Oxidation products of polyamines induce mitochondrial uncoupling and cytochrome c release

Nitric Oxide Induces Autophagy in Triticum aestivum Roots

Autophagy is a highly conserved process that degrades damaged macromolecules and organelles. Unlike animals, only scant information is available regarding nitric oxide (NO)-induced autophagy in plants. Such lack of information prompted us to study the roles of the NO donors' nitrate, nitrite, and sodium nitroprusside in this catabolic process in wheat roots. Furthermore, spermine, a polyamine that is found in all eukaryotic cells, was also tested as a physiological NO donor. Here, we show that in wheat roots, NO donors and spermine can trigger autophagy, with NO and reactive oxygen species (ROS) playing signaling roles based on the visualization of autophagosomes, analyses of the levels of NO, ROS, mitochondrial activity, and the expression of autophagic (ATG) genes. Treatment with nitrite and nitroprusside causes an energy deficit, a typical prerequisite of autophagy, which is indicated by a fall in mitochondrial potential, and the activity of mitochondrial complexes. On the contrary, spermine sustains energy metabolism by upregulating the activity of appropriate genes, including those that encode glyceraldehyde 3-phosphate dehydrogenase GAPDH and SNF1-related protein kinase 1 SnRK1. Taken together, our data suggest that one of the key roles for NO in plants may be to trigger autophagy via diverse mechanisms, thus facilitating the removal of oxidized and damaged cellular constituencies.

Difluoromethylornithine (DFMO) and Neuroblastoma: A Review

Neuroblastoma is a type of cancer that affects the sympathetic nervous system and is the most common extracranial solid tumor in children. Difluoromethylornithine (DFMO) is a drug that has shown promise as a treatment option for high-risk neuroblastoma. This review aims to provide an overview of the current research on the use of DFMO in neuroblastoma treatment. The review includes a discussion of the mechanisms of action of DFMO, as well as its potential for use in combination with other treatments such as chemotherapy and immunotherapy. The review also examines the current clinical trials involving DFMO in high-risk neuroblastoma patients and provides insights into the challenges and future directions for the use of DFMO in neuroblastoma treatment. Overall, the review highlights the potential of DFMO as a promising therapy for neuroblastoma and highlights the need for further research to fully understand its potential benefits and limitations.

Synthesis of a fluorinated pyronin that enables blue light to rapidly depolarize mitochondria

Fluorinated analogues of the fluorophore pyronin B were synthesized as a new class of amine-reactive drug-like small molecules. In water, 2,7-difluoropyronin B was found to reversibly react with primary amines to form covalent adducts. When this fluorinated analogue is added to proteins, these adducts undergo additional oxidation to yield fluorescent 9-aminopyronins. Irradiation with visible blue light enhances this oxidation step, providing a photochemical method to modify the biological properties of reactive amines. In living HeLa cells, 2,7-difluoropyronin B becomes localized in mitochondria, where it is partially transformed into fluorescent aminopyronins, as detected by spectral profiling confocal microscopy. Further excitation of these cells with the blue laser of a confocal microscope can depolarize mitochondria within seconds. This biological activity was only observed with 2,7-difluoropyronin B and was not detected with analogues such as pyronin B or 9-methyl-2,7-difluoropyronin B. This irradiation with blue light enhances the cellular production of reactive oxygen species (ROS), suggesting that increased ROS in mitochondria promotes the formation of aminopyronins that inactivate biomolecules critical for maintenance of mitochondrial membrane potential. The unique reactivity of 2,7-difluoropyronin B offers a novel tool for photochemical control of mitochondrial biology.

What is the role of putrescine accumulated under potassium deficiency?

