Determination of penetration profiles of topically applied substances by means of tape stripping and optical spectroscopy: UV filter substance in sunscreens

An in vivo study to evaluate the influence of oil blotting paper on the efficacy of sunscreen

BACKGROUND

Ultraviolet radiation (UVR) is a major cause of photoaging and photocarcinogenesis. An appropriate application of sunscreen can effectively protect UV damage but cause unpleasant skin oiliness. Oil blotting paper is commonly used to reduce oiliness in some parts of the world although its influence on the efficacy of sunscreen has not been carefully investigated.

OBJECTIVE

To evaluate the efficacy of sunscreen after applying oil blotting paper.

MATERIALS AND METHODS

Measurement of oiliness and sunscreen efficacy was compared before and after the use of oil blotting paper in 11 healthy volunteers, 10 females, and 1 male. Specifically, 3 zones on each subject's back were exposed to UVR from a solar simulator, that is, 1) no sunscreen, 2) sunscreen (organic sunscreen at 2 mg/cm² SPF 30) left on for 30 minutes, and 3) sunscreen left on for 30 minutes followed by application of oil blotting paper. Skin oiliness was also compared before and after oil blotting using a sebumeter. All areas were phototested for the comparison of the minimal erythema dose (MED) and sun protection factor (SPF).

RESULTS

The averaged MED of our subjects is 4.3 standard erythema doses (SED) in the unprotected area. The averaged MED was decreased after oil blotting from 89.8 SED to 59.8 SED. The SPF was also decreased from 20.70 to 13.99.

CONCLUSIONS

Application of oil blotting paper significantly reduces the efficacy of organic sunscreen.

Ex vivo penetration analysis and anti-inflammatory efficacy of the association of ferulic acid and UV filters

BACKGROUND

Unprotected chronic exposure to ultraviolet (UV) radiation generates many harmful effects to human skin and sunscreens are essential to health, however, traditional products do not provide enough protection against cutaneous oxidative stress, a process amplified by UV radiation. Therefore, the development of multifunctional photoprotective formulations seems to be a more efficacious approach, since these enable the absorption/reflection of UV radiation and maintain the cutaneous homeostasis.

OBJECTIVES

In the present study, ferulic acid (FA), a well-known antioxidant, has been combined with two UV filters, bemotrizinol and ethylhexyl triazone, and the safety and efficacy of this formulation has been assessed combining ex vivo and in vivo methods.

METHODS

Skin permeation assays were performed by applying the formulation in the volar forearm of participants, after which consecutive samples of the stratum corneum were collected by tape stripping, and the quantification of FA, bemotrizinol and ethylhexyl triazone was performed by high-performance liquid chromatography (HPLC). Also, the FA anti-inflammatory action in combination with the UV filters was probed through a method employing Laser Doppler flowmetry to measure the vasodilatory response to methyl nicotinate topical application.

RESULTS

Skin permeation assay was able to characterize the penetration depth of each substance. It should also be noted that a specific HPLC analytical method was developed in this study to enable the rapid simultaneous quantification of the three substances. Results from Laser Doppler flowmetry showed that the FA was able to mitigate the vasodilatory response.

CONCLUSIONS

FA proved to be a valuable resource in a multifunction sunscreen, not only providing an increase in the SPF of sunscreens, previously published, but also decreasing the extent of inflammation.

Electrohydrodynamic spray applicator for homogenous application and reduced overspray of sunscreen

BACKGROUND

The recommended amount of sunscreen by hand application (2 mg/cm² ) is in reality not achieved, which decreases the homogeneity and thereby the effective sun protection factor (SPF).

MATERIALS AND METHODS

The homogeneity of sunscreen applied by a newly developed spray applicator using an electrostatically charged aerosol, for which a hand rubbing of the formulation is not necessary, is evaluated. In vivo experiments were performed on the volar forearms of human volunteers using the spray applicator compared to the standardized hand application according to ISO 24444.

