Acrylamide-Induced Changes in the Neurofilament Protein of Rat Cerebrum Fractions

Performance of biomarkers NF-L, NSE, Tau and GFAP in blood and cerebrospinal fluid in rat for the detection of nervous system injury

Background

Target organ toxicity is often a reason for attritions in nonclinical and clinical drug development. Leveraging emerging safety biomarkers in nonclinical studies provides an opportunity to monitor such toxicities early and efficiently, potentially translating to early clinical trials. As a part of the European Union's Innovative Medicines Initiative (IMI), two projects have focused on evaluating safety biomarkers of nervous system (NS) toxicity: Translational Safety Biomarker Pipeline (TransBioLine) and Neurotoxicity De-Risking in Preclinical Drug Discovery (NeuroDeRisk).

Methods

Performance of fluid-based NS injury biomarker candidates neurofilament light chain (NF-L), glial fibrillary acidic protein (GFAP), neuron specific enolase (NSE) and total Tau in plasma and cerebrospinal fluid (CSF) was evaluated in 15 rat in vivo studies. Model nervous system toxicants as well as other compounds were used to evaluate sensitivity and specificity. Histopathologic assessments of nervous tissues and behavioral observations were conducted to detect and characterize NS injuries. Receiver operator characteristic (ROC) curves were generated to compare the relative performance of the biomarkers in their ability to detect NS injury.

Results

NF-L was the best performer in detecting both peripheral nervous system (PNS) and CNS injury in plasma, (AUC of 0.97-0.99; respectively). In CSF, Tau correlated the best with CNS (AUC 0.97), but not PNS injury. NSE and GFAP were suitable for monitoring CNS injury, but with lesser sensitivity. In summary, NF-L is a sensitive and specific biomarker in rats for detecting compound-induced central and peripheral NS injuries. While NF-L measurement alone cannot inform the site of the injury, addition of biomarkers like Tau and NSE and analysis in both blood and CSF can provide additional information about the origin of the NS injury.

Conclusion

These results demonstrate the utility of emerging safety biomarkers of drug-induced NS injury in rats and provide additional supporting evidence for biomarker translation across species and potential use in clinical settings to monitor drug-induced NS injury in patients.

Subchronic Acrylamide Exposure Activates PERK-eIF2α Signaling Pathway and Induces Synaptic Impairment in Rat Hippocampus

Acrylamide (ACR), a well-documented neurotoxicant to humans, is extensively found in starchy foods. More than 30% of the typical daily calorie intake comes from ACR-containing foods. Epidemiological and toxicological studies have found that ACR exposure is associated with mild cognitive change in men and experimental animals. However, there is limited information on the mechanisms by which ACR exposure induces memory deficits. The aberrant activation of the PKR-like ER kinase (PERK)-eukaryotic initiation factor 2α (eIF2α) signaling pathway is emerging as a major common theme in cognitive decline. The present study is designed to explore the effect of subchronic ACR exposure on the PERK signaling and the synaptic impairment to elucidate the potential mechanism of ACR-induced cognitive dysfunction in rat. ACR exposure at 5 and 10 (mg/kg)/day by gavage for 14 weeks results in gait abnormality and cognitive impairment in rats, which were accompanied by neuronal loss, glial cell proliferation, and synaptic ultrastructure damage in the hippocampus. ACR reduced the expression of phosphorylated cAMP response element-binding protein (P-CREB), brain-derived neurotrophic factor (BDNF), and synaptic vesicle proteins synapsin-1 and synaptophysin synthesis. ACR also excessively activates the PERK-eIF2α signaling, resulting in overexpression of C/EBP homologous protein (CHOP) and activating transcription factor 4 (ATF4). This work helps to propose a possible mechanism of subchronic exposure of 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.

Acrylamide treatment alters the level of Ca2+ and Ca2+-related protein kinase in spinal cords of rats

