Browse by Audience
Osteoarthritis (OA) is the most prevalent joint disorder associated with severe chronic pain. Although synovial inflammation is well correlated with pain severity, the molecular mechanism responsible for OA pain remains unclear. Here, we show that extracellular miR-21 released from synovial tissue mediates knee OA pain in surgical OA model rats. miR-21 was the most abundant among increased microRNAs (miRNAs) in the synovial tissue. miR-21 was released into extracellular space from the synovial tissue and increased in the synovial fluid. A single intra-articular injection of miR-21 inhibitor exerted long-term analgesia of knee OA pain, whereas miR-21 injection in naive rats caused knee joint pain. miR-21 mutant, which lacks the Toll-like receptor (TLR) binding motif, but not in the seed sequence, did not cause joint pain, suggesting a non-canonical mode of action different from translational repression. Consistent with this, the algesic effect of miR-21 was blocked by antagonizing TLR7. The TLR7 antagonist also exerted a long-lasting analgesic effect on knee OA pain. Therefore, extracellular miR-21 released from synovial tissue mediates knee OA pain through TLR7 activation in surgical OA model rats. Extracellular miRNA in the joint may be a plausible target for pain therapy, providing a novel analgesic strategy for OA.
Learn More >Triptans are the most commonly used acute treatment for migraine. This study evaluated real-world treatment patterns following an initial triptan prescription to understand refill rates and use of non-triptan medications for the acute treatment of migraine.
Learn More >Platinum-based chemotherapy-induced peripheral neuropathy is one of the most common causes of dose reduction and discontinuation of life-saving chemotherapy in cancer treatment; it often causes permanent impairment of quality of life in cancer patients. The mechanisms that underlie this neuropathy are not defined, and effective treatment and prevention measures are not available. Here, we demonstrate that SIRT2 protected mice against cisplatin-induced peripheral neuropathy (CIPN). SIRT2 accumulated in the nuclei of dorsal root ganglion sensory neurons and prevented neuronal cell death following cisplatin treatment. Mechanistically, SIRT2, an NAD+-dependent deacetylase, protected neurons from cisplatin cytotoxicity by promoting transcription-coupled nucleotide excision repair (TC-NER) of cisplatin-induced DNA crosslinks. Consistent with this mechanism, pharmacological inhibition of NER using spironolactone abolished SIRT2-mediated TC-NER activity in differentiated neuronal cells and protection of neurons from cisplatin-induced cytotoxicity and CIPN in mice. Importantly, SIRT2's protective effects were not evident in lung cancer cells in vitro or in tumors in vivo. Taken together, our results identified SIRT2's function in the NER pathway as a key underlying mechanism of preventing CIPN, warranting future investigation of SIRT2 activation-mediated neuroprotection during platinum-based cancer treatment.
Learn More >The activation of the AMP activated protein kinase (AMPK) exerts antinociceptive effects in acute and neuropathic pain models. Mitochondrial open-reading-frame of the twelve S rRNA-c (MOTS-c), a mitochondrial-derived peptide, regulates many biological activities via activating AMPK. However, the role of MOTS-c in the formalin-induced inflammatory nociception remains unclear. In this study, we investigated the role of MOTS-c in the formalin-induced inflammatory nociception. The antinociceptive effect of MOTS-c was assessed by recording the time spent licking paw. The anti-inflammatory effect of MOTS-c was evaluated by detecting the inflammatory cytokine level changes in the mouse serum. Western blot was used to detect the changes of protein phosphorylation levels in the mouse spinal cord. Changes of c-fos expression in the spinal cord were assessed by immunohistochemistry. Our results showed that the intraperitoneal administration of MOTS-c reduced the time spent on licking in phase 2 in a dose-dependent manner in the formalin test. The antinociceptive effects of MOTS-c (50 mg/kg, i.p.) were attenuated by the AMPK antagonist compound C (10 mg/kg, i.p.). MOTS-c (50 mg/kg, i.p.) significantly reduced pro-inflammatory cytokine levels and elevated the level of anti-inflammatory cytokine in mouse serum. In addition, MOTS-c treatment significantly increased AMPKα phosphorylation level and suppressed formalin-induced extracellular signal-regulated kinase (ERK), c-Jun amino-terminal kinases (JNK), and P38 activation and c-fos expression in the mouse spinal cord. These results suggest that systemic administration of MOTS-c exerts antinociceptive and anti-inflammatory effects, at least partially, through activating AMPK pathway and inhibiting MAP kinases-c-fos signaling pathway in the mouse formalin test.
