Radical Protection by Differently Composed Creams in the UV/VIS and IR Spectral Ranges

Carotenoids in Human SkinIn Vivo: Antioxidant and Photo-Protectant Role against External and Internal Stressors

The antioxidant system of the human body plays a crucial role in maintaining redox homeostasis and has an important protective function. Carotenoids have pronounced antioxidant properties in the neutralization of free radicals. In human skin, carotenoids have a high concentration in the stratum corneum (SC)-the horny outermost layer of the epidermis, where they accumulate within lipid lamellae. Resonance Raman spectroscopy and diffuse reflectance spectroscopy are optical methods that are used to non-invasively determine the carotenoid concentration in the human SC in vivo. It was shown by electron paramagnetic resonance spectroscopy that carotenoids support the entire antioxidant status of the human SC in vivo by neutralizing free radicals and thus, counteracting the development of oxidative stress. This review is devoted to assembling the kinetics of the carotenoids in the human SC in vivo using non-invasive optical and spectroscopic methods. Factors contributing to the changes of the carotenoid concentration in the human SC and their influence on the antioxidant status of the SC in vivo are summarized. The effect of chemotherapy on the carotenoid concentration of the SC in cancer patients is presented. A potential antioxidant-based pathomechanism of chemotherapy-induced hand-foot syndrome and a method to reduce its frequency and severity are discussed.

Eco-friendly sunscreen formulation based on starches and PEG-75 lanolin increases the antioxidant capacity and the light scattering activity in the visible light

Most modern sunscreens contain physical filters, which scatter the sunlight, increasing the photons' pathway in the upper stratum corneum. This effect can lead to a better efficacy of the UV filters and improve the diffuse reflection. However, the addition of nanosized inorganic UV filters reduces the antioxidant capacity of sunscreen formulations. Two cream formulations (F1, F2) which differ in the ingredient PEG75 Lanolin (F2), have been characterized for their radical protection factor (RPF) and their optical properties in vitro using electron paramagnetic resonance (EPR) spectroscopy and UV/VIS spectrometry. The RPF for PEG-75 Lanolin was also determined. Furthermore, their radical protection properties were analyzed on porcine skin ex vivo after visible light irradiation by EPR. The structure of each formulation in the skin surface was determined by reflectance confocal microscopy in vivo. The addition of lanolin increased the reflectance and reduced the transmittance for visible light, improving the scattering drastically. Besides, the antioxidant capacity was also increased for F2, something unpublished until now. F1 presented a lower scattering provided by starches. The sunscreens showed high scattering properties and antioxidant capacity, especially for F2, which presented the lowest radical formation in the skin model. These results are consistent with the RPF measurements where F2 has a higher RPF value (193 ± 3 × 10¹⁴ radicals/mg) than F1 (155 ± 4 × 10¹⁴ radicals/mg) and for PEG-75 Lanolin (37 ± 1 × 10¹⁴ radicals/mg). The combination of starches and PEG-75 Lanolin is the first solution to provide both, light scattering and antioxidant capacity, in sunscreens.

Effects of UV-filter Photostabilizers in the Photostability and Phototoxicity of Vitamin A Palmitate Combined with Avobenzone and Octyl Methoxycinnamate

A challenge for cosmetic and dermatologic products is to develop new high-performance and safer anti-aging products based on new compounds to enhance the stability of retinyl palmitate combined with broad-spectrum UV-filters. Consequently, the aim of this work was to evaluate the effects of three often used avobenzone photostabilizers-ethylhexyl methoxycrylene (EHMCR), tris(tetramethylhydroxypiperidinol) citrate (TTMHP) and tris-biphenyl triazine (TBPT)-on the photostability and phototoxicity of the combination of avobenzone (AVO), octyl methoxycinnamate (OMC) and retinyl palmitate (RP). The photostability studies were performed by the exposure of formulations to UVA radiation. The phototoxicity was evaluated by the 3T3 neutral red uptake phototoxic assay (OECD TG 432). The addition of EHMCR, TBPT, and TTMHP in the formulations, with/or without RP, improved the photostability of AVO and RP, but EHMCR was the most effective in stabilizing RP. In the phototoxicity assay, the combinations AVO-OMC containing or not RP showed phototoxic potential. EHMCR and TTMHP reduced the phototoxicity of the combination AVO-OMC, whereas EHMCR also decreased the phototoxicity of the combination containing RP. Therefore, EHMCR might be used to the photostabilization of formulations of AVO-OMC with/or not RP, while TTMHP can be added to this photounstable UV-filter combination.

