The effect of antidiabetic drugs on genes regulating lipid metabolism

RLIP76, a glutathione-conjugate transporter, plays a major role in the pathogenesis of metabolic syndrome

PURPOSE

Characteristic hypoglycemia, hypotriglyceridemia, hypocholesterolemia, lower body mass, and fat as well as pronounced insulin-sensitivity of RLIP76⁻/⁻ mice suggested to us the possibility that elevation of RLIP76 in response to stress could itself elicit metabolic syndrome (MSy). Indeed, if it were required for MSy, drugs used to treat MSy should have no effect on RLIP76⁻/⁻ mice.

RESEARCH DESIGN AND METHODS

Blood glucose (BG) and lipid measurements were performed in RLIP76⁺/⁺ and RLIP76⁻/⁻ mice, using Ascensia Elite Glucometer® for glucose and ID Labs kits for cholesterol and triglycerides assays. The ultimate effectors of gluconeogenesis are the three enzymes: PEPCK, F-1,6-BPase, and G6Pase, and their expression is regulated by PPARγ and AMPK. The activity of these enzymes was tested by protocols standardized by us. Expressions of RLIP76, PPARα, PPARγ, HMGCR, pJNK, pAkt, and AMPK were performed by Western-blot and tissue staining.

RESULTS

The concomitant activation of AMPK and PPARγ by inhibiting transport activity of RLIP76, despite inhibited activity of key glucocorticoid-regulated hepatic gluconeogenic enzymes like PEPCK, G6Pase and F-1,6-BP in RLIP76⁻/⁻ mice, is a salient finding of our studies. The decrease in RLIP76 protein expression by rosiglitazone and metformin is associated with an up-regulation of PPARγ and AMPK.

CONCLUSIONS/SIGNIFICANCE

All four drugs, rosiglitazone, metformin, gemfibrozil and atorvastatin failed to affect glucose and lipid metabolism in RLIP76⁻/⁻ mice. Studies confirmed a model in which RLIP76 plays a central role in the pathogenesis of MSy and RLIP76 loss causes profound and global alterations of MSy signaling functions. RLIP76 is a novel target for single-molecule therapeutics for metabolic syndrome.

Consumption of soymilk lowers atherogenic lipid fraction in healthy individuals

The effect of soy-based products on lipid profile has not been well established. Whereas some investigators have reported that soy is hypocholesterolemic, others could only demonstrate this in hypercholesterolemic subjects, while a few have not found any marked association between soy and cholesterol levels. This study was therefore aimed at investigating the effect of soymilk on lipid and lipoprotein profile of normocholesterolemic, apparently healthy Nigerian Africans. Five hundred milliliters of soymilk preparation was consumed daily by 42 apparently healthy young to middle-aged subjects for a period of 21 days. Forty-two other volunteers with similar characteristics, who did not drink the soymilk over this time frame, were randomly selected as controls. Plasma total cholesterol (TC), high-density lipoprotein-cholesterol (HDL-C), and triglyceride (TG) concentrations were determined twice by standard spectrophotometric methods (at the initial visit and after 3 weeks). Low-density lipoprotein-cholesterol (LDL-C) was calculated from the TC, TG, and HDL-C concentrations. After 21 days, regulated soymilk consumption significantly reduced mean plasma TC by 11% and LDL-C by 25% (P < .001 and P < .001, respectively) and increased mean plasma HDL-C by 20% (P < .05) in the test population. Plasma TG was not significantly altered. In control subjects, no significant differences were observed in mean TC, LDL-C, HDL-C, and TG. Daily consumption of soymilk significantly decreased atherogenic plasma cholesterol concentration. This suggests that soy drink could be an important non-pharmacological cholesterol-reducing agent.