Anandamide amidohydrolase activity in rat brain microsomes. Identification and partial characterization

Area of Science:

• Biochemistry
• Neuroscience
• Pharmacology

Background:

• Anandamide (N-arachidonoylethanolamine) is an endogenous substance with cannabinoid-like effects.
• Understanding the metabolic pathways of anandamide is crucial for comprehending its physiological roles and potential therapeutic applications.

Purpose of the Study:

• To characterize the amidohydrolase activity in rat brain microsomes responsible for anandamide hydrolysis.
• To investigate the substrate specificity, kinetic properties, and tissue distribution of this anandamide-hydrolyzing enzyme.

Main Methods:

• Enzymatic assays using radiolabeled anandamide ([3H]anandamide) to measure hydrolysis rates.
• Determination of kinetic parameters (Km, Vmax) and optimal pH.
• Inhibition studies using various chemical reagents and substrate analogs.
• Analysis of enzyme activity across different rat tissues and brain regions.

Main Results:

• A specific amidohydrolase activity in rat brain microsomes efficiently hydrolyzes [3H]anandamide to ethanolamine and arachidonic acid.
• The enzyme exhibits optimal activity at pH 6 and 8, is independent of divalent cations, and shows high substrate selectivity for anandamide over other N-acylethanolamines.
• Activity is highest in the liver and brain, particularly in the globus pallidus and hippocampus, regions rich in cannabinoid receptors, and significantly lower in other tissues and brain areas.

Conclusions:

• The characterized brain amidohydrolase activity is highly selective for anandamide.
• Its enrichment in cannabinoid receptor-rich areas suggests a key role in the inactivation of anandamide at its sites of action.
• This enzyme likely represents a primary mechanism for terminating anandamide signaling in the central nervous system.