P11The complex problem of sensitive skin

Small rodent laboratory animals lack the complex cutaneous structure and function of human skin resulting in "all or none"‐responses to mild irritants so that the animals may show a less discriminative reaction pattern compared to human volunteers when studying the tolerability of topical drug formulations. This study compared the tolerance pattern of a 6 composite formulations (SCF A‐F) in human volunteers and in hairless guinea pigs (HLGP). The formulations were 2 basic creams (A and B) and 4 composite creams containing either isopropyl palmitate (C), glycerin (D), canola oil (E) or (‐)‐alfa‐bisabolol (F). The tolerability of 6 selected skin care formulations (SCF A‐F), known to cause a differentiated irritative response in HLGP, was studied in 15 male SGP and 20 human volunteers. The HLGP were treated twice a day on a 5 × 5 cm area on each flank with a SCF for 4 consecutive days. The irritant effects of the SCF were quantified by clinical assessment, measurement of trans epidermal waterloss (TEWL) and colorimetry (a*‐parameter). In humans the tolerability was evaluated clinically using the chamber scarification test. In HLGP SCF A and C were strong irritants followed closely by E, the remaining formulations were indistinguishable. In human volunteers all formulations were tolerated equally and well with the clinical score rising slightly on the first day and remaining stable thereafter. In conclusion, the HLGP appeared to be too sensitive, as formulations showing irritation in HLGP were well tolerated in a human.     

The hairless guinea-pig as a model for treatment of acute irritation in humans

BACKGROUND: The effect of six skin care formulations on experimentally induced acute irritation was studied in hairless guinea-pigs (HLGP) and in human volunteers (HV). The formulations were a basic cream, a carbomer cream and four modifications of the carbomer cream, containing either 10% isopropyl palmitate (IPP cream), 10% glycerol (glycerol cream), 19.5% canola oil (canola oil cream) or 0.5% (-)-alpha-bisabolol (bisabolol cream). METHODS: Acute irritation was induced by occlusive tests with 1% sodium lauryl sulfate aq. in both HLGP and HV, and in HV also by using nonanoic acid in n-propanol (NON) 20%. The irritant reactions were treated twice daily with the formulations from the time of removal of the patches. Evaluation of skin irritation and efficacy of treatments was performed daily for 4 days using clinical scoring, evaporimetry (transepidermal water loss), hydration measurement and colorimetry. RESULTS: The glycerol cream was the only product showing effects potentially better than no treatment in HV. CONCLUSION: The HLGP was too sensitive an animal model as a predictor for effect in humans. There was no difference in efficacy of the formulations against the two different irritants in HV.     

Characterization of sulfur mustard vapor-induced cutaneous lesions on haired guinea pigs*

Background/aims: Sulfur mustard (2,2′-dichlorodiethyl sulfide, HD) is a potent vesicating (blistering) agent. In this report, we describe the time-course and the dose-dependent response following cutaneous exposure to sulfur mustard (HD) in the haired guinea pig model. The purpose of this study was to evaluate the usefulness of the haired guinea pig as a vesicant research model. Methods: Seventy-two animals were divided into nine groups of eight animals each. Hair on the dorsal side of each animal was removed by clipping with an electric clipper followed by application of a chemical depilating agent (MAGIC Shaving Powder). Six dorsal skin sites on each animal of a given group were exposed to saturated HD vapor (1.4 mg/l) for one of nine exposure times between 0-8 min. Lesions were evaluated for erythema (reflectance colorimeter) and edema (ultrasound imaging) at 4, 6, 12, and 24 h postexposure. Damage at the dermal-epidermal junction (DEJ) was evaluated by histopathology at 24 h postexposure. Results: We observed that the hair removal process was time-consuming, produced significant initial erythema, and resulted in increased dorsal skin sensitivity to low HD exposure levels. The time-course of exposure response to HD was observed to be dose-dependent and similar to the hairless guinea pig model. Conclusions: The haired guinea pig is inferior to the hairless guinea pig as a vesicant model due to the complications resulting from the hair removal process. However, the haired guinea pig is a useful model for evaluating the cutaneous effects of HD vapor and can be developed into a routine screening tool for the evaluation of topical barriers against HD vapor exposure.     

