Validation of simple indexes to assess insulin sensitivity during pregnancy in Wistar and Sprague-Dawley rats

Insulin resistance plays a role in the pathogenesis of diabetes, including gestational diabetes. The glucose clamp is considered the gold standard for determining in vivo insulin sensitivity, both in human and in animal models. However, the clamp is laborious, time consuming and, in animals, requires anesthesia and collection of multiple blood samples. In human studies, a number of simple indexes, derived from fasting glucose and insulin levels, have been obtained and validated against the glucose clamp. However, these indexes have not been validated in rats and their accuracy in predicting altered insulin sensitivity remains to be established. In the present study, we have evaluated whether indirect estimates based on fasting glucose and insulin levels are valid predictors of insulin sensitivity in nonpregnant and 20-day-pregnant Wistar and Sprague-Dawley rats. We have analyzed the homeostasis model assessment of insulin resistance (HOMA-IR), the quantitative insulin sensitivity check index (QUICKI), and the fasting glucose-to-insulin ratio (FGIR) by comparing them with the insulin sensitivity (SI(Clamp)) values obtained during the hyperinsulinemic-isoglycemic clamp. We have performed a calibration analysis to evaluate the ability of these indexes to accurately predict insulin sensitivity as determined by the reference glucose clamp. Finally, to assess the reliability of these indexes for the identification of animals with impaired insulin sensitivity, performance of the indexes was analyzed by receiver operating characteristic (ROC) curves in Wistar and Sprague-Dawley rats. We found that HOMA-IR, QUICKI, and FGIR correlated significantly with SI(Clamp), exhibited good sensitivity and specificity, accurately predicted SI(Clamp), and yielded lower insulin sensitivity in pregnant than in nonpregnant rats. Together, our data demonstrate that these indexes provide an easy and accurate measure of insulin sensitivity during pregnancy in the rat.     

Limited predictive ability of surrogate indices of insulin sensitivity/resistance in Asian-Indian men

Insulin resistance is highly prevalent in Asian Indians and contributes to worldwide public health problems, including diabetes and related disorders. Surrogate measurements of insulin sensitivity/resistance are used frequently to study Asian Indians, but these are not formally validated in this population. In this study, we compared the ability of simple surrogate indices to accurately predict insulin sensitivity as determined by the reference glucose clamp method. In this cross-sectional study of Asian-Indian men (n = 70), we used a calibration model to assess the ability of simple surrogate indices for insulin sensitivity [quantitative insulin sensitivity check index (QUICKI), homeostasis model assessment (HOMA2-IR), fasting insulin-to-glucose ratio (FIGR), and fasting insulin (FI)] to predict an insulin sensitivity index derived from the reference glucose clamp method (SI(Clamp)). Predictive accuracy was assessed by both root mean squared error (RMSE) of prediction as well as leave-one-out cross-validation-type RMSE of prediction (CVPE). QUICKI, FIGR, and FI, but not HOMA2-IR, had modest linear correlations with SI(Clamp) (QUICKI: r = 0.36; FIGR: r = -0.36; FI: r = -0.27; P < 0.05). No significant differences were noted among CVPE or RMSE from any of the surrogate indices when compared with QUICKI. Surrogate measurements of insulin sensitivity/resistance such as QUICKI, FIGR, and FI are easily obtainable in large clinical studies, but these may only be useful as secondary outcome measurements in assessing insulin sensitivity/resistance in clinical studies of Asian Indians.     

