Search

In this study, we have studied the cytotoxicity and genotoxic potency of 3 pro-oxidants; H2O2, menadione and KBrO3 in different dosing scenarios, namely acute (1-day dosing) and chronic (5-days). For this purpose, relative population doubling (RPD%) and mononucleated micronucleus (MN) test were used. TK6 cells and NH32 were employed in in vitro experiments. In the study, the total acute dose was divided into 5 days for each prooxidant chemicals by dose fractionation (1/5th per day) method. Acute dosing was compared to chronic dosing. The oxidative stress caused by the exposure of cells with pro-oxidant chemicals to the cells was determined by an optimized 2′,7′-dichlorofluorescein diacetate (DCFHDA) test method. The antioxidant levels of the cell lines were altered with buthionine sulfoxide (BSO) and N-acetyl cysteine (NAC), and the effect of antioxidant capacity on the MN formation in the cells was observed with this method. In the case of H2O2 and menadione, fractional dosing has been observed to result in lower toxicity and lower genotoxicity. But in the case of KBrO3, unlike the other 2 pro-oxidants, higher MN induction was observed with fractionated doses. DCFHDA test clearly demonstrated ROS induction with H2O2 and menadione but not with KBrO3. Unexpectedly, DCFHDA test demonstrated that KBrO3 did not cause an increase ROS levels in both acute and chronic dosing, suggesting an alternative ROS induction mechanism. It was also observed that, treatment with BSO and NAC, caused increasing and decreasing of MN fold change respectively, allowing further ROS specific mechanisms to be explored. Hence, dose fractionation expectedly caused less MN, cytotoxicity and ROS formation with H2O2 and menadione exposure, but not with KBrO3. This implies a unique mechanism of action for KBrO3 induced genotoxicity. Chronic dosing in vitro may be a valuable approach allowing better understanding of how chemicals damage DNA and pose human hazards.

In vitro genotoxicity studies are a quick and high throughput approach to assess the genotoxic potential of chemicals; however, the reliability of these tests and their relevance to in vivo effects depends on the choice of representative cell line and optimisation of assay conditions. For chemicals like urethane that require specific metabolic activation to cause genotoxicity, it is important that in vitro tests are conducted using cell lines exhibiting the activity and induction of CYP450 enzymes, including CYP2E1 enzyme that is important in the metabolism of urethane, at a concentration representing actual or perceived chemical exposure. We compared 2D MCL-5 cells and HepG2 cells with 3D HepG2 hanging drop spheroids to determine the genotoxicity of urethane using the micronucleus assay. Our 2D studies with MCL-5 did not show any statistically significant genotoxicity [99% relative population doubling (RPD)] compared to controls for concentrations and time point tested in vitro. HepG2 cells grown as 2D indicated that exposure to urethane of up to 30 mM for 23 h did not cause any genotoxic effect (102% RPD) but, at higher concentrations, genotoxicity was produced with only 89–85% RPD. Furthermore, an exposure of 20–50 mM for 23 h using 3D hanging drop spheroid assays revealed a higher MN frequency, thus exhibiting in vitro genotoxicity of urethane in metabolically active cell models. In comparison with previous studies, this study indicated that urethane genotoxicity is dose, sensitivity of cell model (2D vs. 3D) and exposure dependent.

Human ENP exposure is inevitable and the novel, size-dependent physicochemical properties that enable ENPs to be beneficial in innovative technologies are concomitantly causing heightened public concerns as to their potential adverse effects upon human health. This study aims to deduce the mechanisms associated with potential ENP mediated (geno)toxicity and impact upon telomere integrity, if any, of varying concentrations of both ∼16 nm (4.34 × 10

The aerial hunting behaviours of birds are strongly influenced by flight morphology and ecology, but little is known of how this relates to the behavioural algorithms guiding flight. Here, we used GPS loggers to record the attack trajectories of captive-bred gyrfalcons (Falco rusticolus) during their maiden flights against robotic aerial targets, which we compared with existing flight data from peregrine falcons (Falco peregrinus). The attack trajectories of both species were well modelled by a proportional navigation (PN) guidance law, which commands turning in proportion to the angular rate of the line-of-sight to target, at a guidance gain N. However, naive gyrfalcons operate at significantly lower values of N than peregrine falcons, producing slower turning and a longer path to intercept. Gyrfalcons are less manoeuvrable than peregrine falcons, but physical constraint is insufficient to explain the lower values of N we found, which may reflect either the inexperience of the individual birds or ecological adaptation at the species level. For example, low values of N promote the tail-chasing behaviour that is typical of wild gyrfalcons and which apparently serves to tire their prey in a prolonged high-speed pursuit. Likewise, during close pursuit of typical fast evasive prey, PN will be less prone to being thrown off by erratic target manoeuvres at low guidance gain. The fact that low-gain PN successfully models the maiden attack flights of gyrfalcons suggests that this behavioural algorithm is embedded in a guidance pathway ancestral to the clade containing gyrfalcons and peregrine falcons, though perhaps with much deeper evolutionary origins., Highlighted Article: Naive gyrfalcons attacking aerial targets are modelled by the same proportional navigation guidance law as peregrine falcons, but with a lower navigation constant that promotes tail-chasing rather than efficient interception.

