Comparison of artificial sebum with human and hamster sebum samples

Methods for the characterisation of dermal uptake: Progress and perspectives for organophosphate esters

Organophosphate esters (OPEs) are a group of pollutants that are widely detected in the environment at high concentrations. They can adversely affect human health through multiple routes of exposure, including dermal uptake. Although attention has been paid to achieving an accurate and complete quantification of the dermal uptake of OPEs, existing evaluation methods and parameters have obvious weaknesses. This study reviewed two main categories of methodologies, namely the relative absorption (RA) model and the permeability coefficient (PC) model, which are widely used to assess the dermal uptake of OPEs. Although the PC model is more accurate and is increasingly used, the most important parameter in this model, the permeability coefficient (Kp), has been poorly characterised for OPEs, resulting in considerable errors in the estimation of the dermal uptake of OPEs. Thus, the detailed in vitro methods for the determination of Kp are summarised and sorted. Furthermore, the commonly used skin membranes are identified and the factors affecting Kp and corresponding mechanisms are discussed. In addition, the experimental conditions, conclusions, and available data on Kp values of the OPEs are thoroughly summarised. Finally, the corresponding knowledge gaps are proposed, and a more accurate and sophisticated experimental system and unknown Kp values for OPEs are suggested.

Sweat and Sebum Preferences of the Human Skin Microbiota

The microorganisms inhabiting human skin must overcome numerous challenges that typically impede microbial growth, including low pH, osmotic pressure, and low nutrient availability. Yet the skin microbiota thrive on the skin and have adapted to these stressful conditions. The limited nutrients available for microbial use in this unique niche include those from host-derived sweat, sebum, and corneocytes. Here, we have developed physiologically relevant, synthetic skin-like growth media composed of compounds present in sweat and sebum. We find that skin-associated bacterial species exhibit unique growth profiles at different concentrations of artificial sweat and sebum. Most strains evaluated demonstrate a preference for high sweat concentrations, while the sebum preference is highly variable, suggesting that the capacity for sebum utilization may be a driver of the skin microbial community structure. In particular, the prominent skin commensal Staphylococcus epidermidis exhibits the strongest preference for sweat while growing equally well across sebum concentrations. Conversely, the growth of Corynebacterium kefirresidentii, another dominant skin microbiome member, is dependent on increasing concentrations of both sweat and sebum but only when sebum is available, suggesting a lipid requirement of this species. Furthermore, we observe that strains with similar growth profiles in the artificial media cluster by phylum, suggesting that phylogeny is a key factor in sweat and sebum use. Importantly, these findings provide an experimental rationale for why different skin microenvironments harbor distinct microbiome communities. In all, our study further emphasizes the importance of studying microorganisms in an ecologically relevant context, which is critical for our understanding of their physiology, ecology, and function on the skin. IMPORTANCE The human skin microbiome is adapted to survive and thrive in the harsh environment of the skin, which is low in nutrient availability. To study skin microorganisms in a system that mimics the natural skin environment, we developed and tested a physiologically relevant, synthetic skin-like growth medium that is composed of compounds found in the human skin secretions sweat and sebum. We find that most skin-associated bacterial species tested prefer high concentrations of artificial sweat but that artificial sebum concentration preference varies from species to species, suggesting that sebum utilization may be an important contributor to skin microbiome composition. This study demonstrates the utility of a skin-like growth medium, which can be applied to diverse microbiological systems, and underscores the importance of studying microorganisms in an ecologically relevant context.

Occupational exposure assessment with solid substances: choosing a vehicle for in vitro percutaneous absorption experiments

Percutaneous occupational exposure to industrial toxicants can be assessed in vitro on excised human or animal skins. Numerous factors can significantly influence skin permeation of chemicals and the flux determination. Among them, the vehicle used to solubilize the solid substances is a tricky key step. A "realistic surrogate" that closely matches the exposure scenario is recommended in first intention. When direct transposition of occupational exposure conditions to in vitro experiments is impossible, it is recommended that the vehicle used does not affect the skin barrier (in particular in terms of structural integrity, composition, or enzymatic activity). Indeed, any such effect could alter the percutaneous absorption of substances in a number of ways, as we will see. Potential effects are described for five monophasic vehicles, including the three most frequently used: water, ethanol, acetone; and two that are more rarely used, but are realistic: artificial sebum and artificial sweat. Finally, we discuss a number of criteria to be verified and the associated tests that should be performed when choosing the most appropriate vehicle, keeping in mind that, in the context of occupational exposure, the scientific quality of the percutaneous absorption data provided, and how they are interpreted, may have long-range consequences. From the narrative review presented, we also identify and discuss important factors to consider in future updates of the OECD guidelines for in vitro skin absorption experiments.

