[Modification of stratum corneum quality by glycerin-containing external ointments]

Vehicles for atopic dermatitis therapies: more than just a placebo

A topical vehicle is a 'carrier system' for an active pharmaceutical (or cosmetic) substance, referred to hereafter as the drug, but a vehicle may also be used on its own as an emollient to ameliorate dry skin. It is well established that the vehicle plays an important role in determining the bioavailability of a given drug at its ultimate target within the skin. Yet in the treatment of atopic eczema/dermatitis (AD), wherein the structure and function of the skin's outer barrier play a pivotal role in the development and course of the condition, the interaction of the vehicle with this barrier carries a particular importance. It is now clear that the often-considered inert excipients of a vehicle bring about changes within the skin at the molecular level that promote barrier restoration and enhance innate immune defenses with therapeutic value to AD patients. Moreover, the vehicle control in randomized controlled trials (RCTs) increasingly displays significant efficacy. In light of this, we consider the implications of vehicle design in relation to AD pathophysiology and the role vehicles play as controls in RCTs of new drug treatments for this condition.

Newborn infant skin: physiology, development, and care

Infant skin is critical to the newborn child's transition from the womb environment to the journey to self-sufficiency. This review provides an integrative perspective on the skin development in full term and premature infants. There is a particular focus on the role of vernix caseosa and on the implications of skin development for epidermal penetration of exogenous compounds. Healthy full-term newborn skin is well-developed and functional at birth, with a thick epidermis and well-formed stratum corneum (SC) layers. Transepidermal water loss is very low at birth, equal to, or lower than adults, indicating a highly effective skin barrier. Vernix facilitates SC development in full-term infants through a variety of mechanisms including physical protection from amniotic fluid and enzymes, antimicrobial effects, skin surface pH lowering, provision of lipids, and hydration. Premature infants, particularly those of very low birth weight, have a poor skin barrier with few cornified layers and deficient dermal proteins. They are at increased risk for skin damage, increased permeability to exogenous agents and infection. The SC barrier develops rapidly after birth but complete maturation requires weeks to months. The best methods for caring for infant skin, particularly in the diaper region, are described and related to these developmental changes.

The Ontogeny of Skin

Significance: During gestation, fetal skin progresses from a single layer derived from ectoderm to a complex, multi-layer tissue with the stratum corneum (SC) as the outermost layer. Innate immunity is a conferred complex process involving a balance of pro- and anti-inflammatory cytokines, structural proteins, and specific antigen-presenting cells. The SC is a part of the innate immune system as an impermeable physical barrier containing anti-microbial lipids and host defense proteins. Postnatally, the epidermis continually replenishes itself, provides a protective barrier, and repairs injuries. Recent Advances: Vernix caseosa protects the fetus during gestation and facilitates development of the SC in the aqueous uterine environment. The anti-infective, hydrating, acidification, and wound-healing properties post birth provide insights for the development of strategies that facilitate SC maturation and repair in the premature infant. Critical Issues: Reduction of infant mortality is a global health priority. Premature infants have an incompetent skin barrier putting them at risk for irritant exposure, skin compromise and life-threatening infections. Effective interventions to accelerate skin barrier maturation are compelling. Future Directions: Investigations to determine the ontogeny of barrier maturation, that is, SC structure, composition, cohesiveness, permeability, susceptibility to injury, and microflora, as a function of gestational age are essential. Clinicians need to know when the premature skin barrier becomes fully competent and comparable to healthy newborn skin. This will guide the development of innovative strategies for optimizing skin barrier development.

Evaluation of acyclovir cream and gel formulations for transdermal iontophoretic delivery

BACKGROUND

Efficient iontophoretic transdermal delivery of hydrophilic drug molecules requires selection of appropriate aqueous formulation. In this study, oil/water cream and gel formulations were investigated for iontophoretic transdermal delivery of acyclovir (ACV), a model hydrophilic small-drug molecule, across hairless rat skin on Franz diffusion cells.

