Vitamin E

The role of the microsomal triglygeride transfer protein in abetalipoproteinemia

The microsomal triglyceride transfer protein (MTP) is a dimeric lipid transfer protein consisting of protein disulfide isomerase and a unique 97-kDa subunit. In vitro, MTP accelerates the transport of triglyceride, cholesteryl ester, and phospholipid between membranes. It was recently demonstrated that abetalipoproteinemia, a hereditary disease characterized as an inability to produce chylomicrons and very low-density lipoproteins in the intestine and liver, respectively, results from mutations in the gene encoding the 97-kDa subunit of the microsomal triglyceride transfer protein. Downstream effects resulting from this defect include malnutrition, very low plasma cholesterol and triglyceride levels, altered lipid and protein compositions of membranes and lipoprotein particles, and vitamin deficiencies. Unless treated, abetalipoproteinemic subjects develop gastrointestinal, neurological, ophthalmological, and hematological abnormalities.

Plasma and hepatic alpha-tocopherol in cattle following oral or intramuscular supplementation

Blood and hepatic tocopherol concentration following i.m. injection or oral supplementation was studied in nonlactating dairy cows and pregnant beef heifers, respectively. In Experiment 1, cows received a single i.m. injection of either 4500 IU of d-alpha-tocopherol or 4500 or 7500 IU of dl-alpha-tocopheryl acetate. Plasma and liver tocopherol concentrations were recorded before and up to 4 wk postinjection. In Experiment 2, heifers received either 0, 1000, 2000, or 4000 IU of dl-alpha-tocopheryl acetate daily in the ration for 3 wk. Serum and hepatic tocopherol concentrations were measured before, during, and 3 wk following supplementation. In Experiment 1, level of tocopheryl acetate given influenced plasma and hepatic tocopherol concentrations. Plasma alpha-tocopherol concentration was greater in cows given unesterified tocopherol than an equivalent amount of tocopherol acetate. There was a quadratic relationship between plasma and hepatic tocopherol concentration. In Experiment 2, increasing dietary intake of dl-alpha-tocopheryl acetate failed to increase markedly tocopherol levels in serum or liver. There was no relationship between serum and hepatic tocopherol concentrations. Prior to the trials, serum levels in Experiment 2 were less than plasma levels in Experiment 1, but hepatic levels were greater. Physiological state can influence the relation between circulating and stored reserves of tocopherol, and circulating tocopherol concentration may not be a good indicator of its reserves.

Safety of megavitamin therapy

Carbon compounds that are needed in small amounts in the diet because they are not made in the body of vertebrates are defined as vitamins. Excluded from this definition are vitamins D, K, and niacin which can be synthesized by the organism or, as in the case of vitamin K, by the host's intestinal bacteria. Lack of such vitamins can result in characteristic deficiency diseases. The therapeutic use of such compounds (megavitamin intake) is based on the spectacular effect of vitamins on deficiency diseases; however, evidence that the ingestion of large amounts of vitamins beyond the "Recommended Daily Allowances" (RDA) is beneficial is not within the basic concept of nutrition. Vitamins, like many substances, may be toxic when taken in large quantities, especially the fat-soluble vitamins, and the concept of "more is better" is a common misconception. Vitamin supplements can be suggested only in the unusual cases of patients having inadequate intake, disturbed absorption (genetic or otherwise), or increased tissue requirements. A well-balanced diet that includes a wide variety of foods from each of the four food groups is adequate for the supply of vitamins, as well as other nutrients, in healthy people. This paper will review some of the recent findings regarding vitamin toxicity and the mechanisms of toxicity.

Thrombophlebitis associated with vitamin E therapy. With a commentary on other medical side effects

I have encountered 50 patients with clinical thrombophlebitis involving the lower extremites, with or without associated edema and pulmonary embolism, in whom longstanding self-medication with large amounts of vitamin E appeared to be a significant factor. The majority improved following cessation of vitamin E. In view of the epidemic nature of thrombophlebitis and deep vein thrombosis in the United States, the presumed innocuousness of vitamin E therapy requires reevaluation. Other clinical side effects also have been noted in patients receiving large doses of vitamin E. They include breast tenderness, elevation of blood pressure, a fatigue syndrome, myopathy, intestinal cramps, urticaria, and the possible aggravation of diabetes mellitus. The influence of concomitant metabolic, endocrine, and cardiovascular disorders on the thrombogenic potential of vitamin E is raised, and several possible mechanisms conducive to thrombophlebitis are reviewed.

Metabolism and physiologic roles of vitamin E

Antioxidant effect of vitamin E averts hemolytic anemia in low-birthweight infants fed formula rich in polyunsaturated fatty acids and iron. Tocopherol supplementation has also been shown to decrease the incidence and severity of retrolental fibroplasia and the development of bronchopulmonary dysplasia. Although the vitamin lowers platelet hyperaggregability, its role as an antithrombotic agent is still unclear.