Toxicologic implications of cutaneous barriers: a molecular, cellular, and anatomical overview

MS imaging and absorption methods visualizing sun filter skin spatial distribution and penetration

Sunscreens must now be effective in protecting skin from ultraviolet, as well as visible/infrared radiation. Here, TriAsorB, a new broad-spectrum sun filter, was formulated with three other sunscreens and their distribution on human skin was studied using a standard penetration protocol and two novel mass spectrometry imaging techniques: atmospheric pressure matrix assisted laser desorption ionization (AP-MALDI) coupled to high resolution mass spectrometry and time of flight - secondary ion mass spectrometry (ToF-SIMS). The standard penetration protocol showed that sun filters absorption was very low, with most of the dose recovered at the surface (none entered the receptor fluid). Absorption was not increased in damaged skin. The results were confirmed by AP-MALDI and ToF-SIMS imaging of the spatial distribution of molecular species in cross-section samples of human skin. Each sun filter was detected on or in the stratum corneum, with a good homogenous coverage over the valleys and peaks of the skin, and correlated well with the distribution of endogenous biomarkers. In conclusion, conventional and novel imaging analysis methods showed that the sun filters remained mainly on the skin surface after topical application. Mass spectrometry imaging is a promising complementary approach to traditional skin penetration studies to visualize penetration of compounds.

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.

Animal- free skin permeation analysis using mass spectrometry imaging

Here we demonstrate an animal-free skin permeation analytical approach suitable for testing pharmaceuticals, cosmetics, occupational skin hazards and skin allergens. The method aims to replace or significantly reduce existing in-vivo models and improve on already established in-vitro models. This by offering a more sensitive and flexible analytical approach that can replace and/or complement existing methods in the OECD guidelines for skin adsorption (no 427 and no 428) and measure multiple compounds simultaneously in the skin while being able to also trace endogenous effects in cells. We demonstrate this here by studying how active ingredients in sunscreen permeate through left-over human skin, from routine surgery, in a in a Franz-cell permeation model. Two common sunscreens were therefore applied to the human skin and Time of flight secondary ion mass spectrometry (ToF-SIMS) was used to trace the molecules through the skin. We show that that ToF-SIMS imaging can be applied in visualizing the distribution of Avobenzone, Bemotrizinol, Biscotrizole and Ethyl hexyl triazine at subcellular resolution in the skin. The UV-blockers could be visualized at the same time in one single experiment without any probes or antibodies used. The UV-blockers mostly remained in the stratum corneum. However, in certain features of the skin, such as sebaceous glands, the penetration of the UV-blockers was more prominent, and the compounds reached deeper into the epidermis.

Chemical exposure reduction: Factors impacting on South African herbicide sprayers' personal protective equipment compliance and high risk work practices

The high exposure risks of workers to herbicides in low- and middle-income countries is an important public health concern because of the potential resulting negative impacts on workers' health. This study investigated workers' personal protective equipment (PPE) compliance as a risk mitigation measure; particularly workers who apply herbicides for Working for Water (WfW) - a South African invasive alien vegetation control programme. The study aim was to understand workers' low PPE compliance by analysing their risk perceptions of herbicide use, working conditions and socio-cultural context. Research methods included ethnographic observations, informal interviews, visual media, questionnaires and a focus group. Study results indicated that low PPE compliance persists despite workers' awareness of herbicide exposure risks and as a result of the influence from workers' socio-cultural context (i.e. gender dynamics and social status), herbicide risk perceptions and working conditions (i.e. environmental and logistical). Interestingly, teams comprised of mostly women had the highest compliance rate. These findings highlighted that given the complexity of PPE compliance, especially in countries with several economic and social constraints, exposure reduction interventions should not rely solely on PPE use promotion. Instead, other control strategies requiring less worker input for effectiveness should be implemented, such as elimination and substitution of highly hazardous pesticides, and altering application methods.

An in vitro skin penetration model for compromised skin: estimating penetration of polyethylene glycol [¹⁴C]-PEG-7 phosphate

BACKGROUND/AIMS

Establishing dermal penetration rates is important to better understand the safety of topically applied materials, especially for premature infant skin with compromised skin barrier function. Skin prematurity involves thinner stratum corneum and underdeveloped epidermis/dermis resulting in decreased barrier function, higher transepidermal water loss and greater chemical penetration, when compared to healthy full-term neonate/adult skin.

METHODS

We developed an in vitro skin penetration model using human ex vivo skin to estimate penetration for premature/compromised skin barrier conditions by tape stripping. Skin barrier deficiency was characterized by transepidermal water loss. Baby wipe lotion containing 5 mg/cm(2) [(14)C]-PEG-7 phosphate was applied 5 times to human skin samples of intact, moderately or highly compromised skin barrier and once at 25 mg/cm(2) over 24 h.

RESULTS

Overall penetration of [(14)C]-PEG-7 phosphate was low (<5%) even for highly compromised skin. The absorption rate was higher (p < 0.001) for compromised skin versus intact skin. No significant difference was seen between moderately and highly compromised skin by repeated dosing. Under single-dose conditions, penetration through highly compromised skin was significantly higher compared to intact skin (p = 0.001).

CONCLUSION

Our model demonstrates that even under highly compromised skin conditions, penetration of [(14)C]-PEG-7 phosphate is low (<5%) and only 4-6 times higher compared to mature/intact skin and does not approach 100%. Penetration was unaffected by single or multiple dosing conditions.

The minipig as nonrodent species in toxicology--where are we now?

Over the past 3 decades minipigs have moved from being an obscure alternative to dogs and nonhuman primates to being a standard animal model in regulatory toxicity studies. This article covers the use of minipigs as a model in the context of nonclinical drug safety and provides an overview of the minipig's developmental history and relates minipigs to other animal species commonly used in toxicology; and the minipig's translational power is supported by 43 case studies of marketed drug products covered. Special focus is given to criteria for selecting minipigs in nonclinical programs supporting the development of new medicines; the use of swine in the assessment of food additives, agrochemicals, and pesticides; as well as a regulatory perspective on the use of minipigs in Food and Drug Administration (FDA)-regulated products. This article presents the main points conveyed at a symposium held at the 2010 American College of Toxicology meeting in Baltimore, Maryland.