Evaluation of In Vitro Metabolism- and Transporter-Based Drug Interactions with Sunscreen Active Ingredients.

PURPOSE: The aim of this study was to examine the ability of sunscreen active ingredients to inhibit in vitro drug metabolism via cytochrome P450 (CYP) enzymes and drug uptake transporters. METHODS: Metabolism assays with human liver microsomes were conducted for CYP2C9, CYP2D6 and CYP3A4 using probe substrates warfarin, bufuralol and midazolam, respectively. Uptake transporter assays with transfected cell lines were conducted for OAT3, OCT2 and OATP1B1 with probe substrates estrone-3-sulfate, metformin and rosuvastatin, respectively. Six sunscreen active ingredients, avobenzone, enzacamene, oxybenzone, octinoxate, trolamine, and homosalate, were evaluated up to their aqueous solubility limits in the assays. RESULTS: None of the sunscreen active ingredients inhibited CYP2D6 or CYP3A4 activities in the microsomes at concentration ranges up to tenfold higher than their known clinical total plasma levels. Only enzacamene, oxybenzone and trolamine were found to be inhibitory to CYP2C9 activity with IC50 values of 14.76, 22.46 and 154.7 µM, respectively. Avobenzone, enzacamene, homosalate and octinoxate were not inhibitory to the uptake transporters at the evaluated concentrations. Oxybenzone was inhibitory to OAT3 and OCT2 with IC50 values of 39.93 and 42.77 µM, respectively. Trolamine also inhibited uptake in OAT3 and OCT2 transfected cells with IC50 values of 448.1 and 1376 µM, respectively. CONCLUSIONS: Although enzacamene, oxybenzone and trolamine inhibited CYP2C9 and the renal transporters OAT3 and OCT2 in vitro, their IC50 values exceeded total plasma levels found in clinical studies. Therefore, it is unlikely that these sunscreen active ingredients in sunscreen products will inhibit the metabolism or transport of co-administered drugs in consumers.

Toxicokinetics of 2-ethylhexyl salicylate (EHS) and its seven metabolites in humans after controlled single dermal exposure to EHS.

The chemical UV filter 2-ethylhexyl salicylate (EHS) is used in various personal-care products. The dermal and oral metabolism of EHS have already been targeted by different studies. However, toxicokinetic data after a single dermal exposure to EHS was missing. In our study, three volunteers were dermally exposed to a commercial EHS-containing sunscreen for 9 h with an application dose of 2 mg sunscreen per cm2 body surface area. The exposure was performed indoors, and sunscreen was applied on about 75% of the total skin area. Complete urine voids were collected over 72 h and eight blood samples were drawn from each subject. Urine samples were analyzed for EHS and seven known metabolites (5OH-EHS, 4OH-EHS, 2OH-EHS, 6OH-EHS, 4oxo-EHS, 5oxo-EHS, and 5cx-EPS) by online-SPE UPLC MS/MS. The peaks of urinary elimination occurred 10-11 h after application. The elimination half-lives (Phase 1) were between 6.6 and 9.7 h. The dominant urinary biomarkers were EHS itself, followed by 5OH-EHS, 5cx-EPS, 5oxo-EHS, and 4OH-EHS. 2OH-EHS, 6OH-EHS, and 4oxo-EHS were detected only in minor amounts. An enhanced analysis of conjugation species revealed marginal amounts of unconjugated metabolites and up to 40% share of sulfate conjugates for 5OH-EHS, 5oxo-EHS, and 5cx-EPS. The results demonstrated a delayed systemic resorption of EHS via the dermal route. Despite an extensive metabolism, the parent compound occurred as main urinary parameter. The delayed dermal resorption as well as the slow elimination of EHS indicate an accumulation up to toxicological relevant doses during daily repeated dermal application to large skin areas.

Use of in vitro ADME methods to identify suitable analogs of homosalate and octisalate for use in a read-across safety assessment.

