Andrographolide Inhibits Mechanical and Thermal Hyperalgesia in a Rat Model of HIV-Induced Neuropathic Pain

P2Y12-mediated HIV gp120 and ddC-induced neuropathic pain improved by esculin

We studied whether esculin (ES) has the effect of alleviating peripheral neuropathic pain (NP) in rat models of HIV glycoprotein 120 (gp120) together with zalcitabine (2',3'-dideoxycytidine; ddC) treatment and explored the possible mechanism of it. The rats pain behaviors were evaluated by observing the paw withdrawal threshold (PWT) and the paw withdrawal latency (PWL). The rats were divided into a control group, sham group, gp120 combined with a ddC treatment group (gp120& ddC group), gp120&ddC combined with ES treatment group (gp120&ddC+ES group), which ES was administered intragastrically, and gp120&ddC combined with short hair RNA of P2Y12 receptor (rP2Y12) treatment group (gp120&ddC+shP2Y12 group), which shRNA of rP2Y12 was injected intrathecally with a dose of 25 µg/20 µl for every rat, and a negative control plasmid was administered to the gp120&ddC+nc group. Western blotting was used to measure the protein expression levels of the rP2Y12, the nuclear factor of activated T-cells type c1 (NFATc1), phospho-NFATc1 and the C-C motif chemokine ligand 3 (CCL3) in the L4-L6 dorsal root ganglia (DRG). Real-time quantitative PCR (RT-qPCR) was used to test the mRNA expression level of the CCL3. Double-labeling immunofluorescence was used to identify the co-localization of the rP2Y12 with glial fibrillary acidic protein (GFAP) in DRG. Fluorescence imaging with calcium indicator fluo-3 AM (7.5 μM) was performed to observe the change of intracellular calcium concentration ([Ca2+]i). Molecular docking was performed to identify the interaction between rP2Y12 and the ligand ES. We found that accompanied by the attenuation of mechanical allodynia and thermal hyperalgesia, rP2Y12 expression in the gp120+ddC+ES group of rats was downregulated compared with the gp120+ddC ones, as was the coexpression of the rP2Y12 and GFAP of satellite glial cells (SGCs) in DRG, and the CCL3 mRNA levels and protein expression were both decreased. In addition, mechanistic studies have found that there is a docking pocket between ES and the rP2Y12 protein, which causes ES to decrease the [Ca2+]i, thus increasing the phosphorylation level of NFATc1. Taken together, the results suggest that ES can combine with the rP2Y12, inhibit DRG SGCs activation caused by gp120&ddC, reduce [Ca2+]i, and prevent the NFATc1-mediated gene transcription of CCL3, finally relieving NP in rats treated with gp120&ddC.

Involvement of sphingosine-1-phosphate receptor 1 in pain insensitivity in a BTBR mouse model of autism spectrum disorder

BACKGROUND

Abnormal sensory perception, particularly pain insensitivity (PAI), is a typical symptom of autism spectrum disorder (ASD). Despite the role of myelin metabolism in the regulation of pain perception, the mechanisms underlying ASD-related PAI remain unclear.

METHODS

The pain-associated gene sphingosine-1-phosphate receptor 1 (S1PR1) was identified in ASD samples through bioinformatics analysis. Its expression in the dorsal root ganglion (DRG) tissues of BTBR ASD model mice was validated using RNA-seq, western blot, RT-qPCR, and immunofluorescence. Pain thresholds were assessed using the von Frey and Hargreaves tests. Patch-clamp techniques measured KCNQ/M channel activity and neuronal action potentials. The expression of S1PR1, KCNQ/M, mitogen-activated protein kinase (MAPK), and cyclic AMP/protein kinase A (cAMP/PKA) signaling proteins was analyzed before and after inhibiting the S1P-S1PR1-KCNQ/M pathway via western blot and RT-qPCR.

RESULTS

Through integrated transcriptomic analysis of ASD samples, we identified the upregulated gene S1PR1, which is associated with sphingolipid metabolism and linked to pain perception, and confirmed its role in the BTBR mouse model of ASD. This mechanism involves the regulation of KCNQ/M channels in DRG neurons. The enhanced activity of KCNQ/M channels and the decreased action potentials in small and medium DRG neurons were correlated with PAI in a BTBR mouse model of ASD. Inhibition of the S1P/S1PR1 pathway rescued baseline insensitivity to pain by suppressing KCNQ/M channels in DRG neurons, mediated through the MAPK and cAMP/PKA pathways. Investigating the modulation and underlying mechanisms of the non-opioid pathway involving S1PR1 will provide new insights into clinical targeted interventions for PAI in ASD.

CONCLUSIONS

S1PR1 may contribute to PAI in the PNS in ASD. The mechanism involves KCNQ/M channels and the MAPK and cAMP/PKA signaling pathways. Targeting S1PR1 in the PNS could offer novel therapeutic strategies for the intervention of pain dysesthesias in individuals with ASD.

