Report of the First ONTOX Stakeholder Network Meeting: Digging Under the Surface of ONTOX Together With the Stakeholders

The first Stakeholder Network Meeting of the EU Horizon 2020-funded ONTOX project was held on 13-14 March 2023, in Brussels, Belgium. The discussion centred around identifying specific challenges, barriers and drivers in relation to the implementation of non-animal new approach methodologies (NAMs) and probabilistic risk assessment (PRA), in order to help address the issues and rank them according to their associated level of difficulty. ONTOX aims to advance the assessment of chemical risk to humans, without the use of animal testing, by developing non-animal NAMs and PRA in line with 21st century toxicity testing principles. Stakeholder groups (regulatory authorities, companies, academia, non-governmental organisations) were identified and invited to participate in a meeting and a survey, by which their current position in relation to the implementation of NAMs and PRA was ascertained, as well as specific challenges and drivers highlighted. The survey analysis revealed areas of agreement and disagreement among stakeholders on topics such as capacity building, sustainability, regulatory acceptance, validation of adverse outcome pathways, acceptance of artificial intelligence (AI) in risk assessment, and guaranteeing consumer safety. The stakeholder network meeting resulted in the identification of barriers, drivers and specific challenges that need to be addressed. Breakout groups discussed topics such as hazard versus risk assessment, future reliance on AI and machine learning, regulatory requirements for industry and sustainability of the ONTOX Hub platform. The outputs from these discussions provided insights for overcoming barriers and leveraging drivers for implementing NAMs and PRA. It was concluded that there is a continued need for stakeholder engagement, including the organisation of a 'hackathon' to tackle challenges, to ensure the successful implementation of NAMs and PRA in chemical risk assessment.

Effects of Exercise during Chemo- or Radiotherapy on Immune Markers: A Systematic Review

INTRODUCTION

Patients with cancer receiving radio- or chemotherapy undergo many immunological stressors. Chronic regular exercise has been shown to positively influence the immune system in several populations, while exercise overload may have negative effects. Exercise is currently recommended for all patients with cancer. However, knowledge regarding the effects of exercise on immune markers in patients undergoing chemo- or radiotherapy is limited. The aim of this study is to systematically review the effects of moderate- and high-intensity exercise interventions in patients with cancer during chemotherapy or radiotherapy on immune markers.

METHODS

For this review, a search was performed in PubMed and EMBASE, until March 2023. Methodological quality was assessed with the PEDro tool and best-evidence syntheses were performed both per immune marker and for the inflammatory profile.

RESULTS

Methodological quality of the 15 included articles was rated fair to good. The majority of markers were unaltered, but observed effects included a suppressive effect of exercise during radiotherapy on some pro-inflammatory markers, a preserving effect of exercise during chemotherapy on NK cell degranulation and cytotoxicity, a protective effect on the decrease in thrombocytes during chemotherapy, and a positive effect of exercise during chemotherapy on IgA.

CONCLUSION

Although exercise only influenced a few markers, the results are promising. Exercise did not negatively influence immune markers, and some were positively affected since suppressed inflammation might have positive clinical implications. For future research, consensus is needed regarding a set of markers that are most responsive to exercise. Next, differential effects of training types and intensities on these markers should be further investigated, as well as their clinical implications.

A practical guide for probiotics applied to the case of antibiotic-associated diarrhea in The Netherlands

BACKGROUND

Antibiotic-associated diarrhea (AAD) is a side-effect frequently associated with the use of broad spectrum antibiotics. Although a number of clinical studies show that co-administration of specific probiotics reduces the risk for AAD, there is still unclarity among healthcare professionals on the recommendation of probiotic products. This paper aims at a practical guide to inform healthcare professionals, patients and consumers about the exact product characteristics of available probiotics with a proven efficacy to prevent AAD.

METHODS

The workflow in this paper includes three consecutive steps: 1) systematic review of relevant clinical studies for effective probiotics by a meta-analysis, 2) compilation of a list of available probiotic products, and 3) recommendation of probiotic products that match effective formulations. Our systematic review on the efficacy of probiotics for the prevention of AAD included only studies with randomized, double blind placebo-controlled trials, a clear definition of antibiotic associated diarrhea, and a probiotic administration regime for at least the duration of the antibiotic therapy.

