Transepidermal potassium ion, chloride ion, and water flux across delipidized and cellophane tape-stripped skin

How many skin barriers haveth we: Percutaneous egression of ions?

INTRODUCTION

Skin provides critical barrier properties that enable terrestrial life. Myriad research has focused on the "water barrier" to transepidermal water loss (TEWL) despite there being a multitude of skin barrier properties. We asked what other barrier properties may have been overlooked and compiled data demonstrating the "electrolyte barrier" to be of potential clinical relevance.

METHODS

A literature search was conducted through PubMed, Embase, Google Scholar, and Web of Science databases for the following keywords: "transepidermal" or "epidermal" or "cutaneous" or "skin" or "percutaneous" and "ion" or "sodium" or "chloride" or "potassium" or "electrolyte" and "flux" or "egression." Textbooks at the University of California, San Francisco were also hand reviewed. Experimental studies quantifying in vivo or ex vivo percutaneous egression of ions in response to human skin barrier perturbation were included.

RESULTS

Experimental damage to skin, mostly by tape-stripping, frequently induced increased ion flux rates through the epidermis, in addition to increases in TEWL values. Interestingly, barrier perturbation did not always result in a concomitant rise in TEWL and transepidermal ion flux rates, such as in delipidization, indicating a distinction between the two barriers.

CONCLUSION

Quantifying the percutaneous egression of ions in response to physical or chemical alterations may offer additional data that are not to be captured with TEWL studies exclusively. Continued efforts should be made to: (1) advance this technique as a method of assessing skin status and (2) enhance our understanding of other barriers and mechanisms.

Howard I. Maibach: Extraordinary Leadership in Integrating Key Concepts Underpinning Our Understanding of Percutaneous Absorption and Occupational Dermatology

The purpose of the present article is to briefly highlight some contributions of Prof. Howard I. Maibach to the field of dermatology. After a few introducing remarks regarding Howard's personal career, the article specifically reviews contributions to the understanding of percutaneous absorption and to occupational dermatology. He and his companions/coworkers established and introduced experimental prerequisites to better study and understand percutaneous absorption - both in vitro and in vivo. Not less influential was his contribution to occupational dermatology acting as a founding member of the International Contact Dermatitis Research Group and coinaugurating the North American Contact Dermatitis Group. These groups have been very active ever since. As an academic teacher, he inspired young colleagues to perform original research work and to establish their own working groups. He has done this most successfully with many fellows who worked with him over the years, and who are now leading departments or companies dedicated to dermatological research all over the world. Probably this is his most important and lasting achievement.

The determination of stratum corneum thickness: an alternative approach

The individual thickness of the stratum corneum is required to normalise drug permeation profiles in dermato-pharmacokinetic studies. The thickness is often estimated using tape-stripping combined with transepidermal water loss measurements. A linear transformation of Fick's first law is used to relate the progressively thinner barrier with the corresponding increase in transepidermal water loss and to estimate the thickness by linear regression. However, the data from an important subset of subjects are poorly fitted to this linear model. This is typically due to the removal of loose outer layers of stratum corneum, which do not contribute significantly to barrier function. This work proposes two alternative non-linear models. All three models were used to fit data from 31 in vivo tape-stripping experiments and their outcomes and goodness-of-fit compared. The results suggest that the linear model may overestimate the stratum corneum thickness and is open to subjectivity regarding the selection of data points to be fitted. The non-linear models satisfactorily fitted all the data, including all data points. No significant differences were found between the thicknesses derived from the two non-linear models. However, the analysis of the goodness-of-fit of the models to the data suggests a preference for a baseline-corrected approach.

Facial skin injuries caused by adhesive tapes in a patient receiving cosmetic skin exfoliants

A 39-yr-old woman underwent general anesthesia for laparoscopic sterilization. We used adhesive tapes to close her eyelids and to secure the tracheal tube. Removal of the tapes caused patchy areas of skin loss. We later discovered that the patient had fragile facial skin from cosmetics containing skin exfoliants. We recommend taking a detailed drug history before anesthesia and avoiding adhesive tapes to the patient's face under general anesthesia.

