Vitamin E and hepatotoxic agents. 2. Lipid peroxidation and poisoning with orotic acid, ethanol and thioacetamide in rats

Orotic acid, a new promoter for experimental liver carcinogenesis

Male Fischer 344 rats initiated with 1,2-dimethylhydrazine 2HCl (100 mg/kg) given 18 hr after partial hepatectomy and exposed to a diet containing 1% orotic acid for 13 months developed a 100% incidence of hepatocellular carcinoma. The creation of nucleotide pool imbalances by dietary orotic acid, for e.g., an increase in uridine nucleotides and a decrease in adenine nucleotides, was considered as a possible mechanism for the promotional effect of orotic acid on liver carcinogenesis. The significance of this hypothesis is that altered nucleotide pools affect both genomic as well as membrane organization. Consistent with this hypothesis is our finding that feeding rats with a diet containing 1% orotic acid for 10 weeks resulted in a liver DNA damage as monitored by its slower sedimentation in alkaline sucrose gradients compared to the corresponding controls. To assess the general applicability of this hypothesis, nucleotide pool imbalances were created by using methods other than feeding orotic acid and their effect on the incidence of gamma-glutamyltransferase positive foci in carcinogen initiated rats was determined. The results obtained indicated that rats initiated with 1,2-dimethylhydrazine.2HCl (100 mg/kg) given 18 hr after partial hepatectomy and exposed to diet deficient in arginine, a regimen that causes an increased synthesis and excretion of orotic acid, or were fed diets containing 1% thymidine or 1% thymine developed greater number of gamma-glutamyltransferase positive foci compared to the corresponding controls fed the basal diets. These results were interpreted to indicate that orotic acid exerts its promotional effect probably by creating an imbalance in nucleotide pools. One of the mechanisms by which an imbalance of nucleotide pools influences the pathogenesis of the carcinogenic process may be by inducing perturbations in the DNA.

Will the 'good fairies' please prove to us that vitamin E lessens human degenerative disease?

Recent research about the role of free radical derivatives of oxygen and nitrogen in biological systems has highlighted the possibility that antioxidants, such as vitamin E, that prevent these processes in vitro may be capable of carrying out a similar function in living organisms in vivo. There is increasing evidence that free radical reactions are involved in the early stages, or sometimes later on, in the development of human diseases, and it is therefore of particular interest to inquire whether vitamin E and other antioxidants, which are found in the human diets, may be capable of lowering the incidence of these diseases. Put simply, the proposition is that by improving human diets by increasing the quantity in them of antioxidants, it might be possible to reduce the incidence of a number of degenerative diseases. Of particular significance to these considerations is the likely role of the primary fat-soluble dietary antioxidant vitamin E in the prevention of degenerative diseases such as arteriosclerosis, which is frequently the cause of consequent heart attacks or stroke, and prevention of certain forms of cancer, as well as several other diseases. Substantial evidence for this proposition now exists, and this review is an attempt to give a brief account of the present position. Two kinds of evidence exist; on the one hand there is very substantial basic science evidence which indicates an involvement of free radical events, and a preventive role for vitamin E, in the development of human disease processes. On the other hand, there is also a large body of human epidemiological evidence which suggests that incidence of these diseases is lowered in populations having a high level of antioxidants, such as vitamin E, in their diet, or who have taken steps to enhance their level of intake of the vitamin by taking dietary supplements. There is also some evidence which suggests that intervention with dietary supplements of vitamin E can result in a lowered risk of disease, in particular of cardiovascular disease, which is a major killer disease among the developed nations of the world. The intense interest in this subject recently has as its objective the possibility that, by making some simple alterations to dietary lifestyle, or by enhancing the intake of vitamin E by fortification of foods, or by dietary supplements, it may be possible to reduce substantially the risk of a large amount of common, highly disabling human disease. By this simple means, therefore it may be possible to improve substantially the quality of human life, in particular for people of advancing years.