Current in vitro genotoxicity tests can produce misleading positive results, indicating an inability to effectively predict a compound’s subsequent carcinogenic potential in vivo. Such oversensitivity can incur unnecessary in vivo tests to further investigate positive in vitro results, supporting the need to improve in vitro tests to better inform risk assessment. It is increasingly acknowledged that more informative in vitro tests using multiple endpoints may support the correct identification of carcinogenic potential. The present study, therefore, employed a holistic, multiple-endpoint approach using low doses of selected carcinogens and non-carcinogens (0.001–770 µM) to assess whether these chemicals caused perturbations in molecular and cellular endpoints relating to the Hallmarks of Cancer. Endpoints included micronucleus induction, alterations in gene expression, cell cycle dynamics, cell morphology and bioenergetics in the human lymphoblastoid cell line TK6. Carcinogens ochratoxin A and oestradiol produced greater Integrated Signature of Carcinogenicity scores for the combined endpoints than the “misleading” in vitro positive compounds, quercetin, 2,4-dichlorophenol and quinacrine dihydrochloride and toxic non-carcinogens, caffeine, cycloheximide and phenformin HCl. This study provides compelling evidence that carcinogens can successfully be distinguished from non-carcinogens using a holistic in vitro test system. Avoidance of misleading in vitro outcomes could lead to the reduction and replacement of animals in carcinogenicity testing. Electronic supplementary material The online version of this article (10.1007/s00204-020-02902-3) contains supplementary material, which is available to authorized users.

Motorboats are a pervasive, growing source of anthropogenic noise in marine environments, with known impacts on fish physiology and behaviour. However, empirical evidence for the disruption of parental care remains scarce and stems predominantly from playback studies. Additionally, there is a paucity of experimental studies examining noise-mitigation strategies. We conducted two field experiments to investigate the effects of noise from real motorboats on the parental-care behaviours of a common coral-reef fish, the Ambon damselfish Pomacentrus amboinensis, which exhibits male-only egg care. When exposed to motorboat noise, we found that males exhibited vigilance behaviour 34% more often and spent 17% more time remaining vigilant, compared to an ambient-sound control. We then investigated nest defence in the presence of an introduced conspecific male intruder, incorporating a third noise treatment of altered motorboat-driving practice that was designed to mitigate noise exposure via speed and distance limitations. The males spent 22% less time interacting with the intruder and 154% more time sheltering during normal motorboat exposure compared to the ambient-sound control, with nest-defence levels in the mitigation treatment equivalent to those in ambient conditions. Our results reveal detrimental impacts of real motorboat noise on some aspects of parental care in fish, and successfully demonstrate the positive effects of an affordable, easily implemented mitigation strategy. We strongly advocate the integration of mitigation strategies into future experiments in this field, and the application of evidence-based policy in our increasingly noisy world.

The file attached to this record is the author's final peer reviewed version. The Publisher's final version can be found by following the DOI link. The liver's role in metabolism of chemicals makes it an appropriate tissue for toxicity testing. Current testing protocols, such as animal testing and two-dimensional liver cell systems, offer limited resemblance to in vivo liver cell behaviour, in terms of gene expression profiles and metabolic competence; thus, they do not always accurately predict human toxicology. In vitro three-dimensional liver cell models offer an attractive alternative. This study reports on the development of a 3D liver model, using HepG2 cells, by a hanging-drop technique, with a focus on evaluating spheroid growth characteristics and suitability for genotoxicity testing. The cytokinesis-blocked micronucleus assay protocol was adapted to enable micronucleus (MN) detection in the 3D spheroid models. This involved evaluating the difference between hanging vs non-hanging drop positions for dosing of the test agents and comparison of automated Metafer scoring with manual scoring for MN detection in HepG2 spheroids. The initial seeding density, used for all experiments, was 5000 cells/20 μl drop hanging spheroids, harvested on day 4, with >75% cell viability. Albumin secretion (7.8 g/l) and both CYP1A1 and CYP1A2 gene expression were highest in the 3D environment at day 4. Exposure to metabolically activated genotoxicants for 24 h resulted in a 6-fold increase in CYP1A1 enzyme activity (3 μM B[a]P) and a 30-fold increase in CYP1A2 enzyme activity (5 μM PhIP) in 3D hanging spheroids. MN inductions in response to B[a]P or PhIP were 2-fold and 3-fold, respectively, and were greater in 3D hanging spheroids than in 2D format, showing that hanging spheroids are more sensitive to genotoxic agents. HepG2 hanging-drop spheroids are an exciting new alternative system for genotoxicity studies, due to their improved structural and physiological properties, relative to 2D cultures.

