A carcinogenicity study of diphenylarsinic acid in C57BL/6J mice in drinking water for 78 weeks.

Diphenylarsinic acid (DPAA), a neurotoxic organic arsenical, is present in groundwater and soil in some regions of Japan owing to illegal dumping. The present study evaluated the potential carcinogenicity of DPAA, including investigating whether bile duct hyperplasia in the liver that was observed in a chronic study on 52 week mouse, develops into a tumor when administered to mice in their drinking water for 78 weeks. DPAA was administered to 4 groups of male and female C57BL/6J mice at concentrations of 0, 6.25, 12.5, and 25 ppm in drinking water for 78 weeks. A significant decrease in the survival rate was found for females in the 25 ppm DPAA group. Body weights of males in the 25 ppm and females in the 12.5 and 25 ppm DPAA groups were significantly lower than those of the controls. Histopathological evaluation of neoplasms in all tissues showed no significant increase in tumor incidence in any organ or tissue of 6.25, 12.5, or 25 ppm DPAA-treated male or female mice. In conclusion, the present study demonstrated that DPAA is not carcinogenic to male or female C57BL/6J mice. Taken together with the fact that the toxic effect of DPAA is predominantly restricted to the central nervous system in humans, and the finding that DPAA was not carcinogenic in a previous 104-week rat carcinogenicity study, our results suggest that DPAA is unlikely to be carcinogenic in humans.

Diphenylarsinic acid induced activation of MAP kinases, transcription factors, and oxidative stress-responsive factors and hypersecretion of cytokines in cultured normal human cerebellar astrocytes.

Diphenylarsinic acid (DPAA) is a non-natural pentavalent organic arsenic and was detected in well water in Kamisu, Ibaraki, Japan in 2003. Individuals that had consumed this arsenic-contaminated water developed cerebellar symptoms such as myoclonus. We previously revealed that DPAA exposure in rats in vitro and in vivo specifically affected astrocytes rather than neurons among cerebellar cells. Here, we evaluated adverse effects of DPAA in cultured normal human cerebellar astrocytes (NHA), which were compared with those in normal rat cerebellar astrocytes (NRA) exposed to DPAA at 10 µM for 96 h, focusing on aberrant activation of astrocytes; increase in cell viability, activation of MAP kinases (ERK1/2, p38MAPK, and SAPK/JNK) and transcription factors (CREB, c-Jun, and c-Fos), upregulation of oxidative stress-responsive factors (Nrf2, HO-1, and Hsp70), and also hypersecretion of brain cytokines (MCP-1, adrenomedullin, FGF-2, CXCL1, and IL-6) as reported in NRA. While DPAA exposure at 10 µM for 96 h had little effect on NHA, a higher concentration (50 µM for 96 h) and longer exposure (10 µM for 288 h) induced similar aberrant activation. Moreover, exposure to DPAA at 50 µM for 96 h or 10 µM for 288 h in NHA induced hypersecretion of cytokines induced in DPAA-exposed NRA (MCP-1, adrenomedullin, FGF-2, CXCL1, and IL-6), and IL-8 besides into culture medium. These results suggested that aberrantly activated human astrocytes by DPAA exposure might play a pivotal role in the pathogenesis of cerebellar symptoms, affecting adjacent neurons, microglia, brain blood vessels, or astrocyte itself through these brain cytokines in human.

Contrasting effects of iron reduction on thionation of diphenylarsinic acid in a biostimulated Acrisol.

