Agmatine as a novel intervention for Alzheimer's disease: Pathological insights and cognitive benefits

Alzheimer's disease (AD) is a devastating neurodegenerative disorder characterized by progressive cognitive decline and a significant societal burden. Despite extensive research and efforts of the multidisciplinary scientific community, to date, there is no cure for this debilitating disease. Moreover, the existing pharmacotherapy for AD only provides symptomatic support and does not modify the course of the illness or halt the disease progression. This is a significant limitation as the underlying pathology of the disease continues to progress leading to the deterioration of cognitive functions over time. In this milieu, there is a growing need for the development of new and more efficacious treatments for AD. Agmatine, a naturally occurring molecule derived from L-arginine, has emerged as a potential therapeutic agent for AD. Besides this, agmatine has been shown to modulate amyloid beta (Aβ) production, aggregation, and clearance, key processes implicated in AD pathogenesis. It also exerts neuroprotective effects, modulates neurotransmitter systems, enhances synaptic plasticity, and stimulates neurogenesis. Furthermore, preclinical and clinical studies have provided evidence supporting the cognition-enhancing effects of agmatine in AD. Therefore, this review article explores the promising role of agmatine in AD pathology and cognitive function. However, several limitations and challenges exist, including the need for large-scale clinical trials, optimal dosing, and treatment duration. Future research should focus on mechanistic investigations, biomarker studies, and personalized medicine approaches to fully understand and optimize the therapeutic potential of agmatine. Augmenting the use of agmatine may offer a novel approach to address the unmet medical need in AD and provide cognitive enhancement and disease modification for individuals affected by this disease.

The prenatal use of agmatine prevents social behavior deficits in VPA-exposed mice by activating the ERK/CREB/BDNF signaling pathway

BACKGROUND

According to reports, prenatal exposure to valproic acid can induce autism spectrum disorder (ASD)-like symptoms in both humans and rodents. However, the exact cause and therapeutic method of ASD is not fully understood. Agmatine (AGM) is known for its neuroprotective effects, and this study aims to explore whether giving agmatine hydrochloride before birth can prevent autism-like behaviors in mouse offspring exposed prenatally to valproic acid.

METHODS

In this study, we investigated the effects of AGM prenatally on valproate (VPA)-exposed mice. We established a mouse model of ASD by prenatally administering VPA. From birth to weaning, we evaluated mouse behavior using the marble burying test, open-field test, and three-chamber social interaction test on male offspring.

RESULTS

The results showed prenatal use of AGM relieved anxiety and hyperactivity behaviors as well as ameliorated sociability of VPA-exposed mice in the marble burying test, open-field test, and three-chamber social interaction test, and this protective effect might be attributed to the activation of the ERK/CREB/BDNF signaling pathway.

CONCLUSION

Therefore, AGM can effectively reduce the likelihood of offspring developing autism to a certain extent when exposed to VPA during pregnancy, serving as a potential therapeutic drug.

Efficacy of Agmatine Treatment in Experimental Acute Pancreatitis Rat Model

BACKGROUND/AIMS

Acute pancreatitis which is characterized by pancreatic inflammation can sometimes be difficult to treat because of limited therapeutic options. The purpose of the study was to assess the effects of agmatine in the acute pancreatitis experimental rat model.

MATERIALS AND METHODS

An acute pancreatitis model was created with the administration of cerulein in 40 female Sprague-Dawley rats. Agmatine was administered as a protective agent at 5 mg/kg (low dose) and 10 mg/kg (high dose). The rats were divided into 5 groups, each with 8 rats: group 1 (acute pancreatitis); group 2 (acute pancreatitis+low-dose agmatine 5 mg/kg); group 3 (acute pancreatitis+high-dose agmatine 10 mg/kg); group 4 (placebo, acute pancreatitis+saline); and group 5 (sham and saline infusion). All rats were sacrificed 24 hours after the last injection, and the levels of superoxide dismutase, interleukin-1 beta, and tumor necrosis factor-alpha were assessed in blood samples collected via cardiac puncture. Histopathological examination was performed by a pathologist, who was blind to the groups, according to the Schoenberg's pancreatitis scoring index.

RESULTS

The amylase (16.67 and 37.89 U/L), glutathione peroxidase (13.62 and 18.44 ng/mL), tumor necrosis factor-α (39.68 and 64 ng/mL), interleukin-1 (484.73 and 561.83 pg/mL), and transforming growth factor-β (110.52 and 126.34 ng/L) levels were significantly lower and superoxide dismutase (1.29 and 0.98 ng/L) and malondialdehyde (0.99 and 0.96 nmol/mL) levels were significantly higher in group 3 compared to group 1 (P < .05). Moreover glutathione peroxidase, tumor necrosis factor-α, and transforming growth factor-β levels were lower, and malondialdehyde levels were higher in the group 3 compared to group 2 (P < .05). Although the Schoenberg's pancreatitis scoring index was not significantly different between the high- and low-dose treatment groups, rats who received high-dose treatment had significantly lower scores compared to those with acute pancreatitis group.

CONCLUSION

This is the first study that evaluated the efficacy of agmatine in an experimental model of acute pancreatitis. Agmatine, an anti-inflammatory and antioxidant agent, had a protective effect in an experimental rat model of acute pancreatitis.

Cholinergic deficit induced memory retrieval impairment and hippocampal CaMKII-alpha deregulation is counteracted by sub-chronic agmatine treatment in mice

Alzheimer's disease (AD) is one of the most prevalent neurodegenerative disease characterized by brain cholinergic dysfunction. Evidence suggests the impairment of memory retrieval phase in AD. It has been shown that CaMKII-α expressing neurons are selectively reduced in the hippocampus in AD brains. The present study aimed to investigate the effect of scopolamine on the memory retrieval phase and the hippocampal CaMKII-α signaling. In addition, the effect of sub-chronic administration of agmatine against scopolamine induced memory and possible hippocampal CaMKII-α deregulation was investigated in mice. Adult male NMRI mice were administered with agmatine at the doses of 5, 10, 20, 30 and 40 mg/kg/i.p. or saline for 11 days. Acquisition and retrieval tests of passive avoidance task were performed on days 10 and 11, respectively (30 Min following agmatine treatment). Scopolamine (1 mg/kg/i.p.) was administered once, 30 Min before retrieval test. Upon completion of the behavioral tasks, the hippocampi were isolated for western blot analysis to detect the phosphorylated and total levels of CaMKII-α and beta actin proteins. The results showed that scopolamine induced memory retrieval deficit and decreased the phosphorylated level of hippocampal CaMKII-α. Sub-chronic agmatine treatment at the dose of 40 mg/kg prevented scopolamine induced memory retrieval deficit and restored the level of hippocampal phosphorylated CaMKII-α. This study suggests that hippocampal CaMKII-α might play a role in scopolamine induced amnesia and sub-chronic agmatine prevents the impairing effect of scopolamine on the retrieval phase of memory and the phosphorylation of hippocampal CaMKII-α protein.

Biodistribution of Agmatine to Brain and Spinal Cord after Systemic Delivery

Agmatine, an endogenous polyamine, has been shown to reduce chronic pain behaviors in animal models and in patients. This reduction is due to inhibition of the GluN2B subunit of the N-methyl-D-aspartate receptor (NMDAR) in the central nervous system (CNS). The mechanism of action requires central activity, but the extent to which agmatine crosses biologic barriers such as the blood-brain barrier (BBB) and intestinal epithelium is incompletely understood. Determination of agmatine distribution is limited by analytical protocols with low sensitivity and/or inefficient preparation. This study validated a novel bioanalytical protocol using high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) for quantification of agmatine in rat biologic matrices. These protocols were then used to determine the plasma pharmacokinetics of agmatine and the extent of distribution to the CNS. Precision and accuracy of the protocol met US Food and Drug Administration (FDA) standards in surrogate matrix as well as in corrected concentrations in appropriate matrices. The protocol also adequately withstood stability and dilution conditions. Upon application of this protocol to pharmacokinetic study, intravenous agmatine showed a half-life in plasma ranging between 18.9 and 14.9 minutes. Oral administration led to a prolonged plasma half-life (74.4-117 minutes), suggesting flip-flop kinetics, with bioavailability determined to be 29%-35%. Intravenous administration led to a rapid increase in agmatine concentration in brain but a delayed distribution and lower concentrations in spinal cord. However, half-life of agmatine in both tissues is substantially longer than in plasma. These data suggest that agmatine adequately crosses biologic barriers in rat and that brain and spinal cord pharmacokinetics can be functionally distinct. SIGNIFICANCE STATEMENT: Agmatine has been shown to be an effective nonopioid therapy for chronic pain, a significantly unmet medical necessity. Here, using a novel bioanalytical protocol for quantification of agmatine, we present the plasma pharmacokinetics and the first report of agmatine oral bioavailability as well as variable pharmacokinetics across different central nervous system tissues. These data provide a distributional rationale for the pharmacological effects of agmatine as well as new evidence for kinetic differences between brain and spinal cord.

Neuroprotection by agmatine: Possible involvement of the gut microbiome?

Agmatine, an endogenous polyamine derived from L-arginine, elicits tremendous multimodal neuromodulant properties. Alterations in agmatinergic signalling are closely linked to the pathogeneses of several brain disorders. Importantly, exogenous agmatine has been shown to act as a potent neuroprotectant in varied pathologies, including brain ageing and associated comorbidities. The antioxidant, anxiolytic, analgesic, antidepressant and memory-enhancing activities of agmatine may derive from its ability to regulate several cellular pathways; including cell metabolism, survival and differentiation, nitric oxide signalling, protein translation, oxidative homeostasis and neurotransmitter signalling. This review briefly discusses mammalian metabolism of agmatine and then proceeds to summarize our current understanding of neuromodulation and neuroprotection mediated by agmatine. Further, the emerging exciting bidirectional links between agmatine and the resident gut microbiome and their implications for brain pathophysiology and ageing are also discussed.

