Bone Mineral Density and Progression of Subclinical Atherosclerosis in African-Americans With Type 2 Diabetes

CONTEXT

Relative to European Americans, calcified atherosclerotic plaque (CP) is less prevalent and severe in African-Americans (AAs).

OBJECTIVE

Predictors of progression of CP in the aorta, carotid, and coronary arteries were examined in AAs over a mean 5.3 ± 1.4-year interval.

DESIGN

This is the African American-Diabetes Heart Study.

SETTING

A type 2 diabetes (T2D)-affected cohort was included.

PARTICIPANTS

A total of 300 unrelated AAs with T2D; 50% female, mean age 55 ± 9 years, baseline hemoglobin A1c 8.1 ± 1.8% was included.

MAIN OUTCOME MEASURES

Glycemic control, renal parameters, vitamin D, and computed tomography-derived measures of adiposity, vascular CP, and volumetric bone mineral density (vBMD) in lumbar and thoracic vertebrae were obtained at baseline and follow-up.

RESULTS

CP increased in incidence and quantity/mass in all three vascular beds over the 5-year study (P < .0001). Lower baseline lumbar and thoracic vBMD were associated with progression of abdominal aorta CP (P < .008), but not progression of carotid or coronary artery CP. Lower baseline estimated glomerular filtration rate was associated with progression of carotid artery CP (P = .0004), and higher baseline pericardial adipose volume was associated with progression of coronary artery (P = .001) and aorta (P = .0006) CP independent of body mass index. There was a trend for an inverse relationship between change in thoracic vBMD and change in aortic CP (P = .05).

CONCLUSIONS

In this longitudinal study, lower baseline thoracic and lumbar vBMD and estimated glomerular filtration rate and higher pericardial adipose volumes were associated with increases in CP in AAs with T2D. Changes in these variables and baseline levels and/or changes in glycemic control, albuminuria, and vitamin D were not significantly associated with progression of CP.

Adiposity is inversely associated with hippocampal volume in African Americans and European Americans with diabetes

AIMS

To assess associations between body mass index (BMI), waist circumference (WC), and computed tomography-determined volumes of pericardial, visceral, and subcutaneous adipose tissue with magnetic resonance imaging-(MRI) based cerebral structure and cognitive performance in individuals with type 2 diabetes (T2D).

METHODS

This study was performed in 348 African Americans (AAs) and 256 European Americans (EAs) with T2D. Associations between adiposity measures with cerebral volumes of white matter (WMV), gray matter (GMV), white matter lesions, hippocampal GMV, and hippocampal WMV, cognitive performance and depression were examined using marginal models incorporating generalized estimating equations. All models were adjusted for age, sex, education, smoking, HbA1c, hypertension, statins, cardiovascular disease, MRI scanner (MRI outcomes only), and time between scans; some neuroimaging measures were additionally adjusted for intracranial volume.

RESULTS

Participants were 59.9% female with mean (SD) age 57.7(9.3)years, diabetes duration 9.6(6.8)years, and HbA1c 7.8(1.9)%. In AAs, inverse associations were detected between hippocampal GMV and both BMI (β [95% CI]-0.18 [-0.30, -0.07], P=0.0018) and WC (-0.23 [-0.35, -0.12], P=0.0001). In the full bi-ethnic sample, inverse associations were detected between hippocampal WMV and WC (P≤0.0001). Positive relationships were observed between BMI (P=0.0007) and WC (P<0.0001) with depression in EAs.

CONCLUSIONS

In patients with T2D, adiposity is inversely associated with hippocampal gray and white matter volumes.

Risk prediction of major complications in individuals with diabetes: the Atherosclerosis Risk in Communities Study

AIMS

To develop a prediction equation for 10-year risk of a combined endpoint (incident coronary heart disease, stroke, heart failure, chronic kidney disease, lower extremity hospitalizations) in people with diabetes, using demographic and clinical information, and a panel of traditional and non-traditional biomarkers.

METHODS

We included in the study 654 participants in the Atherosclerosis Risk in Communities (ARIC) study, a prospective cohort study, with diagnosed diabetes (visit 2; 1990-1992). Models included self-reported variables (Model 1), clinical measurements (Model 2), and glycated haemoglobin (Model 3). Model 4 tested the addition of 12 blood-based biomarkers. We compared models using prediction and discrimination statistics.

RESULTS

Successive stages of model development improved risk prediction. The C-statistics (95% confidence intervals) of models 1, 2, and 3 were 0.667 (0.64, 0.70), 0.683 (0.65, 0.71), and 0.694 (0.66, 0.72), respectively (p < 0.05 for differences). The addition of three traditional and non-traditional biomarkers [β-2 microglobulin, creatinine-based estimated glomerular filtration rate (eGFR), and cystatin C-based eGFR] to Model 3 significantly improved discrimination (C-statistic = 0.716; p = 0.003) and accuracy of 10-year risk prediction for major complications in people with diabetes (midpoint percentiles of lowest and highest deciles of predicted risk changed from 18-68% to 12-87%).

CONCLUSIONS

These biomarkers, particularly those of kidney filtration, may help distinguish between people at low versus high risk of long-term major complications.

Prediabetes and Diabetes Are Associated With Arterial Stiffness in Older Adults: The ARIC Study

BACKGROUND

To determine whether prediabetes and diabetes in older adults are associated with arterial stiffness measured in central and peripheral arteries and to examine characteristics that modify these associations.

METHODS

Cohort members attending the 5th exam (2011-2013) of the Atherosclerosis Risk in Communities (ARIC) study had pulse wave velocity (PWV) measures performed at the carotid-femoral (cfPWV), brachial-ankle (baPWV), and femoral-ankle (faPWV) segments. Fasting glucose ≥126mg/dl, glycated hemoglobin (HbA1c) ≥6.5%, or currently taking diabetes medication defined diabetes. Fasting glucose 100-125mg/dl or HbA1c 5.7%-6.4% among those without diabetes defined prediabetes. Cross-sectional associations were modeled using multivariable linear regression.

RESULTS

Among 4,279 eligible participants with cfPWV measures (mean age 75 years), 22% were African-American, 25.5% had diabetes, and 54.7% had prediabetes. Compared to those with normal glucose, cfPWV was 95.8cm/s higher (stiffer) on average for those with diabetes (for reference: being 1 year older was associated with 14.4cm/s higher cfPWV). Similar findings were seen for diabetes and baPWV, although attenuated. Interestingly, faPWV was 17.6cm/s lower for those with diabetes compared to normal glucose. There was a significant positive association between baPWV and prediabetes. Among those with diabetes, cfPWV was higher for those with albuminuria, reduced kidney function, duration of diabetes ≥10 years, and elevated HbA1c (HbA1c ≥7).

CONCLUSION

Among older adults, diabetes is associated with higher central arterial stiffness and lower peripheral arterial stiffness, and prediabetes is associated with higher baPWV. Cross-sectionally, the magnitude of the effect of diabetes on central stiffness is equivalent to 6 years of arterial aging.

Relationships between measures of adiposity with subclinical atherosclerosis in patients with type 2 diabetes

OBJECTIVE

Assess cross-sectional relationships between body mass index (BMI), waist circumference (WC), pericardial (PAT), visceral (VAT), and subcutaneous adipose tissue (SAT) volumes with calcified plaque (CP) in African Americans (AAs) and European Americans (EAs) with type 2 diabetes.

METHODS

Computed tomography measured PAT, VAT, SAT, and CP in coronary arteries (CAC), carotid arteries, and aorta. Generalized estimating equations models were fitted to test for associations between adiposity and CP, stratified by ethnicity while accounting for familial correlations.

RESULTS

AAs (N = 753) vs. EAs (N = 562) had significantly lower PAT and VAT, despite equal or higher BMI. In multivariable models adjusting for age, gender, education, HbA1c, statins, smoking, cardiovascular disease, hypertension, nephropathy, and C-reactive protein, PAT positively associated with presence of CAC in AAs (P < 0.001), not EAs (P = 0.68; ethnicity interaction P < 0.01). Inverse associations were detected between SAT and severity of aorta CP (P < 0.01) in AAs and between BMI, WC, and SAT with severity of aorta CP in all participants.

CONCLUSIONS

Ethnic- and gender-specific differences in BMI, WC, PAT, SAT, and VAT were present in AAs and EAs with diabetes. Only PAT was positively associated with CAC in AAs; paradoxical inverse associations were seen between several other adiposity measures and subclinical cardiovascular disease.

Genome-Wide Interaction with Insulin Secretion Loci Reveals Novel Loci for Type 2 Diabetes in African Americans

Type 2 diabetes (T2D) is the result of metabolic defects in insulin secretion and insulin sensitivity, yet most T2D loci identified to date influence insulin secretion. We hypothesized that T2D loci, particularly those affecting insulin sensitivity, can be identified through interaction with insulin secretion loci. To test this hypothesis, single nucleotide polymorphisms (SNPs) associated with acute insulin response to glucose (AIRg), a dynamic measure of first-phase insulin secretion, were identified in African Americans from the Insulin Resistance Atherosclerosis Family Study (IRASFS; n = 492 subjects). These SNPs were tested for interaction, individually and jointly as a genetic risk score (GRS), using genome-wide association study (GWAS) data from five cohorts (ARIC, CARDIA, JHS, MESA, WFSM; n = 2,725 cases, 4,167 controls) with T2D as the outcome. In single variant analyses, suggestively significant (Pinteraction<5×10-6) interactions were observed at several loci including LYPLAL1 (rs10746381), CHN2 (rs7796525), and EXOC1 (rs4289500). Notable AIRg GRS interactions were observed with SAMD4A (rs11627203) and UTRN (rs17074194). These data support the hypothesis that additional genetic factors contributing to T2D risk can be identified by interactions with insulin secretion loci.

