Ahmet Ozaydin

Glutathione S transferase M1 and T1 genetic polymorphisms are related to the risk of primary open-angle glaucoma: a study in a Turkish population.

Background: Genetic factors and oxidative damage have been shown to have a role in the development of primary open angle glaucoma (POAG). Aim: To determine the effects of genetic polymorphisms of glutathione S transferase (GST)M1 and GSTT1 on the risk of POAG in a Turkish population. Methods: Using a multiplex polymerase chain reaction (PCR), GSTM1 and GSTT1 gene polymorphisms were analysed in 144 patients with POAG and in 121 otherwise healthy controls of similar age. Results: The GSTM1 positive genotype and the GSTT1 null genotype had an increased risk of developing POAG (p<0.001, OR 2.93, 95% CI 1.66 to 5.20 and OR 4.25, 95% CI 2.30 to 7.80, respectively). The risk of glaucoma also increased significantly in subjects with a combination of GSTM1 positive and GSTT1 null genotypes (p<0.001, OR 3.46, 95% CI 1.64 to 7.38). Conclusion: The GSTM1 positive genotype and GSTT1 null genotype or the combination of both may be associated with the increased risk of development of POAG in the Turkish population.

DNA repair gene XRCC1 and XPD polymorphisms and their association with coronary artery disease risks and micronucleus frequency

Coronary artery disease (CAD) is a multifactorial process that appears to be caused by the interaction of environmental risk factors with multiple predisposing genes. In this study, we investigated the effects of the XPD Lys751Gln and XRCC1 Arg399Gln polymorphisms on the presence and the severity of CAD. We also investigated the presence of DNA damage in the peripheral lymphocytes of patients with CAD by using the micronucleus (MN) test and the effect of XPD Lys751Gln and XRCC1 Arg399Gln polymorphisms on this damage. The study population consisted of 147 patients with angiographically documented CAD and 48 healthy controls. No association between XPD Lys751Gln or XRCC1 Arg399Gln polymorphisms and the presence or the severity of CAD was observed. On the other hand, a significantly higher frequency of MN was observed in CAD patients compared with controls (5.7 ± 1.9 vs 5.0 ± 2.1, respectively, P = 0.018). We found an elevated frequency of MN in CAD patients with the XPD 751Gln allele (Gln/Gln genotype) or the XRCC1 399Gln (Arg/Gln or Gln/Gln genotypes) allele compared with the XPD 751Lys (Lys/Lys genotype) allele or XRCC1 399 Arg (Arg /Arg genotype) allele, respectively. These preliminary results suggest that XPD Lys751Gln and XRCC1 Arg399Gln polymorphisms may not be a significant risk factor for developing CAD. In addition, our results indicate that the MN frequency is associated with presence, but not severity, of CAD and is related to the XRCC1 Arg399Gln and XPD Lys751Gln polymorphisms, suggesting an elevated frequency of MN in CAD patients with the XPD 751Gln or XRCC1 399Gln alleles.

The investıgatıon of GSTT1, GSTM1 and SOD polymorphism in bladder cancer patıents

Glutathione S transferases (GSTT1, GSTM1, GSTP1) are enzymes that activate the detoxification of endogenous and exogenous agents. The genetic polymorphism in these genes may change the response of individuals to environmental toxicants. The genetic polymorphisms of GSTT1, GSTM1, GSTP1 have been studied extensively in the determination of individual cancer risks. Some studies showed a strong relationship between polymorphism of GSTs and superoxidedismutase enzymes. Using the polymerase chain reaction (PCR) the prevalence of genetic polymorphisms of GSTT1, GSTM1 and MnSOD (Manganese Superoxide Dismurase) was investigated in 104 cases and controls to seek any association with the risk of bladder cancer. The frequency of GSTT1 +/+ polymorphism was 65% (33/51) in the cases and 79% (42/53) in the controls. The frequency of the GSTM1 +/+ polymorphism was 33% (17/51) in the cases and 58% (31/53) in the controls. The frequency of the GSTM1 null genotype was 42% (22/53) in the controls and 68% (34/51) in the patients. The frequency of the SOD AA genotype was 36% (17/51) in the cases and 33% (19/53) in the controls. There was no association between the GSTT1 and SOD polymorphism and bladder cancer incidence. The incidence of the GSTM1 null genotype was increased in bladder cancer patients compared to controls (OR = 1.755, 95% CI = 1.119–2.751).

