Conjugation of acrylamide with glutathione catalysed by glutathione-S-transferases of rat liver and brain

Beyond detoxification: Pleiotropic functions of multiple glutathione S-transferase isoforms protect mice against a toxic electrophile

Environmental and endogenous electrophiles cause tissue damage through their high reactivity with endogenous nucleophiles such as DNA, proteins, and lipids. Protection against damage is mediated by glutathione (GSH) conjugation, which can occur spontaneously or be facilitated by the glutathione S-transferase (GST) enzymes. To determine the role of GST enzymes in protection against electrophiles as well as the role of specific GST families in mediating this protection, we exposed mutant mouse lines lacking the GSTP, GSTM, and/or GSTT enzyme families to the model electrophile acrylamide, a ubiquitous dietary contaminant known to cause adverse effects in humans. An analysis of urinary metabolites after acute acrylamide exposure identified the GSTM family as the primary mediator of GSH conjugation to acrylamide. However, surprisingly, mice lacking only this enzyme family did not show increased toxicity after an acute acrylamide exposure. Therefore, GSH conjugation is not the sole mechanism by which GSTs protect against the toxicity of this substrate. Given the prevalence of null GST polymorphisms in the human population (approximately 50% for GSTM1 and 20–50% for GSTT1), a substantial portion of the population may also have impaired acrylamide metabolism. However, our study also defines a role for GSTP and/or GSTT in protection against acrylamide mediated toxicity. Thus, while the canonical detoxification function of GSTs may be impaired in GSTM null individuals, disease risk secondary to acrylamide exposure may be mitigated through non-canonical pathways involving members of the GSTP and/or GSTT families.

Simple, selective and fast detection of acrylamide based on glutathione S-transferase

Acrylamide (AA) is a toxic compound formed in thermally prepared foods by Maillard reaction. Besides foods, AA may be found in cosmetic products as an impurity of the widely-used non-toxic polyacrylamide. We present a novel, fast and selective detection method based on the amperometric monitoring of the coupling reaction between reduced glutathione (GSH) and AA catalyzed by glutathione S-transferase (GST) to produce an electrochemically inactive compound. We have used electrodes modified with cobalt-phthalocyanine to monitor the decrease of GHS concentration at +300 mV. Our system is simple, does not require supplementary substrates such as 1-chloro-2,4-dinitrobenzene (CDNB) nor have disadvantageous competitive kinetics characteristic to inhibition like signals. Using the optimum concentration of 100 μM GSH we have obtained a linear calibration graph from 7 to 50 μM AA and a limit of detection of 5 μM AA. The method is not affected by interfering compounds usually found in foods and was applied for real sample analysis.

Acrylamide alters glycogen content and enzyme activities in the liver of juvenile rat

Acrylamide (AA) is spontaneously formed in carbohydrate-rich food during high-temperature processing. It is neurotoxic and potentially cancer causing chemical. Its harmful effects on the liver, especially in a young organism, are still to be elucidated. The study aimed to examine main liver histology, its glycogen content and enzyme activities in juvenile rats treated with 25 or 50mg/kg bw of AA for 3 weeks. Liver samples were fixed in formalin, routinely processed for paraffin embedding, sectioning and histochemical staining. Examination of haematoxylin and eosin (H&E)-stained sections showed an increase in the volume of hepatocytes, their nuclei and cytoplasm in both AA-treated groups compared to the control. In Periodic acid-Schiff (PAS)-stained sections in low-dose group was noticed glycogen reduction, while in high-dose group was present its accumulation compared to the control, respectively. Serum analysis showed increased activity of aspartate aminotransferase (AST), and decreased activity of alanine aminotransferase (ALT) in both AA-treated groups, while the activity of alkaline phosphatase (ALP) was increased in low-dose, but decreased in high-dose group compared to the control, respectively. Present results suggest a prominent hepatotoxic potential of AA which might alter the microstructural features and functional status in hepatocytes of immature liver.

