![[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
Neuroscience Discovery Research, Wyeth Research, Princeton, New Jersey
Received for publication
February 4, 2005
Accepted
March 8, 2005.
 |
Abstract |
|---|
 Top Abstract Materials and MethodsResultsDiscussionReferences |
|---|
; Kawamata and Omote, 1996; Dickenson et al., 1997). Repeated stimulation of primary afferent fibers can progressively increase the magnitude and duration of action potentials in spinal cord (often termed "windup"), which can lead to central sensitization (Ma and Woolf, 1995). This neuronal hyperexcitability manifests itself in a lowered threshold to evoked activity (i.e., hyperalgesia), an expansion of receptive fields (i.e., secondary hypersensitivity), and an ability of non-noxious input to evoke neuronal activity (i.e., allodynia). In preclinical studies, NMDA receptor antagonists reverse neuronal hyperexcitability and reverse hypersensitivity in several inflammatory and neuropathic animal pain models associated with various pathophysiologic mechanisms (Mao et al., 1993; Chaplan et al., 1997; Suzuki et al., 2001). In clinical studies, NMDA receptor antagonists, such as ketamine and dextromethorphan, reduce windup pain, spontaneous pain, hyperalgesia, and allodynia in patients with postherpetic neuralgia pain, phantom limb pain, and diabetic neuropathy pain (Stubhaug and Breivik, 1997; Rabben et al., 1999; Sang, 2000). However, the narrow separation between effectiveness and adverse effects, including sedation and psychotomimetic effects, of clinically available NMDA receptor antagonists has severely hampered their utility for the treatment of neuropathic pain.
Perzinfotel is a selective, competitive small molecule antagonist that blocks the actions of glutamate at the NMDA receptor (Kinney et al., 1998; Childers et al., 2002; Sun et al., 2004). Previous studies have demonstrated its effectiveness in several animal stroke models and anticonvulsant models (Childers et al., 2002). Importantly, perzinfotel has an adverse effect profile superior to many other reported competitive (e.g., CGS-19755) and uncompetitive (e.g., dizocilpine) antagonists (Kinney et al., 1998; Childers et al., 2002). Given the apparent involvement of NMDA receptors in pain conditions, perzinfotel was evaluated in preclinical pain assays to determine whether the compound would have antinociceptive, antiallodynic, or antihyperalgesic effects.
|
Materials and Methods |
|---|
|
TopAbstractMaterials and MethodsResultsDiscussionReferences |
|---|
). Subjects. Male Sprague-Dawley rats (Charles River Laboratories, Inc., Wilmington, MA) weighing 200 to 250 g at time of arrival were individually housed in wire cages in a climate-controlled room. A 12-h light/dark cycle (lights on at 06:30 AM) was in effect for all animals, and water was available ad libitum. In the operant responding study, rats were food restricted to 10 to 15 g of food postsession and food pellets earned during sessions. For all oral dosing studies, rats were fasted for approximately 16 h before drug administration. With these exceptions, all other rats were fed ad libitum.
Thermal Sensitivity Assessed by Warm-Water Tail Withdrawal. To asses baseline thermal sensitivity, the terminal 10 cm of the tail was placed into water warmed to 34, 38, 42, 46, 50, 54, or 58°C. The latency in seconds for the animal to remove the tail from the water was used as a measure of nociception. If the animal did not remove the tail within 20 s, the experimenter removed the tail and a maximum latency of 20 s was recorded. The antinociceptive effects of morphine or perzinfotel were evaluated in a cumulative dosing paradigm. Under this procedure, doses of morphine or perzinfotel, increasing in 0.5 log unit increments, were administered intraperitoneal (i.p.) every 30 min. Tail-withdrawal latencies were assessed during the 5-min period at the end of each 30-min period (i.e., 25–30 min after drug administration).
Prostaglandin E2 (PGE2)- and Capsaicin-Induced Thermal Hypersensitivity Assessed by Warm-Water Tail Withdrawal. Following the assessment of baseline thermal sensitivity, thermal hypersensitivity was produced by an intradermal 50-µl injection of PGE2 (Sigma-Aldrich, St. Louis, MO) or capsaicin (Sigma-Aldrich) into the distal 1 cm of the tail. Temperature-effect curves were generated before (baseline) and after (15, 30, 60, 90, and 120 min) PGE2 (0.01–0.1 mg) or capsaicin (0.001–0.1 mg) injection. To evaluate whether baseline thermal sensitivity or the magnitude of thermal hypersensitivity changed after repeated PGE2 administration, eight rats were administered PGE2 weekly for 3 weeks, and thermal sensitivities were assessed before and 30 min after the administration of 0.1 mg of PGE2. Based on results from the current study, as well as results of PGE2 and capsaicin in other species, such as rhesus monkeys (Brandt et al., 2001), subjects were tested a maximum of three times with a minimum of 5 days between tests (one baseline 0.1 mg of PGE2 or 0.01 mg of capsaicin assessment and one or two compound tests in the presence of 0.1 mg of PGE2 or 0.01 mg of capsaicin).
