Naringenin more effectively inhibits inducible nitric oxide synthase and cyclooxygenase-2 expression in macrophages than in microglia.

Macrophages and microglia are thought to account for initial disease progression in acute myocardial infarction and acute ischemic stroke. Before our study, the inhibitory effects of naringenin, a flavonoid, on lipopolysaccharide (LPS)-induced inflammation in macrophages and microglia have not been fully reported and compared. We hypothesized that naringenin can effectively inhibit LPS-induced inflammation of macrophages and microglia at different concentrations, the range of which is broader, with the lowest concentration more easily achieved in macrophages. In this study, we compared the anti-inflammatory effects of naringenin on LPS-stimulated RAW 274.6 macrophages and BV2 microglia and the suppression effects of naringenin and vitamin C (a well-known anti-inflammatory agent) on LPS-induced nitrite production. The results show that macrophages could maintain cell viability at higher naringenin concentrations and were more easily activated by LPS in comparison to microglia (200 vs 100 μmol/L; 0.1 vs 1 μg/mL). Under LPS (1 μg/mL) stimulation in both cell types, naringenin (up to 200 μmol/L in macrophages and 100 μmol/L in microglia) inhibited nitrite production and inducible nitric oxide synthase and cyclooxygenase-2 expression in a dose-dependent manner. The range of naringenin concentrations for inhibition was broader, and the lowest concentration was more easily achieved in macrophages; the lowest effective concentrations of naringenin to achieve constant suppression effect were 50 μmol/L in macrophages and 100 μmol/L in microglia, respectively. Vitamin C (100 μmol/L), compared with naringenin (100 μmol/L), had less and no suppression effect on LPS (1 μg/mL)-induced nitrite production in macrophages and microglia, respectively. In conclusion, naringenin more effectively inhibits the LPS-induced inflammatory status, including nitrite production and inducible nitric oxide synthase and cyclooxygenase-2 expression, in macrophages than in microglia. The findings of the present study suggest that consumption of naringenin-containing flavonoids might be beneficial to the cardiovascular and cerebrovascular inflammatory process.