RESULTS

Using our inclusion criteria, we selected 32 out of 128 identified trials and pooled the results of these studies for each specific dairy product and food supplement. The results indicate a total of seven single or multiple-strain formulations favoring the probiotic treatment group, with the strain Lactobacillus rhamnosus GG being the most effective [relative risk ratio of probiotic versus placebo 0.30 (95% CI 0.16-0.5)]. We selected products for recommendation from a compiled list of all probiotic dairy products and food supplements available in The Netherlands and categorized them into groups of products showing effects against the incidence of AAD in at least one, two or three independent clinical studies. We excluded all products which did not unambiguously declare on the label the specific probiotic strain(s) and the number of colony forming units.

CONCLUSION

Here we present a practical guide that informs healthcare professionals and patients on the availability of probiotic products with a proven efficacy for the prevention of AAD.

Regional Expression Levels of Drug Transporters and Metabolizing Enzymes along the Pig and Human Intestinal Tract and Comparison with Caco-2 Cells

Intestinal transporter proteins and metabolizing enzymes play a crucial role in the oral absorption of a wide variety of drugs. The aim of the current study was to characterize better available intestinal in vitro models by comparing expression levels of these proteins and enzymes between porcine intestine, human intestine, and Caco-2 cells. We therefore determined the absolute protein expression of 19 drug transporters and the mRNA expression of 12 metabolic enzymes along the pig intestinal tract (duodenum, jejunum, ileum; N = 4), in human intestine (jejunum; N = 9), and Caco-2 cells. Expression of the included transporters and enzymes was in general well comparable between porcine and human intestinal tissue, although breast cancer resistance protein, monocarboxylate transporter 5, multidrug resistance protein (MRP) 1, MRP1, MRP3 (∼2-fold), and organic anion-transporting polypeptide (OATP) 4A1 (∼6-fold) was higher expressed in pig compared with human jejunum. Alternatively, expression level of relevant transporter proteins (glucose transporter 1, OATP4A1, MRP2, MRP1, and OATP2B1) was significantly higher (3- to 130-fold) in Caco-2 cells compared with human jejunum. Moreover, all examined CYPs showed at least a fivefold lower gene expression in Caco-2 cells compared with human jejunum, with the smallest differences for CYP1A1 and CYP3A5 and the largest difference for CYP3A4 (871-fold higher expression in human jejunum compared with Caco-2 cells). In conclusion, a comprehensive overview is provided of the expression levels of clinically relevant transporter proteins and metabolic enzymes in porcine and human intestinal tissue and Caco-2 cells, which may assist in deciding upon the most suitable model to further improve our understanding of processes that determine intestinal absorption of compounds.

Prediction of the Carcinogenic Potential of Human Pharmaceuticals Using Repeated Dose Toxicity Data and Their Pharmacological Properties

In an exercise designed to reduce animal use, we analyzed the results of rat subchronic toxicity studies from 289 pharmaceutical compounds with the aim to predict the tumor outcome of carcinogenicity studies in this species. The results were obtained from the assessment reports available at the Medicines Evaluation Board of the Netherlands for 289 pharmaceutical compounds that had been shown to be non-genotoxic. One hundred forty-three of the 239 compounds not inducing putative preneoplastic lesions in the subchronic study did not induce tumors in the carcinogenicity study [true negatives (TNs)], whereas 96 compounds were categorized as false negatives (FNs) because tumors were observed in the carcinogenicity study. Of the remaining 50 compounds, 31 showed preneoplastic lesions in the subchronic study and tumors in the carcinogenicity study [true positives (TPs)], and 19 only showed preneoplastic lesions in subchronic studies but no tumors in the carcinogenicity study [false positives (FPs)]. In addition, we then re-assessed the prediction of the tumor outcome by integrating the pharmacological properties of these compounds. These pharmacological properties were evaluated with respect to the presence or absence of a direct or indirect proliferative action. We found support for the absence of cellular proliferation for 204 compounds (TN). For 67 compounds, the presence of cellular hyperplasia as evidence for proliferative action could be found (TP). Therefore, this approach resulted in an ability to predict non-carcinogens at a success rate of 92% and the ability to detect carcinogens at 98%. The combined evaluation of pharmacological and histopathological endpoints eventually led to only 18 unknown outcomes (17 categorized as FN and 1 as FP), thereby enhancing both the negative and positive predictivity of an evaluation based upon histopathological evaluation only. The data show the added value of a consideration of the pharmacological properties of compounds in relation to potential class effects, both in the negative and positive direction. A high negative and a high positive predictivity will both result in waiving the need for conducting 2-year rat carcinogenicity studies, if this is accepted by Regulatory Authorities, which will save large numbers of animals and reduce drug development costs and time.

