Preparation of soluble stable C₆₀/human serum albumin nanoparticles via cyclodextrin complexation and their reactive oxygen production characteristics.

AIMS: The stability of solutions of fullerene C₆₀ with human serum albumin (C₆₀/HSA) has not been studied in detail. In this study, we report on the preparation of stable C₆₀/HSA solutions that are formed via the formation of C₆₀/HP-β-CyD nanoparticles, i.e. by transferring C₆₀ molecules from HP-β-CyD to HSA molecules, and an investigation of the reactive oxygen species on the behavior of the resulting C₆₀/HSA.

MAIN METHODS: Structural and functional properties were examined by spectroscopic techniques, including circular dichroism (CD), fluorescent spectra (FI), and electron spin resonance spin-trapping method, and by cell viability test using A549 cells.

KEY FINDING: Aqueous C₆₀/HSA solutions with a small distribution size, excellent dispersion stability and a high dispersion concentration were obtained without the use of organic solvents. CD and FI spectra indicated that the HSA had undergone structural changes as the result of C₆₀/HSA formation. Binding experiments indicated that C₆₀/HSA had increased Site I and Site II-ligand binding capabilities. The HSA, in the form of C₆₀/HSA was, therefore, conformationally altered, and its binding capabilities were enhanced. Radical scavenging studies using the 1,1'-diphenyl-2-picrylhydrazyl radical showed that C₆₀/HSA had an increased antioxidant activity, compared to HSA alone. Further, C₆₀/HSA efficiently generated not only superoxide anion radicals O₂·- but also singlet oxygen ¹O₂ through photoirradiation. C₆₀/HSA showed cell toxicity characteristics after light irradiation, but no toxicity was observed in the absence of irradiation.

SIGNIFICANCE: C₆₀/HSA not only has an excellent stability and antioxidant activity, but also has substantial phototoxicity properties. It thus appears that HSA can be used as a carrier of C₆₀in drug delivery systems for photodynamic therapy.