Polyenylphosphatidylcholine decreases alcohol-induced oxidative stress in the baboon

Diets supplemented with polyunsaturated fatty acids or triglycerides exacerbate alcohol-induced liver injury in rats, whereas, in baboons, polyenylphosphatidylcholine (PPC) protects against alcohol-induced fibrosis and cirrhosis. Because the aggravation in rats was attributed to enhanced lipid peroxidation, the present study was undertaken to assess parameters of oxidative stress in percutaneous liver biopsies of baboons fed alcohol, with or without PPC (2.8 g per 1000 calories). F2-isoprostanes and 4-hydroxynonenal, breakdown products of lipid peroxidation, were determined by gas chromatography/mass spectrometry, and alpha-tocopherol was measured by HPLC with electrochemical detection. Hepatic 4-hydroxynonenal was significantly increased in animals fed alcohol, but this was fully prevented by PPC. F2-isoprostanes were also significantly lower after PPC and ethanol than after ethanol alone, and the alcohol-induced glutathione decrease was attenuated. All of these parameters were normal in the animals withdrawn from alcohol, even with persistence of significant liver disease. Because peroxidation products are fibrogenic, their decrease could contribute to the antifibrogenic property of the phospholipids. In conclusion, PPC significantly attenuates ethanol-induced oxidative stress, which may explain, at least in part, its protective effect against alcoholic liver injury.

Will the 'good fairies' please prove to us that vitamin E lessens human degenerative disease?

Recent research about the role of free radical derivatives of oxygen and nitrogen in biological systems has highlighted the possibility that antioxidants, such as vitamin E, that prevent these processes in vitro may be capable of carrying out a similar function in living organisms in vivo. There is increasing evidence that free radical reactions are involved in the early stages, or sometimes later on, in the development of human diseases, and it is therefore of particular interest to inquire whether vitamin E and other antioxidants, which are found in the human diets, may be capable of lowering the incidence of these diseases. Put simply, the proposition is that by improving human diets by increasing the quantity in them of antioxidants, it might be possible to reduce the incidence of a number of degenerative diseases. Of particular significance to these considerations is the likely role of the primary fat-soluble dietary antioxidant vitamin E in the prevention of degenerative diseases such as arteriosclerosis, which is frequently the cause of consequent heart attacks or stroke, and prevention of certain forms of cancer, as well as several other diseases. Substantial evidence for this proposition now exists, and this review is an attempt to give a brief account of the present position. Two kinds of evidence exist; on the one hand there is very substantial basic science evidence which indicates an involvement of free radical events, and a preventive role for vitamin E, in the development of human disease processes. On the other hand, there is also a large body of human epidemiological evidence which suggests that incidence of these diseases is lowered in populations having a high level of antioxidants, such as vitamin E, in their diet, or who have taken steps to enhance their level of intake of the vitamin by taking dietary supplements. There is also some evidence which suggests that intervention with dietary supplements of vitamin E can result in a lowered risk of disease, in particular of cardiovascular disease, which is a major killer disease among the developed nations of the world. The intense interest in this subject recently has as its objective the possibility that, by making some simple alterations to dietary lifestyle, or by enhancing the intake of vitamin E by fortification of foods, or by dietary supplements, it may be possible to reduce substantially the risk of a large amount of common, highly disabling human disease. By this simple means, therefore it may be possible to improve substantially the quality of human life, in particular for people of advancing years.

The role of free radicals and antioxidants: how do we know that they are working?

This review briefly discusses how free radicals are formed and the possible participation of free radicals in disease. The review describes the basic radical reactions and the types of products that are formed from the free-radical reactions of cellular constituents. In many cases, in vivo free-radical oxidation can be detected by measuring products that were derived from radical reactions. Since aerobic organisms generate oxygen-containing free radicals during oxygen metabolism, they carry chemicals and enzymes that reduce the threat posed by these radicals. The more common sources of in vivo free radicals are described in the article as well as the methods used by cells to protect themselves from free-radical damage. Generation of free radicals in vivo also may be the result of exposure to certain chemical agents present in the environment. Many of these agents cause pathologic changes to the exposed tissues and organs by initiating free-radical reactions.