This study aimed to analyze the neurological changes induced by acrylamide (ACR) poisoning and their underlying mechanisms within the spinal cords of male adult Wistar rats. The rats were randomly divided into three groups (n = 9 rats per group). ACR was intraperitoneally injected to produce axonopathy according to the daily dosing schedules of 20 or 40 mg/kg/day of ACR for eight continuous weeks (three times per week). During the exposure period, body weights and gait scores were assessed, and the concentration of Ca²⁺ was calculated in 27 mice. Protein kinase A (PKA), protein kinase C (PKC), cyclin-dependent protein kinase 5 (CDK5), and P35 were assessed by electrophoretic resolution and Western blotting. The contents of 3'-cyclic adenosine monophosphate (cAMP) and calmodulin (CaM) were determined using ELISA kits, and the activities of calcium/calmodulin-dependent protein kinase II (CaMKII), PKA, and PKC were determined using the commercial Signa TECTPKAassay kits. Compared with control rats, treatment with 20 and 40 mg/kg of ACR decreased body weight and increased gait scores at 8 weeks. Intracellular Ca²⁺ levels increased significantly in treated rats; CaM, PKC, CDK5, and P35 levels were significantly decreased; and PKA and cAMP levels remained unchanged. CaMKII, PKA, and PKC activities increased significantly. The results indicated that ACR can damage neurofilaments by affecting the contents and activities of CaM, CaMKII, PKA, cAMP, PKC, CDK5, and P35, which could result in ACR toxic neuropathy.

Uptake of TiO2 Nanoparticles into C. elegans Neurons Negatively Affects Axonal Growth and Worm Locomotion Behavior

We employ model organism Caenorhabditis elegans to effectively study the toxicology of anatase and rutile phase titanium dioxide (TiO₂) nanoparticles (NPs). The experimental results show that nematode C. elegans can take up fluorescein isothiocyanate-labeled TiO₂ NPs and that both anatase and rutile TiO₂ NPs can be detected in the cytoplasm of cultured primary neurons imaged by transmission electron microscopy. After TiO₂ NP exposure, these neurons also grow shorter axons, which may be related to the detected impeded worm locomotion behavior. Furthermore, anatase TiO₂ NPs did not affect the worm's body length; however, we determined that a concentration of 500 μg/mL of anatase TiO₂ NPs reduced the worm population by 50% within 72 h. Notably, rutile TiO₂ NPs negatively affect both the body size and worm population. Worms unable to enter the L4 larval stage explain a severe reduction in the worm population at TiO₂ NPs LC₅₀/3d. To obtain a better understanding of the cellular mechanisms involved in TiO₂ NP intoxication, DNA microarray assays were employed to determine changes in gene expression in the presence or absence of TiO₂ NP exposure. Our data reveal that three genes (with significant changes in expression levels) were related to metal binding or metal detoxification (mtl-2, C45B2.2, and nhr-247), six genes were involved in fertility and reproduction (mtl-2, F26F2.3, ZK970.7, clec-70, K08C9.7, and C38C3.7), four genes were involved in worm growth and body morphogenesis (mtl-2, F26F2.3, C38C3.7, and nhr-247), and five genes were involved in neuronal function (C41G6.13, C45B2.2, srr-6, K08C9.7, and C38C3.7).

Protective effect of rosemary on acrylamide motor neurotoxicity in spinal cord of rat offspring: postnatal follow-up study

The direct interactive effects of rosemary and acrylamide on the development of motor neurons in the spinal cord remains unknown. Our goal is to confirm the protective effects of rosemary against motor neuronal degeneration induced by acrylamide in the developing postnatal rat spinal cord using a postnatal rat model. We assigned the offspring of treated female rats into control, rosemary; acrylamide group; and recovery groups. This work depended on clinical, histopathological, morphometrically, immunohistochemical and genetic methods. In the acrylamide group, we observed oxidation, motor neuron degeneration, apoptosis, myelin degeneration, neurofilament reduction, reactive gliosis. Whoever, concomitant rosemary intake and withdrawal of acrylamide modulate these effects. These findings proof that dietary rosemary can directly protect motor neuron against acrylamide toxicity in the mammalian developing spinal cord.

