Synthesis and biliary excretion of tyrosine-conjugated bile salts in Wistar rats

Biliary excretion of chenodeoxycholyllysylrhodamine in Wistar rats: a possible role of a bile acid as a carrier for drugs

The effect on biliary excretion of rhodamine after its conjugation to give chenodeoxycholyl-lysyl-rhodamine (cheno-lys-R) was studied in male Wistar rats. Following its intravenous injection via the jugular vein of animals cheno-lys-R was efficiently excreted into bile with a peak biliary excretion of 31.6 +/- 1.2% dose 5 min-1 and a cumulative biliary excretion of 96.4 +/- 2.0% in 30 min of the total dose administered. Unlike cheno-lys-R, rhodamine had a poor biliary excretion of 1.0 +/- 0.1% dose 5 min-1 and a cumulative biliary excretion of 3.3 +/- 0.6% in 30 min. Cheno-lys-R had a short plasma half-life (t1/2 alpha) of 4.0 +/- 0.5 min, whereas free rhodamine had a longer half life (t1/2 alpha) of 82.1 +/- 1.4 min. The plasma clearances of cheno-lys-R and rhodamine were 41.2 +/- 6.5 and 9.0 +/- 1.2 ml/min per kg, respectively. The data indicate that the cationic fluorescent xenobiotic, rhodamine, when conjugated to the bile salt analogue, greatly increased the biliary excretion of rhodamine and that cheno-lys acted as a carrier for hepatic uptake of rhodamine. Thus, an appropriate bile salt derivative may be used to target a drug to the liver.

Characterization of the transport of a synthetic bile salt, iodinated cholyl-glycyl-tyrosine, in isolated cultured rat hepatocytes

The uptake of tri-hydroxy conjugated bile salts by hepatocytes is principally by a sodium-dependent carrier. We examined the uptake kinetics of the high-specific-activity, hydroxylated, conjugated bile salt 125I-labeled cholyl-glycyl-tyrosine, to determine whether this synthetic bile salt was transported by the sodium-dependent bile salt system. 125I-labeled cholyl-glycyl-tyrosine was synthesized, and its transport kinetics were studied in freshly cultured rat hepatocytes. Uptake into hepatocytes was time and temperature dependent and was decreased by the inhibitors diisothiocyanodisulfonic acid stilbene, probenecid and carbonyl cyanide chlorophenyl hydrazone, demonstrating carrier mediation and energy dependence. At concentrations of iodinated cholyl-glycyl-tyrosine less than 10 mumol/L, uptake was 27% +/- 5% sodium dependent, whereas at concentrations from 10 mumol/L to 40 mumol/L uptake was 52% +/- 4% sodium dependent. The apparent affinity for uptake of 125I-labeled cholyl-glycyl-tyrosine was 8 +/- 2 mumol/L, and the maximal velocity was 50 +/- 20 pmol/micrograms DNA/min. Both taurocholate and indocyanine green inhibited uptake of 125I-labeled cholyl-glycyl-tyrosine. Indocyanine green inhibited the uptake of 125I-labeled cholyl-glycyl-tyrosine (Ki = 10 microns) more effectively than taurocholate (Ki = 20 microns). We conclude that 125I-labeled cholyl-glycyl-tyrosine is not a specific probe for either sodium-dependent bile salt or sodium-independent organic anion carriers, but appears to use both systems in a concentration-dependent manner in cultured rat hepatocytes.

Cholyl-lysylfluorescein: synthesis, biliary excretion in vivo and during single-pass perfusion of isolated perfused rat liver

A fluorescent bile salt, cholyl-lysylfluorescein (cholyl-lys-F), was synthesised so that it retained both an intact steroid ring and a side chain structure with an unblocked carboxyl group. Its biliary kinetics and hepatic extraction were studied in Wistar rats and in the isolated perfused rat liver, respectively. The synthetic method used excess N-epsilon-CBZ-l-lysine methyl ester hydrochloride (7 mmol) and cholic acid (5 mmol) via EEDQ with a yield of 94% for cholyl-lys. Cholyl-lys-F was synthesized employing equimolar amounts of cholyl-lys (sodium salt) and fluorescein isothiocyanate (FITC) in bicarbonate buffer (pH 9.5) over 16 h at room temperature (21 degrees C) with a yield of 70%. The fluorescent property of cholyl-lys-F was similar to fluorescein with a strong apple-green fluorescence. In bile-fistula rats under pentobarbital anaesthesia, the cumulative 20 min biliary excretion as a percentage of injected dose were as follows: cholyl-lys-F, 94.4 +/- 0.3%, [14C]cholylglycine (CG), 93.1 +/- 1.2% and fluorescein (F), 34.8 +/- 0.5. Furthermore the single-pass hepatic extraction of cholyl-lys-F was 64.1 +/- 3.9%, [14C]CG was 66.1 +/- 1.2% and F was 16.5 +/- 2%. The similarity in biliary output and hepatic extraction of cholyl-lys-F to that of the natural bile acid cholylglycine suggest that both compounds are handled in a similar fashion. The greater biliary excretion and hepatic extraction of cholyl-lys-F relative to free fluorescein further suggest that conjugation with a bile salt may be an efficient way of targeting compounds to the liver.

