Tocopheryl acetate absorption

It is fortuitous that indigenous concentrations of vitamin E in the principal food sources are on the order of mg rather than yug/100 g, for the tocopherols and tocotrienols exhibit relatively low intensities of UV absorption. Individual vitamers are characterized by a slightly different absorption maximum within the wavelength range of 292-298 nm in ethanol. Published A] m values for the tocopherols at their Amax in ethanol are a-T 70-73.7 at 292 nm, (3-T 86-87 at 297 nm, y-T 90-93 at 298 nm, and <5-T 91.2 at 298 nm (126). The different absorption characteristics among the vitamers necessitates the running of individual standards for accurate quantitation of each vitamer. The absorption intensity of a-tocopheryl acetate is lower still with an A j m value of only 40-44 at the Amax of 285.5 nm (44). Reported minimum detectable quantities of a-, / -, y-, and (5-tocopherols at 295 nm are, respectively, 50 ng, 70 ng, 90 ng, and 130 ng (127). 

Vitamin E is absorbed as free tocopherol, along with other fat-soluble vitamins and dietary lipids. Tocopheryl acetate, the form commonly used for dietary supplementation, is hydrolyzed before absorption. Uptake requires bile salts. A selective impairment of vitamin E absorption without malabsorption of other fat-soluble vitamins has been identified it was corrected after a large oral intake of the vitamin. Patients with chronic fat malabsorption and abetalipoproteinemia (Chapter 20) may develop vitamin E deficiency. 

Mathias, P.M., Harries, J.T., Peters, T.J., and Muller, D.P., Studies on the in vivo absorption of micellar solutions of tocopherol and tocopheryl acetate in the rat demonstration and partial characterization of a mucosal esterase localized to the endoplasmic reticulum of the enterocyte, J. Lipid. Res. 22 (5), 829-837, 1981. 

Some work has recently been completed in our laboratory which further explores the absorption characteristics of the tocopherols in the chick. Two aspects were of interest, namely, to determine the rate of absorption of a-tocopherol and a-tocopheryl acetate after a single dose at physiological levels and to determine the effect on the quantitative relationships of intake versus plasma and liver tocopherols on increasingly higher levels of vitamin E intake. 

Studies with C -labeled df-a-tocopheryl acetate reveal that absorption occurs rather slowly, reaching maximal concentrations only after a few... 

The second most frequently used internal standard for a-tocopherol is a-tocopheryl acetate. The two compounds possess the same carbon backbone but differ in that the 6-chromanol group is either free or esterifled, respectively. Consequently, the difference in elution position will not be excessively high in reversed-phase systems. However, a-tocopheryl acetate has virtually no retention in normal-phase systems and is neither strongly fluorescent nor electrochemically active, so its use is virtually restricted to reversed-phase chromatography with absorption detection. It cannot be used in conjunction with isolation methods involving saponification as it is hydrolyzed to free a-tocopherol. 

Estimation of a-tocopheryl acetate by a simplified procedure is sometimes possible where (i) the vitamin is present in sufficient quantity to yield organic solvent extracts which have measurable ultra-violet absorption, (ii) interference from such material as steroids and vitamin A is small and constant in magnitude and (iii) simple chromatography removes sufficient of the interfering material to apply baseline correction techniques to ultra-violet spectra recorded continuously in the region 220 mfi to 350 m//. 

Intestinal absorption of vitamin E is dependent upon normal processes of fat absorption. Specifically, both biliary and pancreatic secretions are necessary for solubilization of vitamin E in mixed micelles containing bile acids, fatty acids, and monoglycerides (Figure 3). a-Tocopheryl acetates (or other esters) from vitamin E supplements are hydrolyzed by pancreatic esterases to a-tocopherol prior to absorption. Following micellar uptake by entero-cytes, vitamin E is incorporated into chylomicrons and secreted into the lymph. Once in the circulation, chylomicron triglycerides are hydrolyzed by lipoprotein lipase. During chylomicron catabolism in the... 

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