Inhibition of Hepatobiliary Transport Activity by the Antibacterial Agent Fusidic Acid: Insights into Factors Contributing to Conjugated Hyperbilirubinemia/Cholestasis.
Conjugated hyperbilirubinemia accompanied by cholestasis is a frequent side effect during chronic treatment with the antimicrobial agent fusidic acid. Previous studies from our laboratory, addressing mechanisms of musculoskeletal toxicity arising from coadministration of fusidic acid with statins, demonstrated the ability of fusidic acid to potently inhibit human organic anion transporting polypeptides OATP1B1 (IC50= 1.6 μM) and OATP1B3 (IC50= 2.5 μM), which are responsible for the uptake-limited clearance of statins as well as bilirubin glucuronide conjugates. In the present work, inhibitory effects of fusidic acid were characterized against additional human hepatobiliary transporters [Na+/taurocholate cotransporting polypeptide (NTCP), bile salt export pump (BSEP), and multidrug resistance-associated proteins MRP2 and MRP3] as well as uridine glucuronosyl transferase (UGT1A1), which mediate the disposition of bile acids and bilirubin (and its conjugated metabolites). Fusidic acid demonstrated concentration-dependent inhibition of human NTCP- and BSEP-mediated taurocholic acid transport with IC50values of 44 and 3.8 μM, respectively. Inhibition of BSEP activity by fusidic acid was also consistent with the potent disruption of cellular biliary flux (AC50= 11 μM) in the hepatocyte imaging assay technology assay, with minimal impact on other toxicity end points (e.g., cytotoxicity, mitochondrial membrane potential, reactive oxygen species generation, glutathione depletion, etc.). Fusidic acid also inhibited UGT1A1-catalyzed β-estradiol glucuronidation activity in human liver microsomes with an IC50value of 16 μM. Fusidic acid did not demonstrate any significant inhibition of ATP-dependent LTC4 transport (IC50's > 300 μM) in human MRP2 or MRP3 vesicles. R values, which reflect maximal in vivo inhibition, were estimated from a static mathematical model by taking into consideration the IC50values generated in the various in vitro assays and clinically efficacious unbound fusidic acid concentrations. The magnitudes of in vivo interaction (R values) resulting from the inhibition of OATP1B1, UGT1A1, NTCP, and BSEP transport were ∼1.9-2.6, 1.1-1.2, 1.0-1.1, and 1.4-1.7, respectively, which are indicative of some degree of inherent toxicity risk, particularly via inhibition of OATP and BSEP. Collectively, these observations indicate that inhibition of human BSEP by fusidic acid could affect bile acid homeostasis, resulting in cholestatic hepatotoxicity in the clinic. Lack of direct inhibitory effects on MRP2 transport by fusidic acid suggests that conjugated hyperbilirubinemia does not arise via interference in MRP2-mediated biliary disposition of bilirubin glucuronides. Instead, it is possible that elevation in the level of bilirubin conjugates in blood is mediated through inhibition of hepatic OATPs, which are responsible for their reuptake and/or downregulation of MRP2 transporter as a consequence of cholestatic injury.
Kimberly
K
Lapham
Jonathan
J
Novak
Lisa D
LD
Marroquin
Rachel
R
Swiss
Biological Screening and Assay Development, Cyprotex , Watertown, Massachusetts 02472, United States.
Shuzhen
S
Qin
Biological Screening and Assay Development, Cyprotex , Watertown, Massachusetts 02472, United States.
Christopher J
CJ
Strock
Renato
R
Scialis
Michael D
MD
Aleo
Thomas
T
Schroeter
Heather
H
Eng
A David
AD
Rodrigues
Pharmacokinetics, Dynamics, and Metabolism Department, Pfizer Worldwide Research and Development , Cambridge, Massachusetts 02139, United States.
Amit S
AS
Kalgutkar