Cosmeceutical formulations of pro-vitamin E phosphate: In-vitro release testing and dermal penetration into excised...

Long-term exposure to solar radiation can lead to skin damage such as photoageing, and photocarcinogenesis. This can be prevented by topically applying α-tocopherol phosphate (α-TP). The major challenge is that a significant amount of α-TP needs to reach viable skin layers for effective photoprotection. This study aims to develop candidate formulations of α-TP (gel-like, solution, lotion, and gel), and investigate formulation characteristics' effect on membrane diffusion and human skin permeation. All the formulations developed in the study had an appealing appearance and no signs of separation. All formulations had low viscosity and high spreadability except the gel. The flux of α-TP through the polyethersulfone membrane was the highest for lotion (6.63 ± 0.86 mg/cm²/h), followed by control gel-like (6.14 ± 1.76 mg/cm²/h), solution (4.65 ± 0.86 mg/cm²/h), and gel (1.02 ± 0.22 mg/cm²/h). The flux of α-TP through the human skin membrane was numerically higher for lotion compared to the gel-like (328.6 vs.175.2 µg/cm²/h). The lotion delivered 3-fold and 5-fold higher α-TP in viable skin layers at 3 h and 24 h, respectively, compared to that of the gel-like. The low skin membrane penetration rate and deposition of α-TP in viable skin layers were observed for the solution and gel. Our study demonstrated that dermal penetration of α-TP was influenced by characteristics of formulation such as formulation type, pH, and viscosity. The α-TP in the lotion scavenged higher DPPH free radicals compared to that of gel-like (almost 73% vs. 46%). The IC₅₀ of α-TP in lotion was significantly lower than that of gel-like (397.2 vs. 626.0 µg/mL). The preservative challenge test specifications were fulfilled by Geogard 221 and suggested that the combination of benzyl alcohol and Dehydroacetic Acid effectively preserved 2% α-TP lotion. This result confirms the suitability of the α-TP cosmeceutical lotion formulation employed in the present work for effective photoprotection.