Nickel sulfate induces numerous defects in Caenorhabditis elegans that can also be transferred to progeny

Exploring the impact of Agaricus bisporus on mitigating lead reproductive toxicity using the Caenorhabditis elegans model

Given that Agaricus bisporus, an edible mushroom, has demonstrated antioxidant properties, our investigation aimed to assess whether Agaricus bisporus could mitigate the toxic effects of lead (Pb) on Caenorhabditis elegans (C. elegans) model. A dose-response study was conducted involving Pb and Agaricus bisporus to determine appropriate doses. Subsequently, a co-exposure study utilizing C. elegans strains N2 and CL2166 was implemented, with groups designated as Control, Pb, Agaricus bisporus, and Pb + Agaricus bisporus. Our findings revealed that co-exposure to Pb + 100 mg/mL Agaricus bisporus resulted in reduced embryonic and larval lethality, increased brood size, and enhanced motility compared to nematodes exposed solely to Pb. Notably, our observations indicated a transfer of reproductive toxicity from nematode parents to their offspring. Thus, Agaricus bisporus may play a significant role in Pb detoxification, suggesting its potential as a natural antioxidant for neutralizing the detrimental effects of Pb on reproductive health.

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.

Esterification with a Long-Chain Fatty Acid Elevates the Exposure Toxicity of Tigliane Diterpenoids from Euphorbia fischeriana Roots against Nematodes

In this study, two tigliane diterpenoids, 12-deoxyphorbol-13-hexadecanoate and 12-deoxyphorbol-13-acetate (prostratin), were identified from the methanol extract of the roots of Euphorbia fischeriana and were found to have the ability to significantly reduce the survival of Caenorhabditis elegans. It was determined that exposure to these two compounds had toxic effects on the growth, reproduction, locomotion behavior, and accumulation of lipids and lipofuscin of the nematodes. Moreover, the transcription levels of the genes associated with lipid accumulation, apoptosis, insulin, and nuclear hormone synthesis in C. elegans were significantly influenced. Interestingly, 12-deoxyphorbol-13-hexadecanoate produced exposure toxicity at lower concentrations than that of prostratin. Pearson correlation analysis indicates that the elevated exposure toxicity of 12-deoxyphorbol-13-hexadecanoate may be the result of differing transcription levels, which result from the differential expression of fat-6, egl-38, and cep-1. These results reveal that esterification with a long-chain fatty acid elevates the exposure toxicity of this tigliane diterpenoid, thus providing a basis for the application of tigliane diterpenoids in plant-derived nematicides.

A review of transgenerational and multigenerational toxicology in the in vivo model animal Caenorhabditis elegans

A large number of pollutants existing in the environment can last for a long time, and their potential toxic effects can transfer from parents to their offspring. Thus, it is necessary to investigate the toxicity of environmental pollutants across multigenerations and the underlying mechanisms in organisms. Due to its short life cycle and sensitivity to environmental exposures, Caenorhabditis elegans is an important animal model for toxicity assessment of environmental pollutants across multigenerations. In this review, we introduced the transgenerational and multigenerational toxicity caused by various environmental pollutants in C. elegans. Moreover, we discussed the underlying mechanisms for the observed transgenerational and multigenerational toxicity of environmental contaminants in C. elegans.

Perfluorooctane sulfonate (PFOS) induces several behavioural defects in Caenorhabditis elegans that can also be transferred to the next generations

Perfluorooctane sulfonate (PFOS) is a well-known global persistent organic pollutant of grave concern to ecological and human health. Toxicity of PFOS to animals and humans are well studied. Although few studies have reported the behavioral effect of PFOS on nematode Caenorhabditis elegans, it's transgenerational effects were seldom studied. Therefore, we investigated the toxicity of PFOS on several behavioral responses besides bioaccumulation and transgenerational effects in C. elegans. In contrast to the several published studies, we used lower concentrations (0.5-1000 μg/L or 0.001-2.0 μM) that are environmentally relevant and reported to occur close to the contaminated areas. The 48 h median lethal concentration of PFOS was found to be 3.15 μM (1575 μg/L). PFOS (≥0.01 μM) caused severe toxicity to locomotion, and this effect was even transferred to progeny. However, after a few generations, the defect was rectified in the progeny of single-time exposed parent nematodes. Whereas, continuous exposure at 0.001 μM PFOS, no visible defects were observed in the progeny. PFOS (≥0.01 μM) also significantly decreased the brood size in a concentration-dependent manner. Besides, lifespan was affected by the higher concentration of PFOS (≥1.0 μM). These two behavioral endpoints, lifespan and reproduction defects, became less severe in the progeny. Chemotaxis plasticity was also significantly retarded by ≥ 1.0 μM PFOS compared to the control group. Results indicate that PFOS can exert severe neurobehavioral defects that can be transferred from parents to their offspring. The findings of this study have significant implications for the risk assessment of perfluorinated substances in the environment.

Ketamine induction of physiological functions alterations in Caenorhabditis elegans by chronic and multigenerational exposure and corresponding aquatic environmental risk assessment

Although ketamine (KET) has been widely detected in aquatic environments, the ecotoxicity data in aquatic invertebrates and associated risk remained unclear. This study aimed to investigate the adverse effects on benthos (Caenorhabditis elegans (C.elegans)) posed by KET from chronic (10 days) and multigenerational (four generations) exposure. Such exposure induced dose-dependent alterations on apoptosis, reactive oxygen species (ROS) induction, locomotion activity, feeding rate, chemotaxis, and brood size of nematodes, showing a cumulative damage through generations. KET posed vulva deformations and worm bags of C. elegans with a dosed-dependent increase. As a consequence, the fecundity and viability of worms would be impaired, which could eventually impact aquatic ecosystem equilibrium. Meanwhile, the bioactivation/detoxification process of xenobiotics and longevity regulating pathway induced by KET might be responsible for the physiological function disorders. Accordingly, the risk quotients (RQ) of KET in surface water in China were calculated using the 90% indicator protection concentration (C_0.1) derived from multiple toxicity indicators cumulative analyses. The results would be more objective considering numerous biomarkers changes of one species in comparison with traditional method using no observed effect concentrations (NOEC) of teratogenesis. The risk in surface water in southern China was up to high level (RQ > 1), suggesting long-term monitoring was imperative.

Acute Toxicity and Transgenerational Effects of Perfluorobutane Sulfonate on Caenorhabditis elegans

Perfluorobutane sulfonate (PFBS), due to its increasing use as an alternative to perfluooctane sulfonate (PFOS), is widely detected in humans and the environment, necessitating the evaluation of its potential ecotoxicological risk. We assessed the toxicity and bioaccumulation potential of PFBS in Caenorhabditis elegans, using lethality, locomotion, reproduction, life span, growth, and chemotactic behavior as the effect parameters. In addition, a total of 6 generations of exposed parent animals were monitored for locomotion, brood, and life span behaviors. Life span and brood size were significantly reduced in parent nematodes (P0) following exposure to ≥0.1 mM PFBS, but these negative effects did not transfer to the progeny. Although there was no remarkable effect on reproduction and life span in parent worms exposed to ≤0.01 mM PFBS, multigenerational exposure at 0.0005 mM significantly affected the F4 and F5 progeny. Furthermore, 0.01 to 2.0 mM of PFBS substantially retarded the locomotion behavior of P0 worms. At higher concentrations such as 1.0 mM, this negative effect on locomotion was transferred to the next generation (F1) but later recovered from F2 progeny onward. Our findings demonstrate for the first time that chronic exposure to PFBS at higher concentrations can cause behavioral toxicity and could be transferred to the progeny. These findings have significant implications for the environmental risk assessment of PFBS. Environ Toxicol Chem 2021;40:1973-1982. © 2021 SETAC.

