Higenamine Attenuates Neuropathic Pain by Inhibition of NOX2/ROS/TRP/P38 Mitogen-Activated Protein Kinase/NF-ĸB Signaling Pathway

The interplay of p38 MAPK signaling and mitochondrial metabolism, a dynamic target in cancer and pathological contexts

Mitochondria play a crucial role in cellular metabolism and bioenergetics, orchestrating various cellular processes, including energy production, metabolism, adaptation to stress, and redox balance. Besides, mitochondria regulate cellular metabolic homeostasis through coordination with multiple signaling pathways. Importantly, the p38 mitogen-activated protein kinase (MAPK) signaling pathway is a key player in the intricate communication with mitochondria, influencing various functions. This review explores the multifaced interaction between the mitochondria and p38 MAPK signaling and the consequent impact on metabolic alterations. Overall, the p38 MAPK pathway governs the activities of key mitochondrial proteins, which are involved in mitochondrial biogenesis, oxidative phosphorylation, thermogenesis, and iron homeostasis. Additionally, p38 MAPK contributes to the regulation of mitochondrial responses to oxidative stress and apoptosis induced by cancer therapies or natural substances by coordinating with other pathways responsible for energy homeostasis. Therefore, dysregulation of these interconnected pathways can lead to various pathologies characterized by aberrant metabolism. Consequently, gaining a deeper understanding of the interaction between mitochondria and the p38 MAPK pathway and their implications presents exciting forecasts for novel therapeutic interventions in cancer and other disorders characterized by metabolic dysregulation.

SIRT1-regulated ROS generation activates NMDAR2B phosphorylation to promote central sensitization and allodynia in a male chronic migraine rat model

Background

Central sensitization is one of the pivotal pathological mechanisms in chronic migraine (CM). Silent information regulator 1 (SIRT1) was shown to be involved in CM, but its specific mechanism is unclear. Reactive oxygen species (ROS) are increasingly regarded as important signaling molecules in several models of pain. However, studies about the role of ROS in the central sensitization of CM model are rare. We thus explored the specific process of SIRT1 involvement in the central sensitization of CM, focusing on the ROS pathway.

Methods

Inflammatory soup was repeatedly administered to male Sprague-Dawley rats to establish a CM model. The SIRT1 expression level in trigeminal nucleus caudalis (TNC) tissues was assessed by qRT-PCR and Western blotting analysis. The levels of ROS were detected by a Tissue Reactive Oxygen Detection Kit, DHE staining, and the fluorescence signal intensity of 8-OHdG. A ROS scavenger (tempol), a SIRT1 activator (SRT1720), a SIRT1 inhibitor (EX527), and a mitochondrial fission inhibitor (Mdivi-1) were used to investigate the specific molecular mechanisms involved. NMDAR2B, CGRP, ERK, and mitochondrial fission-related protein were evaluated by Western blotting, and the CGRP level in frozen sections of the TNC was detected via immunofluorescence staining.

Results

After repeated inflammatory soup infusion and successful establishment of the CM rat model, SIRT1 expression was found to be significantly reduced, accompanied by elevated ROS levels. Treatment with Tempol, SRT1720, or Mdivi-1 alleviated allodynia and reduced the increase in NMDAR2B phosphorylation and CGRP and ERK phosphorylation in the CM rat. In contrast, EX527 had the opposite effect in CM rat. SRT1720 and EX527 decreased and increased ROS levels, respectively, in CM rats, and tempol reversed the aggravating effect of EX527 in CM rats. Furthermore, the regulatory effect of SIRT1 on ROS may include the involvement of the mitochondrial fission protein DRP1.

Conclusion

The results indicate the importance of SIRT1 in CM may be due to its role in regulating the production of ROS, which are involved in modulating central sensitization in CM. These findings could lead to new ideas for CM treatment with the use of SIRT1 agonists and antioxidants.

