Metallomic mapping of gut and brain in heavy metal exposed earthworms: A novel paradigm in ecotoxicology

This study explored the uptake of lead in the epigeic earthworm Dendrobaena veneta exposed to 0, 1000, and 2500 μg Pb/g soil. The soil metal content was extracted using strong acid digestion and water leaching, and analysed by means of Inductively Coupled Plasma Mass Spectrometry (ICP-MS) to estimate absolute and bioavailable concentrations of metals in the soil. The guts and heads of lead-exposed earthworms were processed into formalin-fixed and paraffin embedded sections for high-resolution multi-element metallomic imaging via Laser Ablation ICP-MS (LA-ICP-MS). Metallomic maps of phosphorus, zinc, and lead were produced at 15-μm resolution in the head and gut of D. veneta. Additional 4-μm resolution metallomic maps of the earthworm brains were taken, revealing the detailed localisation of metals in the brain. The Pb bioaccumulated in the chloragogenous tissues of the earthworm in a dose-dependent manner, making it possible to track the extent of soil contamination. The bioaccumulation of P and Zn in earthworm tissues was independent of Pb exposure concentration. This approach demonstrates the utility of LA-ICP-MS as a powerful approach for ecotoxicology and environmental risk assessments.

Dysfunction in atox-1 and ceruloplasmin alters labile Cu levels and consequently Cu homeostasis in C. elegans

Copper (Cu) is an essential trace element, however an excess is toxic due to its redox properties. Cu homeostasis therefore needs to be tightly regulated via cellular transporters, storage proteins and exporters. An imbalance in Cu homeostasis has been associated with neurodegenerative disorders such as Wilson's disease, but also Alzheimer's or Parkinson's disease. In our current study, we explored the utility of using Caenorhabditis elegans (C. elegans) as a model of Cu dyshomeostasis. The application of excess Cu dosing and the use of mutants lacking the intracellular Cu chaperone atox-1 and major Cu storage protein ceruloplasmin facilitated the assessment of Cu status, functional markers including total Cu levels, labile Cu levels, Cu distribution and the gene expression of homeostasis-related genes. Our data revealed a decrease in total Cu uptake but an increase in labile Cu levels due to genetic dysfunction, as well as altered gene expression levels of Cu homeostasis-associated genes. In addition, the data uncovered the role ceruloplasmin and atox-1 play in the worm's Cu homeostasis. This study provides insights into suitable functional Cu markers and Cu homeostasis in C. elegans, with a focus on labile Cu levels, a promising marker of Cu dysregulation during disease progression.

Juggling cadmium detoxification and zinc homeostasis: A division of labour between the two C. elegans metallothioneins

The chemical properties of toxic cadmium and essential zinc are very similar, and organisms require intricate mechanisms that drive selective handling of metals. Previously regarded as unspecific "metal sponges", metallothioneins (MTLs) are emerging as metal selectivity filters. By utilizing C. elegans mtl-1 and mtl-2 knockout strains, metal accumulation in single worms, single copy fluorescent-tagged transgenes, isoform specific qPCR and lifespan studies it was possible to demonstrate that the handling of cadmium and zinc by the two C. elegans metallothioneins differs fundamentally: the MTL-2 protein can handle both zinc and cadmium, but when it becomes unavailable, either via a knockout or by elevated cadmium exposure, MTL-1 takes over zinc handling, leaving MTL-2 to sequester cadmium. This division of labour is reflected in the folding behaviour of the proteins: MTL-1 folded well in presence of zinc but not cadmium, the reverse was the case for MTL-2. These differences are in part mediated by a zinc-specific mononuclear His3Cys site in the C-terminal insertion of MTL-1; its removal affected the entire C-terminal domain and may shift its metal selectivity towards zinc. Overall, we uncover how metallothionein isoform-specific responses and protein properties allow C. elegans to differentiate between toxic cadmium and essential zinc.

Environmental carcinogen benzo[a]pyrene alters neutral lipid storage via a cyp-35A2 mediated pathway in Caenorhabditis elegans

Polycyclic aromatic hydrocarbons (PAHs), in particular benzo [a]pyrene (BaP), have been identified as carcinogenic components of tobacco smoke. In mammals, the toxicological response to BaP-diol-epoxide is driven by cytochrome P450 (CYP1A1), a pathway which is absent in Caenorhabditis elegans. In contrast, in worms prominently the CYP-35 enzyme family seems to be induced after BaP exposure. In C. elegans, BaP exposure reduces the accumulation of lysosomal neutral lipids in a dose dependent manner and the deletion of cyp-35A2 results in a significant elevation of neutral lipid metabolism. A cyp-35A2:mCherry;unc-47:GFP dual-labelled reporter strain facilitated the identification of three potential upstream regulators that drive BaP metabolism in worms, namely elt-2, nhr-49 and fos-1. This newly described reporter line is a powerful resource for future large-scale RNAi regarding toxicology and lipid metabolism screens.

MosSCI-mediated exogenous gene expression is modulated by genomic positioning

Although the Mos1-mediated single-copy insertion (MosSCI) technique has been widely used to generate stable transgenic Caenorhabditis elegans strains, the link between stability of expression and integration site still needs to be explored. Here, experimental evidence is provided that transgenes are not able to match the level of transcription of their native counterpart, and that insertions at certain locations can result in an external stress-mediated increase in expression. Insertion site ttTi5605 on chromosome II was shown to be a superior location, at least when introducing reproduction related genes. Thus, this study provides a reference for the selection of an optimal site for MosSCI which provides acceptable expression performance whilst minimizing undesirable secondary effects.

