Abstract: In this work, black sesame melanin was used as template and reducing agent to prepare a melanin-nanoselenium complex. The preparation process was optimized, and its structure and morphology were characterized. Also, its antioxidant capacity in vitro was tested, and its protective effect on oxidative damage of red blood cells and EAhy926 endothelial cells was evaluated. Its anticancer activity and biocompatibility were investigated by using lung cancer cell line A549 and shrimp killing experiment. The results showed that the optimum conditions for the synthesis of melanin-nanoselenium complex were as follows: volume ratio of melanin solution (0.3 mg/mL) to selenium dioxide solution (0.555 mg/mL) 9:5, pH 7, and reaction time 5 h with magnetic stirring (400 r/min). The results of X-ray photoelectron spectroscopy (XPS) showed that Se4+ was completely reduced. The results of infrared (IR) spectroscopy indicated that the carboxyl and conjugate structures of melanin might be involved in the reaction. According to the results of characterization by synchronous light scattering, the particle size of the melanin-nanoselenium complex was approximately 200 nm, and it was stable and could be well distributed in water dispersion system. The complex remained stable for 2 h in simulated gastric juice, and was pH tolerant. It could be released slowly in simulated intestinal juice, thus having the potential for long-term sustained release. In vitro antioxidant results showed that the scavenging capacity against 2,2’-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical cation and total reducing power of the complex were significantly better than those of selenium dioxide. The complex significantly inhibited hemolysis of red blood cells and oxidative damage of EAhy926 endothelial cells induced by hydrogen peroxide, and had inhibitory activity on lung cancer cells. The toxicity of this complex was weaker than that of selenium dioxide, whose semi-lethal concentration (LC50) values were 347.393 and 19.781 µg/mL, respectively. This study is meaningful for guiding further research on melanin resources and the preparation of melanin-nanoselenium complex, and also provides a theoretical basis for the use of melanin-nanoselenium complex as a dietary selenium supplement.

Key words: melanin-nanoselenium complex; sustained release performance; antioxidant activity; anticancer activity