Relationship between Physical Parameters of Various Metal Ions and Binding Affinity for Alginate.

We investigated the relationship between the physical parameters of various metal ions, including toxic metal ions, and the binding affinity of these metal ions for alginate (Alg). The binding constant, K, of Sr2+ was the highest among all tested metal ions. The order of K values was: Sr2+>Pb2+>Tb3+>Dy3+>Ca2+>Cd2+>Mg2+>Fe2+>Fe3+>Co2+>Al3+>Ni2+>Cs+>Cu2+>Ag+>Li+>K+. The metal ions showing the highest K values had ionic radii within the range of about 90-120 pm. Moreover, the K values of divalent or trivalent metal ions tended to be higher than those of monovalent ions. The number of binding sites per 1 mg of Alg (n) was highest for K+, followed by Pb2+ and Cs+. The order of affinity (calculated as the product of n and K) was Pb2+>Dy3+>Tb3+>Sr2+>Ca2+>Mg2+>Cd2+>Fe2+, Fe3+>Cs+>Al3+>Co2+>Ni2+>Cu2+>Ag+>K+>Li+. Our results support the idea that Alg would be effective as an excretion accelerator and/or absorption inhibitor for various toxic metal ions.

Cholesterol-Lowering Effect of Calcium Alginate in Rats.

We examined whether calcium alginate (Ca-Alg) reduces blood cholesterol levels in rats fed a high-cholesterol diet. First, we examined taurocholate adsorption in vitro by various types of sodium alginate (Na-Alg). 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 concentration-dependent 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.