Biological availability of selenosugars in rats.

The biological availability and metabolism of two selenosugars orally administered to rats were investigated. Two other selenium species, selenite and trimethylselenonium ion (TMSe) were included in the study as positive and negative controls, respectively. Male Wistar strain rats (three per group) at 8 weeks of age were exposed to sodium selenite, TMSe, selenosugar 1 (methyl-2-acetamido-2-deoxy-1-seleno-beta-D-galactopyranoside) or selenosugar 2 (methyl-2-acetamido-2-deoxy-1-seleno-beta-D-glucopyranoside) through drinking water for 48 h. Total selenium concentrations (ICPMS) and selenium species concentrations (HPLC/ICPMS) were determined in urine samples collected in two 24h periods during the exposure, and total selenium concentrations in liver, kidney, small intestine and blood were determined at the end of the experiment. The major species found in background urine were selenosugar 1 (major metabolite) and TMSe (minor metabolite). Rats exposed to selenite excreted large quantities of selenosugars and TMSe consistent with efficient uptake and biotransformation of selenite, whereas TMSe-exposed rats excreted large quantities of TMSe, but there was no significant increase of other selenium metabolites, consistent with TMSe being taken up and excreted unchanged. Rats exposed to selenosugars, however, excreted significant quantities of TMSe suggesting that the sugars were at least partly biologically available and biotransformed. Rats exposed to selenite accumulated selenium in the liver, kidney, small intestine and blood, whereas no accumulation was observed for the other samples except for small increases in selenium concentrations of small intestine from the two selenosugar-exposed groups.

Selenium metabolites in urine of cancer patients receiving L-selenomethionine at high doses.

We investigated, with quantitative HPLC/mass spectrometry, the selenium metabolites in urine from five cancer patients receiving high doses of L-selenomethionine over an extended period (2 x 4000 microg Se/day for 7 days, then 4000 microg Se/day for 21 days) as an adjunct to their normal cancer chemotherapy. Urine samples were collected at day 0 (all 5 patients), and at 2-3 additional collection times ranging from 1 to 33 days. The background selenium concentrations ranged from 12 to 55 microg Se/L and increased to 870 to 4420 microg Se/L for the five patients during the study. All five patients had appreciable levels of selenosugars in their background urine sample, and the concentrations increased dramatically after selenium intake. Trimethylselenonium ion (TMSe), on the other hand, was generally present as only a trace metabolite in background urine, and, although the concentration of TMSe increased following selenium exposure, it became a less significant proportion relative to selenosugars. These data refute the currently accepted role of TMSe as the preferred excretion metabolite when selenium exposure is high.

Consequences of vapor enhancement on selenium speciation analysis by HPLC/ICPMS.

Recent work has shown the presence of volatile selenium metabolites in human urine and suggested that these compounds could compromise quantitative selenium analyses by ICPMS. We show that with a commonly used sample introduction system (pneumatic nebulizer and spray chamber), two volatile selenium species recently identified in urine, namely, dimethyl selenide and dimethyl diselenide, gave greatly increased ICPMS responses (up to 58-fold) relative to selenite, an effect related to their volatilization in the spray chamber resulting in enhanced transport to the plasma. The quantitative consequences of this effect were demonstrated by measurement of total selenium and selenium species in certified reference material, NIES CRM 18 human urine. Direct flow injection analysis of the urine gave a total selenium concentration more than 2-fold higher than the certified value. These data suggested that NIES CRM 18 may contain part of its selenium as volatile species, and subsequent reversed-phase HPLC/ICPMS showed the presence of dimethyl selenide in addition to selenosugars and trimethylselenonium ion. Although the practice of quantifying unidentified chromatographic peaks against those of known compounds is common in speciation analysis, this approach when applied to NIES CRM 18 gave a value for the sum of selenium species which was twice the certified total selenium concentration. This work shows that the presence of volatile selenium species in urine precludes the use of flow injection analysis for total selenium measurements and imposes severe restrictions on the quantification of urinary selenium metabolites. In addition, it raises broader issues of the validity of the "dilute and shoot" approach to the determination of metals in clinical analysis of biological fluids.

Marked individual variability in the levels of trimethylselenonium ion in human urine determined by HPLC/ICPMS and HPLC/vapor generation/ICPMS.

