Catalytic Bioswitch of Platinum Nanozymes: Mechanistic Insights of Reactive Oxygen Species Scavenging in the Neurovascular Unit

Abstract

Oxidative stress is known to be the cause of several neurovascular diseases, including neurodegenerative disorders, since the increase of reactive oxygen species (ROS) levels can lead to cellular damage, blood–brain barrier leaking, and inflammatory pathways. Herein, we demonstrate the therapeutic potential of 5 nm platinum nanoparticles (PtNPs) to effectively scavenge ROS in different cellular models of the neurovascular unit. We investigated the mechanism underlying the PtNP biological activities, analyzing the influence of the evolving biological environment during particle trafficking and disclosing a key role of the protein corona, which elicited an effective switch-off of the PtNP catalytic properties, promoting their selective in situ activity. Upon cellular internalization, the lysosomal environment switches on and boosts the enzyme-like activity of the PtNPs, acting as an intracellular “catalytic microreactor” exerting strong antioxidant functionalities. Significant ROS scavenging was observed in the neurovascular cellular models, with an interesting protective mechanism of the Pt-nanozymes along lysosomal–mitochondrial axes.

Platinum Nanozymes Counteract Photoreceptor Degeneration and Retina Inflammation in a Light-Damage Model of Age-Related Macular Degeneration

“…Using transmission electron microscopy (TEM) on primary rat cortical neurons treated with PtNPs, we confirmed the active internalization of the nanozymes that, as previously shown in a mouse model, were found within intracellular vesicles, consistent with their endocytosis and endolysosomal fate (Figure 1F). 51 A quantification of the PtNP cellular uptake was also performed by mass spectrometry, confirming the key role of the protein coating in effective internalization. In fact, pristine PtNPs were only poorly internalized compared to RSAstabilized PtNPs, likely due to their lower colloidal stability in biological media (Figure 1G).…”

“…38 The use of 4 nm sized PtNPs allows for maximizing the surface-to-volume ratio (increasing the surface atom number available for reaction) without losing the size and shape control of the nanostructures. Citrate-capped PtNPs were prepared as previously reported, 51 yielding a reproducible monodisperse product with a narrow size distribution, as shown by transmission electron microscopy (TEM; Figure 1A) and dynamic light scattering (DLS; Figure S1). Considering that albumin is the most abundant protein of the vitreous humor, PtNPs were coated with rat serum albumin (RSA) to obtain a biomimetic cloak and good colloidal stability in the biofluids of interest.…”

“…38,49 Depending on the protein concentration in biological media, PtNPs are coated with protein corona that shields the catalytic activities of the PtNPs in the extracellular environment. 51 However, after cellular internalization and lysosomal accumulation, the antioxidant enzyme-like properties of PtNPs are completely recovered and boosted thanks to the proteolytic environment (corona degradation) and the acidic pH (enhancing PtNP performances). 51 Here we confirmed these properties and intracellular fate in primary rat neurons, showing that PtNPs protect neurons from ROS generation and inflammation-induced apoptosis.…”

“…Considering that albumin is the most abundant protein of the vitreous humor, PtNPs were coated with rat serum albumin (RSA) to obtain a biomimetic cloak and good colloidal stability in the biofluids of interest. 51 This step also allowed us to eliminate excess citrate from the solution, minimizing osmotic and pH changes in the biofluid composition after the in vivo injection. Gel-shift assay analysis of RSA-coated PtNPs showed a sharp band characterized by slower electrophoretic mobility compared to pristine PtNPs, due to the larger size and lower charge of the complex (Figure 1B).…”

Anti-inflammatory potential of platinum nanozymes: mechanisms and perspectives

“…However, once the PtNZs get internalized in the cell, they will end up in lysosomes, where the proteolytic enzymes can digest the protein corona, making the surface atoms (the nanozyme's active sites) available, thus reactivating the PtNZs. 78 Notably, the PtNZ activity is higher at physiological temperature (37 °C) compared to room temperature and is boosted at lysosomal pH (4.5–5) compared to the extracellular pH (7.4, i.e. , in the bloodstream).…”