Catalase-Loaded Silica Nanoparticles Formulated via Direct Surface Modification as Potential Oxygen Generators for Hypoxia Relief

Enzymes are biological catalysts that have many potential industrial and biomedical applications. However, the widespread use of enzymes in the industry has been limited by their instability and poor recovery. In biomedical applications, systemic administration of enzymes has faced two main challenges: limited bioactivity mostly due to rapid degradation by proteases and immunogenic activity, since most enzymes are from nonhuman sources. Herein, we propose a robust enzyme-encapsulation strategy to mitigate these limitations. Catalase (CAT) was encapsulated in nanoporous silica nanoparticles (CAT-SiNPs) by first chemically modifying the enzyme surface with a silica precursor, followed by silica growth and finally poly(ethylene glycol) (PEG) conjugation. The formulation was carried out in mild aqueous conditions and yielded nanoparticles (NPs) with a mean diameter of 230 +/- 10 nm and a concentration of 1.3 +/- 0.8 x 10(12) NPs/mL. CAT-SiNPs demonstrated high enzyme activity, optimal protection from proteolysis by proteinase K and trypsin, and excellent stability over time. In addition, a new electrochemical assay was developed to measure CAT activity in a rapid, simple, and accurate manner without interference from chromophore usually present in biological samples. Concentrations of 2.5 x 10(10) to 80 x 10(10) CAT-SiNPs/mL not only proved to be nontoxic in cell cultures using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay but also conferred cell protection when cells were exposed to 1 mM hydrogen peroxide (H2O2). Finally, the ability of CAT-SiNPs to release oxygen (O-2) when exposed to H2O2 was demonstrated in vivo using a rat model. Following the direct injection of CAT-SiNPs in the left kidney, partial pressure of oxygen (pO(2)) increased by more than 30 mmHg compared to the contralateral control kidney during the systemic infusion of safe levels of H2O2. This pilot study highlights the potential of CAT-SiNPs to generate O-2 to relieve hypoxia in tissues and potentially sensitize tumors against radiation therapy.

Automated summary

Enzymes are essential biological catalysts with diverse industrial and biomedical applications, however, their instability and poor recovery have hindered widespread use. A robust enzyme-encapsulation strategy using nanoporous silica nanoparticles has been proposed to address these limitations. The CAT-SiNPs showed high enzyme activity, protection from proteolysis, stability over time, and the ability to release oxygen in vivo, indicating their potential for tissue oxygenation and tumor sensitization to radiation therapy.