An arm immersion model of compromised skin (I). Influence on irritation reactions

Inorganic ions in the skin: Allies or enemies?

Skin constitutes a barrier protecting the organism against physical and chemical factors. Therefore, it is constantly exposed to the xenobiotics, including inorganic ions that are ubiquitous in the environment. Some of them play important roles in homeostasis and regulatory functions of the body, also in the skin, while others can be considered dangerous. Many authors have shown that inorganic ions could penetrate inside the skin and possibly induce local effects. In this review, we give an account of the current knowledge on the effects of skin exposure to inorganic ions. Beneficial effects on skin conditions related to the use of thermal spring waters are discussed together with the application of aluminium in underarm hygiene products and silver salts in treatment of difficult wounds. Finally, the potential consequences of dermal exposure to topical sensitizers and harmful heavy ions including radionuclides are discussed.

Assessment of sensitization potential of monoterpenes using the rat popliteal lymph node assay

The popliteal lymph node assay (PLNA) has been proposed as a screening test for detecting chemicals with potential of inducing allergic and auto-immune-like reactions in humans. In the present study, we used the rat PLNA to evaluate the immuno-sensitizing potential of 10 monoterpenes found in the essential oils of a variety of aromatic, edible and medicinal plants. The primary or direct PLNA was performed with the monoterpenes, and chlorpromazine (CPZ) and barbital were used as positive and negative controls, respectively. Female, 7-8 week-old Wistar rats were injected subcutaneously (50 microL) with the test substance (0.5, 2.5 or 5mg) into the right hind footpad while the contralateral footpad was injected with the vehicle (DMSO) alone. Weight (WI) and cellularity (CI) indices for draining PLNs were determined 7 days after treatment. PLNA was positive (WI >or= 2 and CI >or= 5) for CPZ, citral, alpha-terpinene, beta-myrcene and (-)-alpha-pinene, and negative for barbital, DMSO, (-)-menthol, 1,8-cineole, (+/-) citronellal, (+)-limonene, (+/-) camphor and terpineol. A secondary PLNA, a T-cell priming test, was carried out with the four substances that had been positive in the primary assay. Six weeks after being locally primed with 5 mg/paw, rats were sc injected into the same footpad with a dose (0.5 mg/paw) of the substance that had been previously found to be insufficient to cause a positive response. WI and CI were then calculated 4 and 7 days after the second injection. CPZ was also positive in the secondary assay thereby confirming that it is a sensitizing agent. Citral, alpha-terpinene, beta-myrcene and (-)-alpha-pinene, however, were negative in the secondary assay. In summary, citral, alpha-terpinene, beta-myrcene and (-)-alpha-pinene induced a clear immuno-stimulatory response due to their irritant properties but no monoterpene proved to be a sensitizing agent in the PLNA.

Are we reaching the limits or our ability to detect skin effects with our current testing and measuring methods for consumer products?

Testing for potential adverse skin effects is a key part of both the overall safety assessment for many consumer products and the evaluation of potential product improvements in mildness. Whilst modern tissue and paper products (i.e. facial tissues, catamenial products, baby wipes and baby and adult diapers) are inherently very mild to skin, current test methodology may not be robust enough to evaluate future improvements in such products. This article provides a commentary on several technologies we have been exploring to improve the sensitivity of test methods for tissue and paper products. The focus has been on three approaches: (i) further exaggerating exposure conditions using novel approaches to sample application, (ii) increasing the sensitivity of the manner in which we score for irritant effects, either visually or via instrumentation and (iii) quantitatively measuring additional endpoints, i.e. subjective sensory effects.

Development of a sensitive test method to evaluate mechanical irritation potential on mucosal skin

BACKGROUND/PURPOSE

The studies presented here are intended to continue the validation of the behind-the-knee test system developed to evaluate the mechanical irritation potential of products such as catemenial pads, baby and adult diapers (which are inherently non-irritating products/chemicals). These products are intended to be worn for prolonged periods of time on body sites that include the mucous membrane and non-keratinized epithelium in addition to normal squamous cell epithelium. These studies had two specific goals. The first was to validate the test model using a variety of conditions, including those that mimic the conditions that exist during normal product use. The second specific goal was to determine the most cost-effective protocol to use for screening different product executions for potential irritant effects. If the model proves to be reliable under a variety of conditions, it will be an ideal test system to use in claims support studies, where it is preferable to mimic use conditions as closely as possible. We were also interested in evaluating sensory responses that consumers often associate with irritation to determine if any of these sensations correlated with objective measures of irritation.

