Toxic Electrophiles Research Articles

Exploring Secondary Amine Carnosine Derivatives: Design, Synthesis, and Properties

Carnosine is a naturally occurring dipeptide that has been advocated by some authors as an interesting scaffold for the development of potential therapeutic agents in view of the positive outcomes of its supplementation in animal models of human diseases. Its mode of action seems to depend on the quenching of toxic electrophiles, such as 4–hydroxynonenal (HNE). However, carnosine’s bioavailability in humans is lower than that in other mammals. The main reason for such an unfavorable pharmacokinetic profile is the activity of the enzyme human serum carnosinase (E.C. 3.4.13.20), which rapidly hydrolyzes carnosine upon absorption. Therefore, some studies have focused on the design of carnosinase-resistant derivatives that retain binding activity toward toxic electrophiles. Nevertheless, the structural modification of the N-terminus amino group of carnosine has rarely been considered, possibly because of its key role in the electrophile scavenging mechanism. This was proven, since some carnosine N-terminus modification generated inactive compounds, despite some derivatives retaining oral bioavailability and gaining resistance to carnosinase hydrolysis. Herein, we therefore report a study aimed at exploring whether the amino group of carnosine can be conveniently modified to develop carnosinase-resistant derivatives retaining the dipeptide activity toward toxic electrophiles.

Solid-Phase Reactivity-Directed Extraction (SPREx): An Alternative Approach for Simultaneous Extraction, Identification, and Prioritization of Toxic Electrophiles Produced in Water Treatment Applications

Solid-Phase Reactivity-Directed Extraction (SPREx): An Alternative Approach for Simultaneous Extraction, Identification, and Prioritization of Toxic Electrophiles Produced in Water Treatment Applications

Design of β-Keto Esters with Antibacterial Activity: Synthesis, In Vitro Evaluation, and Theoretical Assessment of Their Reactivity and Quorum-Sensing Inhibition Capacity.

This work proposes the design of β-keto esters as antibacterial compounds. The design was based on the structure of the autoinducer of bacterial quorum sensing, N-(3-oxo-hexanoyl)-l-homoserine lactone (3-oxo-C6-HSL). Eight β-keto ester analogues were synthesised with good yields and were spectroscopically characterised, showing that the compounds were only present in their β-keto ester tautomer form. We carried out a computational analysis of the reactivity and ADME (absorption, distribution, metabolism, and excretion) properties of the compounds as well as molecular docking and molecular dynamics calculations with the LasR and LuxS quorum-sensing (QS) proteins, which are involved in bacterial resistance to antibiotics. The results show that all the compounds exhibit reliable ADME properties and that only compound 7 can present electrophile toxicity. The theoretical reactivity study shows that compounds 6 and 8 present a differential local reactivity regarding the rest of the series. Compound 8 presents the most promising potential in terms of its ability to interact with the LasR and LuxS QS proteins efficiently according to its molecular docking and molecular dynamics calculations. An initial in vitro antimicrobial screening was performed against the human pathogenic bacteria Pseudomonas aeruginosa and Staphylococcus aureus as well as the phytopathogenic bacteria Pseudomonas syringae and Agrobacterium tumefaciens. Compounds 6 and 8 exhibit the most promising results in the in vitro antimicrobial screening against the panel of bacteria studied.

Out of Thin Air? Catalytic Oxidation of Trace Aqueous Aldehydes with Ambient Dissolved Oxygen.