Biomarker metabolites are of increasing interest in crops since they open avenues for precision agriculture, whereby nutritional needs and stresses can be monitored optimally. Putrescine has the potential to be a useful biomarker to reveal potassium (K⁺ ) deficiency. In fact, although this diamine has also been observed to increase during other stresses such as drought, cold or heavy metals, respective changes are comparably low. Due to its multifaceted biochemical properties, several roles for putrescine under K⁺ deficiency have been suggested, such as cation balance, antioxidant, reactive oxygen species mediated signalling, osmolyte or pH regulator. However, the specific association of putrescine build-up with low K⁺ availability in plants remains poorly understood, and possible regulatory roles must be consistent with putrescine concentration found in plant tissues. We hypothesize that the massive increase of putrescine upon K⁺ starvation plays an adaptive role. A distinction of putrescine function from that of other polyamines (spermine, spermidine) may be based either on its specificity or (which is probably more relevant under K⁺ deficiency) on a very high attainable concentration of putrescine, which far exceeds those for spermidine and spermine. putrescine and its catabolites appear to possess a strong potential in controlling cellular K⁺ and Ca²⁺ , and mitochondria and chloroplasts bioenergetics under K⁺ stress.

The old and new biochemistry of polyamines

Polyamines are ubiquitous positively charged amines found in all organisms. These molecules play a crucial role in many biological functions including cell growth, gene regulation and differentiation. The three major polyamines produced in all mammalian cells are putrescine, spermidine and spermine. The intracellular levels of these polyamines depend on the interplay of the biosynthetic and catabolic enzymes of the polyamine and methionine salvage pathway, as well as the involvement of polyamine transporters. Polyamine levels are observed to be high in cancer cells, which contributes to malignant transformation, cell proliferation and poor patient prognosis. Considering the critical roles of polyamines in cancer cell proliferation, numerous anti-polyaminergic compounds have been developed as anti-tumor agents, which seek to suppress polyamine levels by specifically inhibiting polyamine biosynthesis, activating polyamine catabolism, or blocking polyamine transporters. However, in terms of the development of effective anti-cancer therapeutics targeting the polyamine system, these efforts have unfortunately resulted in little success. Recently, several studies using the iron chelators, O-trensox and ICL670A (Deferasirox), have demonstrated a decline in both iron and polyamine levels. Since iron levels are also high in cancer cells, and like polyamines, are required for proliferation, these latter findings suggest a biochemically integrated link between iron and polyamine metabolism.

Nuclear reprogramming: kinetics of cell cycle and metabolic progression as determinants of success

Establishment of totipotency after somatic cell nuclear transfer (NT) requires not only reprogramming of gene expression, but also conversion of the cell cycle from quiescence to the precisely timed sequence of embryonic cleavage. Inadequate adaptation of the somatic nucleus to the embryonic cell cycle regime may lay the foundation for NT embryo failure and their reported lower cell counts. We combined bright field and fluorescence imaging of histone H_2b-GFP expressing mouse embryos, to record cell divisions up to the blastocyst stage. This allowed us to quantitatively analyze cleavage kinetics of cloned embryos and revealed an extended and inconstant duration of the second and third cell cycles compared to fertilized controls generated by intracytoplasmic sperm injection (ICSI). Compared to fertilized embryos, slow and fast cleaving NT embryos presented similar rates of errors in M phase, but were considerably less tolerant to mitotic errors and underwent cleavage arrest. Although NT embryos vary substantially in their speed of cell cycle progression, transcriptome analysis did not detect systematic differences between fast and slow NT embryos. Profiling of amino acid turnover during pre-implantation development revealed that NT embryos consume lower amounts of amino acids, in particular arginine, than fertilized embryos until morula stage. An increased arginine supplementation enhanced development to blastocyst and increased embryo cell numbers. We conclude that a cell cycle delay, which is independent of pluripotency marker reactivation, and metabolic restraints reduce cell counts of NT embryos and impede their development.

Polyamines in aging and disease

Polyamines are polycations that interact with negatively charged molecules such as DNA, RNA and proteins. They play multiple roles in cell growth, survival and proliferation. Changes in polyamine levels have been associated with aging and diseases. Their levels decline continuously with age and polyamine (spermidine or high-polyamine diet) supplementation increases life span in model organisms. Polyamines have also been involved in stress resistance. On the other hand, polyamines are increased in cancer cells and are a target for potential chemotherapeutic agents. In this review, we bring together these various results and draw a picture of the state of our knowledge on the roles of polyamines in aging, stress and diseases.

