Axel Haupt

Impact of Variation in the FTO Gene on Whole Body Fat Distribution, Ectopic Fat, and Weight Loss

Polymorphisms in the fat mass‐ and obesity‐associated (FTO) gene have been identified to be associated with obesity and diabetes in large genome‐wide association studies. We hypothesized that variation in the FTO gene has an impact on whole body fat distribution and insulin sensitivity, and influences weight change during lifestyle intervention. To test this hypothesis, we genotyped 1,466 German subjects, with increased risk for type 2 diabetes, for single‐nucleotide polymorphism rs8050136 in the FTO gene and estimated glucose tolerance and insulin sensitivity from an oral glucose tolerance test (OGTT). Distribution of fat depots was quantified using whole body magnetic resonance (MR) imaging and spectroscopy in 298 subjects. Two‐hundred and four subjects participated in a lifestyle intervention program and were examined after a follow‐up of 9 months. In the cross‐sectional analysis, the A allele of rs8050136 in FTO was associated with a higher BMI, body fat, and lean body mass (all P < 0.001). There was a significant effect of variation in the FTO gene on subcutaneous fat (P ≤ 0.05) and a trend for liver fat content, nonvisceral adipose tissue, and visceral fat (all P ≤ 0.1). However, the single‐nucleotide polymorphism was not associated with insulin sensitivity or secretion independent of BMI (all P > 0.05). During lifestyle intervention, there was also no influence of the FTO polymorphism on changes in body weight or fat distribution. In conclusion, despite an association with BMI and whole body fat distribution, variation in the FTO locus has no effect on the success of a lifestyle intervention program.

Gene Variants of TCF7L2 Influence Weight Loss and Body Composition During Lifestyle Intervention in a Population at Risk for Type 2 Diabetes

OBJECTIVE The impact of the diabetes risk gene transcription factor 7-like 2 (TCF7L2) on body weight is unclear. As TCF7L2 is expressed in adipose tissue and involved in Wnt-dependent regulation of adipogenesis, we studied the impact of TCF7L2 variants on body composition and weight loss during lifestyle intervention. RESEARCH DESIGN AND METHODS We genotyped 309 German subjects at increased risk for type 2 diabetes for single nucleotide polymorphisms (SNPs) rs7903146, rs12255372, rs11196205, and rs7895340 in TCF7L2 and performed oral glucose tolerance tests before and after a 9-month lifestyle intervention. Fat distribution was quantified using whole-body magnetic resonance imaging/spectroscopy in a subgroup of 210 subjects. RESULTS After adjustment for confounding variables, we observed a negative impact of the type 2 diabetes allele of SNP rs7903146 on change in BMI (P = 0.0034) and on changes in nonvisceral (P = 0.0032) and visceral fat (P = 0.0165) during lifestyle intervention. An association of rs7903146 with lifestyle intervention-induced changes in insulin secretion, glucose concentrations, liver fat, or insulin sensitivity were not detected (all P > 0.2). Essentially the same results were obtained with SNP rs1255372. In contrast, we found no effects of SNPs rs11196205 and rs7895340 on change in BMI (all P ≥ 0.5). CONCLUSIONS Our data reveal that diabetes-associated alleles of TCF7L2 are associated with less weight loss in response to lifestyle intervention. Thus, diabetes-associated TCF7L2 gene variation predicts the success of lifestyle intervention in terms of weight loss and determines individual susceptibility toward environmental factors.

Association of obesity risk SNPs in PCSK1 with insulin sensitivity and proinsulin conversion.

