Nodularin-induced genotoxicity following oxidative DNA damage and aneuploidy in HepG2 cells

Genotoxicity of Natural Water during the Mass Development of Cyanobacteria Evaluated by the Allium Test Method: A Model Experiment with Microcosms

Cyanobacteria, which develop abundantly in aquatic ecosystems, can be harmful to humans and animals not only by releasing toxins that cause poisoning but also by provoking cytogenetic effects. The influence of the mass development of cyanobacteria on the genotoxic properties of natural water has been studied in model ecosystems (microcosms) with different compositions of biotic components (zooplankton, amphipods and fish). The validated plant test system “Allium test” was used in this study. Genotoxic effects were detected at microcystin concentrations below those established by the World Health Organization (WHO) for drinking water. In all experimental treatments, cells with disorders such as polyploidy and mitotic abnormalities associated with damage to the mitotic spindle, including c-mitosis, as well as lagging chromosomes were found. Genotoxic effects were associated with the abundance of cyanobacteria, which, in turn, depended on the composition of aquatic organisms in the experimental ecosystem. Fish, to a greater extent than other aquatic animals, maintain an abundance of cyanobacteria. After one month, in microcosms with fish, mitotic abnormalities and polyploidy continued to be detected, whereas in other treatments, there were no statistically significant genotoxic effects. In microcosms with amphipods, the number and biomass of cyanobacteria decreased to the greatest extent, and only one parameter of genotoxic activity (frequency of polyploidy) significantly differed from the control.

Review of Cyanotoxicity Studies Based on Cell Cultures

Cyanotoxins (CTs) are a large and diverse group of toxins produced by the peculiar photosynthetic prokaryotes of the domain Cyanoprokaryota. Toxin-producing aquatic cyanoprokaryotes can develop in mass, causing “water blooms” or “cyanoblooms,” which may lead to environmental disaster—water poisoning, extinction of aquatic life, and even to human death. CT studies on single cells and cells in culture are an important stage of toxicological studies with increasing impact for their further use for scientific and clinical purposes, and for policies of environmental protection. The higher cost of animal use and continuous resistance to the use of animals for scientific and toxicological studies lead to a progressive increase of cell lines use. This review aims to present (1) the important results of the effects of CT on human and animal cell lines, (2) the methods and concentrations used to obtain these results, (3) the studied cell lines and their tissues of origin, and (4) the intracellular targets of CT. CTs reviewed are presented in alphabetical order as follows: aeruginosins, anatoxins, BMAA (β-N-methylamino-L-alanine), cylindrospermopsins, depsipeptides, lipopolysaccharides, lyngbyatoxins, microcystins, nodularins, cyanobacterial retinoids, and saxitoxins. The presence of all these data in a review allows in one look to advance the research on CT using cell cultures by facilitating the selection of the most appropriate methods, conditions, and cell lines for future toxicological, pharmacological, and physiological studies.

AOP report: Development of an adverse outcome pathway for oxidative DNA damage leading to mutations and chromosomal aberrations

The Genetic Toxicology Technical Committee (GTTC) of the Health and Environmental Sciences Institute (HESI) is developing adverse outcome pathways (AOPs) that describe modes of action leading to potentially heritable genomic damage. The goal was to enhance the use of mechanistic information in genotoxicity assessment by building empirical support for the relationships between relevant molecular initiating events (MIEs) and regulatory endpoints in genetic toxicology. Herein, we present an AOP network that links oxidative DNA damage to two adverse outcomes (AOs): mutations and chromosomal aberrations. We collected empirical evidence from the literature to evaluate the key event relationships between the MIE and the AOs, and assessed the weight of evidence using the modified Bradford-Hill criteria for causality. Oxidative DNA damage is constantly induced and repaired in cells given the ubiquitous presence of reactive oxygen species and free radicals. However, xenobiotic exposures may increase damage above baseline levels through a variety of mechanisms and overwhelm DNA repair and endogenous antioxidant capacity. Unrepaired oxidative DNA base damage can lead to base substitutions during replication and, along with repair intermediates, can also cause DNA strand breaks that can lead to mutations and chromosomal aberrations if not repaired adequately. This AOP network identifies knowledge gaps that could be filled by targeted studies designed to better define the quantitative relationships between key events, which could be leveraged for quantitative chemical safety assessment. We anticipate that this AOP network will provide the building blocks for additional genotoxicity-associated AOPs and aid in designing novel integrated testing approaches for genotoxicity.

