Differential Expression of Neuroinflammatory mRNAs in the Rat Sciatic Nerve Following Chronic Constriction Injury and Pain-Relieving Nanoemulsion NSAID Delivery to Infiltrating Macrophages

A critical review of the novelties in the development of intravenous nanoemulsions

Nanoemulsions have gained increasing attention in recent years as a drug delivery system due to their ability to improve the solubility and bioavailability of poorly water-soluble drugs. This systematic review aimed to collect and critically analyze recent novelties in developing, designing, and optimizing intravenous nanoemulsions appearing in articles published between 2017 and 2022. The applied methodology involved searching two electronic databases PubMed and Scopus, using the keyword "nanoemulsion" in combination with "intravenous" or "parenteral". The resulting original articles were classified by the method of preparation into different categories. An overview of the current methods used for the preparation of such formulations, including high- and low-energy emulsification, was provided. The advantages and disadvantages of these methods were discussed, as well as their potential impact on the properties of the developed intravenous nanoemulsions. The problem of inconsistency in intravenous nanoemulsion terminology may lead to misunderstandings and misinterpretations of their properties and applications was also undertaken. Finally, the regulatory aspects of intravenous nanoemulsions, the state of the art in the field of intravenous emulsifiers, and the future perspectives were presented.

Folate-conjugated near-infrared fluorescent perfluorocarbon nanoemulsions as theranostics for activated macrophage COX-2 inhibition

Activated macrophages play a critical role in the orchestration of inflammation and inflammatory pain in several chronic diseases. We present here the first perfluorocarbon nanoemulsion (PFC NE) that is designed to preferentially target activated macrophages and can deliver up to three payloads (two fluorescent dyes and a COX-2 inhibitor). Folate receptors are overexpressed on activated macrophages. Therefore, we introduced a folate-PEG-cholesterol conjugate into the formulation. The incorporation of folate conjugate did not require changes in processing parameters and did not change the droplet size or fluorescent properties of the PFC NE. The uptake of folate-conjugated PFC NE was higher in activated macrophages than in resting macrophages. Flow cytometry showed that the uptake of folate-conjugated PFC NE occurred by both phagocytosis and receptor-mediated endocytosis. Furthermore, folate-conjugated PFC NE inhibited the release of proinflammatory cytokines (TNF-α and IL-6) more effectively than nonmodified PFC NE, while drug loading and COX-2 inhibition were comparable. The PFC NEs reported here were successfully produced on multiple scales, from 25 to 200 mL, and by using two distinct processors (microfluidizers: M110S and LM20). Therefore, folate-conjugated PFC NEs are viable anti-inflammatory theranostic nanosystems for macrophage drug delivery and imaging.

Ret deficiency decreases neural crest progenitor proliferation and restricts fate potential during enteric nervous system development

The receptor tyrosine kinase RET plays a critical role in the fate specification of enteric neural crest-derived cells (ENCDCs) during enteric nervous system (ENS) development. RET loss of function (LoF) is associated with Hirschsprung disease (HSCR), which is marked by aganglionosis of the gastrointestinal (GI) tract. Although the major phenotypic consequences and the underlying transcriptional changes from Ret LoF in the developing ENS have been described, cell type- and state-specific effects are unknown. We performed single-cell RNA sequencing on an enriched population of ENCDCs from the developing GI tract of Ret null heterozygous and homozygous mice at embryonic day (E)12.5 and E14.5. We demonstrate four significant findings: 1) Ret-expressing ENCDCs are a heterogeneous population comprising ENS progenitors as well as glial- and neuronal-committed cells; 2) neurons committed to a predominantly inhibitory motor neuron developmental trajectory are not produced under Ret LoF, leaving behind a mostly excitatory motor neuron developmental program; 3) expression patterns of HSCR-associated and Ret gene regulatory network genes are impacted by Ret LoF; and 4) Ret deficiency leads to precocious differentiation and reduction in the number of proliferating ENS precursors. Our results support a model in which Ret contributes to multiple distinct cellular phenotypes during development of the ENS, including the specification of inhibitory neuron subtypes, cell cycle dynamics of ENS progenitors, and the developmental timing of neuronal and glial commitment.

