[Follicular penetration. An important pathway for topically applied substances]

Risk Factors for Acute Urticaria in Central California

At least 15–20% of the population in the world suffers from urticaria. Allergy triggers contribute to the development of urticaria. Not much is known about the demographic and environmental risk factors that contribute to the occurrence of acute urticaria. Methods: We utilized emergency department data on acute urticaria-related visits managed by the California Office of Statewide Planning and Operations for 201 zip codes located in southern central California (San Joaquin Valley) collected during the years 2016 and 2017. Census data from the same zip codes were considered as a population at risk. Socioeconomic and environmental parameters using CalEnviroScreen (Office of Environmental Health Hazard Assessment, Sacramento, CA, USA) database for the zip codes were evaluated as risk factors. Results: The incidence rate of acute urticaria in San Joaquin Valley during 2016–2017 was 1.56/1000 persons (n = 14,417 cases). Multivariate Poisson analysis revealed that zip codes with high population density (RR = 2.81), high percentage of farm workers (RR = 1.49), and the composite of those with high and medium percentage of poverty and those with high and medium percentage of non-white residents (RR = 1.59) increased the likelihood of the occurrence of acute urticaria. Conclusion: High population density, farm work, poverty and minority status is associated with a high risk of having acute urticaria.

Microneedling dilates the follicular infundibulum and increases transfollicular absorption of liposomal sepia melanin

Encapsulation of chemicals in liposomes and microneedling are currently used techniques to enhance the penetration of several substances through skin and hair. In this study, we apply a liposomal melanin–fluorescein compound to an ex vivo model of human skin, using a new electrical microneedling device (Nanopore turbo roller). The product was applied by hand massage (A) or with the assistance of the electrical roller for 2 minutes (B). An additional test was performed free of product and with only the E-roller (C). Histological changes and product absorption were evaluated by optical and fluorescent microscopy 60 and 90 minutes after the treatment. Site B showed larger deposits of melanin–fluorescein at superficial and deep levels of hair structures in comparison to site A. Light, epidermal deposits of the melanin–fluorescein complex were also observed. Sites B and C showed a significant widening (47%) of the follicular infundibulum which could explain the increased penetration of the formulation. Microneedling also removed the scales and sebum residues in the neighborhood of the infundibulum. Targeting hair follicles with melanin may be useful to dye poorly pigmented hairs, improving laser hair removal. The procedure accelerates the delivery of melanin into hair structures allowing an even absorption, larger pigment deposits, and deeper penetration of the formulation into the hair.

Modulation of electroosmosis and flux through skin: effect of propylene glycol

The effect of propylene glycol (PG) on transdermal flux under current was investigated using conventional in vitro iontophoresis methodology. The results were evaluated to explain how PG affects the electroosmotic volume flow (EVF) and electromigrational flux through skin. As a marker molecule for the direction and magnitude of EVF, a non-charged neutral molecule, acetaminophen (AAP), was used. At pH 7.4, the direction of EVF was from anode to cathode. During anodal and cathodal current application, PG decreased AAP flux and this decrease was proportional to the concentration of PG, indicating that the presence of PG in the medium decreased the EVF. This decrease is likely due to the decrease in dielectric constant of the medium and the increases in medium viscosity by the addition of PG. The increase in AAP solubility and the viscosity of the medium by PG may also contribute to the decrease in diffusional flux. The magnitude of EVF was estimated to be about 4.2 μl/cm(2 )h. The effect of PG on the flux of a positively charged drug, donepezil hydrochloride (DH), was further investigated using pH 4.6 phosphate buffer solution. The permselectivity of skin in this solution was also investigated and revealed that the isoelectric point of hairless mouse skin is higher than pH 4.6. Anodal delivery showed much higher flux than cathodal and passive flux, indicating that electromigration is playing the major role for DH flux. As the concentration of PG increased, anodal flux of DH decreased. The main reason for this decrease in electromigration is likely due to the increase in medium viscosity. These results and discussions clearly suggest that the incorporation of frequently used organic cosolvents and penetration enhancers into the iontophoretic formulation should be carefully chosen with a thorough investigation for their effect on flux. Overall, these results provided further mechanistic insights into the role of electroosmosis and electromigration in flux across skin, and how they can be modulated by organic cosolvent, PG.

The in vitro use of the hair follicle closure technique to study the follicular and percutaneous permeation of topically applied drugs

Recent studies on follicular permeation emphasise the importance of hair follicles as diffusion pathways, but only a limited amount of data are available about the follicular permeation of topically applied drugs. This study examines the use of a hair follicle closure technique in vitro, to determine the participation of hair follicles in transdermal drug penetration. Various substances, with different lipophilicities, were tested: caffeine, diclofenac, flufenamic acid, ibuprofen, paracetamol, salicylic acid and testosterone. Diffusion experiments were conducted with porcine skin, the most common replacement material for human skin, in Franz-type diffusion cells over 28 hours. Different experimental settings allowed the differentiation between interfollicular and follicular permeation after topical application of the test compounds. A comparison of the apparent permeability coefficients of the drugs demonstrates that the percutaneous permeations of caffeine and flufenamic acid were significantly higher along the hair follicles. In the cases of paracetamol and testosterone, the follicular pathway appears to be of importance, while no difference was found between interfollicular and follicular permeation for diclofenac, ibuprofen and salicylic acid. Thus, the hair follicle closure technique represents an adequate in vitro method for gaining information about follicular or percutaneous permeation, and can replace in vivo testing in animals or humans.

