Monogenic syndromes of abnormal glucose homeostasis: clinical review and relevance to the understanding of the pathology of insulin resistance and beta cell failure

Design and synthesis of 2-amino-4,6-diarylpyrimidine derivatives as potent α-glucosidase and α-amylase inhibitors: structure-activity relationship, in vitro, QSAR, molecular docking, MD simulations and drug-likeness studies

In the present study, a series of 2-amino-4,6-diarylpyrimidine derivatives was designed, synthesized, characterized and evaluated for their in vitro α-glucosidase and α-amylase enzyme inhibition assays. The outcomes proved that this class of compounds exhibit considerable inhibitory activity against both enzymes. Among the target compounds, compounds 4p and 6p demonstrated the most potent dual inhibition with IC50 = 0.087 ± 0.01 μM for α-glucosidase; 0.189 ± 0.02 μM for α-amylase and IC50 = 0.095 ± 0.03 μM for α-glucosidase; 0.214 ± 0.03 μM for α-amylase, respectively as compared to the standard rutin (IC50 = 0.192 ± 0.02 μM for α-glucosidase and 0.224 ± 0.02 μM for α-amylase). Remarkably, the enzyme inhibition results indicate that test compounds have stronger inhibitory effect on the target enzymes than the positive control, with a significantly lower IC50 value. Moreover, these series of compounds were found to inhibit α-glucosidase activity in a reversible mixed-type manner with IC50 between 0.087 ± 0.01 μM to 1.952 ± 0.26 μM. Furthermore, molecular docking studies were performed to affirm the binding interactions of this scaffold to the active sites of α-glucosidase and α-amylase enzymes. The quantitative structure-activity relationship (QSAR) investigations showed a strong association between 1p-15p structures and their inhibitory actions (IC50) with a correlation value (R2) of 0.999916. Finally, molecular dynamic (MD) simulations were carried out to assess the dynamic behavior, stability of the protein-ligand complex, and binding affinity of the most active inhibitor 4p. The experimental and theoretical results therefore exposed a very good compatibility. Additionally, the drug-likeness assay revealed that some compounds exhibit a linear association with Lipinski's rule of five, indicating good drug-likeness and bioactivity scores for pharmacological targets.Communicated by Ramaswamy H. Sarma.

Variants influencing age at diagnosis of HNF1A-MODY

BACKGROUND

HNF1A-MODY is a monogenic form of diabetes caused by variants in the HNF1A gene. Different HNF1A variants are associated with differences in age of disease onset, but other factors are postulated to influence this trait. Here, we searched for genetic variants influencing age of HNF1A-MODY onset.

METHODS

Blood samples from 843 HNF1A-MODY patients from Czech Republic, France, Poland, Slovakia, the UK and the US were collected. A validation set consisted of 121 patients from the US. We conducted a genome-wide association study in 843 HNF1A-MODY patients. Samples were genotyped using Illumina Human Core arrays. The core analysis was performed using the GENESIS package in R statistical software. Kinship coefficients were estimated with the KING and PC-Relate algorithms. In the linear mixed model, we accounted for year of birth, sex, and location of the HNF1A causative variant.

RESULTS

A suggestive association with age of disease onset was observed for rs2305198 (p = 2.09E-07) and rs7079157 (p = 3.96E-06) in the HK1 gene, rs2637248 in the LRMDA gene (p = 2.44E-05), and intergenic variant rs2825115 (p = 2.04E-05). Variant rs2637248 reached nominal significance (p = 0.019), while rs7079157 (p = 0.058) and rs2825115 (p = 0.068) showed suggestive association with age at diabetes onset in the validation set.

CONCLUSIONS

rs2637248 in the LRMDA gene is associated with age at diabetes onset in HNF1A-MODY patients.

Wolframin deficiency is accompanied with metabolic inflexibility in rat striated muscles

The protein wolframin is localized in the membrane of the endoplasmic reticulum (ER), influencing Ca2+ metabolism and ER interaction with mitochondria, but the exact role of the protein remains unclear. Mutations in Wfs1 gene cause autosomal recessive disorder Wolfram syndrome (WS). The first symptom of the WS is diabetes mellitus, so accurate diagnosis of the disease as WS is often delayed. In this study we aimed to characterize the role of the Wfs1 deficiency on bioenergetics of muscles. Alterations in the bioenergetic profiles of Wfs1-exon-5-knock-out (Wfs1KO) male rats in comparison with their wild-type male littermates were investigated using high-resolution respirometry, and enzyme activity measurements. The changes were followed in oxidative (cardiac and soleus) and glycolytic (rectus femoris and gastrocnemius) muscles. There were substrate-dependent alterations in the oxygen consumption rate in Wfs1KO rat muscles. In soleus muscle, decrease in respiration rate was significant in all the followed pathways. The relatively small alterations in muscle during development of WS, such as increased mitochondrial content and/or increase in the OxPhos-related enzymatic activity could be an adaptive response to changes in the metabolic environment. The significant decrease in the OxPhos capacity is substrate dependent indicating metabolic inflexibility when multiple substrates are available.

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Wolfram syndrome (WS) model rats have muscle type-dependent metabolic changes.

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Substrate-dependent modulation of OxPhos in WS model rat muscles.

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Metabolic inflexibility in early-stage WS rat muscle mitochondria.

Adaptation of striated muscles to Wolframin deficiency in mice: Alterations in cellular bioenergetics

BACKGROUND

Wolfram syndrome (WS), caused by mutations in WFS1 gene, is a multi-targeting disease affecting multiple organ systems. Wolframin is localized in the membrane of the endoplasmic reticulum (ER), influencing Ca²⁺ metabolism and ER interaction with mitochondria, but the exact role of the protein remains unclear. In this study we aimed to characterize alterations in energy metabolism in the cardiac and in the oxidative and glycolytic skeletal muscles in Wfs1-deficiency.

