Adipose tissue niacin

Niacin (vitamin B3) has broad applications in the treatment of lipid disorders when used at higher doses than those used as a nutritional supplement. Niacin inhibits fatty acid release from adipose tissue and inhibits fatty acid and triglyceride production in liver cells. This results in an increased intracellular degradation of apolipoprotein B, and in turn, a reduction in the number of VLDL particles secreted (Fig. 9-4). The lower VLDL levels and the lower triglyceride content in these particles leads to an overall reduction in LDL cholesterol as well as a decrease in the number of small, dense LDL particles. Niacin also reduces the uptake of HDL-apolipoprotein A1 particles and increases uptake of cholesterol esters by the liver, thus improving the efficiency of reverse cholesterol transport between HDL particles and vascular tissue (Fig. 9-4). Niacin is indicated for patients with elevated triglycerides, low HDL cholesterol, and elevated LDL cholesterol.3... 

Niacin reduces plasma LDL cholesterol, lipoprotein (a), triglycerides and raises HDL cholesterol in all types of hyperlipoproteinemia [26]. Although available on the market for more than 40 years, the mechanisms of action of niacin are poorly understood. Putative mechanisms are the activation of adipose tissue LPL, diminished HTGL activity, a reduced hepatic production and release of VLDL, and composi-... 

Vitamins are chemically unrelated organic compounds that cannot be synthesized by humans and, therefore, must must be supplied by the diet. Nine vitamins (folic acid, cobalamin, ascorbic acid, pyridoxine, thiamine, niacin, riboflavin, biotin, and pantothenic acid) are classified as water-soluble, whereas four vitamins (vitamins A, D, K, and E) are termed fat-soluble (Figure 28.1). Vitamins are required to perform specific cellular functions, for example, many of the water-soluble vitamins are precursors of coenzymes for the enzymes of intermediary metabolism. In contrast to the water-soluble vitamins, only one fat soluble vitamin (vitamin K) has a coenzyme function. These vitamins are released, absorbed, and transported with the fat of the diet. They are not readily excreted in the urine, and significant quantities are stored in Die liver and adipose tissue. In fact, consumption of vitamins A and D in exoess of the recommended dietary allowances can lead to accumulation of toxic quantities of these compounds. 

Niacin inhibits lipolysis in adipose tissue, resulting in decreased hepatic VLDL and LDL synthesis. 

Correct answer = D. Clofibrate and gemfibrozil Increase the activity of lipoprotein lipase, thereby increasing the removal of VLDL from plasma. Niacin inhibits lipolysis in adipose tissue and thus eliminates the building blocks needed by the liver to produce triacylglycerol and there-... 

Be aware that niacin decreases lipolysis in adipose tissue and very-low-density lipoprotein (VLDL) synthesis in liver. 

Niacin is a vitamin that is used in high doses to treat hypercholesterolemia. Niacin acts to decrease VLDL and LDL plasma levels. Its mechanism of action is not clearly nnderstood but probably involves inhibition of VLDL secretion, which in tnm decreases the production of LDL. Niacin inhibits the release of free fatty acids from adipose tissue which leads to a decrease of free fatty acids entering the liver and decreased VLDL synthesis in the liver. This decreases the availability of VLDL for conversion to LDL (containing cholesterol esters). Niacin also increases high-density lipoprotein (HDL) (the good cholesterol ) by an nnknown mechanism. 

Niacin affects metabolism in adipose tissue, liver, and other tissues via multiple pathways (Figure 39.1). 

The first hypotheses for cholesterol reduction with niacin pointed toward a steep niacin-induced decrease in non-esterified fatty acid (NEFA) mobilization from adipose tissue via inhibition of lipolysis (reviewed by Carlson 2005). Hormone sensitive lipase mediates lipolysis in response to increased cyclic adenosine monophosphate in adipocytes. A G-protein-coupled cell surface receptor (GPR) inhibiting adenylyl cyclase was proposed, and in 2003, three independent groups identified the human niacin receptors as the low-affinity... 

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