Role of glutathione on acrolein-induced cytotoxicity and mutagenicity in Escherichia coli

Mechanisms underlying dose-limiting toxicities of conventional chemotherapeutic agents

Dose-limiting toxicities (DLTs) are severe adverse effects that define the maximum tolerated dose of a cancer drug. In addition to the specific mechanisms of each drug, common contributing factors include inflammation, apoptosis, ion imbalances, and tissue-specific enzyme deficiencies. Among various DLTs are bleomycin-induced pulmonary fibrosis, doxorubicin-induced cardiomyopathy, cisplatin-induced nephrotoxicity, methotrexate-induced hepatotoxicity, vincristine-induced neurotoxicity, paclitaxel-induced peripheral neuropathy, and irinotecan, which elicits severe diarrhea. Currently, specific treatments beyond dose reduction are lacking for most toxicities. Further research on cellular and molecular pathways is imperative to improve their management. This review synthesizes preclinical and clinical data on the pharmacological mechanisms underlying DLTs and explores possible treatment approaches. A comprehensive perspective reveals knowledge gaps and emphasizes the need for future studies to develop more targeted strategies for mitigating these dose-dependent adverse effects. This could allow the safer administration of fully efficacious doses to maximize patient survival.

Reconsidering the Chemical Nature of Strand Breaks Derived from Abasic Sites in Cellular DNA: Evidence for 3'-Glutathionylation

The hydrolytic loss of coding bases from cellular DNA is a common and unavoidable reaction. The resulting abasic sites can undergo β-elimination of the 3'-phosphoryl group to generate a strand break with an electrophilic α,β-unsaturated aldehyde residue on the 3'-terminus. The work reported here provides evidence that the thiol residue of the cellular tripeptide glutathione rapidly adds to the alkenal group on the 3'-terminus of an AP-derived strand break. The resulting glutathionylated adduct is the only major cleavage product observed when β-elimination occurs at an AP site in the presence of glutathione. Formation of the glutathionylated cleavage product is reversible, but in the presence of physiological concentrations of glutathione, the adduct persists for days. Biochemical experiments provided evidence that the 3'-phosphodiesterase activity of the enzyme apurinic/apyrimidinic endonuclease (APE1) can remove the glutathionylated sugar remnant from an AP-derived strand break to generate the 3'OH residue required for repair via base excision or single-strand break repair pathways. The results suggest that a previously unrecognized 3'glutathionylated sugar remnant─and not the canonical α,β-unsaturated aldehyde end group─may be the true strand cleavage product arising from β-elimination at an abasic site in cellular DNA. This work introduces the 3'glutathionylated cleavage product as the major blocking group that must be trimmed to enable repair of abasic site-derived strand breaks by the base excision repair or single-strand break repair pathways.

Reuterin Demonstrates Potent Antimicrobial Activity Against a Broad Panel of Human and Poultry Meat Campylobacter spp. Isolates

Reuterin is a broad-spectrum antimicrobial system produced by specific strains of Lactobacillus reuteri during anaerobic metabolism of glycerol. Acrolein is the main component responsible for its antimicrobial activity. Here, the sensitivity of Campylobacter jejuni (n = 51) and Campylobacter coli (n = 20) isolates from chicken meat and human stool samples to reuterin was investigated. The minimum inhibitory concentration (MIC) of C. jejuni and C. coli strains was measured between 1.5 and 3.0 µM of acrolein, below the MIC of the sensitive indicator strain Escherichia coli K12 (16.5 µM acrolein). The interaction of C. jejuni N16-1419 and the reuterin-producing L. reuteri PTA5_F13 was studied during 24 h co-cultures with or without glycerol. A high C. jejuni growth was observed in cultures without glycerol. In contrast, C. jejuni growth decreased from 7.3 ± 0.1 log CFU/mL to below detection limit (1 log CFU/mL) during co-cultures added with 28 mM glycerol. This bactericidal effect could be attributed to in situ reuterin production. The low MIC observed and the high sensitivity towards in situ produced reuterin suggests L. reuteri combined with glycerol, as a possible intervention option to reduce Campylobacter in the food chain.

