Agmatine, a potential novel therapeutic strategy for depression

Agmatine modulation of gut-brain axis alleviates dysbiosis-induced depression-like behavior in rats

Depression is a global health concern affecting nearly 280 million individuals. It not only imposes a significant burden on economies and healthcare systems but also manifests complex physiological connections and consequences. Agmatine, a putative neuromodulator derived primarily from beneficial gut microbes specially Lactobacillus, has emerged as a potential therapeutic agent for mental health. The microbiota-gut-brain axis is involved in the development of depression through the peripheral nervous system, endocrine system, and immune system and may be a key factor in the effect of agmatine. Therefore, this study aimed to investigate the potential mechanism of agmatine in antibiotic-induced dysbiosis and depression-like behavior in rats, focusing on its modulation of the gut-brain axis. Depression-like behavior associated with dysbiosis was induced through a seven-day regimen of the broad-spectrum antibiotic, comprising ampicillin and metronidazole and validated through microbial, biochemical, and behavioral alterations. On day 8, antibiotic-treated rats exhibited loose fecal consistency, altered fecal microbiota, and depression-like behavior in forced swim test. Pro-inflammatory cytokines were elevated, while agmatine and monoamine levels decreased in the hippocampus and prefrontal cortex. Antibiotic administration disrupted tight junction proteins in the ileum, affecting gut architecture. Oral administration of agmatine alone or combined with probiotics significantly reversed antibiotic-induced dysbiosis, restoring gut microbiota and mitigating depression-like behaviors. This intervention also restored neuro-inflammatory markers, increased agmatine and monoamine levels, and preserved gut integrity. The study highlights the regulatory role of endogenous agmatine in the gut-brain axis in broad-spectrum antibiotic induced dysbiosis and associated depression-like behavior.

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.

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.

Cytoprotective effects of Hangekobokuto against corticosterone-induced cell death in HT22 cells

The hypothalamic-pituitary-adrenal (HPA) system plays an important role in stress response. Chronic stress is thought to induce neuronal damage and contribute to the pathogenesis of psychiatric disorders by causing dysfunction of the HPA system and promoting the production and release of glucocorticoids, including corticosterone and cortisol. Several clinical studies have demonstrated the efficacy of herbal medicines in treating psychiatric disorders; however, their effects on corticosterone-induced neuronal cell death remain unclear. Here, we used HT22 cells to evaluate the neuroprotective potential of herbal medicines used in neuropsychiatry against corticosterone-induced hippocampal neuronal cell death. Cell death was assessed using 3-[4,5-dimethylthiazol-2-yl]-2,5 diphenyl tetrazolium bromide (MTT) reduction and Live/Dead assays. Hangekobokuto, Kamikihito, Saikokaryukotsuboreito, Kamishoyosan, and Yokukansan were supplied in the form of water-extracted dried powders. Exposure of HT22 cells to ≥ 100 μM corticosterone decreased MTT values. Exposure to 500 μM corticosterone alone reduced MTT values to 18%, while exposure to 10 μM Mifepristone (RU486)-a glucocorticoid receptor antagonist-restored values to 36%. Corticosterone-induced cell death was partially suppressed by treatment with RU486. At 100 μg/mL, Hangekobokuto significantly suppressed the decrease in MTT values (15-32%) and increase in the percentage of ethidium homodimer-1-positive dead cells caused by corticosterone exposure (78-36%), indicating an inhibitory effect on cell death. By contrast, Kamikihito, Saikokaryukotsuboreito, Kamishoyosan, and Yokukansan did not affect corticosterone-induced cell death. Therefore, our results suggest that Hangekobokuto may ameliorate the onset and progression of psychiatric disorders by suppressing neurological disorders associated with increased levels of glucocorticoids.

The gut microbiome and metabolites are altered and interrelated in patients with functional constipation

Introduction

Gut microbiota and metabolites have been identified to contribute to the pathogenesis of functional constipation (FC); however, the underlying mechanism(s) have not been elucidated, and the relationship between the gut microbiota and metabolites in FC has received limited attention in the literature.

Methods

16S rDNA sequencing and non-targeted metabolomic detection based on liquid chromatography-mass spectrometry (LC-MS/MS) technologies were combined to analyze the altered gut microbiome and metabolic profile of fecal samples from FC patients and healthy individuals (healthy control; HC).