Diphenylarsinic acid (DPAA) is an emerging phenylarsenic compound derived from chemical warfare agents. It has been suggested that biostimulation of sulfate reduction decreases the concentrations of DPAA in soils. However, biostimulation often induces Fe(III) reduction which may affect the mobility and thereby the transformation of DPAA. Here, a soil incubation experiment was carried out to elucidate the impact of Fe(III) reduction on the mobilization and transformation of DPAA in a biostimulated Acrisol with the addition of sulfate and lactate. DPAA was significantly mobilized and then thionated in the sulfide soil (amended with sulfate and sodium lactate) compared with the anoxic soil (without addition of sulfate or sodium lactate). At the start of the incubation period, 41.8% of the total DPAA in sulfide soil was mobilized, likely by the addition of sodium lactate, and DPAA was then almost completely released into the solution after 2 weeks of incubation, likely due to Fe(III) reduction. The relatively low fraction of oxalate-extractable Fe in Acrisol, which contributes significantly to DPAA sorption and is more active and reduction-susceptible, may explain the observation that only < 40% of the Fe(III) (hydr)oxides were reduced when DPAA was completely released into the solution. A more rapid and final enhanced elimination of DPAA was observed in sulfide soil and the fraction of total DPAA decreased to 60.1 and 91.0%, respectively, at the end of the incubation in sulfide soil and anoxic soil. The difference appears to result from increased DPAA mobilization and sulfate reduction in sulfide soil. On the other hand, the formation of FeS precipitate, a product of Fe and sulfate reduction, may reduce the efficiency of DPAA thionation. Accordingly, the potentially contrasting effects of Fe(III) reduction on DPAA thionation need be considered when planning biostimulated sulfate reduction strategies for DPAA-contaminated soils.

A chronic toxicity study of diphenylarsinic acid in the drinking water of C57BL/6J mice for 52 weeks.

Diphenylarsinic acid (DPAA), a neurotoxic organic arsenical, is present in the groundwater and soil in some regions of Japan due to illegal dumping. The purpose of the present study was to evaluate the potential toxicity of DPAA when administered to mice in their drinking water for 52 weeks. DPAA was administered to mice at concentrations of 0, 6.25, 12.5, and 25 ppm in their drinking water for 52 weeks. There were no significant differences in final body weights between the control groups and the DPAA treatment groups in male or female mice. Relative liver weights were significantly increased in males treated with 25 ppm DPAA, and absolute liver weights were significantly decreased in female mice treated with 25 ppm DPAA. In female mice, cholangitis and simple bile duct hyperplasia were observed in the 12.5 and 25 ppm DPAA groups, and focal necrosis of hepatocytes was observed in the 25 ppm DPAA group. Proteomic analysis and Ingenuity Pathway Analysis identified 18 proteins related to hepatotoxicity that were overexpressed in the female 25 ppm group. The phase I metabolic enzyme CYP2E1 was one of these overexpressed proteins. Immunostaining confirmed high expression of CYP2E1 in the livers of females in the 25 ppm group. These results suggest that DPAA is toxic to the intrahepatic bile duct epithelium and hepatocytes in female mice and that CYP2E1 might be involved in DPAA-associated toxicity. The no-observed-adverse-effect levels of DPAA were 12.5 ppm (1.6 mg/kg bw/day) for males and 6.25 ppm (1.1 mg/kg bw/day) for females under the conditions of this study.

Sorption mechanisms of diphenylarsinic acid on ferrihydrite, goethite and hematite using sequential extraction, FTIR measurement and XAFS spectroscopy.

Diphenylarsinic acid (DPAA) is an organoarsenic compound derived from abandoned chemical weapons. DPAA sorption by iron (hydr)oxides is of considerable importance but remains largely unexplored. The current study aimed at investigating the sorption mechanisms of DPAA on ferrihydrite, goethite and hematite using both macroscopic sorption kinetics and sequential extraction procedure (SEP) as well as microscopic Fourier transformed infrared (FTIR) and extended X-ray absorption fine structure (EXAFS) spectroscopic techniques. Sorption kinetics studies show that >93% of added DPAA (4-100 mg L-1) was sorbed on ferrihydrite and hematite within 5 min, while only 84% of added DPAA (100 mg L-1) was sorbed on goethite after 24 h. The sequential extraction results and FTIR measurements reveal that DPAA formed simultaneously inner- and outer-sphere complexes on goethite and hematite, but predominantly inner-sphere complexes on ferrihydrite with limited formation of outer-sphere complexes (<15%). A combination of SEP, FTIR and EXAFS techniques further enables identification of the interfacial reactions between DPAA and solid surfaces of iron (hydr)oxides and the mechanisms involved. Results indicate that DPAA interacted with these iron (hydr)oxides via (1) electrostatic attraction or hydrogen bonding, (2) surface complexation and (3) complexation embedded inside the mineral particles. EXAFS studies further demonstrate that DPAA formed mainly bidentate binuclear corner-sharing (2C) complexes regardless of the iron substrate, with As-Fe distances at 3.19-3.32 Å. Comparison of these results with available data in the literature on inorganic, methyl and phenyl arsenics (As) suggests that it is the phenyl group substitution that finally determines the predominance of 2C complexes. Results from the present study will improve our knowledge of DPAA interaction with solid surfaces and may help in the prediction of the environmental fate and environmental risk management of DPAA in the soil-water system.

