Intracellular Antioxidant Activity of Biocompatible Citrate-Capped Palladium Nanozymes

Abstract

A method for the aqueous synthesis of stable and biocompatible citrate-coated palladium nanoparticles (PdNPs) in the size range comparable to natural enzymes (4–8 nm) has been developed. The toxicological profile of PdNPs was assessed by different assays on several cell lines demonstrating their safety in vitro also at high particle concentrations. To elucidate their cellular fate upon uptake, the localization of PdNPs was analyzed by Transmission Electron Microscopy (TEM). Moreover, crucial information about their intracellular stability and oxidation state was obtained by Sputtering-Enabled Intracellular X-ray Photoelectron Spectroscopy (SEI-XPS). TEM/XPS results showed significant stability of PdNPs in the cellular environment, an important feature for their biocompatibility and potential for biomedical applications. On the catalytic side, these PdNPs exhibited strong and broad antioxidant activities, being able to mimic the three main antioxidant cellular enzymes, i.e., peroxidase, catalase, and superoxide dismutase. Remarkably, using an experimental model of a human oxidative stress-related disease, we demonstrated the effectiveness of PdNPs as antioxidant nanozymes within the cellular environment, showing that they are able to completely re-establish the physiological Reactive Oxygen Species (ROS) levels in highly compromised intracellular redox conditions.

Synthesis of Citrate-Coated Penta-twinned Palladium Nanorods and Ultrathin Nanowires with a Tunable Aspect Ratio

“… 52 On the other hand, recent studies on the toxicity of the material per se show that Pd NPs synthesized without polymers, surfactants, or toxic stabilizers do not cause cellular damage in vitro , while having beneficial antioxidant properties. 4 Moreover, there is growing evidence from in vitro and in vivo studies that pristine Pd NPs do not modify cellular metabolism. 5 , 53 − 55 …”

“…The assay was carried out following the protocol provided by the manufacturer and previously published protocols. 4 DMEM supplemented with 10% FBS solutions containing Pd nanowires and nanorods at concentrations of 5, 10, and 25 μg/mL were used. After incubation for 24 and 48 h, viability was measured.…”

“…The plasma membrane integrity was measured by detecting lactate dehydrogenase (LDH) release with CytoTox-ONE (Promega), following the protocol previously published. 4 Cells were incubated with a solution containing nanorods and nanowires at increasing concentrations (from 5 to 25 μg/mL) for 24 and 48 h, and the release of LDH was then measured.…”

Micro‐Bio‐Chemo‐Mechanical‐Systems: Micromotors, Microfluidics, and Nanozymes for Biomedical Applications

“…Notably among them was citrate-capped palladium nanozyme that exhibited efficient antioxidant properties within the cellular environment. [134] Noble metal nanoparticles such as Au, Pd, and Pt demonstrate remarkable catalytic activities and intrinsic antioxidant properties. [135,136] Functionalizing these nanomaterials with various ligands can greatly improve their biocompatibility and broaden their biomedical application potentials.…”

“…Notably among them was citrate‐capped palladium nanozyme that exhibited efficient antioxidant properties within the cellular environment. [ 134 ]…”