Permeation of topically applied caffeine through human skin--a comparison of in vivo and in vitro data

Nanoelectrode Atmospheric Pressure Chemical Ionization Mass Spectrometry

A small ionization needle with an ultrasharp, ultrafine tip is introduced. It is lab-fabricated from tungsten wire and serves as a corona discharge emitter in nanoelectrode atmospheric pressure chemical ionization mass spectrometry (nAPCI-MS). Tip radii ranged from 8 to 44 nm, up to 44× smaller than the sharpest previously reported corona needle. Because of this, nAPCI was able to operate at +1.0 kV with no auxiliary counter electrode. Alternatively, at +1.2 kV, nAPCI could be enclosed in a small plastic assembly for headspace analysis with a sampling tube attachment as long as 15 m. No added heat or gas flow was necessary. The efficacy of nAPCI-MS was demonstrated through needle durability studies and direct analysis of vapors from real-world samples. Provisional identifications include ibuprofen from a pharmaceutical tablet, albuterol aerosol sprayed from a medical inhaler, cocaine from paper currency, caffeine from a fingertip, and bisphenol E from a paper receipt.

Rice (Oryza sativa) Stem Cells as a Novel Promising Active Ingredient with Anti-Proliferative Effects for Potential Skin Cancer Prevention and Skin Whitening Activity

Rice is one of the plants proven to possess antioxidant, anti-inflammatory, anti-proliferative, and whitening properties, making it one of the most beneficial plants in this regard. This study aimed to introduce a novel natural cosmetic and pharmaceutical product based on rice callus as a source of active ingredients that can inhibit skin melanoma cell (B16F10) proliferation and brighten the skin. The 2,4-D hormone at concentrations of 1 µg/mL and 1.5 µg/mL was used to induce rice callus formation. Rice callus extracts were then prepared using aqueous and ethanolic solvents, with a concentration of 1 mg/mL used for characterization tests. To determine the optimal hormone concentration, the phenols/flavonoids, antioxidant activity, proteins, and carbohydrates in the extracts were measured. The optimal concentration of the hormone was found to be 1 µg/mL. Finally, the anti-melanocyte and skin-whitening activity of the extracts was assessed through measurements of their cytotoxicity and inhibition of melanin synthesis-related enzymes. Cellular cytotoxicity measurements revealed that the ethanolic extract induced more cytotoxicity than the aqueous extract, with IC50 values of 566.3 µg/mL for the ethanolic extract and 1327 µg/mL for the aqueous extract. Skin-whitening-related tests demonstrated that the extracts were 1.7 times more effective than arbutin in inhibiting factors that cause hyperpigmentation. The aqueous extract achieved 85% inhibition of melanin biosynthesis at a concentration of 3200 µg/mL, compared to 68% for the ethanolic extract and 50% for arbutin. Based on these findings, rice callus extract can be introduced as a new, effective substance for skin-lightening and anti-melanocyte products in cosmeceutical and pharmaceutical formulations.

Anti-obesity effects of chlorogenic acid and caffeine- lipid nanoparticles through PPAR-γ/C/EBP-ɑ pathways

Obesity is considered one of the most crucial health problems of the century. Therefore, reducing obesity is critically important. Caffeine (CF) and chlorogenic acid (CLA), which are substantial components in green bean coffee which maximize thermogenesis in brown adipose tissue. In our study, we have prepared CF, CLA, and CF + CLA loaded-solid lipid nanoparticles (SLN) since the SLNs are cost-effective, tissue-localized, and highly stable. The central composite design model was preferred to select the optimized formulation. UHPLC was used for quantification related to the CF and CLA amounts. The high-pressure homogenization (HPH) method was used while SLN formulations were prepared in the presence of poloxamer® 407 (surfactant) and Compritol® 888 ATO (solid lipid). The nanoparticles were characterized, followed by the utilization of 3T3-F442A cell lines for the evaluation of the adipogenesis activity of the formulations. Then, rt-PCR and ELISA studies of adipogenic markers were conducted. After optimal formulations were selected with an average of 110.2 ± 0.1 nm, CF (1 mM) + CLA (0.5 mM)-loaded SLN formulation has been proven significantly effective by using PPAR-γ/C/EBP-a pathways. In a nutshell, our study has shown that CF + CLA loaded-SLN has been affected 45.8% times more than regular extracted coffee (p < 0.05) on the adipocyte cells.

Methodologies to Evaluate the Hair Follicle-Targeted Drug Delivery Provided by Nanoparticles

Nanotechnology has been investigated for treatments of hair follicle disorders mainly because of the natural accumulation of solid nanoparticles in the follicular openings following a topical application, which provides a drug "targeting effect". Despite the promising results regarding the therapeutic efficacy of topically applied nanoparticles, the literature has often presented controversial results regarding the targeting of hair follicle potential of nanoformulations. A closer look at the published works shows that study parameters such as the type of skin model, skin sections analyzed, employed controls, or even the extraction methodologies differ to a great extent among the studies, producing either unreliable results or precluding comparisons altogether. Hence, the present study proposes to review different skin models and methods for quantitative and qualitative analysis of follicular penetration of nano-entrapped drugs and their influence on the obtained results, as a way of providing more coherent study protocols for the intended application.

