4-Hydroxynonenal inhibits cell proliferation and alters differentiation pathways in human fetal liver hematopoietic stem cells

GPX4 and FSP1 Expression in Lung Adenocarcinoma: Prognostic Implications and Ferroptosis-Based Therapeutic Strategies

Background: Primary lung cancer is among the cancers with the poorest prognosis, having the highest mortality rate among men and the second highest among women in Japan. While surgery is the primary treatment, advanced stages often require pharmacotherapy. Recently, ferroptosis, an iron-dependent form of cell death caused by lipid peroxidation, has gained attention as a potential therapeutic strategy. This study investigated the prognostic impact of lipid peroxidation marker and regulators involved in ferroptosis in lung adenocarcinoma. Methods: We analyzed 207 patients who underwent resection surgery for lung adenocarcinoma at Tokyo Medical and Dental University Hospital. Immunohistochemistry was used to evaluate the expression levels of glutathione peroxidase 4 (GPX4), ferroptosis suppressor protein 1 (FSP1), and 4-hydroxy-2-nonenal (4-HNE). The association between these markers and clinicopathological factors was assessed, and in vitro experiments were conducted to examine the effects of these markers on cell death. Results: Low cytoplasmic accumulation of 4-HNE and low expression of GPX4 were associated with a worse prognosis, and low FSP1 expression was associated with unfavorable relapse-free survival. In vitro experiments demonstrated that 4-HNE inhibited cell proliferation, and combined inhibition of GPX4 and FSP1 induced ferroptosis. Conclusions: These findings suggest that lipid peroxidation markers and regulators can serve as prognostic biomarkers and therapeutic targets in lung adenocarcinoma.

Physiological Signaling Functions of Reactive Oxygen Species in Stem Cells: From Flies to Man

Reactive oxygen species (ROS), superoxide anion and hydrogen peroxide, are generated as byproducts of oxidative phosphorylation in the mitochondria or via cell signaling-induced NADPH oxidases in the cytosol. In the recent two decades, a plethora of studies established that elevated ROS levels generated by oxidative eustress are crucial physiological mediators of many cellular and developmental processes. In this review, we discuss the mechanisms of ROS generation and regulation, current understanding of ROS functions in the maintenance of adult and embryonic stem cells, as well as in the process of cell reprogramming to a pluripotent state. Recently discovered cell-non-autonomous ROS functions mediated by growth factors are crucial for controlling cell differentiation and cellular immune response in Drosophila. Importantly, many physiological functions of ROS discovered in Drosophila may allow for deciphering and understanding analogous processes in human, which could potentially lead to the development of novel therapeutic approaches in ROS-associated diseases treatment.

Modification of stem cell states by alcohol and acetaldehyde

Ethanol (EtOH) is a recreationally ingested compound that is both teratogenic and carcinogenic in humans. Because of its abundant consumption worldwide and the vital role of stem cells in the formation of birth defects and cancers, delineating the effects of EtOH on stem cell function is currently an active and urgent pursuit of scientific investigation to explicate some of the mechanisms contributing to EtOH toxicity. Stem cells represent a primordial, undifferentiated phase of development; thus encroachment on normal physiologic processes of differentiation into terminal lineages by EtOH can greatly alter the function of progenitors and terminally differentiated cells, leading to pathological consequences that manifest as fetal alcohol spectrum disorders and cancers. In this review we explore the disruptive role of EtOH in differentiation of stem cells. Our primary objective is to elucidate the mechanisms by which EtOH alters differentiation-related gene expression and lineage specifications, thus modifying stem cells to promote pathological outcomes. We additionally review the effects of a reactive metabolite of EtOH, acetaldehyde (AcH), in causing both differentiation defects in stem cells as well as genomic damage that incites cellular aging and carcinogenesis.

Different Effects of Knockouts in ALDH2 and ACSS2 on Embryonic Stem Cell Differentiation

BACKGROUND

Ethanol (EtOH) is a teratogen that causes severe birth defects, but the mechanisms by which EtOH affects stem cell differentiation are unclear. Our goal here is to examine the effects of EtOH and its metabolites, acetaldehyde (AcH) and acetate, on embryonic stem cell (ESC) differentiation.

