Pain Therapeutics Research Articles

Prenatal alcohol exposure promotes NLRP3 inflammasome-dependent immune actions following morphine treatment and paradoxically prolongs nerve injury-induced pathological pain in female mice.

Neuroimmune dysregulation from prenatal alcohol exposure (PAE) may contribute to neurological deficits associated with fetal alcohol spectrum disorders (FASD). PAE is a risk factor for developing peripheral immune and spinal glial sensitization and release of the proinflammatory cytokine IL-1β, which lead to neuropathic pain (allodynia) from minor nerve injury. Although morphine acts on μ-opioid receptors, it also activates immune receptors, TLR4, and the NLRP3 inflammasome that induces IL-1β. We hypothesized that PAE induces NLRP3 sensitization by morphine following nerve injury in adult mice. We used an established moderate PAE paradigm, in which adult PAE and non-PAE control female mice were exposed to a minor sciatic nerve injury, and subsequent allodynia was measured using the von Frey fiber test. In control mice with standard sciatic damage or PAE mice with minor sciatic damage, the effects of the NLRP3 inhibitor, MCC950, were examined during chronic allodynia. Additionally, minor nerve-injured mice were treated with morphine, with or without MCC950. Invitro studies examined the TLR4-NLRP3-dependent proinflammatory response of peripheral macrophages to morphine and/or lipopolysaccharide, with or without MCC950. Mice with standard sciatic damage or PAE mice with minor sciatic damage developed robust allodynia. Blocking NLRP3 activation fully reversed allodynia in both control and PAE mice. Morphine paradoxically prolonged allodynia in PAE mice, while control mice with minor nerve injury remained stably non-allodynic. Allodynia resolved sooner in nerve-injured PAE mice without morphine treatment than in morphine-treated mice. MCC950 treatment significantly shortened allodynia in morphine-treated PAE mice. Morphine potentiated IL-1β release from TLR4-activated PAE immune cells, while MCC950 treatment greatly reduced it. In female mice, PAE prolongs allodynia following morphine treatment through NLRP3 activation. TLR4-activated PAE immune cells showed enhanced IL-1β release with morphine via NLRP3 actions. Similar studies are needed to examine the adverse impact of morphine in males with PAE. These results are predictive of adverse responses to opioid pain therapeutics in individuals with FASD.

Gene Transcription Data Are Correlated with Pain-Related Phenotypic Traits in Individuals with Sickle Cell Disease

Background: Sickle cell disease (SCD) pain is acute and chronic and associated with significant morbidity across the lifespan. Interindividual variability in SCD pain exists, despite the same hemoglobin gene defect. The biology that explains this variability is not well understood, which is a barrier to novel analgesics and disease modifying therapy. Our prior work used plasma-based gene transcription via a peripheral blood mononuclear cell (PBMC) reporter assay to identify differentially expressed transcripts between individuals with SCD and healthy Black controls. In this study, we sought to provide clinical meaning to gene transcription data in the context of SCD pain. We hypothesized that we could identify gene modules using Weighted Gene Co-expression Network Analysis (WGCNA) that are significantly associated with pain-related phenotypic traits in individuals with SCD. Methods: We leveraged our prior data from 149 individuals with SCD (median age 13.6, IQR 9.3-17.1) during baseline health and 45 healthy Black controls to discover differentially expressed transcripts between the two groups. Using our well-developed assay, PBMCs from a healthy blood donor functioned as reporter cells to plasma-born factors present in individuals with SCD during baseline health and controls. Gene expression in PBMCs was measured with Affymetrix array. Using our pre-defined filtering criteria of retaining transcripts differentially expressed between individuals with SCD and controls that exhibit a fold change >1.4, ANOVA p-value of <0.05 and an FDR <10%, we identified 3028 genes differentially expressed between individuals with SCD and controls. We then applied this gene list to an independent cohort of newly recruited individuals with SCD during baseline health. Plasma-based transcription using our PBMC reporter cell assay was conducted in the new independent cohort using identical methods to our derivation cohort. The gene list (n=3028) generated from our derivation cohort was used as the input list for WGCNA to investigate the association of gene modules with pain-related phenotypic traits in our new cohort. Clinical pain-related data included: patient-reported outcomes (PROs) (i.e., PROMIS Pain Interference, Pain Behavior, Pain Quality-Neuropathic, PedsQL Pain Impact), acute care pain visits, chronic pain phenotyping. PROs were scored as per developers' guidelines; means and final PRO scores were used as WGCNA traits. Descriptive statistics summarized clinical variables. WGCNA was used to assess the correlation of co-expressed gene modules with SCD pain-related phenotypic data. The correlation coefficient generated by WGCNA is between the module eigengene (i.e., first principal component of a principal component analysis which is representative of expression profiles of all genes within that module) and the phenotypic trait. We retained modules with significant correlations of ≥0.3 between these modules and SCD pain-related data. Database for Annotation, Visualization and Integrated Discovery (DAVID) was used to identify biological processes represented by the differentially expressed transcripts within each module. Results: A total of 87 individuals with SCD at baseline health were included in our current cohort. Mean age was 14.5 (SD 14.2) years, 51.7% were female and 70.1% had HbSS/HbSβ 0thal. Our WGCNA analyses identified 11 modules (Figure 1). Of these, 10 exhibited significant correlations with pain-related phenotypic traits that met our module inclusion criteria of ≥0.3. Modules with the highest number of significant pain-related trait correlations included: 1) pink, black, blue (4 each) and 2) lime, brown, red, turquoise (3 each). DAVID analyses of the biological processes contained within the modules significantly associated with pain-related traits are displayed in Figure 1. A strong immune-mediated component was found across the modules significantly associated with pain-related traits. Conclusions: We identified gene modules significantly associated with pain-related phenotypic data. These analyses give clinical meaning to gene expression data which is imperative for translational SCD pain research. A strong immune-mediated component was identified in the modules significantly associated with pain. The transcriptional data and pathways identified can be leveraged to investigate SCD pain biology and discover targets for novel pain therapeutics.

