Amounts and types of fatty acids in meals affect the pattern of retinoids secreted in human chylomicrons after a high-dose preformed vitamin A intake.Metabolism. 2003 Apr; 52(4):514-9.M
High doses of preformed vitamin A are commonly used to correct vitamin A deficiency. Newly absorbed vitamin A is secreted mainly as retinyl esters in chylomicrons. The effect of changing types and amounts of fatty acids on fatty acid composition of chylomicron retinoid esters when a high dose of vitamin A is ingested have not been studied previously. In the present study, 10 healthy young men ingested, in a random order, mixed meals containing 15,000 retinol equivalents (RE) of vitamin A (as retinyl palmitate) and either no fat or 40 g of fat provided as butter, olive oil, or sunflower oil. Fasting and postprandial blood samples were obtained for 7 hours after meals. Free retinol and the main retinyl esters (retinyl palmitate/oleate, stearate, and linoleate) were measured in chylomicrons by high-performance liquid chromatography (HPLC). Chylomicron retinyl palmitate/oleate and retinyl stearate concentrations significantly increased after intake of the 4 test meals. Conversely, chylomicron retinyl linoleate and chylomicron free retinol significantly increased only after the sunflower and the fat-free meals, respectively. The main retinoid secreted in chylomicrons after the intake of the fat-rich meals was retinyl palmitate/oleate, accounting for 63% to 79% of total RE, but it was free retinol after the fat-free meal (51% of total RE). Thus, the retinoid pattern secreted in chylomicrons after the intake of a high dose of preformed vitamin A depends on type and amounts of fatty acids ingested. To explain this result we suggest that the esterification process of retinol in the enterocyte by lecithin:retinol acyltransferase can be overwhelmed by a high load of vitamin A. Consequently, a significant proportion of the retinol is esterified by acyl coenzyme A:retinol acyltransferase (ARAT) with ingested fatty acids, explaining the appearance of retinyl linoleate in chylomicrons after the sunflower oil meal. If a high dose of preformed vitamin A is ingested with a fat-free meal, a significant proportion of retinol is not esterified, owing to the lack of fatty acids for ARAT, which explains the appearance of free retinol in chylomicrons.