A miniaturized passive sampling-based workflow for monitoring chemicals of emerging concern in water

The miniaturization of a full workflow for identification and monitoring of contaminants of emerging concern (CECs) is presented. Firstly, successful development of a low-cost small 3D-printed passive sampler device (3D-PSD), based on a two-piece methacrylate housing that held up to five separate 9 mm disk sorbents, is discussed. Secondly, a highly sensitive liquid chromatography-tandem mass spectrometry (LC-MS/MS) method reduced the need for large scale in-laboratory apparatus, solvent, reagents and reference material quantities for in-laboratory passive sampler device (PSD) calibration and extraction. Using hydrophilic-lipophilic balanced sorbents, sampling rates (R_s) were determined after a low 50 ng L^-1 exposure over seven days for 39 pesticides, pharmaceuticals, drug metabolites and illicit drugs over the range 0.3 to 12.3 mL day^-1. The high sensitivity LC-MS/MS method enabled rapid analysis of river water using only 10 μL of directly injected sample filtrate to measure occurrence of 164 CECs and sources along 19 sites on the River Wandle, (London, UK). The new 3D-PSD was then field-tested over seven days at the site with the highest number and concentration of CECs, which was down-river from a wastewater treatment plant. Almost double the number of CECs were identified in 3D-PSD extracts across sites in comparison to water samples (80 versus 42 CECs, respectively). Time-weighted average CEC concentrations ranged from 8.2 to 845 ng L^-1, which were generally comparable to measured concentrations in grab samples. Lastly, high resolution mass spectrometry-based suspect screening of 3D-PSD extracts enabled 113 additional compounds to be tentatively identified via library matching, many of which are currently or are under consideration for the EU Watch List. This miniaturized workflow represents a new, cost-effective, and more practically efficient means to perform passive sampling chemical monitoring at a large scale. SYNOPSIS: Miniaturized, low cost, multi-disk passive samplers enabled more efficient multi-residue chemical contaminant characterization, potentially for large-scale monitoring programs.

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

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

Cryptic speciation and blurred species boundaries of the earthworm: A challenge for soil-based toxicological risk assessments

The toxicological risk assessment of chemicals is largely based on the Organization for Economic Co-operation and Development (OECD) guidelines. These internationally approved methodologies help shape policy and political strategy of environment and human health issues. Risk assessments which pertain to soil biota 'recruit' sentinel organisms, including the earthworm Eisenia fetida. Despite E. fetida being morphologically similar to Dendrobaena veneta, they are characterized by a several-fold difference in sensitivity to xenobiotics. Worms, sold as either as pure E. fetida stocks or E. fetida/D. veneta mixed cultures, were obtained from five commercial suppliers. The species identity of 25 earthworms was determined by sequencing the cytochrome c oxidase subunit 2 (COII). We revealed that only one of 25 worms was E. fetida, the remaining worms were all identified as D. veneta. This underlines the notion that E. fetida and D. veneta are easily mis-identified. The occurrence of cryptic speciation combined with the well-documented species-specific variation in toxicological responses highlights the pressing need to accurately classify earthworms to species level prior to any toxicological research. Only this will ensure the validity and reliability of risk assessments.

Molecular genetic and biochemical characterization of a putative family of zinc metalloproteins in Caenorhabditis elegans

The first characterization of W08E12.2, W08E12.3, W08E12.4 and W08E12.5, four putative metalloproteins in C. elegans. (A) phase contrast microscopy, (B) fluorescence microscopy of PW08E12.3;W08E12.4::GFP.

Four highly similar genes (W08E12.2, W08E12.3, W08E12.4 and W08E12.5) which are consecutively aligned on chromosome IV of the C. elegans genome are predicted to code for small (120–141aa) yet cysteine rich (18–19 cysteines) proteins. Cloning and sequencing of the genomic regions of the isoforms confirmed the presence and order of all genes. The generation of transgenic worms strains with an integrated single copy or extrachromosomal multi-copy PW08E12.3;W08E12.4::GFP uncovered that W08E12.3 and W08E12.4 are constitutively expressed in the pharynx and significantly induced in worms exposed to 100 μM Zn. Knockdown by RNAi did not have a marked consequence on reproductive performance nor was a Zn-dependent effect on nematode growth observed. However, RNAi of these genes led to an accumulation of Zn in the intestinal cells. W08E12.3 was recombinantly expressed in E. coli and the purified protein was shown to be able to bind up to 6.5 Zn molecules at neutral pH. Zn-binding was acid-labile and the apo protein was observed at pH < 4.3. This characterization suggests W08E12.2, W08E12.3, W08E12.4 and W08E12.5 belong to a family of putative Metalloproteins which, akin to metallothioneins, may play an important role in Zn-sensing, homeostasis and/or detoxification.

Proanthocyanidins of Natural Origin: Molecular Mechanisms and Implications for Lipid Disorder and Aging-Associated Diseases

Proanthocyanidins are phytonutrients formed by oligomerization or polymerization of subunits catechin, epicatechin, and their gallic acid esters. Proanthocyanidins are a component of many plants and thus form an integral part of the human diet. Oligomeric proanthocyanidins are currently marketed as medicinal products that target vascular disorders and chronic pathological conditions, many of which are age-associated. Proanthocyanidins are also characterized by their effects on energy homeostasis. Not dissimilar to their chemically synthesized counterparts, naturally extracted proanthocyanidins act via inhibition of lipases, stimulation of energy expenditure, or suppression of appetite. Here we review the current knowledge-base and highlight challenges and future impacts regarding involvement of proanthocyanidins in global lipid metabolism, with a focus on the molecular mechanisms and pathological conditions that progress with aging.

Metallothionein 2 and Heat Shock Protein 72 Protect Allolobophora chlorotica from Cadmium But Not Nickel or Copper Exposure: Body Malformation and Coelomocyte Functioning

Earthworms serve as good indicators of heavy metal contamination due to their innate sensitivity towards soil pollution. However, to date, not many studies have focused on endogeic earthworms, such as the omnipresent Allolobophora chlorotica. The current study was designed to verify whether this earthworm could serve as a novel distinctively susceptible species for environmental contamination studies. We show that the dermal exposure to Cu, Ni, and Cd affected the mortality and morphology of A. chlorotica, and the number and functioning of coelomocytes. These features particularly were pronounced in animals treated with Ni and Cu and interestingly to a lesser extend with Cd. In contrast, Cd induced a strong expression of metallothioneins (MT-2) and heat shock proteins (HSP72). The presence of MT-2 was detected not only in coelomocytes but also in the intestine, blood vessels, and epidermis. In conclusion, Allolobophora chlorotica coelomocytes are adopted to respond differentially to various heavy metals, generating powerful response towards potentially most dangerous exogenous non-essential elements.

