Piperlongumine Improves Lipopolysaccharide-Induced Amyloidogenesis by Suppressing NF-KappaB Pathway

Amyloidogenesis is known to cause Alzheimer's disease. Our previous studies have found that lipopolysaccharide (LPS) causes neuroinflammation and amyloidogenesis through activation of nuclear factor kappaB (NF-κB). Piperlongumine (PL) is an alkaloid amide found naturally in long pepper (Piper longum) isolates; it was reported to have inhibitory effects on NF-κB activity. We therefore investigated whether PL exhibits anti-inflammatory and anti-amyloidogenic effects by inhibiting NF-κB. A murine model of LPS-induced memory impairment was made via the intraperitoneal (i.p.) injection of LPS (0.25 mg/kg/day, i.p.). We then injected PL (1.5 or 3.0 mg/kg/day, i.p.) for 7 days in three groups of mice to observe effects on memory. We also conducted an in vitro study with astrocytes and microglial BV-2 cells, which were treated with LPS (1 µg/mL) or PL (0.5 or 1.0 or 2.5 µM). Results from our behavioral tests showed that PL inhibited LPS-induced memory. PL also prevented LPS-induced beta-amyloid (Aβ) accumulation and inhibited the activities of β- and γ-secretases. The expression of inflammatory proteins also was decreased in PL-treated mice, cultured BV-2, and primary astrocyte cells. These effects were associated with the inhibition of NF-κB activity. A docking model analysis and pull-down assay showed that PL binds to p50. Taken together, our findings suggest that PL diminishes LPS-induced amyloidogenesis and neuroinflammation by inhibiting NF-κB signaling; PL therefore demonstrates potential for the treatment of Alzheimer's disease.