Skin irritation and sensitization: mechanisms and new approaches for risk assessment. 1. Skin irritation

Cutaneous irritation presents a major health problem with serious social and occupational impact. The interaction between an irritant and the human skin depends on multiple factors: the intrinsic properties and the nature of the irritant itself, and specific individual- and environment-related variables. The main pathological mechanisms of irritancy include skin barrier disruption, induction of a cytokine cascade and involvement of the oxidative stress network; all of them resulting in a visible or subclinical inflammatory reaction. In vivo, different non-invasive parameters for the evaluation of skin irritation and irritant potential of compounds and their specific formulations have been introduced, such as epidermal barrier function, skin hydration, surface pH, lipid composition, skin colour and skin blood flow. The diverse physiological changes caused by irritating agents require implementation of a multiparametric approach in the evaluation of cutaneous irritancy.     

Sensory irritation: risk assessment approaches

Irritation of eyes and upper airways--sensory irritation--is commonly used as a parameter for setting occupational exposure limits and is a common complaint in occupants of non-industrial buildings. Sensory irritation occurs from stimulation of receptors on trigeminal nerves. In general, chemically reactive compounds are more potent than non-reactive congeners. Animal studies allow prediction of sensory irritation effects in humans; the concentration-effect relationships are often steep. In humans, thresholds and suprathreshold effects can be obtained from short-term ( approximately seconds) exposures and from longer exposures ( approximately hours). Sensory irritation may develop over time and odour cues may influence reported sensory irritation symptoms; generally, the slope of the irritant effect is steeper than the slope of odour cues. A best available no-observed-adverse-effect level (NOAEL) should be based on a combined estimate from the three types of study. The NOAEL/5 is considered sufficient to protect individuals not especially sensitive. The present knowledge suggests that especially sensitive individuals may be protected by an additional uncertainty factor (UF) of 2, suggesting a combined UF of 10. In published studies, the combined UF is up to 300, highlighting the need of evidence-based UFs. Combined effects of sensory irritants can be considered additive as a first approximation.     

马钱子巴布剂对皮肤刺激性和过敏性实验研究

目的探究马钱子巴布剂是否有皮肤刺激性和致敏性。方法以新西兰白兔为模型进行一次给药皮肤刺激和多次给药皮肤刺激实验,以豚鼠为模型观察巴布剂的皮肤致敏作用。结果马钱子巴布剂对新西兰白兔皮肤未见任何刺激作用,也不会引起豚鼠出现皮肤过敏反应。结论马钱子巴布剂是一种比较安全的外用新剂型。     

Skin sensitization testing in potency and risk assessment.

The purpose of this article is to review, and make recommendations for, the use of relevant skin sensitization test methods, for the purposes of determination of relative potency and the threshold dose necessary for the induction of skin sensitization, and for risk assessment. In addressing the first area, the utility of three guinea pig tests (the guinea pig maximization test, the occluded patch test, and the open epicutaneous test) of the local lymph node assay (LLNA) and of human volunteer testing for the assessment of relative potency and identification of thresholds for sensitization were considered. The following conclusions were drawn. (1) Although attempts have been made to modify the guinea pig maximization test for the purposes of deriving dose-response relationships, this method is usually unsuitable for determination of relative sensitizing potency. (2) Guinea pig methods that do not require the use of adjuvant and which employ a relevant route of exposure (the occluded patch test and the open epicutaneous test) are more appropriate for the assessment of relative skin-sensitizing potency. (3) The LLNA is suitable for the determination of relative skin sensitizing potency, and the adaptation of this method for derivation of comparative criteria such as EC3 values (the estimated concentration of test chemical required to induce a stimulation index of 3 in the LLNA) provides an effective and quantitative basis for such measurements. (4) For all the methods identified above, potency is assessed relative to other chemical allergens of known skin sensitizing potential. The estimation of likely threshold concentrations is dependent upon the availability of suitable benchmark chemicals of known potency for human sensitization. (5) Human testing (and specifically, the Human Repeat Insult Patch Test) can provide information of value in confirming the absence of skin sensitizing activity of formulations and products under specific conditions of use and exposure. Based on the above, the following recommendations are made. (1) If results are already available from suitable guinea pig tests, then judicious interpretation of the data may provide information of value in assessing relative skin sensitizing potency. This option should be explored before other analyses are conducted. (2) The LLNA is the recommended method for new assessments of relative potency, and/or for the investigation of the influence of vehicle or formulation on skin sensitizing potency. (3) Whenever available, human skin sensitization data should be incorporated into an assessment of relative potency. With respect to risk assessment, the conclusion drawn is that all the available data on skin-sensitizing activity in animals and man should be integrated into the risk-assessment process. Appropriate interpretation of existing data from suitable guinea pig studies can provide valuable information with respect to potency, as the first step in the development of a risk assessment. However, for de novo investigations, the LLNA is the method favored for providing quantitative estimations of skin-sensitizing potency that are best suited to the risk assessment process. Finally, human testing is of value in the risk assessment process, but is performed only for the purposes of confirming product safety.     

