Variants in MTNR1B influence fasting glucose levels.

To identify previously unknown genetic loci associated with fasting glucose concentrations, we examined the leading association signals in ten genome-wide association scans involving a total of 36,610 individuals of European descent. Variants in the gene encoding melatonin receptor 1B (MTNR1B) were consistently associated with fasting glucose across all ten studies. The strongest signal was observed at rs10830963, where each G allele (frequency 0.30 in HapMap CEU) was associated with an increase of 0.07 (95% CI = 0.06-0.08) mmol/l in fasting glucose levels (P = 3.2 x 10(-50)) and reduced beta-cell function as measured by homeostasis model assessment (HOMA-B, P = 1.1 x 10(-15)). The same allele was associated with an increased risk of type 2 diabetes (odds ratio = 1.09 (1.05-1.12), per G allele P = 3.3 x 10(-7)) in a meta-analysis of 13 case-control studies totaling 18,236 cases and 64,453 controls. Our analyses also confirm previous associations of fasting glucose with variants at the G6PC2 (rs560887, P = 1.1 x 10(-57)) and GCK (rs4607517, P = 1.0 x 10(-25)) loci.

New genetic loci implicated in fasting glucose homeostasis and their impact on type 2 diabetes risk.

Levels of circulating glucose are tightly regulated. To identify new loci influencing glycemic traits, we performed meta-analyses of 21 genome-wide association studies informative for fasting glucose, fasting insulin and indices of beta-cell function (HOMA-B) and insulin resistance (HOMA-IR) in up to 46,186 nondiabetic participants. Follow-up of 25 loci in up to 76,558 additional subjects identified 16 loci associated with fasting glucose and HOMA-B and two loci associated with fasting insulin and HOMA-IR. These include nine loci newly associated with fasting glucose (in or near ADCY5, MADD, ADRA2A, CRY2, FADS1, GLIS3, SLC2A2, PROX1 and C2CD4B) and one influencing fasting insulin and HOMA-IR (near IGF1). We also demonstrated association of ADCY5, PROX1, GCK, GCKR and DGKB-TMEM195 with type 2 diabetes. Within these loci, likely biological candidate genes influence signal transduction, cell proliferation, development, glucose-sensing and circadian regulation. Our results demonstrate that genetic studies of glycemic traits can identify type 2 diabetes risk loci, as well as loci containing gene variants that are associated with a modest elevation in glucose levels but are not associated with overt diabetes.

Glomerular hyperfiltration and increased proximal sodium reabsorption in subjects with type 2 diabetes or impaired fasting glucose in a population of the African region.

BACKGROUND. Glomerular hyperfiltration (GHF) is a well-recognized early renal alteration in diabetic patients. As the prevalence of GHF is largely unknown in populations in the African region with respect to normal fasting glucose (NFG), impaired fasting glucose (IFG) and type 2 diabetes [diabetes mellitus (DM)], we conducted a cross-sectional study in the Seychelles islands among families including at least one member with hypertension. METHODS. The glomerular filtration rate (GFR), effective renal plasma flow (ERPF) and proximal tubular sodium reabsorption were measured using inulin, p-aminohippurate (PAH) and endogenous lithium clearance, respectively. Twenty-four-hour urine was collected on the preceding day. RESULTS. Of the 363 participants (mean age 44.7 years), 6.6% had IFG, 9.9% had DM and 63.3% had hypertension. The prevalence of GHF, defined as a GFR >140 ml/min, was 17.2%, 29.2% and 52.8% in NFG, IFG and DM, respectively (P trend <0.001). Compared to NFG, the adjusted odds ratio for GHF was 1.99 [95% confidence interval (CI) 0.73-5.44] for IFG and 5.88 (2.39-14.45) for DM. Lithium clearance and fractional excretion of lithium were lower in DM and IFG than NFG (P < 0.001). CONCLUSION. In this population of African descent, subjects with impaired fasting glucose or type 2 diabetes had a high prevalence of GHF and enhanced proximal sodium reabsorption. These findings provide further insight on the elevated incidence of nephropathy reported among African diabetic individuals.

Interactions of dietary whole-grain intake with fasting glucose- and insulin-related genetic loci in individuals of European descent: a meta-analysis of 14 cohort studies.

