Development of a murine model to evaluate the effect of vernix caseosa on skin barrier recovery

Effects of Siegesbeckia herba extract against particulate matter 10 (PM10 ) in skin barrier-disrupted mouse models

OBJECTIVES

Skin barrier disruption is a significant problem of the older population in an aging society. It is characterized by increased transepidermal water loss and decreased skin water content, and particulate matter (PM) is a social issue that can contribute to the exacerbation of skin inflammation. Thus, addressing this problem is urgent.

METHODS

Skin barrier-disrupted mouse models were induced by two methods using acetone application or tape-stripping. This study investigated the antioxidative and anti-inflammatory properties of the Siegesbeckia herba extract (SHE) on PM-induced changes in skin barrier-disrupted mouse models. To examine changes in skin water content, inflammatory cytokines, and keratinocyte differentiation markers, mouse models were treated with vehicle 100 μL, PM10 100 μL (100 μg/mL), SHE 100 μL, or PM10 100 μL (100 μg/mL) plus SHE 100 μL.

RESULTS

SHE preserved skin hydration in the skin barrier-disrupted mouse models regardless of the presence of PM10 . SHE also inhibited the upregulation of inflammatory cytokines such as interleukin (IL)-1β, IL-4, IL-6, IL-8, and tumor necrosis factor-α and normalized the downregulation of keratinocyte differentiation markers against PM10 in skin barrier-disrupted mouse models.

CONCLUSIONS

This study elucidated the therapeutic effects of SHE against PM10 in skin barrier-disrupted mouse models.

Animal models for the study of acute cutaneous wound healing

The process of wound healing is critical to maintaining homeostasis after injury. Although a considerable amount has been learned about this complex process, much remains unknown. Whereas, studies with human volunteers are ideal given the unique nature of the human skin anatomy and immune system, the lack of such clinical access has made animal models prime candidates for use in preclinical studies. This review aims to discuss the strengths and limitations of the commonly used mammalian species in wound healing studies: murine, rabbit and porcine. Thereafter, a survey of models of various acute wounds such as cutaneous, ear, and implant are presented and representative studies that use them are described. This review is intended to acquaint readers with the vast spectrum of models available, each of which has a distinct utility. At the same time, it highlights the importance of utilising clinical samples to complement investigations conducted in animal models. Through this strategy, it is hoped that forthcoming research may be more reflective of the acute wound healing process as it occurs in humans.

Epidermal Immunity and Function: Origin in Neonatal Skin

The fascinating story of epidermal immunity begins in utero where the epidermal barrier derives from the ectoderm and evolves through carefully orchestrated biological processes, including periderm formation, keratinocyte differentiation, proliferation, cornification, and maturation, to generate a functional epidermis. Vernix caseosa derives from epidermal cells that mix with sebaceous lipids and coat the fetus during late gestation, likely to provide conditions for cornification. At birth, infants dramatically transition from aqueous conditions to a dry gaseous environment. The epidermal barrier begins to change within hours, exhibiting decreased hydration and low stratum corneum (SC) cohesion. The SC varied by gestational age (GA), transformed over the next 2–3 months, and differed considerably versus stable adult skin, as indicated by analysis of specific protein biomarkers. Regardless of gestational age, the increased infant SC proteins at 2–3 months after birth were involved in late differentiation, cornification, and filaggrin processing compared to adult skin. Additionally, the natural moisturizing factor (NMF), the product of filaggrin processing, was higher for infants than adults. This suggests that neonatal skin provides innate immunity and protection from environmental effects and promotes rapid, continued barrier development after birth. Functional genomic analysis showed abundant differences across biological processes for infant skin compared to adult skin. Gene expression for extracellular matrix, development, and fatty acid metabolism was higher for infant skin, while adult skin had increased expression of genes for the maintenance of epidermal homeostasis, antigen processing/presentation of immune function, and others. These findings provide descriptive information about infant epidermal immunity and its ability to support the newborn’s survival and growth, despite an environment laden with microbes, high oxygen tension, and irritants.

