[Show abstract][Hide abstract] ABSTRACT: Contamination of soil by heavy metals such as Cd causes a serious negative impact on agricultural production and human health. Thus, improvement of tolerance to Cd is one of the major challenges in plant biotechnology. In the present study, we have generated transgenic Nicotiana tabacum (tobacco) plants overexpressing both serine acetyltransferase (SAT) and cysteine synthase (CS) [O-acetylserine (thiol)-lyase], which are committed in the last two steps of cysteine (Cys) biosynthesis, by crossing the respective single-gene transgenic plants. Two enzymatic activities were high in these two-gene overexpressing plants, and these plants exhibited more resistance to Cd stress than wild-type and single-gene transgenic plants. The two-gene transgenic plants also exhibited a higher production of phytochelatins (PCs) in an inducible manner by the Cd stress. The levels of free non-chelated Cd were lower in the two-gene transgenic plants than the wild-type and single-gene transformants. The levels of Cys and gamma-glutamylcysteine (gamma-EC) were also increased in the dual transgenic plants, presumably enhancing the metabolic flow of Cys biosynthesis leading to the ultimate synthesis of PCs which detoxify Cd by chelating. These results suggested that the overexpression of two genes, SAT and CS, could be a promising strategy for engineering Cd resistant plants.
[Show abstract][Hide abstract] ABSTRACT: Quite a few new thioarsenicals have recently been found in urine of arsenic-exposed humans and animals, and some of them have been shown to be highly toxic to cells. However, little is known about their toxic effects and metabolism in the body. In order to elucidate the toxic mechanism of thioarsenicals, we further focused on the distribution and metabolism of monomethylmonothioarsonic acid (MMMTA(V)) in rats. MMMTA(V) was synthesized chemically and injected intravenously into rats at the dose of 0.5mg As/kg, followed by speciation analysis of selected organs and body fluids at 10 min and 12h after the injection. MMMTA(V) was excreted into urine in its intact form, and approximately 35% of the dose was recovered in urine at 12h after the injection, suggesting that MMMTA(V) was taken up more effectively by organs/tissues than non-thiolated, monomethylarsonous acid (MMA(V)) previously studied. On the other hand, the liver and kidneys contained arsenic that was in a protein-binding form with free forms of DMA(V) or DMDTA(V) at 10 min, and disappeared at 12h after the injection. Moreover, these bound arsenic species in kidneys were converted back to MMA(V) after oxidation with H(2)O(2), suggesting that the arsenic bound to proteins had been reduced within the body and was in a trivalent oxidation state. In red blood cells (RBCs), most of the arsenic was in the form of DMA(III) bound to hemoglobin (Hb), and approximately 40% of the dose was recovered in RBCs at 12h after injection. These results indicate that arsenic accumulated preferentially in RBCs after being transformed to DMA(III). In addition, we have also discussed the effect of MMMTA(V) on viability of human bladder cancer T24 cells in comparison with MMA(V). Consequently, MMMTA(V) was assumed to be a more toxic arsenic metabolite than non-thiolated MMA(V).
[Show abstract][Hide abstract] ABSTRACT: Arsenic toxicity and distribution are highly dependent on animal species and its chemical species. Recently, thioarsenical has been recognized in highly toxic arsenic metabolites, which was commonly found in human and animal urine. In the present study, we revealed the mechanism underlying the distribution and metabolism of non-thiolated and thiolated dimethylarsenic compounds such as dimethylarsinic acid (DMA(V)), dimethylarsinous acid (DMA(III)), dimethylmonothioarsinic acid (DMMTA(V)), and dimethyldithioarsinic acid (DMDTA(V)) after the administration of them into femoral vein of hamsters. DMA(V) and DMDTA(V) distributed in organs and body fluids were in their unmodified form, while DMA(III) and DMMTA(V) were bound to proteins and transformed to DMA(V) in organs. On the other hand, DMA(V) and DMDTA(V) were mostly excreted into urine as their intact form 1 h after post-injection, and more than 70% of the doses were recovered in urine as their intact form. By contrast, less than 8-14% of doses were recovered in urine as DMA(V), while more than 60% of doses were distributed in muscles and target organs (liver, kidney, and lung) of hamsters after the injection of DMMTA(V) and DMA(III). However, in red blood cells (RBCs), only a small amount of the arsenicals was distributed (less than 4% of the doses) after the injection of DMA(III) and DMMTA(V), suggesting that the DMA(III) and DMMTA(V) were hardly accumulated in hamster RBCs. Based on these observations, we suggest that although DMMTA(V) and DMDTA(V) are thioarsenicals, DMMTA(V) is taken up efficiently by organs, in a manner different from that of DMDTA(V). In addition, the distribution and metabolism of DMMTA(V) are like in manner similar to DMA(III) in hamsters, while DMDTA(V) is in a manner similar to DMA(V).
