Involvement of Rho-kinase in inflammatory and neuropathic pain through phosphorylation of myristoylated alanine-rich C-kinase substrate (MARCKS)

Characterization of Fasudil in preclinical models of pain

Activation of Rho kinase (ROCK) has been shown to play a role in neuronal regeneration and development of posttraumatic neuropathic pain. The ROCK inhibitor Fasudil, used clinically for the treatment of vasospasm, was used to investigate the analgesic profile of a ROCK inhibitor. Fasudil was evaluated in different preclinical models of neuropathic, osteoarthritic (OA), and inflammatory pain as well as capsaicin-induced acute pain and secondary mechanical hypersensitivity. In addition, Fasudil was tested in in vivo electrophysiology to determine the mechanism by which Fasudil produces analgesia. Fasudil at the highest dose tested (30 mg/kg) significantly attenuated mechanical allodynia in spinal-nerve ligation (SNL; 77%), chronic constriction injury (CCI; 53%), capsaicin-induced secondary mechanical hypersensitivity (63%), sodium iodoacetate-induced OA pain (88%), and capsaicin-induced acute flinching behaviors (56%). However, Fasudil (at 30 mg/kg) failed to attenuate or had only modest effects on inflammatory thermal hyperalgesia following carrageenan injection and mechanical allodynia following Complete Freund's Adjuvant (CFA) injection. Fasudil produced ED(50) of 10.8 mg/kg in the SNL, and 5.7 mg/kg in the OA pain models. The ED(50) and 95% CI could not be obtained in the other models. Furthermore, administration of Fasudil (10 mg/kg, iv) significantly reduced both spontaneous and evoked firing of wide dynamic range (WDR) neurons in SNL, but not sham rats. Finally, Fasudil significantly decreased exploratory behaviors at 30 mg/kg. These results suggest that the acute administration of a ROCK inhibitor produces efficacy in both neuropathic and nociceptive pain states at doses devoid of locomotor side effects, with specific effects on WDR neurons.

PERSPECTIVE

In this article, the potential analgesic effects of Fasudil in a range of preclinical pain models were assessed. Fasudil was shown to have efficacy in neuropathic and nociceptive pain models. These findings may help identify new therapeutic treatments for pain in the clinic.

Rho kinase inhibitor Y-27632 down-regulates norepinephrine synthesis and release in PC12 cells

Rho kinase inhibition is beneficial for neurite outgrowth and nerve disorders, and the Rho kinase inhibitors have been regarded as promising agents to treat neural diseases. The main aim of the study was to elucidate how Rho kinase inhibitor Y-27632 regulates neurotransmitter norepinephrine synthesis and release in PC12 cells when neurite outgrowth was induced. PC12 cells were treated with Y-27632 for 6 days. The amount of norepinephrine synthesized in PC12 cells and the amount released evoked by acetylcholine or by KCl were determined by norepinephrine enzyme-linked immunosorbent assay kits. The results showed that the amount of norepinephrine both synthesized and released was down-regulated with a concentration-dependent relationship. Further results of Western blotting found that the protein expression of tyrosine hydroxylase and synapsin I (especially its active form, synapsin I phosphoSer603) was also down-regulated, which were directly related to synthesis and release of norepinephrine, respectively. All the results suggest that Y-27632 is able to down-regulate norepinephrine synthesis and release, the direct mechanism of which may be associated with down-regulation on expression of some proteins, including tyrosine hydroxylase and synapsin I.