Adipose-derived stem cells modulate neuroinflammation and improve functional recovery in chronic constriction injury of the rat sciatic nerve

Introduction

Compressive neuropathy, a common chronic traumatic injury of peripheral nerves, leads to variable impairment in sensory and motor function. Clinical symptoms persist in a significant portion of patients despite decompression, with muscle atrophy and persistent neuropathic pain affecting 10%-25% of cases. Excessive inflammation and immune cell infiltration in the injured nerve hinder axon regeneration and functional recovery. Although adipose-derived stem cells (ASCs) have demonstrated neural regeneration and immunomodulatory potential, their specific effects on compressive neuropathy are still unclear.

Methods

We conducted modified CCI models on adult male Sprague-Dawley rats to induce irreversible neuropathic pain and muscle atrophy in the sciatic nerve. Intraneural ASC injection and nerve decompression were performed. Behavioral analysis, muscle examination, electrophysiological evaluation, and immunofluorescent examination of the injured nerve and associated DRG were conducted to explore axon regeneration, neuroinflammation, and the modulation of inflammatory gene expression. Transplanted ASCs were tracked to investigate potential beneficial mechanisms on the local nerve and DRG.

Results

Persistent neuropathic pain was induced by chronic constriction of the rat sciatic nerve. Local ASC treatment has demonstrated robust beneficial outcomes, including the alleviation of mechanical allodynia, improvement of gait, regeneration of muscle fibers, and electrophysiological recovery. In addition, locally transplanted ASCs facilitated axon remyelination, alleviated neuroinflammation, and reduced inflammatory cell infiltration of the injured nerve and associated dorsal root ganglion (DRG). Trafficking of the transplanted ASC preserved viability and phenotype less than 7 days but contributed to robust immunomodulatory regulation of inflammatory gene expression in both the injured nerve and DRG.

Discussion

Locally transplanted ASC on compressed nerve improve sensory and motor recoveries from irreversible chronic constriction injury of rat sciatic nerve via alleviation of both local and remote neuroinflammation, suggesting the promising role of adjuvant ASC therapies for clinical compressive neuropathy.

Celecoxib alleviates nociceptor sensitization mediated by interleukin-1beta-primed annulus fibrosus cells

PURPOSE

This study aims to analyze the effect of pro-inflammatory cytokine-stimulated human annulus fibrosus cells (hAFCs) on the sensitization of dorsal root ganglion (DRG) cells. We further hypothesized that celecoxib (cxb) could inhibit hAFCs-induced DRG sensitization.

METHODS

hAFCs from spinal trauma patients were stimulated with TNF-α or IL-1β. Cxb was added on day 2. On day 4, the expression of pro-inflammatory and neurotrophic genes was evaluated using RT-qPCR. Levels of prostaglandin E2 (PGE-2), IL-8, and IL-6 were measured in the conditioned medium (CM) using ELISA. hAFCs CM was then applied to stimulate the DRG cell line (ND7/23) for 6 days. Then, calcium imaging (Fluo4) was performed to evaluate DRG cell sensitization. Both spontaneous and bradykinin-stimulated (0.5 μM) calcium responses were analyzed. The effects on primary bovine DRG cell culture were performed in parallel to the DRG cell line model.

RESULTS

IL-1ß stimulation significantly enhanced the release of PGE-2 in hAFCs CM, while this increase was completely suppressed by 10 µM cxb. hAFCs revealed elevated IL-6 and IL-8 release following TNF-α and IL-1β treatment, though cxb did not alter this. The effect of hAFCs CM on DRG cell sensitization was influenced by adding cxb to hAFCs; both the DRG cell line and primary bovine DRG nociceptors showed a lower sensitivity to bradykinin stimulation.