Selenium species were determined using HPLC/ICPMS and HPLC/vapor generation/ICPMS in the urine from seven human volunteers investigated at background selenium concentrations and at slightly elevated concentrations after ingestion of 200 microg Se as a selenite supplement. Trimethylselenonium ion (TMSe) was present, together with selenosugars, in the urine samples, a result that dispels recent doubts about its possible previous misidentification with a cationic selenosugar. Although TMSe was present as only a trace metabolite in urine from five of the seven volunteers (0.02-0.28 microg Se/L, equivalent to 1-5% of the sum of selenosugars and TMSe), it was a significant metabolite (up to 4.6 microg Se/L, 22%) in one volunteer, and it was the major identified metabolite (up to 15 microg Se/L, 53%) in another volunteer. This marked individual variability in the formation of TMSe was maintained in a duplicate investigation of urine from the same seven volunteers.

Simultaneous administration of sodium selenite and mercuric chloride decreases efficacy of DMSA and DMPS in mercury elimination in rats.

Two chelating agents meso-2,3-dimercaptosuccinic acid (DMSA) and sodium 2,3-dimercapto-propane-1-sulphonate (DMPS) were tested for their efficiency in mercury removal from the body of rats in the presence and in the absence of selenium. Female Wistar rats were given a single intraperitoneal injection of mercuric chloride or an equimolar mixture of mercuric chloride and sodium selenite (1.5 micromol/kg body weight). The chelating agents were given orally, in excess (500 micromol DMSA/kg body weight; 300 micromol DMPS/kg body weight), 30 min after the administration of mercury and selenium. The animals were euthanized 24 h after the treatment and mercury in the kidney, liver, and 24 h urine was determined using cold vapour atomic absorption spectrometry (CV-AAS). The simultaneous administration of mercuric chloride and sodium selenite led to a redistribution of mercury in the organs, so that accumulation of mercury in the kidneys was decreased and in the liver increased. Selenite also caused decrease in the level of urinary mercury excretion. Both chelating agents were effective in mercury removal from the body, by increasing its urinary excretion. However, when animals were simultaneously treated with mercury and selenite, the rise of mercury excreted in the urine due to the treatment with chelating agents was lower when compared to animals receiving mercury without selenite. It is concluded that sodium selenite decreases the efficiency of DMSA and DMPS in mercury removal from the body of rats.

Endotoxin measurement in house dust using the end-point Limulus amoebocyte lysate method.

Endotoxin is a lipopolysaccharide, a part of gram-negative bacteria cell membrane commonly present in general and many occupational environments. This paper describes sample preparation and endotoxin measurement in 16 samples of house dust from urban homes (Zagreb, Croatia) using end-point chromogenic Limulus amoebocyte lysate (LAL) bioassay. House dust was collected on cellulose filters by vacuuming bedroom and living room floors, and was kept frozen until assayed. Samples were extracted from filters with a 0.05% solution of Tween-20 in endotoxin-free water. Serial dilutions of samples were measured in duplicates. The linearity of the standard curve was satisfying (r=0.983), as well as the recovery (92 and 110%) and repeatability (coefficient of variation from 0 to 8.5%). The endotoxin levels found in the house dust samples ranged from 4.8 to 200 EU/mg, with the arithmetic mean of 49.5 EU/mg (standard error of the mean of 12.1 EU/mg), and were in the range of house dust endotoxin values obtained by other authors.

Combined early treatment with chelating agents DMSA and CaDTPA in acute oral cadmium exposure.

The influence of chelating agents: meso-2,3-dimercaptosuccinic acid (DMSA); calcium trisodium diethylenetriaminepentaacetate (CaDTPA) and their combination on mobilisation of cadmium (Cd) was compared in female albino rats. After oral Cd administration chelators were applied either orally (DMSA) or intraperitoneally (CaDTPA) at various short time intervals after Cd. Three experiments were carried out with four treatment groups in each: 1) Cd (control); 2) Cd+DMSA; 3) Cd+CaDTPA; 4) Cd+DMSA+CaDTPA. Time intervals for chelator treatment after Cd administration were: immediate application in the first, half an hour in the second and one hour in the third experiment. At the end of each experiment cadmium was analysed in kidney and liver. Additionally in experiment 3 essential elements (Fe, Cu, Zn) were also determined in the same organs. In experiment 2 the effect of the treatment on urinary elimination of cadmium, copper and zinc were analysed. Results showed that the efficiency of Cd removal from the body (kidneys and liver) is lower when the time between Cd and chelating agents administration is longer. The two chelators differ in efficiency in mobilizing Cd, with DMSA being more efficient than CaDTPA. The combined therapy with the two chelators gave generally better results. It seems that DMSA which is given orally after oral Cd administration removes this element very efficiently from the gastrointestinal tract. CaDTPA, however, which is given parenterally removes absorbed Cd less efficiently, Organs are not significantly depleted in iron and copper after chelation treatment. Only zinc concentration was, however, significantly lower in the liver and higher in kidneys only after CaDTPA and combined DMSA+CaDTPA chelation.

