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Research Techniques Made Simple: Stratum Corneum Tape Stripping

  • Anne J. Keurentjes
    Affiliations
    Department of Public and Occupational Health, Amsterdam Public Health Research Institute, Amsterdam UMC, University of Amsterdam, Amsterdam, The Netherlands
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  • Ivone Jakasa
    Affiliations
    Laboratory for Analytical Chemistry, Department of Chemistry and Biochemistry, Faculty of Food Technology and Biotechnology, University of Zagreb, Zagreb, Croatia
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  • Sanja Kezic
    Correspondence
    Correspondence: Sanja Kezic, Department of Public and Occupational Health, Amsterdam Public Health Research Institute, University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
    Affiliations
    Department of Public and Occupational Health, Amsterdam Public Health Research Institute, Amsterdam UMC, University of Amsterdam, Amsterdam, The Netherlands
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      Stratum corneum (SC)-derived biomarkers can provide relevant information on the skin’s antimicrobial, physical, and immunological barriers. The SC is easily accessible, and collection by adhesive tapes (tape stripping [TS]) is robust and minimally invasive. Given its minimal invasiveness and simplicity, TS is particularly useful for studies in the pediatric population and when repetitive sampling over time is desirable, for example, in clinical trials. The palette of SC biomarkers is expanding in a wide variety of research areas, benefiting from advances in multiplex immunoassays and omics approaches, including proteomics, lipidomics, and transcriptomics. Although there is increasing interest in collecting SC samples, the lack of TS standardization hampers its broader implementation in research and clinical practice. In this article, we address the TS procedure as well as methodological challenges that should be considered in the development of an optimal sampling strategy.

      Abbreviations:

      AD (atopic dermatitis), CER (ceramide), IRD (infrared densitometry), SC (stratum corneum), TS (tape stripping)

      Introduction

      Only micrometers thick, the stratum corneum (SC) is a layer of anucleated, keratin-rich corneocytes embedded in a lipid matrix. It harbors a variety of molecules that participate in the first line of body defense. In addition to constitutively present molecules such as lipids, IL-1 cytokines, and a variety of proteases, there is a continuous influx to the extracellular space within the SC of other macromolecules inducibly expressed by keratinocytes and other cells of the living epidermal layers (
      • Elias P.M.
      Stratum corneum defensive functions: an integrated view.
      ).

      Summary Points

      Advantages

      • Tape stripping (TS) is a simple and minimally invasive way of collecting stratum corneum (SC) samples.
      • SC samples are suitable for the determination of a broad spectrum of biomarkers using various analytical platforms, including proteomics, lipidomics, and transcriptomics.
      • SC biomarkers can provide insight into the physical, immune, and antimicrobial barriers of the skin.

      Limitations

      • The kinetics by which biomarkers are transferred into the SC from the living epidermis are largely unknown.
      • Variability in the spatial expression of biomarkers of interest should be evaluated before applying the TS technique.
      • To correct for the variable amount of SC removed by the tape, it is often necessary to normalize the biomarker expression for the SC amount on the tape.
      SC samples can easily be collected in a minimally invasive way by using adhesive tapes (tape stripping [TS]), a technique that can be applied in vivo and in vitro skin models and with both human and animal skin (
      • Lademann J.
      • Jacobi U.
      • Surber C.
      • Weigmann H.J.
      • Fluhr J.W.
      The tape stripping procedure--evaluation of some critical parameters.
      ). However, there are several methodological challenges that should be considered in relation to the use of TS. The SC is a multilayer structure, and most adhesive tapes remove only a small number of the layers. That raises the question of whether there might be a concentration‒depth gradient across the SC, and, if so, which layers are relevant for a specific biomarker, that is, which consecutive tape is appropriate to use? Furthermore, the amount of SC that is harvested by a single tape is highly variable despite the use of standardized procedures, and for some applications, there is a need for normalization for the amount of SC on the tape.
      In this article, we will describe and discuss various technical aspects of the TS technique with a view to support the development of an optimal sampling strategy. In addition, the various types of SC biomarkers and their application fields are briefly reviewed.

