Anticholinesterase,antioxidant and cognitive enhancing properties of essential oils from black pepper(pipernigrum,) and calabash nutmeg(monodoramyristica)(gaertn).) dunal)
This study determined the chemical composition of the essential oils of the seeds of Monodoramyristica and Piper nigrumand evaluated itsin vitro anticholinesterase, antioxidant and antiamnesic potentials. This was with a view to using these oils in the management of neurodegenerative diseases. Fifty grams (50 g) of the powdered seeds of M. myristica and P. nigrum were separately subjected to hydrodistillation in a Clavenger-type apparatus to isolate their essential oils. The oils were dried with anhydrous sodium sulphate (Na2SO4) and their compositional profiles were analysed by gas chromatography and mass spectrometry(GC-MS). Radical scavenging activities were tested using 2,2΄-diphenyl-1-picrylhydrazyl hydrate (DPPH),2,2΄-azinobis-(3-ethyl-benzothiazoline-6-sulphonic acid) (ABTS˙+), nitric oxide (NO) inhibition, while the antioxidant capacities were investigated with the ferric reducing antioxidant power (FRAP) and total antioxidant capacities (TAC). The inhibitory effects on acetylcholinesterase (AChE) andbutyrylcholinesterase(BuChE) were investigated by standard method. In the in vivoantiamnesic studies, adult mice were used for the test in the cognitive behavioural paradigms. The animals were assessed for performance in the Passive Avoidance and Morris Water-Maze Tasks by measuring the Step-Through Latency Time (SLT) and Escape Latency Time (ELT) respectively. The animals were then sacrificed, whole brain excised, homogenized (10% weight/volume) and then assayed for brain acetylcholinesterase activity. The result showed that M. myristica and P.nigrum oils were characterised by the presence of 51 and 61 components, representing 94.76% and 90.65% respectively of the total oil. The oils were dominated by α-phellandrene (18.13%), 1-methyl-4-1(1-methylethyl) benzene (16.26%) and α-pinene (7.16%) in M.myristica while β-pinene (5.92%), 2,4-quinolinediol (4.74%) and caryophyllene (4.55%) were the major compounds in P.nigrum. M.myristica demonstrated free radical scavenging effects on DPPH (IC50 = 3.01 ± 0.04 mg/ml), NO inhibition (IC50 = 0.372 ± 0.013 mg/ml), ABTS˙+ (IC50 = 0.347 ± 0.019 mg/ml). In terms of antioxidant capacities, FRAP (11.66 ± 0.26 µg AAE/ml) and TAC (274.41 ± 14.40 µg AAE/ml). P. nigrum also elicited free radical scavenging and antioxidant capacity on DPPH (IC50 = 9.89 ± 0.66 mg/ml), NO inhibition (IC50 = 0.384 ± 0.013 mg/ml), ABTS˙+ (IC50 = 0.436 ± 0.012 mg/ml), FRAP (5.27 ± 0.06 µg AAE/ml) and TAC (266.90 ± 4.66 µg AAE/ml). Both oils at 416 µg/ml elicited remarkable and significant (p<0.05) inhibitory activity with M. myristica eliciting IC50 of 0. 205 ± 0.06 mg/ml and 0. 178 ± 0.016 mg/ml against AChE and BuChE respectively. P. nigrum inhibited AChE with IC50 = 272.66 ± 18.05 µg/ml and BuChE with IC50 = 223.75 ± 20.82 µg/ml. Kinetic studies revealed that the mode of inhibition exhibited by M. myristica oil against AChE and BuChE was competitive while P. nigrum on the other hand caused a competitive type of inhibition towards AChE and a mixed type towards BuChE. In the Morris Water-Maze Task, the Escape Latency Time (ELT) were significantly (p<0.05) decreased by both M.myristica and P.nigrum treated group compared to scopolamine treated group. Similarly, in the Passive Avoidance Task, the Step-Through Latency were significantly increased by the administration of the oils when compared to scopolamine treated group. The study concluded that the seeds of M. myristica and P. nigrum were potential sources of active metabolites with anticholinesterase and antioxidant properties with M. myristica showing a higher activity.