A neolignan enantiomer from Piper hancei with anti-neuroinflammatory effect by attenuating NF-κB signaling pathway

Background

In the traditional “Yao” ethno-medicine system, Piper hancei Maxim. is used to treat rheumatism, wind-cold, and inflammation. Previous studies indicate that lignans obtained from P. hancei stems have anti-neuroinflammatory potential in LPS-stimulated microglial cells. However, identification of the lignan enantiomers and the precise mechanism by which they work to reduce inflammation is yet to be explored.

Purpose

To identify the active anti-neuroinflammatory lignan enantiomers isolated from P. hancei stems and to elucidate the mechanism of action both in vitro and in vivo.

Methods

The lignan enantiomers from P. hancei stems were isolated and elucidated using various chromatographic and spectroscopic methods. The anti-neuroinflammatory potential of all the compounds was initially screened by measuring nitric oxide (NO) inhibition in LPS-stimulated BV-2 microglial cells. Then anti-neuroinflammatory efficacy of the most active compound was assessed with LPS-stimulated microglial cell model, microglia-induced neuronal injury SH-SY5Y cell model, and LPS-intracerebroventricular injection neuroinflammation mouse model. The underlying mechanism was further explored by qRT-PCR analysis, Western blot analysis, and immunofluorescence staining experiments to understand the intervention pathway.

Results

Phytochemical analysis of P. hancei stems resulted in the isolation of 13 pairs of neolignan enantiomers (1–13), including 4 new pairs named piperhancin D–G (1–4). All right-handed (+) and left-handed (–) enantiomers of each pair (1–13) were isolated successfully. Notably, (+)-futoquinol (5) demonstrated significant anti-neuroinflammatory activity without cytotoxicity, unlike its inactive enantiomer (–)-5 in LPS-stimulated microglial cells. The representative compound (+)-5 effectively suppressed pro-inflammatory cytokines in LPS stimulated BV-2 cells and mouse brains, and alleviated microglia-induced neuronal damage in SH-SY5Y cells. Behavioral tests showed that (+)-5 alleviated the LPS-induced cognitive dysfunction in mice. Furthermore, the compound was able to reduce LPS-induced neuronal damage and microglial activation in mouse brains. A mechanistic study demonstrated that (+)-5 hindered the nuclear translocation of NF-κB p65 and downregulated the pro-inflammatory mediators to relieve neuroinflammation.

Conclusion

This is the first example of both in vitro and in vivo study on the anti-neuroinflammatory effects and underlying mechanism of the neolignan enantiomers isolated from P. hancei. Notably, (+)-futoquinol (5) emerged as a potential lead for further drug development to treat neurodegenerative diseases.