Whole-grain foods are touted for multiple health benefits, including enhancing insulin sensitivity and reducing type 2 diabetes risk. Recent genome-wide association studies (GWAS) have identified several single nucleotide polymorphisms (SNPs) associated with fasting glucose and insulin concentrations in individuals free of diabetes. We tested the hypothesis that whole-grain food intake and genetic variation interact to influence concentrations of fasting glucose and insulin. Via meta-analysis of data from 14 cohorts comprising ∼ 48,000 participants of European descent, we studied interactions of whole-grain intake with loci previously associated in GWAS with fasting glucose (16 loci) and/or insulin (2 loci) concentrations. For tests of interaction, we considered a P value <0.0028 (0.05 of 18 tests) as statistically significant. Greater whole-grain food intake was associated with lower fasting glucose and insulin concentrations independent of demographics, other dietary and lifestyle factors, and BMI (β [95% CI] per 1-serving-greater whole-grain intake: -0.009 mmol/l glucose [-0.013 to -0.005], P < 0.0001 and -0.011 pmol/l [ln] insulin [-0.015 to -0.007], P = 0.0003). No interactions met our multiple testing-adjusted statistical significance threshold. The strongest SNP interaction with whole-grain intake was rs780094 (GCKR) for fasting insulin (P = 0.006), where greater whole-grain intake was associated with a smaller reduction in fasting insulin concentrations in those with the insulin-raising allele. Our results support the favorable association of whole-grain intake with fasting glucose and insulin and suggest a potential interaction between variation in GCKR and whole-grain intake in influencing fasting insulin concentrations.

Impaired glucose homeostasis in mice lacking the alpha1b-adrenergic receptor subtype.

To assess the role of the alpha1b-adrenergic receptor (AR) in glucose homeostasis, we investigated glucose metabolism in knockout mice deficient of this receptor subtype (alpha1b-AR-/-). Mutant mice had normal blood glucose and insulin levels, but elevated leptin concentrations in the fed state. During the transition to fasting, glucose and insulin blood concentrations remained markedly elevated for at least 6 h and returned to control levels after 24 h whereas leptin levels remained high at all times. Hyperinsulinemia in the post-absorptive phase was normalized by atropine or methylatropine indicating an elevated parasympathetic activity on the pancreatic beta cells, which was associated with increased levels of hypothalamic NPY mRNA. Euglycemic clamps at both low and high insulin infusion rates revealed whole body insulin resistance with reduced muscle glycogen synthesis and impaired suppression of endogenous glucose production at the low insulin infusion rate. The liver glycogen stores were 2-fold higher in the fed state in the alpha1b-AR-/- compared with control mice, but were mobilized at the same rate during the fed to fast transition or following glucagon injections. Finally, high fat feeding for one month increased glucose intolerance and body weight in the alpha1b-AR-/-, but not in control mice. Altogether, our results indicate that in the absence of the alpha1b-AR the expression of hypotalamic NPY and the parasympathetic nervous activity are both increased resulting in hyperinsulinemia and insulin resistance as well as favoring obesity and glucose intolerance development during high fat feeding.

Genome-wide association identifies nine common variants associated with fasting proinsulin levels and provides new insights into the pathophysiology of type 2 diabetes.

