Development of a non-radioactive endpoint in a modified local lymph node assay

Safety Evaluation and Anti-wrinkle Effects of Retinoids on Skin

Retinoids have many beneficial effects on dermatological applications. But, retinoids cause skin irritation. In this study, the safety of retinoids was clarified via both primary skin irritation test in rabbits and sensitization study using an integrated model for the differentiation of chemical-induced allergic and irritant skin reaction (IMDS) , an alternative method to sensitization test. The effects of retinoids on the change of ultraviolet A (UVA) -induced matrix metalloproteinase-1 (MMP-1) in human skin fibroblasts and the modulation of type-1 pN collagen synthesis in hairless mice were examined to clarify the anti-wrinkle effects. All-trans retinol (t-ROL) and its derivative, all-trans retinoic acid (t-RA) , showed mild skin irritation but did not induce the sensitization. t-ROL and t-RA exerted anti-wrinkle effects by inhibiting the UVA-induced MMP-1 in human skin fibroblasts and increasing the type-1 pN collagen synthesis in hairless mice. These findings suggest that retinoids do not induce the allergy, and show anti-wrinkle effects by decreasing MMP-1 activation and increasing collagen synthesis.

A draining lymph node assay (DLNA) for assessing the sensitizing potential of proteins

There is a need for a simple and predictive model to identify the respiratory sensitization potential of (novel) proteins. The present study examined the use of a mouse draining lymph node assay (DLNA) approach, employing several routes of exposure, as a possible starting point for assessing protein sensitization potential. Consistent with the experimental procedure for the standard local lymph node assay (LLNA), female BALB/c mice were dosed dermally (topical), intranasally (IN) or by oropharyngeal aspiration (OP) on days 1, 2 and 3, and proliferation in the relevant draining lymph nodes was measured on day 6. For each route, the auricular, superficial cervical and tracheobronchial lymph nodes (TBLN) were evaluated following treatment with Subtilisin Carlsberg (SUB; a potent sensitizer/allergen), ovalbumin (OVA; a potent food allergen), beta-lactoglobulin (BLG; a moderate food allergen), and keyhole limpet hemocyanin (KLH; a strong immunogen with no reports of respiratory sensitization). Initial studies with OVA indicated that dermal administration did not stimulate lymph node proliferation. Responses in the tracheobronchial lymph node were most dramatic (stimulation indices up to 100) and reproducible for both the IN and OP routes. In a comparative experiment, all proteins induced lymph node proliferation with a rank order potency of SUB>KLH>OVA>BLG. The influence of the endotoxin content on lymph node proliferation was determined to be minimal, and did not impact the rank order potency. Molecular characterization of the TBLN at an equipotent proliferative dose was conducted for select gene transcripts based on research examining chemical sensitizers. Expression profiles differed among the four proteins, but the relevance of these responses was not clear and they did not further discriminate their allergic potential. These data illustrate both the opportunities and challenges associated with the examination of the draining lymph node proliferative response to assess the allergenic potential of proteins.

Characterization and evaluation of a modified local lymph node assay using ATP content as a non-radio isotopic endpoint

INTRODUCTION

The murine local lymph node assay (LLNA) is an accepted and widely used method for assessing the skin-sensitizing potential of chemicals. Here, we describe a non-radio isotopic modified LLNA in which adenosine triphosphate (ATP) content is used as an endpoint instead of radioisotope (RI); the method is termed LLNA modified by Daicel based on ATP content (LLNA-DA).

METHODS

Groups of female CBA/JNCrlj mice were treated topically on the dorsum of both ears with test chemicals or a vehicle control on days 1, 2, and 3; an additional fourth application was conducted on day 7. Pretreatment with 1% sodium lauryl sulfate solution was performed 1 h before each application. On day 8, the amount of ATP in the draining auricular lymph nodes was measured as an alternative endpoint by the luciferin-luciferase assay in terms of bioluminescence (relative light units, RLU). A stimulation index (SI) relative to the concurrent vehicle control was derived based on the RLU value, and an SI of 3 was set as the cut-off value.

RESULTS

Using the LLNA-DA method, 31 chemicals were tested and the results were compared with those of other test methods. The accuracy of LLNA-DA vs LLNA, guinea pig tests, and human tests was 93% (28/30), 80% (20/25), and 79% (15/19), respectively. The estimated concentration (EC) 3 value was calculated and compared with that of the original LLNA. It was found that the EC3 values obtained by LLNA-DA were almost equal to those obtained by the original LLNA.