Case studies are needed to demonstrate the use of human-relevant New Approach Methodologies in cosmetics ingredient safety assessments. For read-across assessments, it is crucial to compare the target chemical with the most appropriate analog; therefore, reliable analog selection should consider physicochemical properties, bioavailability, metabolism, as well as the bioactivity of potential analogs. To complement in vitro bioactivity assays, we evaluated the suitability of three potential analogs for the UV filters, homosalate and octisalate, according to their in vitro ADME properties. We describe how technical aspects of conducting assays for these highly lipophilic chemicals were addressed and interpreted. There were several properties that were common to all five chemicals: they all had similar stability in gastrointestinal fluids (in which no hydrolysis to salicylic occurred); were not substrates of the P-glycoprotein efflux transporter; were highly protein bound; and were hydrolyzed to salicylic acid (which was also a major metabolite). The main properties differentiating the chemicals were their permeability in Caco-2 cells, plasma stability, clearance in hepatic models, and the extent of hydrolysis to salicylic acid. Cyclohexyl salicylate, octisalate, and homosalate were identified suitable analogs for each other, whereas butyloctyl salicylate exhibited ADME properties that were markedly different, indicating it is unsuitable. Isoamyl salicylate can be a suitable analog with interpretation for octisalate. In conclusion, in vitro ADME properties of five chemicals were measured and used to pair target and potential analogs. This study demonstrates the importance of robust ADME data for the selection of analogs in a read-across safety assessment.

Enhanced Sunscreen Effects via Layer-By-Layer Self-Assembly of Chitosan/Sodium Alginate/Calcium Chloride/EHA.

The sunscreen nanocapsules were successfully synthesized by the way of layer-by-layer self-assembly using charged droplets (prepared by emulsification of LAD-30, Tween-80 and EHA (2-Ethylhexyl-4-dimethylaminobenzoate)) as templates. Chitosan/sodium alginate/calcium chloride were selected as wall materials to wrap EHA. The emulsions with the ratio of Tween-80 to EHA (1:1) were stable. A stable NEI negative emulsion can be obtained when the ratio of Tween-80 and LAD-30 was 9:1. Chitosan solutions (50 kDa, 0.25 mg/mL) and sodium alginate solutions (0.5 mg/mL) were selected to prepare nanocapsules. The nanocapsules were characterized via some physico-chemical methods. Based on the synergistic effects of the electrostatic interaction between wall materials and emulsifiers, EHA was effectively encapsulated. DLS and TEM showed that the sunscreen nanocapsules were dispersed in a spherical shape with nano-size, with the increasing number of assembly layers, the size increased from 155 nm (NEI) to 189 nm (NEII) to 201 nm (NEIII) and 205 nm after solidification. The release studies in vitro showed sustained release behavior of the nanocapsules were observed with the increase of the number of deposition layers, implying a good coating effect. The sunscreen nanocapsules could control less than 50% the release of EHA after crosslinking of calcium chloride and sodium alginate, which also could effectively avoid the stimulation of the sun protection agent on the skin.

Sustained effect of two antioxidants (oxothiazolidine and δ-tocopheryl glucoside) for immediate and long-term sun protection in a sunscreen emulsion based on their different penetrating properties.

OBJECTIVE: We investigated the dermal bioavailability and antioxidative properties of a sunscreen formulation containing two antioxidants, oxothiazolidine (OTZ) and δ-tocopheryl glucoside (DTG). OTZ reacts directly with reactive oxygen species to form taurine, while DTG is metabolized in δ-tocopherol to achieve antioxidative activities. METHODS: After topical application to a hair follicle-derived reconstructed human epidermis (RHE) model, followed by solar-simulated radiation, kinetics of bioavailability and antioxidative responses were measured over 24 h. Markers for oxidative stress were malondialdehyde (MDA), superoxide dismutase (SOD) and catalase activities. RESULTS: The two antioxidants had different bioavailability profiles: OTZ was rapidly and extensively absorbed, whereas DTG was slowly absorbed and converted to δ-tocopherol. Compared to OTZ alone, the protection against effects on MDA levels and SOD and catalase activities was higher when DTG was used alone or in combination with OTZ. When used in combination, the degree of protection increased over time and remained constant over 24 h with maximal protection 2 h post-irradiation. DTG slowly penetrated into the skin and was present in the skin at all post-irradiation timepoints, thus allowing a slow but constant supply of δ-tocopherol over at least 24 h. By contrast, the oxidative protection by OTZ was immediate but short-lived due to its rapid penetration through the RHE and into the receptor fluid. CONCLUSION: These results indicate a complementary sunlight protective action of OTZ and DTG with an immediate delivery of OTZ just after topical application of the formulation, and a prolonged skin delivery of δ-tocopherol from the slower penetration and metabolism of DTG.

