Lipoproteins functional derivatives

Using human hepatoma-derived cell lines Kong et al. [268] showed that berberine increased mRNA and protein as well as the function of hepatic linear low density lipoprotein receptor (LDLR). It does not stimulate the transcription of LDLR, as the LDLR promoter activity was not increased by this compound. Post-transcriptional regulation appears to be the main working mechanism underlying the effect of this alkaloid on LDLR expression. It was proposed that berberine can be used as a monotherapy to treat hypercholes-terolemic patients [268]. Very recently it was observed [269] that berberine reduces cholesterol and Upid accumulations in plasma as well as Uver. 

The physiological function of heparin is not completely understood. It is found only in trace amounts in normal circulating blood. It exerts an antihpemic effect by releasing lipoprotein lipase from endothehal cells heparinlike proteoglycans produced by endothelial cells have anticoagulant activity. Heparin decreases platelet and inflammatory cell adhesiveness to endothelial cells, reduces the release of platelet-derived growth factor, inhibits tumor cell metastasis, and exerts an antiproliferative effect on several types of smooth muscle. 

In adipose tissue, TAG is stored in the cytosol of the cells in a nearly anhydrous form. It serves as "depot fat," ready for mobilization when the body requires it for fuel. Little TAG is stored in the liver. Instead, most is exported, packaged with cholesteryl esters, cholesterol, phospholipid, and protein (apolipoprotein B-100, see p. 229) to form lipoprotein particles called very low density lipoproteins (VLDL). Nascent VLDL are secreted into the blood where they mature and function to deliver the endogenously-derived lipids to the peripheral tissues. [Note Recall that chylomicrons deliver primarily dietary (exogenously-derived) lipids.] Plasma lipoproteins are discussed in Chapter 18, p. 225. 

Sarria, A. J., Panini, S. R., and Evans, R. M. (1992). A functional role for vimentin intermediate filaments in the metabolism of lipoprotein-derived cholesterol in human SW-13 cells./. Biol. Chem. 267, 19455-19463. 

HDLs have the opposite function to that of LDLs in that they remove cholesterol from the tissues. The HDLs are synthesized in the blood mainly from components derived from the degradation of other lipoproteins. HDLs then acquire their cholesterol by extracting it from cell membranes and converting it into cholesterol esters by the action of LCAT (Fig. 1). The HDLs are then either taken up directly by the liver or transfer their cholesterol esters to VLDLs, of which about half are taken up by the liver by receptor-mediated endocytosis (Fig. 1). The liver is the only organ that can dispose of significant quantities of cholesterol, primarily in the form of bile salts (see Topic K5). 

Exchangeable apolipoproteins are a class of functionally important proteins which play a key role in plasma lipoprotein metabolism. In this capacity they have been associated with several human disorders, including hyperlipidemia and cardiovascular disease (1,2). Apolipophorin-III (apoLp-III) is a model exchangeable apolipoprotein derived from the insect Manr/Mca sexta (166 residues, Mr 18,380). ApoLp-III is a major hemolymph protein in the adult life stage and... 

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