Expression analysis of hepatic mitochondria-related genes in mice exposed to acrylamide and glycidamide

Acrylamide (AA) is an industrial chemical that has been extensively investigated for central nervous system (CNS), reproductive, and genetic toxicity. However, AA effects on the liver, a major organ of drug metabolism, have not been adequately explored. In addition, the role of mitochondria in AA-mediated toxicity is still unclear. Changes in expression levels of genes associated with hepatic mitochondrial function of male transgenic Big Blue (BB) mice administered 500 mg/L AA or an equimolar concentration (600 mg/L) of its reactive metabolite glycidamide (GA) in drinking water for 3 and 4 wk, respectively, were examined. Transcriptional profiling of 542 mitochondria-related genes indicated a significant downregulation of genes associated with the 3-beta-hydroxysteroid dehydrogenase family in AA- and GA-treated mice, suggesting a possible role of both chemicals in altering hepatic steroid metabolism in BB mice. In addition, genes associated with lipid metabolism were altered by both treatments. Interestingly, only the parental compound (AA) significantly induced expression levels of genes associated with oxidative phosphorylation, in particular ATP synthase, which correlated with elevated ATP levels, indicating an increased energy demand in liver during AA exposure. Acrylamide-treated mice also showed significantly higher activity of glutathione S-transferase in association with decreased levels of reduced glutathione (GSH), which may imply an enhanced rate of conjugation of AA with GSH in liver. These results suggest different hepatic mechanisms of action of AA and GA and provide important insights into the involvement of mitochondria during their exposures.

Prenatal and perinatal acrylamide disrupts the development of cerebellum in rat: Biochemical and morphological studies

Acrylamide is known to cause neurotoxicity in the experimental animals and humans. The literature on its neurotoxic effect in the adult animals is huge, but the effect of acrylamide on the embryonic and postnatal development is relatively less understood. The present study examined its effects on the development of external features and cerebellum in albino rats. Acrylamide was orally administered to non-anesthetized pregnant females by gastric intubation 10 mg/kg/day. The animals were divided into three groups as follows. (1) Group A, newborn from control animals; (2) Group B; newborns from mothers treated with acrylamide from day 7 (D7) of gestation till birth (prenatal intoxicated group); (3) Group C; newborns from mothers treated with acrylamide from D7 of gestation till D28 after birth (perinatally intoxicated group). Acrylamide administered either prenatally or perinatally has been shown to induce significant retardation in the newborns’ body weights development, increase of thiobarbituric acid-reactive substances (TBARS) and oxidative stress (significant reductions in glutathione reduced [GSH], total thiols, superoxide dismutase [SOD] and peroxidase activities) in the developing cerebellum. Acrylamide treatment delayed the proliferation in the granular layer and delayed both cell migration and differentiation. Purkinje cell loss was also seen in acrylamide-treated animals. Ultrastructural studies of Purkinje cells in the perinatal group showed microvacuolations and cell loss. The results of this study show that prenatal and perinatal acrylamide or its metabolites disrupts the biochemical machinery, cause oxidative stress and induce structural changes in the developing rat cerebellum.

Development of a physiologically-based toxicokinetic model of acrylamide and glycidamide in rats and humans

Physiologically-based toxicokinetic ("pharmacokinetic") (PBPK or PBTK) modeling can be used as a tool to compare internal doses of acrylamide (AA) and its metabolite glycidamide (GA) in humans and rats. An earlier PBTK model for AA and GA in rats was refined and extended to humans based on new data. With adjustments to the previous parameters, excellent fits to a majority of the data for male Fisher 344 rats were obtained. Kinetic parameters for the human model were estimated based on fit to available human data for urinary metabolites of AA, and levels of hemoglobin adducts of AA and GA measured in studies in which human volunteers ingested known doses of AA. The simulations conducted with the rat and human models predicted that rats and humans ingesting comparable levels of AA (in mg/kg day) would have similar levels of GA in blood and tissues. This finding stands in contrast to the default approach that assumes a 3.2-fold increase in human risk due to pharmacokinetic differences between rats and humans. This model was used in a companion paper to estimate safe levels of ingested AA.

Effect of prenatal and perinatal acrylamide on the biochemical and morphological changes in liver of developing albino rat