METHODS

Alterations in the bioenergetic profiles in the cardiac and skeletal muscles of Wfs1-knock-out (KO) male mice and their wild type male littermates were determined using high resolution respirometry, quantitative RT-PCR, NMR spectroscopy, and immunofluorescence confocal microscopy.

RESULTS

Oxygen consumption without ATP synthase activation (leak) was significantly higher in the glycolytic muscles of Wfs1 KO mice compared to wild types. ADP-stimulated respiration with glutamate and malate was reduced in the Wfs1-deficient cardiac as well as oxidative and glycolytic skeletal muscles.

CONCLUSIONS

Wfs1-deficiency in both cardiac and skeletal muscles results in functional alterations of energy transport from mitochondria to ATP-ases. There was a substrate-dependent decrease in the maximal Complex I -linked respiratory capacity of the electron transport system in muscles of Wfs1 KO mice. Moreover, in cardiac and gastrocnemius white muscles a decrease in the function of one pathway were balanced by the increase in the activity of the parallel pathway.

GENERAL SIGNIFICANCE

This work provides new insights to the muscle involvement at early stages of metabolic syndrome like WS as well as developing glucose intolerance.

A Review of Type 2 Diabetes Mellitus Predisposing Genes

INTRODUCTION

Scientists are considering the possibility of treating diabetes mellitus (DM) using a personalized approach in which various forms of the diseases will be treated based on the causal gene and its pathogenesis. To this end, scientists have identified mutations in certain genes as probable causes of Type 2 diabetes mellitus (T2DM) with diverse mechanisms.

AIM

This review was aimed at articulating already identified T2DM genes with their mechanisms of action and phenotypic presentations for the awareness of all stakeholders.

METHOD

The Google search engine was used to retrieve relevant information on the subject from reliable academic databases such as PubMed, Medline, and Google Scholar, among others.

RESULTS

At least seventy (70) genes are currently being suspected in the biogenesis of T2DM. However, mutations in, or variants of KCNJ11, PPARG, HNF1B and WFS1 genes, are the most suspected and reported in the pathogenesis of the disease. Mutations in these genes can cause disruption of insulin biosynthesis through the destruction of pancreatic beta cells, change of beta cell morphology, destruction of insulin receptors, among others. These cellular events may lead to insulin resistance and hyperglycemia and, along with environmental triggers such as obesity and overweight, culminate in T2DM. It was observed that each identified gene has its distinct mechanism by which it interacts with other genes and environmental factors to cause T2DM.

CONCLUSION

Healthcare providers are advised to formulate T2DM drugs or treatment by targeting the causal genes along with their mechanisms.

Solution Ensemble of the C-Terminal Domain from the Transcription Factor Pdx1 Resembles an Excluded Volume Polymer

The pancreatic and duodenal homeobox 1 (Pdx1) is an essential pancreatic transcription factor. The C-terminal intrinsically disordered domain of Pdx1 (Pdx1-C) has a heavily biased amino acid composition; most notably, 18 of 83 residues are proline, including a hexaproline cluster near the middle of the chain. For these reasons, Pdx1-C is an attractive target for structure characterization, given the availability of suitable methods. To determine the solution ensembles of disordered proteins, we have developed a suite of ¹³C direct-detect NMR experiments that provide high spectral quality, even in the presence of strong proline enrichment. Here, we have extended our suite of NMR experiments to include four new pulse programs designed to record backbone residual dipolar couplings in a ¹³C,¹⁵N-CON detection format. Using our NMR strategy, in combination with small-angle X-ray scattering measurements and Monte Carlo simulations, we have determined that Pdx1-C is extended in solution, with a radius of gyration and internal scaling similar to that of an excluded volume polymer, and a subtle tendency toward a collapsed structure to the N-terminal side of the hexaproline sequence. This structure leaves Pdx1-C exposed for interactions with trans-regulatory co-factors that contribute with Pdx1 to transcription control in the cell.

An overview of type 2 diabetes and importance of vitamin D3-vitamin D receptor interaction in pancreatic β-cells

One significant health issue that plagues contemporary society is that of Type 2 diabetes (T2D). This disease is characterised by higher-than-average blood glucose levels as a result of a combination of insulin resistance and insufficient insulin secretions from the β-cells of pancreatic islets of Langerhans. Previous developmental research into the pancreas has identified how early precursor genes of pancreatic β-cells, such as Cpal, Ngn3, NeuroD, Ptf1a, and cMyc, play an essential role in the differentiation of these cells. Furthermore, β-cell molecular characterization has also revealed the specific role of β-cell-markers, such as Glut2, MafA, Ins1, Ins2, and Pdx1 in insulin expression. The expression of these genes appears to be suppressed in the T2D β-cells, along with the reappearance of the early endocrine marker genes. Glucose transporters transport glucose into β-cells, thereby controlling insulin release during hyperglycaemia. This stimulates glycolysis through rises in intracellular calcium (a process enhanced by vitamin D) (Norman et al., 1980), activating 2 of 4 proteinases. The rise in calcium activates half of pancreatic β-cell proinsulinases, thus releasing free insulin from granules. The synthesis of ATP from glucose by glycolysis, Krebs cycle and oxidative phosphorylation plays a role in insulin release. Some studies have found that the β-cells contain high levels of the vitamin D receptor; however, the role that this plays in maintaining the maturity of the β-cells remains unknown. Further research is required to develop a more in-depth understanding of the role VDR plays in β-cell function and the processes by which the beta cell function is preserved.