Skin sensitization quantitative risk assessment: A review of underlying assumptions

Toxicological risk assessment informs exposure limits, so the potential for adverse effects to human health are minimised or avoided. For skin sensitisers, the situation is complicated by asymptomatic induction of contact allergy, a necessary prerequisite for expression of the disease allergic contact dermatitis (ACD). For fragrance skin sensitisers, the development of quantitative risk assessment (QRA) arose from the need to improve the extent to which contact allergy occurred. However, the perceived impact has been less than anticipated. Accordingly, the science and assumptions upon which QRA was founded have been scrutinised and proposals for refinement have been made. In addition, areas of uncertainty have been made explicit, e.g. inter-individual variability and the impact of concomitant disease, clarifying where numerical safety assessment factors are based on expert judgement. Also, the relatively small contribution of factors eg. age, gender, ethnic origin, vehicle matrix and skin permeability are highlighted by reference to the (now controversial) human experiments carried out in the second half of the last century. Adoption and widespread implementation of the current recommendations for QRA, taken in concert with improved assessment of aggregate exposure from multiple sources, should ensure that the frequency of contact allergy will decrease over the coming years.     

Potential new approaches for children's inhalation risk assessment

The U.S. Environmental Protection Agency (EPA) practice of risk assessment is moving toward more thoroughly considering children's unique susceptibilities and exposure potential. Childhood is assessed as a sequence of life stages that reflects the fact that as humans develop, windows of susceptibility may appear that lead to enhanced sensitivity to exposure of environmental agents, while changes in behavior and physiology may increase exposure and dose. The U.S. EPA developed guidance in the past few years that addresses some aspects of increased susceptibility and exposure and dose. However, when it comes to considering inhalation exposure, dose, and risk, current U.S. EPA practice does not explicitly address children. The purpose here is to begin studying the adequacy of practice for children's health and to explore possible next steps in developing new methods to more accurately assess life-stage-specific differences. The existing guidelines and policies used to address potentially unique susceptibilities of children for inhaled environmental chemicals were considered, as well as what may be learned from examples of approaches that have been applied by state agencies (such as the California Environmental Protection Agency) or in the literature, to incorporate potentially unique susceptibilities and exposures to children. Finally, there is a discussion of possible approaches for considering inhalation exposure and susceptibility in U.S. EPA risk assessments.     

Integrated testing and assessment approaches for skin sensitization: a commentary

A Bayesian integrated testing strategy (ITS) approach, aiming to assess skin sensitization potency, has been presented, in which data from various types of in vitro assays are integrated and assessed in combination for their ability to predict in vivo skin sensitization data. Here we discuss this approach and compare it to our quantitative mechanistic modeling (QMM) approach based on physical organic chemistry. The main findings of the Bayesian study are consistent with our chemistry‐based approach and our previously published assessment of the key determinants of sensitization potency, in particular the relatively high predictive value found for chemical reactivity data and the relatively low predictive value for bioavailability parameters. As it stands at present the Bayesian approach does not utilize the full range of predictive capability that is already available, and aims only to assign potency categories rather than numerical potency values per se. In contrast, for many chemicals the QMM approach can already provide numerical potency predictions. However, the Bayesian approach may have potential for those chemicals where a chemistry modeling approach cannot provide a complete answer (e.g. pro‐electrophiles whose in cutaneo activation cannot currently be modeled confidently). Nonetheless, our main message is of the importance of leveraging chemistry insights and read‐across approaches to the fullest extent possible. Copyright © 2013 John Wiley & Sons, Ltd.     

Acute irritation tests in risk assessment

The two most important elements in assessing the risk of topical injury from a chemical are its biological properties, in the context of skin and mucous membrane damage, and the likelihood and likely nature of topical contact with the chemical. Appropriate biological tests in model systems should be based on the probable circumstances of exposure. Topical contact takes place under two distinct sets of circumstances--intentional and accidental. Chemicals that are intended to come into contact with skin and mucous membranes include cosmetics and dermatological preparations. For such compounds the frequency and extent of skin contact is predictable and any irritant effects are unacceptable. The absence of irritant effects is established by testing in human volunteers or experimental animals. Since animal skin and mucous membranes are more susceptible to irritants than those of man, the amounts or concentrations tested need not be greater than those intended for human use. It is hoped that validated alternatives to animal models will soon be available. For household or industrial chemicals where skin and/or mucous-membrane contact occurs accidentally, topical contact should generally be avoided. In such cases the objective of irritancy testing should be to establish which compounds are particularly irritant and therefore need extra care in handling. We are convinced that this latter objective can be achieved by simpler and less cruel tests than the Draize eye-irritation test.     