Droplette: A Platform Technology to Directly Deliver Nucleic Acid Therapeutics and Other Molecules into Cells and Deep into Tissue Without Transfection Reagents

Droplette (US 9,700,686 B2 and PCT/US2016/035695) is the first portable and contact-free transdermal technology comprising the unique combination of a piezoelectric transducer and a pneumatic diaphragm pump to deliver large biomolecules including nucleic acid therapeutics (NATs) deep into cells, and into skin and soft tissue for effective delivery over short timescales. The droplets that come out of the device are 10-50× smaller upon impact than what is created through other commercial atomizers, such as the piezoelectric transducer alone. This device has been tested extensively in vitro, in vivo and in IRB approved human studies. The Droplette device delivers metered doses using a water droplet dispersal technology already commonly used in humidifier devices, by utilizing a piezoelectric material. Three key innovations make this device technically novel and tailored specifically for both field and lab use: (1) The combination of the piezo and pump to generate sub-micron drug-loaded droplets that penetrate cells, skin, and soft tissue to effectively deliver a range of large molecules, proteins, and nucleic acids. (2) Their assembly in a modular manner which enables portability, safe sterilization, and ejection without direct device-surface contact or significant force, allowing for improved safety and ease of use in both research and clinical settings. (3) The integration of a single-use, sterile cartridge that contains a therapeutic formulation and allows easy integration of a large number of molecules. The platform has broad applications across multiple fields, such as delivery of drugs for inflammatory skin diseases, antibiotics for skin infections, and gene delivery for gene therapy and biomedical research. In this chapter, we briefly introduce the Droplette delivery technology, instructions for building your own setup (note that fully built devices are available for purchase from Droplette, Inc), and provide protocols for directly transfecting adherent cell cultures and for direct in vivo transfection using the Droplette system without the need for traditional transfection reagents or methods.

Topically applied fatty acids are elongated before incorporation in the stratum corneum lipid matrix in compromised skin

In several skin diseases, both the lipid composition and organization in the stratum corneum (SC) are altered which contributes to the impaired skin barrier function in patients. One of the approaches for skin barrier repair is treatment with topical formulations to normalize SC lipid composition and organization. Vernix caseosa (VC), a white cheesy cream on the skin during gestational delivery, has shown to enhance skin barrier repair. In this study, we examined how a fatty acid (FA) containing formulation mimicking the lipid composition of VC interacts with the lipid matrix in the SC. The formulation was applied on ex vivo human skin after SC removal. Subsequently, the ex vivo human skin generated SC during culture. The effect of FA containing formulations on the lipid organization and composition in the regenerated SC was analysed by Fourier transform infrared (FTIR) spectroscopy and liquid chromatography mass spectroscopy (LC/MS), respectively. FTIR results demonstrate that the FAs are intercalated in the lipid matrix of the regenerated SC and partition in the same lattice with the endogenous SC lipids, thereby enhancing the fraction of lipids forming an orthorhombic (very dense) packing in the SC. LC/MS data show that the topically applied FAs are elongated before intercalation in the lipid matrix and are thus involved in the lipid biosynthesis in the skin.

Confocal Raman microspectroscopy as an alternative method to investigate the extraction of lipids from stratum corneum by emulsifiers and formulations

The purpose of this study was to investigate the impact of emulsifiers and formulations on intercellular lipids of porcine stratum corneum (SC) and evaluate confocal Raman microscopy (CRM) as an alternative method in this research context. To this end, four different formulations were used: three conventional creams that contained ionic and/or non-ionic emulsifiers and one surfactants-free emulsion stabilized by a polymeric emulsifier. Additionally, all emulsifiers were tested in aqueous solution/dispersion in the respective concentrations as present in the formulations. CRM and HPTLC were used to analyse changes in SC lipid content after treatment. Furthermore, lipid extraction was visualized by fluorescence staining and SC thickness was measured by CRM and light microscopy. Various emulsifiers and emulsifier mixtures showed different impact on SC lipid content and SC thickness, while none of the tested formulations had any effect on SC lipids. Emulsifiers and their mixtures that reduced the lipids content also reduced SC thickness, indicating lipid extraction is the reason for SC thinning. Results from CRM and conventional methods showed a strong positive correlation for both lipid content and SC thickness measurements. With easy sample preparation and fast analytical readout, CRM has the potential to be a standardized analytical method for skin lipids investigation.

Topically Applied Ceramides Interact with the Stratum Corneum Lipid Matrix in Compromised Ex Vivo Skin

PURPOSE

To determine whether formulations containing ceramides (including a ceramide with a long hydroxyl acyl chain linked to a linoleate, CER EOS) and fatty acids are able to repair the skin barrier by normalizing the lipid organization in stratum corneum (SC).

METHODS

The formulations were applied on a skin barrier repair model consisting of ex vivo human skin from which SC was removed by stripping. The effect of formulations on the lipid organization and conformational ordering in the regenerated SC were analyzed using Fourier transform infrared spectroscopy and small angle X-ray diffraction.

