Polyamine metabolism revisited

Engineering of Methionine Adenosyltransferase toward Mitigated Product Inhibition for Efficient Production of S-Adenosylmethionine

S-Adenosylmethionine (SAM) is a crucial metabolic intermediate playing irreplaceable roles in organismal activities. However, the synthesis of SAM by methionine adenosyltransferase (MAT) is hindered by low conversion due to severe product inhibition. Herein structure-guided semirational engineering was conducted on MAT from Escherichia coli (EcMAT) to mitigate the product inhibitory effect. Compared with the wild-type EcMAT, the best variant E56Q/Q105R exhibited an 8.13-fold increase in half maximal inhibitory concentration and a 4.46-fold increase in conversion (150 mM ATP and l-methionine), leading to a SAM titer of 47.02 g/L. Another variant, E56N/Q105R, showed superior thermostability with an impressive 85.30-fold increase in half-life (50 °C) value. Furthermore, molecular dynamics (MD) simulation results demonstrate that the alleviation in product inhibitory effect could be attributed to facilitated product release. This study offers molecular insights into the mitigated product inhibition, and provides valuable guidance for engineering MAT toward enhanced catalytic performance.

Polyamine Oxidase Expression Is Downregulated by 17β-Estradiol via Estrogen Receptor 2 in Human MCF-7 Breast Cancer Cells

Polyamine levels decrease with menopause; however, little is known about the mechanisms regulated by menopause. In this study, we found that among the genes involved in the polyamine pathway, polyamine oxidase (PAOX) mRNA levels were the most significantly reduced by treatment with 17β-estradiol in estrogen receptor (ESR)-positive MCF-7 breast cancer cells. Treatment with 17β-estradiol also reduced the PAOX protein levels. Treatment with selective ESR antagonists and knockdown of ESR members revealed that estrogen receptor 2 (ESR2; also known as ERβ) was responsible for the repression of PAOX by 17β-estradiol. A luciferase reporter assay showed that 17β-estradiol downregulates PAOX promoter activity and that 17β-estradiol-dependent PAOX repression disappeared after deletions (−3126/−2730 and −1271/−1099 regions) or mutations of activator protein 1 (AP-1) binding sites in the PAOX promoter. Chromatin immunoprecipitation analysis showed that ESR2 interacts with AP-1 bound to each of the two AP-1 binding sites. These results demonstrate that 17β-estradiol represses PAOX transcription by the interaction of ESR2 with AP-1 bound to the PAOX promoter. This suggests that estrogen deficiency may upregulate PAOX expression and decrease polyamine levels.

Salivary Metabolomics for Oral Cancer Detection: A Narrative Review

The development of low- or non-invasive screening tests for cancer is crucial for early detection. Saliva is an ideal biofluid containing informative components for monitoring oral and systemic diseases. Metabolomics has frequently been used to identify and quantify numerous metabolites in saliva samples, serving as novel biomarkers associated with various conditions, including cancers. This review summarizes the recent applications of salivary metabolomics in biomarker discovery in oral cancers. We discussed the prevalence, epidemiologic characteristics, and risk factors of oral cancers, as well as the currently available screening programs, in India and Japan. These data imply that the development of biomarkers by itself is inadequate in cancer detection. The use of current diagnostic methods and new technologies is necessary for efficient salivary metabolomics analysis. We also discuss the gap between biomarker discovery and nationwide screening for the early detection of oral cancer and its prevention.

Arginase Signalling as a Key Player in Chronic Wound Pathophysiology and Healing

Arginase (ARG) represents an important evolutionarily conserved enzyme that is expressed by multiple cell types in the skin. Arg acts as the mediator of the last step of the urea cycle, thus providing protection against excessive ammonia under homeostatic conditions through the production of L-ornithine and urea. L-ornithine represents the intersection point between the ARG-dependent pathways and the urea cycle, therefore contributing to cell detoxification, proliferation and collagen production. The ARG pathways help balance pro- and anti-inflammatory responses in the context of wound healing. However, local and systemic dysfunctionalities of the ARG pathways have been shown to contribute to the hindrance of the healing process and the occurrence of chronic wounds. This review discusses the functions of ARG in macrophages and fibroblasts while detailing the deleterious implications of a malfunctioning ARG enzyme in chronic skin conditions such as leg ulcers. The review also highlights how ARG links with the microbiota and how this impacts on infected chronic wounds. Lastly, the review depicts chronic wound treatments targeting the ARG pathway, alongside future diagnosis and treatment perspectives.

AMD1 is required for the maintenance of leukemic stem cells and promotes chronic myeloid leukemic growth

Polyamines are critical elements in mammals, but it remains unknown whether adenosyl methionine decarboxylase (AMD1), a rate-limiting enzyme in polyamine synthesis, is required for myeloid leukemia. Here, we found that leukemic stem cells (LSCs) were highly differentiated, and leukemia progression was severely impaired in the absence of AMD1 in vivo. AMD1 was highly upregulated as chronic myeloid leukemia (CML) progressed from the chronic phase to the blast crisis phase, and was associated with the poor prognosis of CML patients. In addition, the pharmacological inhibition of AMD1 by AO476 treatment resulted in a robust reduction of the progression of leukemic cells both in vitro and in vivo. Mechanistically, AMD1 depletion induced loss of mitochondrial membrane potential and accumulation of reactive oxygen species (ROS), resulting in the differentiation of LSCs via oxidative stress and aberrant activation of unfolded protein response (UPR) pathway, which was partially rescued by the addition of polyamine. These results indicate that AMD1 is an essential element in the progression of myeloid leukemia and could be an attractive target for the treatment of the disease.

