Metabolism of arsenic in Drosophila melanogaster and the genotoxicity of dimethylarsinic acid in the Drosophila wing spot test

Methylation and bio-accessibility assessment of arsenate in crickets (Gryllusbimaculatus)

The ability of an organism to biomethylate toxic inorganic arsenic (As) determines both, the amount of As available for uptake higher up the food chain and the toxicity of bioavailable As. An exposure study was conducted to determine ability of farmed crickets to metabolize dietary arsenate. Crickets were exposed to 1.3 ± 0.1, 5.1 ± 2.5 and 36.3 ± 5.6 mg kg-1 dietary arsenate and quantitation of total As showed retention of 0.416 ± 0.003, 1.3 ± 0.04 and 2.46 ± 0.09 mg kg-1, respectively. Speciation analysis revealed that crickets have well developed ability to biomethylate dietary arsenate and the most abundant methylated As compound was DMA followed by MMA, TMAO and an unknown compound. Arsenobetaine, although present in all feed, control and As-rich, was measured only in the control crickets. To assess the bio-accessibility of the As species, crickets were subjected to simulated gastrointestinal digestion. The results showed that majority of As was extracted in saliva, followed by gastric and intestinal juice, which mass fraction was equal to residue. Over 78% of total As was shown to be bio-accessible with methylated species reaching 100% and iAs over 79% bio-accessibility. Additionally, arsenite and arsenate have shown different distributions between sequential leachate solutions. Bioaccumulation of As was observed in the studied crickets although it does not seem to occur to the same extent at higher exposure levels.

Carcinogen sodium arsenite disrupts antioxidant and redox homeostasis in Drosophila melanogaster

OBJECTIVES

The inadvertent exposure to environmental contaminants has been reported to induce cancer in different animal models. Here, we investigated the toxicity of Sodium Arsenite (SA), a Class I Carcinogen in Drosophila melanogaster.

METHODS

Harwich fly strain (1-3 days old) of both sexes were orally exposed to SA (0, 0.0312, 0.0625 and 0.125 mM) for 14 days for survival study. Thereafter, 5 days exposure period was selected to assess the toxic effects of SA on oxidative stress and antioxidant markers.

RESULTS

The results indicated that SA induced significant reduction in survival and emergence rate of flies. Furthermore, SA significantly increased Nitric Oxide (NO, nitrite and nitrate) and Hydrogen Peroxide (H2O2) levels in flies compared with control (p<0.05). In addition, SA inhibited catalase and glutathione-S-transferase (GST) activities, and depleted total thiol and glutathione (GSH) contents. Moreover, acetylcholinesterase activity significantly increased in flies treated with SA when compared with control.

CONCLUSIONS

Sodium arsenite-induced reduction in survival and emergence rates of flies occurred via the disruption of oxidative stress-antioxidant homeostasis in D. melanogaster.

Acute Exposure to Arsenic Affects Pupal Development and Neurological Functions in Drosophila melanogaster

Millions of people in developing countries are affected by arsenic (As) toxicity and its prevalence. Arsenic's detrimental effects on humans have been amplified by an unacceptable level of exposure to food and drinking water, the ongoing rise in industrial usage, and several other occupational conditions. Due to increased cellular absorption and the ability to cross the blood-brain barrier (BBB), inorganic arsenic (iAs) is extremely hazardous to living organisms in its trivalent form. Arsenic toxicity damages an organism's tissues and organs, resulting in skin cancer, circulatory system abnormalities, and central nervous system disorders. However, a competent model system is required to investigate the acute effects of arsenic on the brain, cognition ability, and to assess any behavioral impairment. Hence, Drosophila, with its short generation time, genomic similarities with humans, and its availability for robust behavioral paradigms, may be considered an ideal model for studying arsenic toxicity. The present study helps to understand the toxic effects of acute arsenic treatment on the behavior, cognition, and development of Drosophila in a time-dependent manner. We found that the exposure of fruit flies to arsenic significantly affected their locomotor abilities, pupae size, cognitive functions, and neurobehavioral impairment. Hence, providing a better understanding of how arsenic toxicity affects the brain leading to acute behavioral disorders and neurological alterations, this study will lead to a better understanding of the mechanisms.