Acrolein-stressed threshold adaptation alters the molecular and metabolic bases of an engineered Saccharomyces cerevisiae to improve glutathione production

Acrolein (Acr) was used as a selection agent to improve the glutathione (GSH) overproduction of the prototrophic strain W303-1b/FGP^PT. After two rounds of adaptive laboratory evolution (ALE), an unexpected result was obtained wherein identical GSH production was observed in the selected isolates. Then, a threshold selection mechanism of Acr-stressed adaption was clarified based on the formation of an Acr-GSH adduct, and a diffusion coefficient (0.36 ± 0.02 μmol·min⁻¹·OD₆₀₀⁻¹) was calculated. Metabolomic analysis was carried out to reveal the molecular bases that triggered GSH overproduction. The results indicated that all three precursors (glutamic acid (Glu), glycine (Gly) and cysteine (Cys)) needed for GSH synthesis were at a relativity higher concentration in the evolved strain and that the accumulation of homocysteine (Hcy) and cystathionine might promote Cys synthesis and then improve GSH production. In addition to GSH and Cys, it was observed that other non-protein thiols and molecules related to ATP generation were at obviously different levels. To divert the accumulated thiols to GSH biosynthesis, combinatorial strategies, including deletion of cystathionine β-lyase (STR3), overexpression of cystathionine γ-lyase (CYS3) and cystathionine β-synthase (CYS4), and reduction of the unfolded protein response (UPR) through up-regulation of protein disulphide isomerase (PDI), were also investigated.

Acrolein contributes strongly to antimicrobial and heterocyclic amine transformation activities of reuterin

Glycerol/diol dehydratases catalyze the conversion of glycerol to 3-hydroxypropionaldehyde (3-HPA), the basis of a multi-component system called reuterin. Reuterin has antimicrobial properties and undergoes chemical conjugation with dietary heterocyclic amines (HCAs). In aqueous solution reuterin is in dynamic equilibrium with the toxicant acrolein. It was the aim of this study to investigate the extent of acrolein formation at various physiological conditions and to determine its role in biological and chemical activities. The application of a combined novel analytical approach including IC-PAD, LC-MS and NMR together with specific acrolein scavengers suggested for the first time that acrolein, and not 3-HPA, is the active compound responsible for HCA conjugation and antimicrobial activity attributed to reuterin. As formation of the HCA conjugate was observed in vivo, our results imply that acrolein is formed in the human gut with implications on detoxification of HCAs. We propose to re-define the term reuterin to include acrolein.

Low dose cyclophosphamide: Mechanisms of T cell modulation

Cyclophosphamide is considered one of the most successful chemotherapy drugs and is listed on the World Health Organisations List of Essential Medicines. Since its initial synthesis in 1958, it has been widely used to treat a range of cancers but its use has been declining due to the advent of platinum based and other chemotherapy agents. However, cyclophosphamide is still used either as a single agent or as adjuvant therapy to treat lymphomas, and breast and ovarian cancers at much lower doses. The efficacy of low dose cyclophosphamide is primarily due to its ability to promote anti-tumour immunity, by selectively depleting regulatory T cells and enhancing effector T cell function. Compared to effecter T cells, regulatory T cells have metabolic adaptations that make them more susceptible to cyclophosphamide-mediated cytotoxicity. In this review, we highlight the potential for improving the efficacy of low dose cyclophosphamide by combining insights on the mechanisms of cyclophosphamide-mediated cytotoxicity, and how these cytotoxic effects of cyclophosphamide influence T cell function, thereby contributing to anti-tumour immunity.

Acrolein-exposed normal human lung fibroblasts in vitro: cellular senescence, enhanced telomere erosion, and degradation of Werner's syndrome protein

BACKGROUND

Acrolein is a ubiquitous environmental hazard to human health. Acrolein has been reported to activate the DNA damage response and induce apoptosis. However, little is known about the effects of acrolein on cellular senescence.

OBJECTIVES

We examined whether acrolein induces cellular senescence in cultured normal human lung fibroblasts (NHLF).

METHODS

We cultured NHLF in the presence or absence of acrolein and determined the effects of acrolein on cell proliferative capacity, senescence-associated β-galactosidase activity, the known senescence-inducing pathways (e.g., p53, p21), and telomere length.

RESULTS

We found that acrolein induced cellular senescence by increasing both p53 and p21. The knockdown of p53 mediated by small interfering RNA (siRNA) attenuated acrolein-induced cellular senescence. Acrolein decreased Werner's syndrome protein (WRN), a member of the RecQ helicase family involved in DNA repair and telomere maintenance. Acrolein-induced down-regulation of WRN protein was rescued by p53 knockdown or proteasome inhibition. Finally, we found that acrolein accelerated p53-mediated telomere shortening.