Andrographolide exhibits antinociceptive effects in neuropathic rats via inhibiting class Ⅱ MHC associated response and regulating synaptic plasticity

BACKGROUND

Neuropathic pain (NP) due to nerve injury, disrupts neural plasticity by triggering the release of inflammatory mediators. Alongside the hypothesis that neuro-inflammation contributes to this disruption, Andrographolide (Andro), a traditional bioactive compound derived from Andrographis paniculata, has garnered attention for its potent anti-inflammatory properties. However, whether Andro could ameliorate NP by regulating neuroinflammation remains unknown.

PURPOSE

This study aimed to investigate whether and how Andro regulates neuroinflammation and alleviates NP.

METHODS

The analgesic effects of Andro on NP were evaluated using both the spinal nerve ligation (SNL) and formalin rat models. A combination of network pharmacology, RNA sequencing, and experimental validation was employed to elucidate the underlying mechanism behind Andro's analgesic effects. Additionally, various techniques such as functional ultrasound, immunohistochemistry, quantitative real-time polymerase chain reaction (qPCR), patch clamp, and electron microscopy were employed to investigate the specific neural cell types, neural functions, and changes in neural plasticity influenced by Andro.

RESULTS

Network pharmacology analysis unveiled the crucial roles played by shared targets of Andro and pain in regulating pain-related inflammation, including microglia activation, neuroinflammation, immune modulation, and synaptic transmission. Furthermore, we confirmed Andro's superior efficacy in pain relief compared to the traditional analgesic drug, Gabapentin. In these models, Andro was observed to modulate the haemodynamic response triggered by SNL. Transcriptome analysis and molecular docking studies indicated the involvement of major histocompatibility complex class II (MHCII) genes (Db1, Da, and Bb). Electron microscopy revealed improvements in synaptic ultrastructure, and electrophysiological investigations showed a selective reduction in glutamatergic transmission in neuropathic rats after following Andro treatment. The integration of systems pharmacology analysis and biological validation collectively demonstrated that the mechanism of pain relief involves immune modulation, enhancement of synaptic plasticity, and precise regulation of excitatory neurotransmission.

CONCLUSION

In conclusion, this study has demonstrated that Andro, by targeting MHCII genes, may serve as a promising therapeutic candidate for neuropathic pain.

Andrographolide attenuates sepsis-induced acute kidney injury by inhibiting ferroptosis through the Nrf2/FSP1 pathway

Sepsis is a systemic inflammatory response syndrome caused by infection, which causes renal dysfunction known as sepsis-associated acute kidney injury (S-AKI). Ferroptosis is a form of lipid peroxidation dependent on iron and reactive oxygen species that differs from other forms of programmed cell death at the morphological and biochemical levels. Andrographolide (AG), a natural diterpenoid lactone compound extracted from Andrographis paniculata, has been shown to have therapeutic effects in kidney disease. In this study, we investigated the novel mechanism by which AG attenuates septic acute kidney injury by inhibiting ferroptosis in renal tubular epithelial cells (HK-2) through the Nrf2/FSP1 pathway. Cecum ligation and puncture (CLP)-induced septic rats and lipopolysaccharide (LPS)-induced HK-2 cells were used for in vivo and in vitro experiments. Firstly, in septic rats and HK-2 cells, AG effectively decreased the levels of kidney injury indicators, including blood creatinine, urea nitrogen, and markers of kidney injury such as neutrophil gelatinase-associated lipid transport protein and kidney injury molecule-1 (KIM-1). In addition, AG prevented ferroptotosis, by avoiding the accumulation of iron and lipid peroxidation, and an increase in SLC7A11 and GPX4 in AG-treated HK-2 cells. Furthermore, AG attenuated mitochondrial damage, including mitochondrial swelling, outer membrane rupture, and a reduction in mitochondrial cristae in LPS-treated HK-2 cells. Ferrostatin-1 (Fer-1), a ferroptosis inhibitor, significantly inhibited LPS-induced ferroptosis in HK-2 cells. Importantly, our results confirm that Nrf2/FSP1 is an important pathway for ferroptosis resistance. Nrf2 siRNA hindered the effect of AG in attenuating acute kidney injury and inhibiting ferroptosis. These findings demonstrate that Nrf2/FSP1-mediated HK-2 ferroptosis is associated with AG, alleviates septic acute kidney injury, and indicates a novel avenue for therapeutic interventions in the treatment of acute kidney injury in sepsis.

Andrographolide inhibits the activation of spinal microglia and ameliorates mechanical allodynia

Andrographolide (Andro), a labdane diterpene, possesses anti-inflammatory properties and has been used to treat numerous inflammatory diseases. Novel findings revealed that Andro might be vital in regulating pain. However, the contribution of Andro to chronic inflammatory pain has yet to be determined, and its underlying mechanism of action remains unknown. In this study, we observed that Andro attenuated mechanical allodynia in inflammatory pain mice induced by injecting complete Freund's adjuvant (CFA) into the right hind paws. This analgesic effect of Andro is mainly dependent on its inhibition of microglial overactivation and the release of proinflammatory cytokines (TNF and IL-1β) in lumbar spinal cords of inflammatory pain model mice. More importantly, our data in vivo and in vitro revealed a negative role for Andro in regulating the TLR4/NF-κB signaling pathway, which might contribute to the inhibition of spinal microglial activation and proinflammatory cytokines production, and the improvement of paw withdrawal thresholds in a mouse model of chronic inflammatory pain evoked by CFA. We further found the potential interaction of Andro with TLR4/myeloid differentiation factor 2 heterodimer using molecular modeling, implying that TLR4 might be a potential target for Andro to exert an analgesic effect. Taken together, our findings demonstrated that the modulation of spinal microglial activation by Andro might be substantially conducive to managing chronic pain triggered by neuroinflammation.