Acrylamide has been employed as an experimental probe to investigate biochemical and morphological changes in developing rat liver following toxin administration in pregnant rats. Non-anesthetized pregnant rats were given acrylamide by gastric intubation at a dose of 10 mg/kg/day. The pups were divided into three groups: Group A, mothers were treated with saline (control group); Group B, mothers were treated with acrylamide from day D7 of gestation till birth (prenatal intoxication); Group C, mothers were treated with acrylamide from D7 of gestation to D28 after birth (perinatal intoxication). Acrylamide-induced biochemical changes (in liver and serum) and morphological changes (in liver) were studied in control and acrylamide-treated developing pups. Prenatally and perinatally administered acrylamide significantly increased lipid peroxidation and reduced glutathione and total thiol levels in liver. Significant inhibition of peroxidase and superoxide dismutase activities was observed in liver tissue. Total lipids including cholesterol and triglycerides were significantly increased in the serum. Acrylamide treatment increased serum alanine aminotransferase and aspartate aminotransferase activities and inhibited alkaline phosphatase activity. Sodium and potassium concentrations were increased, but calcium, phosphorus and iron levels were significantly reduced in the serum. Acrylamide produced significant electrophoretic changes in serum proteins. The most noticeable change was splitting of beta-globulin into beta1- and beta2-globulins. Light microscopy showed acrylamide-induced fatty deposits, congested central vein, vacuolization and chromatolysis in hepatocytes. Ultrastructural studies revealed vacuolated cytoplasm, lipid droplets of variable size and mitochondria with damaged cristae and vacuolization. The nuclei in acrylamide-treated groups showed marked decrease in the staining of nuclear DNA.

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.

Metabolism of acrylamide to glycidamide and their cytotoxicity in isolated rat hepatocytes: protective effects of GSH precursors

Acrylamide (AA) is a widely studied industrial chemical that is neurotoxic, mutagenic to somatic and germ cells, and carcinogenic in rodents. The recent discovery of AA at ppm levels in a wide variety of commonly consumed foods has energized research efforts worldwide to define toxicity and prevention. Metabolism and cytotoxicity of AA and its epoxide glycidamide (GA) were studied in the hepatocytes freshly isolated from male Sprague-Dawley rats. The isolated hepatocytes metabolized AA to GA. The formation of GA followed Michaelis-Menten kinetic parameters yielded apparent Km = 0.477 +/- 0.100 and 0.263 +/- 0.016 mM, Vmax = 6.5 +/- 2.1 and 26.4 +/- 3.0 nmol/h/10(6) cells, and CLint = 14 +/- 5 and 100 +/- 12 microl/h/10(6) cells for the hepatocytes from untreated and acetone-treated rats, respectively. There were lower Km and marked increases in Vmax (four-fold) and in CLint (sevenfold) in acetone-treated rat hepatocytes. The data suggest that CYP2E1 played a major role in metabolizing AA to more toxic GA. Both AA and GA induced a concentration- and time-dependent glutathione (GSH) depletion of the hepatocytes. From decreasing rates of GSH contents in hepatocytes, the parameters of glutathione S-transferase (GST) in hepatocytes to AA and GA were calculated to be Km = 1.4 and 1.5 mM, Vmax = 21 and 33 nmol/h/10(6) cells, and CLint = 15 and 23 microl/h/10(6) cells, respectively. GA 1.5-times more readily depleted GSH content than AA. GA decreased the viability of hepatocytes at 3 mM, but AA did not. These data indicate that GA is more toxic than AA as assessed by intracellular GSH depletion and loss of viability of hepatocytes. GSH precursors such as N-acetylcysteine and methionine provided significant anti-cytotoxic effects on the decrease of GSH content and cell viability of hepatocytes induced by GA and AA.

Protective effect of acorus calamus against acrylamide induced neurotoxicity

Exposure of rats to acrylamide (ACR) caused hind limb paralysis in 58% of the animals on day 10 and decreased behavioural parameters, namely distance travelled, ambulatory time, stereotypic time and basal stereotypic movements compared with the control group. These rats also had a decrease in the reduced glutathione (GSH) content and glutathione-S-transferase (GST) activity in the corpus striatum and an increase in striatal dopamine receptors, as evident by an increase in the binding of 3H-spiperone to striatal membranes. Treatment with the ethanol:water (1:1) extract of the rhizomes of Acorus calamus (AC-002) increased the GSH content and GST activity in the corpus striatum while insignificant changes were observed in other parameters. Rats treated with ACR and AC-002 in combination had a lower incidence of paralysis (18%) compared with those treated with ACR alone on day 10 of the experiment. The rats also showed a partial recovery in other behavioural parameters. The levels of GSH content and GST activity increased in the corpus striatum, while the dopamine receptors decreased compared with the ACR treated rats. The results suggest that the neurobehavioural changes produced by ACR may be prevented following treatment with Acorus calamus rhizomes.

