaconate enhances donor lung function in cold preservation settings

BACKGROUND

Lung transplantation is the primary treatment for end-stage lung diseases. However, ischemia-reperfusion injury (IRI) significantly impacts transplant outcomes. 4-Octyl itaconate (4-OI) has shown potential in mitigating organ IRI, although its effects in lung transplantation require further exploration.

METHODS

BEAS-2B cells were used to model transplantation, assessing the effects of 4-OI through viability, apoptosis, and ROS assays. qRT-PCR analyzed cytokine transcription post-cold ischemia/reperfusion (CI/R). RNA sequencing and Gene Ontology analysis elucidated 4-OI's mechanisms of action, confirmed by Western blotting. ALI-airway and lung transplantation organoid models evaluated improvements in bronchial epithelial morphology and function due to 4-OI. ELISA measured IL-6 and IL-8 levels. Rat models of extended cold preservation and non-heart-beating transplantation assessed 4-OI's impact on lung function, injury, and inflammation.

RESULTS

Our findings indicate that 4-OI (100 µM) during cold preservation effectively maintained cell viability, decreased apoptosis, and reduced ROS production in BEAS-2B cells under CI/R conditions. It also downregulated pro-inflammatory cytokine transcription, including IL1B, IL6, and TNF. Inhibition of Nrf2 partially reversed these protective effects. In cold preservation solutions, 4-OI upregulated Nrf2 target genes such as NQO1, HMOX1, and SLC7A11. In ALI airway models, 4-OI enhanced bronchial epithelial barrier integrity and ciliary beat function after CI/R. In rat models, 4-OI administration improved lung function and reduced pulmonary edema, tissue injury, apoptosis, and systemic inflammation following extended cold preservation or non-heart-beating lung transplantation.

CONCLUSIONS

Incorporating 4-OI into cold preservation solutions appears promising for alleviating CI/R-induced bronchial epithelial injury and enhancing lung transplant outcomes via Nrf2 pathway activation.

Polydatin retards the progression of osteoarthritis by maintaining bone metabolicbalance and inhibiting macrophage polarization

Background

Polydatin (PD), also known as tiger cane glycoside, is a natural compound extracted from the Japanese knotweed plant, which is often referred to as white resveratrol. It exhibits anti-inflammatory, antioxidant, and anti-apoptotic effects in the treatment of various diseases. However, the potential molecular mechanisms of PD in osteoarthritis have not been clearly elucidated.

Methods

Anterior cruciate ligament transection (ACLT) surgery was performed to establish an osteoarthritis animal model. Female mice at the age of 12 weeks were intraperitoneally injected with different concentrations of PD (20 and 40 mg/kg). In vitro models were established by isolating mouse articular chondrocytes, which were subsequently treated with lipopolysaccharide or IL-1β for 24 h for subsequent experiments. In addition, different concentrations of PD were administered for 12 h. Morphological changes were observed by toluidine blue staining, joint bone metabolism changes were observed by tartrate-resistant acid phosphatase staining, immunohistochemistry was used to observe the expression levels of inflammatory factors and extracellular matrix. MicroCT analysis was conducted to assess changes in the microstructure of subchondral bone trabeculae, and Western blot was performed to measure the expression of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) signaling pathway and markers of M1 polarization in macrophages.

Results

PD significantly delays the progression of osteoarthritis induced by ACLT, effectively inhibits IL-1β-induced joint inflammation, bone metabolic remodeling and extracellular matrix degradation. In addition, paeoniflorin markedly suppresses the transmission of the NF-κB signaling pathway and reverses M1 polarization in macrophages induced by IL-1β.

Conclusion

Taken together, PD might be a potential therapeutic agent for the prevention and treatment of osteoarthritis.

4-Octyl itaconate inhibits synovitis in the mouse model of post-traumatic osteoarthritis and alleviates pain

PURPOSE

To investigate the pathological changes of the synovium in mice with post-traumatic osteoarthritis (PTOA) treated with 4-octyl itaconate (4-OI) and evaluate the therapeutic effects of 4-OI.

METHODS

In the phenotypic validation experiment, the mice were randomly divided into 3 groups: wild-type (WT) group, sham group, and destabilization of the medial meniscus (DMM) group. Through MRI, micro-CT, and histological analysis, it was determined that the DMM surgery induced a mouse PTOA model with significant signs of synovitis. At 12 weeks post-DMM surgery, synovial tissues from the DMM group and WT group mice were collected for ribonucleic acid sequencing analysis. In the 4-OI treatment experiment, mice were randomly divided into the sham group, DMM group, DMM + 4-OI (50 mg/kg) group, and DMM + 4-OI (100 mg/kg) group. Von Frey tests and open field tests were conducted at intervals during the 12 weeks following the DMM surgery. After 12 weeks of surgery, the efficacy of 4-OI treatment on PTOA in mice was evaluated using MRI, micro-CT, histological analysis, and quantitative real-time polymerase chain reaction. Finally, we utilized network pharmacology analysis to predict the mechanism of 4-OI in treating PTOA synovitis and conducted preliminary validation. Statistical analysis was performed using one-way ANOVA and the Kruskal-Wallis test. Difference was considered statistically significant at p < 0.05.