To assess the chronic effects of perzinfotel, 10 mg/kg perzinfotel was administered, and the duration of PGE2-induced thermal hypersensitivity was assessed 30 min later for 2 h. Subjects were then dosed daily with 10 mg/kg perzinfotel for 2 weeks. The ability of perzinfotel to block thermal hypersensitivity was reassessed 1 week and again 2 weeks after the beginning of chronic daily treatment under conditions identical to the first determination.
The ability of compounds to block 0.1 mg of PGE2- or 0.01 mg of capsaicin-induced thermal hypersensitivity was assessed using a single dose procedure. Under this procedure, a single dose of compound was administered i.p. or p.o. 30 min before the injection of PGE2 or capsaicin, and thermal sensitivities were assessed 30 min after PGE2 or capsaicin injection (i.e., drug effects were evaluated 60 min after administration). This pretreatment time was chosen based on preliminary rodent pharmacokinetic studies, which indicated that the time to peak concentration (tmax) of perzinfotel was between 0.3 and 1 h after p.o. administration (20 and 100 mg/kg) and 0.3 h after i.p. administration (10 mg/kg). Apparent terminal half-lives (t1/2) were 1.3 to 7.8 h after p.o. administration and 0.5 h after i.p. administration. In addition, preliminary time course studies indicated that the behavioral effects of perzinfotel were maximal when administered 30 min before PGE2 by the oral route of administration. For i.t. administration of perzinfotel, rats were anesthetized with isoflurane, and an incision was made along the dorsal midline from approximately L3 to S2. Perzinfotel was administered into the intrathecal space at the level of the lumbar enlargement in a volume of 20 µl using a 50-µl Hamilton syringe. PGE2 was administered at the same time as i.t. perzinfotel, and thermal hypersensitivity was evaluated 30 min later.
Effects of Perzinfotel on Schedule-Controlled Responding. To evaluate the potential for drugs to modify tail-withdrawal latencies by mechanisms unrelated to pain (i.e., sedation), compounds were also evaluated for their ability to suppress operant rates of responding. Experimental sessions were conducted in operant conditioning chambers located inside ventilated sound-attenuating chambers that were equipped with white noise to mask extraneous sounds (MED Associates Inc., Georgia, VT). A response lever and a food trough were located on the front panel of the operant chamber. The operant chambers were controlled and monitored by computers with hardware and software from MED Associates Inc.
Rats were trained to respond on one lever under a fixed ratio-30 schedule of food presentation (Bioserv 45-mg pellets; Bioserv, Frenchtown, NJ). Daily experimental sessions consisted of three components. Each component consisted of a 10-min timeout period followed by a 10-min response period; thus, daily sessions totaled 60 min. During the timeout period, the chamber was dark, and there were no programmed consequences. During the response component, the house light was illuminated, and lever pressing was associated with an audible feedback click. Experimental sessions were conducted daily (Monday through Friday). Test sessions assessing the effects of compounds were typically conducted 2 days per week (Tuesday and Friday), provided response rates were within 20% of the previous 5 training day mean on the day preceding the test. Compounds were administered i.p. or p.o. at the start of the first cycle. To equate rate effects with irritant-induced thermal hypersensitivity, which assessed the effects of drugs 60 min after administration, response rates for only the last cycle (i.e., 50–60 min after drug administration) were used for comparison.
Data Analysis. Temperature-effect curves were generated for each experimental condition for individual rats. The temperature that produced a half-maximal increase in the tail-withdrawal latency (i.e., T10) was calculated from each temperature-effect curve. The T10 was determined by interpolation from a line drawn between the point above and the point below 10 s on the temperature-effect curve. For these studies, thermal hypersensitivity was defined as a leftward shift in the temperature-effect curve and a decrease in the T10 value. Statistical analysis was done using a within-subjects repeated measures analysis of variance on T10 values. The criterion for significant reversal of the T10 value from the chemical irritant alone was p < 0.05.
Reversal of thermal hypersensitivity was defined as a return to baseline of the temperature-effect curve and the T10 value. Blockade of irritant-induced thermal hypersensitivity was quantified as the percentage return to baseline values (% reversal) according to the following equation:
 |
Operant response rates for the last cycle were converted to percentage of vehicle control by using the average rate from the previous training day as the control value (i.e., average of three cycles). ED50 values and 95% confidence limits for both decreases in operant responding and reversal of thermal hypersensitivity were calculated by linear regression when at least three data points were available on the linear portion of the dose-effect curve or by interpolation when two data points (one above and one below 50%) were available. ED50 values were typically not calculated when effects did not reach a magnitude of at least 50%.
