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Pioglitazone, a thiazolidinedione, is a novel antidiabetic compound that can lower blood glucose in diabetic rodents by increasing insulin sensitivity in target tissues. We have previously demonstrated that pioglitazone can enhance the insulin- or insulin-like growth factor-1-regulated differentiation of 3T3-L1 cells, a cell line that undergoes morphological and biochemical differentiation to mature adipocytes [Mol. Pharmacol. 41:393-398 (1992)]. In this study, we have examined the effect of pioglitazone on the expression of the adipocyte fatty acid-binding protein (aFABP) in ob/ob mice and 3T3-L1 cells. Administration of the drug to mice was observed to cause a dose-dependent increase in aFABP mRNA expression in epididymal fat, which was correlated with a decrease in blood glucose and insulin levels. Treatment of 3T3-L1 cells with pioglitazone enhanced aFABP expression in a time-dependent fashion. To explore a possible direct effect of pioglitazone on aFABP expression, a chimeric gene was constructed containing the aFABP promoter fused upstream of the bacterial reporter gene for chloramphenicol acetyltransferase. After transfection into 3T3-L1 cells and selection of stable transformants, regulation of the chimeric gene was studied. Pioglitazone, in combination with insulin or insulin-like growth factor-1, was observed to elicit a dose-dependent increase in expression, indicating a role for pioglitazone in regulating transcription of the aFABP gene. Several thiazolidinedione analogs were tested for their ability to induce the expression of the chimeric gene, and it was found that activity in this assay paralleled the structure-activity relationships observed for enhancement of 3T3-L1 cell differentiation. These observations on control of aFABP gene expression by pioglitazone suggest possible mechanisms by which cellular sensitivity to insulin may be regulated.

To evaluate the long-held concept that acidic guanidines lack glycemic effects, guanidinoalkanoic acids and the biguanide metformin (positive control) were administered to KKAy mice, a model of noninsulin-dependent diabetes. Two acidic guanidines, 3-guanidinopropionic acid (3-GPA) and guanidinoacetic acid, decreased the plasma glucose level; other compounds were ineffective. 3-GPA was more potent than even metformin. Insulin suppression tests in KKAy mice indicated that improved insulin sensitivity was the mode of action for 3-GPA. Glycemic effects in KKAy mice resulted from increased glucose disposal whereas gluconeogenesis, hepatic glycogen content and intestinal glucose absorption were unchanged. 3-GPA's glycemic effect was corroborated in two other models of noninsulin-dependent diabetes. In ob/ob mice, the compound reduced hyperglycemia, polyuria, glycosuria and hyperinsulinemia. In insulin-resistant rhesus monkeys, it increased the disappearance of i.v. glucose. The glycemic action of 3-GPA required the presence of some circulating insulin as well as hyperglycemia because the compound was ineffective in normoglycemic mice, insulinopenic Chinese hamsters and streptozotocin-diabetic rats. These data indicate that acidic guanidine derivatives can ameliorate hyperglycemia in animal models of noninsulin-dependent diabetes. Because acidic derivatives uniquely lack the propensity of guanidine compounds for inducing lactic acidosis, our finding suggests a new approach for developing improved antidiabetes compounds from this chemical class.

A microsomal glycoprotein that catalyzes the hydrolysis of pantetheine to pantothenate and cysteamine was solubilized and purified to homogeneity as determined by sodium dodecyl sulfate electrophoresis. The enzyme from pig kidney cortex was solubilized on exposure to butanol and purified by heat treatment, ammonium sulfate fractionation, hydrophobic chromatography, and hydroxyapatite chromatography. The purified enzyme (Mr = 57,000) has a specific activity of 14 mumol of pantothenate produced per min/mg of protein, a value 35 times that previously reported. A method for localizing enzymatic activity on polyacrylamide gels is presented, and enzyme activity, protein, and carbohydrate are shown to migrate identically by electrophoresis on nondenaturing polyacrylamide gels. Amino acid analysis indicated an absorbance index E1%1cm (280 nm) of 11.3, and carbohydrate analysis revealed the presence of galactose, mannose, fucose, glucose, galactosamine, and sialic acid for a total carbohydrate composition of 11.8%. The enzymatic hydrolysis of various pantetheine analogs indicated the enzyme had a high specificity for the pantothenate moiety but a low specificity for the cysteamine portion.