Transient Receptor Potential Channels: Multiple Modulators of Peripheral Neuropathic Pain in Several Rodent Models

Neuropathic pain, a prevalent chronic condition in clinical settings, has attracted widespread societal attention. This condition is characterized by a persistent pain state accompanied by affective and cognitive disruptions, significantly impacting patients' quality of life. However, current clinical therapies fall short of addressing its complexity. Thus, exploring the underlying molecular mechanism of neuropathic pain and identifying potential targets for intervention is highly warranted. The transient receptor potential (TRP) receptors, a class of widely distributed channel proteins, in the nervous system, play a crucial role in sensory signaling, cellular calcium regulation, and developmental influences. TRP ion channels are also responsible for various sensory responses including heat, cold, pain, and stress. This review highlights recent advances in understanding TRPs in various rodent models of neuropathic pain, aiming to uncover potential therapeutic targets for clinical management.

Higenamine inhibits acute and chronic inflammatory pain through modulation of TRPV4 channels

Pain is the cardinal symptom of many debilitating diseases and results in heavy health and economic burdens worldwide. Asarum (Asarum sieboldii Miq.) is a commonly used analgesic in Chinese medicine. However, the analgesic components and mechanisms of asarum in acute and chronic pain mice model remain unknown. In this study, we first generated asarum water extract and confirmed strong analgesic properties in mice in both the acute thermal and mechanical pain models, as well as in the complete Freund's adjuvant (CFA) induced chronic inflammatory pain model. Second, we identified higenamine as a major component of asarum and found that higenamine significantly inhibited thermal and mechanical induced acute pain and CFA induced chronic inflammatory pain. Then, using Trpv4-/- mice, we found that TRPV4 is necessary for CFA induced thermal and mechanical allodynia, and demonstrated that higenamine analgesia in the CFA model is partly through TRPV4 channel inhibition. Finally, we found that GSK1016790A, a TRPV4 agonist, induced calcium response was significantly inhibited by higenamine in both cultured DRG neurons and TRPV4 transfected HEK293 cells. Consistent with calcium imaging results, higenamine pretreatment also dose-dependently inhibited GSK1016790A induced acute pain. Taken together, our behavior and calcium imaging results demonstrate that the asarum component higenamine inhibits acute and chronic inflammatory pain by modulation of TRPV4 channels.

Tumor necrosis factor-α-induced protein 8-like 2 alleviates morphine antinociceptive tolerance through reduction of ROS-mediated apoptosis and MAPK/NF-κB signaling pathways

Chronic morphine tolerance is a repulsive barrier to the clinical treatment of pain. Whereas the underlying molecular mechanisms of morphine tolerance remain unknown. Here, we proposed that tumor necrosis factor-α-induced protein 8-like 2 (TIPE2) is an essential control point regarding the progression of chronic morphine tolerance. We found that TIPE2 levels in the lumbar spinal cord were significantly downregulated in the morphine tolerance mouse model. Specifically, decreased TIPE2 by morphine tolerance was primarily expressed in spinal neurons, while increased expression of spinal TIPE2 distinctly attenuated the chronic morphine antinociceptive tolerance and tolerance-associated hyperalgesia. We also observed that increased expression of spinal TIPE2 significantly reduced morphine tolerance-induced neuronal ROS production and apoptosis, along with the activation of MAPKs and NF-κB signaling pathways. Moreover, the increased TIPE2 expression inhibited neuronal activation and glial reactivity in the spinal dorsal horn after chronic morphine exposure. Additionally, TIPE2 overexpression in cultured SH-SY5Y cells significantly suppressed ROS production and apoptosis in response to morphine challenge. Therefore, we can conclude that the upregulation of spinal TIPE2 may attenuate the morphine antinociceptive tolerance via TIPE2-dependent downregulation of neuronal ROS, inhibition of neuronal apoptosis, suppression of MAPKs and NF-κB activation. TIPE2 may be a potential strategy for preventing morphine tolerance in the future studies and clinical settings. Schematic diagram for the proposed mechanisms of TIPE2 regulates morphine antinociceptive tolerance. TIPE2 may alleviate morphine antinociceptive tolerance by regulating MAPK/NF-κB signaling pathways and apoptosis, which might be associated with ROS production.

