Antiallodynic Effect Of Gabapentin Research Articles

Intrathecal Gabapentin Increases Interleukin-10 Expression and Inhibits Pro-Inflammatory Cytokine in a Rat Model of Neuropathic Pain

We examined the possible anti-inflammatory mechanisms of gabapentin in the attenuation of neuropathic pain and the interaction between the anti-allodynic effects of gabapentin and interleukin-10 (IL-10) expression in a rat model of neuropathic pain. The anti-allodynic effect of intrathecal gabapentin was examined over a 7-day period. The anti-allodynic effects of IL-10 was measured, and the effects of anti-IL-10 antibody on the gabapentin were assessed. On day 7, the concentrations of pro-inflammatory cytokines and IL-10 were measured. Gabapentin produced an anti-allodynic effect over the 7-day period, reducing the expression of pro-inflammatory cytokines but increasing the expression of IL-10 (TNF-α, 316.0 ± 69.7 pg/mL vs 88.8 ± 24.4 pg/mL; IL-1β, 1,212.9 ± 104.5 vs 577.4 ± 97.1 pg/mL; IL-6, 254.0 ± 64.8 pg/mL vs 125.5 ± 44.1 pg/mL; IL-10, 532.1 ± 78.7 pg/mL vs 918.9 ± 63.1 pg/mL). The suppressive effect of gabapentin on pro-inflammatory cytokine expression was partially blocked by the anti-IL-10 antibody. Expression of pro-inflammatory cytokines was significantly attenuated by daily injections of IL-10. The anti-allodynic effects of gabapentin may be caused by upregulation of IL-10 expression in the spinal cord, which leads to inhibition of the expression of pro-inflammatory cytokines in the spinal cords.

Spinal Mechanism Underlying the Antiallodynic Effect of Gabapentin Studied in the Mouse Spinal Nerve Ligation Model

We studied the antiallodynic effect of gabapentin (GBP) in the mouse model of neuropathic pain, aiming at clarifying the underlying mechanism. The L5 spinal nerve ligation induced tactile allodynia, an increase of CD11b expression, and an increase in the protein expression level of the voltage-dependent Ca2+ channel α2/δ-1 subunit in the spinal dorsal horn on the injured side. The chronic intrathecal administration of GBP (100 μg/body per day) as well as ω-conotoxin MVIIA, an N-type Ca2+-channel blocker, completely suppressed allodynia, but did not attenuate the CD11b expression. The antiallodynic effect of GBP lasted for several days after the termination of the drug, while that of ω-conotoxin MVIIA disappeared immediately after the termination. GBP suppressed the elevation of the protein level of the α2/δ-1 subunit in the spinal dorsal horn, although it did not affect its mRNA level in the L5 DRG. These results suggest that GBP inhibits the development of allodynia by suppressing the up-regulation of N-type Ca2+ channels, through normalization of the protein level of the α2/δ-1 subunit at the primary afferent nerve terminal via the inhibition of its anterograde transport. In addition, we propose that the nerve injury enhances the expression level of α2/δ-1 in the downstream of the activation of microglia.

Molecular Basis for the Dosing Time-Dependency of Anti-Allodynic Effects of Gabapentin in a Mouse Model of Neuropathic Pain

