title: Evaluation of antiviral activities of Houttuynia cordata Thunb. extract, quercetin, quercetrin and cinanserin on murine coronavirus and dengue virus infection.
abstract: OBJECTIVE
  To evaluate the in vitro activities of the ethyl acetate (EA) fraction of Houttuynia cordata (H. cordata) Thunb. (Saururaceae) and three of its constituent flavonoids (quercetin, quercitrin and rutin) against murine coronavirus and dengue virus (DENV).
  
  
  METHODS
  The antiviral activities of various concentrations of the EA fraction of H. cordata and flavonoids were assessed using virus neutralization tests against mouse hepatitis virus (MHV) and DENV type 2 (DENV-2). Cinanserin hydrochloride was also tested against MHV. The EA fraction of H. cordata was tested for acute oral toxicity in C57BL/6 mice.
  
  
  RESULTS
  The EA fraction of H. cordata inhibited viral infectivity up to 6 d. Cinanserin hydrochloride was able to inhibit MHV for only 2 d. The 50% inhibitory concentrations (IC50) of the EA fraction of H. cordata added before the viral adsorption stage were 0.98 μg/mL for MHV and 7.50 μg/mL for DENV-2 with absence of cytotoxicity. The mice fed with the EA fraction up to 2000 mg/kg did not induce any signs of acute toxicity, with normal histological features of major organs. Certain flavonoids exhibited comparatively weaker antiviral activity, notably quercetin which could inhibit both MHV and DENV-2. This was followed by quercitrin which could inhibit DENV-2 but not MHV, whereas rutin did not exert any inhibitory effect on either virus. When quercetin was combined with quercitrin, enhancement of anti-DENV-2 activity and reduced cytotoxicity were observed. However, the synergistic efficacy of the flavonoid combination was still less than that of the EA fraction.
  
  
  CONCLUSIONS
  The compounds in H. cordata contribute to the superior antiviral efficacy of the EA fraction which lacked cytotoxicity in vitro and acute toxicity in vivo. H. cordata has much potential for the development of antiviral agents against coronavirus and dengue infections.
authors: Department of Microbiology, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Kent Ridge, Singapore; Department of Pathology, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Kent Ridge, Singapore; Department of Pharmacology, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Kent Ridge, Singapore.
authors: K H
authors: KH
authors: Chiow
authors: Department of Microbiology, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Kent Ridge, Singapore; Department of Pathology, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Kent Ridge, Singapore; Department of Pharmacology, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Kent Ridge, Singapore.
authors: M C
authors: MC
authors: Phoon
authors: Department of Microbiology, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Kent Ridge, Singapore; Department of Pathology, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Kent Ridge, Singapore; Department of Pharmacology, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Kent Ridge, Singapore.
authors: Thomas
authors: T
authors: Putti
authors: Department of Microbiology, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Kent Ridge, Singapore; Department of Pathology, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Kent Ridge, Singapore; Department of Pharmacology, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Kent Ridge, Singapore.
authors: Benny K H
authors: BK
authors: Tan
authors: Department of Microbiology, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Kent Ridge, Singapore; Department of Pathology, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Kent Ridge, Singapore; Department of Pharmacology, Yong Loo Lin School of Medicine, National University Health System, National University of Singapore, Kent Ridge, Singapore. Electronic address: micctk@nus.edu.sg.
authors: Vincent T
authors: VT
authors: Chow
keywords: Cinanserin; Dengue virus; Houttuynia cordata; Murine coronavirus; Quercetin; Quercetrin