Results

The richness and diversity of gut microbiota significantly (p < 0.01) increased in FC patients. Compared to the HC group, 18 genera, including Intestinibacter, Klebsiella, and Akkermansia, exhibited statistically significant changes (p < 0.05). Metabolic analysis showed that metabolic profiles were also markedly altered with 79 metabolites, such as (-)-caryophyllene oxide, chenodeoxycholic acid, and biliverdin, indicating significant inter-group differences (p < 0.05). Besides, the primary bile acid biosynthesis, as well as the metabolic profile of porphyrin and chlorophyll, were the most dominant enriched pathways (FDR < 0.01), in which chenodeoxycholic acid and biliverdin were significantly enriched, respectively. Correlation analysis demonstrated a strong relationship between 10 genera and 19 metabolites (r > 0.6, FDR < 0.05), and notably, Intestinibacter showed a negative correlation with biliverdin (FDR < 0.001), which highlighted the interplay of the gut microbiota and metabolites in the pathogenesis of FC.

Conclusion

Our research describes the characteristics of the gut microbiota and metabolic profiles and the correlation between the gut microbiota and metabolites in FC patients. This may contribute to the understanding of the underlying mechanisms involved in FC pathogenesis and may provide novel insights into therapeutic interventions.

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.

The effect of maternal separation stress-induced depression on ovarian reserve in Sprague Dawley Rats: The possible role of imipramine and agmatine through a mTOR signal pathway

PURPOSE

To examine the possible role of impramine and agmatine through a mTOR signal pathway on rat ovary after maternal separation stress-induced depression.

METHODS

Sprague Dawley neonatal female rats were divided into control, maternal separation (MS), MS+imipramine, and MS+agmatine groups. Rats were subjected to MS for 4 hours daily from postnatal day (PND) 2 to PND 21 and pups were exposed to social isolation (SI) on PND23 for 37 days for model establishment treated with imipramine (30 mg/kg; ip) or agmatine (40 mg/kg; ip) for 15 days. In order to examine behavioral changes rats were all subjected to locomotor activity and forced swimming tests (FST). Ovaries were isolated for morphological evaluation, follicle counting and mTOR signal pathway protein expression levels were detected.

RESULTS

Increased number of primordial follicles and diminished ovarian reserve in the MS groups were detected. Imipramine treatment caused diminished ovarian reserve and atretic follicle; however, agmatine treatment provided the maintenance of ovarian follicular reserve after MS. mTOR signal pathway may have an important role during rat ovarian follicular development in model of MS.

CONCLUSIONS

Our findings suggest that agmatine may help to protect ovarian reserve during follicular development by controlling cell growth.

The expression of agmatinase manipulates the affective state of rats subjected to chronic restraint stress

Agmatine is an endogenous polyamine produced from l-arginine and degraded by agmatinase (AGMAT). Studies in humans and animals have shown that agmatine has neuroprotective, anxiolytic, and antidepressant-like actions. However, little is known about the role of AGMAT in the action of agmatine or in the pathophysiology of psychiatric disorders. Therefore, this study aimed to investigate the role of AGMAT in the pathophysiology of MDD. In this study, we observed that AGMAT expression increased in the ventral hippocampus rather than in the medial prefrontal cortex in the chronic restraint stress (CRS) animal model of depression. Furthermore, we found that AGMAT overexpression in the ventral hippocampus elicited depressive- and anxiety-like behaviors, whereas knockdown of AGMAT exhibited antidepressant and anxiolytic effects in CRS animals. Field and whole-cell recordings of hippocampal CA1 revealed that AGMAT blockage increased Schaffer collateral-CA1 excitatory synaptic transmission, which was expressed both pre- and post-synaptically and was probably due to the inhibition of AGMAT-expressing local interneurons. Therefore, our results suggest that dysregulation of AGMAT is involved in the pathophysiology of depression and is a potential target for designing more effective antidepressants with fewer adverse effects to offer a better therapy for depression.

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.