CONCLUSION

Cxb can inhibit PGE-2 production in hAFCs in an IL-1β-induced pro-inflammatory in vitro environment. The cxb applied to the hAFCs also reduces the sensitization of DRG nociceptors that are stimulated by the hAFCs CM.

RNA-Seq Reveals Sex Differences in Gene Expression during Peripheral Neuropathic Inflammation and in Pain Relief from a COX-2 Inhibiting Theranostic Nanoemulsion

Given decades of neuroinflammatory pain research focused only on males, there is an urgent need to better understand neuroinflammatory pain in females. This, paired with the fact that currently there is no long-term effective treatment for neuropathic pain furthers the need to evaluate how neuropathic pain develops in both sexes and how it can be relieved. Here we show that chronic constriction injury of the sciatic nerve caused comparable levels of mechanical allodynia in both sexes. Using a COX-2 inhibiting theranostic nanoemulsion with increased drug loading, both sexes achieved similar reduction in mechanical hypersensitivity. Given that both sexes have improved pain behavior, we specifically explored differential gene expression between sexes in the dorsal root ganglia (DRG) during pain and relief. Total RNA from the DRG revealed a sexually dimorphic expression for injury and relief caused by COX-2 inhibition. Of note, both males and females experience increased expression of activating transcription factor 3 (Atf3), however, only the female DRG shows decreased expression following drug treatment. Alternatively, S100A8 and S100A9 expression appear to play a sex specific role in relief in males. The sex differences in RNA expression reveal that comparable behavior does not necessitate the same gene expression.

Khellin as a selective monoamine oxidase B inhibitor ameliorated paclitaxel-induced peripheral neuropathy in mice

BACKGROUND

Treatment of paclitaxel (PTX)-induced peripheral neuropathy (PIPN) is full of challenges because of the unclear pathogenesis of PIPN. Herbal folk medicine Khellin (Khe) is a natural compound extracted from Ammi visnaga for treatment of renal colics and muscle spasms.

PURPOSE

Here, we aimed to assess the potential of Khe in ameliorating PIPN-like pathology in mice and investigate the underlying mechanisms.

METHODS

PIPN model mice were conducted by injection of PTX based on the published approach. The capability of Khe in ameliorating the PTX-induced neurological dysfunctions was assayed by detection of nociceptive hypersensitivities including mechanical hyperalgesia, thermal hypersensitivity, and cold allodynia in mice. The underlying mechanisms were investigated by assays against the PIPN mice with MAOB-specific knockdown in spinal cord and dorsal root ganglion (DRG) tissues by injection of adeno-associated virus (AAV)-MAOB-shRNA.

RESULTS

We determined that MAOB not MAOA is highly overexpressed in the spinal cord and DRG tissues of PIPN mice and Khe as a selective MAOB inhibitor improved PIPN-like pathology in mice. Khe promoted neurite outgrowth, alleviated apoptosis, and improved mitochondrial dysfunction of DRG neurons by targeting MAOB. Moreover, Khe inhibited spinal astrocytes activation and suppressed neuroinflammation of spinal astrocytes via MAOB/NF-κB/NLRP3/ASC/Caspase1/IL-1β pathway.

CONCLUSION

Our work might be the first to report that MAOB not MAOA is selectively overexpressed in the spinal cord and DRG tissues of PIPN mice, and all findings have highly addressed the potency of selective MAOB inhibitor in the amelioration of PIPN-like pathology and highlighted the potential of Khe in treating PTX-induced side effects.

