Ji-Yeon Roh

Ecotoxicological investigation of CeO2 and TiO2 nanoparticles on the soil nematode Caenorhabditis elegans using gene expression, growth, fertility, and survival as endpoints.

In this study, the potential harmful effect of cerium dioxide (CeO(2)), and titanium dioxide (TiO(2)) nanoparticles on the environment was investigated using Caenorhabditis elegans ecotoxicity tests. Multiple toxic endpoints, such as stress-response gene expression, growth, fertility, and survival, were analyzed in C. elegans, in response to the CeO(2) and TiO(2) exposure. To investigate relationship between sizes of nanoparticles and toxicity, C. elegans were exposed to nanoparticles to the different sizes of nanoparticles (15, 45nm for CeO(2) and 7, 20nm for TiO(2)). An increase in the expression of the cyp35a2 gene, decrease in fertility and survival parameters were observed in the 15 and 45nm of CeO(2) and in the 7nm of TiO(2) nanoparticles exposed to C. elegans. Gene knock-down experiment using RNA interference (RNAi) suggested that physiological level disturbances may be related with the cyp35a2 gene expression. Smaller sized nanoparticles (7nm of TiO(2) and 15nm of CeO(2)) seemed to be more toxic than larger sized ones (20nm of TiO(2) and 45nm of CeO(2)) on the observed toxicity. The size-dependent effect in CeO(2) and TiO(2) nanoparticles-induced toxicity needs to be investigated under more detailed experimental settings with the various sizes of nanoparticles. Further studies on the mechanism by which CeO(2) and TiO(2) nanoparticles affect cyp35a2 gene expression, fertility, and survival are warranted to better understand the CeO(2) and TiO(2) nanoparticles-induced ecotoxicity in C. elegans, as are studies with the causal relationships between these parameters. Overall results suggest that CeO(2) and TiO(2) nanoparticles have a potential for provoking ecotoxicity on C. elegans and the data obtained from this study can comprise a contribution to knowledge of the ecotoxicology of nanoparticles in C. elegans, about which little data are available.

Oxidative stress‐related PMK‐1 P38 MAPK activation as a mechanism for toxicity of silver nanoparticles to reproduction in the nematode Caenorhabditis elegans

In the present study, a toxic mechanism of silver nanoparticles (AgNPs) was investigated in the nematode, Caenorhabditis elegans, focusing on the involvement of oxidative stress in reproduction toxicity. Initially, AgNPs were tested as potential oxidative stress inducers, and increased formation of reactive oxygen species (ROS) was observed in AgNP-exposed C. elegans. Subsequently, the potential upstream signaling pathway activated in response to AgNP exposure was investigated, paying special attention to the C. elegans PMK-1 p38 mitogen-activated protein kinase (MAPK). Increased PMK-1 p38 MAPK gene and protein expressions were observed in C. elegans exposed to AgNPs. Expression of the p38-dependent transcription factor genes and glutathione S-transferase (GST) enzyme activity was also investigated in wildtype (N2) and pmk-1 mutant (km25) C. elegans exposed to AgNPs. The results indicated that AgNP exposure led to increased ROS formation, increased expression of PMK-1 p38 MAPK and hypoxia-inducible factor (HIF-1), GST enzyme activity, and decreased reproductive potential in wildtype (N2) C. elegans; whereas in the AgNP-exposed pmk-1 (km25) mutant, ROS formation and HIF-1 and GST activation were not observed, and decreased reproductive potential was rescued. These results suggest that oxidative stress is an important mechanism of AgNP-induced reproduction toxicity in C. elegans, and that PMK-1 p38 MAPK plays an important role in it. The results also suggest that GST and HIF-1 activation by AgNP exposure are PMK-1 p38 MAPK-dependent, and that both play an important role in the PMK-1 p38 MAPK-mediated defense pathway to AgNP exposure in C. elegans.

Assessment of stress-related gene expression in the heavy metal-exposed nematode Caenorhabditis elegans: A potential biomarker for metal-induced toxicity monitoring and environmental risk assessment