Comet assay in reconstructed 3D human epidermal skin models--investigation of intra- and inter-laboratory reproducibility with coded chemicals

Reconstructed 3D human epidermal skin models are being used increasingly for safety testing of chemicals. Based on EpiDerm™ tissues, an assay was developed in which the tissues were topically exposed to test chemicals for 3h followed by cell isolation and assessment of DNA damage using the comet assay. Inter-laboratory reproducibility of the 3D skin comet assay was initially demonstrated using two model genotoxic carcinogens, methyl methane sulfonate (MMS) and 4-nitroquinoline-n-oxide, and the results showed good concordance among three different laboratories and with in vivo data. In Phase 2 of the project, intra- and inter-laboratory reproducibility was investigated with five coded compounds with different genotoxicity liability tested at three different laboratories. For the genotoxic carcinogens MMS and N-ethyl-N-nitrosourea, all laboratories reported a dose-related and statistically significant increase (P < 0.05) in DNA damage in every experiment. For the genotoxic carcinogen, 2,4-diaminotoluene, the overall result from all laboratories showed a smaller, but significant genotoxic response (P < 0.05). For cyclohexanone (CHN) (non-genotoxic in vitro and in vivo, and non-carcinogenic), an increase compared to the solvent control acetone was observed only in one laboratory. However, the response was not dose related and CHN was judged negative overall, as was p-nitrophenol (p-NP) (genotoxic in vitro but not in vivo and non-carcinogenic), which was the only compound showing clear cytotoxic effects. For p-NP, significant DNA damage generally occurred only at doses that were substantially cytotoxic (>30% cell loss), and the overall response was comparable in all laboratories despite some differences in doses tested. The results of the collaborative study for the coded compounds were generally reproducible among the laboratories involved and intra-laboratory reproducibility was also good. These data indicate that the comet assay in EpiDerm™ skin models is a promising model for the safety assessment of compounds with a dermal route of exposure.

Toward a mechanism-based in vitro safety test for pertussis toxin

Pertussis vaccines are routinely administered to infants to protect them from whooping cough. Still, an adequate safety test for pertussis toxin (PT), one of the main antigens in these vaccines, is not available. The histamine sensitization test is currently the only assay accepted by regulatory authorities to test for the absence of active PT in vaccines. This is however, a lethal animal test with poor reproducibility. In addition, it is not clear whether the assumed underlying mechanism, i.e., ADP-ribosylation of G proteins, is the only effect that should be considered in safety evaluation of PT. The in vitro safety test for PT that we developed is based on the clinical effects of PT in humans. For this, human cell lines were chosen based on the cell types involved in the clinical effects of PT. These cell lines were exposed to PT and analyzed by microarray. In this review, we discuss the clinical effects of PT and the mechanisms that underlie them. The approach taken may provide as an example for other situations in which an in vitro assay based on clinical effects in humans is required.