      TS procedure

      The TS procedure involves applying an adhesive tape to the skin and its subsequent removal of an SC layer. Usually, multiple tape samples are collected from the same skin site to increase the amount of SC available for analysis or to collect the sample from a certain SC depth.
      The skin site to which the tape is applied should preferably be free from hairs, which can be removed by using scissors or shaving.
      The basic procedure of TS is outlined in Figure 1. The tape is placed on the skin (Figure 1a), taking care to avoid folding. When multiple stripping is performed from the same skin site, the position of the tape may be marked with a pen or a template. To increase adhesion of the SC to the tape and promote a uniform collection, the pressure applied to the tape is standardized by using a roller, constant weight, or a pressure device (Figure 1b). After applying the pressure for 5‒15 seconds, the tape is pulled off in a swift movement using tweezers or gloved fingers (Figure 1c). To increase uniform removal of the SC by repeated stripping from the same skin site, the successive tapes are pulled off the skin in alternating directions. After removal, each individual tape is placed in a vial with the adhesive side facing inward or on a D-Squame cardboard (Figure 1d). It is important that the tape is not folded during transfer to the vial. The number of successive tapes that are applied depends on the optimal SC depth for the determination of the investigated biomarker and the amount of SC needed for analytical determination. For example, by using multiplex immunoassays, cytokine levels could be determined from a single tape (
      • McAleer M.A.
      • Jakasa I.
      • Hurault G.
      • Sarvari P.
      • McLean W.H.I.
      • Tanaka R.J.
      • et al.
      Systemic and stratum corneum biomarkers of severity in infant atopic dermatitis include markers of innate and T helper cell-related immunity and angiogenesis.
      ). However, for gene expression analysis, up to 20 tapes may be needed (
      • Guttman-Yassky E.
      • Diaz A.
      • Pavel A.B.
      • Fernandes M.
      • Lefferdink R.
      • Erickson T.
      • et al.
      Use of tape strips to detect immune and barrier abnormalities in the skin of children with early-onset atopic dermatitis.
      ).

      Types of tapes

      The adhesive on the tape should allow both for uniform and sufficient removal of the SC and for efficient and quantitatively adequate extraction of the molecules of interest from the tape. Furthermore, adhesive components should not interfere with the analysis. Various commercially available or custom-made tapes have been used for TS (
      • Boiten W.
      • Absalah S.
      • Vreeken R.
      • Bouwstra J.
      • van Smeden J.
      Quantitative analysis of ceramides using a novel lipidomics approach with three dimensional response modelling.
      ;
      • Lademann J.
      • Jacobi U.
      • Surber C.
      • Weigmann H.J.
      • Fluhr J.W.
      The tape stripping procedure--evaluation of some critical parameters.
      ;
      • McAleer M.A.
      • Jakasa I.
      • Hurault G.
      • Sarvari P.
      • McLean W.H.I.
      • Tanaka R.J.
      • et al.
      Systemic and stratum corneum biomarkers of severity in infant atopic dermatitis include markers of innate and T helper cell-related immunity and angiogenesis.
      ). The most widely used are D-Squame tapes available in different sizes (CuDerm, Dallas, TX). The advantage of D-Squame tapes is the availability of both compatible devices for measuring protein (D501 D-Squame Scan 850A Instrument, CuDerm) (Figure 1e) and a pressure applicator (D-Squame Pressure Instrument, CuDerm) (Figure 1b). The suitability of the tape for a specific biomarker should be investigated before starting a study because various compounds present in blank tapes may interfere with the analytical determination (
      • Kaleja P.
      • Emmert H.
      • Gerstel U.
      • Weidinger S.
      • Tholey A.
      Evaluation and improvement of protein extraction methods for analysis of skin proteome by noninvasive tape stripping.
      ).
      Figure thumbnail gr1
      Figure 1Tape stripping procedure. (a) Place the tape and mark the position with a pen or using a template. (b) Apply constant pressure using a pressure device or a roller. (c) Remove the tape using tweezers or gloved fingers. (d) Place the tape in the vial or on the storage card. (e) Measuring the optical density to determine the stratum corneum amount on the tape (optional). (f) Tapes containing stratum corneum: examples of homogeneous (left) and heterogeneous (right) distribution.

