Table 2.

Studies on the protective effect of nanoparticles in biological systems

Nanoparticles	Size		Results	References
Bovine serum albumin-coated magnesium nanoparticles		~ 4–8 nm	BSA-coated magnesium nanoparticles showed catalase-like activity. The synthesized nanoparticles protected the hepatocytes from the 3-AT induced oxidative stress and degraded the hydrogen peroxide into water and oxygen. The 3-AT exposure could not affect the catalase-like activity of the nanoparticle	(Shah et al, 2020)
Nanoceria–gold nanoparticles conjugates with a coating of polyoxometalate, 12-phosphotungstic acid		Nanoceria ~ 27 nm and gold NPs ~ 10 nm	The nanoceria and gold NPs form a multienzyme complex in synthesized conjugates. Polyoxometalate,12-phosphotunstic acid-coated nanoceria improved the catalytic activity of gold NPs and showed 82% better efficiency in converting the 4-nitrophenol into 4-aminophenol in vitro. The gold NPs showed increased peroxidase-like activity in nanocomposites	(Shah et al, 2021)
Nanocomposites of cerium oxide NPs, sulforaphane loaded on silk fibroin NPs (SFSNPs), and carbon dots (CDs)		~ 365–385 nm	CeNPs–CDs–SFSNPs nanocomposites, multifunctional formulations which showed diagnostic and therapeutic properties, were prepared. Sulforaphane is an antioxidant drug. The CeNPs catalyzed the neutralization of the ROS, whereas CDs acted as a probe for fluorescence imaging of cells, simultaneously. Hence, the nanocomposites behaved as carriers, antioxidants, and probes for imaging	(Passi et al, 2020)
Poly (ethylene glycol) and poly (acrylic acid) coated cerium oxide NPs	~ 7.8 nm		The synthesized cerium oxide NPs have been studied for their catalytic activities to mimic antioxidative enzymes. The coatings of poly (ethylene glycol) and poly (acrylic acid) on cerium oxide NPs inhibited the catalase-like activity, impaired oxidase-like activity, had not affected the superoxide dismutase-like activity, and enhanced the peroxidase-like activity of NPs	(Baldim et al. 2020)
Cerium vanadate nanorods	~ 50–150 nm		Superoxide dismutase-like activity of synthesized nanorods was investigated in the SH-SY5Y, neuronal cells. They neutralized the superoxides which were generated due to the exposure of diethyldithiocarbamate (DDC), a SOD inhibitor. The nanorods also retained the structural integrity of mitochondria	(Singh et al, 2021)
A PTEN plasmid and a siRNA carrying cerium oxide nanoparticles	~ 98–136 nm		The PTEN is a tumor suppressor gene and its loss results in overexpression of phosphatidylinositol 3-kinase (PI3K)/AKT pathway which leads to increased cellular proliferation. The cerium oxide nanoliposomes incorporating the PTEN plasmid and AKT3 siRNA were studied internalized in the prostate cancer cell culture model (PC-3) and shown to internalize by endocytosis. The nanoliposomes induced DNA fragmentation then apoptosis which ultimately led to cell death. The cerium oxide NPs in the formulation behaved as the SOD enzyme and reduced the excess levels of free radicals from cancer cells	(Bhagat and Singh, 2020)
Cerium oxide nanorods	~ 1.88 nm		The WRL-68 cells (hepatocyte model) were treated with Buthionine sulfoximine (BSO). BSO depletes the cells of GSH and induces redox imbalance. This study showed the SOD-like activity of synthesized cerium oxide nanorods which catalyzed the neutralization of free radicals generated during the BSO exposure in cells	(Yadav and Singh, 2021a, b)
Cobalt-doped iron oxide nanozymes	~ 94.6 ± 8.6 nm		The Co-Fe3O4 nanoparticles when applied in human renal cancer cells, killed the cells by inducing oxidative stress. The synthesized nanoconjugates switched on the oxidative stress in the presence of H2O2, which led to the bursting and killing of the cancer cells. The nanoparticles typically behaved as peroxidase enzyme activity and killed the cancer cells	(Wang et al, 2019)