Cadmium alters whole animal ionome and promotes the re-distribution of iron in intestinal cells of Caenorhabditis elegans

The chronic exposure of humans to the toxic metal cadmium (Cd), either occupational or from food and air, causes various diseases, including neurodegenerative conditions, dysfunction of vital organs, and cancer. While the toxicology of Cd and its effect on the homeostasis of biologically relevant elements is increasingly recognized, the spatial distribution of Cd and other elements in Cd toxicity-caused diseases is still poorly understood. Here, we use Caenorhabditis elegans as a non-mammalian multicellular model system to determine the distribution of Cd at the tissue and cellular resolution and its effect on the internal levels and the distribution of biologically relevant elements. Using inductively coupled plasma-mass spectrophotometry (ICP-MS), we show that exposure of worms to Cd not only led to its internal accumulation but also significantly altered the C. elegans ionome. Specifically, Cd treatment was associated with increased levels of toxic elements such as arsenic (As) and rubidium (Rb) and a decreased accumulation of essential elements such as zinc (Zn), copper (Cu), manganese (Mn), calcium (Ca), cobalt (Co) and, depending on the Cd-concentration used in the assay, iron (Fe). We regarded these changes as an ionomic signature of Cd toxicity in C. elegans. We also show that supplementing nematode growth medium with Zn but not Cu, rescues Cd toxicity and that mutant worms lacking Zn transporters CDF-1 or SUR-7, or both are more sensitive to Cd toxicity. Finally, using synchrotron X-Ray fluorescence Microscopy (XRF), we showed that Cd significantly alters the spatial distribution of mineral elements. The effect of Cd on the distribution of Fe was particularly striking: while Fe was evenly distributed in intestinal cells of worms grown without Cd, in the presence of Cd, Fe, and Cd co-localized in punctum-like structures in the intestinal cells. Together, this study advances our understanding of the effect of Cd on the accumulation and distribution of biologically relevant elements. Considering that C. elegans possesses the principal tissues and cell types as humans, our data may have important implications for future therapeutic developments aiming to alleviate Cd-related pathologies in humans.

Mercury entomotoxicology

Mercury is an industrial pollutant of global concern. Currently entomofauna is disappearing and chemical pollution is one cause, however, it is unknown whether mercury is an additional threat. Therefore, it is necessary to know the entomotoxicology of mercury. The aim of the present work was to perform a comprehensive literature review on the entomotoxicology of mercury. The toxicokinetics and toxicity of mercury in insects, the participation of insects in the mercury cycle and the fact that this element is a threat to entomofauna are characterized. Insects can be exposed to mercury through ingestion, tracheal respiration, and gill respiration. Organic forms of mercury are better absorbed, bioaccumulated and distributed than inorganic forms. In addition, insects can biotransform mercury, for example, by methylating it. Metal elimination occurs through feces, eggs and exuvia. Toxicity molecular mechanisms include oxidative stress, enzymatic disruptions, alterations in the metabolism of neurotransmitters and proteins, genotoxicity, cell death and unbalances in the energetic state. Moreover, mercury affects lipid, germ, and gut cells, causes deformations, disturbs development, reproduction, behavior, and locomotion, besides to alters insect populations and communities. In terrestrial ecosystems, entomofauna participate in the mercury cycle by bioaccumulating mercury from soil and air, predating, being predated and decomposing organic matter. In aquatic ecosystems insects participate by accumulating mercury from water and sediment, predating, being predated and transporting it to terrestrial ecosystems when they emerge as winged adults. There are still information gaps that need to be addressed.

Short exposure to ethyl and methylmercury prompts similar toxic responses in Drosophila melanogaster

Methylmercury (MeHg) and ethylmercury (EtHg) are important mercury organic forms in terms of human poisoning. Since the comparative effects of compounds are mainly in vitro, this study was designed to investigate the toxicities induced by MeHg and EtHg in an in vivo study using adult Drosophila melanogaster (D. melanogaster). Firstly, we performed a survival curve, where the flies were fed on a medium containing MeHg and EtHg at concentrations ranging from 2.5 to 200 μM, until the end of their lifespan. After that, the concentrations 25 and 200 μM of MeHg and EtHg were chosen to be tested in a short exposure for 5 days. The analysis of survival by Kaplan-Meier plot revealed that all concentrations of MeHg and EtHg reduced significantly the lifespan of the flies. Short exposure to both concentrations of MeHg and EtHg impaired the ability of flies in the climbing assay and induced lipid peroxidation. Only the flies exposed to the highest concentration had viability loss, thiol depletion, and increased reactive species (RS) and Hg levels in the whole body. Our findings indicate that MeHg and EtHg exhibit similar toxic effects in vivo, and that oxidative stress is a phenomenon behind the toxicity of both mercurials. The data obtained also reinforce the use of D. melanogaster as a useful organism for basic toxicological research.

