Reeba K. Vikramadithyan

Ragaglitazar: a novel PPARα & PPARγ agonist with potent lipid‐lowering and insulin‐sensitizing efficacy in animal models

Ragaglitazar [(−) DRF 2725; NNC 61‐0029] is a coligand of PPARα and PPARγ. In ob/ob mice, ragaglitazar showed significant reduction in plasma glucose, triglyceride and insulin (ED50 values <0.03, 6.1 and <0.1 mg kg−1). These effects are three‐fold better than rosiglitazone and KRP‐297. In Zucker fa/fa rats, ragaglitazar showed dose‐dependent reduction in triglyceride and insulin, hepatic triglyceride secretion and triglyceride clearance kinetics (maximum of 74, 53, 32 and 50% at 3 mg kg−1), which are better than rosiglitazone and KRP‐297. In a high‐fat‐fed hyperlipidaemic rat model, the compound showed an ED50 of 3.95, 3.78 mg kg−1 for triglyceride and cholesterol lowering, and 0.29 mg kg−1 for HDL‐C increase. It also showed improvement in clearance of plasma triglyceride and hepatic triglyceride secretion rate. All these effects are 3–10‐fold better than fenofibrate and KRP‐297. Ragaglitazar treatment showed significant reduction in plasma Apo B and Apo CIII levels, and increase in liver CPT1 and CAT activity and ACO mRNA. Significant increase of both liver and fat LPL activity and fat aP2 mRNA was also observed. In a high‐fat‐fed hamster model, ragaglitazar at 1 mg kg−1 showed 83 and 61% reduction in triglyceride and total cholesterol, and also 17% reduction in fat feed‐induced body weight increase. In these hyperlipidaemic animal models, PPARγ ligands failed to show any significant efficacy. Taken together, ragaglitazar shows better insulin‐sensitizing and lipid‐lowering potential, as compared to the standard compounds.

Antidiabetic and hypolipidemic activity of Helicteres isora in animal models

Helicteres isora (Sterculiaceae) root juice has been used in the treatment of diabetes by several ethnic groups in different parts of India. A program was initiated to elucidate the scientific basis for the antidiabetic activity of H. isora. Ethanolic extract of H. isora root caused significant reduction in plasma glucose, triglyceride and insulin levels at 300 mg/kg dose after 9 days of administration to insulin resistant and diabetic C57BL/KsJdb/db mice. In normoglycemic and mildly hypertriglyceridemic Swiss albino mice, the extract also showed significant reduction in plasma triglyceride and insulin levels, without affecting plasma glucose level. An ethanolic extract showed activity distinctly different from glybenclamide and acarbose but similar to troglitazone in these models. In high fat fed hamster model, the extract showed significant reduction in plasma lipid levels. In order to identify the active pharmacophore, the ethanolic extract was further subjected to sequential partitioning with low, medium and high polarity solvents, which yielded a semipurified fraction having both euglycemic and lipid-lowering activity. Our study suggests that the extract of H. isora has insulin-sensitizing and hypolipidemic activity and has the potential for use in the treatment of type-2 diabetes.

Addition of dietary fat to cholesterol in the diets of LDL receptor knockout mice: effects on plasma insulin, lipoproteins, and atherosclerosis

The factors underlying cardiovascular risk in patients with diabetes have not been clearly elucidated. Efforts to study this in mice have been hindered because the usual atherogenic diets that contain fat and cholesterol also lead to obesity and insulin resistance. We compared plasma glucose, insulin, and atherosclerotic lesion formation in LDL receptor knockout (Ldlr−/−) mice fed diets with varying fat and cholesterol content that induced similar lipoprotein profiles. Ldlr−/− mice fed a high-fat diet developed obesity, mild hyperglycemia, hyperinsulinemia, and hypertriglyceridemia. Quantitative and qualitative assessments of atherosclerosis were unchanged in diabetic Ldlr−/− mice fed a high-fat diet compared with lean nondiabetic control mice after 20 weeks of diet. Although one group of mice fed diets for 40 weeks had larger lesions at the aortic root, this was associated with a more atherogenic lipoprotein profile. The presence of a human aldose reductase transgene had no effect on atherosclerosis in fat-fed Ldlr−/− mice with mild diabetes. Our data suggest that when lipoprotein profiles are similar, addition of fat to a cholesterol-rich diet does not increase atherosclerotic lesion formation in Ldlr−/− mice.

Effects of lipoprotein lipase and statins on cholesterol uptake into heart and skeletal muscle

Regulation of cholesterol metabolism in cultured cells and in the liver is dependent on actions of the LDL receptor. However, nonhepatic tissues have multiple pathways of cholesterol uptake. One possible pathway is mediated by LPL, an enzyme that primarily hydrolyzes plasma triglyceride into fatty acids. In this study, LDL uptake and tissue cholesterol levels in heart and skeletal muscle of wild-type and transgenic mice with alterations in LPL expression were assessed. Overexpression of a myocyte-anchored form of LPL in heart muscle led to increased uptake of LDL and greater heart cholesterol levels. Loss of LDL receptors did not alter LDL uptake into heart or skeletal muscle. To induce LDL receptors, mice were treated with simvastatin. Statin treatment increased LDL receptor expression and LDL uptake by liver and skeletal muscle but not heart muscle. Plasma creatinine phosphokinase as well as muscle mitochondria, cholesterol, and lipid droplet levels were increased in statin-treated mice overexpressing LPL in skeletal muscle. Thus, pathways affecting cholesterol balance in heart and skeletal muscle differ.

Synthesis and biological activity of novel pyrimidinone containing thiazolidinedione derivatives

A series of pyrimidinone derivatives of thiazolidinediones were synthesized. Their biological activity were evaluated in insulin resistant, hyperglycemic and obese db/db mice. In vitro PPARgamma transactivation assay was performed in HEK 293T cells. PMT13 showed the best biological activity in this series. PMT13 (5-[4-[2-[2-ethyl-4-methyl-6-oxo-1,6-dihydro-1-pyrimidinyl]ethoxy]phenylmethyl]thiazolidine-2,4-dione) showed better plasma glucose, triglyceride and insulin-lowering activity in db/db mice than rosiglitazone and pioglitazone. PMT13 showed better PPARgamma transactivation than the standard compounds. Pharmacokinetic study in Wistar rats showed good systemic exposure of PMT13. Twenty-eight day oral toxicity study in Wistar rats did not show any treatment-related adverse effects.

PMT13, a pyrimidone analogue of thiazolidinedione improves insulin resistance-associated disorders in animal models of type 2 diabetes

Aim: To evaluate the antidiabetic and hypolipidaemic potential of a novel thiazolidinedione, PMT13, in different animal models of insulin resistance.