The Utility of Peripherally Restricted Kappa-Opioid Receptor Agonists for Inhibiting Below-Level Pain After Spinal Cord Injury in Mice.

Pain after spinal cord injury (SCI) can be difficult to treat. Drugs that target the opioid receptor (OR) outside the central nervous system (CNS) have gained increasing interest in pain control owing to their low risk of central side effects. Asimadoline and ICI-204448 are believed to be peripherally restricted KOR agonists withlimited access to the CNS. This study examined whether they can attenuate pain hypersensitivity in mice subjected to a contusive T10 SCI. Subcutaneous (s.c.) injection of asimadoline (5, 20 mg/kg) and ICI-204448 (1, 10 mg/kg) inhibited heat hypersensitivity at both doses, but only attenuated mechanical hypersensitivity at the high dose. However, the high-dose asimadoline adversely affected animals' exploratory performance in SCI mice and caused aversion, suggesting CNS drug penetration. In contrast, high-dose ICI-204448 did not impair exploration and remained effective in reducing both mechanical and heat hypersensitivities after SCI. Accordingly, we chose to examine the potential peripheral neuronal mechanism for ICI-204448-induced pain inhibition by conducting in vivo calcium imaging of dorsal root ganglion (DRG) in Pirt-GCaMP6s+/- mice. High-dose ICI-204448 (10 mg/kg, s.c.) attenuated the increased fluorescence intensity of lumbar DRG neurons activated by a noxious pinch (400 g) stimulation in SCI mice. In conclusion, systemic administration of ICI-204448 achieved SCI pain inhibition at doses that did not induce notable side effects and attenuated DRG neuronal excitability which may partly contribute to its pain inhibition. These findings suggest that peripherally restricted KOR agonists may be useful for treating SCI pain, but the therapeutic window must be carefully examined.

[Protective effect of ghrelin against paraquat-induced acute lung injury in mice].

OBJECTIVE: To measure the levels of ghrelin-induced expression or activation of nuclear factor erythroid 2-related factor 2 (Nrf2), heme oxygenase-1 (HO-1), and NAD(P)H: quinone oxidoreductase 1 (NQO1) in the PQ-injured lungs of mice and to evaluate the protective effect of ghrelin against paraquat (PQ)-induced acute lung injury in mice. METHODS: According to the random number table method, 50 ICR mice of clean grade were assigned to 5 groups: normal control group (n = 10), PQ group (n = 10), and ghrelin intervention groups (n = 30). For PQ group, mice were injected with a single dose of PQ (20 mg/kg, i.p.); for ghrelin intervention groups, mice were injected with a single dose of PQ (20 mg/kg, i.p.), and then ghrelin was injected at three concentrations (16.58, 33.15, and 49.73 µg/kg). Lung tissues were collected and proceeded to the following studies. HE staining was used for histopathological examination under a light microscope, and the changes in nuclear expression of Nrf2 were evaluated by Western blot. The activities of HO-1 and NQO1 were measured by ELISA. Malondialdehyde (MDA) content and MPO activity were measured by colorimetry. Another 40 mice were divided into PQ group (n = 10) and 16.58, 33.15, and 49.73 µg/kg ghrelin intervention groups (n = 10 for each); mortality and clinical manifestations were recorded within 72 h. RESULTS: Compared with the normal control group, the PQ group showed significant increases in nuclear protein level of Nrf2, content of MDA, and activities of HO-1, NQO1, and MPO (P < 0.05 for all). Compared with the PQ group, ghrelin treatment significantly increased the expression of Nrf2 and activities of HO-1 and NQO1 and significantly reduced the content of MDA and activity of MPO (P < 0.01 for all). Histopathological studies indicated that ghrelin showed an antioxidant property that reduced the histological changes induced by PQ in the lungs. The ghrelin intervention groups had a significantly lower mortality than the PQ group, and there was a significant difference between the high-dose ghrelin intervention group and PQ group (P < 0.05). CONCLUSION: Ghrelin can up-regulate nuclear expression of Nrf2, increase the activities of HO-1 and NQO1, and reduce the activity of MPO and content of MDA, thus protecting PQ-exposed mice from acute lung injury.