Evaluation of diet and dimethylarsinic acid on the urothelium of Syrian golden hamsters.
(9/89)
Few studies have examined the carcinogenicity of chemicals toward the urinary bladder in hamsters, and the effect of diet on hamster urine and urothelium has not been reported. Our laboratory recently began investigating the effects of dimethylarsinic acid (DMA) on the hamster bladder, and we noticed subtle urothelial changes even in controls. The possible effect of various diets on hamster urothelium was evaluated by feeding different diets to 4-week-old Syrian Golden hamsters for 5 weeks. The diets examined were Tekland 8656, Purina 5002, Purina 5L79, and NIH-07. Light microscopic examination showed a slight increase in urothelial hyperplasia in hamsters fed Purina 5L79. An increase in the incidence of urinary bladder necrosis, exfoliation, and mild hyperplasia were noted by scanning electron microscopy (SEM) with all dietary preparations except NIH-07. The constituents in the diets producing the urothelial alterations are not known at present, but NIH-07 diet was chosen for experiments to investigate the effects of DMA on the hamster bladder epithelium. Male and female 5-week-old Syrian Golden hamsters were fed 100 ppm DMA for 10 weeks. Examination of urinary parameters showed no treatment-related changes. Light microscopic examination and SEM revealed no changes of the urothelium of DMA-treated male or female hamsters. (+info)
Uptake kinetics of arsenic species in rice plants.
(10/89)
Arsenic (As) finds its way into soils used for rice (Oryza sativa) cultivation through polluted irrigation water, and through historic contamination with As-based pesticides. As is known to be present as a number of chemical species in such soils, so we wished to investigate how these species were accumulated by rice. As species found in soil solution from a greenhouse experiment where rice was irrigated with arsenate contaminated water were arsenite, arsenate, dimethylarsinic acid, and monomethylarsonic acid. The short-term uptake kinetics for these four As species were determined in 7-d-old excised rice roots. High-affinity uptake (0-0.0532 mM) for arsenite and arsenate with eight rice varieties, covering two growing seasons, rice var. Boro (dry season) and rice var. Aman (wet season), showed that uptake of both arsenite and arsenate by Boro varieties was less than that of Aman varieties. Arsenite uptake was active, and was taken up at approximately the same rate as arsenate. Greater uptake of arsenite, compared with arsenate, was found at higher substrate concentration (low-affinity uptake system). Competitive inhibition of uptake with phosphate showed that arsenite and arsenate were taken up by different uptake systems because arsenate uptake was strongly suppressed in the presence of phosphate, whereas arsenite transport was not affected by phosphate. At a slow rate, there was a hyperbolic uptake of monomethylarsonic acid, and limited uptake of dimethylarsinic acid. (+info)
Carcinogenicity of dimethylarsinic acid in male F344 rats and genetic alterations in induced urinary bladder tumors.
(11/89)
Arsenic is a well-documented human carcinogen, and contamination with this heavy metal is of global concern, presenting a major issue in environmental health. However, the mechanism by which arsenic induces cancer is unknown, in large part due to the lack of an appropriate animal model. In the present set of experiments, we focused on dimethylarsinic acid (DMA), a major metabolite of arsenic in most mammals including humans. We provide, for the first time, the full data, including detailed pathology, of the carcinogenicity of DMA in male F344 rats in a 2-year bioassay, along with the first assessment of the genetic alteration patterns in the induced rat urinary bladder tumors. Additionally, to test the hypothesis that reactive oxygen species (ROS) may play a role in DMA carcinogenesis, 8-hydroxy-2'-deoxyguanosine (8-OHdG) formation in urinary bladder was examined. In experiment 1, a total of 144 male F344 rats at 10 weeks of age were randomly divided into four groups that received DMA at concentrations of 0, 12.5, 50 and 200 p.p.m. in the drinking water, respectively, for 104 weeks. From weeks 97-104, urinary bladder tumors were observed in 8 of 31 and 12 of 31 rats in groups treated with 50 and 200 p.p.m. DMA, respectively, and the preneoplastic lesion, papillary or nodular hyperplasias (PN hyperplasia), was noted in 12 and 14 rats, respectively. DMA treatment did not cause tumors in other organs and no urinary bladder tumors or preneoplastic lesions were evident in the 0 and 12.5 p.p.m.