(+)‑pinoresinol‑O‑β‑D‑glucopyranoside from Eucommia ulmoides Oliver and its anti‑inflammatory and antiviral effects against influenza A (H1N1) virus infection

Functional Characterization of UDP-Glycosyltransferases Involved in Anti-viral Lignan Glycosides Biosynthesis in Isatis indigotica

Isatis indigotica is a popular herbal medicine with its noticeable antiviral properties, which are primarily due to its lignan glycosides such as lariciresinol-4-O-β-D-glucoside and lariciresinol-4,4'-bis-O-β-D-glucosides (also called clemastanin B). UDP-glucose-dependent glycosyltransferases are the key enzymes involved in the biosynthesis of these antiviral metabolites. In this study, we systematically characterized the UGT72 family gene IiUGT1 and two UGT71B family genes, IiUGT4 and IiUGT71B5a, with similar enzymatic functions. Kinetic analysis showed that IiUGT4 was more efficient than IiUGT1 or IiUGT71B5a for the glycosylation of lariciresinol. Further knock-down and overexpression of these IiUGTs in I. indigotica's hairy roots indicates that they play different roles in planta: IiUGT71B5a primarily participates in the biosynthesis of coniferin not pinoresinol diglucoside, and IiUGT1 primarily participates in the biosynthesis of pinoresinol diglucoside, while IiUGT4 is responsible for the glycosylation of lariciresinol and plays a dominant role in the biosynthesis of lariciresinol glycosides in I. indigotica. Analysis of the molecular docking and site-mutagenesis of IiUGT4 have found that key residues for its catalytic activity are H373, W376, E397, and that F151 could be associated with substrate preference. This study elucidates the biosynthetic route of anti-viral lignan glycosides in I. indigotica, and provides the foundation for the production of anti-viral lignan glycosides via synthetic biology under the heterologous model.

Tandem UGT71B5s Catalyze Lignan Glycosylation in Isatis indigotica With Substrates Promiscuity

Lignans are a class of chemicals formed by the combination of two molecules of phenylpropanoids with promising nutritional and pharmacological activities. Lignans glucosides, which are converted from aglycones catalyzed by uridine diphosphate (UDP) glycosyltransferases (UGTs), have abundant bioactivities. In the present study, two UGTs from Isatis indigotica Fort., namely IiUGT71B5a and IiUGT71B5b, were characterized to catalyze the glycosylation of lignans with promiscuities toward various sugar acceptors and sugar donors, and pinoresinol was the preferred substrate. IiUGT71B5a was capable of efficiently producing both pinoresinol monoglycoside and diglycoside. However, IiUGT71B5b only produced monoglycoside, and exhibited considerably lower activity than IiUGT71B5a. Substrate screening indicated that ditetrahydrofuran is the essential structural characteristic for sugar acceptors. The transcription of IiUGT71B5s was highly consistent with the spatial distribution of pinoresinol glucosides, suggesting that IiUGT71B5s may play biological roles in the modification of pinoresinol in I. indigotica roots. This study not only provides insights into lignan biosynthesis, but also elucidates the functional diversity of the UGT family.

A Potent Lignan from Prunes Alleviates Inflammation and Oxidative Stress in Lithium/Pilocarpine-Induced Epileptic Seizures in Rats

Prunus domestica L. is an edible plant that is included in the family Rosaceae and proven to possess potent anti-inflammatory and anxiolytic activity. Pinoresinol-4-O-β-d-glucopyranoside (PGu) was isolated from Prunus domestica methanol extract and its structure was determined using 1-D and 2-D NMR (one- and two-dimensional nuclear magnetic resonance). PGu was evaluated for its anticonvulsant activity using lithium/pilocarpine-induced epileptic seizures in rats. PGu displayed a notable antioxidant and anti-inflammatory activity in vitro. It ameliorates the seizures triggered by pilocarpine in a dose-dependent manner, manifested by retarding seizure onset, reducing the number of rats developing seizures, and enhancing the survival of animals after seizure exposure. PGu reduced MDA (malondialdehyde) level by 24.2% in addition to increasing catalase activity by 44.4% at 50 mg/kg b.w compared to pilocarpine-treated animals. This was confirmed by histopathological examination in which pretreatment with PGu (50 mg/kg b.w.) attenuated neurodegeneration and seizures with no histopathological alteration in neurons of the cerebral cortex. In the immunohistochemical examination, it significantly declined the elevated Cyclooxygenase-2 (COX-2) by 40% and decreased Inducible nitric oxide synthase (iNOS) expression by 18% as expressed by the optical density. PGu revealed a pronounced fitting within the active site of 5-LOX (lipoxygenase-5) with a free binding energy (∆G) equals to −65.05 kcal/mol. PGu could perfectly serve as a potent lead drug for the relief of epileptic seizures, which appeals to many patients owing to its natural origin.

Sinensetin suppresses influenza a virus-triggered inflammation through inhibition of NF-κB and MAPKs signalings

Background

Human respiratory system infected with influenza A virus (IAV) elicited a robust pro-inflammatory response that resulted in severe illness and even death. Currently, limited immunomodulator is available to counteract IAV-associated pneumonia in the clinic. Sinensetin, a polymethoxylated flavone with five methoxy groups, has been found to possess anti-agiogenesis, anti-inflammatory and anti-diabetic activities. However, the effects of sinensetin on IAV-triggered pro-inflammatory response remain unclear. In the present study, the anti-inflammatory effects and corresponding possible mechanism of sinensetin in IAV-infected A549 cells were subjected to investigations.

Methods

The cytotoxic effects of sinensetin towards A549 cells was detected by MTT and LDH assays. The antiviral activity of sinensetin against influenza A virus was assayed in A549 cells with an engineered replication-competent influenza A virus carrying Gaussia luciferase reporter gene infection. The effect of sinensetin on influenza A virus-triggered inflammatory reaction was determined by qRT-PCR, Luminex assays, ELISA and Western blot.

Results

Our results showed that sinensetin did not exhibit antiviral activity against A/PR/8/34 (H1N1). Meanwhile, sinensetin treatment significantly decreased IAV-induced expression of pro-inflammatory mediators at mRNA and protein levels, including IL-6, TNF-α, IP-10, IL-8 and MCP-1. Additionally, levels of cyclooxygenase (COX)-2 and the downstream product prostaglandin E₂ (PGE₂) up-regulated by IAV infection were dramatically suppressed by sinensetin. The mechanistic investigation revealed that sinensetin treatment suppressed the NF-κB transcriptional activity using the NF-κB reporter stable HEK293 cell line stimulated with TNF-α (20 ng/mL) or influenza H1N1 virus. Furthermore, sinensetin abrogated influenza H1N1 virus-induced activation of NF-κB, ERK1/2 MAPK and p38 MAPK signalings.

Conclusion

Collectively, our results indicated that sinensetin has potential capacity to attenuate IAV-triggered pro-inflammatory response via inactivation of NF-κB, ERK1/2 MAPK and p38 MAPK signalings, which implied that sinensetin may be a promising candidate drug for influenza H1N1 virus infection therapeutics.