The plant flavonoid wogonin suppresses death of activated C6 rat glial cells by inhibiting nitric oxide production

Flavonoids are a group of low molecular weight polyphenolic compounds derived from plants. 5,7-dihydroxy-8-methoxyflavone (Wogonin), a flavonoid originated from the root of Scutellaria baicalensis Georgi, has been shown to exert various anti-inflammatory effects such as inhibition of nitric oxide (NO) and prostaglandin E₂ production in macrophages. Because glial cells have been previously shown to undergo NO-dependent apoptosis upon inflammatory activation and this auto-regulatory process may be negatively affected by exogenous factors possessing anti-inflammatory activities, we examined the effects of wogonin on NO production and activation-induced cell death of C6 rat glial cells. Activation of C6 glial cells with lipopolysaccharide (LPS), interferon-γ, and tumor necrosis factor-α induced NO production followed by cell death. Pretreatment of C6 cells with wogonin before LPS and cytokine treatment dose-dependently inhibited NO production as well as death of activated C6 cells. Wogonin-mediated inhibition of NO production was accompanied by suppression of inducible nitric oxide synthase (iNOS) protein induction and nuclear factor kappa B (NF-κB) reporter activity. Wogonin, however, did not affect a NO donor-induced cytotoxicity. Taken together, our results indicate that wogonin inhibits activation-induced death of C6 glial cells by suppressing NO production, and these inhibitory effects of wogonin on NO production are exerted through inhibition of NF-κB-mediated iNOS induction.