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

Dynamic macromolecular material design: the versatility of cucurbituril over cyclodextrin in host-guest chemistry

The keto-enol tautomerism of avobenzone (AVO) is pivotal to its photostability, influenced by microenvironmental factors, such as, the type of solvent and complexation with macrocyclic compounds. This study explores the effect of host-guest complexation on AVO photostabilization, employing cucurbit[7]uril (CB[7]) and β-cyclodextrin (β-CD) to form inclusion complexes. CB[7] exhibits a higher affinity to the keto form of AVO, a UVC radiation absorber. The complexed keto form facilitates the regeneration of the enol form, reducing skin permeation. Spectroscopic and thermal analyses confirm 1 : 1 AVO-CB[7] and AVO-β-CD complex formation. Computational and MD simulations show that host-guest complex is favored over isolated AVO and β-CD or CB[7] molecules by 95-125 kJ mol-1, depending on the presence of implicit solvent. Both macrocycles enhance AVO photostabilization in aqueous environments, with CB[7] displaying greater selectivity for the keto form, while β-CD shows ethanol concentration-dependent binding.

Drug Delivery Strategies for Avobenzone: A Case Study of Photostabilization

Several developments and research methods are ongoing in drug technology and chemistry research to elicit effectiveness regarding the therapeutic activity of drugs along with photoprotection for their molecular integrity. The detrimental effect of UV light induces damaged cells and DNA, which leads to skin cancer and other phototoxic effects. The application of sunscreen shields to the skin is important, along with recommended UV filters. Avobenzone is widely used as a UVA filter for skin photoprotection in sunscreen formulations. However, keto-enol tautomerism propagates photodegradation into it, which further channelizes the phototoxic and photoirradiation effects, further limiting its use. Several approaches have been used to counter these issues, including encapsulation, antioxidants, photostabilizers, and quenchers. To seek the gold standard approach for photoprotection in photosensitive drugs, combinations of strategies have been implemented to identify effective and safe sunscreen agents. The stringent regulatory guidelines for sunscreen formulations, along with the availability of limited FDA-approved UV filters, have led many researchers to develop perfect photostabilization strategies for available photostable UV filters, such as avobenzone. From this perspective, the objective of the current review is to summarize the recent literature on drug delivery strategies implemented for the photostabilization of avobenzone that could be useful to frame industrially oriented potential strategies on a large scale to circumvent all possible photounstable issues of avobenzone.

Hyaluronic acid-cyclodextrin encapsulating paeonol for treatment of atopic dermatitis

The cyclodextrin (CD) was grafted onto hyaluronic acid (HA) to form a topical delivery carrier (HACD) in which Paeonol was loaded in its CD cavity and self-assemble into the polymeric micelles (HACD-PAE) for the treatment of atopic dermatitis. Fluorescence microscope observed that HACD could fast penetrate into the skin and remain stable within 12 h. In vitro penetration test (IVPT) results showed the PAE retentions of HACD-PAE group in the stratum corneum and dermis were 3.35 and 1.78 times improvement than that of PAE group. ATR-FTIR and H&E staining assays indicated HACD could increase the gap of keratinocytes by interacting with corneum lipids and loosening the keratin. Furthermore, HACD-PAE showed the best therapeutic effect on atopic dermatitis mice. Thus HACD could be a promising skin-specific delivery carrier, not only promoting the drug penetrating but increasing its remaining in the skin and play the skin disease therapy and skin-care role.