MARCKS regulates lamellipodia formation induced by IGF-I via association with PIP2 and beta-actin at membrane microdomains

Myristoylated alanine-rich C kinase substrate (MARCKS) is considered to participate in formation of F-actin-based lamellipodia, which represents the first stage of neurite formation. However, the mechanism of how MARCKS is involved in lamellipodia formation is not precisely unknown. Using SH-SY5Y cells, we demonstrated here that MARCKS was translocated from cytosol to detergent-resistant membrane microdomains, known as lipid rafts, within 30 min after insulin-like growth factor-I (IGF-I) stimulation, which was accompanied by MARCKS dephosphorylation, beta-actin accumulation in lipid rafts, and lamellipodia formation. The protein kinase C inhibitor, Ro-31-8220, and Rho-kinase inhibitors, HA1077 and Y27632, themselves decreased basal phosphorylation levels of MARCKS and coincidently elicited translocation of MARCKS to lipid rafts. On the other hand, the phosphoinositide 3-kinase inhibitor, LY294002, abolished IGF-I-induced dephosphorylation, translocation of MARCKS to lipid rafts, and lamellipodia formation. Treatment of cells with neomycin, a PIP2-masking reagent, attenuated the translocation of MARCKS to lipid rafts and the lamellipodia formation induced by IGF-I, although dephosphorylation of MARCKS was not affected. Immunocytochemical and immunoprecipitation analysis indicated that IGF-I stimulation induced the translocation of MARCKS to lipid rafts in the edge of lamellipodia and formation of the complex with PIP2. Moreover, we demonstrated that knockdown of endogenous MARCKS resulted in significant attenuation of IGF-I-induced beta-actin accumulation in the lipid rafts and lamellipodia formation. These results suggest a novel role for MARCKS in lamellipodia formation induced by IGF-I via the translocation of MARCKS, association with PIP2, and accumulation of beta-actin in the membrane microdomains.

The Rac GTPase-activating bacterial protein toxin CNF1 induces analgesia up-regulating mu-opioid receptors

Cytotoxic Necrotizing Factor 1 (CNF1) is a protein toxin from Escherichia coli that constitutively activates the Rho, Rac and Cdc42 GTPases. These regulatory proteins oscillate between a cytosolic GDP-bound inactive form and a membrane-linked GTP-bound active form, orchestrating the actin cytoskeleton assembly and dynamics. We herein describe, for the first time, the ability of CNF1 to potently counteract the formalin-induced inflammatory pain in mice. The analgesic response due to CNF1 requires both the sustained activation of the Rac GTPase, with consequent cerebral actin cytoskeleton remodeling, and the up-regulation of the mu-opioid receptors (MORs), the most important receptors controlling pain perception. The crucial role of Rac is proved by the lack of analgesic activity in mice challenged with a recombinant CNF1, in which the enzymatic activity was abolished by substituting serine with cysteine at position 866. The importance of MORs is proved by the inability of CNF1 to induce any analgesic effect in MORs knockout mice and by the ability of naloxone to antagonize the analgesic effects. Furthermore, it is worth noting that the analgesic effect in mice occurs after both peripheral and central administration of CNF1. Hence, taken altogether, our findings provide new insights into the comprehension of intracellular mechanisms involved in pain modulation, and indicate this bacterial protein toxin as a novel tool in the field of pain control. Conceivably, this might pave the way for new therapeutic strategies.

Involvement of Rho-kinase in tumor necrosis factor-alpha-induced interleukin-6 release from C6 glioma cells