Drugs. Memantine and dizocilpine (MK-801) were purchased from Sigma/RBI (Natick, MA). Amitriptyline, prostaglandin E2, and ifenprodil were purchased from Sigma-Aldrich. Selfotel (CGS-19755), L-701324, and (R,S)CPP were purchased from Tocris Cookson Inc. (Ellisville, MO). Morphine was purchased from Mallinckrodt, Inc. (St. Louis, MO), and ketamine was purchased from J. A. Webster Inc. (Sterling, MA). Ifenprodil and L-701324 were dissolved in 2% Tween 80/0.5% methylcellulose and sterile water. Low concentrations of perzinfotel were dissolved in sterile water, and concentrations for oral dosing higher than 10 mg/ml were dissolved in 2% Tween 80/0.5% methylcellulose and sterile water. All other compounds were dissolved in sterile water. Drug concentration doses were calculated using the molecular weight of the base form and were administered in a volume of 1 ml/kg with the dose administered calculated as milligrams per kilograms.
|
Results |
|---|
|
TopAbstractMaterials and MethodsResultsDiscussionReferences |
|---|
|
Based on these results, drugs were assessed 30 min after the administration of 0.1 mg of PGE2 or 0.01 mg of capsaicin. Figure 2 shows the baseline temperature-effect curve at this time (the dotted line at the 10-s latency represents the T10 value). The intradermal administration of 0.1 mg of PGE2 or 0.01 mg of capsaicin into the distal end of the tail shifted the temperature-effect curve to the left and produced a decrease in the T10. Thirty minutes after administration, rats removed the tail from temperatures of water that were previously innocuous (34–46°C) and rapidly removed the tail from temperatures of water that had previously been partially noxious (50°C). A 0.1-mg dose of PGE2 produced a 4.5°C decrease in the T10, whereas a dose of 0.01 mg of capsaicin produced a larger 8.4°C decrease in the T10.
|
|
|
Morphine dose-dependently blocked PGE2-induced thermal hypersensitivity. Doses higher than 0.3 mg significantly blocked thermal hypersensitivity, and a dose of 3 mg/kg fully blocked hypersensitivity (Fig. 5; left panel). The ED50 for morphine in this assay is shown in Table 1. Similar to morphine, perzinfotel dose-dependently blocked PGE2-induced thermal hypersensitivity. A 3 mg/kg dose of perzinfotel i.p. administered 30 min before PGE2 significantly blocked PGE2-induced hypersensitivity. A higher dose of 10 mg/kg i.p. blocked PGE2-induced thermal hypersensitivity by 79%. Perzinfotel was also effective after oral administration with significant blockade observed after 30 mg/kg and a 62% reversal observed after 100 mg/kg. Based on ED50 values, perzinfotel was 22-fold less potent after oral administration than after i.p. administration (Table 1). Perzinfotel was also effective after i.t. administration. Concentrations of 0.3, 1, and 3 nM reversed PGE2-induced thermal hypersensitivity by 34.8 ± 4.4, 56.3 ± 6.9, and 61.1 ± 5.5%, respectively. The calculated ED50 for i.t. perzinfotel was 0.90 nM (95% CL 0.49–1.65).
|
|
Similar to their effects in the PGE2 assay, morphine and perzinfotel dose-dependently blocked capsaicin-induced thermal hypersensitivity. The potency of morphine in the capsaicin assay (ED50 = 1.43; 95% CL 1.14–1.79) was similar to its potency in the PGE2 assay. Doses of perzinfotel higher than 1 mg/kg i.p. significantly blocked capsaicin-induced hypersensitivity, and a dose of 10 mg/kg produced a 77% reversal. After p.o. administration, all doses of perzinfotel (10–100 mg/kg) significantly blocked capsaicin-induced thermal hypersensitivity. Perzinfotel was 6.6-fold less potent after p.o. administration (ED50 = 31.0; 95% CL 23.3–41.2) compared with i.p. administration (ED50 = 4.7; 95% CL 3.67–6.1).
