Caenorhabditis elegans generates biologically relevant levels of genotoxic metabolites from aflatoxin B1 but not benzo[a]pyrene in vivo

CYP14 family in Caenorhabditis elegans: Mitochondrial function, detoxification, and lifespan

CYP-14 members of the Caenorhabditis elegans (C. elegans) Cytochrome P450 (CYP) enzyme family, plays important roles in mitochondrial dysfunction, detoxification, lipid metabolism, defense and lifespan regulation. The review identifies CYP-14 members: cyp-14A1, cyp-14A2, cyp-14A3, cyp-14A4, cyp-14A5 and their homology with human CYP families. Despite limited studies on C. elegans cyp-14 members, the findings unraveled their complex crosstalk between mitochondrial stress, detoxification mechanisms, and lifespan regulation, emphasizing the complexity of these interconnected pathways as well as how their regulation depends on environmental cues changes including pH, nutrients, ROS and chemical stressors. The review underscores the translational relevance to human health, shedding light on potential human homologues and their implications in age-related, metabolic and respiratory diseases. Among other genes, cyp-14A2 and cyp-14A4 predominate the mitochondrial function, heat resistance, lipid metabolism, detoxification and lifespan pathways. In conclusion, these insights pave the way for future research, offering promising avenues for therapeutic interventions targeting CYP-14 activity to address age-related diseases and promote healthy aging.

Caenorhabditis elegans CYP33 Family in Eicosanoid Regulation, Xenobiotic Metabolism, Nanotoxicity and Spermatogenesis

The CYP33 family in Caenorhabditis elegans is integral to processes like xenobiotic detoxification, eicosanoid regulation, nanotoxicity response and spermatogenesis. Limited research on C. elegans CYP33 suggests its functions are similar to human CYP33, indicating conserved roles in metabolism and disease. This review examines C. elegans CYP33 enzymes, especially CYP-33E1 and CYP-33E2, and their human homologues, focusing on their roles in eicosanoid biosynthesis, xenobiotic metabolism, nanotoxicity and spermatogenesis. Understanding these enzymes enhances insights into cytochrome P450 biology, metabolism and cyp-associated diseases.

vivoBodySeg: Machine learning-based analysis of C. elegans immobilized in vivoChip for automated developmental toxicity testing

Developmental toxicity (DevTox) tests evaluate the adverse effects of chemical exposures on an organism's development. While large animal tests are currently heavily relied on, the development of new approach methodologies (NAMs) is encouraging industries and regulatory agencies to evaluate these novel assays. Several practical advantages have made C. elegans a useful model for rapid toxicity testing and studying developmental biology. Although the potential to study DevTox is promising, current low-resolution and labor-intensive methodologies prohibit the use of C. elegans for sub-lethal DevTox studies at high throughputs. With the recent availability of a large-scale microfluidic device, vivoChip, we can now rapidly collect 3D high-resolution images of ~ 1,000 C. elegans from 24 different populations. In this paper, we demonstrate DevTox studies using a 2.5D U-Net architecture (vivoBodySeg) that can precisely segment C. elegans in images obtained from vivoChip devices, achieving an average Dice score of 97.80. The fully automated platform can analyze 36 GB data from each device to phenotype multiple body parameters within 35 min on a desktop PC at speeds ~ 140× faster than the manual analysis. Highly reproducible DevTox parameters (4-8% CV) and additional autofluorescence-based phenotypes allow us to assess the toxicity of chemicals with high statistical power.

Cyprocide selectively kills nematodes via cytochrome P450 bioactivation

Left unchecked, plant-parasitic nematodes have the potential to devastate crops globally. Highly effective but non-selective nematicides are justifiably being phased-out, leaving farmers with limited options for managing nematode infestation. Here, we report our discovery of a 1,3,4-oxadiazole thioether scaffold called Cyprocide that selectively kills nematodes including diverse species of plant-parasitic nematodes. Cyprocide is bioactivated into a lethal reactive electrophilic metabolite by specific nematode cytochrome P450 enzymes. Cyprocide fails to kill organisms beyond nematodes, suggesting that the targeted lethality of this pro-nematicide derives from P450 substrate selectivity. Our findings demonstrate that Cyprocide is a selective nematicidal scaffold with broad-spectrum activity that holds the potential to help safeguard our global food supply.

Transgenerational toxicity induced by maternal AFB1 exposure in Caenorhabditis elegans associated with underlying epigenetic regulations

Aflatoxin B1 (AFB1), usually seriously contaminates in grain and oil foods or feed, displayed significant acute and chronic toxic effects in human and animal populations. However, little is known about the transgenerational toxic effects induced by a maternal AFB1 intake at a lower dose on offspring. In our study, only parental wild-type Caenorhabditis elegans was exposed to AFB1 (0-8 μg/ml) and the following three filial generations were grown on AFB1-free NGM. Results showed that the toxic effects of AFB1 on the growth (body length) and reproduction (brood size, generation time and morphology of gonad arm) can be transmitted through generations. Moreover, the levels of MMP and ATP were irreversibly inhibited in the filial generations. By using RNomics and molecular biology techniques, we found that steroid biosynthesis, phagosome, valine/leucine/isoleucine biosynthesis and oxidative phosphorylation (p < 0.05) were the core signaling pathways to exert the transgenerational toxic effects on nematodes. Also, notably increased histone methylation level at H3K36me3 was observed in the first generation. Taken together, our study demonstrated that AFB1 has notable transgenerational toxic effects, which were resulted from the complex regulatory network of various miRNAs, mRNAs and epigenetic modification in C. elegans.

Bacteria pyruvate metabolism modulates AFB1 toxicity in Caenorhabditis elegans

Aflatoxin B1 (AFB1), the most potent mycotoxin and Group 1 human carcinogen, continues to pose a significant public health burden, particularly in developing countries. Increasing evidence has shown the gut microbiota as a key mediator of AFB1 toxicity through multiple interactive host-microbiota activities. In our previous study we observed that disturbances in bacterial pyruvate metabolism might have a significant impact on AFB1 in the host. To further investigate the impact of the pyruvate pathway on AFB1 toxicity in C. elegans, we engineered two bacterial strains (triple-overexpressed and triple-knockout strains with aceB, lpd, and pflB). Additionally, we employed two mutant worm strains (pyk-1 and pdha-1 mutants) known to affect pyruvate metabolism. Our results revealed that the co-metabolism of pyruvate by the host and bacterial strains synergistically influences AFB1 toxicity. Remarkable, we found that bacterial pyruvate metabolism, rather than that of the host, plays a pivotal role in modulating AFB1 toxicity in C. elegans. Our study sheds light on the role of gut microbiota involved in pyruvate metabolism in influencing AFB1 toxicity in C. elegans.

Selective control of parasitic nematodes using bioactivated nematicides

Parasitic nematodes are a major threat to global food security, particularly as the world amasses 10 billion people amid limited arable land^1-4. Most traditional nematicides have been banned owing to poor nematode selectivity, leaving farmers with inadequate means of pest control^4-12. Here we use the model nematode Caenorhabditis elegans to identify a family of selective imidazothiazole nematicides, called selectivins, that undergo cytochrome-p450-mediated bioactivation in nematodes. At low parts-per-million concentrations, selectivins perform comparably well with commercial nematicides to control root infection by Meloidogyne incognita, a highly destructive plant-parasitic nematode. Tests against numerous phylogenetically diverse non-target systems demonstrate that selectivins are more nematode-selective than most marketed nematicides. Selectivins are first-in-class bioactivated nematode controls that provide efficacy and nematode selectivity.

