Most
virus infections induce cycloxygenase-2 (COX-2) expression and subsequent
prostaglandin E(2) (
PGE(2)) production in cells, an inflammatory response that might be detrimental to virus replication and pathogenesis. This response in dengue virus
infection remains to be elucidated.
Triptolide and
tetrandrine, compounds derived from two commonly used Chinese herbs, both demonstrate anti-inflammatory and immunosuppressive effects partly through modulation of COX-2 expression and, hence, may have
antiviral effects. In this study, we examined, firstly, the immune response to dengue virus
infection with respect to COX-2 expression and
PGE(2) production in human lung cells (A549), liver cells (HepG2) and dendritic cells. Secondly, we assessed the potential
antiviral effects of
triptolide and
tetrandrine on dengue virus
infection vis-à-vis expression of COX-2,
PGE(2),
transcription factors, as well as virus production. We found that dengue virus
infection enhanced COX-2 expression and
PGE(2) production in A549 cells, similarly to the response in dendritic cells, but not in HepG2 cells. In dengue virus-infected A549 cells,
nuclear factor kappaB (
NF-kappaB) and
activator protein 1 (AP-1) were also activated, and both were dose-dependently inhibited by
triptolide (0.5-4 ng/ml).
Tetrandrine (1-10 microM) had no similar immunosuppressive effects and, moreover, at higher concentrations, enhanced
NF-kappaB and
AP-1 activity, COX-2 expression and
PGE(2) production. However, unexpectedly,
tetrandrine, but not
triptolide, dose-dependently suppressed dengue virus production in A549 cells, independent of
PGE(2) level. Our findings imply that
triptolide and
tetrandrine may attenuate dengue virus
infection in human lung cells, but through distinct pathways.