Showing papers on "Agmatine published in 2008"

Differential Regulation of Root Arginine Catabolism and Polyamine Metabolism in Clubroot-Susceptible and Partially Resistant Arabidopsis Genotypes

Abstract: The hypertrophy and hyperplasia of infected roots into clubs are the intrinsic characteristics of clubroot, one of the economically most important diseases in Brassica crops worldwide. Polyamines, arginine (Arg)-derived metabolites, have long been recognized as cell proliferation and differentiation regulators in plants and consequently are suitable candidates for potential gall development factors. Furthermore, Arg catabolism, through arginase, which is strongly connected to polyamine metabolism, would play an important role in response to wound trauma and pathogen infection. In this study, we exploited the Arabidopsis (Arabidopsis thaliana)-Plasmodiophora brassicae pathosystem to investigate the involvement of polyamine metabolism and Arg catabolism in host responses to the pathogen infection and in partial clubroot resistance mechanisms. We demonstrated at the transcriptional, enzymatic, and metabolic levels that polyamine metabolism and Arg catabolism are induced during the later stages of disease in compatible Arabidopsis-P. brassicae interactions. However, susceptible and partially resistant plants showed strikingly different Arg metabolism signatures. Susceptible plants were characterized by a transient agmatine production, a massive induction of arginase, and a strong accumulation of proline. The potential functions of this marked activation of the arginase pathway in the P. brassicae pathogenicity strategy are discussed. Partially resistant plants showed a continuous agmatine production and a weaker arginase pathway activity than the susceptible genotype. Results suggest that the symptom severity was strongly associated to the differential regulation of root polyamine metabolism and Arg catabolism. Further work using arginase transgenic plants will provide insight into the physiological function of the arginase pathway in partial clubroot resistance.

Characterization of arginine decarboxylase in rat brain and liver: distinction from ornithine decarboxylase.

Abstract: We compared the properties of mammalian arginine decarboxylase (ADC) and ornithine decarboxylase (ODC) in rat liver and brain. Mammalian ADC is thermally unstable and associated with mitochondrial membranes. ADC decarboxylates both arginine (Km = 0.75 mM) and ornithine (Km = 0.25 mM), a reaction not inhibited by the specific ODC inhibitor, difluoromethylornithine. ADC activity is inhibited by Ca2+, Co2+, and polyamines, is present in many organs being highest in aorta and lowest in testis, and is not recognized by a specific monoclonal antibody to ODC. In contrast, ODC is thermally stable, cytosolic, and mitochondrial and is expressed at low levels in most organs except testis. Although ADC and ODC are expressed in cultured rat C6 glioma cells, the patterns of expression during growth and confluence are very different. We conclude that mammalian ADC differs from ADC isoforms expressed in plants, bacteria, or Caenorhabditis elegans and is distinct from ODC. ADC serves to synthesize agmatine in proximity to mitochondria, an organelle also harboring agmatine's degradative enzyme, agmatinase, and a class of imidazoline receptor (I2) to which agmatine binds with high affinity.

Transcriptome Analysis of Agmatine and Putrescine Catabolism in Pseudomonas aeruginosa PAO1

