Oxidation of Ethylene Glycol to Glycolaldehyde by Mammalian Tissues

Abstract

Summary. The mammalian enzymes oxidizing ethylene glycol to glycolaldehyde were investigated with homogenates of horse liver and of rat tissues. The oxidation was followed by measuring either pyridine nucleotide reduction by fluorometry or glycolaldéhyde with diphenylamine. The reaction required either NAD^+ or a biological source of H(2)0(2); NADP^+ was ineffective. In the presence of NAD^+, crude horse liver demonstrated the same relative rates for ethylene glycol oxidation, ethanol oxidation, and acetaldehyde reduction as did crystalline horse liver alcohol dehydrogenase. The oxidation of many flavoprotein oxidoreductase substrates (including glycolic acid, a metabolite of ethylene glycol) could be coupled to that of ethylene glycol, presumably by providing a source of H(2)0(2) for the oxidation of ethylene glycol via tissue catalase. Partially purified L-gulonate: NADP oxidoreductase and glycerol: NADP oxidoreductase (D-glyceraldehyde forming) oxidized ethylene glycol poorly. The results suggest that the important enzymes in the first step of ethylene glycol oxidation are the same as those for ethanol oxidation, namely alcohol dehydrogenase and catalase.

Effect of Ethanol on Ethylene Glycol Oxidation by Mammalian Liver Enzymes

“…Thus, when the reaction media contain 15 mM cysteine, 2 mM of added glycolaldéhyde can be completely recovered after incubation. L-cysteine is oxidized poorly by the L-amino acid oxidases of rat liver homogenates, and under these experimental conditions it does not enhance ethylene glycol oxidation by H202 production as some amino acids do [1].…”

“…Cysteine was used as a trapping agent to prevent the further oxidation of glycolaldéhyde. This NAD+-linked oxidation of ethylene glycol by rat liver is effected almost solely by alcohol dehydrogenase [1].…”

“…First, aldehyde oxidoreductases would oxidize about 40-60 % of the glycolaldéhyde formed, as we have determined by recovery experiments. Secondly, some of the acetaldehyde, glycolal déhyde, and glycolate generated in the incubation media would be oxidized by flavoprotein oxidoreductases to yield H202, which, in the presence of tissue catalase, would oxidize more ethylene glycol to glycolaldéhyde [1]. However, when cysteine is present, it reacts with both glycolaldéhyde and acetaldehyde to produce the corresponding thiazolidine carboxylic acid derivatives [13], thereby preventing the further oxidation of glycolaldéhyde and markedly limiting that of acetaldehyde.…”

“…Homogenates of fresh rat liver were prepared and dialyzed as reported previously [1], The enzymatic oxidation of ethylene glycol was measured by the determination of glycolaldéhyde with diphenylamine [2] after precipitating protein with trichloro acetic acid in an end-concentration of 1 M. When the samples contained cysteine, this was precipitated with the protein by adding 0.5 volumes of 0.2 M HgCl2 in 0.5 M acetic acid [14], placing in an ice bath for 30 minutes, and centrifuging at 5° C. The slightly turbid supernatants were then further acidified and clarified with 0.2 volumes of 6 M trichloroacetic acid before adding the diphenylamine reagent. When propylene glycol was present in the samples, the results were corrected [15] for spectral interference by its oxidation products which were measured at 515 m[x.…”

“…We have shown previ ously [1] that ethylene glycol and ethanol are oxidized to aldehydes by the same enzymes : alcohol dehydrogenase and catalase. This find ing suggested that ethanol might be administered to humans who had accidentally ingested ethylene glycol, to block its oxidation and re duce its toxicity.…”