FOLATE METABOLISM IN ALCOHOLISM

叶酸缺乏是营养不良最常见的迹象

Folate deficiency is the most common sign of malnutrition in chronic alcoholic patients, affecting nucleic acid synthesis and turnover of all cells. On the basis of prior studies in chronic alcohol-fed primates, which showed decreased folate absorption and hepatic uptake with increased urinary folate excretion, we propose 1) that chronic alcoholism leads to physical and chemical changes in membranes involved in folate transport. Alternatively, 2) free radical production during ethanol metabolism could accelerate the catabolism of endogenous folates. During the first period of this grant we established a model of control and alcohol feeding in the miniature pig and found a significant reduction in the activity of jejunal brush border folate hydrolase with decreased in vivo hydrolysis of pteroylpolyglutamate (PteGlun), the principal dietary folate. We also found striking changes in the molar ratios of circulating phospholipid fatty acids, which were partly reflected by the fatty acid composition of the jejunal brush border membrane and which were consistent with a defect in fatty acid desaturation. In the proposed renewal, we plan to test the two hypotheses for folate deficiency in pigs fed a higher concentration of ethanol for a minimum of two to three years. Membrane effects, including changes in lipid composition and order parameter will be measured at 4 to 6 month intervals in plasma and tissue biopsies and hepatic microsomal fatty acid desaturase will be isolated and studied in control and alcoholic groups. After killing, the transport of monoglutamyl folate (PteGlu) will be measured in intestinal hepatic, and renal tubular membranes, correlating changes with membrane microviscosity and lipid composition. The effect of chronic alcoholism on the mucosal synthesis and intracellular processing of jejunal brush border folate hydrolase will be studied by mRNA hybridization and by immunoprecipitation of nascent proteins in mucosal explant cultures. Injecting trace amounts of 3H-PteGlu to label endogenous folates in timed liver biopsies, we will measure the effect of chronic alcohol feeding in vivo on the uptake intracellular binding, and metabolism of folate in the liver. In separate experiments with 14C and 3H doubly labeled PteGlu we will determine whether chronic alcoholism accelerates the catabolism and urinary excretion of folate catabolites. These quantitative data will be correlated with studies of hepatic trace mineral and free radical formation and metabolism in both groups of animals. The proposed studies will identify etiologies for folate deficiency in chronic alcoholism. Using folate as an example, these studies will further understanding of the interactions among chronic alcoholism, membrane changes, nutrient metabolism, and malnutrition.