Cerebral ischemia enhances polyamine oxidation: identification of enzymatically formed 3-aminopropanal as an endogenous mediator of neuronal and glial cell death

Plasma Polyamines and Short-Term Adverse Outcomes Among Patients With Ischemic Stroke: A Prospective Cohort Study

BACKGROUND

Polyamines have been reported to be associated with neurological function, but the associations between polyamines and the prognosis of ischemic stroke remain unclear. We aimed to prospectively investigate whether elevated plasma polyamine levels are associated with adverse outcomes in patients with ischemic stroke.

METHODS AND RESULTS

Plasma polyamine levels were measured at admission in 3570 patients with acute ischemic stroke, and clinical outcomes were assessed at 3 months after stroke onset. The primary outcome was a composite outcome of death and major disability (modified Rankin Scale score≥3), and secondary outcomes included the individual outcomes of death and major disability. During a 3-month follow-up period, 877 participants (25.1%) experienced the primary outcome. Increased putrescines were associated with a decreased risk of the primary outcome (the highest versus the lowest tertile: odds ratio, 0.72 [95% CI, 0.58-0.91]; P=0.005) and major disability (odds ratio, 0.59 [95% CI, 0.47-0.74]; P<0.001). Conversely, increased spermidines were associated with an increased risk of death (hazard ratio, 1.86 [95% CI, 1.10-3.14]; P=0.020), and increased spermines were associated with an increased risk of the primary outcome (odds ratio, 1.36 [95% CI, 1.08-1.71]; P=0.009) and major disability (odds ratio, 1.27 [95% CI, 1.01-1.59]; P=0.041).

CONCLUSIONS

Among patients with ischemic stroke, high plasma putrescine levels were associated with a decreased risk of adverse outcomes, whereas high plasma spermidine and spermine levels were associated with an increased risk of adverse outcomes. Further studies are needed to investigate whether targeting these polyamines can improve the prognosis of patients with ischemic stroke.

REGISTRATION

https://clinicaltrials.gov. Identifier: NCT01840072.

Polyamine-Derived Aminoaldehydes and Acrolein: Cytotoxicity, Reactivity and Analysis of the Induced Protein Modifications

Polyamines participate in the processes of cell growth and development. The degradation branch of their metabolism involves amine oxidases. The oxidation of spermine, spermidine and putrescine releases hydrogen peroxide and the corresponding aminoaldehyde. Polyamine-derived aminoaldehydes have been found to be cytotoxic, and they represent the subject of this review. 3-aminopropanal disrupts the lysosomal membrane and triggers apoptosis or necrosis in the damaged cells. It is implicated in the pathogenesis of cerebral ischemia. Furthermore, 3-aminopropanal yields acrolein through the elimination of ammonia. This reactive aldehyde is also generated by the decomposition of aminoaldehydes produced in the reaction of serum amine oxidase with spermidine or spermine. In addition, acrolein is a common environmental pollutant. It causes covalent modifications of proteins, including carbonylation, the production of Michael-type adducts and cross-linking, and it has been associated with inflammation-related diseases. APAL and acrolein are detoxified by aldehyde dehydrogenases and other mechanisms. High-performance liquid chromatography, immunochemistry and mass spectrometry have been largely used to analyze the presence of polyamine-derived aminoaldehydes and protein modifications elicited by their effect. However, the main and still open challenge is to find clues for discovering clear linkages between aldehyde-induced modifications of specific proteins and the development of various diseases.

Small molecule inhibiting microglial nitric oxide release could become a potential treatment for neuroinflammation

Microglia are the immune effector cells of the central nervous system (CNS) and react to pathologic events with a complex process including the release of nitric oxide (NO). NO is a free radical, which is toxic for all cells at high concentrations. To target an exaggerated NO release, we tested a library of 16 544 chemical compounds for their effect on lipopolysaccharide (LPS)-induced NO release in cell line and primary neonatal microglia. We identified a compound (C1) which significantly reduced NO release in a dose-dependent manner, with a low IC50 (252 nM) and no toxic side effects in vitro or in vivo. Target finding strategies such as in silico modelling and mass spectroscopy hint towards a direct interaction between C1 and the nitric oxide synthase making C1 a great candidate for specific intra-cellular interaction with the NO producing machinery.

The Involvement of Polyamines Catabolism in the Crosstalk between Neurons and Astrocytes in Neurodegeneration

In mammalian cells, the content of polyamines is tightly regulated. Polyamines, including spermine, spermidine and putrescine, are involved in many cellular processes. Spermine oxidase specifically oxidizes spermine, and its deregulated activity has been reported to be linked to brain pathologies involving neuron damage. Spermine is a neuromodulator of a number of ionotropic glutamate receptors and types of ion channels. In this respect, the Dach-SMOX mouse model overexpressing spermine oxidase in the neocortex neurons was revealed to be a model of chronic oxidative stress, excitotoxicity and neuronal damage. Reactive astrocytosis, chronic oxidative and excitotoxic stress, neuron loss and the susceptibility to seizure in the Dach-SMOX are discussed here. This genetic model would help researchers understand the linkage between polyamine dysregulation and neurodegeneration and unveil the roles of polyamines in the crosstalk between astrocytes and neurons in neuroprotection or neurodegeneration.

Polyamines and Their Metabolism: From the Maintenance of Physiological Homeostasis to the Mediation of Disease

The polyamines spermidine and spermine are positively charged aliphatic molecules. They are critical in the regulation of nucleic acid and protein structures, protein synthesis, protein and nucleic acid interactions, oxidative balance, and cell proliferation. Cellular polyamine levels are tightly controlled through their import, export, de novo synthesis, and catabolism. Enzymes and enzymatic cascades involved in polyamine metabolism have been well characterized. This knowledge has been used for the development of novel compounds for research and medical applications. Furthermore, studies have shown that disturbances in polyamine levels and their metabolic pathways, as a result of spontaneous mutations in patients, genetic engineering in mice or experimentally induced injuries in rodents, are associated with multiple maladaptive changes. The adverse effects of altered polyamine metabolism have also been demonstrated in in vitro models. These observations highlight the important role these molecules and their metabolism play in the maintenance of physiological normalcy and the mediation of injury. This review will attempt to cover the extensive and diverse knowledge of the biological role of polyamines and their metabolism in the maintenance of physiological homeostasis and the mediation of tissue injury.

