Skin structure and mode of action of vesicles

The natural function of the skin is to protect the body for unwanted influences from the environment. The main barrier of the skin is located in the outermost layer of the skin, the stratum corneum. Since the lipids regions in the stratum corneum form the only continuous structure, substances applied onto the skin always have to pass these regions. Therefore, in the first part of this paper, the barrier function has been explained, focusing on the lipid composition and organisation. The major obstacle for topical drug delivery is the low diffusion rate of drugs across the stratum corneum. Several methods have been assessed to increase the permeation rate of drugs temporarily. One of the approaches is the application of drugs in formulations containing vesicles. In order to unravel the mechanisms involved in increasing the drug transport across the skin, information on the effect of vesicles on drug permeation rate, the permeation pathway and perturbations of the skin ultrastructure is of importance. In the second part of this paper, the possible interactions between vesicles and skin are described, focusing on differences between the effects of gel-state, liquid-state, and elastic vesicles.     

Skin Penetration and Mechanisms of Action in the Delivery of the D2-Agonist Rotigotine from Surfactant-Based Elastic Vesicle Formulations

Purpose. This study was performed to investigate the effect of elastic and rigid vesicles on the penetration of the D₂ dopamine agonist rotigotine across human skin and to further elucidate the mechanisms of action of the elastic vesicles. Methods. A series of rotigotine-loaded vesicles were prepared, ranging from very elastic to very rigid. The drug penetration from these vesicles across human skin was studied in vitro using flow-through diffusion cells. Micelle and buffer solutions were investigated as controls. For the most elastic vesicle composition, two additional variables were investigated. Coapplication of drug and vesicles was compared to pretreatment, and the effect of the drug entrapment efficiency was investigated. Results. The very elastic vesicle formulation L-595/PEG-8-L (50/50) gave steady-state fluxes of 214.4 ± 27.8 ng/(h · cm²). This formulation was the most effective formulation and significantly better than the rigid vesicle formulations as well as the micelle and buffer controls. However, coapplication and a high drug entrapment efficiency were essential factors for an optimal drug delivery from elastic vesicle formulations. Conclusions. Elastic vesicles are promising vehicles for transdermal drug delivery. It is essential that drug molecules are applied together with and entrapped within the vesicles themselves, suggesting that elastic vesicles act as drug carrier systems and not solely as penetration enhancers.     

Pretreatment with a Water-Based Surfactant Formulation Affects Transdermal Iontophoretic Delivery of R-Apomorphine in Vitro

Purpose. To further increase the transdermal transport rate of R-apomorphine, a nonocclusive pretreatment with an aqueous surfactant formulation in combination with iontophoresis was explored in vitro. Methods. The human stratum corneum was pretreated nonocclusively with formulations composed of laureth-3 oxyethylene ether (C₁₂EO₃), laureth-7 oxyethylene ether (C₁₂EO₇), and cholesterol sulfate (CSO₄) prior to iontophoresis. The effect on the flux of the following parameters was examined: the composition, the charge, and the applied amount of surfactant formulations. Results. The iontophoretic flux of R-apomorphine was appreciably increased by pretreatment with surfactant formulations. A formulation containing C₁₂EO₃/C₁₂EO₇/CSO₄ at a molar ratio of 70:30:5 was very stable and increased the iontophoretic flux of R-apomorphine from 92.2 ± 13.9 nmol/cm²*h to 181.5 ± 22.6 nmol/cm²*h. When further increasing the negative charge of this formulation the iontophoretic transport rate was slightly inhibited. A dose of 40 L/cm² of the formulation with a total surfactant concentration of 5% (w/w) was sufficient for a maximum enhancing effect. Conclusions. The results obviously show that nonocclusive pretreatment with the surfactant formulation enhances the iontophoretic transport of R-apomorphine, and is a promising approach to achieve therapeutic concentrations of R-apomorphine.     

