GSTM1 and GSTT1 polymorphism influences protection against induced oxidative DNA damage by quercetin and ascorbic acid in human lymphocytes in vitro

Antioxidants are of major importance in the protection against cellular oxidative damage caused by endogenous as well as exogenous free radicals. This study aims to establish the impact of genetic polymorphisms in GSTM1 and GSTT1, which encode for enzymatic antioxidative defence, on H₂O₂-induced oxidative DNA damage and on the effectiveness of quercetin and ascorbic acid in preventing this induced damage in human lymphocytes. Lymphocytes from 12 healthy volunteers were pre-incubated either with 10 μM of quercetin or with 10 μM of ascorbic acid, and exposed to 25 μM H₂O₂ for 1 h. The induction of oxidative DNA damage was quantified using the Comet assay. Genotyping of these 12 subjects showed that six individuals were GSTM1+ and six were GSTM1−; eight were GSTT1+ and four GSTT1−.

Results

Baseline levels of oxidative DNA damage did not differ between GSTM1 or GSTT1 variants and their respective wild types. Also with respect to ex vivo induced levels of oxidative DNA damage, no significant difference was seen between variants and wild types of both genotypes. The protection against H₂O₂-induced oxidative DNA damage by quercetin was significantly higher in GSTT1 wild types than in GSTT1 variants (57% and 9% decrease, respectively; p = 0.01); furthermore, GSTT1 wild types were protected against induced oxidative DNA damage by ascorbic acid pre-incubation while GSTT1 variants showed an increase of damage (16% decrease vs. 91% increase; p = 0.01). For GSTM1 variants and wild types, observed differences in protective effects of quercetin or ascorbic acid were not statistically significant. Overall, quercetin proves to be better in protecting human lymphocytes in vitro against oxidative DNA damage upon H₂O₂ challenge than ascorbic acid.