Anemonin reduces hydrogen peroxide-induced oxidative stress, inflammation and extracellular matrix degradation in nucleus pulposus cells by regulating NOX4/NF-κB signaling pathway

BACKGROUND

Excessive oxidative stress plays a critical role in the progression of various diseases, including intervertebral disk degeneration (IVDD). Recent studies have found that anemonin (ANE) possesses antioxidant and anti-inflammatory effects. However, the role of ANE in IVDD is still unclear. Therefore, this study investigated the effect and mechanism of ANE on H₂O₂ induced degeneration of nucleus pulposus cells (NPCs).

METHODS

NPCs were pretreated with ANE, and then treated with H₂O₂. NOX4 was upregulated by transfection of pcDNA-NOX4 into NPCs. Cytotoxicity was detected by MTT, oxidative stress-related indicators and inflammatory factors were measured by ELISA, mRNA expression was assessed by RT-PCR, and protein expression was tested by western blot.

RESULTS

ANE attenuated H₂O₂-induced inhibition of NPCs activity. H₂O₂ enhanced oxidative stress, namely, increased ROS and MDA levels and decreased SOD level. However, these were suppressed and pretreated by ANE. ANE treatment repressed the expression of inflammatory factors (IL-6, IL-1β and TNF-α) in H₂O₂-induced NPCs. ANE treatment also prevented the degradation of extracellular matrix induced by H₂O₂, showing the downregulation of MMP-3, 13 and ADAMTS-4, 5 and the upregulation of collagen II. NOX4 is a key factor regulating oxidative stress. Our study confirmed that ANE could restrain NOX4 and p-NF-κB. In addition, overexpression of NOX4 counteracted the antioxidant and anti-inflammatory activities of ANE in H₂O₂-induced NPCs, and the inhibition of the degradation of extracellular matrix induced by ANE was also reversed by overexpression of NOX4.

CONCLUSION

ANE repressed oxidative stress, inflammation and extracellular matrix degradation in H₂O₂-induced NPCs by inhibiting NOX4/NF-κB pathway. Our study indicated that ANE might be a candidate drug for the treatment of IVDD.

Rac2 enhances activation of microglia and astrocytes, inflammatory response, and apoptosis via activating JNK signaling pathway and suppressing SIRT1 expression in chronic constriction injury-induced neuropathic pain

Neuropathic pain (NP) is pain caused by injury or dysfunction of the somatosensory system. The role of Rac2, a member of the Rac family, which is expressed in neutrophils, macrophages, and adult T cells, in NP remains unclear. Using a chronic constriction injury (CCI)-induced NP model in rats, we found that Rac2 expression was elevated in rats with CCI-induced NP and that overexpression of Rac2 aggravated the NP. Rac2 overexpression also aggravated the inflammatory response, induced activation of microglia and astrocytes, and enhanced apoptosis whereas knockdown of Rac2 had the opposite effects. Rac2 suppressed SIRT1 expression via activating the c-Jun N-terminal kinase (JNK) signaling pathway. In rescue experiments, SRT1720, an activator of SIRT1, reversed the effect of Rac2 on glial activation, inflammatory response, and apoptosis. These findings indicate that Rac2 enhances the activation of microglia and astrocytes, inflammatory response, and apoptosis via activating the JNK signaling pathway and suppressing SIRT1 expression in CCI-induced NP.

Structure, Activation, and Regulation of NOX2: At the Crossroad between the Innate Immunity and Oxidative Stress-Mediated Pathologies

Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX) is a multisubunit enzyme complex that participates in the generation of superoxide or hydrogen peroxide (H₂O₂) and plays a key role in several biological functions. Among seven known NOX isoforms, NOX2 was the first identified in phagocytes but is also expressed in several other cell types including endothelial cells, platelets, microglia, neurons, and muscle cells. NOX2 has been assigned multiple roles in regulating many aspects of innate and adaptive immunity, and human and mouse models of NOX2 genetic deletion highlighted this key role. On the other side, NOX2 hyperactivation is involved in the pathogenesis of several diseases with different etiologies but all are characterized by an increase in oxidative stress and inflammatory process. From this point of view, the modulation of NOX2 represents an important therapeutic strategy aimed at reducing the damage associated with its hyperactivation. Although pharmacological strategies to selectively modulate NOX2 are implemented thanks to new biotechnologies, this field of research remains to be explored. Therefore, in this review, we analyzed the role of NOX2 at the crossroads between immunity and pathologies mediated by its hyperactivation. We described (1) the mechanisms of activation and regulation, (2) human, mouse, and cellular models studied to understand the role of NOX2 as an enzyme of innate immunity, (3) some of the pathologies associated with its hyperactivation, and (4) the inhibitory strategies, with reference to the most recent discoveries.

