Pomegranate polyphenol punicalin ameliorates lipopolysaccharide-induced memory impairment, behavioral disorders, oxidative stress, and neuroinflammation via inhibition of TLR4-NF-кB pathway.

Abstract

Neuroinflammation may play an important role in the development of Alzheimer's disease (AD). Previous studies have reported that lipopolysaccharide (LPS)-induced neuroinflammation causes memory impairments and behavioral disorders. We investigated the potential preventive effects of punicalin (PUN), a polyphenolic component of pomegranate, on LPS-induced memory deficiency and anxiety- and depression-like behaviors, along with the underlying mechanisms. LPS-treated cultured microglial BV2 cells and BV2 cell/Neuro-2a (N2a) cell coculture system were investigated for anti-neuroinflammatory effects of PUN in vitro. The in vivo experiments involved mice administered a 4-week course of oral gavage with 1500 mg/kg/d PUN before intraperitoneal LPS (250 mg/kg daily 7 times) injections. The in vitro results demonstrated that PUN inhibited the LPS-induced inflammatory cytokine (IL-18, IL-1β, TNF-ɑ, and IL-6) production in BV2 cells and protected N2a cells from synaptic damage mediated by BV2 microglia-induced neuroinflammation. In in vivo studies, it was observed that PUN improved memory impairment and anxiety- and depression-like behaviors caused by LPS and reduced the expression of inflammatory proteins such as iNOS, COX-2, IL-1β, IL-2, IL-6, and TNF-α. Furthermore, PUN inhibited the LPS-induced production of MDA; increased the activities of CAT, SOD, and GSH-Px, and inhibited LPS-induced Aβ1-42 generation through down-regulation of APP and BACE1 expression. Moreover, PUN also suppressed the expression of TLR4, IRAK4, TRAF6, IKK-β, NF-κB, p65, and HMGB1 in LPS-treated mouse brain and cultured microglial BV-2 cells. These results suggest that PUN inhibits LPS-induced memory impairment via anti-inflammatory and anti-amylogenic mechanisms through inhibition of TLR4-NF-kB activation.