RESULTS

The DMM surgery effectively induced a PTOA mouse model, which displayed significant symptoms of synovitis. These symptoms included a notable increase in both the number of calcified tissues and osteophytes (p < 0.001), an enlargement of the calcified meniscus and synovial tissue volume (p < 0.001), and thickening of the synovial lining layer attributable to M1 macrophage accumulation (p = 0.035). Additionally, we observed elevated histological scores for synovitis (p < 0.001). Treatment with 4-OI inhibited the thickening of M1 macrophages in the synovial lining layer of PTOA mice (p < 0.001) and reduced fibrosis in the synovial stroma (p = 0.004). Furthermore, it reduced the histological scores of knee synovitis in PTOA mice (p = 0.006) and improved the inflammatory microenvironment associated with synovitis. Consequently, this treatment alleviated pain in PTOA mice (p < 0.001) and reduced spontaneous activity (p = 0.003). Bioinformatics and network pharmacology analyses indicated that 4-OI may exert its therapeutic effects by inhibiting the differentiation of synovial Th17 cells. Specifically, compared to the lipopolysaccharide stimulation group, 4-OI reduced the levels of positive regulatory factors of Th17 cell differentiation (IL-1: p < 0.001, IL-6: p < 0.001), key effector molecules (IL-17A: p < 0.001, IL-17F: p = 0.004), and downstream effector molecules in the IL-17 signaling pathway (CCL2: p < 0.001, MMP13: p < 0.001).

CONCLUSION

4-OI is effective in inhibiting synovitis in PTOA, thereby alleviating the associated painful symptoms.

Regulation of chondrocyte apoptosis in osteoarthritis by endoplasmic reticulum stress

Osteoarthritis (OA), a common degenerative joint disease, is characterized by the apoptosis of chondrocytes as a primary pathophysiological change, with endoplasmic reticulum stress (ERS) playing a crucial role. It has been demonstrated that an imbalance in endoplasmic reticulum (ER) homeostasis can lead to ERS, activating three cellular adaptive response pathways through the unfolded protein response to restore ER homeostasis. Mild ERS exerts a protective effect on cells, while prolonged ERS that disrupts the self-regulatory balance of the ER activates apoptotic signaling pathways, leading to chondrocyte apoptosis and hastening OA progression. Hence, controlling the ERS signaling pathway and its apoptotic factors has become a critical focus for preventing and treating OA. This review aims to elucidate the key mechanisms of ERS pathway-induced apoptosis, associated targets, and regulatory pathways, offering valuable insights to enhance the mechanistic understanding of OA. It also reviews the mechanisms studied for ERS-related drugs or compounds for the treatment of OA.

Chondrocyte autophagy mechanism and therapeutic prospects in osteoarthritis

Osteoarthritis (OA) is the most common type of arthritis characterized by progressive cartilage degradation, with its pathogenesis closely related to chondrocyte autophagy. Chondrocytes are the only cells in articular cartilage, and the function of chondrocytes plays a vital role in maintaining articular cartilage homeostasis. Autophagy, an intracellular degradation system that regulates energy metabolism in cells, plays an incredibly important role in OA. During the early stages of OA, autophagy is enhanced in chondrocytes, acting as an adaptive mechanism to protect them from various environmental changes. However, with the progress of OA, chondrocyte autophagy gradually decreases, leading to the accumulation of damaged organelles and macromolecules within the cell, prompting chondrocyte apoptosis. Numerous studies have shown that cartilage degradation is influenced by the senescence and apoptosis of chondrocytes, which are associated with reduced autophagy. The relationship between autophagy, senescence, and apoptosis is complex. While autophagy is generally believed to inhibit cellular senescence and apoptosis to promote cell survival, recent studies have shown that some proteins are degraded by selective autophagy, leading to the secretion of the senescence-associated secretory phenotype (SASP) or increased SA-β-Gal activity in senescent cells within the damaged region of human OA cartilage. Autophagy activation may lead to different outcomes depending on the timing, duration, or type of its activation. Thus, our study explored the complex relationship between chondrocyte autophagy and OA, as well as the related regulatory molecules and signaling pathways, providing new insights for the future development of safe and effective drugs targeting chondrocyte autophagy to improve OA.

