Lignans from the genus Piper L. and their pharmacological activities: An updated review

Hydroxychavicol derivatives from Piper betle Linn. as natural PDE4 inhibitors with anti-inflammatory effects

PDE4 inhibitors have been developed as anti-inflammatory medications primarily used in the clinical treatment of pulmonary inflammations such as asthma, chronic obstructive pulmonary disease, and idiopathic pulmonary fibrosis. However, the application of these drugs is usually restricted by obvious side effects, such as nausea and vomiting. Our previous study found that several natural PDE4 inhibitors or their modified derivatives showed minimal side effects, particularly reduced incidence of nausea and vomiting, which aroused our interest in searching for natural PDE4 inhibitors. In this study, a chemical investigation of an active fraction of Piper betle L. leaves led to the characterization of 23 hydroxychavicol derivatives, including 18 hydroxychavicol-type lignans. Compounds 1-9 were new lignans, with three of them being racemates that were eventually resolved into isolated (+)- and (-)-enantiomers. Compounds 1-5 and 10, neolignans characterized by a dioxane moiety, were unique to this species within the genus Piper. Compounds 5 and 10 were the sole sesquineolignans found in the genus Piper. Compounds 5, 7-14, 16, 17, and 21 exhibited considerable inhibition towards PDE4 with IC50 values ranging from 1.8 to 10 μM, with hit 7 exhibiting remarkable activity (1.8 μM). Further anti-inflammatory assays revealed that compounds 5, 7, 9, and 16 decreased the expression of several key inflammatory mediators in LPS-stimulated RAW 264.7 cells. Notably, 16 was comparable to the positive control rolipram at the same concentration of 10 μM. A primary study of the mechanism of action revealed that 16 may exert anti-inflammatory effect by inhibiting the NF-κB signaling pathway, displaying significant inhibition of the phosphorylation of IκB-α and p65 at concentrations of 5 and 10 μM. These findings suggest that hydroxychavicol derivatives from P. betle L. leaves may serve as new PDE4 inhibitors, offering promising leads for the development of anti-inflammatory medications.

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.

Undescribed (2-7')-neolignans and polyoxygenated cyclohexene glycosides from the aerial parts of Piper mutabile C. DC. and their inhibitory effects on nitric oxide production

A phytochemical study of the aerial parts of Piper mutabile C. DC. revealed seven undescribed compounds [two (2-7')-neolignans and five polyoxygenated cyclohexene glycosides] and six known propenylcatechol derivatives. The chemical structures of the isolated compounds were elucidated by extensive HR-ESI-MS and NMR analyses, as well as comparison with the literature. The absolute configurations of the (2-7')-neolignans were confirmed by GIAO 13C NMR calculations with a sorted training set strategy and TD-DFT calculation ECD spectra. The (2-7')-neolignans and polyoxygenated cyclohexene glycosides are unusual in natural sources. Undescribed neolignans 1 and 2 inhibited NO production in RAW 264.7 cells, with respective IC50 values of 14.4 and 9.5 μM.

Three new phenylpropanoid glucosides and a new tyramine-type alkamide from Piper puberulum

Three new phenylpropanoid glycosides, piperpubelide (1), 1-propionyl-3-hydroxy-phenyl-4-O-β-D-glucopyranoside (2), and 1-propionyl-4-hydroxy-phenyl-3-O-β-D-glucopyranoside (3), a new tyramine-type alkamide, puberulumine L (4), together with thirteen known compounds (5-17) were isolated from Piper puberulum (Benth.) Maxim. Their structures were elucidated by analysis of spectroscopic data involving NMR, IR, UV, and HRESIMS data. Calculated and experimental ECD was used to confirm the configuration of compound 1. Compounds 14, 16, and 17 exhibited relatively positive DPPH radical scavenging activities, with corresponding EC50 of 10.23, 24.12, and 21.83 μM, respectively. In addition, compound 5 inhibited LPS-induced NO production in BV-2 microglia with an IC50 value of 18.05 μM.

Antiquorum and Antibiofilm Activities of Piper bogotense C. DC. against Pseudomonas aeruginosa and Identification of Bioactive Compounds

The present study describes the anti-biofilm and quorum sensing (QS) inhibitory potential of extracts and chemical constituents from Piper bogotense. Antibiofilm potential was determined through crystal violet assay against Pseudomonas aeruginosa, while QS inhibition efficacy was determined through violacein inhibition assay using Chromobacterium violaceum as a bacterial model. Additionally, this study reports the effects of the chemical constituents isolated in P. bogotense against various virulent factors associated with QS, such as the percentage decrease in pyocyanin, elastase, and protease production. The chemical study led to the isolation and identification of two prenylated benzoic acids (1 and 2) and a prenylated hydroquinone 3, of which compounds 1 and 2 are reported for the first time for P. bogotense. The ethanolic extract and the DCM fraction from P. bogotense stand out for reducing violacein production in C. violaceum, as well as the biofilm formation in P. aeruginosa. Compounds 2 and 3 stand out for having the lowest violacein production (43.8% and 68.3%), as well as the lowest production of virulence factors such as elastase (60.2% and 51.4%) and pyocyanin (39.7% and 33.2%). These results demonstrate the potential of P. bogotense components to be used as an alternative control against multidrug-resistant P. aeruginosa.