Predicting the Rate and Extent of Fragrance Chemical Absorption into and through the Skin

An Investigation into the Transdermal Behavior of Active Ingredients by Combination of Experiments and Multiscale Simulations

Transdermal behavior is a critical aspect of studying delivery systems and evaluating the efficacy of cosmetics. However, existing methods face challenges such as lengthy experiments, high cost, and limited model accuracy. Therefore, developing accurate transdermal models is essential for formulation development and effectiveness assessment. In this study, we developed a multiscale model to describe the transdermal behavior of active ingredients in the stratum corneum. Molecular dynamics simulations were used to construct lipid bilayers and determine the diffusion coefficients of active ingredients in different regions of these bilayers. These diffusion coefficients were integrated into a multilayer lipid pathway model using finite element simulations. The simulation results were in close agreement with our experimental results for three active ingredients (mandelic acid (MAN), nicotinamide (NIC), and pyruvic acid (PYR)), demonstrating the effectiveness of our multiscale model. This research provides valuable insights for advancing transdermal delivery methods.

Fragrance in dermocosmetic emulsions: From microstructure to skin application

Fragrance is added to almost all dermocosmetic emulsions, as it has been found to be a key driver in consumer choice and contributes to the perception of product performance. Fragrance is a complex mixture of odorant chemicals at different concentrations. When incorporated into a formulation, the individual fragrance chemicals partition between the emulsion phases depending on their physicochemical properties, which can impact the structure, stability, texture and odour of the final product. On the other hand, it is well known in the food industry how the composition and structure of food emulsion matrices influence the release of aroma chemicals. Fragranced dermocosmetic emulsions have been studied to a lesser extent but it is interesting to apply findings from the food domain since emulsion structure, composition and aroma compounds share common features. This review aims to give an overview of the literature dealing with the interactions between fragrance and dermocosmetic emulsions. The effects of fragrance on emulsion microstructure, stability and texture are highlighted and discussed. The effects of composition and structure of emulsion on the release of fragrance molecules are also presented. Finally, the interactions between skin and fragranced emulsions are addressed.

New approaches build upon historical studies in dermal toxicology

These are my personal reflections on the history of approaches to understanding dermal toxicology brought together for the Paton Prize Award. This is not a comprehensive account of all publications from in vivo studies in humans to development of in vitro and in silico approaches but highlghts important progress. I will consider what is needed now to influence approaches to understanding dermal exposure with the current development and use of NAMs (new approach methodologies).

Assessment of dermal absorption of beryllium and copper contained in temple tips of eyeglasses

Dermal exposure to hazardous substances such as chemicals, toxics, metallic items and other contaminants may present substantial danger for health. Beryllium (Be) is a hazardous metal, especially when inhaled and/or in direct contact with the skin, associated with chronic beryllium disease (CBD) and Be sensitization (BeS). The objective of this study was to investigate the percutaneous penetration of beryllium and copper contained in metallic items as eyeglass temple tips (specifically BrushCAST® Copper Beryllium Casting Alloys containing Be 0.35 < 2.85%; Cu 95.3-98.7%), using Franz diffusion cells. This work demonstrated that the total skin absorption of Cu was higher (8.86%) compared to Be (4.89%), which was expected based on the high percentage of Cu contained in the eyeglass temple tips. However, Be accumulated significantly in the epidermis and dermis (up to 0.461 µg/cm²) and, to a lesser extent, in the stratum corneum (up to 0.130 µg/cm²) with a flux of permeation of 3.52 ± 4.5 µg/cm²/hour and lag time of 2.3 ± 1.3 h, after cutaneous exposure of temple tip into 1.0 mL artificial sweat for 24 h. Our study highlights the importance of avoiding the use of Be alloys in items following long-term skin contact.

Permeability coefficients and vapour pressure determination for fragrance materials

OBJECTIVE

This study aims to correlate new experimental data relevant to the description of the combined evaporation/permeation process of a perfume applied onto the skin.