Caenorhabditis elegans: a model organism in the toxicity assessment of environmental pollutants

The unfavorable effects of environmental pollutants are becoming increasingly evident. In recent years, Caenorhabditis elegans (C. elegans) has been used as a powerful terrestrial model organism for environmental toxicity studies owing to its various advantages, including ease of culture, short lifespan, small size, transparent body, and well-characterized genome. In vivo bioassays and field studies can analyze and evaluate various toxic effects of the toxicants on the model organism, while emerging technologies allow profound insights into molecular disturbances underlying the observed phenotypes. In this review, we discuss the applications of C. elegans as a model organism in environmental toxicity studies and delineate apical assays such as lifespan, growth rate, reproduction, and locomotion, which are widely used in toxicity evaluation. In addition to phenotype assays, a comprehensive understanding of the toxic mode of action and mechanism can be achieved through a highly sensitive multi-omics approach, including the expression levels of genes and endogenous metabolites. Recent studies on environmental toxicity using these approaches have been summarized. This review highlights the practicality and advantages of C. elegans in evaluating the toxicity of environmental pollutants and presents the findings of recent toxicity studies performed using this model organism. Finally, we propose crucial technical considerations to escalate the appropriate use of C. elegans in examining the toxic effects of environmental pollutants.

Determining Toxic Potencies of Water-Soluble Contaminants in Wastewater Influents and Effluent Using Gene Expression Profiling in C. elegans as a Bioanalytical Tool

With chemical analysis, it is impossible to qualify and quantify the toxic potency of especially hydrophilic bioactive contaminants. In this study, we applied the nematode C. elegans as a model organism for detecting the toxic potency of whole influent wastewater samples. Gene expression in the nematode was used as bioanalytical tool to reveal the presence, type and potency of molecular pathways induced by 24-h exposure to wastewater from a hospital (H), nursing home (N), community (C), and influent (I) and treated effluent (E) from a local wastewater treatment plant. Exposure to influent water significantly altered expression of 464 genes, while only two genes were differentially expressed in nematodes treated with effluent. This indicates a significant decrease in bioactive pollutant-load after wastewater treatment. Surface water receiving the effluent did not induce any genes in exposed nematodes. A subset of 209 genes was differentially expressed in all untreated wastewaters, including cytochromes P450 and C-type lectins related to the nematode's xenobiotic metabolism and immune response, respectively. Different subsets of genes responded to particular waste streams making them candidates to fingerprint-specific wastewater sources. This study shows that gene expression profiling in C. elegans can be used for mechanism-based identification of hydrophilic bioactive compounds and fingerprinting of specific wastewaters. More comprehensive than with chemical analysis, it can demonstrate the effective overall removal of bioactive compounds through wastewater treatment. This bioanalytical tool can also be applied in the process of identification of the bioactive compounds via a process of toxicity identification evaluation.

CYP35 family in Caenorhabditis elegans biological processes: fatty acid synthesis, xenobiotic metabolism, and stress responses

With more than 80 cytochrome P450 (CYP) encoding genes found in the nematode Caenorhabditis elegans (C. elegans), the cyp35 genes are one of the important genes involved in many biological processes such as fatty acid synthesis and storage, xenobiotic stress response, dauer and eggshell formation, and xenobiotic metabolism. The C. elegans CYP35 subfamily consisted of A, B, C, and D, which have the closest homolog to human CYP2 family. C. elegans homologs could answer part of the hunt for human disease genes. This review aims to provide an overview of CYP35 in C. elegans and their human homologs, to explore the roles of CYP35 in various C. elegans biological processes, and how the genes of cyp35 upregulation or downregulation are influenced by biological processes, upon exposure to xenobiotics or changes in diet and environment. The C. elegans CYP35 gene expression could be upregulated by heavy metals, pesticides, anti-parasitic and anti-chemotherapeutic agents, polycyclic aromatic hydrocarbons (PAHs), nanoparticles, drugs, and organic chemical compounds. Among the cyp35 genes, cyp-35A2 is involved in most of the C. elegans biological processes regulation. Further venture of cyp35 genes, the closest homolog of CYP2 which is the largest family of human CYPs, may have the power to locate cyps gene targets, discovery of novel therapeutic strategies, and possibly a successful medical regime to combat obesity, cancers, and cyps gene-related diseases.

Resistance of mitochondrial DNA to cadmium and Aflatoxin B1 damage-induced germline mutation accumulation in C. elegans

Mitochondrial DNA (mtDNA) is prone to mutation in aging and over evolutionary time, yet the processes that regulate the accumulation of de novo mtDNA mutations and modulate mtDNA heteroplasmy are not fully elucidated. Mitochondria lack certain DNA repair processes, which could contribute to polymerase error-induced mutations and increase susceptibility to chemical-induced mtDNA mutagenesis. We conducted error-corrected, ultra-sensitive Duplex Sequencing to investigate the effects of two known nuclear genome mutagens, cadmium and Aflatoxin B1, on germline mtDNA mutagenesis in Caenorhabditis elegans. Detection of thousands of mtDNA mutations revealed pervasive heteroplasmy in C. elegans and that mtDNA mutagenesis is dominated by C:G → A:T mutations generally attributed to oxidative damage. However, there was no effect of either exposure on mtDNA mutation frequency, spectrum, or trinucleotide context signature despite a significant increase in nuclear mutation rate after aflatoxin B1 exposure. Mitophagy-deficient mutants pink-1 and dct-1 accumulated significantly higher levels of mtDNA damage compared to wild-type C. elegans after exposures. However, there were only small differences in mtDNA mutation frequency, spectrum, or trinucleotide context signature compared to wild-type after 3050 generations, across all treatments. These findings suggest mitochondria harbor additional previously uncharacterized mechanisms that regulate mtDNA mutational processes across generations.

Differential expression of genes in C. elegans reveals transcriptional responses to indirect-acting xenobiotic compounds and insensitivity to 2,3,7,8-tetrachlorodibenzodioxin

Caenorhabditis elegans is a well-established model organism for toxicity testing of chemical substances. We recently demonstrated its potential for bioanalysis of the toxic potency of chemical contaminants in water. While many detoxification genes are homologues to those in mammalians, C. elegans is reported to be deficient in cytochrome CYP1-like P450 metabolism and that its aryl hydrocarbon receptor (AhR) homolog encoded by ahr-1 purportedly does not interact with dioxins or any other known xenobiotic ligand. This suggests that C. elegans is insensitive for compounds that require bioactivation (indirectly acting compounds) and for dioxins or dioxin-like compounds. This study analysed genome-wide gene expression of the nematode in response to 30 μM of aflatoxin B1 (AFB1), benzo(a)pyrene (B(a)P), Aroclor 1254 (PCB1254), and 10 μM of 2,3,7,8-tetrachlorodibenzodioxin (TCDD). After 24 h of exposure in the early L4 larval stage, microarray analysis revealed 182, 86, and 321 differentially expressed genes in the nematodes treated with 30 μM of AFB1, B(a)P, and PCB1254, respectively. Among these genes, many encode xenobiotic-metabolizing enzymes, and their transcription levels were among the highest-ranked fold-changed genes. Interestingly, only one gene (F59B1.8) was upregulated in the nematodes exposed to 10 μM TCDD. Genes related to metabolic processes and catalytic activity were the most induced by exposure to 30 μM of AFB1, B(a)P, and PCB1254. Despite the genotoxic nature of AFB1 and B(a)P, no differential expression was found in the genes encoding DNA repair and cell cycle checkpoint proteins. Analysis of concentration-response curves was performed to determine the Lowest Observed Transcriptomic Effect Levels (LOTEL) of AFB1, B(a)P, and PCB1254. The obtained LOTEL values showed that gene expression changes in C. elegans are more sensitive to toxicants than reproductive effects. Overall, transcriptional responses of metabolic enzymes suggest that the nematode does metabolize AFB1, B(a)P, and PCB1254. Our findings also support the assumption that the transcription factor AhR homolog in C. elegans does not bind typical xenobiotic ligands, rendering the nematode transcriptionally insensitive to TCDD effects.

