Chronic Ethanol Induced Impairment of Hepatic Glycosylation Machinery in Rat Is Independent of Dietary Carbohydrate

Abstract

In recent years, a number of studies have been reported that have clearly established that hepatic glycosylation machinery is affected by chronic ethanol treatment in rats. We have previously reported that chronic ethanol treatment in rats resulted in decreased glycosylation of transfenin and apolipoprotein E with concomitant decreases in enzymatic activities of Golgi galactosyltransferases and sialyltransferases. In all these studies investigators have invariably used the well-accepted dietary formulation of alcohol diet as proposed by Lieber and DeCarli. However, questions were raised whether the lower carbohydrate content in Lieber's alcohol diet may be responsible for observed effects of ethanol on hepatic glycosylation machinery. Therefore, to verify whether or not the crucial effects of chronic ethanol treatment on hepatic glycosylation machinery as observed in our studies, were truly caused by ethanol, we have extended our studies on protein glycosylation with the inclusion of a third dietary group that was compensated for carbohydrate content. In this investigation, rats were fed with three dietary regimen corresponding to control, ethanol, and carbohydrate compensated ethanol group and studies were done on (i) labeled leucine, galactose and N-acetylmannosamine incorporation into transferrin and apolipoprotein E, and (ii) hepatic galactosyltransferase and sialyttrans-ferase activities in Golgi rich fraction in rat. Our results clearly showed that regardless of the carbohydrate content, marked decreases in the incorporation of labeled sugars into transferrin and the enzymatic activities of galactosyltransferase and sialyltrans-ferase occurred in rats administered chronic ethanol. Thus, it is reasonable to conclude that it is not the carbohydrate content of the diet but ethanol per se, when administered chronically, greatly impairs the glycosylation machinery of rat liver and that the magnitudes of these effects are selectively specific with regard to the type of sugar or the glycosylation enzyme.