Preventive putative effect of agmatine on cognitive and molecular outcomes in ventral tegmental area of male offspring following physical and psychological prenatal stress

Prenatal stress (PS) results from a maternal experience of stressful events during pregnancy, which has been associated with an increased risk of behavioral disorders including substance abuse and anxiety in the offspring. PS is known to result in heightened dopamine release in the ventral tegmental area (VTA), in part through the effects of corticotropin-releasing hormone, which directly excites dopaminergic cells. It has recently been suggested that agmatine plays a role in modulating anxiety-like behaviors. In this study, we investigated whether agmatine could reduce negative cognitive outcomes in male mice prenatally exposed to psychological/physical stress, and whether this could be associated with molecular changes in VTA. Agmatine (37.5 mg/kg) was administrated 30 min prior to PS induction in pregnant Swiss mice. Male offspring were evaluated in a series of behavioral and molecular assays. Findings demonstrated that agmatine reduced the impairment in locomotor activity induced by both psychological and physical PS. Agmatine also decreased heightened conditioned place preference to morphine seen in PS offspring. Moreover, agmatine ameliorated the anxiety-like behavior and drug-seeking behavior induced by PS in the male offspring. Molecular effects were seen in VTA as the enhanced brain-derived neurotrophic factor (BDNF) induced by PS in the VTA was reduced by agmatine. Behavioral tests indicate that agmatine exerts a protective effect on PS-induced impairments in male offspring, which could be due in part to agmatine-associated molecular alterations in the VTA. Taken together, our data suggest that prenatal treatment with agmatine exerts protective effect against negative consequences of PS on the development of affective circuits in the offspring.

Agmatine improves liver function, balance performance, and neuronal damage in a hepatic encephalopathy induced by bile duct ligation

INTRODUCTION

In the current study, we investigate whether oral administration of agmatine (AGM) could effectively reduce motor and cognitive deficits induced by bile duct ligation (BDL) in an animal model of hepatic encephalopathy (HE) through neuroprotective mechanisms.

METHODS

The Wistar rats were divided into four groups: sham, BDL, BDL+ 40 mg/kg AGM, and BDL+ 80 mg/kg AGM. The BDL rats were treated with AGM from 2 weeks after the surgery for 4 consecutive weeks. The open field, rotarod, and wire grip tests were used to assess motor function and muscle strength. The novel object recognition test (NOR) was performed to evaluate learning and memory. Finally, blood samples were collected for the analysis of the liver markers, the animals were sacrificed, and brain tissues were removed; the CA1 regions of the hippocampus and cerebellum were processed to identify apoptosis and neuronal damage rate using caspase-3 immunocytochemistry and Nissl staining.

RESULTS

The serological assay results showed that BDL severely impaired the function of the liver. Based on histochemical findings, BDL increased the neuronal damage in CA1 and Purkinje cells, whereas apoptosis was significantly observed only in the cerebellum. AGM treatment prevented the increase of serum liver enzymes, balance deficits, and neuronal damage in the brain areas. Apoptosis partially decreased by AGM, and there were no differences in the performance of animals in different groups in the NOR.

CONCLUSIONS

The study suggests AGM as a potential treatment candidate for HE because of its neuroprotective properties and/or its direct effects on liver function.

Analysis of Regulatory Mechanism of AcrB and CpxR on Colistin Susceptibility Based on Transcriptome and Metabolome of Salmonella Typhimurium

With the increasing and inappropriate use of colistin, the emerging colistin-resistant isolates have been frequently reported during the last few decades. Therefore, new potential targets and adjuvants to reverse colistin resistance are urgently needed. Our previous study has confirmed a marked increase of colistin susceptibility (16-fold compared to the wild-type Salmonella strain) of cpxR overexpression strain JSΔacrBΔcpxR::kan/pcpxR (simplified as JSΔΔ/pR). To searching for potential new drug targets, the transcriptome and metabolome analysis were carried out in this study. We found that the more susceptible strain JSΔΔ/pR displayed striking perturbations at both the transcriptomics and metabolomics levels. The virulence-related genes and colistin resistance-related genes (CRRGs) were significantly downregulated in JSΔΔ/pR. There were significant accumulation of citrate, α-ketoglutaric acid, and agmatine sulfate in JSΔΔ/pR, and exogenous supplement of them could synergistically enhance the bactericidal effect of colistin, indicating that these metabolites may serve as potential adjuvants for colistin therapy. Additionally, we also demonstrated that AcrB and CpxR could target the ATP and reactive oxygen species (ROS) generation, but not proton motive force (PMF) production pathway to potentiate antibacterial activity of colistin. Collectively, these findings have revealed several previously unknown mechanisms contributing to increased colistin susceptibility and identified potential targets and adjuvants for potentiating colistin treatment of Salmonella infections. IMPORTANCE Emergence of multidrug-resistant (MDR) Gram-negative (G-) bacteria have led to the reconsideration of colistin as the last-resort therapeutic option for health care-associated infections. Finding new drug targets and strategies against the spread of MDR G- bacteria are global challenges for the life sciences community and public health. In this paper, we demonstrated the more susceptibility strain JSΔΔ/pR displayed striking perturbations at both the transcriptomics and metabolomics levels and revealed several previously unknown regulatory mechanisms of AcrB and CpxR on the colistin susceptibility. Importantly, we found that exogenous supplement of citrate, α-ketoglutaric acid, and agmatine sulfate could synergistically enhance the bactericidal effect of colistin, indicating that these metabolites may serve as potential adjuvants for colistin therapy. These results provide a theoretical basis for finding potential new drug targets and adjuvants.

Agmatine reduces alcohol drinking and produces antinociceptive effects in rodent models of alcohol use disorder

Alcohol use disorder (AUD) is a chronic, relapsing disorder characterized by an escalation of drinking and the emergence of negative affective states over time. Within this framework, alcohol may be used in excessive amounts to alleviate withdrawal-related symptoms, such as hyperalgesia. Future effective therapeutics for AUD may need to exhibit the ability to reduce drinking as well as to alleviate co-morbid conditions such as pain, and to take mechanistic sex differences into consideration. Agmatine is an endogenous neuromodulator that has been previously implicated in the regulation of reward and pain processing. In the current set of studies, we examined the ability of agmatine to reduce escalated ethanol drinking in complementary models of AUD where adult male and female mice and rats were made dependent via chronic, intermittent ethanol vapor exposure (CIE). We also examined the ability of agmatine to modify thermal and mechanical sensitivity in alcohol-dependent male and female rats. Agmatine reduced alcohol drinking in a dose-dependent fashion, with somewhat greater selectivity in alcohol-dependent female mice (versus non-dependent female mice), but equivalent efficacy across male mice and both groups of male and female rats. In mice and female rats, this efficacy did not extend to sucrose drinking, indicating some selectivity for ethanol reinforcement. Female rats made dependent on alcohol demonstrated significant hyperalgesia symptoms, and agmatine produced dose-dependent antinociceptive effects across both sexes. While additional mechanistic studies into agmatine are necessary, these findings support the broad-based efficacy of agmatine to treat co-morbid excessive drinking and pain symptoms in the context of AUD.

Long-term reversal of chronic pain behavior in rodents through elevation of spinal agmatine

Chronic pain remains a significant burden worldwide, and treatments are often limited by safety or efficacy. The decarboxylated form of L-arginine, agmatine, antagonizes N-methyl-d-aspartate receptors, inhibits nitric oxide synthase, and reverses behavioral neuroplasticity. We hypothesized that expressing the proposed synthetic enzyme for agmatine in the sensory pathway could reduce chronic pain without motor deficits. Intrathecal delivery of an adeno-associated viral (AAV) vector carrying the gene for arginine decarboxylase (ADC) prevented the development of chronic neuropathic pain as induced by spared nerve injury in mice and rats and persistently reversed established hypersensitivity 266 days post-injury. Spinal long-term potentiation was inhibited by both exogenous agmatine and AAV-human ADC (hADC) vector pre-treatment but was enhanced in rats treated with anti-agmatine immunoneutralizing antibodies. These data suggest that endogenous agmatine modulates the neuroplasticity associated with chronic pain. Development of approaches to access this inhibitory control of neuroplasticity associated with chronic pain may yield important non-opioid pain-relieving options.

Perspectives on Agmatine Neurotransmission in Acute and Chronic Stressrelated Conditions

Adaptive responses to stressful stimuli in the environment are believed to restore homeostasis after stressful events. Stress activates the hypothalamic-pituitary-adrenocortical (HPA) axis, which releases glucocorticoids (GCs) into the bloodstream. Recently, agmatine, an endogenous monoamine was discovered to have the potential as a pharmacotherapy for stress. Agmatine is released in response to certain stress conditions, especially those involving GCs, and participates in establishing homeostasis disturbed by stress following GC activation. The therapeutic potential of agmatine for the management of psychological diseases involving stress and depression is promising based on a significant amount of literature. When exogenously applied, agmatine leads to reductions in levels of GCs and counteracts stress-related morphologic, synaptic, and molecular changes. However, the exact mechanism of action by which agmatine modifies the effects resulting from stress hormone secretion is not fully understood. This review aims to present the most possible mechanisms by which agmatine reduces the harmful effects of chronic and acute stress. Several studies suggest chronic stress exposure and repeated corticosteroid treatment lower agmatine levels, contributing to stress-related symptoms. Agmatine acts as an antistress agent by activating mTOR signaling, inhibiting NMDA receptors, suppressing iNOS, and maintaining bodyweight by activating α-2adrenergic receptors. Exogenous administration that restores agmatine levels may provide protection against stress-induced changes by reducing GCs release, stimulating anti-inflammatory processes, and releasing neuroprotective factors, which are not found in all therapies currently being used to treat stress-related disorders. The administration of exogenous agmatine should also be considered a therapeutic element that is capable of triggering a neural protective response that counters the effects of chronic stress. When combined with existing treatment strategies, this may have synergistic beneficial effects.

