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.

Carotid atherosclerosis and a reduced likelihood for lowered cognitive performance in a Canadian First Nations population

BACKGROUND

We investigated the associations among cardiovascular risk factors, carotid atherosclerosis and cognitive function in a Canadian First Nations population.

METHODS

Individuals aged > or = 18 years, without stroke, nonpregnant and with First Nations status were assessed by the Trail Making Test Parts A and B. Results were combined into a Trail Making Test executive function score (TMT-exec). Doppler ultrasonography assessed carotid stenosis and plaque volume. Anthropometric, vascular and metabolic risk factors were assessed by interview, clinical examinations and blood tests.

RESULTS

For 190 individuals with TMT-exec scores, the median age of the population was 39 years. Compared to the reference group, individuals with elevated levels of left carotid stenosis (LCS) and total carotid stenosis (TCS) were less likely to demonstrate lowered cognitive performance [LCS, odds ratio (OR): 0.47, 95% confidence interval (CI): 0.24-0.96; TCS, OR: 0.40, 95% CI: 0.20-0.80]. No effect was shown for plaque volume. In structural equation modeling, we found that for every 1-unit change in the anthropometric factor in kg/m(2), there was a 0.86-fold decrease in the percent of TCS (p < 0.05).

CONCLUSIONS

Individuals with elevated levels of LCS and TCS were less likely to demonstrate lowered performance. There was some suggestion that TCS mediates the effect of anthropometric risk factors on cognitive function.

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.

Risk of type 2 diabetes among individuals with high and low glomerular filtration rates

AIMS/HYPOTHESIS

Metabolic abnormalities frequently develop prior to the diagnosis of type 2 diabetes and chronic kidney disease. However, it is not known whether GFR predicts the onset of type 2 diabetes.

METHODS

Incident diabetes was ascertained in the Insulin Resistance Atherosclerosis Study (IRAS) (n = 864; age 40-69 years; median follow-up 5.2 years [4.5-6.6 years]; 141 incident cases of diabetes). GFR was estimated by the Modification of Diet in Renal Disease equation. We assessed the relationship between GFR and incident diabetes by logistic regression analysis. Results were adjusted for age, sex, ethnicity, clinic location, BMI, systolic blood pressure, antihypertensive treatment, family history of diabetes, insulin sensitivity and secretion, albumin to creatinine ratio, and levels of triacylglycerols, HDL-cholesterol, plasminogen activator inhibitor-1, and fasting and 2 h glucose.

RESULTS

The relationship between GFR and incident diabetes was not linear. This relationship was statistically significant (p = 0.039) using a restricted cubic polynomial spline for GFR as a regression modelling strategy. Participants were stratified by GFR quintiles. Mean values for GFR from the first to the fifth quintile were 60.8, 71.6, 79.8, 88.2 and 109.0 ml min(-1) 1.73 m(-2). Relative to the fourth quintile, the odds ratios of incident diabetes for the first, second, third and fifth quintiles were 2.32 (95% CI 1.06-5.05), 1.76 (95% CI 0.80-3.88), 1.26 (95% CI 0.56-2.84) and 2.59 (95% CI 1.18-5.65), respectively.

CONCLUSIONS/INTERPRETATION

Individuals in the upper and lower ranges of GFR are at increased risk of future diabetes. GFR and type 2 diabetes may share common pathogenic mechanisms.

Decreased high-molecular-weight adiponectin in gestational diabetes: implications for the pathophysiology of Type 2 diabetes

AIMS

Low serum concentrations of the insulin-sensitizing protein adiponectin predict the development of incident Type 2 diabetes (T2DM). It has recently emerged that the anti-diabetic activity of adiponectin may be mediated by its high-molecular-weight (HMW) isoform, circulating levels of which are decreased in T2DM. The relevance of decreased HMW adiponectin to incident T2DM, however, has not been assessed. Since gestational diabetes (GDM) identifies a population of young women at high risk of future T2DM (i.e. representing an early stage in the natural history of the disease), we sought to determine if decreased HMW adiponectin is a feature of GDM.

