Gain or loss? Sunscreen efficiency after cosmetic pretreatment of the skin.

Sunscreens are a key pillar of the multimodal protection strategy against short- and long-term impacts of intermittent and continuous UV exposure. Hitherto, an unanswered part of current scientific discourse is the question whether a cosmetic pretreatment has an impact on distribution and adhesiveness of sunscreens on the skin and therefore affects UV protection. In order to evaluate the homogeneity of sunscreen filter distribution, water resistance as a parameter of adhesiveness and effective UV protection of sunscreens after a pretreatment with cream or lotion was investigated in 18 volunteers who were examined before and after swimming, using the established combination of the tape stripping procedure and UV/VIS spectroscopy. It was shown that a cosmetic skin pretreatment affects neither filter homogeneity nor effective UV protection prior to water contact. However, compared to nonpretreated skin, a considerable loss of water resistance is caused. Therefore, using a cream or lotion before application of sunscreens is not to be recommended.

Methods for the evaluation of the protective efficacy of sunscreen products.

The objective of the present investigation was to examine the utilization of optical and spectroscopic methods for the noninvasive characterization of Anthelios XL Fluide Extreme (SPF 50+), an exemplary sunscreen, concerning its homogeneity of distribution on the skin, its spectroscopic properties and its overall protective efficacy. The homogeneity of the distribution of the sunscreen on the skin was investigated with a multiphoton tomography microscope. Additionally, the sum transmission spectrum was determined using tape stripping and spectroscopic measurements. The results revealed a very homogeneous distribution of the sunscreen on the skin surface and also in the deep furrows. The sum transmission spectrum reflects a high protective efficacy of the sunscreen in both the UVA and UVB ranges. The sunscreen Anthelios XL Fluide Extreme (SPF 50+) generates a comfortable feeling on the skin and can be easily distributed. The presented optical methods have been shown to be suitable to investigate the overall protective efficacy of sunscreen products objectively, noninvasively and quickly.

In vivo methods for the analysis of the penetration of topically applied substances in and through the skin barrier.

The efficacy of a drug is characterized by its action mechanism and its ability to pass the skin barrier. In this article, different methods are discussed, which permit this penetration process to be analysed non-invasively. Providing qualitative and quantitative information, tape stripping is one of the oldest procedures for penetration studies. Although single cell layers of corneocytes are removed from the skin surface, this procedure is considered as non-invasive and is applicable exclusively to the stratum corneum. Recently, optical and spectroscopic methods have been used to investigate the penetration process. Fluorescence-labelled drugs can be easily detected in the skin by laser scanning microscopy. This method has the disadvantage that the dye labelling changes the molecular structures of the drug and consequently might influence the penetration properties. The penetration process of non-fluorescent substances can be analysed by Raman spectroscopy, electron paramagnetic resonance, CARS and multiphoton microscopic measurements. Using these methods, the concentration of the topically applied formulations in different depths of the stratum corneum can be detected by moving the laser focus from the skin surface deeper into the stratum corneum. The advantages and disadvantages of these methods will be discussed in this article.

Quantification of the inhomogeneous distribution of topically applied substances by optical spectroscopy: definition of a factor of inhomogeneity.

The inhomogeneous distribution of topically applied substances due to decisive differences in the skin structure (furrows and wrinkles) affects the efficacy of cosmetic products, in particular sunscreens. The combination of tape stripping and optical spectroscopy results in absorption data, which reflect ex vivo the inhomogeneity of the in vivo distribution of topically applied substances. Based on these data, a factor of inhomogeneity is defined describing the individual distribution of formulations on the skin surface of volunteers. Thus, the influence of different skin surface structures and the influence of different formulations on the distribution of the topically applied substances can be determined. Analyzing the inhomogeneity data on 6 volunteers (5 sunscreens per volunteer), it was found that the influence on the distribution of sunscreens caused by the formulation was higher than the inhomogeneity originating from the differences in the skin surface structure of the volunteers. The method is well suited to characterize, for example, sunscreens and antiaging creams in the process of development, as well as for the evaluation of the final products.

Pathways of lateral spreading.