FATS regulates polyamine biosynthesis by promoting ODC degradation in an ERβ-dependent manner in non-small-cell lung cancer

Polyamine biosynthesis is an essential metabolic pathway for cell growth and differentiation in non-small-cell lung cancer (NSCLC). Fragile-site associated tumour suppressor (FATS) is a novel gene involved in cancer. The results of our previous study showed that FATS-mediated polyubiquitination of p53 promotes the activation of p53 in response to DNA damage; however, little is known about the role of FATS in metabolic reprogramming in NSCLC. In the present study, FATS was observed to be significantly downregulated in NSCLC tissues compared with paired adjacent normal tissues and was associated with the survival of NSCLC patients. We further showed that the presence of the tumour suppressor FATS in NSCLC cells led to apoptosis by inducing pro-death autophagy. In addition, FATS was shown to function as a suppressor of polyamine biosynthesis by inhibiting ornithine decarboxylase (ODC) at the protein and mRNA levels, which was partially dependent on oestrogen receptor (ER). Furthermore, FATS was observed to bind to ERβ and translocate to the cytosol, leading to ODC degradation. The findings of our study demonstrate that FATS plays important roles in polyamine metabolism in NSCLC and provides a new perspective for NSCLC progression.

Polyamine Transport Protein PotD Protects Mice against Haemophilus parasuis and Elevates the Secretion of Pro-Inflammatory Cytokines of Macrophage via JNK-MAPK and NF-κB Signal Pathways through TLR4

The potD gene, belonging to the well-conserved ABC (ATP-binding cassette) transport system potABCD, encodes the bacterial substrate-binding subunit of the polyamine transport system. In this study, we found PotD in Haemophilus (Glaesserella) parasuis could actively stimulate both humoral immune and cellular immune responses and elevate lymphocyte proliferation, thus eliciting a Th1-type immune response in a murine immunity and infection model. Stimulation of Raw 264.7 macrophages with PotD validated that Toll-like receptor 4, rather than 2, participated in the positive transcription and expression of pro-inflammatory cytokines IL–1β, IL–6, and TNF–α using qPCR and ELISA. Blocking signal-regulated JNK–MAPK and RelA(p65) pathways significantly decreased PotD-induced pro-inflammatory cytokine production. Overall, we conclude that vaccination of PotD could induce both humoral and cellular immune responses and provide immunoprotection against H. parasuis challenge. The data also suggest that Glaesserella PotD is a novel pro-inflammatory mediator and induces TLR4-dependent pro-inflammatory activity in Raw 264.7 macrophages through JNK–MAPK and RelA(p65) pathways.

Polyamines: therapeutic perspectives in oxidative stress and inflammatory diseases

Polyamines are naturally occurring aliphatic compounds, particularly essential elements for biological functions. These compounds play a central role in regulating molecular pathways which are responsible for cellular proliferation, growth, and differentiation. Importantly, excessive polyamine catabolism can lead to a prominent source of oxidative stress which increases inflammatory response and thought to be involved in several diseases including stroke, renal failure, neurological disease, liver disease, and even cancer. Moreover, polyamine supplementation increases life span in model organisms and may encounter oxidative stress via exerting its potential anti-oxidant and anti-inflammatory properties. The revealed literature indicates that an emerging role of polyamine biosynthetic pathway could be a novel target for drug development against inflammatory diseases. In this review, we expand the knowledge on the metabolism of polyamines, and its anti-oxidant and anti-inflammatory activities which might have future implications against inflammatory diseases in humans and animals.

Modulation of learning and memory by natural polyamines

Spermine and spermidine are natural polyamines that are produced mainly via decarboxylation of l-ornithine and the sequential transfer of aminopropyl groups from S-adenosylmethionine to putrescine by spermidine synthase and spermine synthase. Spermine and spermidine interact with intracellular and extracellular acidic residues of different nature, including nucleic acids, phospholipids, acidic proteins, carboxyl- and sulfate-containing polysaccharides. Therefore, multiple actions have been suggested for these polycations, including modulation of the activity of ionic channels, protein synthesis, protein kinases, and cell proliferation/death, within others. In this review we summarize these neurochemical/neurophysiological/morphological findings, particularly those that have been implicated in the improving and deleterious effects of spermine and spermidine on learning and memory of naïve animals in shock-motivated and nonshock-motivated tasks, from a historical perspective. The interaction with the opioid system, the facilitation and disruption of morphine-induced reward and the effect of polyamines and putative polyamine antagonists on animal models of cognitive diseases, such as Alzheimer's, Huntington, acute neuroinflammation and brain trauma are also reviewed and discussed. The increased production of polyamines in Alzheimer's disease and the biphasic nature of the effects of polyamines on memory and on the NMDA receptor are also considered. In light of the current literature on polyamines, which include the description of an inborn error of the metabolism characterized by mild-to moderate mental retardation and polyamine metabolism alterations in suicide completers, we can anticipate that polyamine targets may be important for the development of novel strategies and approaches for understanding the etiopathogenesis of important central disorders and their pharmacological treatment.