Understanding childhood diabetes mellitus: new pathophysiological aspects

Diabetes mellitus (DM) is not a single disease, but several pathophysiological conditions where synthesis, release, and/or action of insulin are disturbed. A progressive autoimmune/autoinflammatory destruction of islet cells is still considered the main pathophysiological event in the development of T1DM, but there is evidence that T1DM itself is a heterogeneous disease. More than 50 gene regions are closely associated with T1DM and a variety of epigenetic factors and metabolic patterns have been characterized, which may play a role in the development of T1DM. The pathogenesis and genetics of type 2 DM (T2DM) are distinct from T1DM. Genes associated with T2DM are distinct from those in T1DM. Characteristic metabolic patterns, different from those in T1DM were reported in T2DM, and some children with T2DM also express islet-antibodies. Huge progress has been made in the characterization of other specific types of DM, which had been considered very rare before. The molecular clarification of maturity-onset diabetes of the young (MODY) has greatly improved our understanding of the pathophysiology of DM. There are genetic overlaps between T2DM and monogenetic DM. Neonatal DM has been shown to be monogenetic in most cases, and genetic elucidation leads to more precise and individualized therapies. Cystic fibrosis related DM (CFRDM) should be considered a genuine part of cystic fibrosis, and not a complication, since pancreatic fibrosis does not sufficiently explain the pathophysiology of CFRDM. Disturbances of cystic fibrosis transmembrane conductance regulator (CFTR) as well as autoimmunity are involved in the pathogenesis of CFRDM.

Phenotype Heterogeneity in Glucokinase-Maturity-Onset Diabetes of the Young (GCK-MODY) Patients

OBJECTIVE

The aim of the study was to evaluate the clinical phenotypes of glucokinase-maturity-onset diabetes of the young (GCK-MODY) pediatric patients from Southwest Poland and to search for phenotype-genotype correlations.

METHODS

We conducted a retrospective analysis of data on 37 CGK-MODY patients consisting of 21 girls and 16 boys of ages 1.9-20.1 (mean 12.5±5.2) years, treated in our centre in the time period between 2002 and 2013.

RESULTS

GCK-MODY carriers were found in a frequency of 3% among 1043 diabetes mellitus (DM) patients and constituted the second most numerous group of DM patients, following type 1 DM, in our centre. The mean age of GCK-MODY diagnosis was 10.4±4.5 years. The findings leading to the diagnosis were impaired fasting glucose (IFG) (15/37), symptoms of hyperglycemia (4/37), and a GCK-MODY family history (18/37). Mean fasting blood glucose level was 6.67±1.64 mmol/L. In the sample, there were patients with normal values (4/37), those with DM (10/37), and IFG (23/37). In OGTT, 120 min glucose level was normal in 8, diabetic in 2, and characteristic for glucose intolerance in 27 of the 37 cases. Twelve of the 37 cases (32%) were identified as GCK-MODY carriers. In the total group, mean C-peptide level was 2.13±0.65 ng/mL and HbA1c was 6.26±0.45% (44.9±-18 mmol/mol). Thirty-two patients had a family history of DM. DM autoantibodies were detected in two patients. The most common mutations were p.Gly318Arg (11/37) and p.Val302Leu (8/37). There was no correlation between type of mutations and plasma glucose levels.

CONCLUSION

The phenotype of GCK-MODY patients may vary from those characteristic for other DM types to an asymptomatic state with normal FG with no correlation with genotype.

Review: Genetics of the cardiometabolic syndrome: new insights and therapeutic implications

Although the definition of the phenotype is imprecise, cardiometabolic syndrome (CMS) includes a constellation of complex diseases such as type 2 diabetes, dislipidemias, central obesity and hypertension, proinflammatory and prothrombotic states, ovarian polycystosis and fatty liver. The genetics of each disease is complex in itself and varies in spectrum from monogenic and syndromic models of inheritance, usually rare, to the most common polygenic and multifactorial forms. In addition, human studies using the candidate-gene approach indicate that common genetic variants of several genes are associated with the development of CMS. Genome-wide scans have also provided several chromosomal regions associated with some of the components of CMS. In addition, through comparative genomics animal models can generate a map for candidate loci in humans and a promising approach is offered by bioinformatic tools for gene prioritization. Lastly, the involvement of genes whose products are already the targets for approved drugs, such as SLC6A4, PPARα and PPARγ , in the development of CMS suggests new avenues for CMS pharmacological treatment.

Apoptosis in pancreatic β-islet cells in Type 2 diabetes

Apoptosis plays important roles in the pathophysiology of Type 2 diabetes mellitus (T2DM). The etiology of T2DM is multifactorial, including obesity-associated insulin resistance, defective insulin secretion, and loss of β-cell mass through β-cell apoptosis. β-cell apoptosis is mediated through a milliard of caspase family cascade machinery in T2DM. The glucose-induced insulin secretion is the principle pathophysiology of diabetes and insufficient insulin secretion results in chronic hyperglycemia, diabetes. Recently, hyperglycemia-induced β-cell apoptosis has been extensively studied on the balance of pro-apoptotic Bcl-2 proteins (Bad, Bid, Bik, and Bax) and anti-apoptotic Bcl family (Bcl-2 and Bcl-xL) toward apoptosis in vitro isolated islets and insulinoma cell culture. Apoptosis can only occur when the concentration of pro-apoptotic Bcl-2 exceeds that of anti-apoptotic proteins at the mitochondrial membrane of the intrinsic pathway. A bulk of recent research on hyperglycemia-induced apoptosis on β-cells unveiled complex details on glucose toxicity on β-cells in molecular levels coupled with cell membrane potential by adenosine triphosphate generation through K+ channel closure, opening Ca2+ channel and plasma membrane depolarization. Furthermore, animal models using knockout mice will shed light on the basic understanding of the pathophysiology of diabetes as a glucose metabolic disease complex, on the balance of anti-apoptotic Bcl family and pro-apoptotic genes. The cumulative knowledge will provide a better understanding of glucose metabolism at a molecular level and will lead to eventual prevention and therapeutic application for T2DM with improving medications.