Simple fasting methods to assess insulin sensitivity in childhood

The 'gold standard' techniques used to measure insulin sensitivity in children are the hyperinsulinaemic-euglycaemic clamp and Bergman's minimal model. Although precise, these techniques are complex, invasive and time consuming. Alternative indirect measures of insulin sensitivity have been developed that utilize fasting glucose and insulin data in algorithms or computer programs. These methods include homeostatic model assessment (HOMA), the quantitative insulin sensitivity check index (QUICKI) and the glucose to insulin ratio (G:I). Each of these three fasting techniques has been developed and validated in adults, with little or no validation in children. Increasingly, HOMA and QUICKI are being used in childhood studies to assess insulin sensitivity. In a group of 79 pre-pubertal children, we found that the correlation between the minimal model and RHOMA (r = -0.4) was no better than that between the minimal model and fasting insulin (r = 0.4), with an even weaker correlation between the minimal model and QUICKI (r = 0.2). In addition, neither HOMA nor QUICKI were able to detect a reduction in insulin sensitivity with obesity or during growth hormone therapy, unlike the minimal model. In children with normal glucose levels, neither HOMA nor QUICKI was superior to fasting insulin. Validation of the derivation formulae for these methods in children is needed before they are more widely used. The potential benefits of these simple fasting techniques is that they are useful in large field studies. However, if the study groups are small or longitudinal changes in insulin sensitivity are sought, more precise techniques such as the clamp or minimal model should be used.     

Comparison between surrogate indexes of insulin sensitivity and resistance and hyperinsulinemic euglycemic clamp estimates in mice

Insulin resistance contributes to the pathophysiology of diabetes, obesity, and their cardiovascular complications. Mouse models of these human diseases are useful for gaining insight into pathophysiological mechanisms. The reference standard for measuring insulin sensitivity in both humans and animals is the euglycemic glucose clamp. Many studies have compared surrogate indexes of insulin sensitivity and resistance with glucose clamp estimates in humans. However, regulation of metabolic physiology in humans and rodents differs and comparisons between surrogate indexes and the glucose clamp have not been directly evaluated in rodents previously. Therefore, in the present study, we compared glucose clamp-derived measures of insulin sensitivity (GIR and SI(Clamp)) with surrogate indexes, including quantitative insulin-sensitivity check index (QUICKI), homeostasis model assessment (HOMA), 1/HOMA, log(HOMA), and 1/fasting insulin, using data from 87 mice with a wide range of insulin sensitivities. We evaluated simple linear correlations and performed calibration model analyses to evaluate the predictive accuracy of each surrogate. All surrogate indexes tested were modestly correlated with both GIR and SI(Clamp). However, a stronger correlation between body weight per se and both GIR and SI(Clamp) was noted. Calibration analyses of surrogate indexes adjusted for body weight demonstrated improved predictive accuracy for GIR [e.g., R = 0.68, for QUICKI and log(HOMA)]. We conclude that linear correlations of surrogate indexes with clamp data and predictive accuracy of surrogate indexes in mice are not as substantial as in humans. This may reflect intrinsic differences between human and rodent physiology as well as increased technical difficulties in performing glucose clamps in mice.     

Effects of growth hormone therapy on glucose metabolism and insulin sensitivity indices in prepubertal children with Prader-Willi syndrome

In Prader-Willi syndrome (PWS) growth hormone therapy (GHT) improves height, body composition, agility and muscular strength. In such patients it is necessary to consider the potential diabetogenic effect of GHT, since they tend to develop type 2 diabetes, particularly after the pubertal age. The aim of our study was to investigate the effects of GHT on glucose and insulin homeostasis in PWS children. An oral glucose tolerance test (OGTT) was performed in 24 prepubertal PWS children (15 male, 9 female, age: 5.8 +/- 2.8 years), 16 were obese (group A) and 8 had normal weight (group B), before and after 2.7 +/- 1.3 years GHT (0.22 +/- 0.03 mg/kg/week) and, only at baseline, in 35 prepubertal children with simple obesity (19 male, 16 female) (group C). Fasting glucose and insulin, glucose tolerance, insulin sensitivity index (ISI), homeostasis model assessment of insulin resistance (HOMA-IR), quick insulin check index (QUICKI), area under the curves (AUC) of glucose and insulin were estimated. At the start of GHT, all PWS children were normoglycaemic and normotolerant but two developed impaired glucose tolerance after 2.2 and 1.9 years of therapy, respectively. At baseline, group A showed lower fasting insulin levels, HOMA-IR and AUC of insulin, higher ISI, QUICKI and AUC of glucose than group C. Comparing groups A and B, AUC of insulin was higher and ISI lower in group A. During GHT, a significant increase of fasting insulin and glucose, a worsening of insulin resistance (HOMA-IR) and insulin sensitivity (QUICKI) was found only in group A while ISI did not change. The AUC of glucose decreased in both groups instead AUC of insulin did not change. BMI-SDS decreased in group A and increased in group B. The increased insulin resistance and decreased insulin sensitivity in obese PWS patients, as well as the occurrence of impaired glucose tolerance during GHT, suggest that a close monitoring of glucose and insulin homeostasis is mandatory, especially in treated obese PWS children.     