Investigating cannabinoids as P2X purinoreceptor 4 ligands by using surface plasmon resonance and computational docking

P2X purinoceptor 4 (P2X4) is an ATP-gated ion channel receptor with diverse neurophysiological functions, and P2X4 modulators hold promise as potential therapeutics for neuropathic pain, neuroinflammation, and neurodegenerative diseases. While several cannabinoids have been reported as modulators of purinoreceptors, their specific purinoreceptor-binding characteristics remain elusive. In this study, we established a comprehensive workflow that included a binding screening platform and a novel surface plasmon resonance (SPR) competitive assay, complemented by computational docking, to identify potential P2X4 binders among a panel of twenty-eight cannabinoids. Through SPR, we determined the binding affinities of cannabinoids (KD values ranging from 3.4 × 10−4 M to 1 × 10−6 M), along with two known P2X4 antagonists, BX430 (KD = 4.5 × 10−6 M) and 5-BDBD (KD = 7.8 × 10−6 M). The competitive SPR assay validated that BX430 and 5-BDBD acted as non-competitive binders with P2X4. In the following competitive assays, two cannabinoids including cannabidiol (CBD) and cannabivarin (CBV) were identified as competitive P2X4-binders with 5-BDBD, while the remaining cannabinoids exhibited non-competitive binding with either BX430 or 5-BDBD. Our molecular docking experiments further supported these findings, demonstrating that both CBD and CBV shared identical binding sites with residues in the 5-BDBD binding pocket on P2X4. In conclusion, this study provides valuable insights into the P2X4-binding affinity of cannabinoids through SPR and sheds light on the interactions between cannabinoids (CBD and CBV) and P2X4.

Ih current stabilizes excitability in rodent DRG neurons and reverses hyperexcitability in a nociceptive neuron model of inherited neuropathic pain.

We show here that hyperpolarization-activated current (Ih ) unexpectedly acts to inhibit the activity of dorsal root ganglion (DRG) neurons expressing WT Nav1.7, the largest inward current and primary driver of DRG neuronal firing, and hyperexcitable DRG neurons expressing a gain-of-function Nav1.7 mutation that causes inherited erythromelalgia (IEM), a human genetic model of neuropathic pain. In this study we created a kinetic model of Ih and used it, in combination with dynamic-clamp, to study Ih function in DRG neurons. We show, for the first time, that Ih increases rheobase and reduces the firing probability in small DRG neurons, and demonstrate that the amplitude of subthreshold oscillations is reduced by Ih . Our results show that Ih , due to slow gating, is not deactivated during action potentials (APs) and has a striking damping action, which reverses from depolarizing to hyperpolarizing, close to the threshold for AP generation. Moreover, we show that Ih reverses the hyperexcitability of DRG neurons expressing a gain-of-function Nav1.7 mutation that causes IEM. In the aggregate, our results show that Ih unexpectedly has strikingly different effects in DRG neurons as compared to previously- and well-studied cardiac cells. Within DRG neurons where Nav1.7 is present, Ih reduces depolarizing sodium current inflow due to enhancement of Nav1.7 channel fast inactivation and creates additional damping action by reversal of Ih direction from depolarizing to hyperpolarizing close to the threshold for AP generation. These actions of Ih limit the firing of DRG neurons expressing WT Nav1.7 and reverse the hyperexcitability of DRG neurons expressing a gain-of-function Nav1.7 mutation that causes IEM. KEY POINTS: Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels, the molecular determinants of hyperpolarization-activated current (Ih ) have been characterized as a 'pain pacemaker', and thus considered to be a potential molecular target for pain therapeutics. Dorsal root ganglion (DRG) neurons express Nav1.7, a channel that is not present in central neurons or cardiac tissue. Gain-of-function mutations (GOF) of Nav1.7 identified in inherited erythromelalgia (IEM), a human genetic model of neuropathic pain, produce DRG neuron hyperexcitability, which in turn produces severe pain. We found that Ih increases rheobase and reduces firing probability in small DRG neurons expressing WT Nav1.7, and demonstrate that the amplitude of subthreshold oscillations is reduced by Ih . We also demonstrate that Ih reverses the hyperexcitability of DRG neurons expressing a GOF Nav1.7 mutation (L858H) that causes IEM. Our results show that, in contrast to cardiac cells and CNS neurons, Ih acts to stabilize DRG neuron excitability and prevents excessive firing.