Effects of a novel cystine-based glutathione precursor on oxidative stress in vascular smooth muscle cells

Chronic kidney disease (CKD) is associated with accelerated atherosclerosis and cardiovascular disease, which is largely mediated by oxidative stress. We investigated the effect of three glutathione (GSH) precursors: N-acetyl-cysteine (NAC), cystine as the physiological carrier of cysteine in GSH with added selenomethionine (F1), and NAC fortified with selenomethionine (F2) on oxidative stress induced by spermine (a uremic toxin) in cultured human aortic vascular smooth muscle cells (VSMC). VSMC were exposed to spermine (15 microM) with or without the given antioxidants (dose 50, 100, 200, and 500 microg/ml) or vehicle (control) and assessed for intracellular GSH levels, 4-hydroxy-trans-2-nonenal (4-HNE), and incorporation of 13C from glucose into alanine and protein. Spermine exposure reduced intracellular GSH levels, increased 4-HNE, and impaired glucose metabolism through reduction in pyruvate generation and/or transamination. Treatment with NAC had no effect on intracellular glutathione level. In contrast, F1 maintained intracellular GSH at control levels at all four doses. Subsequent studies performed with 200 microg/ml of F1, F2, or NAC (optimal dose) revealed normalization of 4-HNE, whereas restoration of 13C from glucose to alanine or protein to control values was only noted in the F1 group. Spermine-induced alterations in VSMC ultrastructure were prevented in approximately 90% of cells treated with F1 but only approximately 50% of cells treated with either NAC or F2. In conclusion, F1 was more effective than NAC or F2 in ameliorating spermine-induced reduction in intracellular GSH levels and cellular alterations in VSMC. The cystine-based GSH precursor (F1) is a promising antioxidant, and further studies are needed to examine the effect of this compound in preventing CKD-associated vascular disease.

Inhibition of apoptotic signalling in spermine-treated vascular smooth muscle cells by a novel glutathione precursor

CKD (chronic kidney disease) is a public health problem, mediated by haemodynamic and non-haemodynamic events including oxidative stress. We investigated the effect of two GSH (glutathione) precursors, NAC (N-acetylcysteine) and cystine as the physiological carrier of cysteine in GSH with added selenomethionine (F1) in preventing spermine (uraemic toxin)-induced apoptosis in cultured human aortic VSMC (vascular smooth muscle cells). VSMCs exposed to spermine (15 microM) with or without antioxidants (doses 50, 100, 200 and 500 microg/ml) were assessed for apoptosis, JNK (c-Jun-NH2-terminal kinase) activation and iNOS (inducible nitric oxide synthase) induction and activation of intrinsic pathway signalling. Spermine exposure resulted in activation of JNK and iNOS induction and apoptosis. NAC and F1 (dose range 50-500 microg/ml) attenuated spermine-induced acceleration of VSMC apoptosis but only F1 (at 200 and 500 microg/ml) maintained spermine-induced apoptosis at control levels. Spermine-induced JNK activation was prevented by 200 microg/ml of both NAC and F1, while iNOS induction was blocked only by F1. Notably, the adverse effects of spermine on BAX/BCL-2 ratio, cytochrome c release and caspase activation was fully attenuated by F1. In conclusion, F1 was more effective than NAC in preventing spermine-induced apoptosis and downstream changes in related signal transduction pathways in VSMCs. Further studies are needed to examine the effect of these compounds in preventing CKD-associated vascular disease.

Metabolic correlations of glucocorticoids and polyamines in inflammation and apoptosis

