Functional characterization of AVPR2 mutants found in Turkish patients with nephrogenic diabetes insipidus.

Diabetes insipidus is a rare disorder characterized by an impairment in water balance because of the inability to concentrate urine. While central diabetes insipidus is caused by mutations in the AVP, the reason for genetically determined nephrogenic diabetes insipidus can be mutations in AQP2 or AVPR2 After release of AVP from posterior pituitary into blood stream, it binds to AVPR2, which is one of the receptors for AVP and is mainly expressed in principal cells of collecting ducts of kidney. Receptor activation increases cAMP levels in principal cells, resulting in the incorporation of AQP2 into the membrane, finally increasing water reabsorption. This pathway can be altered by mutations in AVPR2 causing nephrogenic diabetes insipidus. In this study, we functionally characterize four mutations (R68W, ΔR67-G69/G107W, V162A and T273M) in AVPR2, which were found in Turkish patients. Upon AVP stimulation, R68W, ΔR67-G69/G107W and T273M showed a significantly reduced maximum in cAMP response compared to wild-type receptor. All mutant receptor proteins were expressed at the protein level; however, R68W, ΔR67-G69/G107W and T273M were partially retained in the cellular interior. Immunofluorescence studies showed that these mutant receptors were trapped in ER and Golgi apparatus. The function of V162A was indistinguishable from the indicating other defects causing disease. The results are important for understanding the influence of mutations on receptor function and cellular trafficking. Therefore, characterization of these mutations provides useful information for further studies addressing treatment of intracellularly trapped receptors with cell-permeable antagonists to restore receptor function in patients with nephrogenic diabetes insipidus.

Identification of a Novel Deletion in AVP-NPII Gene in a Patient with Central Diabetes Insipidus.

Central Diabetes Insipidus (CDI) is caused by a deficiency of antidiuretic hormone and characterized by polyuria, polydipsia and inability to concentrate urine. Our objective was to present the results of the molecular analyses of AVP-neurophysin II (AVP-NPII) gene in a large familial neurohypophyseal (central) DI pedigree. A male patient and his family members were analyzed and the prospective clinical data were collected. The proband applied to hospital for eligibility to be a recruit in Armed Forces. The patient had severe polyuria (20 L/day), polydipsia (20.5 L/day), fatique, and deep thirstiness. CDI was confirmed with the water deprivation-desmopressin test according to an increase in urine osmolality from 162 mOsm/kg to 432 mOsm/kg after desmopressin acetate injection. To evaluate the coding regions of AVP-NPII gene, polymerase chain reactions were performed and amplified regions were submitted to direct sequence analysis. We detected a heterozygous three base pair deletion at codon 69-70 (207_209delGGC) in exon 2, which lead to a deletion of the amino acid alanine. A three-dimensional protein structure prediction was shown for the deleted AVP-NPII and compared with the wild type. The three base pair deletion may yield an abnormal AVP precursor in neurophysin moiety, but further functional analyses are needed to understand the function of the deleted protein.

AVP-NPII gene mutations and clinical characteristics of the patients with autosomal dominant familial central diabetes insipidus.

BACKGROUND: Familial central diabetes insipidus (DI), usually an autosomal dominant disorder, is caused by mutations in arginine vasopressin-neurophysin II (AVP-NPII) gene that leads to aberrant preprohormone processing and gradual destruction of AVP-secreting cells. OBJECTIVE: To determine clinical and molecular characteristics of patients with familial central DI from two different Turkish families. MATERIALS AND METHODS: The diagnosis of central DI was established by 24-h urine collection, water deprivation test, and desmopressin challenge. To confirm the diagnosis of familial central DI, the entire coding region of AVP-NPII gene was amplified and sequenced. A total of eight affected patients and three unaffected healthy relatives from two families were studied. RESULTS: Genetic analysis revealed a previously reported heterozygous mutation (p.C98X) in family A, and a heterozygous novel mutation (p.G45C) in family B, both detected in exon 2 of AVP-NPII gene. When we compared the clinical characteristics of the two families, it was noticed that as the age of onset of symptoms in family A ranges between 4 and 7 years, it was <1 year in family B. Additionally, pituitary bright spot was present in the affected siblings, but absent in their affected parents. CONCLUSION: Familial central DI is a progressive disease, and age of onset of symptoms can differ depending on the mutation. Bright spot on pituitary MRI might be present at onset, but become invisible over time. Genetic testing and appropriate counseling should be given in familial cases of central DI to ensure adequate treatment, and to avoid chronic water deprivation that might result in growth retardation in childhood.