Respiratory sensitization: Advances in assessing the risk of respiratory inflammation and irritation

Respiratory sensitization provides a case study for a new approach to chemical safety evaluation, as the prevalence of respiratory sensitization has increased considerably over the last decades, but animal and/or human experimental/predictive models are not currently available. Therefore, the goal of a working group was to design a road map to develop an ASAT approach for respiratory sensitisers. This approach should aim at (i) creating a database on respiratory functional biology and toxicology, (ii) applying data analyses to understand the multi-dimensional sensitization response, and how this predisposes to respiratory inflammation and irritation, and (iii) building a systems model out of these analyses, adding pharmacokinetic–pharmacodynamic modeling to predict respiratory responses to low levels of sensitisers. To this end, the best way forward would be to follow an integrated testing approach. Experimental research should be targeted to (i) QSAR-type approaches to relate potential as a respiratory sensitizer to its chemical structure, (ii) in vitro models and (iii) in vitro–in vivo extrapolation/validation.     

Methyldibromoglutaronitrile: skin sensitization and quantitative risk assessment

Preservatives can be a frequent cause of allergic contact dermatitis (ACD). A quantitative risk assessment (QRA) method for identifying safe exposure levels has been suggested as a more effective tool for this purpose. This work assesses the validity of QRA by its retrospective application to the sensitizing preservative methyldibromoglutaronitrile (MDGN), which has recently been associated with unacceptable exposure levels in consumer products. Using a recently published QRA analysis of 4 preservatives in 5 consumer product types, the accuracy of the predictions for MDGN was assessed in light of what is known clinically about the nature and incidence of ACD to this material. Based on a local lymph node assay (LLNA) EC3 value (concentration of test chemical required to provoke a 3-fold increase in lymph node cell proliferation) of 0.9% in a weight-of-evidence approach to the identification of thresholds for the induction of skin sensitization, it can be determined that the acceptable levels of exposure to MDGN in a range of products range from as little as 25 ppm to in excess of 10,000 ppm. Thus, proactive use of QRA, used conservatively and in combination with expert judgment, would have limited the problem of ACD to this new preservative that is known to have caused problems on the consumer market.     

Skin moisturization mechanisms: new data

The main function of the skin is to protect the body against exogenous substances and excessive water loss. The skin barrier is located in the outermost layer of the skin, called the stratum corneum, which is composed of corneocytes, originating from the keratinocytes differentiation process, embedded in organized complex lipid domains. Moisturizing of the skin is recognized as the first anti-aging skin care. Skin moisturization is essential for its appearance, protection, complexion, softness and the reinforcement of its barrier properties against deleterious and exogenous environmental factors. The intrinsic water binding capacity of skin is not only due to the complex natural moisturizing factor present in corneocytes, but also to hyaluronic acid and a regulated water transport within the skin. Recent data shows that the water movements between the cells at the different levels of the epidermis are due to dedicated water and glycerol transport proteins named aquaporins. Their role in the skin moisturization is completed by corneodesmosomes and tight junctions. Water and pH are now shown to be of prime importance in the regulation of the epidermal enzymes linked to corneocytes desquamation and lipid synthesis. Furthermore, the level of moisturization of the skin is important in its protection against repeated exposure to various irritant agents or phenomena such as very frequent washing with strong tensioactive materials.     

Skin sensitization in chemical risk assessment: report of a WHO/IPCS international workshop focusing on dose-response assessment

An international workshop was held in 2006 to evaluate experimental techniques for hazard identification and hazard characterization of sensitizing agents in terms of their ability to produce data, including dose-response information, to inform risk assessment. Human testing to identify skin sensitizers is discouraged for ethical reasons. Animal-free alternatives, such as quantitative structure-activity relationships and in vitro testing approaches, have not been sufficiently developed for such application. Guinea pig tests do not generally include dose-response assessment and are therefore not designed for the assessment of potency, defined as the relative ability of a chemical to induce sensitization in a previously naive individual. In contrast, the mouse local lymph node assay does include dose-response assessment and is appropriate for this purpose. Epidemiological evidence can be used only under certain circumstances for the evaluation of the sensitizing potency of chemicals, as it reflects degree of exposure as well as intrinsic potency. Nevertheless, human diagnostic patch test data and quantitative elicitation data have provided very important information in reducing allergic contact dermatitis risk and sensitization in the general population. It is therefore recommended that clinical data, particularly dose-response data derived from sensitized patients, be included in risk assessment.     

