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Acrylamide has been used industrially and also found in certain foods cooked at high temperatures. Previous reports described acrylamide-related human intoxication who presented with ataxia, memory impairment, and/or illusion. The aim of this study was to characterize the molecular mechanisms of neurotoxicity of acrylamide by analyzing the expression levels of various proteins in the hippocampus of rats exposed to acrylamide. Male Wistar rats were administered acrylamide by gavage at 0, 2, and 20 mg/kg for 1 week or 0, 0.2, 2, and 20 mg/kg for 5 weeks. At the end of the experiment, the hippocampus was dissected out and proteins were extracted for two-dimensional difference gel electrophoresis combined with matrix-assisted laser-desorption ionization time-of-flight/time-of-flight mass spectrometry (MALDI-TOF/TOF/MS). MALDI-TOF/TOF/MS identified significant changes in two proteins in the 1-week and 22 proteins in the 5-week exposure groups. These changes were up-regulation in 9 and down-regulation in 13 proteins in the hippocampus of rats exposed to acrylamide at 20 mg/kg for 5 weeks. PANTHER overrepresentation test based on the GO of biological process showed significant overrepresentation in proteins annotated to nicotinamide nucleotide metabolic process, coenzyme biosynthetic process, pyruvate metabolic process, and carbohydrate metabolic process. The test also showed significant overrepresentation in proteins annotated to creatinine kinase activity for the GO of molecular function as well as myelin sheath, cytoplasmic part, and cell body for the GO of cellular component. Comparison with a previous proteomic study on hippocampal proteins in rats exposed to 1-bromopropane identified triosephosphate isomerase, mitochondrial creatine kinase U-type, creatine kinase β-type and proteasome subunit α type-1 as proteins affected by exposure to acrylamide and 1-bromopropane, suggesting a common mechanism of neurotoxicity for soft electrophiles. [ABSTRACT FROM AUTHOR]

Oxidative stress leads to the activation of the Nuclear factor-erythroid-2-related factor 2 (Nrf2) pathway. While most studies have focused on the activation of the Nrf2 pathway after single chemical treatment, little is known about the dynamic regulation of the Nrf2 pathway in the context of repeated exposure scenarios. Here we employed single cell live imaging to quantitatively monitor the dynamics of the Nrf2 pathway during repeated exposure, making advantage of two HepG2 fluorescent protein reporter cell lines, expressing GFP tagged Nrf2 or sulfiredoxin 1 (Srxn1), a direct downstream target of Nrf2. High throughput live confocal imaging was used to measure the temporal dynamics of these two components of the Nrf2 pathway after repeated exposure to an extensive concentration range of diethyl maleate (DEM) and tert-butylhydroquinone (tBHQ). Single treatment with DEM or tBHQ induced Nrf2 and Srxn1 over time in a concentration-dependent manner. The Nrf2 response to a second treatment was lower than the response to the first exposure with the same concentration, indicating that the response is adaptive. Moreover, a limited fraction of individual cells committed themselves into the Nrf2 response during the second treatment. Despite the suppression of the Nrf2 pathway, the second treatment resulted in a three-fold higher Srxn1-GFP response compared to the first treatment, with all cells participating in the response. While after the first treatment Srxn1-GFP response was linearly related to Nrf2-GFP nuclear translocation, such a linear relationship was less clear for the second exposure. siRNA-mediated knockdown demonstrated that the second response is dependent on the activity of Nrf2. Several other, clinically relevant, compounds (i.e., sulphorophane, nitrofurantoin and CDDO-Me) also enhanced the induction of Srxn1-GFP upon two consecutive repeated exposure. Together the data indicate that adaptation towards pro-oxidants lowers the Nrf2 activation capacity, but simultaneously primes cells for the enhancement of an antioxidant response which depends on factors other than just Nrf2. These data provide further insight in the overall dynamics of stress pathway activation after repeated exposure and underscore the complexity of responses that may govern repeated dose toxicity. [ABSTRACT FROM AUTHOR]