The Effects of Essential and Non-Essential Metal Toxicity in the Drosophila melanogaster Insect Model: A Review

The biological effects of environmental metal contamination are important issues in an industrialized, resource-dependent world. Different metals have different roles in biology and can be classified as essential if they are required by a living organism (e.g., as cofactors), or as non-essential metals if they are not. While essential metal ions have been well studied in many eukaryotic species, less is known about the effects of non-essential metals, even though essential and non-essential metals are often chemically similar and can bind to the same biological ligands. Insects are often exposed to a variety of contaminated environments and associated essential and non-essential metal toxicity, but many questions regarding their response to toxicity remain unanswered. Drosophila melanogaster is an excellent insect model species in which to study the effects of toxic metal due to the extensive experimental and genetic resources available for this species. Here, we review the current understanding of the impact of a suite of essential and non-essential metals (Cu, Fe, Zn, Hg, Pb, Cd, and Ni) on the D. melanogaster metal response system, highlighting the knowledge gaps between essential and non-essential metals in D. melanogaster. This review emphasizes the need to use multiple metals, multiple genetic backgrounds, and both sexes in future studies to help guide future research towards better understanding the effects of metal contamination in general.

Copper and Zinc Homeostasis: Lessons from Drosophila melanogaster

Maintenance of metal homeostasis is crucial for many different enzymatic activities and in turn for cell function and survival. In addition, cells display detoxification and protective mechanisms against toxic accumulation of metals. Perturbation of any of these processes normally leads to cellular dysfunction and finally to cell death. In the last years, loss of metal regulation has been described as a common pathological feature in many human neurodegenerative diseases. However, in most cases, it is still a matter of debate whether such dyshomeostasis is a primary or a secondary downstream defect. In this review, we will summarize and critically evaluate the contribution of Drosophila to model human diseases that involve altered metabolism of metals or in which metal dyshomeostasis influence their pathobiology. As a prerequisite to use Drosophila as a model, we will recapitulate and describe the main features of core genes involved in copper and zinc metabolism that are conserved between mammals and flies. Drosophila presents some unique strengths to be at the forefront of neurobiological studies. The number of genetic tools, the possibility to easily test genetic interactions in vivo and the feasibility to perform unbiased genetic and pharmacological screens are some of the most prominent advantages of the fruitfly. In this work, we will pay special attention to the most important results reported in fly models to unveil the role of copper and zinc in cellular degeneration and their influence in the development and progression of human neurodegenerative pathologies such as Parkinson's disease, Alzheimer's disease, Huntington's disease, Friedreich's Ataxia or Menkes, and Wilson's diseases. Finally, we show how these studies performed in the fly have allowed to give further insight into the influence of copper and zinc in the molecular and cellular causes and consequences underlying these diseases as well as the discovery of new therapeutic strategies, which had not yet been described in other model systems.

Effects of Hg(II) exposure on MAPK phosphorylation and antioxidant system in D. melanogaster

The heavy metal mercury is a known toxin, but while the mechanisms involved in mercury toxicity have been well demonstrated in vertebrates, little is known about toxicological effects of this metal in invertebrates. Here, we present the results of our study investigating the effects associated with exposure of fruit fly Drosophila melanogaster to inorganic mercury (HgCl2 ). We quantify survival and locomotor performance as well as a variety of biochemical parameters including antioxidant status, MAPK phosphorylation and gene expression following mercury treatment. Our results demonstrate that exposure to Hg(II) through diet induced mortality and affected locomotor performance as evaluated by negative geotaxis, in D. melanogaster. We also saw a significant impact on the antioxidant system including an inhibition of acetylcholinesterase (Ache), glutathione S-transferase (GST) and superoxide dismutase (SOD) activities. We found no significant alteration in the levels of mRNA of antioxidant enzymes or NRF-2 transcriptional factor, but did detect a significant up regulation of the HSP83 gene. Mercury exposure also induced the phosphorylation of JNK and ERK, without altering p38(MAPK) and the concentration of these kinases. In parallel, Hg(II) induced PARP cleavage in a 89 kDa fragment, suggesting the triggering of apoptotic cell death in response to the treatment. Taken together, this data clarifies and extends our understanding of the molecular mechanisms mediating Hg(II) toxicity in an invertebrate model.

Mining genes involved in insecticide resistance of Liposcelis bostrychophila Badonnel by transcriptome and expression profile analysis

BACKGROUND

Recent studies indicate that infestations of psocids pose a new risk for global food security. Among the psocids species, Liposcelis bostrychophila Badonnel has gained recognition in importance because of its parthenogenic reproduction, rapid adaptation, and increased worldwide distribution. To date, the molecular data available for L. bostrychophila is largely limited to genes identified through homology. Also, no transcriptome data relevant to psocids infection is available.

