Acrylamide Retards the Slow Axonal Transport of Neurofilaments in Rat Cultured Dorsal Root Ganglia Neurons and the Corresponding Mechanisms

Dietary Exposure to Acrylamide Has Negative Effects on the Gastrointestinal Tract: A Review

Changing eating habits and an increase in consumption of thermally processed products have increased the risk of the harmful impact of chemical substances in food on consumer health. A 2002 report by the Swedish National Food Administration and scientists at Stockholm University on the formation of acrylamide in food products during frying, baking and grilling contributed to an increase in scientific interest in the subject. Acrylamide is a product of Maillard's reaction, which is a non-enzymatic chemical reaction between reducing sugars and amino acids that takes place during thermal processing. The research conducted over the past 20 years has shown that consumption of acrylamide-containing products leads to disorders in human and animal organisms. The gastrointestinal tract is a complex regulatory system that determines the transport, grinding, and mixing of food, secretion of digestive juices, blood flow, growth and differentiation of tissues, and their protection. As the main route of acrylamide absorption from food, it is directly exposed to the harmful effects of acrylamide and its metabolite-glycidamide. Despite numerous studies on the effect of acrylamide on the digestive tract, no comprehensive analysis of the impact of this compound on the morphology, innervation, and secretory functions of the digestive system has been made so far. Acrylamide present in food products modifies the intestine morphology and the activity of intestinal enzymes, disrupts enteric nervous system function, affects the gut microbiome, and increases apoptosis, leading to gastrointestinal tract dysfunction. It has also been demonstrated that it interacts with other substances in food in the intestines, which increases its toxicity. This paper summarises the current knowledge of the impact of acrylamide on the gastrointestinal tract, including the enteric nervous system, and refers to strategies aimed at reducing its toxic effect.

Acrylamide Induces Neurotoxicity in SH-SY5Y Cells via NLRP3-mediated Pyroptosis

Acrylamide (ACR), a soft electrophile, is a typical environmental and food contaminant that presents potential health hazards and, consequently, is attracting increasing attention in the quest for its control. ACR neurotoxicity has been widely reported in experimental animals and attributed to neuroinflammation; however, the mechanisms involved therein require clarification. In this study, we used a neuron cell model to investigate the mechanisms of ACR-induced neuroinflammation and pyroptosis. The results showed that ACR treatment induced lytic cell death morphologically under both the canonical pyroptotic pathway (NOD-like receptor protein 3 (NLRP3)-apoptosis-associated speck-like protein containing CARD (ASC)-cysteinyl aspartate specific proteinase 1 (caspase-1)-gasdermin D (GSDMD)-interleukin-1β (IL-1β)/interleukin-18 (IL-18)) and an alternative pyroptotic pathway (cysteinyl aspartate specific proteinase 3 (caspase-3)-gasdermin E (GSDME)-IL-1β/IL-18) in SH-SY5Y cells. Moreover, the lactate dehydrogenase (LDH) production, cytokines release, and lytic cell death induced by ACR were diminished by caspase-1 and -3 inhibitors. Furthermore, the knockdown of caspase-1 by small interfering RNA attenuated ACR-induced lytic cell death, suggesting that canonical pyroptosis (the NLRP3-caspase 1-GSDMD-IL-1β signaling axis) played a primary role in the ACR-induced pyroptosis. Of the two pyroptotic-related pathways, the NLRP3 inflammasome cascade was activated first within the 6-h period of ACR exposure, while the activation of the alternative pyroptotic pathway was delayed. Collectively, these results indicate that ACR mainly induces NLRP3-related neuroinflammation and pyroptosis in SH-SY5Y cells, which is, thus, suggestive of an alternative mechanism for ACR-induced neurotoxicity.

The Mechanism of Acrylamide-Induced Neurotoxicity: Current Status and Future Perspectives

Acrylamide (ACR), a potential neurotoxin, is produced by the Maillard reaction between reducing sugars and free amino acids during food processing. Over the past decade, the neurotoxicity of ACR has caused increasing concern, prompting many related studies. This review summarized the relevant literature published in recent years and discussed the exposure to occupational, environmental, and daily ACR contamination in food. Moreover, ACR metabolism and the potential mechanism of ACR-induced neurotoxicity were discussed, with particular focus on the axonal degeneration of the nervous system, nerve cell apoptosis, oxidative stress, inflammatory response, and gut-brain axis homeostasis. Additionally, the limitations of existing knowledge, as well as new perspectives, were examined, specifically regarding the connection between the neurotoxicity caused by ACR and neurodegenerative diseases, NOD-like receptor protein 3 (NLRP3) inflammasome-related neuroinflammation, and microbiota-gut-brain axis signaling. This review might provide systematic information for developing an alternative pathway approach to assess ACR risk.