CONCLUSIONS

These results suggest that acrolein induces p53-mediated cellular senescence accompanied by enhanced telomere attrition and WRN protein down-regulation.

Acrolein scavengers: reactivity, mechanism and impact on health

Acrolein (ACR) is an α,β-unsaturated aldehyde that exists extensively in the environment and (thermally processed) foods. It can also be generated through endogenous metabolism. Its high electrophilicity makes this aldehyde notorious for its facile reaction with biological nucleophiles, leading to the modification of proteins/DNA and depletion of glutathione. Recent studies also have revealed its roles in disturbing various cell signing pathways in biological systems. With growing evidences of ACR's implication in human diseases, strategies to eliminate its hazardous impacts are of great importance. One of the intervention strategies is the application of reactive scavengers to directly trap ACR. Some known ACR scavengers include sulfur (thiol)-containing and nitrogen (amino)-containing compounds as well as the newly emerging natural polyphenols. In this review, the interactions between ACR and its scavengers are highlighted. The discussion about ACR scavengers is mainly focused on their chemical reactivity, trapping mechanisms as well as their roles extended to biological relevance. In addition to their direct trapping effect on ACR, these scavengers might possess multiple functions and offer additional benefits against ACR-induced toxicity. A comprehensive understanding of the mechanism involved may help to establish ACR scavenging as a novel therapeutic intervention against human diseases that are associated with ACR and/or oxidative stress.

Unraveling the hydroxypropionaldehyde (HPA) system: an active antimicrobial agent against human pathogens

The hydroxypropionaldehyde (HPA) system is a natural defense system synthesized by the probiotic bacterium Lactobacillus reuteri. To elucidate which of the molecules composing the HPA system (3-hydroxypropionaldehyde (3-HPA), reuterin (HPA dimer), and HPA hydrate) is responsible for the potent antimicrobial activity in biological systems, a combination of biochemical, genetic, and proteomic assays was used. The HPA system reacts with sulfhydryl-containing compounds such as cysteine and reduced glutathione (GSH) in solution. In situ, GSH knock-out Escherichia coli is significantly more susceptible to HPA-mediated cell death than E. coli wild type; GSH supplementation protects either bacteria from HPA attack. Proteomic analysis of HPA-treated bacteria ( Haemophilus influenzae ) revealed induction of redox- and heat shock-related proteins. A new antimicrobial mechanism of HPA is proposed, whereby the activity of HPA leads to depletion of free SH- groups in GSH and proteins through the action of 3-hydroxypropionaldehyde, causing an imbalance of the cellular redox status, ultimately resulting in cell death.

Mutagenicity of acrolein and acrolein-induced DNA adducts

Acrolein mutagenicity relies on DNA adduct formation. Reaction of acrolein with deoxyguanosine generates alpha-hydroxy-1, N(2)-propano-2'-deoxyguanosine (alpha-HOPdG) and gamma-hydroxy-1, N(2)-propano-2'-deoxyguanosine (gamma-HOPdG) adducts. These two DNA adducts behave differently in mutagenicity. gamma-HOPdG is the major DNA adduct and it can lead to interstrand DNA-DNA and DNA-peptide/protein cross-links, which may induce strong mutagenicity; however, gamma-HOPdG can be repaired by some DNA polymerases complex and lessen its mutagenic effects. alpha-HOPdG is formed much less than gamma-HOPdG, but difficult to be repaired, which contributes to accumulation in vivo. Results of acrolein mutagenicity studies haven't been confirmed, which is mainly due to the conflicting mutagenicity data of the major acrolein adduct (gamma-HOPdG). The minor alpha-HOPdG is mutagenic in both in vitro and in vivo test systems. The role of alpha-HOPdG in acrolein mutagenicity needs further investigation. The inconsistent result of acrolein mutagenicity can be attributed, at least partially, to a variety of acrolein-DNA adducts formation and their repair in diverse detection systems. Recent results of detection of acrolein-DNA adduct in human lung tissues and analysis of P53 mutation spectra in acrolein-treated cells may shed some light on mechanisms of acrolein mutagenicity. These aspects are covered in this mini review.

Inhibitory activity spectrum of reuterin produced by Lactobacillus reuteri against intestinal bacteria

Background

Reuterin produced from glycerol by Lactobacillus reuteri, a normal inhabitant of the human intestine, is a broad-spectrum antimicrobial agent. It has been postulated that reuterin could play a role in the probiotic effects of Lb. reuteri. Reuterin is active toward enteropathogens, yeasts, fungi, protozoa and viruses, but its effect on commensal intestinal bacteria is unknown. Moreover reuterin's mode of action has not yet been elucidated. Glutathione, a powerful antioxidant, which also plays a key role in detoxifying reactive aldehydes, protects certain bacteria from oxidative stress, and could also be implicated in resistance to reuterin.

