The stripping technique: in vitro absorption and penetration of five UV filters on excised fresh human skin

RP-18 TLC and Computational Descriptors of Skin Permeability of Sunscreens

Abstract The relationships between the reversed-phase thin layer chromatographic retention parameters obtained on octadecyl-modified silica (RP-18) sorbent for mobile phases containing water and one of six water-miscible organic modifiers (acetone, methanol, acetonitrile, tetrahydrofurane, N,N-dimethylformamide, 1,4-dioxane) and skin permeability coefficients were studied for a group of 21 cosmetic raw materials, mainly organic sunscreens and preservatives. The correlations between the skin permeability coefficients log Kd calculated in silico using EpiSuite software and the RP-18 thin layer chromatographic retention parameters are mostly linear, especially for compounds of lower-to-medium lipophilicity.. It was established that skin permeability coefficient models based on retention parameters collected for mobile phases containing acetone or dioxane (75% v/v), proposed for structurally unrelated cosmetic raw materials are also applicable to other actives, as shown using a test set of compounds whose in vivo log Kd data are available. Skin permeability models developed in this study have the benefit of being based on easily obtained, chromatographic descriptors and their applicability extends beyond cosmetic chemistry.

Sunscreens and their usefulness: have we made any progress in the last two decades?

Sunscreens have now been around for decades to mitigate the Sun's damaging ultraviolet (UV) radiation which, although essential for the existence of life, is a recognized prime carcinogen. Accordingly, have suncreams achieved their intended purposes towards protection against sunburns, skin photo-ageing and the like? Most importantly, however, have they provided the expected protection against skin cancers that current sunscreen products claim to do? In the last two decades, there have been tens, if not hundreds of studies on sunscreens with respect to skin protection against UVB (280‒320 nm)-traditionally sunscreens with rather low sun protection factors (SPF) were intended to protect against this type of radiation-and UVA (320‒400 nm) radiation; a distinction between SPF and UVA protection factor (UVA-PF) is made. Many of the studies of the last two decades have focused on protection against the more skin-penetrating UVA radiation. This non-exhaustive article reviews some of the important facets of what is currently known about sunscreens with regard (i) to the physical UV filters titanium dioxide (TiO₂) and zinc oxide (ZnO) and the mostly photo-unstable chemical UVB/UVA filters (e.g., octinoxate (OMC) and avobenzone (AVO), among others), (ii) to novel chemical sunscreen agents, (iii) to means that minimize the breakdown of chemical filters and improve their stability when exposed to UV sunlight, (iv) to SPF factors, and (v) to a short discussion on non-melanoma skin cancers and melanoma. Importantly, throughout the article we allude to the safety aspects of sunscreens and at the end ask the question: do active ingredients in sunscreen products pose a risk to human health, and what else can be done to enhance protection? Significant loss of skin protection from two well-known commercial suncreams when exposed to simulated UV sunlight. Cream I: titanium dioxide, ethylhexyl triazone, avobenzone, and octinoxate; Cream II: octyl salicylate, oxybenzone, avobenzone, and octinoxate.

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.

Skin barrier damaging and repairing process: A new application field of dermoscopy

BACKGROUND

Although more and more noninvasive detection technologies have been used in assessing skin barrier integrity and functions, more accurate, intuitive, and convenient detective methods still needed to be explored and developed.

AIMS

To investigate the characteristic image changes under the dermoscopy and to explore the relationship with skin physiological indexes in skin barrier damaging and repairing process.

PATIENTS/METHODS

25 healthy subjects with normal skin in forearm were included and divided into different groups according to the operated strips numbers (30, 35, and 40 times). Before tape stripping, and immediately, 3, 7, 14, and 21 days after tape stripping, dermoscopic examination and skin transepidermal water loss (TEWL), surface hydration, and L*a*b* value were simultaneously tested in the same region.

RESULTS

Immediately after different times tape stripping, the amount of cuticle cells residues and the microvascular images were different. In skin barrier repairing process, the scab forming time observed under dermoscopy was day 14, day 7, and day 3 on 30 times, 35 times, and 40 times stripped skin, respectively. A small amount of cuticle cells and blurry vessels could be identified in hydration value <40 group, while there was no cuticle cell residue, and the branching vessels were obvious in hydration value >40 group.

CONCLUSIONS

Unique manifestations could be observed under dermoscopy in different time points of skin barrier with various degree of injury and in skin barrier repairing process. By combining dermoscopy and skin indexes assessing technologies, the skin barrier integrity and function could be observed and evaluated more accurately and precisely.

Assessment of non-invasive techniques and herbal-based products on dermatological physiology and intercellular lipid properties

Skin is the largest external organ of the human body. It acts as a barrier to protect the human body from environmental pollution, mechanical stress, and excessive water loss. The defensive function resides primarily on top of the epidermis layer commonly known as stratum corneum (SC). Human SC consists of three major lipids, namely ceramide, free fatty acid, and cholesterol that comprise approximately 50%, 25%, and 25% of the total lipid mass, respectively. The optimal composition of SC lipids is the vital epidermal barrier function of the skin. On the other hand, skin barrier serves to limit passive water loss from the body, reduces chemical absorption from the environment, and prevents microbial infection. In contrast, epidermal lipids are important to maintain the cell structure, growth and differentiation, cohesion and desquamation as well as formation of a permeability barrier. Multiple non-invasive in vivo approaches were implemented on a regular basis to monitor skin physiological and intercellular lipid properties. The measurement of different parameters such as transepidermal water loss (TEWL), hydration level, skin elasticity, collagen intensity, melanin content, sebum, pH, and tape stripping is essential to evaluate the epidermal barrier function. Novel non-invasive techniques such as tape stripping, ultrasound imaging, and laser confocal microscopy offer higher possibility of accurate and detailed characterisation of skin barrier. To date, these techniques have also been widely used to determine the effects of herbal plants in dermatology. Herbal plants have been traditionally used for ages to treat a variety of skin diseases, as reported by the World Health Organisation (WHO). Their availability, lower cost, and minimal or no side effects have created awareness among society, thus increase the demand for natural sources as the remedy to treat various skin diseases. This paper reviews several non-invasive techniques and evaluations of herbal-based product in dermatology.

