A comparative study on the effects of alpha-hexachlorocyclohexane and its metabolite beta-pentachlorocyclohexene on growth and monooxygenase activities in rat liver

Hexachlorocyclohexanes (HCH) in ringed seal (Phoca hispida) from Ulukhaktok (Holman), NT: trends from 1978 to 2006

Trends in alpha-, beta-, and gamma-hexachlorocyclohexane (HCH) concentrations were examined in blubber lipid of ringed seals (Phoca hispida) from Ulukhaktok (Holman), NT (Canada) sampled at intervals between 1978 and 2006. alpha-HCH usually represented approximately 90% of the total HCH isomers. alpha-HCH and gamma-HCH concentrations showed no change over the sampling interval, but beta-HCH concentrations increased significantly, about 8-10-fold in females and 4-5-fold in males. Residue concentrations showed no dependence on age. Concentrations (all data as ng/g lipid, GM (range)) of alpha-HCH were significantly higher (P<0.001 by t-test) in males (217 (93.9-517), n=37) than those in females (138 (40.9-402), n=38). beta-HCH concentrations did not differ between the sexes. Concentrations of gamma-HCH were significantly higher (P<0.05) in males (6.74 (0-46.7)) than in females (4.35 (0-19.0)). Although global emissions of both alpha-HCH and beta-HCH have declined since the early 1980's, the "signal" of HCH emission changes has not yet resulted in a "response" in ringed seal residue concentrations. In the light of our current understanding of the dynamics of HCH in the Arctic, we conclude that any such response may not be detected by retrospective analyses of the sort describe here at least for another decade or so, because of the longevity of the seals.

A comparative study of gene expression profiles in rat liver after administration of alpha-hexachlorocyclohexane and lindane

Alpha-hexachlorocyclohexane (alpha-HCH) is a stereoisomer of gamma-HCH, the active ingredient of lindane (> 99% gamma-HCH). In the present study, cDNA microarray technology was employed to identify changes in gene expression associated with toxicity in livers of male Fischer 344 rats after treatment with alpha-HCH (2, 20 mg/kg/day) and lindane (1, 10 mg/kg/day) by daily oral gavage for up to 28 days. Liver samples were obtained after 1, 3, 7, 14 and 28 days and compared for gene expression profiles. The dose of the alpha-HCH was higher than that of lindane and toxicity was greater, but the numbers of probe sets with differences in expression were fewer for the alpha-HCH-treated group except on Day 3. Only very few probe sets with differences in expression overlapped between alpha-HCH and lindane at each time point and the gene expression profiles were very dissimilar. Important liver-based differences in expression between alpha-HCH and lindane might possibly account for hepato-carcinogenicity of alpha-HCH.

Liver lipid peroxidation-related parameters after short-term administration of hexachlorocyclohexane isomers to rats

Rats treated with diets containing 20 ppm of alpha- or gamma-hexachlorocyclohexane (HCH) for 15 or 30 days showed increased levels of liver cytochrome P-450 followed by increased production of both thiobarbituric acid reactants by liver homogenates and microsomes and superoxide anion production by liver microsomes. In these animals superoxide dismutase (SOD) activity was also increased. In consequence, the ratio between SOD activity and microsomal superoxide radical (O2-.) production showed a slight increase after 15 days of treatment. However, after 30 days, there was a tendency for this ratio to decrease. Other parameters studied were liver glucose-6-phosphate dehydrogenase, glutathione peroxidase, glutathione reductase and catalase (CAT) activities. Among them, only CAT activity showed a 26% and 38% increase after 15 or 30 days of treatment with the alpha-isomer. It is suggested that when lipid peroxidation is involved in the mechanism of toxicity of a xenobiotic, this parameter can be used to determine the no-observed-effect level.

Induction of monooxygenases and growth in rat liver by progesterone

Female Wistar rats were treated with various doses of progesterone orally via the diet or via the SC route. Oral treatment resulted in enhanced progesterone levels in the liver as measured by radioimmunoassay. There were up to 3-fold increases in activity of ethylmorphine demethylation by isolated microsomes; metabolism of aminopyrine and benzphetamine was less enhanced, that of aniline and p-nitroanisol showed no distinct increases. Progesterone also caused increases in liver size and total liver protein by up to 50%; total liver DNA showed only slight, insignificant increments. These studies suggest that hepatic effects of progesterone are similar to those previously described with synthetic steroids such as pregnenolone-16 alpha-carbonitrile (PCN) and cyproterone acetate.

Epoxidation of the lindane metabolite, beta-PCCH, by human- and rat-liver microsomes

Human- and rat-liver microsomes convert the lindane metabolite, beta-PCCH (beta-1,3,4,5,6-pentachlorocyclohex-1-ene (3,4,6/5-PCCH] to the metabolites: 1,2,4-TCB (1,2,4-trichlorobenzene), 1,2,3,4-TTCB (1,2,3,4-tetrachlorobenzene), 2,4,5-TCP (2,4,5-trichlorophenol), 3,4,5/6-PCCOL (1,2,4,5,6-pentachlorocyclohex-1-en-3-ol) and beta-PCCH oxide (1,2,3,4,5-pentachloro-7-oxabicyclo[4.1.0]heptane) or (3,4,6/5-PCCH oxide). The identity of the beta-PCCH oxide is confirmed by column chromatography and g.l.c.-mass spectrometry, in comparison to characterized synthetic material. The stability of the beta-PCCH oxide is indicated by its resistance to hydrolysis by microsomal epoxide hydrolase (EC. 3.3.2.3), or various aqueous acid conditions. It shows no mutagenicity using S. typhimurium strain TM677. However, in levels above 0.05 mg/ml it was lethal to the test cells. It is not a substrate for and is only a weak inhibitor of epoxide hydrolase. A stable halogenated hydrocarbon epoxide metabolite is described. Its toxicological role, if any, remains unaccounted for.

Stability of microsomal mono-oxygenase during incubations for the liver microsomal assay with S9 fractions of mouse liver under various inductions

Aminopyrine-N-demethylase and p-nitroanisole-O-demethylase activities were determined in incubation mixtures for the liver microsomal assay at time zero and after 1 h of incubation in the conditions for the mutagenic assay. The experiments were performed with the S9 liver fraction of mice in the basal state and induced with sodium phenobarbital, beta-naphthoflavone or both. Lipid peroxidation was also determined. The experiments were repeated with female mice and also in the presence of styrene, as an example of a xenobiotic substance. The activity of pNAD was much more stable than that of APD in all the conditions tested. The pattern of stability, however, was similar for the two activities: more stable than controls with S9 fractions from beta-NF-induced mice, less stable than controls in PB-induced mice, intermediate between controls and PB-induced mice in those with combined induction by PB + beta NF. Styrene 50 mM in the incubation mixtures led to a marked inactivation of enzymic activity, similar in all cases and reaching about 90% in 1 h. S9 fractions from female mice gave enzymes slightly more stable in almost all cases. Lipid peroxidation was appreciably more elevated in basal than in induced animals. It was concluded that, for a mutagenesis test on an unknown xenobiotic, S9 fractions from mice following PB and beta-NF induction are to be preferred from the point of view of activation.