Channels In Pancreatic Beta-cells Research Articles

Preliminary Content of Glibenklamide and Its Metabolite 4-trans-hydroxyglibenclamide Using Uv-Vis Spectrophotometry Method

Glibenclamide, another name for glyburide, is one of the antidiabetic drugs oral (ADO) which works by closing the K+-ATP channels in pancreatic beta cells thereby increasing insulin release. 4-trans-hydroxyglibenclamide is the main metabolite of glibenclamide which also has hypoglycemic effects. This study aims to determine the maximum wavelength of glibenclamide and its metabolite 4-trans-hydroxyglibenclamide. The results showed that the maximum wavelength of glibenclamide was at 300.60 nm, while 4-trans-hydroxyglibenclamide was at 299.50 nm and the glibenclamide calibration curve was obtained using the regression equation Y= Y=0.010x+0.001 with a correlation coefficient of 0.998, while 4 -trans-hydroxyglibenclamide Y= 0.0102x-0.0098 with a correlation coefficient of 0.99

Association of KCNJ11 gene (rs5219) polymorphism with HOMA-IR & HOMA B values in type 2 diabetes mellitus in India: A case-control study

Objectives Type 2 diabetes mellitus (T2DM) is a complex illness that results from either insulin resistance or insufficient insulin, which raises blood sugar levels. Numerous genes interact to influence the secretion of insulin. A gene of great interest is KCNJ11 of subfamily-J, member 11, which functions as an inwardly rectifying ATP-sensitive potassium (KATP) channel in pancreatic beta cells and is involved in glucose-stimulated insulin release. Material & Methods The present case-control study attempts to delineate the genetic impact of KCNJ11 (rs5219) gene polymorphism on the risk of T2DM in the Indian population. It involves 55 patients with type 2 diabetes (fasting plasma glucose of >126 mg/dl, 2-h glucose of >200 mg/dl, or HbA1c level of >6.4%) and 55 healthy controls (fasting plasma glucose of <100 mg/dl, 2-h glucose of <140 mg/dl, or HbA1c level of <6.4%). polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP) was used to study KCNJ11 polymorphism through a standard protocol. Enzyme Linked Immunosorbent Assay (ELISA) was used to estimate serum Insulin levels. HOMA-IR & HOMA-β values were calculated. Statistical analysis was done using t-test, Chi-Square test, and One-way analysis of variance (ANOVA) test. Results Serum insulin levels and HOMA-IR values were significantly decreased in cases than in the control group. Logistic regression analysis showed that the frequency of KK genotype in T2DM individuals (21.8%) was higher than the control group (9%) (p = 0.01). Frequency of K allele (38%) in patients was higher than the control group (18%) (p = 0.001). The K allele risk in diabetic patients was 9.9 times higher as compared to controls (p = 0.001, OR 9.9, 95%Cl 0.036–0.36). Homeostatic model assessment β (HOMA-β) values of KK genotype (59.9±27.8315) were lower than that of EK (76.8±33.23) and EE (127.9±44.59) genotypes (p < 0.001). Conclusion The presence of KCNJ11 (rs 5219) gene polymorphism shows a noteworthy correlation with the likelihood of developing T2DM among the North Indian population. K allele is more likely to be present in individuals with T2DM than the control group. Moreover, HOMA-β values of those with the KK genotype were found to be lower than the individuals having EK and EE genotypes.