      Extraction of biomarkers from the tape

      Whereas morphological or biophysical markers, such as corneocyte stiffness or topology, can directly be measured on the tape, molecular markers have to be extracted from the tape before analytical assay. The type of extraction solvent, the extraction technique (shaking, vortexing, or ultrasonication), and the number of tapes needed to obtain a sufficiently large sample are biomarker specific. For immune markers and antimicrobial peptides, various lysis or extraction buffers with added protease inhibitors and/or surfactants are used (
      • Clausen M.L.
      • Slotved H.C.
      • Krogfelt K.A.
      • Agner T.
      Measurements of AMPs in stratum corneum of atopic dermatitis and healthy skin-tape stripping technique.
      ;
      • McAleer M.A.
      • Jakasa I.
      • Hurault G.
      • Sarvari P.
      • McLean W.H.I.
      • Tanaka R.J.
      • et al.
      Systemic and stratum corneum biomarkers of severity in infant atopic dermatitis include markers of innate and T helper cell-related immunity and angiogenesis.
      ). Extraction of highly lipophilic markers such as ceramides (CERs) or free fatty acids often requires multistage extraction using organic solvents of different polarities (
      • Boiten W.
      • Absalah S.
      • Vreeken R.
      • Bouwstra J.
      • van Smeden J.
      Quantitative analysis of ceramides using a novel lipidomics approach with three dimensional response modelling.
      ;
      • Emmert H.
      • Baurecht H.
      • Thielking F.
      • Stölzl D.
      • Rodriguez E.
      • Harder I.
      • et al.
      Stratum corneum lipidomics analysis reveals altered ceramide profile in atopic dermatitis patients across body sites with correlated changes in skin microbiome [e-pub head of print].
      ).
      For gene expression profiling, RNA is commonly extracted using the lysis buffer used for RNA isolation. As the amount of RNA in the SC is very small, extracts from multiple tapes are usually pooled before RNA isolation (
      • Guttman-Yassky E.
      • Diaz A.
      • Pavel A.B.
      • Fernandes M.
      • Lefferdink R.
      • Erickson T.
      • et al.
      Use of tape strips to detect immune and barrier abnormalities in the skin of children with early-onset atopic dermatitis.
      ). To increase yield, the extract from one tape can be used for successive extractions of subsequent tapes. For example,
      • He H.
      • Olesen C.M.
      • Pavel A.B.
      • Clausen M.L.
      • Wu J.
      • Estrada Y.
      • et al.
      Tape-strip proteomic profiling of atopic dermatitis on dupilumab identifies minimally invasive biomarkers.
      performed eight subsequent extractions to obtain sufficient amounts for proteomic analysis.
      Evaluation of the extraction recovery is an important part of the method validation. Evaluation should be performed in the type of skin to be investigated (healthy vs. diseased, various body location, aged vs. young skin, etc.). For examples of the evaluation of extraction of tapes for proteome analysis, the reader is referred to a recent study by
      • Kaleja P.
      • Emmert H.
      • Gerstel U.
      • Weidinger S.
      • Tholey A.
      Evaluation and improvement of protein extraction methods for analysis of skin proteome by noninvasive tape stripping.
      and to a study by
      • Boiten W.
      • Absalah S.
      • Vreeken R.
      • Bouwstra J.
      • van Smeden J.
      Quantitative analysis of ceramides using a novel lipidomics approach with three dimensional response modelling.
      for examples of evaluation of extraction of tapes for CERs.

