Insulin resistance: the link between obesity and cardiovascular disease

Lifestyle changes in women with polycystic ovary syndrome

BACKGROUND

Polycystic ovary syndrome (PCOS) affects 4% to 18% of reproductive-aged women and is associated with reproductive, metabolic and psychological dysfunction. Obesity worsens the presentation of PCOS and weight management (weight loss, maintenance or prevention of excess weight gain) is proposed as an initial treatment strategy, best achieved through lifestyle changes incorporating diet, exercise and behavioural interventions.

OBJECTIVES

To assess the effectiveness of lifestyle treatment in improving reproductive, anthropometric (weight and body composition), metabolic and quality of life factors in PCOS.

SEARCH STRATEGY

Electronic databases (Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library), MEDLINE, EMBASE, PsycINFO, CINAHL, AMED), controlled trials register, conference abstracts, relevant journals, reference lists of relevant papers and reviews and grey literature databases, with no language restrictions applied.

SELECTION CRITERIA

Randomised controlled trials comparing lifestyle treatment (diet, exercise, behavioural or combined treatments) to minimal or no treatment in women with PCOS.

DATA COLLECTION AND ANALYSIS

Two authors independently selected trials, assessed methodological quality and risk of bias and extracted data.

MAIN RESULTS

Six studies were included. Three studies compared physical activity to minimal dietary and behavioural advice or no advice. Three studies compared combined dietary, exercise and behavioural interventions to minimal intervention. There were no studies assessing fertility primary outcomes and no data for meta-analysis on ovulation or menstrual regularity. For secondary outcomes, lifestyle intervention provided benefits when compared to minimal treatment for endpoint values for total testosterone (mean difference (MD) -0.27 nmol/L, 95% confidence interval (CI) -0.46 to -0.09, P = 0.004), hirsutism by the Ferriman-Gallwey score (MD -1.19, 95% CI -2.35 to -0.03, P = 0.04), weight (MD -3.47 kg, 95% CI -4.94 to -2.00, P < 0.00001), waist circumference (MD -1.95 cm, 95% CI -3.34 to -0.57, P = 0.006), waist to hip ratio (MD -0.04, 95% CI -0.07 to -0.00, P = 0.02), fasting insulin (MD -2.02 µU/mL, 95% CI -3.28 to -0.77, P = 0.002) and oral glucose tolerance test insulin (standardised mean difference -1.32, 95% CI -1.73 to -0.92, P < 0.00001) and per cent weight change (MD -7.00%, 95% CI -10.1 to -3.90, P < 0.00001). There was no evidence of effect of lifestyle for body mass index, free androgen index, sex hormone binding globulin, glucose or lipids; and no data for quality of life, patient satisfaction or acne.

AUTHORS' CONCLUSIONS

Lifestyle intervention improves body composition, hyperandrogenism (high male hormones and clinical effects) and insulin resistance in women with PCOS. There was no evidence of effect for lifestyle intervention on improving glucose tolerance or lipid profiles and no literature assessing clinical reproductive outcomes, quality of life and treatment satisfaction.

Comparison between surrogate indexes of insulin sensitivity/resistance and hyperinsulinemic euglycemic glucose clamps in rhesus monkeys

The euglycemic glucose clamp is the reference method for assessing insulin sensitivity in humans and animals. However, clamps are ill-suited for large studies because of extensive requirements for cost, time, labor, and technical expertise. Simple surrogate indexes of insulin sensitivity/resistance including quantitative insulin-sensitivity check index (QUICKI) and homeostasis model assessment (HOMA) have been developed and validated in humans. However, validation studies of QUICKI and HOMA in both rats and mice suggest that differences in metabolic physiology between rodents and humans limit their value in rodents. Rhesus monkeys are a species more similar to humans than rodents. Therefore, in the present study, we evaluated data from 199 glucose clamp studies obtained from a large cohort of 86 monkeys with a broad range of insulin sensitivity. Data were used to evaluate simple surrogate indexes of insulin sensitivity/resistance (QUICKI, HOMA, Log HOMA, 1/HOMA, and 1/Fasting insulin) with respect to linear regression, predictive accuracy using a calibration model, and diagnostic performance using receiver operating characteristic. Most surrogates had modest linear correlations with SI(Clamp) (r ≈ 0.4-0.64) with comparable correlation coefficients. Predictive accuracy determined by calibration model analysis demonstrated better predictive accuracy of QUICKI than HOMA and Log HOMA. Receiver operating characteristic analysis showed equivalent sensitivity and specificity of most surrogate indexes to detect insulin resistance. Thus, unlike in rodents but similar to humans, surrogate indexes of insulin sensitivity/resistance including QUICKI and log HOMA may be reasonable to use in large studies of rhesus monkeys where it may be impractical to conduct glucose clamp studies.

