Vol. 25, Issue 12, 1416-1423, 1997

Gadolinium Chloride Inhibition of Rat Hepatic Microsomal Epoxide Hydrolase and Glutathione S-Transferase Gene Expression

Sang Geon Kim and Sung Hee Choi

College of Pharmacy, Duksung Women's University

The effects of gadolinium chloride, a Kupffer cell toxicant, on the constitutive and inducible expression of hepatic microsomal epoxide hydrolase (mEH) and glutathione S-transferase (GST) genes were examined in rats. Northern blot analysis showed that treatment of rats with GdCl₃ caused suppression of mEH and GST gene expression. mEH mRNA levels were decreased in a time-dependent manner after a single injected dose of GdCl₃ (10 mg/kg, iv), resulting in 95, 55, 17, 36, and 69% of the levels in untreated animals at 6, 12, 18, 24, and 48 hr after treatment, respectively. A maximal reduction in GST Ya, Yb1/2, and Yc1 mRNA levels was also noted at 18 hr after treatment with GdCl₃, followed by a gradual return to levels in untreated rats at later time points. Whereas treatment of rats with thiazole, allyl disulfide, propyl sulfide, oltipraz, or clotrimazole caused 2-13-fold increases in mEH mRNA levels at 18 hr after treatment, concomitant GdCl₃ treatment caused 30-70% reductions in the increases in mEH mRNA levels. The chemical-inducible mRNA levels for GST Ya, Yb1/2, and Yc1 were also significantly inhibited by GdCl₃ at 18 hr after treatment. Rats treated with GdCl₃ (10 mg/kg/day, iv) for 3-5 consecutive days exhibited 40-90% decreases in mEH, GST Ya, and GST Yb1/2 mRNA levels, relative to control, whereas the Yc1 mRNA level was suppressed at early times and returned to levels in untreated animals at day 5 after treatment. The mRNA levels for mEH and GST Ya in rats treated daily with both allyl disulfide (25 mg/kg, po) and GdCl₃ for 3 consecutive days were 20-30% of those in rats treated with allyl disulfide alone. Western immunoblotting showed that mEH and GST Ya protein expression was decreased at 1-3 days after consecutive daily treatment with GdCl₃. Whereas treatment of rats with GdCl₃ at a dose of 1 mg/kg suppressed constitutive hepatic mEH gene expression by 85% at 18 hr, rats treated with CaCl₂ (10 mg/kg, iv) in combination with GdCl₃ (1 mg/kg, iv) showed 45% suppression of the mEH mRNA level, compared with untreated animals. GdCl₃-induced suppression was also significantly reversed for GST Ya mRNA by excessive CaCl₂ administration. These results demonstrate that GdCl₃ effectively inhibits constitutive and inducible mEH and GST expression, with decreases in their mRNA levels. GdCl₃ suppression of detoxifying enzyme expression may be associated with its blocking of intracellular Ca²⁺ influx, which affects signaling pathways for the expression of the genes.