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.