Improvement in HOMA-IR is an independent predictor of reduced carotid intima-media thickness in obese adolescents participating in an interdisciplinary weight-loss program

The aim of this study was to verify whether a 1-year interdisciplinary weight-loss program improved common carotid artery intima-media thickness (IMT) and whether insulin resistance and/or inflammation (as measured by the markers plasminogen activator inhibitor type-1 and adiponectin) might underlie obesity in adolescents. A group of 29 post-pubescent obese adolescents were submitted to an interdisciplinary intervention over the course of 1 year. Common carotid artery IMT was determined ultrasonographically. Body composition, blood pressure (BP), glycemia, insulinemia, homeostasis model assessment of insulin resistance (HOMA-IR), lipid profile and adipokine concentrations were analyzed before and after the intervention. The interdisciplinary weight-loss program promoted a significant improvement in body composition, insulin concentration, HOMA-IR, lipid profile, BP and inflammatory state, in addition to significantly decreasing the common carotid artery IMT. Furthermore, this study demonstrated that the difference between baseline and final values of HOMA-IR (ΔHOMA-IR) was negatively correlated with concomitant changes in the adiponectin concentration (Δadiponectin; r=-0.42; P=0.02) and positively correlated with changes in common carotid artery IMT (Δcarotid IMT; r=0.41; P=0.03). Multiple regression analysis adjusted by age, cardiovascular risk factors and inflammatory markers showed that ΔHOMA-IR was an independent predictor of significant changes in common carotid artery IMT. This investigation demonstrated that an interdisciplinary weight-loss program promoted a reduction of the common carotid artery IMT in obese Brazilian adolescents, and the improvement of HOMA-IR was an independent predictor of carotid IMT changes in this population.

Differential adipogenic and inflammatory properties of small adipocytes in Zucker Obese and Lean rats

We recently reported that a preponderance of small adipose cells, decreased expression of cell differentiation markers, and enhanced inflammatory activity in human subcutaneous whole adipose tissue were associated with insulin resistance. To test the hypothesis that small adipocytes exhibited these differential properties, we characterised small adipocytes from epididymal adipose tissue of Zucker Obese (ZO) and Lean (ZL) rats. Rat epididymal fat pads were removed and adipocytes isolated by collagenase digestion. Small adipocytes were separated by sequential filtration through nylon meshes. Adipocytes were fixed in osmium tetroxide for cell size distribution analysis via Beckman Coulter Multisizer. Quantitative real-time PCR for cell differentiation and inflammatory genes was performed. Small adipocytes represented a markedly greater percentage of the total adipocyte population in ZO than ZL rats (58±4% vs. 12±3%, p<0.001). In ZO rats, small as compared with total adipocytes had 4-fold decreased adiponectin, and 4-fold increased visfatin and IL-6 levels. Comparison of small adipocytes in ZO versus ZL rats revealed 3-fold decreased adiponectin and PPARγ levels, and 2.5-fold increased IL-6. In conclusion, ZO rat adipose tissue harbours a large proportion of small adipocytes that manifest impaired cell differentiation and pro-inflammatory activity, two mechanisms by which small adipocytes may contribute to insulin resistance.

Bioactives in blueberries improve insulin sensitivity in obese, insulin-resistant men and women

