Uncovering the toxicity mechanisms of a series of carboxylic acids in liver cells through computational and experimental approaches

Hepatotoxicity poses a significant concern in drug design due to the potential liver damage that can be caused by new drugs. Among common manifestations of hepatotoxic damage is lipid accumulation in hepatic tissue, resulting in liver steatosis or phospholipidosis. Carboxylic derivatives are prone to interfere with fatty acid metabolism and cause lipid accumulation in hepatocytes. This study investigates the toxic behaviour of 24 structurally related carboxylic acids in hepatocytes, specifically their ability to cause accumulation of fatty acids and phospholipids. Using high-content screening (HCS) assays, we identified two distinct lipid accumulation patterns. Subsequently, we developed structure-activity relationship (SAR) and quantitative structure-activity relationship (QSAR) models to determine relevant molecular substructures and descriptors contributing to these adverse effects. Additionally, we calculated physicochemical properties associated with lipid accumulation in hepatocytes and examined their correlation with our chemical structure characteristics. To assess the applicability of our findings to a wide range of chemical compounds, we employed two external datasets to evaluate the distribution of our QSAR descriptors. Our study highlights the significance of subtle molecular structural variations in triggering hepatotoxicity, such as the presence of nitrogen or the specific arrangement of substitutions within the carbon chain. By employing our comprehensive approach, we pinpointed specific molecules and elucidated their mechanisms of toxicity, thus offering valuable insights to guide future toxicology investigations.

Protectiveness of NAM-based hazard assessment - which testing scope is required?

Hazard assessment (HA) requires toxicity tests to allow deriving protective points of departure (PoDs) for risk assessment irrespective of a compound's mode of action (MoA). The scope of in vitro test batteries (ivTB) thereby necessitated for systemic toxicity is still unclear. We explored the protectiveness regarding systemic toxicity of an ivTB with a scope, which was guided by previous findings from rodent studies, where examining six main targets, including liver and kidney, was sufficient to predict the guideline scope-based PoD with high probability. The ivTB comprises human in vitro models representing liver, kidney, lung and the neuronal system covering transcriptome, mitochondrial dysfunction and neuronal outgrowth. Additionally, 32 CALUX®- and 10 HepG2 BAC-GFP reporters cover a broad range of disturbance mechanisms. Eight compounds were chosen for causing adverse effects such as immunotoxicity or anemia in vivo, i.e., effects not directly covered by assays in the ivTB. PoDs derived from the ivTB and from oral repeated dose studies in rodents were extrapolated to maximum unbound plasma concentrations for comparison. The ivTB-based PoDs were one to five orders of magnitude lower than in vivo PoDs for six of eight compounds, implying that they were protective. The extent of in vitro response varied across test compounds. Especially for hematotoxic substances, the ivTB showed either no response or only cytotoxicity. Assays better capturing this type of hazard would be needed to complement the ivTB. This study highlights the potentially broad applicability of ivTBs for deriving protective PoDs of compounds with unknown MoA.

Update of the Cancer Potency Database (CPDB) to enable derivations of Thresholds of Toxicological Concern (TTC) for cancer potency

The purpose of this study was to update the existing Cancer Potency Database (CPDB) in order to support the development of a dataset of compounds, with associated points of departure (PoDs), to enable a review and update of currently applied values for the Threshold of Toxicological Concern (TTC) for cancer endpoints. This update of the current CPDB, last reviewed in 2012, includes the addition of new data (44 compounds and 158 studies leading to additional 359 dose-response curves). Strict inclusion criteria were established and applied to select compounds and studies with relevant cancer potency data. PoDs were calculated from dose-response modeling, including the benchmark dose (BMD) and the lower 90% confidence limits (BMDL) at a specified benchmark response (BMR) of 10%. The updated full CPDB database resulted in a total of 421 chemicals which had dose-response data that could be used to calculate PoDs. This candidate dataset for cancer TTC is provided in a transparent and adaptable format for further analysis of TTC to derive cancer potency thresholds.

Toward implementing virtual control groups in nonclinical safety studies

Historical data from control groups in animal toxicity studies is currently mainly used for comparative purposes to assess validity and robustness of study results. Due to the highly controlled environment in which the studies are performed and the homogeneity of the animal collectives it has been proposed to use the historical data for building so-called virtual control groups, which could replace partly or entirely the concurrent control. This would constitute a substantial contribution to the reduction of animal use in safety studies. Before the concept can be implemented, the prerequisites regarding data collection, curation and statistical evaluation together with a validation strategy need to be identified to avoid any impairment of the study outcome and subsequent consequences for human risk assessment. To further assess and develop the concept of virtual control groups the transatlantic think tank for toxicology (t⁴) sponsored a workshop with stakeholders from the pharmaceutical and chemical industry, academia, FDA, pharmaceutical, contract research organizations (CROs), and non-governmental organizations in Washington, which took place in March 2023. This report summarizes the current efforts of a European initiative to share, collect and curate animal control data in a centralized database and the first approaches to identify optimal matching criteria between virtual controls and the treatment arms of a study as well as first reflections about strategies for a qualification procedure and potential pitfalls of the concept.

Exposure considerations in human safety assessment: Report from an EPAA Partners' Forum

Understanding and estimating the exposure to a substance is one of the fundamental requirements for safe manufacture and use. Many approaches are taken to determine exposure to substances, mainly driven by potential use and regulatory need. There are many opportunities to improve and optimise the use of exposure information for chemical safety. The European Partnership for Alternative Approaches to Animal Testing (EPAA) therefore convened a Partners' Forum (PF) to explore exposure considerations in human safety assessment of industrial products to agree key conclusions for the regulatory acceptance of exposure assessment approaches and priority areas for further research investment. The PF recognised the widescale use of exposure information across industrial sectors with the possibilities of creating synergies between different sectors. Further, the PF acknowledged that the EPAA could make a significant contribution to promote the use of exposure data in human safety assessment, with an aim to address specific regulatory needs. To achieve this, research needs, as well as synergies and areas for potential collaboration across sectors, were identified.

Workshop report: Challenges faced in developing inhalation thresholds of Toxicological Concern (TTC) - State of the science and next steps

A challenging step in human risk assessment of chemicals is the derivation of safe thresholds. The Threshold of Toxicological Concern (TTC) concept is one option which can be used for the safety evaluation of substances with a limited toxicity dataset, but for which exposure is sufficiently low. The application of the TTC is generally accepted for orally or dermally exposed cosmetic ingredients; however, these values cannot directly be applied to the inhalation route because of differences in exposure route versus oral and dermal. Various approaches of an inhalation TTC concept have been developed over recent years to address this. A virtual workshop organized by Cosmetics Europe, held in November 2020, shared the current state of the science regarding the applicability of existing inhalation TTC approaches to cosmetic ingredients. Key discussion points included the need for an inhalation TTC for local respiratory tract effects in addition to a systemic inhalation TTC, dose metrics, database building and quality of studies, definition of the chemical space and applicability domain, and classification of chemicals with different potencies. The progress made to date in deriving inhalation TTCs was highlighted, as well as the next steps envisaged to develop them further for regulatory acceptance and use.