Comprehensive insights into the occurrence and toxicological issues of nodularins

The occurrence of cyanobacterial toxins is being increasingly reported. Nodularins (NODs) are one of the cyanotoxins group mainly produced by Nodularia spumigena throughout the world. NODs may exert adverse effects on animal and human health, and NOD-R variant is the most widely investigated. However, research focused on them is still limited. In order to understand the realistic risk well, the aim of this review is to compile the available information in the scientific literature regarding NODs, including their sources, distribution, structural characteristics, physicochemical properties, biosynthesis and degradation, adverse effects in vitro and vivo, and toxicokinetics. More data is urgently needed to integrate the cumulative or synergistic effects of NODs on different species and various cells to better understand, anticipate and aggressively manage their potential toxicity after both short- and long-term exposure in ecosystem, and to minimize or prevent the adverse effects on human health, environment and the economy.

In Vivo and In Vitro Toxicity Testing of Cyanobacterial Toxins: A Mini-Review

Harmful cyanobacterial blooms are increasing and becoming a worldwide concern as many bloom-forming cyanobacterial species can produce toxic metabolites named cyanotoxins. These include microcystins, saxitoxins, anatoxins, nodularins, and cylindrospermopsins, which can adversely affect humans, animals, and the environment. Different methods to assess these classes of compounds in vitro and in vivo include biological, biochemical, molecular, and physicochemical techniques. Furthermore, toxic effects not attributable to known cyanotoxins can be observed when assessing bloom material. In order to determine exposures to cyanotoxins and to monitor compliance with drinking and bathing water guidelines, it is necessary to have reliable and effective methods for the analysis of these compounds. Many relatively simple low-cost methods can be employed to rapidly evaluate the potential hazard. The main objective of this mini-review is to describe the assessment of toxic cyanobacterial samples using in vitro and in vivo bioassays. Newly emerging cyanotoxins, the toxicity of analogs, or the interaction of cyanobacteria and cyanotoxins with other toxicants, among others, still requires bioassay assessment. This review focuses on some biological and biochemical assays (MTT assay, Immunohistochemistry, Micronucleus Assay, Artemia salina assay, Daphnia magna test, Radionuclide recovery, Neutral red cytotoxicity and Comet assay, Enzyme-Linked Immunosorbent Assay (ELISA), Annexin V-FITC assay and Protein Phosphatase Inhibition Assay (PPIA)) for the detection and measurement of cyanotoxins including microcystins, cylindrospermopsins, anatoxin-a, saxitoxins, and nodularins. Although most bioassay analyses often confirm the presence of cyanotoxins at low concentrations, such bioassays can be used to determine whether some strains or blooms of cyanobacteria may produce other, as yet unknown toxic metabolites. This review also aims to identify research needs and data gaps concerning the toxicity assessment of cyanobacteria.

