Perturbation of organogenesis by the herbicide atrazine in the amphibian Xenopus laevis

[Open experiment: QuEChERS combined with fluorescence derivatization for the detection of atrazine and its effect on enzyme activity]

Atrazine is a triazine pesticide that interferes with normal physiological activities, induces oxidative stress, and is significantly toxic to plants. Therefore, the ability to quantitatively detect atrazine and study the mechanisms responsible for its toxicity are crucial for ensuring food safety and maintaining plant growth. Herein, a method was developed by QuEChERS combined with fluorescence derivatization to rapidly, sensitively, and quantitatively detect atrazine in real samples. This approach offers excellent selectivity and high sensitivity, and is simple to operate. In addition, we also investigated the effect of atrazine on catalase activity through enzyme-activity assays and molecular-docking studies to explore the mechanism responsible for the toxicity of atrazine on the molecular level. This experiment involves knowledge related to sample pretreatment, spectroscopy, and molecular docking, while the instruments used are widely available in colleges and universities and are very suitable for teaching open experiments. This experiment aims to provide students with a comprehensive understanding of experimental operations integrated with theory, as well as applied research aimed at helping students understand the use of separation materials, the selection and application of fluorescent derivatization reagents, the principles of analytical instruments, the use of enzymes, and the principles of molecular docking. This experiment is expected to enhance students' awareness of people's livelihoods, analytical chemistry concepts, and operational standards, which will guide the development of their scientific research thinking and improve their abilities to solve real-world problems.

Morphological and cellular effects in Boana faber tadpoles (Anura: Hylidae) exposed to atrazine-based herbicide and glyphosate-based herbicide and their mixtures

Atrazine and glyphosate are considered some of the main pollutants for aquatic ecosystems, directly and indirectly affecting non-target organisms, such as amphibians. This study aimed to evaluate the sublethal effects of different concentrations of atrazine-based herbicide (ABH) and glyphosate-based herbicide (GBH) commercial formulations, both individually and in a mixture, through toxicity tests on the larval stage of Boana faber. Tadpoles were exposed to concentrations of ABH (2, 9.33, 10.40, 47.21, and 240 μg L-1) and GBH (65, 144, 280, 500, and 1000 μg L-1), as well as a mixture ABH + GBH, for 7 days. Although survival and swimming activity were not significantly affected by herbicide exposure, tadpoles in all treatments showed damage to the mouth and intestine, changes in size and mass, and an increase in the frequency of micronuclei and other nuclear abnormalities. Despite differences in some variables analyzed, it is not possible to definitively state that there is a difference in the toxicity of these two herbicides, as both caused morphological damage and were cyto-genotoxic. Our findings suggest that exposure to commercial formulations of these herbicides, whether alone or in mixture, can directly impact the quality of life of B. faber tadpoles.

Glyphosate formulations cause mortality and diverse sublethal defects during embryonic development of the amphibian Xenopuslaevis

The human impact on environmental landscapes, such as land use, climate change or pollution, is threatening global biodiversity and ecosystems maintenance. Pesticides like the herbicide glyphosate have garnered considerable attention due to their well-documented harmful effects on non-target species. During application, the active ingredient glyphosate is utilized in various formulations, each containing different additive adjuvants. However, the possible effects of these formulations on amphibians - the group with the highest decline rates among vertebrates - remain largely unknown. Therefore, the present study investigated the effects of four glyphosate formulations (Glyphosat TF, Durano TF, Helosate 450 TF, Kyleo) on the embryonic development of the model organism Xenopus laevis (South African clawed frog). Embryos at the 2-cell stage were exposed to various concentrations of glyphosate formulations (glyphosate: 0.01-100 mg/L), and mortality as well as sublethal effects on different organs and tissues were analyzed. The results indicated that the formulations had different effects, particularly on the mortality of Xenopus laevis embryos. At sublethal concentrations, the formulations altered the embryos' external appearance, leading to malformations such as reduced eye and head size. In addition, exposure to formulations impaired heart morphology and function, and the expression of heart-specific genes was altered at a molecular level. Our results confirmed that glyphosate formulations had a stronger effect on Xenopus laevis embryogenesis than pure glyphosate. Therefore, it is crucial to evaluate the active ingredient and the co-formulations independently, as well as the combined, commercially available products, during pesticide risk assessments and renewal procedures of agrochemicals. The severe global decline of amphibians, partly due to herbicide use, highlights the need for strict and efficient monitoring of environmental pesticide loads and application areas.

Endocrine toxicity of atrazine and its underlying mechanisms

Atrazine (ATR) is one of the most widely utilized herbicides globally and is prevalent in the environment due to its extensive use and long half-life. It can infiltrate the human body through drinking water, ingestion, and dermal contact, and has been recognized as an environmental endocrine disruptor. This study aims to comprehensively outline the detrimental impacts of ATR on the endocrine system. Previous research indicates that ATR is harmful to various bodily systems, including the reproductive system, nervous system, adrenal glands, and thyroi d gland. The toxic effects of ATR on the endocrine system and its underlying molecular mechanisms are summarized as follows: influencing the expression of kisspeptin in the HPG axis, consequently affecting steroid synthesis; disrupting DNA synthesis and meiosis, as well as modifying DNA methylation levels, leading to reproductive and developmental toxicity; impacting dopamine by altering Nurr1, VMAT2, and DAT expression, consequently affecting dopamine synthesis and transporter expression, and influencing other neurotransmitters, resulting in neurotoxicity; and changing adipose tissue synthesis and metabolism by reducing basal metabolism, impairing cellular oxidative phosphorylation, and inducing insulin resistance. Additionally, a compilation of natural products used to mitigate the toxic effects of ATR has been provided, encompassing melatonin, curcumin, quercetin, lycopene, flavonoids, vitamin C, vitamin E, and other natural remedies. It is important to note that existing research predominantly relies on in vitro and ex vivo experiments, with limited population-based empirical evidence available.

Atrazine exposure promotes cardiomyocyte pyroptosis to exacerbate cardiotoxicity by activating NF-κB pathway

Atrazine is a ubiquitous herbicide with persistent environmental presence and accumulation in the food chain, posing potential health hazards to organisms. Increasing evidence suggests that atrazine may have detrimental effects on various organ systems, including the nervous, digestive, and immune systems. However, the specific toxicity and underlying mechanism of atrazine-induced cardiac injury remain obscure. In this study, 4-week-old male C57BL/6 mice were administered atrazine via intragastric administration at doses of 50 and 200 mg/kg for 4 and 8 weeks, respectively. Our findings showed that atrazine exposure led to cardiac fibrosis, as evidenced by elevated heart index and histopathological scores, extensive myofiber damage, and interstitial collagen deposition. Moreover, atrazine induced cardiomyocyte apoptosis, macrophage infiltration, and excessive production of inflammatory factors. Importantly, atrazine upregulated the expressions of crucial pyroptosis proteins, including NLRP3, ASC, CASPASE1, and GSDMD, via the activation of NF-κB pathway, thus promoting cardiomyocyte pyroptosis. Collectively, our findings provide novel evidence demonstrating that atrazine may exacerbate myocardial fibrosis by inducing cardiomyocyte pyroptosis, highlighting its potential role in the development of cardiac fibrosis.

