Spinal 5-HT2A Receptor is Involved in Electroacupuncture Inhibition of Chronic Pain

IUPHAR Article: Psilocybin induces long-lasting effects via 5-HT2A receptors in mouse models of chronic pain

Chronic pain is a debilitating disease with current treatments lacking efficacy and safety, therefore discovery of new treatments is crucial. Initial studies suggest that psychedelics may be feasible for targeting pain, however clinical and preclinical controlled studies are necessary to further investigate that possibility. In this study we assessed the effects of two classical psychedelics psilocybin and 2,5-Dimethoxy-4-iodoamphetamine (DOI) in two models of chronic pain after systemic administration in male and female mice. Psilocybin and DOI dose-dependently reversed mechanical and cold hypersensitivity in the chemotherapy-induced peripheral neuropathy (CIPN) mouse model with different time-course of action. Similarly, psilocybin and DOI dose-dependently reversed thermal hypersensitivity in the chronic inflammatory mouse model of Complete Freud's Adjuvant (CFA). The effects of Psilocybin and DOI in both models were mediated by activation of 5-HT2A receptors (5-HT2AR). Overall, the present study suggests that classical psychedelics psilocybin and DOI are effective in reducing pain-like behaviors via 5-HT2AR activation in two mouse models of chronic pain.

Ibogalogs decrease neuropathic pain in mice through a mechanism involving crosstalk between 5-HT2A and mGlu2 receptors

The objective of this study was to determine the anti-neuropathic activity of a variety of ibogalogs, including tabernanthalog (TBG), ibogaminalog (DM506), ibogainalog (IBG), nor-IBG, catharanthalog (CAG), and PNU-22394 using the oxaliplatin (OXA) neuropathic pain model in mice, and to investigate whether there is crosstalk between the 5-HT2A and mGlu2 receptors. All tested ibogalogs induce pain-relieving activity using both cold plate and paw pressure tests, without toxic effects. The most potent ibogalogs were IBG and CAG, whereas nor-IBG and DM506 were the longest-acting compounds. The anti-neuropathic activity of ibogalogs was inhibited by ketanserin, a 5-HT2A receptor antagonist, indicating a role for the 5-HT2A receptor for these effects. Sub-threshold doses of IBG (1 mg/kg) and nor-IBG (3 mg/kg) produced pain relief only in the presence of a sub-threshold dose of LY379268, a selective mGlu2 receptor agonist, indicating that signaling through both 5-HT2A and mGlu2 receptors improves efficacy. In the functional study using HEK293 cells co-expressing both 5-HT2A and mGlu2 receptors, Glu increased the apparent potency of ibogalogs in a concentration-dependent manner and sub-threshold concentrations of ibogalogs augmented the Glu-induced response through the mGlu2 receptor, which collectively indicate functional crosstalk between both receptors. Ibogalogs increased mGlu2 receptor phosphorylation on Ser843, a proposed key molecular event underlying the functional receptor crosstalk. Our study shows for the first time that diverse ibogalogs induce anti-neuropathic activity through a synergic mechanism involving both 5-HT2A and mGlu2 receptors.

Astragalin relieves inflammatory pain and negative mood in CFA mice by down-regulating mGluR5 signaling pathway

As a flavonoid compound, astragalin (AST) is found in a variety of medicinal plants. In clinical studies, AST has anti-inflammatory and analgesia effects on rheumatoid arthritis, bronchopneumonia diseases and so on, but its specific role and mechanism is still not clear. This study aimed to investigate the effect and molecular mechanism of AST on inflammatory pain and pain-related emotions in complete Freund's adjuvant (CFA) mice. In this study, we observed that AST significantly alleviated CFA-induced inflammatory pain and associated emotional disturbances in mice. The mechanism may be related to down-regulating mGluR5-mediated PKCλ-ERK1/2-FOXO6 signaling pathway in CFA mice. Treatment with the mGluR5-specific inhibitor MTEP resulted in the downregulation of proteins associated with the PKCλ-ERK1/2-FOXO6 pathway, similar to the effects observed with AST administration. These results suggested that AST might play a crucial role in the management of inflammatory pain and related emotions, shedding light on its underlying mechanism for treating such conditions.

