Browsing by Subject "Agmatine"

Now showing 1 - 4 of 4
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    Alleviation of Chronic Neuropathic Pain by Agmatine Requires the GluN2B Subunit of the NMDA Receptor
    (2017-11) Peterson, Cristina
    Effective treatment for chronic pain patients remains an area of largely unmet need. However, chronic pain patients receiving traditional opioid therapy are consistently surrounded by the potential risks and social stigmas of opioid dependence, misuse, and addiction. These concerns are heightened in the face of the expanding opioid epidemic. The need for new, non-opioidergic therapeutics for management of the large population of chronic patients is widely recognized. Agmatine, also known as decarboxylated arginine, is an endogenous small molecule that has been shown to modulate maladaptive neuroplasticity that underlies the experience of chronic pain. Agmatine has been established to meet the criteria of acting as a neurotransmitter including synthesis in neurons, release from nerve terminals, and binding to post-synaptic receptors. We have previously demonstrated the efficacy of exogenously delivered agmatine in reversing chronic pain behaviors in models of neuropathic pain. Targeting primary sensory neurons through gene vectors such as serotypes of the adeno-associated virus has recently been identified as a powerful emerging strategy to treat chronic, intractable pain. Gene therapy has been approved for market use in Europe and the United States, making it a viable tool for translation from bench side to clinic. To this end, a viral vector encoding the synthetic enzyme for agmatine, namely arginine decarboxylase was developed. It has been shown that intrathecally injected viral vector particles distribute to sites of interest for chronic pain. The primary objective of my thesis work has been to expand both the application and mechanistic understanding of agmatine as a non-opioidergic therapeutic in the treatment of chronic pain. The central hypothesis of this work is that enhanced expression of arginine decarboxylase in nociceptive pathways results in long-term reduction of neuropathic pain due to agmatine production and agmatine’s antagonism of the NMDA receptor. The rationale for this research was that delivery of a gene therapy to enhance agmatine’s inhibition of NMDA signaling would be a viable, long term solution for management of chronic pain. In this thesis, I will expand upon the dual public health crises of chronic pain and prescription opioid abuse. These call for new, non-opioid therapeutic approaches for chronic pain, leading to the therapeutic development of agmatine as an NMDA receptor antagonist.
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    The GLUN2B subunit of the NMDA receptor as an effector of inhibitory and pro-nociceptive neuromodulators
    (2024-11) Xie, Tongzhen
    Chronic pain affects over 20% of adults in the U.S., imposing a significant personal and economic burden, while most existing therapies are not suitable for long-term use. Chronic pain patients critically need an alternative effective treatment with minimal side effects. To create such treatments, it is essential to understand the pain circuitry and different mechanisms of how chronic pain can develop. One promising therapeutic target is the GluN2B-containing NMDA receptor in the spinal cord dorsal horn. Antagonizing this receptor has been shown to prevent the development of central sensitization, a key driver of chronic pain. Building on the understanding of NMDA receptors, this thesis described both pronociceptive and inhibitory modulation of spinal GluN2B-NMDA receptors using a novel NMDA-evoked calcium response assay in the mouse spinal cord dorsal horn. The results showed that the spinal NMDA receptor mediates the maladaptive involvement of the VGF-derived peptide TLQP-62. In contrast, the inhibitory effects of agmatine on spinal NMDA receptor activity require intact spinal PSD95-nNOS tethering. While further research is required to fully characterize the direct interactions of these modulators with NMDA receptors, it is hoped that this study will help the goal of developing safe and effective therapeutics for pain patients.
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    The impact of gene transfer of arginine decarboxylase to the central nervous system on opioid analgesic tolerance
    (2014-12) Churchill, Caroline Catharine
    Opioid-based pharmacotherapy remains the most commonly prescribed treatment for patients suffering from neuropathic pain conditions. Although opioids are effective for treating neuropathic pain, when used chronically the development of adverse side effects, such as opioid analgesic tolerance, can develop. Previous studies have shown that exogenously delivered agmatine, (decarboxylated L-arginine) can prevent the development of opioid analgesic tolerance, dependence, and self-administration. This study investigated the impact of intrathecal adeno-associated virus serotype 5-human arginine decarboxylase (AAV5-hADC) in models of opioid analgesic tolerance. Pharmacological dose-response curves were collected from two cohorts using two different models of opioid analgesic tolerance. Tissues from the central nervous system of the subjects were further analyzed for hADC gene expression and for spinal agmatine levels. Investigations of the choroid plexus as a target for intrathecal gene therapeutics were also conducted. Region-directed genetic modulation of the agmatine metabolic pathway within the central nervous system could be a highly innovative approach for the control of opioid tolerance and other neuroplasticity disorders.
