Electrolyte Blood Press.  2011 Jun;9(1):7-15. 10.5049/EBP.2011.9.1.7.

The Role of Proximal Nephron in Cyclophosphamide-Induced Water Retention: Preliminary Data

• Kim S
• Jo CH
• Park JS
• Han HJ
• Kim GH

• KMID: 1497136
• DOI: http://doi.org/10.5049/EBP.2011.9.1.7

Abstract

Cyclophosphamide is clinically useful in treating malignancy and rheumatologic disease, but has limitations in that it induces hyponatremia. The mechanisms by which cyclophosphamide induces water retention in the kidney have yet to be identified. This study was undertaken to test the hypothesis that cyclophosphamide may produce water retention via the proximal nephron, where aquaporin-1 (AQP1) and aquaporin-7 (AQP7) water channels participate in water absorption. To test this hypothesis, we gave a single dose of intraperitoneal cyclophosphamide to male Sprague-Dawley rats and treated rabbit proximal tubule cells (PTCs) with 4-hydroperoxycyclophosphamide (4-HC), an active metabolite of cyclophosphamide. In the short-term 3-day rat study, AQP1 protein expression was significantly increased in the whole kidney homogenates by cyclophosphamide administration at 48 (614 +/- 194%, P < 0.005), and 96 (460 +/- 46%, P < 0.05) mg/kg BW compared with vehicle-treated controls. Plasma sodium concentration was significantly decreased (143 +/- 1 vs. 146 +/- 1 mEq/L, P < 0.05) by cyclophosphamide 100 mg/kg BW in the long-term 6-day rat study. When primary cultured rabbit PTCs were treated with 4-HC for 24 hours, the protein expressions of AQP1 and AQP7 were increased in a dose-dependent manner. Quantitative polymerase chain reaction revealed no significant changes in the mRNA levels of AQP1 and AQP7 from cyclophosphamide-treated rat renal cortices. From these preliminary data, we conclude that the proximal nephron may be involved in cyclophosphamide-induced water retention via AQP1 and AQP7 water channels. Further studies are required to demonstrate intracellular mechanisms that affect the expression of AQP proteins.

Keyword

cyclophosphamide; aquaporin 1; hyponatremia; water; proximal tubule

MeSH Terms

Absorption
Animals
Aquaporin 1
Aquaporins
Cyclophosphamide
Factor IX
Humans
Hyponatremia
Kidney
Male
Nephrons
Plasma
Polymerase Chain Reaction
Proteins
Rats
Rats, Sprague-Dawley
Retention (Psychology)
RNA, Messenger
Sodium
Water
Aquaporin 1
Aquaporins
Cyclophosphamide
Factor IX
Proteins
RNA, Messenger
Sodium
Water

Figure

• 

  Fig. 1 Immunoblot Analysis for Aquaporin-1 (AQP1) and Aquaporin-2 (AQP2) from Whole Kidneys of Animal Experiment I. Each lane was loaded with a protein sample from a different rat. GAPDH, glyceraldehyde-3-phosphate dehydrogenase.*P < 0.05.†P < 0.005 compared with vehicle-treated controls.

• 

  Fig. 2 Immunoblot Analysis for Aquaporin-1 (AQP1) and Aquaporin-2 (AQP2) from Rnal Cortices of Animal Experiment II. Each lane was loaded with a protein sample from a different rat. No statistically significant differences were found between the groups.

• 

  Fig. 3 Reverse Transcription Polymerase Chain Reaction (PCR) from Renal Cortices of Animal Experiment II. Each lane was loaded with a cDNA sample from a different rat. AQP1, aquaporin-1; AQP2, aquaporin-2; V2R, vasopressin-2 receptor; AQP7, aquaporin-7; GAPDH, glyceraldehyde-3-phosphate dehydrogenase.

• 

  Fig. 4 Quantitative Polymerase Chain Reaction (PCR) from Renal Cor tices of Animal Experiment II. AQP1, aquaporin-1; AQP2, aquaporin-2; AQP7, aquaporin-7; V2R, vasopressin-2 receptor. No statistically significant differences were found between the groups.

• 

  Fig. 5 Immunoblot for Aquaporin-1 (AQP1) and Aquaporin-7 (AQP7) from Primary Cultured Rabbit Renal Proximal Tubule Cells. Cells were treated for 24 hours with each concentration of 4-hydroperoxycyclophosphamide (4-HC).

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