Water reuse is expanding due to increased water scarcity. Water reuse facilities treat wastewater effluent to a very high purity level, typically resulting in a product water that is essentially deionized water, often containing less than 100 μg/L organic carbon. However, recent research has found that low-molecular-weight aldehydes, which are toxic electrophiles, comprise a significant fraction of the final organic carbon pool in recycled wastewater in certain treatment configurations. In this manuscript, we demonstrate oxidation of trace aqueous aldehydes to their corresponding acids using a heterogeneous catalyst (5% Pt on C), with ambient dissolved oxygen serving as the terminal electron acceptor. Mass balances are essentially quantitative across a range of aldehydes, and pseudo-first-order reaction kinetics are observed in batch reactors, with kobs varying from 0.6 h-1 for acetaldehyde to 4.6 h-1 for hexanal, while they are low for unsaturated aldehydes. Through kinetic and isotopic labeling experiments, we demonstrate that while oxygen is essential for the reaction to proceed, it is not involved in the rate-limiting step, and the reaction appears to proceed primarily through a base-promoted β-hydride elimination mechanism from the hydrated gem-diol form of the corresponding aldehyde. This is the first report we are aware of that demonstrates useful abiotic oxidation of a trace organic contaminant using dissolved oxygen.

The Influence of Intracellular Glutathione Levels on the Induction of Nrf2-Mediated Gene Expression by α-Dicarbonyl Precursors of Advanced Glycation End Products.

α-Dicarbonyl compounds, particularly methylglyoxal (MGO), glyoxal (GO), and 3-deoxyglucosone (3-DG), are highly reactive precursors for the formation of advanced glycation end products (AGEs). They are formed in vivo and during food processing. This study aimed to investigate the role of intracellular glutathione (GSH) levels in the induction of Nrf2-mediated gene expression by α-dicarbonyl compounds. The reactions between α-dicarbonyl compounds (MGO, GO, and 3-DG) and GSH were studied by LC-MS in a cell-free system. It was shown that these three α-dicarbonyl compounds react instantaneously with GSH, with the GSH-mediated scavenging decreasing in the order MGO > GO > 3DG. Furthermore, in a cell-based reporter gene assay MGO, GO, and 3-DG were able to induce Nrf2-mediated gene expression in a dose-dependent manner. Modulation of intracellular GSH levels showed that the cytotoxicity and induction of the Nrf2-mediated pathway by MGO, GO and 3-DG was significantly enhanced by depletion of GSH, while a decrease in Nrf2-activation by MGO and GO but not 3-DG was observed upon an increase of the cellular GSH levels. Our results reveal subtle differences in the role of GSH in protection against the three typical α-dicarbonyl compounds and in their induction of Nrf2-mediated gene expression, and point at a dual biological effect of the α-dicarbonyl compounds, being reactive toxic electrophiles and -as a consequence- able to induce Nrf2-mediated protective gene expression, with MGO being most reactive.

The Potential Development Sulfonylhydrazines for the Treatment of Alzheimer’s Disease

The anticancer drug BCNU has striking activity against Alzheimer’s disease in humans. This activity is likely due to one of the many reactive electrophiles generated by BCNU. The structure and complex decomposition pathways of BCNU do not allow for the synthesis of analogs that can selectively generate these electrophiles. Therefore, their contributions to the anti-Alzheimer’s efficacy and toxicity of these different electrophiles cannot be determined. The sulfonylhydrazine prodrugs (SHP), which readily cross the blood-brain barrier, can be regarded as functional homologs of BCNU but with substantial design flexibility and tolerance for structural modification. Agents have been synthesized, which generate individual or combinations of identical or similar electrophiles to the electrophilic species produced by the BCNU. This should allow for the determination of which electrophilic species are important in the anti-Alzheimer’s disease activity and how using SHPs, we can generate the most efficacious of these electrophiles, in a more selective and less toxic manner, to generate an improved anti-Alzheimer’s agent.

A comparison of the chemical biology of hydropersulfides (RSSH) with other protective biological antioxidants and nucleophiles

The hydropersulfide (RSSH) functional group has received significant recent interest due to its unique chemical properties that set it apart from other biological species. The chemistry of RSSH predicts that one possible biological role may be as a protectant against cellular oxidative and electrophilic stress. That is, RSSH has reducing and nucleophilic properties that may combat the potentially destructive biochemistry of toxicologically relevant oxidants and electrophiles. However, there are currently numerous other molecules that have established roles in this regard. For example, ascorbate and tocopherols are potent antioxidants that quench deleterious oxidative reactions and glutathione (GSH) is a well-established and highly prevalent biological protectant against electrophile toxicity. Thus, in order to begin to understand the possible role of RSSH species as protectants against oxidative/electrophilic stress, the inherent chemical properties of RSSH versus these other protectants will be discussed and contrasted.

