山本 昇平

We have recently found that the synthetic curcumin derivative CNB-001 suppresses lipopolysaccharide (LPS)-induced nitric oxide (NO) production in cultured microglia, demonstrating that it exerts anti-neuroinflammatory effects by regulating microglial activation. To explore the molecular mechanisms underlying the anti-inflammatory effect of CNB-001, the present study investigated whether CNB-001 is also effective for microglial NO production induced by other stimulants than LPS. Treatment of primary cultured rat microglia with thrombin, a serine protease that has been proposed as a mediator of cerebrovascular injuries, caused the expression of inducible NO synthase (iNOS) and the production of NO. The thrombin-induced NO production was completely blocked by the presence of SCH-79797, a selective protease-activated receptor 1 (PAR-1) antagonist, suggesting that the effect of thrombin is mediated by PAR-1. CNB-001 (1-10 µM) attenuated the thrombin-induced iNOS expression and NO production without affecting the PAR-1 expression. In addition, thrombin treatment caused rapid phosphorylation of extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38 mitogen-activated protein kinase (MAPK). The changes in ERK and p38 MAPK were significantly suppressed by the presence of CNB-001. These results demonstrate that CNB-001 suppresses thrombin-stimulated microglial activation by inhibiting the ERK and p38 MAPK pathways.

Cilnidipine is a dihydropyridine derivative that inhibits N-type and L-type voltage-gated Ca2+ channels (VDCCs). We recently reported that a selective N-type VDCC blocker attenuated the spinal long-term potentiation (LTP) of C-fiber-evoked field potentials recorded in the spinal dorsal horn of rats, which served as a model for examining synaptic function during central pain sensitization. In this study, we investigated the effects of cilnidipine on the changes related to neuropathic pain induced by nerve injury. Mechanical allodynia and hyperalgesia were evaluated by von Frey test and pin prick test, respectively. Spinal LTP of C-fiber-evoked field potentials were evaluated by in vivo electrophysiology. Intrathecally administrated cilnidipine attenuated mechanical allodynia and hyperalgesia in the spared nerve injury mouse model. Using in vivo electrophysiology in rats, cilnidipine (10 mu m) administered spinally inhibited the induction and maintenance of high-frequency stimulation-induced LTP of C-fiber-evoked field potentials, while basal C-fiber-evoked field potentials in naive rats were unaffected. The basal C-fiber-evoked field potentials in nerve-injured rats were strongly inhibited by cilnidipine. Treatment with a specific N-type VDCC blocker, omega o-conotoxin GVIA, which reportedly attenuates C-fiber-evoked field potentials both before and after the induction of LTP, attenuated mechanical allodynia and hyperalgesia in nerve-injured mice. By contrast, an L-type VDCC blocker, nicardipine attenuated only mechanical hyperalgesia, but not mechanical allodynia in nerve-injured mice, and also attenuated the established LTP of C-fiber-evoked field potentials in rats. These results suggested that N-type and L-type VDCC blockers may effectively alleviate the hyperalgesia and allodynia associated with neuropathic pain without affecting normal pain perception.

Oxaliplatin (L-OHP) is a platinum-based chemotherapy drug, used in standard treatment of colorectal cancer. L-OHP frequently causes acute peripheral neuropathies. These adverse effects limit cancer therapy with L-OHP. The present study was designed to reveal the changes in sensory nerve function in L-OHP-injected rats. Mechanical static allodynia, dynamic allodynia, and cold allodynia were evaluated using the von Frey test, brush test, and acetone test, respectively. Sensory nerve fiber responsiveness was measured using a Neurometer. The fifth lumbar ventral root was sectioned to record multi-unit efferent discharges. Single intraperitoneal administration of L-OHP induced mechanical static allodynia, dynamic allodynia, and cold allodynia in Wistar/ST rats. The thresholds for paw withdrawal induced by 2000 Hz (A beta-fiber) and 5 Hz (C-fiber), but not 250 Hz (A delta-fiber) sine-wave electrical stimulation were reduced in L-OHP-treated rats. Multi-unit efferent discharges were increased by mechanical stimulation using a von Frey filament applied to the plantar surface of the hindpaw. The discharges during and after stimulation were increased in the L-OHP-treated rats. Cold stimulation, but not brush stimulation, increased the discharges in L-OHP-treated rats. These results suggest that sensitization of A beta- and C-fibers, but not A delta-fibers, contributes to the development of L-OHP-induced mechanical and cold allodynia. (C) 2015 The Authors. Production and hosting by Elsevier B.V. on behalf of Japanese Pharmacological Society. This is an open access article under the CC BY-NC-ND license.