Guinea pig maximization test

Chemical- and Drug-Induced Allergic, Inflammatory, and Autoimmune Diseases Via Haptenation

Haptens are small molecules that only elicit an immune response when bound to proteins. Haptens initially bind to self-proteins and activate innate immune responses by complex mechanisms via inflammatory cytokines and damage-associated molecular patterns and the subsequent upregulation of costimulatory signals such as cluster of differentiation 86 (CD86) on dendritic cells. Subsequent interactions between CD86 and CD28 on T cells are critically important for properly activating naive T cells and inducing interleukin 2 production, leading to the establishment of adaptive immunity via effector and memory T cells. Accumulating evidence revealed the involvement of haptens in the development of various autoimmune-like diseases such as allergic, inflammatory, and autoimmune diseases including allergic contact dermatitis, atopy, asthma, food allergy, inflammatory bowel diseases, hemolytic anemia, liver injury, leukoderma, and even antitumor immunity. Therefore, the development of in vitro testing alternatives to evaluate in advance whether a substance might lead to the development of these diseases is highly desirable. This review summarizes and discusses recent advances in chemical- and drug-induced allergic, inflammatory, and autoimmune diseases via haptenation and the possible molecular underlying mechanisms, as well as in vitro testing alternatives to evaluate in advance whether a substance might cause the development of these diseases.

Toward of Safer Phenylbutazone Derivatives by Exploration of Toxicity Mechanism

A drug design for safer phenylbutazone was been explored by reactivity and docking studies involving single electron transfer mechanism, as well as toxicological predictions. Several approaches about its structural properties were performed through quantum chemistry calculations at the B3LYP level of theory, together with the 6-31+G(d,p) basis sets. Molecular orbital and ionization potential were associated to electron donation capacity. The spin densities contribution showed a preferential hydroxylation at the para-positions of phenyl ring when compared to other positions. In addition, on electron abstractions the aromatic hydroxylation has more impact than alkyl hydroxylation. Docking studies indicate that six structures 1, 7, 8 and 13–15 have potential for inhibiting human as well as murine COX-2, due to regions showing similar intermolecular interactions to the observed for the control compounds (indomethacin and refecoxib). Toxicity can be related to aromatic hydroxylation. In accordance to our calculations, the derivatives here proposed are potentially more active as well safer than phenylbutazone and only structures 8 and 13–15 were the most promising. Such results can explain the biological properties of phenylbutazone and support the design of potentially safer candidates.

Sensitizing Capacities and Cross-Reactivity Patterns of Some Diisocyanates and Amines Using the Guinea-Pig Maximization Test. Can p-phenylenediamine be Used as a Marker for Diisocyanate Contact Allergy?

Background:

Isocyanates are mainly considered respiratory allergens but can also cause contact allergy. Diphenylmethane-4,4′-diamine (4,4′-MDA) has been considered a marker for diphenylmethane-4,4′-diisocyanate (4,4′-MDI) contact allergy. Furthermore, overrepresentation of positive patch-test reactions top-phenylenediamine (PPD) in 4,4′-MDA positive patients have been reported.

Objectives:

To investigate the sensitizing capacities of toluene-2,4-diisocyanate (2,4-TDI) and PPD and the cross-reactivity of 4,4′-MDA, 2,4-TDI, dicyclohexylmethane-4,4′-diamine (4,4′-DMDA), dicyclohexylmethane-4,4′-diisocyanate (4,4′-DMDI), 4,4′-MDI and PPD.

Methods:

The Guinea Pig Maximization Test (GPMT) was used.

Results:

PPD was shown to be a strong sensitizer (p<0.001). Animals sensitized to PPD showed cross-reactivity to 4,4′-MDA (p<0.001). Animals sensitized to 4,4′-MDA did not show cross-reactivity to PPD. 8 animals sensitized to 2,4-TDI were sacrificed due to toxic reactions at the induction site and could thus not be fully evaluated.

Conclusion:

PPD was shown to be a strong sensitizer. However, it cannot be used as a marker for isocyanate contact allergy. On the other hand, positive reactions to 4,4′-MDA could indicate a PPD allergy. The intradermal induction concentration of 2,4-TDI (0.70% w/v) can induce strong local toxic reactions in guinea-pigs and should be lowered.

Prediction of Chemical Respiratory and Contact Sensitizers by OX40L Expression in Dendritic Cells Using a Novel 3D Coculture System

The use of animal models in chemical safety testing will be significantly limited due to the recent introduction of the 3Rs principle of animal experimentation in research. Although several in vitro assays to predict the sensitizing potential of chemicals have been developed, these methods cannot distinguish chemical respiratory sensitizers and skin sensitizers. In the present study, we describe a novel in vitro assay that can discriminate respiratory sensitizers from chemical skin sensitizers by taking advantage of the fundamental difference between their modes of action, namely the development of the T helper 2 immune response, which is critically important for respiratory sensitization. First, we established a novel three-dimensional (3D) coculture system of human upper airway epithelium using a commercially available scaffold. It consists of human airway epithelial cell line BEAS-2B, immature dendritic cells (DCs) derived from human peripheral blood CD14⁺ monocytes, and human lung fibroblast cell line MRC-5. Respective cells were first cultured in individual scaffolds and subsequently assembled into a 3D multi-cell tissue model to more closely mimic the in vivo situation. Then, three typical chemicals that are known respiratory sensitizers (ortho-phthaldialdehyde, hexamethylene diisocyanate, and trimellitic anhydride) and skin sensitizers (oxazolone, formaldehyde, and dinitrochlorobenzene) were added individually to the 3D coculture system. Immunohistochemical analysis revealed that DCs do not migrate into other scaffolds under the experimental conditions. Therefore, the 3D structure was disassembled and real-time reverse transcriptase-PCR analysis was performed in individual scaffolds to analyze the expression levels of molecules critical for Th2 differentiation such as OX40 ligand (OX40L), interleukin (IL)-4, IL-10, IL-33, and thymic stromal lymphopoietin. Both sensitizers showed similarly augmented expression of DC maturation markers (e.g., CD86), but among these molecules, OX40L expression in DCs was most consistently and significantly enhanced by respiratory sensitizers as compared to that by skin sensitizers. Thus, we have established a 3D coculture system mimicking the airway upper epithelium that may be successfully applied to discriminate chemical respiratory sensitizers from skin sensitizers by measuring the critical molecule for Th2 differentiation, OX40L, in DCs.