METHODS

We designed ESC lines in which aldehyde dehydrogenase (ALDH2, NCBI#11669) and acyl-CoA synthetase short-chain family member 2 (ACSS2, NCBI#60525) were knocked out by CRISPR-Cas9 technology. We selected these genes because of their key roles in EtOH oxidation in order to dissect the effects of EtOH metabolism on differentiation.

RESULTS

By using kinetic assays, we confirmed that AcH is primarily oxidized by ALDH2 rather than ALDH1A2. We found increases in mRNAs of differentiation-associated genes (Hoxa1, Cyp26a1, and RARβ2) upon EtOH treatment of WT and Acss2-/- ESCs, but not Aldh2-/- ESCs. The absence of ALDH2 reduced mRNAs of some pluripotency factors (Nanog, Sox2, and Klf4). Treatment of WT ESCs with AcH or 4-hydroxynonenal (4-HNE), another substrate of ALDH2, increased differentiation-associated transcripts compared to levels in untreated cells. mRNAs of genes involved in retinoic acid (RA) synthesis (Stra6 and Rdh10) were also increased by EtOH, AcH, and 4-HNE treatment. Retinoic acid receptor-γ (RARγ) is required for both EtOH- and AcH-mediated increases in Hoxa1 and Stra6, demonstrating the critical role of RA:RARγ signaling in AcH-induced ESC differentiation.

CONCLUSIONS

ACSS2 knockouts showed no changes in differentiation phenotype, while pluripotency-related transcripts were decreased in ALDH2 knockout ESCs. We demonstrate that AcH increases differentiation-associated mRNAs in ESCs via RARγ.

Carnosine Supplementation Mitigates the Deleterious Effects of Particulate Matter Exposure in Mice

Background Exposure to fine airborne particulate matter ( PM 2.5) induces quantitative and qualitative defects in bone marrow-derived endothelial progenitor cells of mice, and similar outcomes in humans may contribute to vascular dysfunction and the cardiovascular morbidity and mortality associated with PM 2.5 exposure. Nevertheless, mechanisms underlying the pervasive effects of PM 2.5 are unclear and effective interventional strategies to mitigate against PM 2.5 toxicity are lacking. Furthermore, whether PM 2.5 exposure affects other types of bone marrow stem cells leading to additional hematological or immunological dysfunction is not clear. Methods and Results Mice given normal drinking water or that supplemented with carnosine, a naturally occurring, nucleophilic di-peptide that binds reactive aldehydes, were exposed to filtered air or concentrated ambient particles. Mice drinking normal water and exposed to concentrated ambient particles demonstrated a depletion of bone marrow hematopoietic stem cells but no change in mesenchymal stem cells. However, HSC depletion was significantly attenuated when the mice were placed on drinking water containing carnosine. Carnosine supplementation also increased the levels of carnosine-propanal conjugates in the urine of CAPs-exposed mice and prevented the concentrated ambient particles-induced dysfunction of endothelial progenitor cells as assessed by in vitro and in vivo assays. Conclusions These results suggest that exposure to PM 2.5 has pervasive effects on different bone marrow stem cell populations and that PM 2.5-induced hematopoietic stem cells depletion, endothelial progenitor cell dysfunction, and defects in vascular repair can be mitigated by excess carnosine. Carnosine supplementation may be a viable approach for preventing PM 2.5-induced immune dysfunction and cardiovascular injury in humans.

