Insulin sensitivity assessment in uncomplicated obese women: comparison of indices from fasting and oral glucose load with euglycemic hyperinsulinemic clamp

Myths and methodologies: Assessing glycaemic control and associated regulatory mechanisms in human physiology research

Accurate measurements of glycaemic control and the underpinning regulatory mechanisms are vital in human physiology research. Glycaemic control is the maintenance of blood glucose concentrations within optimal levels and is governed by physiological variables including insulin sensitivity, glucose tolerance and β-cell function. These can be measured with a plethora of methods, all with their own benefits and limitations. Deciding on the best method to use is challenging and depends on the specific research question(s). This review therefore discusses the theory and procedure, validity and reliability and any special considerations of a range common methods used to measure glycaemic control, insulin sensitivity, glucose tolerance and β-cell function. Methods reviewed include glycosylated haemoglobin, continuous glucose monitors, the oral glucose tolerance test, mixed meal tolerance test, hyperinsulinaemic euglycaemic clamp, hyperglycaemic clamp, intravenous glucose tolerance test and indices derived from both fasting concentrations and the oral glucose tolerance test. This review aims to help direct understanding, assessment and decisions regarding which method to use based on specific physiology-related research questions.

Shift of Glucose Peak Time During Oral Glucose Tolerance Test is Associated with Changes in Insulin Secretion and Insulin Sensitivity After Therapy with Antidiabetic Drugs in Patients with Type 2 Diabetes

INTRODUCTION

Delay in peak blood glucose during an oral glucose tolerance test (OGTT) predicts declining β-cell function and poor ability to regulate glucose metabolism. Glucose peak time has not been used as a comparative indicator of the improvement in islet function after treatment with exenatide, insulin, or oral antidiabetic drugs (OADs). We evaluated the efficacy of three types of antidiabetic drugs on the basis of blood glucose peak time in patients with non-newly diagnosed type 2 diabetes.

METHODS

The data from 100 patients with diabetes who completed two OGTTs within 6 months were collected. Thirty-seven of them with type 2 diabetes were treated with Humalog Mix25, 28 patients with OADs (metformin, acarbose, and gliclazide), and 35 patients with exenatide.

RESULTS

Glycated hemoglobin improved in all three groups after treatment (P < 0.05). Subcutaneous adipose tissue (P < 0.01) and visceral adipose tissue (P < 0.0001) significantly decreased in the exenatide group. The insulinogenic index (IGI) (P = 0.01) and IGI × oral glucose insulin sensitivity (OGIS) (P = 0.01) improved in the exenatide group only. Homeostatic assessment of β-cell function (HOMA-β) and OGIS were greater in the exenatide and OAD groups than in the Humalog Mix25 group (all P < 0.05). A shift to an earlier peak was observed in 57.1%, 35.7%, and 27.0% of patients in the exenatide, OAD, and Humalog Mix25 groups, respectively (P = 0.029). OGIS (odds ratio [OR] 0.54, 95% confidence interval [CI] 0.33-0.89, P = 0.026) and IGI × OGIS (OR 1.72, 95% CI 0.44-6.68, P = 0.012) were independently related to shifts in glucose peak time.

CONCLUSION

Exenatide, Humalog Mix25, and OADs improved glycemic metabolism. However, exenatide exhibited superior efficacy in shifting blood glucose peak time to an earlier point, while it improved insulin secretion and insulin sensitivity. Hence, the shift of glucose peak time may be considered an indicator for the evaluation of the effect of hypoglycemic drugs.

The effects of diet and lifestyle interventions on insulin resistance in patients with nonalcoholic fatty liver disease: a systematic review

Nonalcoholic fatty liver disease (NAFLD) results from excessive fat accumulation in the liver in the absence of excessive alcohol consumption. Insulin resistance (IR) is proposed to be an underlying pathogenic factor in the development and progression of disease. There are currently no proven pharmacotherapies and weight loss is the only prescribed treatment despite a lack of evidence to support a specific diet or lifestyle therapy. The aim of this review is to evaluate the efficacy of dietary lifestyle interventions on IR measured by Homeostasis model assessment in patients with NAFLD. A systematic electronic search of Medline, Scopus, The Cochrane Library, CINAHL and PubMed databases (1999-2015) was performed by two independent reviewers. Randomized control trials evaluating the efficacy of diet and lifestyle interventions on IR in adults diagnosed with NAFLD were included. A total of 6441 articles were identified; eight randomized control trials fulfilled the inclusion criteria. Three studies involved dietary interventions and five incorporated diet and exercise. The majority of intervention groups resulted in significant reductions in IR, with no significant changes observed in the control groups. Lifestyle interventions compared with controls reduced IR measured by homeostasis model assessment. All diet and diet and lifestyle intervention trials were efficient in reducing IR in participants with NAFLD. A lack of literature and variation across interventions warrants the need for extensive research to establish firm dietary lifestyle recommendations.