Estimation of the Contribution Made to Down-the-Drain Emissions of D5 by Personal Care Product Categories in the European Union

Aquatic risk assessment of personal care chemicals requires quantifying the contribution of all product types containing these ingredients to down-the-drain emissions. We developed a probabilistic model framework embracing stochastic variability associated with individual consumers and their behaviors in the European Union, as well as other sources of uncertainty related to losses following applications (e.g., volatilization). The model was applied to decamethylcyclopentasoloxane (D5), an emollient used in wash-off (WO) and leave-on (LO) products. Quantifying contributions from each product category containing D5 to down-the-drain emissions is necessary to inform optimal risk management options. Simulation results for the baseline scenario in 2012 support the argument that LO products make up a minor contribution (7.1%) to down-the-drain emissions of D5, with only 0.20% of the D5 used in LO products being released to wastewater. The most influential model parameters are the release factor from WO products and the time between application and use for various LO product types, stressing the importance of embracing stochastic variability across individuals' behavior when assessing contributions of various product types to environmental emissions. The downward trend in WO use from 2010 to 2016 is reflected in declining concentrations in wastewater influent during the same period. Uncertainty remains about future levels of D5, once phasing out WO products is complete. The probabilistic model in conjunction with high-tier data of consumer habits is a promising high-tier tool for the characterization of complex emission scenarios of personal care ingredients. Integr Environ Assess Manag 2019;00:1-12. © 2019 SETAC.

Systemic availability of lipophilic organic UV filters through dermal sunscreen exposure

BACKGROUND

Chemical UV filters are common components in sunscreens and cosmetic products and used to protect the skin against harmful effects of sunlight like sunburn. However, the effectiveness of sunscreens in the prevention of skin cancer is in some parts still controversial. Meanwhile, questions about negative effects of the chemical UV filters on human health arise and request an effective risk assessment. Real-life exposure data in humans after application of these products are still rare. Thus, we explored whether and to what extent UV filters are absorbed through the skin into the human body.

MATERIAL AND METHODS

Plasma and urine samples from 20 healthy volunteers were collected before, during and after a real-life exposure scenario (1st application: 2 mg/cm²; 2nd and 3rd (after 2 and 4 h): 1 mg/cm² each) using a commercial sunscreen formulation for one day. These samples were analyzed for their content of the currently prominent UV filters octocrylene and avobenzone as well as 2-cyano-3,3-diphenylacrylic acid (CDAA) as the main octocrylene metabolite by using different liquid chromatography electrospray-ionization tandem mass spectrometric procedures.

RESULTS

Following dermal sunscreen exposure, avobenzone, octocrylene and CDAA reached concentrations up to 11 μg/L, 25 μg/L and 1352 μg/L in plasma. In urine detection rates of avobenzone and octocrylene were low while CDAA showed a high detection rate and reached up to 5207 μg/g creatinine. Kinetic models could be fitted for octocrylene and CDAA in plasma and CDAA in urine. Concentration peaks were reached between 10 and 16 h after first application and half-life periods were in the range of 1.5 to 2 days. The lipophilic UV filter octocrylene and its metabolite CDAA showed a much slower elimination than other more hydrophilic UV filters. Concordantly, the metabolite CDAA in particular showed a markedly increased renal excretion over the whole sampling period and indicated high internal exposure to OC.

DISCUSSION

Real-life sunscreen usage leads to considerable bioavailability of organic UV filters and their metabolites which is rarely seen for other environmental exposures. A combined monitoring of the parent compound and its metabolites is important to fully address internal exposure to the UV filter in humans. Considering the kinetic profiles a prolonged systemic release due to depot formation in skin and a potential accumulation through multi-day exposure is presumed. High in-vivo loads call for a critical toxicological assessment of the UV filters and their metabolites.

Quantification of prominent organic UV filters and their metabolites in human urine and plasma samples

Monitoring human exposure to chemical UV filters is essential for an accurate assessment of the health risk caused by the resorbed compounds. We developed different procedures for the determination of the prominent UV filters octocrylene (OC), avobenzone (AVO) and 2-ethylhexyl salicylate (EHS) as well as for two OC and EHS metabolites in human urine and OC, AVO and 2-cyano-3,3-diphenylacrylic acid (CDAA) in plasma samples using liquid chromatography-tandem mass spectrometry (LC-MS/MS). Since the development of a multi-method for all analytes proved to be difficult, three different procedures were established for the determination of AVO, OC and its metabolite CDAA in urine and plasma as well as for EHS and its metabolite 5-hydroxy-EHS in urine. The methods have been validated with good sensitivity, precision and accuracy. The procedures were satisfactorily applied to the determination of the target compounds in human samples collected from volunteers after sunscreen application. These new analytical procedures can provide information on the internal exposure to the UV filters OC, AVO and EHS, which has been little studied.

Role of solid lipid nanoparticles as photoprotective agents in cosmetics

BACKGROUND

Novel drug delivery systems have gained popularity since last two decades because of its advantages over conventional dosage forms. Effect of UV radiation on skin can cause either acute or chronic damage to our skin. Solid lipid nanoparticles (SLNs) were developed as novel carrier over the conventional carrier systems like liposomes and emulsions. The SLNs were selected as a carrier for the formulation because of its ability to protect the labile drug particles, the ability to make the drug release in a controlled manner, and occlusive property of the SLNs.