In the case of topically applied substances, usually both lateral spreading and competitive penetration into the skin occur in parallel. In the present study, the pathways of lateral spreading were studied quantitatively and visually. The local distribution and lateral spreading of the UV filter substance butyl methoxydibenzoylmethane applied in an o/w emulsion was studied on the forearm and the back. The tape stripping procedure was used to determine the recovery rates inside and outside the area of application. The skin characteristics of transepidermal water loss, pH value, hydration of the stratum corneum and sebum rate were determined at both anatomic sites. Photography and laser scanning microscopy were used to visually investigate the lateral spreading of topically applied dyes. On the back, a preferred direction of lateral spreading parallel to the body axis was observed. This result was caused by differences in the network of furrows. The furrows functioned as a pathway for lateral spreading, whereas the follicles formed a reservoir for the topically applied substance.

The tape stripping procedure--evaluation of some critical parameters.

Tape stripping is a simple and efficient method for the assessment of quality and efficacy of cosmetical and dermatological formulations. After topical application and penetration of formulations, the cell layers of the stratum corneum are successively removed from the same skin area using adhesive films. The tape strips contain the amount of corneocytes and the corresponding amount of the penetrated formulation, which can be determined by classical analytical chemical methods. Different formulations can strongly influence the amount of stratum corneum removed with every tape strip. Therefore, it is essential for the comparison of the penetration of different formulations that the amount of formulation detected on the single tape strip is not related to the tape strip number as a relative measure of the penetration depths, but to their standardized real position in the stratum corneum. Therefore, different methods are reported for the determination of the amount of stratum corneum removed with every tape strip. The tape stripping method in its standardized form is well-suited to determine the dermatopharmacokinetics of topically applied substances. Additionally, the method can be used to obtain information about the homogeneity and the distribution of formulations on the skin and in the stratum corneum. This is used, e.g., for the determination of the homogeneity of the distribution and the ex vivo determination of a universal sun protection factor (USPF) characterizing the efficacy of sunscreens.

Penetration studies of topically applied substances: Optical determination of the amount of stratum corneum removed by tape stripping.

Tape stripping is a standard measuring method for the investigation of the dermatopharmacokinetics of topically applied substances using adhesive films. These tape strips are successively applied and removed from the skin after application and penetration of topically applied substances. Thus, layers of corneocytes and some amount of topical applied substances are removed. The amount of substances and the amount of stratum corneum removed with a single tape strip has to be determined for the calculation of the penetration profile. The topically applied substances removed from the skin can be determined by classical analytical methods like high-pressure liquid chromatography, mass spectroscopy, and spectroscopic measurements. The amount of corneocytes on the tape strips can be easily detected by their pseudoabsorption. In the present paper, an easy and cheap corneocyte density analyzer is presented that is based on a slide projector. Comparing the results of the measurements obtained by the corneocyte density analyzer and by uv-visible spectrometry, identical results were obtained.

Comparison of transepidermal water loss and spectroscopic absorbance to quantify changes of the stratum corneum after tape stripping.

The objective and quantitative application of tape stripping in pharmaceutics and dermatopharmacokinetics requires the determination of the exact position of each removed tape strip inside the stratum corneum (SC) and/or the determination of the relative SC thickness. In this study, transepidermal water loss (TEWL) and the optical spectroscopic data of the corneocytes were measured simultaneously during the complete removal of the SC by tape stripping. The spectroscopic data quantitatively reflect the amount of corneocytes removed by the individual tape strips, whereas TEWL and 1/TEWL are not sensitive enough to measure the relatively small changes in the SC thickness realized by the removal of the individual strips. The relative SC thickness can be determined directly by the spectroscopic data, while the 1/TEWL values require a second independent method. The results demonstrate the importance of tape stripping characterizing the behaviour of topically applied substances.

Estimation of the relative stratum corneum amount removed by tape stripping.