Human Hazard Assessment Using Drosophila Wing Spot Test as an Alternative In Vivo Model for Genotoxicity Testing-A Review

Genomic instability, one of cancer's hallmarks, is induced by genotoxins from endogenous and exogenous sources, including reactive oxygen species (ROS), diet, and environmental pollutants. A sensitive in vivo genotoxicity test is required for the identification of human hazards to reduce the potential health risk. The somatic mutation and recombination test (SMART) or wing spot test is a genotoxicity assay involving Drosophila melanogaster (fruit fly) as a classical, alternative human model. This review describes the principle of the SMART assay in conjunction with its advantages and disadvantages and discusses applications of the assay covering all segments of health-related industries, including food, dietary supplements, drug industries, pesticides, and herbicides, as well as nanoparticles. Chemopreventive strategies are outlined as a global health trend for the anti-genotoxicity of interesting herbal extract compounds determined by SMART assay. The successful application of Drosophila for high-throughput screening of mutagens is also discussed as a future perspective.

Arsenic transformation mediated by gut microbiota affects the fecundity of Caenorhabditis elegans

Arsenic biotransformation has been discovered in guts of soil invertebrates. Reproduction of invertebrates is sensitive to arsenic contamination in soils. However, little is known about the impact of gut microbe-mediated arsenic biotransformation on the fecundity of invertebrates. Here, Caenorhabditis elegans was firstly pre-fed with Escherichia coli BL21 possessing the capability of reducing arsenate [As(V)] or BL21M having the ability to reduce As(V) and methylate arsenite [As(III)], then inoculated worms were transferred to inactive E. coli AW3110 (harboring no arsenic transformation gene)-seeded plates treated with As(V) at different concentrations. Quantification of gut microbes showed that both E. coli BL21 and BL21M stably colonized in the guts after worms were cultured on inactive E. coli AW3110-seeded plates for 72 h. The analysis of arsenic species indicated that there was As(III) in C. elegans guts colonized with E. coli BL21, As(III) and dimethylarsinic acid [DMAs(V)] in C. elegans guts with E. coli BL21M exposed to As(V) for 6 h. After treatment of 100 μM As(V), decrease in brood sizes was observed for worms that were colonized with E. coli BL21 or BL21M compared to that with AW3110 in the guts. The levels of vitellogenin (VTG), glutathione S-transferases (GST) and superoxide dismutase (SOD), closely linked to reproduction and antioxidation-linked indicators, were the highest in worms whose guts colonized with E. coli BL21, followed by worms colonized with E. coli BL21M and worms colonized with inactive E. coli AW3110 exposed to As(V). Our results indicated the toxic impact of As(III) and DMAs(V) produced by gut microbes on reproduction of C. elegans. The work provides novel insight into the interplay between arsenic biotransformation mediated by gut microbes and the host fecundity in soils.

The Wing-Spot and the Comet Tests as Useful Assays for Detecting Genotoxicity in Drosophila

In spite of its pioneer use in detecting mutational processes, Drosophila still plays an important role in those studies aiming to detect and quantify the induction of DNA damage. Here we describe two assays, one detecting primary damage (the Comet assay) and the other detecting somatic mutation and recombination effects (wing-spot test). It is important to emphasize that somatic recombination is a key event in cancer development and no assays exist at present to detect and quantify somatic recombination processes, other than the spot tests developed in Drosophila.

Drosophila melanogaster Models of Metal-Related Human Diseases and Metal Toxicity

Iron, copper and zinc are transition metals essential for life because they are required in a multitude of biological processes. Organisms have evolved to acquire metals from nutrition and to maintain adequate levels of each metal to avoid damaging effects associated with its deficiency, excess or misplacement. Interestingly, the main components of metal homeostatic pathways are conserved, with many orthologues of the human metal-related genes having been identified and characterized in Drosophila melanogaster. Drosophila has gained appreciation as a useful model for studying human diseases, including those caused by mutations in pathways controlling cellular metal homeostasis. Flies have many advantages in the laboratory, such as a short life cycle, easy handling and inexpensive maintenance. Furthermore, they can be raised in a large number. In addition, flies are greatly appreciated because they offer a considerable number of genetic tools to address some of the unresolved questions concerning disease pathology, which in turn could contribute to our understanding of the metal metabolism and homeostasis. This review recapitulates the metabolism of the principal transition metals, namely iron, zinc and copper, in Drosophila and the utility of this organism as an experimental model to explore the role of metal dyshomeostasis in different human diseases. Finally, a summary of the contribution of Drosophila as a model for testing metal toxicity is provided.

