Chondrocyte enlargement is a marker of osteoarthritis severity.

OBJECTIVE: We aimed to assess whether an increase in chondrocyte size might be a feature of the articular cartilage (AC) hypertrophic-like phenotype both in experimental and in human osteoarthritis (OA). The anatomical location of these enlarged cells in the cartilage layers was also evaluated. METHODS: Experimental OA was carried out in female rabbits alone or in combination with osteoporosis (OPOA). The rabbits were subjected to destabilization knee surgery to develop OA. Osteoporosis was induced with ovariectomy and methylprednisolone administration. Human OA samples obtained from knee replacement surgery were also studied. Cartilage lesions and chondrocyte size were assessed in AC sections. Immunostaining of type-X collagen and metalloproteinase-13 were used as markers of the AC hypertrophic transformation. Both the cell size and the gene expression of type-X collagen were further analyzed in primary murine chondrocyte cultures. RESULTS: Compared to healthy AC, chondrocyte size was increased both in experimental and in human OA, in correlation with the severity of cartilage damage. No differences in chondrocyte size were found between deeper or more superficial regions of AC. In cell cultures, accretion of hypertrophic markers and cell enlargement were found to occur synchronized. CONCLUSIONS: We observed an enhancement in the mean size of chondrocytes at the OA cartilage, which showed correlation with cartilage damage, both in human and in experimental OA. The enlarged chondrocytes were homogeneously distributed throughout the AC. Our results suggest that chondrocyte size could be a reliable measure of disease progression, of potential use in the histopathological assessment of OA cartilage.

Tofacitinib restores the inhibition of reverse cholesterol transport induced by inflammation: understanding the lipid paradox associated with rheumatoid arthritis.

BACKGROUND AND PURPOSE: Patients with active rheumatoid arthritis (RA) have increased cardiovascular mortality, paradoxically associated with reduced circulating lipid levels. The JAK inhibitor tofacitinib ameliorates systemic and joint inflammation in RA with a concomitant increase in serum lipids. We analysed the effect of tofacitinib on the lipid profile of hyperlipidaemic rabbits with chronic arthritis (CA) and on the changes in reverse cholesterol transport (RCT) during chronic inflammation. EXPERIMENTAL APPROACH: CA was induced in previously immunized rabbits, fed a high-fat diet, by administering four intra-articular injections of ovalbumin. A group of rabbits received tofacitinib (10 mg·kg-1 ·day-1 ) for 2 weeks. Systemic and synovial inflammation and lipid content were evaluated. For in vitro studies, THP-1-derived macrophages were exposed to high lipid concentrations and then stimulated with IFNγ in the presence or absence of tofacitinib in order to study mediators of RCT. KEY RESULTS: Tofacitinib decreased systemic and synovial inflammation and increased circulating lipid levels. Although it did not modify synovial macrophage density, it reduced the lipid content within synovial macrophages. In foam macrophages in culture, IFNγ further stimulated intracellular lipid accumulation, while the JAK/STAT inhibition provoked by tofacitinib induced lipid release by increasing the levels of cellular liver X receptor α and ATP-binding cassette transporter (ABCA1) synthesis. CONCLUSIONS AND IMPLICATIONS: Active inflammation could be associated with lipid accumulation within macrophages of CA rabbits. JAK inhibition induced lipid release through RCT activation, providing a plausible explanation for the effect of tofacitinib on the lipid profile of RA patients.

Hypercholesterolemia boosts joint destruction in chronic arthritis. An experimental model aggravated by foam macrophage infiltration.