Advances in targeted therapies for age-related osteoarthritis: A comprehensive review of current research

Osteoarthritis (OA) is a common degenerative joint disease that disproportionately impacts the elderly population on a global scale. As aging is a significant risk factor for OA, there is a growing urgency to develop specific therapies that target the underlying mechanisms of aging associated with this condition. This summary seeks to offer a thorough introduction of ongoing research efforts aimed at developing therapies to combat senescence in the context of OA. Cellular senescence plays a pivotal role in both the deterioration of cartilage integrity and the perpetuation of chronic inflammation and tissue remodeling. Consequently, targeting SnCs has emerged as a promising therapeutic approach to alleviate symptoms and hinder the progression of OA. This review examines a range of approaches, including senolytic drugs targeting SnCs, senomorphics that modulate the senescence-associated secretory phenotype (SASP), and interventions that enhance immune system clearance of SnCs. Novel methodologies, such as utilizing novel materials for exosome delivery and administering anti-aging medications with precision, offer promising avenues for the precise treatment of OA. Accumulating evidence underscores the potential of targeting senescence in OA management, potentially facilitating the development of more effective and personalized therapeutic interventions.

4-Octyl itaconate protects chondrocytes against IL-1β-induced oxidative stress and ferroptosis by inhibiting GPX4 methylation in osteoarthritis

The role of oxidative stress and ferroptosis in osteoarthritis (OA) pathogenesis is increasingly recognized. Notably, 4-octyl Itaconate (OI) has been documented to counteract oxidative stress and inflammatory responses, highlighting its therapeutic potential in OA. This study explored the effects of OI on GPX4 methylation, oxidative stress, and ferroptosis in chondrocytes affected by OA. Our results demonstrated that OI mitigated IL-1β-induced chondrocyte degeneration in a dose-dependent manner. It also suppressed reactive oxygen species (ROS) production and sustained GPX4 expression, thereby attenuating the degenerative impact of IL-1β and Erastin on chondrocytes by curtailing ferroptosis. Moreover, we observed that blocking GPX4 methylation could alleviate IL-1β-induced degeneration, oxidative stress, and ferroptosis in chondrocytes. The regulatory mechanism of OI on GPX4 expression in chondrocytes involved the inhibition of GPX4 methylation. In a mouse model of OA, OI's protective effects against OA were comparable to those of Ferrostatin-1. Thus, OI reduced chondrocyte degeneration, oxidative stress, and ferroptosis by inhibiting GPX4 methylation, offering a novel mechanistic insight into its therapeutic application in OA.

Itaconate to treat acute lung injury: recent advances and insights from preclinical models

Acute lung injury (ALI) is defined as the acute onset of diffuse bilateral pulmonary infiltration, leading to PaO2/FiO2 ≤ 300 mmHg without clinical evidence of left atrial hypertension. Acute respiratory distress syndrome (ARDS) involves more severe hypoxemia (PaO2/FiO2 ≤ 200 mmHg). Treatment of ALI and ARDS has received renewed attention as the incidence of ALI caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection has increased. Itaconate and its derivatives have shown therapeutic potential against ALI. This review provides an in-depth summary of the mechanistic research of itaconate in the field of acute lung injury, including inducing autophagy, preventing ferroptosis and pyroptosis, shifting macrophage polarization to an anti-inflammatory M2 phenotype, inhibiting neutrophil activation, regulating epigenetic modifications, and repressing aerobic glycolysis. These compounds merit further consideration in clinical trials. We anticipate that the clinical translation of itaconate-based drugs can be accelerated.

The anti-inflammatory effects of itaconate and its derivatives in neurological disorders

Almost 16 % of the global population is affected by neurological disorders, including neurodegenerative and cerebral neuroimmune diseases, triggered by acute or chronic inflammation. Neuroinflammation is recognized as a common pathogenic mechanism in a wide array of neurological conditions including Alzheimer's disease, Parkinson's disease, postoperative cognitive dysfunction, stroke, traumatic brain injury, and multiple sclerosis. Inflammatory process in the central nervous system (CNS) can lead to neuronal damage and neuronal apoptosis, consequently exacerbating these diseases. Itaconate, an immunomodulatory metabolite from the tricarboxylic acid cycle, suppresses neuroinflammation and modulates the CNS immune response. Emerging human studies suggest that itaconate levels in plasma and cerebrospinal fluid may serve as biomarkers associated with inflammatory responses in neurological disorders. Preclinical studies have shown that itaconate and its highly cell-permeable derivatives are promising candidates for preventing and treating neuroinflammation-related neurological disorders. The underlying mechanism may involve the regulation of immune cells in the CNS and neuroinflammation-related signaling pathways and molecules including Nrf2/KEAP1 signaling pathway, reactive oxygen species, and NLRP3 inflammasome. Here, we introduce the metabolism and function of itaconate and the synthesis and development of its derivatives. We summarize the potential impact and therapeutic potential of itaconate and its derivatives on brain immune cells and the associated signaling pathways and molecules, based on preclinical evidence via various neurological disorder models. We also discuss the challenges and potential solutions for clinical translation to promote further research on itaconate and its derivatives for neuroinflammation-related neurological disorders.

