Enkephalin hydrolysis by mouse plasma in vitro.

Area of Science:

• Biochemistry
• Pharmacology
• Neuroscience

Background:

• Enkephalins are endogenous opioid peptides involved in pain modulation and other physiological processes.
• Understanding the degradation pathways of enkephalins is crucial for developing therapeutic strategies.
• Mouse plasma serves as a relevant model for studying peptide metabolism in vivo.

Purpose of the Study:

• To investigate and compare the hydrolysis rates of [Leu]enkephalin and [Met]enkephalin in mouse plasma.
• To identify the specific peptidases responsible for enkephalin degradation in plasma.
• To determine the half-lives of [Leu]enkephalin and [Met]enkephalin in mouse plasma.

Main Methods:

• High-Performance Liquid Chromatography with Electrochemical Detection (HPLC-ECD) was employed to quantify Tyr-containing metabolites.
• In vitro hydrolysis assays were performed using pooled whole mouse plasma.
• Selective peptidase inhibitors were used to identify enzyme involvement in the hydrolysis process.

Main Results:

• Accumulation of Tyr-Gly-Gly was significantly higher from [Met]enkephalin hydrolysis compared to [Leu]enkephalin.
• [Met]enkephalin exhibited a shorter half-life in mouse plasma (approximately half) than [Leu]enkephalin.
• Enkephalinase, angiotensin-converting enzyme, and a bestatin-sensitive aminopeptidase (likely aminopeptidase M) were identified as key enzymes in plasma hydrolysis.

Conclusions:

• Mouse plasma efficiently metabolizes [Met]enkephalin, with a faster degradation rate than [Leu]enkephalin.
• Multiple peptidases, including aminopeptidase M, enkephalinase, and ACE, contribute to the in vitro hydrolysis of enkephalins in mouse plasma.
• These findings provide insights into the pharmacokinetic profile and enzymatic inactivation of enkephalins.