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Key words alginate; toxic metal; binding mechanism; affinity Metal ions absorbed via the intestinal tract, respiratory system or skin can cause serious damage to various internal organs, depending on their type and amount. For example, lead (Pb) causes acute damage to the central nervous system, and chronic damage to the kidney and hematopoetic and nervous systems.1,2) Long-term, low-dose exposure to cadmium (Cd) damages the lung (chronic bronchitis, fibrosis, emphysema), kidney (renal tubular degeneration, interstitial inflammation, fibrosis, diabetes, proteinuria), and bone (fake fracture, osteomalacia).3) Cadmium is well known to induce itai-itai disease (kidney tubular damage and osteomalacia), 4) and moreover, it is carcinogenic. 3,5) In addition, aluminum (Al) causes encephalopathy and osteodystrophy, 6,7) and copper (Cu) causes hemolytic anemia and gastroenteritis. 8) In the case of acute oral exposure, damage can be reduced by immediate treatments such as induction of vomiting and/or the use of a laxative to promote excretion of the metal. In addition, chelating agents can be administered; for example, ethylenediaminetetraacetic acid and dimercaptopropionylsulfonate are used as antidotes for Pb poisoning, 9-11) and dimercaprol is used for detoxification of Pb and Cu.11,12) However, in the case of chronic exposure, it is essential to use intrinsically safe absorption inhibitors and/or excretion accelerators that are suitable for long-term administration.Alginate (Alg), an intercellular polysaccharide found in brown algae, is used as a health food and food additive to reduce cholesterol in the blood and to inhibit weight gain. [13][14][15] It also protects the gastric mucous membrane.16) Moreover, it was reported that accumulation of strontium (Sr) in the human body decreased when sodium alginate (Na-Alg) was ingested before exposure to Sr. 17) Further, when rats pre-fed with NaAlg for ten days were administered Sr, the cumulative amount of Sr in the body was markedly reduced, compared with the control group.18) Consequently, it has been suggested that daily intake of Na-Alg would offer protection against radiation damage from radioactive fall-out by decreasing the absorption of radioactive Sr. Accordingly, the International Atomic Energy Agency (IAEA) has recommended Na-Alg intake for persons exposed to large amounts of radioactive Sr. 19)We have compared the effects of Na-Alg and Ca-Alg in promoting excretion and decreasing absorption of Sr and cesium (Cs) in rats. 20) Both additives increased the excretion of Sr, though Cs concentration was significantly reduced only in the Ca-Alg group. There have been some reports describing the capacity of Alg for metal binding and the order of affinity between Alg and metals. 21,22) However, there is little information about the relationship between the physical parameters of various metal ions and the binding affinity of these metal ions for Alg. Therefore we performed range and limitation tests of the adapting metals by evaluating the binding constants and the b...

We examined whether calcium alginate (Ca-Alg) reduces blood cholesterol levels in rats fed a highcholesterol diet. First, we examined taurocholate adsorption in vitro by various types of sodium alginate (NaAlg). High molecular-weight, guluronic acid-rich Na-Alg showed the greatest adsorption of taurocholate, and therefore the corresponding Ca-Alg was chosen for the in vivo study. Rats were fed a high-cholesterol diet or a Ca-Alg-containing diet for 2 weeks. Body weight and diet intake were measured, and the general condition of the animals was monitored during this period. After 14 d, the plasma concentration of cholesterol, portal plasma concentration of bile acid, and bile acid in feces were measured. The plasma concentration of cholesterol was significantly reduced in rats fed a 2% Ca-Alg-containing diet. Furthermore, the portal concentration of bile acid was significantly lowered in the 2% Ca-Alg group. A tendency for a Ca-Alg concentrationdependent increase in fecal excretion of bile acid was also seen, although it was not statistically significant. While several changes in biochemical parameters and histopathological findings were observed, all the values remained within the physiological range. These results indicate that Ca-Alg is effective in reducing plasma cholesterol. A possible mechanism would be enhanced fecal excretion of bile acid due to reduced intestinal reabsorption, which in turn might stimulate bile acid synthesis from cholesterol in the liver, leading to a decrease in plasma cholesterol.Key words alginate; cholesterol; bile acid Heart disease and cerebrovascular disease account for about one-quarter of all deaths in Japan, 1) and a major factor in their etiology is considered to be dyslipidemia.2-4) Indeed, dyslipidemia can be considered predominantly a modern lifestylerelated disease.5,6) Therefore, there is considerable interest in food additives or health foods that decrease cholesterol absorption or promote cholesterol excretion. Possible candidates include alginate (Alg), a cationic intercellular polysaccharide derived from brown seaweed. 7,8) We have compared the effects of sodium alginate (Na-Alg) and calcium alginate (Ca-Alg) in promoting excretion and decreasing absorption of Sr and cesium (Cs) in rats.9) Both additives increased the excretion of Sr, though Cs concentration was significantly reduced only in the Ca-Alg group. We also measured the plasma concentration of cholesterol in that study, and interestingly found that Ca-Alg has a greater cholesterol-lowering effect than Na-Alg. 9)At present, Na-Alg is widely used as a food additive (thickening agent) and as a health food to decrease blood cholesterol and inhibit weight gain. [10][11][12] However, sodium intake is associated with hypertension, 13) and Ca-Alg may be preferable to Na-Alg, if it has an equivalent pharmaceutical effect. Therefore, in this study we first examined various types of Na-Alg to evaluate their bile acid-absorbing ability in vitro. Based on the results, we selected high-molecular-weight, guluronic acidri...

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