Fentanyl Analogs Exert Antinociceptive Effects via Sodium Channel Blockade in Mice.

The formalin test is one approach to studying acute pain in rodents. Similar to formalin, injection with glutamate and veratrine can also produce a nociceptive response. This study investigated whether opioid-related compounds could suppress glutamate- and veratrine-induced nociceptive responses in mice at the same dose. The administration of morphine (3 mg/kg), hydromorphone (0.4 mg/kg), or fentanyl (0.03 mg/kg) suppressed glutamate-induced nociceptive response, but not veratrine-induced nociceptive response at the same doses. However, high doses of morphine (10 mg/kg), hydromorphone (2 mg/kg), or fentanyl (0.1 mg/kg) produced a significant reduction in the veratrine-induced nociceptive response. These results indicate that high doses are required when using morphine, hydromorphone, or fentanyl for sodium channel-related neuropathic pain, such as ectopic activity. As a result, concerns have arisen about overdose and abuse if the dose of opioids is steadily increased to relieve pain. In contrast, trimebutine (100 mg/kg) and fentanyl analog isobutyrylfentanyl (iBF; 0.1 mg/kg) suppressed both glutamate- and veratrine-induced nociceptive response. Furthermore, nor-isobutyrylfentanyl (nor-iBF; 1 mg/kg), which is a metabolite of iBF, suppressed veratrine-induced nociceptive response. Besides, the optimal antinociceptive dose of iBF, unlike fentanyl, only slightly increased locomotor activity and did not slow gastrointestinal transit. Cancer pain is a complex condition driven by inflammatory, neuropathic, and cancer-specific mechanisms. Thus, iBF may have the potential to be a superior analgesic than fentanyl.

Antinociceptive activity of the novel RAGE inhibitor, papaverine, in a mouse model of chronic inflammatory pain.

Extracellular high-mobility group box 1 (HMGB1) is known to mediate the inflammatory response through pattern recognition receptors, including the receptor for advanced glycation end products (RAGE) or the toll-like receptors (TLRs). The aim of the present study was to investigate whether papaverine, a novel RAGE inhibitor, could suppress inflammatory pain in mice after several time points, which was induced by the injection of complete Freund's adjuvant (CFA). We also investigated the influence of redox modulation during a state of chronic inflammatory pain. Although papaverine did not suppress CFA-induced mechanical allodynia on Day 7, papaverine significantly suppressed CFA-induced mechanical allodynia on Days 14 and 28. In contrast, the radical scavenger N-tert-Butyl-α-phenylnitrone (PBN) suppressed mechanical allodynia in mice on Days 7 and 14, but not on Day 28. We demonstrated that the RAGE inhibitor improves mechanical allodynia in chronic inflammatory conditions. Moreover, we also found that high levels of reactive oxygen species (ROS) contributed to the early phase of CFA-induced mechanical allodynia. Precisely, lower ROS levels contributed to the inflammatory pain response via the all-thiol HMGB1/RAGE signaling pathway during the chronic state. These findings led us to propose that ROS levels modulate RAGE and/or TLR4-mediated inflammatory allodynia by regulating the concentrations of disulfide HMGB1 or all-thiol HMGB1.

Synergistic Antinociceptive Activity of Tramadol/Acetaminophen Combination Mediated by µ-Opioid Receptors.

We investigated whether tramadol could suppress both neuropathic and inflammatory pain in mice at the same dose level. We also examined the effects of drugs metabolized by glucuronidase, such as acetaminophen (ACAP), indomethacin, probenecid, and valproate, on the antinociceptive activity of tramadol. The administration of 5.6 or 10 mg/kg tramadol suppressed cuff-induced mechanical allodynia, but 10 mg/kg tramadol did not suppress complete Freund's adjuvant (CFA)-induced mechanical allodynia. Although neither tramadol (10 mg/kg) nor ACAP (100 mg/kg) alone produced an antinociceptive effect, their combination suppressed CFA-induced mechanical allodynia. Moreover, pretreatment naloxone, an opioid receptor antagonist, significantly attenuated the antinociceptive effects induced by the combination of tramadol and ACAP and slowed gastrointestinal transit. Similar to ACAP, the combination of tramadol and probenecid or valproate, which has the potential to inhibit uridine 5'-diphosphate (UDP)-glucuronosyltransferase (UGT), also suppressed the CFA-induced mechanical allodynia and slowed gastrointestinal transit. We concluded that tramadol was more beneficial for the treatment of neuropathic pain than inflammatory pain. Furthermore, the antinociceptive effects of the tramadol and ACAP combination were mediated by the µ-opioid receptor, and were thought to be related, at least in part, to the accumulation of the active metabolite, M1.