METHODS

Three test materials were used in these experiments. All three are commercially available catemenial pads that were expected to be similar, but not identical, in irritant properties based on subjective consumer reports of irritation associated with product use. Test materials were applied daily to the area behind the knee and held in place for 6 h by an elastic knee band of appropriate size. Irritation was graded 30-60 min after test product removal, and the following morning before application of the next sample. Two products were compared using four different protocol variations: dry product on intact skin, dry product on tape stripped (compromised) skin, wet product (i.e., product loaded with 8 mL of saline) on intact skin and wet product on compromised skin. An additional study compared the two products using two protocol variations (intact skin/dry product vs. compromised skin/wet product). In addition, a study (#5) was conducted to compare a third product applied wet on intact vs. compromised skin. In the final two studies, information was collected from the panelists on subjective sensations of irritation.

RESULTS

All four protocol variations were capable of detecting significant differences between the products. These differences were directionally similar to what was expected based on subjective consumer comments. In addition, a higher number of certain perceived sensory effects were reported for the more irritating product.

CONCLUSIONS

In these studies, Product A is more irritating than Product B when assessed objectively, i.e., by scoring irritation at the test sites, and subjectively, i.e., by evaluating reports of adverse sensations perceived by panelists. There is no clear relationship between specific test conditions, i.e., compromised skin and/or testing wet samples, and reports of perceived sensory reactions. However, some sensory reactions appear to be associated with higher levels of irritation. The most cost-effective protocol to use for screening for potential irritant effects for catemenial pads, baby and adult diapers is two 6-h sample applications on intact skin, with scoring in the afternoon 30 min after removal of the sample. For claims support testing, a variety of test conditions can be used in the behind-the-knee assay to mimic the exposure conditions for the product under evaluation, including using compromised (tape stripped) skin and wet product samples.

Citral a fragrance allergen and irritant

Citral is a well known contact allergen and a contact irritant. Routine patch testing in the past may have been restricted because of possible irritant (IR) patch test responses. 586 consecutive patients, with hand eczema, were patch tested with a selection of fragrances including citral 2% petrolatum and the European standard series. 28 of the patients showed a positive patch test reaction (+ to +++) to citral and 82 at least 1 IR patch test reaction and no positive patch test reaction to citral. A statistically significant association between a positive patch test reaction to citral and positive patch test reactions to other fragrances compared with IR reactions (n = 82) was established. The difference regarding fragrance history found between those with IR and positive reactions to citral was not significant. Citral could be an allergen and/or irritant, worthy of further more extensive studies.

Non-animal testing strategies for assessment of the skin corrosion and skin irritation potential of ingredients and finished products

The dermatotoxicologist today is faced with a dilemma. Protection of workers and consumers from skin toxicities (irritation and allergy) associated with exposure to products, and the ingredients they contain, requires toxicological skin testing prior to manufacture, transport, or marketing. Testing for skin corrosion or irritation has traditionally been conducted in animals, particularly in rabbits via the long established Draize test method. However, this procedure, among others, has been subject to criticism, both for its limited predictive capacity for human toxicity, as well as for its use of animals. In fact, legislation is pending in the European Union which would ban the sale of cosmetic products, the ingredients of which have been tested in animals. These considerations, and advancements in both in vitro skin biology and clinical testing, have helped drive an intensive effort among skin scientists to develop alternative test methods based either on in vitro test systems (e.g. using rat, pig or human skin ex vivo, or reconstructed human skin models) or ethical clinical approaches (human volunteer studies). Tools are now in place today to enable a thorough skin corrosion and irritation assessment of new ingredients and products without the need to test in animals. Herein, we describe general testing strategies and new test methods for the assessment of skin corrosion and irritation. The methods described, and utilized within industry today, provide a framework for the practicing toxicologist to support new product development initiatives through the use of reliable skin safety testing and risk assessment tools and strategies.

