Selenium Nanoparticles: Synthesis, Stability and In Vitro Evaluation in Human Lens Epithelial Cells

Background/Objectives: Oxidative stress plays a critical role in the development of ocular diseases such as cataracts. Selenium nanoparticles (SeNPs) offer antioxidant benefits with low toxicity. This study aimed to evaluate the antioxidant activity of SeNPs coated with D-α-tocopheryl polyethylene glycol succinate (TPGS) in human lens epithelial (HLE) cells. Methods: SeNPs were synthesised by reducing sodium selenite with ascorbic acid in the presence of TPGS. Physicochemical characterisation was carried out using dynamic light scattering to assess size and surface charge. Antioxidant activity was measured by a 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay. Cytocompatibility was assessed on adult retinal pigment epithelial (ARPE-19) and HLE cells using PrestoBlue. Functional antioxidant performance was determined through enzymatic assays for glutathione peroxidase (GPx), thioredoxin reductase (TrxR), and glutathione (GSH), and lipid peroxidation was assessed using malondialdehyde (MDA) quantification. Catalase mimicry was evaluated under 3-amino-1,2,4-triazole (3-AT)-induced inhibition. Results: The optimal SeNP formulation had an average hydrodynamic diameter of 44 ± 3 nm, low PDI (<0.1), and a surface charge of -15 ± 3 mV. These TPGS-SeNPs demonstrated strong radical scavenging (EC₅₀ ≈ 1.55 µg/mL) and were well tolerated by ARPE-19 cells (IC₅₀ = 524 µg/mL), whereas HLE cells had a narrower biocompatibility window (≤0.4 µg/mL, IC₅₀ = 2.2 µg/mL). Under oxidative stress, SeNPs significantly enhanced GPx and TrxR activity but did not affect GSH or MDA levels. No catalase-mimetic activity was observed. Conclusions: TPGS-SeNPs exhibit potent antioxidant enzyme modulation under stress conditions in HLE cells. Although not affecting all oxidative markers, these nanoparticles show promise for non-invasive strategies targeting lens-associated oxidative damage, including cataract prevention.