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Skin Barrier Function in Healthy Subjects and Patients with Atopic Dermatitis in Relation to Filaggrin Loss-of-Function Mutations

2010; Elsevier BV; Volume: 131; Issue: 2 Linguagem: Inglês

10.1038/jid.2010.307

1523-1747

Ivone Jakaša, Ellen S. Koster, Florentine Calkoen, W.H. Irwin McLean, Linda E. Campbell, Jan D. Bos, Maarten M. Verberk, Sanja Kežić,

Contact Dermatitis and Allergies

atopic dermatitis filaggrin polyethylene glycol stratum corneum transepidermal water loss TO THE EDITOR Patients with atopic dermatitis (AD) have a defective skin barrier that even exists in nonlesional skin and is characterized by increased transepidermal water loss (TEWL) as well as enhanced percutaneous penetration of both lipophilic and hydrophilic compounds (Hata et al., 2002Hata M. Tokura Y. Takigawa M. et al.Assessment of epidermal barrier function by photoacoustic spectrometry in relation to its importance in the pathogenesis of atopic dermatitis.Lab Invest. 2002; 82: 1451-1461Crossref PubMed Scopus (46) Google Scholar; Jakasa et al., 2006Jakasa I. de Jongh C.M. Verberk M.M. et al.Percutaneous penetration of sodium lauryl sulphate is increased in uninvolved skin of atopic dermatitis patients compared to control subjects.Br J Dermatol. 2006; 155: 104-109Crossref PubMed Scopus (95) Google Scholar, Jakasa et al., 2007Jakasa I. Verberk M.M. Esposito M. et al.Altered penetration of polyethylene glycols into uninvolved skin of atopic dermatitis patients.J invest Dermatol. 2007; 127: 129-134Crossref PubMed Scopus (105) Google Scholar; Gupta et al., 2008Gupta J. Grube E. Ericksen M.B. et al.Intrinsically defective skin barrier function in children with atopic dermatitis correlates with disease severity.J Allergy Clin Immunol. 2008; 121: 725-730Abstract Full Text Full Text PDF PubMed Scopus (125) Google Scholar; Proksch et al., 2008Proksch E. Brandner J.M. Jensen J.M. The skin—an indispensable barrier.Exp Dermatol. 2008; 17: 1063-1072Crossref PubMed Scopus (1008) Google Scholar; Jensen et al., 2009Jensen J.M. Pfeiffer S. Witt M. et al.Different effects of pimecrolimus and betamethasone on the skin barrier in patients with atopic dermatitis.J Allergy Clin Immunol. 2009; 124: R19-R28Abstract Full Text Full Text PDF PubMed Scopus (54) Google Scholar). Various causes for the impaired barrier in AD have been suggested, including an aberrant composition and structure of the intercellular lipid bilayers and an altered expression of the cornified envelope and keratinocyte structural proteins (Proksch et al., 2008Proksch E. Brandner J.M. Jensen J.M. The skin—an indispensable barrier.Exp Dermatol. 2008; 17: 1063-1072Crossref PubMed Scopus (1008) Google Scholar). Furthermore, barrier function in nonaffected skin has been shown to be dependent on disease activity (Chamlin et al., 2002Chamlin S.L. Kao J. Freiden I.J. et al.Ceramide-dominant barrier repair lipids alleviate childhood atopic dermatitis: changes in barrier function provide a sensitive indicator of disease activity.J Am Acad Dermatol. 2002; 47: 198-208Abstract Full Text Full Text PDF PubMed Scopus (360) Google Scholar; Jakasa et al., 2006Jakasa I. de Jongh C.M. Verberk M.M. et al.Percutaneous penetration of sodium lauryl sulphate is increased in uninvolved skin of atopic dermatitis patients compared to control subjects.Br J Dermatol. 2006; 155: 104-109Crossref PubMed Scopus (95) Google Scholar; Gupta et al., 2008Gupta J. Grube E. Ericksen M.B. et al.Intrinsically defective skin barrier function in children with atopic dermatitis correlates with disease severity.J Allergy Clin Immunol. 2008; 121: 725-730Abstract Full Text Full Text PDF PubMed Scopus (125) Google Scholar). The well-established association between filaggrin gene (FLG) loss-of-function mutations and AD supports the hypothesis that an intrinsically impaired skin barrier may be a primary step in the development of AD (Brown and McLean, 2009Brown S.J. McLean W.H. Eczema genetics: current state of knowledge and future goals.J Invest Dermatol. 2009; 129: 543-552Crossref PubMed Scopus (129) Google Scholar; O’Regan et al., 2009O’Regan G.M. Sandilands A. McLean W.H. et al.Filaggrin in atopic dermatitis.J Allergy Clin Immunol. 2009; 124: R2-R6Abstract Full Text Full Text PDF PubMed Scopus (142) Google Scholar). This seems plausible because filaggrin is a key epidermal protein that regulates several functions critical for the structure and composition of the stratum corneum (SC) (Kezic et al., 2008Kezic S. Kemperman P.M. Koster E.S. et al.Loss-of-function mutations in the filaggrin gene lead to reduced level of natural moisturizing factor in the stratum corneum.J Invest Dermatol. 