Neuroprotective Effect of Calpeptin on Acrylamide-Induced Neuropathy in Rats

Acrylamide (ACR) is a vinyl monomer with established human neurotoxic effects, which is characterized by the accumulation of neurofilaments (NFs) in the distal swellings of large axons in peripheral and central nervous systems. However, the mechanisms of neurotoxicity remain unclear. The objective is to investigate the neuroprotective effect of calpeptin (CP) on ACR-induced neuropathy and its mechanism. Female adult Wistar rats were randomly divided into four groups (control, CP, ACR, and ACR + CP group). Control group received 0.9 % saline, ACR and ACR + CP groups received 30 mg/kg ACR by intraperitoneal injection. In addition, CP and ACR + CP groups also received 200 µg/kg CP. Gait analysis and hind limb splay were measured weekly to analyze neurobehavioral changes. The calpain activity and the changes of NFs protein levels in spinal cord are determined. Compared with control group, body weight of rats in ACR group decreased by 11.3 % (P < 0.01), while in ACR + CP group body weight increased significantly by 8.3 % (P < 0.01) compared with ACR group by the end of the 4th week; gait score of rats in both ACR and ACR + CP groups increased significantly by 167 % and 100 % (P < 0.01) compared with control group, while it decreased significantly by 25.1 % (P < 0.01) in ACR + CP group compared with ACR group; the distance of hind limb splay in both ACR and ACR + CP groups increased by 76.7 % and 49.5 % (P < 0.01) compared with control group, while it decreased by 15.4 % (P < 0.01) in ACR + CP group compared with ACR group; calpain activity of spinal cord at ACR and ACR + CP groups increased significantly by 14.9 % and 10.0 % (P < 0.01) compared with control group, while it decreased 4.2 % (P < 0.01) in ACR + CP group compared with ACR group; compared with control group, the levels of light NF (NF-L), medium NF (NF-M) and heavy NF (NF-H) subunits increased by 81.2 %, 263.6 % and 22.6 % (P < 0.01) in the supernatant of ACR group in spinal cord tissue and increased by 28.4 %, 96.6 % and 10.6 % (P < 0.01) in ACR + CP group, while the levels of NF-L, NF-M and NF-H subunits decreased by 29.1 %, 45.9 % and 9.8 % (P < 0.01) in ACR + CP group compared with ACR group. The present results suggested that CP can relieve ACR neuropathy by decrease calpain activity and NFs degradation. The changes of calpain activity and NFs may be one of the mechanisms of ACR-induced neuropathy.

Acrylamide neurotoxicity

Acrylamide, a food contaminant, belongs to a large class of structurally similar toxic chemicals, 'type-2 alkenes', to which humans are widely exposed. Besides, occupational exposure to acrylamide has received wide attention through the last decades. It is classified as a neurotoxin and there are three important hypothesis considering acrylamide neurotoxicity: inhibition of kinesin-based fast axonal transport, alteration of neurotransmitter levels, and direct inhibition of neurotransmission. While many researchers believe that exposure of humans to relatively low levels of acrylamide in the diet will not result in clinical neuropathy, some neurotoxicologists are concerned about the potential for its cumulative neurotoxicity. It has been shown in several studies that the same neurotoxic effects can be observed at low and high doses of acrylamide, with the low doses simply requiring longer exposures. This review is focused on the neurotoxicity of acrylamide and its possible outcomes.

Neurotoxicity of acrylamide in exposed workers

Acrylamide (ACR) is a water-soluble chemical used in different industrial and laboratory processes. ACR monomer is neurotoxic in humans and laboratory animals. Subchronic exposure to this chemical causes neuropathies, hands and feet numbness, gait abnormalities, muscle weakness, ataxia, skin and in some cases, cerebellar alterations. ACR neurotoxicity involves mostly the peripheral but also the central nervous system, because of damage to the nerve terminal through membrane fusion mechanisms and tubulovescicular alterations. Nevertheless, the exact action mechanism is not completely elucidated. In this paper we have reviewed the current literature on its neurotoxicity connected to work-related ACR exposure. We have analyzed not only the different pathogenetic hypotheses focusing on possible neuropathological targets, but also the critical behavior of ACR poisoning. In addition we have evaluated the ACR-exposed workers case studies. Despite all the amount of work which have being carried out on this topic more studies are necessary to fully understand the pathogenetic mechanisms, in order to propose suitable therapies.

Ameliorating effect of fish oil on acrylamide induced oxidative stress and neuronal apoptosis in cerebral cortex

Acrylamide (ACR) is a known industrial toxic chemical that produce neurotoxicity characterized by progressive neuronal degeneration. This study was designed to investigate the protective effect of fish oil on ACR-induced neuronal damage in Wistar rats. ACR enhances the production of reactive oxygen species and potentially affects brain. ACR administered rats showed increased levels of lipid peroxidative product, protein carbonyl content, hydroxyl radical and hydroperoxide which were significantly modulated by the supplementation of fish oil. The activities of enzymic antioxidants and levels of reduced glutathione were markedly lowered in ACR-induced rats; fish oil treatment augmented these antioxidant levels in cortex. Free radicals generated during ACR administration reduced the activities of membrane adenosine triphosphatases and acetylcholine esterase. Fish oil enhanced the activities of these enzymes near normal level. Histological observation represented the protective role of fish oil in ACR-induced neuronal damage. Fish oil reduced the ACR-induced apoptosis through the modulation in expressions of B-cell lymphoma 2 (Bcl2)-associated X protein and Bcl2-associated death promoter. Further, fish oil increases the expression of heat shock protein 27 (Hsp27) in ACR-induced rats. This study provides evidence for the neuroprotective effect of fish oil on ACR-induced neurotoxicity by reducing oxidative stress and apoptosis with modulation in the expression of Hsp27.