Sensitization and cross-reactivity patterns of contact allergy to diisocyanates and corresponding amines: investigation of diphenylmethane-4,4'-diisocyanate, diphenylmethane-4,4'-diamine, dicyclohexylmethane-4,4'-diisocyanate, and dicylohexylmethane-4,4'-diamine

Background

Isocyanates are used in polyurethane production. Dermal exposure to isocyanates can induce contact allergy. The most common isocyanate is diphenylmethane diisocyanate used for industrial purposes. The isomer diphenylmethane‐4,4′‐diisocyanate (4,4′‐MDI) is used in patch testing. Diphenylmethane‐4,4′‐diamine (4,4′‐MDA) is its corresponding amine. Concurrent reactions to 4,4′‐MDI and 4,4′‐MDA have been reported, as have concurrent reactions to 4,4′‐MDI and dicyclohexylmethane‐4,4′‐diisocyanate (4,4′‐DMDI).

Objectives

To investigate the sensitization capacities and the cross‐reactivity of 4,4′‐MDI, 4,4′‐MDA, 4,4′‐DMDI, and dicyclohexylmethane‐4,4′‐diamine (4,4′‐DMDA).

Methods

The guinea‐pig maximization test (GPMT) was used.

Results

The GPMT showed sensitizing capacities for all investigated substances: 4,4′‐MDI, 4,4′‐MDA, 4,4′‐DMDI, and 4,4′‐DMDA (all p < 0.001). 4,4′‐MDI‐sensitized animals showed cross‐reactivity to 4,4′‐MDA (p < 0.001) and 4,4′‐DMDI (all p < 0.05). 4,4′‐MDA‐sensitized animals showed cross‐reactivity to 4,4′‐DMDA (p = 0.008).

Conclusion

All of the investigated substances were shown to be strong sensitizers. Animals sensitized to 4,4′‐MDI showed cross‐reactivity to 4,4′‐MDA and 4,4′‐DMDI, supporting previous findings in the literature. The aromatic amine 4,4′‐MDA showed cross‐reactivity to the aliphatic amine 4,4′‐DMDA.

Skin sensitization

Skin sensitization associated with allergic contact dermatitis is a common health problem and is an important consideration for toxicologists in safety assessment. Historically, in vivo predictive tests have been used with good success to identify substances that have the potential to induce skin sensitization, and these tests formed the basis of safety evaluation. These original tests are now being replaced gradually either by in vitro assays or by further refinements of in vivo methods such as the local lymph node assay. Human data have also been available to inform classification decisions for some substances and have been used by risk managers to introduce measures for exposure reduction. However, humans encounter hazards in the context of exposure rather than in the form of intrinsic hazards per se, and so in this article, we have examined critically the extent to which human data have been used to refine classification decisions and safety evaluations. We have also evaluated information on the burden of human allergic skin disease and used this to address the question of whether, and to what extent, the identification and evaluation of skin sensitization hazards has led to an improvement of public and/or occupational health.

Methyl methacrylate and respiratory sensitization: a critical review

Methyl methacrylate (MMA) is a respiratory irritant and dermal sensitizer that has been associated with occupational asthma in a small number of case reports. Those reports have raised concern that it might be a respiratory sensitizer. To better understand that possibility, we reviewed the in silico, in chemico, in vitro, and in vivo toxicology literature, and also epidemiologic and occupational medicine reports related to the respiratory effects of MMA. Numerous in silico and in chemico studies indicate that MMA is unlikely to be a respiratory sensitizer. The few in vitro studies suggest that MMA has generally weak effects. In vivo studies have documented contact skin sensitization, nonspecific cytotoxicity, and weakly positive responses on local lymph node assay; guinea pig and mouse inhalation sensitization tests have not been performed. Cohort and cross-sectional worker studies reported irritation of eyes, nose, and upper respiratory tract associated with short-term peaks exposures, but little evidence for respiratory sensitization or asthma. Nineteen case reports described asthma, laryngitis, or hypersensitivity pneumonitis in MMA-exposed workers; however, exposures were either not well described or involved mixtures containing more reactive respiratory sensitizers and irritants. The weight of evidence, both experimental and observational, argues that MMA is not a respiratory sensitizer.

Skin sensitization, false positives and false negatives: experience with guinea pig assays

The advent of the local lymph node assay (LLNA), and efforts to develop in vitro alternatives for the identification of skin sensitizing chemicals has focused attention on the issue of false positive and false negative results. In essence, the question becomes 'what is the gold standard?' In this context, attention has focused primarily on the LLNA as this is now the preferred assay for skin sensitization testing. However, for many years prior to introduction of the LLNA, the guinea pig maximization test and the occluded patch test of Buehler were the methods of choice. In order to encourage a more informed dialogue about the relative performance, accuracy and applicability of the LLNA and guinea pig tests, we have here considered the extent to which guinea pig methods were themselves subject to false positives and negative results. We describe and discuss here well-characterized examples of instances where both false negatives (including abietic acid and eugenol) or false positives (including vanillin and sulfanilic acid) have been recorded in guinea pig tests. These and other examples are discussed with particular reference to the fabrication of a gold standard dataset that is required for the validation of in vitro alternatives.

