New approach for a reliable in vitro sun protection factor method - Part II: Practical aspects and implementations

In Vitro Photoprotection and Functional Photostability of Sunscreen Lipsticks Containing Inorganic Active Compounds

Titanium dioxide (TiO2) is a safe inorganic ultraviolet (UV) filter with activity against UV damage. However, the recombination of the carrier’s charge and the tendency for TiO2 aggregation are the main disadvantages. Substrate supports, such as mesoporous silica, are biocompatible strategies to incorporate TiO2, altering its interaction with the skin. Since the lips are sensitive to the adversities of the environment, including UV radiation, the application of lipstick sunscreens is of great importance and expected to provide protection for this particular area against sunburn and photoaging, among other unfavorable responses unprotected UV exposure. We investigated the in vitro photoprotective efficacy and photostability of lipstick formulations containing TiO2 incorporated into mesoporous silica (SBA-15). The samples were the lipstick base; SBA-15; TiO2 (free form); and TiO2 incorporated into SBA-15. The photoprotective efficacy was characterized in vitro using a Labsphere UV2000S. Lipsticks were irradiated in a Suntest CPS+ chamber to evaluate functional photostability. Lipstick base and SBA-15 alone did not display photoprotective efficacy. The sample containing 10.0% TiO2 incorporated into the mesoporous silica generated greater photostability and sun protection factor (SPF) value compared to the one containing only 10.0% TiO2 (free state). Our findings suggest that TiO2 + SBA-15 can be considered a broad-spectrum ingredient for innovative sunscreens, particularly for the photoprotection of the lips.

[Characterization of sun protection performance: Quo vadis?]

Die Aufgabe der ersten Sonnenschutzmittel war es, die Entstehung von Sonnenbrand zu verhindern und, dem Zeitgeist der 1950/60er-Jahre folgend, die Bräunung der Haut nicht zu beeinträchtigen. Schnell entstand die Notwendigkeit, die Schutzleistung zu quantifizieren. Ursprünglich unter Zuhilfenahme des natürlichen – heute eines künstlichen – Sonnenlichts wurde eine Methode zur Bestimmung eines Sonnenschutzfaktor (SPF) entwickelt. Dieser ist heute formal als das Verhältnis zwischen minimaler erythemwirksamer UV-Dosis auf mit Sonnenschutzmittel geschützter und minimaler erythemwirksamer UV-Dosis auf ungeschützter Haut definiert (ISO 24444:2019). Drei Beobachtungen stellen die Eignung der Methode infrage: 1) Zwischen-Labor-Variabilität: Trotz strenger Normierung sind Resultate von SPF-Bestimmungen aus verschiedenen Labors und Regionen sehr großen Schwankungen unterworfen. 2) Natürliches vs. künstliches Sonnenlicht: Das Strahlungsspektrum des künstlichen Sonnenlichts unterscheidet sich von dem des natürlichen Sonnenlichts. Die mit künstlichem Sonnenlicht bestimmten SPFs (wie auf allen derzeit im Handel befindlichen Sonnenschutzmitteln abgebildet) sind im Vergleich zur SPF-Bestimmung mit natürlichem Sonnenlicht deutlich zu hoch. 3) Erythembelastung: Bei der Bestimmung des SPF werden die Probanden potenziell schädlicher Strahlung ausgesetzt. Vor diesem Hintergrund werden alternative Methoden – In-vitro-SPF, hybride diffuse Reflexionsspektroskopie (HDRS) und In-silico-Berechnungen – vorgestellt. Diese haben das Potenzial, die heutige mit erheblichen Einschränkungen verbundene Methode abzulösen. Als Sofortmaßnahme wird die Rückbesinnung auf die für alle verständliche Beschreibung niedriger, mittlerer, hoher und sehr hoher Schutz empfohlen, in Zukunft unter Berücksichtigung des Spektrums des natürlichen Sonnenlichtes.