METHODOLOGY AND PRINCIPAL FINDINGS

In this study, we generated de novo assembly of L. bostrychophila transcriptome performed through the short read sequencing technology (Illumina). In a single run, we obtained more than 51 million sequencing reads that were assembled into 60,012 unigenes (mean size = 711 bp) by Trinity. The transcriptome sequences from different developmental stages of L. bostrychophila including egg, nymph and adult were annotated with non-redundant (Nr) protein database, gene ontology (GO), cluster of orthologous groups of proteins (COG), and KEGG orthology (KO). The analysis revealed three major enzyme families involved in insecticide metabolism as differentially expressed in the L. bostrychophila transcriptome. A total of 49 P450-, 31 GST- and 21 CES-specific genes representing the three enzyme families were identified. Besides, 16 transcripts were identified to contain target site sequences of resistance genes. Furthermore, we profiled gene expression patterns upon insecticide (malathion and deltamethrin) exposure using the tag-based digital gene expression (DGE) method.

CONCLUSION

The L. bostrychophila transcriptome and DGE data provide gene expression data that would further our understanding of molecular mechanisms in psocids. In particular, the findings of this investigation will facilitate identification of genes involved in insecticide resistance and designing of new compounds for control of psocids.

Developmental study of mercury effects on the fruit fly (Drosophila melanogaster)

Environmental pollution caused by heavy metals such as mercury is one of the most important human problems. It might have severe teratogenic effects on embryonic development. Some pharmacological and physiological aspects of fruit flies (Drosophila melanogaster) are similar to humans. So the stages of egg to adult fruit fly, as a developmental model, were employed in the study. Wild adult insects were maintained in glass dishes containing standard medium at 25 °C in complete darkness. Five pairs of 3-day old flies were then transferred to standard culture dishes containing different concentrations of mercury ion. They were removed after 8 hours. We considered the following: The rate of larvae becoming pupae and pupae to adults; the time required for the development; the hatching rate in the second generation without mercury in the culture; the morphometric changes during development in both length and width of the eggs through two generations; larvae, pupae and adult thorax length and width. The results showed that mercury in culture (20–100 mg/l) increase the duration of larvae (p<0.01) and pupae (p<0.01) development, the rate of larvae becoming pupae (p<0.001); pupae maturation (p<0.05), the hatching rate (p<0.01), the length (p<0.05) and width of larvae (p<0.01) and pupae (p<0.001) and the length in the adult thorax (p<0.01) decreased significantly. There was no effect upon the size of eggs. There were also no larvae hatching in concentrations of 200 mg/l of mercury. Negative effects of mercury as a heavy metal are possibly due to the interference of this metal in cellular signaling pathways, such as: Notch signaling and protein synthesis during the period of development. Since it bonds chemically with the sulfur hydride groups of proteins, it causes damage to the cell membrane and decreases the amount of RNA. This is the cause of failure of many enzyme mechanisms.

Is the lobster cockroach Nauphoeta cinerea a valuable model for evaluating mercury induced oxidative stress?

Organic and inorganic forms of mercury are highly neurotoxic environmental contaminants. The exact mechanisms involved in mercury neurotoxicity are still unclear. Oxidative stress appears to play central role in this process. In this study, we aimed to validate an insect-based model for the investigation of oxidative stress during mercury poisoning of lobster cockroach Nauphoeta cinerea. The advantages of using insects in basic toxicological studies include the easier handling, rapid proliferation/growing and absence of ethical issues, comparing to rodent-based models. Insects received solutions of HgCl2 (10, 20 and 40mgL(-1) in drinking water) for 7d. 24h after mercury exposure, animals were euthanized and head tissue samples were prepared for oxidative stress related biochemical determinations. Mercury exposure caused a concentration dependent decrease in survival rate. Cholinesterase activity was unchanged. Catalase activity was substantially impaired after mercury treatment 40mgL(-1). Likewise, GST had a significant decrease, comparing to control. Peroxidase and thioredoxin reductase activity was inhibited at concentrations of 20mgL(-1) and 40mgL(-1) comparing to control. These results were accompanied by decreased GSH levels and increased hydroperoxide and TBARS formation. In conclusion, our results show that mercuric compounds are able to induce oxidative stress signs in insect by modulating survival rate as well as inducing impairments on important antioxidant systems. In addition, our data demonstrates for the first time that Nauphoeta cinerea represents an interesting animal model to investigate mercury toxicity and indicates that the GSH and thioredoxin antioxidant systems plays central role in Hg induced toxicity in insects.