Agmatine relieves behavioral impairments in Fragile X mice model

BACKGROUND

Fragile X syndrome (FXS) is the most common heritable form of neurodevelopmental disorder, which is caused by the loss of fragile X mental retardation protein (FMRP) expression. Despite the unceasing efforts to develop therapeutic agents against FXS based on the pathophysiological changes observed in animal models of FXS and human patients, therapeutic candidates including mGluR signaling modulators have failed to provide sufficient effects. Based on the recent successful demonstration of an endogenous polyamine, agmatine, to improve the autism-like symptoms in the valproic acid animal model of autism, we investigated the effects of agmatine against FXS symptoms using Fmr1 knockout (KO) mice.

METHODS

We used male Fmr1 KO mice for behavioral tests such as marble burying, open-field test, memory tasks, social interaction tests and startle response to confirm the symptoms of FXS. We also checked the electrophysiological profile of neural activity in agmatine-treated Fmr1 KO mice.

RESULTS

Agmatine reversed the compulsion, learning and memory deficits, hyperactivity, aberrant social interaction, and communication deficit in Fmr1 KO mice while it normalized the aberrant LTP and LTD in the hippocampus.

CONCLUSIONS

The results highlight the potential of agmatine's novel disease-ameliorating effects in FXS, which warrants further studies to ascertain whether these findings translate into clinical effects in FXS patients.

Agmatine prevents development of tolerance to anti-nociceptive effect of ethanol in mice

Drug tolerance is directly correlated with drug abuse and physical dependence. The development of tolerance is manifested as the decline in pharmacological responses of drugs following repeated administration of the constant dose. The present study evaluated the effect of agmatine in ethanol-induced anti-nociception and tolerance in the tail-flick assay in mice. In an acute protocol, ethanol (1 and 2 g/kg, i.p. [intraperitoneally]) and agmatine (20 and 40 μg/mouse, i.c.v. [intracerebroventricularly]) produced significant analgesic effects in mice, as was evident from the increased baseline tail-flick latency when tested 20 minutes after their administration. Agmatine in a per se non-effective dose (5 μg/mouse, i.c.v.), L-arginine (40 μg/mouse, i.c.v.), and arcaine (25 μg/mouse, i.c.v.) significantly potentiated the anti-nociceptive effect of ethanol. Blood ethanol analysis showed no significant differences in blood ethanol concentration between ethanol/saline- and ethanol/agmatine-treated mice, suggesting that the effects of agmatine were not due to any possible effects on the pharmacokinetics of ethanol. In a separate study, mice were injected with ethanol (2 g/kg, i.p., 12%) or saline (1 mL/kg, i.p.) once daily for 9 days. On days 1, 3, 5, 7, and 9 of the experiment, they were subjected to the tail-flick test. Agmatine (5-20 μg/mouse, i.c.v.), L-arginine (40 μg/mouse, i.c.v.), arcaine (25 μg/mouse, i.c.v.), aCSF (2 μL/mouse, i.c.v.), or saline (1 mL/kg, i.p.) was administered daily prior to the first daily ethanol or saline injections, and reaction latencies were determined in the tail-flick assay. Injections of agmatine, L-arginine, and arcaine prevented the development of tolerance to ethanol-induced analgesia. Given that agmatine and its endogenous modulation can prevent tolerance to the anti-nociceptive effects of ethanol, these data suggest it as a possible new therapeutic strategy for the treatment of alcohol use disorder and associated complications.

Protective Effect of Agmatine Against Cisplatin- Induced Cellular Apoptosis in an Auditory Cell Line

BACKGROUND

The aims of this study were to evaluate the protective effects of agmatine against cisplatin-induced cellular apoptosis in an audi- tory cell line and to prove the protective mechanism of agmatine.

METHODS

The House Ear Institute-Organ of Corti 1 cells were co-treated with agmatine at different concentrations and 15 μM of cisplatin for 48 hours. Cell viability and proliferation were measured. Annexin V-fluorescein isothiocyanate /propidium iodide staining was performed to analyze apoptosis. The levels of intracellular reactive oxygen species were measured using flow cytometry. The expression of BCL2-associated X protein and the enzymatic activity of caspase-3 was measured to examine the pathway of apoptosis induction.

RESULTS

In normal conditions, the maximal protective effect occurred with 10 mM of agmatine. However, in the presence of cisplatin, the maximal protective effect was observed from 8 mM of agmatine. Thus, 8 mM was chosen as the ideal agmatine concentration for the analysis of protective effects against cisplatin-induced cytotoxicity. Agmatine exerted a significant protective effect against 15 μM of cisplatin when applied for 48 hours and reduced the proportion of necrotic and late apoptotic cells. Agmatine did not significantly reduce the cisplatin-induced increase in reactive oxygen species but decreased the expression of BCL2-associated X protein and the activity of caspase-3.

CONCLUSION

Agmatine protected against cisplatin-induced cellular apoptosis in an auditory cell line. These effects were mediated by the pro- tection of mitochondrial function and inhibition of apoptosis.

The effects of subchronic agmatine on passive avoidance memory, anxiety-like behavior and hippocampal Akt/GSK-3β in mice

Agmatine, a polyamine derived from l-arginine, has been suggested to modulate memory. However, the available evidence regarding the effect of agmatine on the memory of intact animals is contradictory. This study aimed to assess the dose-response effect of subchronic agmatine on passive avoidance memory and anxiety-like parameters of elevated plus maze in adult intact mice. Furthermore, considering the roles of Akt/GSK-3β signaling pathway in memory and Alzheimer's disease, the hippocampal contents of phosphorylated and total forms of Akt and GSK-3β proteins were determined using the western blot technique. Agmatine was administered intraperitoneally at the doses of 10, 20, 30, 40 and 80 mg/kg/daily to adult male NMRI mice for 10 days after which the behavioral assessments were performed. Upon completion of the passive avoidance test, the hippocampi were removed for western blot analysis to detect the phosphorylated and total levels of Akt and GSK-3β proteins. Results showed the biphasic effect of agmatine on passive avoidance memory; in lower doses (10, 20 and 30 mg/kg), agmatine impaired memory whereas in higher ones (40 and 80 mg/kg) improved it. Though, agmatine in none of the doses affected animals' anxiety-like parameters in an elevated plus maze. Moreover, the memory-improving doses of agmatine augmented Akt/GSK-3β pathway. This study showed the biphasic effect of agmatine on passive avoidance memory and an augmentation of hippocampal Akt/GSK-3β signaling pathway following the memory-improving doses of this polyamine.

Agmatine improves olfactory and cognitive deficits in Spontaneously Hypertensive Rats (SHR): An animal model of Attention Deficit Hyperactivity Disorder (ADHD)

Attention Deficit Hyperactivity Disorder (ADHD) is a highly prevalent and disabling disorder that frequently persists into adulthood. Many patients are considered nonresponders to typical pharmacological treatments due to insufficient symptoms' reduction or the inability to tolerate the side effects of these medications. Agmatine is an endogenous neuromodulator with emotional- and cognitive-enhancing properties that arises as a promising agent to manage several Central Nervous System disorders. Here, we investigated the effects of chronic treatment with agmatine on behavioral impairments exhibited by adult Spontaneously Hypertensive Rats (SHR), an animal model for the study of ADHD. Adult male Wistar and SHR (3-4 months old) received intraperitoneal (i.p.) treatment with saline (NaCl 0.9%) or agmatine (30 mg/kg/day) during 20 consecutive days and were evaluated in a battery of behavioral tasks. Agmatine treatment improved olfactory and recognition memory impairments of SHR evaluated in the olfactory discrimination, object recognition, and social recognition memory tasks. In addition, agmatine administration improved the cognitive flexibility in the water maze test. Agmatine did not alter SHR's locomotor activity and hedonic-like behaviors observed in the open-field and splash tests, respectively. No changes were observed in SHR's systolic blood pressure following agmatine treatment. This study provides the first evidence that agmatine improves olfactory and cognitive impairments observed in an animal model of ADHD. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Agmatine and glycolipid metabolism

The prevalence of abnormal glucose and lipid metabolism and its relevant diseases has increased year by year, and it has become a problem that threatens human health. Therefore, finding a more effective way to prevent and treat diseases related to abnormal glucose and lipid metabolism has become an urgent public problem. Agmatine is a polyamine substance which widely presents in mammals.It is a metabolite produced by decarboxylation of L-arginine under the action of arginine decarboxylase, hence also known as decarboxylated arginine. Its biological effects have been confirmed. Previous studies have shown that agmatine possesses anti-diabetic effects in diabetic animals. Agmatine not only increases the insulin secretion form β-pancreatic cells to inhibit the hyperglycemia, but also attenuates insulin resistance in rats. Agmatine also plays a positive role in lipid metabolism disorders and related diseases by modulating lipid metabolism and fatty acid oxidation.