Characterization of the molecular mechanisms underlying increased ischemic damage in the aldehyde dehydrogenase 2 genetic polymorphism using a human induced pluripotent stem cell model system

Nearly 8% of the human population carries an inactivating point mutation in the gene that encodes the cardioprotective enzyme aldehyde dehydrogenase 2 (ALDH2). This genetic polymorphism (ALDH2*2) is linked to more severe outcomes from ischemic heart damage and an increased risk of coronary artery disease (CAD), but the underlying molecular bases are unknown. We investigated the ALDH2*2 mechanisms in a human model system of induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) generated from individuals carrying the most common heterozygous form of the ALDH2*2 genotype. We showed that the ALDH2*2 mutation gave rise to elevated amounts of reactive oxygen species and toxic aldehydes, thereby inducing cell cycle arrest and activation of apoptotic signaling pathways, especially during ischemic injury. We established that ALDH2 controls cell survival decisions by modulating oxidative stress levels and that this regulatory circuitry was dysfunctional in the loss-of-function ALDH2*2 genotype, causing up-regulation of apoptosis in cardiomyocytes after ischemic insult. These results reveal a new function for the metabolic enzyme ALDH2 in modulation of cell survival decisions. Insight into the molecular mechanisms that mediate ALDH2*2-related increased ischemic damage is important for the development of specific diagnostic methods and improved risk management of CAD and may lead to patient-specific cardiac therapies.

Chlorpyrifos Induces MLL Translocations Through Caspase 3-Dependent Genomic Instability and Topoisomerase II Inhibition in Human Fetal Liver Hematopoietic Stem Cells

Household pesticide exposure during pregnancy has been associated with a more than 2-fold increased risk in infant leukemia, and chlorpyrifos (CPF) is among the most frequently applied insecticides. During early fetal development, liver is a hematopoietic organ with majority of cells being CD34(+) hematopoietic stem cells (CD34(+)HSC). The in utero injury to CD34(+)HSC has been known to underlie the pathogenesis of several blood disorders, often involving rearrangements of the mixed-lineage leukemia (MLL) gene on 11q23. In this study, we evaluated the leukemogenic potential of CPF in human fetal liver-derived CD34(+)HSC. Specifically, exposure to 10 μM CPF led to decrease in viability, inhibition in proliferation and induction of DNA double-strand breaks (DSBs) and occurrence of MLL(+) rearrangements. In particular, we observed CPF-mediated cell cycle disturbance as shown by G0/G1 arrest, in contrast to etoposide (VP-16), an anticancer drug used as a positive control and known to induce G2/M arrest. Further study on mechanisms underlying DNA DSBs and MLL(+) rearrangements revealed that CPF might act as topoisomerase II poison, a mechanism of action similar to VP-16. On the other hand, CPF was also shown to induce early apoptosis through active caspase-3 activation, a pathway known to underlie DNA DSBs and MLL(+) translocations. Our data indicate that in utero injury of CD34(+)HSC by CPF may contribute to the increased risk of infant leukemia. Future work will elucidate the mechanism and the type of CPF-induced MLL(+) translocations in HSC.

Modulation of keratinocyte expression of antioxidants by 4-hydroxynonenal, a lipid peroxidation end product

4-Hydroxynonenal (4-HNE) is a lipid peroxidation end product generated in response to oxidative stress in the skin. Keratinocytes contain an array of antioxidant enzymes which protect against oxidative stress. In these studies, we characterized 4-HNE-induced changes in antioxidant expression in mouse keratinocytes. Treatment of primary mouse keratinocytes and PAM 212 keratinocytes with 4-HNE increased mRNA expression for heme oxygenase-1 (HO-1), catalase, NADPH:quinone oxidoreductase (NQO1) and glutathione S-transferase (GST) A1-2, GSTA3 and GSTA4. In both cell types, HO-1 was the most sensitive, increasing 86-98 fold within 6h. Further characterization of the effects of 4-HNE on HO-1 demonstrated concentration- and time-dependent increases in mRNA and protein expression which were maximum after 6h with 30 μM. 4-HNE stimulated keratinocyte Erk1/2, JNK and p38 MAP kinases, as well as PI3 kinase. Inhibition of these enzymes suppressed 4-HNE-induced HO-1 mRNA and protein expression. 4-HNE also activated Nrf2 by inducing its translocation to the nucleus. 4-HNE was markedly less effective in inducing HO-1 mRNA and protein in keratinocytes from Nrf2-/- mice, when compared to wild type mice, indicating that Nrf2 also regulates 4-HNE-induced signaling. Western blot analysis of caveolar membrane fractions isolated by sucrose density centrifugation demonstrated that 4-HNE-induced HO-1 is localized in keratinocyte caveolae. Treatment of the cells with methyl-β-cyclodextrin, which disrupts caveolar structure, suppressed 4-HNE-induced HO-1. These findings indicate that 4-HNE modulates expression of antioxidant enzymes in keratinocytes, and that this can occur by different mechanisms. Changes in expression of keratinocyte antioxidants may be important in protecting the skin from oxidative stress.