Impact of the toxicity of Cylindrospermopsis raciborskii (Woloszynska) Seenayya & Subba Raju on laboratory rats in vivo

In vivo laboratory studies of toxicity were performed on Wistar rats using a methanol extract produced by the natural population of Cylindrospermopsis raciborskii (abundance of 2.13 × 10⁵ trichomes mL^-1) collected at Aleksandrovac Lake (Serbia). HPLC analysis showed that the extract contains 6.65 μg cylindrospermopsin (CYN) mg^-1. The rats were killed 24 or 72 h after a single intraperitoneal injection of C. raciborskii extract in concentrations of 1500, 3000, 6000 and 12,000 μg kg^-1 body weight (bw) and an equivalent amount of CYN as present in the highest dose of the extract (79.80 μg CYN kg^-1 bw). The genotoxic effect on the livers treated with C. raciborskii was evaluated using comet assay and potential induction of oxidative stress as the toxicity mechanism associated with the presence of CYN in extract. The results from the analyses of DNA damage in the comet tail length, tail moment and percentage of DNA in the tail in the liver indicated that administration of extract and CYN present statistically significant difference when compared with the negative control group. Although an increase in the frequency of selected parameters induced by the CYN was observed in the liver, this damage was less than the damage resulting from the administration of the highest dose of extract. The changes in the biochemical parameters of the hepatic damage showed that the application of single doses of the extract and CYN did not cause serious liver damage in rats. The extract and CYN significantly increased oxidative stress in rats' liver after a single exposure.

New record of a bloom forming, genotoxic strain Nodularia strain (KT447209) from Andaman and Nicobar Islands, India

Cyanobacteria blooms in marine waters are limited to only a few taxa; with the genus Nodularia (Nostocales) being one among the most commonly observed and widely studied species. A bloom of Nodularia sp. was observed across a vast area along the coast of the Andaman and Nicobar Islands. The bloom occurred during the summer when salinity was >30‰. This differed to previous reports where blooms have crashed at such high salinities. The molecular phylogeny revealed the Nodularia species to be a novel one. A crude extract from the bloom demonstrated lowed toxicity with an LC₅₀ of 5 mg/ml at 48 h towards Artemia salina and slight genotoxicity when tested against human lymphocytes.

Cyanobacterial Toxins in Water Sources and Their Impacts on Human Health

Cyanobacteria are a group of phytoplankton of marine and freshwaters. The accelerated eutrophication of water sources by agricultural and industrial run-off has increased the occurrence and intensity of cyanobacterial blooms. They are of particular concern because of their production for potent hepato-, neuro-, and dermatoxins, being hazardous to human health. Dissemination of knowledge about cyanobacteria and their cyanotoxins assists water supply authorities in developing monitoring and management plans, and provides the public with appropriate information to avoid exposure to these toxins. This chapter provides a broad overview and up-to-date information on cyanobacteria and their toxins in terms of their occurrence, chemical and toxicological characteristics, fate in the environment, guideline limits, and effective treatment techniques to remove these toxins from drinking water. Future research directions were also suggested to fill knowledge and research gaps, and advance the abilities of utilities and water treatment plant designers to deal with these toxins.

Saxitoxins induce cytotoxicity, genotoxicity and oxidative stress in teleost neurons in vitro

The aim of this study was establish a protocol for isolation and primary culture of neurons from tropical freshwater fish species Hoplias malabaricus for assessment of the effects of neurotoxic substances as saxitoxins (STXs). Cells from brain of H. malabaricus were treated with different concentrations of trypsin, dispase and papain for tissue dissociation. Cells type was separated by cellular gradient and basic fibroblast growth factor (bFGF) supplement nutrition media were added. The dissociated cells were plated with medium and different STXs concentrations and the toxic cellular effects such as oxidative stress, neurotoxicity, and genotoxicity and apoptosis process were evaluated. Cultures treated with bFGF showed the greatest adherence, survival and cellular development. STXs increased specific activity of glutathione peroxidase and lipoperoxidation levels, were cytotoxic and genotoxic indicated by the comet assay. Although the STXs effects due the blockage of sodium channels is reported to be reversible, the time exposure and concentration of STXs suggested cellular injuries which can lead to neuropathology. The establishment of primary neuronal culture protocol enables new applications for neurotoxicological assessments.

