Bile canalicular membrane

Transport system Basolateral membrane Bile canalicular membrane... 

The liver plays an important role in determining the oral bioavailability of drags. Drag molecules absorbed into the portal vein are taken up by hepatocytes, and then metabolized and/or excreted into the bile. For hydrophilic drugs, transporters located on the sinusoidal membrane are responsible for the hepatic uptake [1, 2]. Biliary excretion of many drags is also mediated by the primary active transporters, referred to as ATP-binding cassette transmembrane (ABC) transporters, located on the bile canalicular membrane [1, 3-5], Recently, many molecular biological... 

It is important to establish an in vitro system which will allow in vivo transport across the bile canalicular membrane to be predicted quantitatively. By comparing the transport activity between in vivo and in vitro situations in isolated bile canalicular membrane vesicles, it has been shown that there is a significant correlation for nine types of substrates [90]. Here, in vivo transport activity was defined as the biliary excretion rate, divided by the unbound hepatic concentration at steady-state, whereas in vitro transport activity was defined as the initial velocity for the transport into the isolated bile canalicular membrane vesicles divided by the medium concentration [90]. Collectively, it is possible to predict in vivo canalicular transport from in vitro experiments with the isolated bile canalicular membrane vesicles. 

Fig. 12.2. Comparison of ATP-dependent transport activity between rats and humans determined in isolated bile canalicular membrane vesicles. Key 1, SN-38 glucuronide (carboxylate) 2, SN-38 glucuronide (lactone) 3, E3040 (6-hydroxy-5,7-dimethyl-2-methyl-amino-4-(3-pyridylmethyl) benzothiazole) glucuronide 4, 170 estradiol-170-D-glucuro-nide 5, grepafloxacin glucuronide 6, leuko-...

MDCK II cells (Fig. 12.3) [93], Kinetic analysis revealed that the Km value for transcellular transport (24 pM) was similar to the Km for OATP2 (34 pM) [93], Moreover, the efflux across the bile canalicular membrane was not saturated under these experimental conditions. These in vitro observations are consistent with in vivo experimental results in rats which showed that the rate-determining process for the biliary excretion of pravastatin is uptake across the sinusoidal membrane. By normalizing the expression level between the double transfectant and human hepatocytes, it might be possible to predict in vivo hepatobiliary excretion. 

If the unbound drug concentrations in plasma are higher than their K values on the transporters, then transporter function may be significantly affected [106], Following a pharmacokinetic analysis of the effect of probenecid on the hepatobiliary excretion of methotrexate, it has been shown the extent of an in vivo drug-drug interaction can be quantitatively predicted from the kinetic parameters for transport across the sinusoidal and bile canalicular membranes determined in vitro [107]. 

Effect of Drugs on the Activity of Transporters Located on the Bile Canalicular Membrane... 

Aoki, J., Suzuki, H., Sugiyama, Y., Quantitative prediction of in vivo biliary excretion clearance across the bile canalicular membrane from in vitro transport studies with isolated membrane vesicles. Abstract of Millennial World Congress of pharmaceutical Sciences, San Francisco, April 16-20, 2000, p. 92. 

Niinuma, K., Kato, Y., Suzuki, H., Tyson, C. A., Weizer, V., Dabbs, J. E., Froehlich, R., Green, C. E., Sugiyama, Y., Primary active transport of organic anions on bile canalicular membrane in humans, Am. J. Physiol. 1999, 276, G1153-G1164. 

Y., Drug—drug interaction at the biliary excretion process prediction of the potential cholestatic activity using bile canalicular membrane vesicles, Jpn. J. Pharmacol. Ther. 2001, 29S, S243-S245. 

In contrast to P-gp and the MRP proteins, the breast cancer resistance protein (BCRP) contains six transmembrane domains and only one ATP-binding domain. It was first cloned from the breast cancer cell line MCF-7 selected in doxombicin, in the presence of the P-gp inhibitor verapamil. It is found in many human tissues, such as the placenta, small intestine, colon, and liver [133], It is localized to the apical membrane of epithelial cells of the small intestine and colon and to the bile canalicular membrane in the liver and is involved in reducing intestinal uptake, increasing hepatobiliary excretion, etc., leading to diminished oral bioavailability. cDNA sequences identical to BCRP and named MXR and ABCP, respectively, were independently isolated from human colon carcinoma cells and human placenta [134], BCRP requires... 

Many drugs that are taken up and metabolized by hepatocytes are excreted via the bile canahcuh into the bile. One of the remaining topics in liver slice research is the question of whether liver shces are capable of bile excretion via the bile canaliculus. Thompson et aZ.[93] showed that shces are capable of excreting bile acids, however, there is a need for more experiments to determine whether this excretion takes place across the bile canalicular membrane. 

Alteration of ER transport, sinusoidal membrane transport, or bile canalicular membrane transport of the glucuronides... 

Excretion Parenchymal cells Bile Canalicular membrane vesicles, transporter expression system... 

Niinuma K, Kato Y, Suzuki H, et al. Sugiyama. Primary active transport of organic anions on bile canalicular membrane in humans. Am J Physiol 1999 276 G1153-G1164. 

Buschman E, Arceci RJ, Croop JM, et al. mdr2 encodes P-glycoprotein expressed in the bile canalicular membrane as determined by isoform-specific antibodies. J Biol Chem 1992 267(25) 18093-18099. 

Figure 22-3. Transport and hepatic metabolism of bilirubin. Bilirubin that is produced in phagocytes is transported to liver as an albumin-bilirubin complex. Uptake into the hepatocytes takes place in liver sinusoids. Within the hepatocyte, bilirubin is transported to the endoplasmic reticulum (microsomes) bound to glutathione S-transferase (GST). Bilirubin is made water soluble by addition of one or two glucuronic acid moieties obtained from UPD-glucuronic acid, catalyzed by bilirubin-UDP-glucuronyltransferase. The product, conjugated bilirubin, is transported across the bile canalicular membrane for secretion into the biliary system, with subsequent movement into the intestines.

Table 11.3 Major efflux transporters expressed in the bile canalicular membrane of human liver. 

One of the popular experimental systems to investigate the hepatic efflux process is canalicular membrane vesicle (CMV). It is difficult to evaluate the transport activity of efflux transporters in cell systems because substrates cannot easily access the intracellular compartment, so CMV system is often used to rapidly determine the ATP-dependent efflux transport of substrates across bile canalicular membrane. 

Ishizuka, H., Konno, K., Shiina, T., Naganuma, H., Nishimura, K., Ito, K., Suzuki, H. and Sugiyama, Y. (1999) Species differences in the transport activity for organic anions across the bile canalicular membrane. The Journal of Pharmacology and Experimental Therapeutics, 290, 1324—1330. 

A key feature of the liver is the antidromic blood and bile flow system (Fig. lc). Blood enters the lobules in the periphery, passes the sinusoids, and is drained off into the central vein. Bile is secreted by the hepatocytes into the apical bile canaliculi, which form a network organized parallel as well as perpendicular to the sinusoidal vessels. Bile flows to the bile ducts in the periportal field and is finally drained off into the gall bladder and the small intestine. The bile canalicular network is not composed of conventional vessels with endothelial cells. It is formed by the apical membrane of hepatocytes and thereby is a consequence of the polar structure of these cells which have an apical pole (facing the bile canaliculus) and a basolateral side (facing the sinusoid). The direct contact to bile leads to a high vulnerability of hepatocytes. Destruction of the apical hepatocyte membrane may lead to bile acids entering the cell, hepatocyte killing, and inflammation. 

---