A Simple and Effective Method for Speciation Analysis of 13 Arsenic Species Using HPLC on a Fluorocarbon Stationary Phase Coupled to ICP-MS.

The separation properties of arsenic species was investigated using HPLC-ICP-MS with several commercially available fluorocarbon stationary phases and no ion-pair reagents in HPLC. One pentafluorophenyl column showed the highest potential for the separation of a larger number of arsenic species when using simple acid-based mobile phases. After modification of the operational parameters in HPLC, the speciation analysis of 13 representative arsenic species: arsenite, arsenate, methylarsonic acid, dimethylarsinic acid, trimethylarsine oxide, tetramethylarsonium, arsenobetaine, arsenocholine, thio-dimethylarsinic acid, oxo-arsenosugar-glycerol, oxo-arsenosugar-phosphate, oxo-arsenosugar-sulfonate, and oxo-arsenosugar-sulfate, was achieved by HPLC-ICP-MS with the column along with a mobile phase of 0.05% heptafluorobutyric acid-methanol (99:1, volume per volume).

Contribution of aquaporin 9 and multidrug resistance-associated protein 2 to differential sensitivity to arsenite between primary cultured chorion and amnion cells prepared from human fetal membranes.

Arsenic trioxide (arsenite, As(III)) has shown a remarkable clinical efficacy, whereas its side effects are still a serious concern. Therefore, it is critical to understand the effects of As(III) on human-derived normal cells for revealing the mechanisms underlying these side effects. We examined the effects of As(III) on primary cultured chorion (C) and amnion (A) cells prepared from human fetal membranes. A significant dose-dependent As(III)-mediated cytotoxicity was observed in the C-cells accompanied with an increase of lactate dehydrogenase (LDH) release. Higher concentrations of As(III) were required for the A-cells to show cytotoxicity and LDH release, suggesting that the C-cells were more sensitive to As(III) than the A-cells. The expression levels of aquaporin 9 (AQP9) were approximately 2 times higher in the C-cells than those in the A-cells. Both intracellular arsenic accumulation and its cytotoxicity in the C-cells were significantly abrogated by sorbitol, a competitive AQP9 inhibitor, in a dose-dependent manner. The protein expression levels of multidrug resistance-associated protein (MRP) 2 were downregulated by As(III) in the C-cells, but not in the A-cells. No significant differences in the expression levels of MRP1 were observed between C- and A-cells. The protein expression of P-glycoprotein (P-gp) was hardly detected in both cells, although a detectable amount of its mRNA was observed. Cyclosporine A, a broad-spectrum inhibitor for ABC transporters, and MK571, a MRP inhibitor, but not PGP-4008, a P-gp specific inhibitor, potently sensitized both cells to As(III)-mediated cytotoxicity. These results suggest that AQP9 and MRP2 are involved in controlling arsenic accumulation in these normal cells, which then contribute to differential sensitivity to As(III) cytotoxicity between these cells.

Antiproliferative and anti-invasive effects of inorganic and organic arsenic compounds on human and murine melanoma cells in vitro.

OBJECTIVES: For patients with advanced melanoma, no treatment options are available at present that provide either sufficient response rates or a significant prolongation of overall survival. The present study examines the effects of two inorganic and six organic arsenic compounds on cell proliferation and cell invasion of melanoma cells in vitro. METHODS: The effects of arsenic compounds on proliferation of human melanoma A375 cells and murine melanoma B16F10 cells were examined by MTT assay and 5-bromo-2'-deoxyuridine (BrdU) incorporation assay, and the effects of the compounds on cell invasion were examined by the Boyden chamber invasion assay. The amounts of active matrix metalloproteinase (MMP)-2 and pro-MMP-2 in the culture supernatant of A375 cells were determined by an MMP-2 activity assay system. KEY FINDINGS: Arsenate and arsenic trioxide (As(2) O(3) ) inhibited the proliferation of A375 and B16F10 cells significantly at concentration ranges of 0.1-20µg/ml (P<0.001), while the organic compounds arsenobetaine, arsenocholine, dimethylarsinic acid, methylarsonic acid, tetramethylarsonium and trimethylarsine oxide did not show any inhibitory effects even at 20µg/ml. Cell invasion of A375 and B16F10 cells through a layer of collagen IV was significantly inhibited by 0.1-20 µg/ml of arsenate or As(2) O(3) (P<0.05), while the organic compounds did not inhibit cell invasion. Arsenate or As(2) O(3) at 0.2-10µg/ml significantly inhibited the amount of active MMP-2 and pro-MMP-2 secreted into the A375 cell culture supernatant (P<0.05). CONCLUSIONS: Our findings show that the inorganic arsenic compounds arsenate and As(2) O(3) inhibit cell proliferation and prevent the invasive properties of melanoma cells, possibly by decreasing MMP-2 production from the cells.

