Enhanced oral delivery of zeaxanthin via chitosan/alginate nanoparticles: Optimizing stability and antioxidant efficacy in retinal cells

Abstract

Zeaxanthin (ZT), a lipophilic carotenoid with strong antioxidant potential, suffers from poor aqueous solubility and low oral bioavailability, which limits its therapeutic application. In this study, chitosan/alginate nanoparticles (CS/ALG-NPs) were developed and optimized for oral ZT delivery using a Box-Behnken design. The optimized NPs showed a particle size of 268 ± 35 nm, a zeta potential of −25.2 ± 0.8 mV, and an encapsulation efficiency of 75.4 ± 3.4%. In vitro release under simulated gastrointestinal (GI) conditions exhibited sustained release with improved digestive stability and bioaccessibility compared to free ZT. The optimized ZT-CS/ALG-NPs exhibited favorable stability, maintaining particle size, surface charge, and encapsulation efficiency during storage at 4 °C, and retained their spherical morphology and uniform dispersion after simulated GI digestion, supporting their potential for oral delivery applications. In ARPE-19 cells, ZT-CS/ALG-NPs significantly reduced intracellular reactive oxygen species, restored antioxidant enzyme activities (SOD, CAT, GPx), and increased intracellular glutathione (GSH) levels compared to free ZT. Under H<inf>2</inf>O<inf>2</inf>-induced oxidative stress, ZT-CS/ALG-NPs reduced the expression of pro-apoptotic proteins (Bax and cytochrome c) and increased the expression of anti-apoptotic protein (Bcl-2) in ARPE-19 cells (vs H<inf>2</inf>O<inf>2</inf> group). Transmission electron microscopy and flow cytometry confirmed cellular uptake. These findings demonstrate the potential of CS/ALG-NPs as a polysaccharide-based oral delivery system to enhance the stability, bioaccessibility, and antioxidant efficacy of hydrophobic bioactives such as zeaxanthin.