OBJECTIVE: The aim of this study was to determine whether hypercholesterolemia increases articular damage in a rabbit model of chronic arthritis. METHODS: Hypercholesterolemia was induced in 18 rabbits by administrating a high-fat diet (HFD). Fifteen rabbits were fed normal chow as controls. Chronic antigen-induced arthritis (AIA) was induced in half of the HFD and control rabbits, previously immunized, by intra-articular injections of ovalbumin. After sacrifice, lipid and systemic inflammation markers were analyzed in blood serum. Synovium was analyzed by Krenn score, multinucleated cell counting, immunohistochemistry of RAM11 and CD31, and TNF-α and macrophage chemoattractant protein-1 (MCP-1) gene expression. Active bone resorption was assessed by protein expression of receptor activator of nuclear factor kappa-B ligand (RANKL), osteoprotegerin (OPG) and quantification of cathepsin K, contact surface and the invasive area of pannus into bone. RESULTS: Rabbits receiving the HFD showed higher total serum cholesterol, HDL, triglycerides and CRP levels than rabbits fed a normal diet. Synovitis score was increased in HFD, and particularly in AIA and AIA + HFD groups. AIA + HFD synovium was characterized by a massive infiltration of RAM11+ cells, higher presence of multinucleated foam cells and bigger vascularization than AIA. Cathepsin K+ osteoclasts and the contact surface of bone resorbing pannus were also increased in rabbits with AIA + HFD compared with AIA alone. Synovial TNF-α and MCP-1 gene expression was increased in AIA and HFD rabbits compared with healthy animals. RANKL protein expression in AIA and AIA + HFD groups was higher compared with either HFD or normal groups. CONCLUSIONS: This experimental model demonstrates that hypercholesterolemia increments joint tissue damage in chronic arthritis, with foam macrophages being key players in this process.

Inflamación sinovial en un modelo experimental de síndrome metabólico en conejo / Synovial inflammation in an experimental model of metabolic syndrome in the rabbit

Objetivo: Analizar el efecto del síndrome metabólico (SM) sobre la inflamación sinovial en un modelo experimental en conejo. Material y métodos: Se probaron tres intervenciones dietéticas diferentes para inducir un modelo experimental de SM, en 21 conejos New Zealand hembra, de 8 meses de edad: 1) alimentación con dieta enriquecida con 1% de colesterol y 3% de aceite de cacahuete y agua ad libitum; 2) alimentación con dieta normal y agua con 30% de fructosa ad libitum; 3) alimentación con dieta enriquecida con 1% de colesterol y 3% de aceite de cacahuete y agua con 30% de fructosa ad limitum. Los animales se dejaron evolucionar durante 12 semanas y se hizo un seguimiento semanal de peso, glucosa basal, colesterol HDL, triglicéridos. Tras el sacrificio, se tomaron muestras de membrana sinovial para cuantificar el infiltrado macrofágico sinovial mediante inmunohistoquímica. Resultados: La única intervención dietética con la que conseguimos inducir alteraciones asociadas al SM en los conejos fue alimentándolos con una dieta hiperlipémica. Estos animales, además de presentar hiperglucemia y dislipemia, tenían un infiltrado macrofágico sinovial mayor que el del grupo control. Conclusión: La alimentación con dieta hiperlipémica induce alteraciones típicas del SM en el conejo, acompañadas de un aumento del infiltrado macrofágico sinovial, lo que sugiere que el macrófago podría desempeñar un papel importante en el inicio y/o la progresión de la artrosis descrita que se asocia con el SM (AU)

Objetive: To analyze the effect of metabolic syndrome (MS) upon synovial inflammation in an experimental model in the rabbit. Material and methodology: Three different diets were used to induce an experimental model of MS in 21 female New Zealand rabbits (aged 8 months): 1) diet enriched with 1% cholesterol and 3% peanut oil, with water, ad libitum; 2) normal diet, with water, and 30% fructose, ad libitum; 3) diet enriched with 1% cholesterol and 3% peanut oil, with water, and 30% fructose, ad libitum. The animals were followed-up on for 12 weeks, with weekly monitoring of body weight, basal glucose, HDL-cholesterol and triglycerides. Following sacrifice, synovial membrane samples were collected to quantify the synovial macrophage infiltrate using immunohistochemical techniques. Results: The only diet to induce alterations associated with MS in the rabbits was the hyperlipidemic diet. These animals, in addition to presenting hyperglycemia and dyslipidemia, showed greater synovial macrophage infiltration than the control group. Conclusion: A hyperlipidemic diet induces alterations typical of MS in the rabbit, accompanied by an increase in synovial macrophage infiltration (AU)