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

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

Deletion of Phytochelatin Synthase Modulates the Metal Accumulation Pattern of Cadmium Exposed C. elegans

Environmental metal pollution is a growing health risk to flora and fauna. It is therefore important to fully elucidate metal detoxification pathways. Phytochelatin synthase (PCS), an enzyme involved in the biosynthesis of phytochelatins (PCs), plays an important role in cadmium detoxification. The PCS and PCs are however not restricted to plants, but are also present in some lower metazoans. The model nematode Caenorhabditis elegans, for example, contains a fully functional phytochelatin synthase and phytochelatin pathway. By means of a transgenic nematode strain expressing a pcs-1 promoter-tagged GFP (pcs-1::GFP) and a pcs-1 specific qPCR assay, further evidence is presented that the expression of the C. elegans phytochelatin synthase gene (pcs-1) is transcriptionally non-responsive to a chronic (48 h) insult of high levels of zinc (500 μM) or acute (3 h) exposures to high levels of cadmium (300 μM). However, the accumulation of cadmium, but not zinc, is dependent on the pcs-1 status of the nematode. Synchrotron based X-ray fluorescence imaging uncovered that the cadmium body burden increased significantly in the pcs-1(tm1748) knockout allele. Taken together, this suggests that whilst the transcription of pcs-1 may not be mediated by an exposure zinc or cadmium, it is nevertheless an integral part of the cadmium detoxification pathway in C. elegans.

Adsorbable organic bromine compounds (AOBr) in aquatic samples: a nematode-based toxicogenomic assessment of the exposure hazard

Elevated levels of adsorbable organic bromine compounds (AOBr) have been detected in German lakes, and cyanobacteria like Microcystis, which are known for the synthesis of microcystins, are one of the main producers of natural organobromines. However, very little is known about how environmental realistic concentrations of organobromines impact invertebrates. Here, the nematode Caenorhabditis elegans was exposed to AOBr-containing surface water samples and to a Microcystis aeruginosa-enriched batch culture (MC-BA) and compared to single organobromines and microcystin-LR exposures. Stimulatory effects were observed in certain life trait variables, which were particularly pronounced in nematodes exposed to MC-BA. A whole genome DNA-microarray revealed that MC-BA led to the differential expression of more than 2000 genes, many of which are known to be involved in metabolic, neurologic, and morphologic processes. Moreover, the upregulation of cyp- and the downregulation of abu-genes suggested the presence of chronic stress. However, the nematodes were not marked by negative phenotypic responses. The observed difference in MC-BA and microcystin-LR (which impacted lifespan, growth, and reproduction) exposed nematodes was hypothesized to be likely due to other compounds within the batch culture. Most likely, the exposure to low concentrations of organobromines appears to buffer the effects of toxic substances, like microcystin-LR.

The double mutation of cytochrome P450's and fatty acid desaturases affect lipid regulation and longevity in C. elegans

An imbalance between energy uptake and energy expenditure can lead to obesity and increase the risk of coronary heart disease, high blood pressure, stroke, type II diabetes and some cancers. Given that key elements of the energy pathway are evolutionary conserved, invertebrate research is an attractive alternative that overcomes the many legislative, financial and experimental hurdles typical of research with higher metazoan animals. Recent studies have suggested that some members of the cytochrome P450 superfamily are involved in lipid metabolism in addition to the traditional xenobiotic activity. To investigate this notion in more detail, the present study aimed to pinpoint phenotypic, genetic and genomic-level responses of Caenorhabditis elegans using selected deletion mutants including fat-5 (a member of the Δ9 desaturases) and cyp-35A2 (a member of the cytochrome P450 family). The creation of a fat-5(tm420);cyp-35A2(gk317) mutant uncovered that the deletion of both genes resulted in a strain which is marked by an extended lifespan. Furthermore, it diminished the overall level of Nile Red positive compartments, which is indicative of a change in lipid metabolism. Comprehensive transcriptomics revealed that several genes involved in aging and lipid transport/homeostasis were modulated following the double deletion of fat-5 and cyp-35A2. Taken together, the results suggest the presence of a putative correlation between longevity and lipid regulation and given that both genes have human homologs, this finding may offer a new lead to investigate in higher organisms.

Metallothionein gene activation in the earthworm (Lumbricus rubellus)

In order to cope with changing environmental conditions, organisms require highly responsive stress mechanisms. Heavy metal stress is handled by metallothioneins (MTs), the regulation of which is evolutionary conserved in insects and vertebrates and involves the binding of metal transcription factor 1 (MTF-1) to metal responsive elements (MREs) positioned in the promoter of MT genes. However, in most invertebrate phyla, the transcriptional activation of MTs is different and the exact mechanism is still unknown. Interestingly, although MREs are typically present also in invertebrate MT gene promoters, MTF-1 is notably absent. Here we use Lumbricus rubellus, the red earthworm, to study the elusive mechanism of wMT-2 activation in control and Cd-exposed conditions. EMSA and DNase I footprinting approaches were used to pinpoint functional binding sites within the wMT-2 promoter region, which revealed that the cAMP responsive element (CRE) is a promising candidate which may act as a transcriptional activator of invertebrate MTs.

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The wMT-2 promoter region of Lumbricus rubellus was analyzed and revealed a CRE binding site acting as putative transcriptional activator.

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MREs from the wMT-2 promoter region were shown to be functional protein binding sites.

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The wMT-2 transcription revealed an induction at the mRNA and protein level upon Cd exposure.

H2S: A New Approach to Lifespan Enhancement and Healthy Ageing?

Ageing, a progressive structural and functional decline, is considered to be a major risk factor for virtually all ageing-associated pathologies and disabilities, including Alzheimer's disease, Parkinson's disease, stroke, diabetes, atherosclerosis and certain cancers. Biogerontology research has now been largely directed towards finding novel drug targets to decelerate the ageing process and attain healthy ageing in order to delay the onset of all ageing-related diseases. H2S has been reported to exert vasodilatory, antioxidant, antiapoptotic and anti-inflammatory actions and has been shown to act as a signalling molecule, neuromodulator and cytoprotectant. Intriguingly, H2S has been reported to regulate cell cycle and survival in healthy cells which suggests that it may regulate cell fate and hence the ageing process. This chapter sets out to provide an overview of the current knowledge regarding the involvement of H2S in ageing, with a specific focus on the invertebrate model nematode C. elegans.