Detoxification mechanisms of nickel sulfate in nematode Caenorhabditis elegans

Nickel is the most prevailing metal allergen with the highest sensitization rate among the "TOP 25" contact allergens and can affect about 15% of the human population. It is an essential trace metal in plants, animals, and humans. However, the environmental levels of nickel are considerably higher than what is needed for human life. Exposure to high levels of nickel can lead to skin allergies, lung fibrosis, and carcinogenesis. Few existing studies have closely examined the toxicity of nickel, let alone investigated the effective detoxification pathways. Here, we developed a high-throughput screening platform to comprehensively evaluate the nickel toxicity in wild-type C. elegans and explore the underlying detoxification mechanisms in transgenic nematodes. We demonstrated that nickel exerted multiple toxic effects on growth, brood size, feeding, and locomotion in C. elegans. Of which, brood size is the most sensitive endpoint. Nickel was found to first bind to phytochelatin (PC) after entering the worms' body and this PC-Ni complex was further transported by the ABC transporter, CeHMT-1, into the coelomocytes for further detoxification. Our study also demonstrated that the high-throughput screening platform is a promising system for evaluation and investigation of the ecological risks of heavy metals.

A novel micro-injection droplet microfluidic system for studying locomotive behavior responses to Cu2+ induced neurotoxin in individual C.elegans

Analysis of C.elegans by droplet microfluidics has been widely used in study of locomotive behavior responses to neurotoxicity due to the capacity of high-throughput manipulating single cells. However, it has been difficult to manipulate droplets flexibly and actively on account of the limitation of the dimension of individual C. elegans droplets. In this study, a novel MiDMS (Micro-injection Droplet Microfluidic System) was proposed, which consisted of three parts: single C. elegans droplet generator, droplets drug micro-injection channels and drug-incubation observation array. Individual C.elegans droplets were produced initially by regulating the flow rates between oil and water phase as well as the concentration of C.elegans in suspension. Then, the drug solution was precisely injected into each C.elegans droplet, which by electricity induced surface tension of droplet changing. In addition, the effect of neurotoxic Cu²⁺ on locomotive behavior of C. elegans was evaluated at single cell resolution. The results showed that the neurotoxicity induced behavioral disorder of the C. elegans was more obvious with the increase of Cu²⁺ concentration or treatment time, and these dose-effect and time-effect relationship in MiDMS were similar as in petri dish. This study will provide a powerful platform for the study of the response of C. elegans to quantitative drug at single cell resolution.

A new method for measuring the size of nematodes using image processing

Many studies have been made on nematodes, especially Caenorhabditis Elegans, which are used as a model organism. In many studies, the size of the nematode is important. This article describes a method of measuring the length, volume and surface area of nematodes from photographs. The method uses the imaging software ImageJ, which is in the public domain. Two macros are described. The first converts the images into binary form, and the second uses several built-in functions to measure the length of the worm and its diameter along its length. If it is assumed that the worm has a circular cross-section, then the volume and surface area of the nematode can be calculated. This is a cheap and easy technique.

Intergenerational effects of coal dust on Tribolium castaneum, Herbst

Coal dust is a primary air contaminant from coal mining operations that produces harmful health effects. However, it is unclear to what extent its detrimental properties would impact future generations, and whether alterations in the progenies might be concentration-dependent. The aim of this study was to determine the intergenerational effects of chronic exposure to coal dust on the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), at three life stages. Groups of fifty adult insects were exposed during 30 days at different concentrations of coal dust mixed with ground oats as food substrate (0, 0.25, 0.5, 1.0 and 2.0% weight/weight), both with a particle size <38 μm. The LC₅₀ for F0 insects was 1.07%, whereas for larvae and adults from F1, values were 0.53 and 0.89%, respectively. Pathological findings assessed at F1 revealed a coal dust concentration-dependent frequency of several morphological abnormalities, including larvae without antenna or extremities, lack of T1, T2, T3 legs, loss of urogomphi, and the presence of abnormal protuberances. It was found that a considerable number of F1 larvae derived from parental beetles did not achieve a complete conversion into the next growth stage. Pupae with undeveloped eyes and adults with malformed elytra, as well as necrosis, were recurrently observed at high concentrations. Finally, adults exposed to 1% coal dust overexpressed genes related to oxidative stress (nuclear factor erythroid 2-related factor 2, Nrf2) and synaptic transmission (GABA-gated ion channel, Grd). In short, coal dust particles induced intergenerational effects on T. castaneum, highlighting the need to further study the impact of this airborne pollutant on wildlife and human populations.

(-)-Epigallocatechin-3-gallate attenuates the toxicity of methylmercury in Caenorhabditis elegans by activating SKN-1

(-)-Epigallocatechin-3-gallate (EGCG) found in tea is a natural activator of nuclear factor erythroid 2-related factor 2 (Nrf2), a primary regulator of the cellular defense system. The adverse health effects resulting from methylmercury (MeHg) exposure in humans are of worldwide concern. We hypothesized that EGCG could induce a Nrf2-mediated protective response to antagonize MeHg toxicity. Using the Caenorhabditis elegans (C. elegans) nematode model, we observed that EGCG activated SKN-1 (the functional ortholog of Nrf2 in C. elegans), as shown by the increased skn-1 mRNA level, induction of the gene gst-4, and enhanced SKN-1-mediated oxidative stress resistance that were indicated by elevation of total antioxidant ability and reductions in reactive oxygen species and malondialdehyde. Following exposure to MeHg, EGCG-treated C. elegans displayed increased survival rates, improved locomotion behaviors, decreased numbers of damaged neurons, and reduced oxidative damage compared to the controls. Moreover, the protective effects of EGCG against MeHg toxicity were counteracted by RNA-mediated interference of skn-1. These results demonstrated that EGCG could alleviate MeHg toxicity by upregulating the SKN-1-regulated protective response in C. elegans. Our study suggests a potentially beneficial effect of targeting Nrf2 by dietary EGCG in protecting humans against MeHg toxicity.

Reproductive toxicity induced by nickel nanoparticles in Caenorhabditis elegans

To investigate the reproductive toxicity and underlying mechanism of nickel nanoparticles (Ni NPs), Caenorhabditis elegans (C. elegans) were treated with/without 1.0, 2.5, and 5.0 μg cm^-2 of Ni NPs or nickel microparticles (Ni MPs). Generation time, fertilized egg numbers, spermatide activation and motility were detected. Results indicated, under the same treatment doses, that Ni NPs induced higher reproductive toxicity to C. elegans than Ni MPs. Reproductive toxicities observed in C. elegans included a decrease in brood size, fertilized egg and spermatide activation, but an increase in generation time and out-of-round spermatids. The reproductive toxicity of Ni NPs on C. elegans may be induced by oxidative stress. The reproductive toxicity in C. elegans induced by Ni NPs is consistent with our previous results in the rats. Therefore, C. elegans can be used as an alternative model to detect the early reproductive toxicity of Ni NPs exposure. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1530-1538, 2017.

