Action mechanism of 6, 6′-dihydroxythiobinupharidine from Nuphar japonicum, which showed anti-MRSA and anti-VRE activities

• Published in: Biochimica et biophysica acta Vol. 1850; no. 6; pp. 1245 - 1252
• Main Authors: Okamura, Shinya, Nishiyama, Eri, Yamazaki, Tomohiro, Otsuka, Nao, Taniguchi, Shoko, Ogawa, Wakano, Hatano, Tsutomu, Tsuchiya, Tomofusa, Kuroda, Teruo
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01-06-2015
• Subjects: Alkaloids - chemistry; Alkaloids - isolation & purification; Alkaloids - pharmacology; Anti-Bacterial Agents - chemistry; Anti-Bacterial Agents - isolation & purification; Anti-Bacterial Agents - pharmacology; DNA topoisomerase IV; DNA Topoisomerase IV - antagonists & inhibitors; DNA Topoisomerase IV - metabolism; Dose-Response Relationship, Drug; Drug Resistance, Multiple, Bacterial; Enterococcus - drug effects; Enterococcus - enzymology; Methicillin-Resistant Staphylococcus aureus - drug effects; Methicillin-Resistant Staphylococcus aureus - enzymology; Methicillin-Resistant Staphylococcus aureus - genetics; Microbial Sensitivity Tests; Molecular Structure; MRSA; Nuphar - chemistry; Nuphar japonicum; Phytotherapy; Plant Extracts - chemistry; Plant Extracts - isolation & purification; Plant Extracts - pharmacology; Plants, Medicinal; Rhizome; Time Factors; Topoisomerase II Inhibitors - pharmacology; Vancomycin Resistance; VRE; VCM; O.D; MIC; Nuphar japonicum; VRE; DNA topoisomerase IV; NOR; CFU; MeOH; MRSA; DTBN; Et2NH; AcOEt
• ISSN: 0304-4165; 0006-3002; 1872-8006
• DOI: 10.1016/j.bbagen.2015.02.012

Multidrug-resistant bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA) and vancomycin resistant enterococci (VRE), cause serious infections at clinical sites, for which the development of new drugs is necessary. We screened candidates for new antibiotics and investigated its action mechanism.
An antimicrobial compound was isolated from an extract of Nuphar japonicum. Its chemical structure was determined by NMR, MS, and optical rotation. We measured its minimum inhibitory concentration (MIC) using the microdilution method. The effects of the compound on DNA gyrase and DNA topoisomerase IV were investigated with DNA supercoiling, decatenation, and cleavage assay.
We isolated and identified 6,6′-dihydroxythiobinupharidine as the antimicrobial compound. The MIC of this compound was 1–4μg/mL against various MRSA and VRE strains. We also demonstrated that this compound inhibited DNA topoisomerase IV (IC50 was 10–15μM), but not DNA gyrase in S. aureus, both of which are known to be the targets of quinolone antibiotics and necessary for DNA replication. However, this compound only exhibited slight cross-resistance to norfloxacin-resistant S. aureus, which indicated that DTBN might inhibit other targets besides topoisomerase IV. These results suggest that 6,6′-dihydroxythiobinupharidine may be a potent candidate or seed for novel antibacterial agents.
DTBN from N. japonicum showed anti-MRSA and anti-VRE activities. DTBN might be involved in the inhibition of DNA topoisomerase IV.
DTBN might be useful as a seed compound. The information on the inhibition mechanism of DTBN will be useful for the modification of DTBN towards developing novel anti-MRSA and anti-VRE drug.
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•DTBN had antimicrobial activity for Staphylococcus aureus and enterococci.•DTBN strongly inhibited DNA topoisomerase IV of S. aureus in vitro.•DTBN slightly inhibited DNA gyrase of S. aureus in vitro.•DTBN did not exhibit cross-resistance to norfloxacin-resistant S. aureus.