The Role of Calcium in the Pathogenesis of Gallstones: Ca++ Electrode Studies of Model Bile Salt Solutions and Other Biologic Systems†

Abstract

Calcium is present in all pigment gallstones as a sat of one or more of the anions in bile which are most readily precipitable by calcium: (i) carbonate; (ii) bilirubinate; (iii) phosphate, and (iv) "palmitate". We term these "calcium-sensitive" anions. In addition, since cholesterol stones have been found to contain pigment stone centers, we postulate that calcium precipitation in bile is a critical event in the initiation of cholesterol gallstones, so that the latter should be considered a two-stage process: (i) precipitation of calcium salts to form a nidus, and (ii) precipitation of cholesterol from its supersaturated state on this nidus. Any measure which will reduce free [Ca++] in bile will reduce calcium lithogenicity; possible ways to reduce [Ca"] in bile are presented. One way is to increase Ca++ binding by normal biliary constituents; we have recently pointed out that bile salts are important buffers for Ca++ in bile by virtue of binding to both free and micellar bile salts. Here, we consider some of our Ca++ electrode studies of taurocholate, glycocholate, serum albumin, and simple molecules having terminal carboxyl (COO-) or sulfonic (SO;) ions. A brief history of the development of the Ca++ electrode is'given, along with theoretical considerations of ionic activities and techniques of electrode measurements. From the various studies, a unifying hypothesis is proposed for the structural requirements of Ca++-binding to proteins (albumin) and free monomeric bile salts. For proteins, unconjugated bile salts and glycine-conjugated bile salts, it is proposed that Ca++ binding involves a reversible ion-exchange "site" in which a Ca++ ion is interposed between carboxyl (COO-) and hydroxyl (OH) groups. For taurine-conjugated bile salts, this "site" is proposed to involve the interposition of a Ca++ ion between the side-chain SOT and cholanic ring OH groups. These studies are a first step toward modulation of Ca++ activity in bile.Gallstone disease is a major medical and surgical problem in many countries. In the United States, approximately 500,000 cholecystectomies are performed each year for cholelithiasis, with a direct cost of several billion dollars and indirect cost of several billions more due to time lost from work, to say nothing of the suffering and occasional mortality involved. The physical chemistry of bile is therefore of great interest to scientist and clinician This conference is not Only to Our old ideas, but to bring together investigators with different disciplines to focus on the multiplicity of factors involved in gallstone formation. We hypothesize that one icallY the free calcium ion concentration [Ca"] activThis work was supported by Research Grants AM 18887, AM 27104 and Am 32130, National Institute of Arthritis, Diabetes, Digestive and Kidney Diseases, National Institutes of Health.The author wishes to apologize to the reader for not being able to include details of several unpublished studies which were presented at the Kroc Conference. This was necessary so as not to jeopardize ...

The Effect of Biliary Bile Acid Concentration and Composition on the Calcium Level in Human Gallbladder Bile.

“…This finding was compatible with the previous reports (Knyrim et al 1989;Yoneda et al 1991). Non-ionized calcium may be solubilized by binding mainly to bile acid mixed micelles which may play an important buffer-like role in keeping the constant ionized calcium level to minimize the risk of calcium precipitation in bile (Moore et al 1982;Moore 1984). Then, higher ionized to total calcium ratio denotes smaller capacity of this buffer action.…”

“…As calcium binding capacity of small size of aggregates is less than that of mixed micellar bile acids (Moore 1984), UDCA-rich bile may have a high potential to precipitate insoluble calcium salts from the viewpoint of the calcium binding capacity and buffer-like action of bile acid micelles. We hypothesized that the difference in micelle forming properties would influence the stability of solubilized calcium in bile, although ionized calcium levels detected no statistical difference between the CDCA and UDCA group.…”

Influence of Dietary Calcium Concentration on the Digestion of Nutrients along the Intestinal Tract of Broiler Chickens

“…Phospholipids in the bile (van Berge Henegouwen et al, 1987) are other major contributors to the endogenous P flow. Bile is also the major source of endogenous Ca, in which the Ca exists as bile acid conjugates, free ionised Ca or insoluble Ca salts such as calcium bilirubinate, calcium carbonate, calcium orthophosphate and calcium palmitate (Moore, 1984;Gleeson et al, 1990). The existence of continuous duodenal-gizzard refluxes in chickens could also account, in part, for the observed negative digestibility estimates.…”

Isolation of an acidic protein from cholesterol gallstones, which inhibits the precipitation of calcium carbonate in vitro.

“…Calcium is an important constituent of all kinds of gallstones, and is almost always present in the center of even "pure" cholesterol stones (1 1-14). In analogy with cholesterol, calcium salt precipitation is possible only when bile is supersaturated with the salt, i.e., when the product of the activities of the calcium ion and a "calcium sensitive" anion (e.g., carbonate) exceeds the solubility product for that salt (15). Hepatic bile, however, is always supersaturated with calcium carbonate, even in the absence of stones, and normal gallbladder bile can tolerate massive supersaturation with calcium carbonate without precipitation of this salt (16,17).…”