Trans-ethnic Meta-analysis and Functional Annotation Illuminates the Genetic Architecture of Fasting Glucose and Insulin

Knowledge of the genetic basis of the type 2 diabetes (T2D)-related quantitative traits fasting glucose (FG) and insulin (FI) in African ancestry (AA) individuals has been limited. In non-diabetic subjects of AA (n = 20,209) and European ancestry (EA; n = 57,292), we performed trans-ethnic (AA+EA) fine-mapping of 54 established EA FG or FI loci with detailed functional annotation, assessed their relevance in AA individuals, and sought previously undescribed loci through trans-ethnic (AA+EA) meta-analysis. We narrowed credible sets of variants driving association signals for 22/54 EA-associated loci; 18/22 credible sets overlapped with active islet-specific enhancers or transcription factor (TF) binding sites, and 21/22 contained at least one TF motif. Of the 54 EA-associated loci, 23 were shared between EA and AA. Replication with an additional 10,096 AA individuals identified two previously undescribed FI loci, chrX FAM133A (rs213676) and chr5 PELO (rs6450057). Trans-ethnic analyses with regulatory annotation illuminate the genetic architecture of glycemic traits and suggest gene regulation as a target to advance precision medicine for T2D. Our approach to utilize state-of-the-art functional annotation and implement trans-ethnic association analysis for discovery and fine-mapping offers a framework for further follow-up and characterization of GWAS signals of complex trait loci.

Improved Performance of Dynamic Measures of Insulin Response Over Surrogate Indices to Identify Genetic Contributors of Type 2 Diabetes: The GUARDIAN Consortium

Type 2 diabetes (T2D) is a heterogeneous disorder with contributions from peripheral insulin resistance and β-cell dysfunction. For minimization of phenotypic heterogeneity, quantitative intermediate phenotypes characterizing basal glucose homeostasis (insulin resistance and HOMA of insulin resistance [HOMAIR] and of β-cell function [HOMAB]) have shown promise in relatively large samples. We investigated the utility of dynamic measures of glucose homeostasis (insulin sensitivity [SI] and acute insulin response [AIRg]) evaluating T2D-susceptibility variants (n = 57) in Hispanic Americans from the GUARDIAN Consortium (n = 2,560). Basal and dynamic measures were genetically correlated (HOMAB-AIRg: ρG = 0.28-0.73; HOMAIR-SI: ρG = -0.73 to -0.83) with increased heritability for the dynamic measure AIRg Significant association of variants with dynamic measures (P < 8.77 × 10(-4)) was observed. A pattern of superior performance of AIRg was observed for well-established loci including MTNR1B (P = 9.46 × 10(-12)), KCNQ1 (P = 1.35 × 10(-4)), and TCF7L2 (P = 5.10 × 10(-4)) with study-wise statistical significance. Notably, significant association of MTNR1B with AIRg (P < 1.38 × 10(-9)) was observed in a population one-fourteenth the size of the initial discovery cohort. These observations suggest that basal and dynamic measures provide different views and levels of sensitivity to discrete elements of glucose homeostasis. Although more costly to obtain, dynamic measures yield significant results that could be considered physiologically "closer" to causal pathways and provide insight into the discrete mechanisms of action.

The ARIC-PET amyloid imaging study: Brain amyloid differences by age, race, sex, and APOE

OBJECTIVE

To evaluate differences in amyloid deposition in a community-based cohort without dementia by age, sex, race, education, and APOE ε4 allele status.

METHODS

Recruited from the longitudinal Atherosclerosis Risk in Communities study, 329 participants without dementia, ages 67-88 years, were imaged using florbetapir PET at 3 US community sites (Washington County, Maryland; Forsyth County, North Carolina; and Jackson, Mississippi). Standardized uptake value ratios (SUVRs) were calculated; global cortical SUVR >1.2 was evaluated as the primary outcome. Age, race, sex, education level, and number of APOE ε4 alleles were evaluated in multivariable models including vascular risk factors, brain white matter hyperintensity and total intracranial volume, and cognitive status.

RESULTS

A total of 141 of the participants (43%) were black. In multivariable models, odds of elevated SUVR was increased in participants with increasing age (odds ratio [OR] 1.63, 95% confidence interval [CI] 1.01-2.65 per 10 years of age) and black race (OR 2.08, 95% CI 1.23-3.51) but did not differ by educational level. Each ε4 allele was associated with increased odds of elevated SUVR (OR 2.65, 95% CI 1.61-4.39).

CONCLUSIONS

In this community-based cohort without dementia, florbetapir uptake is associated with older age and APOE genotype. Black race was associated with higher SUVR, after adjusting for demographics, vascular risk factors, cognitive status, white matter hyperintensity volume, and APOE genotype, with effect sizes nearing those seen for APOE ε4. Replication of these findings is needed in other cohorts, and reasons for and consequences of these observed differences by race warrant further study.

Admixture mapping of serum vitamin D and parathyroid hormone concentrations in the African American-Diabetes Heart Study

Vitamin D and intact parathyroid hormone (iPTH) concentrations differ between individuals of African and European descent and may play a role in observed racial differences in bone mineral density (BMD). These findings suggest that mapping by admixture linkage disequilibrium (MALD) may be informative for identifying genetic variants contributing to these ethnic disparities. Admixture mapping was performed for serum 25-hydroxyvitamin D, 1,25-dihydroxyvitamin D, vitamin D-binding protein (VDBP), bioavailable vitamin D, and iPTH concentrations and computed tomography measured thoracic and lumbar vertebral volumetric BMD in 552 unrelated African Americans with type 2 diabetes from the African American-Diabetes Heart Study. Genotyping was performed using a custom Illumina ancestry informative marker (AIM) panel. For each AIM, the probability of inheriting 0, 1, or 2 copies of a European-derived allele was determined. Non-parametric linkage analysis was performed by testing for association between each AIM using these probabilities among phenotypes, accounting for global ancestry, age, and gender. Fine-mapping of MALD peaks was facilitated by genome-wide association study (GWAS) data. VDBP levels were significantly linked in proximity to the protein coding locus (rs7689609, LOD=11.05). Two loci exhibited significant linkage signals for 1,25-dihydroxyvitamin D on 13q21.2 (rs1622710, LOD=3.20) and 12q13.2 (rs11171526, LOD=3.10). iPTH was significantly linked on 9q31.3 (rs7854368, LOD=3.14). Fine-mapping with GWAS data revealed significant known (rs7041 with VDBP, P=1.38×10(-82)) and novel (rs12741813 and rs10863774 with VDBP, P<6.43×10(-5)) loci with plausible biological roles. Admixture mapping in combination with fine-mapping has focused efforts to identify loci contributing to ethnic differences in vitamin D-related traits.

Branched-Chain Amino Acids and Insulin Metabolism: The Insulin Resistance Atherosclerosis Study (IRAS)

OBJECTIVE

Recent studies using untargeted metabolomics approaches have suggested that plasma branched-chain amino acids (BCAAs) are associated with incident diabetes. However, little is known about the role of plasma BCAAs in metabolic abnormalities underlying diabetes and whether these relationships are consistent across ethnic populations at high risk for diabetes. We investigated the associations of BCAAs with insulin sensitivity (SI), acute insulin response (AIR), and metabolic clearance of insulin (MCRI) in a multiethnic cohort.

RESEARCH DESIGN AND METHODS

In 685 participants without diabetes of the Insulin Resistance Atherosclerosis Study (IRAS) (290 Caucasians, 165 African Americans, and 230 Hispanics), we measured plasma BCAAs (sum of valine, leucine, and isoleucine) by mass spectrometry and SI, AIR, and MCRI by frequently sampled intravenous glucose tolerance tests.

RESULTS

Elevated plasma BCAAs were inversely associated with SI and MCRI and positively associated with fasting insulin in regression models adjusted for potential confounders (β = -0.0012 [95% CI -0.0018, -0.00059], P < 0.001 for SI; β = -0.0013 [95% CI -0.0018, -0.00082], P < 0.001 for MCRI; and β = 0.0015 [95% CI 0.0008, 0.0023], P < 0.001 for fasting insulin). The association of BCAA with SI was significantly modified by ethnicity, with the association only being significant in Caucasians and Hispanics. Elevated plasma BCAAs were associated with incident diabetes in Caucasians and Hispanics (multivariable-adjusted odds ratio per 1-SD increase in plasma BCAAs: 1.67 [95% CI 1.21, 2.29], P = 0.002) but not in African Americans. Plasma BCAAs were not associated with SI-adjusted AIR.

CONCLUSIONS

Plasma BCAAs are associated with incident diabetes and underlying metabolic abnormalities, although the associations were generally stronger in Caucasians and Hispanics.

Plasma FGF23 and Calcified Atherosclerotic Plaque in African Americans with Type 2 Diabetes Mellitus

BACKGROUND

Fibroblast growth factor 23 (FGF23) is a phosphaturic hormone implicated in disorders of serum phosphorus concentration and vitamin D. The role of FGF23 in vascular calcification remains controversial.

METHODS

Relationships between FGF23 and coronary artery calcified atherosclerotic plaque (CAC), aortoiliac calcified plaque (CP), carotid artery CP, volumetric bone mineral density (vBMD), albuminuria, and estimated glomerular filtration rate (eGFR) were determined in 545 African Americans with type 2 diabetes (T2D) and preserved kidney function in African American-Diabetes Heart Study participants. Generalized linear models were fitted to test associations between FGF23 and cardiovascular, bone, and renal phenotypes, and change in measurements over time, adjusting for age, gender, African ancestry proportion, body mass index, diabetes duration, hemoglobin A1c, blood pressure, renin-angiotensin-system inhibitors, statins, calcium supplements, serum calcium, and serum phosphate.

RESULTS

The sample was 56.7% female with a mean (SD) age of 55.6 (9.6) years, diabetes duration of 10.3 (8.2) years, eGFR 90.9 (22.1) ml/min/1.73 m2, urine albumin:creatinine ratio (UACR) 151 (588) (median 13) mg/g, plasma FGF23 161 (157) RU/ml, and CAC 637 (1,179) mg. In fully adjusted models, FGF23 was negatively associated with eGFR (p < 0.0001) and positively associated with UACR (p < 0.0001) and CAC (p = 0.0006), but not with carotid CP or aortic CP. Baseline FGF23 concentration did not associate with changes in vBMD or CAC after a mean of 5.1 years follow-up.

