Abdominal adiposity and diabetes risk: the importance of precise measures and longitudinal studies

Identification of Sortilin Alternatively Spliced Variants in Mouse 3T3L1 Adipocytes

Type 2 diabetes mellitus is a metabolic disorder defined by systemic insulin resistance. Insulin resistance in adipocytes, an important regulator of glucose metabolism, results in impaired glucose uptake. The trafficking protein, sortilin, regulates major glucose transporter 4 (Glut4) movement, thereby promoting glucose uptake in adipocytes. Here, we demonstrate the presence of an alternatively spliced sortilin variant (Sort^17b), whose levels increase with insulin resistance in mouse 3T3L1 adipocytes. Using a splicing minigene, we show that inclusion of alternative exon 17b results in the expression of Sort^17b splice variant. Bioinformatic analysis indicated a novel intrinsic disorder region (IDR) encoded by exon 17b of Sort^17b. Root mean square deviation (RMSD) and root mean square fluctuation (RMSF) measurements using molecular dynamics demonstrated increased flexibility of the protein backbone within the IDR. Using protein–protein docking and co-immunoprecipitation assays, we show robust binding of Glut4 to Sort^17b. Further, results demonstrate that over-expression of Sort^17b correlates with reduced Glut4 translocation and decreased glucose uptake in adipocytes. The study demonstrates that insulin resistance in 3T3L1 adipocytes promotes expression of a novel sortilin splice variant with thus far unknown implications in glucose metabolism. This knowledge may be used to develop therapeutics targeting sortilin variants in the management of type 2 diabetes and metabolic syndrome.

Longer-term outcomes in offspring of GDM mothers treated with metformin versus insulin

Insulin has traditionally been the gold standard pharmacological treatment for gestational diabetes mellitus (GDM). Insulin requires multiple injections a day, can cause frequent hypoglycaemia, requires careful handling, and is generally more expensive compared to oral agents. Metformin has been increasingly popular in recent years. Based on the short-term data available, metformin appears to be safe and effective for the treatment of GDM but existing studies have all stressed the lack of longer-term offspring data. This article will analyse the evidence available on the longer-term outcomes in the offspring of women with GDM treated with metformin versus insulin. Pubmed, EMBASE, CENTRAL, and CNKI were searched for follow-up studies of randomised controlled trials that compared metformin with insulin for the treatment of GDM. Existing follow-up studies did not find any significant increase in the risk of adverse effects in terms of growth and development in the offspring of GDM mothers managed with metformin versus insulin.

Low Plasma Adiponectin Concentrations Predict Increases in Visceral Adiposity and Insulin Resistance

Context

Plasma adiponectin concentration has been shown to be inversely associated with body mass index (BMI) and insulin resistance in cross-sectional research. However, it is unclear whether adiponectin predicts future body composition and insulin resistance.

Objective

We aimed to investigate the potential relationship between adiponectin concentration and future regional body fat distribution and insulin resistance.

Design and Setting

This was a community-based prospective cohort study with 5 years of follow-up.

Participants

A total of 218 Japanese Americans without diabetes (79 men, 139 women, mean age 51.7 ± 10.1 years) were assessed at baseline and after 5 years of follow-up.

Main Outcome Measures

Abdominal visceral and subcutaneous fat area and thigh subcutaneous fat area were measured by computed tomography (CT). Insulin resistance was evaluated by homeostasis model assessment 2 of insulin resistance (HOMA2-IR). Plasma total adiponectin was measured by radioimmunoassay.

Results

Baseline adiponectin was inversely associated with abdominal visceral fat area (P = 0.037) and HOMA2-IR (P = 0.002) at 5 years in a multiple linear regression model after adjustment for baseline traits (including age, sex, BMI, abdominal visceral fat area, abdominal subcutaneous fat area, thigh subcutaneous fat area, HOMA2-IR) and weight change. However, no association was seen between baseline adiponectin concentration and BMI or other CT-measured regional fat depots at 5 years.

Conclusions

Low plasma adiponectin concentration independently predicted future abdominal visceral fat accumulation and increased insulin resistance in Japanese Americans.

