Cellular and molecular interactions of engineered nanomaterials

Abstract

In the past few years, nanotechnology has grown explosively as an enabling technology. Nanomaterials (NMs) exceptional properties in comparison to their bulk counter parts has led its increased production and wide application in commercial purposes like medicines, sunscreen, paints, bioimaging probes, therapeutic and antimicrobial agents. Several NMs are reported to exhibit natural enzymes like properties which are known as “Nanozymes”, and are used in several biomedical applications. Nanozymes can overcome the drawbacks of natural existing enzymes like difficult synthesis, denaturation, and storage. Certain nanoparticles (NPs), like cerium oxide NPs (CeNPs), gold NPs (AuNPs), iron oxide NPs (IONPs) mimics the natural enzyme activities like superoxide dismutase (SOD), catalase, and peroxidase. Among these NPs, CeNPs are well explored as a free radical scavenger both in in vitro and in vivo system and has also shown to be used in the treatment of several oxidative stress related diseases like tumor, Parkinson’s, Alzheimer disease. CeNPs are known to exhibit unique antioxidant property due to auto-regenerative redox cycle on its surface between Ce3+ and Ce4+ oxidation state. Cerium oxides with high Ce3+ and Ce4+ oxidation state atoms exhibit biological SOD and catalase enzyme like activity, respectively. But due to their high surface area, it is possible that NPs can react with surrounding metal ions which can alter their catalytic properties. Thus, in order to explore the antioxidant properties of NPs it is also important to check their interaction with metal ions present in surrounding medium. Although the metal oxide NPs such as, zinc oxide (ZnO), titanium dioxide (TiO2) are known for their importance in several industrial applications but are reported to produce harmful effect on human health when released in to environment. These NPs are reported to be used in the several commercial products like cosmetics, electronics, paints etc. Extensive use of these particles ends up its fate in municipal sewage treatment plants, where they can exert harmful effect and eliminate microbial community which play vital roles in ecosystem. More use of nano-enabled products throws more NPs in air, soil and water environment, where its persistence and consequent accumulation is possible. Studies to date have reported about the NPs induced oxidative DNA damage in microorganisms which ultimately leads to cell death. Thus, before extensive use it is very important to check the safety assessment of NPs. In the present study, we have evaluated the stability and catalytic properties of CeNPs in different biological relevant buffers and then also evaluated its antioxidant potential in in vitro under oxidative stress conditions. Firstly, CeNPs (4+) stability and its catalase mimetic activity was explored in different biological relevant buffers. Results suggest that catalase mimetic activity and surface chemistry of CeNPs (4+) does not altered by phosphate anions. Similarly, different pH conditions and cell culture media also does not exert any effect on catalytic property of CeNPs (4+). Although, upon dispersion into complete cell culture media, NPs tends to form “protein corona” on their surface but this protein coating also did not alter the catalase mimetic activity. Also, H2O2 exposure confirms that phosphate anions did not block the redox cycling of CeNPs (4+) between 3+/4+. The evidences obtained suggest that CeNPs (4+) retain their catalase mimetic activity even when exposed to the phosphate buffer. Further, CeNPs (4+) antioxidant effect was evaluated against 3-Amino-1,2,4-Triazole (3-AT) induced oxidative stress which is known to act as an irreversible catalase inhibitor. Result suggest that the CeNPs (4+) were significantly internalized into WRL-68 cells and also efficiently scavenge the free radicals formed inside cells due to 3-AT exposure. CeNPs (4+) also protect the 3-AT exposed cells from nuclear fragmentation and increases the viability of cells by preventing them from undergoing apoptosis process. CeNPs (4+) improved the glucose uptake in cells in order to maintain the energy source which diminished due to 3-AT exposure. Further, result also suggests that, CeNPs (4+) itself acts as a radical scavenger and did not exert its protective effect by increasing the level of natural antioxidants like glutathione (GSH) and catalase present in cells. Coating of CeNPs with polyethylene glycol (PEG) increases the retention time of particles and also protect from macrophage detection and clearance by reticuloendothelial system (RES) in mammals. In this study, PEGylated CeNPs (3+) was shown to protect the HaCaT cells from buthionine sulfoximine (BSO) induced oxidative stress which inhibits the GSH production inside cells. CeNPs efficiently scavenge the free radical formed inside cells and also prevent the cells from genotoxic effect caused by BSO. In the presence of PEGylated CeNPs (3+), cells did not require the natural antioxidant proteins and genes like thioredoxin reductase (TrxR) and peroxiredoxin 6 (Prx6) to protect it from oxidative insult. CeNPs itself acts as a radical scavenger and protect cells from oxidative stress caused due to GSH depletion. Safety assessment of NPs were evaluated by exposing it with Deinococcus radiodurans which can protect itself from oxidative stress induced DNA and protein damage. Different metal oxide NPs like CuO, ZnO and TiO2, are used to assess their internalization and effects on the cell viability and ROS generation in D. radiodurans cells. Result shows that among all the tested NPs, ZnO NPs exposed cells shows less viability in comparison to CuO and TiO2 NPs exposed cells. ZnO NPs were shown to induce oxidative stress and thus toxicity in D. radiodurans. Detailed study showed that ZnO NPs was significantly internalized into bacterial cells and causes ROS generation, thiol depletion, DNA and protein damage inside cells which are thought to be the main cause of oxidative stress and thus cell death. It also causes impairment of genes involved in DNA repair and metabolic pathways, which could also be the major cause of toxic response induced by ZnO NPs.