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At least 109 records · Page 6Linked to original sources
PubMed2001

In vitro effect of arsenical compounds on glutathione-related enzymes.

The mechanism of arsenic toxicity is believed to be due to the ability of arsenite (As(III)) to bind protein thiols. Glutathione (GSH) is the most abundant cellular thiol, and both GSH and GSH-related enzymes are important antioxidants that play an important role in the detoxification of arsenic and other carcinogens. The effect of arsenic on the activity of a variety of enzymes that use GSH has been determined using purified preparations of glutathione reductase (GR) from yeast and bovine glutathione peroxidase (GPx) and equine glutathione S-transferase (GST). The effect on enzyme activity of increasing concentrations (from 1 microM to 100 mM) of commercial sodium arsenite (As(III)) and sodium arsenate (As(V)) and a prepared arsenic(III)-glutathione complex [As(III)(GS)(3)] and methylarsenous diiodide (CH(3)As(III)) has been examined. GR, GPx, and GST are not sensitive to As(V) (IC(50) > 50 mM), and none of the enzymes are inhibited or activated by physiologically relevant concentrations of As(III), As(III)(GS)(3), or CH(3)As(III), although CH(3)As(III) is the most potent inhibitor (0.3 mM < IC(50) < 1.5 mM). GPx is the most sensitive to arsenic treatment and GST the least. Our results do not implicate a direct interaction of As with the glutathione-related enzymes, GR, GPx, and GST, in the mechanism of arsenic toxicity. CH(3)As(III) is the most effective inhibitor, but it is unclear whether this product of arsenic metabolism is produced at a sufficiently high concentration in critical target tissues to play a major role in either arsenic toxicity or carcinogenesis.

Arsenicals↗
PubMed1985

Arsenic speciation in urine from humans intoxicated by inorganic arsenic compounds.

Trends in the urinary concentrations of the four arsenic species, pentavalent [As (V)] and trivalent [As (III)] inorganic arsenic, monomethylarsonic acid (MMAA) and dimethylarsinic acid (DMAA), were followed for several days subsequent to the acute intoxication of two human subjects by arsenic trioxide [As (III)2O3] and sodium orthoarsenate [Na2HAs(V)O4 X 7H2O], respectively, in unsuccessful suicide attempts. Total arsenic concentrations ranged from 1.6 to 18.7 mg/l. The increasing predominance of the less toxic methylated species, especially DMAA, after 3 or 4 days supports the concept of methylation as a natural detoxification mechanism as part of an overall reduction/methylation sequence involved in the biotransformation of inorganic arsenic by the human body. However, the additional possibility of oxidation of As(III) to As(V) in vivo under extreme immediate postingestion conditions is suggested by initial high urinary As(V) after arsenic trioxide intoxication. Relative proportions of As(V), As(III), MMAA and DMAA in both cases probably reflect species-dependent differences in rates of direct elimination and reactivity with tissues as well as the efficiency of methylation.

Adult↗
PubMed1997

New retinoids and arsenic compounds for the treatment of refractory acute promyelocytic leukemia: clinical and basic studies for the next generation.

All-trans retinoic acid (ATRA) is a potent differentiation drug for acute promyelocytic leukemia (APL) and is now incorporated into first-line therapy. However, ATRA resistance has become a major clinical problem. This limitation has prompted the development of alternative agents with desirable pharmacologic properties. We describe (1) our recent clinical trial using the new synthetic retinoid Am80 to overcome acquired resistance to ATRA and (2) basic in vitro effects of arsenic trioxide, a possible alternative to ATRA, on APL cells. A total of 19 APL patients who had relapsed after ATRA-induced complete remissions (CRs) received 6 mg/m2 Am80 p.o. daily until CR; 11 (58%) patients achieved a CR between days 20 and 58 (median day 37). The in vitro sensitivity to Am80, based on PML immunostaining, correlated well with the clinical effect in all patients tested. All three patients whose blasts were sensitive to Am80 in vitro despite a poor response to ATRA achieved CRs. Thus, Am80 might be an effective compound for the treatment of refractory APL and is a promising alternative retinoid. Since arsenic compounds have reportedly induced CRs in APL patients in China, we studied the in vitro effect of arsenic and other metal ions on myeloid leukemia cell lines. The effects of arsenic were limited mainly to APL cells, and the arsenic concentration was critical for the APL cell line NB4: 1 microM As3+ induced time-dependent apoptosis, whereas 0.1 microM As3+ allowed partial NB4 cell differentiation. Arsenic trioxide was equally effective when used on ATRA-resistant NB4 cells. Among the clinical leukemia samples tested, the in vitro cytotoxic effects of As3+ were observed selectively in APL cells, regardless of their ATRA sensitivity. These data suggest that APL cells are sensitive to As3+ and that As3+ acts on APL cells via a different pathway to ATRA.

Antineoplastic Agents↗
PubMed1998

Promotion of NCI-Black-Reiter male rat bladder carcinogenesis by dimethylarsinic acid an organic arsenic compound.

