Confinement of Metalloenzymes in PEGylated Liposomes to Formulate Colloidal Catalysts for Antioxidant Cascade

Abstract

Antioxidant cascade reactions detoxifying reactive oxygen species are of significance to control oxidative stresses-triggered diseases. In the present work, the antioxidant catalysts were prepared through the confinement of dual metalloenzymes in liposomes. The amino groups of superoxide dismutase (SOD) were conjugated to the carboxyl groups-bearing liposomes encapsulated with the catalase (CAT) to formulate a spatially organized antioxidant reaction network. The activity of SOD and CAT in the liposomal system was evaluated in detail on the basis of the prolonged xanthine oxidase/xanthine reaction producing superoxide anion radicals (O2̇–) and hydrogen peroxide (H2O2) coupled with redox reactions of cytochrome c. The liposome-confined SOD and CAT molecules were clearly demonstrated to catalyze the sequential disproportionation of O2̇– and H2O2 at 25 °C in a potassium phosphate buffer solution (pH = 7.8) under moderate transfer resistance with respect to the intermediate product (H2O2) within the liposomes. Furthermore, the liposomal catalysts were modified with the poly­(ethylene glycol) (PEG)-conjugated lipids with the molecular mass of the PEG moiety of about 5000 through the post-PEGylation approach. The mean hydrodynamic diameter of the PEGylated liposomal catalysts was 140–150 nm. The dual enzyme activity in liposomes and the thermal stability of the encapsulated CAT were practically unaffected by the PEGylation. The above liposome-based antioxidant catalysts are highly biocompatible, PEG-modifiable, and reactive, thereby making the catalysts potentially applicable to therapeutic materials exhibiting functionality similar to cellular peroxisomes.

Multi-enzyme mimics – cracking the code of subcellular cascade reactions and their potential biological applications

“…Peroxidase enzymes are the enzymes with a heme position that break down peroxide compounds into hydroxyl functionalities containing products, where the heme position acts as a catalytically active site. 36 ROOR' + 2 e À + 2 H + + (POD) -ROH + R'OH (2) PODs are a large family of isozymes that can catalyze the oxidation of products in cells. These biological reactions involve hydrogen peroxide or organic hydroperoxides and an electron donor substrate.…”

“…Researchers tried to study such multiple cascades in living cells by developing artificial peroxisomes, where multiple enzymes are combined over a biofriendly scaffold to mimic the peroxisome present in cells. [1][2][3] Such a system, although completely consisting of biological entities, could not be sustained for a very long time, because it had issues with stability, poor substrate versatility and diversity, low adaptability to non-biological reactions, low tolerance to extreme environmental conditions, denaturation at high temperatures, and storage, recovery and cost issues. 4,5 Therefore, researchers diverted their attention towards the individual smaller entities that are responsible for driving these cascade reactions, i.e., enzymes, and termed the artificial materials that could mimic the natural enzymes as artificial enzymes.…”

“…2 O molecules or carboxyl groups or from the acidic medium. However, the POD-like activity of the GCQDs can be enhanced by increasing the density of functional groups through reducing the size of the GCQDs.131 Song et al synthesized graphene oxide (GO) modified with -COOH groups, where -C-O acted as a catalytically active site, while -CQO acted as the binding site for POD-like activity.…”