DISCUSSION

The SI value based on ATP content is similar to that of the original LLNA as a result of the modifications in the chemical treatment procedure, which contribute to improving the SI value. It is concluded that LLNA-DA is a promising non-RI alternative method for evaluating the skin-sensitizing potential of chemicals.

Targeting effector memory T cells with the small molecule Kv1.3 blocker PAP-1 suppresses allergic contact dermatitis

The voltage-gated potassium channel Kv1.3 has been recently identified as a molecular target that allows for selective pharmacological suppression of effector memory T (T(EM)) cells without affecting the function of naïve and central memory T cells. We here investigated whether PAP-1, a small molecule Kv1.3 blocker (EC50=2 nM), could suppress allergic contact dermatitis (ACD). In a rat model of ACD, we first confirmed that the infiltrating cells in the elicitation phase are indeed CD8+ CD45RC- memory T cells with high Kv1.3 expression. In accordance with its selective effect on T(EM) cells, PAP-1 did not impair sensitization, but potently suppressed oxazolone-induced inflammation by inhibiting the infiltration of CD8+ T cells and reducing the production of the inflammatory cytokines IFN-gamma, IL-2, and IL-17 when administered intraperitoneally or orally during the elicitation phase. PAP-1 was equally effective when applied topically, demonstrating that it effectively penetrates skin. We further show that PAP-1 is not a sensitizer or an irritant and exhibits no toxicity in a 28-day toxicity study. Based on these results we propose that PAP-1 could potentially be developed into a drug for the topical treatment of inflammatory skin diseases such as psoriasis.

Sensitising potential of four textile dyes and some of their metabolites in a modified local lymph node assay

We studied the sensitising and allergenic potentials of the textile dyes disperse yellow 3, disperse orange 30, disperse red 82, disperse yellow 211 and two metabolites of disperse yellow 3, 4-aminoacetanilide and 2-amino-p-cresol, using modified protocols of the murine "local lymph node assay" (LLNA). Test substances were applied either to the dorsum of the mice ears (sensitisation protocol) or they were first applied to the skin of their backs and 2 weeks later to their ears (sensitisation-challenge protocol). In addition to the endpoints weight and cell number of the draining ear lymph nodes we analysed lymphocyte subpopulations by flow cytometry. In the sensitisation protocol, disperse yellow 3 and its metabolite 4-aminoacetanilide did not induce significant effects, whereas in the sensitisation-challenge protocol cell number and lymph node weight increased significantly indicating a sensitising potential in NMRI mice. Hence, two-phase treatment (skin of the back, ear) increased the sensitivity of this assay. The second metabolite of disperse yellow 3, 2-amino-p-cresol, showed distinct effects in both treatment protocols; this applied mainly to the parameters cell number and lymph node weight. The dye disperse red 82 caused ambiguous increases in lymph node weight and cell number in the sensitisation protocol which were not reproduced in the sensitisation-challenge protocol, ruling out a relevant sensitising potential for this dye in NMRI mice. Disperse yellow 211 and disperse orange 30 did not induce relevant changes under our experimental conditions. Phenotyping of lymphocytes did not influence the assessment of these dyes.

Advantage of using CBA/N strain mice in a non-radioisotopic modification of the local lymph node assay

The murine local lymph node assay (LLNA) is currently recognized as a stand-alone test method for determining the skin sensitizing potential of chemicals. It has been incorporated into the official test guidelines published by some authorities, including the OECD. To avoid the use of radioisotopes, efforts have been made recently to develop non-radioisotopic modifications of the LLNA. A non-radioisotopic modification of the LLNA was developed previously using 5-bromo-2'-deoxyuridine (BrdU) incorporation (non-RI LLNA). However, the non-RI LLNA was found to be somewhat less sensitive than the standard assay. This study reports the advantage of using mice of the CBA/N strain in the non-RI LLNA to improve the sensitivity of this method. The non-RI LLNA was performed using CBA/JN and CBA/N mice exposed to one of four confirmed skin sensitizers, 2,4-dinitrochlorobenzene (DNCB), eugenol (EG), isoeugenol (IEG) or alpha-hexylcinnamic aldehyde (HCA), and to one non-sensitizer, propylene glycol (PG). The EC3 values for DNCB, IEG, EG, HCA and PG were calculated to be 0.1%, 9.6%, 40.6%, 45.5% and >50% in CBA/JN mice and 0.08%, 1.9%, 10.7%, 20.3% and >50% in CBA/N mice, respectively. The EC3 values for DNCB, IEG, EG, HCA and PG in the standard LLNA using CBA/Ca mice and radioisotopes were reported elsewhere as being 0.08%, 1.3%, 13.0%, 8.0% and >50%, respectively. The EC3 values derived from the CBA/N mice in the non-RI LLNA were nearly equivalent to the EC3 values obtained using the standard radioisotopic LLNA with CBA/Ca mice. These data suggest that the use of CBA/N mice may provide a realistic opportunity to develop a version of the LLNA that does not have a requirement for the use of radioisotopes, but which nevertheless has sensitivity approaching, or comparable to, the standard method.