The wing-spot and the comet tests as useful assays detecting genotoxicity in Drosophila

In spite of its pioneer use in detecting mutational processes, Drosophila has yet an important role in studies aiming to detect and quantify the induction of DNA damage. Here we describe two assays, one detecting primary damage (the Comet assay) and the other detecting somatic mutation and recombination effects (wing-spot test). It is important to emphasize that somatic recombination is a key event in cancer and no assays exist to detect and quantify somatic recombination processes, other than the spot tests developed in Drosophila.

Cytotoxic and genotoxic effects of metal(oid)s bioactivated in rocket leaves (Eruca vesicaria subsp. sativa Miller)

Rocket is an important source of essential elements. However, it may also accumulate toxic elements such as metal(oids). The objectives of the present work were (i) to study the uptake of arsenic, lead, cadmium and zinc in rocket grown in contaminated soils, (ii) to establish the genotoxic and cytotoxic activities of this vegetable material, and (iii) to study the modulator role of the glucosinolate and metal contents in the genotoxic/cytotoxic activities. Lead, cadmium and zinc leaf concentrations in our study were over the concentrations allowed by the statutory limit set for metal(oid) contents in vegetables. The accessions were non genotoxic at the different concentrations studied, although one of the accessions showed the highest mutation rates doubling those of negative control. The cytotoxicity assays with HL60 human leukaemia cells showed that the tumouricide activities of rocket leaves decreased with the increasing of metal(oid) concentrations and also with the decreasing of glucosinolate concentrations in their tissues. An interaction between metal(oid)s and glucosinolate degradation products contained in rocket leaves is suggested as the main modulator agents of the biological activity of the plants grown in metal-contaminated soils.

Micro x-ray absorption spectroscopic analysis of arsenic localization and biotransformation in Chironomus riparius Meigen (Diptera: Chironomidae) and Culex tarsalis Coquillett (Culicidae)

The distribution and speciation of arsenic (As) were analyzed in individuals of various life stages of a midge, Chironomus riparius, and the mosquito Culex tarsalis exposed to 1000 μg/l arsenate. X-ray absorption spectroscopy (XAS) revealed that C. riparius larvae accumulate As in their midgut, with inorganic arsenate [As(V)] being the predominant form, followed by arsenite [As(III)] and an As-thiol. Reduced concentrations of As in pupal and adult stages of C. riparius indicate excretion of As between the larval and pupal stages. In adults, As was limited to the thorax, and the predominant form was an As-thiol. In Cx. tarsalis, As was not found in high enough concentrations to determine As speciation, but the element was distributed throughout the larva. In adults, As was concentrated in the thorax and eyes of adults. These results have implications for understanding the biotransformation of As and its movement from aquatic to terrestrial environments.

The glutathione reductase GSR-1 determines stress tolerance and longevity in Caenorhabditis elegans

Glutathione (GSH) and GSH-dependent enzymes play a key role in cellular detoxification processes that enable organism to cope with various internal and environmental stressors. However, it is often not clear, which components of the complex GSH-metabolism are required for tolerance towards a certain stressor. To address this question, a small scale RNAi-screen was carried out in Caenorhabditis elegans where GSH-related genes were systematically knocked down and worms were subsequently analysed for their survival rate under sub-lethal concentrations of arsenite and the redox cycler juglone. While the knockdown of γ-glutamylcysteine synthetase led to a diminished survival rate under arsenite stress conditions, GSR-1 (glutathione reductase) was shown to be essential for survival under juglone stress conditions. gsr-1 is the sole GSR encoding gene found in C. elegans. Knockdown of GSR-1 hardly affected total glutathione levels nor reduced glutathione/glutathione disulphide (GSH/GSSG) ratio under normal laboratory conditions. Nevertheless, when GSSG recycling was impaired by gsr-1(RNAi), GSH synthesis was induced, but not vice versa. Moreover, the impact of GSSG recycling was potentiated under oxidative stress conditions, explaining the enormous effect gsr-1(RNAi) knockdown had on juglone tolerance. Accordingly, overexpression of GSR-1 was capable of increasing stress tolerance. Furthermore, expression levels of SKN-1-regulated GSR-1 also affected life span of C. elegans, emphasising the crucial role the GSH redox state plays in both processes.