Increase in cellular pool of low-molecular-weight iron during ethanol metabolism in rat hepatocyte cultures. Relationship with lipid peroxidation

Ethanol-induced lipid peroxidation was studied in primary rat hepatocyte cultures supplemented with ethanol at the concentration of 50 mM. Lipid peroxidation was assessed by two indices: (1) conjugated dienes by second-derivative UV spectroscopy in lipid extract of hepatocytes (intracellular content), and (2) free malondialdehyde (MDA) by HPLC-UV detection and quantitation for the incubation medium (extracellular content). In cultures supplemented with ethanol, free MDA increased significantly in culture media, whereas no elevation of conjugated diene level was observed in the corresponding hepatocytes. The cellular pool of low-mol-wt (LMW) iron was also evaluated in the hepatocytes using an electron spin resonance procedure. An early increase of intracellular LMW iron (< or = 1 hr) was observed in ethanol-supplemented cultures; it was inhibited by 4-methylpyrazole, an inhibitor of alcohol dehydrogenase, whereas alpha-tocopherol, which prevented lipid peroxidation, did not inhibit the increase of LMW iron. Therefore, the LMW iron elevation was the result of ethanol metabolism and was not secondarily induced by lipid hydroperoxides. Thus, ethanol caused lipid peroxidation in rat hepatocytes as shown by the increase of free MDA, although no conjugated diene elevation was detected. During ethanol metabolism, an increase in cellular LMW iron was observed that could enhance conjugated diene degradation.

Mechanisms of ethanol-drug-nutrition interactions

Mechanisms of the toxicologic manifestations of ethanol abuse are reviewed. Hepatotoxicity of ethanol results from alcohol dehydrogenase-mediated excessive hepatic generation of nicotinamide adenine dinucleotide and acetaldehyde. It is now recognized that acetaldehyde is also produced by an accessory (but inducible) pathway, the microsomal ethanol-oxidizing system, which involves a specific cytochrome P450. It generates oxygen radicals and activates many xenobiotics to toxic metabolites, thereby explaining the increased vulnerability of heavy drinkers to industrial solvents, anesthetics, commonly used drugs, over-the-counter medications and carcinogens. The contribution of gastric alcohol dehydrogenase to the first pass metabolism of ethanol and alcohol-drug interactions is now recognized. Alcohol also alters the degradation of key nutrients, thereby promoting deficiencies as well as toxic interactions with vitamin A and beta-carotene. Conversely, nutritional deficits may affect the toxicity of ethanol and acetaldehyde, as illustrated by the depletion in glutathione, ameliorated by S-adenosyl-L-methionine. Other supernutrients include polyenylphosphatidylcholine, shown to correct the alcohol-induced hepatic phosphatidylcholine depletion and to prevent alcoholic cirrhosis in non-human primates. Thus, a better understanding of the pathology induced by ethanol has now generated improved prospects for therapy.