Effect of sub-acute exposure to acrylamide on GABAergic neurons and astrocytes in weaning rat cerebellum

Occupational exposure and experimental intoxication of acrylamide (ACR) can produce skeletal muscle weakness and ataxia. In this study, we tested whether ACR would affect cerebellar function through the regulation of gamma-aminobutyric acid (GABA) and glial fibrillary acidic protein (GFAP) expression in cerebellum. Weaning male Sprague-Dawley rats were gavaged with ACR (5, 15, 30 mg/kg, 5 days per week) or saline for 4 weeks. Effects of ACR on the cerebellum were observed. For the 5 mg/kg group, no obvious change was observed, whereas moderate and severe ataxia were observed in the 15 mg/kg and 30 mg/kg groups, respectively. For the 15 mg/kg and 30 mg/kg groups, cerebellum concentrations of glutamate and GABA were dose-dependently decreased and increased, respectively. Moreover, the expression of GABA, the GABAergic presynaptic marker glutamate acid decarboxylase-65 (GAD65) and GFAP were significantly increased in those 2 groups. The results suggested that weaning rats were sensitive to ACR and that the toxic effects of ACR on the cerebellum may be associated with the increased expression of GABA and reactive astrocytes hypertrophy.

Single-cell ELISA and flow cytometry as methods for highlighting potential neuronal and astrocytic toxicant specificity

The timeline imposed by recent worldwide chemical legislation is not amenable to conventional in vivo toxicity testing, requiring the development of rapid, economical in vitro screening strategies which have acceptable predictive capacities. When acquiring regulatory neurotoxicity data, distinction on whether a toxic agent affects neurons and/or astrocytes is essential. This study evaluated neurofilament (NF) and glial fibrillary acidic protein (GFAP) directed single-cell (S-C) ELISA and flow cytometry as methods for distinguishing cell-specific cytoskeletal responses, using the established human NT2 neuronal/astrocytic (NT2.N/A) co-culture model and a range of neurotoxic (acrylamide, atropine, caffeine, chloroquine, nicotine) and non-neurotoxic (chloramphenicol, rifampicin, verapamil) test chemicals. NF and GFAP directed flow cytometry was able to identify several of the test chemicals as being specifically neurotoxic (chloroquine, nicotine) or astrocytoxic (atropine, chloramphenicol) via quantification of cell death in the NT2.N/A model at cytotoxic concentrations using the resazurin cytotoxicity assay. Those neurotoxicants with low associated cytotoxicity are the most significant in terms of potential hazard to the human nervous system. The NF and GFAP directed S-C ELISA data predominantly demonstrated the known neurotoxicants only to affect the neuronal and/or astrocytic cytoskeleton in the NT2.N/A cell model at concentrations below those affecting cell viability. This report concluded that NF and GFAP directed S-C ELISA and flow cytometric methods may prove to be valuable additions to an in vitro screening strategy for differentiating cytotoxicity from specific neuronal and/or astrocytic toxicity. Further work using the NT2.N/A model and a broader array of toxicants is appropriate in order to confirm the applicability of these methods.

Protective role of dark soy sauce against acrylamide-induced neurotoxicity in rats by antioxidative activity

Dark soy sauce (DSS) exerts antioxidant activity in vitro or in vivo. To test the possibility of chemoprevention by such dietary supplements on acrylamide (ACR)-induced subacute toxicity, Sprague-Dawley male rats were administered DSS dissolved in water (0.5 ml/kgbw x d) for 2 weeks after, before or during ACR exposure (0.2 mg/L in distillate water). DSS significantly improved the body weight gain, relative brain weights, and the gait abnormalities of ACR-treated rats when DSS treated at the same time as ACR-exposure (p < 0.05). DSS significantly improved the axonal degeneration, the ratio of myelinated nerves < 3 microm in diameter, degree of central chromatolysis of the ganglion neurons in peripheral nerves, and numbers of SYP (+) aberrant dots per mm cortex in the cerebellar molecular layer of ACR-treated rats no matter before, after, or during ACR-exposure (p < 0.05). DSS significantly decreased the malondialdehyde level and increased the superoxide dismutase activity in brain of ACR-treated rats when DSS treated during ACR-exposure (p < 0.05). These findings suggest that DSS plays a protective role against ACR-developed neurotoxicity and, partly at least, through an anti-oxidative mechanism. And it is worthy to note that DSS treatment at the same time as ACR exposure plays a more effective protective role than before or after ACR exposure.