α-Asarone attenuates chronic sciatica by inhibiting peripheral sensitization and promoting neural repair

This study explored the therapeutic effect of α-asarone on chronic sciatica. Thirty-two Sprague-Dawley (SD) rats were divided into four groups: the sham group, chronic constriction injury (CCI) group, pregabalin group, and α-asarone group. Hot hyperalgesia was induced after the CCI operation, and α-asarone was found to relieve chronic neuralgia. Furthermore, α-asarone reduced IL1β, IL6, TNF-α, CRP, and LPS levels and increased IL10 levels in serum. α-Asarone decreased the protein levels of TRPA1, TRPM8, and TRPV1-4 and the mRNA levels of TRPA1, TRPM8, TRPV1-4, IL1β, and TNF-α in dorsal root ganglion neurons. In the sciatic nerve, α-asarone treatment reduced the number of inflammatory cells and promoted the proliferation of Schwann cells, favouring recovery of the nerve structure. In cellular experiments, LPS induced Schwann cell apoptosis via TLR4/p38MAPK signalling; α-asarone attenuated LPS-induced Schwann cell apoptosis by decreasing TLR4, p-p38MAPK, cleaved-caspase3, and cleaved-caspase7 levels and increasing Bcl-2 and Bcl-xl expression. Overall, these findings suggest that α-asarone relieves chronic sciatica by decreasing the levels of inflammatory factors, inhibiting peripheral sensitization, and favouring the repair of damaged nerves.

Research progress on the mechanism of chronic neuropathic pain

Chronic neuropathic pain (CNP) refers to pain that lasts for more than three months due to a disease or an injury to the somatosensory nervous system. The incidence of CNP has been increasing in the world, causing it to become a global concern and patients often experience spontaneous pain, hyperalgesia, abnormal pain or even abnormal sensation as some of its main symptoms. In addition to serious pain and poor physical health, CNP also negatively affects patients' mental health, thus impacting the overall quality of their lives. The pathogenesis of CNP is not clear, but some studies have proved that central sensitization, peripheral sensitization, neuroinflammation, dysfunction in descending nociceptive modulatory systems, oxidative stress reaction, activation of glial cells and psychological factors play an important role in the occurrence and development of CNP. In this context, this article summarizes the current research progress on the mechanism of CNP to provide a basis for further research in preventing and treating the disease.

Ferulic acid alleviates sciatica by inhibiting peripheral sensitization through the RhoA/p38MAPK signalling pathway

BACKGROUND

Nonsteroidal anti-inflammatory drugs are used to relieve sciatica, but their effects are not satisfactory.

PURPOSE

This study aimed to explore the therapeutic effects of ferulic acid on sciatica.

METHODS

Thirty-two SD rats were randomly divided into 4 groups, i.e., sham operation group, chronic constriction injury (CCI) group, mecobalamin group, and ferulic acid group. We conducted behavioural tests, ELISA, PCR, Western blots, and immunofluorescence analysis. Specific inhibitors were used in cell experiments to explore the related mechanisms.

RESULTS

Thermal hyperalgesia was induced after CCI operation, and ferulic acid relieved thermal hyperalgesia. In addition, ferulic acid decreased the IL1β, IL6, TNF-α, and CRP mRNA levels; the IBA-1, iNOS, IL1β, RhoA, RhoA-GTP, COX2, Rock1, TRPV1, TRPA1, and p-p38MAPK levels in dorsal root ganglion (DRG) neurons; and the LPS, CRP, substance P (SP), and prostaglandin E2 (PGE2) levels in serum, and these levels were higher in the CCI group. In the cell experiments, LPS induced M1 polarization of GMI-R1 cells via the RhoA/Rock pathway. Ferulic acid attenuated LPS-induced M1 polarization by decreasing the levels of M1 polarization markers, including IL1β, IL6, TNF-α, iNOS, and CD32, and increased M2 polarization by increasing the levels of M2 polarization markers, including CD206 and Arg-1. LPS treatment clearly increased the iNOS, IL1β, RhoA, Rock1, Rock2 and p-p38 MAPK levels and reduced Arg-1 expression, and ferulic acid reversed these changes.

