Glyoxalase I Assay as a Possible Tool for Evaluation of Biological Activity of Antioxidant-Rich Plant Extracts

The health-promoting properties of natural plant bioactive compounds are mainly attributable to their ability to counteract oxidative stress. This is considered a major causative factor in aging and aging-related human diseases, in which a causal role is also ascribed to dicarbonyl stress. This is due to accumulation of methylglyoxal (MG) and other reactive dicarbonyl species, leading to macromolecule glycation and cell/tissue dysfunction. The glyoxalase (GLYI) enzyme, catalyzing the rate-limiting step of the GSH-dependent MG detoxification pathway, plays a key role in cell defense against dicarbonyl stress. Therefore, the study of GLYI regulation is of relevant interest. In particular, GLYI inducers are important for pharmacological interventions to sustain healthy aging and to improve dicarbonyl-related diseases; GLYI inhibitors, allowing increased MG levels to act as proapoptotic agents in tumor cells, are of special interest in cancer treatment. In this study, we performed a new in vitro exploration of biological activity of plant bioactive compounds by associating the measurement of their antioxidant capacity (AC) with the evaluation of their potential impact on dicarbonyl stress measured as capability to modulate GLYI activity. AC was evaluated using TEAC, ORAC, and LOX-FL methods. The GLYI assay was performed using a human recombinant isoform, in comparison with the recently characterized GLYI activity of durum wheat mitochondria. Different plant extracts were tested, obtained from plant sources with very high phytochemical content ('Sun Black' and wildtype tomatoes, black and 'Polignano' carrots, and durum wheat grain). Results showed high antioxidant properties of the tested extracts, associated with different modes (no effect, activation, and inhibition) and effectiveness in modulating both GLYI activity sources. Overall, results indicate the GLYI assay as an advisable and promising tool for researching plant foods as a source of natural antioxidant compounds acting as GLYI enzymatic regulators to be used for dietary management associated the treatment of oxidative/dicarbonyl-promoted diseases.