Involvement of Fenton reaction products in differentiation induction of K562 human leukemia cells

Antioxidant Expression Response to Free Radicals in Active Men and Women Fallowing to a Session Incremental Exercise; Numerical Relationship Between Antioxidants and Free Radicals

Background

Energy production is a necessary process to continue physical activities, and exercise is associated with more oxygen consumption and increase of oxidative stress. what seems important is the numerical relationship between antioxidant and free radicals. Although the activity of some enzymes increases with physical activities, but it is possible that gene expression of this enzyme is not changed during exercise.

Objectives

The aim of the present study is to investigate the antioxidant enzymes gene expression and changes in malondialdehyde (MDA) and total antioxidant capacity (TAC) levels in men and women affected by a session of incremental exercise and to carefully and numerically assess the relationship between MDA changes and gene expression and activity of antioxidant enzymes.

Materials and Methods

12 active men and 12 active women (21 - 24 years old) participated voluntarily in this study. Peripheral blood samples were taken from the subjects in three phases, before and after graduated exercise test (GXT) and 3 hours later (recovery).

Results

The gene expression of manganese superoxide dismutase (MnSOD) enzyme increased significantly in women in the recovery phase (P < 0.05). Catalase gene expression significantly increased in men in both phases (immediately & recovery) (P < 0.05). But the changes in active women were only significant immediately after the exercise. TAC levels increased significantly in men in the recovery phase and in active women immediately after the exercise (P < 0.05). MDA activity also increased significantly in men in both phases (P < 0.05). However, in women the increase was significant only in the recovery phase (P < 0.05). There was a reverse relationship between changes in MnSOD and copper- and zinc-containing superoxide dismutase (Cu/ZnSOD) levels and MDA in men (P < 0.05). In active women there was also a significant relationship between changes in MDA and gene expression of Cu/ZnSOD and TAC (P < 0.05).

Conclusions

The increase in free radicals during incremental exercises challenges gene expression and activity of antioxidant enzymes. However, despite the negative effects of free radicals, in women, activity and gene expression of antioxidant enzymes respond appropriately to free radicals.

Knockdown of malic enzyme 2 suppresses lung tumor growth, induces differentiation and impacts PI3K/AKT signaling

Mitochondrial malic enzyme 2 (ME2) catalyzes the oxidative decarboxylation of malate to yield CO₂ and pyruvate, with concomitant reduction of dinucleotide cofactor NAD⁺ or NADP⁺. We find that ME2 is highly expressed in many solid tumors. In the A549 non-small cell lung cancer (NSCLC) cell line, ME2 depletion inhibits cell proliferation and induces cell death and differentiation, accompanied by increased reactive oxygen species (ROS) and NADP⁺/NADPH ratio, a drop in ATP, and increased sensitivity to cisplatin. ME2 knockdown impacts phosphoinositide-dependent protein kinase 1 (PDK1) and phosphatase and tensin homolog (PTEN) expression, leading to AKT inhibition. Depletion of ME2 leads to malate accumulation and pyruvate decrease, and exogenous cell permeable dimethyl-malate (DMM) mimics the ME2 knockdown phenotype. Both ME2 knockdown and DMM treatment reduce A549 cell growth in vivo. Collectively, our data suggest that ME2 is a potential target for cancer therapy.

Role of ROS in the protective effect of silibinin on sodium nitroprusside-induced apoptosis in rat pheochromocytoma PC12 cells

Silibinin mostly has been used as hepatoprotectants, but it has other interesting activities, e.g. anti-cancer, cardial protective and brain-protective activities. A previous study demonstrated that silibinin protected amyloid β (Aβ)-induced mouse cognitive disorder by behavioural pharmacological observation. This study assessed the effect of silibinin on sodium nitroprusside (SNP)-treated rat pheochromocytoma PC12 cells. Subsequent morphologic observation, flow cytometric analysis and Western blot analysis indicated that treatment with SNP significantly induced apoptosis in PC12 cells. However, silibinin eliminated the apoptotic effect by reactive oxygen species (ROS) generation, especially hydroxyl free radical. Silibinin-induced autophagy through ROS generation when exerting a protective effect and silibinin-induced autophagy also enhanced the ROS generation since 3-methyladenine (3-MA), a specific autophagy inhibitor, decreased the ROS generation and rapamycin, an autophagy inducer, enhanced the ROS generation. Therefore, there exists a positive feedback loop between autophagy and ROS generation. Autophagy prevented SNP-induced apoptosis, since the addition of 3-MA significantly eliminated the protective effect of silibinin. This protective effect was attributed to the generation of ROS and its two downstream Ras/PI3K/NF-κB and Ras/Raf/MEK/ERK pathways. Both prevented PC12 cells from apoptosis. The PI3K/NF-κB pathway induced autophagy to protect PC12 cells, but the Raf/MEK/ERK pathway directly protected PC12 cells bypassing the autophagic effect.

