Modulation des facteurs protéiques impliqués dans la maladie d’Alzheimer par les extraits de Khaya grandifololia C. DC.

Abstract

Neurodegenerative diseases, the most common of which is Alzheimer's disease, represent a major public health problem in the world. The search for new therapeutic sources is imperative because the available treatments only alleviate the symptoms of the disease with a reduced effectiveness and varying from one individual to another. Khaya grandifoliola (Meliaceae) is used in traditional medicine for the treatment of various ailments. Studies with the extracts of this plant have shown anti-inflammatory, immunomodulatory and hepatoprotective activities testifying to the plant’s ability to protect organs. However, studies showing the neouroprotective potential of the plant have not yet been carried out. Thus, the aim of this work was to study neuroprotective activities with emphasis on the modulation of protein factors involved in Alzheimer's disease. For this purpose, a hydroethanolic extract of Khaya grandifoliola (KG) was prepared by maceration of the bark powder in a water/ethanol mixture (65:35, v/v). The extract was fractionated by silica gel column chromatography and the neuroprotective activities as well as the mechanism of protection of extract and fractions were investigated. Regarding the neuroprotective activity of the extracts, the Aβ42 peptideinduced neurotoxicity induced was used. Cell viability tests were conducted with 3-(4.5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium (MTT) bromide and crystal violet. The staining of the nuclei of differentiated neuroblastoma cells was performed with 2',7'- dichlorodihydrofluorescein diacetate (DCDA), Hoescht 33342 and propidium iodide (PI) were performed. The neuroprotective properties of the extracts were subsequently evaluated by fluorescence detection of their effect on cell viability and the generation of reactive oxygen species (ROS). To understand the neuroprotective mechanism of these extracts, the expression of some proteins: mitochondrial SOD, caspase-3, Symptosomal associated protein 25 (SNAP25), synaptosin (SYP), tau protein (tau T181) and Extracellular signal-related kinase (ERK) was quantified by western blot. β-actin was used as an internal control. Regarding antiamnesic activity of the extract, male albino wistar rats were intoxicated with scopolamine to induce amnesia. Behavioral tests were performed to assess depression (tail suspension test), anxiety (novelty suppressed feeding test), and memory (Morris water maze test). The effect of the extract on the activities of enzymes of the intracellular antioxidant system, acetylcholine esterase, phosphatases and the process of fibrillation were evaluated. The results demonstrated the maintenance of cell viability and the inhibition of the production of ROS demonstrated the neuroprotective action of extract. Western blot analysis revealed that KG extracts inhibit mitochondrial dysfunction, apoptosis, synaptic toxicity and tau protein hyperphosphorylation. KG extract exhibits nootrophic and chronic anti-amnesic effects. The chronic anti-amnesic effect was attributed to the increase of activity of antioxidant enzymes (SOD and CAT) and the level of reduced glutathione. The inhibitory effect was manifested by the decrease in acetylcholine esterase activity and the normalization of phosphatase activity. But also, the inhibition of the formation of fibrils which is a key step in the formation of aggregates that are deposited in the form of senile plaques or neurofibrillary tangles. This study demonstrated that KG extracts could possess neuroprotective properties against β-amyloid peptide and scopolamine toxicities. These observations suggest that the hydroethanolic extract of KG could be a good candidate for the development of new treatments against neurodegenerative diseases in general and Alzheimer's disease in particular.