Agmatine sulfate

Agmatine sulfate exerts modulatory action at multiple molecular targets, such as neurotransmitter systems, ion channels and nitric oxide synthesis. It is an endogenous agonist at imidazoline receptor and a NO synthase inhibitor.

In Vitro:Agmatine binds to alpha 2-adrenergic and imidazoline receptors and stimulates release of catecholamines from adrenal chromaffin cells. Its biosynthetic enzyme, arginine decarboxylase, is present in brain. Agmatine, locally synthesized, is an endogenous agonist at imidazoline receptors, a noncatecholamine ligand at alpha 2-adrenergic receptors and may act as a neurotransmitter[1]. Agmatine is synthesized in the brain, stored in synaptic vesicles in regionally selective neurons, accumulated by uptake, released by depolarization, and inactivated by agmatinase. Agmatine inhibits nitric oxide synthase, and induces the release of some peptide hormones[2]. Agmatine, 4-(aminobutyl)guanidine, is produced by decarboxylation of L-arginine by the enzyme arginine decarboxylase. Agmatine is a competitive inhibitor of all NOS isoenzymes but not an NO precursor. Ki values are approximately 660 µM (NOS I), 220 µM (NOS II) and 7.5 mM (NOS III)[3]. Agmatine stimulates nitrite production three-fold above basal nitrite formation by endothelial cells. Agmatine displaces [3H]-idazoxan from endothelial cellmembranes and is found to induce transients in the cytosolic calcium of endothelial cells. The transients could be downregulated by repeated exposure to agmatine but are not affected by pretreatment with norepinephrine[4].

In Vivo:Agmatine produces an antidepressant-like effect when assessed in the forced swimming test and in the tail suspension test in mice (dose range 0.01-50 mg/kg, i.p.), without accompanying changes in ambulation in an open-field[5]. In ischemic stroke, agmatine protects the blood-brain barrier, which can be monitored in vivo by quantification of permeability by using dynamic contrast-enhanced MR imaging[6]. Agmatine substantially augments the antidepressant-like effect of MK-801, reinforcing the notion that this compound modulates NMDA receptor activation[7].

References:
[1]. Li G, et al. Agmatine: an endogenous clonidine-displacing substance in the brain. Science. 1994 Feb 18;263(5149):966-9. [2]. Reis DJ, et al. Is agmatine a novel neurotransmitter in brain? Trends Pharmacol Sci. 2000 May;21(5):187-93. [3]. Galea E, et al. Inhibition of mammalian nitric oxide synthases by agmatine, an endogenouspolyamine formed by decarboxylation of arginine. Biochem J. 1996 May 15;316 ( Pt 1):247-9. [4]. Morrissey JJ, et al. Agmatine activation of nitric oxide synthase in endothelial cells. Proc Assoc Am Physicians. 1997 Jan;109(1):51-7. [5]. Zomkowski AD, et al. Agmatine produces antidepressant-like effects in two models of depression in mice. Neuroreport. 2002 Mar 25;13(4):387-91. [6]. Ahn SS, et al. Effects of agmatine on blood-brain barrier stabilization assessed by permeability MRI in a rat model of transient cerebral ischemia. AJNR Am J Neuroradiol. 2015 Feb;36(2):283-8. [7]. Neis VB, et al. Agmatine enhances antidepressant potency of MK-801 and conventional antidepressants in mice. Pharmacol Biochem Behav. 2015 Mar;130:9-14.

Safety and Efficacy of Dietary Agmatine Sulfate in Lumbar Disc-associated Radiculopathy. An Open-label, Dose-escalating Study Followed by a Randomized, Double-blind, Placebo-controlled Trial.[Pubmed:20447305]

Pain Med. 2010 Mar;11(3):356-68.

Objective. Agmatine, decarboxylated arginine, was shown in preclinical studies to exert efficacious neuroprotection by interacting with multiple molecular targets. This study was designed to ascertain safety and efficacy of dietary Agmatine sulfate in herniated lumbar disc-associated radiculopathy. Study Design. First, an open-label dose escalation study was performed to assess the safety and side-effects of Agmatine sulfate. In the follow-up study, participants diagnosed with herniated lumbar disc-associated radiculopathy were randomly assigned to receive either placebo or Agmatine sulfate in a double-blind fashion. Methods. Participants in the first study were recruited consecutively into four cohorts who took the following escalating regimens: 1.335 g/day Agmatine sulfate for 10 days, 2.670 g/day for 10 days, 3.560 g/day for 10 days, and 3.560 g/day for 21 days. Participants in the follow-up study were assigned to receive either placebo or Agmatine sulfate, 2.670 g/day for 14 days. Primary outcome measures were pain using the visual analog scale, the McGill pain questionnaire and the Oswestry disability index, sensorimotor deficits, and health-related quality of life using the 36-item short form (SF-36) questionnaire. Secondary outcomes included other treatment options, and safety and tolerability assessment. Results. Safety parameters were within normal values in all participants of the first study. Three participants in the highest dose cohort had mild-to-moderate diarrhea and mild nausea during treatment, which disappeared upon treatment cessation. No other events were observed. In the follow-up study, 51 participants were randomly enrolled in the agmatine group and 48 in the placebo. Continuous improvement of symptoms occurred in both groups, but was more pronounced in the agmatine (analyzed n = 31) as compared with the placebo group (n = 30). Expressed as percent of baseline values, significantly enhanced improvement in average pain measures and in quality of life scores occurred after treatment in the agmatine group (26.7% and 70.8%, respectively) as compared with placebo (6.0% [P Agmatine sulfate is safe and efficacious treatment for alleviating pain and improving quality of life in lumbar disc-associated radiculopathy. Study Registration. ClinicalTrials.gov Protocol Registration System Identifier: NCT00405041.