Cd, Cu, Zn, Se, and metallothioneins in two amphibians, Necturus maculosus (Amphibia, Caudata) and Bufo bufo (Amphibia, Anura)

The accumulation of cadmium, its affinity for metallothioneins (MTs), and its relation to copper, zinc, and selenium were investigated in the experimental mudpuppy Necturus maculosus and the common toad Bufo bufo captured in nature. Specimens of N. maculosus were exposed to waterborne Cd (85 μg/L) for up to 40 days. Exposure resulted in tissue-dependent accumulation of Cd in the order kidney, gills > intestine, liver, brain > pancreas, skin, spleen, and gonads. During the 40-day exposure, concentrations increased close to 1 μg/g in kidneys and gills (0.64-0.95 and 0.52-0.76; n = 4), whereas the levels stayed below 0.5 in liver (0.14-0.29; n = 4) and other organs. Cd exposure was accompanied by an increase of Zn and Cu in kidneys and Zn in skin, while a decrease of Cu was observed in muscles and skin. Cytosol metallothioneins (MTs) were detected as Cu,Zn-thioneins in liver and Zn,Cu-thioneins in gills and kidney, with the presence of Se in all cases. After exposure, Cd binding to MTs was clearly observed in cytosol of gills as Zn,Cu,Cd-thionein and in pellet extract of kidneys as Zn,Cu,Cd-thioneins. The results indicate low Cd storage in liver with almost undetectable Cd in liver MT fractions. In field trapped Bufo bufo (spring and autumn animals), Cd levels were followed in four organs and found to be in the order kidney > liver (0.56-5.0 μg/g >0.03-0.72 μg/g; n = 11, spring and autumn animals), with no detectable Cd in muscle and skin. At the tissue level, high positive correlations between Cd, Cu, and Se were found in liver (all r > 0.80; α = 0.05, n = 5), and between Cd and Se in kidney (r = 0.76; n = 5) of autumn animals, possibly connected with the storage of excess elements in biologically inert forms. In the liver of spring animals, having higher tissue level of Cd than autumn ones, part of the Cd was identified as Cu,Zn,Cd-thioneins with traces of Se. As both species are special in having liver Cu levels higher than Zn, the observed highly preferential Cd load in kidney seems reasonable. The relatively low Cd found in liver can be attributed to its excretion through bile and its inability to displace Cu from MTs. The associations of selenium observed with Cd and/or Cu (on the tissue and cell level) point to selenium involvement in the detoxification of excessive cadmium and copper through immobilization.

Transcriptome response to pollutants and insecticides in the dengue vector Aedes aegypti using next-generation sequencing technology

BACKGROUND

The control of mosquitoes transmitting infectious diseases relies mainly on the use of chemical insecticides. However, mosquito control programs are now threatened by the emergence of insecticide resistance. Hitherto, most research efforts have been focused on elucidating the molecular basis of inherited resistance. Less attention has been paid to the short-term response of mosquitoes to insecticides and pollutants which could have a significant impact on insecticide efficacy. Here, a combination of LongSAGE and Solexa sequencing was used to perform a deep transcriptome analysis of larvae of the dengue vector Aedes aegypti exposed for 48 h to sub-lethal doses of three chemical insecticides and three anthropogenic pollutants.

RESULTS

Thirty millions 20 bp cDNA tags were sequenced, mapped to the mosquito genome and clustered, representing 6850 known genes and 4868 additional clusters not located within predicted genes. Mosquitoes exposed to insecticides or anthropogenic pollutants showed considerable modifications of their transcriptome. Genes encoding cuticular proteins, transporters, and enzymes involved in the mitochondrial respiratory chain and detoxification processes were particularly affected. Genes and molecular mechanisms potentially involved in xenobiotic response and insecticide tolerance were identified.

CONCLUSIONS

The method used in the present study appears as a powerful approach for investigating fine transcriptome variations in genome-sequenced organisms and can provide useful informations for the detection of novel transcripts. At the biological level, despite low concentrations and no apparent phenotypic effects, the significant impact of these xenobiotics on mosquito transcriptomes raise important questions about the 'hidden impact' of anthropogenic pollutants on ecosystems and consequences on vector control.

Pb2+: an endocrine disruptor in Drosophila?

Environmental exposure to Pb(2+) affects hormone-mediated responses in vertebrates. To help establish the fruit fly, Drosophila melanogaster, as a model system for studying such disruption, we describe effects of Pb(2+) on hormonally regulated traits. These include duration of development, longevity, females' willingness to mate, fecundity and adult locomotor activity. Developmental Pb(2+) exposure has been shown to affect gene expression in a specific region of the Drosophila genome (approximately 122 genes) involved in lead-induced changes in adult locomotion and to affect regulation of intracellular calcium levels associated with neuronal activity at identified synapses in the larval neuromuscular junction. We suggest ways in which Drosophila could become a new model system for the study of endocrine disruptors at genetic, neural and behavioral levels of analysis, particularly by use of genomic methods. This will facilitate efforts to distinguish between behavioral effects of Pb(2+) caused by direct action on neural mechanisms versus effects of Pb(+2) on behavior mediated through endocrine disruption.