The hairless guinea-pig as a model for treatment of cumulative irritation in humans

BACKGROUND: The effect of six skin-care formulations (SCFs) on experimentally induced cumulative irritation was studied in hairless guinea-pigs (HLGPs) and in human volunteers (HVs). The formulations were a basic cream, a carbomer cream and four modifications of the carbomer cream, containing either 10% isopropyl palmitate (IPP cream), 10% glycerol (glycerol cream), 19.5% canola oil (canola oil cream) or 0.5% (-)-alpha-bisabolol (bisabolol cream). METHODS: In HLGP, irritant dermatitis was induced with 30 min daily exposure for 4 days to 0.5% sodium lauryl sulfate aq. (SLS). In HVs, irritant dermatitis was induced with 10 min daily exposure for 5+4 days (no irritation on weekends) to 3% SLS aq. on the right and 30% nonanoic acid (NON) in n-propanol on the left volar forearm. Clinical scoring was performed daily; evaporimetry (total epidermal water loss (TEWL)), hydration and colorimetry were measured at baseline (day 0) in the middle and at the end of treatment. Treatments were applied twice daily. The basic cream and the IPP cream were excluded from testing in HLGP because they were known from previous studies to be irritant in HLGP, while all formulations were known to be equally and well tolerated locally in humans. RESULTS: All formulations worsened the skin irritation in HLGP: the glycerol cream the least, the canola oil cream the most, while the bisabolol cream and the carbomer cream were indistinguishable. In humans, the glycerol cream was better than 'No Treatment' after cumulative irritation with both SLS and NON. The basic cream was better tolerated in humans than was expected from previous testing in HLGPs. CONCLUSION: In conclusion, the results from the studies in HLGPs and HVs are in agreement with regard to ranking of the SCFs. Further, the glycerol cream showed a positive treatment effect on both SLS- and NON-irritated skin in HVs.     

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 2,3,7,8-tetrachlorodibenzo-p-dioxin on murine skin

The effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) on skin of congenic haired and hairless newborn and adult HRS/J mice was studied. In all adult animals topical application of TCDD caused an involution of sebaceous glands. Epidermal/epithelial hyperplasia and hyperkeratinization was induced in the hairless, but not the haired mice. Trans-glutaminase (TG) activity was stimulated in both haired and hairless animals. A single application of 1 microgram of TCDD did not stimulate significant ornithine decarboxylase activity in the skin in either strain. Other than a reduction in the density of the inflammatory cell infiltrate in the dermis, topical treatment with antiinflammatory agents fluocinolone acetonide and indomethacin did not affect the cutaneous response to TCDD. Skin of newborn mice treated topically with TCDD over a 2-wk period reacted much the same as adult skin in that sebaceous glands were reduced in size and TG activity was stimulated in both haired and hairless neonates; but epidermal hyperplasia occurred only in the hairless, not the haired newborns.     

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.     

Murine auricular transepidermal water loss -- a novel approach for evaluating irritant skin reaction in mice

The standard method for evaluating contact allergy in mice is the ear swelling technique. However, in experimental irritant contact dermatitis, the epidermal barrier disruption, that represents a predominant effect of irritants, cannot be assayed by this METHOD: An appropriate method to evaluate barrier disruption is the measurement of transepidermal water loss (TEWL) but to date this has so far been possible only on the trunk of hairless or shaved mice. We therefore developed a new technique to measure the TEWL of mice ears (murine auricular TEWL: MATEWL). After patch testing with irritants and allergens, respectively, we found that the ear swelling method is most suitable for evaluating allergic skin reactions, whereas MATEWL is most appropriate for evaluating irritant skin reactions.     

A new animal model for contact dermatitis: the hairless guinea pig.

Allergic and irritant contact reactions were evaluated in the recently identified hairless guinea pig, Crl:IAF(HA)BR, a mutant from the Hartley strain. The cutaneous changes were observed macro- and microscopically. The irritant contact dermatitis was induced by croton oil, 2,4-dinitrochlorobenzene (DNCB), or anthralin. Both hairless and hairy guinea pigs developed similar reactions to these chemicals. The density of the epidermal Langerhans cells (LC) of hairless guinea pigs was significantly higher than that in the hairy strain. Allergic contact sensitization was easily induced with DNCB. Photoallergic contact sensitization was also induced with tetrachlorosalicylanilide (TCSA) but not with tribromosalicylanilide (TBS). However, by administration of cyclophosphamide before sensitization, positive photocontact responses were seen with TBS. These results indicate that hairless guinea pigs can be used as animal models for investigation of immunologic and nonimmunologic contact reactions.     

The hairless guinea pig as an experimental animal for photodermatology.

Photobiologic reactions to various modalities of ultraviolet light (UVL) irradiation were evaluated in the recently identified hairless guinea pig, Crl: IAF(HA)BR, a mutant from the Hartley strain. The cutaneous changes were observed macro- and microscopically. The animal developed similar but somewhat stronger reactions than the Hartley guinea pig to the UVB irradiation and topical and systemic PUVA treatments. The density of the epidermal Langerhans cell of the hairless guinea pig was significantly higher than that of the hairy strain. The photoallergic contact sensitization was easily induced by tetrachlorosalicylanilide. These results indicate that the hairless guinea pig can be used as an animal model for photobiologic and photoimmunologic investigations.     

