Luteolin relieves lung cancer-induced bone pain by inhibiting NLRP3 inflammasomes and glial activation in the spinal dorsal horn in mice.

BACKGROUND: Bone cancer pain (BCP) is one of the most severe complications in cancer patients. However, the pharmacological therapeutic approaches are limited. Luteolin, a major component of flavones, is widely distributed in plants and plays a critical role in the antinociceptive effects, but whether luteolin could alleviate cancer pain and its underlying mechanisms are not known. HYPOTHESIS/PURPOSE: This study investigated the molecular mechanisms by which luteolin reduced BCP. METHODS: Behavioral, pharmacological, immunohistochemical, and biochemical approaches were used to investigate the effect of luteolin on BCP. RESULTS: Luteolin treatment ameliorated Lewis lung cancer (LLC)-induced bone pain in mice in a dose-dependent manner. Luteolin treatment could inhibit the activation of neurons, glial cells, and NOD-like receptor protein 3 (NLRP3) inflammasomes in the dorsal spinal cord in the BCP mouse model. Furthermore, phosphorylated p-38 mitogen-activated protein kinase (MAPK) in the spinal dorsal horn (SDH) was suppressed by luteolin treatment that could influence the analgesic and glial inhibition effects of luteolin. CONCLUSION: Our results demonstrated that luteolin inhibited neuroinflammation by obstructing glial cell and NLRP3 inflammasome activation via modulating p38 MAPK activity in SDH, ultimately improving LLC-induced BCP.

Regular Aerobic Exercise Attenuates Pain and Anxiety in Mice by Restoring Serotonin-Modulated Synaptic Plasticity in the Anterior Cingulate Cortex.

PURPOSE: Clinical studies found that regular aerobic exercise has analgesic and antianxiety effects; however, the underlying neural mechanisms remain unclear. Multiple studies have suggested that regular aerobic exercise may exert brain-protective effects by promoting the release of serotonin, which may be a pain modulator. Anterior cingulate cortex (ACC) is a key brain area for pain information processing, receiving dense serotonergic innervation. As a result, we hypothesized that exercise may increase the release of serotonin in the ACC, thus improving pain and anxiety behaviors. METHODS: Integrative methods were used, including behavioral, electrophysiological, pharmacological, biochemical, and genetic approaches, to explore the effects of regular aerobic exercise and the underlying neural mechanisms. RESULTS: Regular aerobic exercise in the form of voluntary wheel running for 30 min daily for 15 d showed significant effectiveness in relieving pain and concomitant anxiety in complete Freund's adjuvant-induced chronic inflammation pain models. c-Fos staining and multielectrode array recordings revealed alterations in neuronal activities and synaptic plasticity in the ACC. Moreover, systemic pharmacological treatment with 4-chloro-dl-phenylalanine (PCPA) to deplete endogenous serotonin and local delivery of serotonin to the ACC revealed that exercise-related serotonin release in the ACC bidirectionally modulates pain sensitization and anxiety behaviors by modulating synaptic plasticity in the ACC. Furthermore, we found that 5-HT1A and 5-HT7 receptors mediated the serotonin modulation effects under conditions of regular aerobic exercise through local infusion of a selective antagonist and shRNA in the ACC. CONCLUSIONS: Our results reveal that regular aerobic exercise can increase serotonin release and modulate synaptic plasticity in the ACC, ultimately improving pain and concomitant anxiety behaviors through the functions of the 5-HT1A and 5-HT7 receptors.