Effect of colchicine-specific Fab fragments on the hepatic clearance of colchicine.

The influence of colchicine-specific Fab fragments on hepatic metabolism and biliary excretion of colchicine was studied in the isolated perfused rat liver. Isolated rat livers were perfused for 180 min with either [3H]colchicine (initial concentration: 50 ng/ml) or Fab-[3H] colchicine in a stoichiometrical proportion at a constant flow of 100 ml/min in a recirculating system. Based on perfusate concentrations, the hepatic extraction ratio of colchicine was more than 15-fold decreased when colchicine was bound to Fab fragments (E = 0.011 +/- 0.001) than when it was infused alone (E = 0.16 +/- 0.01) (p < 0.01). The extensive binding of colchicine to Fab over the experimental period as demonstrated by equilibrium dialysis (97 +/- 2%) prevented hepatic uptake. At the end of the colchicine perfusion experiment, 74.2 +/- 4.9% of the radioactivity infused was excreted by the biliary route. In contrast, biliary excretion of radioactivity was 10-fold lower when [3H]colchicine was perfused complexed with Fab fragments (p < 0.01). However, the metabolic profile of colchicine was not affected by Fab fragments. The apparent half-life of colchicine metabolites calculated from biliary data was similar to that of colchicine, indicating that the biliary excretion of these metabolites was formation rate-limited. Inhibition of colchicine uptake by specific Fab fragment was confirmed in vitro with isolated hepatocytes.