Artificial Human Sweat as a Novel Growth Condition for Clinically Relevant Pathogens on Hospital Surfaces

The emergence of biofilms on dry hospital surfaces has led to the development of numerous models designed to challenge the efficacious properties of common antimicrobial agents used in cleaning. This is in spite of limited research defining how dry surfaces are able to facilitate biofilm growth and formation in such desiccating and nutrient-deprived environments. While it is well established that the phenotypical response of biofilms is dependent on the conditions in which they are formed, most models incorporate a nutrient-enriched, hydrated environment dissimilar to the clinical setting. In this study, we piloted a novel culture medium, artificial human sweat (AHS), which is perceived to be more indicative of the nutrient sources available on hospital surfaces, particularly those in close proximity to patients. AHS was capable of sustaining the proliferation of four clinically relevant multidrug-resistant pathogens (Acinetobacter baumannii, Staphylococcus aureus, Enterococcus faecalis, and Pseudomonas aeruginosa) and achieved biofilm formation at concentration levels equivalent to those found in situ (average, 6.00 log₁₀ CFU/cm²) with similar visual characteristics upon microscopy. The AHS model presented here could be used for downstream applications, including efficacy testing of hospital cleaning products, due to its resemblance to clinical biofilms on dry surfaces. This may contribute to a better understanding of the true impact these products have on surface hygiene. IMPORTANCE Precise modeling of dry surface biofilms in hospitals is critical for understanding their role in hospital-acquired infection transmission and surface contamination. Using a representative culture condition which includes a nutrient source is key to developing a phenotypically accurate biofilm community. This will enable accurate laboratory testing of cleaning products and their efficacy against dry surface biofilms.

Human in vitro percutaneous absorption of bisphenol S and bisphenol A: A comparative study

Bisphenol A (BPA) is widely used in industrial products. Due to the toxicity of this compound, and to comply with restrictions and regulations, manufacturers have progressively replaced it by substitutes. One of the main substitutes used is bisphenol S (BPS). Despite increasing use in many products, the effects of BPS on human health have been little investigated, and studies on percutaneous BPS absorption and particularly toxicokinetic data are lacking. However, the endocrine-disrupting activity of BPA and BPS appears comparable. Dermal contact is a significant source of occupational exposure and is the main route during handling of bisphenol-containing receipts by cashiers. Here, percutaneous BPS absorption was investigated and compared to that of BPA. Experiments were performed according to OECD guidelines. Test compounds dissolved in a vehicle - acetone, artificial sebum or water - were applied in vitro to fresh human skin samples in static Franz diffusion cells. Flux, cumulative absorbed dose and distribution of dose recovered were measured. BPA absorption was vehicle-dependent ranging from 3% with sebum to 41% with water. BPS absorption was much lower than BPA absorption whatever the vehicle tested (less than 1% of applied dose). However, depending on the vehicle 20% to 47% of the applied BPS dose remained in the skin, and was consequently potentially absorbable. Both BPA and BPS were mainly absorbed without biotransformation. Taken together, these results indicate that workers may be exposed to BPS through skin when handling products containing it. This exposure is of concern as its toxicity is currently incompletely understood.

