The UCP2-UCP3 gene cluster maps to chromosome 11q13 in humans, and polymorphisms in these genes may contribute to obesity through effects on energy metabolism. DNA sequencing of UCP2 and UCP3 revealed three polymorphisms informative for association studies: an Ala-->Val substitution in exon 4 of UCP2, a 45 bp insertion/deletion in the 3'-untranslated region of exon 8 of UCP2 and a C-->T silent polymorphism in exon 3 of UCP3. Initially, 82 young (mean age = 30 +/- 7 years), unrelated, full-blooded, non-diabetic Pima Indians were typed for these polymorphisms by direct sequencing. The three sites were in linkage disequilibrium ( P < 0.00001). The UCP2 variants were associated with metabolic rate during sleep (exon 4, P = 0.007; exon 8, P = 0.016) and over 24 h (exon 8, P = 0.038). Heterozygotes for UCP2 variants had higher metabolic rates than homozygotes. The UCP3 variant was not significantly associated with metabolic rate or obesity. In a further 790 full-blooded Pima Indians, there was no significant association between the insertion/deletion polymorphism and body mass index (BMI). However, when only individuals >45 years of age were considered, heterozygotes (subjects with the highest sleeping metabolic rate) had the lowest BMI (P = 0.04). The location of the insertion/deletion polymorphism suggested a role in mRNA stability; however, it appeared to have no effect on skeletal muscle UCP2 mRNA levels in a subset of 23 randomly chosen Pima Indians. In conclusion, these results suggest a contribution from UCP2 (or UCP3) to variation in metabolic rate in young Pima Indians which may contribute to overall body fat content later in life.

Aims/hypothesis. The recent discovery of two adiponectin receptors (AdipoR1 and AdipoR2) will improve our understanding of the molecular mechanisms underlying the insulin-sensitising effect of adiponectin. The aim of this study was to determine for the first time whether skeletal muscle AdipoR1 and/or AdipoR2 gene expression levels are associated with insulin resistance. Methods. Using RT-PCR and northern analysis we measured AdipoR1 and AdipoR2 gene expression in skeletal muscle from healthy Mexican Americans with normal glucose tolerance who had (n=8) or did not have (n=10) a family history of Type 2 diabetes. Results. Gene expression profiling indicated that the AdipoR1 and AdipoR2 isoforms are highly expressed in human skeletal muscle, unlike in mice where AdipoR2 expression was highest in the liver, and AdipoR1 was highest in skeletal muscle. In the study subjects, the expression levels of AdipoR1 (p=0.004) and AdipoR2 (p=0.04), as well as plasma adiponectin concentration (p=0.03) were lower in people with a family history of Type 2 diabetes than in those with no family history of the disease. Importantly, the expression levels of both receptors correlated positively with insulin sensitivity (r=0. 64, p=0.004 and r=0.47, p=0.048 respectively). Conclusions/interpretation. Collectively, these data indicate that both isoforms of the adiponectin receptor play a role in the insulin-sensitising effect of adiponectin.

TCF7L2 is an important regulator of HGP in vitro and binds directly to genes that are important in pathways of glucose metabolism in the liver. These data highlight the possibility that TCF7L2 may affect fasting and postprandial hyperglycaemia in carriers of at-risk TCF7L2 genetic polymorphisms.

To characterize the defects in β-cell function in subjects with impaired fasting glucose (IFG) and compare the results to impaired glucose tolerance (IGT) and normal glucose tolerance (NGT) subjects, β-cell glucose sensitivity and rate sensitivity during the oral glucose tolerance test were measured with the model by Mari in 172 Mexican Americans. A subgroup (n = 70) received a 2-h hyperglycemic clamp (+125 mg/dL), and first- and second-phase insulin secretion were quantitated. Compared with NGT, subjects with IFG and IGT manifested a decrease in β-cell glucose sensitivity; IFG subjects, but not IGT subjects, had decreased β-cell rate sensitivity. In IFG subjects, the defect in β-cell glucose sensitivity was time dependent, began to improve after 60 min, and was comparable to NGT after 90 min. The incremental area under the plasma C-peptide concentration curve during the first 12 min of the hyperglycemic clamp (ΔC-pep[AUC]0–12) was inversely related with the increase in FPG concentration (r = −36, r = 0.001), whereas ΔC-pep[AUC]15–120 positively correlated with FPG concentration (r = 0.29, r < 0.05). When adjusted for the prevailing level of insulin resistance, first-phase insulin secretion was markedly decreased in both IFG and IGT, whereas second-phase insulin secretion was decreased only in IGT. These results demonstrate distinct defects in β-cell function in IFG and IGT.

Interleukin (IL)-18 is a cardiotropic proinflammatory cytokine chronically elevated in the serum of patients with cardiac hypertrophy (LVH). The purpose of this study was to examine the role of IL-18 in pressure-overload hypertrophy using wild type (WT) and IL-18 −/− (null) mice. Adult male C57Bl/ 6 mice underwent transaortic constriction (TAC) for 7 days or sham surgery. Heart weight/body weight ratios showed blunted hypertrophy in IL-18 null TAC mice compared to WT TAC animals. Microarray analyses indicated differential expression of hypertrophy-related genes in WT versus IL-18 nulls. Northern, Western, and EMSA analyses showed Akt and GATA4 were increased in WT but unchanged in IL-18 null mice. Our results demonstrate blunted hypertrophy with reduced expression of contractile-, hypertrophy-, and remodeling-associated genes following pressure overload in IL-18 null mice, and suggest that IL-18 plays a critical role in the hypertrophic response.