[Show abstract][Hide abstract] ABSTRACT: Cadmium was injected sc into female Wistar rats at a dose of 3.0 mg Cd/kg body weight, 4 times a week for 1, 2, 3, 4, 5, and 6 wk. Concentrations of cadmium in the spleen and pancreas were determined, together with essential metals, by inductively coupled plasma-atomic emission spectrometry. Cadmium in both tissues increased even after maximum concentration was attained in the liver. Contents of zinc, calcium, and magnesium in the spleen increased with splenomegaly, while content of iron decreased. Concentrations of calcium, magnesium, and iron decreased in the pancreas, while concentration of zinc showed a transitory increase. Cadmium in the spleen and pancreas supernatants was mostly bound to metallothionein, and metallothionein in the pancreas was highly susceptible to oxidation reaction. The spleen and pancreas were histologically less affected by cadmium loading compared to the liver and kidney, and the pancreas showed only slight alterations after injections for 5 and 6 wk.
Journal of Toxicology and Environmental Health 10/2009; 11(4-6):727-37. DOI:10.1080/15287398309530380 · 2.35 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The role of o-bisguanidinobenzenes (BGBs) as new Brønsted base ligands for arsenic and phosphoric acids was examined. In solution state, complexation was evaluated by Job's plot in (1)H NMR experiment, indicating a 1:1 complex formation, whereas in solid state crystalline structures of complexes obtained were addressed by X-ray crystallographic analysis and/or solid state (13)C NMR experiment, in which 1:2 complexes between the BGB and the acid components were normally formed. Based on these results, Merrifield and Hypogel resin-anchored BGBs were designed and prepared as the corresponding polymer-supported host ligands. Evaluation of their coordination ability with metal salts (ZnCl(2) and CoCl(2)) and arsenic acid in aqueous media by ICP-MS showed that the latter Hypogel resin-anchored BGBs acted as effective immobilized base ligands.
[Show abstract][Hide abstract] ABSTRACT: Arsenic toxicity is dependent on its chemical species. In humans, the bladder is one of the primary target organs for arsenic-induced carcinogenicity. However, little is known about the mechanisms underlying arsenic-induced carcinogenicity, and what arsenic species are responsible for this carcinogenicity. The present study aimed at comparing the toxic effect of DMMTA(V) with that of inorganic arsenite (iAs(III)) on cell viability, uptake efficiency and production of reactive oxygen species (ROS) toward human bladder cancer EJ-1 cells. The results were compared with those of a previous study using human epidermoid carcinoma A431 cells. Although iAs(III) was known to be toxic to most cells, here we show that iAs(III) (LC(50)=112 microM) was much less cytotoxic than DMMTA(V) (LC(50)=16.7 microM) in human bladder EJ-1 cells. Interestingly, pentavalent sulfur-containing DMMTA(V) generated a high level of intracellular ROS in EJ-1 cells. However, this was not observed in the cells exposed to trivalent inorganic iAs(III) at their respective LC(50) dose. Furthermore, the presence of N-acetyl-cysteine completely inhibited the cytotoxicity of DMMTA(V) but not iAs(III), suggesting that production of ROS was the main cause of cell death from exposure to DMMTA(V), but not iAs(III). Because the cellular uptake of iAs(III) is mediated by aquaporin proteins, and because the resistance of cells to arsenite can be influenced by lower arsenic uptake due to lower expression of aquaporin proteins (AQP 3, 7 and 9), the expression of several members of the aquaporin family was also examined. In human bladder EJ-1 cells, mRNA/proteins of AQP3, 7 and 9 were not detected by reverse transcription polymerase chain reaction (RT-PCR)/western blotting. In A431 cells, only mRNA and protein of AQP3 were detected. The large difference in toxicity between the two cell lines could be related to their differences in uptake of arsenic species.
