Abnormalities in chylomicron (apolipoprotein B-48-containing lipoproteins) metabolism are associated with risk of pancreatitis. Figure 4 Chylomicron pathway. The intestine secretes chylomicron particles into the lymphatics. Rate-limiting enzymes limit the rate at which a metabolic pathway proceeds. Empty HDL is produced as a byproduct of steps 3 and 4. Very-low-density lipoproteins (VLDL) contain apoprotein B-100 (apo B), are synthesized in the liver, and transport TGs and cholesterol to peripheral tissues. The Pathways of Lipid Transport. The pharmaceutical industry has taken advantage of this knowledge to lower people's LDL levels with drugs known as statins. (2) Chylomicron Metabolism Chylomicrons are metabolized in adipose tissue and muscle. These surface constituents are transferred from the chylomicron remnant for the formation of high density lipoprotein. The triglycerides carried in VLDL are metabolized in muscle and adipose tissue by lipoprotein lipase releasing free fatty acids and IDL are formed. 5. The chylomicron remnants contain a smaller core of lipids that is enveloped by excess surface components. Although the proportion of the apoE-dependent/non-LDLR pathway in the overall metabolism of chylomicron remnants is only (null)/1;6, chylomicron remnants do not accumulate in the plasma of the LDLR-deficient humans and animals fed a normal chow (14, 15, 25). Chylomicron Metabolism Since the intestine is primarily an absorptive organ, it must have the means of exporting newly absorbed lipids. After unloading their fats, chylomicrons are smaller and referred to as chylomicron remnants. Exogenous pathway for lipid metabolism: Dietary cholesterol and fatty acids are absorbed. 1. for which apo E is a high-affinity ligand. Chylomicrons enter the circulation and travel to peripheral sites. Abnormalities in the metabolism of VLDL, IDL, and LDL [apolipoprotein B-100 (apoB-100)-containing lipoproteins] and HDL (apolipoprotein A-containing lipoproteins) are associated with risk of atherosclerosis. There are three main pathways responsible for the generation and transport of lipids within the body. Triglycerides and cholesterol combine to form chylomicrons. Chylomicron remnants then travel to the liver and are removed by the binding of apoE to their remnant receptor. Triglycerides are formed in the intestinal cell from free fatty acids and glycerol and cholesterol is esterified. The endogenous lipoprotein pathway begins in the liver with the formation of VLDL. The reactions in this initial stage are the same as in ketogenesis (see slide 10.4.1).However, while ketogenesis occurs in the mitochondria, HMG-CoA destined for … Chylomicrons are the ‘orphans’ of the lipoprotein family. Difficulty of measurement has impeded understanding of their metabolism. 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