Pra-C exerts analgesic effect through inhibiting microglial activation in anterior cingulate cortex in complete Freund's adjuvant-induced mouse model

Santacruzamate A Alleviates Pain and Pain-Related Adverse Emotions through the Inhibition of Microglial Activation in the Anterior Cingulate Cortex

Chronic pain is a complex disease. It seriously affects patients' quality of life and imposes a significant economic burden on society. Santacruzamate A (SCA) is a natural product isolated from marine cyanobacteria in Panama. In this study, we first demonstrated that SCA could alleviate chronic inflammatory pain, pain-related anxiety, and depression emotions induced by complete Freund's adjuvant in mice while inhibiting microglial activation in the anterior cingulate cortex. Moreover, SCA treatment attenuated lipopolysaccharide (LPS)-induced inflammatory response by downregulating interleukin 1β and 6 (IL-1β and IL-6) and tumor necrosis factor-α (TNF-α) levels in BV2 cells. Furthermore, we found that SCA could bind to soluble epoxide hydrolase (sEH) through molecular docking technology, and the thermal stability of sEH was enhanced after binding of SCA to the sEH protein. Meanwhile, we identified that SCA could reduce the sEH enzyme activity and inhibit sEH protein overexpression in the LPS stimulation model. The results indicated that SCA could alleviate the development of inflammation by inhibiting the enzyme activity and expression of sEH to further reduce chronic inflammatory pain. Our study suggested that SCA could be a potential drug for treating chronic inflammatory pain.

The traditional uses, pharmacology, and phytochemistry of Peucedanum praeruptorum Dunn

Bai Hua Qian Hu (Qianhu; Peucedanum praeruptorum Dunn) is a classical medicinal plant traditionally prescribed for respiratory ailments, including cough, pulmonary hypertension, and asthma. In this review, we summarize the research progress of the toxicology, pharmacokinetics, pharmacology, phytochemistry, botany, quality control, and traditional uses of P. praeruptorum in order to support future investigations into the scientific and therapeutic promise of this important medicinal plant. Information pertaining to P. praeruptorum was collected from scientific databases (ScienceDirect, Springer, SciFinder, PubMed, Baidu Scholar, Google Scholar, Web of Science), as well as toxicology papers from local conferences, M. Sc. and Ph.D. theses and dissertations, local magazines, classic texts on Chinese botanical drugs, and peer-reviewed journals. The Plant List (www.theplantlist.org) was utilized to verify the taxonomy of P. praeruptorum. P. praeruptorum was found to contain more than 119 distinct phytochemicals, including simple coumarins, pyranocoumarins, furanocoumarins, flavonoids, ketones, organic acids, and sterols, among others (e.g., praeruptorins A and B). Both crude plant extracts and purified metabolites of P. praeruptorum have been reported as treatments for hypertension, osteoporosis, Huntington's disease, and cancer. In addition, extracts of P. praeruptorum are reported to exhibit diverse pharmacological activities, including osteogenic, anti-osteoclastogenic, antidepressant, neuroprotective, antitumor, and anti-inflammatory effects. Research into the pharmacology and phytochemistry of P. praeruptorum partially support both traditional uses and extraction methods. However, further research is required to elucidate the relationships between these metabolites, their molecular mechanisms, their structure-function roles, and their antagonistic and synergistic effects.

Role of magnesium-L-Threonate in alleviating skin/muscle incision and retraction induced mechanical allodynia and anxiodepressive-like behaviors in male rats

