Role of peroxide and superoxide anion during tumour cell apoptosis

Ghrelin attenuates heat-induced degenerative effects in the rat testis

This study was conducted to examine the efficacy of ghrelin in prevention of deleterious effects of heat stress in rat testicular tissue. Forty five adult male rats were scheduled for this study and were divided equally into three groups: heat-saline, heat-ghrelin and control-saline. The scrota of heated-designed rats were immersed once in water bath at 43 °C for 15 min. Immediately upon heating, 2 nmol of ghrelin were given subcutaneously to heat-ghrelin animals every other day up to day 60 and physiological saline to the other two groups using the same method. The animals were sacrificed at 10, 30 and 60 days after heat treatment and their testes were taken for later photomicrograph and immunohistochemical analysis. Testicular histopathology revealed a significant reduction in the means of seminiferous tubules and Sertoli cell nucleus diameters as well as germinal epithelium height on day 10 in both heated groups. Furthermore, other testicular components including miotic index, spermatogenesis rate, presence of spermatocytes and volume densities were dramatically decreased following heat exposure. Notably, ghrelin caused a partial recovery in all of the above-mentioned parameters and accelerated testicular regeneration process by day 30 compared to the heat-saline group (P<0.05). Because of testicular progressive recovery, these indices were similar among groups on day 60 (P>0.05). However, immunohistochemistry evaluation for in situ detection of Bcl-2 protein did not exhibit any germ cells-positive of this factor among groups at different experimental days. In conclusion, the results of the present study indicate for the first time the novel evidences of ghrelin ability in attenuation of heat-induced testicular damage and also that ghrelin therapy may be useful as a suppressor of degenerative effects following testicular hyperthermia.

SOD/catalase mimetic platinum nanoparticles inhibit heat-induced apoptosis in human lymphoma U937 and HH cells

Platinum nanoparticles (Pt-NPs) are known to possess anti-tumouric activity and the ability to scavenge superoxides and peroxides indicating that they can act as superoxide dismutase (SOD)/catalase mimetics. These potentials seem useful in the protection and/or amelioration of oxidative stress-associated pathologies, but, when they are combined with a therapeutic modality that depends upon the mediation of reactive oxygen species in cell killing induction, the effect of Pt-NPs might be questionable. Here, the effects of polyacrylic acid-capped Pt-NPs (nano-Pts) on hyperthermia (HT)-induced apoptosis and the underlying molecular mechanisms were investigated in human myelomonocytic lymphoma U937 and human cutaneous T-cell lymphoma HH cells. The results showed that the pre-treatment with nano-Pts significantly inhibited HT-induced apoptosis in a dose-dependent manner. Superoxide, but not peroxides, was suppressed to varying extents. All pathways involved in apoptosis execution were also negatively affected. The results reveal that the combination of nano-Pts and HT could result in HT-desensitization.

Role of oxidative stress in stem, cancer, and cancer stem cells

The term ‘‘oxidative stress” refers to a cell’s state characterized by excessive production of reactive oxygen species (ROS) and oxidative stress is one of the most important regulatory mechanisms for stem, cancer, and cancer stem cells. The concept of cancer stem cells arose from observations of similarities between the self-renewal mechanism of stem cells and that of cancer stem cells, but compared to normal stem cells, they are believed to have no control over the cell number. ROS have been implicated in diverse processes in various cancers, and generally the increase of ROS in cancer cells is known to play an important role in the initiation and progression of cancer. Additionally, ROS have been considered as the most significant mutagens in stem cells; when elevated, blocking self-renewal and at the same time, serving as a signal stimulating stem cell differentiation. Several signaling pathways enhanced by oxidative stress are suggested to have important roles in tumorigenesis of cancer or cancer stem cells and the self-renewal ability of stem or cancer stem cells. It is now well established that mitochondria play a prominent role in apoptosis and increasing evidence supports that apoptosis and autophagy are physiological phenomena closely linked with oxidative stress. This review elucidates the effect and the mechanism of the oxidative stress on the regulation of stem, cancer, and cancer stem cells and focuses on the cell signaling cascades stimulated by oxidative stress and their mechanism in cancer stem cell formation, as very little is known about the redox status in cancer stem cells. Moreover, we explain the link between ROS and both of apoptosis and autophagy and the impact on cancer development and treatment. Better understanding of this intricate link may shed light on mechanisms that lead to better modes of cancer treatment.

Cellular stress responses: cell survival and cell death

Cells can respond to stress in various ways ranging from the activation of survival pathways to the initiation of cell death that eventually eliminates damaged cells. Whether cells mount a protective or destructive stress response depends to a large extent on the nature and duration of the stress as well as the cell type. Also, there is often the interplay between these responses that ultimately determines the fate of the stressed cell. The mechanism by which a cell dies (i.e., apoptosis, necrosis, pyroptosis, or autophagic cell death) depends on various exogenous factors as well as the cell's ability to handle the stress to which it is exposed. The implications of cellular stress responses to human physiology and diseases are manifold and will be discussed in this review in the context of some major world health issues such as diabetes, Parkinson's disease, myocardial infarction, and cancer.

A new view of carcinogenesis and an alternative approach to cancer therapy

During the last few decades, cancer research has focused on the idea that cancer is caused by genetic alterations and that this disease can be treated by reversing or targeting these alterations. The small variations in cancer mortality observed during the previous 30 years indicate, however, that the clinical applications of this approach have been very limited so far. The development of future gene-based therapies that may have a major impact on cancer mortality may be compromised by the high number and variability of genetic alterations recently found in human tumors. This article reviews evidence that tumor cells, in addition to acquiring a complex array of genetic changes, develop an alteration in the metabolism of oxygen. Although both changes play an essential role in carcinogenesis, the altered oxygen metabolism of cancer cells is not subject to the high genetic variability of tumors and may therefore be a more reliable target for cancer therapy. The utility of this novel approach for the development of therapies that selectively target tumor cells is discussed.

Human papillomavirus type 16 E5 protein inhibits hydrogen-peroxide-induced apoptosis by stimulating ubiquitin-proteasome-mediated degradation of Bax in human cervical cancer cells

To investigate the mechanism by which the human papillomavirus (HPV) E5 protein contributes to the carcinogenesis of uterine cervical cancer, we studied the effect of HPV E5 on apoptosis of cervical cancer cells and its underlying mechanism. Expression of HPV16 E5 protein inhibited hydrogen peroxide-induced apoptosis in C-33A cervical cancer cells. E5 decreased the expression of Bax protein, and exogenous expression of Bax abolished the anti-apoptotic effect of E5. Knockdown of E5 by small interfering RNA sensitized CaSki cervical cancer cells to hydrogen peroxide-induced apoptosis with concurrent increase in Bax expression. Transient expression of E5 significantly increased the degradation rate of Bax protein by inducing the ubiquitination. The E5-induced decrease in Bax expression was inhibited by a cyclooxygenase-2 (COX-2) inhibitor, prostaglandin E2 (PGE(2)) receptor antagonists and cyclic adenosine monophosphate-dependent protein kinase (PKA) inhibitor. Treatment with PGE(2) decreased the expression of Bax and inhibited hydrogen peroxide-induced apoptosis of C-33A cells. We concluded that HPV16 E5 protein inhibits hydrogen peroxide-induced apoptosis of cervical cancer cells by stimulating the ubiquitin-proteasome-mediated degradation of Bax protein, and the pathway involves COX-2, PGE(2) and PKA. This finding suggests the possibility that HPV 16 E5 protein contributes to cervical carcinogenesis by inhibiting apoptosis of transformed cervical epithelial cells.