Hemoglobin α-derived peptides VD-hemopressin (α) and RVD-hemopressin (α) are involved in electroacupuncture inhibition of chronic pain

Introduction

Knee osteoarthritis (KOA) is a chronic degenerative bone metabolic disease that primarily affects older adults, leading to chronic pain and disability that affect patients' daily activities. Electroacupuncture (EA) is a commonly used method for the treatment of chronic pain in clinical practice. Previous studies indicate that the endocannabinoid system is involved in EA analgesia, but whether endocannabinopeptide VD-hemopressin (α) and RVD-hemopressin (α) derived from hemoglobin chains are involved in EA analgesia is unclear.

Methods

RNA-seq technology was used to screen which genes involved in EA analgesia. The expression of hemoglobin α chain and 26S proteasome were determined by Western blotting. The level of VD-hemopressin (α) and RVD-hemopressin (α) were measured by UPLC-MS/MS. Microinjection VD-Hemopressin (α), RVD-Hemopressin (α) and 26S proteasome inhibitor MG-132 into vlPAG, then observe mechanical and thermal pain thresholds.

Results

Therefore, we used RNA-seq to obtain differentially expressed genes Hba-a1 and Hba-a2 involved in EA analgesia in the periaqueductal gray (PAG), which were translated into the hemoglobin α chain. EA significantly increased the expression of the hemoglobin α chain and the level of hemopressin (α) and RVD-hemopressin (α). Microinjection of VD-hemopressin (α) and RVD-hemopressin (α) into the ventrolateral periaqueductal gray (vlPAG) mimicked the analgesic effect of EA, while CB1 receptor antagonist AM251 reversed this effect. EA significantly increased the expression of 26S proteasome in KOA mice. Microinjection of 26S proteasome inhibitor MG132 before EA prevented both the anti-allodynic effect and upregulation of the concentration of RVD-hemopressin (α) by EA treatment and upregulated the expression of the hemoglobin α chain.

Discussion

Our data suggest that EA upregulated the concentration of VD-hemopressin (α) and RVD-hemopressin (α) through enhancement of the hemoglobin α chain degradation by 26S proteasome in the PAG, then activated the CB1 receptor, thereby exerting inhibition of chronic pain in a mouse model of KOA. These results provide new insights into the EA analgesic mechanisms and reveal possible targets for EA treatment of chronic pain.

Effect of Traditional Chinese Non-Pharmacological Therapies on Knee Osteoarthritis: A Narrative Review of Clinical Application and Mechanism

Knee osteoarthritis (KOA) stands as a degenerative ailment with a substantial and escalating prevalence. The practice of traditional Chinese non-pharmacological therapy has become a prevalent complementary and adjunctive approach. A mounting body of evidence suggests its efficacy in addressing KOA. Recent investigations have delved into its underlying mechanism, yielding some headway. Consequently, this comprehensive analysis seeks to encapsulate the clinical application and molecular mechanism of traditional Chinese non-pharmacological therapy in KOA treatment. The review reveals that various therapies, such as acupuncture, electroacupuncture, warm needle acupuncture, tuina, and acupotomy, primarily target localized knee components like cartilage, subchondral bone, and synovium. Moreover, their impact extends to the central nervous system and intestinal flora. More perfect experimental design and more comprehensive research remain a promising avenue in the future.

Research of the analgesic effects and central nervous system impact of electroacupuncture therapy in rats with knee osteoarthritis

It aimed to observe the effects of TongDu TiaoShen (TDTS) electroacupuncture (EA) on the analgesia and central system of knee osteoarthritis (KOA) rats and explore its mechanism. SD rats were rolled into the blank group, model group (KOA), control group (duloxetine 500 mg/kg/d, Ctrl), conventional EA group, and TDTS-EA group. Radiometric pain measurements and the Lequesne MG scale were used to evaluate the behavioral performance of the rats. Dopamine (DA), norepinephrine (NE), 5-hydroxytryptamine (5-HT), β-endorphin (β-EP), and leucine-enkephalin (L-ENK) were detected in the midbrain and spinal cord of lumbar enlargement. Interleukin (IL)-1β protein expression was detected by Western blot. The incubation period of thermal pain and foot contraction was decreased in the KOA group versus blank group, the Lequesne MG score was increased, DA, NE, 5-HT, β-EP, and L-ENK in the midbrain and spinal cord were increased, and synovial tissue IL-1β protein expression was increased (P < 0.05). EA group and TDTS-EA group had an increased incubation period of thermal pain contraction, decreased Lequesne MG score, decreased DA, NE, etc. In the midbrain, increased 5-HT and NE in the spinal cord, and decreased IL-1β in the synovial tissue versus KOA group (P < 0.05). The Lequesne MG score and midbrain DA, NE, 5-HT, β-EP, and synovial tissue IL-1β expression were decreased in TDTS-EA group versus EA group (P < 0.05). EA can effectively improve the behavioral score of KOA and participate in central analgesia by regulating central DA, NE, 5-HT, β-EP, and L-ENK.