Succimer treatment and calcium supplementation reduce tissue lead in suckling rats.

The effect of combined treatment with meso-2,3-dimercaptosuccinic acid (DMSA) and calcium supplementation in reducing lead absorption and enhancing lead elimination was evaluated in suckling rats under two experimental conditions: during ongoing oral lead exposure (lead acetate, 2 mg Pb kg(-1) day(-1), total dose 16 mg Pb kg(-1)) or after lead exposure (72 h after a 2-day lead exposure, total dose 12 mg Pb kg(-1) s.c.). The artificial feeding method was used for calcium supplementation, with 6% Ca (as CaHPO(4)) suspension in cow's milk to increase the daily calcium intake about three times above control values. Artificial feeding lasted for 7 h a day over eight consecutive days. During this period DMSA was administered on 6 days twice a day (0.5 mmol kg(-1) day(-1) p.o.). At the end of the experiments, Pb, Ca and Zn in the carcass and Pb, Fe and Cu in the liver, kidneys and brain were analysed by atomic absorption spectrometry. Calcium supplementation during lead exposure reduced tissue lead but had no effect when applied after lead exposure, and DMSA administered either during or after lead exposure lowered the tissue lead. Combined treatment during ongoing lead exposure caused a greater reduction in tissue lead than either DMSA or calcium treatment alone. When administered after lead exposure, it had no advantage over DMSA treatment alone but did not impair its efficacy. Combined treatment had no influence on growth and did not seriously disturb essential element status. It is concluded that calcium supplementation could be applied during DMSA therapy, when indicated.

Ascorbic acid supplementation does not improve efficacy of meso-dimercaptosuccinic acid treatment in lead-exposed suckling rats.

It was suggested that ascorbic acid as a natural chelating agent can influence lead toxicokinetics and improve chelating properties of dimercaptosuccinic acid (DMSA) in adult rats. In this paper potential benefits of ascorbic acid supplementation, alone or combined with DMSA, in decreasing lead retention in suckling rats were evaluated. Such data in young mammals are not available. L-Ascorbic acid (daily dose 650 mg/kg b.wt.) and/or DMSA (daily dose 91 mg/kg b.wt.) were administered orally to suckling Wistar rats either during ongoing 8-day oral lead exposure (as acetate; daily dose 2 mg lead/kg b.wt.) or after 3-day lead exposure (total dose 12 mg lead/kg b.wt.). Lead concentrations were analysed in the carcass (skeleton), liver, kidneys and brain by atomic absorption spectrometry. By ascorbic acid supplementation lead retention was not reduced under either lead exposure condition. Lead concentration was even increased in the carcass. Treatment with DMSA under both exposure conditions significantly reduced lead in all analysed tissues. Combined treatment with ascorbic acid and DMSA during ongoing lead exposure was substantially less effective than DMSA treatment alone, and did not affect DMSA efficacy when administered after lead exposure. It was concluded that ascorbic acid administered either during or after lead exposure in suckling rats has no beneficial effect on either lead retention or DMSA chelation effectiveness.

Effect of dietary calcium on cadmium absorption and retention in suckling rats.

The effect of calcium supplementation on absorption and retention of cadmium in the suckling period was evaluated in Wistar rat pups of both sexes. Animals were maintained in the litters with the mother rats and supplemented with 1%, 3% or 6% calcium (as CaHPO4 x 2H2O) in cow's milk by artificial feeding from day of birth 6 through 14. All rats were exposed to cadmium (as CdCl2 x H2O) either orally or parenterally. Oral cadmium dose of 0.5 mg/kg body weight a day was administered through nine-day period of calcium supplementation and parenteral cadmium dose was injected subcutaneously in a single dose of 0.5 mg Cd/kg body weight prior to calcium supplementation. On experimental day 10 (at the age of pups of 15 days) all animals were killed and the liver, kidneys, brain and carcass (body without organs and skin) were removed for element analyses. Cadmium and essential elements calcium, zinc and iron were analysed in the tissues by atomic absorption spectrometry. Results showed that after oral exposure cadmium concentrations in all calcium-supplemented groups were significantly decreased in the organs and carcass and that the effect was dose-related. No such effect of calcium was found after parenteral cadmium exposure. Calcium supplementation per se significantly increased calcium concentration in the carcass and had no effect on iron in organs and zinc in carcass. It was concluded that calcium supplementation during the suckling period could be an efficient way of reducing oral cadmium absorption and retention without affecting tissue essential trace element concentrations.