DNA damage, DNA repair and chromosome aberrations of xeroderma pigmentosum cells and controls following exposure to nitrosation products of methylguanidine.

Nitrosation of methylguanidine (MG) led to products that caused DNA fragmentation (shift in sedimentation profiles of velocity centrifugation through alkaline sucrose gradients), a DNA repair synthesis (unscheduled uptake of (3H]TdR), chromosome aberrations and a lethal effect of cultured human fibroblasts. The response of repair-deficient xeroderma pigmentosum cells did not differ from that of controls. The nitrosation of MG must be carried out at a pH level below 3, in order to obtain products that react with cellular DNA. The results show that a DNA repair synthesis of human fibroblasts appears to be a sensitive assay for carcinogenic and mutagenic nitrosation products which may be formed within an organism from non-carcinogenic compounds.