Genes, Genetics, and Environment in Type 2 Diabetes: Implication in Personalized Medicine

Type 2 diabetes (T2D) is a multifactorial anomaly involving 57 genes located on 16 different chromosomes and 136 single nucleotide polymorphisms (SNPs). Ten genes are located on chromosome 1, followed by seven genes on chromosome 11 and six genes on chromosomes 3. Remaining chromosomes harbor two to five genes. Significantly, chromosomes 13, 14, 16, 18, 21, 22, X, and Y do not have any associated diabetogenic gene. Genetic components have their own pathways encompassing insulin secretion, resistance, signaling, and β-cell dysfunction. Environmental factors include epigenetic changes, nutrition, intrauterine surroundings, and obesity. In addition, ethnicity plays a role in conferring susceptibility to T2D. This scenario poses a challenge toward the development of biomarker for quick disease diagnosis or for generating a consensus to delineate different categories of T2D patients. We believe, before prescribing a generic drug, detailed genotypic information with the background of ethnicity and environmental factors may be taken into consideration. This nonconventional approach is envisaged to be more robust in the context of personalized medicine and perhaps would cause lot less burden on the patient ensuring better management of T2D.

A standardized method for in vivo mouse pancreas imaging and semiquantitative β cell mass measurement by dual isotope SPECT

PURPOSE

In order to evaluate future β cell tracers in vivo, we aimed to develop a standardized in vivo method allowing semiquantitative measurement of a prospective β cell tracer within the pancreas.

PROCEDURES

2-[(123)I]Iodo-L-phenylalanine ([(123)I]IPA) and [Lys(40)([(111)In]DTPA)]exendin-3 ([(111)In]Ex3) pancreatic uptake and biodistribution were evaluated using SPECT, autoradiography, and an ex vivo biodistribution study in a controlled unilaterally nephrectomized mouse β cell depletion model. Semiquantitative measurement of the imaging results was performed using [(123)I]IPA to delineate the pancreas and [(111)In]Ex3 as a β cell tracer.

RESULTS

The uptake of [(123)I]IPA was highest in the pancreas. Aside from the kidneys, the uptake of [(111)In]Ex3 was highest in the pancreas and lungs. Autoradiography showed only uptake of [(111)In]Ex3 in insulin-expressing cells. Semiquantitative measurement of [(111)In]Ex3 in the SPECT images based on the delineation of the pancreas with [(123)I]IPA showed a high correlation with the [(111)In]Ex3 uptake data of the pancreas obtained by dissection. A strong positive correlation was observed between the relative insulin positive area and the pancreas-to-blood ratios of [(111)In]Ex3 uptake as determined by counting with a gamma counter and the semiquantitative analysis of the SPECT images.

CONCLUSIONS

[(123)I]IPA is a promising tracer to delineate pancreatic tissue on SPECT images. It shows a high uptake in the pancreas as compared to other abdominal tissues. This study also demonstrates the feasibility and accuracy to measure the β cell mass in vivo in an animal model of diabetes.

Effect of early life stress on pancreatic isolated islets' insulin secretion in young adult male rats subjected to chronic stress

Early stressful experiences may predispose organisms to certain disorders, including those of metabolic defects. This study aimed to explore the effects of early life stress on pancreatic insulin secretion and glucose transporter 2 (GLUT2) protein levels in stressed young adult male rats. Foot shock stress was induced in early life (at 2 weeks of age) and/or in young adulthood (at 8-10 weeks of age) for five consecutive days. Blood samples were taken before and after stress exposure in young adult rats. At the end of the experiment, glucose tolerance, isolated islets' insulin secretion, and pancreatic amounts of GLUT2 protein were measured. Our results show that early life stress has no effect on basal plasma corticosterone levels and adrenal weight, either alone or combined with young adulthood stress, but that early life + young adulthood stress could prevent weight gain, and cause an increase in basal plasma glucose and insulin. The homeostasis model assessment of insulin resistance index did not increase, when the rats were subjected to early life stress alone, but increased when combined with young adulthood stress. Moreover, glucose tolerance was impaired by the combination of early life + young adult stress. There was a decrease in islet's insulin secretion in rats subjected to early life stress in response to 5.6 mM glucose concentration, but an increase with a concentration of 16.7 mM glucose. However, in rats subjected to early life + young adulthood stress, islet's insulin secretion increased in response to both the levels of glucose concentrations. GLUT2 protein levels decreased in response to early life stress and early life + young adulthood stress, but there was a greater decrease in the early life stress group. In conclusion, perhaps early life stress sensitizes the body to stressors later in life, making it more susceptible to metabolic syndrome only when the two are in combination.