Effects of omega-3 fatty acids on apoptosis of human gastric epithelial cells exposed to silica-immobilized glucose oxidase

Oxidative stress plays a critical role in apoptosis of gastric epithelial cells. Omega-3 fatty acids show anti-inflammatory and/or anticancer effects and regulate apoptosis in various cells. In this study, we aimed to investigate whether omega-3 fatty acids inhibit oxidative stress-induced apoptosis of gastric epithelial cells. The cells received oxidative stress caused by silica-immobilized glucose oxidase acting on beta-D-glucose and cultured in the absence or presence of alpha-linolenic acid or docosahexanoic acid. Viable cell numbers, levels of H(2)O(2) in the medium, DNA fragmentation, and protein levels of p53 and Bax were determined. As a result, silica-immobilized glucose oxidase acting on beta-D-glucose consistently and reproducibly produced H(2)O(2), which decreased cell viability and increased DNA fragmentation of the cells. Omega-3 fatty acids inhibited oxidative stress-induced cell death, DNA fragmentation, and induction of p53 and Bax of the cells. The silica-immobilized glucose oxidase could be a useful tool for studies on oxidative stress-induced cellular events because it is reusable and forms a stable enzyme system acting on glucose. Omega-3 fatty acids may be beneficial for preventing oxidative stress-induced apoptosis by inhibiting apoptotic gene expression and DNA fragmentation of gastric epithelial cells.

ROS and protein oxidation in early stages of cytotoxic drug induced apoptosis

Cytotoxic drugs induce cell death through induction of apoptosis. This can be due to activation of a number of cell death pathways. While the downstream events in drug induced cell death are well understood, the early events are less clear. We therefore used a proteomic approach to investigate the early events in apoptosis induced by a variety of drugs in HL60 cells. Using 2D-gel electrophoresis, we were able to identify a number of protein changes that were conserved between different drug treatments. Identification of post-translational modifications (PTM) responsible for these proteome changes revealed an increase in protein oxidation in drug treated cells, as well as changes in protein phosphorylation. We demonstrate an accumulation of oxidised proteins within the ER, which lead to ER stress and calcium release and may result in the induction of apoptosis. This study demonstrates the importance of ROS mediated protein modifications in the induction of the early stages of apoptosis in response to chemotherapeutic drug treatment.

Enhancement of Radiation-induced Apoptosis by 6-Formylpterin

Radiation-induced apoptosis and its possible enhancement in the presence of 6-formylpterin (6-FP), a metabolite of folic acid, were examined in human myelomonocytic lymphoma U937 cells. When cells were treated with 6-FP at a nontoxic concentration of 300 microM, and then exposed to X-rays at a dose of 10 Gy, significant enhancement of radiation-induced apoptosis as determined by nuclear morphological change, phosphatidylserine (PS) externalization and DNA fragmentation were observed. Flow cytometry for the detection of intracellular hydrogen peroxide (H2O2) revealed that 6-FP increased the formation of intracellular H2O2, which further increased when the cells were irradiated. Decrease of mitochondria trans-membrane potential (MMP), release of cytochrome c from mitochondria, and activation of caspase-3 were enhanced after the combined treatment. Remarkable activation of protein kinase C delta (PKC delta) and its translocation from cytosol to mitochondria were detected in combined treatment. Increase of intracellular Ca2+ concentrations ([Ca2+]i) was also observed, however, neither calpain I nor calpain II could inhibit the apoptosis. In addition, c-Jun NH2-terminal kinase (JNK) activation was not enhanced in the combined treatment. A protein involved in a caspase-independent apoptosis pathway, apoptosis inducing factor (AIF), remained unchanged even 3 h after treatment. These results indicate that intracellular H2O2 generated by 6-FP enhances radiation-induced apoptosis via the mitochondria-mediated caspase-dependent pathway, with the active involvement of PKC delta.

Involvement of hydrogen peroxide in histamine-induced modulation of WM35 human malignant melanoma cell proliferation

Histamine is a recognized growth factor in melanoma, and exogenous histamine produces a dual effect on proliferation. We have previously reported that histamine at micromolar concentrations reduces the proliferation of melanoma cell lines. To investigate the mechanism by which histamine inhibits proliferation of WM35 human melanoma cells, we have studied the involvement of histamine in reactive oxygen species production and antioxidant enzyme regulation in these cells. Results indicate that histamine treatment (10 microM) significantly increased hydrogen peroxide levels, whereas it slightly decreased superoxide levels associated with an enhancement of superoxide dismutase and a reduction in catalase activity. Additionally, catalase treatment reversed the inhibitory effect of histamine on proliferation, and various treatments that reduce hydrogen peroxide formation increased proliferation of these cells. Furthermore, we demonstrate that the inhibition of proliferation produced by histamine was mediated at least in part by an induction of cell senescence. We conclude that hydrogen peroxide is involved in histamine-mediated modulation of proliferation in malignant melanoma cells.

Cell survival from chemotherapy depends on NF-kappaB transcriptional up-regulation of coenzyme Q biosynthesis

BACKGROUND

Coenzyme Q (CoQ) is a lipophilic antioxidant that is synthesized by a mitochondrial complex integrated by at least ten nuclear encoded COQ gene products. CoQ increases cell survival under different stress conditions, including mitochondrial DNA (mtDNA) depletion and treatment with cancer drugs such as camptothecin (CPT). We have previously demonstrated that CPT induces CoQ biosynthesis in mammal cells.

METHODOLOGY/PRINCIPAL FINDINGS

CPT activates NF-kappaB that binds specifically to two kappaB binding sites present in the 5'-flanking region of the COQ7 gene. This binding is functional and induces both the COQ7 expression and CoQ biosynthesis. The inhibition of NF-kappaB activation increases cell death and decreases both, CoQ levels and COQ7 expression induced by CPT. In addition, using a cell line expressing very low of NF-kappaB, we demonstrate that CPT was incapable of enhancing enhance both CoQ biosynthesis and COQ7 expression in these cells.

CONCLUSIONS/SIGNIFICANCE

We demonstrate here, for the first time, that a transcriptional mechanism mediated by NF-kappaB regulates CoQ biosynthesis. This finding contributes new data for the understanding of the regulation of the CoQ biosynthesis pathway.

