Alzheimer’s disease (AD) is an irreversible, degenerative brain disease characterized by impairment of cognitive and behavioral deterioration, accounting for 60–80% of all dementia patients [1]. According to the World Alzheimer Report 2021, over 55 million people live with dementia worldwide and this number is projected to rise by threefold, reaching 152 million by 2050, making it the 5^th leading cause of death [2]. A collaborative survey of icddr, b, Directorate General of Health Services (DGHS), and National Institute of Neuroscience & Hospital (NINS) estimated that around 1.1 million people in Bangladesh have dementia, and this number is projected to reach 1.37 million in 2025 and could be doubled in 2041 (2.4 million).

Neuropathological diagnosis of an AD brain reveals the loss of cholinergic neurons from the basal forebrain to the hippocampus, resulting in reduction of choline acetyltransferase (ChAT), an enzyme responsible for the synthesis of acetylcholine (ACh), a neurotransmitter that regulates the sleep cycle, memory and learning functions [3]. Reduction of ChAT activity and ACh levels are significantly corroborated with cognitive impairment in AD cases. Acetylcholine and butyrylcholine signaling are terminated within the synaptic cleft through the breakdown of acetylcholine and butyrylcholine by acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), respectively [4]. Hence, drugs that limit acetylcholine and butyrylcholine breakdown (AChE inhibitors) have provided a therapeutic strategy to augment cholinergic signaling in AD patients. In addition to the cholinergic system, the accumulation of extracellular senile plaques consisting of deposits of amyloid beta (Aβ) peptides ultimately leads to neuronal cell death and brain atrophy [1]. Aβ peptides are generated through successive cleavage of amyloid precursor proteins (APPs) by beta-secretase (BACE-1) and gamma-secretase in brain tissues [5]. Aβ42 is thought to be secreted and aggregated as senile plaques due to their low solubility and more neurotoxic components in amyloid plaques at the earliest stage of AD. Patients with familial AD regularly exhibit a higher ratio of Aβ42 in the brain [6].

Therefore, we hypothesize that the prevention of acetylcholine and butyrylcholine deprivation by inhibiting acetylcholine and butyrylcholine degrading enzymes, acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), and cleavage of APPs by beta-secretase or BACE-1 (b-secretase or beta-site APP-cleaving enzyme) is a key step in amyloid-beta production and could be an attractive target for AD drug development.

Several studies on AD onset and progression have been performed. However, currently, no effective treatments are available to prevent or ameliorate this debilitating neurodegenerative disease. Drug treatments for AD primarily provide temporary and incomplete symptomatic relief accompanied by severe side effects, including nausea, vomiting, and liver damage, instead of disease cure [7]. Traditional medicines from natural products are currently of interest as promising alternative candidates for the treatment of AD because of their consumption safety, cost-effectiveness, limited side effects and multi-target abilities [1, 8]. Diplazium esculentum, Limnophila aromatica, Eichhornia crassipes, and Beta vulgaris are all edible plants. Diplazium esculentum is a common pteridophyte in the family Athyriaceae and grows as an edible vegetable fern. Only the young, curly fronds are used as vegetables. D. esculentum has been reported as a credible source of minerals and bioactive compounds such as phosphorus, potassium, alkaloids, flavonoids, saponins, tannins, and terpenoids, together with antibacterial, antidiabetic, antioxidant, and hepatoprotective activities [1]. The methanolic crude extract of D. esculentum inhibited AChE activity in vitro. Limnophila aromatica belongs to the Scrophulariaceae family known as rice paddy herb, and has been stated as a source of flavonoids, terpenoids, and antimicrobial, antioxidant, and vascular protective activities [9]. The aqueous extract of Limnophila aromatica exhibited antioxidant and acetylcholinesterase (AChE) inhibitory activity in vitro and a memory enhancing effect in rats [10]. Eichhornia crassipes, commonly known as water hyacinth, is a warm-water floating aquatic plant belonging to the family of Pontederiaceae. Water hyacinth flowers and green parts are used as a carotene-rich vegetable in Vietnam, Japan, Taiwan, and Thailand. It has been reported that water hyacinth is a rich source of secondary metabolites which have biological activities such as antiviral, antifungal, antitumor, and antibacterial effects [11]. The plant is a convenient source of antioxidants, including oxidative enzymes and non-enzymatic antioxidant systems, as well as having wound healing effects and anticancer activities. The ethanol extract of water hyacinth showed promising anti-AChE activity in vitro [12]. Beta vulgaris is an herbaceous biennial leafy vegetable belonging to a family cultivated in many parts of the world for its year-round availability and generally known as beetroot or chukandar. It is widely spread in Turkey and is used as an antidiabetic in traditional medicine [13]. Numerous studies in recent years have shown that this plant extract has beneficial properties for health with its antioxidant, antibacterial, hepatoprotective, hypocholesteremic, and anticoagulant activity. It has also been reported that the hypoglycemic effect of Beta vulgaris treatment in the model of type-2 diabetes in rats. Furthermore, Beta vulgaris extract has been shown in vitro to have AChE inhibitory activity as well as antioxidant potential. Based on above statement, it implies that all the selected plants might be a promising candidate for prevention or treatment of AD by supporting cholinergic neurons. However, it is unknown whether these plants possess anti-AD properties particularly in relation to the amyloid pathway. Thus, this proposed research will explain the anti-AD properties of selected plant extracts in vitro and in Drosophila model of AD, as well as the phytochemicals of the selected plant extracts in silico.

Drosophila models have well-defined genetic characteristics including a short life span, simplicity in genetic manipulation, and a powerful binary UAS-GAL4 transgenic system, allowing tissue-specific protein expression [1]. AD-like symptoms can be obtained from flies expressing human AD genes that resemble AD pathology presented in mice AD models [14]. Flies are also a powerful alternative model for drug screening since their anatomy exhibits an open blood vascular system, hence drugs or plant extracts can be distributed to target organs, even the brain. The blood-brain barrier (BBB) is known to restrict the distribution of biomolecules (> 500 kDa), including proteins and drugs. Studies in the cell models cannot overcome this problem. Thus, here, phytochemical analysis, in vitro antioxidant and anti-AD properties of selected edible plant extracts, and in silico anti-AD properties of the GC-MS identified phytochemicals of selected edible plant extracts through inhibition of the key enzymes relevant to AD (AChE, BChE, and BACE-1) will be studied. Additionally, inhibition of BACE-1 and Aβ42 production in Drosophila models will also be elucidated.