Traditional Chinese medicine alleviating neuropathic pain targeting purinergic receptor P2 in purinergic signaling: A review

Past studies have suggested that Chinese herbal may alleviate neuropathic pain, and the mechanism might target the inhibition of purinergic receptor P2. This review discusses whether traditional Chinese medicine target P2 receptors in neuropathic pain and its mechanism in order to provide references for future clinical drug development. The related literatures were searched from Pubmed, Embase, Sinomed, and CNKI databases before June 2023. The search terms included"neuropathic pain", "purinergic receptor P2", "P2", "traditional Chinese medicine", "Chinese herbal medicine", and "herb". We described the traditional Chinese medicine alleviating neuropathic pain via purinergic receptor P2 signaling pathway including P2X2/3 R, P2X3R, P2X4R, P2X7R, P2Y1R. Inhibition of activating glial cells, changing synaptic transmission, increasing painful postsynaptic potential, and activating inflammatory signaling pathways maybe the mechanism. Purine receptor P2 can mediate the occurrence of neuropathic pain. And many of traditional Chinese medicines can target P2 receptors to relieve neuropathic pain, which provides reasonable evidences for the future development of drugs. Also, the safety and efficacy and mechanism need more in-depth experimental research.

Progress in Pathological and Therapeutic Research of HIV-Related Neuropathic Pain

HIV-related neuropathic pain (HRNP) is a neurodegeneration that gradually develops during the long-term course of acquired immune deficiency syndrome (AIDS) and manifests as abnormal sock/sleeve-like symmetrical pain and nociceptive hyperalgesia in the extremities, which seriously reduces patient quality of life. To date, the pathogenesis of HRNP is not completely clear. There is a lack of effective clinical treatment for HRNP and it is becoming a challenge and hot spot for medical research. In this study, we conducted a systematic review of the progress of HRNP research in recent years including (1) the etiology, classification and clinical symptoms of HRNP, (2) the establishment of HRNP pathological models, (3) the pathological mechanisms underlying HRNP from three aspects: molecules, signaling pathways and cells, (4) the therapeutic strategies for HRNP, and (5) the limitations of recent HRNP research and the future research directions and prospects of HRNP. This detailed review provides new and systematic insight into the pathological mechanism of HRNP, which establishes a theoretical basis for the future exploitation of novel target drugs. HIV infection, antiretroviral therapy and opioid abuse contribute to the etiology of HRNP with symmetrical pain in both hands and feet, allodynia and hyperalgesia. The pathogenesis involves changes in cytokine expression, activation of signaling pathways and neuronal cell states. The therapy for HRNP should be patient-centered, integrating pharmacologic and nonpharmacologic treatments into multimodal intervention.

Central role of purinergic receptors with inflammation in neuropathic pain-related macrophage-SGC-neuron triad

Adenosine triphosphate (ATP) acts on P2 purinergic receptors as an extracellular signaling molecule. P2 purinergic receptors include P2X ionotropic receptors and P2Y metabotropic receptors. Satellite glial cells (SGCs) and macrophages express P2X and P2Y receptors. Inflammatory cytokines and pro-nociceptive mediators are released by activated macrophages and SGCs, which can act on neurons to promote excitability and firing. In the primary sensory ganglia, in response to signals of injury, SGCs and macrophages accumulate around primary sensory neurons, forming a macrophage-SGC-neuron triad. In addition to affecting the pathological alterations of inflammation-related neuropathic pain, inflammatory cytokines and pro-nociceptive mediators are released by the action of ATP on P2X and P2Y receptors in macrophages and SGCs. Macrophages and SGCs work together to enhance and prolong neuropathic pain. The macrophage-SGC-neuron triad communicates with each other through ATP and other inflammatory mediators and maintains and promotes the initiation and development of inflammation related-neuropathic pain. This article is part of the Special Issue on "Purinergic Signaling: 50 years".

