Direct oxidative DNA damage, apoptosis and radio sensitivity by spermine oxidase activities in mouse neuroblastoma cells

Spermine oxidase induces DNA damage and sensitizes fusion negative rhabdomyosarcoma cells to irradiation

Rhabdomyosarcoma (RMS) is a pediatric myogenic soft tissue sarcoma that includes fusion-positive (FP) and fusion-negative (FN) molecular subtypes. FP-RMS expresses PAX3-FOXO1 fusion protein and often shows dismal prognosis. FN-RMS shows cytogenetic abnormalities and frequently harbors RAS pathway mutations. Despite the multimodal heavy chemo and radiation therapeutic regimens, high risk metastatic/recurrent FN-RMS shows a 5-year survival less than 30% due to poor sensitivity to chemo-radiotherapy. Therefore, the identification of novel targets is needed. Polyamines (PAs) such as putrescine (PUT), spermidine (SPD) and spermine (SPM) are low-molecular-mass highly charged molecules whose intracellular levels are strictly modulated by specific enzymes. Among the latter, spermine oxidase (SMOX) regulates polyamine catabolism oxidizing SPM to SPD, which impacts cellular processes such as apoptosis and DNA damage response. Here we report that low SMOX levels are associated with a worse outcome in FN-RMS, but not in FP-RMS, patients. Consistently, SMOX expression is downregulated in FN-RMS cell lines as compared to normal myoblasts. Moreover, SMOX transcript levels are reduced FN-RMS cells differentiation, being indirectly downregulated by the muscle transcription factor MYOD. Noteworthy, forced expression of SMOX in two cell lines derived from high-risk FN-RMS: 1) reduces SPM and upregulates SPD levels; 2) induces G0/G1 cell cycle arrest followed by apoptosis; 3) impairs anchorage-independent and tumor spheroids growth; 4) inhibits cell migration; 5) increases γH2AX levels and foci formation indicative of DNA damage. In addition, forced expression of SMOX and irradiation synergize at activating ATM and DNA-PKCs, and at inducing γH2AX expression and foci formation, which suggests an enhancement in DNA damage response. Irradiated SMOX-overexpressing FN-RMS cells also show significant decrease in both colony formation capacity and spheroids growth with respect to single approaches. Thus, our results unveil a role for SMOX as inhibitor of tumorigenicity of FN-RMS cells in vitro. In conclusion, our in vitro results suggest that SMOX induction could be a potential combinatorial approach to sensitize FN-RMS to ionizing radiation and deserve further in-depth studies.

The Impact of Spermidine on C2C12 Myoblasts Proliferation, Redox Status and Polyamines Metabolism under H2O2 Exposure

A central feature of the skeletal muscle is its ability to regenerate through the activation, by environmental signals, of satellite cells. Once activated, these cells proliferate as myoblasts, and defects in this process profoundly affect the subsequent process of regeneration. High levels of reactive oxygen species such as hydrogen peroxide (H₂O₂) with the consequent formation of oxidized macromolecules increase myoblasts’ cell death and strongly contribute to the loss of myoblast function. Recently, particular interest has turned towards the beneficial effects on muscle of the naturally occurring polyamine spermidine (Spd). In this work, we tested the hypothesis that Spd, upon oxidative challenge, would restore the compromised myoblasts’ viability and redox status. The effects of Spd in combination with aminoguanidine (Spd-AG), an inhibitor of bovine serum amine oxidase, on murine C2C12 myoblasts treated with a mild dose of H₂O₂ were evaluated by analyzing: (i) myoblast viability and recovery from wound scratch; (ii) redox status and (iii) polyamine (PAs) metabolism. The treatment of C2C12 myoblasts with Spd-AG increased cell number and accelerated scratch wound closure, while H₂O₂ exposure caused redox status imbalance and cell death. The combined treatment with Spd-AG showed an antioxidant effect on C2C12 myoblasts, partially restoring cellular total antioxidant capacity, reducing the oxidized glutathione (GSH/GSSG) ratio and increasing cell viability through a reduction in cell death. Moreover, Spd-AG administration counteracted the induction of polyamine catabolic genes and PA content decreased due to H₂O₂ challenges. In conclusion, our data suggest that Spd treatment has a protective role in skeletal muscle cells by restoring redox balance and promoting recovery from wound scratches, thus making myoblasts able to better cope with an oxidative insult.