Optogenetic inhibition of spinal inhibitory neurons facilitates mechanical responses of spinal wide dynamic range neurons and causes mechanical hypersensitivity

Inhibitory interneurons in the spinal dorsal horn (DH) play a major role in regulating innocuous and noxious information. Reduction in inhibitory synaptic transmission is thought to contribute to the development of touch-evoked pain (allodynia), a common symptom of neuropathic pain. However, it is not fully understood how inhibitory neurons in the DH regulate sensory responses in surrounding neurons and modulate sensory transmission. In this study, we established a novel experimental method to analyze temporal activity of DH neurons during the optogenetically induced disinhibition state by combining extracellular recording and optogenetics. We investigated how specific and temporally restricted dysfunction of DH inhibitory neurons affected spinal neuronal activities evoked by cutaneous mechanical stimulation. In behavioral experiments, the specific and temporally restricted spinal optogenetic suppression of DH inhibitory neurons induced mechanical hypersensitivity. Furthermore, this manipulation enhanced the mechanical responses of wide dynamic range (WDR) neurons, which are important for pain transmission, in response to brush and von Frey stimulation but not in response to nociceptive pinch stimulation. In addition, we examined whether a neuropathic pain medication, mirogabalin, suppressed these optogenetically induced abnormal pain responses. We found that mirogabalin treatment attenuated the abnormal firing responses of WDR neurons and mechanical hypersensitivity. These results suggest that temporally restricted and specific reduction of spinal inhibitory neuronal activity facilitates the mechanical responses of WDR neurons, resulting in neuropathic-like mechanical allodynia which can be suppressed by mirogabalin. Our optogenetic methods could be useful for developing novel therapeutics for neuropathic pain.

Urokinase-type Plasminogen Activator-induced Mouse Back Pain Model.

A model of persisting lower back pain can be induced in mice with the simple methodology described herein. Step-by-step methods for simple, rapid induction of a persisting back pain model in mice are provided here using an injection of urokinase-type plasminogen activator (urokinase), a serine protease present in humans and other animals. The methodology for induction of persisting lower back pain in mice involves a simple injection of urokinase along the ligamentous insertion region of the lumbar spine. The urokinase inflammatory agent activates plasminogen to plasmin. Typically, the model can be induced within 10 min and hypersensitivity persists for at least 8 weeks. Hypersensitivity, gait disturbance, and other standard anxiety- and depression-like measures can be tested in the persisting model.Back pain is the most prevalent type of pain. To improve awareness of back pain, the International Association for the Study of Pain (IASP) named 2021 the "Global Year about Back Pain" and 2022 the "Global Year for Translating Pain Knowledge to Practice." One limitation of the therapeutic advancement of pain therapeutics is the lack of suitable models for testing persistent and chronic pain. Thefeatures of this modelare suitable for testing potential therapeutics aimed at the reduction of back pain and its ancillary characteristics, contributing to IASP's naming 2022 as the Global Year for Translating Pain Knowledge to Practice.

Endometriosis in the era of precision medicine and impact on sexual and reproductive health across the lifespan and in diverse populations.