CONCLUSIONS

Plasma FGF23 concentrations were independently associated with subclinical coronary artery disease, albuminuria, and kidney function in the understudied African American population with T2D. Findings support relationships between FGF23 and vascular calcification, but not between FGF23 and bone mineral density, in African Americans lacking advanced nephropathy.

Genetic Predisposition to Weight Loss and Regain With Lifestyle Intervention: Analyses From the Diabetes Prevention Program and the Look AHEAD Randomized Controlled Trials

Clinically relevant weight loss is achievable through lifestyle modification, but unintentional weight regain is common. We investigated whether recently discovered genetic variants affect weight loss and/or weight regain during behavioral intervention. Participants at high-risk of type 2 diabetes (Diabetes Prevention Program [DPP]; N = 917/907 intervention/comparison) or with type 2 diabetes (Look AHEAD [Action for Health in Diabetes]; N = 2,014/1,892 intervention/comparison) were from two parallel arm (lifestyle vs. comparison) randomized controlled trials. The associations of 91 established obesity-predisposing loci with weight loss across 4 years and with weight regain across years 2-4 after a minimum of 3% weight loss were tested. Each copy of the minor G allele of MTIF3 rs1885988 was consistently associated with greater weight loss following lifestyle intervention over 4 years across the DPP and Look AHEAD. No such effect was observed across comparison arms, leading to a nominally significant single nucleotide polymorphism×treatment interaction (P = 4.3 × 10(-3)). However, this effect was not significant at a study-wise significance level (Bonferroni threshold P < 5.8 × 10(-4)). Most obesity-predisposing gene variants were not associated with weight loss or regain within the DPP and Look AHEAD trials, directly or via interactions with lifestyle.

A Comprehensive Analysis of Common and Rare Variants to Identify Adiposity Loci in Hispanic Americans: The IRAS Family Study (IRASFS)

Obesity is growing epidemic affecting 35% of adults in the United States. Previous genome-wide association studies (GWAS) have identified numerous loci associated with obesity. However, the majority of studies have been completed in Caucasians focusing on total body measures of adiposity. Here we report the results from genome-wide and exome chip association studies focusing on total body measures of adiposity including body mass index (BMI), percent body fat (PBF) and measures of fat deposition including waist circumference (WAIST), waist-hip ratio (WHR), subcutaneous adipose tissue (SAT), and visceral adipose tissue (VAT) in Hispanic Americans (n_max = 1263) from the Insulin Resistance Atherosclerosis Family Study (IRASFS). Five SNPs from two novel loci attained genome-wide significance (P<5.00x10^-8) in IRASFS. A missense SNP in the isocitrate dehydrogenase 1 gene (IDH1) was associated with WAIST (rs34218846, MAF = 6.8%, P_DOM = 1.62x10^-8). This protein is postulated to play an important role in fat and cholesterol biosynthesis as demonstrated in cell and knock-out animal models. Four correlated intronic SNPs in the Zinc finger, GRF-type containing 1 gene (ZGRF1; SNP rs1471880, MAF = 48.1%, P_DOM = 1.00x10^-8) were strongly associated with WHR. The exact biological function of ZGRF1 and the connection with adiposity remains unclear. SNPs with p-values less than 5.00x10^-6 from IRASFS were selected for replication. Meta-analysis was computed across seven independent Hispanic-American cohorts (n_max = 4156) and the strongest signal was rs1471880 (P_DOM = 8.38x10^-6) in ZGRF1 with WAIST. In conclusion, a genome-wide and exome chip association study was conducted that identified two novel loci (IDH1 and ZGRF1) associated with adiposity. While replication efforts were inconclusive, when taken together with the known biology, IDH1 and ZGRF1 warrant further evaluation.

Obesity, Insulin Resistance, and Incident Small Vessel Disease on Magnetic Resonance Imaging: Atherosclerosis Risk in Communities Study

BACKGROUND AND PURPOSE

The term metabolic syndrome describes the clustering of risk factors found in many individuals with obesity. Because of their pathophysiology, we hypothesized that 2 features of metabolic syndrome, central obesity and insulin resistance (IR), would be associated with cerebrovascular changes on magnetic resonance imaging, and specifically with incident lacunar disease and not white matter hyperintensity (WMH) progression.

METHODS

Risk factors were defined at study baseline in 934 participants in the Atherosclerosis Risk in Communities (ARIC) study, who completed 2 brain magnetic resonance imagings≈10 years apart. WMH progression and incident lacunes between the 2 magnetic resonance imagings were determined. An IR score for each participant was created using principal component analysis of 11 risk factors, including (among others): insulin, homeostatic model assessment-IR, body mass index, and waist circumference. Metabolic syndrome (presence/absence), using standard clinical definitions, and IR score at the first magnetic resonance imaging, were independent variables, evaluated in multivariate logistic regression to determine odds of WMH progression (Q5 versus Q1-Q4) and incident lacunes.

RESULTS

Metabolic syndrome (adjusted odds ratio, 1.98; 95% confidence interval, 1.28-3.05) and IR score (adjusted odds ratio per 1-SD increase, 1.33; 95% confidence interval, 1.05-1.68) were associated with incident lacunes but not with WMH progression. Insulin, homeostatic model assessment-IR, and body mass index were not associated with incident lacunes or WMH progression in separate models.

CONCLUSIONS

The IR score and central obesity are associated with incident lacunar disease but not WMH progression in individuals. Central obesity and IR may be important risk factors to target to prevent lacunar disease.

Vitamin D Associations With Renal, Bone, and Cardiovascular Phenotypes: African American-Diabetes Heart Study

CONTEXT

Vitamin D binding protein (DBP) is an important determinant of bioavailable vitamin D (BAVD) and may provide clues to racial variation in osteoporosis and atherosclerosis.

OBJECTIVE

The objective was to assess relationships between DBP, BAVD, 25-hydroxyvitamin D (25OHD), and 1,25 di-hydroxyvitamin D (1,25OH2D) with kidney, bone, adipose, and atherosclerosis phenotypes in African Americans with type 2 diabetes.

DESIGN

Cross-sectional (N = 545) and longitudinal (N = 288; mean 5.1 ± 0.9-year follow-up) relationships between vitamin D concentrations with renal phenotypes, vertebral bone mineral density, aorto-iliac, coronary artery, and carotid artery calcified plaque (CP), and adipose tissue volumes were studied.

SETTING

African American-Diabetes Heart Study.

PATIENTS

Participants were 56.7% female with mean ± standard deviation (sd) age 55.6 ± 9.6 years, diabetes duration 10.3 ± 8.2 years, and eGFR 90.9 ± 22.1 ml/min/1.73 m(2).

INTERVENTIONS

None.

MAIN OUTCOMES AND MEASURES

Associations tested between vitamin D and the previously mentioned phenotypes adjusting for age, sex, African ancestry proportion, diabetes duration, statins, smoking, changes in estimated glomerular filtration rate, body mass index, hemoglobin A1c, and blood pressure.

RESULTS

1,25OH2D was inversely associated with change in coronary artery CP (parameter estimate [β] -0.005, standard error [SE] 0.002; P = .037), with a trend for change in carotid artery CP (β -0.007, SE 0.004; P = .074). Further adjustment for renin-aldosterone-system blockade revealed inverse association between 1,25OH2D and change in albuminuria (β -0.004, SE 0.002; P = .037). DBP, BAVD, and 25OHD did not associate significantly with changes in albuminuria, CP, or bone mineral density. BAVD was inversely associated with visceral, subcutaneous, intermuscular, and pericardial adipose volumes.

CONCLUSIONS

In contrast to BAVD and 25OHD, only 1,25OH2D levels were significantly and inversely associated with changes in subclinical atherosclerosis and albuminuria in African Americans, suggesting potential beneficial effects.

An Islet-Targeted Genome-Wide Association Scan Identifies Novel Genes Implicated in Cytokine-Mediated Islet Stress in Type 2 Diabetes

Genome-wide association studies in human type 2 diabetes (T2D) have renewed interest in the pancreatic islet as a contributor to T2D risk. Chronic low-grade inflammation resulting from obesity is a risk factor for T2D and a possible trigger of β-cell failure. In this study, microarray data were collected from mouse islets after overnight treatment with cytokines at concentrations consistent with the chronic low-grade inflammation in T2D. Genes with a cytokine-induced change of >2-fold were then examined for associations between single nucleotide polymorphisms and the acute insulin response to glucose (AIRg) using data from the Genetics Underlying Diabetes in Hispanics (GUARDIAN) Consortium. Significant evidence of association was found between AIRg and single nucleotide polymorphisms in Arap3 (5q31.3), F13a1 (6p25.3), Klhl6 (3q27.1), Nid1 (1q42.3), Pamr1 (11p13), Ripk2 (8q21.3), and Steap4 (7q21.12). To assess the potential relevance to islet function, mouse islets were exposed to conditions modeling low-grade inflammation, mitochondrial stress, endoplasmic reticulum (ER) stress, glucotoxicity, and lipotoxicity. RT-PCR revealed that one or more forms of stress significantly altered expression levels of all genes except Arap3. Thapsigargin-induced ER stress up-regulated both Pamr1 and Klhl6. Three genes confirmed microarray predictions of significant cytokine sensitivity: F13a1 was down-regulated 3.3-fold by cytokines, Ripk2 was up-regulated 1.5- to 3-fold by all stressors, and Steap4 was profoundly cytokine sensitive (167-fold up-regulation). Three genes were thus closely associated with low-grade inflammation in murine islets and also with a marker for islet function (AIRg) in a diabetes-prone human population. This islet-targeted genome-wide association scan identified several previously unrecognized candidate genes related to islet dysfunction during the development of T2D.