BACKGROUND/PURPOSE: The tape stripping procedure is a suitable minimal invasive tool to study, e.g. the penetration and dermatopharmacokinetics of topically applied substances. In the present study, this procedure was used to remove the stratum corneum (SC) completely and to study the penetration of the UVA filter substance butyl methoxydibenzoylmethane after application in two different vehicles. METHODS: The amount of corneocytes removed by each tape strip from the flexor forearm of human volunteers was determined via their pseudo-absorption. In a second part, the penetration profiles of a UVA filter substance applied in two different vehicles were determined following the developed standard protocol using the tape stripping procedure in combination with UV/VIS spectroscopy. RESULTS: The amount of corneocytes removed by each tape strip was related to the number of tape strips used for removal. Mean values with a deviation of less than 20% concerning the relative amount of SC removed by a constant number of tape strips were obtained. For instance, a relative amount of 66 +/- 12% was removed with the first 20 tape strips, while nearly the complete SC (95 +/- 3%) was removed using 50 tape strips. In addition, these results were used to estimate the relative SC amounts removed, studying the penetration of the UVA filter substance after application in two different vehicles. No significant differences between the distributions of the UV filter substance applied in both emulsions were obtained (P > 0.05). CONCLUSIONS: The reported procedure for the estimation of the removed SC amount provides the possibility to avoid the complete removal of the SC and to compare the penetration characteristics obtained for different volunteers and different products in relation to the relative horny layer profile.

Reservoir function of the stratum corneum: development of an in vivo method to quantitatively determine the stratum corneum reservoir for topically applied substances.

Investigations on the stratum corneum (SC) reservoir for topically applied substances are of importance in dermatologic science in order to assess the pharmacokinetics of these substances. In the present study, an in vivo method was developed to determine the SC reservoir quantitatively and to investigate the temporal behavior of this reservoir. Therefore, increasing amounts of an oil-in-water emulsion (o/w emulsion) containing 4% of a chemical UV filter were topically applied onto the flexor forearms of 5 healthy volunteers. The saturation of the SC reservoir was determined utilizing the tape stripping technique 1 and 6 h after application. The capacity of the SC reservoir for the o/w emulsion was found to be approximately 2.7 mg/cm(2). Furthermore, a correlation of the capacity of the SC with transepidermal water loss was observed. Extending the time between the topical application and SC removal did not affect the distribution or the recovery rate of the UV filter in the SC. The results indicate that the reservoir of the SC is limited. This is reflected by the saturation level, which depends on the individual volunteer and, presumably, the topically applied substances and formulations used. The results show that the method developed is suited to quantitatively determine in vivo the SC reservoir for topically applied substances.

Lateral spreading of topically applied UV filter substances investigated by tape stripping.

The lateral spreading of topically applied substances is a competitive process to the penetration into the stratum corneum (SC). The penetration of topically applied UV filter substances into the human SC and the lateral spreading were investigated in vivo. Tape stripping in combination with spectroscopic measurements was used to study both processes of two UV filter substances. The concentration of both UV filters was determined inside and outside the application area by varying the application and tape stripping protocol. A spreading of the topically applied substances from the treated to the untreated areas was observed, which caused a concentration gradient. This lateral spreading depends on the time between application and tape stripping and the size of the treated skin area. Significant amounts of topically applied substances were found adjoining the application area, due to the lateral spreading which takes place on the skin surface. In general, the lateral spreading must be considered to be a competitive process when studying penetration processes of topically applied substances. It has to be considered during drug treatment of small limited skin areas and for the interpretation of recovery rates obtained in penetration studies.

UV/VIS absorbance allows rapid, accurate, and reproducible mass determination of corneocytes removed by tape stripping.

The accurate determination of the mass of the horny layer removed by tape stripping is a decisive prerequisite for the application of this technique in penetration studies. A novel method using optical spectroscopy to determine the amount of stratum corneum (SC) is presented. We could show that the absorbance measured in the visible spectral range accurately reflects the mass of the SC fixed on individual tapes. Furthermore, absorbance measurement allows determination of the absolute mass of corneocyte aggregates on the removed tape strips. Topically applied substances do not disturb the spectroscopic measurements in contrast to the conventionally employed weight determination. Identical results were obtained when performing spectroscopic horny layer quantification independently in two separate institutions. Taken together, this new method is rapid, sensitive, reproducible, and accurate. We anticipate a wide application in penetration studies as well as in dermatopharmacokinetics.

Evaluation of the pseudo-absorption method to quantify human stratum corneum removed by tape stripping using protein absorption.

