TRPV1: A Potential Drug Target for Treating Various Diseases

Capsaicin-insensitivity of TRPV1-R575D mutant located at the lipid-water-interface region can be rescued by either extracellular Ca2+-chelation or cholesterol reduction

TRPV1 acts as a unique polymodal ion channel having distinct structure and gating properties. In this context, TRPV1-R575D represents a special mutant located at the inner lipid-water-interface (LWI) region that has less possibility of interaction with membrane cholesterol. In control conditions, this lab-generated mutant of TRPV1 shows no "ligand-sensitivity", reduced surface expression, reduced localization in the lipid rafts, yet induces high cellular lethality. Notably, the cellular lethality induced by TRPV1-R575D expression can be rescued by adding 5'I-RTX (a specific inhibitor of TRPV1) or by introducing another mutation in the next position, i.e. in TRPV1-R575D/D576R. In this work we characterized TRPV1-R575D and TRPV1-R575D/D576R mutants in different cellular conditions and compared with the TRPV1-WT. We report that the "ligand-insensitivity" of TRPV1-R575D can be rescued in certain conditions, such as by chelation of extracellular Ca2+, or by reduction of the membrane cholesterol. Here we show that Ca2+ plays an important role in the channel gating of TRPV1-WT as well as LWI mutants (TRPV1-R575D, TRPV1-R575D/D576R). However, chelation of intracellular Ca2+ or depletion of ER Ca2+ did not have a significant effect on the TRPV1-R575D. Certain properties related to channel gating of mutant TRPV1-R575D/D576R can be rescued partially or fully in a context -dependent manner. Cholesterol depletion also alters these properties. Our data suggests that lower intracellular basal Ca2+ acts as a pre-requisite for further opening of TRPV1-R575D. These findings enable better understanding of the structure-function relationship of TRPV1 and may be critical in comprehending the channelopathies induced by other homologous thermosensitive TRPVs.

TRP Channels in Cancer: Therapeutic Opportunities and Research Strategies

The influence of gut microbiota on transient receptor potential (TRP) channels has been identified as an important element in developing gastrointestinal conditions, yet its involvement in cancer progression is not as thoroughly understood. This review explores the multifaceted roles of TRP channels in oncogenesis and emphasizes their significance in cancer progression and therapeutic outcomes. Critical focus was placed on the influence of traditional medicines, such as traditional Chinese medicine (TCM) related aromatic medicines, on TRP channel functions. Moreover, we explored the interplay between the gut microbiota and TRP channels in cancer signaling, highlighting the therapeutic potential of targeting this axis in cancer treatment. The impact of current therapies on TRP channel function was examined, highlighting the need for a comprehensive understanding of how different modalities affect TRP channels in cancer. Technological advancements, including artificial intelligence (AI) tools and computer-aided drug development (CADD), have been discussed in the context of leveraging TRP channels for innovative cancer therapies. Future directions emphasize the potential applications of TRP channel research in advancing cancer treatment and enhancing patient well-being.

TRPV1 channel in the pathophysiology of epilepsy and its potential as a molecular target for the development of new antiseizure drug candidates

Identification of transient receptor potential cation channel, subfamily V member 1 (TRPV1), also known as capsaicin receptor, in 1997 was a milestone achievement in the research on temperature sensation and pain signalling. Very soon after it became evident that TRPV1 is implicated in a wide array of physiological processes in different peripheral tissues, as well as in the central nervous system, and thereby could be involved in the pathophysiology of numerous diseases. Increasing evidence suggests that modulation of TRPV1 may also affect seizure susceptibility and epilepsy. This channel is localized in brain regions associated with seizures and epilepsy, and its overexpression was found both in animal models of seizures and in brain samples from epileptic patients. Moreover, modulation of TRPV1 on non-neuronal cells (microglia, astrocytes, and/or peripheral immune cells) may have an impact on the neuroinflammatory processes that play a role in epilepsy and epileptogenesis. In this paper, we provide a comprehensive and critical overview of currently available data on TRPV1 as a possible molecular target for epilepsy management, trying to identify research gaps and future directions. Overall, several converging lines of evidence implicate TRPV1 channel as a potentially attractive target in epilepsy research but more studies are needed to exploit the possible role of TRPV1 in seizures/epilepsy and to evaluate the value of TRPV1 ligands as candidates for new antiseizure drugs.