The decrease of PAMAM dendrimer-induced cytotoxicity by PEGylation via attenuation of oxidative stress

Due to their unique structure, poly(amidoamine) (PAMAM) dendrimers have been widely used in medical applications. However, PAMAM dendrimers bearing amino terminals show certain cytotoxicity. In order to improve their biocompatibility, we modified Generation-5 PAMAM dendrimers by conjugating them with poly(ethylene glycol) (PEG) of two different molecular weights and different number of chains. The IC(50) values of PEGylated dendrimers were 12-105 fold higher than those of PAMAM dendrimers. To investigate the influence of PEGylation on PAMAM-induced cytotoxicity, the intracellular responses, reactive oxygen species (ROS) content, mitochondrial membrane potential (MMP), and apoptosis were examined. The results indicated that conjugation with PEG could effectively reduce the PAMAM-induced cell apoptosis by attenuating the ROS production and inhibiting PAMAM-induced MMP collapse. Meanwhile, dendrimers conjugated with less PEG of lower molecular weight did not significantly change the endocytic properties. Dendrimers conjugated with more PEG of higher molecular weight were much less cytotoxic. This study provided a novel insight into the effects of PEGylation on the decrease of cytotoxicity at the molecular level.

Effect of chain length on physicochemical properties and cytotoxicity of cationic vesicles composed of phosphatidylcholines and dialkyldimethylammonium bromides

This study investigated the physicochemical characteristics of cationic vesicles that were prepared from two phosphatidylcholines and three dialkyldimethylammonium bromides (DXDAB) with differing in dialkyl chain lengths, ranging from 2-C(14) to 2-C(18), by measuring particle size and zeta potential. The dependence of particle size, zeta potential and short-storage stability of mixed phosphatidylcholine/DXDAB vesicles on the chain length and composition were also elucidated. Transmission electron microscopy analysis verified that vesicles were formed as a phosphatidylcholine film to which DXDAB was added in a phosphate buffer saline (PBS, pH 7.4). Furthermore, the toxicity to the human keratinocytes (HaCaT) and squamous cell carcinomas (SCC25) cells that were incubated with these vesicles, evaluated by a cell viability assay, increased with the percentage of DXDAB that was incorporated and was inversely proportional to the chain length of DXDAB. The morphological features (round shape, chromatin condensation and apoptosis bodies) and results of flow cytometry analysis (increased sub-G(1) fraction) confirmed the induction of apoptosis in HaCaT and SCC25 cells by cationic vesicles. Apoptosis caused by cationic vesicles without the addition of any drugs was observed for the first time in HaCaT and SCC25 cells. The results of this investigation suggest that cytotoxicity is related to the zeta potential of the cationic vesicles.

Protective role of 1 alpha, 25-dihydroxyvitamin D3 against oxidative stress in nonmalignant human prostate epithelial cells

Overproduction of reactive oxygen species (ROS), through either endogenous or exogenous sources, could induce DNA damage, and accumulation of DNA damage might lead to multistep carcinogenesis. The antioxidative effects of vitamin D have been suggested by epidemiological and many in vitro and in vivo laboratory studies. While exploring the antioxidative effects of vitamin D in prostate cells, we found that the active form of vitamin D, 1 alpha, 25-dihydroxyvitamin D(3) (1,25-VD), can protect nonmalignant human prostate epithelial cell lines, BPH-1 and RWPE-1, but not malignant human prostate epithelial cells, CWR22R and DU 145, from oxidative stress-induced cell death. Glucose-6-phosphate dehydrogenase (G6PD), a key antioxidant enzyme, was dose- and time-dependently induced by 1,25-VD. Mechanistic studies using chromatin immunoprecipitation (ChIP) assay revealed that a direct repeat-3 (DR3) vitamin D response element located in the first intron of the G6PD genome can be bound by liganded vitamin D receptor, thereby regulating G6PD gene expression. Increasing G6PD activity and glutathione level by 1,25-VD can scavenge cellular ROS. Moreover, the protective effects of 1,25-VD were abolished by dehydroepiandrosterone, a noncompetitive inhibitor of G6PD activity. Together, our results showed that 1,25-VD can protect nonmalignant prostate cells from oxidative stress-induced cell death by elimination of ROS-induced cellular injuries through transcriptional activation of G6PD activity. The antioxidative effect of vitamin D strengthens its roles in cancer chemoprevention and adds to a growing list of beneficial effects of vitamin D against cancer.

Effect of xanthohumol and isoxanthohumol on 3T3-L1 cell apoptosis and adipogenesis

Xanthohumol (XN), the chalcone from beer hops has several biological activities. XN has been shown to induce apoptosis in cancer cells and also has been reported to be involved in lipid metabolism. Based on these studies and our previous work with natural compounds, we hypothesized that XN and its isomeric flavanone, isoxanthohumol (IXN), would induce apoptosis in adipocytes through the mitochondrial pathway and would inhibit maturation of preadipocytes. Adipocytes were treated with various concentrations of XN or IXN. In mature adipocytes both XN and IXN decreased viability, increased apoptosis and increased ROS production, XN being more effective. Furthermore, the antioxidants ascorbic acid and 2-mercaptoethanol prevented XN and IXN-induced ROS generation and apoptosis. Immunoblotting analysis showed an increase in the levels of cytoplasmic cytochrome c and cleaved poly (ADP-ribose) polymerase (PARP) by XN and IXN. Concomitantly, we observed activation of the effectors caspase-3/7. In maturing preadipocytes both XN and IXN were effective in reducing lipid content, XN being more potent. Moreover, the major adipocyte marker proteins such as PPARgamma, C/EBPalpha, and aP2 decreased after treatment with XN during the maturation period and that of DGAT1 decreased after treatment with XN and IXN. Taken together, our data indicate that both XN and IXN inhibit differentiation of preadipocytes, and induce apoptosis in mature adipocytes, but XN is more potent.

Decoding dangerous death: how cytotoxic chemotherapy invokes inflammation, immunity or nothing at all

Chemotherapy and immunotherapy can be either synergistic or antagonistic modalities in the treatment of cancer. Cytotoxic chemotherapy not only affects the tumor but also targets dividing lymphocytes, the very cells that are required to develop an immune response. For this reason, chemo- and immunotherapy have been seen as antagonistic. However, cell death can be immunogenic and the way in which chemotherapeutic drug kills a tumor cell is likely to be an important determinant of how that dying cell interacts with the immune system and whether the interaction will lead to an immune response. When a cell dies as the result of infection, the immune system responds rapidly and the system of Toll-like receptors (TLR) plays a key role in this process. In this review, we will briefly summarize the intracellular signaling pathways that link TLR ligation with immune activation and we will address the questions where and how TLRs recognize their targets.