RESULTS

The distribution homogeneity was assessed qualitatively using in vivo laser scanning microscopy and quantitatively by absorption spectroscopy after tape stripping and by the standard deviation of multiple spatially displaced reflectance measurements for non-invasive SPF determination below the minimal erythemal dose, which showed a significantly higher homogeneity by 20.9% after spray application compared to hand application.

CONCLUSION

Non-invasive SPF determination of multiple spatially displaced reflectance measurements was proven to be a suitable method for the non-invasive determination of the sunscreen distribution homogeneity. Electrostatically charged spray application increased the sunscreen distribution homogeneity on the skin and can reduce the amount of overspray.

The influence of different shavers on the skin quantified by non-invasive reflectance confocal microscopy

BACKGROUND

The impact of personal care devices on skin is mainly assessed using subjective tools. However, new objective, accurate non-invasive in vivo imaging techniques have been developed. The aim of this study was to evaluate the ability of reflectance confocal microscopy (RCM) in quantifying morphological impact of shavers on skin. Furthermore, tape stripping (TS) as method to study morphological impact of shavers was evaluated.

METHODS

In 12 healthy male subjects, for two consecutive days, a split-face test was performed in the neck; on one side a shaver was applied, while the other side was exposed to TS. The stratum corneum (SC) thickness was quantified using RCM and sensory observations were evaluated using questionnaires.

RESULTS

Shavers with a different impact on skin, can be discriminated by RCM; shaver B removed more SC after application than the skin friendlier shaver A. Furthermore, the changes in SC thickness induced by TS corresponded well to that of the shavers.

CONCLUSION

RCM is able to quantify the impact of different shavers on skin. Besides, TS appeared to be a suitable model mimicking the mechanical impact of shavers on skin. RCM in combination with the TS model appeared to be a suitable minimally invasive model to obtain morphological and cell biological data on skin-material interactions caused by different personal care devices.

Skin integrity testing and monitoring of in vitro tape stripping by capacitance-based sensor imaging

BACKGROUND

Despite the frequent use of porcine ear skin for tape-stripping experiments, the peculiarities of this skin type have not been characterised in detail yet. Thus, different techniques were employed to investigate the skin surface structure of porcine ear skin and the changes in barrier function during in vitro tape stripping. To this end, the potential of capacitance-based skin hydration imaging as a means of skin quality control was investigated for the first time.

METHODS

The porcine ear model was characterised before and during tape stripping using transepidermal water loss (TEWL) measurements, capacitance-based sensor imaging, attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) and optical light microscopy.

RESULTS

The capacitance-based sensor was found to deliver precise information about the quality of the employed skin sites before and during tape stripping. The removal of stratum corneum proteins was highly reproducible even for different porcine ear types. The mean greyscale values showed an excellent linear correlation to the corresponding TEWL values and the respective penetration depth. Optical light microscopy confirmed the presence of canyons on the surface of porcine ear skin.

CONCLUSION

The results suggest that the capacitance-based sensor is a suitable tool for skin integrity testing of porcine ear skin in vitro and for monitoring changes in skin barrier function.

Influence of skin aging effects on the skin surface profile and the correlated distribution of topically applied sunscreens

The surface profile of human skin influences characteristically the distribution pattern of topically applied formulations and consequently the efficacy of sunscreens. The volumes of furrows and the spectroscopically determined factors of inhomogeneity are investigated for three sunscreens. A clear correlation between both measurands exists. The average values for younger (<32 years) and older (≥51 years) volunteers do not show statistically significant differences. Systematic variations found for the individual values are due to a reduced elasticity of the skin with age improving the homogeneity of the sunscreen distribution.

Carriers in the topical treatment of skin disease

Topical drug application is less prone to severe systemic side-effects than systemic application. Starting with the liposomes, various types of nanosized and microsized drug carriers have been developed to increase the notoriously low penetration of active agents into the skin, which limits not only the topical therapy of skin disease but also transdermal therapy. Today, liposome- and microsponge-based preparations are approved for dermatomycosis, acne and actinic keratosis. Under investigation are drug carriers such as lipid nanoparticles, polymeric particles, dendrimers, and dendritic-core multi-shell nanotransporters. According to the rapidly increasing research in this field, both in academia and industry, a breakthrough appears likely, once stability problems (nanoparticles) and safety concerns (dendrimers) are overcome. Technical approaches and results of in vitro, ex vivo and in vivo testing are described, taking into account pharmacokinetic, efficacy and safety aspects.

