A proteome signature for acute incisional pain in dorsal root ganglia of mice

Widespread hyperexcitability of nociceptor somata outlasts enhanced avoidance behavior after incision injury

ABSTRACT

Nociceptors with somata in dorsal root ganglia (DRGs) readily switch from an electrically silent state to a hyperactive state of tonic, nonaccommodating, low-frequency, irregular discharge of action potentials (APs). Spontaneous activity (SA) during this state is present in vivo in rats months after spinal cord injury (SCI) and has been causally linked to SCI pain. Intrinsically generated SA and, more generally, ongoing activity (OA) are induced by various neuropathic conditions in rats, mice, and humans and are retained in nociceptor somata after dissociation and culturing, providing a powerful tool for investigating its mechanisms and functions. The present study shows that long-lasting hyperexcitability that can generate OA during modest depolarization in probable nociceptors dissociated from DRGs of male and female rats is induced by plantar incision injury. OA occurred when the soma was artificially depolarized to a level within the normal range of membrane potentials where large, transient depolarizing spontaneous fluctuations (DSFs) can approach AP threshold. This hyperexcitability persisted for at least 3 weeks, whereas behavioral indicators of affective pain-hind paw guarding and increased avoidance of a noxious substrate in an operant conflict test-persisted for 1 week or less. The most consistent electrophysiological alteration associated with OA was enhancement of DSFs. An unexpected discovery after plantar incisions was hyperexcitability in neurons from thoracic DRGs that innervate dermatomes distant from the injured tissue. Potential in vivo functions of widespread, low-frequency nociceptor OA consistent with these and other findings are to contribute to hyperalgesic priming and to drive anxiety-related hypervigilance.

Anxa10 and neuropathic pain: Insights into dysregulation of endoplasmic reticulum-mitochondria contact tethering complex and therapeutic potential

The stability of membrane contact sites is critically dependent on Endoplasmic Reticulum mitochondria contact tethering complexes (EMCTCs), and dysregulation of these sites has been implicated in neuropathic diseases. In this study, we examined the role of Annexin A10 (Anxa10), a calcium-dependent protein, in neuropathic pain by investigating its influence on EMCTCs dysregulation. Using RNA sequencing, western blotting, and behavioral assays, we observed that spared nerve injury (SNI)-induced neuropathic pain significantly increased Anxa10 expression levels within the spinal dorsal horn (SDH) of mice. By employing cell-specific gene regulation via the Cre/loxp system, we utilized loxp-modified adeno-associated virus vectors to modulate Anxa10 expression in GAD2-Cre (inhibitory neurons), vGlut2-Cre (excitatory neurons), and Fos-Cre (activity-induced neurons) transgenic mice. Our results demonstrated that specific down-regulation of Anxa10 in excitatory neurons within the SDH alleviated neuropathic pain, whereas up-regulation of Anxa10, regardless of cell type, induced spontaneous pain in mice. Ultrastructural analysis of the endoplasmic reticulum (ER) and mitochondria, as well as double immunofluorescence staining, revealed that downregulation of Anxa10 mitigated the SNI-induced reduction in ER-mitochondrial distance. Additionally, it attenuated the SNI-induced upregulation of key components of EMCTCs, including IP3R, GRP75, and VDAC1, while preventing the SNI-induced downregulation of NCX3 expression. Furthermore, we formulated and validated the hypothesis that SGK1 and PI3K are positioned downstream of Anxa10. The up-regulation of Anxa10 compromised mitochondrial integrity and disrupted mitochondrial networks, ultimately leading to elevated oxidative stress. Collectively, these findings suggest that Anxa10 represents a promising therapeutic target for correcting EMCTCs dysregulation and mitigating neuropathic pain.