Occurrence of Diabetes Mellitus in Obese Nondiabetic Patients, with Correlative Analysis of Visceral Fat, Fasting Insulin, and Insulin Resistance: A 3-year Follow-up Study (Mysore Visceral Adiposity in Diabetes Follow-up Study)

OBJECTIVE

To assess the occurrence of diabetes in obese nondiabetic patients over a 3-year follow-up period with a correlative analysis of visceral fat (VF), fasting insulin levels, (FILs) and insulin resistance (IR).

MATERIAL AND METHODS

Thirty-seven obese and nineteen nonobese nondiabetics of our previous study, Mysore Visceral Adiposity in Diabetes were followed for the next 3 years. Their blood pressure, body mass index, waist circumference (WC), fasting blood sugar (FBS), FIL, lipid profile and subcutaneous fat (SCF), and VF measurement by US method were repeated every 6 months for the next 3 years. The findings were analyzed with appropriate statistical methods.

RESULTS

Twenty-three obese and 18 nonobese nondiabetics completed the study. There were 17 dropouts. The changes in the physical and biochemical characteristics of the two groups before and after the study were not significant. SCF had no correlation with IR whereas VF correlated with FIL and IR. There were three diabetics in the obese group and two from the control group at the end of the study. There were 12 impaired glucose tolerance (IGT) in the test group and 2 in the control group. Those who developed diabetes had higher VF, WC, FBS, FIL, and IR. Those who showed IGT also had these at higher levels compared to others. There was no change in the VF at the end of the study.

CONCLUSIONS

This follow-up study on South Indians has shown that VF is a significant risk factor for the development of IR. IR can develop without any increase in the volume of the VF, is the essential finding of this study. SCF has not shown any significant relationship with IR. We recommend FBS and FIL in all the obese nondiabetics to calculate IR, which has given much insight in the development of IGT and diabetes. Large multicentric, longitudinal studies are required to establish the cause of IR.

Body composition in offspring of New Zealand women: ethnic and gender differences at age 1-3 years in 2005-2009

BACKGROUND

In multi-ethnic New Zealand the prevalence of obesity and diabetes is increasing and varies by ethnic group.

AIM

This study explored ethnic and gender differences in body composition in offspring of women treated for gestational diabetes in the metformin in gestational diabetes (MiG) trial.

SAMPLE AND METHODS

Total and regional body composition measured by dual X-ray absorptiometry were investigated in European, Indian, Polynesian and "Other" children aged 2 years (48 boys; 56 girls).

RESULTS

By ethnicity, boys were not different by height or weight. Compared with European girls, Indian girls weighed less (2.3 ± 0.58 kg) and Polynesian (1.13 ± 0.53 kg) more, but percentage body fat was not different. Adjusted for age, height and weight boys had less total and appendicular fat and higher abdominal fat mass and total bone mineral density than girls (p < 0.001). Adjusted for age, weight and height Indian boys had more fat in the central and abdominal regions and less total lean mass than European boys (p < 0.05).

CONCLUSION

These measurements provide early evidence for gender and ethnic differences in the distribution of fat and might help identify who is most likely to benefit from intervention in the first few years of life to reduce risk of chronic disease including diabetes.

Metformin in gestational diabetes: the offspring follow-up (MiG TOFU): body composition at 2 years of age

OBJECTIVE

In women with gestational diabetes mellitus, who were randomized to metformin or insulin treatment, pregnancy outcomes were similar (Metformin in Gestational diabetes [MiG] trial). Metformin crosses the placenta, so it is important to assess potential effects on growth of the children.

RESEARCH DESIGN AND METHODS

In Auckland, New Zealand, and Adelaide, Australia, women who had participated in the MiG trial were reviewed when their children were 2 years old. Body composition was measured in 154 and 164 children whose mothers had been randomized to metformin and insulin, respectively. Children were assessed with anthropometry, bioimpedance, and dual energy X-ray absorptiometry (DEXA), using standard methods.

RESULTS

The children were similar for baseline maternal characteristics and pregnancy outcomes. In the metformin group, compared with the insulin group, children had larger mid-upper arm circumferences (17.2 ± 1.5 vs. 16.7 ± 1.5 cm; P = 0.002) and subscapular (6.3 ± 1.9 vs. 6.0 ± 1.7 mm; P = 0.02) and biceps skinfolds (6.03 ± 1.9 vs. 5.6 ± 1.7 mm; P = 0.04). Total fat mass and percentage body fat assessed by bioimpedance (n = 221) and DEXA (n = 114) were not different.