Salidroside promotes erythropoiesis and protects erythroblasts against oxidative stress by up-regulating glutathione peroxidase and thioredoxin

ETHNOPHARMACOLOGICAL RELEVANCE

Rhodiola rosea is commonly used in China and Tibet folk medicine for the treatment of high altitude sickness, anoxia and mountain malhypoxia.

AIM OF STUDY

Salidroside (SDS) is an active ingredient of Rhodiola rosea. This study attempted to examine the potential erythropoiesis-stimulating and anti-oxidative effect of SDS in TF-1 erythroblasts.

MATERIALS AND METHODS

The erythropoiesis-promoting effect was determined by treating human TF-1 cells, one of the popular in vitro models for studying erythropoiesis, with SDS in the presence and absence of erythropoietin (EPO) through the measurement of the expression of a series of erythroid markers such as glycophorin A (GPA), transferrin receptor (CD71) and hemoglobin (Hb). The potential protective effect of SDS against H(2)O(2)-induced apoptosis and its underlying mechanism in TF-1 erythroblasts were examined by flow cytometry and Western blot analysis.

RESULTS

SDS promotes erythropoiesis in the EPO-treated cells and it also reduces the number of apoptotic cells in TF-1 erythroblasts after H(2)O(2) treatment probably through the up-regulation of protective proteins thioredoxin-1 (Trx1) and glutathione peroxidase-1 (GPx1).

CONCLUSION

Our study provides evidence to explain the ethnopharmacological role of SDS and Rhodiola rosea in Chinese medicine. Our findings also support the use of SDS as an erythropoiesis-adjuvant agent to correct anemia and malhypoxia.

Induction of erythroid differentiation in human erythroleukemia cells by depletion of malic enzyme 2

Malic enzyme 2 (ME2) is a mitochondrial enzyme that catalyzes the conversion of malate to pyruvate and CO2 and uses NAD as a cofactor. Higher expression of this enzyme correlates with the degree of cell de-differentiation. We found that ME2 is expressed in K562 erythroleukemia cells, in which a number of agents have been found to induce differentiation either along the erythroid or the myeloid lineage. We found that knockdown of ME2 led to diminished proliferation of tumor cells and increased apoptosis in vitro. These findings were accompanied by differentiation of K562 cells along the erythroid lineage, as confirmed by staining for glycophorin A and hemoglobin production. ME2 knockdown also totally abolished growth of K562 cells in nude mice. Increased ROS levels, likely reflecting increased mitochondrial production, and a decreased NADPH/NADP+ ratio were noted but use of a free radical scavenger to decrease inhibition of ROS levels did not reverse the differentiation or apoptotic phenotype, suggesting that ROS production is not causally involved in the resultant phenotype. As might be expected, depletion of ME2 induced an increase in the NAD+/NADH ratio and ATP levels fell significantly. Inhibition of the malate-aspartate shuttle was insufficient to induce K562 differentiation. We also examined several intracellular signaling pathways and expression of transcription factors and intermediate filament proteins whose expression is known to be modulated during erythroid differentiation in K562 cells. We found that silencing of ME2 leads to phospho-ERK1/2 inhibition, phospho-AKT activation, increased GATA-1 expression and diminished vimentin expression. Metabolomic analysis, conducted to gain insight into intermediary metabolic pathways that ME2 knockdown might affect, showed that ME2 depletion resulted in high orotate levels, suggesting potential impairment of pyrimidine metabolism. Collectively our data point to ME2 as a potentially novel metabolic target for leukemia therapy.

