Lipoperoxidation of lung lipids in rats exposed to nitrogen dioxide

Absorption spectra characteristic of diene conjugation and typical for peroxidized polyenoic fatty acids can be induced in rat lung lipids after the rats have been exposed to a scant amount of nitrogen dioxide (1 part per million) for 4 hours. The peroxidative changes do not occur immediately but appear to reach a maximum between 24 and 48 hours after exposure. The prooxidant effect of this atmospheric pollutant in rat lung lipids may be partially prevented by prior treatment of the animal with large doses of alpha-tocopherol.

On the postulated peroxidation of unsaturated lipids in the tissues of vitamin E-deficient rats

1. The micro-iodimetric method has been used to study some factors affecting the concentration of lipid peroxides in the adipose tissue of vitamin E-deficient rats.

2. Cod-liver oil methyl esters (CLOME) or maize oil methyl esters (MOME) with peroxide values ranging from 3 to 330 μ-equiv./g were given by mouth to vitamin E-deficient rats deprived of food before and after the dose. Lipid peroxides did not accumulate in the adipose tissue of these rats.

3. Experiments with dietary CLOME and MOME of varying peroxide values (2–230 μ-equiv./g) showed that exogenous lipid peroxide accumulates in the adipose tissue when the rats received these lipids at 10% in the diet for 4 weeks, but not if the dietary concentration was only 4% or if the diet with 10% lipid was given for 5 days only.

4. Rats were given dietary CLOME for 4 weeks. Their adipose tissue was then found to contain about 50 μ-equiv. lipid peroxide/g. They were divided into three groups. One group was given a fat-free diet and, after 10 days, the adipose tissue concentration of lipid peroxide had decreased to about 10 μ-equiv./g. The other groups were given the fat-free basal diet supplemented with vitamin E or DPPD (N,N′-diphenyl-p-phenylenediamine). Neither supplement significantly affected the rate of disappearance of the peroxides from the adipose tissue.

5. It was shown that neither α-tocopherol nor DPPD reacted with the lipid peroxides of CLOME or MOME in vitro, at room temperature or even after 65 h at 37°.

6. It was concluded that unsaturated lipids do not become peroxidized after incorporation into the adipose tissue of vitamin E-deficient rats. Lipid peroxides taken up from the diet into the adipose tissue are not of fleeting existence, having a half-life of about 6 days. Dietary vitamin E probably prevents the accumulation of exogenous lipid peroxides in the adipose tissue by reinforcing the barrier to their absorption in the gut.

7. These studies provide further evidence that current concepts of lipid peroxidation in vitamin E-deficient animals are incorrect. In fact, vitamin E-deficient animals have low concentrations of peroxide in their adipose tissue, unless they have received large amounts of unsaturated lipid for long periods, and the role of vitamin E in controlling this concentration is not due to any effect on peroxidation in vivo.

The inhibitory effects in vitro of phenothiazines and other drugs on lipid-peroxidation systems in rat liver microsomes, and their relationship to the liver necrosis produced by carbon tetrachloride

1. The effects of several phenothiazine derivatives on lipid-peroxidation systems in rat liver microsomes were studied and the results are considered in relation to the hepatotoxic action of carbon tetrachloride. 2. The lipid-peroxidation system coupled to NADPH(2) oxidation and stimulated by an ADP-Fe(2+) mixture is strongly inhibited in vitro by promethazine (50% inhibition at 29mum). Chlorpromazine and Stelazine also inhibit the peroxidation system but are less effective than promethazine. 3. The effects of promethazine on three other systems involving oxygen uptake (sulphite oxidation, orcinol oxidation and mitochondrial succinate oxidation) were also studied. Promethazine does not inhibit these systems to the same extent as it does the NADPH(2)-ADP-Fe(2+) lipid-peroxidation system. 4. Promethazine also produces an inhibition of the NADPH(2)-ADP-Fe(2+) system in liver microsomes after administration in vivo. It is concluded that the inhibition involves the interaction of the drug (or a metabolite of it) with the microsomal electron-transport chain. 5. Several other compounds known to protect the rat against liver necrosis after the administration of carbon tetrachloride were tested for inhibitory action on the NADPH(2)-ADP-Fe(2+) system. No clear correlation was observed between effectiveness in vivo as a protective agent and inhibitory effects on the NADPH(2)-ADP-Fe(2+) system in vitro. 6. Promethazine was found to inhibit the stimulation of lipid peroxidation produced in rat liver microsomes by low concentrations of carbon tetrachloride. This effect occurs at a concentration similar to that observed in vivo after administration of a normal clinical dose.