Development of a panel of high-throughput reporter-gene assays to detect genotoxicity and oxidative stress

The lack of toxicological information on many of the compounds that humans use or are exposed to, intentionally or unintentionally, poses a big problem in risk assessment. To fill this data gap, more emphasis is given to fast in vitro screening tools that can add toxicologically relevant information regarding the mode(s) of action via which compounds can elicit adverse effects, including genotoxic effects. By use of bioassays that can monitor the activation of specific cellular signalling pathways, many compounds can be screened in a high-throughput manner. We have developed two new specific reporter-gene assays that can monitor the effects of compounds on two pathways of interest: the p53 pathway (p53 CALUX) for genotoxicity and the Nrf2 pathway (Nrf2 CALUX) for oxidative stress. To exclude non-specific effects by compounds influencing the luciferase reporter-gene expression non-specifically, a third assay was developed to monitor changes in luciferase expression by compounds in general (Cytotox CALUX). To facilitate interpretation of the data and to avoid artefacts, all three reporter-gene assays used simple and defined reporter genes and a similar cellular basis, the human U2OS cell line. The three cell lines were validated with a range of reference compounds including genotoxic and non-genotoxic agents. The sensitivity (95%) and specificity (85%) of the p53 CALUX was high, showing that the assay is able to identify various types of genotoxic compound, while avoiding the detection of false positives. The Nrf2 CALUX showed specific responses to oxidants only, enabling the identification of compounds that elicit part of their genotoxicity via oxidative stress. All reporter-gene assays can be used in a high-throughput screening format and can be supplemented with other U2OS-based reporter-gene assays that can profile nuclear receptor activity, and several other signalling pathways.

Identification of biomarkers to detect residual pertussis toxin using microarray analysis of dendritic cells

In this study we aimed to identify genes that are responsive to pertussis toxin (PTx) and might eventually be used as biological markers in a testing strategy to detect residual PTx in vaccines. By microarray analysis we screened six human cell types (bronchial epithelial cell line BEAS-2B, fetal lung fibroblast cell line MRC-5, primary cardiac microvascular endothelial cells, primary pulmonary artery smooth muscle cells, hybrid cell line EA.Hy926 of umbilical vein endothelial cells and epithelial cell line A549 and immature monocyte-derived dendritic cells) for differential gene expression induced by PTx. Immature monocyte-derived dendritic cells (iMoDCs) were the only cells in which PTx induced significant differential expression of genes. Results were confirmed using different donors and further extended by showing specificity for PTx in comparison to Escherichia coli lipopolysaccharide (LPS) and Bordetella pertussis lipo-oligosaccharide (LOS). Statistical analysis indicated 6 genes, namely IFNG, IL2, XCL1, CD69, CSF2 and CXCL10, as significantly upregulated by PTx which was also demonstrated at the protein level for genes encoding secreted proteins. IL-2 and IFN-γ gave the strongest response. The minimal PTx concentrations that induced production of IL-2 and IFN-γ in iMoDCs were 12.5 and 25IU/ml, respectively. High concentrations of LPS slightly induced IFN-γ but not IL-2, while LOS and detoxified pertussis toxin did not induce production of either cytokine. In conclusion, using microarray analysis we evaluated six human cell lines/types for their responsiveness to PTx and found 6 PTx-responsive genes in iMoDCs of which IL2 is the most promising candidate to be used as a biomarker for the detection of residual PTx.

The use of ex vivo human skin tissue for genotoxicity testing

As a result of the chemical legislation concerning the registration, evaluation, authorization and restriction of chemicals (REACH), and the Seventh Amendment to the Cosmetics Directive, which prohibits animal testing in Europe for cosmetics, alternative methods for safety evaluation of chemicals are urgently needed. Current in vitro genotoxicity assays are not sufficiently predictive for the in vivo situation, resulting in an unacceptably high number of misleading positives. For many chemicals and ingredients of personal care products the skin is the first site of contact, but there are no in vitro genotoxicity assays available in the skin for additional evaluation of positive or equivocal responses observed in regulatory in vitro genotoxicity assays. In the present study ex vivo human skin tissue obtained from surgery was used for genotoxicity evaluation of chemicals by using the comet assay. Fresh ex vivo human skin tissue was cultured in an air-liquid interface and topically exposed to 20 chemicals, including true positive, misleading positive and true negative genotoxins. Based on the results obtained in the present study, the sensitivity, specificity and accuracy of the ex vivo skin comet assay to predict in vivo genotoxicity were 89%, 90% and 89%, respectively. Donor and experimental variability were mainly reflected in the magnitude of the response and not the difference between the presence and absence of a genotoxic response. The present study indicates that human skin obtained from surgery is a promising and robust model for safety evaluation of chemicals that are in direct contact with the skin.