Neurotoxic action of microcystin-LR is reflected in the transcriptional stress response of Caenorhabditis elegans

Cyanobacterial blooms in aquatic environments are frequently characterized by elevated levels of microcystins, a potent hepatotoxin. Here we exposed the nematode Caenorhabditis elegans with environmentally realistic concentrations of MC-LR to explore its non-hepatic toxicity. Lifespan, reproduction and growth assays confirmed the toxic potential of 100μg/L MC-LR even in this liver-lacking invertebrate. Whole-genome microarray analysis revealed that a neuromodulating action was the dominant response in nematodes challenged with 100μg/L MC-LR. Indeed, most of the 201 differentially expressed genes were associated with neurobehavior, neurogenesis, and signaling associated pathways. In addition, a whole-genome miRNA-microarray highlighted that, in particular, members of the let-7 family were differentially regulated. These miRNAs are involved in the developmental timing of cell fates, including neurons, and are probably also part of the stress response system. To conclude, neurological modulation is the main transcriptional stress response in C. elegans exposed to MC-LR.

Two organobromines trigger lifespan, growth, reproductive and transcriptional changes in Caenorhabditis elegans

Organobromines of natural and artificial origin are omnipresent in aquatic and terrestrial environments. Although it is well established that exposure to high concentrations of organobromines are harmful to vertebrates, few studies have investigated the effect of environmentally realistic concentrations on invertebrates. Here, the nematode Caenorhabditis elegans was challenged with two organobromines, namely dibromoacetic acid (DBAA) and tetrabromobisphenol-A (TBBP), and monitored for changes in different life trait variables and global gene expression patterns. Fifty micromolar DBAA stimulated the growth and lifespan of the nematodes; however, the onset of reproduction was delayed. In contrast, TBBP changed the lifespan in a hormetic fashion, namely it was stimulated at 0.1 μM but impaired at 50 μM. The reproductive performance was even impaired at 2 μM TBBP. Moreover, DBAA could not reduce the toxic effect of TBBP when applied as a mixture. A whole-genome DNA microarray revealed that both organobromines curtailed signalling and neurological processes. Furthermore on the transcription level, 50 μM TBBP induced proteolysis and DBAA up-regulated biosynthesis and metabolism. To conclude, even naturally occurring concentrations of organobromines can influence the biomolecular responses and life cycle traits in C. elegans. The life extension is accompanied by negative changes in the reproductive behaviour, which is crucial for the stability of populations. Thus, this paper highlights that the effects of exposure to moderate, environmentally realistic concentrations of organobromines should not be ignored.

Mixtures of chemical pollutants at European legislation safety concentrations: how safe are they?

The risk posed by complex chemical mixtures in the environment to wildlife and humans is increasingly debated, but has been rarely tested under environmentally relevant scenarios. To address this issue, two mixtures of 14 or 19 substances of concern (pesticides, pharmaceuticals, heavy metals, polyaromatic hydrocarbons, a surfactant, and a plasticizer), each present at its safety limit concentration imposed by the European legislation, were prepared and tested for their toxic effects. The effects of the mixtures were assessed in 35 bioassays, based on 11 organisms representing different trophic levels. A consortium of 16 laboratories was involved in performing the bioassays. The mixtures elicited quantifiable toxic effects on some of the test systems employed, including i) changes in marine microbial composition, ii) microalgae toxicity, iii) immobilization in the crustacean Daphnia magna, iv) fish embryo toxicity, v) impaired frog embryo development, and vi) increased expression on oxidative stress-linked reporter genes. Estrogenic activity close to regulatory safety limit concentrations was uncovered by receptor-binding assays. The results highlight the need of precautionary actions on the assessment of chemical mixtures even in cases where individual toxicants are present at seemingly harmless concentrations.

Hydrogen sulfide is an endogenous regulator of aging in Caenorhabditis elegans

AIMS

To investigate the role of endogenous hydrogen sulfide (H2S) in the control of aging and healthspan of Caenorhabditis elegans.

RESULTS

We show that the model organism, C. elegans, synthesizes H2S. Three H2S-synthesizing enzymes are present in C. elegans, namely cystathionine γ lyase (CSE), cystathionine β synthetase, and 3-mercaptopyruvate transferase (MPST or 3-MST). Genetic deficiency of mpst-1 (3-MST orthologue 1), but not cth-2 (CSE orthologue), reduced the lifespan of C. elegans. This effect was reversed by a pharmacological H2S donor (GYY4137). GYY4137 also reduced detrimental age-dependent changes in a range of physiological indices, including pharyngeal contraction and defecation. Treatment of C. elegans with GYY4137 increased the expression of several age-related, stress response, and antioxidant genes, whereas MitoSOX Red fluorescence, indicative of reactive oxygen species generation, was increased in mpst-1 knockouts and decreased by GYY4137 treatment. GYY4137 additionally increased the lifespan in short-lived mev-1 mutants with elevated oxidative stress and protected wild-type C. elegans against paraquat poisoning. The lifespan-prolonging and health-promoting effects of H2S in C. elegans are likely due to the antioxidant action of this highly cell-permeable gas.

INNOVATION

The possibility that novel pharmacological agents based on the principle of H2S donation may be able to retard the onset of age-related disease by slowing the aging process warrants further study.

CONCLUSION

Our results show that H2S is an endogenous regulator of oxidative damage, metabolism, and aging in C. elegans and provide new insight into the mechanisms, which control aging in this model organism.

