Gadolinium chloride inhibition of rat hepatic microsomal epoxide hydrolase and glutathione S-transferase gene expression.

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.