Formation and removal of genotoxic activity during UV/H(2)O(2)-GAC treatment of drinking water

The objective of this study was to determine the genotoxic activity of water after UV/H(2)O(2) oxidation and GAC filtration. Pre-treated surface water from three locations was treated with UV/H(2)O(2) with medium pressure (MP) lamps and passed through granulated activated carbon (GAC). Samples taken before and after each treatment step were extracted and concentrated by solid phase extraction (SPE) and analyzed for genotoxicity using the Comet assay with HepG2 cells and the Ames II assay. The Comet assay showed no genotoxic response in any of the samples. In the Ames II, no genotoxic response was obtained with the TAMix (a mix of six strains), but the TA98 strain showed an increase in genotoxic activity after MP-UV/H(2)O(2) for all three locations. GAC post treatment effectively reduced the activities to control levels at two of the three locations and to below the level of the pre-treated water at one site. The results indicate that UV/H(2)O(2) treatment may lead to the formation of genotoxic by-products, which can be removed by subsequent GAC filtration.

Expression profiling of colon cancer cell lines and colon biopsies: towards a screening system for potential cancer-preventive compounds

Interest in mechanisms of colon cancer prevention by food compounds is strong and research in this area is often performed with cultured colon cancer cells. In order to assess utility for screening of potential cancer-preventive (food) compounds, expression profiles of 14 human cell lines derived from colonic tissue were measured using cDNA microarrays with 4000 genes and compared with expression profiles in biopsies of human colon tumours and normal tissue. Differences and similarities in the gene expression profiles of the cell lines were analysed by clustering and principal component analysis (PCA). Cytoskeleton genes and immune response genes are two functional classes of genes that contributed to the differences between the cell lines. A subset of 72 colon cancer-specific genes was identified by comparing expression profiles in human colon biopsies of tumour tissue and normal tissue. A separation of the cell lines based on the tumour stage of the original adenocarcinoma was observed after PCA of expression data of the subset of colon cancer-specific genes in the cell lines. The results of this study may be useful in the ongoing research into mechanisms of cancer prevention by dietary components.

Prediction of in vivo embryotoxic effect levels with a combination of in vitro studies and PBPK modelling

The new EU legislations for chemicals (Registration, Evaluation and Authorization of Chemicals, REACH) and cosmetics (Seventh Amendment) stimulate the acceptance of in vitro and in silico approaches to test chemicals for their potential to cause reproductive effects. In the current study seven compounds with known in vivo developmental effects were tested in the embryonic stem cell test (EST). The EST correctly classified 5-fluorouracil, methotrexate, retinoic acid, 2-ethoxyacetic acid and 2-methoxyacetic acid for their in vivo embryotoxic potential. The toxicity of 2-methoxyethanol and 2-ethoxyethanol was underestimated due to a lack of metabolic capacity in the EST. This study further investigated the possibility to use in silico techniques to extrapolate in vitro effect concentrations determined in the EST to in vivo exposure levels. This approach was evaluated by comparing in silico predicted in vivo effect levels with effect levels measured in rodents. The in vivo effect levels of 2-methoxyethanol, 2-ethoxyethanol, methotrexate and retinoic acid were correctly predicted with in silico modelling. Contrary, in vivo embryotoxicity of 5-fluorouracil was overestimated following this approach. It is concluded that a combination of in vitro and in silico techniques appears to be a promising alternative test method for risk assessment of embryotoxic compounds.