Metalloproteins and phytochelatin synthase may confer protection against zinc oxide nanoparticle induced toxicity in Caenorhabditis elegans

Zinc oxide nanoparticles (ZnONPs) are used in large quantities by the cosmetic, food and textile industries. Here we exposed Caenorhabditis elegans wild-type and a metal sensitive triple knockout mutant (mtl-1;mtl-2;pcs-1) to ZnONPs (0-50mg/L) to study strain and exposure specific effects on transcription, reactive oxygen species generation, the biomolecular phenotype (measured by Raman microspectroscopy) and key endpoints of the nematode life cycle (growth, reproduction and lifespan). A significant dissolution effect was observed, where dissolved ZnO constituted over 50% of total Zn within a two day exposure to the test medium, suggesting that the nominal exposure to pure ZnONPs represents in vivo, at best, a mixture exposure of ionic zinc and nanoparticles. Nevertheless, the analyses provided evidence that the metallothioneins (mtl-1 and mtl-2), the phytochelatin synthase (pcs-1) and an apoptotic marker (cep-1) were transcriptionally activated. In addition, the DCFH-DA assay provided in vitro evidence of the oxidative potential of ZnONPs in the metal exposure sensitive triple mutant. Raman spectroscopy highlighted that the biomolecular phenotype changes significantly in the mtl-1;mtl-2;pcs-1 triple knockout worm upon ZnONP exposure, suggesting that these metalloproteins are instrumental in the protection against cytotoxic damage. Finally, ZnONP exposure was shown to decrease growth and development, reproductive capacity and lifespan, effects which were amplified in the triple knockout. By combining diverse toxicological strategies, we identified that individuals (genotypes) housing mutations in key metalloproteins and phytochelatin synthase are more susceptible to ZnONP exposure, which underlines their importance to minimize ZnONP induced toxicity.

Caenorhabditis elegans in regenerative medicine: a simple model for a complex discipline

Stem cell research is a major focus of regenerative medicine, which amalgamates diverse disciplines ranging from developmental cell biology to chemical and genetic therapy. Although embryonic stem cells have provided the foundation of stem cell therapy, they offer an in vitro study system that might not provide the best insight into mechanisms and behaviour of cells within living organisms. Caenorhabditis elegans is a well defined model organism with highly conserved cell development and signalling processes that specify cell fate. Its genetic amenability coupled with its chemical screening applicability make the nematode well suited as an in vivo system in which regenerative therapy and stem cell processes can be explored. Here, we describe some of the major advances in stem cell research from the worm's perspective.

C. elegans aging is modulated by hydrogen sulfide and the sulfhydrylase/cysteine synthase cysl-2

Exogenous hydrogen sulfide (H2S) administration and endogenous H2S metabolism were explored in the nematode C. elegans. Chronic treatment with a slow-releasing H2S donor, GYY4137, extended median survival by 17-23% and increased tolerance towards oxidative and endoplasmic reticulum (ER) stress. Also, cysl-2, a sulfhydrylase/cysteine synthase in C. elegans, was transcriptionally upregulated by GYY4137 treatment and the deletion of cysl-2 resulted in a significant reduction in lifespan which was partially recovered by the supplementation of GYY4137. Likewise, a mammalian cell culture system, GYY4137 was able to protect bovine aortic endothelial cells (BAECs) from oxidative stress and (H2O2)-induced cell death. Taken together, this provides further support that H2S exerts a protective function which is consistent with the longevity dividend theory. Overall, this study underlines the therapeutic potential of a slow-releasing H2S donor as regulators of the aging and cellular stress pathways.

Hormesis and longevity with tannins: free of charge or cost-intensive?

Hormetic lifespan extension is, for obvious reasons, beneficial to an individual. But is this effect really cost-neutral? To answer this question, four tannic polyphenols were tested on the nematode Caenorhabditis elegans. All were able to extend the lifespan, but only some in a hormetic fashion. Additional life trait variables including stress resistance, reproductive behavior, growth, and physical fitness were observed during the exposure to the most life extending concentrations. These traits represent the quality of life and the population fitness, being the most important parameters of a hormetic treatment besides lifespan. Indeed, it emerged that each life-extension is accompanied by a constraining effect in at least one other endpoint, for example growth, mobility, stress resistance, or reproduction. Thus, in this context, longevity could not be considered to be attained for free and therefore it is likely that other hormetic benefits may also incur cost-intensive and unpredictable side-effects.

Transcript expression patterns illuminate the mechanistic background of hormesis in caenorhabditis elegans maupas

The animal model Caenorhabditis elegans was employed to study polyphenol- and humic substances-induced hormetic changes in lifespan. A detailed insight into the underlying mechanism of hormesis was uncovered by applying whole genome DNA microarray experimentation over a range of quercetin (Q), tannic acid (TA), and humic substances (HuminFeed(®), HF) concentrations. The transcriptional response to all exposures followed a non-linear mode which highlighted differential signaling and metabolic pathways. While low Q concentrations regulated processes improving the health of the nematodes, higher concentrations extended lifespan and modulated substantially the global transcriptional response. Over-represented transcripts were notably part of the biotransformation process: enhanced catabolism of toxic intermediates possibly contributes to the lifespan extension. The regulation of transcription, Dauer entry, and nucleosome suggests the presence of distinct exposure dependent differences in transcription and signaling pathways. TA- and HF-mediated transcript expression patterns were overall similar to each other, but changed across the concentration range indicating that their transcriptional dynamics are complex and cannot be attributed to a simple adaptive response. In contrast, Q-mediated hormesis was well aligned to fit the definition of an adaptive response. Simple molecules are more likely to induce an adaptive response than more complex molecules.

Biosynthesis of luminescent quantum dots in an earthworm

The synthesis of designer solid-state materials by living organisms is an emerging field in bio-nanotechnology. Key examples include the use of engineered viruses as templates for cobalt oxide (Co(3)O(4)) particles, superparamagnetic cobalt-platinum alloy nanowires and gold-cobalt oxide nanowires for photovoltaic and battery-related applications. Here, we show that the earthworm's metal detoxification pathway can be exploited to produce luminescent, water-soluble semiconductor cadmium telluride (CdTe) quantum dots that emit in the green region of the visible spectrum when excited in the ultraviolet region. Standard wild-type Lumbricus rubellus earthworms were exposed to soil spiked with CdCl(2) and Na(2)TeO(3) salts for 11 days. Luminescent quantum dots were isolated from chloragogenous tissues surrounding the gut of the worm, and were successfully used in live-cell imaging. The addition of polyethylene glycol on the surface of the quantum dots allowed for non-targeted, fluid-phase uptake by macrophage cells.

