Mechanism of inhibition of endothelin-1-stimulated proteoglycan and collagen synthesis in rat articular chondrocytes.

The aim of this study was to determine the effects of endothelin-1 (ET-1) on proteoglycan (PG) and collagen synthesis by rat articular chondrocytes (RAC). PG and collagen synthesis was measured by [(35)S]-sulphate and [(3)H]-glycine incorporation, respectively into monolayers of confluent RAC exposed to ET-1 (10(-11) M-10(-7) M). ET-1 stimulated PG and collagen synthesis in these cells in a concentration-dependent manner during the first 24 h of incubation. Prolonged contact of the cells with ET-1 resulted in a gradual decrease, and finally, inhibition of ET-1 effects. This inhibition is mediated by nitric oxide (NO) released in response to ET-1 since: (1) nitric oxide synthase inhibitor, nitro-L-arginine-methyl ester (L-NAME), enhanced both basal and ET-1-induced [(35)S]-sulphate and [(3)H]-glycine incorporations; (2) sodium nitroprusside (SNP), which spontaneously releases NO, inhibited both basal and ET-1-induced incorporations, and was also able to suppress the effects of L-NAME; (3) NO levels in the culture media were also correlated with the inhibition of [(35)S]-sulphate and [(3)H]-glycine incorporation; and (4) SNP also inhibited aggrecan and collagen II transcriptions, probably via cGMP. This effect was mimicked with 8-bromo-cGMP. Interestingly, the LY83583, which blocks the NO-dependent production and release of cGMP, inhibited PG-collagen synthesis but had no effect on their mRNA expressions. Thus, normal levels of cGMP appeared to be necessary for PG-collagen synthesis, whereas decreased levels are detrimental. In conclusion, NO, produced by rat AC in response to ET-1, counteracts the stimulation and finally induces inhibition of PG-collagen synthesis by ET-1 in these cells but NO-induced cGMP is only partially responsible for this inhibition. Copyright 2002 Elsevier Science Ltd. All rights reserved.