Anti-Parkinson's disease polysaccharide PFP50-1 attenuated neuroinflammation via inhibition of TLR4/NF-κB and PI3K/Akt pathways and suppression of NLRP3 inflammasome activation.

Our previous investigations have revealed that Perilla frutescens-derived polysaccharide PFP50-1 exhibited significant neuroprotective activity by attenuating lipopolysaccharide (LPS)-induced neuroinflammatory responses in microglia. Nonetheless, the protection and mechanisms of its anti-neuroinflammatory activities are still poorly understood. The neuroprotection effects of PFP50-1's underlying mechanisms were evaluated in MPTP-stimulated Parkinson's disease (PD) mice and LPS-induced microglia, respectively. In vitro, PFP50-1 effectively suppressed the excessive release of pro-inflammatory cytokines. Meanwhile, PFP50-1 significantly downregulated the levels of Toll-like receptor 4 (TLR4), myeloid differentiation primary response protein gene 88 (MyD88), nuclear factor kappa-B (NF-κB), p-PI3K (phosphorylated phosphatidylinositol 3-Kinase), and p-Akt (phosphorylated Protein Kinase B). Subsequently, investigations revealed that TLR4 inhibitor (TAK242) and PI3K inhibitor (LY294002) significantly potentiated PFP50-1's inhibitory effects on LPS-induced pro-inflammatory mediators. Moreover, the excessive releases of Caspase-1, IL-18, and IL-1β were reversed by suppressing NLRP3 inflammasome activation. In conditioned medium-stimulated N2a cells, PFP50-1 exhibited a strong neuroprotective effect against neuroinflammation-mediated neurotoxicity by preventing MMP depolarization and ROS production. Notably, PFP50-1 effectively ameliorated MPTP-induced dopaminergic (DA) neuronal degeneration in vivo, which was associated with the downregulation of the TLR4-mediated and PI3K-mediated signaling pathways, as well as the NLRP3 inflammasome. Collectively, our data indicated that PFP50-1's anti-neuroinflammation effect is related to downregulating the TLR4/NF-κB and PI3K/Akt signaling pathways and suppressing NLRP3 inflammasome activation, making it a promising candidate for PD.