Thresholds of Genotoxic and Non-Genotoxic Carcinogens

Assessment of genotoxic chemicals using chemogenomic profiling based on gene-knockout library in Saccharomyces cerevisiae

Understanding the adverse effects of genotoxic chemicals and identifying them effectively from non-genotoxic chemicals are of great worldwide concerns. Here, Saccharomyces cerevisiae (yeast) genome-wide single-gene knockout screening approach was conducted to assess two genotoxic chemicals (4-nitroquinoline-1-oxide (4-NQO) and formaldehyde (FA)) and environmental pollutant dichloroacetic acid (DCA, genotoxicity is controversial). DNA repair was significant enriched in the gene ontology (GO) biology process (BP) terms and KEGG pathways when exposed to low concentrations of 4-NQO and FA. Higher concentrations of 4-NQO and FA influenced some RNA metabolic and biosynthesis pathways. Moreover, replication and repair associated pathways were top ranked KEGG pathways with high fold-change for low concentrations of 4-NQO and FA. The similar gene profiles perturbed by DCA with three test concentrations identified, the common GO BP terms associated with aromatic amino acid family biosynthetic process and ubiquitin-dependent protein catabolic process via the multivesicular body sorting pathway. DCA has no obvious genotoxicity as there was no enriched DNA damage and repair pathways and fold-change of replication and repair KEGG pathways were very low. Five genes (RAD18, RAD59, MUS81, MMS4, and BEM4) could serve as candidate genes for genotoxic chemicals. Overall, the yeast functional genomic profiling showed great performance for assessing the signatures and potential molecular mechanisms of genotoxic chemicals.

Connexin-Based Channel Activity Is Not Specifically Altered by Hepatocarcinogenic Chemicals

Connexin-based channels play key roles in cellular communication and can be affected by deleterious chemicals. In this study, the effects of various genotoxic carcinogenic compounds, non-genotoxic carcinogenic compounds and non-carcinogenic compounds on the expression and functionality of connexin-based channels, both gap junctions and connexin hemichannels, were investigated in human hepatoma HepaRG cell cultures. Expression of connexin26, connexin32, and connexin43 was evaluated by means of real-time reverse transcription quantitative polymerase chain reaction analysis, immunoblot analysis and in situ immunostaining. Gap junction functionality was assessed via a scrape loading/dye transfer assay. Opening of connexin hemichannels was monitored by measuring extracellular release of adenosine triphosphate. It was found that both genotoxic and non-genotoxic carcinogenic compounds negatively affect connexin32 expression. However, no specific effects related to chemical type were observed at gap junction or connexin hemichannel functionality level.

Modification of Enteromorpha prolifera with dielectric barrier discharge plasma to enhance malachite green adsorption

Dyes, a kind of visible chemical, have severe deleterious effects on human health and ecological environment. In this work, batch biosorption experiments were carried out under various experimental conditions such as pH value and agitation time to optimize the potentiality of Enteromorpha prolifera for the removal of malachite green (MG) dye from aqueous solution (70·7%). Then, the algal biomass was treated with a dielectric barrier discharge (DBD) in helium for 4 and 10 min to enhance MG removal efficiency (84·7 and 96·6%). In addition, Fourier-transform infrared spectroscopy in combination with scanning electron microscopy was employed to monitor the chemical and physical changes of algal cells treated by DBD. This study illustrates that DBD may serve as an effective tool to activate the functional groups on the cell wall surface for dye binding, and it even offers an alternative new technique to improve the adsorption properties of native biosorbents for the removal of toxic dyes from wastewater.

How to Address Consumers' Concerns and Information Needs about Emerging Chemical and Microbial Contaminants in Drinking Water; The Case of GenX in The Netherlands

The perceived safety of tap water is an important condition for consumers to drink it. Therefore, addressing consumers' concerns should be included in the roadmap towards the UN SDG 6 on safe drinking water for all. This paper studies consumers' information needs regarding emerging contaminants in drinking water using a mental model approach for the development of targeted risk communication. As most consumers expect safe drinking water, free of contamination, communication on emerging contaminants may increase concerns. Here, we showed that communication strategies better tailored to consumers' information needs result in smaller increases in risk perception compared with existing strategies.

Mutagenicity of carcinogenic heterocyclic amines in Salmonella typhimurium YG strains and transgenic rodents including gpt delta

Chemical carcinogens to humans have been usually identified by epidemiological studies on the relationships between occupational or environmental exposure to the agents and specific cancer induction. In contrast, carcinogenic heterocyclic amines were identified under the principle that mutagens in bacterial in the Ames test are possible human carcinogens. In the 1970s to 1990s, more than 10 heterocyclic amines were isolated from pyrolysates of amino acids, proteins, meat or fish as mutagens in the Ames test, and they were demonstrated as carcinogens in rodents. In the 1980s and 1990s, we have developed derivatives of the Ames tester strains that overexpressed acetyltransferase of Salmonella typhimurium. These strains such as Salmonella typhimurium YG1024 exhibited a high sensitivity to the mutagenicity of the carcinogenic heterocyclic amines. Because of the high sensitivity, YG1024 and other YG strains were used for various purposes, e.g., identification of novel heterocyclic amines, mechanisms of metabolic activation, comparison of mutagenic potencies of various heterocyclic amines, and the co-mutagenic effects. In the 1990s and 2000s, we developed transgenic mice and rats for the detection of mutagenicity of chemicals in vivo. The transgenics were generated by the introduction of reporter genes for mutations into fertilized eggs of mice and rats. We named the transgenics as gpt delta because the gpt gene of Escherichia coli was used for detection of point mutations such as base substitutions and frameshifts and the red/gam genes of λ phage were employed to detect deletion mutations. The transgenic rodents gpt delta and other transgenics with lacI or lacZ as reporter genes have been utilized for characterization of mutagenicity of heterocyclic amines in vivo. In this review, we summarized the in vitro mutagenicity of heterocyclic amines in Salmonella typhimurium YG strains and the in vivo mutagenicity in transgenic rodents. We discussed the relationships between in vitro and in vivo mutagenicity of the heterocyclic amines and their relations to the carcinogenicity.

