title: Potent bacterial neuraminidase inhibitors, anthraquinone glucosides from Polygonum cuspidatum and their inhibitory mechanism.
abstract: BACKGROUND
  P. cuspidatum is a popular Chinese medicinal herb, having a long history of usage in traditional Chinese medicine for the treatment of several inflammatory diseases in the form of powders and decoctions. Similarly there are many reports that P. cuspidatum has antibacterial and anti-inflammatory effects, both of which are properties associated with compounds having activity against bacterial neuraminidase (BNA).
  
  
  OBJECTIVE
  We investigated whether P. cuspidatum's metabolites exhibited BNA inhibition. Consistent with our hypothesis, we found several inhibitors from the methanol extract of this plant, and then fully characterized their inhibitory mechanisms.
  
  
  METHODS
  Activity guided separation of methanol extract led to isolation of individual constituents, and subsequently their structures were elucidated by spectroscopic analysis. Detailed kinetic behaviors of BNA inhibitors were explored by showing the changes of Kmand Vmax, the ratios of KI/KISand Kik/Kiv, and fluorescence quenching effect.
  
  
  CONCLUSIONS
  This study attempted to isolate the responsible metabolites and elucidate the BNA inhibitory mechanism. The principal BNA inhibitory compounds (2-6) were identified as emodin (2), physcion-8-O-β-D-glucopyranoside (3), emodin-8-O-β-D-glucopyranoside (4), emodin-1-O-β-D-glucopyranoside (5), and 2-methoxy-6-acetyl-7-methyljuglone (6). Unexpectedly, anthraquinone glucosides (3-5) were much more potent than their corresponding aglycones (1 and 2). For example, emodin (2) had an IC50=5.4μM, whereas its glucosides (4 and 5) had IC50=0.85μM and 0.43μM respectively. A similar trend was observed with physcion (1, IC50>200μM) and its glucoside (3, IC50=6.2μM). The anthraquinone (2) was mixed type I inhibitor, whereas its glucosides (4 and 5) were noncompetitive. In addition, the fluorescence quenching study showed that the affinity constants (KSV) of inhibitors increased in proportion to their inhibitory potencies. Furthermore, we quantified the major and minor metabolites through UPLC-PDA-Q-TOF/MS, and revealed that the most potent inhibitors were the major constituents. This result contributes to our understanding of P. cuspidatum utility as functional food stuff and widely used herbal medicine.
authors.affiliation: Division of Applied Life Science (BK21 plus), IALS, Gyeongsang National University, Jinju 660-701, Republic of Korea. Electronic address: ziauddinrph@gmail.com.
authors.forename: Zia
authors.initials: Z
authors.lastname: Uddin
authors.affiliation: Division of Applied Life Science (BK21 plus), IALS, Gyeongsang National University, Jinju 660-701, Republic of Korea. Electronic address: yh0126@hanmail.net.
authors.forename: Yeong Hun
authors.initials: YH
authors.lastname: Song
authors.affiliation: Department of Chemistry and Chemical Biology, Cornell University, Ithaca, NY 14853, United States. Electronic address: mjl253@cornell.edu.
authors.forename: Marcus J
authors.initials: MJ
authors.lastname: Curtis-Long
authors.affiliation: Division of Applied Life Science (BK21 plus), IALS, Gyeongsang National University, Jinju 660-701, Republic of Korea. Electronic address: yoon24@gnu.ac.kr.
authors.forename: Jeong Yoon
authors.initials: JY
authors.lastname: Kim
authors.affiliation: Division of Applied Life Science (BK21 plus), IALS, Gyeongsang National University, Jinju 660-701, Republic of Korea. Electronic address: cupid6@gnu.ac.kr.
authors.forename: Heung Joo
authors.initials: HJ
authors.lastname: Yuk
authors.affiliation: Division of Applied Life Science (BK21 plus), IALS, Gyeongsang National University, Jinju 660-701, Republic of Korea. Electronic address: khpark@gnu.ac.kr.
authors.forename: Ki Hun
authors.initials: KH
authors.lastname: Park
mesh_terms: D001419:Bacteria / Q000737:chemistry*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D045468:Fallopia japonica / Q000737:chemistry*; D005960:Glucosides / Q000737:chemistry*; D007700:Kinetics; D009439:Neuraminidase / Q000008:administration & dosage*; D011809:Quinones / Q000737:chemistry / Q000494:pharmacology*; D013050:Spectrometry, Fluorescence
chemical_list: D004791:Enzyme Inhibitors; D005960:Glucosides; D011809:Quinones; D009439:Neuraminidase
keywords: Anthraquinone glucosides; Bacterial neuraminidase; Inhibitory mechanism; Polygonum cuspidatum