OBJECTIF: Nous avons étudié la cinétique de pénétration cutanée et les propriétés antioxydantes d'une formulation solaire contenant deux antioxydants, l'oxothiazolidine (OTZ) et le δ-tocophéryl glucoside (DTG). L'OTZ se transforme directement en taurine en présence de stress oxydant sans l'action des enzymes cutanées, tandis que le DTG est métabolisé par les enzymes cutanées pour libérer le δ-tocophérol qui est la molécule ayant les propriétés antioxydantes. MÉTHODES: Après application topique sur un modèle d'épiderme humain reconstruit dérivé de follicules pileux (RHE), suivi d'une irradiation solaire, la cinétique de biodisponibilité et les réponses antioxydantes de ces deux composés ont été mesurées sur 24 h. Les marqueurs du stress oxydatif étaient la production de malondialdéhyde (MDA), l'activité de la superoxyde dismutase (SOD) et de la catalase. RÉSULTATS: Les deux antioxydants ont des profils de biodisponibilité différents. L'OTZ pénètre rapidement dans la peau, tandis que le DTG pénètre lentement et est biotransformé par les enzymes cutanés pour libérer le δ-tocophérol. Par rapport à l'OTZ seul, la protection oxydante sur les niveaux de MDA et les activités SOD et catalase était plus élevée lorsque le DTG était utilisé seul ou en association avec OTZ. Lorsqu'il est utilisé en combinaison, le degré de protection augmente au cours du temps et atteint son maximum 2h post-irradiation et reste constant durant 24 h. Le DTG pénètre lentement dans la peau et est présent dans la peau durant 24h post-irradiation, permettant ainsi un apport lent mais constant de δ-tocophérol. En revanche, la protection oxydante via l'OTZ est immédiate mais de courte durée en raison de sa pénétration rapide à travers le RHE. CONCLUSION: Ces résultats indiquent une action de protection solaire complémentaire de l'OTZ et du DTG avec une absorption immédiate d'OTZ juste après l'application topique de la formulation, et une libération cutanée prolongée de δ-tocophérol grâce à la pénétration et la métabolisation plus lentes du DTG.

A Handful of Sunscreen for Whole-Body Application.

BACKGROUND: The rule of thumb "Fill up a handful of sunscreen and spread it all over your body" has been used in several sun safety campaigns. The intention was to increase the applied sunscreen to obtain a quantity of 2 mg/cm2 to all accessible skin. The present study is the first to investigate how this advice works in practice, evaluated by quantity of sunscreen applied and amount of covered skin. METHODS: Seventeen volunteers wearing swimwear were asked to "Fill up a handful and spread it all over your body." Before and after sunscreen application, the volunteers were photographed in black light. As sunscreen absorbs black light, the darkness of the skin increases with increasing amounts of applied sunscreen, making it possible to identify skin left without coverage. The sunscreen container was weighed before and after to quantify the amount of sunscreen applied. RESULTS: A median of 21% of the accessible skin was left completely without coverage. The 79% covered area was covered with a median of 1.12 mg/cm2, not the expected 2 mg/cm2. CONCLUSION: In practice, the advice "Fill up a handful of sunscreen and spread it all over your body" led to a better but still modest protection, compared to the intended effect.

Effect of Sunscreen Application on Plasma Concentration of Sunscreen Active Ingredients: A Randomized Clinical Trial.

