![[Feedback]](/icons/banner/feedbackACT.gif){kind=icon}
![[For Subscribers]](/icons/banner/subscriberACT.gif){kind=icon}
![[Archive]](/icons/banner/archiveACT.gif){kind=icon}
![[Search]](/icons/banner/searchACT.gif){kind=icon}
![[Contents]](/icons/banner/tocACT.gif){kind=icon}
|
|
|
|
|
||
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
NEUROPHARMACOLOGY
Departments of Pharmaceutics (J.C.R., B.M.G., C.A.F.), Pharmacology (B.M.G., K.F.K., C.A.F.), and Neuroscience (K.F.K., C.A.F.), and Center for Pain Research (J.C.R., K.F.K., C.A.F.), University of Minnesota, Minneapolis, Minnesota
Received March 10, 2005; accepted May 31, 2005.
 |
Abstract |
|---|
 Top Abstract Materials and MethodsResultsDiscussionReferences |
|---|
), opioid tolerance (Trujillo and Akil, 1991; Tiseo and Inturissi, 1993), drug addiction (Semenova et al., 1999), and spinal cord injury (Faden and Simon, 1988). An outcome of the search for the endogenous ligand to the pharmacologically characterized imidazoline receptor was the identification of agmatine (decarboxylated arginine) in the mammalian central nervous system (CNS) receptor (Li et al., 1994). The imidazoline receptor is associated with the cloned family of 
2 adrenergic receptors in that the two receptor systems share a set of imidazoline ring-bearing ligands such as clonidine, moxonidine, rilmenidine, and idazoxan. Although agmatine does not have an imidazoline ring, as a clonidine-displacing substance agmatine was included in this associated set of imidazoline receptor/2 ligands (Codd et al., 1995); it was later shown to also bind to 2 receptors, albeit without demonstrable activity (Pinthong et al., 1995). Subsequent investigations extended the presumed agmatinergic targets and activity to include the observations that agmatine antagonizes NMDA receptors (Yang and Reis, 1999) and inhibits nitric-oxide synthase (Galea et al., 1996), actions suggesting modulation of glutamatergic systems. Since the discovery of agmatine in mammalian CNS, we and others have studied the molecule in vivo and reported that it prevents the development of opioid tolerance (Kolesnikov et al., 1996; Fairbanks and Wilcox, 1997), reverses the maintenance of pain resulting from inflammation, neuropathy, and spinal cord injury (Fairbanks et al., 2000), and attenuates escalation of opioid self-administration (Morgan et al., 2002). Despite the extensive glutamate literature (>74,000 journal articles since 1966), comparatively few studies have been performed with agmatine (
600 journal articles).
In the previous reports examining exogenously administered agmatine on in vivo systems, agmatine sulfate has been administered primarily by systemic routes, including intravenous, subcutaneous, intraperitoneal, and intrarenal administration. The doses, species, dependent measures, and outcomes from greater than 50 such in vivo studies have recently been reviewed (Nguyen et al., 2003). The effective systemic agmatine doses that elicit therapeutic results in these animal models exhibit a wide range (10–400 mg/kg); 100 mg/kg has been the most frequently applied effective systemic dose of agmatine. Many of these studies assert a central site of action for agmatine. However, agmatine is a cation at physiological pH and therefore should not readily cross the blood-brain barrier. Furthermore, an agmatinergic blood-brain barrier transport system has yet to be definitively characterized. In support of the proposal that agmatine exerts its effects through a central site of action, a number of studies have applied agmatine through central routes of administration, including intracerebroventricular (for a complete list, see Nguyen et al., 2003) and intrathecal (Fairbanks and Wilcox, 1997; Horvath et al., 1999; Fairbanks et al., 2000; Hou et al., 2003). Although these pharmacological studies provide proof-of-principle for agmatinergic modulation of many centrally mediated plasticity-requiring phenomena, minimal information is available regarding the pharmacokinetics of agmatine in the serum or the CNS. Two preliminary studies report mouse spinal cord (Nguyen et al., 2003) and brain (Piletz et al., 2003) recovery of agmatine after systemic administration of agmatine. Piletz et al. (2003) also reported a preclinical study of CSF agmatine recovery after systemic administration (30 mg/kg i.v.) in a single retired experimental nonhuman primate. Although these results also provide evidence for agmatine's pharmacological action within the CNS, a full pharmacokinetic evaluation of agmatine in CNS has yet to be reported. Such information is important in defining the therapeutic utility of the molecule as well as its role in CNS processing. The objective of this study was to directly compare spinal cord pharmacokinetics with pharmacodynamic responses to intrathecally administered agmatine in a murine model of acute activation of the neuronal NMDA receptor-nitric-oxide synthase system (Kitto et al., 1992).