Do aberrant crypt foci have predictive value for the occurrence of colorectal tumours? Potential of gene expression profiling in tumours

The effects of different dietary compounds on the formation of aberrant crypt foci (ACF) and colorectal tumours and on the expression of a selection of genes were studied in rats. Azoxymethane-treated male F344 rats were fed either a control diet or a diet containing 10% wheat bran (WB), 0.2% curcumin (CUR), 4% rutin (RUT) or 0.04% benzyl isothiocyanate (BIT) for 8 months. ACF were counted after 7, 15 and 26 weeks. Tumours were scored after 26 weeks and 8 months. We found that the WB and CUR diets inhibited the development of colorectal tumours. In contrast, the RUT and BIT diets rather enhanced (although not statistically significantly) colorectal carcinogenesis. In addition, the various compounds caused different effects on the development of ACF. In most cases the number or size of ACF was not predictive for the ultimate tumour yield. The expression of some tumour-related genes was significantly different in tumours from the control group as compared to tumours from the treated groups. It was concluded that WB and CUR, as opposed to RUT and BIT, protects against colorectal cancer and that ACF are unsuitable as biomarker for colorectal cancer. Effects of the different dietary compounds on metalloproteinase 1 (TIMP-1) expression correlated well with the effects of the dietary compounds on the ultimate tumour yield.

Safety evaluation of an α-cyclodextrin glycosyltranferase preparation

Alpha-cyclodextrin glucosyltransferase (alpha-CGTase, EC 2.4.1.19) is an amylolytic enzyme used for the production of alpha-cyclodextrin (alpha-CD), a novel, soluble dietary fiber, from food-grade starch. The safety of an alpha-CGTase preparation obtained by batch fermentation from a recombinant strain of Escherichia coli K12 harboring the alpha-CGTase gene from Klebsiella oxytoca strain M5a1 was examined. In a 13-week subchronic toxicity study in rats, the administration by gavage of the alpha-CGTase preparation at levels of up to 20 ml/kg bw/day, corresponding to a total organic solids dosage of 260 mg/kg bw/day, did not cause any systemic toxic effect. Some signs of irritation were observed in the respiratory tract which occurred, however, in one sex only and/or were not dose-related. Accordingly, these changes were considered to be an unspecific consequence of the reflux and aspiration of the dosing solution. There was no evidence of a genotoxic activity in Ames tests and a chromosome aberration test in cultured human lymphocytes. It is concluded that the examined alpha-CGTase preparation is safe when used for the production of alpha-CD.

Intragastric formation and modulation of N-nitrosodimethylamine in a dynamic in vitro gastrointestinal model under human physiological conditions

Human exposure to carcinogenic N-alkylnitrosamines can occur exogenously via food consumption or endogenously by formation of these compounds through nitrosation of amine precursors. Information on the intragastric formation of NDMA from complex mixtures of precursors and inhibitors in humans is not available. In this study the formation of N-nitrosodimethylamine (NDMA) has been quantitatively analysed in a dynamic in vitro gastrointestinal model, in which gastric conditions can be modulated and closely simulates the physiological situation in humans. Substantial amounts of NDMA were produced when nitrite and dimethylamine or codfish were simultaneously introduced into the model. However, humans are gradually exposed to nitrite by the intake of nitrate-containing food. Nitrate secreted in saliva is converted to nitrite by oral bacteria. To mimic the human exposure to nitrite in a realistic way, nitrite was gradually added into the gastric compartment, simulating the swallowing of nitrite containing oral fluid after the intake of nitrate at the level of 0.1-10 times the ADI. Under these conditions, the cumulative amounts of NDMA formed were 2.3-422 microg NDMA and 1.8-42.7 microg NDMA at a rapid and slow gastric pH decrease, respectively. Beside codfish, various fish species and batches in combination with nitrite, simulating the intake of for times the ADI of nitrate, were investigated. Herring, pollack and plaice were also able to induce NDMA formation. Mackerel, salmon and pike perch did not result in increased NDMA formation. Furthermore, the effect of nitrosation modulators on NDMA formation was investigated. Thiocyanate (2 mM) increased NDMA formation, but the increase was not statistically significant. In contrast, orange jus and tea effectively, but not totally, reduced the amount of NDMA formed in the gastric compartment. These experiments show that (1). the dynamic in vitro gastrointestinal model is an appropriate tool for mechanistic studies on the intragastric formation of nitrosamines, and (2). that the results obtained with this model are helpful in evaluating human cancer risk for the combined intake of codfish-like fish species and nitrate-containing vegetables.