Medicinal Thiols: Current Status and New Perspectives.

The thiol (-SH) functional group is found in a number of drug compounds and confers a unique combination of useful properties. Thiol-containing drugs can reduce radicals and other toxic electrophiles, restore cellular thiol pools, and form stable complexes with heavy metals such as lead, arsenic, and copper. Thus, thiols can treat a variety of conditions by serving as radical scavengers, GSH prodrugs, or metal chelators. Many of the compounds discussed here have been in use for decades, yet continued exploration of their properties has yielded new understanding in recent years, which can be used to optimize their clinical application and provide insights into the development of new treatments. The purpose of this narrative review is to highlight the biochemistry of currently used thiol drugs within the context of developments reported in the last five years. More specifically, this review focuses on thiol drugs that represent the standard of care for their associated conditions, including N-acetylcysteine, 2,3-meso-dimercaptosuccinic acid, British anti-Lewisite, D-penicillamine, amifostine, and others. Reports of novel dosing regimens, delivery strategies, and clinical applications for these compounds were examined with an eye toward emerging approaches to address a wide range of medical conditions in the future.

Exposure to acrylamide decreases noradrenergic axons in rat brain

PurposeAcrylamide is known to induce disorders in the central nervous system in humans and experimental animals. The present study investigated effects of exposure to acrylamide on adult neurogenesis, noradrenergic axons and the level of norepinephrine in the brain of male rats. MethodFour groups of 12 male Wistar rats each were exposed to acrylamide at 0, 0.2, 2 and 20 mg/kg body weight by gavage for 5 weeks. Six rats of each groups were injected with 5-bromo-2′-deoxy-uridine (BrdU) after five-week exposure to acrylamide to examine proliferative cells in the dentate gyrus using immunostaining. Density of noradrenergic and serotonergic axons in the prefrontal cortex, hippocampus and cortex behind the bregma was quantified. Remaining 6 rats were decapitated after the last exposure and brains were dissected out to measure monoamine level in the hippocampus and prefrontal cortex using high performance liquid chromatography. ResultExposure to acrylamide dose-dependently decreased the density of noradrenergic axons in the prefrontal cortex with a significant change at 20 mg/kg. Norepinephrine level decreased in the hippocampus at 20 mg/kg. Exposure to acrylamide at 20 mg/kg or less did not change the number of BrdU positive cells, but the result should be considered preliminary. ConclusionThe results show that oral exposure to acrylamide induces decrease in noradrenergic axons and norepinephrine level in the brain of rats. Given the similar effects are observed in 1-bromopropane-exposed rats, there may be the common mechanism in the toxicity of soft electrophiles to the central nervous system.

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.

Methyl and Ethylmercury elicit oxidative stress and unbalance the antioxidant system in Saccharomyces cerevisiae

Methylmercury (MeHg) and Ethylmercury (EtHg) are toxic to the central nervous system. Human exposure to MeHg and EtHg results mainly from the consumption of contaminated fish and thimerosal-containing vaccines, respectively. The mechanisms underlying the toxicity of MeHg and EtHg are still elusive. Here, we compared the toxic effects of MeHg and EtHg in Saccharomyces cerevisiae (S. cerevisiae) emphasizing the involvement of oxidative stress and the identification of molecular targets from antioxidant pathways. Wild type and mutant strains with deleted genes for antioxidant defenses, namely: γ-glutamylcysteine synthetase, glutathione peroxidase, catalase, superoxide dismutase, mitochondrial peroxiredoxin, cytoplasmic thioredoxin, and redox transcription factor Yap1 were used to identify potential pathways and proteins from cell redox system targeted by MeHg and EtHg. MeHg and EtHg inhibited cell growth, decreased membrane integrity, and increased the granularity and production of reactive species (RS) in wild type yeast. The mutants were predominantly less tolerant of mercurial than wild type yeast. But, as the wild strain, mutants exhibited higher tolerance to MeHg than EtHg. Our results indicate the involvement of oxidative stress in the cytotoxicity of MeHg and EtHg and reinforce S. cerevisiae as a suitable model to explore the mechanisms of action of electrophilic toxicants.

