Channeling dysglycemia: ion-channel variations perturbing glucose homeostasis

Congenital Hyperinsulinism Caused by Mutations in ABCC8 Gene Associated with Early-Onset Neonatal Hypoglycemia: Genetic Heterogeneity Correlated with Phenotypic Variability

Congenital hyperinsulinism (CHI) is a rare disorder of glucose metabolism and is the most common cause of severe and persistent hypoglycemia (hyperinsulinemic hypoglycemia, HH) in the neonatal period and childhood. Most cases are caused by mutations in the ABCC8 and KCNJ11 genes that encode the ATP-sensitive potassium channel (KATP). We present the correlation between genetic heterogeneity and the variable phenotype in patients with early-onset HH caused by ABCC8 gene mutations. In the first patient, who presented persistent severe hypoglycemia since the first day of life, molecular genetic testing revealed the presence of a homozygous mutation in the ABCC8 gene [deletion in the ABCC8 gene c.(2390+1_2391-1)_(3329+1_3330-1)del] that correlated with a diffuse form of hyperinsulinism (the parents being healthy heterozygous carriers). In the second patient, the onset was on the third day of life with severe hypoglycemia, and genetic testing identified a heterozygous mutation in the ABCC8 gene c.1792C>T (p.Arg598*) inherited on the paternal line, which led to the diagnosis of the focal form of hyperinsulinism. To locate the focal lesions, (18)F-DOPA (3,4-dihydroxy-6-[18F]fluoro-L-phenylalanine) positron emission tomography/computed tomography (PET/CT) was recommended (an investigation that cannot be carried out in the country), but the parents refused to carry out the investigation abroad. In this case, early surgical treatment could have been curative. In addition, the second child also presented secondary adrenal insufficiency requiring replacement therapy. At the same time, she developed early recurrent seizures that required antiepileptic treatment. We emphasize the importance of molecular genetic testing for diagnosis, management and genetic counseling in patients with HH.

Potential Applications of Gliclazide in Treating Type 1 Diabetes Mellitus: Formulation with Bile Acids and Probiotics

A major advancement in therapy of type 1 diabetes mellitus (T1DM) is the discovery of new treatment which avoids and even replaces the absolute requirement for injected insulin. The need for multiple drug therapy of comorbidities associated with T1DM increases demand for developing novel therapeutic alternatives with new mechanisms of actions. Compared to other sulphonylurea drugs used in the treatment of type 2 diabetes mellitus, gliclazide exhibits a pleiotropic action outside pancreatic β cells, the so-called extrapancreatic effects, such as antiinflammatory and cellular protective effects, which might be beneficial in the treatment of T1DM. Results from in vivo experiments confirmed the positive effects of gliclazide in T1DM that are even more pronounced when combined with other hypoglycaemic agents such as probiotics and bile acids. Even though the exact mechanism of interaction at the molecular level is still unknown, there is a clear synergistic effect between gliclazide, bile acids and probiotics illustrated by the reduction of blood glucose levels and improvement of diabetic complications. Therefore, the manipulation of bile acid pool and intestinal microbiota composition in combination with old drug gliclazide could be a novel therapeutic approach for patients with T1DM.

Sulfonylurea challenge test in subjects diagnosed with type 1 diabetes mellitus

BACKGROUND

Patients with early onset diabetes because of defects in glucose-stimulated insulin secretion (GSIS) may respond better to sulfonylureas than insulin treatment. Such patients include those with monogenic disorders, who can be differentiated from autoimmune type 1 diabetes mellitus (T1DM) by genetic testing. Genetic testing is expensive and unknown defects in GSIS would not be diagnosed.

AIMS

We propose a sulfonylurea challenge test to identify patients who have been clinically diagnosed with T1DM, but those who maintain a preferentially sulfonylurea-responsive insulin secretion.

MATERIALS & METHODS

A total of 3 healthy controls, 2 neonatal diabetes mellitus (NDM) subjects, 3 antibody-positive (Ab+T1DM), and 12 antibody-negative (Ab-T1DM) subjects with type 1 diabetes, were given an intravenous bolus of glucose followed by an oral dose of glipizide.

RESULTS

Healthy controls showed a robust C-peptide increase after both glucose and glipizide, but NDM subjects showed a large increase in C-peptide only following glipizide. As expected, 2 of 3 Ab+T1DM, as well as 11 of 12 Ab-T1DM showed no response to either glucose or glipizide. However, 1 Ab-T1DM and 1 Ab+T1DM showed a small C-peptide response to glucose and a marked positive response to glipizide, suggesting defects in GSIS rather than typical autoimmune diabetes.

