Lipid peroxidation: a mechanism involved in acute ethanol toxicity as demonstrated by in vivo pentane production in the rat

Breath alkanes as a marker of oxidative stress in different clinical conditions

We assessed oxidative stress in three different clinical conditions: smoking, human immunodeficiency virus (HIV) infection, and inflammatory bowel disease, using breath alkane output and other lipid peroxidation parameters such as plasma lipid peroxides (LPO) and malondialdehyde (MDA). Antioxidant micronutrients such as selenium, vitamin E, C, beta-carotene and carotenoids were also measured. Lipid peroxidation was significantly higher and antioxidant vitamins significantly lower in smokers compared to nonsmokers. Beta-carotene or vitamin E supplementation significantly reduced lipid peroxidation in that population. However, vitamin C supplementation had no effect. In HIV-infected subjects, lipid peroxidation parameters were also elevated and antioxidant vitamins reduced compared to seronegative controls. Vitamin E and C supplementation resulted in a significant decrease in lipid peroxidation with a trend toward a reduction in viral load. In patients with inflammatory bowel disease, breath alkane output was also significantly elevated when compared to healthy controls. A trial with vitamin E and C is underway. In conclusion, breath alkane output, plasma LPO and MDA are elevated in certain clinical conditions such as smoking, HIV infection, and inflammatory bowel disease. This is associated with lower levels of antioxidant micronutrients. Supplementation with antioxidant vitamins significantly reduced these lipid peroxidation parameters. The results suggest that these measures are good markers for lipid peroxidation.

Lipid peroxidation during n-3 fatty acid and vitamin E supplementation in humans

The purpose of this study was to investigate in healthy humans the effect of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) intake, alone or in combination with dL-alpha-tocopherol acetate (vitamin E) supplements on lipid peroxidation. Eighty men were randomly assigned in a double-blind fashion to take daily for 6 wk either menhaden oil (6.26 g, n-3 fatty acids) or olive oil supplements with either vitamin E (900 IU) or its placebo. Antioxidant vitamins, phospholipid composition, malondialdehyde (MDA), and lipid peroxides were measured in the plasma at baseline and week 6. At the same time, breath alkane output was measured. Plasma alpha-tocopherol concentration increased in those receiving vitamin E (P < 0.0001). In those supplemented with n-3 fatty acids, EPA and DHA increased in plasma phospholipids (P < 0.0001) and plasma MDA and lipid peroxides increased (P < 0.001 and P < 0.05, respectively). Breath alkane output did not change significantly and vitamin E intake did not prevent the increase in lipid peroxidation during menhaden oil supplementation. The results demonstrate that supplementing the diet with n-3 fatty acids resulted in an increase in lipid peroxidation, as measured by plasma MDA release and lipid peroxide products, which was not suppressed by vitamin E supplementation.

Evidence for a novel pentyl radical adduct of the cyclic nitrone spin trap MDL 101,002

3,4-Dihydro-3,3-dimethyl-isoquinoline-2-oxide (MDL 101,002) is a conformationally constrained cyclic analog of the known spin trap alpha-phenyl N-tert-butyl nitrone (PBN). Because of PBN's ability to scavenge free radicals, MDL 101,002 is currently being evaluated in stroke models as a means to ameliorate the oxidative insult associated with reperfusion injury. To augment our understanding of the radical scavenging mechanism of this potential drug, MDL 101,002 was incubated with soybean lipoxygenase in the presence of linoleic acid to study the interaction between MDL 101,002 and free radicals formed during lipid peroxidation. Analysis of the reaction mixture was performed by high performance liquid chromatography using normal phase conditions with detection by atmospheric pressure chemical ionization mass spectrometry (APCI-MS). Similar to the work by Iwahashi et al. [Arch. Biochem. Biophys., 1991, 285, 172], who studied the spin trap alpha-(4-pyridyl-1-oxide)-N-tert-butyl nitrone (4-POBN), an adduct that suggested the trapping of pentyl radicals by MDL 101,002 was observed. However, the apparent molecular ion for this adduct (246 Da) was 1 Da lower than would be predicted if a pentyl radical had simply added to MDL 101,002. In addition, the adduct exhibited significant absorbance at 304 nm, consistent with the unsaturated nitrone structure of MDL 101,002. To account for these observations, it is postulated that, after the initial capture of a pentyl radical, subsequent abstraction of a hydrogen atom by a neighboring radical occurs to regenerate a nitrone (1-pentyl analog of MDL 101,002). We present evidence for this adduct and offer a mechanism for its formation. These findings indicate that mass spectroscopic analysis of stable nitrone radical adducts may be useful in the identification of radical-dependent damage in vivo and possibly in clinical development of MDL 101,002 as an antioxidant pharmaceutical.

High blood pressure, oxygen radicals and antioxidants: etiological relationships

This hypothesis proposes that high blood pressure is a pathological state associated with a loss of the balance between pro-oxidation and antioxidation, energy depletion, and accelerated aging in the target organs, such as heart, kidney and brain. Different nutritional, environmental, pharmacological factors and/or associated pathologies (diabetes, arteriosclerosis, cancer, alcoholism, etc.) and/or genetic components, can induce high blood pressure by breaking the redox equilibrium in the affected organs. Additional evidence, such as increase of oxidative damage, fibrogenesis, inhibition of the cardiocytic sodium-potassium pump, and heart hypertrophy, supports this hypothesis. These facts are analysed in the present paper, showing that they could contribute to the development of high blood pressure and associated pathologies by oxidative mechanisms.

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.