Pain and aging: A unique challenge in neuroinflammation and behavior

Chronic pain is one of the most common, costly, and potentially debilitating health issues facing older adults, with attributable costs exceeding $600 billion annually. The prevalence of pain in humans increases with advancing age. Yet, the contributions of sex differences, age-related chronic inflammation, and changes in neuroplasticity to the overall experience of pain are less clear, given that opposing processes in aging interact. This review article examines and summarizes pre-clinical research and clinical data on chronic pain among older adults to identify knowledge gaps and provide the base for future research and clinical practice. We provide evidence to suggest that neurodegenerative conditions engender a loss of neural plasticity involved in pain response, whereas low-grade inflammation in aging increases CNS sensitization but decreases PNS sensitivity. Insights from preclinical studies are needed to answer mechanistic questions. However, the selection of appropriate aging models presents a challenge that has resulted in conflicting data regarding pain processing and behavioral outcomes that are difficult to translate to humans.

Nerve decompression surgery suppresses TNF-ɑ expression and T cell infiltration in a rat sciatic nerve chronic constriction injury model

Decompression surgery (DS) is a standard treatment for chronic nerve compression injuries; however, the mechanisms underlying its effects remain unclear. Here, we investigated the effects of DS on messenger RNA (mRNA) expression of tumor necrosis factor-α (TNF-α) and T cell recruitment in a rat sciatic nerve (SN) chronic constriction injury (CCI) model. Male Wistar rats were subjected to CCI to establish a model of SN injury (CCI group). DS, in which all ligatures were removed, was performed 3 days after CCI surgery (CCI + dec group). Mechanical sensitivity was assessed using the von Frey test 3, 7, and 14 days after the CCI surgery. Gene expression of Tnfa, Cd3, Cxcl10, and immunolocalization of TNF-α and the pan T cell marker, CD3, was evaluated using quantitative polymerase chain reaction (qPCR) and immunohistochemistry, respectively. In addition, the effects of TNF-α on Cxcl10 expression and CXCL10 protein production were evaluated using qPCR and enzyme-linked immunosorbent assay in SN cell culture. Rats that received DS had significantly higher withdrawal threshold levels than those in the CCI group. In addition, Tnfa, Cd3, and Cxcl10 mRNA expression increased following CCI. DS suppressed this elevated expression, with the CCI + dec group showing significantly reduced expression levels compared to the CCI group. Furthermore, TNF-α induced Cxcl10 expression and CXCL10 protein production in SN cell culture. Therefore, DS reduced TNF-α expression and T cell recruitment in the rat SN CCI model. These observations may partly explain the mechanism underlying the therapeutic effects of DS.

IMT504 blocks allodynia in rats with spared nerve injury by promoting the migration of mesenchymal stem cells and by favoring an anti-inflammatory milieu at the injured nerve

ABSTRACT

IMT504, a noncoding, non-CpG oligodeoxynucleotide, modulates pain-like behavior in rats undergoing peripheral nerve injury, through mechanisms that remain poorly characterized. Here, we chose the spared nerve injury model in rats to analyze the contribution of mesenchymal stem cells (MSCs) in the mechanisms of action of IMT504. We show that a single subcutaneous administration of IMT504 reverses mechanical and cold allodynia for at least 5 weeks posttreatment. This event correlated with long-lasting increases in the percentage of MSCs in peripheral blood and injured sciatic nerves, in a process seemingly influenced by modifications in the CXCL12-CXCR4 axis. Also, injured nerves presented with reduced tumor necrosis factor-α and interleukin-1β and increased transforming growth factor-β1 and interleukin-10 protein levels. In vitro analysis of IMT504-pretreated rat or human MSCs revealed internalized oligodeoxynucleotide and confirmed its promigratory effects. Moreover, IMT504-pretreatment induced transcript expression of Tgf-β1 and Il-10 in MSCs; the increase in Il-10 becoming more robust after exposure to injured nerves. Ex vivo exposure of injured nerves to IMT504-pretreated MSCs confirmed the proinflammatory to anti-inflammatory switch observed in vivo. Interestingly, the sole exposure of injured nerves to IMT504 also resulted in downregulated Tnf-α and Il-1β transcripts. Altogether, we reveal for the first time a direct association between the antiallodynic actions of IMT504, its promigratory and cytokine secretion modulating effects on MSCs, and further anti-inflammatory actions at injured nerves. The recapitulation of key outcomes in human MSCs supports the translational potential of IMT504 as a novel treatment for neuropathic pain with a unique mechanism of action involving the regulation of neuroimmune interactions.