Differential irritant skin responses to tandem application of topical retinoic acid and sodium lauryl sulphate: II. Effect of time between first and second exposure

In clinical practice, the cutaneous exposure to chemical irritants such as surfactants and topical drugs is frequent. Topical all-trans retinoic acid (RA) is often associated with irritation and induces epidermal changes similar to those produced by sodium lauryl sulphate (SLS). Using bioengineering techniques, e.g. assessing transepidermal water loss (TEWL), capacitance and chromametry, we investigated the variations of the skin response to SLS and RA and to both chemicals applied sequentially, allowing different time periods (from 1 h to 2 weeks) between applications of SLS and RA. Both chemicals caused irritation as assessed by visual scoring, but the values from the objective variables differed at different time periods. TEWL increased dramatically shortly after applying SLS but the increase was delayed after RA. After applying SLS, the capacitance generally decreased then returned to basal values; treatment with RA produced an overall increase. Only the results from chromametry were similar. After tandem application, the drugs were synergistic for all variables except capacitance, showing an antagonistic interaction for skin hydration. These results suggest that non-specific skin irritation profoundly reflects different mechanisms of action at tissue level. With sequential application, SLS injury modified the response to RA for at least 1 week after applying SLS. These late effects of detergents should be considered when studying irritant chemical interactions and in developing strategies for the management of occupational and other irritant dermatitis.     

Cutaneous toxicity of chemical irritants on hairless Guinea pigs

To evaluate the toxicity of irritant chemicals on animal skin, investigators have frequently had to apply high concentrations, owing to the fact that its susceptibility is less than that of human skin. High concentrations are so damaging to tissue that specific effects are obscured on the various layers. The aim of the present study was to elucidate the effects of a variety of irritating chemicals on the skin of hairless guinea pigs. Graded concentrations of these irritating substances were applied to the back for varying periods. Histologic changes were analyzed by light and electron microscopy. The structural alterations varied greatly among the chemicals, reflecting quite different mechanisms of action. Hairless guinea pigs are quite susceptible to chemical injury, especially to their hair follicles and dermal components. The hairless guinea pig appears to be an advantageous model to assess the acute and chronic effects of chemical irritants.     

Skin reactions to irritants assessed by non-invasive bioengineering methods

Pathophysiological components of irritant contact dermatitis caused by 3 chemically-different irritants were investigated. 20 healthy volunteers were patch tested with sodium lauryl sulphate, nonanoic acid and hydrochloric acid on the flexor side of the upper arm. The skin response was evaluated after 24, 48 and 96 h by visual scoring and measured by the following bioengineering methods: transepidermal water loss measurement, electrical conductance for measurement of skin hydration, laser Doppler flowmetry for measurement of cutaneous blood flow and 20 MHz ultrasound A-scan for measurement of skin thickness. In spite of homogeneous inflammatory responses, significant differences in the severity of the injury to the skin barrier function caused by the different irritants were found. Also significant differences between irritants were found in the time course of development of maximum irritant reactions. Bioengineering methods indicating inflammatory responses (measurement of blood flow and skin thickness) were helpful in quantifying the irritant response in general, while bioengineering methods indicating epidermal damage (measurement of TEWL and electrical conductance) were helpful in classifying the individual irritants.     

Long-term repetitive sodium lauryl sulfate-induced irritation of the skin: an in vivo study

Skin may adapt to topical irritants through accommodation. This study focuses on long-term exposure to irritants and attempts to demonstrate accommodation. Sodium lauryl sulfate (SLS) induced irritant contact dermatitis at 3 concentrations (0.025% to 0.075%). Distilled water, acetone and an empty chamber served as controls. Experimental compounds were applied to forearms of 7 healthy volunteers for 24 hr before replacing by a fresh chamber for 6 non-consecutive weeks over 103 days. Possible accommodation was quantified by visual scoring (erythema and dryness) and by bioengineering parameters: transepidermal water loss (TEWL), capacitance, chromametry and laser Doppler flowmetry (LDF). Significant erythema, dryness, elevated TEWL, skin colour reflectance and LDF values occurred during the exposure periods. Upon repeat exposure, an immediate and augmented response in erythema, TEWL, skin colour reflectance and LDF developed. However, irritant skin changes were not sustained. Irritation parameters return to baseline after cessation of exposure. There was no evidence of sustained irritation or accommodation after the last exposure. Study findings do not document sustained accommodation or adaptive hyposensitivity after long-term repetitive irritant exposure under these test conditions. Alternative models should be developed to prove or disprove the accommodation hypothesis.     

