The physiological role of the polyamines

Chemotherapy in pediatric brain tumor and the challenge of the blood-brain barrier

BACKGROUND

Pediatric brain tumors (PBT) stand as the leading cause of cancer-related deaths in children. Chemoradiation protocols have improved survival rates, even for non-resectable tumors. Nonetheless, radiation therapy carries the risk of numerous adverse effects that can have long-lasting, detrimental effects on the quality of life for survivors. The pursuit of chemotherapeutics that could obviate the need for radiotherapy remains ongoing. Several anti-tumor agents, including sunitinib, valproic acid, carboplatin, and panobinostat, have shown effectiveness in various malignancies but have not proven effective in treating PBT. The presence of the blood-brain barrier (BBB) plays a pivotal role in maintaining suboptimal concentrations of anti-cancer drugs in the central nervous system (CNS). Ongoing research aims to modulate the integrity of the BBB to attain clinically effective drug concentrations in the CNS. However, current findings on the interaction of exogenous chemical agents with the BBB remain limited and do not provide a comprehensive explanation for the ineffectiveness of established anti-cancer drugs in PBT.

METHODS

We conducted our search for chemotherapeutic agents associated with the blood-brain barrier (BBB) using the following keywords: Chemotherapy in Cancer, Chemotherapy in Brain Cancer, Chemotherapy in PBT, BBB Inhibition of Drugs into CNS, Suboptimal Concentration of CNS Drugs, PBT Drugs and BBB, and Potential PBT Drugs. We reviewed each relevant article before compiling the information in our manuscript. For the generation of figures, we utilized BioRender software.

FOCUS

We focused our article search on chemical agents for PBT and subsequently investigated the role of the BBB in this context. Our search criteria included clinical trials, both randomized and non-randomized studies, preclinical research, review articles, and research papers.

FINDING

Our research suggests that, despite the availability of potent chemotherapeutic agents for several types of cancer, the effectiveness of these chemical agents in treating PBT has not been comprehensively explored. Additionally, there is a scarcity of studies examining the role of the BBB in the suboptimal outcomes of PBT treatment, despite the effectiveness of these drugs for other types of tumors.

Modeling Myotonic Dystrophy Type 2 Using Drosophila melanogaster

Myotonic dystrophy 2 (DM2) is a genetic multi-systemic disease primarily affecting skeletal muscle. It is caused by CCTGn expansion in intron 1 of the CNBP gene, which encodes a zinc finger protein. DM2 disease has been successfully modeled in Drosophila melanogaster, allowing the identification and validation of new pathogenic mechanisms and potential therapeutic strategies. Here, we describe the principal tools used in Drosophila to study and dissect molecular pathways related to muscular dystrophies and summarize the main findings in DM2 pathogenesis based on DM2 Drosophila models. We also illustrate how Drosophila may be successfully used to generate a tractable animal model to identify novel genes able to affect and/or modify the pathogenic pathway and to discover new potential drugs.

Age-associated polyamines in peripheral blood cells and plasma in 20 to 70 years of age subjects

Dietary polyamines have been associated with slowing ageing processes and various pathologies, raising the importance of establishing reference values at different ages throughout life. This study aimed to analyse age-dependent variations in polyamine content using peripheral blood cells and plasma in a healthy and homogeneous population. Peripheral blood of 193 volunteers of both sexes (20-70 years), selected by convenience, was processed to separate cells and plasma. A pre-column derivatization method was used to determine the amines by HPLC (nmol or pmol/mg protein or nmol/ml) to analyse their association with the age (continuous or ordinal in decades) of the subjects. Putrescine and spermine weakly declined significantly in mononuclear cells with age. In erythrocytes and plasma, putrescine showed an evident decrease in the 60-70-year-old group compared to the rest. The ratios between polyamines, mainly in erythrocytes, decreased in the 60-70 years age group and increased the ratio of putrescine in mononuclear cells/erythrocytes. The ratio of putrescine in mononuclear cells/erythrocytes was higher in the 60-70-year-old age group than in the rest. In a sample of subjects (20-29 vs. 60-70 years), whole blood polyamines were not significantly different when differences existed in erythrocytes. Polyamine homeostasis in blood cells and plasma changed with age. Putrescine declined in mononuclear cells and decreased in erythrocytes and plasma in the decade of the 60 s. Further studies should establish an age-dependent phenotype and whether polyamines' supplementation could restore the decreased values and be associated with long-term overall biological benefits.

The role of polyamine metabolism in remodeling immune responses and blocking therapy within the tumor immune microenvironment

The study of metabolism provides important information for understanding the biological basis of cancer cells and the defects of cancer treatment. Disorders of polyamine metabolism is a common metabolic change in cancer. With the deepening of understanding of polyamine metabolism, including molecular functions and changes in cancer, polyamine metabolism as a new anti-cancer strategy has become the focus of attention. There are many kinds of polyamine biosynthesis inhibitors and transport inhibitors, but not many drugs have been put into clinical application. Recent evidence shows that polyamine metabolism plays essential roles in remodeling the tumor immune microenvironment (TIME), particularly treatment of DFMO, an inhibitor of ODC, alters the immune cell population in the tumor microenvironment. Tumor immunosuppression is a major problem in cancer treatment. More and more studies have shown that the immunosuppressive effect of polyamines can help cancer cells to evade immune surveillance and promote tumor development and progression. Therefore, targeting polyamine metabolic pathways is expected to become a new avenue for immunotherapy for cancer.