|
Materials and Methods |
|---|
|
TopAbstractMaterials and MethodsResultsDiscussionReferences |
|---|
Chemicals. MK-801 (dizocilpine maleate) was obtained from Merck Sharpe & Dohme (Rahway, NJ), 7-nitroindazole (7-NINA) sodium salt was from Tocris Cookson Inc. (Ellisville, MO). Agmatine sulfate and NMDA were purchased from Sigma Chemical Co. (St. Louis, MO). All drugs were dissolved in 0.9% saline.
Intrathecal Injection. Agmatine was administered intrathecally (i.t.) in conscious mice according to the method of Hylden and Wilcox (1980) as described in detail by Fairbanks (2003). Briefly, the pelvic girdle (ileac crest) of the mouse is gripped firmly by the thumb and forefinger of the injectors' nondominant hand. The skin above the ileac crest is pulled tautly to create a horizontal plane where the needle is inserted. The needle is a 30-gauge, 0.5-inch sterile disposable needle connected to a 50-µl Luer-hub Hamilton syringe. All injections were delivered in 5 µl of vehicle, a frequently used volume in pharmacodynamic studies of intrathecally delivered agents in mice. Notably, some preliminary experiments were performed to evaluate the CNS recovery of agmatine (120 nmol) at 3 and 10 min after intrathecal injections of 1- and 2.5-µl volumes. However, for both the 1- and 2.5-µl volumes, spinal agmatine recovery was low at 3 min (<10 pmol/mg) and generally below the limit of detection at 10 min. In contrast, the 5-µl volume yielded sufficient concentrations over time to assess the pharmacokinetic parameters of agmatine in spinal cord.
NMDA-Induced Nociceptive Behavioral Responses. NMDA responses were induced by a single intrathecal injection (0.3 nmol) of NMDA according to the method of Aanonsen and Wilcox (1987). The animal's scratching and biting responses in the first minute after injection are counted. After 1 min, NMDA no longer produces the scratching and biting response.
NMDA-Induced Thermal Hyperalgesia. A warm water (49°C) tail immersion test for NMDA-induced thermal hypersensitivity (adapted from the radiant heat method of Kitto and Wilcox, 1992) followed 3 to 5 min after injection of NMDA. Three or 5 min after injection with NMDA (0.3 nmol), the animals show a decrease in latency to tail-flick (1–2 s) in response to applied noxious heat (49°C) relative to their baseline and also to saline-injected controls. Other signs of irritation or discomfort (vocalization and motor impairment) are not present. This test is conducted immediately after and in the same animals in which the NMDA nociceptive scratching and biting behaviors are counted. Since the behaviors occur in the first minute and cease thereafter, it is then possible to conduct a test of thermal hyperalgesia at 3 to 5 min after injection of NMDA.
Dose-Response Analysis. The pharmacological parameters presented in Table 1 were calculated using the using the pharmacological statistics software FlashCalc version 4.3.2 (Dr. Michael Ossipov, University of Arizona, Tucson, AZ) (Wells et al., 2001; Xie et al., 2005), which is based on the methods described by Tallarida and Murray (1987) and Tallarida (2000). A minimum of three doses was used for each drug.
|
Spinal Distribution of Agmatine in ICR Mice. In intrathecal dosing experiments, the mice received 120 nmol of agmatine as a single intrathecal dose. At different times after the injection (1, 3, 10, 30, 60, 180, and 360 min; 24, 48, 72, and 168 h; n = 5 or more for each time point), trunk blood was collected for serum analysis. Spinal cords were extruded by hydraulic pressure (using cold phosphate-buffered saline) and quick-frozen on dry ice. Spinal cords were dissected into cervical, thoracic, and lumbosacral sections using the cervical and lumbosacral enlargements as indicators. Serum and tissue were stored at -80°C until HPLC analysis. In a smaller study, mice were given 60 nmol of agmatine as the intrathecal dose, and tissue and serum were extracted at 1, 10, and 30 min (n = 4–5 per time point). This is the same dose that gives maximum effect in the NMDA nociceptive and thermal hyperalgesia assay.
