Hyperinsulinemic euglycemic step clamping with tracer glucose infusion and labeled glucose infusate for assessment of acute insulin resistance in pigs

d-Allulose Ameliorates Skeletal Muscle Insulin Resistance in High-Fat Diet-Fed Rats

BACKGROUND

d-Allulose is a rare sugar with antiobesity and antidiabetic activities. However, its direct effect on insulin sensitivity and the underlying mechanism involved are unknown.

OBJECTIVE

This study aimed to investigate the effect of d-allulose on high-fat diet (HFD)-induced insulin resistance using the hyperinsulinemic-euglycemic (HE)-clamp method and intramuscular signaling analysis.

METHODS

Wistar rats were randomly divided into three dietary groups: chow diet, HFD with 5% cellulose (HFC), and HFD with 5% d-allulose (HFA). After four weeks of feeding, the insulin tolerance test (ITT), intraperitoneal glucose tolerance test (IPGTT), and HE-clamp study were performed. The levels of plasma leptin, adiponectin, and tumor necrosis factor (TNF)-α were measured using the enzyme-linked immunosorbent assay. We analyzed the levels of cell signaling pathway components in the skeletal muscle using Western blotting.

RESULTS

d-allulose alleviated the increase in HFD-induced body weight and visceral fat and reduced the area under the curve as per ITT and IPGTT. d-Allulose increased the glucose infusion rate in the two-step HE-clamp test. Consistently, the insulin-induced phosphorylation of serine 307 in the insulin receptor substrate-1 and Akt and expression of glucose transporter 4 (Glut-4) in the muscle were higher in the HFA group than HFC group. Furthermore, d-allulose decreased plasma TNF-α concentration and insulin-induced phosphorylation of stress-activated protein kinase/Jun N-terminal kinase in the muscle and inhibited adiponectin secretion in HFD-fed rats.

CONCLUSIONS

d-allulose improved HFD-induced insulin resistance in Wistar rats. The reduction of the proinflammatory cytokine production, amelioration of adiponectin secretion, and increase in insulin signaling and Glut-4 expression in the muscle contributed to this effect.

Perioperative Infusion of Glucagon-Like Peptide-1 Prevents Insulin Resistance After Surgical Trauma in Female Pigs

Insulin resistance is an independent negative predictor of outcome after elective surgery and increases mortality among surgical patients in intensive care. The incretin hormone glucagon-like peptide-1 (GLP-1) potentiates glucose-induced insulin release from the pancreas but may also increase insulin sensitivity in skeletal muscle and directly suppress hepatic glucose release. Here, we investigated whether a perioperative infusion of GLP-1 could counteract the development of insulin resistance after surgery. Pigs were randomly assigned to three groups; surgery/control, surgery/GLP-1, and sham/GLP-1. Both surgery groups underwent major abdominal surgery. Whole-body glucose disposal (WGD) and endogenous glucose release (EGR) were assessed preoperatively and postoperatively using D-[6,6-2H2]-glucose infusion in combination with hyperinsulinemic euglycemic step-clamping. In the surgery/control group, peripheral insulin sensitivity (i.e., WGD) was reduced by 44% relative to preoperative conditions, whereas the corresponding decline was only 9% for surgery/GLP-1 (P < 0.05). Hepatic insulin sensitivity (i.e., EGR) remained unchanged in the surgery/control group but was enhanced after GLP-1 infusion in both surgery and sham animals (40% and 104%, respectively, both P < 0.05). Intraoperative plasma glucose increased in surgery/control (∼20%) but remained unchanged in both groups receiving GLP-1 (P < 0.05). GLP-1 diminished an increase in postoperative glucagon levels but did not affect skeletal muscle glycogen or insulin signaling proteins after surgery. We show that GLP-1 improves intraoperative glycemic control, diminishes peripheral insulin resistance after surgery, and suppresses EGR. This study supports the use of GLP-1 to prevent development of postoperative insulin resistance.

