1
|
Chapkanov A, Schultz TW, Yordanova D, Kirilov K, Ivanova H, Mekenyan OG. Estimating uncertainty in LLNA EC3 data and its impact on regulatory classifications. Regul Toxicol Pharmacol 2023; 139:105357. [PMID: 36805911 DOI: 10.1016/j.yrtph.2023.105357] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2022] [Revised: 02/01/2023] [Accepted: 02/14/2023] [Indexed: 02/18/2023]
Abstract
The murine Local Lymph Node Assay (LLNA) is a test that produces numerical results (EC3 values) quantifying the sensitization potency of chemicals. These results are broadly used in toxicology and serve as a basis for various classifications, which determine subsequent regulatory decisions. The continuing interest in LLNA data and the diminished likelihood of new experimental EC3 data being generated sparked this investigation of uncertainty. Instead of using the Gaussian distribution as a default choice for assessing variability in a data set, two strictly positive distributions were proposed and their performance over the available experimental EC3 values was tested. In the application stage, how the uncertainty in EC3 values affects the possible classifications was analyzed, and the percentage of the chemicals receiving ambiguous classification was determined. It was shown that this percentage is high, which increases the risk of improper classification. Two approaches were suggested in regulatory practice to address the uncertainty in the EC3 data: the approaches based on "grey zones" and the classification distribution. If a chemical cannot be classified unambiguously, the latter appears to be an acceptable means to assess the level of sensitization potency of chemicals and helps provide better regulatory decisions.
Collapse
Affiliation(s)
- Atanas Chapkanov
- Laboratory of Mathematical Chemistry, Prof. As. Zlatarov University, Bourgas, Bulgaria
| | - Terry W Schultz
- The University of Tennessee, College of Veterinary Medicine, Knoxville, TN, 37996-4500, USA
| | - Darina Yordanova
- Laboratory of Mathematical Chemistry, Prof. As. Zlatarov University, Bourgas, Bulgaria
| | - Kalin Kirilov
- Laboratory of Mathematical Chemistry, Prof. As. Zlatarov University, Bourgas, Bulgaria
| | - Hristiana Ivanova
- Laboratory of Mathematical Chemistry, Prof. As. Zlatarov University, Bourgas, Bulgaria
| | - Ovanes G Mekenyan
- Laboratory of Mathematical Chemistry, Prof. As. Zlatarov University, Bourgas, Bulgaria.
| |
Collapse
|
2
|
Johnson C, Anger LT, Benigni R, Bower D, Bringezu F, Crofton KM, Cronin MT, Cross KP, Dettwiler M, Frericks M, Melnikov F, Miller S, Roberts DW, Suarez-Rodriguez D, Roncaglioni A, Lo Piparo E, Tice RR, Zwickl C, Myatt GJ. Evaluating Confidence in Toxicity Assessments Based on Experimental Data and In Silico Predictions. COMPUTATIONAL TOXICOLOGY (AMSTERDAM, NETHERLANDS) 2022; 21:100204. [PMID: 35368849 PMCID: PMC8967148 DOI: 10.1016/j.comtox.2021.100204] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Understanding the reliability and relevance of a toxicological assessment is important for gauging the overall confidence and communicating the degree of uncertainty related to it. The process involved in assessing reliability and relevance is well defined for experimental data. Similar criteria need to be established for in silico predictions, as they become increasingly more important to fill data gaps and need to be reasonably integrated as additional lines of evidence. Thus, in silico assessments could be communicated with greater confidence and in a more harmonized manner. The current work expands on previous definitions of reliability, relevance, and confidence and establishes a conceptional framework to apply those to in silico data. The approach is used in two case studies: 1) phthalic anhydride, where experimental data are readily available and 2) 4-hydroxy-3-propoxybenzaldehyde, a data poor case which relies predominantly on in silico methods, showing that reliability, relevance, and confidence of in silico assessments can be effectively communicated within Integrated approaches to testing and assessment (IATA).
Collapse
Affiliation(s)
- Candice Johnson
- Instem, 1393 Dublin Rd, Columbus, OH 43215, USA,Corresponding author.