Role of 4-hydroxynonenal and its metabolites in signaling

Available evidence from a multitude of studies on the effects of 4-hydroxynonenal (HNE) on cellular processes seem to converge on some common themes: (i) concentration-dependent opposing effects of HNE on key signaling components (e.g. protein kinase C, adenylate cyclase) predict that certain constitutive levels of HNE may be needed for normal cell functions - lowering of this constitutive HNE level in cells promotes proliferative machinery while an increase in this level promotes apoptotic signaling; (ii) HNE is a common denominator in stress-induced apoptosis caused by H(2)O(2), superoxide, UV, heat or oxidant chemicals such as doxorubicin; and (iii) HNE can modulate ligand-independent signaling by membrane receptors such as EGFR or Fas (CD95) and may act as a sensor of external stimuli for eliciting stress-response. Against a backdrop of various reported effects of HNE, in vitro and in vivo, we have critically evaluated the above mentioned hypotheses suggesting a key role of HNE in signaling.

Oxidative stress-induced biomarkers for stem cell-based chemical screening

Stem cells have been considered for their potential in pharmaceutical research, as well as for stem cell-based therapy for many diseases. Despite the potential for their use, the challenge remains to examine the safety and efficacy of stem cells for their use in therapies. Recently, oxidative stress has been strongly implicated in the functional regulation of cell behavior of stem cells. Therefore, development of rapid and sensitive biomarkers, related to oxidative stress is of growing importance in stem cell-based therapies for treating various diseases. Since stem cells have been implicated as targets for carcinogenesis and might be the origin of "cancer stem cells", understanding of how oxidative stress-induced signaling, known to be involved in the carcinogenic process could lead to potential screening of cancer chemopreventive and chemotherapeutic agents. An evaluation of antioxidant states reducing equivalents like GSH and superoxide dismutase (SOD), as well as reactive oxygen species (ROS) and nitric oxide (NO) generation, can be effective markers in stem cell-based therapies. In addition, oxidative adducts, such as 4-hydroxynonenal, can be reliable markers to detect cellular changes during self-renewal and differentiation of stem cells. This review highlights the biomarker development to monitor oxidative stress response for stem cell-based chemical screening.

Effect of bentazon on growth and physiological responses of marine diatom: Chaetoceros gracilis

The herbicide bentazon (CASRN 25057-89-0) is extensively used in agriculture in Brittany (France) to replace atrazine. Bentazon is not readily adsorbed by soil and therefore it enters adjacent freshwater ecosystems, making its way to estuarine and marine waters areas. Information regarding its effects on marine ecosystems is scarce. Phytotoxicity assessments were conducted in the laboratory on the common diatom Chaetoceros gracilis using both the active ingredient and its formulated product (Basamaïs). The 3 day EC(50) using cell counts were, respectively, 150 mg/L and 60 microg/L for bentazon active ingredient and for bentazon-formulated while cellular volume was increased. Although bentazon is known as a photosystem II inhibitor, it produced an increase of pigment (chlorophylls a, c, and carotenoids) content, ATP synthesis, rates of photosynthesis and respiration, and TBARS formation. Therefore, pigments cannot be used as biomarkers of toxicity. Algal cell recovery from bentazon effects occurred after 6-9 days, suggesting a tolerance mechanism.