Integrated 'omics analysis for studying the microbial community response to a pH perturbation of a cellulose-degrading bioreactor culture

Integrated 'omics have been used on pure cultures and co-cultures, yet they have not been applied to complex microbial communities to examine questions of perturbation response. In this study, we used integrated 'omics to measure the perturbation response of a cellulose-degrading bioreactor community fed with microcrystalline cellulose (Avicel). We predicted that a pH decrease by addition of a pulse of acid would reduce microbial community diversity and temporarily reduce reactor function in terms of cellulose degradation. However, 16S rDNA gene pyrosequencing results revealed increased alpha diversity in the microbial community after the perturbation, and a persistence of the dominant community members over the duration of the experiment. Proteomics results showed a decrease in activity of proteins associated with Fibrobacter succinogenes 2 days after the perturbation followed by increased protein abundances 6 days after the perturbation. The decrease in cellulolytic activity suggested by the proteomics was confirmed by the accumulation of Avicel in the reactor. Metabolomics showed a pattern similar to that of the proteome, with amino acid production decreasing 2 days after the perturbation and increasing after 6 days. This study demonstrated that community 'omics data provide valuable information about the interactions and function of anaerobic cellulolytic community members after a perturbation.

Involvement of polyamine binding protein D (PotD) of Synechocystis sp. PCC 6803 in spermidine uptake and excretion

The in vivo function of polyamine binding protein D (PotD) in Synechocystis sp. PCC 6803 for the transport of spermidine was investigated using Synechocystis mutant disrupted in potD gene. The growth rate of potD mutant was similar to that of wild-type when grown in BG11 medium. However, the mutant exhibited severely reduced growth compared to the wild-type when BG11 medium was supplemented with 0.5 mM spermidine. The mutant accumulated a higher spermidine level than the wild-type when grown in the medium with or without spermidine. Transport experiments revealed that the mutant had a reduction in both the uptake and the excretion of spermidine. Moreover, [(14)C]spermidine-loaded wild-type and mutant cells showed a decrease of [(14)C]spermidine excretion when the assay medium contained exogenous spermidine. These data suggest that PotD is involved in both the uptake and the excretion of spermidine in Synechocystis cells.

Polyamine metabolism in fungi with emphasis on phytopathogenic species

Polyamines are essential metabolites present in all living organisms, and this subject has attracted the attention of researchers worldwide interested in defining their mode of action in the variable cell functions in which they are involved, from growth to development and differentiation. Although the mechanism of polyamine synthesis is almost universal, different biological groups show interesting differences in this aspect that require to be further analyzed. For these studies, fungi represent interesting models because of their characteristics and facility of analysis. During the last decades fungi have contributed to the understanding of polyamine metabolism. The use of specific inhibitors and the isolation of mutants have allowed the manipulation of the pathway providing information on its regulation. During host-fungus interaction polyamine metabolism suffers striking changes in response to infection, which requires examination. Additionally the role of polyamine transporter is getting importance because of its role in polyamine regulation. In this paper we analyze the metabolism of polyamines in fungi, and the difference of this process with other biological groups. Of particular importance is the difference of polyamine biosynthesis between fungi and plants, which makes this process an attractive target for the control of phytopathogenic fungi.

Cationic nanohydrogel particles as potential siRNA carriers for cellular delivery

Oligonucleotides such as short, double-stranded RNA (siRNA) or plasmid DNA (pDNA) promise high potential in gene therapy. For pharmaceutical application, however, adequate drug carriers are required. Among various concepts progressing in the market or final development, nanosized hydrogel particles may serve as novel transport media especially for siRNA. In this work, a new concept of synthesizing polymeric cationic nanohydrogels was developed, which offers a promising strategy to complex and transport siRNA into cells. For this purpose, amphiphilic reactive ester block copolymers were synthesized by RAFT polymerization of pentafluorophenyl methacrylate as reactive ester monomer together with tri(ethylene glycol)methyl ether methacrylate. In polar aprotic solvents, a self-assembly of these polymers could be observed leading to the formation of nanometer-sized polymer aggregates. The resulting superstructures were used to convert the reactive precursor block copolymers with amine-containing cross-linker molecules into covalently stabilized hydrogel particles. Detailed dynamic light scattering studies showed that the structure of the self-assembled aggregates can permanently be locked-in by this process. This method offers a new possibility to synthesize precise nanohydrogels of different size starting from various block copolymers. Moreover, via reactive ester approach, further functionalities could be attached to the nanoparticle, such as fluorescent dyes, which allowed distinct tracing of the hydrogels during complexation with siRNA or cell uptake experiments. In this respect, cellular uptake of the particles themselves as well as with its payload could be detected successfully. Looking ahead, these novel cationic nanohydrogel particles may serve as a new platform for proper siRNA delivery systems.

Characterization of the substrate-binding PotD subunit in Synechocystis sp. strain PCC 6803

The potD gene encodes the bacterial substrate-binding subunit of the polyamine transport system. The uptake system, which belongs to the ABC transporters, has been characterized in Escherichia coli, but it has not been previously studied in cyanobacteria. Although the overall sequence identity between Synechocystis sp. strain PCC 6803 (hereafter Synechocystis) PotD and Escherichia coli PotD is 24%, the ligand-binding site in the constructed homology model of Synechocystis PotD is well conserved. The conservation of the five polyamine-binding residues (Asp206, Glu209, Trp267, Trp293, and Asp295 in Synechocystis PotD) between these two species indicated polyamine-binding capacity for Synechocystis PotD. The Synechocystis potD gene is functional and its expression is under environmental regulation at transcriptional as well as post-transcriptional levels. Furthermore, an in vitro binding assay with the purified recombinant PotD protein demonstrated that the Synechocystis PotD protein is able to bind polyamines and favors spermidine over putrescine. Finally, we confirmed that Synechocystis PotD plays a physiological role in the uptake of polyamines in vivo using a constructed Synechocystis potD-disruption mutant.

