Enzymatic dimerization of luteolin enhances antioxidant and antimicrobial activities

Abstract

Antimicrobial resistance and oxidative stress continue to be major challenges globally. The aim of the current study was to enzymatically transform luteolin for the improvement of antioxidant and antimicrobial activities, using the fungal laccase from Trametes pubescens. Laccase-catalysed homocoupling reactions were carried out in a monophasic system with ethanol as co-solvent. A new dimer (m/z 569) was produced and characterized for antioxidant and antibacterial activities. The dimer showed a modest but significant (p < 0.05) increase (1.1–1.2 × ) in antioxidant activity compared to luteolin as demonstrated in standard (DPPH, ABTS and FRAP) antioxidant assays. The antibacterial activity of the dimer also improved as the minimum inhibitory concentrations (MICs) recorded against Escherichia coli and methicillin-resistant Staphylococcus aureus (MRSA) were substantially reduced (approximately halved) when the dimer was used instead of luteolin. A bactericidal mode of action (cell membrane disruption) was evident from the cell integrity and time-kill assays and scanning electron microscopy (SEM) images. These analyses showed loss of cell constituents, the formation of membrane pores, as well as cell fragmentations. The novel dimer with its enhanced biological activity may be exploited in food, health, and nutraceutical industries.