Evidence for oral agmatine sulfate safety--a 95-day high dosage pilot study with rats.[Pubmed:24140462]

Food Chem Toxicol. 2013 Dec;62:758-62.

Agmatine, decarboxylated arginine, exerts beneficial effects in various experimental disease models. Clinical trials indicate the safety and effectiveness of short-term (up to 21 days) high dose regimens of oral Agmatine sulfate, but longer term studies are lacking. This pilot study undertook to assess the safety of a longer term high dosage oral Agmatine sulfate in laboratory rats. Adult Wistar rats consumed 5.3 g/l Agmatine sulfate in their drinking water for 95 days, a regimen estimated to result in a daily dosage of absorbed agmatine of about 100mg/kg. Animals' body weight, water consumption and blood pressure were periodically measured, and general cage behavior, fur appearance, urination and feces appearance monitored. These parameters were also determined at 20 days after treatment cessation (day 115). On days 95 and 115, animals were euthanized for gross necropsy assessment. Agmatine-treated rats showed slight, but significant reductions in body weight and blood pressure, and reduced water consumption during treatment, which recovered completely within 20 days after treatment cessation. Otherwise, no abnormal behaviors or organ pathologies were observed. These findings are first to suggest apparent safety of sub-chronic high dosage dietary Agmatine sulfate in laboratory rats, thus lending further support to the therapeutic applications of agmatine.

Comparison of the properties of agmatine and endogenous clonidine-displacing substance at imidazoline and alpha-2 adrenergic receptors.[Pubmed:7853171]

J Pharmacol Exp Ther. 1995 Feb;272(2):581-7.

Nonadrenergic imidazoline receptors (I receptors) mediate the central antihypertensive effects of clonidine. Agmatine, an arginine metabolite that is synthesized within bovine brain and exhibits clonidine-displacing substance (CDS) activity, might be the endogenous I receptor neurotransmitter. The authors compared the affinity of agmatine versus the potency of endogenous bovine hypothalamic CDS, at bovine adrenomedullary I1 receptors and at human clonidine-binding sites: human alpha-2A, alpha-2B and alpha-2C expressed on transfected cell lines, I1 sites on human platelet plasma membranes and I2b (amiloride-insensitive) sites on human platelet intracellular membranes. The alpha-2 and I1 sites were labeled with [125I]p-iodoclonidine and the I2b sites were labeled with [3H]-idazoxan. Agmatine displayed preferential affinity for I1 receptors, with both high (H) and low (L) affinity components; the rank order was I1(human)(H) > I1(bovine)(H) > I2b = I1(human)(L) = I1(bovine) (L) = alpha-2A = alpha-2B = alpha-2C. By comparison, hypothalamic CDS competition curves modeled to a single site for all receptors, i.e., I1(bovine) > I2b = alpha-2C > I1(human) = alpha-2A = alpha-2B. Thus, agmatine alone cannot explain the rank order of potency of hypothalamic CDS. Moreover, I1 sites on human platelets differ from I1 sites on bovine adrenomedullary cells with respect to CDS potency but not agmatine affinity. These results do not rule out agmatine as an I1 transmitter but suggest that other I-receptor ligands might exist within endogenous CDS.

Agmatine: an endogenous clonidine-displacing substance in the brain.[Pubmed:7906055]

Science. 1994 Feb 18;263(5149):966-9.

Clonidine, an antihypertensive drug, binds to alpha 2-adrenergic and imidazoline receptors. The endogenous ligand for imidazoline receptors may be a clonidine-displacing substance, a small molecule isolated from bovine brain. This clonidine-displacing substance was purified and determined by mass spectroscopy to be agmatine (decarboxylated arginine), heretofore not detected in brain. Agmatine binds to alpha 2-adrenergic and imidazoline receptors and stimulates release of catecholamines from adrenal chromaffin cells. Its biosynthetic enzyme, arginine decarboxylase, is present in brain. Agmatine, locally synthesized, is an endogenous agonist at imidazoline receptors, a noncatecholamine ligand at alpha 2-adrenergic receptors and may act as a neurotransmitter.

Agmatine sulfate exerts modulatory action at multiple molecular targets, such as neurotransmitter systems, ion channels and nitric oxide synthesis. It is an endogenous agonist at imidazoline receptor and a NO synthase inhibitor.

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