[Show abstract][Hide abstract] ABSTRACT: Diphenylarsinic acid (DPAA) is an environmental degradation product of diphenylarsine chloride or diphenylarsine cyanide, which were chemical warfare agents produced by Japan during the World War II. DPAA is now considered a dangerous environmental pollutant in Kamisu, Japan, where it is suspected of inducing health effects that include articulation disorders (cerebellar ataxia of the extremities and trunk), involuntary movements (myoclonus and tremor), and sleep disorders. In order to elucidate the toxic mechanism of DPAA, we focused on the distribution and metabolism of DPAA in rats. Systemic distribution of DPAA was determined by administering DPAA orally to rats at a single dose of 5.0 mg As/kg body weight, followed by speciation analysis of selected organs and body fluids. Most of the total arsenic burden was recovered in the urine (23% of the dose) and feces (27%), with the distribution in most other organs/tissues being less than 1%. However, compared with the typical distribution of inorganic dietary arsenic, DPAA administration resulted in elevated levels in the brain, testes and pancreas. In contrast to urine, in which DPAA was found mostly in its unmodified form, the tissues and organs contained arsenic that was mostly bound to non-soluble and soluble high molecular weight proteins. These bound arsenic species could be converted back to DPAA after oxidation with H(2)O(2), suggesting that the DPAA bound to proteins had been reduced within the body and was in a trivalent oxidation state. Furthermore, we also detected two unknown arsenic metabolites in rat urine, which were assumed to be hydroxylated arsenic metabolites.
[Show abstract][Hide abstract] ABSTRACT: This study compares the transfer from mother to fetuses and pups of selenium (Se) in the form of selenite, selenate, and selenomethionine (SeMet) labeled with different homo-elemental isotopes.
To completely substitute endogenous Se with natural abundance with Se enriched with a single stable isotope (82Se), female Wistar rats delivered by mother fed 82Se-selenite were fed Se-deficient diet and drinking water containing 82Se-selenite immediately after weaning, and then mated with male Wistar rat at the age of 15-17 weeks. The pregnant rats were divided into two groups. One group was fed Se-deficient diet and drinking water containing 76Se-selenite, 78Se-selenate, and 77Se-SeMet from gestation days 11 to 20. The other group was fed the same diet and drinking water containing the three Se species after delivery for 10 days of lactation. Non-pregnant rats were also fed Se mixture and Se-deficient diet for 10 days. KEY FINDING: Tissue and plasma Se concentrations showed significant changes among non-pregnant, pregnant, and lactating rats. The peak corresponding to selenoprotein P (Sel P) in serum of pregnant rats was reduced. The concentration of 77Se originating from SeMet was higher than those of 76Se from selenite and 78Se from selenate in the stomach content of pups.
Inorganic Se species are more preferably transformed into Sel P than SeMet, and Sel P is effectively incorporated into placenta during pregnancy. On the other hand, SeMet is a more efficient Se source than inorganic Se species during lactation.
Life sciences 05/2009; 84(25-26):888-93. DOI:10.1016/j.lfs.2009.03.023 · 2.70 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Copper (Cu) is the active center of some enzymes because of its redox-active property, although that property could have harmful effects. Because of this, cells have strict regulation/detoxification systems for this metal. In this study, multi-disciplinary approaches, such as speciation and elemental imaging of Cu, were applied to reveal the detoxification mechanisms for Cu in cells bearing a defect in Cu-regulating genes. Although Cu concentration in metallothionein (MT)-knockout cells was increased by the knockdown of the Cu chaperone, Atox1, the concentrations of the Cu influx pump, Ctr1, and another Cu chaperone, Ccs, were paradoxically increased; namely, the cells responded to the Cu deficiency despite the fact that cellular Cu concentration was actually increased. Cu imaging showed that the elevated Cu was compartmentalized in cytoplasmic vesicles. Together, the results point to the novel roles of MT and cytoplasmic vesicles in the detoxification of Cu in mammalian cells.
