The neurotoxicity of acrylamide in ultra-processed foods: interventions of polysaccharides through the microbiota–gut–brain axis

Abstract

Ultra-processed foods (UPFs) have become popular in recent years, however, the detrimental effects of their excessive consumption have also become evident. Acrylamide (AA), a processing hazard present in UPFs, can further aggravate the harmful effects of UPFs. AA can cause significant damage to both the intestinal barrier and gut microbiota, thereby affecting the nervous system through the microbiota–gut–brain (MGB) axis. Natural polysaccharides have demonstrated the capacity to significantly alleviate the oxidative stress and inflammatory response associated with AA exposure. In addition, they exhibit neuroprotective properties that may be mediated through the MGB axis. This paper reviews literature on the presence of AA in certain UPFs and its potential to inflict serious harm on the human gut microbiota and brain. Moreover, the possibility of utilizing polysaccharides as a preventative measure against AA-induced neurotoxicity was also proposed. These findings provide new insights into the safety risks associated with the overconsumption of UPFs and highlight the potential of polysaccharides to counteract the neurodegeneration induced by AA.

---

Introduction

The rapid development of the food industry has introduced more and more diversity in food types and processing methods.¹ Due to the accelerated lifestyle of modern people, many consumers prefer to eat convenient and highly processed food instead of freshly prepared foods in order to save time. As a result, traditional dietary patterns have gradually shifted, with ultra-processed foods (UPFs) gaining increasing popularity. Previous studies have established that consuming UPFs elevates the risk of chronic diseases such as cardiovascular diseases (CVDs),^2,3 obesity,⁴ diabetes,⁵ and dementia.⁶ Process contaminants found in UPFs, such as heterocyclic aromatic amines (HAAs), acrylamide (AA), advanced glycation end-products (AGEs), trans fatty acids, and furans, have been identified as significant contributors to the health risks associated with these products, as these process contaminants can disrupt the endocrine system and gut microbiota.^2,6

AA is a key processing contaminant produced in UPFs, known for its neurotoxic effects.⁷ It is formed when carbohydrate-rich foods are heated at high temperatures.⁸ Although AA can also be produced in some simply processed foods, UPFs were reported to contain high levels of AA as they tend to be heated for a long time at high temperatures. For example, the AA content in both French Fries and potato chips can be up to 100 times higher than in boiled potatoes.⁹ Upon ingestion, AA interacts with the intestinal tract during digestion and absorption, and then enters the human body, resulting in toxicity.¹⁰ Exposure to AA induces oxidative stress, inflammation, apoptosis, and DNA damage.¹¹ Various neurodegenerative diseases, as well as brain pathology, such as Parkinson's disease and Alzheimer's disease, are associated with oxidative stress and inflammation.¹²

The gut microbiota, a complex microbial community, significantly influences various aspects of host physiology.¹³ It has been demonstrated that gut microbiota and its metabolites maintain gastrointestinal (GI) functions due to their capacity to affect intestinal permeability and mucosal immune function.¹⁴ Short-chain fatty acids (SCFAs), one of the important metabolites of gut microbiota, play a key role in maintaining the intestinal barrier and regulating intestinal inflammation.¹⁵ The intricate microbiota in the mammalian intestinal tract plays an important role in immunity and defence when pathogenic bacteria invade the host's intestinal tract.¹⁶ For example, Lactobacillus can mediate the production of reactive oxygen species (ROS) via regulating the redox state of host cells, thereby reducing oxidative stress.¹⁷ Besides, the gut microbiota and its metabolites can affect the central nervous system (CNS) and regulate brain function through the microbiota–gut–brain (MGB) axis,¹⁸ thus affecting mood and behaviour, including depression, anxiety, circadian rhythm disorders, etc.^19–21 The bidirectional communication between the GI and the brain is essential for maintaining balance in the body and regulating the nervous system, and provides a potential pathway for the gut microbiota and its metabolites to enter the brain.²²

Long-term intake of UPFs will damage the gut microbiota, leading to metabolic disorders, oxidative stress, and inflammation, thus increasing the risk of brain diseases.²³ One of the major reasons for these damages may be that some UPFs contain AA. AA stimulates the inflammatory response in the brain by disrupting the intestinal barrier integrity and increasing the levels of circulating lipopolysaccharides (LPS), interleukin (IL)-1β, and TNF-α (tumor necrosis factor-α). This further aggravates the harm caused by excessive consumption of UPFs and causes significant damage to both the human gut microbiota and nervous system through the MGB axis.²⁴ Studies have shown that AA can cause neurobehavioural disorders, including cognitive and motor impairments, in zebrafish through the MGB axis.²⁵

Polysaccharides, natural active macromolecules composed of various monosaccharides connected by glycosidic chains, are widely found in nature.²⁶ Polysaccharides have a variety of biological activities, such as immune regulation, anti-inflammation, anti-oxidation, anti-cancer, and hypoglycemia, which play an important role in maintaining human health.²⁷ Further studies have shown that the biological activity of polysaccharides is closely related to its regulation of gut microbiota, so the interaction between polysaccharides and gut microbiota has become a research hotspot.^21,28Ganoderma atrum polysaccharides,²⁹Cyclocarya paliurus polysaccharides,³⁰ and kiwifruit polysaccharides³¹ show regulatory effects on intestinal microbial ecology, and then improve brain damage through the bidirectional communication between the gut and brain.

The consumption of UPFs has been linked to a variety of potential health issues, with AA being a notable concern due to its presence in these products. AA is known to cause significant damage to the gut microbiota and detrimental effects on the nervous system through the MGB axis. Polysaccharides, as a natural ingredient, can promote the growth and reproduction of beneficial gut microbiota. The mechanism by which they regulate gut microbiota-mediated microbial metabolism to alleviate or treat neurodegenerative diseases is gaining recognition.³² This review synthesizes recent relevant literature to elucidate the intervention mechanism and structure–activity relationship of polysaccharides on AA-induced neurotoxicity from multiple aspects, such as biological activity and the MGB axis. It provides new insights into the safety risks associated with excessive consumption of UPFs and lays the foundation for natural polysaccharides to be used to counteract AA-induced neurodegeneration.

The current development of UPFs

The concept of UPFs was first proposed by researchers in 2009, in observation of the link between global trends in obesity and obesity-related chronic diseases and the increasing consumption of convenient/pre-prepared foods.³³ NOVA classification divides foods into four groups according to the degree and purpose of modern food industrial processing: unprocessed or minimally processed foods, such as fresh fruits and vegetables, pasteurized milk, and frozen meat (group 1), processed culinary ingredients, such as sugar, honey, salt, and butter (group 2), processed foods, such as fruits in syrup and vegetables in brine (group 3) and ultra-processed foods (group 4).³⁴

UPFs are increasingly favoured by consumers, especially young people, due to their palatability and convenience. UPFs, such as sweet drinks, biscuits, cakes, potato chips, and fried chicken, are consumed by children and teenagers in countries with different income levels.^35–37 It is reported that UPF consumption has increased sharply around the world. According to the data from the National Health and Nutrition Examination Survey (NHANES), the proportion of total calorie intake from UPFs among young Americans between the ages of 2–19 has risen from 61.4% to 67.0% over the past 20 years.³⁸ Similar increases in the consumption of UPFs have been observed in South Korea (2010–2018: from 23.1% to 26.1%),³⁹ Canada (2004–2015: from 47.8% to 45.7%),⁴ and other countries.^35,36,40 UPFs are gradually replacing minimally processed foods and freshly prepared foods. UPFs accounted for over half of the total energy intake in developed countries.⁴¹ However, most UPFs are nutritionally imbalanced, containing more so-called limiting nutrients (added sugars, sodium, and saturated and trans-fats), while being relatively deficient in promoting nutrients (fibres and micronutrients).⁴² Furthermore, excessive processing at high temperatures leads to significant accumulation of process contaminants, such as AA,⁴³ AGEs,⁴⁴ and HAAs,⁴⁵ which further endanger consumer health.

The safety of UPFs

The consumption of UPFs has been correlated with a heightened risk of developing chronic metabolic diseases.⁴ The emergence of these health issues is multifactorial, and excessive intake of fat and sugars in UPFs is a significant contributor. Furthermore, exposure to processing-induced contaminants in UPFs is also a crucial element in the pathogenesis of these diseases.⁴⁶ Among these contaminants, AA is particularly concerning as it can not only disrupt the gut microbiota but also cause neurotoxicity.²

The production and prevention of AA

AA is primarily formed through the Maillard reaction, which involves the reaction between glucose and asparagine.⁴⁷ The process begins with the reaction of the amino residues (–NH₂) of asparagine and the carbonyl groups (C=O) of glucose, resulting in the formation of the corresponding N-glycosyl conjugation and its corresponding Schiff base. The Schiff base may facilitate decarboxylation, either through the Schiff betaine or through the oxazolidine-5-one intermediate, leading to the formation of the azomethine ylide. This intermediate then undergoes tautomerization to yield the decarboxylated Amadori product. Subsequently, AA may be formed either via the β-elimination of the decarboxylated Amadori compound, or via deamination of 3-aminopropionamide, which is regarded as an important precursor of AA.⁴⁸ Alternatively, the Schiff base can undergo rearrangement to form the Amadori compound, which subsequently generates carbonyl compounds. Previous studies have proved that these carbonyl compounds can also react with asparagine to yield AA.⁴⁹ In addition, AA can be produced through the acrolein pathway. When fats or oils, especially unsaturated oils, are subjected to excessively high temperatures, acrolein is generated.⁵⁰ In the presence of asparagine, acrolein is oxidized to form acrylic acid, which then reacts with ammonia to produce AA.⁵¹

According to European Commission regulations, the residue of AA in potato chips should be under 750 μg kg⁻¹, while for roasted coffee, the limit is set between 400–850 μg kg⁻¹.⁵² However, a survey by the European Food Safety Authority (EFSA) showed that the average concentration of AA in fried potato products was 1000 μg kg⁻¹, and alarmingly, in coffee, it reached as high as 4500 μg kg⁻¹.⁵³ These levels are considerably higher than the recommended by the European Commission.

