Direct effects of ethanol on bone resorption and formation in vitro

In vitro studies indicate that low concentrations of ethanol can have direct effects on bone formation and resorption. Bone resorption was increased when embryonic chick tibiae were exposed to ethanol at 0.03-0.3% ( v v), and bone formation was inhibited when tibiae were exposed to 0.2% ethanol in the presence of NaF or parathyroid hormone (P < 0.01 for each). Ethanol also had direct effects on isolated bone cells in vitro, increasing both cAMP and PGE₂ production (P < 0.001 for each), and affecting cell proliferation in a biphasic, time- and dose-dependent manner. After 24 h of exposure, 0.03% ethanol increased bone cell proliferation (P < 0.001), but 0.3% ethanol was inhibitory (P < 0.01). Paradoxically, mitogenic doses of ethanol prevented the effects of two other mitogens, NaF and human skeletal growth factor, to increase bone cell proliferation (P < 0.001). But how were these effects produced? Several observations suggest that these direct effects of ethanol on skeletal tissues in vitro were mediated by changes in bone cell membrane fluidity, (a) Dimethyl sulfoxide, ethylene glycol, and lecithin, which act, like ethanol, to increase membrane fluidity, mimicked the effects of ethanol on bone cell proliferation. Dimethyl sulfoxide also mimicked the effect of ethanol to increase cAMP (P < 0.001). (b) Cholesterol, which decreases cell membrane fluidity, acted oppositely to ethanol and enhanced the mitogenic response to human skeletal growth factor (P < 0.001). (c) Preincubation of calvarial cells with ethanol or with cholesterol altered the in situ reaction kinetics of the membrane-bound enzyme, alkaline phosphatase. Together, these data demonstrate that ethanol has direct effects on skeletal tissue in vitro, and suggest that those effects may be secondary to changes in bone cell membrane fluidity.