Enhancement of ethanol-induced lipid peroxidation in rat liver by lowered carbohydrate intake

Inhibition of in vitro lipid peroxidation by stable steroidic nitroxyl radicals

4',4'-dimethylspiro (5 alpha-cholestane-3,2'-oxazolidin)-3'-yloxy (IK-1) and 7 alpha,12 alpha-dihydroxy-4',-4'-dimethylspiro (5 beta-cholan-24-oic-3,2'-oxazolidin)-3'-yloxy acid (IK-2), two stable steroidic nitroxyl radicals, were newly synthesized and tested as possible inhibitors of lipid peroxidation, induced by Fenton's reagent in both rat liver microsomes and egg phosphatidylcholine liposomes. The inhibitory activity, evaluated through the formation of thiobarbituric acid reactive substances (TBARS) and the conjugated diene, was compared with that of alpha-tocopherol and 2,2,6,6-tetramethylpiperidine-1-yloxy (TEMPO). In each model system IK-1 and IK-2 exhibited an IC50 of 8 microM and reduced the formation of TBARS and conjugated diene, showing IK-1 a potency comparable to alpha-tocopherol and higher than TEMPO. Moreover IK-1 and, to a lesser extent IK-2, reduced the lipid peroxidation induced in the microsomes by the water-soluble azo-initiator 2,2'-Azobis (2-methylpropionamidine) dihydrochloride (AMPH), indicating the IK-1 and IK-2 ability as chain-breaking antioxidants. The hydroxylamine 4',4'-dimethylspiro (5 alpha-cholestane-3,2'-oxazolidin)-3'-hydroxide (IK-3), obtained by chemical reduction of IK-1, was completely inactive as an inhibitor of lipid peroxidation in heat pre-treated microsomes and in liposomes. However in microsomes it was active since it was oxidized to the corresponding nitroxyl radical IK-1.

Lipid peroxidation, CYP2E1 and arachidonic acid metabolism in alcoholic liver disease in rats

The role of cytochrome P450 metabolism of fatty acids and lipid peroxidation in the alterations of the fatty acid composition of the liver and liver pathology was investigated. The CYP2E1 inhibitors partially prevented CYP2E1 induction by ethanol and completely blocked lipid peroxidation. However, the liver pathology induced by ethanol was only partially prevented as was the decrease in arachidonic acid in total liver lipid, triglycerides and cholesterol esters. This means that liver peroxidation induced by ethanol can not completely account for the liver pathology or the decrease in arachidonic acid caused by ethanol. Lauric acid omega-1 hydroxidation by the liver microsomes in vitro was increased by ethanol and partially blocked by CYP2E1 inhibitors. However, although ethanol feeding increased the total hydroxidation and epoxidation of arachidonic acid, these were not inhibited by CYP2E1 inhibitors. Thus the ethanol-induced arachidonic acid depletion is not likely due to CYP2E1 metabolism of arachidonic acid, since the severity of liver pathology correlated negatively with the decrease in arachidonic acid in the ethanol-fed rats. The increase in its metabolism by microsomes and decrease in synthesis may be an important mechanism of ethanol-induced liver injury.

Dietary modulation of oxidative stress in alcoholic liver disease in rats

Numerous studies dealing with prolonged feeding of rats with ethanol liquid regimens high in fat and low in carbohydrate showed that the resulting hepatic pathologic changes, including increased lipid peroxidation, are due to dietary aberrations rather than to ethanol toxicity. The amount and particularly the type of dietary fat significantly modulate the hepatic oxidative stress and morphofunctional reactivities. Although dietary vitamin E modulated oxidative stress or lipid peroxidation, it did not influence the development of hepatic pathologic changes in different animal models of chronic alcoholism. The old observation that lipotropes modulate the hepatic alterations associated with prolonged excessive ingestion of ethanol has been amply confirmed by even those who for years did not accept the importance of lipotropes. Our recent studies in rats indicated that prolonged feeding of large amounts of ethanol and diets with variable amounts of lipotropes, vitamin E and minerals did not significantly modulate a large series of hepatic prooxidants, but decreased several antioxidants (vitamin E, ubiquinols and glutathione peroxidase). Ethanol regimens relatively low in vitamin E increased the hepatic thiobarbituric acid-reactive substances and chemiluminescence and reduced some of the antioxidant factors. However, the hepatic prooxidant factors were unaffected, and no liver damage was detected. These and other findings indicated that the eventual detection of oxidative stress in experimental alcoholic liver disease primarily depends on the type of diet and that oxidative stress may not play a significant pathogenic role in this condition.

Effects of carbohydrate intake on the blood ethanol level and alcoholic fatty liver damage in rats

Effects of carbohydrate (CHO) intake on the blood ethyl alcohol (ethanol) level were studied in rats with a surgically placed gastric cannula. A basal diet (protein, 2.07; fat, 1.98; CHO, 5.76 g/day), a high-CHO diet (CHO, 4.39 g/day) + ethanol, a medium-CHO diet (CHO, 2.69 g/day) + ethanol or a low-CHO diet (CHO, 0.98 g/day) + ethanol was infused into the stomach for 4 weeks starting from the 2nd postoperative week. The basal diet and the test diets were isocaloric, and the ethanol (2.80 g/day) in the test diets accounted for 39% of the total calories. The liquid diets (50 kcal in 50 ml) were infused over 16 h from 16.00 to 08.00 h each day. The low-CHO diet group had significantly higher blood ethanol levels than the high-CHO diet group 4, 8 and 16 h after the start of infusion. These groups could be ranked by liver triglyceride content at autopsy as follows: low-CHO > medium-CHO > high-CHO > or = basal. Consistent with the triglyceride content, histological changes of the liver could be ranked by the degree of fatty changes in the same order: low-CHO > medium-CHO > high-CHO > basal. Thus, for a given amount of ethanol consumption, lower CHO intake was associated with higher blood ethanol levels and with more severe fatty changes of the liver.