Dynamically monitoring cellular γ-H2AX reveals the potential of carcinogenicity evaluation for genotoxic compounds

Amongst all toxicological endpoints, carcinogenicity might pose the greatest concern. Genetic damage has been considered an important underlying mechanism for the carcinogenicity of chemical substances. The demand for in vitro genotoxic tests as alternative approaches is growing rapidly with the implementation of new regulations for compounds. However, currently available in vitro genotoxicity tests are often limited by relatively high false positive rates. Moreover, few studies have explored carcinogenicity potential by in vitro genotoxicity testing due to the shortage of suitable toxicological biomarkers to link gene damage with cancer risk. γ-H2AX is a recently acknowledged attractive endpoint (biomarker) for evaluating DNA damage and can simultaneously reflect the DNA damage response and repair of cells. We previously reported an ultrasensitive and reliable method, namely stable-isotope dilution-liquid chromatography-tandem mass spectrometry (ID-LC-MS/MS), for detecting cellular γ-H2AX and evaluating genotoxic chemicals. More importantly, our method can dynamically monitor the specific processes of genotoxic compounds affecting DNA damage and repair reflected by the amount of γ-H2AX. To clarify the possibility of using this method to assess the potential carcinogenicity of genotoxic chemicals, we applied it to a set of 69 model compounds recommended by the European Center for the Validation of Alternative Methods (ECVAM), with already-characterized genotoxic potential. Compared to conventional in vitro genotoxicity assays, including the Ames test, the γ-H2AX assay by MS has high accuracy (94-96%) due to high sensitivity and specificity (88% and 100%, respectively). The dynamic profiles of model compounds after exposure in HepG2 cells were explored, and a mathematical approach was employed to simulate and quantitatively model the DNA repair kinetics of genotoxic carcinogens (GCs) based on γ-H2AX time-effect curves up to 8 h. Two crucial parameters, i.e., k (rate of γ-H2AX decay) and t₅₀ (time required for γ-H2AX from maximum decrease to half) estimated by the least squares method, were achieved. An open web server to help researchers calculate these two key parameters and profile simulated curves of the tested compound is available online ( http://ccb1.bmi.ac.cn:81/shiny-server/sample-apps/prediction1/ ). We detected a positive association between carcinogenic levels and k and t₅₀ values of γ-H2AX in tested GCs, validating the potential of using this MS-based γ-H2AX in vitro assay to help preliminarily evaluate carcinogenicity and assess genotoxicity. This approach may be used alone or integrated into an existing battery of in vitro genetic toxicity tests.

FEMA GRAS assessment of natural flavor complexes: Eucalyptus oil and other cyclic ether-containing flavoring ingredients

In 2015, the Expert Panel of the Flavor and Extract Manufacturers Association (FEMA) initiated a program for the re-evaluation of the safety of over 250 natural flavor complexes (NFCs) used as flavor ingredients. This publication, the sixth in the series, will summarize the re-evaluation of eight NFCs whose constituent profiles are characterized by significant amounts of eucalyptol and/or other cyclic ethers. This re-evaluation was based on a procedure first published in 2005 and subsequently updated in 2018 that evaluates the safety of naturally occurring mixtures for their intended use as flavoring ingredients. The procedure relies on a complete chemical characterization of the NFC intended for commerce and the organization of its chemical constituents into well-defined congeneric groups. The safety of the NFC is evaluated using the well-established and conservative threshold of toxicological concern (TTC) concept in addition to data on absorption, metabolism and toxicology of the constituents of the congeneric groups and the NFC under evaluation. Eight NFCs derived from the Eucalyptus, Melaleuca, Origanum, Laurus, Rosmarinus and Salvia genera were affirmed as generally recognized as safe (GRAS) under their conditions of intended use as flavor ingredients based on an evaluation of each NFC and the constituents and congeneric groups therein.

Natural Products: Implication in Cancer Prevention and Treatment through Modulating Various Biological Activities

Cancer is one of the most leading causes of death worldwide. It is one of the primary global diseases that cause morbidity and mortality in millions of people. It is usually caused by different carcinogenic agents that damage the genetic material and alter the cell signaling pathways. Carcinogens are classified into two groups as genotoxic and non-genotoxic agents. Genotoxic carcinogens are capable of directly altering the genetic material, while the non-genotoxic carcinogens are capable of producing cancer by some secondary mechanisms not related to direct gene damage. There is undoubtedly the greatest need to utilize some novel natural products as anticancer agents, as these are within reach everywhere. Interventions by some natural products aimed at decreasing the levels and conditions of these risk factors can reduce the frequency of cancer incidences. Cancer is conventionally treated by surgery, radiation therapy and chemotherapy, but such treatments may be fast-acting and causes adverse effects on normal tissues. Alternative and innovative methods of cancer treatment with the least side effects and improved efficiency are being encouraged. In this review, we discuss the different risk factors of cancer development, conventional and innovative strategies of its management and provide a brief review of the most recognized natural products used as anticancer agents globally.

A review on genotoxicity in connection to infertility and cancer

Genotoxicity has been identified as the main cause of infertility and a variety of cancers. The mechanisms affect the structure, quality of the information or the segregation of DNA and are not inherently correlated with mutagenicity. The concept of genotoxicity, the chemical classes that cause genetic damage and the associated mechanisms of action are discussed here. Hazardous effects of pharmaceuticals, cosmetics, agrochemicals, industrial compounds, food additives, natural toxins and nanomaterials are, in large part, identified by genotoxicity and mutagenicity tests. These are critical and early steps in industrial and regulatory health assessment. Though several in vitro experiments are commonly used and approval by regulatory agencies for commercial licensing of drugs, their accuracy in human predictions for genotoxic and mutagenic effects is frequently questioned. Treatment of real and functional genetic toxicity problems depends in detail on the knowledge of mechanisms of DNA damage in the molecular, subcellular, cellular and tissue or organ system levels. Current strategies for risk assessment of human health need revisions to achieve robust and reliable results for optimizing their effectiveness. Additionally, computerized methods, neo-biomarkers leveraging '-omics' approaches, all of which can provide a convincing genotoxicity evaluation to reduce infertility and cancer risk.