Alcohol, liver, and nutrition

Until two decades ago, dietary deficiencies were considered to be the major reason why alcoholics developed liver disease. As the overall nutrition of the population improved, more emphasis was placed on secondary malnutrition. Direct hepatotoxic effects of ethanol were also established, some of which were linked to redox changes produced by reduced nicotinamide adenine dinucleotide (NADH) generated via the alcohol dehydrogenase (ADH) pathway. It was also determined that ethanol can be oxidized by a microsomal ethanol oxidizing system (MEOS) involving cytochrome P-450: the newly discovered ethanol-inducible cytochrome P-450 (P-450IIE1) contributes to ethanol metabolism, tolerance, energy wastage (with associated weight loss), and the selective hepatic perivenular toxicity of various xenobiotics. P-450 induction also explains depletion (and enhanced toxicity) of nutritional factors such as vitamin A. Even at the early fatty-liver stage, alcoholics commonly have a very low hepatic concentration of vitamin A. Ethanol administration in animals was found to depress hepatic levels of vitamin A, even when administered with diets containing large amounts of the vitamin, reflecting, in part, accelerated microsomal degradation through newly discovered microsomal pathways of retinol metabolism, inducible by either ethanol or drug administration. The hepatic depletion of vitamin A was strikingly exacerbated when ethanol and other drugs were given together, mimicking a common clinical occurrence. Hepatic retinoid depletion was found to be associated with lysosomal lesions and decreased detoxification of chemical carcinogens. To alleviate these adverse effects, as well as to correct problems of night blindness and sexual inadequacies, the alcoholic patient should be provided with vitamin A supplementation. Such therapy, however, is complicated by the fact that in excessive amounts vitamin A is hepatotoxic, an effect exacerbated by long-term ethanol consumption. This results in striking morphologic and functional alterations of the mitochondria with leakage of mitochondrial enzymes, hepatic necrosis, and fibrosis. Thus, treatment with vitamin A and other nutritional factors (such as proteins) is beneficial but must take into account a narrowed therapeutic window in alcoholics who have increased needs for such nutrients, but also display an enhanced susceptibility to their adverse effects. Massive doses of choline also exerted some toxic effects and failed to prevent the development of alcoholic cirrhosis. Acetaldehyde (the metabolite produced from ethanol by either ADH or MEOS) impairs hepatic oxygen utilization and forms protein adducts, resulting in antibody production, enzyme inactivation, and decreased DNA repair. It also enhances pyridoxine and perhaps folate degradation and stimulates collagen production by the vitamin A storing cells (lipocytes) and myofibroblasts.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of chronic ethanol feeding on hepatic and extrahepatic distribution of vitamin E in rats

The effect of chronic ethanol feeding on the status of alpha- and gamma-tocopherol in plasma, liver, lung, and testes of Sprague-Dawley rats was characterized. Rats were pair-fed liquid diets containing 36% of total calories either as ethanol or isocaloric carbohydrates. After 3 weeks, ethanol ingestion resulted in a significant (p less than or equal to 0.05) increase in liver weight and induced fatty liver without affecting total body weight. Ethanol feeding did not affect the plasma concentration of alpha-tocopherol but doubled that of gamma-tocopherol. When expressed per milligram of tissue, liver alpha-tocopherol did not vary with ethanol ingestion, whereas gamma-tocopherol concentration increased 2.5 times that of control animals. However, the concentration of alpha-tocopherol expressed per milligram of total lipids was significantly (p less than or equal to 0.01) decreased in the liver with ethanol feeding. In contrast to the liver, ethanol feeding significantly increased alpha- and gamma-tocopherol levels per milligram of total lipids in the testes. The concentration of gamma-tocopherol (but not alpha-tocopherol) per milligram of lung tissue and per total lung was significantly (p less than or equal to 0.05) increased with ethanol feeding. These data indicate that chronic ethanol ingestion significantly alters the distribution of alpha-tocopherol and gamma-tocopherol in hepatic and extrahepatic tissues of the rat.

Effect of orotic acid on the generation of reactive oxygen and on lipid peroxidation in rat liver

The pyrimidine precursor orotic acid (OA) is a constituent of dairy products and therapeutic drugs. Several recent publications point towards a tumor promoting activity of OA in rat liver. An increased production of reactive oxygen has been discussed as a possible mechanism, leading to lipid peroxidation and DNA single strand breaks. In view of contradictory results, this postulated prooxidative action of OA was reexamined with new experimental techniques. Weanling Sprague-Dawley rats were fed 1% OA in different diets for 4-35 days. The NADPH-mediated lipid peroxidation in liver homogenate and microsomes was determined in vitro by analysis of low-level chemiluminescence (CL) and the strongly correlated formation of malondialdehyde (MDA). In no case did treatment with OA result in an increase of lipid peroxidation in vitro nor did such treatment enhance the generation of reactive oxygen as measured by lucigenin CL. In accordance, the total cytochrome P-450 content as well as the activity of individual P-450 isoenzymes were unchanged. Treatment with OA did not elevate the MDA content of fresh liver homogenate when butylated hydroxytoluene (BHT) was present in the test system. However, when the antioxidant was omitted, increased levels of thiobarbituric acid reactive material were found which correlated with the triglyceride content. This could explain some published data that have been taken as indication for a prooxidative action of OA. Evidence against an increased lipid peroxidation in vivo is given by the analysis of ethane exhalation. Furthermore, no increase in DNA single strand breaks by OA treatment could be observed by the alkaline elution technique. These results do not support the hypothesis of a prooxidative activity of OA. The observed reversible decrease of the GSH/GSSG ratio is assumed to result from the reduced size of the phosphopyridine nucleotide pool due to purine deficiency and an increased consumption of NADPH by the enhanced reductive degradation of pyrimidines.