Persistent sensory changes and sex differences in transgenic mice conditionally expressing HIV-1 Tat regulatory protein

HIV-associated sensory neuropathies (HIV-SN) are prevalent in >50% of patients aged over 45 years many of which report moderate to severe chronic pain. Previous preclinical studies have investigated the mechanisms by which HIV-1 causes sensory neuropathies and pain-like behaviors. The aim of the present study is to delineate the role of chronic HIV-1 trans-activator of transcription protein (Tat) exposure in the development of neuropathy in mice. The temporal effects of conditional Tat expression on the development of hypersensitivity to mechanical (von Frey filaments) and thermal (heat or cold) stimuli were tested in male and female mice that transgenically expressed HIV-1 Tat in a doxycycline-inducible manner. Inducing Tat expression produced an allodynic response to mechanical or cold (but not heat) stimuli that respectively persisted for at least 23-weeks (mechanical hypersensitivity) or at least 8-weeks (cold hypersensitivity). Both allodynic states were greater in magnitude among females, compared to males, and mechanical increased hypersensitivity progressively in females over time. Acute morphine or gabapentin treatment partly attenuated allodynia in males, but not females. Irrespective of sex, Tat reduced intraepidermal nerve fiber density, the mean amplitude of sensory nerve action potentials (but not conductance), engagement in some pain-related ethological behaviors (cage-hanging and rearing), and down-regulated PPAR-α gene expression in lumbar spinal cord while upregulating TNF-α expression in dorsal root ganglion. Taken together, these data reveal fundamental sex differences in mechanical and cold hypersensitivity in response to Tat and demonstrate the intractable nature in female mice to current therapeutics. Understanding the role of Tat in these pathologies may aid the design of future therapies aimed at mitigating the peripheral sensory neuropathies that accompany neuroHIV.

P2X7 receptor in inflammation and pain

Different studies have confirmed P2X7 receptor-mediated inflammatory mediators play a key role in the development of pain. P2X7 receptor activation can induce the development of pain by mediating the release of inflammatory mediators. In view of the fact that P2X7 receptor is expressed in the nervous system and immune system, it is closely related to the stability and maintenance of the nervous system function. ATP activates P2X7 receptor, opens non-selective cation channels, activates multiple intracellular signaling, releases multiple inflammatory cytokines, and induces pain. At present, the role of P2X7 receptor in inflammatory response and pain has been widely recognized and affirmed. Therefore, in this paper, we discussed the pathological mechanism of P2X7 receptor-mediated inflammation and pain, focused on the internal relationship between P2X7 receptor and pain. Moreover, we also described the effects of some antagonists on pain relief by inhibiting the activities of P2X7 receptor. Thus, targeting to inhibit activation of P2X7 receptor is expected to become another potential target for the relief of pain.

Effect of Bufalin-PLGA Microspheres in the Alleviation of Neuropathic Pain via the CCI Model

The treatment of neuropathic pain (NPP) is considered challenging, while the search for alternative medication is striving. NPP pathology is related with the expression of both the purinergic 2X7 (P2X7) receptor and the transient receptor potential vanilloid 1 receptor (TRPV1). Bufalin is a traditional Chinese medication derived from toad venom with pronounced antitumor, analgesic, and anti-inflammatory properties. However, poor solubility, rapid metabolism, and the knowledge gap on its pain alleviation mechanism have limited the clinical application of bufalin. Hence, the purpose of this study is to illustrate the NPP alleviation mechanism of bufalin via chronic constriction injury (CCI). To address the concern on fast metabolism, bufalin-PLGA microspheres (MS) were prepared via membrane emulsification to achieve prolonged pain-relieving effects. Western blot, real-time PCR, immunofluorescence, and molecular docking were employed to demonstrate the therapeutic action of bufalin on NPP. The results showed enhanced thermal withdrawal latency (TWL) and mechanical withdrawal threshold (MWT) after the administration of both bufalin and bufalin-PLGA MS in the CCI rats. Prolonged pain-relieving effects for up to 3 days with reduced dose frequency was achieved via bufalin-PLGA MS. In the CCI rats treated with bufalin-PLGA MS, the expression levels of protein and mRNA in TRPV1 and P2X7, both localized in the dorsal root ganglion (DRG), were reduced. Moreover, bufalin-PLGA MS effectively reduced the levels of IL-1β, IL-18, IL-6, and TNF-α in the CCI group. The results from molecular docking suggested a possible mechanism of NPP alleviation of bufalin through binding to P2X7 receptors directly. The administration of bufalin-PLGA MS prepared by membrane emulsification demonstrated promising applications for sustained effect on the alleviation of NPP.

Escinosomes: Safe and Successful Nanovesicles to Deliver Andrographolide by a Subcutaneous Route in a Mice Model of Oxaliplatin-Induced Neuropathy

Andrographolide (AG) is a natural diterpene lactone endowed with considerable therapeutic potential for treating numerous diseases, including neurological disorders, but its low aqueous solubility and scarce bioavailability limit its clinical use. To overcome this problem, AG was encapsulated in escinosomes, special nanovesicles made of escin (ESN), a natural saponin, and phosphatidylcholine. Escinosomes loaded with AG had an average size of 164.7 ± 13.30 nm, optimal polydispersity index (0.190 ± 0.0890) and high ζ-potential (−35.4 ± 0.451 mV), and significantly loaded the active substance—the encapsulation efficiency of AG was about 88%. Escinosomes allowed the prolonged release of AG over time, without burst effects—about 85% AG was released after 24 h. Morphological analysis by cryo-transmission electron microscopy showed nanovesicles with a spherical shape, unilamellar and oligolamellar structures, and dimensions in agreement with those measured by dynamic light scattering. In addition, stability studies were performed on AG-loaded escinosomes stored for one month at 4 °C. The pain-relieving efficacy of these nanovesicles was tested in a rat model of oxaliplatin-induced neuropathy. AG-loaded escinosomes, subcutaneously administered, effectively reduced the thermal allodynia characteristic of chemotherapy-induced neuropathy, enhancing and prolonging the effect of the natural compound. Overall, AG-loaded escinosomes were found to be excellent for loading AG, physically and chemically stable for one-month storage, and with controlled-release properties, making the formulation an ideal pharmacological approach for persistent pain treatment.