      Correction for variable amount of SC removed by the tape

      The amount of SC collected by a tape is highly variable and depends on numerous factors related to the TS procedure (force of removal from the skin, the pressure applied on the tape, adhesive strength of the glue) as well as intrinsic SC properties such as cohesiveness between the corneocytes and the presence of furrows (
      • Lademann J.
      • Jacobi U.
      • Surber C.
      • Weigmann H.J.
      • Fluhr J.W.
      The tape stripping procedure--evaluation of some critical parameters.
      ). To correct for the variable amount of SC collected, it is often necessary to quantify the amount of SC removed by the tape.
      There are various methods for quantifying the amount of SC removed by TS. The direct approaches include differential weighing of the tape before and after collection and measuring light absorption by the tape with SC attached. In recent years, a simple, robust, and quick method based on near-infrared densitometry (IRD) has been introduced (
      • Voegeli R.
      • Heiland J.
      • Doppler S.
      • Rawlings A.V.
      • Schreier T.
      Efficient and simple quantification of stratum corneum proteins on tape strippings by infrared densitometry.
      ), and the commercially available IRD device (D501 D-Squame Scan 850A Instrument, CuDerm) has become increasingly popular in dermatological research (Figure 1e). Several studies have shown a good correlation between the SC content estimated by IRD and that obtained by weighing in the context of samples from various body sites and ethnic groups (
      • Raj N.
      • Voegeli R.
      • Rawlings A.V.
      • Gibbons S.
      • Munday M.R.
      • Summers B.
      • et al.
      Variation in stratum corneum protein content as a function of anatomical site and ethnic group.
      ). The critical issue with the use of D-Squame Scan is the distribution of the SC over the tape (Figure 1f) because the infrared beam only passes through a window covering approximately 45% of the tape area (
      • Raj N.
      • Voegeli R.
      • Rawlings A.V.
      • Gibbons S.
      • Munday M.R.
      • Summers B.
      • et al.
      Variation in stratum corneum protein content as a function of anatomical site and ethnic group.
      ). Especially where lesional skin samples and tapes from the deeper SC layers are concerned, uneven distribution of SC on the tape might affect the accuracy of this method.
      Another technique used to correct for the variable amount of SC collected by a tape is based on the biochemical analysis of proteins after extraction with an appropriate buffer or solvent. The advantage of such methods is that both soluble and insoluble proteins can be determined. Soluble proteins are extracted mainly from the intercellular space by a buffer, whereas insoluble proteins (mainly keratins), present within the corneocytes, are measured after treating the tape with a strong base (
      • McAleer M.A.
      • Jakasa I.
      • Hurault G.
      • Sarvari P.
      • McLean W.H.I.
      • Tanaka R.J.
      • et al.
      Systemic and stratum corneum biomarkers of severity in infant atopic dermatitis include markers of innate and T helper cell-related immunity and angiogenesis.
      ). In contrast to direct methods, biochemical methods are destructive. In some cases, the biomarker of interest and the amount of protein can be measured from the same extract (
      • McAleer M.A.
      • Jakasa I.
      • Hurault G.
      • Sarvari P.
      • McLean W.H.I.
      • Tanaka R.J.
      • et al.
      Systemic and stratum corneum biomarkers of severity in infant atopic dermatitis include markers of innate and T helper cell-related immunity and angiogenesis.
      ). However, the type of solvent used for the extraction of biomarkers might not be compatible with the protein assay. In that case, the tape can be divided into two parts before extraction: one for the protein analysis and another for the biomarker assay.