Phospholipid-polymer hybrid nanoparticle-mediated transfollicular delivery of quercetin: prospective implement for the treatment of androgenic alopecia

Objectives: The aim of the study was to deliver effective doses of quercetin (Que) to the lower region of hair follicles (HFs) using the transfollicular route through dipalmotylphosphatidylcholine (DPPC)-reinforced poly lactide-co- glycolide nanoparticles (DPPC-PLGA hybrid NPs) for the treatment of alopecia. Method: PLGA and DPPC-PLGA hybrid NPs were prepared by double-emulsification solvent evaporation method. NPs were characterized for size, shape, zeta potential entrapment and drug release. Drug-polymer interactions were determined by infrared spectroscopy (Fourier transform infrared spectroscopy, FTIR) and differential scanning calorimetry (DSC). Follicular uptake of fluorescent marker tagged NPs was assessed on isolated rat skin by fluorescent microscopy. Potential of hybrid NPs to induce hair regrowth was tested on testosterone-induced alopecia in rat models by visual inspection, hair follicular density measurement (no./mm), and histological skin tissue section studies. Key findings: Hybrid NPs had mean vesicles size 339 ± 1.6, zeta potential -32.6 ± 0.51, and entrapment efficiency 78 ± 5.5. Cumulative drug release after 12 h was found to be 47.27 ± 0.79%. FTIR and DSC confirmed that drug was independently dispersed in the amorphous form in the polymer. Data from fluorescence microscopy suggested that NPs were actively taken up by HFs. In-vivo studies on alopecia-induced rat models showed that hybrid NPs improved hair regrowth potential of Que and accumulation of NPs at HFs end region inhibit HFs cells apoptosis. Conclusion: This study concludes that phospholipid-polymer hybrid NPs could be the promising transfollicular delivery system for Que in the treatment of androgenic alopecia management.

Bioaccessibility of Drug Residues on Common Police Station Work Surfaces

The fraction of any surface-adsorbed contaminant available for absorption is considered the bioaccessible fraction. Applied previously to contaminants such as pesticides and heavy metals on surfaces such as soil, food and cosmetics, the term may also be used to describe the fraction of drug residue bound to work surfaces which may be mobilized via contact transfer with human skin. Police station work surfaces have been shown to commonly contain low levels of drug residues as thin films; however, no information is available on how readily these residues may be transferred to human skin during direct or glancing contact. A bioaccessibility study was undertaken in which jojoba oil and artificial sebum were used to mimic human sebum to identify how readily a mix of six licit and illicit drugs were transferred from three commonly used police station work surfaces. Transfer from surfaces was slightly greater for jojoba oil than sebum when using a direct pressure contact or a wiping motion. Generally, less than 5% of applied residues were recovered via direct contact, and up to 10% when a wiping motion was used to simulate a glancing contact. While swabbing of work surfaces with methanol provides a suitable environmental audit of drug residues present, it does not represent the bioaccessible fraction of residues available for contact transfer, and hence, absorption via skin or unintentional ingestion. The current study indicates that the ability of sebum to mobilize drug residues from thin films on work surfaces via casual contact is limited, and sebum may potentially assist in the preservation of residues on pitted work surfaces and on skin.

Host-microbiome interactions and recent progress into understanding the biology of acne vulgaris

Acne is one of the most common skin diseases worldwide and results in major health care costs and significant morbidity to severely affected individuals. However, the pathophysiology of this disorder is not well understood. Host-microbiome interactions that affect both innate and adaptive immune homeostasis appear to be a central factor in this disease, with recent observations suggesting that the composition and activities of the microbiota in acne is perturbed. Staphylococcus epidermidis and Cutibacterium acnes (C. acnes; formerly Propionibacterium acnes) are two major inhabitants of the skin that are thought to contribute to the disease but are also known to promote health by inhibiting the growth and invasion of pathogens. Because C. acnes is ubiquitous in sebaceous-rich skin, it is typically labeled as the etiological agent of acne yet it fails to fulfill all of Koch's postulates. The outdated model of acne progression proposes that increased sebum production promotes over-proliferation of C. acnes in a plugged hair follicle, thereby driving inflammation. In contrast, growing evidence indicates that C. acnes is equally abundant in both unaffected and acne-affected follicles. Moreover, recent advances in metagenomic sequencing of the acne microbiome have revealed a diverse population structure distinct from healthy individuals, uncovering new lineage-specific virulence determinants. In this article, we review recent developments in the interactions of skin microbes with host immunity, discussing the contribution of dysbiosis to the immunobiology of acne and newly emerging skin microbiome-based therapeutics to treat acne.

Determining the Effect of pH on the Partitioning of Neutral, Cationic and Anionic Chemicals to Artificial Sebum: New Physicochemical Insight and QSPR Model

PURPOSE

Sebum is an important shunt pathway for transdermal permeation and targeted delivery, but there have been limited studies on its permeation properties. Here we report a measurement and modelling study of solute partition to artificial sebum.

