Glutathione S-transferase Mu-1 (GSTM1) Deficiency Exaggerates Cisplatin Nephrotoxicity

Background: Cisplatin is the first line chemotherapeutic agent for several cancers. However, its use is limited by significant toxicity, including acute kidney injury (AKI)in up to 30% of patients. Increased reactive oxygen species (ROS) generation plays a key role in cisplatin nephrotoxicity (CN). Glutathione-S-transferase Mu-1 (GSTM1) gene encodes GSTM1 enzyme that functions in the detoxification of electrophilic compounds. We previously reported that Gstm1 knockout (KO) mice have increased oxidative stress and susceptibility to kidney injury in chronic kidney disease (CKD) models, and CKD patients carrying the highly common null variant of GSTM1 gene are more susceptible to CKD progression. Here, we investigate the effect of GSTM1 in a chronic CN mouse model of AKI and in a human HK2 proximal tubular epithelial cell (PTEC) line model. Methods: Wild-type (WT) and Gstm1 KO male mice (12 weeks old) on FVB background were treated with cisplatin (9mg/kg) once per week for 4 weeks via IP injection. HK2 PTEC line deficient in GSTM1 was used to generate a stable GSTM1 overexpressing cell line (HK2-Tg). Cells were treated with cisplatin (60uM) for 24 hrs. Intracellular ROS was measured using ROS Assay Kit, and mitochondrial superoxide was measured by MitoSox. The color intensity of the images (three random fields of each image) was quantitated with Image J. Live cell numbers were counted with Trypan blue. Results: After 4 weeks cisplatin treatment, Gstm1 KO mice had a significant increase in serum creatinine measured by mass spec (0.13±0.157mg/ml), compared to WT mice (0.06±0.006 mg/ml) (n = 6 each, p=0.0043). There was a trend toward increase in BUN level (22.16 vs 14.77, p=0.309) in KO mice. Compared to HK2-Tg cells expressing GSTM1, HK2 cells deficient in GSTM1 displayed fewer % of live cells: HK2 39±2.95 vs HK2-Tg 54±2.37; p=0.003. Compared to vehicle, cisplatin treatment resulted in a higher fold of intracellular ROS production in HK2 compared to HK2-Tg PTECs (6.6 vs 3.9; p=0.03). Similarly, HK2 PTECs showed a larger fold increase in mitochondrial ROS level compared to HK2-Tg PTECs (23.5 vs 17.6; p=0.01). Conclusion: GSTM1 deficiency increases susceptibility to CN, which can be attributable to increased intracellular and mitochondrial ROS generation. Understanding how GSTM1 regulates ROS signaling pathway may lead to a novel therapeutic target in CN. Funding: NIDDK Support