Tape stripping is a well-known method to study the barrier function of the stratum corneum (SC) and penetration processes of topically applied substances into the horny layer. The quantification of the removed corneocytes for each tape strip is the prerequisite for these studies. The pseudo-absorption of the corneocytes was proposed as a measure for the quantification of the removed corneocyte aggregates. In this study, the pseudo-absorption of the corneocytes in the visible range (430 nm) is compared with the protein absorption in the UV range (278 nm) and an absorption at 652 nm obtained after staining of the SC proteins with Trypan blue. Both the protein absorption and the absorption measured after staining correlate well with the pseudo-absorption measured at 430 nm (R(2) = 0.92 +/- 0.04 and R(2) = 0.95 +/- 0.04, respectively).

Investigation of follicular penetration of topically applied substances.

The influence of specific follicle properties, sebum production and hair growth on the follicular penetration of topically applied substances was investigated. The behavior of follicles identified in selected skin areas of volunteers was analyzed by various tape stripping and staining methods in combination with laser scanning microscopy. Furthermore hair growth in the selected skin areas was determined. A correlation between sebum production, hair growth activity and follicular penetration was observed.

Correlation of the local distribution of topically applied substances inside the stratum corneum determined by tape-stripping to differences in bioavailability.

Tape-stripping and optical spectroscopy are used as a suitable combined method to determine the horny layer profile. Firstly, typical ultraviolet filter substances are used as active substances which are fixed inside the horny layer. Secondly, clobetasol propionate was applied topically in two formulations, Temovate Cream and Temovate and Emollient. The measured changes in the local distribution of the drug inside stratum corneum reflect the observed differences in the biological response visualized as blanching. The concentration of the drug in deeper parts of the horny layer proposes the existence of a small channel available for the percutaneous absorption. The observed low intensity blanching is correlated to the follicle orifices of the skin. After application of Temovate and Emollient, a lateral spreading of the drug must be taken into account.

Influence of aromatic hydrocarbons on the metabolism of dichloromethane to carbon monoxide in rats.

The influence of prior or simultaneous oral administration of benzene, toluene, o-, m-, or p-xylene on the carboxyhemoglobin (COHb) level after a single dose of dichloromethane (DCM) was investigated in male rats. Six hours after administration of DCM, 6.2 mmol/kg, the mean maximum COHb level was 9.3 +/- 1.9%. This level was significantly enhanced by prior administration of benzene (16.9 mmol/kg) at 12-24 h, of toluene (18.8 mmol/kg) at 20-28 h, of o- (16.6 mmol/kg) and m-xylene (16.3 mmol/kg) at 20-32 h, and of p-xylene (16.2 mmol/kg) at 24-32 h. The corresponding maximum COHb levels were 20.7 +/- 1.3, 18.6 +/- 1.1, 18.9 +/- 1.1, 22.7 +/- 1.2, and 13.2 +/- 1.0%, respectively. After simultaneous administration of both DCM and the aromatic solvent, the COHb formation was inhibited: values of 1.3 +/- 0.3, 1.7 +/- 0.4, 3.6 +/- 0.2, 1.9 +/- 0.2, and 2.0 +/- 0.2% COHb, respectively, were found. The inhibition was also evident when DCM was administered 12 h after toluene or m-xylene and 12, 16 or 20 h after p-xylene. The inhibition was dose-related as seen after combined gavage of o-, m-, or p-xylene and DCM. The o- and m-, but not the p-methylhippuric acid (MHA) excretion in the urine was significantly reduced after simultaneous administration of equimolar doses of DCM and the corresponding xylenes. In conclusion, it seems that the stimulation or inhibition of the COHb formation after DCM caused by pretreatment with or by simultaneous administration of the aromatic solvents is due to the induction of cytochrome P-450 IIE1 or to competition between DCM and the aromatic solvent on this isozyme of cytochrome P-450.

[Blood alcohol concentration is dependent on the sequence of the combined administration of trichlorethylene and ethanol]. / Blutalkoholwerte in Abhängigkeit von der Sequenz kombinierter Gaben von Trichlorethylen und Ethanol.

In equimolar amounts ethanol and trichloroethylene were administered intraperitoneally to male ICR mice in varying sequences. The sequence of administration proved to be decisive for the blood alcohol levels. In relation to ethanol alone following the simultaneous administration of trichloroethylene and ethanol the blood alcohol levels were elevated. This effect is furthermore enhanced if trichloroethylene was administered 1 h prior to ethanol administration. The reversed sequence had no effect on blood alcohol levels.