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Li S, Yi H, Yuan F, Zhang X, Zhong Y, Huang Y. Oral application of magnesium-L-threonate alleviates radicular pain by inhibiting neuro-inflammation dependent central sensitization of rats. Brain Res 2024; 1839:148910. [PMID: 38604557 DOI: 10.1016/j.brainres.2024.148910] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2023] [Revised: 03/13/2024] [Accepted: 04/01/2024] [Indexed: 04/13/2024]
Abstract
BACKGROUND We have reported neuro-inflammation is involved in radicular pain by enhancing the efficiency of pain synaptic transmission in spinal level. Recently, peers' studies have confirmed that magnesium deficiency leads to neuro-inflammation, thus contributes to memory and emotional deficits and pain hypersensitivity in antineoplastic agents treated rats. In this study, we explore the effect of oral application of magnesium-L-threonate (L-TAMS) in radicular pain induced by lumbar disc herniation (LDH) of rats and the possible mechanisms. METHODS Rat model of LDH was induced by autologous nucleus pulposus (NP) implantation. Mechanical and thermal pain thresholds were assessed by von Frey filaments and hotplate test respectively. L-TAMS was applied from drinking water at dosage of 604 mg/kg/day from 2 day before NP implantation and until the end of the experiment. Free Mg2+ content in serum and cerebrospinal fluid (CSF) was measured by calmagite chromometry. Synaptic transmission efficiency was determined by C-fiber evoked field potentials recorded by electrophysiologic recording in vivo. The activation of microglia in spinal dorsal horn was displayed by immunofluorescence staining and western blotting. The expressions of pro-inflammatory cytokines and glutamic N-methyl-D-aspartate receptor (NMDAR) subunits (NR2A, NR2B) were assessed by western blotting and enzyme-linked immunosorbent assay (ELISA) respectively. RESULTS NP implantation induced mechanical allodynia and thermal hyperalgesia, accompanied by decreased Mg2+ concentration in serum and CSF which were both obscured by oral application of L-TAMS. L-TAMS inhibited spinal microglia activation and pro-inflammatory cytokines (TNF-α, IL-6, IL-1β) expression of rats with NP. L-TAMS decreased C-fiber evoked potentials and NR2B protein level in rats with NP, which were rescued by extra intrathecal delivery of TNF-α or IL-6 or IL-1β. CONCLUSIONS Oral application of L-TAMS alleviates radicular pain by inhibiting neuro-inflammation dependent central sensitization of rats.
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Affiliation(s)
- Siyuan Li
- Department of Spine Surgery, First Affiliated Hospital of Sun Yat-sen University, Guangzhou, 510080, China
| | - Hongjian Yi
- Department of Spine Surgery, First Affiliated Hospital of Sun Yat-sen University, Guangzhou, 510080, China
| | - Fuli Yuan
- Department of Anesthesiology, First Affiliated Hospital of Sun Yat-sen University, Guangzhou, 510080, China
| | - Xuejuan Zhang
- Department of Radiology, First Affiliated Hospital of Sun Yat-sen University, Guangzhou, 510080, China
| | - Yi Zhong
- Key Laboratory of Neuroscience, School of Basic Medical Science, Guangzhou Medical University, Guangzhou, 511436, China.
| | - Yangliang Huang
- Department of Spine Surgery, First Affiliated Hospital of Sun Yat-sen University, Guangzhou, 510080, China.