Structural insights into a bacterial ß-glucosidase capable of degrading sesaminol triglucoside to produce sesaminol: toward the understanding of the aglycone recognition mechanism by the C-terminal lid domain.

The sesaminol triglucoside (STG)-hydrolyzing ß-glucosidase from Paenibacillus sp. (PSTG1), which belongs to glycoside hydrolase family 3 (GH3), is a promising catalyst for the industrial production of sesaminol. We determined the X-ray crystal structure of PSTG1 with bound glycerol molecule in the putative active site. PSTG1 monomer contained typical three domains of GH3 with the active site in domain 1 (TIM barrel). In addition, PSTG1 contained an additional domain (domain 4) at the C-terminus that interacts with the active site of the other protomer as a lid in the dimer unit. Interestingly, the interface of domain 4 and the active site forms a hydrophobic cavity probably for recognizing the hydrophobic aglycone moiety of substrate. The short flexible loop region of TIM barrel was found to be approaching the interface of domain 4 and the active site. We found that n-heptyl-ß-D-thioglucopyranoside detergent acts as an inhibitor for PSTG1. Thus, we propose that the recognition of hydrophobic aglycone moiety is important for PSTG1-catalyzed reactions. Domain 4 might be a potential target for elucidating the aglycone recognition mechanism of PSTG1 as well as for engineering PSTG1 to create a further excellent enzyme to degrade STG more efficiently to produce sesaminol.

Simultaneous Pseudoprogression and an Immune-related Adverse Event of Pulmonary Pleomorphic Carcinoma after Combined Therapy with Cytotoxic Anticancer Agents and Immune Checkpoint Inhibitor.

Pulmonary pleomorphic carcinoma is rare among lung tumors. Pulmonary pleomorphic carcinoma is resistant to chemotherapy. However, treatment with taxane anticancer agents and immune checkpoint inhibitors has been reported to be effective. When using immune checkpoint inhibitors, pseudoprogression and true progression are difficult to distinguish, and immune-related adverse events (irAEs) are common. We herein report a patient with simultaneous pseudoprogression and irAEs after combined therapy with cytotoxic agents and an immune checkpoint inhibitor for pulmonary pleomorphic carcinoma. Immune checkpoint inhibitors are effective against pulmonary pleomorphic carcinoma, but patients should be monitored for pseudoprogression and irAEs.

Differences in the antinociceptive effects of serotonin-noradrenaline reuptake inhibitors via sodium channel blockade using the veratrine test in mice.

Antidepressants exert their analgesic effects by inhibiting the reuptake of noradrenaline. Several antidepressants have been shown to block the sodium channels, which might contribute to their analgesic potency. The aim of this study was to determine whether serotonin-noradrenaline reuptake inhibitors (SNRIs) could produce antinociceptive effects via sodium channel blockade using the veratrine test in mice. Furthermore, the effects of these agents on the veratrine test were examined to elucidate the effects of several antidepressants and tramadol on sodium channels. The administration of duloxetine (10 mg/kg) and venlafaxine (30 mg/kg) suppressed cuff-induced mechanical allodynia; however, these antinociceptive effects were only partially suppressed by atipamezole. Furthermore, duloxetine and venlafaxine demonstrated antinociceptive effects via sodium channel blockade, as assayed by the veratrine test. In addition, several antidepressants, including amitriptyline, paroxetine and mirtazapine, reduced veratrine-induced nociception. In contrast, milnacipran and tramadol did not alter the veratrine-induced nociception. These results indicated that, in addition to the primary action of SNRIs on monoamine transporters, sodium channel blockade might be involved in the antinociceptive activities of duloxetine and venlafaxine, but not milnacipran.