Luigi Gnudi

We studied the relation of serum insulin levels to plasma lipid levels and blood pressure in two groups drawn from among 247 healthy, normotensive nonobese subjects with normal glucose tolerance. One group of 32 subjects was defined as having hyperinsulinemia (serum insulin, greater than 2 SD above the mean) and then compared with 32 normoinsulinemic subjects (serum insulin within 1 SD of the mean) matched for age (mean, 39 years), sex (22 men and 10 women), and body-mass index (24.7). The two groups had similar patterns of smoking, drinking, and physical exercise. Plasma glucose levels after an oral glucose challenge were significantly higher (P less than 0.05) in the hyperinsulinemic group. In addition, the mean (+/- SEM) fasting plasma triglyceride levels in subjects with hyperinsulinemia were significantly higher (1.73 +/- 0.2 vs. 1.24 +/- 0.1 mmol per liter) and the plasma high-density lipoprotein cholesterol concentrations were lower (1.21 +/- 0.06 vs. 1.43 +/- 0.06 mmol per liter) than in subjects with normoinsulinemia. Both systolic (126 vs. 119 mm Hg; P less than 0.05) and diastolic (85 vs. 78 mm Hg; P less than 0.01) blood pressures were significantly elevated in the group with hyperinsulinemia. We conclude that healthy persons with hyperinsulinemia and normal glucose tolerance have an increase in risk factors for coronary artery disease, as compared with a well-matched group of healthy subjects with normal insulin levels.

To gain insight into the molecular pathogenesis of obesity and specifically the role of nutrient partitioning in the development of obesity, we overexpressed the insulin-responsive glucose transporter (GLUT4) in transgenic mice under the control of the fat-specific aP2 fatty acid-binding protein promoter/enhancer. Two lines of transgenic mice were generated, which overexpressed GLUT4 6-9-fold in white fat and 3-5-fold in brown fat with no overexpression in other tissues. In vivo glucose tolerance was enhanced in transgenic mice. In isolated epididymal, parametrial, and subcutaneous adipose cells from transgenic mice, basal glucose transport was 20-34-fold greater than in nontransgenic littermates. Insulin-stimulated glucose transport was 2-4-fold greater in cells from transgenic mice. Total body lipid was increased 2-3-fold in transgenic mice overexpressing GLUT4 in fat. Surprisingly, fat cell size was unaltered and fat cell number was increased > 2-fold. This is the first animal model in which increased fat mass results solely from adipocyte hyperplasia and it will be a valuable model for understanding the mechanisms responsible for fat cell replication and/or differentiation in vivo.

We showed before that in neonatal rat cardiac myocytes partial inhibition of Na+/K+-ATPase by nontoxic concentrations of ouabain causes hypertrophic growth and transcriptional regulations of genes that are markers of cardiac hypertrophy. In view of the suggested roles of Ras and p42/44 mitogen-activated protein kinases (MAPKs) as key mediators of cardiac hypertrophy, the aim of this work was to explore their roles in ouabain-initiated signal pathways regulating four growth-related genes of these myocytes, i.e. those for c-Fos, skeletal alpha-actin, atrial natriuretic factor, and the alpha3-subunit of Na+/K+-ATPase. Ouabain caused rapid activations of Ras and p42/44 MAPKs; the latter was sustained longer than 90 min. Using high efficiency adenoviral-mediated expression of a dominant-negative Ras mutant, and a specific inhibitor of MAPK kinase (MEK), activation of Ras-Raf-MEK-p42/44 MAPK cascade by ouabain was shown. The effects of the mutant Ras, an inhibitor of Ras farnesylation, and the MEK inhibitor on ouabain-induced changes in mRNAs of the four genes indicated that (a) skeletal alpha-actin induction was dependent on Ras but not on p42/44 MAPKs, (b) alpha3 repression was dependent on the Ras-p42/44 MAPK cascade, and (c) induction of c-fos or atrial natriuretic factor gene occurred partly through the Ras-p42/44 MAPK cascade, and partly through pathways independent of Ras and p42/44 MAPKs. All ouabain effects required extracellular Ca2+, and were attenuated by a Ca2+/calmodulin antagonist or a protein kinase C inhibitor. The findings show that (a) signal pathways linked to sarcolemmal Na+/K+-ATPase share early segments involving Ca2+ and protein kinase C, but diverge into multiple branches only some of which involve Ras, or p42/44 MAPKs, or both; and (b) there are significant differences between this network and the related gene regulatory pathways activated by other hypertrophic stimuli, including those whose responses involve increases in intracellular free Ca2+ through different mechanisms.