[Show abstract][Hide abstract] ABSTRACT: Se-methylselenocysteine (MeSeCys) is not only a selenium (Se) supplement but also a more promising precursor of an anti-tumor drug containing Se than selenomethionine, which is currently used as Se supplement. In this study, the metabolism of MeSeCys labeled with an Se isotope, 82Se, in rats depleted of endogenous natural abundance isotopes with another Se isotope, 78Se, was traced for 21 days when MeSeCys was continuously and perorally ingested at a supplemental dose. The tracer experiment was performed with our improved method that utilized an inductively coupled plasma-deuterium reaction-mass spectrometer. The substitution of endogenous Se with a single isotope, 78Se, facilitated the detection of exogenous labeled Se. Exogenous Se in the form of MeSeCys preferably accumulated and/or assimilated in the liver, kidneys and testes with long-term ingestion of MeSeCys and was utilized for the synthesis of selenoproteins, i.e., extracellular and cellular glutathione peroxidases and selenoprotein P. Meanwhile, intact MeSeCys was not excreted into urine although trimethylselenonium was detected in addition to selenosugar. The results suggest that MeSeCys was transformed into selenide via methylselenol by beta-lyase. Consequently, it is surmised that MeSeCys is a precursor of methylselenol under long-term ingestion.
The Journal of Toxicological Sciences 05/2009; 34(2):191-200. DOI:10.2131/jts.34.191 · 1.29 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Selenometabolites transformed from selenomethionine (SeMet) in wheat germ extract (WGE) were identified by complementary use of HPLC-ICP-MS and HPLC-ESI-MS/MS. Three selenium (Se)-containing peaks tentatively named WGE1, WGE2, and WGE3 were detected by HPLC-ICP-MS. WGE1 had [M]+ at m/z 212 on HPLC-ESI-MS analysis, and its fragment ions indicated that WGE1 is selenomethionine methylselenonium (MeSeMet). WGE2 and WGE3 exhibited absorption at 254 nm and molecular ions at m/z 433 and 447, respectively. Their fragment ions revealed that WGE2 and WGE3 are Se-adenosylselenohomocysteine (AdoSeHcy) and Se-adenosylselenomethionine (AdoSeMet), respectively. Their structures were coincident with the absorption of WGE2 and WGE3 at 254 nm. In addition, a trace amount of AdoSeMet was suggested to also exist in rabbit reticulocyte lysate, a mammalian in vitro translation system, because the transformation of AdoSeMet from SeMet was completely inhibited by (2S)-2-amino-4,5-epoxypentanoic acid (AEPA), a potent inhibitor of AdoMet synthetase. These results suggest that SeMet and methionine (Met) share a common metabolic pathway, i.e., SeMet is not only incorporated into proteins in place of Met but also metabolized to AdoSeMet in higher eukaryotes and MeSeMet in plants.
[Show abstract][Hide abstract] ABSTRACT: The availability, distribution, and metabolism of four typical selenium sources [in-organic selenite and selenate, and organic selenomethionine (SeMet) and methylselenocysteine (MeSeCys)] were compared by administering them simultaneously through a parenteral route. The four selenium sources were each labeled with a different enriched selenium isotope ((82)Se, (78)Se, (77)Se, and (76)Se, respectively), and administered intravenously at the dose of 25 mu g Se/kg body weight each to rats that had been depleted of natural abundance selenium with a single isotope, (80)Se, by feeding (80)Se-selenite in drinking water and a selenium-deficient diet. At 1 h post-injection, the amounts of the four tracers recovered from major organs and blood comprised around 70, 55, and 50% of the doses for selenite, MeSeCys and SeMet, and selenate, respectively, being most abundant in the liver. The intact precursors, except for selenite, were recovered from all organs. (77)Se and (76)Se of SeMet and MeSeCys origin, respectively, were much more efficiently recovered from the pancreas than selenite and selenate, in forms mostly bound to proteins together with intact forms, suggesting that SeMet and MeSeCys are preferentially distributed directly to the pancreas. The incorporations of selenium into selenoprotein P (Sel P) and selenosugars were most efficient from selenite and less efficient from SeMet, suggesting that selenite was most efficiently utilized for the syntheses of selenoproteins and selenosugars. Although selenate was partly excreted into the Urine in its intact form, it was retained longer in the plasma in its intact form than the other selenium Sources. The advantage of simultaneous administration of multiple precursors each labeled with a different enriched isotope to depleted hosts followed by simultaneous tracing of the labeled isotopes over the conventional method with a single tracer is emphasized together with cautions that may occur with the new multiple tracer method.
