Misoprostol Stimulates cAMP Generation in Human Leukocytes: Synergy with Colchicine Suggests a New Potential for Established Drugs.

In isolated leukocytes, elevation of cAMP can inhibit various proinflammatory and immune functions. The prostaglandins E (PGEs) are known to stimulate leukocyte cAMP production, and for years they have been viewed as potential immunosuppressive and/or anti-inflammatory agents. However, their clinical use is severely limited by extreme metabolic instability and by poor oral absorption, which necessitates administration by infusion or injection. Misoprostol is a synthetic analog of PGE(1) that is relatively stable and orally absorbable. We examined the effects of misoprostol on cAMP production in leukocytes, in view of the possibility that it mimics PGE(1) and, thus, might represent a clinically useful immunosuppresive or anti-inflammatory drug. Our results indicate the following: (1) Misoprostol increases leukocyte cAMP production in a dose-dependent manner (similar20 nM to >100 &mgr;M) and acts by stimulating adenylate cyclase. (2) Its potency and maximal effect are somewhat less than those of PGE(1) (3) cAMP generation in response to either misoprostol or PGE(1) is transient (in the presence of isobutylmethylxanthine to inhibit endogenous phosphodiesterases). (4) Misoprostol's stimulation of adenylate cyclase is synergistically increased by pretreatment of cells with colchicine, a microtubule-disrupting agent that is currently used for prophylaxis and treatment of gout. (5) Colchicine acts by increasing the initial rate of cAMP production and not by prolonging the response to misoprostol. (6) A clinically relevant dose of colchicine (0.25 &mgr;M) is effective given sufficient pretreatment time. (7) Whereas a clinically relevant dose of misoprostol (3 nM) is ineffective alone, preexposure of cells to colchicine enables such a dose to stimulate cAMP generation significantly. The combination of misoprostol with colchicine might eventually prove useful in the therapy of immune or inflammatory disease.