Importance: A prior pilot study demonstrated the systemic absorption of 4 sunscreen active ingredients; additional studies are needed to determine the systemic absorption of additional active ingredients and how quickly systemic exposure exceeds 0.5 ng/mL as recommended by the US Food and Drug Administration (FDA). Objective: To assess the systemic absorption and pharmacokinetics of the 6 active ingredients (avobenzone, oxybenzone, octocrylene, homosalate, octisalate, and octinoxate) in 4 sunscreen products under single- and maximal-use conditions. Design, Setting, and Participants: Randomized clinical trial at a clinical pharmacology unit (West Bend, Wisconsin) was conducted in 48 healthy participants. The study was conducted between January and February 2019. Interventions: Participants were randomized to 1 of 4 sunscreen products, formulated as lotion (n = 12), aerosol spray (n = 12), nonaerosol spray (n = 12), and pump spray (n = 12). Sunscreen product was applied at 2 mg/cm2 to 75% of body surface area at 0 hours on day 1 and 4 times on day 2 through day 4 at 2-hour intervals, and 34 blood samples were collected over 21 days from each participant. Main Outcomes and Measures: The primary outcome was the maximum plasma concentration of avobenzone over days 1 through 21. Secondary outcomes were the maximum plasma concentrations of oxybenzone, octocrylene, homosalate, octisalate, and octinoxate over days 1 through 21. Results: Among 48 randomized participants (mean [SD] age, 38.7 [13.2] years; 24 women [50%]; 23 white [48%], 23 African American [48%], 1 Asian [2%], and 1 of unknown race/ethnicity [2%]), 44 (92%) completed the trial. Geometric mean maximum plasma concentrations of all 6 active ingredients were greater than 0.5 ng/mL, and this threshold was surpassed on day 1 after a single application for all active ingredients. For avobenzone, the overall maximum plasma concentrations were 7.1 ng/mL (coefficient of variation [CV], 73.9%) for lotion, 3.5 ng/mL (CV, 70.9%) for aerosol spray, 3.5 ng/mL (CV, 73.0%) for nonaerosol spray, and 3.3 ng/mL (CV, 47.8%) for pump spray. For oxybenzone, the concentrations were 258.1 ng/mL (CV, 53.0%) for lotion and 180.1 ng/mL (CV, 57.3%) for aerosol spray. For octocrylene, the concentrations were 7.8 ng/mL (CV, 87.1%) for lotion, 6.6 ng/mL (CV, 78.1%) for aerosol spray, and 6.6 ng/mL (CV, 103.9%) for nonaerosol spray. For homosalate, concentrations were 23.1 ng/mL (CV, 68.0%) for aerosol spray, 17.9 ng/mL (CV, 61.7%) for nonaerosol spray, and 13.9 ng/mL (CV, 70.2%) for pump spray. For octisalate, concentrations were 5.1 ng/mL (CV, 81.6%) for aerosol spray, 5.8 ng/mL (CV, 77.4%) for nonaerosol spray, and 4.6 ng/mL (CV, 97.6%) for pump spray. For octinoxate, concentrations were 7.9 ng/mL (CV, 86.5%) for nonaerosol spray and 5.2 ng/mL (CV, 68.2%) for pump spray. The most common adverse event was rash, which developed in 14 participants. Conclusions and Relevance: In this study conducted in a clinical pharmacology unit and examining sunscreen application among healthy participants, all 6 of the tested active ingredients administered in 4 different sunscreen formulations were systemically absorbed and had plasma concentrations that surpassed the FDA threshold for potentially waiving some of the additional safety studies for sunscreens. These findings do not indicate that individuals should refrain from the use of sunscreen. Trial Registration: ClinicalTrials.gov Identifier: NCT03582215.

Synthesis and Characterization of Nanostructured Lipid Nanocarriers for Enhanced Sun Protection Factor of Octyl p-methoxycinnamate.

Sunlight is important to health, but higher exposure to radiation causes early aging of the skin and skin damage that can lead to skin cancers. This study aimed at producing a stable octyl p-methoxycinnamate (OMC)-loaded nanostructured lipid carrier (NLC) sunscreen, which can help in the photoprotective effect. NLC was produced by emulsification-sonication method and these systems were composed of myristyl myristate (MM), caprylic capric triglyceride (CCT), Tween® 80 (TW), and soybean phosphatidylcholine (SP) and characterized by dynamic light scattering (DLS), zeta potential (ZP) measurement, atomic force microscopy (AFM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and in vitro release studies. Pre-formulation studies were performed changing TW concentrations and no differences were found at concentrations of 1.0 and 2.0%. Two selected formulations were designed and showed an average size of 91.5-131.7, polydispersity index > 0.2, and a negative value of ZP. AFM presented a sphere-like morphology and SEM showed ability to form a thin film. DSC exhibited that the incorporation of OMC promoted reduction of enthalpy due to formation of a more amorphous structure. Drug release shows up to 55.74% and 30.57%, and this difference could be related to the presence of SP in this formulation that promoted a more amorphous structure; the release mechanism study indicated Fickian diffusion and relaxation. Sun protection factor (SPF) evaluation was performed using NLC and presented values around 40, considerably higher than those observed in the literature. The developed formulations provide a beneficial alternative to conventional sunscreen formulations.

Analysis of photokinetics of 2'-ethylhexyl-4-methoxycinnamate in sunscreens.

2'-Ethylhexyl-4-Methoxycinnamate (EHMC), also designated as octinoxate, is an oily UV-absorber used in sunscreens for the protection of human skin against solar UV-radiation and represents one of the most employed UVB absorbers for that application. In water-in-oil emulsions EHMC was adjusted at a constant overall concentration, while changing the EHMC concentration in the oil droplets by adding a non-absorbing oil. In that way the EHMC concentration could be varied at constant optical thickness. Here we show that the kinetics of the photoreaction follows a second-order rate law, in line with the UV-induced [2 + 2]-cycloaddition reaction mechanism known for this UV absorber. The second-order rate constant decreased with higher overall EHMC concentration. This can be explained by the fact, that at higher overall concentration of the UV absorber not every EHMC molecule will absorb a photon due to the increased optical density, so that on average less photons are absorbed per molecule. On the other hand, the rate constant increases with decreasing polarity of the surrounding oil. Since the molar fraction of the trans-isomer of EHMC is augmented at lower polarity, more photons are absorbed in this case, as the strength of the absorption band of the trans-isomer is significantly higher than that of the cis-isomer. In conclusion, our experiments show that a high polarity of the oil phase and a high concentration of EHMC are advantageous for the photostability of this compound.