Pure and Applied Chemistry 12/2008; 80(12):2699-2713. DOI:10.1351/pac200880122699 · 2.49 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The present study describes the synthesis and characterization of thioarsenicals using electro-spray ionization-MS and time of flight-MS. Separation of thioarsenicals was found to be better by size-exclusion column compared to anion exchange column coupled with HPLC-inductively coupled argon plasma mass spectrometer (ICP MS). Although four thioarsenicals were confirmed as dimethylthioarsinous acid (m/z=138), methylmonothioarsonous acid (m/z=122), dimethyldithioarsinic acid (m/z=170) and methyltrithioarsonic acid (m/z=188), it is noted that HPLC-ICP MS alone were not sufficient for their identification. Also, none of them was stable with time. This is the first report detailing the synthesis and identification of methyltrithioarsonic acid. Both dimethyldithioarsinic acid and dimethylthioarsinous acid were detected in human nail samples while dimethyldithioarsinic acid was found in urine samples. So, the above technique could be applicable to the identification of sulfur-containing biomolecules in the biological samples.
Journal of Chromatography B 10/2008; 874(1-2):64-76. DOI:10.1016/j.jchromb.2008.09.004 · 2.73 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Thioarsenicals have been paid much attention due to the toxicity of arsenic, since some of them are highly toxic and commonly found in the urine of mammals. We previously reported that thioarsenicals might be produced in red blood cells (RBCs). Here, we further characterized the mechanism underlying the production and metabolism of thioarsenicals in RBCs using 34S-labeled dimethylmonothioarsinic acid (34S-DMMTAV) and purified rat hemoglobin (Hb) or a rat RBC lysate. 34S-DMMTAV did not bind to Hb on incubation with purified rat Hb, remaining in its original form. However, when 34S-DMMTAV was incubated with a rat RBC lysate, only arsenic, i.e., not sulfur (34S), was detected in a form bound to Hb (As-Hb). In addition, another arsenic product containing sulfur (34S) in the molar ratio of 34S/As = 2 was detected, which was assigned as dimethyldithioarsinic acid (DMDTAV), suggesting that arsenic does not bind to Hb in the form of 34S-DMMTAV but does so in the form of dimethylarsinous acid (DMAIII). Namely, DMMTAV appeared to be hydrolyzed into dimethylarsinic acid (DMAV) and H34S-, and the released H34S- reacted with DMMTAV to produce DMDTAV. Thus, DMMTAV was transformed into DMDTAV and DMAV (2DMMTAV - > DMDTAV + DMAV), the latter product being reduced to DMAIII in the presence of GSH and bound to Hb. In a separate experiment, 34S-DMMTAV was incubated with sulfide (Na2S) and GSH. Although DMMTAV was not transformed into DMDTAV in the presence of only Na2S or GSH, it was transformed into DMDTAV in the presence of both Na2S and GSH. Our results suggest that DMMTAV is hydrolyzed enzymatically into DMAV and sulfide, the former being reduced to DMAIII and bound to Hb, and the latter reacting with DMMTAV to yield DMDTAV. Thus, DMMTAV is transformed into DMDTAV and DMAV through a hydrolytic reaction in a manner similar to a disproportionation reaction, DMAV being reduced and bound to Hb (As-Hb), and DMDTAV being produced more in the presence of sulfides in the medium.
[Show abstract][Hide abstract] ABSTRACT: Buckwheat (Fagopyrum esculentum Moench) and quinoa (Chenopodium quinoa Willdenow) are widely used as food ingredients. The nutritional characteristics of these plants, i.e., high contents of proteins
and amino acids suggest that selenium (Se) is preserved as selenoamino acid derivatives, in particular, selenomethionine (SeMet)
in proteins, similar to selenized yeast. Therefore, buckwheat and quinoa are expected to be a good nutritional source of Se.
