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

Role of signal transduction pathways in IL-1β-induced apoptosis: Pathological and therapeutic aspects

BACKGROUND

Interleukin-1β (IL-1β) is a pro-inflammatory cytokine mainly produced by monocytes and macrophages with a wide range of biological effects. Evidence has shown that IL-1β plays a vital role in the process of apoptosis; however, the specific mechanisms, by which IL-1β induces apoptosis, vary due to different cellular and experimental conditions. Therefore, this present reviewstudy aimed to systematically review the association between the molecular mechanisms of IL-1β-induced apoptosis in pathological processes and the role of signaling pathways. This article also sought to briefly investigate the potential of signaling pathway-targeted therapy in the prevention and treatment of disease.

METHODS

This is a literature review article. The present discourse aim is first to scrutinize and assess the available literature on IL-1β and apoptosis. The relevant studies using the keywords of "IL-1β-induced apoptosis" and "signaling pathways" were searched in the databases of PubMed, Scopus, Google Scholar, and Web of Science. Gathered relevant material, and extracted information was then assessed.

RESULTS

IL-1β can induce apoptosis in various types of cells under different external stimuli via the mitochondrial pathway, death receptor pathway and endoplasmic reticulum pathway, and that the different pathways are often interconnected. The NF-kB signaling pathway, p38MAPK, and JNK signaling pathways mainly play a proapoptotic part, and the ERK1/2 pathway has a bidirectional role in regulating apoptosis, while activation of the PI3K-Akt signaling pathway can inhibit apoptosis.

CONCLUSION

This review indicates that IL-1β-induced apoptosis plays an important role in pathogenesis and development of pathology of many inflammatory diseases. Elucidating the role of the signaling pathways will aid the development of targeted therapeutic treatments.

Melatonin triggers the anticancer potential of phenylarsine oxide via induction of apoptosis through ROS generation and JNK activation

Melatonin, a safe endogenous hormone and a natural supplement, has recently been recognized to have antiproliferative effects and the ability to sensitize cells to other anticancer therapies. Phenylarsine oxide (PAO) has anticancer potential but it is considered as a toxic agent. In this study we combined melatonin to reduce the toxicity while securing the anti-cancer effects of PAO. Cell viability was determined by MTT assay, whereas cytotoxic assays were performed using an LDH cytotoxicity assay kit. Cell cycle analysis, Annexin V/PI staining, the mitochondrial membrane potential (MMP), mitochondrial calcium and reactive oxygen species (ROS) generation were analyzed using flow cytometry. Sytox stained cells were visualized by fluorescence microscopy and the expression of proteins was detected by western blotting. Melatonin increased the anticancer potential of PAO by decreasing the cell viability and increasing LDH release in various cancer cells. The mode of cell death was determined to be typical apoptosis, as evidenced by Annexin V/PI-stained cells, PARP cleavage, and caspase-3 activation, and with significant modulations in the expression of proapoptotic, antiapoptotic and cell cycle-related proteins. ROS generation played a critical role in induction of cell death by this combined treatment, which is validated by reversal of cytotoxicity upon cotreatment with NAC. Furthermore, the activation of MAPKs, especially JNK, contributed to the induction of cell death, accompanied by endoplasmic reticulum stress and autophagy, affirmed by the abrogation of cytotoxicity after JNK-IN-8 and TUDCA application. Melatonin showed promising potential as a chemotherapeutic agent in combination with PAO to achieve a better anticancer response.

Mechanistic study of nonivamide enhancement of hyperthermia-induced apoptosis in U937 cells

Hyperthermia is one therapeutic tool for damaging and killing cancer cells, with minimal injury to normal tissues. However, its cytotoxic effects alone are insufficient for quantitative cancer cell death. To overcome this limitation, several studies have explored non-toxic enhancers for hyperthermia-induced cell death. Capsaicin may be applicable as a therapeutic tool against various types of cancer. In the present study, we employed nonivamide, a less-pungent capsaicin analogue, to investigate its possible enhancing effects on hyperthermia-induced apoptosis; moreover, we analyzed its molecular mechanism. Treatment of U937 cells at 44 °C for 15 min, combined with nonivamide 50 μM, revealed enhancement of apoptosis. Significant increases in reactive oxygen species generation, mitochondrial dysfunction, and cleaved caspase-3 were observed during the combined treatment; these were accompanied by an increase in pro-apoptotic Bcl-2 family proteins and a decrease in anti-apoptotic Bcl-2 proteins. In addition, significant increases in p-JNK and p-p38 were detected, following the combined treatment. In conclusion, nonivamide enhanced hyperthermia-induced apoptosis via a mitochondrial-caspase dependent pathway. The underlying mechanism may include elevation of intracellular reactive oxygen species, mitochondrial dysfunction, and increased activation of JNK and p38.

