Metabolism and bioactivation of 1,2,3-trichloropropane (TCP)

Abstract

1,2,3-Trichloropropane (TCP) causes rat hepatic DNA damage in the form of DNA single strand breaks. This damage was dose and time dependent. In vivo ¹⁴C-TCP equivalents covalently bound to hepatic protein, RNA and DNA. Glutathione depletion with L-buthionine-(R,S)-sulfoximine increased binding to protein by 342% while it decreased binding to DNA by 56%. The in vivo binding data suggest a dual role for glutathione in the bioactivation of TCP. In vitro rat hepatic microsomes activated TCP to species which covalently bound to microsomal protein. Rat liver microsomes also bioactivated TCP to the direct acting mutagen 1,3-dichloroacetone. 1,3-Dichloroacetone was identified as the major microsomal protein binding species through conjugation with N-acetylcysteine to form 1,3-(2-propanone)-bis-S-(N-acetylcysteine) which accounted for 87% of all TCP microsomal metabolism. These findings support a role for 1,3-dichloroacetone as a mutagenic metabolite of TCP. Carbon-13 nuclear magnetic resonance was used to identify directly the urinary metabolite of ¹³C₃-TCP (99 atom % enrichment). Urine was investigated directly using proton-decoupled ¹³C and two-dimensional homonuclear correlated nuclear magnetic resonance spectroscopy. Spectral shifts have been assigned to N-acetyl-S-(2-hydroxy-3-chloropropyl)cysteine, 1,3-(2-propanol)-bis-S-(N-acetylcysteine), N-acetyl-S-(2-hydroxy-2-carboxyethyl)cysteine, 2,3-dichloropropionic acid, 2-chloroethanol, ethylene glycol and oxalic acid by comparison to spectra of authentic standards. No unchanged TCP was detected. From the results obtained it is concluded that metabolism of TCP by cytochromes P450 and by glutathione conjugation can result in the formation of reactive metabolites of TCP which may be responsible for TCP genotoxicity.