Principal role of cholinesterase (ChE) is the termination of nerve impulse transmission at the cholinergic synapses by rapid hydrolysis of acetylcholine (ACh). Inhibition of ChE serves as a strategy for the treatment of Alzheimer's disease (AD), senile dementia, ataxia, myasthenia gravis and Parkinson's disease [33
] A variety of plants has been reported to show ChE inhibitory activity and so may be relevant to the treatment of neurodegenerative disorders such as AD [15
In this study, aqueous extracts prepared from leaves, seeds and roots from R. pentaphyllum
were tested to determine their ability as human BuChE inhibitors. The BuChE inhibition was determined using an adaptation of the method described by Ellman, et al.
All extracts exhibited moderate to good anti BuChE activity, in fact, the inhibition capacity shows the following order: seeds extract > leaves extract > roots extracts. The best inhibitory activity was exhibited by the seeds extract.
On the other hand, the role of oxidative stress in the pathogenesis of diseases such as macular degeneration, certain types of cancer, and Alzheimer's disease (AD) has received substantial attention. For that reason, we also aimed to look into antioxidant capacities of R. pentaphyllum extracts.
Three different reactive species were used to evaluate the antioxidant activity of the R. pentaphyllum
extracts: the DPPH.
radicals. The superoxide anion and other ROS contribute to oxidative stress, and are known contributors to genetic damage, as well as degenerative diseases such as cancer [35
], Parkinson disease, and heart ischemia [36
]. Since, the DPPH.
And the ABTS.+
radicals are not biologically relevant, the DPPH and ABTS.+
assays were performed as a preliminary study to estimate the direct free-radical scavenging abilities of the test extracts. The activity of extracts against the superoxide radical via the non enzymatic NBT/riboflavin assay system has more relevance to physiological conditions. Results show that, compared to leaves and roots extracts, seeds aqueous extract revealed relatively strong antiradical activity towards the ABTS.+
and DPPH free radicals and decreased significantly the O2.-
formation. Thus, we can suggest that the anti-BuChE activities occurs through free radical scavenging capacities.
The antioxidant and anti-BuChE possibilities of R. pentaphyllum
extracts are supported by the detection of flavonoids and phenolic compounds. In fact, several flavonoids and other phenolic compounds are considered antioxidants [37
] and inhibition capacities of BuChE activity [38
It has been reported, oxidative stress, caused by reactive oxygen species (ROS), is known to cause the oxidation of biomolecules leading to cellular damage. It is also speculated to be pathologically important in various neurodegenerative processes including cognitive deficits that occur during normal cerebral aging, Alzheimer's (AD), and Parkinson's diseases [39
]. Nowadays, the most accepted theory about the disturbing effect of free radicals in the process of aging was reported by Harman [41
]. Later on, it was also reported that oxidative stress is associated with the pathogenesis of AD and cellular characteristics of this disease are either causes or effects of oxidative stress [42
]. These evidences clearly show that oxidative stress, an early event in AD, may play a key pathogenic role in the disease [44
]. Thus, we can establish a correlation between the antioxidant and anti-BuChE capacities and quantity of these phenolic components. Curiously, the roots aqueous extract contained a high quantity of tannins but it exhibited lowest both antioxidant and anti-BuChE activities than the two other extracts. We cannot, however, exclude the possibility that other compounds, particularly coumarins in the case of seeds aqueous extract, with decreased the BuChE and free radical properties [45
]. On the other hand, it is not necessarily always to be only one compound that is responsible for these effects, which may as well be depend on several compounds that act in a synergistic manner or on compounds which regulate one another.
In summary, R. pentaphyllum extracts appear to contain compounds with antioxidant and chemoprotective properties. Therefore, these data suggest that high dietary or supplemental consumption of antioxidants in people may reduce the risk of AD. However, further studies are required to fractionate the active extracts, to identify the active compounds, and to determine their exact mechanism of action.