Scar quality and physiologic barrier function restoration after moist and moist-exposed dressings of partial-thickness wounds

BACKGROUND

There is growing evidence of improved healing of full- and partial-thickness cutaneous wounds in wet and moist environments. Retention of biologic fluids over the wound prevents desiccation of denuded dermis or deeper tissues and allows faster and unimpeded migration of keratinocytes over the wound surface. It allows also the naturally occurring cytokines and growth factors to exert their beneficial effect on wound contracture and re-epithelialization. Despite all of these documented benefits, applying the moist healing principles to large surface areas, in particular to large burns, is hindered by the major technical handicap of creating and maintaining a sealed moist environment over these areas.

METHODS

From January to September 2001, healing of partial-thickness skin graft donor sites was studied in a prospective comparative study of two types of moist dressings, Tegaderm (3M Health Care, St. Paul, MN), a semipermeable membrane occlusive dressing, and moist exposed burn ointment (MEBO) (Julphar; Gulf Pharmaceutical Industries, United Arab of Emirates), an ointment that can provide a moist environment without the need of an overlying occlusive dressing. Healing was assessed both clinically and with serial measurements of transepidermal water loss (TEWL) and moisture. Following healing, scar quality was evaluated by two members of the team separately using a visual analog scale. Results were statistically analyzed.

RESULTS

Faster healing was observed clinically with MEBO application. Physiologic healing as determined by TEWL measurements occurred at an extremely significant earlier stage for MEBO, and this was associated with better scar quality, demonstrating a positive relationship between function and cosmetic appearance. Moreover, the ointment is definitely easier to apply than the occlusive self-adhesive membrane, which requires some degree of dexterity and expertise.

CONCLUSION

MEBO application is an effective and valid alternative to conventional occlusive dressings. Moreover, the observed improved anatomic and physiologic healing indicates that MEBO may have a positive effect on healing more that the mere fact of passive moisture retention.

A comparative review of cutaneous pH

This review describes the role of pH in cutaneous structure and function. We first describe the molecules that contribute to the acidity or alkalinity of the skin. Next, differences in cutaneous pH among species, among individuals of the same species and within individuals are described. The potential functions of cutaneous pH in normal and diseased skin are analysed. For example, cutaneous pH has a role in the selection and maintenance of the normal cutaneous microbiota. In addition, cutaneous acidity may protect the skin against infection by microbes. Finally, there is evidence that a cutaneous pH gradient activates pH-dependent enzymes involved in the process of keratinization.

Evidence for the existence of a self-regulated enzymatic process within the human stratum corneum -an unexpected role for urocanic acid

The existence of a flux of proton donors from skin (inner part of the forearm) to the electrode was observed in 12 male and female volunteers. This flux was used to collect and identify the ionic species responsible for skin acidity. It was then found that: (i) pK of these proton donors (pK = 6.13 +/- 0.07) was quasi-identical to that of trans-urocanic acid (6.10), and (ii) the amount of urocanic acid present in stratum corneum was sufficient in itself to explain the acidic level as measured with pH meter (R = 0.8484, n = 10, p = 0.00136). As a result, the contribution of other ionic species can be considered as negligible in normal human skin. The data recorded led us to identify three groups (Fast, Medium, and Slow) characterized by different skin surface pH values (low, medium, and close to neutral) and showing a pH gradient in the outer layers of the stratum corneum, or not. Data analysis suggests that these characteristics depend on urocanic acid production rate within the stratum corneum and that this production rate is self-regulated by its urocanic acid content.

Neonatal skin care: the scientific basis for practice

OBJECTIVE

To review the literature addressing the care of neonatal skin.

DATA SOURCES

Computerized searches in MEDLINE and CINAHL, as well as references cited in articles reviewed. Key concepts in the searches included neonatal skin differences; neonatal skin and care practices for skin integrity; neonatal skin and toxicity; permeability; and contact irritant sensitization.

STUDY SELECTION

Articles and comprehensive works relevant to key concepts and published after 1963, with an emphasis on new findings from 1993 to 1999. One hundred two citations were identified as useful to this review.

DATA EXTRACTION

Data were extracted and organized under the following headings: anatomy and physiology of the skin; physiologic and anatomic differences in neonatal skin; nutritional deficiencies; skin care practices; and care of skin breakdown.

DATA SYNTHESIS

Newborns' skin is at risk for disruption of normal barrier function because of trauma. In light of available evidence about differences in neonatal skin development, clinical practice guidelines are suggested for baths, lubrication, antimicrobial skin disinfection, and adhesive removal. In addition, basic care practices are suggested for maintaining skin integrity, reducing exposure to potentially toxic substances, and promoting skin health beyond the neonatal period. Preventive care recommendations are made for reducing trauma, protecting the skin's immature barrier function, and promoting skin integrity.