Regulation of nodularin-induced apoptosis by epigallocatechin-3-gallate on fish lymphocytes in vitro

Nodularin is one of the most conspicuous and widespread pollutants that elicit water ecological hazards to fish, causing serious damage on the immune system and physiological functions. Nodularin can cause oxidative stress-induced apoptosis on fish lymphocytes. The regulatory effects of epigallocatechin-3-gallate (EGCG) at 10, 100, and 1000 μg/L levels on the antioxidant defense system and apoptosis of Carassius auratus lymphocytes exposed to a high dose of nodularin (100 μg/L) were quantified in vitro. EGCG reduced nodularin-induced oxidative damage on fish immune cells. This compound significantly increased the activities of superoxide dismutase and catalase and the level of glutathione but decreased the levels of intracellular reactive oxygen species and malondialdehyde. Flow cytometry results showed that the percentages of apoptotic cells after treatment with 10, 100, and 1000 μg/L EGCG for 12 h reached 27.9%, 19.1%, and 13.7%, respectively. By contrast, the nodularin alone-induced group showed a high percentage of apoptosis (44.2%). Western blot analysis showed the increased expression of bcl-2 and the decreased expression of bax and caspase-3 in EGCG-treated fish lymphocytes. EGCG also inhibited the potential collapse of the mitochondrial membrane. Overall, EGCG can inhibit nodularin-induced apoptosis and protect the normal immunity of fish by regulating bax/bcl-2 and blocking the downstream of mitochondrial apoptosis pathway with increased intracellular antioxidant enzyme activity.

Apoptotic responses of Carassius auratus lymphocytes to nodularin exposure in vitro

Nodularin, a metabolite of Nodularin spumigena, is widely detected in water blooms worldwide and causes serious negative effects on fish. The apoptosis-related cytotoxic effects and mechanisms of nodularin on Carassius auratus lymphocytes were investigated. Transmission electron microscopy results showed that nodularin-treated lymphocytes display a series of morphological changes, including condensed cytoplasm, nuclear chromatin agglutination and marginalization. DNA fragmentation was verified by the DNA-ladder and formation of sub-G1 DNA peaks. These cell characteristics confirmed the occurrence of apoptosis in lymphocytes. Flow cytometric results showed that the percentages of apoptotic cells incubated with 1, 5, 10, and 100 μg/L nodularin for 12 h reached 15.76%, 17.36%, 20.34% and 44.21%, respectively; controls showed low rates of apoptosis (2.4%). The mechanism of apoptosis induced by nodularin was determined, and results showed that nodularin exposure caused a significant increase in intracellular reactive oxygen species (ROS), loss of mitochondrial transmembrane potential in a dose-dependent manner, upregulation of intracellular Ca²⁺, downregulation of Bcl-2 and upregulation of Bax expression at the mRNA and protein levels, and activation of caspase-3 and caspase-9 without caspase-8. In summary, all the results suggest that nodularin induces lymphocyte apoptosis via the mitochondrial apoptotic pathway and destroys the immune response of fish.

Genotoxicity of crude extracts of cyanobacteria from Taihu Lake on carp (Cyprinus carpio)

Genotoxicity of crude cyanobacteria extracts (CBE) from blooms in Taihu Lake, China toward common carp (Cyprinus carpio) was measured. The primary extracellular product was determined by HPLC to be Microcystin-LR (MC-LR, L for leucine and R for arginine) with an average concentration of 2.4 × 10(2) μg MC g(-1) dry weight of cyanobacteria. Acute toxicity to carp, expressed as the 72-h LC(50,) was 53 mg, dw cyanobacteria L(-1). Genotoxicity, as determined by the micronucleus (MN) and comet assays were both dose- and time-depended. Deformities of cellular organelles in liver and gill were observed by use of transmission electron microscopy (TEM). The results showed that MC-LR from cyanobacteria from Taihu Lake could induce genotoxic response and tissue-level morphological changes in common carp.