Glucocorticoid hormones (GC) are essential in all aspects of human health and disease. Their anti-inflammatory and immunosuppressive properties are reasons for therapeutic application in several diseases. GC suppress immune activation and uncontrolled overproduction and release of cytokines. GC inhibit the release of pro-inflammatory cytokines and stimulate the production of anti-inflammatory cytokines. Investigation of GC's mechanism of action, suggested that polyamines (PA) may act as mediators or messengers of their effects. Beside glucocorticoids, spermine (Spm) is one of endogenous inhibitors of cytokine production. There are many similarities in the metabolic actions of GC and PA. The major mechanism of GC effects involves the regulation of gene expression. PA are essential for maintaining higher order organization of chromatin in vivo. Spermidine and Spm stabilize chromatin and nuclear enzymes, due to their ability to form complexes with negatively charged groups on DNA, RNA and proteins. Also, there is an increasing body of evidence that GC and PA change the chromatin structure especially through acetylation and deacetylation of histones. GC display potent immunomodulatory activities, including the ability to induce T and B lymphocyte apoptosis, mediated via production of reactive oxygen species (ROS) in the mitochondrial pathway. The by-products of PA catabolic pathways (hydrogen peroxide, amino aldehydes, acrolein) produce ROS, well-known cytotoxic agents involved in programmed cell death (PCD) or apoptosis. This review is an attempt in the better understanding of relation between GC and PA, naturally occurring compounds of all eukaryotic cells, anti-inflammatory and apoptotic agents in physiological and pathological conditions connected to oxidative stress or PCD.

Spermine signaling plays a significant role in the defense response of Arabidopsis thaliana to cucumber mosaic virus

We have proposed that the polyamine spermine (Spm) functions as a signaling molecule to evoke defense reactions/cell death in avirulent pathogen-attacked tobacco plants. To understand its molecular basis in depth, Spm-responsive genes in Arabidopsis thaliana were identified by SuperSAGE analysis. Close to 90% of the Spm-responsive genes also responded during cucumber mosaic virus (CMV)-elicited hypersensitive response. Spm modulated the expression of genes of redox components, and genes involved in protein folding and secretion, protein degradation and defense. Two other prominent changes, the coordinately enhanced expression of members of the photorespiration pathway and a diversion in electron flow from the primary electron transfer chain of respiration to an alternative oxidase pathway, occurred in response to Spm. Spm activated the expression of 6 transcription factor genes including ZAT7, ZAT12, AtWRKY40 and AtbZIP60, of which the former three genes' products are currently assigned as components of H(2)O(2) signaling pathway, suggesting the involvement of H(2)O(2) in Spm-triggered responses. Since AtbZIP60 plays a proven master role in the unfolded protein response in Arabidopsis thaliana, it may function to control the expression of genes participating in protein folding and secretion, which were mentioned above. Spm induction and CMV-triggered up-regulation of the genes described mainly coincided and their induction was suppressed by inhibitors of Spm oxidation. Furthermore, treatment with those inhibitors prior to CMV inoculation allowed higher viral multiplication in Arabidopsis thaliana plants. These results support the existence of a Spm-signaling pathway in Arabidopsis thaliana and its significant role in defense against CMV.

Hypothermic storage of isolated human hepatocytes: a comparison between University of Wisconsin solution and a hypothermosol platform

Until now little is known about the functional integrity of human hepatocytes after hypothermic storage. In order to address this limitation, we evaluated several commercially available hypothermic preservation media for their abilities to protect freshly isolated hepatocytes during prolonged cold storage. Human hepatocytes were isolated from non-transplantable/rejected donor livers and resuspended in ice-cold University of Wisconsin solution (UW), HypoThermosol-Base (HTS-Base), or HypoThermosol-FRS (HTS-FRS) with or without the addition of fetal bovine serum. Cells were stored at 4 degrees C for 24-72 h, and evaluated for hepatocyte viability (trypan blue exclusion, or labeling with fluorochromes), cell attachment, and function. The energy status of hepatocytes was evaluated by measurement of intracellular adenosine 5'-triphosphate. To determine whether the test cells expressed metabolic functions of freshly isolated cells, the activities of major phase I (cytochromes P450, FMO) and phase II (UGT, ST) drug-metabolizing enzymes were examined. Although hepatocytes are shown to be satisfactory after 24 h storage in all of the tested solutions, the cell viability, energy status, and xenobiotic metabolism following cold preservation in HTS-FRS was consistently and, in some cases, markedly higher when compared with other systems. The same metabolites for each of the tested substrates were detected in all groups of cells. Moreover, the use of HTS-FRS eliminates the need for serum in preservation solutions. HTS-FRS represents an improved solution compared to HTS-Base and UW for extending the shipping/storage time of human hepatocytes.