METHODS

The vapour pressure data were measured by thermogravimetric analysis (TG-DTA). The Antoine constants and the Clarke and Glew parameters were determined for the same set of fragrance molecules to describe its low vapour pressures at new temperature ranges. The permeability coefficient of a set of 14 fragrance molecules in ethanolic solution was determined by Franz diffusion cell experiments, using porcine skin. The samples were analysed by gas chromatography with a flame ionization detector (GC/FID) and high-performance liquid chromatography with UV visible detector (HPLC/UV). A QSAR model was proposed to correlate the experimental data.

RESULTS

The Antoine constants were determined and presented low standard deviations. The Clarke and Glew physically significant parameters were obtained along with its statistical analysis. The fitting is good since the magnitude order is in accordance with the literature, associated with the low correlation between the estimated parameters and low standard deviations. The presented correlation, based on a mixture using only ethanol as solvent, showed better results than previous QSAR models with a standard relative deviation ( σ r ) of 0.190, a standard error (SE) of 0.397 and a determination coefficient (R² ) of 0.7786.

CONCLUSION

The dataset is still small compared to larger and more general QSAR models; however, it is much more specific as to the type of solvent and class of materials studied. This work represents an advance for the modelling of the perfume diffusion process since it specifies important properties that until then had been treated in a more general way.

Clustering a Chemical Inventory for Safety Assessment of Fragrance Ingredients: Identifying Read-Across Analogs to Address Data Gaps

A valuable approach to chemical safety assessment is the use of read-across chemicals to provide safety data to support the assessment of structurally similar chemicals. An inventory of over 6000 discrete organic chemicals used as fragrance materials in consumer products has been clustered into chemical class-based groups for efficient search of read-across sources. We developed a robust, tiered system for chemical classification based on (1) organic functional group, (2) structural similarity and reactivity features of the hydrocarbon skeletons, (3) predicted or experimentally verified Phase I and Phase II metabolism, and (4) expert pruning to consider these variables in the context of specific toxicity end points. The systematic combination of these data yielded clusters, which may be visualized as a top-down hierarchical clustering tree. In this tree, chemical classes are formed at the highest level according to organic functional groups. Each subsequent subcluster stemming from classes in this hierarchy of the cluster is a chemical cluster defined by common organic functional groups and close similarity in the hydrocarbon skeleton. By examining the available experimental data for a toxicological endpoint within each cluster, users can better identify potential read-across chemicals to support safety assessments.

Agarose-Based Gel-Phase Microextraction Technique for Quick Sampling of Polar Analytes Adsorbed on Surfaces

Sampling and extraction of chemical residues present on flat or curved surfaces as well as touch-sensitive objects are challenging. Hydrogels are characterized by high mechanical flexibility and water content. Thus, they are an ideal medium for transferring water-soluble analytes from a sampled surface to the next stage of an analytical workflow. Here, we demonstrate gel-phase microextraction (GPME), in which disks of blended hydrogels are utilized to lift traces of water-soluble substances adsorbed on surfaces. The protocol has been optimized in a series of tests involving fluorometric and mass spectrometric measurements. Compared with the pure agarose hydrogel, most of the tested blended hydrogels provide a higher efficiency for the sampling/extraction of a model analyte, fluorescein. The blended hydrogel disks are incorporated into three-dimensional (3D)-printed acrylonitrile-butadiene-styrene chips to create easy-to-use sampling probes. We exemplify the suitability of this improved GPME approach in sampling chemical residues present on the skin, glass, and daily use objects. In these tests, the extracts were analyzed on a triple quadrupole mass spectrometer fitted with an electrospray ion source operated in the positive- and negative-ion modes. The method enabled the detection of diclofenac on excised porcine skin fragments exposed to a topical nonsteroidal anti-inflammatory drug and sweat residues (lactic acid) left on surfaces touched by humans. The limits of detection for diclofenac and lactic acid in hydrogel extract were 6.4 × 10-6 and 2.1 × 10-5 M, respectively. In a model experiment, conducted using the presented approach, the amount of lactic acid on a glass slide with fingerprints was estimated to be ∼1.4 × 10-7 mol cm-2.