Stimulatory heterotrimeric GTP-binding protein inhibits hydrogen peroxide-induced apoptosis by repressing BAK induction in SH-SY5Y human neuroblastoma cells

Heterotrimeric stimulatory GTP-binding protein (G(s)) stimulates adenylate cyclases to activate the cAMP signaling pathway. Although the cAMP pathway has been reported to be involved in apoptosis, the role of the G(s)-cAMP signaling pathway during reactive oxygen species (ROS)-mediated apoptosis, which is involved in the resistance of cancer cells to chemotherapy and radiation, is not clearly understood. Thus, in this study we aimed to investigate the role of the alpha subunit of G(s) (Galpha(s)) in the ROS-induced apoptosis of cancer cells. The stable expression of constitutively active Galpha(s) (Galpha(s)QL) inhibited the hydrogen peroxide-induced apoptosis of SH-SY5Y human neuroblastoma cells and reduced the hydrogen peroxide-induced increase in Bak and the decrease in Bcl-x(L) protein expression. Exogenous Bak expression abolished these inhibitory effects of Galpha(s)QL, but Bak small interfering RNA decreased hydrogen peroxide-induced apoptosis. Galpha(s) repressed hydrogen peroxide-induced Bak expression by inhibiting the transcription of Bak mRNA, which resulted from the inhibition of the hydrogen peroxide-induced activation of transcription factors such as AP1, NF-kappaB, and NFAT. Moreover, Galpha(s) also inhibited the hydrogen peroxide-induced binding of AP1, NF-kappaB, and NFAT to the Bak promoter. Furthermore, hydrogen peroxide-induced apoptosis was reduced by treating cells with prostaglandin E(2), which activates Galpha(s), but this was augmented by CCPA, which activates Galpha(i) causing a decrease in cAMP levels. From the results, we conclude that Galpha(s) protects neuroblastoma cells from hydrogen peroxide-induced apoptosis by repressing Bak induction, which is mediated by the inhibition of the hydrogen peroxide-induced activations of AP1, NF-kappaB, and NFAT through cAMP-PKA-CREB signaling system.

Molecular mechanisms of polypeptide from Chlamys farreri protecting HaCaT cells from apoptosis induced by UVA plus UVB

AIM

To investigate the mechanism of polypeptide from Chlamys farreri (PCF) protecting HaCaT cells from apoptosis induced by UVA plus UVB in vitro.

METHODS

An apoptotic model of UV irradiation-induced HaCaT cells was established. The 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide assay, agarose gel electrophoresis, biochemical methods, and Western blotting were employed in the study.

RESULTS

PCF inhibited the UV irradiation-induced apoptosis of HaCaT cells. PCF strongly reduced the intracellular reactive oxygen species level, enhanced activities of superoxide dismutase and glutathione peroxidase and increased the total anti-oxidative capacity in HaCaT cells following UV irradiation. Furthermore, we found that PCF could inhibit the phosphorylation of c-Jun amino-terminal kinase and the activity of caspase-3 in a concentration-dependent manner.

CONCLUSION

PCF protected HaCaT cells from apoptosis induced by UVA plus UVB, mainly through decreasing the intracellular ROS level and increasing the activities of anti-oxidative enzymes to block the ROS-JNK-caspase-3-apoptosis signaling pathway.

Dual role of hydrogen peroxide in cancer: Possible relevance to cancer chemoprevention and therapy

Accumulating evidence suggests that hydrogen peroxide (H(2)O(2)) plays an important role in cancer development. Experimental data have shown that cancer cells produce high amounts of H(2)O(2). An increase in the cellular levels of H(2)O(2) has been linked to several key alterations in cancer, including DNA alterations, cell proliferation, apoptosis resistance, metastasis, angiogenesis and hypoxia-inducible factor 1 (HIF-1) activation. It has also been observed that the malignant phenotype of cancer cells can be reversed just by decreasing the cellular levels of H(2)O(2). On the other hand, there is evidence that H(2)O(2) can induce apoptosis in cancer cells selectively and that the activity of several anticancer drugs commonly used in the clinic is mediated, at least in part, by H(2)O(2). The present report discusses that the high levels of H(2)O(2) commonly observed in cancer cells may be essential for cancer development; these high levels, however, seem almost incompatible with cell survival and may make cancer cells more susceptible to H(2)O(2)-induced cell death than normal cells. An understanding of this dual role of H(2)O(2) in cancer might be exploited for the development of cancer chemopreventive and therapeutic strategies.

Preventive effect of trimidox on oxidative stress in U937 cell line

Trimidox (3,4,5-trihydroxybenzamidoxime) is one of the most potent ribonucleotide reductase inhibitors, revealing an antitumor effect in several experimental studies. We have examined the effect of trimidox on the induction of cytotoxicity and apoptosis via oxidative stress by typical free radical inducers, hydrogen peroxide (H(2)O(2)), tert-butylhydroperoxide (tBuOOH) or ultraviolet (UV) irradiation in a human diffuse histiocytic lymphoma U937 cell line. Trimidox showed strong radical scavenging activity by the DPPH reduction assay. The 50% rate inhibited the DPPH reduction concentration of trimidox, and its derivates didox, or gallic acid were 8.8 microM, 117.5 microM, or 41.8 microM, respectively. Induction of cytotoxicity by H(2)O(2) (500 microM) or tBuOOH (100 microM) was concentration-dependently attenuated by incubation with Trimidox (10-150 microM). Trimidox also prevented the effect of UV-induced apoptosis estimated by both nuclear morphological change and DNA fragmentation. This effect was due to inhibition of the production of reactive oxygen species. Moreover, the activity and mRNA expression of catalase, an antioxidant enzyme, was significantly increased by trimidox. These results indicate that trimidox has radical scavenging activity and prevents exogenous oxidative stress and increase in catalase; therefore, trimidox is suggested as an anticancer agent exhibiting potent antioxidant properties in this study.

Enhancement of hyperthermia-induced apoptosis by a new synthesized class of furan-fused tetracyclic compounds

The combined effects of hyperthermia (44 degrees C, 20 min) or X-rays (10 Gy) and a new class of furan-fused tetracyclic synthesized compounds (DFs), on apoptosis in human lymphoma U937 cells were investigated. Among the tested compounds (DF1 approximately 6), the combined treatment of 10 microM DF with TIPS (triisopropylsilyloxy) (Designated #3 DF3) and hyperthermia showed the largest potency to induce DNA fragmentation at 6 h after hyperthermia but no enhancement was observed if it was combined with X-rays. Enhancement of hyperthermia-induced apoptosis by DF3 in a dose-dependent manner was observed. When the cells were treated first with DF3 at a nontoxic concentration of 20 microM, and exposed to hyperthermia afterwards, a significant enhancement of heat-induced apoptosis was evidenced by DNA fragmentation, morphological changes and phosphatidylserine externalization. The activation of Bid, but no change of Bax and Bcl-2 were observed after the combined treatment. The release of cytochrome c from mitochondria to cytosol, which was induced by hyperthermia, was enhanced by DF3. Mitochondrial transmembrane potential was decreased and the activation of caspase-3 and caspase-8 was enhanced in the cells treated with the combination. Externalization of Fas was observed following the combined treatment. Flow cytometry revealed rapid and sustained increase of intracellular superoxide due to DF3, and showed subsequent and transient increase in the formation of intracellular hydrogen peroxide (H(2)O(2)), which was further increased when hyperthermia was combined. These results indicate that the intracellular superoxide and H(2)O(2) generated by DF3 enhance the hyperthermia-induced apoptosis via the Fas-mediated mitochondrial caspase-dependent pathway.

