IN-VITRO QUANTITATIVE-DETERMINATION OF PHOSPHOLIPID ADDUCTS OF CHLOROFORM INTERMEDIATES IN HEPATIC AND RENAL MICROSOMES FROM DIFFERENT RODENT STRAINS

We have comparatively studied in vitro the oxidative and reductive pat hways of chloroform metabolism in hepatic and renal microsomes of rode nt strains used for carcinogenicity testing (B6C3F1 mice, Osborne Mend el and Sprague Dawley rats). To this aim we exploited the regioselecti ve binding of phosgene to phospholipid (PL) polar heads and of dichlor omethyl radical to PL fatty acyl chains, using a method based on the c hemical transmethylation of PL adducts, followed by phase partitioning of the resulting products (De Biasi et al., 1992). The analysis of re sults let us to conclude at first that a C-14 label partitioning by 89 .2 (+/- 6.5)% or 13.7 (+/- 5.0)% in the aqueous phase is typical of th e pi, adduct with phosgene (PL-PHOS) or with dichloromethyl radical (P L-RAD), respectively. Metabolism of 0.1 mM CHCl3 was mainly oxidative in all the samples, being hepatic microsomes more active than renal on es by about one order of magnitude and levels of CHCl3-derived PL addu cts in B6C3F1 mouse liver microsomes higher than in rat samples. At 5 mM CHCl3, total levels of PL adducts in renal microsomes reached level s almost similar to those found in liver microsomes. However, while B6 C3F1 mouse kidney microsomes produced both reactive metabolites, simil arly as the hepatic samples, Osborne Mendel rat kidney microsomes bioa ctivated CHCl3 only reductively, producing the radical. The relevance of this finding depends on the fact that phosgene is known to be the m ajor cause of CHCl3 toxicity, based on data with the rat liver and mou se liver and kidney, while nephrotoxicity in rats occurs with minimal production of COCl2. Chloroform reductive bioactivation may therefore provide a reasonable explanation for the toxicity of chloroform to the rat kidney. The same finding may be of interest in elucidating the me tabolic reasons of the chloroform-induced kidney tumors in Osborne Men del rats.