Effect of fenofibrate and selective PPARα modulator (SPPARMα), pemafibrate on KATP channel activity and insulin secretion

ObjectiveInsulin secretion is regulated by ATP-sensitive potassium (KATP) channels in pancreatic beta-cells. Peroxisome proliferator-activated receptors (PPAR) α ligands are clinically used to treat dyslipidemia. A PPARα ligand, fenofibrate, and PPARγ ligands troglitazone and 15-deoxy-∆12,14-prostaglandin J2 are known to close KATP channels and induce insulin secretion. The recently developed PPARα ligand, pemafibrate, became a new entry for treating dyslipidemia. Because pemafibrate is reported to improve glucose intolerance in mice treated with a high fat diet and a novel selective PPARα modulator, it may affect KATP channels or insulin secretion.ResultsThe effect of fenofibrate (100 µM) and pemafibrate (100 µM) on insulin secretion from MIN6 cells was measured by using batch incubation for 10 and 60 min in low (2 mM) and high (10 mM) glucose conditions. The application of fenofibrate for 10 min significantly increased insulin secretion in low glucose conditions. Pemafibrate failed to increase insulin secretion in all of the conditions experimented in this study. The KATP channel activity was measured by using whole-cell patch clamp technique. Although fenofibrate (100 µM) reduced the KATP channel current, the same concentration of pemafibrate had no effect. Both fenofibrate and pemafibrate had no effect on insulin mRNA expression.

Case of neonatal diabetes mellitus due to KCNJ11 mutation: Therapeutic implications of a genetic diagnosis

Abstract BACKGROUND: Neonatal diabetes mellitus (NDM) is a rare condition occurring in approximately 1 in 90,000 live births. CASE REPORT: We describe a 2.5-month-old infant with neonatal diabetes who presented with diabetic ketoacidosis due to a mutation affecting the KCNJ11 gene, which encodes the Kir6.2 subunit of the ATP-sensitive potassium channel in pancreatic beta cells. CONCLUSION: Availing a genetic diagnosis has crucial therapeutic implications in the initiation of oral sulfonylureas in KCNJ11 and ABCC8 mutations as against the continued use of subcutaneous insulin in some other causes of neonatal diabetes.

The Association Between genetic variations of KCNj11 gene and type 2 diabetes mellitus in a sample of Iraqi population.

Background: Type 2 diabetes mellitus is a polygenic disorder that develops as a result of a complex interaction between multiple genes and environmental factors. KCNJ11 gene encodes a Kir6.2 protein which forms the inner section of the potassium channels in pancreatic beta cells.
 Methods: This case-control study involved 300 T2DM patients and 300 healthy controls. The KCNJ11 rs5215 and rs5210 polymorphism was genotyped by Restriction Fragment Length Polymorphism (RFLP).
 Results : Hardy Weinberg equation statistics of KCNJ11 rs5210 (A/G) SNP genotypes among patients, control subjects highly significant (p < 0.001). Comparison of KCNJ11 rs5210 (A/G) SNP genotypes the codominance model, the additive model The recessive model and has shown no significant variation between control and patient groups (p = 0.564), (p = 0.806)and (p = 0.284) respectively. confirmed the lack of significant association (p = 0.589). Analysis of alleles has shown no significant association (p = 0.432). Comparison of BMI and HDL is significant to KCNJ11 rs5210 (A/G) SNP genotypes based on codominance model and other biochemical is not . Hardy Weinberg equation statistics of KCNJ11 rs5215 (C:I /T:V) SNP genotypes among patients, control highly significant (p < 0.001). The codominance model has shown no significant difference (p =0.835). The dominant model, the recessive model and the additive model has shown no significant difference (p =0.581),(p =0.606) and (p =0.483). Allele analysis has shown no significant difference (p =0.463). Comparison of BMI and cholesterol is no significant to KCNJ11 rs5215 (C/T) SNP genotypes based on codominance model and other biochemical is significant. The association between risk of disease and haplotypes resulting from KCNJ11 rs5210 (A/G) versus rs5115 (C:I /T:V) interaction is H 1 , H2 haplotypes was associated with highly significant risk of disease (p = 0.004) OR of 1.64, (p < 0.001) with an OR of 0.35. H 3 haplotypes was associated with significant protection against the disease (p = 0.024) with an approximate OR of 0.69. The presence of H 4 haplotypes was associated with highly significant risk of the disease (p < 0.001) with an OR of 2.52.
 Conclusions: This study showed that rs5215and rs5210 polymorphism of the KCNJ11 gene is an important risk factor for type 2 diabetes mellitus in a sample of the Iraqi population.
 Aimed of study :This study was aimed to detect the relationship between the rs5215and rs5210 polymorphism of the KCNJ11 associated with T2DM in Iraqi population ,what is the impact of haplotype analysis on the risk of T2DM as well as the glycemic indices.