Ranking of hair dye substances according to predicted sensitization potency: quantitative structure-activity relationships

Allergic contact dermatitis following the use of hair dyes is well known. Many chemicals are used in hair dyes and it is unlikely that all cases of hair dye allergy can be diagnosed by means of patch testing with p-phenylenediamine (PPD). The objectives of this study are to identify all hair dye substances registered in Europe and to provide their tonnage data. The sensitization potential of each substance was then estimated by using a quantitative structure-activity relationship (QSAR) model and the substances were ranked according to their predicted potency. A cluster analysis was performed in order to help select a number of chemically diverse hair dye substances that could be used in subsequent clinical work. Various information sources, including the Inventory of Cosmetics Ingredients, new regulations on cosmetics, data on total use and ChemId (the Chemical Search Input website provided by the National Library of Medicine), were used in order to identify the names and structures of the hair dyes. A QSAR model, developed with the help of experimental local lymph node assay data and topological sub-structural molecular descriptors (TOPS-MODE), was used in order to predict the likely sensitization potential. Predictions for sensitization potential were made for the 229 substances that could be identified by means of a chemical structure, the majority of these hair dyes (75%) being predicted to be strong/moderate sensitizers. Only 22% were predicted to be weak sensitizers and 3% were predicted to be extremely weak or non-sensitizing. Eight of the most widely used hair dye substances were predicted to be strong/moderate sensitizers, including PPD - which is the most commonly used hair dye allergy marker in patch testing. A cluster analysis by using TOPS-MODE descriptors as inputs helped us group the hair dye substances according to their chemical similarity. This would facilitate the selection of potential substances for clinical patch testing. A patch-test series with potent, frequently used, substances representing various chemical clusters is suggested. This may prove useful in diagnosing PPD-negative patients with symptoms of hair dye allergy and would provide some clinical validation of the QSAR predictions.

Allergenicity evaluation of p-chloro-m-cresol and p-chloro-m-xylenol by non-radioactive murine local lymph-node assay and multiple-dose guinea pig maximization test

p-Chloro-m-cresol (PCMC) and p-chloro-m-xylenol (PCMX) are known to cause allergic contact dermatitis. For risk assessment of skin sensitizers, information on dose-response profiles in the induction and elicitation phases and cross-reactivity with analogous chemicals are important. In the non-radioactive local lymph-node assay (LLNA) using 5-bromo-2'-deoxyuridine instead of 3H-methyl thymidine, significant effect on lymph node cell proliferation was detected at 10% PCMC and 25% PCMX, while in the multiple-dose guinea pig maximization test (GPMT) at least one animal tested in the group was sensitized at a 5 ppm induction dose of either chemical. When mean skin reaction score in an animal group maximally sensitized with each allergen with the GPMT was plotted against log challenge concentration, linear regression lines with high correlations were obtained in both cases. The calculated elicitation threshold was lower for PCMC than PCMX. The area under the linear regression line between the threshold point and 1% of the elicitation concentration, another index of relative elicitation potency, was also greater for PCMC. Bidirectional cross-reactivity between PCMX and PCMC was detected in the GPMT. PCMC was thus identified in both LLNA and GPMT as a stronger sensitizer than PCMX in both the induction and elicitation phases. These results suggest that the non-radioactive LLNA is a simple and useful method for evaluating allergenicity in the induction phase, while the GPMT using a maximally sensitized animal group is more suitable for assessing the dose-response profile and cross-reactivity in the elicitation phase.

