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Heterogeneous lipoprotein (a) size isoforms differ by their interaction with the low density lipoprotein receptor and the low density lipoprotein receptor-related protein/α2-macroglobulin receptor

Lipoprotein (a) (Lp(a)) is a complex of low density lipoprotein (LDL) with apolipoprotein (apo) (a). To examine the size distribution of Lp(a), plasma was separated by fast flow gel filtration and Lp(a): B complexes were determined in the eluate by enzyme immunoassays, in which detection was performed with monoclonal antibodies specific for apoB Lp(a): B particles displayed apparent molecular masses (Mr ) of 2 × 106 to at least 10 × 106. Lp(a) size isoforms differed by the expression of apoB epitopes and their interaction with cultured human skin fibroblasts. LDL was more effective in inhibiting binding, uptake, and degradation of low Mr , Lp(a) than of high Mr Lp(a). In contrast, Glu‐plasmmogen, α2‐macroglobulin and tissue‐type plasminogen activator were more effective in competing for the cellular degradation of high Mr Lp(a) than of low Mr Lp(a). Ligand blotting revealed that Lp(a) bound to the low density lipoprotein receptor, the low density lipoprotein receptor‐related protein/α2‐macroglobulin receptor (LRP) and to two other endosomal membrane proteins. We propose that the LDL receptor preferentially internalizes low Mr Lp(a), whereas LRP may have a role in the clearance of high Mr Lp(a).

Effects of lovastatin and pravastatin on the survival of hamsters with inherited cardiomyopathy.

Cardiomyopathic hamsters develop heart disease early in life, which leads to congestive heart failure and death as these hamsters age. Hydroxymethylglutaryl coenzyme A (HMG-CoA) reductase inhibitors have been reported to reduce ubiquinone concentrations and to deteriorate myocardial function in humans and in experimental animals. HMG-CoA reductase inhibitors differ regarding their ability to penetrate extrahepatic tissues. As a consequence, lovastatin inhibits cholesterol biosynthesis at least 100-Fold more effectively than pravastatin in extrahepatic cells. We examined the effect of lovastatin and pravastatin (approximately 10 mg per kilogram of body weight and per day mixed in the diet) compared with controls on the lifespan of cardiomyopathic hamsters (BIO 8262 strain) in the heart-failure period. In male hamsters, neither lovastatin nor pravastatin significantly affected survival. In female hamsters, lovastatin reduced median survival time from 89 days (control animals) to 30 days (P < .05); pravastatin (median survival, 115 days) had no statistically significant effect. We conclude that lovastatin, but not pravastatin, at a daily dose of 10 mg per kilogram of body weight significantly increases the mortality of cardiomyopathic hamsters. This effect may be the result of inhibition of myocardial ubiquinone supply.

Amplification and direct sequencing of a cDNA encoding human cytosolic 3-hydroxy-3-methylglutaryl-coenzyme A synthase

Cytosolic 3-hydroxy-3-methylglutaryl CoA (HMG-CoA) synthase (E.C. 4.1.3.5) is a highly regulated enzyme involved in isoprenoid biosynthesis and therefore a potential target for cholesterol-lowering drugs. Up to now, primary structure data have only been available for chicken, rat and hamster HMG-CoA synthase. Using in vitro amplification and direct sequencing, we have determined the nucleotide sequence of the coding region of the human cytosolic 3-hydroxy-3-methylglutaryl CoA synthase cDNA.

Application of electrophoretic techniques to the diagnosis of disorders of lipoprotein metabolism. Examples at the levels of lipoproteins and apolipoproteins

Disorders of lipoprotein metabolism are strongly related to the development of chronic degenerative diseases of the cardiovascular and of the central nervous system. The analysis of lipoproteins and apolipoproteins is essential to the assessment of cardiovascular risk and to the monitoring of individuals on treatment. We provide an overview of electrophoretic methods serving the analysis of lipoproteins in body fluids, placing particular emphasis on those techniques that have contributed to the classification of lipoprotein disorders and to the elucidation of the structure and function of lipoproteins. Electrophoresis in agarose separates the major classes of lipoproteins in the plasma. During recent years, considerable progress has been made in the quantification of electrophoretically separated lipoproteins using enzymatic staining of cholesterol and triglycerides. Evidence is now accumulating that the distinction of subclasses of low density lipoproteins and high density lipoproteins is clinically significant as well, and electrophoresis-based methods have become available to examine lipoprotein microheterogeneity. One- and two-dimensional immunoelectrophoresis has been used to characterize and to quantify lipoproteins and apolipoproteins. Apolipoprotein isoforms have been separated according to size and isoelectric point or a combination of both under denaturing conditions. In the clinical laboratory, these techniques have mainly been applied to the analysis of the apolipoprotein (a) size polymorphism and to the determination of the apolipoprotein E phenotype. Although immunoelectrophoretic approaches to the quantification of apolipoproteins will widely be replaced by automated methods like enzyme immunoassays, nephelometry and turbidimetry, we expect that electrophoresis will continue to make significant contributions to our understanding of disorders of the lipoprotein metabolism and thus provide new and more precise tools to identify individuals at an augmented risk of cardiovascular and other chronic diseases.