Mechanism of ethanol induced hepatic injury

Ethanol is hepatotoxic through redox changes produced by the NADH generated in its oxidation via the alcohol dehydrogenase pathway, which in turn affects the metabolism of lipids, carbohydrates, proteins and purines. Ethanol is also oxidized in liver microsomes by an ethanol-inducible cytochrome P-450 (P-450IIE1) which contributes to ethanol metabolism and tolerance, and activates xenobiotics to toxic radicals thereby explaining increased vulnerability of the heavy drinker to industrial solvents, anesthetic agents, commonly prescribed drugs, over-the-counter analgesics, chemical carcinogens and even nutritional factors such as vitamin A. Induction also results in energy wastage and increased production of acetaldehyde. Acetaldehyde, in turn, causes injury through the formation of protein adducts, resulting in antibody production, enzyme inactivation, decreased DNA repair, and alterations in microtubules, plasma membranes and mitochondria with a striking impairment of oxygen utilization. Acetaldehyde also causes glutathione depletion and lipid peroxidation, and stimulates hepatic collagen synthesis, thereby promoting fibrosis.

Lipid peroxidation, iron mobilization and radical generation induced by alcohol

Increasing evidence points to a major role for free radicals in the pathogenesis of alcohol-induced liver injury. In vitro, free radicals may be generated during ethanol metabolism by the further metabolism of acetaldehyde by molybdenum-dependent oxidases such as xanthine oxidase. Ferritin iron mobilized by such free radicals may serve as catalytic iron. Increased stores of ferritin iron and induction of microsomal P-450 reductase activity are mechanisms by which chronic alcohol feeding may potentiate the acute effects of alcohol.

International Commission for Protection against Environmental Mutagens and Carcinogens. ICPEMC Working Paper No. 15/2. Metabolism and metabolic effects of ethanol, including interaction with drugs, carcinogens and nutrition

Different pathways of alcohol metabolism, the alcohol dehydrogenase pathway, the microsomal ethanol-oxidizing system and the catalase pathway are discussed. Alcohol consumption leads to accelerated ethanol metabolism by different mechanisms including an increased microsomal function. Microsomal induction leads to interactions of ethanol with drugs, hepatotoxic agents, steroids, vitamins and to an increased activation of mutagens/carcinogens. A number of ethanol-related complications may be explained by the production of its first metabolite, acetaldehyde, such as alterations of mitochondria, increased lipid peroxidation and microtubular alterations with its adverse effects on various cellular activities, including disturbances of cell division. Nutritional factors in alcoholics such as malnutrition are discussed especially with respect to its possible relation to cancer.

Lack of evidence for increased lipid peroxidation in ethanol-induced centrilobular necrosis of rat liver

The pathogenetic role of lipid peroxidation in ethanol-induced liver injury was previously supported by demonstration of increased formation of diene conjugates and decreased hepatic levels of reduced glutathione in ethanol-fed animals and alcoholic patients with liver injury. The present study was carried out to investigate whether these findings can be extended to a rat model that was shown to produce a spontaneous ethanol-induced liver injury progressing from steatosis to necrosis and fibrosis (Hepatology 6: 814, 1986). Despite the histological evidence of progression from hepatic steatosis to centrilobular necrosis in these animals, diene conjugate formation in mitochondrial and microsomal lipids was not enhanced when compared to pair-fed controls. In addition, hepatic levels of neither methionine nor glutathione were decreased in the ethanol-fed animals. The fatty acid composition of mitochondrial phospholipids from these animals was similar to that in the controls. However, in the microsomal phospholipids, the level of arachidonate (20:4) was depressed by about 50% as compared to the controls. These results demonstrate the lack of evidence for a pathogenetic relationship between lipid peroxidation and ethanol-induced liver injury progressing to centrilobular necrosis. They further suggest that the decreased levels of 20:4 commonly seen after chronic ethanol intake may not be due to a peroxidative loss.