Metformin mitigates osteoarthritis progression by modulating the PI3K/AKT/mTOR signaling pathway and enhancing chondrocyte autophagy

Osteoarthritis (OA) is a chronic degenerative disease characterized by overall joint tissue damage. Metformin (Met) has been shown to inhibit inflammatory reactions, though its potential protective mechanism on cartilage remains unclear. This study investigated Met's potential to protect cartilage in an OA rat model. Various morphological experiments were conducted to assess changes in cartilage tissue morphology before and after Met treatment. Protein and mRNA levels of cartilage-specific genes were measured using western blot, immunohistochemical staining, and RT-qPCR. Additionally, protein levels of autophagy-related and mTOR pathway-related proteins were measured. The results indicate an imbalance in the synthesis and degradation metabolism of chondrocytes, downregulation of cellular autophagy, and activation of the PI3K/Akt/mTOR pathway after surgery. However, treatment with Met could upregulate the expression of synthetic metabolic factors, indicating its contribution to cartilage repair. Furthermore, analysis of autophagy and pathway protein levels indicated that Met effectively attenuated autophagic damage to osteoarthritic cartilage cells and abnormal activation of the PI3K/Akt/mTOR pathway. In conclusion, Met can inhibit the abnormal activation of the PI3K/AKT/mTOR signaling pathway in cartilage tissue, promote the restoration of cartilage cell autophagic function, improve the balance of cartilage cell synthesis and degradation metabolism, and thus exert a protective effect on rat joint cartilage.

Cellular Senescence and Inflammaging in the Bone: Pathways, Genetics, Anti-Aging Strategies and Interventions

Advancing age is associated with several age-related diseases (ARDs), with musculoskeletal conditions impacting millions of elderly people worldwide. With orthopedic conditions contributing towards considerable number of patients, a deeper understanding of bone aging is the need of the hour. One of the underlying factors of bone aging is cellular senescence and its associated senescence associated secretory phenotype (SASP). SASP comprises of pro-inflammatory markers, cytokines and chemokines that arrest cell growth and development. The accumulation of SASP over several years leads to chronic low-grade inflammation with advancing age, also known as inflammaging. The pathways and molecular mechanisms focused on bone senescence and inflammaging are currently limited but are increasingly being explored. Most of the genes, pathways and mechanisms involved in senescence and inflammaging coincide with those associated with cancer and other ARDs like osteoarthritis (OA). Thus, exploring these pathways using techniques like sequencing, identifying these factors and combatting them with the most suitable approach are crucial for healthy aging and the early detection of ARDs. Several approaches can be used to aid regeneration and reduce senescence in the bone. These may be pharmacological, non-pharmacological and lifestyle interventions. With increasing evidence towards the intricate relationship between aging, senescence, inflammation and ARDs, these approaches may also be used as anti-aging strategies for the aging bone marrow (BM).

Luteolin regulating synthesis and catabolism of osteoarthritis chondrocytes via activating autophagy

Osteoarthritis (OA) is a prevalent bone and joint disease characterized by degeneration. The dysregulation between chondrocyte synthesis and breakdown is a key factor in OA development. Targeting the degenerative changes in cartilage tissue degradation could be a potential treatment approach for OA. Previous research has established a strong link between autophagy and the regulation of chondrocyte functions. Activating autophagy has shown promise in mitigating cartilage tissue degeneration. Currently, osteoarthritis treatment primarily focuses on symptom management, as there is no definitive medication to stop disease progression. Previous studies have demonstrated that luteolin, a flavonoid present in Chinese herbal medicine, can activate autophagy and reduce the expression of MMP1 and ADAMTS-5. This study utilized an in vitro osteoarthritis model with chondrocytes stimulated by IL-1β, treated with varying concentrations of luteolin. Treatment with luteolin notably increased the levels of synthesis factors Aggrecan and Collagen II, while decreasing the levels of decomposition factors MMP-1 and ADAMTS-5. Moreover, inhibition of autophagy by Chloroquine reversed the imbalances in chondrocyte activities induced by IL-1β. In an in vivo model of knee osteoarthritis induced by medial meniscal instability (DMM), luteolin was administered as a therapeutic regimen. After 12 weeks, knee cartilage tissues from mice were analyzed. Immunofluorescence and immunohistochemical staining revealed a decrease in P62 expression and an increase in Beclin-1 in the cartilage tissues. Additionally, cartilage wear in the knee joints of mice was alleviated by safranin O and fast green staining. Our study findings underscore the significant role of luteolin in effectively rebalancing chondrocyte activities disrupted by IL-1β. Our results strongly indicate that luteolin has the potential to be developed as a novel therapeutic agent for the treatment of osteoarthritis, offering promising prospects for future drug development.