Oxidative stress and cyto-genotoxicity induced by poly-d-glucosamine in human blood cells in vitro

Poly-N-acetyl-d-glucosamine (CH; chitin) is the main component of the insect skeleton, fungal cell wall, and many crustaceans, including crab and shrimp. CH is the most abundant in nature after cellulose, and it has a complex and hardly soluble structure. Poly-d-glucosamine (CHO; chitosan) is a soluble derivative of CH produced by deacetylation used in many fields, including human health. This study carried out the cytotoxic, genotoxic, and oxidative effects of CHO on human whole blood (hWB) and lymphocytes (LYMs) in dose ranges 6.25-2000 μg/mL, in vitro. Total antioxidant capacity (TAC) and total oxidant status (TOS) analyzes were performed on plasma to appreciate oxidative stress. 3-(4,5-Dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide (MTT) and lactate dehydrogenase (LDH) assays were applied to understand the cytotoxicity. Chromosomal aberration (CA) and micronucleus (MN) methods were practiced to evaluate genotoxicity. 6.25-150 μg/mL doses increased TAC and decreased TOS. A decreasing and increasing curve from 200 to 2000 μg/mL on TAC and TOS values were determined, respectively. 0-250 μg/mL doses did not provide any cytotoxic data. However, 500-2000 μg/mL doses showed increasing cytotoxicity and genotoxicity. The study results showed that CHO does not pose a toxic risk to human health at low doses but may pose a threat at high doses.

Marine Anthraquinones: Pharmacological and Toxicological Issues

The marine ecosystem, populated by a myriad of animals, plants, and microorganisms, is an inexhaustible reservoir of pharmacologically active molecules. Among the multiple secondary metabolites produced by marine sources, there are anthraquinones and their derivatives. Besides being mainly known to be produced by terrestrial species, even marine organisms and the uncountable kingdom of marine microorganisms biosynthesize anthraquinones. Anthraquinones possess many different biological activities, including a remarkable antitumor activity. However, due to their peculiar chemical structures, anthraquinones are often associated with toxicological issues, even relevant, such as genotoxicity and mutagenicity. The aim of this review is to critically describe the anticancer potential of anthraquinones derived from marine sources and their genotoxic and mutagenic potential. Marine-derived anthraquinones show a promising anticancer potential, although clinical studies are missing. Additionally, an in-depth investigation of their toxicological profile is needed before advocating anthraquinones as a therapeutic armamentarium in the oncological area.

Prednisone is genotoxic in mice and Drosophila melanogaster

Prednisone (PD) is one of the most commonly used corticosteroids in immunosuppressive therapy for patients with autoimmune diseases and transplants. Chronic use of corticosteroids is associated with several side effects and an increase in neoplasia. Since genotoxic effects are associated with an increased risk of cancer development, this study evaluated the genotoxic and cytotoxic activities of PD using the SMART/wing assay in Drosophila melanogaster and the micronucleus test and comet assay in mouse bone marrow cells. Further, the toxic effects of PD on mouse organ tissues were assessed using histopathological analyses. In the SMART/wing assay, PD showed a significant genotoxic activity at all concentrations tested (0.375, 0.75, 1.5, and 2.0 mg/mL) compared to the negative control (p < 0.05). The micronucleus test and comet assay also showed an elevated genotoxicity of PD at all treatment conditions (24, 48, and 120 h with doses ranging from 0.5 to 1.5 mg/kg) compared to the negative control (p < 0.05). The histopathological analyses did not show toxicity of PD in mouse cells and tissues. Therefore, our results demonstrate that PD is a potent genotoxic immunosuppressant in mice and D. melanogaster cells. Somatic recombination was the primary contributor (46%-82%) to the induced genotoxicity observed in the SMART test.

A comparison of classical and 21st century genotoxicity tools: A proof of concept study of 18 chemicals comparing in vitro micronucleus, ToxTracker and genomics-based methods (TGx-DDI, whole genome clustering and connectivity mapping)

A key step in the risk assessment process of a substance is the assessment of its genotoxic potential. Irrespective of the industry involved, current approaches rely on combinations of two or three in vitro tests and while highly sensitive, their specificity is thought to be limited. A refined in vitro genotoxicity testing strategy with improved predictive capacity would be beneficial and "3R" friendly as it helps to avoid unnecessary in vivo follow-up testing. Here, we describe a proof of concept study evaluating a balanced set of compounds that have in vivo negative or positive outcomes, but variable in vitro data, to determine if we could differentiate between direct and indirect acting genotoxicants. Compounds were examined in TK6 cells using an approach in which the same sample was used to evaluate both early genomic markers (Affymetrix analysis 4 hr post treatment), and the genotoxic outcome (micronuclei [MN] after 24 hr). The resulting genomic data was then analyzed using the TGx-DDI biomarker, Connectivity mapping and whole genome clustering. Chemicals were also tested in the ToxTracker assay, which uses six different biomarker genes. None of the methods correctly differentiated all direct from indirect acting genotoxicants when used alone, however, the ToxTracker assay, TGx-DDI biomarker and whole genome approaches provided high predictive capacity when used in combination with the MN assay (1/18, 2/18, 1/18 missed calls). Ultimately, a "fit for purpose" combination will depend on the specific tools available to the end user, as well as considerations of the unique benefits of the individual assays.

Anti-seizure medication is not associated with an increased risk to develop cancer in epilepsy patients

Objective

Whether anti-seizure medication (ASM) increases the risk for cancer has been debated for decades. While for some ASM, a carcinoma-promoting effect has been suspected, carcinoma-protective effects have been shown for other ASM. However, the issue remains unresolved as data from preclinical and clinical studies have been inconsistent and contradictory.

Methods

We collected anonymous patient data from practice neurologists throughout Germany between 2009 and 2018 using the IMS Disease Analyzer database (QuintilesIMS, Frankfurt, Germany). People with epilepsy (PWE) with an initial cancer diagnosis and antiepileptic therapy prior to the index date were 1:1 matched with a control group of PWE without cancer according to age, gender, index year, Charlson Comorbidity Index, and treating physician. For both groups, the risk to develop cancer under treatment with different ASMs was analyzed using three different models (ever use vs. never use (I), effect per one (II) and per five therapy years (III).

Results

A total of 3152 PWE were included (each group, n = 1,576; age = 67.3 ± 14.0 years). The risk to develop cancer was not significantly elevated for any ASM. Carbamazepine was associated with a decreased cancer risk (OR Model I: 0.699, p < .0001, OR Model II: 0.952, p = .4878, OR Model III: 0.758, p < .0004).

Significance

Our findings suggest that ASM use does not increase the risk of cancer in epilepsy patients.