The aim of this work was to test the activity of reuterin against a representative panel of intestinal bacteria and to study a possible correlation between intracellular low molecular weight thiols (LMW-SH) such as glutathione, hydrogen peroxide and/or reuterin sensitivity. Reuterin was produced by Lb. reuteri SD2112 in pure glycerol solution, purified and used to test the minimal inhibitory (MIC) and minimal bactericidal concentrations (MBC). Hydrogen peroxide sensitivity and intracellular LMW-SH concentration were also analysed.

Results

Our data showed that most tested intestinal bacteria showed MIC below that for a sensitive indicator Escherichia coli (7.5–15 mM). Lactobacilli and Clostridium clostridioforme were more resistant with MIC ranging from 15 to 50 mM. No correlation between bacterial intracellular concentrations of LMW-SH, including glutathione, and reuterin or hydrogen peroxide sensitivities were found.

Conclusion

Our data showed that intestinal bacteria were very sensitive to reuterin and that their intracellular concentration of LMW-SH was not directly linked to their capacity to resist reuterin or hydrogen peroxide. This suggests that detoxification by LMW-SH such as glutathione is not a general mechanism and that other mechanisms are probably involved in bacterial tolerance to reuterin and hydrogene peroxide.

P38 and ERK mitogen-activated protein kinases mediate acrolein-induced apoptosis in Chinese hamster ovary cells

Acrolein, which is a highly reactive alpha,beta-unsaturated aldehyde generated by lipid peroxidation, can affect cells and tissues and cause various disorders. Increased levels of unsaturated aldehydes play an important role in the pathogenesis of a number of human diseases such as Alzheimer's disease, atherosclerosis and diabetes. Acrolein is a highly ubiquitous toxic environmental pollutant. Because of human exposure, there is a need for investigating the mechanisms involved in acrolein toxicity at the cellular and molecular levels. Acrolein can induce cell death by apoptosis, although the mechanisms are not entirely clear. The present study investigates whether mitogen-activated protein kinases (MAPKs) play a role in activation of apoptosis by acrolein. Our findings show that acrolein-mediated apoptosis is in fact MAPK-dependent in Chinese hamster ovary cells. The MAP family kinases, including ERK and p38 kinase, and the transcription factor c-Jun were all activated by phosphorylation after 1 h exposure to acrolein. Phosphorylation of ERK and p38 kinases and their blockade by an ERK inhibitor, U0126, or a p38 inhibitor, SB203580, respectively, suggested that activation of apoptosis by acrolein is ERK- and p38-dependent. Thus, blockade of ERK and p38 inhibited chromatin condensation, caspase-7 and -9 activation as well as ICAD cleavage induced by acrolein. JNK and AKT kinases seem to be implicated in survival pathways against acrolein insult, since their respective inhibitors, SP600125 and LY294002/Wortmannin switched the mode of cell death from apoptosis to total necrosis. Finally, acrolein induced phosphorylation of the pro-apoptotic factor p53 which is responsible for transcription of pro-apoptotic factors such as Bax and Fas ligand. These results provide new information demonstrating the implication of MAPKs and AKT in acrolein-induced apoptosis, and this information may be useful for understanding the pathogenesis of a number of tissue diseases and environmental toxicity in response to acrolein.

Genotoxicity of diphenyl diselenide in bacteria and yeast

Diphenyl diselenide (DPDS) is an electrophilic reagent used in the synthesis of a variety of pharmacologically active organic selenium compounds. This may increase the risk of human exposure to the chemical at the workplace. We have determined its mutagenic potential in the Salmonella/microsome assay and used the yeast Saccharomyces cerevisiae to assay for putative genotoxicity, recombinogenicity and to determine whether DNA damage produced by DPDS is repairable. Only in exponentially growing cultures was DPDS able to induce frameshift mutations in S. typhimurium and haploid yeast and to increase crossing over and gene conversion frequencies in diploid strains of S. cerevisiae. Thus, DPDS presents a behavior similar to that of an intercalating agent. Mutants defective in excision-resynthesis repair (rad3, rad1), in error-prone repair (rad6) and in recombinational repair (rad52) showed higher than WT-sensitivity to DPDS. It appears that this compound is capable of inducing single and/or double strand breaks in DNA. An epistatic interaction was shown between rad3-e5 and rad52-1 mutant alleles, indicating that excision-resynthesis and strand-break repair may possess common steps in the repair of DNA damage induced by DPDS. DPDS was able to enhance the mutagenesis induced by oxidative mutagens in bacteria. N-acetylcysteine, a glutathione biosynthesis precursor, prevented mutagenesis induced by DPDS in yeast. We have shown that DPDS is a weak mutagen which probably generates DNA strand breaks through both its intercalating action and pro-oxidant effect.