[Recent development in animal testing to predict the skin and respiratory sensitizing potential of chemicals]

The identification of chemicals with skin and/or respiratory sensitizing potential is important for the prevention of allergic diseases in both living and work environments. Although a number of animal models for respiratory allergic diseases have been reported, none of these models meets the goals of broad assessments of chemical sensitizing potential. We are attempting to develop a test for predicting the respiratory sensitization of chemicals. In the evaluation of skin sensitization of chemicals, the mostly used predictive tests are the guinea pig maximization test, Buehler test, and mouse local lymph node assay (LLNA). However, only LLNA has been validated formally and independently. Recent studies have revealed that EC3 estimated by LLNA correlates well with human skin sensitizing potency and the threshold for the induction of skin sensitization in the human repeat patch test. Thus, LLNA can predict the potency of skin sensitizing potential of a chemical and its risk in humans.

Skin sensitization: strategies for the assessment and management of risk

Allergic contact dermatitis (ACD) is to a considerable extent a preventable disease. Limitation can be achieved by correct identification of skin sensitizers, characterization of their potency, understanding human skin exposure and application of good risk assessment/management strategies. Various methods exist which are accurate for the predictive identification of chemicals that possess skin-sensitizing properties. These are enshrined in regulations that aim to provide a harmonized approach to hazard identification. One of the methods, the local lymph node assay, also delivers information on the relative potency of sensitizers. Efforts are continuing in the European Union and at the Organization for Economic Cooperation and Development to use elements of this information for regulatory categorization of skin sensitizers. However, greater use can be made of this potency information in the application of quantitative risk assessments. Such assessments depend also on the availability of accurate data on human skin exposure, one aspect where legislation has little role to play. Management of risks by restriction of skin exposure is, in contrast, a key point where legislation can play an important role, helping to establish a level playing field for industry and setting good standards based on the legislator's ability to access all data. Ultimately, the combination of accurate hazard identification, potency measurement, risk assessment and management, underpinned by enabling legislation, will lead to reduction of ACD. For individuals who do still develop contact allergy, avoidance of ACD should continue to be a goal, based on raising awareness of skin protection, allergen labelling and other skincare strategies.

Comparative analysis of skin sensitization potency of acrylates (methyl acrylate, ethyl acrylate, butyl acrylate, and ethylhexyl acrylate) using the local lymph node assay

There are currently available no systematic experimental data on the skin sensitizing properties of acrylates that are of relevance in occupational settings. Limited information from previous guinea-pig tests or from the local lymph node assay (LLNA) is available; however, these data are incomplete and somewhat contradictory. For those reasons, we have examined in the LLNA 4 acrylates: butyl acrylate (BA), ethyl acrylate (EA), methyl acrylate (MA), and ethylhexyl acrylate (EHA). The LLNA data indicated that all 4 compounds have some potential to cause skin sensitization. In addition, the relative potencies of these acrylates were measured by derivation from LLNA dose-response analyses of EC3 values (the effective concentration of chemical required to induce a threefold increase in proliferation of draining lymph node cells compared with control values). On the basis of 1 scheme for the categorization of skin sensitization potency, BA, EA, and MA were each classified as weak sensitizers. Using the same scheme, EHA was considered a moderate sensitizer. However, it must be emphasized that the EC3 value for this chemical of 9.7% is on the borderline between moderate (<10%) and weak (>10%) categories. Thus, the judicious view is that all 4 chemicals possess relatively weak skin sensitizing potential.

A further characteristic of susceptibility to contact allergy: sensitization to a weak contact allergen is associated with polysensitization. Results of the IVDK

Although genetic factors probably account for differences in susceptibility to contact allergy, they have not yet been identified, partly due to an insufficient understanding of 'susceptibility'. Regarding polysensitization (PS) as a sign of increased susceptibility, we studied the relationship between PS and sensitization to weak versus strong allergens. Patch test data from 66,835 patients registered by the multicentre project, Information Network of Departments of Dermatology (IVDK) between 1 January 1997 and 31 December 2004, were analysed. The association between the number of sensitization to standard series allergens, and contact allergy to a strong allergen methyldibromoglutaronitrile (MDBGN) and to a weak allergen (paraben mix), was analysed with adjusted logistic regression analysis. In paraben-positive (++/+++) patients, the risk of > or = 2, > or = 3 or > or = 4 additional reactions were significantly increased by a factor of 2.1-4.6 compared to MDBGN-sensitized (++/+++) patients. Varying the basic model, a higher risk of additional positive reactions associated with paraben sensitization was consistently identified. The association between PS and sensitization to weak allergens adds a further characteristic of susceptibility to former findings of the IVDK, where PS was related to an increased risk of induction, elicitation, and cytokine polymorphisms. PS can be regarded as a phenotype to be considered in genetic studies.

