A Murine Model Of Kidney Injury: The role of SMPDL3b In Radiation And Cisplatin-Induced Nephrotoxicity

Abstract

Cisplatin is widely used as a chemotherapeutic agent and a known radiosensitizer. The current study aimed to investigate the role of lipid-modulating enzyme sphingomyelin phosphodiesterase acid-like 3B (SMPDL3b) in cisplatin toxicity. Nephrotoxicity is dose-limiting toxicity. Cultured oocytes were treated with rituximab mAb (100 μg/ml) or IgG (100 μg/ml) 30 minutes before irradiation with 0-8 Gy, with or without Cisplatin (2μM). In other experiments, 10–14-week old C57BL/6 male and female mice were given bilateral kidney X-irradiation (4Gyx1, 6 Gyx5, and 2Gyx24) with or without Cisplatin (6mg/kg, IP). Animals received rituximab mAb (RTX) or IgG (50mg/kg; IV) 30 minutes before radiation treatment. Functional kidney parameters (serum BUN, hematocrit, and creatinine), histopathological assessments (oil red staining, H&E, Periodic Acid-Schiff, and TEM) and biochemical changes were studied at baseline, 10- and 20-weeks post-chemo-radiotherapy. Glomerular filtration rate (GFR) was estimated at 10- and 20-weeks post-radiation using FITC-sinistrin based transdermal monitor and iSMAART dynamic contrast-enhanced (DCE) imaging. RT and concurrent Cisplatin (2 μM) produced time-dependent apoptosis in wild-type human podocytes, causing an 85% increase in caspase 3 activity 2h post-RT (8Gy). Different doses of RT, 1x4Gy, 1x10Gy, and 1x14Gy increased glomerular base membrane (GBM) thickness in irradiated mice significantly (100%, 150%, and 200% respectively). Cisplatin and RT (1x4Gy) increased GBM thickness from 225nm to 425nm, respectively (p = 0.01). The eGFR values changed significantly from 1010±214 to 718±205, 687±175, 508±56, 596±180, and 639±221 mL/min after x4Gy, 1x10Gy, 1x14Gy, 5x6Gy, and 24x2Gy, respectively. RTX pretreatment improved eGFR and other functional parameters (serum BUN, hematocrit, serum creatinine, and urine albumin/creatinine ratio (ACR) significantly post chemoradiotherapy. RTX pretreatment protected podocytes cytoskeletal remodeling in vitro and foot process effacement in vivo. SMPDL3b expression and podocytes count significantly decreased post chemoradiotherapy. RTX ameliorated SMPDL3b down-regulation, and improved podocytes count significantly. This study shows that RTX pretreatment protects podocytopathy in vitro and chemoradiation induced kidney injury in vivo. SMPDL3b may be an important therapeutic target for radiation-induced kidney injuries in cancer patients.