Effects of glycerol on human skin damaged by acute sodium lauryl sulphate treatment

Glycerol, widely used as humectant, is known to protect against irritants and to accelerate recovery of irritated skin. However, most studies were done with topical formulations (i.e. emulsions) containing glycerol in relatively high amounts, preventing drawing conclusions from direct effects. In this study, acute chemical irritations were performed on the forearm with application of a 10% sodium lauryl sulphate (SLS) aqueous solution under occlusion for 3 h. Then, glycerol aqueous solutions from 1 to 10% were applied under occlusion for 3 h. After elimination of moist excess consecutive to occlusive condition, in ambient air for 15 and 30 min, skin barrier function was investigated by dual measurement of skin hydration and transepidermal water loss (TEWL). Treatments with SLS solution under occlusion significantly increased TEWL and decreased skin hydration as assessed by capacitance measurements. The SLS irritant property was raised by the occlusion and the water barrier function as well as water content appeared impaired. Recovery with glycerol at low doses was remarkable through a mechanism that implies its hygroscopic properties and which is saturable. This precocious effect acts through skin rehydration by enhancing water-holding capacity of stratum corneum that would facilitate the late physiological repair of impaired skin barrier. Thus, glycerol appears to substitute for natural moisturizing factors that have been washed out by the detergent action of SLS, enhancing skin hydration but without restoring skin barrier function as depicted by TEWL values that remained high. Thus, irritant contact dermatitis treated with glycerol application compensate for skin dehydration, favouring physiological process to restore water barrier function of the impaired skin. Empirical use of glycerol added topical formulations onto detergent altered skin was substantiated in the present physicochemical approach.     

Experimental irritant contact dermatitis due to cumulative epicutaneous exposure to sodium lauryl sulphate and toluene: single and concurrent application

In clinical practice, cutaneous exposure to a variety of irritants such as surfactants and solvents is frequent. Although the induction of irritant dermatitis by single irritants has been extensively studied in recent years, our knowledge of the effects of simultaneous application of different irritants is limited. Using non-invasive techniques for measurements of transepidermal water loss (TEWL) and skin colour reflectance, we quantified the irritant effects of single and concurrent application of 0.5% sodium lauryl sulphate (SLS) and undiluted toluene (TOL) in vivo. The irritants were applied twice daily for 30 min to the volar forearms of 20 volunteers. Repeated application of SLS and TOL induced an irritant reaction, as indicated by an increase in TEWL and skin redness. In contrast to SLS alone, the application of TOL alone induced only a moderate increase in TEWL, confirming previous results. Concurrent application of SLS/TOL and TOL/SLS induced significantly stronger reactions than those caused by twice daily application of each irritant on its own. Our results demonstrate that a mixed application of an anionic detergent and an organic solvent has an additive effect on skin irritation. It is suggested that pretreatment with SLS causes an increased susceptibility to TOL irritation and vice versa. Thus, the necessity for special precautions against skin absorption of TOL when handling detergents such as SLS is emphasized.     

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.     

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.     

Experimental study of cutaneous tolerance to glycol ethers

We tried out the potential irritant and sensitizing effect of the main glycol ethers found in industrial and consumer products. Cutaneous irritation was determined in the rabbit following the EEC method (European Economic Communities) and the Draize protocol, and the sensitizing effect was evaluated in the guinea pig by the maximized Magnusson and Kligman method. The results showed no delayed cutaneous hypersensitivity, and all glycol ethers studied were classified from slightly irritant to severely irritant according to the Draize protocol, though only 2–butoxyethanol and isopropoxyethanol were classified as skin irritants with the EEC method. Glycol ethers should be handled with all the care that should be taken in the safe use of organic solvents.     

Topical application of artesunate on guinea pig allergic contact dermatitis

Artesunate is derived from the Chinese medicinal herb qinghao. Many animal studies suggest that systemic artesunate has immunoregulatory activity. We investigated the effect of topical artesunate on contact sensitivity in guinea pigs sensitized with DNCB. Female hairless guinea pigs were used and the contact reaction graded by visual (5 point) score and erythema measured with a color analyzer. Topical artesunate inhibited the elicitation reaction of contact hypersensitivity when given at the 1st and 12th h after challenge ( p < 0.05), but showed no effect when given from day 3 to day I before challenge ( p > 0.05). Artesunate had no effect on toxic (irritant) contact dermatitis from 20% croton oil ( p > 0.05). The results indicate that topical application of artesunate may offer a novel treatment of allergic contact dermatitis and other cutaneous immune-mediated disorders.