Evaluation of antiviral activity indicators in selected medicinal plants used traditionally for treatment of respiratory viral infections

The continued usage of plants for treatment of diseases and healthcare purposes dates back from time immemorial, including for treatment of respiratory viral infections. The current study was aimed at the evaluation of the antioxidant, anti-neuraminidase and anti-inflammatory properties of selected medicinal plants (Artemisia afra, Lippia javanica, Tetradenia riparia and Tulbaghia violacea) used traditionally for treatment of respiratory viral infections. The plants were extracted using water and 80% ethanol. Phytochemical screening of the plant extracts was evaluated using standard protocols. The quantitative antioxidant activity evaluation was performed using the 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, ferric reducing antioxidant power (FRAP) assay and the hydrogen peroxide (H2O2) assay. Anti-viral potential was evaluated using anti-neuraminidase inhibition assay. The anti-inflammatory effect of the plant extracts was determined by their activity against cyclooxygenase-2 (COX-2) using colorimetric COX-2 inhibitor screening assay kit. The phytochemical screening results of extracts tested showed the presence of different classes of secondary metabolites that included coumarins, flavonoids, terpenoids, saponins, steroids, glycosides, and phenolic compounds. The results showed possession of antioxidant activity by the leaf extracts of the selected medicinal plants through dose dependent inhibition of DPPH, H2O2 and FRAP free radicals. The possessed antioxidant activity was shown at varying strengths amongst different plants as demonstrated by differences in determined IC50s. In addition, the plant extracts showed notable inhibitory activity on the enzymatic action of viral neuraminidase with the lowest IC50 of 50 µg/ml recorded. Furthermore, the plant extracts showed possession of anti-inflammation activity demonstrated by C0X-2 inhibition activity. The results of the current study showed possession of antioxidant, anti-neuraminidase, and anti-inflammatory properties by the extracts of Artemisia afra, Lippia javanica, Tetradenia riparia and Tulbaghia violacea.