Endometriosis is a common estrogen-dependent disorder wherein uterine lining tissue (endometrium) is found mainly in the pelvis where it causes inflammation, chronic pelvic pain, pain with intercourse and menses, and infertility. Recent evidence also supports a systemic inflammatory component that underlies associated co-morbidities, e.g., migraines and cardiovascular and autoimmune diseases. Genetics and environment contribute significantly to disease risk, and with the explosion of omics technologies, underlying mechanisms of symptoms are increasingly being elucidated, although novel and effective therapeutics for pain and infertility have lagged behind these advances. Moreover, there are stark disparities in diagnosis, access to care, and treatment among persons of color and transgender/nonbinary identity, socioeconomically disadvantaged populations, and adolescents, and a disturbing low awareness among health care providers, policymakers, and the lay public about endometriosis, which, if left undiagnosed and under-treated can lead to significant fibrosis, infertility, depression, and markedly diminished quality of life. This review summarizes endometriosis epidemiology, compelling evidence for its pathogenesis, mechanisms underlying its pathophysiology in the age of precision medicine, recent biomarker discovery, novel therapeutic approaches, and issues around reproductive justice for marginalized populations with this disorder spanning the past 100 years. As we enter the next revolution in health care and biomedical research, with rich molecular and clinical datasets, single-cell omics, and population-level data, endometriosis is well positioned to benefit from data-driven research leveraging computational and artificial intelligence approaches integrating data and predicting disease risk, diagnosis, response to medical and surgical therapies, and prognosis for recurrence.

Monoacylglycerol Lipase Protects the Presynaptic Cannabinoid 1 Receptor from Desensitization by Endocannabinoids after Persistent Inflammation.

Cannabinoid-targeted pain therapies are increasing with the expansion of cannabis legalization, however, their efficacy may be limited by pain-induced adaptations in the cannabinoid system. Cannabinoid receptor subtype 1 (CB1R) inhibition of spontaneous, GABAergic miniature IPSCs (mIPSCs) and evoked IPSCs (eIPSCs) in the ventrolateral periaqueductal gray (vlPAG) were compared in slices from naive and inflamed male and female Sprague Dawley rats. Complete Freund's Adjuvant (CFA) injections into the hindpaw induced persistent inflammation. In naive rats, exogenous cannabinoid agonists robustly reduce both eIPSCs and mIPSCs. After 5-7 d of inflammation, the effects of exogenous cannabinoids are significantly reduced because of CB1R desensitization via GRK2/3, as function is recovered in the presence of the GRK2/3 inhibitor, Compound 101 (Cmp101). Inhibition of GABA release by presynaptic μ-opioid receptors in the vlPAG does not desensitize with persistent inflammation. Unexpectedly, while CB1R desensitization significantly reduces the inhibition produced by exogenous agonists, depolarization-induced suppression of inhibition protocols that promote 2-arachidonoylglycerol (2-AG) synthesis exhibit prolonged CB1R activation after inflammation. 2-AG tone is detected in slices from CFA-treated rats when GRK2/3 is blocked, suggesting an increase in 2-AG synthesis after persistent inflammation. Inhibiting 2-AG degradation with the monoacylglycerol lipase (MAGL) inhibitor JZL184 during inflammation results in the desensitization of CB1Rs by endocannabinoids that is reversed with Cmp101. Collectively, these data indicate that persistent inflammation primes CB1Rs for desensitization, and MAGL degradation of 2-AG protects CB1Rs from desensitization in inflamed rats. These adaptations with inflammation have important implications for the development of cannabinoid-based pain therapeutics targeting MAGL and CB1Rs.SIGNIFICANCE STATEMENT Presynaptic G-protein-coupled receptors are resistant to desensitization. Here we find that persistent inflammation increases endocannabinoid levels, priming presynaptic cannabinoid 1 receptors for desensitization on subsequent addition of exogenous agonists. Despite the reduced efficacy of exogenous agonists, endocannabinoids have prolonged efficacy after persistent inflammation. Endocannabinoids readily induce cannabinoid 1 receptor desensitization if their degradation is blocked, indicating that endocannabinoid concentrations are maintained at subdesensitizing levels and that degradation is critical for maintaining endocannabinoid regulation of presynaptic GABA release in the ventrolateral periaqueductal gray during inflammatory states. These adaptations with inflammation have important implications for the development of cannabinoid-based pain therapies.

Curcumin Stereoisomer, Cis-Trans Curcumin, as a Novel Ligand to A1 and A3 Adenosine Receptors.

Adenosine receptors (ARs) are being explored to generate non-opioid pain therapeutics. Vanilloid compounds, curcumin, capsaicin, and vanillin possess antinociceptive properties through their interactions with the transient receptor potential channel family. However, their binding with adenosine receptors has not been well studied. The hypothesis in this study was that a vanilloid compound, cis-trans curcumin (CTCUR), binds to each of the two Gi-linked AR subtypes (A1AR and A3AR). CTCUR was synthesized from curcumin (CUR) using the cavitand-mediated photoisomerization technique. The cell lines transfected with the specific receptor (A1AR or A3AR) were treated with CTCUR or CUR and the binding was analyzed using competitive assays, confocal microscopy, and docking. The binding assays and molecular docking indicated that CTCUR had Ki values of 306 nM (A1AR) and 400 nM (A3AR). These values suggest that CTCUR is selective for Gi-linked ARs (A1AR or A3AR) over Gs-linked ARs (A2AAR or A2BAR), based on our previous published research. In addition, the docking showed that CTCUR binds to the toggle switch domain of ARs. Curcumin (CUR) did not exhibit binding at any of these receptors. In summary, CTCUR and other modifications of CUR can be developed as novel therapeutic ligands for the Gi-linked ARs (A1AR and A3AR) involved with pain and cancer.

