Novel effect of methionine enkephalin against influenza A virus infection through inhibiting TLR7-MyD88-TRAF6-NF-kappa B p65 signaling pathway

The morbidity and mortality associated with influenza A virus infections, have stimulated the search for novel prophylactic and therapeutic drugs. The purpose of this study was to investigate the prophylactic and therapeutic effect of synthetic methionine enkephalin (MENK) on mice infected by A/PR/8/34 influenza virus (H1N1) in vivo. The results showed that MENK could exert both prophylactic and therapeutic influences on infected mice, significantly improve the survival rate, relieve acute lung injury and decrease cytokine (IFN-alpha, IFN-beta, TNF-alpha, IL-6, and IL-1 beta) levels. MENK also inhibited virus replication on day 4 post infection (p.i.) through upregulating opioid receptors (MOR, DOR) and suppressing TLR7-MyD88-TRAF6-NF-kappa B p65 signaling pathways. These results suggest that MENK, given via intranasal administration, could provide a novel drug with a new mode of action as a nonspecific anti-influenza agent or vaccine adjuvant.