Maintenance of the Neuroprotective Function of the Amino Group Blocked Fluorescence-Agmatine

Agmatine, an endogenous derivative of arginine, has been found to be effective in treating idiopathic pain, convulsion, stress-mediated behavior, and attenuate the withdrawal symptoms of drugs like morphine. In the early stages of ischemic brain injury in animals, exogenous agmatine treatment was found to be neuroprotective. Agmatine is also considered as a putative neurotransmitter and is still an experimental drug. Chemically, agmatine is called agmatine 1-(4-aminobutyl guanidine). Crystallographic study data show that positively-charged guanidine can bind to the protein containing Gly and Asp residues, and the amino group can interact with the complimentary sites of Glu and Ser. In this study, we blocked the amino end of the agmatine by conjugating it with FITC, but the guanidine end was unchanged. We compared the neuroprotective function of the agmatine and agmatine-FITC by treating them in neurons after excitotoxic stimulation. We found that even the amino end blocked neuronal viability in the excitotoxic condition, by NMDA treatment for 1 h, was increased by agmatine-FITC, which was similar to that of agmatine. We also found that the agmatine-FITC treatment reduced the expression of nitric oxide production in NMDA-treated cells. This study suggests that even if the amino end of agmatine is blocked, it can perform its neuroprotective function.

Retinoprotective effect of agmatine in streptozotocin-induced diabetic rat model: avenues for vascular and neuronal protection : Agmatine in diabetic retinopathy

Diabetic retinopathy (DR) is the most common diabetic neurovascular complication, and the leading cause of preventable blindness among working-age individuals. Recently, agmatine, the endogenous decarboxylated L-arginine, has gained attention as a pleiotropic agent that modulates the diabetes-associated decline in quality of life, and exhibited varied protective biological effects. Diabetes was induced by a single streptozotocin (STZ, 50 mg/kg, i.p.) injection. When diabetes was verified, the animals were randomly allocated into three groups (16 rat each); diabetic, agmatine-treated diabetic (1 mg/kg, daily, for 12 weeks), and control group. Blood glucose homeostasis, retinal redox status, apoptotic parameters, nitric oxide synthase (NOS), nitric oxide (NO), vascular endothelial growth factor (VEGF), glutamate, glutamine, glutamine synthase (GS) activity, nuclear factor kappa-light-chain-enhancer of activated B cells (NFκB), and mitogen-activated protein kinase (MAPKs) pathways were assayed biochemically. Retinal vascular permeability was measured. Retinal morphology was evaluated by hematoxylin and eosin staining. Retinal N-methyl-D-aspartic acid receptor1 (NMDAR1) and glutamate aspartate transporter (GLAST) mRNA were quantified. Glucose transporter 1, pro-caspase3, and glial fibrillary acidic protein (GFAP) expression were quantified by immunohistochemistry. Chronic agmatine treatment abrogated STZ-induced retinal neurodegeneration features including gliosis, and neuronal apoptosis, restored retinal vascular permeability, mostly through antioxidant, anti-apoptotic capacity, abolishing glutamate excitotoxicity, modulating the activity of NMDARs, MAPKs/NFκB, and NOS/NO pathways. By restoring the molecular and functional background of retinal neurovascular homeostatic balance, agmatine would be appropriate therapeutic option acting upstream of the DR, impeding its progression.

Neuroprotective action of agmatine in rotenone-induced model of Parkinson's disease: Role of BDNF/cREB and ERK pathway

Numerous studies have investigated the role of agmatine in the central nervous system and indicated neuroprotective properties. In addition to its potent antioxidant effects, agmatine is an endogenous neuromodulator and has wide spectrum molecular actions on different receptor subtypes (NMDA, Imidazoline 1-2, alpha-2 adrenoreceptor, 5-HT2a, 5-HT3) and cellular signaling pathways (MAPK, PKA, NO, BDNF). Although the neuroprotective effects of agmatine demonstrated in experimental Parkinson's disease model, the effects of agmatine with the aspect of neuroplasticity and possible signaling mechanisms behind agmatine actions have not been investigated. Herein, in this study, we investigated the role of the of agmatine on rotenone-induced Parkinson's disease model. Agmatine at the dose of 100 mg/kg i.p., was mitigated oxidative damage and alleviated motor impairments which were the results of the rotenone insult. Additionally, agmatine decreased neuronal loss, tyrosine hydroxylase immunoreactivity and increased cREB, BDNF and ERK1/2 expression in the striatum, which are crucial neuroplasticity elements of striatal integrity. Taken together, the present study expands the knowledge of molecular mechanisms behind neuroprotective actions of agmatine in Parkinson's disease, and as far as we have known, this is the first study to delineate agmatine treated activation of cellular pathways which are important elements in neuronal cell survival.

Effect of agmatine on food intake in mandarin fish (Siniperca chuatsi)

Agmatine, an endogenous biogenic amine, is considered to be a central neurotransmitter. And it plays an important role in mammal feeding behavior. However, there were few studies on the effect of agmatine on feeding behavior in fishes. Here, we investigated the impact of intracerebroventricular (ICV) injections of agmatine (1.25-20 nmol/fish) on food intake in mandarin fish (Siniperca chuatsi). At 1-h post-injection, food intake showed a significant decrease in agmatine-treated fishes compared with the saline treated. Furthermore, the food intake in agmatine treatment mostly did not differ from that in saline treatment at 4--24-h post-injection as well as the results of genes expression of neuropeptide Y (NPY), agouti-regulated peptide (AgRP), and anorexigenic melanocortin 4 receptor (MC4R). In accordance with the insulin level increasing in liver, the gene expression of insulin receptor substrate (IRS2) was significantly higher in agmatine treatment compared to saline treatment at 1-h post-injection. Thus, the anorexigenic effect of agmatine is likely to decrease NPY and AgRP expression levels and increase MC4R and IRS2 levels which was coupled with stimulation of insulin secretion. Although these initial findings are limited in dose, the data firstly provides evidence for the anorectic effects of agmatine in fish.

α2-Adrenoceptor signaling in cardiomyocytes of spontaneously hypertensive rats starts to impair already at early age

α2-Adrenoceptors (α2-AR) found in the cardiomyocyte's sarcolemma represent a very important negative feedback for control of myocardial contractility by endogenous catecholamines. Earlier, we showed that the endogenous neurotransmitter agmatine in micromolar concentrations via α2-AR activates the nitric oxide (NO) synthesis, enhancing the Ca²⁺ pumping into sarcoplasmic reticulum (SR). In the millimolar doses it inhibits Ca²⁺ sequestration by SR Ca²⁺ ATPase (SERCA), acting through the first type of imidazoline receptors. Here, we study the functional activity of agmatine, as well as a specific α2-agonist, guanabenz, in respect to spontaneous Ca²⁺-transients in SHR cardiomyocytes of the early age (2-2.5 months), and adulthood animals (8-9 months). α2-mediated cardioprotective effect was almost twofold decreased in SHR cardiac cells compared to normotensive rats of the corresponding age, despite the fact that both α2A- and α2B-AR protein levels were significantly increased in SHR cardiomyocytes. NO-mediated facilitation of SERCA activity is substantially reduced in SHR cardiomyocytes vs. normotensive rats. These data suggest that the SHR phenotype starting from early age shows signs of the impaired sarcolemmal α2-AR signaling, which can aggravate the development of this cardiovascular pathology.

Neuroprotective effects of agmatine in antineoplastic drugs induced neurotoxicity: In vitro study

AIMS

The effects of agmatine, an endogenous substance known to have a neuroprotective effect against neurotoxicity has been investigated.

MATERIAL AND METHODS

The primary neuron culture obtained from neonatal rats was exposed to toxicity with paclitaxel and cisplatin and the effect of agmatine on both acute (1 h) and chronic (24 h) exposure was demonstrated by biochemical and molecular analyses. It was demonstrated that the effect of agmatine before and after agmatine was induced by neurotoxicity before agmatine and the effect of agmatine on the formed and occuring toxicities. In addition to the results of cell viability assay, total oxidant capacity and total antioxidant capacity, we have found the opportunity to elaborate on our molecular mechanisms by elaborating our findings with apoptotic and inflammation markers such as caspase 3, kaspase 9 and TNF alpha.

KEY FINDINGS

The results of our study revealed the effect profile of a protective molecule against pathological neural deaths due to neurodegeneration not only in neurotoxicity due to anticancer drugs.

SIGNIFICANCE

In this context, we tried to reverse neurotoxicity due to anticancer drugs by using agmatine the duration (1 and 24 h) and dosage (10-5 M and 10-6 M) determined.

Agmatine preferentially antagonizes GluN2B-containing N-methyl-d-aspartate receptors in spinal cord

The role of the N-methyl-d-aspartate receptor (NMDAr) as a contributor to maladaptive neuroplasticity underlying the maintenance of chronic pain is well established. Agmatine, an NMDAr antagonist, has been shown to reverse tactile hypersensitivity in rodent models of neuropathic pain while lacking the side effects characteristic of global NMDAr antagonism, including sedation and motor impairment, indicating a likely subunit specificity of agmatine's NMDAr inhibition. The present study assessed whether agmatine inhibits subunit-specific NMDAr-mediated current in the dorsal horn of mouse spinal cord slices. We isolated NMDAr-mediated excitatory postsynaptic currents (EPSCs) in small lamina II dorsal horn neurons evoked by optogenetic stimulation of Nav1.8-containing nociceptive afferents. We determined that agmatine abbreviated the amplitude, duration, and decay constant of NMDAr-mediated EPSCs similarly to the application of the GluN2B antagonist ifenprodil. In addition, we developed a site-specific knockdown of the GluN2B subunit of the NMDAr. We assessed whether agmatine and ifenprodil were able to inhibit NMDAr-mediated current in the spinal cord dorsal horn of mice lacking the GluN2B subunit of the NMDAr by analysis of electrically evoked EPSCs. In control mouse spinal cord, agmatine and ifenprodil both inhibited amplitude and accelerated the decay kinetics. However, agmatine and ifenprodil failed to attenuate the decay kinetics of NMDAr-mediated EPSCs in the GluN2B-knockdown mouse spinal cord. The present study indicates that agmatine preferentially antagonizes GluN2B-containing NMDArs in mouse dorsal horn neurons. NEW & NOTEWORTHY Our study is the first to report that agmatine preferentially antagonizes the GluN2B receptor subunit of the N-methyl-d-aspartate (NMDA) receptor in spinal cord. The preferential targeting of GluN2B receptor is consistent with the pharmacological profile of agmatine in that it reduces chronic pain without the motor side effects commonly seen with non-subunit-selective NMDA receptor antagonists.

