In vitro antibacterial and antioxidant activity of flavonoids from the roots of Tephrosia vogelii: a combined experimental and computational study

Abstract

Tephrosia vogelii is a traditional medicinal plant used to treat hypertension, diarrhea and urinary disorders. Silica gel chromatographic separation of CH₂Cl₂/MeOH (1:1) roots extract of T. vogelii afforded seven compounds namely; β-sitosterol (1a), stigmasterol (1b), 6a, 12a-dehydro-deguelin (2), tephrosin (3), maackiain (4), obovatin (5) and 6-oxo, 6a, 12a-dehydro-deguelin (6). GC-MS analysis of essential oils from the root of T. vogelii displayed a total of 17 compounds of which cis-nerolidol (41.7 %) and cadinol (19.7 %) were the major constituents. CH₂Cl₂/MeOH (1:1) extract, MeOH extract, maackiain (4) and obovatin (5) showed moderate inhibitory activity against Pseudomonas aeruginosa with MIC value of 0.5, 0.66, 0.83 and 0.83 mg/mL, respectively, compared to ciprofloxacin (MIC of 0.078 μg/mL). 6a, 12a-dihydro-deguelin (2), and 6-oxo, 6a, 12a-dehydro-deguelin (6) displayed significant activity against S. epidermis with MIC values of 0.66 mg/mL. Tephrosin (3) and maackiain (4) also showed moderate antibacterial activity against Staphylococcus aureus and Proteus mirabilis with MIC values of 0.83 and 0.5 mg/mL, respectively, compared to ciprofloxacin (0.312 μg/mL). The radical scavenging activity results indicated that tephrosin (3), obovatin (5) and 6-oxo, 6a, 12a-dehydro-deguelin (6) showed potent DPPH scavenging activity with IC₅₀ values of 10.97, 10.43 and 10.73 μg/mL, respectively, compared to ascorbic acid (IC₅₀ of 5.83 μg/mL). The docking prediction results revealed that 6a, 12a-dehydro-deguelin (2) displayed the best binding energy of -8.1 kcal/mol towards pyruvate kinase of S. aureus (PDB ID: 3T07) and -7.9 kcal/mol towards P. mirabilis urease (PDB ID: 1E9Y) and DNA gyrase B of Escherichia coli (PDB: 4F86) receptors compared to ciprofloxacin (-7.2 to -8.0 kcal/mol). Maackiain (4) and obovatin (5) displayed the minimum binding energy of -7.9 and -8.2 kcal/mol towards the LasR protein of P. aeruginosa (PDB: ID 2UV) and S. epidermidis FtsZ (PDB: ID 4M8I), respectively. The SwissADME drug-likeness and Pro Tox II toxicity prediction results indicated that compounds (2-6) obeyed Lipinski's rule of five with 0 violations and none of them were found to be hepatotoxic, mutagenic, and cytotoxic, respectively. The in vitro assessment results supported by the in silico analysis revealed that crude extracts and isolated compounds showed promising antibacterial and antioxidant activity, which proves the therapeutic potential of the roots of T. vogelii.

Keywords: T. vogelii; ADME; antibacterial; antioxidant; binding energy; molecular docking.