Indolethylamine N-methyltransferase (INMT) is not essential for endogenous tryptamine-dependent methylation activity in rats

Nicolas G Glynos; Lily Carter; Soo Jung Lee; Youngsoo Kim; Robert T Kennedy; George A Mashour; Michael M Wang; Jimo Borjigin

doi:10.1038/s41598-023-27538-y

Indolethylamine N-methyltransferase (INMT) is not essential for endogenous tryptamine-dependent methylation activity in rats

Sci Rep. 2023 Jan 6;13(1):280. doi: 10.1038/s41598-023-27538-y.

Authors

Nicolas G Glynos^#^{1

2}, Lily Carter^#¹, Soo Jung Lee^{3

4}, Youngsoo Kim⁵, Robert T Kennedy⁵, George A Mashour^{2

6

7}, Michael M Wang^{1

3

4

7}, Jimo Borjigin^{8

9

10

11}

Affiliations

¹ Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI, USA.
² Michigan Psychedelic Center, University of Michigan, Ann Arbor, MI, USA.
³ Department of Neurology, University of Michigan, Ann Arbor, MI, USA.
⁴ Veterans Affairs Ann Arbor Healthcare System, Ann Arbor, MI, USA.
⁵ Department of Chemistry, University of Michigan, Ann Arbor, MI, USA.
⁶ Department of Anesthesiology, University of Michigan, Ann Arbor, MI, USA.
⁷ Neuroscience Graduate Program, University of Michigan, Ann Arbor, MI, USA.
⁸ Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, MI, USA. borjigin@umich.edu.
⁹ Michigan Psychedelic Center, University of Michigan, Ann Arbor, MI, USA. borjigin@umich.edu.
¹⁰ Department of Neurology, University of Michigan, Ann Arbor, MI, USA. borjigin@umich.edu.
¹¹ Neuroscience Graduate Program, University of Michigan, Ann Arbor, MI, USA. borjigin@umich.edu.

^# Contributed equally.

Abstract

Indolethylamine N-methyltransferase (INMT) is a transmethylation enzyme that utilizes the methyl donor S-adenosyl-L-methionine to transfer methyl groups to amino groups of small molecule acceptor compounds. INMT is best known for its role in the biosynthesis of N,N-Dimethyltryptamine (DMT), a psychedelic compound found in mammalian brain and other tissues. In mammals, biosynthesis of DMT is thought to occur via the double methylation of tryptamine, where INMT first catalyzes the biosynthesis of N-methyltryptamine (NMT) and then DMT. However, it is unknown whether INMT is necessary for the biosynthesis of endogenous DMT. To test this, we generated a novel INMT-knockout rat model and studied tryptamine methylation using radiometric enzyme assays, thin-layer chromatography, and ultra-high-performance liquid chromatography tandem mass spectrometry. We also studied tryptamine methylation in recombinant rat, rabbit, and human INMT. We report that brain and lung tissues from both wild type and INMT-knockout rats show equal levels of tryptamine-dependent activity, but that the enzymatic products are neither NMT nor DMT. In addition, rat INMT was not sufficient for NMT or DMT biosynthesis. These results suggest an alternative enzymatic pathway for DMT biosynthesis in rats. This work motivates the investigation of novel pathways for endogenous DMT biosynthesis in mammals.

Publication types

Research Support, N.I.H., Extramural
Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

Animals
Humans
Mammals
Methylation
N,N-Dimethyltryptamine* / chemistry
Rabbits
Rats
Tryptamines*

Substances

tryptamine N-methyltransferase
tryptamine
Tryptamines
N,N-Dimethyltryptamine

Grants and funding

RF1 NS128522/NS/NINDS NIH HHS/United States