A transgenic Drosophila model for arsenic methylation suggests a metabolic rationale for differential dose-dependent toxicity endpoints

The mechanisms by which exposure to arsenic induces its myriad pathological effects are undoubtedly complex, while individual susceptibility to their type and severity is likely to be strongly influenced by genetic factors. Human metabolism of arsenic into methylated derivatives, once presumed to result in detoxification, may actually produce species with significantly greater pathological potential. We introduce a transgenic Drosophila model of arsenic methylation, allowing its consequences to be studied in a higher eukaryote exhibiting conservation of many genes and pathways with those of human cells while providing an important opportunity to uncover mechanistic details via the sophisticated genetic analysis for which the system is particularly well suited. The gene for the human enzyme, arsenic (+3 oxidation state) methyltransferase, was introduced into nonmethylating Drosophila under inducible control. Transgenic flies were characterized for enzyme inducibility, production of methylated arsenic species, and the dose-dependent consequences for chromosomal integrity and organismal longevity. Upon enzyme induction, transgenic flies processed arsenite into mono and dimethylated derivatives identical to those found in human urine. When induced flies were exposed to 9 ppm arsenite, chromosomal stability was clearly reduced, whereas at much higher doses, adult life span was significantly increased, a seemingly paradoxical pair of outcomes. Measurement of arsenic body burden in the presence or absence of methylation suggested that enhanced clearance of methylated species might explain this greater longevity under acutely toxic conditions. Our study clearly demonstrates both the hazards and the benefits of arsenic methylation in vivo and suggests a resolution based on evolutionary grounds.

Induction of adaptive response in Drosophila after exposure to low doses of UVB

PURPOSE

The aim of this study was to assess the adaptive response induced by low doses of ultraviolet-B (UVB, 290-320 nm) radiation in the Drosophila wing spot test.

MATERIALS AND METHODS

The adaptive response of Drosophila larvae to UVB light was studied by using a somatic mutation and recombination test (SMART). The SMART system used was the wing spot test, which uses morphological markers of the wing blade. This in vivo test has shown to be very useful to study the induction of genetic damage in somatic cells, measuring loss of heterozygosity (LOH) resulting from gene mutation, mitotic recombination, chromosomal rearrangements or chromosome loss.

RESULTS

To determine the induction of adaptive response, two-day-old Drosophila larvae were first irritated with an adaptive dose (58.3 J/m(2)), followed by different challenge doses (178, 224, 288, 338, and 386 J/m(2)). When the results obtained in the different challenge doses were compared with those obtained following the application of adaptive plus challenge doses, significant decreases (74.7-80.8%) in a first experiment, and (65.6-78.4%) in a second experiment, were observed in the frequency of mutant spots on the wing blades.

CONCLUSIONS

Our results show that in Drosophila the adaptive response can be stimulated in vivo by UVB exposure.

Arsenic speciation of terrestrial invertebrates

The distribution and chemical form (speciation) of arsenic in terrestrial food chains determines both the amount of arsenic available to higher organisms, and the toxicity of this metalloid in affected ecosystems. Invertebrates are part of complex terrestrial food webs. This paper provides arsenic concentrations and arsenic speciation profiles for eight orders of terrestrial invertebrates collected at three historical gold mine sites and one background site in Nova Scotia, Canada. Total arsenic concentrations, determined by inductively coupled plasma mass spectrometry (ICP-MS), were dependent upon the classification of invertebrate. Arsenic species were determined by high-performance liquid chromatography (HPLC) ICP-MS and X-ray absorption spectroscopy (XAS). Invertebrates were found by HPLC ICP-MS to contain predominantly arsenite and arsenate in methanol/water extracts, while XAS revealed that most arsenic is bound to sulfur in vivo. Examination of the spatial distribution of arsenic within an ant tissue highlighted the differences between exogenous and endogenous arsenic, as well as the extent to which arsenic is transformed upon ingestion. Similar arsenic speciation patterns for invertebrate groups were observed across sites. Trace amounts of arsenobetaine and arsenocholine were identified in slugs, ants, and spiders.