Effects of Other NMDA Receptor Antagonists on PGE2-Induced Thermal Hypersensitivity. Few other glutamate site NMDA receptor antagonists blocked PGE2-induced thermal hypersensitivity to a similar magnitude as perzinfotel. Doses of 1 and 3 mg/kg CPP significantly blocked thermal hypersensitivity (Fig. 6). A dose of 10 mg/kg CPP produced a 56% reversal; however, a higher dose of 30 mg/kg did not substantially block hypersensitivity further (57%). Selfotel significantly blocked PGE2-induced hypersensitivity at doses of 10 and 30 mg/kg; however, this effect was not greater than a 25% reversal. Similarly, a dose of 10 mg/kg CGP-39653 only produced a 23% reversal.
|
|
Effects of NMDA Receptor Antagonists on Schedule-Controlled Responding. To quantify drug-induced behavioral disruptions, compounds were also evaluated for their ability to suppress operant rates of responding. In rats responding under a fixed ratio-30 schedule of food reinforcement, doses of morphine greater than 1 mg/kg significantly decreased response rates (Fig. 8; left panel). An i.p. dose of 3 mg/kg perzinfotel did not modify rates of responding. Larger i.p. doses of 10 and 30 mg/kg significantly decreased response rates. When administered p.o., doses of perzinfotel up to 178 mg/kg did not modify rates of responding. A larger dose of 300 mg/kg decreased rates of responding by 53% of normal control response rates. Rate-decreasing effects of high doses of perzinfotel produced similar levels of rate suppression over the duration of the 1-h study. For example, 300 mg/kg perzinfotel p.o. decrease response rates to 55.6 ± 17.3, 50.3 ± 17.2, and 46.7 ± 17.0% of control during the first, second, and third cycle, respectively. Similarly, a dose of 30 mg/kg perzinfotel i.p. decreased response rates to 48.2 ± 17.2, 46.8 ± 20.6, and 47.4 ± 20.6% of control during the first, second, and third cycle, respectively.
|
All of the NMDA receptor antagonists evaluated dose-dependently decreased response rates (Fig. 8; right panel). Dizocilpine was the most potent NMDA receptor antagonist for decreasing rates of responding. Other NMDA receptor antagonists decreased response rates over a similar dose range (3–30 mg/kg) and had similar ED50 values (between 5.8 and 23.5 mg/kg). Table 1 shows the ED50 values of compounds for reversing PGE2-induced thermal hypersensitivity, the ED50 values of compounds for decreasing operant rates of responding, and the respective dose ratio for these two effects. Perzinfotel had the largest dose ratios by both i.p. and p.o. routes of administration compared with all other compounds evaluated. Morphine had the next largest ratio followed by L-701324 and (R,S)CPP. All other NMDA receptor antagonists evaluated suppressed rates of responding at doses that were ineffective for reversing PGE2-induced thermal hypersensitivity. Thus, dose ratios for these compounds were less than one.
|
Discussion |
|---|
|
TopAbstractMaterials and MethodsResultsDiscussionReferences |
|---|
Thermal Hypersensitivity Produced by Chemical Irritants. PGE2 is a metabolite of the arachidonic acid cascade, and its effects are mediated by endoperoxide receptors located on primary afferent nociceptors. Agonist stimulation of these receptors activates cAMP-dependent protein kinase, which produces a number of secondary events including enhancement of Ca2+ and NaV currents (Bley et al., 1998). Capsaicin sensitizes primary afferent nociceptors through agonist actions at TRPVR1 (Szallasi and Blumberg, 1999). In the current study, both of these irritants produced hyperalgesia (increased sensitivity to noxious temperatures) and allodynia (increased sensitivity to non-noxious temperatures). These effects of PGE2 and capsaicin in rodents extends previous findings in rhesus monkeys (Negus et al., 1993; Brandt et al., 2001) and in humans (Sciberras et al., 1987; LaMotte et al., 1991). Given the similarities between the dose range and temperature responses in preclinical and clinical studies, these results suggest that capsaicin- and PGE2-induced thermal hypersensitivity could be useful surrogate endpoints when assessing novel compounds having potential clinical utility.
Effects of Perzinfotel and Other NMDA Receptor Antagonists on Chemically Induced Thermal Hypersensitivity. In the present study, perzinfotel lacked antinociceptive effects under conditions where morphine increased tail-withdrawal latencies in normal animals. These results are consistent with the lack of antinociceptive effects observed with other compounds of this class (Dickenson et al., 1997; Lutfy et al., 1997) and indicate that perzinfotel does not modify normal pain sensitivity.
Perzinfotel dose-dependently blocked PGE2-induced thermal hypersensitivity after i.p. and p.o. administration. However, the ability to block PGE2-induced thermal hypersensitivity was not common to all NMDA receptor antagonists. For example, the uncompetitive NMDA receptor antagonists memantine, ketamine, and dizocilpine (MK-801), the NR2B-subunit selective antagonist ifenprodil, and even other competitive glutamate site antagonists (selfotel and CGP-39653) were only minimally effective for preventing PGE2-induced thermal hypersensitivity. It is noteworthy that at doses that produced sedation, ataxia and impairment of operant responding, animals still were able to remove their tails from warm water indicating that animals could still perceive and respond to nociceptive stimuli. Although some studies have demonstrated that ketamine or dizocilpine can decrease inflammatory pain after intrathecal administration (Ren et al., 1992; Klimscha et al., 1998), the current results indicate that dose-limiting adverse effects associated with systemic administration of these compounds impedes observations of therapeutic efficacy, results consistent with other studies in both rodents and humans (Boyce et al., 1999; Sang, 2000).