Cytotoxic and genotoxic effects of nateglinide on human ovarian, prostate, and colon cancer cell lines

Objective: Nateglinide, an oral anti-diabetic medication used to treat type 2 diabetes, activates ATP-dependent potassium channels in pancreatic beta cells and induces insulin secretion. Numerous antidiabetic medicines, particularly metformin, are known to drastically reduce the viability of cancer cells. This study examined the effects of nateglinide on the DNA and viability of human ovarian (A2780), prostate (LNCaP), and colon (Caco-2) cancer cells. Materials and methods: Initially in the study, 1, 10, 100, and 1000 µM doses of nateglinide were administered for 24 hours to A2780, LNCaP, and Caco-2 cells. The 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) test was used to measure cell viability. Using Graphpad Prism 8, the inhibitory logarithmic concentration values (LogIC50) of nateglinide in A2780, LNCaP, and Caco-2 cells were computed based on the results of the MTT experiment. These doses were applied to A2780, LNCaP, and Caco-2 cells for the Comet assay. The Bonferroni-corrected Mann–Whitney U test was used to compare groups, and a value of p<0.05 was considered statistically significant. Results: In A2780 and LNCaP cell lines, only 1000 μM nateglinide concentration decreased cell viability (p<0.05), whereas in Caco-2 cells, all concentrations except 1 μM reduced cell viability (p<0.05). The Comet assay indicated that nateglinide produced DNA damage by increasing the tail lengths and tail moments of A2780, LNCaP, and Caco-2 cells (p<0.05) and reducing the head diameters (p<0.05). Conclusion: According to the findings of this study, nateglinide has cytotoxic effects on human ovarian, prostate and colon cancer cell lines and may possess anticancer properties.

50-LB: Behavior and Learning Challenges in ABCC8-Related Neonatal Diabetes

Background: Activating mutations in KCNJ11 or ABCC8 cause neonatal diabetes (NDM) as well as neurodevelopmental difficulties, related to expression of mutated KATP channels in pancreatic beta cells as well as brain. Even individuals with more mildly activating KCNJ11 mutations underperform on many neurodevelopmental measures compared to sibling controls; however, very little information has been available about those with ABCC8 mutations. Methods: Surveys were used to assess attention-deficit hyperactivity disorder (ADHD), learning and behavioral challenges, sleep disturbances, and other related medical conditions in participants with ABCC8-related NDM from the University of Chicago Monogenic Diabetes Registry. Results: Baseline data including diagnosis and treatment information, and relevant medical records, were available for 19 of 20 participants with ABCC8-NDM (10 permanent, 9 transient), while 10 completed the ADHD/behavior/sleep survey. Participants with ABCC8-related NDM showed a range of neurodevelopmental and behavioral challenges (Table 1). Conclusions: Our results suggest that individuals with ABCC8-NDM have a high prevalence of neurodevelopmental, behavioral and sleep challenges and should therefore receive relevant ongoing evaluation and support to address these challenges. Disclosure N. Brown: None. S. Berry: None. A. Harris: None. L.R. Letourneau-Freiberg: None. S.W. Greeley: None. Funding American Diabetes Association (1-17-JDF-008 to S.A.W.G.); National Institute of Diabetes and Digestive and Kidney Diseases (R01DK104942, P30DK0205950); National Center for Advancing Translational Sciences (UL1TR002389)

Concentration‐Time profiles of Glyburide in Rats: Predictions using a Continuous Absorption Model

