Maria José LópEz-Armada

Recent studies have related mitochondrial impairment with peritoneal membrane damage during peritoneal dialysis (PD) therapy. Here, we assessed the involvement of mitochondrial dysfunction in the inflammatory response in human mesothelial cells, a hallmark in the pathogenesis of PD-related peritoneal membrane damage. Our ex vivo studies showed that IL-1β causes a drop in the mitochondrial membrane potential in cells from peritoneal effluent. Moreover, when mitochondrial damage was induced by inhibitors of mitochondrial function, a low-grade inflammatory response was generated. Interestingly, mitochondrial damage sensitized mesothelial cells, causing a significant increase in the inflammatory response induced by cytokines, in which ROS generation and NF-κB activation appear to be involved, since inflammation was counteracted by both mitoTEMPO (mitochondrial ROS scavenger) and BAY-117085 (NF-κB inhibitor). Furthermore, the natural anti-inflammatory antioxidant resveratrol significantly attenuated the inflammatory response, by reversing the decline in mitochondrial membrane potential and decreasing the expression of IL-8, COX-2 and PGE₂ caused by IL-1β. These findings suggest that IL-1β regulates mitochondrial function in mesothelial cells and that mitochondrial dysfunction could induce an inflammatory scenario that sensitizes these cells, causing significant amplification of the inflammatory response induced by cytokines. Resveratrol may represent a promising strategy in controlling the mesothelial inflammatory response to PD.

Control of excessive mitochondrial oxidative stress could provide new targets for both preventive and therapeutic interventions in the treatment of chronic inflammation or any pathology that develops under an inflammatory scenario, such as rheumatoid arthritis (RA). Increasing evidence has demonstrated the role of mitochondrial alterations in autoimmune diseases mainly due to the interplay between metabolism and innate immunity, but also in the modulation of inflammatory response of resident cells, such as synoviocytes. Thus, mitochondrial dysfunction derived from several danger signals could activate tricarboxylic acid (TCA) disruption, thereby favoring a vicious cycle of oxidative/mitochondrial stress. Mitochondrial dysfunction can act through modulating innate immunity via redox-sensitive inflammatory pathways or direct activation of the inflammasome. Besides, mitochondria also have a central role in regulating cell death, which is deeply altered in RA. Additionally, multiple evidence suggests that pathological processes in RA can be shaped by epigenetic mechanisms and that in turn, mitochondria are involved in epigenetic regulation. Finally, we will discuss about the involvement of some dietary components in the onset and progression of RA.

Preservation of the peritoneal membrane is an essential determinant of the long-term outcome of peritoneal dialysis (PD). Epithelial-to-mesenchymal transition (EMT) plays a central role in the pathogenesis of PD-related peritoneal membrane injury. We hypothesized that mitochondria may be implicated in the mechanisms that initiate and sustain peritoneal membrane damage in this setting. Hence, we carried out ex vivo studies of effluent-derived human mesothelial cells, which disclosed a significant increase in mitochondrial reactive oxygen species (mtROS) production and a loss of mitochondrial membrane potential in mesothelial cells with a fibroblast phenotype, compared to those preserving an epithelial morphology. In addition, in vitro studies of omentum-derived mesothelial cells identified mtROS as mediators of the EMT process as mitoTEMPO, a selective mtROS scavenger, reduced fibronectin protein expression induced by TGF-ß1. Moreover, we quantified mitochondrial DNA (mtDNA) levels in the supernatant of effluent PD solutions, disclosing a direct correlation with small solute transport characteristics (as estimated from the ratio dialysate/plasma of creatinine at 240 min), and an inverse correlation with peritoneal ultrafiltration. These results suggest that mitochondria are involved in the EMT that human peritoneal mesothelial cells suffer in the course of PD therapy. The level of mtDNA in the effluent dialysate of PD patients could perform as a biomarker of PD-induced damage to the peritoneal membrane.

Scope Previous work reported that dietary supplementation with resveratrol lowers synovial hyperplasia, inflammatory markers and oxidative damage in an antigen‐induced arthritis (AIA) model. Here, we investigated whether resveratrol can regulate the abnormal synovial proliferation by inducing autophagy and controlling the associated inflammatory response. Methods and Results Animals treated with resveratrol 8 weeks before AIA induction showed the highest significant signal for microtubule‐associated protein 1 light chain 3 (LC3) by confocal microscopy. Besides, resveratrol significantly reduced p62 expression, but it did not increase the signal of beclin‐1. Also, active caspase‐3 expression, as well as PARP, were up‐regulated in the AIA group, and were significantly reduced in resveratrol‐treated AIA group. Likewise, resveratrol also mitigated Ang‐1 and VEGF signals. Finally, resveratrol significantly reduced the serum levels of IL‐1β, CRP and PGE₂, as well as NF‐kB synovial tissue expression, which showed a significant correlation with p62 expression. Conclusion Dietary supplementation with resveratrol induces the non‐canonical autophagy pathway and limits the cross‐talk existence with inflammation, which in consequence modulates the synovial hyperplasia. Preventive strategies that incorporate dietary intervention with resveratrol may offer a potential therapeutic alternative to drugs to influence the risk of RA and influence its course. This article is protected by copyright. All rights reserved

