Macromolecule-macromolecule interaction in drug distribution. III. Kinetic characterization of the uptake of fractionated [3H]heparin and the effect of plasma proteins in the perfused rat liver

Are novel scavenger-like receptors involved in the hepatic uptake of heparin?

Heparin is an anionic macromolecular drug. It has been widely used as an anticoagulant, and numerous efforts to clarify the mechanism of its disposition in the body have been made to help expand its clinical applications, using its newly found biological activities, as well as to further improve its use in anticoagulant therapy. It has now been shown that heparin is taken up extensively not only by Kupffer cells but also by parenchymal cells in the liver, the major distribution organ, and a receptor-mediated endocytotic mechanism, which is shared by heparin analogs and various anionic macromolecules, is responsible for heparin uptake in both types of cells. Although the characteristics of the receptors for heparin in both cells have lots of similarities to those of scavenger receptors, the receptors in parenchymal cells do not accept acetylated low density lipoprotein (Ac-LDL) as a ligand, which is the only striking difference between them and major scavenger receptors. Although the receptors in Kupffer cells, which accept Ac-LDL as a ligand, may belong to class A scavenger receptors, this remains to be established. We therefore conclude at present that it is likely that novel scavenger-like receptors for heparin (heparin receptors) or unidentified scavenger receptors are responsible for heparin uptake in the liver.

Decreased activity of hepatic P-glycoprotein in the isolated perfused liver of the adjuvant arthritis rat

1. We investigated the hepatobiliary transport of doxorubicin in the isolated perfused liver prepared from the adjuvant arthritis rat, an animal model for rheumatoid arthritis, to examine the hepatic P-glycoprotein activity in the adjuvant arthritis rat. 2. Liver was isolated from the normal and the adjuvant arthritis rat and perfused for 60 min with recirculating buffer and the perfusate and bile samples were collected at timed interval. 3. The elimination of doxorubicin in the adjuvant arthritis rat tended to be reduced, but it was not significantly different from the normal rat. Biliary clearance (CL(bile)) in the normal rat was 1.93 +/- 0.48 ml min(-1), whereas, CL(bile) in the adjuvant arthritis rat was significantly decreased to 0.40 +/- 0.13 ml min(-1). 4. CL(bile) was markedly decreased to about 0.15 ml min(-1) in the presence of 100 microM verapamil in both types of rat. Methotrexate treatment had no effect on CL(bile) in both the normal and adjuvant arthritis rat (2.18 +/- 0.22 and 0.47 +/- 0.22 ml min(-1), respectively). 5. The results suggest that the hepatic P-glycoprotein activity was markedly decreased in the adjuvant arthritis rat and the effect of methotrexate on the hepatic P-glycoprotein activity did not corresponded to its anti-inflammatory effect.