Comparison of human and porcine skin for characterization of sunscreens

The universal sun protection factor (USPF) characterizing sunscreen efficacy based on spectroscopically determined data, which were obtained using the tape stripping procedure. The USPF takes into account the complete ultraviolet (UV) spectral range in contrast to the classical sun protection factor (SPF). Until now, the USPF determination has been evaluated only in human skin. However, investigating new filters not yet licensed excludes in vivo investigation on human skin but requires the utilization of a suitable skin model. The penetration behavior and the protection efficacy of 10 commercial sunscreens characterized by USPF were investigated, comparing human and porcine skin. The penetration behavior found for typical UV filter substances is nearly identical for both skin types. The comparison of the USPF obtained for human and porcine skin results in a linear relation between both USPF values with a correlation factor R(2)=0.98. The results demonstrate the possibility for the use of porcine skin to determine the protection efficacy of sunscreens.

Investigation into the mechanism by which cyclodextrins influence transdermal drug delivery

The objective of this study was to investigate the mechanism by which hydroxypropyl-beta-cyclodextrin (HPCD) increases transdermal permeation. Hairless mouse skin was pretreated with HPCD solutions for up to 4 h. After removing the HPCD, corticosteroid-containing suspensions were applied and the transdermal flux and skin accumulation of two model drugs were investigated. After pretreatment, changes to the stratum corneum endothermic melting transitions were determined as an indication of HPCD-induced lipid disorganization. Results demonstrated that HPCD pretreatment had no significant effect on the transdermal permeation or skin accumulation of the model corticosteroids. These findings suggest that HPCD functions to enhance the apparent solubility of the drug in the formulation, thus increasing transdermal permeation rather than extracting lipids from the skin.

Influence of solid lipid microparticle carriers on skin penetration of the sunscreen agent, 4-methylbenzylidene camphor

The objective of this study was to prepare lipid microparticles (LMs) loaded with the sunscreen agent, 4-methylbenzylidene camphor (4-MBC), to achieve decreased skin penetration of this UV filter. The microparticles were produced by the melt dispersion technique using tristearin as lipidic material and hydrogenated phosphatidylcholine as the surfactant. The obtained microparticles were characterized by scanning electron microscopy and differential scanning calorimetry. Release of 4-MBC from the LMs was found to be slower than its dissolution rate. The influence of the LMs' carrier system on percutaneous penetration was evaluated after their introduction in a model topical formulation (emulsion). In-vitro measurements were performed with cellulose acetate membranes in Franz diffusion cells. The 4-MBC release and diffusion was decreased by 66.7-77.3% with the LM formulation, indicating that the retention capacity of the microparticles was maintained after incorporation into the emulsion. In-vivo human skin penetration of 4-MBC was investigated by tape stripping, a technique for selectively removing the upper cutaneous layers. The amount of sunscreen penetrating into the stratum corneum was greater for the emulsion containing non-encapsulated 4-MBC (36.55% of the applied dose) compared with the formulation with the sunscreen-loaded microparticles (24.57% of the applied dose). The differences between the two formulations were statistically significant in the first (2-4) horny layer strips. Moreover, the LMs' effect measured in-vivo was less pronounced than in-vitro. The increased 4-MBC retention on the skin surface achieved by its incorporation in the LMs should enhance its efficacy and reduce the potential toxicological risk associated with skin penetration.