Neurofilament isoform alterations in the rat cerebellum following cytosine arabinoside administration

A number of neurotoxic agents could potentially exert their action by degrading or modifying cytoskeleton components like neurofilaments (NF). Cytosine arabinoside (AraC) is an anticancer drug commonly used in leukemia treatment. Its side effects include neuronal cell death in the cerebellum and severe motor coordination deficits. We have previously shown that AraC administration (400mg/kg bw) in adult rats reduced NF immunostaining in cerebellar neurons. To further delineate the susceptibility of individual NF isoforms (NF-H, NF-M, NF-L) to AraC, in the present study we used Western blot analysis to quantify their level. A significant and selective reduction of NF-H isoform was observed in the cerebellum of AraC-treated animals, compared to the controls. Administration of the antioxidant N-acetylcysteine (NAC) for a period of 14 days (prior to and during AraC treatment), which was previously shown to ameliorate the AraC-induced motor deficits in these animals, largely prevented the reduction in NF-H isoform. Given the significant role of NF proteins and particularly NF-H in maintaining structural integrity and synaptic transport, the observed loss of this isoform may be a key-target of AraC action in cerebellar neurons. Moreover, this study provides further data on the neuroprophylactic role of NAC in vivo against chemotherapy-induced toxicity.

Acrylamide alters cytoskeletal protein level in rat sciatic nerves

Occupational exposure and experimental intoxication with acrylamide (ACR) produce neuropathy characterized by nerve degeneration. To investigate the mechanism of ACR-induced neuropathy, male adult Wistar rats were given ACR (20, 40 mg/kg i.p. 3 days/week) for 8 weeks. Sciatic nerves were Triton-extracted and centrifuged at a high speed (100,000 x g) to yield pellet and supernatant fractions. The contents of six cytoskeletal proteins (NF-L, NF-M, NF-H, alpha-tubulin, beta-tubulin, and beta-actin) in both fractions were determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting. Results showed that the three neurofilament (NF) subunits (NF-L, NF-M, NF-H) in both the pellet and the supernatant fraction decreased significantly (P < 0.01) in the high-dosing group, except for NF-M in the pellet. alpha-tubulin, beta-tubulin, and beta-actin increased significantly in the supernatant (P < 0.01), whereas both alpha-tubulin and beta-tubulin decreased significantly in the pellet (P < 0.01). However, beta-actin was not altered significantly in the sciatic nerves pellet. These findings suggest that ACR altered the cytoskeletal protein level in sciatic nerve, which may be one of the molecular mechanisms of ACR-induced peripheral neuropathy.

The Changes of Cytoskeletal Proteins in Plasma of Acrylamide-Induced Rats

Acrylamide (ACR) is a known industrial neurotoxic chemical that can induce neurodegeneration. Cytoskeletal protein aggregation is a pathological hallmark of neurodegenerative disorders. This study was an initial exploration on cytoskeletal proteins in plasma as potential biomarkers of ACR neurotoxicity. Low and high ACR groups received 20 mg/kg and 40 mg/kg ACR by intraperitoneal injection in adult Wistar rats and control group received physiological saline. Rats were all killed after 8 weeks to evaluate the levels of neurofilament(NF)-L, NF-M, NF-H, beta-actin, alpha-tubulin, beta-tubulin, tau, MAP2 proteins in plasma using both SDS-PAGE and western blotting. Compared with the control, the levels of NF-L, NF-M, NF-H, beta-actin, tau, MAP2 proteins decreased and the level of alpha-tubulin increased in high ACR group, the levels of alpha-tubulin, beta-tubulin and MAP2 increased in low ACR group. The results suggested that the changes of these proteins might be relevant to the neurotoxicity of ACR. Some of the cytoskeletal proteins in plasma might be used as marker of biological effect in ACR induced neuropathy.