Unraveling the path to osteoarthritis management: targeting chondrocyte apoptosis for therapeutic intervention

Osteoarthritis (OA) is a chronic disease affecting joints and further causing disabilities. This disease affects around 240 million people worldwide. It is a multifactorial disease, and its etiology is difficult to determine. Although numerous therapeutic strategies are available, the therapies are aimed at reducing pain and improving patients' quality of life. Hence, there is an urgent need to develop disease-modifying drugs (DMOAD) that can reverse or halt OA progression. Apoptosis is a cell removal process that is important in maintaining homeostatic mechanisms in the development and sustaining cell population. The apoptosis of chondrocytes is believed to play an important role in OA progression due to poor chondrocytes self-repair abilities to maintain the extracellular matrix (ECM). Hence, targeting chondrocyte apoptosis can be one of the potential therapeutic strategies in OA management. There are various mediators and targets available to inhibit apoptosis such as autophagy, endoplasmic reticulum (ER) stress, oxidative stress, and inflammation. As such, this review highlights the importance and potential targets that can be aimed to reduce chondrocyte apoptosis.

WITHDRAWN: The dysregulated autophagy in osteoarthritis: Revisiting molecular profile

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Emerging Roles of Macrophage Polarization in Osteoarthritis: Mechanisms and Therapeutic Strategies

Osteoarthritis (OA) is the most common chronic degenerative joint disease in middle-aged and elderly people, characterized by joint pain and dysfunction. Macrophages are key players in OA pathology, and their activation state has been studied extensively. Various studies have suggested that macrophages might respond to stimuli in their microenvironment by changing their phenotypes to pro-inflammatory or anti-inflammatory phenotypes, which is called macrophage polarization. Macrophages accumulate and become polarized (M1 or M2) in many tissues, such as synovium, adipose tissue, bone marrow, and bone mesenchymal tissues in joints, while resident macrophages as well as other stromal cells, including fibroblasts, chondrocytes, and osteoblasts, form the joint and function as an integrated unit. In this study, we focus exclusively on synovial macrophages, adipose tissue macrophages, and osteoclasts, to investigate their roles in the development of OA. We review recent key findings related to macrophage polarization and OA, including pathogenesis, molecular pathways, and therapeutics. We summarize several signaling pathways in macrophage reprogramming related to OA, including NF-κB, MAPK, TGF-β, JAK/STAT, PI3K/Akt/mTOR, and NLRP3. Of note, despite the increasing availability of treatments for osteoarthritis, like intra-articular injections, surgery, and cellular therapy, the demand for more effective clinical therapies has remained steady. Therefore, we also describe the current prospective therapeutic methods that deem macrophage polarization to be a therapeutic target, including physical stimulus, chemical compounds, and biological molecules, to enhance cartilage repair and alleviate the progression of OA.

Thrombospondin-1-mediated crosstalk between autophagy and oxidative stress orchestrates repair of blast lung injury

Coal mining carries inherent risks of catastrophic gas explosions capable of inflicting severe lung injury. Using complementary in vivo and in vitro models, we explored mechanisms underlying alveolar epithelial damage and repair following a gas explosion in this study. In a rat model, the gas explosion was demonstrated to trigger inflammation and injury within the alveolar epithelium. The following scRNA-sequencing revealed that alveolar epithelial cells exhibited the most profound transcriptomic changes after gas explosion compared to other pulmonary cell types. In the L2 alveolar epithelial cells, the blast was found to cause autophagic flux by inducing autophagosome formation, LC3 lipidation, and p62 degradation. Transcriptomic profiling of the L2 cells identified PI3K-Akt and p53 pathways as critical modulators governing autophagic and oxidative stress responses to blast damage. Notably, Thrombospondin-1 (Thbs1) was determined for the first time as a pivotal node interconnecting these two pathways. The findings of this study illuminate intricate mechanisms of alveolar epithelial injury and recovery after blast trauma, highlighting autophagic and oxidative stress responses mediated by Thbs1-associated PI3K-Akt and p53 pathways as high-value therapeutic targets, and strategic modulation of these pathways in future studies may mitigate lung damage by reducing oxidative stress while engaging endogenous tissue repair processes like autophagy.

Fabrication of injectable alginate hydrogels with sustained release of 4-octyl itaconate for articular anti-inflammatory

BACKGROUND

Osteoarthritis (OA) is a chronic and degenerative joint disease that remains a great challenge in treatment due to the lack of effective therapies. 4-octyl itaconate (4-OI) is a novel and potent modulator of inflammation for the treatment of inflammatory disease. However, the clinical usage of 4-OI is limited due to its poor solubility and low bioavailability. As a promising drug delivery strategy, injectable hydrogels offers an effective approach to address these limitations of 4-OI.

OBJECTIVE

The aim of the study was to verify that the composite 4-OI/SA hydrogels could achieve a controlled release of 4-OI and reduce damage to articular cartilage in the group of osteoarthritic rats treated with the system.