Most drugs are administered orally due to cost‐efficacy and increased patient compliance. However, the absorption of these drugs is subjected to complex biological processes and depends on the drug’s physicochemical properties. Prior to human trials, preclinical species such as rodents are utilized to evaluate efficacy and safety in vivo. Because animal studies are expensive and time‐consuming, it is beneficial to predict a drug’s pharmacokinetic profiles prior to in vivo studies. Pharmacokinetic modeling and simulation is useful for such predictions.The small intestine and colon of male Sprague Dawley rats were divided into 10 unequal segments to measure the change in luminal pH. Luminal contents were collected and directly measured under fed (n=4) and 12‐hour fasted (n=4) conditions. Glyburide is an oral anti‐diabetic medication that stimulates insulin secretion by blocking ATP‐dependent potassium channels in pancreatic beta cells. In vivo pharmacokinetic studies were performed to determine the effect of food. Fasted (n=4) and fed (n=4) male Sprague Dawley rats were dosed 5mg/kg of glyburide by oral gavage. Rats (n=2) were dosed intravenously to collect pharmacokinetic parameters. Blood samples were collected at 0.1, 0.25, 0.5, 1, 2, 4, 6, 10, and 24 hours post dose. Data were analyzed with non‐compartmental analysis. A continuous rodent absorption model was developed to predict the concentration‐time profiles of compounds based on rodent anatomical data collected in‐house and from the literature. Several physiological parameters were incorporated in the model, including small intestinal transit time, luminal pH, and transporter expression along the intestines.Rats fasted for 12 hours had a higher pH along the intestine that increased slowly, compared to fed rats. While the pH of the colon was higher in fasted rats, the cecum was not altered by fasted conditions. Fasted rats had an average glyburide AUC(0–24) of 2.7 μg*h/ml, while fed rats had an AUC(0–24) of 0.97 μg*h/ml. The mean apparent clearance (CL/F) was 1.8 L/min/kg for fasted rats and 5.1 L/min/kg for fed rats. The mean half‐life increased slightly from 10.6 hours in fasted rats to 11.6 hours in fed rats. Current predictions using the rodent continuous absorption model do not accurately describe the exposure profile of glyburide. To refine the model, further anatomical data collection and incorporation of fasted versus fed conditions are underway.Support or Funding InformationThis work was supported by NIH grants R01GM114369 and R01GM104178 to Swati Nagar and Ken Korzekwa.

The Interaction between KCNJ11 Gene Polymorphism and Refined Carbohydrates Intake on Obesity in Indonesian Adolescents

Background: Obesity has been associated with genetic and environmental factors. Although carbohydrate intake was previously shown to be associated with a high risk of obesity and insulin resistance, some studies reported that genetic factors also have a role in this association. KCNJ11 is a gene involved in protein K-ATP channels of pancreatic beta cells and previously associated with obesity. Objective: The objective of this study was to determine the interaction between KCNJ11 polymorphism with a high intake of refined carbohydrates in relation to the incidence of obesity in adolescents. Method: This was an observational study with a case-control design. The subjects of this study were male and female adolescents from 10 high schools in Yogyakarta. Dietary intake, body weight, and height were collected. KCNJ11 gene polymorphism was detected by polymerase Chain Reaction- Restriction Fragment Length Polymorphism (PCR-RFLP) method. Result: There is a significant association between KCNJ11 polymorphism with a high intake of refined carbohydrates in the incidence of obesity in adolescents (OR = 2.35, p =0.036). Conclusion: There is a significant association between the KCNJ11 polymorphism with a high intake of refined carbohydrates in adolescent obesity.

Ion Channels as Therapeutic Targets for Type 1 Diabetes Mellitus.