Activation of retinoic acid-related orphan receptor γ(t) by parabens and benzophenone UV-filters

Retinoic acid-related orphan receptor γt (RORγt) regulates immune responses and its impaired function contributes to inflammatory and autoimmune diseases and may promote skin cancer. Synthetic inverse RORγt agonists block the production of Th17-associated cytokines including interleukin (IL)-17A and IL-22 and are under investigation for treatment of such pathologies. Unintentional RORγt activation in skin, following exposure to environmental chemicals, may promote inflammatory skin disease. Parabens and UV-filters, frequently used as additives in cosmetics and body care products, are intensively inspected for endocrine disrupting properties. This study assessed whether such compounds can interfere with RORγ activity using a previously established tetracycline-inducible reporter gene assay in CHO cells. These transactivation experiments revealed hexylparaben, benzylparaben and benzophenone-10 as RORγ agonists (EC50 values: 144 ± 97 nM, 3.39 ± 1.74 µM and 1.67 ± 1.04 µM, respectively), and they could restore RORγ activity after suppression by an inverse agonist. Furthermore, they enhanced RORγt-dependent transcription of the pro-inflammatory IL-17A and/or IL-22 genes in the murine T-cell model EL4. Virtual screening of a cosmetics database for structurally similar chemicals and in vitro testing of the most promising hits revealed benzylbenzoate, benzylsalicylate and 4-methylphenylbenzoate as RORγ agonists (low micromolar EC50 values). Moreover, an analysis of mixtures of the newly identified RORγ agonists suggested additive effects. This study presents novel RORγ(t) agonistic structural scaffolds. By activating RORγ(t) the identified parabens and UV-filters may potentially aggravate pathophysiological conditions, especially skin diseases where highest exposure of such chemicals can be expected. Follow-up studies should assess whether such compounds, either alone or as mixtures, can reach relevant concentrations in tissues and target cells to activate RORγ(t) in vivo.

2-Hydroxy-4-methoxybenzophenone Enhances the Suppression of Superoxide Anion Radicals Generated via UVA-induced Photosensitizing by t-Butyl Methoxydibenzoylmethane

4-tert-Butyl-4'-methoxydibenzoylmethane (BMDM) is widely used throughout the world as a highly effective UVA absorber that can prevent the progression of photoaging in skin. However, due to its low photostability, BMDM is also known for the disadvantage of having a reduced capability to absorb UVA during prolonged exposure to sunlight. Although many studies have been carried out to overcome this disadvantage of BMDM, little attention has been paid to how the radicals generated from BMDM during UV exposure influence the skin. Therefore, the purpose of this study was twofold: One goal was to clarify the influence of radicals on human skin using cytotoxicity as a parameter. The second was to propose a solution that could reduce the radical formation while taking photostability into consideration. Using ESR spin trapping and superoxide dismutase (SOD) treatment, the radicals produced by the UV exposure of BMDM were shown to be superoxide anion radicals (•O₂^-). HaCaT keratinocytes exposed to UVA in the presence of BMDM showed a significant reduction in cell viability, indicating that the radicals produced from BMDM have a harmful influence on the skin. UVA exposure coincidently led to a reduction of UVA absorbance by BMDM. Interestingly, 2-hydroxy-4-methoxybenzophenone (Benzophenone-3; BP3) reduced both the radical formation and the cytotoxicity resulting from the UVA-exposure of BMDM, while also restoring its UVA absorbance. In conclusion, the results show that BMDM and BP3 is an effective combination to reduce the influence of UVA-exposed BMDM on the skin and to prevent the loss of UVA absorbance by BMDM during UV exposure.

In Vitro Skin Permeation Methodology for Over-The-Counter Topical Dermatologic Products

For topically applied over-the-counter (OTC) products, the association of unwanted systemic exposure and adverse events may be difficult to ascertain without a recognition or determination of in vivo absorption. Evaluation of skin permeability using a validated in vitro permeation methodology can provide important information for both initial formulation selection and reformulation during the product life cycle. Additionally, a comparison of permeation rates between formulations using a validated methodology could reduce the number of nonclinical studies needed as part of reformulation. However, many in vitro permeation tests (IVPTs) have produced results with high variability and low reproducibility between study sites. It is unclear if this is due to a lack of a standardized protocol, or lack of control of multiple key experimental factors including skin source, preparation, receptor fluid, and study design. This review presents the authors perspective on the potential regulatory utility of IVPT and proposes steps to improve the accuracy and reproducibility of IVPT. The focus of this review is on topical dermatologic drugs with an initial emphasis on the OTC marketplace where reformulations are more common.

