Inorganic Arsenic Metabolites Research Articles

The role of active arsenic species produced by metabolic reduction of dimethylarsinic acid in genotoxicity and tumorigenesis

In recent research of arsenic carcinogenesis, many researchers have directed their attention to methylated metabolites of inorganic arsenics. Because of its high cytotoxicity and genotoxicity, trivalent dimethylated arsenic, which can be produced by the metabolic reduction of dimethylarsinic acid (DMA), has attracted considerable attention from the standpoint of arsenic carcinogenesis. In the present paper, we examined trivalent dimethylated arsenic and its further metabolites for their chemical properties and biological behavior such as genotoxicity and tumorigenicity. Our in vitro and in vivo experiments suggested that the formation of cis-thymine glycol in DNA was induced via the production of dimethylated arsenic peroxide by the reaction of trivalent dimethylated arsenic with molecular oxygen, but not via the production of common reactive oxygen species (ROS; superoxide, hydrogen peroxide, hydroxyl radical, etc.). Thus, dimethylated arsenic peroxide may be the main species responsible for the tumor promotion in skin tumorigenesis induced by exposure to DMA. Free radical species, such as dimethylarsenic radical [(CH 3) 2As·] and dimethylarsenic peroxy radical [(CH 3) 2AsOO·], that are produced by the reaction of molecular oxygen and dimethylarsine [(CH 3) 2AsH], which is probably a further reductive metabolite of trivalent dimethylated arsenic, may be main agents for initiation in mouse lung tumorigenesis.

Induction of glutathione S-transferase placental form positive foci in liver and epithelial hyperplasia in urinary bladder, but no tumor development in male Fischer 344 rats treated with monomethylarsonic acid for 104 weeks

The carcinogenicity of monomethylarsonic acid (MMA(V)), a major metabolite of inorganic arsenics in human and experimental animals, was investigated in male Fischer 344 rats. A total of 129 rats at 10 weeks of age were randomly divided into three groups and received drinking water containing MMA(V) at doses of 0 (Control), 50, and 200 ppm ad libitum for 104 weeks. No significant differences were found between the control and the MMA(V)-treated groups regarding clinical signs, mortality, hematological, and serum biochemistry findings. Quantitative analysis of glutathione S-transferase placental form (GST-P) positive foci in liver revealed a significant increase of numbers and areas in the 200 ppm MMA(V)-treated group. In the urinary bladder MMA(V) induced simple hyperplasia and significantly elevated the proliferating cell nuclear antigen (PCNA)-positive index in the urothelium. A variety of tumors developed in rats of all groups, including the controls, but all were histologically similar to those known to occur spontaneously in F344 rats and there were no significant differences among the groups. Thus, it could be concluded that, under the present experimental conditions, MMA(V) induced lesions in the liver and urinary bladder, but did not cause tumor development in male F344 rats even after 2 years exposure.

Active arsenic species produced by GSH-dependent reduction of dimethylarsinic acid cause micronuclei formation in peripheral reticulocytes of mice

Dimethylarsine and trivalent dimethylated arsenic, metabolites of inorganic arsenics, have received considerable attention in current research because of their biological activities. We attempted to determine the appearance of micronucleated reticulocytes (MNRETs) in mouse peripheral blood following intraperitoneal administration of dimethylarsinous iodide (DMI) and trimethylarsine (TMA), model compounds of trivalent dimethylated arsenic and dimethylarsine, respectively. A significant increase in the number of MNRETs was observed with TMA, but not with DMI. Furthermore, MNRETs only appeared with 10.6 mg/kg of dimethylarsinic acid (DMA) following its co-injection with reduced glutathione (GSH). These results suggest that micronucleus formation may need further metabolic reduction of trivalent dimethylated arsenic, i.e. the production of dimethylarsine, by an excess amount of GSH. Meanwhile, the increase in MNRETs by administration of arsenite at 7.6 mg/kg, an equivalent dose to DMA as As, was remarkably diminished by co-administration with GSH. These results indicate that GSH plays an important role in the genotoxic process of arsenics, particularly by dimethylated arsenic.

