leupeptins and Hypercholesterolemia

In the current study, we examined the mechanisms that regulate hepatic apolipoprotein B (apoB)-containing lipoprotein secretion in Psammomys obesus, a good animal model for the investigation of insulin resistance and diabetes.. When fed chow ad libitum, 22% maintained normoglycemia and normoinsulinemia (group A), 33% exhibited normoglycemia and appreciable hyperinsulinemia (group B), and 45% developed overt diabetes (group C). Body weight gain, plasma free fatty acid elevation, hypertriglyceridemia, and hypercholesterolemia characterized groups B and C. Triton WR-1339 injection, at fasting, resulted in higher plasma VLDL-triglyceride and VLDL-apoB accumulation in groups B and C, suggesting increased VLDL production by the liver. Pulse-chase labeling experiments in cultured hepatocytes with [35S]methionine revealed reduced intracellular degradation and enhanced secretion of newly synthesized apoB in groups B and C. Concomitant with the raised triglyceride and cholesterol contents in the livers of groups B and C, there was an increase in lipogenesis and in the activity of microsomal triglyceride transfer protein, monoacylglycerol acyltransferase, and diacylglycerol transferase. Pretreatment of hepatocytes with proteasomal inhibitors eliminated the differences in apoB secretion among groups A, B, and C.. Our data indicate that both insulin resistance and diabetes triggered the intracellular machinery involved in VLDL assembly and secretion.

Topics: Acetylcysteine; Animals; Apolipoproteins B; Cells, Cultured; Cysteine Endopeptidases; Diabetes Mellitus; Disease Models, Animal; Gerbillinae; Hepatocytes; Hypercholesterolemia; Hyperinsulinism; Hypertriglyceridemia; Insulin; Insulin Resistance; Leupeptins; Lipoproteins, VLDL; Liver; Multienzyme Complexes; Protease Inhibitors; Proteasome Endopeptidase Complex

Low-density lipoprotein (LDL) receptor-related protein (LRP) is highly expressed in vascular smooth muscle cells (VSMCs) of both normal and atherosclerotic lesions. However, little is known about LRP regulation in the vascular wall.. We analyzed the regulation of LRP expression in vitro in human VSMCs cultured with native LDL (nLDL) or aggregated LDL (agLDL) by semiquantitative reverse transcriptase-polymerase chain reaction, real-time polymerase chain reaction, and Western blot and in vivo during diet-induced hypercholesterolemia by in situ hybridization. LRP expression in human VSMCs is increased by nLDL and agLDL in a time- and dose-dependent manner. Maximal induction of LRP mRNA expression was observed after 24 hours of exposure to LDL. However, agLDL induced higher LRP mRNA expression (3.0-fold) than nLDL (1.76-fold). LRP mRNA upregulation was associated with an increase on LRP protein expression with the greatest induction by agLDL. VSMC-LRP upregulation induced by nLDL or agLDL was reduced by an inhibitor of sterol regulatory element binding protein (SREBP) catabolism (N-acetyl-leucyl-leucyl-norleucinal). In situ hybridization analysis indicates that there is a higher VSMC-LRP expression in hypercholesterolemic than in normocholesterolemic pig aortas.. These results indicate that LRP expression in VSMCs is upregulated by intravascular and systemic LDL.

Topics: Animals; Aorta, Abdominal; Blotting, Western; Cells, Cultured; Cholesterol, Dietary; Chromatography, Thin Layer; Disease Models, Animal; DNA-Binding Proteins; Dose-Response Relationship, Drug; Female; Humans; Hypercholesterolemia; In Situ Hybridization; Leupeptins; Lipoproteins, LDL; Low Density Lipoprotein Receptor-Related Protein-1; Macromolecular Substances; Muscle, Smooth, Vascular; Polymers; Receptors, LDL; RNA, Messenger; Signal Transduction; Sterol Regulatory Element Binding Protein 2; Swine; Transcription Factors; Up-Regulation