Retinyl esters supplementation

Theoretically, when blood and liver levels of vitamin A are reduced as in alcoholic hepatitis and alcoholic cirrhosis, subjects should receive supplemental vitamin A. Such supplementation, as high as 3000-10,(X)0 xg daily, has been shown to correct abnormal dark adaptation in some alcoholic cirrhotics uncomplicated by zinc deficiency (Morrison et aL, 1978 Russell et aL, 1978 Mobarhan et aL, 1981). Some studies in rats, however, indicate that acute and chronic administration of ethanol impairs hepatic and/or peripheral tissue uptake of newly ingested retinyl ester and/or causes the release of retinyl esters from hepatic tissue... 

The enzymatic hydrolysis of retinyl esters in liver has been examined in retinol-depleted, retinoic acid-supplemented rats (Harrison et al., 1979) as well as in normal rats (Prystowsky et al., 1981). In both studies, the enzyme retinyl palmitate hydrolase showed an unusual subcellular distribution, being found in the nuclear, mitochondrial, and supernatant fractions and displayed a large variability in activity from rat to rat. For additional information regarding the esterification and hydrolysis of retinol the reader is again referred to Chapters 7 and 10. 

Vitamin A-active compounds [1] are present in foods of animal origin as retinoids (retinol, retinyl esters, retinylaldehyde, retinoic acid) and in those of plant origin as carotenoids (only carotenoids with one unsubstituted P-ionone ring and with an 11-carbon polyene chain at least are provitamins A). Retinyl palmitate is the main form used as a food supplement [4]. 

Another affect of the APR on circulating retinoid levels occurs as a result of reduced lipol-ysis and delayed clearance of chylomicrons and their component retinyl esters [3, 97]. Recent work by Rosales and Ross demonstrated that retinoid supplementation of marginally retinoid-deficient rats undergoing an APR induced by lipopolysaccharide treatment showed lower concentrations of retinyl esters in the liver and perirenal fat, and delayed clearance of circulating retinyl esters [90]. 

Eckhoff C, Collins MD, Nau H (1991) Human plasma sll-trans, 13-cis- and 13-d5-4-oxoretinoic acid profiles during subchronic vitamin A supplementation Comparison to retinol and retinyl ester plasma levels. J Nutr 121 1016-1025... 

The excessive state is characterized by high intakes of preformed vitamin A, usually as supplements, by enhanced total body reserves of vitamin A and by increased steady-state concentrations of retinyl ester in the plasma. No gross signs of toxicity are present. Finally, the toxic state is a clinical condition that will be discussed later. 

Users of supplements that contain retinol or a retinyl ester should evaluate their average combined intake from diet (especially liver, milk, dairy products), fortified foods (including breakfast cereals), and all dietary supplements to ensure that it does not exceed the UL. Children s vitamin supplements should be checked to make sure that the amount of vitamin A is suitable for the child s age. 

Foods are supplemented with vitamin A in the form of standardized preparations of synthetic fatty acyl esters, nowadays chiefly retinyl palmitate. The preparations are available commercially as either dilutions in high-quality vegetable oils containing added vitamin E as an antioxidant or as dry, stabilized beadlets in which the vitamin A is dispersed in a solid matrix of gelatin and sucrose or gum acacia and sucrose. The oily preparations are used to supplement fat-based foods such as margarines the dry preparations are used in dried food products such as milk powder, infant formulas, and dietetic foods (24). 

For the determination of supplemental vitamin E in infant formulas, Woollard and Blott (222) employed a radially compressed Radial-PAK cartridge. This enabled lipid material to be rapidly cleared by stepping up the mobile-phase flow rate from 2 ml/min to 10 ml/min after elution of the a-tocopheryl acetate. Fluorescence detection, using a filter-type fluorometer, allowed the indigenous a-tocopherol to be conveniently estimated, while UV absorbance detection was used to quantify the a-tocopheryl acetate. Supplemental retinyl acetate could be assayed simultaneously with either added or indigenous vitamin E using the appropriate detection mode. With the aid of a dual-monochromator spectrofluorometer, a-tocopheryl acetate and a-tocopherol could be determined simultaneously with wavelengths of 280 nm (excitation) and 335 nm (emission), but the increased selectivity eliminated detection of the vitamin A esters (233). 

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