Decreased regional cerebral blood flow in patients with diphenylarsinic acid intoxication.

BACKGROUND AND PURPOSE: Diphenylarsinic acid (DPAA) intoxication caused by drinking contaminated well water was found in Kamisu, Japan. The symptoms indicated cerebellar-brainstem and temporo-occipital involvement. However, it remains unclear how it affects the human brain. To elucidate the effect of DPAA on the human brain, we analyzed cerebral blood flow (CBF) data after the drinking of DPAA-contaminated water was stopped and investigated the correlation between DPAA exposure level and CBF by single-photon emission computed tomography (CBF-SPECT). METHODS: The DPAA-exposed inhabitants (n = 78) were divided into 35 symptomatic and 43 asymptomatic subjects and compared with 38 healthy controls. The DPAA concentration in nails or hair and well water was measured using a high-performance liquid chromatography system and coupled plasma mass spectrometry after adequate extraction treatment. CBF-SPECT data, obtained within 1 year after the drinking of contaminated well water was stopped, were analyzed by statistical parametric mapping. We also examined the relationship between variations in CBF-SPECT signals and variations in DPAA concentrations in the hair or nails of the subjects. RESULTS: Compared with control subjects, CBF in symptomatic DPAA-exposed subjects was significantly lower in the occipital lobe, including the cuneus and inferior occipital gyri. The DPAA concentration in the nails or hair of subjects was inversely and significantly related to their CBF. CONCLUSION: These data suggest that CBF-SPECT may be useful as a clinical marker to infer the effect of accumulated DPAA on the brain.

A carcinogenicity study of diphenylarsinic acid in F344 rats in drinking water for 104 weeks.

Diphenylarsinic acid (DPAA), a neurotoxic organic arsenical used as a chemical warfare agent, is present in the groundwater and soil in some regions of Japan due to illegal dumping after World War II. We previously demonstrated that DPAA promotes diethylnitrosamine-induced liver carcinogenesis in a medium-term rat liver bioassay. The purpose of the present study was to evaluate the potential carcinogenicity of DPAA, including investigation of whether the bile duct hyperplasia in the liver that was observed in a previous 52 week rat chronic study develops into a tumor, when administered to rats in their drinking water for 104 weeks. DPAA was administered to groups 1-4 at concentrations of 0, 5, 10, and 20 ppm in their drinking water for 104 weeks. A significant decrease in survival rate was found for females in the 20 ppm DPAA group. Body weights of males in the 20 ppm and females in the 10 and 20 ppm DPAA groups were significantly decreased compared to the controls. Overall histopathological evaluation of neoplasms in all tissues showed no significant increase of tumor incidence in any organ or tissue of the 5, 10, or 20 ppm DPAA-treated male or female F344 rats. In conclusion, the present study demonstrated that DPAA is not a complete carcinogen in male or female F344 rats.

Diphenylarsinic acid exerts promotion effects on hepatobiliary carcinogenesis in a rat medium-term multiorgan carcinogenicity bioassay.