Phenotypic heterogeneity in monogenic diabetes: the clinical and diagnostic utility of a gene panel-based next-generation sequencing approach

Single gene mutations that primarily affect pancreatic β-cell function account for approximately 1-2% of all cases of diabetes. Overlapping clinical features with common forms of diabetes makes diagnosis of monogenic diabetes challenging. A genetic diagnosis often leads to significant alterations in treatment, allows better prediction of disease prognosis and progression, and has implications for family members. Currently, genetic testing for monogenic diabetes relies on selection of appropriate individual genes for analysis based on the availability of often-limited phenotypic information, decreasing the likelihood of making a genetic diagnosis. We thus developed a targeted next-generation sequencing (NGS) assay for the detection of mutations in 36 genes known to cause monogenic forms of diabetes, including transient or permanent neonatal diabetes mellitus (TNDM or PNDM), maturity-onset diabetes of the young (MODY) and rare syndromic forms of diabetes. A total of 95 patient samples were analyzed: 19 with known causal mutations and 76 with a clinically suggestive phenotype but lacking a genetic diagnosis. All previously identified mutations were detected, validating our assay. Pathogenic sequence changes were identified in 19 out of 76 (25%) patients: 7 of 32 (22%) NDM cases, and 12 of 44 (27%) MODY cases. In 2 NDM patients the causal mutation was not expected as consanguinity was not reported and there were no clinical features aside from diabetes. A 3 year old patient with NDM diagnosed at 3 months of age, who previously tested negative for INS, KCNJ11 and ABCC8 mutations, was found to carry a novel homozygous mutation in EIF2AK3 (associated with Wolcott-Rallison syndrome), a gene not previously suspected because consanguinity, delayed growth, abnormal bone development and hepatic complications had not been reported. Similarly, another infant without a history of consanguinity was found to have a homozygous GCK mutation causing PNDM at birth. This study demonstrates the effectiveness of multi-gene panel analysis in uncovering molecular diagnoses in patients with monogenic forms of diabetes.

Potent α-glucosidase inhibitors isolated from Ginkgo biloba leaves

In vitro α-glucosidase inhibitory activity of Ginkgo biloba leaves was investigated. The inhibitory activity of methanol extracts from yellow and green leaves was 13.8 and 40.1 μg mL(-1), respectively. Each methanol extract was separated into its respective fraction by solvent-solvent extraction with n-hexane, chloroform, ethyl acetate and n-butanol. The n-hexane fractions (in both methanol extracts from green and yellow leaves) exhibited high α-glucosidase inhibitory activity with IC50 values of 13.6 and 13.4 μg mL(-1), respectively. Further fractionation of the n-hexane fractions by silica gel column chromatography gave the most active fraction which was identified as ginkgolic acid (C13:0) and a mixture (C13:0, C15:0, C15: 1, C17:1 and C17:2). Ginkgolic acid (C13:0) exhibited the highest α-glucosidase inhibitory activity. This is the first study to successfully isolate ginkgolic acids as α-glucosidase inhibitors.

Two novel mutations identified in familial cases with Donohue syndrome

Donohue syndrome (DS) is a rare and lethal autosomal recessive disease caused by mutations in the insulin receptor (INSR) gene, manifesting marked insulin resistance, severe growth retardation, hypertrichosis, and characteristic dysmorphic features. We report the clinical, molecular, and biochemical characterization of three new patients with DS, and address genotype–phenotype issues playing a role in the pathophysiology of DS. A female infant born to first-degree cousins Muslim Arab parents and two brothers born to first-degree cousins Druze parents presented classical features of DS with hypertrophic cardiomyopathy and died in infancy. Each patient was found homozygous for one missense mutation within the extracellular domain of the INSR gene. Western blot analysis identified the proreceptor of INSR, but not its mature subunits alpha and beta. Of 95 healthy Muslims, no heterozygous was found and of 52 healthy Druze from the same village, one was heterozygous. This study presents two novel familial mutations in the alpha subunit of the INSR which appear to impair post-translational processing of the INSR, resulting loss of its function. Both mutations cause DS with hypertrophic cardiomyopathy and early death. Identification of the causative mutation enables prevention of this devastating disease.

Monogenic models: what have the single gene disorders taught us?

Monogenic diabetes constitutes a heterogeneous group of single gene disorders. The molecular background and clinical picture of many of these diseases have been described. While each of these forms is much less prevalent than multifactorial type 1 and type 2 diabetes mellitus (T2DM), together they affect millions of patients worldwide. Genetic diagnosis, which has become widely available, is of great clinical importance for patients with single gene diabetes. It helps to fully understand the pathophysiology of the disease, tailor the optimal hypoglycemic treatment, and define the prognosis for the entire family. Monogenic diabetes forms can be divided into 2 large groups, resulting from impaired insulin secretion or from an abnormal response to insulin. There are several lessons we have been taught by single-gene diabetes. We learned that the gene responsible for the occurrence of diabetes can be identified if an appropriate search strategy is used. In addition, discoveries of genes responsible for monogenic disorders pointed to them as susceptibility candidates for T2DM. Moreover, establishing that some families of proteins or biological pathways, such as transcription factors or potassium channel subunits, are involved in monogenic diabetes sparked research on their involvement in multifactorial diabetes. Finally, the example of single gene diabetes, particularly HNF1A MODY and permanent neonatal diabetes associated with the KCNJ11 and ABCC8 genes, all efficiently controlled on sulfonylurea, inspires us to continue the efforts to tailor individual treatment for T2DM patients. In this review paper, we summarize the impact of single gene disease discoveries on diabetes research and clinical practice.

Enhanced oxidative stress and endocrine pancreas alterations are linked to a novel glucokinase missense mutation in ENU-derived Munich Gck(D217V) mutants

In the large-scale Munich N-ethyl-N-nitrosourea (ENU) mouse mutagenesis project murine models recapitulating human diseases were generated. In one strain, a novel missense mutation (D217V) in the glucokinase (Gck) gene was identified, resulting in decreased glucokinase activity. Heterozygous mutants display mild hyperglycaemia, disturbed glucose tolerance, and decreased glucose-induced insulin secretion. In contrast, homozygous mutants exhibit severe but not survival affecting hyperglycaemia, mild growth retardation, diminished oxidative capacity, and increased abundance of CHOP protein in the islets. Furthermore, the total islet and β-cell volumes and the total volume of isolated β-cells are significantly decreased in adult homozygous mutants, whereas in neonatal mice, β-cell mass is not yet significantly decreased and islet neogenesis is unaltered. Therefore, reduced total islet and β-cell volumes of adult homozygous mutants might predominantly emerge from disturbed postnatal islet neogenesis. Thus, we identified a novel Gck mutation in mice, with relevance in humans, leading to glycaemic disease.