Melatonin enhances hyperthermia-induced apoptotic cell death in human leukemia cells

Melatonin is an endogenous indoleamine with a wide range of biological functions. In addition to modulating circadian rhythms, it plays important roles in the health as an antioxidant. Melatonin has also the ability to induce apoptosis in cancer cells and to enhance the antitumoral activity of chemotherapeutic agents. In this study, the effect of melatonin on hyperthermia-induced apoptosis was explored using human leukemia cells. The results demonstrate that melatonin greatly improved the cytotoxicity of hyperthermia in U937 cells. The potentiation of cell death was achieved with 1 mmol/L concentrations of the indoleamine but not with concentrations close to physiological levels in blood (1 nmol/L). This effect was associated to an enhancement of the apoptotic response, revealed by an increase in cells with hypodiploid DNA content and activation of multiple caspases (caspase-2, caspase-3, caspase-8, and caspase-9). Melatonin also increased hyperthermia-induced Bid activation as well as translocation of Bax from the cytosol to mitochondria and cytochrome c release. Hyperthermia-provoked apoptosis and potentiation by melatonin were abrogated by a broad-spectrum caspase inhibitor (z-VAD-fmk) as well as by specific inhibitors against caspase-8 or caspase-3. In contrast, blocking of the mitochondrial pathway of apoptosis either with a caspase-9 inhibitor or overexpressing the anti-apoptotic protein Bcl-2 (U937/Bcl-2) reduced the number of apoptotic cells in response to hyperthermia but it was unable to suppress melatonin enhancement. Melatonin appears to modulate the apoptotic response triggered by hyperthermia in a cell type-specific manner as similar results were observed in HL-60 but not in K562 or MOLT-3 cells.

On the vasoprotective mechanisms underlying novel β-phosphorylated nitrones: Focus on free radical characterization, scavenging and NO-donation in a biological model of oxidative stress

A series of new hybrid 2-(diethoxyphosphoryl)-N-(benzylidene)propan-2-amine oxide derivatives with different aromatic substitution (PPNs) were synthesized. These molecules were evaluated for their EPR spin trapping potential on eleven different radicals and NO-donation properties in vitro, cytotoxicity and vasoprotective effect on precontracted rat aortic rings. A subfamily of the new PPNs featured an antioxidant moiety occurring in natural phenolic acids. From the experimental screening of these hydroxyphenyl- and methoxyphenyl-substituted PPNs, biocompatible nitrones 4d, and 4g-4i deriving from caffeic, gallic, ferulic and sinapic acids, which combined improved EPR probing of ROS formation, vasorelaxant action and antioxidant potency, might be potential drug candidate alternatives to PBN and its analogues.

Hyperthermia: an effective strategy to induce apoptosis in cancer cells

Heat has been used as a medicinal and healing modality throughout human history. The combination of hyperthermia (HT) with radiation and anticancer agents has been used clinically and has shown positive results to a certain extent. However, the clinical results of HT treatment alone have been only partially satisfactory. Cell death following HT treatment is a function of both temperature and treatment duration. HT induces cancer cell death through apoptosis; the degree of apoptosis and the apoptotic pathway vary in different cancer cell types. HT-induced reactive oxygen species production are responsible for apoptosis in various cell types. However, the underlying mechanism of signal transduction and the genes related to this process still need to be elucidated. In this review, we summarize the molecular mechanism of apoptosis induced by HT, enhancement of heat-induced apoptosis, and the genetic network involved in HT-induced apoptosis.

