Cyclooxygenase metabolizes dihomo-γ-linolenic acid and arachidonic acid to form prostaglandin (PG) E, including PGE1 and PGE2, respectively. Although PGE2 is well known to play an important role in the development and maintenance of hyperalgesia and allodynia, the role of PGE1 in pain is unknown. We confirm whether PGE1 induced pain using orofacial pain behavioral test in mice and determine the target molecule of PGE1 in TG neurons with whole-cell patch-clamp and immunohistochemistry. Intradermal injection of PGE1 to the whisker pads of mice induced a reduced threshold, enhancing the excitability of HCN channel-expressing trigeminal ganglion (TG) neurons. The HCN channel-generated inward current (I_h) was increased by 135.3 ± 4.8% at 100 nM of PGE1 in small- or medium-sized TG, and the action of PGE1 on I_h showed a concentration-dependent effect, with a median effective dose (ED₅₀) of 29.3 nM. Adenylyl cyclase inhibitor (MDL12330A), 8-bromo-cAMP, and the EP2 receptor antagonist AH6809 inhibited PGE1-induced I_h. Additionally, PGE1-induced mechanical allodynia was blocked by CsCl and AH6809. PGE1 plays a role in mechanical allodynia through HCN2 channel facilitation via the EP2 receptor in nociceptive neurons, suggesting a potential therapeutic target in that PGE1 could be involved in pain as endogenous substances under inflammatory conditions.

Chemotherapy-induced peripheral neuropathy (CIPN) is a major drawback in the use of chemotherapeutic agents for patients with cancer. Although studies have investigated a broad number of molecules that might be related to CIPN, the differences in the chemokine pathways between various chemotherapeutic agents, such as vincristine and oxaliplatin, which are some of the most widely used treatments, have not been fully elucidated. We confirmed that the administration (intraperitoneal injections for seven days) of vincristine (0.1 mg/kg) and oxaliplatin (3 mg/kg) induced pain by using the von Frey behavioral test. Subsequent applications with vincristine and oxaliplatin led to mechanical allodynia that lasted more than one week from the fifth day. After the induction of mechanical allodynia, the mRNA expression of CXCR2, CXCL1, CXCL3, and CXCL5 was examined in the dorsal root ganglia (DRG) and spinal cord of the CIPN models. As a result, the mRNA expression of CXCR2 robustly increased in the lumbar spinal cord in the oxaliplatin-treated mice. Next, to evaluate the involvement of CXCR2 in CIPN, reparixin, a CXCR1/2 inhibitor, was administered intrathecally or intraperitoneally with vincristine or oxaliplatin and was further verified by treatment with ruxolitinib, which inhibits Janus kinase 2 downstream of the CXCR1/2 pathway. Reparixin and ruxolitinib blocked oxaliplatin-induced allodynia but not vincristine-induced allodynia, which suggests that CXCR2-related pathways are associated with the development of oxaliplatin-induced neuropathy. Together with the above results, this suggests that the prevention of oxaliplatin-induced neuropathy by CXCR2 inhibition can lead to successful chemotherapy, and it is important to provide appropriate countermeasures against CIPN development for each specific chemotherapeutic agent.