Nanocarriers and Microcarriers for Enhancing the UV Protection of Sunscreens: An Overview

This review addresses a major question of importance to pharmaceutical scientists: how can novel drug delivery systems play a role in maximizing the UV protection of sunscreens? Because more and more people are being diagnosed with skin cancer each year than all other cancers combined, adequate sun protective measures are pivotal. In this context, the present review is to give an up-to-date overview on the different nanocarrier systems that have been explored so far for encapsulating different types of UV filters present on the market. The aim of these carrier systems is to prevent skin penetration and to enhance the photoprotective potential of sunscreen actives. For each supramolecular system, a brief description along with the studies, achievements, and pitfalls, on the type of UV actives inside them, ranging from classical UV filters to new generation of UV actives is given. A brief overview of UV filters encapsulated in microcarriers is also discussed.

Skin absorption and human exposure estimation of three widely discussed UV filters in sunscreens--In vitro study mimicking real-life consumer habits

Due to health concerns about safety, three UV-filters (Benzophenone-3, BP3, 10%; Ethylhexyl Methoxycinnamate, EHMC, 10%; Butyl Methoxydibenzoylmethane, BMDBM; 5%) were examined in vitro for absorption on full-thickness pig-ear skin, mimicking human in-use conditions. Kinetic profiles confirmed the rapid permeation of BP3; after the first hour of skin (frozen-stored) exposure to 2 mg/cm(2) (W/O sunscreen; recommended but unrealistic amount), about 0.5% of the applied dose passed into the receptor fluid. The absorption rate of filters was higher from W/O than from O/W emulsions. The fresh/frozen-stored skin permeability coefficient (0.83-0.54) for each UV filter was taken into account. Systemic Exposure Dosage of BP3, EHMC, BMDBM for humans as a consequence of (i) whole-body and (ii) face treatment with 0.5 mg/cm(2) of W/O sunscreen for 6-h skin exposure followed by washing and subsequent 18-h permeation (a realistic scenario) were estimated to be (i) 4744, 1032 and 1036 μg/kg-bw/day, and (ii) 153, 33 and 34 μg/kg-bw/day, respectively. From Margin of Safety for BP3, EHMC and BMDBM (i) 42, 485 and 192 as well as (ii) 1307; 15,151 and 5882, respectively, only the value of 42 (<100) for BP3 indicated a possible health risk. Escalation of a phobia towards all organic UV filters is undesirable.

Modified-release ointment with nitroglycerin β-cyclodextrin inclusion complex for treatment of anal fissures

Objectives

The aim was to evaluate ointments for local treatment of anal fissures. Nitroglycerin (NTG) was complexed with β-cyclodextrin (β-CD) to provide prolonged NTG release, with the intention of decreasing systemic drug absorption and thus reducing side effects.

Methods

Gels, creams and anhydrous water-emulsifying (AWE) ointment with NTG-CD were compared with preparations containing uncomplexed NTG (diluted with crospovidone, NTG-cP). The in-vitro NTG release and ex-vivo skin absorption were studied.

Key findings

The prolonged-release ointment with the NTG-CD complex was formulated using AWE base or w/o cream (20% water); release of NTG from a hydrogel was very fast with both the complexed and uncomplexed forms. From the AWE ointment base, 16.4% or 4.5% of the total NTG dose was released after 6 h when NTG-cP or NTG-CD was incorporated, respectively. With the complexed form, NTG absorption to the skin after a 5-h application was 18.1 or 11.1 μg/g from AWE ointment or cream, respectively; absorption of the uncomplexed NTG was higher: 52.3 or 21.9 μg/g from AWE ointment and cream, respectively.

Conclusions

Complexation with β-CD results in prolonged release of NTG from AWE ointment and w/o cream, which was confirmed by the ex-vivo skin absorption results.

