Body Insulin-mediated Glucose Uptake Research Articles

Diacylglycerol kinase α deficiency alters inflammation markers in adipose tissue in response to a high-fat diet

Conversion of diacylglycerol to phosphatidic acid is mediated by diacylglycerol kinases (DGKs), with DGKα specifically linked to adaptive immune responses. We determined the role of DGKα in obesity and inflammatory responses to a high-fat diet (HFD). DGKα KO and WT littermates were either a) chow-fed, b) HFD-fed for 12 weeks (Long-Term HFD), or c) HFD-fed for 3 days (Acute HFD). Body weight/composition, oxygen consumption, food intake, and glucose tolerance was unaltered between chow-fed DGKα KO and WT mice. Insulin concentration during the intraperitoneal glucose tolerance (IPGT) test was elevated in chow-fed DGKα KO mice, suggesting mild insulin resistance. Insulin concentration during the IPGT test was reduced in Long-Term HFD-fed DGKα KO mice, suggesting a mild enhancement in insulin sensitivity. Acute HFD increased hormone sensitive lipase protein abundance and altered expression of interleukin 1β mRNA, an inflammatory marker in perigonadal adipose tissue of DGKα KO mice. In conclusion, DGKα ablation is associated with mild alterations in insulin sensitivity. However, DGKα is dispensable for whole body insulin-mediated glucose uptake, hepatic glucose production, and energy homeostasis. Our results suggest DGKα aids in modulating the early immune response of adipose tissue following an acute exposure to HFD, possibly through modulation of acute T-cell action.

Divergence of intracellular and extracellular HSP72 in type 2 diabetes: does fat matter?

Divergence of intracellular and extracellular HSP72 in type 2 diabetes: does fat matter?

Specificity of insulin signalling in human skeletal muscle as revealed by small interfering RNA

Insulin action on metabolically active tissues is a complex process involving positive and negative feedback regulation to control whole body glucose homeostasis. At the cellular level, glucose and lipid metabolism, as well as protein synthesis, are controlled through canonical insulin signalling cascades. The discovery of small interfering RNA (siRNA) allows for the molecular dissection of critical components of the regulation of metabolic and gene regulatory events in insulin-sensitive tissues. The application of siRNA to tissues of human origin allows for the molecular dissection of the mechanism(s) regulating glucose and lipid metabolism. Penetration of the pathways controlling insulin action in human tissue may aid in discovery efforts to develop diabetes prevention and treatment strategies. This review will focus on the use of siRNA to validate critical regulators controlling insulin action in human skeletal muscle, a key organ important for the control of whole body insulin-mediated glucose uptake and metabolism.

Influence of TNF-α and IL-6 infusions on insulin sensitivity and expression of IL-18 in humans

Inflammation is associated with insulin resistance, and both tumor necrosis factor (TNF)-alpha and interleukin (IL)-6 may affect glucose uptake. TNF induces insulin resistance, whereas the role of IL-6 is controversial. High plasma levels of IL-18 are associated with insulin resistance in epidemiological studies. We investigated the effects of TNF and IL-6 on IL-18 gene expression in skeletal muscle and adipose tissue. Nine human volunteers underwent three consecutive interventions, receiving an infusion of recombinant human (rh)IL-6, rhTNF, and saline. Insulin sensitivity was assessed by measurement of whole body glucose uptake with the stable isotope tracer method during a euglycemic hyperinsulinemic clamp (20 mU.min(-1).kg(-1)), which was initiated 1 h after the IL-6-TNF-saline infusion. Cytokine responses were measured in plasma, muscle, and fat biopsies. Plasma concentrations of TNF and IL-6 increased 10- and 38-fold, respectively, during the cytokine infusions. Whole body insulin-mediated glucose uptake was significantly reduced during TNF infusion but remained unchanged during IL-6 infusion. TNF induced IL-18 gene expression in muscle tissue, but not in adipose tissue, whereas IL-6 infusion had no effect on IL-18 gene expression in either tissue. We conclude that TNF-induced insulin resistance of whole body glucose uptake is associated with increased IL-18 gene expression in muscle tissue, indicating that TNF and IL-18 interact, and both may have important regulatory roles in the pathogenesis of insulin resistance.

