Life cycle toxicity assessment of earthworms exposed to cadmium-contaminated soils.

Cadmium (Cd) is of great concern in the soil environment and it can damage terrestrial organisms. The purpose of this study was to employ a toxicokinetic/toxicodynamic (TK/TD) approach to investigate the effects of toxicologically relevant Cd accumulation on the life cycle growth of earthworms (Lumbricus rubellus and Eisenia fetida) and to assess potential terrestrial ecosystem risk. We reanalyzed growth toxicity and whole body and pellet accumulation data linked with TK/TD and life cycle growth models to estimate key rate constants. The growth risk of earthworms exposed to Cd was also assessed. This study found that the estimated whole body killing rate constant (0.114 g d µg-1) was much lower than that of pellet (0.248 g d µg-1). The recovery rate constant for whole body (6.02 d-1) was much higher than that of pellet (2.91 d-1). We also employed a life cycle-based probabilistic risk assessment model to estimate the growth inhibition risk for earthworms in response to environmentally relevant concentrations of Cd in Taiwan. Results showed that earthworms had a 90% growth inhibition probability risk of body weight, which was lower than 872.33 mg based on assessment of toxicologically relevant Cd accumulation. This study suggests that toxicologically relevant Cd accumulation could accurately reflect the capacity of Cd toxicity to earthworms. The integrated life cycle toxicity of earthworms exposed to Cd in this study provides a robust and applicable tool for the management of ecological risk assessment of Cd-contaminated soil.

Selenite enhances immune response against Pseudomonas aeruginosa PA14 via SKN-1 in Caenorhabditis elegans.

BACKGROUND: Selenium (Se) is an important nutrient that carries out many biological processes including maintaining optimal immune function. Here, inorganic selenite (Se(IV)) was evaluated for its pathogen resistance and potential-associated factors in Caenorhabditis elegans. The immune effects of Se(IV) were investigated by examining the responses of C. elegans to Pseudomonas aerugonisa PA14 strain. PRINCIPAL FINDINGS: Se(IV)-treated C. elegans showed increased survival under PA14 infection compared with untreated controls. The significant pathogen resistance of Se(IV) on C. elegans might not be attributed to the effects of Se(IV) on PA14 as Se(IV) showed no effect on bacterial quorum-sensing and virulence factors of PA14. This study showed that Se(IV) enhanced the expression of a gene pivotal for the innate immunity in C. elegans. The study found that the pathogen-resistant phenotypes contributed by Se(IV) was absent from the skn-1 mutant worms. Moreover, Se(IV) influenced the subcellular distribution of SKN-1/Nrf in C. elegans upon PA14 infection. Furthermore, Se(IV) increased mRNA levels of SKN-1 target genes (gst-4 and gcs-1). CONCLUSIONS: This study found evidence of Se(IV) protecting C. elegans against P. aeruginosa PA14 infection by exerting effects on the innate immunity of C. elegans that is likely mediated via regulation of a SKN-1-dependent signaling pathway.

Assessment of selenium toxicity on the life cycle of Caenorhabditis elegans.

Selenium (Se) is a growing problem of global concern. Se can cause adverse effects on reproductive systems, which have been linked to declines in animal populations. The soil nematode Caenorhabditis elegans (C. elegans) is a ubiquitous soil organism that is increasingly utilized as a model organism in aquatic and soil toxicology. In the present study, the experimental data for individual body length, survival rate, brood size, and hatching rate were used to evaluate the possible effects of selenite [Se(IV)] on C. elegans. A stage-classified matrix model was applied to the experimental data to provide information on the population dynamics of C. elegans and to assess the Se(IV)-affected asymptotic population growth rate. Estimates of the survival probability showed significant decreases in survival at all stages when C. elegans was exposed to Se(IV). The growth probability of C. elegans in the L1 stage showed the most significant decline, from 0.11 h(-1) (for the control) to 0.04 h(-1) [for exposure to 3 mM Se(IV)]. These results showed that Se(IV) has a profound impact on C. elegans population dynamics. The asymptotic population growth rate (λ) was found to range from 1.00 to 0.64 h(-1) for increasing Se(IV) concentrations, implying a potential risk of population decrease for C. elegans exposure to a Se(IV)-contaminated environment. Our study shows how a mechanistic view based on the Se(IV) effects on the soil nematode C. elegans can promote a life cycle toxicity assessment. An important implication of this analysis is that mathematical models can be used to produce a population stage structure, to give clarity to the analysis of the key population-level endpoint (the asymptotic population growth rate) of population dynamics, and to evaluate the influences for the response of other species to environmental Se. These models sequentially provide candidate environmental criteria for the evaluation of the population impact of Se.