Trans-generational influences of sulfamethoxazole on lifespan, reproduction and population growth of Caenorhabditis elegans

Trans-generational effects are increasingly used to indicate long-term influences of environmental pollutants. However, such studies can be complex and yield inconclusive results. In this study, the trans-generational effects of sulfamethoxazole (SMX) on Caenorhabditis elegans on lifespan, reproduction and population growth were tested for 7 consecutive generations, which included gestating generation (F0), embryo-exposed generation (F1), germline-exposed generation (F2), the first non-exposed generation (F3) and the three following generations (F4-F6). Results showed that lifespan was significantly affected by embryo exposure (F1) at 400µm SMX with a value as low as 47% of the control. The reproduction (a total brood size as 49% of the control) and population growth (81% of the control) were significantly affected in germline exposure (F2). Lifespan and reproduction were severely inhibited in non-exposed generations, confirming the real trans-generational effects. Notably, initial reproduction and reproduction duration showed opposite generation-related changes, indicating their interplay in the overall brood size. The population growth rate was well correlated with median lethal time, brood size and initial reproduction, which indicated that the population would increase when the nematodes lived longer and reproduced more offspring within shorter duration.

ace-3 plays an important role in phoxim resistance in Caenorhabditis elegans

Organophosphorus and carbamate are widely used in agricultural production. Caenorhabditis elegans is a model organism that is widely used in various toxicology studies. To understand the effects of two types of commonly used pesticides, phoxim (organophosphorus) and carbaryl (carbamate), we determined the activities of acetylcholinesterases (AChEs) and detected the expression of four ace genes by RT-qPCR in C. elegans following treatment with these pesticides. The results showed that phoxim and carbaryl could reduce acetylcholinesterase activities and up-regulate the ace-3 mRNA expression levels. We also detected the toxic effects of these pesticides on the ace-3 deletion mutant dc-2, and found that some characteristics, including LC50, development, movement, reproduction and lifespan, were reduced in the dc-2 mutant. However, the toxic effects of carbaryl were weaker than those of phoxim. Carbaryl treatment did not significantly affect the LC50, movement ability or lifespan. Interestingly, body and brood size increased with carbaryl treatment at low concentrations. These data showed that both phoxim and carbaryl could inhibit AChE but that the ace-3 was necessary for phoxim detoxification. The LC50 of phoxim and carbaryl in wild type N2 and the ace-3 deletion mutant dc-2. **Higher significant differences (P < 0.01).

Multigenerational Effects of Heavy Metals on Feeding, Growth, Initial Reproduction and Antioxidants in Caenorhabditis elegans

Earlier studies showed that toxicities of excessive metals lasted over generations. Yet, these studies mainly employed one-generation exposure, and the effects of multigenerational challenges need further studies. Presently, Caenorhabditis elegans were exposed to cadmium, copper, lead and zinc for four consecutive generations (G1 to G4) at environmental concentrations. The feeding, growth, initial reproduction, superoxide dismutase (SOD) and catalase (CAT) were determined. All data were represented in the percentage of that in control (POC), and POC in the control was normalized to 100%. In G1 and G2, the POC values in feeding, growth and initial reproduction were generally within 10% of the control (100%), indicating non-significant effects. The POC values in SOD and CAT were significantly higher than 100%, showing stimulatory effects. In G3 and G4, the POC values in feeding, growth and initial reproduction were significantly lower than 100%, showing inhibitory effects which were more severe in G4 than in G3. Meanwhile, SOD and CAT continuously showed stimulatory effects, and the stimulatory effects on SOD increased from G1 to G4. The effects with multigenerational challenges were different from those in one-generation exposure. The effects in later generations demonstrated the importance of multigenerational challenges in judging long-term influences of metals.

Transgenerational safety of nitrogen-doped graphene quantum dots and the underlying cellular mechanism in Caenorhabditis elegans

Nitrogen-doped graphene quantum dots (N-GQDs) are safe for environmental release.

The combinational effects between sulfonamides and metals on nematode Caenorhabditis elegans

As emerging pollutants, antibiotic sulfonamides are continuously emitted into the environment and encounter those already-existing contaminants, e.g., heavy metals, which may cause toxicity interactions in polluted habitats. So far, the sulfonamide mixture effects and the combinational effects between sulfonamides and metals have been seldom studied. In this study, lifespan, lethality (24 and 120 h), locomotion behavior and growth (96 h) of Caenorhabditis elegans were measured after exposure to mixtures containing sulfonamides (sulfadiazine, sulfapyridine, sulfamethoxazole and sulfamethazine as representatives) and/or metals (cadmium, copper, lead and zinc as representatives) at environmental concentrations. Results showed that sulfonamides did not cause acute (24 h) lethality at chosen concentrations, but they decreased the lifespan in a concentration dependent fashion. Moreover, sulfonamide mixtures caused synergisms at higher concentrations but antagonisms at lower concentrations on the subacute (120 h) lethal effects. The toxicity interactions of sulfonamide mixtures were addition action on body bending frequency, and antagonism on reversal movement and body length. In sulfonamide and metal mixtures, the toxicity interactions were different in acute and subacute lethal results, indicating the influence of the exposure time. According to the comparison among effects of mixtures containing sulfonamides and/or metals, subacute lethality of sulfonamides was enhanced by metals based on the synergistic mixture effects, while their inhibitions on the growth and behavior were weakened by metals based on the antagonistic mixture effects. Our findings highlighted studies on combinational effects between emerging and common contaminants for more accurate environmental risk evaluation, and also urged further mechanism studies.

Nickel nanoparticles exposure and reproductive toxicity in healthy adult rats

Nickel is associated with reproductive toxicity. However, the reproductive toxicity of nickel nanoparticles (Ni NPs) is unclear. Our goal was to determine the association between nickel nanoparticle exposure and reproductive toxicity. According to the one-generation reproductive toxicity standard, rats were exposed to nickel nanoparticles by gavage and we selected indicators including sex hormone levels, sperm motility, histopathology, and reproductive outcome etc. Experimental results showed nickel nanoparticles increased follicle stimulating hormone (FSH) and luteinizing hormone (LH), and lowered etradiol (E₂) serum levels at a dose of 15 and 45 mg/kg in female rats. Ovarian lymphocytosis, vascular dilatation and congestion, inflammatory cell infiltration, and increase in apoptotic cells were found in ovary tissues in exposure groups. For male rats, the weights decreased gradually, the ratio of epididymis weight over body weight increased, the motility of rat sperm changed, and the levels of FSH and testosterone (T) diminished. Pathological results showed the shedding of epithelial cells of raw seminiferous tubule, disordered arrangement of cells in the tube, and the appearance of cell apoptosis and death in the exposure group. At the same time, Ni NPs resulted in a change of the reproductive index and the offspring development of rats. Further research is needed to elucidate exposure to human populations and mechanism of actions.