Effects of Perzinfotel and Other NMDA Receptor Antagonists on Operant Responding. Doses of perzinfotel that fully blocked PGE2-induced thermal hypersensitivity were not associated with disruptions in other behaviors. For example, doses of perzinfotel that decreased operant responding by 50% were 5- to 10-fold higher than doses that produced a 50% blockage of PGE2-induced thermal hypersensitivity. In contrast, other negative modulators of the NMDA receptor evaluated decreased rates of responding and elicited observable signs of sedation and ataxia at doses that lacked any antihyperalgesic effects. L-701324 and (R,S)CPP were the exceptions and did produce greater than a 50% reversal of PGE2 at doses lower than those that decreased rates of responding; however, the separation between alleviating thermal hypersensitivity and decreasing response rates was small. Pharmacokinetic studies with perzinfotel demonstrate rapid absorption and elimination after both p.o. and i.p. routes of administration. Consistent with peak concentrations, the antihyperalgesic effects of perzinfotel in the PGE2 assay are maximal 1 h after p.o. administration and wane by 5 h after administration (M. R. Brandt, unpublished observation). In the current study, rate-decreasing effects of high doses of perzinfotel produced similar levels of rate suppression over the duration of the 1-h study. These results suggest that the behavioral effects of perzinfotel were not fluctuating at the time of testing and that the behavioral assessments were close to the peak plasma concentrations.
Pharmacology of Perzinfotel. Perzinfotel is a selective, competitive NMDA receptor antagonist with high affinity (30 nM) for the glutamate site (Kinney et al., 1998). Perzinfotel lacks activity at more than 60 other receptors, ion channels, or uptake sites (Childers et al., 2002; Sun et al., 2004). In vitro, perzinfotel blocks NMDA-induced currents with an IC50 of 0.48 µM and glutamate-induced neurotoxicity with an IC50 of 1.6 µM. In contrast, perzinfotel does not have appreciable affinity (up to a concentration of 100 µM) for kainate, 
-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, and strychnine-insensitive glycine receptors and does not block -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid- or kainate-induced neurotoxicity (up to a concentration of 1 mM). To date, the activity of perzinfotel is consistent with actions at the NMDA receptor.
The mechanisms for the unique profile of perzinfotel in the current study are being investigated. One possibility is that perzinfotel does not readily cross the blood-brain barrier, thereby precluding centrally mediated adverse effects typical of other NMDA receptor antagonists. Previous studies have demonstrated that peripheral NMDA receptors are involved in heat hypersensitivity associated with inflammation and that this hypersensitivity can be blocked by the local administration of a NMDA receptor antagonist (Davidson et al., 1997; Davidson and Carlton, 1998; Du et al., 2003). Thus, perzinfotel might be blocking peripheral nociceptor input and subsequent central sensitization. However, other data are not fully consistent with this notion. In vivo, systemic administration of perzinfotel blocks lethality induced by an i.c.v. ED90 dose of NMDA (ED50 = 2.1 mg/kg i.p.) and blocks maximal electroshock convulsions (ED50 = 4.8 mg/kg i.p.) in mice (Kinney et al., 1998; Childers et al., 2002). Perzinfotel also reverses established tactile hypersensitivity produced by L5/L6 spinal nerve ligation and chronic constriction injury of the sciatic nerve (M. R. Brandt, unpublished results), both neuropathic pain models thought to be strongly mediated by central mechanisms (Kawamata and Omote, 1996). Moreover, pharmacokinetic studies have shown that perzinfotel does cross the blood-brain barrier, albeit weakly (M. R. Brandt, unpublished results). Together with the i.t. efficacy in the current study, a purely peripheral action of perzinfotel is not fully consistent with its known activity.
A second possibility for the unique activity of perzinfotel could be related to its actions at subpopulations of NMDA receptors. NMDA receptor complexes are comprised of NR1 subunits (of which there are eight splice variants) and NR2 subunits (of which there are four subtypes, NR2A–D). In addition to having discrete localization, subunit composition imparts unique biophysical and pharmacologic properties (Sirinathsinghji and Hill, 2002). Compounds used in the current study have been shown to have different NMDA receptor subtype selectivity. For example, L-701,324, ketamine, dizocilpine, and memantine show little selectivity among the NR1/NR2 subunit combinations (Yamakura et al., 1993; Sucher et al., 1996; Parsons et al., 1999). Selfotel, CGP-39653, and CPP have slightly higher (2- to 3-fold) selectivity for NR1/NR2A subunits than for other NR2 subunits (Laurie and Seeburg, 1994; Christie et al., 2000). In oocytes expressing different NR1/NR2 subunits, perzinfotel was 8- to 13-fold more selective for the NR1/NR2A than either NR1/NR2B or NR1/NR2C (Sun et al., 2004). Thus, among the compounds evaluated in the current study, only perzinfotel was selective for the NR1/NR2A subunit.