Substantiate a read-across hypothesis by using transcriptome data-A case study on volatile diketones

This case study explores the applicability of transcriptome data to characterize a common mechanism of action within groups of short-chain aliphatic α-, β-, and γ-diketones. Human reference in vivo data indicate that the α-diketone diacetyl induces bronchiolitis obliterans in workers involved in the preparation of microwave popcorn. The other three α-diketones induced inflammatory responses in preclinical in vivo animal studies, whereas beta and gamma diketones in addition caused neuronal effects. We investigated early transcriptional responses in primary human bronchiolar (PBEC) cell cultures after 24 h and 72 h of air-liquid exposure. Differentially expressed genes (DEGs) were assessed based on transcriptome data generated with the EUToxRisk gene panel of Temp-O-Seq^®. For each individual substance, genes were identified displaying a consistent differential expression across dose and exposure duration. The log fold change values of the DEG profiles indicate that α- and β-diketones are more active compared to γ-diketones. α-diketones in particular showed a highly concordant expression pattern, which may serve as a first indication of the shared mode of action. In order to gain a better mechanistic understanding, the resultant DEGs were submitted to a pathway analysis using ConsensusPathDB. The four α-diketones showed very similar results with regard to the number of activated and shared pathways. Overall, the number of signaling pathways decreased from α-to β-to γ-diketones. Additionally, we reconstructed networks of genes that interact with one another and are associated with different adverse outcomes such as fibrosis, inflammation or apoptosis using the TRANSPATH-database. Transcription factor enrichment and upstream analyses with the geneXplain platform revealed highly interacting gene products (called master regulators, MRs) per case study compound. The mapping of the resultant MRs on the reconstructed networks, visualized similar gene regulation with regard to fibrosis, inflammation and apoptosis. This analysis showed that transcriptome data can strengthen the similarity assessment of compounds, which is of particular importance, e.g., in read-across approaches. It is one important step towards grouping of compounds based on biological profiles.

Potential of the zebrafish (Danio rerio) embryo test to discriminate between chemicals of similar molecular structure-a study with valproic acid and 14 of its analogues

Valproic acid is a frequently used antiepileptic drug and known pediatric hepatotoxic agent. In search of pharmaceuticals with increased effectiveness and reduced toxicity, analogue chemicals came into focus. So far, toxicity and teratogenicity data of drugs and metabolites have usually been collected from mammalian model systems such as mice and rats. However, in an attempt to reduce mammalian testing while maintaining the reliability of toxicity testing of new industrial chemicals and drugs, alternative test methods are being developed. To this end, the potential of the zebrafish (Danio rerio) embryo to discriminate between valproic acid and 14 analogues was investigated by exposing zebrafish embryos for 120 h post fertilization in the extended version of the fish embryo acute toxicity test (FET; OECD TG 236), and analyzing liver histology to evaluate the correlation of liver effects and the molecular structure of each compound. Although histological evaluation of zebrafish liver did not identify steatosis as the prominent adverse effect typical in human and mice, the structure–activity relationship (SAR) derived was comparable not only to human HepG2 cells, but also to available in vivo mouse and rat data. Thus, there is evidence that zebrafish embryos might serve as a tool to bridge the gap between subcellular, cell-based systems and vertebrate models.

Application of high-throughput transcriptomics for mechanism-based biological read-across of short-chain carboxylic acid analogues of valproic acid

Chemical read-across is commonly evaluated without specific knowledge of the biological mechanisms leading to observed adverse outcomes in vivo. Integrating data that indicate shared modes of action in humans will strengthen read-across cases. Here we studied transcriptomic responses of primary human hepatocytes (PHH) to a large panel of carboxylic acids to include detailed mode-of-action data as a proof-of-concept for read-across in risk assessment. In rodents, some carboxylic acids, including valproic acid (VPA), are known to cause hepatic steatosis, whereas others do not. We investigated transcriptomics responses of PHHs exposed for 24 h to 18 structurally different VPA analogues in a concentration range to determine biological similarity in relation to in vivo steatotic potential. Using a targeted high-throughput screening assay, we assessed the differential expression of ~3,000 genes covering relevant biological pathways. Differentially expressed gene analysis revealed differences in potency of carboxylic acids, and expression patterns were highly similar for structurally similar compounds. Strong clustering occurred for steatosis-positive versus steatosis-negative carboxylic acids. To quantitatively define biological read-across, we combined pathway analysis and weighted gene co-expression network analysis. Active carboxylic acids displayed high similarity in gene network modulation. Importantly, free fatty acid synthesis modulation and stress pathway responses are affected by active car­boxylic acids, providing coherent mechanistic underpinning for our findings. Our work shows that transcriptomic analysis of cultured human hepatocytes can reinforce the prediction of liver injury outcome based on quantitative and mechanistic biological data and support its application in read-across.

RespiraTox - Development of a QSAR model to predict human respiratory irritants

Respiratory irritation is an important human health endpoint in chemical risk assessment. There are two established modes of action of respiratory irritation, 1) sensory irritation mediated by the interaction with sensory neurons, potentially stimulating trigeminal nerve, and 2) direct tissue irritation. The aim of our research was to, develop a QSAR method to predict human respiratory irritants, and to potentially reduce the reliance on animal testing for the identification of respiratory irritants. Compounds are classified as irritating based on combined evidence from different types of toxicological data, including inhalation studies with acute and repeated exposure. The curated project database comprised 1997 organic substances, 1553 being classified as irritating and 444 as non-irritating. A comparison of machine learning approaches, including Logistic Regression (LR), Random Forests (RFs), and Gradient Boosted Decision Trees (GBTs), showed, the best classification was obtained by GBTs. The LR model resulted in an area under the curve (AUC) of 0.65, while the optimal performance for both RFs and GBTs gives an AUC of 0.71. In addition to the classification and the information on the applicability domain, the web-based tool provides a list of structurally similar analogues together with their experimental data to facilitate expert review for read-across purposes.