Neurobiological Promises of the Bitter Diterpene Lactone Andrographolide

Andrographolide (ANDRO), a bitter diterpene lactone found in Andrographis paniculata (Burm.f.) Nees, possesses several biological effects such as antioxidant, anti-inflammatory, and organo-protective effects. Scientific reports suggest that it also has neuroprotective capacity in various test systems. The purpose of this review was to synthesize the neuropharmacological properties of ANDRO and highlight the molecular mechanisms of action that highlight these activities. A careful search was done in PubMed and Google Scholar databases using specific keywords. Findings suggest that ANDRO possess neuroprotective, analgesic, and antifatigue effects. Prominent effects were stated on neuro-inflammation, cerebral ischemia, Alzheimer's and Parkinson's diseases, multiple sclerosis, and brain cancer in mice and rats. Furthermore, ANDRO and its derivatives can enhance memory and learning capacity in experimental animals (rats) without causing any toxicity in the brain. Thus, ANDRO may be one of the most promising plant-based psychopharmacological lead compounds for new drug development.

Andrographolide: A review of its pharmacology, pharmacokinetics, toxicity and clinical trials and pharmaceutical researches

Andrographis paniculata (Burm. f.) Wall. ex Nees, a renowned herb medicine in China, is broadly utilized in traditional Chinese medicine (TCM) for the treatment of cold and fever, sore throat, sore tongue, snake bite with its excellent functions of clearing heat and toxin, cooling blood and detumescence from times immemorial. Modern pharmacological research corroborates that andrographolide, the major ingredient in this traditional herb, is the fundamental material basis for its efficacy. As the main component of Andrographis paniculata (Burm. f.) Wall. ex Nees, andrographolide reveals numerous therapeutic actions, such as antiinflammatory, antioxidant, anticancer, antimicrobial, antihyperglycemic and so on. However, there are scarcely systematic summaries on the specific mechanism of disease treatment and pharmacokinetics. Moreover, it is also found that it possesses easily ignored security issues in clinical application, such as nephrotoxicity and reproductive toxicity. Thereby it should be kept a lookout over in clinical. Besides, the relationship between the efficacy and security issues of andrographolide should be investigated and evaluated scientifically. In this review, special emphasis is given to andrographolide, a multifunctional natural terpenoids, including its pharmacology, pharmacokinetics, toxicity and pharmaceutical researches. A brief overview of its clinical trials is also presented. This review intends to systematically and comprehensively summarize the current researches of andrographolide, which is of great significance for the development of andrographolide clinical products. Noteworthy, those un-cracked issues such as specific pharmacological mechanisms, security issues, as well as the bottleneck in clinical transformation, which detailed exploration and excavation are still not to be ignored before achieving integration into clinical practice. In addition, given that current extensive clinical data do not have sufficient rigor and documented details, more high-quality investigations in this field are needed to validate the efficacy and/or safety of many herbal products.

Gallic Acid Alleviates Neuropathic Pain Behaviors in Rats by Inhibiting P2X7 Receptor-Mediated NF-κB/STAT3 Signaling Pathway

Neuropathic pain is a complex disease with high incidence. Adenosine triphosphate (ATP) and its activated P2X7 receptor are involved in the signal transmission of neuropathic pain. Gallic acid (3,4,5-trihydroxybenzoic acid) is a traditional Chinese medicine obtained from natural plants that exhibit anti-inflammatory, analgesic, and antitumor effects. However, the underlying mechanism for gallic acid in analgesia remains unknown. This study aims to reveal how gallic acid alleviates neuropathic pain behaviors in a rat model with chronic constriction injury (CCI). Real-time PCR, western blotting, double-label immunofluorescence, molecular docking, and whole-cell patch clamp technology were used to explore the therapeutic action of gallic acid on neuropathic pain. The results showed that after CCI rats were treated with gallic acid for 1 week, the mechanical withdrawal threshold and thermal withdrawal latency were increased, accompanied by inhibition of the upregulated expression of P2X7 and TNF-α at both mRNA and protein levels, and reduced NF-κB and phosphorylated-STAT3 in the dorsal root ganglia. At the same time, gallic acid significantly decreased the coexpression of P2X7 and glial fibrillary acidic protein in the dorsal root ganglia. In addition, gallic acid could suppress ATP-activated current in human embryonic kidney 293 (HEK293) cells transfected with the plasmid expressing P2X7 but had no effect on ATP activation current of P2X7-mutant plasmid (with the point mutation sequence of the key site where gallic acid binds to the P2X7 receptor). Therefore, our work suggests that gallic acid may alleviate neuropathic pain in CCI rats by inhibiting the P2X7 receptor and subsequent activation of the TNF-α/STAT3 signaling pathway.

