Determination of oxidative DNA damage and its correlation with malondialdehyde (MDA) level / Siti Nor Fuadah Sapuan

Oxidative DNA damage was investigated after the intraperitoneal administration of paraquat (PQ) 70 mg/kg in mice by using the comet assay in combination with a specific endonuclease, formamidopyrimidine DNA glycosylase (FPG). On the other hand, the product of lipid peroxidation, malondiladehyde (MDA) was determined by using HPLC method as a measure of oxidative stress. The correlation between oxidative DNA damage and lipid peroxidation was also investigated. The mice were divided into two groups, a PQ-treated group (n = 6) and a control group (n = 6). The former group received PQ (70 mg/kg, i.p.) while the latter, normal saline (i.p.). After 24 hours, the blood and lungs of the mice were collected for the measurement of oxidative DNA damage by the comet assay while MDA was measured by HPLC in lung and plasma samples. FPG was used in combination with the comet assay to specifically detect oxidative DNA damage. For MDA determination, lung and plasma samples were derivatised with 2,4- dinitrophenylhydrazine (DNPH) before HPLC analysis. The results showed no pronounced oxidative DNA damage in the PQ-treated group both in the presence and absence of FPG. There was no significant DNA damage in the PQ-treated group compared to controls. MDA lung levels were not different from those of the controls but MDA plasma levels were higher than those of controls. It is not certain whether lipid peroxidation had occurred in the lungs since MDA lung levels were not different from those of controls. Since DNA damage did not occur with PQ administration, no correlation could be made between the increase in plasma MDA levels (which is an indication of lipid peroxidation) and oxidative DNA damage. Further studies need to be carried out in order to correlate oxidative DNA damage and oxidative stress as measured by an enhanced MDA level.