Formulation of tocopherol nanocarriers and in vitro delivery into human skin

Tocopherol is stronger antioxidant than tocopherol acetate but due to its viscous form, poor water solubility, instability to light and skin irritation issues it is not used in the current marketed formulations. To overcome the drawbacks, tocopherol was formulated as nanostructured lipid carriers and nanoemulsion. The objective of the study was to formulate tocopherol as nanocarriers.

Nanostructured lipid carriers (NLCs) and nanoemulsion (NE) were prepared by homogenization technique. They were characterized for particle size and zeta potential. In vitro release study was performed using dialysis method, and skin permeation was carried out using human cadaver skin. Further, antioxidant activity was tested by ferric reducing antioxidant potential (FRAP) assay and skin irritation testing was performed on Epiderm skin model. Effect of UV degradation was studied using solar simulator.

The size and zeta potential of NLC was 67.0 nm ± 1.2 and -32.0 mV ± 1.2, whereas for NE, it was 586.5 nm ± 209.6 and -10 mV ± 0.6. In vitro release study showed that 30% of tocopherol was released from NLC in the first 2 h of the study as compared to only 4% from NE. Permeation study from human skin showed that 762.3 ng mL(-1) ± 184.6 of tocopherol was delivered into the epidermis when formulated as NLCs as compared to 182.3 ng mL(-1) ± 52.7 from NE. FRAP assay was performed to test the antioxidant activity of formulated tocopherol, and it was seen that both formulations were able to retain the antioxidant activity. Skin irritation testing showed that NLC was non-irritant to the skin. NLC and NE were also able to protect tocopherol from UV degradation.

Based on the studies conducted, it can be concluded that formulating tocopherol as NLCs is beneficial to produce a stable, non-irritant and aqueous formulation.