Safety and neurochemical profiles of acute and sub-chronic oral treatment with agmatine sulfate

Evidence for safety of the dietary ingredient agmatine sulfate as assessed by mutagenicity and genotoxicity studies

Agmatine, 1-Amino-4-guanidinobutane, is a ubiquitous naturally occurring molecule present in low amounts in a wide variety of foodstuff. Clinical trials have demonstrated the safety of oral agmatine sulfate and have led to its development as an effective dietary ingredient for promoting resilient nerve functions. Although clearly required, the mutagenic and genotoxic effects of agmatine have not been previously reported. The present study, therefore, undertook to assess the safety profile of agmatine using currently accepted in vitro and in vivo mutagenicity and genotoxicity tests. The test item was G-Agmatine®, a proprietary brand of agmatine sulfate. Using the bacterial reverse mutation assay (Ames test), the study found that G-Agmatine® has no mutagenic effects. It had no clastogenic effects as observed by the in vitro chromosomal aberration test using Chinese Hamster lung cells. And it lacked genotoxic effects as evidenced by the lack of increased frequency of micronucleated polychromatic immature erythrocytes following oral administration in the mouse micronucleus test. Taken together with previously published data, results of the present study further support the safety of agmatine sulfate as a dietary ingredient.

Pharmacological profile of agmatine: An in-depth overview

Agmatine, a naturally occurring polyamine derived from arginine via arginine decarboxylase, has been shown to play multifaceted roles in the mammalian body, impacting a wide range of physiological and pathological processes. This comprehensive review delineates the significant insights into agmatine's pharmacological profile, emphasizing its structure and metabolism, neurotransmission and regulation, and pharmacokinetics and function. Agmatine's biosynthesis is highly conserved across species, highlighting its fundamental role in cellular functions. In the brain, comparable to established neurotransmitters, agmatine acts as a neuromodulator, influencing the regulation, metabolism, and reabsorption of neurotransmitters that are key to mood disorders, learning, cognition, and the management of anxiety and depression. Beyond its neuromodulatory functions, agmatine exhibits protective effects across various cellular and systemic contexts, including neuroprotection, nephroprotection, cardioprotection, and cytoprotection, suggesting a broad therapeutic potential. The review explores agmatine's interaction with multiple receptor systems, including NMDA, α2-adrenoceptors, and imidazoline receptors, elucidating its role in enhancing cell viability, neuronal protection, and synaptic plasticity. Such interactions underpin agmatine's potential in treating neurological diseases and mood disorders, among other conditions. Furthermore, agmatine's pharmacokinetics, including its absorption, distribution, metabolism, and excretion, are discussed, underlining the complexity of its action and the potential for therapeutic application. The safety and efficacy of agmatine supplementation, demonstrated through various animal and human studies, affirm its potential as a beneficial therapeutic agent. Conclusively, the diverse physiological and therapeutic effects of agmatine, spanning neurotransmission, protection against cellular damage, and modulation of various receptor pathways, position it as a promising candidate for further research and clinical application. This review underscores the imperative for continued exploration into agmatine's mechanisms of action and its potential in pharmacology and medicine, promising advances in the treatment of numerous conditions.

Agmatine mitigates behavioral abnormalities and neurochemical dysregulation associated with 3-Nitropropionic acid-induced Huntington's disease in rats

Huntington's disease (HD) is a progressive neurodegenerative condition characterized by a severe motor incoordination, cognitive decline, and psychiatric complications. However, a definitive cure for this devastating disorder remains elusive. Agmatine, a biogenic amine, has gain attention for its reported neuromodulatory and neuroprotective properties. The present study was designed to examine the influence of agmatine on the behavioral, biochemical, and molecular aspects of HD in an animal model. A mitochondrial toxin, 3-nitro propionic acid (3-NP), was used to induce HD phenotype and similar symptoms such as motor incoordination, memory impairment, neuro-inflammation, and depressive-like behavior in rats. Rats were pre-treated with 3-NP (10 mg/kg, i.p.) on days 1, 3, 5, 7, and 9 and then continued on agmatine treatment (5 - 20 µg/rat, i.c.v.) from day-8 to day-27 of the treatment protocol. 3-NP-induced cognitive impairment was associated with declined in agmatine levels within prefrontal cortex, striatum, and hippocampus. Further, the 3-NP-treated rats showed an increase in IL-6 and TNF-α and a reduction in BDNF immunocontent within these brain areas. Agmatine treatment not only improved the 3-NP-induced motor incoordination, depression-like behavior, rota-rod performance, and learning and memory impairment but also normalized the GABA/glutamate, BDNF, IL-6, and TNF-α levels in discrete brain areas. Similarly, various agmatine modulators, which increase the endogenous agmatine levels in the brain, such as L-arginine (biosynthetic precursor), aminoguanidine (diamine oxidase inhibitor), and arcaine (agmatinase inhibitor) also demonstrated similar effects exhibiting the importance of endogenous agmatinergic pathway in the pathogenesis of 3-NP-induced HD like symptoms. The present study proposed the possible role of agmatine in the pathogenesis and treatment of HD associated motor incoordination, and psychiatric and cognitive complications.

