The Pseudomonas putida NfnB nitroreductase confers resistance to roxarsone

Roxarsone (3-nitro-4-hydroxyphenylarsonic acid, Rox) has been used for decades as an antimicrobial growth promoter for poultry and swine. Roxarsone is excreted in chicken manure unchanged and can be microbially transformed into a variety of arsenic-containing compounds such as 3-amino-4-hydroxyphenylarsonic acid (HAPA(V)) that contaminate the environment and present a potential health hazard. To cope with arsenic toxicity, nearly every prokaryote has an ars (arsenic resistance) operon, some of which confer resistance to roxarsone. Pseudomonas putida KT2440 is a robust environmental isolate capable of metabolizing many aromatic compounds and is used as a model organism for biodegradation of aromatic compounds. Here we report that P. putida KT2440 (ΔΔars) in which the two ars operons had been deleted retains resistance to highly toxic trivalent Rox(III), the likely active form of roxarsone. In this study, a genomic library constructed from P. putida KT2440 (ΔΔars) was used to screen for resistance to Rox(III) in Escherichia coli. One gene, termed, PpnfnB, was identified that encodes a putative 6,7-dihydropteridine reductase. Cells expressing PpnfnB reduce the nitro group of Rox(III), and purified NfnB catalyzes FMN-NADPH-dependent nitroreduction of Rox(III) to less toxic HAPA(III). This identifies a key step in the breakdown of synthetic aromatic arsenicals.

Roxarsone exposure jeopardizes nitrogen removal and regulates bacterial community in biological sequential batch reactors

Roxarsone is widely present in wastewaters of many animal farms in China. However, little is known about how long-term roxarsone exposure influences the nitrogen removal of biological wastewater treatment in agricultural settings. Here we investigated the nitrogen removal performance of a biological sequential batch reactor (SBR) and the changes of bacterial community, upon long-term roxarsone exposure. The long-term roxarsone dosing decreased the SBR nitrogen removal by 52.4%, with an immediate inhibition on denitrification and a delayed inhibition on nitrification. The analyses of bacterial enzymatic activities and 16 S rRNA sequencing revealed that bacterial activities generally decreased, and the nitrogen-cycling bacterial community was changed, particularly by the decrease (Acinetobacter and Methylophilaceae), persistence (Flavobacterium and Methylotenera), and emergence (Aeromonas) of certain bacterial genera. Overall, chronic roxarsone exposure could suppress nitrification and denitrification, which may even have broad implications on the use efficiency and cycling of nitrogen in agroecosystems.

Stress-responsive genes (hsp70 and mt) and genotoxicity elicited by roxarsone exposure in Carassius auratus

In this study, comet assay (single-cell gel electrophoresis), real-time quantitative PCR (qPCR) and proteomics approach were used to comprehensively assess toxicity elicited by roxarsone exposure in C. auratus at 50, 150 and 300 μg/L for 7, 14 and 21 days. Results of comet assay showed that DNA were seriously damaged under the pressure of roxarsone, especially the concentration of 50 μg/L that always maintained a sustained and increased damage effect to fish liver cell during the 21 days experiment. The expressions of biomarker genes showed that hsp70 gene expressions raised significantly and the group of 50 μg/L also showed a continued increased response effect, whereas mt gene was only slightly increased. Results of proteomics for the concentration of 300 μg/L found that thirty six significantly changed proteins were identified by MALDI-TOF/TOF-MS. They are involved in many important processes including energy producing, cytoskeleton stabilization, substance metabolism and stress response. Among these metabolites, carbohydrate metabolism (mainly occurred during day 1-14) and cytoskeleton proteins (mainly occurred during day 14-21) were the most identified proteins. These results revealed that the low levels of 50 μg/L probably led to a continuous damage than the higher groups during the experiment time. Furthermore, proteomics results might implied that though cell system expected to mobilize almost all the functional proteins to quickly establish a new homeostasis together when facing the roxarsone at first, but in the end the destroyed cell cytoskeleton structure might burst the bubble.

