Role of tissue metabolite accumulation in the renal toxicity of diethylene glycol.

Misuse of diethylene glycol (DEG) has led to numerous epidemic poisonings worldwide. DEG produces toxicity because of its metabolism, although the mechanism of its toxicity has not been further defined. The purpose of this study was to investigate the accumulation of specific metabolites in blood and target organ tissues and to determine the relationship between tissue accumulation of metabolites and the resulting toxicity. Wistar rats were treated with water, 2 g/kg DEG (low dose), 10 g/kg DEG (high dose), or 10 g/kg DEG + fomepizole (15 mg/kg then 10 mg/kg per 12 h, to inhibit DEG metabolism), and blood and tissue samples were collected up to 48 h. After high doses of DEG, 2-hydroxyethoxyacetic acid (HEAA) was the primary metabolite in the blood (∼4 mmol/l), with only low concentrations of diglycolic acid (DGA) (∼0.04 mmol/l). In contrast, renal and hepatic concentrations of DGA and of HEAA at 48 h were similar (∼4 mmol/l), indicating a 100-fold concentrative uptake of DGA by kidney tissue. Treatment with fomepizole blocked the formation of HEAA and DGA and the kidney toxicity. Both HEAA and DGA concentrations in the kidney correlated strongly with the degree of kidney damage. Accumulation of HEAA in blood correlated with increased anion gap and decreased blood bicarbonate so appeared responsible for the DEG-induced acidosis. Although these studies suggest that either metabolite may be involved in producing kidney toxicity, the unexpected renal accumulation of DGA at toxic doses of DEG suggests that it must also be considered a possible toxic metabolite of DEG.

Involvement of urinary proteins in the rat strain difference in sensitivity to ethylene glycol-induced renal toxicity.

Ethylene glycol (EG) exposure is a common model for kidney stones, because animals accumulate calcium oxalate monohydrate (COM) in kidneys. Wistar rats are more sensitive to EG than Fischer 344 (F344) rats, with greater COM deposition in kidneys. The mechanisms by which COM accumulates differently among strains are poorly understood. Urinary proteins inhibit COM adhesion to renal cells, which could alter COM deposition in kidneys. We hypothesize that COM accumulates more in Wistar rat kidneys because of lower levels of inhibitory proteins in urine. Wistar and F344 rats were treated with 0.75% EG in drinking water for 8 wk. Twenty-four-hour urine was collected every 2 wk for analysis of urinary proteins. Similar studies were conducted for 2 wk using 2% hydroxyproline (HP) as an alternative oxalate source. Total urinary protein was higher in F344 than Wistar rats at all times. Tamm-Horsfall protein was not different between strains. Osteopontin (OPN) levels in Wistar urine and kidney tissue were higher and were further increased by EG treatment. This increase in OPN occurred before renal COM accumulation. Untreated F344 rats showed greater CD45 and ED-1 staining in kidneys than untreated Wistars; in contrast, EG treatment increased CD45 and ED-1 staining in Wistars more than in F344 rats, indicating macrophage infiltration. This increase occurred in parallel with the increase in OPN and before COM accumulation. Like EG, HP induced markedly greater oxalate concentrations in the plasma and urine of Wistar rats compared with F344 rats. These results suggest that OPN upregulation and macrophage infiltration do not completely protect against COM accumulation and may be a response to crystal retention. Because the two oxalate precursors, EG and HP, produced similar elevations of oxalate, the strain difference in COM accumulation may result more so from metabolic differences between strains than from differences in urinary proteins or inflammatory responses.

Inhibition of metabolism of diethylene glycol prevents target organ toxicity in rats.

Diethylene glycol (DEG) is an industrial chemical, the misuse of which has led to numerous epidemic poisonings worldwide. The mechanism of its toxicity has not been defined as to the precise relationship between the metabolism of DEG and target organ toxicity. The purpose of this study was to investigate the mechanism for the acute toxicity of DEG, and the effect of the alcohol dehydrogenase inhibitor 4-methylpyrazole (fomepizole), by determining the relationship between accumulation of DEG or its metabolites and the resulting kidney and liver toxicity. Rats were treated by oral gavage with water, 2 g/kg DEG (low dose), 10 g/kg DEG (high dose), or 10 g/kg DEG + fomepizole, and blood and urine were collected over 48 h. Rats treated with high-dose DEG had metabolic acidosis, increased BUN and creatinine, and marked kidney necrosis, noted by histopathology. A minor degree of liver damage was noted at the high dose. After low and high doses of DEG, 2-hydroxyethoxyacetic acid (HEAA) was the primary metabolite in the urine, with only minor amounts of urinary diglycolic acid (DGA). Small amounts of ethylene glycol (EG), but not oxalate or glycolate, were observed in the urine. Treatment with fomepizole blocked the formation of HEAA and DGA and the development of metabolic acidosis and the kidney and liver toxicity. These results indicate that the mechanism for the target organ toxicity results from metabolites of DEG, and not DEG itself nor formation of EG from DEG, and that fomepizole may be a useful antidote for treating DEG poisoning.