OBJECTIVE

The current review is an attempt to focus on the characteristics of solid lipid nanoparticles, methods for the preparations, and their cosmetic applications along with some future perspectives of the nanodrug delivery systems.

METHODS

A review of the current literature of solid lipid nanoparticles (SLNs) as novel carrier showed better photoprotection in sunscreens.

RESULTS AND CONCLUSIONS

The disadvantages of conventional sunscreens can be overcome by incorporation of solid lipid nanoparticles. On comparing the lipid nanobased systems with traditional cosmetic products, the occlusion can be achieved without the use of paraffin and other greasy oils. The film formed by lipid nanoparticles will be smooth as compared to the inflexible films formed by the paraffin. Newer approaches may lead to even better results. They also possess excellent UV-blocking activity and showed better photoprotection.

Investigation of cis-trans isomer dependent dermatotoxicokinetics of UV filter ethylhexyl methoxycinnamate through stratum corneum in vivo

2-Ethylhexyl methoxycinnamate (EHMC) is one of the most used ultraviolet filters in personal care products. It undergoes cis/trans isomerization in sunlight, and there is limited toxicological understanding of the effects of the cis-isomer. It is known that two geometric isomers of one compound can have different physico-chemical properties and effects. However, there are no studies focusing on toxicokinetics of EHMC isomerization products to compare their potential difference in dermal exposure to cis-EHMC and trans-EHMC due to the difference in their dermatotoxicokinetics. In this study, dermal absorption of the parental trans-EHMC and its cis isomer was studied. A commercially available sunscreen lotion containing trans-EHMC and spiked with laboratory-prepared cis-EHMC was locally applied on the forearm skin of two volunteers. After 8 h of skin exposure, the stratum corneum (SC) layer was removed by tape stripping. The removed thickness of the SC was determined spectrophotometrically using a total protein assay. The concentration of both isomers in the removed SC was measured by HPLC-DAD. A new diffusion and permeability coefficient of both EHMC isomers in SC were determined by Fick's second law of diffusion in vivo. The difference in dermatotoxicokinetic parameters between the two isomers was not statistically significant. However, separate toxicological studies of isomeric forms and the determination of their dermatotoxicokinetic parameters are crucial for refinement of human risk assessment.

Different DNA damage response of cis and trans isomers of commonly used UV filter after the exposure on adult human liver stem cells and human lymphoblastoid cells

2-ethylhexyl 4-methoxycinnamate (EHMC), used in many categories of personal care products (PCPs), is one of the most discussed ultraviolet filters because of its endocrine-disrupting effects. EHMC is unstable in sunlight and can be transformed from trans-EHMC to emergent cis-EHMC. Toxicological studies are focusing only on trans-EHMC; thus the toxicological data for cis-EHMC are missing. In this study, the in vitro genotoxic effects of trans- and cis-EHMC on adult human liver stem cells HL1-hT1 and human-derived lymphoblastoid cells TK-6 using a high-throughput comet assay were studied. TK-6 cells treated with cis-EHMC showed a high level of DNA damage when compared to untreated cells in concentrations 1.56 to 25μgmL^-1. trans-EHMC showed genotoxicity after exposure to the two highest concentrations 12.5 and 25μgmL^-1. The increase in DNA damage on HL1-hT1 cells induced by cis-EHMC and trans-EHMC was detected at the concentration 25μgmL^-1. The No observed adverse effect level (NOAEL, mg kg^-1bwday^-1) was determined using a Quantitative in vitro to in vivo extrapolation (QIVIVE) approach: NOAEL_trans-EHMC=3.07, NOAEL_cis-EHMC=0.30 for TK-6 and NOAEL_trans-EHMC=26.46, NOAEL_cis-EHMC=20.36 for HL1-hT1. The hazard index (HI) was evaluated by comparing the reference dose (RfD, mgkg^-1bwday^-1) obtained from our experimental data with the chronic daily intake (CDI) of the female population. Using comet assay experimental data with the more sensitive TK-6 cells, HI_cis-EHMC was 7 times higher than HI_trans-EHMC. In terms of CDI, relative contributions were; dermal exposure route>oral>inhalation. According to our results we recommend the RfD_trans-EHMC=0.20 and RfD_cis-EHMC=0.02 for trans-EHMC and cis-EHMC, respectively, to use for human health risk assessment. The significant difference in trans-EHMC and cis-EHMC response points to the need for toxicological reevaluation and application reassessment of both isomers in PCPs.

New probabilistic risk assessment of ethylhexyl methoxycinnamate: Comparing the genotoxic effects of trans- and cis-EHMC

Ethylhexyl methoxycinnamate (EHMC) is a widely used UV filter present in a large number of personal care products (PCPs). Under normal conditions, EHMC occurs in a mixture of two isomers: trans-EHMC and cis-EHMC in a ratio of 99:1. When exposed to sunlight, the trans isomer is transformed to the less stable cis isomer and the efficiency of the UV filter is reduced. To date, the toxicological effects of the cis-EHMC isomer remain largely unknown. We developed a completely new method for preparing cis-EHMC. An EHMC technical mixture was irradiated using a UV lamp and 98% pure cis-EHMC was isolated from the irradiated solution using column chromatography. The genotoxic effects of the isolated cis-EHMC isomer and the nonirradiated trans-EHMC were subsequently measured using two bioassays (SOS chromotest and UmuC test). In the case of trans-EHMC, significant genotoxicity was observed using both bioassays at the highest concentrations (0.5 - 4 mg mL^-1 ). In the case of cis-EHMC, significant genotoxicity was only detected using the UmuC test at concentrations of 0.25 - 1 mg mL^-1 . Based on these results, the NOEC was calculated for both cis- and trans-EHMC, 0.038 and 0.064 mg mL^-1 , respectively. Risk assessment of dermal, oral and inhalation exposure to PCPs containing EHMC was carried out for a female population using probabilistic simulation and by using Quantitative in vitro to in vivo extrapolation (QIVIVE). The risk of cis-EHMC was found to be ∼1.7 times greater than trans-EHMC. In the case of cis-EHMC, a hazard index of 1 was exceeded in the 92nd percentile. Based on the observed differences between the isomers, EHMC application in PCPs requires detailed reassessment. Further exploration of the toxicological effects and properties of cis-EHMC is needed in order to correctly predict risks posed to humans and the environment. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 569-580, 2017.

