Pravastatin transport across the hepatocyte canalicular membrane requires both ATP and a transmembrane pH gradient

Determination of Acid Dissociation Constant of Pravastatin under Degraded Conditions by Capillary Zone Electrophoresis

The acid dissociation constant of pravastatin was determined under degraded conditions. Pravastatin was degraded in an acidic solution (pH = 2.0) for 5 h, and the degradation solution was subjected to the measurement of the effective electrophoretic mobility by capillary zone electrophoresis. Although the amount of pravastatin decreased by the acid degradation, its acid dissociation constant was successfully determined with the residual pravastatin through its effective electrophoretic mobility. The determined acid dissociation constant value agreed well with the one obtained with freshly prepared solution and with some reported values.

Effect of bile acids on the biliary excretion of pravastatin in rats

AIM

The biliary excretion of pravastatin, an HMG-CoA reductase inhibitor, is mediated by the multidrug resistance protein 2, but a recent report suggests that pravastatin is also a substrate of the bile salt export pump, which transports bile acids. We examined the effects of bile acids on biliary pravastatin excretion in rats.

METHODS

The effect of taurocholate on biliary pravastatin excretion, and that of pravastatin on biliary taurocholate excretion was examined in bile-drained rats.

RESULTS

Taurocholate had no effect on biliary pravastatin excretion, whereas pravastatin with a dose to cause biliary excretory maximum significantly inhibited biliary taurocholate excretion.

CONCLUSION

These data indicate that increased serum bile acids will not affect the pharmacokinetics of pravastatin in patients with hepatobiliary diseases. Although pravastatin inhibited biliary taurocholate excretion, it is unlikely that pravastatin significantly inhibits biliary bile acid excretion by its therapeutic doses.

Relationship between drug/metabolite exposure and impairment of excretory transport function

The quantitative impact of excretory transport modulation on the systemic exposure to xenobiotics and derived metabolites is poorly understood. This article presents fundamental relationships between exposure and loss of a specific excretory process that contributes to overall clearance. The mathematical relationships presented herein were explored on the basis of hepatic excretory data for polar metabolites formed in the livers of various transporter-deficient rodents. Experimental data and theoretical relationships indicated that the fold change in exposure is governed by the relationship, 1/(1 - f(e)), where f(e) is the fraction excreted by a particular transport protein. Loss of function of a transport pathway associated with f(e) < 0.5 will have minor consequences (<2-fold) on exposure, but exposure will increase exponentially in response to loss of function of transport pathways with f(e) > 0.5. These mathematical relationships may be extended to other organs, such as the intestine and kidney, as well as to systemic drug exposure. Finally, the relationship between exposure and f(e) is not only applicable to complete loss of function of a transport pathway but also can be extended to partial inhibition scenarios by modifying the equation with the ratio of the inhibitor concentration and inhibition constant.

Improving effect of ethyl eicosapentanoate on statin-induced rhabdomyolysis in Eisai hyperbilirubinemic rats

The effect of ethyl eicosapentanoate (EPA-E) on statin-induced rhabdomyolysis was investigated by co-administration of EPA-E and pravastatin (PV), as a typical statin, to Eisai hyperbilirubinemic rats (EHBR). It was confirmed that the plasma PV concentration was not affected by simultaneous administration of EPA-E, and there was no cumulative increase of PV during prolonged co-administration of EPA-E and PV. Muscular degeneration was prominent (incidence 5/5; average grade 3.5 (range 2-4)) in EHBR treated with PV alone at 200 mg/kg/day for 14 days, but co-administration of EPA-E at doses of 100, 300, and 1000 mg/kg/day decreased the average grades to 1.4 (range 0.3-3.0), 0.5 (0.2-1.0), and 0.6 (0.0-1.7), respectively. Creatine phosphokinase (CPK) and myoglobin levels in plasma were well correlated with the grade of skeletal muscle degeneration. Thus, EPA-E appears to reduce the severity of statin-induced rhabdomyolysis.

Bile salt export pump (BSEP/ABCB11) can transport a nonbile acid substrate, pravastatin

Pravastatin is a well known 3-hydroxy-3-methylglutaryl-CoA reductase inhibitor. Cumulative studies have shown that pravastatin is taken up into hepatocytes by the organic anion transporting polypeptide family transporters and excreted into the bile as an intact form by multidrug resistance-associated protein 2 (MRP2). It is generally accepted that the bile salt export pump (BSEP/ABCB11) mainly transports bile acids and plays an indispensable role in their biliary excretion. Interestingly, we found that BSEP could accept pravastatin as a substrate. Significant ATP-dependent uptake of pravastatin by human BSEP (hBSEP)- and rat BSEP (rBsep)-expressing membrane vesicles was observed, and the ratio of the uptake activity of pravastatin to that of taurocholic acid (TCA) by hBSEP was 3.3-fold higher than that by rBsep. The K(m) value of pravastatin for hBSEP was 124 muM. A mutual inhibition study between TCA and pravastatin revealed that they competitively interact with hBSEP. Several statins inhibited the hBSEP- and rBsep-mediated uptake of TCA; however, the specific uptake of other statins (cerivastatin, fluvastatin, and pitavastatin) by hBSEP and rBSEP was not detected. The inhibitory effects of hydrophilic statins (pravastatin and rosuvastatin) on the uptake of TCA by BSEP were relatively lower than those of lipophilic statins. These data suggest that BSEP may be partly involved in the biliary excretion of pravastatin in both rats and humans.