Molecular pathways of major depressive disorder converge on the synapse

Major depressive disorder (MDD) is a psychiatric disease of still poorly understood molecular etiology. Extensive studies at different molecular levels point to a high complexity of numerous interrelated pathways as the underpinnings of depression. Major systems under consideration include monoamines, stress, neurotrophins and neurogenesis, excitatory and inhibitory neurotransmission, mitochondrial dysfunction, (epi)genetics, inflammation, the opioid system, myelination, and the gut-brain axis, among others. This review aims at illustrating how these multiple signaling pathways and systems may interact to provide a more comprehensive view of MDD's neurobiology. In particular, considering the pattern of synaptic activity as the closest physical representation of mood, emotion, and conscience we can conceptualize, each pathway or molecular system will be scrutinized for links to synaptic neurotransmission. Models of the neurobiology of MDD will be discussed as well as future actions to improve the understanding of the disease and treatment options.

New Insights Into the Pivotal Role of CREB-Regulated Transcription Coactivator 1 in Depression and Comorbid Obesity

Depression and obesity are major public health concerns, and there is mounting evidence that they share etiopathophysiological mechanisms. The neurobiological pathways involved in both mood and energy balance regulation are complex, multifactorial and still incompletely understood. As a coactivator of the pleiotropic transcription factor cAMP response element-binding protein (CREB), CREB-regulated transcription coactivator 1 (CRTC1) has recently emerged as a novel regulator of neuronal plasticity and brain functions, while CRTC1 dysfunction has been associated with neurodegenerative and psychiatric diseases. This review focuses on recent evidence emphasizing the critical role of CRTC1 in the neurobiology of depression and comorbid obesity. We discuss the role of CRTC1 downregulation in mediating chronic stress-induced depressive-like behaviors, and antidepressant response in the light of the previously characterized Crtc1 knockout mouse model of depression. The putative role of CRTC1 in the alteration of brain energy homeostasis observed in depression is also discussed. Finally, we highlight rodent and human studies supporting the critical involvement of CRTC1 in depression-associated obesity.

Agmatine as a novel candidate for rapid-onset antidepressant response

Major depressive disorder (MDD) is a disabling and highly prevalent mood disorder as well as a common cause of suicide. Chronic stress, inflammation, and intestinal dysbiosis have all been shown to play crucial roles in the pathophysiology of MDD. Although conventional antidepressants are widely used in the clinic, they can take weeks to months to produce therapeutic effects. The discovery that ketamine promotes fast and sustaining antidepressant responses is one of the most important breakthroughs in the pharmacotherapy of MDD. However, the adverse psychomimetic/dissociative and neurotoxic effects of ketamine discourage its chronic use. Therefore, agmatine, an endogenous glutamatergic modulator, has been postulated to elicit fast behavioral and synaptogenic effects by stimulating the mechanistic target of rapamycin complex 1 signaling pathway, similar to ketamine. However, recent evidence has demonstrated that the modulation of the NLR family pyrin domain containing 3 inflammasome and gut microbiota, which have been shown to play a crucial role in the pathophysiology of MDD, may also participate in the antidepressant-like effects of both ketamine and agmatine. This review seeks to provide evidence about the mechanisms that may underlie the fast antidepressant-like responses of agmatine in preclinical studies. Considering the anti-inflammatory properties of agmatine, it may also be further investigated as a useful compound for the management of MDD associated with a pro-inflammatory state. Moreover, the fast antidepressant-like response of agmatine noted in animal models should be investigated in clinical studies.

Role of agmatine in the application of neural progenitor cell in central nervous system diseases: therapeutic potentials and effects

Agmatine, the primary decarboxylation product of L-arginine, generated from arginine decarboxylase. Since the discovery of agmatine in the mammalian brain in the 1990s, an increasing number of agmatine-mediated effects have been discovered, demonstrating the benefits of agmatine on ischemic strokes, traumatic brain injury and numerous psychological disorders such as depression, anxiety, and stress. Agmatine also has cellular protective effects and contributes to cell proliferation and differentiation in the central nervous system (CNS). Neural progenitor cells are an important component in the recovery and repair of many neurological disorders due to their ability to differentiate into functional adult neurons. Recent data has revealed that agmatine can regulate and increase proliferation and the fate of progenitor cells in the adult hippocampus. This review aims to summarise and discuss the role of agmatine in the CNS; specifically, the effects and relationship between agmatine and neural progenitor cells and how these ideas can be applied to potential therapeutic application.

