Immunomodulatory and anti-SARS activities of Houttuynia cordata

Abstract

Background: Severe acute respiratory syndrome (SARS) is a life-threatening form of pneumonia caused by SARS coronavirus (SARS-CoV). From late 2002 to mid 2003, it infected more than 8000 people worldwide, of which a majority of cases were found in China. Owing to the absence of definitive therapeutic Western medicines, Houttuynia cordata Thunb. (Saururaceae)(HC) was shortlisted by Chinese scientists to tackle SARS problem as it is conventionally used to treat pneumonia.

Aim of the study: The present study aimed to explore the SARS-preventing mechanisms of HC in the immunological and anti-viral aspects.

Results: Results showed that HC water extract could stimulate the proliferation of mouse splenic lymphocytes significantly and dose-dependently. By flow cytometry, it was revealed that HC increased the proportion of CD4(+) and CD8(+) T cells. Moreover, it caused a significant increase in the secretion of IL-2 and IL-10 by mouse splenic lymphocytes. In the anti-viral aspect, HC exhibited significant inhibitory effects on SARS-CoV 3C-like protease (3CL(pro)) and RNA-dependent RNA polymerase (RdRp). On the other hand, oral acute toxicity test demonstrated that HC was non-toxic to laboratory animals following oral administration at 16 g/kg.

Conclusion: The results of this study provided scientific data to support the efficient and safe use of HC to combat SARS.

Fig. 1

Lymphoproliferation activity of Houttuynia cordata extract on mouse splenic lymphocytes after 48 and 72 h treatment. The results are expressed as mean ± S.D. of six values from one representative experiment. **p < 0.01 vs. control (0 μg/ml).

Fig. 2

Effect of Houttuynia cordata on IL-2 (A), IL-10 (B), IL-4 (C) and IFN-γ (D) production in mouse splenic lymphocytes. Mouse splenic lymphocytes were treated with HC extract for 24, 48 and 72 h. Cytokine production was measured by ELISA. Data are expressed as mean ± S.D. of values from at least three independent experiments. *p < 0.05, **p < 0.01 vs. control (0 μg/ml).

Fig. 3

Effect of Houttuynia cordata on the SARS coronaviral 3CLpro activity. Data are expressed as mean ± S.D. of values from four independent experiments. *p < 0.05 vs. control (0 μg/ml).

Fig. 4

Effect of Houttuynia cordata on the SARS-CoV RdRp activity using radiometric RdRp assay by [α-32P] UTP incorporation. Data are expressed as mean ± S.D. from three individual experiments. *p < 0.05, **p < 0.01 vs. control.