Ion channels are integral proteins expressed in almost all living cells and are involved in muscle contraction and nutrient transport. They play a critical role in the normal functioning of the excitable tissues of the nervous system and regulate the action potential and contraction events. Dysfunction of genes encodes ion channel proteins, which disrupt the channel function and lead to a number of diseases, among which is type 1 diabetes mellitus (T1DM). Therefore, understanding the complex mechanism of ion channel receptors is necessary to facilitate the diagnosis and management of treatment. In this review, we summarize the mechanism of important ion channels and their potential role in the regulation of insulin secretion along with the limitations of ion channels as therapeutic targets. Furthermore, we discuss the recent investigations of the mechanism regulating the ion channels in pancreatic beta cells, which suggest that ion channels are active participants in the regulation of insulin secretion.

Association of KCNJ11 rs5219 gene polymorphism with type 2 diabetes mellitus in a population of Syria: a case-control study

BackgroundType 2 diabetes mellitus is believed to be a polygenic disorder that develops as a result of a complex interaction between multiple genes and environmental factors. KCNJ11 gene encodes a Kir6.2 protein which forms the inner section of the potassium channels in pancreatic beta cells. Several studies found that KCNJ11 polymorphism increases T2DM risk. Our study aimed to investigate the association between rs5219 polymorphism of the KCNJ11 gene and T2DM in Syrian patients.MethodsThis case-control study involved 75 T2DM patients and 63 healthy controls. The KCNJ11 rs5219 polymorphism was genotyped by Restriction Fragment Length Polymorphism (RFLP).ResultsThe frequency of the risk allele K was similar between the two groups (38.7% vs. 38.1%, P = 0.132). The frequency of the KK genotype was higher among the patients’ group (16% vs. 4.8%), and the frequency of the EK genotype was higher among the control group (45.3% vs. 66.6%); however, the differences were statistically insignificant. The KK genotype was significantly associated with T2DM in the recessive model with an OR of 3.81 (95% CI 1.024–14.17, P = 0.035).ConclusionsThis study showed that rs5219 polymorphism of the KCNJ11 gene is an important risk factor for type 2 diabetes mellitus in a sample of the Syrian population.

P-56 - Insights on aquaporins involvement in obesity-induced inflammation in pancreatic β-cells

Aquaporins (AQPs) are membrane channels that facilitate water and/or glycerol permeation through membranes. Among the 13 isoforms, AQP7 is tightly involved in insulin secretion while AQP12 was shown upregulated in pancreatitis. Using a loss-of-function/gain-of-function strategy in the pancreatic RIN-m5F cell line, we evaluated AQP7 and AQP12 expression and function as well as their involvement in cell proliferation, migration and adhesion in healthy conditions, and we investigated their contribution for obesity-induced inflammation in the endocrine pancreas. Our data confirm AQP7 as a functional water and glycerol channel in pancreatic beta-cells with importance for cell proliferation. Both AQP7 and AQP12 overexpressing cells show improved cell adhesion and migration. Their implication in inflammation was evaluated by assessing mRNA expression levels as well as of markers of inflammation in a pro-inflammatory condition (Streptozotocin STZ). Treated cells show upregulated AQP7 and AQP12 and proinflammatory markers (TNFα, IL-1β and IL6). However, AQP12 overexpression downregulates TNFα and IL-6, while AQP12-silencing dramatically upregulates TNFα and IL-6. These results indicate AQP12 may play a protective role in inflammation.

Modulation of Connexin-36 Gap Junction Channels by Intracellular pH and Magnesium Ions.