Glutathione-S-transferase M1 and T1 genetic polymorphisms and the risk of cataract development: a study in the Turkish population.

In this study, we aimed to determine the effects of genetic polymorphisms of glutathione-S-transferase M1 (GSTM1) and glutathione-S-transferase T1 (GSTT1) on risk of developing different subtypes of age-related cataract in the Turkish population. Using a multiplex polymerase chain reaction (PCR), GSTM1 and GSTT1 gene polymorphisms were analyzed in 195 patients with age-related cataract (75 patients with cortical, 53 with nuclear, 37 with posterior subcapsular, and 30 with mixed type) and in 136 patients of an otherwise healthy control group of similar age. GSTM1 null genotype had a significant association with the development of cataract in female subjects (p < 0.0029; OR, 2.98; 95% CI, 1.41–6.34). This relationship in female subjects was only in nuclear and mixed types cataract cases (p < 0.002; OR, 4.58; 95% CI, 1.67–12.78 and p < 0.03, respectively). There was also a statistically significant association between the combination of GSTM1-null and GSTT1-positive genotypes and the risk of cataract development in female subjects (p = 0.01; OR = 2.87; 95% CI = 1.25–6.69). Stratification by the subtypes revealed that this association was only in nuclear type cataract (p = 0.001; OR, 3.92; 95% CI, 1.34–11.71). GSTM1-null genotype or combination of the GSTM1-null and GSTT1-positive genotypes in females may be associated with increased risk of cataract development in the Turkish population.

LKB1 downregulation may be independent of promoter methylation or FOXO3 expression in head and neck cancer.

The serine/threonine kinase liver kinase B 1 (LKB1) is a multifunctional protein and has been associated with various cancer types. Although the tumor suppressor function of LKB1 is attributed mainly to its ability to phosphorylate directly different adenosine monophosphate-activated protein kinases, its regulation is still poorly understood. More recently, it has been shown that LKB1 expression can be regulated by forkhead box O transcription factors via cis-acting elements, which are found in the promoter region of the LKB1 gene. In this study, we investigated LKB1 messenger RNA expression levels in association with the promoter methylation of the gene and forkhead box O member 3 (FOXO3) messenger RNA expression in head and neck squamous cell carcinoma (HNSCC) tumor samples. Our results show that LKB1 expression is downregulated, especially in advanced-stage tumor samples, and this downregulation was not the result of promoter methylation or modulation by FOXO3 (P = 0.656). Despite observing a positive association between the LKB1 and FOXO3 expression levels in the tumors, this association was not statistically significant (P = 0.24). Our results indicate that downregulation of LKB1 is independent of FOXO3 and may be implicated in the progression of HNSCC.

Transport of glutathione conjugate in erythrocytes from aged subjects and susceptibility to oxidative stress following inhibition of the glutathione S-conjugate pump

The aim of the present study was to investigate the effect of donor aging on the glutathione conjugate transport in erythrocytes and whether it plays a role in the resistance to oxidative stress of the erythrocytes of aging subjects. In our comparative study on intact erythrocytes of healthy aging and young adults, in which 2,4-dinitrophenyl-S-glutathione (DNP-SG) was used as model glutathione S-conjugate, we found that the efflux of DNP-SG remained unchanged in the aged subjects. This result suggests that the detoxification function is maintained against the chemical stress employed in erythrocytes of aging subjects. In the assay conditions used, which were optimized to obtain maximal inhibition of glutathione S-conjugate transport, our results also indicated that the susceptibility of erythrocytes to in vitro lipid peroxidation generated by cumene hydroperoxide was enhanced by pretreatment with DNP-SG inhibitors in both age groups. However, the difference in susceptibility was not a function of aging. Further, the results suggested that inhibition of glutathione S-conjugate pump may impair cellular protection of the erythrocytes against oxidative damage.

Inhibition of platelet function by GSTM1-null human peripheral lymphocytes exposed to benzo(a)pyrene-induced challenge.