The DAF-16 FOXO transcription factor regulates natc-1 to modulate stress resistance in Caenorhabditis elegans, linking insulin/IGF-1 signaling to protein N-terminal acetylation

The insulin/IGF-1 signaling pathway plays a critical role in stress resistance and longevity, but the mechanisms are not fully characterized. To identify genes that mediate stress resistance, we screened for C. elegans mutants that can tolerate high levels of dietary zinc. We identified natc-1, which encodes an evolutionarily conserved subunit of the N-terminal acetyltransferase C (NAT) complex. N-terminal acetylation is a widespread modification of eukaryotic proteins; however, relatively little is known about the biological functions of NATs. We demonstrated that loss-of-function mutations in natc-1 cause resistance to a broad-spectrum of physiologic stressors, including multiple metals, heat, and oxidation. The C. elegans FOXO transcription factor DAF-16 is a critical target of the insulin/IGF-1 signaling pathway that mediates stress resistance, and DAF-16 is predicted to directly bind the natc-1 promoter. To characterize the regulation of natc-1 by DAF-16 and the function of natc-1 in insulin/IGF-1 signaling, we analyzed molecular and genetic interactions with key components of the insulin/IGF-1 pathway. natc-1 mRNA levels were repressed by DAF-16 activity, indicating natc-1 is a physiological target of DAF-16. Genetic studies suggested that natc-1 functions downstream of daf-16 to mediate stress resistance and dauer formation. Based on these findings, we hypothesize that natc-1 is directly regulated by the DAF-16 transcription factor, and natc-1 is a physiologically significant effector of the insulin/IGF-1 signaling pathway that mediates stress resistance and dauer formation. These studies identify a novel biological function for natc-1 as a modulator of stress resistance and dauer formation and define a functionally significant downstream effector of the insulin/IGF-1 signaling pathway. Protein N-terminal acetylation mediated by the NatC complex may play an evolutionarily conserved role in regulating stress resistance.

Transgenerational effects of traffic-related fine particulate matter (PM₂.₅) on nematode Caenorhabditis elegans

Numerous studies have demonstrated the toxic effects of fine particle matter less than 2.5 μm (PM2.5) on health of human. However, little information is available on PM2.5 ecotoxicity. We employed Caenorhabditis elegans to investigate the adverse effects of traffic-related PM2.5 on exposed animals and their progeny. Acute exposure to high concentrations of PM2.5 in the range of mg/L caused adverse effects on development, lifespan, reproduction, and locomotion behavior of nematodes. In contrast, prolonged exposure to low concentrations of PM2.5 in the range of μg/L resulted in adverse effects on development, lifespan, reproduction, locomotion behavior, and intestinal development of nematodes. Prolonged exposure to PM2.5 could even cause adverse effects on lifespan, reproduction, locomotion behavior, and intestinal development in progeny of exposed nematodes. PM2.5 toxicity was only partially recovered in progeny of exposed nematodes. For the PM2.5 toxicity on nematodes and their progeny, we hypothesize that it might be the combinational effects of oxidative stress, damage on intestinal barrier, and abnormal defecation behavior. Our data here imply the potential toxic effects of long-term exposure to traffic-related PM2.5 on environmental organisms. Our results further highlight the possible crucial roles of biological barrier and defecation behavior in regulating the PM2.5 toxicity.

Assaying environmental nickel toxicity using model nematodes

Although nickel exposure results in allergic reactions, respiratory conditions, and cancer in humans and rodents, the ramifications of excess nickel in the environment for animal and human health remain largely undescribed. Nickel and other cationic metals travel through waterways and bind to soils and sediments. To evaluate the potential toxic effects of nickel at environmental contaminant levels (8.9-7,600 µg Ni/g dry weight of sediment and 50-800 µg NiCl₂/L of water), we conducted assays using two cosmopolitan nematodes, Caenorhabditis elegans and Pristionchus pacificus. We assayed the effects of both sediment-bound and aqueous nickel upon animal growth, developmental survival, lifespan, and fecundity. Uncontaminated sediments were collected from sites in the Midwestern United States and spiked with a range of nickel concentrations. We found that nickel-spiked sediment substantially impairs both survival from larval to adult stages and adult longevity in a concentration-dependent manner. Further, while aqueous nickel showed no adverse effects on either survivorship or longevity, we observed a significant decrease in fecundity, indicating that aqueous nickel could have a negative impact on nematode physiology. Intriguingly, C. elegans and P. pacificus exhibit similar, but not identical, responses to nickel exposure. Moreover, P. pacificus could be tested successfully in sediments inhospitable to C. elegans. Our results add to a growing body of literature documenting the impact of nickel on animal physiology, and suggest that environmental toxicological studies could gain an advantage by widening their repertoire of nematode species.

High concentration of vitamin E decreases thermosensation and thermotaxis learning and the underlying mechanisms in the nematode Caenorhabditis elegans

α-tocopherol is a powerful liposoluble antioxidant and the most abundant isoform of vitamin E in the body. Under normal physiological conditions, adverse effects of relatively high concentration of vitamin E on organisms and the underlying mechanisms are still largely unclear. In the present study, we used the nematode Caenorhabditis elegans as an in vivo assay system to investigate the possible adverse effects of high concentration of vitamin E on thermosensation and thermotaxis learning and the underlying mechanisms. Our data show that treatment with 100-200 µg/mL of vitamin E did not noticeably influence both thermosensation and thermotaxis learning; however, treatment with 400 µg/mL of vitamin E altered both thermosensation and thermotaxis learning. The observed decrease in thermotaxis learning in 400 µg/mL of vitamin E treated nematodes might be partially due to the moderate but significant deficits in thermosensation, but not due to deficits in locomotion behavior or perception to food and starvation. Treatment with 400 µg/mL of vitamin E did not noticeably influence the morphology of GABAergic neurons, but significantly decreased fluorescent intensities of the cell bodies in AFD sensory neurons and AIY interneurons, required for thermosensation and thermotaxis learning control. Treatment with 400 µg/mL of vitamin E affected presynaptic function of neurons, but had no remarkable effects on postsynaptic function. Moreover, promotion of synaptic transmission by activating PKC-1 effectively retrieved deficits in both thermosensation and thermotaxis learning induced by 400 µg/mL of vitamin E. Therefore, relatively high concentrations of vitamin E administration may cause adverse effects on thermosensation and thermotaxis learning by inducing damage on the development of specific neurons and presynaptic function under normal physiological conditions in C. elegans.

Rapid phenotypic changes in Caenorhabditis elegans under uranium exposure

Pollutants can induce selection pressures on populations, and the effects may be concentration-dependant. The main ways to respond to the stress are acclimation (i.e. plastic changes) and adaptation (i.e. genetic changes). Acclimation provides a short-term response to environmental changes and adaptation can have longer-term implications on the future of the population. One way of studying these responses is to conduct studies on the phenotypic changes occurring across generations in populations experimentally subjected to a selective factor (i.e. multigenerational test). To our knowledge, such studies have not been performed with uranium (U). Here, the phenotypic changes were explored across three generations in experimental Caenorhabditis elegans populations exposed to different U-concentrations. Significant negative effects of U were detected on survival, generation time, brood size, body length and body bend. At lower U-concentrations, the negative effects were reduced in the second or the third generation, indicating an improvement by acclimation. In contrast, at higher U-concentrations, the negative effects on brood size were amplified across generations. Consequently, under high U-concentrations acclimation may not be sufficient, and adaptation of individuals would be required, to permit the population to avoid extinction. The results highlight the need to consider changes across generations to enhance environmental risk assessment related to U pollution.

Inhibitions on the behavior and growth of the nematode progeny after prenatal exposure to sulfonamides at micromolar concentrations

Sulfonamides are one typical antibiotic which is an emerging hazardous material to the ecological stability due to their continuously application and biological effects to non-target organisms. The parent-progeny transgenerational effects need investigations to indicate their long-term consequences. Currently, we tested the transgenerational effects of sulfadiazine (SD), sulfapyridine (SP) and sulfamethazine (SMZ) on L3 larva of Caenorhabditis elegans. The nematodes were exposed to aqueous sulfonamides at micromolar concentrations for 96 h, and then the effects on the behavior and growth in the exposed parent and unexposed progeny were measured. Results showed that SD, SP and SMZ inhibited three behavior indicators including body bending frequency (BBF), reversal movement (RM) and Omega turn (OT), and the growth indicator (body length, BL). Behavior indicators showed higher sensitivities than the growth indicator, and BBF had the highest sensitivity among the behavior indicators. Moreover, the effects of sulfonamides were also observed in the unexposed progeny with partially rescued or more severe inhibitions on the indicators. The behavior also showed higher sensitivity than the growth in the progeny. The transgenerational effects of sulfonamides indicated that parental exposure can multiply the harmful effects of antibiotic pollution in following generations and their potential ecological risks at environmental concentrations were further raised.