Teachings from COVID-19 and aging-An oxidative process

As of June 2020, the COVID‐19 pandemic has totaled over 9 000 000 cases and 470 000 deaths globally (ref. 1). Emerging data from COVID‐19 patients have suggested a clear role for oxidative stress in the pathogenesis of SARS‐CoV‐2, the pathogenic agent of COVID‐19. Several comorbidities, including hypertension, diabetes, obesity, and aging, have been associated with an increase in baseline oxidative stress, likely explaining why such individuals at risk for poor outcomes with SARS‐CoV‐2 infection. Similarly, the concept of oxidative stress remains one of the best supported theories to explain the mechanism behind aging. Oxidative stress through both endogenous and exogenous sources has known deleterious effects in both aging and SARS‐CoV‐2 infection. Herein, we will review the role of oxidative stress as a key player in both aging and COVID‐19 and highlight why some individuals may have better or poorer outcomes because of this. Additionally, we will discuss potential therapeutic pathways for effectively anti‐aging as we take away from our learnings on COVID‐19.

Simultaneous nanoencapsulation of lipoic acid and resveratrol with improved antioxidant properties for the skin

Cutaneous aging is intimately related to redox imbalance, which is mainly caused by ultraviolet radiation exposure. The aim of the present investigation was to develop lipid-core nanocapsules for the co-nanoencapsulation of resveratrol and lipoic acid aiming to improve the chemical stability and photostability of the compounds, as well as their antioxidant properties. Lipid-core nanocapsules were developed and characterized according to their mean size, size distribution, zeta potential, pH value, drug content, encapsulation efficiency, release profile, stability under storage, photostability and skin permeation profile. In vitro antioxidant activity was analyzed by lipid peroxidation method and the in vitro cytotoxicity by MTT assay and cellular count, using BALB/c-3T3 fibroblasts. It was possible to co-nanoencapsulate resveratrol and lipoic acid into particles of average diameter close to 200 nm, low polydispersity index and encapsulation efficiencies around 90 %. Nanoencapsulation increased the substances stability under storage and photostability under UVA light exposure, besides controlling substances release. The actives were able to permeate a skin model membrane when nanoencapsulated, with a faster permeation of lipoic acid. The antioxidant activity was potentiated by the co-nanoencapsulation of resveratrol and lipoic acid, without signs of cytotoxicity to fibroblasts. Therefore, the co-nanoencapsulation of resveratrol and lipoic acid is promising for application in topical formulations aiming antioxidant effects.

The Influence of Short-Wave and Long-Wave Radiation Spectrum on the Photostability of Sunscreens

BACKGROUND

Sunscreen products aim to help protect the skin against UV radiation and consequently reduce the risk of early skin ageing and skin cancer. However, it is well known that some sunscreen ingredients are not photostable, but this usually refers to irradiation with UV light. Moreover, it has to be mentioned that a relative cumulative erythema effectiveness compliant light source is used for the in vivo sun protection factor (SPF) testing. Here, UV simulators equipped with a xenon arc lamp use filters such as WG320 and UG11 (thickness 1 mm) to minimize infrared (IR) radiation and wavelength below 300 nm. However, under practical conditions, the sunscreen product is not only exposed to UVA/B light, but also to visible light (VIS) and IR light. In fact, the spectrum of solar radiation is composed of approximately 7% UV, 39% VIS and 54% IR.

