Excretory/Secretory products of plerocercoids of Spirometra erinaceieuropaei induce the expression of inducible nitric oxide synthase mRNA in murine hepatocytes

In this study, we observed the level of normal murine hepatocyte inducible NOS (iNOS) mRNA by semi-quantitative polymerase chain reaction (SQ-PCR) analysis after stimulation with ES products (ESP) and/or ESP fractions from the plerocercoids. We found that ESP are able to induce the expression of iNOS gene in a dose-dependent fashion. Treatment of ESP with polymyxin B did not affect their ability to induce the expression of iNOS gene, suggesting that bacterial lipopolysaccharide (LPS) is not involved. The iNOS-inducing factor (s) is soluble, and may be a component whose molecular mass exceeds 94kDa as analyzed by a combination of SDS-PAGE and SQ-PCR. The peak of iNOS mRNA level was detected 3 h after stimulation with ESP; the mRNA level decreased sharply from 9 h. Dexamethasone inhibited the induction of mRNA for hepatocyte iNOS. In contrast, cycloheximide stimulated the induction; this suggests that de novo protein synthesis is important in the regulation of the ESP-induced expression of iNOS mRNA. Actinomycin D blocked the induction. In addition, the results of Northern blot analysis showed that ESP suppressed the LPS (10 mu g/ml) and interferon-gamma (IFN-y, 100 U/ml)-induced hepatocyte iNOS mRNA expression in a dose-dependent fashion and the suppressing effect was more marked when hepatocytes were exposed to ESP 3 h prior to LPS and IFN-y. These results demonstrate that the soluble factor (s) of ESP is capable of inducing murine iNOS gene expression in hepatocytes in the absence of added cytokines. (C) 1997 Australian Society for Parasitology. Published by Elsevier Science Ltd.