Unique Chemistry, Intake, and Metabolism of Polyamines in the Central Nervous System (CNS) and Its Body

Polyamines (PAs) are small, versatile molecules with two or more nitrogen-containing positively charged groups and provide widespread biological functions. Most of these aspects are well known and covered by quite a number of excellent surveys. Here, the present review includes novel aspects and questions: (1) It summarizes the role of most natural and some important synthetic PAs. (2) It depicts PA uptake from nutrition and bacterial production in the intestinal system following loss of PAs via defecation. (3) It highlights the discrepancy between the high concentrations of PAs in the gut lumen and their low concentration in the blood plasma and cerebrospinal fluid, while concentrations in cellular cytoplasm are much higher. (4) The present review provides a novel and complete scheme for the biosynthesis of Pas, including glycine, glutamate, proline and others as PA precursors, and provides a hypothesis that the agmatine pathway may rescue putrescine production when ODC knockout seems to be lethal (solving the apparent contradiction in the literature). (5) It summarizes novel data on PA transport in brain glial cells explaining why these cells but not neurons preferentially accumulate PAs. (6) Finally, it provides a novel and complete scheme for PA interconversion, including hypusine, putreanine, and GABA (unique gliotransmitter) as end-products. Altogether, this review can serve as an updated contribution to understanding the PA mystery.

Transgenic Mouse Overexpressing Spermine Oxidase in Cerebrocortical Neurons: Astrocyte Dysfunction and Susceptibility to Epileptic Seizures

Polyamines are organic polycations ubiquitously present in living cells. Polyamines are involved in many cellular processes, and their content in mammalian cells is tightly controlled. Among their function, these molecules modulate the activity of several ion channels. Spermine oxidase, specifically oxidized spermine, is a neuromodulator of several types of ion channel and ionotropic glutamate receptors, and its deregulated activity has been linked to several brain pathologies, including epilepsy. The Dach-SMOX mouse line was generated using a Cre/loxP-based recombination approach to study the complex and critical functions carried out by spermine oxidase and spermine in the mammalian brain. This mouse genetic model overexpresses spermine oxidase in the neocortex and is a chronic model of excitotoxic/oxidative injury and neuron vulnerability to oxidative stress and excitotoxic, since its phenotype revealed to be more susceptible to different acute oxidative insults. In this review, the molecular mechanisms underlined the Dach-SMOX phenotype, linked to reactive astrocytosis, neuron loss, chronic oxidative and excitotoxic stress, and susceptibility to seizures have been discussed in detail. The Dach-SMOX mouse model overexpressing SMOX may help in shedding lights on the susceptibility to epileptic seizures, possibly helping to understand the mechanisms underlying epileptogenesis in vulnerable individuals and contributing to provide new molecular mechanism targets to search for novel antiepileptic drugs.

Overview of the Neuroprotective Effects of the MAO-Inhibiting Antidepressant Phenelzine

Phenelzine (PLZ) is a monoamine oxidase (MAO)-inhibiting antidepressant with anxiolytic properties. This multifaceted drug has a number of pharmacological and neurochemical effects in addition to inhibition of MAO, and findings on these effects have contributed to a body of evidence indicating that PLZ also has neuroprotective/neurorescue properties. These attributes are reviewed in this paper and include catabolism to the active metabolite β-phenylethylidenehydrazine (PEH) and effects of PLZ and PEH on the GABA-glutamate balance in brain, sequestration of reactive aldehydes, and inhibition of primary amine oxidase. Also discussed are the encouraging findings of the effects of PLZ in animal models of stroke, spinal cord injury, traumatic brain injury, and multiple sclerosis, as well other actions such as reduction of nitrative stress, reduction of the effects of a toxin on dopaminergic neurons, potential anticonvulsant actions, and effects on brain-derived neurotrophic factor, neural cell adhesion molecules, an anti-apoptotic factor, and brain levels of ornithine and N-acetylamino acids.

Ablation of polyamine catabolic enzymes provokes Purkinje cell damage, neuroinflammation, and severe ataxia

BACKGROUND

Polyamine catabolism plays a key role in maintaining intracellular polyamine pools, yet its physiological significance is largely unexplored. Here, we report that the disruption of polyamine catabolism leads to severe cerebellar damage and ataxia, demonstrating the fundamental role of polyamine catabolism in the maintenance of cerebellar function and integrity.

METHODS

Mice with simultaneous deletion of the two principal polyamine catabolic enzymes, spermine oxidase and spermidine/spermine N1-acetyltransferase (Smox/Sat1-dKO), were generated by the crossbreeding of Smox-KO (Smox-/-) and Sat1-KO (Sat1-/-) animals. Development and progression of tissue injury was monitored using imaging, behavioral, and molecular analyses.

RESULTS

Smox/Sat1-dKO mice are normal at birth, but develop progressive cerebellar damage and ataxia. The cerebellar injury in Smox/Sat1-dKO mice is associated with Purkinje cell loss and gliosis, leading to neuroinflammation and white matter demyelination during the latter stages of the injury. The onset of tissue damage in Smox/Sat1-dKO mice is not solely dependent on changes in polyamine levels as cerebellar injury was highly selective. RNA-seq analysis and confirmatory studies revealed clear decreases in the expression of Purkinje cell-associated proteins and significant increases in the expression of transglutaminases and markers of neurodegenerative microgliosis and astrocytosis. Further, the α-Synuclein expression, aggregation, and polyamination levels were significantly increased in the cerebellum of Smox/Sat1-dKO mice. Finally, there were clear roles of transglutaminase-2 (TGM2) in the cerebellar pathologies manifest in Smox/Sat1-dKO mice, as pharmacological inhibition of transglutaminases reduced the severity of ataxia and cerebellar injury in Smox/Sat1-dKO mice.

CONCLUSIONS

These results indicate that the disruption of polyamine catabolism, via coordinated alterations in tissue polyamine levels, elevated transglutaminase activity and increased expression, polyamination, and aggregation of α-Synuclein, leads to severe cerebellar damage and ataxia. These studies indicate that polyamine catabolism is necessary to Purkinje cell survival, and for sustaining the functional integrity of the cerebellum.

Nutritional Aspects of Spermidine

Natural polyamines (spermidine and spermine) are small, positively charged molecules that are ubiquitously found within organisms and cells. They exert numerous (intra)cellular functions and have been implicated to protect against several age-related diseases. Although polyamine levels decline in a complex age-dependent, tissue-, and cell type–specific manner, they are maintained in healthy nonagenarians and centenarians. Increased polyamine levels, including through enhanced dietary intake, have been consistently linked to improved health and reduced overall mortality. In preclinical models, dietary supplementation with spermidine prolongs life span and health span. In this review, we highlight salient aspects of nutritional polyamine intake and summarize the current knowledge of organismal and cellular uptake and distribution of dietary (and gastrointestinal) polyamines and their impact on human health. We further summarize clinical and epidemiological studies of dietary polyamines.