Concomitant real-time monitoring of intracellular reactive oxygen species and mitochondrial membrane potential in individual living promonocytic cells

Reactive oxygen species (ROS) have recently been shown to be involved in multiple physiological responses through modulation of signaling pathways. Inappropriate production of these radicals, and their metabolites, leads to the development of various pathologies. Free radicals can induce both positive and negative effects in cells, and their metabolic pathways are very complex. Hence, it is crucial to be able to simultaneously and directly determine their production dynamics and concentrations in individual living cells, in physiological or pathological states, and in response to drugs. The aim of the present study was to monitor in real time the rates of ROS generation in promonocytic cells upon stimulation with hydrogen peroxide and oxidized lipid. Quantitative detection of intracellular ROS concentration in intact living U937 cells was performed by fluorescence intensity (FI) and polarization (FP) measurements utilizing the Optical LiveCell Array technology. The "dihydro" derivative probes of fluorescein (DCF-DA) and rhodamine (DHR123) were used to assess the intracellular levels of ROS. Each probe molecule exhibited a characteristic FI and FP in its non-fluorescent or oxidized form. Analysis of the temporal relationship between the kinetics of ROS generation and the onset of changes in mitochondrial membrane potential shows high variability within a cell population with regard to both processes. The data demonstrated that temporal measurement of ROS generation, in identifiable individual cells, reveals kinetic behavior that otherwise would be undetected.

Ceramide is the key mediator of oxidative stress-induced apoptosis in retinal photoreceptor cells

Nitric oxide and reactive oxygen species play a critical role in photoreceptor apoptosis. However, the exact molecular mechanisms triggered by oxidative stress in photoreceptor cell death remain undefined. Here, we demonstrate that the sphingolipid ceramide is the key mediator of oxidative stress-induced apoptosis in 661W retinal photoreceptor cells. Treatment of 661W cells with the nitric oxide donor, sodium nitroprusside, activates acid sphingomyelinase. As a result, sphingomyelin is hydrolysed, which leads to an increase in the concentration of ceramide. We also show that ceramide is responsible for the activation of the mitochondrial apoptotic pathway in 661W photoreceptor cells and subsequent activation of the caspase cascade. Furthermore, we show for the first time that ceramide is responsible for the increased Ca2+ levels in the mitochondria and cytosol that precedes activation of the calpain-mediated apoptotic pathway. Additionally, we provide evidence that ceramide also activates the endolysosomal protease cathepsin D pathway. In summary, our findings show that ceramide controls the cell death decisions in photoreceptor cells and highlight the relevance of acid sphingomyelinase as a potential therapeutic target for the treatment of retinal pathologies.

Mechanisms of cardiolipin oxidation by cytochrome c: relevance to pro- and antiapoptotic functions of etoposide

Execution of apoptotic program in mitochondria is associated with accumulation of cardiolipin peroxidation products required for the release of proapoptotic factors into the cytosol. This suggests that lipid antioxidants capable of inhibiting cardiolipin peroxidation may act as antiapoptotic agents. Etoposide, a widely used antitumor drug and a topoisomerase II inhibitor, is a prototypical inducer of apoptosis and, at the same time, an effective lipid radical scavenger and lipid antioxidant. Here, we demonstrate that cardiolipin oxidation during apoptosis is realized not via a random cardiolipin peroxidation mechanism but rather proceeds as a result of peroxidase reaction in a tight cytochrome c/cardiolipin complex that restrains interactions of etoposide with radical intermediates generated in the course of the reaction. Using low-temperature and ambient-temperature electron paramagnetic resonance spectroscopy of H(2)O(2)-induced protein-derived (tyrosyl) radicals and etoposide phenoxyl radicals, respectively, we established that cardiolipin peroxidation and etoposide oxidation by cytochrome c/cardiolipin complex takes place predominantly on protein-derived radicals of cytochrome c. We further show that etoposide can inhibit cytochrome c-catalyzed oxidation of cardiolipin competing with it as a peroxidase substrate. Peroxidase reaction of cytochrome c/cardiolipin complexes causes cross-linking and oligomerization of cytochrome c. With nonoxidizable tetraoleoyl-cardiolipin, the cross-linking occurs via dityrosine formation, whereas bifunctional lipid oxidation products generated from tetralinoleoyl-cardiolipin participate in the production of high molecular weight protein aggregates. Protein aggregation is effectively inhibited by etoposide. The inhibition of cardiolipin peroxidation by etoposide, however, is realized at far higher concentrations than those at which it induces apoptotic cell death. Thus, oxidation of cardiolipin by the cytochrome c/cardiolipin peroxidase complex, which is essential for apoptosis, is not inhibited by proapoptotic concentrations of the drug.

Oxidative stress and apoptotic changes in murine splenocytes exposed to cadmium

Cadmium being a potent immunotoxicant, affects both humoral and cell mediated immunity. However, its effect on spleen is not clearly understood. Hence, to delineate the action of Cd, mouse splenic lymphocytes were exposed to Cd (10, 25 and 50 microM) for 60 min, 1.5, 3, 6 and 18 h. At 6 h, apoptosis was reflected by DNA fragmentation, increased sub-G1 population (apoptotic DNA) and apoptotic cells (Annexin V binding assay). The early stage markers of apoptosis, i.e. decreased mitochondrial membrane potential and caspase-3 activation were observed as early as 1.5 h by the highest dose of Cd (50 microM). Significant ROS production by 25 and 50 microM Cd at 60 min occurred prior to the lowering of mitochondrial membrane potential, suggesting involvement of ROS in causing mitochondrial membrane damage. N-acetylcysteine and pyrrolidine dithiocarbamate (thiol antioxidants) lowered the sub-G(1) population, inhibited the ROS generation and raised the GSH levels induced by Cd. Buthionine sulfoximine (GSH depletor) on the other hand, enhanced the ROS production as well as the sub-G1 fraction. These results imply that ROS is a critical mediator of Cd-induced apoptosis and that cadmium may compromise splenic immune function by accelerating apoptosis.

