Activity of acetone and methanol extracts from thirty-one medicinal plant species against herpes simplex virus types 1 and 2

Abstract

Context: Thirty-one medicinal plant species from Hawaii, Morocco, and the Sonoran Desert, USA have been shown in past studies to be highly inhibitory to pathogenic bacteria, fungi, and certain cancer cell lines. However, none were tested for antiviral activity.

Objective: Acetone and methanol extracts from these species were bio-assayed for antiviral activity against herpes simplex virus types 1 and 2, and for cytotoxicity to the Vero C1008 cell line.

Materials and methods: Extracts from these species were tested in vitro for antiviral activity using an immunoperoxidase mini-plaque reduction assay to detect viral structural protein synthesis. A 50% inhibitory concentration (IC₅₀) was computed. Sulforhodamine B and neutral red assays were used to qualitatively and quantitatively assess the cytotoxicity of extracts to C1008 cells, and to compute a 50% cytotoxic concentration (CC₅₀) using a dose response curve.

Results: Eight of the 31 plant species assayed showed significant antiviral activity against HSV 1 and HSV 2 viruses. The acetone extract of Kalanchoe pinnata Pers. (Crassulaceae) produced an IC₅₀ of 0.025 mg/mL and a CC₅₀ of 1.25 mg/mL yielding a therapeutic index of 50. Additionally, this extract reduced plaque numbers to zero or near zero at a concentration of 0.1 mg/mL when added 30 min before or 30 min after virus infection.

Discussion and conclusion: The mechanism of inhibition against HSV 1 and HSV 2 viruses is now being investigated, along with fractionation of the acetone extract in search of the active compound or compounds.

Keywords::

• Antiviral
• cytotoxicity
• HSV
• immunoperoxidase plaque reduction assay
• neutral red assay

Acknowledgements

We thank Jack Donaldson, Brandon Odum, Brad Prestwich and Analiesa Leonhardt for help with this project.

Declaration of Interest

The authors are grateful to the Wesley T. Johnson Memorial Virus Research Fund, the Professional Development Fund in the Department of Biology at Brigham Young University and the Public Education Job Enhancement Committee, in association with the Governor’s Office of the State of Utah, for financial support of this work.