HPLC Analysis. The HPLC protocol is based on two methods for agmatine determination (Raasch et al., 1995; Feng et al., 1997) and modified to use naphthalene dicarboxaldehyde as the derivatization agent (deMontigny et al., 1987). Tissue extracts were concentrated under vacuum and suspended in 100 µl of borate buffer, pH 9.4; NaCN (40 µl; 0.025 M) was added, followed by naphthalene dicarboxaldehyde (100 µl; 0.05 M) in MeOH, which was allowed to react at room temperature for 20 min. Derivatization of agmatine with naphthalene dicarboxaldehyde produces a highly fluorescent molecule of high stability. Five to 10 µl of the reaction mixture were injected onto a 250 x 4.6-mm Alltech Nucleosil C8 10-µm HPLC cartridge and eluted with 80% ACN in a buffer prepared by dissolving 3.42 g of KH2PO4 and 4.32 g of K2HPO4 in 1 liter of HPLC-grade H2O, pH 6.81, at a flow rate of 1.5 ml/min. Fluorescence of the agmatine derivative was recorded over time using an excitation wavelength of 249 nm and an emission wavelength of 466 nm. External agmatine standards were used to calculate the concentration of agmatine in tissue and plasma. Samples exhibiting peak areas outside of the linear range of the agmatine standard curve were diluted accordingly and injected again for quantification.
Pharmacokinetic Analysis. In vivo pharmacokinetic parameters (Cmax, t1/2, AUCcord, and AUCserum) were determined using WinNonlin version 3.1. Noncompartmental analysis, WinNonlin NCA 201, with linear/log trapezoidal rule was used for determination of area under the curves, AUC0–
. Predicted elimination phases for each pharmacokinetic profile were assigned and fitted using a WinNonlin log-transformed linear regression with 1/y weighting.
|
Results |
|---|
|
TopAbstractMaterials and MethodsResultsDiscussionReferences |
|---|
|
Unlike MK-801, the selective neuronal nitric-oxide synthase inhibitor 7-NINA dose dependently inhibited the thermal hyperalgesia but had no impact on the nociceptive behavior (also measured within the same mice) (Fig. 1B; Table 1). These results illustrate that the mechanisms underlying the two behaviors can be distinguished pharmacologically. In contrast to both MK-801 and 7-NINA, coadministration of agmatine with NMDA dose dependently inhibited both the nociceptive behavior and the thermal hyperalgesia at significantly different potencies (Fig. 1C). Agmatine inhibited the nociceptive behavior with 21-fold lower potency than for the thermal hyperalgesia (Table 1); it is noteworthy that the confidence intervals (CIs) of these dose-response curves are nonoverlapping. Additionally, agmatine seemed to act as a partial antagonist against the nociceptive behavior, but a full antagonist against the thermal hyperalgesia. The differential pharmacology between the two dependent measures suggests two separate sites of action for agmatine in the spinal cord. These experiments were all replicated with similar outcomes; a replication of the agmatine experiment was reported previously (Fairbanks et al., 2000). There was no evidence of adverse or toxic effects of agmatine at any of the doses evaluated.
Time-Effect Course of Agmatine-Mediated Inhibition of NMDA-Evoked Behavior and Thermal Hyperalgesia. Intrathecally administered agmatine (60 nmol i.t.) consistently and reproducibly partially antagonized NMDA-evoked nociceptive behavior and fully inhibited the thermal hyperalgesia when coadministered with NMDA. To determine the time-effect relationship of agmatine in these two pharmacodynamic measures, the most effective dose (60 nmol i.t.) of agmatine (or saline) was intrathecally administered as a pretreatment 1, 3, 10, 30, and 60 min before the administration of NMDA (Fig. 2). In both measures, the inhibitory effect of agmatine persisted at 1-, 3-, and 10-min pretreatment. The effect was not present at 30 or 60 min. These results indicate the pharmacodynamic activity of agmatine may be limited to a relatively short time window in acutely measured behavior such as this model. These experiments were replicated with similar outcomes.
|
|
|
In a more restricted study (n = 4–5 per group), a dose of 60 nmol of agmatine was injected (i.t.), and tissue and serum were collected at selected time points (1, 10, and 30 min). The Cmax values of agmatine in lumbosacral (230 ± 34 pmol/mg), thoracic (340 ± 68 pmol/mg), and cervical tissue (120 ± 52 pmol/mg) at this dose were approximately half those quantified at the respective spinal levels after the 120-nmol dose (Table 1), as would be expected for dose-independent pharmacokinetics. Additionally, in this instance, brainstem samples also were collected and evaluated; the Cmax in brainstem was 58 ± 2.0 pmol/mg. As in the samples collected for the 120-nmol dose, the samples from the 60-nmol study showed a clear rostral decline in concentrations from lumbosacral to cervical to brainstem, as would be expected for a molecule that is largely retained within the CNS with minor redistribution to the systemic circulation.
