J-2156, a somatostatin receptor type 4 agonist, alleviates mechanical hyperalgesia in a rat model of chronic low back pain

Drug effects on neuropeptides and their receptors: Big hopes but moderate success in the treatment of chronic pain

Neuropeptides, including tachykinins, CGRP, and somatostatin, are localized in a peptidergic subgroup of nociceptive primary afferent neurons. Tachykinins and CGRP are pronociceptive, somatostatin is an antinociceptive mediator. Intensive drug research has been performed to develop tachykinin and CGRP antagonists, and somatostatin agonists as analgesics. CGRP receptor antagonists are efficacious and well-tolerated drugs in migraine. Monoclonal antibodies against CGRP or its receptor are used for the prophylactic treatment of migraine. Tachykinin NK1 receptor antagonists failed as analgesics but are used for chemotherapy-induced nausea and vomiting. New, orally active somatostatin 4 receptor agonists are promising drug candidates for treating various pain conditions.

J-2156, a small molecule somatostatin type 4 receptor agonist, alleviated hindpaw hypersensitivity in the streptozotocin-induced rat model of painful diabetic neuropathy but with a 2-fold decrease in potency at an advanced stage in the model, mimicking morphine

There is a large unmet need for novel pain-killers to improve relief of painful diabetic neuropathy (PDN). Herein, we assessed the efficacy of the somatostatin type 4 (SST4) receptor agonist, J-2156, for relief of PDN in rats. Diabetes was induced with streptozotocin (STZ; 70 mg/kg) and bilateral hindpaw hypersensitivity was fully developed by 8-week post-STZ. In the intervals, 8-12-weeks (morphine-sensitive phase; Phase 1) and 16-18-weeks (morphine-hyposensitive phase; Phase 2) post-STZ, rats received a single dose of intraperitoneal (i.p.) J-2156 (10, 20, 30 mg/kg), gabapentin (100 mg/kg i.p.), subcutaneous morphine (1 mg/kg) or vehicle. Hindpaw withdrawal thresholds (PWTs) were assessed using von Frey filaments pre-dose and at regular intervals over 3-h post-dose. In Phase 1, J-2156 at 30 mg/kg evoked significant anti-allodynia in the hindpaws with maximal effect at 1.5 h compared with 1 h for gabapentin and morphine. The durations of action for all three compounds were greater than 3 h. The corresponding mean (±SEM) extent and duration of anti-allodynia (ΔPWT AUC) for gabapentin did not differ significantly from that for J-2156 (30 mg/kg) or morphine. However, in Phase 2, the ΔPWT AUC for morphine was reduced to approximately 25% of that in Phase 1, mirroring our previous work. Similarly, the mean (±SEM) ΔPWT AUC for J-2156 (30 mg/kg) in Phase 2 was approximately 45% of that for Phase 1 whereas for gabapentin the mean (±SEM) ΔPWT AUCs did not differ significantly (p > 0.05) between the two phases. Our findings further describe the preclinical pain relief profile of J-2156 and complement previous work in rat models of inflammatory pain, neuropathic pain and low back pain. SST4 receptor agonists hold promise as novel therapeutics for the relief of PDN, a type of peripheral neuropathic pain that is often intractable to relief with clinically used drug treatment options.

Pharmacological Characterization of Veldoreotide as a Somatostatin Receptor 4 Agonist

Veldoreotide, a somatostatin analogue, binds to the somatostatin receptors (SSTR) 2, 4, and 5. The current aim was to assess its pharmacological activity as an SSTR4 agonist. G-protein signaling was assessed using a fluorescence-based membrane potential assay in human embryonic kidney 293 (HEK293) cells stably co-expressing G-protein-coupled inwardly rectifying potassium 2 channels and the individual SSTR2, SSTR4, and SSTR5, and in human BON-1 cells stably expressing these SSTRs. Veldoreotide effects on chromogranin A (CgA) secretion and cell proliferation were examined in BON-1 cells. In HEK293 transfected cells, veldoreotide showed a high efficacy for activating the SSTR4; octreotide and pasireotide had little activity (E_max, 99.5% vs. 27.4% and 52.0%, respectively). Veldoreotide also activated SSTR2 and SSTR5 (E_max, 98.4% and 96.9%, respectively). In BON-1 cells, veldoreotide activated SSTR2, SSTR4, and SSTR5 with high potency and efficacy. CgA secretion was decreased to a greater degree in the BON-1 cells expressing SSTR4 versus the cells expressing SSTR2 and SSTR5 (65.3% vs. 80.3% and 77.6%, respectively). In the BON-1 cells expressing SSTR4, veldoreotide inhibited cell proliferation more than somatostatin SS-14 (71.2% vs. 79.7%) and to a similar extent as the SSTR4 agonist J-2156 in the presence of SSTR2 and SSTR5 antagonists. Veldoreotide is a full agonist of SSTR2, SSTR4, and SSTR5.