Evaluation of the effect of hydroxypropyl-β-cyclodextrin on topical administration of milk thistle extract

Two water in oil emulsions composed by eudermic ingredients as glycerin, cocoa butter, almond oil and a variety of lipids, were enriched respectively with milk thistle dry extract (MT) or with a binary complex composed by MT and hydroxypropyl-β-cyclodextrin (HP) (1:4 w/w) correspondent to 1% (w/w) in sylimarine in order to obtain two different emulsions designed for the skin delivery and determine influence of hydroxypropyl-β-cyclodextrin on the extract delivery and permeation. Uv-vis spectrophotometric analyses demonstrated that phytocomplex formation influences the finding of MT after the complexation process and the in vitro antioxidant activity. Further in vitro and ex vivo experiments demonstrated that the penetration capability of MT from formulations is strictly influenced by the phytocomplex able to control MT permeation; moreover phytocomplex increases flavonoids stability during the in vitro tests. Additionally, in vivo studies showed that the penetration into the stratum corneum of the active ingredients is effectively achieved by the phytocomplex formation, in fact about 80% of MT is absorbed by the skin along 1h despite the 30% of MT not complexed absorbed during the same period.

Evaluation of octyl p-methoxycinnamate included in liposomes and cyclodextrins in anti-solar preparations: preparations, characterizations and in vitro penetration studies

PURPOSE

Awareness of the harmful effects of ultraviolet radiation has led to the increasing use of sunscreens, thus, the development of safe and effective antisolar preparations is important. The inclusion of sunscreen molecules in different release systems, like liposomes (lipo) and cyclodextrins (CD) is therefore required.

METHODS

The in vivo sun protection factor (SPF), water resistance, and in vitro transdermal penetration test of octyl p-methoxycinnamate (OMC) in different dispersions, such as OMC encapsulated in liposomes (lipo/OMC), OMC encapsulated in β-cyclodextrins (β-CD/OMC), OMC encapsulated in both release systems (lipo/OMC and β-CD/OMC), and an OMC-free formulation were determined.

RESULTS

Although the formulation containing only the lipo/OMC system revealed high value of in vivo SPF (11.0 ± 1.3) and water resistance (SPF = 10.3 ± 2.2), the formulation containing both release systems (lipo/OMC + β-cyclodextrin/OMC) showed the best result in the in vivo SPF test (11.6 ± 1.6). In the penetration test, the formulation containing the lipo/OMC system had better performance, since a high amount of OMC in the epidermis (18.04 ± 1.17 μg) and a low amount of OMC in the dermis (9.4 ± 2.36 μg) were observed. These results suggest that liposomes interact with the cells of the stratum corneum, promoting retention of OMC in this layer.

CONCLUSION

According to our study, the lipo/OMC system is the most advantageous release system, due to its ability to both increase the amount of OMC in the epidermis and decrease the risk of percutaneous absorption.

Permeation and distribution of ferulic acid and its α-cyclodextrin complex from different formulations in hairless rat skin

Ferulic acid (FA) is a natural product that occurs in seeds of many plants where it is generally located in the bran. This compound is a multifunctional ingredient endowed with antioxidative, radical scavenging, sunscreening and antibacterial actions. The aim of this study was to analyse the ferulic acid cutaneous permeation and distribution, through and into the skin layers, from different cosmetic vehicles, an O/W emulsion (pH 6.0) and two gel-type formulations at different pH levels (6.0 and 7.4), containing FA alone or an inclusion complex with α-cyclodextrin (CD-FA). In vitro permeation studies were performed in vertical diffusion cells using hairless rat excised skin. At appropriate intervals of time, the amount of permeated sunscreen/radical scavenger was evaluated by high-performance liquid chromatography (HPLC). At the end of experiments, treated skin samples were sectioned with a cryomicrotome and the FA content of the individual slices was analysed by HPLC. FA-containing formulations, O/W emulsion, gels A and B, originated FA fluxes of 8.48 ± 2.31, 8.38 ± 0.89 and 5.72 ± 0.50 μg/cm(2) h, respectively, thus suggesting the pH influence on FA percutaneous permeation. The use of the inclusion complex, CD-FA, determined in all cases a decrease of FA transdermal permeation while no influence of pH was observed. Gel-type formulations containing FA ensured higher sunscreen storage in the superficial layers if compared with O/W emulsion. When FA was included in α-cyclodextrin, FA amount retained into skin layers decreased markedly.