Depressed hepatic glutathione and increased diene conjugates in alcoholic liver disease. Evidence of lipid peroxidation

The role of lipid peroxidation in the pathogenesis of alcoholic liver disease has been a subject of controversy. In order to study this question we measured hepatic glutathione and diene conjugates in liver biopsies from 16 alcoholics with different stages of liver injury and 8 nonalcoholics with liver disease. Patients with alcoholic liver disease were found to have decreased hepatic glutathione compared to patients with liver disease unrelated to alcohol (22.1 +/- 2.5 vs 33.5 +/- 4.6 nmol/mg protein, P less than 0.05). The decrease in glutathione was accompanied by an increase in diene conjugates in hepatic lipids (3.37 +/- 0.14 vs 2.26 +/- 0.21 OD at 232 nm/mg lipid, P less than 0.001). The changes were present in all stages of alcoholic liver damage including fatty liver but unrelated to nutritional status in these patients. They support the concept that lipid peroxidation may be an important mechanism in the pathogenesis of alcoholic liver disease.

Microsomal ethanol oxidizing system (MEOS): interaction with ethanol, drugs and carcinogens

Several studies in our unit showed that in men, baboons, rats and deermice, blood ethanol clearance is significantly accelerated at ethanol concentrations higher than the levels needed to effectively saturate the low Km forms of ADH present in animals, thereby incriminating a high Km non-ADH system such as microsomal ethanol oxidizing system (MEOS). Furthermore, kinetics of blood ethanol clearance were consistent with the Km of MEOS. After chronic ethanol consumption, there was an increase in rates of ethanol elimination and in the activity of MEOS. There was an associated rise in microsomal cytochrome P-450, including a form (different from that of a non-ADH pathway of ethanol metabolism and its increase after chronic ethanol consumption was most conclusively shown in ADH-negative deermice. Microsomal induction was also associated with enhanced metabolism of other drugs, resulting in metabolic drug tolerance. In addition, there was increased activation of known hepatotoxic agents (such as CCl4 and acetaminophen) which may explain the enhanced susceptibility of alcoholics to the toxicity of solvents and commonly used drugs. There was enhanced activation of procarcinogens, sometimes at concentrations much lower than those required for other microsomal inducers. Moreover, catabolism of retinoic acid was accelerated possibly contributing to hepatic vitamin A depletion. In conclusion, after chronic ethanol consumption, enhanced MEOS activity and concomitant cytochrome P-450 changes may contribute to accelerated ethanol and drug metabolism and associated activation of hepatotoxic agents and carcinogens.

Effects of four bisphenolic antioxidants on lipid contents of rat liver

Hepatic lipids were studied in Sprague-Dawley male rats given, 2,2'-methylenebis(4-ethyl-6-tert-butylphenol), 2,2'-methylenebis(4-methyl-6-tert-butylphenol), 4,4'-butylidenebis(3-methyl-6-tert-butylphenol) or 4,4'-methylenebis(2,6-di-tert-butylphenol) at a level of 1.135 mmol% for 1 week. 4,4'-Butylidenebis(3-methyl-6-tert-butylphenol) induced fatty liver and increased triglyceride, diglyceride and cholesteryl-ester concentrations, 7.1-, 5.8- and 6.1-fold, respectively. Plasma triglycerides, total cholesterol and non-esterified fatty acids were markedly decreased. It would appear that the fatty liver resulted mainly from defective fat excretion from the liver. The other bisphenols produced a little change in liver lipids.