Clamp techniques in paediatrics: what have we learned?

The marked increase in conditions associated with insulin resistance in youth, including obesity, polycystic ovary syndrome, type 2 diabetes mellitus etc., has prompted the need to assess insulin sensitivity in this age group. Even though insulin resistance plays an important role in disorders of glucose metabolism and other pathological conditions, both insulin sensitivity and insulin secretion should be determined for a comprehensive evaluation of glucose homeostasis disorders. Insulin sensitivity and secretion are intricately coupled with a delicate feedback mechanism governing their relationship. This article will delineate our paediatric experience with the clamp technique, the hyperinsulinaemic-euglycaemic clamp in assessing in vivo insulin sensitivity, and the hyperglycaemic clamp in assessing insulin secretion.     

Assessment of insulin resistance in vivo: application to the study of type 2 diabetes.

Besides insulin secretion, insulin sensitivity plays a key role in the feedback glucose-insulin closed loop. It can be altered in numerous physiological, pathological and pharmacological conditions. It can be estimated in vivo using methods that open the feedback loop (insulin suppression test, glucose clamp) or that analyze the closed loop by employing mathematical models of glucose kinetics. The most popular method is the euglycemic hyperinsulinemic glucose clamp. This test should be ideally coupled with a priming-constant infusion of a glucose tracer together with indirect calorimetry. This combination allows to study the glucose kinetics (Ra and Rd, and thus endogenous-mainly hepatic-glucose production) and its metabolism (oxidation or storage as glycogen), respectively. One alternative approach is the frequently sampled intravenous glucose tolerance test where the dynamic changes in plasma insulin and glucose levels are analyzed using the so-called 'minimal model' method. Noninsulin-dependent or type 2 diabetes is characterized by a significant defect in both insulin secretion and action. The insulin resistance is located at the liver site (increased glucose production) and at the peripheral tissues (decreased oxidation and, even more, defective storage of glucose in the muscles). This insulin resistance, which predominates at the postreceptor level, seems to be genetically determined but is worsened by weight excess and by hyperglycemia itself. This contributes to a vicious circle which aggravates progressively the severity of the disease.     

For debate: Starling's curve of the pancreas--overuse of a concept?

It is commonly accepted that insulin secretion follows the pattern of an inverted U, also termed 'Starling's curve of the pancreas' during the natural history of hyperglycemia in glucose intolerance and type 2 diabetes. This concept is based on the cross-sectional observation that insulin concentrations initially increase when insulin sensitivity declines (as a consequence of obesity, for example) and decrease when glucose tolerance deteriorates (impaired glucose tolerance or overt type 2 diabetes). The initial increase in insulin concentrations has been viewed as 'hypersecretion' of insulin, thought to indicate that beta cell dysfunction is not etiological but secondary in nature. However, this view is oblivious to the now well-established fact that assessment of insulin secretion must account for individual insulin sensitivity. Here, we revisit the concept of Starling's curve of the pancreas based on first-phase C-peptide concentrations (hyperglycemic clamp) from subjects with normal glucose tolerance (n=66), impaired glucose tolerance (n=19) and mild type 2 diabetes (n=9). In absolute terms, first-phase C-peptide concentrations plotted against increasing fasting glucose concentrations indeed followed an inverted U. However, adjusted for direct and indirect measures of insulin sensitivity (insulin sensitivity index from the hyperglycemic clamp, body mass index, age and sex), first-phase C-peptide concentrations of the same individuals tended to decrease steadily. In conclusion, while the Starling curve exists for insulin concentrations, and perhaps also for insulin secretion, it does not hold for beta-cell function if that term were to imply appropriateness of insulin secretion (based on a formal test of glucose-stimulated insulin secretion) for the degree of insulin resistance, as it should.     

