Ethylene glycol (EG) is nephrotoxic due to its metabolism. Many studies suggest that the toxicity is due to
oxalate accumulation, but others have conversely suggested that toxicity results from effects of metabolites such as
glycolaldehyde or
glyoxylic acid on proximal tubule cells. In vivo studies have indicated that accumulation of
calcium oxalate monohydrate (COM) corresponds closely with development of toxicity in renal tissue. The present studies were therefore designed to clarify the roles of various metabolites in the mechanism for EG toxicity in vitro by comparing the relative cytotoxicity of EG metabolites using three measures of cell death,
ethidium homodimer uptake,
lactate dehydrogenase (LDH) release and the conversion of the
tetrazolium salt XTT to a colorimetric
dye. Human proximal tubule cells in culture were incubated in physiologic
buffers for 6h at 37 degrees C with COM (147-735microg/ml, an
oxalate equivalence of 1-5mM),
glycolate (5-25mM),
glyoxylate (0.2-5mM) and
glycolaldehyde (0.2-2mM). To assess the effects of acidity on the cytotoxicity, incubations were carried out at pH 6-7.4. The results show that COM dose-dependently increased LDH release and
ethidium homodimer uptake, while the other metabolites did not. Conversely, COM had no effect on the XTT assay, while high concentrations of
glycolaldehyde and
glyoxylate decreased XTT activity, but the latter only at acidic pH. The correlation between the uptake of
ethidium homodimer and the release of LDH suggest that COM is cytotoxic to human kidney cells in culture, while the XTT assay does not validly measure cytotoxicity in this system. These results indicate that COM, and not
glyoxylate or
glycolaldehyde, is the toxic metabolite responsible for the acute tubular
necrosis and
renal failure that is observed in EG-poisoned patients.