A read-across case study on chronic toxicity of branched carboxylic acids (1): Integration of mechanistic evidence from new approach methodologies (NAMs) to explore a common mode of action

This read-across case study characterises thirteen, structurally similar carboxylic acids demonstrating the application of in vitro and in silico human-based new approach methods, to determine biological similarity. Based on data from in vivo animal studies, the read-across hypothesis is that all analogues are steatotic and so should be considered hazardous. Transcriptomic analysis to determine differentially expressed genes (DEGs) in hepatocytes served as first tier testing to confirm a common mode-of-action and identify differences in the potency of the analogues. An adverse outcome pathway (AOP) network for hepatic steatosis, informed the design of an in vitro testing battery, targeting AOP relevant MIEs and KEs, and Dempster-Shafer decision theory was used to systematically quantify uncertainty and to define the minimal testing scope. The case study shows that the read-across hypothesis is the critical core to designing a robust, NAM-based testing strategy. By summarising the current mechanistic understanding, an AOP enables the selection of NAMs covering MIEs, early KEs, and late KEs. Experimental coverage of the AOP in this way is vital since MIEs and early KEs alone are not confirmatory of progression to the AO. This strategy exemplifies the workflow previously published by the EUTOXRISK project driving a paradigm shift towards NAM-based NGRA.

Threshold of Toxicological Concern—An Update for Non-Genotoxic Carcinogens

The Threshold of Toxicological Concern (TTC) concept can be applied to organic compounds with the known chemical structure to derive a threshold for exposure, below which a toxic effect on human health by the compound is not expected. The TTC concept distinguishes between carcinogens that may act as genotoxic and non-genotoxic compounds. A positive prediction of a genotoxic mode of action, either by structural alerts or experimental data, leads to the application of the threshold value for genotoxic compounds. Non-genotoxic substances are assigned to the TTC value of their respective Cramer class, even though it is recognized that they could test positive in a rodent cancer bioassay. This study investigated the applicability of the Cramer classes specifically to provide adequate protection for non-genotoxic carcinogens. For this purpose, benchmark dose levels based on tumor incidence were compared with no observed effect levels (NOELs) derived from non-, pre- or neoplastic lesions. One key aspect was the categorization of compounds as non-genotoxic carcinogens. The recently finished CEFIC LRI project B18 classified the carcinogens of the Carcinogenicity Potency DataBase (CPDB) as either non-genotoxic or genotoxic compounds based on experimental or in silico data. A detailed consistency check resulted in a dataset of 137 non-genotoxic organic compounds. For these 137 compounds, NOEL values were derived from high quality animal studies with oral exposure and chronic duration using well-known repositories, such as RepDose, ToxRef, and COSMOS DB. Further, an effective tumor dose (ETD10) was calculated and compared with the lower confidence limit on benchmark dose levels (BMDL10) derived by model averaging. Comparative analysis of NOEL/EDT10/BMDL10 values showed that potentially bioaccumulative compounds in humans, as well as steroids, which both belong to the exclusion categories, occur predominantly in the region of the fifth percentiles of the distributions. Excluding these 25 compounds resulted in significantly higher but comparable fifth percentile chronic NOEL and BMDL10 values, while the fifth percentile EDT10 value was slightly higher but not statistically significant. The comparison of the obtained distributions of NOELs with the existing Cramer classes and their derived TTC values supports the application of Cramer class thresholds to all non-genotoxic compounds, such as non-genotoxic carcinogens.

NAM-supported read-across: From case studies to regulatory guidance in safety assessment

The use of new approach methodologies (NAMs) in support of read-across (RAx) approaches for regulatory purposes is a main goal of the EU-ToxRisk project. To bring this forward, EU-ToxRisk partners convened a workshop in close collaboration with regulatory representatives from key organizations including European regulatory agencies, such as the European Chemicals Agency (ECHA) and the European Food Safety Authority (EFSA), as well as the Scientific Committee on Consumer Safety (SCCS), national agencies from several European countries, Japan, Canada and the USA, as well as the Organisation for Economic Cooperation and Development (OECD). More than a hundred people actively participated in the discussions, bringing together diverse viewpoints across academia, regulators and industry. The discussion was organized starting from five practical cases of RAx applied to specific problems that offered the oppor-tunity to consider real examples. There was general consensus that NAMs can improve confidence in RAx, in particular in defining category boundaries as well as characterizing the similarities/dissimilarities between source and target substances. In addition to describing dynamics, NAMs can be helpful in terms of kinetics and metabolism that may play an important role in the demonstration of similarity or dissimilarity among the members of a category. NAMs were also noted as effective in providing quanti-tative data correlated with traditional no observed adverse effect levels (NOAELs) used in risk assessment, while reducing the uncertainty on the final conclusion. An interesting point of view was the advice on calibrating the number of new tests that should be carefully selected, avoiding the allure of "the more, the better". Unfortunately, yet unsurprisingly, there was no single approach befitting every case, requiring careful analysis delineating the optimal approach. Expert analysis and assessment of each specific case is still an important step in the process.

Combining In Vivo Data with In Silico Predictions for Modeling Hepatic Steatosis by Using Stratified Bagging and Conformal Prediction

Hepatic steatosis (fatty liver) is a severe liver disease induced by the excessive accumulation of fatty acids in hepatocytes. In this study, we developed reliable in silico models for predicting hepatic steatosis on the basis of an in vivo data set of 1041 compounds measured in rodent studies with repeated oral exposure. The imbalanced nature of the data set (1:8, with the "steatotic" compounds belonging to the minority class) required the use of meta-classifiers-bagging with stratified under-sampling and Mondrian conformal prediction-on top of the base classifier random forest. One major goal was the investigation of the influence of different descriptor combinations on model performance (tested by predicting an external validation set): physicochemical descriptors (RDKit), ToxPrint features, as well as predictions from in silico nuclear receptor and transporter models. All models based upon descriptor combinations including physicochemical features led to reasonable balanced accuracies (BAs between 0.65 and 0.69 for the respective models). Combining physicochemical features with transporter predictions and further with ToxPrint features gave the best performing model (BAs up to 0.7 and efficiencies of 0.82). Whereas both meta-classifiers proved useful for this highly imbalanced toxicity data set, the conformal prediction framework also guarantees the error level and thus might be favored for future studies in the field of predictive toxicology.