The Nematode Caenorhabditis elegans, Stress and Aging: Identifying the Complex Interplay of Genetic Pathways Following the Treatment with Humic Substances

Low concentrations of the dissolved leonardite humic acid HuminFeed^® (HF) prolonged the lifespan and enhanced the thermal stress resistance of the model organism Caenorhabditis elegans. However, growth was impaired and reproduction delayed, effects which have also been identified in response to other polyphenolic monomers, including Tannic acid, Rosmarinic acid, and Caffeic acid. Moreover, a chemical modification of HF, which increases its phenolic/quinonoid moieties, magnified the biological impact on C. elegans. To gain a deep insight into the molecular basis of these effects, we performed global transcriptomics on young adult (3 days) and old adult (11 days) nematodes exposed to two different concentrations of HF. We also studied several C. elegans mutant strains in respect to HF derived longevity and compared all results with data obtained for the chemically modified HF. The gene expression pattern of young HF-treated nematodes displayed a significant overlap to other conditions known to provoke longevity, including various plant polyphenol monomers. Besides the regulation of parts of the metabolism, transforming growth factor-beta signaling, and Insulin-like signaling, lysosomal activities seem to contribute most to HF’s and modified HF’s lifespan prolonging action. These results support the notion that the phenolic/quinonoid moieties of humic substances are major building blocks that drive the physiological effects observed in C. elegans.

Meta-Analysis of Global Transcriptomics Suggests that Conserved Genetic Pathways are Responsible for Quercetin and Tannic Acid Mediated Longevity in C. elegans

Recent research has highlighted that the polyphenols Quercetin and Tannic acid are capable of extending the lifespan of Caenorhabditis elegans. To gain a deep understanding of the underlying molecular genetics, we analyzed the global transcriptional patterns of nematodes exposed to three concentrations of Quercetin or Tannic acid, respectively. By means of an intricate meta-analysis it was possible to compare the transcriptomes of polyphenol exposure to recently published datasets derived from (i) longevity mutants or (ii) infection. This detailed comparative in silico analysis facilitated the identification of compound specific and overlapping transcriptional profiles and allowed the prediction of putative mechanistic models of Quercetin and Tannic acid mediated longevity. Lifespan extension due to Quercetin was predominantly driven by the metabolome, TGF-beta signaling, Insulin-like signaling, and the p38 MAPK pathway and Tannic acid's impact involved, in part, the amino acid metabolism and was modulated by the TGF-beta and the p38 MAPK pathways. DAF-12, which integrates TGF-beta and Insulin-like downstream signaling, and genetic players of the p38 MAPK pathway therefore seem to be crucial regulators for both polyphenols. Taken together, this study underlines how meta-analyses can provide an insight of molecular events that go beyond the traditional categorization into gene ontology-terms and Kyoto encyclopedia of genes and genomes-pathways. It also supports the call to expand the generation of comparative and integrative databases, an effort that is currently still in its infancy.

Incidence of maxillary sinusitis and oro-antral fistulae in bisphosphonate-related osteonecrosis of the jaw

OBJECTIVE

Bisphosphonate-related osteonecrosis of the jaw (BRONJ) is a serious side-effect of bisphosphonate therapy. In the majority of cases BRONJ occurs in the mandible. As a consequence a detailed investigation of BRONJ of the maxilla and in particular of involvement of the maxillary sinus has largely so far been neglected. The aim of this study was to analyse the frequency of maxillary sinusitis and oro-antral fistulae in BRONJ of the maxilla.

SUBJECTS AND METHODS

A retrospective multicentre analysis was carried out in three Departments of Oral and Maxillofacial Surgery focussing on patients suffering from BRONJ in the maxilla. The role of involvement of the maxillary sinus, in particular sinusitis and oro-antral fistula, was analysed.

RESULTS

Out of a total of 170 patients suffering from BRONJ 53 cases (31.2%) with involvement of the maxilla were identified. At least one sign of maxillary sinusitis was present in 43.6% (23/53) and an oro-antral fistula in the course of the disease was detected in 35.8% (19/53) of those patients. The mean length of time of bisphosphonate intake was 36.16±16.32 months. Zoledronate was most frequently associated (60.4%) with symptoms, followed by the combination of Zoledronate/Ibandronate (13.2%), and Zoledronate/Pamidronate or Pamidronate alone (both 7.5%).

CONCLUSION

Maxillary sinusitis and oro-antral fistulae are associated with a BRONJ manifestation in the upper jaw in approximately 44%. The involvement of the maxillary sinus should be given special attention and three-dimensional imaging modalities might be necessary, not only to evaluate the extent of necrosis, but also to exclude involvement of the maxillary sinus.

Diversity of polyphenol action in Caenorhabditis elegans: between toxicity and longevity

The model organism Caenorhabditis elegans was utilized to determine, in vivo, the mode(s) of action of four plant polyphenols, namely, tannic acid (TA), gallic acid (GA), ellagic acid (EA), and catechin (CT). The determination of lifespan, stress resistance, growth, reproduction, eating-related behaviors, antioxidative capacities, and lifespan assays with the mev-1 and the eat-2 mutants as well as in the presence of dead bacteria provided new insights into their action. All four compounds prolonged lifespan, but only TA and CT mediated distinct stress protection. Longevity is unlikely the result of antioxidant capacities but rather due to calorie restriction imitating and hormetic properties in the case of TA and EA or antimicrobial capacities of GA and EA. Furthermore, the prominent "disposable soma theory" is only partly reflected by these polyphenols. In summary, this study underlines the diversity of polyphenolic phytochemicals and their mechanistic background.

Nematode and snail metallothioneins

Metallobiologists have, at large, neglected soil dwelling invertebrates; exceptions are the nematode (Caenorhabditis elegans) and snails (Helix pomatia and Cantareus aspersus). This review aims to compare and contrast the molecular, protein and cellular mechanisms of the multifunctional nematode and snail metallothioneins (MTs). The C. elegans genome contains two MT genes, mtl-1, which is constitutively expressed in the pharynx and likely to act as an essential and/or toxic metal sensor, and mtl-2, which plays a negligible role under normal physiological conditions but is strongly induced (as mtl-1) in intestinal cells upon metal exposure. It has been possible to follow the intricate phenotypic responses upon the knockdown/knockout of single and multiple MT isoforms and we have started to decipher the multifunctional role of C. elegans MTs. The snails have contributed to our understanding regarding MT evolution and diversity, structure and metal-specific functionality. The H. pomatia and C. aspersus genomes contain at least three MT isoform genes. CdMT is responsible for cadmium detoxification, CuMT is involved in copper homeostasis and Cd/CuMT is a putative ancestral MT possibly only of minor importance in metal metabolism. Further investigations of nematode, snail and other invertebrate MTs will allow the development of alternative biomarker approaches and lead to an improved understanding of metallobiology, protein evolution and toxicogenomics.