Acrylamide induced immunosuppression in rats and its modulation by 6-MFA, an interferon inducer

In the present communication, we describe acrylamide (ACR) induced immunotoxicity and its modulation by an interferon inducer, the 6th mycelial fraction acetone (6-MFA) of Aspergillus ochraceus ATCC 28706. ACR administration to rats produced a significant decrease in the weight of spleen (p < 0.001), thymus (p < 0.001) and mesenteric lymph nodes (p < 0.05). A decrease in cellularity of spleen (p < 0.001), thymus (p < 0.001), bone marrow (p < 0.001) and circulating blood lymphocyte population (p < 0.001) was also recorded. ACR suppressed the humoral as well as cell mediated immunity as assessed by erythrocyte antibody complement (EAC)-rosettes (p < 0.001), hemagglutination titre (p < 0.001), PFC (p < 0.001) and the delayed type hypersensitivity response against sheep red blood cells (SRBC, p < 0.001). ACR treated immunosuppressed rats when treated with 6-MFA restored the circulating lymphocyte number to the normal level and a partial recovery in the weight of spleen and thymus. Potentiation of EAC-rosettes, hemagglutination titre, IgM-PFC and DTH response against SRBC was observed. It is concluded that 6-MFA ameliorate the ACR induced toxicity. This study may be of significance in prevention of ACR toxicity.

Protein malnourishment: a predisposing factor in acrylamide toxicity in pregnant rats

Exposure to acrylamide (3-10 mg/kg body weight) was found to be lethal for protein-deficient pregnant rats as evidenced by their increased mortality. It had no such effect on the normal protein diet fed pregnant and nonpregnant rats and the protein-malnourished nonpregnant rats. Protein deficiency during pregnancy caused a significant decrease in the activity of brain monoamine oxidase and acetylcholinesterase and striatal [3H]spiperone binding, known to label dopamine receptors; had no significant effect on the binding of 3H-QNB (quinuclidinyl benzilate) to cerebellar and [3H]diazepam to frontocortical membranes, known to label muscarinic and benzodiazepine receptors, respectively; and had no significant effect on brain glutathione (GSH) levels in comparison with pregnant rats fed normal protein diet. Exposure to acrylamide (2 mg/kg body weight) in protein-malnourished pregnant rats caused a marked decrease in the activity of monoamine oxidase and acetylcholinesterase and also in the binding of [3H]spiperone, [3H]QNB, and [3H]diazepam to striatal, cerebellar, and frontocortical membranes, respectively. Kinetic studies revealed that decreased binding of these ligands in the specific brain regions were due to decreased receptor sites (Bmax). A reduction in the brain glutathione content was also observed in these animals in comparison with those fed a low-protein diet during pregnancy. Pregnant rats fed a normal-protein diet on acrylamide exposure, however, showed no such biochemical changes in comparison with the pregnant rats fed normal protein diet. Also, no effect on any of the parameters studied was observed in the adult nonpregnant rats fed a low-protein diet (for 18 d) and those exposed to the monomer (d 6-17) fed either a normal- or low-protein diet in comparison with respective controls. The results indicate that pregnancy under conditions of malnutrition modifies the susceptibility of pregnant rats toward acrylamide.

Effect of methyl bromide on regional brain glutathione, glutathione-S-transferases, monoamines, and amino acids in F344 rats

Both metabolic and neurotransmitter changes have been implicated in the pathogenesis of monohalomethane neurotoxicity in rodents. This study in male and female F344 rats examined the effects of methyl bromide (MeBr) on regional brain glutathione-S-transferase (GST) activities and concentrations of glutathione (GSH), monoamines, and amino acid. Inhalation exposure to 150 ppm MeBr (6 hr/day x 5 days) yielded no histologic evidence of brain lesions but resulted in a number of biochemical changes. GSH depletion and GST inhibition were detected in the frontal cortex, caudate nucleus, hippocampus (examined for GSH only), brain stem, and cerebellum from animals of both sexes. Differences between sexes were detected for GSH depletion. Simultaneous treatment of rats with the inhibitor of monohalomethane toxicity, BW 755C (3-amino-1-[m-(trifluoromethyl)phenyl]-2-pyrazoline; 10 mg/kg bw ip, 1 hr pre- and 1 hr postexposure) completely protected against GST inhibition in all brain regions of both sexes. Partial protection by BW 755C against GSH depletion was observed in the cerebral cortex and in the cerebellum only. In males, MeBr exposure had no effect on the regional concentrations of the monoamines dopamine and serotonin and the amino acids glutamate, glutamine, taurine, and gamma-aminobutyric acid. Regional increases of brain aspartate and glycine levels were observed after exposure of males to MeBr but BW 755C had no effect on these changes induced by MeBr. Thus, of all the parameters studied, only GST, and in some brain areas GSH, correlated with inhibition of toxicity. It is concluded that, in contrast to the monoamines and the amino acids, GST and GSH are sensitive and potentially relevant indicators of MeBr neurotoxicity which could explain sex and regional differences in response to the monohalomethanes.