Liver tumorigenicity of trimethylarsine oxide in male Fischer 344 rats--association with oxidative DNA damage and enhanced cell proliferation.

Arsenic is a notorious environmental toxicant known to be carcinogenic for the skin, lung and urinary bladder in human beings. The carcinogenicity of trimethylarsine oxide (TMAO), one organic metabolite of inorganic arsenics in humans and experimental animals, was investigated here in male Fischer 344 rats in a 2-year carcinogenicity test. TMAO was administered to a total of 129 male rats ad libitum at concentrations of 0 (Control), 50 or 200 p.p.m. in the drinking water. In animals that died or were killed from the 87th week until the end of 104th week, incidences of hepatocellular adenomas were 14.3, 23.8 and 35.6% in the 0, 50 and 200 p.p.m.-treated groups, respectively; the multiplicities were 0.21, 0.33 and 0.53. Both were significantly increased in the 200 p.p.m.-treated group. While a variety of other tumors developed in various organs, they were present in all groups, including the controls, and were histologically diagnosed as those known to occur spontaneously in F344 rats. To test the contribution of reactive oxygen species (ROS) to TMAO tumorigenicity in the liver, 8-hydroxydeoxyguanosine (8-OHdG) formation was assessed by high performance liquid chromatography. The 8-OHdG values for the 200 p.p.m. TMAO group were significantly higher than those for the control group. Furthermore, as assessed by the proliferating cell nuclear antigen index, cell proliferation in the normally appearing parenchyma was elevated by the TMAO treatment. These results indicate that TMAO exerts liver tumorigenicity with possible mechanistic roles for oxidative DNA damage and enhanced cell proliferation.

Simultaneous arsenic‐ and selenium‐specific detection of the dimethyldiselenoarsinate anion by high‐performance liquid chromatography–inductively coupled plasma atomic emission spectrometry

AbstractThe seleno‐bis (S‐glutathionyl) arsinium ion, [(GS)2AsSe]−, which can be synthesized from arsenite, selenite and glutathione (GSH) at physiological pH, fundamentally links the mammalian metabolism of arsenite with that of selenite and is potentially involved in the chronic toxicity/carcinogenicity of inorganic arsenic. A mammalian metabolite of inorganic arsenic, dimethylarsinic acid, reacts with selenite and GSH in a similar manner to form the dimethyldiselenoarsinate anion, [(CH3)2As(Se)2]−. Since dimethylarsinic acid is an environmentally abundant arsenic compound that could interfere with the mammalian metabolism of the essential trace element selenium via the in vivo formation of [(CH3)2As(Se)2]−, a chromatographic method was developed to rapidly identify this compound in aqueous samples. Using an inductively coupled plasma atomic emission spectrometer (ICP‐AES) as the simultaneous arsenic‐ and selenium‐specific detector, the chromatographic retention behaviour of [(CH3)2As(Se)2]− was investigated on styrene–divinylbenzene‐based high‐performance liquid chromatography (HPLC) columns. With a Hamilton PRP‐1 column as the stationary phase (250 × 4.1 mm ID, equipped with a guard column) and a phosphate‐buffered saline buffer (0.01 mol dm−3, pH 7.4) as the mobile phase, [(CH3)2As(Se)2]− was identified in the column effluent according to its arsenic:selenium molar ratio of 1 : 2. With this stationary phase/mobile phase combination, [(CH3)2As(Se)2]− was baseline‐separated from arsenite, selenite, dimethylarsinate, methylarsonate and low molecular weight thiols (GSH, oxidized GSH) that are frequently encountered in biological samples. Thus, the HPLC–ICP‐AES method developed should be useful for rapid identification and quantification of [(CH3)2As(Se)2]− in biological fluids. Copyright © 2003 John Wiley & Sons, Ltd.