METHODS

HMW and total adiponectin were measured in 121 women at the time of oral glucose tolerance testing (OGTT) in late pregnancy, following an abnormal glucose challenge test. Based on the OGTT, there were 41 women with and 80 without GDM.

RESULTS

Median HMW adiponectin concentration was lower in women with GDM (3.5 microg/ml) than in those without GDM (5.5 microg/ml) (P < 0.0001). After full adjustment for covariates, mean HMW adiponectin remained significantly lower in women with GDM compared with their peers (3.6 vs. 5.3 microg/ml, P = 0.0035). HMW adiponectin was positively associated with insulin sensitivity (IS(OGTT)) (r = 0.38, P < 0.0001) and pancreatic B-cell function [insulin secretion-sensitivity index (ISSI)] (r = 0.33, P = 0.0002) and inversely related to blood glucose levels, including area-under-the-glucose-curve during the OGTT (AUC(glucose)) (r = -0.31, P = 0.0007). On separate multiple linear regression analyses, HMW adiponectin emerged as an independent determinant of AUC(glucose), IS(OGTT) and ISSI, respectively, mirroring the relationships of total adiponectin.

CONCLUSIONS

HMW adiponectin is significantly decreased in women with GDM. Deficiency of HMW adiponectin may be an early event in the natural history of T2DM.

Elevated C-reactive protein in Native Canadian children: an ominous early complication of childhood obesity

AIM

Subclinical inflammation has been proposed as a pathophysiologic mechanism linking obesity with vascular and metabolic disease. Native North American populations are experiencing high prevalence rates of both (i) childhood obesity and (ii) adult cardiovascular disease (CVD) and type 2 diabetes. Thus, we sought to determine whether subclinical inflammation is an early complication of obesity in Native children.

METHODS

Serum concentrations of the inflammatory biomarker C-reactive protein (CRP) were assessed in a population-based, cross-sectional study of the Sandy Lake Oji-Cree community of Northern Ontario, Canada, involving 228 children aged 10-19 years (mean age 14.8).

RESULTS

Median CRP in this population was 0.5 mg/l (interquartile range 0.18-1.79 mg/l). CRP levels were higher than age-matched reference data from the Third National Health and Nutrition Examination Survey (NHANES III). Importantly, fully 15.8% of the children of this community had CRP concentrations between 3 and 10 mg/l, a range that identifies adults at high risk of CVD. Moreover, increasing CRP concentration in this paediatric population was associated with an enhanced CV risk profile, consisting of increased adiposity, higher insulin resistance, worsening lipid profile (higher total cholesterol, triglycerides, low-density lipoprotein cholesterol, apolipoprotein B and total cholesterol : high-density-lipoprotein cholesterol ratio), increased leptin and decreased adiponectin. On multivariate analysis, waist circumference and interleukin-6 (IL-6) emerged as independent determinants of CRP concentration.

CONCLUSION

Subclinical inflammation is an early complication of childhood obesity in Native children and may foreshadow an increased burden of CVD and type 2 diabetes in the future.

Preventing type 2 diabetes using combination therapy: design and methods of the CAnadian Normoglycaemia Outcomes Evaluation (CANOE) trial

