Yeo Ok Kim

Role of neuronal nitric oxide synthase in the antiallodynic effects of intrathecal EGCG in a neuropathic pain rat model

Epigallocatechin-3-gallate (EGCG), the major catechin in green tea, is known to have antioxidant activity against nitric oxide (NO) by scavenging free radicals, chelating metal ions, and inducing endogenous antioxidant enzymes. NO and NO synthase (NOS) play an important role in nociceptive processing. In this study, we examined the effects of intrathecal EGCG in neuropathic pain induced by spinal nerve ligation and the possible involvement of NO. Intrathecal EGCG attenuated mechanical allodynia in spinal nerve ligated-rats, compared to sham-operated rats, with a maximal possible effect of 69.2%. This antinociceptive effect was reversed by intrathecal pretreatment with l-arginine, a precursor of NO. Intrathecal EGCG also blocked the increase in nNOS expression in the spinal cord of spinal nerve-ligated rats, but iNOS expression was not significantly suppressed. These findings suggest that intrathecal EGCG could produce an antiallodynic effect against spinal nerve ligation-induced neuropathic pain, mediated by blockade of nNOS protein expression and inhibition of the pronociceptive effects of NO.

Evaluation for the interaction between intrathecal melatonin and clonidine or neostigmine on formalin-induced nociception.

AIMS We examined the nature of pharmacological interaction after coadministration of melatonin with clonidine or neostigmine on formalin-induced nociception at the spinal level. Further, the role of melatonin receptor subtypes in melatonin-induced antinociception was clarified. MAIN METHODS Catheters were inserted into the intrathecal space of male Sprague-Dawley rats. Pain was assessed using the formalin test (induced by a subcutaneous injection of 50 microl of a 5% formalin solution to the hindpaw). Isobolographic analysis was used for the evaluation of drug interaction between melatonin and clonidine or neostigmine. Non-selective MT1/MT2 receptors antagonist (luzindole), MT2 receptor antagonist (4-P-PDOT), and MT3 receptor/alpha-1 adrenoceptor antagonist (prazosin) were intrathecally given to verify the involvement of the melatonin receptor subtypes in the antinociception of melatonin. Furthermore, the effect of intrathecal MT3 receptor ligand (GR 135531) was observed. KEY FINDINGS Intrathecal melatonin, clonidine, and neostigmine dose-dependently suppressed the flinching response during phase 1 and phase 2 in the formalin test. Isobolographic analysis showed additivity between melatonin and clonidine or neostigmine in both phases. The antinociceptive effect of melatonin was antagonized by luzindole, 4-P-PDOT, and prazosin in the spinal cord. Intrathecal GR 135531 was ineffective against the formalin-induced flinching response. SIGNIFICANCE These results suggest that melatonin interacts additively with clonidine and neostigmine in the formalin-induced nociception at the spinal level. Furthermore, the antinociception of melatonin is mediated through the MT2 receptor, but not the MT3 receptor. However, it seems that alpha-1 adrenoceptor plays in the effect of melatonin.

Roles of opioid receptor subtypes on the antinociceptive effect of intrathecal sildenafil in the formalin test of rats

Recently, it has been known that the antinociception of sildenafil, a phosphodiesterase 5 inhibitor, is mediated through the opioid receptors. There are common three types of opioid receptors mu, delta, and kappa. We characterized the role of subtypes of opioid receptor for the antinociception of sildenafil at the spinal level. Intrathecal catheters were placed for drug delivery and formalin solution (5%, 50 microl) was injected for induction of nociception within male SD rats. The effect of mu opioid receptor antagonist (CTOP), delta opioid receptor antagonist (naltrindole), and kappa opioid receptor antagonist (GNTI) on the activity of sildenafil was examined. Intrathecal sildenafil decreased the flinching responses during phases 1 and 2 in the formalin test. Intrathecal CTOP and naltrindole reversed the antinociception of sildenafil during both phases in the formalin test. Intrathecal GNTI reversed the effect of sildenafil during phase 2, but not phase 1. These results suggest that sildenafil is effective to acute pain and the facilitated pain state at the spinal level. Both mu and delta opioid receptors are involved. However, it seems that kappa opioid receptors play in the effect of sildenafil.

Additive Antinociception between Intrathecal Sildenafil and Morphine in the Rat Formalin Test

The possible characteristics of spinal interaction between sildenafil (phosphodiesterase 5 inhibitor) and morphine on formalin-induced nociception in rats was examined. Then the role of the opioid receptor in the effect of sildenafil was further investigated. Catheters were inserted into the intrathecal space of male Sprague-Dawley rats. For induction of pain, 50 µL of 5% formalin solution was applied to the hind-paw. Isobolographic analysis was used for the evaluation of drug interaction between sildenafil and morphine. Furthermore, naloxone was intrathecally given to verify the involvement of the opioid receptor in the antinociception of sildenafil. Both sildenafil and morphine produced an antinociceptive effect during phase 1 and phase 2 in the formalin test. The isobolographic analysis revealed an additive interaction after intrathecal delivery of the sildenafil-morphine mixture in both phases. Intrathecal naloxone reversed the antinociception of sildenafil in both phases. These results suggest that sildenafil, morphine, and the mixture of the two drugs are effective against acute pain and facilitated pain state at the spinal level. Thus, the spinal combination of sildenafil with morphine may be useful in the management of the same state. Furthermore, the opioid receptor is contributable to the antinocieptive mechanism of sildenafil at the spinal level.