Numerous strategies have been proposed to inhibit the formation of AA, including modifications to food processing techniques and the incorporation of specific inhibitors. For instance, Zhong et al.⁵⁴ found that a pre-treatment freezing process at 10 °C effectively reduces AA concentration in potato chips and chips, with minimal impact on the product's appearance. Vacuum frying has been shown to produce French Fries with a low AA content while maintaining quality characteristics.⁵⁵ Antunes-Rohling et al.⁵⁶ demonstrated that a 30-minute water pre-treatment for potatoes, followed by high-intensity ultrasound, led to a 90% decrease in AA concentration. Besides, the addition of amino acids, antioxidants, enzymes, salts, and vitamins can reduce the AA content in food.^57,58 Asparaginase can catalyse the hydrolysis of asparagine to ammonia and aspartic acid, thereby reducing the concentration of the precursor necessary for the Maillard reaction and inhibiting the production of AA.⁵⁹ Treating potato chips and bread with 300 U asparaginase resulted in reductions of 85% and 78% in asparagine content, respectively, while the AA content in potato chips and baked bread decreased by 94% and 86%, respectively.⁶⁰

The harm of AA

AA is classified as a Class 2A carcinogen by the International Agency for Research on Cancer.⁶¹ Upon entering the body, it is distributed to various tissues, such as the heart, kidney, and brain.⁴⁷ The genotoxicity, neurotoxicity, reproductive toxicity, and potential carcinogenicity of AA were demonstrated in animal experiments.^62–64 Moreover, exposure to AA is associated with the onset of CVDs, coronary heart disease, and neurodegenerative diseases, which are also closely related to the consumption of UPFs.^65,66

Long-term exposure to low concentrations of AA, particularly through food intake, poses potential risks to human health.⁶⁷ Such exposure may result in neurotoxic effects, including difficulties in learning, memory, cognition, and numbness in the hands and feet.^62,67 Increasing evidence indicates that the inflammatory response, oxidative stress, and apoptosis of neurocytes significantly contributes to neurodegenerative diseases.^68,69 The levels of ROS, 8-hydroxy-2-deoxyguanosine, and malondialdehyde (MDA) increased, while glutathione (GSH) content decreased in mice administered with 5–50 mg kg⁻¹ AA, leading to oxidative stress.⁷⁰ Inflammation-induced immune system disorders are related to the increase of several inflammatory cytokines caused by AA, including IL-1α, IL-1β, IL6, and TNF-α peripheral tissues.⁷¹ Zhao et al.⁷² found increased TNF-α, IL-6, and IL-1β levels in the primary microglia during the latter stages of AA exposure, further confirming the involvement of the immune-inflammatory response in AA-induced neurotoxicity. In addition, AA can induce apoptosis in various neurocytes, such as human neuroblastoma SH-SY5Y cells and astrocytoma U1240-MG cells.⁷³ Therefore, AA may damage brain homeostasis and induce neurotoxicity by inducing nerve cell apoptosis.

The effect of AA on nerves through gut microbiota

The effect mechanism of AA on gut microbiota

Destruction of the intestine tissue. AA is rapidly absorbed into the bloodstream via the intestinal tract through a passive process, and subsequently distributed to the liver and other tissues.⁷⁴ Notably, AA has a negative impact on the structure and absorption of the intestinal mucosa, resulting in intestinal barrier dysfunction and immune balance disorder.^29,75 The oxidative damage and inflammatory response induced by AA in the intestine are significant mechanisms of intestinal mucosal injury.⁷⁶ Specifically, AA treatment significantly decreased the level of GSH and activities of antioxidants, increased the level of MDA in both the small and large intestine of rats, and impaired the intestinal mucosa due to oxidative stress.⁷⁷ In addition, a study showed that compared to the control group, the levels of pro-inflammatory factors IL-2, IL-1β, and TNF-α in the AA group were significantly increased, while the levels of anti-inflammatory cytokines IL-4 and IL-10 were markedly decreased. This led to intestinal inflammation and diminished the local immune function of intestinal mucosa in rats.²⁹ AA-induced inflammation often results in alterations to the intestinal barrier, characterized by compromised defence function and heightened permeability.⁷⁸ Such alterations promote the infiltration of liquid and plasma proteins into the intestinal cavity, leading to the translocation of intestinal bacteria into the systemic circulation, thereby causing intestinal dysfunction and injury.²⁹

Apart from inflammatory reactions and oxidative stress, AA can cause other obvious destructive effects on intestinal tissue.^29,79 A prior investigation revealed that exposure to AA destroyed the structural integrity of ileal villi in rats, resulting in obvious atrophy and deformation, and this causes significant damage to the intestinal epithelial cells.⁷⁹ Intestinal epithelial cells play a crucial role in defending against intestinal pathogens and maintaining intestinal transport and barrier functions. Similarly, studies showed that AA changes the morphology and histology of the small intestinal wall, reducing the proliferation of the intestinal wall, muscular and submucosal thickness, villus length, crypt depth, crypt number, and intestinal absorption surface. On the contrary, there was an increase in the apoptosis rate, enterocyte number, the level of hemoglobin adducts, the staining intensity of epithelial cells, the thickness of villus epithelial, and the width of crypt.⁷⁵ Therefore, AA has a negative effect on the tissue structure, regeneration, and innervation of the small intestinal wall, and indirectly affects the absorption function of the small intestinal mucosa.

Impacts on the gut microbiota. On the one hand, AA exposure can directly alter the richness and diversity of gut microbiota. Both in normal and AA-treated rats, Firmicutes, Bacteroidetes, and Proteobacteria were the main taxa.⁷⁹ The study showed that the relative abundance of Firmicutes decreased, while the relative abundance of Bacteroidetes increased in the AA-exposed group compared with the control group.⁸⁰ Previous evidence has shown a significant increase in the Firmicutes/Bacteroidetes (F/B) ratio in obese hosts and a decrease in this ratio in lean hosts.⁸¹ Obviously, the F/B ratio decreased, which suggests that AA-induced weight loss may be related to the abundance and composition of the gut microbiota. Furthermore, AA can reduce the number of probiotics and increase the number of pathogens in rats and mice, indicating that gut microbiota may be the main target of AA toxicity.^29,77 Furthermore, AA induces the activation of the NOD-like receptor protein 3 inflammasome by activating oxidative stress and endoplasmic reticulum stress, which acts as the steady-state sensor and regulator of the microbiota, resulting in the alteration of the gut microbiota.^82,83

On the other hand, AA can also change the metabolism of gut microbiota, which in turn influences host metabolism by regulating metabolites, such as bile acids (BAs) and SCFAs.⁸⁴ BAs can promote the absorption and transport of fat in the intestinal tract, thereby regulating intestinal incretin secretion, hepatic gluconeogenesis, glycogen synthesis, energy expenditure, inflammation, and gut microbiota configuration.⁸⁵ AA exposure significantly reduced the content of microbial genes involved in the secondary biosynthesis of BAs. Compared with the control group, the expression levels of genes involved in BA synthesis, reabsorption, and signal transduction were significantly decreased in AA-treated rats.⁷⁹ SCFAs, such as butyric acid, propionic acid, and acetate, are by-products of intestinal microbial fermentation. They serve not only as the energy source for intestinal epithelial cells but also play a crucial role in reducing inflammation and improving the integrity of the intestinal barrier.¹⁵ SCFAs can inhibit the NF-κB (nuclear factor κB) pathway and reduce the production of proinflammatory cytokines.⁸⁶ However, Bacteroides, Escherichia_Shigella, Dubosiella, and Alloprevotella, which are related to the synthesis of SCFAs, were negatively affected by AA. This resulted in a significant reduction in SCFAs levels and promoted inflammation.⁸⁷

The effect of AA on the nervous system

 Introduction of the microbiota–gut–brain axis. In recent years, the convergence of microbiology and neuroscience has intensified. Increasing evidence indicated that gut microbiota significantly influences brain development, function, and behaviour.⁸⁸ The MGB axis was introduced approximately 60 years ago.⁸⁹ This axis is subject to numerous internal and external factors that modulate signal transmission and influence the functionality of both the intestine and CNS.⁹⁰ Various potential communication pathways exist in the MGB axis, ranging from intricate neuronal pathways to subtle small molecular information transmission systems.⁹¹ Among them, neural, immune and endocrine pathways constitute the three main communication pathways of the MGB axis.⁹²

