Gegen Qinlian Decoction can effectively treat cognitive dysfunction. However, its active ingredients and the underlying biological mechanisms remain unclear. In this study, a network pharmacological analysis is performed for the pharmacological components of 4 Chinese herbs (puerariae lobatae radix, scutellariae radix, coptidis rhizoma and glycyrrhizae radix et rhizoma praeparata cum melle) in the Gegen Qinlian Decoction and targets of cognitive dysfunction. Gegen Qinlian Decoction has affected 88 core targets associated with cognitive dysfunction. Subsequently, GO and KEGG enrichment analysis indicates that these core targets may be involved in the response to extracellular stimulus and oxidative stress. Finally, appropriate active ingredients and potential target proteins are identified by gene-pathway relationship network maps and molecular docking. Moreover, there is a PPI interaction network to supplement it. The results reveal that quercetin, licochalcone A, tetrahydroberberine and naringenin are intended to be the active components related to most disease pathways. The outcomes of molecular docking have also validated their good binding properties with the target genes.
Along with the social aging intensifies, the incidence of cognitive dysfunction is increasing year by year. As the most serious type of cognitive dysfunction, the incidence of dementia almost doubles every 20 years. The sum of healthcare costs and income loss from dementia is expected to rise to $2 trillion [1] by 2030. Due to the poor treatment effect of middle and late dementia, it causes a heavy burden to the society and the family, and wastes a lot of human and material resources. Therefore, it is a feasible way to explore a mechanism to control cognitive dysfunction from TCM compound medicine.
Gegen Qinlian Decoction comes from the Treatise on Febrile and Miscellaneous Disease in the Eastern Han Dynasty. Its major function is similar to treating modern intestinal inflammatory diseases. Hence, it is mostly used in the clinical treatment of intestinal diseases. However, this book also records the basis of this Chinese medicine prescription in the treatment of brain diseases. Besides. many practitioners of later generations have drawn similar conclusions through clinical practice. It expounds the characteristics of multi-targets and diversification in the TCM treatment of cognitive dysfunction.
Some animal experiments [2] have proved that Gegen Qinlian Decoction can protect the viability of hippocampal cells, inhibit the apoptosis of hippocampal cells, maintain the dendritic spine density by activating the activity of PI3K-Akt signaling pathway in rats with diabetic cognitive dysfunction, thus improving the learning and memory function in rats. A randomized controlled clinical trial [3] including 60 cases of vascular dementia shows that taking Gegen Qinlian Decoction may improve the patients’ cognitive function (MMSE) score and ability of daily living (ADL) score, and effectively prevent the disease converting to end-stage disease. Nevertheless, Gegen Qinlian Decoction is not perfect in the mechanism of the treatment of cognitive dysfunction and there is a lack of systematic analysis. Therefore, we try to understand the mechanism of Gegen Qinlian Decoction in treating cognitive dysfunction from the perspective of network pharmacology and molecular docking in this study.
As shown in this paper, the PPI topology analysis of 88 crossover genes reveals 28 strongly related genes, including major gene targets (AKT1, IL6, IL1B, CASP3, CCL2, IL10, STAT3, CXCL8, EGF, ICAM1, CRP, IL4, IL2, SIRT1, NOS2, GSK3B and MAPK1) in regulating immunity and apoptosis. In the PPI network, by the size of degree values, the series are AKT1, IL6, IL1B, VEGFA, MMP9, etc. AKT1 that is one of the three serine/threonine protein kinases (AKT1, AKT2 and AKT3) can regulate the balance of apoptosis, thereby inhibiting the activity of pro-apoptotic cytokines and activating the activity of anti-apoptotic cytokines, and then affecting the survival[4]of neurons. Activated AKT is an important upstream regulator of GSK-3 β proteins. AKT may promote the phosphorylation of Ser9 of GSK-3 β, thus inhibiting GSK-3 β protein activation, further reducing the phosphorylation level of Tau and improving cognitive function[5] in Alzheimer's disease mice. IL6 regulates the inflammatory response in the human body and ADPN may protect nerve cells [6] by inhibiting IL6 expression. Clinical data indicate that the expression of postoperative inflammation is closely related with postoperative cognitive dysfunction, especially the levels [7.8] of IL6 and IL1B. VEGFA has special protective effects [9] in patients with Alzheimer's disease and people with high-risk cognitive decline. MMP9 is a key factor affecting the permeability of blood-brain barrier (BBB). By activating the self-autonomous CypA-MMP9 BBB degradation pathway in the endothelium, it leads to the spontaneous disintegration of the cerebral vascular system, resulting in the loss of key endothelial tight junction proteins and collagen IV, thereby leading to structural damage of BBB, leaking blood-derived neurotoxic proteins (such as fibrinogen), and causing relevant neurodegenerative processes [10].