Long-term cultivation of a neuroblastoma cell line in medium with reduced serum content as a model system for neuronal aging?

Impaired energy metabolism and increased vulnerability to additional stress are some of the pivotal characteristics of the aging brain. This study was designed to establish a cell culture model for long-term investigations of some mechanisms underlying the process of aging using the neuroblastoma cell line SK-N-MC. As high serum concentrations in the culture medium are a major disadvantage for the investigation of regulatory or toxic influences, the effects of serum reduction in the culture medium on growth, viability and energy metabolism during long-term cultivation were determined. Serum reduction resulted in a decrease in the proliferation rate and in increased vulnerability of the cells, measured as release of lactate dehydrogenase into the culture medium. The rates of glucose consumption and lactate production were elevated, whereas the energetic state was markedly compromised, as was obvious from a 40% reduction of creatine phosphate. The observed increased vulnerability and the decreased energy state of the SK-N-MC cells were even more pronounced after induction of free radicals by addition of FeSO(4) to the medium with reduced serum content. Increased oxidative stress was indicated by elevated cellular contents of glutathione both after serum reduction and after incubation with FeSO(4). It is concluded that the SK-N-MC cells cultured chronically in medium with low serum content display biochemical characteristics that are similar to those observed in aging studies with animal models.

Hemin-mediated regulation of an antioxidant-responsive element of the human ferritin H gene and role of Ref-1 during erythroid differentiation of K562 cells

An effective utilization of intracellular iron is a prerequisite for erythroid differentiation and hemoglobinization. Ferritin, consisting of 24 subunits of H and L, plays a crucial role in iron homeostasis. Here, we have found that the H subunit of the ferritin gene is activated at the transcriptional level during hemin-induced differentiation of K562 human erythroleukemic cells. Transfection of various 5' regions of the human ferritin H gene fused to a luciferase reporter into K562 cells demonstrated that hemin activates ferritin H transcription through an antioxidant-responsive element (ARE) that is responsible for induction of a battery of phase II detoxification genes by oxidative stress. Gel retardation and chromatin immunoprecipitation assays demonstrated that hemin induced binding of cJun, JunD, FosB, and Nrf2 b-zip transcription factors to AP1 motifs of the ferritin H ARE, despite no significant change in expression levels or nuclear localization of these transcription factors. A Gal4-luciferase reporter assay did not show activation of these b-zip transcription factors after hemin treatment; however, redox factor 1 (Ref-1), which increases DNA binding of Jun/Fos family members via reduction of a conserved cysteine in their DNA binding domains, showed induced nuclear translocation after hemin treatment in K562 cells. Consistently, Ref-1 enhanced Nrf2 binding to the ARE and ferritin H transcription. Hemin also activated ARE sequences of other phase II genes, such as GSTpi and NQO1. Collectively, these results suggest that hemin activates the transcription of the ferritin H gene during K562 erythroid differentiation by Ref-1-mediated activation of these b-zip transcription factors to the ARE.

cDNA microarray analysis of altered gene expression in Ara-C-treated leukemia cells

The acute lymphoblastic leukemia cell line CCRF-CEM is sensitive to Ara-C and undergoes apoptosis. In contrast, the chronic myelogenous leukemia (CML) cell line K562 is highly resistant to Ara-C, which causes the cells to differentiate into erythrocytes before undergoing apoptosis. We used cDNA microarrays to monitor the alterations in gene expression in these two cell lines under conditions leading to apoptosis or differentiation. Ara-C-treated CCRF-CEM cells were characterized by a cluster of down-regulated chaperone genes, whereas Ara-C-treated K562 cells were characterized by a cluster of up-regulated hemoglobin genes. In K562 cells, Ara-C treatment induced significant down-regulation of the asparagine synthetase gene, which is involved in resistance to L-asparaginase. Sequential treatment with Ara-C and L-asparaginase had a synergistic effect on the inhibition of K562 cell growth, and combination therapy with these two anticancer agents may prove effective in the treatment of CML, which cannot be cured by either drug alone.