RESULTS

Application of the formulation containing only one ceramide on regenerating SC resulted in a higher fraction of lipids adopting an orthorhombic organization. A similar fraction of lipids forming an orthorhombic organization was observed after application of a formulation containing two ceramides and a fatty acid on regenerating SC. No effects on the lamellar lipid organization were observed.

CONCLUSIONS

Application of a formulation containing either a single ceramide or two ceramides and a fatty acid on regenerating SC, resulted in a denser lateral lipid packing of the SC lipids in compromised skin. The strongest effect was observed after application of a formulation containing a single ceramide.

Applying a vernix caseosa based formulation accelerates skin barrier repair by modulating lipid biosynthesis

Restoring the lipid homeostasis of the stratum corneum (SC) is a common strategy to enhance skin barrier function. Here, we used a ceramide containing vernix caseosa (VC)-based formulation and were able to accelerate barrier recovery in healthy volunteers. The recovery was examined over 16 days by monitoring trans-epidermal water loss (TEWL) after barrier disruption by tape-stripping. Four skin sites were used to examine the effects of both treatment and barrier recovery. After 16 days, samples were harvested at these sites to examine the SC ceramide composition and lipid organization. Changes in ceramide profiles were identified using principal component analysis. After barrier recovery, the untreated sites showed increased levels of ceramide subclass AS and ceramides with a 34 total carbon-atom chain length, while the mean ceramide chain length was reduced. These changes were diminished by treatment with the studied formulation, which concurrently increased the formulated ceramides. Correlations were observed between SC lipid composition, lipid organization, and TEWL, and changes in the ceramide subclass composition suggest changes in the ceramide biosynthesis. These results suggest that VC-based formulations enhance skin barrier recovery and are attractive candidates to treat skin disorders with impaired barrier properties.

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.

An emulsion restores the skin barrier by decreasing the skin pH and inflammation in a canine experimental model

The aim of this study was to investigate the effect of Douxo(®) Calm Mousse (Sogeval, Laval, France) on restoration of the skin barrier in a canine model of barrier disruption. Tape strips were performed, daily for 6 days, on the lateral thorax of five healthy beagle dogs. Douxo(®) Calm Mousse was applied daily for 5 days to one side of the thorax and the opposite side was left untreated. The effects of treatment were evaluated by measurement of transepidermal water loss (TEWL) and pH and by histological assessment of disrupted skin at various times during barrier repair. Although no effect on TEWL was observed, Douxo(®) Calm Mousse maintained an acidic pH after three applications and reduced skin inflammation, which was most pronounced after five applications. The results of the study suggest that Douxo(®) Calm Mousse exerts a beneficial effect on barrier restoration and on markers of inflammation.

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.

Expansion of epidermal progenitors with high p63 phosphorylation during wound healing of mouse epidermis

The transcription factor p63 plays an essential role in maintaining the proliferative potential of epidermal stem cells. We have shown recently that under homoeostatic conditions, phosphorylation of p63 increases during the early transition of stem cells to transit-amplifying cells in human epidermis. However, how p63 phosphorylation relates to the regenerative processes during wound healing remains unknown. In this study, we characterize epidermal cells that contribute to wound repair in mouse models using phosphorylated p63 as a marker for stem cell differentiation. Our studies reveal that epidermal progenitors with high p63 phosphorylation preferentially expand in response to wounding in both full-thickness wound and surface injury models. As phosphorylated p63 levels inversely correlate with the proliferative potential of epidermal progenitors, p63 phosphorylation may serve as a therapeutic target to modulate the function of these regenerative cells during wound healing.

Dietary sphingolipids improve skin barrier functions via the upregulation of ceramide synthases in the epidermis

Sphingolipids are ubiquitous in eukaryotic organisms and are significant components in foods. It has been reported that treatment with sphingolipids prevents colon cancer, improves skin barrier function and suppresses inflammatory responses. However, the mechanisms for those effects of dietary sphingolipids are not well understood. In this study, to investigate the effects of dietary glucosylceramide (GluCer) and sphingomyelin (SM) on skin function, we characterized the recovery of skin barrier function and the change in sphingolipid metabolism-related enzymes in the epidermis using a special Mg-deficient diet-induced atopic dermatitis-like skin and tape-stripping damaged skin murine models. Our results show that dietary GluCer and SM accelerate the recoveries of damaged skin barrier functions. Correspondingly, dietary sphingolipids significantly upregulated the expression of ceramide synthases 3 and 4 in the epidermis of the atopic dermatitis-like skin model (P < 0.05). In the case of cultured cells, the expression of ceramide synthases 2-4 in normal human foreskin keratinocytes was significantly upregulated by treatment with 0.001-0.1 μm sphingoid bases (sphinganine, sphingosine and trans-4,cis-8-sphingadienine) (P < 0.05). These results suggest that the effects of dietary sphingolipids might be due to the activation of ceramide synthesis in the skin, rather than the direct reutilization of dietary sphingolipids. Our findings provide a novel insight into the mechanisms of the skin barrier improving effect and a more comprehensive understanding of dietary sphingolipids.