Aggregate consumer exposure to UV filter ethylhexyl methoxycinnamate via personal care products

Ultraviolet (UV) filters are substances designed to protect our skin from UV-induced damage and can be found in many categories of personal care products (PCPs). The potential endocrine-disrupting effects attributed to UV filter ethylhexyl methoxycinnamate (EHMC) are being debated. We evaluated the aggregate exposure of the Swiss-German population (N=1196; ages ≤1-97years) to EHMC via the use of PCPs; thus we provide the first comprehensive information about the current EHMC exposure sources and aggregate exposure levels. In our probabilistic modeling method performed at an individual level, PCP use data obtained by a postal questionnaire were linked to concentration data on EHMC gained from chemical analyses of PCPs used by the questionnaire respondents. The modeled median and 99.9th percentile of the internal aggregate exposure for the general population were 0.012 and 0.873mgday(-1)kg(-1) and 0.008 and 0.122mgday(-1)kg(-1) for the summer/autumn and winter/spring period, respectively. The major contributors to internal aggregate exposure were sunscreen products in summer/autumn (females: 64%; males: 85%; children aged ≤12years 93%). In winter/spring, lip care dominated for females (30%) and sunscreen for males (38%) and children aged ≤12years (50%). Overall, the internal aggregate exposure estimates for the studied population are shown to be below the Derived No Effect Level (DNEL) for EHMC i.e., the level of exposure above which humans should not be exposed; however, when an intense short-term exposure via sunscreen is accounted for during a sunbathing day, at the high-end percentiles (99.9th) the predicted aggregate exposure exceeds the DNEL for thyroid-disrupting effects such as for children aged ≤4years, who might be particularly susceptible to endocrine disrupting events. It is nevertheless critical to acknowledge that quantitative data on transdermal penetration of EHMC from PCPs are currently insufficient. Since long-term effects of endocrine disruptors are not known, future studies are warranted to provide accurate quantitative data on transdermal penetration of EHMC and to determine its metabolic fate in humans.

Influence of vegetable oil on the synthesis of bioactive nanocarriers with broad spectrum photoprotection

Due to their unique features, most nanostructured lipid carriers (NLCs) in association with vegetable oils that exhibit UV filtering properties and bioactivity could be used in many cosmetic formulations. Therefore, in this work, a new application of pomegranate seed oil (PSO) in the cosmetic sector was developed, based on the synthesis of bioactive lipid nanocarriers loaded with various UV filters by the hot high pressure homogenization technique. To get broad spectrum photoprotection, different UVA and UVB filters have been used (Avobenzone — AVO, Octocrylen-OCT, Bemotrizinol — BEMT). The influence of the solid lipids combined with PSO on the particle size, physical stability and entrapment efficiency was investigated using 8 nanocarrier systems. An improved physical stability and an appropriate size were obtained for NLCs prepared with Emulgade, carnauba wax and PSO (e.g. −30.9÷-36.9 mV and 160÷185 nm). NLCs showed an entrapment efficiency above 90% and assured slow release rates of UV filters, especially for BEMT (5%). The developed nanocarriers have been formulated into safe and effective sunscreens containing low amounts of synthetic UV filters coupled with a high percent of natural ingredients. The highest SPF of 34.3 was obtained for a cream comprising of 11% PSO and 3.7% BEMT

Quality by Design-Based Development of a Stability-Indicating RP-HPLC Method for the Simultaneous Determination of Methylparaben, Propylparaben, Diethylamino Hydroxybenzoyl Hexyl Benzoate, and Octinoxate in Topical Pharmaceutical Formulation

A stability-indicating RP-HPLC method has been developed and validated for the simultaneous determination of methylparaben (MP), propylparaben (PP), diethylamino hydroxybenzoyl hexyl benzoate (DAHHB), and octinoxate (OCT) in topical pharmaceutical formulation. The desired chromatographic separation was achieved on the Kinetex(TM) C18 (250 × 4.6 mm, 5 μm) column using gradient elution at 257 nm detection wavelength. The optimized mobile phase consisted of a buffer : acetonitrile : tetrahydrofuran (60 : 30 : 10, v/v/v) as solvent A and acetonitrile : tetrahydrofuran (70 : 30, v/v) as solvent B. The method showed linearity over the range of 0.19-148.4 μg/mL, 0.23-15.3 μg/mL, 1.97-600.5 μg/mL, and 1.85-451.5 μg/mL for MP, PP, DAHHB, and OCT, respectively. Recovery for all the components was found to be in the range of 98-102%. The stability-indicating capability of the developed method was established by analysing the forced degradation samples in which the spectral purity of MP, PP, DAHHB, and OCT, along with the separation of the degradation products from the analyte peaks, was achieved. The proposed method was successfully applied for the quantitative determination of MP, PP, DAHHB, and OCT in the lotion sample. The design expert with ANOVA software with the linear model was applied and a 2(4) full factorial design was employed to estimate the model coefficients and also to check the robustness of the method. Results of the two-level full factorial design, 2(4) with 20 runs including four centrepoint analysis based on the variance analysis (ANOVA), demonstrated that all four factors, as well as the interactions of resolution between DAHHB and OCT are statistically significant.