A phase II randomized controlled trial of tiopronin for aneurysmal subarachnoid hemorrhage

OBJECTIVE

Delayed cerebral ischemia (DCI) is a significant contributor to poor outcomes after aneurysmal subarachnoid hemorrhage (aSAH). The neurotoxin 3-aminopropanal (3-AP) is upregulated in cerebral ischemia. This phase II clinical trial evaluated the efficacy of tiopronin in reducing CSF 3-AP levels in patients with aSAH.

METHODS

In this prospective, randomized, double-blind, placebo-controlled, multicenter clinical trial, 60 patients were assigned to receive tiopronin or placebo in a 1:1 ratio. Treatment was commenced within 96 hours after aSAH onset, administered at a dose of 3 g daily, and continued until 14 days after aSAH or hospital discharge, whichever occurred earlier. The primary efficacy outcome was the CSF 3-AP level at 7 ± 1 days after aSAH.

RESULTS

Of the 60 enrolled patients, 29 (97%) and 27 (93%) in the tiopronin and placebo arms, respectively, received more than one dose of the study drug or placebo. At post-aSAH day 7 ± 1, CSF samples were available in 41% (n = 12/29) and 48% (n = 13/27) of patients in the tiopronin and placebo arms, respectively. No difference in CSF 3-AP levels at post-aSAH day 7 ± 1 was observed between the study arms (11 ± 12 nmol/mL vs 13 ± 18 nmol/mL; p = 0.766). Prespecified adverse events led to early treatment cessation for 4 patients in the tiopronin arm and 2 in the placebo arm.

CONCLUSIONS

The power of this study was affected by missing data. Therefore, the authors could not establish or refute an effect of tiopronin on CSF 3-AP levels. Additional observational studies investigating the role of 3-AP as a biomarker for DCI may be warranted prior to its use as a molecular target in future clinical trials.Clinical trial registration no.: NCT01095731 (ClinicalTrials.gov).

Arginase Pathway in Acute Retina and Brain Injury: Therapeutic Opportunities and Unexplored Avenues

Ischemic retinopathies represent a major cause of visual impairment and blindness. They include diabetic retinopathy (DR), acute glaucoma, retinopathy of prematurity (ROP), and central (or branch) retinal artery occlusion (CRAO). These conditions share in common a period of ischemia or reduced blood supply to the retinal tissue that eventually leads to neuronal degeneration. Similarly, acute brain injury from ischemia or trauma leads to neurodegeneration and can have devastating consequences in patients with stroke or traumatic brain injury (TBI). In all of these conditions, current treatment strategies are limited by their lack of effectiveness, adverse effects or short time window for administration. Therefore, there is a great need to identify new therapies for acute central nervous system (CNS) injury. In this brief review article, we focus on the pathway of the arginase enzyme as a novel therapeutic target for acute CNS injury. We review the recent work on the role of arginase enzyme and its downstream components in neuroprotection in both retina and brain acute injury models. Delineating the similarities and differences between the role of arginase in the retina and brain neurodegeneration will allow for better understanding of the role of arginase in CNS disorders. This will also facilitate repurposing the arginase pathway as a new therapeutic target in both retina and brain diseases.

Targeting Smox Is Neuroprotective and Ameliorates Brain Inflammation in Cerebral Ischemia/Reperfusion Rats

Spermine oxidase (Smox) is a member of the polyamine oxidases and has been demonstrated to be involved in ischemic brain damage. In this study, we found that Smox expression was increased in a rat middle cerebral artery occlusion (MCAO) model and in cultured primary neurons after oxygen-glucose deprivation and reoxygenation (OGD/R). Smox downregulation by the adeno-associated virus RNA interference system significantly reduced the MCAO-induced brain infarct volume and neurological deficits and decreased neuronal apoptosis and inflammatory reactions. In addition, significant microglial activation and increased IL-6 and TNF-α expression were observed in microglia treated with supernatant from neurons after OGD/R. However, a significant reduction in microglial activation as well as IL-6 and TNF-α expression was observed in microglia treated with supernatant from Smox downregulated neurons after OGD/R. Therefore, the results indicated that Smox is an important mediator of cerebral ischemia injury and may be a therapeutic target for cerebral ischemia patients.

Methyl 5-MeO-N-aminoanthranilate, a minimalist fluorogenic probe for sensing cellular aldehydic load

A minimalist fluorogenic probe is presented capable of the mapping of aldehydic load through live cell microscopy.

Hydrazo-CEST: Hydrazone-Dependent Chemical Exchange Saturation Transfer Magnetic Resonance Imaging Contrast Agents

The rapid formation of hydrazones under physiological conditions was exploited for the detection of aldehydes through chemical exchange saturation transfer magnetic resonance imaging (CEST-MRI). A metal-free, diamagnetic contrast agent derived from N-amino anthranilic acid was introduced, which selectively "turned-on" upon hydrazone formation through an effect termed Hydrazo-CEST. While the hydrazine form of the probe produced no CEST-MRI signal enhancement, the formation of the aryl hydrazone resulted in >20 % intensity decrease in the bulk water signal through the CEST effect, as measured by 300 MHz ¹ H NMR, 3 T and 7 T MRI. Both the electronic contributions of the N-amino anthranilate and the aldehyde binding partner were shown to directly impact the exchange rate of the proton on the ring-proximal nitrogen, and thus the imaging signal. Additionally, the presence of the carboxylic acid moiety ortho to the hydrazine was necessary not only for contrast production, but also for rapid hydrazone formation and prolonged hydrazone product stability under physiological conditions. This work provided the first example of an MRI-based contrast agent capable of a "turn on" response upon reaction with bioactive aldehydes, and outlined both the structural and electronic requirements to expand on Hydrazo-CEST, a novel, hydrazone-dependent subtype of diamagnetic CEST-MRI.

Spermine synthase deficiency causes lysosomal dysfunction and oxidative stress in models of Snyder-Robinson syndrome

Polyamines are tightly regulated polycations that are essential for life. Loss-of-function mutations in spermine synthase (SMS), a polyamine biosynthesis enzyme, cause Snyder-Robinson syndrome (SRS), an X-linked intellectual disability syndrome; however, little is known about the neuropathogenesis of the disease. Here we show that loss of dSms in Drosophila recapitulates the pathological polyamine imbalance of SRS and causes survival defects and synaptic degeneration. SMS deficiency leads to excessive spermidine catabolism, which generates toxic metabolites that cause lysosomal defects and oxidative stress. Consequently, autophagy-lysosome flux and mitochondrial function are compromised in the Drosophila nervous system and SRS patient cells. Importantly, oxidative stress caused by loss of SMS is suppressed by genetically or pharmacologically enhanced antioxidant activity. Our findings uncover some of the mechanisms underlying the pathological consequences of abnormal polyamine metabolism in the nervous system and may provide potential therapeutic targets for treating SRS and other polyamine-associated neurological disorders.