Developmental regulation of cellular metabolism is required for intestinal elongation and rotation

Malrotation of the intestine is a prevalent birth anomaly, the etiology of which remains poorly understood. Here, we show that late-stage exposure of Xenopus embryos to atrazine, a widely used herbicide that targets electron transport chain (ETC) reactions, elicits intestinal malrotation at high frequency. Interestingly, atrazine specifically inhibits the cellular morphogenetic events required for gut tube elongation, including cell rearrangement, differentiation and proliferation; insufficient gut lengthening consequently reorients the direction of intestine rotation. Transcriptome analyses of atrazine-exposed intestines reveal misexpression of genes associated with glycolysis and oxidative stress, and metabolomics shows that atrazine depletes key glycolytic and tricarboxylic acid cycle metabolites. Moreover, cellular bioenergetics assays indicate that atrazine blocks a crucial developmental transition from glycolytic ATP production toward oxidative phosphorylation. Atrazine-induced defects are phenocopied by rotenone, a known ETC Complex I inhibitor, accompanied by elevated reactive oxygen species, and rescued by antioxidant supplementation, suggesting that malrotation may be at least partly attributable to redox imbalance. These studies reveal roles for metabolism in gut morphogenesis and implicate defective gut tube elongation and/or metabolic perturbations in the etiology of intestinal malrotation.

Anuran heart development and critical developmental periods: a comparative analysis of three Neotropical anuran species

The heart begins to form early during vertebrate development and is the first functional organ of the embryo. This study aimed to describe and compare the heart development in three Neotropical anuran species, Physalaemus albonotatus, Elachistocleis bicolor, and Scinax nasicus. Different Gosner Stages (GS) of embryos (GS 18-20) and premetamorphic (GS 21-25), prometamorphic (GS 26-41) and metamorphic (GS 42-46) tadpoles were analyzed using stereoscopic microscopy and Scanning Electronic Microscopy. Heart development was similar in the three analyzed species; however, some heterochronic events were identified between P. albonotatus and S. nasicus compared to E. bicolor. In addition, different patterns of melanophores arrangement were observed. During the embryonic and metamorphic periods, the main morphogenetic events occur: formation of the heart tube, regionalization of the heart compartments, development of spiral valve, onset of heartbeat, looping, and final displacement of the atrium and its complete septation. Both periods are critical for the normal morphogenesis and the correct functioning of the anuran heart. These results are useful to characterize the normal anuran heart morphology and to identify possible abnormalities caused by exposure to environmental contaminants.

Trans-ovo permethrin exposure affects growth, brain morphology and cardiac development in quail

Permethrin is a commonly used, highly effective pesticide in poultry agriculture, and has recently been trialed in conservation efforts to protect Galápagos finch hatchlings from an invasive ectoparasite. Although permethrin is considered safe for adults, pesticides can have health consequences when animals are exposed during early life stages. The few studies that have examined permethrin's effects in embryonic chicks and rats have shown hydrocephaly, anencephaly, reduced cellular energy conversion, and disruption of developing heart muscle. To test whether trans-ovo exposure of permethrin affects early development in birds, we exposed Japanese quail (Coturnix japonica) eggs to cotton treated with 1% permethrin that was incorporated into nests in two amounts (0.2, 0.8 g), each with a paired untreated cotton control group. When measured on incubation Day 15, we found permethrin-treated developing birds were smaller and showed signs of microcephaly, although mortality rates were the same. Despite no difference in heart mass, ventricular tissue was less compact, cardiac arteries were reduced and heart rates were slower in permethrin-treated birds. Differences in heart development were also observed at 5 days of incubation, indicating that abnormalities are present from early in cardiac development. Future studies are needed to examine permethrin's effects on developmental pathways and to determine if these effects persist after hatching to affect offspring health. This study provides evidence that permethrin can cross the eggshell to cause non-lethal but adverse effects on embryonic development, and studies should look beyond hatching when monitoring the efficacy of permethrin on wild bird populations.

Why We Will Continue to Lose Our Battle with Cancers If We Do Not Stop Their Triggers from Environmental Pollution

Besides our current health concerns due to COVID-19, cancer is a longer-lasting and even more dramatic pandemic that affects almost a third of the human population worldwide. Most of the emphasis on its causes has been posed on genetic predisposition, chance, and wrong lifestyles (mainly, obesity and smoking). Moreover, our medical weapons against cancers have not improved too much during the last century, although research is in progress. Once diagnosed with a malignant tumour, we still rely on surgery, radiotherapy, and chemotherapy. The main problem is that we have focused on fighting a difficult battle instead of preventing it by controlling its triggers. Quite the opposite, our knowledge of the links between environmental pollution and cancer has surged from the 1980s. Carcinogens in water, air, and soil have continued to accumulate disproportionally and grow in number and dose, bringing us to today's carnage. Here, a synthesis and critical review of the state of the knowledge of the links between cancer and environmental pollution in the three environmental compartments is provided, research gaps are briefly discussed, and some future directions are indicated. New evidence suggests that it is relevant to take into account not only the dose but also the time when we are exposed to carcinogens. The review ends by stressing that more dedication should be put into studying the environmental causes of cancers to prevent and avoid curing them, that the precautionary approach towards environmental pollutants must be much more reactionary, and that there is an urgent need to leave behind the outdated petrochemical-based industry and goods production.

Amiodarone bioconcentration and suppression of metamorphosis in Xenopus

Trace concentrations of a number of pharmaceutically active compounds have been detected in the aquatic environment in many countries, where they are thought to have the potential to exert adverse effects on non-target organisms. Amiodarone (AMD) is one such high-risk compound commonly used in general hospitals. AMD is known to alter normal thyroid hormone (TH) function, although little information is available regarding the specific mechanism by which this disruption occurs. Anuran tadpole metamorphosis is a TH-controlled developmental process and has proven to be useful as a screening tool for environmental pollutants suspected of disrupting TH functions. In the present study, our objective was to clarify the effects of AMD on Xenopus metamorphosis as well as to assess the bioconcentration of this pharmaceutical in the liver. We found that AMD suppressed spontaneous metamorphosis, including tail regression and hindlimb elongation in pro-metamorphic stage tadpoles, which is controlled by endogenous circulating TH, indicating that AMD is a TH antagonist. In transgenic X. laevis tadpoles carrying plasmid DNA containing TH-responsive element (TRE) and a 5'-upstream promoter region of the TH receptor (TR) βA1 gene linked to a green fluorescent protein (EGFP) gene, triiodothyronine (T₃) exposure induced a strong EGFP expression in the hind limbs, whereas the addition of AMD to T₃ suppressed EGFP expression, suggesting that this drug interferes with the binding of T₃ to TR, leading to the inhibition of TR-mediated gene expression. We also found AMD to be highly bioconcentrated in the liver of pro-metamorphic X. tropicalis tadpoles, and we monitored hepatic accumulation of this drug using mass spectrometry imaging (MSI). Our findings suggest that AMD imposes potential risk to aquatic wildlife by disrupting TH homeostasis, with further possibility of accumulating in organisms higher up in the food chain.

