Metabolic basis of ethanol-induced hepatic and pancreatic injury in hepatic alcohol dehydrogenase deficient deer mice

Abstract

Alcoholic liver disease (ALD) and alcoholic pancreatitis (AP) are major diseases causing high mortality and morbidity among chronic alcohol abusers. Neutral lipid accumulation (steatosis) is an early stage of ALD or AP and progresses to inflammation and other advanced stages of diseases in a subset of chronic alcohol abusers. However, the mechanisms of alcoholic steatosis leading to ALD and AP are not well understood. Chronic alcohol abuse impairs hepatic alcohol dehydrogenase (ADH, a major enzyme involved in ethanol oxidative metabolism) and facilitates nonoxidative metabolism of ethanol to fatty acid ethyl esters (FAEEs, nonoxidative metabolites of ethanol). These esters are implicated in the pathogenesis of various alcoholic diseases and shown to cause hepatocellular and pancreatitis-like injury. Ethanol exposure is known to increase synthesis of FAEEs by several-fold in the livers and pancreata of rats pretreated with hepatic ADH inhibitor. Therefore, studies were undertaken to evaluate hepatocellular and pancreatic injury in hepatic ADH-deficient (ADH −) deer mice versus ADH-normal (ADH +) deer mice fed ethanol (4% wt/vol) via Lieber-DeCarli liquid diet for 60 days. A significant mortality was found in ethanol-fed ADH − deer mice (11 out of 18) versus ADH + deer mice (1 out of 16); most of the deaths occurred during the first 2 weeks of ethanol exposure. The surviving animals, sacrificed at the end of 60th day, showed distinct changes in hepatic and pancreatic histology and several-fold increases in nonoxidative metabolism of ethanol in ethanol-fed ADH − versus ADH + deer mice. Extensive vacuolization with displacement or absence of nucleus in some hepatocytes, and significant increase in hepatic neutral lipids were found in ethanol-fed ADH − versus ADH + deer mice. Ultrastructural changes showed perinuclear space, edema, presence of apoptotic bodies and disintegration, and/or dilatation of endoplasmic reticulum (ER) in the pancreata of ethanol-fed ADH − deer mice. FAEE levels were significantly higher in ADH − versus ADH + deer mice, approximately four-fold increases in the livers and seven-fold increases in the pancreata. Ethyl esters of oleic, linoleic, and arachidonic acids were the major FAEEs detected in ethanol-fed groups. The role of FAEEs in pancreatic lysosomal fragility is reflected by higher activity of cathepsin B (five-fold) in ethanol-fed ADH − versus ADH + deer mice. Although the present studies clearly indicate a metabolic basis of ethanol-induced hepatic and pancreatic injury, detailed dose- and time-dependent toxicity studies in this ADH − deer mouse model could reveal further a better understanding of mechanism(s) of ethanol-induced hepatic and pancreatic injuries.