OBJECTIVE: Proinsulin is a precursor of mature insulin and C-peptide. Higher circulating proinsulin levels are associated with impaired β-cell function, raised glucose levels, insulin resistance, and type 2 diabetes (T2D). Studies of the insulin processing pathway could provide new insights about T2D pathophysiology. RESEARCH DESIGN AND METHODS: We have conducted a meta-analysis of genome-wide association tests of ∼2.5 million genotyped or imputed single nucleotide polymorphisms (SNPs) and fasting proinsulin levels in 10,701 nondiabetic adults of European ancestry, with follow-up of 23 loci in up to 16,378 individuals, using additive genetic models adjusted for age, sex, fasting insulin, and study-specific covariates. RESULTS: Nine SNPs at eight loci were associated with proinsulin levels (P < 5 × 10(-8)). Two loci (LARP6 and SGSM2) have not been previously related to metabolic traits, one (MADD) has been associated with fasting glucose, one (PCSK1) has been implicated in obesity, and four (TCF7L2, SLC30A8, VPS13C/C2CD4A/B, and ARAP1, formerly CENTD2) increase T2D risk. The proinsulin-raising allele of ARAP1 was associated with a lower fasting glucose (P = 1.7 × 10(-4)), improved β-cell function (P = 1.1 × 10(-5)), and lower risk of T2D (odds ratio 0.88; P = 7.8 × 10(-6)). Notably, PCSK1 encodes the protein prohormone convertase 1/3, the first enzyme in the insulin processing pathway. A genotype score composed of the nine proinsulin-raising alleles was not associated with coronary disease in two large case-control datasets. CONCLUSIONS: We have identified nine genetic variants associated with fasting proinsulin. Our findings illuminate the biology underlying glucose homeostasis and T2D development in humans and argue against a direct role of proinsulin in coronary artery disease pathogenesis.

The Lin28/let-7 axis regulates glucose metabolism.

The let-7 tumor suppressor microRNAs are known for their regulation of oncogenes, while the RNA-binding proteins Lin28a/b promote malignancy by inhibiting let-7 biogenesis. We have uncovered unexpected roles for the Lin28/let-7 pathway in regulating metabolism. When overexpressed in mice, both Lin28a and LIN28B promote an insulin-sensitized state that resists high-fat-diet induced diabetes. Conversely, muscle-specific loss of Lin28a or overexpression of let-7 results in insulin resistance and impaired glucose tolerance. These phenomena occur, in part, through the let-7-mediated repression of multiple components of the insulin-PI3K-mTOR pathway, including IGF1R, INSR, and IRS2. In addition, the mTOR inhibitor, rapamycin, abrogates Lin28a-mediated insulin sensitivity and enhanced glucose uptake. Moreover, let-7 targets are enriched for genes containing SNPs associated with type 2 diabetes and control of fasting glucose in human genome-wide association studies. These data establish the Lin28/let-7 pathway as a central regulator of mammalian glucose metabolism.

Moderate amounts of fructose consumption impair insulin sensitivity in healthy young men: a randomized controlled trial.

OBJECTIVE: Adverse effects of hypercaloric, high-fructose diets on insulin sensitivity and lipids in human subjects have been shown repeatedly. The implications of fructose in amounts close to usual daily consumption, however, have not been well studied. This study assessed the effect of moderate amounts of fructose and sucrose compared with glucose on glucose and lipid metabolism. RESEARCH DESIGN AND METHODS: Nine healthy, normal-weight male volunteers (aged 21-25 years) were studied in this double-blind, randomized, cross-over trial. All subjects consumed four different sweetened beverages (600 mL/day) for 3 weeks each: medium fructose (MF) at 40 g/day, and high fructose (HF), high glucose (HG), and high sucrose (HS) each at 80 g/day. Euglycemic-hyperinsulinemic clamps with [6,6]-(2)H(2) glucose labeling were used to measure endogenous glucose production. Lipid profile, glucose, and insulin were measured in fasting samples. RESULTS: Hepatic suppression of glucose production during the clamp was significantly lower after HF (59.4 ± 11.0%) than HG (70.3 ± 10.5%, P < 0.05), whereas fasting glucose, insulin, and C-peptide did not differ between the interventions. Compared with HG, LDL cholesterol and total cholesterol were significantly higher after MF, HF, and HS, and free fatty acids were significantly increased after MF, but not after the two other interventions (P < 0.05). Subjects' energy intake during the interventions did not differ significantly from baseline intake. CONCLUSIONS: This study clearly shows that moderate amounts of fructose and sucrose significantly alter hepatic insulin sensitivity and lipid metabolism compared with similar amounts of glucose.

Exercise prevents fructose-induced hypertriglyceridemia in healthy young subjects.

