Impact of ursodeoxycholic acid on a CCK1R cholesterol-binding site may contribute to its positive effects in digestive function

Abstract

Dysfunction of the type 1 cholecystokinin (CCK) receptor (CCK1R) as a result of increased gallbladder muscularis membrane cholesterol has been implicated in the pathogenesis of cholesterol gallstones. Administration of ursodeoxycholic acid, which is structurally related to cholesterol, has been shown to have beneficial effects on gallstone formation. Our aims were to explore the possible direct effects and mechanism of action of bile acids on CCK receptor function. We studied the effects of structurally related hydrophobic chenodeoxycholic acid and hydrophilic ursodeoxycholic acid in vitro on CCK receptor function in the setting of normal and elevated membrane cholesterol. We also examined their effects on a cholesterol-insensitive CCK1R mutant (Y140A) disrupting a key site of cholesterol action. The results show that, similar to the impact of cholesterol on CCK receptors, bile acid effects were limited to CCK1R, with no effects on CCK2R. Chenodeoxycholic acid had a negative impact on CCK1R function, while ursodeoxycholic acid had no effect on CCK1R function in normal membranes but was protective against the negative impact of elevated cholesterol on this receptor. The cholesterol-insensitive CCK1R mutant Y140A was resistant to effects of both bile acids. These data suggest that bile acids compete with the action of cholesterol on CCK1R, probably by interacting at the same site, although the conformational impact of each bile acid appears to be different, with ursodeoxycholic acid capable of correcting the abnormal conformation of CCK1R in a high-cholesterol environment. This mechanism may contribute to the beneficial effect of ursodeoxycholic acid in reducing cholesterol gallstone formation.

Molecular Mechanism of Action of Triazolobenzodiazepinone Agonists of the Type 1 Cholecystokinin Receptor. Possible Cooperativity across the Receptor Homodimeric Complex

“…Biological activity of CE-326597 or PF-04756956 at the various CCK receptor-based mutants was measured by quantifying intracellular calcium responses in intact cells 42–44 . These responses are reported as percentages of maximal responses to 10 nM CCK.…”

Beneficial effects of β-sitosterol on type 1 cholecystokinin receptor dysfunction induced by elevated membrane cholesterol

“…In order to test the effect of β-sitosterol on CCK binding characteristics, whole cell radioligand binding assays were performed, with a similar treatment protocol as described previously for bile acids (17). Briefly, cells were seeded and grown to achieve 80–85 percent confluence in 24-well tissue culture plates.…”

“…Another site to target might be outside of this helical bundle, also within the lipid bilayer, where cholesterol has been postulated to interact with CCK1R to exert its negative impact on receptor function (4). We recently reported a proof-of-principle for the latter approach by studying CCK1R function in the presence of bile acids that are structurally similar to cholesterol (17). In that work, ursodeoxycholic acid was observed to correct the defective biological response of this receptor to CCK in the setting of high cholesterol (17).…”

“…We recently reported a proof-of-principle for the latter approach by studying CCK1R function in the presence of bile acids that are structurally similar to cholesterol (17). In that work, ursodeoxycholic acid was observed to correct the defective biological response of this receptor to CCK in the setting of high cholesterol (17). …”

Metabolic Actions of the Type 1 Cholecystokinin Receptor: Its Potential as a Therapeutic Target

“…Other structurally-related sterols, such as bile acids, seem to be capable of interacting with the same site on CCK1R, with ursodeoxycholic acid able to compete for cholesterol interaction and to reverse the negative effects of that lipid [58]. This may provide proof-of-principle for ultimate development of a drug that might act similarly.…”