Cytochromes P450 of Caenorhabditis elegans: Implication in Biological Functions and Metabolism of Xenobiotics

Caenorhabditis elegans is an important model used for many aspects of biological research. Its genome contains 76 genes coding for cytochromes P450 (P450s), and few data about the biochemical properties of those P450s have been published so far. However, an increasing number of articles have appeared on their involvement in the metabolism of xenobiotics and endobiotics such as fatty acid derivatives and steroids. Moreover, the implication of some P450s in various biological functions of C. elegans, such as survival, dauer formation, life span, fat content, or lipid metabolism, without mention of the precise reaction catalyzed by those P450s, has been reported in several articles. This review presents the state of our knowledge about C. elegans P450s.

Ecotoxicological Effects of Aflatoxins on Earthworms under Different Temperature and Moisture Conditions

Aflatoxin contamination remains one of the most important threats to food safety and human health. Aflatoxins are mainly found in soil, decaying plant material and food storage systems and are particularly abundant during drought stress. Regulations suggest the disposal of aflatoxin-contaminated crops by incorporation into the soil for natural degradation. However, the fate and consequences of aflatoxin in soil and on soil organisms providing essential ecological services remain unclear and could potentially pose a risk to soil health and productivity. The protection of soil biodiversity and ecosystem services are essential for the success of the declared United Nations Decade on Ecosystem Restoration. The focus of this study was to investigate the toxicological consequences of aflatoxins to earthworms’ survival, growth, reproduction and genotoxicity under different temperature and moisture conditions. Results indicated an insignificant effect of aflatoxin concentrations between 10 and 100 µg/kg on the survival, growth and reproduction but indicated a concentration-dependent increase in DNA damage at standard testing conditions. However, the interaction of the toxin with different environmental conditions, particularly low moisture, resulted in significantly reduced reproduction rates and increased DNA damage in earthworms.

Stem cells based in vitro models: trends and prospects in biomaterials cytotoxicity studies

Advanced biomaterials are increasingly used for numerous medical applications from the delivery of cancer-targeted therapeutics to the treatment of cardiovascular diseases. The issues of foreign body reactions induced by biomaterials must be controlled for preventing treatment failure. Therefore, it is important to assess the biocompatibility and cytotoxicity of biomaterials on cell culture systems before proceeding to in vivo studies in animal models and subsequent clinical trials. Direct use of biomaterials on animals create technical challenges and ethical issues and therefore, the use of non-animal models such as stem cell cultures could be useful for determination of their safety. However, failure to recapitulate the complex in vivo microenvironment have largely restricted stem cell cultures for testing the cytotoxicity of biomaterials. Nevertheless, properties of stem cells such as their self-renewal and ability to differentiate into various cell lineages make them an ideal candidate for in vitro screening studies. Furthermore, the application of stem cells in biomaterials screening studies may overcome the challenges associated with the inability to develop a complex heterogeneous tissue using primary cells. Currently, embryonic stem cells, adult stem cells, and induced pluripotent stem cells are being used as in vitro preliminary biomaterials testing models with demonstrated advantages over mature primary cell or cell line based in vitro models. This review discusses the status and future directions of in vitro stem cell-based cultures and their derivatives such as spheroids and organoids for the screening of their safety before their application to animal models and human in translational research.

Xenobiotic metabolism and transport in Caenorhabditis elegans

Caenorhabditis elegans has emerged as a major model in biomedical and environmental toxicology. Numerous papers on toxicology and pharmacology in C. elegans have been published, and this species has now been adopted by investigators in academic toxicology, pharmacology, and drug discovery labs. C. elegans has also attracted the interest of governmental regulatory agencies charged with evaluating the safety of chemicals. However, a major, fundamental aspect of toxicological science remains underdeveloped in C. elegans: xenobiotic metabolism and transport processes that are critical to understanding toxicokinetics and toxicodynamics, and extrapolation to other species. The aim of this review was to initially briefly describe the history and trajectory of the use of C. elegans in toxicological and pharmacological studies. Subsequently, physical barriers to chemical uptake and the role of the worm microbiome in xenobiotic transformation were described. Then a review of what is and is not known regarding the classic Phase I, Phase II, and Phase III processes was performed. In addition, the following were discussed (1) regulation of xenobiotic metabolism; (2) review of published toxicokinetics for specific chemicals; and (3) genetic diversity of these processes in C. elegans. Finally, worm xenobiotic transport and metabolism was placed in an evolutionary context; key areas for future research highlighted; and implications for extrapolating C. elegans toxicity results to other species discussed.

Benzo[a]pyrene and Caenorhabditis elegans: defining the genotoxic potential in an organism lacking the classical CYP1A1 pathway

Benzo[a]pyrene (BaP) is bioactivated in most organisms by the cytochrome P450 (CYP) enzymes, mainly CYP1A1, ultimately resulting in the reactive metabolite BaP-7,8-dihydrodiol-9,10-epoxide (BPDE) capable of covalently binding to DNA and forming adducts. This step has been defined as the key process in cancer initiation in humans. However, limited knowledge is available about the consequences of BaP exposure in organisms lacking this classical CYP1A1 pathway, one example is the model nematode Caenorhabditis elegans. The aim of this study was to define the genotoxic potential of BaP in C. elegans and to advance our understanding of xenobiotic processing in the absence of the CYP1A1 pathway. Exposure to high concentrations of BaP (0-40 µM) significantly affected life cycle endpoints of C. elegans, which were manifested by a reduced reproductive output and shortened life span. An optimised comet assay revealed that DNA damage increased in a dose-dependent manner; however, no bulky DNA adducts (dG-N²-BPDE) were observed by ³²P-postlabelling. Global transcriptomic analysis by RNA-Seq identified responsive transcript families, most prominently members of the cyp-35 and UDP-glucuronosyltransferases (UGTs) enzyme families, both of which are linked to xenobiotic metabolism. Strains harbouring mutations in the cyp-35A2 and cyp-35A3 genes were notably less prone to BaP-mediated toxicity, and BaP led to longevity in cyp-35A5 mutants. In summary, BaP induces transcriptional, genotoxic and phenotypic responses in C. elegans, despite the absence of the classical CYP1A1 bioactivation pathway. This provides first evidence that parallel pathways are implicated in BaP metabolism in C. elegans and this seems to be mediated via the cyp-35 pathway.

Quantitative analysis of PAH compounds in DWH crude oil and their effects on Caenorhabditis elegans germ cell apoptosis, associated with CYP450s upregulation

The Deepwater Horizon (DWH) oil spill marked the largest environmental oil spill in human history, where it was estimated a large amount of the polycyclic aromatic hydrocarbons (PAHs) were released with crude oil into the environment. In this study, common PAH compounds were quantitatively determined in crude oil from the DWH spill by gas chromatography-mass spectroscopy (GC-MS). Twelve PAH compounds were identified and quantified from a 100× dilution of DWH crude oil: naphthalene (7800 ng/mL), acenaphthylene (590 ng/mL), acenaphtehen (540 ng/mL), fluorene (2550 ng/mL), phenanthrene (2910 ng/mL), anthracene (840 ng/mL), fluoranthene (490 ng/mL), pyrene (290 ng/mL), benzo(k) fluoranthene (1050 ng/mL), benzo(b)fluoranthene (1360 ng/mL), dibenz(a,h)anthracene (2560 ng/mL), and benzo(g, h, i) perylene (630 ng/mL). Toxicity assays using the nematode, Caenorhabditis elegans (C. elegans), indicated a single PAH compound naphthalene, exposure increased C. elegans germ cell apoptosis which may adversely affect progeny reproduction. The number of apoptotic germ cells significantly increased from 1.4 to 2.5 when worms were treated with 10 μg/mL of naphthalene and from 1.3 to 2.5 and 3.5 cells in presence of 1 μg/mL and 5 μg/mL of benzo(a)pyrene, respectively. Five CYP450 genes (CYP14A3, CYP35A1, CYP35A2, CYP35A5, and CYP35C1) were significantly upregulated following 500× dilution of dispersed crude oil exposure (p < 0.05). These results suggest that CYP450s may play a role in bioactivation of PAHs in crude oil, resulting in DNA damage related germ cell apoptosis.

