Characterization of resistance to bromobenzene-induced hepatotoxicity by microarray

Area of Science:

• Hepatotoxicity and Toxicology
• Molecular Biology and Genomics
• Drug Metabolism and Pharmacokinetics

Background:

• Previous studies demonstrated acquired hepatic resistance to bromobenzene (BB)-induced hepatotoxicity in rats.
• The molecular mechanisms underlying this resistance remained to be fully elucidated.

Purpose of the Study:

• To characterize the molecular changes associated with acquired resistance to BB-induced hepatotoxicity using microarray analysis.
• To identify key genes and pathways involved in the liver's protective response against BB.

Main Methods:

• F344 rats were treated with bromobenzene (150 mg/kg) to induce initial injury, followed by sustained dosing.
• Liver samples were analyzed using Affymetrix RG_U34A arrays to compare gene expression profiles between BB-treated and vehicle-treated groups.
• Key gene expression changes related to metabolic activation, detoxification, and elimination pathways were assessed.

Main Results:

• Decreased expression of CYP3A9 (Phase I metabolism) and increased expression of glutathione S-transferase Yc2 (GST Yc2) and glutathione peroxidase (GPX) (Phase II detoxification) were observed.
• Upregulation of epoxide hydrolase (EH) and NAD(P)H:quinone oxidoreductase (NQO1) suggested alternative Phase II detoxification routes.
• Significantly increased expression of multidrug resistance-associated protein 3 (Mrp3) (Phase III elimination) was noted.

Conclusions:

• Acquired resistance to BB hepatotoxicity involves suppression of Phase I metabolic activation and induction of Phase II detoxification.
• The multidrug resistance-associated protein 3 (Mrp3) in Phase III drug elimination also contributes significantly to this resistance.
• Increased GST Yc2 and Mrp3 expression were identified as the primary contributors to the observed resistance based on gene expression levels.