Lipid hydroperoxide induced mitochondrial dysfunction following acute ethanol intoxication in rats. The critical role for mitochondrial reduced glutathione

It has been found that acute ethanol (EtOH) intoxication of rats caused depletion of mitochondrial reduced glutathione (GSH) of approximately 40%. A GSH reduction of similar extent was also observed after the administration to rats of buthionine sulphoximine (BSO), a specific inhibitor of GSH synthesis. Combined treatment with BSO plus EtOH further decreased mitochondrial GSH up to 70% in comparison to control. Normal functional efficiency was encountered in BSO-treated mitochondria, as evaluated by membrane potential measurements during a complete cycle of phosphorylation. In contrast a partial loss of coupled functions occurred in mitochondria from EtOH- and BSO plus EtOH-treated rats. The presence in the incubation system of either GSH methyl monoester (GSH-EE), which normalizes GSH levels, or of EGTA, which chelates the available Ca2+, partially restores the mitochondrial phosphorylative efficiency. Following EtOH and BSO plus EtOH intoxication, the presence of fatty-acid-conjugated diene hydroperoxides, such as octadecadienoic acid hydroperoxide (HPODE), was detected in the mitochondrial membrane. Exogenous HPODE, when added to BSO-treated mitochondria, induced, in a concentration-dependent system, membrane potential derangement. The presence of either GSH-EE or EGTA fully prevented a drop in membrane potential. The results obtained suggest that fatty acid hydroperoxides, endogenously formed during EtOH metabolism, brought about non-specific permeability changes in the mitochondrial inner membrane whose extent was strictly dependent on the level of mitochondrial GSH.

Blood and liver lipid peroxide status after chronic ethanol administration in rats

During the last decades a vast number of reports have aimed at elucidating the mechanisms behind alcohol-related organ injury, but the manner in which ethanol induces, e.g., liver damage is still an enigma. Increased oxidative stress has been put forward as one possible mechanism behind alcohol-related tissue damage. This paper focuses on the effect of chronic ethanol consumption on antioxidant status and lipid peroxide levels in blood and liver of rats. Alcohol was given twice daily in a total dose of 5 g ethanol/kg body wt. per day divided into two 2.5 g ethanol/kg body wt. doses as a 50% water solution, by gavage over 4 weeks. Chronic ethanol ingestion led neither to a significant change in lipid peroxide formation nor to a significant change in enzymatic antioxidant activities. Only concentrations of oxidized glutathione and of other non-enzymatic antioxidant such as vitamin E showed a tendency to decrease after alcohol application. The data presented could serve to emphasize no involvement of free radical-induced lipoperoxidation in the pathogenesis of ethanolic liver diseases.

Production of lipid hydroperoxides and depletion of reduced glutathione in liver mitochondria after acute ethanol administration to rats

It has been found that acute ethanol (EtOH) intoxication to rats caused approximately 40% depletion of mitochondrial reduced glutathione (GSH). A GSH reduction of similar extent was also observed after the administration to rats of buthionine sulfoximine (BSO), a specific inhibitor of GSH synthesis. The combined treatment of EtOH plus BSO induced a further mitochondrial GSH decrease up to 70% with respect to control. The presence of lipid hydroperoxides in the mitochondrial membrane was observed whenever an additional oxidative stress was associated to a condition of GSH depletion as in the case of EtOH or EtOH plus BSO. Under these conditions a severe derangement in mitochondrial oxidative functions occurred.

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

In order to investigate the effect of carbohydrate intake on ethanol-induced lipid peroxidation and cytotoxicity, rats were maintained on four different test diets, a medium-carbohydrate (carbohydrate intake, 8.4 g/day/rat on average), a low-carbohydrate (carbohydrate intake, 2.8 g/day/rat on average), an ethanol-containing medium-carbohydrate (carbohydrate and an ethanol intake, 8.4 and 2.9 g/day/rat on average, respectively), and an ethanol-containing low-carbohydrate diet (2.8 and 2.9 g/day/rat on average, respectively). Ethanol and the low-carbohydrate diet each increased the liver malondialdehyde content, but the combined effect of both (ethanol-containing low-carbohydrate diet) was much more prominent than either alone. The degree of increase in malondialdehyde content almost paralleled the activity of the microsomal ethanol oxidizing system. Both the low-carbohydrate and the ethanol-containing low-carbohydrate diets decreased the liver glutathione content, but ethanol combined with the medium-carbohydrate diet had no effect on the content. Ethanol treatment increased the liver triglyceride content only when combined with the low-carbohydrate diet. The rate of NADPH-dependent microsomal malondialdehyde formation was much higher in microsomes from rats maintained on the ethanol-containing low-carbohydrate diet than in those from rats on the ethanol-containing medium-carbohydrate diet, indicating that lowered carbohydrate intake augments ethanol-induced malondialdehyde accumulation in the liver by enhancing the rate of lipid peroxidation. In addition, when incubated with red blood cells in the presence of NADPH, microsomes from rats fed the ethanol-containing low-carbohydrate diet caused marked hemolysis, which was prevented by the addition of 5 mM glutathione to the incubation system. Furthermore, addition of 50 mM ethanol to the reaction system greatly accentuated the hemolysis. These results suggest that lowered carbohydrate intake at the time of ethanol consumption potentiates ethanol cytotoxicity by enhancing ethanol-induced lipid peroxidation.

Zinc deficiency, ethanol, and myocardial ischemia affect lipoperoxidation in rats

The production of oxygen free radicals can be stimulated by excess iron, cadmium, nickel, and the like. Inversely, copper, zinc, and selenium inhibit production, either via their own action or via antiradical metalloenzymes. The study involved determining the effect of zinc deficiency combined with chronic ethanol administration on the status of blood and tissue free radicals, as well as on cardiac function in isolated, perfused rats' hearts. Animals were fed a basic diet containing residual zinc at 0.2-0.3 ppm. Following a zinc deficiency lasting 5 wk, which during the last 4 wk was accompanied by chronic ethanol administration, hearts were submitted to ischemia for 30 min in vitro, followed by reperfusion. Biochemical analyses (zinc, superoxide dismutase, malondialdehyde, conjugated dienes, and so on) were performed in the blood and in the homogenates of different organs. The experimental zinc deficiency caused a slight decrease of superoxide dismutase activity, accompanied by increased production of peroxidated lipids. Ethanol administration appeared to increase the levels of peroxidated lipids in the heart. Finally, the combination of zinc deficiency and ethanol administration had very harmful effects, especially on lipid peroxidation and contractile function of the isolated, perfused heart in preischemic conditions.

