Olive oil phenols inhibit human hepatic microsomal activity

Area of Science:

• Biochemistry
• Pharmacology
• Nutritional Science

Background:

• Olive oil contains complex phenols with potential biological activities.
• Human hepatic microsomal enzymes play crucial roles in steroid metabolism.
• Androstenedione 6beta-hydroxylation and 17beta-hydroxysteroid dehydrogenase (17beta-HSD) are key enzymes in steroid hormone pathways.

Purpose of the Study:

• To investigate the inhibitory effects of olive oil phenols on human hepatic microsomal androstenedione 6beta-hydroxylation and 17beta-HSD activity.
• To compare the inhibitory potential of structurally similar compounds.
• To identify structural features responsible for the observed inhibitory effects.

Main Methods:

• Enzyme inhibition assays using human hepatic microsomes.
• Assay of androstenedione 6beta-hydroxylation and both reductive and oxidative 17beta-HSD activities.
• Kinetic analysis to determine inhibition constants (K(i)).
• Structure-activity relationship analysis of phenolic compounds.

Main Results:

• Oleuropein glycoside, hydroxytyrosol, and gallic acid inhibited androstenedione 6beta-hydroxylase activity with apparent K(i) values of 80, 77, and 70 micromol/L, respectively.
• Oleuropein glycoside, hydroxytyrosol, gallic acid, and dihydroxybenzoic acid inhibited reductive 17beta-HSD activity.
• Oxidative 17beta-HSD activity was not inhibited, but gallic acid showed a 30% stimulation.
• A 3,4-dihydroxyphenyl ethanol structure was identified as essential for the inhibition of androstenedione 6beta-hydroxylase.

Conclusions:

• Complex phenols in olive oil, particularly those with a 3,4-dihydroxyphenyl ethanol moiety, can inhibit critical enzymes in human steroid metabolism.
• These findings suggest a potential mechanism for the biological effects of olive oil consumption related to steroid hormone regulation.
• Further research is warranted to explore the in vivo implications of these enzymatic inhibitions.