Hyperglycemia-induced insulin resistance in diabetic dyslipidemic Yucatan swine

Hyperglycemia, dyslipidemia, and associated insulin resistance are hallmarks of diabetes mellitus. Purposes of the study reported here were to develop practical methods for assessment of in vivo insulin sensitivity and determine contributions of hyperglycemia and dyslipidemia to insulin resistance in the porcine model of alloxan-induced diabetes mellitus and dyslipidemia. Male Yucatan swine groups were treated for 20 weeks: control (C), high fat-fed (2% cholesterol) hyperlipidemic (H), alloxan-induced diabetic normolipidemic (D), diabetic high fat-fed (diabetic dyslipidemic, DD), and diabetic dyslipidemic treated with the lipid-lowering agent atorvastatin (DDA). Plasma cholesterol concentration increased sixfold in animals of groups H, DD, and DDA, whereas triglyceride concentration increased threefold in animals of group DD only. Diabetics had decreases in glucose tolerance and pancreatic immunostaining for insulin. Use of the gold standard hyperinsulinemic euglycemic clamp procedure indicated that maximal insulin-stimulated glucose uptake was similar to that in humans, but this method was not practical for use in pigs. Instead, a more convenient and valid insulin sensitivity test involving suppression of insulin secretion with somatostatin and a single insulin injection was used. Insulin sensitivity was greatly impaired by anesthesia with isoflurane, but was not affected by use of the anxiolytic agent diazepam. Insulin sensitivity decreased by 75% in diabetics (groups D, DD, DDA), compared with animals of groups C and H, and was inversely related to fasting blood glucose concentration (r = -0.72). Insulin treatment to restore blood glucose values of diabetics (> 250 mg/dl) to near control values (< 100 mg/dl) promptly restored insulin sensitivity to control values. We conclude that hyperglycemia is a major cause of insulin resistance in the porcine model of alloxan-induced diabetes mellitus and dyslipidemia.     

Insulin sensitivity and beta-cell function in healthy cats: assessment with the use of the hyperglycemic glucose clamp.

A hyperglycemic clamp (HGC) was developed for use in conscious cats. In 21 healthy, normal glucose tolerant cats glucose disposal rate (M), insulin sensitivity (ISI (HGC)), and beta-cell response (I) at arterial plasma glucose of 9 mmol.l (-1) were measured. The HGC was tolerated well and steady state glucose infusion was achieved. Compared to values reported for humans, M values for the cats were low, which appeared to relate to both a low ISI (HGC) and a low I. HGC measures correlated with fasting plasma glucose and insulin concentrations as well as with their HOMA (homeostasis model assessment) and QUICKI (quantitative insulin sensitivity check index) counterparts. Also, I and ISI (HGC) correlated with their counterparts derived from intravenous glucose tolerance tests. In conclusion, this is the first report of hyperglycemic glucose clamping in cats. The procedure (HGC) allows for measurements of glucose disposal, beta-cell response and insulin sensitivity. Compared to human data, both insulin sensitivity and insulin secretion appeared to be low in cats. This is compatible with the carnivorous nature of this species, for which insulin resistance would be advantageous during periods of restricted food availability.     

Hyperinsulinemia, insulin resistance and essential hypertension.