(C. Johnson)
| | | | | | - David Bower
- Instem, 1393 Dublin Rd, Columbus, OH 43215, USA
| | | | | | - Mark T.D. Cronin
- School of Pharmacy and Biomolecular Sciences, Liverpool
John Moores University, Liverpool, L3 3AF, UK
| | | | - Magdalena Dettwiler
- Idorsia Pharmaceuticals Ltd, Hegenheimermattweg 91, 4123
Allschwill, Switzerland
| | - Markus Frericks
- BASF SE, APD/ET, Li 444, Speyerer St 2, 67117
Limburgerhof, Germany
| | - Fjodor Melnikov
- Genentech, Inc., 1 DNA Way, South San Francisco, CA,
94080, USA
| | | | - David W. Roberts
- School of Pharmacy and Biomolecular Sciences, Liverpool
John Moores University, Liverpool, L3 3AF, UK
| | | | - Alessandra Roncaglioni
- Laboratory of Environmental Chemistry and Toxicology,
Department of Environmental Health Sciences, Istituto di Ricerche Farmacologiche
Mario Negri IRCCS, Milan, Italy
| | - Elena Lo Piparo
- Chemical Food Safety Group, Nestlé Research,
Lausanne, Switzerland
| | | | - Craig Zwickl
- Transendix LLC, 1407 Moores Manor, Indianapolis, IN
46229, USA
| | | |
Collapse
|
3
|
Arts J. How to assess respiratory sensitization of low molecular weight chemicals? Int J Hyg Environ Health 2020; 225:113469. [PMID: 32058937 DOI: 10.1016/j.ijheh.2020.113469] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2019] [Revised: 12/29/2019] [Accepted: 01/27/2020] [Indexed: 12/13/2022]
Abstract
There are no validated and regulatory accepted (animal) models to test for respiratory sensitization of low molecular weight (LMW) chemicals. Since several decades such chemicals are classified as respiratory sensitizers almost exclusively based on observations in workers. However, both respiratory allergens (in which process the immune system is involved) as well as asthmagens (no involvement of the immune system) may induce the same type of respiratory symptoms. Correct classification is very important from a health's perspective point of view. On the other hand, over-classification is not preferable in view of high costs to overdue workplace engineering controls or the chemical ultimately being banned due to Authorities' decisions. It would therefore be very beneficial if respiratory sensitizers can be correctly identified and distinguished from skin sensitizers and non-sensitizers/respiratory irritants. The purpose of this paper is to consider whether LMW chemicals can be correctly identified based on the currently available screening methods in workers, and/or via in silico, in vitro and/or in vivo testing. Collectively, based on the available information further effort is still needed to be able to correctly identify respiratory sensitizers and to distinguish these from skin sensitizers and irritants, not at least because of the far-reaching consequences once a chemical is classified as a respiratory sensitizer.
Collapse
Affiliation(s)
- Josje Arts
- Nouryon, Velperweg 76, 6824 BM Arnhem, the Netherlands.
| |
Collapse
|
4
|
Developing a framework for assessing chemical respiratory sensitization: A workshop report. Regul Toxicol Pharmacol 2016; 80:295-309. [PMID: 27396307 DOI: 10.1016/j.yrtph.2016.06.006] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2016] [Accepted: 06/10/2016] [Indexed: 12/29/2022]
Abstract
Respiratory tract sensitization can have significant acute and chronic health implications. While induction of respiratory sensitization is widely recognized for some chemicals, validated standard methods or frameworks for identifying and characterizing the hazard are not available. A workshop on assessment of respiratory sensitization was held to discuss the current state of science for identification and characterization of respiratory sensitizer hazard, identify information facilitating development of validated standard methods and frameworks, and consider the regulatory and practical risk management needs. Participants agreed on a predominant Th2 immunological mechanism and several steps in respiratory sensitization. Some overlapping cellular events in respiratory and skin sensitization are well understood, but full mechanism(s) remain unavailable. Progress on non-animal approaches to skin sensitization testing, ranging from in vitro systems, -omics, in silico profiling, and structural profiling were acknowledged. Addressing both induction and elicitation phases remains challenging. Participants identified lack of a unifying dose metric as increasing the difficulty of interpreting dosimetry across exposures. A number of research needs were identified, including an agreed list of respiratory sensitizers and other asthmagens, distinguishing between adverse effects from immune-mediated versus non-immunological mechanisms. A number of themes emerged from the discussion regarding future testing strategies, particularly the need for a tiered framework respiratory sensitizer assessment. These workshop present a basis for moving towards a weight-of-evidence assessment.