      Sampling: Spatial variability

      The amount of SC removed by TS is not linearly proportional to the number of tapes used, and the consecutive tape number is only a rough indicator of the depth of SC removal (
      • Clausen M.L.
      • Slotved H.C.
      • Krogfelt K.A.
      • Agner T.
      Tape stripping technique for stratum corneum protein analysis.
      ). Preferably, the sample should originate from the depth where the concentration of the biomarker is greatest and the concentration‒depth variability is smallest. Various studies have shown that SC depth has a biomarker-specific effect. For example, a strong depth dependence has been found for total lipid level and lipid composition (
      • Sadowski T.
      • Klose C.
      • Gerl M.J.
      • Wójcik-Maciejewicz A.
      • Herzog R.
      • Simons K.
      • et al.
      Large-scale human skin lipidomics by quantitative, high-throughput shotgun mass spectrometry.
      ). By contrast, the levels of various cytokines measured in lesional and nonlesional skin samples from patients with atopic dermatitis (AD) showed only a slight concentration‒depth gradient (
      • Clausen M.L.
      • Kezic S.
      • Olesen C.M.
      • Agner T.
      Cytokine concentration across the stratum corneum in atopic dermatitis and healthy controls.
      ). Next to depth-related variability, a significant spatial effect has been observed with respect to the distance of the skin sampling site from the lesion (
      • Jurakic Toncic R.
      • Kezic S.
      • Hadzavdic S.L.
      • Marinovic B.
      • Jakasa I.
      Stratum corneum biomarkers in atopic dermatitis: biological and spatial variability.
      ) and the body location (
      • Emmert H.
      • Baurecht H.
      • Thielking F.
      • Stölzl D.
      • Rodriguez E.
      • Harder I.
      • et al.
      Stratum corneum lipidomics analysis reveals altered ceramide profile in atopic dermatitis patients across body sites with correlated changes in skin microbiome [e-pub head of print].
      ). Very few studies have yet measured spatial variability of gene expression across the SC.
      In the case of significant depth-related variability, tapes from different depths (e.g., upper, middle, and lower parts of the SC) could be collected and their extracts pooled before analytical determination.
      Another potential source of variability when using TS is related to the kinetics by which the molecules of interest are transferred into the SC from the living epidermis, the skin layer from which these molecules originate. Temporal variability of SC biomarkers is largely unknown, whereas it may be of crucial importance for the sampling strategy, especially when studying monitoring of therapy or skin barrier repair.