Studies suggest that compounds having NR1/NR2B selectivity are more effective for alleviating pain and lack adverse effects compared with nonselective antagonists (Boyce et al., 1999; Chazot, 2004). For example, ifenprodil has 400-fold selectivity for NR1/NR2B over NR1/NR2A (Williams, 1993) and blocks both mechanical hypersensitivity associated with sciatic nerve ligation and carrageenan administration (Boyce et al., 1999). However, like the current study, these effects occurred over a similar dose range as those that impaired rotarod performance (Boyce et al., 1999). Although ifenprodil has selectivity for NR1/NR2B, it also has activity at other non-NMDA receptors such as 1-adrenoceptors (Chenard et al., 1995) and Ca2+ channels (Bath et al., 1996) that might contribute to the impairment of other behaviors. More selective NR1/NR2B compounds (e.g., CP-101606) might reverse PGE2-induced thermal hypersensitivity at doses that are not associated with side effects. However, there are accumulating data suggesting that NR2A plays a significant role in inflammatory pain. For example, mRNA and protein levels of the NR2A subunit are up-regulated to a greater extent than NR2B mRNA in the rostral ventromedial medulla (RVM) after carrageenan injection in the hindpaw of rats (Miki et al., 2002). In another study, formalin injected into the paw increased NR2A mRNA expression in the spinal cord (Gaunitz et al., 2002). However, up-regulation of NR2A mRNA might be specific for inflammatory pain states since nerve injury decreased NR2A in the spinal cord (Karlsson et al., 2002). Taken together, the current study indicates that NR2B selectivity is not the only avenue for improving the adverse effect profile of NMDA antagonists; selectivity for other NMDA receptor subunits might also be important for identifying compounds with therapeutic potential.
|
Acknowledgements |
|---|
|
Footnotes |
|---|
ABBREVIATIONS: NMDA, N-methyl-D-aspartate; selfotel or CGS-19755, cis-4-(phosphonomethyl) piperidine-2-carboxylic acid; PG, prostaglandin; perzinfotel or EAA-090, [2-(8,9-dioxo-2,6-diazabicyclo[5.2.0]non1(7)-en-2-yl)-ethyl]phosphonic acid; dizocilpine or MK-801, (5S,10R)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclohepten-5,10-imine hydrogen maleate; L-701324, 7-chloro-4-hydroxy-3-(3-phenoxy)phenyl-2(1H)-quinolone; CPP, 3-(2-carboxypiperazin-4-yl)propyl-1-phosphonic acid; CL, confidence limits; CGP-39653; D,L-(E)-2-amino-4-propyl-5-phosphono-3-pentenoic acid; CP-101606, (1S,2S)-1-(4-hydroxyphenyl)-2-(4-hydroxy-4-phenylpiperidino)-1-propanol.
Address correspondence to: Dr. Michael R. Brandt, Analgesics Drug Discovery, Johnson and Johnson PRDUS, Welsh and McKean Roads, Spring House, PA 19477-0776. E-mail: mbrandt4{at}prdus.jnj.com
|
References |
|---|
|
TopAbstractMaterials and MethodsResultsDiscussionReferences |
|---|
Bath CP, Farrell LN, Gilmore J, Ward MA, Hicks CA, O'Neill MJ, and Bleakman D (1996) The effects of ifenprodil and eliprodil on voltage-dependent Ca2+ channels and in gerbil global cerebral ischaemia. Eur J Pharmacol 299: 103-112.[CrossRef][Medline]
Bley KR, Hunter JC, Eglen RM, and Smith JAM (1998) The role of ip prostanoid receptors in inflammatory pain. Trends Pharmacol Sci 19: 141-147.[CrossRef][Medline]
Boyce S, Wyatt A, Webb JK, O'Donnell R, Mason G, Rigby M, Sirinathsinghji D, Hill RG, and Rupniak NMJ (1999) Selective NMDA NR2B antagonists induce antinociception without motor dysfunction: correlation with restricted localisation of NR2B subunit in dorsal horn. Neuropharmacology 38: 611-623.[CrossRef][Medline]
Brandt MR, Furness MS, Mello NK, Rice KC, and Negus SS (2001) Antinociceptive effects of delta-opioid agonists in rhesus monkeys: effects on chemically induced thermal hypersensitivity. J Pharmacol Exp Ther 296: 939-946.
