Hinokitiol inhibits compound action potentials in the frog sciatic nerve.

Area of Science:

• Pharmacology
• Neuroscience
• Natural Products Chemistry

Background:

• Hinokitiol (β-thujaplicin), a tropolone derivative from Chamaecyparis taiwanensis, exhibits anti-inflammatory properties.
• The effect of hinokitiol on nerve conduction, specifically compound action potentials (CAPs), has not been previously investigated.
• Plant-derived compounds often modulate CAPs based on their chemical structures.

Purpose of the Study:

• To investigate whether hinokitiol inhibits CAPs.
• To identify the structural features of hinokitiol responsible for CAP inhibition.
• To explore the potential contribution of nerve conduction inhibition to hinokitiol's pharmacological effects.

Main Methods:

• Experiments were conducted on frog sciatic nerves using the air-gap method.
• The effects of hinokitiol and related compounds on fast-conducting CAPs were measured.
• Concentration-dependent inhibition and half-maximal inhibitory concentration (IC50) were determined.

Main Results:

• Hinokitiol demonstrated a concentration-dependent reduction in CAP peak amplitude, with an IC50 of 0.54mM.
• A stereoisomer, γ-thujaplicin, also inhibited CAPs.
• Compounds lacking hinokitiol's isopropyl group (tropolone, kojic acid) did not inhibit CAPs, while those with isopropyl and hydroxyl groups (biosol, 4-isopropylphenol) did.

Conclusions:

• Hinokitiol inhibits frog CAPs, indicating an ability to impede nerve conduction.
• The isopropyl, carbonyl, and hydroxyl groups of hinokitiol appear essential for its nerve-inhibiting action.
• This nerve conduction inhibition may partially explain the broader pharmacological activities of hinokitiol.