Berberine-oleanolic acid self-assembled nanoparticles: Enhanced stability, cellular uptake, and anti-inflammatory activity

Berberine (BBR) and oleanolic acid (OA) are natural bioactive compounds with recognized anti-inflammatory properties. However, their therapeutic potential is often limited due to poor solubility and low bioavailability. Different from the traditional polymeric or lipidic-encapsulation strategies, this study successfully prepared carrier-free co-assembly BBR-OA nanoparticles (B-O NPs) using a solvent exchange method, which could achieve higher payload. Under optimal conditions, BBR and OA self-assembled to form uniform spherical nanoparticles, with an average particle size of approximately 130 nm. B-O NPs were negatively charged with a zeta potential of -42.43 mV and demonstrated improved water solubility and stability compared to the BBR and OA alone. The self-assemble mechanism of BBR and OA was further elucidated by molecular dynamics simulations and molecular docking analysis, highlighting the role of electrostatic and hydrogen bonding interactions. In vitro studies revealed that B-O NPs displayed obvious pH responsiveness and sustained BBR release capabilities in simulated gastric fluid (pH 2.0) and physiological buffer (pH 7.4) when compared to free BBR. Cellular experiments revealed that B-O NPs had enhanced cellular uptake and transmembrane transport ability. Moreover, in a lipopolysaccharide (LPS)-stimulated inflammatory model of RAW 264.7 macrophages, B-O NPs effectively reduced the intracellular reactive oxygen species (ROS) and downregulated the inflammatory mediators, including NO, TNF-α, IL-1β, and IL-6, showing significantly higher anti-inflammatory activity than free BBR, OA, or their physical mixture. These findings suggested that B-O NPs may provide a promising approach to improve the bioavailability and biological activity of small natural molecules.