The liver’s role in metabolism of chemicals makes it an appropriate tissue for toxicity testing. Current testing protocols, such as animal testing and two-dimensional liver cell systems, offer limited resemblance to in vivo liver cell behaviour, in terms of gene expression profiles and metabolic competence; thus, they do not always accurately predict human toxicology. In vitro three-dimensional liver cell models offer an attractive alternative. This study reports on the development of a 3D liver model, using HepG2 cells, by a hanging-drop technique, with a focus on evaluating spheroid growth characteristics and suitability for genotoxicity testing. The cytokinesis-blocked micronucleus assay protocol was adapted to enable micronucleus (MN) detection in the 3D spheroid models. This involved evaluating the difference between hanging vs non-hanging drop positions for dosing of the test agents and comparison of automated Metafer scoring with manual scoring for MN detection in HepG2 spheroids. The initial seeding density, used for all experiments, was 5000 cells/20 μl drop hanging spheroids, harvested on day 4, with >75% cell viability. Albumin secretion (7.8 g/l) and both CYP1A1 and CYP1A2 gene expression were highest in the 3D environment at day 4. Exposure to metabolically activated genotoxicants for 24 h resulted in a 6-fold increase in CYP1A1 enzyme activity (3 μM B[a]P) and a 30-fold increase in CYP1A2 enzyme activity (5 μM PhIP) in 3D hanging spheroids. MN inductions in response to B[a]P or PhIP were 2-fold and 3-fold, respectively, and were greater in 3D hanging spheroids than in 2D format, showing that hanging spheroids are more sensitive to genotoxic agents. HepG2 hanging-drop spheroids are an exciting new alternative system for genotoxicity studies, due to their improved structural and physiological properties, relative to 2D cultures.

Human exposure to carcinogens occurs via a plethora of environmental sources, with 70–90% of cancers caused by extrinsic factors. Aberrant phenotypes induced by such carcinogenic agents may provide universal biomarkers for cancer causation. Both current in vitro genotoxicity tests and the animal-testing paradigm in human cancer risk assessment fail to accurately represent and predict whether a chemical causes human carcinogenesis. The study aimed to establish whether the integrated analysis of multiple cellular endpoints related to the Hallmarks of Cancer could advance in vitro carcinogenicity assessment. Human lymphoblastoid cells (TK6, MCL-5) were treated for either 4 or 23 h with 8 known in vivo carcinogens, with doses up to 50% Relative Population Doubling (maximum 66.6 mM). The adverse effects of carcinogens on wide-ranging aspects of cellular health were quantified using several approaches; these included chromosome damage, cell signalling, cell morphology, cell-cycle dynamics and bioenergetic perturbations. Cell morphology and gene expression alterations proved particularly sensitive for environmental carcinogen identification. Composite scores for the carcinogens’ adverse effects revealed that this approach could identify both DNA-reactive and non-DNA reactive carcinogens in vitro. The richer datasets generated proved that the holistic evaluation of integrated phenotypic alterations is valuable for effective in vitro risk assessment, while also supporting animal test replacement. Crucially, the study offers valuable insights into the mechanisms of human carcinogenesis resulting from exposure to chemicals that humans are likely to encounter in their environment. Such an understanding of cancer induction via environmental agents is essential for cancer prevention. Electronic supplementary material The online version of this article (10.1007/s00204-017-2102-y) contains supplementary material, which is available to authorized users.