Risk assessment for irritating chemicals - Derivation of extrapolation factors

Irritation of the eyes and the upper respiratory tract are important endpoints for setting guide values for chemicals. To optimize the use of the often-limited data, we analysed controlled human exposure studies (CHS) with 1-4 h inhalation of the test substance, repeated dose inhalation studies in rodents, and Alarie-Tests and derived extrapolation factors (EF) for exposure duration, inter- and intraspecies differences. For the endpoint irritating effects in the respiratory tract in rodents, geometric mean (GM) values of 1.9 were obtained for the EF for subacute→subchronic (n = 16), 2.1 for subchronic→chronic (n = 40), and 2.9 for subacute→chronic (n = 10) extrapolation. Based on these data we suggest an EF of 2 for subchronic→chronic and of 4 for subacute→chronic extrapolation. In CHS, exposure concentration determines the effects rather than exposure duration. Slight reversible effects during 4 h exposure indicate that an EF of 1 can be considered for assessing chronic exposures. To assess species extrapolation, 10 chemicals were identified with both, reliable rat inhalation studies and CHS. The GM of the ratio between the No Observed Adverse Effect Concentration (NOAEC) in rats and humans was 2.3 and increased to 3.6 when expanding the dataset to all available EF (n = 25). Based on these analyses, an EF of 3 is suggested to extrapolate from a NOAEC in a chronic rat study to a NOAEC in a CHS. The analysis of EFs for the extrapolation from a 50% decrease in respiratory frequency in the Alarie test in mice (RD₅₀) to a NOAEC in a CHS resulted in a GM of 40, for both, the reliable (n = 11) and the overall dataset (n = 19). We propose to use the RD₅₀ from the Alarie test for setting guide values and to use 40 as EF. Efs for intraspecies differences in the human population must account for susceptible persons, most importantly for persons with chemical intolerance (CI), who show subjective signs of irritation at low concentrations. The limited data available do not justify to deviate from an EF of 10 - 20 as currently used in different regulatory settings.

Setting the stage for next-generation risk assessment with non-animal approaches: the EU-ToxRisk project experience

In 2016, the European Commission launched the EU-ToxRisk research project to develop and promote animal-free approaches in toxicology. The 36 partners of this consortium used in vitro and in silico methods in the context of case studies (CSs). These CSs included both compounds with a highly defined target (e.g. mitochondrial respiratory chain inhibitors) as well as compounds with poorly defined molecular initiation events (e.g. short-chain branched carboxylic acids). The initial project focus was on developing a science-based strategy for read-across (RAx) as an animal-free approach in chemical risk assessment. Moreover, seamless incorporation of new approach method (NAM) data into this process (= NAM-enhanced RAx) was explored. Here, the EU-ToxRisk consortium has collated its scientific and regulatory learnings from this particular project objective. For all CSs, a mechanistic hypothesis (in the form of an adverse outcome pathway) guided the safety evaluation. ADME data were generated from NAMs and used for comprehensive physiological-based kinetic modelling. Quality assurance and data management were optimized in parallel. Scientific and Regulatory Advisory Boards played a vital role in assessing the practical applicability of the new approaches. In a next step, external stakeholders evaluated the usefulness of NAMs in the context of RAx CSs for regulatory acceptance. For instance, the CSs were included in the OECD CS portfolio for the Integrated Approach to Testing and Assessment project. Feedback from regulators and other stakeholders was collected at several stages. Future chemical safety science projects can draw from this experience to implement systems toxicology-guided, animal-free next-generation risk assessment.

Integrated In Silico Models for the Prediction of No-Observed-(Adverse)-Effect Levels and Lowest-Observed-(Adverse)-Effect Levels in Rats for Sub-chronic Repeated-Dose Toxicity

Repeated-dose toxicity (RDT) is a critical endpoint for hazard characterization of chemicals and is assessed to derive safe levels of exposure for human health. Here we present the first attempt to model simultaneously no-observed-(adverse)-effect level (NO(A)EL) and lowest-observed-(adverse)-effect level (LO(A)EL). Classification and regression models were derived based on rat sub-chronic repeated dose toxicity data for 327 compounds from the Fraunhofer RepDose database. Multi-category classification models were built for both NO(A)EL and LO(A)EL though a consensus of statistics- and fragment-based algorithms, while regression models were based on quantitative relationships between the endpoints and SMILES-based attributes. NO(A)EL and LO(A)EL models were integrated, and predictions were compared to exclude inconsistent values. This strategy improved the performance of single models, leading to R² greater than 0.70, root-mean-square error (RMSE) lower than 0.60 (for regression models), and accuracy of 0.61-0.73 (for classification models) on the validation set, based on the endpoint and the threshold applied for selecting predictions. This study confirms the effectiveness of the modeling strategy presented here for assessing RDT of chemicals using in silico models.

Internationalization of read-across as a validated new approach method (NAM) for regulatory toxicology

Read-across (RAx) translates available information from well-characterized chemicals to a substance for which there is a toxicological data gap. The OECD is working on case studies to probe general applicability of RAx, and several regulations (e.g., EU-REACH) already allow this procedure to be used to waive new in vivo tests. The decision to prepare a review on the state of the art of RAx as a tool for risk assessment for regulatory purposes was taken during a workshop with international experts in Ranco, Italy in July 2018. Three major issues were identified that need optimization to allow a higher regulatory acceptance rate of the RAx procedure: (i) the definition of similarity of source and target, (ii) the translation of biological/toxicological activity of source to target in the RAx procedure, and (iii) how to deal with issues of ADME that may differ between source and target. The use of new approach methodologies (NAM) was discussed as one of the most important innovations to improve the acceptability of RAx. At present, NAM data may be used to confirm chemical and toxicological similarity. In the future, the use of NAM may be broadened to fully characterize the hazard and toxicokinetic properties of RAx compounds. Concerning available guidance, documents on Good Read-Across Practice (GRAP) and on best practices to perform and evaluate the RAx process were identified. Here, in particular, the RAx guidance, being worked out by the European Commission’s H2020 project EU-ToxRisk together with many external partners with regulatory experience, is given.

Potential emerging chemical risks in the food chain associated with substances registered under REACH

A screening procedure for the identification of potential emerging chemical risks in the food and feed chain developed in a previous EFSA-sponsored pilot study was applied to 15021 substances registered under the REACH Regulation at the time of evaluation. Eligible substances were selected from this dataset by excluding (a) intermediates handled under strictly controlled conditions, (b) substances lacking crucial input data and (c) compounds considered to be outside the applicability domain of the models used. Selection of eligible substances resulted in a considerable reduction to 2336 substances. These substances were assessed and scored for environmental release (tonnage and use information from REACH registration dossiers), biodegradation (predictions from BIOWIN models 3, 5 and 6 evaluated in a battery approach), bioaccumulation in food/feed (ACC-HUMANsteady modelling) and chronic human health hazards (classification according to the CLP Regulation for carcinogenicity, mutagenicity, reproductive toxicity and repeated dose toxicity as well as IARC classification for carcinogenicity). Prioritisation based on the scores assigned and additional data curation steps identified 212 substances that are considered potential emerging risks in the food chain. Overall, 53% of these substances were prioritised due to chronic hazards identified in REACH registrations dossiers only (i.e. hazards not identified in classifications from other sources). Bioaccumulation in food and feed predicted on the basis of ACC-HUMANsteady modelling identified many substances that are not considered bioaccumulative in aquatic or terrestrial organisms based on screening criteria of the relevant ECHA guidance documents. Furthermore, 52% of the priority substances have not yet been assessed for their presence in food/feed by EU regulatory agencies. This finding and illustrative examples suggest that the screening procedure identified substances that have the potential to be emerging chemical risks in the food chain. Future research should investigate whether they actually represent emerging chemical risks as defined in EFSA's mandate.