Behavioral and inflammatory sex differences revealed by celecoxib nanotherapeutic treatment of peripheral neuroinflammation

Neuropathic pain affects millions of people worldwide, yet the molecular mechanisms of how it develops and persists are poorly understood. Given that males have historically been utilized as the primary sex in preclinical studies, less is known about the female neuroinflammatory response to injury, formation of pain, or response to pain-relieving therapies. Macrophages contribute to the development of neuroinflammatory pain via the activation of their cyclooxygenase-2 (COX-2) enzyme, which leads to the production of prostaglandin E₂ (PGE₂). PGE₂ activates nociception and influences additional leukocyte infiltration. Attenuation of COX-2 activity decreases inflammatory pain, most commonly achieved by nonsteroidal anti-inflammatory drugs (NSAIDs), yet NSAIDs are considered ineffective for neuropathic pain due to off target toxicity. Using chronic constriction injury of the rat sciatic nerve, we show that males and females exhibit quantitatively the same degree of mechanical allodynia post injury. Furthermore, a low-dose nanotherapeutic containing the NSAID celecoxib is phagocytosed by circulating monocytes that then naturally accumulate at sites of injury as macrophages. Using this nanotherapeutic, we show that treated males exhibit complete reversal of hypersensitivity, while the same dose of nanotherapeutic in females provides an attenuated relief. The difference in behavioral response to the nanotherapy is reflected in the reduction of infiltrating macrophages at the site of injury. The observations contained in this study reinforce the notion that female neuroinflammation is different than males.

A retrospective comparative study of local anesthesia only and local anesthesia with sedation for percutaneous endoscopic lumbar discectomy

It is still an unsolved problem to achieve both immediate intraoperative feedback and satisfactory surgical experience in percutaneous endoscopic lumbar discectomy under local anesthesia for lumbar disk herniation (LDH) patients. Herein, we compared the analgesic and sedative effects of local anesthesia alone and local anesthesia with conscious sedation in LDH patients during percutaneous endoscopic lumbar discectomy. Ninety-two LDH patients were enrolled and divided into the following groups: control group (Con Group), dexmedetomidine group (Dex Group), oxycodone group (Oxy Group), and dexmedetomidine + oxycodone group (Dex + Oxy Group). Various signs, including mean arterial pressure (MAP), heart rate (HR), pulse oximeter oxygen saturation (SpO₂) and Ramsay score, were compared before anesthesia (T1), working cannula establishment (T2), nucleus pulposus removal (T3), and immediately postoperation (T4). Clinical outcomes, including VAS score, operation time, hospitalization period, Macnab criteria, and SF-36 score, were also evaluated. The Dex + Oxy Group showed the most stable MAP and HR at T2 and T3 in all groups. The clinical outcomes, such as VAS, hospitalization period, Macnab criteria, and SF-36 score, have no significant differences among groups (p > 0.05). Local anesthesia combined with conscious sedation is a safe and effective method to improve the surgical experience and achieve satisfying clinical outcomes for LDH patients during percutaneous endoscopic lumbar discectomy.

Maresin 1 promotes nerve regeneration and alleviates neuropathic pain after nerve injury

Background

Peripheral nerve injury (PNI) is a public health concern that results in sensory and motor disorders as well as neuropathic pain and secondary lesions. Currently, effective treatments for PNI are still limited. For example, while nerve growth factor (NGF) is widely used in the treatment of PNI to promote nerve regeneration, it also induces pain. Maresin 1 (MaR1) is an anti-inflammatory and proresolving mediator that has the potential to regenerate tissue. We determined whether MaR1 is able to promote nerve regeneration as well as alleviating neuropathic pain, and to be considered as a putative therapeutic agent for treating PNI.