The role of peroxidation during chronic and acute exposure to ethanol as determined by pentane expiration in the rat

Weanling rats were fed one of 3 diets containing 0, 11 or 200 international units (IU) dl-alpha-tocopherol acetate/kg diet for 4 weeks. Following this period, the drinking water was replaced with an 18% solution of ethanol (v/v). An isocaloric D-glucose solution was substituted for the drinking water of a control group of rats fed the vitamin-E-deficient diet for 4 weeks. The 4 treatment groups were maintained on the diet and drinking regimen for 20 weeks. Basal levels of expired pentane were determined at weeks 0, 1, 3, 5, 7 and 9. Chronic ethanol consumption did not influence basal pentane production during the 9-week treatment. Basal levels of expired pentane were affected by dietary vitamin E. Rats supplemented with vitamin E had basal pentane levels less than one-half of the level of rats fed a vitamin-E-deficient diet (p less than 0.001). After 14 weeks of treatment, the 2 groups of rats fed a vitamin-E-deficient diet were administrated p.o. an acute dose of 6 g of ethanol/kg body wt. Pentane expired above basal levels during the following 4-hr period correlated with the amount of hepatic triglycerides determined at the conclusion of the experiment. The etiology of ethanol toxicity is a complex and multifactorial system made up of many biological variables that influence lipid peroxidation. The appropriate choices of experimental designs and methods are important in examining the role of lipid peroxidation.

The antioxidant vitamins

This article is an attempt to study the metabolic functions of vitamin C and E together. Such a study must necessarily be imcomplete owing to the extreme richness of the literature. The increasing importance of the work on free radical reactions, their toxicity and carcinogenic action, and also their relation to the metabolism of metals, particularly iron, copper, selenium, and zinc, shows a number of metabolic pathways with which both vitamins interact. It is hoped that this article will indicate future research possibilities.

Interaction of vitamin E and selenium with the hepatotoxic agent dimethylnitrosamine

Pretreatment of rats with vitamin E, 0.02% w/w of the diet and a sc dose, 200 mg/kg, given 48 hrs. before dimethylnitrosamine, DMNA, was found to ameliorate the acute hepatotoxicity of DMNA (30 mg/kg) as reflected in reduced plasma asparagine-amino-transferase (AspAT) activity. This effect was confirmed by histological evaluation. No significant effect of DMNA on plasma levels of vitamin E was observed, however, DMNA significantly increased the hepatic level of vitamin E supplemented rats. Pretreatment with selenium, 0.5 mg/kg given intraperitoneally 48 hrs. before DMNA, was found to enhance the acute hepatotoxicity of DMNA as reflected in increased elevation of plasma AspAT activity. This effect was not confirmed morphologically. DMNA did not have any effect on the hepatic selenium state in selenium pretreated rats; however, selenium pretreatment tended to decrease hepatic and plasma tocopherol levels. To explain the effects observed in the present investigation, various mechanisms were discussed. If the compounds were acting as antioxidants, then the difference in intracellular localization had to be important. More likely a specific biochemical function involving drug metabolizing enzymes could be involved. Finally vitamin E could protect membranes from damage during the necrotizing action of DMNA.

A possible mechanism for the peroxidation of lipids due to chronic ethanol ingestion

The effects of chronic ethanol ingestion on NADPH-oxidase and on the NADPH-catalyzed peroxidation of lipids in rat liver microsomes have been studied. It was demonstrated that the rates of NADPH oxidation, of oxygen consumption, and of malondialdehyde formation increased significantly above control values after one month of ethanol ingestion. Further, the fatty acid composition of these microsomes revealed a decrease in arachidonate and in the C22 polyenes. Also, the energies of activation for the formation of malondialdehyde increased in the microsomes from the ethanol-treated animals. These results were interpreted to mean that ethanol ingestion had induced changes in the microsomal membranes such that additional or alternate, possibly abnormal, pathways for lipid peroxidation were functional. Finally, these data suggest a mechanism whereby chronic ethanol ingestion inhances the production of lipid peroxides via the microsomal-catalyzed oxidation of NADPH.