Collapse
|
5
|
Whritenour J, Casinghino S, Collinge M, Zhu X. Nonclinical Tools to Assess Risk of Drug Hypersensitivity Reactions. Annu Rev Pharmacol Toxicol 2016; 56:561-76. [DOI: 10.1146/annurev-pharmtox-010715-103354] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- J. Whritenour
- Pfizer Inc., Drug Safety Research and Development, Groton, Connecticut 06340;
| | - S. Casinghino
- Pfizer Inc., Drug Safety Research and Development, Groton, Connecticut 06340;
| | - M. Collinge
- Pfizer Inc., Drug Safety Research and Development, Groton, Connecticut 06340;
| | - X. Zhu
- Pfizer Inc., Drug Safety Research and Development, Groton, Connecticut 06340;
| |
Collapse
|
6
|
Ji Z, LeBaron MJ, Schisler MR, Zhang F, Bartels MJ, Gollapudi BB, Pottenger LH. Dose-Response for Multiple Biomarkers of Exposure and Genotoxic Effect Following Repeated Treatment of Rats with the Alkylating Agents, MMS and MNU. Mutagenesis 2015; 31:297-308. [PMID: 26040483 DOI: 10.1093/mutage/gev035] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The nature of the dose-response relationship for various in vivo endpoints of exposure and effect were investigated using the alkylating agents, methyl methanesulfonate (MMS) and methylnitrosourea (MNU). Six male F344 rats/group were dosed orally with 0, 0.5, 1, 5, 25 or 50mg/kg bw/day (mkd) of MMS, or 0, 0.01, 0.1, 1, 5, 10, 25 or 50 mkd of MNU, for 4 consecutive days and sacrificed 24h after the last dose. The dose-responses for multiple biomarkers of exposure and genotoxic effect were investigated. In MMS-treated rats, the hemoglobin adduct level, a systemic exposure biomarker, increased linearly with dose (r (2) = 0.9990, P < 0.05), indicating the systemic availability of MMS; however, the N7MeG DNA adduct, a target exposure biomarker, exhibited a non-linear dose-response in blood and liver tissues. Blood reticulocyte micronuclei (MN), a genotoxic effect biomarker, exhibited a clear no-observed-genotoxic-effect-level (NOGEL) of 5 mkd as a point of departure (PoD) for MMS. Two separate dose-response models, the Lutz and Lutz model and the stepwise approach using PROC REG both supported a bilinear/threshold dose-response for MN induction. Liver gene expression, a mechanistic endpoint, also exhibited a bilinear dose-response. Similarly, in MNU-treated rats, hepatic DNA adducts, gene expression changes and MN all exhibited clear PoDs, with a NOGEL of 1 mkd for MN induction, although dose-response modeling of the MNU-induced MN data showed a better statistical fit for a linear dose-response. In summary, these results provide in vivo data that support the existence of clear non-linear dose-responses for a number of biologically significant events along the pathway for genotoxicity induced by DNA-reactive agents.
Collapse
|
7
|
Davis M, Boekelheide K, Boverhof DR, Eichenbaum G, Hartung T, Holsapple MP, Jones TW, Richard AM, Watkins PB. The new revolution in toxicology: The good, the bad, and the ugly. Ann N Y Acad Sci 2013; 1278:11-24. [DOI: 10.1111/nyas.12086] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Affiliation(s)
- Myrtle Davis
- Toxicology and Pharmacology Branch, Developmental Therapeutics Program Division of Cancer Treatment and Diagnosis; The National Cancer Institute, National Institutes of Health; Bethesda; Maryland
| | - Kim Boekelheide
- Deparment of Pathology and Laboratory Medicine; Brown University; Providence; Rhode Island
| | - Darrell R. Boverhof
- Toxicology and Environmental Research and Consulting; The Dow Chemical Company; Midland; Michigan
| | - Gary Eichenbaum
- Department of Drug Safety Science; Johnson & Johnson Pharmaceutical R&D, LLC; Raritan; NJ
| | - Thomas Hartung
- Department of Environmental Health Sciences. Johns Hopkins Bloomberg School of Public Health; Baltimore; Maryland
| | | | - Thomas W. Jones
- Department of Toxicology and Pathology; Elil Lilly and Company; Indianapolis; Indiana
| | - Ann M. Richard
- National Center for Computational Toxicology; Environmental Protection Agency, Research Triangle Park; North Carolina
| | - Paul B. Watkins
- Institute for Drug Safety Sciences; Hamner University of North Carolina, Research Triangle Park; North Carolina
| |
Collapse
|
8
|
Adenuga D, Woolhiser MR, Gollapudi BB, Boverhof DR. Differential Gene Expression Responses Distinguish Contact and Respiratory Sensitizers and Nonsensitizing Irritants in the Local Lymph Node Assay. Toxicol Sci 2012; 126:413-25. [DOI: 10.1093/toxsci/kfs071] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
|
9
|
Oshida K, Maeda A, Kitsukawa M, Suga S, Iwano S, Miyoshi T, Miyamoto Y. Novel gene markers of immunosuppressive chemicals in mouse lymph node assay. Toxicol Lett 2011; 205:79-85. [PMID: 21621594 DOI: 10.1016/j.toxlet.2011.05.1017] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2011] [Revised: 05/11/2011] [Accepted: 05/12/2011] [Indexed: 01/07/2023]