BackgroundNeuropathic pain is characterized by hypersensitivity to innocuous stimuli (tactile allodynia) that is nearly always resistant to NSAIDs or even opioids. Gabapentin, a GABA analogue, was originally developed to treat epilepsy. Accumulating clinical evidence supports the effectiveness of this drug for diverse neuropathic pain. In this study, we showed that the anti-allodynic effect of gabapentin was changed by the circadian oscillation in the expression of its target molecule, the calcium channel α2δ-1 subunit.ResultsMice were underwent partial sciatic nerve ligation (PSL) to create a model of neuropathic pain. The paw withdrawal threshold (PWT) in PSL mice significantly decreased and fluctuated with a period length about 24 h. The PWT in PSL mice was dose-dependently increased by intraperitoneal injection of gabapentin, but the anti-allodynic effects varied according to its dosing time. The protein levels of α2δ-1 subunit were up-regulated in the DRG of PSL mice, but the protein levels oscillated in a circadian time-dependent manner. The time-dependent oscillation of α2δ-1 subunit protein correlated with fluctuations in the maximal binding capacity of gabapentin. The anti-allodynic effect of gabapentin was attenuated at the times of the day when α2δ-1 subunit protein was abundant.ConclusionsThese findings suggest that the dosing time-dependent difference in the anti-allodynic effects of gabapentin is attributable to the circadian oscillation of α2δ-1 subunit expression in the DRG and indicate that the optimizing its dosing schedule helps to achieve rational pharmacotherapy for neuropathic pain.

Basis for dosing time-dependent change in the anti-allodynic effect of gabapentin in mice

Basis for dosing time-dependent change in the anti-allodynic effect of gabapentin in mice

Gabapentin reverses microglial activation in the spinal cord of streptozotocin-induced diabetic rats

Diabetes mellitus is the leading cause of peripheral neuropathy worldwide. Despite this high level of incidence, underlying mechanisms of the development and maintenance of neuropathic pain are still poorly understood. Evidence supports a prominent role of glial cells in neuropathic pain states. Gabapentin is used clinically and shows some efficacy in the treatment of neuropathic pain. Here we investigate the distribution and activation of spinal microglia and astrocytes in streptozotocin (STZ)-diabetic rats and the effect of the gold standard analgesic, Gabapentin, on these cells. Mechanical allodynia was observed in four week-diabetic rats. Oral administration of Gabapentin significantly attenuated mechanical allodynia. Quantification of cell markers Iba-1 for microglia and GFAP for astrocytes revealed extensive activation of microglia in the dorsal horn of diabetic rats, whereas a reduction in the number of astrocytes could be observed. In addition, an attenuation of microglial activation correlated with reduced allodynia following Gabapentin treatment, while Gabapentin had no effect on the number of astrocytes. Here we show a role of microglia in STZ-induced mechanical allodynia and furthermore, that the anti-allodynic effect of Gabapentin may be linked to a reduction of spinal microglial activation. Astrocytic activation in this model appears to be limited and is unaffected by Gabapentin treatment. Consequently, spinal microglial activation is a key mechanism underlying diabetic neuropathy. Furthermore, we suggest that Gabapentin may exert its anti-allodynic actions partially through alterations of microglial cell function.

( l)-Phenylglycine, but not necessarily other α 2δ subunit voltage-gated calcium channel ligands, attenuates neuropathic pain in rats

Gabapentin and pregabalin have been demonstrated, both in animal pain models and clinically, to be effective analgesics particularly for the treatment of neuropathic pain. The precise mechanism of action for these two drugs is unknown, but they are generally believed to function via initially binding to the α 2δ subunit of voltage-gated Ca 2+ channels. In this study, we used a pharmacological approach to test the hypothesis whether high affinity interactions with the α 2δ subunit alone could lead to attenuation of neuropathic pain in rats. The anti-allodynic effects of gabapentin and pregabalin, along with three other compounds – ( l)-phenylglycine, m-chlorophenylglycine and 3- exo-aminobicyclo[2.2.1]heptane-2- exo-carboxylic acid (ABHCA) – discovered to be potent α 2δ ligands, were tested in the rat spinal nerve ligation model of neuropathic pain. Gabapentin ( K i = 120 nM), pregabalin (180 nM) and ( l)-phenylglycine (180 nM) were shown to be anti-allodynic, with respective ED 50 values of 230, 90 and 80 μmol/kg (p.o.). ( l)-Phenylglycine was as potent as pregabalin and equi-efficacious in reversing mechanical allodynia. In contrast, two ligands with comparable or superior α 2δ binding affinities, m-chlorophenylglycine ( K i = 54 nM) and ABHCA (150 nM), exhibited no anti-allodynic effects at doses of 30–300 μmol/kg (p.o.), although these compounds achieved substantial brain levels. The data demonstrate that, at least in the rat spinal nerve ligation model of neuropathic pain, ( l)-phenylglycine has an anti-allodynic effect, but two equally potent α 2δ subunit ligands do not. These results suggest that additional mechanisms, besides α 2δ interactions, may contribute to the effects of compounds like gabapentin, pregabalin and ( l)-phenylglycine in neuropathic pain.

