Abstract
Exploring new antimicrobial and cytotoxic drugs has been one of the most active areas of research. Rhamnus purpurea (Edgew.) buckthorn (Rhamnaceae) is a wild shrub traditionally used in Pakistan for the treatment of various ailments including cancer and infectious diseases. The aim of this study is to find novel antimicrobial and cytotoxic agents of plant origin. The crude methanol extract and full range of fractions of R. purpurea leaves were screened for the said activities using in vitro antimicrobial, antioxidant, and cytotoxic models following standard protocols. The antimicrobial activity was evaluated using the agar well diffusion method, while the antioxidant activity was assessed with 1,1-diphenyl-2-picryl hydrazyl (DPPH) and ferric reducing antioxidant power (FRAP) assays. The cytotoxic effect was investigated against the human cancer cell lines i.e. Caco-2 (gut), A549 (lung), HepG2 (liver), and MDA-MB-231 (breast) by MTS assay. In addition, toxicity studies were conducted on renal and alveolar primary epithelial cells (HRPTEpiC and HPAEpiC, respectively). Phytochemical investigation showed the presence of secondary metabolites such as alkaloids, saponins, tannins, glycosides, phenols, carbohydrates, proteins, and flavonoids. The n-hexane and chloroform fractions showed significant activity against Staphylococcus aureus (MIC 0.60 and 0.68 mg/mL, respectively), Salmonella typhi (MIC 0.48 and 0.45 mg/mL, respectively), and Bacillus subtilis (MIC 0.54 and 0.76 mg/mL, respectively). Among fungal strains, crude methanol and chloroform fractions exhibited significant activity against Fusarium solani (MIC 0.53 and 0.44 mg/mL, respectively) and Aspergillus niger (MIC 0.47 and 0.42 mg/mL, respectively). The crude methanol, n-hexane and chloroform fractions revealed the highest antioxidant activity at 1000 μg/mL, compared to that of ascorbic acid. The n-hexane fraction showed a significant cytotoxic effect against Caco-2, A549, and HepG2 cell lines with IC50 values of 5.65 ± 0.88, 5.50 ± 0.90, and 4.95 ± 1.0 μg/mL, respectively. Similarly, the chloroform fraction depicted significant activity against Caco-2, A549, and HepG2 cell lines with IC50 values of 4.55 ± 1.25, 4.65 ± 1.55, and 2.85 ± 0.98 μg/mL, respectively. The crude methanol extract and almost all fractions exhibited the highest selectivity index (>2.0) for Caco-2, A549, and HepG2 cancer cell lines, providing safety data for this study. The results showed that R. purpurea leaves have excellent antimicrobial, antioxidant, and cytotoxic potential and warrant further studies to search for novel compounds for the said activities.