Investigation of the threshold for allergic reactivity to chromium

Allergy to chromium is relatively common, often in association with exposure to cement or in leather manufacture. However, in certain locations, there appears to be a relatively large cohort of chromium-sensitive individuals whose allergy cannot be explained by these common sources. In particular, this group include Israeli housewives with persistent hand eczema and concomitant patch test positivity to chromium. The causation of their allergy has been linked with relatively high levels of chromium contamination in household products. To provide further information in respect of the definition of safe levels for such products, we examined 17 chromium-allergic individuals to determine their threshold for reaction under closed patch test and repeated open application test (ROAT) conditions. The data derived indicated that, on normal skin, the patch test threshold was 10 ppm chromium; in the presence of an irritant (sodium lauryl sulfate) the threshold was closer to 1 ppm, 2/17 subjects giving 1+ reactions at this concentration. In the more realistic exposure conditions of the ROAT, 8/14 individuals failed to react to 50 ppm, whilst 3/15 reacted to 5 ppm. Interestingly, there was very poor correlation between patch test sensitivity and ROAT sensitivity. To ensure the large majority of chromium-allergic individuals do not suffer elicitation of their allergy, as well as to limit the development of new chromium-sensitive subjects, it is recommended that household products adhere to a previously published standard of a maximum limit of 5 ppm, with an ultimate target of 1 ppm contamination by chromium.

Comparison between 2 test models in evaluating the effect of a moisturizer on irritated human skin

The purpose of the present study was to compare 2 experimental models of moisturizer efficacy on the recovery of irritated skin on the hands and the volar forearms. 12 healthy volunteers had their hands immersed in sodium lauryl sulfate (SLS) 10 min 2x daily for 2 days, and at the same time the volunteers had patch tests with SLS (0.125%, 0.25% and 0.5%) applied on their forearms for 24 h. After irritation of the skin, the volunteers had a moisturizer applied on one arm/hand 3x daily for the following 9 days. The other arm/hand served as untreated control. Evaluation was done on days (D) 1, 3, 5, 8 and 12 by transepidermal water loss, electrical capacitance, laser Doppler flowmetry and DermaSpectrometry. Both models were found useful, and the moisturizer was found to accelerate regeneration of the skin barrier function in both the hands (D8, p<0.05) and the volar forearms (0.5% SLS, D5 and D8, p<0.01). When the forearm model is used in the present set-up, a relatively high concentration of SLS (>0.25%) should be used and evaluation measurements are best performed on D5-D8. The forearm model proved reliable and easy to handle and we suggest that this model is used in future studies on moisturizer evaluation.

Epidermal Langerhans cell apoptosis is induced in vivo by nonanoic acid but not by sodium lauryl sulphate

Exposure to irritants may cause chronic irritant contact dermatitis (ICD), characterized by irregular epidermal thickening and a predominantly dermal mononuclear cell infiltrate. The mechanisms involved, and why only certain individuals are affected, are not clearly understood. Different irritants may trigger different cellular and molecular interactions between resident skin cells and recruited inflammatory cells. In some individuals these interactions may become self-perpetuating resulting in persistent inflammation in the absence of continued exposure. This study examined Langerhans cell (LC) density in clinically normal skin of 46 patients with chronic ICD and 10 healthy individuals, and compared the action of the two irritants nonanoic acid (NA) and sodium lauryl sulphate (SLS) on the LCs and keratinocytes of clinically normal skin in patients with chronic ICD. There was a higher number of LCs/mm basement membrane in patients compared with controls, although there was no difference in the number of dendrites/LC nor in dendrite length. SLS induced keratinocyte proliferation after 48 h exposure, had no effect on LC number or distribution, and induced keratinocyte apoptosis after 24 and 48 h exposure. In contrast, NA decreased keratinocyte proliferation after 24 h exposure but this returned to basal levels after 48 h, and induced epidermal cell apoptosis after only 6 h exposure. NA dramatically decreased LC number after 24 and 48 h exposure, which was accompanied by basal redistribution and decreased dendrite length. Most significantly, NA induced apoptosis in over half of the LCs present after 24 and 48 h exposure.

Guidelines on sodium lauryl sulfate (SLS) exposure tests. A report from the Standardization Group of the European Society of Contact Dermatitis

This report reviews the clinical and histopathological reactions caused by sodium lauryl sulfate (SLS), and the non-invasive methods that can characterize these reactions. Furthermore, SLS exposure techniques and factors that may influence the outcome of these exposures are discussed. Finally, guidelines are introduced for each exposure technique in order to have a uniform approach to SLS testing in man. Since different study aims warrant different testing conditions, we have proposed 2 categories, namely susceptibility testing and provocative testing, tailored to the aim with which the study is performed.