Rapid biotransformation of arsenate into oxo-arsenosugars by a freshwater unicellular green alga, Chlamydomonas reinhardtii.

We examined the short-term metabolic processes of arsenate for 24 h in a freshwater unicellular green alga, Chlamydomonas reinhardtii wild-type strain CC-125. The arsenic species in the algal extracts were identified by high-performance liquid chromatography/inductively coupled plasma mass spectrometry after water extraction using a sonicator. Speciation analyses of arsenic showed that the levels of arsenite, arsenate, and methylarsonic acid in the cells rapidly increased for 30 min to 1 h, and those of dimethylarsinic acid and oxo-arsenosugar-glycerol also tended to increase continuously for 24 h, while that of oxo-arsenosugar-phosphate was quite low and fluctuated throughout the experiment. These results indicate that this alga can rapidly biotransform arsenate into oxo-arsenosugar-glycerol for at least 10 min and then oxo-arsenosugar-phosphate through both reduction of incorporated arsenate to arsenite and methylation of arsenite and/or arsenate retained in the cells to dimethylarsinic acid via methylarsonic acid as an possible intermediate.

Regulation of the human CHOP gene promoter by the stress response transcription factor ATF5 via the AARE1 site in human hepatoma HepG2 cells.

AIMS: Activating transcription factor (ATF) 5 is a member of the cAMP response element-binding protein (CREB)/ATF family of transcription factors. We have shown that ATF5 is a stress response transcription factor that responds to amino acid limitation, arsenite exposure, or cadmium exposure. In this study we investigated whether ATF5 is involved in the regulation of CCAAT/enhancer-binding protein (C/EBP) homologous protein (CHOP) gene expression. MAIN METHODS: We used a transient transfection system to express ATF5 and analyzed the regulation of CHOP gene promoter in human hepatoma, HepG2 cells. We also studied the effect of ATF5 knockdown on arsenite-induced CHOP protein expression and arsenite-induced cell death of HepG2 cells. KEY FINDINGS: We showed that ATF5 activates the CHOP gene promoter in HepG2 cells. Both deletion analysis and point mutations of the promoter revealed that amino acid response element (AARE) 1 is responsible for ATF5-dependent promoter activation. Furthermore, the existence of either AARE1 or activating protein-1 (AP-1) site is sufficient for transcriptional activation of the CHOP gene promoter by arsenite exposure, although complete induction requires the existence of both elements. We also demonstrated that knockdown of ATF5 reduced arsenite-induced CHOP protein expression and arsenite-induced cell death of HepG2 cells. SIGNIFICANCE: These results suggested that the CHOP gene is a potential target for ATF5, and that ATF5 raises the arsenite-induced CHOP gene expression level via the AARE1 site in HepG2 cells.

[Biological effects and metabolism of arsenic compounds present in seafood products].

Marine organisms contain arsenic at various concentrations, and so human consumption of seafood products results in arsenic intake. Therefore, identification and quantification of all arsenic compounds present in seafood products are important from the viewpoint of food hygiene, because the toxicity of arsenic strongly depends on its chemical form. Hence, determination of total arsenic concentration and speciation analysis of arsenic compounds in seafood products have been extensively performed. This review covers the large number of arsenic compounds identified in seafood products, and summarizes recent findings on their biological effects and metabolism in humans and experimental animals.

Effects of naturally occurring polymethyoxyflavonoids on cell growth, p-glycoprotein function, cell cycle, and apoptosis of daunorubicin-resistant T lymphoblastoid leukemia cells.