EFFECTS OF PHYTOL AND ETHANOL ON THE FATE OF RADIOTOCOPHEROL IN SHEEP

The effects of orally administered phytol or ethanol on the metabolism of tritium-labelled tocopherol was studied in 12 sheep fed hay ad libitum. Significantly higher levels of radioactivity were found in the liver, adrenals, rumen tissues, and heart of the two alcohol-treated groups than in the corresponding tissues of the unsupplemented group. In the nontreated sheep specific activities of their blood lipids inclined to be higher than those in the ethanol- or phytol-treated sheep. The higher tritium levels in the livers of the ethanol- and phytol-administered groups may have been related to the reported increase in tocopherol requirement resulting from alcohol-induced stress.

Vitamin E and hepatotoxic agents. 3. Vitamin E, synthetic antioxidants and carbon tetrachloride toxicity in the rat

1. The acute toxicity of orally administered CCl4and its subacute toxicity (liver necrosis and hepatic fat accumulation) were studied in young adult male and female rats. CCl4was more toxic in males than in females. The protective effects of vitamin E (D-α-tocopheryl acetate) and three synthetic antioxidants, DPPD (N,N'-diphenyl-p-phenylenediamine), ethoxyquin (6-ethoxy-1,2-dihydro-2,2,4-trimethylquinoline) and BHT (butylated hydroxytoluene) were studied.

2. Three daily oral doses (450 mg/kg) of vitamin E given before CCl4increased survival in male rats but not consistently in females. Single oral doses (450 mg/kg) given previously at times between 24 and 72 h were also protective in males, but slightly decreased survival in females. Single intraperitoneal doses (500 mg/kg) given to female rats 1–48 h before CCl4had no effect on survival. None of these treatments with vitamin E significantly decreased CC14-induced hepatic triglyceride accumulation. A large oral dose (2000 mg/kg) 6 h before CCl4not only significantly increased hepatic fat accumulation but also increased mortality.

3. Three daily doses (600 mg/kg) of DPPD or a single oral dose given 72 h before CCl4increased survival in male and female rats. When single doses of DPPD were given 6–48 h before CCl4they had no effect on survival. In contrast, DPPD usually significantly decreased the CC14-induced hepatic triglyceride rise when given orally 6–72 h before CCl4. Single intra-peritoneal doses (100–1500 mg/kg) of DPPD, given 1–48 h before CCl4, decreased the hepatic triglyceride rise. Multiple doses of DPPD decreased CC14-induced liver necrosis, but single doses were generally less effective.

4. Three daily oral doses (300–500 mg/kg) of ethoxyquin given before CCl4were highly effective in preventing mortality, liver necrosis and the rise in hepatic triglycerides. Single oral doses (500 mg/kg) given 72 or 48 h before CCl4produced the same effect, but these single doses 24 or 6 h before CCl4were without effect. The effective treatments usually increased liver weight markedly. Intraperitoneal treatment with ethoxyquin also substantially reduced the toxicity of CC14. Ethoxyquin was the most effective of all four treatments studied, and livers from animals given this substance were often nearly normal in histological appearance.

5. The activity of oral doses (400–600 mg/kg) of BHT, given 48 h or more before CCl4was, in general, similar to that of ethoxyquin, but less marked. This substance also caused a large increase in liver weight after 48 h. Oral doses given 6–24 h before CC14 increased the CC14-induced triglyceride rise still further. Intraperitoneal doses of BHT were ineffective against acute toxicity, liver necrosis or the triglyceride rise.

6. Concentrations of a-tocopherol and the three synthetic antioxidants were measured in liver in many of the experiments. Very high hepatic concentrations of a-tocopherol could be obtained without affecting either the acute or subacute toxicity of CCl4. Ethoxyquin and BHT were rapidly eliminated from the liver after oral dosage, and when maximum concentrations were reached (24 h or less after administration) they were without protective effect. In contrast, when ethoxyquin and BHT were most active (48–96 h after administration) they could not be found in appreciable concentration in the liver.