Hormesis is defined as a biphasic dose-response where biological effects of low doses of a stressor demonstrate the opposite effect to high-dose effects of the same stressor. Hormetic, or J-shaped, dose-response relationships are relatively rarely observed in toxicology, resulting in a limited understanding and even some skepticism of the concept. Low dose-response studies for genotoxicity endpoints have been performed at Swansea University for over a decade. However, no statistically significant decreases below control genotoxicity levels have been detected until recently. A hormetic-style dose-response following a 24h exposure to the alkylating agent N-methyl-N-nitrosourea (MNU) was observed in a previous study for HPRT mutagenesis in the human lymphoblastoid cell line AHH-1. A second recent study demonstrated a J-shaped dose-response for the induction of micronuclei by MNU in a 24h treatment in a similar test system. Following mechanistic investigations, it was hypothesized that p53 may be responsible for the observed hormetic phenomenon. As genotoxic carcinogens are a major causative factor of many cancers, consideration of hormesis in carcinogenesis could be important in safety assessment. The data examined here offer possible insights into hormesis, including its estimated prevalence, underlying mechanisms and lack of generalizability.

Genotoxicity testing methods in vitro provide a means to predict the DNA damaging effects of chemicals on human cells. This is hindered in the case of hydrophobic test compounds, however, which will partition to in vitro components such as plastic-ware and medium proteins, in preference to the aqueous phase of the exposure medium. This affects the freely available test chemical concentration, and as this freely dissolved aqueous concentration is that bioavailable to cells, it is important to define and maintain this exposure. Passive dosing promises to have an advantage over traditional ‘solvent spiking’ exposure methods and involves the establishment and maintenance of known chemical concentrations in the in vitro medium, and therefore aqueous phase. Passive dosing was applied in a novel format to expose the MCL-5 human lymphoblastoid cell line to the pro-carcinogen, benzo[a]pyrene (B[a]P) and was compared to solvent (dimethyl sulphoxide) spiked B[a]P exposures over 48 h. Passive dosing induced greater changes, at lower concentrations, to micronucleus frequency, p21 mRNA expression, cell cycle abnormalities, and cell and nuclear morphology. This was attributed to a maintained, definable, free chemical concentration using passive dosing and the presence or absence of solvent, and highlights the influence of exposure choice on genotoxic outcomes.

The micronucleus (MN) assay, a mainstay of DNA damage testing for over 30 years, has been applied to dozens of human cell model systems and used to generate hazard identification data on hundreds of chemical (and physical) agents in vitro. Standardisation of the MN assay procedures and strict adherence of cell culture best practise has ensured high quality reproducible data is being generated. We compare here key characteristics of different human cell models used in MN studies across recent years and show technical details of 19 different human cell lines used for MN assessment as well as several 3D human tissue models. We discuss some of the key aspects of the methodology and/or cell culture characteristics which influence the level of MN in these human cells.

Background The rapid production and incorporation of engineered nanomaterials into consumer products alongside research suggesting nanomaterials can cause cell death and DNA damage (genotoxicity) makes in vitro assays desirable for nanosafety screening. However, conflicting outcomes are often observed when in vitro and in vivo study results are compared, suggesting more physiologically representative in vitro models are required to minimise reliance on animal testing. Method BASF Levasil® silica nanoparticles (16 and 85 nm) were used to adapt the 3D reconstructed skin micronucleus (RSMN) assay for nanomaterials administered topically or into the growth medium. 3D dose-responses were compared to a 2D micronucleus assay using monocultured human B cells (TK6) after standardising dose between 2D / 3D assays by total nanoparticle mass to cell number. Cryogenic vitrification, scanning electron microscopy and dynamic light scattering techniques were applied to characterise in-medium and air-liquid interface exposures. Advanced transmission electron microscopy imaging modes (high angle annular dark field) and X-ray spectrometry were used to define nanoparticle penetration / cellular uptake in the intact 3D models and 2D monocultured cells. Results For all 2D exposures, significant (p

