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Selenium in industrial wastewater at sub-ppm level was determined by PIXE spectrometry at the Tokyo Institute of Technology Van de Graaff Laboratory using a 2.5 MeV proton beam. A chemical concentration method was applied for elemental analysis. Other elements (Mn, Fe, Ni, Cu, Zn, Pb, Hg, Cd, As) were also found simultaneously. Anion chromatography revealed that selenium forms an oxyanion SeO₃^2- in wastewater studied. Pb, As and Se of these chemical species are required to lower below the discharge standard to the public water, 0.1ppm, while that of Hg is 0.005ppm. The combined use of these two analysis tools will help for rapid monitoring of the quality in the public water environment.

The groundwater pollution by arsenic in Bangladesh causes a serious problem for millions of people who are exposed to poisoning by this toxic element. In an attempt to evaluate the extent of arsenic poisoning, hair samples of people living in Pabna district were collected. The hair samples were analyzed using Proton Induced X-ray Emission (PIXE) through exciting the atoms of a specimen so that their intensities can be converted into elemental concentrations in the specimen. The elements present in the specimen are identified by the corresponding X-ray energies and their concentrations are deduced from the X-ray intensities. The results from hair samples indicate substantially higher level of arsenic than those demarcated as toxic levels, in people from member families both affected and non-affected by poisoning. We correlate it with exceedingly high arsenic concentration in drinking water far above the permissible limit. The analytical results are compared with the results of arsenic and other elemental analysis of 160 Bangladeshi hair samples with that of 250 Japanese samples. The results show markedly higher levels of arsenic, manganese, iron and lead where the latter three elements show a positive relation with arsenic in the case of Bangladeshi as compared to the samples from Japan. On the other hand, selenium concentrations show very low level in the Bangladeshi samples compared to Japanese, displaying an inverse relationship with arsenic. The mechanism of arsenic in relation to other elements in the human body needs further investigation. The preliminary results call for detailed experimental and epidemiological studies to further characterize these aspects.

In 30 healthy persons (control), 17 renal cell carcinoma (RCC) patients, 30 hemodialysis patients (HD) and 15 healthy persons in the Takko town (Aomori prefecture), the selenium concentration in serum was determined by PIXE. The mean serum selenium concentration in healthy controls was 1.4 ± 0.6 μmol/l, in RCC patients 1.1 ± 0.4 μmol/l, in HD patients 1.3 ± 0.9 μmol/l and in healthy persons in the Takko town 1.7 ± 0.7 μmol/l. There was a significant statistical difference between RCC patients and healthy persons in the Takko town (p < 0.05). Takko town is famous for the production of garlic. Epidemiological studies have established an inverse relationship between garlic consumption and incidence of gastric, colon, and laryngeal cancers. Garlic is a rich source of selenium in the food. Contents of selenium in normal and carcinoma fractions in kidneys of RCC patients were determined by PIXE. The results indicate that RCC patients caused significant decrease of selenium contents in the carcinoma fraction (p < 0.05).

The soil bacterium Cupriavidus metallidurans CH34 resist selenite by reducing it into the insoluble and less toxic elemental selenium. Two mechanisms of reduction of selenium oxides in C. metallidurans CH34 were highlighted: assimilation leading to organic species and detoxification leading to precipitation of selenite in nanoparticules of elemental selenium. The alkyl selenide detected as an intermediate product during assimilation of selenite or as the major accumulated chemical form during assimilation of selenate was identified as selenomethionine.

Soluble and membrane proteins were extracted from C. metallidurans CH34 submitted to selenium oxides challenge. After separation by SDS-PAGE, µPIXE analyses were used for Se identification and quantification at a micrometer scale. The profiles of Se distribution in the different samples suggest a non-specific incorporation of selenium probably reflecting the incorporation of selenomethionin in place of the naturally occurring methionin.

A total of 4269 beard samples were collected from the same person every day over a 12-year period and analyzed by PIXE using a standard-free method. It was found that the concentrations of copper and zinc showed certain short-term changes but did not show a noticeable long-term trend over the study period, with only iron showing a slightly decreasing tendency with age. All of these elements showed clear yearly variations with a cycle of a few years possibly due to periodic metabolic changes in the subject’s body or long-term changes in eating habits. In contrast, however, selenium showed clear seasonal variations. Its concentration significantly increased in the summer and decreased in the winter, just as was observed with arsenic and mercury. This suggests that most of the subject’s selenium intake was from marine products, whose supply and consumption were increased in the summer. These findings confirmed that beard analyses are useful not only for evaluating essential-element intake but also for estimating the relationship between the body-element concentrations and ingestion of certain foods.