Abstract 4738: Lipid peroxidation mediates the effects of topoisomerase poisons on their targets

Abstract Our studies characterizing responses of cancer cells to oxidative stress have implicated the topoisomerases TOP1 and TOP2 as key mediators linking reactive oxygen species to DNA damage. Normally, TOP1 and TOP2 maintain chromosome integrity by transiently cleaving and rejoining DNA, thereby releasing topological strain and facilitating transcription, replication, and other processes critical for cancer cell proliferation. The topoisomerase poisons are a structurally diverse group of chemotherapy agents such as camptothecin, doxorubicin and etoposide that trap topoisomerases as cleavage complexes, TOP1cc and/or TOP2cc, where the enzymes remain covalently bound at single or double strand breaks, respectively. Prior studies identified a common mechanism of interfacial inhibition, but the constraints of locking protein onto DNA are hard to reconcile with the diversity of topoisomerase poisons, including simple compounds like H2O2 and 1,4-benzoquinone. Pointing to an alternative mechanism, camptothecin, doxorubicin, etoposide, and other topoisomerase poisons share the potential to markedly increase cellular oxidative stress. Among the most toxic consequences of oxidative stress is lipid peroxidation, leading to formation of lipid aldehydes such as 4-hydroxynonenal that modify and crosslink proteins at nucleophilic residues. In prior work, we showed that sequestering aldehydes blocked cellular effects of topoisomerase poisons while treating cells with 4-hydroxynonenal recapitulated many of their effects. Here, we have examined whether lipid aldehydes also mediate effects of topoisomerase poisons on their protein targets. Thus, we modulated oxidative stress in cells along with directly assaying formation TOP1cc and/or TOP2cc by detection in situ, flow cytometry, and Western blotting. We confirmed that camptothecin, doxorubicin, and etoposide induce lipid peroxidation, leading to production of aldehydes and other electrophiles. Under conditions where TOP1cc and/or TOP2cc are normally formed, blocking lipid peroxidation with butylated hydroxytoluene (BHT) was sufficient to protect cells from topoisomerase poisons. Among candidate mediators, 4-hydroxy-2-nonenal, 1- and E-2-hexadecanal, and 15-deoxy-Δ12, 14-prostaglandin J2 could each induce TOP1cc and TOP2cc. The toxicity of the lipid-derived electrophiles was also dependent on the activity of TDP1, which serves a key role in removing TOP1cc and TOP2cc from DNA. Our results suggest a distinct, shared mechanism of action of topoisomerase poisons that depends on oxidative stress, lipid peroxidation, accumulation of lipid aldehydes and covalent modification of surface nucleophiles on topoisomerase enzymes. These covalent modifications may be sufficient to poison topoisomerases on their own and drive formation of TOP1cc and TOP2cc, independent of whether the cleaved conformation is stabilized by interfacial inhibition. Citation Format: Amy C. Flor, Jing Li, Leslyn A. Hanakahi, Stephen J. Kron. Lipid peroxidation mediates the effects of topoisomerase poisons on their targets [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4738.

Sulfane Sulfur in Toxicology: A Novel Defense System Against Electrophilic Stress.

