Accumulating evidence indicates that purinergic P2X4 receptors (P2X4R: cation channels activated by extracellular ATP) expressed in spinal microglia are crucial for pathological chronic pain caused by nerve damage, suggesting a potential target for drug discovery. We identified NP-1815-PX (5-[3-(5-thioxo-4H-[1,2,4]oxadiazol-3-yl)phenyl]-1H-naphtho[1, 2-b][1,4]diazepine-2,4(3H,5H)-dione) as a novel antagonist selective for P2X4R with high potency and selectivity compared with other P2XR subtypes. In in vivo assay for acute and chronic pain, intrathecal administration of NP-1815-PX produced an anti-allodynic effect in mice with traumatic nerve damage without affecting acute nociceptive pain and motor function (although its oral administration did not produce the effect). Furthermore, in a mouse model of herpetic pain, P2X4R upregulation in the spinal cord exclusively occurred in microglia, and intrathecal NP-1815-PX suppressed induction of mechanical allodynia. This model also showed K+/Cl− cotransporter 2 (KCC2) downregulation, which is implicated in dorsal horn neuron hyperexcitability; this downregulation was restored by intrathecal treatment with NP-1815-PX or by interfering with brain-derived neurotrophic factor (BDNF) signaling, a P2X4R-activated microglial factor implicated in KCC2 downregulation. Taken together, the newly developed P2X4R antagonist NP-1815-PX produces anti-allodynic effects in chronic pain models without altering acute pain sensitivity, suggesting that microglial P2X4R could be an attractive target for treating chronic pain.

We compared the inhibitory action of gabapentin, which is used to treat neuropathic pain, on mechanical allodynia induced by chemotherapeutic agents, paclitaxel, oxaliplatin, and vincristine, in mice. Single injections of paclitaxel, oxaliplatin, and vincristine at the doses corresponding to doses clinically used caused mechanical allodynia of similar intensity. Oral administration of gabapentin (30, 100 mg/kg) produced a dose-dependent inhibition of allodynia caused by paclitaxel and oxaliplatin, but not vincristine. Intrathecal injection of gabapentin (30, 100microg/site) significantly inhibited allodynia induced by paclitaxel, but not oxaliplatin and vincristine. Intraplantar injection of gabapentin (30, 100 microg/site) did not significantly inhibit allodynia induced by paclitaxel and oxaliplatin. Paclitaxel increased the expression of mRNA of voltage-dependent calcium channel alpha(2)delta-1 subunit, an action site of gabapentin, in the dorsal spinal cord, and oxaliplatin increased it in the dorsal root ganglia. Vincristine was without effects on alpha(2)delta-1 subunit mRNA in these regions. These results suggest that the efficacy of gabapentin in the treatment of mechanical allodynia is dependent on chemotherapy agent used. It may be partly due to the distinct effects of chemotherapy agents on the expression of alpha(2)delta-1 subunit of voltage-dependent calcium channel.

Abstract. This study examined in mice whether limaprost, a prostaglandin E 1 analog, would relieve allodynia induced by chemotherapeutic agents. Single intraperitoneal injections of paclitaxel, oxaliplatin, and vincristine sulfate induced and gradually increased mechanical allodynia. Repeated administration of limaprost alfadex inhibited the late, but not early, phase of mechanical allodynia induced by paclitaxel and oxaliplatin, but not vincristine. Paclitaxel and oxaliplatin, but not vincristine, gradually decreased peripheral blood flow, which was prevented by limaprost. These results suggest that limaprost is effective against mechanical allodynia induced by paclitaxel and oxaliplatin, which may be due to inhibition of the decrease in peripheral blood flow.

Antihypertensive activities derived from porcine skeletal muscle proteins were investigated. Thermolysin hydrolysates of porcine muscle water-insoluble proteins demonstrated antihypertensive activities in spontaneously hypertensive rats when administrated in single oral doses. Hydrolysates of porcine myosin and peptides (Met-Asn-Pro-Pro-Lys, Ile-Thr-Thr-Asn-Pro, Met-Asn-Pro, Pro-Pro-Lys) with parts of the sequence of myosin showed antihypertensive activities. This is the first report of antihypertensive activities of peptides derived from muscle proteins of domestic animals. The hydrolysates of porcine muscle protein and their corresponding bioactive peptides might be utilized for physiologically functional foods.

A series of 1-benzyl-4-[2-(N-benzoylamino)ethyl]piperidine derivatives was synthesized and evaluated for anti-acetylcholinesterase (anti-AChE) activity. Substituting the benzamide with a bulky moiety in the para position led to a substantial increase in activity. Introduction of an akyl or phenyl group at the nitrogen atom of benzamide dramatically enhanced the activity. The basic quality of the nitrogen atom of piperidine appears to play an important role in the increased activity, since the N-benzoylpiperidine derivative was almost inactive. We found that 1-benzyl-4-[2-(N-[4'-(benzylsulfonyl) benzoyl]-N-methylamino]ethyl]piperidine hydrochloride (21) (IC50 = 0.56 nM) is one of the most potent inhibitors of acetylcholinesterase. Compound 21 showed an affinity 18,000 times greater for AChE than for BuChE. At a dose of 3 mg/kg, 21 produced a marked and significant increase in acetylcholine (ACh) content in the cerebral vortex and hippocampus of rats. Compound 21 was chosen for advanced development as an antidementia agent.