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.

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.

Translational control of polyamine metabolism by CNBP is required for Drosophila locomotor function

Microsatellite expansions of CCTG repeats in the cellular nucleic acid-binding protein (CNBP) gene leads to accumulation of toxic RNA and have been associated with myotonic dystrophy type 2 (DM2). However, it is still unclear whether the dystrophic phenotype is also linked to CNBP decrease, a conserved CCHC-type zinc finger RNA-binding protein that regulates translation and is required for mammalian development. Here, we show that depletion of Drosophila CNBP in muscles causes ageing-dependent locomotor defects that are correlated with impaired polyamine metabolism. We demonstrate that the levels of ornithine decarboxylase (ODC) and polyamines are significantly reduced upon dCNBP depletion. Of note, we show a reduction of the CNBP-polyamine axis in muscles from DM2 patients. Mechanistically, we provide evidence that dCNBP controls polyamine metabolism through binding dOdc mRNA and regulating its translation. Remarkably, the locomotor defect of dCNBP-deficient flies is rescued by either polyamine supplementation or dOdc1 overexpression. We suggest that this dCNBP function is evolutionarily conserved in vertebrates with relevant implications for CNBP-related pathophysiological conditions.

Function of Polyamines in Regulating Cell Cycle Progression of Cultured Silkworm Cells

Simple Summary

The mechanism of the polyamine pathway in the lepidopteran silkworm is largely unknown. In the current study, we aimed to characterize the function of polyamines and polyamine pathway genes in silkworm cells as a regulator of cell cycle progression. For the first time, we identified the homologous genes of the polyamine pathway in silkworm, and analyzed their expression characteristics in different tissues and their subcellular localizations in cultured silkworm cells. We measured the abundant levels of polyamines in silkworm cells by HPLC analysis. We found that exogenous supplementation of spermidine in cells promoted DNA replication and cell cycle progression and, in contrast, treatment with polyamine biosynthesis inhibitors DFMO and MGBG prevented DNA replication and cell cycle progression. Indeed, the mechanism studies indicated that spermidine increased the expression of cell cycle-related genes, whereas this increase could be abolished by treatment with inhibitors. Taken together, our findings highlight that appropriate levels of polyamines have beneficial effects on the progression of the cell cycle by regulating cell cycle genes in silkworm.

Abstract

Background: Putrescine, spermidine, and spermine are polyamines that are ubiquitously distributed in prokaryotic and eukaryotic cells, which play important roles in cell proliferation and differentiation. Methods: We investigated the expression profiles of polyamine pathway genes by qRT-PCR in different tissues of the lepidopteran silkworm. The polyamine levels in cultured silkworm cells were measured by HPLC. Spermidine and polyamine biosynthetic inhibitors were used for treating the cultured silkworm cells in order to clarify their effects on cell cycle progression. Results: We identified the anabolic and catabolic enzymes that are involved in the polyamine biosynthetic pathway in silkworm. Transcriptional expression showed at least seven genes that were expressed in different silkworm tissues. Treatments of the cultured silkworm cells with spermidine or inhibitor mixtures of DFMO and MGBG induced or inhibited the expression of cell cycle-related genes, respectively, and thus led to changed progression of the cell cycle. Conclusions: The present study is the first to identify the polyamine pathway genes and to demonstrate the roles of polyamines on cell cycle progression via regulation of the expression of cell cycle genes in silkworm.

Total synthesis of ent-pavettamine

Pavettamine, a plant toxin first isolated from Pavetta harborii in 1995, was previously identified as a polyamine with C₂ symmetry and a 1,3-syn-diol moiety on a C₁₀ carbon backbone – one of very few substituted polyamines to be isolated from nature. Its absolute configuration was later established by our first reported total synthesis in 2010. Herein we report the first total synthesis of the enantiomer of pavettamine, ent-pavettamine. The symmetrical structure of the molecule allows for the synthesis of a common C₅ fragment that can be divergently transformed into two synthons for later convergent coupling to furnish the target carbon framework. Based on the success of the protocol we employed for the synthesis of the naturally occurring pavettamine, (S)-malic acid was again the starting material of choice for the synthesis of the two individual C₅ fragments, with strategic differences in terminal-group manipulation allowing for the synthesis of ent-pavettamine rather than pavettamine. Chain extension and stereoselective ketone reduction were achieved using the (R)-methyl p-tolyl sulfoxide chiral auxiliary to give the desired 1,3-syn-diol C₅ unit. A protecting-group strategy was also developed for the orthogonal protection of the alcohol and amine functional groups as they were unveiled. The functionalized C₅ fragments were coupled via reductive amination revealing the C₁₀ carbon backbone. Deprotection of the alcohol and amine functional groups successfully provided ent-pavettamine as a TFA salt.

