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.

白过江藤（Lippia alba）因具有解痉、镇痛、镇静及抗焦虑活性，在传统实践中常被用于制备浸剂、药茶、浸渍剂及水醇提取物。柠檬醛（citral）是反式香叶醛（trans-geranial）与顺式橙花醛（cis-neral）的混合物，为白过江藤精油的主要成分，同时具备镇痛、抗焦虑、抗惊厥及镇静活性。本研究评估了白过江藤精油（EOLa）与柠檬醛对Wistar大鼠坐骨神经复合动作电位（compound action potentials，CAPs）的影响。两种受试物质均以浓度依赖性方式抑制复合动作电位。经计算，白过江藤精油与柠檬醛的复合动作电位峰峰值振幅半数抑制浓度（half-maximal inhibitory concentrations，IC50）分别为53.2 µg/mL与35.00 µg/mL（或230 µM）。当使用浓度为30 µg/mL的白过江藤精油与10 µg/mL的柠檬醛时，可显著降低复合动作电位的峰峰值振幅。当浓度分别为60 µg/mL与30 µg/mL（接近二者各自阻断复合动作电位的半数抑制浓度）时，白过江藤精油与柠檬醛可显著升高时值（chronaxy）与基强度（rheobase）。10 µg/mL的白过江藤精油与3 µg/mL的柠檬醛可使第一、第二复合动作电位组分的传导速度分别降至对照组的约86%与90%，差异具有统计学意义。本研究表明，白过江藤精油可抑制神经兴奋性，该效应可通过其所含的柠檬醛成分得以解释。相较于其他具备局部麻醉活性的精油及成分，白过江藤精油与柠檬醛在更低浓度下即可展现抑制活性。综上，本研究数据证实，白过江藤精油与柠檬醛是开发具有局部麻醉活性的新型药物的潜在候选物质。