Studies of Inhibition of Intestinal Absorption of Radioactive Strontium: IV. Estimation of the Suppressant Effect of Sodium Alginate

A method is reported which permits selective suppression of absorption of radioactive strontium from ingested food material, allowing calcium to be available to the body. Studies were carried out on the inhibitory effect of various amounts of sodium alginate and the dose-response relationship of Sr⁸⁹ and bone uptake. The results obtained indicated that under laboratory conditions sodium alginate effectively reduces Sr⁸⁹ uptake in a constant proportion. This effect was observed at the three levels of administration of 1.4%, 12% and 24% of sodium alginate. The linear relationship between the dosage of the radioisotope and the bone uptake in the presence of sodium alginate suggests that the same proportion is maintained at the lower levels of intake of radioactive strontium.Previous studies with small constant doses of sodium alginate were extended in rats to a period corresponding approximately to three years of human life span. Low doses were sufficient to reduce appreciably bone uptake of radiostrontium.     

Studies on Inhibition of Intestinal Absorption of Radioactive Strontium: II. Effects of Administration of Sodium Alginate by Orogastric Intubation and Feeding

A method is reported that enables selective suppression of absorption of radioactive strontium from ingested food material, permitting calcium to remain available to the body. Studies were carried out by measuring blood levels and bone uptake of Sr⁸⁹ and Ca⁴⁵ at different time intervals after orogastric intubation of rats. The addition of sodium alginate, derived from brown marine algae, to the radioactive isotopes increased the overall physiological discrimination against strontium by amounts up to 60% after 24 hours. This discrimination was further increased by feeding sodium alginate mixed with standard diet in the proportions of 20:80 and 30:70. The observed ratio was reduced by administration of sodium alginate from 0.25 to 0.09.Determination of the limiting dosage in rats is restricted to the amounts which rats will consume. In the event of an inadvertent release of radioactive strontium, human subjects probably could increase their intake of alginate at will, permitting a greater effectiveness of sodium alginate than could be obtained in experimental animals.     

Studies on Inhibition of Intestinal Absorption of Radioactive Strontium: I. Prevention of Absorption from Ligated Intestinal Segments

A method is reported which permits selective suppression of absorption of radioactive strontium from ingested food material, permitting the calcium to be available to the body. Studies were carried out in vivo by injection of Sr⁸⁹ and Ca⁴⁵ in the presence of inert carrier into ligated intestinal segments in rats, and the amount of absorption was measured by standard monitoring techniques. The pattern of absorption of both ions is very similar but the rate of absorption is different. It was found that the polyelectrolyte, sodium alginate, obtained from brown algae (Phaeophyceae), injected simultaneously with radiostrontium effectively reduces the absortion of Sr⁸⁹ from all segments of the intestine by as much as 50-80% of the control values. No significant reduction in absorption of Ca⁴⁵ was observed in equivalent concentrations. The reduction in blood levels of Sr⁸⁹ and in bone uptake corresponded to the absorption pattern. The difference in the effect on strontium and calcium absorption may be due to differences in the binding capacity of sodium alginate from the two metal ions under the conditions present in vivo.     

Studies on the Inhibition of Intestinal Absorption of Radioactive Strontium: V. The Effect of Administration of Calcium Alginate

A method of selective suppression of absorption of radioactive strontium from ingested food material is described which allows calcium to be available to the body. In the present study the effects of administering calcium alginate were determined. Studies on the relative binding of Ca and Sr by calcium alginate in vivo are also important to the investigation of calcium-strontium exchange.Samples of calcium alginate were obtained commercially or prepared from sodium salts and the binding properties with Ca⁴⁵ and Sr⁸⁹ were tested in vivo. There was a free exchange of radioactive calcium as well as of strontium with bound inactive calcium. The amount of Ca⁴⁵ retained in the gut by calcium alginate is proportionally less than Sr⁸⁹, so that the ratio Sr⁸⁹/Ca⁴⁵ in the bone is consistently and significantly lower in treated rats. Calcium alginate acts differently from other calcium salts, although in a manner similar to sodium alginate.     

