Toxicology of Industrial Compounds

324 ANTIOXIDANTS AND LIGHT STABILISERS: TOXIC EFFECT
plasma transaminase activities. Upon electron microscopical examination,
a striking peroxisome proliferation was the major finding.
Compound F, a di-ester ‘product by process’ obtained upon esterification
of 3-[3-(2H-benzotriazole-2-yl)-5-tert-buty1–4-hydroxyphenyl] propionic
acid with polyethyleneglycol 300, when tested for its toxicity to rat
reproduction in a Segment I study, gave rise to increased numbers of stillborn
pups, decreased pup survival, decreased weight gain of surviving pups, and
dark discoloured abdominal skin regions in a number of pups at higher
dose levels.
The common nature of general toxicology findings with all investigated
derivatives of the addressed benzotriazole-based light stabilisers suggested a
common basis of action and, depending upon this action, perhaps a very
similar behaviour and extent of potency as foetotoxic agents. In order to
investigate these interrelationships a series of mechanistic studies were
conducted focusing on the kinetics, primary metabolism of the parent
compounds in vitro and in vivo and their effect on selected biochemical
liver parameters in rats. Compound F was selected as a model compound
to investigate the mechanism of toxicity in pregnant female rats and
foetuses.
In vitro hydrolysis
Compound D, the methyl ester of 3-[3-(2H-benzotriazole-2-yl)-5-tertbutyl-4-hydroxyphenyl]
propionic acid was readily hydrolysed in vitro by
rat serum as well as rat liver homogenate while a homogenate of rat small
intestine when compared on a gram tissue basis, appeared to be less
efficient by three orders of magnitude than the liver. Increasing the sterical
hindrance around the ester bond by formation of the di-ester with a short
chain alcohol reduced the rate of in vitro hydrolysis considerably as
demonstrated for Compound F, the diester of hexane-l,6-diol with
Compound C. When offered at a test concentration of 0.2 mM, essentially
no hydrolysis of this compound was observed with rat serum, and the
hydrolysis by liver and small intestine homogenate was estimated to
proceed at least two and one orders of magnitude slower, respectively, than
calculated for Compound D (Table 23.1 and 23.4).
Blood kinetics and blood metabolites
Assuming comparable extents of intestinal absorption in vivo, the observed
differences in the in vitro hydrolysis rates might as well suggest
significantly different in vivo hydrolysis rates and consequently quite
different residence times for both parent compounds in the rat in vivo.
Different residence times, on the other hand, may eventually allow not only
for additional routes of metabolism but also for an intensification of toxic