Reverse iontophoresis: monitoring prostaglandin E2 associated with cutaneous inflammation in vivo

Abstract In response to topical application of irritants, increased concentrations of prostaglandin E₂ (PGE₂) are found in human skin exudate and in cultured dermal fibroblasts. In this study, PGE₂ generated in response to transdermal delivery of irritant drug compounds was monitored in hairless guinea pig (HOP) by a non-invasive method, reverse iontophoresis. Reverse iontophoresis is the movement of molecules from the skin under the influence of an applied electric field. Irritant drug compounds were applied with iontophoresis (electrotransport), and reverse iontophoresis of PGE₂ from skin was monitored by radioimmunoassay (RIA) after extraction from the delivery system. Chlorpromazine was used as a model drug irritant. When chlorpromazine and saline were applied over a range of current densities from 0 to 200 μA/cm², visual scores of erythema and edema yielded a correlation with measured skin efflux of PGE₂ (r=0.86). Delivery of chlorpromazine resulted in greater efflux of PGE₂ than delivery of non-irritant saline controls under the same delivery conditions. Five drug compounds, chloroquine, promazine, chlorpromazine, tetracaine, metoclopramide, and saline were applied to hairless guinea pig skin. The 6 agents were similarly rank ordered by visual erythema/edema scores and by PGE₂ efflux, indicating that the quantity of PGE₂ effluxed reflects the intensity of skin irritation. In contrast, vasoconstriction or vasodilation produced by the local delivery of vasoactive agents did not correlate with PGE₂ skin efflux, indicating that this measurement is specific for an inflammatory response. In summary, PGE₂ generated in response to transdermally applied drug irritants can be monitored non-invasively in vivo by reverse iontophoresis.     

Influence of tumour necrosis factor‐α polymorphism −308 and atopy on irritant contact dermatitis in healthcare workers*

Background. Chronic irritant hand dermatitis is an issue for healthcare workers and may negatively impact infection control. Objectives. We examined the effects of a G to A transition at position ?308 on the tumour necrosis factor‐α (TNF‐α) gene on chronically damaged skin of healthcare workers during exposure and recovery from repetitive hand hygiene, after intensive treatment, and on the irritant response in normal skin. Patients/Materials/Methods. In 68 healthcare workers with irritant hand dermatitis, we genotyped TNF‐α?308 and measured the epidermal response via quantitative digital imaging, erythema, dryness, and barrier integrity. Results. Excess hand erythema decreased with hand hygiene exposure and increased during time off for AA/GA genotypes, but had opposite effects for GG. AA/GA had smaller reductions in dryness with lotion treatment and larger reductions in excess erythema than GG. The atopic diathesis and heightened neurosensory irritation resulting from water and lactic acid significantly influenced the responses. Repeated exposure to water and sodium lauryl sulfate (0.05, 0.1%) produced higher erythema in normal skin for AA/GA than for GG. Conclusions. This study provides evidence that the TNF‐α polymorphism at ?308 and an atopic history impact the severity of irritation and recovery from exposure and response to treatment for common hand skin products in both chronic irritant hand dermatitis and normal skin.     

An animal model for altering the irritability threshold of normal skin

Theory behind conditioned hyperirritability (autoeczematization) predicts the lowering of the irritation threshold in the presence of a pre-existing dermatitis. We have attempted to develop an animal model that parallels the syndrome seen in man. Groups of 10 guinea pigs were shaved and depilated; irritation thresholds to benzalkonium chloride and trichloroacetic acid were determined using 1 cm diameter open patches. Reactions were scored 24 h later on the basis of erythema and induration. Animals having as little as 1.56 cm2 of skin acutely inflamed with a known irritant had lowered irritation thresholds to the same irritant on normal skin at remote sites (p less than 0.01). Mild irritation of a much larger surface area produced the same effect (p less than 0.01). More extensive, severe dermatitis did not lower the irritation threshold further. Acute dermatitis induced by a contact allergen (DNCB) lowered the irritation threshold of normal skin to the same level as that obtained with irritants (p less than 0.01). Induction of chronic cutaneous ulcers 3-4 cm in diameter lowered the irritation threshold of normal skin to the same point defined by the acute studies (p less than 0.01). These results indicate that an acute irritant or contact dermatitis, as well as chronic skin ulceration, may alter the reactivity of unaffected normal skin to exhibit a heightened response to irritation. This model appears to differ from that seen in humans, in that a more extensive or chronic dermatitis did not further heighten the susceptibility to irritation.     