Inhibitory Effects of Palmatine on P2X7 Receptor Expression in Trigeminal Ganglion and Facial Pain in Trigeminal Neuralgia Rats

Trigeminal Neuralgia (TN) refers to recurrent severe paroxysmal pain in the distribution area of the trigeminal nerve, which seriously affects the quality of life of patients. This research applied the chronic constriction injury of the infraorbital nerve (CCI—ION) approach to induce an animal model of TN in rats. The mechanical pain threshold of each group of rats was determined postoperatively; the expression of P2X7 receptor in trigeminal ganglion (TG) was assessed by qRT-PCR, immunofluorescence and Western blot; and the changes of the proinflammatory cytokines IL-1β and TNF-α in serum of rats were detected by ELISA. The results showed that the administration of palmatine in the TN rats could reduce the mechanical pain threshold, significantly decrease the expression of P2X7 receptor in TG, and lower the serum concentrations of IL-1β and TNF-α, compared to the sham group. In addition, the phosphorylation level of p38 in TG of TN rats was significantly decreased after treatment with palmatine. Likewise, inhibition of P2X7 expression by shRNA treatment could effectively counteract the adversary changes of pain sensitivity, IL-1β and TNF-α production, and p38 phosphorylation in TN rats. Our data suggest that palmatine may alleviate mechanical facial pain in TN rats possibly by reducing the expression of P2X7 receptor in TG of TN rats, which may be attributable to inhibiting p38 phosphorylation and reducing the release of IL-1β and TNF-α.

HIV-1 Tat promotes age-related cognitive, anxiety-like, and antinociceptive impairments in female mice that are moderated by aging and endocrine status

Hypogonadism is a common comorbidity associated with HIV-1 that is more prevalent among infected individuals over the age of 45. The underlying mechanisms are unknown, but both combined antiretroviral therapeutics and HIV-1 proteins, such as trans-activator of transcription protein (Tat), dysregulate steroid-synthetic mechanisms including lipid storage/synthesis and mitochondrial function. Thus, Tat expression may accelerate age-related comorbidities partly by impairing endocrine function. Few studies exist of Tat-mediated behavioral deficits in aged animals and effects of endocrine status have not been investigated. Accordingly, we tested whether conditional Tat expression in aged (~ 1.5 years old), female, Tat-transgenic [Tat(+)] mice increases anxiety-like behavior, impairs cognition, and augments mechanical allodynia, when compared to age-matched controls that do not express Tat protein [Tat(-)]. We further tested whether aged mice that maintained their endocrine status (pre-estropausal) were more resilient to Tat/age-related comorbidities than peri- or post-estropausal mice. Tat and endocrine aging status exerted separate and interacting effects that influenced anxiety-like and cognitive behaviors. Peri- and post-estropausal mice exhibited greater anxiety-like behavior in the elevated plus-maze and impaired learning in the radial arm water maze compared to pre-estropausal mice. Irrespective of estropause status, Tat(+) mice demonstrated impaired learning, reduced grip strength, and mechanical allodynia compared to Tat(-) mice. Tat exposure reduced circulating estradiol in post-estropausal mice and increased the estradiol-to-testosterone ratio in pre-estropausal mice. Changes in circulating estradiol, testosterone, and progesterone correlated with grip strength. Thus, endocrine status is an important factor in age-related anxiety, cognition, neuromuscular function, and allodynia that can be accelerated by HIV-1 Tat protein.

Transplantation of olfactory ensheathing cells combined with chitosan down-regulates the expression of P2X7 receptor in the spinal cord and inhibits neuropathic pain

BACKGROUND

Neuropathic pain (NPP) is the common symptom of most clinical diseases, and its treatment has always been a difficult problem at present. Therefore, the purpose of this study is to explore a new method for the treatment of NPP by transplanting olfactory ensheathing cells combined with chitosan (OECs-CS).

METHODS

Animal model of chronic compression sciatic nerve injury (CCI) was made, olfactory ensheathing cells (OECs) were cultured, chitosan (CS) biomaterials were prepared, and biocompatibility of OECs and CS were detected by MTT method, OECs and OECs-CS were transplanted into the site of the injured sciatic nerve respectively, behavioral method was used to measured the mechanical withdrawal thresholds (MWT) and thermal withdrawal latency (TWL) of rats. On days 7 and 14 after surgery, the expression level of P2X7 receptor (P2X7R) in the L4-5 spinal cord was measured by using in situ hybridization, western-blotting and qRT-PCR. To explore the therapeutic effect of OECs-CS transplantation on pain suppression.