Excess fructose intake causes hypertriglyceridemia and hepatic insulin resistance in sedentary humans. Since exercise improves insulin sensitivity in insulin-resistant patients, we hypothesized that it would also prevent fructose-induced hypertriglyceridemia. This study was therefore designed to evaluate the effects of exercise on circulating lipids in healthy subjects fed a weight-maintenance, high-fructose diet. Eight healthy males were studied on three occasions after 4 days of 1) a diet low in fructose and no exercise (C), 2) a diet with 30% fructose and no exercise (HFr), or 3) a diet with 30% fructose and moderate aerobic exercise (HFrEx). On all three occasions, a 9-h oral [(13)C]-labeled fructose loading test was performed on the fifth day to measure [(13)C]palmitate in triglyceride-rich lipoprotein (TRL)-triglycerides (TG). Compared with C, HFr significantly increased fasting glucose, total TG, TRL-TG concentrations, and apolipoprotein (apo)B48 concentrations as well as postfructose glucose, total TG, TRL-TG, and [(13)C]palmitate in TRL-TG. HFrEx completely normalized fasting and postfructose TG, TRL-TG, and [(13)C]palmitate concentration in TRL-TG and apoB48 concentrations. In addition, it increased lipid oxidation and plasma nonesterified fatty acid concentrations compared with HFr. These data indicate that exercise prevents the dyslipidemia induced by high fructose intake independently of energy balance.

Basal insulin and cardiovascular and other outcomes in dysglycemia.

BACKGROUND: The provision of sufficient basal insulin to normalize fasting plasma glucose levels may reduce cardiovascular events, but such a possibility has not been formally tested. METHODS: We randomly assigned 12,537 people (mean age, 63.5 years) with cardiovascular risk factors plus impaired fasting glucose, impaired glucose tolerance, or type 2 diabetes to receive insulin glargine (with a target fasting blood glucose level of ≤95 mg per deciliter [5.3 mmol per liter]) or standard care and to receive n-3 fatty acids or placebo with the use of a 2-by-2 factorial design. The results of the comparison between insulin glargine and standard care are reported here. The coprimary outcomes were nonfatal myocardial infarction, nonfatal stroke, or death from cardiovascular causes and these events plus revascularization or hospitalization for heart failure. Microvascular outcomes, incident diabetes, hypoglycemia, weight, and cancers were also compared between groups. RESULTS: The median follow-up was 6.2 years (interquartile range, 5.8 to 6.7). Rates of incident cardiovascular outcomes were similar in the insulin-glargine and standard-care groups: 2.94 and 2.85 per 100 person-years, respectively, for the first coprimary outcome (hazard ratio, 1.02; 95% confidence interval [CI], 0.94 to 1.11; P=0.63) and 5.52 and 5.28 per 100 person-years, respectively, for the second coprimary outcome (hazard ratio, 1.04; 95% CI, 0.97 to 1.11; P=0.27). New diabetes was diagnosed approximately 3 months after therapy was stopped among 30% versus 35% of 1456 participants without baseline diabetes (odds ratio, 0.80; 95% CI, 0.64 to 1.00; P=0.05). Rates of severe hypoglycemia were 1.00 versus 0.31 per 100 person-years. Median weight increased by 1.6 kg in the insulin-glargine group and fell by 0.5 kg in the standard-care group. There was no significant difference in cancers (hazard ratio, 1.00; 95% CI, 0.88 to 1.13; P=0.97). CONCLUSIONS: When used to target normal fasting plasma glucose levels for more than 6 years, insulin glargine had a neutral effect on cardiovascular outcomes and cancers. Although it reduced new-onset diabetes, insulin glargine also increased hypoglycemia and modestly increased weight. (Funded by Sanofi; ORIGIN ClinicalTrials.gov number, NCT00069784.).

Protocol for the modeling the epidemiologic transition study: a longitudinal observational study of energy balance and change in body weight, diabetes and cardiovascular disease risk.