Determinants of inorganic arsenic methylation capability among residents of the Lanyang Basin, Taiwan: arsenic and selenium exposure and alcohol consumption

The objective of this study was to assess individual variation in inorganic arsenic methylation capability and the association between selenium levels in urine and blood, and inorganic arsenic methylation capability among residents of the Lanyang Basin who drank groundwater and were exposed to high concentrations of inorganic arsenic. According to the arsenic concentration of their drinking water, they were equally and randomly classified into four groups of 252 persons. It turned out that the higher the concentration of arsenic in well water was and thus the cumulative arsenic exposure, the higher the total inorganic arsenic metabolites in urine (total As i) and the overall inorganic and organic arsenic in urine (overall As i+o) were. The percentage of inorganic arsenic significantly decreased and the DMA percentage significantly increased as the concentration of urinary selenium and serum α-tocopherol increased. It appeared that urinary selenium levels increased the metabolism by methylation of arsenic, a finding that requires further investigation.

Monitoring of arsenic exposure with speciated urinary inorganic arsenic metabolites for ion implanter maintenance engineers

For wafer fabrication in the semiconductor industry, maintenance engineers are potentially exposed to hazards during their work of disassembling machine components for cleanup. One special concern is the presence of arsenic or arsenic compounds in the working environment. This study analyzed speciated urinary inorganic arsenic metabolites of the maintenance engineers using high-performance liquid chromatography–hydride generation atomic absorption spectrometry to study the potential arsenic exposure during their maintenance work. In total, from six wafer fabrication facilities, 30 maintenance engineers were recruited as the exposed group and another 12 office-based engineers served as the control group. First morning-voided urine samples of each study subject were collected for 7 consecutive days. The levels of total urinary inorganic arsenic metabolites for the exposed group were 1.7±1.4, 1.4±1.1, 6.2±6.7, 20.2±14.1, and 29.5±17.2 μg/L for As 3+, As 5+, monomethylarsonic acid, dimethylarsinic acid, and total inorganic arsenic, respectively. Both the concentration of monomethylarsonic acid and its percentage in total urinary inorganic arsenic metabolites showed significantly ascending trends for the control group, for the engineers without preventative maintenance work prior to their urine sampling, and for the engineers with such work prior to their urine sampling ( P<0.05 and P<0.0005, respectively). The data also suggested that, at low-level occupational arsenic exposure, the concentration of total urinary inorganic arsenic metabolites might be misleading due to the confounding effect resulting from intake of seafood, such as arsenosuger. Nevertheless, monitoring of urinary arsenic species by using the percentage change of monomethylarsonic acid in total urinary inorganic arsenic metabolites as an indicator for the verification of arsenic exposure is helpful and appropriate in such cases.

Intra-individual variation in the metabolism of inorganic arsenic.

Inorganic arsenic is metabolized to methylarsonic acid (MMA) and dimethylarsinic acid (DMA), which are excreted in the urine. Previous studies have shown a marked inter-individual variation in the metabolism, but the within-person variation is unknown. Therefore, we determined the variation in the relative amount of urinary arsenic metabolites, i.e., inorganic arsenic, MMA and DMA, over time in women living in an Andean village with elevated arsenic levels in drinking water. For our investigation of the individual day-to-day variation, daily spot urine samples were collected (at the same time of the day) for 5 consecutive days by 15 women. For our investigation of the within-day variation, seven women collected all the urine voided over a 72-h period, each voided into a separate container. Repeated measures analysis of variance (ANOVA) revealed no significant day-to-day variation, either in the relative distribution of inorganic arsenic metabolites (inorganic arsenic, MMA and DMA), or in the concentration of the metabolites. However, the percentage of DMA was slightly higher (on average 5.0%; P=0.003) and the percentage of inorganic arsenic lower (on average 5.8%; P=0.001) during the morning/day (03:00-15:00) compared with the evening/night (15:00-03:00). No within-day variation in the percentage of MMA was observed. The arsenic methylation efficiency of an individual is remarkably stable over time.

Promoting effects of monomethylarsonic acid, dimethylarsinic acid and trimethylarsine oxide on induction of rat liver preneoplastic glutathione S-transferase placental form positive foci: a possible reactive oxygen species mechanism.