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Abolarin PO, Owoyele BV. Tannic acid inhibits pain mediators, inflammation and oxidative stress in mice exposed to glyphosate-based herbicide. Environ Anal Health Toxicol 2024; 39:e2024019-0. [PMID: 39054833 PMCID: PMC11294660 DOI: 10.5620/eaht.2024019] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2024] [Accepted: 05/17/2024] [Indexed: 07/27/2024] Open
Abstract
Chronic exposure to glyphosate-based herbicide (Gly) has been associated with neurological disorders. Tannic acid (TA) is an antioxidant with attenuating action against neuroinflammation-associated conditions. This study evaluated the effect of Gly on pain perception alongside antinociceptive and anti-inflammatory actions of TA in Gly-exposed mice. Male Swiss mice were randomly divided into six groups (n=8): control (distilled water 0.2 ml/kg), Gly (Gly 500 mg/kg), Pre-TA + Gly (TA 50 mg/kg pre-treatment, afterwards Gly-administered), TA + Gly (TA 50 mg/kg and Gly co-administered), Pre-AA + Gly (ascorbic acid (AA) 10 mg/kg pre-treatment, afterwards Gly-administered), and AA + Gly (AA 10 mg/kg and Gly co-administered). Mechanical, thermal, and chemical pain were evaluated six weeks post vehicle/drugs administrations orally, followed by brain biochemical measurements. TA treatment alleviated Gly-induced hyperalgesia in similar version to the values of control and AA groups by increasing significantly (p < 0.05) nociceptive thresholds. Moreover, TA-treatment significantly decreased malondialdehyde (MDA) and pro-inflammatory cytokines (TNF-α, IL-1β, and IL-6) levels, significantly increased anti-inflammatory cytokines (IL-10, IL-4, and TGF-1β) levels, and antioxidant enzymes, catalase (CAT), glutathione peroxidase (GPx), and superoxide dismutase (SOD) activities compared to Gly-treated mice (p < 0.05). Conclusively, TA treatment exerted antinociceptive and anti-inflammatory actions, possibly through its antioxidant and anti-inflammatory actions in Gly-exposed mice. Notably, TA pre-treatment showed a better response than TA and Gly co-administration. We propose the potential neuroprotective and ameliorative functions of TA in Gly-induced hyperalgesia. This merits further clinical research into protective roles of TA against pesticide-related conditions.
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Affiliation(s)
- Patrick Oluwole Abolarin
- Department of Physiology/Pharmacology, Chrisland University, College of Basic Medical Sciences, Abeokuta, Ogun state, Nigeria
- Department of Physiology, Neuroscience and Pain Laboratory, College of Health Sciences, University of Ilorin, Ilorin, Kwara state, Nigeria
| | - Bamidele Victor Owoyele
- Department of Physiology/Pharmacology, Chrisland University, College of Basic Medical Sciences, Abeokuta, Ogun state, Nigeria
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Ye Y, Cheng H, Wang Y, Sun Y, Zhang LD, Tang J. Macrophage: A key player in neuropathic pain. Int Rev Immunol 2024:1-14. [PMID: 38661566 DOI: 10.1080/08830185.2024.2344170] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2023] [Accepted: 04/13/2024] [Indexed: 04/26/2024]
Abstract
Research on the relationship between macrophages and neuropathic pain has flourished in the past two decades. It has long been believed that macrophages are strong immune effector cells that play well-established roles in tissue homeostasis and lesions, such as promoting the initiation and progression of tissue injury and improving wound healing and tissue remodeling in a variety of pathogenesis-related diseases. They are also heterogeneous and versatile cells that can switch phenotypically/functionally in response to the micro-environment signals. Apart from microglia (resident macrophages of both the spinal cord and brain), which are required for the neuropathic pain processing of the CNS, neuropathic pain signals in PNS are influenced by the interaction of tissue-resident macrophages and BM infiltrating macrophages with primary afferent neurons. And the current review looks at new evidence that suggests sexual dimorphism in neuropathic pain are caused by variations in the immune system, notably macrophages, rather than the neurological system.