Inhibitory potential of traditional herbs on α-amylase activity

CONTEXT

There has been enormous interest in the development of alternative medicines for the control of diabetes. Use of carbohydrate-hydrolyzing enzyme inhibitors proved to be an important strategy for the management of postprandial hyperglycemia by delaying the process of carbohydrate hydrolysis and absorption.

OBJECTIVE

Three common traditional herbs, namely, stem bark of Terminalia arjuna (Combretaceae), seeds of Eugenia cumini (Myrtaceae), and leaves of Aegle marmelos (Rutaceae), were tested for their α-amylase inhibitory activities to establish antidiabetic potential.

MATERIALS AND METHODS

The plant extracts (aqueous, 50%, and 100% methanol) obtained were subjected to an in vitro amylase inhibitory assay using starch as a substrate and pancreatic amylase as the enzyme. Statistical differences and linear regression analysis were performed using GraphPad prism 5 software.

RESULTS

The 50% methanol extracts of T. arjuna, E. cumini, and A. marmelos at a concentrations 50-500 μg/mL showed maximum percentage inhibition on amylase activity with IC(50) values of 302 ± 0.55, 632 ± 0.21, and 503 ± 0.28 μg/mL, respectively. However, the 100% methanol extracts of all the three plants showed the least inhibitory activity.

DISCUSSION AND CONCLUSION

The results show that T. arjuna > E. cumini > A. marmelos have excellent inhibitory activity and, therefore, might be effective in lowering postprandial hyperglycemia.

Glucosensing and glucose homeostasis: from fish to mammals

This review is focused on two topics related to glucose in vertebrates. In a first section devoted to glucose homeostasis we describe how glucose levels fluctuate and are regulated in different classes of vertebrates. The detection of these fluctuations is essential for homeostasis and for other physiological processes such as regulation of food intake. The capacity of that detection is known as glucosensing, and the different mechanisms through which it occurs are known as glucosensors. Different glucosensor mechanisms have been demonstrated in different tissues and organs of rodents and humans whereas the information obtained for other vertebrates is scarce. In the second section of the review we describe the present knowledge regarding glucosensor mechanisms in different groups of vertebrates, with special emphasis in fish.

Saturation of the human phenome

The phenome is the complete set of phenotypes resulting from genetic variation in populations of an organism. Saturation of a phenome implies the identification and phenotypic description of mutations in all genes in an organism, potentially constrained to those encoding proteins. The human genome is believed to contain 20-25,000 protein coding genes, but only a small fraction of these have documented mutant phenotypes, thus the human phenome is far from complete. In model organisms, genetic saturation entails the identification of multiple mutant alleles of a gene or locus, allowing a consistent description of mutational phenotypes for that gene. Saturation of several model organisms has been attempted, usually by targeting annotated coding genes with insertional transposons (Drosophila melanogaster, Mus musculus) or by sequence directed deletion (Saccharomyces cerevisiae) or using libraries of antisense oligonucleotide probes injected directly into animals (Caenorhabditis elegans, Danio rerio). This paper reviews the general state of the human phenome, and discusses theoretical and practical considerations toward a saturation analysis in humans. Throughout, emphasis is placed on high penetrance genetic variation, of the kind typically asociated with monogenic versus complex traits.

Wolfram syndrome 1 gene (WFS1) product localizes to secretory granules and determines granule acidification in pancreatic beta-cells

Wolfram syndrome is an autosomal recessive disorder characterized by juvenile-onset insulin-dependent diabetes mellitus and optic atrophy. The gene responsible for the syndrome (WFS1) encodes an endoplasmic reticulum (ER) resident transmembrane protein. The Wfs1-null mouse exhibits progressive insulin deficiency causing diabetes. Previous work suggested that the function of the WFS1 protein is connected to unfolded protein response and to intracellular Ca(2+) homeostasis. However, its precise molecular function in pancreatic β-cells remains elusive. In our present study, immunofluorescent and electron-microscopic analyses revealed that WFS1 localizes not only to ER but also to secretory granules in pancreatic β-cells. Intragranular acidification was assessed by measuring intracellular fluorescence intensity raised by the acidotrophic agent, 3-[2,4-dinitroanilino]-3'-amino-N-methyldipropyramine. Compared with wild-type β-cells, there was a 32% reduction in the intensity in WFS1-deficient β-cells, indicating the impairment of granular acidification. This phenotype may, at least partly, account for the evidence that Wfs1-null islets have impaired proinsulin processing, resulting in an increased circulating proinsulin level. Morphometric analysis using electron microscopy evidenced that the density of secretory granules attached to the plasma membrane was significantly reduced in Wfs1-null β-cells relative to that in wild-type β-cells. This may be relevant to the recent finding that granular acidification is required for the priming of secretory granules preceding exocytosis and may partly explain the fact that glucose-induced insulin secretion is profoundly impaired in young prediabetic Wfs1-null mice. These results thus provide new insights into the molecular mechanisms of β-cell dysfunction in patients with Wolfram syndrome.

