Assessment of DNA nucleo base oxidation and antioxidant defense in postmenopausal women under hormone replacement therapy.

Background and Objective: The aim of the present study was to evaluate oxidative stress byinvesting oxidatively damaged DNA AS Formamidopyrimidine DNA glycosylase (Fpg) -sensitive sites, glutathione peroxidase (GPx), superoxide dismutase (SOD) activities reduced glutathione (GSH) level and nitrite level as satble end product of in women receiving hormone replacement therapy (HRT). Materials and Methods: 127 healthy postmenopausal women receiving HRT and 25 healthy control postmenopausal women were included in this study. Women receiving HRT, comprised surgical menopausal women who underwent surgery for benign conditionsand received conjugated equine estrogen, 0.625 mg/day for 1year (group 1), 5 years (group 2) and more than 10 years (group 3), spontaneous postmenopausal women received conjugated equine estrogen, 0.625 (Premarin) mg/day and medroxyprogesterone acetate, 2.5 mg/day (Premelle) for 1 year (group 4), 5 years (group 5) and more than 5 years (group 6).We investigated in the present study the effects of HRT on nitrite level and GSH level, activities of SOD and GPx and oxidative damage to DNA by comet assays by measuring levels of Fpg-sensitive sites. Results: Although no significant differences were found in the SOD activities, in total group receiving HRT, increased DNA oxidation (P<0.001) together with an increased GPx activity (P<0.001) and nitrite level (P<0.001) as well as a decreased GSH level (P < 0.05) as compared with controls were observed. Conclusion: Estrogen alone or oestrogen in combination with progesterone and duration of use did not significantly alter the results. We evaluated that caused oxidative stress by investigating oxidative DNA damage as Fp-sensitive sites and GSH.NO levels in women receiving HRT.

Base excision repair synthesis of DNA containing 8-oxoguanine in Escherichia coli

8-oxo-7,8-dihydroguanine (8-oxo-G) in DNA is a mutagenic adduct formed by reactive oxygen species. In Escherichia coli, 2,6-dihydroxy-5N-formamidopyrimidine (Fapy)-DNA glycosylase (Fpg) removes this mutagenic adduct from DNA. In this report, we demonstrate base excision repair (BER) synthesis of DNA containing 8-oxo-G with Fpg in vitro. Fpg cut the oligonucleotide at the site of 8-oxo-G, producing one nucleotide gap with 3' and 5' phosphate termini. Next, 3' phosphatase(s) in the supernatant obtained by precipitating a crude extract of E. coli with 40% ammonium sulfate, removed the 3' phosphate group at the gap, thus exposing the 3' hydroxyl group to prime DNA synthesis. DNA polymerase and DNA ligase then completed the repair. These results indicate the biological significance of the glycosylase and apurinic/ apyrimidinic (AP) lyase activities of Fpg, in concert with 3' phosphatase(s) to create an appropriately gapped substrate for efficient BER synthesis of DNA containing 8-oxo-G.