Genetic regulation of spermine oxidase activity and cancer risk: a Mendelian randomization study

Spermine oxidase (SMOX) catalyzes the oxidation of spermine to spermidine. Observational studies have reported SMOX as a source of reactive oxygen species associated with cancer, implying that inhibition of SMOX could be a target for chemoprevention. Here we test causality of SMOX levels with cancer risk using a Mendelian randomization analysis. We performed a GWAS of spermidine/spermine ratio to identify genetic variants associated with regulation of SMOX activity. Replication analysis was performed in two datasets of SMOX gene expression. We then did a Mendelian randomization analysis by testing the association between the SMOX genetic instrument and neuroblastoma, gastric, lung, breast, prostate, and colorectal cancers using GWAS summary statistics. GWAS of spermidine/spermine ratio identified SMOX locus (P = 1.34 × 10-49) explaining 32% of the variance. The lead SNP rs1741315 was also associated with SMOX gene expression in newborns (P = 8.48 × 10-28) and adults (P = 2.748 × 10-8) explaining 37% and 6% of the variance, respectively. Genetically determined SMOX activity was not associated with neuroblastoma, gastric, lung, breast, prostate nor colorectal cancer (P > 0.05). A PheWAS of rs1741315 did not reveal any relevant associations. Common genetic variation in the SMOX gene was strongly associated with SMOX activity in newborns, and less strongly in adults. Genetic down-regulation of SMOX was not significantly associated with lower odds of neuroblastoma, gastric, lung, breast, prostate and colorectal cancer. These results may inform studies of SMOX inhibition as a target for chemoprevention.

Is the Arginase Pathway a Novel Therapeutic Avenue for Diabetic Retinopathy?

Diabetic retinopathy (DR) is the leading cause of blindness in working age Americans. Clinicians diagnose DR based on its characteristic vascular pathology, which is evident upon clinical exam. However, extensive research has shown that diabetes causes significant neurovascular dysfunction prior to the development of clinically apparent vascular damage. While laser photocoagulation and/or anti-vascular endothelial growth factor (VEGF) therapies are often effective for limiting the late-stage vascular pathology, we still do not have an effective treatment to limit the neurovascular dysfunction or promote repair during the early stages of DR. This review addresses the role of arginase as a mediator of retinal neurovascular injury and therapeutic target for early stage DR. Arginase is the ureohydrolase enzyme that catalyzes the production of L-ornithine and urea from L-arginine. Arginase upregulation has been associated with inflammation, oxidative stress, and peripheral vascular dysfunction in models of both types of diabetes. The arginase enzyme has been identified as a therapeutic target in cardiovascular disease and central nervous system disease including stroke and ischemic retinopathies. Here, we discuss and review the literature on arginase-induced retinal neurovascular dysfunction in models of DR. We also speculate on the therapeutic potential of arginase in DR and its related underlying mechanisms.

Pharmacological Inhibition of Spermine Oxidase Reduces Neurodegeneration and Improves Retinal Function in Diabetic Mice

Diabetic retinopathy (DR) is a significant cause of blindness in working-age adults worldwide. Lack of effective strategies to prevent or reduce vision loss is a major problem. Since the degeneration of retinal neurons is an early event in the diabetic retina, studies to characterize the molecular mechanisms of diabetes-induced retinal neuronal damage and dysfunction are of high significance. We have demonstrated that spermine oxidase (SMOX), a mediator of polyamine oxidation is critically involved in causing neurovascular damage in the retina. The involvement of SMOX in diabetes-induced retinal neuronal damage is completely unknown. Utilizing the streptozotocin-induced mouse model of diabetes, the impact of the SMOX inhibitor, MDL 72527, on neuronal damage and dysfunction in the diabetic retina was investigated. Retinal function was assessed by electroretinography (ERG) and retinal architecture was evaluated using spectral domain-optical coherence tomography. Retinal cryosections were prepared for immunolabeling of inner retinal neurons and retinal lysates were used for Western blotting. We observed a marked decrease in retinal function in diabetic mice compared to the non-diabetic controls. Treatment with MDL 72527 significantly improved the ERG responses in diabetic retinas. Diabetes-induced retinal thinning was also inhibited by the MDL 72527 treatment. Our analysis further showed that diabetes-induced retinal ganglion cell damage and neurodegeneration were markedly attenuated by MDL 72527 treatment. These results strongly implicate SMOX in diabetes-induced retinal neurodegeneration and visual dysfunction.