Renal Denervation for Resistant Hypertension Fails to Improve Insulin Resistance as Assessed by Hyperinsulinemic-Euglycemic Step Clamp

We assessed whether insulin sensitivity improved after renal denervation (RDN) for resistant hypertension. Twenty-three patients underwent a two-step hyperinsulinemic-euglycemic clamp (HEC) with glucose tracer and labeled glucose infusion and oral glucose tolerance test (OGTT) before and 6 months after RDN. Eighteen patients had metabolic syndrome at baseline. Blood pressure declined significantly after RDN, whereas mean (SD) fasting plasma glucose concentration (5.9 ± 0.7 mmol/L), median (minimum-maximum) insulin concentration (254 pmol/L [88-797 pmol/L]), and median C-peptide concentration (2.4 nmol/L [0.9-5.7 nmol/L]) remained unchanged. Endogenous glucose release during HEC was less suppressed after RDN, suggesting a slight decrease in hepatic insulin sensitivity. During high-dose insulin infusion, whole-body glucose disposal was low and remained unchanged after RDN, indicating persistent peripheral insulin resistance (IR). Area under the curve for 0-120 min for glucose and insulin during OGTT, Quantitative Insulin Sensitivity Check Index, Simple Index Assessing Insulin Sensitivity Oral Glucose Tolerance, and HOMA-IR were high, and did not improve after RDN. Despite a significant decrease in blood pressure, neither peripheral nor hepatic insulin sensitivity improved 6 months after RDN treatment in this group of insulin-resistant patients without diabetes and with resistant hypertension, as measured with gold standard methods.

Interaction of low dose of fish oil and glucocorticoids on insulin sensitivity and lipolysis in healthy humans: A randomized controlled study

SCOPE

This study examined the interaction of fish oil (FO) with dexamethasone on glucose and lipid metabolisms in healthy subjects.

METHODS AND RESULTS

The study included two consecutive parts. Part A (randomized) in 16 subjects studied the effects of dexamethasone (2 days, 2 mg/day) versus placebo (lactose), part B (two parallel subgroups of eight) studied the interaction of FO (3 wk, 840 mg/day of EPA + DHA) with dexamethasone. Insulin sensitivity of lipolysis (d5-glycerol infusion + microdialysis), endogenous glucose production, and muscle glucose uptake were assessed by a three-step hot insulin clamp and substrate oxidation by indirect calorimetry. Dexamethasone induced liver and peripheral insulin resistance, an increase in fat oxidation, and a decrease in suppression of plasma nonesterified fatty acids (NEFAs). FO amplified the effects of dexamethasone by increasing liver and muscle insulin resistance, by reducing suppression of plasma NEFAs and fat oxidation and by increasing adipose tissue (AT) lipolysis.

CONCLUSION

FO, given at a moderate dose in healthy subjects prior to a very short-term (2 days) low dose of a synthetic glucocorticoid, worsened its deleterious effects on insulin sensitivity. The enhancing effect of FO on fat oxidation and AT lipolysis might be a protective effect toward an increase in fat mass.

Skeletal muscle mitochondria exhibit decreased pyruvate oxidation capacity and increased ROS emission during surgery-induced acute insulin resistance

Development of acute insulin resistance represents a negative factor after surgery, but the underlying mechanisms are not fully understood. We investigated the postoperative changes in insulin sensitivity, mitochondrial function, enzyme activities, and release of reactive oxygen species (ROS) in skeletal muscle and liver in pigs on the 2nd postoperative day after major abdominal surgery. Peripheral and hepatic insulin sensitivity were assessed by D-[6,6-²H₂]glucose infusion and hyperinsulinemic euglycemic step clamping. Surgical trauma elicited a decline in peripheral insulin sensitivity (∼34%, P<0.01), whereas hepatic insulin sensitivity remained unchanged. Intramyofibrillar (IFM) and subsarcolemma mitochondria (SSM) isolated from skeletal muscle showed a postoperative decline in ADP-stimulated respiration (V(ADP)) for pyruvate (∼61%, P<0.05, and ∼40%, P<0.001, respectively), whereas V(ADP) for glutamate and palmitoyl-L-carnitine (PC) was unchanged. Mitochondrial leak respiration with PC was increased in SSM (1.9-fold, P<0.05) and IFM (2.5-fold, P<0.05), indicating FFA-induced uncoupling. The activity of the pyruvate dehydrogenase complex (PDC) was reduced (∼32%, P<0.01) and positively correlated to the decline in peripheral insulin sensitivity (r=0.748, P<0.05). All other mitochondrial enzyme activities were unchanged. No changes in mitochondrial function in liver were observed. Mitochondrial H₂O₂ and O₂·⁻ emission was measured spectrofluorometrically, and H₂O₂ was increased in SSM, IFM, and liver mitochondria (∼2.3-, ∼2.5-, and ∼2.3-fold, respectively, all P<0.05). We conclude that an impairment in skeletal muscle mitochondrial PDC activity and pyruvate oxidation capacity arises in the postoperative phase along with increased ROS emission, suggesting a link between mitochondrial function and development of acute postoperative insulin resistance.

