THE ROLE OF CYCLIC-3',5'-ADENOSINE MONOPHOSPHATE IN PROSTAGLANDIN-MEDIATED INHIBITION OF BASIC CALCIUM-PHOSPHATE CRYSTAL-INDUCED MITOGENESIS AND COLLAGENASE INDUCTION IN CULTURED HUMAN FIBROBLASTS

Synovial fluid basic calcium phosphate (BCP) crystals are associated w ith severe destructive arthropathies characterised by synovial prolife ration and non-inflammatory degradation of intra-articular collagenous structures. BCP crystals stimulate fibroblast and chondrocyte mitogen esis, metalloprotease secretion and prostaglandin production. As a tis sue protective effect of prostaglandins has been suggested, we recentl y studied the effect of PGE(1) on BCP crystal-induced mitogenesis and collagenase mRNA accumulation in human fibroblasts (HF). We demonstrat ed a dose-dependent inhibition of BCP crystal-induced mitogenesis and collagenase mRNA accumulation. The mechanism of PGE(1) inhibition of B CP crystal-induced mitogenesis and collagenase mRNA accumulation was t herefore explored. PGE(1) (100 ng/ml) increased HF intracellular cAMP 40-fold over control. BCP alone caused no such change but inhibited th e PGE(1)-induced increase in intracellular cAMP by at least 60%. The P GE(1)-induced increase in intracellular cAMP was also blocked by the a denyl cyclase inhibitor, 2',5'-dideoxyadenosine (ddA) (10 mu M) and dd A reversed the PGE(1)-mediated inhibition of BCP crystal-induced mitog enesis. Dibutyryl cAMP also inhibited BCP crystal-induced mitogenesis in a concentration-dependent manner. Agents which increase intracellul ar cAMP levels such as the adenyl cyclase activator forskolin and the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (IBMX) mimicke d the effect of PGE(1) on HF collagenase mRNA levels. PGE(1) inhibits the biologic effects of BCP crystals through the cAMP signal transduct ion pathway and such inhibition may have significant therapeutic impli cations.