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Insulin-and glyburide-stimulated changes in cytosolic free calcium concentrations (QCa2+Ii) were studied in gluteal adipocytes obtained from six obese women (139±3% ideal body wt) and six healthy, normal weight age-and sex-matched controls. Biopsies were performed after an overnight fast and twice (at 3 and 6 h) during an insulin infusion (40 mU/m2 per min) (euglycemic clamp). In adipocytes obtained from normal subjects before insulin infusion, insulin (10 ng/ml) increased [Ca2+ji from 146±26 nM to 391±66 nM. Similar increases were evoked by 2 tiM glyburide (329±41 nM). After 3 h of insulin infusion, basal ICa2+ii rose to 234±21 nM, but the responses to insulin and glyburide were completely abolished. In vitro insulin-stimulated 2-deoxyglucose uptake was reduced by insulin and glucose infusion (25% stimulation before infusion, 5.4% at 3 h, and 0.85% at 6 h of infusion). Rat adipocytes were preincubated with 1-10 mM glucose and 10 ng/ml insulin for 24 h. Measurements of 2-deoxyglucose uptake demonstrated insulin resistance in these cells.Under these experimental conditions, increased levels of [Ca2+Ii that were no longer responsive to insulin were demonstrated. Verapamil in the preincubation medium prevented the development of insulin resistance.

Caspase-1 is a member of the intracellular cysteine protease family that mediates inflammation through the activation of the cytokines interleukin-1β (IL-1β) and interleukin-18 (IL-18). As mice lacking IL-18 become obese and insulin resistant, and both IL-18 and IL-1β have a role in overall energy balance, we sought to determine whether caspase-1 deficiency also causes obesity. Male and female caspase-1-deficient (caspase-1-/-) and control (wild-type (WT)) mice were fed either a high-fat (HF, 45% of kcal) or a low-fat (LF, 10% of kcal) synthetic diet starting at 6 weeks of age. Caspase-1-/- mice maintained lower but detectable levels of IL-18 compared with WT mice. Plasma IL-1β levels were below the detection limit for both KO and WT mice. Male caspase-1-/- mice gained extra fat mass by 16 weeks on the HF diet, but not until 40 weeks on the LF diet. Female capase-1-/- mice gained more fat by 28 weeks but only on the HF diet. These data indicate that caspase-1-/- mice develop obesity with an age and sex-dependent differences, and only male mice display obesity on LF diet. Overall, this study suggests that the lower level of IL-18 in caspase-1-/- mice might be causing obesity development similarly to IL-18-deficient mice.

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Transgenic mice overexpressing GLUT-4 selectively in adipose tissue using the aP2 promoter/enhancer develop obesity, enhanced glucose tolerance, and increased insulin sensitivity. The current study was designed to determine whether altering glucose transport affects lipoprotein lipase (LPL) activity. Female transgenic mice (10-12 mo old) have increased parametrial fat pad weight, adipocyte size, total body lipid and fasting plasma triglycerides, fatty acids, and glycerol compared with nontransgenics. Stimulation of LPL activity by feeding is blunted in parametrial and perirenal fat from 15- and 22-fold in nontransgenic mice to three- to sevenfold in transgenics. LPL activity in the fed state in transgenic mice is reduced 60-75% in fat. In heart and skeletal muscle of transgenic mice, LPL activity in the fasted state is 55-65% lower than in nontransgenics and feeding induces an unexpected rise in LPL activity. Muscle LPL activity is strongly and inversely correlated with glucose transport in adipocytes (r = -0.942, P < 0.005), which is increased 15- to 27-fold in the basal state and 4.5- to 6.9-fold in the insulin-stimulated state in transgenics. Whereas stimulation of adipose LPL may be blunted by lower plasma insulin levels in transgenics, fasting muscle LPL may be suppressed by elevated plasma lipids. Thus altering the partitioning of glucose between adipose tissue and muscle alters a critical step for the partitioning of lipoprotein fatty acids between these tissues.