A novel Nudix hydrolase for oxidized purine nucleoside triphosphates encoded by ORFYLR151c (PCD1 gene) in Saccharomyces cerevisiae

A search for candidates for a functional homologue of Escherichia coli MutT in yeast Saccharomyces cerevisiae was made in the NCBI-BLAST database using the Nudix box, a short amino acid sequence conserved among E.coli MutT, Pseudomonoas vulgaris MutT, and human, rat and mouse MTH1. Among five candidates, we focused on the open reading frame YLR151c, because it had a region with approximately 76% similarity to the N-terminal half of MutT including the Nudix box. We thus evaluated the ability of YLR151c as a functional homologue of E.coli MutT in S.cerevisiae. Expression of YLR151c was able to suppress the transversion from A:T to C:G caused by misincorporation of the oxidized nucleotide 8-oxo-dGTP in the E.coli mutT-deficient strain. The disruption of the YLR151c in yeast strain caused approximately 14-fold increase in the frequency of spontaneous mutation compared to the wild type. Additionally, biochemical analysis indicated that GST-YLR151c fusion protein possessed pyrophosphatase activity for both 7,8-dihydro-8-oxo-2'-deoxyguanosine triphosphate (8-oxo-dGTP) and 1,2-dihydro-2-hydroxy-2'-deoxyadenosine triphosphate (2-OH-dATP). The specific activity of GST-YLR151c for 8-oxo-dGTP was 5.6 x 10(-3) microM(-1) s(-1), which was similar to that of RibA, a backup enzyme for MutT in E.coli, but was 150-fold lower than that of hMTH1. From these results, we conclude that YLR151c has an ability to prevent spontaneous mutagenesis via sanitization of oxidized nucleotides, and that it may be the functional homologue of E.coli MutT in S.cerevisiae.

Mutagenic target for hydroxyl radicals generated in Escherichia coli mutant deficient in Mn- and Fe- superoxide dismutases and Fur, a repressor for iron-uptake systems

We previously reported that mutations in Mn- and Fe-superoxide dismutases and Fur, a repressor for iron uptake systems, simulated generation of hydroxyl radicals, and caused hypermutability in Escherichia coli. The predominant type of spontaneous mutation was GC --> TA, followed by AT --> CG, suggesting the involvement of 7,8-dihydro-8-oxoguanine (8-oxoG) and 1,2-dihydro-2-oxoadenine (2-oxoA) in DNA as well as 7,8-dihydro-8-oxodeoxyguanosine triphosphate (8-oxodGTP) and 1,2-dihydro-2-oxodeoxyadenosine triphosphate (2-oxodATP) in the nucleotide pool. To determine the targets contributing to oxidative mutagenesis, DNA or nucleotides, we characterized spontaneous mutations and compared the distribution to those in mutMY and mutT strains, in which GC --> TA and AT --> CG were predominantly induced, respectively. The hotspots and sequence contexts where AT --> CG occurred frequently in sodAB fur strain were almost identical to those in mutT strain,whereas, those where GC --> TA occurred frequently in sodAB fur strain were quite different from those in mutMY strain. These observations suggested that AT --> CG is due to 8-oxodGTP, while GC --> TA is produced by some other lesion(s). The 2-oxodATP is also a major oxidative lesion in nucleotides, and strongly induces GC --> TA. The expression of cDNA for MTH1, which can hydrolyze 2-oxodATP as well as 8-oxodGTP, partially but significantly, suppressed the GC --> TA mutator phenotype of the sodAB fur strain, whereas, it did not for the mutMY strain. Additionally, the sequence contextby 2-oxodATP in E. coli was similar to that in sodAB fur strain. These results suggested that the targets contributing to oxidative mutagenesis in sodAB fur strain are nucleotides such as dGTP and dATP, rather than DNA.