The pathokinetics of acrylamide intoxication: a reassessment of the problem

Increased IP3R-3 degradation induced by acrylamide promoted Ca2+-dependent calpain activation and axon damage in rats

Occupational and environmental exposure to acrylamide (ACR) can cause selective peripheral and central nerve fiber degeneration. IP3R-3 is an important transmembrane Ca²⁺ channel on the endoplasmic reticulum (ER), previous studies have found that ACR could induce Ca²⁺-dependent calpain activation and axon injury, but the exact role of IP3R-3 in ACR neuropathy is still unclear. Here we show that ACR exposure (40mg/kg) markedly increased the ubiquitination of IP3R-3 in rat spinal cords, and promoted the degradation of IP3R-3 through the ubiquitin-proteasome pathway. Furthermore, the normal structure of ER, especially the mitochondrial associated membranes (MAMs) component, was significantly impaired in ACR neuropathy, and the ER stress pathway was activated, which indicated that the aberrant increase of cytoplasmic Ca²⁺ could be attributed the destruction of IP3R-3. Further investigation demonstrated that the proteasome inhibitor MG-132 effectively rescued the IP3R-3 loss, attenuated the intracellular Ca²⁺ increase, and reduced the axon loss of Neuron 2a (N2a) cells following ACR exposure. Moreover, the calpain inhibitor ALLN also reduced the loss of IP3R-3 and axon injury in N2a cells, but did not alleviate the Ca²⁺ increase in cytosol, supporting that the abnormal ubiquitination of IP3R-3 was the upstream of the cellular Ca²⁺ rise and axon damage in ACR neuropathy. Taken together, our results suggested that the aberrant IP3R-3 degradation played an important role in the disturbance of Ca²⁺ homeostasis and the downstream axon loss in ACR neuropathy, thus providing a potential therapeutic target for ACR neurotoxicity.

Long-term acrylamide exposure exacerbates brain and lung pathology in a mouse malaria model

The consumption of dietary acrylamide (ACR), a carcinogen, results in the dysfunction of various organs and the immune system. However, the impact of ACR exposure on the progression of infectious diseases is unknown. This study investigated the effect of ACR on the progression of malaria infection using a mouse model of malaria. C57BL/6 mice were continuously treated with ACR at a dose of 20 mg/kg bodyweight/day for six weeks (long-term exposure) or phosphate-buffered saline (PBS). Next, the mice were infected with the rodent malaria parasite, Plasmodium berghei NK65 (PbNK). Parasitemia and survival rate were analyzed in the different treatment groups. Magnetic resonance imaging (MRI) and histopathological analyses were performed to evaluate the effect of ACR exposure on the morphology of various organs. Long-term ACR exposure exacerbated PbNK-induced multiorgan dysfunction. MRI and histopathological analysis revealed signs of encephalomeningitis and acute respiratory distress syndrome in the PbNK-infected long-term ACR exposure mice, which decreased the survival rate of mice, but not in the PbNK-infected long-term PBS exposure group. These findings enhance our understanding of the impact of ACR on the progression of infectious diseases, such as malaria.

Determination of Critical Cellular Neurotoxic Concentrations in Human Neuroblastoma (SH-SY5Y) Cell Cultures

The effects of the neurotoxic compounds acrylamide, triethyltin chloride (TET), methyl mercury (II) chloride (MeHg) and lindane on selected neurospecific and general cell functions in differentiated human neuroblastoma SH-SY5Y cells were investigated in an attempt to determine critical cellular neurotoxic concentrations. The cultures were exposed to the neurotoxicants for three days, and then the effects on cell growth, neuronal signal transaction and the induction of axonopathy were measured. For comparison, general cytotoxicity was also determined in human epithelial (HeLa) cells. The cytotoxic activities (IC20 values) in the SH-SY5Y cells were 0.18 ± 0.03μM for TET, 0.20 ± 0.03μM for MeHg, 32 ± 10μM for lindane and 810 ± 170μM for acrylamide. Inhibition of cell growth was similar in HeLa cells. Significantly lower concentrations of MeHg, acrylamide and TET than the IC20 values were sufficient to induce axonopathy. In addition, MeHg and acrylamide increased the basal intracellular free calcium concentration, [Ca2+]i,as well as the carbachol-induced Ca2+fluxes and the depolarisation-stimulated increase of [Ca2+]icompared to control cells. The elevated [Ca2+]imay be a primary cause of the acrylamide-induced and MeHg-induced neuropathy. Treatment with lindane (1μM) slightly decreased the depolarisation-evoked Ca2+influx in the neuroblastoma cells. A parallel to the documented neurotoxic mechanism of lindane (i.e. inhibition of the γ-aminobutyric acid-activated Cl-channels) is possible.

Acrylamide, 2,5-Hexanedione and β-Aminopropionitrile Toxicity Tested in Rat Embryo Mid-brain Cell Cultures

The abilities of three substances, acrylamide, 2,5-hexanedione and β-aminopropionitrile to affect nerve cell differentiation were compared with their general cytotoxicities (ability to affect cell survival) over five days in rat embryo mid-brain micromass cultures. ACA and 25HD are neurotoxins in the adult, but only ACA is known to have transplacental effects on the developing central nervous system. BAPN is a model teratogen, but not a neurotoxin, in the adult and was used as a positive control. ACA inhibited neuronal differentiation (assayed by reduction of number of foci of differentiated neurons) by 50% at a concentration (the IC50) of 15μg/ml. The corresponding IC50 for cell survival (assayed by reduction in cell number) was 36μg/ml. In 25HD-exposed cultures, IC50 values of 729 and 872μg/ml were obtained for the inhibition of differentiation and cell survival, respectively. BAPN inhibited differentiation with an IC50 of 226μg/ml, but had very little effect on cell viability up to 500μg/ml. This pronounced difference in sensitivity of the two endpoints is in agreement with previous reports of its teratogenicity. The more-limited but significant difference detected for ACA, but not for 25HD, suggests that rat embryo mid-brain micromass cultures can be used to study subteratogenic effects of ACA on brain development.

In Vitro Testing of Neurotoxicity

Many of the toxic compounds that are at large in the environment represent a risk to our neuronal functions. Chemicals may have a direct or indirect effect on the nervous system and they may interfere with general biochemical properties or specific neuronal structures and processes. In this review, a brief presentation of the major neurotoxicological targets is given, together with a discussion of some aspects of the use of different in vitro models for screening purposes and mechanistic studies. It is believed that in vitro methods offer special opportunities for the development of new neurotoxicological assays, and that this development will mainly involve cultured model systems. Therefore, a presentation of nerve and glia tissue culture methods is given, followed by an overview of how information on the action of mercury and mercurials, excitotoxins and acrylamide has been obtained through the use of cultured cell models. It is concluded that the developmental potential in cell neurotoxicology lies within the areas of separation and identification of cells representative for different structures in the nervous system, co-cultivation of different cell types, in vivo/in vitro (ex vivo) procedures, chemically defined media, metabolic competent cultures of human cells and improved physiological conditions for cultivation and exposure.