Electrophiles can undergo covalent modification of cellular proteins associated with its dysfunction, thereby exerting toxicity. Small nucleophilic molecules such as glutathione protect cells from electrophilic insult by binding covalently to electrophiles to form adducts that are excreted into the extracellular space. Recent studies indicate that sulfane sulfur, which is defined as a sulfur atom with 6 valence electrons and no charge, plays an essential role in protection against electrophile toxicity because sulfane sulfur can be highly nucleophilic compared to the corresponding thiol group. Advances in the development of assays to detect sulfane sulfur have revealed that sulfane sulfur-containing molecules such as persulfide/polysulfide species are ubiquitous in cells and tissues. Also, there is growing evidence that the binding of sulfane sulfur to electrophiles forms sulfur adducts as detoxified metabolites. Although the biosynthesis pathways of sulfane sulfur are known, its regulatory function in toxicology is still unclear. This review outlines the current knowledge of the synthesis, chemical properties, detection methods, interactions with electrophiles, and toxicological significance of sulfane sulfur, as well as suggesting directions for future research.

Trimethylphosphate as a Methylating Agent for Cross Coupling: A Slow-Release Mechanism for the Methylation of Arylboronic Esters.

A methyl group on an arene, despite its small size, can have a profound influence on biologically active molecules. Typical methods to form a methylarene involve strong nucleophiles or strong and often toxic electrophiles. We report a strategy for a new, highly efficient, copper and iodide co-catalyzed methylation of aryl- and heteroarylboronic esters with the mild, nontoxic reagent trimethylphosphate, which has not been used previously in coupling reactions. We show that it reacts in all cases tested in yields that are higher than those of analogous copper-catalyzed reactions of MeOTs or MeI. The combination of C-H borylation and this methylation with trimethylphosphate provides a new approach to the functionalization of inert C-H bonds and is illustrated by late-stage methylation of four medicinally active compounds. In addition, reaction on a 200 mmol scale demonstrates reliability of this method. Mechanistic studies show that the reaction occurs by a slow release of methyl iodide by reaction of PO(OMe)3 with iodide catalyst, rather than the typical direct oxidative addition to a metal center. The low concentration of the reactive electrophile enables selective reaction with an arylcopper intermediate, rather than nucleophilic groups on the arylboronate, and binding of tert-butoxide to the boronate inhibits reaction of the electrophile with the tert-butoxide activator to form methyl ether.

Evaluation of the Efficacy and Safety of Topical and Oral Glutathione in Treatment of Melasma

AbstractBackground: Melasma is an acquired symmetrical hyper-pigmentation that typically presents on the face. Its etiology is multifactorial; its treatment remains a challenge and unsat-isfactory. Glutathione is a major antioxidant which plays critical roles in protecting cells from oxidative damage and the toxicity of xenobiotic electrophiles, and maintaining redox homeostasis.Aim of the Work: To assess the efficacy and safety of topical and oral glutathione in the treatment of melasma.Patients and Methods: This study included 30 female patients with melasma were selected among those attending the Outpatient Clinic of Dermatology and Venereology De-partment, Tanta University Hospitals during the period between December, 2015 and February, 2017. The studied patients were divided into 3 groups. Group I (10 patients) applied glutathione (2%) cream to right side of the face while placebo cream to left side (as a control) twice daily for 10 weeks. Group II (10 patients) received oral glutathione capsules (500mg/day) for 4 weeks. Group III (10 patients) received oral placebo capsules (as a control) once daily for 4 weeks. Modified melasma area and severity index (MASI) score was calculated before and after therapy. The patients were followed up for a period of 3 months.Results: Significant reduction in modified MASI was observed in patients treated with topical and oral glutathione (p=0.011) and (p=0.007) respectively, while patients treated with topical or oral placebo had no response. Topical and oral forms of glutathione were safe and well tolerated.Conclusion: Glutathione is safe, tolerable and effective whitening agent when used in topical cream (2%) and also in oral form in treatment of melasma.

Polymorphisms and Protein Expressions of Glutathione S-Transferase M1 and T1 in Non-Small Cell Lung Cancer.