ABSTRACT: BACKGROUND: The prevalence of obesity has increased in societies of all socio-cultural backgrounds. To date, guidelines set forward to prevent obesity have universally emphasized optimal levels of physical activity. However there are few empirical data to support the assertion that low levels of energy expenditure in activity is a causal factor in the current obesity epidemic are very limited. METHODS: The Modeling the Epidemiologic Transition Study (METS) is a cohort study designed to assess the association between physical activity levels and relative weight, weight gain and diabetes and cardiovascular disease risk in five population-based samples at different stages of economic development. Twenty-five hundred young adults, ages 25-45, were enrolled in the study; 500 from sites in Ghana, South Africa, Seychelles, Jamaica and the United States. At baseline, physical activity levels were assessed using accelerometry and a questionnaire in all participants and by doubly labeled water in a subsample of 75 per site. We assessed dietary intake using two separate 24-h recalls, body composition using bioelectrical impedance analysis, and health history, social and economic indicators by questionnaire. Blood pressure was measured and blood samples collected for measurement of lipids, glucose, insulin and adipokines. Full examination including physical activity using accelerometry, anthropometric data and fasting glucose will take place at 12 and 24 months. The distribution of the main variables and the associations between physical activity, independent of energy intake, glucose metabolism and anthropometric measures will be assessed using cross-section and longitudinal analysis within and between sites. DISCUSSION: METS will provide insight on the relative contribution of physical activity and diet to excess weight, age-related weight gain and incident glucose impairment in five populations' samples of young adults at different stages of economic development. These data should be useful for the development of empirically-based public health policy aimed at the prevention of obesity and associated chronic diseases.

Relation between atherogenic dyslipidemia and the Adult Treatment Program-III definition of metabolic syndrome (Genetic Epidemiology of Metabolic Syndrome Project).

Genetic Epidemiology of Metabolic Syndrome is a multinational, family-based study to explore the genetic basis of the metabolic syndrome. Atherogenic dyslipidemia (defined as low plasma high-density lipoprotein cholesterol with elevated triglycerides (&lt;25th and &gt;75th percentile for age, gender, and country, respectively) identified affected subjects for the metabolic syndrome. This report examines the frequency at which atherogenic dyslipidemia predicts the metabolic syndrome of the National Cholesterol Education Program Adult Treatment Panel III (ATP-III). One thousand four hundred thirty-six (854 men/582 women) affected patients by our criteria were compared with 1,672 (737 men/935 women) unaffected persons. Affected patients had more hypertension, obesity, and hyperglycemia, and they met a higher number of ATP-III criteria (3.2 +/- 1.1 SD vs 1.3 +/- 1.1 SD, p &lt;0.001). Overall, 76% of affected persons also qualified for the ATP-III definition (Cohen's kappa 0.61, 95% confidence interval 0.59 to 0.64), similar to a separate group of 464 sporadic, unrelated cases (75%). Concordance increased from 41% to 82% and 88% for ages &lt; or =35, 36 to 55, and &gt; or =55 years, respectively. Affected status was also independently associated with waist circumference (p &lt;0.001) and fasting glucose (p &lt;0.001) but not systolic blood pressure (p = 0.43). Thus, the lipid-based criteria used to define affection status in this study substantially parallels the ATP-III definition of metabolic syndrome in subjects aged &gt;35 years. In subjects aged &lt;35 years, atherogenic dyslipidemia frequently occurs in the absence of other metabolic syndrome risk factors.

Metabolically healthy obesity: different prevalences using different criteria.

To estimate the prevalence of metabolically healthy obesity (MHO) according to different definitions. Population-based sample of 2803 women and 2557 men participated in the study. Metabolic abnormalities were defined using six sets of criteria, which included different combinations of the following: waist; blood pressure; total, high-density lipoprotein or low-density lipoprotein-cholesterol; triglycerides; fasting glucose; homeostasis model assessment; high-sensitivity C-reactive protein; personal history of cardiovascular, respiratory or metabolic diseases. For each set, prevalence of MHO was assessed for body mass index (BMI); waist or percent body fat. Among obese (BMI 30 kg/m(2)) participants, prevalence of MHO ranged between 3.3 and 32.1% in men and between 11.4 and 43.3% in women according to the criteria used. Using abdominal obesity, prevalence of MHO ranged between 5.7 and 36.7% (men) and 12.2 and 57.5% (women). Using percent body fat led to a prevalence of MHO ranging between 6.4 and 43.1% (men) and 12.0 and 55.5% (women). MHO participants had a lower odd of presenting a family history of type 2 diabetes. After multivariate adjustment, the odds of presenting with MHO decreased with increasing age, whereas no relationship was found with gender, alcohol consumption or tobacco smoking using most sets of criteria. Physical activity was positively related, whereas increased waist was negatively related with BMI-defined MHO. MHO prevalence varies considerably according to the criteria used, underscoring the need for a standard definition of this metabolic entity. Physical activity increases the likelihood of presenting with MHO, and MHO is associated with a lower prevalence of family history of type 2 diabetes.