METHODS

Equilibrium experiments were carried out for the sebum-water partition coefficients of 23 neutral, cationic and anionic compounds at different pH.

RESULTS

Sebum-water partition coefficients not only depend on the hydrophobicity of the chemical but also on pH. As pH increases from 4.2 to 7.4, the partition of cationic chemicals to sebum increased rapidly. This appears to be due to increased electrostatic attraction between the cationic chemical and the fatty acids in sebum. Whereas for anionic chemicals, their sebum partition coefficients are negligibly small, which might result from their electrostatic repulsion to fatty acids. Increase in pH also resulted in a slight decrease of sebum partition of neutral chemicals.

CONCLUSIONS

Based on the observed pH impact on the sebum-water partition of neutral, cationic and anionic compounds, a new quantitative structure-property relationship (QSPR) model has been proposed. This mathematical model considers the hydrophobic interaction and electrostatic interaction as the main mechanisms for the partition of neutral, cationic and anionic chemicals to sebum.

Potential of short-wave infrared spectroscopy for quantitative depth profiling of stratum corneum lipids and water in dermatology

We demonstrate the feasibility of short wave infrared (SWIR) spectroscopy combined with tape stripping for depth profiling of lipids and water in the stratum corneum of human skin. The proposed spectroscopic technique relies on differential detection at three wavelengths of 1720, 1750, and 1770 nm, with varying ratio of the lipid-to-water absorption coefficient and an 'isosbestic point'. Comparison of the data acquired using SWIR spectroscopy with that obtained by a gold standard for non-invasive quantitative molecular-specific skin measurements, namely confocal Raman spectroscopy (CRS), revealed specificity of the proposed modality for water and lipid quantification. At the same time, we provide evidence showing aberrant sensitivity of Corneometer hydration read-outs to the presence of skin surface lipids, and a lack of sensitivity of the Sebumeter when attempting to measure the lipids of the cornified lipid envelope and intracellular lipid layers. We conclude that a spectroscopic SWIR-based spectroscopic method combined with tape stripping has the potential for depth profiling of the stratum corneum water and lipids, due to superior measurement sensitivity and specificity compared to the Corneometer and Sebumeter.

The influence of cellulosic coacervate composition on the flux of an entrained agent through a coacervate/sebum barrier

Complex coacervation is the primary mechanism used in rinse-off formulations to deliver topical agents to the skin and hair; this process produces polycation-surfactant anion coacervates that entrain the agent and enhance its substantivity at these sites. This study investigates the relationship between the transport of agents released from a coacervate vehicle into artificial sebum and the coacervate's composition and properties. The flux of a model compound, kinetin, through a variety of cellulosic coacervate/sebum composite barriers prepared on cell culture inserts was determined. These values were interpreted according to a semi-empirical model based on the composition of the coacervate, polymer properties, and the material stiffness. A multivariate analysis using composition and polymer descriptors yielded a strong correlation (r²=0.72) to the experimental kinetin transport data. Variables that describe the degree of entanglement of the surfactant-linked polymer chain web (specifically, the molar ratio of anions to cations and wt% water) emerged as important predictive variables for kinetin transport. According to the developed model, compositional or ingredient manipulations that expand and untangle the web favor a more rapid release of entrained agents from the coacervate into sebum and, consequently, higher bioavailability on the skin surface.

Developing an in vitro artificial sebum model to study Propionibacterium acnes biofilms

AIM

The aim of the present study was to develop a new model system to study Propionibacterium acnes biofilms. This model should be representative for the conditions encountered in the pilosebaceous unit.

METHODS AND RESULTS

The new model, consists of an artificial sebum pellet supported by a silicone disc. Sebum pellets were inoculated with various P. acnes strains isolated from both normal and acneic skin. Growth and biofilm formation was verified by conventional plating at different time points, as well as by resazurin assays and fluorescence microscopy after LIVE/DEAD staining. The artificial sebum pellets were also used in assays to measure the production of certain virulence factors implicated in the pathogenesis of acne, including lipase, protease and the presence of CAMP factors.

