Glutathione and mitochondria determine acute defense responses and adaptive processes in cadmium-induced oxidative stress and toxicity of the kidney.

Cadmium (Cd) induces oxidative stress that ultimately defines cell fate and pathology. Mitochondria are the main energy-producing organelles in mammalian cells, but they also have a central role in formation of reactive oxygen species, cell injury, and death signaling. As the kidney is the major target in Cd toxicity, the roles of oxidative signature and mitochondrial function and biogenesis in Cd-related stress outcomes were investigated in vitro in cultured rat kidney proximal tubule cells (PTCs) (WKPT-0293 Cl.2) for acute Cd toxicity (1-30 µM, 24 h) and in vivo in Fischer 344 rats for sub-chronic Cd toxicity (1 mg/kg CdCl subcutaneously, 13 days). Whereas 30 µM Cd caused ~50 % decrease in cell viability, apoptosis peaked at 10 µM Cd in PTCs. A steep, dose-dependent decline in reduced glutathione (GSH) content occurred after acute exposure and an increase of the oxidized glutathione (GSSG)/GSH ratio. Quantitative PCR analyses evidenced increased antioxidative enzymes (Sod1, Gclc, Gclm), proapoptotic Bax, metallothioneins 1A/2A, and decreased antiapoptotic proteins (Bcl-xL, Bcl-w). The positive regulator of mitochondrial biogenesis Pparγ and mitochondrial DNA was increased, and cellular ATP was unaffected with Cd (1-10 µM). In vivo, active caspase-3, and hence apoptosis, was detected by FLIVO injection in the kidney cortex of Cd-treated rats together with an increase in Bax mRNA. However, antiapoptotic genes (Bcl-2, Bcl-xL, Bcl-w) were also upregulated. Both GSSG and GSH increased with chronic Cd exposure with no change in GSSG/GSH ratio and augmented expression of antioxidative enzymes (Gpx4, Prdx2). Mitochondrial DNA, mitofusin 2, and Pparα were increased indicating enhanced mitochondrial biogenesis and fusion. Hence, these results demonstrate a clear involvement of higher mitochondria copy numbers or mass and mitochondrial function in acute defense against oxidative stress induced by Cd in renal PTCs as well as in adaptive processes associated with chronic renal Cd toxicity. [ABSTRACT FROM AUTHOR]