Urinary metabolites of the UV filter octocrylene in humans as biomarkers of exposure.

Octocrylene (OC) is a UV filter used in sun screens and other personal care products, but also in polymers and food contact materials for stabilization. In this study, we investigate human OC metabolism and urinary excretion after oral dosage of approx. 5 mg OC [≙ 61.8-89.5 µg/(kg body weight)] in three male volunteers. In a screening approach, we tentatively identified six urinary OC metabolites. For three, renal elimination kinetics was quantitatively investigated using authentic standards: the sidechain oxidation product 2-ethyl-5-hydroxyhexyl 2-cyano-3,3-diphenyl acrylate (5OH-OC), the beta-oxidation product 2-(carboxymethyl)butyl 2-cyano-3,3-diphenyl acrylate (dinor OC carboxylic acid; DOCCA), and the ester hydrolysis product 2-cyano-3,3-diphenylacrylic acid (CPAA). CPAA was the major urinary metabolite, representing 45% (range 40-50%) of the OC dose. 5OH-OC and DOCCA were only minor metabolites with low, but highly consistent renal conversion factors of 0.008% (0.005-0.011%) and 0.13% (0.11-0.16%), respectively. Peak urinary metabolite concentrations were observed between 3.2 h and 4.2 h postdose. All three metabolites were excreted with biphasic elimination kinetics, with considerably longer elimination half-lives for DOCCA (1st phase: 3.0 h; 2nd phase: 16 h) and CPAA (5.7 h and 16 h) compared to 5OH-OC (1.3 h and 6.4 h). 99% of all 5OH-OC was excreted within 24 h compared to 82% of DOCCA and 77% of CPAA. After dermal exposure, we detected the same metabolites with similar ratios in urine, however, at much lower concentrations and with considerably delayed elimination.

Review of the safety of octocrylene used as an ultraviolet filter in cosmetics.

Octocrylene or octocrilene is an organic ultraviolet (UV) filter which absorbs mainly UVB radiation and short UVA wavelengths. It is used in various cosmetic products to either provide an appropriate sun protection factor in sunscreen products or to protect cosmetic formulations from UV radiation. There is no discussion that UV filters are beneficial ingredients in cosmetics since they protect from skin cancer, but octocrylene has been recently incriminated to potentially induce adverse effects on the endocrine system in addition to having allergic and/or photoallergic potential. However, the substance has the advantage to work synergistically with other filters allowing a beneficial broad photoprotection, e.g. it stabilizes the UVA filter avobenzone (i.e. butylmethoxydibenzoylmethane). Like all chemicals used in cosmetics, the safety profile of octocrylene is constantly under assessment by the European Chemical Agency (ECHA) since it has been registered according to the European regulation Registration, Evaluation, Authorisation and Restriction of Chemicals. Summaries of safety data of octocrylene are publicly available on the ECHA website. This review aims to present the main safety data from the ECHA website, as well as those reported in scientific articles from peer-reviewed journals. The available data show that octocrylene does not have any endocrine disruption potential. It is a rare sensitizer, photocontact allergy is more frequent and it is considered consecutive to photosensitization to ketoprofen. Based on these results, octocrylene can be considered as safe when used as a UV filter in cosmetic products at a concentration up to 10%.

Safety of titanium dioxide nanoparticles in cosmetics.