Therapeutic Targets for the Treatment of Comorbidities Associated with Epilepsy

One of the most common neurological disorders, which occurs among 1% of the population worldwide, is epilepsy. Therapeutic failure is common with epilepsy and nearly about 30% of patients fall in this category. Seizure suppression should not be the only goal while treating epilepsy but associated comorbidities, which can further worsen the condition, should also be considered. Treatment of such comorbidities such as depression, anxiety, cognition, attention deficit hyperactivity disorder and, various other disorders which co-exist with epilepsy or are caused due to epilepsy should also be treated. Novel targets or the existing targets are needed to be explored for the dual mechanism which can suppress both the disease and the comorbidity. New therapeutic targets such as IDO, nNOS, PAR1, NF-κb are being explored for their role in epilepsy and various comorbidities. This review explores recent therapeutic targets for the treatment of comorbidities associated with epilepsy.

Agmatine has beneficial effect on harmaline-induced essential tremor in rat

Essential tremor (ET) is one of the most prevalent movement disorders and the most common cause of abnormal tremors. However, it cannot be treated efficiently with the currently available pharmacotherapy options. The pathophysiology of harmaline-induced tremor, most commonly used model of ET, involves various neurotransmitter systems including glutamate as well as ion channels. Agmatine, an endogenous neuromodulator, interacts with various glutamate receptor subtypes and ion channels, which have been associated with its' beneficial effects on several neurological disorders. The current study aims to assess the effect of agmatine on the harmaline model of ET. Two separate groups of male rats were injected either with saline or agmatine (40 mg/kg) 30 min prior to single intraperitoneal injection of harmaline (20 mg/kg). The percent duration, intensity and frequency of tremor and locomotor activity were evaluated by a custom-built tremor and locomotion analysis system. Pretreatment with agmatine reduced the percent tremor duration and intensity of tremor induced by harmaline, without affecting the tremor frequency. However, it did not affect the decreased spontaneous locomotor activity due to harmaline. This pattern of ameliorating effects of agmatine on harmaline-induced tremor provide the first evidence for being considered as a treatment option for ET.

Agmatine improves the behavioral and cognitive impairments associated with chronic gestational ethanol exposure in rats

Chronic maternal ethanol exposure leads to poor intelligence, impaired cognition and array of neurological symptoms in offsprings and commonly referred as fetal alcohol spectrum disorder (FASD). Despite high prevalence and severity, the neurochemical basis of FASD remains largely unexplored. The present study evaluated the pharmacological effects of agmatine in cognitive deficits associated with FAS in rat's offsprings prenatally exposed to alcohol. Pregnant rats received ethanol in liquid modified diet during the entire gestational period of 21 days. Offsprings were treated with agmatine (20-80 mg/Kg, i.p.) during early postnatal days (PND: 21-35) and subsequently evaluated for anxiety in elevated plus maze (EPM), depression in forced swim test (FST) and learning and memory in Morris's water maze (MWM) during post adolescent phase. Hippocampal agmatine, BDNF, TNF-α and IL-6 levels were also analyzed in prenatally ethanol exposed pups. Offsprings prenatally exposed to ethanol demonstrated delayed righting reflex, reduced exploratory behavior along with anxiety, depression-like behavior and impaired memory. These behavioral abnormalities were correlated with a significant reduction in hippocampal agmatine and BDNF levels and elevation in TNF-α and IL-6 immunocontent. Chronic agmatine (40 and 80 mg/Kg, i.p.) administration for 15 days (PND: 21-35), improved entries and time spent in open arm of EPM, decreased immobility time in FST. It also reduced latency to reach the platform location; increased the number of entries, time spent in platform quadrant and also number of crossing over platform quadrant when subjected to MWM test in prenatally ethanol exposed offsprings. This study provides functional evidences for the therapeutic potential of agmatine in cognitive impairment and other neurological complications associated with FASD.