We have previously demonstrated that diphenylarsinic acid (DPAA) promotes liver carcinogenesis in rats in a medium-term liver carcinogenicity bioassay. However, the effects of DPAA on other organs have not been determined. In the present study, the effects of DPAA on carcinogenesis were investigated using a rat multiorgan carcinogenicity bioassay. A total of 60 six-week-old male F344 rats were treated with the carcinogens diethylnitrosamine, N-butyl-N-(4-hydroxybutyl) nitrosamine, N-methyl-N-nitrosourea, N-bis (2-hydroxypropyl) nitrosamine, and 1,2-dimethylhydrazine dihydrochloride to initiate carcinogenesis in multiple organs. After initiation, DPAA was given at a dose of 0, 5, or 20 ppm in drinking water for 27 weeks. The incidences of moderate and severe bile duct hyperplasia were significantly increased in the 20 ppm DPAA group (29.4%, 70.6%, respectively) compared with the 0 ppm DPAA group (0%, 0%, respectively), and the incidence and multiplicity of cholangioma were significantly increased in the 20 ppm DPAA group (29.4%, 0.4 ± 0.8/rat) compared with the 0 ppm DPAA group (0%, 0/rat). The total number and average area of glutathione S-transferase placenta form-positive foci, preneoplastic lesions in rat livers, were significantly increased in the 20 ppm DPAA group (10.5 ± 2.2/cm2, 5.3 ± 1.7 mm2/cm2) compared with the 0 ppm DPAA group (6.2 ± 2.9/cm2, 2.4 ± 1.4 mm2/cm2). In conclusion, our results demonstrate that DPAA promotes hepatobiliary carcinogenesis in a rat medium-term multiorgan carcinogenicity bioassay; no promotion effects were observed in other organs.

Dysregulation of MAP Kinase Signaling Pathways Including p38MAPK, SAPK/JNK, and ERK1/2 in Cultured Rat Cerebellar Astrocytes Exposed to Diphenylarsinic Acid.

Diphenylarsinic acid (DPAA) was a major compound found in the arsenic poisoning incident that occurred in Kamisu, Ibaraki, Japan in 2003. People exposed to DPAA via contaminated well water suffered from several neurological disorders, including cerebellar symptoms. We previously reported that DPAA induces cellular activation in cultured rat cerebellar astrocytes, dose-dependent promotion of cell growth (low DPAA), cell death (high DPAA), and increased phosphorylation of mitogen-activated protein (MAP) kinases (p38MAPK, SAPK/JNK, and ERK1/2). Moreover, DPAA induces up-regulation of oxidative stress-counteracting proteins, activation of CREB phosphorylation, increased protein expression of c-Jun and c-Fos, and aberrant secretion of brain-active cytokines (MCP-1, adrenomedullin, FGF2, CXCL1, and IL-6). Here, we explored the role of MAP kinases in DPAA-induced activation of astrocytes using specific MAP kinase signaling inhibitors [SB203580 (p38MAPK), SP600125 (SAPK/JNK), SCH772984 (ERK1/2), and U0126 (MEK1/2, a kinase for ERK1/2)]. DPAA-induced activation of MAP kinases had little contribution to DPAA-induced cell growth and death. On the other hand, a power relationship among MAP kinases was also observed, in which p38MAPK suppressed DPAA-induced SAPK/JNK and ERK1/2 activation, whereas ERK1/2 and MEK1/2 facilitated p38MAPK and SAPK/JNK activation. In addition, SAPK/JNK had minimal effects on the activation of other MAP kinases. DPAA-induced activation of transcription factors and secretion of brain-active cytokines were submissively but intricately dominated by MAP kinases. Collectively, our results indicate that DPAA-induced activation of MAP kinases is neither a cell growth-promoting response nor a cytoprotective one but leads to transcriptional disruption and aberrant secretion of brain-active cytokines in cerebellar astrocytes.

A chronic toxicity study of diphenylarsinic acid in F344 rats in drinking water for 52 weeks.