Genetic Variants Associated With Quantitative Glucose Homeostasis Traits Translate to Type 2 Diabetes in Mexican Americans: The GUARDIAN (Genetics Underlying Diabetes in Hispanics) Consortium

Insulin sensitivity, insulin secretion, insulin clearance, and glucose effectiveness exhibit strong genetic components, although few studies have examined their genetic architecture or influence on type 2 diabetes (T2D) risk. We hypothesized that loci affecting variation in these quantitative traits influence T2D. We completed a multicohort genome-wide association study to search for loci influencing T2D-related quantitative traits in 4,176 Mexican Americans. Quantitative traits were measured by the frequently sampled intravenous glucose tolerance test (four cohorts) or euglycemic clamp (three cohorts), and random-effects models were used to test the association between loci and quantitative traits, adjusting for age, sex, and admixture proportions (Discovery). Analysis revealed a significant (P < 5.00 × 10(-8)) association at 11q14.3 (MTNR1B) with acute insulin response. Loci with P < 0.0001 among the quantitative traits were examined for translation to T2D risk in 6,463 T2D case and 9,232 control subjects of Mexican ancestry (Translation). Nonparametric meta-analysis of the Discovery and Translation cohorts identified significant associations at 6p24 (SLC35B3/TFAP2A) with glucose effectiveness/T2D, 11p15 (KCNQ1) with disposition index/T2D, and 6p22 (CDKAL1) and 11q14 (MTNR1B) with acute insulin response/T2D. These results suggest that T2D and insulin secretion and sensitivity have both shared and distinct genetic factors, potentially delineating genomic components of these quantitative traits that drive the risk for T2D.

Changes in body composition over 8 years in a randomized trial of a lifestyle intervention: the look AHEAD study

OBJECTIVE

To determine the effects of an intensive lifestyle intervention versus a comparison group on body composition in obese or overweight persons with type 2 diabetes at baseline and at 1, 4, and 8 years.

METHODS

Body composition was measured by dual-energy X-ray absorptiometry in a subset of 1019 Look AHEAD study volunteers randomized to intervention or comparison groups. The intervention was designed to achieve and maintain ≥7% weight loss through increased physical activity and reduced caloric intake. The comparison group received social support and diabetes education.

RESULTS

At 1 year, the intervention group lost fat (5.6 ± 0.2 kg) and lean mass (2.3 ± 0.1 kg) but regained fat (∼100%) and lost lean mass between years 1 and 8. Between baseline and year 8, weight loss was greater in intervention versus comparison groups (4.0 ± 0.4 vs. 2.3 ± 0.4 kg); comparison group weight loss was mostly lean mass (2.1 ± 0.17 kg). Fat mass in the intervention group was lower than that of the comparison group at all post-baseline time points.

CONCLUSIONS

Reduced fat mass may place the intervention group at a lower risk of obesity-linked sequelae, a hypothesis that can be tested by future studies of this cohort.

Metabolomic profile associated with insulin resistance and conversion to diabetes in the Insulin Resistance Atherosclerosis Study

CONTEXT

Metabolomic profiling of amino acids and acylcarnitines has revealed consistent patterns associated with metabolic disease.

OBJECTIVE

This study used metabolomic profiling to identify analytes associated with insulin sensitivity (SI) and conversion to type 2 diabetes (T2D).

DESIGN

A multiethnic cohort from the Insulin Resistance Atherosclerosis Study.

SETTING

Community-based.

PATIENTS

A total of 196 subjects (European American, Hispanic, and African American) were selected to represent extremes of the SI distribution and conversion to T2D between baseline and followup exams.

MAIN OUTCOME

Mass spectrometry-based profiling of 69 metabolites. Subjects participated in a frequently sampled i.v. glucose tolerance test to measure SI and acute insulin response. T2D status was determined by a 2-hour oral glucose tolerance test.

RESULTS

Logistic regression analysis from 72 high and 75 low SI subjects revealed significantly decreased glycine and increased valine, leucine, phenylalanine, and combined glutamine and glutamate (P = .0079-7.7 × 10(-6)) in insulin-resistant subjects. Ethnic-stratified results were strongest in European Americans. Comparing amino acid profiles between subjects that converted to T2D (76 converters; 70 nonconverters) yielded a similar pattern of associations: decreased glycine and increased valine, leucine, and combined glutamine and glutamate (P = .016-.00010). Importantly, β-cell function as a covariate revealed a similar pattern of association.

CONCLUSIONS

A distinct pattern of differences in amino acids were observed when comparing subjects with high and low levels of SI. This pattern was associated with conversion to T2D, remaining significant when accounting for β-cell function, emphasizing a link between this metabolic profile and insulin resistance. These results demonstrate a consistent metabolic signature associated with insulin resistance and conversion to T2D, providing potential insight into underlying mechanisms of disease pathogenesis.

Low-frequency and rare exome chip variants associate with fasting glucose and type 2 diabetes susceptibility

Fasting glucose and insulin are intermediate traits for type 2 diabetes. Here we explore the role of coding variation on these traits by analysis of variants on the HumanExome BeadChip in 60,564 non-diabetic individuals and in 16,491 T2D cases and 81,877 controls. We identify a novel association of a low-frequency nonsynonymous SNV in GLP1R (A316T; rs10305492; MAF=1.4%) with lower FG (β=-0.09±0.01 mmol l(-1), P=3.4 × 10(-12)), T2D risk (OR[95%CI]=0.86[0.76-0.96], P=0.010), early insulin secretion (β=-0.07±0.035 pmolinsulin mmolglucose(-1), P=0.048), but higher 2-h glucose (β=0.16±0.05 mmol l(-1), P=4.3 × 10(-4)). We identify a gene-based association with FG at G6PC2 (pSKAT=6.8 × 10(-6)) driven by four rare protein-coding SNVs (H177Y, Y207S, R283X and S324P). We identify rs651007 (MAF=20%) in the first intron of ABO at the putative promoter of an antisense lncRNA, associating with higher FG (β=0.02±0.004 mmol l(-1), P=1.3 × 10(-8)). Our approach identifies novel coding variant associations and extends the allelic spectrum of variation underlying diabetes-related quantitative traits and T2D susceptibility.

APOL1 associations with nephropathy, atherosclerosis, and all-cause mortality in African Americans with type 2 diabetes

Albuminuria and reduced estimated glomerular filtration rate (eGFR) associate with two apolipoprotein L1 gene (APOL1) variants in nondiabetic African Americans (AAs). Whether APOL1 associates with subclinical atherosclerosis and survival remains unclear. To determine this, 717 African American-Diabetes Heart Study participants underwent computed tomography to determine coronary artery-, carotid artery-, and aorta-calcified atherosclerotic plaque mass scores in addition to the urine albumin:creatinine ratio (UACR), eGFR, and C-reactive protein (CRP). Associations between mass scores and APOL1 were assessed adjusting for age, gender, African ancestry, body mass index (BMI), hemoglobin A1c, smoking, hypertension, use of statins and angiotensin-converting enzyme inhibitors, albuminuria, and eGFR. Participants were 58.9% female with mean age 56.5 years, eGFR 89.5 ml/min per 1.73 m(2), UACR 169.6 mg/g, and coronary artery-, carotid artery-, and aorta-calcified plaque mass scores of 610, 171, and 5378, respectively. In fully adjusted models, APOL1 risk variants were significantly associated with lower levels of carotid artery-calcified plaque (β=-0.42, s.e. 0.18; dominant model) and marginally lower coronary artery plaque (β=-0.36, s.e. 0.21; dominant model), but not with aorta-calcified plaque, CRP, UACR, or eGFR. By the end of a mean follow-up of 5.0 years, 89 participants had died. APOL1 nephropathy risk variants were significantly associated with improved survival (hazard ratio 0.67 for one copy; 0.44 for two copies). Thus, APOL1 nephropathy variants associate with lower levels of subclinical atherosclerosis and reduced risk of death in AAs with type 2 diabetes mellitus.

Diabetes in midlife and cognitive change over 20 years: a cohort study

BACKGROUND

Type 2 diabetes is associated with dementia risk, but evidence is limited for possible associations of diabetes and prediabetes with cognitive decline.

OBJECTIVE

To determine whether diabetes in midlife is associated with 20-year cognitive decline and to characterize long-term cognitive decline across clinical categories of hemoglobin A1c (HbA1c) levels.

DESIGN

Prospective cohort study.

SETTING

The community-based ARIC (Atherosclerosis Risk in Communities) study.

PARTICIPANTS

13,351 black and white adults aged 48 to 67 years at baseline (1990 to 1992).

MEASUREMENTS

Diabetes was defined by self-reported physician diagnosis or medication use or HbA1c level of 6.5% or greater. Undiagnosed diabetes, prediabetes, and glucose control in persons with diagnosed diabetes were defined by clinical categories of HbA1c level. Delayed word recall, digit symbol substitution, and word fluency tests were used to assess cognitive performance and were summarized with a global Z score.

RESULTS

Diabetes in midlife was associated with a 19% greater cognitive decline over 20 years (adjusted global Z-score difference, -0.15 [;95% CI, -0.22 to -0.08];) compared with no diabetes. Cognitive decline was significantly greater among persons with prediabetes (HbA1c level of 5.7% to 6.4%) than among those with an HbA1c level less than 5.7%. Participants with poorly controlled diabetes (HbA1c level ≥ 7.0%) had greater decline than those whose diabetes was controlled (adjusted global Z-score difference, -0.16; P = 0.071). Longer-duration diabetes was also associated with greater late-life cognitive decline (P for trend < 0.001). Rates of decline did not differ significantly between white and black persons (P for interaction = 0.44).

LIMITATION

Single HbA1c measurement at baseline, 1 test per cognitive domain, and potential geographic confounding of race comparisons.

CONCLUSION

Diabetes prevention and glucose control in midlife may protect against late-life cognitive decline.

PRIMARY FUNDING SOURCE

National Institutes of Health.

Serum pentadecanoic acid (15:0), a short-term marker of dairy food intake, is inversely associated with incident type 2 diabetes and its underlying disorders

BACKGROUND

Growing evidence suggests that dairy consumption is associated with lower type 2 diabetes risk. However, observational studies have reported inconsistent results, and few have examined dairy's association with the underlying disorders of insulin resistance and β-cell dysfunction.