Alcohol-induced oxidative stress in rat liver

1. Livers from rats treated acutely with ethanol showed increased chemiluminescence, malondialdehyde production, and diene formation. Previous administration of (+)-cyanidanol-3 completely abolished acute ethanol-induced chemiluminescence. 2. Rats fed alcohol liquid diets for 3 weeks showed significant increases in microsomal and mitochondrial malondialdehyde formation, and in microsomal H2O2 and O2-. generation. 3. Rats fed a solid basal diet plus ethanol solution for 12 weeks also showed increased microsomal production of O2-. and increased content of microsomal cytochrome P-450. Hydroperoxide-induced chemiluminescence was higher in homogenates, mitochondria and microsomes from ethanol-treated rats than from controls. Vitamins E and A were more effective inhibitors of hydroperoxide-stimulated chemiluminescence in liver homogenates from ethanol-treated rats than from control animals. 4. Results are consistent with peroxidative stress leading to increased lipid peroxidation in liver of rats fed ethanol both acutely and after long-term dosing.

Isolation and identification of alpha-(4-pyridyl-1-oxide)-N-tert-butylnitrone radical adducts formed by the decomposition of the hydroperoxides of linoleic acid, linolenic acid, and arachidonic acid by soybean lipoxygenase

alpha-(4-Pyridyl-1-oxide)-N-tert-butylnitrone (4-POBN) radical adducts, which are formed in the reactions of soybean lipoxygenase with linoleic acid, arachidonic acid, and linolenic acid, were isolated using HPLC-ESR spectroscopy. Both linoleic acid and arachidonic acid gave one radical adduct, whereas in the case of linolenic acid, two radical adducts were isolated. These radical adducts all showed virtually identical uv spectra with lambda max at 292 and 220 nm in hexane. The absence of absorbance with lambda max at 234 nm indicates that a conjugated diene structure is not contained in these radical adducts. The mass spectra of the radical adducts formed from linoleic and arachidonic acids were identical and contained a molecular ion of m/z 264, consistent with the trapping of the pentyl radical by 4-POBN. Indeed, authentic 4-POBN pentyl radical adduct obtained from the reaction between pentylhydrazine and 4-POBN gave the same mass spectrum as the product obtained from the reaction of linoleic acid and arachidonic acid with 4-POBN. The two 4-POBN radical adducts formed in the linolenic acid reaction were shown by mass spectrometry to be isomers of pentenyl radicals. The 4-POBN-pentyl radical adduct was also detected in the reaction mixture of 13-hydroperoxy-linoleic acid, soybean lipoxygenase, and 4-POBN, indicating that the pentyl radical and pentenyl radical are formed by the decomposition of the hydroperoxides.

Absorption, transport and metabolism of vitamin E

Vitamin E includes eight naturally occurring fat-soluble nutrients called tocopherols and dietary intake of vitamin E activity is essential in many species. alpha-Tocopherol has the highest biological activity and the highest molar concentration of lipid soluble antioxidant in man. Deficiency of vitamin E may cause neurological dysfunction, myopathies and diminished erythrocyte life span. alpha-Tocopherol is absorbed via the lymphatic pathway and transported in association with chylomicrons. In plasma alpha-tocopherol is found in all lipoprotein fractions, but mostly associated with apo B-containing lipoproteins in man. In rats approximately 50% of alpha-tocopherol is bound to high density lipoproteins (HDL). After intestinal absorption and transport with chylomicrons alpha-tocopherol is mostly transferred to parenchymal cells of the liver were most of the fat-soluble vitamin is stored. Little vitamin E is stored in the non-parenchymal cells (endothelial, stellate and Kupffer cells). alpha-Tocopherol is secreted in association with very low density lipoprotein (VLDL) from the liver. In the rat about 90% of total body mass of alpha-tocopherol is recovered in the liver, skeletal muscle and adipose tissue. Most alpha-tocopherol is located in the mitochondrial fractions and in the endoplasmic reticulum, whereas little is found in cytosol and peroxisomes. Clinical evidence from heavy drinkers and from experimental work in rats suggests that alcohol may increase oxidation of alpha-tocopherol, causing reduced tissue concentrations of alpha-tocopherol. Increased demand for vitamin E has also been observed in premature babies and patients with malabsorption, but there is little evidence that the well balanced diet of the healthy population would be improved by supplementation with vitamin E.

Vitamin E suppresses increased lipid peroxidation in cigarette smokers

Cigarette smoke contains many xenobiotics, including oxidants and free radicals, which can increase lipid peroxidation. Recently, breath pentane output (BPO) has been recognized as a good indicator of lipid peroxidation. Vitamin E is known to be a potent free radical scavenger which can protect biological membranes against oxidative damage. We investigated the effect of vitamin E (dl-alpha-tocopherol) on lipid peroxidation in 13 healthy smokers. The results showed (1) smokers had increased BPO as compared with 19 healthy non-smokers (16.3 +/- 1.9 vs 5.8 +/- 0.5, pmol/kg body weight/min, p less than 0.001) although both groups had comparable plasma vitamin E and selenium concentrations, (2) supplementation with vitamin E (800 mg/day for 2 weeks) decreased BPO in smokers, and (3) the concentration of plasma selenium-dependent glutathione peroxidase was restored to normal in those smokers (five out of 13) in whom this was low initially. We conclude that a normal plasma concentration of vitamin E does not prevent this increase of lipid peroxidation in smokers but that substantial doses of vitamin E will significantly reduce this increased lipid peroxidation. If a major function of vitamin E is to protect lipids from peroxidation, then smokers have a conditioned insufficiency of vitamin E on a normal diet.