Imidazoline Receptor System: The Past, the Present, and the Future

Imidazoline receptors historically referred to a family of nonadrenergic binding sites that recognize compounds with an imidazoline moiety, although this has proven to be an oversimplification. For example, none of the proposed endogenous ligands for imidazoline receptors contain an imidazoline moiety but they are diverse in their chemical structure. Three receptor subtypes (I₁, I₂, and I₃) have been proposed and the understanding of each has seen differing progress over the decades. I₁ receptors partially mediate the central hypotensive effects of clonidine-like drugs. Moxonidine and rilmenidine have better therapeutic profiles (fewer side effects) than clonidine as antihypertensive drugs, thought to be due to their higher I₁/α ₂-adrenoceptor selectivity. Newer I₁ receptor agonists such as LNP599 [3-chloro-2-methyl-phenyl)-(4-methyl-4,5-dihydro-3H-pyrrol-2-yl)-amine hydrochloride] have little to no activity on α ₂-adrenoceptors and demonstrate promising therapeutic potential for hypertension and metabolic syndrome. I₂ receptors associate with several distinct proteins, but the identities of these proteins remain elusive. I₂ receptor agonists have demonstrated various centrally mediated effects including antinociception and neuroprotection. A new I₂ receptor agonist, CR4056 [2-phenyl-6-(1H-imidazol-1yl) quinazoline], demonstrated clear analgesic activity in a recently completed phase II clinical trial and holds great promise as a novel I₂ receptor-based first-in-class nonopioid analgesic. The understanding of I₃ receptors is relatively limited. Existing data suggest that I₃ receptors may represent a binding site at the Kir6.2-subtype ATP-sensitive potassium channels in pancreatic β-cells and may be involved in insulin secretion. Despite the elusive nature of their molecular identities, recent progress on drug discovery targeting imidazoline receptors (I₁ and I₂) demonstrates the exciting potential of these compounds to elicit neuroprotection and to treat various disorders such as hypertension, metabolic syndrome, and chronic pain.

Accumulation of Agmatine, Spermidine, and Spermine in Sprouts and Microgreens of Alfalfa, Fenugreek, Lentil, and Daikon Radish

Sprouts and microgreens are a rich source of various bioactive compounds. Seeds of lentil, fenugreek, alfalfa, and daikon radish seeds were germinated and the contents of the polyamines agmatine (AGM), putrescine (PUT), cadaverine (CAD), spermidine (SPD), and spermine (SPM) in ungerminated seeds, sprouts, and microgreens were determined. In general, sprouting led to the accumulation of the total polyamine content. The highest levels of AGM (5392 mg/kg) were found in alfalfa microgreens, PUT (1079 mg/kg) and CAD (3563 mg/kg) in fenugreek sprouts, SPD (579 mg/kg) in lentil microgreens, and SPM (922 mg/kg) in fenugreek microgreens. A large increase in CAD content was observed in all three legume sprouts. Conversely, the nutritionally beneficial polyamines AGM, SPD, and SPM were accumulated in microgreens, while their contents of CAD were significantly lower. In contrast, daikon radish sprouts exhibited a nutritionally better profile of polyamines than the microgreens. Freezing and thawing of legume sprouts resulted in significant degradation of CAD, PUT, and AGM by endogenous diamine oxidases. The enzymatic potential of fenugreek sprouts can be used to degrade exogenous PUT, CAD, and tyramine at pH values above 5.

Inhibitory influence of agmatine in ethanol withdrawal-induced depression in rats: Behavioral and neurochemical evidence

Although ethanol withdrawal depression is one of the prominent reasons for ethanol consumption reinstatement and ethanol dependence, its neurochemical basis is not clearly understood. The present study investigated the role of the agmatinergic system in ethanol withdrawal-induced depression using the forced swim test (FST) in rats. Chronic exposure of animals to ethanol for 21 days and its abrupt withdrawal produced depression-like behavior, as evidenced by increased immobility time in the FST, compared to the pair-fed control animals. The ethanol withdrawal-induced depression was significantly attenuated by agmatine (20-40 μg/rat, i.c.v. [intracerebroventricularly]), moxonidine (50 μg/rat, i.c.v.), 2-BFI (20 μg/rat, i.c.v.), L-arginine (80 μg/rat, i.c.v.), amino-guanidine (25 μg/rat, i.c.v.), and arcaine (50 μg/rat, i.c.v.) by their once-daily administration during the withdrawal phase (Days 21, 22, and 23). The antidepressant effect of agmatine in ethanol-withdrawn rats was potentiated by the imidazoline receptor I₁ agonist moxonidine (25 μg/rat, i.c.v.) and the imidazoline receptor I₂ agonist, 2-BFI (10 μg/rat, i.c.v.) at their sub-effective doses. On the other hand, it was completely blocked by the imidazoline receptor I₁ antagonist, efaroxan (10 μg/rat, i.c.v.) and the imidazoline receptor I₂ antagonist, idazoxan (4 μg/rat, i.c.v.). In addition, agmatine levels were significantly reduced in brain samples of ethanol-withdrawn rats as compared to the pair-fed control animals. In conclusion, the present study suggests the importance of the endogenous agmatinergic system and the imidazoline receptors system in ethanol withdrawal-induced depression. The data project agmatine as a potential therapeutic target for the alcohol withdrawal-induced depression.

