Antimicrobial activity and DNA-fragmentation effect of isoflavonoids isolated from seeds of Millettia ferruginea, an endemic legume tree in Ethiopia

Objective: To investigate the seeds of Millettia ferruginea (M. ferruginea) to unravel its antibacterial, antifungal, antitubercular, and antileishmanial potential for the first time. Methods: M. ferruginea seeds were refluxed separately with chloroform, methanol and water to prepare the three extracts, which were tested against the reference strains of Gram-positive and Gram-negative bacteria, yeast cells, Mycobacterium tuberculosis and Leishmania donovani (L. donovani) promastigotes. Next, the seeds were chemically analysed to isolate three constituent compounds, viz., barbigerone, calopogonium isoflavone-A and durmillone, which were purified, characterised and evaluated for antibacterial and antileishmanial activity. Further, Comet assay was conducted to observe DNA fragmentation effects on human peripheral blood mononuclear cells pretreated with the isoflavonoid compounds. Results: The chloroform and methanol extracts of M. ferruginea seeds exhibited antibacterial and antileishmanial activity. The pure compounds also showed inhibitory activity against Gram-negative ATCC strains (minimum inhibitory concentration ~0.5 µmol/L), and L. donovani promastigotes (IC50 8.2–87.3 µg/mL). However, they had little or no activity against yeast cells and tubercle bacilli. The DNA fragmentation study showed that the isoflavonoid constituents of M. ferruginea seeds were safe at therapeutic doses. Conclusions: The antibacterial efficacy of the non-aqueous extracts of M. ferruginea seed was observed against both Gram-positive and Gram-negative ATCC strains. Moreover, the constituents isoflavonoids, viz., barbigerone, calopogonium isoflavone-A and durmillone, exhibited inhibitory activity against Gram-negative ATCC strains and L. donovani promastigotes. The comet assay showed that the compounds were safe to be considered for human consumption.