Free radical production and labile iron pool decrease triggered by subtoxic concentration of aclarubicin in human leukemia cell lines

Aclarubicin (ACLA), which belongs to the antracycline class of antineoplasic agents, has been demonstrated as a differentiating agent for a broad range of human solid tumors and leukemia. By using dihydroethidium as a fluorescent probe, we show the ability of subtoxic (i.e. differentiating) concentration of ACLA to generate reactive oxygen species in both K562 and HL-60 leukemia cell lines. Besides, we have used a calcein-based spectrofluorimetric assay to determine the influence of ACLA treatment on the cellular labile iron pool (LIP). In both cell lines, the LIP level was markedly decreased in the presence of ACLA. Nevertheless, whereas ACLA-induced differentiation was obviously ROS-dependent, the LIP decrease was rather ROS-independent.

A77 1726 induces differentiation of human myeloid leukemia K562 cells by depletion of intracellular CTP pools

A77 1726 (LEF) is the active metabolite of leflunomide, a recently approved immunosuppressive agent. We examined the ability of LEF to induce differentiation of a human erythroleukemia (K562) cell line and show that LEF induces a dose- and time-dependent differentiation of these cells as characterized by growth inhibition, hemoglobin production, and erythroid membrane protein glycophorin A expression. This effect was dependent on depletion of the intracellular pyrimidine ribonucleotides (UTP and CTP), and preceded by a specific S-phase arrest of the cell cycle. Supplementation of the cultures with exogenous uridine restored intracellular UTP and CTP to normal levels and prevented the LEF-induced cell cycle block and differentiation of K562 cells. Interestingly, addition of cytidine alone blocked the LEF-induced differentiation of K562 cells but only restored the CTP pool. By contrast, neither deoxycytidine nor thymidine prevented the effects of LEF on these cells. Similarly, pyrimidine starvation of a cell line lacking the de novo pyrimidine pathway (G9c) resulted in an S-phase arrest that was reversed by the addition of cytidine. Thus these studies demonstrate an important role for CTP in regulating cell cycle progression and show that LEF is an effective inducer of tumor cell differentiation through depletion of this ribonucleotide.

Inhibition of nucleoside transport by p38 MAPK inhibitors

While investigating the ability of p38 MAPK to regulate cytarabine (Ara C)-dependent differentiation of erythroleukemia K562 cells, we observed effects that indicated that the imidazoline class of p38 MAPK inhibitors prevented nucleoside transport. Incubation of K562 cells with SB203580, SB203580-iodo, or SB202474, an analogue of SB203580 that does not inhibit p38 MAPK activity, inhibited the uptake of [3H]Ara C or [3H]uridine and the differentiation of K562 cells. Consistent with the effects of these compounds on the nitrobenzylthioinosine (NBMPR)-sensitive equilibrative nucleoside transporter (ENT1), incubation with SB203580 or SB203580-iodo eliminated the binding of [3H]NBMPR to K562 cells or membranes isolated from human erythrocytes. Furthermore, using a uridine-dependent cell type (G9c), we observed that SB203580 or SB203580-iodo efficiently inhibited the salvage synthesis of pyrimidine nucleotides in vivo. Thus these studies demonstrate that the NBMPR-sensitive equilibrative nucleoside transporters are novel and unexpected targets for the p38 MAPK inhibitors at concentrations typically used to inhibit protein kinases.

The SOD2 gene, encoding a manganese-type superoxide dismutase, is up-regulated during conidiogenesis in the plant-pathogenic fungus Colletotrichum graminicola

The SOD2 gene, encoding a manganese-type superoxide dismutase (MnSOD), was identified from Colletotrichum graminicola among a collection of cDNAs representing genes that are up-regulated during conidiogenesis. The SOD2 gene consists of a 797-bp open reading frame that is interrupted by three introns and is predicted to encode a polypeptide of 208 amino acids. All conserved residues of the MnSOD protein family, including four consensus metal binding domains, are present in the predicted SOD2 protein. However, the predicted protein does not appear to contain a signal peptide that would target it to the mitochondria. Northern hybridizations revealed that expression of the approximately 900-bp SOD2 transcript is closely associated with differentiation of both oval and falcate conidia. Southern analysis indicated that there is only a single copy of the gene. SOD2 disruption strains were morphologically and pathogenically indistinguishable from wild-type strains. The dispensability of the MnSOD enzyme may be due to the activities of two other SOD enzymes, a highly expressed iron-type superoxide dismutase and a much less abundant copper/zinc type, that were also detected in C. graminicola.