Deep proteomics and network pharmacology reveal sex- and age-shared neuropathic pain signatures in mouse dorsal root ganglia

Our understanding of how sex and age influence chronic pain at the molecular level is still limited with wide-reaching consequences for adolescent patients. Here, we leveraged deep proteome profiling of mouse dorsal root ganglia (DRG) from adolescent (4-week-old) and adult (12-week-old) male and female mice to investigate the establishment of neuropathic pain in the spared nerve injury (SNI)-model in parallel. We quantified over 12,000 proteins, including notable ion channels involved in pain, highlighting the sensitivity of our approach. Differential expression revealed sex- and age-dependent proteome changes upon nerve injury. In contrast to most previous studies, our comprehensive dataset enabled us to determine differentially expressed proteins (DEPs), which were shared between male and female mice of both age groups. Among these, the vast majority (94 %) were also expressed and, in part, altered in human DRG of neuropathic pain patients, indicating evolutionary conservation. Proteome signatures represented numerous targets of FDA-approved drugs comprising both (i) known pain therapeutics (e.g. Pregabalin and opioids) and, importantly, (ii) compounds with high potential for future re-purposing, e.g. Ptprc-modulators and Epoetins. Protein network and multidimensional analysis uncovered distinct hubs of sex- and age-shared biological pathways impacted by neuropathic pain, such as neuronal activity and synaptic function, DNA-damage, and neuroimmune interactions. Taken together, our results capture the complexity of nerve injury-associated DRG alterations in mice at the network level, moving beyond single-candidate studies. Consequently, we provide an innovative resource of the molecular landscape of neuropathic pain, enabling novel opportunities for translational pain research and network-based drug discovery.

Proteomic analysis of dorsal root ganglia in a mouse model of paclitaxel-induced neuropathic pain

Paclitaxel is a chemotherapy drug widely used for the treatment of various cancers based on its ability to potently stabilize cellular microtubules and block division in cancer cells. Paclitaxel-based treatment, however, accumulates in peripheral system sensory neurons and leads to a high incidence rate (over 50%) of chemotherapy induced peripheral neuropathy in patients. Using an established preclinical model of paclitaxel-induced peripheral neuropathy (PIPN), we examined proteomic changes in dorsal root ganglia (DRG) of adult male mice that were treated with paclitaxel (8 mg/kg, at 4 injections every other day) relative to vehicle-treated mice. High throughput proteomics based on liquid chromatography electrospray ionization mass spectrometry identified 165 significantly altered proteins in lumbar DRG. Gene ontology enrichment and bioinformatic analysis revealed an effect of paclitaxel on pathways for mitochondrial regulation, axonal function, and inflammatory purinergic signaling as well as microtubule activity. These findings provide insight into molecular mechanisms that can contribute to PIPN in patients.

Proteomic Analysis of Dorsal Root Ganglia in a Mouse Model of Paclitaxel-Induced Neuropathic Pain

Paclitaxel is a chemotherapy drug widely used for the treatment of various cancers based on its ability to potently stabilize cellular microtubules and block division in cancer cells. Paclitaxel-based treatment, however, accumulates in peripheral system sensory neurons and leads to a high incidence rate (over 60%) of chemotherapy induced peripheral neuropathy. Using an established preclinical model of paclitaxel-induced peripheral neuropathy (PIPN), we examined proteomic changes in dorsal root ganglia (DRG) of adult male mice that were treated with paclitaxel (8 mg/kg, at 4 injections every other day) relative to vehicle-treated mice. High throughput proteomics based on liquid chromatography electrospray ionization mass spectrometry identified 165 significantly altered proteins in lumbar DRG. Gene ontology enrichment and bioinformatic analysis revealed an effect of paclitaxel on pathways for mitochondrial regulation, axonal function, and inflammatory purinergic signaling as well as microtubule activity. These findings provide insight into molecular mechanisms that can contribute to PIPN in patients.