Tumor-promoting and pro-angiogenic effects of roxarsone via VEGFR2/PLCγ/PKC signaling

Roxarsone is an organoarsenic feed additive used in livestock and poultry production that is released into the environment, where it poses a risk to human health. It is known to have a tumor-promoting effect that is brought about by pro-angiogenic factors such as vascular endothelial growth factor (VEGF) and it receptors (VEGFR). However, little information is available about the other signaling molecules that could be involved. This study aims to investigate the role of PLCγ/PKC signaling in roxarsone-induced angiogenesis in a mouse B16-F10 melanoma xenograft model and rat vascular endothelial cells (ECs). Results showed treatment with 5 mg/kg and 25 mg/kg roxarsone resulted in an obvious increase in the weight and volume of B16-F10 xenografts and PLCγ/PKC phosphorylation in a dose-dependent manner in C57BL/6 mice. SU5416, a VEGFR2 inhibitor, significantly attenuated the tumor growth induced by roxarsone. Further, 1.0 μmol/L roxarsone treatment in rat ECs was observed to significantly increase the optical density rate in the MTT assay, the number of BrdU-positive cells in the proliferation assay, the migration distance in the scratch test, and the number of meshes formed in the tube formation assay. In addition, treatment with 1.0 μmol/L roxarsone was associated with significantly higher phosphorylation of PLCγ/PKC than the control treatment. U73122, a PLCγ inhibitor, was found significantly to combat the effects of 1.0 μmol/L roxarsone on the ECs. Roxarsone is capable of promoting the growth of mouse B16-F10 xenografts and tube formation in vascular ECs. Moreover, VEGFR2/PLCγ/PKC signaling may play a regulatory role in in vivo and in vitro roxarsone-induced angiogenesis.

Response of soil microbial communities to roxarsone pollution along a concentration gradient

The extensive use of roxarsone (3-nitro-4-hydroxyphenylarsonic acid) as a feed additive in the broiler poultry industry can lead to environmental arsenic contamination. This study was conducted to reveal the response of soil microbial communities to roxarsone pollution along a concentration gradient. To explore the degradation process and degradation kinetics of roxarsone concentration gradients in soil, the concentration shift of roxarsone at initial concentrations of 0, 50, 100, and 200 mg/kg, as well as that of the arsenic derivatives, was detected. The soil microbial community composition and structure accompanying roxarsone degradation were investigated by high-throughput sequencing. The results showed that roxarsone degradation was inhibited by a biological inhibitor, confirming that soil microbes were absolutely essential to its degradation. Moreover, soil microbes had considerable potential to degrade roxarsone, as a high initial concentration of roxarsone resulted in a substantially increased degradation rate. The concentrations of the degradation products HAPA (3-amino-4-hydroxyphenylarsonic acid), AS(III), and AS(V) in soils were significantly positively correlated. The soil microbial community composition and structure changed significantly across the roxarsone contamination gradient, and the addition of roxarsone decreased the microbial diversity. Some bacteria tended to be inhibited by roxarsone, while Bacillus, Paenibacillus, Arthrobacter, Lysobacter, and Alkaliphilus played important roles in roxarsone degradation. Moreover, HAPA, AS(III), and AS(V) were significantly positively correlated with Symbiobacterium, which dominated soils containing roxarsone, and their abundance increased with increasing initial roxarsone concentration. Accordingly, Symbiobacterium could serve as indicator of arsenic derivatives released by roxarsone as well as the initial roxarsone concentration. This is the first investigation of microbes closely related to roxarsone degradation.

Phytotoxicity and uptake of roxarsone by wheat (Triticum aestivum L.) seedlings

Roxarsone (ROX), the primary aromatic arsenical additive (AAA) used in animal feeding operations, is of increasing concern to environmental and human health due to land application of ROX-laden animal manure. Few studies have investigated the phytotoxicity, uptake mechanisms, and speciation of AAA in crop plants. In this study, wheat seedlings were employed to address these issues under hydroponic conditions. Compared to inorganic arsenic, ROX was less toxic to wheat root elongation. Wheat roots were more sensitive to ROX stress than shoots. For the first time, metabolized inorganic arsenic was detected in plants, although ROX was the predominant detected arsenic species in wheat seedlings. ROX uptake and toxicity to roots were inhibited by humic acid at concentrations higher than 50 mg/L due to interaction with ROX. Phosphate enhanced ROX uptake, but no trends were observed for ROX uptake in the presence of glycerol at concentrations lower than 250 mM. In addition, ROX uptake was significantly decreased by silicate (Si(IV), 0.5-10 mM) and the metabolic inhibitor, 2,4-dinitrophenol (0.5-2 mM), indicating that ROX transport into wheat roots was actively mediated by Si(IV)-sensitive transporters. These findings provide important insights into the fate and speciation of AAA in soil-water-plant systems relevant to human health.