The neuroprotective effect of agmatine against amyloid β-induced apoptosis in primary cultured hippocampal cells involving ERK, Akt/GSK-3β, and TNF-α

β-Amyloid peptide (Aβ), the major element of senile plaques in Alzheimer's disease (AD), has been found to accumulate in brain regions critical for memory and cognition. Deposits of Aβ trigger neurotoxic events which lead to neural apoptotic death. The present study examined whether agmatine, an endogenous polyamine formed by the decarboxylation of L-arginine, possesses a neuroprotective effect against Aβ-induced toxicity. Primary rat hippocampal cells extracted from the brains of 18-19-day-old embryos were exposed to 10 µM of Aβ (25-35) in the absence or presence of agmatine at 150 or 250 µM. Additionally, the involvement of Akt (Protein Kinae B), GSK-3β (glycogen synthase kinase 3-β), ERK (Extracellular Signal-Regulated Kinase) and TNF-α (Tumor necrosis factor-α) in the agmatine protection against Aβ-induced neurotoxicity was investigated. Agmatine significantly prevented the effect of Aβ exposure on cell viability and caspase-3 assays. Furthermore, agmatine considerably restored Aβ-induced decline of phospho-Akt and phospho-GSK and blocked Aβ-induced increase of phospho-ERK and TNF-alpha. Taken together, these findings might shed light on the protective effect of agmatine as a potential therapeutic agent for AD.

Antidepressant-like action of agmatine in the acute and sub-acute mouse models of depression: a receptor mechanism study

Previous studies have shown that agmatine, a potential neuromodulator or co-transmitter, exhibited antidepressant-like action in animal models, yet its mechanism, especially the receptor mechanism, remains unclear. In the present study, using efaroxan, a preferential antagonist of I₁ imidazoline receptor (I₁R) and yohimbine, an antagonist of α₂ adrenergic receptor (α₂AR), we investigated the roles of I₁R and α₂AR in agmatine's antidepressant-like effect in acute and sub-acute depression models in mice. We found that in the tail-suspension test (TST) and the forced swimming test (FST), acute administration of agmatine (20 and 40 mg/kg, p.o.) significantly shortened the immobility time. Concurrent administration of efaroxan (1 mg/kg, i.p.) completely abolished the antidepressant-like effects of agmatine (40 mg/kg, p.o.) whereas yohimbine (5 mg/kg, i.p.) failed to exert similar effects, suggesting that the acute antidepressant-like effects of agmatine was mainly mediated by I₁R but not α₂AR. Additionally, in the learned helplessness (LH) test, repeated administration of agmatine (20 mg/kg, p.o., q.d.) for 5 days significantly decreased the escape latency and the number of escape failure, and these effects were respectively abolished by concurrent administration of efaroxan (0.5 mg/kg,i.p., q.d.) and yohimbine (3 mg/kg, i.p., q.d.) for 5 days, suggesting that the antidepressant-like action of agmatine in the LH test was achieved via the activation of both I₁R and α₂AR. In summary, we found that the antidepressant-like effects of agmatine in the TST and the FST were mediated by activating I₁R and in the sub-acute LH test were mediated by activating both I₁R and α₂AR.

[Exogenous agmatine inhibits lipopolysaccharide-induced activation and dysfunction of human umbilical vein endothelial cells]

OBJECTIVE

To investigate whether exogenous agmatine inhibits lipopolysaccharide (LPS)-induced activation and dysfunction of human umbilical vein endothelial cells (HUVECs) by modulating nuclear factor-κB (NF-κB) and MAPK signal pathways and the production of reactive oxygen species (ROS).

METHODS

Cultured HUVECs were treated with agmatine at the optimized concentration of 1.0 mmolγL, LPS (10 µgγmL), and LPS + agmatine, with or without pretreatment with the inhibitors of NF-κB (PDTC), p38 (SB203580), and ERK (PD98059) for 1 h. The levels of soluble vascular cell adhesion molecule 1 (VCAM-1), soluble intercellular adhesion molecule 1 (sICAM-1), soluble E-selectin and monocyte chemoattractant protein 1 (MCP-1) in the supernatant were determined using ELISA, and their mRNA expressions, along with heme oxygenase-1 (HO-1), and NAD(P)H: quinone oxidoreductase 1 (NQO-1), were assessed using real-time PCR. ROS production in the cells was determined using 2, 7-dichlorofluoresce in diacetate (DCFH-DA) as the fluorescence probe. The protein expressions of VCAM-1, ICAM-1, p65, phospho-p65 (p-p65), IκBα, p-IκBα, ERK, p-ERK, p38, p-p38, JNK, and p-JNK were detected using Western blotting.

RESULTS

LPS stimulation for 6 and 24 h significantly increased the levels of sVCAM-1, sICAM-1, sE-selectin and MCP-1 in the supernatant, intracellular ROS production, and the mRNA expressions of these molecules (P<0.05). Intervention with 1 mmolγL agmatine, similar with pretreatment with p38, ERK and NF-κB inhibitors, obviously inhibited such effects of LPS in HUVECs (P<0.05). Agmatine significantly up-regulated the mRNA expression of HO-1 (P<0.05), inhibited LPS-induced phosphorylation of p38, ERK, nuclear p65 and cytoplasmic IκBα, and up-regulated the protein expression of cytoplasmic IκBα.

CONCLUSION

Agmatine inhibits LPS-induced activation and dysfunction of HUVECs by modulating NF-κB and MAPK signal pathways to down-regulate the expressions of adhesion molecules and chemokines and by up-regulating the expression of HO-1 to reduce ROS production.

[Exogenous agmatine inhibits lipopolysaccharide-induced activation and dysfunction of human umbilical vein endothelial cells]

OBJECTIVE

To investigate whether exogenous agmatine inhibits lipopolysaccharide (LPS)-induced activation and dysfunction of human umbilical vein endothelial cells (HUVECs) by modulating nuclear factor-κB (NF-κB) and MAPK signal pathways and the production of reactive oxygen species (ROS).

METHODS

Cultured HUVECs were treated with agmatine at the optimized concentration of 1.0 mmolγL, LPS (10 µgγmL), and LPS + agmatine, with or without pretreatment with the inhibitors of NF-κB (PDTC), p38 (SB203580), and ERK (PD98059) for 1 h. The levels of soluble vascular cell adhesion molecule 1 (VCAM-1), soluble intercellular adhesion molecule 1 (sICAM-1), soluble E-selectin and monocyte chemoattractant protein 1 (MCP-1) in the supernatant were determined using ELISA, and their mRNA expressions, along with heme oxygenase-1 (HO-1), and NAD(P)H: quinone oxidoreductase 1 (NQO-1), were assessed using real-time PCR. ROS production in the cells was determined using 2, 7-dichlorofluoresce in diacetate (DCFH-DA) as the fluorescence probe. The protein expressions of VCAM-1, ICAM-1, p65, phospho-p65 (p-p65), IκBα, p-IκBα, ERK, p-ERK, p38, p-p38, JNK, and p-JNK were detected using Western blotting.

RESULTS

LPS stimulation for 6 and 24 h significantly increased the levels of sVCAM-1, sICAM-1, sE-selectin and MCP-1 in the supernatant, intracellular ROS production, and the mRNA expressions of these molecules (P<0.05). Intervention with 1 mmolγL agmatine, similar with pretreatment with p38, ERK and NF-κB inhibitors, obviously inhibited such effects of LPS in HUVECs (P<0.05). Agmatine significantly up-regulated the mRNA expression of HO-1 (P<0.05), inhibited LPS-induced phosphorylation of p38, ERK, nuclear p65 and cytoplasmic IκBα, and up-regulated the protein expression of cytoplasmic IκBα.

CONCLUSION

Agmatine inhibits LPS-induced activation and dysfunction of HUVECs by modulating NF-κB and MAPK signal pathways to down-regulate the expressions of adhesion molecules and chemokines and by up-regulating the expression of HO-1 to reduce ROS production.

