GLP-1-related proteins attenuate the effects of mitochondrial membrane damage in pancreatic ß cells.

Glucagon-like peptide (GLP)-1 analog based therapies are used not only for their insulinotropic effects, but also for their pleiotropic effects that improve pancreatic ß cell function. Liraglutide is a long acting derivative of human GLP-1(7-37), which is a cleavage product encompassing amino acids 7-37 of GLP-1. In this study, we examined whether Liraglutide treatment restore the glucose-stimulated mitochondrial response of ß cells with chemically induced mitochondrial damage. We tested three GLP-1-related proteins: human GLP-1(1-37), GLP-1(7-37) and Liraglutide. To measure changes of the mitochondrial pH quantitatively in real-time, we have developed a bioengineered ß cell line. We generated a mitochondrial damaged model by treating ß cells with ethidium bromide (EtBr; 0.5 or 1 µg/mL for 48 h). EtBr treatment reduced the response to 25 mM glucose in mitochondrial pH in a dose- and time-dependent manner. GLP-1(7-37) (100 nM) enhanced the response of mitochondria to glucose stimulation in undamaged ß cells. Preincubation with Liraglutide (1 nM) or GLP-1 (100 nM) for 3h recovered the mitochondrial response to glucose in damaged ß cells, however, GLP-1(7-37) (100 nM) did not. When GLP-1(7-37) was administered in stepwise increments (i.e., starting with 20 nM to reach 100 nM in 3h), similar recovery of the mitochondrial function was observed. The results suggest that Liraglutide is effective to recover glucose-stimulated mitochondrial response in damaged ß cells.

Identification of KCNJ15 as a susceptibility gene in Asian patients with type 2 diabetes mellitus.

Recent advances in genome research have enabled the identification of new genomic variations that are associated with type 2 diabetes mellitus (T2DM). Via fine mapping of SNPs in a candidate region of chromosome 21q, the current study identifies potassium inwardly-rectifying channel, subfamily J, member 15 (KCNJ15) as a new T2DM susceptibility gene. KCNJ15 is expressed in the beta cell of the pancreas, and a synonymous SNP, rs3746876, in exon 4 (C566T) of this gene, with T allele frequency among control subjects of 3.1%, showed a significant association with T2DM affecting lean individuals in three independent Japanese sample sets (p = 2.5 x 10(-7), odds ratio [OR] = 2.54, 95% confidence interval [CI] = 1.76-3.67) and with unstratified T2DM (p = 6.7 x 10(-6), OR = 1.76, 95% CI = 1.37-2.25). The diabetes risk allele frequency was, however, very low among Europeans in whom no association between this variant and T2DM could be shown. Functional analysis in human embryonic kidney 293 cells demonstrated that the risk allele of the synonymous SNP in exon 4 increased KCNJ15 expression via increased mRNA stability, which resulted in the higher expression of protein as compared to that of the nonrisk allele. We also showed that KCNJ15 is expressed in human pancreatic beta cells. In conclusion, we demonstrated a significant association between a synonymous variant in KCNJ15 and T2DM in lean Japanese patients with T2DM, suggesting that KCNJ15 is a previously unreported susceptibility gene for T2DM among Asians.

A new mitochondrial pH biosensor for quantitative assessment of pancreatic ß-cell function.

Mitochondrial pH is a key determinant of mitochondrial energy metabolism. We have developed a new fluorescence-based ratiometric pH biosensor using a chloride-insensitive and hydrogen-sensitive probe for direct, quantitative and bleaching-free measurement in a living cell. Fusing this biosensor with a mitochondrial localization signal (MTpHGV) allowed us to determine mitochondrial pH. This new system was applied to measure mitochondrial pH in pancreatic ß-cells, in which mitochondrial function plays a pivotal role in insulin secretion. Rat INS1 cells and mouse MIN6 cells are transfected with MTpHGV stably to monitor mitochondrial pH. While carbonyl cyanide 3-chlorophenylhydrazone (CCCP) treatment rapidly decreased mitochondrial pH in cultured rat MTpHGV-INS-1 cells, MTpHGV-MIN6 cells showed a rapid increase. These data suggest that MTpHGV probe exist in matrix side in INS-1 cells, but on the outer side of mitochondrial inner membrane in MIN6 cells. Moreover, while MTpHGV-INS-1 cells showed a rapid increase of pH by glucose stimulation, mitochondrial pH decreased quickly by glucose stimulation in all MTpHGV-MIN6 cells examined and recovered smoothly. Perfusion study of glucose load in MTpHGV-MIN6 cells under aminooxyacetate (AOA) or 100µM diazoxide showed that this mitochondrial pH acidification was dependent on nicotinamide adenine dinucleotide (NADH) shuttle, but independent from KATP channel. This new system for measuring mitochondrial pH is sensitive across the range of physiologic conditions and may be a useful tool for evaluating mitochondrial function in living cells.

Genetic polymorphisms in organic cation transporter 1 (OCT1) in Chinese and Japanese populations exhibit altered function.