To determine whether the source of the serum agmatine was redistribution from the intrathecal space to the vasculature or from possible leakage to the systemic circulation from the musculoskeletal tissue surrounding injection site, we conducted a side-by-side comparison of serum collected from mice injected with agmatine (120 nmol/5 µl) either i.t. or intramuscularly (i.m.) at the 1-min time point. The i.m. route was included to control for the possibility that leakage from the intrathecal injection into the muscle surrounding the spinal column could account for the presence of agmatine in the serum. Intrathecally injected agmatine resulted in significantly greater serum concentrations of 12 ± 2.0 pmol/µl (n = 8) compared with agmatine serum concentrations of 3.5 ± 0.76 pmol/µl(n = 8) from i.m. injection (Student's t test; p < 0.01). These data support the hypothesis that the source of the serum agmatine represented in Figs. 3 and 4 is most likely to be the agmatine delivered to the intrathecal space (rather than leakage to the musculoskeletal area surrounding the column) and subsequently redistributed to the systemic circulation via the CNS microvasculature.
For pharmacokinetic comparison with the i.t. injections, a set of systemic administrations (n = 5–6 per group), with a dose of 100 mg/kg (11 µmol/mouse) agmatine was injected intraperitoneally (i.p.) or intravenously (i.v.) by tail vein delivery, and tissue and serum were collected at selected time points. The Cmax value of i.p.-delivered agmatine in serum was 907 ± 212 pmol/µl) at 1-min postinjection and declined to 12 ± 5 (S.D.) pmol/µl by 180 min. Agmatine was undetectable in spinal cord tissue under these conditions at this dose given by the i.p. route of administration. In contrast, the Cmax value of i.v.-delivered agmatine in serum was 4020 ± 1220 (S.D.) pmol/µl at 1-min postinjection and declined to 42 ± 17 pmol/mg by 60 min. Agmatine was detectable in spinal cord tissue after i.v. administration with a maximum concentration (58 ± 7 pmol/mg) at 1-min postinjection, which declined to 17 ± 9 pmol/mg by 30 min. These data confirm that although CNS levels may be very limited, agmatine is detectable in CNS after i.v. administration of 100 mg/kg, a dose commonly used in pharmacological studies of exogenously applied agmatine (Nguyen et al., 2003).
Pharmacokinetic Parameter Estimates for Intrathecally Administered Agmatine. Noncompartmental analysis of mean concentrations revealed decreasing agmatine exposure, with increasing distance from the site of the intrathecal injection (Table 2). Less than a 3-fold difference was seen in agmatine exposure between the most separated spinal cord regions, suggesting widespread spinal cord distribution of agmatine upon intrathecal injection. AUC ratios between spinal cord and serum were more than 1000-fold higher for all spinal cord regions (supporting a centrally mediated agmatine effect in the behavioral assays discussed in Introduction). The half-lives were similar in all spinal cord regions ranging from t1/2 = 11.1 to 12.6 h, in contrast to the serum half-life, t1/2 = 6.9 min. In the restricted lower dose experiment (60-nmol injection), the serum t1/2 was comparable to the 120-nmol dose experiment.
|
|
Discussion |
|---|
|
TopAbstractMaterials and MethodsResultsDiscussionReferences |
|---|
). Asserting that claim requires, among other things, testing the hypothesis that, when administered exogenously, agmatine produces pharmacological effects comparable with the proposed physiological effects of the putative endogenous molecule (Kandel et al., 2000). Since its discovery in the CNS (Li et al., 1994), there have been approximately 60 studies evaluating a variety of physiological effects produced by exogenous administration of agmatine. Most of these studies applied a systemic (rather than a central) route of administration. Despite the positive pharmacodynamic results demonstrated by many of these reports, the duration of high serum or plasma agmatine levels after systemic delivery is very short (Raasch et al., 2002; Nguyen et al., 2003; Piletz et al., 2003). Furthermore, CNS levels of agmatine after standard systemic doses have had limited description (Raasch et al., 2002; Nguyen et al., 2003; Piletz et al., 2003). The pharmacokinetics of CNS agmatine have not been evaluated. To begin to address these issues, the present study directly compared spinal cord pharmacokinetic parameters with acute pharmacodynamic responses to agmatine after a single intrathecal injection in mice.