CONCLUSIONS

Children exposed to metformin had larger measures of subcutaneous fat, but overall body fat was the same as in children whose mothers were treated with insulin alone. Further follow-up is required to examine whether these findings persist into later life and whether children exposed to metformin will develop less visceral fat and be more insulin sensitive. If so, this would have significant implications for the current pandemic of diabetes.

Combined impact of adiponectin and retinol-binding protein 4 on metabolic syndrome in elderly people: the Korean Longitudinal Study on Health and Aging

The prevalence of metabolic syndrome (MS) increases with progressing and is potentially associated with changes in adipose-derived cytokines, including adiponectin and retinol-binding protein 4 (RBP4). We aimed to determine the prevalence of MS, and the relationships between these factors and MS in elderly people. A population-based cohort study, the Korean Longitudinal Study on Health and Aging (KLoSHA), was performed on subjects aged > or =65 years by random stratified sampling in 2005-2006 (439 men and 561 women). Anthropometrics, biochemical factors including adiponectin and RBP4 levels, body composition, and abdominal fat by computed tomography (CT) were measured. The prevalence of MS was 61.0% in women and 39.9% in men. After adjustment for age, gender, smoking, alcohol, and exercise status and muscle mass, participants with the lowest quartile of adiponectin had a higher risk for having MS than those with the highest quartile (odds ratio (OR) = 4.12, P < 0.01). Similarly, subjects with the highest quartile of RBP4 showed an increased risk for having MS (OR = 1.73, P < 0.01). When both the lowest adiponectin and the highest RBP4 quartiles were combined, the OR increased to 6.22 compared with the opposite quartiles (i.e., highest adiponectin and lowest RBP4 concentrations). Furthermore, circulating levels of adiponectin and RBP4 were significantly correlated with visceral fat and insulin resistance index. In this study, the increased prevalence of MS in elderly but relatively lean population was associated with low adiponectin and high RBP4 levels. The combination of these factors might predict older subjects at high risk for having MS.

Insulin resistance, beta cell dysfunction and visceral adiposity as predictors of incident diabetes: the Insulin Resistance Atherosclerosis Study (IRAS) Family study

AIMS/HYPOTHESIS

Central obesity, insulin resistance and beta cell dysfunction are independent risk factors for incident type 2 diabetes, although few studies have used detailed measures of these disorders. Our objective was to study the association of directly measured visceral and subcutaneous adipose tissue (VAT, SAT), insulin sensitivity (S (I)) and the acute insulin response (AIR) with incident type 2 diabetes.

METHODS

Participants were 1,230 Hispanic-Americans and African-Americans in the Insulin Resistance Atherosclerosis Study (IRAS) Family Study who were free of type 2 diabetes at baseline (2000-2002). S (I) and AIR were determined from frequently sampled IVGTTs with minimal model analysis. VAT and SAT were determined by computed tomography. Impaired fasting glucose and type 2 diabetes were defined according to American Diabetes Association criteria.

RESULTS

Incident type 2 diabetes was diagnosed in 90 participants after 5 years. After adjustment for age, sex, ethnicity, centre, impaired fasting glucose, triacylglycerol, HDL-cholesterol and systolic BP, both S(I) and AIR were inversely associated with type 2 diabetes (S (I), OR 0.53, 95% CI 0.39-0.73; AIR, OR 0.22, 95% CI 0.14-0.34 per SD; both p < 0.001), while both VAT and SAT were positively associated with type 2 diabetes (VAT, OR 1.68, 95% CI 1.22-2.33; SAT, OR 1.49, 95% CI 1.13-1.99; both p < 0.01). In a model including all four factors, S (I) and AIR (S (I), OR 0.55, 95% CI 0.37-0.80; AIR, OR 0.21, 95% CI 0.13-0.33; both p < 0.01) were significant predictors of type 2 diabetes, although associations with VAT and SAT were no longer significant. A significant sex x VAT interaction indicated a stronger association of VAT with type 2 diabetes in women than in men.

CONCLUSIONS/INTERPRETATION

Insulin resistance, beta cell dysfunction and VAT predicted incident type 2 diabetes, with evidence of a stronger association of VAT with type 2 diabetes among women.