Titanium dioxide (TiO2 ) is widely used in a variety of products including cosmetics. TiO2 in its nanoparticle form (nano-TiO2 ) is now the only form used as an ultraviolet (UV) filter in sunscreens, but also in some day creams, foundations and lip balms. While its efficacy as a UV filter is proven in the prevention of skin cancers and sunburns, some concerns have been raised about its safety. Indeed, considering its small size, nano-TiO2 is suspected to penetrate dermal, respiratory or gastrointestinal barriers, disseminate in the body and therefore constitute a potential risk to the consumer. At the skin level, most studies performed in humans or animals showed that nano-TiO2 did not penetrate beyond the outer layers of stratum corneum to viable cells and did not reach the general circulation, either in healthy or in compromised skin. The Scientific Committee on Consumer Safety (SCCS) considers nano-TiO2 as a non-sensitizer and as mild- or non-irritant to skin and concludes in no evidence of carcinogenicity (supported by the European Chemicals Agency), mutagenicity or reproductive toxicity after dermal exposure to nano-TiO2 . According to the SCCS, nano-TiO2 from sunscreens does not present any health risk when applied on the skin at a concentration up to 25%. However, the SCCS does not recommend the use of nano-TiO2 in formulations that may lead to exposure of the consumer's lungs by inhalation (sprayable products and powders). Indeed, even if human data are sparse and inconsistent, lung inflammation was reported in animals. In 2016, the EU Cosmetic Regulation made nano-TiO2 as an authorized UV filter, except in products that could lead to exposure of the lungs. After oral exposure, nano-TiO2 absorption and toxicity are limited. The incidental oral exposure to nano-TiO2 contained in lip balms is thus not expected to induce adverse health effects.

Effect of Sunscreen Application Under Maximal Use Conditions on Plasma Concentration of Sunscreen Active Ingredients: A Randomized Clinical Trial.

Importance: The US Food and Drug Administration (FDA) has provided guidance that sunscreen active ingredients with systemic absorption greater than 0.5 ng/mL or with safety concerns should undergo nonclinical toxicology assessment including systemic carcinogenicity and additional developmental and reproductive studies. Objective: To determine whether the active ingredients (avobenzone, oxybenzone, octocrylene, and ecamsule) of 4 commercially available sunscreens are absorbed into systemic circulation. Design, Setting, and Participants: Randomized clinical trial conducted at a phase 1 clinical pharmacology unit in the United States and enrolling 24 healthy volunteers. Enrollment started in July 2018 and ended in August 2018. Interventions: Participants were randomized to 1 of 4 sunscreens: spray 1 (n = 6 participants), spray 2 (n = 6), a lotion (n = 6), and a cream (n = 6). Two milligrams of sunscreen per 1 cm2 was applied to 75% of body surface area 4 times per day for 4 days, and 30 blood samples were collected over 7 days from each participant. Main Outcomes and Measures: The primary outcome was the maximum plasma concentration of avobenzone. Secondary outcomes were the maximum plasma concentrations of oxybenzone, octocrylene, and ecamsule. Results: Among 24 participants randomized (mean age, 35.5 [SD, 1.5] years; 12 (50%] women; 14 [58%] black or African American; 14 [58%]), 23 (96%) completed the trial. For avobenzone, geometric mean maximum plasma concentrations were 4.0 ng/mL (coefficient of variation, 6.9%) for spray 1; 3.4 ng/mL (coefficient of variation, 77.3%) for spray 2; 4.3 ng/mL (coefficient of variation, 46.1%) for lotion; and 1.8 ng/mL (coefficient of variation, 32.1%). For oxybenzone, the corresponding values were 209.6 ng/mL (66.8%) for spray 1, 194.9 ng/mL (52.4%) for spray 2, and 169.3 ng/mL (44.5%) for lotion; for octocrylene, 2.9 ng/mL (102%) for spray 1, 7.8 ng/mL (113.3%) for spray 2, 5.7 ng/mL (66.3%) for lotion, and 5.7 ng/mL (47.1%) for cream; and for ecamsule, 1.5 ng/mL (166.1%) for cream. Systemic concentrations greater than 0.5 ng/mL were reached for all 4 products after 4 applications on day 1. The most common adverse event was rash, which developed in 1 participant with each sunscreen. Conclusions and Relevance: In this preliminary study involving healthy volunteers, application of 4 commercially available sunscreens under maximal use conditions resulted in plasma concentrations that exceeded the threshold established by the FDA for potentially waiving some nonclinical toxicology studies for sunscreens. The systemic absorption of sunscreen ingredients supports the need for further studies to determine the clinical significance of these findings. These results do not indicate that individuals should refrain from the use of sunscreen. Trial Registration: ClinicalTrials.gov Identifier: NCT03582215.

Metabolism and disposition of 2-ethylhexyl-p-methoxycinnamate following oral gavage and dermal exposure in Harlan Sprague Dawley rats and B6C3F1/N mice and in hepatocytes in vitro.

