Antimicrobial activity, toxicity and anti-inflammatory potential of methanolic extracts of four ethnomedicinal plant species from Punjab, Pakistan

BACKGROUND The plant species Aristolochia indica (AI), Melilotus indicus (MI), Tribulus terrestris (TT) and Cuscuta pedicellata (CP) are widely used in folk medicine in the villages around Chowk Azam, South Punjab, Pakistan. The aim of this study was to evaluate the antioxidant activity, phytochemical composition, and the antibacterial, antifungal, cytotoxic and anti-inflammatory potential of the four medicinal plants listed above. For CP stem, this study represents (to the best of our knowledge) the first time phytochemicals have been identified and the antioxidant and anti-inflammatory potential determined. METHODS Phytochemicals were analyzed through chemical tests, thin layer chromatography (TLC) and spectrophotometric methods. Antioxidant activities (DPPH and H2O2) were also determined through spectrophotometric methods. Extracts were evaluated for antibacterial potential via the agar well diffusion method against Staphylococcus aureus, Pseudomonas aeruginosa, Klebsiella pneumonia and Acinetobacter baumannii. The minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) were determined by the microdilution method. Antifungal activities were tested using the agar tube dilution method against three species: Aspergillus fumigatus, Aspergillus flavus and Rhizopus oryzae. The cytotoxic potential of the plant extracts was checked using the brine shrimp assay. In vitro anti-inflammatory activity of the selected plant extracts was evaluated using albumin denaturation, membrane stabilization and proteinase inhibitory assays. RESULTS Of all the methanolic extracts tested, those from CP (stem) and TTF (T. terrestris fruit) had the highest phenolic, flavonoid and flavonol contents (497±4 mg GAE/g, 385±8 mg QE/g and 139±4 mg QE/g; 426±5 mg GAE/g, 371±8 mg QE/g and 138±6 mg QE/g, respectively) and also exhibited strong antioxidant potential in scavenging DPPH and hydrogen peroxide (IC50 values; 20±1 and 18±0.7 μg/mL; 92±2 and 26±2 μg/mL, respectively). CP, TTF and TTL (T. terrestris leaf) extracts substantially inhibited the growth of the bacteria A. baumannii, S. aureus, and K. pneumonia and also exhibited the highest antifungal potential. The ranking of the plant extracts for cytotoxicity was TTF > TTL > AI > CP > MI, while the ranking for in vitro anti-inflammatory potential at a concentration of 200 μg/mL of the selected plant extracts was CP > TTL, TTF > AI > MI. The lowest IC50 (28 μg/mL) observed in the albumin denaturation assay was for CP. Positive correlations were observed between total phenolics, antioxidants, antibacterial, antifungal and anti-inflammatory potential of the selected plant extracts, indicating a significant contribution of phenolic compounds in the plant extracts to these activities. CONCLUSIONS This study revealed the strong antimicrobial, antioxidant, cytotoxic and anti-inflammatory potential of the plant species CP and TT used in folk medicine.