Association of Type 2 Diabetes Candidate Polymorphisms in KCNQ1 With Incretin and Insulin Secretion

OBJECTIVE

KCNQ1 gene polymorphisms are associated with type 2 diabetes. This linkage appears to be mediated by altered β-cell function. In an attempt to study underlying mechanisms, we examined the effect of four KCNQ1 single nucleotide polymorphisms (SNPs) on insulin secretion upon different stimuli.

RESEARCH DESIGN AND METHODS

We genotyped 1,578 nondiabetic subjects at increased risk of type 2 diabetes for rs151290, rs2237892, rs2237895, and rs2237897. All participants underwent an oral glucose tolerance test (OGTT); glucagon-like peptide (GLP)-1 and gastric inhibitory peptide secretion was measured in 170 participants. In 519 participants, a hyperinsulinemic-euglycemic clamp was performed, in 314 participants an intravenous glucose tolerance test (IVGTT), and in 102 subjects a hyperglycemic clamp combined with GLP-1 and arginine stimuli.

RESULTS

rs151290 was nominally associated with 30-min C-peptide levels during OGTT, first-phase insulin secretion, and insulinogenic index after adjustment in the dominant model (all P ≤ 0.01). rs2237892, rs2237895, and rs2237897 were nominally associated with OGTT-derived insulin secretion indexes (all P < 0.05). No SNPs were associated with β-cell function during intravenous glucose or GLP-1 administration. However, rs151290 was associated with glucose-stimulated gastric inhibitory polypeptide and GLP-1 increase after adjustment in the dominant model (P = 0.0042 and P = 0.0198, respectively). No associations were detected between the other SNPs and basal or stimulated incretin levels (all P ≥ 0.05).

CONCLUSIONS

Common genetic variation in KCNQ1 is associated with insulin secretion upon oral glucose load in a German population at increased risk of type 2 diabetes. The discrepancy between orally and intravenously administered glucose seems to be explained not by altered incretin signaling but most likely by changes in incretin secretion.Recent genome-wide association (GWA) studies confirmed the significance of established candidate gene regions for type 2 diabetes, i.e., PPARã, KCNJ11, TCF7L2, and WFS1, and also revealed several novel type 2 diabetes susceptibility loci, i.e., SLC30A8, HHEX, CDKAL1, IGF2BP2, and CDKN2A/B, none of which were considered as functional candidates (1–5). Comprehensive metabolic analysis of genotyped cohorts, comprising measurement of insulin sensitivity and insulin secretion with state-of-the-art methods, revealed that the novel variants influence insulin secretion but show little, if any, impact on insulin sensitivity (6–11).Two recent GWA studies identified KCNQ1 as a novel diabetes susceptibility gene (12–13). Similar to the other novel gene variants that are associated with type 2 diabetes, the KCNQ1 risk alleles for type 2 diabetes also appear to be associated with impaired pancreatic β-cell function as assessed by fasting state– and oral glucose tolerance test (OGTT)-derived indexes of insulin secretion (13).KCNQ1 contains 19 exons and spans more than 400 kb on chromosome 11p15.5 (14). The KCNQ1 gene encodes the pore-forming α-subunit of the voltage-gated K⁺ channel (KvLQT1), which plays an important role in controlling the ventricular repolarization process (15). Mutations in KCNQ1 have been associated with inherited cardiac disorders, such as long QT syndrome and familial atrial fibrillation. The long QT syndrome may occur in a recessive form that is associated with deafness (Jervell and Lange-Nielsen syndrome) or in an autosomal dominant variant not associated with deafness (Romano-Ward syndrome) (16). In addition to the heart and cochlea, KCNQ1 is ubiquitously expressed in epithelial cells, including the exocrine and endocrine pancreas (17). KCNQ1 was reported previously to be expressed in insulin-secreting INS-1 cells, and inhibition of this potassium channel by the sulfonamide analog 293B was found to significantly increase insulin secretion in the presence of tolbutamide (18).The aim of the present study was to investigate the influence of common type 2 diabetes–associated KCNQ1 single nucleotide polymorphisms (SNPs) on insulin secretion kinetics in response to orally and intravenously administered glucose during an OGTT and intravenous glucose tolerance test (IVGTT) as well as a hyperglycemic clamp combined with glucagon-like peptide (GLP)-1 and arginine administration.     