Essential oil alloaromadendrene from mixed-type Cinnamomum osmophloeum leaves prolongs the lifespan in Caenorhabditis elegans.

Cinnamomum osmophloeum Kaneh. is an indigenous tree species in Taiwan. The present study investigates phytochemical characteristics, antioxidant activities, and longevity of the essential oils from the leaves of the mixed-type C. osmophloeum tree. We demonstrate that the essential oils from leaves of mixed-type C. osmophloeum exerted in vivo antioxidant activities on Caenorhabditis elegans. In addition, minor (alloaromadendrene, 5.0%) but not major chemical components from the leaves of mixed-type C. osmophloeum have a key role against juglone-induced oxidative stress in C. elegans. Additionally, alloaromadendrene not only acts protective against oxidative stress but also prolongs the lifespan of C. elegans. Moreover, mechanistic studies show that DAF-16 is required for alloaromadendrene-mediated oxidative stress resistance and longevity in C. elegans. The results in the present study indicate that the leaves of mixed-type C. osmophloeum and essential oil alloaromadendrene have the potential for use as a source for antioxidants or treatments to delay aging.

Antioxidant activity and delayed aging effects of hot water extract from Chamaecyparis obtusa var. formosana leaves.

The antioxidant activity and delayed aging effects of hot water extracts from leaves of Chamaecyparis obtusa var. formosana were investigated. Free radical, superoxide radical scavenging, and total phenolic content assays were employed to evaluate the in vitro activities of the extracts. In addition, in vivo assays using the nematode Caenorhabditis elegans were also performed in this study. The results showed that among all soluble fractions obtained from the extracts, the ethyl acetate-soluble fraction has the best in vitro and in vivo antioxidant activities. Moreover, it decreased significantly the deposition of lipofuscin (aging pigment) and extended the lifespan of C. elegans. Bioactivity-guided fractionation yielded six potent antioxidant constituents from the ethyl acetate-soluble fraction, namely, catechin, quercetin, quercetin-3-O-α-rhamnoyranoside, myricetin-3-O-α-rhamnoyranoside, vanillic acid, and 4-hydroxybenzoic acid. Quercetin-3-O-α-rhamnoyranoside pretreatment showed the highest survival of C. elegans upon juglone exposure. Taken together, the results revealed that hot water extracts from C. obtusa var. formosana leaves have the potential to be used as a source for antioxidant or delayed aging health food.

Selenite protects Caenorhabditis elegans from oxidative stress via DAF-16 and TRXR-1.

SCOPE: Selenium is an essential micronutrient. In the present study, trace amount of selenite (0.01 µM) was evaluated for oxidative stress resistance and potential associated factors in Caenorhabditis elegans. METHODS AND RESULTS: Selenite-treated C. elegans showed an increased survival under oxidative stress and thermal stress compared to untreated controls. Further studies demonstrated that the significant stress resistance of selenite on C. elegans could be attributed to its in vivo free radical-scavenging ability. We also found that the oxidative and thermal stress resistance phenotypes by selenite were absent from the forkhead transcription factor daf-16 mutant worms. Moreover, selenite influenced the subcellular distribution of DAF-16 in C. elegans. Furthermore, selenite increased mRNA levels of stress-resistance-related proteins, including superoxide dismutase-3 and heat shock protein-16.2. Additionally, selenite (0.01 µM) upregulated expressions of transgenic C. elegans carrying sod-3::green fluorescent protein (GFP) and hsp-16.2::GFP, whereas this effect was abolished by feeding daf-16 RNA interference in C. elegans. Finally, unlike the wild-type N2 worms, the oxidative stress resistance phenotypes by selenite were both absent from the C. elegans selenoprotein trxr-1 mutant worms and trxr-1 mutants feeding with daf-16 RNA interference. CONCLUSION: These findings suggest that the antioxidant effects of selenite in C. elegans are mediated via DAF-16 and TRXR-1.