Pro-oxidant and cytotoxic activities of atractylenolide I in human promyeloleukemic HL-60 cells

The dried rhizome of Bai Zhu (Atractylodes ovata) is widely used as a Chinese herbal medicine. Two sesquiterpenolides of similar structures (atractylenolide I, AT-I; atractylenolide III, AT-III) were isolated from dried rhizome of Atractylodes ovata. Incubation of AT-I with recombinant human Cu,Zn-superoxide dismutase (rhCu,Zn-SOD) resulted in rhCu,Zn-SOD fragmentations and Zn releases. However, these were not observed in the AT-III reaction. The AT-1 showed dose-dependent cytotoxic activities (7.5, 15, and 30 microg/ml) on the human promyeloleukemic HL-60 cells while AT-III did not, and the IC50 of the former being 10.6 microg/ml (corresponding to 46 microM) on 12 h-treated cells. The results of DNA ladder and DNA contents in sub-G1 type revealed that AT-I induced apoptosis in human promyeloleukemic HL-60 cells. The cytotoxic and pharmacological mechanisms of AT-I against human promyeloleukemic HL-60 cells was investigated. The AT-I appeared to exhibit both pro-oxidant and antioxidant properties after an ESR spectrometer was used to detect hydroxyl radical productions in vitro and flow cytometry to detect intracellular ROS productions in AT-I treated cells. The AT-1 also showed dose-dependent Cu,Zn-SOD inhibitory activity in HL-60 cells treated for 12 h, confirmed by activity and immune stainings. However, catalase, Mn-SOD, and glutathione peroxidase did not apparently change activities under the same treatments. The addition of commercial rhCu,Zn-SOD (25-100 U/mL) to the AT-I-treated HL-60 cells (15 microg/ml) resulted in significant differences (p<0.01) and could reduce the AT-I cytotoxicity from 78% to 28% on HL-60 cells. It was proposed that the AT-I might work via Cu,Zn-SOD inhibition in HL-60 cells to induce apoptosis and bring about cytotoxicity.

Involvement of endonuclease G in nucleosomal DNA fragmentation under sustained endogenous oxidative stress

We have previously shown that inhibition of catalase and glutathione peroxidase activities by 3-amino-1,2,4-triazole (ATZ) and mercaptosuccinic acid (MS), respectively, in rat primary hepatocytes caused sustained endogenous oxidative stress and apoptotic cell death without caspase-3 activation. In this study, we investigated the mechanism of this apoptotic cell death in terms of nucleosomal DNA fragmentation. Treatment with ATZ+MS time-dependently increased the number of deoxynucleotidyl transferase-mediated nick end-labeling (TUNEL)-positive nuclei from 12 h, resulting in clear DNA laddering at 24 h. The deoxyribonuclease (DNase) inhibitor, aurintricarboxylic acid (ATA), completely inhibited nucleosomal DNA fragmentation but the pan-caspase inhibitor, z-VAD-fmk was without effects; furthermore, the cleavage of inhibitor of caspase-activated DNase was not detected, indicating the involvement of DNase(s) other than caspase-activated DNase. Considering that endonuclease G (EndoG) reportedly acts in a caspase-independent manner, we cloned rat EndoG cDNA for the first time. Recombinant EndoG alone digested plasmid DNA and induced nucleosomal DNA fragmentation in isolated hepatocyte nuclei. Recombinant EndoG activity was inhibited by ATA but not by hydrogen peroxide, even at 10 mm. ATZ+MS stimulation elicited decreases in mitochondrial membrane potential and EndoG translocation from mitochondria to nuclei. By applying RNA interference, the mRNA levels of EndoG were almost completely suppressed and the amount of EndoG protein was decreased to approximately half the level of untreated cells. Under these conditions, decreases in TUNEL-positive nuclei were significantly suppressed. These results indicate that EndoG is responsible, at least in part, for nucleosomal DNA fragmentation under endogenous oxidative stress conditions induced by ATZ+MS.

Involvement of oxidative stress in the pre-malignant and malignant states of cervical cancer in women

OBJECTIVES

To evaluate the potential role of oxidative stress in the evolution of cervical cancer, including its pre-malignant states.

DESIGN AND METHODS

Erythrocytes thiobarbituric acid reactive substances (TBARS) levels, plasma vitamin C and thiol content and total blood delta-ALA-D levels were estimated in 46 untreated cervical cancer and pre-malignant patients and in 46 age-sex-matched controls.

RESULTS

Erythrocytes from patients, regardless of disease state, pre-malignant (low squamous intraepithelial lesion--LSIL and high squamous intraepithelial lesion--HSIL) or cancer, showed a significant 2-3 times increase in TBARS levels (P<0.01). Plasma vitamin C was lower in the carcinoma group (P<0.01). The reactivation index of delta-aminolevulinate dehydratase (delta-ALA-D) was higher in the patient group, when compared to control (P<0.01).

CONCLUSION

LSIL, HSIL or cervical cancer can be associated with changes in 3 indicators of oxidative stress: increase in erythrocyte TBARS, ALA-D reactivation index and a decrease in vitamin C content, that may play an important role in carcinogenesis.

Heat shock proteins and acute leukemias

Heat shock proteins (HSPs) acts as molecular chaperones by helping in the refolding of misfolded proteins and assisting in their elimination if they become irreversibly damaged. HSPs induced by stress treatment have a role in the modulation of apoptosis. The reduction in protein expression levels was correlated with an increased susceptibility to drug-induced apoptosis. HSPs have also been implicated in the resistance of leukemia cells to potential therapeutic agents. The mechanisms of cellular protection used by HSPs have yet to be fully defined. HSPs were shown highly expressed by acute myeloid leukemia (AML) cells as well as by acute lymphoblastic leukemia (ALL) cells. HSP expressions were correlated with that of differentiation antigens and that of drug-resistance and apoptosis proteins. Complete remission (CR) rates were higher in patients with lower expression of HSPs. Overall survival (OS) was significantly longer in patients with lower expression of HSPs. Therapeutically, inhibition of inducible HSP expression or activity should not cause any undesired side effects. HSPs emerge as novel therapeutic targets in anticancer protocols. Early results of phase I studies indicate that 17-allylamino-17-demethoxygeldamycin (17-AAG), capable of binding and disrupting the function of HSP90, results in an acceptable toxicity profile while achieving in vivo disruption of multiple oncogenic client proteins.

The Effect of Quercetin on Topotecan Cytotoxicity in MCF-7 and MDA-MB 231 Human Breast Cancer Cells1

BACKGROUND

Topotecan, which is a Camptothecin derivative, shows a large spectrum in anti-tumor activity. Topotecan exerts its cytotoxic effect on tumor cells mainly by inhibition of topoisomerase I activity resulting in double-strand DNA breaks. In our study, we investigated the combined cytotoxic action of Topotecan and Quercetin in MCF-7 and MDA-MB 231 human breast cancer cells. To examine the possible relation between the cytotoxic activity of Topotecan and oxidative stress, we measured ROS and nitrite levels in both human breast cell lines.

MATERIALS AND METHODS

MCF-7 and MDA-MB 231 cells were exposed to Topotecan, Quercetin, or a combination of both agents for 24 h at 37 degrees C. The viability of the cells was measured using the colorimetric MTT (3-(4,5)-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay. We determined reactive oxygen species and nitrite levels as indicators of oxidative stress in both cell lines with and without Topotecan and/or Quercetin incubations using fluorometric dichlorofluorescin diacetate (DCFH-DA) and diaminonaphtalene (DAN) assay.

RESULTS

The IC(50) concentration of Topotecan was 100 ng/ml in MCF-7 cell line and 160 ng/ml in MDA-MB231 cell line. Treatment with Quercetin enhanced cytotoxicity of Topotecan as 1.4-fold in MCF-7 and 1.3-fold in MDA-MB-231 cell line. A significant increment on ROS and nitrite levels was found in MCF-7 and MDA-MB-231 cells following Topotecan incubation.