Glucose intolerance and noninsulin-dependent diabetes are commonly associated with hypertension. Epidemiological data suggest that this association is independent of age and obesity. Much evidence indicates that the link between diabetes and essential hypertension is hyperinsulinemia. When hypertensive patients whether obese or of normal weight are compared with matched normotensive control subjects, an increased plasma insulin response to a glucose challenge is consistently observed. Studies using insulin glucose clamp techniques in combination with tracer glucose infusion and indirect calorimetry have demonstrated that the insulin resistance in hypertensive subjects is located in muscles and restricted to glycogen synthesis. The relations between hyperinsulinemia and blood pressure do not prove that the relationship is a causal one. However, at least four mechanisms may link hyperinsulinemia with hypertension: Na+ retention, sympathetic nervous system overactivity, disturbed membrane ion transport and proliferation of vascular smooth muscle cells. Diuretics and beta-blockers may enhance insulin resistance, which is not affected by calcium antagonists, but decreased by the ACE inhibitor captopril. Weight reduction and regular physical exercise can improve insulin sensitivity and decrease blood pressure values. These nonpharmacological interventions should be more strongly recommended to diabetic and nondiabetic hypertensive patients.     

Influence of PPAR-alpha agonist fenofibrate on insulin sensitivity and selected adipose tissue-derived hormones in obese women with type 2 diabetes

PPAR-alpha agonists improve insulin sensitivity in rodent models of obesity/insulin resistance, but their effects on insulin sensitivity in humans are less clear. We measured insulin sensitivity by hyperinsulinemic-isoglycemic clamp in 10 obese females with type 2 diabetes before and after three months of treatment with PPAR-alpha agonist fenofibrate and studied the possible role of the changes in endocrine function of adipose tissue in the metabolic effects of fenofibrate. At baseline, body mass index, serum glucose, triglycerides, glycated hemoglobin and atherogenic index were significantly elevated in obese women with type 2 diabetes, while serum HDL cholesterol and adiponectin concentrations were significantly lower than in the control group (n=10). No differences were found in serum resistin levels between obese and control group. Fenofibrate treatment decreased serum triglyceride concentrations, while both blood glucose and glycated hemoglobin increased after three months of fenofibrate administration. Serum adiponectin or resistin concentrations were not significantly affected by fenofibrate treatment. All parameters of insulin sensitivity as measured by hyperinsulinemic-isoglycemic clamp were significantly lower in an obese diabetic group compared to the control group before treatment and were not affected by fenofibrate administration. We conclude that administration of PPAR-alpha agonist fenofibrate for three months did not significantly affect insulin sensitivity or resistin and adiponectin concentrations in obese subjects with type 2 diabetes mellitus. The lack of insulin-sensitizing effects of fenofibrate in humans relative to rodents could be due to a generally lower PPAR-alpha expression in human liver and muscle.     

Elevated insulin sensitivity and β-cell function during pregnancy in mothers of growth-restricted newborns

The "Barker hypothesis" suggests that low birth weight might predict future risk of developing obesity, cardiovascular disease, and type 2 diabetes. Identification of the causes of fetal growth restriction (FGR) is critical for preventive and management strategies. Some studies indicate that maternal carbohydrate metabolism might be involved in FGR development. We aimed to evaluate, in a large number of normotensive pregnant women with normal glucose tolerance, the effect of insulin sensitivity and β-cell function on unexplained fetal growth. A total of 1,814 Caucasian pregnant women with normal prepregnancy body mass index were tested with a 75-g, 2-h glucose load (24-28 gestation wk). Insulin sensitivity was evaluated with fasting (QUICKI) and dynamic index (OGIS) and β-cell function with a modified insulinogenic index as ΔAUC(insulin)/ΔAUC(glucose) and disposition index. FGR was a birth weight below the 5th percentile for gestational age. FGR developed in 99 (5.5%) pregnant women that showed significantly higher QUICKI, OGIS, insulinogenic, and disposition index with respect to women with normal-weight babies (P < 0.0001). By using multiple regression analysis in the FRG group, QUICKI and OGIS appeared as significant independent variables (P < 0.0001 and P < 0.0366, respectively). We conclude that elevated insulin sensitivity seems to be one of the factors involved in determining unexplained fetal growth retardation; its assessment, even only in the fasting state, could be useful to guide any possible monitoring and therapeutic strategies to reduce fetal complications.     

Co-administration of etomoxir and RU-486 mitigates insulin resistance in hepatic and muscular tissues of STZ-induced diabetic rats.