The deletion polymorphisms of glutathione S-transferase (GST) GSTM1 and GSTT1 genes result in the absence of the corresponding protein, which decreases the detoxification of carcinogens. Studies evaluating polymorphisms and protein expressions in the same patients are limited. Therefore, in this study, we aimed to investigate the association between polymorphisms and protein expressions of GSTM1 and GSTT1 in lung tissues of patients with non-small cell lung cancer (NSCLC). For protein expression and gene deletion studies, tumor and surrounding tumor free (normal) tissue of 33 patients with NSCLC were used. In paraffin-embedded tissues, immunohistochemistry was used to detect protein expressions, and multiplex polymerase chain reaction amplification was used to identify gene deletions. GSTM1 and GSTT1 protein expressions were not detected in patients with GSTM1 and GSTT1 gene deletions, whereas protein expressions were detected in lung tissues of all patients carrying GSTM1 and GSTT1 genes. The protein expression level of GSTT1 was 2.0-fold higher in tumors of patients lacking GSTM1 genes than those with GSTM1 genes (p=0.018). Protein expression of GSTM1 was statistically higher in tumor tissues than in normal tissues of patients with GSTM1 genes (p=0.001). These results show that a) there is an association between gene deletions and protein expressions of GSTM1 and GSTT1 in patients with NSCLC, b) in the absence of GSTM1 genes, enhancement of expression of GSTT1 in tumors is likely to show that GSTT1 increases its capacity to detoxify the toxic electrophiles in tumors, and c) GSTM1 protein expression is higher in tumors compared with normal lung tissues of patients with NSCLC.

Characterization of equine GST A3-3 as a steroid isomerase

Glutathione transferases (GSTs) comprise a superfamily of enzymes prominently involved in detoxication by making toxic electrophiles more polar and therefore more easily excretable. However some GSTs have developed alternative functions. Thus, a member of the Alpha class GSTs in pig and human tissues is involved in steroid hormone biosynthesis, catalyzing the obligatory double-bond isomerization of Δ5-androstene-3,17-dione to Δ4-androstene-3,17-dione and of Δ5-pregnene-3,20-dione to Δ4-pregnene-3,20-dione on the biosynthetic pathways to testosterone and progesterone. The human GST A3-3 is the most efficient steroid double-bond isomerase known so far in mammals. The current work extends discoveries of GST enzymes that act in the steroidogenic pathways in large mammals. The mRNA encoding the steroid isomerase GST A3-3 was cloned from testis of the horse (Equus ferus caballus). The concentrations of GSTA3 mRNA were highest in hormone-producing organs such as ovary, testis and adrenal gland. EcaGST A3-3 produced in E. coli has been characterized and shown to have highly efficient steroid double-bond isomerase activity, exceeding its activities with conventional GST substrates. The enzyme now ranks as one of the most efficient steroid isomerases known in mammals and approaches the activity of the bacterial ketosteroid isomerase, one of the most efficient enzymes of all categories known today. The high efficiency and the tissue distribution of EcaGST A3-3 support the view that the enzyme plays a physiologically significant role in the biosynthesis of steroid hormones.

Enolate-Forming Compounds as a Novel Approach to Cytoprotection.

Evidence from laboratory studies and clinical trials suggests that plant-derived polyphenolic compounds such as curcumin, resveratrol, or phloretin might be useful in the treatment of certain diseases (e.g., Alzheimer's disease) and acute tissue injury states (e.g., spinal cord trauma). However, despite this potential, the corresponding chemical instability, toxic potential, and low bioavailability of these compounds could limit their ultimate clinical relevance. We have shown that pharmacophores of curcumin (e.g., 2-acetylcyclopentanone) and phloretin (e.g., 2',4',6'-trihydroxyacetophenone; THA) can provide cytoprotection in cell culture and animal models of oxidative stress injury. These pharmacophores are 1,3-dicarbonyl and polyphenol derivatives, the enol groups of which can ionize in biological solutions to form an enolate. This carbanionic moiety can chelate metal ions and, as a nucleophile, can scavenge toxic electrophiles (e.g., acrolein, 4-hydroxy-2-nonenal, and N-acetyl-p-benzoquinone imine) involved in many pathogenic conditions. Aromatic derivatives such as THA can also trap free oxygen and nitrogen radicals and thereby provide another layer of cytoprotection. The multifunctional character of these enolate-forming compounds suggests an ability to block pathogenic processes (e.g., oxidative stress) at several steps. The purpose of this review is to discuss research supporting our theory that enolate formation is a significant cytoprotective property that represents a platform for development of pharmacotherapeutic approaches to a variety of toxic and pathogenic conditions. Our discussion will focus on mechanism and structure-activity studies that define enolate chemistry and their corresponding relationships to cytoprotection.