Supplementary Information

The online version of this article (10.1007/s00415-020-10379-4) contains supplementary material, which is available to authorized users.

Bruce Nathan Ames - Paradigm shifts inside the cancer research revolution

Dr. Bruce Ames turned 92 on December 16, 2020. He considers his most recent work linking adequate consumption of 30 known vitamins and minerals with successful aging to be his most important contribution. With the passage of time, it is not uncommon for the accomplishments of a well-known scientist to undergo a parsimonious reductionism in the public mind - Pasteur's vaccine, Mendel's peas, Pavlov's dogs, Ames' test. Those of us in the research generation subsequent to Dr. Ames' are undoubtedly affected by our own unconscious tendencies toward accepting the outstanding achievements of the past as commonplace. In doing so, seminal advances made by earlier investigators are often inadvertently subsumed into common knowledge. But having followed Ames' work since the mid-1970s, we are cognizant that the eponymous Ames Test is but a single chapter in a long and rich narrative. That narrative begins with Ames' classic studies on the histidine operon of Salmonella, for which he was elected to the National Academy of Sciences. A summary of the historical progression of the understanding of chemical carcinogenesis to which Ames and his colleagues contributed is provided. Any summary of a topic as expansive and complex as the ongoing unraveling of the mechanisms underlying chemical carcinogenesis will only touch upon some of the major conceptual advances to which Ames and his colleagues contributed. We hope that scientists of all ages familiar with Ames only through the eponymous Ames Test will further investigate the historical progression of the conceptualization of cancer caused by chemical exposure. As the field of chemical carcinogenesis gradually moves away from primary reliance on animal testing to alternative protocols under the rubric of New Approach Methodologies (NAM) an understanding of where we have been might help to guide where we should go.

Insight into the formation of N-nitrosodimethylamine in metformin products

An effective analytical method for the quantification of N-nitrosodimethylamine (NDMA) using a liquid chromatography coupled with tandem mass spectrometry was developed and applied to a process optimization study of the production of metformin film coated tablets in order to identify the key factors behind the NDMA formation in metformin products. The method uses a linear gradient elution with mobile phases 0.1 % formic acid in water for chromatography and methanol for chromatography and a column Acquity UPLC HSS T3 1.8 μm. The use of the tandem mass spectrometry in a positive ion mode with an atmospheric pressure chemical ionization allows for the use of an isotopically labelled internal standard and an external calibration standard. The method was validated according to the guidelines of International Council for Harmonization in terms of limit of detection and quantification, linearity, precision, accuracy and method selectivity. To further justify the effectiveness of the method, a comparison between two laboratories was performed using a linear regression testing. Both methods give comparable results. 469 samples of both metformin active pharmaceutical ingredient and film coated tablets were analysed and the key factors behind NDMA formation were identified. Hypotheses explaining the mechanism were formulated and confronted with measurements and scientific literature. Protective measures to prevent NDMA contamination in metformin products were drawn.

Hallmarks of Health

Health is usually defined as the absence of pathology. Here, we endeavor to define health as a compendium of organizational and dynamic features that maintain physiology. The biological causes or hallmarks of health include features of spatial compartmentalization (integrity of barriers and containment of local perturbations), maintenance of homeostasis over time (recycling and turnover, integration of circuitries, and rhythmic oscillations), and an array of adequate responses to stress (homeostatic resilience, hormetic regulation, and repair and regeneration). Disruption of any of these interlocked features is broadly pathogenic, causing an acute or progressive derailment of the system coupled to the loss of numerous stigmata of health.

Targeting gap junctional intercellular communication by hepatocarcinogenic compounds

Gap junctions in liver, as in other organs, play a critical role in tissue homeostasis. Inherently, these cellular constituents are major targets for systemic toxicity and diseases, including cancer. This review provides an overview of chemicals that compromise liver gap junctions, in particular biological toxins, organic solvents, pesticides, pharmaceuticals, peroxides, metals and phthalates. The focus in this review is placed upon the mechanistic scenarios that underlie these adverse effects. Further, the potential use of gap junctional activity as an in vitro biomarker to identify non-genotoxic hepatocarcinogenic chemicals is discussed.

FEMA GRAS assessment of natural flavor complexes: Clove, cinnamon leaf and West Indian bay leaf-derived flavoring ingredients

In 2015, the Expert Panel of the Flavor and Extract Manufacturers Association initiated the safety re-evaluation of over 250 natural flavor complexes (NFCs) used as flavor ingredients. This publication, 4th in a series focusing on the safety evaluation of NFCs, presents an evaluation of NFCs rich in hydroxyallylbenzene and hydroxypropenylbenzene constituents using a procedure initially published in 2005 and updated in 2018 that evaluates the safety of naturally occurring mixtures for their intended use as flavoring ingredients. The procedure requires the characterization of the chemical composition for each NFC and subsequent organization of the constituents into defined congeneric groups. The safety of each NFC is evaluated using the conservative threshold of toxicological concern (TTC) approach together with studies on absorption, metabolism and toxicology of the NFC and its constituent congeneric groups. By the application of this procedure, seven NFCs, derived from clove, cinnamon leaf and West Indian bay leaf were affirmed as "generally recognized as safe (GRAS)" under their conditions of intended use as flavor ingredients. An eighth NFC, an oleoresin of West Indian bay leaf, was affirmed based on its estimated intake, which is below the TTC of 0.15 μg/person per day for compounds with structural alerts for genotoxicity.

FEMA GRAS assessment of natural flavor complexes: Lavender, Guaiac Coriander-derived and related flavoring ingredients

In 2015, the Expert Panel of the Flavor and Extract Manufacturers Association (FEMA) initiated a program for the re-evaluation of the safety of over 250 natural flavor complexes (NFCs) used as flavor ingredients. This publication, fifth in the series, evaluates the safety of NFCs containing linalool and/or other characteristic mono- and sesquiterpenoid tertiary alcohols and esters using the safety evaluation procedure published by the FEMA Expert Panel in 2005 and updated in 2018. The procedure relies on a complete chemical characterization of the NFC intended for commerce and organization of the chemical constituents of each NFC into well-defined congeneric groups. The safety of each NFC is evaluated using the well-established and conservative threshold of toxicological concern (TTC) concept in addition to data on absorption, metabolism and toxicology of both the constituent congeneric groups and the NFCs. Sixteen NFCs, derived from the Lavandula, Aniba, Elettaria, Daucus, Salvia, Coriandrum, Ribes, Guaiacum/Bulnesia, Citrus, Pogostemon, Melaleuca and Michelia genera, were affirmed as generally recognized as safe (GRAS) under their conditions of intended use as flavor ingredients based on an evaluation of each NFC and the constituents and congeneric groups therein.