Recent epidemiological studies proposed that the glutathione S-transferase (GST) M1-null genotype may contribute to diseases associated with oxidative stress. The genetic polymorphism exhibited by theGSTM1 may be an important factor in risk toward oxidant chemicals. In this study, we investigated the effect ofGSTM1-null genotype in lymphocyte and oxidative stress-dependent inhibition of platelet aggregation. To determine whether GSTM1 deficiency is a genetic determinant of cell toxicity toward oxidant chemicals, lymphocytes were incubatedin vitro with low levels of benzo(a)pyrene (BaP), cumene hydroperoxide (CumOOH), ortrans-stilbene oxide that do not decrease cell viability, and were assessed for oxidative damage and for the lymphocyte-dependent inhibition of platelet response. Malondialdehyde and carbonyl levels, and the oxidation ofcis-parinaric acid, were used as biomarkers of oxidative stress in lymphocytes. Following stimulation by BaP or CumOOH, when peroxidation-dependent changes in these parameters were compared between theGSTM1-null genotype and the positive genotype, no significant differences were found between the two genotypes. On the other hand, preincubation of the lymphocytes with BaP or CumOOH attenuated their inhibitory action on ADP-induced platelet aggregation. However, our results indicate that lymphocytes of individuals with theGSTM1-null genotype have greater inhibitory activity on platelet function after exposure to BaP, but not CumOOH, although they are not more susceptible toin vitro oxidative stress.

Abstract 5382: LKB1 downregulation in head and neck cancer is independent of promoter methylation or FOXO3 expression.

Cancers of the head and neck comprise a diverse group of tumors with squamous cell carcinoma (HNSCC) as the predominant form. Epidemiological data suggest that the etiology and pathogenesis of HNSCC are influenced by environmental and life-style-related factors, such as tobacco use, dietery factors and exposure to toxic substances. However, only a small fraction of tobacco users develop HNSCC suggesting that genetic factors may play a key role in the development of HNSCC. Therefore, genetic abnormalities in HNSCC have been studied extensively. The genetic changes associated with HNSCC affect a variety of different pathways and vary from point mutations to chromosomal aberrations which impair the function or expression of both oncogenes and tumor suppressor genes. Liver Kinase B1 (LKB1) is one of the recently identified tumor suppressor genes which is mutated in Peutz-Jeghers syndrome. It codes for a well-conserved serine-threonine kinase and regulates multiple biological processes and signaling pathways including the control of cell-cycle arrest, p53-mediated apoptosis, Wnt signaling, TGF-s-signaling, ras-induced cell transformation and energy metabolism. Somatic LKB1 alterations have been reported in a variety of carcinomas. Different studies have shown that the LKB1 protein can be inactivated by a wide spectrum of mutations that are scattered all over the protein or by promoter methylation in different types of cancer. Recently, it has been reported that LKB1 is transcriptionally regulated by binding of the FOXO3 protein to the cis-regulatory elements in the promoter region of the LKB1 gene. The FOXO proteins can affect a wide range of biological processes such as cell cycle, stress resistance, development, reproduction, and ageing. In this study we investigated the effect of FOXO3 in the silencing of LKB1 expression in head and neck cancer. For this purpose LKB1 and FOXO3 expression levels and methylation status of the LKB1 promoter were analyzed by real-time PCR and methylation-specific PCR in LKB1-mutant and wild-type HNC tumor samples and matched normal tissue from 49 patients with HNSCC. The average decrease in FOXO3 mRNA expression in the tumor samples was 40%. Downregulation of LKB1 mRNA expression was also observed in a similar fraction of the patients (44%). However, the association was not statistically significant. We observed partial promoter methylation only in 3 of the tumor samples. LKB1 mRNA was downregulated particularly in grade IV tumors indicating that alterations of LKB1 take place during the later stages of HNC carcinogenesis. Our results suggest that LKB1 downregulation is not the result of promoter methylation or modulation by FOXO3. Therefore, the exact understanding of the regulation of LKB1 and FOXO3 in HNSCC requires further studies. Citation Format: Nejat Dalay, Seda Ekizoglu, Emin Karaman, Demet Akdeniz, Ahmet Ozaydin, Nur Buyru. LKB1 downregulation in head and neck cancer is independent of promoter methylation or FOXO3 expression. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5382. doi:10.1158/1538-7445.AM2013-5382