Subtoxic concentrations of allergenic haptens induce LC migration and maturation in a human organotypic skin explant culture model: a novel method for identifying potential contact allergens

The accelerated migration of Langerhans cells (LCs) out of the epidermis and up-regulation of maturation markers, upon treatment with subtoxic concentrations of chemicals, were used as the criteria to determine the potential of allergenic chemicals capable of inducing a hapten-specific delayed-type hypersensitivity reaction. Here we report the findings of a study in which seven chemicals, coded and tested in a blind fashion, were classified as contact allergens or non-allergens using the human organotypic skin explant culture (hOSEC) model. All chemicals that were identified as a contact sensitizer on decoding induced a definite decrease in the number of CD1a and HLA-DR-positive epidermal LCs in the epidermis of the skin explants, as determined by both semiquantitative immunohistochemistry and quantitative flow cytometric analysis. A significant increase in the number of CD83(+) cells was accompanied by up-regulation of activation molecules in the epidermis of hOSEC exposed specifically to contact allergens. In contrast, there were only minor alterations in epidermal LC numbers, expression of CD83 and other activation markers by LCs when the biopsies were treated with non-toxic concentrations of non-allergenic irritants and vehicles. The data suggest that an increased epidermal LC migration and maturation accompanied by increased expression of activation markers could be used as end-point determinants to screen allergens in a non-animal alternative hOSEC model.

Predictive identification of human skin sensitization thresholds

For years, methods have been available for the predictive identification of chemicals that possess the intrinsic potential to cause skin sensitization. However, many have proven less suitable for the determination of relative sensitizing potency. In this respect, the local lymph node assay (LLNA) has been shown to have a number of important advantages. Through interpolation of LLNA dose-response data, the concentration of a chemical required to produce a threshold positive response (a 3-fold increase in activity compared with concurrent vehicle controls, the EC3 value) can be measured. The robustness of this parameter has been demonstrated rigorously in terms of inter- and intralaboratory reproducibility. Additionally, the relationship between potency estimates from the LLNA and an appreciation of human potency based on clinical experience has been reported previously. In the present investigations, we have sought to consolidate further our understanding of the association between EC3 values and human skin-sensitization potency by undertaking a thorough and extensive analysis of existing human predictive assays, particularly where dose-response information is available, from historical human repeated insult patch tests (HRIPTs). From these human data, information on the approximate threshold for the induction of skin sensitization in the HRIPT was determined for 26 skin-sensitizing chemicals. These data were then compared with LLNA-derived EC3 values. The results from each assay, expressed as dose per unit area (microg/cm(2)), revealed a clear linear relationship between the 2 values, thereby substantiating further the utility of LLNA EC3 values for prediction of the relative human sensitizing potency of newly identified skin sensitizers.

An European inter-laboratory validation of alternative endpoints of the murine local lymph node assay

The original local lymph node assay (LLNA) is based on the use of radioactive labelling to measure cell proliferation. Other endpoints for the assessment of proliferation are also authorized by the OECD Guideline 429 provided there is appropriate scientific support, including full citations and description of the methodology (OECD, 2002. OECD Guideline for the Testing of Chemicals; Skin Sensitization: Local Lymph Node Assay, Guideline 429. Paris, adopted 24th April 2002.). Here, we describe the outcome of the second round of an inter-laboratory validation of alternative endpoints in the LLNA conducted in nine laboratories in Europe. The validation study was managed and supervised by the Swiss Agency for Therapeutic Products (Swissmedic) in Bern. Ear-draining lymph node (LN) weight and cell counts were used to assess LN cell proliferation instead of [3H]TdR incorporation. In addition, the acute inflammatory skin reaction was measured by ear weight determination of circular biopsies of the ears to identify skin irritation properties of the test items. The statistical analysis was performed in the department of statistics at the university of Bern. Similar to the EC(3) values defined for the radioactive method, threshold values were calculated for the endpoints measured in this modification of the LLNA. It was concluded that all parameters measured have to be taken into consideration for the categorisation of compounds due to their sensitising potencies. Therefore, an assessment scheme has been developed which turned out to be of great importance to consistently assess sensitisation versus irritancy based on the data of the different parameters. In contrast to the radioactive method, irritants have been picked up by all the laboratories applying this assessment scheme.

Evaluation of the skin sensitizing potency of chemicals by using the existing methods and considerations of relevance for elicitation

The Technical Committee of Classification and Labelling dealing with harmonized classification of substances and classification criteria under Directive 67/548/EEC on behalf of the European Commission nominated an expert group on skin sensitization in order to investigate further the possibility for potency consideration of skin sensitizers for future development of the classification criteria. All substances and preparations should be classified on the basis of their intrinsic properties and should be labelled accordingly with the rules set up in the Directive 67/548/EEC. The classification should be the same under their full life cycle and in the case that there is no harmonized classification the substance or preparation should be self-classified by the manufacturer in accordance with the same criteria. The Directive does not apply to certain preparations in the finished state, such as medical products, cosmetics, food and feeding stuffs, which are subject to specific community legislation. The main questions that are answered in this report are whether it would be possible to give detailed guidance on how to grade allergen potency based on the existing methods, whether such grading could be translated into practical thresholds and whether these could be set for both induction and elicitation. Examples are given for substances falling into various potency groups for skin sensitization relating to results from the local lymph node assay, the guinea pig maximization test, the Buehler method and human experience.