Phthalates induce neurotoxicity affecting locomotor and thermotactic behaviors and AFD neurons through oxidative stress in Caenorhabditis elegans.

BACKGROUND: Phthalate esters are ubiquitous environmental contaminants and numerous organisms are thus exposed to various levels of phthalates in their natural habitat. Considering the critical, but limited, research on human neurobehavioral outcomes in association with phthalates exposure, we used the nematode Caenorhabditis elegans as an in vivo model to evaluate phthalates-induced neurotoxicity and the possible associated mechanisms. PRINCIPAL FINDINGS: Exposure to phthalates (DEHP, DBP, and DIBP) at the examined concentrations induced behavioral defects, including changes in body bending, head thrashing, reversal frequency, and thermotaxis in C. elegans. Moreover, phthalates (DEHP, DBP, and DIBP) exposure caused toxicity, affecting the relative sizes of cell body fluorescent puncta, and relative intensities of cell bodies in AFD neurons. The mRNA levels of the majority of the genes (TTX-1, TAX-2, TAX-4, and CEH-14) that are required for the differentiation and function of AFD neurons were decreased upon DEHP exposure. Furthermore, phthalates (DEHP, DBP, and DIBP) exposure at the examined concentrations produced elevated intracellular reactive oxygen species (ROS) in C. elegans. Finally, pretreatment with the antioxidant ascorbic acid significantly lowered the intracellular ROS level, ameliorated the locomotor and thermotactic behavior defects, and protected the damage of AFD neurons by DEHP exposure. CONCLUSIONS: Our study suggests that oxidative stress plays a critical role in the phthalate esters-induced neurotoxic effects in C. elegans.

Protective efficacy of selenite against lead-induced neurotoxicity in Caenorhabditis elegans.

BACKGROUND: Selenium is an essential micronutrient that has a narrow exposure window between its beneficial and toxic effects. This study investigated the protective potential of selenite (IV) against lead (Pb(II))-induced neurotoxicity in Caenorhabditis elegans. PRINCIPAL FINDINGS: The results showed that Se(IV) (0.01 µM) pretreatment ameliorated the decline of locomotion behaviors (frequencies of body bends, head thrashes, and reversal ) of C. elegans that are damaged by Pb(II) (100 µM) exposure. The intracellular ROS level of C. elegans induced by Pb(II) exposure was significantly lowered by Se(IV) supplementation prior to Pb(II) exposure. Finally, Se(IV) protects AFD sensory neurons from Pb(II)-induced toxicity. CONCLUSIONS: Our study suggests that Se(IV) has protective activities against Pb(II)-induced neurotoxicity through its antioxidant property.

Protein engineering of oxidosqualene-lanosterol cyclase into triterpene monocyclase.

A computational modeling/protein engineering approach was applied to probe H234, C457, T509, Y510, and W587 within Saccharomyces cerevisiae oxidosqualene-lanosterol cyclase (ERG7), which spatially affects the C-10 cation of lanosterol formation. Substitution of Trp587 to aromatic residues supported the "aromatic hypothesis" that the π-electron-rich pocket is important for the stabilization of electron-deficient cationic intermediates. The Cys457 to Gly and Thr509 to Gly mutations disrupted the pre-existing H-bond to the protonating Asp456 and the intrinsic His234 : Tyr510 H-bond network, respectively, and generated achilleol A as the major product. An H234W/Y510W double mutation altered the ERG7 function to achilleol A synthase activity and generated achilleol A as the sole product. These results support the concept that a few-ring triterpene synthase can be derived from polycyclic cyclases by reverse evolution, and exemplify the power of computational modeling coupled with protein engineering both to study the enzyme's structure-function-mechanism relationships and to evolve new enzymatic activity.

The cysteine 703 to isoleucine or histidine mutation of the oxidosqualene-lanosterol cyclase from Saccharomyces cerevisiae generates an iridal-type triterpenoid.

