Inhibitory effect of naringin on lipopolysaccharide (LPS)-induced endotoxin shock in mice and nitric oxide production in RAW 264.7 macrophages

Lipopolysaccharide (LPS) has been known to induce endotoxin shock via production of inflammatory modulators such as tumor necrosis factor alpha (TNF-α), or nitric oxide (NO). In this study, we have examined the effect of naringin (NG), one of the flavonoids, on LPS-induced endotoxin shock in mice and NO production in RAW 264.7 macrophages. For intraperitoneal (i.p., 20 mg/kg) injection of LPS at 48 h, the survival rate of mice administered with LPS alone (n = 10) or pretreated with NG at 10, 30 and 60 mg/kg (i.p.) group (n = 10) was 0% or 10%, 50% and 70%, respectively. NG dose-dependently suppressed LPS-induced production of TNF-α. LPS-induced production of NO at 6 h (125.89 ± 16.35 μM), as measured by nitrite formation, was significantly reduced by NG at 30 or 60 mg/kg for 49.49 ± 4.81 or 27.91 ± 1.81 μM (P < 0.01 vs. LPS alone), respectively. To further examine the mechanism by which NG suppresses LPS-induced endotoxin shock, we used an in vitro model, RAW 264.7 mouse macrophage cells. NG (1 mM) suppressed LPS (0.01, 0.1 or 1 μg/ml)-induced production of NO and the expression of inflammatory gene products such as inducible NO synthase (iNOS), TNF-α, inducible cyclooxygenase (COX-2) and interleukin-6 (IL-6) as determined by RT-PCR assay. NG was found to have blocked the LPS-induced transcriptional activity of NF-κB in electrophoretic mobility shift assay and reporter assay. These findings suggest that suppression of the LPS-induced mortality and production of NO by NG is due to inhibition of the activation of NF-κB.