METHODS

In this study, an injectable composite hydrogel containing sodium alginate (SA) and 4-octyl itaconate (4-OI) has been developed for continuous intra-articular administration in the treatment of OA.

RESULTS

After intra-articular injection in arthritic rats, the as-prepared 4-OI/SA hydrogel containing of 62.5 μM 4-OI effectively significantly reduced the expression of TNF-α, IL-1β, IL-6 and MMP3 in the ankle fluid. Most importantly, the as-prepared 4-OI/SA hydrogel system restored the morphological parameters of the ankle joints close to normal.

CONCLUSION

4-OI/SA hydrogel shows a good anti-inflammatory activity and reverse cartilage disruption, which provide a new strategy for the clinical treatment of OA.

4-Octyl itaconate inhibits inflammation to attenuate psoriasis as an agonist of oxeiptosis

Psoriasis is a highly prevalent chronic disease associated with a substantial social and economic burden. Oxeiptosis is a programmed cell death that occurs when cells are in a state of high oxidative stress, which has a potent anti-inflammatory effect. However, there is still no research on oxeiptosis in psoriasis, and the agonists or antagonists of oxeiptosis remain an unclear field. Here, we found that oxeiptosis of keratinocytes was inhibited in psoriasis lesions. KEAP1, as the upstream molecular component of oxeiptosis, is highly expressed in psoriasis lesions. Knockdown of KEAP1 in HaCaT cells caused oxeiptosis in the condition of M5 cocktail stimulation. Next, we found that the cell-permeable derivative of itaconate, 4-octylitaconate (OI) promoted oxeiptosis of keratinocytes by inhibiting KEAP1 and then activating PGAM5 which are two upstream molecular components of oxeiptosis. At the same time, OI can reduce the expression of inflammatory cytokines induced by M5 cocktail stimulation in vitro. Similarly, we found that OI can alleviate IMQ-induced psoriatic lesions in mice and downregulate the levels of inflammatory cytokines in psoriatic lesions. In summary, our findings suggest that oxeiptosis of keratinocytes was inhibited in psoriasis and OI can significantly inhibit inflammation and alleviate psoriasis as an agonist of oxeiptosis, indicating that oxeiptosis may be involved in regulating the progression of psoriasis, which may provide new therapeutic targets for psoriasis treatment.

Osteoarthritis: Role of Peroxisome Proliferator-Activated Receptors

Osteoarthritis (OA) represents the foremost degenerative joint disease observed in a clinical context. The escalating issue of population aging significantly exacerbates the prevalence of OA, thereby imposing an immense annual economic burden on societies worldwide. The current therapeutic landscape falls short in offering reliable pharmaceutical interventions and efficient treatment methodologies to tackle this growing problem. However, the scientific community continues to dedicate significant efforts towards advancing OA treatment research. Contemporary studies have discovered that the progression of OA may be slowed through the strategic influence on peroxisome proliferator-activated receptors (PPARs). PPARs are ligand-activated receptors within the nuclear hormone receptor family. The three distinctive subtypes-PPARα, PPARβ/δ, and PPARγ-find expression across a broad range of cellular terminals, thus managing a multitude of intracellular metabolic operations. The activation of PPARγ and PPARα has been shown to efficaciously modulate the NF-κB signaling pathway, AP-1, and other oxidative stress-responsive signaling conduits, leading to the inhibition of inflammatory responses. Furthermore, the activation of PPARγ and PPARα may confer protection to chondrocytes by exerting control over its autophagic behavior. In summation, both PPARγ and PPARα have emerged as promising potential targets for the development of effective OA treatments.

4-Octyl itaconate attenuates LPS-induced acute kidney injury by activating Nrf2 and inhibiting STAT3 signaling

BACKGROUND

Septic acute kidney injury (S-AKI) is the leading form of acute kidney failure among hospitalized patients, and the inflammatory response is involved in this process. 4-octyl itaconate (4-OI) is a multi-target itaconate derivative with potent anti-inflammatory action. However, it remains elusive whether and how 4-OI contributes to the regulation of S-AKI.

METHODS

We employed a lipopolysaccharide (LPS)-induced AKI murine model and explored the potential renoprotective effect of 4-OI in vivo. In vitro experiments, BUMPT cells, a murine renal tubular cell line, were conducted to examine the effects of 4-OI on inflammation, oxidative stress, and mitophagy. Moreover, STAT3 plasmid was transfected in BUMPT cells to investigate the role of STAT3 signaling in the 4-OI-administrated state.

