N-nitrosodialkylamines do not function as substrates for liver monoamine oxidase

Area of Science:

• Biochemistry
• Pharmacology
• Toxicology

Background:

• Hepatic monoamine oxidase (MAO) is implicated in the metabolic activation of N-nitrosodialkylamines to mutagens.
• Understanding the precise enzymatic pathways involved in N-nitrosodialkylamine activation is crucial for assessing their toxicological risks.

Purpose of the Study:

• To investigate whether N-nitrosodiethylamine, N-nitrosodimethylamine, and N-nitrosodibenzylamine are direct substrates or inhibitors of hepatic monoamine oxidase (MAO).
• To clarify the role of MAO in the mutagenic activation of these specific N-nitrosodialkylamines.

Main Methods:

• In vitro enzymatic assays were performed using purified liver monoamine oxidase.
• N-nitrosodiethylamine, N-nitrosodimethylamine, and N-nitrosodibenzylamine were tested for substrate, competitive inhibition, and irreversible inhibition activity against MAO.

Main Results:

• The tested N-nitrosodialkylamines (N-nitrosodiethylamine, N-nitrosodimethylamine, N-nitrosodibenzylamine) were found not to be substrates for liver monoamine oxidase.
• These compounds also did not act as competitive or irreversible inhibitors of hepatic monoamine oxidase activity.

Conclusions:

• Hepatic monoamine oxidase does not appear to directly participate in the mutagenic activation of N-nitrosodiethylamine, N-nitrosodimethylamine, or N-nitrosodibenzylamine.
• The mutagenic activation of these N-nitrosodialkylamines likely involves an initial conversion to their respective secondary amines, followed by a separate activation step.