Bioactivity of Natural Products from Larrea divaricata Cav. (Zygophyllaceae) against Monkeypox Virus (Orthopoxvirus)

Abstract

Monkeypox, caused by the monkeypox virus (MpoxV, Orthopoxvirus), has spread globally and has been declared a public health emergency by the WHO. Although there is no specific treatment, the antiviral drug tecovirimat has been approved for severe cases. The lack of effective therapies has driven the search for new antiviral agents, including plant-derived natural compounds. Our research group has been studying the plant species Larrea divaricata Cav. (Zygophyllaceae) ("jarilla") for some time and has demonstrated,  its effectiveness against a wide range of viruses in in vitro studies. We aimed to evaluate the potential antiviral activity of natural products obtained from L. divaricata against MpoxV, to expand the knowledge about the antiviral activity of this plant species and to identify a safe and effective treatment for this disease.

Ethanolic and chloroformic extracts of jarilla, previously obtained as part of a doctoral thesis, were used in this study. Nordihydroguaiaretic acid (NDGA), the primary metabolite of the species, was isolated from the chloroformic extract with a purity of 90%. For in vitro assays, the Vero clone 76 cell line was used. The cytotoxicity of the natural products was evaluated using the Neutral Red Uptake assay. The antiviral and virucidal activity was evaluated using the plaque reduction method,  with a strain of MpoxV isolated and characterized at InViV-UNC during the outbreak of December 2022.

Using the Neutral Red Uptake method, we determined the 50% cytotoxic concentration (CC50) of the natural products. The chloroformic extract was found to be the most cytotoxic, with a CC50 of 52.64 µg/ml, followed by NDGA (CC50 of 59.34 µg/ml) and the ethanolic extract (CC50 of 86.52 µg/ml). Regarding antiviral and virucidal activity, all natural products showed inhibition values below 50%, indicating that they do not possess significant antiviral activity against MpoxV.

Although the results were not as expected, as the natural products did not inhibit MpoxV replication, they contribute to the knowledge of the bioactivities of the plant species under study.