Abstract: Polyamines (putrescine, spermidine, and spermine) are major organic polycations essential for a wide spectrum of cellular processes. The cells require mechanisms to maintain homeostasis of intracellular polyamines to prevent otherwise severe adverse effects. We performed a detailed transcriptome profile analysis of Pseudomonas aeruginosa in response to agmatine and putrescine with an emphasis in polyamine catabolism. Agmatine serves as the precursor compound for putrescine (and hence spermidine and spermine), which was proposed to convert into 4-aminobutyrate (GABA) and succinate before entering the tricarboxylic acid cycle in support of cell growth, as the sole source of carbon and nitrogen. Two acetylpolyamine amidohydrolases, AphA and AphB, were found to be involved in the conversion of agmatine into putrescine. Enzymatic products of AphA were confirmed by mass spectrometry analysis. Interestingly, the alanine-pyruvate cycle was shown to be indispensable for polyamine utilization. The newly identified dadRAX locus encoding the regulator alanine transaminase and racemase coupled with SpuC, the major putrescine-pyruvate transaminase, were key components to maintaining alanine homeostasis. Corresponding mutant strains were severely hampered in polyamine utilization. On the other hand, an alternative γ-glutamylation pathway for the conversion of putrescine into GABA is present in some organisms. Subsequently, GabD, GabT, and PA5313 were identified for GABA utilization. The growth defect of the PA5313 gabT double mutant in GABA suggested the importance of these two transaminases. The succinic-semialdehyde dehydrogenase activity of GabD and its induction by GABA were also demonstrated in vitro. Polyamine utilization in general was proven to be independent of the PhoPQ two-component system, even though a modest induction of this operon was induced by polyamines. Multiple potent catabolic pathways, as depicted in this study, could serve pivotal roles in the control of intracellular polyamine levels.

Agmatine and imidazoline receptors: their role in opioid analgesia, tolerance and dependence.

Abstract: Agmatine is an endogenous amine that is synthesized following the decarboxylation of l-arginine by arginine decarboxylase. Agmatine exists in mammalian brain and has been proposed as a neurotransmitter and/or neurotransmodulator. Agmatine binds to several targets and is considered as an endogenous ligand for imidazoline receptors. This review, mainly based on our research work in the past decade, focused on the modulations by agmatine action on imidazoline receptors to opioid analgesia, tolerance and dependence, and its possible neurochemical mechanisms. We went on to propose that agmatine and imidazoline receptors constitute a novel system of modulating opioid functions.

Agmatine is essential for the cell growth of Thermococcus kodakaraensis

Abstract: TK0149 (designated as Tk-PdaD) of a hyperthermophilic archaeon, Thermococcus kodakaraensis, was annotated as pyruvoyl-dependent arginine decarboxylase, which catalyzes agmatine formation by the decarboxylation of arginine as the first step of polyamine biosynthesis. In order to investigate its physiological roles, Tk-PdaD was purified as a recombinant form, and its substrate dependency was examined using the candidate compounds arginine, ornithine and lysine. Tk-PdaD, expressed in Escherichia coli, was cleaved into α and β subunits, as other pyruvoyl-dependent enzymes, and the resulting subunits formed an (αβ)6 complex. The Tk-PdaD complex catalyzed the decarboxylation of arginine but not that of ornithine and lysine. A gene disruptant lacking Tk-pdaD was constructed, showing that it grew only in the medium in the presence of agmatine but not in the absence of agmatine. The obtained results indicate that Tk-pdaD encodes a pyruvoyl-dependent arginine decarboxylase and that agmatine is essential for the cell growth of T. kodakaraensis.

Spatial learning results in elevated agmatine levels in the rat brain.

Abstract: Accumulating evidence suggests that agmatine, a metabolite of L-arginine by arginine decarboxylase, is a novel neurotransmitter, and exogenous agmatine can modulate behavior functions including learning and memory. However, direct evidence of its involvement in learning and memory processes is currently lacking. This study measured agmatine levels in the hippocampus, parahippocampal region, cerebellum, and vestibular nucleus in rats that were trained to find a hidden escape platform in the water-maze task, or forced to swim in the pool with no platform presented, or kept in the holding-box, using liquid chromatography/mass spectrometry. Compared with the swimming only group and holding-box group, agmatine levels were significantly increased in the CA1 and dentate gyrus subregions of the hippocampus, the entorhinal cortex and the vestibular nucleus in the water-maze training group. These results, for the first time, demonstrate spatial learning-induced region-specific elevation in agmatine, and raise a novel issue of the involvement of agmatine in the processes of learning and memory. © 2008 Wiley-Liss, Inc.

