Synthesis and Characterisation of Marine Docosahexaenoic Acid-Encapsulated Chitosan Nanoparticles (DHA@CSNP) and Evaluation of their Antioxidant and Cytotoxic Activities

Docosahexaenoic acid (DHA) is an essential ω-3 polyunsaturated fatty acid with demonstrated health benefits, including neuroprotection, anti-inflammatory effects and anticancer activity. However, its poor water solubility, susceptibility to oxidative degradation and low bioavailability limit therapeutic applications. This study aimed to improve the stability and therapeutic efficacy of DHA through nano-encapsulation within chitosan nanoparticles (DHA@CSNPs), synthesised through ionic gelation method using sodium tripolyphosphate as a crosslinking agent. The synthesised nanoparticles were characterised by SEM, FE-SEM with EDX, FTIR, XRD, DLS and zeta potential analysis. DHA@CSNPs exhibited nanoscale morphology (average particle size 76.53 ± 3.41 nm), semi-crystalline structure and a positive surface charge of 21.63 mV, confirming colloidal stability and successful encapsulation. Encapsulation efficiency was 83.38 ± 1.48% and in vitro release studies demonstrated pH-dependent sustained release, with higher release at acidic pH, mimicking tumor microenvironments. Antioxidant potential was evaluated using ABTS, DPPH, hydroxyl, superoxide, nitric oxide and reducing power assays, showing enhanced radical-scavenging activity and lower IC50 values for DHA@CSNPs than for free DHA. Cytotoxicity against MDA-MB-231 triple-negative breast cancer cells revealed a dose-dependent decrease in cell viability with an IC50 of 59.30 µg/mL and pronounced morphological changes indicative of apoptosis. These results highlight that chitosan-based nanocarriers effectively improve DHA’s stability, bioavailability and therapeutic potential.