Interaction of alkali and alkaline earth ions with Ochratoxin A

The effect of alkali and alkaline earth ions on the chemical equilibrium of mono- and dianionic forms of the mycotoxin Ochratoxin A (OTA) and their bonding onto the surface of Bovine Serum Albumin (BSA) have been investigated by fluorescence spectroscopy and fluorescence polarization techniques. Our results show that alkali metal ions shift the chemical equilibrium towards formation of dianionic form of OTA. Furthermore, the alkaline earth ions can compete with BSA for binding to OTA when these ions are present in millimolar concentrations. Our data also highlight the possibility that the "free" fraction of OTA (not bound onto the surface of albumin) or at least a part of it is present in cation-bound form in body fluids. These observations are supported by stability constants and quantum-chemical calculations. Among the studied alkaline metal ions magnesium showed the highest affinity towards OTA under physiological conditions. Further research is required to analyze the potential significance of Mg2+–OTA complex in cellular uptake and/or elimination of the toxin in the human body. - Highlights: ► Fluorescence spectroscopy reveals cation–Ochratoxin A (OTA) interactions. ► Alkali ions shift the equilibrium of OTA to formation of a dianionic structure. ► Alkaline earth ions directly bind to OTA in the order: Mg2+, Ca2+, Ba2+. ► Quantum chemical calculations and logK values support our experimental data.