Development and Validation of a Stability Indicating RP-HPLC Method for the Determination of Two Sun Protection Factors (Koptrizon and Tinosorb S) in Topical Pharmaceutical Formulations Using Experimental Designs

A novel, simple, validated stability indicating HPLC method was developed for determination of Koptrizon and Tinosorb S. Stability indicating power of the method was established by forced degradation study. The chromatographic separation was achieved with Waters X Bridge column, by using mobile phase consisting of a mixture of acetonitrile : tetrahydrofuran : water (38 : 38 : 24, v/v/v). The method fulfilled validation criteria and was shown to be sensitive, with limits of detection (LOD) and quantitation (LOQ) of 0.024 and 0.08 μg  for Koptrizon and 0.048 and 0.16 μg  for Tinosorb S, respectively. The developed method is validated for parameters like precision, accuracy, linearity, solution stability, specificity, and ruggedness as per ICH norms. Design expert with ANOVA software with linear model was applied and a 23 full factorial design was employed to estimate the model coefficients and also to check the robustness of the method. Results of the two-level full factorial design, 23 with 10 runs including two-centre-point analysis based on the variance analysis (ANOVA), demonstrated that all three factors, as well as the interactions between retention time of Koptrizon, Tinosorb S, and USP plate count for Koptrizon, are statistically significant.

Preparation, characterization and evaluation of moisturizing and UV protecting effects of topical solid lipid nanoparticles

Solid lipid nanoparticles (SLN) were recently proposed as carriers for various pharmaceutical and cosmetic actives. These lipid nanoparticles can act as moisturizers and physical sunscreens on their own. Therefore, the full potential of these carriers has yet to be determined. The present study was aimed to determine and compare moisturizing and UV-protecting effects of different solid lipid nanoparticles (SLN) prepared by different solid lipids including Glyceryl monostearate (GMS), Precirol® (P) and cetyl palmitate (CP) as carrier systems of moisturizers and sunscreens. The influence of the size and matrix crystallinity of the solid lipids on the occlusive factor, skin hydration and UV-protection were evaluated by in vitro and in vivo methods. The SLN were prepared by high-shear homogenization and ultrasound methods. Size, zeta potential and morphological characteristics of the samples were assessed by transmission electron microscopy (TEM) and thermotropic properties with differential scanning calorimetry (DSC) technique. Results of the assessments showed that SLN-CP significantly increases skin hydration and UV-protection, compared to SLN-GMS and SLN-P. It was demonstrated that the size of SLN, crystallinity index of solid lipid in SLN and probably other mechanisms besides the occlusive factor can influence skin hydration and UV-protection indices. Furthermore, findings of the assessments demonstrated significant difference between in vitro and in vivo assessments regarding occlusive factor and moisturizing effects. Findings of the present study indicate that the SLN-CP could be a promising carrier for sunscreens and moisturizers.

Quantification of sunscreen ethylhexyl triazone in topical skin-care products by normal-phase TLC/densitometry

Ethylhexyl triazone (ET) was separated from other sunscreens such as avobenzone, octocrylene, octyl methoxycinnamate, and diethylamino hydroxybenzoyl hexyl benzoate and from parabens by normal-phase HPTLC on silica gel 60 as stationary phase. Two mobile phases were particularly effective: (A) cyclohexane-diethyl ether 1 : 1 (v/v) and (B) cyclohexane-diethyl ether-acetone 15 : 1 : 2 (v/v/v) since apart from ET analysis they facilitated separation and quantification of other sunscreens present in the formulations. Densitometric scanning was performed at 300 nm. Calibration curves for ET were nonlinear (second-degree polynomials), with R > 0.998. For both mobile phases limits of detection (LOD) were 0.03 and limits of quantification (LOQ) 0.1 μg spot⁻¹. Both methods were validated.

A reversed-phase ion-interaction chromatographic method for in-vitro estimation of the percutaneous absorption of water-soluble UV filters

An analytical method based on ion-interaction chromatography with UV detection for simultaneous in-vitro estimation of the percutaneous absorption of the most used water-soluble UV filters in sunscreen cosmetics is proposed. These UV filters were phenylbenzimidazole sulfonic acid, disodium phenyl dibenzimidazole tetrasulfonate, benzophenone-4, and terephthalylidene dicamphor sulfonic acid. The methodology is based on applying the sunscreen containing the target UV filters to human epidermis in a diffusion cell. Analytes are determined in the receptor solution. To ensure skin integrity, screening of the cells was carried out by analytical determination of a marker. Analytical variables such as percentage ethanol, concentration of ion-pairing agent, pH of the mobile phase, and temperature were studied in order to achieve high resolution of the chromatographic peaks in the lowest possible time of analysis. The conditions selected consisted of a mobile phase composed of 35:65 (v/v) ethanol-ammonium acetate buffer solution (pH 4, containing 50 mmol L(-1) tetra-n-butylammonium bromide). The chromatographic determination was carried out with the analytical column at 50 degrees C. UV detection was carried out at the maximum absorption wavelength for each analyte. The limit of detection (3s(y/x)/b) ranged from 16 to 65 ng mL(-1), depending on the analyte.

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.