The toxicity of cadmium, lead, chromium, and arsenite on Caenorhabditis elegans was investigated to identify sensitive biomarkers for environmental monitoring and risk assessment. Effects of these metals on stress-related gene expression, growth, reproduction, and mortality of C. elegans were investigated under laboratory conditions. The possibility of using C. elegans as a biosensor for environmental toxicity monitoring was also tested using a green fluorescent protein transgenic nematode. The 24-h median lethal concentrations of cadmium, lead, chromium, and arsenite in C. elegans were 846, 34, 115, and 92 mg/L, respectively. Cadmium exposure led to an increase in the expression of most of the genes tested. The degree of increase was more than threefold compared to control in heat shock protein 16.2, heat shock protein 70, metallothionein 2, cytochrome P450 family protein 35A2, glutathione-S-transferase 4, superoxide dismutase 1, catalase 2, C. elegans p53-like protein 1, and apoptosis enhancer 1 genes. The lead-, chromium-, and arsenite-exposed nematode, on the other hand, showed little change in gene expression. Alterations in growth and reproduction were observed in cadmium- and chromium-exposed worms. To consider a transgenic nematode as a biosensor for toxicity monitoring, the responses of stress-related gene promoters need to be tested with a variety of metals. The overall results suggest that cadmium exhibits a high level of tolerance compared to the other metals tested. Use of the responses of stress-related gene expression therefore has considerable potential as a sensitive biomarker for the diagnosis of cadmium contamination, and C. elegans seems to be a good biological model for this approach.

Toxic effects of di(2-ethylhexyl)phthalate on mortality, growth, reproduction and stress-related gene expression in the soil nematode Caenorhabditis elegans

In this study, di(2-ethylhexyl)phthalate (DEHP) toxicities to Caenorhabditis elegans were investigated using multiple toxic endpoints, such as mortality, growth, reproduction and stress-related gene expression, focusing on the identification of chemical-induced gene expression as a sensitive biomarker for DEHP monitoring. The possible use of C. elegans as a sentinel organism in the monitoring of soil ecosystem health was also tested by conducting the experiment on the exposure of nematode to field soil. Twenty-four-hour median lethal concentration (LC50) data suggest that DEHP has a relatively high potential of acute toxicity to C. elegans. Decreases in body length and egg number per worm observed after 24h of DEHP exposure may induce long-term alteration in the growth and reproduction of the nematode population. Based on the result from the C. elegans genome array and indicated in the literatures, stress proteins, metallothionein, vitellogenin, xenobiotic metabolism enzymes, apoptosis-related proteins, and antioxidant enzyme genes were selected as stress-related genes and their expression in C. elegans by DEHP exposure was analyzed semi-quantitatively. Expression of heat shock protein (hsp)-16.1 and hsp-16.2 genes was decreased by DEHP exposure. Expression of cytochrome P450 (cyp) 35a2 and glutathione-S-transferease (gst)-4, phase I and phase II of xenobiotic metabolism enzymes, was increased by DEHP exposure in a concentration-dependent manner. An increase in stress-related gene expressions occurred concomitantly with the deterioration on the physiological level, which suggests an increase in expression of those genes may not be considered as a homeostatic response but as a toxicity that might have physiological consequences. The experiment with the soil from the landfill site suggests that the potential of the C. elegans biomarker identified in laboratory conditions should be calibrated and validated for its use in situ.

Ecotoxicological evaluation of chlorpyrifos exposure on the nematode Caenorhabditis elegans

To investigate the effects of chlorpyrifos (CP), an organophosphorus insecticide, on the soil nematode Caenorhabditis elegans, the toxicity of the insecticide on the molecular, biochemical, and physiological levels were investigated upon sublethal exposure, and an acute toxicity test was conducted using lethality as an endpoint. To assess the molecular-level effect, stress-related gene expression was investigated, and the neurotoxicity indicator, acetylcholinesterase (AChE) activity was assessed as the biochemical-level response. Growth, reproduction and development were also studied as physiological-level responses. The overall results indicate that CP exposure leads to the alteration of the expression of some stress genes, such as of heat shock protein, metallothionein, vitellogenin and C. elegans p53-like protein genes; the inhibition of AChE activity; and the retardation of development. These data suggest that the toxicity of CP on C. elegans occurred in multiple biological organizations; nevertheless this is not sufficient to conclude that there is a casual relationship between them. Thus, direct experimental demonstrations of the wider relationships between the molecular/biochemical effects of CP exposure and their consequences at higher levels of biological organization are needed to fully understand the effects of this compound on C. elegans.