Self-regulatory role of 4-hydroxynonenal in signaling for stress-induced programmed cell death

Within the last two decades, 4-hydroxynonenal has emerged as an important second messenger involved in the regulation of various cellular processes. Our recent studies suggest that HNE can induce apoptosis in various cells through the death receptor Fas (CD95)-mediated extrinsic pathway as well as through the p53-dependent intrinsic pathway. Interestingly, through its interaction with the nuclear protein Daxx, HNE can self-limit its apoptotic role by translocating Daxx to cytoplasm where it binds to Fas and inhibits Fas-mediated apoptosis. In this paper, after briefly describing recent studies on various biological activities of HNE, based on its interactions with Fas, Daxx, and p53, we speculate on possible mechanisms through which HNE may affect a multitude of cellular processes and draw a parallel between signaling roles of H(2)O(2) and HNE.

The role of mitochondrial and oxidative injury in BDE 47 toxicity to human fetal liver hematopoietic stem cells

The polybrominated diphenyl ethers (PBDEs) are a group of flame retardants whose residues have markedly increased in the environment and in human tissues during the last decade. Of the various congeners, BDE 47 (2,2',4,4'-tetrabromodiphenyl ether) is typically the predominant congener observed in fish and wildlife samples, as well as in human tissues. Several studies indicate in utero transfer of PBDEs during pregnancy with residues accumulating in fetal tissues, and thus the potential for BDE 47-mediated injury in utero is of concern. In this study, we examined the mechanisms of BDE 47-mediated injury to primary human fetal liver hematopoietic stem cells (HSCs), which comprise a large proportion of fetal hepatic cells and play a key role in hematopoiesis during fetal development. Incubation of fetal liver HSCs with BDE 47 led to a loss of mitochondrial membrane potential and the onset of apoptosis. These effects were observed in the low micromolar range of BDE 47 exposures. At higher concentrations, BDE 47 elicited a loss of viability, which was accompanied by the generation of reactive oxygen species and peroxidation of HSC lipids. Preincubation of fetal liver HSCs with N-acetylcysteine, a glutathione (GSH) precursor, caused an increase in cellular GSH concentrations, restored mitochondrial redox status, and ameliorated the toxicity of BDE 47. BDE 47-mediated cytotoxicity or oxidative injury was not evident at the lower concentrations (< 1microM). Collectively, these data support a role for oxidative stress in the cytotoxicity of BDE 47 and indicate that oxidative stress-associated biomarkers may be useful in assessing the sublethal effects of BDE 47 toxicity in other models. However, the fact that BDE 47 undergoes a concentration-dependent accumulation in other primary cells in media that can underestimate cellular concentrations (W. R. Mundy et al., 2004, Toxicol. Sci. 82, 164-169) suggests that the HSC cell injury observed in our study may be of less relevance to human in utero PBDE exposures.

Transfection of HepG2 cells with hGSTA4 provides protection against 4-hydroxynonenal-mediated oxidative injury

4-Hydroxynonenal (4-HNE) is a mutagenic alpha,beta-unsaturated aldehyde produced during oxidative injury that is conjugated by several glutathione S-transferase (GST) isoforms. The alpha class human GSTA4-4 enzyme (hGSTA4-4) has a particularly high catalytic efficiency toward 4-HNE conjugation. However, hGST4-4 expression is low in most human cells and there are other aldehyde metabolizing enzymes that detoxify 4-HNE. In the current study, we determined the effect of over-expression of hGSTA4 mRNA on the sensitivity of HepG2 cells to 4-HNE injury. HepG2 cells transfected with an hGSTA4 vector construct exhibited high steady-state hGSTA4 mRNA, high GST-4-HNE catalytic activities, but lower basal glutathione (GSH) concentrations relative to insert-free vector (control) cells. Exposure to 4-HNE elicited an increase in GSH concentrations in the control and hGSTA4 cells, although the dose-response of GSH induction differed among the two cell types. Specifically, hGSTA4 cells had significantly higher GSH concentrations when exposed to 5-15 microM 4-HNE, but not at 20 microM 4-HNE, suggesting extensive GSH utilization at high concentrations of 4-HNE. The hGSTA4 cells exhibited a significant growth advantage relative to control cells in the absence of 4-HNE, and a trend towards increased growth at low dose exposures to 4-HNE. However, the hGSTA4 cells did not exhibit a growth advantage relative to control cells at higher 4-HNE exposures associated with increased GSH utilization. As expected, the hGSTA4 cells showed resistance to 4-HNE stimulated lipid peroxidation at all 4-HNE doses. In summary, our data indicates that over-expression of hGSTA4 at levels conferring high GST-4-HNE conjugating activity confers a partial growth advantage to HepG2 cells and protects against 4-HNE oxidative injury. However, the loss of proliferative capacity of hGSTA4 cells challenged with levels of 4-HNE associated with severe oxidative stress indicates a role of other aldehyde metabolizing enzymes, and/or GSH-electrophile transporter proteins, in providing full cellular protection against 4-HNE toxicity.