Insight into the molecular mechanism of heme oxygenase-1 induction by docosahexaenoic acid in U937 cells

Heme oxygenase-1 (HO-1) has anti-inflammatory effects on myeloid cells in response to various stimuli. To date, little is known about whether fatty acids can affect HO-1 induction. Here, we report the induction of HO-1 by docosahexaenoic acid (DHA) and the associated molecular mechanisms in human myelomonocytic lymphoma U937 cells. When U937 cells were treated with DHA, eicosapentaenoic acid, palmitic acid or oleic acid, DHA was the most effective inducer of HO-1. The activation of AKT and glycogen synthase kinase-3β did not significantly change after DHA treatment. However, DHA increased the activation of extracellular signal-regulated kinases 1 and 2 (ERK1/2), but not of other mitogen-activated protein kinases such as p38 and JNK. The increase in HO-1 expression was significantly inhibited by U0126, an ERK1/2 inhibitor. Nuclear translocation of nuclear factor erythroid 2-related factor 2 (Nrf-2) and its binding to the HO-1 promoter significantly increased upon DHA treatment. An increase in intracellular reactive oxygen species was detected by dichlorofluorescein diacetate, but not by hydroethidium or 2-[6-(4-hydroxy)phenoxy-3H-xanthen-3-on-9-yl] benzoic acid after DHA treatment. Pretreatment with NAC dramatically inhibited the ERK1/2 activation, binding of Nrf-2 to antioxidant response elements (AREs) located in the HO-1 promoter and the induction of HO-1 by DHA. In conclusion, DHA increased HO-1 expression in U937 cells via activation of ERK1/2 and increased Nrf-2 binding to ARE in the HO-1 promoter. These findings will help develop better strategies for treating inflammatory disorders with DHA.

Isofraxidin, a potent reactive oxygen species (ROS) scavenger, protects human leukemia cells from radiation-induced apoptosis via ROS/mitochondria pathway in p53-independent manner

Ionizing radiation (IR) leads to oxidizing events such as excessive reactive oxygen species (ROS) in the exposed cells, resulting in further oxidative damage to lipids, proteins and DNA. To screen the potential radio-protective drug, the intracellular ROS was measured in irradiated U937 cells pretreated with 80 candidate traditional herbal medicine, respectively. Isofraxidin (IF) was one possible radio-protector in these 80 drugs. This study investigated the radio-protective role of IF, a Coumarin compound, in human leukemia cell lines, for the first time. Results indicate that IF protects against IR-induced apoptosis in U937 cells in the time- and concentration- dependent manner. IF decreases IR-induced intracellular ROS generation, especially hydroxyl radicals formation, inhibits IR-induced mitochondrial membrane potential loss and reduces IR-induced high intracellular Ca(2+) levels regardless of ER stress. IF down-regulates the expression of caspase-3, phospho-JNK, phospho-p38 and activates Bax in mitochondria. IF inhibits cytochrome c release from mitochondria to cytosol. IF also moderates IR-induced Fas externalization and caspase-8 activation. IF also exhibits significant protection against IR-induced cell death in other leukemia cell lines such as Molt-4 cells and HL60 cells regardless of p53. Taken together, the data demonstrate that IF protects leukemia cells from radiation-induced apoptosis via ROS/mitochondria pathway in a p53-independent manner.

Molecular mechanisms of apoptosis induction by 2-dodecylcyclobutanone, a radiolytic product of palmitic acid, in human lymphoma U937 cells

The irradiation of fat-containing food forms 2-dodecylcyclobutanone (2-DCB) from palmitic acid (PA). In this study, we investigated whether 2-DCB and PA induce apoptosis in human lymphoma U937 cells. We found that cell viability decreased by 2-DCB and apoptosis was induced by 2-DCB and PA. 2-DCB and PA significantly enhanced the formation of intracellular reactive oxygen species (ROS). Apoptosis induced by 2-DCB and PA was strongly prevented by an antioxidant, N-acetyl-L: -cysteine. The treatment with 2-DCB and PA resulted in the loss of mitochondrial membrane potential, and Fas, caspase-8 and caspase-3 activation. Pretreatment with a pan-caspase inhibitor (z-VAD) significantly inhibited apoptosis induced by 2-DCB and PA. Moreover, 2-DCB and PA also induced Bax up-regulation, the reduction in Bcl-2 expression level, Bid cleavage and the release of cytochrome c from the mitochondria to the cytosol. In addition, an increase in intracellular Ca(2+) concentration ([Ca(2+)](i)) was observed after the treatment with 2-DCB and PA. Our results indicated that intracellular ROS generation, the modulation of the Fas-mitochondrion-caspase-dependent pathway and the increase in [Ca(2+)](i) involved in apoptosis are induced by 2-DCB and PA in U937 cells.