Effects of polymethoxyflavonoids tangeretin and nobiletin and the related polyphenolic compounds baicalein, wogonin, quercetin, and epigallocatechin gallate on the cell growth, P-glycoprotein function, apoptosis, and cell cycle of human T lymphoblastoid leukemia MOLT-4 and its daunorubicin-resistant cells were investigated. The IC50 values of these compounds on the cell growth were 7.1-32.2 micromol/L, and the inhibitory effects were observed to be almost equal to the parent MOLT-4 and the daunorubicin-resistant cells. Tangeretin and nobiletin showed the strongest effects with the IC50 values of 7.1-14.0 micromol/L. These polymethoxyflavonoids inhibited the P-glycoprotein function and significantly influenced the cell cycle (p<.05), whereas they did not induce apoptosis.

Speciation of arsenic trioxide penetrates into cerebrospinal fluid in patients with acute promyelocytic leukemia.

We assessed concentrations of arsenic trioxide (As(2)O(3)) and its metabolites in the plasma and cerebrospinal fluid in acute promyelocytic leukemia patients who achieved complete remission with intravenous As(2)O(3). Arsenic trioxide exists as high molecular mass proteins and low molecular mass proteins in the plasma, and metabolites seem to be able to penetrate blood-brain barrier. Methylarsonic acid (MA) in the cerebrospinal fluid is stably detected and its level was higher than that in plasma after As(2)O(3) treatment. Trivalent arsenic (AS(III)) and dimethylarsinic acid (DMA) became detectable after As(2)O(3) infusion, though the levels of arsenic metabolites in the cerebrospinal fluid was lower than plasma levels. Results suggest that a combinatory treatment of As(2)O(3) with other chemotherapeutics could be effective for APL patients with CNS involvement.

Ingestion and excretion of arsenic compounds present in edible brown algae, Hijikia fusiforme, by mice.

The element arsenic is a carcinogen and toxic for humans and other living organisms. Some seaweeds contain high amounts of inorganic arsenic (iAs). In particular, Hijikia fusiforme has a high iAs content of approximately 50%. In this study, we examined the absorption, metabolism, excretion, and accumulation of arsenic compounds in mice after the administration of Hijiki. The single-dose experiment, wherein a single dose of cooked Hijiki was administered to the mice, revealed that the urinary and fecal excretion of arsenic compounds was the highest on the first day of dosing, and it became clear that 66-92% of arsenic was excreted within 3 days after administration of the first dose. The repeated-dose experiment, wherein repeated doses of cooked or dried Hijiki were administered to the mice, arsenic was detected in all the tissues, but only approximately 5% of the administered dose of arsenic was detected as residual arsenic. These results suggest that the arsenic present in cooked Hijiki is accumulated in very small amounts in mice.

Rapid determination of arsenic species in freshwater organisms from the arsenic-rich Hayakawa River in Japan using HPLC-ICP-MS.

Speciation analyses of water-soluble arsenicals from freshwater and biological samples collected from the Hayakawa River (Kanagawa, Japan), which contains a high concentration of arsenic, were performed using high performance liquid chromatography/inductively coupled plasma mass spectrometry (HPLC-ICP-MS). River water contained only arsenate, which is a pentavalent inorganic arsenical. The water bug Stenopsyche marmorata contained inorganic arsenicals accounting for 77% of the water-soluble arsenicals, followed by oxo-arsenosugar-glycerol, which is a type of dimethylarsinoylriboside (arsenosugar). The freshwater green macroalga Cladophora glomerata contained oxo-arsenosugar-glycerol and oxo-arsenosugar-phosphate as 64% of the water-soluble arsenicals. Production of the same types of arsenosugars was confirmed in the freshwater green microalga Chlamydomonas reinhardtii CC125 experimentally exposed to arsenate. The muscle tissues of all freshwater fish and crustaceans analyzed contained arsenobetaine, oxo-arsenosugar-glycerol, and/or oxo-arsenosugar-phosphate in various concentrations. Seven freshwater fish (Cobitis biwae, Leuciscus hakonensis, Phoxinus lagowski steindachneri, Plecoglossus altivelis, Rhinogobius sp. CB, Rhinogobius sp. CO, Sicyopterus japonicus) and the crustacean Macrobracbium nipponenese contained arsenobetaine in their muscle tissues as the predominant form, contributing up to 80% of the water-soluble arsenicals, while the freshwater fish Anguilla japonica muscle tissues primarily contained dimethylarsinic acid as 77% of the water-soluble arsenicals, followed by arsenobetaine. The freshwater fish Zacco platypus muscle tissues predominantly contained oxo-arsenosugar-phosphate, accounting for 51% of the water-soluble arsenicals, followed by dimethylarsinic acid and arsenobetaine. These biological samples possessed non-extractable arsenical(s) accounting for more than 50% of the total arsenic concentration.