CONCLUSION

The artificial sebum model can sustain biofilm growth of P. acnes, as was determined by increasing CFU counts for up to 1 week after inoculation. Metabolic activity and biofilm formation were confirmed using resazurin staining and fluorescence microscopy respectively. The production of virulence factors in this model was demonstrated as well.

Development of a Two-Dimensional Model for Predicting Transdermal Permeation with the Follicular Pathway: Demonstration with a Caffeine Study

Purpose

The development of a new two-dimensional (2D) model to predict follicular permeation, with integration into a recently reported multi-scale model of transdermal permeation is presented.

Methods

The follicular pathway is modelled by diffusion in sebum. The mass transfer and partition properties of solutes in lipid, corneocytes, viable dermis, dermis and systemic circulation are calculated as reported previously [Pharm Res 33 (2016) 1602]. The mass transfer and partition properties in sebum are collected from existing literature. None of the model input parameters was fit to the clinical data with which the model prediction is compared.

Results

The integrated model has been applied to predict the published clinical data of transdermal permeation of caffeine. The relative importance of the follicular pathway is analysed. Good agreement of the model prediction with the clinical data has been obtained. The simulation confirms that for caffeine the follicular route is important; the maximum bioavailable concentration of caffeine in systemic circulation with open hair follicles is predicted to be 20% higher than that when hair follicles are blocked.

Conclusions

The follicular pathway contributes to not only short time fast penetration, but also the overall systemic bioavailability. With such in silico model, useful information can be obtained for caffeine disposition and localised delivery in lipid, corneocytes, viable dermis, dermis and the hair follicle. Such detailed information is difficult to obtain experimentally.

Diclofenac Loaded Lipid Nanovesicles Prepared by Double Solvent Displacement for Skin Drug Delivery

PURPOSE

Herein, we detail a promising strategy of nanovesicle preparation based on control of phospholipid self-assembly: the Double Solvent Displacement. A systematic study was conducted and diclofenac as drug model encapsulated. In vitro skin studies were carried out to identify better formulation for dermal/transdermal delivery.

METHODS

This method consists in two solvent displacements. The first one, made in a free water environment, has allowed triggering a phospholipid pre-organization. The second one, based on the diffusion into an aqueous phase has led to liposome formation.

RESULTS

Homogeneous liposomes were obtained with a size close to 100 nm and a negative zeta potential around -40 mV. After incorporation of acid diclofenac, we obtained nanoliposomes with a size between 101 ± 45 and 133 ± 66 nm, a zeta potential between 34 ± 2 and 49 ± 3 mV, and the encapsulation efficiency (EE%) was between 58 ± 3 and 87 ± 5%. In vitro permeation studies showed that formulation with higher EE% dispayed the higher transdermal passage (18,4% of the applied dose) especially targeting dermis and beyond.

CONCLUSIONS

Our results suggest that our diclofenac loaded lipid vesicles have significant potential as transdermal skin drug delivery system. Here, we produced cost effective lipid nanovesicles in a merely manner according to a process easily transposable to industrial scale. Graphical Abstract ᅟ.

In vivo cleansing efficacy of biodegradable exfoliating beads assessed by skin bioengineering techniques

BACKGROUND/PURPOSE

The plastic microbeads, used in many cleansers, will be banned in cosmetic and personal care products within 2017 since they are non-degradable and can disturb the living organisms in water reservoirs. Various choices of biodegradable beads are commercially available, but their efficacy has not been proven yet. This study aimed to compare the cleansing efficacy in dirt and sebum removal aspects of three types of exfoliating beads.

METHODS

The gel scrubs with polyethylene (PE) beads, mannan beads or wax beads, were formulated and evaluated for their stability. The in vivo evaluation was done in 38 healthy volunteers and the skin irritation, efficacy for dirt and sebum removal were measured by Mexameter^® , Colorimeter^® , and Sebumeter^® , respectively.

RESULTS

The selected gel scrubs did not cause an irritation in any volunteers. The differences in dirt residues between before and after scrubbing were not statistically significant among three gel scrubs and the similar result was also reported in the sebum removal study.

CONCLUSION

All gel scrubs demonstrated the comparable cleansing efficacy in term of dirt and sebum removal. Thus, mannan beads and wax beads may be replaced non-biodegradable PE beads to achieve the similar cleansing effect.