Pharmacodynamic Studies of Spinal Agmatine. We have previously observed that intrathecally administered agmatine (decarboxylated arginine) inhibits carrageenan-evoked mechanical hyperalgesia (Fairbanks et al., 2000), prevents morphine-induced acute tolerance (Fairbanks and Wilcox, 1997), and reverses neuropathy-induced hyperalgesia (Fairbanks et al., 2000) in mice. These behavioral models of plasticity require 3-, 8-, and 24-h induction periods, respectively, and all have shown a dependence on the NMDA receptor/NOS cascade. These induction periods inherently contain an induction phase and a maintenance phase, the borders of which are not clearly defined. Therefore, it is challenging to temporally pinpoint the action of a modulator (e.g., MK-801, L-NAME, or agmatine). In other words, the point at which the modulator exerts its effect is not clearly defined. We have also observed that agmatine acutely inhibits both the nociceptive scratching and biting behavior (NMDA receptor-dependent) and the thermal hyperalgesia (NMDA receptor- and NOS-dependent) that arises when NMDA is directly injected into the intrathecal space (Fairbanks et al., 2000) (Fig. 1C). These NMDA-induced responses take place on 5-s to 5-min time frames, respectively. Compared with the models of longer induction, maintenance, and duration described above, these time periods can be more comprehensively parsed for timing of action. We therefore evaluated whether agmatine could differentially inhibit two phases of a rapid induction model of behavioral plasticity (NMDA receptor/NOS cascade behavioral and thermal hyperalgesia) to determine whether the temporal characteristics of this model are useful for examining agmatine action in the CNS.
Antagonism of NMDA-Induced Nociceptive Behavior and Thermal Hyperalgesia. Agmatine has been previously shown to antagonize NMDA receptors (Yang and Reis, 1999; Fairbanks et al., 2000) and inhibit NOS (Auguet et al., 1995; Galea et al., 1996). Because induction of neuronal NOS follows NMDA-induced activation, we compared the ability of agmatine to inhibit two NMDA-induced behavioral sequelae. NMDA (0.3 nmol) delivered intrathecally produces a scratching and biting behavior that persists for about a minute after injection. This behavior is dose dependently antagonized by coinjection of NMDA with a variety of classically defined noncompetitive (MK-801, dextromethorphan, ketamine, and memantine), competitive (LY235959), NR2B subunit-selective (ifenprodil) NMDA receptor antagonists (Fairbanks et al., 2000). Like the NMDA receptor antagonists, agmatine dose dependently inhibited the NMDA-evoked behavior, although with a lower potency (Fairbanks et al., 2000; Fig. 1C). The rank order of potency for antinociceptive activity of NMDA antagonists in this model was LY235959 > ketamine = ifenprodil = mementaine = aminoguanidine > MK-801 > agmatine. We also tested agmatine in a model of NMDA-evoked thermal hyperalgesia. This behavior is dependent on three steps: NMDA receptor activation, NOS activation, and extracellular diffusion of nitric oxide (Kitto and Wilcox, 1992). The thermal hyperalgesia response was inhibited by the noncompetitive NMDA receptor antagonist, MK-801, with approximately the same potency observed for prevention of the nociceptive behaviors. The equal potency of MK-801 in both measures would be expected, since the NMDA receptor operates upstream of NOS, such that blockade of NMDA receptor should prevent activation of NOS.
Previous studies have shown that intrathecal delivery of NOS inhibitors (e.g., L-NAME) prevents the development of NMDA-induced thermal hyperalgesia in rodents (Kitto et al., 1992; Malmberg and Yaksh, 1993), but it does not affect the NMDA-evoked nociceptive behavioral component of the response in mice (Kitto et al., 1992; Fairbanks et al., 2000). This would also be expected since the NOS inhibitors, acting downstream of NMDA receptors, should not affect their initial activation. The present demonstration that the selective neuronal NOS inhibitor 7-NINA (Moore et al., 1993) also inhibited development of the thermal hyperalgesia without affecting the behavior (Fig. 1B) is consistent with this inference and our previous results using the nonselective NOS inhibitor L-NAME (Kitto et al., 1992; Fairbanks et al., 2000); the 7-NINA results suggest that the behavior may depend upon neuronal NOS. However, further studies would be needed to evaluate the potential relative contributions of inducible NOS and endothelial NOS.
