Pesticide residues in food — 2007: Toxicological ... - ipcs inchem

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recovery period. The microsomal protein content was elevated in the mice treated with the three reference
substances. The protein content of the cytosolic liver fractions was not different between the
control and treated groups.
Microsomal cytochrome P450 contents were significantly elevated in mice treated with difenoconazole
at 100 and 400 mg/kg bw per day. The values returned to the control levels after a 28-day
recovery period. Cytochrome P450 contents were also markedly elevated in mice treated with the
three reference substances.
Examination of the cytochrome P450 gene families detected by cross-reaction with different
monoclonal antibodies showed that the P450 families CYP1A and CYP3A were detectable at enhanced
concentrations in mice treated with difenoconazole at 100 or 400 mg/kg bw per day. There appeared
to be a dose-dependent decrease in the expression of the CYP2B isoenzymes. A similar profile was
obtained with phenobarbitone, while 3-MC caused a 45-fold increase in CYP1A and NAF caused a
9-fold increase in CYP4A. Microsomal epoxide hydrolase activity was markedly elevated in mice
treated with difenoconazole at 100 and 400 mg/kg bw per day relative to mice in the control group, by
about 50% and 250%, respectively. No differences were seen after the 28-day recovery period. Substantial
increases were also noted for phenobarbitone and NAF, but not for 3-MC. Activities of morphine
UDP-glucuronosyltransferase were slightly increased in a dose-related manner in the mice treated with
difenoconazole; this increase was reversed after the 28-day recovery period. Similar increases were
seen in mice treated with phenobarbitone, 3-MC and NAF. Microsomal 1-naphthol UDP-glucuronosyltransferase
activities were essentially unchanged by treatment with difenoconazole, while significant
increases were seen after treatment with phenobarbitone, 3-MC and NAF. EROD and PROD activities
were increased approximately 3- and 30-fold, respectively, in the mice treated with difenoconazole at
400 mg/kg bw; these increases were comparable in magnitude to the increases produced by phenobarbitone.
Changes were also induced by 3-MC, but much greater changes were noted in EROD than
PROD (opposite of difenoconazole). NAF only marginally induced PROD activities. All changes were
reversible after the 28-day recovery period. The activity of cytosolic glutathione S-transferase in mice
treated with difenoconazole at 500 mg/kg bw was increased about 50% over that for mice in the control
group; a similar level of induction was seen with phenobarbitone, and to a lesser extent with NAF.
Total testosterone hydroxylation, dependent on cytochrome P450, was induced in a dose-related
manner to about sixfold the control value in mice treated with difenoconazole at 400 mg/kg bw. Testosterone
hydroxylation rates were also significantly increased with phenobarbitone, 3-MC and NAF.
Except for 7α-hydroxy-testosterone, all testosterone metabolites were increased by between 3- and 120-
fold in mice treated with difenoconazole at 400 mg/kg bw compared with mice in the control group. The
increases of 6β- and 15β-hydroxy-testosterone indicate either a strong barbiturate- or steroid-type induction.
The extent of 6α-hydroxylation also suggests difenoconazole to be a phenobarbitone-type inducer.
Testosterone metabolite profiles of animals treated with 3-MC and NAF were clearly different in magnitude
and distribution, indicating that difenoconazole is not likely to be a 3-MC- or NAF-type inducer.
Treatment with difenoconazole at 100 and 400 mg/kg bw per day resulted in approximately
2-fold increases in lauric acid 11-hydroxylation, while lauric acid 12-hydroxylation decreased at all
doses. Mice treated with phenobarbitone had increases in lauric acid 11-hydroxylation that were
comparable to those in mice treated with difenoconazole and 12-hydroxylation remained unchanged.
On the other hand, 3-MC did not increase 11-hydroxylation and significantly reduced 12-hydroxylation,
while NAF increased both 11- and 12-hydroxylation markedly.
Cyanide-insensitive peroxisomal fatty acid β-oxidation appeared to be slightly and dose-dependently
decreased by treatment with difenoconazole, although this change was not statistically
significant and was reversible after 28 days of recovery. Neither phenobarbitone nor 3-MC affected
peroxisomal β-oxidation, but NAF resulted in a more than fourfold increase in this process.
Titration of liver microsomal suspensions from mice treated with difenoconazole, phenobarbitone,
3-MC or NAF revealed type II binding spectra, which are indicative of an inhibitory action
DIFENOCONAZOLE 201–272 JMPR 2007