Connexin-36 (Cx36) protein forms gap junction (GJ) channels in pancreatic beta cells and is also the main Cx isoform forming electrical synapses in the adult mammalian brain. Cx36 GJs can be regulated by intracellular pH (pHi) and cytosolic magnesium ion concentration ([Mg2+]i), which can vary significantly under various physiological and pathological conditions. However, the combined effect and relationship of these two factors over Cx36-dependent coupling have not been previously studied in detail. Our experimental results in HeLa cells expressing Cx36 show that changes in both pHi and [Mg2+]i affect junctional conductance (gj) in an interdependent manner; in other words, intracellular acidification cause increase or decay in gj depending on whether [Mg2+]i is high or low, respectively, and intracellular alkalization cause reduction in gj independently of [Mg2+]i. Our experimental and modelling data support the hypothesis that Cx36 GJ channels contain two separate gating mechanisms, and both are differentially sensitive to changes in pHi and [Mg2+]i. Using recombinant Cx36 we found that two glutamate residues in the N-terminus could be partly responsible for the observed interrelated effect of pHi and [Mg2+]i. Mutation of glutamate at position 8 attenuated the stimulatory effect of intracellular acidification at high [Mg2+]i, while mutation at position 12 and double mutation at both positions reversed stimulatory effect to inhibition. Moreover, Cx36*E8Q lost the initial increase of gj at low [Mg2+]i and double mutation lost the sensitivity to high [Mg2+]i. These results suggest that E8 and E12 are involved in regulation of Cx36 GJ channels by Mg2+ and H+ ions.

The inhibitor of connexin Cx36 channels, mefloquine, inhibits voltage-dependent Ca2+ channels and insulin secretion.

The antimalarial agent, mefloquine, inhibits the function of connexin Cx36 gap junctions and hemichannels and has thus become a tool to investigate their physiological relevance in pancreatic islets. In view of earlier reports on a KATP channel-block by mefloquine, the specificity of mefloquine as a pharmacological tool was investigated. Mouse pancreatic islets and single beta cells were used to measure membrane potential, whole cell currents, Ca2+ channel activity, cytosolic Ca2+ concentration ([Ca2+]i) and insulin secretion. Mefloquine was tested in the concentration range of 5-50μM 25μM mefloquine was as effective as 500μM tolbutamide to depolarize the plasma membrane of beta cells, but did not induce action potentials. Rather, it abolished tolbutamide-induced action potentials and the associated increase of [Ca2+]i. In the range of 5-50μM mefloquine inhibited voltage-dependent Ca2+ currents in primary beta cells as effectively as 1μM nisoldipine, a specific blocker of L-type Ca2+ channels. The Ca2+ channel opening effect of Bay K8644 was completely antagonized by mefloquine. Likewise, the increase of [Ca2+]i and of insulin secretion stimulated by 40mM KCl, but not that by 30mM glucose was antagonized by 50μM mefloquine. Neither at 5μM nor at 50μM did mefloquin stimulate insulin secretion at basal glucose. In conclusion, mefloquine blocks KATP channels and L-type Ca2+ channels in pancreatic beta cells in the range from 5 to 50μM. Thus it inhibits depolarization-induced insulin secretion, but in the presence of a stimulatory glucose concentration additional effects of mefloquine, possibly on intracellular Ca2+ mobilization, and the metabolic amplification by glucose permit a sustained rate of secretion.

Nesfatin-1 inhibits voltage gated K+ channels in pancreatic beta cells

The anorexigenic neuropeptide NEFA/nucleobindin 2 (NUCB2)/nesfatin-1-containing neurons are distributed in the brain regions involved in feeding regulation. In spite of the growing knowledge of its physiological functions through extensive studies, its molecular mechanism of reaction, including its receptor, remains unknown. NUCB2/nesfatin-1 is also involved in various peripheral regulations, including glucose homeostasis. In pancreatic beta-cells, NUCB2/nesfatin-1 is reported to enhance glucose-stimulated insulin secretion (GSIS) but its exact mechanism remains unknown.To clarify this mechanism, we measured the effect of nesfatin-1 on the electrical activity of pancreatic beta-cells. Using mouse primary beta cells, we measured changes in the ATP-sensitive K+ (KATP) channel current, the voltage-gated K+ (Kv) channel current, and insulin secretion upon application of nesfatin-1.Nesfatin-1 inhibited the Kv channel, but KATP channel activity was unaffected. Nesfatin-1 enhanced insulin secretion to a same level as Kv channel blocker tetraethylammonium (TEA). The effect was not further enhanced when nesfatin-1 and TEA were applied simultaneously. The inhibition binding assay with [125I]nesfatin-1 in Kv2.1 channels, major contributor of Kv current in beta cell, expressing HEK239 cells indicated the binding of nesfatin-1 on Kv2.1 channel.Because Kv channel inhibition enhances insulin secretion under high glucose conditions, our present data suggest a possible mechanism of nesfatin-1 on enhancing GSIS through regulation of ion channels rather than its unidentified receptor.