Challenges in working towards an internal threshold of toxicological concern (iTTC) for use in the safety assessment of cosmetics: Discussions from the Cosmetics Europe iTTC Working Group workshop

The Threshold of Toxicological Concern (TTC) is an important risk assessment tool which establishes acceptable low-level exposure values to be applied to chemicals with limited toxicological data. One of the logical next steps in the continued evolution of TTC is to develop this concept further so that it is representative of internal exposures (TTC based on plasma concentration). An internal TTC (iTTC) would provide threshold values that could be utilized in exposure-based safety assessments. As part of a Cosmetics Europe (CosEu) research program, CosEu has initiated a project that is working towards the development of iTTCs that can be used for the human safety assessment. Knowing that the development of an iTTC is an ambitious and broad-spanning topic, CosEu organized a Working Group comprised a balance of multiple stakeholders (cosmetics and chemical industries, the EPA and JRC and academia) with relevant experience and expertise and workshop to critically evaluate the requirements to establish an iTTC. Outcomes from the workshop included an evaluation on the current state of the science for iTTC, the overall iTTC strategy, selection of chemical databases, capture and curation of chemical information, ADME and repeat dose data, expected challenges, as well as next steps and ongoing work.

Development of a novel scoring system for identifying emerging chemical risks in the food chain

The European Food Safety Authority (EFSA) is responsible for risk assessment of all aspects of food safety, including the establishment of procedures aimed at the identification of emerging risks to food safety. Here, a scoring system was developed for identifying chemicals registered under the European REACH Regulation that could be of potential concern in the food chain using the following parameters: (i) environmental release based on maximum aggregated tonnages and environmental release categories; (ii) biodegradation in the environment; (iii) bioaccumulation and in vivo and in vitro toxicity. The screening approach was tested on 100 data-rich chemicals registered under the REACH Regulation at aggregated volumes of at least 1000 tonnes per annum. The results show that substance-specific data generated under the REACH Regulation can be used to identify potential emerging risks in the food chain. After application of the screening procedure, priority chemicals can be identified as potentially emerging risk chemicals through the integration of exposure, environmental fate and toxicity. The default approach is to generate a single total score for each substance using a predefined weighting scenario. However, it is also possible to use a pivot table approach to combine the individual scores in different ways that reflect user-defined priorities, which enables a very flexible, iterative definition of screening criteria. Possible applications of the approaches are discussed using illustrative examples. Either approach can then be followed by in-depth evaluation of priority substances to ensure the identification of substances that present a real emerging chemical risk in the food chain.

The application of new HARD-descriptor available from the CORAL software to building up NOAEL models

Continuous QSAR models have been developed and validated for the prediction of no-observed-adverse-effect (NOAEL) in rats, using training and test sets from the Fraunhofer RepDose® database and EFSA's Chemical Hazards Database: OpenFoodTox. This paper demonstrates that the HARD index, as an integrated attribute of SMILES, improves the prediction power of NOAEL values using the continuous QSAR models and Monte Carlo simulations. The HARD-index is a line of eleven symbols, which represents the presence, or absence of eight chemical elements (nitrogen, oxygen, sulfur, phosphorus, fluorine, chlorine, bromine, and iodine) and different kinds of chemical bonds (double bond, triple bond, and stereo chemical bond). Optimal molecular descriptors calculated with the Monte Carlo technique (maximization of correlation coefficient between the descriptor and endpoint) give satisfactory predictive models for NOAEL. Optimal molecular descriptors calculated in this way with the Monte Carlo technique (maximization of correlation coefficient between the descriptor and endpoint) give amongst the best results available in the literature. The models are built up in accordance with OECD principles.

Curated human hyperbilirubinemia data and the respective OATP1B1 and 1B3 inhibition predictions

Hyperbilirubinemia is a pathological condition, very often indicative of underlying liver condition that is characterized by excessive accumulation of conjugated or unconjugated bilirubin in sinusoidal blood. In literature there are several indications associating the inhibition of the basolateral hepatic transporters Organic anion transporting polypeptide 1B1 and 1B3 (OATP1B1 and 1B3) with hyperbilirubinemia. In this article, we present a curated human hyperbilirubinemia dataset and the respective OATP1B1 and 1B3 inhibition predictions obtained from an effort to generate a classification model for hyperbilirubinemia. These data originate from the research article "Linking organic anion transporting polypeptide 1b1 and 1b3 (oatp1b1 and oatp1b3) interaction profiles to hepatotoxicity- the hyperbilirubinemia use case" (E. Kotsampasakou, S.E. Escher, G.F. Ecker, 2017) [1]. We further provide the full list of descriptors used for generating the hyperbilirubinemia classification models as well as the calculated descriptors for each compound of the dataset that was used to build the classification model.

Linking organic anion transporting polypeptide 1B1 and 1B3 (OATP1B1 and OATP1B3) interaction profiles to hepatotoxicity - The hyperbilirubinemia use case

Hyperbilirubinemia is a pathological condition of excessive accumulation of conjugated or unconjugated bilirubin in blood. It has been associated with neurotoxicity and non-neural organ dysfunctions, while it can also be a warning of liver side effects. Hyperbilirubinemia can either be a result of overproduction of bilirubin due to hemolysis or dyserythropoiesis, or the outcome of impaired bilirubin elimination due to liver transporter malfunction or inhibition. There are several reports in literature that inhibition of organic anion transporting polypeptides 1B1 and 1B3 (OATP1B1 and OATP1B3) might lead to hyperbilirubinemia. In this study we created a set of classification models for hyperbilirubinemia, which, besides physicochemical descriptors, also include the output of classification models of human OATP1B1 and 1B3 inhibition. Models were based on either human data derived from public toxicity reports or animal data extracted from the eTOX database VITIC. The generated models showed satisfactory accuracy (68%) and area under the curve (AUC) for human data and 71% accuracy and 70% AUC for animal data. However, our results did not indicate strong association between OATP inhibition and hyperbilirubinemia, neither for humans nor for animals.

