Photostability of alpha-tocopherol ester derivatives in solutions and liposomes. Spectroscopic and LC-MS studies

Self-assembled low molecular weight chitosan-based cationic micelle for improved water solubility, stability and sustained release of α-tocopherol

New amphiphilic low molecular weight chitosan-graft-nicotinic acid bearing decyl groups (LCND) was synthesized by two-step reaction and spontaneously assembled into cationic micelle by ultra-sonication method to improve water solubility and photostability properties of α-tocopherol. The chemical structure of LCND was characterized and physical properties of cationic micelle were evaluated. Results displayed that cationic micelle exhibited strong self-assemble ability with nanoscale spherical morphology and showed best loading ability with loading content of 18.50% when the feeding ratio of LCND to α-tocopherol reached 10:3. Meanwhile, the greatly enhanced water solubility, photostability and sustained release behavior of α-tocopherol in cationic micelle were observed. The cumulative release of α-tocopherol in cationic micelle reached up 82.18% within 96 h while free α-tocopherol was completely released within 10 h. Additionally, release kinetics models were also fitted. The LCND cationic micelle could be promising nanocarrier for improving the physicochemical properties of α-tocopherol in food fields.

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

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.

The photoprotective properties of α-tocopherol phosphate against long-wave UVA1 (385 nm) radiation in keratinocytes in vitro

UVA1 radiation (340–400 nm), especially longwave UVA1 (> 370 nm), is often ignored when assessing sun protection due to its low sunburning potential, but it generates reactive oxygen species (ROS) and is poorly attenuated by sunscreens. This study aimed to investigate if α-tocopherol phosphate, (α-TP) a promising new antioxidant, could protect against long-wave UVA1 induced cell death and scavenge UVA1 induced ROS in a skin cell model. HaCaT keratinocyte cell viability (24 h) was assessed with Alamar Blue and Neutral Red assays. The metabolism of α-TP into α-T, assessed using mass spectrometry, and the compound's radical scavenging efficacy, assessed by the dichlorodihydrofluorescein (H2DCFDA) ROS detection assay, was monitored in HaCaTs. The mechanism of α-TP ROS scavenging was determined using non-cell based DPPH and ORAC assays. In HaCaT keratinocytes, irradiated with 226 J/cm² UVA1 in low-serum (2%, starved) cell culture medium, pretreatment with 80 µM α-TP significantly enhanced cell survival (88%, Alamar Blue) compared to control, whereas α-T pre-treatment had no effect survival (70%, Alamar Blue). Pre-treatment of cells with 100 μM α-TP or 100 μM α-T before 57 J/cm² UVA1 also significantly reduced ROS generation over 2 h (24.1% and 23.9% respectively) compared to the control and resulted in α-TP bioconversion into α-T. As α-TP displayed weak antioxidant activity in the cell-free assays thus its photoprotection was assigned to its bioconversion to α-T by cellular phosphatases. Through this mechanism α-TP prevented long-wave UVA1 induced cell death and scavenged UVA1 induced ROS in skin cells when added to the starved cell culture medium before UVA1 exposure by bioconversion into α-T.

Spectroscopic Evidence for Photooxidation of Tocopherols in n-Hexane

This paper presents the results of an investigation into the photooxidation of tocopherols (Tocs) dissolved in argonated and non-argonated n-hexane. During irradiation, steady-state absorption and fluorescence spectra as well as lifetimes were measured. In all experiments, the photoreactions were of the first order type. The reaction rate was higher for all Tocs in argonated solvent. A new emission band with a maximum at 298 nm as well as new absorption and fluorescence bands beyond the 300 nm connected with charge-transfer (C-T) complexes for all Tocs appeared during the irradiation of γ- and δ-Toc. The above results indicate that the photooxidation process is very complex and that the observed phenomena strongly depend on the number and position of methyl groups in the chromanol ring.

Molecular photoprotection of human keratinocytes in vitro by the naturally occurring mycosporine-like amino acid palythine

Background

Solar ultraviolet radiation (UVR) induces molecular and genetic changes in the skin, which result in skin cancer, photoageing and photosensitivity disorders. The use of sunscreens is advocated to prevent such photodamage; however, most formulations contain organic and inorganic UVR filters that are nonbiodegradable and can damage fragile marine ecosystems. Mycosporine‐like amino acids (MAAs) are natural UVR‐absorbing compounds that have evolved in marine species for protection against chronic UVR exposure in shallow‐water habitats.

Objectives

To determine if palythine, a photostable model MAA, could offer protection against a range of UVR‐induced damage biomarkers that are important in skin cancer and photoageing.

Methods

HaCaT human keratinocytes were used to assess the photoprotective potential of palythine using a number of end points including cell viability, DNA damage (nonspecific, cyclobutane pyrimidine dimers and oxidatively generated damage), gene expression changes (linked to inflammation, photoageing and oxidative stress) and oxidative stress. The antioxidant mechanism was investigated using chemical quenching and Nrf2 pathway activation assays.

Results

Palythine offered statistically significant protection (P < 0·005) against all end points tested even at extremely low concentrations (0·3% w/v). Additionally, palythine was found to be a potent antioxidant, reducing oxidatively generated stress, even when added after exposure.

Conclusions

Palythine is an extremely effective multifunctional photoprotective molecule in vitro that has potential to be developed as a natural and biocompatible alternative to currently approved UVR filters.

What's already known about this topic?

Mycosporine‐like amino acids (MAAs) are photoprotective molecules found in marine organisms but there are few data on their ability to protect skin cells from the adverse effects of solar ultraviolet radiation (UVR).

The European Chemicals Agency (ECHA) is concerned about the potential adverse health and ecotoxic effects of eight of 16 commonly used sunscreen filters in Europe. The Environmental Effects Assessment Panel (EEAP) of the United Nations Environment Programme has expressed similar concerns.

What does this study add?

Palythine, an MAA extracted from an edible seaweed, affords photoprotection against a wide range of adverse effects in HaCaT keratinocytes exposed to solar simulating and ultraviolet A radiation. Of note is protection against two types of DNA photolesions; cyclobutane pyrimidine dimers and 8‐oxo‐7,8‐dihydroguanine.

Palythine is also a potent antioxidant that offers protection even when added after UVR exposure.

What is the translational message?

MAAs should be considered for development as natural biocompatible sunscreens that may address the concerns of the ECHA and EEAP.

Linked Comment: https://doi.org/10.1111/bjd.16598.

https://goo.gl/Uqv3dl