AMP kinase regulates ligand-gated K-ATP channels in substantia nigra dopamine neurons

AMP-activated protein kinase (AMPK) is a master enzyme that regulates ATP-sensitive K+ (K-ATP) channels in pancreatic beta-cells and cardiac myocytes. We used patch pipettes to record currents and potentials to investigate effects of AMPK on K-ATP currents in substantia nigra compacta (SNC) dopamine neurons in slices of rat midbrain. When slices were superfused repeatedly with the K-ATP channel opener diazoxide, we were surprised to find that diazoxide currents gradually increased in magnitude, reaching 300% of the control value 60min after starting whole-cell recording. However, diazoxide current increased significantly more, to 472% of control, when recorded in the presence of the AMPK activator A769662. Moreover, superfusing the slice with the AMPK blocking agent dorsomorphin significantly reduced diazoxide current to 38% of control. Control experiments showed that outward currents evoked by the K-ATP channel opener NN-414 also increased over time, but not currents evoked by the GABAB agonist baclofen. Delaying the application of diazoxide after starting whole-cell recording correlated with augmentation of current. Loose-patch recording showed that diazoxide produced a 34% slowing of spontaneous firing rate that did not intensify with repeated applications of diazoxide. However, superfusion with A769662 significantly augmented the inhibitory effect of diazoxide on firing rate. We conclude that K-ATP channel function is augmented by AMPK, which is activated during the process of making whole-cell recordings. Our results suggest that AMPK and K-ATP interactions may play an important role in regulating dopamine neuronal excitability.

Searching for Maturity-Onset Diabetes of the Young (MODY): When and What for?

Maturity-onset diabetes of the young (MODY) is a group of monogenic diseases that results in primary defects in insulin secretion and dominantly inherited forms of nonautoimmune diabetes. Although many genes may be associated with monogenic diabetes, heterozygous mutations in 6 of them are responsible for the majority of cases of MODY. Glucokinase (GCK)-MODY is due to mutations in the glucokinase gene, 3 MODY subtypes are associated with mutations in the hepatocyte nuclear factor (HNF) transcription factors, and 2 others with mutations in ABCC8 and KCNJ11, which encode the subunits of the ATP-dependent potassium channel in pancreatic beta cells. GCK-MODY and HNF1A-MODY are the most common subtypes. The clinical presentation of MODY subtypes has been reported to differ according to the gene involved, and the diagnosis of MODY may be considered in various clinical circumstances. However, except in patients with GCK-MODY whose phenotype is very homogeneous, in most cases the penetrance and expressivity of a given molecular abnormality vary greatly among patients and, conversely, alterations in various genes may lead to similar phenotypes. Moreover, differential diagnosis among more common forms of diabetes may be difficult, particularly with type 2 diabetes. Thus, careful assessment of the personal and family histories of patients with diabetes is mandatory to select those in whom genetic screening is worthwhile. The diagnosis of monogenic diabetes has many consequences in terms of prognosis, therapeutics and family screening.

Evidence for glucagon-like peptide-1 receptor signaling to activate ATP-sensitive potassium channels in pancreatic beta cells