Acrylamide Induced Toxicity and the Propensity of Phytochemicals in Amelioration: A Review

Acrylamide is widely found in baked and fried foods, produced in large amount in industries and is a prime component in toxicity. This review highlights various toxicities that are induced due to acrylamide, its proposed mode of action including oxidative stress cascades and ameliorative mechanisms using phytochemicals. Acrylamide formation, the mechanism of toxicity and the studies on the role of oxidative stress and mitochondrial dysfunctions are elaborated in this paper. The various types of toxicities caused by Acrylamide and the modulation studies using phytochemicals that are carried out on various type of toxicity like neurotoxicity, hepatotoxicity, cardiotoxicity, immune system, and skeletal system, as well as embryos have been explored. Lacunae of studies include the need to explore methods for reducing the formation of acrylamide in food while cooking and also better modulators for alleviating the toxicity and associated dysfunctions along with identifying its molecular mechanisms.

Hazardous effects of fried potato chips on the development of retina in albino rats

OBJECTIVE

To evaluate the hazardous effects of fried potato chips upon the retina of two developmental stages of the albino rats aged 7 and 14 days from parturition.

METHODS

PREGNANT RATS WERE ARRANGED INTO TWO GROUPS: control pregnant rats and consequently their delivered newborns until reaching 7 and 14 days old from parturition and fried potato chips group in which pregnant rats at the 6th day of gestation maintained on diet formed of fried potato chips supplied from the market mixed with standard diet at a concentration of 50% per each till 7 and 14 post-partum. Three fold integrated approaches were adopted, namely, histological, ultrastructural and proteomic analysis.

RESULTS

Histological examination of the retina of the experimental offsprings revealed many histopathological changes, including massive degeneration, vacuolization and cell loss in the ganglion cell layer, as well as general reduction in retinal size. At the ultrastructural level, the retina of experimental offsprings exhibited number of deformities, including ill differentiated and degenerated nuclear layer, malformed and vacuolated pigment epithelium with vesiculated and fragmented rough endoplasmic reticulum, degenerated outer segment of photoreceptors, as well as swollen choriocapillaris and loss of neuronal cells. Proteomic analysis of retina of the two experimental developmental stages showed variations in the expressed proteins as a result of intoxication which illustrated the adverse toxic effects of fried potato chips upon the retina.

CONCLUSIONS

It can be concluded that the effect of fried potato chips on the development of retina in rats may be due to the presence of acrylamide or its metabolite.

Effectiveness of selenium on acrylamide toxicity to retina

AIM

To investigate the hematological parameters, biochemical and electrophysiological role of acrylamide (ACR) in the retina and to assess whether selenium (Se) has protective potential in experimental oral intoxication with ACR.

METHODS

Sixty Wistar age matched-albino rats (3mo) weighing 195-230 g comprised of both sex were divided into 4 groups. Group I served as the control one in which animals take saline; group II was animals administrated ACR in dose of 15 mg/kg body weight per day for 28d; group III was animals received ACR then additionally Se (0.1 mg/kg body weight) for 28d; and group IV was animals received Se only (0.1 mg/kg body weight) for 28d. Blood analysis and serum trace element levels (Fe, Cu, and Zn) were measured. The electroretinogram (ERG) was recorded, the levels of malondialdehyde (MDA) and glutathione peroxidase (GSH-Px) in the retinal tissues were determined. Moreover the regulation of ion channels such as calcium, sodium and potassium were studied. All measurements were done for all groups after 28d.

RESULTS

Administration of ACR in group II caused a significant decrease (P<0.05) in hemoglobin (Hb), red blood cells (RBCs), hematocrit (HCT), white blood cells (WBCs) and lymphocyte of rats. A significant decrease (P<0.05) in Zn level, and alkaline phosphatase enzyme was observed compared to control. ERG which is a reflection of the electric activity in the retina; a- and-b wave amplitudes in ACR group had a reduction of 40% and 20% respectively. These changes accompanied by significant increases (P<0.05) in MDA level in the ACR group, in contrast with GSH-Px which is significant decreased (P<0.05). Moreover sodium and calcium were significant increased but potassium was significant decreased (P<0.05) compared to control group. There were no significant differences between group III (treated with Se) and control in all hematological parameter. Also serum trace elements levels (Cu, Fe and Zn), alkaline phosphatase enzyme and electric activity of the retina didn't change compared to control due to Se treatment.

CONCLUSION

This study provides evidence for the protective effect of Se on acrylamide induced toxicity by reducing oxidative stress.

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.

Toxicity of acrylamide and evaluation of its exposure in baby foods

Contaminants are a vast subject area of food safety and quality and can be present in our food chain from raw materials to finished products. Acrylamide, an α,β-unsaturated (conjugated) reactive molecule, can be detected as a contaminant in several foodstuffs including baby foods and infant formulas. It is anticipated that children will generally have intakes that are two to three times those of adults when expressed on a body-weight basis. Though exposure to acrylamide is inevitable, it is necessary to protect infant and children from high exposure. The present review focuses on the several adverse health effects of acrylamide including mutagenicity, genotoxicity, carcinogenicity, neurotoxicity and reproductive toxicity, and the possible outcomes of childhood exposure from baby foods and infant formulas.

Acrylamide-induced nerve terminal damage: relevance to neurotoxic and neurodegenerative mechanisms

Acrylamide (ACR) has demonstrable neurotoxic effects in animals and humans that stem from its chemical behavior as a soft electrophilic alpha,beta-unsaturated carbonyl compound. Evidence is presented that the nerve terminal is a primary site of ACR action and that inhibition of neurotransmission mediates the development of neurological deficits. At the mechanistic level, recent proteomic, neurochemical, and kinetic data are considered, which suggest that ACR inhibits neurotransmission by disrupting presynaptic nitric oxide (NO) signaling. Nerve-terminal damage likely mediates the neurological complications that accompany the occupational exposure of humans to ACR. In addition, the proposed molecular mechanism of synaptotoxicity has substantial implications for the pathogenesis of Alzheimer's disease and other neurodegenerative conditions that involve neuronal oxidative stress and the secondary endogenous generation of acrolein and other conjugated carbonyl chemicals.

Molecular mechanisms of the conjugated alpha,beta-unsaturated carbonyl derivatives: relevance to neurotoxicity and neurodegenerative diseases

Conjugated alpha,beta-unsaturated carbonyl derivatives such acrylamide, acrolein, and 4-hydroxy-2-nonenal (HNE) are members of a large class of chemicals known as the type-2 alkenes. Human exposure through diet, occupation, and pollution is pervasive and has been linked to toxicity in most major organs. Evidence suggests that these soft electrophiles produce toxicity by a common mechanism involving the formation of Michael-type adducts with nucleophilic sulfhydryl groups. In this commentary, the adduct chemistry of the alpha,beta-unsaturated carbonyls and possible protein targets will be reviewed. We also consider how differences in electrophilic reactivity among the type-2 alkenes impact corresponding toxicokinetics and toxicological expression. Whereas these concepts have mechanistic implications for the general toxicity of type-2 alkenes, this commentary will focus on the ability of these chemicals to produce presynaptic damage via protein adduct formation. Given the ubiquitous environmental presence of the conjugated alkenes, discussions of molecular mechanisms and possible neurotoxicological risks could be important. Understanding the neurotoxicodynamic of the type-2 alkenes might also provide mechanistic insight into neurodegenerative conditions where neuronal oxidative stress and presynaptic dysfunction are presumed initiating events. This is particularly germane to a recent proposal that lipid peroxidation and the subsequent liberation of acrolein and HNE in oxidatively stressed neurons mediate synaptotoxicity in brains of Alzheimer's disease patients. This endogenous neuropathogenic process could be accelerated by environmental type-2 alkene exposure because common nerve terminal proteins are targeted by alpha,beta-unsaturated carbonyl derivatives. Thus, the protein adduct chemistry of the conjugated type-2 alkenes offers a mechanistic explanation for the environmental toxicity induced by these chemicals and might provide insight into the pathogenesis of certain human neurodegenerative diseases.