Effects of aging on agmatine levels in memory‐associated brain structures

Abstract: Agmatine is a metabolite of L-arginine by arginine decarboxylase. Recent evidence suggests that it exists in mammalian brain and is a novel neurotransmitter. The present study measured agmatine levels in several memory-associated brain structures in aged (24-month-old), middle-aged (12-month-old), and young (4-month-old) male Sprague Dawley rats using liquid chromatography/mass spectrometry. Agmatine levels were significantly decreased in the CA1, but increased in the CA2/3 and dentate gyrus, subregions of the hippocampus in aged and middle-aged rats relative to the young adults. In the prefrontal cortex, a dramatic decrease in agmatine level was found in aged rats as compared with middle-aged and young rats. There were significantly increased levels of agmatine in the entorhinal and perirhinal cortices in aged relative to middle-aged and young rats. In the postrhinal and temporal cortices, agmatine levels were significantly increased in aged and middle-aged rats as compared with young adults. The present findings, for the first time, demonstrate age-related changes in agmatine levels in memory-associated brain structures and raise a novel issue of the potential involvement of agmatine in the aging process. © 2008 Wiley-Liss, Inc.

Exogenous agmatine has neuroprotective effects against restraint-induced structural changes in the rat brain

Abstract: Agmatine is an endogenous amine derived from decarboxylation of arginine catalysed by arginine decarboxylase. Agmatine is considered a novel neuromodulator and possesses neuroprotective properties in the central nervous system. The present study examined whether agmatine has neuroprotective effects against repeated restraint stress-induced morphological changes in rat medial prefrontal cortex and hippocampus. Sprague-Dawley rats were subjected to 6 h of restraint stress daily for 21 days. Immunohistochemical staining with β-tubulin III showed that repeated restraint stress caused marked morphological alterations in the medial prefrontal cortex and hippocampus. Stress-induced alterations were prevented by simultaneous treatment with agmatine (50 mg/kg/day, i.p.). Interestingly, endogenous agmatine levels, as measured by high-performance liquid chromatography, in the prefrontal cortex and hippocampus as well as in the striatum and hypothalamus of repeated restraint rats were significantly reduced as compared with the controls. Reduced endogenous agmatine levels in repeated restraint animals were accompanied by a significant increase of arginine decarboxylase protein levels in the same regions. Moreover, administration of exogenous agmatine to restrained rats abolished increases of arginine decarboxylase protein levels. Taken together, these results demonstrate that exogenously administered agmatine has neuroprotective effects against repeated restraint-induced structural changes in the medial prefrontal cortex and hippocampus. These findings indicate that stress-induced reductions in endogenous agmatine levels in the rat brain may play a permissive role in neuronal pathology induced by repeated restraint stress.

Factors affecting the production of putrescine from agmatine by Lactobacillus hilgardii X1B isolated from wine

Abstract: Aims: To elucidate and characterize the metabolic putrescine synthesis pathway from agmatine by Lactobacillus hilgardii X1B. Methods and Results: The putrescine formation from agmatine by resting cells (the normal physiological state in wine) of lactic acid bacteria isolated from wine has been determined for the first time. Agmatine deiminase and N-carbamoylputrescine hydrolase enzymes, determined by HPLC and LC-Ion Trap Mass Spectrometry, carried out the putrescine synthesis from agmatine. The influence of pH, temperature, organic acids, amino acids, sugars and ethanol on the putrescine formation in wine was determined. Conclusions: Resting cells of Lact. hilgardii X1B produce putrescine in wine. The putrescine production was carried out from agmatine through the agmatine deiminase system. Significance and Impact of the Study: These results have significance from two points of view, wine quality and toxicological and microbiological aspects, taking account that putrescine, which origin is still controversial, is quantitatively the main biogenic amine found in wine.

Central L-arginine reduced stress responses are mediated by L-ornithine in neonatal chicks.

