Activation of mast cells by bile acids

To test whether bile acids interact with mast cells, dilute, aqueous solutions of five pure unconjugated natural bile acids and their corresponding glycine or taurine conjugates were incubated with murine PT-18 cells (a mast cell line functionally and cytochemically similar to mucosal mast cells) or with freshly isolated rat peritoneal mast cells. Bile acid solutions ranged in concentration from 0.3 to 10 mmol/L; histamine release was assessed by a fluorimetric assay, and cell lysis by cytosolic enzyme (lactate dehydrogenase) release. Lipophilic, dihydroxy bile acids (chenodeoxycholic acid and deoxycholic acid as well as their glycine and taurine conjugates) caused histamine release in a dose-related manner; cholic acid and its conjugates caused much less or no histamine release. Two hydrophilic bile acids (ursodeoxycholic acid and ursocholic acid and their conjugates) were virtually devoid of activity. Histamine release, which was independent of extracellular Ca2+, occurred at 0.3 mmol/L, well below the critical micellization concentration. For a given concentration, unconjugated bile acids and glycine-conjugated bile acids induced more histamine release than taurine-conjugated bile acids; maximal release was observed at 3 mmol/L for lipophilic, dihydroxy bile acids. To test whether bile acids could also cause histamine release from cutaneous mast cells in vivo, rats were injected intradermally with bile acid solutions and histamine release assessed by capillary leakage of Evan's blue dye. Cutaneous blueing was greater with cytotoxic bile acids, chenodeoxycholyglycine or deoxycholylglycine, than with ursodeoxycholylglycine and was inhibited by prior antihistamine treatment. Histamine release correlated highly and positively with lipophilicity and with bile acid surface activity. It was concluded that lipophilic but not hydrophilic bile acids possess concentration-dependent cytotoxicity toward mast cells causing histamine release, that unconjugated and glycine-conjugated bile acids are more potent than taurine-conjugated bile acids, and that mast cell histamine release is highly correlated with lipophilicity of bile acids as well as their surface activity.