Acrylamide: review of toxicity data and dose-response analyses for cancer and noncancer effects

Acrylamide (ACR) is used in the manufacture of polyacrylamides and has recently been shown to form when foods, typically containing certain nutrients, are cooked at normal cooking temperatures (e.g., frying, grilling or baking). The toxicity of ACR has been extensively investigated. The major findings of these studies indicate that ACR is neurotoxic in animals and humans, and it has been shown to be a reproductive toxicant in animal models and a rodent carcinogen. Several reviews of ACR toxicity have been conducted and ACR has been categorized as to its potential to be a human carcinogen in these reviews. Allowable levels based on the toxicity data concurrently available had been developed by the U.S. EPA. New data have been published since the U.S. EPA review in 1991. The purpose of this investigation was to review the toxicity data, identify any new relevant data, and select those data to be used in dose-response modeling. Proposed revised cancer and noncancer toxicity values were estimated using the newest U.S. EPA guidelines for cancer risk assessment and noncancer hazard assessment. Assessment of noncancer endpoints using benchmark models resulted in a reference dose (RfD) of 0.83 microg/kg/day based on reproductive effects, and 1.2 microg/kg/day based on neurotoxicity. Thyroid tumors in male and female rats were the only endpoint relevant to human health and were selected to estimate the point of departure (POD) using the multistage model. Because the mode of action of acrylamide in thyroid tumor formation is not known with certainty, both linear and nonlinear low-dose extrapolations were conducted under the assumption that glycidamide or ACR, respectively, were the active agent. Under the U.S. EPA guidelines (2005), when a chemical produces rodent tumors by a nonlinear or threshold mode of action, an RfD is calculated using the most relevant POD and application of uncertainty factors. The RfD was estimated to be 1.5 microg/kg/day based on the use of the area under the curve (AUC) for ACR hemoglobin adducts under the assumption that the parent, ACR, is the proximate carcinogen in rodents by a nonlinear mode of action. When the mode of action in assumed to be linear in the low-dose region, a risk-specific dose corresponding to a specified level of risk (e.g., 1 x 10-5) is estimated, and, in the case of ACR, was 9.5 x 10-2 microg ACR/kg/day based on the use of the AUC for glycidamide adduct data. However, it should be noted that although this review was intended to be comprehensive, it is not exhaustive, as new data are being published continuously.

Acrylamide Neurotoxicity: Neurological, Morhological and Molecular Endpoints in Animal Models

Acrylamide (AA) monomer is used in numerous chemical industries and is a contaminant in potato- and grain-based foods prepared at high temperatures. Although experimental animal studies have implicated carcinogenicity and reproductive toxicity as possible consequences of exposure, neurotoxicity is the only outcome identified by epidemiological studies of occupationally exposed human populations. Neurotoxicity in both humans and laboratory animals is characterized by ataxia and distal skeletal muscle weakness. Early neuropathological studies suggested that AA neurotoxicity was mediated by distal axon degeneration. However, more recent electrophysiological and quantitative morphometric analyses have identified nerve terminals as primary sites of AA action. A resulting defect in neurotransmitter release appears to be the pathophysiological basis of the developing neurotoxicity. Corresponding mechanistic research suggests that AA impairs release by adducting cysteine residues on functionally important presynaptic proteins. In this publication we provide an overview of recent advances in AA research. This includes a discussion of the cumulative nature of AA neurotoxicity and the putative sites and molecular mechanisms of action.

Protective role ofPanax ginseng extract standardized with ginsenoside Rg3 against acrylamide-induced neurotoxicity in rats

Acrylamide (ACR) is an industrial neurotoxic chemical that has been recently found in carbohydrate-rich foods cooked at high temperatures. ACR was designated as a probable human carcinogen by IARC (1994) and USEPA (1988). Panax ginseng extract has efficacies such as anticancer, antihypertension, antidiabetes and antinociception. The objective of the current study is to evaluate the protective effects of Panax ginseng extract against ACR-induced toxicity in rats. Sixty adult Sprague Dawley female rats were divided into six groups included a control group, a group treated orally with ACR (50 mg kg(-1) body weight; b.w.) for 11 days, a group treated orally with Panax ginseng extract (20 mg kg(-1) b.w.) for 11 days and groups treated orally with Panax ginseng for 11 days before, during or after 11 days of ACR treatment. The results indicated that treatment with ACR alone resulted in a significant increase in lipid peroxidation level and LDH activity in brain homogenate as well as in serum CK activity, whereas it caused a significant decrease in SOD activity and a small but statistically insignificant decrease in Na(+)K(+)-ATPase activity in brain homogenate. Serum serotonin, corticosterone, T3, T4, TSH, estradiol, progesterone and plasma adrenaline were significantly decreased in ACR-treated rats. Treatment with Panax ginseng before, during or after ACR treatment reduced or partially antagonized the effects induced by ACR towards the normal values of controls. It could be concluded that Panax ginseng extract exhibited a protective action against ACR toxicity and it is worth noting that treatment with Panax ginseng extract before or at the same time as ACR treatment was more effective than when administered after ACR treatment.

Proteomic analysis of acrylamide-protein adduct formation in rat brain synaptosomes

Evidence suggests that the neurological defects (gait abnormalities, foot splay, and skeletal muscle weakness) associated with acrylamide (ACR) intoxication are mediated by impaired neurotransmission at central and peripheral synapses. ACR can form adducts with nucleophilic residues on proteins and thereby alter corresponding structure and function. To evaluate protein adduction in nerve terminals as a possible mechanism of action, recombinant N-ethylmaleimide sensitive factor (NSF) was exposed in vitro to ACR (10 micromol) and mass spectrometry (MS) was used to identify adduct sites. MS analyses demonstrated that ACR formed adducts with sulfhydryl groups on cysteine residues (carbamoylethylcysteine, or CEC) of NSF. Ex vivo incubation of whole brain synaptosomes with ACR (0.001-1.0 M) produced concentration-dependent increases in CEC that were inversely correlated to reductions in neurotransmitter release that occurred over the same neurotoxicant concentration range. In synaptosomes isolated from rats intoxicated at a higher (50 mg/kg per day x 3, 5, 8, or 11 days) or a lower (21 mg/kg per day x 14, 21, or 28 day) ACR dose rate, CEC levels increased progressively up to a moderate level of neurotoxicity. To identify protein adducts, synaptosomal proteins labeled by ex vivo 14C-ACR exposure were separated by gel electrophoresis and probed by immunoblot analysis. Results showed that NSF and the SNARE protein, SNAP-25, were tentative ACR targets. Subsequent experiments indicated that ACR exposure increased synaptosomal levels of the 7S SNARE core complex, which is consistent with inhibition of NSF, SNAP-25 function, or both. These data suggest that adduction of cysteine residues on NSF and certain SNARE proteins might be causally involved in the nerve terminal dysfunction induced by ACR.