Methods

PNI models were constructed with 8-week-old adult male ICR mice and treated with NGF, MaR1 or saline by local application, intrathecal injection or intraplantar injection. Behavioral analysis and muscle atrophy test were assessed after treatment. Immunofluorescence assay was performed to examine the expression of ATF-3, GFAP, IBA1, and NF200. The expression transcript levels of inflammatory factors IL1β, IL-6, and TNF-α were detected by quantitative real-time RT-PCR. AKT, ERK, mTOR, PI3K, phosphorylated AKT, phosphorylated ERK, phosphorylated mTOR, and phosphorylated PI3K levels were examined by western blot analysis. Whole-cell patch-clamp recordings were executed to detect transient receptor potential vanilloid 1 (TRPV1) currents.

Results

MaR1 demonstrated a more robust ability to promote sensory and motor function recovery in mice after sciatic nerve crush injury than NGF. Immunohistochemistry analyses showed that the administration of MaR1 to mice with nerve crush injury reduced the number of damaged DRG neurons, promoted injured nerve regeneration and inhibited gastrocnemius muscle atrophy. Western blot analysis of ND7/23 cells cultured with MaR1 or DRG neurons collected from MaR1 treated mice revealed that MaR1 regulated neurite outgrowth through the PI3K–AKT–mTOR signaling pathway. Moreover, MaR1 dose-dependently attenuated the mechanical allodynia and thermal hyperalgesia induced by nerve injury. Consistent with the analgesic effect, MaR1 inhibited capsaicin-elicited TRPV1 currents, repressed the nerve injury-induced activation of spinal microglia and astrocytes and reduced the production of proinflammatory cytokines in the spinal cord dorsal horn in PNI mice.

Conclusions

Application of MaR1 to PNI mice significantly promoted nerve regeneration and alleviated neuropathic pain, suggesting that MaR1 is a promising therapeutic agent for PNI.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02405-1.

Tetrodotoxin, a Potential Drug for Neuropathic and Cancer Pain Relief?

Tetrodotoxin (TTX) is a potent neurotoxin found mainly in puffer fish and other marine and terrestrial animals. TTX blocks voltage-gated sodium channels (VGSCs) which are typically classified as TTX-sensitive or TTX-resistant channels. VGSCs play a key role in pain signaling and some TTX-sensitive VGSCs are highly expressed by adult primary sensory neurons. During pathological pain conditions, such as neuropathic pain, upregulation of some TTX-sensitive VGSCs, including the massive re-expression of the embryonic VGSC subtype Na_V1.3 in adult primary sensory neurons, contribute to painful hypersensitization. In addition, people with loss-of-function mutations in the VGSC subtype Na_V1.7 present congenital insensitive to pain. TTX displays a prominent analgesic effect in several models of neuropathic pain in rodents. According to this promising preclinical evidence, TTX is currently under clinical development for chemo-therapy-induced neuropathic pain and cancer-related pain. This review focuses primarily on the preclinical and clinical evidence that support a potential analgesic role for TTX in these pain states. In addition, we also analyze the main toxic effects that this neurotoxin produces when it is administered at therapeutic doses, and the therapeutic potential to alleviate neuropathic pain of other natural toxins that selectively block TTX-sensitive VGSCs.

Investigation of Neuropathology after Nerve Release in Chronic Constriction Injury of Rat Sciatic Nerve

Peripheral compressive neuropathy causes significant neuropathic pain, muscle weakness and prolong neuroinflammation. Surgical decompression remains the gold standard of treatment but the outcome is suboptimal with a high recurrence rate. From mechanical compression to chemical propagation of the local inflammatory signals, little is known about the distinct neuropathologic patterns and the genetic signatures after nerve decompression. In this study, controllable mechanical constriction forces over rat sciatic nerve induces irreversible sensorimotor dysfunction with sustained local neuroinflammation, even 4 weeks after nerve release. Significant gene upregulations are found in the dorsal root ganglia, regarding inflammatory, proapoptotic and neuropathic pain signals. Genetic profiling of neuroinflammation at the local injured nerve reveals persistent upregulation of multiple genes involving oxysterol metabolism, neuronal apoptosis, and proliferation after nerve release. Further validation of the independent roles of each signal pathway will contribute to molecular therapies for compressive neuropathy in the future.