PBK modelling of topical application and characterisation of the uncertainty of Cmax estimate: A case study approach

Combined with in vitro bioactivity data, physiologically based kinetic (PBK) models has increasing applications in next generation risk assessment for animal-free safety decision making. A tiered framework of building PBK models for such application has been developed with increasing complexity and refinements, as model parameters determined in silico, in vitro, and with human pharmacokinetic data become progressively available. PBK modelling has been widely applied for oral/intravenous administration, but less so on topically applied chemicals. Therefore, building PBK models for topical applications and characterizing their uncertainties in the tiered approach is critical to safety decision making. The purpose of this study was to assess the confidence of PBK modelling of topically applied chemicals following the tiered framework, using non-animal methods derived parameters. Prediction of maximum plasma concentration (C_max) and area under the curve were compared to observed kinetics from published dermal clinical studies for five chemicals (diclofenac, salicylic acid, coumarin, nicotine, caffeine). A bespoke Bayesian statistical model was developed to describe the distributions of C_max errors between the predicted and observed data. We showed a general trend that confidence in model predictions increases when more quality in vitro data, particularly those on hepatic clearance and dermal absorption, are available as model input. The overall fold error distributions are useful for characterizing model uncertainty. We concluded that by identifying and quantifying the uncertainties in the tiered approach, we can increase the confidence in using PBK modelling to help make safety decisions on topically applied chemicals in the absence of human pharmacokinetic data.

Safflower oil body nanoparticles deliver hFGF10 to hair follicles and reduce microinflammation to accelerate hair regeneration in androgenetic alopecia

Androgenetic alopecia (AGA) affects physical and mental health with limited therapeutic options. Novel materials and delivery methods have considerable potential to improve the current paradigm of treatment. In this study, we used a novel plant nanoparticle of safflower oil body (SOB) loaded with human fibroblast growth factor 10 (hFGF10) to target hair follicles and accelerate hair regeneration in AGA mice with few adverse effects. Our data revealed that the average particle size of SOB-hFGF10 was 226.73 ± 9.98 nm, with a spherical and uniform structure, and that SOB-hFGF10 was quicker to preferentially penetrate into hair follicles than hFGF2 alone. Using a mouse model of AGA, SOB-hFGF10 was found to significantly improve hair regeneration without any significant toxicity. Furthermore, SOB-hFGF10 inhibited dihydrotestosterone (DHT)-induced TNF-α, IL-1β, and IL-6 overproduction in macrophages in relation to hair follicle microinflammation, thereby enhancing the proliferation of dermal papilla cells. Overall, this study provides an applicable therapeutic method through targeting hair follicles and reducing microinflammation to accelerate hair regeneration in AGA.

Microdialysis on Ex Vivo Porcine Ear Skin Can Validly Study Dermal Penetration including the Fraction of Transfollicular Penetration-Demonstrated on Caffeine Nanocrystals

Common ex vivo methods for penetration investigations often fail to monitor transfollicular penetration appropriately. In the present investigation, the validity of dermal microdialysis on the ex vivo porcine ear skin to investigate penetration kinetics, including transfollicular penetration, was studied. In setup A, a caffeine nanocrystal formulation was compared to a non-particular caffeine gel formulation. In setup B, two caffeine nanocrystal formulations of different sizes (200 nm, 700 nm) were compared to each other. Microdialysis samples were collected for 46 h. After sampling, the skin layers were separated, homogenized, and caffeine was quantified in all samples. In setup A the area under the curve (AUC) after crystal gel formulation application was 12 times higher than after non-particular formulation application. Setup B showed an increased AUC of 42% in the microdialysis data when the 700 nm caffeine crystals were applied compared to the 200 nm crystals. The microdialysis data was supported by the separation, homogenization and extraction data. Microdialysis performed on ex vivo porcine ear skin is a novel experimental setup. It is of high interest for further investigations since it is able to also capture the impact of follicular and transfollicular penetration kinetics as no other ex vivo setup can.

Influence of nanocrystal size on the in vivo absorption kinetics of caffeine after topical application

The absorption of topically applied substances is challenging due to the effective skin barrier. Encapsulation of substances into nanoparticles was expected to be promising to increase the bioavailability of topically applied products. Since nanoparticles cannot traverse the intact skin barrier, but penetrate into the hair follicles, they could be used to deliver substances via hair follicles, where the active is released and can translocate independently transfollicularly into the viable epidermis. In the present in vivo study, this effect was investigated for caffeine. Caffeine nanocrystals of two sizes, 206 nm and 694 nm, with equal amounts of caffeine were used to study caffeine serum concentration kinetics after topical application on 5 human volunteers. The study demonstrated that at early time points, the smaller nanocrystals were more effective in increasing the bioavailability of caffeine, whereas after 20 min, the serum concentration of caffeine was higher when caffeine was applied by larger nanocrystals. Caffeine was still detectable after 5 days. The area under the curve could be increased by 82% when the 694 nm nanocrystals were applied. Especially larger sized nanocrystals seem to be a promising type of nanoparticulate preparation to increase the bioavailability of topically applied drugs via the transfollicular penetration pathway.

Polysaccharide-based skin scaffolds with enhanced mechanical compatibility with native human skin

We report a custom-made technique to synthesize process-convenient skin scaffolds by tuning the mechanical properties of hydrogels based on a few naturally occurring polysaccharides to match the rheological properties of previously established benchmarks, i.e., the ex vivo native human skins. We studied the mechanical parameters using oscillatory shear rheology. At small strain amplitudes, the intrinsic elastic modulus showed an almost linear dependence in the middle and a changing rate profile at the two ends with concentration of the principal hydrogel component variant, i.e., kappa (κ)-carrageenan. At large strain amplitudes, the hydrogels demonstrated intercycle strain-softening behavior, the onset of which was directly proportional to the κ-carrageenan concentration. We observed a concentration match for the intrinsic elastic modulus of the benchmark within this sigmoidal curve fit. Contextually, we need to explore other potent polymeric hydrogel systems to achieve mechanical affinity in terms of multiple rheological parameters derived from both strain amplitude and angular frequency sweeps. Additionally, we carried out diffusion experiments to study caffeine permeation attributes. The hydrogels show improved barrier features with increasing κ-carrageenan concentration. In terms of the penetration flux and total cumulative amount of permeated caffeine, this enhanced mechanical adherence demonstrates comparable penetration features with the commercial 3D skin model.

