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 attributableto their ability to counteract oxidative stress. This is considered a major causative factor inaging 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, leadingto macromolecule glycation and cell/tissue dysfunction. The glyoxalase (GLYI) enzyme, catalyzingthe rate-limiting step of the GSH-dependent MG detoxification pathway, plays a key role in celldefense against dicarbonyl stress. Therefore, the study of GLYI regulation is of relevant interest. Inparticular, GLYI inducers are important for pharmacological interventions to sustain healthy agingand to improve dicarbonyl-related diseases; GLYI inhibitors, allowing increased MG levels to actas proapoptotic agents in tumor cells, are of special interest in cancer treatment. In this study, weperformed a new in vitro exploration of biological activity of plant bioactive compounds by associatingthe measurement of their antioxidant capacity (AC) with the evaluation of their potential impacton dicarbonyl stress measured as capability to modulate GLYI activity. AC was evaluated usingTEAC, ORAC, and LOX-FL methods. The GLYI assay was performed using a human recombinantisoform, in comparison with the recently characterized GLYI activity of durum wheat mitochondria.Different plant extracts were tested, obtained from plant sources with very high phytochemicalcontent ('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 (noeffect, 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 asource of natural antioxidant compounds acting as GLYI enzymatic regulators to be used for dietarymanagement associated the treatment of oxidative/dicarbonyl-promoted diseases.