Anti-nociceptive effects of ECa 233 a standardized extract of Centella asiatica (L.) Urban on chronic neuropathic orofacial pain in mice.

Ethnopharmacological Relevance: ECa 233 is a standardized extract of Centella asiatica (L.) Urban, a herb traditionally used to treat a number of diseases including neurological disorders. Accordingly, ECa 233 showed benefits on animal models of cognitive deficits, chronic stress and Parkinson's disease. Analgesic activity of ECa 233 was shown in Tail's flick test in rodent and relieving aphthous ulcer pain in man. Moreover, acute and sub-chronic toxicity testing in rodents and pharmacokinetic study in healthy volunteers, clinical trial phase I demonstrated good safety profiles of ECa 233.

Aim Of The Study: This study aims to evaluate the anti-nociceptive effects of ECa 233 and its synergistic effect with gabapentin on chronic neuropathic orofacial pain after 3 weeks infraorbital nerve chronic constriction injury in mice. The peripheral and central nociceptive activities are also examined.

Materials And Methods: Chronic neuropathic orofacial pain was induced by 3 weeks infraorbital nerve chronic constriction injury. Mice were treated with ECa 233 (30, 100 and 300 mg/kg) and gabapentin (10 mg/kg) by oral gavage starting on day 21 and going on for 14 consecutive days. Mechanical hyperalgesia and allodynia were measured on day 7, 14, 21, 28 and 35 after infraorbital nerve chronic constriction injury. At the end of the experiment, mice were observed for the sedative effect using the locomotor activity, the calcitonin gen-related peptide in trigeminal ganglion and c-fos expression in trigeminal nucleus caudalis were investigated after euthanasia.

Results: Infraorbital nerve chronic constriction injury gradually induced marked ipsilateral mechanical hyperalgesia and allodynia. The maximum hyperalgesia and allodynia response presented on day 21 and the response was remained constant until day 35. Treatment with either 300 mg/kg ECa 233 or 10 mg/kg gabapentin were able to attenuate mechanical hyperalgesia and allodynia. The downregulation of calcitonin gen-related peptide on ipsilateral trigeminal ganglion were observed in ECa 233 at 100 and 300 mg/kg and 10 mg/kg gabapentin-treated groups. The c-fos expression on ipsilateral trigeminal nucleus caudalis was also decreased in 300 mg/kg ECa 233 and 10 mg/kg gabapentin-treated groups.

Conclusion: ECa 233 reduced hyperalgesia and allodynia by modulating the peripheral calcitonin gen-related peptide expression consequently alleviate the nociceptive activity in trigeminal nucleus caudalis. Further clinical trial to proof ECa 233's efficacy in neuropathic pain in man as well as possible attributable mechanism of action should be further investigated.