CONCLUSION

Ferulic acid can inhibit peripheral sensitization by reducing the levels of inflammatory factors, TRPA1 and TRPV1 through the RhoA/p38 MAPK pathway to alleviate sciatica.

Upregulation of TLR4/MyD88 pathway in alcohol-induced Wernicke’s encephalopathy: Findings in preclinical models and in a postmortem human case

Wernicke’s encephalopathy (WE) is a neurologic disease caused by vitamin B1 or thiamine deficiency (TD), being the alcohol use disorder its main risk factor. WE patients present limiting motor, cognitive, and emotional alterations related to a selective cerebral vulnerability. Neuroinflammation has been proposed to be one of the phenomena that contribute to brain damage. Our previous studies provide evidence for the involvement of the innate immune receptor Toll-like (TLR)4 in the inflammatory response induced in the frontal cortex and cerebellum in TD animal models (animals fed with TD diet [TDD] and receiving pyrithiamine). Nevertheless, the effects of the combination of chronic alcohol consumption and TD on TLR4 and their specific contribution to the pathogenesis of WE are currently unknown. In addition, no studies on TLR4 have been conducted on WE patients since brains from these patients are difficult to achieve. Here, we used rat models of chronic alcohol (CA; 9 months of forced consumption of 20% (w/v) alcohol), TD hit (TDD + daily 0.25 mg/kg i.p. pyrithiamine during 12 days), or combined treatment (CA + TDD) to check the activation of the proinflammatory TLR4/MyD88 pathway and related markers in the frontal cortex and the cerebellum. In addition, we characterized for the first time the TLR4 and its coreceptor MyD88 signature, along with other markers of this proinflammatory signaling such as phospo-NFκB p65 and IκBα, in the postmortem human frontal cortex and cerebellum (gray and white matter) of an alcohol-induced WE patient, comparing it with negative (no disease) and positive (aged brain with Alzheimer’s disease) control subjects for neuroinflammation. We found an increase in the cortical TLR4 and its adaptor molecule MyD88, together with an upregulation of the proinflammatory signaling molecules p-NF-ĸB and IĸBα in the CA + TDD animal model. In the patient diagnosed with alcohol-induced WE, we observed cortical and cerebellar upregulation of the TLR4/MyD88 pathway. Hence, our findings provide evidence, both in the animal model and the human postmortem brain, of the upregulation of the TLR4/MyD88 proinflammatory pathway in alcohol consumption–related WE.

Pharmacological effects of higenamine based on signalling pathways and mechanism of action

Higenamine (HG) is a chemical compound found in various plants, such as aconite. Recent pharmacological studies have demonstrated its effectiveness in the management of many diseases. Several mechanisms of action of HG have been proposed; however, they have not yet been classified. This review summarises the signalling pathways and pharmacological targets of HG, focusing on its potential as a naturally extracted drug. Articles related to the pharmacological effects, signalling pathways and pharmacological targets of HG were selected by searching the keyword “Higenamine” in the PubMed, Web of Science and Google Scholar databases without limiting the search by publication years. HG possesses anti-oxidant, anti-apoptotic, anti-inflammatory, electrophysiology regulatory, anti-fibrotic and lipid-lowering activities. It is a structural analogue of catecholamines and possesses characteristics similar to those of adrenergic receptor ligands. It can modulate multiple targets, including anti-inflammation- and anti-apoptosis-related targets and some transcription factors, which directly or indirectly influence the disease course. Other naturally occurring compounds, such as cucurbitacin B (Cu B) and 6-gingerol (6-GR), can be combined with HG to enhance its anti-apoptotic activity. Although significant research progress has been made, follow-up pharmacological studies are required to determine the exact mechanism of action, new signalling pathways and targets of HG and the effects of using it in combination with other drugs.

