Abstract: BACKGROUND: Sulfasalazine has been commonly used in the treatment of ulcerative colitis. Traditional administration methods have poor absorption, low availability, and are often accompanied by serious toxic side effects. Compared with traditional drug delivery methods, colon-targeted nano-delivery can protect the drug from adverse environment and improve the local absorption and bioavailability of the drug. 
OBJECTIVE: Sulfasalazine@polylactic acid-glycolic acid copolymer-chitosan-pectin-chitosan nanoparticles were prepared for characterization and vitro evaluation, and the safety of nanoparticles as drug carriers was verified at the cellular level.
METHODS: The O/W emulsion method and electrostatic layer-by-layer self-assembly technique were used to prepare sulfasalazine@polylactic acid-glycolic acid copolymer-chitosan-pectin-chitosan nanoparticles. The morphology of the nanoparticles was observed using transmission electron microscopy. Laser particle sizer was used to detect nanoparticle potential and particle size. Drug loading and encapsulation rates of nanoparticles were determined by ultraviolet spectrophotometry. The nanoparticles were dissolved in PBS with different pH values (1.2, 6.8, 7.4) to detect the release of sulfasalazine by the nanoparticles. The nanoparticle solutions of different mass concentrations (10, 20, 50, 100, 200 mg/L) were co-cultured with macrophages, and after 48 hours, the cell viability was detected by CCK8 assay. The 20 mg/L nanoparticle solution was co-cultured with macrophages, and after 24 hours, rhodamine fluorescent staining was performed for the uptake of nanoparticles by cells.
RESULTS AND CONCLUSION: (1) Transmission electron microscopy images showed that the nanoparticles were ellipsoidal with uniform particle size; with a particle size of 290.9 nm, a potential of 19.8 mV and a dispersion index of 0.295, with good dispersion of the individual nanoparticles. The encapsulation rate of the nanoparticles was 75.68% and the drug loading was 22.24%. (2) In vitro release experiments showed that within 36 hours, the release rate of nanoparticles increased with the increase of PBS pH. The prepared nanoparticles barely released sulfasalazine at low pH=1.2 and released slowly and continuously up to pH 7.4, indicating that the nanoparticles had pH-dependent and good slow release characteristics. (3) Different concentrations of nanoparticles had no obvious effects on the activity of macrophages and did not show cytotoxic effects. (4) Cellular uptake experiments showed that nanoparticles could be taken up by cells after 6 hours of culture. The nanoparticles entered the macrophages within 12-24 hours. (5) The sulfasalazine@polylactic acid-glycolic acid copolymer-chitosan-pectin-chitosan nanoparticles have good slow-release properties and cytocompatibility, can be taken up by macrophages with high uptake efficiency. 

Key words: sulfasalazine, polylactic acid-glycolic acid copolymer, chitosan, pectin, nanoparticles, in vitro evaluation, ulcerative colitis