Eisai hyperbilirubinemic rat (EHBR) as an animal model affording high drug-exposure in toxicity studies on organic anions

The Eisai hyperbilirubinemic rat (EHBR) should be a useful animal model for studies on the toxicity of organic anions which are substrates of multidrug resistance-associated protein 2 (Mrp2), since the systemic exposure to these compounds is expected to be increased in EHBR. In this study, we tested the value of EHBR for this purpose, using pravastatin (PV) and methotrexate (MTX) as model compounds. In the case of a single oral dose of PV (200 mg/kg), C(max) in plasma was 4.0-fold higher and AUC(0-infinity) was 3.6-fold larger than those of normal Sprague-Dawley rats (SDR), respectively. When multiple doses of PV were given to EHBR without co-administration of any other compound, drug-induced skeletal muscle toxicity (myopathy/rhabdomyolysis) and increased creatine phosphokinase (CPK) level were observed, whereas a control experiment using SDR did not show any toxic change. When a single dose of MTX (0.6 mg/kg) was given to EHBR orally, C(max) was 1.7-fold higher and AUC(0-infinity) was 1.6-fold larger than those of SDR, respectively. When multiple doses of MTX were given to EHBR, the changes in bone marrow, spleen and intestines were more severe than those in SDR. These findings support the view that EHBR would be a valuable animal model for toxicity studies on organic anion compounds which are substrates of Mrp2.

Changes in biliary excretory mechanisms in rats with ethinyloestradiol-induced cholestasis

Several excretory pathways for cholephilic compounds have been known. To examine the changes in excretory pathways in cholestasis induced by ethinyloestradiol, various bile acids, organic anions and organic cations were intravenously administered to ethinyloestradiol-treated rats and their biliary excretion was studied. Biliary excretion of taurocholate was slightly delayed, but its excretory maximum was markedly decreased. Biliary excretion of lithocholate-3-O-glucuronide, leukotriene C4, sulphobromophthalein and pravastatin was markedly impaired to a similar extent. Biliary excretion of vinblastine, a P-glycoprotein substrate, was increased, suggesting increased expression of P-glycoprotein. In contrast, biliary excretion of erythromycin, a cationic antibiotic, was markedly impaired. In conclusion, ethinyloestradiol treatment altered the biliary excretion of organic compounds, which may partly be related to changes of the canalicular transporters.

Effects of organic anions and bile acid conjugates on biliary excretion of pravastatin in the rat

PURPOSE

Biliary organic anion excretion is mediated by an ATP-dependent primary active transporter, a so-called canalicular multispecific organic anion transporter (cMOAT). As there appear to be many canalicular organic anion transports, we examined the effects of various organic anions and bile acid conjugates on the biliary excretion of pravastatin in rats.

METHODS

[14C]pravastatin was intravenously injected into rats with bile drainage in the presence and absence of the continuous infusion of organic anions and bile acids, and radioactivity of its biliary excretion was studied.

RESULTS

Biliary excretion of [14C]pravastatin was markedly inhibited by sulfobromophthalein-glutathione, taurolithocholate-3-sulfate, ursodeoxycholate-3, 7-sulfate, and ursodeoxycholate-3-O-glucuronide. In contrast, dibromosulfophthalein only slightly inhibited biliary pravastatin excretion, and cefpiramide did not affect biliary pravastatin excretion.

CONCLUSIONS

These findings further support the multiplicity of canalicular organic anion transport, and pravastatin is considered to be excreted through a canalicular transporter which is absent in EHBR in addition to through cMOAT.

Effects of organic anions and bile acid conjugates on biliary excretion of LTC4 in the rat

Biliary organic anion excretion is mediated by an ATP-dependent primary active transporter, so-called canalicular multispecific organic anion transporter (cMOAT). On the other hand, a multiplicity of canalicular organic anion transport has been suggested. Therefore, to examine the substrate specificity of cMOAT using inhibition of excretion of [3H] LTC4-derived radioactive products in the bile as a marker, we examined the effects of various organic anions and bile acid conjugates on the biliary excretion of LTC4 in rats. Biliary excretion of the metabolites of [3H] LTC4, which was injected via the femoral vein, was markedly inhibited by sulfobromophthalein-glutathione, taurolithocholate-3-sulfate, and ursodeoxycholate-3-O-glucuronide. In contrast, dibromosulfophthalein and cefpiramide slightly inhibited, and pravastatin, taurocholate, and 3,7-sul-UDC did not affect biliary LTC4 excretion. Furthermore, vinblastine and phenothiazine, a P-glycoprotein substrate and inducer, did not affect biliary LTC4 excretion. Among various organic anions and bile acid conjugates, LTC4, sulfobromophthalein-glutathione, taurolithocholate-3-sulfate, and ursodeoxycholate-3-O-glucuronide may be good substrates for cMOAT.