Aneugen Versus Clastogen Evaluation and Oxidative Stress-Related Mode-of-Action Assessment of Genotoxic Compounds Using the ToxTracker Reporter Assay

Understanding the mode-of-action (MOA) of genotoxic compounds and differentiating between direct DNA interaction and indirect genotoxicity is crucial for their reliable safety assessment. ToxTracker is a stem cell-based reporter assay that detects activation of various cellular responses that are associated with genotoxicity and cancer. ToxTracker consists of 6 different GFP reporter cell lines that can detect the induction of DNA damage, oxidative stress, and protein damage in a single test. The assay can thereby provide insight into the MOA of compounds. Genotoxicity is detected in ToxTracker by activation of 2 independent GFP reporters. Activation of the Bscl2-GFP reporter is associated with induction of DNA adducts and subsequent inhibition of DNA replication and the Rtkn-GFP reporter is activated following the formation of DNA double-strand breaks. Here, we show that the differential activation of these 2 genotoxicity reporters could be used to further differentiate between a DNA reactive and clastogenic or a non-DNA-reactive aneugenic MOA of genotoxic compounds. For further classification of aneugenic and clastogenic compounds, the ToxTracker assay was extended with cell cycle analysis and aneuploidy assessment. The extension was validated using a selection of 16 (genotoxic) compounds with a well-established MOA. Furthermore, indirect genotoxicity related to the production of reactive oxygen species was investigated using the DNA damage and oxidative stress ToxTracker reporters in combination with different reactive oxygen species scavengers. With these new extensions, ToxTracker was able to accurately classify compounds as genotoxic or nongenotoxic and could discriminate between DNA-reactive compounds, aneugens, and indirect genotoxicity caused by oxidative stress.

The 2-year rodent bioassay in drug and chemical carcinogenesis testing: Sensitivity, according to the framework of carcinogenic action

The long-term rodent bioassay (RCB) has been the gold-standard for the pre-marketing prediction of chemical and drug carcinogenicity to humans. Nonetheless, the validity of this toxicity test has remained elusive for several decades. In the quest to uncover the performance of the RCB, its sensitivity (SEN) was charted as the first step. This appraisal was based on (a) chemicals with sufficient epidemiological evidence of carcinogenicity, and (b) other substances with limited epidemiological evidence, or remarkable classifications of carcinogenicity based on mechanistic or pharmacological data. In the present study, chemicals evaluated for their carcinogenicity to humans in IARC Monographs volumes 1-123, U.S. EPA IRIS Assessments, and U.S. NTP RoC were considered. This investigation gathered additional evidence supporting that, in hazard identification, the RCB is unwarranted for mutagenic or direct-acting genotoxicants. However, for purposes of risk assessment or management, the RCB might be justified whenever there is a lack of reliable and/or comprehensive epidemiological data. The RCB exhibited a significantly different SEN for threshold-based human carcinogens compared to non-threshold-based ones. With threshold-based chemicals, to increase the SEN of the testing from 80% (rat-RCB) to 90%, the 2-species RCB might be warranted. Nevertheless, the resolve would depend on the viewpoint, and on the future analysis of the overall performance of the RCB. In terms of SEN, and cancer hazard identification, the comparison between the RCB and alternative methods (e.g. rasH2 mouse, Tg.AC mouse) is now enabled.

Application of transcriptomic and microRNA profiling in the evaluation of potential liver carcinogens

Hepatocarcinogens are agents that increase the incidence of liver cancer in exposed animals or humans. It is now established that carcinogenic exposures have a widespread impact on the transcriptome, inducing both adaptive and adverse changes in the activities of genes and pathways. Chemical hepatocarcinogens have also been shown to affect expression of microRNA (miRNA), the evolutionarily conserved noncoding RNA that regulates gene expression posttranscriptionally. Considerable effort has been invested into examining the involvement of mRNA in chemical hepatocarcinogenesis and their potential usage for the classification and prediction of new chemical entities. For miRNA, there has been an increasing number of studies reported over the past decade, although not to the same degree as for transcriptomic studies. Current data suggest that it is unlikely that any gene or miRNA signature associated with short-term carcinogen exposure can replace the rodent bioassay. In this review, we discuss the application of transcriptomic and miRNA profiles to increase mechanistic understanding of chemical carcinogens and to aid in their classification.

Plastics in Cyanobacterial Blooms-Genotoxic Effects of Binary Mixtures of Cylindrospermopsin and Bisphenols in HepG2 Cells

Ever-expanding environmental pollution is causing a rise in cyanobacterial blooms and the accumulation of plastics in water bodies. Consequently, exposure to mixtures of cyanotoxins and plastic-related contaminants such as bisphenols (BPs) is of increasing concern. The present study describes genotoxic effects induced by co-exposure to one of the emerging cyanotoxins-cylindrospermopsin (CYN)-(0.5 µg/mL) and BPs (bisphenol A (BPA), S (BPS), and F (BPF); (10 µg/mL)) in HepG2 cells after 24 and 72 h of exposure. The cytotoxicity was evaluated with an MTS assay and genotoxicity was assessed through the measurement of the induction of DNA double strand breaks (DSB) with the γH2AX assay. The deregulation of selected genes (xenobiotic metabolic enzyme genes, DNA damage, and oxidative response genes) was assessed using qPCR. The results showed a moderate reduction of cell viability and induction of DSBs after 72 h of exposure to the CYN/BPs mixtures and CYN alone. None of the BPs alone reduced cell viability or induced DSBs. No significant difference was observed between CYN and CYN/BPs exposed cells, except with CYN/BPA, where the antagonistic activity of BPA against CYN was indicated. The deregulation of some of the tested genes (CYP1A1, CDKN1A, GADD45A, and GCLC) was more pronounced after exposure to the CYN/BPs mixtures compared to single compounds, suggesting additive or synergistic action. The present study confirms the importance of co-exposure studies, as our results show pollutant mixtures to induce effects different from those confirmed for single compounds.