An Understudied Dimension: Why Age Needs to Be Considered When Studying Epigenetic-Environment Interactions

We live in a complex chemical environment where there are an estimated 350 000 chemical compounds or mixtures commercially produced. A strong body of literature shows that there are time points during early development when an organism’s epigenome is particularly sensitive to chemicals in its environment. What is less understood is how gene-environment and epigenetic-environment interactions change with age. This question is bidirectional: (1) how do chemicals in the environment affect the aging process and (2) how does aging affect an organism’s response to its chemical environment? The study of gene-environment interactions with age is especially important because, in many parts of the world, older individuals are a large and rapidly growing proportion of the population and because aging is a process universal to most of the animal kingdom. Epigenetics has emerged as a crucial framework for studying aging as epigenetic pathways, often triggered by environmental stimuli, have been shown to be essential regulators of the aging process. In this perspective article, we delineate the connection between aging, epigenetics, and environmental exposures. We discuss why it is essential to consider age when researching how an organism interacts with its environment. We describe recent advances in understanding how the chemical environment affects aging and the gap in research on how age affects an organism’s response to the environment. Finally, we highlight how model organisms and network approaches can help fill this crucial gap. Taken together, systemic changes that occur in the epigenome with age indicate that adult organisms cannot be treated as a homogeneous population and that there are discrete mechanisms modulating the aging epigenome that we do not yet understand.

Zebrafish CYP1A expression in transgenic Caenorhabditis elegans protects from exposures to benzo[a]pyrene and a complex polycyclic aromatic hydrocarbon mixture

Polycyclic aromatic hydrocarbons (PAHs) are environmental toxicants primarily produced during incomplete combustion; some are carcinogens. PAHs can be safely metabolized or, paradoxically, bioactivated via specific cytochrome P450 (CYP) enzymes to more reactive metabolites, some of which can damage DNA and proteins. Among the CYP isoforms implicated in PAH metabolism, CYP1A enzymes have been reported to both sensitize and protect from PAH toxicity. To clarify the role of CYP1A in PAH toxicity, we generated transgenic Caenorhabditis elegans that express CYP1A at a basal (but not inducible) level. Because this species does not normally express any CYP1 family enzyme, this approach permitted a test of the role of basally expressed CYP1A in PAH toxicity. We exposed C. elegans at different life stages to either the PAH benzo[a]pyrene (BaP) alone, or a real-world mixture dominated by PAHs extracted from the sediment of a highly contaminated site on the Elizabeth River (VA, USA). This site, the former Atlantic Wood Industries, was declared a Superfund site due to coal tar creosote contamination that caused very high levels (in the [mg/mL] range) of high molecular weight PAHs within the sediments. We demonstrate that CYP1A protects against BaP-induced growth delay, reproductive toxicity, and reduction of steady state ATP levels. Lack of sensitivity of a DNA repair (Nucleotide Excision Repair)-deficient strain suggested that CYP1A did not produce significant levels of DNA-reactive metabolites from BaP. The protective effects of CYP1A in Elizabeth River sediment extract (ERSE)-exposed nematodes were less pronounced than those seen in BaP-exposed nematodes; CYP1A expression protected against ERSE-induced reduction of steady-state ATP levels, but not other outcomes of exposure to sediment extracts. Overall, we find that in C. elegans, a basal level of CYP1A activity is protective against the examined PAH exposures.

Mitochondria as a target of organophosphate and carbamate pesticides: Revisiting common mechanisms of action with new approach methodologies

Mitochondrial toxicity has been proposed as a potential cause of developmental defects in humans. We evaluated 51 organophosphate and carbamate pesticides using the U.S. EPA ToxCast and Tox21 databases. Only a small number of them bind directly to cholinesterases in the parent form. The hydrophobicity of organophosphate pesticides is correlated significantly to TSPO binding affinity, mitochondrial membrane potential reduction in HepG2 cells, and developmental toxicity in Caenorhabditis elegans and Danio rerio (p < 0.05). Structural analysis suggests that in some cases the Krebs cycle is a potential target of organophosphate and carbamate exposure at early life stages. The results support the hypothesis that mitochondrial effects of some organophosphate pesticides-particularly those that require enzymatic activation to the oxon form-may augment the documented effects of disruption of acetylcholine signaling. This study provides a proof of concept for applying new approach methodologies to interrogate mechanisms of action for cumulative risk assessment.

Polypeptides secreted from the columnar vesicles of the sea anemone Bunodosoma cangicum and their in vivo effects on Caenorhabditis elegans

In this study we provide new evidence that the columnar vesicles of the sea anemone Bunodosoma cangicum are toxic in vivo and contain at least two active polypeptides, a neurotoxic and an apoptosis inducing polypeptide. Here we show that it is also an effective inducer of apoptosis in vivo in the nematode Caenorhabditis elegans. In addition, the anemone peptides rapidly paralyze C. elegans, and set in motion a sequence of events that result in the complete dissolution of the internal organs in adult animals within 60 min. Nematodes that survive the toxin treatment exhibit a decreased reproductive capacity. Interestingly, adult animals appear to be much more susceptible to the effects of the toxins than larval stages, suggesting possible developmentally dependent targets of the toxins. Here we also provide chemical characterization of the compounds through chromatographic analysis and mass spectrometry. Gel filtration chromatography coupled with reverse phase HPLC shows that our partially purified extract contains at least two principle components. Additionally, MALDI-TOF mass spectrometry analysis of our extract shows three principal compounds at 814.6, 2914.1, and 4360.3 m/z plus three other minor components or fragments. Mass spectrometry analysis also indicates the presence of three disulfide bridges. Which is in agreement with other characterizations of anemone venoms.

Comparative metabolism of xenobiotic chemicals by cytochrome P450s in the nematode Caenorhabditis elegans

We investigated the metabolic capabilities of C. elegans using compounds whose metabolism has been well characterised in mammalian systems. We find that similar metabolites are produced in C. elegans as in mammals but that C. elegans is deficient in CYP1-like metabolism, as has been seen in other studies. We show that CYP-34A9, CYP-34A10 and CYP-36A1 are the principal enzymes responsible for the metabolism of tolbutamide in C. elegans. These are related to the mammalian enzymes that metabolise this compound but are not the closest homologs suggesting that sequence comparison alone will not predict functional conservation among cytochrome P450s. In mammals, metabolite production from amytryptiline and dextromethorphan is dependent on specific cytochrome P450s. However, in C. elegans we did not find evidence of similar specificity: the same metabolites were produced but in small amounts by numerous cytochrome P450s. We conclude that, while some aspects of cytochrome P450 mediated metabolism in C. elegans are similar to mammals, there are differences in the production of some metabolites and in the underlying genetics of metabolism.

