Chronic ethanol consumption interferes with the metabolism of phospholipids, and as a consequence, the membranes in animals chronically fed ethanol acquire an altered lipid composition. Changes in the synthesis of phospholipids and their subsequent intracellular translocation to specific membranes can have significant effects on cell function, since phospholipids are important determinants of membrane structure and functions. Certain phospholipids also play critical roles in receptor-mediated signal transduction events. We will investigate possible mechanisms by which ethanol interferes with phospholipid metabolism by determining the effects of ethanol on the synthesis and intracellular translocation of functionally distinct pools of phosphatidylcholine (PC) and phosphatidylethanolamine (PE) derived from phosphatidylserine (PS). We have found that ethanol interferes with the metabolism of this pool. The generation of these lipids occurs by the synthesis of PS on the endoplasmic reticulum, from which it is translocated to the mitochondria where it is decarboxylated to form PE. The PE is then transferred back to the endoplasmic reticulum, where it is converted to PC by PE-N-methyltransferase. By using radioactive serine to label the polar headgroup of these phospholipids, we will determine the effects of chronic ethanol consumption and acute ethanol treatment on their translocation between the microsomes and mitochondria during their synthesis, as well as their subsequent transfer to the plasma membrane in hepatocytes. To examine the mechanism of interference by ethanol on this process, we will study the effects on the individual enzymes in a reconstituted in vitro system of microsomes and mitochondria. There is evidence that hormones affect the final step in the generation of PC by the N-methylation of PE and that chronic ethanol consumption inhibits glucagon-stimulated N-methylation. We will determine which pools of PE are methylated in response to glucagon and vasopressin, and the effects of chronic and acute ethanol treatment on these processes. In addition to studying the pools of phospholipids, we will use reversed-phase HPLC to determine the effects of ethanol on the generation and translocation of specific molecular species of the serine- derived phospholipids and the molecular species methylated in response to hormones. Disturbances in the synthesis and translocation of specific pools of phospholipid molecular species and their N-methylation in response to hormones are mechanisms by which ethanol could alter cellular processes and contribute to the development of liver disease.