Like MK-801, agmatine dose dependently inhibited both the nociceptive behavior and the thermal hyperalgesia. However, a notable difference was that agmatine inhibited the thermal hyperalgesia with significantly higher potency compared with antagonism of the nociceptive behaviors measured in the same subject. Additionally, agmatine fully inhibits the thermal hyperalgesia but only partially antagonizes the nociceptive behavior. These differences are consistent with previous reports that agmatine acts at both NOS (Galea et al., 1996) and NMDA receptors (Yang and Reis, 1999). In this case, perhaps blockade at both sites acts in an autopotentiating manner. Since we have previously observed (Fairbanks et al., 2000) that agmatine exhibits relatively long-term effectiveness in two models of carrageenan-evoked hyperalgesia (on the order of hours) and in two chronic models of mechanical hyperalgesia (dynorphin- and spinal nerve ligation-induced, on the order of weeks), we evaluated the time course for agmatine in both NMDA-evoked nociceptive behavior and thermal hyperalgesia. Interestingly, the effectiveness of agmatine as a pretreatment to the NMDA diminished relatively rapidly, on the order of minutes. This result would imply either a rapid clearance of agmatine from the CNS or a redistribution of agmatine from its pharmacological targets (e.g., clearance from the synapse or intracellular proximity to NOS). The pharmacokinetic data support the latter argument. However, it is evident that agmatine residence in the CNS is significantly longer than its ability to inhibit acute NMDA-evoked pharmacodynamic events.
Pharmacokinetic Studies. After a single intrathecal bolus delivery of agmatine, serum and spinal cord tissue (lumbo-sacral, thoracic, and cervical levels) were collected and analyzed by HPLC. At 1-min postinjection, agmatine was present in the serum at its peak concentration (Cmax), which means that a small but significant component of agmatine was redistributed to the systemic circulation rapidly (if not immediately) after injection. Consistent with other preliminary reports evaluating the half-life of agmatine in serum or plasma after its systemic injection (Raasch et al., 2002; Nguyen et al., 2003; Piletz et al., 2003), elimination of agmatine from serum occurred rapidly, on the order of minutes. In contrast, agmatine reached its maximum concentration in the spinal cord at all levels by 60 min and persisted at levels comparable with the peak concentration as long as 6 h. This finding is consistent with a preclinical pilot study where a retired experimental monkey received agmatine intracerebroventricularly (300 µg/kg); CSF sampled at 24 h postinjection showed agmatine in the 300 µM range. Therefore, two independent studies in two species show that exogenous agmatine persists in the CNS (CSF and spinal cord tissue) on the order of hours to days rather than minutes to hours as is observed in serum. The fact that intrathecally administered agmatine persists in mouse spinal cord tissue on the order of hours to days is consistent with the longer pharmacodynamic efficacy observed in the inflammation and chronic pain models. However, it contrasts with the acute pharmacodynamic effects presented in Figs. 1 and 2. Together, these observations imply a CNS cellular uptake and storage system for agmatine as yet to be defined.
In conclusion, previous reports have shown that exogenously applied agmatine inhibits NMDA receptor/NOS-dependent phenomena (e.g., persistent pain and opioid tolerance) with an either documented or implied duration of action on the order of hours to days. However, this study shows that in one model of acutely induced NMDA-evoked behavior and hyperalgesia agmatine's duration of action is on the order of minutes. These results would on the surface seem incongruent with the previous reports except that the spinal pharmacokinetic data presented here indicate a clear prolonged duration of agmatine residence within spinal tissue, consistent with previous pharmacodynamic studies; these pharmacodynamic results stand in contrast to serum levels and kinetics. The short duration of agmatine's action in the NMDA-evoked behavior and hyperalgesia model together with its long duration of residence in the spinal cord tissue suggests yet unidentified mechanisms of retention in and clearance from its pharmacological targets. Further studies are needed to clarify this aspect of agmatinergic neuropharmacology.
|
Acknowledgements |
|---|
|
Footnotes |
|---|
Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
ABBREVIATIONS: CNS, central nervous system; NMDA, N-methyl-D-aspartate; CSF, cerebrospinal fluid; 7-NINA, 7-nitroindazole; HPLC, high-performance liquid chromatography; AUC, areas under the curve; CI, confidence interval; L-NAME, N
-nitro-L-arginine methyl ester; NOS, nitric-oxide synthase; LY235959, (-)-6-phosphonomethyl-deca-hydroisoquiinoline-3-carboxylic acid.
