Inhibitors of Chylomicron Formation and Secretion
Most of the lipid absorbed by the enterocytes leaves these cells as reesterified lipid in the form of chylomicrons (CM). CM formation and secretion is a complex process requiring proteins, phospholipids, and cholesterol in addition to triacylglycerols to form these lipoprotein particles. The first three compounds are also required to synthesize membranes and enzymes located in these absorbing cells that are involved in this process. The first step involved in CM formation is the reesterification of the products of triacylglycerol digestion, fatty acids and monoacylglycerols, that have been absorbed into the enterocytes (Johnson, 1978; Thomson and Dietschy, 1981). There are two pathways for reesterification in the enterocytes. The more important pathway for reesterification of the absorbed products of digested dietary lipid is the monoglyceride pathway, which utilizes 2-monoglyceride and free fatty acids as substrates (Mattson and Volpenhein, 1964). This involves reesterifying enzymes located on the cytoplasmic surface of the smooth endoplasmic reticulum (Bell et al., 1981). As 2-monoacylglycerol is present in the enterocytes in significant amounts during the process of digestion and absorption of a lipid meal, this pathway is obviously efficient. The other pathway for triacylglycerol synthesis utilizes α-glycerol phosphate to donate the glycerol portion of the molecule and is therefore known as the a-glycerol phosphate pathway (Johnson, 1978). This pathway, which involves more steps than the monoglyceride pathway and is therefore less rapid, has to be utilized when triacylglycerol is being synthesized by the enterocytes under conditions when no 2-monoacylglycerol is being absorbed, which is the case while fasting.
KeywordsCholesteryl Ester Essential Fatty Acid Deficiency Intestinal Lymph Large Lipid Droplet Intestinal Lipid
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