Selenized buckwheat and quinoa were cultivated on Se-fortified soil using sparingly soluble Se salts, such as barium selenate
and barium selenite. Se concentration in the edible parts of these plants was determined, and Se extraction efficiency with
enzyme or alkali was evaluated. In addition, the chemical species of Se in the low molecular weight fraction of these plants
were determined by HPLC-ICP-MS. Total Se concentrations in the edible parts of selenized buckwheat and quinoa were 170.4±2.9μg/g
and 102.7±2.4μg/g wet weight, respectively. Thus, these selenized seeds were found to be Se accumulators. The results indicate
that Se in selenized buckwheat exists mainly as SeMet, while Se in selenized quinoa exists not only as SeMet but also as selenate
(Se(VI)) and non-protein forms.
European Food Research and Technology 09/2008; 227(5):1455-1460. DOI:10.1007/s00217-008-0866-2 · 1.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Tellurium (Te) has shown recent increase in use as a component of optical magnetic disks having phase-change property, such as digital versatile disk-random access memory (DVD-RAM) and DVD-rewritable (DVD-RW). However, the toxicity and metabolic pathway of Te remain unclear despite its being known as a non-essential and harmful metalloid. This study was performed to gain an insight into Te metabolism in the body. The mechanism for the distinction of Te from selenium (Se), an essential metalloid belonging to the same group as Te, was also clarified. Rats were given drinking water containing tellurite and (82)Se-labeled selenite at the same concentration, and the concentrations of these metalloids in organs, body fluid and excreta were determined 2 days later. The results demonstrate that urinary and fecal excretion of Te was, respectively, lower and higher than that of exogenous (labeled) Se, suggesting that Te was less absorbed than Se. The ingested Te was transformed, i.e., methylated in organs and effluxed into bloodstream, and the effluxed Te was highly accumulated in rat red blood cells (RBCs) in the form of dimethylated Te. In contrast, Se was not accumulated in RBCs. Finally, Te was excreted in urine as trimethyltelluronium and might be exhaled as dimethyltelluride. The results suggest that the metabolism of Te was distinct from that of Se in rats.
[Show abstract][Hide abstract] ABSTRACT: Nitric oxide (NO) enhanced the nuclear lo- calization of metallothionein (MT) in digitonin- permeabilized semi-intac tH eLacells. Although 1-Hydroxy-2-oxo-3-(3-aminopropyl)-3-isopropyl-1- triazene (NOC5), an NO donor, enhanced the nuclear localization of MT in a manner similar to hydrogen peroxide (H2O2), a tenfold higher concentration of NOC5 was required to achieve the same effect as H2O2 ,s uggesting that an endogenous NO scavenger existed in the reaction mixture of the nuclear import assay system that we used. We also evaluated the effect of NO on the nuclear localization of MT in intact HeLa cells. Treatment with NOC5 induced the nuclear localization of MT pre-induced with zinc, and its effect was greater than that of H2O2. The induced MT was localized in the nucleus and the cytoplasm. The results suggest that MT can scavenge NO using the sulfhydryl groups of cysteines in its molecule to form nitrosothiol, thereby reducing nuclear and cytoplasmic damage by NO.
Journal of health science 06/2008; 54(3):339-342. DOI:10.1248/jhs.54.339 · 0.80 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Minute amounts of tissue supernatants from mouse neonates bearing a mutation in the copper (Cu)-transporter gene, Atp7a, were injected into narrow-bore HPLC coupled with an inductively coupled plasma-mass spectrometer (ICP-MS) to examine Cu metabolism. In the 14-day-old mutant neonates, Cu accumulated in the intestine in the metallothionein (MT)-bound form, and mRNA expression of the two MT isoforms was increased. Meanwhile, Cu in the MT-bound form (Cu-MT) was depleted in the liver and mRNA expression decreased in comparison with wild-type mice. These results suggest that Cu is not secreted by intestinal microvillus cells into bloodstream due to the defect of Atp7a, and systemic depletion of Cu occurred. On the other hand, in the kidneys of mutant mice, Cu accumulated in the MT-bound form despite the fact that mRNA expression of the two MT isoforms was low. Part of Cu-MT in microvillus cells may be released into bloodstream at turnover and be preferably taken up by the kidneys. Consequently, the mRNA expression of MT isoforms was not always coincident with the amounts of MT proteins binding Cu, and narrow bore HPLC-ICP-MS used for MT protein determination is a complementary technique to real-time RT-PCR used for MT mRNA determination in Cu speciation.