Maternal malnutrition programs pancreatic islet mitochondrial dysfunction in the adult offspring

Accumulating evidence has shown that maternal malnutrition increases the risk of metabolic disease in the progeny. We previously reported that prenatal exposure to a low-protein diet (LP) leads to mitochondrial dysfunction in pancreatic islets from adult rodent offspring that could relate physiological and cellular alterations due to early diet. We aim to determine whether mitochondrial dysfunction could be a common consequence of prenatal nutritional unbalances. Pregnant Wistar rats received either a global food restriction (GFR), consisting in the reduction by 50% of the normal daily food intake, or a high-fat diet (HF) throughout gestation. GFR or HF diet during pregnancy leads to a lack of increase in insulin release and ATP content in response to glucose stimulation in islets from 3-month-old male and female offspring. These similar consequences originated from impairment in either glucose sensing or glucose metabolism, depending on the type of early malnutrition and on the sex of the progeny. Indeed, the glucose transport across β-cell membrane seemed compromised in female HF offspring, since GLUT-2 gene was markedly underexpressed. Additionally, for each progeny, consequences downstream the entry of glucose were also apparent. Expression of genes involved in glycolysis, TCA cycle and oxidative phosphorylations was altered in GFR and HF rats in a sex- and diet-dependent manner. Moreover, prenatal malnutrition affected the regulators of mitochondrial biogenesis, namely, PPAR coactivator 1 alpha (PGC-1α), since its expression was higher in islets from GFR rats. In conclusion, programming of mitochondrial dysfunction is a consequence of maternal malnutrition, which may predispose to glucose intolerance in the adult offspring.

LMNA gene mutation search in Polish patients: new features of the heterozygous Arg482Gln mutation phenotype

Mutations of the LMNA gene have been shown to cause an autosomal dominant form of insulin resistance with familial partial lipodystrophy (PLD), frequently accompanied by diabetes. LMNA mutations are considered to be a rare cause of monogenic diabetes; however, they are probably sometimes misdiagnosed as type 2 diabetes (T2DM). We examined whether skin fold thickness measurements may be an effective screening procedure to select individuals with T2DM for molecular testing of the LMNA gene. We also aimed to search for mutations in diabetic patients with evident clinical features of lipodystrophy. Skin fold measurements were performed in 249 not pre-selected T2DM patients. The sum of two trunk skin fold measurements divided by the sum of two peripheral was obtained. Men with a skin fold ratio above 2.5 and women above 1.5 were selected for further molecular analysis of the LMNA gene by direct sequencing. We also examined eight patients presenting typical clinical features of lipodystrophy. We selected 16 patients with T2DM on the basis of skin fold measurements. LMNA gene sequencing in this group revealed no mutation that could be attributable to diabetic phenotype. However, in the group of subjects with apparent lipodystrophic phenotype, we identified one Arg482Gln mutation. This female, diagnosed with diabetes at the age of 51 years, was characterized by insulin resistance but, unlike previously reported LMNA Arg48Gln mutation carriers, she was not overweight. The patient also presented with chronic kidney disease and pulmonary fibrosis that could potentially be a part of the phenotype related to the identified LMNA mutation. We did not find the evidence that screening based on skin fold measurements alone could be an efficient approach to select T2DM patients for molecular testing of the LMNA gene; the presence of features typical for laminopathy seems to be required for such testing. A clinical picture related to the LMNA Arg482Gln mutation may be more diversified than it was previously considered and include low BMI and pulmonary fibrosis.

Can geneticists help clinicians to understand and treat non-autoimmune diabetes?

Approximately, a few percent of the European population suffers from diabetes. Scientific evidence showed that specific treatment of this disease could be successfully tailored on the basis of proper differential diagnosis that in many instances also requires genetic testing. This may be helpful in achieving metabolic control of the disease, increasing quality of life and potentially reducing the prevalence of chronic complications. Identification of the molecular background of these specific forms of diabetes gives new insight into the underlying aetiology. This knowledge helps to optimize treatment in specific clinical situations. Monogenic diabetes is an excellent example of a clinical area where new advances in molecular genetics can aid patient care and treatment decisions. The most frequently diagnosed forms of monogenic diabetes are MODY, mitochondrial diabetes, permanent and transient neonatal diabetes (PNDM and TNDM). These rare forms probably constitute at least a few percent of all diabetes cases seen in diabetic clinics. The proper differential diagnosis also helps to predict the progress of diabetes in affected individuals and defines the prognosis in the family. Recently, several genome wide association studies added new facts to the knowledge on complex forms of type 2 diabetes mellitus (T2DM) as the scientists substantially extended the short list of previously identified genes. Most newly identified variants influence beta-cell insulin secretion, while a few modulate peripheral insulin action. It is not clear whether in the future the genetic testing of frequent polymorphisms will influence the treatment of T2DM. In this review, we present the clinical application of genetic testing in non-autoimmune diabetes, mostly monogenic forms of disease.

Monogenic diabetes: implications for therapy of rare types of disease

There are two major forms of diabetes: type 1 and type 2. However, monogenic diabetes, associated with severe beta-cell dysfunction or with severe resistance to insulin action, is diagnosed with increasing frequency by genetic testing. The list of such forms of diabetes includes MODY, mitochondrial diabetes, permanent neonatal diabetes (PNDM) and transient neonatal diabetes, familial lipodystrophies and some others. These rare forms constitute probably at least a few per cent of all diabetes cases seen in diabetic clinics. The identification of the molecular background of specific forms of diabetes gives new insight into the underlying aetiology. This knowledge helps to optimize treatment in specific clinical situations. The proper differential diagnosis also helps to predict the progress of diabetes in affected individuals and defines the prognosis in the family. For example, in patients with MODY2 because of glucokinase mutations who have very mild diabetes characterized by modest fasting, hyperglycaemia diet is frequently sufficient. Some other forms of monogenic diabetes associated with impaired function of the beta-cell, such as MODY3 and PNDM linked to mutations in Kir6.2 and SUR1 genes, can be successfully managed by sulphonylurea agents. Although the examples of pharmacogenetics seem to be less spectacular in rare syndromes of insulin resistance, those patients can also benefit from genetic testing. In this paper, the aetiology of some monogenic diabetes forms is reviewed together with the clinical aspects of management of the affected individuals.