Subjects with impaired fasting glucose (IFG) are at increased risk for type 2 diabetes. We recently demonstrated that IFG subjects have increased hepatic insulin resistance with normal insulin sensitivity in skeletal muscle. In this study, we quantitated the insulin secretion rate from deconvolution analysis of the plasma C-peptide concentration during an oral glucose tolerance test (OGTT) and compared the results in IFG subjects with those in subjects with impaired glucose tolerance (IGT) and normal glucose tolerance (NGT). One hundred and one NGT subjects, 64 subjects with isolated IGT, 24 subjects with isolated IFG, and 48 subjects with combined (IFG + IGT) glucose intolerance (CGI) received an OGTT. Plasma glucose, insulin, and C-peptide concentrations were measured before and every 15 min after glucose ingestion. Insulin secretion rate (ISR) was determined by deconvolution of plasma C-peptide concentration. Inverse of the Matsuda index of whole body insulin sensitivity was used as a measure of insulin resistance; 56 subjects also received a euglycemic hyperinsulinemic clamp. The insulin secretion/insulin resistance (disposition) index was calculated as the ratio between incremental area under the ISR curve (∆ISR[AUC]) to incremental area under the glucose curve (∆G[AUC]) factored by the severity of insulin resistance (measured by Matsuda index during OGTT or glucose disposal during insulin clamp). Compared to NGT, the insulin secretion/insulin resistance index during first 30 min of OGTT was reduced by 47, 49, and 74% in IFG, IGT, and CGI, respectively (all < 0.0001). The insulin secretion/insulin resistance index during the second hour (60-120 min) of the OGTT in subjects with IFG was similar to that in NGT (0.79 ± 0.6 vs. 0.72 ± 0.5, respectively, P = NS), but was profoundly reduced in subjects with IGT and CGI (0.31 ± 0.2 and 0.19 ± 0.11, respectively; P < 0.0001 vs. both NGT and IFG). Early-phase insulin secretion is impaired in both IFG and IGT, while the late-phase insulin secretion is impaired only in subjects with IGT.

OBJECTIVEThe study objective was to assess the relationship between β-cell function and HbA1c.RESEARCH DESIGN AND METHODSA total of 522 Mexican American subjects participated in this study. Each subject received a 75-g oral glucose tolerance test (OGTT) after a 10- to 12-h overnight fast. Insulin sensitivity was assessed with the Matsuda index. Insulin secretory rate was quantitated from deconvolution of the plasma C-peptide concentration. β-Cell function was assessed with the insulin secretion/insulin resistance (IS/IR) (disposition) index and was related to the level of HbA1c.RESULTSAt HbA1c levels <5.5%, both the Matsuda index of insulin sensitivity and IS/IR index were constant. However, as the HbA1c increased >5.5%, there was a precipitous decrease in both the Matsuda index and the IS/IR index. Subjects with HbA1c = 6.0–6.4% had a 44 and 74% decrease in the Matsuda index and the IS/IR index, respectively, compared with subjects with HbA1c <5.5% (P < 0.01 for both indices). Subjects with normal glucose tolerance and HbA1c <5.7% had β-cell function comparable to that of subjects with normal glucose tolerance with HbA1c = 5.7–6.4%. However, subjects with impaired fasting glucose or impaired glucose tolerance had a marked decrease in β-cell function independent of their HbA1c level.CONCLUSIONSThe results of the current study demonstrate that in Mexican Americans, as HbA1c increases >6.0%, both insulin sensitivity and β-cell function decrease markedly. Performing an OGTT is pivotal for accurate identification of subjects with impaired β-cell function.

Brain dopaminergic pathways play a major role in the control of movement. Absence of the murine dopamine D2 receptor gene (drd2) produces bradykinesia and hypothermia. A Ser311Cys mutation of the human DRD2 produces a marked functional impairment of the receptor and is associated with higher BMI in some populations. We hypothesized that the Ser311Cys mutation of DRD2 may inhibit energy expenditure. Here we report that total energy expenditure (doubly labeled water) measured in 89 nondiabetic Pima Indians was 244 kcal/ day lower in homozygotes for the Cys311-encoding allele when compared with those heterozygous and homozygous for the Ser311-encoding allele (P ‫؍‬ 0.056). The 24-h resting energy expenditure (respiratory chamber) measured in 320 nondiabetic Pimas was also 87 kcal/day lower in homozygotes for the Cys311-encoding allele when compared with those heterozygous and homozygous for the Ser311-encoding allele (P ‫؍‬ 0.026). These findings are the first evidence that a genetic mutation is associated with reduced energy expenditure in humans. Because the impact of this mutation on human obesity is small, we suggest that either the energy deficit induced is not large enough to significantly influence body weight in this population and/or that the Cys311-encoding allele is also associated with reduced energy intake. Diabetes 50:901-904, 2001