Neurotoxicological evaluation of microcystin-LR exposure at environmental relevant concentrations on nematode Caenorhabditis elegans

Previous studies have not examined the adverse effects of microcystin-LR (MC-LR) at environmental relevant concentrations on the development and functions of nervous system. The neurotoxic effects of MC-LR exposure on neurotransmitter systems were investigated in Caenorhabditis elegans. After exposing L1 larvae to 0.1, 1, 10, and 100 μg l(-1) of MC-LR for 8 and 24 h, the adverse effects on GABAergic, cholinergic, serotonergic, dopaminergic, and glutamatergic neurons were examined. The expression levels of genes required for development and functions of GABAergic neurons were further investigated. Body bend frequency and head thrash frequency decreased significantly after MC-LR exposure for 8 h at concentrations more than 1 μg l(-1) and after MC-LR exposure for 24 h at concentrations more than 0.1 μg l(-1). Loss of GABAergic neurons increased significantly in a dose-dependent manner after MC-LR exposure at concentrations more than 0.1 μg l(-1). In contrast, no obvious neuronal losses or morphologic changes were observed in cholinergic, serotonergic, dopaminergic, and glutamatergic neurons in MC-LR-exposed nematodes. Quantitative real-time PCR assay further showed that expression levels of unc-30, unc-46, unc-47, and exp-1 genes required for development and function of GABAergic neurons decreased significantly in nematodes exposed to MC-LR at concentrations more than 0.1 or 1 μg l(-1). MC-LR at environmental relevant concentrations caused neurobehavioral defects, which may be largely due to the neuronal loss and the alterations of expression level of genes required for GABAergic neurotransmitter system in C. elegans.

Opinion: nickel and urease in plants: still many knowledge gaps

We propose experimental strategies to expand our understanding of the role of Ni in plants, beyond the Ni-metallocenter of urease, still the only identified Ni-containing plant enzyme. While Ni has been considered an essential mineral for plants there is a clear lack of knowledge of its involvement in metabolic steps except the urease-catalyzed conversion of urea to ammonia and bicarbonate. We argue that urease (and hence, Ni) plays an important role in optimal N-use efficiency under various N regimes by recycling urea-N, which is generated endogenously exclusively from arginase action on arginine. We further suggest that urease and arginase may connect different metabolic compartments under stress situations, and therefore may be involved in stress tolerance. To determine possible non-urease roles of Ni we call for experimental manipulation of both Ni and N availability in urease-negative mutants. Plant ureases have been shown to have defense roles, distinct from their ureolytic activity, and we call for investigation of whether Ni helps maintain a urease conformation or stability for these non-ureolytic defense roles. The beneficial effects of Ni at upper concentration limits have not been fully examined. We posit a "Ni strategy" of plants whose growth/performance is stimulated by unusual amounts of soil Ni, for defense and/or for maximal N-use efficiency. While we know little about Ni and urease roles in N metabolism and defense, virtually nothing is known about Ni roles in plant-microbial 'consortia.' And, much of what we know of Ni and urease is limited to only a few plants, e.g. soybean, potato and Arabidopsis, and we suggest studies vigorously extended to other plants.

Transgenerational effects of heavy metals on L3 larva of Caenorhabditis elegans with greater behavior and growth inhibitions in the progeny

Heavy metals are ubiquitous environmental pollutants, and their toxic effects have been widely studied. However, their transgenerational effects between parent and progeny at environmental relevant concentrations need further investigations. Currently, L3 stage of Caenorhabditis elegans was exposed to aqueous metals (Cd, Cu, Pb and Zn) at environmentally realistic concentrations for 96 h. The whole exposure time covered the formation of sperm, ovum and eggs. Subsequently the behavior and growth indicators were measured. The parent nematodes were then bleached to gain synchronized eggs, which were cultured under non-toxic conditions to L3 stage when the same indicators were measured in the progeny. The parent suffered concentration-dependent inhibitions on behavior and growth. Based on the median effective concentration (EC(50)) values, body bending frequency showed relatively higher sensitivity than other behavior indicators. The inhibitions on growth and behavior of progeny were more severe than those of the parent, based on their respective EC(50) values. Interestingly, Cd was not the most toxic metal in either parent or progeny according to EC(50) values, but its EC(50) ratios between parent and progeny (EC(50, parent)/EC(50, progeny)) were the most significant, indicating its greatest transgenerational effects. The results demonstrated the higher sensitivity of L3 larva stage of C. elegans in the transgenerational effect studies than other life stages used before. Our findings suggested that parental exposure to heavy metals can multiply their harmful effects in following generations.

Exposure to mercury causes formation of male-specific structural deficits by inducing oxidative damage in nematodes

Metal exposure causes reproductive damage in hermaphrodite nematodes, but effects of metals on male development are unclear. We here investigated the effects of mercury chloride exposure on development of males. Hg exposure severely increased the percentage of abnormal males, disrupted the development of male-specific structures, and caused high reactive oxygen species (ROS) production in male tails. Pre-treatment with antioxidant (vitamin E) protected the nematodes against toxicity from Hg exposure on development of male-specific structures. The ROS production in tails was closely correlated with formation of abnormal male-specific structures in males induced by Hg exposure. Moreover, mutations of clk-1, encoding ortholog of COQ7/CAT5, and daf-2, encoding an insulin/IGF receptor, functioned in two different pathways to suppress the formation of deficits in development of male-specific structures. Thus, three different lines of evidence support our conclusion that HgCl(2) causes male structure-specific teratogenesis via production of oxidative stress.

Aluminium exposure disrupts elemental homeostasis in Caenorhabditis elegans

Aluminium (Al) is highly abundant in the environment and can elicit a variety of toxic responses in biological systems. Here we characterize the effects of Al on Caenorhabditis elegans by identifying phenotypic abnormalities and disruption in whole-body metal homeostasis (metallostasis) following Al exposure in food. Widespread changes to the elemental content of adult nematodes were observed when chronically exposed to Al from the first larval stage (L1). Specifically, we saw increased barium, chromium, copper and iron content, and a reduction in calcium levels. Lifespan was decreased in worms exposed to low levels of Al, but unexpectedly increased when the Al concentration reached higher levels (4.8 mM). This bi-phasic phenotype was only observed when Al exposure occurred during development, as lifespan was unaffected by Al exposure during adulthood. Lower levels of Al slowed C. elegans developmental progression, and reduced hermaphrodite self-fertility and adult body size. Significant developmental delay was observed even when Al exposure was restricted to embryogenesis. Similar changes in Al have been noted in association with Al toxicity in humans and other mammals, suggesting that C. elegans may be of use as a model for understanding the mechanisms of Al toxicity in mammalian systems.