OBJECTIVE

We investigated the association of the dairy fatty acid biomarkers pentadecanoic acid (15:0) and trans-palmitoleic acid (trans 16:1n-7) with type 2 diabetes traits by evaluating 1) prospective associations with incident diabetes after 5 y of follow-up and 2) cross-sectional associations with directly measured insulin resistance and β-cell dysfunction.

DESIGN

The study analyzed 659 adults without diabetes at baseline from the triethnic multicenter Insulin Resistance Atherosclerosis Study (IRAS). Diabetes status was assessed by using oral-glucose-tolerance tests. Frequently sampled intravenous-glucose-tolerance tests measured insulin sensitivity (SI) and β-cell function [disposition index (DI)]. Serum fatty acids were quantified by using gas chromatography. Logistic and linear regression models were adjusted for demographic, lifestyle, and dietary variables.

RESULTS

Serum 15:0 was a significant biomarker for total dairy intake in the IRAS cohort. It was associated with a decreased incident diabetes risk (OR: 0.73, P = 0.02) and was positively associated with log SI (β: 0.84, P = 0.03) and log DI (β: 2.21, P = 0.02) in fully adjusted models. trans 16:1n-7 was a marker of total partially hydrogenated dietary fat intake and was not associated with outcomes in fully adjusted models.

CONCLUSIONS

Serum 15:0, a marker of short-term intake of this fatty acid, was inversely associated with diabetes risk in this multiethnic cohort. This study may contribute to future recommendations regarding the benefits of dairy products on type 2 diabetes risk.

Egg consumption and insulin metabolism in the Insulin Resistance Atherosclerosis Study (IRAS)

OBJECTIVE

To examine the association between egg consumption and measures of insulin sensitivity (SI), acute insulin response (AIR) and metabolic clearance rate of insulin (MCRI).

DESIGN

Cross-sectional analysis.

SETTINGS

Egg consumption, categorized as <1/week, 1 to <3/week, 3 to <5/week and ≥5/week, was measured using a validated FFQ. SI, AIR and MCRI were determined from frequently sampled intravenous glucose tolerance tests.

SUBJECTS

Non-diabetic participants (n 949) in the Insulin Resistance Atherosclerosis Study (IRAS).

RESULTS

Egg consumption was inversely associated with SI and MCRI, and positively associated with fasting insulin in regression models adjusted for demographic, socio-economic, lifestyle and dietary factors (β = -0·22, 95 % CI -0·38, -0·045, P = 0·05 for SI; β = -0·20, 95 % CI -0·34, -0·055, P = 0·005 for MCRI; β = 0·35, 95 % CI 0·15, 0·54, P = 0·002 for fasting insulin; all P values for linear trend). These associations remained significant after additionally adjusting for energy intake or dietary saturated fat, although dietary cholesterol and BMI attenuated these associations to non-significance. Egg consumption was not associated with AIR.

CONCLUSIONS

Dietary cholesterol and BMI appear to mediate the inverse association of egg consumption with insulin sensitivity and clearance. Alternatively, egg consumption may be clustered with other dietary behaviours which increase BMI, hence negatively impacting on insulin sensitivity and clearance.

Racial differences in the association of insulin resistance with stroke risk: the REasons for Geographic And Racial Differences in Stroke (REGARDS) study

BACKGROUND AND PURPOSE

Insulin resistance is associated with increased stroke risk, but the effect has not been adequately examined separately in white and black populations.

METHODS

The association of baseline insulin resistance with risk of cerebral infarction (CI) and intracerebral hemorrhage (ICH) was assessed in 12 366 white and 6782 black participants from the REasons for Geographic And Racial Differences in Stroke (REGARDS) cohort, recruited between 2003 and 2007 and followed for an average of 5.7 years. Insulin resistance was measured with the homeostasis model assessment-insulin resistance.

RESULTS

There were 364 incident CI and 41 incident ICH events. The risk for CI increased with the log of insulin resistance in whites (hazards ratio [HR]ln(IR)=1.17; 95% confidence interval [CI], 1.00-1.38) but was largely attenuated by adjustment for stroke risk factors (HRln(IR)=1.05; 95% CI, 0.88-1.26). There was no association in blacks (HRln(IR)=1.01; 95% CI, 0.81-1.25). After adjustment for demographic factors and risk factors, there was a significant difference by race in the association of insulin resistance with risk of ICH (P=0.07), with a decrease in the risk of ICH in whites (HRln(IR)=0.61; 95% CI, 0.35-1.04) but a nonsignificant increase in blacks (HRln(IR)=1.20; 95% CI, 0.60-2.39).

CONCLUSIONS

These data support the growing evidence that insulin resistance may play a more important role in stroke risk among white than black individuals and suggest a potentially discordant relationship of insulin resistance on CI and ICH among whites.

Carotid intima-media thickness is associated with incident heart failure among middle-aged whites and blacks: the Atherosclerosis Risk in Communities study

Background

Increased carotid intima‐media thickness (IMT) is associated with subclinical left ventricular myocardial dysfunction, suggesting a possible role of carotid IMT in heart failure (HF) risk determination.

Methods and Results

Mean far wall carotid IMT, measured by B‐mode ultrasound, was available for 13 590 Atherosclerosis Risk in Communities study participants aged 45 to 64 years and free of HF at baseline. HF was defined using ICD‐9 428 and ICD‐10 I‐50 codes from hospitalization records and death certificates. The association between carotid IMT and incident HF was assessed using Cox proportional hazards analysis with models adjusted for demographic variables, major CVD risk factors, and interim CHD. There were 2008 incident HF cases over a median follow‐up of 20.6 years (8.1 cases per 1000 person‐years). Mean IMT was higher in those with HF than in those without (0.81 mm±0.23 versus 0.71 mm±0.17, P<0.001). Unadjusted rate of HF for the fourth compared with the first quartile of IMT was 15.4 versus 3.9 per 1000 person‐years; P<0.001. In multivariable analysis, after adjustment, each standard deviation increase in IMT was associated with incident HF (HR 1.20 [95% CI: 1.16 to 1.25]). After adjustment, the top quartile of IMT was associated with HF (HR 1.60 [95% CI: 1.37 to 1.87]). Results were similar across race and gender groups.

Conclusions

Increasing carotid IMT is associated with incident HF in middle‐aged whites and blacks, beyond risks explained by major CVD risk factors and CHD. This suggests that carotid IMT may be associated with HF through mechanisms different from myocardial ischemia or infarction.

Impact of differential attrition on the association of education with cognitive change over 20 years of follow-up: the ARIC neurocognitive study

Studies of long-term cognitive change should account for the potential effects of education on the outcome, since some studies have demonstrated an association of education with dementia risk. Evaluating cognitive change is more ideal than evaluating cognitive performance at a single time point, because it should be less susceptible to confounding. In this analysis of 14,020 persons from a US cohort study, the Atherosclerosis Risk in Communities (ARIC) Study, we measured change in performance on 3 cognitive tests over a 20-year period, from ages 48-67 years (1990-1992) through ages 70-89 years (2011-2013). Generalized estimating equations were used to evaluate the association between education and cognitive change in unweighted adjusted models, in models incorporating inverse probability of attrition weighting, and in models using cognitive scores imputed from the Telephone Interview for Cognitive Status for participants not examined in person. Education did not have a strong relationship with change in cognitive test performance, although the rate of decline was somewhat slower among persons with lower levels of education. Methods used to account for selective dropout only marginally changed these observed associations. Future studies of risk factors for cognitive impairment should focus on cognitive change, when possible, to allow for reduction of confounding by social or cultural factors.

Genome-wide family-based linkage analysis of exome chip variants and cardiometabolic risk

Linkage analysis of complex traits has had limited success in identifying trait-influencing loci. Recently, coding variants have been implicated as the basis for some biomedical associations. We tested whether coding variants are the basis for linkage peaks of complex traits in 42 African-American (n = 596) and 90 Hispanic (n = 1,414) families in the Insulin Resistance Atherosclerosis Family Study (IRASFS) using Illumina HumanExome Beadchips. A total of 92,157 variants in African Americans (34%) and 81,559 (31%) in Hispanics were polymorphic and tested using two-point linkage and association analyses with 37 cardiometabolic phenotypes. In African Americans 77 LOD scores greater than 3 were observed. The highest LOD score was 4.91 with the APOE SNP rs7412 (MAF = 0.13) with plasma apolipoprotein B (ApoB). This SNP was associated with ApoB (P-value = 4 × 10(-19)) and accounted for 16.2% of the variance in African Americans. In Hispanic families, 104 LOD scores were greater than 3. The strongest evidence of linkage (LOD = 4.29) was with rs5882 (MAF = 0.46) in CETP with HDL. CETP variants were strongly associated with HDL (0.00049 < P-value <4.6 × 10(-12)), accounting for up to 4.5% of the variance. These loci have previously been shown to have effects on the biomedical traits evaluated here. Thus, evidence of strong linkage in this genome wide survey of primarily coding variants was uncommon. Loci with strong evidence of linkage was characterized by large contributions to the variance, and, in these cases, are common variants. Less compelling evidence of linkage and association was observed with additional loci that may require larger family sets to confirm.

Insulin sensitivity and insulin clearance are heritable and have strong genetic correlation in Mexican Americans

OBJECTIVE

The GUARDIAN (Genetics UndeRlying DIAbetes in HispaNics) consortium is described, along with heritability estimates and genetic and environmental correlations of insulin sensitivity and metabolic clearance rate of insulin (MCRI).

METHODS

GUARDIAN is comprised of seven cohorts, consisting of 4,336 Mexican-American individuals in 1,346 pedigrees. Insulin sensitivity (SI ), MCRI, and acute insulin response (AIRg) were measured by frequently sampled intravenous glucose tolerance test in four cohorts. Insulin sensitivity (M, M/I) and MCRI were measured by hyperinsulinemic-euglycemic clamp in three cohorts. Heritability and genetic and environmental correlations were estimated within the family cohorts (totaling 3,925 individuals) using variance components.

