Pycnoporus laccase-mediated bioconversion of rutin to oligomers suitable for biotechnology applications

The Pycnoporus fungi are white-rot basidiomycetes listed as food- and cosmetic-grade microorganisms. Three high redox potential laccases from Pycnoporus coccineus and Pycnoporus sanguineus were tested and compared, with the commercial Suberase® as reference, for their ability to synthesise natural active oligomers from rutin (quercetin-3-rutinoside, one of the best-known naturally occurring flavonoid glycosides). The aim of this work was to develop a process with technical parameters (solvent, temperature, reaction time and raw materials) that were easy to scale up for industrial production and compatible with cosmetic and pharmaceutical formulation guidelines. The aqueous mixture of glycerol/ethanol/buffer described in this study met this requirement and allowed the solubilisation of rutin and its oxidative bioconversion into oligomers. The four flavonoid oligomer mixtures synthesised using laccases as catalysts were analysed by high performance liquid chromatography-diode array detection-negative electrospray ionisation-multistage mass spectrometry. Their chromatographic elution profiles were compared and 16 compounds were characterised and identified as dimers and trimers of rutin. The oligorutins were different in Suberase® and Pycnoporus laccase reaction mixtures. They were evaluated for their antioxidant, anti-inflammatory and anti-ageing activities on specific enzymatic targets such as cyclooxygenase (COX-2) and human matrix metalloproteinase 3 (MMP-3). Expressed in terms of IC(50), the flavonoid oligomers displayed a 2.5- to 3-fold higher superoxide scavenging activity than monomeric rutin. Pycnoporus laccase and Suberase® oligorutins led to an inhibition of COX-2 of about 35% and 70%, respectively, while monomeric rutin showed a near-negligible inhibition effect, less than about 10%. The best results on MMP-3 activity were obtained with rutin oligomers from P. sanguineus IMB W006-2 laccase and Suberase® with about 70-75% inhibition.