Tumor necrosis factor (TNF)-alpha stimulated interleukin (IL)-6 release and induced the phosphorylation of myosin phosphatase targeting subunit (MYPT)-1, a Rho-kinase substrate. The IL-6 release was significantly suppressed by Y-27632 and fasudil, Rho-kinase inhibitors. Although IkappaB inhibitor suppressed the TNF-alpha-induced IL-6 release, the Rho-kinase inhibitors did not affect the TNF-alpha-induced IkappaB phosphorylation. TNF-alpha induced the phosphorylation of p38 mitogen-activated protein (MAP) kinase, stress-activated protein kinase (SAPK)/c-Jun N-terminal kinase (JNK), and p44/p42 MAP kinase. The TNF-alpha-induced IL-6 release was suppressed by SB203580, a p38 MAPK inhibitor, or SP600125, a SAPK/JNK inhibitor, but not by PD98059, a MAP kinase/extracellular signal-regulated kinase kinase inhibitor. The Rho-kinase inhibitors attenuated the TNF-alpha-induced phosphorylation of both p38 MAP kinase and SAPK/JNK. Rho-kinase, which has been used for the clinical treatment of cerebral vasospasms, may be involved in other central nervous system (CNS) disorders such as traumatic injury, stroke, neurodegenerative disease and neuropathic pain. TNF-alpha, a proinflammatory cytokine that affects the CNS through cytokines, such as IL-6, release from neurons, astrocytes and microglia. Therefore, we investigated the involvement of Rho-kinase in the TNF-alpha-induced IL-6 release from rat C6 glioma cells. These results strongly suggest that Rho-kinase regulates the TNF-alpha-induced IL-6 release at a point upstream from p38 MAPK and SAPK/JNK in C6 glioma cells. Therefore, Rho-kinase inhibitor may be considered to be a new clinical candidate for the treatment of CNS disorders in addition to cerebral vasospasms.

Antiepileptic effects of two Rho-kinase inhibitors, Y-27632 and fasudil, in mice

BACKGROUND AND PURPOSE

Rho/Rho-kinase signalling is involved in many cellular events, including some in the CNS. However, the role of this pathway in epilepsy has not yet been assessed. Therefore, we determined the effects of two Rho-kinase inhibitors, Y-27632 and fasudil, on seizures induced by pentylenetetrazole (PTZ) or maximal electroconvulsive shock (MES).

EXPERIMENTAL APPROACH

Effects of Y-27632 (5-10 mg kg(-1)) and fasudil (5-25 mg kg(-1)) on duration of myoclonic jerks, clonic and tonic convulsions, tonic hindlimb extensions and percentage of tonic convulsion index, as well as recovery latency for righting reflex were investigated in mice stimulated with PTZ (65 mg kg(-1)) or MES (50 Hz, 50 mA and 0.4 s). These inhibitors were also tested on a model of kindling induced by PTZ (35 mg kg(-1), for 11 days). Membrane and cytosolic levels of RhoA protein were measured in brain homogenates from kindled mice.

KEY RESULTS

Y-27632 and fasudil diminished onset of myoclonic jerks, clonic convulsions and tonic hindlimb extensions in mice given PTZ. These inhibitors suppressed the percentage of tonic convulsion index and recovery latency for righting reflex in the mice excited with MES. Western blotting demonstrated that Rho translocation to plasma membrane increased in the brain homogenates obtained from PTZ-kindled mice. However, the Rho-kinase inhibitors at the given doses did not change motor coordination of the mice.

CONCLUSIONS AND IMPLICATIONS

Rho/Rho-kinase signalling may play a role in epilepsy induced by PTZ and MES. Furthermore, Rho-kinase inhibitors could be novel important antiepileptic agents.

Mevalonate sensitizes the nociceptive transmission in the mouse spinal cord

Isoprenylation is crucial for the biological activation of small molecular G proteins. Activation of Rho/Rho kinase (ROCK) signaling has been reported to be involved in the initiation and maintenance of hyperalgesia caused by nerve injury and inflammation. The present study was then undertaken to examine whether the protein isoprenylation could affect thermal nociceptive threshold in the mouse spinal cord. Intrathecal administration of mevalonate (0.05-5.0 micromol) dose-dependently decreased the paw-withdrawal latencies for the thermal stimulation, indicating that mevalonate induces thermal hyperalgesia. Intrathecal pretreatment with a geranylgeranyl transferase I inhibitor GGTI-2133 (0.001-1.0 nmol) or a ROCK inhibitor Y27632 (0.001-1.0 nmol) completely blocked the mevalonate-induced thermal hyperalgesia. On the other hand, mevalonate-induced thermal hyperalgesia was only slightly attenuated by a farnesyl transferase inhibitor FTI-277 (0.01-1.0 nmol). Intrathecal injection of mevalonate increased the amount of geranylgeranylated RhoA in the spinal cord, which was completely blocked by intrathecal pretreatment with GGTI-2133. Intrathecal injection of mevalonate also produced RhoA translocation from cytosol to plasma membrane. This mevalonate-induced RhoA translocation was also blocked by intrathecal pretreatment with GGTI-2133, indicating that the RhoA translocation is triggered by RhoA geranylgeranylation. Moreover, inhibition of mevalonate synthesis by HMG-CoA reductase inhibition with simvastatin attenuated the second phase, but not the first phase, of nociceptive response to formalin. Our present results suggest that mevalonate sensitizes the spinal nociceptive transmission, which is mediated by the activation of ROCK following the RhoA geranylgeranylation.