AIMS

To investigate the influence of short-wave and long-wave radiation on the photostability of sunscreens.

METHODS

Irradiation was performed with the Suntest CPS+ that is considered to closely imitate solar radiation. The filter UG11 (thickness 1 mm), which absorbs much of the VIS and IR light, and the glass filter WG320 (thickness 2 mm), which effectively absorbs radiation of wavelengths less than 300 nm, were used in the Suntest CPS+ both individually and in combination and were inserted between the light source and the samples. The following transmission measurements were carried out with Labsphere's UV-2000s device. Here, the effectiveness (percentage change of SPF before irradiation to SPF after irradiation) as a measure of the photostability was calculated.

RESULTS

As expected after total solar spectrum irradiation, the effectiveness in all tested sunscreens is lower compared to relative cumulative erythema effectiveness light used for in vitro testing of SPF. In the reference sunscreen formula S2 as well as in the two different sunscreen products, especially long-wave radiation (>400 nm) had an effect on photostability, whereas short-wave radiation had only a minor impact. In contrast, in the BASF sun care gel line only short-wave radiation below 300 nm had an effect on photostability, and blocking VIS and IR light had no effect at all.

CONCLUSION

Based on these data, we can conclude that short waves and/or VIS + IR light have an influence on the photostability of sunscreens.

Application of an Easy-to-Perform High-Energy and Low-End Visible Light Transmittance Method and the Influence of Tinted Sunscreens on High-Energy/Low-End Visible Light Transmittance and Infrared Protection

BACKGROUND

About 50% of the sun's radiation arriving on earth is visible light (VIS). For a long time, its effects on human health have not been fully investigated. But recently, the influence of VIS has gained more attention, especially regarding skin physiology. Studies showed various effects, many of them harmful, comparable to UV radiation. As a result, there are now a few sunscreens commercially available which claim protection against VIS. The question of whether protection is necessary is still much discussed.

AIMS

The objective of this study was to develop an easy-to-perform high-energy visible (HEV) and low-end visible (LEV) light transmittance method to determine the direct VIS protection of sunscreens and other cosmetic samples. Furthermore, the influence of the brightness of the tested products on the HEV, LEV, and infrared A protection was investigated.

METHODS

An experimental setup consisting of a light source, a VIS-transmissible filter system, and a sensor unit was built to measure the direct VIS protection of sunscreens and other daily skin care products in two ranges of the VIS area. For a closer look, the brightness of the samples was evaluated by photometric assessment.

RESULTS/CONCLUSION

The experimental setup could be validated. It could be demonstrated for the first time that there is a strong positive linear correlation between transmittance and brightness of tinted sunscreen and daily skin care products with sunscreen properties in the HEV, LEV, and infrared A range. However, tinted samples worked best in the blue light region, and the higher the wavelength range, the lower the protection.

Chitosan Nanoparticles with Encapsulated Natural and UF-Purified Annatto and Saffron for the Preparation of UV Protective Cosmetic Emulsions

The aim of the present work is to evaluate the preparation of sunscreen emulsions based on chitosan (CS) nanoparticles with annatto, ultrafiltrated (UF) annatto, saffron, and ultrafiltrated saffron. Ionic gelation was used for the preparation of chitosan nanoparticles, while their morphological characteristics and physicochemical properties were evaluated via Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and dynamic light scattering (DLS). Results showed that the prepared nanoparticles ranged from ~150 to ~500 nm and had a spherical or irregular shape. In the case of annatto and UF annatto, due to the formation of H-bonds, the sunscreen agents were amorphously dispersed within CS nanoparticles, while in the case of saffron and UF saffron, crystalline dispersion was observed. All encapsulated materials had good thermal stability as well as color stability. In a further step, sunscreen emulsions were prepared based on the formed CS-sunscreen nanoparticles and evaluated for their stability in terms of pH and viscosity, along with their ultraviolet (UV) radiation protection ability in terms of sun protection factor (SPF). All prepared emulsions showed low cytotoxicity and good storage stability for up to 90 days, while minimum sunscreen protection was observed with SPF values varying from 2.15 to 4.85.

