Dynamics of the Interaction of Rare-Earth-Based Nanoparticles with Glutathione at Physiological pH

This study aimed to investigate the influence of pH on the interaction between CeO2 and LnVO4:Eu3+ (Ln = La, Gd, Y) nanoparticles (NPs) and low molecular weight antioxidants, such as glutathione, in both oxidized and reduced forms. Dynamic light scattering was utilized to assess the colloidal stability parameters of NPs, including GdYV04/Eu3+ (2 nm), CeO2 (2 nm and 10 nm), GdYVO4/Eu3+ (8 × 25 nm), and LaVO4/Eu3+ (8 × 80 nm), in the presence of glutathione in aqueous and buffer solutions within the physiological pH range of 6.7 to 7.8. Measurements of hydrodynamic diameter and zeta potential were conducted using a ZetaPAls/bi-masanalyzer (Brookhaven Instruments Corp., USA), operating in phase analysis light scattering mode. The experiments were performed at a scattering angle of 90° and λ = 659 nm, at a temperature of 25 °C. Notably, the zeta potential was found to be negative. The NP solutions, at final concentrations ranging from 250 to 500 μg/mL, were mixed in 10 mM HEPES buffer (at pH 6.7, pH 7.4, or pH 7.8). The samples also contained either reduced (GSH) or oxidized (GSSG) forms of glutathione, along with 0.2% albumin (BSA). The results revealed that both forms of glutathione interacted with NPs in aqueous and buffer solutions, leading to an increase in hydrodynamic diameter and agglomeration. The most significant changes occurred during the initial stages of the process, typically within the first 30 minutes. Notably, solutions exhibited stabilization due to diffusion during 24-hour incubation. Interestingly, for nanoceria (10 nm), no enlargement was observed in any of the studied systems. In contrast, for orthovanadate NPs of all types, the aggregation process was more pronounced, irrespective of the form of glutathione used, and proved irreversible under weakly alkaline conditions. These alterations in the aggregation stability of orthovanadate NPs in the presence of glutathione were accompanied by changes in zeta potential, which contrasted with both types of nanoceria, where potential changes remained negative. The addition of 0.2% BSA effectively prevented NP agglomeration and stabilized the systems under all studied conditions. In conclusion, our findings suggest interactions between both forms of glutathione and orthovanadate nanoparticles, potentially influencing the level and bioavailability of these molecules in biological systems and triggering adjustments in cellular glutathione-dependent antioxidant defense systems.