To explore the molecular mechanism of acrylamide-induced ND, we searched the ChEMBL, Super-PRED, STP, SEA, STITCH, GeneCards, and OMIM databases and identified 142 potential targets of ND associated with acrylamide. We subsequently used the STRING database and Cytoscape to screen 18 core targets, including TP53, PIK3CA, PIK3R1, PTK2, and GRB2, which are considered core targets of acrylamide-induced ND and have been associated with ND. We subsequently constructed the PPI network. Using the DAVID platform, we performed GO and KEGG enrichment analyses for the core targets. The results showed that acrylamide induced ND mainly through the PI3K-Akt and PLD signaling pathways. Molecular docking results showed that the five core target proteins could bind stably to acrylamide with a binding energy less than 0 kcal/mol.
The TP53 gene, which is also known as P53 and is located on chromosome 17, is an important tumor suppressor gene that prevents normal cells from becoming cancer cells and plays a crucial role in promoting cell apoptosis and inhibiting tumor formation. Previous studies showed that TP53 mutations exist in the somatic cells of diseased tissues in patients with various nerve injuries, such as nervous system tumors and malignant peripheral schwannomas[15–16]. Qu Shuang reported that TP53 deletion was present in two newly treated patients with multiple myeloma with intracranial invasion and was a clinical manifestation of impaired central nervous system function[17]. In addition, the TP53 subtype has been shown to modulate the toxic and protective effects of astrocytes on neurons. Abnormal expression of TP53 may be related to neurodegenerative diseases such as Alzheimer’s disease (AD) and Parkinson’s syndrome[18–19]. In human neuroblastoma cells, acrylamide exert cytotoxic effects by phosphorylating the P53 protein at Ser15[20]. Molecular docking experiments showed that acrylamide could easily bind to the TP53 protein.
PIK3CA is an oncogene that is expressed in the brain, mammary gland, and intestine of normal humans and plays an important role in regulating somatic cell proliferation, differentiation, and other physiological functions. As a catalytic subunit of PI3K, PIK3CA plays a key role in the PI3K/AKT signaling pathway and protects against Aβ toxicity by inhibiting tyrosine phosphatase, thereby affecting the regulation of AD pathogenesis[21]. According to relevant studies, the PI3KCA mutation is associated with peripheral neurolipomatosis[22].
PI3K is located downstream of tyrosine kinase, G protein-coupled receptors, and GTPase and is involved in regulating cell metabolism, proliferation, and migration[23]. In vivo, PI3KR1 and its gene product p85α inhibit the catalytic activity of PI3K in tumors and exert a tumor suppressive effect[24]. In addition, PI3KR1 is underexpressed in most tumors, and its deletion may play a role in abnormal cell proliferation, increased invasion, and decreased apoptosis[25]. According to relevant research, miR-153-3p causes insulin resistance in the brain through PIK3R1 and participates in the neurotoxicity induced by cigarette smoke[26]. PIK3R1 has also been shown to be associated with the development of neurodegenerative diseases[27].
The PTK2 protein, which is also known as FAK, is involved in cell adhesion and diffusion and is related to the normal apoptosis of cells. The upregulation of PTK2 expression, which includes high PTK2 protein expression and overactivation, occurs in almost all tumor tissues, such as common lung cancer, stomach cancer, colorectal cancer, uterine cancer, and melanoma tissues[28]. Existing studies have shown that PTK2 is associated with axon growth[29–30]. The PTK2B protein, which is the expression product of the PTK2B gene, may be a risk factor for AD. The expression level of PTK2B in the hippocampus of rats with Aβ-induced cognitive dysfunction is increased, accompanied by increased phosphorylation of the Aβ1–42 and Tau proteins[31].
The GRB2 protein, which is also known as the ASH protein, is involved in EGF receptor-mediated signal transduction and is indirectly involved in insulin receptor-mediated signal transduction by binding to the Shc phosphorylated tyrosine. The GRB2 protein can also bind to the Shc-SOS complex and activate the Ras protein, thus participating in various cell development processes[32–33]. GRB2-associated binding protein 1 has been shown to be critical for peripheral nerve myelination, and it regulates the formation of neuromuscular synapses in skeletal muscle[34–35]. Studies have shown that GRB2-associated binder 2 gene knockout mice exhibit neural repair defects after nerve transection[36].