Insulin resistance is a condition of central importance in a cluster of clinical disorders including diabetes mellitus, hypertension, dyslipidemia, central obesity and coronary heart disease. Despite its association with numerous health problems, the mechanism responsible for the development of this phenomenon remains to be established. A novel theory has proposed that insulin resistance in diabetes stems, at least in part, from enhanced free fatty acid (FFA) oxidation and/or excessive production of glucocorticoids (GCs). Several key predictions of this premise were subjected to experimental testing using streptozotocin (STZ)-treated rats as a model for insulin-dependent diabetes mellitus and euglycemic-hyperinsulinemic clamp technique for the in vivo measurement of insulin actions. Euglycemic clamp studies with an insulin infusion index of 5 mU/kg/min were used to measure endogenous glucose production (EGP), glucose infusion rate (GIR), glucose disposal rate (GDR) and skeletal muscle glucose utilization index (GUI). Post-absorptive basal EGP and plasma levels of glucose and free fatty acids (FFA) were elevated in the STZ diabetic rats compared to their corresponding control values. In contrast, hypoinsulinemia was evident in these animals. Steady-state GIR and GDR during euglycemic-hyperinsulinemic clamp were markedly decreased in the STZ diabetic rats. Similarly, insulin-mediated suppression of EGP and plasma FFA concentration was also impaired in these animals. GUI, a measure of 2-deoxyglucose (2-DG) uptake, was increased in response to insulin in the order of white gastrocnemus (WG), red gastrocnemus (RG), extensor digitorum longus and soleus muscles. This parallels the percentage of red fibers in these muscles. Diabetes interferes with insulin's ability to increase 2-DG uptake in all of the above muscles with the exception of WG. Nullification of the associated hyperlipidemic and hypercortisolemic states of diabetes with etomoxir (hyperlipidemic) and the glucocorticoid receptor blocker RU-486 (hypercortisolemic) ameliorated the diabetes-related impairment of the in vivo insulin action. Overall these results together with those garnered from the literature support the notion that hypercortisolemia and the enhancement of FFA oxidation are involved, at least in part, in the development of hepatic and skeletal muscle insulin resistance in poorly controlled type I diabetes.     

Serum adipocyte fatty acid binding protein levels in patients with type 2 diabetes mellitus and obesity: the influence of fenofibrate treatment

Recent studies have demonstrated that adipocyte fatty acid binding proteins (FABP) may play a role in the etiopathogenesis of insulin resistance. The aim of our study was to assess serum FABP levels in obese patients with type 2 diabetes mellitus (T2DM) before and after 3 months of treatment with PPAR-alpha agonist fenofibrate (F) and to explore the relationship of FABP to biochemical parameters and measures of insulin sensitivity assessed by hyperinsulinemic-isoglycemic clamp. We measured biochemical parameters by standard laboratory methods, insulin sensitivity by hyperinsulinemic-isoglycemic clamp and serum concentrations of FABP by commercial ELISA kit in 11 obese females with T2DM before and after three months of treatment with PPAR-alpha agonist fenofibrate and in 10 lean healthy control women (C). Serum FABP levels were 2.5-fold higher in T2DM group relative to C and were not affected by fenofibrate treatment (C: 20.6+/-2.1 microg/l, T2DM before F: 55.6+/-5.7 microg/l, T2DM after F: 54.2+/-5.4 microg/l, p 0.0001 for C vs. T2DM before F). Hyperinsulinemia during the clamp significantly suppressed FABP levels in both C and T2DM group. FABP levels positively correlated with BMI, triglyceride levels, blood glucose, glycated hemoglobin, atherogenic index and insulin levels. An inverse relationship was found between FABP and HDL levels, metabolic clearance rate of glucose, M/I and MCR(glc)/I sensitivity indexes. We conclude that FABP levels are closely related to BMI, parameters of insulin sensitivity, HDL levels and measures of diabetes compensation. This combination makes FABP a valuable marker of metabolic disturbances in patients with type 2 diabetes mellitus.     

Impaired non-esterified fatty acid suppression is associated with endothelial dysfunction in insulin resistant subjects.