Chaplan SR, Malmberg AB, and Yaksh TL (1997) Efficacy of spinal NMDA receptor antagonism in formalin hyperalgesia and nerve injury evoked allodynia in the rat. J Pharmacol Exp Ther 280: 829-838.
Chazot PL (2004) The NMDA receptor NR2B subunit: a valid therapeutic target for multiple CNS pathologies. Curr Med Chem 11: 389-396.[CrossRef][Medline]
Chenard BL, Bordner J, Butler TW, Chambers LK, Collins MA, De Costa DL, Ducat MF, Dumont ML, Fox CB, Mena EE, et al. (1995) (1S,2S)-1-(4-Hydroxyphenyl)-2-(4-hydroxy-4-phenylpiperidino)-1-propanol: a potent new neuroprotectant which blocks N-methyl-D-aspartate responses. J Med Chem 38: 3138-3145.[CrossRef][Medline]
Childers WE, Abou-Gharbia MA, Moyer JA, and Zaleska MM (2002) EAA-090—neuroprotectant, competitive NMDA antagonist. Drugs Future 27: 633-638.[CrossRef]
Christie JM, Jane DE, and Monaghan DT (2000) Native N-methyl-D-aspartate receptors containing NR2A and NR2B subunits have pharmacologically distinct competitive antagonist binding sites. J Pharmacol Exp Ther 292: 1169-1174.
Davidson EM and Carlton SM (1998) Intraplantar injection of dextrorphan, ketamine or memantine attenuates formalin-induced behaviors. Brain Res 785: 136-142.[CrossRef][Medline]
Davidson EM, Coggeshall RE, and Carlton SM (1997) Peripheral NMDA and non-NMDA glutamate receptors contribute to nociceptive behaviors in the rat formalin test. Neuroreport 8: 941-946.[Medline]
Dickenson AH, Chapman V, and Green GM (1997) The pharmacology of excitatory and inhibitory amino acid-mediated events in the transmission and modulation of pain in the spinal cord. Gen Pharmacol 28: 633-638.[CrossRef][Medline]
Du J, Zhou S, Coggeshall RE, and Carlton SM (2003) N-Methyl-D-aspartate-induced excitation and sensitization of normal and inflamed nociceptors. Neuroscience 118: 547-562.[CrossRef][Medline]
Gaunitz C, Schuttler A, Gillen C, and Allgaier C (2002) Formalin-induced changes of NMDA receptor subunit expression in the spinal cord of the rat. Amino Acids (Vienna) 23: 177-182.
Karlsson U, Sjodin J, Moller KA, Johansson S, Wikstrom L, and Nasstrom J (2002) Glutamate-induced currents reveal three functionally distinct NMDA receptor populations in rat dorsal horn—effects of peripheral nerve lesion and inflammation. Neuroscience 112: 861-868.[CrossRef][Medline]
Kawamata M and Omote K (1996) Involvement of increased excitatory amino acids and intracellular Ca2+ concentration in the spinal dorsal horn in an animal model of neuropathic pain. Pain 68: 85-96.[CrossRef][Medline]
Kinney WA, Abou-Gharbia M, Garrison DT, Schmid J, Kowal DM, Bramlett DR, Miller TL, Tasse RP, Zaleska MM, and Moyer JA (1998) Design and synthesis of [2-(8,9-dioxo-2,6-diazabicyclo[5.2.0]non-1(7)-en-2-yl)-ethyl]phosphonic acid (EAA-090), a potent N-methyl-D-aspartate antagonist, via the use of 3-cyclobutene-1,2-dione as an achiral alpha-amino acid bioisostere. J Med Chem 41: 236-246.[CrossRef][Medline]
Klimscha W, Horvath G, Szikszay M, Dobos I, and Benedek G (1998) Antinociceptive effect of the S(+)-enantiomer of ketamine on carrageenan hyperalgesia after intrathecal administration in rats. Anesth Analg 86: 561-565.[Abstract]
LaMotte RH, Shain CN, Simone DA, and Tsai EF (1991) Neurogenic hyperalgesia: psychophysical studies of underlying mechanisms. J Neurophysiol 66: 190-211.