Dimethylarsinic acid (DMA) is a major metabolite of inorganic arsenicals, which are epidemiologically significant chemicals in relation to liver cancer in mammals. The present study was conducted to determine the promoting effects of organic arsenicals related to DMA [monomethylarsonic acid (MMA) and trimethylarsine oxide (TMAO)] on rat liver carcinogenesis using a liver medium-term bioassay (the Ito test). Male, 10-week-old, F344 rats were given a single i.p. injection of diethylnitrosamine at a dose of 200 mg/kg b.w. as an initiator. Starting 2 weeks thereafter they received 100 ppm of MMA, DMA or TMAO in their drinking water, or no supplement as a control, for 6 weeks. All animals underwent 2/3 partial hepatectomy in week 3 after initiation. Quantification of glutathione S-transferase placental form (GST-P)-positive foci as preneoplastic lesions in liver sections revealed significantly increased numbers and areas in all 3 treated groups compared with controls. Hepatic microsome cytochrome P-450 content was markedly increased with all 3 arsenic treatments. Markedly elevated CYP 2B1 protein levels and CYP 2B1/2 mRNA levels were thus observed in all cases. The potency of promotion was similar for MMA, DMA and TMAO. Since hydroxyradicals were found to be generated in the relatively early phase while methylated arsenicals were metabolized in liver, the resultant oxidative stress might have promoted lesion development.

A review of animal models for the study of arsenic carcinogenesis

As inorganic arsenic is a proven human carcinogen, significant effort has been made in recent decades in an attempt to understand arsenic carcinogenesis using animal models, including rodents (rats and mice) and larger mammals such as beagles and monkeys. Transgenic animals were also used to test the carcinogenic effect of arsenicals, but until recently all models had failed to mimic satisfactorily the actual mechanism of arsenic carcinogenicity. However, within the past decade successful animal models have been developed using the most common strains of mice or rats. Thus dimethylarsinic acid (DMA), an organic arsenic compound which is the major metabolite of inorganic arsenicals in mammals, has been proven to be tumorigenic in such animals. Reports of successful cancer induction in animals by inorganic arsenic (arsenite and arsenate) have been rare, and most carcinogenetic studies have used organic arsenicals such as DMA combined with other tumor initiators. Although such experiments used high concentrations of arsenicals for the promotion of tumors, animal models using doses of arsenicals species closed to the exposure level of humans in endemic areas are obviously the most significant. Almost all researchers have used drinking water or food as the pathway for the development of animal model test systems in order to mimic chronic arsenic poisoning in humans; such pathways seem more likely to achieve desirable results.

Urinary arsenic speciation in subjects with or without restriction from seafood dietary intake

In order to understand whether ingestion of seafood affects the urinary arsenic metabolites. About 42 women and 36 men were recruited from the students, parents and teachers in Taipei Medical University and National Taiwan University. The study subjects were interviewed about dietary habits, cigarette smoking habits, drug and vitamin intake, and consumption of seafood. Urine samples were collected from study subjects before and after refraining from eating seafood for 3 days, respectively. The urine samples were frozen at −20 °C separated by high-performance liquid chromatography (HPLC), and on line linked to hydride generator atomic absorption spectrometry (HGAAS) to quantify the levels of various species of inorganic arsenic and its metabolites. The levels of arsenite (AsIII), arsenate (AsV), monomethylarsonic acid (MMA), dimethylarsinic acid (DMA), total inorganic arsenic metabolites, inorganic arsenic percent, MMA percent and DMA percent were similar before and after refraining from eating seafood for 3 days. The frequencies of fish, shellfish and seaweed dietary intake were not significantly correlated with urinary arsenic species.

Species variations in the biliary and urinary excretion of arsenate, arsenite and their metabolites

