Selenium Nanoparticles Based on Morinda officinalis Polysaccharides: Characterization, Anti-Cancer Activities, and Immune-Enhancing Activities Evaluation In Vitro

**Background:** Selenium is an essential trace element with important roles in immune function and cancer prevention, but inorganic selenium can be toxic. Nano-selenium offers lower toxicity and higher bioactivity, but tends to aggregate without a suitable dispersant. Morinda officinalis polysaccharides (MOP) have multiple pharmacological activities including immune enhancement and are non-toxic with good water solubility, making them a potential dispersant for selenium nanoparticles. This study aimed to prepare and characterize selenium nanoparticles stabilized with MOP (Se-MOP) and evaluate their anti-cancer and immune-enhancing activities in vitro.

**Methods:** Se-MOP was synthesized via a redox reaction between sodium selenite and ascorbic acid using MOP as a dispersant. Characterization included particle size and zeta potential measurement (Malvern Zetasizer), UV spectrometry (200–800 nm), ATR-FTIR spectrometry (4000–400 cm⁻¹), and transmission electron microscopy (TEM). Selenium content was determined spectrophotometrically after digestion. Anti-cancer activity was assessed using CCK8 assay on five cancer cell lines (HepG2, MCF-7, AGS, PC9, HCT8) at concentrations of 0–400 μg/mL for 48 and 72 h. Cell cycle analysis was performed on HepG2 cells using propidium iodide staining and flow cytometry after 24 h treatment with Se-MOP (0–400 μg/mL). Immune-enhancing activity was evaluated using mouse spleen lymphocytes from 5-week-old ICR male mice, measuring proliferation via CCK8 assay and cytokine gene expression (IFN-γ, IL-2, IL-4) by quantitative RT-PCR after 48 h treatment with Se-MOP (0.195–200 μg/mL) alone or in combination with PHA (10 μg/mL) or LPS (5 μg/mL).

**Key Results:** Se-MOP particles had a mean size of 67.25 ± 0.99 nm, PDI of 0.10 ± 0.02, and zeta potential of −21.17 ± 0.47 mV, indicating good stability. TEM confirmed spherical, evenly-sized, well-dispersed particles of 40–80 nm. UV spectrometry showed a maximum absorption peak at 266 nm for Se-MOP, distinct from sodium selenite (212 nm) and MOP (no peak). ATR-FTIR revealed hydroxyl vibration peak shifts from 3257 cm⁻¹ to 3238 cm⁻¹ and a new peak at 668 cm⁻¹ (Se-H bond). Selenium content was 0.99 ± 0.01%. Se-MOP showed significant inhibition of all five cancer cell lines (p < 0.01), with the strongest effect on HepG2 cells (IC50 of 2 μg/mL at 48 h and 1 μg/mL at 72 h). MOP alone showed only weak anti-tumor activity. Cell cycle analysis demonstrated G0/G1 phase arrest: G1 phase decreased from 53.43% to 4.33%, while G2 phase increased from 15.35% to 64.87% after Se-MOP treatment (p < 0.05 to p < 0.0001). For immune enhancement, Se-MOP promoted lymphocyte proliferation with maximum proliferation rate at 12.5 μg/mL. Cytokine expression analysis showed significantly increased IFN-γ (up to 5.31-fold at 1.56 μg/mL, p < 0.0001), IL-2 (up to 3.75-fold at 1.56 μg/mL, p < 0.0001), and IL-4 (up to 7.42-fold at 0.78 μg/mL, p < 0.0001) compared to PHA control.

**Clinical Implications:** Se-MOP demonstrates potent anti-cancer activity against multiple cancer cell lines, particularly liver cancer cells, through G0/G1 cell cycle arrest, while simultaneously enhancing immune function by promoting lymphocyte proliferation and increasing cytokine expression. The combination of selenium nanoparticles with MOP not only improves nanoparticle stability but also significantly enhances the biological activity of MOP. With a selenium content of 0.99%, the WHO maximum daily selenium intake of 400 μg would require only 0.04 g of Se-MOP per day, suggesting high supplementation efficiency. These findings support Se-MOP as a promising candidate for cancer therapy and immune modulation, though the binding mechanisms between selenium and MOP require further NMR verification, and in vivo studies are needed to confirm these in vitro results.