Gypenosides derived from Gynostemma pentaphyllum suppress NO synthesis in murine macrophages by inhibiting iNOS enzymatic activity and attenuating NF-kappaB-mediated iNOS protein expression.
Gypenosides isolated from Gynostemma pentaphyllum are widely used in traditional Chinese medicine, with beneficial effects reported in numerous diseases, including inflammation and atherosclerosis, although the mechanism underlying these therapeutic effects is unknown. Because increased nitric oxide (NO) plays a role in these pathological conditions, we investigated whether the pharmacological activity of gypenosides is due to suppression of NO synthesis. The markedly increased production of nitrite by stimulation of RAW 264.7 murine macrophages with 1 microg/mL lipopolysaccharide (LPS) for 20 h (unstimulated: 0.3+/-0.3 microM vs. LPS: 32.5+/-1.2 microM) was dose-dependently inhibited by gypenosides (0.1-100 microg/mL). When cells were pretreated with gypenosides (for 1h) prior to LPS stimulation, subsequent NO production was significantly attenuated (IC(50) of 3.1+/-0.4 microg/mL) (P<0.05). Gypenosides (25 microg/mL) produced the same maximum inhibition of LPS-induced NO production as aminoguanidine, a standard inhibitor of NOS enzymes. Suppression of NO production occurred both by direct inhibition of the activity and expression of iNOS. Inhibition of iNOS protein expression appears to be at the transcriptional level, since gypenosides decreased LPS-induced NF-kappaB activity in a dose-dependent manner (P<0.05), with significant inhibition achieved following pretreatment with 10 microg/mL gypenoside. Taken together, these results suggest that gypenosides derived from G. pentaphyllum suppress NO synthesis in murine macrophages by inhibiting iNOS enzymatic activity and attenuating NF-kappaB-mediated iNOS protein expression, thereby implicating a mechanism by which gypenosides may exert their therapeutic effects.
Aktan
Fugen
F
Faculty of Pharmacy, University of Sydney, Building A15, Room S222, Sydney NSW 2006, Australia.
Henness
Sheridan
S
Roufogalis
Basil D
BD
Ammit
Alaina J
AJ
D000818:Animals; D002460:Cell Line; D002470:Cell Survival; D004305:Dose-Response Relationship, Drug; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006146:Guanidines / Q000494:pharmacology; D029774:Gynostemma / Q000737:chemistry*; D008070:Lipopolysaccharides / Q000494:pharmacology; D008264:Macrophages / Q000187:drug effects* / Q000201:enzymology / Q000378:metabolism; D051379:Mice; D016328:NF-kappa B / Q000187:drug effects / Q000378:metabolism*; D009569:Nitric Oxide / Q000096:biosynthesis*; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors* / Q000378:metabolism; D009573:Nitrites / Q000037:antagonists & inhibitors / Q000737:chemistry; D010936:Plant Extracts / Q000494:pharmacology*
D004791:Enzyme Inhibitors; D006146:Guanidines; D008070:Lipopolysaccharides; D016328:NF-kappa B; D009573:Nitrites; D010936:Plant Extracts; C474918:gypenoside; D009569:Nitric Oxide; D019001:Nitric Oxide Synthase; C004479:pimagedine