Electroacupuncture attenuates spared nerve injury-induced neuropathic pain possibly by promoting the progression of AMPK/mTOR-mediated autophagy in spinal microglia

Background

Neuropathic pain (NP) is a syndrome that arises from central or peripheral nerve injury, which manifests primarily as hyperalgesia, spontaneous pain, and allodynia. The recent trend has exhibited a shift towards the development of therapies for managing NP. Activation of autophagy is involved in the function of the glial cells, which may be implicated further to attenuate pain.

Methods

In this study, the analgesic effects of electroacupuncture (EA) were evaluated among NP rats developed using spared nerve injury (SNI). Acupuncture treatment or EA was carried out after 7 days of SNI at two acupoints, i.e., the Zusanli (ST36) and Huantiao (GB30).

Results

The application of EA was found to attenuate mechanical hyperalgesia. The marker protein for microglial cells (CD11b) alone, without either the astrocyte marker or neuronal marker, was co-expressed with the autophagy indicator p62, as illustrated with immunofluorescence staining. Western blotting demonstrated that the expression levels of p62, Beclin-1, and LC3-II/LC3-I were elevated in the spinal cords of rats in the SNI group compared to the control levels. EA treatment resulted in reduced expression of p62, while the expressions of Beclin-1 and LC3-II/LC3-I were increased. The electron microscopy results indicated that EA could induce autophagy progression in the microglia of the spinal dorsal horn in SNI rats. Furthermore, we explored the causal relationship between EA-induced inhibition of NP and increased autophagic levels in microglia using the AMPK inhibitor compound C, and found that the mechanism of EA-induced analgesia may contribute to the promotion of AMPK/mTOR-mediated autophagy in spinal microglia.

Conclusions

Our work showed that the analgesic impact of EA is partly related to AMPK/mTOR pathway activation and autophagy induction in microglial cells, providing a potential therapeutic target for NP.

Electroacupuncture alleviates neuropathic pain caused by spared nerve injury by promoting AMPK/mTOR-mediated autophagy in dorsal root ganglion macrophage

Background

Dorsal root ganglia (DRG) plays an important role in mediating the peripheral sensation transduction through the primary afferent neurons in pain research. Neuropathic pain (NP) is a syndrome of hyperalgesia, spontaneous pain and allodynia caused by central or peripheral nerve injury. Recent trends of study are turning towards the development of therapies for the management of NP. Activation of autophagy in glial cells in the spinal cord has been reported to be associated with attenuation of NP, but the autophagic process in DRG is rarely studied.

Methods

The analgesic effect of electroacupuncture (EA) was evaluated in NP-induced rats developed using spared nerve injury (SNI). Acupuncture or EA was performed after 7 days of SNI at Zusanli (ST36) and Huantiao (GB30) acupoints. Then, the activation status of autophagy process in DRGs of rats treated with SNI and EA were investigated, and the possible mechanism of the analgesic effect of EA were explored.

Results

Application of EA has been found to reduce mechanical hyperalgesia. Autophagy indicator p62 was colocalized with the marker proteins for macrophages (CD11b), but not with NeuN (marker protein for neurons) or GFAP (marker protein for satellite glial cells), as shown by immunofluorescence. Western blots results indicate that the expression levels of p62, Beclin-1 and LC3-II in the L4-L6 DRG of rats in the SNI group were increased, compared with that in the control group. EA treatment resulted in decreased expression of p62 and increased expression of Beclin-1 and LC3-II/LC3-I. Furthermore, we explored the causal relationship between EA-induced suppression of NP and increased levels of autophagy in DRG using electron microscopy and the AMPK (AMP-activated protein kinase) inhibitor compound C.

Conclusions

SNI achieved a significant upregulation of autophagy levels in DRG macrophages. Furthermore, EA attenuated NP, which may contribute to the promotion of AMPK/mTOR (mammalian target of rapamycin)-mediated autophagy in DRG macrophages. Therefore, this strategy provides a new target for therapeutic intervention of NP.

Screening of disease-related biomarkers related to neuropathic pain (NP) after spinal cord injury (SCI)

BACKGROUND

Based on the molecular expression level, this paper compares lncRNA and mRNA expressions respectively in peripheral blood samples of the patients after SCI with NP and without NP, and screens disease-related biomarkers related to NP after SCI in peripheral blood samples of patients.

METHOD

The expression spectrum of 25 human peripheral blood samples (12 samples of refractory NP patients after SCI) was downloaded and data were normalized. Screening of GO annotations significantly associated with significant differentially expressed mRNAs and significant involvement of the KEGG pathway. The WGCNA algorithm was used to screen for modules and RNAs that were significantly associated with disease characterization. A co-expression network was constructed to extract the genes involved in the disease pathway from the co-expression network, construct a network of SCI pain-related pathways, and screen important disease-related biomarkers. Quantitative real-time PCR was used to detect the mRNA expression of hub genes.