Morphological and histological abnormalities of the neotropical toad, Rhinella arenarum (Anura: Bufonidae) larvae exposed to dexamethasone

Dexamethasone (DEX) is a glucocorticoid highly effective as an anti-inflammatory, immunosuppressant and decongestant drug. In the present study, a preliminary acute toxicity test was assayed in order to determinate DEX median-lethal, lowest-observed-effect and the no-observed-effect concentrations (LC₅₀, LOEC and NOEC, respectively) on the common toad embryos (Rhinella arenarum). Also, morphological and histological abnormalities from five body larval regions, liver melanomacrophages (MM) and glutathione S-transferase (GST) activity were evaluated in the toad larvae to characterize the chronic sublethal effects of DEX (1-1,000 µg L^-L). Results of the acute test showed that the LC₅₀ of DEX at 96 h of exposure for the toad embryos (GS 18-20) was 10.720 mg L^-g, and the LOEC was 1 µg L^-g. In the chronic assay, the larval development and body length were significantly affected. DEX exposition also induced teratogenic effects. Most frequent external abnormalities observed in DEX-treated larvae included abdominal edema and swollen body, abnormal gut coiling and visceral congestion. Intestinal dysplasia was recurrent in cross-section of all DEX-treated larvae. Neural, conjunctive and renal epithelial cells were also affected. Significant increase in liver MM number and size, and GST activity levels were also registered in DEX treatments with respect to controls. The evaluation of a variety of biomarkers provided clear evidence of toad larvae sensitivity to DEX, and the ecotoxicological risk of these pharmaceuticals, commonly found in different water bodies worldwide on aquatic animals.

Bacterial catabolism of s-triazine herbicides: biochemistry, evolution and application

The synthetic s-triazines are abundant, nitrogen-rich, heteroaromatic compounds used in a multitude of applications including, herbicides, plastics and polymers, and explosives. Their presence in the environment has led to the evolution of bacterial catabolic pathways in bacteria that allow use of these anthropogenic chemicals as a nitrogen source that supports growth. Herbicidal s-triazines have been used since the mid-twentieth century and are among the most heavily used herbicides in the world, despite being withdrawn from use in some areas due to concern about their safety and environmental impact. Bacterial catabolism of the herbicidal s-triazines has been studied extensively. Pseudomonas sp. strain ADP, which was isolated more than thirty years after the introduction of the s-triazine herbicides, has been the model system for most of these studies; however, several alternative catabolic pathways have also been identified. Over the last five years, considerable detail about the molecular mode of action of the s-triazine catabolic enzymes has been uncovered through acquisition of their atomic structures. These structural studies have also revealed insights into the evolutionary origins of this newly acquired metabolic capability. In addition, s-triazine-catabolizing bacteria and enzymes have been used in a range of applications, including bioremediation of herbicides and cyanuric acid, introducing metabolic resistance to plants, and as a novel selectable marker in fermentation organisms. In this review, we cover the discovery and characterization of bacterial strains, metabolic pathways and enzymes that catabolize the s-triazines. We also consider the evolution of these new enzymes and pathways and discuss the practical applications that have been considered for these bacteria and enzymes. One Sentence Summary: A detailed understanding of bacterial herbicide catabolic enzymes and pathways offer new evolutionary insights and novel applied tools.

Biotoxicity of diclofenac on two larval amphibians: Assessment of development, growth, cardiac function and rhythm, behavior and antioxidant system

The non-steroidal anti-inflammatory drug diclofenac (DCF) threatens the health of aquatic animals and ecosystems. In the present study, different biological endpoints (mortality, development and growth, abnormalities, cardiotoxicity, neurotoxicity and antioxidant system) were used to characterize the acute and chronic effects of DCF (at concentrations ranging between 125 and 4000 μg L^-1) on two amphibian species from Argentina (Trachycephalus typhonius and Physalaemus albonotatus). Results showed that the larval developmental, growth rates, and body condition of DCF-exposed individuals of both species were significantly reduced. DCF-exposed individuals also showed several morphological abnormalities, including significantly altered body axis, chondrocranium and hyobranchial skeleton, and organ and visceral abnormalities including cardiac hypoplasia, malrotated guts, asymmetrically inverted guts, and cholecystitis. DCF also had a significant effect on the swimming performance of both species: at low concentrations (125 and 250 μg L^-1), swimming distance, velocity and global activity decreased, whereas, at high concentrations (1000 and 2000 μg L^-1), these behavioral responses increased. Regarding cardiac function and rhythm, at DCF concentrations higher than 1000 μg L^-1, the heart frequency and ventricular systole interval of both species were significantly reduced. Regarding the antioxidant system, the activity of acetylcholinesterase indicated that DCF is neurotoxic and thus related to the changes in behavioral performance. The DCF concentrations studied produced a biochemical imbalance between radical oxygen species production and antioxidant systems. The sensitivities to sublethal and chronic DCF exposure in both anuran species were similar, thus indicating the inherent complexity involved in understanding the biotoxic effects of DCF.

Exposures to chemical contaminants: What can we learn from reproduction and development endpoints in the amphibian toxicology literature?

Environmental contamination is one of the major factors or cofactors affecting amphibian populations. Since 2000, the number of studies conducted in laboratory conditions to understand impacts of chemical exposures increased. They aimed to characterize biological effects on amphibians. This review proposes an overview of biological responses reported after exposures to metals, phytopharmaceuticals or emerging organic contaminants and focuses on endpoints relating to reproduction and development. Due to amphibian peculiar features, these periods of their life cycle are especially critical to pollutant exposures. Despite the large range of tested compounds, the same model species are often used as biological models and morphological alterations are the most studied observations. From the results, the laboratory-to-field extrapolation remained uneasy and exposure designs have to be more elaborated to be closer to environmental conditions. Few studies proposed such experimental approaches. Lastly, gametes, embryos and larvae constitute key stages of amphibian life cycle that can be harmed by exposures to freshwater pollutants. Specific efforts have to be intensified on the earliest stages and notably germ cells.

Lethal and Sublethal Effects of the Herbicide Atrazine in the Early Stages of Development of Physalaemus gracilis (Anura: Leptodactylidae)

Water sources used as reproductive sites by crying frog, Physalaemus gracilis, are extensively associated with agroecosystems in which the herbicide atrazine is employed. To evaluate the lethal and sublethal effects of atrazine commercial formulation, acute and chronic toxicity tests were performed in the embryonic phase and the beginning of the larval phase of P. gracilis. Tests were started on stage 19 of Gosner (Herpetologica 16:183-190, 1960) and performed in 24-well cell culture plates. Acute tests had a duration of 96 h with embryo mortality monitoring every 24 h. Chronic assays contemplated the transition from the embryonic to larval stages and lasted 168 h. Every 24 h the embryos/larvae were observed for mortality, mobility, and malformations. The LC50 of atrazine determined for P. gracilis embryos was 229.34 mg L^-1. The sublethal concentrations did not affect the development of the larvae but were observed effects on mobility and malformations, such as spasmodic contractions, reduced mobility, malformations in mouth and intestine, and edema arising. From 1 mg L^-1 atrazine, the exposed larvae began to have changes in mobility and malformations. The atrazine commercial formulation has caused early life effects of P. gracilis that may compromise the survival of this species but at higher concentrations than recorded in the environment, so P. gracilis can be considered tolerant to this herbicide at environmentally relevant concentrations.

A novel mechanism underlies atrazine toxicity in quails (Coturnix Coturnix coturnix): triggering ionic disorder via disruption of ATPases

The widely used atrazine has been reported to exhibit extensive ecological hazards. Due to the biological accumulation, atrazine elicits widespread toxic effects on different organisms. However, true proof for the mechanism of atrazine-induced toxicity is lacking. To determine the potential mechanism by which atrazine exerted toxic effects, quails were treated with atrazine (0, 50, 250 and 500 mg/kg) by gavage administration for 45 days. Atrazine significantly increased the histological alterations and serum creatine kinase, lactate dehydrogenase and choline esterase levels. A marked disorder in ionic (Na+, K+, Ca2+ and Mg2+)contents and the decrease of ATPases (Na+-K+-ATPase, Ca2+-ATPase, Mg2+-ATPase and Ca2+-Mg2+-ATPase) activities were observed in the heart and liver of atrazine-exposed quails. Of note, it was also observed that atrazine suppressed the transcription of Na+, K+ transfer associated genes (Na+-K+-ATPase subunits) and Ca2+ transfer associated genes (Ca2+-ATPase subunits, solute carriers) in heart and liver. In conclusion, atrazine induced cardiac and hepatic damage via causing the ionic disorder, triggering the transcription of the ion transporters and leading the histopathological and functional alternations in the heart and liver of quails. This study demonstrated atrazine significantly induced the ionic disorder via decreasing the ATPases activities and disturbing the transcription of the ion transporters.