Engineering a multicompartment in vitro model for dorsal root ganglia phenotypic assessment.

Despite the significant global prevalence of chronic pain, current methods to identify pain therapeutics often fail translation to the clinic. Phenotypic screening platforms rely on modeling and assessing key pathologies relevant to chronic pain, improving predictive capability. Patients with chronic pain often present with sensitization of primary sensory neurons (that extend from dorsal root ganglia [DRG]). During neuronal sensitization, painful nociceptors display lowered stimulation thresholds. To model neuronal excitability, it is necessary to maintain three key anatomical features of DRGs to have a physiologically relevant platform: (1) isolation between DRG cell bodies and neurons, (2) 3D platform to preserve cell-cell and cell-matrix interactions, and (3) presence of native non-neuronal support cells, including Schwann cells and satellite glial cells. Currently, no culture platforms maintain the three anatomical features of DRGs. Herein, we demonstrate an engineered 3D multicompartment device that isolates DRG cell bodies and neurites and maintains native support cells. We observed neurite growth into isolated compartments from the DRG using two formulations of collagen, hyaluronic acid, and laminin-based hydrogels. Further, we characterized the rheological, gelation and diffusivity properties of the two hydrogel formulations and found the mechanical properties mimic native neuronal tissue. Importantly, we successfully limited fluidic diffusion between the DRG and neurite compartment for up to 72 h, suggesting physiological relevance. Lastly, we developed a platform with the capability of phenotypic assessment of neuronal excitability using calcium imaging. Ultimately, our culture platform can screen neuronal excitability, providing a more translational and predictive system to identify novel pain therapeutics to treat chronic pain.

Oxycodone withdrawal induces HDAC1/HDAC2-dependent transcriptional maladaptations in the reward pathway in a mouse model of peripheral nerve injury.

The development of physical dependence and addiction disorders due to misuse of opioid analgesics is a major concern with pain therapeutics. We developed a mouse model of oxycodone exposure and subsequent withdrawal in the presence or absence of chronic neuropathic pain. Oxycodone withdrawal alone triggered robust gene expression adaptations in the nucleus accumbens, medial prefrontal cortex and ventral tegmental area, with numerous genes and pathways selectively affected by oxycodone withdrawal in mice with peripheral nerve injury. Pathway analysis predicted that histone deacetylase (HDAC) 1 is a top upstream regulator in opioid withdrawal in nucleus accumbens and medial prefrontal cortex. The novel HDAC1/HDAC2 inhibitor, Regenacy Brain Class I HDAC Inhibitor (RBC1HI), attenuated behavioral manifestations of oxycodone withdrawal, especially in mice with neuropathic pain. These findings suggest that inhibition of HDAC1/HDAC2 may provide an avenue for patients with chronic pain who are dependent on opioids to transition to non-opioid analgesics.

ID: 208858 The NIH HEAL Initiative Preclinical Screening Platform for Pain

As part of the National Institutes of Health Helping to End Addiction Long-termSM Initiative, or NIH HEAL InitiativeSM, the Preclinical Screening Platform for Pain (PSPP) evaluates novel therapeutic approaches towards the goal of accelerating the discovery and development of new non-opioid, non-addictive pain therapeutics.

The Mechanism of Cannabichromene and Cannabidiol Alone Versus in Combination in the Alleviation of Arthritis-Related Inflammation.

Patients suffering from arthritis have limited treatment options for nonoperative management. In search of pain relief, patients have been taking over-the-counter cannabinoids. Cannabidiol (CBD) and cannabichromene (CBC) are minor cannabinoids with reported analgesic and anti-inflammatory properties and have been implicated as potential therapeutics for arthritis-related pain. To this end, we utilized a murine model to investigate the effectiveness of and mechanism by which CBC alone, CBD alone, or CBD and CBC in combination may provide a reduction in arthritis-associated inflammation. Forty-eight mice were included in the study, which were separated into 4 groups: control group (n = 12), treatment with CBD alone (n = 12), treatment with CBC alone (n = 12), and treatment with CBD + CBC (n = 12). We induced inflammation in each mouse utilizing the collagen-induced arthritis model. At scheduled timepoints, mice were clinically assessed for weight gain, swelling, and arthritis severity. In addition, inflammation-associated serum cytokine levels were analyzed for each animal. Thirty-five of 48 mice survived the duration of the study resulting in the following group numbers: control group (n = 8), treatment with CBD alone (n = 9), treatment with CBC alone (n = 9), and treatment with CBD + CBC (n = 9). Animals treated with CBC and CBD + CBC showed significant weight gain between 3 and 5 weeks. Irrespective of treatment, regression analysis comparing all cytokine measurement and physical outcomes found a significant positive correlation between levels of 5 individual cytokines and both arthritis scores and swelling. Animals treated with CBD + CBC showed a significant decrease in swelling between 3 and 5 weeks compared with the control group. Cannabinoid treatment selectively affected the gene expression of eotaxin and lipopolysaccharide-induced CXC chemokine with combined treatment of CBC + CBD. Treatment with cannabinoids resulted in decreased clinical markers of inflammation. Further, the anti-inflammatory effect of CBC and CBD in conjunction was associated with a greater anti-inflammatory effect than either minor cannabinoid alone. Future work will elucidate the possibility of synergistic or entourage effects of minor cannabinoids used in combination for the treatment of arthritis-related pain and inflammation.