Variable reliability of surrogate measures of insulin sensitivity after Roux-en-Y gastric bypass

Roux-en-Y gastric bypass (RYGB) induces weight loss and improves insulin sensitivity when evaluated by the hyperinsulinemic-euglycemic clamp (HEC). Surrogate indices of insulin sensitivity calculated from insulin and glucose concentrations at fasting or after an oral glucose tolerance test (OGTT) are frequently used, but have not been validated after RYGB. Our aim was to evaluate whether surrogate indices reliably estimate changes in insulin sensitivity after RYGB. Four fasting surrogates (inverse-HOMA-IR, HOMA2-%S, QUICKI, revised-QUICKI) and three OGTT-derived surrogates (Matsuda, Gutt, OGIS) were compared with HEC-estimated peripheral insulin sensitivity (R_d or R_d/I, depending on how the index was originally validated) and the tracer-determined hepatic insulin sensitivity index (HISI) in patients with preoperative type 2 diabetes (n = 10) and normal glucose tolerance (n = 10) 1 wk, 3 mo, and 1 yr postoperatively. Post-RYGB changes in inverse-HOMA-IR and HOMA2-%S did not correlate with changes in R_d at any visit, but were comparable to changes in HISI at 1 wk. Changes in QUICKI and revised-QUICKI correlated with R_d/I after surgery. Changes in the Matsuda and Gutt indices did not correlate with changes in R_d/I and R_d, respectively, whereas OGIS changes correlated with R_d changes at 1 yr post-RYGB. In conclusion, surrogate measures of insulin sensitivity may not reflect results obtained with gold standard methodology after RYGB, underscoring the importance of critical reflection when surrogate endpoints are used. Fasting surrogate indices may be particularly affected by post-RYGB changes in insulin clearance, whereas the validity of OGTT-derived surrogates may be compromised by surgical rearrangements of the gut.

Insulin resistance index (HOMA-IR) in the differentiation of patients with non-alcoholic fatty liver disease and healthy individuals

CONTEXT

Due to its good correlation to glycemic clamp, HOMA-IR has been widely utilized as insulin resistance index in clinical and epidemiological studies involving non-alcoholic fatty liver disease carriers. However, values used for this parameter have shown large variability.

OBJECTIVE

To identify the HOMA-IR cut value that best distinguishes non-diabetic non-alcoholic fatty liver disease patients from a control group.

METHODS

One hundred sixteen non-alcoholic fatty liver disease patients were studied, diagnosed by clinical, biochemical, and liver image or biopsy criteria, and 88 healthy individuals, without any liver disease and testing for oral glucose tolerance within normality. These groups did not differ in age and gender. All were submitted to oral glucose tolerance test and blood samples were collected for glucose and insulin measurements by immunofluorometric method. HOMA-IR was calculated according to the formula: fasting insulin (microU/L) x fasting glucose (nmol/L)/22.5.

RESULTS

NAFLD patients showed higher insulin, glycemia, and HOMA-IR values than control group, even when excluding glucose intolerant and diabetes mellitus patients by their glycemic curves. HOMA-IR 75th percentile for control group was 1.78 and the best area under the curve index was obtained for HOMA-IR values of 2.0 [AUC= 0.840 (0.781-0.899 CI 95%), sensitivity (Se): 85%, specificity (Sp): 83%] while value 2.5 showed best specificity without important loss in sensitivity [AUC=0,831 (0.773-0.888) Se = 72%, Sp = 94%].

CONCLUSION

HOMA-IR values above or equal to 2.0 or 2.5 show enhanced diagnostic value in distinguishing non-alcoholic fatty liver disease carriers from control group individuals.

Comparison between several insulin sensitivity indices and metabolic risk factors in overweight and obese postmenopausal women: a MONET study

BACKGROUND AND AIMS

The purpose of this study was to compare the relationship of several insulin sensitivity indices with cardiometabolic risk factors in overweight and obese postmenopausal women.

