Increased superoxide anion production by platelets in hypercholesterolemic patients

Objectives: The purpose of this study was to investigate the relationship between hypercholesterolemia and Superoxide anion production.Background: Experimental Studies demonstrated that hypercholesterolemia is associated with enhanced cellular Superoxide anion (O-2(-)) production. Aim of the study was to assess whether the same phenomenon occurs in humans.Methods: Lipid profile and platelet O-2(-) production Acre measured in 28 patients with hypercholesterolemia, compared with 25 age- and sex-matched healthy subjects. and in 21 out of the 28 patients after 8-week treatment with 10 mg/day atorvastatin (a HMGCoA reductase inhibitor). In order to assess the mechanism by which LDL cholesterol interferes kith platelet production of O-2(-), human platelets were incubated with LDL cholesterol in the presence of either an inhibitor of the phospholipaseA2 enzyme, AACOCF3 or an inhibitor of NADH/NADPH oxidases. DPI.Results: O-2(-) platelet generation was significantly higher (p<0.001) and significantly related to LDL cholesterol (p<0.001) in patient,, as Compared to controls. 8-keek treatment with 10 mg/day atorvastatin significantly reduced both LDL cholesterol and O-2(-) platelet production. This effect was partially related to the cholesterol-lowering, in that three days of treatment with atorvastatin significantly decreased platelet O-2(-) production, While no significant change in LDL-cholesterol levels was observed. Platelets incubated kith LDL cholesterol showed an increased O-2(-) production, which as significantly inhibited by, AACOCF3 (-78%) and DPI (-56%).Conclusions: LDL cholesterol increases platelet O-2(-) production by activating PLA2 and NADH/NADPH enzymes. Inhibition of platelet O-2(-) release by atorvastatin is partially related to cholesterol lowering effect, suggesting that other mechanisms could he responsible for the antioxidant activity of the drug

GLUT2 and glucokinase expression is coordinately regulated by sulfonylurea

In the present study we examined the effect of sulfonylurea on the expression of the glucose transporter GLUT2 and the glucose phosphorylating enzyme Glucokinase (GK) in beta TC6-F7 cells; furthermore, we studied the modifications induced by sulfonylurea on glucose-responsiveness and -sensitivity. Results demonstrate that sulfonylurea increases GLUT2 and GK mRNA expression after 24 h in a dose-dependent manner. On the contrary, after 48 and 72 h a time-dependent reduction of both GLUT2 and GK mRNA. occurs. GLUT2 and GK protein expression follow the same modifications. Therefore, GLUT2 and GK are coordinately regulated by sulfonylurea, probably by a common mechanism. Glucose-induced insulin release is increased by sulfonylurea as well as glucose sensitivity. Our study suggests that short-term effect of sulfonylurea increases while long-term effect reduces the expression of glucose sensing elements. The long-term inhibitory effect on glucose sensing elements would explain the reduced insulin secretion occurring after chronic sulfonylurea treatment. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved

Molecular and functional characterization of pituitary adenylate cyclase-activating polypeptide (PACAP-38)/vasoactive intestinal polypeptide receptors in pancreatic beta-cells and effects of PACAP-38 on components of the insulin secretory system

It has been previously demonstrated that pituitary adenylate cyclase-activating polypeptide (PACAP) regulates insulin secretion. PACAP exerts its biological action by binding to at least three different receptor subtypes coupled to different signal transduction mechanisms. The signaling pathways underlying the insulinotropic effect of PACAP involve mainly the activation of adenylate cyclase to form cAMP, which directly and indirectly, through increased intracellular Ca+2, stimulates insulin exocytosis. In the present study we have characterized the functional and molecular expression of PACAP/vasoactive intestinal polypeptide receptors isoforms and subtypes and its isoforms in a beta-cell Line and in isolated rat pancreatic islets. Although insulinoma cells express the messenger RNA encoding PAC1 (-R and -hop variants), VPAC1 and VPAC2, binding experiments indicate the preponderance of PAC1 over VPAC1-2 receptors. We have also shown that the main signaling pathway of PACAP in beta-cells is mediated by adenylate cyclase, whereas the inositol 1,4,5-trisphosphate pathway is almost inactive. Furthermore, we have demonstrated that PACAP exerts long-term effects on beta-cells, such as transcriptional regulation of the insulin gene and genes of the glucose-sensing system (GLUT1 and hexokinase 1)