Objective: Alterations in mitochondria play a key role in the pathogenesis of osteoarthritis (OA). The role of inflammation in the progression of OA has also acquired important new dimensions. This study was undertaken to evaluate the potential role of mitochondrial dysfunction in increasing the inflammatory response of normal human chondrocytes to cytokines.Methods: Mitochondrial dysfunction was induced by commonly used inhibitors. Interleukin‐1β (IL‐1β) and tumor necrosis factor α (TNFα) were used as inflammatory mediators. IL‐8 and cyclooxygenase 2 (COX‐2) protein and messenger RNA (mRNA) expression and prostaglandin E₂ (PGE₂) levels were assessed. The chemotactic activity of neutrophils was assayed. Additionally, inhibitors of reactive oxygen species (ROS) and NF‐κB were used to identify possible inflammatory response pathways induced by mitochondrial dysfunction, and the effects of the natural antioxidant resveratrol were tested.Results: Pretreatment with antimycin A or oligomycin (inhibitors of mitochondrial respiratory chain complexes III and V, respectively) triggered a strong potentiation of IL‐1β–induced IL‐8 mRNA and protein expression (mean ± SEM at 18 hours 5,932 ± 1,995 pg/50,000 cells for IL‐1β alone versus 16,241 ± 5,843 pg/50,000 cells for antimycin A plus IL‐1β and 20,087 ± 5,407 pg/50,000 cells for oligomycin plus IL‐1β; P < 0.05). Similar results were observed with TNFα or when expression of the inflammatory mediator COX‐2 or PGE₂ production was assessed. Mitochondrial dysfunction increased the chemotactic activity induced by cytokines, and ROS and NF‐κB inhibitors decreased the production of IL‐8. Resveratrol significantly reduced the inflammatory response.Conclusion: Our findings indicate that mitochondrial dysfunction could amplify the responsiveness to cytokine‐induced chondrocyte inflammation through ROS production and NF‐κB activation. This pathway might lead to the impairment of cartilage and joint function in OA.

Objective: Mitochondrial alterations play a key role in the pathogenesis of osteoarthritis (OA). This study evaluated a potential role of mitochondrial respiratory chain (MRC) dysfunction in the inflammatory response of normal human chondrocytes.Methods: Commonly used inhibitors of the MRC were utilized to induce mitochondrial dysfunction in normal human chondrocytes. Levels of prostaglandin E₂ (PGE₂) protein and expression of cyclooxygenase 2 (COX‐2) and COX‐1 messenger RNA (mRNA) and protein were analyzed. To identify the underlying mechanisms responsible for PGE₂ liberation, reactive oxygen species (ROS) were measured. Inhibitors of ROS, including vitamin E, and inhibitors of mitochondrial Ca²⁺ and NF‐κB were used to test their effects on the MRC.Results: Antimycin A and oligomycin (inhibitors of mitochondrial complexes III and V, respectively) significantly increased the levels of PGE₂ (mean ± SEM 505 ± 132 pg/50,000 cells and 288 ± 104 pg/50,000 cells, respectively, at 24 hours versus a basal level of 29 ± 9 pg/50,000 cells; P < 0.05) and increased the expression of COX‐2 at both the mRNA and protein levels. Expression of COX‐1 did not show any modulation with either inhibitor. Further experiments revealed that antimycin A and oligomycin induced a marked increase in the levels of ROS. Production of PGE₂ and expression of COX‐2 protein were inhibited by antioxidants, vitamin E, and mitochondrial Ca²⁺ and NF‐κB inhibitors. The response to blockers of mitochondrial Ca²⁺ movement showed that ROS production was dependent on mitochondrial Ca²⁺ accumulation.Conclusion: These results strongly suggest that, in human chondrocytes, the inhibition of complexes III and V of the MRC induces an inflammatory response, which could be especially relevant in relation to PGE₂ production via mitochondrial Ca²⁺ exchange, ROS production, and NF‐κB activation. These data may prove valuable for a better understanding of the participation of mitochondria in the pathogenesis of OA.