The Changing View of Acrylamide Neurotoxicity

Acrylamide (ACR) is a water-soluble, vinyl monomer that has multiple chemical and industrial applications: e.g., waste water management, ore processing. In addition, ACR is used extensively in molecular laboratories for gel chromatography and is present in certain foods that have been prepared at very high temperatures. Extensive studies in rodents and other laboratory animals have provided evidence that exposure to monomeric ACR causes cellular damage in both the nervous and reproductive systems, and produces tumors in certain hormonally responsive tissues. Whereas human epidemiological studies have demonstrated a significantly elevated incidence of neurotoxicity in occupationally exposed populations, such research has not, to date, revealed a corresponding increase in cancer risk. Since the announcement by a Swedish research group in April 2002 [J. Ag. Food Chem. 50 (2002) 4998] regarding the presence of ACR in potato and grain-based foods, there has been a renewed interest in the toxic actions of this chemical. Therefore, in this review, we consider the different toxic effects of ACR. The neurotoxic actions of ACR will be the focal point since neurotoxicity is a consequence of both human and laboratory animal exposure and since this area of investigation has received considerable attention over the past 30 years. As will be discussed, a growing body of evidence now indicates that the nerve terminal is a primary site of ACR action and that inhibition of corresponding membrane-fusion processes impairs neurotransmitter release and promotes eventual degeneration. The electrophilic nature of ACR suggests that this neurotoxicant adducts nucleophilic sulfhydryl groups on certain proteins that are critically involved in membrane fusion. Adduction of thiol groups also might be common to the reproductive and carcinogenic effects of ACR. A final goal of this review is to identify data gaps that retard a comprehensive understanding of ACR pathophysiological processes.

Patterned Purkinje cell death in the cerebellum

The object of this review is to assemble much of the literature concerning Purkinje cell death in cerebellar pathology and to relate this to what is now known about the complex topography of the cerebellar cortex. A brief introduction to Purkinje cells, and their regionalization is provided, and then the data on Purkinje cell death in mouse models and, where appropriate, their human counterparts, have been arranged according to several broad categories--naturally-occurring and targeted mutations leading to Purkinje cell death, Purkinje cell death due to toxins, Purkinje cell death in ischemia, Purkinje cell death in infection and in inherited disorders, etc. The data reveal that cerebellar Purkinje cell death is much more topographically complex than is usually appreciated.

Acrylamide axonopathy revisited

Distal swelling and eventual degeneration of axons in the CNS and PNS have been considered to be the characteristic neuropathological features of acrylamide (ACR) neuropathy. These axonopathic changes have been the basis for classifying ACR neuropathy as a central-peripheral distal axonopathy and, accordingly, research over the past 30 years has focused on the primacy of axon damage and on deciphering underlying mechanisms. However, based on accumulating evidence, we have hypothesized that nerve terminals, and not axons, are the primary site of ACR action and that compromise of corresponding function is responsible for the autonomic, sensory, and motor defects that accompany ACR intoxication (NeuroToxicology 23 (2002) 43). In this paper, we provide a review of data from a recently completed comprehensive, longitudinal silver stain study of brain and spinal cord from rats intoxicated with ACR at two different daily dosing rates, i.e., 50 mg/kg/day, ip or 21 mg/kg/day, po. Results show that, regardless of dose-rate, ACR intoxication was associated with early, progressive nerve terminal degeneration in all CNS regions and with Purkinje cell injury in cerebellum. At the lower dose-rate, initial nerve terminal argyrophilia was followed by abundant retrograde axon degeneration in white matter tracts of spinal cord, brain stem, and cerebellum. The results support and extend our nerve terminal hypothesis and suggest that Purkinje cell damage also plays a role in ACR neurotoxicity. Substantial evidence now indicates that axon degeneration is a secondary effect and is, therefore, not pathophysiologically significant. These findings have important implications for future mechanistic research, classification schemes, and assessment of neurotoxicity risk.

Acrylamide neuropathy. III. Spatiotemporal characteristics of nerve cell damage in forebrain

Previous studies of acrylamide (ACR) neuropathy in rat PNS [Toxicol. Appl. Pharmacol. (1998) 151:211-221] and in spinal cord, brainstem and cerebellum [NeuroToxicology (2002a) 23:397-414; NeuroToxicology (2002b) 23:415-429] have suggested that axon degeneration was not a primary effect and was, therefore, of unclear neurotoxicological significance. To conclude our studies of neurodegeneration in rat CNS during ACR neurotoxicity, a cupric silver stain method was used to define spatiotemporal characteristics of nerve cell body, dendrite, axon and terminal argyrophilia in forebrain regions and nuclei. Rats were exposed to ACR at a dose-rate of either 50 mg/kg per day (i.p.) or 21 mg/kg per day (p.o.) and at selected times brains were removed and processed for silver staining. Results show that intoxication at either ACR dose-rate produced a terminalopathy, i.e. nerve terminal degeneration and swelling were present in the absence of significant argyrophilic changes in neuronal cell bodies, dendrites or axons. Exposure to the higher ACR dose-rate caused early onset (day 5), widespread nerve terminal degeneration in most of the major forebrain areas, e.g. cerebral cortex, thalamus, hypothalamus and basal ganglia. At the lower dose-rate, nerve terminal degeneration in the forebrain developed early (day 7) but exhibited a relatively limited spatial distribution, i.e. anteroventral thalamic nucleus and the pars reticulata of the substantia nigra. Several hippocampal regions were affected at a later time point (day 28), i.e. CA1 field and subicular complex. At both dose-rates, argyrophilic changes in forebrain nerve terminals developed prior to the onset of significant gait abnormalities. Thus, in forebrain, ACR intoxication produced a pure terminalopathy that developed prior to the onset of significant neurological changes and progressed as a function of exposure. Neither dose-rate used in this study was associated with axon degeneration in any forebrain region. Our findings indicate that nerve terminals were selectively affected in forebrain areas and, therefore, might be primary sites of ACR action.

Acrylamide neuropathy. II. Spatiotemporal characteristics of nerve cell damage in brainstem and spinal cord

Previous studies of acrylamide (ACR) neuropathy in rat PNS [Toxicol. Appl. Pharmacol. 151 (1998) 211] and cerebellum [NeuroToxicology 23 (2002) 397] have suggested that axon degeneration was not a primary effect and was, therefore, of unclear neurotoxicological significance. To continue morphological examination of ACR neurotoxicity in CNS, a cupric silver stain method was used to define spatiotemporal characteristics of nerve cell body, dendrite, axon and terminal degeneration in brainstem and spinal cord. Rats were exposed to ACR at a dose-rate of either 50 mg/kg per day (i.p.) or 21 mg/kg per day (p.o.), and at selected times brains and spinal cord were removed and processed for silver staining. Results show that intoxication at the higher ACR dose-rate produced a nearly pure terminalopathy in brainstem and spinal cord regions, i.e. widespread nerve terminal degeneration and swelling were present in the absence of significant argyrophilic changes in neuronal cell bodies, dendrites or axons. Exposure to the lower ACR dose-rate caused initial nerve terminal argyrophilia in selected brainstem and spinal cord regions. As intoxication continued, axon degeneration developed in white matter of these CNS areas. At both dose-rates, argyrophilic changes in brainstem nerve terminals developed prior to the onset of significant gait abnormalities. In contrast, during exposure to the lower ACR dose-rate the appearance of axon degeneration in either brainstem or spinal cord was relatively delayed with respect to changes in gait. Thus, regardless of dose-rate, ACR intoxication produced early, progressive nerve terminal degeneration. Axon degeneration occurred primarily during exposure to the lower ACR dose-rate and developed after the appearance of terminal degeneration and neurotoxicity. Spatiotemporal analysis suggested that degeneration began at the nerve terminal and then moved as a function of time in a somal direction along the corresponding axon. These data suggest that nerve terminals are a primary site of ACR action and that expression of axonopathy is restricted to subchronic dosing-rates.