METHODS AND RESULTS

This was a cross-sectional study involving 137 overweight and obese postmenopausal women (age: 57.7+/-4.8 yrs; body mass index: 32.4+/-4.6 kg/m(2); body fat: 38.6+/-9.2 kg). Insulin sensitivity was determined by the euglycaemic-hyperinsulinemic (EH) clamp technique as well as by oral glucose tolerance test (OGTT) derived indices (Stumvoll, Matsuda and SI(is)) and fasting surrogate indices (HOMA, QUICKI). Cardiometabolic risk factors included: body composition and visceral fat that were measured using dual energy X-ray absorptiometry and computed tomography, respectively. Peak oxygen consumption, lower body muscle strength (using weight training equipment), physical activity energy expenditure (doubly labeled water), plasma lipids and C-reactive protein were also measured. Correlations of insulin sensitivity indices with metabolic risk factors showed some similarities, however, a wide range of variations were also observed. Furthermore, our results showed that visceral fat was the primary predictor for surrogate and OGTT indices, explaining 15-28% of the variance and the triglycerides/HDL-C ratio was the primary predictor for the EH clamp indices, explaining 15-17% of the variance.

CONCLUSION

The present study indicates that the different methods of measuring and/or expressing insulin sensitivity display variations for associations with cardiometabolic risk factors. Therefore, interpretations of relationships between insulin sensitivity indices and cardiometabolic risk factors should take into account the method used to estimate and express insulin sensitivity.

Comparative evaluation of whole body and hepatic insulin resistance using indices from oral glucose tolerance test in morbidly obese subjects with nonalcoholic Fatty liver disease

Nonalcoholic Fatty Liver Disease (NAFLD) is the hepatic manifestation of metabolic syndrome and is a marker of Insulin Resistance (IR). Euglycemic-hyperinsulinemic clamp is the gold standard for measuring whole body IR (hepatic + peripheral IR). However, it is an invasive and expensive procedure. Homeostasis Model Assessment Index for Insulin Sensitivity (HOMA-IS), Quantitative Insulin Sensitivity Check Index (QUICKI) for hepatic IR and Insulin Sensitivity Index (ISI(0,120)), and Whole Body Insulin Sensitivity Index (WBISI) for whole body IR are the indices calculated after Oral Glucose Tolerance Test (OGTT). We used these indices as noninvasive methods of IR (inverse of insulin sensitivity) estimation and compared hepatic/peripheral components of whole body IR in NAFLD. Methods. 113 morbidly obese, nondiabetic subjects who underwent gastric bypass surgery and intraoperative liver biopsy were included in the study. OGTT was performed preoperatively and the indices were calculated. Subjects were divided into closely matched groups as normal, fatty liver (FL) and Non-Alcoholic Steatohepatitis (NASH) based on histology. Results. Whole body IR was significantly higher in both FL and NASH groups (NAFLD) as compared to Normal, while hepatic IR was higher only in NASH from Normal. Conclusions. FL is a manifestation of peripheral IR but not hepatic IR.

Mediterranean diet and insulin sensitivity, lipid profile and blood pressure levels, in overweight and obese people; the Attica study

BACKGROUND

We aimed to investigate if overweight and obese adults "close" to Mediterranean diet present better insulin, lipids profile and better pressure levels, compared to individuals close to a more Westernized diet.

METHODS

The ATTICA study is a population-based cohort that has randomly enrolled 3042 adult men and women, stratified by age - gender, from the greater area of Athens, during 2001-2002. Of them, in this work were have studied 1762 participants with excess body weight, meaning overweight (BMI: 25-29.9 kg/m2) and obese (BMI>30 kg/m2). 1064 were men and 698 women (20-89 years old). Adherence to Mediterranean diet was assessed through a diet-score that was based on a validated food-frequency questionnaire. Blood pressure was measured and also fasting glucose, insulin and blood lipids. Insulin sensitivity was also assessed by the homeostasis model assessment (HOMA) approach (glucose x insulin/22.5).

RESULTS

Individuals with excess bodyweight in the highest tertile of diet score, were more insulin sensitive than those in the lowest tertile (11.4% lower HOMA, p = 0.06), had 13% lower levels of total cholesterol (p = 0.001) and 3 mmHg decrease of systolic blood pressure levels (p < 0.001), when adjusted for age, sex and BMI. Multivariate analysis after taking into account several confounders demonstrated that insulin sensitivity, total cholesterol and systolic blood pressure were independently but only modestly correlated with Mediterranean diet in people with excess bodyweight.

CONCLUSION

Adherence to Mediterranean diet is modestly associated with a better insulin sensitivity, lower levels of total cholesterol and lower levels of systolic blood pressure in overweight and obese subjects. This may suggest that compared to general population, the beneficial effect of this diet in cardiovascular system of excess body weight people is limited.

Relationship between the hyperinsulinemic-euglycaemic clamp and a new simple index assessing insulin sensitivity in overweight and obese postmenopausal women

OBJECTIVE

The purpose of this study was to compare assessment of insulin sensitivity from hyperinsulinemic euglycaemic (HIEG) clamp with indexes derived from fasting and oral glucose tolerance test (OGTT).

