Nitric oxide-releasing emulsion with hyaluronic acid and vitamin E†
S-Nitrosoglutathione (GSNO) is a naturally available S-nitrosothiol that can be incorporated into non-toxic formulations intended for topical use. The value of nitric oxide (NO) delivered topically relates to its well-studied physiological functions such as vasodilation, angiogenesis, cell proliferation and broad-spectrum antibacterial activity. Previously reported topical NO-releasing substrates include polymeric materials that exhibit non-toxic behaviors on dermal tissue such as polyethylene glycol. However, they do not serve as humectants nor provide vitamins to the skin. In this study, GSNO was added to an emulsion that was fortified with α-tocopheryl acetate (vitamin E) and hyaluronic acid. The average total NO content for the NO-releasing emulsion was 58 ± 8 μmol g−1 at 150 °C and the cumulative NO release over 53 h at physiological temperature (37.4 °C) was 46 ± 4 μmol g−1. The GSNO concentration in the lotion was optimized in order to reach a pH value similar to that of human skin (pH 5.5). The viscosity was analyzed using a rotational viscometer for the S-nitrosated and the non-nitrosated emulsions to obtain a material that can be readily spread on dermal tissue. The viscosity values obtained ranged from 7.88 ± 0.99 to 8.50 ± 0.36 Pa s. Previous studies have determined that the viscosity maximum for lotions is 100 Pa s. A low viscosity increases the diffusion coefficient of active ingredients to the skin given that they are inversely proportional as described by the Einstein–Smoluchowski equation. The effect of the S-nitrosated and non-nitrosated emulsions on adult human dermal fibroblasts (HDFs) was assessed in comparison to untreated HDFs using Colorimetric Cell Viability Kit I-WST-8. The findings indicate that neither the S-nitrosated nor non-nitrosated emulsions induced cytotoxicity in HDFs.