Chromogenic Chemodosimeter Based on Capped Silica Particles to Detect Spermine and Spermidine

A new hybrid organic–inorganic material for sensing spermine (Spm) and spermidine (Spd) has been prepared and characterized. The material is based on MCM-41 particles functionalized with an N-hydroxysuccinimide derivative and loaded with Rhodamine 6G. The cargo is kept inside the porous material due to the formation of a double layer of organic matter. The inner layer is covalently bound to the silica particles, while the external layer is formed through hydrogen and hydrophobic interactions. The limits of detection determined by fluorimetric titration are 27 µM and 45 µM for Spm and Spd, respectively. The sensor remains silent in the presence of other biologically important amines and is able to detect Spm and Spd in both aqueous solution and cells.

Dual targeting of polyamine synthesis and uptake in diffuse intrinsic pontine gliomas

Diffuse intrinsic pontine glioma (DIPG) is an incurable malignant childhood brain tumor, with no active systemic therapies and a 5-year survival of less than 1%. Polyamines are small organic polycations that are essential for DNA replication, translation and cell proliferation. Ornithine decarboxylase 1 (ODC1), the rate-limiting enzyme in polyamine synthesis, is irreversibly inhibited by difluoromethylornithine (DFMO). Herein we show that polyamine synthesis is upregulated in DIPG, leading to sensitivity to DFMO. DIPG cells compensate for ODC1 inhibition by upregulation of the polyamine transporter SLC3A2. Treatment with the polyamine transporter inhibitor AMXT 1501 reduces uptake of polyamines in DIPG cells, and co-administration of AMXT 1501 and DFMO leads to potent in vitro activity, and significant extension of survival in three aggressive DIPG orthotopic animal models. Collectively, these results demonstrate the potential of dual targeting of polyamine synthesis and uptake as a therapeutic strategy for incurable DIPG.

The multiple effects of aspirin in prostate cancer patients

Aspirin is a commonly used medication with anti-inflammatory and analgesic properties, and it is widely used to reduce the risk of ischaemic heart disease-related events and/or cerebrovascular accidents. However, there is also evidence from epidemiological and interventional studies to suggest that regular aspirin use can reduce the risk of prostate cancer development and progression, and can reduce the risk of disease recurrence following anti-prostate cancer therapy. Aspirin use in African-American men is associated with a reduced incidence of advanced PCa and reduced disease recurrence, and there is evidence from other studies of an association between regular aspirin use and decreased PCa-related mortality. The cyclooxygenase-2 enzyme inhibited by Aspirin and other NSAIDs, and which catalyses prostaglandin synthesis and mediates inflammation, is overexpressed in prostate cancer, therefore inhibition of cyclooxygenase-2 may have direct, and indirect, therapeutic effects. This review explores the evidence suggesting that aspirin use can modify prostate cancer biology and disease characteristics, and explores the potential mechanisms underpinning the observed associations between aspirin use and modification of prostate cancer risk. It also summarises the potential for adjuvant aspirin use to combine with other therapeutic approaches such as radical surgery and radiotherapy.

The regulation of triglyceride storage by ornithine decarboxylase (Odc1) in Drosophila

Polyamines are low molecular weight, organic cations that play a critical role in many major cellular processes including cell cycle regulation and apoptosis, cellular division, tissue proliferation, and cellular differentiation; however, the functions of polyamines in regulating the storage of metabolic fuels such as triglycerides and glycogen is poorly understood. To address this question, we focused on the Drosophila homolog of ornithine decarboxylase (Odc1), the first rate-limiting enzyme in the synthesis of polyamines. Mutants in Odc1 are lethal, but heterozygotes were viable to adulthood. Odc1 heterozygotes appeared larger than their genetic background control flies and consistent with this observation, weighed more than the controls. However, the increased weight was not due to increased food consumption as heterozygotes ate less than the controls. Interestingly, Odc1 heterozygous flies had augmented triglyceride storage, and this lipid phenotype was due to increased triglyceride storage per cell and an increase in the number of fat cells produced. Odc1 heterozygous flies also displayed increased expression of the lipid synthesis genes fatty acid synthase (FASN) and acetyl-CoA carboxylase (ACC), suggesting increased lipid synthesis was the cause of the augmented triglyceride phenotype. These results provide a link between the expression of Odc1 and triglyceride storage suggesting that the polyamine pathway plays a role in regulating lipid metabolism.

Altered brain arginine metabolism in a mouse model of tauopathy

Tauopathies consist of intracellular accumulation of hyperphosphorylated and aggregated microtubule protein tau, which remains a histopathological feature of Alzheimer's disease (AD) and frontotemporal dementia. L-Arginine is a semi-essential amino acid with a number of bioactive molecules. Its downstream metabolites putrescine, spermidine, and spermine (polyamines) are critically involved in microtubule assembly and stabilization. Recent evidence implicates altered arginine metabolism in the pathogenesis of AD. Using high-performance liquid chromatographic and mass spectrometric assays, the present study systematically determined the tissue concentrations of L-arginine and its nine downstream metabolites in the frontal cortex, hippocampus, parahippocampal region, striatum, thalamus, and cerebellum in male PS19 mice-bearing human tau P301S mutation at 4, 8, and 12-14 months of age. As compared to their wild-type littermates, PS19 mice displayed early and/or prolonged increases in L-ornithine and altered polyamine levels with age. There were also genotype- and age-related changes in L-arginine, L-citrulline, glutamine, glutamate, and γ-aminobutyric acid in a region- and/or chemical-specific manner. The results demonstrate altered brain arginine metabolism in PS19 mice with the most striking changes in L-ornithine, polyamines, and glutamate, indicating a shift of L-arginine metabolism to favor the arginase-polyamine pathway. Given the role of polyamines in maintaining microtubule stability, the functional significance of these changes remains to be explored in future research.