Abstract: Recently, we observed that central administration of l-arginine attenuated stress responses in neonatal chicks, but the contribution of nitric oxide (NO) to this response was minimal. The sedative and hypnotic effects of l-arginine may be due to l-arginine itself and/or its metabolites, excluding NO. To clarify the mechanism, the effect of intracerebroventricular (i.c.v.) injection of l-arginine metabolites on behavior under social separation stress was investigated. The i.c.v. injection of agmatine, a guanidino metabolite of l-arginine, had no effect during a 10 min behavioral test. In contrast, the i.c.v. injection of l-ornithine clearly attenuated the stress response in a dose-dependent manner, and induced sleep-like behavior. The l-ornithine concentration in the telencephalon and diencephalon increased following the i.c.v. injection of l-arginine. In addition, several free amino acids including L-alanine, glycine, l-proline and l-glutamic acid concentrations increased in the telencephalon. In conclusion, it appears that l-ornithine, produced by arginase from l-arginine in the brain, plays an important role in the sedative and hypnotic effects of l-arginine observed during a stress response. In addition, several other amino acids having a sedative effect might partly participate in the sedative and hypnotic effects of l-arginine.

Regulatory mechanisms underlying agmatine homeostasis in humans.

Abstract: Regulation of agmatine homeostasis has so far only been poorly defined. In the present study, three mechanisms regulating human agmatine homeostasis were investigated. 1) Enzymatic regulation: expr...

Agmatine inhibits hypoxia-induced TNF-alpha release from cultured retinal ganglion cells

Abstract: The effect of hypoxia on the release of tumor necrosis factor-alpha (TNF-alpha) in transformed rat retinal ganglion cells (RGCs) and the effect of agmatine on the hypoxia-induced production of TNF-alpha in RGCs were evaluated. RGCs were cultured under hypoxic conditions with 5% oxygen, with or without 100 microM agmatine. The expression levels of TNF-alpha and its receptor-1 (TNF-R1) were investigated by Western blot analysis. After 6 hours of hypoxia, we noted an increase in TNF-alpha production in RGCs. Agmatine significantly reduced TNF-alpha level after 12 hours of hypoxic treatment. The expression of TNF-R1 was not affected by the hypoxia or agmatine treatment. Our results show that agmatine inhibits the TNF-alpha production of RGCs in hypoxic condition. These results demonstrate a possible neuroprotective mechanism for agmatine against hypoxic damage in RGCs.

Agmatine pretreatment protects retinal ganglion cells (RGC-5 cell line) from oxidative stress in vitro.

Abstract: Agmatine, 2-(4-aminobutyl)guanidine, has been reported to have neuroprotective effects against various neuronal damages. In this study it was investigated whether agmatine pretreatment rescues the retinal ganglion cells from oxidative injury in vitro. After differentiation of transformed rat retinal ganglion cells (RGC-5 cell line) with staurosporine, agmatine (0.0 to 100.0 μM) pretreatment was performed for 2 hours. Subsequently, they were exposed to hydrogen peroxide (0.0 to 2.5 mM) as an oxidative stress. Cell viability was monitored for up to 48 hours with the lactate dehydrogenase (LDH) assay and apoptosis was examined by the terminal deoxynucleotide transferase-mediated terminal uridine deoxynucleotidyl transferase nick end-labeling (TUNEL) method. As a result, differentiated RGC-5 cells were found to have decreased viability after addition of hydrogen peroxide in a dose-dependent manner. This hydrogen peroxide induced cytotoxicity caused apoptosis characterized by DNA fragmentation. Agmatine pretreatment not only increased cell viability but also attenuated DNA fragmentation. In conclusion, agmatine pretreatment demonstrated neuroprotective effects against oxidative stress induced by hydrogen peroxide in differentiated RGC-5 cells in vitro. This suggests a novel therapeutic strategy rescuing retinal ganglion cells from death caused by oxidative injury

Effects on kidney filtration rate by agmatine requires activation of ryanodine channels for nitric oxide generation.

Abstract: Agmatine, decarboxylated arginine, is produced in the kidney and can increase nephron and kidney filtration rate via renal vasodilatation and increases in plasma flow This increase in filtration r

Behavioral effects of intracerebroventricular microinfusion of agmatine in adult rats.