Activation of endoplasmic reticulum stress response by enhanced polyamine catabolism is important in the mediation of cisplatin-induced acute kidney injury

Cisplatin-induced nephrotoxicity limits its use in many cancer patients. The expression of enzymes involved in polyamine catabolism, spermidine/spermine N1-acetyltransferase (SSAT) and spermine oxidase (SMOX) increase in the kidneys of mice treated with cisplatin. We hypothesized that enhanced polyamine catabolism contributes to tissue damage in cisplatin acute kidney injury (AKI). Using gene knockout and chemical inhibitors, the role of polyamine catabolism in cisplatin AKI was examined. Deficiency of SSAT, SMOX or neutralization of the toxic products of polyamine degradation, H2O2 and aminopropanal, significantly diminished the severity of cisplatin AKI. In vitro studies demonstrated that the induction of SSAT and elevated polyamine catabolism in cells increases the phosphorylation of eukaryotic translation initiation factor 2α (eIF2α) and enhances the expression of binding immunoglobulin protein BiP/GRP78) and CCAAT-enhancer-binding protein homologous protein (CHOP/GADD153). The increased expression of these endoplasmic reticulum stress response (ERSR) markers was accompanied by the activation of caspase-3. These results suggest that enhanced polyamine degradation in cisplatin AKI may lead to tubular damage through the induction of ERSR and the consequent onset of apoptosis. In support of the above, we show that the ablation of the SSAT or SMOX gene, as well as the neutralization of polyamine catabolism products modulate the onset of ERSR (e.g. lower BiP and CHOP) and apoptosis (e.g. reduced activated caspase-3). These studies indicate that enhanced polyamine catabolism and its toxic products are important mediators of ERSR and critical to the pathogenesis of cisplatin AKI.

Astrocyte-Dependent Vulnerability to Excitotoxicity in Spermine Oxidase-Overexpressing Mouse

Transgenic mice overexpressing spermine oxidase (SMO) in the cerebral cortex (Dach-SMO mice) showed increased vulnerability to excitotoxic brain injury and kainate-induced epileptic seizures. To investigate the mechanisms by which SMO overexpression leads to increased susceptibility to kainate excitotoxicity and seizure, in the cerebral cortex of Dach-SMO and control mice we assessed markers for astrocyte proliferation and neuron loss, and the ability of kainate to evoke glutamate release from nerve terminals and astrocyte processes. Moreover, we assessed a possible role of astrocytes in an in vitro model of epileptic-like activity in combined cortico-hippocampal slices recorded with a multi-electrode array device. In parallel, as the brain is a major metabolizer of oxygen and yet has relatively feeble protective antioxidant mechanisms, we analyzed the oxidative status of the cerebral cortex of both SMO-overexpressing and control mice by evaluating enzymatic and non-enzymatic scavengers such as metallothioneins. The main findings in the cerebral cortex of Dach-SMO mice as compared to controls are the following: astrocyte activation and neuron loss; increased oxidative stress and activation of defense mechanisms involving both neurons and astrocytes; increased susceptibility to kainate-evoked cortical epileptogenic activity, dependent on astrocyte function; appearance of a glutamate-releasing response to kainate from astrocyte processes due to activation of Ca(2+)-permeable AMPA receptors in Dach-SMO mice. We conclude that reactive astrocytosis and activation of glutamate release from astrocyte processes might contribute, together with increased reactive oxygen species production, to the vulnerability to kainate excitotoxicity in Dach-SMO mice. This mouse model with a deregulated polyamine metabolism would shed light on roles for astrocytes in increasing vulnerability to excitotoxic neuron injury.

Effect of chronic intraperitoneal aminoguanidine on memory and expression of Bcl-2 family genes in diabetic rats

Long-term hyperglycemia associates with memory defects via hippocampal cells damaging. The aim of the present study was to examine the effect of 1 month of i.p. injections of AG on passive avoidance learning (PAL) and hippocampal apoptosis in rat. Eighty male rats were divided into 10 groups: control, nondiabetics and STZ-induced diabetics treated with AG (50, 100, 200, and 400 mg/kg, i.p.). PAL and the Bcl-2 family gene expressions were determined. Diabetes resulted in memory and Bcl-2 family gene expression deficits. AG (50 and 100 mg/kg) significantly improved the learning and Bcl-2, Bcl-xl, Bax, and Bak impairment in diabetic rats. However, negative effects were indicated by higher doses of the drug (200 and 400 mg/kg). Present study suggests that 1 month of i.p. injections of lower doses of AG, may improve the impaired cognitive tasks in STZ-induced diabetic rats possibly by modulating Bcl-2 family gene expressions.

The role of glia in stress: polyamines and brain disorders

This review focuses on the roles of glia and polyamines (PAs) in brain function and dysfunction, highlighting how PAs are one of the principal differences between glia and neurons. The novel role of PAs, such as putrescine, spermidine, and spermine and their precursors and derivatives, is discussed. However, PAs have not yet been a focus of much glial research. They affect many neuronal and glial receptors, channels, and transporters. They are therefore key elements in the development of many diseases and syndromes, thus forming the rationale for PA-focused and glia-focused therapy for these conditions.

Proximal tubule epithelial cell specific ablation of the spermidine/spermine N1-acetyltransferase gene reduces the severity of renal ischemia/reperfusion injury

BACKGROUND

Expression and activity of spermidine/spermine N1-acetyltransferase (SSAT) increases in kidneys subjected to ischemia/reperfusion (I/R) injury, while its ablation reduces the severity of such injuries. These results suggest that increased SSAT levels contribute to organ injury; however, the role of SSAT specifically expressed in proximal tubule epithelial cells, which are the primary targets of I/R injury, in the mediation of renal damage remains unresolved.

METHODS

Severity of I/R injury in wt and renal proximal tubule specific SSAT-ko mice (PT-SSAT-Cko) subjected to bilateral renal I/R injury was assessed using cellular and molecular biological approaches.

RESULTS

Severity of the loss of kidney function and tubular damage are reduced in PT-SSAT-Cko- compared to wt-mice after I/R injury. In addition, animals treated with MDL72527, an inhibitor of polyamine oxidases, had less severe renal damage than their vehicle treated counter-parts. The renal expression of HMGB 1 and Toll like receptors (TLR) 2 and 4 were also reduced in PT-SSAT-Cko- compared to wt mice after I/R injury. Furthermore, infiltration of neutrophils, as well as expression of tumor necrosis factor-α (TNF-α), monocyte chemoattractant protein-1 (MCP-1) and interleukin-6 (IL-6) transcripts were lower in the kidneys of PT-SSAT-Cko compared to wt mice after I/R injury. Finally, the activation of caspase3 was more pronounced in the wt compared to PT-SSAT-Cko animals.