BackgroundProhormone convertase 1 is involved in maturation of peptides. Rare mutations in gene PCSK1, encoding this enzyme, cause childhood obesity and abnormal glucose homeostasis with elevated proinsulin concentrations. Common single nucleotide polymorphisms (SNPs) within this gene, rs6232 and rs6235, are associated with obesity. We studied whether these SNPs influence the prediabetic traits insulin resistance, β-cell dysfunction, or glucose intolerance.MethodsWe genotyped 1498 German subjects for SNPs rs6232 and rs6235 within PCSK1. The subjects were metabolically characterized by oral glucose tolerance test with glucose, insulin, proinsulin, and C-peptide measurements. A subgroup of 512 subjects underwent a hyperinsulinemic-euglycemic clamp.ResultsThe minor allele frequencies were 25.8% for SNP rs6235 and 6.0% for rs6232. After adjustment for sex and age, we found no association of SNPs rs6235 and rs6232 with BMI or other weight-related traits (all p ≥ 0.07). Both minor alleles, adjusted for sex, age, BMI and insulin sensitivity were associated with elevated AUCproinsulin and AUCproinsulin/AUCinsulin (rs6235: padditive model ≤ 0.009, effect sizes 8/8%, rs6232: pdominant model ≤ 0.01, effect sizes 10/21%). Insulin secretion was not affected by the variants (different secretion parameters, all p ≥ 0.08). The minor allele of SNP rs6232 was additionally associated with 15% higher OGTT-derived and 19% higher clamp-derived insulin sensitivity (pdom ≤ 0.0047), 4.5% lower HOMAIR (pdom = 0.02) and 3.5% lower 120-min glucose (pdom = 0.0003) independently of BMI and proinsulin conversion. SNP rs6235 was not associated with parameters of glucose metabolism.ConclusionsLike rare mutations in PCSK1, the more common variants tested determine glucose-stimulated proinsulin conversion, but not insulin secretion. In addition, rs6232, encoding the amino acid exchange N221D, influences insulin sensitivity and glucose homeostasis.

Impact of Variation Near MC4R on Whole-body Fat Distribution, Liver Fat, and Weight Loss

Polymorphisms near the melanocortin‐4 receptor (MC4R) gene locus are associated with body weight. Recent studies have shown that they influence insulin sensitivity and incidence of the metabolic syndrome. Thus, we hypothesized that the candidate single‐nucleotide polymorphism (SNP) rs17782313 near MC4R additionally influences body fat distribution and its change during lifestyle intervention. To test this, 343 German subjects were genotyped for SNP rs17782313. Body composition was assessed using magnetic resonance technique. Subjects were characterized by an oral glucose tolerance test (OGTT). A subgroup of 242 subjects participated in a 9‐month lifestyle intervention. In the overall cohort, the C allele was associated with a higher BMI (P = 0.0013), but had no impact on glucose tolerance or insulin sensitivity (all P ≥ 0.10). There was an effect of the SNP on total body fat (P = 0.022) and nonvisceral fat (P = 0.017), but not on liver fat and visceral fat (all P ≥ 0.33). In the subgroup undergoing lifestyle intervention, SNP rs17782313 had no impact on changes in body weight or fat distribution. Despite an association with BMI and nonvisceral adipose tissue, the SNP rs17782313 did not influence visceral adipose tissue. Thus, this candidate SNP for human obesity may preferentially affect the accumulation of subcutaneous adipose tissue. Furthermore, the variation near MC4R has no effect on success of weight loss during lifestyle intervention.

11β-Hydroxysteroid Dehydrogenase 2 Activity Is Elevated in Severe Obesity and Negatively Associated With Insulin Sensitivity

Alterations in glucocorticoid (GC) metabolism may contribute to the development of obesity and insulin resistance. We aimed to study the role of 11β‐hydroxysteroid dehydrogenase type 2 (11β‐HSD2) in human adiposity, paying special attention to the association between altered GC metabolism and insulin sensitivity. In 24‐h urine samples of 72 extremely obese (mean BMI 45.5 ± 1.1 kg/m2), but otherwise healthy patients urinary free cortisol (UFF), urinary free cortisone (UFE), tetrahydrocortisol (THF), 5α‐tetrahydrocortisol (5α‐THF), and tetrahydrocortisone (THE) were quantified by radioimmunoassay. The sum of the three major tetrahydrometabolites is an estimate for daily GC secretion, and the sum of UFF and UFE represents potentially bioactive‐free‐GCs. Thirty healthy lean subjects (BMI 22.3 ± 0.3 kg/m2) served as controls. In obese subjects, absolute daily GC secretion and the potentially bioactive‐free‐GCs were significantly (P < 0.005) higher than in lean controls (11.8 ± 0.7 vs. 8.0 ± 0.6 mg/d; and 171.8 ± 11.2 vs. 117.6 ± 9.2 μg/d, respectively). However, when these values were corrected for body surface area (BSA), significant differences were no longer detectable. While enzyme activity indices for 5α‐reductase and 11β‐hydroxysteroid dehydrogenase type 1 (11β‐HSD1) were similar in lean and obese subjects, 11β‐HSD2 was markedly elevated in adiposity (3.7 ± 0.2 vs. 2.1 ± 0.1; P < 0.0001). This increase was accompanied by a significant reduction in UFF excretion corrected for BSA (16.5 ± 1.2 vs. 21.7 ± 2.0 μg/d/m2; P = 0.0222). Besides, 11β‐HSD2 activity was significantly correlated with insulin sensitivity (P = 0.0262). When body size is accounted for, both adrenal GC secretion and potentially bioactive‐free‐GCs are indistinguishable between lean and extremely obese subjects. However in obesity, the kidney appears to intensify its supply of the direct substrate cortisone for extrarenal 11β‐HSD1, which may fuel visceral adiposity and insulin resistance.