Effect of acute ethanol administration on the subcellular distribution of iron in rat liver and cerebellum

An acute ethanol load (50 mmol/kg, i.p.) produced altogether a decrease in the non-heme iron content of the serum and an increase in the iron content in liver and cerebellum. Subcellular fractionation studies indicated that the non-heme iron accumulated by the liver, 4 hr after the ethanol load, was recovered in light mitochondria, microsomes and cytosol, and that iron accumulated by the cerebellum was localized in heavy mitochondria, light mitochondria, microsomes and cytosol. The low molecular weight chelatable (LMWC) iron content as well as the percentage of total non-heme iron represented by LMWC-iron were increased in the cytosol of liver and cerebellum after the ethanol load. These results suggest that an acute ethanol load induces (i) a shift in the distribution between circulating and tissular non-heme iron; (ii) an increase in the cytosolic LMWC-iron which, by favouring the biosynthesis of reactive free radicals, may contribute to lipid peroxidation in liver and cerebellum.

Effect of chronic ethanol consumption on the content of alpha-tocopherol in subcellular fractions of rat liver

The effects of long-term administration of ethanol (35% of total energy for 6-8 weeks) on the distribution and concentration of alpha-tocopherol in subcellular fractions of rat liver have been studied. Marker enzymes were measured in all fractions. The highest concentration of alpha-tocopherol was found in the light mitochondrial fraction both in ethanol-fed and control rats, 754 +/- 104 and 1127 +/- 126 pmol/mg protein, respectively. The microsomal, heavy mitochondrial, and nuclear fractions also had high concentrations of alpha-tocopherol, whereas the cytosolic fraction contained minor amounts. In the light mitochondrial fraction we found the highest concentration of alpha-tocopherol in lysosomes, whereas small amounts were detected in peroxisomes. In the microsomal fraction the highest concentration was found in the Golgi apparatus. The content of alpha-tocopherol in the light mitochondrial fraction was reduced by 33% (p less than 0.02) in the ethanol-fed group as compared to the controls. In the other fractions no significant differences between the two groups were observed. Long term administration of ethanol promoted, however, a further enrichment of alpha-tocopherol (178% higher than controls) in the Golgi apparatus, possibly due to reduced secretion of very low density lipoprotein-associated alpha-tocopherol.

Chemiluminescence from acetaldehyde oxidation by xanthine oxidase involves generation of and interactions with hydroxyl radicals

The ability of acetaldehyde to generate free radicals is often ascribed to its oxidation by xanthine oxidase, with the subsequent production of reactive oxygen intermediates. Chemiluminescence associated with the oxidation of acetaldehyde by xanthine oxidase was inhibited by superoxide dismutase, catalase, or several hydroxyl radical scavenging agents, and was stimulated by the addition of EDTA or ferric-EDTA. This suggests that the light emission is primarily due to the production of hydroxyl radicals via an iron-catalyzed Haber-Weiss type of reaction. Chemiluminescence with hypoxanthine as substrate for xanthine oxidase was much lower than that found with acetaldehyde, yet rates of hydroxyl radical production were greater with hypoxanthine. Acetaldehyde increased light emission in the presence of hypoxanthine by a greater than additive effect. These results suggest a complex role for acetaldehyde in catalyzing xanthine oxidase-dependent chemiluminescence. It appears that besides being a substrate for xanthine oxidase, acetaldehyde also reacts with the generated hydroxyl radical to produce acetaldehyde radicals, which yield chemiluminescence upon their decay. Further studies will be required to evaluate whether the production of such species contributes to or plays a role in the generation of reactive oxygen intermediates and toxicity associated with acetaldehyde metabolism.

The metabolism of acetaldehyde and not acetaldehyde itself is responsible for in vivo ethanol-induced lipid peroxidation in rats

A single oral administration of ethanol (5 g/kg) to rats induced a marked increase in lipid peroxidation, in the liver and kidney within 9 hr, as assessed by malondialdehyde accumulation. The pretreatment with alcohol dehydrogenase (ADH) inhibitor, 4-methylpyrazole (1 mmol/kg) caused approximately 50% inhibition of the hepatic ADH activity and abolished this ethanol-induced lipid peroxidation. The disulfiram treatment (100 mg/kg) significantly inhibited 63% of the hepatic low Km aldehyde dehydrogenase (ALDH) but not the high Km ALDH. The cyanamide treatment (15 mg/kg) effectively decreased 83% of the low Km and 70% of the high Km ALDH in the liver. Although there was more than a 20-fold elevation of acetaldehyde levels by the inhibition of acetaldehyde metabolism with disulfiram or cyanamide, the ethanol-induced lipid peroxidation was significantly suppressed by pretreatment with these drugs. More than 90% inhibition of xanthine oxidase and dehydrogenase by the pretreatment with allopurinol (100 mg/kg), with no effect on the hepatic ADH and ALDH activities, did not alter the enhancement of lipid peroxidation following ethanol administration. We propose that the metabolism of acetaldehyde (probably via the low Km ALDH) and not acetaldehyde itself is responsible for the ethanol-induced lipid peroxidation in vivo and that the contribution of xanthine oxidase, as an initiator of lipid peroxidation through acetaldehyde oxidation is minute during acute intoxication.

Association between alcoholism and increased hepatic iron stores

Although alcoholic liver disease is often associated with some increase in hepatic iron stores, it is now established that when gross iron overload is present, this is due to genetic hemochromatosis. Furthermore, there appears to be a critical iron concentration necessary for the induction of hepatic fibrosis. Lipid peroxidation induced by ethanol and/or iron would appear to play a major role in hepatic damage in both humans and experimental animals. Although the exact mechanism(s) of induction of lipid peroxidation by ethanol and iron remains to be elucidated, both toxins can exert a synergistic effect upon hepatic lipid peroxidation. Iron overload has also been shown to stimulate directly hepatocyte and hepatic procollagen mRNA expression, which is further stimulated by ethanol. The observed synergism between iron and alcohol with respect to both hepatic lipid peroxidation and collagen biosynthesis offers a possible explanation of the apparent early onset of fibrosis and cirrhosis in patients with iron overload who have an excessive alcohol intake.