The value of time-dependent toxicity (TDT) data in predicting mixture toxicity was examined. Single chemical (A and B) and mixture (A + B) toxicity tests using Microtox ® were conducted with inhibition of bioluminescence ( Vibrio fischeri ) being quantified after 15, 30 and 45-min of exposure. Single chemical and mixture tests for 25 sham (A 1 :A 2 ) and 125 true (A:B) combinations had a minimum of seven duplicated concentrations with a duplicated control treatment for each test. Concentration/response ( x / y ) data were fitted to sigmoid curves using the five-parameter logistic minus one parameter (5PL-1P) function, from which slope, EC 25 , EC 50 , EC 75 , asymmetry, maximum effect, and r 2 values were obtained for each chemical and mixture at each exposure duration. Toxicity data were used to calculate percentage-based TDT values for each individual chemical and mixture of each combination. Predicted TDT values for each mixture were calculated by averaging the TDT values of the individual components and regressed against the observed TDT values obtained in testing, resulting in strong correlations for both sham ( r 2 = 0.989, n = 25) and true mixtures ( r 2 = 0.944, n = 125). Additionally, regression analyses confirmed that observed mixture TDT values calculated for the 50% effect level were somewhat better correlated with predicted mixture TDT values than at the 25 and 75% effect levels. Single chemical and mixture TDT values were classified into five levels in order to discern trends. The results suggested that the ability to predict mixture TDT by averaging the TDT of the single agents was modestly reduced when one agent of the combination had a positive TDT value and the other had a minimal or negative TDT value. [ABSTRACT FROM AUTHOR]

Humans have widespread exposure to both oxidants, and soft electrophilic compounds such as alpha,beta-unsaturated aldehydes and quinones. Electrophilic motifs are commonly found in a drugs, industrial chemicals, pollutants and are also generated via oxidant-mediated degradation of biomolecules including lipids (e.g. formation of 4-hydroxynonenal, 4-hydroxyhexenal, prostaglandin J2). All of these classes of compounds react efficiently with Cys residues, and the particularly the thiolate anion, with this resulting in Cys modification via either oxidation or adduct formation. This can result in deleterious or beneficial effects, that are either reversible (e.g. in cell signalling) or irreversible (damaging). For example, acrolein is a well-established toxin, whereas dimethylfumarate is used in the treatment of multiple sclerosis and psoriasis. This short review discusses the targets of alpha,beta-unsaturated aldehydes, and particularly two prototypic cases, acrolein and dimethylfumarate, and the factors that control the selectivity and kinetics of reaction of these species. Comparison is made between the reactivity of oxidants versus soft electrophiles. These rate constants indicate that electrophiles can be significant thiol modifying agents in some situations, as they have rate constants similar to or greater than species such as H 2 O 2 , can be present at higher concentrations, and are less efficiently removed by protective systems when compared to H 2 O 2. They may also induce similar or higher levels of modification than highly reactive oxidants, due to the very low concentrations of oxidants formed in most in vivo situations. [Display omitted] • Humans are widely exposed to oxidants and soft electrophiles (e.g. α,β-unsaturated aldehydes, quinones). • Both electrophiles and oxidants react rapidly with thiols/thiolates, resulting in modification to proteins. • This can be deleterious or beneficial depending on the modifying agent and target protein(s). • Targets of major reactive aldehydes (acrolein, dimethylfumarate) and controlling factors are reviewed. • Modification by oxidants vs. electrophiles is compared; the latter can be quantitatively important. [ABSTRACT FROM AUTHOR]

Replacement of a carbon atom of an aromatic compound by a more electronegative heteroatom gives rise to suppression of reactivities of the remaining carbon atoms in electrophilic substitution (SE2) reactions. To prove this experiment-based rule, the reactivities are related to the relevant extents of the intermolecular charge transfer. General algebraic expressions are derived and analyzed for these extents for various directions of the attack of electrophile. The reactant is considered as a perturbed alternant hydrocarbon, the perturbation coinciding with the alteration in the Coulomb parameter of the carbon atom undergoing the replacement, whereas the reagent is represented explicitly by an external vacant orbital. Changes in the intermolecular charge transfer due to introduction of heteroatom are shown to consist of two components, viz. of an initial-population-dependent component contributing increments of alternating signs for shifting positions of electrophile along the hydrocarbon chain and of an additional negative contribution originating from the increased interval between diagonal Hamiltonian matrix elements for orbitals participating in the charge transfer. For soft electrophiles, the negative contribution is shown to predominate over the alternating one. This implies the charge transfer between heteroaromatic reactants and electrophiles to be suppressed vs. the relevant values for hydrocarbons-containing system. [ABSTRACT FROM AUTHOR]