Lipid nanocapsules loaded with prilocaine and lidocaine and incorporated in gel for topical application

Lipid nanocapsules (LNC) are special drug delivery system (DDS) carriers obtained by the phase-inversion temperature method (PIT). This study describes the encapsulation of the local anesthetics (LA) prilocaine (PLC) and lidocaine (LDC) in lipid nanocapsules (LNC_PLC+LDC) optimized by 2³ factorial design, characterized through DLS, NTA, CRYO-EM and release kinetics and incorporated in carbopol gel (Gel_{LNC PLC+LDC}) prior to in vivo anesthetic effect (in mice) evaluation. A very homogeneous population of small (50 nm; polydispersity index = 0.05) spherical nanocapsules with negative zeta potentials (-21 mV) and ca. 2.3 × 10¹⁵ particles/mL was obtained. The encapsulation efficiency was high (81% and 89% for prilocaine and lidocaine, respectively). The release rate profile was free PLC = free LDC > LNC_PLC+LDC > Gel_{LNC PLC+LDC}. The hybrid system increased (4x) the anesthesia time in comparison to an equipotent gel formulation prepared without LNC. No tissue damage was detected on the tail skin of mice that received the formulations. This study shows that lipid nanocapsules are suitable carriers for PLC and LDC, promoting longer and safer topical anesthesia. Gel_{LNC PLC+LDC} is mucoadhesive and suitable for application in the mouth, where it could be used as a pre-anesthetic, to reduce pain of needle stick (infiltrative anesthesia).

Effect of Application Amounts on In Vitro Dermal Absorption Test Using Caffeine and Testosterone

Dermal absorption of chemicals is a key factor in risk assessment. This study investigated the effects of different amounts of application on dermal absorption and suggested an appropriate application dose for proper dermal absorption. Caffeine and testosterone were chosen as test compounds. An in vitro dermal absorption test was performed using a Franz diffusion cell. Different amounts (5, 10, 25, and 50 mg (or µL)/cm²) of semisolid (cream) and liquid (solution) formulations containing 1% caffeine and 0.1% testosterone were applied to rat and minipig (Micropig^®) skins. After 24 h, the concentrations of both compounds remaining on the skin surface and in the stratum corneum, dermis and epidermis, and receptor fluid were determined using LC-MS / MS or HPLC. Dermal absorption of both compounds decreased with increasing amounts of application in both skin types (rat and minipig) and formulations (cream and solution). Especially, dermal absorptions (%) of both compounds at 50 mg (or µL)/cm² was significantly lower compared to 5 or 10 mg (or µL)/cm² in both rat and minipig skins. Therefore, a low dose (5 or 10 mg (or µL)/cm²) of the formulation should be applied to obtain conservative dermal absorption.

New framework for a non-animal approach adequately assures the safety of cosmetic ingredients - A case study on caffeine

This case study on the model substance caffeine demonstrates the viability of a 10-step read-across (RAX) framework in practice. New approach methodologies (NAM), including RAX and physiologically-based kinetic (PBK) modelling were used to assess the consumer safety of caffeine. Appropriate animal systemic toxicity data were used from the most relevant RAX analogue while assuming that no suitable animal toxicity data were available for caffeine. Based on structural similarities, three primary metabolites of the target chemical caffeine (theophylline, theobromine and paraxanthine) were selected as its most relevant analogues, to estimate a point of departure in order to support a next generation risk assessment (NGRA). On the basis of the pivotal mode of action (MOA) of caffeine and other methylxanthines, theophylline appeared to be the most potent and suitable analogue. A worst-case aggregate exposure assessment determined consumer exposure to caffeine from different sources, such as cosmetics and food/drinks. Using a PBK model to estimate human blood concentrations following exposure to caffeine, an acceptable Margin of Internal Exposure (MOIE) of 27-fold was derived on the basis of a RAX using theophylline animal data, which suggests that the NGRA approach for caffeine is sufficiently conservative to protect human health.

Animal- free skin permeation analysis using mass spectrometry imaging

Here we demonstrate an animal-free skin permeation analytical approach suitable for testing pharmaceuticals, cosmetics, occupational skin hazards and skin allergens. The method aims to replace or significantly reduce existing in-vivo models and improve on already established in-vitro models. This by offering a more sensitive and flexible analytical approach that can replace and/or complement existing methods in the OECD guidelines for skin adsorption (no 427 and no 428) and measure multiple compounds simultaneously in the skin while being able to also trace endogenous effects in cells. We demonstrate this here by studying how active ingredients in sunscreen permeate through left-over human skin, from routine surgery, in a in a Franz-cell permeation model. Two common sunscreens were therefore applied to the human skin and Time of flight secondary ion mass spectrometry (ToF-SIMS) was used to trace the molecules through the skin. We show that that ToF-SIMS imaging can be applied in visualizing the distribution of Avobenzone, Bemotrizinol, Biscotrizole and Ethyl hexyl triazine at subcellular resolution in the skin. The UV-blockers could be visualized at the same time in one single experiment without any probes or antibodies used. The UV-blockers mostly remained in the stratum corneum. However, in certain features of the skin, such as sebaceous glands, the penetration of the UV-blockers was more prominent, and the compounds reached deeper into the epidermis.