Acrolein and Human Disease: Untangling the Knotty Exposure Scenarios Accompanying Several Diverse Disorders.

Acrolein is a highly toxic electrophile that participates in many diseases, yet efforts to delineate its precise mechanistic contributions to specific conditions are complicated by its wide distribution within human environments. This Perspective develops the proposal that due to its mixed status as environmental pollutant, metabolic byproduct, and endotoxicant which forms via ubiquitous pathophysiological processes, many diseases likely involve acrolein released from multiple sources. Although the category boundaries are indistinct, at least four identifiable exposure scenarios are identifiable. First, in some syndromes, such as those accompanying chronic or acute intoxication with smoke, whatever role acrolein plays in disease pathogenesis mainly traces to exogenous sources such as the combustion of tobacco or other organic matter. A second exposure category involves xenobiotics that undergo metabolism within the body to release acrolein. Still other health conditions, however, involve acrolein that forms via several endogenous pathways, some of which are activated upon intoxication with xenobiotics (i.e., Exposure Category 3), while still others accompany direct physical trauma to body tissues (Exposure Category 4). Further complicating efforts to clarify the role of endogenous acrolein in human disease is the likelihood that many such syndromes are complex phenomena that resemble "chemical mixture exposures" by involving multiple toxic substances simultaneously. This Perspective contends that while recent decades have witnessed much progress in describing the deleterious effects of acrolein at the cellular and molecular levels, more work is needed to define the contributions of different acrolein sources to "real-world" health conditions in human subjects.

Read-across of 90-day rat oral repeated-dose toxicity: A case study for selected β-olefinic alcohols

There are no in vivo repeated-dose data for the vast majority of β-olefinic alcohols. However, there are robust and consistent ex vivo data suggesting many of these chemicals are metabolically transformed, especially in the liver, to reactive electrophilic toxicants which react in a mechanistically similar manner to acrolein, the reactive metabolite of 2-propen-1-ol. Hence, an evaluation was conducted to determine suitability of 2-propen-1-ol as a read-across analogue for other β-olefinic alcohols. The pivotal issue to applying read-across to the proposed category is the confirmation of the biotransformation to metabolites having the same mechanism of electrophilic reactivity, via the same metabolic pathway, with a rate of transformation sufficient to induce the same in vivo outcome. The applicability domain for this case study was limited to small (C3 to C6) primary and secondary β-olefinic alcohols. Mechanistically, these β-unsaturated alcohols are considered to be readily metabolised by alcohol dehydrogenase to polarised α,β-unsaturated aldehydes and ketones. These metabolites are able to react via the Michael addition reaction mechanism with thiol groups in proteins resulting in cellular apoptosis and/or necrosis. The addition of the non-animal in chemico reactivity data (50% depletion of free glutathione) reduced the uncertainty so the read-across prediction for the straight-chain olefinic β-unsaturated alcohols is deemed equivalent to a standard test. Specifically, the rat oral 90-day repeated-dose No Observed Adverse Effect Level (NOAEL) for 2-propen-1-ol of 6mg/kg body weight (bw)/d in males based on increase in relative weight of liver and 25mg/kg bw/d in females based on bile duct hyperplasia and periportal hepatocyte hypertrophy in the liver, is read across to fill data gaps for the straight-chained analogues.