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    Pharmacokinetics and Pharmacodynamics of Strategically Substituted Agmatines
    (2022-10) Clements, Benjamin
    Chronic pain remains a major issue affecting patients, with current pharmacotherapy limited to drugs with low efficacy, negative side effects, and/or social stigma. Thus, there is a critical need to develop novel pharmacotherapies that are effective in reducing chronic pain while being safe for long-term use. Agmatine has been extensively shown to reduce chronic pain behaviors in animal models with no cardiac, motor, or neurological adverse effects1. This reduction is due to antagonism of the N-methyl-D-aspartate (NMDA) receptor, specifically at the GluN2B subunit2-4. This specificity allows agmatine to modulate the biological changes underlying chronic pain without the negative side effects observed with complete inhibition of the NMDA receptor. However, agmatine is a polar small molecule and does not efficiently diffuse passively across biological membranes. It has been shown to cross the intestinal epithelium and blood-brain barrier (BBB)5,6, but these distributions are limited, requiring high doses to generating quantifiable disposition. Additionally, the barrier in drug appearance in the CNS necessitates high doses (30-300 mg/kg in animal models) to achieve pharmacological effects. Furthermore, although agmatine has a long half-life in the CNS, its short elimination half-life in plasma restricts efficacy as a systemic therapeutic7. Therefore, our team and collaborators have designed and synthesized a series of agmatine-based prodrugs, the Strategically Substituted Agmatines (SSAs), which are designed to have increased lipophilicity, prolonged plasma half-lives, and equivalent pharmacological activity to agmatine. The central hypothesis of this thesis research is that the SSAs reduce pain behaviors in preclinical models of chronic pain in a manner comparable to agmatine while exhibiting improved pharmacokinetic parameters in rat. From this hypothesis, my objective has been to answer several questions: How can these compounds be measured in plasma and the central nervous system (CNS)? Do strategic substitutions improve pharmacokinetic parameters over agmatine? Do the SSAs distribute more readily to the CNS? Are the SSAs metabolized to agmatine within the CNS? And do the SSAs show improved potency over agmatine following oral administration? To answer these questions, my goals have been to develop techniques to quantify agmatine and the SSAs in complex tissues, determine the pharmacokinetic parameters of agmatine and the SSAs after IV and oral administration, investigate the prodrug activity of the SSAs, and explore the efficacy on chronic pain of these compounds as oral therapeutics. I accomplished these goals by completing the following specific aims: Specific Aim 1: Develop and Validate Analytical Methods to Accurately Quantify Agmatine and the SSAs in Complex MatricesUsing HPLC-MS/MS, a series of tissue preparation methods and chromatographic techniques were developed and validated according to FDA guidance8 to determine the concentration of agmatine, SSA1, SSA2, SSA3, and SSA4 in rat plasma, and quantify agmatine and SSA3 in rat brain and spinal cord. Specific Aim 2: Determine the Plasma Pharmacokinetic Parameters of Agmatine and the SSAs in Rat Following Intravenous and Oral DeliveryI hypothesized that the lipophilic substitutions of the SSAs would increase plasma half-life and volume of distribution over agmatine, as well as improve the oral bioavailability over agmatine. Sprague-Dawley rats with surgically implanted catheters received IV or oral agmatine, SSA1, SSA2, SSA3, or SSA4. Serial blood samples were collected, and plasma was analyzed using HPLC-MS/MS. These plasma concentrations were used to generate individual pharmacokinetic profiles of each drug in individual rats. Specific Aim 3: Assess the Tissue Distribution Profiles of Agmatine and SSA3 in RatI hypothesized that SSA3 would show increased CNS distribution across all tissues compared to agmatine. Furthermore, I hypothesized that SSA3 would be metabolized to agmatine within the CNS. Following IV administration of agmatine or SSA3 via tail-vein in Sprague-Dawley rat, multiple tissues from within the CNS were collected and heat-treated, along with plasma. Agmatine and SSA3 content were assessed using HPLC-MS/MS in each tissue, from which I determined distribution and pharmacokinetic profiles of each compound within individual tissues, such as spinal cord, cortex, ventral tegmental area (VTA), and nucleus accumbens (NAcc). Agmatine content was also assessed in CNS tissues following IV SSA3 and SSA4 to estimate prodrug activity. Specific Aim 4: Evaluate the Efficacy of Agmatine and the SSAs on NMDA-Evoked Responses and Chronic Pain Following Systemic Administration Intrathecal NMDA evokes characteristic behaviors in mice, including biting/scratching and tail-flick hyperalgesia. I hypothesized that the SSAs, due to their increased lipophilicity, would have increased systemic activity at lower doses than agmatine in the NMDA-evoked behavioral model. Additionally, I hypothesized that increased activity at lower doses would be observed in reversal of tactile hypersensitivity in inflammatory pain. I assessed changes in NMDA-evoked behaviors following subcutaneous and oral administration of agmatine and the SSAs to determine the CNS effects of these compounds from non-central delivery. Furthermore, these compounds were tested after oral administration for reduction of tactile hypersensitivity following inflammatory injury via CFA administration.