Long Non-coding RNAs: Major Regulators of Cell Stress in Cancer

Cellular stress can occur in many forms; oxidative stress caused by reactive oxygen species (ROS), metabolic stress from increased metabolic programs and genotoxic stress in the form of DNA damage and disrepair. In most instances, these different types of cell stress initiate programmed cell death. However, in cancer, cells are able to resist cellular stress and by-pass growth limiting checkpoints. Recent findings have now revealed that the large and heterogenous RNA species known as long non-coding RNAs (lncRNAs) are major players in regulating and overcoming cancer cell stress. lncRNAs constitute a significant fraction of the genes differentially expressed in response to cell stress and contribute to the management of downstream cellular processes, including the regulation of key stress responses such as metabolic stress, oxidative stress and genotoxic stress. This review highlights the complex regulatory role of lncRNAs in the cell stress response of cancer by providing an overview of key examples from recent literature.

The safety evaluation of food flavoring substances: the role of genotoxicity studies

The Flavor and Extract Manufacturers Association (FEMA) Expert Panel relies on the weight of evidence from all available data in the safety evaluation of flavoring substances. This process includes data from genotoxicity studies designed to assess the potential of a chemical agent to react with DNA or otherwise cause changes to DNA, either in vitro or in vivo. The Panel has reviewed a large number of in vitro and in vivo genotoxicity studies during the course of its ongoing safety evaluations of flavorings. The adherence of genotoxicity studies to standardized protocols and guidelines, the biological relevance of the results from those studies, and the human relevance of these studies are all important considerations in assessing whether the results raise specific concerns for genotoxic potential. The Panel evaluates genotoxicity studies not only for evidence of genotoxicity hazard, but also for the probability of risk to the consumer in the context of exposure from their use as flavoring substances. The majority of flavoring substances have given no indication of genotoxic potential in studies evaluated by the FEMA Expert Panel. Examples illustrating the assessment of genotoxicity data for flavoring substances and the consideration of the factors noted above are provided. The weight of evidence approach adopted by the FEMA Expert Panel leads to a rational assessment of risk associated with consumer intake of flavoring substances under the conditions of use.

Evaluation of the Suitability of Mammalian In Vitro Assays to Assess the Genotoxic Potential of Food Contact Materials

Background: Non-targeted screening of food contact materials (FCM) for non-intentionally added substances (NIAS) reveals a great number of unknown and unidentified substances present at low concentrations. In the absence of toxicological data, the application of the threshold of toxicological concern (TTC) or of EU Regulation 10/2011 requires methods able to fulfill safety threshold criteria. In this review, mammalian in vitro genotoxicity assays are analyzed for their ability to detect DNA-damaging substances at limits of biological detection (LOBD) corresponding to the appropriate safety thresholds. Results: The ability of the assays to detect genotoxic effects varies greatly between substance classes. Especially for direct-acting mutagens, the assays lacked the ability to detect most DNA reactive substances below the threshold of 10 ppb, making them unsuitable to pick up potential genotoxicants present in FCM migrates. However, suitability for the detection of chromosomal damage or investigation of other modes of action makes them a complementary tool as part of a standard test battery aimed at giving additional information to ensure safety. Conclusion: improvements are necessary to comply with regulatory thresholds to consider mammalian genotoxicity in vitro assays to assess FCM safety.

Dietary phytochemicals as the potential protectors against carcinogenesis and their role in cancer chemoprevention

Health-threatening consequences of carcinogen exposure are mediated via occurrence of electrophiles or reactive oxygen species. As a result, the accumulation of biomolecular damage leads to the cancer initiation, promotion or progression. Accordingly, there is an association between lifestyle factors including inappropriate diet or carcinogen formation during food processing, mainstream, second or third-hand tobacco smoke and other environmental or occupational carcinogens and malignant transformation. Nevertheless, increasing evidence supports the protective effects of naturally occurring phytochemicals against carcinogen exposure as well as carcinogenesis in general. Isolated phytochemicals or their mixtures present in the whole plant food demonstrate efficacy against malignancy induced by carcinogens widely spread in our environment. Phytochemicals also minimize the generation of carcinogenic substances during the processing of meat and meat products. Based on numerous data, selected phytochemicals or plant foods should be highly recommended to become a stable and regular part of the diet as the protectors against carcinogenesis.

International landscape of limits and recommendations for occupational exposure to engineered nanomaterials

The increasing concern of possible adverse effects on human health derived from occupational engineered nanomaterials (ENMs) exposure is an issue addressed by entities related to provide guidelines and/or protocols for ENMs regulation. Here we analysed 17 entities from America, Europe and Asia, and some of these entities provide limits of exposure extrapolated from the non-nanosized counterparts of ENMs. The international landscape shows that recommendations are mostly made for metal oxide based ENMs and tonnage is one of the main criteria for ENMs registration, however, sub-nanometric ENMs are emerging and perhaps a novel category of ENMs will appear soon. We identify that besides the lack of epidemiological evidence of ENMs toxicity in humans and difficulties in analysing the toxicological data derived from experimental models, the lack of information on airborne concentrations of ENMs in occupational settings is an important limitation to improve the experimental designs. The development of regulations related to ENMs exposure would lead to provide safer work places for ENMs production without delaying the nanotechnology progress but will also help to protect the environment by taking opportune and correct measures for nanowaste, considering that this could be a great environmental problem in the coming future.

Protecting Children from Toxic Waste: Data-Usability Evaluation Can Deter Flawed Cleanup

Nearly 25 percent of US children live within 2 km of toxic-waste sites, most of which are in urban areas. They face higher rates of cancer than adults, partly because the dominant contaminants at most US hazardous-waste sites include genotoxic carcinogens, like trichloroethylene, that are much more harmful to children. The purpose of this article is to help protect the public, especially children, from these threats and to improve toxics-remediation by beginning to test our hypothesis: If site-remediation assessments fail data-usability evaluation (DUE), they likely compromise later cleanups and public health, especially children’s health. To begin hypothesis-testing, we perform a focused DUE for an unremediated, Pasadena, California toxic site. Our DUE methods are (a) comparing project-specific, remediation-assessment data with the remediation-assessment conceptual site model (CSM), in order to identify data gaps, and (b) using data-gap directionality to assess possible determinate bias (whether reported toxics risks are lower/higher than true values). Our results reveal (1) major CSM data gaps, particularly regarding Pasadena-toxic-site risks to children; (2) determinate bias, namely, risk underestimation; thus (3) likely inadequate remediation. Our discussion shows that if these results are generalizable, requiring routine, independent, DUEs might deter flawed toxic-site assessment/cleanup and resulting health threats, especially to children.