      Application fields

      There are three main application fields for TS: (i) determination of biomarkers in various skin pathologies, (ii) assessment of dermal absorption of drugs and toxic substances, and (iii) induction of standardized skin barrier damage (Table 1).
      Table 1Overview of Application Fields
      Application FieldPotential UseSC MarkerReferences
      Inflammatory skin diseases (e.g., AD, psoriasis)PathophysiologyImmune mediators (proteins or gene expression)
      • He H.
      • Bissonnette R.
      • Wu J.
      • Diaz A.
      • Saint-Cyr Proulx E.
      • Maari C.
      • et al.
      Tape strips detect distinct immune and barrier profiles in atopic dermatitis and psoriasis.
      Immune mediators.
      Differentiation between inflammatory skin diseasesStructural proteins
      • He H.
      • Olesen C.M.
      • Pavel A.B.
      • Clausen M.L.
      • Wu J.
      • Estrada Y.
      • et al.
      Tape-strip proteomic profiling of atopic dermatitis on dupilumab identifies minimally invasive biomarkers.
      Immune mediators.
      Marker of disease severity Monitoring therapyFLG breakdown products
      • Guttman-Yassky E.
      • Diaz A.
      • Pavel A.B.
      • Fernandes M.
      • Lefferdink R.
      • Erickson T.
      • et al.
      Use of tape strips to detect immune and barrier abnormalities in the skin of children with early-onset atopic dermatitis.
      Immune mediators.
      ,
      Structural proteins.
      Stratification of patientsLipids
      • McAleer M.A.
      • Jakasa I.
      • Hurault G.
      • Sarvari P.
      • McLean W.H.I.
      • Tanaka R.J.
      • et al.
      Systemic and stratum corneum biomarkers of severity in infant atopic dermatitis include markers of innate and T helper cell-related immunity and angiogenesis.
      Immune mediators.
      ,
      FLG breakdown products.
      Antimicrobial peptides
      • Clausen M.L.
      • Slotved H.C.
      • Krogfelt K.A.
      • Agner T.
      Measurements of AMPs in stratum corneum of atopic dermatitis and healthy skin-tape stripping technique.
      Antimicrobial peptides.
      Microbiome
      • Emmert H.
      • Baurecht H.
      • Thielking F.
      • Stölzl D.
      • Rodriguez E.
      • Harder I.
      • et al.
      Stratum corneum lipidomics analysis reveals altered ceramide profile in atopic dermatitis patients across body sites with correlated changes in skin microbiome [e-pub head of print].
      Lipids.
      ,
      Microbiome.
      Corneocyte surface topography
      • Riethmuller C.
      • McAleer M.A.
      • Koppes S.A.
      • Abdayem R.
      • Franz J.
      • Haftek M.
      • et al.
      Filaggrin breakdown products determine corneocyte conformation in patients with atopic dermatitis.
      Corneocyte surface topography.
      Skin cancerIdentification of the cancerization fieldCorneocyte surface topography
      • Keurentjes A.J.
      • de Witt K.D.
      • Jakasa I.
      • Rüther L.
      • Kemperman P.M.J.H.
      • Kezic S.
      • et al.
      Actinic keratosis and surrounding skin exhibit changes in corneocyte surface topography and decreased levels of filaggrin degradation products.
      Corneocyte surface topography.
      Transdermal penetrationBioequivalence of dermally applied drugsDrug amount
      • N’Dri-Stempfer B.
      • Navidi W.C.
      • Guy R.H.
      • Bunge A.L.
      Improved bioequivalence assessment of topical dermatological drug products using dermatopharmacokinetics.
      Model for skin barrier damageEfficacy of topical therapy on skin barrier repair
      • Berkers T.
      • Boiten W.A.
      • Absalah S.
      • van Smeden J.
      • Lavrijsen A.P.M.
      • Bouwstra J.A.
      Compromising human skin in vivo and ex vivo to study skin barrier repair.
      Abbreviations: AD, atopic dermatitis; SC, stratum corneum.
      1 Immune mediators.
      2 Structural proteins.
      3 FLG breakdown products.
      4 Lipids.
      5 Antimicrobial peptides.
      6 Microbiome.
      7 Corneocyte surface topography.
      SC biomarkers have been investigated mainly in inflammatory skin diseases such as AD and psoriasis. A wide range of candidate biomarkers, including FLG degradation products, lipids, antimicrobial peptides, and cytokines, have been investigated as markers of disease activity (
      • McAleer M.A.
      • Jakasa I.
      • Hurault G.
      • Sarvari P.
      • McLean W.H.I.
      • Tanaka R.J.
      • et al.
      Systemic and stratum corneum biomarkers of severity in infant atopic dermatitis include markers of innate and T helper cell-related immunity and angiogenesis.
      ) to monitor therapy (
      • He H.
      • Olesen C.M.
      • Pavel A.B.
      • Clausen M.L.
      • Wu J.
      • Estrada Y.
      • et al.