1. 2-Ethylhexyl-p-methoxycinnamate (EHMC) is commonly used as an ingredient in sunscreens, resulting in potential oral and dermal exposure in humans. 2. Clearance and metabolism of EHMC in hepatocytes and disposition and metabolism of EHMC in rodents following oral (8-800 mg/kg) intravenous (IV) (8 mg/kg) or dermal (0.8-80 mg/kg representing 0.1-10% formulation concentration) exposure to [14C]EHMC were investigated in rats and mice. 3. EHMC was rapidly cleared from rat and mouse hepatocytes (half-life ≤3.16 min) and less rapidly (half-life ≤48 min) from human hepatocytes. 4. [14C]EHMC was extensively absorbed and excreted primarily in urine by 72 h after oral administration to rats (65-80%) and mice (63-72%). Oral doses to rats were excreted to a lesser extent (3-8%) in feces and as CO2 (1-4%). Radioactive residues in tissues were <1% of the dose. There were no sex or species differences in disposition in rats. 5. Following dermal application, 34-42% of an 8-mg/kg dose was absorbed in rats, and 54-62% in mice in 72-h. 6. Among numerous urinary metabolites associated with hydrolysis of the ester, two potential reproductive and developmental toxicants, 2-ethylhexanol and 2-ethylhexanoic acid were produced by metabolism of EHMC.

Sunscreen creams containing naringenin nanoparticles: Formulation development and in vitro and in vivo evaluations.

BACKGROUND: The aim of this study was to develop sunscreen creams containing polymeric nanoparticles (NPs) of naringenin for photoprotective and antioxidant effects. METHODS: Polymeric NPs of naringenin were prepared and optimized. The NPs were incorporated into sunscreen creams and evaluated for in vitro and in vivo skin retention. RESULTS: The optimized naringenin NPs showed a size of 131.2 nm, zeta potential -25.4 mV, and entrapment efficiency 32.45%. The absence of drug-excipient interaction was confirmed by Fourier transform infrared spectroscopy and differential scanning calorimetry. X-Ray diffraction analysis demonstrated the amorphization of naringenin in nanoparticles. Transmission electron microscopy showed the sphericity of the NPs with the size of <200 nm. Cytotoxicity assessment in HaCaT cells indicated non-toxic nature of naringenin NPs. In vitro skin permeation studies demonstrated that higher amount of naringenin permeated at the end of 12 hours (Q12 hours  = 184.03 ± 3.37 µg/cm2 ) and deposited in the skin (10.38 ± 0.48 µg/cm2 ) from NPs as compared to plain naringenin. Sunscreen creams (SC1-SC5) containing plain naringenin or NPs with/without nano-zinc oxide and nano-titanium dioxide were prepared and evaluated. Optimized cream (SC5) containing naringenin NPs showed highest SPF value and enhanced skin retention of naringenin in comparison with NPs in suspension form and other cream formulations. CONCLUSION: Optimized nanoparticulate sunscreen cream exhibited highest skin retention and negligible skin permeation of naringenin besides showing excellent SPF value.

Realistic Sunscreen Durability: A Randomized, Double-blinded, Controlled Clinical Study.

BACKGROUND: Studies show that sunscreen under real-life conditions is often not reapplied and/or applied insufficiently. This study investigated the durability of 2 current sunscreens with different SPF protection over an 8-hour period under simulated real-life conditions. METHODS: Participants (n=24) were randomized into two study groups utilizing either 2 mg/cm2 (FDA testing concentration) or 1 mg/cm2 (real-life application levels) of sunscreen. Two current SPF 15 and 70 sunscreens were applied to test spots on each participant's back. SPF values were obtained at baseline, 3.5, and 8 hours after initial application, during which subjects completed 30 minutes of moderate exercise followed by 80 minutes of water exposure. RESULTS: Participants in both dose study groups revealed only a 15-40% overall decrease in their SPF protection 8 hours after application. The study group that received half the FDA test concentration of sunscreen achieved approximately half or less the labeled SPF. At 8 hours, the test sites that received SPF 70 maintained an average SPF greater than 64 (2 mg/cm2 application) and 26 (1 mg/cm2 application). Similarly, the SPF 15 product test sites revealed an in vivo protection of 13 (2 mg/cm2) and 7 (1 mg/cm2). CONCLUSION: This study demonstrates that current sunscreens may be durable on skin even following significant exercise and water exposure, suggesting that reapplication intervals may be longer than currently recommended. In addition, the higher SPF sunscreen maintained a skin cancer-protective level of SPF following extended use.

J Drugs Dermatol. 2018;17(1):116-117.

In Vivo Human Skin Penetration Study of Sunscreens by Confocal Raman Spectroscopy.

