Carolyn A. Lister

Mice overexpressing human uncoupling protein-3 in skeletal muscle are hyperphagic and lean

Uncoupling protein-3 (UCP-3) is a recently identified member of the mitochondrial transporter superfamily that is expressed predominantly in skeletal muscle. However, its close relative UCP-1 is expressed exclusively in brown adipose tissue, a tissue whose main function is fat combustion and thermogenesis. Studies on the expression of UCP-3 in animals and humans in different physiological situations support a role for UCP-3 in energy balance and lipid metabolism. However, direct evidence for these roles is lacking. Here we describe the creation of transgenic mice that overexpress human UCP-3 in skeletal muscle. These mice are hyperphagic but weigh less than their wild-type littermates. Magnetic resonance imaging shows a striking reduction in adipose tissue mass. The mice also exhibit lower fasting plasma glucose and insulin levels and an increased glucose clearance rate. This provides evidence that skeletal muscle UCP-3 has the potential to influence metabolic rate and glucose homeostasis in the whole animal.

Repeat Treatment of Obese Mice With BRL 49653, a New Potent Insulin Sensitizer, Enhances Insulin Action in White Adipocytes: Association With Increased Insulin Binding and Cell-Surface GLUT4 as Measured by Photoaffinity Labeling

(±)-5-([4-[2-Methyl-2(pyridylamino)ethoxy]phenyl]methyl) 2,4-thiazolidinedione (BRL 49653) is a new potent antidiabetic agent that improves insulin sensitivity in animal models of NIDDM. In C57BL/6 obese (ob/ob) mice, BRL 49653, included in the diet for 8 days, improved glucose tolerance. The half-maximal effective dose was 3 μmol/kg diet, which is equivalent to ∼0.1 mg/kg body wt. Improvements in glucose tolerance were accompanied by significant reductions in circulating triacylglycerol, nonesterified fatty acids, and insulin. The insulin receptor number of epididymal white adipocytes prepared from obese mice treated with BRL 49653 (30 μmol/kg diet) for 14 days was increasedtwofold. The affinity of the receptor for insulin was unchanged. In the absence of added insulin, the rates of glucose transport in adipocytes from untreated and BRL 49653-treated obese mice were similar. Insulin (73 nmol/l) produced only a 1.5-fold increase in glucose transport in adipocytes from control obese mice, whereas after BRL 49653 treatment, insulin stimulated glucose transport 2.8-fold. BRL 49653 did not alter the sensitivity of glucose transport to insulin. The increase in insulin responsiveness was accompanied by a 2.5-fold increase in the total tissue content of the glucose transporter GLUT4. Glucose transport in adipocytes from lean littermates was not altered by BRL 49653. To establish the contribution of changes in glucose transporter trafficking to the BRL 49653-mediated increase in insulin action, the cell-impermeant bis-mannose photolabel 2-N-[4-(1-azi-2,2,2-trifluoroethyl)benzoyl]-1,3-bis-(D-mannos-4-yloxy)-2-[2-3H]-propylamine was used to measure adipocyte cell-surface–associated glucose transporters. In these experiments, the increase in maximal insulin-stimulated glucose transport (4.2-fold) produced after BRL 49653 treatment was correlated with a 2.6-fold increase in cell-surface–associated GLUT4. Photolabeled cell-sur-face GLUT1 was not detectable in any adipocyte preparation. These results suggest that the improvement in glycemic control produced by repeated administration of BRL 49653 to obese mice is mediated by increased insulin responsiveness of target tissues. BRL 49653 potentiates insulin-stimulated glucose transport in adipocytes from insulin-resistant obese mice, both by increasing insulin receptor number and by facilitating translocation of GLUT4, from an expanded intracellular pool, to the cell surface. In addition, the increased intrinsic activity of cell-surface glucose transporters may also contribute to an increased insulin responsiveness of adipose tissue.

Non thiazolidinedione antihyperglycaemic agents. 1: α-Heteroatom substituted β-phenylpropanoic acids

The 5-benzylthiazolidine-2,4-dione moiety of insulin sensitising antidiabetic agents can be replaced by a range of α-heteroatom functionalised β-phenylpropanoic acids. α-Oxy-carboxylic acids show potent antidiabetic activity and one compound, the α-ethoxyacid 15 (SB 213068), is one of the most potent antihyperglycaemic agents yet reported.

Non-thiazolidinedione antihyperglycaemic agents. Part 3 : The effects of stereochemistry on the potency of α-methoxy-β-phenylpropanoic acids

Rhizopus delemar lipase catalysed ester hydrolysis of the alpha-methoxy-beta-phenylpropanoate 1 affords the (R)-(+) and (S)-(-) isomers in > 84% enantiomeric excess. Absolute stereochemistry was determined by a single crystal X-ray analysis of a related synthetic analogue. The activity of these two enantiomers on glucose transport in vitro and as anti-diabetic agents in vivo is reported and their unexpected equivalence attributed to an enzyme-mediated stereospecific isomerisation of the (R)-(+) isomer. Binding studies using recombinant human PPARgamma (peroxisomal proliferator activated receptor gamma), now established as a molecular target for this compound class, indicate a 20-fold higher binding affinity for the (S) antipode relative to the (R) antipode.

Improved glycemic control in C57Bl/KsJ (db/db) mice after treatment with the thermogenic beta-adrenoceptor agonist, BRL 26830.

BRL 26830, (R*,R*)-(±)-methyl-4-(2-[{2-hydroxy-2-phenylethyl} amino]propyl)-benzoate, is a new type of β-adrenoceptor receptor agonist that combines antihyperglycemic and thermogenic properties. In C57BI/KsJ db/db mice, treatment with BRL 26830 (50 mg of the hemifumarate salt/kg diet) decreased blood glucose concentration and normalized water intake. As judged by the normalization of polydipsia, BRL 26830 was effective within 2 days and the effect was maintained throughout a treatment period of up to 11 wk. Treatment of db/db mice with BRL 26830 resulted in an increase in both plasmaand pancreatic insulin concentrations and a partial restoration of first-phase insulin secretion by the isolated, perfused pancreas in response to a high (16.7 mM) glucose pulse. Given acutely, BRL 26830 increased energy expenditure in both fed and fasted db/db mice. When given chronically, BRL 26830 increased significantly the dietary and thermoregulatory component of metabolic rate. It is suggested that the antidiabetic and thermogenic properties of BRL 26830 are linked and that blood glucose acts either directly or indirectly as a substrate for thermogenesis.

Non thiazolidinedione antihyperglycaemic agents. 2: α-Carbon substituted β-phenylpropanoic acids1

The thiazolidine-2,4-dione ring of insulin sensitising antidiabetic agents can be replaced by α-acyl-, α-alkyl- and α-(aralkyl)-carboxylic acids. Inclusion of an additional lipophilic moiety affords compounds 14 and 16, equipotent to BRL 48482.