Cardiac sensitization: methodology and interpretation in risk assessment

An increased sensitivity of the heart to endogenous epinephrine (adrenaline), a phenomenon referred to as cardiac sensitization, has long been recognized as a risk during exposure to hydrocarbons, principally halogenated hydrocarbons. Cardiac sensitization, which can result in serious arrhythmia and death, requires a certain critical blood level of both the sensitizing agent and epinephrine. The original research and methods utilized an exogenous epinephrine challenge during inhalation exposure to a chemical to assess cardiac sensitization potential in Beagle dogs. These screening tests were developed about 30 years ago, although in the last 15 years some modifications of these methods have occurred in response to testing chlorofluorocarbon (CFC) replacements. Results from these experimental cardiac sensitization studies have been used for semi-quantitative risk evaluation for occupational exposures but now are being used more quantitatively for regulatory purposes. The risks associated with cardiac sensitization from CFC replacements are unknown but expected to be low based on cardiac sensitization studies in the 1970s where dogs were made to generate their own adrenaline. With the advent of physiologically based pharmacokinetic (PBPK) modeling, greater emphasis is being placed on quantitative risk assessment for cardiac sensitization. In this investigation, we have examined the various methodologies used for detection of cardiac sensitization and discussed their limitations and advantages. In addition, we examined the potential concerns involved in using experimental cardiac sensitization data and PBPK modeling to predict exposure scenarios.     

A risk assessment process for allergic contact sensitization

This review describes an approach that has been used to assess the skin sensitization risk of new chemicals and product formulations prior to launching the new chemical or product on the market. The risk assessment process utilizes a comparative toxicological approach, in which data on the inherent toxicity of a material, and the exposure to it through manufacturing or consumer use or foreseeable misuse, are integrated and compared with data generated by 'benchmark' materials of similar chemistry or product application, or both. This approach has been valuable in providing an accurate assessment of the skin sensitization potential for a wide range of consumer products and pharmaceuticals, ranging from products with a very transient skin exposure (e.g. some paper products), to cosmetics, to products whose ingredients may be deposited on fabrics and thus result in chronic skin exposure. The risk assessment process described includes both guinea-pig (Buehler) and human skin sensitization test methodologies to evaluate inherent toxicity under relevant epicutaneous exposure conditions. Alternative guinea-pig test methods have been reported to be more sensitive than the Buehler method, particularly those employing intradermal injection of the test material in Freund's complete adjuvant (e.g. maximization test). However, by bypassing the skin barrier at induction, these methods can overstate the sensitization risk of epicutaneous exposure to weak sensitizers (Andersen and Hamann, 1983 and 1984; Matsushita et al., 1975a,b), and can understate the risk to very strong sensitizers possibly through tolerance induction (Buehler, 1985). In addition, materials are tested and classified at concentrations that may not be relevant to anticipated human exposure. The Buehler guinea-pig test data are important in assessing skin sensitization risk in the early phases of product development, where human exposure can be limited, controlled and monitored (e.g. manufacturing employees). The Buehler test can often define consumer skin sensitization risk; however, the ultimate consumer skin safety assessment should in general be developed through a series of controlled human tests; the human repeat insult patch test and, when necessary, the provocative or extended product use tests. Post-market monitoring of skin-related consumer comments is the final phase of the data gathering process. These results can be used to assess further each product and to provide valuable feedback to confirm the validity of the overall risk assessment process. Risk assessment for skin sensitization potential is seldom a simple process.(ABSTRACT TRUNCATED AT 400 WORDS)     

Quantitative component analysis of mixtures for risk assessment: application to eye irritation

A methodology called quantitative component analysis of mixtures (QCAM) was used to analyze an existing set of product formulation data to determine if the irritating ingredients in the mixtures could be identified. Eye irritation scores, based on a rat model, for 18 mixtures having a composite total of 37 components, were analyzed by QCAM. QCAM relates a net toxicity measure of a mixture to the toxicities of the individual components of the mixture through linear, quadratic, and pairwise cross-component concentration-dependent interactions. A correlation model is established using a particular genetic algorithm employing either multidimensional linear regression or partial least-squares regression fitting. Cornea eye irritation and average eye irritation are well-explained in terms of a linear model of, at most, three components over the set of mixtures. Moreover, extensive cornea and average eye irritations are due to only one of these three components of the mixtures. Also, one of the three significant components was predicted to decrease the extent of eye irritation, and subsequently identified as an "anti-irritant" in contact lens solutions. A reasonable linear correlation model could also be developed for conjunctiva irritation, but no significant iris irritation model could be constructed. The addition of quadratic and/or cross-component concentration terms to a linear correlation model did not statistically improve the overall resultant model. The QCAM models permit estimation of the intrinsic (self) toxicity of each of the components of a mixture, and may aid in the reduction, and ultimate elimination, of the need for animal eye irritation studies.     