P09Comparison between mild irritant response in haired and hairless guinea pigs

The hairless guinea pig offers the possibility of performing irritant studies without the use of depilatory agents or clipping. Studies have shown a response to allergens and simple irritants comparable to that of the haired guinea pig. Histoanatomical studies have demonstrated differences in cutaneous structure in the two strains, differences that might influence the response to mild irritants such as topical drug vehicles. The purpose of this study was to compare the usability of hairless (HLGP) and shaved haired guinea pigs (SGP) in tolerability studies of complex topical formulations. The tolerability of 6 selected skin care formulations (SCF), known to cause a differentiated irritative response in HLGP, was studied in 15 male SGP and 15 male HLGP. All animals were treated on a 5 × 5 cm area on each flank twice daily for 4 consecutive days with SCF. The irritant effects of the SCF were quantified clinically and by measurement of transepidermal water loss (TEWL) and colorimetry (a*‐parameter). Both species were able to differentiate between SCF in relation to skin tolerance and although the response pattern was somewhat different in the two species the ranking of the SCF was essentially the same using TEWL and clinical scoring. However, colorimetry was found to be unsuited for the evaluation of cutaneous irritation in the SGP over a period of days as regrowth of fur obfuscated the underlying erythema. In conclusion the HLGP appears to be a more suitable model for tolerability testing of composite formulations.     

Cumulative irritation patch test of sanitary pads on sensitive skin

Background Tools are needed to assess the effects of various products on sensitive skin. Aim To investigate the cutaneous compatibility of various sanitary pads in people with self‐declared sensitive skin. Patients/methods Eight subjects, who considered their skin to be sensitive and who reported adverse skin responses to everyday products or clothing, were patch tested on the arm with two, low‐irritancy sanitary pads for four consecutive 24‐hour periods. Test products differed only in their surface covering. Sodium lauryl sulfate solution (0.1% w/v) and physiological saline served as standard irritant and nonirritant controls, respectively. Skin irritation (erythema) was graded after each 24‐hour period. Results No significant difference in skin erythema scores was observed between groups (scores on day 4: 1.06 ± 0.11 vs. 1.25 ± 0.13, on a five‐point scale, P < 0.05). The temporal development of cumulative irritation associated with the pads was comparable to that observed with the nonirritant control (a plateau in maximal group scores) and distinct from that of the irritant control (continuously rising scores). Conclusion Sanitary pads under investigation elicited negligible cumulative irritation in a four‐day patch test on subjects with self‐declared sensitive skin. The temporal pattern of cumulative response was consistent with the inherently low irritation potential of the products.     

Acyclovir skin depot characterization following in vivo iontophoretic delivery

Background/purpose: Current Herpes labialis infection treatment by oral, parenteral or topical routes is inefficient. The objective of this study was to investigate the use of iontophoresis for improved topical delivery of acyclovir (ACV) in vivo in hairless rat. Methods: Iontophoresis was performed for 10 min using a 5% ACV gel formulation. Tape stripping and skin extractions were performed at different time points following treatment for drug quantification in stratum corneum (SC) and underlying skin, respectively. Results: Fourfold more ACV was detected in the SC immediately following 10‐min iontophoresis as compared with passive delivery. Similarly, high ACV levels (29.27±3.52 μg/cm²) were achieved in the underlying skin following a single 10‐min iontophoretic treatment while no drug detected following passive delivery (P<0.05). At 24‐h post‐iontophoresis, ACV levels in the SC decreased with a corresponding increase in the underlying skin due to drug migration. After 24‐h post‐iontophoresis, drug levels gradually decreased in both skin compartments until no ACV was detected at 72‐h post‐iontophoresis. Conclusion: Iontophoretic delivery of ACV resulted in high drug levels in skin layers to form a drug depot, which persisted over 2–3 days.     