Evaluating the Transport Kinetics of a Model Compound Released From Cellulosic Coacervate Compositions Into Artificial Sebum

Complex coacervates of cationic polymers and anionic surfactants, which are produced spontaneously during the use of rinse-off formulations, represent an important delivery vehicle for topical agents to the skin surface and appendages. In this study, an artificial sebum-loaded cell culture insert method for determining the sebum diffusion properties of topical agents was optimized for in vitro release testing. This method was subsequently used to evaluate the transport kinetics of a model compound, kinetin, released from semi-solid coacervate formulations into sebum. Coacervate compositions were prepared with cationic-hydroxyethyl cellulose dodecyl sulfate (cat-HECDS), sodium dodecyl sulfate (NaDS), and water. Tested compositions ranged from 90 to 50 wt% water and had a cat-HECDS to NaDS wt% ratio of 2:1, 1:1, or 1:2, mimicking the in vivo hydration range and relative excess surfactant content expected from commercial rinse-off formulations. Steady-state flux of the model compound from each coacervate composition was found to vary with water content of the composition. When flux was plotted versus [(cat-HECDS:NaDS) × (1 - weight fraction water)]^-1, a strong linear correlation (R² = 0.89) emerged. The in vitro release testing method proved capable of discriminating between clinically relevant differences in transport kinetics from different coacervate formulations using a practical sample size.

Methamphetamine absorption by skin lipids: accumulated mass, partition coefficients, and the influence of fatty acids

Occupants of former methamphetamine laboratories, often residences, may experience increased exposure through the accumulation of the methamphetamine in the organic films that coat skin and indoor surfaces. The objectives of this study were to determine equilibrium partition coefficients of vapor-phase methamphetamine with artificial sebum (AS-1), artificial sebum without fatty acids (AS-2), and real skin surface films, herein called skin oils. Sebum and skin oil-coated filters were exposed to vapor-phase methamphetamine at concentrations ranging from 8 to 159 ppb, and samples were analyzed for exposure time periods from 2 h to 60 days. For a low vapor-phase methamphetamine concentration range of ~8-22 ppb, the equilibrium partition coefficient for AS-1 was 1500 ± 195 μg/g/ppb. For a high concentration range of 98-112 ppb, the partition coefficient was lower, 459 ± 80 μg/g/ppb, suggesting saturation of the available absorption capacity. The low partition coefficient for AS-2 (33 ± 6 μg/g/ppb) suggests that the fatty acids in AS-1 and skin oil are responsible for much high partition coefficients. We predict that the methamphetamine concentration in skin lipids coating indoor surfaces can exceed recommended surface remediation standards even for air concentrations well below 1 ppb.

Influence of artificial sebum on the dermal absorption of chemicals in excised human skin: A proof-of-concept study

In an initial diffusion cell study, the influence of artificial sebum on dermal penetration and intradermal reservoir of ethanol and toluene was investigated in comparison with the effects of a skin cream (o/w- and w/o-emulsion) and untreated (control) skin. Human skin was exposed to neat ethanol and toluene for 4h, respectively. During the experiments, the penetration of the compounds was assessed in the receptor fluid. The amounts of the test compounds in the skin were determined at the end of exposure. In the control experiments, 42% of the total resorbed ethanol amounts were found in the intradermal reservoir after 4h, whereas 82% of the toluene amounts were found in the skin compartments. The treatment with artificial sebum showed no significant differences in dermal absorption of both test compounds compared to control skin. In contrast, the treatment with skin cream increased the percutaneous penetration (p<0.001) and the intradermal reservoir of ethanol ~2-fold but not of toluene. In all exposure scenarios, a relevant intradermal reservoir was formed. The results indicate that sebum does not influence the percutaneous penetration and the intradermal reservoir of epidermally applied chemicals, whereas the application of skin creams may increase the dermal penetration of the compounds.

