Various pharmacokinetic parameters in relation to enzyme-inducing abilities of 1,2,4-trichlorobenzene and 1,2,4-tribromobenzene

Subchronic Hepatotoxicity Evaluation of 1,2,4-Tribromobenzene in Sprague-Dawley Rats

Male Sprague-Dawley rats were exposed to 1,2,4-tribromobenzene (TBB) by gavage for 5 days, 2, 4, and 13 weeks at 0, 2.5, 5, 10, 25, or 75 mg/kg per d. There were no TBB exposure-related clinical signs of toxicity or changes in body weight. Liver weight increases were dose and exposure time related and statistically significant at ≥10 mg/kg per d. Incidence and severity of centrilobular cytoplasmic alteration and hepatocyte hypertrophy were dose and time related. The 75 mg/kg per d group had minimally increased mitoses within hepatocytes (5 days only). Hepatocyte vacuolation was observed (13 weeks) and was considered TBB exposure related at ≥25 mg/kg per d. Concentrations of blood TBB increased linearly with dose and at 13 weeks, ranged from 0.5 to 17 µg/mL (2.5-75 mg/kg per d). In conclusion, rats administered TBB doses of 10-75 mg/kg per d for 13 weeks had mild liver effects. A no observed adverse effect level of 5 mg/kg per d was selected based on the statistically significant incidence of hepatocyte hypertrophy at doses ≥10 mg/kg per d.

Effects of 1,2,4-trichlorobenzene on the enzyme activities and ultrastructure of earthworm Eisenia fetida

Adult Eisenia fetida earthworms were exposed to sub-lethal concentrations of 1,2,4-trichlorobenzene to assess the toxicity of contaminated soils. The LC₅₀ of 1,2,4-TCB at 7 and 14 d were 945±175 and 890±169 mg kg⁻¹. A lower dose of 1,2,4-TCB (25 mg g⁻¹) had stimulatory effects on SOD and AChE activities, but AChE activities were significantly inhibited at higher treatment levels (100 and 400 mg g⁻¹). SOD activities increased after 2, 7, and 14 d of exposure, but AChE activities were significantly inhibited at 400 mg/kg 1,2,4-TCB after 2, 7, and 14 d of exposure, and the inhibition rates were 25.41%, 28.65%, and 25.05%. Ultrastructural observation of the intestinal epithelium at three concentrations (control, 50, and 400 mg g⁻¹) revealed that the epicuticle, cuticle layer, and microvilli were damaged with increasing 1,2,4-TCB concentration. At 400 mg kg⁻¹, mitochondria were seriously injured and the smooth endoplasmic reticulum was seriously dilated.

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.