Spermine oxidase: A promising therapeutic target for neurodegeneration in diabetic retinopathy

Diabetic Retinopathy (DR), is a significant public health issue and the leading cause of blindness in working-aged adults worldwide. The vision loss associated with DR affects patients' quality of life and has negative social and psychological effects. In the past, diabetic retinopathy was considered as a vascular disease; however, it is now recognized to be a neuro-vascular disease of the retina. Current therapies for DR, such as laser photocoagulation and anti-VEGF therapy, treat advanced stages of the disease, particularly the vasculopathy and have adverse side effects. Unavailability of effective treatments to prevent the incidence or progression of DR is a major clinical problem. There is a great need for therapeutic interventions capable of preventing retinal damage in DR patients. A growing body of evidence shows that neurodegeneration is an early event in DR pathogenesis. Therefore, studies of the underlying mechanisms that lead to neurodegeneration are essential for identifying new therapeutic targets in the early stages of DR. Deregulation of the polyamine metabolism is implicated in various neurodegenerative diseases, cancer, renal failure, and diabetes. Spermine Oxidase (SMOX) is a highly inducible enzyme, and its dysregulation can alter polyamine homeostasis. The oxidative products of polyamine metabolism are capable of inducing cell damage and death. The current review provides insight into the SMOX-regulated molecular mechanisms of cellular damage and dysfunction, and its potential as a therapeutic target for diabetic retinopathy. Structural and functional changes in the diabetic retina and the mechanisms leading to neuronal damage (excitotoxicity, loss of neurotrophic factors, oxidative stress, mitochondrial dysfunction etc.) are also summarized in this review. Furthermore, existing therapies and new approaches to neuroprotection are discussed.

Targeting Polyamine Oxidase to Prevent Excitotoxicity-Induced Retinal Neurodegeneration

Dysfunction of retinal neurons is a major cause of vision impairment in blinding diseases that affect children and adults worldwide. Cellular damage resulting from polyamine catabolism has been demonstrated to be a major player in many neurodegenerative conditions. We have previously shown that inhibition of polyamine oxidase (PAO) using MDL 72527 significantly reduced retinal neurodegeneration and cell death signaling pathways in hyperoxia-mediated retinopathy. In the present study, we investigated the impact of PAO inhibition in limiting retinal neurodegeneration in a model of NMDA (N-Methyl-D-aspartate)-induced excitotoxicity. Adult mice (8–10 weeks old) were given intravitreal injections (20 nmoles) of NMDA or NMLA (N-Methyl-L-aspartate, control). Intraperitoneal injection of MDL 72527 (40 mg/kg body weight/day) or vehicle (normal saline) was given 24 h before NMDA or NMLA treatment and continued until the animals were sacrificed (varied from 1 to 7 days). Analyses of retinal ganglion cell (RGC) layer cell survival was performed on retinal flatmounts. Retinal cryostat sections were prepared for immunostaining, TUNEL assay and retinal thickness measurements. Fresh frozen retinal samples were used for Western blotting analysis. A marked decrease in the neuronal survival in the RGC layer was observed in NMDA treated retinas compared to their NMLA treated controls, as studied by NeuN immunostaining of retinal flatmounts. Treatment with MDL 72527 significantly improved survival of NeuN positive cells in the NMDA treated retinas. Excitotoxicity induced neurodegeneration was also demonstrated by reduced levels of synaptophysin and degeneration of inner retinal neurons in NMDA treated retinas compared to controls. TUNEL labeling studies showed increased cell death in the NMDA treated retinas. However, treatment with MDL 72527 markedly reduced these changes. Analysis of signaling pathways during excitotoxic injury revealed the downregulation of pro-survival signaling molecules p-ERK and p-Akt, and the upregulation of a pro-apoptotic molecule BID, which were normalized with PAO inhibition. Our data demonstrate that inhibition of polyamine oxidase blocks NMDA-induced retinal neurodegeneration and promotes cell survival, thus offering a new therapeutic target for retinal neurodegenerative disease conditions.

Treatment with polyamine oxidase inhibitor reduces microglial activation and limits vascular injury in ischemic retinopathy

Retinal vascular injury is a major cause of vision impairment in ischemic retinopathies. Insults such as hyperoxia, oxidative stress and inflammation contribute to this pathology. Previously, we showed that hyperoxia-induced retinal neurodegeneration is associated with increased polyamine oxidation. Here, we are studying the involvement of polyamine oxidases in hyperoxia-induced injury and death of retinal vascular endothelial cells. New-born C57BL6/J mice were exposed to hyperoxia (70% O2) from postnatal day (P) 7 to 12 and were treated with the polyamine oxidase inhibitor MDL 72527 or vehicle starting at P6. Mice were sacrificed after different durations of hyperoxia and their retinas were analyzed to determine the effects on vascular injury, microglial cell activation, and inflammatory cytokine profiling. The results of this analysis showed that MDL 72527 treatment significantly reduced hyperoxia-induced retinal vascular injury and enhanced vascular sprouting as compared with the vehicle controls. These protective effects were correlated with significant decreases in microglial activation as well as levels of inflammatory cytokines and chemokines. In order to model the effects of polyamine oxidation in causing microglial activation in vitro, studies were performed using rat brain microvascular endothelial cells treated with conditioned-medium from rat retinal microglia stimulated with hydrogen peroxide. Conditioned-medium from activated microglial cultures induced cell stress signals and cell death in microvascular endothelial cells. These studies demonstrate the involvement of polyamine oxidases in hyperoxia-induced retinal vascular injury and retinal inflammation in ischemic retinopathy, through mechanisms involving cross-talk between endothelial cells and resident retinal microglia.