Acrylamide neuropathy. I. Spatiotemporal characteristics of nerve cell damage in rat cerebellum

Based on evidence from morphometric studies of PNS, we suggested that acrylamide (ACR)-induced distal axon degeneration was a secondary effect related to duration of exposure [Toxicol. Appl. Pharmacol. 151 (1998) 211]. To test this hypothesis in CNS, the cupric-silver stain method of de Olmos was used to define spatiotemporal characteristics of nerve somal, dendritic, axonal and terminal degeneration in rat cerebellum. Rats were exposed to ACR at either 50 mg/kg per day (i.p.) or 21 mg/kg per day (p.o.) and at selected times (i.p. = 5, 8 and 11 days; p.o. = 7, 14, 21, 28 and 38 days) brains were removed and processed for silver staining. Results demonstrate that intoxication at the higher ACR dose-rate produced early (day 5) and progressive degeneration of Purkinje cell dendrites in cerebellar cortex. Nerve terminal degeneration occurred concurrently with somatodendritic argyrophilia in cerebellar and brainstem nuclei that receive afferent input from Purkinje neurons. Relatively delayed (day 8), abundant axon degeneration was present in cerebellar white matter but not in cortical layers or in tracts carrying afferent fibers (cerebellar peduncles) from other brain nuclei. Axon argyrophilia coincided with the appearance of perikaryal degeneration, which was selective for Purkinje cells since silver impregnation of other cerebellar neurons was not evident in the different cortical layers or cerebellar nuclei. Intoxication at the lower ACR dose-rate produced simultaneous (day 14) dendrite, axon and nerve terminal argyrophilia and no somatic Purkinje cell degeneration. The spatiotemporal pattern of dendrite, axon and nerve terminal loss induced by both ACR dose-rates is consistent with Purkinje cell injury. Injured neurons are likely to be incapable of maintaining distal processes and, therefore, axon degeneration in the cerebellum is a component of a "dying-back" process of neuronal injury. Because cerebellar coordination of somatomotor activity is mediated solely through efferent projections of the Purkinje cell, injury to this neuron might contribute significantly to gait abnormalities that characterize ACR neurotoxicity.

Acrylamide neuropathy. II. Spatiotemporal characteristics of nerve cell damage in brainstem and spinal cord

Previous studies of acrylamide (ACR) neuropathy in rat PNS [Toxicol. Appl. Pharmacol. 151 (1998) 211] and cerebellum [Neurotoxicology, 2002a] have suggested that axon degeneration was not a primary effect and was, therefore, of unclear neurotoxicological significance. To continue morphological examination of ACR neurotoxicity in CNS, a cupric silver stain method was used to define spatiotemporal characteristics of nerve cell body, dendrite, axon and terminal degeneration in brainstem and spinal cord. Rats were exposed to ACR at a dose-rate of either 50 mg/kg per day (i.p.) or 21 mg/kg per day (p.o.), and at selected times brains and spinal cord were removed and processed for silver staining. Results show that intoxication at the higher ACR dose-rate produced a nearly pure terminalopathy in brainstem and spinal cord regions, ie. widespread nerve terminal degeneration and swelling were present in the absence of significant argyrophilic changes in neuronal cell bodies, dendrites or axons. Exposure to the lower ACR dose-rate caused initial nerve terminal argyrophilia in selected brainstem and spinal cord regions. As intoxication continued, axon degeneration developed in white matter of these CNS areas. At both dose-rates, argyrophilic changes in brainstem nerve terminals developed prior to the onset of significant gait abnormalities. In contrast, during exposure to the lower ACR dose-rate the appearance of axon degeneration in either brainstem or spinal cord was relatively delayed with respect to changes in gait. Thus, regardless of dose-rate, ACR intoxication produced early, progressive nerve terminal degeneration. Axon degeneration occurred primarily during exposure to the lower ACR dose-rate and developed after the appearance of terminal degeneration and neurotoxicity. Spatiotemporal analysis suggested that degeneration began at the nerve terminal and then moved as a function of time in a somal direction along the corresponding axon. These data suggest that nerve terminals are a primary site of ACR action and that expression of axonopathy is restricted to subchronic dosing-rates.

Nerve terminals as the primary site of acrylamide action: a hypothesis

Acrylamide (ACR) is considered to be prototypical among chemicals that cause a central-peripheral distal axonopathy. Multifocal neurofilamentous swellings and eventual degeneration of distal axon regions in the CNS and PNS have been traditionally considered the hallmark morphological features of this axonopathy. However, ACR has also been shown to produce early nerve terminal degeneration of somatosensory, somatomotor and autonomic nerve fibers under a variety of dosing conditions. Recent research from our laboratory has demonstrated that terminal degeneration precedes axonopathy during low-dose subchronic induction of neurotoxicity and occurs in the absence of axonopathy during higher-dose subacute intoxication. This relationship suggests that nerve terminal degeneration, and not axonopathy, is the primary or most important pathophysiologic lesion produced by ACR. In this hypothesis paper, we review evidence suggesting that nerve terminal degeneration is the hallmark lesion of ACR neurotoxicity, and we propose that this effect is mediated by the direct actions of ACR at nerve terminal sites. ACR is an electrophile and, therefore, sulfhydryl groups on presynaptic proteins represent rational molecular targets. Several presynaptic thiol-containing proteins (e.g. SNAP-25, NSF) are critically involved in formation of SNARE (soluble N-ethylmaleimide (NEM)-sensitive fusion protein receptor) complexes that mediate membrane fusion processes such as exocytosis and turnover of plasmalemmal proteins and other constituents. We hypothesize that ACR adduction of SNARE proteins disrupts assembly of fusion core complexes and thereby interferes with neurotransmission and presynaptic membrane turnover. General retardation of membrane turnover and accumulation of unincorporated materials could result in nerve terminal swelling and degeneration. A similar mechanism involving the long-term consequences of defective SNARE-based turnover of Na+/K(+)-ATPase and other axolemmal constituents might explain subchronic induction of axon degeneration. The ACR literature occupies a prominent position in neurotoxicology and has significantly influenced development of mechanistic hypotheses and classification schemes for neurotoxicants. Our proposal suggests a reevaluation of current classification schemes and mechanistic hypotheses that regard ACR axonopathy as a primary lesion.