Cytochrome p450 and glutathione s-transferase mRNA expression in human fetal liver hematopoietic stem cells

During fetal development, the liver serves as the primary hematopoietic organ in which hematopoietic stem cells (HSC) capable of initiating long-term hematopoiesis comprise a large proportion of the hepatic cell population. Although HSC are potential targets for transplacental chemicals, little is known regarding their xenobiotic biotransformation ability. We quantitated the steady-state mRNA expression of six cytochrome P450 (P450) and 11 glutathione S-transferase (GST) isoforms in CD34(+)-selected HSC isolated from second trimester human fetal liver donors, genotyped donors for polymorphic hGSTM1 and hGSTT1 status, and analyzed gene expression in HSC relative to total liver from donors of similar gestational ages. Several P450 isoforms, including CYP1A1, CYP2E1, CYP3A4, and CYP3A5, were expressed at low levels in HSC (relative mRNA expression CYP3A5 > CYP1A1 > CYP2E1 > CYP3A4). CYP1A2 and CYP3A7 were not detected in HSC. The CYP3A4/5 mRNA expression in HSC was accompanied by detectable CYP3A protein and low midazolam oxidation activity. Several GST isoforms, including hGSTM1, hGSTM2, hGSTM4, and hGSTP1, were significantly higher in HSC as compared with total fetal liver. With the exception of hGSTA4, alpha class GST were not detected in HSC. GST expression in HSC was accompanied by substantial GST catalytic activity toward 1-chloro-2,4-dinitrobenzene. In summary, our data indicate that fetal liver CD34(+)-derived HSC constitutively express several P450 isoforms at low levels relative to total hepatic cell populations but have a higher capacity for GST conjugation reactions through mu and pi class isoforms. The functional ramifications of these observations are discussed relative to the sensitivity of human fetal HSC to transplacental chemical injury.

Cytotoxic effects of various stressors on PC12 cells: involvement of oxidative stress and effect of antioxidants

In order to specifically elucidate the involvement of oxidative stress, the effects of various types of stressors and antioxidants on PC12 cells were examined. In this study, the following four stressors were studied in detail: free radicals generated from 2,2'-azobis(2-amidinopropane) dihydrochloride (AAPH), 4-hydroxynonenal (HNE), 7-ketocholesterol (KC), and arsenic trioxide (As2O3). Undifferentiated PC12 cells were treated with 50% lethal concentration (LC50) of these stressors, and subsequently the viability, apoptosis/necrosis ratio, reactive oxygen species (ROS) production, caspase-3 activity, and protection by antioxidants were measured to elucidate the underlying mechanisms that determine the action of these stressors on PC12 cells. The cytotoxicity did not correlate directly with the intracellular formation of ROS. For example, as compared to AAPH, As2O3 produced considerably smaller amounts of ROS at LC50. As observed in the cells incubated with As2O3, KC and HNE exerted cell toxicity, but with a moderate production of ROS. With the exception of HNE, the apoptosis/necrosis ratio of all the stressors evaluated by annexin V and propidium iodide assays increased with an increase in the incubation time at the LC50 values of these stressors. In accordance with apoptosis ratio, caspase activity was detected in the cells incubated with AAPH, As2O3, and KC, but not HNE at LC50 for 24 h. The protective effect of alpha-tocopherol, 17beta-estradiol, 2,3-dihydro-5-hydroxy-2,2-dipentyl-4,6-di-tert-butylbenzofuran (BO653), glutathione, and N-acetylcysteine (NAC) against cytotoxicity depended on the type of stressors. These antioxidants were found to be effective against the abovementioned stressors, except As2O3 against which only NAC was effective. These results suggest that the involvement of ROS and the protective effect of antioxidants depend on the type of stressors.