Annexin A1 in the nervous and ocular systems

The therapeutic potential of Annexin A1, an important member of the Annexin superfamily, has become evident in results of experiments with multiple human systems and animal models. The anti-inflammatory and pro-resolving effects of Annexin A1 are characteristic of pathologies involving the nervous system. In this review, we initially describe the expression sites of Annexin A1, then outline the mechanisms by which Annexin A1 maintains the neurological homeostasis through either formyl peptide receptor 2 or other molecular approaches; and, finally, we discuss the neuroregenerative potential qualities of Annexin A1. The eye and the nervous system are anatomically and functionally connected, but the association between visual system pathogenesis, especially in the retina, and Annexin A1 alterations has not been well summarized. Therefore, we explain the beneficial effects of Annexin A1 for ocular diseases, especially for retinal diseases and glaucoma on the basis of published findings, and we explore present and future delivery strategies for Annexin A1 to the retina.

Widespread latent hyperactivity of nociceptors outlasts enhanced avoidance behavior following incision injury

Nociceptors with somata in dorsal root ganglia (DRGs) exhibit an unusual readiness to switch from an electrically silent state to a hyperactive state of tonic, nonaccommodating, low-frequency, irregular discharge of action potentials (APs). Ongoing activity (OA) during this state is present in vivo in rats months after spinal cord injury (SCI), and has been causally linked to SCI pain. OA induced by various neuropathic conditions in rats, mice, and humans is retained in nociceptor somata after dissociation and culturing, providing a powerful tool for investigating its mechanisms and functions. An important question is whether similar nociceptor OA is induced by painful conditions other than neuropathy. The present study shows that probable nociceptors dissociated from DRGs of rats subjected to postsurgical pain (induced by plantar incision) exhibit OA. The OA was most apparent when the soma was artificially depolarized to a level within the normal range of membrane potentials where large, transient depolarizing spontaneous fluctuations (DSFs) can approach AP threshold. This latent hyperactivity persisted for at least 3 weeks, whereas behavioral indicators of affective pain - hindpaw guarding and increased avoidance of a noxious substrate in an operant conflict test - persisted for 1 week or less. An unexpected discovery was latent OA in neurons from thoracic DRGs that innervate dermatomes distant from the injured tissue. The most consistent electrophysiological alteration associated with OA was enhancement of DSFs. Potential in vivo functions of widespread, low-frequency nociceptor OA consistent with these and other findings are to amplify hyperalgesic priming and to drive anxiety-related hypervigilance.

Spinal GABA transporter 1 contributes to evoked-pain related behavior but not resting pain after incision injury

The inhibitory function of GABA at the spinal level and its central modulation in the brain are essential for pain perception. However, in post-surgical pain, the exact mechanism and modes of action of GABAergic transmission have been poorly studied. This work aimed to investigate GABA synthesis and uptake in the incisional pain model in a time-dependent manner. Here, we combined assays for mechanical and heat stimuli-induced withdrawal reflexes with video-based assessments and assays for non-evoked (NEP, guarding of affected hind paw) and movement-evoked (MEP, gait pattern) pain-related behaviors in a plantar incision model in male rats to phenotype the effects of the inhibition of the GABA transporter (GAT-1), using a specific antagonist (NO711). Further, we determined the expression profile of spinal dorsal horn GAT-1 and glutamate decarboxylase 65/67 (GAD65/67) by protein expression analyses at four time points post-incision. Four hours after incision, we detected an evoked pain phenotype (mechanical, heat and movement), which transiently ameliorated dose-dependently following spinal inhibition of GAT-1. However, the NEP-phenotype was not affected. Four hours after incision, GAT-1 expression was significantly increased, whereas GAD67 expression was significantly reduced. Our data suggest that GAT-1 plays a role in balancing spinal GABAergic signaling in the spinal dorsal horn shortly after incision, resulting in the evoked pain phenotype. Increased GAT-1 expression leads to increased GABA uptake from the synaptic cleft and reduces tonic GABAergic inhibition at the post-synapse. Inhibition of GAT-1 transiently reversed this imbalance and ameliorated the evoked pain phenotype.