The risk allele load accelerates the age-dependent decline in beta cell function

Aims/hypothesisAmong the novel type 2 diabetes risk loci identified by genome-wide association studies, TCF7L2, HHEX, SLC30A8 and CDKAL1 appear to affect beta cell function. In the present study we examined the effect of these genes’ risk alleles on the age-dependent decline in insulin secretion.MethodsThe SNPs rs7903146 (TCF7L2), rs7754840(CDKAL1), rs7923837 (HHEX) and rs13266634 (SLC30A8) were genotyped in 1,412 non-diabetic patients, who were subsequently grouped according to their number of risk alleles. All participants underwent an OGTT. Insulin secretion was assessed by validated indices and proinsulin conversion by calculating AUCproinsulin/AUCinsulin.ResultsThe number of risk alleles revealed a Gaussian distribution, with most participants carrying four risk alleles. Stratification into groups with low (LAL, up to three alleles), median (MAL, four alleles) and high (HAL, five to eight alleles) allele load resulted in MAL and HAL participants displaying significantly lower insulin secretion and proinsulin conversion than LAL participants (p ≤ 0.0014 and p = 0.0185, respectively). In the overall cohort, age was negatively associated with insulin secretion and proinsulin conversion (both p < 0.0001). MAL and HAL participants showed a significantly more pronounced decline in insulin secretion with increasing age than LAL participants (p ≤ 0.0325; analysis of covariance), and after stratification for BMI this relationship was maintained in obese, but not non-obese, participants. Proinsulin conversion decreased with increasing age in MAL and HAL, but not LAL, participants (p ≤ 0.0003 vs p = 0.2).Conclusions/interpretationThe risk allele load significantly accelerates the age-dependent decline in beta cell function, and this might be of particular importance in obese people.

Novel obesity risk loci do not determine distribution of body fat depots: a whole-body MRI/MRS study.

A recent meta‐analysis of genome‐wide association studies has identified six new risk‐loci for common obesity. We studied whether these risk loci influence the distribution of body fat depots. We genotyped 1,469 nondiabetic subjects for the single‐nucleotide polymorphisms (SNPs) TMEM18 rs6548238, KCTD15 rs11084753, GNPDA2 rs10938397, SH2B1 rs7498665, MTCH2 rs10838738, and NEGR1 rs2815752. We assessed BMI, waist circumference, total body fat, and lean body mass (bioimpedance). All subjects underwent an oral glucose tolerance test (OGTT) for estimation of insulin sensitivity. In 332 subjects, we measured total adipose tissue (TAT), visceral adipose tissue (VAT), nonvisceral adipose tissue (NVAT), liver fat content, and intramyocellular lipids (IMCLs) using whole‐body magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS). In the dominant inheritance model, the risk alleles of TMEM18 rs6548238 and MTCH2 rs10838738 were nominally associated with higher BMI (P = 0.04, both). The risk allele of TMEM18 rs6548238 was additionally associated with higher waist circumference and total body fat (P ≤ 0.03), the risk allele of NEGR1 rs2815752 with higher waist circumference (P = 0.05) and unexpectedly with lower BMI (P = 0.01). In the MR cohort, we found an association of the risk allele of SH2B1 rs7498665 with higher VAT (P = 0.009) and of GNPDA2 rs10938397 with increased IMCLs (P = 0.03). After Bonferroni correction for multiple comparisons (corrected α‐level: P = 0.0085), none of the SNPs was significantly associated with measures of adiposity or body fat distribution (all P > 0.009, dominant inheritance model). Therefore, our results suggest that these new obesity SNPs, despite their influence on BMI, are neither associated with a metabolically unfavorable nor with a favorable body composition.