Diphenylarsinic acid (DPAA), a chemical warfare-related neurotoxic organic arsenical, is present in the groundwater and soil in some regions of Japan due to illegal dumping after World War II. The purpose of the present study was to evaluate the potential toxicity of DPAA when administered to rats in their drinking water for 52 weeks. DPAA was administered to groups 1-4 at concentrations of 0, 5, 10, and 20ppm in their drinking water for 52 weeks. There were no significant differences in the final body weights between the control groups and the treatment groups in male or female rats. In serum biochemistry, in females 20ppm DPAA significantly increased alkaline phosphatase and γ-glitamyl transferase compared to controls, and 10 and 20ppm DPAA significantly increased total cholesterol compared to controls. Absolute and relative liver weights were significantly increased in females treated with 20ppm DPAA compared to the control group. Dilation of the common bile duct outside the papilla of Vater and stenosis of the papilla of Vater was observed in all male and female rats administered 20ppm DPAA. The incidence of intrahepatic bile duct hyperplasia was significantly increased in male and female rats treated with 20ppm DPAA compared to the control groups. These results suggest that DPAA is toxic to the bile duct epithelium in rats. The no-observed adverse effect levels of DPAA were estimated to be 10ppm (0.48mg/kg b.w./day) for males and 5ppm (0.35mg/kg b.w./day) for females under the conditions of this study.

Phytoremediation of diphenylarsinic-acid-contaminated soil by Pteris vittata associated with Phyllobacterium myrsinacearum RC6b.

A pot experiment was conducted to explore the phytoremediation of a diphenylarsinic acid (DPAA)-spiked soil using Pteris vittata associated with exogenous Phyllobacterium myrsinacearum RC6b. Removal of DPAA from the soil, soil enzyme activities, and the functional diversity of the soil microbial community were evaluated. DPAA concentrations in soil treated with the fern or the bacterium were 35-47% lower than that in the control and were lowest in soil treated with P. vittata and P. myrsinacearum together. The presence of the bacterium added in the soil significantly increased the plant growth and DPAA accumulation. In addition, the activities of dehydrogenase and fluorescein diacetate hydrolysis and the average well-color development values increased by 41-91%, 37-78%, and 35-73%, respectively, in the treatments with P. vittata and/or P. myrsinacearum compared with the control, with the highest increase in the presence of P. vittata and P. myrsinacearum together. Both fern and bacterium alone greatly enhanced the removal of DPAA and the recovery of soil ecological function and these effects were further enhanced by P. vittata and P. myrsinacearum together. Our findings provide a new strategy for remediation of DPAA-contaminated soil by using a hyperaccumulator/microbial inoculant alternative to traditional physicochemical method or biological degradation.

Solid-solution partitioning and thionation of diphenylarsinic acid in a flooded soil under the impact of sulfate and iron reduction.

Diphenylarsinic acid (DPAA) is a major organic arsenic (As) compound derived from abandoned chemical weapons. The solid-solution partitioning and transformation of DPAA in flooded soils are poorly understood but are of great concern. The identification of the mechanisms responsible for the mobilization and transformation of DPAA may help to develop effective remediation strategies. Here, soil and Fe mineral incubation experiments were carried out to elucidate the partitioning and transformation of DPAA in anoxic (without addition of sulfate or sodium lactate) and sulfide (with the addition of sulfate and sodium lactate) soil and to examine the impact of sulfate and Fe(III) reduction on these processes. Results show that DPAA was more effectively mobilized and thionated in sulfide soil than in anoxic soil. At the initial incubation stages (0-4weeks), 6.7-74.5% of the total DPAA in sulfide soil was mobilized likely by sorption competition with sodium lactate. At later incubation stage (4-8weeks), DPAA was almost completely released into the solution likely due to the near-complete Fe(III) reduction. Scanning transmission X-ray microscopy (STXM) results provide further direct evidence of elevated DPAA release coupled with Fe(III) reduction in sulfide environments. The total DPAA fraction decreased significantly to 24.5% after two weeks and reached 3.4% after eight weeks in sulfide soil, whereas no obvious elimination of DPAA occurred in anoxic soil at the initial two weeks and the total DPAA fraction decreased to 10.9% after eight weeks. This can be explained in part by the enhanced mobilization of DPAA and sulfate reduction in sulfide soil compared with anoxic soil. These results suggest that under flooded soil conditions, Fe(III) and sulfate reduction significantly promote DPAA mobilization and thionation, respectively, and we suggest that it is essential to consider both sulfate and Fe(III) reduction to further our understanding of the environmental fate of DPAA.

