Gene expression analysis of EpiDerm TM following exposure to SLS using cDNA microarrays S.T. Fletcher a, *, V.A. Baker a , J.H. Fentem a , D.A. Basketter a , D.P. Kelsell b a SEAC Toxicology Unit, Unilever Research, Sharnbrook, Bedfordshire MK44 1LQ, UK b Centre for Cutaneous Research, St Bartholomews and The Royal London School of Medicine and Dentistry, Queen Mary and Westfield College, 2 Newark Street, London E1 2AT, UK Abstract There is a need to investigate the mechanistic basis of the human skin irritation response if relevant in vitro test systems for the predictive identification of skin irritation hazards are to be developed. Recent progress in genomics technologies mean that tools for the identification and investigation of important biochemical events in the processes of skin irritation are now available. The aim of this work was to identify genes (for further mechanistic investigation) which may be regulated in response to skin irritation, fol- lowing exposure of the EpiDerm TM skin model to the known skin irritant sodium lauryl sulphate (SLS). EpiDerm cultures were treated in triplicate with a non-cytotoxic dose of SLS (0.1 mg/ml, as determined by the MTT assay and histological examination) for 15 min, 30 min, 1 h, 2 h, 3 h, 4 h and 24 h. Total RNA was extracted from the pooled EpiDerm cultures and used to probe Atlas TM human arrays (Clontech) covering approximately 3600 genes. Preliminary data indicated an up-regulation at early time points (15–30 min) of a number of genes involved in transportation (e.g. the sodium and chloride dependent taurine transporter) and receptors (e.g. ZAP70 and protocadherin 42 precursor). The gene encoding the UV excision repair protein and other DNA repair genes (e.g. DNA-directed RNA polymerase II) were up-regulated after 1–3 h, along with TGFb3 and other tumour sup- pressors, which play a role in cellular development and wound healing. At the later time points of 4–24 h, genes involved in protein translation (e.g. Cathepsin D receptor) and metabolism (e.g. CYP27A) were up-regulated. In addition, a number of genes were down-regulated in response to treatment with SLS, although these followed less of a time dependent pattern. These results indicate the differential regulation of a number of genes in response to treatment with SLS, some of which may provide additional clues to the molecular events underpinning the irritation response to this particular surfactant and possibly to other chemical irritants. # 2001 Elsevier Science Ltd. All rights reserved. Keywords: Skin irritation; EpiDerm TM ; cDNA microarrays; Genomics 1. Introduction Development of relevant in vitro test systems for the predictive identification of skin irritation hazards requires an understanding of the mechanistic basis of the human skin irritation response. Recent progress in genomics technologies means that tools for the identifi- cation and investigation of important biochemical events in the processes of skin irritation are now avail- able (e.g. large-scale differential gene expression using microarray hybridisation technology). These tools can be used to identify genes critical in the human skin response following exposure to irritants. It is currently difficult to differentiate between irritant contact derma- titis and allergic contact dermatitis both clinically and histopathologically. However, they are believed to initi- ate responses via different pathways (Harvell and Mai- bach, 1994), a period of induction after initiation being required for an immune mediated (i.e. allergic) response but not for irritant responses. A strong allergen may serve as both inductor and elicitor on exposure to skin, making the distinction between irritation and allergy difficult. In practice, time course assessments do not provide a reliable distinction between irritant and aller- gic reactions because in patch testing, irritants can mimic weak allergens by intensifying the reaction after an initial reading is taken (Rietschel, 1997). Basketter (1998) hypothesised that all chemicals are skin irritants 0887-2333/01/$ - see front matter # 2001 Elsevier Science Ltd. All rights reserved. PII: S0887-2333(01)00042-X Toxicology in Vitro 15 (2001) 393–398 www.elsevier.com/locate/toxinvit Abbreviations: CYP, cytochrome P450; cDNA, complementary deoxyribonucleic acid; ER, endoplamic reticulum; LDH, lactate dehydrogenase; NHEK, normal human-derived epidermal keratino- cytes; PBS, phosphate buffered saline; SLS, sodium lauryl sulphate. * Corresponding author. Tel.: +44-1234-222581; fax: +44-1234- 222122. E-mail address: samantha.fletcher@unilever.com (S.T. Fletcher).