Modulation of the Inflammatory Response by Pre-emptive Administration of IMT504 Reduces Postoperative Pain in Rats and has Opioid-Sparing Effects

Despite the available knowledge on underlying mechanisms and the development of several therapeutic strategies, optimal management of postoperative pain remains challenging. This preclinical study hypothesizes that, by promoting an anti-inflammatory scenario, pre-emptive administration of IMT504, a noncoding, non-CpG oligodeoxynucleotide with immune modulating properties, will reduce postincisional pain, also facilitating therapeutic opioid-sparing. Male adult Sprague-Dawley rats with unilateral hindpaw skin-muscle incision received pre-emptive (48 and 24 hours prior to surgery) or postoperative (6 hours after surgery) subcutaneous vehicle (saline) or IMT504. Various groups of rats were prepared for pain-like behavior analyses, including subgroups receiving morphine or naloxone, as well as for flow-cytometry or quantitative RT-PCR analyses of the spleen and hindpaws (for analysis of inflammatory phenotype). Compared to vehicle-treated rats, pre-emptive IMT504 significantly reduced mechanical allodynia by 6 hours after surgery, and accelerated recovery of basal responses from 72 hours after surgery and onwards. Cold allodynia was also reduced by IMT504. Postoperative administration of IMT504 resulted in similar positive effects on pain-like behavior. In IMT504-treated rats, 3 mg/kg morphine resulted in comparable blockade of mechanical allodynia as observed in vehicle-treated rats receiving 10 mg/kg morphine. IMT504 significantly increased hindpaw infiltration of mesenchymal stem cells, CD4+T and B cells, and caused upregulated or downregulated transcript expressions of interleukin-10 and interleukin-1β, respectively. Also, IMT504 treatment targeted the spleen, with upregulated or downregulated transcript expressions, 6 hours after incision, of interleukin-10 and interleukin-1β, respectively. Altogether, pre-emptive or postoperative IMT504 provides protection against postincisional pain, through participation of significant immunomodulatory actions, and exhibiting opioid-sparing effects. PERSPECTIVE: This preclinical study introduces the noncoding non-CpG oligodeoxynucleotide IMT504 as a novel modulator of postoperative pain and underlying inflammatory events. The opioid-sparing effects observed for IMT504 appear as a key feature that could contribute, in the future, to reducing opioid-related adverse events in patients undergoing surgical intervention.

Label-free serum proteomics for the identification of the putative biomarkers of postoperative pain in patients with gastric cancer

Background: Individualized pain therapy conforms to the concept of precision medicine and contributes to adequate pain management after surgery. Preoperative biomarkers associated with postoperative pain may instruct anesthesiologists to improve personalized suitable analgesia. Therefore, it is essential to explore the association between preoperative proteins and postoperative acute pain using the proteomics platform. Methods: In this study, the 24 hours postoperative sufentanil consumption of 80 male patients with gastric cancer was ranked. Patients with sufentanil consumption in the lowest 12% were included in the sufentanil low consumption group, while patients with sufentanil consumption in the highest 12% were included in the sufentanil high consumption group. The secretion of serum proteins in both groups was analyzed using label-free proteomics technology. The results were validated by ELISA. Results: Proteomics identified 29 proteins that were significantly differentially expressed between groups. ELISA confirmed that secretion of TNC and IGFBP2 was down-regulated in the SLC group. The differential proteins were mainly extracellular and were involved in several terms, including calcium ion binding, laminin-1 binding, and so on. Pathway analysis showed that they were mainly enriched in focal adhesion and extracellular matrix-receptor interaction. The protein-protein interaction network analysis showed 22 proteins that interacted with other proteins. F13B had the strongest correlation with sufentanil consumption and its AUC value was 0.859. Conclusions: Several differential proteins are associated with postoperative acute pain and are involved in ECM-related processes, inflammation, and blood coagulation cascades. F13B may be a novel marker for postoperative acute pain. Our results may benefit postoperative pain management.