Earthworms as agents for ecotoxicity in roxarsone-contaminated soil ecosystem: a modeling study of ultrastructure and proteomics

Contamination of roxarsone has been recognized as a potential environmental hazard. In this study, Eisenia fetida samples were collected after roxarsone exposures to analyze their intestinal epithelium ultrastructure, expression levels of stress-related genes, and proteomics. Our results showed that mitochondria and endoplasmic reticulum in roxarsone-treated earthworms demonstrated variety of damages. Furthermore, 149 proteins were displayed in 2-DE, and 36 of them were identified by MALDI-TOF/TOF-MS. Those identified proteins are involved in several important processes including cell immunity, cell stress responses, and cell genetic behaviors. Our study demonstrates the toxicity responses of earthworms toward arsenic-based animal drug roxarsone with practical usefulness and demonstrates a proteomic profile change that may be critical for the roxarsone stress survival mechanisms of E. fetida. Graphical Abstract Inspiration of this referred to the form of Fig. 4 in the article "Proteomic analysis of a high aluminum tolerant yeast Rhodotorula taiwanensis RS1 in response to aluminum stress" of Chao, W et al.

Degradation of roxarsone in a silt loam soil and its toxicity assessment

The land application of poultry or swine litter, containing large amounts of roxarsone, causes serious arsenic pollution in soil. Understanding biotransformation process of roxarsone and its potential risks favors proper disposal of roxarsone-contaminated animal litter, yet remains not achieved. We report an experimental study of biotransformation process of roxarsone in a silt loam soil under various soil moisture and temperature conditions, and the toxicity of roxarsone and its products from degradation. Results showed that soil moisture and higher temperature promoted roxarsone degradation, associating with emergent pentavalent arsenic. Analysis of fluorescein diacetate (FDA) hydrolysis activity revealed that roxarsone does not exert acute toxic on soil microbes. With the release of inorganic arsenic, FDA hydrolysis activity was inhibited gradually, as evidenced by ecotoxicological assessment using Photobacterium leiognathi. The results shade new lights on the dynamic roxarsone biotransformation processes in soil, which is important for guiding appropriate disposal of poultry or swine litter in the environment.

Biological phosphorus removal inhibition by roxarsone in batch culture systems

Roxarsone has been extensively used in the feed of animals, which is usually excreted unchanged in the manure and eventually enter into animal wastewater, challenging the biological phosphorus removal processes. Knowledge of its inhibition effect is key for guiding treatment of roxarsone-contaminated wastewater, and is unfortunately keeping unclear. We study the inhibition of roxarsone on biological phosphorus removal processes for roxarsone-contaminated wastewater treatment, in terms of the removal and rates of chemical oxygen demand (COD), phosphate. Results showed that presence of roxarsone considerably limited the COD removals, especially at roxarsone concentration exceeding 40 mg L(-1). Additionally, roxarsone inhibited both phosphorus release and uptake processes, consistent with the phosphate profiles during the biological phosphorus removal processes; whereas, roxarsone is more toxic to phosphorus uptake process, than release function. The results indicated that it is roxarsone itself, rather than the inorganic arsenics, inhibit biological phosphorus removal processes within both aerobic and anaerobic roxarsone-contaminated wastewater treatment.

Angiogenic potential of 3-nitro-4-hydroxy benzene arsonic acid (roxarsone)

BACKGROUND

Roxarsone (3-nitro-4-hydroxy benzene arsonic acid) is an arsenic compound widely used in the poultry industry as a feed additive to prevent coccidiosis, stimulate growth, and to improve tissue pigmentation. Little is known about the potential human health effects from roxarsone released into the environment from chicken waste or from residual compound in chicken products.