Involvement of Caenohabditis elegans MAPK Signaling Pathways in Oxidative Stress Response Induced by Silver Nanoparticles Exposure

In the present study, toxicity of silver nanoparticles (AgNPs) was investigated in the nematode, Caenohabditis elegans focusing on the upstream signaling pathway responsible for regulating oxidative stress, such as mitogen-activated protein kinase (MAPK) cascades. Formation of reactive oxygen species (ROS) was observed in AgNPs exposed C.elegans, suggesting oxidative stress as an important mechanism in the toxicity of AgNPs towards C. elegans. Expression of genes in MAPK signaling pathways increased by AgNPs exposure in less than 2-fold compared to the control in wildtype C.elegans, however, those were increased dramatically in sod-3 (gk235) mutant after 48 h exposure of AgNPs (i.e. 4-fold for jnk-1 and mpk-2; 6-fold for nsy-1, sek-1, and pmk-1, and 10-fold for jkk-1). These results on the expression of oxidative stress response genes suggest that sod-3 gene expression appears to be dependent on p38 MAPK activation. The high expressions of the pmk-1 gene 48 h exposure to AgNPs in the sod-3 (gk235) mutant can also be interpreted as compensatory mechanisms in the absence of important stress response genes. Overall results suggest that MAPK-based integrated stress signaling network seems to be involved in defense to AgNPs exposure in C.elegans.

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.

A cadmium toxicity assay using stress responsive Caenorhabditis elegans mutant strains.

To test the applicability of Caenorhabditis elegans mutant for toxicity screening, the sensitivity of cadmium (Cd) in C. elegans was investigated on 14 mutant strains using median lethal concentration (LC50) tests, with further analysis on growth and reproduction conducted on five selected strains. The 24h LC50 of Cd observed on the wildtype and mutant strains of C. elegans was in the order of age-1(hx546)>mtl-2(gk125)>sod-3(gk235)>daf-21(p673)>cyp35a2(gk317)>skn-1(or13)>daf-12(rh62rh157)>hsp-16.2(gk249)>daf-18(e1375)>ctl-2(ok1137)>wildtype(N2)>sod-1(or13)>daf-16(mu86)>cep-1(gk138)>cdr-2(ok1996). Compared to the wildtype response, a decreased reproduction potential was observed in mtl-2(gk125), sod-3(gk235), cdr-2(ok1996) and cep-1(gk138) strains. To gain a mechanistic understanding of different sensitivities of the mutant strains, a time-course gene expression analysis was also performed on the five genes. A dramatic increase in the expression of the mtl-2 gene due to Cd exposure confirmed the importance of this gene in C. elegans Cd toxicity. An increased expression of the sod-3 gene at the longer exposure time period (48h) suggests that oxidative stress may not be a direct toxic mechanism, but may rather be a consequence of Cd toxicity. Even though, LC50 values for the age-1(hx546) mutant strain were the highest among the tested strains, the response on the reproduction potential in age-1(hx546) mutant was unchanged compared to the wildtype, and the age-1 gene expression remained unaltered on exposure to Cd, which may be interpreted as the maintenance of age-1 expression level is needed for the exertion of Cd toxicity; however, the role of the age-1 gene in Cd toxicity may not be via a reproduction-related pathway. The overall results suggest that the C. elegans mutant assay seems to be a promising tool for the study of toxic mechanisms, as well as for toxicity screening in ecotoxicological research.

Maintaining the Constant Exposure Condition for an Acute Caenorhabditis elegans Mortality Test Using Passive Dosing

Objectives Maintaining the constant exposure to hydrophobic organic compouds in acute toxicity tests is one of the most difficult issues in the evaluation of their toxicity and corresponding risks. Passive dosing is an emerging tool to keep constant aqueous concentration because of the overwhelming mass loaded in the dosing phase. The primary objectives of this study were to develop the constant exposure condition for an acute mortality test and to compare the performance of the passive dosing method with the conventional spiking with co-solvent. Methods A custom cut polydimethylsiloxane (PDMS) tubing loaded with benzyl butyl phthalate (BBP) was placed in each well of a 24-well plate containing assay medium. The rate of the release of BBP from PDMS was evaluated by measuring the change in the concentration of BBP in the assay medium. The efficiency of maintaining constant exposure condition was also evaluated using a simple two-compartment mass transport model employing a film-diffusion theory. An acute mortality test using 10 C. elegans in each well was conducted for the evaluation of the validity of passive dosing and the comparative evaluation of the passive dosing method and the conventional spiking method. Results Free concentration in the assay medium reached 95% steady state value within 2.2 hours without test organisms, indicating that this passive dosing method is useful for an acute toxicity test in 24 hours. The measured concentration after the mortality test agreed well with the estimated values from partitioning between PDMS and the assay medium. However, the difference between the nominal and the free concentration became larger as the spiked concentration approached water solubility, indicating the instability of the conventional spiking with a co-solvent. Conclusions The results in this study support that passive dosing provides a stable exposure condition for an acute toxicity test. Thus, it is likely that more reliable toxicity assessment can be made for hydrophobic chemicals using passive dosing.