Potentiation of ethanol-induced lipid peroxidation of biological membranes by vitamin C

The hydroxyl free radical (.OH) was generated by the system of ADP-Fe++ and H2O2, trapped by 5,5-dimethyl-1-pyrroline-N-oxide (DMPO) and analyzed by electron spin resonance (ESR) spectroscopy. The addition of vitamin C to the system decreased considerably the amount of hydroxyl adduct of DMPO formed. In the presence of ethanol, the ESR spectrum observed was a composite signal of the hydroxyl and hydroxyethyl (HE) adducts of DMPO. However, in the presence of vitamin C and ethanol, pure HE adduct of DMPO was detected. We also detected the increase in lipid peroxidation in the presence of ethanol and vitamin C. These data lead us to hypothesize that in the biological system, formation of these long-lived HE free radicals may result in membrane damage due to an increase in lipid peroxidation.

Reactive free radical generation in vivo in heart and liver of ethanol-fed rats: correlation with radical formation in vitro

Rats fed a high-fat ethanol-containing diet for 2 weeks were found to generate free radicals in liver and heart in vivo. The radicals are believed to be carbon-centered radicals, were detected by administering spin-trapping agents to the rats, and were characterized by electron paramagnetic resonance spectroscopy. The radicals in the liver were demonstrated to be localized in the endoplasmic reticulum. Rats fed ethanol in a low-fat diet showed significantly less free radical generation. Control animals given isocaloric diets without ethanol showed no evidence of free radicals in liver and heart. When liver microsomes prepared from rats fed the high-fat ethanol diet were incubated in a system containing ethanol, NADPH, and a spin-trapping agent, the generation of 1-hydroxyethyl radicals was observed. The latter was verified by using 13C-substituted ethanol. Microsomes from animals fed the high-fat ethanol-containing diet had higher levels of cytochrome P-450 than microsomes from rats fed the low-fat ethanol-containing diet. The results suggest that the consumption of ethanol results in the production of free radicals in rat liver and heart in vivo that appear to initiate lipid peroxidation.

Zinc, ethanol, and lipid peroxidation in adult and fetal rats

Studies were performed on adult and fetal rats receiving either a zinc-deficient (<0.5 ppm) diet and/or ethanol (20%) throughout pregnancy. Liver zinc levels were depressed in fetuses exposed toin utero zinc deficiency, but brain zinc levels were unchanged. Ethanol had no effect on the concentration of zinc in the several fetal and adult tissues studies. Lipid peroxidation, as measured by endogenous levels of malondialdehyde (MDA) increased following food restriction, zinc improverishment, and alcoholism in adult and fetal livers, but not in fetal brains. Generally, levels of MDA were highest when both zinc deficiency and the ingestion of alcohol occurred concurrently. Glutathione (GSH) was depressed by zinc restriction in several adult and fetal tissues, but not in the fetal brain. Ethanol alone had no effect on GSH levels. The activity of the enzyme glutathione peroxidase (GSH-Px) was not changed in either organism by alcohol or zinc deficiency.Overall, the data point to increased lipid peroxidation in maternal and fetal rat tissues following zinc depletion and/or treatment with alcohol and draw attention to the apparent vulnerability of the fetal liver toin utero alcoholism. By contrast, the fetal brain seems to be especially resistant to alcohol and zinc-related lipoperoxidation. An association is suggested between the increased lipoperoxidation accompanying zinc deficiency and reduced levels of GSH, but this does not appear to relate to changes in the activity of GSH-Px. A similar relationship is not evident with respect to the increased levels of MDA in fetal and adult livers following chronic alcohol intoxication. A possible basis for the zinc-GSH interaction is discussed.

Age-dependent changes in rat liver lipid peroxidation and glutathione content induced by acute ethanol ingestion

The study of the influence of the age of animals (13 to 53 weeks) on total liver thiobarbituric acid reactive substances (TBAR) content showed an increase which is maximal in rats of 39 weeks of age compared to young animals (13 weeks), followed by a dimunition in the 53 weeks old group. In this situation, the content of hepatic GSH and total GSH equivalents as well as the GSH/GSSG ratio were decreased with ageing, while GSSG levels were enhanced in the oldest group studied. Acute ethanol intoxication resulted in a marked increase in liver TBAR content in young animals, together with a decline in GSH, total GSH equivalents and GSH/GSSG ratio, and an enhancement in GSSG. These changes elicited by ethanol intake were reduced with ageing. It is concluded that ethanol-induced oxidative stress in the liver is diminished during ageing, despite the progressive decrease in the glutathione content of the tissue observed in control animals.

Reduced hepatic alpha-tocopherol content after long-term administration of ethanol to rats

We have studied the effects of long-term administration of ethanol on the distribution and pharmacokinetics of alpha-tocopherol. In rats fed ethanol (35% of total energy) for 5-6 weeks concentration of alpha-tocopherol in whole liver was reduced by 25% as compared to the pair-fed controls (P less than 0.003). This reduction was significant in the parenchymal cells (28%, P less than 0.004), whereas no significant difference was observed for the nonparenchymal cells. Mitochondrial alpha-tocopherol content was reduced by 55% in the ethanol-treated rats as compared to the controls (P less than 0.002), whereas no significant difference was observed in microsomes, light mitochondria or cytosol. The serum levels of alpha-tocopherol showed no significant difference between the groups. When in vivo labeled chylomicron alpha-[3H]tocopherol was injected intravenously to anesthetized rats, we found a significant increase in serum half-life of alpha-tocopherol in the ethanol-treated group as compared to the controls (P less than 0.025). Hepatic alpha-[3H]tocopherol content was similar in the two groups 24 h after injection.