Cellular and Animal Model Studies on the Growth Inhibitory Effects of Polyamine Analogues on Breast Cancer

Polyamine levels are elevated in breast tumors compared to those of adjacent normal tissues. The female sex hormone, estrogen is implicated in the origin and progression of breast cancer. Estrogens stimulate and antiestrogens suppress the expression of polyamine biosynthetic enzyme, ornithine decarboxylate (ODC). Using several bis(ethyl)spermine analogues, we found that these analogues inhibited the proliferation of estrogen receptor-positive and estrogen receptor negative breast cancer cells in culture. There was structure-activity relationship in the efficacy of these compounds in suppressing cell growth. The activity of ODC was inhibited by these compounds, whereas the activity of the catabolizing enzyme, spermidine/spermine N¹-acetyl transferase (SSAT) was increased by 6-fold by bis(ethyl)norspermine in MCF-7 cells. In a transgenic mouse model of breast cancer, bis(ethyl)norspermine reduced the formation and growth of spontaneous mammary tumor. Recent studies indicate that induction of polyamine catabolic enzymes SSAT and spermine oxidase (SMO) play key roles in the anti-proliferative and apoptotic effects of polyamine analogues and their combinations with chemotherapeutic agents such as 5-fluorouracil (5-FU) and paclitaxel. Thus, polyamine catabolic enzymes might be important therapeutic targets and markers of sensitivity in utilizing polyamine analogues in combination with other therapeutic agents.

3D-Membrane Stacks on Supported Membranes Composed of Diatom Lipids Induced by Long-Chain Polyamines

Long-chain polyamines (LCPAs) are intimately involved in the biomineralization process of diatoms taking place in silica deposition vesicles being acidic compartments surrounded by a lipid bilayer. Here, we addressed the question whether and how LCPAs interact with lipid membranes composed of glycerophospholipids and glyceroglycolipids mimicking the membranes of diatoms and higher plants. Solid supported lipid bilayers and monolayers containing the three major components that are unique in diatoms and higher plants, i.e., monogalactosyldiacylglycerol (MGDG), digalactosyldiacylglycerol (DGDG), and sulfoquinovosyldiacylglycerol (SQDG), were prepared by spreading small unilamellar vesicles. The integrity of the membranes was investigated by fluorescence microscopy and atomic force microscopy showing continuous flat bilayers and monolayers with small protrusions on top of the membrane. The addition of a synthetic polyamine composed of 13 amine groups separated by a propyl spacer (C3N13) results in flat but three-dimensional membrane stacks within minutes. The membrane stacks are connected with the underlying membrane as verified by fluorescence recovery after photobleaching experiments. Membrane stack formation was found to be independent of the lipid composition; i.e., neither glyceroglycolipids nor negatively charged lipids were required. However, the formation process was strongly dependent on the chain length of the polyamine. Whereas short polyamines such as the naturally occurring spermidine, spermine, and the synthetic polyamines C3N4 and C3N5 do not induce stack formation, those containing seven and more amine groups (C3N7, C3N13, and C3N18) do form membrane stacks. The observed stack formation might have implications for the stability and expansion of the silica deposition vesicle during valve and girdle band formation in diatoms.

Decreased sensitivity to aspirin is associated with altered polyamine metabolism in human prostate cancer cells

Aspirin is a well-known analgesic, anti-inflammatory and antipyretic drug and is recognised as a chemopreventative agent in cardiovascular disease and, more recently, in colorectal cancer. Although several studies indicate that aspirin is capable of reducing the risk of developing cancers, there is a lack of convincing evidence that aspirin can prevent prostate cancer in man. In this study, aspirin was shown to be an effective inhibitor of the growth of human prostate cancer cells. In order to investigate the link between polyamine catabolism and the effects of aspirin we used a “Tet off” system that induced the activity of spermidine/spermine N¹-acetyltransferase (SSAT) in human prostate cancer cells (LNCap). Treatment with aspirin was found to decrease induced SSAT activity in these cells. A negative correlation was observed between increased polyamine catabolism via increased SSAT activity and the sensitivity to aspirin. In the presence of increased SSAT activity high amounts of N¹-acetylspermidine and putrescine were observed. These cells were also found to grow more slowly than the non-induced cells. The results indicate that SSAT and its related polyamine metabolism may play a key role in sensitivity of cancer cells to aspirin and possibly other NSAIDs and this may have implications for the development of novel chemopreventative agents.