The local lymph node assay: past, present and future

The local lymph node assay (LLNA) was developed originally as a method for the identification of chemicals that have the potential to cause skin sensitization and allergic contact dermatitis. The assay is based on an understanding that the acquisition of contact sensitization is associated with, and dependent upon, the stimulation by chemical allergens of lymphocyte proliferative responses in skin-draining lymph nodes. Those chemicals that provoke a defined level of lymph node cell (LNC) proliferation (a 3-fold or greater increase compared with concurrent vehicle controls) are classified as skin sensitizers. Following its original inception and development, the LLNA was the subject of both national and international interlaboratory collaborative trials, and of very detailed comparisons with other test methods and with human skin sensitization data. The assay has now been validated fully as a stand-alone test for the purposes of hazard identification. In recent years, there has been a growing interest also in the use of the LLNA to assess the potency of contact allergens and in risk assessment. There is reason to believe that the extent of skin sensitization achieved is associated with the vigour of LNC proliferation induced in draining nodes. Given this relationship, the relative potency of skin sensitizing chemicals is measured in the LLNA by derivation of an EC3 value, this being the concentration of chemical required to provoke a 3-fold increase in the proliferation of LNC compared with controls. Experience to date indicates that relative potency as determined using this approach correlates closely with what is known of the activity of skin sensitizing chemicals in humans. In this article, we review the development, evaluation and validation of the LLNA for the purposes of hazard identification, and the more recent application of the method for evaluation of potency in the context of risk assessment. In addition, we consider what new applications and modifications are currently being investigated.

Local lymph node assay with non-radioisotope alternative endpoints

The local lymph node assay has recently been accepted by regulatory agencies as a stand-alone alternate method for predicting allergic contact dermatitis. To compare the sensitivity of non-radioisotope methods with that of the standard assay, we determined if these modified methods would affect evaluation of sensitization potency. For this reason, we used 2,4-dinitrochlorobenzene (DNCB) and benzocaine for different sensitizing criteria. Female CBA mice were treated for 3 days with a test compound or vehicle applied to each side of both ears. Bilateral auricular lymph node proliferative activity was assessed by the following endpoints with incorporation of 3H-methyl thymidine (3H-TdR), bromodeoxyuridine (BrdU) in vivo, and BrdU ex vivo, IL-2 production, and proliferating cell nuclear antigen (PCNA) expression. Ear thickness was also tested. The strong sensitizer DNCB was detectable by any of the non-radioisotope endpoints as well as by radioisotope-dependent standard assay. On the other hand, when evaluating the weak sensitizer benzocaine, significant changes were evident in BrdU incorporation ex vivo and in vivo, and IL-2 production. We believe that these non-radioisotope methods can assess allergic contact dermatitis caused by chemicals even in the laboratory, where it can be difficult to handle radioisotopes.

A nonradioisotopic endpoint for measurement of lymph node cell proliferation in a murine allergic contact dermatitis model, using bromodeoxyuridine immunohistochemistry

INTRODUCTION

The murine local lymph node assay (LLNA) was developed as an alternative to guinea pig models for the assessment of the xenobiotic contact sensitization potential. However, it would be advantageous to have an alternative endpoint to the usual radioisotopic-dependent measures. In the present study, we investigated the development of a nonradioisotopic endpoint for LLNA using immunohistochemistry.

METHODS

Female Balb/c mice were treated by the topical application of strong sensitizers, 2,4-dinitrochlorobenzene (DNCB) and toluene diisocyanate (TDI), and a strong irritant, sodium lauryl sulfate (SLS), on the dorsum of both ears once daily for three consecutive days. The proliferation of cells in the auricular lymph node and ears was analyzed by means of the labeling index (LI) of bromodeoxyuridine (BrdU) incorporation into cells.

RESULTS

Skin reactions, consisting of increased ear thickness and the presence of inflammatory cell infiltrates, were observed in mice treated with DNCB and TDI. The cell number and the weight of the lymph nodes in the mice treated with the allergens, DNCB and TDI, were increased compared to vehicle control. We observed an increase in the areas of the B220(+) cells in the lymph nodes of mice treated with allergens, as determined by immunohistochemistry. There was an increase in the percentage of B220(+) cells in mice treated with DNCB and TDI compared to the vehicle control, but not in those treated with SLS. Because we observed an increase in the percentage of B cells in the allergen-treated group, we measured the stimulation index (SI) in the cortex and medulla (C+M) of the lymph node. The SI values of the C+M in the lymph nodes of the mice treated with DNCB and TDI were increased more than threefold compared with that of the control. However, the SI of the C+M in the lymph nodes of the mice exposed to 25% SLS was not significantly increased compared to the vehicle control, although the lymph node weight of the SLS group was significantly increased.