RESULTS

Data were normalized and re-annotated by detection of platform information, resulting in a total of 289 lncRNA and 18197 mRNAs. Screening resulted in 338 significant differentially expressed RNAs that met the threshold requirements. Differentially expressed RNAs were significantly enriched with the brown and magenta modules. Six KEGG signaling pathways were screened in the co-expression network, and three KEGG pathways with direct neuropathic pain were identified. The expression levels of E2F1, MAX, MITF, CTNNA1, and ADORA2B in the disease group were all significantly upregulated (p < 0.01). Compared with the normal group, the expression of OXTR was upregulated.

CONCLUSION

We speculate that there are 7 genes and 2 lncRNAs directly involved in the pain pathway: E2F1, MAX, MITF, CTNNA1, ADORA2B, GRIK3, OXTR, LINC01119, and LINC02447. These molecules may be important for NP after SCI.

Interleukin-1 Receptor Associated Kinase 1 Mediates the Maintenance of Neuropathic Pain after Chronic Constriction Injury in Rats

Neuropathic pain (NP) has complicated pathogenesis as it mainly involves a lesion or dysfunction of the somatosensory nervous system and its clinical treatment remains challenging. Chronic constriction injury (CCI) model is a widely used neuropathic pain model and involved in mechanisms including both nerve inflammatory and injury. Cytokines and their receptors play essential roles in the occurrence and persistence of neuropathic pain, but the underlying mechanisms have not well been understood. Therefore, Interleukin-1 receptor-associated kinase 1 (IRAK1) is chosen to explore the possible mechanisms of NP. In the present study, IRAK1 was found to persistently increase in the dorsal root ganglion (DRG) and spinal cord (SC) during CCI detected by western blot. The staining further confirmed that IRAK1 was mainly co-located in the DRG astrocytes or SC neurons, but less in the DRG microglia or SC astrocytes. Moreover, the region of increased IRAK1 expression was observed in superficial laminae of the spinal dorsal horn, which was the nociceptive neuronal expression domain, suggesting that IRAK1 may mediated CCI-induced pain by nociceptive primary afferent. In addition, intrathecal injection of Toll-like receptor 4 (TLR4) inhibitor or IRAK1 siRNA decreased the expression of IRAK1 accompanied with the alleviation of CCI-induced neuropathic pain. The upregulation of p-NF-κB expression was reversed by IRAK1 siRNA in SC, and intrathecal injection of p-NF-κB inhibitor relieved neuropathic pain. Taking together, targeting IRAK1 may be a potential treatment for chronic neuropathic pain.

Role of curcumin in the management of pathological pain

BACKGROUND

Pathological pain conditions can be triggered after peripheral nerve injury and/or inflammation. It is a major clinical problem that is poorly treated with available therapeutics. Curcumin is a phenolic compound derived from Curcuma longa, being widely used for its antioxidant, anti-inflammatory and immunomodulatory effects.

PURPOSE

This review systematically summarized updated information on the traditional uses of curcumin in order to explore antinociceptive effects in pathological pain and evaluate future therapeutic opportunities clinically. Moreover, some structure-activity relationships would greatly enrich the opportunity of finding new and promising lead compounds and promote the reasonable development of curcumin.

METHODS

PubMed were searched and the literature from the year 1976 to January 2018 was retrieved using keywords pain and curcumin.

RESULTS

This review systematically summarized updated information on the traditional uses, chemical constituents and bioactivities of curcumin, and highlights the recent development of the mechanisms of curcumin in the pathological pain by sciatic nerve injury, spinal cord injury, diabetic neuropathy, alcoholic neuropathy, chemotherapy induced peripheral neuroinflammtion, complete Freund's adjuvant (CFA) injection or carrageenan injection. Importantly, the clinical studies provide a compelling justification for its use as a dietary adjunct for pain relief. And we also present multiple approaches to improve bioavailability of curcumin for the treatment of pathological pain.

CONCLUSION

This review focuses on pre-clinical and clinical studies in the treatment of pathological pain. Although the mechanisms of pain mitigating effects are not very clear, there is compelling evidence proved that curcumin plays an essential role. However, further high-quality clinical studies should be undertaken to establish the clinical effectiveness of curcumin in patients suffering from pathological pain. Potential methods of increase the water solubility and bioavailability of curcumin still need to be studied. These approaches will help in establishing it as remedy for pathological pain.