In the neural pathway, the autonomic nervous system (ANS), combined with the activity of the enteric nervous system (ENS) and the regulation of the CNS, is responsible for maintaining physiological balance and responding to endocrine, motor, autonomic, and behavioural regions. ANS, connected with neuroendocrine and neuroendocrine signals, can induce changes in the regulation of the CNS in the intestinal tract (the top-down effect).¹⁴ ENS, a neural network located at the interface between the microbiota and the host, is positioned to respond either directly, or indirectly, to the microbiota and its metabolites. In the context of gut–brain signals, ENS communicates with CNS by separating neurons from the intestine to the sympathetic ganglion, and sensory information is transmitted through external primary afferent neurons that follow the afferent routes of the spinal cord and vagus nerve.⁹³ Microbiota–host interaction at the intestinal level leads to the release of cytokines, chemokines, neurotransmitters, neuropeptides, endocrine messengers, and microbial by-products, which can infiltrate the blood and lymphatic system, or affect the neural information carried by the vagus nerve and spinal cord afferent neurons, thus constantly communicating with the brain, and regulate the brain and behaviour.⁹¹

The immune regulation of microbiota is becoming a major way to coordinate MGB communication.⁹⁴ Gut microbiota has the function of regulating the maturation of resident immune cells in the CNS. Therefore, the gut microbiota and immune system are associated with the etiology or manifestation of neurodevelopmental, mental, and neurodegenerative diseases, such as autism spectrum disorders, depression, and Alzheimer's disease.¹³ The interaction between microorganisms and local immune cells may lead to functional changes other than GI, such as altering the release of cytokines into the systemic circulation or regulating immune cells in other parts of the body, including the brain. In addition to the effects of microorganisms on peripheral immune cells, the gut microbiota has also been reported to regulate the development, maturation, and function of microglia, which are resident immune cells in the brain.⁹⁵ In turn, the inflammatory response in the brain caused by neurodegenerative diseases has been shown to alter the composition of the gut microbiota consequently aggravating the neuroimmune response and exacerbating the pathology development.⁹²

Besides, endocrine pathways are also important for the MGB axis. Enteroendocrine cells (EECs) can secrete a variety of signal molecules, and they are essential for maintaining gut homeostasis. Enteroendocrine L cells, one of the major EECs, secrete glucagon-like peptide-1 (GLP-1) and peptide YY in a postprandial state, and the receptors of these peptides are locally expressed in the gut enteric neurons and vagal afferents, as well as CNS.⁹⁶ Enterochromaffin cells (ECCs) produce the majority of 5-hydroxytryptamine (5-HT) in the body from dietary tryptophan.⁹¹ 5-HT activates a variety of receptor families on the internal and external afferent nerve fibers of the GI tract and mediates many GI functions, including intestinal peristalsis, electrolyte secretion, pain, and inflammation.⁹⁷ Besides, 5-HT released by ECCs may affect gut–brain signals by regulating vagus nerve afferent activity⁹⁷ and inflammation in the gut.⁹⁸ Microbial products and metabolites, such as secondary BAs and SCFAs, regulate the secretion of neuropeptides (such as GLP-1) and neuromodulators (such as hormones and 5-HT) through EECs and ECCs. The gut microbiota also interacts with the neuroendocrine signalling pathway mediated by the hypothalamus-pituitary-adrenal (HPA) axis. The activation of the HPA axis induced by stress affects GI function and then changes the composition of gut microbiota.⁹⁵

The MGB axis is a bidirectional communication system that integrates the neural, immune, and endocrine pathways between the intestinal tract and the brain. These three pathways are highly complex and interrelated. For example, stimulating immune cells in the intestinal tract can lead to the local and systemic release of inflammatory cytokines and affect the permeability of the intestinal tract and brain, which is conducive to the entry of microbial by-products into the portal circulation and intestinal parenchyma, resulting in the excitability of local nerve endings, and eventually modify the brain homeostasis.⁹⁵

Effect of AA on nerves through the MGB axis. The intake of AA will damage the gut microbiota, potentially influencing the nervous system through the MGB axis.^31,67,77,80 AA has been observed to change the diversity of microbiota in rat feces, reduce the abundance of some beneficial bacteria, and significantly increase the abundance of pathogens. This alteration can result in an imbalance in the gut microbiota, leading to a decrease in the production of SCFAs and further stimulating neurotoxicity via the MGB axis (Fig. 1).⁸⁹ Intestinal epithelial tight junction (TJ) proteins play an important role in the intestinal mucosal barrier, forming seals between adjacent epithelial cells and maintaining the integrity of the mucosal epithelial barrier.⁹⁹ However, AA treatment decreases the expression of TJ protein (occludin), which can increase intestinal permeability,¹⁰⁰ and elevate the concentration of LPS and pro-inflammatory cytokines IL-6 and IL-1β in both the intestine and serum.²⁴ The presence of excessive LPS and inflammatory factors in the bloodstream can trigger an immune-inflammatory response, which destroys the tight connection of the blood–brain barrier, aggravates neurogenic inflammation, and damages neurons, ultimately leading to memory impairment. In addition, LPS has been reported to reduce brain-derived neurotrophic factor (BDNF) levels.¹⁰¹ The BDNF was a small dimer protein that could regulate brain development, neuroplasticity, and synaptogenesis in the CNS.¹⁰² Researchers also found that the expression of BDNF plays an important role in cognitive function, particularly in processes related to learning and memory.¹⁰³ AA-treated mice also showed a decrease in BDNF expression at night, which indicated that AA treatment exhibited more neurotoxicity at night and caused cognitive disorder and memory impairment.²⁴ The potential explanation for this result was that AA disturbed the cross-talk between the gut and brain. It has been well established that Toll-like receptor 4 (TLR4) can recognize LPS and activate NF-κB to regulate the production of pro-inflammatory cytokines such as TNF-α and IL-1β.¹⁰⁴ In addition, AA has been observed to significantly increase the expression of TLR4 and myeloid differentiation factor 88 (MyD88).⁸⁷ This upregulation may cause an imbalance that contributes to a wide range of inflammation-associated syndromes and diseases.¹⁰⁵ Therefore, AA has been reported to cause intestinal barrier injury and inflammation through the TLR4/MyD88/NF-κB signalling pathway.¹⁰⁶ Studies have confirmed that this pathway not only results in intestinal damage, but also participates in the pathogenesis of the intracranial aneurysm and seriously damage the nervous system.¹⁰⁷

Fig. 1 Nerve injury induced by AA through MGB axis. AA can harm the intestinal tissue and the gut microbiota, leading to the occurrence of neurodegenerative diseases through the MGB axis.

Research has demonstrated that AA induces Parkinson-like neurobehavioural abnormalities in adult zebrafish through the MGB axis. This is mainly attributed to the alteration in antioxidant levels in the intestine and brain, such as increased oxidative stress and changes in the nuclear factor E2-related factor-2 (Nrf2) signal pathway, a key pathway that regulates the balance of intracellular oxidation and anti-oxidation.¹⁰⁸ Additionally, there are modifications in the level of inflammatory mediators, specifically in the NF-κB signalling pathway, which contribute to neurobehavioural disorders.²⁵ Meanwhile, studies have shown that AA treatment can cause circadian rhythm disorder and inhibit the expression of circadian rhythm-related proteins, especially TJ proteins occludin and claudin-1in the mouse intestine.^24,100 In general, these findings suggest that AA-induced cognitive and memory decline may be due to defects in the MGB axis, and the underlying neurotoxic mechanism via the MGB axis homeostasis requires further investigation.

Intervention effects of polysaccharides on AA related neurotoxicity

Natural polysaccharides are a therapeutic agent for neurotoxicity through oxidative stress, inflammatory response, and intestinal barrier damage. Due to the lack of polysaccharide hydrolase in organisms, many polysaccharides cannot be digested and absorbed directly after entering the body, and the gut microbiota can play an effective role in intermediate transformation.¹⁰⁹ It has been shown that some polysaccharides can improve the disease related to the gut microbiota as prebiotics, then further improve brain injury through the MGB axis (Table 1).^32,110 In addition, they can also play a neuroprotective role through their biological activities, including antioxidation, anti-inflammation, and immunomodulatory activities (Fig. 2). Therefore, polysaccharides have broad application prospects in the treatment of neurotoxicity caused by AA.

Fig. 2 Regulation effects of polysaccharides on the gut and brain. Polysaccharides have a wide range of biological activities, which can adjust the intestinal barrier and gut microbiota, playing a neuroprotective role in the brain through the MGB axis.

Table 1 Summary of intervention of polysaccharides on neurodegenerative diseases through the MGB axis