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Affiliation(s)
- Ying Ye
- Department of Anesthesiology, Jinling Hospital, Affiliated Hospital of Nanjing Medical University, Nanjing, PR China
| | - Hao Cheng
- Department of Anesthesiology, Jinling Hospital, Affiliated Hospital of Medical School, Nanjing University, Nanjing, PR China
| | - Yan Wang
- Department of Anesthesiology, Jinling Hospital, Affiliated Hospital of Nanjing Medical University, Nanjing, PR China
| | - Yan Sun
- Department of Anesthesiology, Jinling Hospital, Affiliated Hospital of Nanjing Medical University, Nanjing, PR China
| | - Li-Dong Zhang
- Department of Anesthesiology, Jinling Hospital, Affiliated Hospital of Nanjing Medical University, Nanjing, PR China
| | - Jun Tang
- Department of Anesthesiology, Jinling Hospital, Affiliated Hospital of Nanjing Medical University, Nanjing, PR China
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4
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Pak R, Cho M, Pride K, Abd-Elsayed A. The Gut Microbiota and Chronic Pain. Curr Pain Headache Rep 2024; 28:259-269. [PMID: 38345694 DOI: 10.1007/s11916-024-01221-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/30/2024] [Indexed: 03/16/2024]
Abstract
PURPOSE OF REVIEW To examine the effects and interactions between gut microbia and chronic pain. RECENT FINDINGS The gut microbiome has been an area of interest in both the scientific and general audience due to a growing body of evidence suggesting its influence in a variety of health and disease states. Communication between the central nervous system (CNS) and gut microbiome is said to be bidirectional, in what is referred to as the gut-brain axis. Chronic pain is a prevalent costly personal and public health burden and so, there is a vested interest in devising safe and efficacious treatments. Numerous studies, many of which are animal studies, have been conducted to examine the gut microbiome's role in the pathophysiology of chronic pain states, such as neuropathy, inflammation, visceral pain, etc. As the understanding of this relationship grows, so does the potential for therapeutic targeting of the gut microbiome in chronic pain.
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Affiliation(s)
- Ray Pak
- Department of Physical Medicine and Rehabilitation, New York Medical College/Metropolitan, New York, NY, USA
| | - Michelle Cho
- Department of Physical Medicine and Rehabilitation, New York Medical College/Metropolitan, New York, NY, USA
| | - Keth Pride
- Department of Anesthesiology, University of Wisconsin School of Medicine and Public Health, 600 Highland Avenue, B6/319 CSC, Madison, WI, 53792-3272, USA
| | - Alaa Abd-Elsayed
- Department of Anesthesiology, University of Wisconsin School of Medicine and Public Health, 600 Highland Avenue, B6/319 CSC, Madison, WI, 53792-3272, USA.
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Sim J, O'Guin E, Monahan K, Sugimoto C, McLean SA, Albertorio-Sáez L, Zhao Y, Laumet S, Dagenais A, Bernard MP, Folger JK, Robison AJ, Linnstaedt SD, Laumet G. Interleukin-10-producing monocytes contribute to sex differences in pain resolution in mice and humans. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.11.03.565129. [PMID: 37961295 PMCID: PMC10635095 DOI: 10.1101/2023.11.03.565129] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2023]
Abstract
Pain is closely associated with the immune system, which exhibits sexual dimorphism. For these reasons, neuro-immune interactions are suggested to drive sex differences in pain pathophysiology. However, our understanding of peripheral neuro-immune interactions on sex differences in pain resolution remains limited. Here, we have shown, in both a mouse model of inflammatory pain and in humans following traumatic pain, that males had higher levels of interleukin (IL)-10 than females, which were correlated with faster pain resolution. Following injury, we identified monocytes (CD11b+ Ly6C+ Ly6G-F4/80 mid ) as the primary source of IL-10, with IL-10-producing monocytes being more abundant in males than females. In a mouse model, neutralizing IL-10 signaling through antibodies, genetically ablating IL-10R1 in sensory neurons, or depleting monocytes with clodronate all impaired the resolution of pain hypersensitivity in both sexes. Furthermore, manipulating androgen levels in mice reversed the sexual dimorphism of pain resolution and the levels of IL-10-producing monocytes. These results highlight a novel role for androgen-driven peripheral IL-10-producing monocytes in the sexual dimorphism of pain resolution. These findings add to the growing concept that immune cells play a critical role in resolving pain and preventing the transition into chronic pain. Graphical abstract
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Jing F, Zou Q, Pu Y. GLP-1R agonist liraglutide attenuates pain hypersensitivity by stimulating IL-10 release in a nitroglycerin-induced chronic migraine mouse model. Neurosci Lett 2023; 812:137397. [PMID: 37442520 DOI: 10.1016/j.neulet.2023.137397] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2023] [Revised: 06/27/2023] [Accepted: 07/10/2023] [Indexed: 07/15/2023]
Abstract
Glucagon-like peptide-1 receptor (GLP-1R) has been indicated to involve in chronic pain, however, the mechanism by which GLP-1R alleviates the central sensitization of chronic migraine (CM) remains unclear. Treatment with GLP-1R agonist liraglutide attenuated trigeminal allodynia and suppressed the protein levels of CM-associated molecules in the trigeminal nucleus caudalis (TNC). Further analysis showed that injection of liraglutide stimulated the release of IL-10 in the TNC. Treatment with IL-10 also alleviated pain hyperalgesia. Our findings illustrated that liraglutide might alleviate the central sensitization of CM by stimulating the release of IL-10, which reveals a novel mechanism of CM.