Unphosphorylated MARCKS is involved in neurite initiation induced by insulin-like growth factor-I in SH-SY5Y cells

Myristoylated alanine-rich C kinase substrate (MARCKS) has been suggested to be involved in various aspects of neuronal cell differentiation, including neurite outgrowth. However, the precise mechanisms by which MARCKS phosphorylation is regulated, and how MARCKS contributes to neurite outgrowth, are poorly understood. Here, we found that treatment of SH-SY5Y cells with insulin-like growth factor-I (IGF-I) induced a rapid and transient decrease in the level of phosphorylated MARCKS (P-MARCKS) to below the basal level. The decrease in P-MARCKS induced by IGF-I was blocked by pretreatment of cells with phosphoinositide 3-kinase (PI3K) inhibitors, LY294002 and wortmannin. A decrease in P-MARCKS was also observed in cells treated with a Rho-dependent kinase (ROCK) inhibitor, Y27632. Furthermore, IGF-I induced transient inactivation of RhoA, an upstream effector of ROCK. We showed that MARCKS was translocated to the membrane and colocalized with F-actin at the lamellipodia and the tips of neurites in the cells stimulated with IGF-I. Finally, overexpression of wild-type MARCKS or an unphosphorylatable mutant of MARCKS enhanced the number of neurite-bearing cells relative to vector-transfected cells. Taken together, these findings suggest that unphosphorylated MARCKS is involved in neurite initiation, and highlight the important role played by MARCKS in organization of the actin cytoskeleton.

Protein kinases as potential targets for the treatment of pathological pain

Pathological pain or clinical pain refers to tissue injury-induced inflammatory pain and nerve injury-induced neuropathic pain and is often chronic. Pathological pain is an expression of neural plasticity that occurs both in the peripheral nervous system (e.g., primary sensory nociceptors), termed peripheral sensitization, and in the central nervous system (e.g., dorsal horn and brain neurons), termed central sensitization. Our insufficient understanding of mechanisms underlying the induction and maintenance of injury-induced neuronal plasticity hinders successful treatment for pathological pain. The human genome encodes 518 protein kinases, representing one of the largest protein families. There is growing interest in developing protein kinase inhibitors for the treatment of a number of diseases. Although protein kinases were not favored as targets for analgesics, studies in the last decade have demonstrated important roles of these kinases in regulating neuronal plasticity and pain sensitization. Multiple protein kinases have been implicated in peripheral and central sensitization following intense noxious stimuli and injuries. In particular, mitogen-activated protein kinases (MAPKs), consisting of extracellular signal-regulated kinase (ERK), p38, and c-Jun N-terminal kinase (JNK), are downstream to many kinases and are activated in primary sensory and dorsal horn neurons by nociceptive activity, growth factors and inflammatory mediators, contributing to the induction and maintenance of pain sensitization via posttranslational, translational, and transcriptional regulation. MAPKs are also activated in spinal glial cells (microglia and astrocytes) after injuries, leading to the synthesis of inflammatory mediators/neuroactive substances that act on nociceptive neurons, enhancing and prolonging pain sensitization. Inhibition of multiple kinases has been shown to attenuate inflammatory and neuropathic pain in different animal models. Development of specific inhibitors for protein kinases to target neurons and glial cells will shed light on the development of new therapies for debilitating chronic pain.