Skin tolerance, efficacy, and quality of life of patients with red facial skin using a skin care regimen containing Licochalcone A

Background Patients with rosacea and red facial skin often show sensitivity to skin care products which can exacerbate inflammation and subjective irritation. Besides pharmacologic management, special skin care is prudent to avoid cosmetically induced irritation and address cosmetic concerns. Appropriate skin care should provide gentle cleansing, UVA/UVB protection, effective moisturization, and concealing pigments to neutralize the appearance of redness. Aims To evaluate skin compatibility and efficacy of a skin care regimen containing licochalcone A (Lic A), an anti‐irritant from the licorice plant Glycyrrhiza inflata, for subjects with mild to moderate facial redness. Patients/methods Sixty‐two patients with mild to moderate red facial skin used a four‐product skin care regimen for 8 weeks. Clinical assessments of erythema and subjective irritation, cross‐polarized photography, and self‐assessment questionnaires were completed at baseline, and after 4 and 8 weeks of use. A quality of life questionnaire was given at baseline and week 8. Results Clinical evaluations, subject response, and photography confirmed very good tolerability of the regimen and effective neutralization of redness by the pigmented products. Significant improvements in average erythema scores were observed at 4 and 8 weeks (P < 0.05), and an improvement in quality of life was confirmed by the patient questionnaires. Discussion The skin care regimen containing Lic A was found to be compatible with the sensitive facial skin of patients with rosacea and improved the appearance of persistent facial redness. The products were also observed to be compatible with daily metronidazole treatment.     

Quantitative in vitro assessment of N-alkyl sulphate-induced cytotoxicity in human keratinocytes (HaCaT). Comparison with in vivo human irritation tests

Summary A spontaneously immortalized human keratinocyte line, HaCaT, was used as an in vitro model to predict the cutaneous irritation of anionic surfactants. For this purpose, a number of sodium salts of N-alkyl sulphates with hydrocarbon chain lengths varying between C₈ and C₁₆ were studied for possible cytotoxic effects. The endpoints used to assess toxicity were uptake of the vital dye neutral red (NR) and cell morphology criteria 24 h after dosing. A linear proportionality between keratinocyte number and NR uptake was established. All tested surfactants had cytotoxic effects as demonstrated by a decreased NR uptake, which showed a clear dose–response relationship. Concentrations resulting in 50% inhibition of NR uptake (IC-50) ranged from 0·15 mmol (sodium lauryl sulphate, C₁₂) to 1·23 mmol (sodium octyl sulphate, C₈). The in vitro cytotoxicity data were highly reproducible when the test was repeated after several weeks. The cytotoxicity data from these assays were compared with the irritant responses (as evaluated by measurement of erythema and transepidermal water loss) obtained after 24 h application of the same compounds (300 μ1 of 20 mmol aqueous solution) to the volar forearm of human volunteers. There were significant linear correlations between the IC-50 values and both barrier damage (transepidermal water loss) and erythema (as evaluated by skin colour reflectance measurements). For the test substances, however, the sensitivity of the in vitro system was between 10 and 100 times higher than that observed in human skin in vivo. This quantitative difference can largely be ascribed to the effective permeability barrier of normal human skin in vivo, which protects living keratinocytes from the cytotoxic effects of surfactant molecules. The results indicate that normal human keratinocytes in culture are a promising screening method for predicting the irritation potential of anionic surfactants. Confirmation, however, has still to be obtained by appropriate in vivo testing in human volunteers.     

Specific barrier response profiles after experimentally induced skin irritation in vivo

Background

Recently, natural moisturizing factors (NMFs) and corneocyte surface topography were suggested as biomarkers for irritant dermatitis.

Objectives

To investigate how exposure to different irritants influences corneocyte surface topography, NMF levels and the barrier function of human skin in vivo.