Transdermal Penetration of UV Filters

A penetration study of 2-ethylhexyl-4-methoxycinnamate (EHMC), 4-methyl benzylidenecamphor (MBC), butyl methoxydibenzoylmethane (BMBM), 2-ethylhexyl-2,4,5-trimethoxycinnamate (EHTMC) and di(2-ethylhexyl)-2,4,5-trimethoxybenzalmalonate (TMB) through baby mouse skin (Mus musculus Linn.) was carried out using a vertical Franz diffusion cell. At 4.4 mg/cm(2) coverage of UV filter on the skin, 2.98 +/- 0.38, 1.15 +/- 0.14 and 0.80 +/- 0.28% of the applied EHMC, MBC and BMBM were detected in the receptor fluid at 24 h after application. Penetrations of UV filter in an ethanolic solution and lotion forms were comparable. EHTMC and TMB showed insignificant penetration across the baby mouse skins. Baby mouse skins kept at 4, -20 and -80 degrees C gave similar EHMC penetration results. Penetrations of EHMC, BMBM, EHTMC and TMB across human epidermis were carried out upon 5 volunteers using the suction blister technique. The results also confirmed the significant penetrations of EHMC and BMBM and the insignificant penetrations of EHTMC and TMB.

Optimization of the skin multiple analyte profile bioanalytical method for determination of skin biomarkers from D-Squame tape samples

BACKGROUND/PURPOSE

This work was performed to optimize extraction conditions for D-Squame tape skin samples for use in the skin multiple analyte profile (SkinMAP) method, a Linco Research Corporation bead-based assay for skin analytes. The experiments were designed to help identify sources of variability during extraction that may be amenable to further control.

METHODS

Two experimental designs were used to study factors influencing the extraction of skin samples from D-Squame tapes. Visually healthy skin samples were obtained from both female and male adult volar forearms. Factors studied in two experiments included: four surfactant (SDS) levels (0.02-0.2%), two buffer types [Citrate-phosphate buffered saline at pH 5.5, phosphate-buffered saline (PBS) at pH 7.4], two buffer volumes (1.0, 1.5 mL), two propylene glycol (PG) levels (0.1%, 1.0%), two extraction temperatures (7-10 degrees C, 22-30+ degrees C), two extraction times (30, 60 min), and location in sonication bath (two vectors). The response biomarkers were cortisol, fibronectin, human serum albumin, involucrin, keratin-6 and keratins 1, 10. Skin sampling sites were also evaluated as sources of variation.

RESULTS

There was no single set of extraction conditions in our experiments that maximized recovery of all the biomarkers. SDS level had the most consistently significant (P<0.05) and directional effects on biomarker recoveries. In general, higher SDS resulted in higher recovery of all biomarkers. There was less consistency and fewer significant results for the other extraction factors.

CONCLUSIONS

These data enable us to better manage SkinMAP studies and interpret their results. The use of 1.5 mL PBS containing 0.2% SDS and 0.5% PG with 30 min sonication at low (near 4 degrees C) temperature is optimal for the quantitation of a range of SkinMAP analytes. In order to protect researchers from obtaining inflated false positive rates, it is crucial to design such studies and analyze the data using appropriate statistical methodology, especially for those studies involving only a small number of subjects.

Ex-vivo spectroscopic quantification of sunscreen efficacy: proposal of a universal sun protection factor

The sun protection factor (SPF) describes the protective behavior of sunscreens insufficiently, because this factor takes into account only the UVB spectral range, and strains the volunteers during its determination by invasively invoking an erythema. A new noninvasive method is proposed that is based on the UV spectroscopic measurement of tape strips taken from a sunscreen-treated skin area. The resulting sum transmission spectra of the tape strips reflect the in-vivo distribution of the absorber on the skin and quantify the protective efficacy of the applied sunscreens over the complete UV spectral range. The spectroscopic data provide a basis for the calculation of a universal sun protection factor (USPF). The comparison of the concrete values of USPF and SPF results in the following statements. 1. An unique functional correlation is not to be expected because a different UVB / UVA dependence exists. 2. The size of the differences between both values is influenced clearly by the intensity relation of the average sum transmission in the UVB in comparison to the UVA range. 3. The USPF values objectively assess the efficacy of sunscreens considering a protection against all irradiation injuries.