Abstract: The present study investigated the behavioral effects of intracerebroventricular microinfusion of agmatine. Rats with low dose (10 microg), but not high dose (100 microg), of agmatine spent significantly less time in the enclosed arm and more time in the open arm in the elevated plus maze. In the water maze task, the high dose group displayed a transient impairment in searching for a hidden platform, whereas the low dose group had reduced latency in the first probe test. In the object recognition task, all groups could detect the novel object, but the low dose group spent significantly more time exploring displaced objects. Furthermore, the low dose group made significantly fewer errors in the working, but not the reference, memory version of the radial arm maze task. These results suggest that the behavioral effects of agmatine are task- and dose-dependent, and agmatine may be an anxiolytic and memory modulator.

Protective effect of agmatine on ischemia/reperfusion-induced renal injury in rats.

Abstract: Enhanced renal sympathetic nerve activity (RSNA) during ischemic period and the renal venous norepinephrine (NE) overflow after reperfusion play important roles in the development of ischemic/reperfusion (I/R)-induced acute renal failure (ARF) in rats. This study evaluated whether agmatine, which is known to reduce sympathetic nerve activity and NE overflow by electrical stimulation, would prevent the I/R-induced renal dysfunction. Ischemic ARF was induced by clamping the left renal artery and vein for 45 minutes followed by reperfusion 2 weeks after the contralateral nephrectomy. Intravenous (IV) injection of agmatine (100 and 300 micromol/kg) to ischemic ARF rats dose-dependently suppressed the enhanced RSNA and attenuated the I/R-induced renal dysfunction and histological damage. Intracerebroventricular (ICV) injection of agmatine (600 nmol/kg) to ischemic ARF rats suppressed the enhanced RSNA during the ischemic period and attenuated the I/R-induced renal injury. Furthermore, both IV and ICV injection of agmatine significantly suppressed the renal venous NE overflow after the reperfusion. These results indicate that agmatine prevents the development of I/R-induced renal injury, and the effect is accompanied by suppression of the enhanced RSNA during ischemic period and NE overflow from renal sympathetic nerve endings.

Occurrence of Agmatine Pathway for Putrescine Synthesis in Selenomonas ruminatium

Abstract: Selenomonas ruminantium synthesizes cadaverine and putrescine from L-lysine and L-ornithine as the essential constituents of its peptidoglycan by a constitutive lysine/ornithine decarboxylase (LDC/ODC). S. ruminantium grew normally in the presence of the specific inhibitor for LDC/ODC, DL-α-difluoromethylornithine, when arginine was supplied in the medium. In this study, we discovered the presence of arginine decarboxylase (ADC), the key enzyme in agmatine pathway for putrescine synthesis, in S. ruminantium. We purified and characterized ADC and cloned its gene (adc) from S. ruminantium chromosomal DNA. ADC showed more than 60% identity with those of LDC/ODC/ADCs from Gram-positive bacteria, but no similarity to that from Gram-negative bacteria. In this study, we also cloned the aguA and aguB genes, encoding agmatine deiminase (AguA) and N-carbamoyl-putrescine amidohydrolase (AguB), both of which are involved in conversion from agmatine into putrescine. AguA and AguB were expressed in S. ruminantium. Henc...

Agmatine: identification and inhibition of methamphetamine, kappa opioid, and cannabinoid withdrawal in planarians.