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.

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.

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.

Agmatine prevents the manifestation of impulsive burying and depression-like behaviour in progesterone withdrawn female rats

Premenstrual dysphoric disorder (PMDD) is characterized by various physical and affective symptoms, including anxiety, irritability, anhedonia, social withdrawal, and depression. The present study investigated the role of the agmatinergic system in animal model of progesterone withdrawal in female rats. Chronic progesterone exposure of female rats for 21 days and its abrupt withdrawal showed enhanced marble burying, increased immobility time, and reduced no. of entries in open arm as compared to control animals. The progesterone withdrawal-induced enhanced marble burying anxiety and immobility time was significantly attenuated by agmatine (5-20 mg/kg, i.p.), and its endogenous modulators like L-arginine (100 mg/kg, i.p.), amino-guanidine (25 mg/kg, i.p.) and arcaine (50 mg/kg, i.p.) by their once-daily administration from day 14-day 21 of the protocol. We have also analysed the levels of agmatine, progesterone, and inflammatory cytokines in the hippocampal region of progesterone withdrawn rats. There was a significant decline in agmatine and progesterone levels and an elevation in cytokine levels in the hippocampal region of progesterone withdrawn rats compared to the control animals. In conclusion, the present studies suggest the importance of the endogenous agmatinergic system in progesterone withdrawal-induced anxiety-like and depression-like behaviour. The data also projects agmatine as a potential therapeutic target for the premenstrual dysphoric disorder.

Agmatine Administration Effects on Equine Gastric Ulceration and Lameness

Osteoarthritis (OA) accounts for up to 60% of equine lameness. Agmatine, a decarboxylated arginine, may be a viable option for OA management, based on reports of its analgesic properties. Six adult thoroughbred horses, with lameness attributable to thoracic limb OA, received either daily oral phenylbutazone (6.6 mg/kg), agmatine sulfate (25 mg/kg) or a control for 30 days, with 21-day washout periods between treatments. Subjective lameness, thoracic limb ground reaction forces (GRF), plasma agmatine and agmatine metabolite levels were evaluated using an established rubric, a force platform, and mass spectrometry, respectively, before, during and after each treatment period. Gastric ulceration and plasma chemistries were evaluated before and after treatments. Braking GRFs were greater after 14 and 29 days of agmatine compared to phenylbutazone administration. After 14 days of phenylbutazone administration, vertical GRFs were greater than for agmatine or the control. Glandular mucosal ulcer scores were lower after agmatine than phenylbutazone administration. Agmatine plasma levels peaked between 30 and 60 min and were largely undetectable by 24 h after oral administration. In contrast, plasma citric acid levels increased throughout agmatine administration, representing a shift in the metabolomic profile. Agmatine may be a viable option to improve thoracic limb GRFs while reducing the risk of glandular gastric ulceration in horses with OA.

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.

Partial Endothelial Nitric Oxide Synthase Deficiency Exacerbates Cognitive Deficit and Amyloid Pathology in the APPswe/PS1ΔE9 Mouse Model of Alzheimer’s Disease

Increasing evidence implicates endothelial dysfunction in the pathogenesis of Alzheimer’s disease (AD). Nitric oxide (NO) derived from endothelial NO synthase (eNOS) is essential in maintaining cerebrovascular function and can modulate the production and clearance of amyloid beta (Aβ). APPswe/PSdE1 (APP/PS1) mice display age-related Aβ accumulation and memory deficits. In order to make the model more clinically relevant with an element of endothelial dysfunction, we generated APP/PS1/eNOS+/− mice by crossing complete eNOS deficient (eNOS−/−) mice and APP/PS1 mice. APP/PS1/eNOS+/− mice at 8 months of age displayed a more severe spatial working memory deficit relative to age-matched APP/PS1 mice. Moreover, immunohistochemistry and immunoblotting revealed significantly increased Aβ plaque load in the brains of APP/PS1/eNOS+/− mice, concomitant with upregulated BACE-1 (hence increased Aβ production), downregulated insulin-degrading enzyme (hence reduced Aβ clearance) and increased immunoreactivity and expression of microglia. The present study, for the first time, demonstrated that partial eNOS deficiency exacerbated behavioral dysfunction, Aβ brain deposition, and microglial pathology in APP/PS1 mice, further implicating endothelial dysfunction in the pathogenesis of AD. The present findings also provide the scientific basis for developing preventive and/or therapeutic strategies by targeting endothelial dysfunction.