Investigation of transfollicular caffeine penetration using microdialysis on ex vivo porcine ear skin

The aim of this study was to develop an ex vivo method that allows to quantify the transfollicular penetration of topically applied substances by combining microdialysis and selective follicular closure with varnish. An experimental setup with three skin areas on ex vivo intact porcine ear skin was designed (varnish on hair follicle, varnish next to hair follicle, no varnish). On each area, 10 µl/cm² caffeine-hydroxyethyl-cellulose-gel was applied. Samples were collected for 22 h by microdialysis. After sampling, the skin layers were separated, homogenized and caffeine was quantified by high pressure liquid chromatography (HPLC) in all samples. Potential impact of the varnish placed next to the follicle by tension on the follicle during the drying process was monitored by a microscopic setup and could be excluded. The microdialysis and homogenization study showed a significantly reduced penetration of caffeine when the hair follicles were closed. In areas with open hair follicles caffeine was detected already in the first ten minutes after application. The reported novel combination of two methods is suitable to investigate ex vivo transfollicular penetration. Possible impact of the closure material in the control area can be ruled out by adjusting the design of the control area in future studies.

Lecithins-Zein nanoparticles for antifungal treatment: Enhancement and prolongation of drug retention in skin with reduced toxicity

Fungal infections are one of the major skin healthcare issues and cause significant morbidity. Ketoconazole (KC) as a broad-spectrum antifungal drug is widely used to treat skin fungal diseases. However, its therapeutic effects are limited by low concentration, short duration of drug efficacy in the skin and severe systemic toxicity. Here, the ketoconazole loaded Lecithins-Zein nanoparticles (KLZ-NPs) with core-shell structure were designed to resolve above problems. In vitro penetration test confirmed that the ketoconazole concentration of the KLZ-NPs group in the stratum corneum and deeper layers increased significantly (2.98-fold, 1.51-fold higher to free ketoconazole, respectively). Meanwhile, follicular closing technique showed the formed nanoparticles via follicle pathway into the skin had been significantly enhanced, and the results of the visual fluorescent images also confirmed it. Additionally, in the in vivo imaging experiment, the fluorescence intensity of the single applying of the DiR-LZ-NPs was higher than that of the thrice usage of the free DiR. More importantly, the results also indicated that the accumulation of nanoparticles in the liver and spleen was significantly reduced. Hence, Lecithins-Zein nanoparticles are a promising strategy to enhance the drug concentration, prolong efficacy and reduce systemic toxicity in the topical administration for antifungal treatment.

Effect of Rubbing on the Distribution of Topically Applied Drugs into the Hair Follicles

Rubbing actions are often conducted to apply topical formulations onto the skin. Although rubbing was found to increase the skin permeation of drugs, few reports have revealed whether rubbing enhanced either drug permeation through the stratum corneum (SC) or hair follicles (HFs) pathways, or through both. In the present study, we investigated the effects of rubbing on caffeine (CAF) distribution in the SC and HFs. The effect of rubbing direction on the skin penetration of CAF was also investigated. The skin concentration of CAF and its cumulative permeation amount were increased clearly by rubbing. More than six times higher CAF concentrations in the viable epidermis and dermis were observed 5 min after rubbing application compared with no rubbing. On the other hand, slightly increased CAF concentrations were observed in the SC, suggesting that CAF was delivered through the HF pathway by rubbing. Rubbing against the natural hair direction provided the highest skin permeation as well as skin concentrations. Changes in the morphology of the HF opening area might be related to the enhancement effect. These results may provide useful information to understand the effect of rubbing on the skin permeation of applied drugs.

Caffeine and Its Pharmacological Benefits in the Management of Androgenetic Alopecia: A Review

Caffeine, particularly after ingestion, is well known to exert various pharmacological effects. A growing body of evidence implicates the ingestion of caffeine with beneficial effects on several diseases. The easy penetration of caffeine across the skin barrier and into human skin makes caffeine an ideal compound for topical application. Hair loss is known to negatively affect the quality of life and predispose to depression and anxiety. Androgenetic alopecia (AGA) is the most common type of hair loss in both men and women. To date, only few approved drug-based treatments for AGA exist, and these are inevitably associated with side effects. Therefore, the development of topical treatments based on well-tolerated natural ingredients such as caffeine to alleviate hair loss may provide a much-needed alternative to drug-based approaches.

Design of dialdehyde cellulose crosslinked poly(vinyl alcohol) hydrogels for transdermal drug delivery and wound dressings

2,3-Dialdehyde cellulose (DAC) was used as an efficient and low-toxicity crosslinker to prepare thin PVA/DAC hydrogel films designed for topical applications such as drug-loaded patches, wound dressings or cosmetic products. An optimization of hydrogel properties was achieved by the variation of two factors - the amount of crosslinker and the weight-average molecular weight (M_w) of the source PVA. The role of each factor to network parameters, mechanical, rheological and surface properties, hydrogel porosity and transdermal absorption is discussed. The best results were obtained for hydrogel films prepared using 0.25 wt% of DAC and PVA with M_w = 130 kDa, which had a high porosity and drug-loading capacity (high water content), mechanical properties allowing easy handling, best adherence to the skin from all tested samples and improved transdermal drug-delivery. Hydrogel films are biocompatible, show no cytotoxicity and have no negative impact on cell growth and morphology in their presence. Furthermore, hydrogels do not support cell migration and attachment to their surface, which should ensure easy removal of hydrogel patches even from wounded or damaged skin after use.