Organic cation transporter 1 (OCT1; SLC22A1) seems to play a role in the efficacy and disposition of the widely used antidiabetic drug metformin. Genetic variants in OCT1 have been identified largely in European populations. Metformin is increasingly being used in Asian populations where the incidence of type 2 diabetes (T2D) is on the rise. The goal of this study is to identify genetic variants of OCT1 in Chinese and Japanese populations, which may potentially modulate response to metformin. We used recent data from the 1000 Genomes Project (Chinese and Japanese) and direct sequencing of selected amplicons of OCT1 in 66 DNA samples from Japanese patients with T2D. A total of six nonsynonymous variants were identified. Three of them (Q97K, P117L, and R206C) had not been functionally characterized previously and had allele frequencies of 0.017, 0.023 and 0.008, respectively. The uptake of metformin in cells expressing Q97K, P117L, and R206C was significantly reduced relative to the OCT1 reference (62 ± 4.3, 55 ± 6.8, and 22 ± 1.5% for Q97K, P117L, and R206C, respectively). Kinetic studies indicated that P117L and R206C exhibited a reduced V(max), whereas Q97K showed an increased K(m). The green fluorescent protein (GFP)-tagged Q97K and P117L variants localized to the plasma membrane, whereas the GFP-tagged R206C was retained mainly in the endoplasmic reticulum. Replacement of the highly conserved R206 with different amino acids modulated the subcellular localization and function of the transporter. This study suggests that nonsynonymous variants of OCT1 in Chinese and Japanese populations may affect the differential response to metformin.

Role of vitamin D in energy and bone metabolism in postmenopausal women with type 2 diabetes mellitus: A 6-month follow-up evaluation.

AIMS/INTRODUCTION: Resting energy expenditure was associated with a serum bone turnover marker in postmenopausal women with type 2 diabetes (T2DMPW) in the present cross-sectional study. To clarify the fundamental pathological factor for the correlation of bone metabolism and basal metabolism in type 2 diabetes, a 6-month prospective follow-up study was carried out with supplementation of vitamin D. MATERIALS AND METHODS: A total of 44 T2DMPW were enrolled. The following factors were evaluated at the beginning and the end of the summer: procollagen type 1 N-terminal propeptide, carboxy-terminal collagen crosslinks-1, intact parathyroid hormone and 25-hydroxyvitamin D (25[OH]D), as well as diabetic complications, body composition, respiratory quotient and resting energy expenditure. A total of 23 patients with low 25(OH)D levels (˂20 ng/mL) were instructed to increase vitamin D levels by lifestyle change. Among them, 15 patients with osteoporosis were also administered alfacalcidol. RESULTS: Serum 25(OH)D increased in 25 patients and decreased in 19 patients. Patients who did not receive the study intervention at the start tended to have a decreased 2525(OH)D level; therefore, the average 25(OH)D level of all patients was not changed. Changes in resting energy expenditure were positively correlated with those of procollagen type 1 N-terminal propeptide/carboxy-terminal collagen crosslinks-1. Changes in the respiratory quotient correlated with the mean glycated hemoglobin levels; procollagen type 1 N-terminal propeptide levels positively correlated with serum 25(OH)D after the intervention. These correlations were prominent in patients with increased 25(OH)D and those with alfacalcidol supplementation. CONCLUSIONS: Restoration of vitamin D level might be a prerequisite for a normal correlation between bone and basal metabolism in T2DMPW. Lifestyle intervention for retention of vitamin D level is important even in summer, in T2DMPW.

Pancreatic developmental defect evaluated by celiac artery angiography in a patient with MODY5.

The hepatocyte nuclear factor 1ß gene (HNF1B) is responsible for maturity-onset diabetes of the young type 5 (MODY5), which is characterized by early-onset diabetes mellitus and urogenital malformations. HNF1B is expressed during visceral endoderm formation. We identified a disruption of the great pancreatic artery in a patient with MODY5 with no pancreatic body or tail. Our finding supports the significance of HNF1B in the development of the pancreas.

Association between basal metabolic function and bone metabolism in postmenopausal women with type 2 diabetes.

OBJECTIVE: Diabetes is a risk factor for osteoporosis, and glycemic control is critical during osteoporosis treatment in patients with type 2 diabetes (T2D). However, diabetic therapies have potentially adverse effects on bone metabolism. Additionally, biomarkers for bone metabolism are directly affected by drug therapies for osteoporosis. This study examined resting energy expenditure (REE) and respiratory quotient (RQ) as indices of bone metabolism in postmenopausal Japanese women with T2D. METHODS: Forty-six postmenopausal Japanese women with T2D were examined. Procollagen type 1 N-terminal propeptide (P1NP, a fasting serum bone formation marker) and carboxy-terminal collagen cross-links-1 (CTX-1, a resorption marker) were evaluated, along with intact parathyroid hormone, 25-hydroxyvitamin D (25[OH]D), urine microalbumin, motor nerve conduction velocity, sensory nerve conduction velocity, R-R interval, body composition, REE, RQ, and bone mineral density at the nondominant distal radius. RESULTS: The mean T-score was low with high variance (-1.7 ± 1.6), and 18 patients (39%) met the criteria for osteoporosis. REE was positively correlated with body mass index (ß = 0.517; r(2) = 0.250), serum calcium (ß = 0.624; r(2) = 0.200), glycated hemoglobin A1C for the previous 6 mo (ß = 0.395; r(2) = 0.137), and the serum P1NP/CTX-1 ratio (ß = 0.380; r(2) = 0.144). RQ was positively correlated with serum 25(OH)D (ß = 0.387; r(2) = 0.131). CONCLUSION: The basal metabolic rate and diabetic pathophysiology are interrelated with bone turnover.