A two-centre evaluation of the human organotypic skin explant culture model for screening contact allergens

Animal models are considered to be the "gold standard" for determining the potential contact allergenicity of low molecular weight chemicals. However, governmental regulations and ethical considerations limit the use of animals for such purposes. There is therefore a need for in vitro alternative models. The human organotypic skin explant culture (HOSEC) model is reported to be a promising alternative method for the predictive testing of contact allergens. The accelerated migration of Langerhans cells from the epidermis upon exposure to contact allergens is used to identify chemicals that are potentially capable of inducing a delayed-type hypersensitivity. In the study described in this paper, the model was further refined, and used, in two independent laboratories, to screen 23 low molecular weight compounds of known classification for their allergenicity. Each laboratory was able to accurately detect the contact allergens, despite small variations in the protocols used. However, the classification of dermal irritants, which have often been falsely classified as allergens, varied between the two laboratories. Despite the current limitations of the HOSEC model, the accuracy of the predictions made (sensitiser or non-sensitiser) compare favourably with classifications obtained with commonly used animal models. The HOSEC model has the potential to be developed further as an in vitro alternative to animal models for screening for contact allergens.

Strong irritants masquerading as skin allergens: the case of benzalkonium chloride

Chemicals may possess a number of hazards to human health including the ability to cause skin irritation and contact allergy. Identification and characterization of these properties should fall within predictive toxicology, but information derived from human exposure, including clinical experience, is also of importance. In this context, it is of interest to review the case of benzalkonium chloride, a cationic surfactant. This chemical is a well-known skin irritant, but on occasions it has also been reported to have allergenic properties, typically on the basis of positive diagnostic patch test data. Because the accumulated knowledge concerning the properties of a chemical is employed as the basis for its regulatory classification (e.g. in Europe), as well as for informing the clinical community with respect to the diagnosis of irritant versus allergic contact dermatitis (ACD), it is important to distinguish properly which chemicals are simply irritants from those which are both irritant and allergenic on skin. A review of the information on benzalkonium chloride confirms that it is a significant skin irritant. However, both predictive test results and clinical data lead to the conclusion that benzalkonium chloride is, at most, an extremely rare allergen, except perhaps in the eye, but with many supposed cases of ACD being likely to arise from the misinterpretation of patch test data. As a consequence, this substance should not normally be regarded as, or classified as, a significant skin sensitizer.

Increased airway responsiveness of a common fragrance component, 3-carene, after skin sensitisation—a study in isolated guinea pig lungs

Lungs from skin-sensitised and non-sensitised guinea pigs were exposed via the airways to 3-carene (1900 mg/m3) and perfused with buffer containing either autologous plasma or lymphocytes. The experiments were performed in order to investigate the importance of blood components for the increased lung responsiveness seen in skin-sensitised animals. A reduction in lung function was noted in all lungs during 3-carene exposure. There was no difference in the 3-carene response between lungs from skin-sensitised animals versus lungs from non-sensitised animals when the perfusion buffer contained lymphocytes. However, when plasma diluted with buffer was used as perfusion medium, there was a significant enhancement in the response in lungs from sensitised versus lungs from non-sensitised animals. This implies that skin sensitisation increases lung responses to inhaled 3-carene and those components in plasma, and not the lymphocyte fraction, contributes to the observed increased lung responsiveness.

Peptide-binding assessment using mass spectrometry as a new screening method for skin sensitization

Skin sensitization potential of low molecular weight chemicals was assessed by analyzing peptide-conjugate formation. Chemicals were incubated with a peptide, glutathione, and resultant mixtures were analyzed by mass spectrometry. Eighteen chemicals were assessed, and new peaks corresponding to chemical-peptide conjugates were detected for 13 of 14 known sensitizers. Conjugates were not detected for 4 negative chemicals. The method has advantages as a simple screening assay for assessing the sensitization potential of chemicals.

Increased airway responsiveness after skin sensitisation to 3-carene, studied in isolated guinea pig lungs

Inhalation of 3-carene has been shown to induce bronchoconstriction in concentrations not far from the threshold limit value. In this study, one group of guinea-pigs were sensitised by dermal exposure to 3-carene according to the modified Cumulative Contact Enhancement Test protocol and another group of animals was used as controls. Lungs from the skin-sensitised and control guinea-pigs were perfused with diluted autologous blood (13 ml blood/87 ml buffer) and exposed to 3-carene at an air concentration of 3000 mg/m(3). In both groups there was a reduction in compliance and conductance but this reduction was significantly (P<0.05) more pronounced (2.5-3 times) in lungs obtained from sensitised animals than from control animals. In a previous study with similar design, but with plain buffer instead of diluted autologous blood as perfusate, we found no statistically significant difference in lung bronchoconstriction. Thus, it is concluded that skin sensitisation can increase lung reactivity to 3-carene and that important mediators of this effect seem to be present in the blood.

Dose-response studies of contact allergens using 3 guinea pigs models

A multi-dose-response induction protocol for the guinea pig maximization test (GPMT), including a statistical computer program, has earlier been developed to improve the power of predictive tests for identification of contact allergens. This dose-response protocol, with 2 modifications (i.e., increased number of animals in each group and increased number of challenge concentrations) was evaluated in the GPMT, the cumulative contact enhancement test (CCET) and the Freund's complete adjuvant test (FCAT), using potassium dichromate and hydroxycitronellal as model contact allergens. Application of the dose-response protocol on the CCET and the FCAT resulted in either monotone or non-monotone curves with significant dose-response. However, application of the dose-response protocol on the GPMT gave curves with no significant dose-response. The protocol makes it possible to obtain an EC50 value, thus improving the possibility of ranking contact allergens, which is of substantial use for risk assessments. The dose-response protocol could benefit from a few adjustments: a wider span in the induction doses; change to simultaneous increase in intradermal and topical induction doses to obtain a proper dose-response for the GPMT; the addition of further challenge concentrations. In addition the computer program should allow calculation of threshold concentration for sensitization and EC50 value for a non-monotone curve.