Human Somatostatin SST4 Receptor Transgenic Mice: Construction and Brain Expression Pattern Characterization

Somatostatin receptor subtype 4 (SST₄) has been shown to mediate analgesic, antidepressant and anti-inflammatory functions without endocrine actions; therefore, it is proposed to be a novel target for drug development. To overcome the species differences of SST₄ receptor expression and function between humans and mice, we generated an SST₄ humanized mouse line to serve as a translational animal model for preclinical research. A transposon vector containing the hSSTR4 and reporter gene construct driven by the hSSTR4 regulatory elements were created. The vector was randomly inserted in Sstr4-deficient mice. hSSTR4 expression was detected by bioluminescent in vivo imaging of the luciferase reporter predominantly in the brain. RT-qPCR confirmed the expression of the human gene in the brain and various peripheral tissues consistent with the in vivo imaging. RNAscope in situ hybridization revealed the presence of hSSTR4 transcripts in glutamatergic excitatory neurons in the CA1 and CA2 regions of the hippocampus; in the GABAergic interneurons in the granular layer of the olfactory bulb and in both types of neurons in the primary somatosensory cortex, piriform cortex, prelimbic cortex and amygdala. This novel SST₄ humanized mouse line might enable us to investigate the differences of human and mouse SST₄ receptor expression and function and assess the effects of SST₄ receptor agonist drug candidates.

Characterisation of a rat model of mechanical low back pain at an advanced stage using immunohistochemical methods

Chronic low back pain (LBP) has high prevalence in the adult population which is associated with enormous disability. Hence, our aim was to further characterise our LBP rat model by using immunohistological and immunohistochemical methods at an advanced stage (day 49) of the model. Male Sprague-Dawley rats were anaesthetised and their lumbar L4/L5 and L5/L6 intervertebral discs (IVDs) were punctured (0.5 mm outer diameter, 2 mm-deep) 10 times per disc. Sham-rats underwent similar surgery, but no discs were punctured. For LBP- but not sham-rats, noxious pressure hyperalgesia was fully developed in the lumbar axial deep tissues on day 21 post-surgery, which was maintained until at least day 49. In the lumbar (L4-L6) dorsal root ganglia (DRGs), somatostatin (SRIF) and the somatostatin receptor type 4 (SST4 receptor) were co-localised with substance P and IB4, markers of small diameter unmyelinated peptidergic and non-peptidergic C-fibres respectively as well as with NF200, a marker of medium to large diameter neurons. On day 49, there was increased expression of SRIF but not the somatostatin receptor type 4 (SST4 receptor) in the lumbar DRGs and the spinal dorsal horns. There were increased DRG expression levels of the putative pro-nociceptive mediators: phosphorylated p38 (pp38) mitogen-activated protein kinase (MAPK) and phosphorylated p44/p42 MAPK (pp44/pp42 MAPK) as well as pp38 MAPK expression levels in the lumbar spinal cord. Taken together, the increased expression of SRIF in the lumbar DRGs and spinal cord and its co-localisation with nociceptive fibres in DRG sections suggest a potential role of SRIF in modulating chronic mechanical LBP.

Assessment of the anti-hyperalgesic efficacy of J-2156, relative to clinically available analgesic/adjuvant agents in a rat model of mild to moderate chronic mechanical low back pain (LBP)

Chronic mechanical low back pain (cLBP) is a leading cause of disability and a major socio-economic burden internationally. The lifetime prevalence of non-specific LBP is approximately 84%, with the prevalence of cLBP at about 23%. Clinically available analgesic/adjuvant medications often provide inadequate pain relief in patients experiencing cLBP. Hence, the urgency for discovery of effective and better tolerated medications. Fourteen days after the induction of five shallow annular punctures (5X) in the lumbar intervertebral discs at L4/L5 and L5/L6 in male Sprague-Dawley rats, mechanical hyperalgesia was fully developed in the lumbar axial deep tissues at L4/L5 (primary) and L1 (secondary). Importantly, mechanical allodynia in the hindpaws was absent. From day 28, we assessed the face validity of our mild to moderate LBP-5X rat model using four clinically available analgesic/adjuvant drugs, namely gabapentin, morphine, meloxicam and amitriptyline relative to vehicle. Additionally, the anti-hyperalgesic effects of J-2156, a highly selective small molecule somatostatin type 4 receptor agonist was assessed. Single i.p. bolus doses of gabapentin and meloxicam at the highest doses tested (100 and 30 mg/kg, respectively) alleviated secondary hyperalgesia (L1) but not primary hyperalgesia (L4/5). Morphine at 1 mg/kg alleviated both primary and secondary hyperalgesia in these tissues, whereas amitriptyline at the doses tested, lacked efficacy. These findings attest to the face validity of our model. J-2156 at 10 and 30 mg/kg alleviated secondary hyperalgesia in the lumbar axial deep tissues at L1 with a non-significant trend for relief of primary hyperalgesia in the corresponding tissues at L4/L5 in these animals.

