Abstract
Sunlight is vital for several biochemical processes of the skin organ. However, acute or chronic exposure to ultraviolet radiation (UVR) has several harmful effects on the skin structure and function, especially in the case of the failing function of antioxidative enzymes, which may lead to substantial tissue damage due to the increased presence of reactive oxygen species (ROS). The aim of this work was to investigate the combined effect of ultraviolet B (UVB) irradiation and oxidative stress on the skin barrier integrity. For this, we employed electrical impedance spectroscopy (EIS) to characterize changes of the electrical properties of excised pig skin membranes after various exposure conditions of UVB irradiation, oxidative stress, and the inhibition of antioxidative enzymatic processes. The oxidative stress was regulated by adding hydrogen peroxide (H2O2) as a source of ROS, while sodium azide (NaN3) was used as an inhibitor of the antioxidative enzyme catalase, which is naturally present throughout the epidermis. By screening for the combined effect of UVB and oxidative stress on the skin membrane electrical properties, we developed a new protocol for evaluating these parameters in a simple in vitro setup. Strikingly, the results show that exposure to extreme UVB irradiation does not affect the skin membrane resistance, implying that the skin barrier remains macroscopically intact. Likewise, exposure to only oxidative stress conditions, without UVB irradiation, does not affect the skin membrane resistance. In contrast to these observations, the combination of UVB irradiation and oxidative stress conditions results in a drastic decrease of the skin membrane resistance, indicating that the integrity of the skin barrier is compromised. Further, the skin membrane effective capacitance remained more or less unaffected by UVB exposure, irrespective of simultaneous exposure of oxidative stress. The EIS results were concluded to be associated with clear signs of macroscopic tissue damage of the epidermis as visualized with microscopy after exposure to UVB irradiation under oxidative stress conditions. Finally, the novel methodology was tested by performing an assessment of cosmetic sunscreen formulations with varying sun protection factor (SPF), with an overall successful outcome, showing good correlation between SPF value and protection capacity in terms of skin resistance change. The results from this study allow for the development of new skin sensors based on EIS for the detection of skin tissue damage from exposure to UVB irradiation and oxidative stress and provide a new, more comprehensive methodology, taking into account both the influence of UVB irradiation and oxidative stress, for in vitro determination of SPF in cosmetic formulations.
Highlights
The skin is the largest organ in the body and performs many important functions, such as being a transport barrier against water loss and the entrance of toxic xenobiotics, defending against microbial pathogens, and providing a general protection against injuries [1,2]
We developed a new simple in vitro method based on electrical impedance spectroscopy (EIS) measurements of excised pig skin membranes
The aim of this work was to investigate the combined effect of ultraviolet B (UVB) radiation and oxidative stress on the electrical properties of the skin barrier
Summary
The skin is the largest organ in the body and performs many important functions, such as being a transport barrier against water loss and the entrance of toxic xenobiotics, defending against microbial pathogens, and providing a general protection against injuries [1,2]. Progress is being made on how to use topical or clinical therapies to reverse or alleviate the symptoms of defective or diseased skin; still, establishing the evidence of beneficial effects from various therapies in human populations remains elusive [2,3]. To approach this challenging topic and advance our general knowledge of how to maintain healthy skin, it is important to have access to reliable in vitro methods that allow for simple, fast, and inexpensive evaluation of relevant mechanisms responsible for defective skin and how topical therapies can be beneficially implemented. The protective capacity of cosmetic sunscreen formulations against the combined assault from UVR and oxidative stress is examined with the aim to illustrate that the proposed in vitro methodology can be used to evaluate the sun protection factor (SPF) of cosmetic sunscreens
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