Glucagon-like peptide-1 (GLP-1) is a gut peptide that promotes insulin release from pancreatic beta cells. GLP-1 has been shown to confer glucose-insensitive beta cells with glucose sensitivity by modulation of the activity of the ATP-sensitive potassium (KATP) channel. The channel closing effect of GLP-1, interacting with corresponding G-protein-coupled receptors, has been well established; however, to our knowledge, no study has shown whether GLP-1 directly induces activation of beta-cell KATP channels. Here, we aimed to evaluate whether the activation of beta-cell KATP channels by GLP-1 exists and affects intracellular Ca2+ levels ([Ca2+]i). KATP channel activity was measured in isolated rat pancreatic beta cells by whole-cell perforated patch-clamp recordings with a diazoxide-containing pipette solution. Changes in [Ca2+]i and the subcellular localization of KATP channels were observed using the calcium-sensitive dye fura-4/AM and anti-Kir6.2 antibodies in INS-1 beta cells, respectively. To eliminate the well-known inhibitory effects of GLP-1 on KATP channel activity, channels were fully inhibited by pretreatment with methyl pyruvate and epigallocatechin-3-gallate. In the pretreated beta cells, GLP-1 and exendin-4 promptly activated the channels, reducing [Ca2+]i. The phosphoinositide 3-kinase (PI3K) inhibitor LY294002 blocked the effects of GLP-1 on channel activity. Moreover, phosphatidylinositol-3,4,5-trisphosphate mimicked the effects of GLP-1. These results suggested that beta-cell GLP-1 receptor signaling involved activation of KATP channels via a PI3K-dependent pathway. This alternative mechanism of GLP-1 function may act as a negative feedback pathway, modulating the glucose-dependent GLP-1 inhibition on KATP channel activity.

Association of KCNJ11 (E23K) gene polymorphism with susceptibility to type 2 diabetes in Iranian patients.

Background:Type 2 diabetes (T2D) is a multifactorial disease with susceptibility of several genes that are related to T2D. Insulin secretion pathway starts with potassium channels in pancreatic beta cells. KCNJ11 gene encodes ATP-sensitive potassium channel subunits. Some studies suggested that KCNJ11 (E23K) mutation increases the risk of T2D. Therefore, present study was designed to investigate the association between E23K polymorphism of KCNJ11 gene and type 2 diabetes mellitus (T2DM) in the Iranian population.Materials and Methods:The type of study was case-control and 40 unrelated subjects, including 20 healthy controls and 20 diabetic patients were recruited (diagnosed based on American Diabetes Association criteria). Blood samples were used for isolation of genomic deoxyribonucleic acid (DNA). Having extracted the genomic DNA from human blood leukocytes by means of High Pure PCR Template Preparation Kit, PCR-restriction fragment length polymorphism method was used to detect KCNJ11 E23K gene polymorphism. BanII restriction enzyme was used for digestion. Data were analyzed using Chi-square or Fisher exact test or independent t-test, as appropriate. P < 0.05 was considered.Results:We found that the carrier homozygous for KK genotype are susceptible to T2D (0.049) and in patients the frequency of K allele was higher than control subjects (0.048).Conclusion:The present study suggests that KCNJ11 (E23K) gene polymorphism is associated with T2DM.

KCNJ11: Genetic Polymorphisms and Risk of Diabetes Mellitus

Diabetes mellitus (DM) is a major worldwide health problem and its prevalence has been rapidly increasing in the last century. It is caused by defects in insulin secretion or insulin action or both, leading to hyperglycemia. Of the various types of DM, type 2 occurs most frequently. Multiple genes and their interactions are involved in the insulin secretion pathway. Insulin secretion is mediated through the ATP-sensitive potassium (KATP) channel in pancreatic beta cells. This channel is a heteromeric protein, composed of four inward-rectifier potassium ion channel (Kir6.2) tetramers, which form the pore of the KATP channel, as well as sulfonylurea receptor 1 subunits surrounding the pore. Kir6.2 is encoded by the potassium inwardly rectifying channel, subfamily J, member 11 (KCNJ11) gene, a member of the potassium channel genes. Numerous studies have reported the involvement of single nucleotide polymorphisms of the KCNJ11 gene and their interactions in the susceptibility to DM. This review discusses the current evidence for the contribution of common KCNJ11 genetic variants to the development of DM. Future studies should concentrate on understanding the exact role played by these risk variants in the development of DM.