Identification of biologically active δ-lactone eicosanoids as paraoxonase substrates

Area of Science:

• Biochemistry
• Enzymology
• Lipid Metabolism

Background:

• Mammalian paraoxonases (PON1, PON2, PON3) are conserved esterases with antioxidant and anti-inflammatory roles.
• Their physiological functions and natural substrates remain largely unknown.
• Previous studies suggest PONs may hydrolyze lipophilic lactones.

Purpose of the Study:

• To investigate the ability of PON1, PON2, and PON3 to hydrolyze specific bioactive δ-lactones derived from arachidonic acid.
• To determine the contribution of PONs to lactone hydrolysis in liver homogenates.
• To elucidate the role of PON3 in the metabolism of these lactone compounds.

Main Methods:

• Enzyme kinetics assays using purified PON1, PON2, and PON3 with 5,6-dihydroxy-eicosatrienoic acid lactone (5,6-DHTL) and cyclo-epoxycyclopentenone (cyclo-EC).
• Inhibition studies using EDTA and serine esterase inhibitors in human and mouse liver homogenates.
• Enzyme activity assays using liver homogenates from PON3 knockout mice.

Main Results:

• PON3 exhibited high efficiency in hydrolyzing both 5,6-DHTL and cyclo-EC.
• PON1 efficiently hydrolyzed 5,6-DHTL but poorly hydrolyzed cyclo-EC.
• PON2 showed minimal activity against both lactones.
• PON3 was responsible for over 80% of the lactonase activity in mouse liver homogenates.

Conclusions:

• PON1 and PON3 effectively hydrolyze specific arachidonic acid-derived lactones, supporting their role in regulating these lipid mediators.
• These findings provide insights into the substrate specificity of PONs and their evolutionary role in lipid metabolism.
• PON3 is identified as a major enzyme responsible for hydrolyzing these bioactive lactones in vivo.