Development of machine learning models of β-cyclodextrin and sulfobutylether-β-cyclodextrin complexation free energies

A new set of 142 experimentally determined complexation constants between sulfobutylether-β-cyclodextrin and diverse organic guest molecules, and 78 observations reported in literature, were used for the development of the QSPR models by the two machine learning regression methods - Cubist and Random Forest. Similar models were built for β-cyclodextrin using the 233-compound dataset available in the literature. These results demonstrate that the machine learning regression methods can successfully describe the complex formation between organic molecules and β-cyclodextrin or sulfobutylether-β-cyclodextrin. In particular, the root mean square errors for the test sets predictions by the best models are low, 1.9 and 2.7kJ/mol, respectively. The developed QSPR models can be used to predict the solubilizing effect of cyclodextrins and to help prioritizing experimental work in drug discovery.

Microencapsulation of a cyclodextrin complex of the UV filter, butyl methoxydibenzoylmethane: in vivo skin penetration studies

Lipid microparticles loaded with the complex between hydroxypropyl-β-cyclodextrin (HP-β-CD) and the sunscreen agent, butyl methoxydibenzoylmethane (BMDBM) were evaluated for their effect on the UV filter percutaneous penetration. The microparticles were prepared by the melt emulsification technique using tristearin as lipidic material and hydrogenate phosphatidylcholine as the surfactant. Human skin penetration was investigated in vivo by the tape stripping technique, a minimal invasive procedure based on the progressive removal of the upper cutaneous layers (stratum corneum) with adhesive tape strips. The amount of sunscreen fixed to each strip was determined by HPLC after solvent extraction. The recovery of the UV filter from spiked adhesive tapes was >94.4% and the precision of the method was better than 7.6% relative standard deviation. Non-encapsulated BMDBM, its complex with HP-β-CD, the lipid microparticles loaded with the sunscreen alone or the BMDBM/HP-β-CD complex were introduced into oil-in-water emulsions and applied to human volunteers. Compared to the cream with the non-encapsulated sunscreen agent (percentage of the applied dose penetrated, 9.7%±2.5), the amount of BMDBM diffusing into the stratum corneum was increased by the formulations containing the BMDBM/HP-β-CD complex (17.1%±3.2 of the applied dose) or the microparticles loaded with BMDBM only (15.1%±2.7 of the applied dose). On the contrary, a significant decrease in the level of UV filter penetrated into the stratum corneum was achieved by the cream containing the microencapsulated BMDBM/HP-β-CD complex (percentage of the applied dose penetrated, 6.0%±1.5). The reduced BMDBM percutaneous penetration attained by the latter system should enhance the UV filter efficacy and limit potential toxicological risks.

Cyclodextrins – Fields of Application. Part I

This review is dedicated to different fields of use of cyclodextrins, a family of three cyclic natural oligosaccharides and their derivatives. The first part of the review gives a brief description of the main and the most recent developed applications of cyclodextrins in food, cosmetic industry, environmental protection technologies and agriculture. Different products based on inclusion complexes with cyclodextrins and technologies with different use of cyclodextrins and inclusion complexes are described.

Percutaneous absorption of metopimazine and effect of cyclodextrins

Metopimazine (MPZ) is used to prevent emesis during chemotherapies. A transdermal delivery system of MPZ may present a great advantage in patients to improve compliance. Hydroxypropyl beta cyclodextrin (HPbetaCD) and partially methylated beta cyclodextrin (PMbetaCD) were tested to enhance the percutaneous absorption of MPZ through pig skin using Franz's cells. The MPZ hydrochloride flux was low with 0.176 +/- 0.054 microg/h/cm(2) and no flux was detected with a suspension of MPZ (base). The used characterization analyses demonstrated the formation of an inclusion complex with cyclodextrin and this complex improved percutaneous absorption of MPZ. Flux was increased to 0.240 +/- 0.032 microg/h/cm(2) and 0.566 +/- 0.057 mug/h/cm(2) for HPbetaCD and PMbetaCD, respectively, with a concentration of 20%. This study has shown that HPbetaCD and PMbetaCD improved the percutaneous penetration of MPZ. Cyclodextrin complexes increased MPZ bioavailability at the skin surface and PMbetaCD was also able to extract cutaneous fatty acids.