RESULTS

After chronic compression sciatic nerve injury, the MWT and TWL of rats were significantly reduced, and the expression levels of P2X7R protein and mRNA in the L4-5 spinal cord was significantly increased. After the transplantation of OECs and OECs-CS, the expression levels of P2X7R was significantly reduced, and the MWT and TWL of rats were significantly increased. Importantly, compared with the transplantation of OECs, OECs-CS transplantation could better reduce the expression levels of P2X7R, and relieve hyperalgesia in rats. Moreover, compared with the CCI + OECs-CS group on days 7 after surgery, the expression levels of P2X7R in the CCI + OECs-CS group was reduced on days 14 after surgery, and the pain in rats was relieved.

CONCLUSION

OECs and OECs-CS transplantation can inhibit P2X7R overexpression mediated NPP, while OECs-CS transplantation has better therapeutic effect than OECs transplantation alone. Our results provide a novel method and theoretical basis for the treatment of NPP.

Compounds of traditional Chinese medicine and neuropathic pain

Neuropathic pain (NP) has become a serious global health issue and a huge clinical challenge without available effective treatment. P2 receptors family is involved in pain transmission and represents a promising target for pharmacological intervention. Traditional Chinese medicine (TCM) contains multiple components which are effective in targeting different pathological mechanisms involved in NP. Different from traditional analgesics, which target a single pathway, TCMs take the advantage of multiple components and multiple targets, and can significantly improve the efficacy of treatment and contribute to the prediction of the risks of NP. Compounds of TCM acting at nucleotide P2 receptors in neurons and glial cells could be considered as a potential research direction for moderating neuropathic pain. This review summarized the recently published data and highlighted several TCMs that relieved NP by acting at P2 receptors.

Crosstalk between endoplasmic reticulum stress and anti-viral activities: A novel therapeutic target for COVID-19

The outbreak of COVID-19 caused by 2019–nCov/SARS-CoV-2 has become a pandemic with an urgent need for understanding the mechanisms and identifying a treatment. Viral infections including SARS-CoV are associated with increased levels of reactive oxygen species, disturbances of Ca⁺⁺ caused by unfolded protein response (UPR) mediated by endoplasmic reticulum (ER) stress and is due to the exploitation of virus's own protein i.e., viroporins into the host cells. Several clinical trials are on-going including testing Remdesivir (anti-viral), Chloroquine and Hydroxychloroquine derivatives (anti-malarial drugs) etc. Unfortunately, each drug has specific limitations. Herein, we review the viral protein involvement to activate ER stress transducers (IRE-1, PERK, ATF-6) and their downstream signals; and evaluate combination therapies for COVID-19 mediated ER stress alterations. Melatonin is an immunoregulator, anti-pyretic, antioxidant, anti-inflammatory and ER stress modulator during viral infections. It enhances protective mechanisms for respiratory tract disorders. Andrographolide, isolated from Andrographis paniculata, has versatile biological activities including immunomodulation and determining SARS-CoV-2 binding site. Considering the properties of both compounds in terms of anti-inflammatory, antioxidant, anti-pyrogenic, anti-viral and ER stress modulation and computational approaches revealing andrographolide docks with the SARS-CoV2 binding site, we predict that this combination therapy may have potential utility against COVID-19.

The role and pharmacological properties of the P2X7 receptor in neuropathic pain

Neuropathic Pain (NPP) is caused by direct or indirect damage to the nervous system and is a common symptom of many diseases. Clinically, drugs are usually used to suppress pain, such as (lidocaine, morphine, etc.), but the effect is short-lived, poor analgesia, and there are certain dependence and side effects. Therefore, the investigation of the treatment of NPP has become an urgent problem in medical, attracting a lot of research attention. P2X7 is dependent on Adenosine triphosphate (ATP) ion channel receptors and has dual functions for the development of nerve damage and pain. In this review, we explored the link between the P2X7 receptor (P2X7R) and NPP, providing insight into the P2X7R and NPP, discussing the pathological mechanism of P2 X7R in NPP and the biological characteristics of P2X7R antagonist inhibiting its over-expression for the targeted therapy of NPP.

β-Caryophyllene, a CB2-Receptor-Selective Phytocannabinoid, Suppresses Mechanical Allodynia in a Mouse Model of Antiretroviral-Induced Neuropathic Pain

Neuropathic pain associated with nucleoside reverse transcriptase inhibitors (NRTIs), therapeutic agents for human immunodeficiency virus (HIV), responds poorly to available drugs. Smoked cannabis was reported to relieve HIV-associated neuropathic pain in clinical trials. Some constituents of cannabis (Cannabis sativa) activate cannabinoid type 1 (CB1) and cannabinoid type 2 (CB2) receptors. However, activation of the CB1 receptor is associated with side effects such as psychosis and physical dependence. Therefore, we investigated the effect of β-caryophyllene (BCP), a CB2-selective phytocannabinoid, in a model of NRTI-induced neuropathic pain. Female BALB/c mice treated with 2′-3′-dideoxycytidine (ddC, zalcitabine), a NRTI, for 5 days developed mechanical allodynia, which was prevented by cotreatment with BCP, minocycline or pentoxifylline. A CB2 receptor antagonist (AM 630), but not a CB1 receptor antagonist (AM 251), antagonized BCP attenuation of established ddC-induced mechanical allodynia. β-Caryophyllene prevented the ddC-induced increase in cytokine (interleukin 1 beta, tumor necrosis factor alpha and interferon gamma) transcripts in the paw skin and brain, as well as the phosphorylation level of Erk1/2 in the brain. In conclusion, BCP prevents NRTI-induced mechanical allodynia, possibly via reducing the inflammatory response, and attenuates mechanical allodynia through CB2 receptor activation. Therefore, BCP could be useful for prevention and treatment of antiretroviral-induced neuropathic pain.