The Cys703 to Ile or His mutation within Saccharomyces cerevisiae oxidosqualene-lanosterol cyclase ERG7 (ERG7(C703I/H)) generates an unusual truncated bicyclic rearranged intermediate, (8R,9R,10R)-polypoda-5,13E,17E,21-tetraen-3ß-ol, related to iridal-skeleton triterpenoid. Numerous oxidosqualene-cyclized truncated intermediates, including tricyclic, unrearranged tetracyclic with 17α/ß exocyclic hydrocarbon side chain, rearranged tetracyclic, and chair-chair-chair tricyclic intermediates (compounds 3-9), were also isolated from the ERG7(C703X) site-saturated mutations or the ERG7(F699T/C703I) double mutation, indicating the functional role of the Cys703 residue in stabilizing the bicyclic C-8 cation and the rearranged intermediate or interacting with Phe699, and opened a new avenue of engineering ERG7 for producing biological active agents.

In vivo antioxidant activities of essential oils and their constituents from leaves of the Taiwanese Cinnamomum osmophloeum.

Cinnamomum osmophloeum Kaneh is an indigenous tree species in Taiwan. In this study, phytochemical characteristics and antioxidant activities of the essential oils and key constituents from the leaves of two C. osmophloeum clones were investigated. The two trees possess two chemotypes, which were classified as the cinnamaldehyde type and camphor type. We demonstrated that the essential oils from C. osmophloeum leaves exerted in vivo antioxidant activities in Caenorhabditis elegans. In addition, trans-cinnamaldehyde and D-(+)-camphor, which respectively represent the major compounds in the cinnamaldehyde-type and camphor-type trees, exerted significant in vivo antioxidant activities against juglone-induced oxidative stress in C. elegans. Moreover, expressions of antioxidative-related genes, including superoxide dismutase (SOD) and glutathione S-transferase (GST), were significantly induced by trans-cinnamaldehyde and D-(+)-camphor from C. osmophloeum leaves. Our results showed that the essential oils from C. osmophloeum leaves and their major compounds might have good potential for further development as nutraceuticals or antioxidant remedies.

Curcumin-mediated lifespan extension in Caenorhabditis elegans.

Curcumin is the active ingredient in the herbal medicine and dietary spice, turmeric (Curcuma longa). It has a wide range of biological activities, including anti-inflammatory, antioxidant, chemopreventive, and chemotherapeutic activities. We examined the effects of curcumin on the lifespan and aging in Caenorhabditis elegans, and found that it responded to curcumin with an increased lifespan and reduced intracellular reactive oxygen species and lipofuscin during aging. We analyzed factors that might influence lifespan extension by curcumin. We showed that lifespan extension by curcumin in C. elegans is attributed to its antioxidative properties but not its antimicrobial properties. Moreover, we showed that lifespan extension had effects on body size and the pharyngeal pumping rate but not on reproduction. Finally, lifespan tests with selected stress- and lifespan-relevant mutant strains revealed that the lifespan-extending phenotype was absent from the osr-1, sek-1, mek-1, skn-1, unc-43, sir-2.1, and age-1 mutants, whereas curcumin treatment prolonged the lifespan of mev-1 and daf-16 mutants. Our study has unraveled a diversity of modes of action and signaling pathways to longevity and aging with curcumin exposure in vivo.

Lung cancer risk in relation to traffic-related nano/ultrafine particle-bound PAHs exposure: a preliminary probabilistic assessment.

Exposures to carcinogenic polycyclic aromatic hydrocarbons (PAHs) have been linked to human lung cancer. The purpose of this study was to assess lung cancer risk caused by inhalation exposure to nano/ultrafine particle-bound PAHs at the population level in Taiwan appraised with recent published data. A human respiratory tract model was linked with a physiologically based pharmacokinetic model to estimate deposition fraction and internal organic-specific PAHs doses. A probabilistic risk assessment framework was developed to estimate potential lung cancer risk. We reanalyzed particle size distribution, total-PAHs, particle-bound benzo(a)pyrene (B[a]P) and PM concentrations. A dose-response profile describing the relationships between external B[a]P concentration and lung cancer risk response was constructed based on population attributable fraction (PAF). We found that 90% probability lung cancer risks ranged from 10(-5) to 10(-4) for traffic-related nano and ultrafine particle-bound PAHs, indicating a potential lung cancer risk. The particle size-specific PAF-based excess annual lung cancer incidence rate due to PAHs exposure was estimated to be less than 1 per 100,000 population, indicating a mild risk factor for lung cancer. We concluded that probabilistic risk assessment linked PAF for limiting cumulative PAHs emissions to reduce lung cancer risk plays a prominent role in future government risk assessment program.

