No Effect of Phenobarbital Pretreatment of Rats on Methotrexate Pharmacokinetics in the Isolated Liver Perfused in a Single-Pass Way

Abstract

Pretreatment of the rat with phenobarbital (PB) is known to increase gene expression of the canalicular multispecific organic anion transporter (cMOAT) and hepatobiliary transport of its substrates (glutathione, sulfobromophthalein). To determine the effect of PB on the hepatobiliary transport of methotrexate (MTX, another substrate of cMOAT) and its metabolism to 7-hydroxymethotrexate (7-OHMTX) in the rat, we compared the steady-state pharmacokinetics of MTX in the isolated liver of either PB-pretreated (80 mg/day/kg bw for 4 days, i.p.) or nonpretreated rats. The livers were perfused in a single-pass way at a flow rate of 15 ml/min using a perfusate which consisted of Krebs-Henseleit buffer containing glucose, taurocholate, bovine albumin and erythrocytes. During the perfusion with 50 µmol/l MTX, the steady-state biliary clearance (1.26 ± 0.24 ml/min) in 7 nonpretreated rats accounted for a major proportion of the hepatic clearance (1.30 ± 0.33 ml/min), metabolism of MTX to 7- OHMTX was minor (partial metabolic clearance = 0.041 ± 0.023 ml/min). MTX concentrations in bile surpassed those in the input perfusate by approximately 100-fold. Pretreatment of rats (n = 7) with PB did not change significantly the steady-state hepatic, biliary and partial metabolic clearances of 50 µmol/l MTX. An interesting result is a 38% increase in the hepatic vascular resistance of non-pretreated livers caused by MTX. The results suggest that in rats, pretreatment with PB has no effect on the hepatobiliary transport and hydroxylation of MTX.

Dose-Dependent Inhibition of Transporter-Mediated Hepatic Uptake and Biliary Excretion of Methotrexate by Cyclosporine A in an Isolated Perfused Rat Liver Model

“…1 and Figs. 2 and 4) are in agreement with previous reports16, 34, 42, 43 on the hepatobiliary disposition of MTX in different IPRL models. In one of the earlier studies, Strum and Liem34 demonstrated that the hepatic uptake of MTX in a recirculating IPRL is a saturable process with a maximum velocity ( V max ) of 11.1 µmol/h/g and a Michaelis–Menten constant ( K m ) of 1.3 mM.…”

“…A similar observation was also made by Strum and Liem34 who showed that the biliary excretion rate of MTX paralleled its hepatic uptake rate at low perfusate concentrations of MTX. Furthermore, an unexpected lack of effect of Mrp2 induction by phenobarbital on the biliary excretion rate of MTX in a recirculating IPRL model with an initial MTX concentration similar to ours was attributed to a rate‐limiting hepatic sinusoidal uptake 43. Collectively, these studies indicate that at or below the concentrations used in our studies, the hepatic uptake is the rate‐limiting step in the biliary excretion of MTX.…”

“…3, middle) is strikingly close to this reported value. In yet another study,43 it was shown that the biliary clearance of MTX accounted for 97% of its hepatic clearance, suggesting an extensive biliary excretion and minimal role for metabolism of MTX in IPRL. Nevertheless, all of these studies are in agreement with the observations made in our current study with the Control livers.…”

Melatonin protects against methotrexate hepatotoxicity in young rats: Impact of PI3K/Akt/mTOR signaling

“…MTX, a commonly used antimetabolite drug in cancer treatment, is known to have toxic effects through the dysregulation of oxidative stress that occurs during its metabolism in the liver. [ 13 ] These oxidative reactions can cause hepatotoxicity, which consists of hepatic steatosis, cholestasis, fibrosis, and cirrhosis. [ 14 ] In addition, several studies have shown that the interaction of oxidants and antioxidants is linked with the development of several pathological processes associated with chemotherapy‐induced organ injury, particularly in the liver and kidney.…”