An in vitro model for toxicological investigations of environmental neurotoxins in primary neuronal cell cultures

Currently, most neurotoxicological investigations are still conducted using various animal models (e.g. chickens, rodents). In this report, alternative strategies of testing were examined to detect the neurotoxic potency of foreign compounds. Primary neuronal cell cultures from fetal rats are already an accepted model for mechanistic and pharmacological studies in drug research. Their suitability for neurotoxicological studies was examined by using industrial model compounds, which are well-known inductors of neuropathies: acrylamide, hexachlorophene, paraquat, n-hexane, and its neurotoxic metabolites acetylaceton and 2,5-hexandione. As a control compound, the nonneurotoxic solvent n-heptane was used. General cytotoxicity and the intracellular content of glial fibrillary acid protein, neuron-specific enolase, and neurofilaments were measured. n-Heptane induced an acute cytotoxicity and acrylamide and 2,5-hexandione produced a delayed cytotoxicity in primary neuronal cells, whereas the others showed no cytotoxic potency in the tested concentration range. These results were in agreement with the quantification of neurons by neuron-specific enolase. In contrast, with the exception of acetylaceton, glia cells were significantly affected by all neurotoxins at the later time. Signs of axonopathies were demonstrated for acrylamide, n-hexane and its metabolites, as well as for hexachlorophene and paraquat in vitro, by determining the intracellular neurofilament level. Therefore, the determination of cell-specific end points is necessary to detect the neurotoxic potency and quality of a compound, whereas the cytotoxicity assay limited the tested concentration range.

Acrylamide-induced neuropathic changes in rat enteric nerves: similarities with effects of streptozotocin-diabetes

The effect of acrylamide intoxication (a widely used model for autonomic neuropathy) on the fluorescence intensity and density of catecholamine- and peptide-containing nerve fibres and tissue content of noradrenaline and the peptides vasoactive intestinal polypeptide, calcitonin gene-related peptide, substance P and neuropeptide Y in the enteric nerves of rat ileum was examined. Histochemical and immunohistochemical techniques were used to localize catecholamine- and peptide-containing nerve fibres. The tissue content of noradrenaline was measured using high-performance liquid chromatography, and an enzyme-linked immunosorbent assay technique was used to determine the tissue content of the peptides investigated. Acrylamide intoxication caused a significant decrease in the density of catecholamine-containing nerve fibres and tissue content of noradrenaline in the myenteric plexus of rat ileum. A decrease in tissue content and immunoreactivity of calcitonin gene-related peptide and an increase in vasoactive intestinal polypeptide was seen in the myenteric plexus of ileum from acrylamide-intoxicated rats. In the submucous plexus, the acrylamide treatment caused a decrease in calcitonin gene-related peptide immunoreactivity and an increase in vasoactive intestinal polypeptide and neuropeptide Y immunoreactivity. There was no change in either tissue content or immunoreactivity of substance P in both myenteric and submucous plexuses of the treated rat ileum. These changes have a striking similarity with those found in the enteric nerves of streptozotocin-diabetic rat ileum, suggesting the possible presence of an underlying common mechanism(s) in the development of neuropathic changes in the autonomic nerves of acrylamide-intoxicated and streptozotocin-diabetic rats.

The volume of Purkinje cells decreases in the cerebellum of acrylamide-intoxicated rats, but no cells are lost

The effects of acrylamide intoxication on the numbers of granule and Purkinje cells and the volume of Purkinje cell perikarya have been evaluated with stereological methods. The analysis was carried out in the cerebella of rats that had received a dose of 33.3 mg/kg acrylamide, twice a week, for 7.5 weeks. The total numbers of cerebellar granule and Purkinje cells were estimated using the optical fractionator and the mean volume of the Purkinje cell perikarya was estimated with the vertical rotator technique. The volumes of the molecular layer, the granular cell layer and the white matter were estimated using the Cavalieri principle. The mean weight of the cerebellum of the intoxicated rats was 7% lower than that of the control rats (2P = 0.001). The numbers of the Purkinje cells and granule cells were the same in both groups, but the mean volume of the perikarya of the Purkinje cells in the intoxicated rats was 10.5% less than that of the control group (2P = 0.004). The volume of the granular cell layer was reduced by 15% (2P = 0.006) but there were no differences in the volumes of the molecular layer and the white matter in the intoxicated and control animals.

Number and volume of rat dorsal root ganglion cells in acrylamide intoxication

Acrylamide intoxication induces a filamentous neuropathy with breakdown of distal axons and chromatolytic reaction of dorsal root ganglion cells. To obtain quantitative information about the perikaryal alterations neurons of the fifth lumbar dorsal root ganglion of rats were examined with stereological techniques following intoxication with a total dose of 500 mg acrylamide. Number, mean volume and distribution of neuron volume were estimated for each of the two cell subpopulations using optical disectors, the four-way-nucleator and systematic sampling techniques. In intoxicated rats perikaryal volume of A-cells was significantly reduced by 28%, from 63,200 micron3 (CV = 0.16) to 45,500 micron3 (CV = 0.19), whereas the volume of B-cells was unchanged. Numbers of A- and B-cells were preserved. The finding of a selective atrophy of A-cell perikaryal volume is in accordance with previous observations of predominant alterations of large myelinated sensory fibres and most likely reflects an attack on the perikaryal neurofilaments abundant in this cell type.

Neurotoxicity of glycidamide, an acrylamide metabolite, following intraperitoneal injections in rats

Acrylamide (2-propenamide) monomer produces central-peripheral distal axonopathy in humans and some animal species. Its neurotoxicity is characterized by abnormal sensation, decreased motor strength, and ataxia. Acrylamide forms adducts with glutathione, proteins, and DNA. Recent studies demonstrated that acrylamide is metabolized to its epoxide, glycidamide (2,3-epoxy-1-propanamide). We studied the neurotoxicity potential of glycidamide in male Sprague-Dawley rats. Animals (groups of 6) were injected ip daily with either aqueous acrylamide or glycidamide at an acrylamide-equivalent dose of 50 mg/kg (0.70 mmol/kg). Both treatments resulted initially in the rats circling, which was followed by the onset of ataxia at 7-9 d and hindlimb paralysis at 12-14 d. Treated animals showed muscle wasting. At termination, acrylamide- and glycidamide-treated rats weighed 105% and 86% of initial weight, respectively, compared to 145% for controls. Animals were anesthetized and perfused with 10% neutral phosphate-buffered formalin 12 or 14 d after beginning of treatment. Both treatment groups exhibited similar neuropathologic changes in the central and peripheral nervous systems. More severe lesions were produced by glycidamide. A marked increase in the number of affected Purkinje cells in the cerebellum, which exhibited changes ranging from pyknosis to cell death, were present. The brainstem exhibited axonal degeneration with chromatolytic necrosis in midbrain medial and lateral reticular nuclei. The spinal cord was characterized by spongy form changes with vacuoles of different sizes in various levels. These results suggest that glycidamide is an active neurotoxic metabolite of acrylamide.