Profiling brain expression of the spermidine/spermine N1-acetyltransferase 1 (SAT1) gene in suicide

Altered stress reactivity is considered to be a risk factor for both major depressive disorder and suicidal behavior. The authors have sought to expand their previous findings implicating altered expression of spermidine/spermine N(1)-acetyltransferase 1 (SAT1), the rate-limiting enzyme involved in catabolism of the polyamines spermidine and spermine in the polyamine stress response (PSR), across multiple brain regions between control individuals and depressed individuals who have died by suicide. Microarray expression of probesets annotated to SAT1 were examined across 17 brain regions in 13 controls and 26 individuals who have died by suicide (16 with a diagnosis of major depression and 10 without), all of French-Canadian origin. Profiling conducted on the Affymetrix U133A/B chipset was further examined on a second chipset (U133 Plus 2.0) using RT-PCR, and analyzed in a second, independent sample. A reduction in SAT1 expression identified through multiple probesets was observed across 12 cortical regions in depressed individuals who have died by suicide compared with controls. Of these, five cortical regions showed statistically significant reductions which were supported by RT-PCR and analysis on the additional chipset. SAT1 cortical expression levels were also found to be significantly lower in an independent sample of German subjects with major depression who died by suicide in comparison with controls. These findings suggest that downregulation of SAT1 expression may play a role in depression and suicidality, possibly by impeding the normal PSR program or through compensation for the increased polyamine metabolism accompanying the psychological distress associated with depressive disorders.

Development of an expression macroarray for amine metabolism-related genes

Cationic amino acids are the precursors of biogenic amines, histamine from histidine, and putrescine, spermidine and spermine from arginine/ornithine (and methionine), as well as nitric oxide. These amines play important biological roles in inter- and intracellular signaling mechanisms related to inflammation, cell proliferation and neurotransmission. Biochemical and epidemiological relationships between arginine-derived products and histamine have been reported to play important roles in physiopathological problems. In this communication, we describe the construction of an expression macroarray containing more than 30 human probes for most of the key proteins involved in biogenic amines metabolisms, as well as other inflammation- and proliferation-related probes. The array has been validated on human mast HMC-1 cells. On this model, we have got further support for an inverse correlation between polyamine and histamine synthesis previously observed on murine basophilic models. These tools should also be helpful to understand the amine roles in many other inflammatory and neoplastic pathologies.

Recognition of age-damaged (R,S)-adenosyl-L-methionine by two methyltransferases in the yeast Saccharomyces cerevisiae

The biological methyl donor S-adenosylmethionine (AdoMet) can exist in two diastereoisomeric states with respect to its sulfonium ion. The S configuration, (S,S)-AdoMet, is the only form that is produced enzymatically as well as the only form used in almost all biological methylation reactions. Under physiological conditions, however, the sulfonium ion can spontaneously racemize to the R form, producing (R,S)-AdoMet. As of yet, (R,S)-AdoMet has no known physiological function and may inhibit cellular reactions. In this study, we found two Saccharomyces cerevisiae enzymes that are capable of recognizing (R,S)-AdoMet and using it to methylate homocysteine to form methionine. These enzymes are the products of the SAM4 and MHT1 genes, identified previously as homocysteine methyltransferases dependent upon AdoMet and S-methylmethionine, respectively. We found here that Sam4 recognizes both (S,S)- and (R,S)-AdoMet, but that its activity is much higher with the R,S form. Mht1 reacts with only the R,S form of AdoMet, whereas no activity is seen with the S,S form. R,S-Specific homocysteine methyltransferase activity is also shown here to occur in extracts of Arabidopsis thaliana, Drosophila melanogaster, and Caenorhabditis elegans, but has not been detected in several tissue extracts of Mus musculus. Such activity may function to prevent the accumulation of (R,S)-AdoMet in these organisms.

Platinum drug effects on the expression of genes in the polyamine pathway: time-course and concentration-effect analysis based on Affymetrix gene expression profiling of A2780 ovarian carcinoma cells

PURPOSE

As a follow-up to our previous findings that platinum drugs induce a key enzyme in polyamine catabolism, gene expression profiling and mathematical modeling were used to define the effects of cisplatin and oxaliplatin on the expression of polyamine metabolic pathway genes in A2780 human ovarian carcinoma cells.

METHODS

Time-course and concentration-effect experiments were each carried out with cisplatin or oxaliplatin in two separate experiments and cells subjected to gene expression profiling using Affymetrix array technology. Time-course data were modeled using exponential increase and decrease models. Concentration-effect data were modeled using a four parameter Hill model.

RESULTS

Gene expression profiling of human ovarian carcinoma A2780 cells after exposure to either cisplatin or oxaliplatin indicates that the expression of several genes involved in polyamine pathway is affected by the platinum drugs. Mathematical/Statistical modeling of the data from time-course and concentration-effect experiments of gene expression from nine polyamine pathway genes represented on the HGU95Av2 chip, indicates that three biosynthetic pathway genes (SAMDC, ODC1 and SRM) are down-regulated and one catabolic pathway gene (SSAT) is up-regulated. Expression changes were similar for different probesets for a given gene on the array. Studies on the induction of SSAT by platinum drugs suggested by the Affymetrix data have been previously validated from this laboratory (Hector et al. in Mol Cancer Ther 3:813-822, 2004). Here, the effects of oxaliplatin exposure on SAMDC and ODC observed by Affymetix are validated with real time QRT-PCR.

CONCLUSION

The data indicate a concerted effect of platinum drugs on the polyamine metabolic pathway with down-regulation in the expression of several enzyme genes involved in biosynthesis and many-fold up-regulation in expression of SSAT, an acetylating enzyme gene that is critically involved in polyamine catabolism and export.