2008; 128: 2117-2119Crossref PubMed Scopus (218) Google Scholar; Brown and McLean, 2009Brown S.J. McLean W.H. Eczema genetics: current state of knowledge and future goals.J Invest Dermatol. 2009; 129: 543-552Crossref PubMed Scopus (129) Google Scholar; O’Regan et al., 2009O’Regan G.M. Sandilands A. McLean W.H. et al.Filaggrin in atopic dermatitis.J Allergy Clin Immunol. 2009; 124: R2-R6Abstract Full Text Full Text PDF PubMed Scopus (142) Google Scholar). Previous investigators have reported contrasting findings regarding the influence of FLG mutations on the skin barrier in AD (Hubiche et al., 2007Hubiche T. Ged C. Benard A. et al.Analysis of SPINK 5, KLK 7 and FLG genotypes in a French atopic dermatitis cohort.Acta Derm Venereol. 2007; 87: 499-505Crossref PubMed Scopus (105) Google Scholar; Nemoto-Hasebe et al., 2009Nemoto-Hasebe I. Akiyama M. Nomura T. et al.Clinical severity correlates with impaired barrier in filaggrin-related eczema.J Invest Dermatol. 2009; 129: 682-689Crossref PubMed Scopus (138) Google Scholar; Jungersted et al., 2010Jungersted J.M. Scheer H. Mempel M. et al.Stratum corneum lipids, skin barrier function and filaggrin mutations in patients with atopic eczema.Allergy. 2010; 65: 911-918Crossref PubMed Scopus (219) Google Scholar). Furthermore, because only one-third of AD patients have FLG loss-of-function mutations, these mutations only explain the barrier abnormalities in a subset of AD patients. Therefore, the main objective of this study was to investigate whether the barrier reduction of nonlesional skin on AD patients was limited to carriers of FLG mutations. This study was based on our previous investigations that reported an impaired skin barrier for polyethylene glycols (PEG) of different molecular weights and sodium lauryl sulfate (Jakasa et al., 2006Jakasa I. de Jongh C.M. Verberk M.M. et al.Percutaneous penetration of sodium lauryl sulphate is increased in uninvolved skin of atopic dermatitis patients compared to control subjects.Br J Dermatol. 2006; 155: 104-109Crossref PubMed Scopus (95) Google Scholar, Jakasa et al., 2007Jakasa I. Verberk M.M. Esposito M. et al.Altered penetration of polyethylene glycols into uninvolved skin of atopic dermatitis patients.J invest Dermatol. 2007; 127: 129-134Crossref PubMed Scopus (105) Google Scholar). In this investigation, we genotyped the subjects who participated in the previous studies. To obtain a sufficient sample size for the groups, we recruited more subjects from the outpatient clinic of the Academic Medical Centre and through a public advertisement. After recruitment, our study population consisted of 20 healthy individuals who were wild type for FLG mutations (CTRL-wt), 15 AD patients who were wild type for FLG (AD-wt), and 17 AD patients who were heterozygous for FLG (AD-Flg). All subjects were of Dutch Caucasian decent. The characteristics of all subjects are presented in Table 1. The medical ethics committee of the Academic Medical Center, University of Amsterdam, approved the experimental protocol. All subjects gave their written, informed consent. The study was conducted according to the Declaration of Helsinki Principles.Table 1Characteristics of the subjects and SC thicknessCTRL-wt (n=20)AD-wt (n=15)AD-Flg (n=17)Age27 (21–56)24 (18–52)26 (19–60)Female gender (%)11 (55)11 (73)10 (59)EASI score*—1.2 (0.4–22.8)0.9 (0.0–3.0)SC thickness/μm7.9 (5.1–13.8)9.3 (7.2–10.8)8.2 (5.1–12.0)Abbreviations: AD-Flg, AD patients with FLG mutations; AD-wt, AD patients without FLG mutations; CTRL-wt, control subjects without FLG mutations; EASI, eczema area and severity index; SC, stratum corneum.The results are shown as the median value (range). *EASI (maximum 72 points) (Hanifin et al., 2001Hanifin J.M. Thurston M. Omoto M. the EASI Evaluator Group The eczema area and severity index (EASI): assessment of reliability in atopic dermatitis.Exp Dermatol. 2001; 10: 11-18Crossref PubMed Scopus (672) Google Scholar). Open table in a new tab Abbreviations: AD-Flg, AD patients with FLG mutations; AD-wt, AD patients without FLG mutations; CTRL-wt, control subjects without FLG mutations; EASI, eczema area and severity index; SC, stratum corneum. The results are shown as the median value (range). *EASI (maximum 72 points) (Hanifin et al., 2001Hanifin J.M. Thurston M. Omoto M. the EASI Evaluator Group The eczema area and severity index (EASI): assessment of reliability in atopic dermatitis.Exp Dermatol. 