In most mammalian species, inorganic arsenicals are extensively biotransformed and excreted both in unchanged form and as metabolites. In the bile of rats receiving arsenate (AsV) or arsenite (AsIII) we have identified monomethylarsonous acid (MMAsIII), purportedly the most toxic metabolite of inorganic arsenic. As rats are not commonly accepted for studying arsenic metabolism, we carried out a comparative investigation on the excretion of AsV, AsIII and their metabolites in five animal species in order to determine whether they also form MMAsIII from AsV and AsIII. Anaesthetised bile duct-cannulated rats, mice, hamsters, rabbits, and guinea pigs were injected with AsV or AsIII (50 μmol/kg, i.v.) and their bile and urine was collected for 2 h. Arsenic in bile and urine was speciated by HPLC-hydride generation-atomic fluorescence spectrometry and the excretion rates of AsV, AsIII, monomethylarsonic acid (MMAsV), MMAsIII and dimethylarsinic acid (DMAsV) were quantified. All species injected with AsV excreted arsenic preferentially into urine, whereas all animals receiving AsIII, except rabbits, delivered more arsenic into bile than urine. Bile contained almost exclusively trivalent arsenic (i.e. AsIII and/or MMAsIII), whereas AsV, AsIII and DMAsV appeared in urine. Except for guinea pigs, which do not methylate arsenic, the other species formed MMAsIII and excreted it into bile. Having excreted as much as 8% of the dose of AsIII or AsV in 2 h as MMAsIII, rats were by far the most efficient producers of this supertoxic metabolite. Thus, although the rat is not a good model for studying long-term arsenic disposition, this species appears especially valuable in studies on AsIII methyltransferase and in vivo formation of MMAsIII.

Lack of promoting effect due to oral administration of dimethylarsinic acid on rat lung carcinogenesis initiated with N-bis(2-hydroxypropyl)nitrosamine

Dimethylarsinic acid (DMA), a major metabolite of inorganic arsenics, and arsenic exposure is associated with tumor development in a wide variety of human tissues. In the present study, we examined whether DMA has tumor-promoting activity on rat lung carcinogenesis initiated with N-bis(2-hydroxypropyl)nitrosamine (DHPN). Male, 8-week-old, F344 rats were treated with DHPN at a concentration of 0.1% in drinking water for 1 week, and starting 1 week thereafter, DMA was administered at concentrations of 0, 100, 200 or 400 ppm in the drinking water for 30 weeks. Induction of epithelial lesions, classified as alveolar epithelial hyperplasia, adenoma, and adenocarcinoma was evident in the lungs of DHPN-initiated animals, but no significant differences were found between DMA-treated groups and control groups. Furthermore, no significant differences in 5-bromo-2′-deoxyuridine labeling indices, as a marker of cell proliferation were observed among the groups. An additional group treated with DMA at concentrations of 200 ppm alone, without prior DHPN initiation was found to develop no epithelial lesions in the lung. There was no significant gain in 8-hydroxydeoxyguanosine formation, as a marker of oxidative stress, in the lungs of rats treated with DMA in their drinking water. In conclusion, oral-administered DMA does not exert promoting effects on rat lung carcinogenesis initiated with DHPN.

Oral Exposure of Dimethylarsinic Acid, a Main Metabolite of Inorganic Arsenics, in Mice Leads to an Increase in 8-Oxo-2′-deoxyguanosine Level, Specifically in the Target Organs for Arsenic Carcinogenesis

We have proposed that oral administration of dimethylarsinic acid (DMA), a metabolite of inorganic arsenics in mammals, rather than inorganic arsenics themselves, promotes lung and skin tumors by way of the metabolic production of free radicals such as dimethylarsenic peroxy radical [(CH3)2AsOO•]. The purpose of the present study was to examine if dimethylarsenic has the ability to induce oxidative damage. 8-oxo-2′-deoxyguanosine (8-oxodG) was used as a biomarker of DNA oxidation. The oral administration of DMA enhanced significantly the amounts of 8-oxodG specifically in the target organs (skin, lung, liver, and urinary bladder) of arsenic carcinogenesis and also in urine, whereas arsenite did not. The dimethylarsenics thus may play an important role in arsenic carcinogenesis through the induction of oxidative damage, particularly of base oxidation.