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.

Liposomal doxorubicin increases radiofrequency ablation-induced tumor destruction by increasing cellular oxidative and nitrative stress and accelerating apoptotic pathways

PURPOSE

To determine if oxidative and nitrative stress and/or apoptosis contribute to increased coagulation when combining radiofrequency (RF) ablation with liposomal doxorubicin.

MATERIALS AND METHODS

Animal care committee approval was obtained. R3230 mammary adenocarcinomas in Fischer rats were treated with either RF ablation (n = 43), 1 mg of intravenously injected liposomal doxorubicin (n = 26), or combined therapy (n = 30) and were compared with control subjects (n = 11). A subset of animals receiving combination therapy (n = 24) were treated in the presence or absence of N-acetylcysteine (NAC) administered 24 hours and 1 hour before RF ablation. Tumors were analyzed 2 minutes to 72 hours after treatment to determine the temporal range of response by using immunohistochemical staining of the apoptosis marker cleaved caspase-3, phosphorylated gammaH2AX, and HSP70 and of markers of oxidative and nitrative stress (8-hydroxydeoxyguanosine [8-OHdG], 4-hydroxynonenal [4-HNE]-modified proteins, and nitrotyrosine [NT]). Statistical analyses, including t tests and analysis of variance for comparisons where appropriate, were performed.

RESULTS

By 4 hours after RF ablation alone, a 0.48-mm +/- 0.13 (standard deviation) peripheral band with 57.0% +/- 7.3 cleaved caspase-3 positive cells was noted at the ablation margin, whereas a 0.73-mm +/- 0.18 band with 77.7% +/- 6.3 positivity was seen for combination therapy (P < .03 for both comparisons). Combination therapy caused increased and earlier staining for 4-HNE-modified proteins, 8-OHdG, NT, and gammaH2AX with colocalization to cleaved caspase-3 staining. A rim of increased HSP70 was identified peripheral to the area of cleaved caspase-3. Parameters of oxidative and nitrative stress were significantly inhibited by NAC 1 hour following RF ablation, resulting in decreased cleaved caspase-3 positivity (0.28-mm +/- 0.09 band of 25.9% +/- 7.4 positivity vs 0.59-mm +/- 0.11 band of 62.9% +/- 6.0 positivity, P < .001 for both comparisons).

CONCLUSION

Combining RF ablation with liposomal doxorubicin increases cell injury and apoptosis in the zone of increased coagulation by using a mechanism that involves oxidative and nitrative stress that leads to accelerated apoptosis.

Gene expression in enhanced apoptosis of human lymphoma U937 cells treated with the combination of different free radical generators and hyperthermia

The effects of various free radicals derived from 6-formylpterin (6-FP), alpha-phenyl-tert-butyl nitrone (PBN) and 2,2'-azobis (2-amidinopropane) dihydrochloride (AAPH) combined with hyperthermia, on gene expression in similarly enhanced apoptosis of human lymphoma U937 cells were investigated using cDNA microarrays containing approximately 16,600 genes and computational gene expression analysis tools. When the cells were treated for 10 min at 44 degrees C (15% apoptosis level), 39 up-regulated and 3 down-regulated genes were identified. In the up-regulated genes, apoptosis- and unfolded protein response-associated genes were contained. The combined treatment with heat and either chemical enhanced apoptosis level (approximately 30%) and showed a chemical-specific gene expression pattern. Furthermore, the expression levels of selected genes were confirmed by a real-time quantitative PCR. The present results will provide a basis for further understanding the molecular mechanisms in enhancement of heat-induced apoptosis by different intracellular oxidative stress.

Reactive oxygen species regulate F-actin dynamics in neuronal growth cones and neurite outgrowth

Reactive oxygen species are well known for their damaging effects due to oxidation of lipids, proteins and DNA that ultimately result in cell death. Accumulating evidence indicates that reactive oxygen species also have important signaling functions in cell proliferation, differentiation, cell motility and apoptosis. Here, we tested the hypothesis whether reactive oxygen species play a physiological role in regulating F-actin structure and dynamics in neuronal growth cones. Lowering cytoplasmic levels of reactive oxygen species with a free radical scavenger, N-tert-butyl-alpha-phenylnitrone, or by inhibiting specific sources of reactive oxygen species, such as NADPH oxidases or lipoxygenases, reduced the F-actin content in the peripheral domain of growth cones. Fluorescent speckle microscopy revealed that these treatments caused actin assembly inhibition, reduced retrograde actin flow and increased contractility of actin structures in the transition zone referred to as arcs, possibly by activating the Rho pathway. Reduced levels of reactive oxygen species ultimately resulted in disassembly of the actin cytoskeleton. When neurons were cultured overnight in conditions of reduced free radicals, growth cone formation and neurite outgrowth were severely impaired. Therefore, we conclude that physiological levels of reactive oxygen species are critical for maintaining a dynamic F-actin cytoskeleton and controlling neurite outgrowth.