The Antiallodynic Action Target of Intrathecal Gabapentin: Ca2+ Channels, KATP Channels or N-Methyl-d-Aspartic Acid Receptors?

Gabapentin is a novel analgesic whose mechanism of action is not known. We investigated in a postoperative pain model whether adenosine triphosphate (ATP)-sensitive K+ (K(ATP)) channels, N-methyl-d-aspartic acid (NMDA) receptors, and Ca2+ channels are involved in the antiallodynic effect of intrathecal gabapentin. Mechanical allodynia was induced by a paw incision in isoflurane-anesthetized rats. Withdrawal thresholds to von Frey filament stimulation near the incision site were measured before and after incision and after intrathecal drug administration. The antiallodynic effect of gabapentin (100 mug) was not affected by intrathecal pretreatment with antagonists of K(ATP) channels, NMDA receptors or gamma-aminobutyric acid (GABA)(A) receptors. K(ATP) channel openers and GABA(A) receptor agonist, per se, had little effect on the postincision allodynic response. The Ca2+ channel blocker of N-type (omega-conotoxin GVIA, 0.1-3 microg), but not of P/Q-type (omega-agatoxin IVA), L-type (verapamil, diltiazem or nimodipine), or T-type (mibefradil), attenuated the incision-induced allodynia, as did gabapentin. Both the antiallodynic effects of gabapentin and omega-conotoxin GVIA were attenuated by Bay K 8644, an L-type Ca2+ channel activator. These results provide correlative evidence to support the contention that N-type Ca2+ channels, but not K(ATP) channels or NMDA or GABA(A) receptors, might be involved in the antiallodynic effect of intrathecal gabapentin.

Role of descending noradrenergic system and spinal α2‐adrenergic receptors in the effects of gabapentin on thermal and mechanical nociception after partial nerve injury in the mouse

1. To gain further insight into the mechanisms underlying the antihyperalgesic and antiallodynic actions of gabapentin, a chronic pain model was prepared by partially ligating the sciatic nerve in mice. The mice then received systemic or local injections of gabapentin combined with either central noradrenaline (NA) depletion by 6-hydroxydopamine (6-OHDA) or alpha-adrenergic receptor blockade. 2. Intraperitoneally (i.p.) administered gabapentin produced antihyperalgesic and antiallodynic effects that were manifested by elevation of the withdrawal threshold to a thermal (plantar test) or mechanical (von Frey test) stimulus, respectively. 3. Similar effects were obtained in both the plantar and von Frey tests when gabapentin was injected intracerebroventricularly (i.c.v.) or intrathecally (i.t.), suggesting that it acts at both supraspinal and spinal loci. This novel supraspinal analgesic action of gabapentin was only obtained in ligated neuropathic mice, and gabapentin (i.p. and i.c.v.) did not affect acute thermal and mechanical nociception. 4. In mice in which central NA levels were depleted by 6-OHDA, the antihyperalgesic and antiallodynic effects of i.p. and i.c.v. gabapentin were strongly suppressed. 5. The antihyperalgesic and antiallodynic effects of systemic gabapentin were reduced by both systemic and i.t. administration of yohimbine, an alpha2-adrenergic receptor antagonist. By contrast, prazosin (i.p. or i.t.), an alpha1-adrenergic receptor antagonist, did not alter the effects of gabapentin. 6. It was concluded that the antihyperalgesic and antiallodynic effects of gabapentin are mediated substantially by the descending noradrenergic system, resulting in the activation of spinal alpha2-adrenergic receptors.

