Resumo
Background: The number of antiviral studies using plant extracts has increased in the last decades, and the results have shown that plants are potential sources of compounds that are able to inhibit and/or decrease viral infections. The selection of these plants by ethnopharmacological criteria increases the probability of fi nding new substances with significant pharmacological and biological activities. Hence, Brazil has an advantage in this area due to its extensive biodiversity and ethnological diversity. Guettarda angelica is a plant from the Brazilian Caatinga region the roots of which are popularly used for various therapeutic purposes, including veterinary use. The aim of this work was to investigate the in vitro antiviral activity of extracts of plant parts from G. angelica against three animal herpesviruses: bovine (BoHV-1), suid (SuHV-1) and equine (EHV-1) herpesviruses type 1. Materials, Methods & Results: The extracts of roots, leaves and seeds of G. angelica were initially screened for in vitro antiviral activity against these herpesviruses using the virus yield reduction assay. The MDBK cells were used in assays with BoHV-1 and SuHV-1, and the Vero cells with EHV-1. For these assays, the cells previously treated with the extracts in non-cytotoxic concentrations were inoculated with logarithmic dilutions of each virus. The viral inhibitory activity of extracts was calculated by difference of virus titer between treated infected cells and non-treated infected cells. Only the aqueous extract from seeds (AEs) showed a significant antiviral activity (P < 0.01, ANOVA followed by Tukey test) against all herpesviruses leading continuous studies. Thus, the selectivity index (SI) of this extract was determined by MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] colorimetric assay by calculating the ratio CC50 over IC50. The 50% cytotoxic concentration (CC50) was defined as the extract concentration that reduced the cell viability by 50% when compared to untreated controls; the 50% inhibitory concentration (IC50) was defined as the concentration of the extract that inhibited 50% of viral replication when compared to the virus control. The CC50 and IC50 were obtained from nonlinear regression analysis of concentration-effect curves by the GraphPad Prism 5 Demo program and represented the means ± standard deviation of three independent experiments. The CC50 for Vero cells was 400.60 ± 0.20 µg/mL, while the CC50 for MDBK cells was 920.50 ± 0.19 µg/mL. The IC50 values of the AEs on the BoHV-1, SuHV-1 and EHV-1 were 22.79 µg/mL, 91.30 µg/mL and 19.95 µg/mL, respectively. The SI values of this extract for each virus obtained from these data were 40.39, 10.08 and 20.08 for BoHV-1, SuHV-1, and EHV-1, respectively. Discussion: To ensure the antiviral activity of a plant extract and consequently its future use as antiviral agent is crucial the obtainment of its selectivity index or safety index. It is guarantee of a true antiviral effect and not the result of cytotoxicity of the extract on cells, and that could be confused with an antiviral activity. Other important point are the extract IC50 values less than 100 µg/mL. The results of the AEs of G. angelica are in accordance with these considerations indicating that the G. angelica seeds may be a potential source of antiviral compounds insurance and encouraging further investigation of them.