Lipoproteins metabolism

Lipoproteins transport hydrophobic fats in plasma (Fig. 13-2). The major lipoproteins (Chap. 6) circulating in the blood are chylomicrons, VLDLs (very low density lipoproteins), LDLs (low-density lipoproteins), and HDLs (high-density lipoproteins). IDLs (intermediate density lipoproteins) are derived from VLDLs in the formation of LDLs. Fatty acids are important cellular 

Cholesteryl esters are transferred out of HDL by cholesteryl ester transfer protein (CETP). CETP promotes the transfer of cholesteryl esters to VLDL and LDL in exchange for triacylglycerol. In this way, CETP enables HDL to transport more cholesteryl esters derived from the LCAT reaction. 

Linoleic acid is the fatty acid most commonly transferred from phosphatidylcholine to cholesterol, forming the cholesteryl ester, linoleoylcholesterol  

The action of an enzyme lipoprotein lipase in adipose tissue depletes chylomicrons and VLDLs of their triacylglycerol. The enzyme is activated by apolipoprotein C, with which it specifically interacts on the surface of chylomicrons and VLDLs. 

Question What is the reaction catalyzed by lipoprotein lipase  

Dyslipoproteinemia is diagnosed in most patients using plasma lipid and lipoprotein cholesterol concentrations. Dyslipoproteinemias have previously been defined in terms of arbitrarily defined cut points for lipids and lipoprotein, but are now based on the relationship between fipoprotein levels and the risk for CHD (see discussion later in this chapter). 

Drugs corticosteroids isotretmoin (Accutane), thiazides, anticonvulsants, j5 blockers, anabolic steroids, certain oral contraceptives Alcohol Obesity 

Cystine storage disease Gaucher s disease Glycogen stora ge disease Juvenile, Tay-Sachs disease Niemann-Pick disease Tay-Sachs disease Chronic renal failure Hemolytic-uremic syndrome Nephrotic syndrome Benign recurrent intrahepatic cholestasis 

Myocardial infarction Bacterial and viral infections Anorexia nervosa Starvation 

Idiopathic hypercalcemia Klinefelter s syndrome Progeria (Hutchinson-Giiford syndrome) 

---

Defects in Lipoprotein Metabolism Can Lead to Elevated Serum Cholesterol... 

Intestinally derived triglyceride-rich lipoprotein. Lipoprotein Metabolism... 

HMG-CoA-Reductase-Inhibitors Lipoprotein Metabolism Lipid Transfer Proteins... 

Lipid-lowering diugs are diugs that affect the lipoprotein metabolism and that used in therapy to lower plasma lipids (cholesterol, triglycerides). The main classes of... 

Lipoprotein metabolism is the process by which hydrophobic lipids, namely triglycerides and cholesterol, are transported within the interstitial fluid and plasma. It includes the transport of energy in the form of triglycerides from intestine and liver to muscles and adipose, as well as the transport of cholesterol both from intestine and liver to peripheral tissues, as well as from peripheral tissues back to the liver. 

Lipoprotein Metabolism. Figure 1 Exogenous pathway of lipoprotein metabolism. 

Disorders of lipoprotein metabolism involve perturbations which cause elevation of triglycerides and/or cholesterol, reduction of HDL-C, or alteration of properties of lipoproteins, such as their size or composition. These perturbations can be genetic (primary) or occur as a result of other diseases, conditions, or drugs (secondary). Some of the most important secondary disorders include hypothyroidism, diabetes mellitus, renal disease, and alcohol use. Hypothyroidism causes elevated LDL-C levels due primarily to downregulation of the LDL receptor. Insulin-resistance and type 2 diabetes mellitus result in impaired capacity to catabolize chylomicrons and VLDL, as well as excess hepatic triglyceride and VLDL production. Chronic kidney disease, including but not limited to end-stage... 

Lipoprotein Metabolism. Figure 3 HDL metabolism and reverse cholesterol transport. 

Lipoprotein Metabolism Antihypertensive Drugs Antiobesity Drugs... 

Nicotinic acid is used in the treatment of hyperlipidemia. It causes various changes in lipid and lipoprotein metabolism when administered in high doses (up to 5 g/d) ... 

Lipoprotein Metabolism Antidiabetic Diugs other than Insulin Adipokines... 

Lipoprotein Metabolism Lipoproteins Liposomes 5-Lipoxygenase Lipoxygenases Lithocholic Acid Local Anaesthetics Locus... 

LEES RS, LEES A (1976) Sitosterol therapy on plasma lipid and lipoprotein Concentrations. In Lipoprotein Metabolism, Ed. Greten, H, Berlin Springer, 119-24. 

Patients with abetalipoproteinaemia, a rare inborn disorder of lipoprotein metabolism, are totally deficient in vitamin E fiom birth and, if untreated, invariably develop a characteristic pigmentary retinopathy similar to that seen in retinitis pigmentosa and peroxisomal disorders. The same retinopathy has been observed in other patients with severe and chronic vitamin E deficiency. A essive vitamin E replacement therapy in all these patients has been shown either to prevent, to halt the progression of, or in some cases, to improve the characteristic visual abnormalities (Muller and Lloyd, 1982). 

Because lipoprotein metabolism and the pathophysiology of atherosclerosis are closely linked, treatment of dyslipidemias is critical for both primary and secondary prevention of IHD-related cardiac events. In 2001, the Adult Treatment Panel III of the National Cholesterol Education Program... 

Identify the major components within each lipoprotein and their role in lipoprotein metabolism and the development of atherosclerosis. 

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. 

Apolipoprotein AIV (apo AIV) is produced in the intestine and is found in chylomicrons, VLDL and HDL. It may modulate enzymes involved in lipoprotein metabolism and may serve as a saturation signal [49]. In a study with 144 participants the apo AIV His360Glu polymorphism showed no significant effect on cholesterol lowering in response to statin therapy [50]. 

---