Follow-up of drug permeation through excised human skin with confocal Raman microspectroscopy

Skin is a multilayered organ which covers and protects the surface of human body by providing a barrier function against exogenous agents. Meanwhile, the efficacy of several topically applicated drugs is directly related to their penetration through the skin barrier. Several techniques are commonly used to evaluate the rate, the speed and the depth of penetration of these drugs, but few of them can provide real-time results. Therefore, the use of nondestructive and structurally informative techniques permits a real breakthrough in the investigations on skin penetration at a microscopic scale. Confocal Raman microspectroscopy is a nondestructive and rapid technique which allows information to be obtained from deep layers under the skin surface, giving the possibility of a real-time tracking of the drug in the skin layers. The specific Raman signature of the drug enables its identification in the skin. In this study, we try to follow the penetration of Metronidazole, a drug produced by Galderma as a therapeutic agent for Rosacea treatment, through the skin. The first step was the spectral characterization of Metronidazole in the skin. Then micro-axial profiles were conducted to follow the penetration of the drug in the superficial layers, on excised human skin specimens. For more accurate information, transverse sections were cut from the skin and spectral images were conducted, giving information down to several millimeters deep. Moreover, the collected spectra permit us to follow the structural modifications, induced by the Metronidazole on the skin, by studying the changes in the spectral signature of the skin constituents.

Complexation of the sunscreen agent, 4-methylbenzylidene camphor with cyclodextrins: effect on photostability and human stratum corneum penetration

The interaction between the sunscreen agent, 4-methylbenzylidene camphor (4-MBC) and hydrophilic alpha-, beta- and gamma-cyclodextrin derivatives was investigated in water by phase-solubility analysis. Among the studied cyclodextrins, random methyl-beta-cyclodextrin (RM-beta-CD) had the greatest solubilizing activity. The complexation of the sunscreen agent with RM-beta-CD was confirmed by nuclear magnetic resonance spectroscopy and powder X-ray diffractometry. The light-induced decomposition of 4-MBC in emulsion vehicles was markedly decreased by complexation with RM-beta-CD (the extent of degradation, determined by HPLC, was 7.1% for the complex compared to 21.1% for free 4-MBC). The influence of RM-beta-CD on the human skin penetration of the sunscreen was investigated in vivo using the tape stripping method, a useful procedure for selectively removing the outermost cutaneous layers. Considerable quantities (21.2-25.1% of the applied dose) of 4-MBC permeated in the stratum corneum. However, no significant differences in the amounts of UV filter in the 10 first strips of the horny layer were observed between the formulations containing 4-MBC free or complexed with RM-beta-CD. Therefore, RM-beta-CD complexation did not alter the retention of 4-MBC in the superficial layers of the stratum corneum, where its action is more desirable.

Investigation of the homogeneity of the distribution of sunscreen formulations on the human skin: characterization and comparison of two different methods

The efficacy of sun protection, mostly realized by the application of sunscreen formulations, is commonly described by the sun protection factor (SPF). Previous investigations have shown that the efficacy of the sun protection inter alia depends on the homogeneity of the distribution of the topically applied sunscreen formulation on the human skin. Therefore, suitable methods are required to determine the homogeneity of topically applied substances on the skin surface. This study provides and compares two different methods, which enable this determination. Laser scanning microscopy allows the analysis of tape strips removed from skin treated with a sunscreen. These reflect the inhomogeneous distribution on the skin that can complementary be determined directly, utilizing a dermatological laser scanning microscope. For the second method, a chromatic confocal setup was utilized, which enables the study of the microtopography of skin replicas before and after the application of a sunscreen product. The two methods were applied for the evaluation of three different sunscreen formulations for each method. A correlation of the homogeneity of distribution with the in vivo SPF could be confirmed. Both methods are suitable to investigate the homogeneity of the tested sunscreen formulations, although they provide different advantages and disadvantages.

Topical Bioavailability of Triamcinolone Acetonide: Effect of Occlusion

BACKGROUND/AIMS

Occlusion by covering the skin with an impermeable wrap enhances skin hydration, affects drug absorption and can induce the formation of a drug reservoir within the stratum corneum. This is desired in local therapy with topical corticosteroids. The aim of the study was to investigate the effect of occlusion before (experiment 1) and after (experiment 2) application on the penetration of triamcinolone acetonide (TACA) into the stratum corneum.

