Abstract
Hepatic clearance of erythromycin (Ery) is significantly reduced in patients with end stage renal disease. Since Ery is primarily eliminated via excretion of unchanged drug in the bile, we suspect that this change could be due to the effect of uremic toxins on hepatic uptake and/or efflux transporters. Using rat hepatocytes and microsomes as model proof of concept systems, we examined six uremic toxins, 3-carboxy-4-methyl-5-propyl-2-furan-propanoic acid (CMPF), indoxyl sulfate (IS), hippuric acid (HA), indole acetic acid (IA), guanidinosuccinic acid (GSA), and indoxyl-β-d-glucuronide (IG), for their effects on Ery uptake and metabolism. Ery and the metabolite N-demethyl-Ery were measured by liquid chromatography/tandem mass spectrometry. The uptake of Ery by rat hepatocytes was markedly inhibited by rifampin and digoxin, but not by quinidine, suggesting that Oatp2 plays a major role in the uptake of Ery. At 50 μM, CMPF significantly (p < 0.05) reduced hepatocyte accumulation of Ery and N-demethyl-Ery. At higher concentrations (>200 μM), CMPF appears to also inhibit the enzymatic metabolism of Ery. In contrast, IS did not significantly inhibit the hepatocyte uptake of Ery, even at the highest concentration (800 μM) tested, but reduced metabolite generation (p < 0.001). The other uremic toxins, HA, IA, IG, and GSA, did not affect either hepatic uptake or microsomal metabolism of Ery. CMPF, IS, and HA were shown not to inhibit differential P-glycoprotein transport of Ery in cellular systems. Our results suggest that CMPF can directly inhibit the uptake of Ery by inhibiting Oatp2, whereas IS is more likely to inhibit the enzymatic metabolism of Ery.
Footnotes
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During the course of this work, H.S. received stipend support initially through National Institutes of Health Clinical Pharmacology Training Grant T32 GM07456 and subsequently through a PhRMA postdoctoral fellowship in pharmacology. These studies were supported in part by National Institutes of Health Grant GM61390.
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Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
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doi:10.1124/dmd.104.000521.
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ABBREVIATIONS: Ery, erythromycin; Oatp, organic anion-transporting polypeptide; ESRD, end stage renal disease; CMPF, 3-carboxy-4-methyl-5-propyl-2-furan-propanoic acid; GSA, guanidinosuccinic acid; IG, indoxyl-β-d-glucuronide; IS, indoxyl sulfate; HA, hippuric acid; UCSF, University of California, San Francisco; GG918, GF120918: N-(4-[2-(1,2,3,4-tetrahydro-6,7-dimethoxy-2-isoquinolinyl)ethyl]-phenyl)-9,10-dihydro-5-methoxy-9-oxo-4-acridine carboxamide; LC/MS/MS, liquid chromatography/tandem mass spectrometry; HBSS-H, Hanks' balanced salt solution with 22.5 mM HEPES; B, basolateral; A, apical; IA, indole acetic acid; P-gp, P-glycoprotein; fu, unbound fraction.
- Received May 7, 2004.
- Accepted July 30, 2004.
- The American Society for Pharmacology and Experimental Therapeutics
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