Atrazine affects the morphophysiology, tissue homeostasis and aromatase expression in the efferent ductules of adult rats with mild alterations in the ventral prostate

The widely used herbicide atrazine is a potent endocrine disruptor known to cause increased aromatase expression and transient increase in testicular weight followed by remarkable testis atrophy. However, whether the effects of atrazine on the testes are primary or secondary to dysfunctions in other components of male reproductive tract remains unknown. Given the high sensitivity of the efferent ductules to estrogen imbalance and the similarity to alterations previously described for other disruptors of these ductules function, and the testicular alterations observed after atrazine exposure, we hypothesized that the efferent ductules could be a target for atrazine. Herein we characterized the efferent ductules and the ventral prostate of adult Wistar rats treated with 200 mg/kg/day of atrazine for 7, 15, and 40 days. Additionally, we evaluated if the effects of atrazine in these organs could be reduced after discontinuation of the treatment. Atrazine exposure resulted in mild effects on the ventral prostate, but remarkable alterations on the efferent ductules, including luminal dilation, reduced epithelial height, and disruption of the epithelial homeostasis, which coincides with increased aromatase expression. Together with our previous data, these results suggest that at least part of the testicular effects of atrazine may be secondary to the alterations in the efferent ductules.

Chronic toxicity of 1,3,5-triazine herbicides in the postembryonic development of the western clawed frog Silurana tropicalis

Seven 1,3,5- triazine (s-triazine) herbicides (ametryn, prometryn, dimethametryn, simazine, atrazine, propazine, and cyanazine) were tested using an amphibian (Silurana tropicalis) metamorphosis assay focusing on morphometric, gravimetric, and thyroid-histological endpoints. Premetamorphic tadpoles were exposed to each s-triazine at 2 concentrations between 1/1000 and 1/10 of the 96-h acute toxicity values, until all tadpoles in the control group reached either the late prometamorphosic stages or the initial stage of metamorphic climax. All s-triazines tested induced significant retardation in growth and development at the higher concentrations (0.2-1.0mg/L), and some of them induced similar effects even at the lower concentrations (0.02-0.1mg/L) while each showing a linear dose-response. Total size of the thyroid glands tended to be reduced corresponding to the delayed development, but without showing histomorphological lesions typical of anti-thyroid chemicals. These consistent results suggest that the s-triazines can act as a chemical stressor inhibiting tadpole growth and development, possibly without disrupting the thyroid axis. In addition, tadpoles exhibiting spinal curvatures appeared in either one or both of the lower and higher concentration groups for each s-triazine tested. The incidence rate in the s-triazine exposure groups where tadpoles with scoliosis were observed ranged from 3.3% to 63.3%, some of which were significantly higher than that in the respective control groups (0-6.7%). It is speculated that the s-triazines may promote to occur axial malformations in developing tadpoles.

Altered development, oxidative stress and DNA damage in Leptodactylus chaquensis (Anura: Leptodactylidae) larvae exposed to poultry litter

Poultry litter (PL), which is usually used as organic fertilizer, is a source of nutrients, metals, veterinary pharmaceuticals and bacterial pathogens, which, through runoff, may end up in the nearest aquatic ecosystems. In this study, Leptodactylus chaquensis at different development stages (eggs, larval stages 28 and 31 here referred to as stages I, II and III respectively) were exposed to PL test sediments as follows: 6.25% (T1), 12.5% (T2); 25% (T3); 50% (T4); 75% (T5); 100% PL (T6) and to dechlorinated water as control. Larval survival, development endpoints (growth rate -GR-, development rate -DR-, abnormalities), antioxidant enzyme activities (Catalase -CAT- and Glutathione-S-Transferase -GST-), and genotoxic effect (DNA damage index by the Comet assay) were analyzed at different times. In stage I, no egg eclosion was observed in treatments T3-T6, and 50% of embryo mortality was recorded after 24h of exposure to T2. In stages II and III, mortality in treatments T3-T6 reached 100% between 24 and 48h. In the three development stages evaluated, the DR and GR were higher in controls than in PL treatments (T1, T2), except for those T1-treated larvae of stage II. Larvae of stage I showed five types of morphological abnormalities, being diamond body shape and lateral displacement of the intestine the most prevalent in T1, whereas larvae of stages II and III presented lower prevalence of abnormalities. In stage I, CAT activity was similar to that of control (p>0.05), whereas it was higher in T1- and T2- treated larvae of stages II and III than controls (p<0.05). In stages I and III, GST activity was similar to that of controls (p>0.05), whereas it was inhibited in T1-treated larvae of stage II (p<0.05). T1- and T2-treated larvae of stages II and III caused higher DNA damage respect to controls (p<0.05), varying from medium to severe damage (comet types II, III and IV). These results showed that PL treatments altered development and growth and induced oxidative stress and DNA damage, resulting ecotoxic for L. chaquensis larvae.

The chemopreventive potential of lycopene against atrazine-induced cardiotoxicity: modulation of ionic homeostasis

People who drink water contaminated with atrazine (ATR) over many years can experience problems with their cardiovascular system. Lycopene (LYC) has been shown to exhibit cardiovascular disease preventive effects. However, chemopreventive potential of LYC against ATR-induced cardiotoxicity remains unclear. To determine the effects of ATR and/or LYC on heart, mice were treated with ATR (50 mg/kg or 200 mg/kg) and/or LYC (5 mg/kg) by intragastric administration for 21 days. Histopathological and biochemical analyses, including analysis of ion concentrations (Na⁺, K⁺, Ca²⁺ and Mg²⁺), ATPases (Na⁺-K⁺-ATPase, Ca²⁺-ATPase, Mg²⁺-ATPase and Ca²⁺-Mg²⁺-ATPase) activities and the transcription of their subunits, were performed on heart. The results revealed that ATR led to decreased Creative Kinase (CK) activity and increased histological alterations. Furthermore, a significant change in Na⁺, K⁺ and Ca²⁺ content and the down-regulation of Na⁺-K⁺-ATPase and Ca²⁺-ATPase activities and the mRNA expression of their subunits were observed in ATR-exposed mice. Notably, supplementary LYC significantly protected the heart against ATR-induced damage. In conclusion, ATR induced cardiotoxicity by modulating cardiac ATPase activity and the transcription of its subunits, thereby triggering ionic disturbances. However, supplementary LYC significantly combated ATR-induced cardiotoxicity via the regulation of ATPase activity and subunit transcription. Thus, LYC exhibited a significant chemopreventive potential against ATR-induced cardiotoxicity.