A Surface Energy Analysis of Mucoadhesion: Contact Angle Measurements on Polycarbophil and Pig Intestinal Mucosa in Physiologically Relevant Fluids

The possible role of surface energy thermodynamics in mucoadhesion was investigated with Polycarbophil and pig intestinal mucosa. In separate experiments, the surface energy parameters of the substrate (mucosa) and the adhesive (polymer film) were determined by contact angle measurements on captive air/octane bubbles in three physiologically relevant test fluids (isotonic saline, artificial gastric fluid, and artificial intestinal fluid). Whereas the swollen Polycarbophil films were relatively hydrophilic as indicated by small water contact angles (22, 23, and 16°), the water contact angles measured on mucosal tissue were significantly larger (61, 48, and 57°). Hence, mucus was found to possess an appreciable hydrophobicity. The measured adhesive performance (force of detachment) between Polycarbophil and pig small intestinal mucosa was highest in non-buffered saline medium, intermediate in gastric fluid, and minimal in intestinal fluid. In agreement with this trend, the mismatch in surface polarities between substrate and adhesive, calculated from the contact angle data, increased in the same order.     

Dissolving Microneedle Patches for Dermal Vaccination

The dermal route is an attractive route for vaccine delivery due to the easy skin accessibility and a dense network of immune cells in the skin. The development of microneedles is crucial to take advantage of the skin immunization and simultaneously to overcome problems related to vaccination by conventional needles (e.g. pain, needle-stick injuries or needle re-use). This review focuses on dissolving microneedles that after penetration into the skin dissolve releasing the encapsulated antigen. The microneedle patch fabrication techniques and their challenges are discussed as well as the microneedle characterization methods and antigen stability aspects. The immunogenicity of antigens formulated in dissolving microneedles are addressed. Finally, the early clinical development is discussed.     

Effects of iontophoresis and electroporation on the stratum corneum. Review of the biophysical studies

This review focuses on the effects induced by iontophoresis and electroporation on the stratum corneum of the skin. Hence, the aims were: (1) to contribute to the understanding of the mechanisms of drug transport by these methods; (2) to evaluate the safety issues associated with current application. Complementary biophysical methods were used to provide a complete picture of the stratum corneum. Even though the mechanism of drug transport is believed to be different, i.e., electrophoresis for iontophoresis and creation of new aqueous pathways for electroporation, the effects on the stratum corneum detected minutes after current application are very similar. For both methods, the major findings were: (1) a disorganisation of the lipid bilayers of the stratum corneum; (2) an increase in skin hydration; (3) a larger decrease in skin resistance induced by electroporation as compared to iontophoresis. These changes were partly reversible and depended on the amount of electrical charges transferred. The mechanisms of stratum corneum perturbations are discussed. These perturbations could explain partly the increase in drug transport. If iontophoresis is considered as a safe method of drug delivery, the data augurs for the safety of electroporation.     

Investigation of conditions involved in the susceptibility of the dermatophyte Trichophyton rubrum to photodynamic treatment

BACKGROUND: Photodynamic treatment (PDT) refers to a treatment with light-activated agents (photosensitizers) in combination with visible light and molecular oxygen. Recently, we have demonstrated that the porphyrins, 5,10,15-tris(4-methylpyridinium)-20-phenyl-[21H,23H]-porphine trichloride (Sylsens B) and deuteroporphyrin monomethylester (DP mme) are excellent photosensitizers to be used against Trichophyton rubrum both in vitro and ex vivo. OBJECTIVES AND METHODS: The objective of this study was to investigate the key factors involved in PDT efficacy of both photosensitizers in an ex vivo situation during different fungal growth stages using a recently developed ex vivo model. The study focused on the influence of pH and ion strength of incubation media, photochemical properties of the photosensitizers (spectra and singlet oxygen production), and the effect of several scavengers of reactive oxygen species (sodium azide, histidine, mannitol) and phenylmethylsulphonylfluoride (keratinase inhibitor) on the PDT efficacy. RESULTS AND CONCLUSIONS: The results show that an optimal pH and low concentrations of calcium are crucial for a selective binding of Sylsens B to the fungus, leading to an increased PDT efficacy. This selective binding to T. rubrum cannot be accomplished for DP mme. It can be concluded that the prerequisite for successful treatment is a use of a low molarity solution of pH 5, supplemented with a chelating agent and a keratinase activity-repressing agent. Under these conditions, PDT with Sylsens B inactivates, initially via singlet oxygen, effectively the fungus in different fungal growth stages.     