The antidepressant effects of l-arginine on chronic mild stress-induced depression by augmenting the expression of brain-derived neurotrophic factor in rats

In the present study, the antidepressant effects of l-arginine in a rat model of chronic mild stress-induced depression were investigated. Animals were divided into group I (sham), group II (control, depression), group III (10 mg/kg l-arginine), group IV (20 mg/kg l-arginine), and group V (10 mg/kg venlafaxine, positive control). The doses were orally administered for 30 consecutive days. Sucrose preference analysis as well as forced swim and open field tests were performed. Serum cortisol, nitric oxide (NO), and monoamine levels in brain tissue were then measured. Brain-derived neurotrophic factor (BDNF) expression was also examined. Supplementation with l-arginine significantly increased the sucrose preference ratio, locomotor activity, and monoamines and decreased serum cortisol and NO levels. The mRNA and protein expression of BDNF in the brain tissue was significantly reduced (>50 %) in control rats. However, supplementation with l-arginine significantly increased BDNF mRNA expression (>50 %) in both groups. Similarly, increased BDNF protein expression after l-arginine treatment was confirmed using Western blot and immunohistochemical analyses. In conclusion, l-arginine supplementation may be effective against chronic stress-induced depression.

Altered plasma levels of arginine metabolites in depression

L-Arginine pathway metabolites appear to play differential roles in the pathogenesis of major depressive disorder (MDD). Studies have revealed an antidepressant and anxiolytic effect of agmatine and putrescine. Possible mechanisms of these effects include inhibition of nitric oxide synthase and N-methyl-D-aspartate receptors. The present study sought to determine whether MDD is associated with altered levels of arginine metabolites and whether these metabolites are associated with depression, anxiety and stress severity. Seventy seven MDD patients 21-65 years of age with a minimum score of 18 on the Hamilton Depression Scale, and 27 age and sex matched healthy controls (HC) were included. Patients with uncontrolled physical diseases, abnormal routine lab tests, other psychiatric diagnoses, or under psychotropic medication were excluded. HC subjects were recruited from the community. Rating instruments included Hamilton Depression and Anxiety Scales, Beck Depression and Anxiety Inventory and Perceived Stress Scale. Fasting blood was drawn between 8:30 and 11:00 a.m. and High Performance Liquid Chromatography (HPLC) was used to measure plasma arginine metabolites. ADMA (Asymmetrical dimethylarginine) and putrescine were significantly lower while SDMA (Symmetric dimethylarginine), agmatine and ornithine were significantly higher in MDD patients (p˂0.05). Depression, anxiety and stress severity were negatively correlated with ADMA and putrescine (p˂0.05). Stress was positively correlated with citrulline, NOHA (N-omega-hydroxy-nor-l-arginine), SDMA, agmatine and ornithine (p˂0.05). Lower putrescine levels predicted depression diagnosis (p = 0.039) and depression severity (p = 0.003). Low ADMA level predicted depression severity as well. Arginine pathway metabolites are associated with the pathophysiology of depression. Putrescine may be a biomarker to predict MDD.

Nrf2 Activators as Dietary Phytochemicals Against Oxidative Stress, Inflammation, and Mitochondrial Dysfunction in Autism Spectrum Disorders: A Systematic Review

Autism spectrum disorder (ASD) is a pervasive neurodevelopmental disorder with limited available treatments and diverse causes. In ASD patients, numerous researches demonstrated various alterations in inflammation/immune, oxidative stress, and mitochondrial dysfunction, and these alterations could be regulated by Nrf2. Hence, we aimed to systematically review the current evidence about the effects of Nrf2 activator supplementation on ASD objects from in vitro studies, animal studies, and clinical studies. Relevant articles were retrieved through searching for the Cochrane Library, PubMed, Web of Science, Scope, Embase, and CNKI databases (through September 23, 2020). Ultimately, we identified 22 preclinical studies, one cell culture study, and seven clinical studies, covering a total of five Nrf2 activators. For each Nrf2 activator, we focused on its definition, potential therapeutic mechanisms, latest research progress, research limitations, and future development directions. Our systematic review provided suggestive evidence that Nrf2 activators have a potentially beneficial role in improving autism-like behaviors and abnormal molecular alterations through oxidant stress, inflammation, and mitochondrial dysfunction. These dietary phytochemicals are considered to be relatively safer and effective for ASD treatment. However, there are few clinical studies to support the Nrf2 activators as dietary phytochemicals in ASD, even though several preclinical studies. Therefore, caution should be warranted in attempting to extrapolate their effects in human studies, and better design and more rigorous research are required before they can be determined as a therapeutic option.