RESULTS

Across studies, age, and gender-adjusted heritability of insulin sensitivity (SI , M, M/I) ranged from 0.23 to 0.48 and of MCRI from 0.35 to 0.73. The ranges for the genetic correlations were 0.91 to 0.93 between SI and MCRI; and -0.57 to -0.59 for AIRg and MCRI (all P < 0.0001). The ranges for the environmental correlations were 0.54 to 0.74 for SI and MCRI (all P < 0.0001); and -0.16 to -0.36 for AIRg and MCRI (P < 0.0001-0.06).

CONCLUSIONS

These data support a strong familial basis for insulin sensitivity and MCRI in Mexican Americans. The strong genetic correlations between MCRI and SI suggest common genetic determinants.

Incidence and survival of hospitalized acute decompensated heart failure in four US communities (from the Atherosclerosis Risk in Communities Study)

Most population-based estimates of incident hospitalized heart failure (HF) have not differentiated acute decompensated heart failure (ADHF) from chronic stable HF nor included racially diverse populations. The Atherosclerosis Risk in Communities Study conducted surveillance of hospitalized HF events (age ≥55 years) in 4 US communities. We estimated hospitalized ADHF incidence and survival by race and gender. Potential 2005 to 2009 HF hospitalizations were identified by International Classification of Diseases, Ninth Revision, Clinical Modification, codes; 6,168 records were reviewed to validate ADHF cases. Population estimates were derived from US Census data; 50% of eligible hospitalizations were classified as ADHF, of which 63.6% were incident ADHF and 36.4% were recurrent ADHF. The average incidence of hospitalized ADHF was 11.6 per 1,000 persons, aged ≥55 years, per year, and recurrent hospitalized ADHF was 6.6 per 1,000 persons/yr. Age-adjusted annual ADHF incidence was highest for black men (15.7 per 1,000), followed by black women (13.3 per 1,000), white men (12.3 per 1,000), and white women (9.9 per 1,000). Of incident ADHF events with heart function assessment (89%), 53% had reduced the ejection fraction (heart failure with reduced ejection fraction [HFrEF]) and 47% had preserved ejection fraction (heart failure with preserved ejection fraction [HFpEF]). Black men had the highest proportion of acute HFrEF events (70%); white women had the highest proportion of acute HFpEF (59%). Age-adjusted 28-day and 1-year case fatality after an incident ADHF was 10.4% and 29.5%, respectively. Survival did not differ by race or gender. In conclusion, ADHF hospitalization and HF type varied by both race and gender, but case fatality rates did not. Further studies are needed to explain why black men are at higher risk of hospitalized ADHF and HFrEF.

Sclerostin is positively associated with bone mineral density in men and women and negatively associated with carotid calcified atherosclerotic plaque in men from the African American-Diabetes Heart Study

CONTEXT

Bone mineral density (BMD) and calcified atherosclerotic plaque (CP) demonstrate inverse relationships. Sclerostin, an endogenous regulator of the Wnt pathway and bone formation, has been associated with impaired osteoblast activation and may play a role in vascular calcification.

OBJECTIVE

Our objective was to assess the relationships between sclerostin, BMD, and CP.

DESIGN

Generalized linear models were fitted to test for associations between sclerostin, volumetric BMD (vBMD), and CP.

PARTICIPANTS

A targeted population of 450 unrelated African Americans (AAs) with type 2 diabetes (T2D) was 56% female with mean/SD/median age of 55.4/9.5/55.0 years and a diabetes duration of 10.3/8.2/8.0 years.

MAIN OUTCOME MEASURES

Plasma sclerostin, computed tomography-derived thoracic and lumbar vertebrae trabecular vBMD, coronary artery, carotid artery, and aortoiliac CP were measured.

RESULTS

Plasma sclerostin was 1119/401/1040 pg/mL, thoracic vBMD was 206.3/52.4/204.8 mg/cm3, lumbar vBMD was 180.7/47.0/179.0 mg/cm3, coronary artery CP score was 284/648/13, carotid artery CP score was 46/132/0, and aortoiliac CP score was 1613/2910/282. Sclerostin levels were higher in men than women (P<.0001). Before and after adjusting for age, sex, body mass index, blood pressure, smoking, hemoglobin A1c, and low-density lipoprotein-cholesterol, plasma sclerostin levels were positively associated with thoracic and lumbar vertebrae vBMD (P<.0001). Sex-stratified analyses verified significant relationships in both men and women (both P<.001). Sclerostin was not associated with CP except for an inverse relationship with carotid CP in men (fully adjusted model, P=.03).

CONCLUSIONS

In this cross-sectional study of AA men and women with T2D, circulating sclerostin was positively associated with vBMD in the spine in both sexes and inversely associated with carotid artery CP in men. Sclerostin may play a role in skeletal mineral metabolism in AA but fails to explain inverse relationships between BMD and CP.

The metabolic syndrome and cognitive decline in the Atherosclerosis Risk in Communities study (ARIC)

BACKGROUND

Midlife metabolic syndrome (MetS) may impact cognitive health as a construct independently of hypertension, hyperlipidemia and other components.

METHODS

10,866 participants aged 45-64 years at baseline were assessed for MetS and completed cognitive testing at two later time points (3 and 9 years from the baseline visit).

RESULTS

MetS is associated with increased odds of low cognitive performance in the domains of executive function and word fluency, but not with 6-year cognitive decline. Individual MetS components explained this association (hypertension, diabetes, low HDL, elevated triglycerides and increased waist circumference).

CONCLUSIONS

A focus on the individual risk factors as opposed to MetS during midlife is important to reduce the incidence of cognitive impairment in later life.

Genetic analysis of adiponectin variation and its association with type 2 diabetes in African Americans

OBJECTIVE

Adiponectin is an adipocytokine that has been implicated in a variety of metabolic disorders, including T2D and cardiovascular disease. Studies evaluating genetic variants in ADIPOQ have been contradictory when testing association with T2D in different ethnic groups.

DESIGN AND METHODS

In this study, 18 SNPs in ADIPOQ were tested for association with plasma adiponectin levels and diabetes status. SNPs were examined in two independent African-American cohorts (nmax = 1,116) from the Insulin Resistance Atherosclerosis Family Study (IRASFS) and the African American-Diabetes Heart Study (AA-DHS).

RESULTS

Five polymorphisms were nominally associated with plasma adiponectin levels in the meta-analysis (P = 0.035-1.02 × 10(-6) ) including a low frequency arginine to cysteine mutation (R55C) which reduced plasma adiponectin levels to <15% of the mean. Variants were then tested for association with T2D in a meta-analysis of these and the Wake Forest T2D case-control study (n = 3,233 T2D, 2645 non-T2D). Association with T2D was not observed (P ≥ 0.08), suggesting limited influence of ADIPOQ variants on T2D risk.

CONCLUSIONS

Despite identification of variants associated with adiponectin levels, a detailed genetic analysis of ADIPOQ revealed no association with T2D risk. This puts into question the role of adiponectin in T2D pathogenesis: whether low adiponectin levels are truly causal for or rather a consequence.

A metabolically healthy obese phenotype in hispanic participants in the IRAS family study

OBJECTIVE

Some obese individuals appear to be protected from developing type 2 diabetes mellitus and cardiovascular disease (CVD). This has led to characterizing body size phenotypes based on cardiometabolic risk factors specifically as obese or overweight, and as metabolically healthy (MH) or metabolically abnormal (MA) based upon blood pressure, lipids, glucose homeostasis, and inflammatory parameters. The aim of this study was to measure the prevalence of and describe fat distribution across these phenotypes in a minority population.

DESIGN AND METHODS

Hispanic participants (N = 1054) in the IRAS Family Study were categorized into different body size phenotypes. Computed tomography (CT) abdominal scans were evaluated for measures of nonalcoholic fatty liver disease (NAFLD) and abdominal fat distribution. Statistical models adjusting for familial relationships were estimated.

RESULTS

Seventy percent (70%) of the Hispanic cohort was overweight (32%) or obese (38%). Forty-one percent (n = 138) of overweight participants and 19% (n = 74) of obese participants met criteria for MH. Adjusted analyses showed the MH phenotype was associated with lower visceral adipose tissue (VAT) and higher liver density (indicating lower fat content) in obese participants (p = 0.0005 and p = 0.0002, respectively), and lower VAT but not liver density in overweight participants (p = 0.008 and p = 0.162, respectively) compared to their MA counterparts. Odds of NAFLD were reduced in MH obese (OR = 0.34, p = 0.0007) compared to MA obese. VAT did not differ between MH obese or overweight and normal weight groups.

CONCLUSIONS

These findings suggest that lower levels of visceral and liver fat, despite overall increased total body fat, may be a defining feature of MH obesity in Hispanic Americans.

Longitudinal decline of β-cell function: comparison of a direct method vs a fasting surrogate measure: the Insulin Resistance Atherosclerosis Study

CONTEXT

β-Cell function (BCF) declines over the course of type 2 diabetes, but little is known about BCF changes across glucose tolerance status (GTS) categories, and comparisons of direct vs surrogate measures.

OBJECTIVE

To assess longitudinal changes in BCF across GTS.

DESIGN

The Insulin Resistance Atherosclerosis Study is a multicenter, observational, epidemiologic study.

SETTING

Four clinical centers in the US that could identify subjects likely to have impaired fasting glucose (IFG) or impaired glucose tolerance (IGT).

PATIENTS

We compared longitudinal changes in BCF in 1052 subjects over 5 years. Subjects were categorized according to baseline GTS: normal glucose tolerance (NGT: n = 547), impaired fasting glucose or impaired glucose tolerance (IFG/IGT: n = 341), and newly diagnosed type 2 diabetes (n = 164).

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

BCF was assessed from a frequently sampled iv glucose tolerance test (AIR, acute insulin response), and the homeostasis model assessment of BCF (HOMA B).

RESULTS

NGT and IFG/IGT subjects increased their insulin secretion over time, whereas those with type 2 diabetes experienced either decline or little change in BCF. After adjustment for demographic variables and change in insulin resistance, change in HOMA B underestimated the magnitude of changes in BCF, as assessed by change in AIR. Relative to NGT, the 5-year change in insulin secretion in IFG/IGT and type 2 diabetes was 31% and 70% lower (by HOMA B) and 50% and 80% lower (by AIR).

