Skin Penetration

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.

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.

Non-invasive Production of Multi-Compartmental Biodegradable Polymer Microneedles for Controlled Intradermal Drug Release of Labile Molecules

Transdermal drug delivery represents an appealing alternative to conventional drug administration systems. In fact, due to their high patient compliance, the development of dissolvable and biodegradable polymer microneedles has recently attracted great attention. Although stamp-based procedures guarantee high tip resolution and reproducibility, they have long processing times, low levels of system engineering, are a source of possible contaminants, and thermo-sensitive drugs cannot be used in conjunction with them. In this work, a novel stamp-based microneedle fabrication method is proposed. It provides a rapid room-temperature production of multi-compartmental biodegradable polymeric microneedles for controlled intradermal drug release. Solvent casting was carried out for only a few minutes and produced a short dissolvable tip made of polyvinylpyrrolidone (PVP). The rest of the stamp was then filled with degradable poly(lactide-co-glycolide) (PLGA) microparticles (μPs) quickly compacted with a vapor-assisted plasticization. The outcome was an array of microneedles with tunable release. The ability of the resulting microneedles to indent was assessed using pig cadaver skin. Controlled intradermal delivery was demonstrated by loading both the tip and the body of the microneedles with model therapeutics; POXA1b laccase from Pleurotus ostreatus is a commercial enzyme used for the whitening of skin spots. The action and indentation of the enzyme-loaded microneedle action were assessed in an in vitro skin model and this highlighted their ability to control the kinetic release of the encapsulated compound.

Strip patch testing does not affect reaction profiles of standard allergens

BACKGROUND

It has been hypothesized that positive reactions in the strip patch test are irritant rather than allergic.

OBJECTIVE

To study reaction profiles of the baseline series patch test substances applied routinely on tape-stripped skin according to the reaction index (RI) and the positivity ratio (PR).

PATIENTS AND METHODS

One thousand two hundred and twenty-eight consecutive patients were routinely strip patch tested with the baseline series between January 2011 and June 2013 (intervention group). On the basis of test reactions at D3/D4, the RI, and the PR, 25 standard allergens were analysed, and the results were compared with those obtained in 1161 patients patch tested conventionally from July 2008 to December 2010 (historical control group).

RESULTS

Nickel sulfate, fragrance mix I, cobalt chloride, Myroxylon pereirae (balsam of Peru) and colophonium showed the highest frequencies of positive reactions in both groups, without any significant differences. Of 25 patch test substances of the baseline series, 18 showed good reaction profiles in the intervention group, and 16 in the historical control group.

CONCLUSIONS

Reaction profiles of baseline series patch test substances remained largely unaffected by tape stripping the skin prior to patch testing. Thus, if conventional patch test results are presumed to be false-negative, performance of the strip patch test can be recommended independently of the standard allergen.

What determines skin sensitization potency-myths, maybes and realities. Part 1. The 500 molecular weight cut-off

BACKGROUND

It is widely accepted that there is a molecular weight (MW) cut-off of 500, such that single chemicals with MWs higher than 500 cannot be skin sensitizers. If true, this could serve as a useful principle for designing non-sensitizing chemicals.

OBJECTIVES

To assess whether the 500 MW cut-off is a myth or a reality.

METHODS

A database of 699 chemicals tested for skin sensitization in guinea pigs or mice was analysed to establish the number of tested chemicals with MW > 500, and to establish whether any of these were sensitizers.

RESULTS

Only 13 (2%) of the 699 chemicals in the database have MW > 500. Of the 13 tested compounds with MW > 500 in the database, five are sensitizers and eight are non-sensitizers.

CONCLUSIONS

The 500 MW cut-off for skin sensitization is a myth, probably derived from the widespread misconception that ability to efficiently penetrate the stratum corneum is a key determinant of sensitization potency. The scarcity of sensitizers with MW > 500 simply reflects the general scarcity of chemicals with MW > 500.