Abstract: Agmatine blocks morphine physical dependence in mammals, but its effects on withdrawal signs caused by other abused drugs have been less studied. One of the reasons is that withdrawal to some of these drugs is difficult to quantify in mammals. An alternative to mammals is planarians, a type of flatworm. Planarians possess mammalian-like neurotransmitters and display withdrawal from amphetamines, benzodiazepines, cannabinoids, cocaine, and opioids. The withdrawal is manifested as a reduction in locomotor behavior following discontinuation of drug exposure. In the present study, our goal was to identify agmatine in planarians and to determine if planarians exposed to agmatine display withdrawal to methamphetamine, a cannabinoid receptor agonist (WIN 55,212-2), or a kappa-opioid receptor agonist (U-50,488H). Neurochemical experiments revealed that the concentration of agmatine in planarians was 185 +/- 33.7 pmol per mg of planarian weight (dry weight). In behavioral experiments, withdrawal (i.e., reduced locomotor activity) was observed when planarians exposed to each drug (10 microM) for 60 min were placed into water. The withdrawal was attenuated when methamphetamine- or U-50,488H-exposed planarians were tested in agmatine (100 microM). Withdrawal was inhibited similarly when planarians coexposed to agmatine (100 microM) plus methamphetamine (10 microM), WIN 55,212-2 (10 microM), or U-50,488H (10 microM) were tested in water. Arginine, the metabolic precursor to agmatine, was ineffective. Our results identify endogenous agmatine in planarians and demonstrate that agmatine exposure blocks withdrawal to three different drugs in planarians. This suggests that a change in agmatine signaling is a common mechanism in the withdrawal caused by these drugs, at least in planarians.

[5-HT1A/1B receptors, alpha2-adrenoceptors and the post-receptor adenylate cyclase activation in the mice brain are involved in the antidepressant-like action of agmatine].

Abstract: This study is to explore the possible mechanisms of the antidepressant-like effect of agmatine. By using two traditional "behavior despair" model, tail suspension test and forced swimming test, we examined the effects of some monoamine receptor antagonists (including beta-adrenergic receptor antagonist propranolol, beta-adrenergic receptor antagonist/5-HT1A/1B receptor antagonist pindolol, alpha2-adrenergic receptor antagonists yohimbine and idazoxan and 5-HT3 receptor antagonist tropisetron) on the antidepressant-like action of agmatine in mice. Activity of adenylate cyclase (AC) in the synapse membrane from rat frontal cortex was determined by radioimmunoassay. Single dose of agmatine (5-40 mg x kg(-1), ig) dose-dependently decrease the immobility time in tail suspension test in mice, indicating an antidepressant-like effect. The effect of agmatine (40 mg x kg(-1), ig) was antagonized by co-administration of beta-adrenergic receptor antagonist/5-HT1A/1B receptor antagonist pindolol (20 mg x kg(-1), ip), alpha2-adrenergic receptor antagonists yohimbine (5-10 mg x kg(-1), ip) or idazoxan (4 mg x kg(-1), ip), but not beta-adrenergic receptor antagonist propranolol (5-20 mg x kg(-1), ip) and 5-HT3 receptor antagonist tropisetron (5-40 mg x kg(-1), ip). Agmatine (5-40 mg x kg(-1), ig) also dose-dependently decrease the immobility time in forced swimming test in mice. The effect of agmatine (40 mg x kg(-1), ig) was also antagonized by pindolol (20 mg x kg(-1), ip), yohimbine (5-10 mg x kg(-1), ip), or idazoxan (4 mg x kg(-1), ip). Incubation of agmatine (0.1-6.4 micromol x L(-1)) with the synaptic membrane extracted from rat frontal cortex activated the AC in a dose-dependent manner in vitro. While the effect of agmatine (6.4 micromol x L(-1)) was dose-dependently antagonized by pindolol (1 micromol x L(-1)) or yohimbine (0.25-1 micromol x L(-1)). Chronic treatment with agmatine (10 mg x kg(-1), ig, bid, 2 w) or fluoxetine (10 mg x kg(-1), ig, bid, 2 w) increased the basic activity, as well as the Gpp (NH)p (1-100 micromol x L(-1)) stimulated AC activity in rat prefrontal cortex. These results indicate that regulation on 5-HT1A/1B and alpha2 receptors, and activation AC in the frontal cortex is one of the important mechanisms involving in agmatine's antidepressant-like action.