The effect of melanin and glutathione on the formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine by singlet molecular oxygen oxidation of 2'-deoxyguanosine
Kurihara, T.A.1; Oliveira, M.B.M.1; Cadena, S.M.S.C.1; Carnieri, E.G.S.1; Di Mascio, P.2; Rocha, M.E.M.1; Martinez, G.R.1
1 Depto de Bioquímica e Biologia Molecular – Setor de Ciências Biológicas – UFPR - PR. E-mail: grmartinez@ufpr.br; 2 Depto de Bioquímica – Instituto de Química – USP - SP
Studies of singlet molecular oxygen (1O2) reaction with 2'-deoxyguanosine (dGuo) in aqueous solution had shown that two products are formed: a pair of diastereomeric spiroiminodihydantoin 2'-deoxyribonucleosides (dSp) and 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodGuo). The evaluation of their formation may be used to investigate the role of some molecules as possible protecting agents of DNA damage. In the present study, we investigated the effect of melanin (from Sepia officinalis and synthetic, 24 mg/mL) and glutathione (reduced -GSH and oxidized – GSSG, 1 mmol/L) on the oxidation of dGuo by 1O2 in neutral aqueous solution. For this purpose, 1O2 was generated by type II photosensitization with methylene blue. It was monitored the formation of 8-oxodGuo using HPLC analysis with electrochemical and UV detection. Previously, we had shown that, in the presence of Sepia´s melanin (24 mg/mL), the level of 8-oxodGuo was around 20% higher independently of the source of 1O2. Interestingly, we observed in the present study, that the formation of 8-oxodGuo in the presence of GSH or GSSG was 45 and 38 % higher than in the absence of this compounds. Also, the presence of Sepia´s melanin in the system with GSH showed a protection, while melanin in the system with GSSG resulted in an increase of 8-oxodGuo. The same tendency was observed when synthetic melanin was employed. These results indicate that the presence of GSH and GSSG favor the oxidation of dGuo by 1O2 and the presence of melanin in the system containing GSH offers a protection. Considering these observations, it may be important the determination of the redox state of cells (GSH/GSSG ratio) when DNA damage is under evaluation. Supported by CNPq
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