Methods

Eight healthy adult volunteers were exposed to aqueous solutions of 60% n‐propanol, 0.5% sodium lauryl sulfate (SLS), 0.15% sodium hydroxide, and 2.0% acetic acid, and distilled water, in a repeated irritation test over a period of 96 hours. Erythema, transepidermal water loss (TEWL), skin hydration, the dermal texture index (DTI) and NMF levels were measured at baseline, and after 24 and 96 hours.

Results

SLS and sodium hydroxide had the most pronounced effects on erythema and TEWL. Although n‐propanol caused only slight changes in TEWL and erythema, it showed pronounced effects on skin hydration, NMF levels, and the DTI. NMF was the only parameter that was significantly altered by all investigated irritants. The changes in the DTI were inversely associated with NMF levels and skin hydration.

Conclusion

Skin barrier impairment and the inflammatory response are irritant‐specific, emphasizing the need for a multiparametric approach to the study of skin irritation. NMF levels seem to be the most sensitive parameter in detecting irritant‐induced skin barrier alterations.     

Skin irritation by dithranol (anthralin) and its 10-acyl analogues in 3 animal models

The skin irritant properties of a single application of dithranol (anthralin), a typical "delayed irritant", and its 10-acyl analogues in acetone or while petrolatum were compared in 3 animals models. Maximal irritation was reached at about 24 h in mouse ear, 48 h in guinea pig back and 1 week ill miniature swine back, the last-mentioned serving as a good model of human skin. In all animal species, butantrone was significantly less irriant than dithranol, 10-acetyl dithranol or 10-propionyl dithranol. 10-acetyl dithranol was the most irritant compound. Clinical trials with butantrone on psoriasis are justified.     

Reduced skin threshold to irritation in the presence of allergic contact dermatitis in the guinea pig

The skin is more susceptible to irritation when an active eczematous process is present. This reduced threshold to irritation occurs in skin distant from the site of the eczematous skin. Data is presented to demonstrate the appearance of irritant dermatitis to lower concentrations of sodium lauryl sulfate during the presence of an allergic contact dermatitis in the guinea pig.     

Photosensitivity of murine skin greatly depends on the genetic background: clinically relevant dose as a new measure to replace minimal erythema dose in mouse studies

Artificial UV irradiation of murine skin is a frequently used method for testing photosensitivity, study carcinogenesis and photoprotective effects of different compounds. However, doses of UV radiation and mouse strains used in experiments vary greatly. The genetic background of mice may influence the photosensitivity as melanin content, pigmentation and hair cycle parameters are dissimilar. Doses of UV are often expressed in relation to the minimal erythema dose (MED) that was not necessarily determined for the given strain. We set out to standardize the method of measuring photosensitivity in three commonly used mouse strains, C57BL/6N, Balb/c and SKH‐1. We found that MED may not be determined for some strains as erythema development in mice with diverse genotypes differs greatly. We measured the oedema response in vivo and ex vivo by using OCT. Given the strain‐specific variability of erythema, we introduced Clinically Relevant Dose (CRD) as a new term to replace MED in experiments, to describe the lowest dose that triggers a perceptible skin reaction in mice. Not only the CRD but the proportion of erythema and oedema were different in strains examined. C57BL/6N mice display skin reactions at the lowest UVB dose, while SKH‐1 hairless mice show changes, mostly oedema, after higher doses of UVB. The cellular composition and skin thickness were examined by histopathology. IL‐1beta and IL‐6 levels in skin correlated with the increasing doses of UVB. Despite the variations in the degree of erythema and oedema, no major differences in cytokine expressions were seen among various strains of mice.     

Cutaneous side-effects of transdermal iontophoresis with and without surfactant pretreatment: a single-blinded, randomized controlled trial