      Tape-strip proteomic profiling of atopic dermatitis on dupilumab identifies minimally invasive biomarkers.
      ), for differentiation of inflammatory skin diseases (
      • He H.
      • Bissonnette R.
      • Wu J.
      • Diaz A.
      • Saint-Cyr Proulx E.
      • Maari C.
      • et al.
      Tape strips detect distinct immune and barrier profiles in atopic dermatitis and psoriasis.
      ), or for stratification of patients into endotypes (
      • Leung D.Y.M.
      • Calatroni A.
      • Zaramela L.S.
      • LeBeau P.K.
      • Dyjack N.
      • Brar K.
      • et al.
      The nonlesional skin surface distinguishes atopic dermatitis with food allergy as a unique endotype.
      ). Whereas older studies involved the determination of limited numbers of protein or lipid biomarkers, recent studies have involved extensive proteomic (
      • He H.
      • Olesen C.M.
      • Pavel A.B.
      • Clausen M.L.
      • Wu J.
      • Estrada Y.
      • et al.
      Tape-strip proteomic profiling of atopic dermatitis on dupilumab identifies minimally invasive biomarkers.
      ) and lipidomic (
      • Emmert H.
      • Baurecht H.
      • Thielking F.
      • Stölzl D.
      • Rodriguez E.
      • Harder I.
      • et al.
      Stratum corneum lipidomics analysis reveals altered ceramide profile in atopic dermatitis patients across body sites with correlated changes in skin microbiome [e-pub head of print].
      ) profiles. Recently, owing to improved procedures for the isolation of RNA from tapes and technological advances in RNA sequencing, an increasing number of studies have focused on the expression of genes involved in immune response and skin barrier in inflammatory skin diseases (
      • Guttman-Yassky E.
      • Diaz A.
      • Pavel A.B.
      • Fernandes M.
      • Lefferdink R.
      • Erickson T.
      • et al.
      Use of tape strips to detect immune and barrier abnormalities in the skin of children with early-onset atopic dermatitis.
      ;
      • He H.
      • Bissonnette R.
      • Wu J.
      • Diaz A.
      • Saint-Cyr Proulx E.
      • Maari C.
      • et al.
      Tape strips detect distinct immune and barrier profiles in atopic dermatitis and psoriasis.
      ;
      • Leung D.Y.M.
      • Calatroni A.
      • Zaramela L.S.
      • LeBeau P.K.
      • Dyjack N.
      • Brar K.
      • et al.
      The nonlesional skin surface distinguishes atopic dermatitis with food allergy as a unique endotype.
      ).
      In addition to molecular biomarkers, SC tapes can provide information on morphological characteristics such as corneocyte surface topography (
      • Riethmuller C.
      • McAleer M.A.
      • Koppes S.A.
      • Abdayem R.
      • Franz J.
      • Haftek M.
      • et al.
      Filaggrin breakdown products determine corneocyte conformation in patients with atopic dermatitis.
      ). Altered corneocyte surface texture assessed by atomic force microscopy has been demonstrated in AD (
      • Riethmuller C.
      • McAleer M.A.
      • Koppes S.A.
      • Abdayem R.
      • Franz J.
      • Haftek M.
      • et al.
      Filaggrin breakdown products determine corneocyte conformation in patients with atopic dermatitis.
      ). A quantitative measure of surface topography has proven to be useful for the determination of field cancerization in actinic keratosis (
      • Keurentjes A.J.
      • de Witt K.D.
      • Jakasa I.
      • Rüther L.
      • Kemperman P.M.J.H.
      • Kezic S.
      • et al.
      Actinic keratosis and surrounding skin exhibit changes in corneocyte surface topography and decreased levels of filaggrin degradation products.
      ). Furthermore, TS may provide insight into the skin microbiome (
      • Emmert H.
      • Baurecht H.
      • Thielking F.
      • Stölzl D.
      • Rodriguez E.
      • Harder I.
      • et al.
      Stratum corneum lipidomics analysis reveals altered ceramide profile in atopic dermatitis patients across body sites with correlated changes in skin microbiome [e-pub head of print].
      ).
      Another application field of the TS technique is related to the percutaneous penetration kinetics and bioequivalence assessment of topically applied drugs and toxic chemicals (
      • N’Dri-Stempfer B.
      • Navidi W.C.
      • Guy R.H.
      • Bunge A.L.
      Improved bioequivalence assessment of topical dermatological drug products using dermatopharmacokinetics.
      ).
      TS has also been used as a standardized method of disrupting the skin barrier and studying the barrier repair mechanism (
      • Berkers T.
      • Boiten W.A.
      • Absalah S.
      • van Smeden J.
      • Lavrijsen A.P.M.
      • Bouwstra J.A.
      Compromising human skin in vivo and ex vivo to study skin barrier repair.
      ).