Gene Transcript Alterations in the Spinal Cord, Anterior Cingulate Cortex, and Amygdala in Mice Following Peripheral Nerve Injury

Chronic neuropathic pain caused by nerve damage is a most common clinical symptom, often accompanied by anxiety- and depression-like symptoms. Current treatments are very limited at least in part due to incompletely understanding mechanisms underlying this disorder. Changes in gene expression in the dorsal root ganglion (DRG) have been acknowledged to implicate in neuropathic pain genesis, but how peripheral nerve injury alters the gene expression in other pain-associated regions remains elusive. The present study carried out strand-specific next-generation RNA sequencing with a higher sequencing depth and observed the changes in whole transcriptomes in the spinal cord (SC), anterior cingulate cortex (ACC), and amygdala (AMY) following unilateral fourth lumbar spinal nerve ligation (SNL). In addition to providing novel transcriptome profiles of long non-coding RNAs (lncRNAs) and mRNAs, we identified pain- and emotion-related differentially expressed genes (DEGs) and revealed that numbers of these DEGs displayed a high correlation to neuroinflammation and apoptosis. Consistently, functional analyses showed that the most significant enriched biological processes of the upregulated mRNAs were involved in the immune system process, apoptotic process, defense response, inflammation response, and sensory perception of pain across three regions. Moreover, the comparisons of pain-, anxiety-, and depression-related DEGs among three regions present a particular molecular map among the spinal cord and supraspinal structures and indicate the region-dependent and region-independent alterations of gene expression after nerve injury. Our study provides a resource for gene transcript expression patterns in three distinct pain-related regions after peripheral nerve injury. Our findings suggest that neuroinflammation and apoptosis are important pathogenic mechanisms underlying neuropathic pain and that some DEGs might be promising therapeutic targets.

Investigational drugs in early phase clinical trials targeting thermotransient receptor potential (thermoTRP) channels

INTRODUCTION

Thermo transient receptor potential (thermoTRP) channels are some of the most intensely pursued therapeutic targets of the past decade. They are considered promising targets of numerous diseases including chronic pain and cancer. Modulators of these proteins, in particular TRPV1-4, TRPM8 and TRPA1, have reached clinical development, but none has been approved for clinical practice yet.

AREAS COVERED

The therapeutic potential of targeting thermoTRP channels is discussed. The discussion is centered on our experience and on available data found in SciFinder, PubMed, and ClinicalTrials.gov database from the past decade. This review focuses on the therapeutic progress concerning this family of channels, including strategies to improve their therapeutic index for overcoming adverse effects.

EXPERT OPINION

Although thermoTRPs are pivotal drug targets, translation to the clinic has faced two key problems, (i) unforeseen side effects in Phase I trials and, (ii) poor clinical efficacy in Phase II trials. Thus, there is a need for (i) an enhanced understanding of the physiological role of these channels in tissues and organs and (ii) the development of human-based pre-clinical models with higher clinical translation. Furthermore, progress in nanotechnology-based delivery strategies will positively impact thermoTRP human pharmacology.

