Early endolysosomal dysfunction is a contributing factor to gadolinium-based contrast agent mouse renal proximal tubule epithelial cell injury

The prevalence of contrast-enhanced magnetic resonance imaging (MRI) examinations and the absence of safer alternatives to gadolinium-based contrast agents (GBCAs) make the associated adverse effects of GBCAs much more concerning. Safety concerns arise from the toxic behavior of heavy metal gadolinium (Gd³⁺) and the potential release of the metal from the chelating ligand. Renal insufficiency and other patient factors increase the susceptibility to the toxic effects of GBCAs. It is, therefore, imperative that the molecular and cellular mechanisms underlying GBCA toxicity be defined. This study aims to determine GBCA-induced endolysosomal dysfunction in mouse renal proximal tubule epithelial cells. Loss of cell viability was agent- and time-dependent, and proximal tubule injury was detectable following 24 h linear GBCA exposure. Both classes of GBCAs displayed lysosomotropic behaviors, characterized by early lysosomal enlargement and lysosomal injury. Hijacking of the endolysosomal system by these agents inhibited cathepsin processing by blocking the transport and maturation of cathepsin B (CTSB) and cathepsin D (CTSD). Lysosomal enlargement coincided with the translocation of CTSB and CTSD from the lysosomal lumen to the cytosol, suggesting lysosomal membrane destabilization. Even though both agents displayed a similar response, linear exposures appeared to exhibit a greater effect. Disturbance of mitochondrial activity and loss of cell viability occurs downstream of early lysosome damage. This effect was partially restored by lysosomal protease inhibitor co-treatment. This data suggests that GBCA exposures induce a lysosomal stress response, and partial LMP occurs upstream of mitochondrial dysfunction and resultant cellular injury.