Association of VNTR polymorphisms in DRD4, 5-HTT and DAT1 genes with obesity.

OBJECTIVE: To investigate the association between VNTR polymorphisms of DRD4, DAT1 and 5-HTT genes and obesity. MATERIAL AND METHODS: Peripheral blood samples of 234 obese (BMI ≥ 30) and 148 healthy individuals (BMI ≤ 25) were objected to PCR to detect the VNTR of the 2nd intron of 5-HTT, 3rd exon of DRD4 and 3'UTR of DAT1 genes. RESULTS: The association between obesity and genotype distributions of 5-HTT, DAT1 and DRD4 genes and between obesity and distributions of allele frequencies were tested by Chi Square (χ(2)) test and were not found statistically significant. BMI values for genotype of obese and morbidly obese (BMI > 40) individuals were analyzed by Kruskal-Wallis and not found statistically significant differences between BMI values for the most frequent genotypes of 5-HTT, DAT1 and DRD4 genes. CONCLUSIONS: As a conclusion, there was no association between 5-HTT, DAT1 and DRD4 genes VNTR polymorphisms and obesity.

Evaluation of Cytogenetic and Genotoxic Effects of Oxalic Acid by the Alkaline Comet Assay and QRT PCR in Human Buccal Epithelial Cells.

OBJECTIVE: To evaluate the cytogenetic and genotoxic effects of oxalic acid. STUDY DESIGN: Buccal epithelial cells were obtained and cells were suspended in phosphate buffered saline. Increasing amounts of oxalic acids were added to cell suspensions and incubated in 37 degrees C, 5% CO2 for 30 minutes. Comets were scored using a computer-based image analysis system, and tail moments were taken as a measure of DNA damage. The transcriptional changes of HIPK2, GADD45A, DDB2, p53, PCNA, NBS1, and MDM2 genes were also investigated by qRT-PCR using B2M and GAPDH genes as references. RESULTS: It was found that DNA damage occurred in parallel with increasing amounts of oxalic acid according to tail moment measurements, and also expressions of the selected genes have increased. CONCLUSION: It can be concluded that along with increasing amounts of oxalic acid, cell damage was detected, and both comet assay and expression of the selected genes can be used in the assessment of the damage caused by oxalic acid.

Promoter hypermethylation of p16 and APC in gastrointestinal cancer patients.

BACKGROUND/AIMS: Cancer is a consequence of the disruption of cellular regulation. Epigenetic is one of the reasons of this disruption. Epigenetic factors play a role in the carcinogenesis by affecting proto-oncogenes and tumor suppressor genes and it is one of the most popular research areas in recent years. DNA methylation, which is an epigenetic mechanism, occurs in the early stages of tumorigenesis. Promoter methylation which causes the silence of tumor suppressor genes have been studied extensively in various tumor types. The aim of this study was to investigate promoter methylation of certain tumor suppressor genes, Cyclin-dependent kinase inhibitor 2A (p16) and Adenomatous polyposis coli (APC), which take part in gastrointestinal tumorigenesis. MATERIALS AND METHODS: To detect the promoter methylation of p16 and APC genes, tissue samples from 20 gastrointestinal cancer patients and peripheral blood samples from 15 healthy individuals were collected for Methylation-Specific Polymerase Chain Reaction (MSP) analysis. RESULTS: According to the statistical analysis, in tumor tissue, positive methylation ratio of p16 and APC genes was found respectively 30% (6/20) and 50% (10/20). The difference of promoter methylation of these genes between tumor tissues and control group was significantly observed (p=0.02 and 0.001, respectively). An alteration of promoter methylation of APC gene according to tumor localization was found (p=0.007), but there was no significant difference observed in p16. CONCLUSION: In our study, promoter methylation which was considered to be occurred as an early event in gastrointestinal carcinogenesis was observed in p16 and APC genes.