Effect of glove occlusion on human skin. (I). short-term experimental exposure

Skin barrier function was studied after use of occlusive gloves on normal and compromised skin. 2 studies were performed (Study A and B), and the effects were evaluated by non-invasive methods. Participants in the studies were instructed to wear an occlusive glove on one hand, while the other hand served as control. The gloves used were hypoallergenic, non-latex. Study A: 20 volunteers wore a glove on normal skin 6 h/day for 3 days. Study B: 20 volunteers wore a glove on sodium lauryl sulfate(SLS)-compromised skin 6 h/day for 3 days. Skin barrier function was evaluated by measurement of transepidermal water loss (TEWL) (Evaporimeter), skin hydration by electrical capacitance (Corneometer) and inflammation was evaluated by erythema index (DermaSpectrometer).

RESULTS

Study A. Glove occlusion on normal skin 6 h/day for 3 days caused no significant influence on the water barrier function. Study B: Glove occlusion on SLS-compromised skin for the same period of time had a significantly negative effect on the water barrier function. It is concluded that occlusion may be an additional factor in the pathogenesis of cumulative irritant contact dermatitis.

Immediate vasoactive effect of citral on the adolescent rat ventral prostate

The vasoactive effect of a fragrance compound, citral, on rat ventral prostate is presented. A combined method of Indian-ink perfusion and postfixation transparency was used. One single dose of citral applied on the back skin of the rat induced an immediate triple response-like effect on the prostatic vascular bed. A slight vasodilatation appeared already after 2 1/2 min, followed by a marked vasoconstriction process after 5-min postcitral administration. Toward the period of 10 min, a second vasodilatation process was noted which persisted for the following 24 hr of observation. This study has demonstrated that changes in the microvascularization of the rat prostate can be estimated by counting the number of carbon-stained blood vessels. The results obtained by this technique are closely related with the findings in the vascular network profile of the macroangiographic observations. The mechanism of action of citral on the microvascularization of the rat ventral prostate is yet unknown. Based on the present findings, we suggest that the neoplastic capacity of citral upon the prostatic epithelia is activated via a nonspecific inflammatory reaction modulated either by local release of neurotransmitters or throughout a direct effect of citral on the endothelial cells.

The effect of repeated open exposure to low levels of nickel on compromised hand skin of nickel-allergic subjects

Nickel is a very common contact allergen, with some reports showing that more than 10% of women are affected. It is therefore important to be able to assess the risk of elicitation of nickel dermatitis in such individuals, particularly in relation to repeated exposure to low levels of this metal. It has been shown previously that under the conditions of a 48-h occluded patch test, some subjects will react to as little as 0.5 ppm nickel on compromised skin. In the present study, the effect of repeated open nickel application combined with repeated treatment with the anionic surfactant sodium dodecyl sulphate has been evaluated on the hand skin of 4 nickel-allergic subjects. Despite 2 of these being known to be particularly sensitive, there was no evidence of a nickel-allergic reaction following 2x daily immersion of hand skin sites in up to 1 ppm nickel over a period of 23 days.

An arm immersion model of compromised skin (II). Influence on minimal eliciting patch test concentrations of nickel

The transition metal nickel is a very common cause of allergic contact dermatitis (ACD). In the general population, adults with hand eczema have a high incidence of allergy to nickel, and nickel allergy is high in occupational dermatoses and is often linked to wet work. Nickel may be found as a trace contaminant in some consumer products, e.g., household cleaning agents. It has therefore been debated whether these levels, whilst not a primary cause, might be sufficient to maintain ACD. The minimal concentration of nickel in patch tests on normal skin that will elicit an allergic reaction in highly sensitised subjects is 1-10 ppm. This trial assessed whether reactivity to nickel was altered on compromised dorsal forearm skin and compared this to normal skin on the contralateral dorsal forearm and on the back. Skin damage consequent upon arm immersion in sodium dodecyl sulphate (SDS) greatly enhanced reactivity to nickel on the forearm, with the dorsal aspect reacting most both in number of reactions at each concentration and in the minimal eliciting concentration, which was 0.5 ppm in 2/20 under the conditions of a 48 h occluded patch.