Frogs as integrative models for understanding digestive organ development and evolution

The digestive system comprises numerous cells, tissues and organs that are essential for the proper assimilation of nutrients and energy. Many aspects of digestive organ function are highly conserved among vertebrates, yet the final anatomical configuration of the gut varies widely between species, especially those with different diets. Improved understanding of the complex molecular and cellular events that orchestrate digestive organ development is pertinent to many areas of biology and medicine, including the regeneration or replacement of diseased organs, the etiology of digestive organ birth defects, and the evolution of specialized features of digestive anatomy. In this review, we highlight specific examples of how investigations using Xenopus laevis frog embryos have revealed insight into the molecular and cellular dynamics of digestive organ patterning and morphogenesis that would have been difficult to obtain in other animal models. Additionally, we discuss recent studies of gut development in non-model frog species with unique feeding strategies, such as Lepidobatrachus laevis and Eleutherodactylous coqui, which are beginning to provide glimpses of the evolutionary mechanisms that may generate morphological variation in the digestive tract. The unparalleled experimental versatility of frog embryos make them excellent, integrative models for studying digestive organ development across multiple disciplines.

Low concentrations of metal mixture exposures have adverse effects on selected biomarkers of Xenopus laevis tadpoles

Polluted ecosystems may contain mixtures of metals, such that the combinations of metals, even in low concentrations, may cause adverse effects. In the present study, we focused on toxic effects of mixtures of selected metals, the LC50 values, and also their safety limit in aquatic systems imposed by the European legislation using a model organism. Xenopus laevis tadpoles were used as test organisms. They were exposed to metals or their combinations due to 96-h LC50 values. Glutathione S-transferase (GST), glutathione reductase (GR), acetylcholinesterase (AChE), carboxylesterase (CaE), glutathione peroxidase (GPx), and catalase (CAT) levels were evaluated. Metallothionein concentrations were also determined. The LC50s for Cd, Pb, and Cu were calculated as 5.81mg AI/L, 123.05mg AI/L, and 0.85mg AI/L, respectively. Low lethality ratios were observed with unary exposure of each metal in lower concentrations. Double or triple combinations of LC50 and LC50/2 concentrations caused 100% lethality with Cd+Cu and Pb+Cd+Cu mixtures, while the Pb+Cu mixture also caused high lethal ratios. The selected enzyme activities were significantly affected by metals or mixtures, and dose-related effects were determined. The metallothionein levels generally increased as related to concentration in unary metals and mixtures. Acceptable limit values of unary metals and mixtures did not significantly change metallothionein levels. The results suggest that oxidative stress-related mechanisms are involved in the toxicity induced by selected metals with combinations of very low concentrations.

Plasma retinoids concentration in Leptodactylus chaquensis (Amphibia: Leptodactylidae) from rice agroecosystems, Santa Fe province, Argentina

Retinoids are known to regulate important processes such as differentiation, development, and embryogenesis of vertebrates: Alteration in endogenous retinoids concentration is linked with teratogenic effects. Retinol (ROH), retinoid acid (RA), and isoform 13-Cis-retinoic acid (13-Cis-RA), in plasma of a native adults frog, Leptodactylus chaquensis from a rice field (RF) and a forest (reference site; RS) were measured. ROH did not vary between treatment sites. RA and 13-Cis-RA activities were higher (93.7±8.6 μg mL(-1) and 131.7±11.4 μg mL(-1), respectively) in individuals collected from RF than in those from RS (65.5±8.6 μg mL(-1) and 92.2±10.2 μg mL(-1), respectively). The ratios retinoic acid-retinol (RA/ROH) and 13-Cis-RA/ROH revealed significantly higher values in RF than in RS. RA and 13-Cis-RA concentrations in plasma on wild amphibian's species such as L. chaquensis would be suitable biomarkers of pesticide exposure in field monitoring. Finally, the mechanism of alteration in retinoid metabolites alteration should be further explored both in larvae and adult, considering that the potential exposition and uptake contaminants vary between the double lives of these vertebrates.

Proteomics analysis of Xenopus laevis gonad tissue following chronic exposure to atrazine

Atrazine is the most commonly detected pesticide contaminant in ground and surface water. Previous studies have shown that atrazine is an endocrine disruptor owing to its adverse effects on the male reproductive system in several vertebrates, but very few molecular mechanisms for these effects have been revealed. In the present study, Xenopus laevis were exposed to 100 ppb of atrazine for 120 d, and then the isobaric tags for relative and absolute quantitation (iTRAQ) technique was used to detect global changes in protein profiles of the testes and ovaries. The results showed that 100 ppb of atrazine exposure adversely affected the growth of X. laevis and did not induce hermaphroditism but delayed or prevented the development of male seminiferous tubules. Proteomic analysis showed that atrazine altered expression of 143 and 121 proteins in the testes and ovaries, respectively, and most of them are involved in cellular and metabolic processes and biological regulation based on their biological processes. In addition, apoptosis, tight junctions, and metabolic pathways were significantly altered in the atrazine-treated gonads. Based on the above results, it is postulated that the reproductive toxicity of atrazine may be the result of disruption of tight junctions and metabolic signaling pathways and/or induction of apoptosis in germ cells.

Effects of atrazine in fish, amphibians, and reptiles: an analysis based on quantitative weight of evidence

A quantitative weight of evidence (WoE) approach was developed to evaluate studies used for regulatory purposes, as well as those in the open literature, that report the effects of the herbicide atrazine on fish, amphibians, and reptiles. The methodology for WoE analysis incorporated a detailed assessment of the relevance of the responses observed to apical endpoints directly related to survival, growth, development, and reproduction, as well as the strength and appropriateness of the experimental methods employed. Numerical scores were assigned for strength and relevance. The means of the scores for relevance and strength were then used to summarize and weigh the evidence for atrazine contributing to ecologically significant responses in the organisms of interest. The summary was presented graphically in a two-dimensional graph which showed the distributions of all the reports for a response. Over 1290 individual responses from studies in 31 species of fish, 32 amphibians, and 8 reptiles were evaluated. Overall, the WoE showed that atrazine might affect biomarker-type responses, such as expression of genes and/or associated proteins, concentrations of hormones, and biochemical processes (e.g. induction of detoxification responses), at concentrations sometimes found in the environment. However, these effects were not translated to adverse outcomes in terms of apical endpoints. The WoE approach provided a quantitative, transparent, reproducible, and robust framework that can be used to assist the decision-making process when assessing environmental chemicals. In addition, the process allowed easy identification of uncertainty and inconsistency in observations, and thus clearly identified areas where future investigations can be best directed.

Atrazine affects phosphoprotein and protein expression in MCF-10A human breast epithelial cells

Atrazine, a member of the 2-chloro-s-triazine family of herbicides, is the most widely used pesticide in the world and often detected in agriculture watersheds. Although it was generally considered as an endocrine disruptor, posing a potential threat to human health, the molecular mechanisms of atrazine effects remain unclear. Using two-dimensional gel electrophoresis, we identified a panel of differentially expressed phosphoproteins and total proteins in human breast epithelial MCF-10A cells after being exposed to environmentally relevant concentrations of atrazine. Atrazine treatments for 6 h resulted in differential expression of 4 phosphoproteins and 8 total-proteins as compared to the control cells (>1.5-fold, p < 0.05). MALDI-TOF MS/MS analysis revealed that the differentially expressed proteins belong to various cellular compartments (nucleus, cytosol, membrane) and varied in function, including those regulating the stress response such as peroxiredoxin I, HSP70 and HSP27; structural proteins such as tropomyosin and profilin 1; and oncogenesis proteins such as ANP32A. Six of the 12 identified proteins were verified by quantitative PCR for their transcript levels. The most up-regulated phosphoprotein by atrazine treatment, ANP32A, was further analyzed for its expression, distribution and cellular localization using Western blot and immunocytochemical approaches. The results revealed that ANP32 expression after atrazine treatment increased dose and time dependently and was primarily located in the nucleus. This study may provide new evidence on the potential toxicity of atrazine in human cells.