On the fate of methanol and ethanol in the adult larva of the cotton leaf worm (Prodenia litura F)

The metabolic fate of C14-methanol and 1-C14-ethanol in the adult larva of Prodenia litura has been investigated in vivo. Following the intersegmental injection of C14-methanol (1.2 mg/g. insect), about 70% of the radioactivity was recovered as C14O2 in the expired air, after 20 hours. Also, about one fourth of the administered dose was recovered as unchanged methanol, during the first six hours. Only a minute trace of C14-formate was found in the excreta. It is suggested that a catalase-peroxide system is involved in the oxidation of methanol. Ethanol and its metabolites were eliminated at a slower rate than methanol. After 20 hours, C14O2 - being the major C14-metabolite - accounted for 56% of the applied dose. In addition, there is at least one minor non-volatile C14-metabolite eliminated in the excreta of ethanol-treated larvae.

The inhibitory effect of reduced glutathione on the lipid peroxidation of the microsomal fraction and mitochondria

1. GSH efficiently inhibited the ascorbate-stimulated lipid peroxidation of the unsaturated fatty acids in the fresh microsomal fraction and mitochondria of rat liver, whereas the peroxidation in heat-denatured particles was little inhibited. 2. Cysteamine and diethyldithiocarbamate inhibited the peroxidation in both fresh and boiled particles. Thioglycollate and 2-mercaptoethanol had no inhibiting effect. Cysteine and homocysteine both stimulated the lipid peroxidation even in the absence of ascorbate. 3. The added GSH disappeared at nearly the same rate in the presence of fresh and of boiled particles to which ascorbate had been added, although considerably more malonaldehyde was formed in the boiled particles. In the absence of ascorbate little GSH disappeared. 4. It is suggested that the protective effect of GSH against lipid peroxidation depends on the preservation of heat-labile structures in the microsomal fraction and mitochondria.

Vitamin E and stress. 5. The effect of high and low oxygen tension on the metabolism of [14C]D-alpha-tocopherol in the vitamin E-deficient rat

1. Vitamin E-deficient rats were found to be more susceptible than vitamin E-supplemented controls to the toxic effects of hyperbaric oxygen (60 lb/in.2 for 20 min). This agrees with the findings of other workers.

2. Hyperbaric O2 treatment did not increase the metabolic destruction of a small amount (46.65 μg) of [14C-5-Me]D-α-tocopherol given to adult vitamin E-deficient rats 24 h previously. The O2 treatment also did not affect the soluble sulphydryl compounds and ascorbic acid of rat liver, nor the percentag haemolysis in vivo of rat blood.

3. Hyperbaric O2 treatment did not increase the true lipid peroxide content of rat brain, compared to control rats treated with hyperbaric air, which has no toxic effects. Increases in ‘lipid peroxidation’ reported by previous workers are considered to have been due to the use of inadequate controls (untreated rats) and of in vitro techniques that are open to criticism.

4. The toxic effects of hyperbaric O2 in the vitamin E-deficient rat cannot be attributed to peroxidation in vivo.

5. Vitamin E was not found to protect rats against the effects of reduced O2 tension (anoxic anoxia). This finding contrasts with some reports by earlier workers. Reduced O2 tension had no effect on the metabolism of radioactive tocopherol, on blood haemolysis in vivo, or on the soluble sulphydryl compounds and ascorbic acid of liver.

Peroxidation of liver lipids in the pathogenesis of the ethanol-induced fatty liver

Administration of an acutely intoxicating dose of ethanol produced significant increases in the concentration of liver triglyceride and enhanced the peroxidation of liver lipids in rats. Adipose triglyceride and lipid peroxide concentrations were unaltered. Coenzyme Q(4), an effective antioxidant, significantly inhibited accumulation of liver triglyceride following ethanol intoxication and prevented the peroxidation of liver lipids. These results, which demonstrate the selective ability of ethanol to induce peroxidation of liver lipids, together with the effectiveness of antioxidants, support the previously proposed hypothesis that peroxidation of liver lipids following ethanol intoxication is a factor in the pathogenesis of ethanol-induced liver injury.

Release of enzymes from lysosomes by irradiation and the relation of lipid peroxide formation to enzyme release

1. Acid phosphatase, cathepsin and beta-glucuronidase are released from rat-liver lysosomes by irradiation in vitro. Enzyme release is detectable after a dose of 1krad and increases with dose up to 100krads. 2. Maximum radiation effects were observed when the lysosomes were kept for 20hr. at 4 degrees or 20 degrees after irradiation. 3. An atmosphere of nitrogen considerably decreases enzyme release from lysosomes. 4. Enzyme release is enhanced by ascorbic acid and decreased by vitamin E. 5. Irradiation causes formation of lipid peroxides in lysosomes, and enzyme release increases with lipid peroxide formation. 6. It is suggested that lipid peroxide formation leads to rupture of the lysosome membrane and allows release of the contained hydrolytic enzymes.