l-Arginine metabolism before and after 10 weeks of antipsychotic treatment in first-episode psychotic patients

Agmatine is an endogenous NMDA (N-methyl-d-aspartate) antagonist which is synthesized from l-Arginine and described as a novel neurotransmitter. Agmatine is considered to play an important role for the development of schizophrenia. The aim of the present study is to explore the role of agmatine and l-arginine metabolism in medication-naive first-episode psychosis (FEP). We conducted a case control study in medication-naive patients with FEP (n = 40). The healthy volunteers with no family history of schizophrenia (n = 35) matched for age, gender and education level were selected as a control group. The patients were recruited to the study and followed up for 10 weeks. The plasma l-arginine, l-citrulline, l-ornithine and agmatine levels were measured using modified liquid chromatography/mass spectrometry. The plasma levels of l-arginine, l-citrulline and agmatine (p < 0.0001), but not l-ornithine and agmatinase (p > 0.05), were significantly increased during baseline analysis. After 10 weeks of treatment, plasma l-arginine and l-citrulline levels were still significantly increased (p < 0.05) while l-ornithine and agmatinase levels remained unchanged (p > 0.05). Conversely, plasma agmatine levels were significantly decreased after the treatment (p < 0.0001). Positive and negative predictive values of agmatine used for evaluating the diagnostic accuracy were 95.1% and 97.1%, respectively (p < 000.1). This is the first study of arginine metabolism and agmatine in medication-naive first-episode patients and provides evidence of increased levels of an endogenous NMDA antagonist which decreases following antipsychotic treatment.

Novel Targets for Fast Antidepressant Responses: Possible Role of Endogenous Neuromodulators

The available medications for the treatment of major depressive disorder have limitations, particularly their limited efficacy, delayed therapeutic effects, and the side effects associated with treatment. These issues highlight the need for better therapeutic agents that provide more efficacious and faster effects for the management of this disorder. Ketamine, an N-methyl-D-aspartate receptor antagonist, is the prototype for novel glutamate-based antidepressants that has been shown to cause a rapid and sustained antidepressant effect even in severe refractory depressive patients. Considering the importance of these findings, several studies have been conducted to elucidate the molecular targets for ketamine's effect. In addition, efforts are under way to characterize ketamine-like drugs. This review focuses particularly on evidence that endogenous glutamatergic neuromodulators may be able to modulate mood and to elicit fast antidepressant responses. Among these molecules, agmatine and creatine stand out as those with more published evidence of similarities with ketamine, but guanosine and ascorbic acid have also provided promising results. The possibility that these neuromodulators and ketamine have common neurobiological mechanisms, mainly the ability to activate mechanistic target of rapamycin and brain-derived neurotrophic factor signaling, and synthesis of synaptic proteins in the prefrontal cortex and/or hippocampus is presented and discussed.

Metabolic strategies for the degradation of the neuromodulator agmatine in mammals

Agmatine (1-amino-4-guanidinobutane), a precursor for polyamine biosynthesis, has been identified as an important neuromodulator with anticonvulsant, antineurotoxic and antidepressant actions in the brain. In this context it has emerged as an important mediator of addiction/satiety pathways associated with alcohol misuse. Consequently, the regulation of the activity of key enzymes in agmatine metabolism is an attractive strategy to combat alcoholism and related addiction disorders. Agmatine results from the decarboxylation of L-arginine in a reaction catalyzed by arginine decarboxylase (ADC), and can be converted to either guanidine butyraldehyde by diamine oxidase (DAO) or putrescine and urea by the enzyme agmatinase (AGM) or the more recently identified AGM-like protein (ALP). In rat brain, agmatine, AGM and ALP are predominantly localised in areas associated with roles in appetitive and craving (drug-reinstatement) behaviors. Thus, inhibitors of AGM or ALP are promising agents for the treatment of addictions. In this review, the properties of DAO, AGM and ALP are discussed with a view to their role in the agmatine metabolism in mammals.