Anticancer drugs and hyperthermia enhance cytotoxicity induced by polyamine enzymatic oxidation products

A correlation between regulation of cell proliferation and polyamine metabolism is described. The latter can enter protein synthesis through the modification of eukaryotic initiation factor 5A (eIF5A) and the formation of the peculiar amino acid hypusine. Specific inhibitors of hypusine formation induce apoptosis that can be potentiated by the combination with cytokines such as interferonalpha (IFNalpha) that itself decreases hypusine synthesis. We have also demonstrated that the concomitant treatment of cancer cells with IFNalpha and the protein synthesis inhibitor fusion protein TGFalpha/Pseudomonas Aeruginosa toxin synergize in inducing cancer cell growth inhibition. Another way used by polyamines to induce apoptosis is the generation of intracellular oxidative stress through the interaction with bovine serum amine oxidase (BSAO). This enzyme used simultaneously to spermine induces apoptosis, necrosis, inhibition of cell proliferation and inhibition of DNA and protein synthesis in several cell types. The enzymatic oxidation products of polyamine, H2O2 and aldehyde(s) cause these effects. We have recently found that the cytotoxicity of anti-cancer agents, either etoposide or docetaxel, in cancer cells is potentiated in the presence of BSAO/Spermine. In conclusion, polyamine metabolites could be useful in the design of new therapeutic strategies.

Targeting polyamine metabolism and function in cancer and other hyperproliferative diseases

The polyamines spermidine and spermine and their diamine precursor putrescine are naturally occurring, polycationic alkylamines that are essential for eukaryotic cell growth. The requirement for and the metabolism of polyamines are frequently dysregulated in cancer and other hyperproliferative diseases, thus making polyamine function and metabolism attractive targets for therapeutic intervention. Recent advances in our understanding of polyamine function, metabolic regulation, and differences between normal cells and tumour cells with respect to polyamine biology, have reinforced the interest in this target-rich pathway for drug development.

Energy metabolism of the inner cell mass and trophectoderm of the mouse blastocyst

Mammalian pre-implantation development culminates in the formation of the blastocyst consisting of two distinct cell lineages, approximately a third of the cells comprise the pluripotent inner cell mass (ICM) and the remainder the differentiated trophectoderm (TE). However, the contribution made by these two cell types to the overall energy metabolism of the intact blastocyst has received relatively little attention. In this study, the metabolism of the intact mouse blastocyst and isolated ICMs were determined in terms of total ATP formation (calculated from oxygen consumption and lactate formation), mitochondrial distribution and amino acid turnover to provide an indication of protein synthesis. The TE consumed significantly more oxygen, produced more ATP and contained a greater number of mitochondria than the ICM. Amino acid turnover was significantly greater (p<0.001) in the TE compared with the ICM. Specifically, there was a significant difference in the utilization of aspartate (p=0.020), glutamate (p=0.024), methionine (p=0.037), and serine (p=0.041) between the cells of the ICM and TE. These data suggest that the TE produces approximately 80% of the ATP generated and is responsible for 90% of amino acid turnover compared with the ICM. The major fate of the energy produced by the TE is likely to be the Na(+), K(+)ATPase (sodium pump enzyme) located on the TE basolateral membrane. In conclusion, the pluripotent cells of the ICM display a relatively quiescent metabolism in comparison with that of the TE.

Amine oxidases in apoptosis and cancer

Amine oxidases, the major enzymes of biogenic amines metabolism, are considered to be biological regulators, especially for cell growth and differentiation. A primary involvement of amine oxidases in cancer growth inhibition and progression, especially by means of aldehydes, H(2)O(2) and other reactive oxygen species, the amine oxidase-mediated products of biogenic amines oxidation, has been demonstrated. Amine oxidases are involved in cancer growth inhibition because of the higher content in tumour cells of biogenic amines in comparison to normal cells. The cytotoxic effect can be explained by a damage to cell membranes and/or nuclei or, indirectly, through modulation of membrane permeability transition and therefore apoptosis. The oxidation products of biogenic amines appears to be also carcinogenic, while acrolein, produced from the oxidation of spermine and spermidine, should be a key compound both carcinogenic and cytotoxic. The cancer inhibition/promotion effect of amine oxidases could be explained by taking into consideration the full pattern of the enzyme content of the cell. The balance of amine oxidases and antioxidant enzymes appear to be a crucial point for cancer inhibition or progression. A long lasting imbalance of these enzymes appears to be carcinogenic, while, for a short time, amine oxidases are cytotoxic for cancer cells.

