Vol. 281, Issue 2, 1005-1012, 1997

Prostaglandin E₂ Production Dependent upon Cyclooxygenase-1 and Cyclooxygenase-2 and Its Contradictory Modulation by Auranofin in Rat Peritoneal Macrophages

Masateru Yamada , Hisae Niki, Masamichi Yamashita, Suetsugu Mue and Kazuo Ohuchi

Department of Pathophysiological Biochemistry, Faculty of Pharmaceutical Sciences, Tohoku University, Sendai (M.Y., H.N., M.Y., K.O.) and Department of Health and Welfare Science, Faculty of Physical Education, Sendai College, Funaoka (S.M.), Miyagi, Japan

Rat peritoneal macrophages were incubated in the presence of cycloheximide or dexamethasone to inhibit the induction of cyclooxygenase (COX)-2 protein synthesis. Thereafter, when the macrophages were incubated in the presence of arachidonic acid, PGE₂ production was increased. Western blot analysis demonstrated that COX-2 protein levels were low and were not affected by arachidonic acid treatment. COX-1 protein levels were not affected by arachidonic acid treatment either. The COX-2 inhibitors NS-398 and nimesulide only slightly inhibited PGE₂ production, whereas the COX-1/COX-2 inhibitors indomethacin, piroxicam and tenoxicam strongly inhibited PGE₂ production. This suggests that under these conditions, PGE₂ production is dependent on COX-1. After the macrophages were treated with aspirin to inactivate existing COX-1 and COX-2, however, treatment with 12-0-tetradecanoylphorbol 13-acetate increased PGE₂ production. Furthermore, COX-2 protein levels were markedly increased by 12-0-tetradecanoylphorbol 13-acetate treatment, whereas COX-1 protein levels did not change. In this case, both the COX-2 and the COX-1/COX-2 inhibitors inhibited PGE₂ production. This suggests that under these conditions, PGE₂ production is dependent on COX-2. Effects of auranofin on COX-1-dependent and COX-2-dependent PGE₂ production were examined. We found that auranofin stimulated COX-1-dependent PGE₂ production but inhibited COX-2-dependent PGE₂ production in a concentration-dependent manner. The latter effect was found to be due to the inhibition of COX-2 protein induction. These findings might explain the mechanism of the antirheumatic and anti-inflammatory activities of auranofin.