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.