-treated groups. Urinary levels of arsenicals increased significantly in a dose-responsive manner except for arsenobetaine (AsBe). DMA and trimethylarsine oxide (TMAO) were the major compounds detected in the urine, with small amounts of monomethylarsonic acid (MMA) and tetramethylarsonium (TeMa) also detected. Significantly increased 5-bromo-2'-deoxyuridine (BrdU) labeling indices were observed in the morphologically normal epithelium of the groups treated with 50 and 200 p.p.m. DMA. Mutation analysis showed that DMA-induced rat urinary bladder tumors had a low rate of H-ras mutations (2 of 20, 10%). No alterations of the p53, K-ras or beta-catenin genes were detected. Only one TCC (6%) demonstrated nuclear accumulation of p53 protein by immunohistochemistry. In 16 of 18 (89%) of the TTCs and 3 of 4 (75%) of the papillomas, decreased p27(kip1) expression could be demonstrated. Cyclin D1 overexpression was observed in 26 of 47 (55%) PN hyperplasias, 3 of 4 (75%) papillomas, and 10 of 18 (56%) TCCs. As a molecular marker of oxidative stress, increased COX-2 expression was noted in 17 of 18 (94%) TCCs, 4 of 4 (100%) papillomas, and 39 of 47 (83%) PN hyperplasias. In experiment 2, 8-OHdG formation in urinary bladder was significantly increased after treatment with 200 p.p.m. DMA in the drinking water for 2 weeks compared with the controls. The studies demonstrated DMA to be a carcinogen for the rat urinary bladder and suggested that DMA exposure may be relevant to the carcinogenic risk of inorganic arsenic in humans. Diverse genetic alterations observed in DMA-induced urinary bladder tumors imply that multiple genes are involved in stages of DMA-induced tumor development. Furthermore, generation of ROS is likely to play an important role in the early stages of DMA carcinogenesis. (+info)
Stability of arsenic species and insoluble arsenic in human urine.
(12/89)
Urinary arsenic species are important short-term biomarkers that have been used in epidemiological studies. However, the stability of soluble arsenic species and the amount of arsenic lost during sample pretreatment remain unclear. The objective of this study is to evaluate the stability of soluble arsenic species in urine and aqueous standards, as well as to assess the amount of insoluble and soluble arsenic lost during pretreatment (centrifugation and filtration, respectively). High-performance liquid chromatogram inductively coupled plasma mass spectrometry was used to speciate arsenic species [Arsenite [As(III)], arsenate [As(V)], monomethylarsonic acid [MMA(V)], monomethylarsonous acid [MMA(III)], dimethylarsinic acid [DMA(V)], and arsenobetaine [AsB]] in aqueous standards and in urine samples. The arsenic levels in both freshly collected urine samples (pH = 5.5-7.0) and National Institute of Standards and Technology Standard Reference Material 2670 toxic elements in frozen-dried urine (pH 4.4) remained constant up to 6 months when stored at -20 degrees C. In an aqueous solution mixed with 10 micro g/liter of As(III), As(V), MMA, and DMA standards, and stored at 4 degrees C, As(III) and As(V) were stable only up to 4 weeks, and MMA and DMA remained stable up to 4.5 months. The same phenomenon was observed for 100 micro g/liter mixed aqueous standards. There was no significant loss of arsenic species in urine (<5%) when passed through a 0.45- micro m filter. The amounts of insoluble arsenic in urine lost during centrifuge ranged from 1/2 to 1/17 of soluble arsenic. These findings indicated that the urinary matrix plays an important role in stabilizing arsenic species. Also, the loss of insoluble arsenic in urine during centrifuging results in underestimation of arsenic exposure, and may explain the lack of an association between arsenic exposure and the risk of health outcomes reported in some epidemiological studies. (+info)
Carcinogenicity of dimethylarsinic acid in p53 heterozygous knockout and wild-type C57BL/6J mice.
(13/89)
There is abundant epidemiological evidence that arsenic is an environmental carcinogen related to human cancers of the skin, lung, liver and urinary bladder, in particular. Dimethylarsinic acid (DMA) has also been reported to act as a carcinogen/or a promoter in rat models. To elucidate molecular mechanisms, we conducted an 18 month carcinogenicity study of DMA in p53 heterozygous (+/-) knockout mice, which are susceptible to early spontaneous development of various types of tumors, and wild-type (+/+) C57BL/6J mice. Totals of 88-90 males, 7-8 weeks of age, were divided into three groups each administered 0, 50 or 200 p.p.m. DMA in their drinking water for 18 months. Mice that were found moribund or died before the end of the study were autopsied to evaluate the tumor induction levels, as well as those killed at the end. Both p53(+/-) knockout and wild-type mice demonstrated spontaneous tumor development, but lesions were more prevalent in the knockout case. Carcinogenic effect of DMA was evident by significant early induction of tumors in both treated p53(+/-) knockout and wild-type mice, significant increase of the tumor multiplicity in 200 p.p.m.-treated p53(+/-) knockout mice, and by significant increase in the incidence and multiplicity of tumors (malignant lymphomas) in the treated wild-type mice. By the end of 80 weeks, tumor induction, particularly malignant lymphomas and sarcomas, were similar in treated and control p53(+/-) knockout mice. No evidence for organ-tumor specificity of DMA was obtained. Molecular analysis using PCR-SSCP techniques revealed no p53 mutations in lymphomas from either p53(+/-) knockout or wild-type mice. In conclusion, DMA primarily exerted its carcinogenic effect on spontaneous development of tumors with both of the animal genotypes investigated here. (+info)
Induction of oxidative DNA damage by arsenite and its trivalent and pentavalent methylated metabolites in cultured human cells and isolated DNA.