Acupuncture's long-term impact on depression prevention in primary dysmenorrhea: A 19-year follow-up of a Taiwan cohort with neuroimmune insights

BACKGROUND

Primary dysmenorrhea (PD) is a common gynecological condition causing depression. Acupuncture is an effective option for PD management but its effects on PD-associated depression remain unclear.

METHODS

A retrospective cohort study involving 35,099 propensity score-matched pairs of acupuncture users and non-users with PD was conducted using data from Taiwan's Longitudinal Generation Tracking Database 2000. Cox proportional hazard models were used to estimate depression risk, and bioinformatics analyses were performed to uncover underlying molecular mechanisms.

RESULTS

The risk of developing depression was reduced by 64 % in acupuncture users compared with non-acupuncture users during the 19-year follow-up period. The decrease was dose-dependent. Bioinformatics analyses identified 34 co-expressed targets for acupuncture, PD, and depression; and eight hub genes (coding for interleukin 6 and 1B, tumor necrosis factor, albumin, vascular endothelial growth factor A, C-reactive protein, prostaglandin-endoperoxide synthase 2, and brain-derived neurotrophic factor) potentially involved in the therapeutic effects of acupuncture. Several molecular pathways were found to be involved, including cytokine-cytokine receptor interaction, neuroactive ligand-receptor interaction, cyclic adenosine 3',5'-monophosphate signaling pathway, mitogen-activated protein kinase signaling pathway, serotonergic synapse, and estrogen signaling pathway.

LIMITATIONS

Bias in the selection of participants could have been introduced as a consequence of the retrospective nature of the study. Data were derived from a single national database, and acupuncture treatment details were unavailable.

CONCLUSION

Acupuncture may protect against the development of depression in patients with PD. This study provides insight into the potential molecular mechanisms underlying the therapeutic effects of acupuncture in PD management and depression prevention.

Validation of the Chinese version of the Brief Pain Inventory in patients with knee osteoarthritis

BACKGROUND

Knee osteoarthritis (KOA) primarily presents with symptoms of pain and compromised functionality. Pain is a subjective manifestation that necessitates the employment of reliable evaluation tools for practical assessment, thereby enabling the formulation of appropriate interventional strategies. The Brief Pain Inventory (BPI) is a widely utilized questionnaire for evaluating the status of chronic pain. The purpose of the present study is to translate the short form of BPI into Chinese version (BPI-CV) and conduct cross-cultural adaptation to evaluate the psychometric characteristics of BPI-CV in KOA patients.

METHODS

BPI-CV was translated and cross-culturally adapted according to internationally recognized guidelines. A cohort comprising 150 patients diagnosed with KOA successfully completed the demographic questionnaire, BPI-CV, Western Ontario and McMaster University Osteoarthritis Index (WOMAC), and the EuroQoL Group's five-dimension questionnaire (EQ-5D). Internal consistency and test-retest analysis were used to evaluate the reliability. The internal consistency of the scale items was evaluated by calculating the Cronbach's α value (> 0.7). We chose to employ two scales commonly used in the evaluation of KOA patients: the disease-specific WOMAC scale and the universal EQ-5D scale. Construct validity was determined through Pearson correlation analysis, comparing BPI scores with those obtained from the WOMAC and EQ-5D scales. Exploratory factor analysis was used to structural validity.

RESULTS

The BPI-CV was well accepted with no ceiling or floor effect. Cronbach's α for assessing internal consistency was 0.894. Test-retest reliability was excellent with an ICC of 0.852 (95%CI 0.785-0.905). The BPI-CV showed moderate to strong correlations with the pain dimension (r = 0.496-0.860) and the functional interference dimension (r = 0.517-0.712) of the WOMAC and the EQ-5D (r = 0.527-0.743). Three factors resulted using exploratory factor analysis: pain severity, activity interference, and emotional interference, accounting for 79.0% of the total variance. Standard error of measurement was 0.539.

CONCLUSION

BPI-CV has good feasibility, reliability, and validity. It can be recommended for KOA patients in mainland China.