DISCUSSION

These data demonstrate the feasibility of the sulfonylurea challenge test, and suggest that responder individuals may be identified.

CONCLUSIONS

We propose that this sulfonylurea challenge test should be explored more extensively, as it may prove useful as a clinical and scientific tool.

ABCC8 Single Nucleotide Polymorphisms are Associated with Cerebral Edema in Severe TBI

OBJECTIVE

Cerebral edema (CE) in traumatic brain injury (TBI) is the consequence of multiple underlying mechanisms and is associated with unfavorable outcomes. Genetic variability in these pathways likely explains some of the clinical heterogeneity observed in edema development. A role for sulfonylurea receptor-1 (Sur1) in CE is supported. However, there are no prior studies examining the effect of genetic variability in the Sur1 gene (ABCC8) on the development of CE. We hypothesize that ABCC8 single nucleotide polymorphisms (SNPs) are predictive of CE.

METHODS

DNA was extracted from 385 patients. SNPs in ABCC8 were genotyped using the Human Core Exome v1.2 (Illumina). CE measurements included acute CT edema, mean and peak intracranial pressure (ICP), and need for decompressive craniotomy.

RESULTS

Fourteen SNPs with minor allele frequency >0.2 were identified. Four SNPS rs2283261, rs3819521, rs2283258, and rs1799857 were associated with CE measures. In multiple regression models, homozygote-variant genotypes in rs2283261, rs3819521, and rs2283258 had increased odds of CT edema (OR 2.45, p = 0.007; OR 2.95, p = 0.025; OR 3.00, p = 0.013), had higher mean (β = 3.13, p = 0.000; β = 2.95, p = 0.005; β = 3.20, p = 0.008), and peak ICP (β = 8.00, p = 0.001; β = 7.64, p = 0.007; β = 6.89, p = 0.034). The homozygote wild-type genotype of rs1799857 had decreased odds of decompressive craniotomy (OR 0.47, p = 0.004).

CONCLUSIONS

This is the first report assessing the impact of ABCC8 genetic variability on CE development in TBI. Minor allele ABCC8 SNP genotypes had increased risk of CE, while major SNP alleles were protective-potentially suggesting an evolutionary advantage. These findings could guide risk stratification, treatment responders, and the development of novel targeted or gene-based therapies against CE in TBI and other neurological disorders.

Discovery and characterization of a potent and selective inhibitor of Aedes aegypti inward rectifier potassium channels

Vector-borne diseases such as dengue fever and malaria, which are transmitted by infected female mosquitoes, affect nearly half of the world's population. The emergence of insecticide-resistant mosquito populations is reducing the effectiveness of conventional insecticides and threatening current vector control strategies, which has created an urgent need to identify new molecular targets against which novel classes of insecticides can be developed. We previously demonstrated that small molecule inhibitors of mammalian Kir channels represent promising chemicals for new mosquitocide development. In this study, high-throughput screening of approximately 30,000 chemically diverse small-molecules was employed to discover potent and selective inhibitors of Aedes aegypti Kir1 (AeKir1) channels heterologously expressed in HEK293 cells. Of 283 confirmed screening ‘hits’, the small-molecule inhibitor VU625 was selected for lead optimization and in vivo studies based on its potency and selectivity toward AeKir1, and tractability for medicinal chemistry. In patch clamp electrophysiology experiments of HEK293 cells, VU625 inhibits AeKir1 with an IC₅₀ value of 96.8 nM, making VU625 the most potent inhibitor of AeKir1 described to date. Furthermore, electrophysiology experiments in Xenopus oocytes revealed that VU625 is a weak inhibitor of AeKir2B. Surprisingly, injection of VU625 failed to elicit significant effects on mosquito behavior, urine excretion, or survival. However, when co-injected with probenecid, VU625 inhibited the excretory capacity of mosquitoes and was toxic, suggesting that the compound is a substrate of organic anion and/or ATP-binding cassette (ABC) transporters. The dose-toxicity relationship of VU625 (when co-injected with probenecid) is biphasic, which is consistent with the molecule inhibiting both AeKir1 and AeKir2B with different potencies. This study demonstrates proof-of-concept that potent and highly selective inhibitors of mosquito Kir channels can be developed using conventional drug discovery approaches. Furthermore, it reinforces the notion that the physical and chemical properties that determine a compound's bioavailability in vivo will be critical in determining the efficacy of Kir channel inhibitors as insecticides.