Effects of DNA polymerase kappa and mismatch repair on dose-responses of chromosome aberrations induced by three oxidative genotoxins in human cells

Genotoxic carcinogens are regulated under the policy that there is no threshold or safe dose. It has been pointed out, however, that self-defense mechanisms, such as detoxification, DNA repair, and error-free translesion synthesis, may protect chromosome DNA from genotoxic insults, thereby constituting practical threshold. In this study, we examined dose responses of chromosome aberrations induced by three oxidative genotoxins, that is, hydrogen peroxide (H₂ O₂ ), menadione and paraquat, with or without DNA polymerase kappa (Polκ) activities and mismatch repair capacities in human cells. Polκ is involved in translesion synthesis across DNA damage and mismatch repair is responsible for correction of base-base mismatch in DNA. Polκ activity of the cells was inactivated either by point mutations in the catalytically essential amino acids (catalytically dead or CD) or by deletion of the POLK gene (knockout or KO). In the absence of mismatch repair, frequencies of chromosome aberrations induced by H₂ O₂ and menadione were not significantly different among CD, KO, and the wild type (WT) cells. In the presence of mismatch repair, however, cytotoxicity and clastogenicity were enhanced and Polκ modulated the sensitivity of the cells. No-observed-genotoxic-effect-levels (NOGELs) for H₂ O₂ and menadione were CD = KO < WT cells. In contrast, the sensitivities of the cells to paraquat were not significantly affected by the status of mismatch repair or Polκ activity. The results suggest that mismatch repair and Polκ coordinately modulate NOGELs for the clastogenicity of H₂ O₂ and menadione and also that DNA lesion(s) responsible for paraquat-induced chromosome aberrations are different from those induced by H₂ O₂ and menadione. Environ. Mol. Mutagen. 61:193-199, 2020. © 2019 Wiley Periodicals, Inc.

Determination of Lymphocyte Cytokinesis-Block Micronucleus Values in Apparently Healthy Children by means of Age and Sex

The cytokinesis-block micronucleus (MN) assay on blood lymphocytes is one of the most important tests implemented in cytogenetics for the measurement of genotoxicity. For the purpose of biological dosing, it is crucial to know the spontaneous frequency of MN and its normal values in general population, especially in children, which are used for the population databases. In this study, MN levels were investigated in cytokinesis-blocked lymphocytes of 150 apparently healthy children aged 1 to 15. Our aim was to assess the variability of MN values according to age and sex. The mean MN frequency among boys was 3.69 ± 1.747‰ and 4.12 ± 1.867‰ in girls where there was no significant difference in relation to age and sex. However, when we separated age groups as 0–2 years, 3–5 years, 6–10 years, and 11–15 years, one-way ANOVA test showed significant association. Significance was obvious in the 0–2 years age group with the 3–5 years age group and 6–10 years age group. When we grouped our study population as 0–2 years and 3–15 years, the mean MN frequency among the 0–2 years age group was 2.85 ± 1.599‰ and 4.07 ± 1.867‰ in the 3–15 years age group which was also statistically significant. This difference may be attributed to age-related increase of close contact with environmental hazardous agents. In conclusion, normal values of MN obtained in this study will add valuable information in regard to update the current childhood population data and will act as a reference for further genotoxicity studies.

My career development with Ames test: A personal recollection

I first became acquainted with the Ames test at the very beginning of my career in 1978, when my task at the National Institute of Health Sciences (Tokyo) was to screen for mutagenicity of food additives used in Japan, using the Ames test. I also used this test to research the metabolic activation mechanisms of chemical carcinogens, in particular, the analgesic drug, phenacetin. This chemical was not mutagenic in Salmonella typhimurium TA100 with standard 9000 × g supernatant of liver homogenates (S9) from rat but was mutagenic with hamster S9. It was revealed that hamster S9 had much higher deacetylation activities than rat S9, which accounts for the species difference. Then, my work was focused on molecular biology. We cloned the genes encoding nitroreductase and acetyltransferase in Salmonella typhimurium TA1538. Plasmids carrying these genes made strain TA98 more sensitive to mutagenic nitroarenes and aromatic amines. Because of their high sensitivity, the resulting strains such as YG1021 and YG1024 are widely used to monitor mutagenic nitroarenes and aromatic amines in complex mixtures. Later, we disrupted the genes encoding DNA polymerases in TA1538 and classified chemical mutagens into four classes depending on their use of different DNA polymerases. I was also involved in the generation of gpt delta transgenic rodent gene mutation assays, which examine the results of the Ames test in vivo. I have unintentionally developed my career under the influence of Dr. Ames and I would like to acknowledge his remarkable achievements in the field of environmental mutagenesis and carcinogenesis.

Extrapolation of Hepatic Concentrations of Industrial Chemicals Using Pharmacokinetic Models to Predict Hepatotoxicity

In this review, we describe the absorption rates (Caco-2 cell permeability) and hepatic/plasma pharmacokinetics of 53 diverse chemicals estimated by modeling virtual oral administration in rats. To ensure that a broad range of chemical structures is present among the selected substances, the properties described by 196 chemical descriptors in a chemoinformatics tool were calculated for 50,000 randomly selected molecules in the original chemical space. To allow visualization, the resulting chemical space was projected onto a two-dimensional plane using generative topographic mapping. The calculated absorbance rates of the chemicals based on cell permeability studies were found to be inversely correlated to the no-observed-effect levels for hepatoxicity after oral administration, as obtained from the Hazard Evaluation Support System Integrated Platform in Japan (r = -0.88, p < 0.01, n = 27). The maximum plasma concentrations and the areas under the concentration-time curves (AUC) of a varied selection of chemicals were estimated using two different methods: simple one-compartment models (i.e., high-throughput toxicokinetic models) and simplified physiologically based pharmacokinetic (PBPK) modeling consisting of chemical receptor (gut), metabolizing (liver), and central (main) compartments. The results obtained from the two methods were consistent. Although the maximum concentrations and AUC values of the 53 chemicals roughly correlated in the liver and plasma, inconsistencies were apparent between empirically measured concentrations and the PBPK-modeled levels. The lowest-observed-effect levels and the virtual hepatic AUC values obtained using PBPK models were inversely correlated (r = -0.78, p < 0.05, n = 7). The present simplified PBPK models could estimate the relationships between hepatic/plasma concentrations and oral doses of general chemicals using both forward and reverse dosimetry. These methods are therefore valuable for estimating hepatotoxicity.