Risk assessment of human exposure to chemicals is crucial for understanding whether such agents can cause cancer. The current emphasis on avoidance of animal testing has placed greater importance on in vitro tests for the identification of genotoxicants. Selection of an appropriate in vitro dosing regime is imperative in determining the genotoxic effects of test chemicals. Here, the issue of dosing approaches was addressed by comparing acute and chronic dosing, uniquely using low-dose experiments. Acute 24 h exposures were compared with equivalent dosing every 24 h over 5-day, fractionated treatment periods. The in vitro micronucleus assay was used to measure clastogenicity induced by methyl methanesulfonate (MMS) and N-methyl-N-nitrosourea (MNU) in human lymphoblastoid cell line, TK6. Quantitative real-time (qRT) PCR was used to measure mRNA level induction of DNA repair enzymes. Lowest observed genotoxic effect levels (LOGELs) for MMS were obtained at 0.7 µg/ml for the acute study and 1.0 µg/ml for the chronic study. For acute MNU dosing, a LOGEL was observed at 0.46 µg/ml, yet genotoxicity was completely removed following the chronic study. Interestingly, acute MNU dosing demonstrated a statistically significant decrease at 0.009 µg/ml. Levels of selected DNA repair enzymes did not change significantly following doses tested. However, p53 deficiency (using the TK6-isogenic cell line, NH32) increased sensitivity to MMS during chronic dosing, causing this LOGEL to equate to the acute treatment LOGEL. In the context of the present data for 2 alkylating agents, chronic dosing could be a valuable in vitro supplement to acute dosing and could contribute to reduction of unnecessary in vivo follow-up tests.

Micronucleus (MN) induction is an established cytogenetic end point for evaluating structural and numerical chromosomal alterations in genotoxicity testing. A semi-automated scoring protocol for the assessment of MN preparations from human cell lines and a 3D skin cell model has been developed and validated. Following exposure to a range of test agents, slides were stained with 4'-6-diamidino-2-phenylindole (DAPI) and scanned by use of the MicroNuc module of metafer 4, after the development of a modified classifier for selecting MN in binucleate cells. A common difficulty observed with automated systems is an artefactual output of high false positives, in the case of the metafer system this is mainly due to the loss of cytoplasmic boundaries during slide preparation. Slide quality is paramount to obtain accurate results. We show here that to avoid elevated artefactual-positive MN outputs, diffuse cell density and low-intensity nuclear staining are critical. Comparisons between visual (Giemsa stained) and automated (DAPI stained) MN frequencies and dose-response curves were highly correlated (R (2) = 0.70 for hydrogen peroxide, R (2) = 0.98 for menadione, R (2) = 0.99 for mitomycin C, R (2) = 0.89 for potassium bromate and R (2) = 0.68 for quantum dots), indicating the system is adequate to produce biologically relevant and reliable results. Metafer offers many advantages over conventional scoring including increased output and statistical power, and reduced scoring subjectivity, labour and costs. Further, the metafer system is easily adaptable for use with a range of different cells, both suspension and adherent human cell lines. Awareness of the points raised here reduces the automatic positive errors flagged and drastically reduces slide scoring time, making metafer an ideal candidate for genotoxic biomonitoring and population studies and regulatory genotoxic testing.

Nineteen children with biopsy-proven rhabdomyosarcoma were selected for a 1-2-year study utilizing surgery, supervoltage, and electron-beam radiation therapy, and combination chemotherapy with vincristine, cyclophosphamide, and dactinomycin. At the time of diagnosis, 4 patients had localized tumor, 9 had regional spread of tumor, 5 had extensive spread of tumor, and 1 had bone marrow involvement. Complete response to therapy was seen in 17 patients, 2 had partial response followed by progressive disease, and 4 died with disease at 15, 11, 8, and 6 months respectively. Eleven patients were free of disease for 4-49 months; 2 had extension of disease at 2 and 4 months. Two patients were just entered on the study and response data is being investigated currently. This approach of extended combination therapy of childhood rhabdomyosarcoma was well tolerated and offers an alternative to radical surgery in the growing child.

Mitochondrial DNA mutation and toxicity have been linked to several inherited and acquired diseases; however, these are challenging to diagnose and characterize due to clinical and genetic heterogeneity. This review investigates current techniques for the analysis of mitochondrial perturbations, and novel, emerging endpoints for routine application within the clinical setting. Particular focus is given to the biochemistry of the mitochondria influencing each endpoint and the relation of these to toxicity. Current approaches such as the use of metabolic markers (e.g. lactate production), and muscle biopsies to measure mitochondrial proteins were found to lack specificity. Newly emerging identified endpoints were: fibroblast growth factor-21, glucose uptake, mitochondrial membrane potential, mitochondrial morphology, mtDNA heteroplasmy, and mutation of mtDNA and nuclear DNA. Owed to the advancement in genetic analysis techniques, it is suggested by this review that genotypic endpoints of mtDNA mutation and heteroplasmy show particular promise as indicators of mitochondrial disease. It is, however, acknowledged that any single endpoint in isolation offers limited information; therefore, it is recommended that analysis of several endpoints simultaneously will offer the greatest benefit in terms of disease diagnosis and study. It is hoped that this review further highlights the need for advancement in understanding mitochondrial disease.