Developmental expression and subcellular localization of glutaminyl cyclase in mouse brain

Glutaminyl cyclase (QC) converts N-terminal glutaminyl residues into pyroglutamate (pE), thereby stabilizing these peptides/proteins. Recently, we demonstrated that QC also plays a pathogenic role in Alzheimer's disease by generating the disease-associated pE-Abeta from N-terminally truncated Abeta peptides in vivo. This newly identified function makes QC an interesting pharmacological target for Alzheimer's disease therapy. However, the expression of QC in brain and peripheral organs, its cell type-specific and subcellular localization as well as developmental profiles in brain are not known. The present study was performed to address these issues in mice. In brain, QC mRNA expression was highest in hypothalamus, followed by hippocampus and cortex. In liver, QC mRNA concentration was almost as high as in brain while lower QC mRNA levels were detected in lung and heart and very low expression levels were found in kidney and spleen. In the developmental course, stable QC mRNA levels were detected in hypothalamus from postnatal day 5 to 370. On the contrary, in cortex and hippocampus QC mRNA levels were highest after birth and declined during ontogenesis by 20–25%. These results were corroborated by immunocytochemical analysis in mouse brain demonstrating a robust QC expression in a subpopulation of lateral and paraventricular hypothalamic neurons and the labeling of a significant number of small neurons in the hippocampal molecular layer, in the hilus of the dentate gyrus and in all layers of the neocortex. Hippocampal QC-immunoreactive neurons include subsets of parvalbumin-, calbindin-, calretinin-, cholecystokinin- and somatostatin-positive GABAergic interneurons. The density of QC labeled hippocampal neurons declined during postnatal development matching the decrease in QC mRNA expression levels. Subcellular double immunofluorescent analysis localized QC within the endoplasmatic reticulum, Golgi apparatus and secretory granules, consistent with a function of QC in protein maturation and/or modification. Our results are in compliance with a role of QC in hypothalamic hormone maturation and suggest additional, yet unidentified QC functions in brain regions relevant for learning and memory which are affected in Alzheimer's disease.     

Somatostatin receptor expression in a parathyroid hormone-related peptide-secreting pancreatic neuroendocrine tumour causing severe hypercalcaemia

BACKGROUND: Humoral hypercalcaemia is a common complication of malignancy with parathyroid hormone-related protein (PTHrP) as a major cause. Breast and lung cancer are relatively common sources of ectopic PTHrP secretion leading to increased osteoclastic bone resorption. CASE REPORT: We report the rare case of a 40-year-old man with severe hypercalcaemia due to a PTHrP-secreting poorly differentiated endocrine carcinoma of the pancreas. On immunohistochemistry, the tumour was positive for PTHrP and somatostatin receptors sst1, sst2, and sst3, whereas sst4 and sst5 were not detected. We demonstrate the transient improvement of hypercalcaemia after adding octreotide to the treatment mainstays in hypercalcaemia of malignancy (fluid repletion, administration of bisphosphonates, loop diuretics, and glucocorticoids). CONCLUSION: To the best of our knowledge, this is the first report showing somatostatin receptor expression in a PTHrP-secreting pancreatic neuroendocrine tumour.     

Impact of oxygen inhalation on the pulmonary circulation: assessment by magnetic resonance (MR)-perfusion and MR-flow measurements

PURPOSE: Oxygen-enhanced magnetic resonance (MR)-ventilation imaging of the lung is based on the inhalation of a high concentration of oxygen (hyperoxia). However, the effect of hyperoxia on the pulmonary circulation is not yet fully understood. In this study the impact of hyperoxia on the pulmonary circulation was evaluated. MATERIALS AND METHODS: Ten healthy volunteers were examined in a 1.5 T MRI system with contrast-enhanced perfusion MRI (saturation recovery 2D turboFLASH) of the lung and phase-contrast flow measurements in the pulmonary trunk. Both measurements were performed breathing room air (RA) and, subsequently, 100% oxygen (15 L/min) (O(2)). RESULTS: The perfusion measurements showed a significant difference between RA and O(2) for the pulmonary blood flow (181 vs. 257 mL/min/100 mL, P = 0.04) and blood volume (14 vs. 21 mL/100 mL, P = 0.008). The mean transit time of the contrast bolus was not changed (P = 0.4) in the dorsal part of the lung, whereas it was significantly prolonged (P = 0.006) in the central part. The mean heart rate during flow measurements breathing RA (67 +/- 11 beats/min) and O(2) (61 +/- 12 beats/min) were not significantly different (P = 0.055). The average cardiac output (pulmonary trunk) was not significantly lower while breathing O(2) (RA: 5.9 vs. O(2): 5.5 L/min, P = 0.054). CONCLUSION: Hyperoxia causes a significant increase and redistribution of the pulmonary perfusion, whereas it leads to a not significant decrease in cardiac output. Thus, for MR-perfusion and MR-flow measurements oxygen inhalation should be avoided, if possible. In the context of oxygen-enhanced MR-ventilation imaging of the lung the contribution of this effect needs to be further evaluated.     