2001; 10: 11-18Crossref PubMed Scopus (672) Google Scholar). The skin barrier in the nonlesional skin was assessed by TEWL and by percutaneous penetration of PEG (PEG 370). The penetration of PEG 370 was characterized by the diffusivity (D), diffusion rate constant (D/L2), and partition of PEG 370 into the SC (Ksc/v). For a detailed method description, please refer to our previous study (Jakasa et al., 2007Jakasa I. Verberk M.M. Esposito M. et al.Altered penetration of polyethylene glycols into uninvolved skin of atopic dermatitis patients.J invest Dermatol. 2007; 127: 129-134Crossref PubMed Scopus (105) Google Scholar). Genotype analysis was performed for the four most prevalent mutations in European Caucasians: R501X, 2282del4, R2447X, and S3247X, according to the procedure described elsewhere (Sandilands et al., 2007Sandilands A. Smith F.J. Irvine A.D. et al.Filaggrin's fuller figure: a glimpse into the genetic architecture of atopic dermatitis.J Invest Dermatol. 2007; 127: 1282-1284Crossref PubMed Scopus (100) Google Scholar). The results of this study showed that AD patients, irrespective of their FLG genotype, have an altered skin barrier. As seen in Figure 1a, a significant difference in TEWL was found between CTRL-wt and AD patients with or without FLG mutations. Similar results were also obtained for the percutaneous penetration of PEG 370. Compared with CTRL-wt, both AD patient subgroups had a higher apparent diffusion coefficient D and diffusion rate (D/L2) of PEG 370 (Figure 1b and c). Increased diffusivity of PEG 370 resulted in a higher permeability coefficient (Kp) of PEG 370 in AD-Flg patients (Figure 1e). However, in AD-wt patients, the higher diffusivity of PEG was offset by a decrease in the partition coefficient of PEG 370 (Figure 1d). Lower partition of PEG in AD patients had previously been reported (Jakasa et al., 2007Jakasa I. Verberk M.M. Esposito M. et al.Altered penetration of polyethylene glycols into uninvolved skin of atopic dermatitis patients.J invest Dermatol. 2007; 127: 129-134Crossref PubMed Scopus (105) Google Scholar); nevertheless, this study showed that this effect was limited to only AD-wt patients. A reduction in the partition of PEG 370 suggests an altered composition and/or structure of the SC in AD-wt patients; however, the reason for this is not clear. In most studies related to AD, skin barrier function was assessed by measuring TEWL. It is still unclear whether TEWL is also a good parameter of the skin barrier for the ingress of compounds (Proksch et al., 2008Proksch E. Brandner J.M. Jensen J.M. The skin—an indispensable barrier.Exp Dermatol. 2008; 17: 1063-1072Crossref PubMed Scopus (1008) Google Scholar; Jensen et al., 2009Jensen J.M. Pfeiffer S. Witt M. et al.Different effects of pimecrolimus and betamethasone on the skin barrier in patients with atopic dermatitis.J Allergy Clin Immunol. 2009; 124: R19-R28Abstract Full Text Full Text PDF PubMed Scopus (54) Google Scholar). Scharschmidt et al., 2009Scharschmidt T.C. Man M.Q. Hatano Y. et al.Filaggrin deficiency confers a paracellular barrier abnormality that reduces inflammatory thresholds to irritants and haptens.J Allergy Clin Immunol. 2009; 124: 496-506Abstract Full Text Full Text PDF PubMed Scopus (203) Google Scholar reported increased penetration of a water-soluble compound in filaggrin-deficient flaky tail (ft/ft) mice when compared with wt/wt mice, however basal TEWL values in ft/ft mice were in the range of normal values. The enhanced TEWL and increased diffusivity of PEG 370 observed in the present study suggests impairment of the skin barrier in both directions. This was further supported by a positive correlation between TEWL and D/L2 (r=0.34; P=0.006). In summary, this study demonstrated a reduced skin barrier in AD patients, irrespective of FLG genotype, implying that other factors besides FLG loss-of-function mutations modulate skin barrier integrity. Enhanced TEWL and diffusivity in AD suggests defects in the intercellular lipid bilayers of the SC. The mechanisms underlying the disturbance of lipid organization in the SC might be different in AD patients with and without FLG mutations. Therefore, an investigation that examined the composition and the organization of intercellular lipids of the SC in AD patients in relation to FLG genotype and state of disease would be interesting.