Chronic postsurgical pain (CPSP) and its emotional comorbidities poses health burden to patients who have received the surgical treatment. However, its underlying mechanism remains unclear. Emerging studies indicate that magnesium deficiency is associated with neurological diseases, and magnesium supplement confers protection under these disease conditions. In this study, we examined the role and mechanism of magnesium deficiency in the pathology of surgery-induced allodynia and negative emotion using a rat model of skin/muscle incision and retraction (SMIR) and investigated the therapeutic effects of magnesium supplementation by oral magnesium-L-Threonate (L-TAMS) in SMIR-injured rats. In the SMIR model, rats developed mechanical allodynia and anxiodepressive-like behaviors. Further, SMIR caused microglia and astrocyte activation and enhanced expression of pro-inflammatory cytokine (TNF-α, IL-1β and IL-6) in the anterior cingulate cortex (ACC). Importantly, magnesium ion (Mg2+) levels decreased in the serum and cerebrospinal fluid (CSF) of SMIR-injured rats, which exhibited high correlation with pain and emotion behavioral phenotypes in these rats. Repeated oral administration of L-TAMS increased serum and CSF levels of Mg2+ in SMIR-injured rats. Notably, L-TAMS administration reversed SMIR-induced mechanical allodynia and anxiodepressive-like behaviors but did not affect pain and emotional behaviors in sham rats. Moreover, L-TAMS administration suppressed SMIR-caused glial activation and proinflammatory cytokine expression in the ACC but had no such effect in sham rats. Together, our study demonstrates the contributing role of magnesium deficiency in the pathology of surgery-induced chronic pain and negative emotion. Moreover, we suggest that L-TAMS might be a novel approach to treat CPSP and its emotional comorbidities.

Praeruptorin C alleviates cognitive impairment in type 2 diabetic mice through restoring PI3K/AKT/GSK3β pathway

Diabetic encephalopathy is a common consequence of diabetes mellitus that causes cognitive dysfunction and neuropsychiatric disorders. Praeruptorin C (Pra-C) from the traditional Chinese medicinal herb Peucedanum praeruptorum Dunn. is a potential antioxidant and neuroprotective agent. This study was conducted to investigate the molecular mechanisms underlying the effect of Pra-C on diabetic cognitive impairment. A novel object recognition test and the Morris water maze test were performed to assess the behavioral performance of mice. Electrophysiological recordings were made to monitor synaptic plasticity in the hippocampus. A protein-protein interaction network of putative Pra-C targets was constructed, and molecular docking simulations were performed to predict the potential mechanisms of the action of Pra-C. Protein expression levels were detected by western blotting. Pra-C administration significantly lowered body weight and fasting blood glucose levels and alleviated learning and memory deficits in type 2 diabetic mice. Network pharmacology and molecular docking results suggested that Pra-C affects the PI3K/AKT/GSK3β signaling pathway. Western blot analysis confirmed significant increases in phosphorylated PI3K, AKT, and GSK3β levels in vivo and in vitro upon Pra-C administration. Pra-C alleviated cognitive impairment in type 2 diabetic mice by activating PI3K/AKT/GSK3β pathway.

Electroacupuncture Attenuates Neuropathic Pain in a Rat Model of Cervical Spondylotic Radiculopathy: Involvement of Spinal Cord Synaptic Plasticity

Purpose

Cervical spondylotic radiculopathy (CSR) is a common neurologic condition that causes chronic neck pain and motor functions, with neuropathic pain (NP) being the primary symptom. Although it has been established that electroacupuncture (EA) can yield an analgesic effect in clinics and synaptic plasticity plays a critical role in the development and maintenance of NP, the underlying mechanisms have not been fully elucidated. In this study, we explored the potential mechanisms underlying EA's effect on synaptic plasticity in CSR rat models.

Materials and Methods

The CSR rat model was established by spinal cord compression (SCC). Electroacupuncture stimulation was applied to LI4 (Hegu) and LR3 (Taichong) acupoints for 20 min once a day for 7 days. Pressure pain threshold (PPT) and mechanical pain threshold (MPT) were utilized to detect the pain response of rats. A gait score was used to evaluate the motor function of rats. Enzyme-linked immunosorbent assay (ELISA), Western blot (WB), immunohistochemistry (IHC), immunofluorescence (IF), and transmission electron microscopy (TEM) were performed to investigate the effects of EA.

