Molecular mechanism of alpha-tocopheryl-phosphate transport across the cell membrane

alpha-Tocopheryl-phosphate (alpha-TP) is synthesized and hydrolyzed in animal cells and tissues where it modulates several functions. alpha-TP is more potent than alpha-T in inhibiting cell proliferation, down-regulating CD36 transcription, inhibiting atherosclerotic plaque formation. Administration of alpha-TP to cells or animals requires its transfer through membranes, via a transporter. We show here that alpha-TP is passing the plasma membrane via a system that is inhibited by glibenclamide and probenecid, inhibitors of a number of transporters. Glibenclamide and probenecid prevent dose-dependently alpha-TP inhibition of cell proliferation. The two inhibitors act on ATP binding cassette (ABC) and organic anion transporters (OAT). Since ABC transporters function to export solutes and alpha-TP is transported into cells, it may be concluded that alpha-TP transport may occur via an OAT family member. Due to the protection by glibenclamide and probenecid on the alpha-TP induced cell growth inhibition it appears that alpha-TP acts after its uptake inside cells

Vitamin E and Cancer

Protection by vitamin E against free radical-induced DNA mutations appears not to be an effective occurrence. On the other hand, in vitro evidence that different tocopherols slow down cell proliferation is an accepted observation. However, such an event may not be sufficient to result in beneficial clinical outcomes. Tocopheryl phosphate, a more active, natural derivative of tocopherol, endowed with prevention and therapeutic potential, represents a possible key to the understanding of the present conflict between laboratory and clinical results

Vitamin E inhibits CD36 scavenger receptor expression in hypercholesterolemic rabbits

A numerous studies suggest that Vitamin E has a preventive role in atherosclerosis, although the mechanism of action still remains unclear. CD36, a member of the scavenger receptor family is centrally involved in the uptake of oxidized low density proteins (oxLDLs) from bloodstream. During the atherosclerotic process, the lipid cargo of oxLDL accumulates in macrophages and smooth muscle cells, inducing their pathological conversion to foam cells. In the present study, we investigate the role of Vitamin E on CD36 expression in an in vivo model. Atherosclerosis was induced by a 2% cholesterol containing Vitamin E poor diet. Three groups of six rabbits each were studied. The first group (control) was fed on Vitamin E poor diet. The second group was fed with Vitamin E poor diet containing 2% cholesterol and the rabbits in the third group were fed with Vitamin E poor diet containing 2% cholesterol and received injections of 50 mg/kg of Vitamin E i.m. After 4 weeks, aortas were removed and analysed by light microscopy for atherosclerotic lesions. Aortic samples were analysed for CD36 mRNA expression. The aortas of cholesterol-fed rabbits showed typical atherosclerotic lesions, detected by macroscopic and microscopic examination, and exhibited an increase in CD36 mRNA expression. Vitamin E fully prevented cholesterol induced atherosclerotic lesions and the induction of CD36 mRNA expression. The effects observed at the level of CD36 scavenger receptor expression in vivo suggest an involvement of reduced foam cell formation in the protective effect of Vitamin E against atherosclerosis

The effect of tocopheryl phosphates on atherosclerosis progression in rabbits fed with a high cholesterol diet

The effect of tocopheryl phosphate on atherosclerosis progression has been studied in rabbits, fed with a 2% cholesterol diet and compared with an equivalent amount of alpha-tocopheryl acetate. The results show that the atherosclerotic-preventing effect of the phosphate derivative was more pronounced than that of the acetate derivative. alpha-Tocopheryl phosphate was also more potent in diminishing the expression of CD36 than the acetate derivative

a-Tocopheryl phosphate: a novel, natural form of vitamin E

We have detected a-tocopheryl phosphate in biological tissues including liver and adipose tissue, as well as in a variety of foods, suggesting a ubiquitous presence in animal and plant tissue. a-Tocopheryl phosphate is a water-soluble molecule that is resistant to both acid and alkaline hydrolysis, making it undetectable using standard assays for vitamin E. A new method was therefore developed to allow the extraction of both a-tocopheryl phosphate and a-tocopherol from a single specimen. We used ESMS to detect endogenous a-tocopheryl phosphate in biological samples that also contained a-tocopherol. Due to the significance of these findings, further proof was required to unequivocally demonstrate the presence of endogenous a-tocopheryl phosphate in biological samples. Four independent methods of analysis were examined: HPLC, LCMS, LCMS/MS, and GCMS. a-Tocopherol phosphate was identified in all instances by comparison between standard a-tocopheryl phosphate and extracts of biological tissues. The results show that a-tocopheryl phosphate is a natural form of vitamin E. The discovery of endogenous a-tocopheryl phosphate has implications for the expanding knowledge of the roles of a-tocopherol in biological systems