[Chemical treatment and decomposition technique of the chemical warfare agents containing arsenicals].

The old Japanese army developed several chemical warfare agents on Ohkuno Island in Seto inland sea, Hiroshima Japan, during the period between 1919 and 1944. These chemical agents including yperite (mustard; irritating agent), lewisite (irritating agent), diphenylchloroarsine (DA; vomiting agent), diphenylcyanoarsine (DC; vomiting agent) and other poisonous gases were manufactured to be used in China. After World War II, the old Japanese army abandoned or dumped these agents into seas inside or outside of Japan and interior of China. Rather than being used for terrorism, these chemical warfare agents containing arsenicals may cause injury to some workers at the digging site of abandoned chemical weapons. Moreover, the leakage of chemical agents or an explosion of the bomb may result in environmental pollution, as a result, it is highly possible to cause serious health damage to the residents. There are still many abandoned or dumped warfare agents in Japan and China, therefore chemical agents containing arsenic are needed to be treated with alkaline for decomposition or to decompose with oxidizing agent. Presently, a large quantity of chemical agents and the contaminated soil are processed by combustion, and industrial waste is treated with sulfur compounds as the insoluble sulfur arsenic complex. This report describes the methods for the disposal of these organic arsenic agents that have been implemented until present and examines the future prospects.

Speciation of arsenic trioxide metabolites in blood cells and plasma of a patient with acute promyelocytic leukemia.

Arsenic trioxide (As(2)O(3)) has been widely accepted as the second-best choice for the treatment of relapsed and refractory acute promyelocytic leukemia (APL) patients. However, a few studies have been conducted on a detailed speciation of As(2)O(3) metabolites in blood samples of patients. To clarify the speciation of arsenic, the blood samples were collected at various time points from a patient with APL after remission induction therapy and during consolidation therapy. The total amounts of arsenic in blood cells and plasma, and the plasma concentrations of inorganic arsenic and methylated metabolites were determined by inductively coupled plasma mass spectrometry (ICP-MS) and high-performance liquid chromatography/ICP-MS, respectively. The total amounts of arsenic in the blood cells were 4-10 times higher than those in plasma. Among all arsenic metabolites, the pentavalent arsenate (As(V)) in plasma was more readily eliminated. During the drug-withdrawal period, the initial plasma concentrations of trivalent arsenic (As(III)) declined more rapidly than those of methylarsonic acid and dimethlyarsinic acid, which are known as the major methylated metabolites of As(III). On the other hand, during the consecutive administration in the consolidation therapy period, the plasma concentrations of total arsenic and arsenic metabolites increased with time. In conclusion, these results may support the idea that methylated metabolites of As(2)O(3) contribute to the efficacy of arsenic in APL patients. These results also suggest that detailed studies on the pharmacokinetics as well as the pharmacodynamics of As(2)O(3) in the blood cells from APL patients should be carried out to provide an effective treatment protocol.

Urine analysis of patients exposed to phenylarsenic compounds via accidental pollution.

New methods involving high-performance liquid chromatography/inductively coupled plasma mass spectrometry were examined for the determination of phenylarsenic compounds derived from chemical warfare agents. Several methods were examined for the separation of diphenylarsinic acid (DPAA), phenylarsonic acid, phenylmethylarsinic acid (PMAA), phenyldimethylarsine oxide, and diphenylmethylarsine oxide. Analysis of the urine samples of the patients exposed to phenylarsenic compounds indicated that the main phenylarsenic components were DPAA and PMAA; moreover, some unknown arsenicals, which were also found in contaminated groundwater and rice samples, were also detected.

Pharmacokinetics of arsenic species in Japanese patients with relapsed or refractory acute promyelocytic leukemia treated with arsenic trioxide.