CONCLUSIONS

Enhanced SSAT expression by proximal tubule epithelial cells leads to tubular damage, and its deficiency reduces the severity of renal I/R injury through reduction of cellular damage and modulation of the innate immune response.

Arginase 2 deficiency reduces hyperoxia-mediated retinal neurodegeneration through the regulation of polyamine metabolism

Hyperoxia treatment has been known to induce neuronal and glial death in the developing central nervous system. Retinopathy of prematurity (ROP) is a devastating disease in premature infants and a major cause of childhood vision impairment. Studies indicate that, in addition to vascular injury, retinal neurons are also affected in ROP. Using an oxygen-induced retinopathy (OIR) mouse model for ROP, we have previously shown that deletion of the arginase 2 (A2) significantly reduced neuro-glial injury and improved retinal function. In the current study, we investigated the mechanism of A2 deficiency-mediated neuroprotection in the OIR retina. Hyperoxia treatment has been known to induce neuronal death in neonates. During the hyperoxia phase of OIR, a significant increase in the number of apoptotic cells was observed in the wild-type (WT) OIR retina compared with A2-deficient OIR. Mass spectrometric analysis showed alterations in polyamine metabolism in WT OIR retina. Further, increased expression level of spermine oxidase was observed in WT OIR retina, suggesting increased oxidation of polyamines in OIR retina. These changes were minimal in A2-deficient OIR retina. Treatment using the polyamine oxidase inhibitor, N, N'-bis (2, 3-butadienyl)-1, 4-butanediamine dihydrochloride, significantly improved neuronal survival during OIR treatment. Our data suggest that retinal arginase is involved in the hyperoxia-induced neuronal degeneration in the OIR model, through the regulation of polyamine metabolism.

Toxicity of polyamines and their metabolic products

Polyamines are ubiquitous and essential components of mammalian cells. They have multiple functions including critical roles in nucleic acid and protein synthesis, gene expression, protein function, protection from oxidative damage, the regulation of ion channels, and maintenance of the structure of cellular macromolecules. It is essential to maintain a correct level of polyamines, and this amount is tightly regulated at the levels of transport, synthesis, and degradation. Catabolic pathways generate reactive aldehydes including acrolein and hydrogen peroxide via a number of oxidases. These metabolites, particularly those from spermine, can cause significant toxicity with damage to proteins, DNA, and other cellular components. Their production can be increased as a result of infection or cell damage that releases free polyamines and activates the oxidative catabolic pathways. Since polyamines also have an important physiological role in protection from oxidative damage, the reduction in polyamine content may exacerbate the toxic potential of these agents. Increases in polyamine catabolism have been implicated in the development of diseases including stroke, other neurological diseases, renal failure, liver disease, and cancer. These results provide new opportunities for the early diagnosis, prevention, and treatment of disease.

Arginase in retinopathy

Ischemic retinopathies, such as diabetic retinopathy (DR), retinopathy of prematurity and retinal vein occlusion are a major cause of blindness in developed nations worldwide. Each of these conditions is associated with early neurovascular dysfunction. However, conventional therapies target clinically significant macula edema or neovascularization, which occur much later. Intra-ocular injections of anti-VEGF show promise in reducing retinal edema, but the effects are usually transient and the need for repeated injections increases the risk of intraocular infection. Laser photocoagulation can control pathological neovascularization, but may impair vision and in some patients the retinopathy continues to progress. Moreover, neither treatment targets early stage disease or promotes repair. This review examines the potential role of the ureahydrolase enzyme arginase as a therapeutic target for the treatment of ischemic retinopathy. Arginase metabolizes l-arginine to form proline, polyamines and glutamate. Excessive arginase activity reduces the l-arginine supply for nitric oxide synthase (NOS), causing it to become uncoupled and produce superoxide and less NO. Superoxide and NO react and form the toxic oxidant peroxynitrite. The catabolic products of polyamine oxidation and glutamate can induce more oxidative stress and DNA damage, both of which can cause cellular injury. Studies indicate that neurovascular injury during retinopathy is associated with increased arginase expression/activity, decreased NO, polyamine oxidation, formation of superoxide and peroxynitrite and dysfunction and injury of both vascular and neural cells. Furthermore, data indicate that the cytosolic isoform arginase I (AI) is involved in hyperglycemia-induced dysfunction and injury of vascular endothelial cells whereas the mitochondrial isoform arginase II (AII) is involved in neurovascular dysfunction and death following hyperoxia exposure. Thus, we postulate that activation of the arginase pathway causes neurovascular injury by uncoupling NOS and inducing polyamine oxidation and glutamate formation, thereby reducing NO and increasing oxidative stress, all of which contribute to the retinopathic process.

A phase I clinical trial of tiopronin, a putative neuroprotective agent, in aneurysmal subarachnoid hemorrhage

BACKGROUND

The neurotoxic aldehyde 3-aminopropanal (3-AP) contributes to brain injury following cerebral ischemia. Tiopronin (N-2-mercaptopropionyl-glycine[N-2-MPG]) is a US Food and Drug Administration (FDA)-approved drug for the treatment of cystinuria and a putative neuroprotective agent that has been shown to bind and neutralize 3-AP and reduce infarct volumes.

OBJECTIVE

The objective of this trial was to establish the safety of tiopronin administration in patients with aneurysmal subarachnoid hemorrhage (aSAH) in preparation for further trials of its efficacy as a neuroprotective agent in this disease process.

METHODS

This Phase I dose-escalation trial enrolled three-patient cohorts using a conventional "3+3" study design. Tiopronin dose began at 1 g/d until aSAH Day 14. Each subsequent cohort received a dose of tiopronin based on predetermined guidelines. A maximum dose of 3 g/d was selected, because this is the maximum FDA-approved dose for long-term cystinuria treatment. Subjects were monitored for known side effects of tiopronin.

RESULTS

Nine patients were enrolled, the minimum number required based on the study design. None of these patients experienced serious side effects attributable to tiopronin, and no adverse events were noted that could not be attributed to the pathophysiology of aSAH.

CONCLUSION

The administration of 3 g/d of tiopronin following aSAH for up to 14 days appears to be safe and without the side effects associated with long-term use. Plans for a randomized, placebo-controlled Phase II trial of tiopronin for neuroprotection following aSAH are underway.