Fate and exposure modeling in regulatory chemical evaluation: new directions from retrospection

The development and application of fate and exposure modeling has undergone fundamental changes over the last 20 years. This has, in part, been driven by different needs within the regulatory community to address chemicals of concern using different approaches. Here we present a retrospective look at fate and exposure model application over the last two decades keeping an international regulatory perspective and using the Government of Canada's Chemicals Management Plan to illustrate concepts. We discuss the important role fate and exposure modeling has played to help address key data gaps when evaluating the risk of chemicals for both human health and ecological reasons. Yet limitations for more widespread model application within a regulatory context remain. Consequently, we identify specific data gaps and regulatory needs with an eye towards new directions for 21^st century chemical evaluation. We suggest that one factor limiting greater model application is the need for increased awareness and agreement of what chemical exposure assessment encompasses within the risk assessment paradigm. This is of particular importance today because of the increased availability of computational and high-throughput data and methods for chemical assessment allowing evaluators to potentially examine exposure from site of release to site of toxic action, thus linking exposure with toxicology. We further suggest there is a need for discussion at a global level to promote the awareness of new tools and approaches available for fate and exposure modeling and suggest that this could be organized using the aggregate exposure pathways concept.

RIFM fragrance ingredient safety assessment, 1-(1,2,3,4-tetrahydro-4,4-dimethyl-1-naphthyl)propan-1-one, CAS Registry Number 74499-60-8

The use of this material under current use conditions is supported by the existing information. This material was evaluated for genotoxicity, repeated dose toxicity, developmental and reproductive toxicity, local respiratory toxicity, phototoxicity/photoallergenicity, skin sensitization, as well as environmental safety. Data from the target material and the suitable read across analog 6-acetyl-1,1,2,4,4,7-hexamethyltetraline (CAS # 21145-77-7) show that this material is not genotoxic. Data from the suitable read across analog 6-acetyl-1,1,2,4,4,7-hexamethyltetraline (CAS # 21145-77-7) provided a MOE > 100 for the repeat dose and developmental toxicity endpoints. The reproductive and local respiratory toxicity endpoints were completed using the TTC (Threshold of Toxicological Concern) for a Cramer Class II material (0.009 mg/kg/day and 0.47 mg/day, respectively). Data on the target material showed that this material is below the non-reactive DST for skin sensitization and did not have the potential for phototoxicity or photoallergenicity. The environmental endpoint was completed as described in the RIFM Framework.

Human skin permeation of emerging mycotoxins (beauvericin and enniatins)

Currently, dermal exposure data of cyclic depsipeptide mycotoxins are completely absent. There is a lack of understanding about the local skin and systemic kinetics and effects, despite their widespread skin contact and intrinsic hazard. Therefore, we provide a quantitative characterisation of their dermal kinetics. The emerging mycotoxins enniatins (ENNs) and beauvericin (BEA) were used as model compounds and their transdermal kinetics were quantitatively evaluated, using intact and damaged human skin in an in vitro Franz diffusion cell set-up and ultra high-performance liquid chromatography (UHPLC)-MS analytics. We demonstrated that all investigated mycotoxins are able to penetrate through the skin. ENN B showed the highest permeation (kp,v=9.44 × 10(-6) cm/h), whereas BEA showed the lowest (kp,v=2.35 × 10(-6) cm/h) and the other ENNs ranging in between. Combining these values with experimentally determined solubility data, Jmax values ranging from 0.02 to 0.35 μg/(cm(2) h) for intact skin and from 0.07 to 1.11 μg/(cm(2) h) for damaged skin were obtained. These were used to determine the daily dermal exposure (DDE) in a worst-case scenario. On the other hand, DDE's for a typical occupational scenario were calculated based on real-life mycotoxin concentrations for the industrial exposure of food-related workers. In the latter case, for contact with intact human skin, DDE's up to 0.0870 ng/(kg BW × day) for ENN A were calculated, whereas for impaired skin barrier this can even rise up to 0.3209 ng/(kg BW × day) for ENN B1. This knowledge is needed for the risk assessment after skin exposure of contaminated food, feed, indoor surfaces and airborne particles with mycotoxins.

Transdermal drug delivery: 30+ years of war and still fighting!