Hormetins, antioxidants and prooxidants: defining quercetin-, caffeic acid- and rosmarinic acid-mediated life extension in C. elegans

Quercetin, Caffeic- and Rosmarinic acid exposure extend lifespan in Caenorhabditis elegans. This comparative study uncovers basic common and contrasting underlying mechanisms: For all three compounds, life extension was characterized by hormetic dose response curves, but hsp-level expression was variable. Quercetin and Rosmarinic acid both suppressed bacterial growth; however, antibacterial properties were not the dominant reason for life extension. Exposure to Quercetin, Caffeic- and Rosmarinic acid resulted in reduced body size, altered lipid-metabolism and a tendency towards a delay in reproductive timing; however the total number of offspring was not affected. An indirect dietary restriction effect, provoked by either chemo-repulsion or diminished pharyngeal pumping was rejected. Quercetin and Caffeic acid were shown to increase the antioxidative capacity in vivo and, by means of a lipofuscin assay, reduce the oxidative damage in the nematodes. Finally, it was possible to demonstrate that the life and thermotolerance enhancing properties of Caffeic- and Rosmarinic acid both rely on osr-1, sek-1, sir-2.1 and unc-43 plus daf-16 in the case of Caffeic acid. Taken together, hormesis, in vivo antioxidative/prooxidative properties, modulation of genetic players, as well as the re-allocation of energy all contribute (to some extent and dependent on the polyphenol) to life extension.

Systems toxicology approaches for understanding the joint effects of environmental chemical mixtures

Environmental mixtures of chemicals constitute a prevalent issue in ecotoxicology and the development of new methods to reduce the uncertainties associated with their ecological risk assessment is a critical research need. Historically, a number of models have been explored to predict the potential combined effects of chemicals on species. These models, especially concentration addition and the independent action, have been applied to a number of mixtures. While often providing a good prediction of joint effect, there are cases where these models can have limitations: notably in cases where there are interactions for which they fail to adequately predict joint effects. To support the better mechanistic understanding of interactions in mixture toxicology a framework to support experimental studies to investigate the basis of observed interactions is proposed. The conceptual framework is derived from the extension of a three stage scheme which has previously been applied to understand chemical bioavailability. The framework considers that interactions in mixtures result from processes related to 1) the speciation, binding and transport of chemicals in the exposure medium (external exposure); 2) the adsorption, distribution, metabolism and excretion of chemicals within the organisms (toxicokinetics); 3) associations governing the binding and toxicity of the chemical(s) at the target site (toxicodynamics). The current state of the art in (eco)toxicology in relation to investigation of the mechanisms of interactions between chemicals is discussed with particular emphasis towards the multi-disciplinary tools and techniques within environmental chemistry; toxicology; biochemistry and systems biology that can be used to address such effects.

The two Caenorhabditis elegans metallothioneins (CeMT-1 and CeMT-2) discriminate between essential zinc and toxic cadmium

The nematode Caenorhabditis elegans expresses two metallothioneins (MTs), CeMT-1 and CeMT-2, that are believed to be key players in the protection against metal toxicity. In this study, both isoforms were expressed in vitro in the presence of either Zn(II) or Cd(II). Metal binding stoichiometries and affinities were determined by ESI-MS and NMR, respectively. Both isoforms had equal zinc binding ability, but differed in their cadmium binding behaviour, with higher affinity found for CeMT-2. In addition, wild-type C. elegans, single MT knockouts and a double MT knockout allele were exposed to zinc (340 microm) or cadmium (25 microm) to investigate effects in vivo. Zinc levels were significantly increased in all knockout strains, but were most pronounced in the CeMT-1 knockout, mtl-1 (tm1770), while cadmium accumulation was highest in the CeMT-2 knockout, mtl-2 (gk125) and the double knockout mtl-1;mtl-2 (zs1). In addition, metal speciation was assessed by X-ray absorption fine-structure spectroscopy. This showed that O-donating, probably phosphate-rich, ligands play a dominant role in maintaining the physiological concentration of zinc, independently of metallothionein status. In contrast, cadmium was shown to coordinate with thiol groups, and the cadmium speciation of the wild-type and the CeMT-2 knockout strain was distinctly different to the CeMT-1 and double knockouts. Taken together, and supported by a simple model calculation, these findings show for the first time that the two MT isoforms have differential affinities towards Cd(II) and Zn(II) at a cellular level, and this is reflected at the protein level. This suggests that the two MT isoforms have distinct in vivo roles.

Linking toxicant physiological mode of action with induced gene expression changes in Caenorhabditis elegans

Background

Physiologically based modelling using DEBtox (dynamic energy budget in toxicology) and transcriptional profiling were used in Caenorhabditis elegans to identify how physiological modes of action, as indicated by effects on system level resource allocation were associated with changes in gene expression following exposure to three toxic chemicals: cadmium, fluoranthene (FA) and atrazine (AZ).

Results

For Cd, the physiological mode of action as indicated by DEBtox model fitting was an effect on energy assimilation from food, suggesting that the transcriptional response to exposure should be dominated by changes in the expression of transcripts associated with energy metabolism and the mitochondria. While evidence for effect on genes associated with energy production were seen, an ontological analysis also indicated an effect of Cd exposure on DNA integrity and transcriptional activity. DEBtox modelling showed an effect of FA on costs for growth and reproduction (i.e. for production of new and differentiated biomass). The microarray analysis supported this effect, showing an effect of FA on protein integrity and turnover that would be expected to have consequences for rates of somatic growth. For AZ, the physiological mode of action predicted by DEBtox was increased cost for maintenance. The transcriptional analysis demonstrated that this increase resulted from effects on DNA integrity as indicated by changes in the expression of genes chromosomal repair.