Association of apolipoprotein E-219T>G promoter polymorphism with primary open angle glaucoma in Turkish population.

AIM: To investigate the association between apolipoprotein E (APOE) -219 T>G promoter polymorphism and primary open angle glaucoma (POAG). METHODS: Patients and healthy subjects were genotyped with polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Genotype/allele frequencies were compared between 122 healthy subjects and in 75 POAG patients using Chi-square test. RESULTS: Although the frequency of APOE -219 GG genotype was higher in POAG group (13.3%) than in control group (6.6%), this finding was not statistically significant (P=0.09). In glaucoma patients carrying GG genotype, mean linear C/D ratio was higher and progression was more compared to glaucoma patients with GT genotype. CONCLUSION: APOE -219 T>G polymorphism does not seem to be a risk factor for the presence of glaucoma, but might play a role in deterioration of the disease, which needs further evaluation.

Assessment of ER Stress and autophagy induced by ionizing radiation in both radiotherapy patients and ex vivo irradiated samples.

Acute radiation leads to several toxic clinical states and triggers some molecular pathways. To shed light on molecular mechanisms triggered by ionizing radiation (IR), we examined the expression profiles of endoplasmic reticulum (ER) stress and autophagy-related genes in individuals who were exposed to IR. Blood samples were collected from 50 cancer patients before radiotherapy and on the 5th, 15th, and 25th days of the treatment. Peripheral blood samples from 10 healthy volunteers were also obtained for ex vivo irradiation, divided into five and irradiated at a rate of 373 kGy/h to 0, 0.1, 0.5, 1, and 3Gy γ-rays using a constant gamma source. GRP78, ATG5, LC3, ATF4, XBP1, and GADD153 genes were analyzed by quantitative real-time polymerase chain reaction (QRT-PCR) using beta 2 microglobulin (B2M) and glyceraldehyde 3-phosphate dehydrogenase (GAPDH) as references. In both groups, expressions of the selected genes have increased. It can be concluded that IR induces ER stress and related authophagy pathway in the peripheral lymphocyte cells proportionally by dose.

A large deletion of the AVPR2 gene causing severe nephrogenic diabetes insipidus in a Turkish family.

X-linked nephrogenic diabetes insipidus (NDI) is a rare hereditary disease caused by mutations in arginine vasopressin type 2 receptor (AVPR2) and characterized by the production of large amounts of urine and an inability to concentrate urine in response to the antidiuretic hormone vasopressin. We have identified a novel 388 bp deletion starting in intron 1 and ending in exon 2 in the AVPR2 gene in a patient with NDI and in his family. We have revealed that this mutation is a de novo mutation for the mother of the proband patient. Prospective clinical data were collected for all family members. The water deprivation test confirmed the diagnosis of diabetes insipidus. The patient has severe symptoms like deep polyuria nocturia, polydipsia, and fatigue. He was given arginine vasopressin treatment while he was a child. However, he could not get well due to his nephrogenic type of illness. Both of his nephews have the same complains in addition to failure to grow. We have sequenced all exons and intron-exon boundaries of the AVPR2 gene of all family members. The analyses of bioinformatics and comparative genomics of the deletion were done via considering the DNA level damage. AVPR2 gene mutation results in the absence of the three transmembrane domains, two extracellular domains, and one cytoplasmic domain. Three-dimensional protein structure prediction was shown. We concluded that X-linked NDI and severity of illness in this family is caused by a novel 388 bp deletion in the AVPR2 gene that is predicted to truncate the receptor protein, and also this deletion may lead to dysfunctioning in protein activity and inefficient or inadequate binding abilities.