Applications and limitations of lipid nanoparticles in dermal and transdermal drug delivery via the follicular route

Lipid nanoparticles (LN) such as solid lipid nanoparticles (SLN) and nanolipid carriers (NLC) feature several claimed benefits for topical drug therapy including biocompatible ingredients, drug release modification, adhesion to the skin, and film formation with subsequent hydration of the superficial skin layers. However, penetration and permeation into and across deeper skin layers are restricted due to the barrier function of the stratum corneum (SC). As different kinds of nanoparticles provide the potential for penetration into hair follicles (HF) LN are applicable drug delivery systems (DDS) for this route in order to enhance the dermal and transdermal bioavailability of active pharmaceutical ingredients (API). Therefore, this review addresses the HF as application site, published formulations of LN which showed follicular penetration (FP), and characterization methods in order to identify and quantify the accumulation of API delivered by the LN in the HF. Since LN are based on lipids that appear in human sebum which is the predominant medium in HF an increased localization of the colloidal carriers as well as a promoted drug release may be assumed. Therefore, sebum-like lipid material and a size of less or equal 640 nm are appropriate specifications for FP of particulate formulations.

1H NMR-based lipidomics of rodent fur: species-specific lipid profiles and SCD1 inhibitor-related dermal toxicity

A method is described that allows noninvasive identification and quantitative assessment of lipid classes present in sebaceous excretions in rodents. The method relies on direct high-field proton NMR analysis of common group lipid protons in deuterated organic solvent extracts of fur. Extracts from as little as 15 mg of fur from rat, mouse, and hamster provided acceptable results on a 600 MHz NMR equipped with a cryogenically cooled proton-observe probe. In rats, sex- and age-related differences in lipid composition are larger than differences in fur collected from various body regions within an individual and much larger than interanimal differences in age- and sex-matched specimens. The utility of this method to noninvasively monitor drug-induced sebaceous gland atrophy in rodents is demonstrated in rats dosed with a stearoyl-CoA desaturase 1 (SCD1) inhibitor. In this model, a 35% reduction in sebum lipids, extracted from fur, was observed. Finally, structural elucidation of cholesta-7,24-dien-3β-ol ester as the most prominent, previously unidentified sebum sterol ester in male Syrian hamsters is described. The utility of this method for drug and cosmetic safety and efficacy assessment is discussed.

Bioelectrocatalytic sensor for triglycerides in human skin sebum based on enzymatic cascade reaction of lipase, glycerol kinase and glycerophosphate oxidase

We report the development of an electrochemical biosensor for the quantification of triglycerides in human skin sebum, based on a multienzyme cascade reaction. The presence of excessive triglycerides in human sebum is one of the leading causes of various skin ailments. However, to the best of our knowledge, no bioelectrocatalytic approach for the quantification of sebum triglycerides has been made. In order to develop triglyceride biosensor, we fabricated a multienzyme-associated electrode incorporating lipase, glycerol kinase, and glycerophosphate oxidase. Enzymes were deposited by electrostatic force and further stabilized via crosslinking between enzymes and polymer matrices. The enzyme-modified biosensing electrode maintained its bioelectrocatalytic activity for five days. An additional constraint was the limited solubility of sebum triglycerides in aqueous electrolytes, impeding the analysis. To address this issue, triglyceride samples were prepared in the form of micelles, enabling efficient sample preparation for biosensor signaling. Calibration tests revealed that the designed assay had a detection range of 15-200mg/dL of micellar triglyceride, which covered the required determination range. The developed biosensing approach was successfully used to determine triglyceride concentrations in real sebum samples of unknown triglyceride content.

Effect of ethnicity, gender and age on the amount and composition of residual skin surface components derived from sebum, sweat and epidermal lipids

BACKGROUND/PURPOSE

The superficial layer on the skin surface, known as the acid mantle, comprises a mixture of sebum, sweat, corneocyte debris and constituents of natural moisturizing factor. Thus, the phrase 'residual skin surface components' (RSSC) is an appropriate term for the mixture of substances recovered from the skin surface. There is no general agreement about the effects of ethnicity, gender and age on RSSC. The aim of this human volunteer study was to evaluate RSSC in relation to ethnicity, gender and age. A suitable acquisition medium for RSSC collection was identified and samples of RSSC were subsequently analysed using gas chromatography-mass spectrometry (GC-MS) and gravimetry.

METHODS

A total of 315 volunteers participated in the study from a range of self-declared ethnic backgrounds. Six acquisition media were compared to determine the most suitable media for RSSC collection. The effect of age, gender and ethnicity on RSSC collection was evaluated by gravimetric analysis while GC-MS was used to determine the composition of RSSC.