(14/89)
Even though a well-known human carcinogen the underlying mechanisms of arsenic carcinogenicity are still not fully understood. For arsenite, proposed mechanisms are the interference with DNA repair processes and an increase in reactive oxygen species. Even less is known about the genotoxic potentials of its methylated metabolites monomethylarsonous [MMA(III)] and dimethylarsinous [DMA(III)] acid, monomethylarsonic [MMA(V)] and dimethylarsinic [DMA(V)] acid. Within the present study we compared the induction of oxidative DNA damage by arsenite and its methylated metabolites in cultured human cells and in isolated PM2 DNA, by frequencies of DNA strand breaks and of lesions recognized by the bacterial formamidopyrimidine-DNA glycosylase (Fpg). Only DMA(III) (> or =10 micro M) generated DNA strand breaks in isolated PM2 DNA. In HeLa S3 cells, short-term incubations (0.5-3 h) with doses as low as 10 nM arsenite induced high frequencies of Fpg-sensitive sites, whereas the induction of oxidative DNA damage after 18 h incubation was rather low. With respect to the methylated metabolites, both trivalent and pentavalent metabolites showed a pronounced induction of Fpg-sensitive sites in the nanomolar or micromolar concentration range, respectively, which was present after both short-term and long-term incubations. Furthermore MMA(III) and DMA(V) generated DNA strand breaks in a concentration-dependent manner. Taken together our results show that very low physiologically relevant doses of arsenite and the methylated metabolites induce high levels of oxidative DNA damage in cultured human cells. Thus, biomethylation of inorganic arsenic may be involved in inorganic arsenic-induced genotoxicity/carcinogenicity. (+info)
Kinetics of the interaction between aspartic aminotransferase and anions.
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The kinetics of the interaction between deionized supernatant aspartic aminotransferase and various anions (cacodylate, phosphate and chloride) were studied by the temperature-jump technique. The anion concentration in the range covered by our experiments does not affect the transamination rate. On the other hand the conformational transition, recently observed at the active site of the enzyme, is hindered by an excess of anions. A single relaxation effect was observed at the enzyme chromophore wavelength in systems containing the aldimine form of the enzyme and the above anions. It is shown that this effect corresponds to the protonation of the chromophore. The relaxation times were of about 10 mus with phosphate, 20-100 mus with cacodylate and 1-2 ms with chloride. The pH and concentration dependence of this effect were studied. The fits of experimental data to a rate equations for various models were tested by a chi2 analysis. The best fit was obtained with models where anions bind rapidly to a site close to the chromophore, so that the pK of the chromophore is affected by anions binding. The rate of the observed relaxation considerably increased when the anion has buffering capacities; this indicates, in the case of cacodylate and phosphate, that the acidic component of the buffer directly exchanges a proton with the enzyme chromophore. (+info)
Protective role of metallothionein (I/II) against pathological damage and apoptosis induced by dimethylarsinic acid.
(16/89)
AIM: To better clarify the main target organs of dimethylarsinic acid toxicity and the role of metallothionein (MTs) in modifying dimethylarsinic acid (DMAA) toxicity. METHODS: MT-I/II null (MT(-/-)) mice and the corresponding wild-type mice (MT(+/+)), six in each group, were exposed to DMAA (0-750 mg/kg body weight) by a single oral injection. Twenty four hours later, the lungs, livers and kidneys were collected and undergone pathological analysis, induction of apoptotic cells as determined by TUNEL and MT concentration was detected by radio-immunoassay. RESULTS: Remarkable pathological lesions were observed at the doses ranging from 350 to 750 mg/kg body weight in the lungs, livers and kidneys and MT(+/+) mice exhibited a relatively slight destruction when compared with that in dose matched MT(-/-) mice. The number of apoptotic cells was increased in a dose dependent manner in the lungs and livers in both types of mice. DMAA produced more necrotic cells rather than apoptotic cells at the highest dose of 750 mg/kg, however, no significant increase was observed in the kidney. Hepatic MT level in MT(+/+) mice was significantly increased by DMAA in a dose-dependent manner and there was no detectable amount of hepatic MT in untreated MT(-/-) mice. CONCLUSION: DMAA treatment can lead to the induction of apoptosis and pathological damage in both types of mice. MT exhibits a protective effect against DMAA toxicity. (+info)