Kinetics of ascorbate and dithiothreitol oxidation by soluble copper, iron, and manganese, and 1,4-naphthoquinone: Influence of the species concentration and the type of fluid

• Published in: Chemosphere (Oxford) 2024-08, Vol.361, p.142435, Article 142435
• Main Authors: Expósito, A., Maillo, J., Uriarte, I., Santibáñez, M., Fernández-Olmo, I.
• Format: Article
• Language: English
• Subjects: AA and DTT assays; active ingredients; Artificial lysosomal fluid; ascorbic acid; copper; dithiothreitol; iron; Kinetics; manganese; naphthoquinones; oxidation; Oxidative potential; particulates; Phosphate buffer; phosphates; PM active compounds; reactive oxygen species; species; toxicity
• ISSN: 0045-6535; 1879-1298; 1879-1298
• DOI: 10.1016/j.chemosphere.2024.142435

An alternative metric to account for particulate matter (PM) composition-based toxicity is the ability of PM-species to generate reactive oxygen species (ROS) and deplete antioxidants, the so-called oxidative potential (OP). Acellular OP assays are the most used worldwide, mainly those based on ascorbic acid (AA) and dithiothreitol (DTT) depletion; OP values are calculated from AA/DTT concentration over time kinetic curves. Since a great variability in OP-DTT and OP-AA values can be found in the literature, the understanding of those factors affecting the kinetic rate of AA and DTT oxidation in the presence of PM-bound species will improve the interpretation of OP values. In this work, a kinetic study of the oxidation rate of AA and DTT driven by species usually found in PM (transition metals and naphthoquinone (NQ)) was carried out. In particular, the influence of the concentration of Cu(II), Fe(II), Fe(III), Mn(II), Mn(III), and 1,4-NQ, and the type of fluid used in the assay (phosphate buffer (PB), phosphate buffer saline (PBS) and artificial lysosomal fluid (ALF)) is analysed and discussed. The reaction orders with respect to the AA/DTT and the active compound, and the kinetic rate constants were also determined. The results show great variability in OP values among the studied species depending on the fluid used; the OP values were mostly higher in PB0.05 M, followed by PBS1x and ALF. Moreover, different species concentration-responses for OP-DTT/OP-AA were obtained. These differences were explained by the different reaction orders and kinetic rate constants obtained for each active compound in each fluid. [Display omitted] •AA and DTT oxidation kinetics driven by metals are highly affected by the fluid used.•The order concerning the active compound concentration varies with the fluid used.•The presence of chloride reduces the kinetic rate of AA oxidation catalyzed by Cu.•Mn(III) is more active than Mn(II) in the OP-DTT assay.