This research work mainly deals with the application of confocal Raman spectroscopic technique to study in vivo human skin penetration of sunscreen products, as there are a lot of controversies associated with their skin penetration. Healthy human volunteers were tested for penetration of two commercial sunscreen products into their volar forearm skin for a period of 2 h. Measurements were taken before and after application of these sunscreen products. All the confocal Raman spectra were pre-processed and then subjected to multivariate two-dimensional principal component analysis and classical least squares analysis to determine the skin penetration of these sunscreens in comparison to the "sunscreen product spectrum" which was considered as the control. Score plots of principal component analysis of confocal Raman spectra indicated clear separation between the spectra before and after application of sunscreen products. Loading plots showed the maximum differences in the spectral region from 1590 to 1626 cm-1 where the characteristic peak of the pure sunscreen products was observed. Classical least squares analysis has shown a significant penetration to a depth of 10 µm in the volar forearm skin of healthy human volunteers for both these sunscreen products. The results confirm that the penetration of these tested sunscreen products was restricted to stratum corneum and also prove that confocal Raman spectroscopy is a simple, fast, nondestructive, and noninvasive semi-quantitative analytical technique for these studies.

Dermal Uptake of Benzophenone-3 from Clothing.

Benzophenone-3 (also known as BP-3 or oxybenzone) is added to sunscreens, plastics, and some coatings to filter UV radiation. The suspected endocrine disruptor BP-3 has been detected in the air and settled dust of homes and is expected to redistribute from its original sources to other indoor compartments, including clothing. Given its physical and chemical properties, we hypothesized that dermal uptake from clothing could contribute to the body burden of this compound. First, cotton shirts were exposed to air at an elevated concentration of BP-3 for 32 days; the final air concentration was 4.4 µg/m3. Next, three participants wore the exposed shirts for 3 h. After 3 h of exposure, participants wore their usual clothing during the collection of urine samples for the next 48 h. Urine was analyzed for BP-3, a metabolite (BP-1), and six other UV filters. The rate of urinary excretion of the sum of BP-1 and BP-3 increased for all participants during and following the 3 h of exposure. The summed mass of BP-1 and BP-3 excreted during the first 24 h attributable to wearing exposed t-shirts were 12, 9.9, and 82 µg for participants 1, 2, and 3, respectively. Analysis of these results, coupled with predictions of steady-state models, suggest that dermal uptake of BP-3 from clothing could meaningfully contribute to overall body burden.

Development of a HPLC method for determination of four UV filters in sunscreen and its application to skin penetration studies.

This study describes the development, validation and application of a high-performance liquid chromatography (HPLC) method for the simultaneous determination of the in vitro skin penetration profile of four UV filters on porcine skin. Experiments were carried out on a gel-cream formulation containing the following UV filters: diethylamino hydroxybenzoyl hexyl benzoate (DHHB), bis-ethylhexyloxyphenol methoxyphenyl triazine (BEMT), methylene bis-benzotriazolyl tetramethylbutylphenol (MBBT) and ethylhexyl triazone (EHT). The HPLC method demonstrated suitable selectivity, linearity (10.0-50.0 µg/mL), precision, accuracy and recovery from porcine skin and sunscreen formulation. The in vitro skin penetration profile was evaluated using Franz vertical diffusion cells for 24 h after application on porcine ear skin. None of the UV filters penetrated the porcine skin. Most of them stayed on the skin surface (>90%) and only BEMT, EHT and DHHB reached the dermis plus epidermis layer. These results are in agreement with previous results in the literature. Therefore, the analytical method was useful to evaluate the in vitro skin penetration of the UV filters and may help the development of safer and effective sunscreen products.

Standardization of an in vitro Model for Evaluating the Bioavailability of Topically Applied Compounds on Damaged Skin: Application to Sunscreen Analysis.

BACKGROUND: Information is lacking on the dermal penetration of topically applied formulations on in vitro skin models, under conditions where the stratum corneum (SC) is damaged. Therefore, we have developed a standardized in vitro barrier-disrupted skin model using tape stripping. METHODS: Different tape stripping conditions were evaluated using histology, transepidermal water loss, infrared densitometry, and caffeine absorption. RESULTS: The effects of tape stripping were comparable using pig and human skin. Optimized conditions were used to test the effect of SC damage and UV irradiation on the absorption of an UV filter combination present in a sunscreen. The bioavailability of the filters was extremely low regardless of the extent of skin damage, suggesting bioavailability would not be increased if the consumer applied the sunscreen to sun-damaged skin. CONCLUSION: This standardized in vitro methodology using pig or human skin for damaged skin will add valuable information for the safety assessment of topically applied products.