Inhibition of ROS elevation and damage to mitochondrial function prevents lead-induced neurotoxic effects on structures and functions of AFD neurons in Caenorhabditis elegans

Here we investigated the possible roles of oxidative stress in the formation of decreased thermotaxis to cultivation temperature in lead (Pb)-exposed nematodes Caenorhabditis elagans. Exposure to Pb at the examined concentrations decreased thermotaxis behaviors, and induced severe deficits in the structural properties of AFD sensory neurons. Meanwhile, Pb exposure caused the induction of severe oxidative damage, reactive oxygen species (ROS) production, and mitochondrial dysfunction in young adults. Moreover, pre-treatment with the antioxidants dimethyl sulfoxide (DMSO), ascorbate and N-acetyl-L-cysteine (NAC), used to inhibit both the ROS elevation and the mitochondrial dysfunction caused by Pb exposure, at the L2-larval stage prevented the induction of oxidative damage and the formation of severe deficits in thermotaxis and structural properties of AFD sensory neurons in Pb-exposed young adults. Therefore, the formation of oxidative stress caused by Pb exposure may be due to both the induction of ROS elevation and damage to mitochondrial function, and oxidative stress may play a key role in inducing the neurotoxic effects on the structures and function of AFD sensory neurons in Pb-exposed nematodes.

Association of oxidative stress with the formation of reproductive toxicity from mercury exposure on hermaphrodite nematode Caenorhabditis elegans

Here we selected HgCl(2) to investigate the mechanism of Hg toxicity on reproduction in hermaphrodite nematodes. Accompanied with decrease of brood size, Hg exposure caused severe deficits in egg number in uterus, egg laying and reproductive structures, including gonad arms and vulva, and formation of protruding phenotype for vulva. Meanwhile, Hg exposure induced severe stress response and oxidative damage in gonad and vulva. Pre-treatment with vitamin E, a potent antioxidant, at the L2-larval stage prevented the oxidative damage and formation of reproductive deficits in Hg exposed nematodes; however, pre-treatment with paraquat, a regent generating superoxide anions, induced more severe reproductive deficits in Hg exposed nematodes. Moreover, Hg exposure increased expression of clk-2 and isp-1 genes, whose mutations decrease ROS production, and decreased expression of mev-1 and gas-1 genes, whose mutations increase ROS production. Thus, oxidative stress may be essential for the induction of reproductive deficits in Hg exposed hermaphrodite nematodes.

Modulation of the assay system for the sensory integration of 2 sensory stimuli that inhibit each other in nematode Caenorhabditis elegans

OBJECTIVE

To perform the modulation of an assay system for the sensory integration of 2 sensory stimuli that inhibit each other.

METHODS

The assay system for assessing the integrative response to 2 reciprocally-inhibitory sensory stimuli was modulated by changing the metal ion barrier. Moreover, the hen-1, ttx-3 and casy-1 mutants having known defects in integrative response were used to evaluate the modulated assay systems. Based on the examined assay systems, new genes possibly involved in the sensory integration control were identified.

RESULTS

In the presence of different metal ion barriers and diacetyl, locomotion behaviors, basic movements, pan-neuronal, cholinergic and GABAergic neuronal GFP expressions, neuronal development, structures of sensory neurons and interneurons, and stress response of nematodes in different regions of examined assay systems were normal, and chemotaxis toward different concentrations of diacetyl and avoidance of different concentrations of metal ions were inhibited. In the first group, most of the nematodes moved to diacetyl by crossing the barrier of Fe(2+), Zn(2+), or Mn(2+). In the second group, almost half of the nematodes moved to diacetyl by crossing the barrier of Ag(+), Cu(2+), Cr(2+), or Cd(2+). In the third group, only a small number of nematodes moved to diacetyl by crossing the barrier of Pb(2+) or Hg(2+). Moreover, when nematodes encountered different metal ion barriers during migration toward diacetyl, the percentage of nematodes moving back and then turning and that of nematodes moving straight to diacetyl were very different. With the aid of examined assay systems, it was found that mutations of fsn-1 that encodes a F-box protein, and its target scd-2 that encodes a receptor tyrosine kinase, caused severe defects in integrative response, and the sensory integration defects of fsn-1 mutants were obviously inhibited by scd-2 mutation.

CONCLUSION

Based on the nematode behaviors in examined assay systems, 3 groups of assay systems were obtained. The first group may be helpful in evaluating or identifying the very subtle deficits in sensory integration, and the third group may be useful for the final confirmation of sensory integration defects of mutants identified in the first or the second group of assay systems. Furthermore, the important association of sensory integration regulation with stabilization or destabilization of synaptic differentiation may exist in C. elegans.

Behavior toxicity to Caenorhabditis elegans transferred to the progeny after exposure to sulfamethoxazole at environmentally relevant concentrations

Sulfamethoxazole (SMX) is one of the most common detected antibiotics in the environment. In order to study whether SMX can affect behavior and growth and whether these effects could be transferred to the progeny, Caenorhabditis elegans was exposed at environmentally relevant concentrations for 24, 48, 72 and 96 hr, respectively. After exposure, the exposed parent generation (P0) was measured for behavior and growth indicators, which were presented as percentage of controls (POC). Then their corresponding unexposed progeny (F1) was separated and measured for the same indicators. The lowest POC for P0 after 96 hr-exposure at 100 mg/L were 37.8%, 12.7%, 45.8% and 70.1% for body bending frequency (BBF), reversal movement (RM), Omega turns (OT) and body length (BL), respectively. And F1 suffered defects with the lowest POC as 55.8%, 24.1%, 48.5% and 60.7% for BBF, RM, OT and BL, respectively. Defects in both P0 and F1 showed a time- and concentration-dependent fashion and behavior indicators showed better sensitivity than growth indicator. The observed effects on F1 demonstrated the transferable properties of SMX. Defects of SMX at environmental concentrations suggested that it is necessary to perform further systematical studies on its ecological risk in actual conditions.

The Caenorhabiditis elegans model as a reliable tool in neurotoxicology

Caenorhabiditis elegans (C. elegans) offers an attractive experimental platform as it has a short life cycle, is inexpensive to maintain and most importantly has high degree of evolutionary conservation with higher eukaryotes. Understanding the contribution of inherent genes that regulate neurotoxicity and antioxidant stress responses in the worm provides critical insight into mechanisms of mammalian neurotoxicity. The C. elegans model readily enables multi-gene approach, allowing for combinatorial genetic variation to be studied within the context of the influence of multigenic polymorphisms in environmental risk and vulnerability. This review provides a synopsis of recent studies on metal and pesticides toxicity in C. elegans, highlighting the utility of the model system in understanding molecular mechanisms that underlie developmental, reproductive and neuronal damage. The continuation of these investigations combining basic toxicological experimentation with novel genetic and high throughput methods will continue to make C. elegans an invaluable tool for future research, providing insight into molecular and cellular mechanisms of toxicity.

