4,4'-Methylene-bis(2-chloroaniline) (MOCA) is an aromatic amine used widely in industry, and human exposure to this compound is well documented. MOCA induces lung and liver tumors in rodents and urinary bladder tumors in dogs, and it is regarded as a suspect urinary bladder carcinogen in humans. In this pilot study, we investigated the occurrence of MOCA-DNA adducts in exfoliated urothelial cells of a MOCA-exposed worker by 32P-postlabeling analysis. Urine samples were collected from the worker at various times after accidental acute exposure to MOCA. DNA isolated from exfoliated urothelial cells collected from each urine sample was enzymatically digested and postlabeled with excess [32P]ATP. Thin-layer chromatographic analysis of the labeled digests revealed the presence of a single, major DNA adduct that cochromatographed with the major N-hydroxy-MOCA-DNA adduct, N-(deoxyadenosin-8-yl)-4-amino-3-chlorobenzyl alcohol, formed in vitro. The MOCA-DNA adduct was detected in samples obtained between 4 and 98 h after initial exposure but not in samples collected at later times. The level of DNA adducts 4 h after exposure was determined to be 516 adducts/10(8) nucleotides. A 5-fold decrease in adduct level was observed 14 h later, followed by a gradual decrease over subsequent days. The results indicate that MOCA is potentially genotoxic to human urinary bladder in vivo and that 32P-postlabeling analysis of exfoliated urothelial cells provides a noninvasive means for biomonitoring the formation of MOCA-DNA adducts resulting from occupational exposure.

This content is only available via PDF.