RESULTS

We demonstrate that 4-OI protects against S-AKI through suppressing inflammation and oxidative stress and enhancing mitophagy. 4-OI significantly reduced the levels of Scr, BUN, Ngal as well as the tubular injury in LPS-induced AKI mice. 4-OI restrained inflammation by reducing macrophage infiltration and suppressing the expression of IL-1β and NLRP3 in the septic kidney. 4-OI also reduced ROS levels, as well as cleaved caspase-3 and boosted antioxidants such as HO-1, and NQO1 in mice. In addition, the 4-OI treatment significantly promoted mitophagy. Mechanistically, 4-OI activated Nrf2 signaling and suppressed phosphorylated STAT3 in vivo and vitro. Molecular docking revealed the binding affinity of 4-OI towards STAT3. ML385, a specific Nrf2 inhibitor, partially repressed the anti-inflammatory and anti-oxidative effects of 4-OI and partially restricted the mitophagy induced by 4-OI in vivo and in vitro. Transfected with STAT3 plasmid partially suppressed mitophagy and the anti-inflammatory effect provoked by 4-OI in vitro.

CONCLUSION

These data suggest that 4-OI ameliorates LPS-induced AKI by suppressing inflammation and oxidative stress and enhancing mitophagy through the overactivation of the Nrf2 signaling pathway, and inactivation of STAT3. Our study identifies 4-OI as a promising pharmacologic for S-AKI.

Dimethyl itaconate is effective in host-directed antimicrobial responses against mycobacterial infections through multifaceted innate immune pathways

BACKGROUND

Itaconate, a crucial immunometabolite, plays a critical role in linking immune and metabolic functions to influence host defense and inflammation. Due to its polar structure, the esterified cell-permeable derivatives of itaconate are being developed to provide therapeutic opportunities in infectious and inflammatory diseases. Yet, it remains largely uncharacterized whether itaconate derivatives have potentials in promoting host-directed therapeutics (HDT) against mycobacterial infections. Here, we report dimethyl itaconate (DMI) as the promising candidate for HDT against both Mycobacterium tuberculosis (Mtb) and nontuberculous mycobacteria by orchestrating multiple innate immune programs.

RESULTS

DMI per se has low bactericidal activity against Mtb, M. bovis Bacillus Calmette-Guérin (BCG), and M. avium (Mav). However, DMI robustly activated intracellular elimination of multiple mycobacterial strains (Mtb, BCG, Mav, and even to multidrug-resistant Mtb) in macrophages and in vivo. DMI significantly suppressed the production of interleukin-6 and -10, whereas it enhanced autophagy and phagosomal maturation, during Mtb infection. DMI-mediated autophagy partly contributed to antimicrobial host defenses in macrophages. Moreover, DMI significantly downregulated the activation of signal transducer and activator of transcription 3 signaling during infection with Mtb, BCG, and Mav.

CONCLUSION

Together, DMI has potent anti-mycobacterial activities in macrophages and in vivo through promoting multifaceted ways for innate host defenses. DMI may bring light to new candidate for HDT against Mtb and nontuberculous mycobacteria, both of which infections are often intractable with antibiotic resistance.

Injectable hydrogel loaded with 4-octyl itaconate enhances cartilage regeneration by regulating macrophage polarization

Macrophages play a distinctive role in the early stage of inflammation after cartilage defects. Previous studies have shown that macrophages can express different phenotypes, among which M2 polarization is important to maintain the balance of the inflammatory microenvironment and promote cartilage regeneration. In this study, 4-octyl itaconic acid (4-OI), a derivative of the endogenous metabolite itaconic acid, was used to regulate the polarization behavior of macrophages and enhance cartilage repair. Oxidized sodium alginate (OSA) and gelatin (GEL) were selected as materials to form injectable hydrogels with the function of sustained release of 4-OI. In vivo and in vitro experiments have verified that the OSA/GEL hydrogel system loaded with 4-OI could promote M2 macrophage polarization and inhibit the inflammatory reaction. A rat knee joint cartilage defect model further confirmed its role in promoting cartilage regeneration in the later stage. In this study, the OSA/GEL hydrogel was successfully fabricated as a vehicle for delivering 4-OI, which could evidently alleviate the inflammatory reaction and thus accelerate tissue regeneration. The results of this study provide a new method for promoting subsequent tissue regeneration by regulating the early immune response.

Mulberroside A alleviates osteoarthritis via restoring impaired autophagy and suppressing MAPK/NF-κB/PI3K-AKT-mTOR signaling pathways

Osteoarthritis (OA) is a trauma-/age-related degenerative disease characterized by chronic inflammation as one of its pathogenic mechanisms. Mulberroside A (MA), a natural bioactive withanolide, demonstrates anti-inflammatory properties in various diseases; however, little is known about the effect of MA on OA. We aim to examine the role of MA on OA and to identify the potential mechanisms through which it protects articular cartilage. In vitro, MA improved inflammatory response, anabolism, and catabolism in IL-1β-induced OA chondrocytes. The chondroprotective effects of MA were attributed to suppressing the MAPK, NF-κB, and PI3K-AKT-mTOR signaling pathways, as well as promoting the autophagy process. In vivo, intra-articular injection of MA reduced the cartilage destruction and reversed the change of anabolic and catabolic-related proteins in destabilized medial meniscus (DMM)-induced OA models. Thus, the study indicates that MA exhibits a chondroprotective effect and might be a promising agent for OA treatment.

