Monitoring the oxidative function of hydroxytyrosol and potential interactions with glutathione produced by human cells

Hydroxytyrosol (HT) has outstanding antioxidant properties, however, the lack of information regarding its potential interactions with biological systems prevents the direct application of HT in the field of medicine. In particular, the interaction of HT with antioxidant defense systems based on tripeptides containing thiols (glutathione, GSH) remains elusive and requires further investigation. Herein, we investigated the electrochemical behavior of HT in Britton-Robinson buffer solution (B-R) in the absence and presence of GSH using bulk electrolysis (BE) and cyclic voltammetry (CV). The posssible reaction pathways of HT and oxidation products were identified by combining ultrahigh-performance liquid chromatography and mass spectrometry (UHPLC-MS). The findings of the study indicate that the phenolic ring of HT experiences a quasi-reversible oxidation process. This process is associated with the oxidation of the catechol moiety through the transfer of 2e(-)/2H(+) in the presence of existing GSH. As a result of this oxidation, a quinone is produced. The quinone molecule can undergo reduction, leading to the regeneration of the HT molecule or interacting with GSH, resulting in the formation of mono-GSH-HT, bi-GSH-HT, and bi-GSH-HT trimer conjugates. Using density functional theory (DFT), the ratio of disulfide, mono-GSH-HT, bi-GSH-HT, and bi-GSH-HT trimer formation energies (E-f) was determined to be 4.5:1.8:1.1:1.4, which are consistent with UHPLC-MS measurement. Accordingly, the formation of the disulfide form of GSH and parent HT is preferred over the formation of other conjugates. The higher values of electrophilicity index (omega) for the HT trimer and quinone suggest a remarkable ability to interact with cells in biological systems