CONCLUSIONS

Our results suggest that Topotecan has cytotoxic activity against both of the breast cancer cell lines in vitro. A combination with Quercetin increases efficacy of Topotecan in the treatment of breast cancers. Our results indicate that increased oxidative stress plays a role in the cytotoxic action of Topotecan.

Immune cell-induced synthesis of NO and reactive oxygen species in lymphoma cells causes their death by apoptosis

Induction of apoptosis in a lymphoma cell line using immune cell-conditioned medium, etoposide or an nitric oxide (NO) donor, resulted in the production of reactive oxygen species (ROS). Agents that inhibited NO production or scavenged ROS or species formed by reaction of NO with ROS, protected the cells from apoptosis. These data support the suggestion that immune rejection of an immunogenic derivative of this lymphoma in vivo involves the induced synthesis of both NO and ROS by the tumour cells.

Analysis of gene expression in apoptosis of human lymphoma U937 cells induced by heat shock and the effects of α-phenyl N-tert-butylnitrone (PBN) and its derivatives

Hyperthermia, a modality of cancer therapy, has been known as a stress to induce apoptosis. However, the molecular mechanism of heat shock-induced apoptosis, especially on roles of intracellular oxidative stress, is not fully understood. First, when human lymphoma U937 cells were treated with heat shock (44 degrees C, 30 min), the fraction of apoptosis, revealed by phosphatidylserine externalization, increased gradually and peaked at 6 hr after the treatment. In contrast, intracellular superoxide formation increased early during the heat shock treatment and peaked at 30 min after the treatment. When the cells were treated with heat shock in the presence of alpha -phenyl-N-tert-butylnitrone (PBN) and its derivatives, which are potent antioxidants, the DNA fragmentation was inhibited in an order according to the agents' hydrophobicity. PBN showing the highest inhibitory effects suppressed not only intracellular superoxide formation but also various apoptosis indicators. cDNA microarray was employed to analyze gene expression associated with heat shock-induced apoptosis, and the time-course microarray analysis revealed 5 groups showing changes in their pattern of gene expression. Among these genes, c-jun mRNA expression showed more than 40 fold increase 2 hr after heat treatment. The expression level of c-jun mRNA verified by quantitative real-time PCR was about 20 fold increase, and c-jun expression was similarly suppressed by PBN and its derivatives. These results suggest that the change of c-jun expression is an excellent molecular marker for apoptosis mediated by intracellular oxidative stress induced by heat shock.

Simultaneous intra- and extracellular superoxide monitoring using an integrated optical and electrochemical sensor system

A new integrated optical and electrochemical sensor system for simultaneous monitoring of intra- and extracellular superoxide (O(2)(-)) was developed using an array-based cell chip. For in vitro assays, A172 human glioblastoma cells were transferred into the cell chip and stimulated by phorbol 12-myristate 13-acetate (PMA). Intracellular O(2)(-) generation was detected via fluorescence image analysis with a dye probe, dihydrorhodamine 123 (DHR 123). Extracellular O(2)(-) was detected using an amperometric sensor constructed by immobilisation of cytochrome c using a binder, 3,3'-dithiobis(sulphosuccinimidylpropionate), to attach the redox protein onto the surface of electrodeposited Au electrodes incorporated into the optically transparent cell chip. The simultaneous intra- and extracellular production of O(2)(-) was successfully observed from PMA-stimulated A172 cells and inhibited by superoxide dismutase (SOD). The quantification of O(2)(-) concentration based on a mathematical model study and possible applications using the sensor system developed were discussed. The results confirm that there was no detectable interference or crosstalk between the optical and electrochemical assays. Feasibility of the integration of the two methods, optical and electrochemical, and the neutralisation of the intra- and extracellular O(2)(-) levels by SOD have been demonstrated.

Enhancement of apoptosis by nitric oxide released from α-phenyl-tert-butyl nitrone under hyperthermic conditions

The aim of this study was to examine whether a neuroprotector, PBN (alpha-phenyl-tert-butyl nitrone), enhances apoptosis induced by hyperthermia, which generates superoxide (O2-) intracellularly, since the release of nitric oxide (NO) from PBN under oxidative stress has been reported. When human myelomonocytic lymphoma U937 cells were treated with hyperthermia (44 degrees C, 10 min) and PBN, an increase in the concentration of nitrite in the culture medium, and a decrease in the hyperthermia-induced production of O2- was observed. Imaging using a fluorescence dye for intracellular NO, diaminofluorescein-2 diacetate (DAF-2 DA), revealed the formation of NO in the apoptotic cells treated with hyperthermia and PBN combined. Apoptotic endpoints were significantly enhanced by the combined treatment: a decrease in mitochondrial trans-membrane potential, cleavage of Bid, release of cytochrome c, and activation of caspase-8 and -3. An increase in the intracellular Ca2+ concentration ([Ca2+]i), externalization of Fas, and decrease in Hsp70 and phosphorylated HSF1 were observed following the combined treatment. Furthermore, scavengers of NO an d ONOO- significantly inhibited the enhancement of apoptosis, the externalization of Fas and the increase in [Ca2+]i. These results suggest that, (1) NO is released from PBN by hyperthermia, and subsequently reacts with O2- to form ONOO-, (2) NO and ONOO- are involved in the enhancement of apoptosis through Fas-mitochondria-caspase and [Ca2+]i-dependent pathways, and (3) a decrease in Hsp70 and phosphorylated HSF1 also contributed to the enhancement of apoptosis.

An increase in reactive oxygen species by dietary fish oil coupled with the attenuation of antioxidant defenses by dietary pectin enhances rat colonocyte apoptosis

We showed previously that the dietary combination of fish oil, rich in (n-3) fatty acids, and the fermentable fiber pectin enhances colonocyte apoptosis in a rat model of experimentally induced colon cancer. In this study, we propose that the mechanism by which this dietary combination heightens apoptosis is via modulation of the colonocyte redox environment. Male Sprague-Dawley rats (n = 60) were fed 1 of 2 fats (corn oil or fish oil) and 1 of 2 fibers (cellulose or pectin) for 2 wk before determination of reactive oxygen species (ROS), oxidative DNA damage, antioxidant enzyme activity [superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx)] and apoptosis in isolated colonocytes. Fish oil enhanced ROS, whereas the combination of fish oil and pectin suppressed SOD and CAT and enhanced the SOD/CAT ratio compared with a corn oil and cellulose diet. Despite this modulation to a seemingly prooxidant environment, oxidative DNA damage was inversely related to ROS in the fish oil and pectin diet, and apoptosis was enhanced relative to other diets. Furthermore, apoptosis increased exponentially as ROS increased. These results suggest that the enhancement of apoptosis associated with fish oil and pectin feeding may be due to a modulation of the redox environment that promotes ROS-mediated apoptosis.