Percutaneous absorption of organic sunscreens

The increased awareness of protection against skin cancer has led to a rise in the use of topically applied chemical sunscreen agents. There is a concern about the systemic absorption of organic filters in sunscreen formulations. The present study briefly reviews theoretical models for the prediction of the percutaneous penetration of the organic molecules and the accepted methods for the in vitro and in vivo evaluations of the penetration. The influence of the vehicle and the formulation viscosity on the penetration of sunscreens are examined. The development of novel methods for the minimization of sunscreen absorption is also discussed.

Monitoring 2-ethylhexyl-4-methoxycinnamate photoisomerization on skin using attenuated total reflection fourier transform infrared spectroscopy

Photoisomerization and photodimerization of a widely used UVB filter, 2-ethylhexy-4-methoxycinnamate (EHMC) on a ZnSe surface and baby mouse (Mus musculus Linn.) skin were monitored using attenuated total reflection Fourier transform infrared spectroscopy (ATR-FT-IR). Differentiation between the E- and the Z-EHMC could be achieved by examining the infrared (IR) peak at 981 cm(-1) (b peak), which corresponds to the CH rocking deformation vibration of Ph-CH=CH- detected only in the E configuration. By plotting the ratios of the peak area of the b peak and an internal standard peak (1060-998 cm(-1)) against mole percentage of Z-isomer in the E-Z mixtures, a linear calibration plot was obtained. Thus, a simple estimation of the mole percentage of each configuration in a sample was obtained. At the same UVB exposure, photostationary equilibrium of the E/Z isomerization on the surface varied with the applied amounts of EHMC. Photoisomerizations on ZnSe and on baby mouse skin were comparable. Less than 10% of E-EHMC changed configuration when the mouse skins applied with 1.0-4.0 mg/cm(2) E-EHMC were exposed to sunlight for 60 min (UVB radiant exposure of approximately 0.30 J/cm(2)). This corresponded to less than 5% loss in UV filtering efficiency. However, at a typical EHMC skin coverage ( approximately 0.2 mg/cm(2)), 0.30 J/cm(2) UVB exposure induced approximately 50% photoisomerization resulting in 25% loss of UV filtering efficiency. No photodimerization was detected even at the extreme EHMC coverage of 4.0 mg/cm(2) after a UVB exposure of 0.90 J/cm(2).

In vitro percutaneous absorption and in vivo stratum corneum distribution of an organic and a mineral sunscreen

Sunscreens, whose main function is to protect the skin against the harmful effects of solar irradiation, should remain at the skin surface or impregnate the first layers of the stratum corneum only and not penetrate into the underlying living tissue. The goal of this work was to assess the penetration of titanium dioxide (TiO(2)) and methylene bis-benzotriazoyl tetramethylbutylphenol (MBBT), included in a broad-spectrum sunscreen formulation, into human skin in vivo, using the tape stripping method, and in vitro, using a compartmental approach. An additional objective was to propose an easy and minimally invasive approach to determining the percutaneous uptake of sunscreens following topical application. TiO(2) and MBBT were quantified using colorimetric assay and HPLC analysis, respectively. The transmission electron microscopy and particle-induced X-ray emission techniques were used to localize the TiO(2) in skin sections. More than 90% of both sunscreens was recovered in the first 15 tape strippings. In addition we have shown that the remaining 10% did not penetrate the viable tissue, but was localized in the furrows and in the opened infundibulum. Less than 0.1% of MBBT was detected in the receptor medium, and no TiO(2) was detected in the follicle, viable epidermis or dermis. Thus, this in vivo and in vitro penetration study showed an absence of TiO(2) penetration into the viable skin layers through either transcorneal or transfollicular pathways and negligible transcutaneous absorption of MBBT. However, differences in distribution within the stratum corneum reinforced the need for a complementary approach, using minimally invasive in vivo methodology and in vitro compartmental analysis. This combination represents a well-adapted method for testing the safety of topically applied sunscreen formulations in real-life conditions.

Determination of molecular conformation and permeation in skin via IR spectroscopy, microscopy, and imaging

Skin tissue, in addition to its specific use in dermal research, provides an excellent model for developing the techniques of vibrational microscopy and imaging for biomedical applications. In addition to permitting characterization of various regions of skin, the relative paucity of major biological constituents in the stratum corneum (the outermost layer of skin), permits us to image, with microscopic resolution, conformational alterations and concentration variations in both the lipid and protein components. Thus we are able to monitor the effects of exogenous materials such as models for drug delivery agents (liposomes) and permeation enhancers (DMSO) on stratum corneum lipid organization and protein structure. In addition, we are able to monitor protein conformational changes in single corneocytes. The current article demonstrates these procedures, ranging from direct univariate measures of lipid chain conformational disorder, to factor analysis which permits us to image conformational differences between liposomes that have permeated through the stratum corneum from those which have remained on the surface in a reservoir outside the skin.

A liquid chromatography–fluorimetric method for the in vitro estimation of the skin penetration of disodium phenyldibenzimidazole tetrasulfonate from sunscreen formulations through human skin

Disodium phenyldibenzimidazole tetrasulfonate (PDT) is a new organic UV filter with hydrophilic properties used in modern sunscreen spray formulations. The aim of this work was to develop and validate an analytical method that can be used to study skin absorption of PDT from sunscreens. Results obtained in vitro for human skin showed a low level of absorption. The proposed in vitro method employs a diffusion cell. Sunscreen lotion was applied onto pretreated human skin, which was then placed in the cell. PDT was collected in a receptor liquid, the surface of which was in contact with the skin. The solutions obtained were diluted appropriately and analyzed by liquid chromatography without any interference. The analytical features of chromatographic determination with fluorimetic detection were suited to this analytical problem, since this method gave a limit of detection of 1 ng ml(-1). Phenol red (PR) was used as a marker to check the skin integrity, and a sensitive method based on sequential injection on-line solid-phase extraction coupled with spectrophotometric detection was developed for determining this marker in the receptor liquid in order to screen the cells.

