Fluorescent bile acid derivatives: Relationship between chemical structure and hepatic and intestinal transport in the rat

Abstract

Studies were performed to characterize hepatic and intestinal transport, as well as biotransformation during transport, of a spectrum of fluorescent bile acids containing a fluorophore attached to the side chain. The following two classes of compounds were studied: 1) aminofluorescein (amF) coupled directly to the carboxylic group of a bile acid which was cholic, ursodeoxycholic, or cholylglycine; and 2) nitrobenzoxadiazolyl (NBD) coupled to the epsilon-amino group of a lysine conjugated bile acid, which was cholic or ursodeoxycholic. Fluorescein, a cholephilic organic anion, was studied as a control. Fluorescent bile acids were synthesized and their structures confirmed by nuclear magnetic resonance and mass spectrometry. Using the biliary fistula rat, hepatic transport, biotransformation, and choleretic activity were defined; intestinal absorption was assessed by jejunal or ileal perfusion studies. All fluorescent bile acids had hepatic transport maxima about one-sixth that reported for cholyltaurine, but derivatives of cholylglycine were transported best. Bile acids underwent little (<5%) biotransformation during hepatocyte transport. Only the amF conjugate of cholylglycine had normal choleretic activity; other compounds were hypocholeretic or cholestatic. In contrast, fluorescein was well transported, was partly glucuronidated, and had normal choleretic activity. NBD-tagged, but not amF-tagged, bile acids were actively transported by the intestine (ileum > jejunum), and no fluorescent bile acid had passive intestinal permeability; NBD-tagged bile acids were biotransformed during intestinal transport (jejunum > ileum). We conclude that the structure of the fluorophore as well as that of the bile acid influences transport by the hepatocyte and enterocyte. These fluorescent bile acids differ from fluorescein in being impermeable to cell membranes and undergoing little biotransformation during hepatocyte transport. Of these fluorescent bile acids, cholylglycylamF has hepatocyte transport and choleretic properties most closely resembling those of a natural bile acid.

Atp8b1 deficiency in mice reduces resistance of the canalicular membrane to hydrophobic bile salts and impairs bile salt transport

“…The gallbladder, portal vein, and superior vena cava were cannulated. The liver (left in situ) was perfused in orthograde direction (3 mL/h) with carbogen (95%O 2 /5%CO 2 )-gassed Krebs-bicarbonate buffer (120 mmol/L NaCl, 24 mmol/L NaHCO 3 24 was perfused for 20 minutes at a 25 nmol/min*100g rate followed by 2 minutes' Krebs buffer; livers were excised and snap-frozen in liquid nitrogen, and liver sections (6 m) were studied using a fluorescent microscope.…”

Interstitial Accumulation of Na+ and K+ During Flush–Out and Cold Storage of Rat Livers: Implications for Graft Survival

“…Livers were reperfused through the portal vein in a closed system with KHB (gassed with O 2 /CO 2 , 37°C), at a constant portal vein pressure of 12 cm H 2 O as described previously. 16 Portal flow and bile production were measured over a period of 1 hour. After 5 and 60 minutes, samples were taken from the perfusate, and aspartate transaminase, alanine transaminase, and lactate dehydrogenase were measured with an automated Hitachi 911-analyzer.…”

Apical Sodium Dependent Bile Acid Transporter (ASBT, SLC10A2): A Potential Prodrug Target

“…Although conjugates exhibited hASBT inhibition, they were not transported by hASBT 57 . Similarly, the absorption of the C-24 dipeptide bile acid conjugate cholylglycyltyrosine was low compared to taurocholic acid 58 . Swaan et al evaluated the transport of peptides of varying length that were conjugated at the 24-position of cholic acid via an amide linkage 59 .…”