Integration of microbiota and metabolomics reveals the analgesic mechanisms of emodin against neuropathic pain.

BACKGROUND AND OBJECTIVE: Neuropathic pain (NeP) induced dysbiosis of intestinal microbiota in chronic constriction injury (CCI) rats. Emodin has analgesic effect but the detailed mechanism is not clear at the present time. This study aims to explore the underling mechanism of action of emodin against NeP with in CCI model. METHODS: Male SD rats (180-220 g) were randomly divided into three groups: sham group, CCI group, and emodin group. Behavioral tests were performed to evaluate the therapeutic effects of emodin on CCI model. Feces and spinal cords of all rats were collected 15 days after surgery. 16S rDNA sequencing, untargeted metabolomics, qPCR and ELISA were performed. RESULTS: Mechanical withdrawal thresholds (MWT), thermal withdrawal latency (TWL) and Sciatic functional index (SFI) in emodin group were significantly higher than CCI group (P < 0.05). Emodin not only inhibited the expression of pro-inflammatory cytokines in the spinal cords and colonic tissue, but also increased the expression of tight junction protein in colonic tissue. 16S rDNA sequencing showed that emodin treatment changed the community structure of intestinal microbiota in CCI rats. Untargeted metabolomics analysis showed that 33 differential metabolites were screened out between CCI group and emodin group. After verification, we found that emodin increased the level of S-adenosylmethionine (SAM) and Histamine in the spinal cord of CCI rats. CONCLUSION: Emodin was effective in relieving neuropathic pain, which is linked to inhibition inflammatory response, increasing the proportion of beneficial bacteria and beneficial metabolites.

Alterations of endogenous pain-modulatory system of the cerebral cortex in the neuropathic pain.

Neuropathic pain (NeP) remains a significant clinical challenge owing to insufficient awareness of its pathological mechanisms. We elucidated the aberrant metabolism of the cerebral cortex in NeP induced by the chronic constriction injury (CCI) using metabolomics and proteomics analyses. After CCI surgery, the values of MWT and TWL markedly reduced and maintained at a low level. CCI induced the significant dysregulation of 57 metabolites and 31 proteins in the cerebral cortex. Integrative analyses showed that the differentially expressed metabolites and proteins were primarily involved in alanine, aspartate and glutamate metabolism, GABAergic synapse, and retrograde endocannabinoid signaling. Targeted metabolomics and western blot analysis confirmed the alterations of some key metabolites and proteins in endogenous pain-modulatory system. In conclusion, our study revealed the alterations of endocannabinoids system and purinergic system in the CCI group, and provided a novel perspective on the roles of endogenous pain-modulatory system in the pathological mechanisms of NeP.

Proteomic Analysis of Emodin Treatment in Neuropathic Pain Reveals Dysfunction of the Calcium Signaling Pathway.

BACKGROUND: Neuropathic pain (NP) is a syndrome of pain mediated by distinct pathophysiological processes, and current treatments are not fully satisfactory. Emodin is an effective component of Chinese traditional medicine and has an alleviating effect on NP, but the pharmacological mechanism is not clear. METHODS: We used isobaric tags for relative and absolute quantitation (iTRAQ) technique integrated with liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis to identify potential targets of emodin in a rat peripheral nerve chronic constriction injury (CCI) model. RESULTS: A total of 177 differentially expressed proteins were identified among the sham group, CCI group, and emodin group, with a threshold of 1.2-fold change and a P value ≤ 0.05. Among them, 100 differentially expressed proteins (51 up-regulated and 49 down-regulated) were identified in the CCI group compared with sham group. Moreover, 108 differentially expressed proteins (65 up-regulated and 43 down-regulated) were identified in the emodin group with the CCI group as reference. The enrichment analysis of Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) revealed an important role of calcium signaling pathway, neurotransmitter regulation, and long-term potentiation (LTP) in emodin-treated CCI model. Real-time quantitative fluorescence PCR (qRT-PCR) and Western blot analysis revealed that emodin decreased expression of calcium signaling related proteins, including calmodulin (CaM) dependent protein kinase II (CaMK II), phospholipase Cß1 (PLCß1), protein kinase C (PKC), protein kinase C (PKA), and tropomyosin-related kinase B (TrkB), compared with the CCI group. CONCLUSION: Overall, these findings indicated that emodin might alleviate NP by regulating the calcium signaling pathway.