Effect of exposure to 2,5-hexanediol in light or darkness on the retina of albino and pigmented rats. I. Morphology

Male albino (Sprague Dawley) and pigmented (Norwegian Brown) rats received 1% 2,5-hexanediol (H) in their drinking water for 5 or 8 weeks, respectively. The rats were housed either in 12 h light (average 30 cd/cm2 inside cage) and 12 h darkness (group LH) or in total darkness (group DH). Two control groups (Light only, LC; Darkness only, DC) were studied in parallel under identical conditions. The animals were sacrificed at the end of H exposure or after an ensuing 13-week period without H but under the same lighting conditions. The retinas of albino rats in the LH group showed a reduction (compared to the LC, DH and DC groups) in the number of nuclei per unit area of the outer nuclear layer (ONL; p < 0.05) and degeneration of the outer segment and the inner segment layers (photoreceptor cells). A less pronounced loss of nuclei was seen in the LC group. No decrease in the number of nuclei, or signs of degeneration, were demonstrated in the albino DH or DC groups. Thirteen weeks after exposure to H, the albino LH rats had lost about 50% of the nuclei in the ONL (p < 0.05) and the outer plexiform layer (OPL) had almost disappeared. At the corresponding time, in the pigmented rats the LH and DH groups differed from the LC and DC groups. The degenerative process resulted in no inflammatory changes in the retina. The results imply an interaction exceeding simple summation after exposure to light and H, in destroying photoreceptors and OPL (p < 0.001) in albino rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Acrylamide induces immediate-early gene expression in rat brain

Northern blot analysis was used to study the effects of acrylamide, a potent neurotoxin, on the induction of c-fos and c-jun mRNA in rat brain. Male Sprague-Dawley rats (10-12 weeks old) treated with acrylamide as a single dose (100 mg/kg, i.p.) or via drinking water (0.03% w/v) for 4 weeks, were used to study acute and chronic effects on immediate-early gene expression, respectively. Acute administration of acrylamide caused a statistically significant increase in the expression of c-fos (approx. 37%) and c-jun (approx. 17%) mRNA in rat brain. By contrast, the level of c-fos mRNA in chronic acrylamide treatment was not altered significantly, but the expression of c-jun mRNA was increased almost 100% as compared to control. These data show that the neurotoxin acrylamide induces immediate-early gene expression in the brain. The effects appear to be related to the route of administration, dose and duration of acrylamide treatment.

Effect of acrylamide on the distribution of microtubule-associated proteins (MAP1 and MAP2) in selected regions of rat brain

The effect of acrylamide treatment on the immunocytochemical localization of microtubule-associated proteins (MAP1 and MAP2) was studied in different brain regions (cerebellum, cerebral cortex, and hippocampus) of adult rats. Animals were treated with acrylamide (estimated mean dose: 15 mg/kg/d) orally for 2 wk when they showed slight hindlimb weakness. Immunoreactivity for MAP1 and MAP2 was detected in tissue sections with monoclonal antibodies according to the Sternberger's peroxidase-antiperoxidase technique. Intense MAP1 immunoreactivity was observed in neuronal perikarya and dendrites, with faint staining in axons. By contrast, MAP2 immunostaining was selectively observed in dendrites and neuronal perikarya. Treatment of animals with acrylamide reduced immunoreactivity for both MAP1 and MAP2 in hippocampus and cerebellum, with relatively little change in cerebral cortex. Loss of MAPs immunoreactivity in affected brain areas likely proceeded from dendrite to perikaryon. The results of this study indicate that hippocampal compromise is part of the neurotoxic picture associated with rodent exposure to acrylamide.

Acrylamide-induced depletion of microtubule-associated proteins (MAP1 and MAP2) in the rat extrapyramidal system

Acrylamide, an occupational neurotoxicant, reduced MAP1 and MAP2 distribution in different regions of rat brain. Different components of the extrapyramidal system (caudate-putamen, globus pallidus, substantia nigra and red nucleus) revealed differential distribution of MAP1 and MAP2 in acrylamide-treated animals. Rats were treated with acrylamide (estimated mean dose: 15 mg/kg/day) for 2 weeks and MAP1 and MAP2 were localized according to Sternberger's peroxidase-anti-peroxidase technique. MAP1 labelled neuronal perikarya and dendrites almost with a similar intensity, but MAP2 immunostaining was more intense in dendrites than neuronal perikarya. Acrylamide caused a near-total loss of MAP1 and MAP2 immunoreactivity in caudate-putamen. Other components of the extrapyramidal system were relatively less affected by acrylamide. These results indicate that caudate-putamen is more susceptible to the action of acrylamide than other components of the extrapyramidal system studied. The depletion of MAP1 and MAP2 immunoreactivity by acrylamide appears to be an early biochemical event preceding peripheral neuropathy. The loss of MAPs immunoreactivity occurs first in dendrites and proceeds toward the perikarya. This study indicates that acrylamide not only causes axonal damage but may also induce dendritic degeneration.

Acrylamide-induced alterations in axonal transport. Biochemical and autoradiographic studies

Alterations in the axonal transport of proteins, glycoproteins, and gangliosides in sensory neurons of the sciatic nerve were examined in adult male rats exposed to acrylamide (40 mg ip/kg body wt/d for nine consecutive days). Twenty-four hours after the last dose, the L5 dorsal root ganglion (DRG) was injected with either [35S]methionine to label proteins or [3H]glucosamine to label glycoproteins and gangliosides. The downflow patterns of radioactivity for [35S]methionine-labeled proteins and [3H]glucosamine-labeled gangliosides were unaltered by acrylamide treatment. In contrast, the outflow pattern of labeled glycoproteins displayed a severely attenuated crest with no alteration in velocity, suggesting a preferential transfer with the unlabeled stationary components in the axolemma. Retrograde accumulation of transported glycoproteins and gangliosides was unaltered for at least 6 h; however, by 24 h, there was a 75% decrease in the amount of accumulated material. The accumulation of [35S]methionine-labeled proteins was not altered. Autoradiographic analysis revealed an acrylamide-induced paucity of transported radiolabeled glycoproteins selectively in myelinated axons with no effect on "nonmyelinated" axons. The pattern of transported proteins was similar in both control and acrylamide-exposed animals. These results suggest a preferential inhibition of glycosylation or axonal transport of glycoproteins in neurons bearing myelinated axons. More importantly, it suggests that interpretations of axonal transport data must be made with the consideration of alterations in selective nerve fibers and not with the tacit assumption that all fibers in the nerve population are equally affected.

The number and mean volume of neurons in the cerebral cortex of rats intoxicated with acrylamide

Acrylamide was given in an accumulated dose of 500 mg/kg to rats by intraperitoneal injection in two different dosing schedules: 50 mg/kg twice a week for 5 weeks and 33.3 mg/kg twice a week for 7.5 weeks. The effect of acrylamide intoxication on the neurons in the cerebral cortex of the rat was studied using unbiased stereological methods. A reduction of brain weight of 8% was seen in both the intoxicated groups. The volume of neocortex was significantly decreased in the experimental groups, but the density of neurons was increased resulting in an unchanged total number of neurons. The mean volume of neurons in neocortex was significantly decreased in both acrylamide intoxicated groups. There was no difference between the two different intoxication schedules. The possibility that acrylamide causes neuronal death and the effect of eventual differential cellular sensitivity is discussed.