"Watching the Detectives" report of the general assembly of the EU project DETECTIVE Brussels, 24-25 November 2015

SEURAT-1 is a joint research initiative between the European Commission and Cosmetics Europe aiming to develop in vitro- and in silico-based methods to replace the in vivo repeated dose systemic toxicity test used for the assessment of human safety. As one of the building blocks of SEURAT-1, the DETECTIVE project focused on a key element on which in vitro toxicity testing relies: the development of robust and reliable, sensitive and specific in vitro biomarkers and surrogate endpoints that can be used for safety assessments of chronically acting toxicants, relevant for humans. The work conducted by the DETECTIVE consortium partners has established a screening pipeline of functional and "-omics" technologies, including high-content and high-throughput screening platforms, to develop and investigate human biomarkers for repeated dose toxicity in cellular in vitro models. Identification and statistical selection of highly predictive biomarkers in a pathway- and evidence-based approach constitute a major step in an integrated approach towards the replacement of animal testing in human safety assessment. To discuss the final outcomes and achievements of the consortium, a meeting was organized in Brussels. This meeting brought together data-producing and supporting consortium partners. The presentations focused on the current state of ongoing and concluding projects and the strategies employed to identify new relevant biomarkers of toxicity. The outcomes and deliverables, including the dissemination of results in data-rich "-omics" databases, were discussed as were the future perspectives of the work completed under the DETECTIVE project. Although some projects were still in progress and required continued data analysis, this report summarizes the presentations, discussions and the outcomes of the project.

Inhalation threshold of toxicological concern (TTC) - Structural alerts discriminate high from low repeated-dose inhalation toxicity

The threshold of toxicological concern (TTC) of a compound represents an exposure value below which the associated human health risk is considered negligible. As such, this approach offers assessing the risk of potential toxicants when little or no toxicological information is available. For the inhalation repeated-dose TTC, the goal was to derive structural alerts that discriminate between high- and low-toxic compounds. A further aim was to identify physicochemical parameters related to the inhalation-specific bioavailability of the compounds, and to explore their use as predictors of high vs low toxicity. 296 compounds with subacute, subchronic and chronic inhalation toxicity NOEC (no-observed effect concentration) values were subdivided into three almost equal-sized high-, medium- and low-toxic (HTox, MTox, LTox) potency classes. Whereas the derived 14 HTox and 7 LTox structural alerts yield an only moderate discrimination between these three groups, the high-toxic vs low-toxic mis-classification is very low: LTox-predicted compounds are not HTox to 97.5%, and HTox-predicted compounds not LTox to 88.6%. The probability of a compound being HTox vs LTox is triggered further by physicochemical properties encoding the tendency to evaporate from blood. The new structural alerts may aid in the predictive inhalation toxicity assessment of compounds as well as in designing low-toxicity chemicals, and provide a rationale for the chemistry underlying the toxicological outcome that can also be used for scoping targeted experimental studies.

n-Nonanoyl-CCL14 (NNY-CCL14), a novel inhibitor of allergic airway inflammation is a partial agonist of human CCR2

BACKGROUND

Modulation of leukocyte recruitment through blocking of chemokine receptors has been proposed as an attractive therapeutic strategy. We have previously demonstrated that n-Nonanoyl-CC chemokine ligand 14 (NNY-CCL14), a modified analog of the naturally occurring chemokine CCL14(9-74) internalizes and desensitizes human CCR3 resulting in the inactivation of eosinophils. However, inhibitory effects of NNY-CCL14 in murine models of allergic airway inflammation are assigned to its interaction with CCR1 and CCR5.

AIM OF THE STUDY

As CCL2 and its receptor CCR2 have been shown to play important roles in the development of Th2 inflammation, we further evaluated the effects of NNY-CCL14 treatment on CCL2-mediated activation of CCR2.

METHODS

Effects of NNY-CCL14 treatment were studied on cell lines transfected with human CCR2 and primary leukocytes. Functional effects were assessed by calcium efflux assays, flow cytometry and chemotaxis.

RESULTS

Prestimulation with NNY-CCL14 desensitized CCR2-mediated responses to further stimulation with its selective ligand CCL2. No significant internalization of CCR2 was observed when the cells were stimulated with NNY-CCL14, even at concentrations eliciting maximal [Ca(2+)]i mobilization. Above all, NNY-CCL14 pretreatment blocked CCL2-induced chemotaxis of monocytes.

CONCLUSIONS

This study demonstrates that NNY-CCL14 is a partial agonist of CCR2, inhibiting responses of monocytes to the CCR2-selective ligand CCL2. NNY-CCL14 attenuates CCR2-mediated responses by rapidly desensitizing the receptor and preventing chemotaxis, although it is able to induce calcium mobilization but does not lead to CCR2 internalization. Hence this study provides further insights into the possible mechanisms of action of NNY-CCL14, which interacts with multiple chemokine receptors inhibiting the migration and activation of different cell populations involved, thus acting as a potential therapeutic compound to alleviate allergic inflammation.

Inhibition of CD26/dipeptidyl peptidase IV enhances CCL11/eotaxin-mediated recruitment of eosinophils in vivo

Chemokines mediate the recruitment of leukocytes to the sites of inflammation. N-terminal truncation of chemokines by the protease dipeptidyl peptidase IV (DPPIV) potentially restricts their activity during inflammatory processes such as allergic reactions, but direct evidence in vivo is very rare. After demonstrating that N-terminal truncation of the chemokine CCL11/eotaxin by DPPIV results in a loss of CCR3-mediated intracellular calcium mobilization and CCR3 internalization in human eosinophils, we focused on the in vivo role of CCL11 and provide direct evidence for specific kinetic and rate-determining effects by DPPIV-like enzymatic activity on CCL11-mediated responses of eosinophils. Namely, it is demonstrated that i.v. administration of CCL11 in wild-type F344 rats leads to mobilization of eosinophils into the blood, peaking at 30 min. This mobilization is significantly increased in DPPIV-deficient F344 rats. Intradermal administration of CCL11 is followed by a dose-dependent recruitment of eosinophils into the skin and is significantly more effective in DPPIV-deficient F344 mutants as well as after pharmacological inhibition of DPPIV. Interestingly, CCL11 application leads to an up-regulation of DPPIV, which is not associated with negative feedback inhibition via DPPIV-cleaved CCL11((3-74)). These findings demonstrate regulatory effects of DPPIV for the recruitment of eosinophils. Furthermore, they illustrate that inhibitors of DPPIV have the potential to interfere with chemokine-mediated effects in vivo including but not limited to allergy.