Laurie DJ and Seeburg PH (1994) Ligand affinities at recombinant N-methyl-D-aspartate receptors depend on subunit composition. Eur J Pharmacol 268: 335-345.[CrossRef][Medline]
Lutfy K, Cai SX, Woodward RM, and Weber E (1997) Antinociceptive effects of NMDA and non-NMDA receptor antagonists in the tail flick test in mice. Pain 70: 31-40.[CrossRef][Medline]
Ma QP and Woolf CJ (1995) Noxious stimuli induce an N-methyl-D-aspartate receptor-dependent hypersensitivity of the flexion withdrawal reflex to touch: implications for the treatment of mechanical allodynia. Pain 61: 383-390.[CrossRef][Medline]
Mao J, Price DD, Hayes RL, Lu J, Mayer DJ, and Frenk H (1993) Intrathecal treatment with dextrorphan or ketamine potently reduces pain-related behaviors in a rat model of peripheral mononeuropathy. Brain Res 605: 164-168.[CrossRef][Medline]
Miki K, Zhou QQ, Guo W, Guan Y, Terayama R, Dubner R, and Ren K (2002) Changes in gene expression and neuronal phenotype in brain stem pain modulatory circuitry after inflammation. J Neurophysiol 87: 750-760.
Negus SS, Butelman ER, Al Y, and Woods JH (1993) Prostaglandin E2-induced thermal hyperalgesia and its reversal by morphine in the warm-water tail-withdrawal procedure in rhesus monkeys. J Pharmacol Exp Ther 266: 1355-1363.
Parsons CG, Danysz W, and Quack G (1999) Memantine is a clinically well tolerated N-methyl-D-aspartate (NMDA) receptor antagonist—a review of preclinical data. Neuropharmacology 38: 735-767.[CrossRef][Medline]
Rabben T, Skjelbred P, and Oye I (1999) Prolonged analgesic effect of ketamine, an N-methyl-D-aspartate receptor inhibitor, in patients with chronic pain. J Pharmacol Exp Ther 289: 1060-1066.
Ren K, Williams GM, Hylden JL, Ruda MA, and Dubner R (1992) The intrathecal administration of excitatory amino acid receptor antagonists selectively attenuated carrageenan-induced behavioral hyperalgesia in rats. Eur J Pharmacol 219: 235-243.[CrossRef][Medline]
Sang CN (2000) NMDA-receptor antagonists in neuropathic pain: experimental methods to clinical trials. J Pain Symptom Manage 19: S21-S25.[CrossRef][Medline]
Sciberras DG, Goldenberg MM, Bolognese JA, James I, and Baber NS (1987) Inflammatory responses to intradermal injection of platelet activating factor, histamine and prostaglandin E2 in healthy volunteers: a double blind investigation. Br J Clin Pharmacol 24: 753-761.[Medline]
Sirinathsinghji DJS and Hill RG (2002) NMDA Antagonists as Potential Analgesic Drugs. Birkhauser Verlag, Boston.
Sluka KA and Westlund KN (1993) Spinal cord amino acid release and content in an arthritis model: the effects of pretreatment with non-NMDA, NMDA and NK1 receptor antagonists. Brain Res 627: 89-103.[CrossRef][Medline]
Stubhaug A and Breivik H (1997) Long-term treatment of chronic pain with NMDA (N-methyl-D-aspartate) receptor antagonist ketamine. Acta Anaesth Scand 41: 427-429.[Medline]
Sucher NJ, Awobuluyi M, Choi YB, and Lipton SA (1996) NMDA receptors: from genes to channels. Trends Pharmacol Sci 17: 348-355.[CrossRef][Medline]
Sun L, Chiu D, Kowal D, Simon R, Smeyne M, Zukin RS, Olney J, Baudy R, and Lin S (2004) Characterization of two novel N-methyl-D-aspartate antagonists: EAA-090 (2-[8,9-dioxo-2,6-diazabicyclo [5.2.0]non-1(7)-en2-yl]ethylphosphonic acid) and EAB-318 (R-alpha-amino-5-chloro-1-(phosphonomethyl)-1H-benzimidazole-2-propanoic acid hydrochloride). J Pharmacol Exp Ther 310: 563-570.
Suzuki R, Matthews EA, and Dickenson AH (2001) Comparison of the effects of MK-801, ketamine and memantine on responses of spinal dorsal horn neurones in a rat model of mononeuropathy. Pain 91: 101-109.[CrossRef][Medline]
Szallasi A and Blumberg PM (1999) Vanilloid (capsaicin) receptors and mechanisms. Pharmacol Rev 51: 159-212.
Williams K (1993) Ifenprodil discriminates subtypes of the N-methyl-D-aspartate receptor: selectivity and mechanisms at recombinant heteromeric receptors. Mol Pharmacol 44: 851-859.[Abstract]
Yamakura T, Mori H, Masaki H, Shimoji K, and Mishina M (1993) Different sensitivities of NMDA receptor channel subtypes to non-competitive antagonists. Neuroreport 4: 687-690.[Medline]
Zimmermann M (1983) Ethical guidelines for investigations of experimental pain in conscious animals. Pain 16: 109-110.[CrossRef][Medline]
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
 |
 |
 |
|
 |
 |
 |