Association between the ornithine decarboxylase G316A polymorphism and breast cancer survival

Ornithine decarboxylase (ODC) is a significant rate-limiting enzyme in polyamine synthesis, required for normal cell growth, and is highly expressed in various malignancies, including colorectal and breast cancer. In the present study, the associations between the ODC G316A single nucleotide polymorphism (SNP) and breast cancer-specific survival were investigated. In addition, the functional effects of this SNP were examined in the MCF-7 human breast cancer cell line. The present study recruited 300 stage I-III breast cancer cases, which were diagnosed at the Affiliated Cancer Hospital of Zhengzhou University (Zhengzhou, China) between 2002 and 2003, with follow-up visits conducted until May 2013. ODC G316A was genotyped (ODC GG vs. ODC AG/AA) in the 300 cases and the association of the genotypes with cancer-specific survival was analyzed. In the MCF-7 cell line, the ODC allele-specific binding of E-box transcription factors was determined using western blot and chromatin immunoprecipitation assays. Survival differences were observed between the two genotypes: Compared with the ODC GG genotype, patients with ODC GA/AA exhibited significantly higher survival rates (P<0.05). In cultured cells, the ODC SNP, which is flanked by two E-boxes, appeared to predict ODC promoter activity. Furthermore, the E-box activator c-MYC and repressor MAX interactor 1 were found to preferentially bind to ODC minor A-alleles compared with major G-alleles, in cultured MCF-7 cells. In conclusion, the results of the current study suggest that the regulation of ODC may affect survival in breast cancer patients and indicate a model in which the ODC SNP may be protective for breast adenoma recurrence and detrimental for survival following a diagnosis of breast cancer.

Interaction of linear polyamines with negatively charged phospholipids: the effect of polyamine charge distance

The binding of cationic polyamines to negatively charged lipid membranes is driven by electrostatic interactions and additional hydrophobic contributions. We investigated the effect of polyamines with different number of charges and charge separation on the phase transition behavior of vesicles of phosphatidylglycerols (dipalmitoylphosphatidylglycerol and dimyristoylphosphatidylglycerol) to differentiate between effects caused by the number of charges, the charge distance, and the hydrophobicity of the methylene spacer. Using differential scanning calorimetry and Fourier transform infrared spectroscopy complemented with monolayer experiments, we found that the binding constant of polyamines to negatively charged lipid vesicles depends as expected on the number of charges. However, for diamines, the effect of binding on the main phase transition of phosphatidylglycerols (PGs) is also strongly influenced by the charge distance between the ammonium groups in the backbone. Oligoamines with charges separated by two or three methylene groups bind more strongly and have larger stabilizing effects on the lipid gel phase of PGs. With multivalent polyamines, the appearance of several transition peaks points to effects of molecular crowding on the surface, i.e., binding of only two or three charges to the surface in the case of spermine, and possible concomitant domain formation.

Polyamines metabolism and breast cancer: state of the art and perspectives

Breast cancer (BC) is a common disease that generally occurs in women over the age of 50, and the risk is especially high for women over 60 years of age. One of the major BC therapeutic problems is that tumors initially responsive to chemotherapeutic approaches can progress to more aggressive forms poorly responsive to therapies. Polyamines (PAs) are small polycationic alkylamines, naturally occurring and essential for normal cell growth and development in eukaryotes. The intracellular concentration of PA is maintained within strongly controlled contents, while a dysregulation occurs in BC cells. Polyamines facilitate the interactions of transcription factors, such as estrogen receptors with their specific response element, and are involved in the proliferation of ER-negative and highly invasive BC tumor cells. Since PA metabolism has a critical role in cell death and proliferation, it represents a potential target for intervention in BC. The goal of this study was to perform a literature search reviewing the association between PA metabolism and BC, and the current evidence supporting the BC treatment targeting PA metabolism. We here describe in vitro and in vivo models, as well as the clinical trials that have been utilized to unveil the relationship between PA metabolism and BC. Polyamine pathway is still an important target for the development of BC chemotherapy via enzyme inhibitors. Furthermore, a recent promising strategy in breast anticancer therapy is to exploit the self-regulatory nature of PA metabolism using PA analogs to affect PA homeostasis. Nowadays, antineoplastic compounds targeting the PA pathway with novel mechanisms are of great interest and high social impact for BC chemotherapy.

Autocrine/paracrine regulatory mechanisms in adrenocortical neoplasms responsible for primary adrenal hypercorticism

A wide variety of autocrine/paracrine bioactive signals are able to modulate corticosteroid secretion in the human adrenal gland. These regulatory factors, released in the vicinity of adrenocortical cells by diverse cell types comprising chromaffin cells, nerve terminals, cells of the immune system, endothelial cells, and adipocytes, include neuropeptides, biogenic amines, and cytokines. A growing body of evidence now suggests that paracrine mechanisms may also play an important role in the physiopathology of adrenocortical hyperplasias and tumors responsible for primary adrenal steroid excess. These intra-adrenal regulatory systems, although globally involving the same actors as those observed in the normal gland, display alterations at different levels, which reinforce the capacity of paracrine factors to stimulate the activity of adrenocortical cells. The main modifications in the adrenal local control systems reported by now include hyperplasia of cells producing the paracrine factors and abnormal expression of the latter and their receptors. Because steroid-secreting adrenal neoplasms are independent of the classical endocrine regulatory factors angiotensin II and ACTH, which are respectively suppressed by hyperaldosteronism and hypercortisolism, these lesions have long been considered as autonomous tissues. However, the presence of stimulatory substances within the neoplastic tissues suggests that steroid hypersecretion is driven by autocrine/paracrine loops that should be regarded as promising targets for pharmacological treatments of primary adrenal disorders. This new potential therapeutic approach may constitute an alternative to surgical removal of the lesions that is classically recommended in order to cure steroid excess.