Intravascular inactivation of CCR5 by n-Nonanoyl-CC chemokine ligand 14 and inhibition of allergic airway inflammation

Modulation of leukocyte recruitment through intervention with chemokine receptors is an attractive, therapeutic strategy. Recently, we have shown that n-Nonanoyl (NNY)-CCL14 internalizes and desensitizes human (h)CCR3, resulting in the inactivation of eosinophils. In this study, we investigated the interaction of NNY-CCL14 with CCR1 and CCR5 and the relevance of these NNY-CCL14 receptors on its in vivo effects in allergic airway inflammation. NNY-CCL14 has inactivating properties on CCR1(+) and CCR5(+) cell lines and primary leukocytes. It desensitizes hCCR1- and hCCR5-mediated calcium release and internalizes these receptors from the cellular surface. Treatment of OVA-sensitized BALB/c mice with NNY-CCL14 resulted in reduced pulmonary inflammation. Above all, it is demonstrated that systemic treatment with NNY-CCL14 down-modulates CCR5 from the surface of lymphocytes in vivo. Although NNY-CCL14 acts on murine lymphocytes and internalizes CCR5, it does not internalize CCR3 on mouse eosinophils, showing species selectivity regarding this particular receptor. Therefore, the inhibitory effects of NNY-CCL14 in murine models of allergic airway inflammation can be assigned to its interaction with CCR5. The presented results substantiate the relevance of CCR5 as a target for allergic airway inflammation.

Differential pattern of CCR1 internalization in human eosinophils: prolonged internalization by CCL5 in contrast to CCL3

BACKGROUND

Whereas recent studies underlie the fundamental importance of the CC chemokine receptor 3 (CCR3) for the recruitment of eosinophils in allergic diseases, controversial data exist about the relevance of CCR1 on eosinophils. Therefore, the purpose of this study was to investigate the expression and regulation of CCR1 on eosinophils.

METHODS

Flow cytometric analysis of whole blood eosinophils and CD16-negative selected eosinophils from healthy nonatopic donors and from patients with atopic disorders was performed and CCR1 receptor internalization and re-expression were studied.

RESULTS

Flow cytometric analysis of whole blood eosinophils revealed that 17.8% of the donors expressed high levels of CCR1 (CCR1high) and 82.2% low levels of CCR1 (CCR1low). A significant down-regulation of CCR1 was induced by 24 h preincubation of isolated eosinophils from CCR1high donors either with IL-3, CC chemokine ligand 3 (CCL3), CCL5, CCL7, or CCL13. Internalization experiments using eosinophils from CCR1high donors revealed that CCL5 is more effective to induce CCR1 internalization than CCL3. Whereas CCR1 re-expression after stimulation with CCL3 reached prestimulation levels (120 min: 81.3% relative CCR1 surface expression) CCL5 induced a prolonged CCR1 internalization (120 min: 15.7%).

CONCLUSIONS

This study demonstrates a distinct pattern of CCR1 internalization and re-expression in human eosinophils between CCL3 and CCL5, as CCL5 induces a prolonged CCR1 internalization and the basic value is not reached after 24 h. Since prolonged receptor internalization plays a central role in chemokine-mediated inhibition of receptor function, CCR1 seems to be an attractive target on human eosinophils for chemokine receptor blockade besides CCR3.

T-helper 2 cytokines attenuate senescent eosinophil activation by the CXCR4 ligand stromal-derived factor-1alpha (CXCL12)

BACKGROUND

Different chemokine receptors have been suggested to play a pivotal role in allergic diseases and therefore to be relevant for the activation of effector cells and propagation of the inflammatory response. The CXC chemokine receptor CXCR4 has recently been found on the surface of eosinophils implicating a role in allergic diseases.

OBJECTIVE

The aim of this study was to investigate the functional expression of CXCR4 on senescent eosinophils. Moreover, we questioned whether the cytokine profile--T-helper (Th)1 and Th2 cytokines--affect the activation of eosinophils via the CXCR4 that could be important for the different phases of the allergic reaction.

METHODS

CXCR4 expression on human eosinophils was analysed by flow cytometry and RT-PCR. Functional analyses of intracellular calcium fluxes, actin polymerization, release of reactive oxygen species and, chemotaxis were carried out using spectrofluorometry, flow cytometry, chemiluminescence and modified Boyden chamber technique.

RESULTS

Whole blood and freshly isolated eosinophils weakly express CXCR4 surface protein. Incubation in culture medium without addition of cytokines for 24 h always lead to strong CXCR4 surface expression that paralleled with stromal-derived factor-1alpha (CXCL12)-induced eosinophil activation. Stimulation of eosinophils with CXCL12 leads to an internalization of CXCR4, which could be prevented by phenylarsine oxide. Co-incubation of eosinophils with Th2 cytokines such as IL-3, IL-4, IL-5, IL-13, and granulocyte macrophage-colony stimulating factor prevented the expression of CXCR4 and affected eosinophil activation after stimulation with the CXCR4 ligand CXCL12. From these cytokines, IL-3 was the only cytokine completely inhibited intracellular calcium fluxes and chemotaxis of eosinophils in response to CXCL12.

CONCLUSION

Senescent eosinophils express functional CXCR4 receptors, which are prevented by Th2 cytokines that are found in the early phase of allergic reaction. Therefore, CXCR4 activation of eosinophils seems to be important in the chronic phase of allergic reaction, which is dominated by a Th1 cytokine profile.

Chemokine receptor antagonists: a novel therapeutic approach in allergic diseases

The aim of this review is to give an overview of the role of chemokines, particularly ligands of the CC chemokine receptor CCR3, in allergic diseases and to show the new concept in the treatment of allergies using chemokine receptor antagonists. Allergic diseases such as allergic asthma, allergic rhinitis and atopic dermatitis are characterized by a complex interaction of different cell types and mediators. Among this, Th2 cells, mast cells, basophils and eosinophils are found in the inflamed tissue due to the attraction of chemokines. Of all the known chemokine receptors, the chemokine receptor CCR3 seems to play the major role in allergic diseases which is supported by the detection of this receptor on the cell types mentioned above. Therefore, academic and industrial research focus on compounds to block this receptor. To date, certain chemokine receptor antagonists derived from peptides and small molecules exist to block the chemokine receptor CCR3. However, the in vivo data about these compounds and the mechanisms of receptor interaction are poorly understood, as yet. For the development of additional chemokine receptor antagonists, more details about the interaction between the ligands and their receptors are required. Therefore, additional studies will lead to the identification of novel CCR3 chemokine receptor antagonists, which can be therapeutically used in allergic asthma, allergic rhinitis, and atopic dermatitis.

