Relationship between chemical structure and activity. III. Dose-response or time-course of induction in microsomal enzymes following treatment with 1,2,4-trichlorobenzene

The contribution of 2,3,5-trichlorophenyl methyl sulfone, a metabolite of 1,2,4-trichlorobenzene, to the delta-aminolevulinic acid synthetase induction by 1,2,4-trichlorobenzene in rat liver

In the present study, we investigated the contribution of methylsulfonyl metabolite derived from 1,2,4-trichlorobenzene (1,2,4-TCB) on the delta-aminolevulinic acid (ALA) synthetase induction by the parent compound in rats. The time courses of increasing of hepatic microsomal total cytochrome P450 content after a single i.p. administration of 1,2,4-TCB (1.36 mmol/kg), and 2,3,5- and 2,4,5-trichlorophenyl methyl sulfones (2,3,5- and 2,4,5-TCPSO2Mes) (50 micromol/kg each) were in parallel with those of increasing of the total heme content in liver microsomes. 1,2,4-TCB significantly increased the heme oxygenase activity, but 2,3,5- and 2,4,5-TCPSO2Mes did not. On the other hand, 1,2,4-TCB and 2,3,5-TCPSO2Me markedly enhanced the ALA synthetase activity. No change was observed in this enzyme activity after the administration of 2,4,5-TCPSO2Me. After the administration of 1,2,4-TCB to the rats treated with DL-buthionine-(S,R)-sulfoximine (BSO) and to the non-BSO-treated rats, the concentrations of both 2,3,5- and 2,4,5-TCPSO2Mes were significantly lower in liver of the BSO-treated rats than in liver of the non-BSO-treated rats. Additionally, the 1,2,4-TCB did not elevate the ALA synthetase activity in the BSO-treated rats. On the other hand, the administration of 2,3,5-TCPSO2Me to BSO-treated rats resulted in induction of ALA synthetase. The results strongly suggest that the methyl sulfone derived from 1,2,4-TCB, i.e., 2,3,5-TCPSO2Me, contributes highly to the induction of the ALA synthetase activity by the parent compound.

Contribution of methylsulfonyl metabolites of m-dichlorobenzene to the heme metabolic enzyme induction by the parent compound in rat liver

In the present study, we investigated the contribution of methylsulfonyl metabolites derived from m-dichlorobenzene (m-DCB) on the heme metabolic enzyme induction by the parent compound in rats. The time courses of the effects of a single ip administration of m-DCB (200 mg/kg, 1.36 mmol/kg) and 2,4- and 3,5-dichlorophenyl methyl sulfones (2,4- and 3,5-DCPSO2Mes) (each 50 mumol/kg) on hepatic microsomal cytochrome P450 content were almost in parallel with those on the total heme content in liver microsomes. m-DCB significantly increased the heme oxygenase activity, but 2,4- and 3,5-DCPSO2Mes did not. On the other hand, m-DCB and both methyl sulfones markedly enhanced the delta-aminolevulinic acid (ALA) synthetase activity. No change was observed in percentage saturation of the tryptophan pyrrolase activity after administration of m-DCB, whereas this ratio at 6 hr after injection of 3,5-DCPSO2Me was increased. In the liver of the DL-buthionine-(S,R)-sulfoximine (BSO)-treated rats dosed with m-DCB, both of 2,4- and 3,5-DCPSO2Mes were present at significantly lower concentrations than in non-BSO-treated rats. Additionally, the m-DCB did not elevate the ALA synthetase activity in the BSO-treated rat. On the other hand, the administration of either 2,4- or 3,5-DCPSO2Mes to BSO-treated rats resulted in induction of ALA synthetase. m-DCB and 2,4- and 3,5-DCPSO2Mes produced a dose-related increase in liver levels of methyl sulfones. The changes in the ALA synthetase activity after the administration of varying doses of m-DCB were similar to those after the administration of 2,4- or 3,5-DCPSO2Mes, whereas the sum of the concentration of two methyl sulfones in the liver of rats dosed with m-DCB was almost the same as the concentration of methyl sulfone after the administration of either 2,4- or 3,5-DCPSO2Mes. The results strongly suggest that the methyl sulfones derived from m-DCB, i.e., 2,4- and 3,5-DCPSO2Mes, contribute highly to the induction of the ALA synthetase activity by the parent compound.