Matrine treatment reduces retinal ganglion cell apoptosis in experimental optic neuritis

Inflammatory demyelination and axonal injury of the optic nerve are hallmarks of optic neuritis (ON), which often occurs in multiple sclerosis and is a major cause of visual disturbance in young adults. Although a high dose of corticosteroids can promote visual recovery, it cannot prevent permanent neuronal damage. Novel and effective therapies are thus required. Given the recently defined capacity of matrine (MAT), a quinolizidine alkaloid derived from the herb Radix Sophorae flavescens, in immunomodulation and neuroprotection, we tested in this study the effect of matrine on rats with experimental autoimmune encephalomyelitis, an animal model of multiple sclerosis. MAT administration, started at disease onset, significantly suppressed optic nerve infiltration and demyelination, with reduced numbers of Iba1⁺ macrophages/microglia and CD4⁺ T cells, compared to those from vehicle-treated rats. Increased expression of neurofilaments, an axon marker, reduced numbers of apoptosis in retinal ganglion cells (RGCs). Moreover, MAT treatment promoted Akt phosphorylation and shifted the Bcl-2/Bax ratio back towards an antiapoptotic one, which could be a mechanism for its therapeutic effect in the ON model. Taken as a whole, our results demonstrate that MAT attenuated inflammation, demyelination and axonal loss in the optic nerve, and protected RGCs from inflammation-induced cell death. MAT may therefore have potential as a novel treatment for this disease that may result in blindness.

NLRP3 inflammasome inhibition attenuates subacute neurotoxicity induced by acrylamide in vitro and in vivo

Acrylamide (AA) constitutes an important industrial chemical agent and well-known neurotoxin. However, the mechanism underlying AA-mediated neurotoxicity is extremely complicated and controversial. In this study, we found that activation of the NLR family pyrin domain containing 3 (NLRP3) inflammasome and its subsequent downstream inflammatory responses plays an important role in AA-induced neurotoxicity mechanisms. In vitro experiments revealed that AA (2.5 mM) induced BV2 microglial cytotoxicity and triggered NLRP3 inflammasome activation along with downstream proinflammatory cytokine interleukin-1β and interleukin-18 expression. Treatment with inhibitor or NLRP3 siRNA efficiently protected BV2 microglial cells against AA-induced cytotoxicity and reversed NLRP3 inflammasome activation and its mediated inflammatory reaction. Similarly, AA exposure (50 mg/kg) for 10 consecutive days caused significant activation of NLRP3 inflammasomes and neuroinflammation in C57BL/6 mice, whereas inhibiting these effects through specific NLRP3 inflammasome blocker MCC950 (5 mg/kg) intervention or NLRP3 knock-out significantly ameliorated AA-induced ataxia, cerebellar Purkinje cells degeneration, and apoptosis. Furthermore, we demonstrated that antagonism of NLRP3 could also up-regulate the Nrf2 signalling pathway and related antioxidant genes. In conclusion, our findings indicate that activation of the NLRP3 inflammasome pathway is involved in AA-induced neurotoxicity, whereas MCC950 treatment or NLRP3 knock-out could effectively protect against AA-induced neurotoxic injury through the inhibition of neuroinflammation and activation of the Nrf2 antioxidant pathway. Therefore, the NLRP3 inflammasome might serve as a promising therapeutic target, with drugs designed to specifically inhibit this pathway potentially providing new avenues for preventing or ameliorating AA poisoning.