Objectives. In RA, synoviocytes cause increased oxidative stress, leading to mitochondrial alterations that may participate in the pathogenesis of RA. Here we investigated whether mitochondrial dysfunction induces inflammatory responses in cultured normal human synoviocytes, a hallmark of RA. Methods. Mitochondrial dysfunction was induced with the inhibitor oligomycin. The effects of mitochondrial dysfunction on cyclooxygenase-2 (COX-2), prostaglandin E₂ (PGE₂) and IL-8 expression; cellular and mitochondrial reactive oxygen species (ROS) production; nuclear factor-κB (NF-κB) activation and p65 translocation were studied. ROS scavengers (N-acetylcysteine and mitoTEMPO) and an NF-κB inhibitor (BAY-117085) were used to investigate the pathways involved. The natural anti-inflammatory antioxidant resveratrol was also tested. Results. Mitochondrial dysfunction per se significantly stimulated mitochondrial ROS production as well as low-grade expressions of COX-2, PGE₂ and IL-8. Interestingly, mitochondrial dysfunction induced by pretreatment of synoviocytes with oligomycin synergized with IL-1β to increase the expression of these inflammatory mediators. The inflammatory effects of mitochondrial damage appeared to be dependent on ROS production and NF-κB activation since the inflammatory response was counteracted by both N-acetylcysteine and mitoTEMPO and it was also reduced by BAY-117085. Antimycin A and paraquat (inhibitors of mitochondrial function) also induced inflammatory responses. Furthermore, resveratrol significantly reduced the inflammatory response by decreasing ROS production and NF-κB activation. Conclusion. These data suggest that mitochondrial dysfunction could induce an inflammatory response in normal human synoviocytes and sensitize these cells, causing a significant amplification of the inflammatory response induced by IL-1β. Resveratrol may represent a promising strategy in controlling the synovial inflammatory response.

Green seaweeds are a widespread group of marine macroalgae that could be regarded as biorenewable source of valuable compounds, in particular sulfated polysaccharides like ulvans with interesting biological properties. Among them, anti-inflammatory activity represents an interesting target, since ulvans could potentially avoid side effects of conventional therapies. However, a great variability in ulvan content, composition, structure and properties occurs depending on seaweed specie and growth and processing conditions. All these aspects should be carefully considered in order to have reproducible and well characterized products. This review presents some concise ideas on ulvan composition and general concepts on inflammation mechanisms. Then, the main focus is on the importance of adequate selection of extraction, depolymerization and purification technologies followed by an updated survey on anti-inflammatory properties of ulvans through modulation of different signaling pathways. The potential application in a number of diseases, with special emphasis on inflammaging, gut microbiota dysbiosis, wound repair, and metabolic diseases is also discussed. This multidisciplinary overview tries to present the potential of ulvans considering not only mechanistic, but also processing and applications aspects, trusting that it can aid in the development and application of this widely available and renewable resource as an efficient and versatile anti-inflammatory agent.

Accumulation of advanced glycation end-products (AGEs) is involved in age-related osteoarthritis (OA). Glyoxalase (Glo)-1 is the main enzyme involved in the removal of AGE precursors, especially carboxymethyl-lysine (CML). We aimed to investigate the expression of several AGEs and Glo-1 in human OA cartilage and to study chondrocytic Glo-1 regulation by inflammation, mediated by interleukin (IL)-1β. Ex vivo, we quantified AGEs (pentosidine, CML, methylglyoxal-hydroimidazolone-1) in knee cartilage from 30 OA patients. Explants were also incubated with and without IL-1β, and we assessed Glo-1 protein expression and enzymatic activity. In vitro, primary cultured murine chondrocytes were stimulated with increasing concentrations of IL-1β to assess Glo-1 enzymatic activity and expression. To investigate the role of oxidative stress in the IL-1β effect, cells were also treated with inhibitors of mitochondrial oxidative stress or nitric oxide synthase. Ex vivo, only the human cartilage CML content was correlated with patient age (r = 0.78, p = 0.0031). No statistically significant correlation was found between Glo-1 protein expression and enzymatic activity in human cartilage and patient age. We observed that cartilage explant stimulation with IL-1β decreased Glo-1 protein expression and enzymatic activity. In vitro, we observed a dose-dependent decrease in Glo-1 mRNA, protein quantity, and enzymatic activity in response to IL-1β in murine chondrocytes. Inhibitors of oxidative stress blunted this downregulation. Glo-1 is impaired by inflammation mediated by IL-1β in chondrocytes through oxidative stress pathways and may explain age-dependent accumulation of the AGE CML in OA cartilage.