Peroxisome proliferator-activated receptor gamma as a molecular target of resveratrol-induced modulation of polyamine metabolism

Previous results indicate that the polyphenol resveratrol inhibits cell growth of colon carcinoma cells via modulation of polyamine metabolic key enzymes. The aim of this work was to specify the underlying molecular mechanisms and to identify a possible role of transcription factor peroxisome proliferator-activated receptor gamma (PPARgamma). Cell growth was determined by bromodeoxyuridine incorporation and crystal violet staining. Protein levels were examined by Western blot analysis. Spermine/spermidine acetyltransferase (SSAT) activity was determined by a radiochemical assay. PPARgamma ligand-dependent transcriptional activity was measured by a luciferase assay. A dominant-negative PPARgamma mutant was transfected in Caco-2 cells to suppress PPARgamma-mediated functions. Resveratrol inhibits cell growth of both Caco-2 and HCT-116 cells in a dose- and time-dependent manner (P < 0.001). In contrast to Caco-2-wild type cells (P < 0.05), resveratrol failed to increase SSAT activity in dominant-negative PPARgamma cells. PPARgamma involvement was further confirmed via ligand-dependent activation (P < 0.01) as well as by induction of cytokeratin 20 (P < 0.001) after resveratrol treatment. Coincubation with SB203580 abolished SSAT activation significantly in Caco-2 (P < 0.05) and HCT-116 (P < 0.01) cells. The involvement of p38 mitogen-activated protein kinase (MAPK) was further confirmed by a resveratrol-mediated phosphorylation of p38 protein in both cell lines. Resveratrol further increased the expression of PPARgamma coactivator PGC-1alpha (P < 0.05) as well as SIRT1 (P < 0.01) in a dose-dependent manner after 24 hours of incubation. Based on our findings, p38 MAPK and transcription factor PPARgamma can be considered as molecular targets of resveratrol in the regulation of cell proliferation and SSAT activity, respectively, in a cell culture model of colon cancer.

Infected Chronic Wounds Show Different Local and Systemic Arginine Conversion Compared With Acute Wounds

BACKGROUND

Several experimental studies have shown the importance of arginine in wound healing. However, little is known about its role in human wound healing. In this study, we investigated arginine metabolism in impaired wound healing.

MATERIALS AND METHODS

Twenty patients with chronic wounds and 10 patients with acute wounds were included in a prospective study. Amino acids, nitrate/nitrite, and arginase concentrations were determined in plasma and wound fluid using high-performance liquid chromatography and enzyme-linked immunosorbent assay. Chronic wounds were divided into two groups: noninfected chronic wounds (n = 11) and infected chronic wounds (n = 9), based on quantitative bacterial analysis of wound fluid samples.

RESULTS

Plasma arginine levels, next to total plasma amino acid levels, were significantly decreased in patients with infected chronic wounds compared with patients having acute or noninfected wounds. Citrulline and ornithine levels were significantly increased in infected chronic wounds and related to decreased nitrate/nitrite levels, whereas wound fluid arginine levels were similar in all groups. In addition, wound fluid arginase levels of infected chronic wounds were significantly enhanced.

CONCLUSIONS

This study demonstrates that patients with infected chronic wounds have decreased plasma arginine levels and suggests enhanced arginine conversion in the wound. In contrast to noninfected chronic wounds, arginine seems to be mainly metabolized by arginase in infected chronic wounds. In conclusion, our hypothesis is that impaired wound healing is related to an altered arginine usage.

Mathematical modeling of polyamine metabolism in mammals

Polyamines are considered as essential compounds in living cells, since they are involved in cell proliferation, transcription, and translation processes. Furthermore, polyamine homeostasis is necessary to cell survival, and its deregulation is involved in relevant processes, such as cancer and neurodegenerative disorders. Great efforts have been made to elucidate the nature of polyamine homeostasis, giving rise to relevant information concerning the behavior of the different components of polyamine metabolism, and a great amount of information has been generated. However, a complex regulation at transcriptional, translational, and metabolic levels as well as the strong relationship between polyamines and essential cell processes make it difficult to discriminate the role of polyamine regulation itself from the whole cell response when an experimental approach is given in vivo. To overcome this limitation, a bottom-up approach to model mathematically metabolic pathways could allow us to elucidate the systemic behavior from individual kinetic and molecular properties. In this paper, we propose a mathematical model of polyamine metabolism from kinetic constants and both metabolite and enzyme levels extracted from bibliographic sources. This model captures the tendencies observed in transgenic mice for the so-called key enzymes of polyamine metabolism, ornithine decarboxylase, S-adenosylmethionine decarboxylase and spermine spermidine N-acetyl transferase. Furthermore, the model shows a relevant role of S-adenosylmethionine and acetyl-CoA availability in polyamine homeostasis, which are not usually considered in systemic experimental studies.