CONCLUSIONS

This review generated evidence with which to create a new and comprehensive practice guideline for clinicians. Evaluation of the guideline is under way at 58 U.S. sites.

Neonatal skin care: the scientific basis for practice

OBJECTIVE

To review the literature addressing the care of neonatal skin.

DATA SOURCES

Computerized searches in MEDLINE and CINAHL, as well as references cited in articles reviewed. Key concepts in the searches included neonatal skin differences; neonatal skin and care practices for skin integrity; neonatal skin and toxicity; permeability; and contact irritant sensitization.

STUDY SELECTION

Articles and comprehensive works relevant to key concepts and published after 1963, with an emphasis on new findings from 1993 to 1999. One hundred two citations were identified as useful to this review.

DATA EXTRACTION

Data were extracted and organized under the following headings: anatomy and physiology of the skin; physiologic and anatomic differences in neonatal skin; nutritional deficiencies; skin care practices; and care of skin breakdown.

DATA SYNTHESIS

Newborns' skin is at risk for disruption of normal barrier function because of trauma. In light of available evidence about differences in neonatal skin development, clinical practice guidelines are suggested for baths, lubrication, antimicrobial skin disinfection, and adhesive removal. In addition, basic care practices are suggested for maintaining skin integrity, reducing exposure to potentially toxic substances, and promoting skin health beyond the neonatal period. Preventive care recommendations are made for reducing trauma, protecting the skin's immature barrier function, and promoting skin integrity.

CONCLUSIONS

This review generated evidence with which to create a new and comprehensive practice guideline for clinicians. Evaluation of the guideline is under way at 58 U.S. sites.

Acute barrier perturbation abolishes the Ca2+ and K+ gradients in murine epidermis: quantitative measurement using PIXE

Epidermal permeability barrier homeostasis requires the delivery of lipids and hydrolytic enzymes by lamellar body exocytosis from the uppermost granular cells, a process that is upregulated following barrier disruption. As lamellar body secretion is controlled by ionic concentrations, especially Ca2+ and K+, we used a quantitative technique, microbeam proton-induced X-ray emission, to measure Ca2+, K+, Cl-, and P concentrations before and after acute barrier perturbation by acetone applications. We found a steep gradient of Ca2+ in normal tissue, peaking in the outer stratum granulosum, which disappeared after barrier disruption, and partially reformed as the barrier recovered. A similar gradient, peaking somewhat lower in the epidermis (i.e., at the stratum granulosum-stratum corneum interface), was found for K+. Epidermal concentrations of K+ also decreased after barrier abrogation, although to a lesser extent than Ca2+. In contrast, P and Cl- demonstrated distribution gradients at baseline, which remained unchanged after barrier disruption. These studies quantitate the levels of Ca2+, K+, Cl-, and P within specific epidermal cell layers at baseline, and in relation to changes in permeability barrier integrity. Ca2+ and K+, but not Cl- or P, decrease after barrier disruption, consistent with these two ion's role in barrier repair.

Disruption of barrier function in neonatal skin associated with adhesive removal

OBJECTIVE

Patients in the neonatal intensive care unit require life support and monitoring equipment that must be securely attached to the skin; removal or replacement often causes skin trauma. In this study, we compared the effects of application and removal of three different adhesives on the skin barrier function of premature neonates. The effects were measured by transepidermal water loss (TEWL), colorimetric measurements, and visual inspection.

DESIGN

Thirty neonates, between 26 and 40 weeks of gestational age and with birth weights ranging from 690 to 3000 gm, were enrolled in the study during the first week of life. Pieces of plastic tape (1 cm2), pectin barrier, and hydrophilic gel were applied to previously undisturbed sites on the back. A fourth site was used as a control. We measured TEWL, colorimetric readings, and visual inspection scores of skin irritation and stripping at each of the four sites serially: before adhesive application, 30 minutes after adhesive removal, and 24 hours later.