CONCLUSIONS

The decline in BCF over time in IFG/IGT and type 2 diabetes may be more pronounced than previously estimated; HOMA B may underestimate this decline significantly.

Human cardiovascular disease IBC chip-wide association with weight loss and weight regain in the look AHEAD trial

BACKGROUND/AIMS

The present study identified genetic predictors of weight change during behavioral weight loss treatment.

METHODS

Participants were 3,899 overweight/obese individuals with type 2 diabetes from Look AHEAD, a randomized controlled trial to determine the effects of intensive lifestyle intervention (ILI), including weight loss and physical activity, relative to diabetes support and education, on cardiovascular outcomes. Analyses focused on associations of single nucleotide polymorphisms (SNPs) on the Illumina CARe iSelect (IBC) chip (minor allele frequency >5%; n = 31,959) with weight change at year 1 and year 4, and weight regain at year 4, among individuals who lost ≥ 3% at year 1.

RESULTS

Two novel regions of significant chip-wide association with year-1 weight loss in ILI were identified (p < 2.96E-06). ABCB11 rs484066 was associated with 1.16 kg higher weight per minor allele at year 1, whereas TNFRSF11A, or RANK, rs17069904 was associated with 1.70 kg lower weight per allele at year 1.

CONCLUSIONS

This study, the largest to date on genetic predictors of weight loss and regain, indicates that SNPs within ABCB11, related to bile salt transfer, and TNFRSF11A, implicated in adipose tissue physiology, predict the magnitude of weight loss during behavioral intervention. These results provide new insights into potential biological mechanisms and may ultimately inform weight loss treatment.

Characterization of European ancestry nonalcoholic fatty liver disease-associated variants in individuals of African and Hispanic descent

Nonalcoholic fatty liver disease (NAFLD) is an obesity-related condition affecting over 50% of individuals in some populations and is expected to become the number one cause of liver disease worldwide by 2020. Common, robustly associated genetic variants in/near five genes were identified for hepatic steatosis, a quantifiable component of NAFLD, in European ancestry individuals. Here we tested whether these variants were associated with hepatic steatosis in African- and/or Hispanic-Americans and fine-mapped the observed association signals. We measured hepatic steatosis using computed tomography in five African American (n = 3,124) and one Hispanic American (n = 849) cohorts. All analyses controlled for variation in age, age(2) , gender, alcoholic drinks, and population substructure. Heritability of hepatic steatosis was estimated in three cohorts. Variants in/near PNPLA3, NCAN, LYPLAL1, GCKR, and PPP1R3B were tested for association with hepatic steatosis using a regression framework in each cohort and meta-analyzed. Fine-mapping across African American cohorts was conducted using meta-analysis. African- and Hispanic-American cohorts were 33.9/37.5% male, with average age of 58.6/42.6 years and body mass index of 31.8/28.9 kg/m(2) , respectively. Hepatic steatosis was 0.20-0.34 heritable in African- and Hispanic-American families (P < 0.02 in each cohort). Variants in or near PNPLA3, NCAN, GCKR, PPP1R3B in African Americans and PNPLA3 and PPP1R3B in Hispanic Americans were significantly associated with hepatic steatosis; however, allele frequency and effect size varied across ancestries. Fine-mapping in African Americans highlighted missense variants at PNPLA3 and GCKR and redefined the association region at LYPLAL1.

CONCLUSION

Multiple genetic variants are associated with hepatic steatosis across ancestries. This explains a substantial proportion of the genetic predisposition in African- and Hispanic-Americans. Missense variants in PNPLA3 and GCKR are likely functional across multiple ancestries.

Do genetic modifiers of high-density lipoprotein cholesterol and triglyceride levels also modify their response to a lifestyle intervention in the setting of obesity and type-2 diabetes mellitus?: The Action for Health in Diabetes (Look AHEAD) study

BACKGROUND

High-density lipoprotein cholesterol (HDL-C) and triglycerides are cardiovascular risk factors susceptible to lifestyle behavior modification and genetics. We hypothesized that genetic variants identified by genome-wide association studies as associated with HDL-C or triglyceride levels modify 1-year treatment response to an intensive lifestyle intervention, relative to a usual care of diabetes mellitus support and education.

METHODS AND RESULTS

We evaluated 82 single-nucleotide polymorphisms, which represent 31 loci demonstrated by genome-wide association studies to be associated with HDL-C and triglycerides, in 3561 participants who consented for genetic studies and met eligibility criteria. Variants associated with higher baseline HDL-C levels, cholesterol ester transfer protein (CETP) rs3764261 and hepatic lipase (LIPC) rs8034802, were found to be associated with HDL-C increases with intensive lifestyle intervention (P=0.0038 and 0.013, respectively) and had nominally significant treatment interactions (P=0.047 and 0.046, respectively). The fatty acid desaturase-2 rs1535 variant, associated with low baseline HDL-C (P=0.017), was associated with HDL-C increases with intensive lifestyle intervention (0.0037) and had a nominal treatment interaction (P=0.035). Apolipoprotein B (rs693) and LIPC (rs8034802) single-nucleotide polymorphisms showed nominally significant associations with HDL-C and triglyceride changes with intensive lifestyle intervention and a treatment interaction (P<0.05). Phosphatidylglycerophosphate synthase-1 single-nucleotide polymorphisms (rs4082919) showed the most significant triglyceride treatment interaction in the full cohort (P=0.0009).

CONCLUSIONS

This is the first study to identify genetic variants modifying lipid responses to a randomized lifestyle behavior intervention in overweight or obese individuals with diabetes mellitus. The effects of genetic factors on lipid changes may differ from the effects on baseline lipids and are modifiable by behavioral intervention.

Cardiovascular effects of intensive lifestyle intervention in type 2 diabetes

BACKGROUND

Weight loss is recommended for overweight or obese patients with type 2 diabetes on the basis of short-term studies, but long-term effects on cardiovascular disease remain unknown. We examined whether an intensive lifestyle intervention for weight loss would decrease cardiovascular morbidity and mortality among such patients.

METHODS

In 16 study centers in the United States, we randomly assigned 5145 overweight or obese patients with type 2 diabetes to participate in an intensive lifestyle intervention that promoted weight loss through decreased caloric intake and increased physical activity (intervention group) or to receive diabetes support and education (control group). The primary outcome was a composite of death from cardiovascular causes, nonfatal myocardial infarction, nonfatal stroke, or hospitalization for angina during a maximum follow-up of 13.5 years.

RESULTS

The trial was stopped early on the basis of a futility analysis when the median follow-up was 9.6 years. Weight loss was greater in the intervention group than in the control group throughout the study (8.6% vs. 0.7% at 1 year; 6.0% vs. 3.5% at study end). The intensive lifestyle intervention also produced greater reductions in glycated hemoglobin and greater initial improvements in fitness and all cardiovascular risk factors, except for low-density-lipoprotein cholesterol levels. The primary outcome occurred in 403 patients in the intervention group and in 418 in the control group (1.83 and 1.92 events per 100 person-years, respectively; hazard ratio in the intervention group, 0.95; 95% confidence interval, 0.83 to 1.09; P=0.51).

CONCLUSIONS

An intensive lifestyle intervention focusing on weight loss did not reduce the rate of cardiovascular events in overweight or obese adults with type 2 diabetes. (Funded by the National Institutes of Health and others; Look AHEAD ClinicalTrials.gov number, NCT00017953.).

Cardiovascular effects of intensive lifestyle intervention in type 2 diabetes

BACKGROUND

Weight loss is recommended for overweight or obese patients with type 2 diabetes on the basis of short-term studies, but long-term effects on cardiovascular disease remain unknown. We examined whether an intensive lifestyle intervention for weight loss would decrease cardiovascular morbidity and mortality among such patients.

METHODS

In 16 study centers in the United States, we randomly assigned 5145 overweight or obese patients with type 2 diabetes to participate in an intensive lifestyle intervention that promoted weight loss through decreased caloric intake and increased physical activity (intervention group) or to receive diabetes support and education (control group). The primary outcome was a composite of death from cardiovascular causes, nonfatal myocardial infarction, nonfatal stroke, or hospitalization for angina during a maximum follow-up of 13.5 years.

RESULTS

The trial was stopped early on the basis of a futility analysis when the median follow-up was 9.6 years. Weight loss was greater in the intervention group than in the control group throughout the study (8.6% vs. 0.7% at 1 year; 6.0% vs. 3.5% at study end). The intensive lifestyle intervention also produced greater reductions in glycated hemoglobin and greater initial improvements in fitness and all cardiovascular risk factors, except for low-density-lipoprotein cholesterol levels. The primary outcome occurred in 403 patients in the intervention group and in 418 in the control group (1.83 and 1.92 events per 100 person-years, respectively; hazard ratio in the intervention group, 0.95; 95% confidence interval, 0.83 to 1.09; P=0.51).

CONCLUSIONS

An intensive lifestyle intervention focusing on weight loss did not reduce the rate of cardiovascular events in overweight or obese adults with type 2 diabetes. (Funded by the National Institutes of Health and others; Look AHEAD ClinicalTrials.gov number, NCT00017953.).

Components of metabolic syndrome and 5-year change in insulin clearance - the Insulin Resistance Atherosclerosis Study

AIMS

Cross-sectional evidence indicates that abdominal adiposity, hypertension, dyslipidaemia and glycaemia are associated with reduced metabolic clearance rate of insulin (MCRI). Little is known about the progression of MCRI and whether components of metabolic syndrome are associated with the change in MCRI. In this study, we examined the association between components of metabolic syndrome and the 5-year change of MCRI.

METHODS

At baseline and 5-year follow-up, we measured fasting plasma triglycerides (TG), high-density lipoprotein (HDL) cholesterol, blood pressure (BP), waist circumference (WC) and fasting blood glucose (FBG) in 784 non-diabetic participants in the Insulin Resistance Atherosclerosis Study. MCRI, insulin sensitivity (SI ) and acute insulin response (AIR) were determined from frequently sampled intravenous glucose tolerance tests.