Results

Our results showed that EA alleviated SCC-induced spontaneous pain and gait disturbance. ELISA showed that EA could decrease the concentration of pain mediators in the cervical nerve root. WB, IHC, and IF results showed that EA could downregulate the expression of synaptic proteins in spinal cord tissues and promote synaptic plasticity. TEM revealed that the EA could reverse the synaptic ultrastructural changes induced by CSR.

Conclusion

Our findings reveal that EA can inhibit SCC-induced NP by modulating the synaptic plasticity in the spinal cord and provide the foothold for the clinical treatment of CSR with EA.

Microglia sustain anterior cingulate cortex neuronal hyperactivity in nicotine-induced pain

BACKGROUND

Long-term smoking is a risk factor for chronic pain, and chronic nicotine exposure induces pain-like effects in rodents. The anterior cingulate cortex (ACC) has been demonstrated to be associated with pain and substance abuse. This study aims to investigate whether ACC microglia are altered in response to chronic nicotine exposure and their interaction with ACC neurons and subsequent nicotine-induced allodynia in mice.

METHODS

We utilized a mouse model that was fed nicotine water for 28 days. Brain slices of the ACC were collected for morphological analysis to evaluate the impacts of chronic nicotine on microglia. In vivo calcium imaging and whole-cell patch clamp were used to record the excitability of ACC glutamatergic neurons.

RESULTS

Compared to the vehicle control, the branch endpoints and the length of ACC microglial processes decreased in nicotine-treated mice, coinciding with the hyperactivity of glutamatergic neurons in the ACC. Inhibition of ACC glutamatergic neurons alleviated nicotine-induced allodynia and reduced microglial activation. On the other hand, reactive microglia sustain ACC neuronal excitability in response to chronic nicotine, and pharmacological inhibition of microglia by minocycline or liposome-clodronate reduces nicotine-induced allodynia. The neuron-microglia interaction in chronic nicotine-induced allodynia is mediated by increased expression of neuronal CX3CL1, which activates microglia by acting on CX3CR1 receptors on microglial cells.

CONCLUSION

Together, these findings underlie a critical role of ACC microglia in the maintenance of ACC neuronal hyperactivity and resulting nociceptive hypersensitivity in chronic nicotine-treated mice.

Huc-MSCs-derived exosomes attenuate inflammatory pain by regulating microglia pyroptosis and autophagy via the miR-146a-5p/TRAF6 axis

Background

Chronic inflammatory pain significantly reduces the quality of life and lacks effective interventions. In recent years, human umbilical cord mesenchymal stem cells (huc-MSCs)-derived exosomes have been used to relieve neuropathic pain and other inflammatory diseases as a promising cell-free therapeutic strategy. However, the therapeutic value of huc-MSCs-derived exosomes in complete Freund's adjuvant (CFA)-induced inflammatory pain remains to be confirmed. In this study, we investigated the therapeutic effect and related mechanisms of huc-MSCs-derived exosomes in a chronic inflammatory pain model.

Methods

C57BL/6J male mice were used to establish a CFA-induced inflammatory pain model, and huc-MSCs-derived exosomes were intrathecally injected for 4 consecutive days. BV2 microglia cells were stimulated with lipopolysaccharide (LPS) plus adenosine triphosphate (ATP) to investigate the effect of huc-MSCs-derived exosomes on pyroptosis and autophagy. Bioinformatic analysis and rescue experiments were used to demonstrate the role of miR-146a-5p/ TRAF6 in regulating pyroptosis and autophagy. Western blotting, RT-qPCR, small interfering RNA and Yo-Pro-1 dye staining were performed to investigate the related mechanisms.