BACKGROUND: Iontophoresis, a method that facilitates drug transport across skin by an external electrical field, offers the possibility for long-term transdermal delivery of compounds in a well-controlled manner. In general, the literature supports the contention that iontophoresis is a safe procedure. However, there are important medical issues concerning the epidermal and dermal effects of iontophoresis that have not been extensively investigated. Specific and strictly controlled studies on the dermal effect of iontophoresis are scarce. OBJECTIVES: The aim of this study was to investigate the cutaneous side-effects of transdermal iontophoresis application in healthy human volunteers. METHODS: This was a single-blinded, randomized and parallel design study. In one group (n=12) subjects were treated nonocclusively with a surfactant formulation followed by iontophoresis (3-h application at a current density of 250 microA cm(-2)). In another group (n=12) iontophoresis alone was performed. No drug was included in these studies. The corresponding passive treatments served as controls. Noninvasive methods including sensation record, transepidermal water loss (TEWL), skin colour and the visual scoring were used to assess cutaneous effects. RESULTS: Tingling and itching were commonly experienced in the first 30 min of the current application. Iontophoresis in combination with the pretreatment induced significant increases in TEWL values and in skin redness, and resulted in slight to mild erythema and oedema compared with the control. Compared with the iontophoresis alone, the presence of surfactant pretreatment caused slightly more skin irritation (erythema and oedema) but did not further disturb the skin barrier function. CONCLUSIONS: The transdermal iontophoresis challenges the skin barrier function and induces transient mild skin irritation, but does not cause any permanent damage to the skin when applied for 3 h at a current density of 0.25 mA cm(-2).     

Efficacy of skin barrier creams

An animal model for the evaluation of skin protective creams against chemical irritants is described. The irritants were applied daily for 2 weeks to shaved back skin of young guinea pigs: sodium tauryl sulphate (5% aq.: 30 min), sodium hydroxide (0,5% aq.; 2 min). and toluene (20'i. eth.; 2 mint. "The harrier cream was applied 2 h prior to and immediately after exposure to the irritant. Control animals were treated with the irritant only. The irritant reaction was scored on a 4–point scale for erythema and quantified with regard to transepidennal water loss (TEWL) by evaporime-try and skin blood flow volume (BFV) by laser Doppler velocimetry. A total of 90 guinea pigs, consisting of" individual panels of 5 to 10 animals, was tested. While one barrier cream (Slokoderm) significantly suppressed the irritation due 10 sodium lauryl sulphate and toluene, the other (Contra-Alkalh failed to do so and even aggravated the response, which was particularly evident with sodium hydroxide. This model may be useful in developing more effective barrier creams.     

Topical D-vitamins: multiparametric comparison of the irritant potential of calcipotriol, tacalcitol and calcitriol in a hairless guinea pig model

The irritant potential of calcipotriol. 1α.24-diliydroxy vitamin D₃, (tacalcitol) and 1α, 25-dihyd rosy-vitamin- D₃ (calcitriol) was compared in a hairless guinea pig model. Randomized, occlusive patch testing for 2 days was used. Each group of X animals was tested simultaneously with the 3 substances and a placebo vehicle. 3 dose levels i.e. 500 μg/ml, 50 μg/ml and 5 μg/ml were used, Test sites were evaluated at day 2 (2 h after removal of the patches) and again at day 3. Evaluation was blinded and based on a multiple parameter assessment of skin irritancy. comparing clinical scoring. skin perfusion using high resolution laser Doppler image scanning, skin colour (a*, Minolta ChromaMeter) and skin thickening (20 MHz ultrasound) indicating oedema. Skin biopsies were taken for histological preparation and assessment of epidermal hyperplasia. No difference was observed between the irritant potential of calcipotriol, tacalcitol and calcitriol bused on clinical scoring as well as objective non-invasive measuring techniques. All 3 substances showed a dose-dependent and equal increase in clinical irritation score. cutaneous blood flow, skin colour and epidermal hyperplasia. The cutaneous inflammatory reaction was dominated by vasodilation and increased cutaneous perfusion. Oedema formation was only seen ill the highest dosages tested. Skin barrier damage was not induced as TEWL remained unaffected. The hairless guinea pig appears a valid model to test irritancy of topical D-vitamins since the same profile of irritancy was previously established in humans for 2 of the compounds tested. calcitriol and calcipotriol.     