Behavioral Voluntary and Social Bioassays Enabling Identification of Complex and Sex-Dependent Pain-(-Related) Phenotypes in Rats with Bone Cancer

Cancer-induced bone pain (CIBP) is a common and devastating symptom with limited treatment options in patients, significantly affecting their quality of life. The use of rodent models is the most common approach to uncovering the mechanisms underlying CIBP; however, the translation of results to the clinic may be hindered because the assessment of pain-related behavior is often based exclusively on reflexive-based methods, which are only partially indicative of relevant pain in patients. To improve the accuracy and strength of the preclinical, experimental model of CIBP in rodents, we used a battery of multimodal behavioral tests that were also aimed at identifying rodent-specific behavioral components by using a home-cage monitoring assay (HCM). Rats of all sexes received an injection with either heat-deactivated (sham-group) or potent mammary gland carcinoma Walker 256 cells into the tibia. By integrating multimodal datasets, we assessed pain-related behavioral trajectories of the CIBP-phenotype, including evoked and non-evoked based assays and HCM. Using principal component analysis (PCA), we discovered sex-specific differences in establishing the CIBP-phenotype, which occurred earlier (and differently) in males. Additionally, HCM phenotyping revealed the occurrence of sensory-affective states manifested by mechanical hypersensitivity in sham when housed with a tumor-bearing cagemate (CIBP) of the same sex. This multimodal battery allows for an in-depth characterization of the CIBP-phenotype under social aspects in rats. The detailed, sex-specific, and rat-specific social phenotyping of CIBP enabled by PCA provides the basis for mechanism-driven studies to ensure robustness and generalizability of results and provide information for targeted drug development in the future.

Phenotype- and species-specific skin proteomic signatures for incision-induced pain in humans and mice

BACKGROUND

Acute pain after surgery is common and often leads to chronic post-surgical pain, but neither treatment nor prevention is currently sufficient. We hypothesised that specific protein networks (protein-protein interactions) are relevant for pain after surgery in humans and mice.

METHODS

Standardised surgical incisions were performed in male human volunteers and male mice. Quantitative and qualitative sensory phenotyping were combined with unbiased quantitative mass spectrometry-based proteomics and protein network theory. The primary outcomes were skin protein signature changes in humans and phenotype-specific protein-protein interaction analysis 24 h after incision. Secondary outcomes were interspecies comparison of protein regulation as well as protein-protein interactions after incision and validation of selected proteins in human skin by immunofluorescence.

RESULTS

Skin biopsies in 21 human volunteers revealed 119/1569 regulated proteins 24 h after incision. Protein-protein interaction analysis delineated remarkable differences between subjects with small (low responders, n=12) and large incision-related hyperalgesic areas (high responders, n=7), a phenotype most predictive of developing chronic post-surgical pain. Whereas low responders predominantly showed an anti-inflammatory protein signature, high responders exhibited signatures associated with a distinct proteolytic environment and persistent inflammation. Compared to humans, skin biopsies in mice habored even more regulated proteins (435/1871) 24 h after incision with limited overlap between species as assessed by proteome dynamics and PPI. Immunohistochemistry confirmed the expression of high priority candidates in human skin biopsies.

CONCLUSIONS

Proteome profiling of human skin after incision revealed protein-protein interactions correlated with pain and hyperalgesia, which may be of potential significance for preventing chronic post-surgical pain. Importantly, protein-protein interactions were differentially modulated in mice compared to humans opening new avenues for successful translational research.

Unbiased proteomic analysis detects painful systemic inflammatory profile in the serum of nerve-injured mice

ABSTRACT

Neuropathic pain is a complex, debilitating disease that results from injury to the somatosensory nervous system. The presence of systemic chronic inflammation has been observed in patients with chronic pain but whether it plays a causative role remains unclear. This study aims to determine the perturbation of systemic homeostasis by an injury to peripheral nerve and its involvement in neuropathic pain. We assessed the proteomic profile in the serum of mice at 1 day and 1 month after partial sciatic nerve injury (PSNL) or sham surgery. We also assessed mouse mechanical and cold sensitivity in naïve mice after receiving intravenous administration of serum from PSNL or sham mice. Mass spectrometry-based proteomic analysis revealed that PSNL resulted in a long-lasting alteration of serum proteome, where most of the differentially expressed proteins were in inflammation-related pathways, involving cytokines and chemokines, autoantibodies, and complement factors. Although transferring sham serum to naïve mice did not change their pain sensitivity, PSNL serum significantly lowered mechanical thresholds and induced cold hypersensitivity in naïve mice. With broad anti-inflammatory properties, bone marrow cell extracts not only partially restored serum proteomic homeostasis but also significantly ameliorated PSNL-induced mechanical allodynia, and serum from bone marrow cell extracts-treated PSNL mice no longer induced hypersensitivity in naïve mice. These findings clearly demonstrate that nerve injury has a long-lasting impact on systemic homeostasis, and nerve injury-associated systemic inflammation contributes to the development of neuropathic pain.