3D-Printed Franz cells - update on optimization of manufacture and evaluation

OBJECTIVES

Laboratory in vitro permeation processes require the use of modified Franz type diffusion cells which are conventionally fabricated from glass. Fragility and high cost are frequently associated with this type of laboratory apparatus. The purpose of our present research was to develop a simple, economical and versatile approach to manufacture Franz type cells using additive manufacturing (AM).

METHODS

Graphical Franz diffusion cell designs were reproduced with a stereolithography (SLA) 3D printer and assessed over a minimum period of 24 h. The surface morphology of AM printouts was analysed before and after compatibility studies using scanning electron microscopy (SEM). Comparative permeation studies in both glass and AM Franz type diffusion cells were conducted using a caffeine solution (1.5 mg mL^-1 ), applied to a model silicone membrane.

RESULTS

Testing of the 3D printed scaffolds confirmed similar recovery of the permeant when compared to glass cells: 1.49 ± 0.01 and 1.50 ± 0.01 mg mL^-1 , respectively, after 72 h. No significant differences were visible from the SEM micrographs demonstrating consistent, smooth and non-porous surfaces of the AM Franz cells' core structure. Permeation studies using transparent 3D printed constructs resulted in 12.85 ± 0.53 µg cm^-2 caffeine recovery in the receptor solution after 180 min with comparable permeant recovery, 11.49 ± 1.04 µg cm^-2 , for the glass homologues.

CONCLUSION

AM constructs can be considered as viable alternatives to the use of conventional glass apparatus offering a simple, reproducible and cost-effective method of replicating specialised laboratory glassware. A wider range of permeants will be investigated in future studies with these novel 3D printed Franz diffusion cells.

Improvement of a slimming cream's efficacy using a novel fabric as a transdermal drug delivery system: An in vivo and in vitro study

Penetration of any compound into the body from the outside is prevented primarily by the corneal layer of the epidermis. The only way to circumvent the properties of the corneal layer is to disrupt it. Currently, transdermal systems can currently only deliver drugs that are of low molecular weight. The purpose of the present study was to assess the improvement of the slimming cream's efficacy using a novel fabric, with the aim of developing an improved method for transdermal drug delivery. The current study was conducted on four groups of guinea pigs. The control group was untreated, whereas the test groups were treated with either slimming cream and no fabric, slimming cream with 100% cotton fabric or slimming cream with the novel fabric. Ultrasound and microscopic histological analysis were used to assess animals. The results demonstrated that compared with the other groups, the novel fabric group demonstrated the greatest reductions in fat layer thickness, adipocyte size and number and proliferator-activated receptor-γ levels in adipose tissue. Furthermore, the novel fabric also enhanced the transdermal delivery of rhodamine B base and caffeine penetration compared with the control fabric (3.18-fold). In conclusion, the results of the present study demonstrated that the novel fabric can potentially be used to enhance transdermal drug delivery.

Solvent-Containing Closure Material Can Be Used to Prevent Follicular Penetration of Caffeine and Fluorescein Sodium Salt on Porcine Ear Skin

AIM

The skin represents a drug delivery portal. The establishment of a skin model capable of distinguishing between the follicular and intercellular penetration pathways remains a challenge. The study described herein was aimed at showing the influence of two nail varnishes as closure material and four application techniques to spread the active pharmaceutical ingredient (API) on a successful follicular closure without inducing penetration-enhancing effects.

MATERIALS AND METHODS

For all experiments, ex vivo porcine ear skin was used. In study design A, a standard and a solvent-free nail varnish were compared. It was tested whether the different application techniques (spreading with pipette, careful finger massage, 5-Hz finger massage, 5-Hz automatic massage) potentially destroy an intact follicular closure. Laser scanning microscopy imaging was used to measure if the model drug (fluorescein sodium salt) penetrated into the hair follicles. Study design B investigated how the penetration is affected when applying standard nail varnish containing solvents to skin. It was tested if the varnish blocks the API (caffeine) on completely covered areas and if adjacent areas show increased penetration. Furthermore, lateral diffusion of the API was investigated. After 20 h, the skin layers were separated by tape stripping and heat separation. The tissue samples were homogenized. Caffeine was quantified by chromatography.

RESULTS

In study design A, the standard nail varnish showed a secure follicular closure, while the solvent-free nail varnish was not able to prevent follicular penetration. Moreover, rapid application techniques were found to destroy an intact follicular closure. Only the two most gentle application techniques kept the follicular closing intact. In study design B, no caffeine was detected in both skin areas that were completely covered. Since no significant difference in caffeine penetration between the two uncovered groups was found, any influence of the applied closure material on adjacent areas was excluded.

CONCLUSION

This study clearly demonstrates that a standard nail varnish in combination with a gentle application technique of the API provides a secure follicular closure. The presented study only investigated the closure for the substances caffeine and fluorescein sodium salt. The results might not be transferable to all kinds of APIs.

Transepidermal UV radiation of scalp skin ex vivo induces hair follicle damage that is alleviated by the topical treatment with caffeine

Objectives

Although the effect of ultraviolet radiation (UVR) on human skin has been extensively studied, very little is known on how UVR impacts on hair follicle (HF) homeostasis. Here, we investigated how solar spectrum UVR that hits the human skin surface impacts on HF biology, and whether any detrimental effects can be mitigated by a widely used cosmetic and nutraceutical ingredient, caffeine.