Nanodelivery of antioxidant Agents: A promising strategy for preventing sensorineural hearing loss

Sensorineural hearing loss (SNHL), often stemming from reactive oxygen species (ROS) generation due to various factors such as ototoxic drugs, acoustic trauma, and aging, remains a significant health concern. Oxidative stress-induced damage to the sensory cells of the inner ear, particularly the non-regenerating hair cells, is a critical pathologic mechanism leading to SNHL. Despite the proven efficacy of antioxidants in mitigating oxidative stress, their clinical application for otoprotection is hindered by the limitations of conventional drug delivery methods. This review highlights the challenges associated with systemic and intratympanic administration of antioxidants, including the blood-labyrinthine barrier, restricted permeability of the round window membrane, and inadequate blood flow to the inner ear. To overcome these hurdles, the application of nanoparticles as a delivery platform for antioxidants emerges as a promising solution. Nanocarriers facilitate indirect drug delivery to the cochlea through the round and oval window membrane, optimising drug absorption while reducing dosage, Eustachian tube clearance, and associated side effects. Furthermore, the development of nanoparticles carrying antioxidants tailored to the intracochlear environment holds immense potential. This literature research aimed to critically examine the root causes of SNHL and ROS overproduction in the inner ear, offering insights into the application of nanoparticle-based drug delivery systems for safeguarding sensorineural hair cells. By focusing on the intricate interplay between oxidative stress and hearing loss, this research aims to contribute to the advancement of innovative therapeutic strategies for the prevention of SNHL.

Bifidobacterium longum subsp. longum BG-L47 boosts growth and activity of Limosilactobacillus reuteri DSM 17938 and its extracellular membrane vesicles

The aim of this study was to identify a Bifidobacterium strain that improves the performance of Limosilactobacillus reuteri DSM 17938. Initial tests showed that Bifidobacterium longum subsp. longum strains boosted the growth of DSM 17938 during in vivo-like conditions. Further characterization revealed that one of the strains, BG-L47, had better bile and acid tolerance compared to BG-L48, as well as mucus adhesion compared to both BG-L48 and the control strain BB536. BG-L47 also had the capacity to metabolize a broad range of carbohydrates and sugar alcohols. Mapping of glycoside hydrolase (GH) genes of BG-L47 and BB536 revealed many GHs associated with plant-fiber utilization. However, BG-L47 had a broader phenotypic fiber utilization capacity. In addition, B. longum subsp. longum cells boosted the bioactivity of extracellular membrane vesicles (MV) produced by L. reuteri DSM 17938 during co-cultivation. Secreted 5'-nucleotidase (5'NT), an enzyme that converts AMP into the signal molecule adenosine, was increased in MV boosted by BG-L47. The MV exerted an improved antagonistic effect on the pain receptor transient receptor potential vanilloid 1 (TRPV1) and increased the expression of the immune development markers IL-6 and IL-1ß in a peripheral blood mononuclear cell (PBMC) model. Finally, the safety of BG-L47 was evaluated both by genome safety assessment and in a human safety study. Microbiota analysis showed that the treatment did not induce significant changes in the composition. In conclusion, B. longum subsp. longum BG-L47 has favorable physiological properties, can boost the in vitro activity of L. reuteri DSM 17938, and is safe for consumption, making it a candidate for further evaluation in probiotic studies.

IMPORTANCE

By using probiotics that contain a combination of strains with synergistic properties, the likelihood of achieving beneficial interactions with the host can increase. In this study, we first performed a broad screening of Bifidobacterium longum subsp. longum strains in terms of synergistic potential and physiological properties. We identified a superior strain, BG-L47, with favorable characteristics and potential to boost the activity of the known probiotic strain Limosilactobacillus reuteri DSM 17938. Furthermore, we demonstrated that BG-L47 is safe for consumption in a human randomized clinical study and by performing a genome safety assessment. This work illustrates that bacteria-bacteria interactions differ at the strain level and further provides a strategy for finding and selecting companion strains of probiotics.

Three-Dimensional Quantitative Structure-Activity Relationship Study of Transient Receptor Potential Vanilloid 1 Channel Antagonists Reveals Potential for Drug Design Purposes

Transient receptor potential vanilloid 1 (TRPV1) was reported to be a putative target for recovery from chronic pain, producing analgesic effects after its inhibition. A series of drug candidates were previously developed, without the ability to ameliorate the therapeutic outcome. Starting from previously designed compounds, derived from the hybridization of antagonist SB-705498 and partial agonist MDR-652, we performed a virtual screening on a pharmacophore model built by exploiting the Cryo-EM 3D structure of a nanomolar antagonist in complex with the human TRPV1 channel. The pharmacophore model was described by three pharmacophoric features, taking advantage of both the bioactive pose of the antagonist and the receptor exclusion spheres. The results of the screening were implemented inside a 3D-QSAR model, correlating with the negative decadic logarithm of the inhibition rate of the ligands. After the validation of the obtained 3D-QSAR model, we designed a new series of compounds by introducing key modifications on the original scaffold. Again, we determined the compounds' binding poses after alignment to the pharmacophoric model, and we predicted their inhibition rates with the validated 3D-QSAR model. The obtained values resulted in being even more promising than parent compounds, demonstrating that ongoing research still leaves much room for improvement.