Strontium-89 and Strontium-90 Levels in Breast Milk and in Mineral-Supplement Preparations

Strontium-90, strontium-89 and S.U. values were determined in human milk before and after the resumption of atmospheric nuclear testings in 1961, and the levels were compared to cows'' milk values reported during the same time. S.U.⁹⁰ levels in human milk were approximately one-fifth of those found in cows'' milk. Assuming an average dietary intake of 11-13 S.U.⁹⁰ during the period tested, the mean strontium/calcium ratio of 1.78 found in human milk represents an Observed Ratio milk-diet of approximately 0.14-0.16. Although strontium-89 was present in cows'' milk already in September 1961, it did not appear in human milk until November 1961. It seems, therefore, that there was a two-month lag period between the appearance of fresh fallout in cows'' milk and human milk. Calcium-supplement mineral preparations used by pregnant and lactating women were tested to find their strontium-89, strontium-90 and S.U. levels, because strontium isotopes, if present in these products, will be transferred to the fetus and to breast-fed infants. The compounds tested had S.U.⁹⁰ levels of 0.13-2.62; in none of the preparations was Sr⁸⁹ present.     

Some environmental factors influencing radiostrontium uptake by plants

Summary The amounts of Sr⁹⁰ taken up from Vina soil varied among several different crop plants by a factor as high as 10 on the basis of dry weight. The relative decreasing order of Sr⁹⁰ uptake by mature plant tops was turnip = millet > Swiss chard > Ladino clover > broccoli > soybeans > barley > oats > wheat > spinach. For each of the cereal crops, the concentration of Sr⁹⁰ in the grain was only about one-fifth of the Sr⁹⁰ in the forage. The tubers of White Rose potato grown on Sassafras, Hanford and Sorrento soils contained only about one-fiftieth of the Sr⁹⁰ concentrated in the tops. The Sr⁹⁰ uptake by potato was inversely correlated with the level of plant-available calcium in Sassafras, Hanford and Sorrento soils.Lowering of root temperature from 17° to 7°C significantly reduced Sr⁹⁰ uptake by barley and beans during a 24-hour absorption period. Q10 values indicated that strontium uptake was chemically controlled rather than the result of physical phenomena.A decrease in light intensity from 1,000 to 450 foot-candle significantly reduced Sr⁹⁰ uptake by barley and beans. The uptake of Sr⁹⁰ also was reduced as the light exposure period was decreased. One-third to one-half of the total amount of Sr⁹⁰ obtained during a 24-hour absorption period was taken up independent of exposure to light.These studies were supported by Contract AT(04-1)-GEN-12 between the Atomic Energy Commission and the University of California.     

ATP-dependent strontium uptake by basolateral membrane vesicles from rat renal cortex in the absence or presence of calcium

ATP-dependent Sr²⁺ transport was examined in vitro using basolateral membrane (BLM) vesicles isolated from rat renal cortex to clarify the discrimination mechanisms between strontium (Sr) and calcium (Ca) in renal tubules during reabsorption. ATP-dependent Sr²⁺ uptake and Ca²⁺ uptake were observed in renal BLM vesicles and were inhibited by vanadate. Hill plots indicate similar kinetic behavior for Ca²⁺ and Sr²⁺ uptake. The apparentK _m andV _max of ATP-dependent Sr²⁺ uptake were both higher than those for Ca²⁺ uptake. ATP-dependent Sr²⁺ uptake by BLM vesicles diminished in the presence of 0.1 μM Ca²⁺ and was more markedly inhibited by 1 μM Ca²⁺. Hill plots of Sr²⁺ uptake data with and without 0.1 μM Ca²⁺ showed that the cooperative behavior of Sr²⁺ uptake was not changed by Ca²⁺. In the presence of 0.1 μM Ca²⁺, the affinity of the transport system for Sr²⁺ and the velocity of Sr²⁺ uptake in the BLM were both decreased. However, the rate of Ca²⁺ uptake was not diminished by Sr²⁺ concentrations of <1.6 μM. These results suggest that Ca²⁺ is preferentially transported in the renal cortex BLM when Ca²⁺ and Sr²⁺ are present at the same time.     

The Effect of Sodium Alginate on the Absorption of Strontium and Calcium in Human Subjects

The effect of sodium alginate on the gastrointestinal absorption of the tracers strontium-85 and calcium-47 was investigated in 19 human subjects. The tracers were administered orally with 100 mg. of a calcium carrier—calcium chloride. At the same time, sodium alginate was given in a commercial jelly. The sevenday per cent retentions of tracers were measured with a whole-body counter. After one month, the experiments were repeated without alginate so that each subject acted as his own control. Fifteen volunteers were given 1.5 g. of alginate, two were given 3.0 g. and two 0.3 g. 1.5 g. of alginate reduced the absorption of strontium by a factor of two with no significant effect on calcium absorption. The smaller dose of alginate (0.3 g.) appeared to have no effect on strontium or calcium absorption and the larger dose (3.0 g.) had no greater effect than the 1.5 g. dose.     

