title: Lithocholylcholine, a bile acid/acetylcholine hybrid, is a muscarinic receptor antagonist.
abstract: Previous work from our laboratory indicates that bile acids, specifically lithocholic acid conjugates, interact with muscarinic receptors on gastric chief cells. Structural similarities between acetylcholine and lithocholyltaurine suggest a potential molecular basis for their interaction with the same receptor. We synthesized a hybrid molecule consisting of the steroid nucleus of lithocholyltaurine and the choline moiety of acetylcholine. The new molecule, lithocholylcholine, is hydrolyzed by acetyl-cholinesterase. Lithocholylcholine inhibited binding of a cholinergic radioligand to Chinese hamster ovary cells expressing each of the five muscarinic receptor subtypes. The binding affinities (K(i); micromolar) of lithocholylcholine for these receptors were: M3 (1.0) > M1 (2.7) > M2 (4.1) = M4 (4.9) > M5 (6.2). Lithocholylcholine inhibited intracellular signaling pathways mediated by interaction with M1, M2, and M3 muscarinic receptors. Regarding M3 receptors, lithocholylcholine was 10-fold more potent than lithocholyltaurine in terms of binding affinity and inhibition of acetylcholine-induced increases in inositol phosphate formation and mitogen-activated protein kinase phosphorylation. In a functional assay, lithocholylcholine inhibited acetylcholine-induced relaxation of rat aortic rings. These observations indicate that lithocholylcholine is a muscarinic receptor antagonist and provide further evidence that bile acids may have gastrointestinal signaling functions that extend beyond their effects on sterol metabolism, lipid absorption, and cholesterol elimination. Hybrid molecules created from bile acids and acetylcholine may be used to develop selective muscarinic receptor ligands.
authors.affiliation: Division of Gastroenterology and Hepatology, Central Arkansas Veterans Healthcare System and University of Arkansas for Medical Sciences, Little Rock, USA.
authors.forename: Kunrong
authors.initials: K
authors.lastname: Cheng
authors.forename: Sandeep
authors.initials: S
authors.lastname: Khurana
authors.forename: Ying
authors.initials: Y
authors.lastname: Chen
authors.forename: Richard H
authors.initials: RH
authors.lastname: Kennedy
authors.forename: Piotr
authors.initials: P
authors.lastname: Zimniak
authors.forename: Jean-Pierre
authors.initials: JP
authors.lastname: Raufman
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000110:Acetylcholinesterase / Q000378:metabolism*; D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects / Q000502:physiology*; D001285:Atropine / Q000494:pharmacology; D016466:CHO Cells; D002217:Carbachol / Q000494:pharmacology; D006224:Cricetinae; D066298:In Vitro Techniques; D007295:Inositol Phosphates / Q000378:metabolism; D007700:Kinetics; D008095:Lithocholic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology*; D008297:Male; D018727:Muscarinic Antagonists / Q000494:pharmacology*; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D011869:Radioligand Assay; D051381:Rats; D017207:Rats, Sprague-Dawley; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000502:physiology*; D011994:Recombinant Proteins / Q000378:metabolism; D013658:Taurolithocholic Acid / Q000494:pharmacology*
chemical_list: D007295:Inositol Phosphates; D018727:Muscarinic Antagonists; D011976:Receptors, Muscarinic; D011994:Recombinant Proteins; C466790:lithocholylcholine; D013658:Taurolithocholic Acid; D008095:Lithocholic Acid; D001285:Atropine; D002217:Carbachol; D000110:Acetylcholinesterase; D000109:Acetylcholine; C027746:glycolithocholic acid