Effect of a topical corticosteroid, a retinoid and a vitamin D3 derivative on sodium dodecyl sulphate induced skin irritation

Exposure of the skin to sodium dodecyl sulfate (SDS) leads to disruption of barrier and skin irritation. We used repetitive short exposure to a low molarity SDS solution as an in vivo model to mimic the development of irritant contact dermatitis. In this model, we studied clinical (erythema), functional (transepidermal water loss(TEWL)) and cell biological changes, 24 healthy volunteers were patch tested with SDS (0.2%) for 4 h a the day for 5 consecutive days. After removal of the patches, the exposed sites were treated 1 × daily either with a topical corticosteroid (triamcinolon acetoide cream 0.05%). a retinoid (tretinoin cream 0.025%). or a vitamin D₃ derivative (calcipotriol ointment 50 microgram/g). Irritant reactions were assessed by erythema scoring and measurement of barrier function with TEWL up to 14 days after the first challenge. Skin biopsies were taken for cell biological changes at day 4. Vehicle-treated sites served as controls. Repetitive exposure of human skin to SDS resulted in a gradual increase in erythema scoring and TEWL associated with the upregulation of proliferative cells as measured by the expression of Ki-67-antigen and of differentiation markers, visualized by increased expression of involucrin and epidermal-fatty-acid binding protein (E-FABP). Skin irritation as assessed by erythema scoring and TEWL was not significantly suppressed by triamcinolone cream. However, a significant reduction of the number of cycling keratinocytes and a decrease in involucrin positive cell layers was observed in this group. Neither treatment with calcipotriol ointment nor with tretinoin cream induced improvement of skin irritation as judged by visual scoring and TEWL. In contrast to steroid treatment no significant elf eel of calcipotriol ointment or tretinoin cream treatment was observed with regard to the number of cycling cells and differentiation markers. Further studies are needed to assess whether treatment with topical corticosteroids is an effective modality in skin irritation and irritant contact dermatitis.     

Allergic contact dermatitis from di-isodecyl phthatate in a polyvinyl chloride identity band

An animal model for the evaluation of skin protective creams against chemical irritants is described. The irritants were applied daily for 2 weeks to shaved back skin of young guinea pigs: sodium tauryl sulphate (5% aq.: 30 min), sodium hydroxide (0,5% aq.; 2 min). and toluene (20′i. eth.; 2 mint. “The harrier cream was applied 2 h prior to and immediately after exposure to the irritant. Control animals were treated with the irritant only. The irritant reaction was scored on a 4–point scale for erythema and quantified with regard to transepidennal water loss (TEWL) by evaporime-try and skin blood flow volume (BFV) by laser Doppler velocimetry. A total of 90 guinea pigs, consisting of” individual panels of 5 to 10 animals, was tested. While one barrier cream (Slokoderm) significantly suppressed the irritation due 10 sodium lauryl sulphate and toluene, the other (Contra-Alkalh failed to do so and even aggravated the response, which was particularly evident with sodium hydroxide. This model may be useful in developing more effective barrier creams.     

Effect of sodium lauryl sulfate-induced skin irritation on in vitro percutaneous absorption of four drugs.

The influence of irritant contact dermatitis on percutaneous penetration was investigated for four 14C-labeled compounds with diverse physicochemical properties: hydrocortisone (HC), indomethacin (IM), ibuprofen (IB), and acitretin (AC). Hairless guinea pigs were pretreated in vivo for 24 h with either 0.5% sodium lauryl sulfate (SLS) to induce irritant contact dermatitis or with water (controls). Twenty-four hours after pretreatment animals were sacrificed. Percutaneous penetration was then measured using in vitro diffusion cells and the removed (pretreated) skin. The following parameters were determined: cumulative amount of compound penetrated, steady state flux, lag time, and permeability coefficient, skin concentration per unit area, and the relative amount of drug remaining in the skin (as a percentage of the cumulative amount of compound penetrated through the skin). SLS pretreatment resulted in moderate irritant dermatitis in all animals and increased in vivo transepidermal water loss 4.5 times. Flux was increased in SLS-pretreated skin as compared with controls for all four compounds, with the greatest enhancement for hydrocortisone (HC) (5.9 times), followed by indomethacin (IM) (4.6 times), ibuprofen (IB) (3.9 times), and acitretin (AC) (3.4 times). Skin concentrations increased to a smaller degree from 1.6 times (IB) and 2.6 times (HC) to 3.4 times (IM). However, AC skin concentrations were not different between the two groups. Thus, percutaneous penetration parameters were equivocally influenced by SLS-induced irritation. Increased skin concentrations were paralleled by even higher increases in flux.     