Spermine metabolism and radiation-derived reactive oxygen species for future therapeutic implications in cancer: an additive or adaptive response

Destruction of cells by irradiation-induced radical formation is one of the most frequent interventions in cancer therapy. An alternative to irradiation-induced radical formation is in principle drug-induced formation of radicals, and the formation of toxic metabolites by enzyme catalyzed reactions. Thus, combination therapy targeting polyamine metabolism could represent a promising strategy to fight hyper-proliferative disease. The aim of this work is to discuss and evaluate whether the presence of a DNA damage provoked by enzymatic ROS overproduction may act as an additive or adaptive response upon radiation and combination of hyperthermia with lysosomotropic compounds may improve the cytocidal effect of polyamines oxidation metabolites. Low level of X-irradiations delivers challenging dose of damage and an additive or adaptive response with the chronic damage induced by spermine oxidase overexpression depending on the deficiency of the DNA repair mechanisms. Since reactive oxygen species lead to membrane destabilization and cell death, we discuss the effects of BSAO and spermine association in multidrug resistant cells that resulted more sensitive to spermine metabolites than their wild-type counterparts, due to an increased mitochondrial activity. Since mammal spermine oxidase is differentially activated in a tissue specific manner, and cancer cells can differ in term of DNA repair capability, it could be of interest to open a scientific debate to use combinatory treatments to alter spermine metabolism and deliver differential response.

Reactive oxygen species spermine metabolites generated from amine oxidases and radiation represent a therapeutic gain in cancer treatments

The most frequent interventions in cancer therapy are currently the destruction of cells by irradiation or administration of drugs both able to induce radical formation and toxic metabolites by enzyme-catalyzed reactions. The aim of this study was to determine the cell viability of cells undergoing a DNA damage threshold accomplished by ROS overproduction via both ectopic expression of murine spermine oxidase (mSMOX) and bovine serum amine oxidase (BSAO) enzymes. Low dose of X-irradiation delivers a challenging dose of damage as evaluated in proficient Chinese hamster AA8 cell line and both deficient transcription-coupled nucleotide excision repair (NER) UV61 cells and deficient base excision repair (BER) EM9 cells, at 6 and 24 h after exposure. The priming dose of ROS overexposure by mSMOX provokes an adaptive response in N18TG2, AA8 and EM9 cell lines at 24 h. Interestingly, in the UV61 cells, ROS overexposure by mSMOX delivers an earlier adaptive response to radiation. The enzymatic formation of toxic metabolites has mainly been investigated on wild-type (WT) and multidrug-resistant (MDR) cancer cell lines, using and spermine as substrate of the BSAO enzyme. MDR cells are more sensitive to the toxic polyamine metabolites than WT cells, thus indicating a new therapeutic strategy to overcome MDR tumors. Since SMOX in mammals is differentially activated in a tissue-specific manner and cancer cells can differ in terms of DNA repair and MDR capabilities, it could be of interest to simultaneously treat with very low dose of X-rays and/or to alter SMOX metabolism to generate a differential response in healthy and cancer tissues.

Spermine oxidase: ten years after

Spermine oxidase (SMO) was discovered much more recently than other enzymes involved in polyamine metabolism; this review summarizes 10 years of researches on this enzyme. Spermine oxidase (SMO) is a FAD-dependent enzyme that specifically oxidizes spermine (Spm) and plays a dominant role in the highly regulated mammalian polyamines catabolism. SMO participates in drug response, apoptosis, response to stressful stimuli and etiology of several pathological conditions, including cancer. SMO is a highly inducible enzyme, its deregulation can alter polyamine homeostasis, and dysregulation of polyamine catabolism is often associated with several disease states. The oxidative products of SMO activity are spermidine, and the reactive oxygen species H(2)O(2) and the aldehyde 3-aminopropanal each with the potential to produce cellular damages and pathologies. The SMO substrate Spm is a tetramine that plays mandatory roles in several cell functions, such as DNA synthesis, cellular proliferation, modulation of ion channels function, cellular signaling, nitric oxide synthesis and inhibition of immune responses. The goal of this review is to cover the main biochemical, cellular and physiological processes in which SMO is involved.