Topical hesperidin improves epidermal permeability barrier function and epidermal differentiation in normal murine skin

Orange peel extract appears to exhibit beneficial effects on skin whitening, inflammation, UVB protection, as well as keratinocyte proliferation. In the present study, we determine whether topical hesperidin influences epidermal permeability barrier function and its underlying mechanisms. Hairless mice were treated topically with 2% hesperidin or 70% ethanol alone twice daily for 6 days. At the end of treatment, basal transepidermal water loss (TEWL) was measured 2 and 4 h post barrier disruption. Epidermal proliferation and differentiation were evaluated by immunohistochemical staining and Western blot analysis. Additionally, lamellar body density and secretion were assessed by electron microscopy. Although there were no significant differences in basal barrier function, in comparison with control animals, topical hesperidin significantly accelerated barrier recovery at both 2 and 4 h after acute barrier abrogation. Enhanced barrier function in hesperidin-treated skin correlated with stimulation of both epidermal proliferation and differentiation, as well as enhanced lamellar body secretion. These results indicate that topical hesperidin enhances epidermal permeability barrier homeostasis at least in part due to stimulation of epidermal proliferation, differentiation, as well as lamellar body secretion.

Characterization of the canine skin barrier restoration following acute disruption by tape stripping

The stratum corneum (SC) forms the main part of the permeability barrier of the skin. In mice and in humans, cutaneous barrier disruption can be generated by removing the SC with tape stripping (TS) and the skin barrier function can be assessed by measurement of transepidermal water loss (TEWL). The aim of the present study was to characterize the skin barrier restoration in the dog following mechanical disruption and to analyse the correlation between the skin barrier recovery and TEWL measurement. Thirty sequential TS were performed on 12 sites on four healthy beagle dogs. The number of TS was chosen to ensure a sufficient barrier disruption with a slow recovery. Skin repair was assessed for 72 h by clinical and histological examinations, and TEWL measurements. The results showed that performing 30 TS was adequate to disrupt the skin barrier in the dog. The homeostatic repair response, initiated in the skin, was rapid and characterized by complete restoration of the SC within 72 h, accompanied by greater basal cell proliferation, and dermal eosinophilic inflammation. TEWL was significantly increased by complete removal of the SC but recovered along with restoration of the SC (Scheffe test, P ≤ 0.05). Characterization of a canine model of barrier disruption and restoration and assessment of the skin barrier function by TEWL measurements could help better understand the events implied in skin barrier function. Development of this canine model is also necessary for future studies on the effects of treatments aimed at restoring the skin barrier.

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.

Current aspects of formulation efforts and pore lifetime related to microneedle treatment of skin

IMPORTANCE OF THE FIELD

The efficacy of microneedles in the area of transdermal drug delivery is well documented. Multiple studies have shown that enhancement of skin permeation by means of the creation of microscopic pores in the stratum corneum can greatly improve the delivery rates of drugs. However, skin pretreatment with microneedles is not the only factor affecting drug transport rates. Other factors, including drug formulation and rate of micropore closure, are also important for optimizing delivery by this route.

AREAS COVERED IN THIS REVIEW

This review aims to highlight work that has been done in these areas, with an emphasis on drug formulation parameters that affect transdermal flux.

WHAT THE READER WILL GAIN

This review creates an appreciation for the many factors affecting microneedle-enhanced delivery. Most results clearly indicate that microneedle skin pretreatment by itself may have different effects on drug transport depending on the formulation used, and formulation characteristics have different effects on the transport through untreated skin and microneedle-treated skin. Several formulation approaches are reported to optimize microneedle-enhanced drug delivery, including co-solvent use, vesicular, nanoparticulate and gel systems.

TAKE HOME MESSAGE

In addition to well-established factors that affect microneedle-assisted delivery (geometry, type of microneedle, etc.), formulation and pore viability are also critical factors that must be considered.