Polyamines inhibit apoptosis in porcine parthenotes developing in vitro

Polyamines, namely putrescine, spermidine, and spermine, are biogenic low-molecular-weight aliphatic amines which play essential roles in cell growth and proliferation. The aim of this study was to determine the effects of polyamines on the viability and development of porcine diploid parthenotes developing in vitro. The addition of 0.1 or 1.0 microM of putrescine, spermidine, or spermine, individually, to the culture medium did not enhance the development of 2-cell parthenotes to the blastocyst stage and did not change the total number of nuclei in the blastocysts. However, combined addition of these three compounds increased developmental rate to blastocyst and total cell numbers. Apoptosis in blastocyst stage parthenotes was decreased in the presence of exogenous polyamines. Real time PCR revealed that addition of polyamines to the culture media decreased the ratio of mRNA expression of Bak/Bcl-xL, Fas/Bcl-xL, and caspase 3, and enhanced mRNA expression of ornithine decarboxylase (ODC) and spermidine synthase, enzymes of polyamine biosynthesis. In the presence of L-alpha-difluoromethyl ornithine (an inhibitor of ODC) or cyclohexylamine (an inhibitor of spermidine synthase) development of porcine parthenotes decreased, apoptosis increased, and mRNA expression of the ratio of Bak/Bcl-xL and Fas/Bcl-xL, and caspase 3 increased. These results suggest that exogenous polyamines in the culture medium prevent apoptosis of porcine parthenotes and results in the net enhancement of porcine embryo viability.

A subset of hypersensitive response marker genes, including HSR203J, is the downstream target of a spermine signal transduction pathway in tobacco

A cellular signal transduction pathway induced by the polyamine, spermine (Spm), and transmitted by mitochondrial dysfunction is proposed in tobacco. In this investigation, we further resolve the pathway by identifying a subset of hypersensitive response (HR) marker genes as downstream components. In a previous report, we identified harpin-induced 1 (HIN1) and two closely related genes as responsive to Spm. Other HR marker genes, HSR203J, HMGR, HSR201, and HSR515, are also Spm-responsive. Induction of these HR marker genes, including HIN1, by Spm was suppressed by pre-treatment with antioxidants, calcium channel blockers, inhibitor of mitochondrial permeability transition pore openings, and blockers of amine oxidase/polyamine oxidase. Such quenching is also observed for Spm-induced activation of two mitogen-activated protein kinases (MAPKs), salicylic acid-induced protein kinase (SIPK), and wound-induced protein kinase (WIPK), and upregulation of the WIPK gene, suggesting that all these components are part of the same signaling pathway. Furthermore, gain-of-function and loss-of-function studies on MAPK cascade members reveal that the expression of Spm-induced HR marker genes varies with respect to involvement of SIPK/WIPK activation.

Induction of polyamine oxidase 1 by Helicobacter pylori causes macrophage apoptosis by hydrogen peroxide release and mitochondrial membrane depolarization

