In vitro Bioactivities of Azadirachta indica (Kohomba) and Oroxylum indicum (Thotila)

Abstract

Background: Traditional Sri Lankan medicine have been serving as a cornerstone of healthcare for approximately 70% of our rural population. In traditional Sri Lankan medicine, formulations combine multiple plants, with a few main components and others act as supportive agents to enhance their effectiveness. Azadirachta indica (AI) and Oroxylum indicum (OI) are components of Denabadiya Kasaya, which traditional healers use to treat viral infections. Objective: To assess the bioactivity of AI and OI bark extracts using in vitro bioassays Methods: Hot water extracts (100°C) of the barks of AI and OI were prepared by boiling 30 g of powdered bark material with 1940 mL of distilled water and condensed to 240 mL. Subsequently, the Total Phenolic Content (TPC) and Total Flavonoid Content (TFC) were determined. Antioxidant activity by 1,1-diphenyl-2-picrylhydrazyl DPPH assay and anti-inflammatory activity by human red blood cell (HRBC) assay were carried out. Finally, cytotoxicity was assessed by (3 (4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide) MTT assay at 24 and 120 h, with Vero cells cultured in DMEM complete media at 37°C in 5% CO2. Results: TPC of AI and OI were recorded as 15.6 and 20.2 mg/g GAE, respectively. TFC of AI and OI were 40.0 and 15.1 mg/g QE. For DPPH assay, IC50 was 0.4 mg/mL for both samples, while standard ascorbic acid showed an IC50 of 0.016 mg/mL. HRBC depicted an IC50 of <0.0625 mg/mL for both AI and OI, while ibuprofen showed an IC50 of <0.0625 mg/mL. Finally, cytotoxicity of AI and OI were recorded as CC50 0.60 and 0.80 mg/mL for 24 h and >1 and 0.62 mg/mL for 120 h. Conclusions: AI showed a remarkably higher TFC value, while both plant extracts depicted moderate antioxidant activity. Both extracts also showed potent anti-inflammatory activity which can help mitigate the detrimental effects of DENV infection by reducing oxidative stress and protecting host cells. However, among the two plants tested AI showed a slightly high CC50 value which might be a more promising candidate for further research as a potential anti-viral therapy.