Photodegradation of diphenylarsinic acid by UV-C light: Implication for its remediation.

Diphenylarsinic acid (DPAA) is a major contaminant in environments polluted by chemical weapons and abandoned after World Wars I and II and poses high risks to biota but remediation methods for this contaminant are rare. Here, the photodegradtion of DPAA was studied under high-pressure Hg lamp irradiation. DPAA was degraded completely into inorganic arsenic species in 30 min under UV-C irradiation. The photodegradation of DPAA depended mainly on its direct photolysis through excited-state DPAA. By contrast, the generation of (1)O2 during the photodegradation of DPAA was confirmed by electron paramagnetic resonance (EPR) studies, but (1)O2 had little effect on the photodegradation of DPAA. Phtotodegradation of DPAA was also studied in soil leachates and groundwater and the photolytic rate of DPAA was controlled by the total organic carbon (TOC) content in soil leachates and by the NO3(-) concentration in groundwater. Finally, studies on the effects of common solutes on the photodegradation of DPAA show that Cl(-) can increase the photolytic rate of DPAA by prolonging the lifetime of excited-state DPAA. Moreover, NO3(-), NO2(-), and humic acid (HA) can decrease the photolytic rate of DPAA by suppressing the production of excited-state DPAA. This research shows the detailed mechanism of DPAA photodegradation and provides a new and effective method for DPAA decontamination.

Diphenylarsinic acid contaminated soil remediation by titanium dioxide (P25) photocatalysis: Degradation pathway, optimization of operating parameters and effects of soil properties.

Diphenylarsinic acid (DPAA) is formed during the leakage of arsenic chemical weapons in sites and poses a high risk to biota. However, remediation methods for DPAA contaminated soils are rare. Here, the photocatalytic oxidation (PCO) process by nano-sized titanium dioxide (TiO2) was applied to degrade DPAA in soil. The degradation pathway was firstly studied, and arsenate was identified as the final product. Then, an orthogonal array experimental design of L9(3)(4), only 9 experiments were needed, instead of 81 experiments in a conventional one-factor-at-a-time, was used to optimize the operational parameters soil:water ratio, TiO2 dosage, irradiation time and light intensity to increase DPAA removal efficiency. Soil:water ratio was found to have a more significant effect on DPAA removal efficiency than other properties. The optimum conditions to treat 4 g soil with a DPAA concentration of 20 mg kg(-1) were found to be a 1:10 soil: water ratio, 40 mW cm(-2) light intensity, 5% TiO2 in soil, and a 3-hour irradiation time, with a removal efficiency of up to 82.7%. Furthermore, this method (except for a change in irradiation time from 3 to 1.5h) was validated in nine different soils and the removal efficiencies ranged from 57.0 to 78.6%. Removal efficiencies were found to be negatively correlated with soil electrical conductivity, organic matter content, pH and total phosphorus content. Finally, coupled with electron spin resonance (ESR) measurement, these soil properties affected the generation of OH• by TiO2 in soil slurry. This study suggests that TiO2 photocatalytic oxidation is a promising treatment for removing DPAA from soil.

Diphenylarsinic Acid Induced Activation of Cultured Rat Cerebellar Astrocytes: Phosphorylation of Mitogen-Activated Protein Kinases, Upregulation of Transcription Factors, and Release of Brain-Active Cytokines.