An update on amine oxidase inhibitors: multifaceted drugs

Although not used as extensively as other antidepressants for the treatment of depression, the monoamine oxidase (MAO) inhibitors continue to hold a niche in psychiatry and to have a relatively broad spectrum with regard to treatment of psychiatric and neurological disorders. Experimental and clinical research on MAO inhibitors has been expanding in the past few years, primarily because of exciting findings indicating that these drugs have neuroprotective properties (often independently of their ability to inhibit MAO). The non-selective and irreversible MAO inhibitors tranylcypromine (TCP) and phenelzine (PLZ) have demonstrated neuroprotective properties in numerous studies targeting elements of apoptotic cascades and neurogenesis. l-Deprenyl and rasagiline, both selective MAO-B inhibitors, are used in the management of Parkinson's disease, but these drugs may be useful in the treatment of other neurodegenerative disorders given that they demonstrate neuroprotective/neurorescue properties in a wide variety of models in vitro and in vivo. Although the focus of studies on the involvement of MAO inhibitors in neuroprotection has been on MAO-B inhibitors, there is a growing body of evidence demonstrating that MAO-A inhibitors may also have neuroprotective properties. In addition to MAO inhibition, PLZ also inhibits primary amine oxidase (PrAO), an enzyme implicated in the etiology of Alzheimer's disease, diabetes and cardiovascular disease. These multifaceted aspects of amine oxidase inhibitors and some of their metabolites are reviewed herein.

The protective effect of geniposide on human neuroblastoma cells in the presence of formaldehyde

Background

Formaldehyde can induce misfolding and aggregation of Tau protein and β amyloid protein, which are characteristic pathological features of Alzheimer’s disease (AD). An increase in endogenous formaldehyde concentration in the brain is closely related to dementia in aging people. Therefore, the discovery of effective drugs to counteract the adverse impact of formaldehyde on neuronal cells is beneficial for the development of appropriate treatments for age-associated cognitive decline.

Methods

In this study, we assessed the neuroprotective properties of TongLuoJiuNao (TLJN), a traditional Chinese medicine preparation, against formaldehyde stress in human neuroblastoma cells (SH-SY5Y cell line). The effect of TLJN and its main ingredients (geniposide and ginsenoside Rg1) on cell viability, apoptosis, intracellular antioxidant activity and the expression of apoptotic-related genes in the presence of formaldehyde were monitored.

Results

Cell counting studies showed that in the presence of TLJN, the viability of formaldehyde-treated SH-SY5Y cells significantly recovered. Laser scanning confocal microscopy revealed that the morphology of formaldehyde-injured cells was rescued by TLJN and geniposide, an effective ingredient of TLJN. Moreover, the inhibitory effect of geniposide on formaldehyde-induced apoptosis was dose-dependent. The activity of intracellular antioxidants (superoxide dismutase and glutathione peroxidase) increased, as did mRNA and protein levels of the antiapoptotic gene Bcl-2 after the addition of geniposide. In contrast, the expression of the apoptotic-related gene - P53, apoptotic executer - caspase 3 and apoptotic initiator - caspase 9 were downregulated after geniposide treatment.

Conclusions

Our results indicate that geniposide can protect SH-SY5Y cells against formaldehyde stress through modulating the expression of Bcl-2, P53, caspase 3 and caspase 9, and by increasing the activity of intracellular superoxide dismutase and glutathione peroxidase.

Monoamine oxidase inhibitors and neuroprotection: a review

Monoamine oxidase inhibitors have been available for more than 50 years, initially developed as antidepressants but currently used in a variety of psychiatric and neurological conditions. There has been a recent surge of interest in monoamine oxidase inhibitors because of their reported neuroprotective and/or neurorescue properties. Interestingly, it seems that often these properties are independent of their ability to inhibit monoamine oxidase. This review article presents an overview of the neuroprotective/neurorescue properties of these multifaceted drugs and focuses on phenelzine, (-)-deprenyl, rasagiline, ladostigil, tranylcypromine, moclobemide, and clorgyline and their possible neuroprotective mechanisms.

Effects of carnosine on polyamine levels in red blood cells of patients with hypertonic discirculatory encephalopathy

The levels of polyamines (putrescine, spermine, spermidine) in erythrocytes from patients with hypertonic discirculatory encephalopathy are reduced (by 37, 45, and 50%, respectively) in comparison with the corresponding parameters in the control group. Addition of carnosine to the treatment protocol for chronic brain ischemia normalized the content of putrescine and spermine. The mechanisms of carnosine influence on polyamine metabolism are discussed: trapping of acrolein, end-product of polyamine oxidation, and compensation of NMDA-receptor excitotoxicity.

Protein-conjugated acrolein as a biochemical marker of brain infarction

The relationship between acrolein (CH(2) =CH-CHO) and brain infarction is the focus of this review. It has been found that acrolein is produced mainly within cells from polyamines by polyamine oxidases (PAOs), especially from spermine by spermine oxidase during cell damage, and that acrolein is more toxic than reactive oxygen species (ROS) in a cell culture system. Thus, the possibility that acrolein and PAOs are good biochemical markers of stroke was tested because there are no other reliable biochemical markers at the early stage of stroke. Levels of protein-conjugated acrolein (PC-Acro) and PAOs (acrolein-producing enzymes) were significantly increased in the plasma of stroke patients. The multiplied value of PC-Acro by PAOs was nearly parallel with the size of stroke. Furthermore, when the combined measurements of PC-Acro, interleukin-6 (IL-6) and C-reactive protein (CRP) were evaluated along with age using a receiver operating characteristic (ROC) curve, even silent brain infarction (SBI), which is a small brain infarction, was indicated with approximately 84% sensitivity and specificity. These findings clearly indicate that acrolein is strongly correlated with cell damage during brain infarction.

Mechanisms of amine accumulation in, and egress from, lysosomes

The human body is continuously exposed to small organic molecules containing one or more basic nitrogen atoms. Many of these are endogenous (i.e., neurotransmitters, polyamines and biogenic amines), while others are exogenously supplied in the form of drugs, foods and pollutants. It is well-known that many amines have a strong propensity to specifically and substantially accumulate in highly acidic intracellular compartments, such as lysosomes, through a mechanism referred to as ion trapping. It is also known that cells have acquired the unique ability to sense and respond to amine accumulation in lysosomes in an effort to prevent potential negative consequences associated with hyperaccumulation. We describe here methods that are used to evaluate the dynamics of amine accumulation in, and egress from, lysosomes. Moreover, we highlight specific proteins that are thought to play important roles in these pathways. A theoretical model describing lysosomal amine dynamics is described and shown to adequately fit experimental kinetic data. The implications of this research in understanding and treating disease are discussed.

Aminoguanidine administration ameliorates hippocampal damage after middle cerebral artery occlusion in rat

The effects of a selective inducible nitric oxide synthase inhibitor aminoguanidine (AG) on neuronal cells survival in hippocampal CA1 region after middle cerebral artery occlusion (MCAO) were examined. Transient focal cerebral ischemia was induced in rats by 60 or 90 min of MCAO, followed by 7 days of reperfusion. AG treatment (150 mg/kg i.p.) significantly reduced total infarct volumes: by 70% after 90 min MCAO and by 95% after 60 min MCAO, compared with saline-treated ischemic group. The number of degenerating neurons in hippocampal CA1 region was also markedly lower in aminoguanidine-treated ischemic groups compared to ischemic groups without AG-treatment. The number of iNOS-positive cells significantly increased in the hippocampal CA1 region of ischemic animals, whereas it was reduced in AG-treated rats. Our findings demonstrate that aminoguanidine decreases ischemic brain damage and improves neurological recovery after transient focal ischemia induced by MCAO.