Polysaccharide	Neurodegenerative disease	Model	Results	Potential mechanisms	Ref.
Dendrobium officinale polysaccharide	Depression-like symptoms	Mouse perimenopausal depression model	1. Campilobacterota, Desulfobacterota and Cyanobacteria ↓	Regulation of gut microbiota-neuroinflammation	133
			2. Bacteroidota↑
			3. Lachnospiraceae and Helicobacter ↓
			4. Lactobacillus and Muribaculaceae ↑
			5. IL-1β, IL-6 and TNF-α ↓
			6. Corticotropin-releasing hormone, adrenocorticotropic hormone and corticosterone levels ↓
Ganoderma lucidum polysaccharides	Depression	Chronic social defeat stress depression animal model	1. IL-1β and TNF-α ↓	Inflammation regulation; regulation of neuroimmune system	134
			2. IL-10 and BDNF ↑
			3. Activation of microglia and proliferation of astrocytes ↓
			4. GluA1 S845 phosphorylation, GluA1 and GluA2 expression ↑
			5. Dectin-1 expression ↑
Inulin	Alzheimer's disease	Asymptomatic apolipoprotein ε4 allele transgenic mice	1. Prevotella and Lactobacillus ↑	Regulation of gut microbiota; suppression of brain inflammation; increase in metabolism	135
			2. Escherichia, Turicibacter and Akkermansia ↓
			3. SCFAs, tryptophan-derived metabolites, BAs, glycolytic metabolites and scyllo-inositol ↑
			4. Brain inflammation ↓
Flammulina velutipes polysaccharides	Learning and memory impairment	Cognitive impairment mice induced by scopolamine	1. The ratio of F/B ↓	Regulation of gut microbiota; suppression of neuroinflammation	136
			2. Clostridia and Bacilli ↓
			3. Bacteroidia, Erysipelotrichia and Actinobacteria ↑
			4. E. fergusonii ↓
			5. IL-1β, TNF-α and IL-6 ↓
			6. IL-10 ↑
Polymannuronic acid in the brown seaweed polysaccharides	Parkinson's disease	1-Methyl-4-phenyl-1,2,3,6tetrahydropyridine induced Parkinson's disease mice model	1. Striatal homovanillic acid, 5-HT, 5-hydroxyindole acetic acid and γ-aminobutyric acid ↑	Suppression of inflammation; improvement in the integrity of the intestinal barrier and blood–brain barrier; regulation of gut microbiota	137
			2. SCFAs, including acetic acid and propionic acid and butyric acid ↑
			3. TNF-α and IL-6 ↓
			4. ZO-1 and occluding mRNA expressions ↑
			5. Turicibacter and Lactobacillus↓
			6. Clostridiales, Coprococcus and Ruminococcus ↑
			7. MAPK signalling pathway ↓
Polygonatum sibiricum polysaccharides	Alzheimer's disease	5xFAD mice	1. Synaptic density ↑	Gut microbiota remodeling; Inflammation regulation; repair of intestinal barrier; prevention of intestinal Amyloid-β deposition	138
			2. Amyloid-β1–40 and amyloid-β1–42 ↓
			3. Microglial M2 phenotype transition and microglial recruitment around the 2. amyloid-β plaques ↑
			4. Helicobacter mastomyrinus and Helicobacter typhlonius↓
			5. Akkermansia muciniphila ↑
			6. TNF-α and IL-6 ↓
			7. The mRNA levels of occludin and ZO-1 ↑

---

Structural characterization of polysaccharides

Polysaccharides are prebiotics and are widely found in nature. With the advantages of being non-toxic, stable, and easy to obtain, natural polysaccharides have attracted significant attention in various fields.¹¹¹ Based on their composition, polysaccharides can be divided into homopolysaccharides and heteropolysaccharides. Homopolysaccharides consist of a single type of monosaccharide, while heteropolysaccharides are composed of various monosaccharides. Polysaccharides have been reported to have health benefits such as antioxidant, anti-inflammatory, intestinal protective, and neuroprotective activities.³² These biological activities of polysaccharides are intricately linked to their primary structure, which encompasses molecular weights (MWs), monosaccharide compositions, and glycosidic bond types.¹¹² Studies have shown that most polysaccharides with intestinal barrier protection capabilities exhibit high MWs. This is because high-MWs polysaccharides have elevated viscosity and can form a hydrophilic gel layer like the intestinal mucosa layer, facilitating cross-linking with membrane receptors to maintain the integrity of the intestinal barrier structure.¹¹³ For example, the polysaccharides from Ganoderma atrum with an MW of 1013.0 kDa have been shown to mend the intestinal barrier function damage induced by AA in mice through the TLR4/MyD88/NF-κB pathway.¹⁰⁶

The monosaccharide composition and glycosidic bond type influence the affinity of polysaccharides with targets in vivo. It is generally accepted that a more complex monosaccharide composition correlates with enhanced biological activity.¹¹⁴ Most polysaccharides with intestinal barrier protection functions are heteropolysaccharides, primarily composed of galactose (Gal), mannose (Man), arabinose (Ara), xylose (Xyl), rhamnose (Rha) and other monosaccharides.¹¹³ In addition, polysaccharides containing Man and Rha have been shown to exhibit tumor suppression and antioxidant activities, respectively.^115,116 However, the specific rules and mechanisms have not yet been clarified and need further exploration.

Additionally, it is generally believed that polysaccharides with β-configuration have a higher activity.¹¹⁷ The majority of polysaccharides that modulate the gut microbiota are characterized by (1 → 3) glycosidic linkages. For example, Hericium erinaceus polysaccharides, primarily consisting of β-(1 → 3)-D-glucose, have been shown to augment both the diversity and richness of rat gut microbiota, as well as optimize the ratio of acetic acid and butyric acid.¹¹⁸

Regulation effect of polysaccharides on gut microbiota

Repairing the intestinal barrier. Obviously, AA can cause intestinal barrier imbalance through various pathways. However, polysaccharides can significantly repair the intestinal barrier by regulating TJ protein and intestinal epithelial cells.¹¹⁹ In a previous study, polysaccharides from Ganoderma lucidum significantly reduced the original surface epithelial erosion, crypt destruction, mucosal muscularis destruction, submucosal edema, and inflammatory cell infiltration. Besides, Ganoderma lucidum polysaccharides can reverse the expression of the key TJ proteins, occludin and ZO-1 (zonula occludens protein 1) in the impaired intestinal barrier.¹²⁰Dendrobium officinale polysaccharides also showed the effect of relieving colonic inflammation, restoring intestinal barrier function and intestinal mucosal immunity. Dendrobium huoshanense polysaccharides can not only change the physiological state of the intestinal tract, but also improve the intestinal physical barrier function by regulating the mucosal structure and up-regulating the expression of TJ proteins, enhancing the intestinal biochemical barrier function by increasing the expression and secretion of mucin-2, β-defensin and secretory immunoglobulin A (SIgA), and regulating the intestinal immune barrier function by stimulating the production of cytokines and the functional development of immune cells.¹²¹Ganoderma atrum polysaccharides can down-regulate the expression of proinflammatory cytokines IL-2, IL-1β and TNF-α, increase the contents of anti-inflammatory cytokines IL-4 and IL-10, and significantly reduce the inflammatory response in the rat intestine. It is suggested that Ganoderma atrum polysaccharides can reduce the oxidative stress of AA, reduce inflammation and inhibit the absorption of AA by protecting the intestinal barrier.²⁹ Therefore, it can be speculated that many polysaccharides have the potential to improve the intestinal barrier damage caused by AA.

Improving the gut microbiota and its metabolites. Injury caused by AA to the richness and diversity of gut microbiota can trigger a series of pathological changes. Research has shown that dysregulation of the gut microbiota can lead to metabolic disorders, reduced production of neuroprotective factors, elevated levels of pro-inflammatory cytokines, and faulty immune responses to neuronal proteins. This highlights the potential role of the gut microbiota dysregulation as a risk factor for neurodegenerative diseases.¹²² As the energy of the gut microbiota, dietary polysaccharides have significant beneficial impacts on the intestinal microbial ecology and the health of the host.¹²³ Therefore, it is possible to improve the related diseases caused by AA. After being ingested by the human body, polysaccharides can be degraded by specific intestinal microorganisms and produce masses of oligosaccharides, which can be directly absorbed by the human body.¹²⁴ Undigested polysaccharides and oligosaccharides are further fermented by gut microbiota to produce SCFAs and other secondary metabolites, which have beneficial effects on human health.^125,126 In addition, polysaccharides can significantly improve the richness and diversity of gut microbiota during digestion in vivo, which provides advantageous conditions for the growth of beneficial bacteria.¹²⁷ Therefore, polysaccharides are of great significance in improving the imbalance of gut microbiota induced by AA.

A study on the effects of compound polysaccharides (Lycium barbarum polysaccharides, Poria cocos polysaccharides and Lentinan, 1 : 1 : 1) on gut microbiota in rats showed that, according to 16S rRNA analysis, the relative abundance of four bacterial genera (Bifidobacterium, Lactobacillus, Allobaculum and Oligella) in the compound polysaccharides treatment group was significantly higher than that in the control group, while the relative abundance of one bacterial genus (Enterococcus) decreased significantly. At the same time, compound polysaccharides treatment promoted the functional maturity of the intestinal bacterial community, which was characterized by an increase in basic metabolism (amino acid metabolism and energy metabolism), SCFAs related metabolism and nucleotide metabolism.¹²⁸ It is worth noting that intestinal microorganisms, including Lactobacillus fermentum, Lactobacillus acidophilus, Bifidobacterium lactis, and so forth, are of great significance in improving cognitive impairment.¹¹⁰ For example, it has been suggested that Lactobacillus fermentum can have beneficial effects on cognitive function, physiological behaviour and immune response in aged mice.¹²⁹ Many studies have also shown that polysaccharides can have a beneficial effect on the nervous system by regulating the gut microbiota. Fucoidan increased the relative abundances of Prevotellaceae, Rikenellaceae, Prevotella, Barnesiella, and Alistipes and decreased the relative abundance of Verrucomicrobiaceae, to ameliorate depression.¹³⁰ Ginkgo biloba leaves polysaccharides¹³¹ and inulin¹³² upregulated the relative abundances of lactic acid bacteria (especially Lactobacillus reuteri) and Bifidobacterium, thereby ameliorating nerve injury via modulating the MGB axis. Thus, polysaccharides have great potential in the treatment of AA-induced cognitive impairment through improving gut microbiota.