Helicobacter pylori infects the human stomach by escaping the host immune response. One mechanism of bacterial survival and mucosal damage is induction of macrophage apoptosis, which we have reported to be dependent on polyamine synthesis by arginase and ornithine decarboxylase. During metabolic back-conversion, polyamines are oxidized and release H(2)O(2), which can cause apoptosis by mitochondrial membrane depolarization. We hypothesized that this mechanism is induced by H. pylori in macrophages. Polyamine oxidation can occur by acetylation of spermine or spermidine by spermidine/spermine N(1)-acetyltransferase prior to back-conversion by acetylpolyamine oxidase, but recently direct conversion of spermine to spermidine by the human polyamine oxidase h1, also called spermine oxidase, has been demonstrated. H. pylori induced expression and activity of the mouse homologue of this enzyme (polyamine oxidase 1 (PAO1)) by 6 h in parallel with ornithine decarboxylase, consistent with the onset of apoptosis, while spermidine/spermine N(1)-acetyltransferase activity was delayed until 18 h when late stage apoptosis had already peaked. Inhibition of PAO1 by MDL 72527 or by PAO1 small interfering RNA significantly attenuated H. pylori-induced apoptosis. Inhibition of PAO1 also significantly reduced H(2)O(2) generation, mitochondrial membrane depolarization, cytochrome c release, and caspase-3 activation. Overexpression of PAO1 by transient transfection induced macrophage apoptosis. The importance of H(2)O(2) was confirmed by inhibition of apoptosis with catalase. These studies demonstrate a new mechanism for pathogen-induced oxidative stress in macrophages in which activation of PAO1 leads to H(2)O(2) release and apoptosis by a mitochondrial-dependent cell death pathway, contributing to deficiencies in host defense in diseases such as H. pylori infection.

Neuroprotective effects of spermine following hypoxia‐ischemia‐induced brain damage: A mechanistic study

The polyamines (spermine, putrescine, and spermidine) can have neurotoxic or neuroprotective properties in models of neurodegeneration. However, assessment in a model of hypoxia-ischemia (HI) has not been defined. Furthermore, the putative mechanisms of neuroprotection have not been elucidated. Therefore, the present study examined the effects of the polyamines in a rat pup model of HI and determined effects on key enzymes involved in inflammation, namely, nitric oxide synthase (NOS) and arginase. In addition, effects on mitochondrial function were investigated. The polyamines or saline were administered i.p. at 10mg/kg/day for 6 days post-HI. Histological assessment 7 days post-HI revealed that only spermine significantly (P<0.01) reduced infarct size from 46.14 +/- 10.4 mm3 (HI + saline) to 4.9 +/- 2.7 mm3. NOS activity was significantly increased following spermine treatment in the left (ligated) hemisphere compared with nonintervention controls (P<0.01) and HI + saline (P<0.05). In contrast, spermine decreased arginase activity compared with HI + saline but was still significantly elevated in comparison to nonintervention controls (P<0.01). Assessment of mitochondrial function in the HI + saline group, revealed significant and extensive damage to complex-I (P<0.01) and IV (P<0.001) and loss of citrate synthase activity (P<0.05). No effect on complex II-III was observed. Spermine treatment significantly prevented all these effects. This study has therefore confirmed the neuroprotective effects of spermine in vivo. However, for the first time, we have shown that this effect may, in part, be due to increased NOS activity and preservation of mitochondrial function.

Spermine signalling in tobacco: activation of mitogen-activated protein kinases by spermine is mediated through mitochondrial dysfunction

Polyamines (PAs) play important roles in cell proliferation, growth and environmental stress responses of all living organisms. In this study, we examine whether these compounds act as signal mediators. Spermine (Spm) specifically activated protein kinases of tobacco leaves, which were identified as salicylic acid (SA)-induced protein kinase (SIPK) and wound-induced protein kinase (WIPK), using specific antibodies. Upon Spm treatment, upregulation of WIPK, but not SIPK, was observed. Spm-induced mitogen-activated protein kinases (MAPKs) activation and WIPK upregulation were prevented upon pre-treatment with antioxidants and Ca2+ channel blockers. Additionally, Spm specifically stimulated expression of the alternative oxidase (AOX) gene, which was disrupted by these antioxidants and Ca2+ channel blockers. Bongkrekic acid (BK), an inhibitor of the opening of mitochondrial permeability transition (PT) pores, suppressed MAPKs activation and accumulation of WIPK and AOX mRNA. Our data collectively suggest that Spm causes mitochondrial dysfunction via a signalling pathway in which reactive oxygen species and Ca2+ influx are involved. As a result, the phosphorylation activities of the two MAPK enzymes SIPK and WIPK are stimulated.