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Affiliation(s)
- Feng Jing
- Department of Pathology, Chongqing General Hospital, No. 118 Xingguang Avenue, Liangjiang New Area, Chongqing 400014, China.
| | - Qian Zou
- Chongqing Key Laboratory of Neurodegenerative Diseases, No. 312 Zhongshan First Road, Yuzhong District, Chongqing 400013, China
| | - Yinshuang Pu
- Chongqing Key Laboratory of Neurodegenerative Diseases, No. 312 Zhongshan First Road, Yuzhong District, Chongqing 400013, China
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7
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Wang X, Li X. Regulation of pain neurotransmitters and chondrocytes metabolism mediated by voltage-gated ion channels: A narrative review. Heliyon 2023; 9:e17989. [PMID: 37501995 PMCID: PMC10368852 DOI: 10.1016/j.heliyon.2023.e17989] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2023] [Revised: 05/15/2023] [Accepted: 07/04/2023] [Indexed: 07/29/2023] Open
Abstract
Osteoarthritis (OA) is one of the leading causes of chronic pain and dysfunction. It is essential to comprehend the nature of pain and cartilage degeneration and its influencing factors on OA treatment. Voltage-gated ion channels (VGICs) are essential in chondrocytes and extracellular matrix (ECM) metabolism and regulate the pain neurotransmitters between the cartilage and the central nervous system. This narrative review focused primarily on the effects of VGICs regulating pain neurotransmitters and chondrocytes metabolism, and most studies have focused on voltage-sensitive calcium channels (VSCCs), voltage-gated sodium channels (VGSCs), acid-sensing ion channels (ASICs), voltage-gated potassium channels (VGKCs), voltage-gated chloride channels (VGCCs). Various ion channels coordinate to maintain the intracellular environment's homeostasis and jointly regulate metabolic and pain under normal circumstances. In the OA model, the ion channel transport of chondrocytes is abnormal, and calcium influx is increased, which leads to increased neuronal excitability. The changes in ion channels are strongly associated with the OA disease process and individual OA risk factors. Future studies should explore how VGICs affect the metabolism of chondrocytes and their surrounding tissues, which will help clinicians and pharmacists to develop more effective targeted drugs to alleviate the progression of OA disease.
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Mahmoud M, Kokozidou M, Gögele C, Werner C, Auffarth A, Kohl B, Mrosewski I, Schulze-Tanzil GG. Does Vitamin K2 Influence the Interplay between Diabetes Mellitus and Intervertebral Disc Degeneration in a Rat Model? Nutrients 2023; 15:2872. [PMID: 37447201 DOI: 10.3390/nu15132872] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2023] [Revised: 06/14/2023] [Accepted: 06/20/2023] [Indexed: 07/15/2023] Open
Abstract
Intervertebral disc (IVD) degeneration is a common cause of low back pain in diabetes mellitus type 2 (T2DM) patients. Its pathogenesis and the vitamin (vit.) K2 influence on this disease remain unclear. Lumbar motion segments of male Zucker Diabetes Fatty (ZDF) rats (non-diabetic [control] and diabetic; fed without or with vit. K2) were used. Femur lengths and vertebral epiphyseal cross-section areas were measured. IVDs were histopathologically examined. Protein synthesis and gene expression of isolated IVD fibrochondrocytes were analyzed. T2DM rats showed histopathological IVD degeneration. Femur lengths and epiphyseal areas were smaller in T2DM rats regardless of vit. K2 feeding. Fibrochondrocytes synthesized interleukin (IL)-24 and IL-10 with no major differences between groups. Alpha smooth muscle actin (αSMA) was strongly expressed, especially in cells of vit. K2-treated animals. Gene expression of aggrecan was low, and that of collagen type 2 was high in IVD cells of diabetic animals, whether treated with vit. K2 or not. Suppressor of cytokine signaling (Socs)3 and heme oxygenase (Hmox)1 gene expression was highest in the cells of diabetic animals treated with vit. K2. Vit. K2 influenced the expression of some stress-associated markers in IVD cells of diabetic rats, but not that of IL-10 and IL-24.