Functional analysis of chemically synthesized derivatives of the human CC chemokine CCL15/HCC-2, a high affinity CCR1 ligand

The CCL15 is a human CC chemokine that activates the receptors, CCR1 and CCR3. Unlike other chemokines, it contains an unusually long N-terminal domain of 31 amino acids preceding the first cysteine residue and a third disulfide bond. To elucidate the functional role of distinct structural determinants, a series of sequential amino-terminal truncated and point-mutated CCL15 derivatives as well as mutants lacking the third disulfide bond and the carboxy-terminal alpha-helix were synthesized using 9-fluorenylmethoxycarbonyl (Fmoc) chemistry. We demonstrate that a truncation of 24 amino acid residues (delta24-CCL15) converts the slightly active 92-residue delta0-CCL15 into a potent agonist of CC chemokine receptor 1 (CCR1) and a weak agonist of CCR3 in cell-based assays. The biological activity decreases from delta24-CCL15 to delta29-CCL15, and re-increases from delta29-CCL15 to delta30-CCL15. Thus, an exocyclic N-terminal region of only one amino acid residue is sufficient for efficient CCR1 activation. As none of the peptides investigated except for delta24-CCL15 activates CCR3, we suggest that CCR1 is the major receptor for CCL15 in vivo. Further we demonstrate that the third disulfide bond of CCL15 and an exchange of tyrosine in position 70 by a leucine residue, which is conserved in CXC chemokines, do not alter the interaction with CCR1. In contrast, a CCL15 derivative lacking the carboxy-terminal alpha-helix exhibits a complete loss of tertiary structure and hence loss of CCR1 agonistic and binding activity. This study demonstrates that specific protein residues in chemokines, which contribute to receptor-ligand interaction, vary significantly between chemokines and cannot be extrapolated using data from functionally related chemokines.

n-Nonanoyl-CC chemokine ligand 14, a potent CC chemokine ligand 14 analogue that prevents the recruitment of eosinophils in allergic airway inflammation

CCR3 is responsible for tissue infiltration of eosinophils, basophils, mast cells, and Th2 cells, particularly in allergic diseases. In this context, CCR3 has emerged as a target for the treatment of allergic asthma. It is well known that the N-terminal domain of chemokines is crucial for receptor binding and, in particular, its activation. Based on this background, we investigated a number of N-terminally truncated or modified peptides derived from the chemokine CCL14/hemofiltrate CC chemokine-1 for their ability to modulate the activity of CCR3. Among 10 derivatives tested, n-nonanoyl (NNY)-CCL14[10-74] (NNY-CCL14) was the most potent at evoking the release of reactive oxygen species and inducing chemotaxis of human eosinophils. In contrast, NNY-CCL14 has inactivating properties on human eosinophils, because it is able to induce internalization of CCR3 and to desensitize CCR3-mediated intracellular calcium release and chemotaxis. In contrast to naturally occurring CCL11, NNY-CCL14 is resistant to degradation by CD26/dipeptidyl peptidase IV. Because inhibition of chemokine receptors through internalization is a reasonable therapeutic strategy being pursued for HIV infection, we tested a potential inhibitory effect of NNY-CCL14 in two murine models of allergic airway inflammation. In both OVA- and Aspergillus fumigatus-sensitized mice, i.v. treatment with NNY-CCL14 resulted in a significant reduction of eosinophils in the airways. Moreover, airway hyper-responsiveness was shown to be reduced by NNY-CCL14 in the OVA model. It therefore appears that an i.v. administered agonist internalizing and thereby inhibiting CCR3, such as NNY-CCL14, has the potential to alleviate CCR3-mediated diseases.

Hemofiltrate CC chemokines with unique biochemical properties: HCC-1/CCL14a and HCC-2/CCL15

The hemofiltrate CC chemokines CCL14a (formerly HCC-1), CCL14b (formerly HCC-3), and CCL15 (formerly HCC-2) are encoded by mono- as well as bicistronic transcripts from a tandem gene arrangement on human chromosome 17q11.2. The transcription and splicing into several mono- and bicistronic transcripts of this gene complex are unique for human genes. No corresponding mechanism is known in nonprimate mammalian species such as mice and rats. The extremely high concentration of CCL14a in human plasma is exceptional for chemokines and led to the identification of this chemokine. Several molecular forms of CCL14a have been isolated and investigated. The mature propeptide CCL14a(1-74) is a low-affinity agonist of CCR1 which is converted to a high-affinity agonist of CCR1 and CCR5 on proteolytic processing by serine proteases. In contrast, CCL15 is characterized using molecular forms deduced from the mRNA/cDNA and shown to activate cells via CCR1 and CCR3, also dependent on the amino-terminal length. Hemofiltrate CC chemokines are chemoattractants for different types of leukocytes including monocytes, eosinophils, T cells, dendritic cells, and neutrophils. In this review, we emphasize the genomic organization, expression patterns, and biochemical properties of CCL14a, CCL14b, and CCL15. We report results of significance for the development of therapeutic strategies, especially concerning HIV infection and inflammatory diseases.

Synthesis and characterization of the human CC chemokine HCC-2

Human CC chemokine 2 (HCC-2) is a novel member of the chemokine peptide family that induces chemotaxis of monocytes, T lymphocytes and eosinophils via activation of the CCR-1 and CCR-3 receptors. Fmoc chemistry was optimized and used to synthesize the biologically active 66-residue peptide HCC-2-(48-113). Introduction of the three disulfide bonds was achieved by oxidative folding in the presence of the redox system cysteine/cystine. Alternatively, a semiselective approach utilizing a mixed Acm/Trt protection scheme for disulfide formation was applied. It was found that, without participation of the two HCC-2-specific cysteine residues in positions 64 and 104, the two typical chemokine disulfides are formed predominantly during oxidative folding. In addition, the mutant [Ala64,104]HCC-2-(48-113) lacking the third disulfide bond that discriminates HCC-2 from most other chemokines was synthesized. For disulfide bond formation, oxidative folding was compared with the use of Acm/Trt protection. HCC-2-(48-113) and the mutant [Ala64,104]HCC-2-(48-113) were further analyzed by CD and one-dimensional 1H NMR-spectroscopy. Both peptides adopt a similar stable secondary and tertiary structure in solution.

Solution structure of the human CC chemokine 2: A monomeric representative of the CC chemokine subtype

HCC-2, a 66-amino acid residue human CC chemokine, was reported to induce chemotaxis on monocytes, T-lymphocytes, and eosinophils. The three-dimensional structure of HCC-2 has been determined by 1H nuclear magnetic resonance (NMR) spectroscopy and restrained molecular dynamics calculations on the basis of 871 experimental restraints. The structure is well-defined, exhibiting average root-mean-square deviations of 0.58 and 0.96 A for the backbone heavy atoms and all heavy atoms of residues 5-63, respectively. In contrast to most other chemokines, subtle structural differences impede dimer formation of HCC-2 in a concentration range of 0.1 microM to 2 mM. HCC-2, however, exhibits the same structural elements as the other chemokines, i.e., a triple-stranded antiparallel beta-sheet covered by an alpha-helix, showing that the chemokine fold is not influenced by quaternary interactions. Structural investigations with a HCC-2 mutant prove that a third additional disulfide bond present in wild-type HCC-2 is not necessary for maintaining the relative orientation of the helix and the beta-sheet.