modification by acetaldehyde correlates well with the severity Liver proteins form adducts with acetaldehyde and are of liver injury in ethanol-fed rats, whereas modification by modified by products of lipid peroxidation in alcohol-fed anithe lipid peroxidation product 4-HNE shows no correlation mals. It has been hypothesized that the formation of these with the severity of liver injury. (HEPATOLOGY 1997;26:650modified liver proteins may contribute to liver injury in alco-657.) holic liver disease. The present work was performed to determine the extent of protein modification in rats with experimental alcoholic liver disease. Rats were fed ethanol
The major pathway for ethanol disposition involves alcointragastrically with medium chain triglycerides (MCTs), hol dehydrogenase, an enzyme that catalyzes the conversion palm oil, corn oil, or fish oil. The group fed MCTs and ethanol of ethanol to acetaldehyde. 1 With prolonged alcohol conshowed no liver injury, rats fed palm oil and ethanol showed sumption, the metabolic pathway through cytochrome P450 only fatty liver, rats fed corn oil and ethanol showed fatty 2E1 becomes important. 2 Both alcohol dehydrogenase and liver with moderate necrosis and inflammation, and rats fed cytochrome P450 2E1 generate acetaldehyde from ethanol. 1,2 fish oil and ethanol showed fatty liver with severe necrosis
In recent years, extensive evidence supporting a role for acetand inflammation. Antibodies were raised by using keyhole aldehyde in the detrimental actions of ethanol on the liver limpet hemocyanin modified in vitro by 4-hydroxynonenal (4has been accumulated. One basis of the toxic effect of acetal-HNE) or acetaldehyde as immunogens. When liver extracts dehyde is the covalent binding of this highly reactive chemiwere examined by Western blot analysis, the intensities of the cal to proteins. Although the adduct formation between acetacetaldehyde-modified protein band (37 kd) in the alcohol-fed aldehyde and hepatic proteins has been well established, 5-11 animals were significantly different among the ethanol-treated its precise role in causing liver injury remains unclear. We groups and correlated with plasma acetaldehyde concentrahave previously detected a protein-acetaldehyde adduct tions. It was strongest in rats fed fish oil and ethanol, followed (PAA) in the livers of rats fed ethanol with both low-and by rats fed palm oil and ethanol and rats fed corn oil and high-fat diets. The 37-kd liver protein that forms acetaldeethanol, whereas rats fed MCTs and ethanol showed the hyde adduct in vivo has been identified recently as D 4 -3weakest intensity. The 37-kd protein-adetaldehyde adduct ketosteroid-5b reductase, 13 a key enzyme involved in bile was located mainly in the pericentral region of the liver. No acid syntheses. acetaldehyde adduct was detected in the control rats that were Another area of investigation in which adduct formation pair-fed with isocaloric amounts of dextrose. Western blot has been proposed to be of pathogenic importance to alcoanalysis using the anti-4-HNE antibody showed four distincholic and other liver diseases is with products of lipid peroxitive bands (48, 45, 40, and 38 kd) in the liver extracts of dation. There is increasing, although not conclusive, evialcohol-fed rats. Control animals showed only a weak 38-kd dence that aldehydes generated endogenously during the band. Although the intensities of the 48-, 40-, and 38-kd bands process of lipid peroxidation are causally involved in some were similar among the different ethanol-treated groups, the of pathophysiological effects associated with alcohol-induced intensity of the 45-kd band decreased from MCTs and ethanol liver injury. One of the aldehyde products of lipid peroxiΓΊ palm oil and ethanol Β’ corn oil and ethanol ΓΊ fish oil dation that has been studied intensively is 4-hydroxynonenal and ethanol. The data indicate that the degree of liver protein (4-HNE). 17 Increased levels of 4-HNE occur in the livers of alcohol-fed animals. 18,19 Furthermore, 4-HNE protein adducts (HPA) have been observed in the centrilobular region Abbreviations: PAA, protein-acetaldehyde adduct; 4-HNE, 4-hydroxynonenal; HPA, of the liver in micropigs fed ethanol for 12 months. 14 4-HNE protein adduct; MCT, medium chain triglyceride; KLH, keyhole limpet hemocy-One of the shortcomings of the various studies that have anin; ELISA, enzyme-linked immunosorbent assay. From the Departments of 1 Medicine,