Address correspondence to: Dr. Carolyn A. Fairbanks, Department of Pharmaceutics, University of Minnesota, 9-177 Weaver Densford Hall, 308 Harvard St. S.E., Minneapolis, MN 55455. E-mail: carfair{at}umn.edu
|
References |
|---|
|
TopAbstractMaterials and MethodsResultsDiscussionReferences |
|---|
Aanonsen LM and Wilcox GL (1987) Nociceptive action of excitatory amino acids in the mouse: effects of spinally administered opioids, phencyclidine and 
agonists. J Pharmacol Exp Ther 243: 9-19.
Auguet M, Viossat I, Marin JG, and Chabrier PE (1995) Selective inhibition of inducible nitric oxide synthase by agmatine. Jpn J Pharmacol 69: 285-287.[Medline]
Codd EE, Press JB, and Raffa RB (1995) Alpha 2-adrenoceptors vs. imidazoline receptors: implications for alpha 2-mediated analgesia and other noncardiovascular therapeutic uses. Life Sci 56: 63-74.[CrossRef][Medline]
deMontigny P, Stobach JF, Givens RS, Carlson RG, Srinivasachar K, Sternson LA, and Higuchi T (1987) Naphthalene-2-3-dicarboxaldehyde/cyanide ion: a rationally designed fluorogenic reagent for primary amines. Anal Chem 59: 1096-1101.[CrossRef]
Faden AI and Simon RP (1988) A potential role for excitotoxins in the pathophysiology of spinal cord injury. Ann Neurol 23: 623-626.[CrossRef][Medline]
Fairbanks CA (2003) Spinal delivery of analgesics in experimental models of pain and analgesia. Adv Drug Deliv Rev 55: 1007-1041.[CrossRef][Medline]
Fairbanks CA, Schreiber KL, Brewer KL, Yu CG, Stone LS, Kitto KF, Nguyen HO, Grocholski BM, Shoeman DW, Kehl LJ, et al. (2000) Agmatine reverses pain induced by inflammation, neuropathy and spinal cord injury. Proc Natl Acad Sci USA 97: 19584-19589.
Fairbanks CA and Wilcox GL (1997) Acute tolerance to spinally administered morphine compares mechanistically with chronically induced morphine tolerance. J Pharmacol Exp Ther 282: 1408-1417.
Feng Y, Halaris AE, and Piletz JE (1997) Determination of agmatine in brain and plasma using high-performance liquid chromatography with fluorescence detection [erratum appears in J Chromatogr B Biomed Sci Appl 1997;696:173]. J Chromatogr Biomed Appl 691: 277-286.
Galea E, Regunathan S, Eliopoulos V, Feinstein DL, and Reis DJ (1996) Inhibition of mammalian nitric oxide synthases by agmatine, an endogenous polyamine formed by decarboxylation of arginine. Biochem J 316: 247-249.
Horvath G, Kekesi G, Dobos I, Szikszay M, Klimscha W, and Benedek G (1999) Effect of intrathecal agmatine on inflammation-induced thermal hyperalgesia in rats. Eur J Pharmacol 368: 197-204.[CrossRef][Medline]
Hou SW, Qi JS, Zhang Y, and Qiao JT (2003) Spinal antinociceptive effect of agmatine and tentative analysis of involved receptors: study in an electrophysiological model of rats. Brain Res 968: 277-280.[CrossRef][Medline]
Hylden JLK and Wilcox GL (1980) Intrathecal morphine in mice: a new technique. Eur J Pharmacol 67: 313-316.[CrossRef][Medline]
Kandel EA, Schwartz JH, and Jessell TM (2000) Principles of Neuroscience, 4th ed, McGraw-Hill Companies, New York.
Kitto KF, Haley JE, and Wilcox GL (1992) Involvement of nitric oxide in spinally mediated hyperalgesia in the mouse. Neurosci Lett 148: 1-5.[CrossRef][Medline]
Kolesnikov Y, Jain S, and Pasternak GW (1996) Modulation of opioid analgesia by agmatine. Eur J Pharmacol 296: 17-22.[CrossRef][Medline]
Li G, Regunathan S, Barrow CJ, Eshraghi J, Cooper R, and Reis DJ (1994) Agmatine: an endogenous clonidine-displacing substance in the brain [see comments]. Science (Wash DC) 263: 966-969.