Cyanobacterial toxins and liver diseaseThis article is one of a selection of papers published in a special issue celebrating the 125th anniversary of the Faculty of Medicine at the University of Manitoba

Blue-green algae, also known as cyanobacteria, produce a variety of toxins, some of which have been implicated in the pathogenesis of severe and potentially life-threatening diseases in humans. As the growth of cyanobacteria within freshwater lakes increases worldwide, it is important to review our present understanding of their toxicity and potential carcinogenicity to gain insight into how these organisms impact human health. This review addresses each of these topics, with special emphasis given to cyanobacterial hepatotoxins within freshwater environments.

Combination of in vitro bioassays for the determination of cytotoxic and genotoxic potential of wastewater, surface water and drinking water samples

In this study we evaluated genotoxicity and cytotoxicity of native samples of wastewaters (15 samples), surface waters (28 samples) and potable waters (8 samples) with the SOS/umuC assay with Salmonella typhimurium TA1535/pSK1002 and MTT assay with human hepatoma HepG2 cells. The genotoxicity of selected samples was confirmed with the comet assay with HepG2 cells. In the SOS/umuC assay 13 out of the 51 samples were genotoxic: two effluent samples from chemical industry; one sample of wastewater treatment plant effluent; two hospital wastewater samples; three river water samples and four lake water samples. Six samples were cytotoxic for HepG2 cells: both effluent samples of chemical industry, two wastewater treatment plant effluent samples, and two river water samples, however, only the chemical industry effluent samples were genotoxic and cytotoxic, indicating that different contaminants are responsible for genotoxic and toxic effects. Comparing genotoxicity of river and lake water samples with the chemical analytical data of the presence of the residues of pharmaceutical and personal care products (non-steroidal anti-inflammatory drugs, UV filters and disinfectants) in these samples, indicated that the presence of UV filters might be linked to the genotoxicity of these samples. The results showed that the application of the bacterial SOS/umuC assay and mammalian cell assays (MTT and comet assay) with HepG2 cells was suitably sensitive combination of assays to monitor genotoxicity and cytotoxicity of native samples of wastewaters and surface waters. With this study we also confirmed that the toxicity/genotoxicity bioassays should be an integral tool in the evaluation of toxicity of complex wastewaters before the release into environment, as well as for the monitoring of surface water quality, providing data useful in risk assessment.

Nucleotide excision repair impairment by nodularin in CHO cell lines due to ERCC1/XPF inactivation

The problem of toxicity of cyanobacterial toxins is of increasing concern, as the incidence of such blooms grows. Among the toxins, the most abundant in the environment are hepatotoxins known as nodularins and microcystins. These toxins are responsible for almost all known cases of fresh and brackish water intoxication and are responsible for recurrent episodes of human and animal illness and death. Moreover, they are believed to be potent tumor promoters and initiators. However, the mechanisms by which these toxins induce liver cancer are not well understood. The aim of the present study was to determine the effect of nodularin on the kinetics of nucleotide excision repair (NER) in Chinese hamster ovary (CHO) cells exposed to UV radiation. The first set of experiments was performed to define the optimal treatment conditions for nodularin to avoid the possibility of encountering false positive signals in the comet assay due to the apoptogenic activity of nodularin. Based on the analysis of apoptosis, the 6-h treatment time of cells with nodularin (1mug/ml, 10mug/ml and 20mug/ml) was chosen for the alkaline comet assay. The kinetics of NER was determined in CHO cell lines: AA8 (wild-type) and mutant cell lines: UV135 (XPG(-)), UV41 (XPF(-)) and UV20 (ERCC1(-)) exposed to 20J/m(2) UV radiation. The micronucleus assay was performed to determine a residual DNA damage in four cell lines treated with nodularin (10mug/ml) and exposed to equitoxic doses UV radiation. Radiation doses of UV producing 50% of survival for AA8, UV135, UV20 and UV41 cell lines were calculated from UV survival curves. The results show that nodularin impairs the incision/excision step of NER in CHO cells by the ERCC1/XPF inactivation and leads to an increased level of UV-induced cytogenetic DNA damage.