Osthole Suppresses Knee Osteoarthritis Development by Enhancing Autophagy Activated via the AMPK/ULK1 Pathway

Knee osteoarthritis (KOA) is an increasingly prevalent heterogeneous disease characterized by cartilage erosion and inflammation. As the main chemical constituent of Angelicae Pubescentis Radix (APR), an anti-inflammatory herbal medicine, the potential biological effects and underlying mechanism of osthole on chondrocytes and KOA progression remain elusive. In this study, the potential effect and mechanism of osthole on KOA were investigated in vitro and in vivo. We found that osthole inhibited IL-1β-induced apoptosis and cartilage matrix degeneration by activating autophagy in rat chondrocytes. In addition, osthole could activate autophagy through phosphorylation of AMPK/ULK1, and AMPK serves as a positive upstream regulator of ULK1. Furthermore, KOA rats treated with osthole showed phosphorylation of the AMPK/ULK1 pathway and autophagy activation, as well as cartilage protection. Collectively, the AMPK/ULK1 signaling pathway can be activated by osthole to enhance autophagy, thereby suppressing KOA development. Osthole may be a novel and effective therapeutic agent for the clinical treatment of KOA.

Icariin alleviates osteoarthritis through PI3K/Akt/mTOR/ULK1 signaling pathway

OBJECTIVES

This study aims to investigate the effects of Icariin (ICA) on interleukin-1β (IL-1β)-induced osteoarthritis (OA) and its potential mechanism of action.

METHODS

SW1353 chondrocytes were pretreated with ICA for 2 h, followed by stimulation with IL-1β to mimic OA. Expression levels of matrix metalloproteinases (MMP-3) and collagen II were determined using real-time PCR and Western blot assays. Autophagy activation (by ICA) or inhibition (by shRNA) was determined based on the expression levels of ULK1, Beclin-1, LC3-II/I, and p62, using Western blot analysis. The phosphorylation levels of PI3K, Akt, mTOR, and ULK1 were also detected using Western blot analysis.

RESULTS

IL-1β increased MMP-3 overproduction, induced collagen II degradation, and reduced the level of autophagy-associated proteins, including ULK1, Beclin-1, and LC3-II/I. In contrast, ICA pretreatment attenuated IL-1β-induced MMP-3 overproduction, increased collagen II expression, and induced expression of autophagy-related proteins. ICA also decreased PI3K, Akt, and mTOR phosphorylation, increased the production of ULK1, and induced autophagy. Short hairpin RNA-mediated knockdown of ULK1 led to activation of the PI3K/Akt/mTOR pathway, which reversed the protective effects of ICA.

CONCLUSIONS

Our findings indicate that ICA can induce autophagy by regulating the PI3K/AKT/mTOR/ULK1 signaling pathway. This study suggests that ICA may be effective for treating OA.

tRNA-Derived Fragment tRF-5009A Regulates Autophagy and Degeneration of Cartilage in Osteoarthritis via Targeting mTOR

tRNA-derived fragments (tRFs) have been reported to have critical regulatory roles in osteoarthritis (OA). Recent studies have suggested that autophagy promotes the homeostasis of the extracellular matrix of chondrocytes in OA. However, the role of tRFs in posttranscriptional gene regulation during autophagy in OA is unknown. Therefore, we explored the role of tRF-5009A in the posttranscriptional gene regulation of autophagy and cartilage degeneration in OA. Using RNA sequencing, we identified tRF-5009A, the tRNA^ValCAC-derived fragment, in OA tissues and explored its expression by quantitative reverse transcription PCR and fluorescence in situ hybridization. We further investigated the relationship between the expression of tRF-5009A and clinical factors in OA. Chondrocytes were transfected with a tRF-5009A inhibitor or mimic to determine their functions, including in relation to autophagy and the cartilage phenotype. A rescue experiment and dual-luciferase reporter assay were conducted to determine whether the 3′-untranslated region (UTR) of mTOR contains a tRF-5009A-binding site. tRF-5009A was downregulated in the cartilage of OA knees, especially in damaged areas. mTOR was highly expressed in damaged cartilage and negatively correlated with the expression of tRF-5009A; transfection with a tRF-5009A inhibitor promoted the expression of mTOR and suppressed autophagy, whereas transfection with a tRF-5009A mimic had the opposite effect. A dual-luciferase reporter assay showed that tRF-5009A silenced the expression of mTOR by binding to its 3′-UTR. Thus, tRF-5009A regulates autophagy and cartilage degeneration in OA by targeting mTOR. In summary, these findings provide an additional tool for the clinical diagnosis and novel targeted therapy of OA.