L-Carnitine Improves Glucose Disposal in Type 2 Diabetic Patients

Objective: Aim of the present study is to evaluate the effects of L-carnitine on insulin-mediated glucose uptake and oxidation in type II diabetic patients and compare the results with those in healthy controls.Design: Fifteen type II diabetic patients and 20 healthy volunteers underwent a short-term (2 hours) euglycemic hyperinsulinemic clamp with simultaneous constant infusion of L-carnitine (0.28 μmole/kg bw/minute) or saline solution. Respiratory gas exchange was measured by an open-circuit ventilated hood system. Plasma glucose, insulin, non-esterified fatty acids (NEFA) and lactate levels were analyzed. Nitrogen urinary excretion was calculated to evaluate protein oxidation.Results: Whole body glucose uptake was significantly (p<0.001) higher with L-carnitine than with saline solution in the two groups investigated (48.66±4.73 without carnitine and 52.75±5.19 μmoles/kgffm/minute with carnitine in healthy controls, and 35.90±5.00 vs. 38.90±5.16 μmoles/kgffm/minute in diabetic patients). Glucose oxidation significantly increased only in the diabetic group (17.61±3.33 vs. 16.45±2.95 μmoles/kgffm/minute, p<0.001). On the contrary, glucose storage increased in both groups (controls: 26.36±3.25 vs. 22.79±3.46 μmoles/kgffm/minute, p<0.001; diabetics: 21.28±3.18 vs. 19.66±3.04 μmoles/kgffm/minute, p<0.001). In type II diabetic patients, plasma lactate significantly decreased during L-carnitine infusion compared to saline, going from the basal period to the end-clamp period (0.028±0.0191 without carnitine and 0.0759±0.0329 with carnitine, p<0.0003).Conclusions: L-carnitine constant infusion improves insulin sensitivity in insulin resistant diabetic patients; a significant effect on whole body insulin-mediated glucose uptake is also observed in normal subjects. In diabetics, glucose, taken up by the tissues, appears to be promptly utilized as fuel since glucose oxidation is increased during L-carnitine administration. The significantly reduced plasma levels of lactate suggest that this effect might be exerted through the activation of pyruvate dehydrogenase, whose activity is depressed in the insulin resistant status.

Insulin action on glucose transport and plasma membrane GLUT4 content in skeletal muscle from patients with NIDDM.

We investigated the response of the glucose transport system to insulin, in the presence of ambient glucose concentrations, in isolated skeletal muscle from seven patients with non-insulin-dependent diabetes mellitus (NIDDM) (age, 55 +/- 3 years, BMI 27.4 +/- 1.8 kg/m2) and seven healthy control subjects (age, 54 +/- 3 years, BMI 26.5 +/- 1.1 kg/m2). Insulin-mediated whole body glucose utilization was similar between the groups when studied in the presence of ambient glucose concentrations (approximately 10 mmol/l for the NIDDM patients and 5 mmol/l for the control subjects). Samples were obtained from the vastus lateralis muscle, by means of an open muscle biopsy procedure, before and after a 40-min insulin infusion. An increase in serum insulin levels from 54 +/- 12 to 588 +/- 42 pmol/l, induced a 1.6 +/- 0.2-fold increase in glucose transporter protein (GLUT4) in skeletal muscle plasma membranes obtained from the control subjects (p < 0.05), whereas no significant increase was noted in plasma membrane fractions prepared from NIDDM muscles, despite a similar increase in serum insulin levels. At concentrations of 5 mmol/l 3-O-methylglucose in vitro, insulin (600 pmol/l) induced a 2.2-fold (p < 0.05) increase in glucose transport in NIDDM muscles and a 3.4-fold (p < 0.001) increase in the control muscles. Insulin-stimulated 3-O-methylglucose transport was positively correlated with whole body insulin-mediated glucose uptake in all participants (r = 0.78, p < 0.001) and negatively correlated with fasting plasma glucose levels in the NIDDM subjects (r = 0.93, p < 0.001). Muscle fibre type distribution and capillarization were similar between the groups. Our results suggest that insulin-stimulated glucose transport in skeletal muscle from patients with NIDDM is down-regulated in the presence of hyperglycaemia. The increased flux of glucose as a consequence of hyperglycaemia may result in resistance to any further insulin-induced gain of GLUT4 at the level of the plasma membrane.

