Chloroacetaldehyde as a Sulfhydryl Reagent: The Role of Critical Thiol Groups in Ifosfamide Nephropathy

Chloroacetaldehyde (CAA) is a metabolite of the alkylating agent ifosfamide (IFO) and putatively responsible for renal damage following anti-tumor therapy with IFO. Depletion of sulfhydryl (SH) groups has been reported from cell culture, animal and clinical studies. In this work the effect of CAA on human proximal tubule cells in primary culture (hRPTEC) was investigated. Toxicity of CAA was determined by protein content, cell number, LDH release, trypan blue exclusion assay and caspase-3 activity. Free thiols were measured by the method of Ellman. CAA reduced hRPTEC cell number and protein, induced a loss in free intracellular thiols and an increase in necrosis markers. CAA but not acrolein inhibited the cysteine proteases caspase-3, caspase-8 and cathepsin B. Caspase activation by cisplatin was inhibited by CAA. In cells stained with fluorescent dyes targeting lysosomes, CAA induced an increase in lysosomal size and lysosomal leakage. The effects of CAA on cysteine protease activities and thiols could be reproduced in cell lysate. Acidification, which slowed the reaction of CAA with thiol donors, could also attenuate effects of CAA on necrosis markers, thiol depletion and cysteine protease inhibition in living cells. Thus, CAA directly reacts with cellular protein and non-protein thiols, mediating its toxicity on hRPTEC. This effect can be reduced by acidification. Therefore, urinary acidification could be an option to prevent IFO nephropathy in patients.