OBJECTIVE

The growth potentiation and enhanced tissue pigmentation suggest that low levels of roxarsone exposure may have an angiogenic potential similar to that of inorganic arsenite (As(III)). The goal of this investigation was to test the hypothesis described above using cultured human aortic and lung microvascular endothelial cells in high-content imaging tube-forming assays and begin developing a molecular level understanding of the process.

METHODS

We used a three-dimensional Matrigel assay for probing angiogenesis in cultured human endothelial cells, and a polymerase chain reaction (PCR) array to probe the gene changes as a function of roxarsone or As(III) treatment. In addition, we used Western blot analysis for changes in protein concentration and activation.

RESULTS

Roxarsone was found to exhibit a higher angiogenic index than As(III) at lower concentrations. Increased endothelial nitric oxide synthase (eNOS) activity was observed for roxarsone but not for As(III)-induced angiogenesis. However, As(III) caused more rapid and pronounced phosphorylation of eNOS. Quantitative PCR array on select genes revealed that the two compounds have different and often opposite effects on angiogenic gene expression.

CONCLUSIONS

The results demonstrate that roxarsone and As(III) promote angiogenic phenotype in human endothelial cells through distinctly different signaling mechanisms.

Oral treatment of mule ducks with arsenicals for inducing fatty liver

The aim of this study was to determine the dosage and the compounds of arsenic that induce fatty liver in mule ducks and also to investigate their effects on tissue residues. One hundred four ducks, 8 wk old, were randomly selected for one of six dietary treatments in Trial 1 or one of seven dietary treatments in Trial 2. Different levels of roxarsone were administrated: 0, 10, 20, 30, 40, or 50 mg/d, respectively, in Trial 1. In Trial 2, the experimental treatments were of the same level (11.36 mg/d) with different sources of arsenic that included the control without As, roxarsone (3-nitro-4-hydroxyphenylarsonic acid), arsanilic acid, phenylarsonic acid, O-nitro-phenylarsonic acid, As2O3, or As2O5. Both trials lasted 3 wk, with 1 wk on the treatment followed by 2 wk of withdrawal. Results in Trial 1 showed that a dose of 40 mg roxarsone/d increased liver weight and caused fatty liver, whereas administration of 50 mg/d was lethal. In Trial 2, administration of arsenic (11.36 mg/d) for 1 wk significantly depressed feed intake in the roxarsone, As2O3, and As2O5 groups (P < 0.05), whereas the treatment significantly decreased only live weight gain in the roxarsone group (P < 0.05). Administration of roxarsone alone increased (P < 0.05) serum cholesterol (CHOL), albumin (ALB), and total protein (TP), whereas only As2O3 among treatments significantly decreased serum triacylglycerol (TG) concentration (P < 0.05). In the roxarsone, arsanilic acid, and phenylarsonic acid groups, serum high density lipoprotein (HDL) decreased to a greater extent (P < 0.05), and arsanilic acid treatment significantly increased the very low density lipoprotein (VLDL) (P < 0.05). After 2 wk of withdrawal, liver weights and relative liver weights were heavier in the treatment groups of roxarsone, As2O3, and As2O5 as compared to the control (P < 0.05). Levels of CHOL, TG, TP, and ALB were significantly higher in the groups treated with As2O3 or As2O5 as compared to the control (P < 0.05). The roxarsone and arsanilic acid treatments significantly decreased HDL and increased VLDL in plasma (P < 0.05). The creatine kinase (CK) level in the roxarsone, As2O3, and As2O5 groups was significantly higher compared to the control group (P < 0.05). Among the As sources, roxarsone, As2O3, and As2O5 caused fatty liver in mule ducks.

Effects of roxarsone and monensin on digital flexoral tendons of broiler chickens