The inhibition of inducible nitric oxide synthase and oxidative stress by agmatine attenuates vascular dysfunction in rat acute endotoxemic model

Vascular dysfunction leading to hypotension is a major complication in patients with septic shock. Inducible nitric oxide synthase (iNOS) together with oxidative stress play an important role in development of vascular dysfunction in sepsis. Searching for an endogenous, safe and yet effective remedy was the chief goal for this study. The current study investigated the effect of agmatine (AGM), an endogenous metabolite of l-arginine, on sepsis-induced vascular dysfunction induced by lipopolysaccharides (LPS) in rats. AGM pretreatment (10mg/kg, i.v.) 1h before LPS (5mg/kg, i.v.) prevented the LPS-induced mortality and elevations in serum creatine kinase-MB isoenzyme (CK-MB) activity, lactate dehydrogenase (LDH) activity, C-reactive protein (CRP) level and total nitrite/nitrate (NOx) level after 24h from LPS injection. The elevation in aortic lipid peroxidation illustrated by increased malondialdehyde (MDA) content and the decrease in aortic glutathione (GSH) and superoxide dismutase (SOD) were also ameliorated by AGM. Additionally, AGM prevented LPS-induced elevation in mRNA expression of iNOS, while endothelial NOS (eNOS) mRNA was not affected. Furthermore AGM prevented the impaired aortic contraction to KCl and phenylephrine (PE) and endothelium-dependent relaxation to acetylcholine (ACh) without affecting endothelium-independent relaxation to sodium nitroprusside (SNP).

IN CONCLUSION

AGM may represent a potential endogenous therapeutic candidate for sepsis-induced vascular dysfunction through its inhibiting effect on iNOS expression and oxidative stress.

Anti-Atherosclerotic Action of Agmatine in ApoE-Knockout Mice

Atherosclerosis is an inflammatory disease in which dysfunction of mitochondria play an important role, and disorders of lipid management intensify this process. Agmatine, an endogenous polyamine formed by decarboxylation of arginine, exerts a protective effect on mitochondria and modulates fatty acid metabolism. We investigated the effect of exogenous agmatine on the development of atherosclerosis and changes in lipid profile in apolipoprotein E knockout (apoE-/-) mice. Agmatine caused an approximate 40% decrease of atherosclerotic lesions, as estimated by en face and cross-section methods with an influence on macrophage but not on smooth muscle content in the plaques. Agmatine treatment did not changed gelatinase activity within the plaque area. What is more, the action of agmatine was associated with an increase in the number of high density lipoproteins (HDL) in blood. Real-Time PCR analysis showed that agmatine modulates liver mRNA levels of many factors involved in oxidation of fatty acid and cholesterol biosynthesis. Two-dimensional electrophoresis coupled with mass spectrometry identified 27 differentially expressed mitochondrial proteins upon agmatine treatment in the liver of apoE-/- mice, mostly proteins related to metabolism and apoptosis. In conclusion, prolonged administration of agmatine inhibits atherosclerosis in apoE-/- mice; however, the exact mechanisms linking observed changes and elevations of HDL plasma require further investigation.

Agmatine attenuates chronic unpredictable mild stress-induced anxiety, depression-like behaviours and cognitive impairment by modulating nitrergic signalling pathway

Agmatine, a neurotransmitter/neuromodulator, has shown to exert numerous effects on the CNS. Chronic stress is a risk factor for development of depression, anxiety and deterioration of cognitive performance. Compelling evidences indicate an involvement of nitric oxide (NO) pathway in these disorders. Hence, investigation of the beneficial effects of agmatine on chronic unpredictable mild stress (CUMS)-induced depression, anxiety and cognitive performance with the involvement of nitrergic pathway was undertaken. Mice were subjected to a battery of stressors for 28days. Agmatine (20 and 40mg/kg, i.p.) alone and in combination with NO modulators like L-NAME (15mg/kg, i.p.) and l-arginine (400mg/kg i.p.) were administered daily. The results showed that 4-weeks CUMS produces significant depression and anxiety-like behaviour. Stressed mice have also shown a significant high serum corticosterone (CORT) and low BDNF level. Chronic treatment with agmatine produced significant antidepressant-like behaviour in forced swim test (FST) and sucrose preference test, whereas, anxiolytic-like behaviour in elevated plus maze (EPM) and open field test (OFT) with improved cognitive impairment in Morris water maze (MWM). Furthermore, agmatine administration reduced the levels of acetylcholinesterase and oxidative stress markers. In addition, agmatine treatment significantly increased the BDNF level and inhibited serum CORT level in stressed mice. Treatment with L-NAME (15mg/kg) potentiated the effect of agmatine whereas l-arginine abolished the anxiolytic, antidepressant and neuroprotective effects of agmatine. Agmatine showed marked effect on depression and anxiety-like behaviour in mice through nitrergic pathway, which may be related to modulation of oxidative-nitrergic stress, CORT and BDNF levels.

Agmatine modulates melanogenesis via MITF signaling pathway

Agmatine contained in soybean is also found in Manaca, an anti-aging plant, inhabited in Amazon and induces vasodilation by the promotion of NO synthesis in blood vessel. However, the research of agmatine on melanin synthesis related to hair greying is lacking. The aim of this study was to investigate the melanogenic effect of agmatine via regulation of MITF signaling pathway in B16F1 cells. It was determined whether agmatine regulates melanin synthesis at cellular level in addition to the effect of agmatine on mushroom tyrosinase in vitro in the presence of different concentrations of agmatine. Furthermore, the effect of agmatine on the protein expressions of tyrosinase, TRP-1, TRP-2, BMP-4, BMP-6, C-KIT, p-p38, MITF and C-FOS were examined by western blot analysis. In addition, immunofluorescence staining was carried out to visualize the location of MITF expression in cell. Agmatine at 256μM or more increased melanin synthesis as well as tyrosinase activity. Moreover, whereas agmatine increased the expression levels of TRP-1, BMP-6, p-p38 and MITF, it reduced the expression level of BMP-4. It was also found that agmatine enhanced the expression level of MITF in nucleus. These results suggest that agmatine could induce melanin synthesis though the regulation of MITF transcription factor via BMP-6/p38 signaling pathway.

Suppression of MicroRNA let-7a Expression by Agmatine Regulates Neural Stem Cell Differentiation

PURPOSE

Neural stem cells (NSCs) effectively reverse some severe central nervous system (CNS) disorders, due to their ability to differentiate into neurons. Agmatine, a biogenic amine, has cellular protective effects and contributes to cellular proliferation and differentiation in the CNS. Recent studies have elucidated the function of microRNA let-7a (let-7a) as a regulator of cell differentiation with roles in regulating genes associated with CNS neurogenesis.

MATERIALS AND METHODS

This study aimed to investigate whether agmatine modulates the expression of crucial regulators of NSC differentiation including DCX, TLX, c-Myc, and ERK by controlling let-7a expression.

RESULTS

Our data suggest that high levels of let-7a promoted the expression of TLX and c-Myc, as well as repressed DCX and ERK expression. In addition, agmatine attenuated expression of TLX and increased expression of ERK by negatively regulating let-7a.

CONCLUSION

Our study therefore enhances the present understanding of the therapeutic potential of NSCs in CNS disorders.

Interactions of nitric oxide with α2 -adrenoceptors within the locus coeruleus underlie the facilitation of inhibitory avoidance memory by agmatine

BACKGROUND AND PURPOSE

Agmatine, a putative neurotransmitter, plays a vital role in learning and memory. Although it is considered an endogenous ligand of imidazoline receptors, agmatine exhibits high affinity for α-adrenoceptors, NOS and NMDA receptors. These substrates within the locus coeruleus (LC) are critically involved in learning and memory processes.

EXPERIMENTAL APPROACH

The hippocampus and LC of male Wistar rat were stereotaxically cannulated for injection. Effects of agmatine, given i.p. or intra-LC, on acquisition, consolidation and retrieval of inhibitory avoidance (IA) memory were measured. The NO donor S-nitrosoglutathione, non-specific (L-NAME) and specific NOS inhibitors (L-NIL, 7-NI, L-NIO), the α2 -adrenoceptor antagonist (yohimbine) or the corresponding agonist (clonidine) were injected intra-LC before agmatine. Intra-hippocampal injections of the NMDA antagonist, MK-801 (dizocilpine), were used to modify the memory enhancing effects of agmatine, SNG and yohimbine. Expression of tyrosine hydroxylase (TH) and eNOS in the LC was assessed immunohistochemically.

KEY RESULTS

Agmatine (intra-LC or i.p.) facilitated memory retrieval in the IA test. S-nitrosoglutathione potentiated, while L-NAME and L-NIO decreased, these effects of agmatine. L-NIL and 7-NI did not alter the effects of agmatine. Yohimbine potentiated, whereas clonidine attenuated, effects of agmatine within the LC. The effects of agmatine, S-nitrosoglutathione and yohimbine were blocked by intra-hippocampal MK-801. Agmatine increased the population of TH- and eNOS-immunoreactive elements in the LC.

CONCLUSIONS AND IMPLICATIONS

The facilitation of memory retrieval in the IA test by agmatine is probably mediated by interactions between eNOS, NO and noradrenergic pathways in the LC.

[Not Available]

This study is an attempt to elucidate of agmatine effects upon leukocyte apoptosis in experimental diabetes mellitus (EDM). We demonstrated the increase in numbers of the leukocytes with both early and late signs of apoptosis at diabetes. Further changes in the morphofunctional state of the leukocytes include the increased amount of fragmented DNA, elevated apoptotic index and violated ratio of p53 to Bcl-2 proteins. Agmatine has been shown to exert direct corrective effects on leukocyte apoptosis: the content of р53 and Bcl-2 proteins was normalized, apoptotic index was decreased, the process of nuclear DNA degradation was ceased, while the amount of cells with early and late signs of apoptosis was diminished.

