The Effect of Maternal Ethanol Ingestion on Fetal Rat Heart Vitamin A: A Model for Fetal Alcohol Syndrome

Abstract

Ethanol consumption during pregnancy can cause fetal alcohol syndrome (FAS). Although the exact mechanism is unknown, nutritional alterations caused by ethanol exposure may be an etiologic factor in FAS. Thc congenital heart defects seen in FAS are similar to those found in vitamin A teratogenesis. Because ethanol ingestion alters vitamin A metabolism, we hypothesized that the cardiac manifestations seen in FAS result from an altcration in vitamin A metabolism or function in the developing fetus. Twenty-day gestation fetal rat hearts from ethanol-exposed and control pregnancies were analyzed for I ) levels of endogenous retinol, rctinyl palmitate, and retinoic acid by quantitative HPLC; 2) binding activity levels of both retinol by cellular retinol binding protein and retinoic acid by cellular retinoic acid binding protein using specific competitive binding assays; and 3 ) relative abundance of cellular retinol binding protein and rctinoic acid receptor a, 0, and y subtype message as expressed in mRNA. Levels of retinol and retinyl palmitate were significantly higher ( p < 0.01) and the level of retinoic acid was significantly lower (p < 0.02) in the ethanol-exposed fetal hearts. Binding activity levels of cellular retinol binding protein Consumption of ethanol during pregnancy results in an increased incidence of spontaneous abortions (I), an increase in perinatal mortality (2), and the birth of a child with FAS, which is defined by the clinical triad of growth retardation, CNS dysfunction, and craniofacial abnormalities (3). Other common features of FAS may include congenital heart defects and skeletal anomalies (3, 4).The mechanism by which ethanol causes FAS is unknown. Various hypotheses include a direct teratogenic effect of ethanol and/or acctaldehydc on the fetus, altered maternalJplacenta1 physiology, and nutritional alterations caused by ethanol ingestion (5-8). An alteration in vitamin A metabolism or function resulting from ethanol ingestion may potentially explain some of the dcvelopme~~tal abnormalities seen in FAS.Rcccivcd July 5, 1994; accepted Octohcr 30, 1904 GAPDH, glyceraldehyde 3-phosphate dehydrogenaseRetinol is the main circulating form of vitamin A. It can be estcrified for storage, mainly in the liver, or it can bind to CRBP. This binding step is necessary for entrance into the ccllular cytosol. In the cytosol, some of the retinol is metabolized to retinoic acid, which can then bind to CRABP. Retinoic acid can be broken down to other metabolites or it can be transferred into the nucleus and serve as a ligand for RAR ( a , p, and y isoforms). Bound RAR acts as a transcription factor, which can bind to several retinoic acid responsive genes and regulate promoter activity (9,10).Vitamin A status is effected by ethanol ingestion. Adult alcoholics have decreased liver retinol levels and increased levels of retinol in their esophagus and trachea (11). Ethanol ingestion by pregnant rats increases retinol levcls in 10-d embryo and 20-d fetal brain (12) and increases both retinol and retinyl pal...

Mechanisms for persistent microphthalmia following ethanol exposure during retinal neurogenesis in zebrafish embryos

“…In the present study, an earlier ethanol exposure regime also resulted in photoreceptor differentiation abnormalities, suggesting that this retinal cell population is sensitive to ethanol from the time of cell birth (and possibly earlier) through the time of outer segment maturation. One mechanism proposed to mediate the teratogenic effects of ethanol is inhibition of synthesis of retinoic acid (RA) (DeJonge & Zachman, 1995;Deltour et al, 1996;Zachman & Grummer, 1998). This inhibition may take place either by ethanol competing with retinol for alcohol dehydrogenase, or by acetaldehyde, an ethanol metabolite, competing with retinaldehyde for aldehyde dehydrogenase (Han et al, 1998).…”

Prenatal Ethanol Consumption Increases Retinol and Cellular Retinol-Binding Protein Expression in the Rat Fetal Snout

“…However, in the fetal heart, ethanol decreased RAR ß mRNA and again increased RAR · expression, but had no effects on CRBP mRNA. The RA level in these fetal rat hearts was also decreased [19]. In the present work, there were no differences in any of the RARs or RXR ß in fetal rat snouts of control and ethanol-consuming pregnancies.…”

“…However, there are definite ethanol diet effects such as an increase in the number of resorptions, fetal anomalies and lower fetal weight [17][18][19][20] compared to control diet pregnancies. Prenatal ethanol intake in this model results in depletion of fetal liver retinyl palmitate but, paradoxically, an increase in endogenous retinol and retinyl palmitate in the 12-day embryo, the 20-day fetal brain [18] and the 20-day fetal heart [19].…”

“…In previous work using this FAS rat model, ethanol altered certain RARs and RA in other tissues at the same 20-day fetal gestation [19,20]. Ethanol consumption was accompanied by an increase in RAR · mRNA, but no change in RAR ß mRNA in fetal brain.…”

“…Using these solvents and a flow rate of 1.5 ml/min, peak retention times were 5.7 min for retinyl palmitate and 4.8 min for retinol. RA was also determined as previously described [19]. Aqueous snout homogenates were extracted with 2.5 vol extraction solvent (butanol:acetonitrile:hexane, 50:49:1) and 1 mg/ml butylated toluene.…”