Diphenylarsinic acid (DPAA) was detected as the primary compound responsible for the arsenic poisoning that occurred in Kamisu, Ibaraki, Japan, where people using water from a well that was contaminated with a high level of arsenic developed neurological (mostly cerebellar) symptoms and dysregulation of regional cerebral blood flow. To understand the underlying molecular mechanism of DPAA-induced cerebellar symptoms, we focused on astrocytes, which have a brain-protective function. Incubation with 10 µM DPAA for 96 h promoted cell proliferation, increased the expression of antioxidative stress proteins (heme oxygenase-1 and heat shock protein 70), and induced the release of cytokines (MCP-1, adrenomedullin, FGF2, CXCL1, and IL-6). Furthermore, DPAA overpoweringly increased the phosphorylation of three major mitogen-activated protein kinases (MAPKs) (ERK1/2, p38MAPK, and SAPK/JNK), which indicated MAPK activation, and subsequently induced expression and/or phosphorylation of transcription factors (Nrf2, CREB, c-Jun, and c-Fos) in cultured rat cerebellar astrocytes. Structure-activity relationship analyses of DPAA and other related pentavalent organic arsenicals revealed that DPAA at 10 µM activated astrocytes most effective among organic arsenicals tested at the same dose. These results suggest that in a cerebellum exposed to DPAA, abnormal activation of the MAPK-transcription factor pathway and irregular secretion of these neuroactive, glioactive, and/or vasoactive cytokines in astrocytes can be the direct/indirect cause of functional abnormalities in surrounding neurons, glial cells, and vascular cells: This in turn might lead to the onset of cerebellar symptoms and disruption of cerebral blood flow.

Detection of diphenylarsinic acid and its derivatives in human serum and cerebrospinal fluid.

BACKGROUND: Residents (n=157) of Kamisu City, Ibaraki, Japan, were orally exposed to diphenylarsinic acid (DPAA) via the ingestion of contaminated underground water. Subsequently, a clinical syndrome associated with a variety of cerebellar and brainstem symptoms, was observed in 20 of the 30 residents who consumed high concentrations of DPAA in the contaminated well water. While the clinical symptoms of DPAA were defined, the toxicokinetics of DPAA remained unclear. METHODS: In order to investigate the underlying toxicokinetics of DPAA, we collected serum and cerebrospinal fluid (CSF) samples from 5 patients with DPAA intoxication, and attempted to estimate the half-life of serum DPAA and the CSF/serum ratio of DPAA. RESULTS: DPAA, and its derivatives, such as phenylmethylarsinic acid (PMAA) and phenylarsinic acid (PAA), were detected in serum from residents exposed to DPAA. Serum DPAA was observed for >200 days after the last ingestion of contaminated water. The half-life of serum DPAA was 22.5 days in children and 39.4 days in youths and adults, which was nearly double that observed in children. DPAA was found in CSF, and the CSF/serum ratios of DPAA in 2 patients were 3.0% and 3.7%, respectively, suggesting that this toxicant is able to cross the blood-brain barrier. CONCLUSION: An established animal model of DPAA intoxication was examined regarding the toxicokinetics, distribution and direct DPAA accumulation in the cerebrum. On the basis of existing animal data, and the present results arising from human subjects, the development of new therapies for DPAA intoxication should be enhanced, such as accelerated DPAA excretion.

An EXAFS study on the adsorption structure of phenyl-substituted organoarsenic compounds on ferrihydrite.

Adsorption structures of mono- and diphenyl substituted organoarsenic compounds (PAA and DPAA, respectively) on ferrihydrite were analyzed by extended X-ray absorption fine structure (EXAFS), which suggested that PAA and DPAA form inner-sphere complexes with ferrihydrite regardless of their bulky functional groups. In addition, coexistence of two types of inner-sphere complex modes, i.e. bidentate-binuclear and monodentate surface complexes was suggested by EXAFS fitting with two type of the As-Fe shell.

Developmental subchronic exposure to diphenylarsinic acid induced increased exploratory behavior, impaired learning behavior, and decreased cerebellar glutathione concentration in rats.