RESULTS

We observed a 29% decline of MCRI at follow-up. TG, systolic BP and WC at baseline were inversely associated with a decline of MCRI regression models adjusted for age, sex, ethnicity, smoking, alcohol consumption, energy expenditure, family history of diabetes, BMI, SI and AIR [β = -0.057 (95% confidence interval, CI: -0.11, -0.0084) for TG, β = -0.0019 (95% CI: -0.0035, -0.00023) for systolic BP and β = -0.0084 (95% CI: -0.013, -0.0039) for WC; all p < 0.05]. Higher HDL cholesterol at baseline was associated with an increase in MCRI [multivariable-adjusted β = 0.0029 (95% CI: 0.0010, 0.0048), p = 0.002]. FBG at baseline was not associated with MCRI at follow-up [multivariable-adjusted β = 0.0014 (95% CI: -0.0026, 0.0029)].

CONCLUSIONS

MCRI declined progressively over 5 years in a non-diabetic cohort. Components of metabolic syndrome at baseline were associated with a significant change in MCRI.

Relationships between serum adiponectin and bone density, adiposity and calcified atherosclerotic plaque in the African American-Diabetes Heart Study

CONTEXT

Adiposity, bone mineral density (BMD), and calcified atherosclerotic plaque (CP) exhibit complex interrelationships that are not well understood. Adipokines vary in relation to changes in body composition and may play roles in regulation of BMD and risk of cardiovascular disease.

OBJECTIVE

Our objective was to examine the relationship between serum adiponectin and quantitative computed tomography-derived measures of volumetric BMD (vBMD) in thoracic and lumbar vertebrae, adipose tissue volumes, and CP in coronary, carotid, and infrarenal aortoiliac arteries. Generalized linear models were fitted to test for associations between adiponectin and measured phenotypes.

PARTICIPANTS

A total of 479 unrelated African Americans with type 2 diabetes, 57% female with a mean ± SD (median) age of 55.6 ± 9.5 (55.0) years and diabetes duration of 10.3 ± 8.2 (8.0) years.

RESULTS

Serum adiponectin was 8.26 ± 7.41 (6.10) μg/mL, coronary artery CP mass score was 280 ± 634 (14), carotid artery CP was 47 ± 133 (0), and aortoiliac CP was 1616 ± 2864 (319). Women had significantly higher body mass index and serum adiponectin and lower coronary and carotid artery calcium than males (all P < .05). Before and after adjusting for age, sex, body mass index, mean arterial pressure, smoking status, hemoglobin A1c, thiazolidinedione use, and low-density lipoprotein-cholesterol, adiponectin was inversely associated with thoracic and lumbar vertebral vBMD [parameter estimates (PEs) of -0.06 and -0.021, respectively; both P < .0005], visceral adipose tissue (PE -0.02; P < 0.0001), and C-reactive protein (PE -0.07; P < .0001) and positively associated with intermuscular adipose tissue (PE 0.01; P = .03). After covariate adjustment, significant associations were not observed between adiponectin and CP in any vascular bed (P > .1).

CONCLUSION

Serum adiponectin levels were inversely associated with cross-sectional measures of thoracic and lumbar vertebral vBMD, inflammation, and visceral adiposity in African Americans but not with vascular CP after adjustment for covariates. The data support a regulatory/signaling role for adiponectin in the modulation of bone density.

Impaired fasting glucose and impaired glucose tolerance have distinct lipoprotein and apolipoprotein changes: the insulin resistance atherosclerosis study

CONTEXT

Cardiovascular risk is increased in individuals with impaired glucose tolerance (IGT) and impaired fasting glucose (IFG); however, those with IGT appear to be at greater risk. Lipoprotein abnormalities occur also in the prediabetic state.

OBJECTIVE

The authors examined lipoprotein composition in IGT and IFG.

DESIGN AND SETTING

Cross-sectional analysis of a large epidemiological study was done.

PARTICIPANTS

The Insulin Resistance Atherosclerosis Study had a total of 1107 participants.

MAIN MEASURES

Lipoproteins and apolipoproteins were measured by conventional methods and lipoprotein composition by nuclear magnetic resonance spectroscopy.

RESULTS

Compared with normal glucose tolerance, apolipoprotein B (105.2 vs 99.8 mg/dL, P < .05) was high in isolated IFG, triglyceride (1.48 vs 1.16 mmol/L, P < .001) was high in isolated IGT, and high-density lipoprotein cholesterol was low in combined IFG/IGT (1.12 vs 1.26 mmol/L, P < .001). Nuclear magnetic resonance spectroscopy revealed additional changes: increased total low-density lipoprotein (LDL) particles (1190 vs 1096 nmol/L, P < .01) in isolated IFG; increased large very-low-density lipoprotein (3.61 vs 2.47 nmol/L, P < .01) and small LDL subclass particles (665 vs 541 nmol/L, P < .05) and decreased large LDL subclass particles (447 vs 513 nmol/L, P < .01) in isolated IGT; and decreased large high-density lipoprotein subclass particles in combined IFG/IGT (4.24 vs 5.39 μmol/L, P < .001).

CONCLUSIONS

Isolated IFG is characterized by increased apolipoprotein B and total LDL particles, whereas isolated IGT is associated with increased triglycerides, large very-low-density lipoprotein subclass particles, and structural remodeling of LDL particles. These results may help to explain differences in cardiovascular disease risk in the prediabetic state.

Insulin clearance and the incidence of type 2 diabetes in Hispanics and African Americans: the IRAS Family Study

OBJECTIVE

We aimed to identify factors that are independently associated with the metabolic clearance rate of insulin (MCRI) and to examine the association of MCRI with incident type 2 diabetes in nondiabetic Hispanics and African Americans.

RESEARCH DESIGN AND METHODS

We investigated 1,116 participants in the Insulin Resistance Atherosclerosis Study (IRAS) Family Study with baseline examinations from 2000 to 2002 and follow-up examinations from 2005 to 2006. Insulin sensitivity (S(I)), acute insulin response (AIR), and MCRI were determined at baseline from frequently sampled intravenous glucose tolerance tests. MCRI was calculated as the ratio of the insulin dose over the incremental area under the curve of insulin. Incident diabetes was defined as fasting glucose ≥126 mg/dL or antidiabetic medication use by self-report.

RESULTS

We observed that S(I) and HDL cholesterol were independent positive correlates of MCRI, whereas fasting insulin, fasting glucose, subcutaneous adipose tissue, visceral adipose tissue, and AIR were independent negative correlates (all P < 0.05) at baseline. After 5 years of follow-up, 71 (6.4%) participants developed type 2 diabetes. Lower MCRI was associated with a higher risk of incident diabetes after adjusting for demographics, lifestyle factors, HDL cholesterol, indexes of obesity and adiposity, and insulin secretion (odds ratio 2.01 [95% CI 1.30-3.10], P = 0.0064, per one-SD decrease in loge-transformed MCRI).

CONCLUSIONS

Our data showed that lower MCRI predicts the incidence of type 2 diabetes.

The long-term effectiveness of a lifestyle intervention in severely obese individuals

OBJECTIVE

Severe obesity (body mass index [BMI] ≥40 kg/m(2)) is a serious public health concern. Although bariatric surgery is an efficacious treatment approach, it is limited in reach; thus, nonsurgical treatment alternatives are needed. We examined the 4-year effects of an intensive lifestyle intervention on body weight and cardiovascular disease risk factors among severely obese, compared with overweight (25 ≤BMI <30), class I (30 ≤BMI <35), and class II obese (35 ≤BMI <40) participants.

METHODS

There were 5145 individuals with type 2 diabetes (45-76 years, BMI ≥25 kg/m(2)) randomized to an intensive lifestyle intervention or diabetes support and education. The lifestyle intervention group received a behavioral weight loss program that included group and individual meetings, a ≥10% weight loss goal, calorie restriction, and increased physical activity. Diabetes support and education received a less intense educational intervention. Four-year changes in body weight and cardiovascular disease risk factors were assessed.

RESULTS

Across BMI categories, 4-year changes in body weight were significantly greater in lifestyle participants compared with diabetes support and education (Ps <.05). At year 4, severely obese lifestyle participants lost 4.9%±8.5%, which was similar to class I (4.8%±7.2%) and class II obese participants (4.4%±7.6%), and significantly greater than overweight participants (3.4%±7.0%; P <.05). Four-year changes in low-density-lipoprotein cholesterol, triglycerides, diastolic blood pressure, HbA(1c), and blood glucose were similar across BMI categories in lifestyle participants; however, the severely obese had less favorable improvements in high-density-lipoprotein cholesterol (3.1±0.4 mg/dL) and systolic blood pressure (-1.4±0.7 mm Hg) compared with the less obese (Ps <.05).

CONCLUSION

Lifestyle interventions can result in important long-term weight losses and improvements in cardiovascular disease risk factors among a significant proportion of severely obese individuals.

Relationship of insulin sensitivity, insulin secretion, and adiposity with insulin clearance in a multiethnic population: the insulin Resistance Atherosclerosis study

OBJECTIVE

We aimed to examine insulin clearance, a compensatory mechanism to changes in insulin sensitivity, across sex, race/ethnicity populations, and varying states of glucose tolerance.

RESEARCH DESIGN AND METHODS

We measured insulin sensitivity index (S(I)), acute insulin response (AIR), and metabolic clearance rate of insulin (MCRI) by the frequently sampled intravenous glucose tolerance test in 1,295 participants in the Insulin Resistance Atherosclerosis Study.

RESULTS

MCRI was positively related to S(I) and negatively to AIR and adiposity across sex, race/ethnicity populations, and varying states of glucose tolerance, adiposity, and family history of diabetes. Differences in MCRI by race/ethnicity (lower in African Americans and Hispanics compared with non-Hispanic whites) and glucose tolerance were largely explained by differences in adiposity, S(I), and AIR.

CONCLUSIONS

Insulin sensitivity, insulin secretion, and adiposity are correlates of insulin clearance and appear to explain differences in insulin clearance by race/ethnicity and glucose tolerance status.