DOI
https://doi.org/10.25772/BY29-Q140
Defense Date
2012
Document Type
Dissertation
Degree Name
Doctor of Philosophy
Department
Pharmaceutical Sciences
First Advisor
Douglas H. Sweet
Abstract
Fluoroquinolones (FQ) are broad-spectrum charged antimicrobials exhibiting excellent tissue/fluid permeation. Thus, FQ disposition depends essentially on active transport and facilitative diffusion. Although most early transporter studies investigating renal elimination of FQs have focused on apical efflux of FQs from renal proximal tubule cell (RPTC) into urine, their basolateral uptake mechanism(s) from blood into RPTC (i.e., first step to tubular secretion) has not yet been explored in detail. Renally expressed SLC22 members: organic anion (OATs) and cation (OCTs) transporters are known to transport such small organic ionic substrates (molecular weight ~400 Da). Hence it is of interest to explore the role of these basolateral transporters in renal elimination of FQs, and to further quantitatively assess their impact in clinically observed FQ drug-drug interactions (DDI). An initial systematic review of clinical literature for FQs (n=18) demonstrated substantial differences among their renal clearance (CLren~46-fold) and unbound renal clearance (CLrenu~20-fold), and suggested that tubular secretion and reabsorption could be major determinants of FQ half-life, efficacy, and DDIs. FQs (n=13) identified from the above review were investigated by in-vitro transport studies using stably transfected cell lines, for potential interactions with organic cation [human (h) OCT1, hOCT2 and hOCT3] and anion [mouse (m) and hOAT3, hOAT1; and hOAT4] transporters. Further, kinetic inhibition studies were conducted to determine inhibition potency (Ki/IC50 values) for those FQs exhibiting significant OCT/OAT inhibition in preliminary interaction experiments. Gatifloxacin, moxifloxacin, prulifloxacin, and sparfloxacin were determined to be competitive inhibitors of hOCT1 with Ki = 250±18, 161±19, 136±33, and 94±8 μM, respectively. Moxifloxacin competitively inhibited hOCT3-mediated uptake, Ki = 1,598±146 μM. Enoxacin, fleroxacin, levofloxacin, lomefloxacin, moxifloxacin, prulifloxacin, and sparfloxacin exhibited competitive inhibition for mOat3 with Ki = 396±15, 817±31, 515±22, 539±27, 1356±114, 299±35, 205±12 μM, respectively. Fleroxacin and pefloxacin were found to inhibit hOAT1 with IC50 = 2228±84 and 1819±144 respectively. Despite expression in enterocytes, hepatocytes, and RPTC, hOCT3 does not appear to contribute significantly to FQ disposition. However, due to hepatic and potential RPTC expression, hOCT1 could play an important role in elimination of these antimicrobials. Among renally expressed OATs in humans, hOAT1 and hOAT3 are likely to be involved in FQ elimination.
Rights
© The Author
Is Part Of
VCU University Archives
Is Part Of
VCU Theses and Dissertations
Date of Submission
August 2012