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OBJECTIVE—Insulin resistance, the underlying pathophysiological mechanism of the metabolic syndrome, can not only predict type 2 diabetes development but also cardiovascular disease. Thus, precise insulin resistance measurement in individuals at risk for metabolic diseases would support clinical risk stratification. However, the gold standard for measuring insulin resistance, the hyperinsulinemic clamp test, is too labor intensive to be performed in large clinical studies/settings. RESEARCH DESIGN AND METHODS—Using plasma glucose and C-peptide concentrations from oral glucose tolerance tests (OGTTs), we developed the novel “clamp-like index” (CLIX) for insulin sensitivity calculation and compared CLIX to clamp glucose infusion rates (GIR) (100–120 min). We evaluated CLIX in 89 nondiabetic subjects (58 female and 31 male, aged 45 ± 1 years, BMI 27.5 ± 0.8 kg/m2) who underwent frequently sampled 3-h 75-g OGTTs and 2-h hyperinsulinemic-isoglycemic clamp (40 mU/min per m2) tests. RESULTS—CLIX, calculated as serum creatinine (×0.85 if male)/(mean AUCglucose × mean AUCC-peptide) × 6,600, was highly correlated (r = 0.670, P < 10−12) with and comparable to clamp GIRs100–120 min. In subgroup analyses, GIRs100–120 min were lower (P < 0.005) in type 2 diabetic offspring (6.2 ± 0.7 mg · min−1 · kg−1) than in sex-, age-, and BMI-matched subjects without a family history of type 2 diabetes (8.6 ± 0.5 mg · min−1 · kg−1), which was also reflected by CLIX (insulin-resistant offspring 6.4 ± 0.6 vs. those without a family history of type 2 diabetes 9.0 ± 0.5; P < 0.002). When compared with normal-weight subjects (GIR 8.8 ± 0.4 mg · min−1 · kg−1; CLIX 9.0 ± 0.5), both GIRs100–120 min and CLIX of obese (5.2 ± 0.9 mg · min −1 · kg−1; 5.7 ± 0.9) and morbidly obese (2.4 ± 0.4 mg · min −1 · kg−1; 3.3 ± 0.5) humans were lower (each P < 0.02). CONCLUSIONS—CLIX, a novel index obtained from plasma OGTT glucose and C-peptide levels and serum creatinine, without inclusion of anthropometrical measures to calculate insulin sensitivity in nondiabetic humans, highly correlates with clamp GIRs and reveals even slight insulin sensitivity alterations over a broad BMI range and is as sensitive as the hyperinsulinemic clamp test.

Roux-en-Y-Gastric-Bypass (RYGB) reduces overall and diabetes-specific mortality by 40% and over 90%. This study aims to gain insight into the underlying mechanisms of this effect. We evaluated time-courses of glucose, insulin, C-peptide, and the incretin glucagon like peptide-1 (GLP-1) following an oral glucose load. Insulin-sensitivity was measured by a hyperinsulinemic-isoglycemic-clamp-test; glucose-turnover was determined using D-[6,6-(2)H(2)] glucose. Examinations were performed in six nondiabetic patients with excess weight before (PRE: BMI: 49.3 +/- 3.2 kg/m(2)) and 7 months after RYGB (POST: BMI: 36.7 +/- 2.9 kg/m(2)), in a lean (CON: BMI: 22.6 +/- 0.6 kg/m(2)) and an obese control group (CONob) without history of gastrointestinal surgery (BMI: 34.7 +/- 1.2 kg/m(2)). RYGB reduced fasting plasma concentrations of insulin and C-peptide (P < 0.01, respectively) whereas fasting glucose concentrations remained unchanged. After RYGB increase of C-peptide concentration following glucose ingestion was significantly higher compared to all other groups (dynamic-area under the curve (Dyn-AUC): 0-90 min: POST: 984 +/- 115 ng.min/ml, PRE: 590 +/- 67 ng.min/ml, CONob: 440 +/- 44 ng.min/ml, CON: 279 +/- 22 ng.min/ml, P < 0.01 respectively). Early postprandial increase of glucose concentration was however not affected. GLP-1 concentrations following glucose ingestion were sixfold higher after RYBG than before (P = 0.01). Insulin-stimulated glucose uptake tended to increase postoperatively (M-value: PRE: 1.8 +/- 0.5, POST: 3.0 +/- 0.3, not significant (n.s.)). Endogenous glucose production (EGP) was unaffected by RYGB. Hepatic insulin resistance index improved after RYGB and was then comparable to both control groups (PRE: 29.2 +/- 4.3, POST: 12.6 +/- 1.1, P < 0.01). RYGB results in hyper-secretion of insulin and C-peptide, whereas improvements of insulin resistance are minor and seem to occur rather in the liver and the adipose tissue than in the skeletal muscle.

OBJECTIVE So far it is unclear whether chronic peripheral hyperinsulinemia per se might contribute to ectopic lipid accumulation and consequently insulin resistance. We investigated the effects of systemic instead of portal insulin release in type 1 diabetic patients after successful pancreas-kidney transplantation (PKT) with systemic venous drainage on the intracellular lipid content in liver and soleus muscle, endogenous glucose production (EGP), and insulin sensitivity. RESEARCH DESIGN AND METHODS In nine PKT patients and nine matching nondiabetic control subjects, intrahepatocellular lipids (IHCLs) and intramyocellular lipids (IMCLs) were measured using 1H nuclear magnetic resonance spectroscopy. Fasting EGP was measured using d-[6,6-2H2]glucose tracer dilution. A 3-h 75-g oral glucose tolerance test (OGTT) allowed us to assess kinetics of glucose, free fatty acids, insulin, and C-peptide concentrations in plasma and to calculate the clamp-like index (CLIX) for insulin sensitivity and the hepatic insulin resistance (HIR) index. RESULTS The PKT patients displayed approximately twofold increased fasting insulin (20 ± 6 vs. 9 ± 3 μU/ml; P < 0.0002) compared with that in nondiabetic control subjects and ∼10% increased fasting glucose (P < 0.02) concentrations, but during the OGTT areas under the concentration curves of C-peptide and insulin were similar. IHCL (PKT, 2.9 ± 2.5%; nondiabetic control subjects, 4.4 ± 6.6%), IMCL (PKT, 1.0 ± 0.4%; nondiabetic control subjects, 1.0 ± 0.5%), CLIX (PKT, 8 ± 2; nondiabetic control subjects, 7 ± 3), HIR (PKT, 25.6 ± 13.2; nondiabetic control subjects, 35.6 ± 20 [mg · min−1 · kg−1] × [μU/ml]), and EGP (PKT, 1.6 ± 0.2; nondiabetic control subjects, 1.7 ± 0.2 mg · min−1 · kg−1) were comparable between PKT patients and nondiabetic control subjects. IHCL was negatively correlated with CLIX in all participants (r = −0.55; P < 0.04). CONCLUSIONS Despite fasting peripheral hyperinsulinemia because of systemic venous drainage, type 1 diabetic patients after PKT show similar IHCL, IMCL, insulin sensitivity, and fasting EGP in comparison with nondiabetic control subjects. These results suggest that systemic hyperinsulinemia per se does not cause ectopic lipid accumulation in liver and skeletal muscle.