In addition, polysaccharides not only directly influence the richness and diversity of gut microbiota, but also significantly affect microbial metabolites, such as SCFAs and BAs. It has been indicated that Ganoderma lucidum polysaccharides could increase the level of SCFAs (acetate and butyrate in particular), improve the intestinal barrier function, reduce the LPS level, and regulate the microbiota to increase the production of beneficial bacteria. Specifically, some SCFAs-producing bacteria and potential probiotics such as Allobaculum, Bifidobacterium, and Christensenellaceae_R-7_group increased due to the Ganoderma lucidum polysaccharides in serum and adipose tissue.¹³⁹ The polysaccharides derived from Xiaoyaosan have been shown to modulate the composition and abundance of gut microbiota, restore the diversity of SCFAs-producing bacteria, and increase the content of SCFAs, thereby playing an antidepressant role in rats.¹⁴⁰ Besides, polysaccharides also have a significant regulatory effect on BA metabolism. For instance, Grifola frondosa polysaccharides significantly enhanced the expression of cholesterol 7α-hydroxylase (CYP7A1), facilitating the biotransformation of BAs, and activated the bile salt export pump (BSEP), contributing to the synthesis and absorption of BAs in the liver.¹⁴¹ A sulfated polysaccharide from Gracilaria Lemaneiformis has been found to promote the excretion of total BAs in mouse feces by regulating gut microbiota, hereby ameliorating the disorders related to BAs metabolism.¹⁴² In conclusion, because of their probiotic properties, polysaccharides are involved in maintaining or restoring microecological balance, so they have been increasingly developed as health food adjuvants. They are also becoming a promising way to alleviate or prevent diseases associated with gut microbiota.¹⁴³

Mitigating the effect of polysaccharides on neurotoxicity

As mentioned earlier, AA has the potential to induce neurotoxic effects in humans, primarily through the mechanisms of oxidative stress and inflammation. Obviously, polysaccharides play a significant role by improving the above oxidative stress and inflammatory response in the treatment of many diseases associated with gut microbiota. Therefore, they are expected to alleviate AA-induced neurotoxicity through the MGB axis, due to their biological activities and beneficial effects on gut microbiota.

In vivo studies showed that some polysaccharides have beneficial antioxidant effects by decreasing the level of lipid peroxidation and increasing the activity of antioxidant enzymes.^144,145 A study revealed that Ganoderma lucidum polysaccharides mitigated exercise-induced oxidative stress by increasing the activity of antioxidant enzymes: superoxide dismutase (from 110–170 U mg⁻¹ protein), catalase (from 1.58–1.95 U mg⁻¹ protein), and glutathione peroxidase (from 6.0–15.0 U mg⁻¹ protein).¹⁴⁶Astragalus polysaccharides can also alleviate 6-hydroxydopamine-induced neurotoxicity by reducing oxidative stress, regulating the apoptosis pathway and cholinergic system.¹⁴⁷ Silent information regulator 1 (Sirt1) can regulate the expression of antioxidant molecules through various mechanisms, and Sirt1 is closely related to the stability and activity of Nrf2, which may be involved in the oxidative stress regulation mediated by Nrf2.¹⁴⁸ In vitro experiments have shown that a polysaccharide (AFP-2) derived from the flowers of Apios americana Medik activated the intracellular antioxidant system through the Sirt1/Nrf2 signalling pathway. This activation effectively mitigates ROS accumulation and ameliorates mitochondrial dysfunction. Further studies have shown that AFP-2 can induce autophagy, which was found to be involved in the antioxidative process of AFP-2 in rat pheochromocytoma line 12 (PC12) cells.¹⁰⁸

Polysaccharides possess potential anti-neuroinflammatory effects, effectively targeting the inhibition of excessive microglial activation, reduction of pro-inflammatory factors, and modulation of related signalling pathways.¹⁴⁹ Some polysaccharides can reduce the levels of inflammatory cytokines IL-1β, IL-6, IL-8, and IL-17, increase the level of anti-inflammatory cytokines IL-10, and thus play an anti-inflammatory role.¹⁵⁰ For example, Fu et al.¹⁵¹ studied the structure of polysaccharides from the leaves of Chinese aconitum (Aconitum Carmichaelii) and proved that these polysaccharides have anti-inflammatory effects on intestinal epithelial cell inflammation induced by LPS. Furthermore, Ganoderma lucidum polysaccharides can also attenuate the LPS-mediated inflammatory response by inhibiting NF-κB or the mitogen activated protein kinases (MAPK) signalling pathway (the main signal pathway that controls the macrophage immune response), reducing the release of above pro-inflammatory cytokines and improving resistance to neurodegenerative diseases.¹¹⁰ Similarly, Zhong et al.¹⁵² studied the neuroprotective and anti-neuroinflammatory effects of Acorus tatarinowii polysaccharides by using the BV2 microglia model, which is induced by LPS. The mechanism of action involves inhibiting the overactivation of the LPS-induced pro-inflammatory BV2 microglia, blocking the TLR4-mediated phosphoinositide 3-kinase/protein kinase B and MyD88/NF-κB signalling pathways, thereby reducing the levels of inflammatory mediators and cytokines. Additionally, Acorus tatarinowii polysaccharides have been shown to protect cortical and hippocampal primary neurons from neurotoxic damage. Additionally, current biochemical and clinical studies have shown that some polysaccharides are effective immunomodulators. The immunomodulatory activity is related to their effects on effector cells, such as macrophages, B and T lymphocytes, natural killer cells and dendritic cells.¹⁵³ For instance, Bupleurum polysaccharides could inhibit the overexpression of pro-inflammatory mediators (TNF-α, IL-1β, and IL-6) in LPS-induced macrophages, which confer benefits on autoimmune inflammatory diseases.¹⁵⁴ Studies have shown that Ganoderma lucidum polysaccharides produced great protection of the spleen and thymus, which are both important organs closely related to immune function. They were also effective in promoting hematopoiesis and increasing the levels of IgA in serum.¹⁵⁵ In addition, polysaccharides from Anemarrhena asphodeloides Bunge (AAP70-1) have been shown to protect the SH-SY5Y cell from CoCl₂-induced apoptosis. The results suggest that AAP70-1 has potential as a therapeutic agent for CNS diseases or as an immunomodulatory agent.¹⁵⁶ Because of the existence of bidirectional communication between the nervous and immune systems, polysaccharides can be used as an immunomodulator to promote the development of the nervous system.¹³

In summary, numerous studies have demonstrated that polysaccharides can positively impact the intestinal barrier through their various biological activities. Specifically, these polysaccharides can decrease lipid peroxidation, reduce ROS levels in the intestine, and inhibit oxidative stress through multiple pathways. They can also exhibit anti-inflammatory properties by reducing pro-inflammatory factors in the intestine and inhibiting the overactivation of microglia. Additionally, they can protect the CNS by modulating immunity and reducing cell apoptosis. Therefore, it is speculated that polysaccharides have great potential in improving the neurotoxicity caused by AA.

Conclusions

AA, produced during the processing of many UPFs, can cause severe neurotoxicity in humans. AA damages the intestinal tissue by injuring the intestinal barrier and changing the composition and abundance of the gut microbiota, resulting in neurotoxicity through the MGB axis. Therefore, it is advisable to reduce the intake of UPFs and develop healthy eating habits. Polysaccharides play a key role in improving the intestinal barrier and microbiota and because of their extensive biological activities, they have great potential in the treatment of neurotoxicity caused by AA. Current research on the neuroprotective effects of polysaccharides predominantly focuses on animal and cell models. Future clinical trials are necessary to validate the therapeutic effects of these polysaccharides on patients with neurodegenerative diseases. In addition, most experiments utilize crude polysaccharides, which may cause antagonistic effects between different components, thereby interfering with the research. Thus, additional purification experiments and structural analyses are needed to obtain polysaccharides of higher purity and better activity. Given the pivotal role of the gut microbiota and the brain in the host, future studies could concentrate on polysaccharide-based foods aimed at promoting gut health. In addition, the structure–activity relationships of natural polysaccharides also warrant further investigation to better comprehend how various structural characteristics influence gut microbiota and the MGB axis.

In daily diets, individuals can modulate gut microbiota and reduce the harm of AA in UPFs by consuming more polysaccharide-rich foods. Additionally, the development of more microbiota-oriented foods may emerge as a new trend, and medicines or functional foods with natural polysaccharides as primary ingredients may find extensive clinical applications in treating neurodegenerative diseases.

Author contributions

Chen Cai: investigation, writing–original draft. Zheyi Song: writing–review and editing. Xinrui Xu: writing–review and editing. Xin Yang: writing–original draft. Siyu Wei: conceptualization, investigation. Fang Chen: conceptualization, investigation. Xu Dong: supervision, writing–review and editing. Xin Zhang: supervision, writing–review and editing. Yuchen Zhu: writing–review and editing, funding acquisition, supervision.

Data availability

Data sharing is not applicable to this article as no datasets were generated or analysed during the current study.

Conflicts of interest

There are no conflicts to declare.

Acknowledgements

This work was supported by the National Natural Science Foundation of China (No. 32072333) and the Young Elite Scientists Sponsorship Program by CAST (No. 2020QNRC001).