Roxarsone and monensin are common poultry feed additives that are used alone or in combination with other drugs to improve growth and feed utilization in young birds. The effects of monensin and roxarsone on the physiology of flexoral tendons of broiler chickens were examined to understand their relationships to leg weakness that have been occasionally associated with these drugs. Day-old chickens were fed either roxarsone or monensin for a period of 6 wk with two regimens of each of the drugs (roxarsone, 45.4 or 90.8 g/ton feed; monensin, 100 or 150 g/ton feed). None of the treatments had any adverse effect on the growth of the birds or caused any significant leg problem. Roxarsone at 45.4 g/ton caused a significant gain in body weight. The biomechanical strength of digital flexoral tendons was measured in several ways. There were no statistical differences in load at break, the modulus of elasticity, or stress or strain levels between different treatment groups and birds that received no medication. There were no differences in collagen, proteoglycan, and pyridinoline content of tendons. Sequential extraction of tendons with different solvents revealed a significant increase in the percentage of guanidine HCl extractible collagens in monensin-treated birds, and a decrease in the acid extractible collagen in both roxarsone- and monensin-treated groups. The relative content of collagen in acid extractible collagens were significantly small relative to total collagen content. Majority of collagen (84 to 90%) was extractible with pepsin. About 8 to 11% of total collagen was resistant to pepsin that was extractible with collagenase; this did not differ between treatment groups. Roxarsone treatment had no effect on the guanidine soluble collagen pool. The effect of monensin on the increase in guanidine soluble pool of collagen may relate to its disruptive effects on cellular secretory processes, which may be of significance in modulating connective tissue function in conjunction with other factors. However, in the present study, neither roxarsone nor monensin alone produced any significant leg problems nor caused any significant differences in the physiology of flexoral tendons or altered their biomechanical properties.

Toxic responses in F344 rats and B6C3F1 mice given roxarsone in their diets for up to 13 weeks

Thirteen-week toxicity studies were conducted in groups of 10 F344 rats and B6C3F1 mice of each sex fed roxarsone at 0, 50, 100, 200, 400, or 800 ppm in the diet. Arsenic levels in blood, urine, kidneys, and liver of rats were measured in additional animals of each sex dosed with 100 or 400 ppm roxarsone. Compound-related mortality occurred in both sexes of rats at 800 ppm and mice at 800 and 400 ppm. Significant body weight gain depression occurred in both sexes of rats at 200, 400, and 800 ppm and mice at 800 ppm. Clinical signs of toxicity (trembling, ataxia, and pale skin) were seen primarily in rats and mice at 800 ppm. Lesions associated with roxarsone administration were noted only in the kidney of rats and were characterized by tubular necrosis and mineralization at the corticomedullary junction. Arsenic levels in urine, blood, liver, and kidneys increased over time and were directly proportional to the level of roxarsone in feed. These levels were greater than 6 times higher in rats than in mice and were about 2 time higher in males than in females. The no-observable-effect level for roxarsone toxicity was estimated at 100 ppm for rats and 200 ppm for mice. No hematology or clinical chemistry effects were found in rats or mice of either sex.

Toxic effects of supplemental copper and roxarsone when fed alone or in combination to young pigs

Three experiments were conducted to investigate the roxarsone (3-nitro-4-hydroxyphenylarsonic acid) X copper (Cu) interaction in weanling pigs. Supplemental roxarsone at 400 mg/kg diet decreased rate and efficiency of weight gain and caused visible neurological signs of toxicosis. Copper addition (CuSO4 X 5H2O) at a level of 650 mg Cu/kg diet likewise decreased weight gain and feed efficiency, and it also increased hepatic Cu deposition. The combination of these growth-depressing dosages of roxarsone and Cu resulted in a far greater reduction in gain and efficiency of feed utilization than was the case when either compound was fed alone. A growth-promoting dosage of Cu (250 mg/kg) increased weight gain by 32% in one experiment but showed no efficacy in alleviating the growth-depression resulting from feeding 400 mg/kg roxarsone. A roxarsone dosage of 100 mg/kg increased gain and feed efficiency. Surprisingly, the decreased weight gain in pigs fed 650 mg/kg Cu was ameliorated by feeding 100 mg/kg roxarsone concomitantly. This level of roxarsone also reduced liver Cu concentration substantially. It thus appears that the nature of the roxarsone X Cu interaction is dependent on the dose of each compound administered. Moreover, low-dose roxarsone administration appears to ameliorate Cu toxicity, but low-dose Cu feeding does not show efficacy against roxarsone toxicity.