RESULTS

Of the six candidate materials assessed, cigarette paper provided the most practical and reproducible sample acquisition medium. There was no significant difference in the amount of RSSC collected when based on gender and ethnicity and no significant correlation between RSSC recovery and age. Up to 49 compounds were detected from human RSSC when analysed by GC-MS.

CONCLUSIONS

The results of the present study suggest that RSSC can be effectively collected using cigarette paper and analysed by GC-MS. Ethnicity, gender and age had no significant impact on the quantity of RSSC recovered from the skin surface.

A honey trap for the treatment of acne: manipulating the follicular microenvironment to control Propionibacterium acnes

Today, as 40 years ago, we still rely on a limited number of antibiotics and benzoyl peroxide to treat inflammatory acne. An alternative way of suppressing the growth of Propionibacterium acnes is to target the environment in which it thrives. We conjecture that P. acnes colonises a relatively “extreme” habitat especially in relation to the availability of water and possibly related factors such as ionic strength and osmolarity. We hypothesise that the limiting “nutrient” within pilosebaceous follicles is water since native sebum as secreted by the sebaceous gland contains none. An aqueous component must be available within colonised follicles, and water may be a major factor determining which follicles can sustain microbial populations. One way of preventing microbial growth is to reduce the water activity (a_w) of this component with a biocompatible solute of very high water solubility. For the method to work effectively, the solute must be small, easily diffusible, and minimally soluble in sebaceous lipids. Xylose and sucrose, which fulfil these criteria, are nonfermentable by P. acnes and have been used to reduce water activity and hence bacterial colonisation of wounds. A new follicularly targeted topical treatment for acne based on this approach should be well tolerated and highly effective.

In vitro antibacterial activity of NB-003 against Propionibacterium acnes

NB-003 and NB-003 gel formulations are oil-in-water nanoemulsions designed for use in bacterial infections. In vitro susceptibility of Propionibacterium acnes to NB-003 formulations and comparator drugs was evaluated. Both NB-003 formulations were bactericidal against all P. acnes isolates, including those that were erythromycin, clindamycin, and/or tetracycline resistant. In the absence of sebum, the MIC(90)s/minimum bactericidal concentrations (MBC(90)s) for NB-003, NB-003 gel, salicylic acid (SA), and benzoyl peroxide (BPO) were 0.5/2.0, 1.0/2.0, 1,000/2,000, and 50/200 μg/ml, respectively. In the presence of 50% sebum, the MIC(90)s/MBC(90)s of NB003 and BPOs increased to 128/1,024 and 400/1,600 μg/ml, respectively. The MIC(90)s/MBC(90)s of SA were not significantly impacted by the presence of sebum. A reduction in the MBC(90)s for NB-003 and BPO was observed when 2% SA or 0.5% BPO was integrated into the formulation, resulting in MIC(90)s/MBC(90)s of 128/256 μg/ml for NB003 and 214/428 μg/ml for BPO. The addition of EDTA enhanced the in vitro efficacy of 0.5% NB-003 in the presence or absence of 25% sebum. The addition of 5 mM EDTA to each well of the microtiter plate resulted in a >16- and >256-fold decrease in MIC(90) and MBC(90), yielding a more potent MIC(90)/MBC(90) of ≤1/<1 μg/ml. The kinetics of bactericidal activity of NB-003 against P. acnes were compared to those of a commercially available product of BPO. Electron micrographs of P. acnes treated with NB-003 showed complete disruption of bacteria. Assessment of spontaneous resistance of P. acnes revealed no stably resistant mutant strains.

Rational design of a topical androgen receptor antagonist for the suppression of sebum production with properties suitable for follicular delivery

A novel nonsteroidal androgen receptor antagonist, (R)-4-(1-benzyl-4,4-dimethyl-2-oxopyrrolidin-3-yloxy)-2-(trifluoromethyl)benzonitrile (1), for the topical control of sebum production is reported. This compound, which is potent, selective, and efficacious in the clinically validated golden Syrian hamster ear animal model, was designed to be delivered to the pilosebaceous unit, the site of action, preferentially by the follicular route.