Neurotensin expressing lateral hypothalamic neurons alleviate neuropathic and inflammatory pain via Nts signaling

The plague of chronic pain has fueled the U.S. opioid epidemic, creating a critical need for novel pain therapeutics that do not cause dependence. In preclinical models, central treatment with the neuropeptide Neurotensin (Nts) or Nts receptor agonists promotes analgesia, suggesting that augmenting Nts system signaling may be useful to treat pain. However, the lack of clarity of the endogenous Nts mechanisms regulating pain has hindered understanding of how to leverage the Nts system for pain relief. The objective of this study was to determine whether the large population of lateral hypothalamic area (LHA) neurons expressing Nts (referred to as LHA Nts neurons) contribute to analgesia. We hypothesized that activating LHA Nts neurons can alleviate chronic pain in an Nts-dependent manner. To test this, we injected Nts Cre mice in the LHA with AAVs to cre-dependently express either mCherry (Control) or excitatory Designer Receptors Exclusively Activated by Designer Drugs (DREADDs) in LHA Nts neurons, permitting their activation after treatment with the DREADD ligand clozapine N-oxide (CNO, 0.3 mg/kg, i.p.). We then measured how DREADD-activation of LHA Nts neurons impacts acute thermal pain (using the hot plate test), spared nerve injury (SNI) pain or complete Freund’s adjuvant (CFA)-induced inflammatory pain measured using the von Frey test. Activating LHA Nts neurons had no effect on thermal pain responses in naïve mice. By contrast, SNI-induced pain hypersensitivity (indicated by reduced paw withdrawal threshold at 7- and 28-days post-injury) was completely reversed by CNO-mediated activation of LHA Nts neurons compared to VEH control. In CFA-treated mice (a model of inflammatory pain), CNO-activating LHA Nts neurons also relieved pain hypersensitivity, increasing paw withdrawal threshold by 30 mins post treatment that gradually reduced to baseline in 5 hours. However, pretreatment with the brain permeable Nts receptor pan-antagonist SR142948 (1mg/kg, i.p, 30 min before VEH/CNO) blocked CNO-mediated analgesia, indicating that LHA Nts neurons alleviate chronic pain in an Nts-dependent manner. Intriguingly, RNAscope analysis revealed that Nts mRNA expression was increased in the LHA in response to CFA and SNI, suggesting that prolonged pain may increase endogenous Nts, with potential to provide analgesia. Taken together these data suggest that activation of LHA Nts neurons alleviates neuropathic and inflammatory pain via Nts signaling, and augmenting Nts signaling via these neurons could hold promise for treating pain. This research was supported by an award from the National Institute of Neurological Disorders under an award to Geoffroy Laumet (R01-NS121259) and an award from the National Institute of Diabetes and Digestive and Kidney Diseases to Gina Leinninger (R01-DK103808). This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Studies on diketopiperazine and dipeptide analogs as opioid receptor ligands

Using the structure of gliotoxin as a starting point, we have prepared two different chemotypes with selective affinity to the kappa opioid receptor (KOR). Using medicinal chemistry approaches and structure-activity relationship (SAR) studies, structural features required for the observed affinity were identified, and advanced molecules with favorable Multiparameter Optimization (MPO) and Ligand Lipophilicity (LLE) profiles were prepared. Using the Thermal Place Preference Test (TPPT), we have shown that compound2 blocks the antinociceptive effect of U50488, a known KOR agonist. Multiple reports suggest that modulation of KOR signaling is a promising therapeutic strategy in treating neuropathic pain (NP). As a proof-of-concept study, we tested compound 2 in a rat model of NP and recorded its ability to modulate sensory and emotional pain-related behaviors. Observed in vitro and in vivo results suggest that these ligands can be used to develop compounds with potential application as pain therapeutics.