Lipid peroxidation and mechanisms of toxicity

Aerobic organisms by definition require oxygen, and the importance of iron in aerobic respiration has long been recognized, but despite their beneficial roles, these elements can pose a real threat to the organism. During oxygen reduction, reactive species such as O2-. and H2O2 are formed readily. Iron can combine with these species, or with molecular oxygen itself, to generate free radicals which will attack the polyunsaturated fatty acids of membrane lipids. This oxidative deterioration of membrane lipids is known as lipid peroxidation. To protect itself against this form of attack, the organism possesses several types of defense mechanisms. Under normal conditions, these defenses appear to offer adequate protection for cell membranes, but the possibility exists that certain foreign compounds may interfere with or even overwhelm these defenses, and herein could lie a general mechanism of toxicity. This possible cause of toxicity is discussed in relation to other suggested causes.

Effect of ethanol, acetaldehyde and acetate on the antioxidant-sensitive respiration in the perfused rat liver: influence of fasting and diethylmaleate treatment

The infusion of 45 mM ethanol or 50 microM acetaldehyde into the perfused rat liver produced comparable and significant antioxidant-sensitive respiratory rates, while marginal responses were obtained with 10 mM acetate. Ethanol-induced antioxidant-sensitive respiration was markedly increased in perfused livers from fasted rats or animals given diethylmaleate which exhibit low hepatic glutathione levels, compared to fed rats. These data point out the significant role of acetaldehyde in ethanol-induced liver oxidative stress, which can be exacerbated by glutathione depletion.

Lipid peroxidation in alcoholic myopathy and cardiomyopathy

The hypothesis is presented that lipid peroxidation is responsible for the damage in skeletal and cardiac muscle of chronic alcoholic subjects. The enhanced lipid peroxidation is caused by the accumulation of oxygen radicals. Both excessive production and decreased disposal of oxygen radicals can arise from the acetaldehyde formed in the oxidation of ethanol. Although acetaldehyde from hepatic sources may contribute, muscle itself can generate significant amounts of acetaldehyde through the action of muscle catalase. The effects of alcohol on other tissues, and its known long-term effects on membranes lend support to this hypothesis. The ultrastructural features of the alcoholic myopathies provide further support. The resemblance between vitamin E-deficiency myopathy and the alcoholic myopathies is strong additional evidence in favor of this hypothesis.

Cytochrome P-450 oxidation of alkanes originating as scission products during lipid peroxidation

Alkanes of low molecular weight, as well as malondialdehyde, originate during lipid peroxidation. Ethane and pentane are the most prominent and are probably scission products of omega-3 and omega-6 unsaturated fatty acids, respectively. Measurement of exhaled alkanes is the most reliable procedure for determining lipid peroxidation in vivo. Alkanes appear in the breath of rats 15 min after administration of CBrCl3 i.p., and are also formed in small amounts endogenously. Alkanes exhaled from untreated rats in a closed system, in which CO2 is absorbed and O2 supplied, reached steady-state levels after different times, indicating that these volatile gases are metabolized at variable rates. Metabolism was verified by injecting alkanes into the closed system. Pentane was metabolized 5-10 times faster than ethane, and was species- and strain-dependent. Administration of drugs which inhibit or induce cytochrome P-450 indicated that a particular isoenzyme might be involved in the oxidation of small alkanes. SKF 525-A or benzoflavone did not inhibit, but tetrahydrofuran and ethanol were effective inhibitors. Inducing effects of phenobarbital, methylcholanthrene or ethanol were insignificant. Incubation of microsomes with NADPH and O2, either with or without Fe-ADP, to elicit lipid peroxidation confirmed the findings in vivo. Ethane and pentane were formed in similar quantities. Inhibition of alkane oxidation with CO or ethanol increased the amount of pentane three- to four-fold, indicating that inhibition of metabolism enhances alkane release. The ratio of unmetabolized pentane to ethane reflects the membrane ratio of omega-6 to omega-3 unsaturated acids. Different types of alkane release were observed following administration of paracetamol or CCl4 to mice, indicating differences in the peroxidative attack. CCl4 destroys cytochrome P-450 dose dependently, so that it loses its capacity to oxidize pentane, whereas paracetamol does not inactivate the mono-oxygenase. Monitoring the elimination rate of injected pentane is recommended as a reliable non-invasive procedure for testing the functional state of hepatic cytochrome P-450.

Ethane release during metabolism of aldehydes and monoamines in perfused rat liver

Infusion of aldehyde such as acetaldehyde, propionaldehyde or benzaldehyde to perfused rat liver leads to an increase in hepatic ethane production. Half-maximal effect was obtained with about 20 microM acetaldehyde, a concentration range found in plasma during ethanol metabolism. Compounds which metabolically generate aldehydes such as monoamines (benzylamine, phenylethylamine) as substrates for monoamine oxidase or ethanol as substrate for alcohol dehydrogenase [A. Müller and H. Sies (1982) Biochem. J. 206, 153-156] are also able to elicit ethane release. Results obtained with inhibitors of hepatic aldehyde metabolism (pargyline or cyanamide) or of monamine oxidase (pargyline or tranylcypromine) suggest that metabolism of the aldehydes is required for ethane production. Radical scavenging by the addition of the flavonoid, cyanidanol, or by pretreatment with vitamin E (alpha-tocopherol) abolished ethane release, in agreement with lipid peroxidation as a source of alkane production during aldehyde metabolism.