Differential responses on energy metabolic pathway reprogramming between genotoxic and non-genotoxic hepatocarcinogens in rat liver cells

To clarify difference in the responses on the reprogramming of metabolism toward carcinogenesis between genotoxic and non-genotoxic hepatocarcinogens in the liver, rats were repeatedly administered genotoxic hepatocarcinogens (N-nitrosodiethylamine, aflatoxin B₁, N-nitrosopyrrolidine, or carbadox) or non-genotoxic hepatocarcinogens (carbon tetrachloride, thioacetamide, or methapyrilene hydrochloride) for 28, 84, or 90 days. Non-genotoxic hepatocarcinogens revealed transcript expression changes suggestive of suppressed mitochondrial oxidative phosphorylation (OXPHOS) after 28 days and increased glutathione S-transferase placental form-positive (GST-P⁺) foci downregulating adenosine triphosphate (ATP) synthase subunit beta, mitochondrial precursor (ATPB), compared with genotoxic hepatocarcinogens after 84 or 90 days, suggesting that non-genotoxic hepatocarcinogens are prone to suppress OXPHOS from the early stage of treatment, which is in contrast to genotoxic hepatocarcinogens. Both genotoxic and non-genotoxic hepatocarcinogens upregulated glycolytic enzyme genes and increased cellular membrane solute carrier family 2, facilitated glucose transporter member 1 (GLUT1) expression in GST-P⁺ foci for up to 90 days, suggesting induction of a metabolic shift from OXPHOS to glycolysis at early hepatocarcinogenesis by hepatocarcinogens unrelated to genotoxic potential. Non-genotoxic hepatocarcinogens increased c-MYC⁺ cells after 28 days and downregulated Tp53 after 84 or 90 days, suggesting a commitment to enhanced metabolic shift and cell proliferation. Genotoxic hepatocarcinogens also enhanced c-MYC activation-related metabolic shift until 84 or 90 days. In addition, both genotoxic and non-genotoxic hepatocarcinogens upregulated glutaminolysis-related Slc1a5 or Gls, or both, after 28 days and induced liver cell foci immunoreactive for neutral amino acid transporter B(0) (SLC1A5) in the subpopulation of GST-P⁺ foci after 84 or 90 days, suggesting glutaminolysis-mediated facilitation of cell proliferation toward hepatocarcinogenesis. These results suggest differential responses between genotoxic and non-genotoxic hepatocarcinogens on reprogramming of energy metabolic pathways toward carcinogenesis in liver cells from the early stage of hepatocarcinogen treatment.

Risk assessment of lithium-ion battery explosion: chemical leakages

Use of lithium-ion batteries has raised safety issues owing to chemical leakages, overcharging, external heating, or explosions. A risk assessment was conducted for hydrofluoric acid (HF) and lithium hydroxide (LiOH) which potential might leak from lithium-ion batteries. The inhalation no-observed-adverse-effect-level (NOAEL) for HF was 0.75 mg/kg/d. When a lithium-ion battery explodes in a limited space, HF emissions amount to 10-100 ppm. Assuming the worst-case scenario, the conversion rate was calculated to be 81.8 mg/m3, and the average daily dose (ADD) was 19.5 mg/kg/d. Consequently, the margin of exposure (MOE = NOAEL/ADD) was 0.034, a value which constitutes an unsafe inhalation exposure for HF. Conversely, skin toxicity NOAEL for LiOH was 41.35 mg/kg/d-. This LiOH value reflects the amount of lithium in the lithium-ion battery, which is generated upon contact between water and the electrolyte. The quantity of lithium in a mobile phone is approximately 295 mg, and systemic exposure dose (SED) was 4.92 mg/kg/d. Accordingly, the MOE (NOAEL/SED) value was 8.41, and skin exposure of LiOH was deemed as safe for humans. However, it is important that Energy Storage System batteries still require safety measures and technologies for next-generation batteries, to prevent any potential explosions of lithium-ion batteries.

Risk Assessment of 5-Chloro-2-Methylisothiazol-3(2H)-One/2-Methylisothiazol-3(2H)-One (CMIT/MIT) Used as a Preservative in Cosmetics

The mixture of 5-chloro-2-methylisothiazol-3(2H)-one (CMIT) and 2-methylisothiazol-3(2H)-one (MIT), CMIT/MIT, is a preservative in cosmetics. CMIT/MIT is a highly effective preservative; however, it is also a commonly known skin sensitizer. Therefore, in the present study, a risk assessment for safety management of CMIT/MIT was conducted on products containing 0.0015% of CMIT/MIT, which is the maximum MIT level allowed in current products. The no observed adverse effect level (NOAEL) for CMIT/MIT was 2.8 mg/kg bw/day obtained from a two-generation reproductive toxicity test, and the skin sensitization toxicity standard value for CMIT/MIT, or the no expected sensitization induction level (NESIL), was 1.25 μg/cm2/day in humans. According to a calculation of body exposure to cosmetics use, the systemic exposure dosage (SED) was calculated as 0.00423 mg/kg bw/day when leave-on and rinse-off products were considered. Additionally, the consumer exposure level (CEL) amounted to 0.77512 μg/cm2/day for all representative cosmetics and 0.00584 μg/cm2/day for rinse-off products only. As a result, the non-cancer margin of safety (MOS) was calculated as 633, and CMIT/MIT was determined to be safe when all representative cosmetics were evaluated. In addition, the skin sensitization acceptable exposure level (AEL)/CEL was calculated as 0.00538 for all representative cosmetics and 2.14225 for rinse-off products; thus, CMIT/MIT was considered a skin sensitizer when all representative cosmetics were evaluated. Current regulations indicate that CMIT/MIT can only be used at concentrations 0.0015% or less and is prohibited from use in other cosmetics products. According to the results of this risk assessment, the CMIT/MIT regulatory values currently used in cosmetics are evaluated as appropriate.