Several studies have demonstrated that type 2 diabetes mellitus (DM) can be prevented/delayed in subjects with impaired glucose tolerance (IGT) by using pharmacologic agents and/or lifestyle interventions. However, a number of challenges remain, including the translation of lifestyle programmes to the general population and the need to achieve greater risk reductions by using pharmacologic approaches. IGT, like DM, is characterized by insulin resistance, beta-cell dysfunction and increased hepatic glucose production. We believe that the use of combination diabetes therapy would be a particularly effective diabetes prevention strategy. In this context, we initiated the Canadian Normoglycemia Outcomes Evaluation (CANOE) study, a moderately sized, randomized, double-blind, controlled trial. The primary objective of CANOE is to determine whether treatment with metformin plus rosiglitazone, in addition to a healthy living lifestyle programme, will prevent the development of DM. The secondary objective of CANOE is to determine whether this treatment approach will improve cardiovascular risk factors associated with IGT. A total of 200 patients will be recruited in Toronto and London, Ontario, and followed for an average of 4 years (range 3-5 years). Active treatment with metformin (500 mg) plus rosiglitazone (2 mg), administered as one capsule twice daily, will be compared to matched placebo. Subjects will be eligible for randomization if they have IGT and are between the ages of 30-75 years. The primary outcome will be the development of new-onset DM, diagnosed by either two fasting plasma glucose values of >or=7 mmol/l or one positive oral glucose tolerance test with a 2-h plasma glucose value of >11.0 mmol/l during the active drug phase of the trial. With a sample size of 100 participants per group, we will be able to detect a relative risk reduction of 45%, with a two-sided log-rank test with a significance level of 0.05 and 80% power, assuming that the median time to progression is 8 years in the control group and that participants will be recruited over 2 years and followed for an average of 4 years. In conclusion, the CANOE study will determine whether combination pharmacological therapy combined with a lifestyle intervention programme can significantly modify the development of diabetes in high-risk Canadians.

Clinical and genetic associations with hypertriglyceridemic waist in a Canadian aboriginal population

OBJECTIVES

To determine the prevalence of 'hypertriglyceridemic waist' (HTGW) in Oji-Cree, to examine its interaction with hepatic nuclear factor-1alpha (HNF1A) in association with type 2 diabetes, and to characterize its putative genetic determinants.

METHOD

The presence or absence of HTGW was determined in 522 Oji-Cree subjects (223 males, 299 females), >or=18 years of age, in whom physical measurements and fasting plasma analyte concentrations were gathered, and a 75-g oral glucose tolerance test was administered, as part of a cross-sectional study. Subjects were genotyped for HNF1A codon 319, angiotensinogen (AGT) codons 174 and 235, G-protein beta3-subunit (GNB3) nucleotide 825, fatty acid-binding protein (FABP2) codon 54, nucleotides -455 and -482 of the apolipoprotein (apo) C-III (APOC3) promoter, and a 5-bp insertion/deletion polymorphism within the 3'-untranslated region of protein phosphatase 1 regulatory subunit 3 (PPP1R3).

RESULTS

The unadjusted prevalence of HTGW in Oji-Cree adults was 20.5%, with more males affected than females (27.8 vs 15.1%, P=0.0004). Logistic regression analysis, adjusted for age and gender, showed type 2 diabetes was associated with both HNF1A G319S (odds ratio (OR) 4.85, 95% CI 2.45, 9.58) and HTGW (OR 4.96, 95% CI 2.49, 9.88). When the HNF1A mutation and HTGW were present in combination, the OR for type 2 diabetes was markedly increased (OR 43.2, 95% CI 12.4, 150). In women only, both GNB3 825C>T and FABP2 A54T genotypes were significantly associated with HTGW (OR 2.02, 95% CI 1.01, 4.05 and OR 1.95, 95% CI 1.01, 3.74, respectively).

CONCLUSIONS

HTGW is prevalent in Oji-Cree, especially in men. The ORs for type 2 diabetes were similar ( approximately 5-fold) for subjects with either the presence of HTGW or the private HNF1A G319S mutation. These two independent risk factors acted synergistically to confer an even greater increased risk of type 2 diabetes.

Characteristics and prevalence of the metabolic syndrome among three ethnic groups in Canada

OBJECTIVE

To compare the characteristics and prevalence of the metabolic syndrome (MetS) among Native Indians, Inuit, and non-Aboriginal Canadians.

METHODS

The study was based on four cross-sectional studies conducted in the late 1980s and early 1990s involving three ethnic groups living in contiguous regions in central Canada: Oji-Cree Indians from several reserves in northern Ontario and Manitoba, Inuit from the Keewatin region of the Northwest Territories, and non-Aboriginal Canadians (predominantly of European heritage) in the province of Manitoba. The MetS was identified among adult subjects according to the National Cholesterol Education Program (NCEP) definition. Prevalence rates were standardized to the 1991 Canadian national population.