Changes in ultraviolet absorbance and hence in protective efficacy against lipid peroxidation of organic sunscreens after UVA irradiation

Owing to the spectral distribution of solar UV, the UVA component of sunlight is now believed to be the main cause of photoaging and photocarcinogenesis and is much more effective than UVB in inducing peroxidative damage. Consequently, most skin care cosmetic products now include UVA filters in their formulations along with UVB filters. These modern sunscreens should provide and maintain their initial absorbance, hence protection, throughout the entire period of exposure to sunlight. However, not all UVA and UVB filters are sufficiently photostable. In this study, we examine the correlation between the photochemical degradation of sunscreen agents under UVA irradiation, with particular reference to the UVA-absorber 4-tert-butyl-4'-methoxydibenzoylmethane, alone and in combination with other organic UV filters (2-ethylhexyl 4 methoxycinnamate and 2-ethylhexyl 2-cyano-3,3-diphenylacrylate) and their ability to prevent UVA-induced lipid peroxidation. Since antioxidants are also added to formulations to deactivate free radicals generated during UVA exposure, vitamin E and the synthetic antioxidant, bis(2,2,6,6-tetramethyl-1-oxyl-piperidine-4-yl)sebacate, a nitroxide derivative, were also included in this study. By using simple in vitro tests, the results show that a decrease in spectral absorbance of the UV filters correlates in most cases with increased UVA-induced lipid peroxidation; this depends on the specific UV absorber analysed and also on whether they are alone or in combination. Furthermore, the combined presence or absence of antioxidants has a profound effect on this oxidative event. In particular, the nitroxide appears to be a more efficient photo-antioxidant than vitamin E. Similar experiments were also performed under natural sunlight and the results obtained did not differ substantially from those performed under UVA. The results presented and discussed in this work may help in understanding the effects of UVA/UVB absorbers and antioxidants upon the level of UV-induced ROS generated under UVA exposure and in natural sunlight which could be relevant for improving the photoprotection and efficacy of skin care cosmetic formulations.

Cutaneous distribution and localization of dyes affected by vehicles all with different lipophilicity

The penetration of topically applied substances into the stratum corneum (SC) depends on several factors, e.g., the physicochemical properties of the vehicle used for application. The penetration of highly hydrophilic and lipophilic dyes into the skin was studied using a pure oil (o) or water (w) for the application compared to an o/w emulsion. The penetration and localization of both dyes, the lipophilic curcumin and the hydrophilic Patent blue V, was investigated in vivo using the method of tape stripping and microscopy. In addition, histological sections of biopsies, removed from porcine ear skin were studied using microscopy. Differences in the distribution and the localization of both dyes within the SC were observed. These differences depend on the physicochemical properties of both the vehicles and the dyes. The vehicle appears to affect, in particular, the pathways of penetration.

Liposomes and niosomes as topical drug delivery systems

The skin acts as a major target as well as a principle barrier for topical/transdermal (TT) drug delivery. The stratum corneum plays a crucial role in barrier function for TT drug delivery. Despite major research and development efforts in TT systems and the advantages of these routes, low stratum corneum permeability limits the usefulness of topical drug delivery. To overcome this, methods have been assessed to increase permeation. One controversial method is the use of vesicular systems, such as liposomes and niosomes, whose effectiveness depends on their physicochemical properties. This review focuses on the effect of liposomes and niosomes on enhancing drug penetration, and defines the effect of composition, size and type of the vesicular system on TT delivery.

Factors affecting the formation of a skin reservoir for topically applied solutes

The reservoir function of the skin is an important determinant of the duration of action of a topical solute. The reservoir can exist in the stratum corneum, in the viable avascular tissue (viable epidermis and supracapillary dermis) and in the dermis. A steroid reservoir in the stratum corneum has been demonstrated by the reactivation of a vasoconstrictor effect by occlusion or application of a placebo cream to the skin some time after the original topical application of steroid. Other solutes have also been reported to show a reservoir effect in the skin after topical application. A simple compartmental model is used to understand why reactivation of vasoconstriction some time after a topical steroid application shows dependency on time, topical solute concentration and the product used to cause reactivation. The model is also used to show which solutes are likely to show a reservoir effect and could be potentially affected by desquamation, especially when the turnover of the skin is abnormally rapid. A similar form of the model can be used to understand the promotion of reservoir function in the viable tissue and in the dermis in terms of effective removal by blood perfusing the tissues.

Influence of cyclodextrins on in vitro human skin absorption of the sunscreen, butyl-methoxydibenzoylmethane

The effects of hydroxypropyl-beta-cyclodextrin (HP-beta-CD) and sulfobutylether-beta-CD (SBE7-beta-CD) on in vitro human skin penetration and retention of the sunscreen agent butyl-methoxydibenzoylmethane (BM-DBM) were investigated. The interaction between the UV filter and the cyclodextrins was studied in water by phase-solubility analysis. Solid complexes were prepared by the co-evaporation method and characterized by (1)H NMR spectroscopy, thermal analysis and powder X-ray diffraction. Solutions containing BM-DBM free or complexed with cyclodextrins were applied to excised human skin in Franz diffusion cells and the amount of sunscreen permeated after 6 h into the stratum corneum, viable epidermis, dermis and receptor fluid was assessed by HPLC. As much as 14.10-16.78% of the applied dose of BM-DBM penetrated within the skin tissue. No sunscreen was detected in the dermis and in the receiver phase. The greater proportion (84.6-95.5%) of the absorbed UV filter was localized in the stratum corneum with no significant differences between uncomplexed or complexed BM-DBM. Notable levels (2.29% of the applied dose) of the sunscreen agent accumulated in the epidermis from the preparation containing free BM-DBM. The epidermal concentration of the UV filter was markedly reduced (0.66% of the applied dose) by complexation with SBE7-beta-CD, whereas HP-beta-CD had no effect. The decreased BM-DBM retention in the epidermal region achieved by SBE7-beta-CD limits direct contact of the sunscreen and of its reactive photolytic products with the skin viable tissues.