Caenorhabditis elegans as an emerging model system in environmental epigenetics

The roundworm Caenorhabitis elegans has been an established model organism for the study of genetics and developmental biology, including studies of transcriptional regulation, since the 1970s. This model organism has continued to be used as a classical model system as the field of transcriptional regulation has expanded to include scientific advances in epigenetics and chromatin biology. In the last several decades, C. elegans has emerged as a powerful model for environmental toxicology, particularly for the study of chemical genotoxicity. Here, we outline the utility and applicability of C. elegans as a powerful model organism for mechanistic studies of environmental influences on the epigenome. Our goal in this article is to inform the field of environmental epigenetics of the strengths and limitations of the well-established C. elegans model organism as an emerging model for medium-throughput, in vivo exploration of the role of exogenous chemical stimuli in transcriptional regulation, developmental epigenetic reprogramming, and epigenetic memory and inheritance. As the field of environmental epigenetics matures, and research begins to map mechanisms underlying observed associations, new toolkits and model systems, particularly manipulable, scalable in vivo systems that accurately model human transcriptional regulatory circuits, will provide an essential experimental bridge between in vitro biochemical experiments and mammalian model systems. Environ. Mol. Mutagen. 59:560-575, 2018. © 2018 Wiley Periodicals, Inc.

Ecotoxicological impacts of surface water and wastewater from conventional and advanced treatment technologies on brood size, larval length, and cytochrome P450 (35A3) expression in Caenorhabditis elegans

Anthropogenic micropollutants and transformation products (TPs) negatively affect aquatic ecosystems and water resources. Wastewater treatment plants (WWTP) represent major point sources for (micro)pollutants and TPs in urban water cycles. The aim of the current study was to assess the removal of micropollutants and toxicity during conventional and advanced wastewater treatment. Using wild-type and transgenic Caenorhabditis elegans, the endpoint reproduction, growth, and cytochrome P450 (CYP) 35A3 induction (via cyp-35A3::GFP) were assessed. Samples were collected at four WWTPs and a receiving surface water. One WWTP included the advanced treatments: ozonation followed by granular activated carbon (GAC) or biological filtration (BF), respectively. Relevant micropollutants and WWTP parameters (n = 111) were included. Significant reproductive toxicity was detected for one WWTP effluent (31-83% reduced brood size). Three of four effluents significantly promoted the growth of C. elegans larvae (49-55% increased lengths). This effect was also observed for the GAC (34-41%) and BF (30%) post-treatments. Markedly, significant cyp-35A3::GFP induction was detected for one effluent before and after ozonation, being more pronounced for the ozonated samples (5- and 7.4-fold above controls). While the advanced treatments decreased the concentrations of most micropollutants, the observed effects may be attributed to effects of residual target compounds and/or compounds not included in the target chemical analysis. This highlights the need for an integrated assessment of (advanced) wastewater treatment covering both biological and chemical parameters.

Development of an adverse outcome pathway for chemically induced hepatocellular carcinoma: case study of AFB1, a human carcinogen with a mutagenic mode of action

Adverse outcome pathways (AOPs) are frameworks starting with a molecular initiating event (MIE), followed by key events (KEs) linked by KE relationships (KERs), ultimately resulting in a specific adverse outcome. Relevant data for the pathway and each KE/KER are evaluated to assess biological plausibility, weight-of-evidence, and confidence. We aimed to describe an AOP relevant to chemicals directly inducing mutation in cancer critical gene(s), via the formation of chemical-specific pro-mutagenic DNA adduct(s), as an early critical step in tumor etiology. Such chemicals have mutagenic modes-of-action (MOA) for tumor induction. To assist with developing this AOP, Aflatoxin B1 (AFB1) was selected as a case study because it has a rich database and is considered to have a mutagenic MOA. AFB1 information was used to define specific KEs, KERs, and to inform development of a generic AOP for mutagen-induced hepatocellular carcinoma (HCC). In assessing the AFB1 information, it became clear that existing data are, in fact, not optimal and for some KEs/KERs, the definitive data are not available. In particular, while there is substantial information that AFB1 can induce mutations (based on a number of mutation assays), the definitive evidence - the ability to induce mutation in the cancer critical gene(s) in the tumor target tissue - is not available. Thus, it is necessary to consider the patterns of results in the weight-of-evidence for KEs and KERs. It was important to determine whether there was sufficient evidence that AFB1 can induce the necessary critical mutations early in the carcinogenic process, which was the case.

Aflatoxin B₁-Induced Developmental and DNA Damage in Caenorhabditis elegans

Aflatoxin B₁ (AFB₁) is a ubiquitous mycotoxin produced by toxicogenic Aspergillus species. AFB₁ has been reported to cause serious adverse health effects, such as cancers and abnormal development and reproduction, in animals and humans. AFB₁ is also a potent genotoxic mutagen that causes DNA damage in vitro and in vivo. However, the link between DNA damage and abnormal development and reproduction is unclear. To address this issue, we examined the DNA damage, germline apoptosis, growth, and reproductive toxicity following exposure to AFB₁, using Caenorhabditis elegans as a study model. Results found that AFB₁ induced DNA damage and germline apoptosis, and significantly inhibited growth and reproduction of the nematodes in a concentration-dependent manner. Exposure to AFB₁ inhibited growth or reproduction more potently in the DNA repair-deficient xpa-1 nematodes than the wild-type N2 strain. According to the relative expression level of pathway-related genes measured by real-time PCR, the DNA damage response (DDR) pathway was found to be associated with AFB₁-induced germline apoptosis, which further played an essential role in the dysfunction of growth and reproduction in C. elegans.

Internal Concentration and Time Are Important Modifiers of Toxicity: The Case of Chlorpyrifos on Caenorhabditis elegans

The internal concentration of chemicals in exposed organisms changes over time due to absorption, distribution, metabolism, and excretion processes since chemicals are taken up from the environment. Internal concentration and time are very important modifiers of toxicity when biomarkers are used to evaluate the potential hazards and risks of environmental pollutants. In this study, the responses of molecular biomarkers, and the fate of chemicals in the body, were comprehensively investigated to determine cause-and-effect relationships over time. Chlorpyrifos (CP) was selected as a model chemical, and Caenorhabditis elegans was exposed to CP for 4 h using the passive dosing method. Worms were then monitored in fresh medium during a 48-h recovery regime. The mRNA expression of genes related to CYP metabolism (cyp35a2 and cyp35a3) increased during the constant exposure phase. The body residue of CP decreased once it reached a peak level during the early stage of exposure, indicating that the initial uptake of CP rapidly induced biotransformation with the synthesis of new CYP metabolic proteins. The residual chlorpyrifos-oxon concentration, an acetylcholinesterase (AChE) inhibitor, continuously increased even after the recovery regime started. These delayed toxicokinetics seem to be important for the extension of AChE inhibition for up to 9 h after the start of the recovery regime. Comprehensive investigation into the molecular initiation events and changes in the internal concentrations of chemical species provide insight into response causality within the framework of an adverse outcome pathway.

The application of the comet assay to assess the genotoxicity of environmental pollutants in the nematode Caenorhabditis elegans

This study aimed to establish a protocol for cell dissociation from the nematode Caenorhabditis elegans (C. elegans) to assess the genotoxicity of the environmental pollutant benzo[a]pyrene (BaP) using the alkaline version of the single cell electrophoresis assay (comet assay). BaP genotoxicity was assessed in C. elegans (wild-type [WT]; N2, Bristol) after 48h exposure (0-40μM). Induction of comets by BaP was concentration-dependent up to 20μM; comet% tail DNA was ∼30% at 20μM BaP and ∼10% in controls. Similarly, BaP-induced DNA damage was evaluated in C. elegans mutant strains deficient in DNA repair. In xpa-1 and apn-1 mutants BaP-induced comet formation was diminished to WT background levels suggesting that the damage formed by BaP that is detected in the comet assay is not recognised in cells deficient in nucleotide and base excision repair, respectively. In summary, our study provides a protocol to evaluate DNA damage of environmental pollutants in whole nematodes using the comet assay.

