Chylomicron metabolism

Chylomicron metabolism. Smoke, administered to rats injected intravenously with C- and H-labeled chylomicrons, produced no difference in the initial plasma clearance time of labeled chylomicrons between smoke-treated and control animals. Hepatic uptake of chylomicron cholesterol was slower in smoke-treated animals than in controls. More labeled chylomicrons remained in the heart of smoke-treated rats than controls . 

NT284 Pan, X. M., I. Staprans, T. E. Read, and NT294 ]. H. Rapp. Cigarette smoke alters chylomicron metabolism in rats. J Vase Surg 1993 18(2) 161-167. 

Lipoprotein lipase (EC 3.1.1.34) is an enzyme or group of enzymes which catalyze the hydrolysis of the 1(3) ester bond(s) of triacylglycerols and the 1 ester bond of phospholipids. The enzyme plays a central role in lipoprotein metabolism, being responsible in particular for the hydrolysis of chylomicron and VLDL triglycerides and the formation of remnant particles from these lipoproteins. There have been reviews of this enzyme [e.g., (N9, Ql)] and lipoprotein lipase will not be discussed in detail in this review. Familial lipoprotein lipase deficiency and related disorders of chylomicron metabolism have also been reviewed (B58, N8) and will not be discussed in detail. 

N8. Nikkila, E. A., Familial lipoprotein lipase deficiency and related disorders of chylomicron metabolism. In The Metabolic Basis of Inherited Disease 0. B. Stanbury, J. B. Wyngaarden, D. S. Fredrickson, J. L. Goldstein, and M. S. Brown, eds.), 5th Ed., pp. 622-642. McGraw-Hill, New York, 1983. 

Lipoproteins are fat carriers in the circulation. Figure 19.3 summarizes human lipoprotein traffic. We focus first on the chylomicrons, which are produced in the intestinal cells and are exported into the general circulation via lymph. Chylomicron metabolism is often referred to as exogenous lipoprotein metabolism. 

The newly synthesized triacylglycerol becomes organized into chylomicrons (a type of lipoprotein see next section), which are secreted by the intestinal epithelial cell into the lacteals, small lymph vessels in the villi of the small intestine. Then from the lymphatics, the chylomicrons pass into the thoracic duct, from which they enter the blood and thus contribute to the transport of lipid fuel to various tissues. A feature of chylomicron metabolism is their ability to deliver lipid fuels to extrahepatic tissues. 

Each newly synthesized intestinal apo B-containing lipoprotein particle (chylomicron) consists of a core lipid droplet rich in TG, surrounded by a monolayer made up mainly of protein, phospholipids, and cholesterol. The chylomicron lipid core contains a small amount of CE. The lipids of TG-rich particles are in a dynamic equilibrium where each lipid can exchange rapidly between the surface and core. As a result, while the great majority of TG is in the core, the surface contains a small but rapidly replenished pool ofTG which is the direct substrate of the plasma lipases responsible for chylomicron metabolism in the circulation. 

Hussain, M. M., R. W. Mahley, J. R. Boyles, P. A. Lindquist, W. J. Brecht, and T. L. Iimerarity. 1989. Chylomicron metabolism. Chylomicron uptake by bone marrow in different animal species. Journal of Biological Chemistry 264 17931-17938. 

Dietary cholesterol from chylomicron metabolism (Figure 42.1)... 

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