RESULTS

The age-standardized prevalence of the MetS varied by ethnic group, ranging from as high as 45% among Native Indian women to as low as 8% among Inuit men. Compared with Canadians of European origin, Indians had a worse metabolic profile, while Inuit had a better metabolic profile except for a high rate of abdominal obesity. The NCEP criteria in identifying individuals with the MetS were compared to those of the World Health Organization (WHO) in a subset of subjects with the requisite laboratory data. There was moderate agreement between the NCEP and WHO definitions, with a kappa value of 0.63 (95% confidence interval 0.56-0.70).

CONCLUSIONS

The results indicate that the MetS is prevalent in diverse ethnic groups in Canada but varies in the pattern of phenotypic expression. Given the diverse nature of these populations, careful consideration should be given to developing culturally appropriate community-based prevention strategies aimed at reducing the frequency of this syndrome.

Synergism between mutant HNF1A and the metabolic syndrome in Oji-Cree Type 2 diabetes

AIMS

To determine the prevalence of the metabolic syndrome in the Sandy Lake Oji-Cree and to examine its interaction with HNF1A in association with impaired glucose tolerance and Type 2 diabetes.

METHODS

Using data collected from the Sandy Lake Health and Diabetes Project (1993-1995), the presence or absence of the metabolic syndrome was determined in 515 Oji-Cree subjects, > or = 18 years of age. In the original study, fasting plasma analytes were measured, a 75-g oral glucose tolerance test was administered, and subjects were genotyped for HNF1A G319S.

RESULTS

The unadjusted prevalence of the metabolic syndrome in the Oji-Cree adults was 29.9%. The adjusted odds ratio (OR) and 95% confidence interval for Type 2 diabetes among subjects who carried the HNF1A G319S mutation and had the modified metabolic syndrome (excluding hyperglycaemia) was 20.3 (6.94, 59.6). Adjusted ORs for Type 2 diabetes for subjects with either the HNF1A G319S mutation alone or the modified metabolic syndrome alone were 5.56 (2.85, 10.9) and 4.84 (2.53, 9.27), respectively. The risk of having impaired glucose tolerance was not influenced by the presence of either factor.

CONCLUSIONS

The risk of Type 2 diabetes was similar (approximately five-fold increased) for subjects with either the presence of the modified metabolic syndrome or the private HNF1A G319S mutation. Interestingly, when present in combination, the two independent risk factors appeared to act synergistically to confer an even greater increased risk of Type 2 diabetes.

Adiponectin and beta cell dysfunction in gestational diabetes: pathophysiological implications

AIMS/HYPOTHESIS

Gestational diabetes mellitus (GDM) identifies a population of young women at high risk of developing type 2 diabetes and thus provides an excellent model for studying early events in the natural history of this disease. Adiponectin, a novel adipocyte-derived protein with insulin-sensitising properties, has been proposed as a factor linking insulin resistance and beta cell dysfunction in the pathogenesis of type 2 diabetes. We conducted the current investigation to determine whether adiponectin is associated with beta cell dysfunction in GDM.

METHODS

We studied 180 women undergoing OGTT in late pregnancy. Based on the OGTT results, participants were stratified into three groups: (1) NGT (n=93); (2) IGT (n=39); and (3) GDM (n=48). First-phase insulin secretion was determined using a validated index previously proposed by Stumvoll. Insulin sensitivity was assessed using the validated OGTT insulin sensitivity index of Matsuda and DeFronzo (IS(OGTT)).

RESULTS

To evaluate beta cell function in relation to ambient insulin sensitivity, an insulin secretion-sensitivity index (ISSI) was derived from the product of the Stumvoll index and the IS(OGTT), based on the existence of the predicted hyperbolic relationship between these two measures. Mean ISSI was highest in the NGT group (6,731), followed by that in the IGT group (4,976) and then that in the GDM group (3,300) (overall p<0.0001), compatible with the notion of declining beta cell function across these glucose tolerance groups. Importantly, adiponectin was significantly correlated with ISSI (r=0.34, p<0.0001), with a stepwise increase in mean ISSI observed per tertile of adiponectin concentration (trend p<0.0001). In multivariate linear regression analysis, ISSI was positively correlated with adiponectin and negatively correlated with GDM, IGT and C-reactive protein (r(2)=0.54).