Rho-kinase inhibitor, Y-27632, has an antinociceptive effect in mice

The possible antinociceptive effect of a Rho-kinase inhibitor, (+)-(R)-trans-4-(1-aminoethyl)-N-(4-pyridyl) cyclohexanecarboxamide dihydrochloride monohydrate (Y-27632), was investigated in mice by using the hot-plate and abdominal constriction response (writhing) tests. In addition, the expression of Rho-kinase protein (ROCK-2) was studied in the mouse brain and spinal cord by Western blotting. Male balb/c mice (n=8, for each group) were used in the experiment. Hot-plate latency and the number of writhes were recorded in control and in Y-27632-treated (1-5 mg/kg, i.p.) groups. Y-27632 (1 mg/kg) did not affect hot-plate latency; however, it considerably diminished the number of writhes, from 89+/-12 in control to 30+/-6 in the mice treated with 1 mg/kg Y-27632 (P=0.001). At a higher dose (5 mg/kg), Y-27632 prolonged the hot-plate latency from 8.7+/-1.0 s to 14.4+/-1.7 s (P=0.005) and decreased the number of writhes from 80+/-8 to 24+/-7 (P=0.002). Western blot analysis revealed that mouse spinal cord and brain homogenates expressed ROCK-2 protein. These results indicate that Rho-kinase may be involved in nociception and that its inhibitors, such as Y-27632, may represent a new type of antinociceptive drug.

Rho-kinase mediates spinal nitric oxide formation by prostaglandin E2 via EP3 subtype

Prostaglandin E2 (PGE2), the principal pro-inflammatory prostanoid, is known to play versatile roles in pain transmission via four PGE receptor subtypes, EP1-EP4. We recently demonstrated that continuous production of nitric oxide (NO) by neuronal NO synthase (nNOS) following phosphorylation of myristoylated alanine-rich C-kinase substrate (MARCKS) and NMDA receptor NR2B subunits is essential for neuropathic pain. These phosphorylation and nNOS activity visualized by NADPH-diaphorase histochemistry were blocked by indomethacin, a PG synthesis inhibitor. To clarify the interaction between cyclooxygenase and nNOS pathways in the spinal cord, we examined the effect of EP subtype-selective agonists on NO production. NO formation was stimulated in the spinal superficial layer by EP1, EP3, and EP4 agonists. While the EP1- and the EP4-stimulated NO formation was markedly blocked by MK-801, an NMDA receptor antagonist, the EP3-stimulated one was completely inhibited by H-1152, a Rho-kinase inhibitor. Phosphorylation of MARCKS and NADPH-diaphorase activity stimulated by the EP3 agonist were also blocked by H-1152. These results suggest that PGE2 stimulates NO formation by Rho-kinase via EP3, a mechanism(s) different from EP1 and EP4.

Rho kinase, a promising drug target for neurological disorders

Rho kinases (ROCKs), the first Rho effectors to be described, are serine/threonine kinases that are important in fundamental processes of cell migration, cell proliferation and cell survival. Abnormal activation of the Rho/ROCK pathway has been observed in various disorders of the central nervous system. Injury to the adult vertebrate brain and spinal cord activates ROCKs, thereby inhibiting neurite growth and sprouting. Inhibition of ROCKs results in accelerated regeneration and enhanced functional recovery after spinal-cord injury in mammals, and inhibition of the Rho/ROCK pathway has also proved to be efficacious in animal models of stroke, inflammatory and demyelinating diseases, Alzheimer's disease and neuropathic pain. ROCK inhibitors therefore have potential for preventing neurodegeneration and stimulating neuroregeneration in various neurological disorders.