Comparison of the Antinociceptive Profiles of Gabapentin and 3-Methylgabapentin in Rat Models of Acute and Persistent Pain: Implications for Mechanism of Action

The anticonvulsant gabapentin (GBP) has been shown effective for the treatment of neuropathic pain, although its mechanism of action remains unclear. A recent report has suggested that binding to the alpha(2)delta subunit of voltage-gated calcium channels contributes to its antinociceptive effect, based on the stereoselective efficacy of two analogs: (1S,3R)3-methylgabapentin (3-MeGBP) (IC(50) = 42 nM), which is effective in neuropathic pain models; and (1R,3R)3-MeGBP (IC(50) > 10,000 nM), which is ineffective (Field et al., 2000). The present study was designed to further examine the profiles of GBP and 3-MeGBP in rat models of acute and persistent pain. Systemic administration of GBP or (1S,3R)3-MeGBP inhibited tactile allodynia in the spinal nerve ligation model of neuropathic pain, whereas (1R,3R)3-MeGBP was ineffective. The antiallodynic effect of GBP, but not (1S,3R)3-MeGBP, was blocked by i.t. injection of the GABA(B) receptor antagonist [3-[[(3,4-dichlorophenyl)methyl]amino]propyl](diethoxymethyl)phosphinic acid (CGP52432). Systemic GBP or (1S,3R)3-MeGBP also inhibited the second phase of formalin-evoked nociceptive behaviors, whereas (1R,3R)3-MeGBP was ineffective. However, both (1S,3R)3-MeGBP and (1R,3R)3-MeGBP, but not GBP, inhibited first phase behaviors. In the carrageenan model of inflammatory pain, systemic GBP or (1R,3R)3-MeGBP failed to inhibit thermal hyperalgesia, whereas (1S,3R)3-MeGBP had a significant, albeit transient, effect. Systemic (1S,3R)3-MeGBP, but not GBP or (1R,3R)3-MeGBP, also produced an antinociceptive effect in the warm water tail withdrawal test of acute pain. These data demonstrate that GBP and 3-MeGBP display different antinociceptive profiles, suggesting dissimilar mechanisms of antinociceptive action. Thus, the stereoselective efficacy of 3-MeGBP, presumably related to alpha(2)delta binding, likely does not completely account for the mechanism of action of GBP.

Effect of K + channel modulators on the antiallodynic effect of gabapentin

The effect of K + channel inhibitors on the antiallodynic activity induced by spinal gabapentin was assessed in rats. Ligation of L5 and L6 spinal nerves made the rats allodynic, whereas that intrathecal administration of gabapentin (25–200 μg) reduced tactile allodynia in a dose-dependent manner. Spinal pretreatment with glibenclamide (12.5–50 μg, ATP-sensitive K + channel inhibitor), charybdotoxin (0.01–1 ng) or apamin (0.1–3 ng, large-and small-conductance Ca 2+-activated K + channel blockers, respectively), but not margatoxin (0.01–10 ng, voltage-dependent K + channel inhibitor), significantly prevented gabapentin-induced antiallodynia. Pinacidil (1–30 μg, K + channel opener) significantly reduced nerve ligation-induced allodynia. Intrathecal glibenclamide (50 μg), charybdotoxin (1 ng) and apamin (3 ng), but not margatoxin (10 ng), significantly reduced pinacidil-induced antiallodynia. K + channel inhibitors alone did not modify allodynia produced by spinal nerve ligation. Results suggest that gabapentin and pinacidil may activate Ca 2+-activated and ATP-sensitive K + channels in order to produce part of its spinal antiallodynic effect in the Chung model.