Tele-Methylhistamine is a specific MAO B substrate in man

Area of Science:

• Biochemistry
• Neuroscience
• Pharmacology

Background:

• Histamine is a crucial biogenic amine involved in various physiological processes.
• Tele-methylhistamine is a primary metabolite of histamine in tissues lacking diamine oxidase.
• Understanding the metabolic pathways of histamine is essential for comprehending its biological roles and potential therapeutic interventions.

Purpose of the Study:

• To investigate whether tele-methylhistamine is a substrate for human monoamine oxidase B (MAO B).
• To elucidate the metabolic fate of tele-methylhistamine in human liver homogenates.
• To determine the implications of tele-methylhistamine's interaction with MAO B for clinical MAO inhibitors.

Main Methods:

• Incubation of human liver homogenates with 3H-tele-methylhistamine.
• Separation of reaction products using thin-layer chromatography.
• Enzyme inhibition studies using (-)deprenyl, a specific MAO B inhibitor, and other substrates like phenylethlamine and 5-hydroxytryptamine.

Main Results:

• Tele-methylhistamine was identified as a substrate for human MAO B.
• The major metabolic product was 3-methylimidazoleacetic acid, resulting from oxidative deamination.
• The reaction was significantly inhibited by low concentrations of (-)deprenyl.
• Tele-methylhistamine competitively inhibited phenylethlamine oxidation, but not 5-hydroxytryptamine oxidation, confirming MAO B involvement.

Conclusions:

• Tele-methylhistamine is directly oxidized by human MAO B.
• This interaction indicates that clinically used MAO inhibitors, such as (-)deprenyl, may interfere with histamine metabolism.
• Further research is warranted to explore the clinical significance of MAO B's role in tele-methylhistamine metabolism.