Effect of sildenafil on neuropathic pain and hemodynamics in rats.

Purpose The inhibition of phosphodiesterase 5 produces an antinociception through the increase of cyclic guanosine monophosphate (cGMP), and increasing cGMP levels enhance the release of γ-aminobutyric acid (GABA). Furthermore, this phosphodiesterase 5 plays a pivotal role in the regulation of the vasodilatation associated to cGMP. In this work, we examined the contribution of GABA receptors to the effect of sildenafil, a phosphodiesterase 5 inhibitor, in a neuropathic pain rat, and assessed the hemodynamic effect of sildenafil in normal rats. Materials and Methods Neuropathic pain was induced by ligation of L5/6 spinal nerves in Sprague-Dawley male rats. After observing the effect of intravenous sildenafil on neuropathic pain, GABAA receptor antagonist (bicuculline) and GABAB receptor antagonist (saclofen) were administered prior to delivery of sildenafil to determine the role of GABA receptors in the activity of sildenafil. For hemodynamic measurements, catheters were inserted into the tail artery. Mean arterial pressure (MAP) and heart rate (HR) were measured over 60 min following administration of sildenafil. Results Intravenous sildenafil dose-dependently increased the withdrawal threshold to the von Frey filament application in the ligated paw. Intravenous bicuculline and saclofen reversed the antinociception of sildenafil. Intravenous sildenafil increased the magnitude of MAP reduction at the maximal dosage, but it did not affect HR response. Conclusion These results suggest that sildenafil is active in causing neuropathic pain. Both GABAA and GABAB receptors are involved in the antinociceptive effect of sildenafil. Additionally, intravenous sildenafil reduces MAP without affecting HR.

Antinociceptive effects of amiloride and benzamil in neuropathic pain model rats.

Amiloride and benzamil showed antinocicepitve effects in several pain models through the inhibition of acid sensing ion channels (ASICs). However, their role in neuropathic pain has not been investigated. In this study, we investigated the effect of the intrathecal amiloride and benzamil in neuropathic pain model, and also examined the role of ASICs on modulation of neuropathic pain. Neuropathic pain was induced by L4-5 spinal nerve ligation in male Sprague-Dawley rats weighing 100-120 g, and intrathecal catheterization was performed for drug administration. The effects of amiloride and benzamil were measured by the paw-withdrawal threshold to a mechanical stimulus using the up and down method. The expression of ASICs in the spinal cord dorsal horn was also analyzed by RT-PCR. Intrathecal amiloride and benzamil significantly increased the paw withdrawal threshold in spinal nerve-ligated rats (87%±12% and 76%±14%, P=0.007 and 0.012 vs vehicle, respectively). Spinal nerve ligation increased the expression of ASIC3 in the spinal cord dorsal horn (P=0.01), and this increase was inhibited by both amiloride and benzamil (P<0.001 in both). In conclusion, intrathecal amiloride and benzamil display antinociceptive effects in the rat spinal nerve ligation model suggesting they may present an alternative pharmacological tool in the management of neuropathic pain at the spinal level.

The intrathecally administered kappa-2 opioid agonist GR89696 and interleukin-10 attenuate bone cancer-induced pain through synergistic interaction.

BACKGROUND:Although bone cancer–related pain is one of the most disruptive symptoms in patients with advanced cancer, patients are often refractory to pharmacological treatments; thus, more effective treatments for bone cancer pain are needed. We evaluated the analgesic efficacy of and interaction between intrathecal GR89696, a &kgr;2-opioid receptor agonist, and interleukin (IL)-10 in a rat model of bone cancer pain. METHODS:The rat model of bone cancer pain was produced by right tibia intramedullary injection of rat breast cancer cells, and an intrathecal catheterization was performed. Ten days later, a paw-withdrawal threshold to mechanical stimulus by von Frey hairs was measured using the up-down method, after intrathecal administration of GR89696 and IL-10. The interaction between the 2 drugs was also evaluated using an isobolographic analysis. RESULTS:Intrathecal GR89696 and IL-10 significantly increased the paw withdrawal threshold of the cancer cell–implanted rat, in a dose-dependent manner, with 50% effective dose values (95% confidence interval) of 50.78 &mgr;g (31.80–80.07&mgr;g) and 0.83 &mgr;g (0.59–1.15 &mgr;g), respectively. Isobolographic analysis revealed a synergistic interaction between intrathecal GR89696 and IL-10. CONCLUSIONS:Intrathecally administered GR89696 and IL-10 attenuated bone cancer–induced pain, and the 2 drugs interacted synergistically in the spinal cord. These results raise the intriguing possibility of &kgr;2-opioid receptor agonists and IL-10 as a new therapeutic approach for the management of bone cancer–associated pain.