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Affiliation(s)
- Mohamed Mahmoud
- Institute of Anatomy and Cell Biology, Paracelsus Medical University, Nuremberg and Salzburg, Prof. Ernst Nathan Str. 1, 90419 Nuremberg, Germany
| | - Maria Kokozidou
- Institute of Anatomy and Cell Biology, Paracelsus Medical University, Nuremberg and Salzburg, Prof. Ernst Nathan Str. 1, 90419 Nuremberg, Germany
| | - Clemens Gögele
- Institute of Anatomy and Cell Biology, Paracelsus Medical University, Nuremberg and Salzburg, Prof. Ernst Nathan Str. 1, 90419 Nuremberg, Germany
| | - Christian Werner
- Institute of Anatomy and Cell Biology, Paracelsus Medical University, Nuremberg and Salzburg, Prof. Ernst Nathan Str. 1, 90419 Nuremberg, Germany
| | - Alexander Auffarth
- Department of Orthopedics and Traumatology, Paracelsus Medical University, Müllner-Hauptstraße 48, 5020 Salzburg, Austria
| | - Benjamin Kohl
- Department of Traumatology and Reconstructive Surgery, Charité-Universitätsmedizin Berlin, Corporate Member of Freie Universität Berlin, Humboldt-Universität zu Berlin, Campus Benjamin Franklin, Hindenburgdamm 30, 12203 Berlin, Germany
| | - Ingo Mrosewski
- MVZ MDI Limbach Berlin, Aroser Alle 84, 13407 Berlin, Germany
| | - Gundula Gesine Schulze-Tanzil
- Institute of Anatomy and Cell Biology, Paracelsus Medical University, Nuremberg and Salzburg, Prof. Ernst Nathan Str. 1, 90419 Nuremberg, Germany
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Yang H, Shan Z, Guo W, Wang Y, Cai S, Li F, Huang Q, Liu JA, Cheung CW, Cai S. Reversal of Peripheral Neuropathic Pain by the Small-Molecule Natural Product Narirutin via Block of Na v1.7 Voltage-Gated Sodium Channel. Int J Mol Sci 2022; 23:ijms232314842. [PMID: 36499167 PMCID: PMC9738487 DOI: 10.3390/ijms232314842] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2022] [Revised: 11/12/2022] [Accepted: 11/24/2022] [Indexed: 12/05/2022] Open
Abstract
Neuropathic pain is a refractory chronic disease affecting millions of people worldwide. Given that present painkillers have poor efficacy or severe side effects, developing novel analgesics is badly needed. The multiplex structure of active ingredients isolated from natural products provides a new source for phytochemical compound synthesis. Here, we identified a natural product, Narirutin, a flavonoid compound isolated from the Citrus unshiu, showing antinociceptive effects in rodent models of neuropathic pain. Using calcium imaging, whole-cell electrophysiology, western blotting, and immunofluorescence, we uncovered a molecular target for Narirutin's antinociceptive actions. We found that Narirutin (i) inhibits Veratridine-triggered nociceptor activities in L4-L6 rat dorsal root ganglion (DRG) neurons, (ii) blocks voltage-gated sodium (NaV) channels subtype 1.7 in both small-diameter DRG nociceptive neurons and human embryonic kidney (HEK) 293 cell line, (iii) does not affect tetrodotoxin-resistant (TTX-R) NaV channels, and (iv) blunts the upregulation of Nav1.7 in calcitonin gene-related peptide (CGRP)-labeled DRG sensory neurons after spared nerve injury (SNI) surgery. Identifying Nav1.7 as a molecular target of Narirutin may further clarify the analgesic mechanism of natural flavonoid compounds and provide an optimal idea to produce novel selective and efficient analgesic drugs.