Agmatine suppresses peripheral sympathetic tone by inhibiting N-type Ca(2+) channel activity via imidazoline I2 receptor activation

Agmatine, a putative endogenous ligand of imidazoline receptors, suppresses cardiovascular function by inhibiting peripheral sympathetic tone. However, the molecular identity of imidazoline receptor subtypes and its cellular mechanism underlying the agmatine-induced sympathetic suppression remains unknown. Meanwhile, N-type Ca(2+) channels are important for the regulation of NA release in the peripheral sympathetic nervous system. Therefore, it is possible that agmatine suppresses NA release in peripheral sympathetic nerve terminals by inhibiting Ca(2+) influx through N-type Ca(2+) channels. We tested this hypothesis by investigating agmatine effect on electrical field stimulation (EFS)-evoked contraction and NA release in endothelium-denuded rat superior mesenteric arterial strips. We also investigated the effect of agmatine on the N-type Ca(2+) current in superior cervical ganglion (SCG) neurons in rats. Our study demonstrates that agmatine suppresses peripheral sympathetic outflow via the imidazoline I2 receptor in rat mesenteric arteries. In addition, the agmatine-induced suppression of peripheral vascular sympathetic tone is mediated by modulating voltage-dependent N-type Ca(2+) channels in sympathetic nerve terminals. These results suggest a potential cellular mechanism for the agmatine-induced suppression of peripheral sympathetic tone. Furthermore, they provide basic and theoretical information regarding the development of new agents to treat hypertension.

Agmatine produces antidepressant-like effects by activating AMPA receptors and mTOR signaling

The activation of AMPA receptors and mTOR signaling has been reported as mechanisms underlying the antidepressant effects of fast-acting agents, specially the NMDA receptor antagonist ketamine. In the present study, oral administration of agmatine (0.1mg/kg), a neuromodulator that has been reported to modulate NMDA receptors, caused a significant reduction in the immobility time of mice submitted to the tail suspension test (TST), an effect prevented by the administration of DNQX (AMPA receptor antagonist, 2.5μg/site, i.c.v.), BDNF antibody (1μg/site, i.c.v.), K-252a (TrkB receptor antagonist, 1μg/site, i.c.v.), LY294002 (PI3K inhibitor, 10nmol/site, i.c.v.) or rapamycin (selective mTOR inhibitor, 0.2nmol/site, i.c.v.). Moreover, the administration of lithium chloride (non-selective GSK-3β inhibitor, 10mg/kg, p.o.) or AR-A014418 (selective GSK-3β inhibitor, 0.01μg/site, i.c.v.) in combination with a sub-effective dose of agmatine (0.0001mg/kg, p.o.) reduced the immobility time in the TST when compared with either drug alone. Furthermore, increased immunocontents of BDNF, PSD-95 and GluA1 were found in the prefrontal cortex of mice just 1h after agmatine administration. These results indicate that the antidepressant-like effect of agmatine in the TST may be dependent on the activation of AMPA and TrkB receptors, PI3K and mTOR signaling as well as inhibition of GSK-3β, and increase in synaptic proteins. The results contribute to elucidate the complex signaling pathways involved in the antidepressant effect of agmatine and reinforce the pivotal role of these molecular targets for antidepressant responses.

[The effects of agmatine on acute peritoneal inflammatory injury and neutrophil infiltration induced by zymosan in mice]

OBJECTIVE

To investigate the protective effect of agmatine (AGM) against peritoneal inflammatory response and neutrophil (PMN) infiltration induced by zymosan (ZYM) in mice.

METHODS

Thirty-six adult male C57BL/6 mice were randomly divided into sham group, model group, and AGM treatment group. Peritonitis model was reproduced by intra-peritoneal injection of 1 mg/mL ZYM (0.5 mL), while equivalent phosphate buffer saline (PBS) was given to sham group. 200 mg/kg AGM was injected into peritoneal cavity after ZYM challenge in AGM treatment group. Six mice in each group were sacrificed at 2 hours and 6 hours, respectively, after reproduction of the model. Blood sample and peritoneal lavage fluid (PLF) were collected. The levels of keratinocyte-derived chemokine (KC), macrophage inflammatory protein 2 (MIP-2), tumor necrosis factor-α (TNF-α), interleukins-6 (IL-6) in serum and PLF were determined by enzyme linked immunosorbent assay (ELISA). The number of leukocytes and PMN in PLF were determined by hemocytometer and flow cytometry, respectively.

RESULTS

Compared with sham group, all serum and PLF levels of KC, MIP-2, TNF-α and IL-6 were greatly elevated at 2 hours after ZYM injection in model group, while AGM treatment could dramatically reduce the levels of the above-mentioned cytokines in serum and PLF as compared with those of the model group [serum KC (ng/L): 990.7±137.9 vs. 2 053.2±262.7, MIP-2 (ng/L): 642.2±124.4 vs. 1 369.7±146.5, TNF-α (ng/L): 608.6±38.1 vs. 1 044.7±101.0, IL-6 (ng/L): 1 058.2±129.1 vs. 1 443.3±190.1; PLF KC (ng/L): 7 462.3±839.6 vs. 12 723.5±1 515.7, MIP-2 (ng/L): 1 570.8±193.4 vs. 3 471.4±384.7, TNF-α (ng/L): 1 115.8±156.7 vs. 1 499.2±231.2, IL-6 (ng/L): 2 646.5±223.2 vs. 3 126.7±291.4; all P < 0.05]. The expressions of KC, MIP-2 and TNF-α at 6 hours were significantly lower than those at 2 hours in model group and AGM treatment group, but IL-6 levels were further increased. The levels of KC and MIP-2 in serum and PLF at 6 hours were decreased to the levels of sham group. At 6 hours after the reproduction of the model, the number of total inflammatory cells and PMN of PLF in the model group was significantly higher than those of the sham group. In contrast, AGM notably lowered the number of inflammatory cells and PMN in peritoneal fluid after ZYM attack [total inflammatory cells (×109/L): 14.7±1.1 vs. 2.0±0.4, 10.1±1.2 vs. 14.7±1.1; PMN (×109/L): 11.37±1.22 vs. 0.18±0.05, 7.69±0.57 vs. 11.37±1.22, all P < 0.05].

CONCLUSION

AGM can effectively alleviate acute peritoneal inflammatory injury induced by ZYM, mainly through reducing the secretion of inflammatory mediators and chemokines, and inhibiting the infiltration of leukocytes and neutrophils.

The effect of amixin and agmatine on cytochrome C release from isolated mitochondria

Mitochondrial nicotinic acetylcholine receptors (nAChRs) control permeability transition pore formation and cytochrome c release in the presence of apoptogenic factors. This study demonstrates that pharmacological agents amixin and agmatine affect mitochondrial nAChR functioning: they slightly suppress cytochrome c release from mouse brain and liver mitochondria stimulated with apoptogenic dose of Са2+ and prevent the effect of α7 nAChR agonist PNU282987. We conclude that mitochondria may be one of therapeutic targets of amixin and agmatine.

Poly(Amido Amine)s Containing Agmatine and Butanol Side Chains as Efficient Gene Carriers

A new type of bioreducible poly(amido amine) copolymer is synthesized by the Michael addition polymerization of cystamine bisacrylamide (CBA) with 4-aminobutylguanidine (agmatine, AGM) and 4-aminobutanol (ABOL). Since the positively charged guanidinium groups of AGM and the hydroxybutyl groups of ABOL in the side chains have shown to improve the overall transfection efficiency of poly(amido amine)s, it is hypothesized that poly(CBA-ABOL/AGM) synthesized at the optimal ratio of both components would result in high transfection efficiency and minimal toxicity. In this study, a series of the poly(CBA-ABOL/AGM) copolymers is synthesized as gene carriers. The polymers are characterized and luciferase transfection efficiencies of the polymers in various cell lines are investigated to select the ideal ratio between AGM and ABOL. The poly(CBA-ABOL/AGM) containing 80% AGM and 20% ABOL has shown the best transfection efficiency with the lowest cytotoxicity, indicating that this polymer is very promising as a potent and nontoxic gene carrier.

Effect of agmatine on experimental vascular endothelial dysfunction

This study was designed to investigate the effect of agmatine sulfate (AG, CAS2482-00-0) in nicotine (NIC)-induced vascular endothelial dysfunction (VED) in rabbits. NIC was administered to produce VED in rabbits with or without AG for 6 weeks. Serum lipid profile, serum thiobarbituric acid reactive substances, reduced glutathione, superoxide dismutase generation, serum nitrite/nitrate, serum vascular cellular adhesion molecule-1 (VCAM-1), and aortic nuclear factor κB (NF-κB) levels were analyzed.Treatment with AG markedly improves lipid profile and prevented NIC-induced VED and oxidative stress. The mechanism of AG in improving NIC-induced VED may be due to the significant reduction in serum VCAM-1 levels and aortic NF-κB. Thus, it may be concluded that AG reduces the oxidative stress, nitric oxide production, VCAM-1 levels, and aortic NF-κB expression, thereby consequently improving the integrity of vascular endothelium.

Sub-chronic agmatine treatment modulates hippocampal neuroplasticity and cell survival signaling pathways in mice

Agmatine is an endogenous neuromodulator which, based on animal and human studies, is a putative novel antidepressant drug. In this study, we investigated the ability of sub-chronic (21 days) p.o. agmatine administration to produce an antidepressant-like effect in the tail suspension test and examined the hippocampal cell signaling pathways implicated in such an effect. Agmatine at doses of 0.01 and 0.1 mg/kg (p.o.) produced a significant antidepressant-like effect in the tail suspension test and no effect in the open-field test. Additionally, agmatine (0.001-0.1 mg/kg, p.o.) increased the phosphorylation of protein kinase A substrates (237-258% of control), protein kinase B/Akt (Ser(473)) (116-127% of control), glycogen synthase kinase-3β (Ser(9)) (110-113% of control), extracellular signal-regulated kinases 1/2 (119-137% and 121-138% of control, respectively) and cAMP response elements (Ser(133)) (127-152% of control), and brain-derived-neurotrophic factor (137-175% of control) immunocontent in a dose-dependent manner in the hippocampus. Agmatine (0.001-0.1 mg/kg, p.o.) also reduced the c-jun N-terminal kinase 1/2 phosphorylation (77-71% and 65-51% of control, respectively). Neither protein kinase C nor p38(MAPK) phosphorylation was altered under any experimental conditions. Taken together, the present study extends the available data on the mechanisms that underlie the antidepressant action of agmatine by showing an antidepressant-like effect following sub-chronic administration. In addition, our results are the first to demonstrate the ability of agmatine to elicit the activation of cellular signaling pathways associated with neuroplasticity/cell survival and the inhibition of signaling pathways associated with cell death in the hippocampus.