Quantitative 3D pulmonary MR-perfusion in patients with pulmonary arterial hypertension: correlation with invasive pressure measurements

PURPOSE: Pathological changes of the peripheral pulmonary arteries induce pulmonary arterial hypertension (PAH). Aim of this study was to quantitatively assess the effect of PAH on pulmonary perfusion by 3D-MR-perfusion techniques and to compare findings to healthy controls. Furthermore, quantitative perfusion data were correlated with invasive pressure measurements. MATERIAL AND METHODS: Five volunteers and 20 PAH patients (WHO class II or III) were examined using a 1.5T MR scanner. Measurement of pulmonary perfusion was done in an inspiratory breathhold (FLASH3D; 3.5 mm x 1.9 mm x 4mm; TA per 3D dataset 1.5s). Injection of contrast media (0.1 mmol Gd-DTPA/kg BW) and image acquisition were started simultaneously. Evaluation of 3D perfusion was done using singular value decomposition. Lung borders were outlined manually. Each lung volume was divided into three regions (anterior, middle, posterior), and the following parameters were assessed: Time-to-Peak (TTP), blood flow (PBF), blood volume (PBV), and mean transit time (MTT). In 10 patients invasive pulmonary artery pressure measurements were available and correlated to the perfusion measurements. RESULTS: In both, controls and patients, an anterior-to-posterior gradient with higher PBF and PBV posterior was observed. In the posterior lung region, a significant difference (p<0.05) was found for TTP (12s versus 16s) and MTT (4s versus 6s) between volunteers and patients. PBF and PBV were lower in patients than in volunteers (i.e. dorsal regions: 124 versus 180 ml/100 ml/min and 10 versus 12 ml/100 ml), but the difference failed to be significant. The ratio of PBF and PBV between the posterior and the middle or ventral regions showed no difference between both groups. A moderate linear correlation between mean pulmonary arterial pressure (mPAP) and PBV (r=0.51) and MTT (r=0.56) was found. CONCLUSION: The only measurable effect of PAH on pulmonary perfusion is a prolonging of the MTT. There is only a moderate linear correlation of invasive mPAP with PBV and MTT.     

Age related changes of human aortic distensibility: evaluation with ECG-gated CT

Aortic distensibility is a parameter to grade vascular diseases and age-related effects because it is related to the elastic properties of the vessel wall. In this study vascular cross-sectional area changes have been determined using ECG-gated CT to analyse the age dependency of aortic distensibility. Distensibility measurements of the aorta were performed in 31 subjects (28 to 85 years). Time-resolved images were acquired either with a 4- or 16-detector row CT system using a modified CT angiography protocol. Cross-sectional area changes of the aorta were calculated by semiautomatic segmentation, and distensibility values were obtained using additional systemic blood pressure measurements. The aorta could be segmented successfully in all subjects. A decrease of aortic distensibility with age was found (r=0.50). Below (above) the renal arteries, the annual decrease was Δ D _infrarenal =(−2.1±0.7)·10⁻⁷ Pa⁻¹a⁻¹, (D _suprarenal Δ=(−3.5±1.1)·10⁻⁷ Pa⁻¹a⁻¹). Differences between the ages, the youngest third and oldest third studied, were found to be significant (P _suprarenal =0.003; P _infrarenal =0.025). An age-dependent decrease of aortic wall elasticity can be determined in a modified routine CT angiography study.     

Clinical aspects of the apparent diffusion coefficient in 3He MRI: results in healthy volunteers and patients after lung transplantation

PURPOSE: To measure the apparent diffusion coefficient (ADC) after inhalation of hyperpolarized (3)He in healthy volunteers and lung transplant recipients, and demonstrate the gravity dependence of ADC values. MATERIALS AND METHODS: Six healthy volunteers, 10 patients after single-lung transplantation, and six patients after double-lung transplantation were examined at 1.5T during inspiration and expiration. The inhalation of 300 mL of hyperpolarized (3)He was performed with a computer-controlled delivery device. A two-dimensional fast low-angle shot (FLASH) sequence measured the (3)He diffusive gas movement. From these data the ADC was calculated. RESULTS: The mean ADC was 0.143 cm(2)/second in healthy individuals, 0.162 cm(2)/second in transplanted healthy lungs, and 0.173 cm(2)/second in rejected transplanted lungs, whereas it was 0.216 cm(2)/second in native fibrotic lungs and 0.239 cm(2)/second in emphysematous lungs. The difference in mean ADC values among healthy lungs, healthy transplanted lungs, and native diseased lungs was significant (P < 0.001). In inspiration the healthy volunteers showed higher ADC values in the anterior than in the posterior parts of the lungs. In expiration this gradient doubled. CONCLUSION: An anterior-posterior (A/P) gradient was found in inspiration and expiration in healthy lungs. Healthy, transplanted, and native diseased lungs had significantly different mean ADC values. From our preliminary results, (3)He MRI appears to be sensitive for detecting areas of abnormal ventilation in transplanted lungs.