Inhibition of Thioredoxin and Thioredoxin Reductase by 4-Hydroxy-2-nonenal in Vitro and in Vivo

Lipid peroxidation is a cellular process that takes place under physiological conditions and particularly after oxidative stress. 4-Hydroxy-2-nonenal (HNE), a major end product of lipid peroxidation, is known to exert a multitude of biological effects and has high reactivity to various cellular components, including DNA and protein. The thioredoxin system, composed of the selenoenzyme thioredoxin reductase (TrxR), thioredoxin (Trx), and NADPH, plays a key role in redox regulation and is involved in many signaling pathways. The selenocysteine (Sec) and cysteine (Cys) residues (Cys-496/Sec-497) in the active site of TrxR and a pair of Cys residues (Cys-32/Cys-35) in Trx are sensitive to various alkylating reagents. Herein, we report a mechanistic study on the inhibition of rat TrxR by HNE. The inhibition occurs with TrxR only in its reduced form and persists after removal of HNE. Inhibition of TrxR by HNE added to cultured HeLa cells is also observed. In addition, HNE inactivates reduced Escherichia coli Trx irreversibly. We proved that the redox residues (Cys-496/Sec-497 in TrxR and Cys-32/Cys-35 in Trx) were primary targets for HNE modification. The covalent adducts formed between HNE and Trx were also confirmed by mass spectrum. Because the thioredoxin system is one of the core regulation enzymes of cells' function, inhibition of both TrxR and Trx by HNE provides a possibly novel mechanism for explanation of its cytotoxic effect and signaling activity, as well as the further damage indirectly caused under oxidative stress conditions.

MLL rearrangements are induced by low doses of etoposide in human fetal hematopoietic stem cells

During fetal development, the liver serves as the primary hematopoietic organ in which hematopoietic stem cells (HSC) comprise a large proportion of hepatic cell populations. Because HSC are capable of initiating long-term hematopoiesis, injury to these cells during pregnancy may play a role in the development of hematopoietic disorders manifested after birth. Of interest is the role of genetic injury to fetal HSC in the etiology of the infant acute leukemias, which are characterized by chromosomal rearrangements in the 11q23 region involving the mixed lineage leukemia (MLL) gene. These gene fusions also occur in leukemias in adults following chemotherapy with etoposide and other inhibitors of DNA topoisomerase II. We used etoposide as a model compound to determine the sensitivity of human fetal HSC to DNA damage and to determine whether we could induce MLL rearrangements in cultured human fetal HSC. Exposure of HSC to etoposide resulted in a dose-dependent loss of viability, with effects observed at low nanomolar concentrations. DNA strand breaks were observed on exposure to 140 nM etoposide, and higher etoposide concentrations stimulated an increase in early lymphoid populations and elicited G2/M cell cycle arrest. Immunophenotyping of MLL translocations revealed a significant increase in positive flow cytometry events at low etoposide concentrations and were consistent with MLL recombination. MLL translocations were confirmed using fluorescent in situ hybridization. In vitro inhibition of DNA topoisomerase II was observed at >or=25 microM etoposide, but was not evident at lower etoposide concentrations associated with DNA damage. Our data indicate that low acute doses of etoposide can cause DNA strand breaks and chromosomal rearrangements involving MLL in human fetal HSC. Ultimately, such injury may have ramifications with regards to transplacental exposures to environmental chemicals linked to the etiology of infant acute leukemias.