Through the analysis of KEGG enriched pathway, we have discovered that six genes (MAPK1, IL6, AKT1, CASP3, IL1B and STAT3) involve in the most pathways. Quercetin may interact with IL6I, AKT1, CASP3 and IL1B; licochalcone may affect STAT3; and tetrahydroberberine may bind with HTR2C. These components may play an important role in treating cognitive dysfunction. Quercetin is an important flavonoid prevalent in a diet with various fruits and vegetables. It is considered a phytochemical that may modulate pathways related to mitochondrial biogenesis, mitochondrial membrane potential, oxidative respiration and ATP anabolism, intramitochondrial redox status, and subsequent mitochondria-induced apoptosis. It plays a protective role against mitochondrial damage in response to several exogenous and endogenous cellular stressors, especially the toxicity [11] caused by oxidative stress. Animal experiments have shown that quercetin can relieve the brain insulin resistance caused by β amyloid and neuroinflammation, either by acting directly on the brain or by regulating the gut-brain axis, and ultimately alleviate the cognitive dysfunction resulting from the β amyloid-induced cognitive dysfunction [12]. Licochalcone A is a chalone isolated from ural licorice, with a variety of antioxidant, antitumor and anti-inflammatory activity [13]. It is shown that licochalcone A may reduce triglyceride level [14] in HFD-induced obese mice. Although there are no studies of licochalcone A in improving cognitive impairment, there are clinical studies [15] demonstrate that statins that reduce TC may decrease the human serum β amyloid and cut down the AD incidence by 70%. Tetrahydroberberine has multiple biological activities [16]. It has been shown to be a new generation of dopamine (DA) antagonist in biochemistry and neuropharmacology, and also to increase the spontaneous discharge of DA neurons. It may reversibly block the opening [17] of the K-ATP channel in a dose-dependent manner. The experiment suggests that A β is significantly reduced with increasing drug concentration and tetrahydroberberine concentration. Moreover, the effect of reducing the number of apoptotic cells is more obvious [18]. Naringenin increases superoxide dismutase and glutathione peroxidase activity in the hippocampus of VaD rats by reducing the production of reactive oxygen species, reducing the malondialdehyde content and recombining the expression of reactive oxygen species regulator 1 (Romo-1), thus reliving the hippocampal oxidative stress. Furthermore, it mitigates the cognitive impairment [19] in VaD rats via suppressing hippocampal inflammatory response as well as restoring NMDARs signaling pathway.
The pathogenesis of cognitive dysfunction is complex. The progression of this disease is associated with cerebrovascular lesions, β amyloidogenesis, intestinal flora, hypothyroxinemia and hyperlipidemia. The KEGG enrichment results indicate that the therapeutic mechanisms are mainly concentrated on the following pathways: AGE-RAGE signaling pathway in diabetic complications, lipid and atherosclerosis, fluid shear stress and atherosclerosis, PI3K-Akt signaling pathway and neuroactive ligand-receptor interaction. (1) The AGE-RAGE signaling pathway in diabetic complications is the most important signaling pathway, which indicates that the AGE-RAGE has a deleterious effect [20] on neuronal damage and inflammation in diabetic patients. (2) Lipids and atherosclerosis are involved [21] in the formation of atherosclerotic plaques. (3) Fluid shear stress and atherosclerosis pathways play an important role [22] in the vulnerability of atherosclerotic plaques. (4) The PI3K/AKT signaling pathway is considered an important signaling pathway for neuronal survival. It modulates neuronal cell survival and synaptic plasticity [23] in aging and many neurodegenerative diseases. (5) Neuroactive ligand-receptor interaction pathway: In this pathway, neurotransmitter receptors are rich and diverse, comprising acetylcholine receptors, monoamine neurotransmitter receptors and inhibitory amino acid neurotransmitter receptors, etc. Some scholars have found that reduced cholinergic innervation is one [24] of the causes of cognitive decline in cognitive and neurodegenerative diseases, especially in patients with Alzheimer's disease. The dopamine system also has functions in regulating aging and cognitive abilities, such as the dopamine D1 receptor (DRD1), which is critical in the neurotransmission of various brain pathways, regulating key functions including autonomic movement, memory, attention and reward, etc. Selective activation of DRD1 could provide new ideas [25] for target treatment of neurodegenerative and neuropsychiatric disorders. Inhibitory interneuron receptors such as γ-aminobutyric acid (GABA) may produce phasic and tonic inhibition, thereby modulating neural activity. This helps establish proper network dynamics in cortical circuits and maintain normal cognition [26]. Consequently, altered γ -GABA signaling is associated with cognitive deficits related to psychiatric and neurological disorders.
However, there are many shortcomings in studying the mechanism of traditional Chinese medicine and traditional Chinese medicine prescriptions using network pharmacology methods. Network pharmacology is based on modern biological pharmacy classification system, which is suitable for the prediction of single chemical composition rather than on complex TCM system. TCM is different from chemical drugs with single chemical composition. TCM formula is not a simple sum [27] of chemical composition. In the parameter settings to filter the so-called active component, many other properties besides oral bioavailability (OB) and drug-like properties (DL) may also influence the drug activity. These influencing factors need to be fully considered when determining the active ingredients. Whereas the network database screening is based on the absorption, distribution, metabolism, excretion (ADME) and so on data processing methods, which has lost sign of the effect of the component content on the efficacy; neglected the interaction among TCM components, including mutual regulation of in vivo absorption and in vivo processes; and ignored that drug components may play an indirect therapeutic role by regulating intestinal flora.In particular, it ignores the regulation effect of polysaccharides in traditional Chinese medicine as prebiotics on intestinal flora [28]. However, intestinal microbiota and inflammatory bowel disease play an important role in the development of cognitive dysfunction [29]. As a consequence, we have discussed the size of binding energy of relevant molecules ((R) -Canadine and HTR2C) in molecular docking. From this we can see that there are still great limitations in the theoretical analysis of drugs relying on network pharmacology technology. Further experiments are required to prove a more accurate mechanism of drug action.