SUBJECTS AND METHODS

Cross-sectional study with 107 sedentary non-diabetic overweight and obese postmenopausal (BMI=32.4+/-0.4 kg/m(2)) women undergoing both HIEG clamp and OGTT. Pairs of data were analyzed using Pearson correlation and Bland-Altman graphs analysis. Comparison between correlations was made using the method reported by Zar.

RESULTS

All the indexes derived from either the OGTT or surrogate indexes were highly correlated with all the clamp-derived formulas (P<0.0001). However, HOMA and QUICKI were generally less correlated than OGTT-derived indexes. Analogically to QUICKI, we calculated a new formula derived from the OGTT measurements of glucose and insulin named simple index assessing insulin sensitivity (SI(is)OGTT)=1/[log(sum glucose t(0-30-90-120)) (mmol/l)+log(sum insulin t(0-30-90-120)) (microUI/ml)]. By using this formula, we found high significant correlations (r's=0.61-0.65; P<0.0001) with the clamp results. Moreover, the correlations of SI(is)OGTT with the clamp data were higher than for other previously published indexes.

CONCLUSION

In that large group of non-diabetic overweight and obese postmenopausal women insulin sensitivity index derived from OGTT provided more accurate information than fasting based formula. We propose a new simple index for the assessment of insulin sensitivity from the OGTT data (SI(is)OGTT). The advantage of this new formula over all previously published OGTT-derived indexes of insulin sensitivity is that it is 1) easy to calculate 2) better correlated than other indexes of insulin sensitivity and 3) not affected by the way clamp results are expressed. Further studies are needed to validate SI(is)OGTT index in other populations.

The Clinical Biochemistry of Obesity—More Than Skin Deep

While obesity has a high prevalence in developed countries, the routine abnormalities seen from the clinical biochemistry laboratory that may be caused by obesity related pathology do not seem to be as common. Insulin resistance, which is often associated with obesity, is difficult to assess as formal procedures are too complex for clinical practice. Furthermore the interpretation of insulin levels is hampered by their in vivo variability, assay differences and the lack of reference intervals from an unaffected reference population. Interpretation of fasting glucose levels between 5.5 and 6.0mmol/L are also being debated however, it is useful to understand the age related changes in this parameter, which may also be due to increasing obesity in the reference population. The association of obesity and dyslipidaemia in the metabolic syndrome should focus on elevated triglycerides (>1.5mmol/L), which is associated with low HDLC and correlates with atherogenic small dense LDL. High triglycerides are also predictive of fatty liver and the common abnormality of an elevated ALT may not be appreciated if laboratories allow their reference intervals to increase as the population gets more obese with aging. SHBG levels fall with insulin resistance/hyperinsulinaemia and this needs to be taken into account when testosterone is measured. However, low SHBG is showing huge potential as a disease and prognostic marker in obesity. These commonly available tests provide useful insights for the obese patient and their utility may improve with future research into the growing problem of obesity.

Hostility and urine norepinephrine interact to predict insulin resistance: the VA Normative Aging Study

OBJECTIVE

Previous research has produced mixed results pertaining to the association between hostility and insulin resistance. These inconsistent findings may be the result of a lack of studies examining potential moderators of this relationship and inconsistent measures of insulin resistance and/or hostility. We hypothesized that hostility may interact with circulating norepinephrine (NEPI) levels, indexed by 24-hour urine concentrations, to affect insulin resistance.

METHODS

Six hundred forty-three men (mean age = 63.1 years) free of diabetic medications completed the Minnesota Multiphasic Personality Inventory and participated in a laboratory assessment. The Cook-Medley Hostility (Ho) and 24-hour urine NEPI were used to predict insulin resistance defined by the homeostatic model assessment (HOMA) index, 2-hour postchallenge glucose (PCGL), and insulin levels (PCIL) after controlling for nine common covariates.

RESULTS

Multiple regression showed that the two-way interaction between Ho and NEPI significantly predicted HOMA and PCIL, but not PCGL, after controlling for covariates. Simple regression slopes of Ho on HOMA and PCIL were explored and indicated that, at higher levels of NEPI, higher Ho was associated with higher HOMA (beta = 0.14, p < .05). Ho was not a significant predictor of HOMA at mean and lower levels of NEPI. Similar results were obtained for PCIL, but not PCGL. Cynicism, but not other subscales of Ho, was similarly related to insulin resistance and NEPI.

CONCLUSION

Individuals with high stress and high hostility were more likely to have insulin resistance. It is important to study moderators in the relationship between hostility and insulin resistance.