title: Cyclophosphamide-induced vasopressin-independent activation of aquaporin-2 in the rat kidney.
abstract: Because cyclophosphamide-induced hyponatremia was reported to occur without changes in plasma vasopressin in a patient with central diabetes insipidus, we hypothesized that cyclophosphamide or its active metabolite, 4-hydroperoxycyclophosphamide (4-HC), may directly dysregulate the expression of water channels or sodium transporters in the kidney. To investigate whether intrarenal mechanisms for urinary concentration are activated in vivo and in vitro by treatment with cyclophosphamide and 4-HC, respectively, we used water-loaded male Sprague-Dawley rats, primary cultured inner medullary collecting duct (IMCD) cells, and IMCD suspensions prepared from male Sprague-Dawley rats. In cyclophosphamide-treated rats, significant increases in renal expression of aquaporin-2 (AQP2) and Na-K-2Cl cotransporter type 2 (NKCC2) were shown by immunoblot analysis and immunohistochemistry. Apical translocation of AQP2 was also demonstrated by quantitative immunocytochemistry. In both rat kidney and primary cultured IMCD cells, significant increases in AQP2 and vasopressin receptor type 2 (V2R) mRNA expression were demonstrated by real-time quantitative PCR analysis. Confocal laser-scanning microscopy revealed that apical translocation of AQP2 was remarkably increased when primary cultured IMCD cells were treated with 4-HC in the absence of vasopressin stimulation. Moreover, AQP2 upregulation and cAMP accumulation in response to 4-HC were significantly reduced by tolvaptan cotreatment in primary cultured IMCD cells and IMCD suspensions, respectively. We demonstrated that, in the rat kidney, cyclophosphamide may activate V2R and induce upregulation of AQP2 in the absence of vasopressin stimulation, suggesting the possibility of drug-induced nephrogenic syndrome of inappropriate antidiuresis (NSIAD).
authors.affiliation: Institute of Biomedical Sciences, Hanyang University College of Medicine, Seoul, Korea;
authors.forename: Sua
authors.initials: S
authors.lastname: Kim
authors.affiliation: Department of Biochemistry and Cell Biology, Kyungpook National University School of Medicine, Taegu, Korea; and.
authors.forename: Hyo-Jung
authors.initials: HJ
authors.lastname: Choi
authors.affiliation: Institute of Biomedical Sciences, Hanyang University College of Medicine, Seoul, Korea;
authors.forename: Chor Ho
authors.initials: CH
authors.lastname: Jo
authors.affiliation: Division of Nephrology, Department of Internal Medicine, Hanyang University College of Medicine, Seoul, Korea.
authors.forename: Joon-Sung
authors.initials: JS
authors.lastname: Park
authors.affiliation: Department of Biochemistry and Cell Biology, Kyungpook National University School of Medicine, Taegu, Korea; and.
authors.forename: Tae-Hwan
authors.initials: TH
authors.lastname: Kwon
authors.affiliation: Institute of Biomedical Sciences, Hanyang University College of Medicine, Seoul, Korea; Division of Nephrology, Department of Internal Medicine, Hanyang University College of Medicine, Seoul, Korea kimgh@hanyang.ac.kr.
authors.forename: Gheun-Ho
authors.initials: GH
authors.lastname: Kim
mesh_terms: D000818:Animals; D051399:Aquaporin 2 / Q000378:metabolism*; D002478:Cells, Cultured; D003520:Cyclophosphamide / Q000031:analogs & derivatives* / Q000494:pharmacology*; D007668:Kidney / Q000187:drug effects* / Q000378:metabolism; D007685:Kidney Tubules, Collecting / Q000187:drug effects* / Q000378:metabolism; D008297:Male; D051381:Rats; D017207:Rats, Sprague-Dawley; D064466:Solute Carrier Family 12, Member 1 / Q000378:metabolism; D014667:Vasopressins / Q000378:metabolism*
chemical_list: D051399:Aquaporin 2; D064466:Solute Carrier Family 12, Member 1; D014667:Vasopressins; D003520:Cyclophosphamide; C011272:perfosfamide
keywords: Na-K-2Cl cotransporter type 2; aquaporin-2; cyclophosphamide; hyponatremia; vasopressin receptor type 2