A279 EVIDENCE OF TRANSIENT RECEPTOR POTENTIAL MELASTATIN 3 (TRPM3) CHANNEL SENSITIZATION IN A MOUSE MODEL OF COLITIS

Abstract Background Abdominal pain is a primary symptom of inflammatory bowel disease (IBD). Opioids provide relief from IBD-associated pain, but they are addictive and associated with excess mortality in IBD patients. Thus, there is a need to develop novel therapeutics for IBD-associated pain. The mechanosensitive ion channel, transient receptor potential melastatin 3 (TRPM3) is upregulated in sensory neurons innervating inflamed tissue and contributes to pain from inflamed joints and cystitis. However, TRPM3’s role in abdominal pain has not been investigated. Purpose To evaluate whether TRPM3 contributes to abdominal pain using a mouse model of colitis. Method We used ratiometric Ca2+ imaging and extracellular afferent nerve recording to determine the effects of pharmacological activation or inhibition of TRPM3 on T13-L5 dorsal root ganglia (DRG) neurons and lumbar splanchnic nerves, respectively. Increased intracellular Ca2+ indicates neuronal excitation. Furthermore, the effects of TRPM3 activation in neurons and nerves from healthy mice and mice with dextran sulphate sodium-induced colitis were compared. Result(s) The TRPM3 agonists, CIM-0216 (0.1-10µM) and pregnenolone sulphate sodium (PSS; 1-300µM), concentration-dependently increased intracellular Ca2+ concentration in mouse DRG neurons and this was blocked using the TRPM3 inhibitor isosakuranetin (5µM; p<0.0001, Mann-Whitney Test). CIM-0216 (5µM)-induced increases in intracellular Ca2+ were significantly larger in neurons from mice with colitis (326±16% of baseline) compared to neurons from healthy mice (257±13% of baseline; p<0.01, Kruskal-Wallis with Dunn’s Multiple Comparison Test). The percentage of neurons responding to CIM-0216 was significantly increased in mice with colitis compared to healthy mice (79% vs 62%; p<0.001, Fischer’s Exact Test). Similarly, the percentage of neurons responding to PSS from mice with colitis was increased compared to healthy mice; however, this did not reach statistical significance (75% vs 70%, p=0.351, Fischer’s Exact Test). Furthermore, CIM-0216 (20µM)-induced change in the basal firing of lumbar splanchnic nerves was significantly increased in mice with colitis (1.23±0.24Hz) compared to healthy mice (0.60±0.14Hz, p<0.05, unpaired t-test). Conclusion(s) TRPM3 activation excited DRG neurons and lumbar splanchnic nerves and these excitatory effects were augmented in mice with colitis. Disclosure of Interest None Declared

A brain-wide genome-wide association study of candidate quantitative trait loci associated with structural and functional phenotypes of pain sensitivity.

Individual pain sensitivity is modulated by the brain's structural and functional features, but its heritability remains unclear. This paper conducted a brain-wide genome-wide association study (GWAS) to explore the genetic bases of neuroimage phenotypes of pain sensitivity. In total, 432 normal participants were divided into high and low pain sensitivity groups according to the laser quantitative test threshold. Then, the brain's gray matter density (GMD) features correlated with pain sensitivity were identified. Next, GWAS was performed on each GMD phenotype using quality-controlled genotypes. Based on the heatmap and hierarchical clustering results, the right insula was identified for further refined analysis in terms of subregions GMD and resting-state functional connectivity (rs-FC) phenotypes. The results indicate that the right insula GMD in the high sensitivity group is significantly lower than that in the low sensitivity group. Also, the TT/TC group at locus rs187974 has lower right insula GMD than the CC group. Further, loci at gene CYP2D6 may lead to a variation of rs-FC between the right insula and left putamen. In conclusion, our study suggests that the right insula and multiple candidate loci may be importantly involved in pain sensitivity modulation, which may guide the future development of precision pain therapeutics.

Development of a functional human induced pluripotent stem cell-derived nociceptor MEA system as a pain model for analgesic drug testing.

