Ethanol, oxidative stress, reactive aldehydes, and the fetus

The fetotoxic effects of maternal ethanol (E) consumption have been documented for over two decades, yet the mechanisms underlying this devastating phenomenon remain uncertain. The wide variety of cellular/biochemical effects of E on fetal tissues is itself a puzzle and strongly suggests that fetotoxic responses to E reflect a multifactorial setting. Many of these responses can be conceptually connected to effects on membrane structure and function. Representative of this, are studies in our laboratory documenting E effects on fetal cell replication, membrane transport systems, membrane fluidity, Na+-K+ pump expression, and EGF receptor expression. Recent studies have provided evidence that oxidative stress may be one mechanism by which E produces these membrane-related events. We initially observed E-induced oxidative stress in cultured fetal rat hepatocytes, the latter exhibiting morphological and biochemical signs of mitochondrial damage. E increased H2O2, O2-, lipid peroxidation products, along with signs of membrane damage. Supplementation with antioxidants or agents that enhance glutathione stores reversed these effects. E was found to inhibit activities of mitochondrial respiratory chain components (a potential source of the enhanced levels of H2O2, and O2-) and this could be reversed by antioxidant treatment. Subsequent studies have documented oxidative stress and membrane lipid peroxidation in fetal brain and liver (gestation day 19) following a two day maternal E consumption and in gestation day 14 and 17 "embryos" immediately following a single dose of E to the pregnant dam. The means by which E can induce oxidative stress in fetal cells is under investigation. We have examined effects of E on activities of key antioxidant enzymes and found no depressant responses. However, the low levels of antioxidants in fetal tissues and an exaggerated response of fetal mitochondria to prooxidant stimulation in vitro, suggest that fetal cells are strongly predisposed to oxidative stress. Additionally, recent studies have suggested that fetal tissues are likewise prone to the formation and subsequent accumulation of at least one toxic lipid peroxidation product, 4-hydroxynonenal. We conclude that maternal E consumption induces oxidative stress in fetal tissues and that this is responsible for some toxic responses to E. Additionally, the low antioxidant defenses in fetal tissues and accumulation of toxic aldehyde products of lipid peroxidation predispose the fetus to oxidative damage.