Studies on Inhibition of the Intestinal Absorption of Radioactive Strontium: IX. Relationship Between Biological Activity and Electron Microscopic Appearance of Alginic Acid Components

The inhibitory action of alginate on intestinal absorption of radioactive strontium was investigated in order to correlate the biological activity with the chemical composition. Alginate from Laminaria hyperborea was partially hydrolyzed with oxalic acid and the degradation products were fractionated into polymannuronic and polyguluronic acid. The activity of these products was assessed biologically in rats and morphologically by electron microscopy. Sodium polymannuronate was found to be less effective than sodium polyguluronate in preventing absorption of radiostrontium. The inhibition of absorption of radio-calcium was low and not affected by hydrolysis or fractionation. When dried from dilute aqueous solutions, the polymannuronate retained the original helical structure of alginate, while the polyguluronate showed a strong tendency to coagulate, forming granules. The variation in the biological activity was attributed to the morphological differences between these alginic acid components and it is suggested that the degree of uncoiling of the polyguluronate chain in water is greater than that of the polymannuronate chain, thus making the carboxylate ions more accessible to strontium.     

Effect of calcium levels on redistribution of Sr85 in bush bean plants

Summary When bush bean plants previously exposed to Sr⁸⁵ were transferred to solutions containing different levels of calcium without further addition of Sr⁸⁵, and calcium had relatively little, but some, effect on the redistribution of the Sr⁸⁵ in the plants. Calcium did tend to restrict movement of strontium. Sr⁸⁵ tended to concentrate in stems or old leaves, usually more so than calcium. New leaves particularly had lower Sr/Ca ratios than other plant parts indicating some discrimination in favor of calcium.     

Active Calcium and Strontium Transport in Human Erythrocyte Ghosts

Both calcium and strontium could be transported actively from erythrocytes if adenosine triphosphate, guanosine triphosphate, or inosine triphosphate were included in the hypotonic medium used to infuse calcium or strontium into the cells. Acetyl phosphate and pyrophosphate were not energy sources for the transport of either ion. Neither calcium nor strontium transport was accompanied by magnesium exchange, and the addition of Mg⁺⁺ to the reaction medium in a final concentration of 3.0 mmoles/liter did not promote the transport of either ion. In the absence of nucleotide triphosphates, the addition of 1.5 mmoles/liter of Sr⁺⁺ to the reaction solution did not bring about active calcium transport and similarly 1.5 mmoles/liter of Ca⁺⁺ did not bring about active strontium transport. The inclusion of 1.5 mmoles/liter of Ca⁺⁺ or Sr⁺⁺ in the reaction medium did not interfere with the transport of the other ion when the erythrocytes were infused with adenosine triphosphate.     

The effect of silica fume on biodegradation of cement paste and its capacity to immobilize strontium during exposure to microbial sulfur oxidation

The disposal of low-level radioactive waste containing isotopes such as strontium by immobilization in cement paste has become common practice. However, the stability of cement paste in the environment may be impaired by sulfuric acid produced by sulfur-oxidizing bacteria. Since biodegradation rates in the environment of most radioactive waste burial sites are too low to be measured, determination of the degradation kinetics of cement paste is a difficult task. This study reports on the development of an accelerated biodegradation system for cement pastes in which the cement paste is exposed to a continuous culture of the sulfur-oxidizing bacterium Halothiobacillus neapolitanus. This system facilitated detection of the biodegradation processes in cement paste after as short a time as 15 days. A comparison of the durability of a cement paste blended with silica fume with that of unblended cement paste showed that the silica fume induced an increase in the leaching of Ca⁺² and Si and enhanced weight loss, indicating rapid deterioration in the structural integrity of the cement paste. The leaching of Sr⁺² from the silica fume amended cement paste was slightly reduced as compared with the non amended cement paste, indicating an increase in immobilization of strontium. Nevertheless, our findings do not support the use of silica fume as a suitable additive for immobilization of low-level radioactive waste.     