A comparison of statistical approaches to the derivation of EC3 values from local lymph node assay dose responses

Effective risk assessment and management of allergic contact dermatitis require three key factors: adequate hazard identification, measurement of the relative potency of identified hazards and an understanding of the nature, extent and duration of exposure. Suitable methods for hazard identification, such as the murine local lymph node assay (LLNA) and the guinea-pig maximization test, are well established and conditions of human exposure normally can be well anticipated. Thus, the need is for a robust and quantitative method for the estimation of relative skin sensitizing potency. One possible approach is via the analysis of LLNA dose-response data. In the LLNA, contact allergens are defined currently as those chemicals that cause a threefold or greater increase in lymph node cell proliferative activity compared with concurrent vehicle-treated controls. It is possible to estimate the concentration of a sensitizer required to generate a threefold stimulation of proliferation in draining lymph nodes; such a concentration is known as the EC3 value. Using a variety of statistical approaches to derive EC3 values from LLNA dose-response data for 10 chemicals, it has been demonstrated that simple linear interpolation between the values either side of the threefold stimulation index provides a robust assessment of the EC3 value without the need for recourse to more sophisticated statistical techniques. Provided that the appropriate concentrations of test chemical have been selected, EC3 values obtained in this way are reproducible both within and between laboratories and form the basis for examination of the utility of this approach for the estimation of relative skin sensitizing potency.

Contact allergy to the monomers of p-tert-butylphenol-formaldehyde resin in the guinea pig

In patients hypersensitive to p-tert-butylphenol-formaldehyde resin (PTBP-F-R), and butylphenol derivatives therein, it is for diagnostic, therapeutic and preventive reasons necessary to know the identity of the primary sensitizing substances, their sensitizing capacities as well as their cross-reaction patterns. The monomers in PTBP-F-R, 2-methylol p-tert-butylphenol (2-MPTBP) and 2,6-dimethylol p-tert-butylphenol (2,6-MPTBP), have been shown to be contact sensitizers in man. The aim of this study was to investigate the sensitizing capacities of the monomers and establish cross-reacting patterns in the guinea pig with the guinea pig maximization test. 2,6-MPTBP was shown to be a strong sensitizer while it was indicated that 2-MPTBP was a sensitizer. Animals sensitized to 2,6-MPTBP showed cross-reactions to 2-MPTBP and p-tert-butylcatechol. No cross-reactions were shown to p-tert-butylphenol, tert-butyl 4-hydroxyanisole (BHA) and 3,5-di-tert-butyl 4-hydroxytoluene (BHT).

Strategies for identifying false positive responses in predictive skin sensitization tests

It is important that predictive toxicological test methods are selective for their intended endpoint and that their limitations are understood and acknowledged. The local lymph node assay (LLNA) is a relatively new predictive test for skin sensitization potential that can replace traditional guinea pig tests and offers significant scientific and animal welfare advantages. However, there has been some concern that certain irritant materials may yield false positive results, although it must be emphasized that false positives also occur in guinea pig methods. Consequently, we have examined the performance in the LLNA of a range of skin irritants, from varying chemical classes and covering a range of irritation potency. The results presented here demonstrate clearly that the majority of skin irritants are negative in the LLNA. These results are reviewed in the context of the occurrence of false positive reactions in the guinea pig maximization test and the strategies for dealing with such results are discussed. The need for careful scientific evaluation of the results in all predictive tests for sensitization is thus emphasized. In terms of specificity, the LLNA has been more fully evaluated than other predictive test methods and is at least as accurate. In terms of animal welfare, objectivity, reproducibility and reliability it is superior to other methods. In summary, all predictive skin sensitization test results should be evaluated in a scientifically rigorous manner and the additional data provided herein further support the adoption of the LLNA as a complete replacement for the traditional guinea pig methods.

The guinea-pig skin sensitization test revisited: an evaluation formula to predict possible sensitization levels for eight chemicals used in household products

In predicting human skin sensitization due to possible risky chemicals, it is not sufficient to evaluate solely the minimum induction dose (MID) or the standard challenge dose (SCD) in the Guinea Pig Maximization Test (GPMT). Nakamura et al. (1994) (Nakamura, A., Momma, J., Sekiguchi, H., Noda, T., Yamano, T., Kaniwa, M., Kojima, S., Tsuda, M., Kurokawa, Y., 1994. A new protocol and criteria for quantitative determination of sensitization potencies of chemicals by guinea pig maximization test. Contact Dermatitis 31, 72-85) previously measured the residual dose of chemicals in the products implicated in human allergic accidents, and stated that '... the level of chemical in the products (direct exposure-dose = DED) was similar to or higher than value of sensitization potency.' However, several of the chemicals listed in their article, show an even lower value of sensitization potency than the DED, although a potential correlation between results of the GPMT and the DED was seemed to be evident; a key question about the essential rule of those parameters therefore remains open. Using the data of Nakamura et al. (1994), we analyzed the functional rules of the three independent parameters, the MID, the SCD, and the DED on which the GPMT is based. Calculations of the degree of allergic reactions elicited in humans provided a range of discrimination constants (D) using the formula; D = DED/(MID*SCD). Possible human allergic accidents may be predicted when the dose of a candidate chemical in a chemical product (equal to DED) exceeds the value; D*(MID*SCD), following the correct evaluation of the MID as well as the SCD.