Antiallodynic effect through spinal endothelin-B receptor antagonism in rat models of complex regional pain syndrome

Complex regional pain syndrome (CRPS) is a very complicated chronic pain disorder that has been classified into two types (I and II). Endothelin (ET) receptors are involved in pain conditions at the spinal level. We investigated the role of spinal ET receptors in CRPS. Chronic post-ischemia pain (CPIP) was induced in male Sprague-Dawley rats as a model for CRPS-I by placing a tourniquet (O-ring) at the ankle joint for 3h, and removing it to allow reperfusion. Ligation of L5 and L6 spinal nerves to induce neuropathic pain was performed as a model for CRPS-II. After O-ring application and spinal nerve ligation, the paw withdrawal threshold was significantly decreased at injured sites. Intrathecal administration of the selective ET-B receptor antagonist BQ 788 dose-dependently increased the withdrawal threshold in both CRPS-I and CRPS-II. In contrast, ET-A receptor antagonist BQ 123 did not affect the withdrawal threshold in either CRPS type. The ET-1 levels of plasma and spinal cord increased in both CRPS types. Intrathecal BQ 788 decreased the spinal ET-1 level. These results suggest that ET-1 is involved in the development of mechanical allodynia in CRPS. Furthermore, the ET-B receptor appears to be involved in spinal cord-related CRPS.

The role of alpha-2 adrenoceptor subtype in the antiallodynic effect of intraplantar dexmedetomidine in a rat spinal nerve ligation model

The purpose of this study was to examine the effects of intraplantar dexmedetomidine to relieve neuropathic pain and determine the role of peripheral α2-adrenoceptors. Neuropathic pain was induced by ligating the L5 and L6 spinal nerves in male Sprague-Dawley rats, and mechanical allodynia was assessed using von Frey filaments. Several antagonists were injected into the hindpaws to evaluate the mechanisms of action of dexmedetomidine, a nonselective α2-adrenoceptor antagonist yohimbine, an α2A-adrenoceptor antagonist BRL 44408, an α2B-adrenoceptor antagonist ARC 239, and a α2C-adrenoceptor antagonist JP 1302. The expression of α2A-adrenoceptor, α2B-adrenoceptor, and α2C-adrenoceptor genes in the lumbar segment of the spinal cord and the plantar skin of the nerve-injured leg was detected by reverse transcription-polymerase chain reaction. Ipsilateral intraplantar injection of dexmedetomidine produced dose-dependent antiallodynia. Ipsilateral, but not contraleral, intraplantar injection of yohimbine reversed the antinociception of dexmedetomidine. Intraplantar BRL 44408, ARC 239, and JP 1302 reversed the antinociception of dexmedetomidine. The expression levels of α2-adrenoceptor genes in the lumbar spinal cord did not differ between rats with neuropathic pain and naïve rats. The expression levels of α2B-adrenoceptor and α2C-adrenoceptor genes of plantar skin were upregulated significantly in the model group, whereas α2A-adrenoceptor expression was unchanged. These results suggest that intraplantar injection of dexmedetomidine produced an antiallodynic effect in spinal nerve ligation-induced neuropathic pain. All three types of peripheral α2A, α2B, and α2C-adrenoceptors were involved in the antiallodynic mechanism of dexmedetomidine.

Analgesic Effect of Intrathecal Ginsenosides in a Murine Bone Cancer Pain

Background Bone cancer pain has a disruptive effect on the cancer patients quality of life. Although ginsenosides have been used as traditional medicine in Eastern Medicine, the effect on bone cancer pain has not been thoroughly studied. The aim of this study was to determine whether ginsenosides may alter the bone cancer pain at the spinal level. Methods NCTC 2472 tumor cells (2.5 × 105) were injected into the femur of adult male C3H/HeJ mice to evoke bone tumor and bone cancer pain. To develop bone tumor, radiologic pictures were obtained. To assess pain, the withdrawal threshold was measured by applying a von Frey filament to the tumor cells inoculation site. The effect of intrathecal ginsenosides was investigated. Effect of ginsenosides (150, 500, 1,000 µg) was examined at 15, 30, 60, 90, 120 min after intrathecal delivery. Results The intrafemoral injection of NCTC 2472 tumor cells induced a radiological bone tumor. The withdrawal threshold with tumor development was significantly decreased compared to the sham animals. Intrathecal ginsenosides effectively increased the withdrawal threshold in the bone cancer site. Conclusions NCTC 2472 tumor cells injection into the mice femur caused bone tumor and bone cancer pain. Intrathecal ginsenosides attenuated the bone cancer-related pain behavior. Therefore, spinal ginsenosides may be an alternative analgesic for treating bone cancer pain.