Effect of HPbetaCD on solubility and transdermal delivery of capsaicin through rat skin

We evaluated the ability of hydroxypropyl-beta-cyclodextrin (HPbetaCD) to influence the percutaneous absorption of capsaicin (CP) through isolated rat skin. Phase solubility analysis and phase distribution studies suggested the potential of HPbetaCD as a solubilizer and permeation enhancer for CP. In vitro permeation studies showed the trend that, the penetration flux (J(s)) of CP increased with the increasing concentration of HPbetaCD from 0 to 2.20% (w/v), and then decreased dramatically when the concentration of HPbetaCD kept on increasing up to 15% (w/v). 2.20% (w/v) of HPbetaCD provided both just adequate solubilization and preferred J(s) for the permeation of CP (0.075%, w/v). Similar change patterns of the permeation parameters were also observed in the hydrogels, but the J(s) of CP was reduced significantly along with the increasing concentration of Carbopol U21. Histological analysis showed an invasive action of HPbetaCD on the stratum corneum (SC) of rat skin, which could only reduce the lag time (T(L)) but could not increase the J(s) of CP. On the other hand, the complexation of HPbetaCD with CP could attenuate this invasive action. It is inferred that excess of HPbetaCD could not only disturb the percutaneous absorption of CP but also disrupt the structure of SC.

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.

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

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

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.

Human Safety and Efficacy of Ultraviolet Filters and Sunscreen Products

Ultraviolet (UV) filters are the active ingredients in sunscreens. The concentration and combination of UV filters determine the efficacy of sunscreens as measured by sun protection factor. The safety of individual UV filters, and, more generally, sunscreen products, is a matter of a few related components: objective toxicologic evaluation, phototoxicologic potential, and human health consequences of using products that may reduce some but not all of the solar UV. Of 16 UV filters approved by the US Food and Drug Administration, 9 are used in different combinations in the most currently marketed sunscreens. Most of these compounds are considered safe and effective alone or in combination with other UV filters based on extensive toxicologic/phototoxicologic evaluations and market history. The benefits from proper use of sunscreens outweigh real or perceived human health concerns, establishing a favorable benefit-to-risk ratio. Future UV filters will require complete human safety evaluations alone and in combination with select benchmark ingredients.

A new sunscreen of the cinnamate class: Synthesis and enzymatic hydrolysis evaluation of glyceryl esters of p-methoxycinnamic acid

Glyceryl esters of p-methoxycinnamic acid, 1,3-dipalmitoyl-2-p-methoxycinnamoyl-1,2,3-propanetriol and 1,3-dioctanoyl-2-p-methoxycinnamoyl-1,2,3-propanetriol were synthesised in an attempt to increase substantivity and decrease eventual undesirable effects of sunscreens of this class. To assess if the glyceryl esters could present a higher stability towards hydrolysis by lipases in the stratum corneum, hydrolysis rates were determined in vitro using a commercial fungal lipase from Rhizomucor miehei. Results presented herein show that the glyceryl esters have similar lambda(max) and epsilon values to sunscreens of the cinnamate class. The ester 1,3-dipalmitoyl-2-p-methoxycinnamoyl-1,2,3-propanetriol presented a 2.8 times lower hydrolysis rate by lipase, in vitro, than the commercial sunscreen 2-ethylhexyl-p-methoxycinnamate (alkyl ester). This finding suggests that this triacylglycerol can possibly have a longer retention time in the skin and consequently promote a more intense and effective antisolar action than the commercial sunscreen.