Dimethylarsinic acid targets tubulin in mitotic cells to induce abnormal spindles

AbstractDimethylarsinic acid (DMA) is the most effective inducer of cell‐cycle disruption among the arsenic compounds and their metabolites. The present study was conducted to gain further insight into cell‐cycle disruption induced by DMA. The inhibition of cell proliferation and the mitotic arrest induced by DMA were significant and dose‐dependent in Chinese hamster V79 cells and the two seemed to be closely related. At less than 140 µM the DMA did not inhibit the proliferation of cells, but it significantly induced mitotic arrest. An indirect immunofluorescence assay using anti‐α‐tubulin antibodies revealed that DMA induced the formation of abnormal spindles in the metaphase cells even at 350 µM with 5 h of treatment. At 1.4 mM DMA no metaphase cells could form a definite spindle structure. The spindle figures were similar to those induced by colchicine (125 nM) or vinblastine (110 nM), major antimitotic agents. In DMA‐treated interphase cells, the microtubule networks were indistinguishable from those of normal cells. With the tubulin‐assembly assay estimated by turbidity, DMA at less than 200 µM suppressed tubulin assembly in a dose‐dependent manner, whereas at more than 700 µM it enhanced tubulin polymerization remarkably with or without addition of excess guanosine‐5′‐triphosphate. According to the above findings, we discussed the possibility that DMA, a primary metabolite of inorganic arsenic in mammals, is related to arsenic carcinogenicity. Copyright © 2001 John Wiley &amp; Sons, Ltd.

Monomethylarsonous acid (MMA(III)) and arsenite: LD(50) in hamsters and in vitro inhibition of pyruvate dehydrogenase.

Monomethylarsonous acid (MMA(III)), a metabolite of inorganic arsenic, has received very little attention from investigators of arsenic metabolism in humans. MMA(III), like sodium arsenite, contains arsenic in the +3 oxidation state. Although we have previously demonstrated that it is more toxic than arsenite in cultured Chang human hepatocytes, there are no data showing in vivo toxicity of MMA(III). When MMA(III) or sodium arsenite was administered intraperitoneally to hamsters, the LD(50)s were 29.3 and 112.0 micromol/kg of body wt, respectively. In addition, inhibition of hamster kidney or purified porcine heart pyruvate dehydrogenase (PDH) activity by MMA(III) or arsenite was determined. To inhibit hamster kidney PDH activity by 50%, the concentrations (mean +/- SE) of MMA(III) as methylarsine oxide, MMA(III) as diiodomethylarsine, and arsenite were 59.9 +/- 6.5, 62.0 +/- 1.8, and 115.7 +/- 2.3 microM, respectively. To inhibit activity of purified porcine heart PDH activity by 50%, the concentrations (mean +/- SE) of MMA(III) as methylarsine oxide and arsenite were 17.6 +/- 4.1 and 106.1 +/- 19.8 microM, respectively. These data demonstrate that MMA(III) is more toxic than inorganic arsenite, both in vivo and in vitro, and call into question the hypothesis that methylation of inorganic arsenic is a detoxication process.

Metabolism of dimethylarsinic acid in rats: production of unidentified metabolites in vivo

AbstractOur previous study revealed that two unidentified metabolites, M‐1 and M‐2, were excreted in urine after long‐term oral administration of dimethylarsinic acid (DMA), the main metabolite of inorganic arsenic. In the present study, we attempted to clarify the mechanism of production of these unknown metabolites. Male F344/DuCrj rats were administered a single dose of DMA (50 mg kg−1) orally or intraperitoneally with or without pretreatment with L‐buthionine‐SR‐sulfoximine (BSO), which inhibits glutathione (GSH) synthesis. Urine was collected by forced urination at various time points after administration of DMA. Arsenic metabolites in urine were analyzed by ion chromatography with inductively coupled plasma mass spectrometry (IC–ICP‐MS). The unidentified metabolites M‐1 and M‐2 were excreted later than elimination of DMA and trimethylarsine oxide (TMAO). GSH depletion decreased in TMAO elimination, suggesting that GSH plays important roles in the methylation of DMA to TMAO in rats. There was no difference in the amount of production of either M‐1 or M‐2 between BSO‐pretreated rats and controls, suggesting that M‐1 and M‐2 cannot be formed during methylation in the liver. The amounts of elimination of M‐1 and M‐2 were less after intraperitoneal administration than after oral administration.Male F344/DuCrj rats were given 100 mg As l−1 DMA via drinking water for 20 weeks. Urine and feces were collected forcibly and were analyzed by IC–ICP‐MS. A new unidentified metabolite, M‐3, was detected only in feces as a metabolite of DMA after 20 weeks exposure to DMA, although M‐1 and M‐2 were found in both urine and feces. The unidentified metabolites M‐1, M‐2, and M‐3 were excreted mainly as fecal metabolites along with unmetabolized DMA. This finding also suggests that M‐1, M‐2, and M‐3 might be produced in the intestinal tract. Copyright © 2001 John Wiley &amp; Sons, Ltd.