Background Previously, we have demonstrated that dietary supplementation with resveratrol (RSV) lowers synovial hyperplasia, chemokines and oxidative damage in an acute antigen-induced arthritis (AIA) model developed in rats, and that autophagic cell death and limiting angiogenic response were involved¹. Objectives Here, we investigated the autophagic flux induced by RSV and its relation with serum interleukin (IL)−1β levels, since autophagy could regulate IL-1β via inflammasome. Moreover, C-reactive protein (CRP) and prostaglandin E₂ (PGE₂), which are also closely linked to inflammation and correlated with disease activity, were also evaluated. Methods Animals were randomly divided into 3 groups: healthy, AIA, and RSV-treated AIA group. RSV (12,5 mg/kg/day) was given orally 8 weeks before AIA induction until sacrifice day (48 hour after intra-articular injection). Healthy and AIA animals were administered 100 µl of water. RSV effects on autophagy were evaluated by the expression of the autophagy proteins, microtubule-associated protein 1 light chain 3 (LC3), and Beclin1 (an autophagic-related protein which up-regulation is associated with increased autophagosome formation), and p62 (an autophagic adaptor protein whose accumulation is associated with autophagic degradation dysfunction), by confocal and immunohistochemistry, respectively. Specific enzyme-linked immunosorbent assay kits and cytokine magnetic milliplex were used to measure CRP and PGE₂ and IL-1β in serum samples, respectively. Results At the end of the study, RSV significantly reduced the serum levels of IL-1 β, CRP and PGE₂ (p≤0.01 for IL-1β and PCR, and p≤0.05 for PGE₂). In relation to autophagy proteins, results showed that the expression of LC3 was greater in the AIA synovial membranes than in control synovial samples, in which the presence of vesicles was easily observed. Interestingly, the synovial tissues from the RSV group showed a significatively (p≤0.001) higher signal for LC3, compared with the AIA samples. As compared with healthy controls, AIA synovial membranes showed increased p62 expression, which was markedly inhibited by RSV treatment (p≤0.01). The protein level of Beclin 1 was higher in AIA synovial membranes than in healthy samples; however, RSV did not increase the signal of Beclin 1. Moreover, there was a significant correlation between p62 expression and serum IL-1β levels (p≤0.05 and r=0.617), PGE₂ (p≤0.01 and r=0. 604), and PCR (p≤0.001 and r=0.692). Conclusions These data suggest that resveratrol is capable of inducing the non-canonical (Beclin1 independent) autophagy pathway, and in consequence, modulates the cross-talk existence with inflammation in an acute AIA model, which could also ameliorate the severity of rheumatoid arthritis. Reference [1] Riveiro-Naveira R, Valcárcel N, Almonte M, Vaamonde C, Hermida L, López E, Blanco F, López-Armada MJ. Resveratrol lowers synovial hyperplasia, inflammatory markers and oxidative damage in an acute antigen-induced arthritis model. Rheumatology2016;55(10):1889–900. Disclosure of Interest None declared

Recent findings support a connection between mitochondrial dysfunction and activation of inflammatory pathways in articular cells. This study investigates in vivo in an acute model whether intra-articular administration of oligomycin, an inhibitor of mitochondrial function, induces an oxidative and inflammatory response in rat knee joints. Oligomycin was injected into the rat left knee joint on days 0, 2, and 5 before joint tissues were obtained on day 6. The right knee joint served as control. Results were evaluated by macroscopy and histopathology and by measuring cellular and mitochondrial reactive oxygen species (ROS), 4-hydroxy-2-nonenal (4-HNE, a marker of lipid peroxidation), nuclear factor erythroid 2-related factor 2 (Nrf2), and CD68 (macrophages) and chemokine levels. The marker of mitochondrial mass COX-IV was also evaluated. The macroscopic findings showed significantly greater swelling in oligomycin-injected knees than in control knees. Likewise, the histological score of synovial damage was also increased significantly. Immunohistochemical studies showed high expression of IL-8, coinciding with a marked infiltration of polymorphonuclears and CD68+ cells in the synovium. Mitochondrial mass was increased in the synovium of oligomycin-injected joints, as well as cellular and mitochondrial ROS production, and 4-HNE. Relatedly, expression of the oxidative stress-related transcription factor Nrf2 was also increased. As expected, no histological differences were observed in the cartilage; however, cytokine-induced neutrophil chemoattractant-1 mRNA and protein expression were up-regulated in this tissue. Mitochondrial failure in the joint is able to reproduce the oxidative and inflammatory status observed in arthritic joints.

Objective. The present study aimed to determine the protective effects of dietary supplementation with resveratrol (RSV) in an acute antigen-induced arthritis (AIA) model.

In patients undergoing peritoneal dialysis (PD), chronic exposure to nonphysiologic PD fluids elicits low-grade peritoneal inflammation, leading to fibrosis and angiogenesis. Phenotype conversion of mesothelial cells into myofibroblasts, the so-called mesothelial-to-mesenchymal transition (MMT), significantly contributes to the peritoneal dysfunction related to PD. A number of factors have been described to induce MMT in vitro and in vivo, of which TGF-β1 is probably the most important. The vasoconstrictor peptide endothelin-1 (ET-1) is a transcriptional target of TGF-β1 and mediates excessive scarring and fibrosis in several tissues. This work studied the contribution of ET-1 to the development of peritoneal damage and failure in a mouse model of PD. ET-1 and its receptors were expressed in the peritoneal membrane and upregulated on PD fluid exposure. Administration of an ET receptor antagonist, either bosentan or macitentan, markedly attenuated PD-induced MMT, fibrosis, angiogenesis, and peritoneal functional decline. Adenovirus-mediated overexpression of ET-1 induced MMT in human mesothelial cells in vitro and promoted the early cellular events associated with peritoneal dysfunction in vivo. Notably, TGF-β1-blocking peptides prevented these actions of ET-1. Furthermore, a positive reciprocal relationship was observed between ET-1 expression and TGF-β1 expression in human mesothelial cells. These results strongly support a role for an ET-1/TGF-β1 axis as an inducer of MMT and subsequent peritoneal damage and fibrosis, and they highlight ET-1 as a potential therapeutic target in the treatment of PD-associated dysfunction.