Considering the results of GO and KEGG enrichment analyses, we found that several key signaling pathways play a role in acrylamide-induced neurotoxicity. For example, the PI3K-Akt signaling pathway plays a role in the expression of microRNAs in cancer, lipid and atherosclerosis, hepatitis B, and phospholipase D (PLD) signaling. The PI3K-Akt signaling pathway is activated by various types of cell stimulation or toxic damage and regulates basic cell functions such as transcription, translation, proliferation, growth, and survival[37]. PI3K catalyzes the production of PIP3 on the cell membrane. PIP3 acts as a second messenger to activate Akt. Activated Akt controls key cellular processes by phosphorylating substrates involved in apoptosis, protein synthesis, metabolism, and the cell cycle[38]. Studies have shown that nerve growth factor (NGF) promotes the formation of filamentous pseudopods and branches of axons through the PI3K-Akt signaling pathway[39]. The PI3K-Akt signaling pathway has been shown to be associated with ND[40–42]. Considering the regulatory effect of the PI3K-Akt signaling pathway and key targets such as TP53, PI3KCA, PIK3R1, RTK2, and GRB2 on nerve injury and combined with the findings of previous studies, acrylamide was found to regulate the PI3K-Akt signaling pathway[43–44]. acrylamide may have a substantial effect on nerve injury by regulating the PI3K-AKT signaling pathway. Glioblastoma is the most common primary malignant tumor in the nervous system of humans and is formed by the malignant transformation of astrocytes[45]. Studies have shown that microRNA-3938 inhibits glioblastoma by downregulating multiple oncogenes and upregulating p53, suggesting a close relationship between microRNAs and nerve injury[46]. In addition to stimulating neuron differentiation and survival, NGF plays an important role in lipid metabolism and atherosclerosis progression[47]. Moreover, studies have shown that acrylamide is closely related to the development of atherosclerosis[48]. Current studies have indicated that hepatitis B can cause ND[49]. PLDs are responsible for the production of the lipid second messenger phosphatidic acid (PA) in cells, and PAs are involved in basic cellular processes such as membrane transport, actin cytoskeleton remodeling, cell proliferation, and cell survival[50]. Previous studies have shown that PLD is related to the stretch sensitivity of sensory nerve endings, which is crucial for maintaining the stretch reactivity of the primary end of the mechanical sensor of the muscle spindle[51]. Moreover, the regulation of the PLD signaling pathway is closely related to nerve injury[52].
Despite evidence indicating that acrylamide can cause neurological damage, the underlying mechanism of its toxicity remains unclear. acrylamide is widely used in a variety of industries, which is why residual acrylamide monomers enter environmental media such as water, soil, and the atmosphere through industrial wastewater and waste residue during production and polyacrylamide production. Smoking and high-temperature cooking processes, especially frying or baking high-starch food, can also produce acrylamide. In addition, acrylamide can be metabolized into its carcinogenic active metabolite, epoxide propanamide, by animals and humans. Long-term exposure to or ingestion of acrylamide may increase the risk of cancer.
In addition to revealing the molecular mechanism underlying the potential neurological damage caused by acrylamide, we also attempted to develop an effective and rapid strategy for screening and studying the toxicity of environmental pollutants. Traditional toxicological studies rely on animal models, and pathological and immunological experimental techniques are used to identify toxic effects of drugs and environmental factors. However, certain limitations exist, not least in dealing with potential chemical poisons that quickly emerge in the environment. Network toxicology involves describing the toxicological properties of research objects by constructing network models that can quickly construct network models of chemical-toxicity target effect pathway interactions and provide strong technical support for exploring the toxicity mechanism of chemical substances. In addition, molecular docking and molecular dynamics simulation techniques can explain the interactions between molecules in depth and visually explain the mechanism of interaction. These approaches have become important research methods for explaining biological mechanisms. Molecular docking and molecular dynamics techniques also provide important tools for predicting the binding types and interaction patterns of biomacromolecular complexes and provide useful references and theoretical support for further experiments. The use of network-based toxicology and molecular docking paradigms may expand the efficiency, depth, and prediction accuracy of toxicological screening and provide a new perspective for the assessment and mechanism prediction of a large number of understudied emergent environmental toxicants.
However, some limitations remain with regard to analyzing the mechanism of action of acrylamide in producing neurotoxicity based on the existing limited database. Therefore, further validation experiments are needed to confirm the results of network-based analysis.