Dimethylarsinic acid (DMAA) is a major metabolite of inorganic arsenicals in mammals. In the present study, we investigated its promoting effects on urinary bladder carcinogenesis in NCI-Black-Reiter (NBR) rats, which lack alpha2u-globulin synthesizing ability. Male 9-14-week-old NBR rats were treated sequentially with 0.05% N-butyl-N-(4-hydroxybutyl)-nitrosamine (BBN) for 4 weeks and then given 100 ppm DMAA in their drinking water (group 1) for 32 weeks. Induction of preneoplastic lesions (papillary or nodular hyperplasia) in this DMAA-treated group was significantly increased as compared to the carcinogen alone control group (P < 0.01). The development of carcinomas was also enhanced and a significant increase in the 5-bromo-2'-deoxyuridine (BrdU) labeling index of the urinary bladder epithelial cells was observed for the DMAA treatment group. These results indicate that DMAA has promoting effects on urinary bladder carcinogenesis even in NBR rats, so its effects are not dependent on the presence of alpha2u-globulin.

Alpha-Globulins↗
PubMed2006

Improved chromatographic separation of thio-arsenic compounds by reversed-phase high performance liquid chromatography-inductively coupled plasma mass spectrometry.

A new group of arsenic species, thio-arsenicals, have recently been reported in several natural samples such as molluscs, algae, and urine. These compounds are the sulfur analogues of oxo-arsenicals, a large group of naturally-occurring compounds, whereby the arsinoyl (As=O) group is substituted by an arsinothioyl group (As=S). The most common separation technique for oxo-arsenicals is anion-exchange HPLC with polymer-based columns, but under these conditions the thio-arsenicals show strong retention, resulting in unacceptably long analysis times and broad peaks. We report the development of a reversed-phase HPLC method, with ICPMS detection, which allows separation of the known thio-arsenicals within 15 min with significantly improved peak shapes. The detection limit is about 0.6 microg As/L based on 10 microL injection volume. Further, we have applied the method to the identification and quantification of thio-arsenic species in two standard reference materials, BCR 710 oyster tissue and NIES 18 human urine.

Animals↗
PubMed1996

Enzymatic methylation of arsenic compounds. III. The marmoset and tamarin, but not the rhesus, monkeys are deficient in methyltransferases that methylate inorganic arsenic.

The methylation of inorganic arsenic to monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) have been generally considered to be the major pathway for inorganic arsenic biotransformation and detoxification. Yet, when arsenate/arsenite is injected into the Callithrix jacchus (marmoset) monkey or chimpanzee, monomethylarsonic acid and dimethylarsinic acid are not found in the urine. With the development of a rapid assay for the methyltransferases of arsenic metabolism, we have investigated the methyltransferases of the marmoset monkey liver. We have found that the marmoset, a New World animal, is deficient in liver arsenite and monomethylarsonic acid methyltransferase activities. However, the rhesus monkey, an Old World animal, has ample amounts of such methyltransferase activities. The tamarin, another New World species, is also deficient in these methyltransferases. Polymorphism and deficiency of these methyltransferases may have allowed high levels of arsenite to be maintained in the blood and liver of the marmoset and tamarin. Such high levels of arsenite may have been selective for survival of the species. The rhesus liver methyltransferases for arsenite and MMA have been purified and found to have some properties different from those of the previously reported purified rabbit liver activities. The rhesus and rabbit liver arsenite and MMA methyltransferases are devoid of catechol O-methyltransferase activity.

Animals↗
PubMedDate not supplied

A suicide by ingestion of a mixture of copper, chromium and arsenic compounds.

A suicide resulting from the ingestion of copper, chromium and arsenic is reported. Death was delayed for 36 hours, during which time copper was rapidly eliminated from the body but chromium and arsenic remained in substantial quantities. The different metabolism of these elements is discussed and the tissue levels discovered are compared with the normal levels.

Arsenic↗
PubMed2004

Methanogenic inhibition by arsenic compounds.

The acute acetoclastic methanogenic inhibition of several inorganic and organic arsenicals was assayed. Trivalent species, i.e., methylarsonous acid and arsenite, were highly inhibitory, with 50% inhibitory concentrations of 9.1 and 15.0 microM, respectively, whereas pentavalent species were generally nontoxic. The nitrophenylarsonate derivate, roxarsone, displayed moderate toxicity.

Arsenicals↗
PubMed2001

Enzymatic methylation of arsenic compounds. IX. Liver arsenite methyltransferase and arsenate reductase activities in primates.

Inorganic arsenic is an important environmental toxicant of both natural and anthropogenic sources. It is a human carcinogen for which appropriate animal models of most arsenic-induced cancers are missing. Although methylation of inorganic arsenic has been considered its primary mechanism for detoxification, the results of recent investigations disagree. We have investigated 17 species of non-human primates, including great apes, New and Old World monkeys and prosimians, and have found that thirteen of them lacked hepatic arsenite methyltransferase activity in vitro. Four primate species, three from the Old World genus Macaca, and one of three animals from the New World genus Saimiri, had arsenite methyltransferase activity. That all the tissues examined were viable was demonstrated by their all having arsenate reductase activity. These data suggest that methylation of inorganic arsenic is not a detoxification mechanism for many non-human primates. Thus, alternative methods of detoxifying inorganic arsenic in mammals need to be considered and investigated. In addition, there appears to be a phylogenetic component to having arsenite methyltransferase activity, as evidenced by the result of our study of the Macaca species.

Adenosine Triphosphatases↗