The memory modulatory effect of agmatine in passive avoidance task coincides with alterations of hippocampal CaMKII-α and ERK signaling in mice

Agmatine is a polyamine suggested to act as a supposed neurotransmitter in the brain. Evidence has indicated that acute agmatine administration might modulate memory. The present study aimed to investigate the effect of repeated agmatine treatment on passive avoidance memory, hippocampal calcium-calmodulin-dependent protein kinase II-alpha (CaMKII-α), and Extracellular Signal-Regulated Kinase (ERK) signaling pathways in naive mice. Adult male NMRI mice were treated with agmatine (10, 20, 30, 40, and 80 mg/kg/ip) or saline for 11 days. Acquisition and retention tests of passive avoidance memory were performed on days 10 and 11, respectively. Following the memory retention test, the hippocampi were assessed for the levels of CaMKII-α and ERK using the western blotting technique. The results revealed the dose-dependent effect of agmatine on the passive avoidance memory. Accordingly, the memory was impaired in lower doses, but was improved in higher ones. Agmatine in none of the doses affected the nociception of the mice in tail-flick test. Furthermore, agmatine increased the phosphorylation of CaMKII-α and ERK in the hippocampus at memory enhancing doses, while ERK phosphorylation decreased following the impairing doses of agmatine. Thus, the dose-dependent effect of agmatine on memory might be related to its modulatory effect on CaMKII-α and ERK signal transduction, eventually regulating the memory process.

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.

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.

Effects of sex and estrous cycle on the brain and plasma arginine metabolic profile in rats

L-arginine is a versatile amino acid with a number of bioactive metabolites. Increasing evidence implicates altered arginine metabolism in the aging and neurodegenerative processes. The present study, for the first time, determined the effects of sex and estrous cycle on the brain and blood (plasma) arginine metabolic profile in naïve rats. Female rats displayed significantly lower levels of L-arginine in the frontal cortex and three sub-regions of the hippocampus when compared to male rats. Moreover, female rats had significantly higher levels of L-arginine and γ-aminobutyric acid, but lower levels of L-ornithine, agmatine and putrescine, in plasma relative to male rats. The observed sex difference in brain L-arginine appeared to be independent of the enzymes involved in its metabolism, de novo synthesis and blood-to-brain transport (cationic acid transporter 1 protein expression at least), as well as circulating L-arginine. While the estrous cycle did not affect L-arginine and its metabolites in the brain, there were estrous cycle phase-dependent changes in plasma L-arginine. These findings demonstrate the sex difference in brain L-arginine in the estrous cycle-independent manner. Since peripheral blood has been increasingly used to identify biomarkers of brain pathology, the influences of sex and estrous cycle on blood arginine metabolic profile need attention when experimental research involves female rodents.

Agmatine ameliorates manifestation of depression-like behavior and hippocampal neuroinflammation in mouse model of Alzheimer's disease

Extensive clinical and experimental studies established that depression and mood disorders are highly prevalent neuropsychiatric conditions in Alzheimer's disease (AD). However, its neurochemical basis is not clearly understood. Thus, understanding the neural mechanisms involved in mediating the co-morbidity of depression and AD may be crucial in exploring new pharmacological treatments for this condition. The present study investigated the role of the agmatinergic system in β-amyloid (Aβ_β1-42) peptide-induced depression using forced swim test (FST) in mice. Following the 28th days of its administration, Aβ_1-42 peptide produced depression-like behavior in mice as evidenced by increased immobility time in FST and increased expression of pro-inflammatory cytokines like IL-6 and TNF-α compared to the control animals. The Aβ_1-42 peptide-induced depression and neuroinflammatory markers were significantly inhibited by agmatine -, moxonidine, 2-BFI and l-arginine by once-daily administration during day 8-27 of the protocol. The antidepressant-like effect of agmatine in Aβ_1-42 peptide in mice was potentiated by imidazoline receptor I₁ agonist, moxonidine and imidazoline receptor I₂ agonist 2-BFI at their sub-effective doses. On the other hand, it was completely blocked by imidazoline receptor I₁ antagonist, efaroxan and imidazoline receptor I₂ antagonist, idazoxan Also, agmatine levels were significantly reduced in brain samples of β-amyloid injected mice as compared to the control animals. In conclusion, the present study suggests the importance of endogenous agmatinergic system and imidazoline receptors system in β-amyloid induced a depressive-like behavior in mice. The data projects agmatine as a potential therapeutic target for the AD-associated depression and comorbidities.