Hydroxyl free radicals induce cell differentiation in SK-N-MC neuroblastoma cells

The SK-N-MC cell line is frequently used as a model of neuronal differentiation induced by 5-bromodeoxyuridine (BrdU). In this study, the differentiation properties of this cell line were investigated under hydroxyl free radical generation, and compared to BrdU treatment. Hydroxyl free radicals were generated in the cultures by the Fenton reaction, i.e. by simultaneous addition of ADP-Fe2+ complex and H2O2. Microscopic morphological signs, as well as the acetylcholinesterase and ganglioside sialidase activities were considered as markers of neuronal differentiation of this cholinergic neuroblastoma cell line. Apart from the altered morphological appearance, the marker enzymes displayed significant increases after both types of intervention. We suggest that hydroxyl free radicals can induce in vitro cell differentiation. They apparently play a more complex role in cell physiology than simply causing oxidative damage.

Experimental gerontology in Hungary

Gerontological research has some past and sporadically also some highlights in Hungary, but its present state can be easily deduced from the following data. During the last 12 years and more, well over 10,000 Hungarian scientific papers have been published in well-recognized national or international journals. Altogether approximately 1% of them have been classified as gerontological publications from Hungary. This low figure shows that gerontology has low priority and--unfortunately low support--in Hungary. This statement does not intend to downgrade Hungarian gerontologists, however points out that the Hungarian trends are not far from those of European or world wide interest in aging. Despite the recognition that we have to accept the inevitable fact that industrial societies will have (they already have) an aging population with all the social and medical problems arising, the focus of interest is wide from this significant and interesting (sub)population, which is neglected (sometimes even despised); yet everybody is absolutely eager to join this club. The average of the Hungarian research achievements and publication activities are among the better European achievements. There are some highlights and new trends even initiated by some outstanding Hungarian scientists, yet the overall weight of gerontology research is still an orphan in the Hungarian scientific life. We deal in this short and far from complete summary almost exclusively with experimental gerontology. We have to apologize if we have not included everybody, who also contributed even significantly to this field because the time for the preparation of this overview was short.

The involvement of hydroxyl free radicals in differentiation of the PC-12 rat pheochromocytoma cell line

These experiments tested the differentiation properties of the PC-12 cell line under conditions of in vitro generation of OH&z.rad; free radicals by Fenton reaction. This involves the simultaneous addition of the following reactants: ADP-Fe(2+)-complex (0.1 mM for iron) and H(2)O(2) (0.025 mM), final concentrations. Superoxide dismutase activity, the increase of which is considered as a marker of differentiation, catalase and glutathione peroxidase enzyme activities were investigated, which all displayed significant increases after single and repeated interventions with hydroxyl free radicals, while the cell number remained nearly at the starting-value. It is known that the differentiation takes place when the cell number has reached a plateau. These data, therefore, suggest that hydroxyl free radicals can induce in vitro cell differentiation, and that they play a more complex role in cell physiology than simply causing oxidative damages. It is interesting that the cells can maintain high levels of these enzyme activities for a relatively long time (2 or 4 days) after a very short flux of hydroxyl free radicals.

On the true role of oxygen free radicals in the living state, aging, and degenerative disorders

Oxyradicals are generally considered harmful byproducts of oxidative metabolism, causing molecular damage in living systems. They are implicated in various processes such as mutagenesis, aging, and series of pathological events. Although all this may be justified, evidence is accumulating that it is an oversimplified view of the real situation. We can assume nowadays that the living state of cells and organisms implicitly requires the production of oxyradicals. This idea is supported by experimental facts and arguments as follows. (1) Complete inhibition of the oxyradical production by KCN (or by any block of respiration) kills the living organisms much before the energy reserves would be exhausted. (2) Construction of the supramolecular organization of the cells (especially of their membranous compounds) requires the cross-linking effect of oxyradicals, particularly that of OH* radicals. (3) Blast type cells produce much fewer oxyradicals than do differentiated ones, and interventions increasing the production of OH* radicals induce differentiation of various lines of leukemic (HL-60 and K562) and normal (fibroblasts, chondroblasts, etc.) cells, while SOD expression increases greatly. (4) It is reasonable to assume that the continuous flux of OH* radicals is prerequisite to maintenance of constant electron delocalization on the proteins, which is a semiconductive phenomenon suggested in 1941 by Szent-Györgyi, but it has never been proven experimentally. It is theoretically possible to describe the function of the synapses as that of a single p-n-p transistor, assuming that the free radical flux maintains electron movements on the subsynaptic structures, while the actual membrane potential is governing the electron flux. This theoretical approach may open completely new possibilities for our understanding of the normal functions of living organisms, such as basic memory mechanisms in brain cells, their aging processes, and therapeutic approaches to many degenerative disorders, such as various types of dementia.