RESULTS

Iontophoresis (0.2 mA/cm2) enhanced ACV delivery from both 5% cream (pH 6.8) and 4% gel (pH II) formulations. However, sixfold higher drug levels were delivered across the skin using gel formulation (12.25 +/- 4.04 microg/cm2) as compared with cream formulation (2.03 +/- 0.05 microg/cm2). Significantly higher drug levels were delivered when iontophoresis was performed at higher current density (0.32 mA/cm2; p < 0.05). Influence of formulation co-solvents (glycerin and propylene glycol) on drug delivery was also investigated in vitro using Franz cells and in vivo in hairless rats using microdialysis.

CONCLUSION

Iontophoretic transdermal delivery of ACV was feasible and dependent on the selection of formulation components and delivery parameters.

The skin-blanching assay

The skin-blanching assay is used for the determination and bioequivalence of dermatologic glucocorticoids (GCs). The exact mechanism of the production of blanching is not fully understood, but it is considered that local vasoconstriction of the skin microvasculature and the consequent blood-flow reduction cause this phenomenon. Several factors influence skin blanching, including drug concentration, duration of application, nature of vehicle, occlusion, posture and location. The intensity of vasoconstriction can be measured in several ways: visual or quantitative methods, such as reflectance spectroscopy, thermography, laser Doppler velocimetry and chromametry. In literature, contradicting results in the correlation of the skin-blanching assay with different tests to determine GC sensitivity have been reported, limiting its clinical usefulness.

Neonatal skin maturation--vernix caseosa and free amino acids

Neonatal skin hydration decreases rapidly postnatally and then increases, indicating adaptive changes in stratum corneum water handling properties. Transition from high to low humidity at birth may initiate filaggrin proteolysis to free amino acids. Neonatal skin with vernix caseosa retained is more hydrated than skin with vernix removed. This study examines the potential roles of free amino acids and vernix in postnatal adaptation of infant stratum corneum in vivo. Specifically, the ontogeny of free amino acid generation in neonatal stratum corneum and the role of vernix caseosa in postnatal adaptation were examined using high performance liquid chromatography. Free amino acids were quantified for infant skin samples collected at (i) birth and 1 month and (ii) birth and 24 hours after vernix caseosa retention or removal and compared to neonatal foreskin, vernix caseosa, and adult stratum corneum using t-tests, analysis of variance, or univariate procedures. Free amino acids were extremely low at birth, significantly higher 1 month later but lower than in adults. Vernix caseosa retention led to significantly higher free amino acids 24 hours after birth compared to infants with vernix caseosa removed, and it paralleled the higher stratum corneum hydration of vernix caseosa-retained skin. Vernix caseosa contained free amino acids, with glutamic acid and histidine levels higher than in infants. Free amino acids in vernix caseosa-retained skin appear to originate from vernix caseosa. Free amino acids were lower in neonatal foreskin than adult forearm stratum corneum. Arginine was higher than citrulline at birth, but levels were comparable in older infants. The free amino acid increase at 1 month may be initiated by the humidity transition at birth and supports results in animals. The findings have implications for infant skin care practices.

Amputee skin condition: occlusion, stratum corneum hydration and free amino acid levels

Patients with a prosthetic limb report negative skin effects, including irritation, rash and chafing, which can lead to infection, discomfort and reduced wear time to significantly impact normal activities. The aims were to examine the epidermal integrity (transepidermal water loss, TEWL), stratum corneum (SC) hydration [moisture accumulation rate (MAT)], friction and biomechanical properties in active below the knee amputees and to determine the effects of an inert sock liner on skin condition. The liner reduced hydration, TEWL and friction and increased elasticity versus the amputee's conventional skin care methods. Residual limb TEWL was increased and MAT was reduced versus the contralateral normal skin. In a second study, we hypothesized that complete occlusion would decrease free amino acids (FAA) and quantified them by high performance liquid chromatography in an adult volar forearm model. Occlusion with a water vapor impermeable wet dressing led to increased TEWL, erythema and dryness and reduced MAT versus normal skin, comparable to the results in the amputees. The FAA levels were significantly reduced for the occluded sites. The results suggest that residual limb occlusion in amputees may block the formation of FAA in the upper SC. Therapies based on replacement of water binding FAAs, may alleviate the consequences of long-term occlusion.