By any measure, transdermal drug delivery (TDD) is a successful controlled release technology. Over the last 30+ years, a steady flux of transdermal products have received regulatory approval and reached the market. For the right compounds, TDD is an effective and preferred route of administration; for others, delivery across the skin makes no sense at all. Currently, the "rules" that govern (passive) TDD feasibility are clearly understood, and research activity is focused on novel approaches that strive to subvert skin's excellent barrier function, and broaden the range of active species amenable to percutaneous administration.

Can acute dermal systemic toxicity tests be replaced with oral tests? A comparison of route-specific systemic toxicity and hazard classifications under the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)

Acute systemic toxicity data (LD50 values) and hazard classifications derived in the rat following oral administration and dermal application have been analysed to examine whether or not orally-derived hazard classification or LD50 values can be used to determine dermal hazard classification. Comparing the oral and dermal classifications for 335 substances derived from oral and dermal LD50 values respectively revealed 17% concordance, and indicated that 7% of substances would be classified less severely while 76% would be classified more severely if oral classifications were applied directly to the dermal route. In contrast, applying the oral LD50 values within the dermal classification criteria to determine the dermal classification reduced the concordance to 15% and the relative 'under-classification' to 1%, but increased the relative 'over-classification' to 84%. Both under- and over-classification are undesirable, and mitigation strategies are discussed. Finally, no substance with an oral LD50 of >2000mg/kg was classified for acute systemic toxicity by the dermal route, suggesting that dermal testing for acute systemic toxicity of such substances adds nothing to the hazard characterisation and should be removed from routine regulatory data requirements.

Explaining skin permeation of 2-butoxyethanol from neat and aqueous solutions

Absorption of 2-butoxyethanol (BE) from neat and aqueous solutions of BE was measured through rat skin in vitro and in vivo and through silicone membranes. Like previous studies in human and guinea pig skin, BE flux increased proportional to BE concentration only when the weight fraction of BE (w(BE))<about 0.2. The flux of BE was relatively constant for 0.2<w(BE)<0.8, and it decreased dramatically for w(BE)>0.8. Experimental values of thermodynamic activity for BE and water in aqueous solutions of BE are presented. Except when the water content in the vehicle is small, skin is fully hydrated and the flux of a BE through it is proportional to the thermodynamic activity of BE. When w(BE)>0.8, there is a sharp drop in the activity-normalized BE flux through skin, which coincides with a decrease in water activity from 0.9 at w(BE)=0.8 to zero for neat BE. These observations are consistent with reduced BE flux arising from skin dehydration. From an analysis of previously published data, the activity-normalized flux of BE through hydrated human skin was determined to be 2-4 mg cm(-2)h(-1), which is in reasonable agreement with predictions of its maximum flux.

Assessment of dermal exposure to pesticide residues during re-entry

Currently, the determination of health risks to pesticide applicators from dermal exposure to these chemicals is assessed using either a concentrate of the compound or a relevant aqueous dilution. Neither of these conditions reflects a normal exposure of an individual when re-entering an area after pesticide application, that is, contact with dried residue of the diluted product on foliage. Methodology has therefore been developed to determine a relevant estimate of this potential dermal re-entry exposure from pesticide residues. Potential delivery platforms have been characterized for the transfer of pesticide residue to skin. Spin coating has been used to deposit uniform pesticide layers on to each platform. Five pesticides have been chosen to encompass a wide range of physicochemical properties: atrazine, 2,4-dichlorophenoxyacetic acid (2,4-D), chlorpyrifos, monocrotophos, and acetochlor. In vitro (Franz diffusion cell) experiments have been performed to monitor the transfer of these pesticides from the delivery platforms onto and through excised porcine skin. Parallel experiments were also conducted with aqueous pesticide dilutions for comparison, and a final in vivo measurement using ibuprofen (as a model compound) complemented the in vitro data. The results demonstrate that transfer of chemical residue onto and subsequently through the skin is dependent on the physical attributes of the residue formed. Thus, assessing dermal exposure to pesticides based on skin contact with either the chemical concentrate or a relevant aqueous dilution may incorrectly estimate the risk for re-entry scenarios.