Methods

Human scalp skin with terminal HFs was irradiated transepidermally ex vivo using either 10 J/cm²UVA (340–440 nm) + 20 mJ/cm²UVB (290–320 nm) (low dose) or 50 J/cm²UVA + 50 mJ/cm²UVB (high dose) and organ‐cultured under serum‐free conditions for 1 or 3 days. 0.1% caffeine (5.15 mmol/L) was topically applied for 3 days prior to UV exposure with 40 J/cm²UVA + 40 mJ/cm²UVB and for 3 days after UVR. The effects on various toxicity and vitality read‐out parameters were measured in defined skin and HF compartments.

Results

Consistent with previous results, transepidermal UVR exerted skin cytotoxicity and epidermal damage. Treatment with high and/or low UVA+UVB doses also induced oxidative DNA damage and cytotoxicity in human HFs. In addition, it decreased proliferation and promoted apoptosis of HF outer root sheath (ORS) and hair matrix (HM) keratinocytes, stimulated catagen development, differentially regulated the expression of HF growth factors, and induced perifollicular mast cell degranulation. UVR‐mediated HF damage was more severe after irradiation with high UVR dose and reached also proximal HF compartments. The topical application of 0.1% caffeine did not induce skin or HF cytotoxicity and stimulated the expression of IGF‐1 in the proximal HF ORS. However, it promoted keratinocyte apoptosis in selected HF compartments. Moreover, caffeine provided protection towards UVR‐mediated HF cytotoxicity and dystrophy, keratinocyte apoptosis, and tendential up‐regulation of the catagen‐promoting growth factor.

Conclusion

Our study highlights the clinical relevance of our scalp UV irradiation ex vivo assay and provides the first evidence that transepidermal UV radiation negatively affects important human HF functions. This suggests that it is a sensible prophylactic strategy to integrate agents such as caffeine that can act as HF photoprotectants into sun‐protective cosmeceutical and nutraceutical formulations.

Recent advances in follicular drug delivery of nanoparticles

Introduction: The improvement of percutaneous absorption represents a clear dermatopharmaceutical aim. Recently, the hair follicle was recognized to be an important penetration pathway. Especially nanoparticles show an enhanced intrafollicular penetration and can be utilized to target specific cell populations within the hair follicle.Areas covered: The present review briefly summarizes the recent advances in follicular drug delivery of nanoparticles. Moreover, the particularities of the hair follicle as a penetration pathway are summarized which include its structure and specific barrier properties. Recently, the mechanism of the follicular penetration process has been clarified.In the meantime, different strategies have been developed to successfully improve follicular drug delivery of nanoparticles. One approach is to equip the nanocarriers with a triggered release system enabling them to release their drug load at the right time and place.Expert opinion: Follicular drug delivery with smart nanocarrier-based drug delivery systems represents a promising approach to increase the percutaneous absorption of topically applied substances. Although technical achievements and efficacy proofs concerning an increased penetration of substances are already available, the practical implementation into clinical application still represents an additional challenge and should be in the focus of interest in future research.

The use of phosphodiesterase inhibitors for the treatment of alopecia

Background: Hair loss encompasses a group of scarring and nonscarring diseases with limited treatment options. Understanding the pathogenesis of alopecias has led to the experimental use of phosphodiesterase inhibitors (PDEi).Objective: To perform a systematic review of literature surrounding the use of PDEi for alopecia.Materials and methods: A search was conducted using PubMed in February 2019 on PDEi and alopecia. Inclusion criteria were clinical trials, prospective or retrospective studies, case series and case reports written in English, using PDEi in human subjects for the treatment of alopecia.Results: Fifteen articles were included for review - eight discussing the use of topical caffeine 0.2%-2.5% for the treatment of androgenetic alopecia (AGA) and telogen effluvium (TE), one using injectable caffeine for AGA, one using topical sildenafil for pediatric alopecia areata (AA), and five using oral apremilast for adult AA.Conclusions: Preliminary results using topical caffeine for AGA or TE are promising with minimal adverse events. However, these studies are primarily single-center trials with few patients. Studies using topical or systemic PDEi for AA demonstrate limited success. Current research using PDEi for alopecia is limited, however new clinical trials are being conducted.

Pramipexole nanocrystals for transdermal permeation: Characterization and its enhancement micro-mechanism

The purpose of the study was to improve transdermal delivery of pramipexole via nanocrystals and investigate the enhancement micro-mechanism. Pramipexole nanocrystals were prepared using wet media milling method and incorporated into carbomer gel. In vitro permeation studies through rabbit ear skin indicated that the cumulative permeation amount of pramipexole from nanocrystals in 24 h was 2.75 times more than that from coarse suspension. Investigations of selective follicular closing technique indicated that approximately 33.88% of the total permeation from nanocrystals was contributed to the follicular pathway, which was confirmed by scanning electron microscopy images. In vitro permeation and in vivo pharmacokinetic studies indicated that pramipexole from nanocrystal gel showed a higher permeation profile than that from coarse suspension gel. Overall, nanocrystals could improve transdermal delivery of pramipexole through transepidermal and transfollicular pathways by the nanosized particles.