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Affiliation(s)
- Haoyi Yang
- Department of Anatomy and Histology, Shenzhen University Health Science Center, Shenzhen 518060, China
| | - Zhiming Shan
- Laboratory and Clinical Research Institute for Pain, Department of Anaesthesiology, School of Clinical Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong 999077, China
- Department of Anesthesiology, Shenzhen People’s Hospital (The First Affiliated Hospital, Southern University of Science and Technology; The Second Clinical Medical College, Jinan University), Shenzhen 518020, China
- Shenzhen Engineering Research Center of Anesthesiology, Shenzhen 518020, China
| | - Weijie Guo
- Department of Anatomy and Histology, Shenzhen University Health Science Center, Shenzhen 518060, China
| | - Yuwei Wang
- Department of Anatomy and Histology, Shenzhen University Health Science Center, Shenzhen 518060, China
| | - Shuxian Cai
- Department of Anatomy and Histology, Shenzhen University Health Science Center, Shenzhen 518060, China
| | - Fuyi Li
- Department of Anatomy and Histology, Shenzhen University Health Science Center, Shenzhen 518060, China
| | - Qiaojie Huang
- Department of Anatomy and Histology, Shenzhen University Health Science Center, Shenzhen 518060, China
| | - Jessica Aijia Liu
- Department of Neuroscience, City University of Hong Kong, Hong Kong 999077, China
| | - Chi Wai Cheung
- Laboratory and Clinical Research Institute for Pain, Department of Anaesthesiology, School of Clinical Medicine, Li Ka Shing Faculty of Medicine, The University of Hong Kong, Hong Kong 999077, China
- Correspondence: (C.W.C.); (S.C.)
| | - Song Cai
- Department of Anatomy and Histology, Shenzhen University Health Science Center, Shenzhen 518060, China
- Correspondence: (C.W.C.); (S.C.)
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Liu XG. Normalization of Neuroinflammation: A New Strategy for Treatment of Persistent Pain and Memory/Emotional Deficits in Chronic Pain. J Inflamm Res 2022; 15:5201-5233. [PMID: 36110505 PMCID: PMC9469940 DOI: 10.2147/jir.s379093] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2022] [Accepted: 08/18/2022] [Indexed: 12/12/2022] Open
Abstract
Chronic pain, which affects around 1/3 of the world population and is often comorbid with memory deficit and mood depression, is a leading source of suffering and disability. Studies in past decades have shown that hyperexcitability of primary sensory neurons resulting from abnormal expression of ion channels and central sensitization mediated pathological synaptic plasticity, such as long-term potentiation in spinal dorsal horn, underlie the persistent pain. The memory/emotional deficits are associated with impaired synaptic connectivity in hippocampus. Dysregulation of numerous endogenous proteins including receptors and intracellular signaling molecules is involved in the pathological processes. However, increasing knowledge contributes little to clinical treatment. Emerging evidence has demonstrated that the neuroinflammation, characterized by overproduction of pro-inflammatory cytokines and glial activation, is reliably detected in humans and animals with chronic pain, and is sufficient to induce persistent pain and memory/emotional deficits. The abnormal expression of ion channels and pathological synaptic plasticity in spinal dorsal horn and in hippocampus are resulting from neuroinflammation. The neuroinflammation is initiated and maintained by the interactions of circulating monocytes, glial cells and neurons. Obviously, unlike infectious diseases and cancer, which are caused by pathogens or malignant cells, chronic pain is resulting from alterations of cells and molecules which have numerous physiological functions. Therefore, normalization (counterbalance) but not simple inhibition of the neuroinflammation is the right strategy for treating neuronal disorders. Currently, no such agent is available in clinic. While experimental studies have demonstrated that intracellular Mg2+ deficiency is a common feature of chronic pain in animal models and supplement Mg2+ are capable of normalizing the neuroinflammation, activation of upregulated proteins that promote recovery, such as translocator protein (18k Da) or liver X receptors, has a similar effect. In this article, relevant experimental and clinical evidence is reviewed and discussed.
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Affiliation(s)
- Xian-Guo Liu
- Pain Research Center and Department of Physiology, Zhongshan School of Medicine of Sun Yat-sen University, Guangzhou, People's Republic of China
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