Abstract
The murine local lymph node assay (LLNA) is an immunologically based test of the sensitizing potential of immunotoxicants, but also evaluates immunosuppressive potential with good sensitivity and specificity. We conducted the LLNA with calcineurin inhibitors (tacrolimus and cyclosporin A), antimetabolites (methotrexate and azathioprine), steroids (dexamethasone and prednisolone), and an alkylator (cyclophosphamide). We performed a comprehensive analysis of results of gene expression in lymph nodes obtained in the LLNA using a highly sensitive DNA chip, 3D-Gene™, and the quantitative reverse transcription-polymerase chain reaction (qPCR). Zfp459 expression increased in all animals treated with immunosuppressive chemicals. Ltf, Cbll1 and Lias expression changed specifically in response to the calcineurin inhibitors, Fmo2 and 9630033F20Rik in response to the antimetabolites, Krt8, Gjb1, Hmha1 and Sfrs7 in response to the steroids, and Gbp1 and Mup5 in response to the alkylator. Therefore, these genes were considered novel markers for immunosuppression and their expression could be used to evaluate the mechanism of action of immunosuppressive chemicals.
Collapse
Affiliation(s)
- Keiyu Oshida
- Toxicology and Pharmacokinetics Laboratories, Pharmaceutical Research Laboratories, Toray Industries, Inc., 6-10-1, Tebiro, Kamakura, Kanagawa 248-8555, Japan
| | | | | | | | | | | | | |
Collapse
|
10
|
Ku HO, Jeong SH, Kang HG, Son SW, Yun SM, Ryu DY. Pathway analysis of gene expression in local lymph nodes draining skin exposed to three different sensitizers. J Appl Toxicol 2011; 31:455-62. [DOI: 10.1002/jat.1646] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2010] [Revised: 11/26/2010] [Accepted: 11/26/2010] [Indexed: 11/08/2022]
Affiliation(s)
- Hyun-Ok Ku
- National Veterinary Research and Quarantine Service; Anyang; 430-824; Republic of Korea
| | - Sang-Hee Jeong
- Toxicological Research Center; Hoseo University; Asan; 336-795; Republic of Korea
| | - Hwan-Goo Kang
- National Veterinary Research and Quarantine Service; Anyang; 430-824; Republic of Korea
| | - Seong-Wan Son
- National Veterinary Research and Quarantine Service; Anyang; 430-824; Republic of Korea
| | - So-mi Yun
- National Veterinary Research and Quarantine Service; Anyang; 430-824; Republic of Korea
| | - Doug-Young Ryu
- College of Veterinary Medicine; Seoul National University; Seoul; 151-742; Republic of Korea
| |
Collapse
|
11
|
Frawley R, White K, Brown R, Musgrove D, Walker N, Germolec D. Gene expression alterations in immune system pathways in the thymus after exposure to immunosuppressive chemicals. ENVIRONMENTAL HEALTH PERSPECTIVES 2011; 119:371-376. [PMID: 21041162 PMCID: PMC3060001 DOI: 10.1289/ehp.1002358] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/27/2010] [Accepted: 11/01/2010] [Indexed: 05/30/2023]
Abstract
BACKGROUND Dysregulation of positive and negative selection, antigen presentation, or apoptosis in the thymus can lead to immunosuppression or autoimmunity. Diethylstilbestrol (DES), dexamethasone (DEX), cyclophosphamide (CPS), and 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) are immunosuppressive chemicals that induce similar immunotoxic effects in the thymus, however, the mechanism of toxicity is purported to be different for each compound. OBJECTIVES We hypothesized that genomic analysis of thymus after chemical-induced atrophy would yield transcriptional profiles that suggest pathways of toxicity associated with reduced function. METHODS Female B6C3F1 mice were exposed to these immunosuppressive agents and changes in gene expression and immune cell subpopulations were evaluated. RESULTS All four chemicals induced thymic atrophy and changes in both the relative proportion and absolute number of CD3(+), CD4(+)/CD8(-), CD4(-)/CD8(+), and CD4(+)/CD8(+) thymocytes. The most significant impact of exposure to DEX, DES, and CPS was modulation of gene expression in the T-cell receptor (TCR) complex and TCR and CD28 signaling pathways; this could represent a common mechanism of action and play a pivotal role in lineage commitment and development of T cells. Up-regulation of genes associated with the antigen presentation and dendritic cell maturation pathways was the most distinctive effect of TCDD exposure. These elements, which were also up-regulated by DEX and DES, contribute to positive and negative selection. CONCLUSIONS Genomic analysis revealed gene expression changes in several pathways that are commonly associated with xenobiotic-induced immune system perturbations, particularly those that contribute to the development and maturation of thymic T cells.
