Showing papers by "Jerrold M. Olefsky published in 2001"

Decreased Susceptibility to Fatty Acid–Induced Peripheral Tissue Insulin Resistance in Women

Abstract: Elevation of plasma nonesterified fatty acid (NEFA) levels has been shown in various studies to induce peripheral tissue insulin resistance and impair the suppression of endogenous glucose production (EGP). These studies have been conducted predominantly in men. We compared the effects of elevated plasma NEFA levels on basal and insulin-stimulated glucose metabolism in 8 normal women (age 42 +/- 8 years [mean +/- SD], BMI 25 +/- 3 kg/m(2)) and 10 normal men (35 +/- 6 years, 24 +/- 3 kg/m(2)). Each subject underwent two 5-h 80 mU. m(-2). min(-1) hyperinsulinemic-euglycemic clamps with measurement of glucose kinetics (intravenous [3-(3)H]glucose) and substrate oxidation. Plasma NEFA levels were elevated in one study for 3 h before and during the clamp ( approximately 1 mmol/l in both groups) by infusion of 20% Intralipid (60 ml/h) and heparin (900 U/h). In the control studies, the men and women had similar insulin-stimulated glucose disposal rates (R(d)) and substrate oxidation rates. In the men, elevated NEFA levels decreased insulin-stimulated glucose R(d) during the final 40 min of the clamp by 23% (P < 0.001). By contrast, no significant change in glucose R(d) was found in the women (control 10.4 +/- 1.1, lipid study 9.9 +/- 1.3 mg. kg(-1). min(-1)). Glucose R(d) was also unchanged in six women studied at a lower insulin dose (40 mU. m(-2). min(-1)). During the last 40 min of the high-insulin dose clamps with elevated NEFA, glucose oxidation was decreased by 33% in the men (P < 0.001) and by 23% in the women (P < 0.02). Nonoxidative glucose R(d) at this time was decreased by 15% in the men (P = 0.02) but was not significantly affected in women. Basal EGP was unaffected by elevation of plasma NEFA levels in both groups. Suppression of EGP during the glucose clamps, however, was impaired. At the insulin infusion rate used, the magnitude of this defect was comparable in men and women. In summary, our findings suggest that although the effects on EGP appear comparable, the inhibitory effects of NEFA on peripheral tissue insulin sensitivity are observed in men but cannot be demonstrated in women.

Insulin can regulate GLUT4 internalization by signaling to Rab5 and the motor protein dynein

Abstract: Insulin stimulates glucose transport by promoting translocation of the insulin-sensitive glucose transporter isoform 4 (GLUT4) from an intracellular compartment to the cell surface. This movement is accomplished by stimulation of GLUT4 exocytosis as well as inhibition of endocytosis. However, the molecular mechanisms for these effects remain unclear. In this study, we found that the GTP-binding protein Rab5 physically associated with the motor protein dynein in immunoprecipitants from both untransfected cells and cells transfected with GFP-Rab5 constructs. Microinjection of anti-Rab5 or anti-dynein antibody into 3T3-L1 adipocytes increased the basal level of surface GLUT4, did not change the insulin-stimulated surface GLUT4 level, and inhibited GLUT4 internalization after the removal of insulin. Photoaffinity labeling of Rab5 with [γ-32P]GTP-azidoanilide showed that insulin inhibited Rab5-GTP loading. By using microtubule-capture assays, we found that insulin also caused a significant decrease in the binding of dynein to microtubules. Furthermore, pretreatment of cells with the PI3-kinase inhibitor LY294002 inhibited the effects of insulin on both Rab5-GTP loading and dynein binding to microtubules. In conclusion, these data indicate that insulin signaling inhibits Rab5 activity and the interaction of dynein with microtubules in a PI3-kinase-dependent manner, and that these effects may inhibit the rate of GLUT4 internalization. As such, our results present a previously uncharacterized insulin-signaling pathway involving Rab5, the motor protein dynein, and the cytoskeleton to regulate directional GLUT4 movement, facilitating GLUT4 distribution to the cell surface.