Microarray analysis of cytokine activation of apoptosis pathways in the thyroid

It has been suggested that Fas-mediated apoptosis plays an important role in the pathogenesis of autoimmune thyroid diseases. Our previous studies have demonstrated that normal primary thyroid epithelial cells are resistant to Fas-mediated apoptosis, but the resistance can be overcome by pretreatment with a combination of interferon-gamma (IFN-gamma) and IL-1beta. To understand the molecular mechanism responsible for the IFN-gamma/IL-1beta effects, we profiled changes in the transcription induced by these two cytokines in normal human thyroid cells, using cDNA microarrays. We found that IFN-gamma/IL-1beta showed a significant increase in apoptosis-related genes such as inducible nitric oxide synthase (iNOS), receptor-interacting protein 2 (RIP2), and caspases 10. These increases were confirmed by other methods, including real-time PCR and Western blot. Furthermore, the sensitization of primary thyroid epithelial cells to Fas-mediated apoptosis by IFN-gamma/IL-1beta was significantly blocked by a general caspase inhibitor, z-VAD, or by the combination of two specific individual caspase inhibitors. In addition, our results showed that IFN-gamma/IL-1beta enhance p38 MAPK phosphorylation and that SB 203580, a p38 MAPK inhibitor, can inhibit IFN-gamma/IL-1beta-induced p38 MAPK phosphorylation. SB 203580 also significantly prevented cytokine-induced iNOS expression and caspase activation and thus blocked Fas-mediated apoptosis of thyroid cells sensitized by IFN-gamma/IL-1beta. In conclusion, our data suggest that both p38 MAPK and iNOS are involved in IFN-gamma/IL-1beta-induced sensitization of the thyroid cells to Fas-mediated apoptosis via the activation of caspases 3, 7, and 10 and that this pathway may be further activated by BID. This hints that inflammatory cytokines regulate death-receptor-mediated apoptosis at multiple points in the process.

Neuroprotective antioxidant STAZN protects against myocardial ischemia/reperfusion injury

BACKGROUND

Protecting the myocardium from ischemia-reperfusion injury has significant potential to reduce the complications of myocardial infarction and interventional revascularization procedures. Reperfusion damage is thought to result, in part, from oxidative stress. Here we use a novel method of percutaneous coronary occlusion to show that the potent antioxidant and neuroprotective free-radical scavenger, stilbazulenyl nitrone (STAZN), confers marked cardioprotection when given immediately prior to reperfusion.

METHODS AND RESULTS

Physiologically controlled male Sprague-Dawley rats were anesthetized with isoflurane, paralyzed with pancuronium and mechanically ventilated. A guide wire was introduced via the femoral artery and advanced retrogradely via the aorta into the left coronary artery under fluoroscopic guidance. Rats with established coronary ischemia (85 min after occlusion) were given STAZN 3.5 mg/kg or its vehicle 5 min before and 2 h after reperfusion, and were subjected to functional and histopathologic studies at 3 days. Ischemia-associated Q wave amplitude was reduced by 73% in STAZN-treated rats (P=0.01), while infarct-related ejection fraction, fractional shortening and severe regional wall-motion impairments were improved by 48%, 54% and 37%, respectively, relative to vehicle-treated controls (P=0.05). Total myocardial infarct volume in STAZN-treated rats was correspondingly reduced by 43% (P<0.05), representing a sparing of 14% of the total left ventricular myocardium.

CONCLUSIONS

STAZN, a second-generation azulenyl nitrone with potent neuroprotective efficacy in brain ischemia, is also a rapidly acting and highly effective cardioprotective agent in acute coronary ischemia. Our results suggest the potential for clinical benefit in the setting of acute coronary syndromes.

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.