Learn More >Pituitary adenylate cyclase activating polypeptide-38 (PACAP38) may play an important role in primary headaches. Preclinical evidence suggests that PACAP38 modulates trigeminal nociceptive activity mainly through PAC1 receptors while clinical studies report that plasma concentrations of PACAP38 are elevated in spontaneous attacks of cluster headache and migraine and normalize after treatment with sumatriptan. Intravenous infusion of PACAP38 induces migraine-like attacks in migraineurs and cluster-like attacks in cluster headache patients. A rodent-specific PAC1 receptor antibody Ab181 was developed and its effect on nociceptive neuronal activity in the trigeminocervical complex was investigated in vivo in an electrophysiological model relevant to primary headaches. Ab181 is potent and selective at the rat PAC1 receptor and provides near maximum target coverage at 10 mg/kg for more than 48 hours. Without affecting spontaneous neuronal activity, Ab181 effectively inhibits stimulus-evoked activity in the trigeminocervical complex. Immunohistochemical analysis revealed its binding in the trigeminal ganglion and sphenopalatine ganglion but not within the CNS suggesting a peripheral site of action. The pharmacological approach using a specific PAC1 receptor antibody could provide a novel mechanism with a potential clinical efficacy in the treatment of primary headaches.
Learn More >We have previously shown that endogenous adenosine 5'-triphosphate (ATP), via P2X3 and P2X2/3 receptors, plays an essential role in carrageenan-induced articular hyperalgesia model in rats' knee joint. In the present study, we used the rat knee joint incapacitation test, Enzyme-Linked Immunosorbent Assay (ELISA), and myeloperoxidase enzyme activity assay, to test the hypothesis that the activation of P2X3 and P2X2/3 receptors by their agonist induces articular hyperalgesia mediated by the inflammatory mediators bradykinin, prostaglandin, sympathomimetic amines, pro-inflammatory cytokines and by neutrophil migration. We also tested the hypothesis that the activation of P2X3 and P2X2/3 receptors contributes to the articular hyperalgesia induced by the inflammatory mediators belonging to carrageenan inflammatory cascade. The non-selective P2X3 and P2X2/3 receptors agonist αβ-meATP induced a dose-dependent articular hyperalgesia, which was significantly reduced by the selective antagonists for P2X3 and P2X2/3 receptors (A-317491), bradykinin B- (DALBK) or B-receptors (bradyzide), β-(atenolol) or β-adrenoceptors (ICI-118,551), by the pre-treatment with cyclooxygenase inhibitor (indomethacin) or with the nonspecific selectin inhibitor (Fucoidan). αβ-meATP induced the release of pro-inflammatory cytokines TNFα, IL-1β, IL-6, and CINC-1, as well as the neutrophil migration. Moreover, the co-administration of A-317491 significantly reduced the articular hyperalgesia induced by bradykinin, prostaglandin E (PGE), and dopamine. These findings suggest that peripheral P2X3 and P2X2/3 receptors activation induces articular hyperalgesia by an indirect sensitization of the primary afferent nociceptor of rats' knee joint through the release of inflammatory mediators. Further, they also indicate that the activation of these purinergic receptors by endogenous ATP mediates the bradykinin-, PGE-, and dopamine-induced articular hyperalgesia.
Learn More >Gastrin-releasing peptide (GRP) receptor-expressing (GRPR) neurons have a central role in the spinal transmission of itch. Because their fundamental regulatory mechanisms are not yet understood, it is important to determine how such neurons are excited and integrate itch sensations. In this study, we investigated the mechanisms for the activation of itch-responsive GRPR neurons in the spinal dorsal horn (SDH). GRPR neurons expressed the α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) containing the GluR2 subunit. In mice, peripherally elicited histaminergic and non-histaminergic itch was prevented by intrathecal (i.t.) administration of the AMPAR antagonist NBQX, which was consistent with the fact that firing of GRPR neurons in SDH under histaminergic and non-histaminergic itch was completely blocked by NBQX, but not by the GRPR antagonist RC-3095. Because GRP neurons in SDH contain glutamate, we investigated the role of GRP (GRP/Glu) neurons in regulating itch. Chemogenetic inhibition of GRP neurons suppressed both histaminergic and non-histaminergic itch without affecting the mechanical pain threshold. In nonhuman primates, i.t. administration of NBQX also attenuated peripherally elicited itch without affecting the thermal pain threshold. In a mouse model of diphenylcyclopropenone (DCP)-induced contact dermatitis, GRP, GRPR, and AMPAR subunits were upregulated in SDH. DCP-induced itch was prevented by either silencing GRP neurons or ablation of GRPR neurons. Altogether, these findings demonstrate that GRP and glutamate cooperatively regulate GRPR AMPAR neurons in SDH, mediating itch sensation. GRP-GRPR and the glutamate-AMPAR system may play pivotal roles in the spinal transmission of itch in rodents and nonhuman primates.