Polyamines and cancer: implications for chemotherapy and chemoprevention

Polyamines are small organic cations that are essential for normal cell growth and development in eukaryotes. Under normal physiological conditions, intracellular polyamine concentrations are tightly regulated through a dynamic network of biosynthetic and catabolic enzymes, and a poorly characterised transport system. This precise regulation ensures that the intracellular concentration of polyamines is maintained within strictly controlled limits. It has frequently been observed that the metabolism of, and the requirement for, polyamines in tumours is frequently dysregulated. Elevated levels of polyamines have been associated with breast, colon, lung, prostate and skin cancers, and altered levels of rate-limiting enzymes in both biosynthesis and catabolism have been observed. Based on these observations and the absolute requirement for polyamines in tumour growth, the polyamine pathway is a rational target for chemoprevention and chemotherapeutics. Here we describe the recent advances made in the polyamine field and focus on the roles of polyamines and polyamine metabolism in neoplasia through a discussion of the current animal models for the polyamine pathway, chemotherapeutic strategies that target the polyamine pathway, chemotherapeutic clinical trials for polyamine pathway-specific drugs and ongoing clinical trials targeting polyamine biosynthesis.

Effects of prolonged agmatine treatment in aged male Sprague-Dawley rats

Increasing evidence suggests that altered arginine metabolism contributes to cognitive decline during ageing. Agmatine, decarboxylated arginine, has a variety of pharmacological effects, including the modulation of behavioural function. A recent study demonstrated the beneficial effects of short-term agmatine treatment in aged rats. The present study investigated how intraperitoneal administration of agmatine (40mg/kg, once daily) over 4-6weeks affected behavioural function and neurochemistry in aged Sprague-Dawley rats. Aged rats treated with saline displayed significantly reduced exploratory activity in the open field, impaired spatial learning and memory in the water maze and object recognition memory relative to young rats. Prolonged agmatine treatment improved animals' performance in the reversal test of the water maze and object recognition memory test, and significantly suppressed age-related elevation in nitric oxide synthase activity in the dentate gyrus of the hippocampus and prefrontal cortex. However, this prolonged supplementation was unable to improve exploratory activity and spatial reference learning and memory in aged rats. These findings further demonstrate that exogenous agmatine selectively improves behavioural function in aged rats.

Ageing alters behavioural function and brain arginine metabolism in male Sprague-Dawley rats

A growing body of evidence suggests the involvement of L-arginine and its metabolites in the ageing and neurodegenerative processes. The present study assessed behavioural performance in 4- (young), 12- (middle-aged) and 24- (aged) month-old male Sprague-Dawley rats, and investigated age-related changes in the activity of two key arginine metabolic enzymes, nitric oxide synthase (NOS) and arginase, and the levels of L-arginine and its downstream metabolites in a number of memory-related brain structures. Aged rats were less anxious and performed poorly in the water maze task relative to the young and middle-aged rats, and both middle-aged and aged rats displayed reduced exploratory activity relative to the young ones. There were significant age-related changes in NOS and arginase activities, and the levels of L-arginine, L-citrulline, L-ornithine, agmatine, putrescine, spermidine, spermine and glutamate, but not γ-aminobutyric acid, in the CA1, CA2/3 and dentate gyrus sub-regions of the hippocampus and the prefrontal, entorhinal, perirhinal, postrhinal and temporal (an auditory cortex) cortices in a region-specific manner. Cluster analyses revealed that the nine related neurochemical variables formed distinct groups, which changed as a function of ageing. Multiple regression analyses revealed a number of significant correlations between the neurochemical and behavioural variables. The present study further supports the involvement of arginine metabolism in the ageing process, and provides further evidence of the effects of animals' behavioural experience on arginine metabolism.

Agmatine, a metabolite of L-arginine, reverses scopolamine-induced learning and memory impairment in rats

Agmatine (l-amino-4-guanidino-butane), a metabolite of L-arginine through the action of arginine decarboxylase, is a novel neurotransmitter. In the present study, effects of agmatine on cognitive functions have been evaluated by using one trial step-down passive avoidance and three panel runway task. Agmatine (20, 40, 80 mg/kg i.p.) was administered either in the presence or absence of a cholinergic antagonist, scopolamine (1 mg/kg i.p.). Scopolamine significantly impaired learning and memory in both passive avoidance and three panel runway test. Agmatine did not affect emotional learning, working and reference memory but significantly improved scopolamine-induced impairment of learning and memory in a dose dependent manner. Our results indicate that agmatine, as an endogenous substance, may have an important role in modulation of learning and memory functions.