Effect of exposure to contaminated pond sediments on survival, development, and enzyme and blood biomarkers in veined treefrog (Trachycephalus typhonius) tadpoles

Sediments are important elements of aquatic ecosystems and in general sediments accumulate diverse toxic substances. Amphibians potentially have a greater risk of exposure to contaminants in sediments, and the test of sediments provides first lines of evidences. Sediment outdoor microcosm experiments were conducted to analyze biological endpoints (survival, development, growth, and morphological and organ malformation), enzyme activity (butyrylcholinesterase, BChE; glutathione-S-transferase, GST; and catalase, CAT) and blood biomarkers in veined treefrog Trachycephalus typhonius tadpoles, a widespread neotropical species. Hatching (stage 23) of T. thyphonius was exposed until they reached metamorphosis (stage 46). Sediment tests were performed and four different treatments were used: three ponds (LTPA, ISP, and SSP) influenced by industrial and agricultural activities and a reference treatment from a forest (RFS). Physical and chemical variables and concentration of nutrients, pesticide residues, and metals were determined. One treatment was metal-rich (LPTA) and two were nutrient-rich (ISP and SSP). Sediment treatments had no significant effect on survival; in contrast they had significant sublethal effects on T. typhonius larval development and growth rates, and affected overall size and shape at stage 38. Principally, in LPTA animals were significantly larger than in RFS, exhibiting swollen bodies, tail muscles and tail fin. In addition, metamorphs from LPTA, ISP, and SSP were smaller and showed signs of emaciation by the end of the experiment. Statistical comparisons showed that the proportions of each type of morphological abnormalities (swollen bodies and diamond shape, gut uncoiling, diverted gut, stiff tails, polydactyly, and visceral and hindlimb hemorrhaging) were significantly greater in metal- and nutrient-rich sediment treatments. Moreover, activities of BChE, GST and CAT, as well as and presence of micronuclei, immature, mitotic, anucleated erythrocytes varied significantly among treatments. Our biological effects-based sediment study highlights the use of different biological endpoints and biomarkers on anuran larvae at sites where pond sediment is risky and sediment management should be considered. Finally, the information of those biological endpoints and biomarkers would be useful as a management tool to decide if there are sufficient exposures of tadpoles to suspected pollutants on sediment.

Comparative sensitivities of larval stages of the cane toad, Rhinella marina, and the striped marsh frog, Limnodynastes peronii, to atrazine

Variations in larval sensitivities to atrazine were determined in the Australian native striped marsh frog, Limnodynastes peronii, and the introduced cane toad, Rhinella marina. The static acute test design involved six nominal concentrations of atrazine, including control, solvent control, 3, 6, 12, and 24 mg L–1. Gosner stages 22–23 as hatchlings, stages 25–26, 28–29, and 32–33 as premetamorphic, 36–37 as prometamorphic and 40–41 as metamorphic climax stages of cane toads and the first four sets of Gosner stages of striped marsh frogs were exposed to atrazine treatments for 96 h. Results showed that late larval stages were more sensitive than early stages and different premetamorphic stages showed variations in sensitivities in both test species. The striped marsh frog showed a stronger concentration- and stage-dependent response and greater sensitivity to atrazine than the cane toad. In both experimental species, Gosner stages 28–29 showed better concentration-dependent increase in sensitivities to atrazine compared with other larval stages. It can be concluded that inter- and intra-species variations in sensitivities to atrazine may occur in Australian anurans and native species may show greater sensitivity to acute concentrations of atrazine than the introduced cane toad.

Atrazine-induced changes in the myocardial structure of peripubertal rats

The aim of the present study was to investigate the effect of atrazine (6-chloro-N(2)-ethyl-N(4)-isopropyl-1,3,5-triazine-2,4-diamine) on the left ventricle myocardium in juvenile/peripubertal male Wistar rats. Atrazine was administered orally at 50 or 200 mg/kg of body weight dose for 28 consecutive days. In order to assess possible structural alterations, tissue sections were examined histologically and then subjected to quantification analysis using stereological methods. The tissue specimens were routinely processed and stained with Mallory trichrome method in order to clearly distinguish muscle cells from the connective tissue components. A toluidine blue staining method was additionally used for the demonstration of mast cells. Statistically significant increase in length density and numerical density of capillaries were found at both the investigated doses of atrazine compared with the control. The increase in surface density and volume density of capillaries found at lower dosage of atrazine was significant in comparison with the control. The extensive mast cell degranulation was noted on the histological examination at both doses of the applied chemical. No significant changes were demonstrated for the stereological parameters of cardiomyocytes. Based on the available published data and the present results, it can be concluded that atrazine promoted angiogenesis in the rat myocardium, which might be partially mediated by mast cells.

Organochlorine pesticide, endosulfan induced cellular and organismal response in Drosophila melanogaster

The effect of endosulfan (0.02-2.0μgmL(-1)) to Drosophila melanogaster (Oregon R(+)) at the cellular and organismal levels was examined. Third instar larvae of D. melanogaster and the strains transgenic for hsp70, hsp83 and hsp26 were exposed to endosulfan through food for 12-48h to examine the heat shock proteins (hsps), reactive oxygen species (ROS) generation, anti-oxidant stress markers and xenobiotic metabolism enzymes. We observed a concentration- and time-dependent significant induction of only small hsps (hsp23>hsp22) in the exposed organism in concurrence with a significant induction of ROS generation, oxidative stress and xenobiotic metabolism markers. Sub-organismal response was to be propagated towards organismal response, i.e., delay in the emergence of flies and decreased locomotor behaviour. Organisms with diminished locomotion also exhibited significantly lowered acetylcholinesterase activity. A significant positive correlation observed among ROS generation and different cellular endpoints (small hsps, oxidative stress markers, cytochrome P450 activities) in the exposed organism indicate a modulatory role of ROS in endosulfan-mediated cellular toxicity. The study thus suggests that the adverse effects of endosulfan in exposed Drosophila are manifested both at cellular and organismal levels and recommends Drosophila as an alternative animal model for screening the risk caused by environmental chemicals.

Sublethal effects of atrazine on embryo-larval development of Rhinella arenarum (Anura: Bufonidae)

Atrazine (ATR), one of the most widely used herbicides in the world, affects not only target organisms but also the biota in general. Here, the teratogenic and neurotoxic effects of ATR on Rhinella arenarum (South American toad) embryos, and larvae were evaluated by means of standardized bioassays during acute and chronic exposures. The herbicide had a significant incidence of malformations, with a Teratogenic Index (TI) of 3.28. The main effects were delayed development, reduced body size, microcephaly, axial flexures, wavy tail and edema. In addition, delayed development, reduced development of forelimbs, and edema were recorded at metamorphosis stages. Scanning electron microscopy allowed observing different degrees of cellular dissociation and persistent cilliar cells in specific regions like the adhesive structure and tail fin. Results obtained by ATR 24 h pulse exposures at six developmental stages pointed out blastula as the most susceptible developmental stage both for immediate and delayed adverse effects. A noteworthy recovery capacity from acute toxic effects was recorded from the neural plate stage onwards. Regarding neurotoxic effects, abnormal, and erratic swimming and spasmodic contractions were recorded. Both the teratogenic and neurotoxic effects reported in this study demonstrate the importance of evaluating sublethal effects in non-target organisms as they could imply reduced fitness of individuals and eventually a population decline. The Hazard Quotients (HQ) for ATR ranged from 0.14 to 10.80, and the fact that some of these values are above USEPA's level of concern indicate that ATR is likely a risk to R. arenarum.

