Isolation and identification of 3-hydroxy-3-methyloxindole, the major murine metabolite of 3-methylindole

Abstract

3-Methylindole (3MI) is pneumotoxic to ruminants and rodents subsequent to metabolic oxidative activation by cytochrome P-450 monooxygenases. Goats are much more susceptible than mice and rats to 3MI-mediated lung damage, and these differences in species susceptibility may be reflected by differences in the metabolic products of 3MI. Radioactive 3MI was administered ip to Swiss-Webster mice, and the major nonpolar urinary metabolites were fractionated and separated by HPLC. Although 3-methyloxindole has been shown to be the major urinary metabolite of 3MI in goats, it was not detected in mouse urine. Instead, the major metabolite, 3-hydroxy-3-methyloxindole, was isolated and purified and its structure elucidated by 1H and 13C NMR, mass spectrometry, and IR spectroscopy. This is the first identification of this highly oxidized indole from mammalian sources. The production of this metabolite may be indicative of the formation of an electrophilic methyleneoxindole intermediate, which could be responsible for pneumotoxicity in this species.

Fecal Metabolomics of Type 2 Diabetic Rats and Treatment with Gardenia jasminoides Ellis Based on Mass Spectrometry Technique

“…Tryptamine is a monoamine compound generally generated by the biosynthesis of the amino acid tryptophan, in turn acting as a precursor for other compounds such as hormones and neurotransmitters. 3-Methyldioxyindole is an in vivo oxidation product formed during metabolism of 3-methylindole, which is a metabolic product of tryptophan generated by bacteria in the colon. , As shown in Figure , 3-methyldioxyindole could be obtained from tryptamine via three biological reactions. 4-(2-Aminophenyl)-2,4-dioxobutanoic acid is a substrate related to tryptophan as well.…”

Oxidative Reaction of Oxindole-3-acetic Acids

“…3-Hydroxy-oxindoles have been detected as the metabolites of indoles, not only of plants but also animals, 17,18) and the oxidative modiˆcation of indoles would be an important step in their biological activity. [19][20][21] However, the metabolic pathway was not fully established.…”

Putative Mechanisms of Toxicity of 3-Methylindole: From Free Radical to Pneumotoxicosis

“…The extensive study of metabolism of 3MI is essential in uncov ering the mechanism of toxicity. The major urinary metabolite of 3MI in goats, 3MOI, is not even detected in mice (35). Jugular infusion of [methyP 4 C]3MI in goats resulted in a minute accumulation of 14C-3MI in plasma with a half-life of 20-25 min (32,33).…”

“…3MI can be metabolized to inert compounds that are excreted as detoxification products , but 3MI can also become a reactive intermediate producing pneumotoxicity (31). The major murine urinary metabolite of 3MI is 3-hydroxy-3-methylindole and is also present in human urine (35,36). The pulmonary concentration of the parent compound of 3MI was low, yet the presence of 3MI metabolites was high.…”

“…Instead, random binding of toxins to non-vital proteins in the cell may simply offer an additional means of detoxification. In species that are susceptible to 3MI pneumotoxic ity, 3MI also binds to hepatic proteins, yet only the lung is susceptible to 3MI toxicity (35,41,66). The formation of adducts of 3Ml with protein probably depends on the number of available reactive sulfhydryls, and the target is probably randomly chos e n. There are other examples of cellular proteins binding to toxins that serve a protective function.…”