Alcohol consumption and incidence of type 2 diabetes. Results from the CoLaus study.

BACKGROUND AND AIMS: Moderate alcohol consumption has been shown to decrease the risk of type 2 diabetes (T2DM), but whether this association is also valid for impaired fasting glucose (IFG) is less well known. We aimed at assessing the impact of alcohol consumption and of type of alcoholic beverage on the incidence of T2DM and T2DM + IFG. METHODS AND RESULTS: As many as 4765 participants (2613 women, mean age 51.7 ± 10.5 years) without T2DM at baseline and followed for an average of 5.5 years. The association between alcohol consumption, type of alcoholic beverage and outcomes was assessed after adjustment for a validated T2DM risk score. During follow-up 284 participants developed T2DM and 643 developed IFG. On bivariate analysis, alcohol consumption was positively associated with the risk of developing T2DM or T2DM + IFG. Moderate (14-27 units/week) alcohol consumption tended to be associated with a lower risk of T2DM, but no protective effect was found for T2DM + IFG. Multivariable-adjusted odds ratio (OR) and (95% confidence interval) for T2DM: 0.89 (0.65-1.22), 0.66 (0.42-1.03) and 1.63 (0.93-2.84) for 1-13, 14-27 and 28 + units/week, respectively (p for quadratic trend < 0.005). For T2DM + IFG, the corresponding ORs were 1.09 (0.90-1.32), 1.33 (1.02-1.74) and 1.54 (0.99-2.39), respectively, p for trend = 0.03. No specific effect of alcoholic beverage (wine, beer or spirits) was found for T2DM or for T2DM + IFG. CONCLUSION: Moderate alcohol consumption is associated with a reduced risk of developing T2DM, but not of developing T2DM + IFG. No specific effect of type of alcoholic beverage was found.

n-3 fatty acids and cardiovascular outcomes in patients with dysglycemia.

BACKGROUND: The use of n-3 fatty acids may prevent cardiovascular events in patients with recent myocardial infarction or heart failure. Their effects in patients with (or at risk for) type 2 diabetes mellitus are unknown. METHODS: In this double-blind study with a 2-by-2 factorial design, we randomly assigned 12,536 patients who were at high risk for cardiovascular events and had impaired fasting glucose, impaired glucose tolerance, or diabetes to receive a 1-g capsule containing at least 900 mg (90% or more) of ethyl esters of n-3 fatty acids or placebo daily and to receive either insulin glargine or standard care. The primary outcome was death from cardiovascular causes. The results of the comparison between n-3 fatty acids and placebo are reported here. RESULTS: During a median follow up of 6.2 years, the incidence of the primary outcome was not significantly decreased among patients receiving n-3 fatty acids, as compared with those receiving placebo (574 patients [9.1%] vs. 581 patients [9.3%]; hazard ratio, 0.98; 95% confidence interval [CI], 0.87 to 1.10; P=0.72). The use of n-3 fatty acids also had no significant effect on the rates of major vascular events (1034 patients [16.5%] vs. 1017 patients [16.3%]; hazard ratio, 1.01; 95% CI, 0.93 to 1.10; P=0.81), death from any cause (951 [15.1%] vs. 964 [15.4%]; hazard ratio, 0.98; 95% CI, 0.89 to 1.07; P=0.63), or death from arrhythmia (288 [4.6%] vs. 259 [4.1%]; hazard ratio, 1.10; 95% CI, 0.93 to 1.30; P=0.26). Triglyceride levels were reduced by 14.5 mg per deciliter (0.16 mmol per liter) more among patients receiving n-3 fatty acids than among those receiving placebo (P<0.001), without a significant effect on other lipids. Adverse effects were similar in the two groups. CONCLUSIONS: Daily supplementation with 1 g of n-3 fatty acids did not reduce the rate of cardiovascular events in patients at high risk for cardiovascular events. (Funded by Sanofi; ORIGIN ClinicalTrials.gov number, NCT00069784.).