Elucidation of molecular events leading to neutrophil apoptosis following phagocytosis: cross-talk between caspase 8, reactive oxygen species, and MAPK/ERK activation

Phagocytosis of complement-opsonized targets is a primary function of neutrophils at sites of inflammation, and the clearance of neutrophils that have phagocytosed microbes is important for the resolution of inflammation. Our previous work suggests that phagocytosis leads to rapid neutrophil apoptosis that is inhibited by antibody to the beta2 integrin, Mac-1, and requires NADPH oxidase-derived reactive oxygen species (ROS) generated during phagocytosis. Here we report that phagocytosis-induced cell death (PICD) does not occur in Mac-1-deficient murine neutrophils, suggesting that PICD proceeds through a bona fide Mac-1-dependent pathway. A sustained, intracellular oxidative burst is associated with PICD. Furthermore, PICD does not require traditional death receptors, Fas, or tumor necrosis factor (TNF) receptor. TNF but not Fas synergizes with phagocytosis to enhance significantly PICD by increasing the oxidative burst, and this is Mac-1-dependent. Phagocytosis-induced ROS promote cleavage/activation of caspases 8 and 3, key players in most extrinsic ("death receptor") mediated pathways of apoptosis, and caspases 8 and 3 but not caspase 9/mitochondria, are required for PICD. This suggests that ROS target the extrinsic versus the intrinsic ("stress stimulus") apoptotic pathway. Phagocytosis also triggers a competing MAPK/ERK-dependent survival pathway that provides resistance to PICD likely by down-regulating caspase 8 activation. The anti-apoptotic factor granulocyte-macrophage colony-stimulating factor (GM-CSF) significantly enhances ROS generation associated with phagocytosis. Despite this, it completely suppresses PICD by sustaining ERK activation and inhibiting caspase 8 activation in phagocytosing neutrophils. Together, these studies suggest that Mac-1-mediated phagocytosis promotes apoptosis through a caspase 8/3-dependent pathway that is modulated by NADPH oxidase-generated ROS and MAPK/ERK. Moreover, TNF and GM-CSF, likely encountered by phagocytosing neutrophils at inflammatory sites, exploit pro-(ROS) and anti-apoptotic (ERK) signals triggered by phagocytosis to promote or suppress PICD, respectively, and thus modulate the fate of phagocytosing neutrophils.

Creating conditions similar to those that occur during exposure of cells to microgravity induces apoptosis in human lymphocytes by 5-lipoxygenase-mediated mitochondrial uncoupling and cytochrome c release

Creating conditions similar to those that occur during exposure of cells to microgravity induced a sixfold increase of apoptotic bodies and DNA fragments in human lymphocytes, paralleled by an early (within 2 h) fourfold increase in 5-lipoxygenase (5-LOX) activity and a fivefold decrease in mitochondrial membrane potential and increase in cytochrome c release (within 4 and 8 h, respectively). Similar membrane potential and cytochrome c release were observed in isolated mitochondria treated with physiological amounts of 5-LOX and were enhanced by creating conditions similar to those that occur during exposure of cells to microgravity. 5-LOX inhibitors, 5,8,11,14-eicosatetraynoic acid and caffeic acid, completely prevented apoptosis, whereas the phospholipase A(2) inhibitor methyl-arachidonoyl fluorophosphonate and the 5-LOX activating protein inhibitor MK886 reduced it to 65-70%. The intracellular calcium chelator EGTA-acetoxymethylester reduced 5-LOX activity and apoptosis to 30-40% of controls, whereas the p38 mitogen-activated protein kinase inhibitor SB203580 was ineffective. The caspase-3 and caspase-9 inhibitors Z-Asp(OCH(3))-Glu(OCH(3))-Val-Asp(OCH(3))-fluoromethylketone (FMK) and Z-Leu-Glu(OCH(3))-His-Asp(OCH(3))-FMK reduced apoptotic bodies to 25-30% of the control cells. Finally, creating conditions similar to those that occur during exposure of cells to microgravity did not induce apoptosis in human lymphoma U937 cells, which did not express an active 5-LOX.