Single-dose carbohydrate treatment in the immediate preoperative phase diminishes development of postoperative peripheral insulin resistance

BACKGROUND & AIMS

Preoperative oral carbohydrate (CHO) treatment is known to reduce postoperative insulin resistance, but the necessity of a preoperative evening dose is uncertain. We investigated the effect of single-dose CHO treatment two hours before surgery on postoperative insulin sensitivity.

METHODS

Thirty two pigs (∼ 30 kg) were randomized to 4 groups (n = 8) followed by D-[6,6-(2)H2] glucose infusion and hyperinsulinemic-euglycemic step clamping. Two groups received a morning drink of 25 g carbohydrate (CHO/surgery and CHO/control). Animals in the other two groups were fasted overnight (fasting/surgery and fasting/control). Counter-regulatory hormones, free fatty acids (FFA) and liver and muscle glycogen content were measured serially.

RESULTS

Glucose infusion rates needed to maintain euglycemia were higher after CHO/surgery than fasting/surgery during low (8.54 ± 0.82 vs. 6.15 ± 0.27 mg/kg/min, P < 0.05), medium (17.26 ± 1.08 vs. 14.02 ± 0.56 mg/kg/min, P < 0.02) and high insulin clamping (19.83 ± 0.95 vs. 17.16 ± 0.58 mg/kg/min, P < 0.05). The control groups exhibited identical insulin sensitivity. Compared to their respective controls, insulin-stimulated whole-body glucose disposal was significantly reduced after fasting/surgery (-41%, P < 0.001), but not after CHO/surgery (-16%, P = 0.180). CHO reduced FFA perioperatively (P < 0.05) and during the clamp procedures (P < 0.02), but did not affect hepatic insulin sensitivity, liver and muscle glycogen content or counter-regulatory hormone profiles. A strong negative correlation between peripheral insulin sensitivity and mean cortisol levels was seen in fasted (R = -0.692, P = 0.003), but not in CHO loaded pigs.

CONCLUSIONS

Single-dose preoperative CHO treatment is sufficient to reduce postoperative insulin resistance, possibly due to the antilipolytic effects and antagonist properties of preoperative hyperinsulinemia on the suppressant actions of cortisol on carbohydrate oxidation.

Porcine somatotropin alters insulin response in growing pigs by reducing insulin sensitivity rather than changing responsiveness

Exogenous porcine somatotropin (pST) treatment consistently improves growth performance and reduces fat deposition in pigs, and it is hypothesized that one component of the mechanism is through altering the sensitivity and/or responsiveness to insulin. Therefore, a study was conducted to investigate the effect of pST treatment on whole-body glucose metabolism in response to varying doses of insulin. Eight barrows were surgically prepared with indwelling catheters and randomly assigned to one of two treatment groups (0 or 120 μg pST/kg BW · d) for 13 d. Whole-body glucose kinetics were measured during infusion of [6-(3)H]-glucose under basal conditions and during hyperinsulinemic-euglycemic clamps at various insulin infusion rates (7, 28, and 140, and 14, 70, and 280 ng insulin/kg BW · min) and alterations in the dose-response parameters were calculated with nonlinear regression. Treatment with pST increased basal plasma concentrations of glucose (36%; P = 0.005), insulin (276%; P = 0.001), and NEFAs (177%; P = 0.01) and decreased the rate of glucose disappearance (-59%; P = 0.001). The responsiveness (maximum response) for steady state glucose infusion rate to maintain glycemia was not altered by pST (112 vs 106 μmol/min · kg; P = 0.78), whereas the sensitivity (effective dose at 50% of maximum response) was increased almost 7-fold (1.3 vs 8.7 ng/mL; P = 0.027). Similar responses were observed for rate of glucose disappearance and insulin-dependent glucose utilization. Therefore, pST-induced insulin resistance with regard to whole-body glucose uptake is due to a reduced sensitivity to insulin, rather than a change in responsiveness.