Dietary supplementation with whole blueberries in a preclinical study resulted in a reduction in glucose concentrations over time. We sought to evaluate the effect of daily dietary supplementation with bioactives from blueberries on whole-body insulin sensitivity in men and women. A double-blinded, randomized, and placebo-controlled clinical study design was used. After screening to resolve study eligibility, baseline (wk 0) insulin sensitivity was measured on 32 obese, nondiabetic, and insulin-resistant subjects using a high-dose hyperinsulinemic-euglycemic clamp (insulin infusion of 120 mU(861 pmol)⋅m(-2)⋅min(-1)). Serum inflammatory biomarkers and adiposity were measured at baseline. At the end of the study, insulin sensitivity, inflammatory biomarkers, and adiposity were reassessed. Participants were randomized to consume either a smoothie containing 22.5 g blueberry bioactives (blueberry group, n = 15) or a smoothie of equal nutritional value without added blueberry bioactives (placebo group, n = 17) twice daily for 6 wk. Both groups were instructed to maintain their body weight by reducing ad libitum intake by an amount equal to the energy intake of the smoothies. Participants' body weights were evaluated weekly and 3-d food records were collected at baseline, the middle, and end of the study. The mean change in insulin sensitivity improved more in the blueberry group (1.7 ± 0.5 mg⋅kg FFM(-1)⋅min(-1)) than in the placebo group (0.4 ± 0.4 mg⋅kg FFM(-1)⋅min(-1)) (P = 0.04). Insulin sensitivity was enhanced in the blueberry group at the end of the study without significant changes in adiposity, energy intake, and inflammatory biomarkers. In conclusion, daily dietary supplementation with bioactives from whole blueberries improved insulin sensitivity in obese, nondiabetic, and insulin-resistant participants.

MRI sagittal abdominal diameter is a stronger predictor of metabolic syndrome than visceral fat area or waist circumference in a high-risk vascular cohort

Objective:

To determine whether sagittal abdominal diameter (SAD) is associated with the metabolic syndrome independently of visceral fat area (VFA) and waist circumference (WC).

Methods:

Forty-three high-risk vascular patients were evaluated for metabolic syndrome criteria and underwent magnetic resonance imaging (MRI) to quantify SAD and VFA at the L4–L5 disc.

Comparisons:

1. Baseline differences in patients with and without the metabolic syndrome 2. Forward binary logistic regression analysis of predictors of the metabolic syndrome with SAD, VFA and WC as independents 3. Correlates of SAD.

Results:

Patients with metabolic syndrome had greater SAD, VFA and WC than patients without the metabolic syndrome (P < 0.01). Of SAD, VFA and WC, only SAD was associated with metabolic syndrome on forward binary logistic regression; beta 0.68, Wald’s statistic 10.8 (P = 0.001) and c-statistic 0.89 (P < 0.001). A > 22.7 cm SAD threshold identified metabolic syndrome with a 91% sensitivity and 80% specificity. SAD correlated with waist circumference (r = 0.918), high-density lipoprotein-cholesterol (r = −0.363), triglyceride (r = 0.401), fasting glucose (r = 0.428) and the QUICK index of insulin sensitivity (r = −0.667) (all P < 0.05).

Conclusions:

MRI-measured SAD is associated with the metabolic syndrome and renders the current gold standard of VFA redundant. This measure of obesity-related cardiovascular risk requires validation and evaluation in a prospective cohort.

Metabolic dysfunction in women with bipolar disorder: the potential influence of family history of type 2 diabetes mellitus

OBJECTIVE

Overweight/obesity, insulin resistance (IR), and other types of metabolic dysfunction are common in patients with bipolar disorder (BD); however, the pathophysiological underpinnings of metabolic dysfunction in BD are not fully understood. Family history of type 2 diabetes mellitus (FamHxDM2), which has been shown to have deleterious effects on metabolic function in the general population, may play a role in the metabolic dysfunction observed in BD.

METHODS

Using multivariate analysis of variance, the effects of BD illness and/or FamHxDM2 were examined relative to metabolic biomarkers in 103 women with BD and 36 healthy, age-matched control women.

RESULTS

As a group, women with BD had higher levels of fasting plasma insulin (FPI) and fasting plasma glucose (FPG), higher homeostatic assessment of IR (HOMA-IR) scores, body mass index (BMI), waist circumference (WC), and hip circumference (HC) compared to control women. FamHxDM2 was associated with significantly worse metabolic biomarkers among women with BD but not among healthy control women. Among women with BD, there was a significant main effect of FamHxDM2 on FPI, HOMA-IR, BMI, WC, and HC, even after controlling for type of BD illness, duration of medication exposure, and depression severity. Metabolic biomarkers were not influenced by use of weight-liable psychotropic medication (WLM), even after controlling for type of BD illness, duration of medication exposure, and depression severity.