Establishment of an evaluation method to detect drug distribution in hair follicles

Development of an appropriate method to evaluate drug disposition or targeting ability in hair follicles (HFs) is urgently needed in order to develop useful pharmaceutical products with pharmacological effects in HFs. In the present study, a cyanoacrylate biopsy (CB) method was used to measure drug disposition in HFs using a model hydrophilic drug, caffeine (CAF), and a lipophilic drug, 4-butylresorcinol (BR), in excised porcine skin. As a result, the height of HF replicas and the recovery ratio decreased with an increase in the application times of the CB method. HF replicas with a length of approximately 175 µm were obtained using a single application of the CB method. Drug distribution in the HF was detected even 5 min after topical application regardless of the lipophilicity of the drugs, although no drug disposition was observed in the deeper layers of the stratum corneum at the same time (5 min). Furthermore, significantly higher amounts of BR were observed in the stratum corneum and HF, compared with those of CAF. These results suggested that the CB method could be useful to evaluate the safety and efficacy as well as the disposition of topically applied chemicals, especially for HF-targeting drugs.

Effect of stratum corneum heterogeneity, anisotropy, asymmetry and follicular pathway on transdermal penetration

The impact of the complex structure of the stratum corneum on transdermal penetration is not yet fully described by existing models. A quantitative and thorough study of skin permeation is essential for chemical exposure assessment and transdermal delivery of drugs. The objective of this study is to analyze the effects of heterogeneity, anisotropy, asymmetry, follicular diffusion, and location of the main barrier of diffusion on percutaneous permeation. In the current study, the solution of the transient diffusion through a two-dimensional-anisotropic brick-and-mortar geometry of the stratum corneum is obtained using the commercial finite element program COMSOL Multiphysics. First, analytical solutions of an equivalent multilayer geometry are used to determine whether the lipids or corneocytes constitute the main permeation barrier. Also these analytical solutions are applied for validations of the finite element solutions. Three illustrative compounds are analyzed in these sections: diethyl phthalate, caffeine and nicotine. Then, asymmetry with depth and follicular diffusion are studied using caffeine as an illustrative compound. The following findings are drawn from this study: the main permeation barrier is located in the lipid layers; the flux and lag time of diffusion through a brick-and-mortar geometry are almost identical to the values corresponding to a multilayer geometry; the flux and lag time are affected when the lipid transbilayer diffusivity or the partition coefficients vary with depth, but are not affected by depth-dependent corneocyte diffusivity; and the follicular contribution has significance for low transbilayer lipid diffusivity, especially when flux between the follicle and the surrounding stratum corneum is involved. This study demonstrates that the diffusion is primarily transcellular and the main barrier is located in the lipid layers.

Anti-obesity effect of a novel caffeine-loaded dissolving microneedle patch in high-fat diet-induced obese C57BL/6J mice

Natural products such as caffeine have been found to be effective in reducing body weight through lipolysis. Here, we report the successful loading of caffeine onto dissolving microneedle following inhibition of its crystal growth by hyaluronic acid (HA), the matrix material of the dissolving microneedle (DMN). Further, the anti-obesity activity of caffeine was evaluated in high-fat diet-induced obese C57BL/6J mice. After 6weeks of caffeine loaded dissolving microneedle patch (CMP) administration, lipolysis improved significantly as shown by leptin and adiponectin activity, which resulted in considerable weight loss of about 12.8±0.75% in high-fat diet-induced obese mice. Comparison of the levels of triglyceride, total cholesterol, high-density lipoprotein (HDL)-cholesterol, and low-density lipoprotein (LDL)-cholesterol after CMP administration with the initial levels in obese mice indicated significant anti-obesity activity of CMP. These findings suggested that a novel CMP with an increased amount of caffeine loaded onto DMN has therapeutic activity against obesity.

Contribution of the Hair Follicular Pathway to Total Skin Permeation of Topically Applied and Exposed Chemicals

Generally, the blood and skin concentration profiles and steady-state skin concentration of topically applied or exposed chemicals can be calculated from the in vitro skin permeation profile. However, these calculation methods are particularly applicable to chemicals for which the main pathway is via the stratum corneum. If the contribution of hair follicles to the total skin permeation of chemicals can be obtained in detail, their blood and skin concentrations can be more precisely predicted. In the present study, the contribution of the hair follicle pathway to the skin permeation of topically applied or exposed chemicals was calculated from the difference between their permeability coefficients through skin with and without hair follicle plugging, using an in vitro skin permeation experiment. The obtained results reveal that the contribution of the hair follicle pathway can be predicted by using the chemicals’ lipophilicity. For hydrophilic chemicals (logarithm of n-octanol/water partition coefficient (log K_o/w) < 0), a greater reduction of permeation due to hair follicle plugging was observed than for lipophilic chemicals (log K_o/w ≥ 0). In addition, the ratio of this reduction was decreased with an increase in log K_o/w. This consideration of the hair follicle pathway would be helpful to investigate the efficacy and safety of chemicals after topical application or exposure to them because skin permeation and disposition should vary among skins in different body sites due to differences in the density of hair follicles.