Mutation of isoleucine 705 of the oxidosqualene-lanosterol cyclase from Saccharomyces cerevisiae affects lanosterol's C/D-ring cyclization and 17α/ß-exocyclic side chain stereochemistry.

Site-saturated substitution in Saccharomyces cerevisiae oxidosqualene-lanosterol cyclase at Ile705 position produced three chair-boat-chair (C-B-C) truncated tricyclic compounds, two 17α-exocyclic protosteryl intermediates, two protosteryl C-17 truncated rearranged intermediates and the normal biosynthetic product, lanosterol. These results indicated the importance of the Ile705 residue in affecting lanosterol's C/D ring stabilization including 6-6-5 tricyclic and protosteryl C-17 cations and 17α/ß-exocyclic side chain stereochemistry.

The ameliorative and toxic effects of selenite on Caenorhabditis elegans.

Selenium is an essential trace nutrient that has a narrow exposure window between its beneficial and detrimental effects. We investigated how selenium affected the development, fertility, and cholinergic signaling of the nematode, Caenorhabditis elegans. Our results showed that selenite supplementation at 0.01 and 0.05 µM accelerated development and increased the brood size, while the addition of 20 µM selenite retarded the developmental rate and decreased the brood size. We also showed that the 0.01 µM selenite-pretreated nematodes were more resistant to paralysis induced by an acetylcholinesterase inhibitor, aldicarb, and a nicotinic acetylcholine receptor agonist, levamisole, compared to untreated worms. In contrast, 20 µM selenite-pretreated animals were more sensitive to aldicarb- and levamisole-induced paralysis compared to untreated worms. We measured the internal selenium in supplemented worms using inductively coupled plasma atomic emission spectroscopy, and the data obtained suggested that selenite added to growth medium was taken up by the worms. Taken together, these results suggest that selenite exerts both ameliorative and toxic effects on C.elegans, depending on the amount. Our investigations here thus reinforce our understanding of the ameliorative and toxic effects of selenium on development, reproduction, and cholinergic signaling.

Caenorhabditis elegans bicarbonate transporter ABTS-1 is involved in arsenite toxicity and cholinergic signaling.

Arsenic poisoning affects millions of people worldwide. Although there is accumulating evidence to suggest that the nervous system is a target of arsenic, relatively little information is known regarding its effects on the nervous system. The effects of arsenite on the nervous system in Caenorhabditis elegans were investigated in the present study. We found that abts-1, which encodes a Na(+)-dependent Cl(-)/HCO(3)(-) transporter, is required to protect C. elegans from arsenite toxicity. The abts-1::GFP transgene is primarily expressed in neurons and the hypodermis, but stronger expression was also observed in the pharynx and body wall muscle cells after exposure to arsenite. The steady-state level of ABTS-1 mRNA increased in response to arsenite exposure. We showed that worms lacking abts-1 are hypersensitive to the paralytic effects of the cholinesterase inhibitor, aldicarb, and the nicotinic acetylcholine receptor agonist, levamisole. We also showed that arsenite enhanced sensitivity to aldicarb and levamisole in abts-1 mutant worms. Our results indicate neuronal effects of arsenite and the ABTS-1 bicarbonate transporter.

Alteration of the substrate's prefolded conformation and cyclization stereochemistry of oxidosqualene-lanosterol cyclase of Saccharomyces cerevisiae by substitution at phenylalanine 699.

The Saccharomyces cerevisiae ERG7(Phe699) mutants produced one chair-chair-chair (C-C-C) and two chair-boat-chair (C-B-C) truncated tricyclic compounds, one tetracyclic 17alpha-exocyclic unrearranged intermediate, and two 17beta-exocyclic truncated rearranged intermediates. These results provided direct evidence for the importance of the residue in affecting mechanistic transitions between C-B-C and C-C-C substrate conformation and between the 17alpha- and 17beta-exocyclic side chain stereochemistry as well as in stabilizing the 6-6-5 tricyclic and the protosteryl C-17 cations.