Chronic endothelin-1 treatment leads to heterologous desensitization of insulin signaling in 3T3-L1 adipocytes

Abstract: We recently reported that insulin and endothelin-1 (ET-1) can stimulate GLUT4 translocation via the heterotrimeric G protein Gαq/11 and through PI3-kinase–mediated pathways in 3T3-L1 adipocytes. Because both hormones stimulate glucose transport through a common downstream pathway, we determined whether chronic ET-1 pretreatment would desensitize these cells to acute insulin signaling. We found that ET-1 pretreatment substantially inhibited insulin-stimulated 2-deoxyglucose uptake and GLUT4 translocation. Cotreatment with the ETA receptor antagonist BQ 610 prevented these effects, whereas inhibitors of Gαi or Gβγ were without effect. Chronic ET-1 treatment inhibited insulin-stimulated tyrosine phosphorylation of Gαq/11 and IRS-1, as well as their association with PI3-kinase and blocked the activation of PI3-kinase activity and phosphorylation of Akt. In addition, chronic ET-1 treatment caused IRS-1 degradation, which could be blocked by inhibitors of PI3-kinase or p70 S6-kinase. Similarly, expression of a constitutively active Gαq mutant, but not the wild-type Gαq, led to IRS-1 degradation and inhibited insulin-stimulated phosphorylation of IRS-1, suggesting that the ET-1–induced decrease in IRS-1 depends on Gαq/11 and PI3-kinase. Insulin-stimulated tyrosine phosphorylation of SHC was also reduced in ET-1 treated cells, resulting in inhibition of the MAPK pathway. In conclusion, chronic ET-1 treatment of 3T3-L1 adipocytes leads to heterologous desensitization of metabolic and mitogenic actions of insulin, most likely through the decreased tyrosine phosphorylation of the insulin receptor substrates IRS-1, SHC, and Gαq/11.

Thiazolidinedione Treatment Prevents Free Fatty Acid–Induced Insulin Resistance in Male Wistar Rats

Abstract: We sought to ascertain whether pretreatment with troglitazone (20 days) could prevent acute free fatty acid (FFA)–induced insulin resistance in male Wistar rats. Animals were divided into three groups: 1 ) control, 2 ) FFA infusion alone (FFA1), and 3 ) thiazolidinedione (TZD)-treated + FFA infusion (FFA1). Days before a hyperinsulinemic-euglycemic clamp, all animals were cannulated in the jugular vein (infusion) and carotid artery (sampling). Animals were allowed 5 days to recover from surgery and fasted 12 h before the experiment. Glucose (variable), insulin (40 mU · kg−1 · min−1), and Liposyn (heparinized 10% lipid emulsion) infusions were initiated simultaneously and continued from 0–120 min. Steady-state glucose, 8.3 ± 0.14 mmol/l, and insulin concentrations, 7.3 ± 2.45 nmol/l, were the same between groups. Interestingly, steady-state FFA levels were significantly lower in animals pretreated with TZD compared with FFA alone (1.83 ± 0.26 vs. 2.96 ± 0.25 mmol/l; P = 0.009), despite matched intralipid infusion rates. A second group of TZD-treated animals (TZD + FFA2) were infused with intralipid at a higher infusion rate (44%) to match the arterial concentrations of FFA1. The glucose infusion and insulin-stimulated glucose disposal rates (GDRs) were significantly decreased (40%) for untreated Liposyn infused (FFA1) compared with control rats. In addition, insulin receptor substrate-1 (IRS-1) phosphorylation and IRS-1–associated phosphatidylinositol (PI) 3-kinase activity was significantly reduced, 30–50%, in FFA1 rats. TZD pretreatment prevented the FFA-induced decrement in insulin signaling. Fatty acid translocase (FAT/CD36) also was significantly reduced (56%) in untreated FFA1 rats after the clamp but remained identical to control values for TZD-treated rats. In conclusion, acutely elevated FFA levels 1 ) induced a significant reduction in tracer-determined GDR paralleled by impaired tyrosine phosphorylation of IRS-1 and reduced IRS-1–associated PI 3-kinase activity and 2 ) induced a significant reduction in FAT/CD36 total protein. TZD pretreatment prevented FFA-induced decrements in insulin action and prevented the reduction in FAT/CD36 protein.