[Show abstract][Hide abstract] ABSTRACT: The bladder and skin are the primary targets for arsenic-induced carcinogenicity in mammals. Thioarsenicals dimethylmonothioarsinic (DMMTA(V)) and dimethyldithioarsinic (DMDTA(V)) acids are common urinary metabolites, the former being much more toxic than non-thiolated dimethylarsinic acid (DMA(V)) and comparable to dimethylarsinous acid (DMAIII) in epidermoid cells, suggesting that the metabolic production of thioarsenicals may be a risk factor for the development of cancer in these organs. To reveal their production sites (tissues/body fluids), we examined the uptake and transformation of the four dimethylated arsenicals by incubation with rat and human red blood cells (RBCs). Although DMA(V) and DMDTA(V) were not taken up by either type of RBCs, DMAIII and DMMTA(V) were taken up by both (more efficiently by rat ones), though DMMTA(V) was taken up slowly, and then the arsenic transformed into DMDTA(V) was excreted from both types of animal RBCs. On the other hand, although DMA(III) taken up rapidly by rat RBCs was retained in the RBCs, that taken up by human RBCs was immediately transformed into DMMTA(V) and then excreted into the incubation medium without being retained in the RBCs. In a separate experiment, arsenic remaining in primary rat hepatocytes after incubation with 1.5 microM DMAIII was recovered from the incubation medium in the forms of DMA(V) and DMMTA(V) in the presence of human RBCs, but not in the presence of rat RBCs (in which the arsenic was bound to hemoglobin). Thus, DMMTA(V) was detected in the medium only in the presence of human RBCs and increased with incubation time. It was proposed that arsenic is excreted from hepatocytes into the bloodstream in the form of DMAIII and then taken up by RBCs in humans, where it is transformed into DMMTA(V) and then excreted again into the bloodstream.
[Show abstract][Hide abstract] ABSTRACT: Chronic exposure to arsenic causes a wide range of diseases such as hyperkeratosis, cardiovascular diseases, and skin, lung, and bladder cancers, and millions of people are chronically exposed to arsenic worldwide. However, little is known about the mechanisms underlying these toxic actions. The metabolism of arsenic is essential for understanding the toxic actions. Here, we identified the major arsenic-binding protein (As-BP) in the plasma of rats after oral administration of arsenite by the use of two different HPLC columns, gel filtration and anion exchange ones, coupled with an inductively coupled argon plasma mass spectrometer (ICP MS). The molecular mass of the As-BP was estimated to be 90 kDa based on results using the former column, and arsenic bound to this protein only in the form of dimethylarsinous acid (DMA (III)) in the plasma in vivo. In addition, the purified As-BP was shown to consist of two different proteins, haptoglobin (Hp) of 37 kDa (three bands) and the hemoglobin (Hb) alpha chain of 14 kDa (single band), using sodium dodecylsulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and matrix-assisted laser desorption ionization-time-of-flight mass spectrometry (MALDI-TOF MS), respectively, suggesting that the As-BP was the ternary DMA (III)-Hb-Hp complex. To confirm the present observations, an arsenic-binding assay was carried out in vitro . Although DMA (III) bound directly to fresh rat plasma proteins, they were different from that identified in vivo. However, when a DMA (III)-exposed rat RBC lysate (DMA (III) binds to Hb in rat RBCs) was added to control rat plasma, a new arsenic peak increased at the expense of the arsenic-Hb one. Furthermore, this new arsenic peak was consistent with the As-BP identified in the plasma in vivo, suggesting that arsenic bound to Hb further binds to haptoglobin (Hp), forming the ternary As-Hb-Hp complex.
Chemical Research in Toxicology 04/2008; 21(3):678-85. DOI:10.1021/tx700383g · 3.53 Impact Factor