Caenorhabditis elegans, a Biological Model for Research in Toxicology

Caenorhabditis elegans is a nematode of microscopic size which, due to its biological characteristics, has been used since the 1970s as a model for research in molecular biology, medicine, pharmacology, and toxicology. It was the first animal whose genome was completely sequenced and has played a key role in the understanding of apoptosis and RNA interference. The transparency of its body, short lifespan, ability to self-fertilize and ease of culture are advantages that make it ideal as a model in toxicology. Due to the fact that some of its biochemical pathways are similar to those of humans, it has been employed in research in several fields. C. elegans' use as a biological model in environmental toxicological assessments allows the determination of multiple endpoints. Some of these utilize the effects on the biological functions of the nematode and others use molecular markers. Endpoints such as lethality, growth, reproduction, and locomotion are the most studied, and usually employ the wild type Bristol N2 strain. Other endpoints use reporter genes, such as green fluorescence protein, driven by regulatory sequences from other genes related to different mechanisms of toxicity, such as heat shock, oxidative stress, CYP system, and metallothioneins among others, allowing the study of gene expression in a manner both rapid and easy. These transgenic strains of C. elegans represent a powerful tool to assess toxicity pathways for mixtures and environmental samples, and their numbers are growing in diversity and selectivity. However, other molecular biology techniques, including DNA microarrays and MicroRNAs have been explored to assess the effects of different toxicants and samples. C. elegans has allowed the assessment of neurotoxic effects for heavy metals and pesticides, among those more frequently studied, as the nematode has a very well defined nervous system. More recently, nanoparticles are emergent pollutants whose toxicity can be explored using this nematode. Overall, almost every type of known toxicant has been tested with this animal model. In the near future, the available knowledge on the life cycle of C. elegans should allow more studies on reproduction and transgenerational toxicity for newly developed chemicals and materials, facilitating their introduction in the market. The great diversity of endpoints and possibilities of this animal makes it an easy first-choice for rapid toxicity screening or to detail signaling pathways involved in mechanisms of toxicity.

Multi-Toxic Endpoints of the Foodborne Mycotoxins in Nematode Caenorhabditis elegans

Aflatoxins B₁ (AFB₁), deoxynivalenol (DON), fumonisin B₁ (FB₁), T-2 toxin (T-2), and zearalenone (ZEA) are the major foodborne mycotoxins of public health concerns. In the present study, the multiple toxic endpoints of these naturally-occurring mycotoxins were evaluated in Caenorhabditis elegans model for their lethality, toxic effects on growth and reproduction, as well as influence on lifespan. We found that the lethality endpoint was more sensitive for T-2 toxicity with the EC50 at 1.38 mg/L, the growth endpoint was relatively sensitive for AFB₁ toxic effects, and the reproduction endpoint was more sensitive for toxicities of AFB₁, FB₁, and ZEA. Moreover, the lifespan endpoint was sensitive to toxic effects of all five tested mycotoxins. Data obtained from this study may serve as an important contribution to knowledge on assessment of mycotoxin toxic effects, especially for assessing developmental and reproductive toxic effects, using the C. elegans model.

A systems toxicology approach on the mechanism of uptake and toxicity of MWCNT in Caenorhabditis elegans

The increased volumes of carbon nanotubes (CNTs) being utilized in industrial and biomedical processes carries with it an increased risk of unintentional release into the environment, requiring a thorough hazard and risk assessment. In this study, the toxicity of pristine and hydroxylated (OH-) multiwall CNTs (MWCNTs) was investigated in the nematode Caenorhabditis elegans using an integrated systems toxicology approach. To gain an insight into the toxic mechanism of MWCNTs, microarray and proteomics were conducted for C. elegans followed by pathway analyses. The results of pathway analyses suggested endocytosis, phagocytosis, oxidative stress and endoplasmic reticulum (ER) stress, as potential mechanisms of uptake and toxicity, which were subsequently investigated using loss-of-function mutants of genes of those pathways. The expression of phagocytosis related genes (i.e. ced-10 and rab-7) were significantly increased upon exposure to OH-MWCNT, concomitantly with the rescued toxicity by loss-of-function mutants of those genes, such as ced-10(n3246) and rab-7(ok511). An increased sensitivity of the hsp-4(gk514) mutant by OH-MWCNT, along with a decreased expression of hsp-4 at both gene and protein level suggests that MWCNTs may affect ER stress response in C. elegans. Collectively, the results implied phagocytosis to be a potential mechanism of uptake of MWCNTs, and ER and oxidative stress as potential mechanisms of toxicity. The integrated systems toxicology approach applied in this study provided a comprehensive insight into the toxic mechanism of MWCNTs in C. elegans, which may eventually be used to develop an "Adverse Outcome Pathway (AOP)", a recently introduced concept as a conceptual framework to link molecular level responses to higher level effects.

Phenanthrene bioaccumulation in the nematode Caenorhabditis elegans

The contribution of food to the bioaccumulation of xenobiotics and hence toxicity is still an ambiguous issue. It is becoming more and more evident that universal statements cannot be made, but that the relative contribution of food-associated xenobiotics in bioaccumulation depends on species, substance, and environmental conditions. Yet, small-sized benthic or soil animals such as nematodes have largely been disregarded so far. Bioaccumulation of the polycyclic aromatic hydrocarbon phenanthrene in the absence and presence of bacterial food was measured in the nematode Caenorhabditis elegans. Elimination of phenanthrene in the nematodes was biphasic, suggesting that there was a slowly exchanging pool within the nematodes or that biotransformation of phenanthrene took place. Even with food present, dissolved phenanthrene was still the major contributor to bioaccumulated compound in nematode tissues, whereas the diet only contributed about 9%. Toxicokinetic parameters in the treatment without food were different from the ones of the treatment with bacteria, possibly because nematodes depleted their lipid reserves during starvation.

Exposure to mitochondrial genotoxins and dopaminergic neurodegeneration in Caenorhabditis elegans

Neurodegeneration has been correlated with mitochondrial DNA (mtDNA) damage and exposure to environmental toxins, but causation is unclear. We investigated the ability of several known environmental genotoxins and neurotoxins to cause mtDNA damage, mtDNA depletion, and neurodegeneration in Caenorhabditis elegans. We found that paraquat, cadmium chloride and aflatoxin B₁ caused more mitochondrial than nuclear DNA damage, and paraquat and aflatoxin B₁ also caused dopaminergic neurodegeneration. 6-hydroxydopamine (6-OHDA) caused similar levels of mitochondrial and nuclear DNA damage. To further test whether the neurodegeneration could be attributed to the observed mtDNA damage, C. elegans were exposed to repeated low-dose ultraviolet C radiation (UVC) that resulted in persistent mtDNA damage; this exposure also resulted in dopaminergic neurodegeneration. Damage to GABAergic neurons and pharyngeal muscle cells was not detected. We also found that fasting at the first larval stage was protective in dopaminergic neurons against 6-OHDA-induced neurodegeneration. Finally, we found that dopaminergic neurons in C. elegans are capable of regeneration after laser surgery. Our findings are consistent with a causal role for mitochondrial DNA damage in neurodegeneration, but also support non mtDNA-mediated mechanisms.

Changes in the expression of cyp35a family genes in the soil nematode Caenorhabditis elegans under controlled exposure to chlorpyrifos using passive dosing

In order to use sensitive molecular-level biomarkers for the evaluation of environmental risks, it is necessary to establish a quantitative dose-response relationship. Passive dosing is regarded as a promising new technique for maintaining a constant exposure condition of hydrophobic chemicals in the assay medium. The main goals of the present study were (1) to quantitatively compare gene expression results obtained using the passive dosing method and the conventional spiking method and (2) to investigate changes in gene expression with respect to the free concentration and exposure duration using passive dosing. Chlorpyrifos (CP), which is oxidized by the cytochrome P450 monooxygenases, was selected as a model chemical, and the expression of cytochrome P450 subfamily protein 35A gene series (cyp-35a1-5) was analyzed by quantitative real-time PCR on soil nematode Caenorhabditis elegans. Whereas the free concentration of CP rapidly decreased and the expression of cyp genes varied with the volume of exposure medium and the test duration when the spiking method was used, the free concentration in the assay medium was stable throughout the experiment when the passive dosing method was used. In addition, the level of gene expression increased with exposure time up to 8 h and with increasing CP concentration. The observed increased gene expression could be explained by increasing body residue concentration of CP with exposure time. In conclusion, quantitative dose-response relationships for gene expression biomarkers could be obtained for highly hydrophobic chemicals when the constant exposure condition is provided and the free concentration is used as the dose-metric.