Histological observation on unique phenotypes of malformation induced in Xenopus tropicalis larvae by tributyltin

Tributyltin (TBT), a biocide used in antifouling paints, has shown strong teratogenic effects on Xenopus tropicalis embryos at environmentally relevant concentrations. X. tropicalis embryos were exposed to 50, 100 and 200 ng/L tributyltin chloride for 72 hr. The histological changes were further observed on abnormal eyes, enlarged trunks, enlarged proctodaeums and absence of fins induced by TBT. The lens and the retinal layers of abnormal eyes were slightly or barely differentiated, and that the pigment epithelium was neither continuous nor smooth. The abdomens were full of undifferentiated gut tissue with yolk-rich inclusions in the tadpoles with enlarged trunks. The proctodaeums formed a bump-like or columnar structure. The mass of yolk-rich cells occupied the lumen, blocked the opening and even turned inside out of the proctodaeum. Both the ventral and dorsal fins in trunks and tails became narrow or even disappeared totally. Our results suggest that great changes of histology took place corresponding to the unique phenotypes. The gut tissue was poorly differentiated, which led to the failed elongation of the guts and subsequently the enlarged trunks. The enlarged proctodaeums were due to the undifferentiation of inner layer, the expansion of outer epidermal part and the absence of fins around them. In brief, the histological observations provided insights into the reason of the unique external malformations in some degree.

Alterations in jejunal morphology and serotonin-containing enteroendocrine cells in peripubertal male rats associated with subchronic atrazine exposure

The effect of atrazine on jejunum was investigated by histopathological examination and quantification analysis related to the morphological parameters of the jejunum. The experiment was performed on male Wistar rats from postnatal day 23-51. Atrazine was administered by gavage daily to one group of rats at 50 mg/kg of body weight (bw) dose, to the second at 200 mg/kg bw while the third group was the control. At the end of the experiments after 28 days of treatment, tissue samples were routinely processed and stained with haematoxylin eosin. Additionally, the histochemical staining with periodic acid Schiff-alcian blue was used to demonstrate goblet cells and the immunohistochemistry protocol for serotonin-containing enteroendocrine cells. A significant decrease in the height of epithelial cells covering the intestinal villi, the villus height to total mucosa thickness ratio and the villus height to crypt depth ratio was found at both doses of atrazine. The crypt depth, total mucosa thickness and the thickness of tunica muscularis were significantly increased by the high dose of atrazine only. The number of serotonin-positive endocrine cells significantly decreased in rats treated with the low dose of atrazine. Overall, these results suggest the alterations in intestinal absorption and support the role of atrazine as an endocrine-disrupting compound.

Atrazine-induced apoptosis of splenocytes in BALB/C mice

BACKGROUND

Atrazine (2-chloro-4-ethytlamino-6-isopropylamine-1,3,5-triazine; ATR), is the most commonly applied broad-spectrum herbicide in the world. Unintentional overspray of ATR poses an immune function health hazard. The biomolecular mechanisms responsible for ATR-induced immunotoxicity, however, are little understood. This study presents on our investigation into the apoptosis of splenocytes in mice exposed to ATR as we explore possible immunotoxic mechanisms.

METHODS

Oral doses of ATR were administered to BALB/C mice for 21 days. The histopathology, lymphocyte apoptosis and the expression of apoptosis-related proteins from the Fas/Fas ligand (FasL) apoptotic pathway were examined from spleen samples.

RESULTS

Mice administered ATR exhibited a significant decrease in spleen and thymus weight. Electron microscope histology of ultrathin sections of spleen revealed degenerative micromorphology indicative of apoptosis of splenocytes. Flow cytometry revealed that the percentage of apoptotic lymphocytes increased in a dose-dependent manner after ATR treatment. Western blots identified increased expression of Fas, FasL and active caspase-3 proteins in the treatment groups.

CONCLUSIONS

ATR is capable of inducing splenocytic apoptosis mediated by the Fas/FasL pathway in mice, which could be the potential mechanism underlying the immunotoxicity of ATR.

Atrazine exposure affects growth, body condition and liver health in Xenopus laevis tadpoles

Six studies were performed regarding the effects of atrazine, the most frequently detected pesticide in fresh water in the US, on developing Xenopus laevis tadpoles exposed 5 days post-hatch through Nieuwkoop Faber Stage 62. The levels of atrazine tested included those potentially found in puddles, vernal ponds and runoff soon after application (200 and 400 μg/L) and a low level studied by a number of other investigators (25 μg/L). One study tested 0, 25 and 200 μg/L, another tested 0, 200 and 400 μg/L, while the remaining four studies tested 0 and 400 μg/L. During all exposures, mortality, growth, metamorphosis, sex ratio, fat body (a lipid storage organ) size and liver weights, both relative to body weight, were evaluated. In selected studies, feeding behavior was recorded, livers and fat bodies were histologically evaluated, liver glycogen and lipid content were determined by image analysis, and immunohistochemical detection of activated caspase-3 in hepatocytes was performed. The NOEC was 25 μg/L. None of these exposure levels changed sex ratios nor were intersex gonads noted, however, no definitive histological evaluation of the gonads was performed. Although a marginal increase in mortality at the 200 μg/L level was noted, this was not statistically significant. Nor was there an increase in mortality at 400 μg/L versus controls. At the 400 μg/L level, tadpoles were smaller than controls by 72 h of exposure and remained smaller throughout the entire exposure. Appetite was not decreased at any exposure level. Slowed metamorphosis was noted only at 400 μg/L in two of five studies. Livers were significantly smaller in the study that tested both 200 and 400 μg/L, yet no pathological changes or differences in glycogen or lipid stores were noted. However, livers from 400 μg/L exposed tadpoles had higher numbers of activated caspase-3 immunopositive cells suggesting increased rates of apoptosis. Fat body size decreased significantly after exposure to 200 and 400 μg/L although these organs still contained some lipid and lacked any pathology. Since this was noted across all studies, it was considered the most sensitive indicator of atrazine exposure measured. The changes noted in body and organ size at 200 and 400 μg/L atrazine indicated exposure throughout development compromised the tadpoles. Significant reductions in fat body size could potentially decrease their ability to survive the stresses of metamorphosis or reduce reproductive fitness as frogs rely on stored lipids for these processes.

Acute atrazine exposure disrupts matrix metalloproteinases and retinoid signaling during organ morphogenesis in Xenopus laevis

Exposure to the herbicide atrazine disrupts many developmental processes in non-target animals. Atrazine exposure during organ morphogenesis in amphibians results in dramatic malformations; the mechanism by which this happens has not been described. We have taken a candidate gene approach to explore two possible mechanisms by which acute atrazine exposure causes extensive malformations in several tissues in Xenopus laevis tadpoles. Using a static renewal system, we exposed tadpoles to atrazine for 6-48 h during organ morphogenesis (Nieuwkoop and Faber stage 42). We observed degradation of cranial cartilage and differentiated muscle in the head, gut and somites of exposed tadpoles. Additionally, transcript levels of matrix metalloproteinases (MMPs), specifically both MMP9TH and MMP18, increased in atrazine-exposed tadpoles in a dose-response test, and MMP18 increased as early as 6 h after exposure began. Gelatinase MMP activity was also altered by atrazine exposure, indicating that atrazine disrupts gene function at the level of transcription and protein activity. Furthermore, transcript levels of the enzyme Xcyp26, an enzyme in the retinoic acid signaling pathway, significantly decreased in the intestines of tadpoles exposed to 10 or 35 mg l(-1) atrazine for 48 h. Our results suggest two mechanisms by which atrazine can disrupt tissue morphogenesis: through misregulation of MMPs that are critical in extracellular matrix remodeling throughout development and the disruption of retinoic acid signaling. This study begins to describe conserved vertebrate developmental processes that are disrupted by atrazine exposure.

