Detection of lignin biopolymer- and vitamin E-stimulated reduction of DNA strand breaks in H2O2- and MNNG-treated mammalian cells by the comet assay

In this study the possible protective effects of water-soluble sulfur-free lignin biopolymer and vitamin E (alpha-tocopherol) on DNA in human VH10 cel ls and hamster V79 cells exposed to H2O2 a nd N-methyl-N'-nitro-N-nitrosogu anidine (MNNG) were investigated The level of DNA damage (DNA strand breaks ) was measured using single-cell gel electrophoresis, i.e., comet assay. Li gnin biopolymer and vitamin E exhibited a protective effect against the ove rall DNA damage induced after H2O2 treatment. If H2O2-treated human cells w ere incubated for 90 minutes to ligate frank breaks of DNA, two lesion-spec ific enzymes, endonuclease III and formamidopyrimidine DNA glycosylase (FPG ), significantly increased the level of DNA strand breaks originating from oxidized pyrimidines and purines. Preincubation of cells with lignin or vit amin E reduced mainly the level of oxidized pyrimidines. Reduction of oxidi zed purines was less evident. In addition, lignin biopolymer exhibited a pr otective effect against MNNG-induced DNA damage, whereas vitamin E exhibite d a protective effect only against H2O2-induced DNA damage. These findings suggest that the antioxidant nature of lignin biopolymer enables a reductio n of the level of frank breaks and of oxidized DNA bases in H2O2-treared ce lls, and its adsorptive capacity enables binding of nitroso compounds and r eduction of alkylation in MNNG-treated cells.