C. elegans whole-genome sequencing reveals mutational signatures related to carcinogens and DNA repair deficiency

Mutation is associated with developmental and hereditary disorders, aging, and cancer. While we understand some mutational processes operative in human disease, most remain mysterious. We used Caenorhabditis elegans whole-genome sequencing to model mutational signatures, analyzing 183 worm populations across 17 DNA repair-deficient backgrounds propagated for 20 generations or exposed to carcinogens. The baseline mutation rate in C. elegans was approximately one per genome per generation, not overtly altered across several DNA repair deficiencies over 20 generations. Telomere erosion led to complex chromosomal rearrangements initiated by breakage–fusion–bridge cycles and completed by simultaneously acquired, localized clusters of breakpoints. Aflatoxin B₁ induced substitutions of guanines in a GpC context, as observed in aflatoxin-induced liver cancers. Mutational burden increased with impaired nucleotide excision repair. Cisplatin and mechlorethamine, DNA crosslinking agents, caused dose- and genotype-dependent signatures among indels, substitutions, and rearrangements. Strikingly, both agents induced clustered rearrangements resembling “chromoanasynthesis,” a replication-based mutational signature seen in constitutional genomic disorders, suggesting that interstrand crosslinks may play a pathogenic role in such events. Cisplatin mutagenicity was most pronounced in xpf-1 mutants, suggesting that this gene critically protects cells against platinum chemotherapy. Thus, experimental model systems combined with genome sequencing can recapture and mechanistically explain mutational signatures associated with human disease.

Integrative assessment of benzene exposure to Caenorhabditis elegans using computational behavior and toxicogenomic analyses

In this study, we investigated the toxic effects of benzene to the nematode Caenorhabditis elegans in an integrative manner, using computational behavior and toxicogenomics analyses, along with survival and reproduction. Benzene exposure led to changes in locomotive behavior and reproduction decline in C. elegans. Microarray followed by pathway analysis revealed that 228 genes were differentially expressed by benzene exposure, and cyp-35a2, pmk-1, and cep-1 were selected for further reproduction and multiparametric behavior analysis. Mutant analysis showed that benzene induced reproduction decline was rescued in cyp-35a2(gk317) mutant, whereas it was significantly exacerbated in pmk-1(km25) mutant, compared with the wildtype. The multiparametric behavior analysis on the mutants of selected genes revealed that each strain exhibits different response patterns, particularly, enhanced linear movement in the cyp-35a2(gk317) mutant, whereas the changes in partial body movement were observed in the pmk-1(km25) mutant by benzene exposure. A self-organizing map revealed that the pmk-1(km25) mutant group was the most densely clustered and located on the opposite side of the map of the cyp-35a2(gk317) mutant, each crossing that of the wildtype. Overall results suggest distinct roles of cyp-35a2 and pmk-1 genes in benzene-induced alterations in behavior and reproduction in C. elegans. This study also suggests computational behavior analysis is a suitable tool for addressing the integrative impact of chemical stress alongside with toxicogenomic approach.

Adverse effects from clenbuterol and ractopamine on nematode Caenorhabditis elegans and the underlying mechanism

In the present study, we used Caenorhabditis elegans assay system to investigate in vivo toxicity from clentuberol and ractopamine and the possible underlying mechanism. Both acute and prolonged exposures to clentuberol or ractopamine decreased brood size and locomotion behavior, and induced intestinal autofluorescence and reactive oxygen species (ROS) production. Although acute exposure to the examined concentrations of clentuberol or ractopamine did not induce lethality, prolonged exposure to 10 µg/L of clentuberol and ractopamine reduced lifespan. At relatively high concentrations, ractopamine exhibited more severe toxicity than clentuberol on nematodes. Overexpression of sod-2 gene encoding a Mn-SOD to prevent induction of oxidative stress effectively inhibited toxicity from clentuberol or ractopamine. Besides oxidative stress, we found that clentuberol might reduce lifespan through influencing insulin/IGF signaling pathway; however, ractopamine might reduce lifespan through affecting both insulin/IGF signaling pathway and TOR signaling pathway. Ractopamine more severely decreased expression levels of daf-16, sgk-1, skn-1, and aak-2 genes than clentuberol, and increased expression levels of daf-2 and age-1 genes at the examined concentration. Therefore, the C. elegans assay system may be useful for assessing the possible toxicity from weight loss agents, and clentuberol and ractopamine may induce toxicity through different molecular mechanisms.

The tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) induces mitochondrial and nuclear DNA damage in Caenorhabditis elegans

The metabolites of the tobacco-specific nitrosamine 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) form DNA adducts in animal models. While there are many reports of formation of nuclear DNA adducts, one report also detected NNK-induced damage to the mitochondrial genome in rats. Using a different DNA damage detection technology, we tested whether this finding could be repeated in the nematode Caenorhabditis elegans. We treated N2 strain (wild-type) nematodes with NNK in liquid culture, and applied quantitative PCR to analyze NNK-induced nuclear and mitochondrial DNA (mtDNA) damage. Our results confirm that NNK causes both nuclear and mtDNA damage. However, we did not detect a difference in the level of nuclear versus mtDNA damage in C. elegans. To test whether the mtDNA damage was associated with mitochondrial dysfunction, we used a transgenic nematode strain that permits in vivo measurement of ATP levels and found lower levels of ATP in NNK-exposed animals when compared with the unexposed controls. To test whether the lower levels of ATP could be attributed to inhibition of respiratory chain components, we investigated oxygen consumption in whole C. elegans and found reduced oxygen consumption in exposed animals when compared with the unexposed controls. Our data suggest a model in which NNK exposure causes damage to both C. elegans nuclear and mitochondrial genomes, and support the hypothesis that the mitochondrial damage is functionally important in this model. These results also represent a first step in developing this genetically tractable organism as a model for assessing NNK toxicity.

Biosafety assessment of titanium dioxide nanoparticles in acutely exposed nematode Caenorhabditis elegans with mutations of genes required for oxidative stress or stress response

We used Caenorhabditis elegans to investigate whether acute exposure to TiO2-NPs at the concentration of 20 μg L(-1) reflecting predicted environmental relevant concentration and 25 mg L(-1) reflecting concentration in food can cause toxicity on nematodes with mutations of susceptible genes. Among examined mutants associated with oxidative stress and stress response, we found that genes of sod-2, sod-3, mtl-2, and hsp-16.48 might be susceptible for TiO2-NPs toxicity. Mutations of these genes altered functions of both possible primary and secondary targeted organs in nematodes exposed to 25 mg L(-1) of TiO2-NPs for 24-h. Mutations of these genes caused similar expression patterns of genes required for oxidative stress in TiO2-NPs exposed mutant nematodes, implying their similar mechanisms to form the susceptible property. Nevertheless, acute exposure to 20 μg L(-1) of TiO2-NPs for 24-h and 25 mg L(-1) of TiO2-NPs for 0.48-h or 5.71-h did not influence functions of both possible primary and secondary targeted organs in sod-2, sod-3, mtl-2, and hsp-16.48 mutants. Therefore, our results suggest the relatively safe property of acute exposure to TiO2-NPs with certain durations at predicted environmental relevant concentrations or concentrations comparable to those in food in nematodes with mutations of some susceptible genes.

