INDUCTION OF DNA-DAMAGE BY RISK-FACTORS OF COLON-CANCER IN HUMAN COLON CELLS DERIVED FROM BIOPSIES

In order to increase the understanding of the factors responsible for causing human colon cancer, a technique was developed to detect genoto xic effects of chemicals in human colon cells. Risk factors suspected to be associated with the aetiology of human colon cancer were subsequ ently investigated: the method is based on the measurement of DNA dama ge in primary cells freshly isolated from human colon biopsies with th e single cell microgel ectrophoresis technique ('Comet Assay'). 2-Amin o-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), 2-amino-3-methyl-3H- imidazo[4,5f]quinoline (IQ), N-methyl-N-nitro-N-nitrosoguanidine (MNNG ), dinitrosocaffeidine (DNC) lithocholic acid (LCA), hydrogen peroxide (H2O2) and benzo[a]pyrene (B[a]P) were investigated for their genotox ic and cytotoxic effects following 30 min incubation with colon cells of human, and for comparative purposes also of the rat colon, The nitr osamides (MNNG, DNC) were very genotoxic in human colon cells. MNNG wa s more genotoxic in human than in rat colon cells. In contrast, the ra t colon carcino ens PhIP and IQ were not genotoxic in human colon cell s. PhIP did induce DNA damage in rat colon cells, which correlates to its capacity of inducing tumors in this animal tissue. LCA was toxic ( rat > human) and concomitantly caused DNA damage in higher concentrati ons. The widespread contaminant B[a]P was not genotoxic in colon cells of either species using this system. H2O2 was found to be a potent ge notoxic agent to both rat and human colon cells (human > rat). In summ ary, those compounds chosen as representatives of endogenously formed risk factors (MNNG, H2O2, LCA) have a higher toxic and/or genotoxic po tency in human colon tissue than in rat colon. They are also more effe ctive in this system than the contaminants tested so far (B[a]P, PhIP, IQ). The newly developed technique is rapid and yields relevant resul ts, It is a novel and useful approach to assess different chemical com pounds for genotoxic activities in tumour tar et tissues of the human.