RESULTS

Thirty minutes after adhesive removal, TEWL, colorimetric measurements, and visual inspection scores were all significantly higher at the sites of plastic tape and pectin barrier removal than at the control and gel adhesive sites (p < 0.01), demonstrating greater disruption of skin barrier function with removal of the plastic tape and pectin barrier. When the neonates were divided into three groups on the basis of birth weight (< 1000 gm [n = 10], 1000 to 1500 gm [n = 11], and > 1500 gm [n = 9], the same pattern of greater disruption in skin barrier function, as measured by TEWL, was observed in each birth weight group. Twenty-four hours after adhesive removal, TEWL of the plastic tape and pectin barrier sites were not significantly different from the control site, indicating recovery of skin barrier function.

CONCLUSIONS

This study demonstrates that a single application and removal of two commonly used adhesives, plastic tape and pectin barrier, disrupts skin barrier function in neonates of varying gestational ages.

Continuous monitoring of lactate during exercise in humans using subcutaneous and transcutaneous microdialysis

We have evaluated the possibility of monitoring the plasma lactate concentration in human volunteers during cycle ergometer exercise using subcutaneous and transcutaneous microdialysis. In transcutaneous microdialysis, the relative increase in dialysate lactate concentration exceeded that of plasma lactate concentration by a factor of 6 during exercise due to exercise-induced lactate secretion in sweat. During exercise the subcutaneous microdialysis dialysate lactate concentration underestimated the plasma lactate concentration possibly due to diffusion limitation or adipose tissue lactate production. While it was demonstrated that microdialysis can be used for on-line lactate monitoring, neither subcutaneous nor transcutaneous dialysate lactate concentration were linearly related to the plasma lactate concentration during exercise, and it was found therefore that it was not possible to monitor directly plasma lactate concentration during exercise.

Metals and the skin

Certain metals, and many metal-based compounds, are inherently toxic, and their presence in occupational and environmental settings raises appropriate questions concerning human exposure. Contact of these materials with the skin represents an important route of exposure, which is not well characterized. The purpose of this review, therefore, is to assemble the available, useful information pertinent to risk assessment following dermal contact. Specifically, we summarize here: (1) data relevant to the qualitative and (where possible) quantitative evaluation of metal compound permeation through the skin; (2) the role of each metal in metabolism, particularly with respect to the skin, and the potentially toxic effects that may result from dermal contact; and (3) the immunological characteristics (including allergenicity) of the metals and their derivatives. In total, information on 31 metals has been reviewed. It is clear that many diverse factors determine the ability of metal-based species to permeate biological membranes, not all of which have been fully defined. Therefore, considerably more experimentation, targeted at the development of high-quality transport data, will be required before the specification of practically useful structure-activity relationships are possible.

Calcium and potassium are important regulators of barrier homeostasis in murine epidermis

Topical solvent treatment removes lipids from the stratum corneum leading to a marked increase in transepidermal water loss (TEWL). This disturbance stimulates a variety of metabolic changes in the epidermis leading to rapid repair of the barrier defect. Using an immersion system we explored the nature of the signal leading to barrier repair in intact mice. Initial experiments using hypotonic to hypertonic solutions showed that water transit per se was not the crucial signal. However, addition of calcium at concentrations as low as 0.01 mM inhibited barrier repair. Moreover, both verapamil and nifedipine, which block calcium transport into cells, prevented the calcium-induced inhibition of TEWL recovery. Additionally, trifluoroperazine or N-6-aminohexyl-5-chloro-1-naphthalenesulfonamide, which inhibit calmodulin, prevented the calcium-induced inhibition of TEWL recovery. Although these results suggest an important role for calcium in barrier homeostasis, calcium alone was only modestly effective in inhibiting TEWL recovery. Potassium alone (10 mM) and phosphate alone (5 mM) also produced a modest inhibition of barrier repair. Together, however, calcium and potassium produced a synergistic inhibition of barrier repair (control 50% recovery vs. calcium + potassium 0-11% recovery in 2.5 h). Furthermore, in addition to inhibiting TEWL recovery, calcium and potassium also prevented the characteristic increase in 3-hydroxy-3-glutaryl CoA reductase activity that occurs after barrier disruption. Finally, the return of lipids to the stratum corneum was also blocked by calcium and potassium. These results demonstrate that the repair of the epidermal permeability barrier after solvent disruption can be prevented by calcium, potassium, and phosphate. The repair process may be signalled by a decrease in the concentrations of these ions in the upper epidermis resulting from increased water flux leading to passive loss of these ions.