In a recent study, we found a significant association between insulin resistance (IR) and disturbed flow-associated (endothelial-dependent) vasodilation in first-degree relatives of subjects with type 2 diabetes. However, the mechanisms linking insulin resistance and endothelial dysfunction (ED) have not been fully elucidated. Experimental data have pointed out that non-esterified fatty acids (NEFA) have a modulating effect on NO-synthase activity, and therefore on endothelial function. The aim of our study was to evaluate whether insulin resistance associated impaired NEFA suppression is present in subjects with ED. We examined 53 first-degree relatives (FDR) of patients with type 2 diabetes (32f, 21 m, mean age 35 years). Endothelial function was measured as flow-associated vasodilation (FAD%) of the brachial artery. Insulin sensitivity was evaluated with a standard hyperinsulinemic glucose clamp (insulin infusion rate of 1 mU/kg/min). While under fasting conditions, NEFA did not differ between groups with high or low FAD (0.415+/-0.033 vs. 0.394 +/- 0.040 mmol/l; p = n. s.), reduced FAD% was significantly associated with higher non-esterified fatty acids concentrations during steady state of the glucose clamp (0.072+/-0.022 vs. 0.039+/-0.016mmol/l; p=0.04). This association was independent of insulin levels under fasting conditions and during the glucose clamp. In conclusion, our results reveal a significant association between endothelial dysfunction and impaired non-esterified fatty acid suppression in insulin resistant subjects. As insulin resistance of lipolysis is a feature of the insulin resistance syndrome, these results suggest that elevated NEFA concentrations could play a role linking endothelial dysfunction and insulin resistance in vivo.     

The euglycemic clamp in patients with thalassaemia intermedia

In order to evaluate the influence of haemosiderosis on the glucose metabolism we studied tissue sensitivity to insulin and the metabolic clearance rate (M.C.R.) of this hormone by means of euglycemic clamp technique using an artificial endocrine pancreas in 8 patients with thalassaemia intermedia and 8 control subjects. During the steady-state of euglycemic-hyperinsulinemic clamp (40 mU/m2/min) plasma insulin values were significantly lower and the insulin M.C.R. was significantly higher in thalassaemic patients compared to the controls. To achieve a comparable steady-state insulin concentration to the controls, we performed for a second time the euglycemic clamp in the thalassaemic patients increasing the insulin infusion rate to 80/mU/m2/min. The insulin M.C.R., the M index and the M/IRIs-s ratio were significantly higher in the thalassaemic patients compared to the controls. These results are indicative of an increased tissue peripheral sensitivity to insulin as well as the metabolic clearance rate of this hormone.     

CRY1 circadian gene variant interacts with carbohydrate intake for insulin resistance in two independent populations: Mediterranean and North American

Dysregulation in the circadian system induced by variants of clock genes has been associated with type 2 diabetes. Evidence for the role of cryptochromes, core components of the system, in regulating glucose homeostasis is not supported by CRY1 candidate gene association studies for diabetes and insulin resistance in human, suggesting possible dietary influences. The purpose of this study was to test for interactions between a CRY1 polymorphism, rs2287161, and carbohydrate intake on insulin resistance in two independent populations: a Mediterranean (n?=?728) and an European origin North American population (n?=?820). Linear regression interaction models were performed in two populations to test for gene–diet interactions on fasting insulin and glucose and two insulin-related traits, homeostasis model assessment of insulin resistance (HOMA-IR) and quantitative insulin sensitivity check index (QUICKI). In addition, fixed effects meta-analyses for these interactions were performed. Cohort-specific interaction analyses showed significant interactions between the CRY1 variant and dietary carbohydrates for insulin resistance in both populations (p?<?0.05). Findings from the meta-analyses of carbohydrate–single nucleotide polymorphism interactions indicated that an increase in carbohydrate intake (% of energy intake) was associated with a significant increase in HOMA-IR (p?=?0.011), fasting insulin (p?=?0.007) and a decrease in QUICKI (p?=?0.028), only among individuals homozygous for the minor C allele. This novel finding supports the link between the circadian system and glucose metabolism and suggests the importance this CRY1 locus in developing personalized nutrition programs aimed at reducing insulin resistance and diabetes risk.     