Cryopreservation of Canine Primary Dorsal Root Ganglion Neurons and Its Impact upon Susceptibility to Paramyxovirus Infection

Canine dorsal root ganglion (DRG) neurons, isolated post mortem from adult dogs, could provide a promising tool to study neuropathogenesis of neurotropic virus infections with a non-rodent host spectrum. However, access to canine DRG is limited due to lack of donor tissue and the cryopreservation of DRG neurons would greatly facilitate experiments. The present study aimed (i) to establish canine DRG neurons as an in vitro model for canine distemper virus (CDV) infection; and (ii) to determine whether DRG neurons are cryopreservable and remain infectable with CDV. Neurons were characterized morphologically and phenotypically by light microscopy, immunofluorescence, and functionally, by studying their neurite outgrowth and infectability with CDV. Cryopreserved canine DRG neurons remained in culture for at least 12 days. Furthermore, both non-cryopreserved and cryopreserved DRG neurons were susceptible to infection with two different strains of CDV, albeit only one of the two strains (CDV R252) provided sufficient absolute numbers of infected neurons. However, cryopreserved DRG neurons showed reduced cell yield, neurite outgrowth, neurite branching, and soma size and reduced susceptibility to CDV infection. In conclusion, canine primary DRG neurons represent a suitable tool for investigations upon the pathogenesis of neuronal CDV infection. Moreover, despite certain limitations, cryopreserved canine DRG neurons generally provide a useful and practicable alternative to address questions regarding virus tropism and neuropathogenesis.

Changes in VIP-, SP- and CGRP- like immunoreactivity in intramural neurons within the pig stomach following supplementation with low and high doses of acrylamide

Acrylamide is one of the food toxins to which the human body is exposed. Although researchers' interest in acrylamide has been growing in recent years, the knowledge of its effect on the gastrointestinal tract, especially on intramural neurons which form the enteric nervous system is scarce. The aim of this experiment was to determine the influence of acrylamide, administered at doses equivalent to the human tolerable daily intake (TDI, 0.5 μg/kg b.w./day) and ten times higher than the TDI (5 μg/kg b.w./day), on the distribution of vasoactive intestinal peptide (VIP), substance P (SP), and calcitonin gene related peptide (CGRP) in intramural neurons of the domestic pig stomach. Using double immunofluorescent labelling we revealed that the ENS neurons underwent adaptive changes in response to the supplementation of acrylamide, which manifested themselves as increased expression of VIP, SP and CGRP, both in intramural neurons and by an increase in the nerve density in submucous and muscular layers in the porcine stomach. These substances take part in defensive reactions of neurons and transmission of sensory reactions may play an important role in protecting the stomach against the harmful effect of acrylamide. Moreover, it has been shown that acrylamide induces a significant response of ENS neurons even in TDI dose, which suggests that it is not neutral to the body. These findings may be the basis for further toxicological studies addressing the question if currently permitted minimal content of acrylamide in the food does jeopardize the health of human consumers?

Axonal outgrowth, neuropeptides expression and receptors tyrosine kinase phosphorylation in 3D organotypic cultures of adult dorsal root ganglia

Limited knowledge from mechanistic studies on adult sensory neuronal activity was generated, to some extent, in recapitulated adult in vivo 3D microenvironment. To fill this gap there is a real need to better characterize the adult dorsal root ganglia (aDRG) organotypic cultures to make these in vitro systems exploitable for different approaches, ranging from basic neurobiology to regenerative therapies, to address the sensory nervous system in adult stage. We conducted a direct head-to-head comparison of aDRG and embryonic DRG (eDRG) organotypic culture focusing on axonal growth, neuropeptides expression and receptors tyrosine kinase (RTK) activation associated with neuronal survival, proliferation and differentiation. To identify alterations related to culture conditions, these parameters were also addressed in retrieved aDRG and eDRG and compared with organotypic cultures. Under similar neurotrophic stimulation, aDRG organotypic cultures displayed lower axonal outgrowth rate supported by reduced expression of growth associated protein-43 and high levels of RhoA and glycogen synthase kinase 3 beta mRNA transcripts. In addition, differential alteration in sensory neuropeptides expression, namely calcitonin gene-related peptide and substance P, was detected and was mainly pronounced at gene expression levels. Among 39 different RTK, five receptors from three RTK families were emphasized: tropomyosin receptor kinase A (TrkA), epidermal growth factor receptors (EGFR, ErbB2 and ErbB3) and platelet-derived growth factor receptor (PDGFR). Of note, except for EGFR, the phosphorylation of these receptors was dependent on DRG developmental stage and/or culture condition. In addition, EGFR and PDGFR displayed alterations in their cellular expression pattern in cultured DRG. Overall we provided valuable information particularly important when addressing in vitro the molecular mechanisms associated with development, maturation and regeneration of the sensory nervous system.