Spermidine synthase is prominently expressed in the striatal patch compartment and in putative interneurones of the matrix compartment

The ubiquitous polyamines spermidine and spermine are known as modulators of glutamate receptors and inwardly rectifying potassium channels. They are synthesized by a set of specific enzymes in which spermidine synthase is the rate-limiting step catalysing the formation of the spermine precursor spermidine from putrescine. Spermidine and spermine were previously localized to astrocytes, probably reflecting storage rather than synthesis in these cells. In order to identify the cellular origin of spermidine and spermine synthesis in the brain, antibodies were raised against recombinant mouse spermidine synthase. As expected, strong spermidine synthase-like immunoreactivity was obtained in regions known to express high levels of spermidine and spermine, such as the hypothalamic paraventricular and supraoptic nuclei. In the striatum, spermidine synthase was found in neurones and the neuropil of the patch compartment (striosome) as defined by expression of the micro opiate receptor. The distinct expression pattern of spermidine synthase, however, only partially overlapped with the distribution of the products spermidine and spermine in the striatum. In addition, spermidine synthase-like immunoreactivity was seen in patch compartment-apposed putative interneurones. These spermidine synthase-positive neurones did not express any marker characteristic of the major striatal interneurone classes. The neuropil labelling in the patch compartment and in adjacent putative interneurones may indicate a role for polyamines in intercompartmental signalling in the striatum.

A comprehensive view of polyamine and histamine metabolism to the light of new technologies

Polyamines and histamine are biogenic amines with multiple biological roles. In spite of the evidence for the involvement of both polyamines and histamine metabolism impairment in several highly prevalent pathological conditions, multiple questions concerning the molecular processes behind these effects remain to be elucidated. More comprehensive and systemic studies integrating molecular biology, biophysical and bioinformatics tools could contribute to accelerate the advances in this research area. This review is designed to underscore the main questions to be answered in polyamine and histamine research and how these new systemic approaches could help to find these answers.

Spermine increases arginase activity in the liver after carbon tetrachloride-induced hepatic injury in Long-Evans rats

Arginase is the enzyme which synthesizes urea and ornithine, a precursor from which putrescine, spermidine and spermine are formed. These natural polyamines have been implicated in cell growth, replication and wound healing. The present study evaluated the possibility that spermine increases arginase activity and reduces liver damage caused by carbon tetrachloride. Intraperitoneally injected spermine at a dose of 1 mg/kg after a single intragastric administration of carbon tetrachloride (1.6 ml/kg) increased arginase activity (6.30-7.79 microg urea/mg protein per min) (P<0.05) as well as total protein content (0.29-0.37 mg/mg dry weight) in hepatic tissue, compared to the group which only received carbon tetrachloride. When liver cell damage was biochemically assessed, the carbon tetrachloride-treated group showed a 20-fold increase in serum glutamic oxaloacetate transaminase, compared to the control group (P<0.05), and this was significantly diminished by the administration of spermine (P<0.05). Serum triglycerides increased four times compared to the control group as a result of the carbon tetrachloride treatment and were diminished by spermine as well. These results indicate that spermine may play a role in the recovery of liver tissue after carbon tetrachloride-induced liver injury, maybe by increasing the synthesis of putrescine, a polyamine which has been found out to participate in the recovery of the hepatic tissue after an insult with carbon tetrachloride.

Alternative antiglycation mechanisms: are spermine and fructosamine-3-kinase part of a carbonyl damage control pathway?

Spermine is an ubiquitous molecule that bears unique structural features of regularly spaced positive charges interrupted by hydrophobic methylene bridges. In previous studies we have shown significant antiglycation effects of physiological concentrations of spermine and spermidine. The effect is apparent in four different protein models, two targeting structural changes on histones and ubiquitin, and two targeting impairment of catalytic activities of AT III and plasminogen. We hypothesize that polyamines inhibit glycation and that might be one of their elusive molecular functions. A mammalian fructosamine-3-kinase (FN-3-K), which phosphorylates fructoselysine (FL) residues on glycated proteins, to FL-3-phosphate has been isolated and cloned by two independent groups. This enzyme may function as a deglycating enzyme. Being its Km for FL two orders of magnitude lower than for its protein substrate, we propose the enzyme has a dual role and also functions as a recycler of spermine-carbonyl adducts. Spermine and FN-3-K may be part of a carbonyl damage control pathway. Thirdly, due to critically functional lysine residues, we underscore the vulnerability to glycation of ornithine decarboxylase, the main enzyme in spermine biosynthesis. If glycation is modulated by polyamines and glycation itself impairs polyamine synthesis, a dangerous loop of excessive spermine consumption and slower spermine biosynthesis might ensue in chronic hyperglycemic conditions. In this perspective, small changes in flow rates in the spermine (where ODC and antizyme are key players) and/or FN-3-K pathway could contribute to enhance the effects of hyperglycemia and explain why there are diabetic subjects with higher glycation phenotypes and incidence of complications. They could have altered steady state levels of polyamines and/or decreased FN-3-K expression or activity.

Induction of a SSAT isoform in response to hypoxia or iron deficiency and its protective effects on cell death

Spermidine/spermine N(1)-acetyltransferase (SSAT) is the key enzyme with regard to the maintenance of intracellular polyamine levels. It is an inducible enzyme, which may participate in adaptive responses to environmental stress. However, little is known regarding its responses to oxygen or nutrient deficiencies. Using microarray assays, we discovered that SSAT was enhanced under both oxygen- and iron-deficient conditions. However, RT-PCR revealed that the SSAT mRNA was not induced; rather, an mRNA variant was newly expressed. In this variant, the splicing-in of 110 bases induces early termination, generating a truncated isoform which lacks catalytic motifs. The variant expression occurs in other cancer cells and was irrelevant to both hypoxia-inducible factor 1 and to the redox state. We attempted to determine its role, using stable cell-lines. The expressed isoform was found to promote cell survival under iron-deficient conditions and blocked the cleavage of poly(ADP-ribose) polymerase. This isoform may contribute to the progression of tumors of a more malignant phenotype under poor conditions and may constitute a potential target for anticancer therapy.