The role of spermidine/spermine N1-acetyltransferase in endotoxin-induced acute kidney injury

The expression of catabolic enzymes spermidine/spermine N(1)-acetyltransferase (SSAT) and spermine oxidase (SMO) increases after ischemic reperfusion injury. We hypothesized that polyamine catabolism is upregulated and that this increase in catabolic response contributes to tissue damage in endotoxin-induced acute kidney injury (AKI). SSAT mRNA expression peaked at threefold 24 h following LPS injection and returned to background levels by 48 h. The activity of SSAT correlated with its mRNA levels. The expression of SMO also increased in the kidney after LPS administration. Serum creatinine levels increased significantly at approximately 15 h, peaking by 24 h, and returned to background levels by 72 h. To test the role of SSAT in endotoxin-induced AKI, we injected wild-type (SSAT-wt) and SSAT-deficient (SSAT-ko) mice with LPS. Compared with SSAT-wt mice, the SSAT-ko mice subjected to endotoxic-AKI had less severe kidney damage as indicated by better preservation of kidney function. The role of polyamine oxidation in the mediation of kidney injury was examined by comparing the severity of renal damage in SSAT-wt mice treated with MDL72527, an inhibitor of both polyamine oxidase and SMO. Animals treated with MDL72527 showed significant protection against endotoxin-induced AKI. We conclude that increased polyamine catabolism through generation of by-products of polyamine oxidation contributes to kidney damage and that modulation of polyamine catabolism may be a viable approach for the treatment of endotoxin-induced AKI.

The antidepressant phenelzine protects neurons and astrocytes against formaldehyde-induced toxicity

Reactive aldehydes have been implicated in the etiology of several neurological and psychiatric disorders, and there is considerable interest in drugs to counteract the actions of these aldehydes. Increased formaldehyde (FA) and up-regulation of semicarbazide-sensitive amine oxidase, which forms FA from methylamine, have been implicated in disorders such as cerebrovascular disorders, alcohol abuse, diabetes and Alzheimer's disease. Phenelzine (PLZ), a monoamine oxidase inhibitor, is an antidepressant that has recently received attention for its neuroprotective/neurorescue properties. We investigated FA-induced toxicity and the effects of PLZ using rat primary cortical neurons and astrocytes and found that FA induced toxicity in neurons and astrocytes by multiple means. In astrocytes, FA decreased glutamate transporter expression, inhibiting glutamate uptake. PLZ reversed the decrease of glutamate uptake and the alteration of the second messengers, AKT and p38, induced by FA. PLZ alone affected the GLT-1 glutamate transporter in opposite directions in astrocytes and neurons. Thus, PLZ has multiple actions in neurons and astrocytes that may contribute to its neuroprotection.

Peripheral administration of fetuin-A attenuates early cerebral ischemic injury in rats

Cerebral ischemia-elicited inflammatory responses are driven by inflammatory mediators produced both by central (e.g., neurons and microglia) and infiltrating peripheral immune cells (e.g., macrophage/monocyte), and contribute to the evolution of tissue injury. A ubiquitous molecule, spermine, is released from injured cells, and counter-regulates release of various proinflammatory cytokines. However, the spermine-mediated anti-inflammatory activities are dependent on the availability of fetuin-A, a liver-derived negative acute-phase protein. Using an animal model of focal cerebral ischemia (i.e., permanent middle cerebral artery occlusion, MCAo), we found that levels of fetuin-A in the ischemic brain tissue were elevated in a time-dependent manner, starting between 2 and 6 h, peaking around 24 to 48 h, and returning to baseline 72 h after MCAo. When administered peripherally, exogenous fetuin-A gained entry across the BBB into the ischemic brain tissue, and dose dependently reduced brain infarct volume at 24 h after MCAo. Meanwhile, fetuin-A effectively attenuated (i) ischemia-induced HMGB1 depletion from the ischemic core; (ii) activation of centrally (e.g., microglia) and peripherally derived immune cells (e.g., macrophage/monocytes); and (iii) TNF production in ischemic brain tissue. Taken together, these experimental data suggest that fetuin-A protects against early cerebral ischemic injury partly by attenuating the brain inflammatory response.

Effect of L-arginine on metabolism of polyamines in rat's brain with extrahepatic cholestasis

Cholestatic encephalopathy results from accumulation of unconjugated bilirubin and hydrophobic bile acids in the brain. The aim of this study was to determine disturbances of polyamine metabolism in the brains of rats with experimental extrahepatic cholestasis and the effects of L-arginine administration. Wister rats were divided into groups: I: sham-operated, II: rats treated with L-arginine, III: animals with bile-duct ligation (BDL), and IV: cholestatic-BDL rats treated with L-arginine. Increased plasma gamma-glutamyltransferase and alkaline phosphatase activity and increased bile-acids and bilirubin levels in BDL rats were reduced by administration of L-arginine (P < 0.001). Cholestasis increased the brain's putrescine (P < 0.001) and decreased spermidine and spermine concentration (P < 0.05). The activity of polyamine oxidase was increased (P < 0.001) and diamine oxidase was decreased (P < 0.001) in the brains of BDL rats. Cholestasis increased the activity of arginase (P < 0.05) and decreased the level of citrulline (P < 0.001). Administration of L-arginine in BDL rats prevents metabolic disorders of polyamines and establishes a neuroprotective role in the brain during cholestasis.

Modulation of cellular function by polyamines

Polyamines (putrescine, spermidine and spermine) are essential for normal cell growth. The polyamine levels in cells are regulated by biosynthesis, degradation, and transport. Polyamines can modulate the functions of DNA, nucleotide triphosphates, proteins, and especially RNA because most polyamines exist in a polyamine-RNA complex in cells. Thus, the major focus on this review is on the role of polyamines in protein synthesis. In addition, effects of polyamines on B to Z conversion of DNA, transcription, phosphorylation of proteins, cell cycle progression, apoptosis and ion channels, especially NMDA receptors, are outlined. The function of eIF5A is also briefly discussed. Finally, a correlation between acrolein, produced from polyamines by polyamine oxidases, and chronic renal failure or brain stroke is summarized. Increased levels of polyamine oxidases and acrolein are good markers of chronic renal failure and brain stroke.

