A formation mechanism for 8-hydroxy-2′-deoxyguanosine mediated by peroxidized 2′-deoxythymidine

Abstract

The oxidative formation of 8-hydroxy-2'-deoxyguanosine (8-OHdG) in DNA is closely associated with the induction of degenerative diseases, including cancer. However, the oxidant species participating in the formation of 8-OHdG has yet to be fully clarified. On the basis that peroxyl radicals are a strong candidate for this species, we employed 2,2'-azobis(2-amidinopropane) (AAPH) as a peroxyl radical generator. Exposure of calf thymus DNA to AAPH formed 8-OHdG, but the exposure of 2'-deoxyguanosine (dG) alone did not. From the exposure of various combinations of nucleotides, 8-OHdG was formed only in the presence of dG and thymidine (dT). A mix of dG with an oxidation product of dT, 5-(hydroperoxymethyl)-2'-deoxyuridine, produced 8-OHdG, but the amount formed was small. In contrast, 8-OHdG was produced abundantly by the addition of dG to peroxidized dT with AAPH. Thus, the formation of 8-OHdG was mediated by the peroxidized dT. Instead of artificial AAPH, endogenous peroxyl radicals are known to be lipid peroxides, which are probably the oxidant species for 8-OHdG formation mediated by thymidine in vivo.

Reactions of the OOH radical with guanine: Mechanisms of formation of 8-oxoguanine and other products

“…2, 4 and 5). It is in agreement with experimental finding that 8-oxoGua is formed due to the oxidation of guanine by superoxide radical anion [40] and by peroxyl radicals [7,9,10,19]. In the schemes 1 and 3, the OH radical abstracts a hydrogen atom producing a complex of 8-oxoGua radical and a water molecule each (PC1, PC1 0 respectively) while in scheme 4, the OH radical gets added to C5 producing 5-hydroxy-8-oxoGua (PC2) (Figs.…”

“…Guanine has been found to be most reactive while adenine has been found to be least reactive with regard to oxidation of DNA bases by peroxyl radicals [18]. Occurrence of 8-oxoGua due to oxidation of DNA by peroxyl radicals has been observed experimentally [7,9,19]. Base level DNA damage caused by different environmental agents and prevention of the damage are subjects of great importance in chemistry, biology and medicine [20][21][22][23][24][25][26][27][28].…”

Urinary 8‐OHdG elevations in a partial lesion rat model of parkinson's disease correlate with behavioral symptoms and nigrostriatal dopaminergic depletion

“…The neurotoxicity of 6‐OHDA in animal models of PD initially involves damage to intracellular lipids, proteins or DNA with consequent impairment of cell function (Fornstedt et al, 1986; Thakar and Hassan, 1988; Schober, 2004; Bové et al, 2005; Goto et al, 2008). Notably 6‐OHDA‐induced mitochondrial dysfunction and oxidative stress have been implicated as key neurotoxic events contributing to the pathogenesis of PD (Blum et al, 2001; Yuan et al, 2008).…”

Black soybean seed coat polyphenols prevent AAPH-induced oxidative DNA-damage in HepG2 cells

“…(20) Briefly, the cells were scraped with 100 µl of PBS, washed three times with ice-cold PBS, and centrifuged at 1,000 ×  g for 10 min at 4°C. The pellet was gently homogenized in an ice cold 5 mM 4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid (HEPES) buffer (pH 7.5) containing 0.25 M sucrose and 0.5 mM ethylene glycol tetraacetic acid, and again centrifuged at 1,000 ×  g for 10 min at 4°C.…”