PURPOSE: To investigate the pharmacokinetics of arsenic species in Japanese patients with relapsed or refractory acute promyelocytic leukemia (APL) treated with arsenic trioxide (ATO) at a daily dose of 0.15 mg/kg. METHODS: Inorganic arsenic (AsIII and AsV) and the major metabolites monomethylarsonic acid (MAA(V)) and dimethylarsinic acid (DMAA(V)) in plasma and urine collected from 12 Japanese patients were quantified by HPLC/ICP-MS. RESULTS: The plasma concentrations of AsIII and AsV on day 1 reached the similar Cmax (12.4 +/- 8.4 and 10.2 +/- 3.9 ng/ml) immediately after completion of administration followed by a biphasic elimination. The AUC(0-infinity) of AsV was about twice that of AsIII. The appearance of methylated metabolites in the blood was delayed. During the repeated administration, the plasma concentrations of inorganic arsenic reached the steady state. In contrast, the MAA(V) and DMAA(V) concentrations increased in relation to increased administration frequency. The mean total arsenic excretion rate including inorganic arsenic and methylated arsenic was about 20% of daily dose on day 1 and remained at about 60% of daily dose during week 1-4. CONCLUSIONS: This study demonstrates that ATO is metabolized when administered intravenously to APL patients and methylated metabolites are promptly eliminated from the blood and excreted into urine after completion of administration, indicating no measurable accumulation of ATO in the blood.

Glutathione plays a role in regulating the formation of toxic reactive intermediates from diphenylarsinic acid.

The role of glutathione (GSH) in the cytotoxicity of diphenylarsinic acid [DPAA(V)], which was detected in drinking well water after a poisoning incident in Kamisu, Japan, was investigated in cultured human HepG2 cells. DPA-GS(III), which is the GSH adduct of DPAA, was synthesized and analyzed by HPLC/ESI-MS. DPA-GS(III) was highly toxic to cells and the potency was about 1000 times that of DPAA(V). DPAA(V) was stable in culture medium, while DPA-GS(III) was unstable and changed to protein-bound As (protein-As). By contrast, DPA-GS(III) remained stable with the addition of exogenous GSH, thereby reducing transformation to protein-As. In addition, DPA-GS(III) was transformed to bis(diphenylarsine)oxide [BDPAO(III)], which was observed under serum-free conditions. BDPAO(III) was very unstable and disappeared conversely with an increase in protein-As. In contrast, the presence of GSH suppressed the transformation of BDPAO(III) to protein-As while it enhanced the transformation of BDPAO(III) to DPA-GS(III). Depletion of cell GSH enhanced the cytotoxic effects of DPA-GS(III) and BDPAO(III). Moreover, exogenously-added GSH suppressed the cytotoxic effects of DPA-GS(III) and BDPAO(III). The dynamic behavior of arsenicals in the culture medium and the resultant cytotoxic effects suggested that GSH played a role in regulating the formation of toxic intermediates, such as DPA-GS(III) and BDPAO(III). Moreover, the results suggested that the formation of protein-As in culture medium was compatible with the cytotoxic effects and that GSH was a factor capable of regulating the formation of protein-As from either DPA-GS(III) or BDPAO(III).

Clinical pharmacokinetic study of arsenic trioxide in an acute promyelocytic leukemia (APL) patient: speciation of arsenic metabolites in serum and urine.

The pharmacokinetics of arsenic species in a Japanese patient with relapsed acute promyelocytic leukemia (APL) treated with arsenic trioxide at a daily dose of 0.08 mg/kg was investigated. After achieving complete remission on Day 35 during the induction therapy of arsenic trioxide, we collected the serum and urine samples on Days 4 and 5 during the consolidation therapy of arsenic trioxide. The concentrations of inorganic arsenic and the methylated metabolites in serum and urine were measured by HPLC/ICP-MS. The patient restricted taking the seafood for 3 d before the start of administration and during the sampling period in order to avoid the influence of arsenic derived from seafood. Arsenite (As(III)), methylarsonic acid (MMAs(V)), and dimethylarsinic acid (DMAs(V)) were detected in serum and urine. The total concentration of As(III), MMAs(V) and DMAs(V) in serum ranged from 18 to 41 microg/l (240-547 nM) during 24 h on Day 4. The amount of total arsenic (As(III)+MMAs(V)+DMAs(V)) in urine was 4464 microg/d on Day 4. These results suggest that not the micro-molar but the nano-molar order of arsenic in serum is sufficient to produce the therapeutic effect on APL cells.

The role of glutathione on the cytotoxic effects and cellular uptake of diphenylarsinic acid, a degradation product of chemical warfare agents.