Molecular and functional characterization of Anopheles gambiae inward rectifier potassium (Kir1) channels: a novel role in egg production

Inward rectifier potassium (Kir) channels play essential roles in regulating diverse physiological processes. Although Kir channels are encoded in mosquito genomes, their functions remain largely unknown. In this study, we identified the members of the Anopheles gambiae Kir gene family and began to investigate their function. Notably, we sequenced the A. gambiae Kir1 (AgKir1) gene and showed that it encodes all the canonical features of a Kir channel: an ion pore that is composed of a pore helix and a selectivity filter, two transmembrane domains that flank the ion pore, and the so-called G-loop. Heterologous expression of AgKir1 in Xenopus oocytes revealed that this gene encodes a functional, barium-sensitive Kir channel. Quantitative RT-PCR experiments then showed that relative AgKir1 mRNA levels are highest in the pupal stage, and that AgKir1 mRNA is enriched in the adult ovaries. Gene silencing of AgKir1 by RNA interference did not affect the survival of female mosquitoes following a blood meal, but decreased their egg output. These data provide evidence for a new role of Kir channels in mosquito fecundity, and further validates them as promising molecular targets for the development of a new class of mosquitocides to be used in vector control.

Direct activation of β-cell KATP channels with a novel xanthine derivative

ATP-regulated potassium (KATP) channel complexes of inward rectifier potassium channel (Kir) 6.2 and sulfonylurea receptor (SUR) 1 critically regulate pancreatic islet β-cell membrane potential, calcium influx, and insulin secretion, and consequently, represent important drug targets for metabolic disorders of glucose homeostasis. The KATP channel opener diazoxide is used clinically to treat intractable hypoglycemia caused by excessive insulin secretion, but its use is limited by off-target effects due to lack of potency and selectivity. Some progress has been made in developing improved Kir6.2/SUR1 agonists from existing chemical scaffolds and compound screening, but there are surprisingly few distinct chemotypes that are specific for SUR1-containing KATP channels. Here we report the serendipitous discovery in a high-throughput screen of a novel activator of Kir6.2/SUR1: VU0071063 [7-(4-(tert-butyl)benzyl)-1,3-dimethyl-1H-purine-2,6(3H,7H)-dione]. The xanthine derivative rapidly and dose-dependently activates Kir6.2/SUR1 with a half-effective concentration (EC50) of approximately 7 μM, is more efficacious than diazoxide at low micromolar concentrations, directly activates the channel in excised membrane patches, and is selective for SUR1- over SUR2A-containing Kir6.1 or Kir6.2 channels, as well as Kir2.1, Kir2.2, Kir2.3, Kir3.1/3.2, and voltage-gated potassium channel 2.1. Finally, we show that VU0071063 activates native Kir6.2/SUR1 channels, thereby inhibiting glucose-stimulated calcium entry in isolated mouse pancreatic β cells. VU0071063 represents a novel tool/compound for investigating β-cell physiology, KATP channel gating, and a new chemical scaffold for developing improved activators with medicinal chemistry.

Effects of probiotic therapy on metabolic and inflammatory parameters of rats with ligature-induced periodontitis associated with restraint stress

BACKGROUND

This study evaluates the effects of probiotic therapy (PT) in rats with ligature-induced periodontitis associated with restraint stress.

METHODS

Sixty-four rats were divided into control, stress (STR), probiotic (PROB), periodontal disease (PD), STR-PROB, STR-PD, STR-PROB-PD, and PROB-PD groups. The probiotic was added to the drinking water for 44 days. PD was induced by a ligature. In STR groups, the animals were subjected to restraint stress for 2.5 hours per day for 30 days.

RESULTS

Rats with PD exhibited increased alveolar bone loss (P <0.05), as well as increased levels of cyclooxygenase-2, serum C-terminal telopeptide (CTX), p38 mitogen-activated protein kinase (p38), and receptor activator of nuclear factor-κB ligand and decreased levels of osteoprotegerin (OPG). Stressed rats presented high levels of C-peptide, corticosterone, and glucose (P <0.05). In general, the presence of stress reduced the expression of CTX and p38 (P <0.05). PT reduced alveolar bone loss in unstressed animals. It also decreased expression of CTX and induced increased expression of OPG in unstressed animals with PD. However, PT was not effective in preventing bone loss or altering the expression of inflammatory markers in stressed animals. PT decreased the number of inflammatory cells in the periodontal tissue (P <0.05). Groups with stress and PD showed decreased villous height and crypt depth. Stress seemed to prevent part of the probiotic beneficial effects on the small intestine.

CONCLUSIONS

Based on the methodology used, PT may reduce tissue breakdown resulting from PD in unstressed rats. The protocol used for restraint stress influenced the immunomodulatory effects of PT in intestinal and periodontal tissues.