Emerging applications of nanomedicine in dermatology

BACKGROUND

Nanotechnology is a new branch of engineering consisting of the usage of nanoscale particles (100 nm and smaller). Nanomedicine is the application of nanoscale technologies for diagnostic and therapeutic purposes in medicine. Nanodermatology, nanotechnology applied to dermatology, represents one of the most advanced field for which an increasing interest, both economic and scientific, is rising. The skin is the first point of contact for a whole host of nanomaterials, ranging from topical preparations, articles of clothing and household products, to sporting goods and industrial manufactured goods. Applications of nanomedicine in dermatology include new direction in medical diagnosis, monitoring and treatment. Gold nanoparticle, quantum dots and magnetic nanoparticles are used in non-invasive nanoimaging of high-resolution dermoscopy, microscopy, nanopunch, and spectroscopy, offering advanced diagnostic and therapeutic modalities. Nanotherapeutics has been considered in immunotherapy, genetherapy, and drug therapy. In drug therapy, because of size reduction or encapsulation of drug particles, the therapeutic potential of water insoluble and unstable drugs improve, and also facilitate the delivery of small molecules across blood, skin, nails, and pilosebaceous unit.

AIMS

To review therapeutic applications and benefits of nanomedicine in esthetic dermatology, treatment of malignancies, and inflammatory skin diseases.

Human skin penetration of a copper tripeptide in vitro as a function of skin layer

OBJECTIVE AND DESIGN

Skin retention and penetration by copper applied as glycyl-L-histidyl-L-lysine cuprate diacetate was evaluated in vitro in order to assess its potential for its transdermal delivery as an anti-inflammatory agent.

MATERIALS AND METHODS

Flow-through diffusion cells with 1 cm(2) exposure area were used under infinite dose conditions. 0.68% aq. copper tripeptide as permeant was applied on isolated stratum corneum, heat-separated epidermis and dermatomed skin and receptor fluid collected over 48 h in 4 h intervals using inductively coupled plasma mass spectrometry to analyze for copper in tissues and receptor fluid.

RESULTS

The permeability coefficient of the compound through dermatomed skin was 2.43 ± 0.51 × 10(-4) cm/h; 136.2 ± 17.5 μg/cm(2) copper permeated 1 cm(2) of that tissue over 48 h, while 97 ± 6.6 μg/cm(2) were retained as depot.

CONCLUSIONS

Copper as tripeptide was delivered in potentially therapeutically effective amounts for inflammatory disease.

Human skin retention and penetration of a copper tripeptide in vitro as function of skin layer towards anti-inflammatory therapy

OBJECTIVE AND DESIGN

The skin retention and penetration characteristics of copper applied as glycyl-L-histidyl-L-lysine cuprate diacetate were evaluated in vitro in order to assess the potential for its transdermal delivery as anti-inflammatory agent.

MATERIALS AND METHODS

Flow-through diffusion cells with 1 cm(2) exposure area were used under infinite dose conditions. 0.68% aq. Copper as a tripeptide was applied on isolated stratum corneum, on heat-separated epidermis and on dermatomed skin. Receptor fluid collected over 48 h in 4 h intervals was analyzed by inductively coupled plasma mass spectrometry for copper in tissues and receptor fluid.

RESULTS

The permeability coefficient of the compound through dermatomed skin was 2.43 ± 0.51 × 10(-4) cm/h; 136.2 ± 17.5 μg/cm(2) copper permeated 1 cm(2) of that tissue over 48 h, while 82 ± 8.1 μg/cm(2) of copper were retained there as depot.

CONCLUSIONS

Applied tansdermally as the tripeptide on human skin ex vivo, copper permeated the skin and was also retained in skin tissue in amounts potentially effective for the treatment of inflammatory diseases.

In situ permeation study of drug through the stratum corneum using attenuated total reflectance [corrected] Fourier transform infrared spectroscopic imaging

Infrared (IR) spectroscopy is one of the most chemically specific analytical methods that gives information about composition, structure, and interactions in a material. IR spectroscopy has been successfully applied to study the permeation of xenobiotics through the skin. Combining IR spectroscopy with an IR array detector led to the development of Fourier transform infrared (FTIR) spectroscopic imaging, which generates chemical information from different areas of a sample at the microscopic level. This is particularly important for heterogeneous samples, such as skin. Attenuated total reflectance [corrected] (ATR)-FTIR imaging has been applied to measure, in situ, the diffusion of benzyl nicotinate (BN) through the outer layer of human skin [stratum corneum (SC)]. In vitro experiments have demonstrated the heterogeneous distribution of SC surface lipids before the penetration of a saturated solution of BN. Image analysis demonstrated a strong correlation between the distribution of lipids and drugs, while ethanol appeared to be homogenously distributed in the SC. These results show the ability of ATR-FTIR imaging to measure simultaneously the affinities of drug and solvent to the lipid-rich and lipid-poor skin domains, respectively, during permeation. This information may be useful in better understanding drug-diffusion pathways through the SC.