Proposal for a risk assessment methodology for skin sensitization based on sensitization potency data

In this paper, we propose a quantitative risk assessment methodology for skin sensitization aiming at the derivation of 'safe' exposure levels for sensitizing chemicals, used e.g., as ingredients in consumer products. Given the limited number of sensitizers tested in human sensitization tests, such as the human repeat-insult patch test (HRIPT) or the human maximization test (HMT), we used EC3 values from the local lymph node assay (LLNA) in mice because they provide the best quantitative measure of the skin sensitizing potency of a chemical. A comparison of LLNA EC3 values with HRIPT and HMT LOEL, and NOEL values was carried out and revealed that the EC3, expressed as area dose, can be used as a surrogate value for the human NOEL in risk assessment. The uncertainty/extrapolation factor approach was used to derive (a) an 'acceptable non-sensitizing area dose' (ANSAD) to protect non-allergic individuals against skin sensitization and (b) an 'acceptable non-eliciting area dose' (ANEAD) to protect allergic individuals against elicitation of allergic contact dermatitis. For ANSAD derivation, interspecies, intraspecies and time extrapolation factors are applied to the LLNA EC3. For ANEAD derivation, additional application of a variable sensitization-elicitation extrapolation factor is proposed. Values for extrapolation factors are derived and discussed, the proposed methodology is applied to the sensitizers methylchloroisothiazolinone/methylisothiazolinone, cinnamic aldehyde and nickel and results are compared to published risk assessments.     

Skin sensitization risk assessment model using artificial neural network analysis of data from multiple in vitro assays

The sensitizing potential of chemicals is usually identified and characterized using in vivo methods such as the murine local lymph node assay (LLNA). Due to regulatory constraints and ethical concerns, alternatives to animal testing are needed to predict skin sensitization potential of chemicals. For this purpose, combined evaluation using multiple in vitro and in silico parameters that reflect different aspects of the sensitization process seems promising.We previously reported that LLNA thresholds could be well predicted by using an artificial neural network (ANN) model, designated iSENS ver.1 (integrating in vitro sensitization tests version 1), to analyze data obtained from two in vitro tests: the human Cell Line Activation Test (h-CLAT) and the SH test. Here, we present a more advanced ANN model, iSENS ver.2, which additionally utilizes the results of antioxidant response element (ARE) assay and the octanol–water partition coefficient (Log P, reflecting lipid solubility and skin absorption). We found a good correlation between predicted LLNA thresholds calculated by iSENS ver.2 and reported values. The predictive performance of iSENS ver.2 was superior to that of iSENS ver.1. We conclude that ANN analysis of data from multiple in vitro assays is a useful approach for risk assessment of chemicals for skin sensitization.     

Adiponectin and cardiovascular disease: mechanisms and new therapeutic approaches

Adiponectin is an abundant plasma protein secreted from adipocytes. Its role in energy homeostasis is well-known, including the regulation of hydrocarbons and lipids metabolism as well as the improvement of insulin resistance. It has been thought to be a key molecule in the development of type 2 diabetes mellitus and metabolic syndrome, which are epidemiological targets for preventing cardiovascular disease. In addition to beneficial metabolic effects, adiponectin seems to have anti-inflammatory, anti-atherosclerotic and vasoprotective actions. Furthermore, adiponectin affects signalling in myocardial cells and exerts beneficial actions on the heart after pressure overload and ischemia-reperfusion injury. The ability of adiponectin to reduce insulin resistance in conjunction with its antiinflammatory and cardioprotective properties makes this adipocytokine a promising therapeutic target. On clinical interest, agents that enhance endogenous adiponectin production or action have potential for the treatment of cardiovascular disease. Management strategies that increase adiponectin levels include weight reduction, Mediterranean diet, thiazolidinediones, antihypertensive and lipid lowering drugs. Current knowledge on the main actions of adiponectin and therapeutic approaches for cardiovascular disease is summarized in this review.