Antiviral Activity Against Infectious Bronchitis Virus and Bioactive Components of Hypericum perforatum L

Hypericum perforatum L., also known as Saint John’s Wort, has been well studied for its chemical composition and pharmacological activity. In this study, the antiviral activities of H. perforatum on infectious bronchitis virus (IBV) were evaluated in vitro and in vivo for the first time. The results of in vitro experiments confirmed that the antiviral component of H. perforatum was ethyl acetate extraction section (HPE), and results showed that treatment with HPE significantly reduced the relative messenger ribonucleic acid (mRNA) expression and virus titer of IBV, and reduced positive green immunofluorescence signal of IBV in chicken embryo kidney (CEK) cells. HPE treatment at doses of 480–120 mg/kg for 5 days, reduced IBV induced injury in the trachea and kidney, moreover, reduced the mRNA expression level of IBV in the trachea and kidney in vivo. The mRNA expression levels of IL-6, tumor necrosis factor alpha (TNF-α), and nuclear factor kappa beta (NF-κB) significantly decreased, but melanoma differentiation-associated protein 5 (MDA5), mitochondrial antiviral signaling gene, interferon alpha (IFN-α), and interferon beta (IFN-β) mRNA levels significantly increased in vitro and in vivo. Our findings demonstrated that HPE had significant anti-IBV effects in vitro and in vivo, respectively. In addition, it is possible owing to up-regulate mRNA expression of type I interferon through the MDA5 signaling pathway and down-regulate mRNA expression of IL-6 and TNF-α via the NF-κB signaling pathway. Moreover, the mainly active compositions of HPE analyzed by high-performance liquid chromatography/electrospray ionization–mass spectroscopy (ESI-MS) are hyperoside, quercitrin, quercetin, pseudohypericin, and hypericin, and a combination of these compounds could mediate the antiviral activities. This might accelerate our understanding of the antiviral effect of H. perforatum and provide new insights into the development of effective therapeutic strategies.

Voltage-gated sodium channel 1.7 expression decreases in dorsal root ganglia in a spinal nerve ligation neuropathic pain model

The role of the voltage-gated sodium channel 1.7 (Nav1.7) is unclear in models of neuropathic pain induced by nerve injury. In the present study, we measured expression levels of Nav1.7 in two distinct neuropathic pain models: spinal nerve ligation (SNL) and chronic constriction injury (CCI). In the SNL model, both mRNA and protein levels of Nav1.7 were markedly lower in the L5 dorsal root ganglia (DRG) but were significantly higher in the L4 DRG. Nav1.7 protein levels were notably higher in both L4 and L5 DRGs under CCI conditions. We found that excessive damage of L5 nerves such as SNL reduced expression levels of Nav1.7 in the injured L5 DRG and activated the adjacent uninjured DRG, resulting in Nav1.7 level increases in the adjacent L4 DRG. We confirmed again that Nav1.7 was closely related to neuropathic pain induced by nerve injury. More importantly, our results suggest that tracing the molecular changes exclusively in the L5 DRG in SNL model may not completely explain the pain mechanism; it is necessary to study the adjacent uninjured L4 DRG.

Role of hesperidin in P2X3 receptor-mediated neuropathic pain in the dorsal root ganglia

Aim: This study investigated whether the neuronal P2X3 receptor in rat dorsal root ganglia (DRG) mediated the effects of hesperidin on neuropathic pain. Materials and methods: The chronic constriction injury (CCI) model was used as a model of neuropathic pain. The mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) were measured. The mRNA and protein expression levels were assayed by real-time RT-PCR and Western blotting. Results: The results showed that mechanical and thermal hyperalgesia in the CCI rats were increased as compared to those in the sham group. The expression levels of P2X3 mRNA and protein in CCI rats were higher than those in the sham group. Dual-labelling immunofluorescence showed that the elevated P2X3 receptor was co-expressed with the neuronal marker NeuN in the DRG of CCI rats. Hesperidin treatment decreased both the mechanical and thermal hyperalgesia, and upregulated P2X3 expression in the CCI rats. Hesperidin treatment also reduced the ERK1/2 phosphorylation in the DRG of CCI rats. Moreover, hesperidin inhibited the P2X3 agonist ATP-induced currents in HEK293 cells transfected with the P2X3 plasmid. Therefore, hesperidin treatment could reverse the elevated expression of neuronal P2X3 receptor and reduce the activation of ERK1/2 in the DRG of CCI rats. Conclusions: Our findings suggested that hesperidin inhibited the nociceptive transmission mediated by the P2X3 receptor in neurons of DRG, and thus, relieved the mechanical and thermal hyperalgesia in CCI rats.