Strategy of topical vaccination with nanoparticles

Liposomes in the nanosize range have been recognized as a versatile drug delivery system of both hydrophilic and lipophilic molecules. In order to develop a liposome-based topical vaccination strategy, five different types of liposomes were tested as a putative vaccine delivery system on pig ear skin. The investigated liposomes mainly varied in size, lipid composition, and surface charge. Using hydrophilic and hydrophobic fluorescent dyes as model drugs, penetration behavior was studied by means of confocal laser scanning microscopy of intact skin and histological sections, respectively. Follicular penetration of the liposomes was measured in comparison to a standard, nonliposomal formulation at different time points. Dependent on time but independent of their different characters, the liposomes showed a significantly higher penetration depth into the hair follicles compared to the standard formulation. The standard formulation reached a relative penetration depth of 30% of the full hair follicle length after seven days, whereas amphoteric and cationic liposomes had reached approximately 70%. Penetration depth of negatively charged liposomes did not exceed 50% of the total follicle length. The fluorescence dyes were mainly detected in the hair follicle; only a small amount of dye was found in the upper parts of the epidermis.

In vivo methods for the assessment of topical drug bioavailability

This paper reviews some current methods for the in vivo assessment of local cutaneous bioavailability in humans after topical drug application. After an introduction discussing the importance of local drug bioavailability assessment and the limitations of model-based predictions, the focus turns to the relevance of experimental studies. The available techniques are then reviewed in detail, with particular emphasis on the tape stripping and microdialysis methodologies. Other less developed techniques, including the skin biopsy, suction blister, follicle removal and confocal Raman spectroscopy techniques are also described.

Percutaneous Penetration Enhancers: An Overview

Transdermal drug delivery is the controlled release of drugs through the skin to obtain therapeutic levels systematically. Several technological advances have been made in the recent decades to enhance percutaneous drug penetration. This overview focuses on the physical, biochemical, and chemical means of penetration enhancement, as well as the classification and mechanisms of chemical penetration enhancers, their application in transdermal drug delivery, and trends and development in penetration enhancement.

Innovative Liposomes as a Transfollicular Drug Delivery System: Penetration into Porcine Hair Follicles

Liposomes had been widely used for drug delivery in the past. In this study, five different liposomes were used as a follicular delivery system in pig ear skin. The liposomes mainly differed in their sphere diameter, lipid composition, and surface charge. A novel class of liposomes being amphoteric in their charge behavior are compared to established anionic and cationic liposomes. Two different fluorescent dyes, hydrophilic carboxyfluoresceine or lipophilic curcumin, were enclosed in the liposomes and used as model drugs. The fluorescent dyes were also applied in a standard formulation for reference. The penetration depth of the dyes was measured by laser scanning microscopy in histological sections. One hour, 3, 5, and 7 days after application, biopsies were taken and the penetration depth into the hair follicle was measured in longitudinal sections. The liposomes showed a higher penetration depth compared to the standard formulation. The relative penetration depth of the dyes, applied in the standard formulation, averaged 30% of the full follicle length during the whole observation period, whereas the liposomal formulations penetrated considerably deeper into the hair follicles. Amphoteric and cationic liposomes reached an average relative penetration depth of approximately 70% of the full hair follicle length.

Overcoming the Stratum Corneum: The Modulation of Skin Penetration

It is preferred that topically administered drugs act either dermally or transdermally. For that reason they have to penetrate into the deeper skin layers or permeate the skin. The outermost layer of the human skin, the stratum corneum, is responsible for its barrier function. Most topically administered drugs do not have the ability to penetrate the stratum corneum. In these cases modulations of the skin penetration profiles of these drugs and skin barrier manipulations are necessary. A skin penetration enhancement can be achieved either chemically, physically or by use of appropriate formulations. Numerous chemical compounds have been evaluated for penetration-enhancing activity, and different modes of action have been identified for skin penetration enhancement. In addition to chemical methods, skin penetration of drugs can be improved by physical options such as iontophoresis and phonophoresis, as well as by combinations of both chemical and physical methods or by combinations of several physical methods. There are cases where skin penetration of the drug used in the formulation is not the aim of the topical administration. Penetration reducers can be used to prevent chemicals entering the systemic circulation. This article concentrates on the progress made mainly over the last decade by use of chemical penetration enhancers. The different action modes of these substances are explained, including the basic principles of the physical skin penetration enhancement techniques and examples for their application.