Drosophotoxicology: the growing potential for Drosophila in neurotoxicology

Understanding neurotoxic mechanisms is a challenge of deciphering which genes and gene products in the developing or mature nervous system are targeted for disruption by chemicals we encounter in our environment. Our understanding of nervous system development and physiology is highly advanced due in large part to studies conducted in simple non-mammalian models. The paucity of toxicological data for the more than 80,000 chemicals in commercial use today, and the approximately 2000 new chemicals introduced each year, makes development of sensitive and rapid assays to screen for neurotoxicity paramount. In this article I advocate the use of Drosophila in the modern regimen of toxicological testing, emphasizing its unique attributes for assaying neurodevelopment and behavior. Features of the Drosophila model are reviewed and a generalized overall scheme for its use in toxicology is presented. Examples of where the fly has proven fruitful in evaluating common toxicants in our environment are also highlighted. Attention is drawn to three areas where development and application of the fly model might benefit toxicology the most: 1) optimizing sensitive endpoints for pathway-specific screening, 2) accommodating high throughput demands for analysis of chemical toxicant libraries, 3) optimizing genetic and molecular protocols for more rapid identification toxicant-by-gene interactions. While there are shortcomings in the Drosophila model, which exclude it from effective toxicological testing in certain arenas, conservation of fundamental cellular and developmental mechanisms between flies and man is extensive enough to warrant a central role for the Drosophila model in toxicological testing of today.

Genotoxic evaluation of two halonitromethane disinfection by-products in the Drosophila wing-spot test

Few studies on the genotoxicity of halonitromethanes (HNMs) have been done. This limited information on their potential genotoxic risk gives special relevance to the collection of new data on their potential genotoxic activity. In the present study we have analyzed the genotoxicity of two HNMs namely bromonitromethane (BNM) and trichloronitromethane (TCNM) in the in vivo wing somatic mutation and recombination test in Drosophila, also known as the wing-spot assay. This test is based on the principle that loss of heterozygosis and the corresponding expression of the suitable recessive markers, multiple wing hairs (mwh) and flare-3 (flr(3)), can lead to the formation of mutant clones in larval cells, which are then expressed as spots on the wings of adult flies. BNM and TCNM were supplied to third instar larvae (72+/-4 h-old) at concentrations ranging from 0.1 to 2 mM. The results showed that none of the three categories of mutant spots recorded (small, large, and twin) increased significantly by the treatments, independently of the dose supplied, indicating that the selected HNMs exhibit a lack of genotoxic activity in the wing-spot assay of Drosophila melanogaster. These results contribute to increase the genotoxicity database on the HNMs.

Genotoxic evaluation of two mercury compounds in the Drosophila wing spot test

Few studies on the genotoxicity of mercury compounds have been carried out in Drosophila melanogaster, most of them focused in the effects on germinal cells, whereas studies in somatic cells are scarce. In the present study we have analyzed for the first time the genotoxic activity of mercury (II) chloride (MC) and methyl mercury (II) chloride (MMC) in the in vivo wing somatic mutation and recombination test in Drosophila, also known as the wing spot assay. This test is based on the principle that loss of heterozygosis and the corresponding expression of the suitable recessive markers, multiple wing hairs (mwh) and flare-3 (flr(3)), can lead to the formation of mutant clones in larval cells, which are then expressed as spots on the wings of adult flies. The mercury compounds were supplied to third instar larvae (72+/-2h old) at concentrations ranging from 1 to 50 microM for mercury chloride (MC) and from 0.5 to 5 microM for methyl mercury chloride (MMC). Both mercury compounds showed high toxicity; however, MMC was more toxic than MC. The results showed that none of the three categories of mutant spots recorded (small, large, and twin) increased significantly by the treatments, independently of the dose supplied, indicating that the mercury compounds tested exhibit a lack of genotoxic activity in the wing spot assay of D. melanogaster. These results contribute to increase the genotoxicity database on the in vivo evaluation of mercury compounds in Drosophila.

Gene-mutation induction by arsenic compounds in the mouse lymphoma assay

Arsenic compounds are generally considered as poor inducers of gene mutations. To investigate the mutagenicity of several arsenic compounds at the thymidine kinase (Tk) gene, a reporter gene for mutation induction, we used the mouse lymphoma assay (MLA). This test is widely applied and detects a broad spectrum of mutational events, from point mutations to chromosome alterations. The selected arsenic compounds were two inorganic (sodium arsenite and arsenic trioxide) and four organic compounds (monomethylarsonic acid, dimethylarsinic acid, tetraphenylarsenium and arsenobetaine). The results show that sodium arsenite, arsenic trioxide, monomethylarsonic acid and dimethylarsinic acid are mutagenic, showing a clear dose-response pattern. On the other hand, tetraphenylarsenium and arsenobetaine are not mutagenic. Inorganic arsenic compounds are the more potent agents producing significant effects in the micromolar range, while the mutagenic organic arsenic compounds induce similar effects but in the millimolar range.