Malmberg AB and Yaksh TL (1993) Spinal nitric oxide synthesis inhibition blocks NMDA-induced thermal hyperalgesia and produces antinociception in the formalin test in rats. Pain 54: 291-300.[CrossRef][Medline]
Mao J, Price DD, Mayer DJ, Lu J, and Hayes RL (1992) Intrathecal MK-801 and local nerve anesthesia synergistically reduce nociceptive behaviors in rats with experimental peripheral mononeuropathy. Brain Res 576: 254-562.[CrossRef][Medline]
Moore PK, Wallace P, Gaffen Z, Hart SL, and Babbedge RC (1993) Characterization of the novel nitric oxide synthase inhibitor 7-nitro indazole and related indazoles: antinociceptive cardiovascular effects. Br J Pharmacol 110: 219-224.[Medline]
Morgan AD, Campbell UC, Fons RD, and Carroll ME (2002) Effects of agmatine on the escalation of i.v. cocaine and fentanyl self-administration in rats. Pharmacol Biochem Behav 72: 873-880.[CrossRef][Medline]
Nguyen HO, Goracke-Postle CJ, Kaminski LL, Overland AO, Morgan AD, and Fairbanks CA (2003) Neuropharmacokinetic and dynamic studies of agmatine. Ann NY Acad Sci 1009: 82-105.[CrossRef][Medline]
Piletz JE, May PJ, Wang G, and Zhu H (2003) Agmatine crosses the blood-brain barrier. Ann NY Acad Sci 1009: 64-74.[CrossRef][Medline]
Pinthong D, Wright IK, Hanmer C, Millns P, Mason R, Kendall DA, and Wilson VG (1995) Agmatine recognizes alpha 2-adrenoceptor binding sites but neither activates nor inhibits alpha 2-adrenoceptors. Naunyn-Schmiedeberg's Arch Pharmacol 351: 10-16.[Medline]
Raasch W, Regunathan S, Li G, and Reis DJ (1995) Agmatine, the bacterial amine, is widely distributed in mammalian tissues. Life Sci 56: 2319-2330.[CrossRef][Medline]
Raasch W, Schafer U, Qadri F, and Dominiak P (2002) Agmatine, an endogenous ligand at imidazoline binding sites, does not antagonize the clonidine-mediated blood pressure reaction. Br J Pharmacol 135: 663-672.[CrossRef][Medline]
Reis DJ and Regunathan S (1998) Agmatine: a novel neurotransmitter? Adv Pharmacol 42: 645-649.
Semenova S, Danysz W, and Bespalov A (1999) Low-affinity NMDA receptor channel blockers inhibit acquisition of intravenous morphine self-administration in naive mice. Eur J Pharmacol 378: 1-8.[CrossRef][Medline]
Tallarida RJ (2000) Drug Synergism and Dose-Effect Data Analysis, Chapman-Hall/CRC Press, Boca Raton, FL.
Tallarida RJ and Murray RB (1987) Manual of Pharmacological Calculations with Computer Programs, pp 26-31, Springer, New York.
Tiseo PJ and Inturissi CE (1993) Attenuation and reversal of morphine tolerance by the competitive NMDA receptor antagonist, LY274614. J Pharmacol Exp Ther 264: 1090-1096.
Trujillo KA and Akil H (1991) Inhibition of morphine tolerance and dependence by the NMDA receptor antagonist MK-801. Science (Wash DC) 251: 85-87.
Wells JL, Bartlett JL, Ananthan S, and Bilsky EJ (2001) In vivo pharmacological characterization of SoRI 9409, a nonpeptidic opioid µ-agonist/
-antagonist that produces limited antinociceptive tolerance and attenuates morphine physical dependence. J Pharmacol Exp Ther 297: 597-605.
Xie JY, Herman DS, Stiller CO, Gardell LR, Ossipov MH, Lai J, Porreca F, and Vanderah TW (2005) Cholecystokinin in the rostral ventromedial medulla mediates opioid-induced hyperalgesia and antinociceptive tolerance. J Neurosci 25: 409-416.
Yang XC and Reis DL (1999) Agmatine selectively blocks the N-methyl-L-aspartate subclass of glutamate receptor channels in rat hippocampal neurons. J Pharmacol Exp Ther 288: 544-549.
This article has been cited by other articles:
|
|
 |
|
  C. Courteix, A.-M. Privat, T. Pelissier, A. Hernandez, A. Eschalier, and J. Fialip Agmatine Induces Antihyperalgesic Effects in Diabetic Rats and a Superadditive Interaction with R( )-3-(2-Carboxypiperazine-4-yl)-propyl-1-phosphonic Acid, a N-Methyl-D-aspartate-Receptor Antagonist J. Pharmacol. Exp. Ther., September 1, 2007; 322(3): 1237 - 1245. [Abstract] [Full Text] [PDF]
|
|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 |
 |
 |
|
 |
 |
 |