The mechanism underlying enhancement of the cytotoxic effects of diphenylarsinic acid (DPAA) by sulfhydryl (SH) compounds, such as glutathione (GSH) and dimercaptopropane sulfonate (DMPS), was investigated in terms of not only the effects of SH compounds on DPAA uptake by cells, but also the cytotoxic effects of the GSH adduct of DPAA, DPA-GS. In addition, the cytotoxic effects of DPA-GS and cellular uptake were investigated in conjunction with the effects of GSH depletion. Cells took up DPAA in a time- and temperature-dependent manner for up to 2 h, then the uptake leveled off for 6 h. Arsenic species other than DPAA were not detected in the cells. The presence of GSH and DMPS did not influence the rate of uptake of DPAA by the cells. By contrast, when the cytotoxic potential of DPA-GS was compared with that of DPAA, DPA-GS was about 1,000 times more toxic than DPAA, suggesting that enhancement of DPAA toxicity by SH compounds might be due to the formation of adducts in the culture medium. The cytotoxic effects of DPA-GS were suppressed markedly by the presence of GSH and DMPS, and the suppression was attributed to an inhibition of more than 90% by the SH compounds of DPA-GS uptake. Depletion of cell GSH enhanced the cytotoxic effects of DPA-GS by two to three times and the enhancement attributed to an increased cellular uptake of DPA-GS. These results suggest that GSH plays a role in regulating the formation of DPA-GS and cellular uptake.

High intracellular phosphorus contents exhibit a correlation with arsenate resistance in chlamydomonas mutants.

Pi in the medium relieved the toxicity of arsenate against cellular growth of Chlamydomonas reinhardtii. To investigate the relationship between intracellular P contents and arsenate resistance, we determined the intracellular P contents of arsenate-sensitive and arsenate-resistant mutants, which had been generated by random insertional mutagenesis. All 13 arsenate-resistant mutants showed higher P contents than the parent strain, while arsenate-sensitive mutants with high P contents were not found. In one of the arsenate-resistant mutants, AR3, the intracellular P content was about twice that in the wild type during growth in the absence of arsenate. Arsenate incorporation in AR3 was suppressed within 10 min after the addition of 1 mM arsenate, while Pi incorporation continued even after arsenate uptake ceased. Whereas the P content of the wild type decreased to half in the presence of 0.5 mM arsenate, almost the same degree (about 50%) of decrease was observed in AR3 cells grown in the presence of as much as 3 mM arsenate. AR3, in which PTB1, a homolog of a Pi transporter gene, had been disrupted, exhibited a higher activity of a high-affinity Pi transporter, suggesting that it may be due to a compensatory transport activity. These data suggest that the intracellular level of P is one of the important factors of arsenate resistance.

In vitro cytotoxic and genotoxic effects of diphenylarsinic acid, a degradation product of chemical warfare agents.

Diphenylarsinic acid [DPAs(V)], a degradation product of diphenylcyanoarsine or diphenylchloroarsine, both of which were developed as chemical warfare agents, was investigated in terms of its capacity to induce cytotoxic effects, numerical and structural changes of chromosomes, and abnormalities of centrosome integrity and spindle organizations in conjunction with the effects of glutathione (GSH) depletion. DPAs(V) had toxic effects on cultured human hepatocarcinoma HepG2 cells at concentrations more than 0.5 mM. Depletion of GSH reduced the toxic effects of DPAs(V) as well as dimethylarsinic acid [DMAs(V)] toxicity, while toxicity by arsenite [iAs(III)] was enhanced. Exogenously added sulfhydryl (SH) compounds, such as dimercapropropane sulfonate (DMPS), GSH, and dithiothreitol (DTT), enhanced the toxic effects of DPAs(V) while they suppressed iAs(III) toxicity. DPAs(V) caused an increase in the mitotic index, and also structural and numerical changes in chromosomes in V79 Chinese hamster cells. Abnormality of centrosome integrity in mitotic V79 cells and multipolar spindles was also induced by DPAs(V) in a time- and concentration-dependent manner. These results suggested that highly toxic chemicals were generated by the interaction of DPAs(V) with SH compounds. Moreover, enhancements of toxicity by a combination of DPAs(V) and SH compounds suggested a risk in the use of SH compounds as a remedy for intoxication by diphenylarsenic compounds. Investigations on the effects of SH compounds on animals intoxicated with DPAs(V) are warranted.