Determination of the correlative association between phytochemical content and nitrite inhibition in selected medicinal plants used traditionally to treat respiratory infections

Introduction: Several medicinal plants, including Artemisia afra Jacq. Ex Willd, Lippia javanica (Burm.f.) Spreng, Tetradenia riparia (Hochst.) Codd, and Tulbaghia violacea Harv have been used in treating illnesses such as respiratory infections and their associated inflammatory dysregulation. The study aimed to evaluate the quantitative phytochemical content and the nitrite inhibition strength of the selected medicinal plant extracts. Methods: A cold-maceration aqueous extraction procedure was employed for phytoconstituent extraction from dried plant material. The total phenolic content (TPC), along with total flavonoid content (TFC), total tannin content (TTC), and total saponin content (TSC), was quantitatively analyzed in the plant extracts. Cytotoxicity evaluation was done using the MTT assay to measure the minimum lethal concentrations against RAW ۲۶۴.۷ macrophage cell lines, and inhibition of nitrite production was assessed using a RAW macrophage cell-based assay. Results: All plant extracts contained measurable levels of the tested phytochemicals, with A. afra roots showing the highest phenolic and flavonoid content at ۴۸.۵۴ ± ۱.۳۳ mg GAE (gallic acid equivalent)/g and ۳۹.۷۶ ± ۱.۵۶ mg QE (quercetin equivalents)/g, respectively. The extracts exhibited relatively low cytotoxicity against RAW macrophage cells, with LC۵۰ values ranging between ۶۴ ± ۲.۲ and ۱۴۴۳ ± ۸۶.۲ µg/mL. The most nitrite inhibition was observed in T. riparia leaf extracts, with ۸۶% inhibition at ۱۲.۵ µg/mL. Correlation analysis further showed that extracts with higher phenolic content exhibited stronger nitrite inhibition properties. Conclusion: Overall, all extracts demonstrated nitrite inhibition activity, showing the possible medicinal uses of these plants against respiratory infections with their associated inflammation.