Learn More >Effective, non-addictive therapeutics for chronic pain remain a critical need. While there are several potential therapeutics that stimulate anti-inflammatory mechanisms to restore homeostasis in the spinal dorsal horn microenvironment, the effectiveness of drugs for neuropathic pain are still inadequate. The convergence of increasing knowledge about the multi-factorial mechanisms underlying neuropathic pain and the mechanisms of drug action from preclinical studies are providing the ability to create pharmaceuticals with better clinical effectiveness. By targeting and activating the peroxisome proliferator-activated receptor gamma subunit (PPARγ), numerous preclinical studies report pleiotropic effects of thiazolidinediones (TDZ) beyond their intended use of increasing insulin, including their anti-inflammatory, renal, cardioprotective, and oncopreventative effects. Several studies find TDZs reduce pain-related behavioral symptoms, including ongoing secondary hypersensitivity driven by central sensitization. Previous studies find increased PPARγ in the spinal cord and brain regions innervated by incoming afferent nerve endings after the induction of neuropathic pain models. PPARγ agonist treatment provides an effective reduction in pain-related behaviors, including anxiety. Data further suggest that improved brain mitochondrial bioenergetics after PPARγ agonist treatment is a key mechanism for reducing hypersensitivity. This review emphasizes two points relevant for the development of better chronic pain therapies. First, employing neuropathic pain models with chronic duration is critical since they can encompass the continuum of molecular and brain circuitry alterations arising over time when pain persists, providing greater relevance to clinical pain syndromes. Assisting in that effort are preclinical models of chronic trigeminal pain syndromes. Secondly, considering the access to nerve and brain neurons and glia across the blood-brain barrier is important. While many therapies have low brain penetrance, a PPARγ agonist with better brain penetrance, ELB00824, has been developed. Purposeful design and recent comparative testing indicate that ELB00824 is extraordinarily efficient and efficacious. ELB00824 provides greatly improved attenuation of pain-related behaviors, including mechanical hypersensitivity, anxiety, and depression in our chronic trigeminal nerve injury models. Physiochemical properties allowing significant brain access and toxicity testing are discussed.
Learn More >The kappa opioid receptor (κOR) is an important target for pain therapeutics to reduce depression and other harmful side effects of existing medications. The analgesic activity is mediated by κOR signaling through the adenylyl cyclase-inhibitory family of Gi protein. Here, we report the three-dimensional (3D) structure for the active state of human κOR complexed with both heterotrimeric Gi protein and MP1104 agonist. This structure resulted from long molecular dynamics (MD) and metadynamics (metaMD) simulations starting from the 3.1-Å X-ray structure of κOR-MP1104 after replacing the nanobody with the activated Gi protein and from the 3.5-Å cryo-EM structure of μOR-Gi complex after replacing the 168 missing residues. Using MD and metaMD we discovered interactions to the Gi protein with strong anchors to two intracellular loops and transmembrane helix 6 of the κOR. These anchors strengthen the binding, contributing to a contraction in the binding pocket but an expansion in the cytoplasmic region of κOR to accommodate G protein. These remarkable changes in κOR structure reveal that the anchors are essential for activation.
Learn More >Clinically, chronic postsurgical pain (CPSP) is very common. Many CPSP patients may experience depression. Thus far, little is known about the mechanism of the comorbidity of CPSP and depression. Ketamine has been confirmed to possess analgesic and rapid antidepressant effects, but it is unclear whether ketamine can relieve the comorbidity of CPSP and depression.
Learn More >