BackgroundAlthough neuropathic pain is frequently observed in demyelinating diseases such as Guillain-Barré syndrome and multiple sclerosis, the molecular basis for the relationship between demyelination and neuropathic pain behaviors is poorly understood. Previously, we found that lysophosphatidic acid receptor (LPA1) signaling initiates sciatic nerve injury-induced neuropathic pain and demyelination.ResultsIn the present study, we have demonstrated that sciatic nerve injury induces marked demyelination accompanied by myelin-associated glycoprotein (MAG) down-regulation and damage of Schwann cell partitioning of C-fiber-containing Remak bundles in the sciatic nerve and dorsal root, but not in the spinal nerve. Demyelination, MAG down-regulation and Remak bundle damage in the dorsal root were abolished in LPA1 receptor-deficient (Lpar1-/-) mice, but these alterations were not observed in sciatic nerve. However, LPA-induced demyelination in ex vivo experiments was observed in the sciatic nerve, spinal nerve and dorsal root, all which express LPA1 transcript and protein. Nerve injury-induced dorsal root demyelination was markedly attenuated in mice heterozygous for autotaxin (atx+/-), which converts lysophosphatidylcholine (LPC) to LPA. Although the addition of LPC to ex vivo cultures of dorsal root fibers in the presence of recombinant ATX caused potent demyelination, it had no significant effect in the absence of ATX. On the other hand, intrathecal injection of LPC caused potent dorsal root demyelination, which was markedly attenuated or abolished in atx+/- or Lpar1-/- mice.ConclusionsThese results suggest that LPA, which is converted from LPC by ATX, activates LPA1 receptors and induces dorsal root demyelination following nerve injury, which causes neuropathic pain.

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Lysophosphatidic acid (LPA) is a bioactive lipid mediator that exerts a wide range of biological actions. In recent decades, LPA has been demonstrated as an important initiator of neuropathic pain based on the mechanisms of LPA-induced feed-forward LPA amplification. In this study, we examined the possible involvement of interleukin (IL)-1β in such LPA production. Intrathecal (i.t.) LPA injection rapidly increased the expression of IL-1β mRNA in the spinal dorsal horn as early as 0.5 h after injection, and the level reached peak at 2 h. Through a developed quantitative mass spectrometry for detecting LPA species, the elevated levels of 18:1, 16:0, and 18:0 LPA in the spinal dorsal horn were observed at 3 h after 18:1 LPA injection and this elevation was completely blocked by the pretreatment of IL-1β-neutralizing antibody. Moreover, enzyme assay experiments showed that LPA (i.t.) significantly activated calcium-independent phospholipase A2 (iPLA2) and cytosolic phospholipase A2 (cPLA2) in the spinal dorsal horn at 1 and 2 h, respectively, and these biochemical changes were also significantly inhibited by IL-1β-neutralizing antibody. Similarly, IL-1β-neutralizing antibody reversed LPA-induced neuropathic pain-like behavior. These findings suggest that the early release of IL-1β is involved in LPA-induced amplification of LPA production, which underlies the initial mechanisms of LPA-induced neuropathic pain.

Rhabdomyosarcoma (RMS) is a common soft tissue sarcoma usually observed in children. However, RMS rarely occurs in adults. The prognosis of adult RMS is poor and a standard chemotherapy regimen has not yet been established. Herein, we report the case of a 60-year-old Japanese woman with primary anterior mediastinal alveolar RMS (T3N0M0, stage III). The tumor increased aggressively despite first-line treatment with doxorubicin (60 mg/m 2 every 3 weeks for 1 cycle) and second-line treatment with eribulin (1.4 mg/m 2 every 3 weeks for 2 cycles). Although her shortness of breath and chest tightness worsened as the tumor compressed her heart and left main bronchus, and her performance status (PS) decreased to 3, third-line treatment with pazopanib (800 mg once daily) was commenced. The treatment led to suppression of tumor growth and resulted in 4-month progression-free survival. Therefore, in cases of adult RMS, considering pazopanib treatment as an option may be beneficial, even with previous ineffective treatments or poor PS.

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