Exposure of Saccharomyces cerevisiae to acetaldehyde induces sulfur amino acid metabolism and polyamine transporter genes, which depend on Met4p and Haa1p transcription factors, respectively

Acetaldehyde is a toxic compound produced by Saccharomyces cerevisiae cells under several growth conditions. The adverse effects of this molecule are important, as significant amounts accumulate inside the cells. By means of global gene expression analyses, we have detected the effects of acetaldehyde addition in the expression of about 400 genes. Repressed genes include many genes involved in cell cycle control, cell polarity, and the mitochondrial protein biosynthesis machinery. Increased expression is displayed in many stress response genes, as well as other families of genes, such as those encoding vitamin B1 biosynthesis machinery and proteins for aryl alcohol metabolism. The induction of genes involved in sulfur metabolism is dependent on Met4p and other well-known factors involved in the transcription of MET genes under nonrepressing conditions of sulfur metabolism. Moreover, the deletion of MET4 leads to increased acetaldehyde sensitivity. TPO genes encoding polyamine transporters are also induced by acetaldehyde; in this case, the regulation is dependent on the Haa1p transcription factor. In this paper, we discuss the connections between acetaldehyde and the processes affected by this compound in yeast cells with reference to the microarray data.

Amifostine has antiangiogenic properties in vitro by changing the redox status of human endothelial cells

Amifostine is a broad-spectrum cytoprotective agent, selective for normal tissues. It is a pro-drug metabolised to the free thiol WR-1065 that may act as a scavenger of free radicals, generated in tissues exposed to chemotherapeutic agents or radiation. WR-1065 can be further oxidized to its symmetric disulfide WR-33278 or degraded to hydrogen peroxide (H2O2). Both WR-1065 and WR-33278 resemble endogenous polyamines. Although amifostine is used in some cases in the clinic, there are only few studies concerning its actions at the cellular level. We have previously shown that amifostine inhibits angiogenesis in vivo, affecting the expression of several angiogenic genes. In the present work, we studied the effect of amifostine on human umbilical vein endothelial cell (HUVEC) functions in vitro, in order to further clarify its mechanism(s) of action. Amifostine increased HUVEC proliferation, an effect that was reversed by the intracellular H2O2 scavenger sodium pyruvate, agents that increase intracellular cAMP levels and L-valine. On the other hand, amifostine decreased HUVEC migration, an effect that was reversed by L-valine or L-arginine but not sodium pyrouvate. The decrease in migration was in line with decreased tube formation on matrigel and decreased amounts of metalloproteinase-2 released into the culture medium of HUVEC. Finally, amifostine reduced tyrosine nitration of the cytoskeletal proteins actin and alpha-tubulin in a time dependent manner. This last action could be due to the reduced production of nitric oxide (NO) or to other not yet identified mechanisms. Collectively, our results suggest that amifostine acts on endothelial cells through pathways that affect the redox status of the cells, either by producing H2O2 or by modulating NO production.

Agmatine signaling: odds and threads

Agmatine is a metabolite of L-arginine. It is formed by the decarboxylation of L-arginine via arginine decarboxylase in bacteria, plants and mammals. It is becoming clear that it has multiple physiological functions as a potential transmitter. Agmatine binds to alpha2-adrenoceptors and to imidazoline binding sites. It blocks NMDA receptors and other ligand-gated cation channels. It also inhibits nitric oxide synthase, induces release of peptide hormones and antizyme and plays a role during cell proliferation by interacting with the generation and transport of polyamines. Although the precise function of endogenously released agmatine is presently still unclear, this review will summarize several aspects concerning the biological function of agmatine.

Polyamine catabolism in platinum drug action: Interactions between oxaliplatin and the polyamine analogue N1,N11-diethylnorspermine at the level of spermidine/spermine N1-acetyltransferase

A great deal of experimental evidence connects induction of polyamine catabolism via spermidine/spermine N1-acetyltransferase (SSAT) to antiproliferative activity and apoptosis. Following our initial observation from gene expression profiling that platinum drugs induce SSAT, we undertook this present study to characterize platinum drug induction of SSAT and other polyamine catabolic enzymes and to examine how these responses might be enhanced with the well-known inducer of SSAT and clinically relevant polyamine analogue, N1,N11-diethylnorspermine (DENSPM). The results obtained in A2780 ovarian cancer cells by real-time quantitative RT-PCR and Northern blot analysis show that a 2-hour exposure of A2780 cells to platinum drugs induces expression of SSAT, a second SSAT (SSAT-2), spermine oxidase, and polyamine oxidase in a dose-dependent manner. At equitoxic doses, oxaliplatin is more effective than cisplatin in SSAT induction. The most affected enzyme, SSAT, increased 15-fold in mRNA expression and 2-fold in enzyme activity. When combined with DENSPM to further induce SSAT and to enhance conversion of mRNA to activity, oxaliplatin increased SSAT mRNA 50-fold and activity, 210-fold. Polyamine pools declined in rough proportion to levels of SSAT induction. At pharmacologically relevant oxaliplatin exposure times (20 hours) and drug concentrations (5 to 15 μmol/L), these responses were increased even further. Combining low-dose DENSPM with oxaliplatin produced a greater than additive inhibition of cell growth based on the sulforhodamine-B assay. Taken together, the findings confirm potent induction of polyamine catabolic enzymes, such as SSAT by platinum drugs, and demonstrate that these biochemical responses as well as growth inhibition can be potentiated by co-treatment with the polyamine analogue DENSPM. With appropriate in vitro and in vivo optimization, these findings could lead to clinically relevant therapeutic strategies.