Preoperative Chronic and Acute Pain Affects Postoperative Cognitive Function Mediated by Neurotransmitters

The effective prevention of postoperative cognitive dysfunction (POCD) needs to be explored, and the effect of preoperative pain on POCD remains unclear. We established a chronic pain model induced by chronic constriction injury (CCI) and models of acute pain and anxiety without pain in mice that were subsequently subjected to partial hepatectomy surgery. Morris water maze (MWM) tests were performed to evaluate the learning and memory abilities of the mice. ELISA was used to measure IL-1β, IL-6, and TNF-α in serum, and HPLC-MS was used to detect neurotransmitters in the prefrontal cortices and hippocampi of the mice. The results indicated that chronic pain induced by CCI might have significantly impaired the learning and memory abilities of mice, while acute pain and anxiety without pain only affected the memory abilities of mice. Perioperative acute pain increased the level of IL-1β in serum, and CCI might have increased the level of IL-6. CCI and acute pain increased dopamine (DA) levels in the cortex, similar to anxiety. Like anxiety, CCI increased 5-hydroxytryptamine (5-HT) levels in the prefrontal cortex and hippocampus. Acute pain led to a decrease in the acetylcholine (ACH) level in the hippocampus. Our results suggest that acute pain and CCI-induced chronic pain might aggravate postoperative cognitive dysfunction via neurotransmitters and by changing the levels of inflammatory factors such as IL-1β and IL-6.

A Novel Fabrication of Dose-Dependent Injectable Curcumin Biocomposite Hydrogel System Anesthetic Delivery Method for Care and Management of Musculoskeletal Pain

Chronic musculoskeletal pain has biological, psychological, and social components. In this article, we have demonstrated the easily injectable nanocomposite carrier for the treatment of chronic musculoskeletal pain. Briefly, the curcumin (Cur) loaded with lipid nanocapsules (LNCs; Cur@LNCs) using the phase invasion method. The synthesized Cur@LNCs were characterized by using scanning electron microscopy, transmittance electron microscopy, and the size of the fabricated nanoparticles confirmed by dynamic light scattering analysis. The synthesized Cur@LNC injectable hydrogel shows excellent results in vivo in the rat model. We have examined the efficiency of the chronic constriction injury in the rat model and induced the pain using thermal paw withdrawal latency. The injectable hydrogels Cur@LNCs display a remarkable reduction in pain 7 days post administrations compared to the untreated group animals. This work could establish the preclinical candidate of the neuropathic pain response in the future.

Targeted cyclooxygenase-2 inhibiting nanomedicine results in pain-relief and differential expression of the RNA transcriptome in the dorsal root ganglia of injured male rats

Chronic constriction injury of the sciatic nerve in rats causes peripheral neuropathy leading to pain-like behaviors commonly seen in humans. Neuropathy is a leading cause of neuropathic pain, which involves a complex cellular and molecular response in the peripheral nervous system with interactions between neurons, glia, and infiltrating immune cells. In this study, we utilize a nonsteroidal anti-inflammatory drug -loaded nanoemulsion to deliver the cyclooxygenase-2 inhibitor, Celecoxib, directly to circulating monocytes following nerve injury, which provides long-lasting pain relief. However, it is not fully understood how cyclooxygenase-2 inhibition in a macrophage traveling to the site of injury impacts gene expression in the dorsal root ganglia. To elucidate aspects of the molecular mechanisms underlying pain-like behavior in chronic constriction injury, as well as subsequent pain relief with treatment, we employ RNAseq transcriptome profiling of the dorsal root ganglia associated with the injured sciatic nerve in rats. Using high throughput RNA sequencing in this way provides insight into the molecular mechanisms involved in this neuroinflammatory response. We compare the transcriptome from the dorsal root ganglias of the following study groups: chronic constriction injury animals administered with cyclooxygenase-2 inhibiting celecoxib-loaded nanoemulsion, chronic constriction injury animals administered with vehicle treatment, a drug-free nanoemulsion, and a group of naïve, unoperated and untreated rats. The results show an extensive differential expression of 115 genes. Using the protein annotation through evolutionary relationship classification system, we have revealed pain-related signaling pathways and underlying biological mechanisms involved in the neuroinflammatory response. Quantitative polymerase chain reaction validation confirms expression changes for several genes. This study shows that by directly inhibiting cyclooxygenase-2 activity in infiltrating macrophages at the injured sciatic nerve, there is an associated change in the transcriptome in the cell bodies of the dorsal root ganglia.