Agmatine induces Nrf2 and protects against corticosterone effects in hippocampal neuronal cell line

Hyperactivation of the hypothalamic-pituitary-adrenal axis is a common finding in major depression; this may lead to increased levels of cortisol, which are known to cause oxidative stress imbalance and apoptotic neuronal cell death, particularly in the hippocampus, a key region implicated in mood regulation. Agmatine, an endogenous metabolite of L-arginine, has been proposed for the treatment of major depression. Corticosterone induced apoptotic cell death and increased ROS production in cultured hippocampal neuronal cells, effects that were abolished in a concentration- and time-dependent manner by agmatine. Interestingly, the combination of sub-effective concentrations of agmatine with fluoxetine or imipramine afforded synergic protection. The neuroprotective effect of agmatine was abolished by yohimbine (α2-adrenoceptor antagonist), ketanserin (5-HT2A receptor antagonist), LY294002 (PI3K inhibitor), PD98059 (MEK1/2 inhibitor), SnPP (HO-1 inhibitor), and cycloheximide (protein synthesis inhibitor). Agmatine increased Akt and ERK phosphorylation and induced the transcription factor Nrf2 and the proteins HO-1 and GCLc; induction of these proteins was prevented by yohimbine, ketanserin, LY294002, and PD98059. In conclusion, agmatine affords neuroprotection against corticosterone effects by a mechanism that implicates Nrf2 induction via α2-adrenergic and 5-HT2A receptors, Akt and ERK pathways, and HO-1 and GCLc expression.

Effects of agmatine and resveratrol on RGC-5 cell behavior under light stimulation

A light radiation causes dysfunction and death of retinal cells and leads to degeneration. Present study, investigated the light-induced cell dysfunction, and their activity. Further, the effects of agmatine and resveratrol on light-induced damage and these underlying photo-oxidative and protective mechanisms were monitored by real-time bio-impedance system. After light exposure retinal ganglion cells underwent death in a time dependent manner. During light exposure the cells elevate free radicals and Ca(2+), followed by nitric oxide (NO) and tumor necrosis factor-α (TNF-α), which can be facilitated to cell demise. The results revealed that these drugs can control the elevation of free radical, calcium gating, NO level, and increased TNF-α, which could diminish cell photo-damage. In summary, resveratrol helps more to rescue damaged cells compared to agmatine. The proposed system suggested mechanism could meet to identify the photo-toxic effects in retinal cells, and provides high throughput screening for early stages photo-damage.

[Protective effects of agmatine on lipopolysaccharide -induced acute hepatic injury in mice]

OBJECTIVE

To observe the effect of agmatine ( AGM) on lipopolysaccharide ( LPS )-induced acute hepatic injury in mice, and to explore its related mechanism.

METHODS

Sixty C57BU6 mice were randomly divided into control group ( n = 20, with intra-peritoneal injection of phosphate buffer saline 10 mg/kg), model group ( n = 20, with intra-peritoneal injection of LPS 10 mg/kg), and AGM group (n=20, with intra-peritoneal injection of LPS 10 mg/kg and AGM 200 mg/kg). Ten mice in each group were sacrificed at 6 hours and 24 hours, respectively, after modeling, blood samples were collected for the determination of tumor necrosis factor-a ( TNF -a) and interleukin ( IL-113 and IL-6) by enzyme linked immunosorbent assay (ELISA) at 6 hours after modeling , and for determination of alanine aminotransferase (ALT), aspartate transaminase (AST) and total bilirubin (TBil) by automatic biochemistry analyzer at 24 hours after modeling. Hepatic homogenate was also collected for determining the endo nuclear nuclear factor-KB ( NF -KB) p65 by Western blotting at 6 hours after modeling, and for observation of pathological changes at 24 hours after modeling.

RESULTS

At 6 hours after modeling, .the mice in model group became lethargic and quiet, and their food and water assumption was reduced, but AGM was found to be able to greatly improve the general status of animals in AGM group. AGM was found to lower the contents of serum TNF-a ( IJ.g/L: 296.3 ± 42.5 vs. 627.2 ± 81.3, t=7.327, P=0.002), IL-113 ( f.Lg/L: 109.1 ± 12.3 vs. 264.2 ± 18.8, t= 11.958, P=0.001), IL-6 ( mg/L: 11.4 ± 1.9 vs. 23.6 ± 2.5, t=6.729, P=0.003), ALT (U!L: 107.9 ± 8.5 vs. 189.9 ± 13.6, t=8.856, P=0.001 ), AST (UIL: 347.4 ± 24.9 vs. 716.8 ± 60.4, t=9.793, P=0.001) and TBil ( f.Lmol!L: 8.3 ± 0.9 vs. 10.6 ± 0.5, t=3.869, P=0.018) in mice with acute hepatic injury induced by LPS. AGM also depressed TNF -a ( ng/g: 287.4 ± 32.5 vs. 461.5 ± 31.4, t=6.673, P= 0.003), IL-113 (pg/g: 146.7 ± 13.5 vs. 351.6 ± 28.7, t=11.190, P=0.001) and intranuclear NF-KB p65 level (NF-KBp65/TBP: 0.515 ± 0.060 vs. 0.853 ± 0.080, t=5.849, P=0.004) in liver tissue. Histological examination demonstrated that AGM significantly reduced liver injury caused by LPS, as manifested in amelioration of hepatocytes swelling, necrosis and neutrophil infiltration.

CONCLUSION

Agmatine can reduce LPS-induced acute hepatic injury in mice via suppressing NF-κB translocation and reduction of the synthesis and release of cytokines.

Possible involvement of neuropeptide Y Y1 receptors in antidepressant like effect of agmatine in rats

Agmatine and neuropeptide Y (NPY) are widely distributed in central nervous system and critically involved in modulation of depressive behavior in experimental animals. However their mutual interaction, if any, in regulation of depression remain largely unexplored. In the present study we explored the possible interaction between agmatine and neuropeptide Y in regulation of depression like behavior in forced swim test. We found that acute intracerebroventricular (i.c.v.) administration of agmatine (20-40μg/rat), NPY (5 and 10μg/rat) and NPY Y1 receptor agonist, [Leu(31), Pro(34)]-NPY (0.4 and 0.8ng/rat) dose dependently decreased immobility time in forced swim test indicating their antidepressant like effects. In combination studies, the antidepressant like effect of agmatine (10μg/rat) was significantly potentiated by NPY (1 and 5μg/rat, icv) or [Leu(31), Pro(34)]-NPY (0.2 and 0.4ng/rat, icv) pretreatment. Conversely, pretreatment of animals with NPY Y1 receptor antagonist, BIBP3226 (0.1ng/rat, i.c.v.) completely blocked the antidepressant like effect of agmatine (20-40μg/rat) and its synergistic effect with NPY (1μg/rat, icv) or [Leu(31), Pro(34)]-NPY (0.2ng/rat, icv). The results of the present study showed that, agmatine exerts antidepressant like effects via NPYergic system possibly mediated by the NPY Y1 receptor subtypes and suggest that interaction between agmatine and neuropeptide Y may be relevant to generate the therapeutic strategies for the treatment of depression.

Agmatine induced NO dependent rat mesenteric artery relaxation and its impairment in salt-sensitive hypertension

l-Arginine and its decarboxylated product, agmatine are important mediators of NO production and vascular relaxation. However, the underlying mechanisms of their action are not understood. We have investigated the role of arginine and agmatine in resistance vessel relaxation of Sprague-Dawley (SD) and Dahl salt-sensitive hypertensive rats. Second or 3rd-order mesenteric arterioles were cannulated in an organ chamber, pressurized and equilibrated before perfusing intraluminally with agonists. The vessel diameters were measured after mounting on the stage of a microscope fitted with a video camera. The gene expression in Dahl rat vessel homogenates was ascertained by real-time PCR. l-Arginine initiated relaxations (EC50, 5.8±0.7mM; n=9) were inhibited by arginine decarboxylase (ADC) inhibitor, difluoromethylarginine (DFMA) (EC50, 18.3±1.3mM; n=5) suggesting that arginine-induced vessel relaxation was mediated by agmatine formation. Agmatine relaxed the SD rat vessels at significantly lower concentrations (EC50, 138.7±12.1μM; n=22), which was compromised by l-NAME (l-N(G)-nitroarginine methyl ester, an eNOS inhibitor), RX821002 (α-2 AR antagonist) and pertussis toxin (G-protein inhibitor). The agmatine-mediated vessel relaxation from high salt Dahl rats was abolished as compared to that from normal salt rats (EC50, 143.9±23.4μM; n=5). The α-2A AR, α-2B AR and eNOS mRNA expression was downregulated in mesenteric arterioles of high-salt treated Dahl hypertensive rats. These findings demonstrate that agmatine facilitated the relaxation via activation of α-2 adrenergic G-protein coupled receptor and NO synthesis, and this pathway is compromised in salt-sensitive hypertension.