Aristolactam I a metabolite of aristolochic acid I upon activation forms an adduct found in DNA of patients with Chinese herbs nephropathy

Aristolochic acid (AA) a naturally occuring nephrotoxin and carcinogen is i mplicated in a unique type of renal fibrosis, designated Chinese herbs neph ropathy (CHN). We identified AA-specific DNA adducts in kidneys and in a ur eter obtained from CHN patients after renal transplantation. AA is a plant extract of aristolochia species containing AA I as the major component. Ari stolactams are the principal detoxication metabolites of AA, which were det ected in urine and faeces from animals and humans. They are activated by cy tochrome P450 (P450) and peroxidase to form DNA adducts. Using the P-32-pos tlabelling assay we investigated the formation of DNA adducts by aristolact am I in these two activation systems. A combination of two independent chro matographic systems lion-exchange chromatography TLC and reversed-phase HPL C) with reference compounds was used for the identification of adducts. Ari stolactam I activated by peroxidase led to the formation of several adducts . Two major adducts were identical to adducts previously observed in vivo. 7-(deoxyguanosin-N-2-yl) ari stolactam I (dG-AAI) and 7-(deoxyadenosin-N-6- yl)aristolactam I(dA-AAI) were formed in DNA during the peroxidase-mediated one-electron oxidation of aristolactam I. Aristolactam I activated by P450 led to one major adduct and four minor ones. Beside the principal AA-DNA a dducts identified recently in the ureter of one patient with CHN, an additi onal minor adduct was detected, which was found to have indistinguishable c hromatographic properties on TLC and HPLC from the major adduct formed from aristolactam I by P450 activation. Thus, this minor AA-adduct might be evo lved from the AAI detoxication metabolite (aristolactam I) by P450 activati on. These results indicate a potential carcinogenic effect of aristolactam I in humans.