[Basic studies on the utility of ursodeoxycholic acid derivatives for clinical medicine]

The aim of this study was to determine whether the derivatives of ursodeoxycholic acid (UDCA) are useful compounds for clinical medicine. 1-1) A conjugate (5-ASA-UDCA monophosphate) of UDCA monophosphate with 5-aminosalicylic acid (5-ASA) was newly synthesized, and basic studies on this compound were carried out. This compound was efficiently deconjugated by cholylglycine hydrolase (CGH) to release 5-ASA, whereas it was completely resistant to deconjugation by pancreatic and intestinal mucosal enzymes. In animal experiments, the urinary excretion of N-acetyl-5-ASA (Ac-5ASA) was measured for 24 h following the oral administration of 20 mg of 5-ASA-UDCA monophosphate. Control rats excreted 276.3 +/- 89.0 micrograms (mean +/- S.E.) of Ac-5ASA whereas rats with intestinal bacterial overgrowth excreted more (1224.1 +/- 231.5 micrograms; p < 0.01). These basic studies indicate that this compound is likely to offer a simple method for the evaluation of intestinal microorganisms without the use of radioisotopes or expensive, special apparatus. 1-2) The disulphate ester of ursodeoxycholyl-p-aminobenzoic acid (PABA-UDCA) was synthesized and compared with PABA-UDCA for its use in the detection of intestinal bacteria. This compound, PABA-UDCA disulphate, had characters in common with PABA-UDCA in that it was deconjugated by CGH to release free PABA. Further, in rat experiments the urinary excretion of PABA was measured for 6 h after oral administration of 15 mg PABA-UDCA disulphate. Ten control rats excreted 188.2 +/- 13.6 micrograms (mean +/- S.E.) of PABA; 10 rats with an intestinal stagnantloop excreted more (530.1 +/- 30.1 micrograms; p < 0.001): whereas 10 rats in each of three groups pretreated with oral administration of various antibiotics excreted less. PABA-UDCA disulphate is a single pass type substance in the gut and its oral administration test reflects the sum of the activities of bacteria in the small intestine and colon. From the results the obtained PABA-UDCA disulphate was considered a good material to detect intestinal bacteria. 2) A conjugate (Lys-UDCA) of UDCA with L-lysine was newly synthesized. In the incubation experiments with plasma, homogenates of the liver and small intestine, various pancreatic enzymes and CGH, Lys-UDCA was deconjugated by carboxypeptidases B and CGH. In the experiment using rodent everted gut sac, Lys-UDCA was actively absorbed from the terminal ileum. Lys-UDCA was recovered well in the bile after intravenous or intraileal administration of Lys-UDCA in biliary fistula rat. These data suggest that Lys-UDCA is a good prodrug of UDCA for intravenous administration. 3) A novel calcium-chelating agent, N"-ursodeoxycholyl-diethylenetriamine-N,N,N'-triacetic acid (UDCA-DTTA), was synthesized to study its ability to dissolve calcified gallstones. In the presence of the agent, sliced human gallstone with a composition of more than 50% calcium bilirubinate was thoroughly dissolved, indicating that calcium bilirubinate was dissolved from the gallstone. The ability to dissolve calcium was comparable to that of EDTA. However, the laminar structure of the sliced gallstone did not disappear in the presence of EDTA, whereas the structure disappeared in the presence of UDCA-DTTA. These results indicate that UDCA-DTTA is an interesting compound as a parent substance for developing a prodrug for an oral or intravenous agent to dissolve calcium-containing gallstones.