Candidate gene association study of insulin signaling genes and Alzheimer's disease: evidence for SOS2, PCK1, and PPARgamma as susceptibility loci

Epidemiological evidence supports the existence of a possible link between type II diabetes mellitus (T2DM) and late-onset Alzheimer's disease (LOAD). Polymorphisms from candidate genes for T2DM were genotyped in a two-stage approach to identify novel risk factors for LOAD. One hundred fifty-two polymorphisms were initially genotyped in a case:control cohort: nine SNPs showed individual association with disease status under at least one genetic model, while an additional two SNPs showed a haplotype association. In a replication study, we confirmed significant association of SNPs within three genes--PPARgamma, SOS2, and PCK1--with Alzheimer's disease. In particular, our data suggest that the effect of variants within these genes might be influenced by gender.

Glycemic control of apoptosis in the pancreatic beta cell: danger of extremes?

Excessive formation of oxygen radicals is a well-established mediator of hyperglycemic damage in diabetes to a wide range of tissues, such as neurons, retinal cells, and vascular endothelium. Increased oxygen radical formation is generally considered a toxic side effect of excessive rates of mitochondrial oxidative metabolism and electron transport in high glucose-exposed cells. Along the same line, metabolic oxidative stress is currently also regarded as crucial mediator of beta cell dysfunction and apoptosis under hyperglycemic conditions. Here the authors argue that a healthy beta cell is well equipped to deal adequately with elevated glucose metabolic rates, and demonstrate that decreased glucose catabolism leads to ROS production and apoptosis. They therefore propose that adverse metabolic conditions in poorly controlled diabetes (hyperglycemia and/or dyslipidemia) or genetic defects could decrease the viability of beta cells by interfering with normal glucose sensing and metabolism, rather than by overactivating it. This view is supported by the fragmentary data currently available on the pathways for hypergycemic and hypoglycemic beta cell death.

Microcephaly and simplified gyral pattern of the brain associated with early onset insulin-dependent diabetes mellitus

Two families are presented with a child suffering from microcephaly with a simplified gyral pattern of the brain (SGP) and early onset insulin dependent diabetes mellitus (IDDM). The first patient was diagnosed postmortally with Wolcott-Rallison syndrome, after her younger brother developed IDDM, and a homozygous mutation in the eukaryotic translation initiation factor 2-alpha kinase 3 was found. The younger brother did not undergo magnetic resonance imaging (MRI). The patient from the second family has no EIF2AK3 mutation. SGP is considered to arise from decreased neuronal proliferation or increased apoptosis at an early stage of embryonal development, but insight into the pathways involved is minimal. EIF2AK3 is involved in translation initiation. It has been proposed that loss of function mutations reduce the ability of the cell to respond to endoplasmic reticulum stress, resulting in apoptosis of pancreatic Langerhans cells. Our findings suggest that in some cases, early onset IDDM and SGP can arise from common mechanisms leading to increased apoptosis.

Glucose-sensing mechanisms in pancreatic beta-cells

The appropriate secretion of insulin from pancreatic beta-cells is critically important to the maintenance of energy homeostasis. The beta-cells must sense and respond suitably to postprandial increases of blood glucose, and perturbation of glucose-sensing in these cells can lead to hypoglycaemia or hyperglycaemias and ultimately diabetes. Here, we review beta-cell glucose-sensing with a particular focus on the regulation of cellular excitability and exocytosis. We examine in turn: (i) the generation of metabolic signalling molecules; (ii) the regulation of beta-cell membrane potential; and (iii) insulin granule dynamics and exocytosis. We further discuss the role of well known and putative candidate metabolic signals as regulators of insulin secretion.

WFS1-deficiency increases endoplasmic reticulum stress, impairs cell cycle progression and triggers the apoptotic pathway specifically in pancreatic beta-cells

Wolfram syndrome, an autosomal recessive disorder associated with diabetes mellitus and optic atrophy, is caused by mutations in the WFS1 gene encoding an endoplasmic reticulum (ER) membrane protein. Herein, we report that pancreatic islets of wfs1-deficient mice exhibit increases in phosphorylation of RNA-dependent protein kinase-like ER kinase, chaperone gene expressions and active XBP1 protein levels, indicating an enhanced ER stress response. We established wfs1-deficient MIN6 clonal beta-cells by crossing wfs1-deficient mice with mice expressing simian virus 40 large T antigen in beta-cells. These cells show essentially the same alterations in ER stress responses as wfs1-deficient islets, which were reversed by re-expression of WFS1 protein or overexpression of GRP78, a master regulator of the ER stress response. In contrast, these changes are not observed in heart, skeletal muscle or brown adipose tissues with WFS1-deficiency. The increased ER stress response was accompanied by reduced BrdU incorporation and increased caspase-3 cleavage, indicating impaired cell cycle progression and accelerated apoptotic processes in the mutant islets. These changes are associated with increased expression of the cell cycle regulator p21(CIP1) in wfs1-deficient islets and clonal beta-cells. Treatment of islets with thapsigargin, an ER stress inducer, caused upregulation of p21(CIP1). In addition, forced expression of p21(CIP1) resulted in reduced MIN6 beta-cell numbers, suggesting the ER stress-induced increase in p21(CIP1) expression to be involved in beta-cell loss in the mutant islets. These data indicate that WFS1-deficiency activates the ER stress response specifically in beta-cells, causing beta-cell loss through impaired cell cycle progression and increased apoptosis.