Purification and partial characterization of an extracellular alginate lyase from <Emphasis Type="Italic">Aspergillus oryzae</Emphasis> isolated from brown seaweed

The extracellular enzyme alginate lyase produced from marine fungus Aspergillus oryzae isolated from brown alga Dictyota dichotoma was purified, partially characterized, and evaluated for its sodium alginate depolymerization abilities. The enzyme characterization studies have revealed that alginate lyase consisted of two polypeptides with about 45 and 50 kDa each on 10% sodium dodecyl sulfate polyacrylamide gel electrophoresis and showed 140-fold higher activity than crude enzyme under optimized pH (6.5) and temperature (35°C) conditions. Zn²⁺, Mn²⁺, Cu²⁺, Mg²⁺, Co²⁺ and NaCl were found to enhance the enzyme activity while (Ca²⁺, Cd²⁺, Fe²⁺, Hg²⁺, Sr²⁺, Ni²⁺), glutathione, and metal chelators (ethylenediaminetetraacetic acid and ethylene glycol tetraacetic acid) suppressed the activity. Fourier transform infrared and thin-layer chromatography analysis of depolymerized sodium alginate indicated the enzyme specificity for cleaving at the β-1,4 glycosidic bond between polyM and polyG blocks of sodium alginate and therefore resulted in estimation of relatively higher polyM content than polyG. Comparison of chemical shifts in ¹³C nuclear magnetic resonance spectra of both polyM and polyG from that of sodium alginate also showed further evidence for enzymatic depolymerization of sodium alginate.     

Comparative Study of Cr(VI) Removal by Exiguobacterium sp. in Free and Immobilized Forms

Cr(VI) is a toxic environmental pollutant. To determine the potential role of microbes towards chromate bioremediation, two bacterial strains, E1 and E4, that could tolerate Cr(VI) at levels up to 2250 μg ml^?1 were isolated from the soil of a tannery. They were identified as Exiguobacterium sp. To estimate the removal of Cr(VI) using immobilized bacterial cells, 2% sodium alginate and 2.5% agar were used as immobilizing matrices. In the case of sodium alginate, 89% and 93% of Cr(VI) removal by E1 and E4, respectively, were observed. When agar beads were used as an immobilizing matrix, removal was recorded as 39% and 48% for E1 and E4, respectively. Removal of Cr(VI) was also estimated in sterile and nonsterile tannery effluent. More Cr(VI) removal was noted in the nonsterile effluent than in the sterile effluent. The maximum uptake of Cr(VI) of bound cells of E1 and E4 was found to be 17.54 and 20.04 μg ml^?1, respectively. Fourier transform infrared (FTIR) spectra of cells of E4 with Cr(VI), without Cr(VI), and immobilized cells depicted several absorption peaks, mainly for P?OH group, C?H bending, C?O bond, and amide II groups, reflecting the complex nature of the bacterial cells and the contribution of these functional groups to the Cr(VI) binding process.     

Effects of manganese and other divalent cations on calcium uptake and catecholamine secretion by primary cultures of bovine adrenal medulla cells

Primary cultures of bovine adrenal medullary chromaffin cells were used to examine the effect of replacing divalent cations in the extracellular media on secretion. When calcium was replaced by manganese, nicotine-stimulated secretion was delayed in onset for 3 to 5 minutes, but continued for approximately 60 minutes. In contrast, calcium-supported secretion began immediately on stimulation and plateaued by 10 minutes. ⁵⁴Mn²⁺ uptake occurred on stimulation but at a lower rate than ⁴⁵Ca²⁺ uptake. There was no delay of ⁵⁴Mn²⁺ uptake upon stimulation and ⁵⁴Mn²⁺ uptake was considerably prolonged compared to ⁴⁵Ca²⁺ uptake. Replacement of calcium with strontium gave results similar to those with calcium, and, in addition, strontium was able to bring about secretion by itself in a manner similar to barium. Inhibition experiments showed that the potency for inhibiting calcium uptake was Cd²⁺>Mn²⁺>Ca²⁺>Sr²⁺.     

Regulation of apoptotic signal by strontium in immunocytes

Exposure to heavy metals can initiate the development of negative effects in different organs and systems, including the immune system, and can be manifested as dysfunction of receptor systems and intracellular signaling. The participation of stable strontium (Sr²⁺) in the regulation of apoptotic signals in immunocompetent cells was analyzed. Various mechanisms of strontium-induced modulation of the apoptotic lymphocyte reaction were described, and the formation of intracellular signal transduction involving Sr²⁺ was defined. The flow cytometry method was used to study changes in membrane and intracellular markers of apoptosis in children who consumed drinking water with the elevated levels of strontium. It was shown that the content of strontium in blood in the range of 0.0129–0.173 mg/dm³ affected different ways of apoptosis regulation (CD95-, p53-, and TNF-induced apoptosis) and their integration sites, thereby reducing the transmission of apoptotic signal in immunocompetent cells, and formed an alternative pathway of the cell elimination based on the mechanism of necrosis.     

