Essential oil of Lippia alba and its main constituent citral block the excitability of rat sciatic nerves

Lippia alba is empirically used for infusions, teas, macerates, and hydroalcoholic extracts because of its antispasmodic, analgesic, sedative, and anxiolytic effects. Citral is a mixture of trans-geranial and cis-neral and is the main constituent of L. alba essential oil and possesses analgesic, anxiolytic, anticonvulsant, and sedative effects. The present study evaluated the effects of the essential oil of L. alba (EOLa) and citral on compound action potentials (CAPs) in Wistar rat sciatic nerves. Both drugs inhibited CAP in a concentration-dependent manner. The calculated half-maximal inhibitory concentrations (IC50) of peak-to-peak amplitude were 53.2 µg/mL and 35.00 µg/mL (or 230 µM) for EOLa and citral, respectively. Peak-to-peak amplitude of the CAP was significantly reduced by 30 µg/mL EOLa and 10 µg/mL citral. EOLa and citral (at 60 and 30 µg/mL, values close to their respective IC50 for CAP blockade) significantly increased chronaxy and rheobase. The conduction velocity of the first and second CAP components was statistically reduced to ∼86% of control with 10 µg/mL EOLa and ∼90% of control with 3 µg/mL citral. This study showed that EOLa inhibited nerve excitability and this effect can be explained by the presence of citral in its composition. Both EOLa and citral showed inhibitory actions at lower concentrations compared with other essential oils and constituents with local anesthetic activity. In conclusion, these data demonstrate that EOLa and citral are promising agents in the development of new drugs with local anesthetic activity.

由于具备解痉、镇痛、镇静及抗焦虑活性，橙香过江藤（Lippia alba）在传统经验中常被用于制备浸剂、茶饮、浸渍物及水醇提取物。柠檬醛（citral）是反式香叶醛与顺式橙花醛的混合物，是橙香过江藤精油的主要成分，同时具备镇痛、抗焦虑、抗惊厥与镇静功效。本研究评估了橙香过江藤精油（EOLa）与柠檬醛对Wistar大鼠坐骨神经中复合动作电位（compound action potentials, CAPs）的影响。两种受试物质均以浓度依赖性方式抑制CAP信号。经计算，EOLa与柠檬醛针对CAP峰峰值振幅的半数抑制浓度（half-maximal inhibitory concentrations, IC50）分别为53.2 μg/mL与35.00 μg/mL（或230 μM）。当EOLa浓度为30 μg/mL、柠檬醛浓度为10 μg/mL时，CAP的峰峰值振幅均出现显著降低。当EOLa与柠檬醛分别以接近各自CAP阻断半数抑制浓度的60 μg/mL与30 μg/mL浓度给药时，可显著升高时值（chronaxy）与基强度（rheobase）。经统计学分析，10 μg/mL的EOLa可将CAP第一、二组分的传导速度降至对照组的约86%，而3 μg/mL的柠檬醛则可将其降至对照组的约90%。本研究证实，EOLa可抑制神经兴奋性，该效应可通过其组分中含有的柠檬醛得到解释。相较于其他具备局部麻醉活性的精油及其成分，EOLa与柠檬醛可在更低浓度下展现抑制效应。综上，本研究数据表明，EOLa与柠檬醛是开发具备局部麻醉活性新型药物的极具潜力的候选制剂。