Associate Professor  Istvan  Szilagyi
University of Szeged,  Hungary

Title: Design of Inorganic-Organic Hybrid Nanomaterial Dispersions for Biocatalytic Decomposition of Reactive Oxygen Species

Abstract:

Oxidative stress caused by reactive oxygen species (ROS) induces several diseases by damaging cell constituents. Antioxidant enzymes including superoxide dismutase (SOD) and horseradish peroxidase (HRP) are members of the primary defence system developed against ROS. However, their supplementation to living organisms is limited due to their high sensitivity to the environmental conditions such as pH, ionic strength and presence of protein inhibitors. To improve the resistance, enzyme immobilization on biocompatible nanomaterials is a promising way, where nanocomposites of antioxidant activity can be obtained. These delivery systems must possess high colloidal stability to avoid aggregation, once the particles are dispersed in bio-fluids. 

To overcome these challenges, we aimed at the development of antioxidant hybrid materials consisting of SOD and/or HRP enzymes as well as polyelectrolyte-functionalized inorganic nanoparticles such as layered double hydroxides, halloysite nanotubes and titania nanosheets [1]. 

Surface functionalization of the inorganic nanoparticles was carried out with natural (heparin and protamine) [2] and synthetic (poly(styrene sulfonate) or poly(diallyldimethylammonium chloride)) [3] polyelectrolytes via electrostatic interaction and hydrogen bonding. Due to the precise optimization of the experimental conditions during preparation, stable dispersions were obtained, which possessed high resistance against salt-induced aggregation. Immobilization of SOD and/or HRP enzymes was carried out individually and also together by physical adsorption on the polyelectrolyte-functionalized surfaces of the inorganic particles. The obtained particlepolyelectrolyte- enzyme hybrids possessed remarkable structural stability, i.e., no enzyme leakage was detected even in long-term experiments. The composites showed high activity in decomposition of superoxide radicals and hydrogen peroxide in standard biochemical assays. The behaviour of hybrid particles containing both SOD and HRP enzymes was tested in the presence of living cells and the results of the experiments revealed that (i) they are not toxic, (ii) they penetrate through the cell wall and (iii) they decrease the intracellular ROS concentration and thus, reduce the oxidative stress significantly. 

Summarily, the obtained bionanocomposites consisting of inorganic particles, antioxidant enzymes and polyelectrolytes showed excellent structural, colloidal and functional stability and they are promising antioxidant candidates in applications, wherever the goal is to reduce oxidative stress in biological systems.

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