Active ingredients in sunscreens act as topical penetration enhancers for the herbicide 2,4-dichlorophenoxyacetic acid

Agricultural workers are encouraged to use sunscreen to decrease the risk of UV-related skin cancer. Our previous studies have shown certain commercial sunscreens to be penetration enhancers. The focus of this project is to determine whether active ingredients in sunscreen formulations (i.e., the UV absorbing components and insect repellants for the sunscreen/bug repellant combinations) also act as dermal penetration enhancers for herbicides in vitro. The total percentages of 2,4-dichlorophenoxyacetic acid (2,4-D) penetrating through hairless mouse skin in 24 h ranged from 54.9 +/- 4.7 for the no sunscreen control to 86.9 +/- 2.5 for padimate-o. Of the active ingredients tested (7.5% octyl methoxycinnamate, 7% octocrylene, 0.6% oxybenzone, 5% homosalate, 5% octyl salicylate, 8% padimate-o, 10% sulisobenzone, and 9.5% and 19% N,N-diethyl-m-toluamide [DEET]), all but octocrylene led to a significant increase in total 2,4-D penetration as compared to the control (P < 0.05), and only octocrylene and oxybenzone did not significantly decrease the corresponding lag time. Octyl salicylate (P < 0.01) and octyl methoxycinnimate (P < 0.05) significantly increased the 3H2O penetration across mouse skin, indicating physical damage to the stratum corneum. Additional studies demonstrated that the penetration enhancement seen across hairless mouse skin also occurred with human skin. Thus, the active ingredients of sunscreen formulations enhance dermal penetration of the moderately lipophilic herbicide 2,4-D.

Percutaneous absorption of Mexoryl SX in human volunteers: comparison with in vitro data

The potential human health risk of UV filters depends on their toxicity and the human systemic exposure which is a function of the extent of percutaneous absorption of the topically applied substance into the human organism. Using a 'mass balance' approach, a study was designed to investigate the systemically absorbed dose of [(14)C]-Mexoryl SX((R)) in humans after topical application of a typical sunscreen emulsion. In addition, to assess the correlation with in vitro experiments, the percutaneous absorption of this UVA filter through isolated human skin was measured under identical exposure conditions. When applied in vivo for a period of 4 h, 89-94% of the applied radioactivity was recovered from the wash-off samples. In urine samples, the radioactivity slightly exceeded background levels and corresponded maximally to 0.014% of the topically applied dose. No radioactivity was measured in blood or faeces sampled up to 120 h after application. In vitro, 24 h after a 4-hour application, [(14)C]-Mexoryl SX remained primarily on the skin surface. The mean in vitro absorption over 24 h, adding up the amounts found in the dermis and receptor fluid, was 0.16% of the applied dose. It is concluded from the in vivo pharmacokinetic results that the systemically absorbed dose of [(14)C]-Mexoryl SX is less than 0.1%. The order of magnitude of this value correlates well with the corresponding in vitro data which overestimate the in vivo results as previously observed with other hydrophilic compounds. This study demonstrates that, under realistic exposure conditions, the human systemic exposure to this UVA filter is negligible and poses no risk to human health.

Effect of heat on the percutaneous absorption and skin retention of three model penetrants

The effect of heat on the transdermal delivery of model penetrants of differing lipophilicity through artificial membranes (non-rate limiting) and human epidermis was investigated in vitro. Saturated suspensions of the model penetrants; methyl paraben (MP), butyl paraben (BP) and caffeine (CF) in deionised water (vehicle) were used to attain maximal thermodynamic activity. Franz cell experiments were performed at temperatures ranging from 23 to 45 degrees C using the infinite dose method. Artificial membrane studies showed the penetrant diffusivity (diffusion coefficient) in the vehicle to be totally dependent on temperature and not changes in donor solubility. Epidermal flux and retention of all penetrants was found to be affected by temperature. The amount of penetrant retained in the epidermis was found to be in the order BP>CF>MP whilst the transdermal fluxes increased in the order MP>BP>CF with increasing receptor temperature. Estimated epidermal diffusivity of MP was found to be significantly affected by temperature (P< or =0.05) compared to BP and CF. Using Arrhenius plots, a lower activation energy was recorded for CF and may suggest a difference in permeation kinetics compared to the other penetrants.

Solid lipid nanoparticles as carrier for sunscreens: in vitro release and in vivo skin penetration

The aim of this study was the comparison of two different formulations (solid lipid nanoparticles (SLN) and conventional o/w emulsion) as carrier systems for the molecular sunscreen oxybenzone. The influence of the carrier on the rate of release was studied in vitro with a membrane-free model. The release rate could be decreased by up to 50% with the SLN formulation. Further in vitro measurements with static Franz diffusion cells were performed. In vivo, penetration of oxybenzone into stratum corneum on the forearm was investigated by the tape stripping method. It was shown that the rate of release is strongly dependent upon the formulation and could be decreased by 30-60% in SLN formulations. In all test models, oxybenzone was released and penetrated into human skin more quickly and to a greater extent from the emulsions. The rate of release also depends upon the total concentration of oxybenzone in the formulation. In vitro-in vivo correlations could be made qualitatively.