Investigation into the mechanism by which cyclodextrins influence transdermal drug delivery

The objective of this study was to investigate the mechanism by which hydroxypropyl-beta-cyclodextrin (HPCD) increases transdermal permeation. Hairless mouse skin was pretreated with HPCD solutions for up to 4 h. After removing the HPCD, corticosteroid-containing suspensions were applied and the transdermal flux and skin accumulation of two model drugs were investigated. After pretreatment, changes to the stratum corneum endothermic melting transitions were determined as an indication of HPCD-induced lipid disorganization. Results demonstrated that HPCD pretreatment had no significant effect on the transdermal permeation or skin accumulation of the model corticosteroids. These findings suggest that HPCD functions to enhance the apparent solubility of the drug in the formulation, thus increasing transdermal permeation rather than extracting lipids from the skin.

Assessment of topical corticosteroid activity using the vasoconstriction assay in healthy volunteers

OBJECTIVE AND DESIGN

The aim of the study was to evaluate the vasoconstrictive activity of four new galenic preparations of hydrocortisone and to compare it with concentration-equivalent reference preparations. The study comprised two study phases: the pilot study phase and the main study phase. During open, nonrandomized pilot study, the optimal administration period was tested. The main study was performed in a randomized, double-blind intraindividual comparative design.

SUBJECTS

Twenty male and female volunteers with healthy skin who responded to topically applied clobetasol-17-propionate before entering the trial participated in this study.

TREATMENT

All subjects received the same treatments. The test preparations new galenic formulation (NGF) hydrocortisone 0.25% cream, NGF hydrocortisone acetate 0.25% cream, NGF hydrocortisone 0.5% cream, and NGF hydrocortisone 1.0% cream were compared with the respective reference preparations Soventol hydrocortisone (hydrocortisone acetate 0.25%), Hydroderm HC 0.5% cream (hydrocortisone 0.5%), Hydrogalen cream (hydrocortisone 1.0%) and placebo (vehicle of test preparations).

METHOD

The topical preparations were applied occlusively for 2 h (pilot study) or 24 h (main study) on outlined areas (5 x 5 cm with a distance of 3 cm) of both forearms (4 areas for each). Assessment of vasoconstriction was performed before treatment, and 0.5, 4, 6 and 24 h after treatment (observation period) using a subjective rating scale (OLSEN vasoconstriction score) and measuring the colorimetric parameter a* (redness) by use of the Chroma-Meter (Minolta company, Ahrensburg, Germany).

RESULTS

A significant vasoconstriction (positive blanching effect) was measured by use of chromametry for test preparations hydrocortisone 0.25% cream, hydrocortisone 0.5% cream, hydrocortisone 1.0% cream and for the reference preparation Hydrogalen cream compared to placebo 30 min after the end of treatment. In contrast, the reference preparations Soventol hydrocortisone and Hydroderm HC 0.5% did not differ significantly from placebo 30 min after treatment. No statistically significant effect of all formulations was observed 4-24 h after treatment in comparison with placebo.

CONCLUSIONS

The vasoconstrictive efficacy of test preparations was mostly stronger than the concentration-equivalent reference preparations. This effect was achieved by use of new galenics of test preparations resulting in enhanced skin penetration and improved efficiency. No unwanted side effects were observed during the course of the study despite increased efficacy of the topically applied test preparations.

Biomedical assessment and instrumental evaluation of healthy infant skin

The skin forms a critical structural boundary and a perceptual interface for the organism, yet the definition "healthy skin" is surprisingly difficult to describe. The present study's goal was to generate a technical definition of healthy infant skin by quantifying specific biophysical parameters before and after bathing in infants and correlating such parameters to a perceptual maternal evaluation. Fifty-two healthy infants, 3-6 months old, were evaluated before and after freshwater bathing. Diapered skin had a higher transepidermal water loss (TEWL), surface hydration, moisture accumulation rate (MAT), and friction than nondiapered skin before the bath (p < 0.01). Bathing dramatically altered the biophysical properties at both skin sites, with decreased MAT and lower friction, indicating a drier skin surface (p < 0.01). Visual redness and dryness decreased after bathing (p < 0.01). Blinded grading of optical images showed a significant preference for the skin after bathing (p < 0.01). This study provides the first quantitative technical definition of healthy infant skin with positive correlation to perceptual assessment by independent observers (mothers). The findings support the hypothesis that water binding properties of the stratum corneum are altered by occlusion (diapering) and that bathing introduces acute changes in stratum corneum water interactions, leading to a drier skin surface and a preferred skin appearance.