Antidepressant and pro-neurogenic effects of agmatine in a mouse model of stress induced by chronic exposure to corticosterone

Agmatine is an endogenous neuromodulator that has been shown to have beneficial effects in the central nervous system, including antidepressant-like effects in animals. In this study, we investigated the ability of agmatine (0.1mg/kg, p.o.) and the conventional antidepressant fluoxetine (10mg/kg, p.o.) to reverse the behavioral effects and morphological alterations in the hippocampus of mice exposed to chronic corticosterone (20mg/kg, p.o.) treatment for a period of 21days as a model of stress and depressive-like behaviors. Chronic corticosterone treatment increased the immobility time in the tail suspension test (TST), but did not cause anhedonic-like and anxiety-related behaviors, as assessed with the splash test and the open field test (OFT), respectively. Of note, the depressive-like behaviors induced by corticosterone were accompanied by a decrease in hippocampal cell proliferation, although no changes in hippocampal neuronal differentiation were observed. Our findings provide evidence that, similarly to fluoxetine, agmatine was able to reverse the corticosterone-induced depressive-like behaviors in the TST as well as the deficits in hippocampal cell proliferation. Additionally, fluoxetine but not agmatine, increased hippocampal differentiation. Agmatine, similar to fluoxetine, was capable of increasing both dendritic arborization and length in the entire dentate hippocampus, an effect more evident in the ventral portion of the hippocampus, as assessed with the modified Sholl analysis. Altogether, our results suggest that the increase in hippocampal proliferation induced by agmatine may contribute, at least in part, to the antidepressant-like response of this compound in this mouse model of stress induced by chronic exposure to corticosterone.

Agmatine: multifunctional arginine metabolite and magic bullet in clinical neuroscience?

Agmatine, the decarboxylation product of arginine, was largely neglected as an important player in mammalian metabolism until the mid-1990s, when it was re-discovered as an endogenous ligand of imidazoline and α2-adrenergic receptors. Since then, a wide variety of agmatine-mediated effects have been observed, and consequently agmatine has moved from a wallflower existence into the limelight of clinical neuroscience research. Despite this quantum jump in scientific interest, the understanding of the anabolism and catabolism of this amine is still vague. The purification and biochemical characterization of natural mammalian arginine decarboxylase and agmatinase still are open issues. Nevertheless, the agmatinergic system is currently one of the most promising candidates in order to pharmacologically interfere with some major diseases of the central nervous system, which are summarized in the present review. Particularly with respect to major depression, agmatine, its derivatives, and metabolizing enzymes show great promise for the development of an improved treatment of this common disease.

Agmatine for combined treatment of epilepsy, depression and cognitive impairment in chronic epileptic animals

Epilepsy is fourth most common neurological disorders associated with depression and cognitive deficits. As per present scenario, none of the antiseizure drugs have been reported successful to have ameliorative effect on epilepsy associated depression and cognitive deficits. Thus, the study was envisioned to assess an ameliorative potential of agmatine on epilepsy and its efficacy and safety for management of associated depression and cognitive deficits. The animals were made epileptic employing pentylenetetrazole (35mg/kg i.p. every 48±2h) kindling model of epilepsy and subsequently were treated with vehicle, valproic acid (300mg/kg/day i.p.) and agmatine (2.5, 5, and 10mg/kg)/day/i.p. for 15days. Except naïve, all the groups were challenged with same pentylenetetrazole dose as employed during kindling on days 5, 10, and 15 to evaluate seizure severity. Two hours after seizure severity test, tail suspension test and passive shock avoidance paradigm was employed to evaluate depression and cognitive behavior respectively. Results suggested that epileptic animals were significantly associated with depression and cognitive impairment. Chronic valproate treatment significantly reduced seizure severity, but was found unable to mitigate depression and cognitive deficits. However, agmatine treatment dose dependently ameliorated seizure severity as well as associated depression and cognitive deficits. On 15th day, animals were euthanized and pertinent neurochemical estimations were carried out in cortical and hippocampal areas of the mice brain. Thus, study concluded that agmatine ameliorated seizure severity, depression and cognitive impairment in epileptic animals, possibly via restoring glutamate-GABA neurotransmission and serotonin synthesis with decreased nitrosative stress.