The role of sodium in the uptake of ursodeoxycholic acid in isolated hamster hepatocytes

Abstract

The uptake of ursodeoxycholic acid (UDCA) was studied in isolated hamster hepatocytes. The uptake was rapid and linear up to 60 seconds for each concentration studied. When the uptake rate was plotted against UDCA concentration, the curve was nonlinear, indicating both saturable and nonsaturable uptake mechanisms. The nonsaturable process had a diffusion constant of 0.01 nmol.s-1.g of cell.mumol/L-1. The saturable component was characterized by a maximum rate of uptake (Vmax) of 5.68 nmol.s-1.g of cell-1 and a Michaelis constant (Km) of 224 mumol/L. In the presence of monensin, ouabain, and amiloride, the uptake of UDCA was significantly decreased by 35% to 55%, whereas the sodium-independent uptake of UDCA was not affected by either monensin or amiloride, thereby confirming sodium dependence of UDCA uptake. The sodium-dependent uptake of UDCA was characterized by a Vmax and a Km of 1.57 nmol.s-1.g of cell-1 and 46 mumol/L, respectively. The rate of uptake of UDCA was maximal at extracellular sodium concentrations > or = 20 mmol/L. Furthermore, the uptake of UDCA was competitively inhibited by both taurocholic acid and cholic acid with an inhibitory constant (Ki) of 60 mumol/L and 48 mumol/L, respectively. Finally, 1 mmol/L of 4,4'-diisothiocyano-2,2'-disulfonic stilbene (DIDS) inhibited solely the sodium-dependent uptake of cholic acid and UDCA. These findings confirm that the hepatocellular uptake of UDCA involves, at least in part, a sodium-dependent, ouabain, amiloride, and DIDS-sensitive transporter.

Uptake of Ursodeoxycholate and Its Conjugates by Human Hepatocytes: Role of Na+-Taurocholate Cotransporting Polypeptide (NTCP), Organic Anion Transporting Polypeptide (OATP) 1B1 (OATP-C), and OATP1B3 (OATP8)

“…Regarding the hepatic uptake of UDCA, it has been reported that the contributions of the Na + -dependent and -independent pathways to its hepatic uptake were almost identical in isolated hamster hepatocytes, which is consistent with our results . On the other hand, we did not see any significant uptake of UDCA via OATP1B1 and OATP1B3, which we expected to work as high-affinity Na + -independent transport systems.…”

“…Regarding the hepatic uptake of UDCA, it has been reported that the contributions of the Na + -dependent and -independent pathways to its hepatic uptake were almost identical in isolated hamster hepatocytes, which is consistent with our results. 28 On the other hand, we did not see any significant uptake of UDCA via OATP1B1 and OATP1B3, which we expected to work as high-affinity Na + -independent transport systems. Britz et al have reported that Bamet-UD2 (cisplatin conjugated with two molecules of UDCA) can be taken up by OATP1A2 (OATP-A), OATP1B1 (OATP-C), organic cation transporter (OCT) 1, OCT2, and NTCP.…”

Extrahepatic deposition and cytotoxicity of lithocholic acid: Studies in two hamster models of hepatic failure and in cultured human fibroblasts

“…16 Initial rate of bile acid uptake was plotted as a function of the corresponding respective bile acid concentration, and data were analyzed by linear curve fitting. 31 …”

Cholestasis: The Close Relationship between Bile Acids and Coenzyme Q10

“…UDCA is a weak acid (pKa = 5), and poorly water soluble, however, its solubility increases directly to the increase of the solution pH. After orally administrations, UDCA must be solubilized in mixed micelles present in small intestinal content in order to allow absorption [19,20]. During the cholestasis disease, the UDCA bioavailability is limited due to the reduction of endogenous BA micelles in the duodenal lumen.…”