Identification of Potential Visceral Pain Biomarkers in Colon Exudates from Mice with Experimental Colitis: An Exploratory In Vitro Study

Chronic visceral pain (CVP) is extremely difficult to diagnose, and available analgesic treatment options are quite limited. Identifying the proteins secreted from the colonic nociceptors, or their neighbor cells within the tube walls, in the context of disorders that course with visceral pain, might be useful to decipher the mechanism involved in the establishment of CVP. Addressing this question in human with gastrointestinal disorders entails multiple difficulties, as there is not a clear classification of disease severity, and colonic secretion is not easy to manage. We propose using of a murine model of colitis to identify new algesic molecules and pathways that could be explored as pain biomarkers or analgesia targets. Descending colons from naïve and colitis mice with visceral hyperalgesia were excised and maintained ex vivo. The proteins secreted in the perfusion fluid before and during acute noxious distension were evaluated using high-resolution mass spectrometry (MS). Haptoglobin (Hp), PZD and LIM domain protein 3 (Pdlim3), NADP-dependent malic enzyme (Me1), and Apolipoprotein A-I (Apoa1) were increased during visceral insult, whilst Triosephosphate isomerase (Tpi1), Glucose-6-phosphate isomerase (Gpi1), Alpha-enolase (Eno1), and Isoform 2 of Tropomyosin alpha-1 chain (Tpm1) were decreased. Most identified proteins have been described in the context of different chronic pain conditions and, according to gene ontology analysis, they are also involved in diverse biological processes of relevance. Thus, animal models that mimic human conditions in combination with unbiased omics approaches will ultimately help to identify new pathophysiological mechanisms underlying pain that might be useful in diagnosing and treating pain. PERSPECTIVE: Our study utilizes an unbiased proteomic approach to determine, first, the clinical relevance of a murine model of colitis and, second, to identify novel molecules/pathways involved in nociception that would be potential biomarkers or targets for chronic visceral pain.

Acute postoperative pain and dorsal root ganglia transcriptomic signatures following total knee arthroplasty (TKA) in rats: An experimental study

Total knee arthroplasty (TKA) is the final treatment option for patients with advanced knee osteoarthritis (OA). Unfortunately, TKA surgery is accompanied by acute postoperative pain that is more severe than arthroplasty performed in other joints. Elucidating the molecular mechanisms specific to post-TKA pain necessitates an animal model that replicates clinical TKA procedures, induces acute postoperative pain, and leads to complete functional recovery. Here, we present a new preclinical TKA model in rats and report on functional and behavioral outcomes indicative of pain, analgesic efficacy, serum cytokine levels, and dorsal root ganglia (DRG) transcriptomes during the acute postoperative period. Following TKA, rats exhibited marked deficits in weight bearing that persisted for 28 days. Home cage locomotion, rearing, and gait were similarly impacted and recovered by day 14. Cytokine levels were elevated on postoperative days one and/or two. Treatment with morphine, ketorolac, or their combination improved weight bearing while gabapentin lacked efficacy. When TKA was performed in rats with OA, similar functional deficits and comparable recovery time courses were observed. Analysis of DRG transcriptomes revealed upregulation of transcripts linked to multiple molecular pathways including inflammation, MAPK signaling, and cytokine signaling and production. In summary, we developed a clinically relevant rat TKA model characterized by resolution of pain and functional recovery within five weeks and with pain-associated behavioral deficits that are partially alleviated by clinically administered analgesics, mirroring the postoperative experience of TKA patients.