EA participates in pain transition through regulating KCC2 expression by BDNF-TrkB in the spinal cord dorsal horn of male rats

The pathogenesis of chronic pain is complex and poorly treated, seriously affecting the quality of life of patients. Electroacupuncture (EA) relieves pain by preventing the transition of acute pain into chronic pain, but its mechanism of action is still unclear. Here, we aimed to investigate whether EA can inhibit pain transition by increasing KCC2 expression via BDNF-TrkB. We used hyperalgesic priming (HP) model to investigate the potential central mechanisms of EA intervention on pain transition. HP model male rats showed significant and persistent mechanically abnormal pain. Brain derived neurotrophic factor (BDNF) expression and Tropomyosin receptor kinase B (TrkB) phosphorylation were upregulated in the affected spinal cord dorsal horn (SCDH) of HP model rats, accompanied by K⁺-Cl^-- Cotransporter-2 (KCC2) expression was down-regulated. EA significantly increased the mechanical pain threshold in HP model male rats and decreased BDNF and p-TrkB overexpression and upregulated KCC2 expression. Blockade of BDNF with BDNF neutralizing antibody attenuated mechanical abnormal pain in HP rats. Finally, administration of exogenous BDNF by pharmacological methods reversed the EA-induced resistance to abnormal pain. In all, these results suggest that BDNF-TrkB contributes to mechanical abnormal pain in HP model rats and that EA ameliorates mechanical abnormal pain through upregulation of KCC2 by BDNF-TrkB in SCDH. Our study further supports EA as an effective treatment to prevent the transition of acute pain into chronic pain.

Ionic Plasticity: Common Mechanistic Underpinnings of Pathology in Spinal Cord Injury and the Brain

The neurotransmitter GABA is normally characterized as having an inhibitory effect on neural activity in the adult central nervous system (CNS), which quells over-excitation and limits neural plasticity. Spinal cord injury (SCI) can bring about a modification that weakens the inhibitory effect of GABA in the central gray caudal to injury. This change is linked to the downregulation of the potassium/chloride cotransporter (KCC2) and the consequent rise in intracellular Cl- in the postsynaptic neuron. As the intracellular concentration increases, the inward flow of Cl- through an ionotropic GABA-A receptor is reduced, which decreases its hyperpolarizing (inhibitory) effect, a modulatory effect known as ionic plasticity. The loss of GABA-dependent inhibition enables a state of over-excitation within the spinal cord that fosters aberrant motor activity (spasticity) and chronic pain. A downregulation of KCC2 also contributes to the development of a number of brain-dependent pathologies linked to states of neural over-excitation, including epilepsy, addiction, and developmental disorders, along with other diseases such as hypertension, asthma, and irritable bowel syndrome. Pharmacological treatments that target ionic plasticity have been shown to bring therapeutic benefits.

Long March Toward Safe and Effective Analgesia by Enhancing Gene Expression of Kcc2: First Steps Taken

Low intraneuronal chloride in spinal cord dorsal horn pain relay neurons is critical for physiologic transmission of primary pain afferents because low intraneuronal chloride dictates whether GABA-ergic and glycin-ergic neurotransmission is inhibitory. If the neuronal chloride elevates to pathologic levels, then spinal cord primary pain relay becomes leaky and exhibits the behavioral hallmarks of pathologic pain, namely hypersensitivity and allodynia. Low chloride in spinal cord dorsal horn neurons is maintained by proper gene expression of Kcc2 and sustained physiologic function of the KCC2 chloride extruding electroneutral transporter. Peripheral nerve injury and other forms of neural injury evoke greatly diminished Kcc2 gene expression and subsequent corruption of inhibitory neurotransmission in the spinal cord dorsal horn, thus causing derailment of the gate function for pain. Here I review key discoveries that have helped us understand these fundamentals, and focus on recent insights relating to the discovery of Kcc2 gene expression enhancing compounds via compound screens in neurons. One such study characterized the kinase inhibitor, kenpaullone, more in-depth, revealing its function as a robust and long-lasting analgesic in preclinical models of nerve injury and cancer bone pain, also elucidating its mechanism of action via GSK3β inhibition, diminishing delta-catenin phosphorylation, and facilitating its nuclear transfer and subsequent enhancement of Kcc2 gene expression by de-repressing Kaiso epigenetic transcriptional regulator. Future directions re Kcc2 gene expression enhancement are discussed, namely combination with other analgesics and analgesic methods, such as spinal cord stimulation and electroacupuncture, gene therapy, and leveraging Kcc2 gene expression-enhancing nanomaterials.