Collapse
Affiliation(s)
- Rachel Frawley
- National Institute of Environmental Health Sciences, National Toxicology Program, Research Triangle Park, North Carolina, USA.
| | | | | | | | | | | |
Collapse
|
12
|
Boverhof DR, Gollapudi BB, Hotchkiss JA, Osterloh-Quiroz M, Woolhiser MR. A draining lymph node assay (DLNA) for assessing the sensitizing potential of proteins. Toxicol Lett 2010; 193:144-51. [PMID: 20060446 DOI: 10.1016/j.toxlet.2009.12.020] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2009] [Revised: 12/29/2009] [Accepted: 12/30/2009] [Indexed: 10/20/2022]
Abstract
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.
Collapse
Affiliation(s)
- Darrell R Boverhof
- Toxicology & Environmental Research and Consulting, The Dow Chemical Company, Midland, MI 48674, USA.
| | | | | | | | | |
Collapse
|
13
|
Abstract
A brief historical perspective of immunotoxicology is presented describing the early development of predictive screening tests to identify xenobiotics that may cause immunosuppression or skin sensitization. This includes a discussion of the evolution of the discipline to support a better understanding of basic -science and improvement of human risk assessment. The last section describes the need for additional validated screening tests and recent efforts to address this gap in the other areas of immunotoxicology including food and respiratory allergy, autoimmunity and immunostimulation.
Collapse
|
14
|
Natsch A. The Nrf2-Keap1-ARE toxicity pathway as a cellular sensor for skin sensitizers--functional relevance and a hypothesis on innate reactions to skin sensitizers. Toxicol Sci 2009; 113:284-92. [PMID: 19767620 DOI: 10.1093/toxsci/kfp228] [Citation(s) in RCA: 119] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
With the tight deadlines set both by the public and by the regulatory authorities to replace animal tests for toxicological endpoints relevant to the development of cosmetic products, a large number of research projects have recently focused on cellular endpoints affected by skin sensitizing compounds. The general aim stated in these projects was to find "markers" for skin sensitizers, be it at the level of the transcriptome or at the protein level. Rather than talking of "cellular markers," the new paradigm "Toxicity testing in the 21st century" formulated by the National Academy of Sciences in the United States focuses on "Toxicity pathways." A specific marker for any given toxicological endpoint can only exist, if specific toxicity pathways, comprising specific sensors, are linked to this endpoint. In the context of skin sensitization, one has to ask whether there is an innate cellular signaling pathway activated by skin sensitizers. Here a significant body of evidence, mainly accumulated in the last 20 months, is reviewed, indicating that indeed the Nrf2-Keap1-ARE regulatory pathway is such a toxicity pathway activated by cysteine-reactive skin sensitizers. Whereas first indications on the in vivo relevance are available, key questions remain open and can now specifically be addressed. A minority of sensitizers, more specifically reacting with lysine residues, appears not to activate the Nrf2-Keap1-ARE pathway and might trigger yet another unknown toxicity pathway.
Collapse
Affiliation(s)
- Andreas Natsch
- Bioscience Department, Fragrance Research, Givaudan Schweiz AG, Duebendorf, Switzerland.
| |
Collapse
|