Choi S H, Kim S G
College of Pharmacy, Duksung Women's University, Seoul, Korea.
Biochem Pharmacol. 1998 Dec 1;56(11):1427-36. doi: 10.1016/s0006-2952(98)00204-4.
Lipopolysaccharide (LPS) is an endotoxin involved in septic shock syndrome and potentiates toxicant-induced liver injury. The effects of LPS on the constitutive and inducible expression of hepatic microsomal epoxide hydrolase (mEH) and glutathione S-transferase (GST) genes were studied in rats. Northern blot analysis showed that treatment of rats with LPS caused suppression in mEH and GST gene expression. The mEH mRNA level was decreased in a time-dependent manner following a single dose of LPS (1 mg/kg, i.v.), resulting in levels of 52%, 22%, 17%, and 94% of those in untreated animals at 2, 6, 12, and 24 hr, respectively. The levels of rGSTA2 and rGSTA3 mRNA were suppressed in response to an LPS injection to the similar extents as observed in mEH mRNA, whereas rGSTM1 and rGSTM2 mRNA levels were less affected. LPS inhibited mEH gene expression at the doses of 1 microg or greater. Whereas treatment of rats with allyl disulfide (ADS), oltipraz (OZ) or pyrazine (PZ) at the dose of 50 mg/kg caused increases in the mEH mRNA level at 12 hr, a concomitant LPS injection (1 mg/kg) resulted in 80%-95% suppression of the inducible gene expression. The inducible rGSTA2, rGSTA3, rGSTM1, and rGSTM2 mRNA levels were also 50%-90% decreased at 12 hr after LPS treatment, with the relative change in rGSTA being greater than that in rGSTM. Three consecutive daily treatments with LPS (10 microg/kg/day) resulted in significant decreases of the constitutive and PZ (50 mg/kg/day, i.p. for 3 days)-inducible mEH and GST mRNA levels, which were consistent with those in the protein levels. Gel shift retardation analysis showed that LPS substantially activated the hepatic nuclear p65/p50 nuclear factor-kappaB (NF-kappaB) complex with the maximal effect observed at 1 hr at the doses of 1 microg/kg or greater. LPS-induced activation of nuclear NF-kappaB (1 microg/kg, i.v.) failed to be inhibited by concomitant treatment with the mEH and GST inducers, including ADS (300 mg/kg, p.o.), OZ (300 mg/kg, p.o.), and PZ (300 mg/kg, i.p.), indicating that NF-kappaB activation was not required for suppression of the gene expression by LPS. In contrast, GdCl3, an inhibitor of mEH and GST expression, inhibited LPS-induced activation of the p65/p50 NF-kappaB. These gel shift analyses provided evidence that LPS-induced activation of the NF-kappaB was not responsible for alterations in the gene expression. In summary, the results of this research demonstrate that LPS effectively inhibits constitutive and inducible mEH and GST expression with decreases in their mRNA levels, and that LPS suppression in the expression of the detoxifying enzymes is not mediated with its activation of NF-kappaB.
脂多糖（LPS）是一种参与脓毒症休克综合征的内毒素，可增强毒物诱导的肝损伤。本研究在大鼠中探讨了LPS对肝微粒体环氧化物水解酶（mEH）和谷胱甘肽S-转移酶（GST）基因组成型和诱导型表达的影响。Northern印迹分析显示，用LPS处理大鼠会导致mEH和GST基因表达受到抑制。单次静脉注射LPS（1 mg/kg）后，mEH mRNA水平呈时间依赖性下降，在2、6、12和24小时时分别为未处理动物的52%、22%、17%和94%。rGSTA2和rGSTA3 mRNA水平对LPS注射的反应与mEH mRNA相似程度的抑制，而rGSTM1和rGSTM2 mRNA水平受影响较小。LPS在1μg或更高剂量时抑制mEH基因表达。当以50 mg/kg的剂量用二烯丙基二硫化物（ADS）、奥替普拉（OZ）或吡嗪（PZ）处理大鼠时，在12小时时mEH mRNA水平会升高，但同时注射LPS（1 mg/kg）会导致诱导型基因表达受到80%-95%的抑制。LPS处理12小时后，诱导型rGSTA2、rGSTA3、rGSTM1和rGSTM2 mRNA水平也降低了50%-90%，rGSTA的相对变化大于rGSTM。连续三天每天用LPS（10μg/kg/天）处理会导致组成型和PZ（50 mg/kg/天，腹腔注射3天）诱导型mEH和GST mRNA水平显著降低，这与蛋白质水平一致。凝胶迁移阻滞分析显示，LPS在1μg/kg或更高剂量时，在1小时时能显著激活肝细胞核p65/p50核因子-κB（NF-κB）复合物。LPS诱导的核NF-κB激活（1μg/kg，静脉注射）不能被mEH和GST诱导剂同时处理所抑制，包括ADS（300 mg/kg，口服）、OZ（300 mg/kg，口服）和PZ（300 mg/kg，腹腔注射），这表明NF-κB激活不是LPS抑制基因表达所必需的。相反，mEH和GST表达的抑制剂GdCl3抑制了LPS诱导的p65/p50 NF-κB激活。这些凝胶迁移分析提供了证据，表明LPS诱导的NF-κB激活与基因表达改变无关。总之，本研究结果表明，LPS有效抑制组成型和诱导型mEH和GST表达，使其mRNA水平降低，且LPS对解毒酶表达的抑制不是通过激活NF-κB介导的。