Selective hepatobiliary transport of nordeoxycholate side chain conjugates in mutant rats with a canalicular transport defect

Canalicular transport of bilirubin diglucuronide, dibromosulfophthalein and several glutathione conjugates is deficient in mutant TR- rats. In contrast, transport of cholyltaurine (taurocholate), a conjugated bile acid, is normal. Previous studies using normal rats have shown that C23 nor-dihydroxy bile acids are conjugated with sulfate or glucuronide during hepatic transport in contrast to the natural C24 bile acids, which are amidated with glycine or taurine. Studies were performed to test the hypothesis that (a) in the TR- rat, nordeoxycholate would be conjugated with glucuronate or sulfate just as in the normal rat, and (b) that such conjugates would have defective biliary secretion. [C23-14C]Nordeoxycholate was administered intravenously to bile fistula rats (TR- and normal), and the biliary recovery of metabolites was assessed by chromatography and mass spectrometry. In both groups of rats, the major biotransformation product of nordeoxycholate was the side chain (23-ester) glucuronide. Conjugation on the nucleus with sulfate and glucuronide at the 3-position (ethereal linkage) also occurred, as well as amidation at the C23 carboxylic acid group. In the mutant rats, biliary secretion of the 3-sulfate and 3-glucuronide conjugates was less than 10% and 1%, respectively, of that of normal rats, whereas biliary secretion of the 23-ester glucuronide and the 23-taurine amidate, as well as unchanged nordeoxycholate, was not decreased. Canalicular secretion of nor-bile acid 3-ether glucuronides and 3-sulfates appears to involve the "bilirubin transport system," which is deficient in mutant rats. Canalicular secretion of unconjugated, amidated or esterified nordeoxycholate is mediated via another pathway, probably the "bile acid transport system."(ABSTRACT TRUNCATED AT 250 WORDS)

Ileal absorption of tyrosine-conjugated bile acids in Wistar rats

We recently reported that tyrosine-conjugated bile acids, when injected intravenously into bile-fistula rats, are extracted by the liver and secreted intact into bile with an efficiency similar to that seen for taurocholate. Now the effect of tyrosine and glycyltyrosine conjugation of bile acids on ileal absorption has been studied in Wistar rats. 125I-labelled tyrosine- and glycyltyrosine-conjugated bile acid or [14C]taurocholate was injected in 400 microliters aliquots of physiological saline buffered to pH 7.8 into the ileal lumen of bile-fistula rats. Recovery of bile salts in bile was taken as proof of ileal absorption. In comparison with taurocholate, ileal absorption was about 10% less for cholyltyrosine and chenodeoxycholyltyrosine and about 50% less for deoxycholyltyrosine. Thus, tyrosine-conjugated bile acids are absorbed by the ileum and excreted into bile and may undergo enterohepatic circulation. Low recoveries of deoxycholyltyrosine relative to deoxycholylglycine suggested that side chain structure was important for ileal absorption of 3 alpha,12 alpha-dihydroxy bile acids. Elongation of cholic acid to form cholylglycyltyrosine markedly reduced 90-min cumulative ileal absorption relative to cholyltyrosine. Although initial rates of recovery of cholylglycyltyrosine were comparable to those of the other bile acids, very little further absorption was seen in the last hour of the experiment, suggesting that this compound was rapidly degraded within the intestinal lumen.

The effect of tyrosine conjugation on the critical micellar concentration of free and glycine-conjugated bile salts

We investigated the effect of conjugation with the aromatic amino acid tyrosine on the critical micellar concentration (CMC) of bile salts. The CMC values were determined by surface tension and by dye solubilization. The surface tension measurement employed the Du Nouy ring detachment method and the dye solubilization measurement utilized a water-insoluble dye, 1-O-tolylazo-2-naphthol. We compared the CMC values of the sodium salts of cholyltyrosine (cholylTyr), deoxycholyltyrosine (deoxycholylTyr), deoxycholylglycyltyrosine (deoxycholylGlyTyr) chenodeoxycholyltyrosine (chenodeoxycholylTyr), chenodeoxycholylglycyltyrosine (chenodeoxycholylGlyTyr), cholyldiglycyltyrosine (cholylGlyGlyTyr) and cholylglycyltyrosine (cholylGlyTyr) with their respective glycine conjugated bile salts. Both techniques of CMC determination indicated that tyrosine conjugation to free and glycine-conjugated bile salts reduced their CMC significantly.