Alzheimer's disease is a progressive neurodegenerative condition that involves multiple biological processes. Single-targeted therapy is no longer in fashion. Traditional Chinese medicine (TCM) treatment takes a holistic approach, using a multi-targeted and multi-pathway therapeutic approach. This provides a new way of thinking about the treatment of Alzheimer's disease. This study screened 10 active ingredients from Polygonatum using Network pharmacology. The active ingredients include methylprotodioscin_qt and sibiricoside A_qt of saponins, beta-sitosterol, sitosterol, and zhonghualiaoine1 of phytosterols, and flavonoids. Additionally, Liquiritigenin, 4',5-Dihydroxyflavone, DFV, baicalein, and 3'-Methoxydaidzein were identified. Saponins are natural plant compounds that can be classified into two main groups: triterpene saponins and steroidal saponins.37 These compounds have various pharmacological properties, such as promoting learning and memory,38 reducing inflammation and oxidative stress,39,40 lowering Aβ levels, inhibiting tau protein hyperphosphorylation,41,42 and decreasing apoptosis in neuronal cells.43,44 Screening based on Ellman's method and HPLC-QTOF MS technique revealed that Zhimai steroidal saponins exhibit moderate or weak AChE inhibitory activity,45 indicating their potential as an anti-AD drug. On the other hand, Diosgenin exerts its therapeutic effect on AD by modulating NOX 4/NOX 4-mediated oxidative stress and inflammatory responses.46 Phytosterols are a class of natural compounds that cannot be synthesized by the human body. They play an important role in regulating cholesterol levels, combating atherosclerosis, and maintaining brain health.47,48 In this study, β-sitosterol, a significant dietary phytosterol, inhibited cholinesterase activity in the hippocampus and frontal cortex and decreased the free radical load in brain tissue.49 The mechanism of neuroinflammatory action during the course of AD has not been fully elucidated.50 However, the inflammatory process in AD certainly involves several proinflammatory factors, such as cytokines (e.g., IL-6, TNF-α), transcription factors (e.g., NF-κB), and enzymes (e.g., COX-2).51 Experimental studies have shown that β-sitosterol can induce anti-neuro injury effects by inhibiting COX-2, IL-6, and NO.52 Tau proteins are phosphorylated proteins found in the normal human brain. In AD patients' brains, the number of phosphorylated Tau proteins per molecule can increase to 5–9, compared to the normal 2–3, causing them to lose their normal biological functions. In a cellular assay conducted in vitro, the resistance of cell membranes to oxidative stress and lipid peroxidation mediated by glucose oxidase (GOX) was enhanced by the addition of beta-sitosterol.53 Several studies have demonstrated a close relationship between mitochondrial dysfunction and the development of AD.54–56 Beta-sitosterol increases ATP levels in the inner mitochondrial membrane, which is beneficial for AD. Cholesterol has been found to play a role in amyloid-β-producing enzyme activity.53 Low levels of cholesterol inhibit Aβ accumulation, and β-sitosterol significantly reduces serum cholesterol levels.57,58 Additionally, an experimental study found that chronic intake of phytosterols in mice caused irreversible accumulation of phytosterols in the brain.59 Flavonoids are the third group of anti-AD potentials in Polygonatum. Baicalein, a flavonoid, has been shown to have neuroprotective effects both in vivo and ex vivo.60 It inhibits disease-associated amyloid production and deposition, reduces oxidative stress and inflammatory response, promotes neural differentiation, and increases resistance to apoptosis.61 Xie et al. discovered that baicalein stimulates the phenotypic transformation of activated microglia through the CX3CR1/NF-κB pathway and reduces neuroinflammatory responses, improving learning ability in model mice.62 Ji et al. demonstrated that baicalein inhibits Aβ25-35-induced oxidative damage, thereby reducing apoptosis.63 Research has demonstrated that baicalein can reverse memory and cognitive deficits induced by Aβ by repairing damaged neurons.64 Impaired cognitive function in the brain is closely related to abnormal functioning of the cholinergic system. Clinical practice has utilized a variety of acetylcholinesterase inhibitor drugs, and preclinical studies have provided ample evidence that restoration of the cholinergic system not only improves cognitive function symmetrically but also attenuates the pathological features of AD, such as β-amyloid aggregation and hyperphosphorylation of tau proteins.65 In contrast, Liquiritigenin prevents the formation of Tau amyloidogenic fibrils and the exposure of hydrophobic plaques.66 Additionally, Liquiritigenin significantly reduces oligomeric levels of Aβ proteins in the mouse brain in related mouse experiments, although it does not alter β-amyloid precursor protein (APP) levels.67 Liquiritigenin improves scopolamine-induced learning and memory deficits by enhancing and protecting the BDNF/ERK/CREB signaling pathway.68 Yang et al. discovered that 4',5-dihydroxyflavone significantly increased the survival of PC12 cells after Aβ25–35 attack and elevated the Ca2 + concentration in these cells. This suggests that 4',5-dihydroxyflavone may have neuroprotective effects through dopaminergic synaptic pathways.69