In Japan, people using water from the well contaminated with high-level arsenic developed neurological, mostly cerebellar, symptoms, where diphenylarsinic acid (DPAA) was a major compound. Here, we investigated the adverse effects of developmental exposure to 20mg/l DPAA in drinking water (early period [0-6 weeks of age] and/or late period [7-12]) on behavior and cerebellar development in male rats. In the open field test at 6 weeks of age, early exposure to DPAA significantly increased exploratory behaviors. At 12 weeks of age, late exposure to DPAA similarly increased exploratory behavior independent of the early exposure although a 6-week recovery from DPAA could reverse that change. In the passive avoidance test at 6 weeks of age, early exposure to DPAA significantly decreased the avoidance performance. Even at 12 weeks of age, early exposure to DPAA significantly decreased the test performance, which was independent of the late exposure to DPAA. These results suggest that the DPAA-induced increase in exploratory behavior is transient, whereas the DPAA-induced impairment of passive avoidance is long lasting. At 6 weeks of age, early exposure to DPAA significantly reduced the concentration of cerebellar total glutathione. At 12 weeks of age, late, but not early, exposure to DPAA also significantly reduced the concentration of cerebellar glutathione, which might be a primary cause of oxidative stress. Early exposure to DPAA induced late-onset suppressed expression of NMDAR1 and PSD95 protein at 12 weeks of age, indicating impaired glutamatergic system in the cerebellum of rats developmentally exposed to DPAA.

Formation of diphenylthioarsinic acid from diphenylarsinic acid under anaerobic sulfate-reducing soil conditions.

Diphenylarsinic acid (DPAA) is a toxic phenylarsenical compound often found around sites contaminated with phenylarsenic chemical warfare agents, diphenylcyanoarsine or diphenylchloroarsine, which were buried in soil after the World Wars. This research concerns the elucidation of the chemical structure of an arsenic metabolite transformed from DPAA under anaerobic sulfate-reducing soil conditions. In LC/ICP-MS analysis, the retention time of the metabolite was identical to that of a major phenylarsenical compound synthesized by chemical reaction of DPAA and hydrogen sulfide. Moreover the mass spectra for the two compounds measured using LC/TOF-MS were similar. Subsequent high resolution mass spectral analysis indicated that two major ions at m/z 261 and 279, observed on both mass spectra, were attributable to C12H10AsS and C12H12AsSO, respectively. These findings strongly suggest that the latter ion is the molecular-related ion ([M+H](+)) of diphenylthioarsinic acid (DPTA; (C6H5)2AsS(OH)) and the former ion is its dehydrated fragment. Thus, our results reveal that DPAA can be transformed to DPTA, as a major metabolite, under sulfate-reducing soil conditions. Moreover, formation of diphenyldithioarsinic acid and subsequent dimerization were predicted by the chemical reaction analysis of DPAA with hydrogen sulfide. This is the first report to elucidate the occurrence of DPAA-thionation in an anaerobic soil.

Diphenylarsinic acid, a chemical warfare-related neurotoxicant, promotes liver carcinogenesis via activation of aryl hydrocarbon receptor signaling and consequent induction of oxidative DNA damage in rats.

Diphenylarsinic acid (DPAA), a chemical warfare-related neurotoxic organic arsenical, is present in the groundwater and soil in some regions of Japan due to illegal dumping after World War II. Inorganic arsenic is carcinogenic in humans and its organic arsenic metabolites are carcinogenic in animal studies, raising serious concerns about the carcinogenicity of DPAA. However, the carcinogenic potential of DPAA has not yet been evaluated. In the present study we found that DPAA significantly enhanced the development of diethylnitrosamine-induced preneoplastic lesions in the liver in a medium-term rat liver carcinogenesis assay. Evaluation of the expression of cytochrome P450 (CYP) enzymes in the liver revealed that DPAA induced the expression of CYP1B1, but not any other CYP1, CYP2, or CYP3 enzymes, suggesting that CYP1B1 might be the enzyme responsible for the metabolic activation of DPAA. We also found increased oxidative DNA damage, possibly due to elevated CYP1B1 expression. Induction of CYP1B1 has generally been linked with the activation of AhR, and we found that DPAA activates the aryl hydrocarbon receptor (AhR). Importantly, the promotion effect of DPAA was observed only at a dose that activated the AhR, suggesting that activation of AhR and consequent induction of AhR target genes and oxidative DNA damage plays a vital role in the promotion effects of DPAA. The present study provides, for the first time, evidence regarding the carcinogenicity of DPAA and indicates the necessity of comprehensive evaluation of its carcinogenic potential using long-term carcinogenicity studies.