Unveiling Targets for Treating Postoperative Pain: The Role of the TNF-α/p38 MAPK/NF-κB/Nav1.8 and Nav1.9 Pathways in the Mouse Model of Incisional Pain

Although the mouse model of incisional pain is broadly used, the mechanisms underlying plantar incision-induced nociception are not fully understood. This work investigates the role of Nav1.8 and Nav1.9 sodium channels in nociceptive sensitization following plantar incision in mice and the signaling pathway modulating these channels. A surgical incision was made in the plantar hind paw of male Swiss mice. Nociceptive thresholds were assessed by von Frey filaments. Gene expression of Nav1.8, Nav1.9, TNF-α, and COX-2 was evaluated by Real-Time PCR in dorsal root ganglia (DRG). Knockdown mice for Nav1.8 and Nav1.9 were produced by antisense oligodeoxynucleotides intrathecal treatments. Local levels of TNF-α and PGE2 were immunoenzymatically determined. Incised mice exhibited hypernociception and upregulated expression of Nav1.8 and Nav1.9 in DRG. Antisense oligodeoxynucleotides reduced hypernociception and downregulated Nav1.8 and Nav1.9. TNF-α and COX-2/PGE2 were upregulated in DRG and plantar skin. Inhibition of TNF-α and COX-2 reduced hypernociception, but only TNF-α inhibition downregulated Nav1.8 and Nav1.9. Antagonizing NF-κB and p38 mitogen-activated protein kinase (MAPK), but not ERK or JNK, reduced both hypernociception and hyperexpression of Nav1.8 and Nav1.9. This study proposes the contribution of the TNF-α/p38/NF-κB/Nav1.8 and Nav1.9 pathways to the pathophysiology of the mouse model of incisional pain.

Moderate-Intensity Ultrasound-Triggered On-Demand Analgesia Nanoplatforms for Postoperative Pain Management

Introduction

The restricted duration is a fundamental drawback of traditional local anesthetics during postoperative pain from a single injection. Therefore, an injectable local anesthetic that produces repeatable on-demand nerve blocks would be ideal.

Methods

We offer ultrasound-triggered on-demand analgesia consisting of dendritic mesoporous silica nanoparticles (DMSN) carried with ultrasound-sensitive perfluoropentane (PFP) and levobupivacaine (DMSN-bupi-PFP) to achieve repeatable and customizable on-demand local anesthetics.

Results

The vaporization of liquid PFP was triggered by ultrasound irradiation to produce a gas environment. Subsequently, the enhanced cavitation effect could improve the release of levobupivacaine to achieve pain relief under a moderate-intensity ultrasound irradiation. DMSN-bupi-PFP demonstrated a controlled-release pattern and showed a reinforced ultrasonic sensitivity compared to levobupivacaine loaded DMSN (DMSN-bupi). The sustained release of levobupivacaine produced continuous analgesia of more than 9 hours in a model of incision pain, approximately 3 times longer than a single free levobupivacaine injection (3 hours). The external ultrasound irradiation can trigger the release of levobupivacaine repeatedly, resulting in on-demand analgesia. In addition, DMSN-bupi-PFP nanoplatforms for ultrasound-enabled analgesia showed low neurotoxicity and good biocompatibility in vitro and in vivo.

Conclusion

This DMSN-bupi-PFP nanoplatform can be used in pain management by providing long-lasting and on-demand pain alleviation with the help of moderate-intensity ultrasound.