Metallothioneins are required for formation of cross-adaptation response to neurobehavioral toxicity from lead and mercury exposure in nematodes

Metallothioneins (MTs) are small, cysteine-rich polypeptides, but the role of MTs in inducing the formation of adaptive response is still largely unknown. We investigated the roles of metallothionein genes (mtl-1 and mtl-2) in the formation of cross-adaptation response to neurobehavioral toxicity from metal exposure in Caenorhabditis elegans. Pre-treatment with mild heat-shock at L2-larva stage effectively prevented the formation of the neurobehavioral defects and the activation of severe stress response in metal exposed nematodes at concentrations of 50 and 100 µM, but pre-treatment with mild heat-shock did not prevent the formation of neurobehavioral defects in 200 µM of metal exposed nematodes. During the formation of cross-adaptation response, the induction of mtl-1 and mtl-2 promoter activity and subsequent GFP gene expression were sharply increased in 50 µM or 100 µM of metal exposed Pmtl-1::GFP and Pmtl-2::GFP transgenic adult animals after mild heat-shock treatment compared with those treated with mild heat-shock or metal exposure alone. Moreover, after pre-treatment with mild heat-shock, no noticeable increase of locomotion behaviors could be observed in metal exposed mtl-1 or mtl-2 mutant nematodes compared to those without mild heat-shock pre-treatment. The defects of adaptive response to neurobehavioral toxicity induced by metal exposure formed in mtl-1 and mtl-2 mutants could be completely rescued by the expression of mtl-1 and mtl-2 with the aid of their native promoters. Furthermore, over-expression of MTL-1 and MTL-2 at the L2-larval stage significantly suppressed the toxicity on locomotion behaviors from metal exposure at all examined concentrations. Therefore, the normal formation of cross-adaptation response to neurobehavioral toxicity induced by metal exposure may need the enough accumulation of MTs protein in animal tissues.

Formation of a combined Ca/Cd toxicity on lifespan of nematode Caenorhabditis elegans

We investigated the possible formation of combined toxicity from Ca/Cd exposure on nematode lifespan. Ca exposure at concentrations more than 1.56 mM significantly reduced lifespan, accelerated aging-related declines, and induced severe stress response in wild-type nematodes. Combined Ca (25 mM)/Cd (200 microM) exposure decreased the lifespans compared to Cd (200 microM) exposure; whereas no lifespan differences were found between Ca (1.56 mM)/Cd (200 microM) exposure and Cd (200 microM) exposure. Combined Ca (25 mM)/Cd (200 microM) exposure caused a more significant induction of hsp-16.2::gfp expression, and a more severe increase in oxidative damage than Cd (200 microM) exposure. Moreover, mutation of mev-1, encoding a subunit of succinate dehydrogenase cytochrome b, enhanced the combined Ca/Cd toxicity on lifespan. Furthermore, mutation of daf-16, encoding a fork-head-family transcription factor, enhanced the combined Ca/Cd toxicity on lifespan, and mutation of daf-2, encoding an insulin receptor-like protein, alleviated the combined Ca/Cd toxicity on lifespan.

Effects of metal exposure on associative learning behavior in nematode Caenorhabditis elegans

In the present study, the thermotaxis model was used to evaluate the effects of metal exposure at different concentrations on associative learning behavior in nematodes. The examined nematodes were cultured at 25 or 17 degrees C, and then shifted to 20 degrees C condition. Based on the ability of nematodes to trace the temperature of 20 degrees C, exposure to 10 microM of all examined metals and 2.5 microM Pb and Hg caused significant decrease of associative learning behavior at time intervals of 5 and 18 h; however, exposure to 2.5 microM Cu, Zn, and Ag did not influence associative learning behavior. Moreover, exposure to 2.5 and 10 microM of examined metals did not influence body bend and thermotaxis to cultivation temperature, whereas exposure to 50 microM of examined metals caused significant reduction of body bend and thermotaxis to cultivation temperature. Furthermore, Pb and Hg were the more toxic among the examined metals, with severe toxicity on associative learning behavior, thermotaxis, and locomotion behavior in nematodes.

Pre-treatment with mild UV irradiation increases the resistance of nematode Caenorhabditis elegans to toxicity on locomotion behaviors from metal exposure

UV irradiation at 10J/m(2)/min induced a mild toxicity on locomotion behaviors and stress response in Caenorhabditis elegans. Pre-treatment with UV irradiation at 10J/m(2)/min at L2-larva stage prevented the formation of locomotion behavioral defects, and activated a noticeable reduction of stress response and oxidative damage in 50 and 100μM metal (Hg, Pb, and Cr) exposed nematodes. Pre-treatment with UV irradiation at 20J/m(2)/min caused a significant decrease of locomotion behaviors in metal exposed nematodes, and pre-treatment with mild UV irradiation could not prevent the formation of locomotion behavioral defects in 200μM metal exposed nematodes. Moreover, the adaptive response to toxicity on locomotion behaviors induced by metal exposure was not formed in mev-1 mutants. Therefore, pre-treatment to mild UV irradiation activates the cross-adaptation response to toxicity on locomotion behaviors induced by metal exposure, and this kind of adaptive response may be under the control of MEV-1 function.

Pre-treatment with mild UV irradiation suppresses reproductive toxicity induced by subsequent cadmium exposure in nematodes

In nematodes, 10 J/m(2)/min of UV irradiation induced a mild reproductive toxicity. Pre-treatment with UV irradiation at 10 J/m(2)/min suppressed the formation of reproductive defects, and activated a noticeable reduction of percentage of population with hsp-16.2::gfp expression, an obvious elevation of superoxide dismutase activities, and decrease of oxidative damage in 50 and 100 microM Cd exposed nematodes; however, pre-treatment with UV irradiation at 20 J/m(2)/min caused a significant decrease of brood sizes or increase of generation times in Cd-exposed nematodes. Pre-treatment with mild UV irradiation did not suppress the formation of reproductive defects in 150 microM Cd-exposed nematodes. Furthermore, the adaptive response to reproductive toxicity from Cd exposure was not observed in a reactive oxygen species sensitive mev-1(kn1) mutant. Therefore, pre-treatment with mild UV irradiation triggers the resistance to reproductive toxicity from Cd exposure by at least partially inducing adaptation to oxidative stress and through a mev-1-dependent pathway.

Confirmation of combinational effects of calcium with other metals in a paper recycling mill effluent on nematode lifespan with toxicity identification evaluation method

We used toxicity identification evaluation (TIE) method to confirm the combinational effects of identified toxic metals in a paper recycling mill effluent in inducing the decreased lifespan in nematode Caenorhabditis elegans. Exposure to Ca + Al caused more severely decreased lifespan than that exposed to Ca, or Al; and exposure to Ca + Fe induced more severely decreased lifespan than that exposed to Ca, or Fe. Exposure to Ca+Al+Fe caused more severely decreased lifespan than that exposed to Ca, or Ca+Fe. Moreover, the baseline toxicity on lifespan was doubled by doubling the concentration of combined metals (Ca+Al+Fe) in spiking test in original effluent (oe), and lifespan defects in oe+Ca+Al+Fe exposed nematodes were more severe than that in Ca+Al+Fe exposed nematode. Therefore, Ca+Al+Fe exposure may largely explain the formation of decreased lifespan induced by the examined industrial effluent. Furthermore, the observed reduction of lifespan induced by the combination of high level of Ca with other metals may be at least partially independent of the insulin-like pathway.

Pre-treatment with mild metal exposure suppresses the neurotoxicity on locomotion behavior induced by the subsequent severe metal exposure in Caenorhabditis elegans

Adaptive response to neurotoxicity on locomotion behavior by severe metal exposure was investigated in Caenorhabditis elegans. Exposure to 2.5μM of metals induced a moderate but significant reduction of locomotion behavior and induction of hsp-16.2::gfp expression. After pre-exposure to 2.5μM of metals, the reduced locomotion behavior induced by subsequent 50 and 100μM of metal exposure were significantly prevented, and the induction of hsp-16.2::gfp expression caused by subsequent 50 and 100μM of metal exposure were significantly suppressed. In contrast, after pre-exposure to 50μM examined metals, the reduced locomotion behavior induced by subsequent 50 and 100μM metal exposure were further decreased, and the noticeable induction of hsp-16.2::gfp expression caused by subsequent severe metal exposure were further enhanced. Therefore, pre-treatment with mild metal exposure can activate the adaptive response to neurotoxicity on locomotion behavior induced by subsequent severe metal exposure in nematodes.