CONCLUSIONS

Women with BD have overall worse metabolic biomarkers than age-matched control women. The use of WLM, duration of medication use, type of BD illness, and depression severity did not appear to be associated with more pronounced metabolic dysfunction. FamHxDM2 may represent a risk factor for the development of IR in women with BD. Further, focused studies of the endocrine profiles of families of BD patients are needed.

Liver fat percent is associated with metabolic risk factors and the metabolic syndrome in a high-risk vascular cohort

Objective

To determine whether liver fat percent (LFP) is associated with the metabolic syndrome independently of visceral fat area (VFA).

Methods

43 High-risk vascular patients not on lipid-lowering therapy were evaluated for the Adult Treatment Panel III (ATPIII) metabolic syndrome criteria and underwent magnetic resonance imaging (MRI) to quantify VFA and subcutaneous fat area (SFA) at the L4-L5 disc and liver magnetic resonance spectroscopy (MRS) to quantify LFP. Comparisons: 1. Baseline differences in patients with and without the metabolic syndrome 2. Forward binary logistic regression analysis of predictors of the metabolic syndrome with VFA, SFA and LFP as independents 3. Correlates of LFP.

Results

43 patients were included in analysis. Patients with metabolic syndrome had greater VFA, SFA and LFP than patients without the metabolic syndrome (all p < 0.01). Of VFA, SFA and LFP, only LFP was associated with the diagnosis of the metabolic syndrome on forward binary logistic regression with an OR of 1.17 per 1% increase in LFP (p = 0.015). A 4% LFP threshold identified the metabolic syndrome with 84% sensitivity and 82% specificity. LFP correlated with waist circumference (r = 0.768), HDL-cholesterol (r = -0.342), triglyceride (r = 0.369), fasting glucose (r = 0.584) and the QUICK Index of insulin sensitivity (r = -0.679) (all p < 0.05)

Conclusions

LFP is associated with the metabolic syndrome and renders the current gold standard of VFA redundant in this analysis. This measure of obesity-related cardiovascular risk requires further validation and evaluation in a prospective cohort.

Candidate gene association study conditioning on individual ancestry in patients with type 2 diabetes and metabolic syndrome from Mexico City

BACKGROUND

Type 2 diabetes (T2D) is influenced by diverse environmental and genetic risk factors. Metabolic syndrome (MS) increases the risk of cardiovascular disease and diabetes. We analysed 14 cases of polymorphisms located in 10 candidate loci, in a sample of patients with T2D and controls from Mexico City.

METHODS

We analysed the association of 14 polymorphisms located within 10 genes (TCF7L2, ENPP1, ADRB3, KCNJ11, LEPR, PPARgamma, FTO, CDKAL1, SIRT1 and HHEX) with T2D and MS. The analysis included 519 subjects with T2D defined according to the ADA criteria, 389 with MS defined according to the AHA/NHLBI criteria and 547 controls. Association was tested with the program ADMIXMAP including individual ancestry, age, sex, education and in some cases body mass index (BMI), in a logistic regression model.

RESULTS

The two markers located within the TCF7L2 gene showed strong associations with T2D (rs7903146, T allele, odd ratio (OR) = 1.76, p = 0.001 and rs12255372, T allele, OR = 1.78, p = 0.002), but did not show significant association with MS. The non-synonymous rs4994 polymorphism of the ADRB3 gene was associated with T2D (Trp allele, OR = 0.62, p = 0.001) and MS (Trp allele, OR = 0.74, p = 0.018). Nominally significant associations were also observed between T2D and the SIRT1 rs3758391 SNP and MS and the HHEX rs5015480 polymorphism.

CONCLUSIONS

Variants located within the gene TCF7L2 are strongly associated with T2D but not with MS, providing support to previous evidence indicating that polymorphisms at the TCF7L2 gene increase T2D risk. In contrast, the non-synonymous ADRB3 rs4994 polymorphism is associated with T2D and MS.

HOMA1-IR and HOMA2-IR indexes in identifying insulin resistance and metabolic syndrome: Brazilian Metabolic Syndrome Study (BRAMS)

OBJECTIVE

To investigate cut-off values for HOMA1-IR and HOMA2-IR to identify insulin resistance (IR) and metabolic syndrome (MS), and to assess the association of the indexes with components of the MS.