An Obesity Risk SNP (rs17782313) near the MC4R Gene Is Associated with Cerebrocortical Insulin Resistance in Humans

Activation of melanocortin-4 receptor (MC4R) by insulin sensitive neurons is a central mechanism in body weight regulation, and genetic variants in the MC4R gene (e.g., rs17782313) are associated with obesity. By using magnetoencephalography, we addressed whether rs17782313 affects the cerebrocortical insulin response. We measured the cerebrocortical insulin response by using magnetoencephalography in a hyperinsulinemic euglycemic clamp (versus placebo) in 51 nondiabetic humans (26 f/25 m, age 35 ± 3 years, BMI 28 ± 1 kg/m2). The C-allele of rs17782313 was minor allele (frequency 23%), and the genotype distribution (TT 30, TC 19, CC 2) was in Hardy-Weinberg-Equilibrium. Insulin-stimulated cerebrocortical theta activity was decreased in the presence of the C-allele (TT 33 ± 16 fT; TC/CC −27 ± 20 fT; P = .023), and this effect remained significant after adjusting for BMI and peripheral insulin sensitivity (P = .047). Cerebrocortical theta activity was impaired in carriers of the obesity risk allele. Therefore, cerebral insulin resistance may contribute to the obesity effect of rs17782313.

The Inhibitory Effect of Recent Type 2 Diabetes Risk Loci on Insulin Secretion Is Modulated by Insulin Sensitivity

CONTEXT/OBJECTIVE Recently novel type 2 diabetes risk loci were identified and reported to associate with beta-cell dysfunction. We assessed whether the risk alleles in TCF7L2, CDKAL1, HHEX, SLC30A8, IGF2BP2, CDKN2A/2B, JAZF1, and WFS1 reduce insulin secretion in an additive manner and whether their impact is influenced by insulin sensitivity. DESIGN/METHODS We genotyped 1397 nondiabetic subjects for the aforementioned risk alleles and performed risk allele summation. Participants underwent an oral glucose tolerance test and in a subgroup also an iv glucose tolerance test with C-peptide and insulin measurements. In our cohort, only polymorphisms in SLC30A8, HHEX, TCF7L2, and CDKAL1 influenced insulin secretion. So we tested only these polymorphisms and, in a separate analysis, all above-mentioned polymorphisms. RESULTS We observed a 28% decline in insulin secretion with increment of risk alleles (P <or= 0.0018). Subjects with two to four risk alleles displayed a progressive decline in ss-cell function, which was not further enhanced in carriers of five to seven alleles. After stratification for insulin sensitivity, subjects with low insulin sensitivity revealed a significant decline in insulin secretion with increment of risk alleles (P = 0.0086), whereas this was not seen in subjects with high insulin sensitivity (P = 0.07). The additional study with eight risk alleles provided similar results. CONCLUSIONS The negative effects of the risk alleles on ss-cell function appear additive in subjects with low insulin sensitivity but not in subjects with high insulin sensitivity. Effective compensatory mechanisms may exist in subjects with high insulin sensitivity that limit the impact of these genes.

Influence of common polymorphisms in the SLC5A2 gene on metabolic traits in subjects at increased risk of diabetes and on response to empagliflozin treatment in patients with diabetes

Objective Inhibition of the renal sodium–glucose cotransporter 2 (SGLT2) is a novel concept in the therapy of diabetes mellitus. In this study, we first assessed whether common single nucleotide polymorphisms (SNPs) in the SGLT2-encoding gene SLC5A2 affect diabetes-related metabolic traits in subjects at risk for type 2 diabetes and, second, whether these have pharmacogenetic relevance by interfering with the response to empagliflozin treatment in patients with type 2 diabetes. Patients and methods Samples from a metabolically well-phenotyped cross-sectional study population (total N=2600) at increased risk for type 2 diabetes and pooled pharmacogenetic samples from patients from four phase III trials of empagliflozin (in total: 603 receiving empagliflozin, 305 receiving placebo) were genotyped for five common SNPs (minor allele frequencies ≥5%) present in the SLC5A2 gene locus. Results In the cross-sectional study, none of the SLC5A2 SNPs significantly influenced metabolic traits such as body fat, insulin sensitivity/resistance, insulin release, HbA1c, plasma glucose, or systolic blood pressure when multiple testing was taken into account (all P≥0.0083). Further, no relevant effect on response to treatment with empagliflozin on HbA1c, fasting glucose, weight, or systolic blood pressure was observed for the SNPs tested in the pharmacogenetic study. Conclusion Common genetic variants in the SLC5A2 gene neither affects diabetes-related metabolic traits nor have a clinically relevant impact on response to treatment with the SGLT2 inhibitor empagliflozin.