Anthracycline-induced erythroid differentiation of K562 cells is inhibited by p28, a novel mammalian glutathione-binding stress protein

When exposed to the anthracycline doxorubicin, K562 cells undergo differentiation which is characterized by arrested cell division, an increased mean cell diameter, and the production of hemoglobin. The influence of expression of p28, a low-molecular weight stress protein, on the differentiation of K562 cells was examined. Expression of p28 was modulated by transfection of K562 cells with expression vectors containing the murine p28 cDNA in either the sense or antisense orientation, or without the p28 cDNA. In K562 cells where p28 expression was either unaltered or downregulated, exposure to 40 nM Doxorubicin resulted in an arrest of cell division, the production of hemoglobin, and an increased cell diameter consistent with cells undergoing differentiation. K562 cells that overexpressed p28 continued to divide, had fewer hemoglobin-producing cells, had a smaller mean cell diameter and had a 5.5-fold increase in cell survival. Consistent with an inhibition of doxorubicin-induced erythroid differentiation, p28 may act by changes in redox regulation via the glutathione-binding activity of p28 and suggests a general role for p28 in cellular differentiation. Furthermore, p28 expression may be useful in predicting resistance to chemo- or radiation therapy in the treatment of leukemia and lymphoma.

On the useful role of OH&z.rad; free radicals in differentiation of cultured human fibroblasts

The working hypothesis assuming that oxygen free radicals cannot be considered only as harmful by-products of the oxidative metabolism has been experimentally tested. Human fibroblasts were grown in culture from the following five types of tissues: (1) normal orbital fat; (2) orbital fat of patients with endocrine ophtalmopathy (EOP); (3) normal orbital muscle; (4) orbital muscle of EOP patients; (5) skin. These fibroblasts (second to 12th passages) were treated for 2x72 h with the Fenton reactants: ADP-Fe(2+)-complex (0.1 mM for iron) and H(2)O(2) (0.055 mM), final concentrations. This treatment caused a slowing down of the cell proliferation, induced various morphological signs of differentiation, and significantly increased (40-150%) the total superoxide dismutase (SOD) and catalase (CAT) activities of the fibroblasts. Authors suggest that the increased expression of these enzymes may play a general role in the cell differentiation mechanisms, meaning that the generation of oxygen free radicals is an essential, useful factor even during the early phases of development, and may not be taken only as a harmful process during aging.

Correlation of urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG), a biomarker of oxidative DNA damage, and clinical features of hematological disorders: a pilot study

The 8-hydroxy-2'-deoxyguanosine (8-OHdG), presently the most popular marker for oxidative DNA damage, level has been reported to be elevated in patients with various malignancies. In the present study, urinary 8-OHdG was examined in 44 patients with hematological disorders (13 malignant lymphoma, 11 adult T cell leukemia/lymphoma (ATL), 10 acute leukemia, and 10 myelodysplastic syndrome (MDS)) by an enzyme-linked immunosorbent assay. The pre-therapy level of urinary 8-OHdG in ATL patients was significantly elevated compared with normal controls (25.3+/-12.9 vs. 11.9+/-7.3 ng/mg, P<0.05). Although patients with lymphoma, acute leukemia and MDS also showed higher urinary 8-OHdG levels than normal controls, the differences were not significant. However, two patients with refractory anemia with excess blasts in transformation (RAEB-t) having extreme monocytosis and neutrophilia showed exceptionally high urinary 8-OHdG levels (161.0 and 218.9 ng/mg). Urinary 8-OHdG excretion increased transiently with chemotherapy, and this fluctuation was significant irrespective of the disorder (P<0.05). Interestingly, lymphoma patients with high LDH, advanced stage, poor performance status or International Prognostic Index (IPI) of high/high-intermediate risk had significantly elevated urinary 8-OHdG levels (P<0.05-<0.001). These latter results suggest that urinary 8-OHdG may be a reliable prognostic marker in lymphoma patients and should encourage large scale and long term follow up studies.