Methods for depleting brain glutathione

To search for a technique to deplete reduced glutathione (GSH) in brain, the influence of various types of compounds on brain GSH levels was investigated in mice. Of the compounds tested, cyclohexene-1-one, cycloheptene-1-one and diethyl maleate were shown to be potent GSH depletors in brain as well as in liver. The depletion of cerebral GSH ranged about 40-60% of control levels at 1 and 3 hr after intraperitoneal injection. Cyclohexene, cycloheptene, phorone, acetaminophen, and benzyl chloride caused mild depletion of cerebral GSH, but buthionine sulfoximine did not alter cerebral GSH levels. Further, intracerebroventricular injection of cyclohexene-1-one and cycloheptene-1-one caused depletion of brain GSH to about 60-80% of control levels at 1 hr after injection, and the effects persisted for at least 6 hr. Under these conditions, hepatic GSH was not altered. These results demonstrated that cyclohexene-1-one and cycloheptene-1-one can cause not only a marked depletion of brain GSH by systemic administration, but also depletion of cerebral GSH by intracerebroventricular injection by virtue of being water-soluble compounds. Thus, methods for depleting brain GSH employing both compounds are available for exploring possible functions of cerebral GSH in in vivo systems.

Characterization and localization of glutathione-S-transferases in rat brain and binding of hormones, neurotransmitters, and drugs

Rat brain glutathione-S-transferases are rich in Yb type subunits with major RNA transcripts coding for a relatively uncommon Yb3 form. The Yb-containing isoenzymes of brain cytosol bind glucocorticoids and are covalently labeled with dexamethasone 21-methanesulfonate. Certain neurotransmitters, hormones, and drugs, such as serotonin, dopamine, glucocorticoids, thyroxine, apomorphine, and benzodiazepine derivatives, are effective inhibitors of brain glutathione transferase activity. Immunocytochemical studies show that Yb forms are localized in ependymal cells, subventricular zone cells, astrocytes, tanycytes, and astrocyte foot processes on blood vessels, but Yb was not detected in oligodendrocytes or neurons. Based on their localization and binding properties, brain glutathione-S-transferases have the potential to function in intracellular binding of a variety of compounds and thereby govern their uptake and release in brain, transport to neurons, as well as in their detoxification.

Acrylamide: its metabolism, developmental and reproductive effects, genotoxicity, and carcinogenicity

Monomeric acrylamide is an important industrial chemical primarily used in the production of polymers and copolymers. It is also used for producing grouts and soil stabilizers. Acrylamide's neurotoxic properties have been well documented. This review will focus on pertinent information concerning other, non-neurotoxic, effects observed after exposure to acrylamide, including: its genotoxic, carcinogenic, reproductive, and developmental effects. It will also cover its absorption, metabolism, and distribution. The data show that acrylamide is capable of inducing genotoxic, carcinogenic, developmental, and reproductive effects in tested organisms. Thus, acrylamide may pose more than a neurotoxic health hazard to exposed humans. Acrylamide is a small organic molecule with very high water solubility. These properties probably facilitate its rapid absorption and distribution throughout the body. After absorption, acrylamide is rapidly metabolized, primarily by glutathione conjugation, and the majority of applied material is excreted within 24 h. Preferential bioconcentration of acrylamide and/or its metabolites is not observed although it appears to persist in tests and skin. Acrylamide can bind to DNA, presumably via a Michael addition-type reaction, which has implications for its genotoxic and carcinogenic potential. The available evidence suggests that acrylamide does not produce detectable gene mutations, but that the major concern for its genotoxicity is its clastogenic activity. This clastogenic activity has been observed in germinal tissues which suggest the possible heritability of acrylamide-induced DNA alterations. Since there is 'sufficient evidence' of carcinogenicity in experimental animals as outlined under the U.S. EPA proposed guidelines for carcinogen risk assessment, acrylamide should be categorized as a 'B2' carcinogen and therefore be considered a 'probable human carcinogen.' The very limited human epidemiological data do not provide sufficient evidence to enable one to judge the actual carcinogenic risk to humans. Acrylamide is able to cross the placenta, reach significant concentrations in the conceptus and produce direct developmental and post-natal effects in rodent offspring. It appears that acrylamide may produce neurotoxic effects in neonates from exposures not overtly toxic to the mothers. Acrylamide has an adverse effect on reproduction as evidenced by dominant lethal effects, degeneration of testicular epithelial tissue, and sperm-head abnormalities.

