Improving the Stability, Water Solubility, and Antioxidant Activity of α-Tocopherol by Encapsulating It into Niosomes Modified with Cationic Carbamate-Containing Surfactants

Abstract

The low solubility of α-tocopherol in water and its susceptibility to photodegradation make it difficult for biological systems to absorb this natural antioxidant. To overcome these limitations, α-tocopherol was encapsulated in low-toxicity nanocontainers, namely, niosomes based on Tween 80 and cholesterol. The niosomes were modified with cationic surfactants containing a carbamate fragment. The size and charge of the particles were determined and their stability was assessed using dynamic and electrophoretic light scattering methods. It was found that the introduction of cationic surfactants to niosome formulations significantly improved their physicochemical properties and increased stability due to a positive charge of up to +40 mV being generated. Modified niosomes loaded with α-tocopherol were characterized by a hydrodynamic diameter of 100–120 nm, a narrow particle size distribution, and a high encapsulation efficiency of more than 90%. Testing the photochemical stability of α-tocopherol using a spectrophotometric method demonstrated that niosomes were able to protect this substance from UV irradiation. Luminescence analysis showed that the inclusion of α-tocopherol in niosomes increased their antioxidant activity by 30%. An acute toxicity study has demonstrated the safety of the systems. The LD₅₀ value for niosomes modified with carbamate-containing surfactants and loaded with α-tocopherol exceeded 10,000 mg·kg^–1 (mice, intraperitoneal and oral administration).