Impact of sublethal levels of environmental pollutants found in sewage sludge on a novel Caenorhabditis elegans model biosensor

A transgenic strain of the model nematode Caenorhabditis elegans in which bioluminescence reports on relative, whole-organism ATP levels was used to test an environmentally-relevant mixture of pollutants extracted from processed sewage sludge. Changes in bioluminescence, following exposure to sewage sludge extract, were used to assess relative ATP levels and overall metabolic health. Reproductive function and longevity were also monitored. A short (up to 8 h) sublethal exposure of L4 larval stage worms to sewage sludge extract had a concentration-dependent, detrimental effect on energy status, with bioluminescence decreasing to 50-60% of the solvent control (1% DMSO). Following longer exposure (22-24 h), the energy status of the nematodes showed recovery as assessed by bioluminescence. Continuous exposure to sewage sludge extract from the L4 stage resulted in a shorter median lifespan relative to that of solvent or medium control animals, but only in the presence of 400-600 µM 5-fluoro-2'-deoxyuridine (FUdR), which was incorporated to inhibit reproduction. This indicated that FUdR increased lifespan, and that the effect was counteracted by SSE. Exposure to sewage sludge extract from the L1 stage led to slower growth and a delayed onset of egg laying. When L1 exposed nematodes reached the reproductive stage, no effect on egg laying rate or egg number in the uterus was observed. DMSO itself (1%) had a significant inhibitory effect on growth and development of C. elegans exposed from the L1 stage and on reproduction when exposed from the L4 stage. Results demonstrate subtle adverse effects on C. elegans of a complex mixture of environmental pollutants that are present, individually, in very low concentrations and indicate that our biosensor of energy status is a novel, sensitive, rapid, quantitative, whole-organism test system which is suitable for high throughput risk assessment of complex pollutant mixtures.

In vivo repair of alkylating and oxidative DNA damage in the mitochondrial and nuclear genomes of wild-type and glycosylase-deficient Caenorhabditis elegans

Base excision repair (BER) is an evolutionarily conserved DNA repair pathway that is critical for repair of many of the most common types of DNA damage generated both by endogenous metabolic pathways and exposure to exogenous stressors such as pollutants. Caenorhabditis elegans is an increasingly important model organism for the study of DNA damage-related processes including DNA repair, genotoxicity, and apoptosis, but BER is not well understood in this organism, and has not previously been measured in vivo. We report robust BER in the nuclear genome and slightly slower damage removal from the mitochondrial genome; in both cases the removal rates are comparable to those observed in mammals. However we could detect no deficiency in BER in the nth-1 strain, which carries a deletion in the only glycosylase yet described in C. elegans that repairs oxidative DNA damage. We also failed to detect increased lethality or growth inhibition in nth-1 nematodes after exposure to oxidative or alkylating damage, suggesting the existence of at least one additional as-yet undetected glycosylase.

A novel 3-hydroxysteroid dehydrogenase that regulates reproductive development and longevity

Endogenous small molecule metabolites that regulate animal longevity are emerging as a novel means to influence health and life span. In C. elegans, bile acid-like steroids called the dafachronic acids (DAs) regulate developmental timing and longevity through the conserved nuclear hormone receptor DAF-12, a homolog of mammalian sterol-regulated receptors LXR and FXR. Using metabolic genetics, mass spectrometry, and biochemical approaches, we identify new activities in DA biosynthesis and characterize an evolutionarily conserved short chain dehydrogenase, DHS-16, as a novel 3-hydroxysteroid dehydrogenase. Through regulation of DA production, DHS-16 controls DAF-12 activity governing longevity in response to signals from the gonad. Our elucidation of C. elegans bile acid biosynthetic pathways reveals the possibility of novel ligands as well as striking biochemical conservation to other animals, which could illuminate new targets for manipulating longevity in metazoans.

Mechanism of silver nanoparticle toxicity is dependent on dissolved silver and surface coating in Caenorhabditis elegans

The rapidly increasing use of silver nanoparticles (Ag NPs) in consumer products and medical applications has raised ecological and human health concerns. A key question for addressing these concerns is whether Ag NP toxicity is mechanistically unique to nanoparticulate silver, or if it is a result of the release of silver ions. Furthermore, since Ag NPs are produced in a large variety of monomer sizes and coatings, and since their physicochemical behavior depends on the media composition, it is important to understand how these variables modulate toxicity. We found that a lower ionic strength medium resulted in greater toxicity (measured as growth inhibition) of all tested Ag NPs to Caenorhabditis elegans and that both dissolved silver and coating influenced Ag NP toxicity. We found a linear correlation between Ag NP toxicity and dissolved silver, but no correlation between size and toxicity. We used three independent and complementary approaches to investigate the mechanisms of toxicity of differentially coated and sized Ag NPs: pharmacological (rescue with trolox and N-acetylcysteine), genetic (analysis of metal-sensitive and oxidative stress-sensitive mutants), and physicochemical (including analysis of dissolution of Ag NPs). Oxidative dissolution was limited in our experimental conditions (maximally 15% in 24 h) yet was key to the toxicity of most Ag NPs, highlighting a critical role for dissolved silver complexed with thiols in the toxicity of all tested Ag NPs. Some Ag NPs (typically less soluble due to size or coating) also acted via oxidative stress, an effect specific to nanoparticulate silver. However, in no case studied here was the toxicity of a Ag NP greater than would be predicted by complete dissolution of the same mass of silver as silver ions.

Caenorhabditis elegans as a model in developmental toxicology

A number of practical advantages have made the nematode Caenorhabditis elegans a useful model for genetic and developmental biological research. These same advantages, along with conservation of disease and stress response pathways, availability of mutant and transgenic strains, and wealth of biological information, have led to the increased use of C. elegans in toxicological studies. Although the potential to study the mechanisms of developmental toxicology in C. elegans is promising, embryonic and larval growth tests to identify compounds that affect the nematode have remained the primary use of C. elegans in developmental toxicology. Here, we describe a C. elegans larval growth and development assay for medium- and high-throughput screening using the COPAS Biosort flow cytometer and provide descriptions of the data and subsequent analysis.

Cyp35a2 gene expression is involved in toxicity of fenitrothion in the soil nematode Caenorhabditis elegans

In this study, the effect of organophosphorous (OP) pesticide, fenitrothion (FT), on the non-target organism was investigated using the soil nematode, Caenorhabditis elegans. Toxicity was investigated on multiple biological levels, from organism to molecular levels, such as, immoblity, growth, fertility, development, acetyl cholinesterase (AChE) activity and stress-response gene expressions. FT may provoke serious consequences on the C. elegans population, as it induced significant developmental disturbance. As expected, FT exposure inhibits AChE activity of C. elegans. The increased expression of the cytochrome p450 family protein 35A2 (cyp35a2) gene was also observed in FT exposed worms. To experimentally demonstrate the relationships between organism-level effects and the cyp35a2 gene expression in FT-exposed C. elegans, the integration of the gene expression with biochemical-, and organism level endpoints were attempted using a C. elegans cyp35a2 RNA interference (RNAi) and cyp35a2 mutant (gk317). The 24 h-EC50s of C. elegans on FT exposure were in the order of cyp35a2 RNAi in cyp35a2 mutant (gk317)>cyp35a2 mutant (gk317)>cyp35a2 RNAi in wildtype (N2)>wildtype (N2). The higher EC50 values of cyp35a2 RNAi and cyp35a2 mutant (gk317) compared to that of wildtype C. elegans strongly supported that cyp35a2 gene plays an important role in the toxicity of FT towards C. elegans. The experiments with cyp35a2 RNAi also indicated that the development disturbance and decreased AChE activity, which were observed in FT exposed wildtype C. elegans were significantly rescued in the cyp35a2 RNAi C. elegans. Overall results suggest that the cyp35a2 may be an important gene for exerting FT toxicity in C. elegans.