S. Gemma et al., IN-VITRO QUANTITATIVE-DETERMINATION OF PHOSPHOLIPID ADDUCTS OF CHLOROFORM INTERMEDIATES IN HEPATIC AND RENAL MICROSOMES FROM DIFFERENT RODENT STRAINS, Environmental toxicology and pharmacology, 2(2-3), 1996, pp. 233-242
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.