The irritant potential of n-propanol (nonanoic acid vehicle) in cumulative skin irritation: a validation study of two different human in vivo test models

Background/purpose: Human in vivo cumulative irritation tests with low‐grade irritants simulate real‐life exposure to skin irritants. The test outcome depends not only on the substance tested but also on the design of the assay. More than one experimental irritant is usually used because chemicals have diverse mechanisms of action on the skin. We used sodium lauryl sulfate (SLS) and nonanoic acid (NON) in three different concentrations plus their vehicles, water and n‐propanol, respectively, to validate our test models and to optimize test concentrations. Methods: Healthy volunteer forearm skin was exposed in two different cumulative test models: a repeated open model (ROAT) and an exaggerated wash test model. ROAT: 10‐min daily exposures for 5+4 days (no irritation on weekend) to SLS 0% (water), 0.5%, 1.0% and 2.0% on the right arm and NON 0% (n‐propanol neat), 10%, 20% and 30% on the left arm. Wash test: induction of irritation by three daily washings for 6 days and maintenance of the dermatitis by two daily washings for 12 days with SLS 0%, 5%, 10% and 15% or NON 0%, 30%, 40% and 50%. Reactions were evaluated clinically and instrumentally (transepidermal water loss, colorimetry and hydration) at sequential time points. Additionally, for the wash test, subjective pain scores were obtained from the volunteers. Results: In the ROAT, n‐propanol exhibited irritation potential at the level of SLS 1.0% and, by visual scoring, was only found to be significantly different from the two highest concentrations of NON (20% and 30%). In the wash test, n‐propanol was much less irritating than SLS, and it could only be distinguished statistically from NON (any concentration) by visual reading. For both test models, n‐propanol, by instrumental measurements, was not significantly different from any NON concentration. Conclusion: In cumulative irritation test assays, n‐propanol appears to be quite irritant itself and may thus be a significant contributor to NON irritation. Moreover, n‐propanol was more irritant in the ROAT compared with the wash test.     

Tandem repeated irritation in aged skin induces distinct barrier perturbation and cytokine profile in vivo

Background The barrier perturbation pattern and molecular markers of inflammation upon tandem repeated irritation in chronologically aged skin have not been previously studied. Objectives We aimed to investigate the barrier impairment kinetic and in vivo cytokine profile following sequential irritation with sodium lauryl sulfate (SLS) and undiluted toluene (Tol) in aged compared with young skin. Methods Four fields on the volar forearm of healthy aged and young volunteers (median age, respectively, 63·9 and 32·6 years) were sequentially exposed to 0·5% SLS and undiluted toluene in a controlled tandem repeated irritation test; an adjacent nontreated field served as control. The permeability barrier function was monitored by repeated measurements of transepidermal water loss (TEWL), capacitance and erythema every 24 h up to 96 h. The stratum corneum cytokines were harvested by sequential tape stripping and quantified by multiplex bead array and enzyme‐linked immunosorbent assay. Results Compared with young skin, aged skin was characterized by delayed and/or less pronounced alterations in the visual irritation score, TEWL, chromametry a*‐value and capacitance, assessed by the respective Δ‐values for each parameter and monitoring time point. In both groups, exposure to SLS/SLS, SLS/Tol and Tol/SLS resulted in decreased interleukin (IL)‐1α levels, whereas the application of Tol/Tol induced an increase in IL‐1α. Furthermore, decreased IL‐1 receptor antagonist (IL‐1RA) levels and a lower IL‐1RA/IL‐1α ratio were found following repeated exposure to the irritants. Conclusions Our results provide evidence for selective alterations in the cytokine profile and distinct barrier impairment kinetic following tandem repeated irritation with SLS and Tol in aged compared with young skin in vivo.