Lethality toxicities induced by metal exposure during development in nematode Caenorhabditis elegans

Lethality changes were investigated during development in 4 h metal exposed Caenorhabditis elegans. Exposure to examined metals caused severe lethality toxicities in L1- and L2-larvae, in L3-larvae exposed to examined metals at concentrations of 50 and 100 microM and to Pb, Hg, and Cr at the concentration of 2.5 microM, in L4-larvae exposed to examined metals at concentrations of 50 and 100 microM, and in adults exposed to Pb, Hg, and Cr at the concentration of 100 microM. Moreover, the lethality toxicities induced by Pb and Hg in L1 larvae for 4 h could be largely comparable to those in young adults for 24 h.

Using the larvae nematode Caenorhabditis elegans to evaluate neurobehavioral toxicity to metallic salts

In this study, we investigated the locomotion behavior changes at different developmental stages in Caenorhabditis elegans exposed to metals for 4h. No obvious differences could be observed in young adults exposed to examined metals, and only exposure to 100 microM of examined metals could significantly decrease the locomotion behaviors of L4 larvae. In contrast, exposure to 50 and 100 microM of examined metals induced noticeable repression of locomotion behaviors at L1-L3 larval stages, and a significant decrease of locomotion behaviors could be observed in L1 larvae exposed to Pb and Hg, and in L2 larvae exposed to Hg at the concentration of 2.5 microM. Moreover, the L1-, L2-, and L3-larvae exposed to metals for 4h exhibited similar neurobehavioral toxicity manner to L4-larvae exposed to metals for 24h. Therefore, younger larvae showed more severe deficits in neurobehavioral phenotypes than L4 larvae and young adults in metal-exposed nematodes.

Exposure to metals induces morphological and functional alteration of AFD neurons in nematode Caenorhabditis elegans

Previous studies have revealed that metal exposure will cause severe deficits in perception behaviors. Here we investigated the effects of metal (Hg, Cu, Ag, and Cr) exposure on thermotaxis to cultivation temperature in Caenorhabditis elegans. Our data suggest that exposure to higher concentrations of examined metals induced severe deficits in thermotaxis, and a significant reduction in thermotaxis could be even observed in nematodes exposed to 2.5μM of Hg. Moreover, exposure to higher concentrations of examined metals and 2.5μM of Hg induced significant decreases in relative intensities and relative sizes of fluorescent puncta of cell bodies in AFD thermosensory neurons. In addition, exposure to higher concentrations of examined metals resulted in a significant reduction in relative intensities and relative lengths of sensory endings in AFD neurons. Furthermore, the relative transcript levels of ttx-1, which functions in specifying the fate of AFD neuron, were significantly decreased in nematodes exposed to 2.5μM of Hg, and 50 and 100μM of examined metals. Thus, metal exposure at high concentrations will induce the severe deficits in thermotaxis to cultivation temperature possibly by altering the morphology or development of AFD neuron and damaging the molecular basis for function of AFD neuron in nematodes.

The neurotoxic effects of heavy metal exposure on GABAergic nervous system in nematode Caenorhabditis elegans

The number of cell body or synapse made by Caenorhabditis elegans GABAergic neurons is constant during development. The neurotoxic effects of metal (Pb, Hg, Cu, Cd, Cr, and Mn) exposure on GABAergic motor neurons were investigated in C. elegans. Exposure to examined metals could not alter the position of GABA neurons, whereas exposure to high concentrations (75μM and 200μM) of metals caused noticeable axonal degeneration and neuronal loss in nerve cords, suggesting neurodegeneration will be induced by metal exposure to different degrees. In addition, exposure to Pb, Hg, Cu, and Cd at the low concentration (2.5μM) could also induce obviously neuronal loss. Moreover, exposure to high concentrations (75μM and/or 200μM) of most of examined metals significantly reduced the relative size and fluorescent intensities of AVL, RMEs, and RIS neurons. Therefore, the neurodegeneration and abnormal structures may be formed in GABAergic motor neurons after metal exposure, and the endpoint of neuronal loss will be useful for the neurotoxicity assessment from trace metal exposure.

Adverse effects of metal exposure on chemotaxis towards water-soluble attractants regulated mainly by ASE sensory neuron in nematode Caenorhabditis elegans

Chemotaxis to water-soluble attractants is mainly controlled by ASE sensory neuron whose specification is regulated by che-1 in Caenorhabditis elegans. Our data suggested that exposure to high concentrations of metals, such as Pb, Cu, Ag, and Cr, would result in severe defects of chemotaxis to water-soluble attractants of NaCl, cAMP, and biotin. Moreover, the morphology of ASE neuron structures as observed by relative fluorescent intensities and relative size of fluorescent puncta of cell bodies, relative lengths of sensory endings in ASE neurons, and the expression patterns of che-1 were obviously altered in metal exposed animals when they meanwhile exhibited obvious chemotaxis defects to water-soluble attractants. In addition, the dendrite morphology could be noticeably changed in animals exposed to 150 micromol/L of Pb, Cu, and Ag. Furthermore, we observed significant decreases of chemotaxis to water-soluble attractants in Pb exposed che-1 mutant at concentrations more than 2.5 micromol/L, and in Cu, Ag, and Cr exposed che-1 mutant at concentrations more than 50 micromol/L. Therefore, impairment of the ASE neuron structures and functions may largely contribute to the appearance of chemotaxis defects to water-soluble attractants in metal exposed nematodes.

Evaluation of pesticide toxicities with differing mechanisms using Caenorhabditis elegans

The aim of this study was to (1) determine whether model organism Caenorhabditis elegans was sensitive to pesticides at the maximum concentration limits regulated by national agency standards, and (2) examine the multi-biological toxicities occurring as a result of exposure to pesticides. Five pesticides, namely, chlorpyrifos, imibacloprid, buprofezin, cyhalothrin, and glyphosate, with four different mechanisms of action were selected for the investigation. In accordance with national agency requirements, 4 exposed groups were used for each tested pesticide with the concentration scales ranging from 1.0 x 10(-3) to 1 mg/L. L4 larvae were exposed for 24 and 72 h, respectively. Endpoints of locomotion, propagation, and development were selected for the assay as parameters of toxicity. After exposure for 24 h, both the body bend frequency and head thrash frequency of nematodes exposed to chlorpyrifos, imibacloprid, and cyhalothrin decreased in a concentration-dependent manner, and there were significant differences between exposed groups at maximum concentration level (MCL) compared to control. The generation time of nematodes exposed to buprofezin 24 h significantly increased in a concentration-dependent manner in the highest exposed group. When exposed for 72 h, the body bend frequency and head thrash frequency of nematodes exposed to cyhalothrin markedly decreased at MCL. The generation time and brood size of nematodes exposed to buprofezin were reduced in a concentration-dependent manner. The behavior of nematodes was sensitive to pesticides with neurotoxic properties, while pesticides affecting insect growth modified the reproductive system. The effects of pesticides on nematodes exposed for 24 h appeared more sensitive than with exposure for 72 h. Caenorhabditis elegans may thus be used for assessing the adverse effects of pesticide residues in aquatic environment.