Results

Huc-MSCs-derived exosomes alleviated mechanical allodynia and thermal hyperalgesia in CFA-induced inflammatory pain. Furthermore, huc-MSCs-derived exosomes attenuated neuroinflammation by increasing the expression of autophagy-related proteins (LC3-II and beclin1) and inhibiting the activation of NLRP3 inflammasomes in the spinal cord dorsal horn. In vitro, NLRP3 inflammasome components (NLRP3, caspase1-p20, ASC) and gasdermin D (GSDMD-F, GSDMD-N) were inhibited in BV2 cells pretreated with huc-MSCs-derived exosomes. Western blot and Yo-Pro-1 dye staining demonstrated that 3-MA, an autophagy inhibitor, weakened the protective effect of huc-MSCs-derived exosomes on BV2 cell pyroptosis. Importantly, huc-MSCs-derived exosomes transfected with miR-146a-5p mimic promoted autophagy and inhibited BV2 cell pyroptosis. TRAF6, as a target gene of miR-146a-5p, was knocked down via small-interfering RNA, which increased pyroptosis and inhibited autophagy.

Conclusion

Huc-MSCs-derived exosomes attenuated inflammatory pain via miR-146a-5p/TRAF6, which increased the level of autophagy and inhibited pyroptosis.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s12951-022-01522-6.

Neuroimmune Mechanisms Underlying Neuropathic Pain: The Potential Role of TNF-α-Necroptosis Pathway

The neuroimmune mechanism underlying neuropathic pain has been extensively studied. Tumor necrosis factor-alpha (TNF-α), a key pro-inflammatory cytokine that drives cytokine storm and stimulates a cascade of other cytokines in pain-related pathways, induces and modulates neuropathic pain by facilitating peripheral (primary afferents) and central (spinal cord) sensitization. Functionally, TNF-α controls the balance between cell survival and death by inducing an inflammatory response and two programmed cell death mechanisms (apoptosis and necroptosis). Necroptosis, a novel form of programmed cell death, is receiving increasing attraction and may trigger neuroinflammation to promote neuropathic pain. Chronic pain is often accompanied by adverse pain-associated emotional reactions and cognitive disorders. Overproduction of TNF-α in supraspinal structures such as the anterior cingulate cortex (ACC) and hippocampus plays an important role in pain-associated emotional disorders and memory deficits and also participates in the modulation of pain transduction. At present, studies reporting on the role of the TNF-α–necroptosis pathway in pain-related disorders are lacking. This review indicates the important research prospects of this pathway in pain modulation based on its role in anxiety, depression and memory deficits associated with other neurodegenerative diseases. In addition, we have summarized studies related to the underlying mechanisms of neuropathic pain mediated by TNF-α and discussed the role of the TNF-α–necroptosis pathway in detail, which may represent an avenue for future therapeutic intervention.

Tetrahydropalmatine exerts analgesic effects by promoting apoptosis and inhibiting the activation of glial cells in rats with inflammatory pain

BACKGROUND

Pain is an unpleasant sensory experience that usually plays a protective role. Inflammatory pain is often severe and stubborn, which has a great impact on the quality of life of patients. However, there has been no breakthrough in the treatment strategy and mechanism of inflammatory pain.

METHODS

This study investigated the analgesic effect of tetrahydropalmatine (THP) in rats injected with complete Freund's adjuvant (CFA)-induced inflammatory pain. Allodynia and gait analysis of rats were used to evaluate the analgesic effect at different time points before and after operation. THP (2.5, 5, and 10 mg/kg) was administered intraperitoneally once daily for 7 days post Day 3. The expression levels of TNF-α and IL-1β in the spinal cord were measured by enzyme-linked immunosorbent assay. The activation of astrocytes and microglial cells in the spinal cord was tested by western blot before and after THP treatment. The apoptosis of glial cells was tested by flow cytometry after treatment with THP in the primary cultured glial cell model.

RESULTS

CFA treatment induced significant allodynia and caused abnormal gait in rats. Administration of THP at 10 mg/kg significantly alleviated CFA-induced inflammatory pain behaviors. Moreover, CFA-induced activation of glial cells and the increased levels of TNF-α and IL-1β were inhibited by THP administration. In addition, THP promotes apoptosis in primary cultured glial cells. This study suggests the possible clinical utility of THP in the treatment of inflammatory pain.

CONCLUSION

THP plays an analgesic role by inhibiting the activation of glial cells and promoting apoptosis.