METHODS

Nondiabetic subjects from the Brazilian Metabolic Syndrome Study were studied (n = 1,203, 18 to 78 years). The cut-off values for IR were determined from the 90th percentile in the healthy group (n = 297) and, for MS, a ROC curve was generated for the total sample.

RESULTS

In the healthy group, HOMA-IR indexes were associated with central obesity, triglycerides and total cholesterol (p < 0.001). The cut-off values for IR were: HOMA1-IR > 2.7 and HOMA2-IR > 1.8; and, for MS were: HOMA1-IR > 2.3 (sensitivity: 76.8%; specificity: 66.7%) and HOMA2-IR > 1.4 (sensitivity: 79.2%; specificity: 61.2%).

CONCLUSION

The cut-off values identified for HOMA1-IR and HOMA2-IR indexes have a clinical and epidemiological application for identifying IR and MS in Westernized admixtured multi-ethnic populations.

Diet-induced obesity prevents interstitial dispersion of insulin in skeletal muscle

OBJECTIVE

Obesity causes insulin resistance, which has been interpreted as reduced downstream insulin signaling. However, changes in access of insulin to sensitive tissues such as skeletal muscle may also play a role. Insulin injected directly into skeletal muscle diffuses rapidly through the interstitial space to cause glucose uptake. When insulin resistance is induced by exogenous lipid infusion, this interstitial diffusion process is curtailed. Thus, the possibility exists that hyperlipidemia, such as that seen during obesity, may inhibit insulin action to muscle cells and exacerbate insulin resistance. Here we asked whether interstitial insulin diffusion is reduced in physiological obesity induced by a high-fat diet (HFD).

RESEARCH DESIGN AND METHODS

Dogs were fed a regular diet (lean) or one supplemented with bacon grease for 9-12 weeks (HFD). Basal insulin (0.2 mU x min(-1) x kg(-1)) euglycemic clamps were performed on fat-fed animals (n = 6). During clamps performed under anesthesia, five sequential doses of insulin were injected into the vastus medialis of one hind limb (INJ); the contralateral limb (NINJ) served as a control.

RESULTS

INJ lymph insulin showed an increase above NINJ in lean animals, but no change in HFD-fed animals. Muscle glucose uptake observed in lean animals did not occur in HFD-fed animals.

CONCLUSIONS

Insulin resistance induced by HFD caused a failure of intramuscularly injected insulin to diffuse through the interstitial space and failure to cause glucose uptake, compared with normal animals. High-fat feeding prevents the appearance of injected insulin in the interstitial space, thus reducing binding to skeletal muscle cells and glucose uptake.

Joint association of obesity and metabolic syndrome with incident mobility limitation in older men and women--results from the Health, Aging, and Body Composition Study

BACKGROUND

Although both obesity and the metabolic syndrome (MetS) are known risk factors for decline in physical function, the joint association of obesity and metabolic alterations with risk of incident mobility limitation is unknown.

METHODS

Data are from 2,984 women and men aged 70-79 years participating in the Health, Aging, and Body Composition Study without mobility limitation at baseline. Obesity was defined as body mass index greater than or equal to 30 kg/m(2) and the MetS as meeting greater than or equal to 3 of the ATP III criteria. Mobility limitation was defined as any difficulty walking one-quarter mile or climbing 10 steps during two consecutive semiannual assessments for more than 6.5 years.

RESULTS

Incidence of mobility limitation was 55% in women and 44% in men. In women, adjusted risk of developing mobility limitation was progressively greater in nonobese participants with the MetS (hazard ratio [HR] = 1.49, 95% confidence interval [CI] = 1.24-1.80), obese participants without the MetS (HR = 1.95, 95% CI = 1.51-2.53), and obese participants with the MetS (HR = 2.16, 95% CI = 1.78-2.63) relative to the nonobese without the MetS. In men, the corresponding adjusted HRs (95% CI) were 1.07 (0.87-1.32), 1.64 (1.19-2.25), and 1.41 (1.12-1.78). Elevated inflammatory markers partly explained the association between obesity, the MetS, and mobility limitation, particularly in nonobese and obese participants with the MetS.

CONCLUSIONS

Obesity itself, independent of its metabolic consequences, is a risk factor for mobility limitation among obese older adults. In addition, having the MetS increases the risk of functional decline in older nonobese women but not in men.