Impaired clearance of methotrexate in organic anion transporter 3 (Slc22a8) knockout mice: a gender specific impact of reduced folates.
OBJECTIVE
To elucidate the role of the renal basolateral transporter, Oat3, in the disposition of methotrexate.


METHODS
Chinese hamster ovary cells expressing mouse Oat3 were used to determine kinetics and specificity of inhibition of methotrexate transport. Methotrexate clearance was then examined in vivo in wildtype and Oat3 knockout mice.


RESULTS
NSAIDs, beta-lactams, and uremic toxins inhibited mOat3-mediated methotrexate uptake by 70-100%, while folate, leucovorin, and 5-methyltetrahydrofolate inhibited transport by 25-50%. A Km of 60.6 +/- 9.3 microM for methotrexate transport was determined. Oat3 knockout mice exhibited reduced methotrexate-to-inulin clearance ratios versus wildtype. Male wildtype mice, but not knockouts or females, demonstrated significantly accelerated methotrexate clearance in response to reduced folates. Reduced folates also markedly inhibited hepatic methotrexate accumulation in males, but not females, and the response was independent of Oat3 function.


CONCLUSIONS
Oat3 contributes to methotrexate clearance, but represents only one component responsible for methotrexate's elimination. Therefore, in patients, dysfunctional hOAT3 polymorphisms or drug competition for hOAT3 transport may severely impact methotrexate elimination only when redundant means of methotrexate removal are also compromised. Furthermore, the present findings suggest that reduced-folate administration only influences methotrexate disposition in males, with the renal reduced-folate response influenced by OAT3 function.
Department of Pharmaceutical Sciences, Medical University of South Carolina, 280 Calhoun Street Rm. QE218, PO Box 250140, Charleston, South Carolina 29425, USA.
Adam L
AL
VanWert
Douglas H
DH
Sweet
D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D003412:Cricetulus; D005260:Female; D005492:Folic Acid / Q000378:metabolism*; D007668:Kidney / Q000378:metabolism; D008297:Male; D008657:Metabolic Clearance Rate; D008727:Methotrexate / Q000493:pharmacokinetics*; D051379:Mice; D018345:Mice, Knockout; D029362:Organic Anion Transporters, Sodium-Independent / Q000502:physiology*; D012727:Sex Characteristics
D029362:Organic Anion Transporters, Sodium-Independent; C114338:organic anion transport protein 3; D005492:Folic Acid; D008727:Methotrexate