References

1. A. Aguirre, M. T. Borneo, S. El Khori and R. Borneo, Food Res. Int., 2019, 115, 535–540.
2. R. J. Ostfeld and K. E. Allen, J. Am. Coll. Cardiol., 2021, 77, 1532–1534.
3. F. Juul, G. Vaidean, Y. Lin, A. L. Deierlein and N. Parekh, J. Am. Coll. Cardiol., 2021, 77, 1520–1531.
4. M. Nardocci, B. S. Leclerc, M. L. Louzada, C. A. Monteiro, M. Batal and J. C. Moubarac, Can. J. Public Health, 2019, 110, 4–14.
5. R. B. Levy, F. Rauber, K. Chang, M. Louzada, C. A. Monteiro, C. Millett and E. P. Vamos, Clin. Nutr., 2021, 40, 3608–3614.
6. Y. Zhang and E. L. Giovannucci, Crit. Rev. Food Sci. Nutr., 2023, 63, 10836–10848.
7. B. Y. Wu, X. Y. Chai, A. M. He, Z. Huang, S. Chen, P. F. Rao, L. J. Ke and L. W. Xiang, Food Chem. Toxicol., 2021, 154, 112315.
8. M. A. Adimas, B. D. Abera, Z. T. Adimas, H. W. Woldemariam and M. A. Delele, Heliyon, 2024, 10, e30258.
9. V. Paul, R. Ezekiel and R. Pandey, Acta Physiol. Plant., 2016, 38, 276.
10. B. Zödl, D. Schmid, G. Wassler, C. Gundacker, V. Leibetseder, T. Thalhammer and C. Ekmekcioglu, Toxicology, 2007, 232, 99–108.
11. E. Sengul, V. Gelen, S. Yildirim, S. Tekin and Y. Dag, Biol. Trace Elem. Res., 2020, 199, 173–184.
12. M. Zhao, L. Deng, X. Lu, L. Fan, Y. Zhu and L. Zhao, Environ. Sci. Pollut. Res., 2022, 29, 41151–41167.
13. T. C. Fung, C. A. Olson and E. Y. Hsiao, Nat. Neurosci., 2017, 20, 145–155.
14. E. A. Mayer, K. Tillisch and A. Gupta, J. Clin. Invest., 2015, 125, 926–938.
15. B. M. Tian, J. H. Zhao, M. Zhang, Z. F. Chen, Q. Y. Ma, H. C. Liu, C. X. Nie, Z. Q. Zhang, W. An and J. X. Li, Mol. Nutr. Food Res., 2021, 65, 2000745.
16. M. Kreuzer and W. D. Hardt, Annu. Rev. Microbiol., 2020, 74, 787–813.
17. Y. L. Hu, D. W. Chen, P. Zheng, J. Yu, J. He, X. B. Mao and B. Yu, BioMed Res. Int., 2019, 2019, 5403761.
18. A. H. Al-Khafaji, S. D. Jepsen, K. R. Christensen and L. K. Vigsnæs, J. Funct. Foods, 2020, 74, 104176.
19. Y. Y. Cheng, Y. Wang, W. Zhang, J. B. Yin, J. C. Dong and J. T. Liu, Medicine, 2022, 101, e28910.
20. D. Song, C. S. Yang, X. Zhang and Y. Wang, Crit. Rev. Food Sci. Nutr., 2020, 61, 139–148.
21. X. Z. Wang, L. Cheng, Y. A. Liu, R. L. Zhang, Z. F. Wu, P. F. Weng, P. Zhang and X. Zhang, Front. Microbiol., 2022, 13, 807076.
22. J. F. Cryan and S. M. O'Mahony, Neurogastroenterol. Motil., 2011, 23, 187–192.
23. M. Zinöcker and I. Lindseth, Nutrients, 2018, 10, 365.
24. X. Tan, J. Ye, W. Liu, B. Zhao, X. Shi, C. Zhang, Z. Liu and X. Liu, Arch. Toxicol., 2018, 93, 467–486.
25. A. Singh, Parkinsonism Relat. Disord., 2020, 79, E21–E21.
26. G. M. Shashidhar, P. Giridhar and B. Manohar, RSC Adv., 2015, 5, 16050–16066.
27. L. Yuan, Z. C. Zhong and Y. Liu, Int. J. Biol. Macromol., 2020, 154, 1400–1407.
28. C. García-Montero, O. Fraile-Martínez, A. M. Gómez-Lahoz, L. Pekarek, A. J. Castellanos, F. Noguerales-Fraguas, S. Coca, L. G. Guijarro, N. García-Honduvilla, A. Asúnsolo, L. Sanchez-Trujillo, G. Lahera, J. Bujan, J. Monserrat, M. Álvarez-Mon, M. A. Álvarez-Mon and M. A. Ortega, Nutrients, 2021, 13, 699.
29. Y. Yang, L. Zhang, G. Jiang, A. Lei, Q. Yu, J. Xie and Y. Chen, Food Funct., 2019, 10, 5863–5872.
30. Y. Yao, L. J. Yan, H. Chen, N. Wu, W. B. Wang and D. S. Wang, Phytomedicine, 2020, 77, 153268.
31. M. Chen, X. Chen, K. Wang, L. Cai, N. Liu, D. Zhou, W. Jia, P. Gong, N. Liu and Y. Sun, Front. Nutr., 2023, 10, 1080825.
32. Y. X. Guo, X. F. Chen, P. Gong, Z. X. Li, Y. P. Wu, J. Zhang, J. T. Wang, W. B. Yao, W. J. Yang and F. X. Chen, Phytomedicine, 2023, 109, 154566.
33. C. A. Monteiro, Public Health Nutr., 2009, 12, 729–731.
34. C. A. Monteiro, J. C. Moubarac, R. B. Levy, D. S. Canella, M. Louzada and G. Cannon, Public Health Nutr., 2018, 21, 18–26.
35. F. Lauria, M. Dello Russo, A. Formisano, S. De Henauw, A. Hebestreit, M. Hunsberger, V. Krogh, T. Intemann, L. Lissner, D. Molnar, L. A. Moreno, L. A. Reisch, M. Tornaritis, T. Veidebaum, G. Williams, A. Siani, P. Russo and I. F. Consortium, Nutr. Metab. Cardiovasc. Dis., 2021, 31, 3031–3043.
36. V. Magalhaes, M. Severo, D. Correia, D. Torres, R. Costa de Miranda, F. Rauber, R. Levy, S. Rodrigues and C. Lopes, J. Nutr. Sci., 2021, 10, e89.
37. E. Ruggiero, S. Esposito, S. Costanzo, A. Di Castelnuovo, C. Cerletti, M. B. Donati, G. de Gaetano, L. Iacoviello, M. Bonaccio and I. S. Investigators, Public Health Nutr., 2021, 24, 6258–6271.
38. L. Wang, E. Martínez Steele, M. Du, J. L. Pomeranz, L. E. O'Connor, K. A. Herrick, H. Luo, X. Zhang, D. Mozaffarian and F. F. Zhang, J. Am. Med. Assoc., 2021, 326, 519–530.
39. J. S. Shim, S. Y. Shim, H. J. Cha, J. Kim and H. C. Kim, Nutrients, 2021, 13, 1120.
40. P. V. L. Moreira, L. Hyseni, J.-C. Moubarac, A. P. B. Martins, L. G. Baraldi, S. Capewell, M. O'Flaherty and M. Guzman-Castillo, Public Health Nutr., 2017, 21, 181–188.
41. M. J. Gibney, Curr. Dev. Nutr., 2019, 3, nzy077.
42. D. Martini, J. Godos, M. Bonaccio, P. Vitaglione and G. Grosso, Nutrients, 2021, 13, 3390.
43. B. P. Riboldi, Á. M. Vinhas and J. D. Moreira, Food Chem., 2014, 157, 310–322.
44. F. Juul, G. Vaidean and N. Parekh, Adv. Nutr., 2021, 12, 1673–1680.
45. E. Oz, Food Chem., 2021, 352, 129378.
46. A. Fardet and E. Rock, Trends Food Sci. Technol., 2019, 93, 174–184.
47. V. Matoso, P. Bargi-Souza, F. Ivanski, M. A. Romano and R. M. Romano, Food Chem., 2019, 283, 422–430.
48. Z. L. Li, C. Y. Zhao and C. W. Cao, Molecules, 2023, 28, 3476.
49. A. Hamzalioglu and V. Gökmen, Food Chem., 2020, 318, 126467.
50. D. Jiang, S. Wang, H. P. Li, L. J. Xu, X. Hu, B. Barati and A. Q. Zheng, ACS Sustainable Chem. Eng., 2021, 9, 3095–3103.
51. I. Govindaraju, M. Sana, I. Chakraborty, M. H. Rahman, R. Biswas and N. Mazumder, Foods, 2024, 13, 556.
52. E. Commission, Off. J. Eur. Communities, 2017, 304, 24–44.
53. EFSA CONTAM Panel (EFSA Panel on Contaminants in the Food Chain), EFSA J., 2015, 13, 4140.
54. S. P. Zhong, Z. He, M. N. Chaudhary, Y. X. Mu, K. Zhou, A. Yang, L. Y. Luo, L. Zeng and W. Luo, LWT – Food Sci. Technol., 2024, 200, 116174.
55. E. Devseren, D. Okut, M. Koç, Ö. Ocak, H. Karatas and F. Kaymak-Ertekin, Acta Chim. Slov., 2021, 68, 25–36.