Promotion of skin carcinogenesis by dimethylarsinic acid in keratin (K6)/ODC transgenic mice.

Dimethylarsinic acid (DMA) is a major metabolite of inorganic arsenicals in mammals, and arsenic exposure is associated with tumor development in a wide variety of human tissues, particularly the skin. Transgenic mice with ornithine decarboxylase (ODC) targeted to hair follicle keratinocytes are much more sensitive than littermate controls to carcinogens. In this study we investigated the promoting effect of DMA on skin carcinogenesis in such K6/ODC transgenic mice. The back skin of female C57BL/6J K6/ODC transgenic mice, 10 to 14 weeks old, was initiated with topical application of 7,12‐dimethylbenz[α]anthracene (DMBA) at a dose of 50 μg or acetone alone on day 1 of the experiment, followed by treatment with 3.6 mg of DMA, 5 μg of 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA) or neutral vehicle (control) twice a week for 18 weeks. Mice were killed 1 week after the end of the treatment. Induction of skin tumors was significantly accelerated in the DMA‐treated group, as well as in the TPA‐treated group, indicating that DMA has a promoting effect on skin tumorigenesis in K6/ODC transgenic mice.

The role of orally administered dimethylarsinic acid, a main metabolite of inorganic arsenics, in the promotion and progression of UVB-induced skin tumorigenesis in hairless mice

The effect of dimethylarsinic acid (DMA) on skin tumorigenesis by UVB irradiation was examined. Hairless mice (Hos: HR-1) irradiated with UVB at a dose of 2 kJ/m 2 twice weekly, were fed with drinking water containing 1000 ppm DMA, a main metabolite of inorganic arsenics, produced more skin tumors than DMA-untreated mice. Histopathological examination revealed that the mouse malignant tumors with severe atypism appeared only in the treatment group of UVB plus 1000 ppm DMA. These positive results point out the importance of dimethylated metabolites of inorganic arsenic in the process of skin carcinogenesis.

Lack of Promoting Potential of Dimethylarsinic Acid in the Kidney of Male NCI-Black Reiter Rats.

Humans encounter exposure to arsenic (As) in numerous ways. Dimethylarsinic acid (DMA), one of the major metabolites of inorganic arsenics in most mammals promotes kidney, urinary bladder, liver, and thyroid carcinogeneses in F344 rats. Dimethylarsenic peroxyl radical ((CH3)2 AsOO.) has been postulated to be responsible for the DNA damage induced by DMA. In a preliminary experiment conducted in our laboratory, subacute doses of DMA induced formation of 8-hydroxy-2’-deoxyguanosine (8-OHdG) and increased proliferation indices in the renal cells of NCI-Black Reiter (NBR) rats which lack α2u-globulin, which has been attributed to influence renal carcinogenesis. This prompted us to study the promoting effects of DMA on renal carcinogenesis in this strain of rats by employing the initiation-promotion model. Animals were divided into two groups (11 rats in each group). Group 1 was treated with N-ethyl-N-hydroxyethylnitrosamine (EHEN), at a concentration of 0.1% in the drinking water for 2 weeks followed by basal diet for 30 weeks. Group 2 was treated with EHEN with the same dosage as Group 1 for 2 weeks followed by 200 ppm DMA in the drinking water for 29 weeks. Neither atypical tubules nor renal cell tumors were induced in both groups, suggesting that absence of α2u-globulin may contribute to the resistance to the above stimulus by this strain of rats. Since EHEN also initiated liver carcinogenesis, we analyzed the liver for glutathione S-transferase placental form (GST-P)-positive foci, which is a marker in rat liver carcinogenesis. There was no significant change between the two groups. Thus, DMA lacked the potential to promote kidney and liver carcinogeneses in male NBR rats.