Intact glucose transport in morphologically altered denervated skeletal muscle from quadriplegic patients.

The present study was undertaken to investigate the nature of the whole body insulin resistance that characterizes patients with complete cervical spinal cord lesion. Nine patients with C5-C7 lesions and ten age-matched healthy individuals were studied. Whole body insulin-mediated glucose utilization was reduced by 43% in the quadriplegic patients compared with the controls (P < 0.001). In the quadriplegic patients, lean body mass corresponded to 66 +/- 3% of total body mass. Despite whole body insulin resistance, in isolated vastus lateralis muscle, basal and insulin-stimulated 3-O-methylglucose transport, as well as protein expression of the insulin or exercise-regulatable glucose transporter, GLUT-4, and glycogen content were comparable between the patients and controls. Strikingly, muscle fiber area was reduced by 44% (P < 0.05), percentage of type IIb fibers was increased (P < 0.01), and there was a complete loss of type I fibers in the patients. In conclusion, the dissociation between whole body insulin-mediated glucose uptake and skeletal muscle glucose transport in quadriplegic patients primarily reflects the decreased muscle mass. Furthermore, these findings demonstrate a remarkable capacity of skeletal muscle to maintain an intact glucose transport system despite severe morphological alterations.

D-Fenfluramine improves hepatic insulin action in streptozotocin-diabetic rats

We have examined the effect of chronic (21 days) oral administration of the serotoninergic anorectic drug d-fenfluramine (5 mg/kg) in a rat model of non-insulin-dependent diabetes (without obesity), as induced by injection of a low dose (45 mg/kg) of streptozotocin at 6 weeks, and characterized by marked hyperglycaemia and hepatic and peripheral insulin resistance. The following parameters were assessed: (1) basal blood glucose and insulin levels, and (2) basal and insulin-stimulated in vivo glucose production and glucose utilization, using the insulin-clamp technique in conjunction with isotopic measurement of glucose turnover. In the d-fenfluramine-treated diabetic rats, postabsorptive basal plasma glucose levels were decreased (7.8 ± 0.3 mM as compared to 14.9 ± 0.1 mM in the untreated diabetic rats) while the basal plasma insulin levels were unchanged. A similar reduction of the basal plasma glucose levels was observed in the pair-fed untreated diabetic group (8.3 ± 0.2 mM). Basal glucose turnover was reduced by 45% ( P < 0.01) in the d-fenfluramine-treated diabetic rats as well as in the pair-fed untreated diabetic rats. The impaired suppression of hepatic glucose output by insulin, caused by diabetes, was totally reversed by d-fenfluramine, while pair-feeding did not modify hepatic insulin resistance. The whole body insulin-mediated glucose uptake in the diabetic rats was also significantly improved by d-fenfluramine treatment. Such an effect was also found in the pair-fed untreated group. Thus the beneficial effect on peripheral glucose utilization in the rats receiving d-fenfluramine is mainly due to chronic food restriction (as a consequence of the anorectic properties of the drug). By contrast, d-fenfluramine counteracts liver insulin resistance in the present rat model of diabetes by a mechanism not related to its anorectic properties.

Effects of epinephrine on insulin-mediated glucose uptake in whole body and leg muscle in humans: role of blood flow.