Lithium ion uptake associated with the stimulation of action potential ionophores of cultured human neuroblastoma cells

Cultured human neuroblastoma cell lines were tested for the action potential sodium ionophore utilizing the Li⁺ ion rather than the ²²Na⁺ ion. The cell lines studied included CHP-134, CHP-100, CHP-126, CHP-212 and LA-N-1. Veratridine-dependent uptake of Li⁺ and ²²Na⁺ and its inhibition by tetrodotoxin implies the presence of the action-potential sodium ionophore. CHP-165, and undifferentiated tumor and RAJI a lymphoblast had no veratridine-dependent Li⁺ uptake. Thus, veratridine-dependent Li⁺ uptake provides a convenient means of assaying human neural cells for the action-potential sodium ionophore without the use of the radioactive Na⁺ ion.     

Uptake and accumulation of Mn2+ and Sr2+ in Saccharomyces cerevisiae

Initial uptake of Mn²⁺ and Sr²⁺ in the yeast Saccharomyces cerevisiae was studied in order to investigate the selectivity of the divalent cation uptake system and the possible involvement of the plasma-membrane ATPase in this uptake. The initial uptake rates of the two ions were not significantly different. This ruled out a direct role of the plasma-membrane ATPase, since this ATPase is specific for Mn²⁺ compared to Sr²⁺. After 1 h uptake, Mn²⁺ had accumulated 10-times more than Sr²⁺. Influx of Mn²⁺ and Sr²⁺ remained unchanged during that time, however. The differences in accumulation level found for Mn²⁺ and Sr²⁺ could be ascribed to a greater efflux of Sr²⁺ as compared with Mn²⁺. Probably this greater efflux of Sr²⁺ was only apparent, since differential extraction of the yeast cells revealed that Mn²⁺ is more compartmentalised than Sr²⁺, giving rise to a lower relative cytoplasmic Mn²⁺ concentration.     

Effects of dietary supplementation with aluminum and citrate on iron metabolism in the rat

The metabolism of iron (Fe) has been shown to interact with that of aluminum (Al) in relation to intestinal absorption, transport in the blood plasma, and the induction of lipid peroxidation and cellular damage. Also, dietary supplementation with citrate has been shown to increase the absorption of both metals and, in the presence of high intakes of Fe and Al, leads to excessive accumulation of both metals in the body. In this study, the likely interaction between Al and internal Fe metabolism was investigated using rats fed diets that were either deficient, sufficient, or loaded with Fe, with or without the addition of Al and sodium citrate. These diets commenced when the rats were 4 wk old and were continued for 9–11 wk. At that time, Fe metabolism as assessed by measurement of organ uptake of⁵⁹Fe and¹²⁵I-transferrin, after iv injection of transferrin labeled with both isotopes, plus measurement of tissue concentrations of nonheme Fe and Al. The Fedeficient diet and Fe-loaded diet led to states of Fe deficiency and Fe overload in the rats, and supplementation of the diet with Al increased Al levels in the kidneys, liver, and femurs, but, generally, only when the diet also contained citrate. Neither Al nor citrate supplementation of the diet had any effect on nonheme Fe concentrations in the liver, kidney, or brain, or on the uptake of⁵⁹Fe or¹²⁵I-transferrin by liver, kidney, brain, or spleen. Only with the femurs was a significant effect observed: increased⁵⁹Fe uptake in association with increased Al intake. Therefore, using this animal model, there was little evidence for interaction between Fe and Al metabolism, and no support was obtained for the hypothesis that dietary supplementation with Fe and citrate can lead to excessive Fe absorption and deposition in the tissues.     

Effects of strontium on the absorption of calcium, magnesium and phosphate ions from the ovine reticulo-rumen

The net absorption rates of strontium ions from the ovine reticulo-rumen, isolated in situ in trained conscious animals, were measured under controlled conditions. A linear positive response was obtained from the addition of Sr²⁺ ions to the artificial rumen fluid. This increase in the absorption of Sr was reflected in an increase in the plasma Sr concentration. In contrast to the discrimination observed elsewhere in favour of the absorption of Ca relative to Sr, the absorption rate of Sr from the reticulo-rumen was significantly greater than that of Ca, from solutions containing the same molar concentration. A graded increase in the Sr concentration in the ruminal fluid from 1 mmol/l to 4 mmol/l led to a corresponding reduction in the absorption rate of Ca but an increase in that of phosphate. The latter result is similar to that observed when the intra-ruminal concentration of Ca²⁺ ions is increased. It is suggested that Ca and Sr share a common pathway for absorption from the reticulo-rumen and that this may involve coupling with the absorption of phosphate ions. Accepted: 18 January 2000