Relationship between genetic variants in the adenosine pathway and outcome of methotrexate treatment in patients with recent‐onset rheumatoid arthritis

Objective

Among patients with rheumatoid arthritis (RA), there is a high degree of interindividual variability in the degree of response to methotrexate (MTX) treatment. This study was undertaken to explore polymorphisms in genes contributing to antiinflammatory adenosine release as novel predictors of MTX treatment outcome.

Methods

In 205 patients with newly diagnosed RA, 5 polymorphisms in 5 genes coding for enzymes related to the release of adenosine were analyzed. All patients received standardized MTX treatment (up to 25 mg per week orally), combined with folic acid. MTX efficacy was evaluated by the Disease Activity Score (DAS) and compared among genotypes. The association between MTX‐related adverse events and genotype was also assessed. The following polymorphisms were determined: AMPD1 34C>T, ATIC 347C>G, ITPA 94C>A, MTR 2756A>G, and MTRR 66A>G. When significant differences were found by chi‐square analysis, odds ratios (ORs) and 95% confidence intervals were calculated.

Results

Patients carrying the AMPD1 34T allele, ATIC 347CC, or ITPA 94CC were more likely to have a good clinical response, as defined by a DAS of ≤2.4 (OR [95% confidence interval] 2.1 [1.0–4.5], 2.5 [1.3–4.7], and 2.7 [1.1–8.1], respectively). The likelihood of a good clinical response was increased if patients possessed all 3 favorable genotypes (OR 27.8 [95% confidence interval 3.2–250]). Regarding toxicity, only ATIC G allele carriers experienced a greater frequency of adverse events (OR 2.0 [95% confidence interval 1.1–3.7]).

Conclusion

Polymorphisms in the AMPD1, ATIC, and ITPA genes are associated with good clinical response to MTX treatment. These findings indicate that genotyping may help in the identification of patients who will benefit most from MTX treatment and may assist clinicians in making treatment decisions regarding patients with recent‐onset RA.

     

Barrier lipid composition and response to plasma lipids: A direct comparison of mouse dorsal back and ear skin

The skin of the ear and the back are frequently selected sites in skin research using mouse models. However, distinct responses to treatment have been described between these two sites in several studies. Despite the crucial role of the stratum corneum (SC) in the skin barrier function of both dorsal back and ear skin, it remains unclear whether differences in lipid composition might underlie altered responses. Here, we compared the skin morphology and the barrier lipid composition of the ear with the back skin of wild-type mice. The ear contained more corneocyte layers in the SC and its barrier lipid composition was enriched with sphingosine ceramide subclasses, especially the short ones with a total chain length of 33-34 carbons. The free fatty acid (FFA) profile in the ear skin shifted towards shorter chains, significantly reducing the mean chain length to 23.3 vs 24.7 carbons in the back skin. In line, FFA species in the ear displayed a twofold increase in unsaturation index (P < .001). Gene expression in the ear skin revealed low expression of genes involved in lipid synthesis and uptake, indicating a reduced metabolic activity. Finally, the effects of hypercholesterolaemia on SC FFA composition was compared in ear and back skin of apolipoprotein E knockout (APOE^−/−) mice. Interestingly, the FFA profile in APOE^−/− ear skin was minimally affected, while the FFA composition in the back skin was markedly changed in response to hypercholesterolaemia. In conclusion, ear and back skin have distinct barrier lipids and respond differently to elevated plasma cholesterol.     

Measurement Properties of the Barthel Index in Geriatric Rehabilitation

Objective

The Barthel index (BI) is a widely used observer-based instrument to measure physical function. Our objective is to assess the structural validity, reliability, and interpretability of the BI in the geriatric rehabilitation setting.