Protective effects of Centella asiaticas ethyl acetate fraction against pentylenetetrazole-induced seizure and learning impairment

Abstract

Investigates the effects and underlying mechanisms of Centella asiaticas ethyl acetate fraction (EACA) in animal model of epilepsy. We investigated an anticonvulsant activity of EACA against pentylenetetrazole (PTZ)-induced seizure, toxicity, drug interaction, possible mechanisms on neurochemical (amino acids neurotransmitter level in the hippocampus) and electrophysiological changes (GABA receptor current) as well as its effects on epileptogenesis and learning impairment in different animal models. Orally given EACA, produced anticonvulsant activity against PTZ test in mice exhibiting the median effective dose (ED[subscript 50]) of 673(299-1575) mg/kg BW, whereas the median neurotoxic dose (TD[subscript 50]) as assessed by rotarod test was 415(147-1169) mg/kg BW. EACA seems to be very safe as the LD[subscript 50] was found to be higher than 5,000 mg/kg BW. In isobolographic analysis for drug interaction, its additivity on some currently available antiepileptic drug namely phenytoin, valproate and gabapentin were observed. In relation to neurotoxicity, combination of gabapentin and EACA demonstrated a broader margin between the effective and the neurotoxic doses, while the other two combinations did not. Further study using microdialysis technique, demonstrated that in rats that EACA 700 mg/kg BW could protect the animals from PTZ-induced seizure, both aspartate and glutamate were gradually decreased while the glycine and GABA tended to increase. On the contrary, an increment of aspartate induced by PTZ was noted in animals receiving the same dose of EACA but demonstrated convulsion. By electrophysiological study, a slight potentiation of the GABA-induced current was observed when EACA at low concentration of 0.1 3 microgram/ml were co-applied with GABA. However, the GABA-induced current was partially blocked at higher concentration of EACA (50 microgram/ml). Taken all together the results obtained suggest the existence of several active constituents with antagonizing pharmacological profiles in EACA. In addition, EACA produced no effect on epileptogenesis and had no effect on lipid peroxidation. Though EACA seemed to have positive effect on learning and memory deficit and survival pyramidal neurons in PTZ-kindled mice, the results obtained was not yet conclusive. The present studies suggested that the anticonvulsant activity of EACA might be, at least, related to a slight decrease of the level of excitatory amino acid neurotransmitter in conjunction with a small increase of inhibitory amino acid neurotransmitter of hippocampus including a slight potentiation of GABA-induced current. In addition, the additivity on some AEDs suggested the potential of EACA to be further developed as adjunctive medication for epileptic patients after identification and separation of the active substances which may be numerous and exhibiting different pharmacological profiles