CONCLUSIONS/INTERPRETATION

Adiponectin concentration is an independent correlate of beta cell function in late pregnancy. As such, adiponectin may play a key role in mediating insulin resistance and beta cell dysfunction in the pathogenesis of diabetes.

Abdominal obesity predicts declining insulin sensitivity in non-obese normoglycaemics: the Insulin Resistance Atherosclerosis Study (IRAS)

AIM

Cross-sectional studies have demonstrated a relationship between obesity and insulin sensitivity (S(I)); however, there is a lack of evidence from longitudinal studies.

METHODS

The Insulin Resistance Atherosclerosis Study (IRAS) estimated S(I) (x10(-4)/min.microU/ml) directly using a frequently sampled intravenous glucose tolerance test with minimal model analysis in 504 normoglycaemic subjects. Partial correlation coefficients (r) were calculated to compare the relationship of change in S(I) from baseline to 5 years later (DeltaS(I)) with baseline waist circumference (waist) as a measure of abdominal obesity and body mass index (BMI) as a measure of overall obesity. Mean DeltaS(I) was -1.06 (SD = 1.85).

RESULTS

Higher baseline waist (r = -0.16; p = 0.0005), but not BMI (r = -0.005; p = 0.91), was associated with (-) DeltaS(I) in models including sex, ethnicity, clinical centre and baseline S(I), BMI, waist, age and physical activity. The waist-DeltaS(I) relationship differed across the levels of baseline BMI, being significant only in normal weight (r = -0.21) and overweight subjects (r = -0.16), but not in obese subjects. DeltaS(I) was correlated with a 5-year change in either obesity measure (Deltawaist: r = -0.22 and DeltaBMI: r = -0.20; p = 0.0001).

CONCLUSIONS

Among non-diabetics, waist circumference was a strong predictor of declining S(I) among lean subjects, a modest predictor among overweight subjects, but was not predictive among obese individuals. Waist circumference should be considered, in addition to BMI, when identifying individuals at high risk of diabetes or the insulin resistance syndrome.

Hypoadiponectinaemia in South Asian women during pregnancy: evidence of ethnic variation in adiponectin concentration

AIMS

People of South Asian descent face an increased risk of Type 2 diabetes mellitus (DM) and coronary artery disease (CAD) compared with other ethnic groups. One candidate factor underlying this risk may be adiponectin, as circulating levels of this adipocyte-derived protein are reduced in both Type 2 DM and CAD. In a recent study, we assessed the relationship between adiponectin and gestational diabetes (GDM), a potential model of early events in the natural history of Type 2 DM. Here, we report the impact of ethnicity on plasma adiponectin concentration in that study.

METHODS

A cross-sectional study was performed in 180 women undergoing oral glucose tolerance testing in late second or early third trimester to investigate the relationship between adiponectin and glucose tolerance in pregnancy. Based on self-reported ethnicity, participants were stratified into three groups: (i) Caucasian (n = 116), (ii) South Asian (n = 31), and (iii) Asian (n = 28).

RESULTS

Median adiponectin concentration was much lower in the South Asian group (9.7 micro g/ml) than in Caucasians (15.8 micro g/ml) or Asians (16.1 micro g/ml) (overall P < 0.0001). With adjustment for age, prepregnancy body mass index, weight gain in pregnancy, previous history of GDM, family history of DM, fasting insulin and glucose intolerance, mean adiponectin remained significantly lower among South Asians compared with either Caucasians (P < 0.0001) or Asians (P = 0.0034).

CONCLUSIONS

Women of South Asian descent exhibit significantly reduced plasma concentrations of adiponectin in pregnancy compared with Caucasian and Asian counterparts. This observation raises the possibility of hypoadiponectinaemia as a potential factor contributing to the increased risk of diabetes and cardiovascular disease in South Asians.