Preparation, characteristics and antioxidant activity of polysaccharides and proteins-capped selenium nanoparticles synthesized by Lactobacillus casei ATCC 393

Selenium (Se) is an essential element nutrient for human and animal health. Biogenic selenium nanoparticles (SeNPs) by microorganism possesses unique physical and chemical properties and biological activities compared to inorganic selenium and organic selenium. The study was conducted to establish a green, efficient and low-cost biotechnology for biogenic synthesis of SeNPs by Lactobacillus casei ATCC 393 (L. casei 393), and investigate its characteristics and antioxidant activities in vitro. The results showed that L. casei 393 transforms sodium selenite to SeNPs under anaerobic conditions. Moreover, 50-80 nm SeNPs were accumulated in the intracellular L. casei 393. The whole bacteria present distinct bright red color. SeNPs were isolated and characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray spectrometry (EDX), X-ray photoelectron spectroscopy (XPS), and fourier transform infrared spectroscopy (FT-IR). The results showed that the extracted SeNPs were capped by proteins and polysaccharides. Extracted biogenic SeNPs by L. casei 393 at a concentration less than 25 μg Se/mL had no cytotoxicity on the growth and proliferation of human normal epithelial cell (NCM460). The toxicity order of different selenium forms was: Sodium selenite > Selenium methionine > SeNPs synthesized by L. casei 393. Moreover, biogenic SeNPs by L. casei 393 induced HepG2 cells apoptosis via caspase cascade signaling and endocytosis of SeNPs. Moreover, SeNPs alleviated diquat or hydrogen peroxide (H2O2)-caused oxidative damage in intestinal epithelial cells, and reduced malondialdehyde (MDA) concentration and increased glutathione peroxidase (GPx) activity in culture medium. The findings suggest that biomolecules capped-SeNPs synthesized by probiotic L. casei 393 possess significant antioxidant and anticancer activities, and probiotic bacteria can provide a better alternative to synthesize biogenic elemental selenium particles with potential applications as anticancer and antioxidant agents.