56. A. Antunes-Rohling, S. Ciudad-Hidalgo, J. Mir-Bel, J. Raso, G. Cebrián and I. Álvarez, Innovative Food Sci. Emerging Technol., 2018, 49, 158–169.
57. L. Rifai and F. A. Saleh, Int. J. Toxicol., 2020, 39, 93–102.
58. T. P. Rajesh, V. A. Basheer, A. S. B. Packirisamy, S. N. Ravi and S. Vallinayagam, Top. Catal., 2024, 67, 300–312.
59. R. Y. Jia, X. Wan, X. Geng, D. M. Xue, Z. X. Xie and C. R. Chen, Microorganisms, 2021, 9, 1659.
60. A. K. Meghavarnam and S. Janakiraman, LWT – Food Sci. Technol., 2018, 89, 32–37.
61. IARC, Acrylamide, Lyon, France, 1994.
62. Y. Liu, X. Zhang, D. D. Yan, Y. Q. Wang, N. Wang, Y. F. Liu, A. J. Tan, X. Y. Chen and H. Yan, Toxicol. Appl. Pharmacol., 2020, 393, 114949.
63. H. Mojska, I. Gielecinska, J. Winiarek and W. Sawicki, Toxics, 2021, 9, 298.
64. J. S. Park, P. Samanta, S. Lee, J. Lee, J. W. Cho, H. S. Chun, S. Yoon and W. K. Kim, Int. J. Mol. Sci., 2021, 22, 3518.
65. B. Srour, L. K. Fezeu, E. Kesse-Guyot, B. Allès, C. Méjean, R. M. Andrianasolo, E. Chazelas, M. Deschasaux, S. Hercberg, P. Galan, C. A. Monteiro, C. Julia and M. Touvier, BMJ [Br. Med. J.], 2019, 365, l1451.
66. Y. Zhang, M. M. Huang, P. Zhuang, J. J. Jiao, X. Y. Chen, J. Wang and Y. N. Wu, Environ. Int., 2018, 117, 154–163.
67. S. Lee, H. R. Park, J. Y. Lee, J. H. Cho, H. M. Song, A. H. Kim, W. Lee, Y. Lee, S. C. Chang, H. S. Kim and J. Lee, J. Toxicol. Environ. Health, Part A, 2018, 81, 254–265.
68. B. Newland, P. Wolff, D. Z. Zhou, W. Wang, H. Zhang, A. Rosser, W. X. Wang and C. Werner, Biomater. Sci., 2016, 4, 400–404.
69. M. Zhao, B. Zhang and L. Deng, Front. Nutr., 2022, 9, 859189.
70. M. Y. Zhao, L. L. Deng, X. X. Lu, L. Q. Fan, Y. Zhu and L. M. Zhao, Environ. Sci. Pollut. Res., 2022, 29, 41151–41167.
71. J. G. Wang, H. H. Dou and Q. Y. Liang, Eur. J. Haematol., 2024 DOI:10.1111/ejh.14310.
72. M. Y. Zhao, F. S. L. Wang, X. S. Hu, F. Chen and H. M. Chan, Food Chem. Toxicol., 2017, 106, 25–35.
73. J. G. Lee, Y. S. Wang and C. C. Chou, Toxicol. In Vitro, 2014, 28, 562–570.
74. E. Altinoz, Y. Turkoz and N. Vardi, Bratislava Med. J., 2015, 116, 252–258.
75. P. Dobrowolski, P. Huet, P. Karlsson, S. Eriksson, E. Tomaszewska, A. Gawron and S. G. Pierzynowski, Nutrition, 2012, 28, 428–435.
76. I. Ghorbel, A. Elwej, K. Jamoussi, T. Boudawara, N. G. Kamoun and N. Zeghal, Food Funct., 2015, 6, 1126–1135.
77. S. Gedik, M. E. Erdemli, M. Gul, B. Yigitcan, H. Gozukara Bag, Z. Aksungur and E. Altinoz, Biotech. Histochem., 2018, 93, 267–276.
78. L. Pastorelli, C. De Salvo, J. R. Mercado, M. Vecchi and T. T. Pizarro, Front. Immunol., 2013, 4, 280.
79. Z. Yue, Y. Chen, Q. Dong, D. Li, M. Guo, L. Zhang, Y. Shi, H. Wu, L. Li and Z. Sun, Food Res. Int., 2022, 157, 111405.
80. Z. Wang, H. Liu, J. Liu, X. Ren, G. Song, X. Xia and N. Qin, Foods, 2021, 10, 2990.
81. P. J. Turnbaugh, M. Hamady, T. Yatsunenko, B. L. Cantarel, A. Duncan, R. E. Ley, M. L. Sogin, W. J. Jones, B. A. Roe, J. P. Affourtit, M. Egholm, B. Henrissat, A. C. Heath, R. Knight and J. I. Gordon, Nature, 2009, 457, U480–U487.
82. S. H. Guo, M. Nighot, R. Al-Sadi, T. Alhmoud, P. Nighot and T. Y. Ma, J. Immunol., 2015, 195, 4999–5010.
83. B. Nan, C. Y. Yang, L. Li, H. Q. Ye, H. Y. Yan, M. H. Wang and Y. Yuan, Food Chem. Toxicol., 2021, 148, 111937.
84. K. A. Krautkramer, J. Fan and F. Bäckhed, Nat. Rev. Microbiol., 2021, 19, 77–94.
85. H. Shapiro, A. A. Kolodziejczyk, D. Halstuch and E. Elinav, J. Exp. Med., 2018, 215, 383–396.
86. J. S. Park, E. J. Lee, J. C. Lee, W. K. Kim and H. S. Kim, Int. Immunopharmacol., 2007, 7, 70–77.
87. Y. Yuan, L. Lu, N. Bo, Y. Chaoyue and Y. Haiyang, J. Agric. Food Chem., 2021, 69, 12837–12852.
88. T. R. Sampson and S. K. Mazmanian, Cell Host Microbe, 2015, 17, 565–576.
89. E. M. M. Quigley, Curr. Neurol. Neurosci. Rep., 2017, 17, 94.
90. K. G. Margolis, J. F. Cryan and E. A. Mayer, Gastroenterology, 2021, 160, 1486–1501.
91. J. F. Cryan, K. J. O'Riordan, C. S. M. Cowan, K. V. Sandhu, T. F. S. Bastiaanssen, M. Boehme, M. G. Codagnone, S. Cussotto, C. Fulling, A. V. Golubeva, K. E. Guzzetta, M. Jaggar, C. M. Long-Smith, J. M. Lyte, J. A. Martin, A. Molinero-Perez, G. Moloney, E. Morelli, E. Morillas, R. O'Connor, J. S. Cruz-Pereira, V. L. Peterson, K. Rea, N. L. Ritz, E. Sherwin, S. Spichak, E. M. Teichman, M. van de Wouw, A. P. Ventura-Silva, S. E. Wallace-Fitzsimons, N. Hyland, G. Clarke and T. G. Dinan, Physiol. Rev., 2019, 99, 1877–2013.
92. Z. Song, R. Song, Y. Liu, Z. Wu and X. Zhang, Food Res. Int., 2023, 167, 112730.
93. J. B. Furness, Nat. Rev. Gastroenterol. Hepatol., 2012, 9, 286–294.
94. J. Cryan, Psychoneuroendocrinology, 2021, 131, S35–S35.
95. G. Agirman and E. Y. Hsiao, Cell, 2021, 184, 2524–2525.
96. A. D. Silva and S. R. Bloom, Gut Liver, 2012, 6, 10–20.
97. G. M. Mawe and J. M. Hoffman, Nat. Rev. Gastroenterol. Hepatol., 2013, 10, 473–486.
98. M. S. Shajib, A. Baranov and W. I. Khan, ACS Chem. Neurosci., 2017, 8, 920–931.
99. J. Liang, H. L. Li, J. Q. Chen, L. He, X. H. Du, L. Zhou, Q. P. Xiong, X. P. Lai, Y. Q. Yang, S. Huang and S. Z. Hou, Pharmacol. Res., 2019, 148, 104417.
100. K. Oh-oka, H. Kono, K. Ishimaru, K. Miyake, T. Kubota, H. Ogawa, K. Okumura, S. Shibata and A. Nakao, PLoS One, 2014, 9, e98016.
101. J. Guo, P. Lin, X. Zhao, J. Zhang, X. Wei, Q. Wang and C. Wang, Neuroscience, 2014, 263, 1–14.
102. C. Hyman, M. Hofer, Y. A. Barde, M. Juhasz, G. D. Yancopoulos, S. P. Squinto and R. M. Lindsay, Nature, 1991, 350, 230–232.
103. A. H. Nagahara, D. A. Merrill, G. Coppola, S. Tsukada, B. E. Schroeder, G. M. Shaked, L. Wang, A. Blesch, A. Kim, J. M. Conner, E. Rockenstein, M. V. Chao, E. H. Koo, D. Geschwind, E. Masliah, A. A. Chiba and M. H. Tuszynski, Nat. Med., 2009, 15, 331–337.
104. L. P. Zhao, Nat. Rev. Microbiol., 2013, 11, 639–647.
105. K. U. Saikh, Immunol. Res., 2021, 69, 117–128.
106. D. Su, A. T. Lei, C. C. Nie and Y. Chen, Food Chem. Toxicol., 2023, 171, 113548.
107. X. Z. Zhang, Y. L. Wan, J. G. Feng, M. H. Li and Z. Q. Jiang, Mol. Med. Rep., 2021, 23, 230.
108. Q. Chu, M. Chen, D. X. Song, X. X. Li, Y. Y. Yang, Z. H. Zheng, Y. L. Li, Y. Y. Liu, L. S. Yu, Z. Hua and X. D. Zheng, Int. J. Biol. Macromol., 2019, 123, 1115–1124.
