Cisplatin-induced injury of the renal distal convoluted tubule is associated with hypomagnesaemia in mice.

BACKGROUND Cisplatin is an effective anti-neoplastic drug, but its clinical use is limited due to dose-dependent nephrotoxicity. The majority of cisplatin-treated patients develop hypomagnesaemia, often associated with a reduced glomerular filtration rate (GFR), polyuria and other electrolyte disturbances. The aim of this study is to unravel the molecular mechanism responsible for these particular electrolyte disturbances. METHODS Two groups of 10 mice were injected intraperitoneally three times, once every 4 days, with cisplatin (5 mg/kg body weight,) or vehicle. Serum and urine electrolyte concentrations were determined. Next, renal mRNA levels of distal convoluted tubule (DCT) genes epithelial Mg(2+) channel TRPM6, the Na(+)-Cl(-) cotransporter (NCC), and parvalbumin (PV), as well as marker genes for other tubular segments were measured by real-time qPCR. Subsequently, renal protein levels of NCC, PV, aquaporin 1 and aquaporin 2 were determined using immunoblotting and immunohistochemistry (IHC). RESULTS The cisplatin-treated mice developed significant polyuria (2.5 ± 0.3 and 0.9 ± 0.1 mL/24 h, cisplatin versus control, P < 0.05), reduced creatinine clearance rate (CCr) (0.18 ± 0.02 and 0.26 ± 0.02 mL/min, cisplatin versus control, P < 0.05) and a substantially reduced serum level of Mg(2+) (1.23 ± 0.03 and 1.58 ± 0.03 mmol/L, cisplatin versus control, P < 0.05), whereas serum Ca(2+), Na(+) and K(+) values were not altered. Measurements of 24 h urinary excretion demonstrated markedly increased Mg(2+), Ca(2+), Na(+) and K(+) levels in the cisplatin-treated group, whereas Pi levels were not changed. The mRNA levels of TRPM6, NCC and PV were significantly reduced in the cisplatin group. The expression levels of the marker genes for other tubular segments were unaltered, except for claudin-16, which was significantly up-regulated by the cisplatin treatment. The observed DCT-specific down-regulation was confirmed at the protein level. CONCLUSIONS The present study identified the DCT as an important cisplatin-affected renal segment, explaining the high prevalence of hypomagnesaemia following treatment.