Spermine protects mice against lethal sepsis partly by attenuating surrogate inflammatory markers

The pathogenesis of sepsis is partly attributable to dysregulated inflammatory response mediated by pathogen-associated molecular patterns (PAMPs) (for example, endotoxin) and damage-associated molecular patterns (DAMPs) (for example, high-mobility group box 1 [HMGB1]). An endogenous ubiquitous polyamine, spermine, inhibits endotoxin-induced cytokine release in vitro, but its capacities to attenuate sepsis- and HMGB1-induced inflammatory responses was previously unknown. We thus tested the hypothesis that spermine protects mice against lethal sepsis by attenuating sepsis-induced local and systemic inflammatory responses. Intraperitoneal (i.p.) administration of spermine (10 mg/kg, twice daily, for 3 d) conferred a significant protection against lethal sepsis. The protective effects were associated with a significant reduction in peritoneal and serum levels of several surrogate markers of sepsis (for example, Interleukin-6 [IL-6], keratinocyte-derived chemokine [KC], monocytes chemoattractant protein-1 [MCP-1], macrophage inflammatory protein-2 [MIP-2], tissue inhibitor of metalloproteinase-1 [TIMP-1], soluble tumor necrosis factor-alpha receptor I [sTNFRI], and soluble tumor necrosis factor-alpha receptor II [sTNFRII]) during a late stage of sepsis. In vitro, spermine effectively inhibited HMGB1-induced release of the above surrogate markers in peritoneal macrophages. Thus, spermine confers protection against lethal sepsis partly by attenuating sepsis- and HMGB1-induced inflammatory responses.

Metabolism of polyamines and oxidative stress in the brain of cholestatic rats

In a recently published article in "Amino Acids" it was shown that obstructive jaundice of 9 days' duration in rats induces significant alterations of polyamines' metabolism in the brain, which might play an important pathogenetic role in cholestatic brain injury. The authors proposed that alterations of polyamines in cholestatic brain might induce neuronal toxicity through a mechanism that implicates the production of reactive oxygen species and oxidative stress, although this parameter was not evaluated in their study. This hypothesis is supported by our recent findings on brain oxidative status in rats with obstructive jaundice of 10 days' duration. Potential interrelations of the two studies' findings are discussed in this commentary.

The role of polyamine metabolism in neuronal injury following cerebral ischemia

Stroke is a leading cause of morbidity and mortality in the US, with secondary damage following the initial insult contributing significantly to overall poor outcome. Prior investigations have shown that the metabolism of certain polyamines such as spermine, spermidine, and putrescine are elevated in ischemic parenchyma, resulting in an increase in their metabolite concentration. Polyamine metabolites tend to be cytotoxic, leading to neuronal injury in the penumbra following stroke and expansion of the area of infarcted tissue. Although the precise mechanism is unclear, the presence of reactive aldehydes produced through polyamine metabolism, such as 3-aminopropanal and acrolein, have been shown to correlate with the incidence of cerebral vasospasm, disruption of oxidative metabolism and mitochondrial functioning, and disturbance of cellular calcium ion channels. Regulation of the polyamine metabolic pathway, therefore, may have the potential to limit injury following cerebral ischemia. To this end, we review this pathway in detail with an emphasis on clinical applicability.

Spermidine/spermine-N1-acetyltransferase ablation protects against liver and kidney ischemia-reperfusion injury in mice

Expression of spermine/spermidine-N1-acetyltransferase (SSAT), the rate-limiting enzyme of polyamine backconversion cascade, increases after ischemia-reperfusion injuries (IRI). We hypothesized that SSAT plays an important role in the mediation of IRI. To test our hypothesis, wild-type (SSAT-wt) and SSAT-deficient (SSAT-ko) mice were subjected to liver or kidney IRI by ligation of hepatic or renal arteries. The liver and kidney content of putrescine (Put), a downstream by-product of SSAT activity, increased in SSAT-wt animals but not in SSAT-ko animals after IRI, indicating that polyamine backconversion is not functional in SSAT-deficient mice. When subjected to hepatic IRI, SSAT-ko mice were significantly protected against liver damage compared with SSAT-wt mice. Similarly, SSAT-ko animals subjected to renal IRI showed significantly greater protection against damage to kidney tubules than SSAT-wt mice. These studies indicate that SSAT-deficient animals are protected against IRI and suggest that SSAT is an important mediator of the tissue damage in IRI.

Niemann-Pick C1 functions in regulating lysosomal amine content

Mutations in the late endosomal/lysosomal membrane protein Niemann-Pick C1 (NPC1) are known to cause a generalized block in retrograde vesicle-mediated transport, resulting in the hyper-accumulation of multiple lysosomal cargos. An important, yet often overlooked, category of lysosomal cargo includes the vast array of small molecular weight amine-containing molecules that are substrates for ion trapping in the highly acidic organelle lumen. We show here that the introduction of amine-containing molecules in lysosomes can significantly stimulate NPC1-mediated late endosome/lysosome fusion, and subsequently the secretion of lysosomal cargo. To illustrate the physiological importance of this NPC1-mediated transport pathway, we show that NPC1-deficient cells are more susceptible to the toxic effects of a lysosomotropic polyamine metabolite 3-aminopropanal. Moreover, NPC fibroblasts are shown to have higher levels of polyamine oxidase, an enzyme involved in the formation of 3-aminopropanal. Collectively, these findings provide strong support for a novel functional role for NPC1 and may also provide clues toward understanding NPC disease progression.

Neuroprotective effect of aminoguanidine on iron-induced neurotoxicity

Iron is a commonly used metal to induce neuronal hyperactivity and oxidative stress. Iron levels rise in the brain in some neurodegenerative disorders such as Parkinson's and Alzheimer's diseases. A body of evidence indicates a link between neuronal death and nitric oxide. The present study was performed to investigate whether nitric oxide produced by inducible nitric oxide synthase is involved in iron-induced neuron death. For this purpose rats were divided into four groups: control, iron, aminoguanidine and iron+aminoguanidine. Animals in iron and iron+aminoguanidine groups received intracerebroventricular FeCl3 injection (200 mM, 2.5 microl). Rats belonging to control and aminoguanidine groups received the same amount of saline into the cerebral ventricles. All animals were kept alive for 10 days following the operation and animals in aminoguanidine and iron+aminoguanidine groups received intraperitoneal aminoguanidine injections once a day (100mg/kg day) during this period. After 10 days, rats were perfused intracardially under deep urethane anesthesia. Removed brains were processed using the standard histological techniques. The total numbers of neurons in hippocampus of all rats were estimated with the unbiased stereological techniques. It was found that aminoguanidine decreased mean neuron loss from 43.4% to 20.3%. Results of the present study suggest that aminoguanidine may attenuate the neurotoxic effects of iron by inhibiting inducible nitric oxide synthase.