Confocal Raman microscopy and multivariate statistical analysis for determination of different penetration abilities of caffeine and propylene glycol applied simultaneously in a mixture on porcine skin ex vivo

Propylene glycol is one of the known substances added in cosmetic formulations as a penetration enhancer. Recently, nanocrystals have been employed also to increase the skin penetration of active components. Caffeine is a component with many applications and its penetration into the epidermis is controversially discussed in the literature. In the present study, the penetration ability of two components - caffeine nanocrystals and propylene glycol, applied topically on porcine ear skin in the form of a gel, was investigated ex vivo using two confocal Raman microscopes operated at different excitation wavelengths (785nm and 633nm). Several depth profiles were acquired in the fingerprint region and different spectral ranges, i.e., 526-600cm(-1) and 810-880cm(-1) were chosen for independent analysis of caffeine and propylene glycol penetration into the skin, respectively. Multivariate statistical methods such as principal component analysis (PCA) and linear discriminant analysis (LDA) combined with Student's t-test were employed to calculate the maximum penetration depths of each substance (caffeine and propylene glycol). The results show that propylene glycol penetrates significantly deeper than caffeine (20.7-22.0μm versus 12.3-13.0μm) without any penetration enhancement effect on caffeine. The results confirm that different substances, even if applied onto the skin as a mixture, can penetrate differently. The penetration depths of caffeine and propylene glycol obtained using two different confocal Raman microscopes are comparable showing that both types of microscopes are well suited for such investigations and that multivariate statistical PCA-LDA methods combined with Student's t-test are very useful for analyzing the penetration of different substances into the skin.

Novel perspectives in the tuberculosis treatment: Administration of isoniazid through the skin

Despite its high efficacy in anti-tuberculosis therapy, the oral administration of isoniazid (INH) may lead to poor patient compliance due to hepatotoxicity events. In this context, the transdermal administration of INH was evaluated, for the first time, since this route avoids hepatic first pass effect. INH was applied to porcine skin in Franz diffusion chambers alone and with 5% menthol, limonene or Transcutol(®). Infrared and DSC analyses were selected for mechanistic studies. The transdermal absorption of INH was sufficient to ensure a systemic therapeutic effect. Menthol was not able to improve the absorption of INH, but it increased the drug accumulation in skin compared to the control (1.4-fold). Transcutol(®) reduced permeation flux of INH (2.2-fold) and also increased the amount of drug retained in skin (1.7-fold). Limonene was the most effective excipient since it increased permeation flux of INH (1.5-fold) and lag time was greatly shortened (2.8-fold). DSC and FTIR analyses of limonene-treated skin suggest higher degree of disorder in lipid bilayers. Transdermal delivery of INH was positively correlated with logP of chemical enhancers. INH can be efficiently delivered by skin route and specific excipients may be selected depending on intended use.

Efficacy of Slimming Cream Containing 3.5% Water-Soluble Caffeine and Xanthenes for the Treatment of Cellulite: Clinical Study and Literature Review

Background

Cellulite is a 'cottage cheese-like' cutaneous change caused by subcutaneous fat bulging into the dermis that usually leads to cosmetic problems. Slimming cream containing 3.5% water-soluble caffeine and xanthenes exhibits a lipolytic effect with penetration into the dermis.

Objective

To evaluate the efficacy and safety of slimming cream for the treatment of cellulite.

Methods

Fifteen subjects with cellulite applied slimming cream to the thighs and inner side of the upper arms twice daily for 6 weeks. Efficacy was assessed using a standard visual scale, changes in the circumferences of the thighs and upper arms, and patient satisfaction by a questionnaire at baseline, week 3, and week 6. Safety was assessed by inquiring about adverse events through questionnaires.

Results

The standard visual scale score improved significantly by 0.49 points (19.8%) at week 6. Thigh and upper-arm circumferences decreased by 0.7 cm (1.7%) and 0.8 cm (2.3%), respectively, at week 6. Slight itching and transient flushing were commonly reported, but no serious adverse event occurred.

Conclusion

The slimming cream tested appears to be effective for the treatment of cellulitis without serious adverse effects. However, additional large clinical trials are required to confirm the efficacy and safety of slimming cream for the treatment of cellulitis.

Topical and transdermal delivery of caffeine

Caffeine is administered topically and transdermally for a variety of pharmaceutical and cosmetic applications and it is also used as a model hydrophilic compound in dermal risk assessment studies. This review considers the physicochemical and permeation properties of caffeine with reference to its delivery to and through the skin. Since it has been used as a model compound the findings have implications for the delivery of many hydrophilic compounds having similar properties. Various passive and active formulation strategies to promote enhanced skin permeation of caffeine are considered. Models to study percutaneous caffeine penetration are also discussed in detail.

Comparison of international guidelines of dermal absorption tests used in pesticides exposure assessment for operators

The number of farmers who have suffered from non-fatal acute pesticide poisoning has been reported to vary from 5.7% to 86.7% in South Korea since 1975. Absorption through the skin is the main route of exposure to pesticides for farmers who operate with them. Several in vitro tests using the skins of humans or animal and in vivo tests using laboratory animals are introduced for the assessment of human dermal absorption level of pesticides. The objective of this study is to evaluate and compare international guidelines and strategies of dermal absorption assessments and to propose unique approaches for applications into pesticide registration process in our situation. Until present in our situation, pesticide exposure level to operator is determined just using default value of 10 as for skin absorption ratio because of data shortage. Dermal absorption tests are requested to get exposure level of pesticides and to ultimately know the safety of pesticides for operators through the comparison with the value of AOEL. When the exposure level is higher than AOEL, the pesticide cannot be approved. We reviewed the skin absorption test guidelines recommended by OECD, EFSA and EPA. The EPA recommends assessment of skin absorption of pesticides for humans through the TPA which includes all the results of in vitro human and animal and animal in vivo skin absorption studies. OECD and EFSA, employ a tiered approach, which the requirement of further study depends on the results of the former stage study. OECD guidelines accept the analysis of pesticide level absorbed through skin without radioisotope when the recovery using the non-labeled method is within 80~120%. Various factors are reviewed in this study, including the origin of skin (gender, animal species and sites of skin), thickness, temperature and, etc., which can influence the integrity of results.