Apoptotic and necrotic cells induced by different agents vary in their expression of MHC and costimulatory genes

We have recently reported, in a murine tumor model, that apoptotic cells induced by different agents may vary in their ability to elicit host immunity. The basis for this observation is unclear but may involve varying efficiencies of cross-presentation and/or direct activation of immunity by different apoptotic preparations. As a first step in addressing this issue, we compared expression patterns of selected immune genes (MHC class I, class II, CD40, B7-1, B7-2) on viable and apoptotic populations induced by four different agents. The histone deacetylase inhibitor trichostatin A (TSA) induced MHC class II expression on viable and apoptotic cell populations, while LPAM, H2O2 and gamma-irradiation did not activate class II. Each agent employed elicited a different expression pattern of costimulatory molecules (CD40, B7-1, B7-2) on both apoptotic and 7-AAD+ 'necrotic' populations. In striking contrast to the TSA induction of MHC class II, class I cell surface protein was diminished on the apoptotic populations. These effects were not a result of changes in the cell cycle produced by the various treatments. The data demonstrate that distinctive gene expression patterns on viable and apoptotic cells are elicited by different apoptosis inducing agents. We discuss how expression patterns on dead or dying tumor cells could potentially affect the tumor's ability to elicit immunity.

Acidic polysaccharide isolated from Phellinus linteus enhances through the up-regulation of nitric oxide and tumor necrosis factor-alpha from peritoneal macrophages

Medicinal mushrooms are increasingly used to treat a wide variety of disease processes. Aqueous extract from the fruiting body or mycelia of Phellinus linteus has been reported to produce antitumor and immunomodulatory activities in vivo and in vitro. However, the mechanisms underlying its tumoricidal effects are poorly understood. The tumoricidal activity of peritoneal macrophages (PM) cultured with acidic polysaccharide (PL) isolated from Phellinus linteus against B16 melanoma cells was enhanced in a dose-dependent manner; growth inhibition increased 4-fold with 200 microg/ml of PL. To further characterize the mechanisms of PL, we investigated the effects of PL on phagocytosis and the release of nitric oxide (NO), tumor necrosis factor-alpha (TNF-alpha) and reactive oxygen intermediates (ROI). To investigate the phagocytosis of PM, the uptake of Dextran (Dex)-FITC between PL-untreated and PL-treated PM was compared. We found some augment in phagocytosis of PL-treated PM compared untreated group. PL stimulated a dose-dependent increase in NO and TNF-alpha, but not in ROI production in PM. We suggested that PL has cytotoxicity against Yac-1 cells through the up-regulation of NO and TNF-alpha production. Also, PL enhanced the expression of costimulatory molecules, CD80 and CD86, and major histocompatibility complex (MHC) molecules II in PM. The ability of PL upon the up-regulation of these surface molecules involved in antigen-presenting processes may, by inference, activate T-cell-mediated immunity against malignant cells in vivo. Taken together, these results suggest that PL act as an effective immunomodulator and enhances the anti-tumoral activity of PM.

Dehydrocrotonin and its derivative, dimethylamide-crotonin induce apoptosis with lipid peroxidation and activation of caspases-2, -6 and -9 in human leukemic cells HL60

A variety of stimuli can induce cells to undergo apoptosis, with one of the most reproducible inducers being mild oxidative stress following exposure to anticancer agents. Apoptosis involves events mediated by cysteine proteases (caspases) that are classified as initiators (-8, -9 and -12) or executors (-2, -3, -6 and -7). In this study, we examined the mechanisms of apoptosis induced by dehydrocrotonin (DHC), a diterpene lactone isolated from the Amazonian plant Croton cajucara, and its synthetic derivative, dimethylamide-crotonin (DCR), in human HL60 promyelocytic leukemia cells. Flow cytometric analysis of HL60 cells after treatment for 72 h showed that DCR- and DHC-induced apoptosis, with maximum cell death at a concentration of 250 microM for both compounds. DCR and DHC were effective in triggering the activation of caspases-2, -6 and -9. The level of reduced glutathione (GSH) decreased, whereas there was an increase in thiobarbituric acid-reactive substance (TBARS) production and in mitochondrial swelling. These effects on mitochondrial swelling, GSH content and lipid peroxidation were abolished by cyclosporine A, an inhibitor of the membrane permeability transition. The cytotoxicity of DHC and DCR was prevented by a high concentration of GSH (15 mM) in the culture medium. These results indicate that DCR and DHC produced apoptosis partly by oxidative stress-induced lipid peroxidation, which triggered the caspase cascade, that lead to apoptotic cell death in HL60 cells. Based on the pattern of caspase activation, on the increase in mitochondrial swelling and on the inhibitory action of cyclosporine A, we conclude that DCR and DHC triggered apoptosis in HL60 cells probably through cytochrome c release and apoptosome formation.

Oxidative Stress-induced Apoptosis in Retinal Photoreceptor Cells Is Mediated by Calpains and Caspases and Blocked by the Oxygen Radical Scavenger CR-6

A critical role for reactive oxygen species (ROS) in photoreceptor apoptosis has been established. However, the exact molecular mechanisms triggered by oxidative stress in photoreceptor cell death remain undefined. This study delineates the molecular events that occur after treatment of the photoreceptor cell line 661W with the nitric oxide donor sodium nitroprusside (SNP). Cytosolic calcium levels increased during photoreceptor apoptosis, leading to activation of the calcium-dependent proteases calpains. Furthermore, caspase activation also occurred following SNP insult. However, although treatment with the pan-caspase inhibitor benzyloxycarbonyl-Val-Ala-Asp fluoromethyl ketone inhibited caspase activity per se in SNP-treated 661W cells, it did not prevent apoptosis. On the other hand, CR-6 (3,4-dihydro-6-hydroxy-7-methoxy-2,2-dimethyl-1(2H)-benzopyran) acted as a scavenger of ROS and reduced 661W photoreceptor apoptosis induced by SNP by preventing the activation of a pathway in which calpains have a key role. In summary, we report for the first time that both caspases and calpains are involved in 661W photoreceptor apoptosis and that calpain activation can be prevented by the ROS scavenger CR-6.

An aging-related cell surface NADH oxidase (arNOX) generates superoxide and is inhibited by coenzyme Q

This report describes a novel ECTO-NOX protein with an oscillating activity having a period length of ca. 26 min encountered with buffy coat fractions and sera of aged individuals (70-100 years) that generates superoxide as measured by the reduction of ferricytochrome c. The oscillating, age-related reduction of ferricytochrome c is sensitive to superoxide dismutase, is inhibited by coenzyme Q and is reduced or absent from sera of younger individuals (20-40 years). An oscillating activity with a regular period length is a defining characteristic of ECTO-NOX proteins (a group of cell surface oxidases with enzymatic activities that oscillate). The period length of ca. 26 min is longer than the period length of 24 min for the usual constitutive (CNOX) ECTO-NOX proteins of the cell surface and sera which neither generate superoxide nor reduce ferricytochrome c. The aging-related ECTO-NOX protein (arNOX) provides a mechanism to transmit cell surface oxidative changes to surrounding cells and circulating lipoproteins potentially important to atherogenesis. Additionally, the findings provide a rational basis for the use of dietary coenzyme Q to retard aging-related arterial lesions.