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Thaliporphine selectively inhibits expression of the inducible, but not the constitutive, nitric oxide synthase.

ABSTRACT: Formation of nitrites/nitrates caused by lipopolysaccharide (LPS) in J774.2 macrophages was inhibited by thaliporphine, an aporphine derivative isolated from the plant Neolitsea konishii K. This inhibition of nitrite synthesis in LPS-stimulated macrophages by thaliporphine was similar to that by cycloheximide, NG-methyl-L-arginine (MeArg) and dexamethasone. Thaliporphine, but not MeArg, inhibited expression of inducible NO synthase without directly affecting enzyme activity. However, thaliporphine did not inhibit nitrite production by NO synthase that had already been induced by prior exposure to LPS for which any possible further induction was inhibited by cycloheximide. In endothelial cells, nitrite formation induced by bradykinin (in the presence of 0.2 mM Ca2+) was inhibited by MeArg. However, incubation of endothelial cells with dexamethasone, cycloheximide and thaliporphine did not affect this Ca(2+)-dependent nitrite production. Thaliporphine (0.1-100 microM) dose-dependently inhibited nitrite accumulation in macrophages stimulated by interleukin-1 beta (IL-1 beta) whereas nitrite formation induced by tumour necrosis factor alpha was not inhibited. LPS-stimulated IL-1 beta synthesis in macrophages was significantly inhibited by thaliporphine, but thaliporphine had only minimal effect on LPS-stimulated IL-1 beta synthesis in endothelial cells. These results demonstrate that thaliporphine inhibits LPS induction of NO synthase expression, and that the mechanism of action of thaliporphine is via inhibition of LPS-stimulated IL-1 beta synthesis in macrophages. In anaesthetized rats subjected to LPS, pretreatment with thaliporphine partially restored the fall in mean arterial pressure and the vascular hyporeactivity to noradrenaline 3 h after LPS injection. In conclusion, thaliporphine selectively inhibited expression of inducible NO synthase, and may thus hold potential for the treatment of endotoxaemia.

SUBMITTER: Yu SM

PROVIDER: S-EPMC1137589 | biostudies-other | 1994 Oct

REPOSITORIES: biostudies-other

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Project description:Inducible nitric oxide synthase (iNOS) activity increases in acute and chronic inflammatory lung diseases. Imaging iNOS expression may be useful as an inflammation biomarker for monitoring lung disease activity. We developed a novel tracer for PET that binds to iNOS in vivo, (18)F-NOS. In this study, we tested whether (18)F-NOS could quantify iNOS expression from endotoxin-induced lung inflammation in healthy volunteers.Healthy volunteers were screened to exclude cardiopulmonary disease. Qualifying volunteers underwent a baseline, 1-h dynamic (18)F-NOS PET/CT scan. Endotoxin (4 ng/kg) was then instilled bronchoscopically in the right middle lobe. (18)F-NOS imaging was performed again approximately 16 h after endotoxin instillation. Radiolabeled metabolites were determined from blood samples. Cells recovered by bronchoalveolar lavage (BAL) after imaging were stained immunohistochemically for iNOS. (18)F-NOS uptake was quantified as the distribution volume ratio (DVR) determined by Logan plot graphical analysis in volumes of interest placed over the area of endotoxin instillation and in an equivalent lung region on the left. The mean Hounsfield units (HUs) were also computed using the same volumes of interest to measure density changes.Seven healthy volunteers with normal pulmonary function completed the study with evaluable data. The DVR increased by approximately 30%, from a baseline mean of 0.42 ± 0.07 to 0.54 ± 0.12, and the mean HUs by 11% after endotoxin in 6 volunteers who had positive iNOS staining in BAL cells. The DVR did not change in the left lung after endotoxin. In 1 volunteer with low-level iNOS staining in BAL cells, the mean HUs increased by 7% without an increase in DVR. Metabolism was rapid, with approximately 50% of the parent compound at 5 min and 17% at 60 min after injection.(18)F-NOS can be used to image iNOS activity in acute lung inflammation in humans and may be a useful PET tracer for imaging iNOS expression in inflammatory lung disease.

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Thaliporphine selectively inhibits expression of the inducible, but not the constitutive, nitric oxide synthase.

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