The PPI network diagram depicts the interactions among different proteins involved in cell cycle, energy metabolism, and signaling. The diagram illustrates the interactions among various proteins. AKT1, a serine/threonine protein kinase, is activated by insulin and various growth and survival factors. It serves as a crucial target of the PI3K-Akt signaling pathway, which regulates cell division, proliferation, apoptosis, and glucose metabolism.70 Abnormal brain insulin metabolism has long been considered a pathogenic mechanism of AD and has been experimentally demonstrated.71 AKT1 activation is not only related to learning and memory,72–74 but also normalizes insulin signaling. This enables the PI 3 K/Akt signaling pathway to operate normally, avoiding neuroinflammation, oxidative stress, and other pathological processes.75
STAT3 encodes a protein that belongs to the STAT family of proteins. It plays a crucial role in various cellular processes such as cell growth and apoptosis. STAT3 is activated by several cytokines, including IL-6 and IL-10, as well as growth factors such as EGF and FGF. Activation of STAT3 was found to be effective in rescuing hTau-induced synaptic dysfunction and memory impairment in mice in animal experiments.76 However, specific knockdown of STAT3 in AD model mice significantly reduced their brain amyloid levels and plaque load.77 This suggests that the role of STAT3 in Alzheimer's disease is two-fold. JUN is a transcription factor that regulates gene transcription in cells and influences biological processes such as cell proliferation, differentiation, and apoptosis. Down-regulating JUN reduces the expression of inflammatory factors.78 Additionally, inhibiting c-Jun rescues neuronal death and damage in AD progenitor cells.79 The TP53-encoded p53 protein induces cell cycle arrest, apoptosis, senescence, DNA repair, or metabolic alterations. Aberrant alterations in p53 activity and Alzheimer's disease (AD) are closely related. The first time p53 activity was found to be altered in AD was in skin fibroblasts from SAD patients.80 Since then, numerous studies have shown that p53 dysregulation induces or exacerbates AD.81,82 The mTOR signaling pathway has been implicated in p53 activity in several studies. It is worth noting that this pathway is activated in early AD, as demonstrated by multiple studies.83,84 Therefore, p53 dysregulation may activate the mTOR signaling pathway and induce AD. Additionally, casp3, a cysteine-aspartic acid protease, maybe a potent target in early AD.85
The KEGG pathway enrichment analysis revealed that Polygonatum regulates the PI3K-Akt signaling pathway, Pathways in cancer, Pathways of neurodegeneration - multiple diseases, and Lipid and atherosclerosis pathways to treat Alzheimer's disease. For instance, the PI 3 K/AKT signaling pathway participates in various in vivo biological processes, including apoptosis, inflammatory response, proliferation, and growth. Its activation inhibits GSK-3β and mTOR signaling, which, in turn, reduces tau protein phosphorylation.86 Previous experiments have shown that activation of metabotropic γ-aminobutyric acid receptors inhibits neuronal apoptosis and increases levels of SOD, GSH-Px, and CAT through the PI 3 K/Akt signaling pathway.87 This signaling pathway also regulates the amelioration of dysfunctional synaptic plasticity.88 In addition, a correlation has been found between estrogen loss and an increased risk of AD.89 Estrogen also protects nerves from toxic damage and reduces inflammatory signaling in neurons by regulating calcium flow.90 Numerous studies have confirmed the association between elevated cholesterol levels and an increased likelihood of developing AD. Specifically, elevated serum LDL levels are involved in the development of AD amyloid pathology.91,92 It is possible that vascular diseases, such as atherosclerosis, caused by abnormal cholesterol levels, are related to the pathology of AD. Research has shown that vascular dysfunction caused by atherosclerosis can disrupt the blood-brain barrier, induce inflammation, and impede β-amyloid clearance.93 The NF-κB signaling pathway and VEGF signaling pathway are also involved in the AD process, in addition to the pathways mentioned above.94–96 In conclusion, our Network pharmacology analysis suggests that Polygonatum has the potential to treat Alzheimer's disease through a multi-component, multi-target, and multi-pathway approach. For instance, baicalein targets TP53, CASP3, AKT1, and methylprotodioscin_qt simultaneously, while sibiricoside A_qt targets STAT3. Additionally, we found that 43 genes were enriched in Pathways in cancer and 23 genes were enriched in the PI3 K/Akt signaling pathway.
Molecular docking is a technique used to predict ligand-receptor binding and calculate binding energies. We validated the docking of 10 active components of Polygonatum and five critical targets using molecular docking. The results demonstrated favorable binding energy for all 50 dockings, confirming our hypothesis regarding the potential of Polygonatum for treating Alzheimer's disease. While network pharmacology aided in identifying active ingredients and corresponding targets of Polygonatum, and molecular docking validation yielded positive results, it is important to note that these findings were based on the analysis of numerous databases and network computer technology. Therefore, caution should be exercised when interpreting these results. Clinical studies are necessary to further validate the results, as we cannot guarantee the scientific validity of the database data or the accuracy of the computerized analyses.