Low levels of the herbicide atrazine alter sex ratios and reduce metamorphic success in Rana pipiens tadpoles raised in outdoor mesocosms

BACKGROUND

There are conflicting reports regarding the effects of atrazine (ATZ) on amphibian development. Therefore, further studies are needed to examine the potential mechanisms of action of ATZ in amphibians.

OBJECTIVES

Our aim in this study was to determine whether low concentrations of ATZ affect gonadal development and metamorphosis in the Northern leopard frog, Rana pipiens.

METHODS

Tadpoles were exposed in outdoor mesocosms to nominal concentrations of 0.1 and 1.8 microg/L of formulated ATZ from Gosner stage 27 (G27) to metamorphic climax (G42). Exposure to 17alpha-ethinylestradiol (EE2; 1.5 microg/L) provided a positive control for induction of testicular oocytes in males. Endocrine-related gene expression and gonadal histopathology were examined at G42 and in a subset of premetamorphic G34 tadpoles that failed to metamorphose.

RESULTS

Gonadal gross morphology revealed that the 1.8-microg/L ATZ treatment produced 20% more females compared with the control. Histologic analysis revealed that 22% of EE2-treated males had testicular oocytes, whereas none were observed in any animals from the control or either ATZ groups. ATZ increased brain estrogen receptor alpha mRNA to 2.5 times that of the control at premetamorphosis and altered liver levels of 5beta-reductase activity at metamorphosis. In contrast, brain aromatase mRNA level and activity did not change. ATZ treatments significantly reduced metamorphic success (number of animals reaching metamorphosis) without affecting body weight, snout-vent length, or age at metamorphosis. Gene expression analysis indicated that ATZ decreased the expression of deiodinase type 3 in the tail at premetamorphosis.

CONCLUSIONS

Our study indicates that exposure to low concentrations of ATZ in experimental mesocosms alters gonadal differentiation and metamorphosis in developing R. pipiens.

Effects of the endocrine disruptors atrazine and PCB 153 on the protein expression of MCF-7 human cells

Polychlorinated biphenyls (PCBs) and a number of pesticides can act as endocrine disrupting compounds (EDCs). These molecules exhibit hormonal activity in vivo, and can therefore interact and perturb normal physiological functions. Many of these compounds are persistent in the environment, and their bioaccumulation may constitute a significant threat for human health. Physiological abnormalities following exposure to these xenobiotic compounds go along with alterations at the protein level of individual cells. In this study, MCF-7 cells were exposed to environmentally relevant concentrations of atrazine, PCB153 (100 ppb, respectively), 17-beta estradiol (positive control, 10 nM) and a negative control (solvent) for t = 24 h (n = 3 replicates/exposure group). After trizol extraction and protein solubilization, protein expression levels were studied by 2D-DIGE. Proteins differentially expressed were excised, trypsin-digested, and identified by MALDI-ToF-ToF, followed by NCBInr database search. 2D-DIGE experiments demonstrated that 49 spots corresponding to 29 proteins were significantly differentially expressed in MCF-7 cells (>1.5-fold, P < 0.05, Student's paired t test). These proteins belonged to various cellular compartments (nucleus, cytosol, membrane), and varied in function; 88% of proteins were down-regulated during atrazine exposure, whereas 75% of proteins were up-regulated by PCB153. Affected proteins included those regulating oxidative stress such as superoxide dismutase and structural proteins such as actin or tropomyosin, which may explain morphological changes of cells already observed under the microscope. This study highlights the susceptibility of human cells to compounds with endocrine disrupting properties.

Low concentrations of atrazine, glyphosate, 2,4-dichlorophenoxyacetic acid, and triadimefon exposures have diverse effects on Xenopus laevis organ morphogenesis

Many chemicals are released into the environment, and chemical contamination has been suggested as a contributing factor to amphibian declines. To add to a growing body of knowledge about the impact of individual chemicals on non-target organisms, we examined the specificity of deformities induced by exposure to four pesticides (atrazine, 2,4-dichloropheoxyacetic acid (2,4-D), triadimefon, and glyphosate) in the model amphibian species, Xenopus laevis. We focused on the period of organ morphogenesis, as it is frequently found to be particularly sensitive to chemical exposure yet also commonly overlooked. We found similar levels of intestine malformations and edemas, as well as disruption of skeletal muscle, in atrazine and triadimefon exposed tadpoles. The effects of 2,4-D were only apparent at the highest concentrations we examined; glyphosate did not induce dramatic malformations at the concentrations tested. While researchers have shown that it is important to understand how chemical mixtures affect non-target organisms, our results suggest that it is first crucial to determine how these chemicals act independently in order to be able to identify consequences of individual pesticide exposure.

Amphibians and agricultural chemicals: review of the risks in a complex environment

Agricultural landscapes, although often highly altered in nature, provide habitat for many species of amphibian. However, the persistence and health of amphibian populations are likely to be compromised by the escalating use of pesticides and other agricultural chemicals. This review examines some of the issues relating to exposure of amphibian populations to these chemicals and places emphasis on mechanisms of toxicity. Several mechanisms are highlighted, including those that may disrupt thyroid activity, retinoid pathways, and sexual differentiation. Special emphasis is also placed on the various interactions that may occur between different agro-chemicals and between chemicals and other environmental factors. We also examine the indirect effects on amphibian populations that occur when their surrounding pond communities are altered by chemicals.

Chronic exposure to high levels of atrazine alters expression of genes that regulate immune and growth-related functions in developing Xenopus laevis tadpoles

Atrazine is the most commonly detected pesticide in ground and surface waters, with seasonal spikes that often exceed the Environmental Protection Agency's "Recommended Water Quality Criterion" of 350 parts per billion (ppb). Although numerous studies have shown atrazine produces adverse effects on growth, development, immune and endocrine system functions in a wide range of species, few describe gene expression changes concurrent with atrazine-induced changes in phenotype during development. In this report, developing Xenopus laevis tadpoles were chronically exposed to 400 ppb atrazine, an environmentally relevant concentration. Affymetrix microarrays and Taqman qRT-PCR were used to define gene expression changes that underlie atrazine-induced phenotypic alterations. Atrazine significantly reduced survival and growth (weight, length and fat body size) in male and female tadpoles. Microarray analysis showed atrazine altered expression of 44 genes in male tadpoles (18 upregulated, 26 downregulated) and 77 genes in female tadpoles (23 upregulated, 54 downregulated). Classification of the genes into functional groups showed the majority of genes were associated with the following biological functions: growth and metabolism, proteolysis, fibrinogen complex formation and immune regulation. Seven genes associated with immune system function, specifically defense molecules present in the skin (e.g. magainin II, levitide A, preprocarulein, skin granule protein), were significantly downregulated in female tadpoles. These results support the idea that environmental contaminants such as atrazine compromise important gene pathways during frog development that may, ultimately, be relevant to global amphibian decline.