Oxidative stress involvement in chemically induced differentiation of K562 cells

The erythroid differentiation of K562 cells could be achieved by exposure to several pharmacologic agents, including hemin, butyric acid (BA), and anthracycline antitumor drugs such as aclarubicin (ACLA) and doxorubicin (DOX). When used at subtoxic concentrations, these drugs induce the overexpression of erythroid genes, leading to hemoglobinization of cells. Because anthracyclines are known to generate oxidative damage, we intended to demonstrate the involvement of an oxidative stress in the chemically induced differentiation process. The addition of antioxidants to anthracycline- and BA-induced cells decreased their growth and dramatically reduced the percentage of differentiated cells at day 3. Northern blot analysis showed that antioxidants also decrease the expression of erythroid genes and related transcription factors in induced cells. Moreover, analyses of oxidative stress markers showed that treatment with BA, ACLA, and DOX lead to a decrease in reduced glutathione and antioxidant enzymes (glutathione peroxidase [GPx], glutathione reductase [GRase], CuZn superoxide dismutase [SOD], and catalase [CAT]). In addition, DOX increased thiobarbituric acid reactants (TBARs), and MnSOD activity was decreased by BA and DOX. Finally, the production of reactive oxygen species (ROS) by differentiating agents was demonstrated using the dihydroethidium probe in a microspectrofluorometric assay. Altogether, these results strongly suggest the involvement of an oxidative stress generated by BA or anthracyclines as the first step in the irreversible differentiation process. Additionally, these results underline the differences between BA, ACLA, and DOX molecular mechanisms.

Differential expression of glutaredoxin and thioredoxin during monocytic differentiation

Macrophages generate reactive oxygen intermediates (ROIs) as the effectors of anti-bacterial defense mechanism. Intracellular ROIs and reduction/oxidation (redox) status play crucial roles in signal transduction. We therefore investigated the expression of redox-regulating proteins such as glutaredoxin (GRX) and thioredoxin (TRX) during the differentiation of murine monocytic leukemia cell line M1 cells and human monocytic leukemia cell line U937 cells. When M1 cells were treated by IL-6, GRX mRNA markedly increased and TRX mRNA also increased slightly. In contrast, there was no increase of GRX mRNA in D-cell, which is a sub-cell line derived from M1 lacking in the capacity of differentiation. GRX mRNA also increased in U937 cells differentiated by phorbol 12-myristate 13-acetate (PMA). By immunohistochemistry, unstimulated M1 cells showed strong staining of TRX and marginal staining of GRX. In contrast, TRX expression in IL-6 treated M1 cells is as strong as in unstimulated M1 cells, whereas GRX expression is slightly enhanced in IL-6 treated M1 cells. Phagocytosis is markedly enhanced and hydrogen peroxide production is slightly enhanced in IL-6 treated M1 cells. These results showed that TRX is steadily expressed whereas GRX is induced in association with the differentiation in macrophage-like cell line cells, suggesting differential roles of these redox regulators in macrophage lineage.

Oxidative stress and superoxide dismutase in development, aging and gene regulation

Free radicals and other reactive oxygen species are produced in the metabolic pathways of aerobic cells and affect a number of biological processes. Oxidation reactions have been postulated to play a role in aging, a number of degenerative diseases, differentiation and development as well as serving as subcellular messengers in gene regulatory and signal transduction pathways. The discovery of the activity of superoxide dismutase is a seminal work in free radical biology, because it established that free radicals were generated by cells and because it made removal of a specific free radical substance possible for the first time, which greatly accelerated research in this area. In this review, the role of reactive oxygen in aging, amyotrophic lateral sclerosis (a neurodegenerative disease), development, differentiation, and signal transduction are discussed. Emphasis is also given to the role of superoxide dismutases in these phenomena.