Prospects for research in diabetes mellitus.

Abstract: Diabetes mellitus is the sixth leading cause of death in the United States, and morbidities resulting from diabetes-related complications such as retinopathy, kidney disease, and limb amputation cause a huge burden to the national health care system Identification of the genetic components of type 1 and type 2 diabetes is the most important area of research because elucidation of the diabetes genes will influence all efforts toward a mechanistic understanding of the disease, its complications, and its treatment, cure, and prevention Also, the link between obesity and type 2 diabetes mandates a redoubled effort to understand the genetic and behavioral contributions to obesity

Synthesis of an organoinsulin molecule that can be activated by antibody catalysis

Abstract: We have developed a methodology of prodrug delivery by using a modified insulin species whose biological activity potentially can be regulated in vivo. Native insulin was derivatized with aldol-terminated chemical modifications that can be selectively removed by the catalytic aldolase antibody 38C2 under physiologic conditions. The derivatized organoinsulin (insulin(D)) was defective with respect to receptor binding and stimulation of glucose transport. The affinity of insulin(D) for the insulin receptor was reduced by 90% in binding studies using intact cells. The ability of insulin(D) to stimulate glucose transport was reduced by 96% in 3T3-L1 adipocytes and by 55% in conscious rats. Incubation of insulin(D) with the catalytic aldolase antibody 38C2 cleaved all of the aldol-terminated modifications, restoring native insulin. Treatment of insulin(D) with 38C2 also restored insulin(D)'s receptor binding and glucose transport-stimulating activities in vitro, as well as its ability to lower glucose levels in animals in vivo. We propose that these results are the foundation for an in vivo regulated system of insulin activation using the prohormone insulin(D) and catalytic antibody 38C2 with potential therapeutic application.

Exercise-Stimulated Glucose Turnover in the Rat Is Impaired by Glucosamine Infusion

Abstract: The infusion of glucosamine causes insulin resistance, presumably by entering the hexosamine biosynthetic pathway; it has been proposed that this pathway plays a role in hyperglycemia-induced insulin resistance. This study was undertaken to determine if glucosamine infusion could influence exercise-stimulated glucose uptake. Male SD rats were infused with glucosamine at 0.1 mg · kg-1 · min-1 (low-GlcN group), 6.5 mg · kg-1 · min-1 (high-GlcN group), or saline (control group) for 6.5 h and exercised on a treadmill for 30 min (17 m/min) at the end of the infusion period. Glucosamine infusion caused a modest increase in basal glycemia in both experimental groups, with no change in tracer-determined basal glucose turnover. During exercise, glucose turnover increased ∼2.2-fold from 46 ± 2 to 101 ± 5 μmol · kg-1 · min-1 in the control group. Glucose turnover increased to a lesser extent in the glucosamine groups and was limited to 88% of control in the low-GlcN group (47 ± 2 to 90 ± 3 μmol · kg-1 · min-1; P < 0.01) and 72% of control in the high-GlcN group (43 ± 1 to 73 ± 3 μmol · kg-1 · min-1; P < 0.01). Similarly, the metabolic clearance rate (MCR) in the control group increased 72% from 6.1 ± 0.2 to 10.5 ± 0.7 ml · kg-1 · min-1 in response to exercise. However, the increase in MCR was only 83% of control in the low-GlcN group (5.2 ± 0.5 to 8.7 ± 0.5 ml · kg-1 · min-1; P < 0.01) and 59% of control in the high-GlcN group (4.5 ± 0.2 to 6.2 ± 0.3 ml · kg-1 · min-1; P < 0.01). Neither glucosamine infusion nor exercise significantly affected plasma insulin or free fatty acid (FFA) concentrations. In conclusion, the infusion of glucosamine, which is known to cause insulin resistance, also impaired exercise-induced glucose uptake. This inhibition was independent of hyperglycemia and FFA levels.