Acrylamide exposure preferentially impairs axonal transport of glycoproteins in myelinated axons

The right L5 dorsal root ganglion of adult rats exposed to acrylamide (40 mg/kg body weight/day for nine consecutive days) was injected with either [3H]methionine or [3H]glucosamine. After allowing incorporation into macromolecules and axonal transport to proceed for 5 hr, the distribution of radioactivity in cross sections and longitudinal sections of sciatic nerve was determined by autoradiography. Control and treated animals showed no difference in distribution of label within the sciatic nerve with respect to rapidly transported proteins labelled with [3H]methionine. In control animals the distribution of rapidly transported glycoproteins labelled with [3H]glucosamine was similar to that found for [3H]methionine-labelled proteins. In contrast, acrylamide-exposed rats had a very different distribution of labelled glycoproteins; there was a marked paucity of label in the myelinated axons. We interpret this result as indicating that acrylamide preferentially inhibits glycosylation or axonal transport of glycoproteins in neurons bearing myelinated axons.

The same chemicals induce different neurotoxicity when administered in high doses for short term or low doses for long term to rats and dogs

Dose- and term-dependent differences in the location and nature of brain lesions induced in rats and dogs by 2,5-hexanedione (2,5-HD), misonidazole, clioquinol, and acrylamide are reported. Subchronic neuropathies ("distal axonopathy") were induced by low-dose administration of these neurotoxicants and at high doses, lesions caused by acute or subacute neurotoxicity were found in the central nervous system (CNS). In rats, 2,5-HD induced extracellular edema, nerve cell degeneration, and axonal degeneration in the cerebellar and vestibular nuclei. Similar lesions were observed in misonidazole-treated dogs and clioquinol induced nerve cell degeneration in the hippocampus and malacia in the piriform lobes of these animals. In rats, acrylamide induced degeneration of Purkinje cells. Although the mechanism(s) underlying the differential neurotoxicity of high and low doses of these neurotoxicants remains unclear, we suggest certain biochemical mechanisms, cytotoxic edema and excitotoxicity, as factors in the production of such lesions after high-dose treatment.

Somatofugal axonal atrophy precedes development of axonal degeneration in acrylamide neuropathy

Somatofugal axonal atrophy is part of the neuronal perikaryal response to axonal injury (axon reaction). Chronic administration of acrylamide (AC) produces proximal atrophy in virtually all sensory fibers in lumbar dorsal root ganglion (DRG) despite the presence of many intact axons in the distal portion of the sciatic nerve. This suggests that the development of axonal atrophy in AC-intoxicated animals is not solely due to a toxic chemical-induced axonal degeneration (axotomy). In this study, we asked whether axonal atrophy arises before onset of axonal degeneration. Rats were given a single intraperitoneal (i.p.) high dose of AC (75 mg/kg), which blocks retrograde axonal transport, followed by daily intraperitoneal injections (30 mg/kg, for 4 days). At 5 days, sensory fibers in the L4 and L5 DRG appeared smaller in caliber and less circular in shape compared to fibers from age-matched normal animals. Axonal diameters of sensory fibers in the L5 dorsal root were significantly (p less than 0.05) reduced at distances up to 2 mm from the DRG. Quantitative electron microscopy demonstrated that the reduction in caliber was due to a decreased neurofilament (NF) content. Axonal degeneration was not present in the distal portion of both centrally (dorsal root) and peripherally (sciatic nerve) projecting sensory fibers at this time, although primary afferent terminals in muscles of the hindfeet were packed with NFs. The somatofugal progression of the atrophy was evident following more prolonged exposures (10-28 days). It is suggested that AC produces somatofugal axonal atrophy by inhibiting the delivery of a retrogradely transported target-derived "trophic" signal to the neuronal perikaryon.

Peripheral pain fiber function is relatively insensitive to the neurotoxic actions of acrylamide in the rat

Acrylamide causes degeneration of sensory nerve axons in a range of experimental animals and in humans. Evidence of selective vulnerability of large diameter fibers has been derived largely from histological and electrophysiological measurements. We have examined the effect of repeated doses of acrylamide on the function of small diameter peripheral pain fibers in rats by measuring the intensity of neurogenic edema initiated by chemosensitive nerve endings and assessing the sensitivity of the hind paws to a noxious stimulus. These effects have been compared to the impaired sensorimotor performance (landing foot spread) resulting from acrylamide treatment and the change in functional integrity of the pain fibers following surgical lesioning of the sciatic nerves. Our results show that the selective vulnerability of large over small diameter sensory fibers previously reported in the literature is reflected in the differential impairment of proprioceptive and pain-related functions in the rat.

Neurotoxic acrylamide and neurotrophic melanocortin peptides--can contrasting actions provide clues about modes of action?

Experimental acrylamide neuropathy has been studied as a model of degenerative neurological disorders of the 'dying-back' type for over 30 years. Functional, histological, ultrastructural, electrophysiological and biochemical aspects of acrylamide neuropathy have been described and several hypotheses concerning the mode of action proposed. However, the mechanism whereby acrylamide causes axonal degeneration and inhibits nerve sprouting remains unknown. By analogy with agonist/antagonist comparisons used by the pharmacologist, we have reconsidered the acrylamide problem in the light of the opposite effects summarized in Table 1, of neurotrophic peptides related to ACTH/MSH (collectively termed melanocortins). The contrasting effects on sprouting and the eventual quality of repair of mechanically lesioned nerves have suggested a mechanism whereby sprouting may regulate perikaryal adjustments to injury. We have also posed the question as to whether a common biochemical mechanism, namely selective proteolysis of neurofilament protein may underlie the opposing effects of acrylamide and melanocortins on nerve sprouting. This possibility implies a hitherto unknown role for neurofilament protein turnover in neuronal maintenance and repair, a suggestion that may provoke further research and discussion.

A Method Based on the Roller Chamber Technique for Determination of CO2 Production in Cultured Cells: Effects of Acrylamide in Neuroblastoma N1E115 Cultures

The effects of acrylamide on CO2 production from [14C]-labelled glucose, pyruvate and glutamine have been studied in a mouse neuroblastoma cell line C1300, clone N1E115. A rotation metabolism chamber, permitting closed incubation of monolayer, anchorage-dependent cell cultures under good physiological conditions, was developed for making the determinations. The cells were exposed to acrylamide (0.35mM) for 14 days. The total amunt of CO2 produced from glucose and pyruvate was increased by exposure to acrylamide, whereas a slight inhibition was found in the production from glutamine. The production of lactate remained unchanged. Comparison of these results with other data obtained in our laboratory leads us to conclude that the method described is relevant for the determination of energy metabolic processes through the quantification of CO2 production. Furthermore, we assume that acrylamide causes an increased demand for energy in the cells and that this demand is met by the cells through the increased oxidative phosphorylation of glucose.

Neurotoxicity of 1-methoxycycloheptatriene--a Purkinje cell toxicant

The toxicity of 1-methoxycycloheptatriene (1-MCHT), a sensory irritant, has been investigated in beagles. It was found to produce gross inco-ordination of the limbs at intravenous doses greater than 10 mg kg-1. The main histological abnormalities were in the cerebellum and consisted of Purkinje cell death and subsequent reactive gliosis. A few necrotic neurons were seen in the diencephalon, pons and medulla. Haematological abnormalities, e.g. leucocytosis with relative lymphopenia, were seen, while biochemical changes included hyperglycaemia and a rise in plasma aminotransferases. The no-effect dose for the histological and biochemical changes was the same. These abnormalities are compared with cerebellar changes observed in acrylamide and other toxic states.