In vivo insulin-mediated glucose uptake (IMGU) occurs chiefly in skeletal muscle, where it is determined by the product of arteriovenous glucose difference (delta AVG) and blood flow (BF) rate into muscle. Epinephrine (Epi) reduces the rate of IMGU in whole body. To examine whether this is due to a reduction in delta AVG across or BF into skeletal muscle we constructed insulin dose-response curves for whole body IMGU and leg muscle IMGU- using euglycemic clamp ((+)[3-3H]glucose infusion) and leg balance techniques during insulin infusions ranging from 10 to 1,200 mU.m-2.min-1. We studied six subjects [wt 70 +/- 2 (SE) kg] during an Epi infusion at a single rate of 0.002 mg.kg-1.min-1 and six subjects (70 +/- 3 kg) during a saline infusion alone. Maximum whole body glucose uptake (WBGU) was similar during Epi and saline infusions [71.4 vs. 73.6 mmol.kg-1.min-1, P = not significant (NS)]. Compared with saline, maximum delta AVG was decreased during Epi infusion (1.04 vs. 1.31 mM, P less than 0.01). Compared with saline alone maximum leg BF was increased (5.3 vs. 4.3 dl/min, P less than 0.01) during Epi infusion. Thus maximum leg glucose uptake (LGU) was similar (696 vs. 821 pmol.leg-1.min-1, P = NS) during infusion of Epi and saline, respectively. Half-maximal effective dose for insulin's effect to stimulate WBGU, delta AVG, BF, and LGU was increased two- to threefold during Epi vs. saline infusions (P less than 0.01 for all values).(ABSTRACT TRUNCATED AT 250 WORDS)

Reduced capacity and affinity of skeletal muscle for insulin-mediated glucose uptake in noninsulin-dependent diabetic subjects. Effects of insulin therapy.

We have estimated the capacity and affinity of insulin-mediated glucose uptake (IMGU) in whole body and in leg muscle of obese non-insulin-dependent diabetics (NIDDM, n = 6) with severe hyperglycemia, glycohemoglobin (GHb 14.4 +/- 1.2%), lean controls (ln, n = 7) and obese nondiabetic controls (ob, n = 7). Mean +/- SEM weight (kg) was 67 +/- 2 (ln), 100 +/- 7 (ob), and 114 +/- 11 (NIDDM), P = NS between obese groups. NIDDM were also studied after 3 wk of intensive insulin therapy, GHb post therapy was 10.1 +/- 0.9, P less than 0.01 vs. pretherapy. Insulin (120 mu/m2 per min) was infused and the arterial blood glucose (G) sequentially maintained at approximately 4, 7, 12, and 21 mmol/liter utilizing the G clamp technique. Leg glucose uptake (LGU) was calculated as the product of the femoral arteriovenous glucose difference (FAVGd) and leg blood flow measured by thermodilution. Compared to ln, ob and NIDDM had significantly lower rates of whole body IMGU and LGU at all G levels. Compared to ob, the NIDDM exhibited approximately 50% and approximately 40% lower rates of whole body IMGU over the first two G levels (P less than 0.02) but did not differ at the highest G, P = NS. LGU was 83% lower in NIDDM vs. ob, P less than 0.05 at the first G level only. After insulin therapy NIDDM were indistinguishable from ob with respect to whole body IMGU or LGU at all G levels. A significant correlation was noted between the percent GHb and the EG50 (G at which 1/2 maximal FAVGd occurs) r = 0.73, P less than 0.05. Thus, (a) insulin resistance in NIDDM and obese subjects are characterized by similar decreases in capacity for skeletal muscle IMGU, but differs in that poorly controlled NIDDM display a decrease in affinity for skeletal muscle IMGU, and (b) this affinity defect is related to the degree of antecedent glycemic control and is reversible with insulin therapy, suggesting that it is an acquired defect.