Development of an in vitro Test Procedure to Determine the Direct Infrared A Protection of Sunscreens and Non-Cosmetic Samples

BACKGROUND

Every day human skin is exposed to infrared A (IRA) radiation as part of the natural sun rays. As IRA radiation accounts for around one third of the solar radiation, it has gained great attention concerning its effects on the human body and skin. In the past few years it has been discussed controversially whether IRA radiation (of solar origin) is harmful or not. Nonetheless, there are several sunscreens on the German market that claim IRA protection for themselves.

AIMS

The present study seeks to find an experimental set-up and a test procedure for the determination and quantification of direct IRA protection (realized via reflection or absorption of the IRA radiation), since to our knowledge these do not yet exist.

METHODS

In this study we proved the usability of a set-up consisting of a light source, an IRA-transmissible filter system and a sensor unit, for the determination and quantification of the IRA protection of cosmetic and non-cosmetic samples.

RESULTS/CONCLUSION

The applicability of the IRA emission of the light source, the spectral detector, transmissivity of the filter systems and the sample carriers could be validated. This experimental set-up can be used as an in vitro test procedure for the determination of direct IRA protection.

The Use of Directional Reflectance Measurement for in vivo Assessment of Protective Properties of Cosmetics in the Infrared Radiation Range

Photoprotection of skin is now focused on UV radiation. The aim of this study was to evaluate in vivo cosmetic products in terms of protection against infrared radiation (IR) and propose a methodology for conducting such measurements. The directional reflectance (DR) of 12 UV filters, six care creams and two preparations containing fumed silica applied on the forearm of 36 volunteers was examined in six spectral bands for two angles of incidence. SOC-410 Directional Hemispherical Reflectometer was used to measure DR. There is very little change in DR for all spectral bands for both incident angles for both UV filters, care creams and preparations containing fumed silica. For example, for 15% of fumed silica in glycerin for the spectral band of 0.9-1.1 μm and the incident angle of 20°, skin DR prior to application was 0.543; 5 min after application was 0.533 and 30 min after application was 0.559. Both UV filters, care creams and fumed silica do not protect skin against IR. The proposed method of in vivo measurements is superior to in vitro studies which have been conducted so far because it takes into account both the refractive index at the tissue/air interface and the absorption of IR by adipose tissue.

Radical-Scavenging Activity of a Sunscreen Enriched by Antioxidants Providing Protection in the Whole Solar Spectral Range

BACKGROUND/AIM

The main reason for extrinsic skin aging is the negative action of free radicals. The formation of free radicals in the skin has been associated with ultraviolet (UV) exposure and also to visible (VIS) and near-infrared (NIR) irradiations. The aim of the present study was to evaluate the efficacy of a sunscreen in the whole solar range.

METHODS

The radical-scavenging activity of a sunscreen in the UV, VIS, and NIR ranges was evaluated using electron paramagnetic resonance spectroscopy. Ex vivo penetration profiles were determined using confocal Raman microscopy on porcine ear skin at different time points after application.

RESULTS

Compared to the untreated skin, the sunscreen decreased the skin radical formation in the UV and VIS regions. Additional protection in the VIS and NIR ranges was observed for the sunscreen containing antioxidants (AO). The penetration depth of the cream was less than 11.2 ± 3.0 µm for all time points.

CONCLUSION

A sunscreen containing AO improved the photoprotection in the VIS and NIR ranges. The sunscreen was retained in the stratum corneum. Therefore, these results show the possibility of the development of effective and safer sunscreen products.