Expression of spermidine/spermine N1-acetyltransferase in HeLa cells is regulated by amino acid sufficiency

The effect of amino acids on the regulation of the expression of spermidine/spermine N(1)-acetyltransferase (SSAT), the key enzyme of polyamine catabolism, was studied in HeLa cells. When compared with similar exposure to complete medium, deprivation of arginine, methionine or leucine gave rise to a time-dependent, slowly reversible increase in the cellular level of SSAT mRNA that started to be significant after 8, 12 or 16h and reached four-, five- and two-fold after 16h, respectively. Experiments utilizing (i) constructs containing fragments of the SSAT promoter linked to a luciferase reporter gene or (ii) actinomycin D (Act-D)-treated cells indicated that the increase in the SSAT mRNA level was due to an augmentation in gene transcription and message stability after omission of one of the polyamine precursor amino acids. By contrast, SSAT mRNA stabilisation was only observed when leucine was the omitted amino acid. Amino acid deprivation was also found to cause increased intracellular activity of SSAT concurrent with changes in the cell polyamine content, namely increased putrescine but decreased spermine levels. Furthermore, stable expression of a dominant negative mutant of stress-activated protein kinase/extracellular signal-regulated protein kinase (SAPK/ERK) kinase 1 in HeLa cells was found to inhibit the increase in SSAT mRNA by amino acid deprivation. The data suggest that c-Jun N-terminal kinase/SAPK (JNK/SAPK) may be involved in the amino acid-dependent regulation of SSAT expression.

The polyamines spermine and spermidine protect proteins from structural and functional damage by AGE precursors: a new role for old molecules?

Due to the importance of glycation in the genesis of diabetic complications, an intense search for synthetic new antiglycation agents is ongoing. However, a somewhat neglected avenue is the search for endogenous compounds that may inhibit the process and be a source of protodrugs. Based on their ubiquity, their polycationic nature, their essential role in growth, their relatively high concentrations in tissues, and their high concentrations in sperm, we hypothesized that polyamines inhibit glycation and that might be one of their so far elusive functions. In this study we demonstrate a potent antiglycation effect of physiological concentrations of the polyamines spermine and spermidine. We employed two approaches: in the first, we monitored structural changes on histones and ubiquitin in which polyamines inhibit glycation-induced dimer and polymer formation. In the second we monitored functional impairment of catalytic activity of antithrombin III and plasminogen. Protection is afforded against glycation by hexoses, trioses and dicarbonyls AGE precursors and is comparable to those of aminoguanidine and carnosine.

Insufficiently charged isosteric analogue of spermine: interaction with polyamine uptake, and effect on Caco-2 cell growth

We characterised a novel, charge-insufficient isosteric analogue of spermine, 11-[(amino)oxy]-4,9-diaza-1-aminoundecane (AOSPM). This analogue was synthesised by displacing aminopropyl group by aminooxyethyl group, the latter having pK(a) of about 5. Charge deficiency of the AOSPM molecule was fixed at a definite atom, while pK(a) of the rest nitrogen was similar to the parent polyamine. AOSPM competed with putrescine, spermidine and spermine for the uptake into the cell, and was accumulated in the cells in high amounts when exogenous polyamine synthesis was impaired. It was not recognised by the cells as growth-promoting polyamine, since it was unable to restore growth arrest due to polyamine deprivation. Like natural spermine, this polyamine analogue prevented oxidative DNA damage. AOSPM could be used not only as a tool to study polyamine homeostasis in the cell, but may have distinct applications either as radiation protector, a stable and non-toxic inhibitor of polyamine uptake or, as an appropriate vector, to enhance the uptake of impermeable compounds into the cell.

Growth, morphological and biochemical changes in oxa-spermine derivative-treated MCF-7 human breast cancer cells

The growth inhibitory properties of two oxa-spermine derivatives named compound 1 and compound 2, representatives of a novel type of polyamine derivatives, were studied. Dose-response growth inhibitory curves obtained after 48h drug exposure demonstrated the much higher cytotoxic activity of compound 1 towards MCF-7 human breast cancer cells. Further experiments with compound 1 showed that this oxa-spermine derivative exhibited considerable cytotoxicity with IC(50) values of 3.74 microM and 2.93 microM after 24h and 48h drug exposure respectively. In MCF-7 cells, after 8h drug (10 microM) exposure it caused shrinkage, chromatin condensation and nuclear fragmentation. However, no clear DNA laddering was detected in treated cells. Drug treatment provoked an increase in polyamine oxidase (PAO) activity. This enzyme is able to produce cytotoxic H(2)O(2) and 3-acetamidopropanal, catalyzing the oxidative deamination of N(1)-acetylated derivatives of spermine and spermidine to spermidine and putrescine respectively. Taken together these data demonstrate that the novel oxa-polyamine derivative compound 1 has considerable cytotoxic activity towards MCF-7 cells and indicate that an induction of PAO may be involved in its cytotoxic and apoptotic effects.

Polyamines in the human gut

Intracellular polyamine concentrations are maintained by endogenous synthesis and uptake of exogenous polyamines from the gastrointestinal lumen. Recently, much attention has been focused on the role of polyamines in tumour pathogenesis and the possible therapeutic value of reducing polyamine concentrations in tumour tissue. Unfortunately, polyamines also appear to be essential for the maintenance of normal gastrointestinal structure and function. The immediate analytical challenge is to make progress in laboratory methods for polyamine class analyses and assessment of polyamine metabolism. An obvious gastroenterological target is to make up for past neglect of the function of these important dietary components.