Increased spermine oxidase (SMO) activity as a novel differentiation marker of myogenic C2C12 cells

Spermine oxidase (SMO) is a FAD-containing enzyme involved in animal cell polyamines (PA) homeostasis, selectively active on spermine and producing H(2)O(2), spermidine, and the 3-aminopropanal. In the present study, we have examined the SMO gene expression during the mouse myoblast C2C12 cell differentiation induced with two different stimuli by RT-PCR analysis, polysome-mRNP distribution and enzyme activity. SMO transcript accumulation and enzymatic activity increases during C2C12 cell differentiation and correlates with the decrease of spermine content. Many proteins are highly regulated during the phenotypic conversion of rapidly dividing C2C12 myoblasts into fully differentiated post-mitotic myotubes. The SMO gene induction represents a novel and additional marker of C2C12 cell differentiation. The sub-cellular localization of the SMOalpha and SMOmu splice variants is not involved in the differentiation processes. Nuclear localization of only the SMOmu protein was confirmed.

Physiological polyamines: simple primordial stress molecules

Physiological polyamines are ubiquitous polycations with pleiotropic biochemical activities, including regulation of gene expression, cell proliferation and modulation of cell signalling. Reports that the polyamines with cytoprotective activities were induced by diverse stresses raised the hypothesis that physiological polyamines may play a role in inducing stress response. In a wide range of organisms, physiological polyamines were not only induced by diverse stresses, such as reactive oxygen species (ROS), heat, ultraviolet (UV) and psychiatric stress but were able to confer beneficial effects for survival. Recent biochemical and genetic evidences show that polyamines can function as an ROS scavenger, acid tolerance factor and chemical chaperone, and positive regulators for expression of stress response genes which may explain their protective functions against diverse stresses. Taken together, these data suggest that physiological polyamines can function as primordial stress molecules in bacteria, plants and mammals, and may play an essential role in regulation of pathogen-host interactions.

Chronic sub-lethal oxidative stress by spermine oxidase overactivity induces continuous DNA repair and hypersensitivity to radiation exposure

In the aging process and in most degenerative diseases, the oxidant by-products of cellular metabolism lead to oxidative stress. Oxidative stress plays an important role in switching from cell proliferation to its opposite outcome, cell death. The metabolic pathways in charge of the interconversion and degradation of the polyamines are responsible for oxidant by-products. In the past few years, spermine metabolism has been found closely related to DNA oxidation and apoptosis. Moreover, that the ectopical expression of murine spermine oxidase induced DNA damage in the neuroblastoma cell line, and this was uncoupled with any increase in cell mortality, thus suggests an activation of DNA repair. In this work, we provide new evidence showing that only spermine oxidase overactivity can deliver sub-lethal chronic DNA damage and repair without affecting transcriptional and enzymatic levels of the PA key regulatory enzymes ODC and SSAT. Chronic sub-lethal DNA damage is below the cell cycle arrest induction threshold, but is able to activate apurinic/apyrimidinic endonuclease protein (APE1) and gamma H2AX. Of therapeutic interest, the chronic sub-lethal DNA damage and activation of the repair processes are in turn responsible for inducing hypersensitivity after exposure to radiation with no induction of adaptive response to damage.

Mammalian polyamine catabolism: a therapeutic target, a pathological problem, or both?

With the recent discovery of the polyamine catabolic enzyme spermine oxidase (SMO/PAOh1), the apparent complexity of the polyamine metabolic pathway has increased considerably. Alone or in combination with the two other known members of human polyamine catabolism, spermidine/spermine N(1)-acetyltransferase, and N(1)-acetylpolyamine oxidase (PAO), SMO/PAOh1 expression has the potential to alter polyamine homeostasis in response to normal cellular signals, drug treatment and environmental and/or cellular stressors. The activity of the oxidases producing toxic aldehydes and the reactive oxygen species (ROS) H(2)O(2), suggest a mechanism by which these oxidases can be exploited as an antineoplastic drug target. However, inappropriate activation of the pathways may also lead to pathological outcomes, including DNA damage that can lead to cellular transformation. The most recent data suggest that the two polyamine catabolic pathways exhibit distinct properties and understanding these properties should aid in their exploitation for therapeutic and/or chemopreventive strategies.

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.