Podocyte-Specific Smpdl3b Modulates Radiation-Induced Renal Dysfunction

Background: The underlying mechanisms responsible for the renal failure and proteinuria in radiation nephropathy remain largely unknown. Radiotherapy with or without chemotherapy may result in radiation-induced kidney injury in pelvic malignancies such as gynecologic cancers, lymphomas, gastrointestinal cancers, sarcomas of the upper abdomen and during total body irradiation. The current study investigates the role of sphingolipids in radiation-induced podocytopathy using a murine model. The molecular and functional effects of kidney irradiation were evaluated after single-dose exposures. Material/Methods: In cell culture, SMPDL3b expression post radiation (8Gy) was determined by real-time PCR (RT-PCR) and Western blotting. Morphological changes and DNA damage were detected post radiation using immunofluorescence microscopy. Wild-type C57BL/6 male and female mice (age 10-14 weeks) were irradiated with a single dose of X-ray (14 Gy) using an image guided small animal arc radiation treatment system (iSMAART). Rituximab/IgG was administered (50 mg/kg, intraperitoneal injection) 30 min before the single dose of irradiation. Functional kidney parameters, kidney histology, and gene expression were analyzed at 20, 30 and 40 weeks after irradiation. Results: Following irradiation, SMPDL3b expression at protein level was significantly reduced in vitro and in vivo. However, no significant changes were observed at the transcriptional level. Podocyte number also decreased significantly post radiation in vivo. iSMAART dynamic contrast enhanced (DCE) imaging data analysis showed reduced glomerular filtration rate post radiation. In agreement with the functional data, hematoxylin and eosin staining of kidney sections showed a multifocal increase in the number of pericytes, tubular atrophy, and glomerular damage. Periodic Acid-Schiff (PAS) staining showed an increase in glomerular mesangial matrix accumulation post radiation. Sirius red staining showed diffuse intertubular fibrosis, especially in the renal cortex post radiation. These histological changes were paralleled by the change in serum Creatinine, urine albumin. Rituximab pretreatment to mice, improved kidney functional parameters, vascular structure, normalization of pericyte coverage, suppress the development of fibrosis and tubular damage post irradiation. Conclusion: This study shows that rituximab pretreatment protects mice against radiation-induced nephrotoxicity, which may have therapeutic implications for radiation-induced injuries in cancer patients. Citation Format: Anis Ahmad, Alla Mitrofanova, Saba Ansari, Thirupandiyur Udayakumar, Jacek Bielawski, Alan Pollack, Alesia Fornoni, Brian Marples, Youssef Zeidan. Podocyte-specific SMPDl3b modulates radiation-induced renal dysfunction [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 904. doi:10.1158/1538-7445.AM2017-904