[New aspects in the development of sunscreening agents]

Sunlight is indispensable for life. Skin aging is determined not only by genetic factors but also by the influence of solar radiation which in all its spectral regions induces free radicals in the human skin. Below a critical concentration, free radicals are important for signaling processes in the human body. Exceeding a critical threshold value (FRTV), however, free radicals lead to cellular damage which, in turn, can induce skin aging, immunosuppression and even skin cancer. Recently it could be shown that 50% of the free radicals induced in the human skin by solar radiation were caused by the visible and infrared spectral regions. Taking into consideration that people who use sunscreen stay considerably longer in the sun than unprotected people, their skin could be exposed to free radical formation in the visible and infrared spectral regions, which far exceeds the critical threshold. Filter substances like those used in sunscreens for skin protection in the ultraviolet region are not available for the visible and infrared spectral regions. Using the natural protection mechanisms of the human skin as examples, however, the protective effect of sunscreens can be considerably enhanced by the addition of scattering and reflective pigments, such as titanium dioxide, as well as of antioxidants which neutralize the free radicals. Currently the focus of sunscreen development is shifting from mere UV protection to protection covering the entire solar spectrum.

From UV Protection to Protection in the Whole Spectral Range of the Solar Radiation: New Aspects of Sunscreen Development

Sunscreens have been constantly improving in the past few years. Today, they provide an efficient protection not only in the UVB but also in the UVA spectral region of the solar radiation. Recently it could be demonstrated that 50% of all free radicals induced in the skin due to solar radiation are formed in the visible and infrared spectral region. The good protective efficacy of sunscreens in the UV region prompts people to stay much longer in the sun than if they had left their skin unprotected. However, as no protection in the visible and infrared spectral region is provided, high amounts of free radicals are induced here that could easily exceed the critical radical concentration. This chapter describes how the effect of sunscreens can be extended to cover also the visible and infrared spectral region of the solar radiation by adding pigments and antioxidants with high radical protection factors to the sunscreen formulations.

An appraisal of the need for infrared radiation protection in sunscreens

Many sunscreens incorporate agents that are said to protect against infrared (IR) damage in the skin but we lack any real data on their benefit in the context of normal human behaviour in the sun. The object of this study was to examine typical IR exposure levels to the sun and industrial sources in order to decide whether there is a need for sunscreens to contain agents that protect against IR radiation, specifically the IR-A waveband. We reviewed claims currently made by products offering protection against IR-A and studies on the biological and clinical effects attributed to IR-A, and compared IR-A exposure levels from these studies with those typically received from the sun and from industrial sources. We found that annual levels of IR-A exposure resulting from typical behaviour in the sun are commensurate with those experienced occupationally by workers exposed to industrial sources of IR, such as steel and glass furnaces. Yet these workers appear to suffer little in the way of chronic skin damage. We conclude that there is not compelling evidence to demonstrate that observable, deleterious cutaneous effects are occurring at doses of solar IR radiation corresponding to those experienced by populations in their normal environments and for this reason we believe it is premature to incorporate IR protection into topical sunscreens and to make claims related to ageing of the skin that consumers may expect to see.

Evaluation of carotenoids and reactive oxygen species in human skin after UV irradiation: a critical comparison between in vivo and ex vivo investigations

UV irradiation is one of the most harmful exogenous factors for the human skin. In addition to the development of erythema, free radicals, that is reactive oxygen species (ROS), are induced under its influence and promote the development of oxidative stress in the skin. Several techniques are available for determining the effect of UV irradiation. Resonance Raman spectroscopy (RRS) measures the reduction of the carotenoid concentration, while electron paramagnetic resonance (EPR) spectroscopy enables the analysis of the production of free radicals. Depending on the method, the skin parameters are analysed in vivo or ex vivo. This study provides a critical comparison between in vivo and ex vivo investigations on the ROS formation and carotenoid depletion caused by UV irradiation in human skin. The oxygen content of tissue was also determined. It was shown that the antioxidant status measured in the skin samples in vivo and ex vivo was different. The depletion in the carotenoid concentration in vivo exceeded the value determined ex vivo by a factor of about 1.5, and the radical formation after UV irradiation was significantly greater in vivo by a factor of 3.5 than that measured in excised human skin, which can be explained by the lack of oxygen ex vivo.

