Evidence for species differences in the regulation of MMPs by all-trans retinoic acid in cytokine-stimulated chondrocytes.

In inflammatory conditions, chondrocytes produce large amounts of matrix metalloproteases (MMP) and nitric oxide (NO) thought to contribute to joint degradation. We tested the ability of all-trans retinoic acid (ATRA, a retinoic acid receptor (RAR) agonist) to modulate these inflammatory genes in chondrocytes from humans or rats, chosen as representative of animal models of arthritis. All RAR subtypes and RXR-alpha or -beta were expressed at the mRNA level in both species, although IL-1beta (10 ng/ml) inhibited RAR subtypes more markedly in rat than in human cells. ATRA (300 or 1000 nM) inhibited IL-1-induced expression of iNOS and nitrites level in both species, although the NO pathway was induced maximally in rat cells. ATRA displayed controversial effects on MMPs between rat and human chondrocytes, especially for MMP-9 expression. The effects of ATRA were irrelevant to the nuclear translocation of AP-1. The present data underlines that retinoids have a species-dependent impact on IL-1-induced responses in chondrocytes, suggesting that extrapolation of their pharmacological properties from animal cells has a poor relevance to clinical situation.

Modulatory effect of rhein on IL-1alpha-induced responses in human chondrocytes: a comparative study between antibody microarrays and specific ELISAs.

The present work aimed to take advantage of the screening capacity of protein arrays to search for additional targets of rhein in interleukin (IL)-1-stimulated chondrocytes. Primary cultures of chondrocytes from osteoarthritic (OA) patients were stimulated for 24 and 48 h with 1 ng/ml of IL-1alpha, in the presence or absence of 10(-5) M of rhein. Culture supernatants were analyzed with arrays membranes consisting of 120 antibodies directed against cytokines, chemokines, and angiogenic or growth factors and were controlled for 8 proteins by specific immuno-enzymatic assays (ELISA). Protein arrays showed that several CC or CXC chemokines, the growth factor GM-CSF, the cytokines IL-6, IL-7 and IL-10 (but unexpectedly not IL-1beta or TNFalpha) and the adhesion molecule ICAM-1 were induced maximally by IL-1alpha. In IL-1-stimulated chondrocytes, rhein reduced slightly the production of MCP-1 and increased those of IL-1Ra, of the cytokine receptors sgp130, IL-6R, sTNFR I and R II, but also of some chemokines or ICAM-1. Specific ELISAs confirmed the effect of rhein on MCP-1, IL-1Ra, sgp130, IL-6R and sTNFR II but was discrepant for GROalpha and were always more sensitive than protein arrays to detect IL-1 effects such as IL-1Ra and TNFalpha release. The present data show that rhein modulated some IL-1-induced responses contributing possibly to its chondroprotective (IL-1Ra, MCP-1) or cytokine modifying (sTNFR II, sgp130) properties, but that protein arrays were poorly sensitive to check for IL-1- and/or rhein-induced changes.