Oligoamine analogues in combination with 2-difluoromethylornithine synergistically induce re-expression of aberrantly silenced tumour-suppressor genes

Epigenetic gene silencing is an important mechanism in the initiation and progression of cancer. Abnormal DNA CpG island hypermethylation and histone modifications are involved in aberrant silencing of tumour-suppressor genes. LSD1 (lysine-specific demethylase 1) was the first enzyme identified to specifically demethylate H3K4 (Lys⁴ of histone H3). Methylated H3K4 is an important mark associated with transcriptional activation. The flavin adenine dinucleotide-binding amine oxidase domain of LSD1 is homologous with two polyamine oxidases, SMO (spermine oxidase) and APAO (N¹-acetylpolyamine oxidase). We have demonstrated previously that long-chain polyamine analogues, the oligoamines, are inhibitors of LSD1. In the present paper we report the synergistic effects of specific oligoamines in combination with DFMO (2-difluoromethylornithine), an inhibitor of ornithine decarboxylase, in human colorectal cancer cells. DFMO treatment depletes natural polyamines and increases the uptake of exogenous polyamines. The combination of oligoamines and DFMO results in a synergistic re-expression of aberrantly silenced tumour-suppressor genes, including SFRP2 (secreted frizzled-related protein 2), which encodes a Wnt signalling pathway antagonist and plays an anti-tumorigenic role in colorectal cancer. The treatment-induced re-expression of SFRP2 is associated with increased H3K4me2 (di-methyl H3K4) in the gene promoter. The combination of LSD1-inhibiting oligoamines and DFMO represents a novel approach to epigenetic therapy of cancer.

Chronic difluoromethylornithine treatment impairs spatial learning and memory in rats

Recent evidence suggests that polyamines putrescine, spermidine and spermine are essential in maintaining normal cellular function. The present study investigated the effects of chronic treatment of difluoromethylornithine (DFMO, 3% in drinking water), a potent inhibitor of putrescine synthesis, for 54 consecutive days on animals'behavior and neurochemical levels in the CA1, CA2/3 and dentate gyrus sub-regions of the hippocampus and the prefrontal cortex. The DFMO group showed performance impairments in the place navigation and the probe test conducted 24 h after the training in the reference memory version of the water maze task, but not in the elevated plus maze, open field, object recognition, cued navigation and the working memory version of the water maze task when compared to the control group (drinking water only). DFMO treatment resulted in approximately 80-90% and 20% of reductions in the putrescine and spermidine levels, respectively, in the four brain regions examined, and a small reduction in agmatine level in the CA2/3, with no effects on spermine, glutamate and γ-aminobutyrate. The DFMO group showed decreased body weight relative to the control one. However, there were no significant differences between groups in the normalized brain, kidney and liver weights. The present study demonstrates that chronic treatment of DFMO depletes putrescine and decreases spermidine levels in the brain, inhibits growth, and impairs spatial learning and memory in the reference memory version of the water maze specifically. These findings merit further investigation to fully understand the functional role of endogenous polyamines in learning and memory.

Spatial learning-induced increase in agmatine levels at hippocampal CA1 synapses

Agmatine, a metabolite of L-arginine, is considered as a novel putative neurotransmitter. It has been detected in axon terminals that synapse with pyramidal cells in the hippocampus, a brain region that is critically involved in spatial learning and memory. However, the role of agmatine in learning and memory is poorly understood. Recently, we demonstrated water maze training-induced increases in tissue levels of agmatine in the CA1 subregion of the hippocampus. This finding has raised an issue whether an endogenous agmatine could directly participate in learning and memory processes as a neurotransmitter. In the present study, quantitative immunogold-labeling and electron-microscopical techniques were used to analyze the levels of agmatine in CA1 stratum radiatum (SR) terminals (n = 600) of male Sprague-Dawley rats that had been trained to find a hidden escape platform in the water maze (WM) task or forced to swim (SW) in the pool with no platform presented. Agmatine levels were significantly increased by ∼85% in the synaptic terminals of SR of trained WM group compared with the SW control group (all P < 0.001). These results, for the first time, demonstrate spatial learning-induced elevation in agmatine levels at synapses in the hippocampus and provide evidence of its participation in learning and memory processing as a novel neurotransmitter.

Associations of a polymorphism in the ornithine decarboxylase gene with colorectal cancer survival

PURPOSE

Activity of ornithine decarboxylase (ODC), the first enzyme in polyamine synthesis, is required for normal growth and is elevated in many cancers, including colorectal cancer. We examined associations of the +316 ODC1 single nucleotide polymorphism (SNP) with colorectal cancer-specific survival among colorectal cancer cases, and then investigated its functional significance in colon cancer cells.

EXPERIMENTAL DESIGN

The study included 400 incident stage I-III colorectal cancer cases from the population-based University of California Irvine Gene-Environment Study of Familial Colorectal Cancer (diagnosed from 1994 to 1996 with follow-up through March 2008). The primary outcome was colorectal cancer-specific survival dependent on ODC1 (rs2302615) genotype (GG versus GA/AA). In human colon cancer cell lines, ODC1 allele-specific binding of E-box transcription factors was determined via Western blotting and chromatin immunoprecipitation assays. ODC1 allele-specific promoter activity was determined using promoter constructs in combination with vectors expressing either the transcriptional activator c-MYC or the repressor MAD1.

