Phosphodiesterase isoenzyme families in human osteoarthritis chondrocytes-functional importance of phosphodiesterase 4

1 We studied whether selective inhibitors of cyclic nucleotide hydrolysing phosphodiesterase (PDE) isoenzymes influence IL-1beta-induced nitric oxide (NO) release from human articular chondrocytes. In addition, the pattern of PDE isoenzymes contributing to cyclic nucleotide hydrolysis in human chondrocytes was characterized. 2 Chondrocytes were isolated from human osteoarthritic cartilage and cultured in alginate beads. IL-1beta-induced chondrocyte products (nitric oxide and prostaglandin E-2) were measured in culture supernatants after 48 h incubation time. PDE activities were assessed in chondrocyte lysates. Inducible nitric oxide synthase (iNOS) and PDE4A-D proteins were detected by immunoblotting. 3 The selective PDE4 inhibitors Piclamilast and Roflumilast partially attenuated IL-1beta-induced NO production whereas selective inhibitors of PDE2 (EHNA), PDE3 (Motapizone) or PDE5 (Sildenafil) were inactive. Indomethacin reversed the reduction of IL-1beta-induced NO by PDE4 inhibitors. It was shown that autocrine prostaglandin E-2 (PGE(2)) enabled PDE4 inhibitors to reduce IL-1beta-induced NO in this experimental setting. 4 Major PDE4 and PDE1 activities were identified in chondrocyte lysates whereas only minor activities of PDE2, 3 and 5 were found. IL-1beta and cyclic AMP-mimetics upregulated PDE4 activity and this was associated with an augmentation of PDE4B2 protein. 5 Based on the view that nitric oxide contributes to cartilage degradation in osteoarthritis our study suggests that PDE4 inhibitors may have chondroprotective effects.