The citrus flavanone naringenin inhibits inflammatory signalling in glial cells and protects against neuroinflammatory injury

Neuroinflammation plays an integral role in the progression of neurodegeneration. In this study we investigated the anti-inflammatory effects of different classes of flavonoids (flavanones, flavanols and anthocyanidins) in primary mixed glial cells. We found that the flavanones naringenin and hesperetin and the flavanols (+)-catechin and (−)-epicatechin, but not the anthocyanidins cyanidin and pelargonidin, attenuated LPS/IFN-γ-induced TNF-α production in glial cells. Naringenin also inhibited LPS/IFN-γ-induced iNOS expression and nitric oxide production in glial cells, thus showing the strongest anti-inflammatory activity among all flavonoids tested. Moreover, naringenin protected against inflammatory-induced neuronal death in a primary neuronal–glial co-culture system. Naringenin also inhibited LPS/IFN-γ-induced p38 mitogen-activated protein kinase (MAPK) phosphorylation and downstream signal transducer and activator of transcription-1 (STAT-1) in LPS/IFN-γ stimulated primary mixed glial cells. Taken together, our results suggest that naringenin may produce an anti-inflammatory effect in LPS/IFN-γ stimulated glial cells that may be due to its interaction with p38 signalling cascades and the STAT-1 transcription factor.