Functional skin adaptation in infancy - almost complete but not fully competent

Early postnatal life is a period of active functional reorganization and cutaneous physiological adaptation to the extrauterine environment. Skin as the outermost organ of mammalians is endowed of multiple functions such as protection, secretion, absorption and thermoregulation. Birth stimulates the epidermal barrier maturation and the skin surface acidification especially in premature infants. In full-term infants the developed stratum corneum accomplishes competent barrier function, in contrast to prematures. Complete barrier maturation in preterm infants is fulfilled by 2-4 weeks of the postnatal life. However, in preterms with 23-25 weeks gestational age this process takes longer. Versatile regulatory mechanisms, namely skin surface acidity, calcium ion gradient and nuclear hormone receptors/ligands are interrelated in the complex postnatal newborn adaptation. The skin of newborns is adjusting quickly to the challenging environmental conditions of the postpartum. However, certain functions, for example, microcirculation, continue to develop even beyond the neonatal period, that is, up to the age of 14-17 weeks. Different environmental factors (for instance, dry and cold climate, diapers and cosmetic care procedures) influence the postnatal development of skin functional parameters such as stratum corneum hydration and the permeability barrier especially in premature infants. The aim of this article is to summarize the current knowledge on skin physiology in newborn and infants with a practical approach and to discuss the possible clinical consequences. This review offers the readership a critical and practical overview of skin physiology in newborns and infants. It emphasizes possible new research fields in neonatal and infantile skin physiology.

Skin barrier disruption by acetone: observations in a hairless mouse skin model

To disrupt the barrier function of the skin, different in vivo methods have been established, e.g., by acetone wiping or tape-stripping. In this study, the acetone-induced barrier disruption of hairless mice was investigated in order to establish a reliable model to study beneficial, long-term effects on barrier recovery after topical application. For both treatments (i.e., acetone treatment and tape-stripping) the transepidermal water loss directly after disruption and the subsequent barrier recovery profile were similar. Histological assessment showed significant lower number of corneocyte layers in acetone-treated and tape-stripped skin compared to untreated skin, while there was no statistical difference between the two treatments. Lipid analysis of acetone-treated skin revealed that only small fraction of lipids were extracted consisting of predominantly nonpolar lipids. Importantly, the ratio of the barrier lipids, i.e., cholesterol, free fatty acids and ceramides, remained similar between control and acetone-treated skin. This reflects the undisrupted lipid organization, as determined by small-angle X-ray diffraction measurements: the long-periodicity lamellar phase was still present after acetone treatment. Our results contradict earlier studies which reported no mechanical stratum corneum removal, a substantial extraction of lipids and disruption in lipid organization. In conclusion, our studies demonstrate that barrier disruption due to acetone treatment is mainly due to removal of corneocytes.

Quantitative determination of skin penetration of PEG-coated CdSe quantum dots in dermabraded but not intact SKH-1 hairless mouse skin

Many cosmetics, sunscreens, and other consumer products are reported to contain nanoscale materials. The possible transdermal absorption of nanoscale materials and the long-term consequences of the absorption have not been determined. We used polyethylene glycol coated cadmium selenide (CdSe) core quantum dots (QD; 37 nm diameter) to evaluate the penetration of nanoscale material into intact, tape stripped, acetone treated, or dermabraded mouse skin. QD were suspended in an oil-in-water emulsion (approximately 9 microM) and the emulsion was applied at 2 mg/cm(2) to mouse dorsal skin pretreated as follows: intact; tape stripped to remove the stratum corneum; acetone pretreated; dermabraded to remove stratum corneum and epidermis. QD penetration into the skin was monitored in sentinel organs (liver and regional draining lymph nodes) using inductively coupled plasma mass spectrometry analysis of cadmium (from the CdSe QD). No consistent cadmium elevation was detected in the sentinel organs of mice with intact, acetone pretreated, or tape-stripped skin at 24- and 48-h post-QD application; however, in dermabraded mice, cadmium elevations were detected in the lymph nodes and liver. QD accumulation (as cadmium) in the liver was approximately 2.0% of the applied dose. The passing of QD through the dermabraded skin was confirmed using confocal fluorescence microscopy. These results suggest that transdermal absorption of nanoscale materials depends on skin barrier quality, and that the lack of an epidermis provided access to QD penetration. Future dermal risk assessments of nanoscale materials should consider key barrier aspects of skin and its overall physiologic integrity.