Mechanisms by which vegetable consumption reduces genetic damage in humans

A previous intervention study had shown that consumption of carotenoid-containing vegetable juices reduces oxidative DNA damage in lymphocytes of 23 male subjects. It was the aim of this study to elucidate the potential mechanisms involved. Specifically, we studied the modulation of protein expression and determined susceptibility factors. Cryopreserved lymphocytes from the study were analyzed for genetic polymorphisms of glutathione S-transferase (GSTM1, GSTP1, and GSTT1) using multiplex PCR, GSTP1-protein with an ELISA, total protein by a colorimetric enzyme reaction, and DNA-repair enzymes with the Comet Assay. Analyses of the genotoxicity data revealed a more steady state of protection for GSTM1*+ than for GSTM1*0 (15 and 8 of 23, respectively) genotypes. Increased expression of cytosolic protein was observed in 11 of 23 subjects, increased expression of GSTP1 in 6 of 23 subjects, and capacity of repair of oxidized DNA bases in 9 of 21 subjects. GSTP1 induction was independent of the GSTP1 genotype (GSTP1a or GSTP1b/c alleles). Kinetics of induction of cytosolic protein and of GSTP1 were compared in one GSTM1*+ and one GSTM1*0 subject and showed an efficacy of tomato and carrots, but not of spinach. Reduced genetic DNA damage in lymphocytes may be due to the enhancement of cytosolic GSTP1, and DNA-repair proteins by tomato and carrot juices. Enhancement of cytosolic proteins may be indicative of increased gene expression by vegetable juices, some of which may be associated with protective activities.