Investigation of DNA damage by the alkaline comet assay in 131I-treated thyroid cancer patients.

OBJECTIVE: To assess the possible applicability of comet assay in the evaluation of DNA damage caused by ionizing radiation. The alkaline comet assay or single-cell gel electrophoresis has been used as a standard method for measuring and analyzing DNA damage. STUDY DESIGN: Peripheral blood samples were collected from papillary thyroid cancer patients who received 131I by oral administration. Blood samples were taken just before the treatment, on the first day of treatment, and 1 week posttreatment. To determine the radiation-induced DNA damage, alkaline comet assay was performed. RESULTS: It was found that significantly high levels of DNA damage occurred in first day samples when compared to control samples according to tail moment measurements. Also, a decrease in the level of damage was observed in the 1-week samples. CONCLUSION: Our observations and data confirmed that treatment with 131I for papilloma thyroid cancer can cause DNA damage in circulating lymphocytes, and the comet assay seemed suitable to assess the effect of radioactive iodine for the patients.

Mutations in the AVPR2, AVP-NPII, and AQP2 genes in Turkish patients with diabetes insipidus.

The aim of this study was to identify mutations in three different genes, the arginine-vasopressin-neurophysin II (AVP-NPII) gene, the arginine-vasopressin receptor 2 (AVPR2) gene, and the vasopressin-sensitive water channel aquaporin-2 (AQP2) gene in Turkish patients affected by central diabetes insipidus or nephrogenic diabetes insipidus. This study included 15 patients from unrelated families. Prospective clinical data were collected for all patients including the patients underwent a water deprivation-desmopressin test. The coding regions of the AVPR2, AQP2, and AVP-NPII genes were amplified by polymerase chain reaction and submitted to direct sequence analysis. Of the 15 patients with diabetes insipidus referred to Gulhane Military Medical Academy, Department of Endocrinology and Metabolism, eight patients have AVPR2 mutations, five patients have AQP2 mutations and two patients have AVP-NPII mutations. Of the patients, which have AVPR2 mutations, one is compound heterozygous for AVPR2 gene. Seven of these mutations are novel. Comparison of the clinical outcomes of these mutations may facilitate in understanding the functions of AVP-NPII, AQP2, and AVPR2 genes in future studies.

Poly(hydroxyethyl methacrylate) based affinity cryogel for plasmid DNA purification.

The aim of this study is to prepare supermacroporous pseudospecific cryogel which can be used for the purification of plasmid DNA (pDNA) from bacterial lysate. N-methacryloyl-(l)-histidine methyl ester (MAH) was chosen as the pseudospecific ligand and/or comonomer. Poly(hydroxyethyl methacrylate-N-methacryloyl-(l)-histidine methyl ester) [PHEMAH] cryogel was produced by free radical polymerization initiated by N,N,N',N'-tetramethylene diamine (TEMED) and ammonium persulfate (APS) pair in an ice bath. Compared with the PHEMA cryogel (50 µg/g polymer), the pDNA adsorption capacity of the PHEMAH cryogel (13,350 µg/g polymer) was improved significantly due to the MAH incorporation into the polymeric matrix. The amount of pDNA bound onto the PHEMAH cryogel disks first increased and then reached a saturation value (i.e., 13,350µg/g) at around 300 µg/ml pDNA concentration. pDNA adsorption amount decreased from 1137 µg/g to 160 µg/g with the increasing NaCl concentration. The maximum pDNA adsorption was achieved at 25 °C. The overall recovery of pDNA was calculated as 90%. The PHEMAH cryogel could be used 3 times without decreasing the pDNA adsorption capacity significantly. The results indicate that the PHEMAH cryogel disks promise high selectivity for pDNA.