Gram-Negative Infection Increases Noninsulin-Mediated Glucose Disposal*

Peripheral glucose uptake can occur by either insulin- or noninsulin-mediated mechanisms, and the two pathways appear to be regulated independently. Using the euglycemic hyperinsulinemic clamp technique, we have previously demonstrated that sepsis induces whole body insulin resistance. The purpose of the present study was to determine whether infection also alters noninsulin-mediated glucose uptake (NIMGU) and, if so, which tissues are affected. Studies were performed in chronically catheterized conscious rats under either basal (6 mM glucose, 30 microU/ml insulin) or insulinopenic conditions to determine NIMGU. Hypermetabolic sepsis was induced by sc injections of live Escherichia coli, and 24 h later a tracer amount of [U-14C]deoxy-2-glucose was injected for the determination of the in vivo glucose metabolic rate (Rg) in selected tissues. Our results indicate that NIMGU is the predominant route of glucose disposal in both septic and nonseptic rats, accounting for 79-83% of the total rate of glucose disposal. Because the rate of whole body glucose disposal was increased by sepsis, the absolute rate of NIMGU was 46% higher in septic rats than in nonseptic animals. This increase was the result of the elevated Rg in liver, spleen, ileum, and lung. Sepsis also increased whole body insulin-mediated glucose uptake by 88% under basal conditions, and this was due to an enhanced glucose uptake by muscle and skin. In insulinopenic animals in which the plasma glucose concentration was elevated to 17 mM, whole body glucose disposal increased by 107% in nonseptic animals, but by only 32% in septic rats. The hyperglycemic-induced increment in organ Rg was smaller in all tissues examined from septic animals. However, the absolute rate of whole body and tissue glucose utilization was not different between the two groups. These results indicate that gram-negative infection increases whole body NIMGU, which results from an enhanced rate of glucose utilization by tissues rich in mononuclear phagocytes, including the liver, spleen, ileum, and lung, but not by muscle.

Decreased effect of insulin to stimulate skeletal muscle blood flow in obese man. A novel mechanism for insulin resistance.

Obesity is characterized by decreased rates of skeletal muscle insulin-mediated glucose uptake (IMGU). Since IMGU equals the product of the arteriovenous glucose difference (AVGd) across muscle and blood flow into muscle, reduced blood flow and/or tissue activity (AVGd) can lead to decreased IMGU. To examine this issue, we studied six lean (weight 68 +/- 3 kg, mean +/- SEM) and six obese (94 +/- 3 kg) men. The insulin dose-response curves for whole body and leg IMGU were constructed using the euglycemic clamp and leg balance techniques over a large range of serum insulin concentrations. In lean and obese subjects, whole body IMGU, AVGd, blood flow, and leg IMGU increased in a dose dependent fashion and maximal rates of all parameters were reduced in obese subjects compared to lean subjects. The dose-response curves for whole body IMGU, leg IMGU, and AVGd were right-shifted in obese subjects with an ED50 two- to threefold higher than that of lean subjects for each parameter. Leg blood flow increased approximately twofold from basal 2.7 +/- 0.2 to 4.4 +/- 0.2 dl/min in lean, P less than 0.01, and from 2.5 +/- 0.3 to 4.4 +/- 0.4 dl/min in obese subjects, P less than 0.01. The ED50 for insulin's effect to increase leg blood flow was about fourfold higher for obese (957 pmol/liter) than lean subjects (266 pmol/liter), P less than 0.01. Therefore, decreased insulin sensitivity in human obesity is not only due to lower glucose extraction in insulin-sensitive tissues but also to lower blood flow to these tissues. Thus, in vivo insulin resistance can be due to a defect in insulin action at the tissue level and/or a defect in insulin's hemodynamic action to increase blood flow to insulin sensitive tissues.

Insulin response of components of whole-body and muscle carbohydrate metabolism in humans.

We measured total body insulin-mediated glucose uptake, carbohydrate oxidation, storage (nonoxidative disposal), muscle glycogen synthase activity, and muscle glucose 6-phosphate (G-6-P) content in response to five levels of insulinemia (means 16, 52, 152, 573, and 5,550 microU/ml) in 16 male glucose-tolerant volunteers. Insulin dissociation constants (KDs) for disposal, storage, and synthase activity (but not for oxidation) are coincident, suggesting that storage via glycogen synthesis could be a major determinant of glucose disposal. Increases in glucose disposal were associated with decreases in muscle G-6-P concentration. These data suggest that the principal control over carbohydrate disposal is exerted after G-6-P. The coincidence of insulin sensitivities for disposal, storage, and synthase activity suggest that storage via glycogen synthesis could be a major determinant of glucose disposal.