Investigation of Model Sunscreen Formulations Comparing the Sun Protection Factor, the Universal Sun Protection Factor and the Radical Formation Ratio

In view of globally rising skin cancer rates and harmful effects exerted by sunlight throughout the ultraviolet, visible and infrared ranges, an objective, safe and comprehensive method for determining sunscreen efficacy is required in order to warrant safe sun exposure. In this study, the influence of characteristic active ingredients (chemical filters, physical filters and antioxidants) on different sunscreen indicators, including the universal sun protection factor and the radical formation ratio, was determined and compared to their influence on sun protection factor values. Spectroscopic universal sun protection factor measurements were conducted ex vivo by analyzing tape strips taken from human skin, and radical formation ratio determination was performed via electron paramagnetic resonance spectroscopy using porcine ear skin ex vivo. The sun protection factor determination was conducted according to ISO standards (ISO 24444:2010). It was shown that chemical filters provide a protective effect which was measurable by all methods examined (spectroscopy, electron paramagnetic resonance spectroscopy and erythema formation). Physical filters, when used as single active ingredients, increased protective values in universal sun protection factor and sun protection factor measurements but exhibited no significant effect on universal sun protection factor measurements when used in combination with chemical filters or antioxidants. Antioxidants were shown to increase sun protection factor values. Radical formation ratio values were shown to be influenced merely by chemical filters, leading to the conclusion that the universal sun protection factor is the most suitable efficacy indicator for the ultraviolet range.

Molecular action mechanisms of solar infrared radiation and heat on human skin

The generation of ROS underlies all solar infrared-affected therapeutic and pathological cutaneous effects. The signaling pathway NF-kB is responsible for the induced therapeutic effects, while the AP-1 for the pathological effects. The different signaling pathways of infrared-induced ROS and infrared-induced heat shock ROS were shown to act independently multiplying the influence on each other by increasing the doses of irradiation and/or increasing the temperature. The molecular action mechanisms of solar infrared radiation and heat on human skin are summarized and discussed in detail in the present paper. The critical doses are determined. Protection strategies against infrared-induced skin damage are proposed.

Reactive molecule species and antioxidative mechanisms in normal skin and skin aging

Reactive oxygen and nitrogen species (ROS/RNS) which may exist as radicals or nonradicals, as well as reactive sulfur species and reactive carbon species, play a major role in aging processes and in carcinogenesis. These reactive molecule species (RMS), often referred to as 'free radicals' or oxidants, are partly by-products of the physiological metabolism. When RMS concentrations exceed a certain threshold, cell compartments and cells are injured and destroyed. Endogenous physiological mechanisms are able to neutralize RMS to some extent, thereby limiting damage. In the skin, however, pollutants and particularly UV irradiation are able to produce additional oxidants which overload the endogenous protection system and cause early aging, debilitation of immune functions, and skin cancer. The application of antioxidants from various sources in skin care products and food supplements is therefore widespread, with increasingly effective formulations being introduced. The harmful effects of RMS (aside from impaired structure and function of DNA, proteins, and lipids) are: interference with specific regulatory mechanisms and signaling pathways in cell metabolism, resulting in chronic inflammation, weakening of immune functions, and degradation of tissue. Important control mechanisms are: MAP-kinases, the aryl-hydrocarbon receptor (AhR), the antagonistic transcription factors nuclear factor-κB and Nrf2 (nuclear factor erythroid 2-related factor 2), and, especially important, the induction of matrix metalloproteinases which degrade dermal connective tissue. Recent research, however, has revealed that RMS and in particular ROS/RNS are apparently also produced by specific enzyme reactions in an evolutionarily adapted manner. They may fulfill important physiologic functions such as the activation of specific signaling chains in the cell metabolism, defense against infectious pathogens, and regulation of the immune system. Normal physiological conditions are characterized by equilibrium of oxidative and antioxidative mechanisms. The application of antioxidants in the form of 'cosmeceuticals' or systemic 'nutraceuticals' should aim to support a physiologically balanced oxidation status in the skin.