109. X. Xie, Y. Wu, H. Xie, H. Wang, X. Zhang, J. Yu, S. Zhu, J. Zhao, L. Sui and S. Li, Front. Pharmacol., 2022, 13, 790136.
110. Y. Sun, C. T. Ho, Y. Zhang, M. Hong and X. Zhang, J. Tradit. Complementary Med., 2023, 13, 128–134.
111. M. Yin, Y. Zhang and H. Li, Front. Immunol., 2019, 10, 145.
112. Y. X. Guo, X. F. Chen and P. Gong, Int. J. Biol. Macromol., 2021, 183, 1753–1773.
113. J. Y. Huo, Z. Y. Wu, W. Z. Sun, Z. H. Wang, J. H. Wu, M. Q. Huang, B. W. Wang and B. G. Sun, J. Agric. Food Chem., 2022, 70, 711–735.
114. B. Wang, L. L. Yan, S. C. Guo, L. Wen, M. L. Yu, L. Feng and X. B. Jia, Front. Nutr., 2022, 9, 908175.
115. Y. Saito, M. Kinoshita, A. Yamada, S. Kawano, H. S. Liu, S. Kamimura, M. Nakagawa, S. Nagasawa, T. Taguchi, S. Yamada and H. Moritake, Cancer Sci., 2021, 112, 4944–4956.
116. R. Sorourian, A. E. Khajehrahimi, M. Tadayoni, M. H. Azizi and M. Hojjati, Int. J. Biol. Macromol., 2020, 160, 758–768.
117. B. Du, M. Meenu, H. Z. Liu and B. J. Xu, Int. J. Mol. Sci., 2019, 20, 4032.
118. S. Shao, D. D. Wang, W. Zheng, X. Y. Li, H. Zhang, D. Q. Zhao and M. X. Wang, Int. Immunopharmacol., 2019, 71, 411–422.
119. Q. Song, Y. Wang, L. Huang, M. Shen, Y. Yu, Q. Yu, Y. Chen and J. Xie, Food Res. Int., 2021, 140, 109858.
120. C. Guo, D. Guo, L. Fang, T. Sang, J. Wu, C. Guo, Y. Wang, Y. Wang, C. Chen, J. Chen, R. Chen and X. Wang, Carbohydr. Polym., 2021, 267, 118231.
121. S. Z. Xie, B. Liu, H. Y. Ye, Q. M. Li, L. H. Pan, X. Q. Zha, J. Liu, J. Duan and J. P. Luo, Carbohydr. Polym., 2019, 206, 149–162.
122. H. Tremlett, K. C. Bauer, S. Appel-Cresswell, B. B. Finlay and E. Waubant, Ann. Neurol., 2017, 81, 369–382.
123. H. J. Flint, E. A. Bayer, M. T. Rincon, R. Lamed and B. A. White, Nat. Rev. Microbiol., 2008, 6, 121–131.
124. Q. Fang, J. Hu, Q. Nie and S. Nie, Trends Food Sci. Technol., 2019, 92, 65–70.
125. Q. Shang, H. Jiang, C. Cai, J. Hao, G. Li and G. Yu, Carbohydr. Polym., 2018, 179, 173–185.
126. N. M. Koropatkin, E. A. Cameron and E. C. Martens, Nat. Rev. Microbiol., 2012, 10, 323–335.
127. N. Zmora, J. Suez and E. Elinav, Nat. Rev. Gastroenterol. Hepatol., 2019, 16, 35–56.
128. M. Wang, Z. Xie, L. Li, Y. Chen, Y. Li, Y. Wang, B. Lu, S. Zhang, F. Ma, C. Ma, L. Lin and Q. Liao, Food Funct., 2019, 10, 2658–2675.
129. M. R. Park, M. Shin, D. Mun, S. Y. Jeong, D. Y. Jeong, M. Song, G. Ko, T. Unno, Y. Kim and S. Oh, Sci. Rep., 2020, 10, 21701.
130. M. L. Xue, X. Y. Teng, H. Liang, J. L. Zhao, Y. S. Jiang, X. Qiu, Z. Zhang, Z. Q. Pei, N. Zhang and Y. M. Qin, J. Funct. Foods, 2021, 86, 104726.
131. P. Chen, M. F. Hei, L. L. Kong, Y. Y. Liu, Y. Yang, H. B. Mu, X. Y. Zhang, S. T. Zhao and J. Y. Duan, Food Funct., 2019, 10, 8161–8171.
132. L. Guo, P. L. Xiao, X. X. Zhang, Y. Yang, M. Yang, T. Wang, H. X. Lu, H. Y. Tian, H. Wang and J. Liu, Food Funct., 2021, 12, 1156–1175.
133. Q. P. Zhang, J. Cheng, Q. Liu, G. H. Xu, C. F. Li and L. T. Yi, J. Funct. Foods, 2022, 88, 104912.
134. H. R. Li, Y. H. Xiao, H. Li, Y. Jia, S. L. Luo, D. D. Zhang, L. Zhang, P. Wu, C. J. Xiao, W. J. Kan, J. Du and H. K. Bao, Brain Res. Bull., 2021, 171, 16–24.
135. J. D. Hoffman, L. M. Yanckello, G. Chlipala, T. C. Hammond, S. D. McCulloch, I. Parikh, S. Sun, J. M. Morganti, S. J. Green and A. L. Lin, PLoS One, 2019, 14, e0221828.
136. A. X. Su, W. J. Yang, L. Y. Zhao, F. Pei, B. Yuan, L. Zhong, G. X. Ma and Q. H. Hu, Food Funct., 2018, 9, 1424–1432.
137. X. L. Dong, X. Wang, F. Liu, X. Liu, Z. R. Du, R. W. Li, C. H. Xue, K. H. Wong, W. T. Wong, Q. Zhao and Q. J. Tang, Int. J. Biol. Macromol., 2020, 164, 994–1005.
138. S. L. Luo, X. Zhang, S. Huang, X. P. Feng, X. J. Zhang and D. X. Xiang, Int. J. Biol. Macromol., 2022, 213, 404–415.
139. T. Sang, C. Guo, D. Guo, J. Wu, Y. Wang, Y. Wang, J. Chen, C. Chen, K. Wu, K. Na, K. Li, L. Fang, C. Guo and X. Wang, Carbohydr. Polym., 2021, 256, 117594.
140. L. L. Xiong, Y. N. Wu, Q. L. Shu and W. Xiong, J. Appl. Microbiol., 2023, 134, lxad052.
141. W. L. Guo, J. C. Deng, Y. Y. Pan, J. X. Xu, J. L. Hong, F. F. Shi, G. L. Liu, M. Qian, W. D. Bai, W. Zhang, B. Liu, Y. Y. Zhang, P. J. Luo, L. Ni, P. F. Rao and X. C. Lv, Int. J. Biol. Macromol., 2020, 153, 1231–1240.
142. S. M. Huang, D. R. Pang, X. Li, L. J. You, Z. G. Zhao, P. C. K. Cheung, M. W. Zhang and D. Liu, Food Funct., 2019, 10, 3224–3236.
143. R. T. Wu, L. F. Wang, Y. F. Yao, T. Sang, Q. L. Wu, W. W. Fu, M. Wan and W. J. Li, Biomed. Pharmacother., 2022, 155, 113681.
144. D. Cör, Z. Knez and M. K. Hrncic, Molecules, 2018, 23, 649.
145. Y. Liu, Y. Y. Sun and G. L. Huang, Int. J. Biol. Macromol., 2018, 111, 780–786.
146. Z. H. Zhao, X. W. Zheng and F. Fang, Saudi J. Biol. Sci., 2014, 21, 119–123.
147. H. Li, R. Shi, F. Ding, H. Wang, W. Han, F. Ma, M. Hu, C. W. Ma and Z. Huang, Oxid. Med. Cell. Longevity, 2016, 2016, 1–10.
148. J. B. Pi, Q. Zhang, J. Q. Fu, C. G. Woods, Y. Y. Hou, B. E. Corkey, S. Collins and M. E. Andersen, Toxicol. Appl. Pharmacol., 2010, 244, 77–83.
149. X. L. Xu, S. Li, R. Zhang and W. D. Le, Neural Regener. Res., 2022, 17, 1907–1912.
150. S. Zhang, M. Zhang, W. Li, L. Ma, X. Liu, Q. Ding, W. Yu, T. Yu, C. Ding and W. Liu, Int. J. Biol. Macromol., 2023, 253, 126799.
151. Y. P. Fu, C. Y. Li, X. Peng, Y. F. Zou, F. Rise, B. S. Paulsen, H. Wangensteen and K. T. Inngjerdingen, Carbohydr. Polym., 2022, 291, 119655.
152. J. Zhong, X. Qiu, Q. Yu, H. Y. Chen and C. Y. Yan, Int. J. Biol. Macromol., 2020, 163, 464–475.
153. S. L. Zhang, G. B. Pang, C. Chen, J. Z. Qin, H. Yu, Y. M. Liu, X. H. Zhang, Z. T. Song, J. Zhao, F. J. Wang, Y. Y. Wang and L. W. Zhang, Carbohydr. Polym., 2019, 205, 192–202.
154. X. Q. Cheng, H. Li, X. L. Yue, J. Y. Xie, Y. Y. Zhang, H. Y. Di and D. F. Chen, J. Ethnopharmacol., 2010, 130, 363–368.
155. J. Li, F. Gu, C. Cai, M. Hu, L. Fan, J. Hao and G. Yu, Int. J. Biol. Macromol., 2019, 143, 806–813.
156. S. J. Zhang, Q. Zhang, L. J. An, J. J. Zhang, Z. G. Li, J. Zhang, Y. H. Li, M. Tuerhong, Y. Ohizumi, J. Jin, J. Xu and Y. Q. Guo, Carbohydr. Polym., 2020, 229, 115477.

---