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

alpha-Tocopherol (vitamin E) content of lung, liver, and blood in the newborn rat and human infant: influence of hyperoxia

Increases in liver and lung alpha-tocopherol (vitamin E) content occur concurrent with birth and the onset of suckling in the newborn rat and are prevented by denying pups access to dams. Liver alpha-tocopherol concentration peaks at 24 hours of age and then declines, whereas the lung concentration of alpha-tocopherol continues to increase in the early neonatal period. These tissue changes are not reflected by changes in the blood alpha-tocopherol concentration. Significant increases in lung alpha-tocopherol result from administering alpha-tocopherol (100 mg/kg body weight, sc) on days 0, 2, and 4 of age. Studies of lung alpha-tocopherol concentrations in infants with varying histories of alpha-tocopherol exposure confirm the findings in the rat, and suggest that increases in lung alpha-tocopherol concentration result from administration of alpha-tocopherol in the immediate newborn period. Studies of alpha-tocopherol values in alpha-tocopherol-treated and control newborn rats reveal no significant changes in lung tocopherol concentration resulting from exposure to hyperoxia.

Effect of vitamin E deficiency on the lipid class and fatty acid composition of rat brain gray and white matter

Three-week old male Sprague-Dawley rats were placed on a control or vitamin E-deficient diet for 9 months. The total lipid and cholesterol contents of brain gray and white matter areas in the vitamin E-deficient group did not differ from controls. The concentration of cerebrosides was lower in white matter but higher in gray matter of deficient animals. However, sulfatide was significantly (P less than 0.001) higher in white and gray matter of deficient animals compared with controls. Lysolecithin was not found in vitamin E-deficient gray matter but was present in control gray matter lipids. No marked differences were found in the concentrations or relative amounts of sphingomyelin, phosphatidyl choline, phosphatidyl ethanolamine, phosphatidyl serine, or phosphatidyl inositol in the phospholipids of gray or white matter of vitamin E-deficient rats as compared to controls. In addition, no remarkable differences were found in the fatty acid composition of total lipid extracts of gray or white matter from vitamin E-deficient rats when compared with controls.

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.

Vitamin E and hepatotoxic agents. 1. Carbon tetrachloride and lipid peroxidation in the rat

1. It has been suggested that carbon tetrachloride damages rat liver by accelerating processes of lipid peroxidation at subcellular sites and that the protective action of vitamin E is due to its functioning as an antioxidant in vivo. Direct evidence for these mechanisms in vivo has been sought and is critically examined.

2. The increased production of malondialdehyde by rat liver microsomal fractions during incubation with CCl4 was shown to be a function of the vitamin E status of the rat and of an in vitro reaction, which could not be correlated with the hepatotoxic action of CCI4.

3. Evidence for the production of lipid peroxides by CCl4 in the livers of vitamin E-deficient and vitamin E-supplemented rats was sought (I) by measurement of ultraviolet spectral changes ('diene' formation) and (2) by direct micro-iodimetric determination of the peroxide. No differences in peroxide content were found between CC14-treated and control rats, nor were the spectrophotometric changes in the ultraviolet region related to the presence of vitamin E.

4. The effect of CCI4 (2.0 ml/kg orally) on ATP levels in rat liver was studied at intervals from 3 to 68 h. The primary lesion leading to necrosis and fat accumulation after CCl4 treatment occurred many hours before the eventual slight decline in ATP. Although the levels of ATP were somewhat higher in vitamin E-deficient rats, vitamin E did not prevent the slight decline in ATP that took place. Since ATP is known to be highly sensitive to peroxidation, the results suggest that lipid peroxidation is not the primary event in CCl4 poisoning.

5. The effect of CC14on the metabolism of [14C]D-α-tocopherol in the rat was studied. A single intraperitoneal dose of CCl4 (2.0 m/kg) did not increase the destruction of α-tocopherol in the liver or carcass after 24 h. Three smaller daily doses of CC14 (0.25 ml/kg) also did not increase α-tocopherol catabolism; on the contrary, significantly more α-tocopherol was found in the livers of rats treated with CCI4. These results suggest that CCl4 does not increase lipid peroxidation in vivo.

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

1. Fatty liver was induced in 4-month-old male rats by oral dosing with ethanol. The marked increase in liver fat was not accompanied by a rise in lipid peroxides.

2. Homogenates were prepared from the livers of vitamin E-deficient rats and incubated with ethanol. In the concentration range of 10–50 μl/3 ml, ethanol increased the production of malondialdehyde. Methanol, which is not a hepatotoxin, showed a similar effect at 10–35 μl/3 ml homogenate. These findings indicate that the pro-oxidative effect of alcohols in vitro is unrelated to their hepatotoxic action in vivo.

3. Fatty liver was induced in 3.g-month-old, vitamin E-deficient male rats by oral dosingwith ethanol. The effect of pretreatment with vitamin E and N,N'-diphenyl-p-phenylenediamine (DPPD) was studied. D-α-Tocopheryl acetate, given as three doses of 350 mg/kg at 48, 24 and 2 h before the ethanol, failed to decrease the fat accumulation and seemed rather to increase the fat content of the liver. DPPD, given as three doses of 600 mg'kg at similar intervals before the ethanol dose, reduced the fat content of the liver almost to normal.

4. Weanling rats of both sexes were given a vitamin E-deficient diet containing 1% orotic acid for 15 days to induce fatty liver. Dietary supplements of D-a-tocopheryl acetate (500 ppm), selenium (I ppm) or DPPD (100 ppm) did not reduce the lipid accumulation. Lipid peroxides and malondialdehyde levels were lower in the livers of animals treated with orotic acid than in controls, regardless of the presence of vitamin E.

j. Liver necrosis was produced in 9-week-old female vitamin E-deficient rats by the intra-peritoneal injection of zoo mg thioacetamide. Promethazine hydrochloride (Phenergan), given intraperitoneally as two doses (25 mg/kg at the same time as the thioacetamide and 12.5 mg/kg 6 h later), markedly reduced the necrosis. D-α-Tocopheryl acetate, given as two oral doses of 1000mg/kg 48 h and 24 h before the thioacetamide, tended to exacerbate the necrosis.

6. The results are discussed in relation to the question of lipid peroxidation as a cause of hepatotoxicity.

Vitamin E and stress. 6. Iron overloading and the metabolism of D-alpha-tocopherol in the rat

1. The effects of iron overloading and unsaturation of dietary lipid on the metabolism of α-tocopherol in the rat were studies.

2. Young adult male vitamin E-deficient rats were given 1000 i.u. of vitamin A and 100 μg of [14C-5-Me]D-α-tocopherol and then given diets containing 5% methyl oleate or 5% cod-liver oil fatty-acid methyl esters. Rats from each group were given intramuscular injections of iron-dextran (50 mg Fe/kg rat) at 48 h intervals for 15 days, and compared with controls given dextran. After this time, liver, kidney and the remainder of the carcass were analysed for [14C]α-tocopherol, and liver and kidney were also analysed for vitamin A.

3. There was no evidence that Fe overloading caused any increase in the destruction of either tocopherol or vitamin A in vivo, whether or not the diet contained polyunsaturated fatty acids. Indeed, treatment with Fe significantly decreased the metabolism of the radioactive tocopherol dose in all three tissues studied.

4. These experiments show that the stress effect of Fe in the vitamin E-deficient animal is unrelated to an increase in oxidative reactions. They provide further evidence that ‘lipid peroxidation’ is not causally concerned in ‘anti-vitamin E’ stress conditions and that α-tocopherol does not function, in vivo, as an antioxidant.