Preclinical and clinical studies to evaluate cutaneous biodistribution, safety and efficacy of UV filters encapsulated in mesoporous silica SBA-15

Innovative technologies have been designed to improve efficacy and safety of chemical UV filters. Encapsulation can enhance efficacy and reduce transdermal permeation and systemic exposure. The aims of this work were (i) to determine the cutaneous biodistribution of avobenzone (AVO), oxybenzone (OXY), and octyl methoxycinnamate (OMC) incorporated in mesoporous silica SBA-15 and (ii) to perform preclinical (in vitro) and (iii) clinical safety studies to demonstrate their innocuity and to evaluate sun protection factor (SPF) in humans. Skin penetration studies showed that deposition of OXY and AVO in porcine and human skin after application of stick formulation with incorporated filters (stick incorporated filters) was significantly lower than from a marketed (non-encapsulated) stick. Cutaneous deposition and transdermal permeation of OXY in and across human skin were 3.8-and 13.4- fold lower, respectively, after application of stick entrapped filters. Biodistribution results showed that encapsulation in SBA-15 decreased AVO and OXY penetration reaching porcine and human dermis. Greater deposition (and permeation) of OXY in porcine skin than in human skin, pointed to the role of follicular transport. Stick incorporated filters had good biocompatibility in vivo and safety profiles, even under sun-exposed conditions. Entrapment of UV filters improved the SPF by 26% and produced the same SPF profile as a marketed stick. Overall, the results showed that SBA-15 enabled safety and efficacy of UV filters to be increased.

Validation of a new in vitro Sun Protection Factor method to include a wide range of sunscreen product emulsion types

In 2017, Cosmetics Europe performed a double‐blinded ring test of 24 emulsion‐type sunscreen products, across 3 in vivo test laboratories and 3 in vitro test laboratories, using a new candidate in vitro SPF test method. Based on the results of this work, an article was published showing how data derived from a new lead candidate method conform to new International Standards (ISO) acceptance criteria for alternative SPF test methods (Any alternative method should consider the matrix effect and if required, specify the matrix applicability of the method; Criterion 1a: Systematic differences between methods should be negligible: 95% of all individual results of an alternative method are within the range of ±2× reproducibility standard deviation of the in vivo method, that is overall bias must be below 0.5× reproducibility standard deviation of the in vivo method; Criterion 1b: Measurement uncertainty of an alternative method should be below the measurement uncertainty of the in vivo method. Candidate method predicted values must fall within the full ‘funnel’ (SPF 6‐50+) limits proposed by Cosmetics Europe (derived from the same minimum test design, that is using the ISO24444 Method to measure at least 24 products across at least 3 laboratories using at least 5 test subjects/laboratory, in a blinded fashion).). Of the 24 sunscreen products tested, the majority of emulsions were of the oil‐in‐water (O/W) type, whereas only one was water‐in‐oil (W/O) and there were no products with a mineral‐only sun filter system. In order to confirm the scope of this method, therefore, a new study was conducted that included 73 W/O (12 mineral + organic, 44 mineral only and 17 organic only) and 3 O/W mineral‐only, emulsion‐type sunscreen products (a total of 76 new sunscreen products). When combined with the previous 24 products (tested in 3 different laboratories), this yielded a new data set comprising a total of 100 emulsion‐type sunscreen products, with SPF values ranging from 6 to 50+ (with a total of 148 data points). These products were tested using the double‐plate in vitro SPF test method and compared with the ISO TC217/WG7 acceptance criteria for alternative SPF test methods. Over 95% of paired in vitro: in vivo SPF values lay within the upper and lower limits of the ISO acceptance criteria funnel, with no bias. This new in vitro SPF test method, therefore, meets the minimum requirements for an alternative SPF test method to ISO24444:2010, for emulsion‐type sunscreen products (which make up the majority of marketed sunscreen products).

Evaluating sunscreen ultraviolet protection using a polychromatic diffuse reflectance device

Background

Sun protection factor (SPF) and UVA protection factor (UVA‐PF) are determined using in vivo tests, with high exposures of subjects to ultraviolet (UV) radiation. Hybrid diffuse reflectance spectroscopy (HDRS) enables estimation of both indices using only trace amounts UVB. However, the equipment requires two expensive monochromators that must synchronously scan the spectrum.