The control of severe or chronic pain has relied heavily on opioids and opioid abuse and addiction have recently become a major global health crisis. Therefore, it is imperative to develop new pain therapeutics which have comparable efficacy for pain suppression but lack of the harmful effects of opioids. Due to the nature of pain, any in vivo experiment is undesired even in animals. Recent developments in stem cell technology has enabled the differentiation of nociceptors from human induced pluripotent stem cells. This study sought to establish an in vitro functional induced pluripotent stem cells-derived nociceptor culture system integrated with microelectrode arrays for nociceptive drug testing. Nociceptors were differentiated from induced pluripotent stem cells utilizing a modified protocol and a medium was designed to ensure prolonged and stable nociceptor culture. These neurons expressed nociceptor markers as characterized by immunocytochemistry and responded to the exogenous toxin capsaicin and the endogenous neural modulator ATP, as demonstrated with patch clamp electrophysiology. These cells were also integrated with microelectrode arrays for analgesic drug testing to demonstrate their utilization in the preclinical drug screening process. The neural activity was induced by ATP to mimic clinically relevant pathological pain and then the analgesics Lidocaine and the opioid DAMGO were tested individually and both induced immediate silencing of the nociceptive activity. This human-based functional nociceptive system provides a valuable platform for investigating pathological pain and for evaluating effective analgesics in the search of opioid substitutes.

Developing Digital Therapeutics for Chronic Pain in Primary Care: A Qualitative Human-Centered Design Study of Providers' Motivations and Challenges.

Digital therapeutics are growing as a solution to manage pain for patients; yet, they are underused in primary care where over half of the patients with chronic pain seek care. Little is known about how to successfully engage primary care providers in recommending digital therapeutics to their patients. Exploring provider motivations in chronic pain management would potentially help to improve their engagement and inform the development of digital therapeutics. This study examined primary care providers' motivations for chronic pain management, including their strategies and challenges, to inform the future development of chronic pain-related digital therapeutics tailored to primary care settings. We conducted qualitative semistructured interviews with health care providers recruited from 3 primary care clinics in Washington and 1 clinic in Colorado between July and October 2021. The sample (N=11) included 7 primary care physicians, 2 behavioral health providers, 1 physician assistant, and 1 nurse. Most providers worked in clinics affiliated with urban academic health systems. Guided by the human-centered design approach and Christensen's Job-to-be-Done framework, we asked providers their goals and priorities in chronic pain management, their experiences with challenges and strategies used to care for patients, and their perceptions of applying digital therapeutics in clinical practice. Transcripts were analyzed using a thematic analysis approach. We found that primary care providers were motivated but challenged to strengthen the patient-provider alliance, provide team-based care, track and monitor patients' progress, and address social determinants of health in chronic pain management. Specifically, providers desired additional resources to improve patient-centered communication, pain education and counseling, and goal setting with patients. Providers also requested greater accessibility to multidisciplinary care team consultations and nonpharmacological pain treatments. When managing chronic pain at the population level, providers need infrastructure and systems to systematically track and monitor patients' pain and provide wraparound health and social services for underserved patients. Recommendations on digital therapeutic features that might address provider challenges in achieving these motivations were discussed. Given the findings, to engage primary care providers, digital therapeutics for chronic pain management need to strengthen the patient-provider alliance, increase access to nonpharmacological treatment options, support population health tracking and management, and provide equitable reach. Leveraging digital therapeutics in a feasible, appropriate, and acceptable way to aid primary care providers in chronic pain management may require multimodal features that address provider motivations at an individual care and clinic or system level.

Simulations reveal molecular mechanisms of high affinity and selective binding of the tarantula venom protoxin-2 to the human NaV1.7 channel.

Human voltage-gated sodium channels (hNaV) are responsible for initiating and propagating action potentials in excitable cells and have been associated with numerous cardiac and neurological disorders. hNaV1.7 channels, present at the endings of pain-sensing nerves, have garnered a lot of scientific interest as potential targets for pain therapeutics by channel inhibition. Certain natural peptide toxins, such as the tarantula protoxin-2 (ProTx2), have high selectivity for hNaV1.7, and hence they serve as valuable scaffolds for peptide design in pain therapeutics. Here, we present the mechanisms by which ProTx2 can bind and modulate hNaV1.7 channel gating kinetics. Using Rosetta biomolecular modeling software, we constructed atomistic structural models of the hNaV1.7 Voltage-Sensing Domain (VSD) 2 and 4 in the activated and deactivated states. Then, we docked ProTx2 onto the VSDs, embedded the structures into lipid bilayers solvated by aqueous NaCl solution, and performed microsecond-long all-atom molecular dynamics (MD) simulations of those systems using the CHARMM36m force field and Amber PMEMD software. Afterward, we performed binding energetics analysis using molecular mechanics Poisson-Boltzmann surface area (MM/PBSA) calculations and conducted Brownian Dynamics simulations using BrownDye to calculate the second-order association rate constants. Our analysis revealed numerous important inter-residue contacts that contribute to the toxin's high affinity for the channel. By understanding the various state- and subtype-specific mechanisms of toxin binding to the channel, we can develop strategies to improve the selectivity and potency of peptide toxins to create effective and safe pain therapeutics. In addition, the results could be incorporated into functional kinetic models to elucidate how ProTx2 can modulate electrical signal propagation in dorsal root ganglion neurons and thus pain sensing.