Conclusions

Our results have established that outputs from process based models and transcriptomics analyses can help to link mechanisms of action of toxic chemicals with resulting demographic effects. Such complimentary analyses can assist in the categorisation of chemicals for risk assessment purposes.

The use of FUdR can cause prolonged longevity in mutant nematodes

The nematode Caenorhabditis elegans is a popular model organism that is used to study longevity and aging. One drawback of nematode lifespan assays is the labour intensive separation of offspring from adults during the reproductive period. To circumvent this, the worm community frequently adds 5-fluoro-2'-deoxyuridine (FUdR), a drug that induces parental sterility, to the nematode culture. Here, we report that FUdR causes a significant artefactual increase in the longevity of tub-1 mutants which is not observed in wild-type nematodes. This suggests that the effect of FUdR is not neutral and the mechanism of action may result in misleading data, or indeed the misinterpretation of gerontogenes.

Molecular genetic differentiation in earthworms inhabiting a heterogeneous Pb-polluted landscape

A Pb-mine site situated on acidic soil, but comprising of Ca-enriched islands around derelict buildings was used to study the spatial pattern of genetic diversity in Lumbricus rubellus. Two distinct genetic lineages ('A' and 'B'), differentiated at both the mitochondrial (mtDNA COII) and nuclear level (AFLPs) were revealed with a mean inter-lineage mtDNA sequence divergence of approximately 13%, indicative of a cryptic species complex. AFLP analysis indicates that lineage A individuals within one central 'ecological island' site are uniquely clustered, with little genetic overlap with lineage A individuals at the two peripheral sites. FTIR microspectroscopy of Pb-sequestering chloragocytes revealed different phosphate profiles in residents of adjacent acidic and calcareous islands. Bioinformatics found over-representation of Ca pathway genes in EST(Pb) libraries. Subsequent sequencing of a Ca-transport gene, SERCA, revealed mutations in the protein's cytosolic domain. We recommend the mandatory genotyping of all individuals prior to field-based ecotoxicological assays, particularly those using discriminating genomic technologies.

The Caenorhabditis elegans Elongator complex regulates neuronal alpha-tubulin acetylation

Although acetylated alpha-tubulin is known to be a marker of stable microtubules in neurons, precise factors that regulate alpha-tubulin acetylation are, to date, largely unknown. Therefore, a genetic screen was employed in the nematode Caenorhabditis elegans that identified the Elongator complex as a possible regulator of alpha-tubulin acetylation. Detailed characterization of mutant animals revealed that the acetyltransferase activity of the Elongator is indeed required for correct acetylation of microtubules and for neuronal development. Moreover, the velocity of vesicles on microtubules was affected by mutations in Elongator. Elongator mutants also displayed defects in neurotransmitter levels. Furthermore, acetylation of alpha-tubulin was shown to act as a novel signal for the fine-tuning of microtubules dynamics by modulating alpha-tubulin turnover, which in turn affected neuronal shape. Given that mutations in the acetyltransferase subunit of the Elongator (Elp3) and in a scaffold subunit (Elp1) have previously been linked to human neurodegenerative diseases, namely Amyotrophic Lateral Sclerosis and Familial Dysautonomia respectively highlights the importance of this work and offers new insights to understand their etiology.

Accumulated metal speciation in earthworm populations with multigenerational exposure to metalliferous soils: cell fractionation and high-energy synchrotron analyses

Predicting metal bioaccumulation and toxicity in soil organisms is complicated by site-specific biotic and abiotic parameters. In this study we exploited tissue fractionation and digestion techniques, combined with X-ray absorption spectroscopy (XAS), to investigate the whole-body and subcellular distributions, ligand affinities, and coordination chemistry of accumulated Pb and Zn in field populations of the epigeic earthworm Lumbricus rubellus inhabiting three contrasting metalliferous and two unpolluted soils. Our main findings were (i) earthworms were resident in soils with concentrations of Pb and Zn ranging from 1200 to 27,000 mg kg(-1) and 200 to 34,000 mg kg(-1), respectively; (ii) Pb and Zn primarily accumulated in the posterior alimentary canal in nonsoluble subcellular fractions of earthworms; (iii) site-specific differences in the tissue and subcellular partitioning profiles of populations were observed, with earthworms from a calcareous site partitioning proportionally more Pb to their anterior body segments and Zn to the chloragosome-rich subcellular fraction than their acidic-soil inhabiting counterparts; (iv) XAS indicated that the interpopulation differences in metal partitioning between organs were not accompanied by qualitative differences in ligand-binding speciation, because crystalline phosphate-containing pyromorphite was a predominant chemical species in the whole-worm tissues of all mine soil residents. Differences in metal (Pb, Zn) partitioning at both organ and cellular levels displayed by field populations with protracted histories of metal exposures may reflect theirinnate ecophysiological responses to essential edaphic variables, such as Ca2+ status. These observations are highly significant in the challenging exercise of interpreting holistic biomarker data delivered by "omic" technologies.

Caenorhabditis elegans metallothioneins protect against toxicity induced by depleted uranium

Depleted uranium (DU) is a dense and heavy metal used in armor, ammunition, radiation shielding, and counterbalances. The military usage has led to growing public concern regarding the health effects of DU. In this study, we used the nematode, Caenorhabditis elegans, to evaluate the toxicity of DU and its effects in knockout strains of metallothioneins (MTs), which are small thiol-rich proteins that have numerous functions, such as metal sequestration, transport, and detoxification. We examined nematode viability, the accumulation of uranium, changes in MT gene expression by quantitative reverse transcription-PCR, and the induction of green fluorescent protein under the control of the MT promoters, following exposure to DU. Our results indicate that (1) DU causes toxicity in a dose-dependent manner; (2) MTs are protective against DU exposure; and (3) nematode death by DU is not solely a reflection of intracellular uranium concentration. (4) Furthermore, only one of the isoforms of MTs, metallothionein-1 (mtl-1), appears to be important for uranium accumulation in C. elegans. These findings suggest that these highly homologous proteins may have subtle functional differences and indicate that MTs mediate the response to DU.