Neuropathology of experimental 3-nitro-4-hydroxyphenylarsonic acid toxicosis in pigs

Twenty pigs were fed a diet containing 187.5 mg kg-1 of 3-nitro-4-hydroxyphenylarsonic acid (3-nitro). Ten pigs were euthanized at intervals up to 29 days, 3-nitro was withdrawn from the diet of the remaining pigs on day 30, and these animals were subsequently euthanized at intervals up to 49 days after commencement of the experiment. A nervous syndrome characterized by clonic convulsive episodes inducible by exercise, developed at day 11. Paraparesis was apparent at day 22 progressing to paraplegia by day 33 (3 days after cessation of 3-nitro feeding). Histopathologic examination revealed myelin and axonal degeneration in the white matter of the spinal cord coincident with the onset of nervous signs. Marchi-positive degeneration was present in the dorsal funiculus at cervical level at day 22. Lesions intensified with increasing duration of toxicosis and while degenerate fibers were seen in all funiculi, there was preferential involvement of the fasciculi gracilis and cuneatus, the peripheral regions of the ventral and lateral funiculi, and a discrete area of the dorsal region of the lateral funiculus. Peripheral and optic neuropathies were evident from day 32 but were always mild and focal. The experiment establishes 3-nitro as a central-peripheral neurotoxicant of pigs.

Investigations of toxicity episodes involving chemotherapeutic agents in Victorian poultry and pigeons

This series of case reports details observations on toxicity episodes in poultry due to a variety of chemotherapeutic agents. These problems arose owing to overdosage, variation in species susceptibility, potentiation of the toxic effects of one substance by the presence of another substance, and particular disease or other on-farm factors. Ignorance and accident were responsible for some of these situations. The episodes involved monensin, salinomycin, nicarbazin, sulphaquinoxaline, dinitolmide, dimetridazole, nitrofurans, streptomycin, and 3-nitro-4-hydroxyphenylarsonic acid.

Arsenic-sulfur amino acid interactions in the chick

Experiments were conducted with growing crossbred chicks to determine the reasons why cysteine exacerbates roxarsone (3-nitro-4-hydroxyphenylarsonic acid) toxicity. A fortified corn-soybean meal diet that met or exceeded all nutrient requirements of the young chick was fed. While cysteine enhanced roxarsone toxicity, it had little effect on the toxicity of the inorganic arsenicals As2O3 and As2O5. The toxicity of another pentavalent organic arsenical, phenylarsonic acid, was also exacerbated by cysteine. In contrast, the growth-depression resulting from feeding the trivalent form of phenylarsonic acid, i.e., phenylarsine oxide, was not affected by dietary addition of cysteine. Supplementation of the diet with cystine, methionine or K2SO4 did not exacerbate roxarsone toxicity. Reduced glutathione (GSH), however, slightly increased the gain/feed depression resulting from feeding 300 mg roxarsone/kg diet. When injected ip 1) roxarsone and cysteine, or 2) roxarsone and ascorbic acid killed 100 or 60% of the birds, respectively, within 48 h postinjection. Few (6.7%) deaths resulted from ip injections of the same level of roxarsone alone. Therefore, the potentiation of toxicity requires pentavalent organic arsenicals and compounds that can act as reducing agents. We concluded that cysteine exacerbates roxarsone toxicity by reducing it to the more toxic trivalent state.

Roxarsone toxicity in the chick as influenced by dietary cysteine and copper and by experimental infection with Eimeria acervulina

A series of experiments was conducted with crossbred chicks to determine the effects of L-cysteine, copper, and coccidiosis on roxarsone toxicity. Levels of roxarsone in excess of 50 mg/kg depressed performance and increased kidney arsenic concentration. L-cysteine x HCl x H2O (59%) increased rate and efficiency of gain when added to the basal diet, but depressed performance, increased kidney arsenic concentration, and enhanced mortality when added to diets containing toxic levels of roxarsone (200 mg/kg or higher). Moreover, excess copper (500 mg/kg) partially alleviated the gain/feed depression due to the combination of cysteine and roxarsone. Cysteine, in fact, increased feed efficiency in birds fed excess copper in the absence of roxarsone. Eimeria acervulina infection (duodenal coccidiosis) depressed gain and feed efficiency. The depression in feed efficiency was more severe in the presence of roxarsone (50 or 300 mg/kg). In the absence of coccidiosis, 50 mg/kg roxarsone slightly increased gain/feed ratio.