Effects of Misoprostol on Bone Resorption and Formation in Organ Culture

Prostaglandins are potent stimulators of bone resorption and formation. Because misoprostol is an analog of prostaglandin E(1) (PGE(1)), we have examined its effects on resorption and formation in organ culture. The results were compared with PGE(2) which can stimulate resorption and both stimulate and inhibit bone formation. Resorption, measured as the release of previously incorporated (45)Ca from 5-day cultures of 19-day fetal-rat long bones, was increased by misoprostol 1.5-fold at 10(minus sign6) M and twofold at 10(minus sign5) M. The effect at 10(minus sign6) M was abolished by addition of indomethacin (10(minus sign6) M). PGE(2) was approximately 100 times more potent and was not affected by indomethacin in this system. In 21-day fetal-rat calvariae, cultured for 24 h in the presence of cortisol (10(minus sign7) M), misoprostol produced a dose-related increase in TdR incorporation between 10(minus sign5) and 10(minus sign7) M. PGE(2) appeared to be only 10-fold more potent in this response. The effects of misoprostol on incorporation of [(3)H]proline into collagenase digestible protein (CDP) and noncollagen protein (NCP) were measured in 72-h cultures, either with continuous treatment or 24-h treatment followed by 48 h in control medium. With continuous treatment at 10(minus sign6) M, misoprostol increased labeling of CDP twofold. A similar effect was observed with 24 h of treatment at 10(minus sign5) M, followed by 48 h in control medium. Again, PGE(2) was approximately 10-fold more potent than misoprostol. When calvariae were treated with insulin-like growth factor I, which increases CDP labeling by 2.5-fold, the effects of misoprostol and PGE(2) were inhibitory. We conclude that misoprostol resembles PGE(2) in its effects on bone but is less potent. Moreover, misoprostol may be relatively less effective in stimulating resorption than in stimulating formation. Therefore, an increase in bone turnover, possibly with a net anabolic effect, might occur in vivo with long-term misoprostol treatment. Misoprostol effects on bone turnover in humans could be evaluated using the sensitive biochemical markers for bone resorption and formation which are currently available.