Does airway responsiveness increase after skin sensitisation to 3-carene: a study in isolated guinea pig lungs

Guinea pigs were sensitised by dermal exposure to 3-carene according to the modified cumulative contact enhancement test (CCET) protocol. Lungs from sensitised and non-sensitised animals were then perfused with buffer and exposed for a period of 10 min to two different air concentrations of 3-carene, 600 and 3000 mg/m3. 3-Carene caused a statistically significant bronchoconstriction even at the relatively low concentration of 600 mg/m3 and the constriction was dose dependent. 600 mg/m3 of 3-carene caused a reduction of 19% in conductance capacity and 16% in compliance capacity. 3000 mg/m3 of 3-carene decreased lung compliance and conductance by 43 and 31%, respectively. The lungs from sensitised animals tended to show a greater response than lungs obtained from control animals. The lower concentration of 3-carene is close to and may even be below, occupational limit values in Sweden, Germany and USA.

Biocompatibility of alumina ceramic and polyethylene as materials for pivot bearings of a centrifugal blood pump

The double pivot bearings in the Gyro C1E3 centrifugal blood pump incorporate a high-purity alumina (Al2O3) ceramic and an ultra-high-molecular-weight polyethylene (UHMWPE). This centrifugal pump has been developed as a completely sealless pump for long-term usage. The combination of Al2O3 and UHMWPE are the materials of choice for the acetabular bearing in artificial joints, which have proven to be clinically reliable for over 10 years. Previous studies have examined the biocompatibility of Al2O3 and UHMWPE as bulky implant materials. The present study investigated this material as a blood-contacting material using a standard assessment in vitro and in vivo analysis. The examined items were systemic toxicity, sensitization (guinea pig maximization test), cytotoxicity (elution test), mutagenicity (Ames test), direct contact hemolysis, and thrombogenicity. The studies were performed according to the United States Pharmacopoeia and published previous studies. The samples of both Al2O3 and UHMWPE demonstrated no differences from the negative controls in all tests. These findings indicate that both Al2O3 and UHMWPE are biocompatible materials for double-pivot bearings in the centrifugal blood pump.

The local lymph node assay: a viable alternative to currently accepted skin sensitization tests

The prospective identification of skin sensitizing chemicals is a vital prerequisite for their proper risk management. Traditionally this has been achieved largely by the conduct of guinea pig assays such as the maximization and Buehler tests. These methods are recommended by the Organisation for Economic Cooperation and Development (OECD) and are required by the European Union (EU) for the evaluation of new substances. However, a novel mechanistically based method, the local lymph node assay (LLNA), has been the focus of substantial validation activity in recent years. This material is reviewed in this paper. It is shown that the LLNA has been validated successfully by five interlaboratory assessments as well as by comparisons with guinea pig tests and human data. The method also offers clear advantages to the user in terms of objectivity, time and cost, and delivers important animal welfare benefits. In consequence, it is recommended that the LLNA be formally adopted by the OECD in Guideline 406 and accepted by the EU and US EPA as a method suitable for the classification of the skin sensitizing potential of chemicals.

Sulphanilic acid: divergent results in the guinea pig maximization test and the local lymph node assay

The guinea pig maximization test (GPMT) has proven to be a valuable tool for the identification of the skin sensitization potential of chemicals. The method identifies a hazard which can lead in the EC to compulsory labelling of that chemical. In the present study, data on sulphanilic acid derived from the GPMT has been compared with results from a second guinea pig assay (the cumulative contact enhancement test) and the murine local lymph node assay, both of which require only topical application of chemical. Except for the GPMT, no test identified any sensitizing activity associated with exposure to sulphanilic acid. These latter results are consistent with the experience gained from substantial human exposure in an occupational setting and from which no cases of allergic contact dermatitis to sulphanilic acid have arisen over a 20-year period. In consequence, it is questioned which test protocol in practice has given the more accurate identification of sensitization hazard relevant to man.

Comparison of the local lymph node assay with the guinea-pig maximization test for the detection of a range of contact allergens

The guinea-pig maximization test (GMPT) has been in use as a method for the prediction of skin sensitization potential for over 20 years, and is widely accepted by regulatory authorities because of its reliable detection of a wide variety of potential human contact allergens. Nevertheless, the method has some limitations and drawbacks, including the use of an adjuvant, the injection of the test substance at induction thus bypassing the normal skin barrier and metabolic function, a subjective endpoint, interference by irritant and/or coloured chemicals, and a relatively long and complex protocol. To address these points, an alternative technique, the local lymph node assay (LLNA), has been proposed and has become the focus of much attention. Recent data from interlaboratory trials have shown a good level of agreement between test facilities and with existing guinea-pig data. The present work investigated the correlation between LLNA results and those derived from the GPMT for 40 chemicals covering a range of chemical types and levels of skin sensitization potential. The LLNA assay was capable of detecting chemicals that exhibit a strong sensitization potential in the GPMT. For chemicals classified as moderate sensitizers in the GPMT, the LLNA was usually positive or provided an indication of sensitizing activity (that was not sufficient to satisfy the current criteria for regarding the result as positive). Weaker sensitizers in the GPMT were usually not detected by the LLNA. With the single exception of copper chloride, non-sensitizers were not positive in the LLNA. The results support the view that the LLNA can provide a rapid and objective screening test for strong sensitizers.