The “WWHow” Concept for Prospective Categorization of Post-operative Severity Assessment in Mice and Rats

The prospective severity assessment in animal experiments in the categories' non-recovery, mild, moderate, and severe is part of each approval process and serves to estimate the harm/benefit. Harms are essential for evaluating ethical justifiability, and on the other hand, they may represent confounders and effect modifiers within an experiment. Catalogs and guidelines provide a way to assess the experimental severity prospectively but are limited in adaptation due to their nature of representing particular examples without clear explanations of the assessment strategies. To provide more flexibility for current and future practices, we developed the modular Where-What-How (WWHow) concept, which applies findings from pre-clinical studies using surgical-induced pain models in mice and rats to provide a prospective severity assessment. The WWHow concept integrates intra-operative characteristics for predicting the maximum expected severity of surgical procedures. The assessed severity categorization is mainly congruent with examples in established catalogs; however, because the WWHow concept is based on anatomical location, detailed analysis of the tissue trauma and other intra-operative characteristics, it enables refinement actions, provides the basis for a fact-based dialogue with authority officials and other stakeholders, and helps to identify confounder factors of study findings.

Tmem160 contributes to the establishment of discrete nerve injury-induced pain behaviors in male mice

Chronic pain is a prevalent medical problem, and its molecular basis remains poorly understood. Here, we demonstrate the significance of the transmembrane protein (Tmem) 160 for nerve injury-induced neuropathic pain. An extensive behavioral assessment suggests a pain modality- and entity-specific phenotype in male Tmem160 global knockout (KO) mice: delayed establishment of tactile hypersensitivity and alterations in self-grooming after nerve injury. In contrast, Tmem160 seems to be dispensable for other nerve injury-induced pain modalities, such as non-evoked and movement-evoked pain, and for other pain entities. Mechanistically, we show that global KO males exhibit dampened neuroimmune signaling and diminished TRPA1-mediated activity in cultured dorsal root ganglia. Neither these changes nor altered pain-related behaviors are observed in global KO female and male peripheral sensory neuron-specific KO mice. Our findings reveal Tmem160 as a sexually dimorphic factor contributing to the establishment, but not maintenance, of discrete nerve injury-induced pain behaviors in male mice.

Investigating the Role of Ly6G+ Neutrophils in Incisional and Inflammatory Pain by Multidimensional Pain-Related Behavioral Assessments: Bridging the Translational Gap

In recent years, preclinical pain research has failed to develop genuinely new analgesics for clinical use. This fact is reflected by a high number of patients, limited drug efficacy accompanied by side effects, and a long-term opioid intake. Two main aspects have been addressed, which hinder translation: the use of non-relevant pain models and a mismatch between pain-related outcomes in preclinical and clinical studies. Conversely, disease-specific pain models that mirror more closely the clinical situation and multidimensional behavioral outcome measures that objectively and reproducibly assess relevant pain-related symptoms in a preclinical setting could improve translation. Mechanistically, a matter of debate is the role of Ly6G⁺ neutrophil granulocytes (NGs) for pain. NGs are essential to eliminate pathogens and promote the wound healing process. For this purpose, there is a need to release various pro- and anti-inflammatory mediators, some of which could ameliorate or enhance pain. However, the contribution of NGs to different pain entities is contradictory for reflex-based tests, and completely unknown in the context of non-evoked pain (NEP) and movement-evoked pain (MEP). First, we combined withdrawal reflex-based assays with novel video-based assessments for NEP- and MEP-related behavior in two mouse pain models. The pain models utilized in this study were incision (INC) and pathogen/adjuvant-induced inflammation (CFA), translating well to postsurgical and inflammatory pain entities. Second, we depleted NGs and applied a set of behavioral assessments to investigate the role of NG migration in different pain modalities. Our comprehensive behavioral approach identified pain-related behaviors in mice that resemble (NEP) or differentiate (MEP) behavioral trajectories in comparison to mechanical and heat hypersensitivity, thereby indicating modality-dependent mechanisms. Further, we show that injury-induced accumulation of NGs minimally affects pain-related behaviors in both pain models. In conclusion, we report a novel assessment to detect NEP in mice after unilateral injuries using a more unbiased approach. Additionally, we are capable of detecting an antalgic gait for both pain entities with unique trajectories. The different trajectories between MEP and other pain modalities suggest that the underlying mechanisms differ. We further conclude that NGs play a subordinate role in pain-related behaviors in incisional and inflammatory pain.