Comparative tissue distribution and excretion of [1-14C]acrylamide in beagle dogs and miniature pigs

Male beagle dogs and miniature pigs were given acrylamide in the diet for 3-4 wk at a dosage of 1 mg/kg/day. They were then given [1-14C]acrylamide as a single oral dose of 1 mg/kg. The animals were killed 6 hr or 1, 2, 4 or 14 days after administration of the radioactive compound and tissues were analysed for radioactivity. The radiolabelled material was distributed to a major extent in muscle tissue in both species (31-35% of the dose at 6 hr and 5-7% at 14 days). Although the nervous system is the primary target for acrylamide monomer toxicity, less than 1% of the administered 14C was found in the brain in both species. No neurotoxic signs were evident during the exposure period at the dosage used. Analysis of discrete areas of the brain for radioactivity revealed that the levels of penetration of [1-14C]acrylamide in brain paralleled the vascularization pattern of the tissues. Approximately 60% of the administered radiolabel was excreted in the urine in both species and smaller amounts were excreted in the faeces. However, recovery in the faeces was higher in pigs (c. 25%) than in dogs (c. 7%) and this and the considerably higher levels demonstrated in the gastro-intestinal tract of the pigs indicated that the absorption of acrylamide was more rapid and more extensive in dogs than in pigs.

Effects of mixed-function oxidase modifiers on neurotoxicity of acrylamide in rats

The effects of modifiers of the microsomal mixed-function oxidase system on acrylamide-induced hind-limb paralysis were investigated in rats. Pretreatment of rats with phenobarbital, trans-stilbene oxide or dichloro diphenyl trichloroethane (DDT) resulted in an earlier onset and subsequent development of acrylamide-induced hind-limb paralysis than that observed in animals treated only with acrylamide. Cobalt chloride pretreatment of rats caused a significant delay in the onset and development of hind-limb paralysis. Our results suggest that an intermediate formed by the cytochrome P-450 system may be responsible for acrylamide neurotoxicity.

Interaction of acrylamide with glutathione in rat erythrocytes

Evidence is presented for an enzyme-catalyzed conjugation of acrylamide (ACR) in rat erythrocytes. Daily exposure of rats to ACR for a period of 7, 14 and 21 days resulted in a time-dependent decrease in glutathione content. In vitro incubation of ACR with rat erythrocytes suspension caused a concentration-dependent decrease in glutathione levels. Red blood cell (RBC) enzyme-catalyzed conjugation of ACR with glutathione increased with protein concentration and was dependent on pH and time of incubation. Glutathione-S-transferase (GST) activity using acrylamide and 1-chloro 2,4-dinitrobenzene (CDNB) as substrates followed the order: liver greater than kidney greater than brain greater than erythrocytes. Glutathione peroxidase activity of RBC's was inhibited by the in vitro addition of ACR to erythrocytes. These results suggest that rat erythrocytes are equipped with the mechanism which can inactivate toxic electrophilic chemicals, such as acrylamide.

Detoxication of industrial pollutants by the glutathione glutathione-S-transferase system in the liver of Anabas testudineus (Bloch)

The interrelationship of reduced glutathione (GSH) and glutathione-S-transferase in the liver of a freshwater climbing perch Anabas testudineus (Bloch) exposed to common industrial pollutants has been studied. In both short- and long-term treatments there was a concomitant decrease in reduced glutathione profile and an increase in glutathione-S-transferase activity. It may be surmised that the majority of xenobiotics of industrial origin are detoxicated by the glutathione glutathione-S-transferase pathways enabling the fish to survive exposure to the additive and/or synergistic toxicity of mixtures of poisons.

Regulation of brain and hepatic glutathione-S-transferase by sex hormones in rats

Our results indicate that sex hormones play an important role in the regulation of brain and hepatic GST protein during maturity. The conjugating factor GSH does not appear to be under the influence of sex hormones. These observations are of great significance in view of the possibility of continued exposure to neurotoxic chemicals like DDT and Kepone which can cause significant alterations in levels of sex hormones. A reduced GSH activity could lead to a retarded biotransformation of electrophiles and thus to an enhanced toxicity.