Lysophosphatidylcholine: Potential Target for the Treatment of Chronic Pain

The bioactive lipid lysophosphatidylcholine (LPC), a major phospholipid component of oxidized low-density lipoprotein (Ox-LDL), originates from the cleavage of phosphatidylcholine by phospholipase A2 (PLA2) and is catabolized to other substances by different enzymatic pathways. LPC exerts pleiotropic effects mediated by its receptors, G protein-coupled signaling receptors, Toll-like receptors, and ion channels to activate several second messengers. Lysophosphatidylcholine (LPC) is increasingly considered a key marker/factor positively in pathological states, especially inflammation and atherosclerosis development. Current studies have indicated that the injury of nervous tissues promotes oxidative stress and lipid peroxidation, as well as excessive accumulation of LPC, enhancing the membrane hyperexcitability to induce chronic pain, which may be recognized as one of the hallmarks of chronic pain. However, findings from lipidomic studies of LPC have been lacking in the context of chronic pain. In this review, we focus in some detail on LPC sources, biochemical pathways, and the signal-transduction system. Moreover, we outline the detection methods of LPC for accurate analysis of each individual LPC species and reveal the pathophysiological implication of LPC in chronic pain, which makes it an interesting target for biomarkers and the development of medicine regarding chronic pain.

Targeting Oxidative Stress and Inflammation in Intervertebral Disc Degeneration: Therapeutic Perspectives of Phytochemicals

Low back pain is a major cause of disability worldwide that declines the quality of life; it poses a substantial economic burden for the patient and society. Intervertebral disc (IVD) degeneration (IDD) is the main cause of low back pain, and it is also the pathological basis of several spinal degenerative diseases, such as intervertebral disc herniation and spinal stenosis. The current clinical drug treatment of IDD focuses on the symptoms and not their pathogenesis, which results in frequent recurrence and gradual aggravation. Moreover, the side effects associated with the long-term use of these drugs further limit their use. The pathological mechanism of IDD is complex, and oxidative stress and inflammation play an important role in promoting IDD. They induce the destruction of the extracellular matrix in IVD and reduce the number of living cells and functional cells, thereby destroying the function of IVD and promoting the occurrence and development of IDD. Phytochemicals from fruits, vegetables, grains, and other herbs play a protective role in the treatment of IDD as they have anti-inflammatory and antioxidant properties. This article reviews the protective effects of phytochemicals on IDD and their regulatory effects on different molecular pathways related to the pathogenesis of IDD. Moreover, the therapeutic limitations and future prospects of IDD treatment have also been reviewed. Phytochemicals are promising candidates for further development and research on IDD treatment.

Therapeutic effect of paeoniflorin on chronic constriction injury of the sciatic nerve via the inhibition of Schwann cell apoptosis

Therapeutic drugs of chronic neuralgia have a high risk of addiction, making it crucial to identify novel drugs for chronic neuralgia. This study aimed to explore the therapeutic effect of paeoniflorin on chronic sciatica via inhibiting Schwann cell apoptosis. 28 SD rats were randomly divided into four groups, including the sham operation group, chronic constriction injury (CCI) group, mecobalamin group, and paeoniflorin group. The therapeutic effect and mechanism of paeoniflorin were evaluated via rat and cell experiments. Mechanical, hot, or cold hyperalgesia was induced in the rats after CCI operation, while paeoniflorin relieved chronic neuralgia. Besides, paeoniflorin decreased the levels of IL1, IL6, TNF‐α, CRP, and LPS and increased the level of IL10 in serum. As for the sciatic nerve, the number of inflammatory cells was decreased, and Schwann cells were present after paeoniflorin treatment, and paeoniflorin promoted the recovery of nerve structure. In cell experiments, LPS induced Schwann cell apoptosis via the TLR4/NF‐kB pathway. And paeoniflorin attenuated LPS‐induced Schwann cell apoptosis by decreasing the levels of TLR4, p‐NF‐kB, caspase3, cleaved‐caspase3, and cleaved‐caspase7. Overall, these results suggest that paeoniflorin alleviates chronic sciatica by decreasing inflammatory factor levels and promotes the repair of damaged nerves by reducing Schwann cell apoptosis.