Abstract
Nephrotoxicity is the dose-limiting factor for colistin, but the exact mechanism is unknown. This study aimed to investigate the roles of the mitochondrial, death receptor, and endoplasmic reticulum pathways in colistin-induced nephrotoxicity. Mice were intravenously administered 7.5 or 15 mg of colistin/kg of body weight/day (via a 3-min infusion and divided into two doses) for 7 days. Renal function, oxidative stress, and apoptosis were measured. Representative biomarkers involved in the mitochondrial, death receptor, and endoplasmic reticulum pathways were investigated, and the key markers involved in apoptosis and autophagy were examined. After 7-day colistin treatment, significant increase was observed with blood urea nitrogen, serum creatinine, and malondialdehyde, while activities of superoxide dismutase (SOD) and catalase decreased in the kidneys. Acute tubular necrosis and mitochondrial dysfunction were detected, and colistin-induced apoptosis was characterized by DNA fragmentation, cleavage of poly(ADP-ribose) polymerase (PARP-1), increase of 8-hydroxydeoxyguanosine (8-OHdG), and activation of caspases (caspase-8, -9, and -3). It was evident that colistin-induced apoptosis involved the mitochondrial pathway (downregulation of Bcl-2 and upregulation of cytochrome C [cytC] and Bax), death receptor pathway (upregulation of Fas, FasL, and Fas-associated death domain [FADD]), and endoplasmic reticulum pathway (upregulation of Grp78/Bip, ATF6, GADD153/CHOP, and caspase-12). In the 15-mg/kg/day colistin group, expression of the cyclin-dependent kinase 2 (CDK2) and phosphorylated JNK (p-JNK) significantly increased (P < 0.05), while in the 7.5-mg/kg/day colistin group, a large number of autophagolysosomes and classic autophagy were observed. Western blot results of Beclin-1 and LC3B indicated that autophagy may play a protective role in colistin-induced nephrotoxicity. In conclusion, this is the first study to demonstrate that all three major apoptosis pathways and autophagy are involved in colistin-induced nephrotoxicity.