Evidence that methylsulfonyl metabolites of m-dichlorobenzene are causative substances of induction of hepatic microsomal drug-metabolizing enzymes by the parent compound in rats

This study was undertaken to clarify the relationship between the formation of 2,4- and 3,5-dichlorophenyl methyl sulfones, metabolites of m-dichlorobenzene (DCB), and their inducing effect on hepatic microsomal drug-metabolizing enzymes in rats. When m-DCB was injected ip into bile duct-cannulated rats, little or no methyl sulfones were detected in blood, liver, kidneys, adipose tissue, or bile. In the antibiotic-pretreated rats dosed with m-DCB, metabolite concentrations in the blood and the three tissues markedly decreased. These findings suggest that the formation of methylsulfonyl metabolites from m-DCB depends largely upon the metabolism of some precursor(s) excreted in the bile by intestinal microflora. The increasing effects of m-DCB administration on the activities of aminopyrine and aniline metabolizing enzymes and the contents of cytochromes P-450 and b5 in hepatic microsomes were scarcely observed in the bile duct-cannulated and antibiotic-pretreated rats, in which the drug-metabolizing enzymes were able to be induced by phenobarbital treatment. On the other hand, in rats administered 2,4- or 3,5-dichlorophenyl methyl sulfone hepatic distribution of each methyl sulfone was similar to that in intact rats, and the degree of increase of the above four parameters was nearly the same as that in the intact rats. These findings provide evidence that the induction of drug-metabolizing enzymes by m-DCB is not due to the action of m-DCB but is due to its methylsulfonyl metabolites.

Differential induction of hepatic drug metabolizing enzymes in Japanese quail by 1,2,4-trichlorobenzene

The effects of single oral administration of 1,2,4-trichlorobenzene (TCB), 200, 400, 800 or 1600 mg/kg, and of daily oral administration of TCB, 400 mg/kg, for 3 consecutive days, on components of the microsomal monooxygenase system, glutathione, and the activities of cytosolic glutathione S-transferase and microsomal epoxide hydrolase in Japanese quail liver were studied. Cytochromes P-450 and b5 contents of liver microsomes and the activities of 7-ethoxyresorufin deethylase (7-ERD) and glutathione S-transferase were significantly increased 1 day after administration of single doses of TCB. Liver GSH and 7-ethoxycoumarin deethylase (7-ECD) activity were unchanged. Microsomal epoxide hydrolase activity was significantly decreased at TCB doses above 400 mg/kg. Increases in cytochromes and activities of 7-ERD and glutathione S-transferase were also seen following the 3-day administration of TCB, 400 mg/kg. In addition, liver GSH and the activity of NADPH-cytochrome c reductase were significantly increased whereas 7-ECD was significantly decreased by the 3-day treatment. These findings indicate that in Japanese quail, TCB is an inducer of 7-ERD and glutathione S-transferase but not of 7-ECD and epoxide hydrolase.

Studies on the porphyrinogenic action of 1,2,4-trichlorobenzene in birds

The porphyrinogenic action of 1,2,4-trichlorobenzene (TCB) was examined in 17-day-old embryos, day-old chicks, 18-day-old chickens and adult Japanese quail. The quail was found to be the most sensitive species towards TCB induced porphyria whereas the chick embryo was totally non-responsive. The liver porphyrins of Japanese quail were increased in a dose-dependent manner 1 day after TCB. Elevation in porphyrin levels in quail was associated with comparable increases in delta-aminolevulinic acid synthetase (ALA-S) activity 1 day after TCB treatment. In contrast, ferrochelatase activity was found to be unchanged 1 day after TCB. Multiple administration of TCB produced only a slight increase in liver porphyrin levels and ALA-S activity in quail. However, there was a marked induction in ferrochelatase activity suggesting increased porphyrin turnover. Liver glutathione and glutathione S-transferase activity were also significantly increased following repeated administration of TCB in quail, which could indicate an enhancement of detoxication of reactive metabolites of TCB. Thus, it is suggested that the inability of low multiple doses of TCB to cause porphyria in Japanese quail may be related to the low responsiveness of ALA-S but high inducibility of ferrochelatase liver GSH and glutathione S-transferase.

Induction of hepatic microsomal drug-metabolizing enzymes by sulfur-containing metabolites of chlorinated benzenes in rats

3,5-Dichlorophenyl methyl sulfide and its oxidized compounds, metabolites of m-dichlorobenzene, increased the activity of aniline hydroxylase and aminopyrine N-demethylase and the content of cytochromes P-450 and b5 in rat liver microsomes. Hexobarbital sleeping time was reduced by these three compounds. After the administration of the sulfide to rats, 3,5-dichlorophenyl methyl sulfone appeared in blood, liver, and kidneys, and remained detectable in the blood and the tissues between 120 and 240 hr. The sulfone was considered to play a principal role in the induction by these compounds. Other chlorophenyl methyl sulfones also showed similar induction activity.