Ethylene Glycol Monomethyl Ether–Induced Toxicity Is Mediated through the Inhibition of Flavoprotein Dehydrogenase Enzyme Family

Ethylene glycol monomethyl ether (EGME) is a widely used industrial solvent known to cause adverse effects to human and other mammals. Organs with high metabolism and rapid cell division, such as testes, are especially sensitive to its actions. In order to gain mechanistic understanding of EGME-induced toxicity, an untargeted metabolomic analysis was performed in rats. Male rats were administrated with EGME at 30 and 100 mg/kg/day. At days 1, 4, and 14, serum, urine, liver, and testes were collected for analysis. Testicular injury was observed at day 14 of the 100 mg/kg/day group only. Nearly 1900 metabolites across the four matrices were profiled using liquid chromatography-mass spectrometry/mass spectrometry and gas chromatography-mass spectrometry. Statistical analysis indicated that the most significant metabolic perturbations initiated from the early time points by EGME were the inhibition of choline oxidation, branched-chain amino acid catabolism, and fatty acid β-oxidation pathways, leading to the accumulation of sarcosine, dimethylglycine, and various carnitine- and glycine-conjugated metabolites. Pathway mapping of these altered metabolites revealed that all the disrupted steps were catalyzed by enzymes in the primary flavoprotein dehydrogenase family, suggesting that inhibition of flavoprotein dehydrogenase–catalyzed reactions may represent the mode of action for EGME-induced toxicity. Similar urinary and serum metabolite signatures are known to be the hallmarks of multiple acyl-coenzyme A dehydrogenase deficiency in humans, a genetic disorder because of defects in primary flavoprotein dehydrogenase reactions. We postulate that disruption of key biochemical pathways utilizing flavoprotein dehydrogenases in conjugation with downstream metabolic perturbations collectively result in the EGME-induced tissue damage

Formation of cholesterol ozonolysis products in vitro and in vivo through a myeloperoxidase-dependent pathway

3β-Hydroxy-5-oxo-5,6-secocholestan-6-al (secosterol-A) and its aldolization product 3β-hydroxy-5β-hydroxy-B-norcholestane-6β-carboxaldehyde (secosterol-B) were recently detected in human atherosclerotic tissues and brain specimens, and they may play pivotal roles in the pathogenesis of atherosclerosis and neurodegenerative diseases. However, as their origin remains unidentified, we examined the formation mechanism, the stability, and the fate of secosterols in vitro and in vivo. About 40% of secosterol-A remained unchanged after 3 h incubation in the FBS-free medium, whereas 20% and 40% were converted to its aldehyde-oxidation product, 3β-hydroxy-5-oxo-secocholestan-6-oic acid, and secosterol-B, respectively. In the presence of FBS, almost all secosterol-A was converted immediately to these compounds. Secosterol-B in the medium, with and without FBS, was relatively stable, but ∼30% was converted to its aldehyde-oxidation product, 3β-hydroxy-5β-hydroxy-B-norcholestane-6-oic acid (secoB-COOH). When neutrophil-like differentiated human leukemia HL-60 (nHL-60) cells activated with PMA were cultured in the FBS-free medium containing cholesterol, significantly increased levels of secosterol-A and its aldehyde-oxidation product, but not secosterol-B, were formed. This secosterol-A formation was decreased in the culture of PMA-activated nHL-60 cells containing several reactive oxygen species (ROS) inhibitors and scavengers or in the culture of PMA-activated neutrophils isolated from myeloperoxidase (MPO)-deficient mice. Our results demonstrate that secoterol-A is formed by an ozone-like oxidant generated with PMA-activated neutrophils through the MPO-dependent mechanism