Selenium (Se) concentrations in plasma, urine, and feces were determined by PIXE analysis before and after intravenous (iv) / oral (po) administration of sodium selenite (a dose equivalent to 2 mg/kg of selenium) to rats. The concentration-time profiles of Se were analyzed by a pharmacokinetic approach. The plasma Se profile after iv injection was biphasic and well-fit to a 2-compartment open model, showing two half lives (t1/2). The first t1/2 was about 0.3 hr and the second t1/2 was 6.9 hrs. The plasma concentration reached almost basal level after about 80 hrs of injection. On the other hand, plasma profiles after po administration showed absorption rate-limiting elimination. The bioavailability of oral sodium selenite (about 49%) and significantly higher amount of fecal Se excretion indicated relatively poor intestinal absorption of sodium selenite, compared to the previously published data. Urinary Se excretion was almost comparable between iv and po groups. The total recovery of the dose excreted in urine and feces was 30 ± 10 % in iv and 56 ± 15 % in po group. The renal excretion was considered to be a major route of Se excretion after absorption. Significant amount of Se that was not fully excreted was noted, suggesting Se distribution or accumulation in organs, together with volatile excretion.

Selenium (Se) concentration-time profiles in plasma and organs including liver, kidney, heart, lung, spleen and brain of rats (Jcl Wister, 9 wks old, n = 32) were investigated after a single intravenous (iv) / oral (po) administration of sodium selenite (dose is equivalent to 2 mg/kg b.w. of Se), The Se concentration was determined by PIXE analysis. Among the investigated biological samples, Se concentration was the highest in the kidney or liver, followed by the heart, lung or spleen, then plasma, and the brain. Se concentrations in these organs were 0.5 to 5 times of plasma Se. The distribution profiles of Se in the organs were dependent on the route of administration. Furthermore, their profiles appeared almost parallel to the plasma Se-concentration in a logarithmic scale. Compared to the Se concentration-time profiles in plasma and organs by the route of administration, po group showed about 1/4-1/2 of the Se concentration in iv group except for kidney. Kidney kept relatively higher concentration of Se, which was similar in the both groups. This may explain our recently published data that urinary excretion was similar in the both groups. The relative oral bioavailability of plasma and each organ was calculated by the ratio of area under the concentration-time curve after oral administration (AUCpo) to AUCiv. Each organ appeared to have their own bioavailability (i.e., liver 39%, kidney 97%, heart 37%, lung 18%, spleen 10%, and brain 72%), where plasma was 46%. These results highly suggested that different Se distribution in organs by the different route of administration was due to the different metabolic profile.

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Three possible catalytic cycles for ebselen have been comprehensively modeled by theoretical calculations using density functional theory (DFT) at a mixed basis set level; the 6-31G(d) basis set for hydrocarbon fragments and the 6-31$++$G(d,p) basis set for other atoms. The 2$\to 3\to 3^{\prime }\to 3^{\prime }{}^{\prime }\to 4^{\prime }\to 4\to 2$ cycle is the main pathway in the glutathione peroxidase (GPx) cycle (cycle A), and IM3$\to$TS3 is the rate controlling process. The 1$\to 5\to 8\to 8^{\prime }{}^{\prime }\to$1 cycle is the main pathway for the oxidation cycle (cycle B), and the rate controlling step is the $8^{\prime }{}^{\prime }\to 1$ step. Ebselen reacts with the selenol 3 to form the diselenide 9, and this is the rate controlling step for cycle C. The extremely high energy barrier for the IM9$\to$TS9 process indicates that cycle C is unlikely to occur in vivo. Although cycle B is favored based on the energy analysis, with a maximum energy barrier of only 26.68kcal/mol at the mixed basis set level, it is generally unlikely to have very high concentrations of peroxides present in vivo. The results indicate that in order to improve the antioxidant activity of ebselen, it would be necessary to suitably modify the molecular structure of ebselen to reduce the energy barrier of the IM3$\to$TS3 process.

The following sections are included:

• Summary

• Introduction and Historical Perspective

• The Thioredoxin System
  • Thioredoxin Reductase and Selenium
  • Structure of Mammalian Thioredoxin Reductase
  • Mechanism of Mammalian Thioredoxin Reductase

• The Glutaredoxin System

• Redox Regulation of Cellular Function

• Future Perspectives

• Acknowledgments

• References

The following sections are included:

• Introduction

• The Thioredoxin System

• The Glutaredoxin System

• Redox Regulation by Thioredoxin and Glutaredoxin

• Effects of Oxidants and Antioxidants

• Future Perspectives

• Acknowledgments

• References