Hypoglycemia Observed on Continuous Glucose Monitoring Associated With IGF-2-Producing Solitary Fibrous Tumor.

CONTEXT: Tumors producing IGF-2 (IGF-2oma) are a major cause of spontaneous hypoglycemia. The treatment mainstay is surgical resection. Many case reports note resolution of hypoglycemia after IGF-2oma resection; however, outcomes are variable according to tumor type. We report a case of resolving hypoglycemia, observed on continuous glucose monitoring, after resection of an IGF-2-producing solitary fibrous tumor of pleura and review the current literature. CASE REPORT: A 69-year-old woman presented with impaired consciousness because of hypoglycemia. An IGF-2oma was diagnosed as the cause for hypoglycemia because of decreased serum insulin and IGF-1, the presence of a pleural tumor, and a high-molecular-weight form of serum IGF-2 detected by Western immunoblot. Surgical resection was performed; pathological examination demonstrated a solitary fibrous tumor with low-grade malignancy. Continuous glucose monitoring showed reversal of hypoglycemia after tumor resection. Approximately 2 years after resection, the patient has no signs of tumor recurrence or hypoglycemia. CONCLUSIONS: An IGF-2-producing solitary fibrous tumor of pleura in this case caused hypoglycemia. From a search of the literature of 2004-2014, 32 cases of IGF-2oma with hypoglycemia that underwent radical surgery were identified; in 19 (59%) patients, hypoglycemia was reversed, and there was no subsequent recurrence. The remaining 13 (41%) patients experienced tumor recurrence or metastasis an average of 43 months after initial tumor resection. The tumor of the present case was a low-grade malignancy. Regular follow-up with biomarker monitoring of glucose metabolism and assessment of hypoglycemic symptomatology, in conjunction with imaging tests, is important for detecting possible tumor recurrence and metastasis.

Tetrabutylammonium 2-pyridyltriolborate salts for Suzuki-Miyaura cross-coupling reactions with aryl chlorides.

Palladium-catalyzed Suzuki-Miyaura cross-coupling reactions of tetrabutylammonium 2-pyridyltriolborate salts with various aryl (heteroaryl) chlorides can produce the corresponding desired coupling products with good to excellent yields. These tetrabutylammonium salts are more reactive than the corresponding lithium salts. The coupling reactions with aryl chlorides progressed in the presence of PdCl2dcpp (3 mol %) and CuI/MeNHCH2CH2OH (20 mol %) in anhydrous DMF without bases.

Localization of hepatocyte nuclear factor-4α in the nucleolus and nucleus is regulated by its C-terminus.

UNLABELLED: Aims/Introduction: Mutations in hepatocyte nuclear factor-4α (HNF4α) lead to various diseases, among which C-terminal deletions of HNF4α are exclusively responsible for maturity onset diabetes of the young 1 (MODY1). MODY is an autosomal dominant disease characterized by a primary defect in insulin response to glucose, suggesting that the C-terminus of HNF4α is important for pancreatic ß-cell function. To clarify the role of the C-terminus of HNF4α, changes in cellular localization and the binding ability to its regulator were examined, specifically in the region containing Q268, which deletion causes MODY1. MATERIALS AND METHODS: Cellular localization of mutant HNF4α were examined in monkey kidney 7 (COS7), Chinese hamster ovary, rat insulinoma and mouse insulinoma cells, and their binding activity to other proteins were examined by fluorescence resonance energy transfer (FRET) in COS7 cells. RESULTS: Although wild-type HNF4α was localized in the nucleoplasm in transfected cultured cells, Q268X-HNF4α was located predominantly in the nucleolus. Deletion analysis of the C-terminus of HNF4α showed that the S337X-HNF4α mutant, and other mutants with shorter amino acid sequences (S337-K194), were mostly localized in the nucleolus. HNF4α mutants with amino acid sequences shorter than the W192X-HNF4α mutant gradually spread to the nucleoplasm in accordance with their lengths. The A250X-HNF4α mutant was capable of causing the accumulation of HNF4α or the small heterodimer partner (SHP), one of the HNF4α regulators, in the nucleolus. However, the R154X-HNF4α mutant did not have binding ability to wild-type HNF4α or SHP, and thus was seen in the nucleus. CONCLUSIONS: The C-terminus sites might play a key role in facilitating the nucleolar and subnucleolar localization of HNF4α. (J Diabetes Invest, doi: 10.1111/j.2040-1124.2012.00210.x, 2012).