Central mechanisms of pain in orofacial pain patients: Implications for management

BACKGROUND

Central sensitization (CS) is a form of neuroplasticity characterized by changes in the neural sensitivity, responsiveness, and/or output that are not contingent on peripheral input nor activity-dependent. CS is characterized by activation of unmyelinated C-fibers resulting in a cascade of events at molecular and cellular levels which eventuate into generation of synaptic currents at rest. CS, therefore, contributes to heightened generalized pain sensitivity, further complicates the process of reaching a diagnosis, and increases the possibility of treatment failure. BODY: Trigeminal nerve is the main sensory supplier of the anterior part of the head, including the intraoral structures. Primary afferent nociceptors of the trigeminal nerve and low threshold mechanoreceptors synapse with wide dynamic range (WDR) neurons in the pons. This multifaceted network of nerve interactions which is further complicated by the modulatory circuits that can suppress or heighten the activity of WDR neurons is one of the main contributors to CS. The importance of CS in orofacial pain disorders is emphasized in the context of chronic pain development. As for all chronic pain conditions, it is crucial to consider the biopsychosocial aspects of chronic orofacial pain in managing this diverse group of conditions. This review highlights current understanding of the biopsychosocial model and central mechanisms contributing to the pathogenesis of chronic orofacial pain.

Identification of significant gene biomarkers of low back pain caused by changes in the osmotic pressure of nucleus pulposus cells

The incidence of intervertebral disc (IVD) degeneration disease, caused by changes in the osmotic pressure of nucleus pulposus (NP) cells, increases with age. In general, low back pain is associated with IVD degeneration. However, the mechanism and molecular target of low back pain have not been elucidated, and there are no data suggesting specific biomarkers of low back pain. Therefore, the research aims to identify and verify the significant gene biomarkers of low back pain. The differentially expressed genes (DEGs) were screened in the Gene Expression Omnibus (GEO) database, and the identification and analysis of significant gene biomarkers were also performed with various bioinformatics programs. A total of 120 patients with low back pain were recruited. Before surgery, the degree of pain was measured by the numeric rating scale (NRS), which enables comparison of the pain scores from individuals. After surgery, IVD tissues were obtained, and NP cells were isolated. The NP cells were cultured in two various osmotic media, including iso-osmotic media (293 mOsm/kg H₂O) to account for the morbid environment of NP cells in IVD degeneration disease and hyper-osmotic media (450 mOsm/kg H₂O) to account for the normal condition of NP cells in healthy individuals. The relative mRNA expression levels of CCL5, OPRL1, CXCL13, and SST were measured by quantitative real-time PCR in the in vitro analysis of the osmotic pressure experiments. Finally, correlation analysis and a neural network module were employed to explore the linkage between significant gene biomarkers and pain. A total of 371 DEGs were identified, including 128 downregulated genes and 243 upregulated genes. Furthermore, the four genes (CCL5, OPRL1, SST, and CXCL13) were identified as significant gene biomarkers of low back pain (P < 0.001) based on univariate linear regression, and CCL5 (odds ratio, 34.667; P = 0.003) and OPRL1 (odds ratio, 19.875; P < 0.001) were significantly related to low back pain through multivariate logistic regression. The expression of CCL5 and OPRL1 might be correlated with low back pain in patients with IVD degeneration disease caused by changes in the osmotic pressure of NP cells.

Novel Drug-Like Somatostatin Receptor 4 Agonists are Potential Analgesics for Neuropathic Pain

Somatostatin released from the capsaicin-sensitive sensory nerves mediates analgesic and anti-inflammatory effects via the somatostatin sst4 receptor without endocrine actions. Therefore, sst4 is considered to be a novel target for drug development in pain including chronic neuropathy, which is an emerging unmet medical need. Here, we examined the in silico binding, the sst4-linked G-protein activation on stable receptor expressing cells (1 nM to 10 μM), and the effects of our novel pyrrolo-pyrimidine molecules in mouse inflammatory and neuropathic pain models. All four of the tested compounds (C1-C4) bind to the same binding site of the sst4 receptor with similar interaction energy to high-affinity reference sst4 agonists, and they all induce G-protein activation. C1 is the more efficacious (γ-GTP-binding: 218.2% ± 36.5%) and most potent (EC50: 37 nM) ligand. In vivo testing of the actions of orally administered C1 and C2 (500 µg/kg) showed that only C1 decreased the resiniferatoxin-induced acute neurogenic inflammatory thermal allodynia and mechanical hyperalgesia significantly. Meanwhile, both of them remarkably reduced partial sciatic nerve ligation-induced chronic neuropathic mechanical hyperalgesia after a single oral administration of the 500 µg/kg dose. These orally active novel sst4 agonists exert potent anti-hyperalgesic effect in a chronic neuropathy model, and therefore, they can open promising drug developmental perspectives.