      Conclusions

      TS is a simple, painless, and minimally invasive way of collecting samples of the SC, which enables the determination of a broad spectrum of biomarkers of skin barrier and immune response. Its fields of application are numerous, and more are still emerging. Owing to its minimal invasiveness and simplicity, TS has opened up new perspectives for studies in children and for monitoring therapy where repetitive skin sampling over time is required. A major obstacle to the wider use of TS in clinics is the lack of standardization and biomarker-specific standard operating protocols.

      Conflict of Interest

      The authors state no conflict of interest.

      Multiple Choice Questions

      • 1.
        Which statement is TRUE regarding tape stripping (TS)?
        • A.
          TS is a procedure to collect the stratum corneum (SC) layers of the skin.
        • B.
          TS is used to remove the epidermal layer of the skin.
        • C.
          TS is an invasive technique similar to biopsy.
        • D.
          TS technique can only be applied in vivo in human skin.
      • 2.
        The amount of SC on the tape can NOT be assessed
        • A.
          From the tape strip number
        • B.
          By weighing the tape before and after collection
        • C.
          By measuring the light absorption of the tape
        • D.
          By measuring the proteins on the tape, for example, by a biochemical assay
      • 3.
        SC samples collected by TS are NOT suitable for the following:
        • A.
          Collection of DNA
        • B.
          Transcriptomic analysis
        • C.
          Markers produced by other cells than keratinocytes
        • D.
          Microbiome
      • 4.
        Which statement is FALSE regarding the collection of the SC by TS?
        • A.
          The amount of SC removed by a tape depends on the adhesive properties of the tape.
        • B.
          The amount of SC removed by a tape depends on the cohesiveness of the SC.
        • C.
          The amount of SC removed by a tape decreases with SC depth.
        • D.
          Commercially available tapes such as D-Squame are suitable for all types of biomarkers.
      • 5.
        Correction for the variable amount of SC is NOT needed
        • A.
          When standardized pressure is applied, sampling is performed in the same subject, and the same type of tape is used.
        • B.
          For imaging of the corneocyte surface topography.
        • C.
          For proteomic analysis.
        • D.
          For lipidomics analysis.

      Acknowledgments

      AJK is a PhD student, and SK and IJ are senior scientists and subject matter experts.

      Author Contributions

      Conceptualization: AJK, IJ, SK; Investigation: AJK, IJ, SK; Project Administration: SK; Supervision: SK; Validation: AJK, IJ, SK; Visualization: IJ, AJK; Writing - Original Draft Preparation: AJK, IJ; Writing - Review and Editing: AJK, IJ, SK

      Supplementary Material

      Detailed Answers

      • 1.
        Which statement is TRUE regarding tape stripping (TS)?
      • CORRECT ANSWER: A. TS is a procedure to collect the stratum corneum (SC) layers of the skin.
      • Tape strips remove only SC layers. The technique is minimally invasive and can be applied in vitro and in vivo in human or animal skin.
      • 2.
        The amount of SC on the tape can NOT be assessed
      • CORRECT ANSWER: A. From the tape strip number.
      • The amount of SC removed by a tape depends on numerous factors such as adhesive properties of the tape, cohesiveness of the SC, and the duration and intensity of the pressure applied on the tape. Usually, the amount of the SC is largest in the first tapes and decreases with SC depth, but the tape number does not provide information on the amount of SC on the tape.
      • 3.
        SC samples collected by TS are NOT suitable for the following:
      • CORRECT ANSWER: A. Collection of DNA.
      • SC comprises dead anucleated cells called corneocytes. Thus, DNA is not present. In contrast, RNA can be isolated from the SC and can be used for transcriptomic analysis. Biomarkers that have been detected in the SC are not exclusively produced by keratinocytes.
      • 4.
        Which statement is FALSE regarding the collection of the SC by TS?
      • CORRECT ANSWER: D. Commercially available tapes such as D-Squame are suitable for all types of biomarkers.
      • Tapes used for tape stripping, including the frequently used D-Squame, may contain ingredients that interfere with the analytical assay for the biomarker of interest (e.g., this has been shown for free fatty acids and various proteins).
      • 5.
        Correction for the variable amount of SC is NOT needed
      • CORRECT ANSWER: B. For imaging of the corneocyte surface topography.
      • Imaging of the corneocyte surface can be performed directly on the tapes, for example, by using atomic force microscopy.

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