METHODS

The experiments were conducted on the forearms of 10 healthy volunteers. In experiment 1, 100 microg/cm(2) TACA in acetone were applied on 3 sites per arm, one arm having been pre-occluded for 16 h. In experiment 2, the same dose was applied on 2 sites per arm, and one arm was occluded after application until skin sampling. Stratum corneum samples were removed by tape stripping at 0.5, 4 and 24 h (experiment 1) and 4 and 24 h (experiment 2) after application. Corneocytes and TACA were quantified by ultraviolet-visible spectroscopy and HPLC, respectively. The total TACA amount penetrated into the stratum corneum was evaluated by multifactor ANOVA.

RESULTS

TACA penetration into the stratum corneum with and without pre-occlusion (experiment 1) showed no significant difference and decreased with time. Occlusion after application (experiment 2) produced a marked TACA accumulation within the stratum corneum, which persisted for 24 h.

CONCLUSION

Pre-occlusion showed no effect on the topical bioavailability of TACA in the stratum corneum. In contrast, post-occlusion enhanced the TACA penetration by a factor of 2, favouring the development of a drug reservoir.

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.

Topical bioavailability of triamcinolone acetonide: effect of dose and application frequency

The application frequency of topical corticosteroids is a recurrently debated topic. Multiple-daily applications are common, although a superior efficacy compared to once-daily application is not unequivocally proven. Only few pharmacokinetic studies investigating application frequency exist. The aim of the study was to investigate the effect of dose (Experiment 1) and application frequency (Experiment 2) on the penetration of triamcinolone acetonide (TACA) into human stratum corneum (SC) in vivo. The experiments were conducted on the forearms of 15 healthy volunteers. In Experiment 1, single TACA doses (300 microg/cm(2) and 100 microg/cm(2)) dissolved in acetone were applied on three sites per arm. In experiment 2, single (1 x 300 microg/cm(2)) and multiple (3 x 100 microg/cm(2)) TACA doses were similarly applied. SC samples were harvested by tape stripping after 0.5, 4 and 24 h (Experiment 1) and after 4, 8 and 24 h (Experiment 2). Corneocytes and TACA were quantified by UV/VIS spectroscopy and HPLC, respectively. TACA amounts penetrated into SC were statistically evaluated by a paired-sample t-test. In Experiment 1, TACA amounts within SC after application of 1 x 300 microg/cm(2) compared to 1 x 100 microg/cm(2) were only significantly different directly after application and similar at 4 and 24 h. In Experiment 2, multiple applications of 3 x 100 microg/cm(2) yielded higher TACA amounts compared to a single application of 1 x 300 microg/cm(2) at 4 and 8 h. At 24 h, no difference was observed. In conclusion, using this simple vehicle, considerable TACA amounts were retained within SC independently of dose and application frequency. A low TACA dose applied once should be preferred to a high dose, which may promote higher systemic exposure.

Effect of size of TiO2 nanoparticles embedded into stratum corneum on ultraviolet-A and ultraviolet-B sun-blocking properties of the skin

Recently there has been a strong demand to protect human skin against negative effects of the UV solar light. This problem is interesting due to the increased frequency of human diseases caused by such radiation. We aim to evaluate how the optical properties of the horny layer of skin can be effectively changed by imbedding TiO2 fine particles to achieve the maximal attenuation of the UV solar radiation. In-depth distribution of TiO2 particles embedded into the skin by multiple administration of sunscreens is determined experimentally using the tape-stripping technique. A computer code implementing the Monte Carlo method is developed to simulate photon migration within the 20-microm-thick horny layer filled with nanosized TiO2 spheres, 25 to 200 nm in diameter. Dependencies of the UV radiation of two wavelengths (310 and 400 nm) absorbed by and totally reflected from, as well as transmitted through the horny layer on the size of TiO2 particles are obtained and analyzed. The most attenuating particles are found to be 62 and 122 nm in diameter for 310- and 400-nm light, respectively. The former could be suggested as the main fraction to be used in sunscreens to prevent erythema.