Methods

An alternate approach was developed using a polychromatic source that illuminates the skin via a custom light guide array, and the diffuse reflected light is measured with a photomultiplier. The ratio of the diffuse reflectance with and without the sunscreen on the skin determines the polychromatic diffuse reflectance UVA‐PF (PDRS UVA‐PF₀). This factor was used to adjust in vitro UV spectroscopy scans of the sunscreen (with and without UV exposure to assess photostability), to calculate SPF and UVA protection factors. Ten sunscreens were evaluated and compared to in vivo SPF and UVA‐PF values.

Results

The data show an excellent correlation with known in vivo determinations.

Conclusion

This polychromatic HDRS approach uses simpler, faster, and less expensive equipment to determine both UVA‐PF and SPFs without high doses of UV radiation to the test subjects.

Development of the multispectral UV polarization reflectance imaging system (MUPRIS) for in situ monitoring of the UV protection efficacy of sunscreen on human skin

Background

Protection of the human skin from ultraviolet (UV) damage is one of the main issues in dermatology and cosmetology. The UV protection efficacy (UVPE) of the sunscreen film is decreased by sweat, sebum, and friction during the day. However, the technical relationship between the UVPE evaluated in a laboratory and the actual protection in daily use has not been clarified, because the UVPE measurement method in real‐life setting has not been established. This study aimed to develop a novel UVPE evaluation system that allows in situ monitoring of the UVPE in real‐life activities.

Methods

The multispectral UV polarization reflectance imaging system (MUPRIS) and a UVPE estimation algorithm were developed. The diffuse reflectance spectra were measured for a total of 48 sunscreen materials that were applied on 59 subjects. The UVPEs estimated from the diffuse reflectance spectra were compared with the in vivo SPFs. Finally, the UVPE before and after a marine leisure activity was evaluated using the MUPRIS as the practical use test.

Results

Compared with the conventional UV camera, the MUPRIS could visualize the applied sunscreen more clearly and showed good UVPE estimation accuracy (correlation coefficient for in vivo SPF, 0.82). In the practical use test, the degradation of the UVPE during a marine leisure activity was quantitatively monitored and was validated by the actual occurrence of sunburn.

Conclusions

A novel in situ UVPE monitoring tool had been successfully developed. It can strongly support the development of innovative sunscreen products that can perfectly protect customers against UV irradiation in real‐life situation.

Validation of an in vitro sun protection factor (SPF) method in blinded ring-testing

OBJECTIVE

The objective of this work was to investigate the utility of a new in vitro SPF test method in blinded ring-testing, against new ISO acceptance criteria.

METHODS

Twenty four blinded, commercial, emulsion-type, primary sunscreen products, covering the full range of labelled SPF in Europe (SPF6 - 50+), were tested by three test institutes using the current ISO24444:2010 In Vivo SPF Test Method and simultaneously by three separate test laboratories using a new candidate in vitro SPF test method, developed under the leadership of Cosmetics Europe (CE). The resulting relationship between in vitro SPF and in vivo SPF values was then compared with acceptance criteria developed recently by the International Standards (ISO) TC217/WG7 Sun Protection Test Methods Working Group.

RESULTS

Analysis of the mean inter-laboratory in vitro and mean inter-institute in vivo SPF values revealed a strong correlation between in vitro and in vivo values, with a Pearson correlation coefficient of r2  = 0.88 (P < 0.0001), a slope of 1.01 and a non-significant intercept (-1.48; P = 0.62). When these data were compared to the new ISO WG7 acceptance criteria, method bias was found to be extremely low and over 95% of the coupled data lay within the model 'funnel' (defined by upper and lower confidence intervals).

CONCLUSION

In conclusion, the results of blinded ring testing and comparison to new ISO WG7 acceptance criteria indicate that a new in vitro SPF test method meets (and exceeds) these minimum criteria and is an interesting candidate for possible deployment as an industry test methodology.

The perplexing dilemma of measuring sun protection factors

Truth, like knowledge, is surprisingly difficult to define. Indeed, every definition of truth that philosophers have developed falls prey to the question, 'Is it true?' In this essay, we consider what is the true SPF of a sunscreen product and whether it can ever be realizable.