Effect of an acute dose of ethanol on lipid peroxidation and on the activity of microsomal glutathione S-transferase in rat liver

Acute ethanol administration (1.5 g/kg) to fasted rats resulted in a small but significant increase in the content of conjugated dienes in the microsomal fraction of liver. Treatment with 4-methylpyrazole prior to ethanol ingestion was able to reduce the ethanol-induced lipid peroxide formation (measured as conjugated dienes). No depletion of glutathione occurred within the first 2 hrs following ethanol administration by which time lipid peroxide formation is well established. The ethanol-induced inhibition of N-ethylmaleimide-stimulated microsomal glutathione S-transferase activity correlates positively to the concentration of conjugated dienes in the microsomal fraction of liver.

Hepatic and biliary levels of glutathione and lipid peroxides following iron overload in the rat: effect of simultaneous ethanol administration

The administration of 125 mg of iron/kg (iron-dextran-Imferon) to fed rats was followed by an increase in the non-hem iron content in plasma and liver over a period of 22 hr, reaching a peak value after 6 hr. Plasma and hepatic iron levels were not modified by ethanol ingestion (5 g/kg). Iron and ethanol treatments enhanced liver lipid peroxidation (malondialdehyde (MDA) formation) by 70 and 35%, respectively, at 6 hr. Since the hepatic MDA formation increased by 92% after the joint iron-ethanol treatment, an additive effect in lipid peroxidation was suggested to occur in this condition. Both iron and ethanol treatments increased biliary levels and release of MDA, in the absence of changes in bile flow. These parameters were further enhanced by the joint iron-ethanol exposure, in that hepatic MDA levels and biliary MDA release were significantly correlated (r = 0.86; p less than 0.05). Plasma MDA levels also increased after iron, ethanol, and iron-ethanol treatments, but they did not reflect the changes in MDA levels in liver. Iron exposure resulted in 26 to 33% decreases in hepatic GSH content at the 6-hr treatment, associated with the peak effect on lipid peroxidation. In this situation, glutathione disulfide (GSSG) levels in liver were not changed, but its biliary release increased by 76%. Hepatic reduced glutathione (GSH) levels were recovered by 18 hr and increased by 23% after 22 hr of iron ingestion. Acute ethanol intake diminished liver GSH content by 30% and enhanced that of GSSG by 73%, thus eliciting a net decrease of 20% in total GSH equivalents (GSH + 2GSSG). Biliary release of total GSH was reduced in this condition. The combined administration of iron and ethanol further influenced the decrease in hepatic GSH and the increase in GSSG levels elicited by the separate treatments, but no alterations in the biliary content and release of total GSH were observed in this situation. These data indicate that iron exposure accentuates the changes in lipid peroxidation and in the glutathione status of the liver cell induced by acute ethanol intoxication.

Time course of the carbon tetrachloride-induced decrease in mitochondrial aldehyde dehydrogenase activity

Hepatic microsomal enzymes like cytochrome P-450 and glucose 6-phosphatase are inhibited after exposure to CCl4 in vivo. Since comparatively less is known about the effects of CCl4 on nonmicrosomal enzymes, we investigated the rapidity by which CCl4 inhibits the low Km mitochondrial aldehyde dehydrogenase (ALDH) isozyme, an enzyme known to be inhibited 24 hr after CCl4 treatment. The activity of this ALDH isozyme was significantly lowered 6 and 12 hr after a single 1 ml/kg intragastric dose of CCl4. The mitochondrial low Km ALDH specific activities exhibited a similar pattern of destruction/inhibition to the documented target enzyme microsomal cytochrome P-450 in that lowest values were observed 6 hr after CCl4. These values were 44 and 37% of control for cytochrome P-450 content and the low Km ALDH activity, respectively. Alcohol dehydrogenase activity, expressed as activity per gram liver, was depressed 12 hr after CCl4 dosing. Finally, the activity of the low Km cytosolic ALDH, the isozyme that metabolizes malondialdehyde at low concentrations, was not affected by CCl4 treatment. The CCl4-induced decline in the activity of the matrix ALDH isozyme occurs earlier than previously reported mitochondrial damage. The study of sensitive enzymes like the low Km ALDH may provide valuable information by which it may be possible to determine the relationship of the truly rapid biochemical effects of CCl4 such as microsomal lipid peroxidation with later effects on nonmicrosomal components.

Quantitative evaluation of ethane and n-pentane as indicators of lipid peroxidation in vivo

The use of exhalation of ethane and n-pentane in experimental animals as parameters of lipid peroxidation led to an examination of pharmacokinetics of both compounds in rats. When rats were exposed, in a closed desiccator jar chamber, to a wide range of ethane concentrations, linear elimination pharmacokinetics were observed. n-Pentane, when concentrations higher than 100 ppm were applied, displayed saturation kinetics. These were formally explained by action of two competing metabolizing pathways or enzymes. Application of preexisting models could describe exhalation of both ethane and n-pentane by untreated control rats. Stimulation of lipid peroxidation by ferrous ions or by carbon tetrachloride resulted in dissimilar quantitative behaviours of ethane and n-pentane. Ethane production rates were enhanced after application of both compounds. Because of relatively slow metabolic eliminations this led to markedly elevated concentrations of ethane in the gas phase of the system. Pentane production rates were simultaneously enhanced. However, difficulties in interpretation arise because of rapid metabolic elimination of n-pentane. Compounds that diminish pentane metabolism are shown to evoke higher pentane concentrations in the system than compounds which only enhance the pentane production rate. Determinations of ethane exhalation should provide a more favourable parameter of lipid peroxidation than exhalation of pentane.

