Human plasma and tissue alpha-tocopherol concentrations in response to supplementation with deuterated natural and synthetic vitamin E.

We report a comparison of natural and synthetic vitamin E in humans using deuterium labeling to permit the two forms of vitamin E to be measured independently in plasma and tissues of each subject. Differences in natural and synthetic vitamin E concentrations were measured directly under equal dosage conditions using an equimolar mixture of deuterated RRR-alpha-tocopheryl acetate and all-rac-alpha-tocopheryl acetate. Two groups of five adults took 30 mg of the mixture as a single dose and as eight consecutive daily doses, respectively. After a 1-mo interval the schedule was repeated but with a 10-fold higher dose (ie, 300 mg). In each case, the ratio of plasma d3-RRR-alpha-tocopherol to d6-all-rac-alpha-tocopherol (RRR:rac) increased from approximately 1.5-1.8 to approximately 2 after dosing ended. In an elective surgery study in which 22 patients were given 150 mg/d for up to 41 d before surgery, the RRR:rac in tissues was lower than in plasma and the percentage of deuterated alpha-tocopherol was lower in all tissues except gallbladder and liver. In a terminally ill patient given 30 mg/d for 361 d, plasma and tissue (x+/-SD) RRR-rac ratios (and % deuterated alpha-tocopherol) at autopsy were 2.06 (6.3%) and 1.71+/-0.24 (5.9+/-2.2%), respectively. In a second terminally ill patient given 300 mg/d for 615 d, the corresponding values were 2.11 (68%) and 2.01+/-0.17 (65+/-10%), respectively. The results indicated that natural vitamin E has roughly twice the availability of synthetic vitamin E. This 2:1 ratio is significantly higher than the currently accepted RRR:rac of 1.36:1.00. Gamma-Tocopherol, expressed as a fraction of total unlabeled tocopherols in 15 elective surgery patients, was 1.4-4.6 (mean: 2.6) times greater in adipose tissue, muscle, skin, and vein than in plasma, which is a substantially larger fraction than had been recognized previously.

Antioxidant transport by the human placenta.

We investigated the transfer of three antioxidants - melatonin, S-adenosyl methionine (SAM) and various forms of vitamin E - across the term, normal human placenta. The transport technique involved the single, isolated placental cotyledon system in vitro. Melatonin crossed the placental rapidly, equally to the freely diffusible marker, antipyrine. There was no biotransformation of the agent. SAM was transferred slowly, similarly to passively transported L-glucose as a marker. There was a breakdown of SAM to at least one other derivative; the process appeared to be nonenzymatic. Vitamin E was transferred slowly, at a rate only 10% of L-glucose. The natural RRR (nonracemic) form of vitamin E was transported best. Free vitamin, rather than the acetate seems to be transferred best, a finding that will require further study.

Prolonged, intravenous paraquat infusion in the rat. I. Failure of coinfused putrescine to attenuate pulmonary paraquat uptake, paraquat-induced biochemical changes, or lung injury.

Paraquat (PQ) was administered to rats for 7 days by iv infusion from osmotic minipump at dosage rates of 250 and 500 nmol PQ/hr. The efficacy of putrescine in attenuating pulmonary PQ accumulation in vivo and the resulting PQ-induced biochemical changes and lung injury were assessed in these animals by coinfusion of putrescine at rates of 2500 or 5000 nmol/hr. Dose-dependent, steady-state blood levels of both PQ and putrescine were achieved by 18 hr and maintained throughout the infusion period. Lung PQ content at 7 days was dose-dependent and up to 18-fold greater than corresponding blood levels. No evidence of toxicity was observed in low-dose PQ animals while weight loss and overt toxicity was observed in high-dose PQ rats between Days 4 and 5. Histopathological examination of high-dose PQ rat lungs revealed qualitative changes typical of PQ toxicity. Significant (p less than 0.05) increases in lung glutathione and activities of glucose-6-phosphate dehydrogenase and GSSG reductase resulted from both PQ doses, reflecting PQ-induced oxidant stress and increased demand on lung NADPH. A net decrease in lung NADPH (p less than 0.05) was directly measured in high-dose PQ rats and may have contributed to the PQ-induced lung injury. Although putrescine is an effective inhibitor of pulmonary PQ uptake in vitro, the blood putrescine levels achieved in this study did not appear to inhibit this process in vivo. This was evidenced by putrescine's failure to decrease 7-day lung PQ content, PQ-induced biochemical changes, or lung injury.

The influence of cysteine and methionine supplements on polyamine biosynthesis in the rat.

Previous reports from this laboratory have shown that supplementation of diets containing the optimal level (0.02%) of dietary inorganic sulfate (SO4(2-] with cysteine instead of methionine can affect several metabolic pathways. It is possible that these results reflect alterations in the biosynthesis of potent physiological compounds, the polyamines. Adult male albino rats were fed diets containing 15% casein and a constant level of inorganic sulfate (0.02%) supplemented with cysteine (0.505%) or methionine (0.62%). The polyamines (putrescine, spermidine and spermine) and the controlling enzymes for their biosynthesis ornithine decarboxylase (ODC) and S-adenosylmethionine decarboxylase (SAMD) were evaluated in liver, kidney and brain tissue homogenates following a 17-day dietary period. Rats fed the diet supplemented with cysteine had increased ODC activity and decreased SAMD activity when compared to rats fed diets supplemented with methionine. Polyamine concentrations varied in tissues with a trend toward increasing amounts in animals fed the cysteine-supplemented diet. Based on these data, it appears that dietary cysteine stimulates the biosynthesis and increased tissue concentration of polyamines.

A metabolic comparison of cysteine and methionine supplements in the diet of a rat.

Adult male Long-Evans rats (250-300 g) were fed diets containing 15% of casein not supplemented with amino acids, supplemented with 0.505% cysteine or supplemented with 0.620% methionine for a period of 17 days. Rats fed the diets supplemented with cysteine had an increased incorporation of the 14C-radioactivity from [U-14C]alanine into liver glycogen and a decreased incorporation from [U-14C]acetate into fatty acids. Pyruvate carboxylase activity was slightly increased and citrate cleavage enzyme activity decreased in the livers of those rats fed the diets supplemented with cysteine. Rats fed diets supplemented with methionine had a decreased liver phosphoenolpyruvate carboxykinase activity. Based on these data it appears that rats fed diets supplemented with cysteine adapt metabolically to store energy as glycogen, while those fed diets supplemented with methionine tend to store energy as lipid.