Value of the cutaneous basophil hypersensitivity (CBH) response for distinguishing weak contact sensitization from irritation reactions in the guinea pig

Numerous studies of the histology of allergic contact dermatitis reactions to potent allergens in guinea pigs and humans have indicated that there is significant tissue infiltration with basophilic leukocytes. In this study we determined whether this histologic finding could be of value in distinguishing weak sensitization reactions from primary irritation, thereby aiding in the predictive identification of weak or moderate contact allergens. Guinea pigs were sensitized by the Buehler test method. Skin reactions were graded 24, 48, and 72 h post-challenge with duplicate patch sites biopsied at the 24- or 72-h grading timepoints. The biopsies were fixed, embedded in glycol methacrylate, thin sectioned, and Giemsa stained. The number of basophils per 400 leukocytes were counted along the upper dermis just below the dermal/epidermal junction. Challenge patch sites from animals sensitized to a relatively low dose of the strong contact allergen, oxazolone, were compared with patch sites from animals challenged only with a strong irritant, sodium lauryl sulfate (SLS). Compared to normal skin (7.5 +/- 1.0 basophils/400 leukocytes +/- SEM) only the oxazolone patch sites showed significant basophil infiltration (36.8 +/- 6.5), despite the fact that the skin reactions to the low oxazolone challenge dose were relatively weak. SLS patch sites showed no basophil infiltration above normal skin levels (4.8 +/- 0.9). Subsequent blinded studies compared weak/moderate presumptive sensitization reactions (as defined by accepted visual skin grading criteria) to various chemicals (citronellal, vanillin, cinnamic aldehyde, and ethylenediamine) to primary irritation reactions to the same chemicals. In each case, low-challenge-dose sensitization sites on previously treated (induced) animals showed mean basophil infiltration (range, 11.9-69.2 basophils/400 leukocytes) significantly greater than higher-dose irritant reactions (range, 1.6-13.3). The range for normal skin was 0.2-10.2 and the range for strong patch reactions to higher concentrations of oxazolone was 59.8-209.3. These data strongly indicate that light-microscopic quantitation of the CBH response can be used to distinguish relatively weak to moderate contact sensitization reactions from primary irritation reactions to the same chemicals.

A review of the Buehler guinea pig skin sensitization test and its use in a risk assessment process for human skin sensitization

The Buehler test is a valuable procedure for screening the sensitization potential of chemicals prior to human exposure. Our experience of over 20 years has shown it to be effective in detecting strong, moderate, and most weak sensitizers. The topical exposure inherent in the Buehler test allows it to be utilized to investigate dose responses, cross reactivity between structurally related chemicals, and the sensitization potential of contaminants in raw material mixtures. For safety assessment purposes, Buehler test results provide an initial indication of the sensitization potential of the material in question under relevant, but exaggerated, exposure conditions. These results can be compared to results on benchmark chemicals to assess sensitization risk for subsequent human exposure. Optimizing the sensitivity of the Buehler test requires adherence to the published methodology and proper interpretation of the challenge and rechallenge data obtained. Adjuvant-type test methods are generally considered to be more sensitive than topical methods. However, when done properly, topical test procedures such as the Buehler test or the open epicutaneous test can accurately detect most chemicals with any realistic potential for sensitizing humans by the topical route. Moreover, from a risk assessment perspective, these topical tests avoid the problems of overestimating the weak sensitization potential of many topically applied materials or underestimating the sensitization potential of very strong sensitizers; both are potential concerns with invasive adjuvant-type test methods. The Buehler test or other topical test methods are particularly valuable for comparative sensitization risk assessment since human sensitization data on benchmark materials are all derived from topical exposure. The risk assessment is developed by comparing the guinea pig data on the new material versus relevant benchmark chemicals or formulations and also by evaluating the existing human sensitization data on the benchmark material. These data are then utilized to predict human sensitization risk from topical exposure to the new material. Confirmation of human safety can be derived from human repeat insult patch testing (HRIPT) and other clinical tests such as the product use test and the diagnostic patch test. Utilized in this manner, the Buehler test is an integral component of an overall skin sensitization safety assessment program for a new chemical or product formulation.

The maximization test for skin sensitization potential--updating the standard protocol and validation of a modified protocol

Since Magnusson and Kligman (1969) first described the maximization test, for assessing skin sensitization potential, the test has been substantially validated and data have been obtained on dose-activity relationships. The original method remains acceptable for qualified risk assessment but several modified protocols have been developed to overcome problems with particular test materials. A modified maximization test is described for compounds that are not soluble in the standard vehicles and, therefore, not injectable, and for formulations, to simulate user exposure conditions. The test compounds 2,4-dinitrochlorobenzene, p-phenylenediamine, 1-(3-chlorophenyl)-3- (4-chlorophenyl)-2-pyrazoline, formaldehyde, benzocain, penicillin G, benzylsalicylate, potassium dichromate and isoeugenol, all gave positive reactions. The incidences of positive reactions varied with the sensitization potentials of the compounds. The results for the first six compounds listed above were compared with those obtained by the standard procedure and were found to be similar. We propose that testing guidelines for skin sensitization should accommodate validated modifications of existing standard procedures.

Contact allergy to colour developing agents in the guinea pig

Colour developing agents, derivatives of p-phenylenediamine, can cause contact allergy. Patch test reactions to more than one colour developer are sometimes seen in patients. To study whether this is due to simultaneous sensitization or cross-reactivity, guinea pig maximization tests (GPMT) with CD-2, CD-3 and CD-4 were carried out. 5 experiments were performed, using pet. or water as vehicles. When pet. was used, the challenge concentrations could be raised and cross-reactivity between the colour developers, but not with p-phenylenediamine-dihydrochloride, was revealed. When water was used as vehicle, the challenge concentrations were limited because of staining of the test sites and irritation. CD-2, CD-3 and CD-4 were found to be extreme sensitizers according to the classification by Magnusson and Kligman. The importance of using an appropriate vehicle to obtain optimal conditions for the GPMT is stressed. To study the purity and stability of the chemicals used, analysis by HPLC of the test substances at different stages of the GPMT procedure was performed. Aqueous solutions of the colour developers were found to be unstable, while pet. mixtures were stable.