Inhibition of ethanol- and aldehyde-induced release of ethane from isolated perfused rat liver by pargyline and disulfiram

Acute addition of ethanol or acetaldehyde to the isolated, perfused rat liver leads to an increase in ethane and n-pentane release. These volatile hydrocarbons are known to originate from the peroxidation of polyunsaturated fatty acids. The effects are half-maximal at 0.5 mM ethanol or 20 microM acetaldehyde in the entering perfusate. Propionaldehyde and benzaldehyde are also able to elicit ethane release. Pargyline and disulfiram, inhibitors of aldehyde oxidation, inhibited the extra ethane release in all cases. The inhibitory effect of pargyline is suppressed during addition of metyrapone. The study indicates that the oxidation of acetaldehyde and not of ethanol itself is the step responsible for increased ethane formation by the perfused rat liver during ethanol infusion.

Hepatic aldehyde dehydrogenases and lipid peroxidation

Recent findings have shown that microsomal membrane lipid peroxidation generates a variety of reactive aldehydic products. The interaction of lipid peroxidation products with hepatic aldehyde dehydrogenases (ALDH) was studied using rat liver subcellular fractions. The well-documented membrane peroxidation product malondialdehyde (MDA) was studied to determine if ALDH isozymes play a role in metabolism of this aldehyde. The cytosolic and mitochondrial hepatic subcellular fractions were found to contain ALDH isozymes capable of oxidizing MDA. The kinetic properties of a cytosolic ALDH (Km of approximately 16 microM) suggest that this enzyme may be involved in the metabolism of MDA in vivo. Both the cytosolic and mitochondrial fractions also contained an ALDH isozyme with Km values in the millimolar range. Addition of the cytosolic fraction of rat liver produced a significant decrease in the accumulation of MDA during CCl4-induced microsomal membrane lipid peroxidation but did not protect cytochrome P-450 from destruction. The mitochondrial low Km ALDH isozyme was found to be a target enzyme for inhibition during in vitro microsomal lipid peroxidation. These studies show that a select ALDH isozyme is sensitive to inhibition during membrane lipid peroxidation whereas other isozymes may be involved in the metabolism of aldehydic peroxidation products.

Alcohol ingestion, liver glutathione and lipoperoxidation: metabolic interrelations and pathological implications

Data reviewed here indicate that acute and chronic ethanol ingestion induce a decrease in the concentration of GSH and an increase in lipoperoxidation in the liver both in experimental animals and in man, changes that are closely interrelated GSH depletion is suggested to be due to an oxidation in the liver tissue and to a translocation into the extrahepatic medium as free glutathione and/or as conjugates with ethanol-derived acetaldehyde. As a result, the hepatic GSH/GSSG ratio is drastically reduced. Lipoperoxidation seems to be related to the metabolism of ethanol and acetaldehyde by secondary pathways that are known to generate oxygen-related free radicals. Being lipoperoxidation a process associated with cell damage and death, its stimulation by ethanol ingestion could play a role in the production of alcoholic liver damage in man. The involvement of several contributory factors in the development of a high lipoperoxidative index in the liver in this situation is discussed.

Effect of vitamin E on pentane exhaled by rats treated with methyl ethyl ketone peroxide

One useful method to monitor in vivo lipid peroxidation is the measurement of volatile hydrocarbons, mainly pentane and ethane, that derive from unsaturated fatty acid hydroperoxides. Vitamin E, the biological antioxidant, inhibits lipid peroxidation and the production of pentane and ethane. The rates of pentane production by male Sprague-Dawley rats fed a diet that contained 10% vitamin E-stripped corn oil and 0, 1, 3, 5 or 10 IU dl-alpha-tocopherol acetate/kg were monitored over a 12-wk period. During the eleventh and twelfth weeks, the rats were injected intraperitoneally with 3.3 and 13 mg of methyl ethyl ketone peroxide (MEKP)/kg body wt, respectively. Pentane production was then measured at intervals over a 50-min period, and the total amount of pentane produced over this time interval was estimated. An asymptotic function was found to describe the relationship between exhaled pentane and the low levels of dietary vitamin E that were fed to the rats. As measured by pentane production, rats had a higher minimal vitamin E requirement after they were treated with the potent peroxidation initiator MEKP than they did prior to treatment. The level of pentane exhaled by rats injected with 13 mg MEKP/kg body wt was significantly correlated with kidney and spleen tocopherol levels.

Role of alcohol dehydrogenase activity and the acetaldehyde in ethanol- induced ethane and pentane production by isolated perfused rat liver

The volatile hydrocarbons ethane and n-pentane are produced at increased rates by isolated perfused rat liver during the metabolism of acutely ethanol. The effect is half-maximal at 0.5 mM-ethanol, and its is not observed when inhibitors of alcohol dehydrogenase such as 4-methyl- or 4-propyl-pyrazole are also present. Propanol, another substrate for the dehydrogenase, is also active. Increased alkane production can be initiated by adding acetaldehyde in the presence of 4-methyl- or 4-propyl-pyrazole. An antioxidant, cyanidanol, suppresses the ethanol-induced alkane production. The data obtained with the isolated organ demonstrate that products known to arise from the peroxidation of polyunsaturated fatty acids are formed in the presence of ethanol and that the activity of alcohol dehydrogenase is required for the generation of the active radical species. The mere presence of ethanol, e.g. at binding sites of special form(s) of cytochrome P-450, it not sufficient to elicit an increased production of volatile hydrocarbons by rat liver.

Carbon tetrachloride-induced lipid peroxidation: simultaneous in vivo measurements of pentane and chloroform exhaled by the rat

Simultaneous measurements of pentane, an index of lipid peroxidation, and chloroform (CHCl3), an index of carbon tetrachloride (CCl4) metabolism, were made on samples of breath from rats injected with 30 microliter CCL4/100 g body wt. In the first 3 h after administration of CCl4, rats fasted overnight metabolized less CCl4 and exhaled less pentane than did fed rats. Multiple injections of CCl4 decreased both the metabolism of CCl4 to CHCl3 and the level of in vivo lipid peroxidation following administration of a subsequent dose of CCl4. Dietary vitamin E provided limited protection from CCl4-induced lipid peroxidation and had no effect on the rate of CCl4 metabolism to CHCl3.