DISCUSSION

In Balb/c mice, BrdU immunohistochemistry showed its potential use for the identification and differentiation of chemicals with the capacity to induce irritation and sensitization. The results suggest that the measurement of the SI in the cortex and medulla of the lymph node using BrdU immunohistochemistry could provide a useful method to screen irritants and allergens.

ICCVAM evaluation of the murine local lymph node assay. Conclusions and recommendations of an independent scientific peer review panel

The validation status of the murine local lymph node assay (LLNA), a method for assessing the allergic contact dermatitis potential of chemicals, was evaluated by an independent peer review panel (Panel) convened by the Interagency Coordinating Committee on the Validation of Alternative Methods (ICCVAM). The LLNA measures lymphocyte proliferation using incorporation of radioactive thymidine or iododeoxyuridine into cells of the draining lymph nodes of mice topically exposed to a test article. The Panel concluded that the assay performed as well as currently accepted guinea pig methods [guinea pig maximization test (GPMT)/Buehler assay (BA)] for the hazard identification of strong to moderate chemical sensitizing agents, but that it might not correctly identify all weak sensitizers or metals (potential false negative response) or all strong irritants (potential false positive response). The Panel concluded also that the LLNA involves less pain and distress than conventional guinea pig methods. The Panel unanimously recommended the LLNA as a stand-alone alternative for contact sensitization hazard assessment, provided that certain protocol modifications were made. These included collection of individual, rather than pooled, animal response data; the inclusion of a concurrent positive control; and consideration of dose-response information and statistical analyses. A standardized LLNA protocol is provided.

Development of non-radio isotopic endpoint of murine local lymph node assay based on 5-bromo-2'-deoxyuridine (BrdU) incorporation

Allergic contact dermatitis is a serious health problem. Over the last decade, the murine local lymph node assay (LLNA) has been developed to detect chemical allergens, and international validation studies have been conducted. We have tried to establish an alternative non-radioisotopic endpoint for the LLNA by using 5-bromo-2'-deoxyuridine (BrdU) incorporation in place of radioisotopes, such as [3H]thymidine, employed in the standard method. BrdU was given as a single administration at 5 mg/animal 2 days following three consecutive daily applications of a test chemical. BrdU incorporation into draining lymph node cells was measured using an enzyme immunosorbent assay technique. In this study, p-benzoquinone(PBQ), trimellitic anhydride (TMA), citral(CT) and dextran (DEX) were used as pilot chemicals. PBQ, TMA and CT, which are classified as moderate to strong sensitizers in the guinea pig maximization test and were positive in the original LLNA, were also found to elicit positive responses in the alternative LLNA using BrdU incorporation. In contrast, DEX tested negative in the modified assay consistent with previous guinea pig and LLNA data. Consequently, the modified LLNA endpoint using BrdU incorporation may represent a useful alternative to the standard assay in situations, where there is a need to avoid the use of radioisotopes.

Local lymph node assay: use in hazard and risk assessment

The murine local lymph node assay (LLNA) was developed as an alternative method for the identification of chemicals that have the ability to cause skin sensitization and allergic contact dermatitis. The assay now has been evaluated extensively in the context of both national and international inter-laboratory collaborative trials and has been the subject of detailed comparisons with guinea pig test methods and human skin sensitization data. On the basis of these evaluations the LLNA has been endorsed recently by the US Interagency Coordinating Committee on the Validation of Alternative Methods (ICCVAM) as a stand-alone method for skin sensitization testing. The assay offers a number of important benefits compared with conventional guinea pig test methods, among these being provision of an objective and quantitative endpoint. Moreover, the LLNA provides advantages in the context of animal welfare; compared with guinea pig tests, fewer animals are required and these animals are subject to less trauma. It is important now that the validation status of the LLNA is recognized and the method applied widely so that these advantages may be realized. Hazard identification represents only the first step in the risk assessment process. A full toxicological evaluation of skin sensitization activity requires an understanding of relative potency. Guinea pig methods do not lend themselves readily to assessment of potency, and interest recently has focused on the utility of the LLNA for this purpose. Contained within this review article are brief descriptions of the history of the LLNA and the immunobiological basis for the method, together with detailed accounts of the conduct and interpretation of the assay. Procedural modifications to, and alternative endpoints for, the LLNA are considered also. Finally, the current regulatory status of the LLNA is summarized and the application of the method for the purposes of defining relative potency and developing risk assessments is reviewed.