Estimations of muscle interstitial insulin, glucose, and lactate in type 2 diabetic subjects

Previous measurement of insulin in human muscle has shown that interstitial muscle insulin and glucose concentrations are approximately 30-50% lower than in plasma during hyperinsulinemia in normal subjects. The aims of this study were to measure interstitial muscle insulin and glucose in patients with type 2 diabetes to evaluate whether transcapillary transport is part of the peripheral insulin resistance. Ten patients with type 2 diabetes and ten healthy controls matched for sex, age, and body mass index were investigated. Plasma and interstitial insulin, glucose, and lactate (measured by intramuscular in situ-calibrated microdialysis) in the medial quadriceps femoris muscle were analyzed during a hyperinsulinemic euglycemic clamp. Blood flow in the contralateral calf was measured by vein plethysmography. At steady-state clamping, at 60-120 min, the interstitial insulin concentration was significantly lower than arterial insulin in both groups (409 +/- 86 vs. 1,071 +/- 99 pmol/l, P < 0.05, in controls and 584 +/- 165 vs. 1, 253 +/- 82 pmol/l, P < 0.05, in diabetic subjects, respectively). Interstitial insulin concentrations did not differ significantly between diabetic subjects and controls. Leg blood flow was significantly higher in controls (8.1 +/- 1.2 vs. 4.4 +/- 0.7 ml. 100 g(-1).min(-1) in diabetics, P < 0.05). Calculated glucose uptake was less in diabetic patients compared with controls (7.0 +/- 1.2 vs. 10.8 +/- 1.2 micromol. 100 g(-1).min(-1), P < 0.05, respectively). Arterial and interstitial lactate concentrations were both higher in the control group (1.7 +/- 0.1 vs. 1.2 +/- 0.1, P < 0. 01, and 1.8 +/- 0.1 vs. 1.2 +/- 0.2 mmol/l, P < 0.05, in controls and diabetics, respectively). We conclude that, during hyperinsulinemia, muscle interstitial insulin and glucose concentrations did not differ between patients with type 2 diabetes and healthy controls despite a significantly lower leg blood flow in diabetic subjects. It is suggested that decreased glucose uptake in type 2 diabetes is caused by insulin resistance at the cellular level rather than by a deficient access of insulin and glucose surrounding the muscle cell.     

Fatness, fitness, and insulin sensitivity among 7- to 9-year-old children

Objective: The purpose of this study was to examine the relationships among fatness and aerobic fitness on indices of insulin resistance and sensitivity in children. Research Design and Methods: A total of 375 children (193 girls and 182 boys) 7 to 9 years of age were categorized by weight as normal‐weight, overweight, or obese and by aerobic fitness based on a submaximal physical working capacity test (PWC). Fasting blood glucose (GLU) and insulin (INS) were used to calculate various indices of insulin sensitivity (GLU/INS), the homeostasis model assessment (HOMA), and the quantitative insulin sensitivity check index (QUICKI). Surrogate measures of pancreatic β cell function included the insulinogenic index (INS/GLU) and the HOMA estimate of pancreatic β‐cell function (HOMA %B). Results: Insulin sensitivity and secretion variables were significantly different between the normal‐weight children and the overweight and obese subjects. Fasting insulin (FI), HOMA, QUICKI, and INS/GLU were significantly different between the overweight and obese subjects. Likewise, the high fitness group possessed a better insulin sensitivity profile. In general, the normal‐weight–high fit group possessed the best insulin sensitivity profile and the obese‐unfit group possessed the worst insulin sensitivity profile. Several significant differences existed among the six fat‐fit groups. Of particular note are the differences within BMI groups by fitness level and the comparison of values between the normal‐weight–unfit subjects and the overweight and obese subjects with high fitness. Conclusions: The results indicate that aerobic fitness attenuates the difference in insulin sensitivity within BMI categories, thus emphasizing the role of fitness even among overweight and obese children.