Flavonoid fraction of guava leaf extract attenuates lipopolysaccharide-induced inflammatory response via blocking of NF-κB signalling pathway in Labeo rohita macrophages

• FGLE inhibited LPS-induced nitric oxide (NO) and prostaglandin E2 (PGE2) production.
• It also effectively inhibited TNF-α, IL-1β, IL-10, iNOS, and COX-2 production in a concentration-dependent manner.
• FGLE suppresses the phosphorylation of MAPK molecules and LPS-induced NF-κB transcriptional activity.

Psidium guajava L. is a well-known traditional medicinal plant widely used in folk medicine. To explore the anti-inflammatory activity of the flavonoid fraction of guava leaf extract (FGLE), we investigated its ability to suppress the levels of inflammatory mediators elevated by lipopolysaccharide (LPS) in Labeo rohita head-kidney (HK) macrophages. HK macrophages of L. rohita were treated with LPS in the presence or absence of the FGLE. We examined the inhibitory effect of FGLE on LPS-induced nitric oxide (NO) and prostaglandin E2 (PGE2) production. The inhibitory effect of FGLE on nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) were investigated by RT-PCR and western blot. The effect of FGLE on proinflammatory cytokines tumour necrosis factor alpha (TNF-α) or interleukin-1β (IL-1β) was also investigated by ELISA and RT-PCR. The phosphorylation of three mitogen activated protein kinases (MAPK) molecules ERK, JNK and p38 was analysed by western blot analysis. FGLE inhibited LPS-induced NO and PGE2 production. It also effectively inhibited TNF-α, IL-1β, IL-10, iNOS, and COX-2 production in a concentration-dependent manner. In addition, FGLE suppressed the mRNA expression levels of TNF-α and IL-1β in LPS-stimulated HK macrophages. RT-PCR and western blot analysis showed that FGLE decreased both the mRNA and protein expression levels of LPS-induced iNOS and COX-2 in HK macrophages. FGLE suppresses the phosphorylation of MAPK molecules in LPS-stimulated HK macrophages. FGLE also significantly inhibited LPS-induced NF-κB transcriptional activity. The molecular mechanism by which FGLE suppresses the expression of inflammatory mediators appears to involve the inhibition of NF-κB activation, through the suppression of LPS-induced IκB-α degradation. Together these results suggest that FGLE contains potential therapeutic agent(s), which regulate NF-κB activation, for the treatment of inflammatory conditions in L. rohita macrophages.