Triglycerides endogenous, fatty acids

It, thus, appears that the capacity to catalyze reactions of transesterification and esterification is a characteristic of various hydrolases (Chapt. 3). Apart from the carboxylesterases discussed here, lipoprotein lipase has the capacity to synthesize fatty acid ethyl esters from ethanol and triglycerides, or even fatty acids [127]. Ethanol, 2-chloroethanol, and other primary alcohols serve to esterify endogenous fatty acids and a number of xenobiotic acids [128-130]. In this context, it is interesting to note that the same human liver carboxylesterase was able to catalyze the hydrolysis of cocaine to benzoylecgonine, the transesterification of cocaine, and the ethyl esterification of fatty acids [131]. 

FIGURE 9. Endogenous lipoprotein metabolism. In liver cells, cholesterol and triglycerides are packaged into VLDL particles and exported into blood where VLDL is converted to IDL. Intermediate-density lipoprotein can be either cleared by hepatic LDL receptors or further metabolized to LDL. LDL can be cleared by hepatic LDL receptors or can enter the arterial wall, contributing to atherosclerosis. Acetyl CoA, acetyl coenzyme A Apo, apolipoprotein C, cholesterol CE, cholesterol ester FA, fatty acid HL, hepatic lipase HMG CoA, 3-hydroxy-3-methyglutaryl coenzyme A IDL, intermediate-density lipoprotein LCAT, lecithin-cholesterol acyltransferase LDL, low-density lipoprotein LPL, lipoprotein lipase VLDL, very low-density lipoprotein. 

Hepatocytes have the ability to synthesize triglycerides from carbohydrates and fatty acids. In addition, when dietary cholesterol acquired firom the receptor-mediated uptake of chylomicron remnants is insufficient, hepatocytes also synthesize their own cholesterol by increasing the activity of HMG-CoA reductase. The endogenously made triglycerides and choiesteroi are packaged in secretory vesicles in the... 

Figure 26-19 Endogenous lipoprotein metabolism pathway. TG, Triglyceride CE, cholesterol ester FC, free cholesterol PL, phospholipids HDL, high-density lipoproteins LDL low-density lipoproteins IDL, intermediate-density lipoproteins VLDL very low-density lipoproteins FA, fatty acid LPL, lipoprotein lipase LCAL lecithin cholesterol acyltransferase B, apolipoproteln B-tOO A, apolipoprotein A-l C, apolipoprotein C-fl , apofipoprotein E. (From RIfai N. Lipoproteins and apolipoproteins Composition, metabolism, and association with coronary heart disease. Arch Pathol Lab Med 1986 110 694-701. Copyright 1986, American Medical Association.)...

The endogenous pathway begins in the iiver with the formation of VLDL. Simiiar to chyiomicrons, triglycerides are present in a higher concentration than either choiesteroi or choiesteroi esters however, the concentration difference between these lipids is much less than that seen in chylomicrons. The metabolism of VLDL also is similar to chylomicrons in that lipoprotein lipase reduces the triglyceride content of VLDL and increases the availability of free fatty acids to the muscle and adipose tissue. The resulting lipoprotein, IDL, either can be further metabolized to LDL or can be transported to the liver for receptor-mediated endocytosis. This latter effect involves an... 

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