RESULTS

Genotype-specific survival differences were observed among colorectal cancer cases: compared with cases with the ODC1 GG genotype (hazards ratio, 1; reference) the adjusted colorectal cancer-specific survival hazards ratio was 2.02 (95% confidence interval, 1.17-3.50) for ODC1 GA/AA cases (P = 0.012). In colon cancer cells, the ODC1 SNP, flanked by two E-boxes, predicts ODC1 promoter activity. The E-box activator c-MYC and repressors MAD1 and MAD4 preferentially bind to ODC1 minor A-alleles, compared with major G-alleles, in cultured cells.

CONCLUSIONS

These results have implications for conditional regulation of polyamine homeostasis and suggest a model in which the ODC1 SNP may be protective for colon adenoma recurrence and detrimental for survival after colon cancer diagnosis.

Behavioral effects of agmatine in naive rats are task- and delay-dependent

The present study systematically investigated the effects of agmatine administered i.p. in several commonly used behavioral tasks. In Experiment 1, pre-test treatment of agmatine (1 and 40 mg/kg) appeared to improve animals' performance in the water maze probe test conducted 24 h, but not 120 s, after training, when the effect was evaluated within subjects. In Experiment 2, pre-test agmatine treatment (40 mg/kg) did not affect animals' performance in the open field, and the place navigation, probe tests (1-4 and 6), reversal test and cued navigation in the water maze, but significantly facilitated performance in probe 5 which was conducted 96 h after training. In Experiment 3, rats with pre-test agmatine treatment (40 mg/kg) were less anxious relative to the controls, with no performance changes in the open field. In the water maze task, post-training agmatine treatment (40 mg/kg) did not affect place and cued navigation, but significantly improved animals' performance in the probe test conducted 24 h after training and the reversal test. In the working memory version of the task, agmatine treated rats took significantly less time and generated markedly shorter path length to reach the platform at the 180 s, but not 30 s, delay relative to the controls. In the object recognition task, rats with pre-test agmatine treatment (40 mg/kg) spent significantly more time exploring displaced objects, but not novel object, as compared to the controls. In Experiment 4, pre-test agmatine treatment (40 mg/kg) had no effect on the task acquisition in the delayed non-match to position task in the T-maze, but significantly facilitated performance at the 600 s delay. These results suggest that the behavioral effects of agmatine are task- and delay-dependent, and agmatine facilitates memory particularly when the task difficulty is increased due to memory trace decay and/or greater interference.

Age-related changes in polyamines in memory-associated brain structures in rats

Polyamines putrescine, spermidine and spermine are positively charged aliphatic amines and have important roles in maintaining normal cellular function, regulating neurotransmitter receptors and modulating learning and memory. Recent evidence suggests a role of putrescine in hippocampal neurogenesis, that is significantly impaired during aging. The present study measured the polyamine levels in memory-related brain structures in 24- (aged), 12- (middle-aged) and 4- (young) month-old rats using liquid chromatography/mass spectrometry and high performance liquid chromatography. In the hippocampus, the putrescine levels were significantly decreased in the CA1 and dentate gyrus, and increased in the CA2/3 with age. Significant age-related increases in the spermidine levels were found in the CA1 and CA2/3. There was no difference between groups in spermine in any sub-regions examined. In the parahippocampal region, increased putrescine level with age was observed in the entorhinal cortex, and age did not alter the spermidine levels. The spermine level was significantly decreased in the perirhinal cortex and increased in the postrhinal cortex with age. In the prefrontal cortex, there was age-related decrease in putrescine, and the spermidine and spermine levels were significantly increased with age. This study, for the first time, demonstrates age-related region-specific changes in polyamines in memory-associated structures, suggesting that polyamine system dysfunction may potentially contribute to aged-related impairments in hippocampal neurogenesis and learning and memory.

Structural and biochemical basis for polyamine binding to the Tp0655 lipoprotein of Treponema pallidum: putative role for Tp0655 (TpPotD) as a polyamine receptor

Tp0655 of Treponema pallidum, the causative agent of syphilis, is predicted to be a 40 kDa membrane lipoprotein. Previous sequence analysis of Tp0655 noted its homology to polyamine-binding proteins of the bacterial PotD family, which serve as periplasmic ligand-binding proteins of ATP-binding-cassette (ABC) transport systems. Here, the 1.8 A crystal structure of Tp0655 demonstrated structural homology to Escherichia coli PotD and PotF. The latter two proteins preferentially bind spermidine and putrescine, respectively. All of these proteins contain two domains that sandwich the ligand between them. The ligand-binding site of Tp0655 can be occupied by 2-(N-morpholino)ethanesulfanoic acid, a component of the crystallization medium. To discern the polyamine binding preferences of Tp0655, the protein was subjected to isothermal titration calorimetric experiments. The titrations established that Tp0655 binds polyamines avidly, with a marked preference for putrescine (Kd=10 nM) over spermidine (Kd=430 nM), but the related compounds cadaverine and spermine did not bind. Structural comparisons and structure-based sequence analyses provide insights into how polyamine-binding proteins recognize their ligands. In particular, these comparisons allow the derivation of rules that may be used to predict the function of other members of the PotD family. The sequential, structural, and functional homology of Tp0655 to PotD and PotF prompt the conclusion that the former likely is the polyamine-binding component of an ABC-type polyamine transport system in T. pallidum. We thus rename Tp0655 as TpPotD. The ramifications of TpPotD as a polyamine-binding protein to the parasitic strategy of T. pallidum are discussed.