Functional nanotransducer-mediated wireless neural modulation techniques

Functional nanomaterials have emerged as versatile nanotransducers for wireless neural modulation because of their minimal invasion and high spatiotemporal resolution. The nanotransducers can convert external excitation sources (e.g. NIR light, x-rays, and magnetic fields) to visible light (or local heat) to activate optogenetic opsins and thermosensitive ion channels for neuromodulation. The present review provides insights into the fundamentals of the mostly used functional nanomaterials in wireless neuromodulation including upconversion nanoparticles, nanoscintillators, and magnetic nanoparticles. We further discussed the recent developments in design strategies of functional nanomaterials with enhanced energy conversion performance that have greatly expanded the field of neuromodulation. We summarized the applications of functional nanomaterials-mediated wireless neuromodulation techniques, including exciting/silencing neurons, modulating brain activity, controlling motor behaviors, and regulating peripheral organ function in mice. Finally, we discussed some key considerations in functional nanotransducer-mediated wireless neuromodulation along with the current challenges and future directions.

Transient receptor potential vanilloid 1 interacts with Toll-like receptor 4 (TLR4)/cluster of differentiation 14 (CD14) signaling pathway in lipopolysaccharide-mediated inflammation in macrophages

Transient receptor potential vanilloid 1 (TRPV1), a ligand-gated cation channel, is a receptor for vanilloids on sensory neurons and is also activated by capsaicin, heat, protons, arachidonic acid metabolites, and inflammatory mediators on neuronal or non-neuronal cells. However, the role of the TRPV1 receptor in pro-inflammatory cytokine secretion and its potential regulatory mechanisms in lipopolysaccharide (LPS)-induced inflammation has yet to be entirely understood. To investigate the role and regulatory mechanism of the TRPV1 receptor in regulating LPS-induced inflammatory responses, bone marrow-derived macrophages (BMDMs) harvested from wild-type (WT) and TRPV1 deficient (Trpv1-/-) mice were used as the cell model. In WT BMDMs, LPS induced an increase in the levels of tumor necrosis factor-α, IL-1β, inducible nitric oxide synthase, and nitric oxide, which were attenuated in Trpv1-/- BMDMs. Additionally, the phosphorylation of inhibitor of nuclear factor kappa-Bα and mitogen-activated protein kinases, as well as the translocation of nuclear factor kappa-B and activator protein 1, were all decreased in LPS-treated Trpv1-/- BMDMs. Immunoprecipitation assay revealed that LPS treatment increased the formation of TRPV1-Toll-like receptor 4 (TLR4)-cluster of differentiation 14 (CD14) complex in WT BMDMs. Genetic deletion of TRPV1 in BMDMs impaired the LPS-triggered immune-complex formation of TLR4, myeloid differentiation protein 88, and interleukin-1 receptor-associated kinase, all of which are essential regulators in LPS-induced activation of the TLR4 signaling pathway. Moreover, genetic deletion of TRPV1 prevented the LPS-induced lethality and pro-inflammatory production in mice. In conclusion, the TRPV1 receptor may positively regulate the LPS-mediated inflammatory responses in macrophages by increasing the interaction with the TLR4-CD14 complex and activating the downstream signaling cascade.

The combined effect of oxidative stress and TRPV1 on temperature-induced asthma: Evidence in a mouse model

Temperature is one of the possible activators for asthma. As global warming continues, the health hazard of high temperatures is increasing. It is unclear, nevertheless, how high temperatures affect asthma. The research aims to examine how asthma is affected by high temperatures and underlying molecular mechanisms. The BALB/c mice were adopted in a model of asthma. The mice were exposed at 24 °C, 38 °C and 40 °C for 4h on weekdays from day 1 to day 30. After the experiment, the lung function was measured in vivo, and then serum protein, pulmonary inflammation and immunohistochemistry assay was assessed in vitro. As the temperature increased from 24 °C to 40 °C, there was a significant increase in serum protein, while there is no discernible difference in serum protein of OVA-sIgE and OVA-sIgG between the OVA (38 °C) group and OVA (24 °C) group. The immunohistochemistry assay showed a change in the pro-inflammatory cytokines. The histopathological analysis exhibited the change of airway structure after high-temperature exposure, especially for exposure at 40 °C. The results of signals protein showed a remarkable rise of TRPV1 for OVA+40 °C. Our results revealed that high temperatures may make asthmatic airway dysfunction severe, and the higher the temperature, the more serious asthma. The oxidative stress and TRPV1 receptor can be a potential drug target for asthma. It will provide a new tool for precision medicine in asthma.

The effect of perineural injection therapy on neuropathic pain: a retrospective study

Background

Among the various pain-related diseases that can be encountered at the clinic, there is a neuropathic pain that is difficult to treat. Numerous methods have been proposed to treat neuropathic pain, such as taking medication, nerve block with lidocaine, or neurolysis with alcohol or phenol. Recently, a method of perineural injection using dextrose instead of lidocaine was proposed. This study was designed to compare the effects of perineural injection therapy (PIT) with buffered 5% dextrose or 0.5% lidocaine on neuropathic pain.

Methods

The data were collected from the database of pain clinic from August 1st, 2019 to December 31st, 2022 without any personal information. The inclusion criteria were patients diagnosed with postherpetic neuralgia (PHN), trigeminal neuralgia (TN), complex regional pain syndrome (CRPS), or peripheral neuropathy (PN), and patients who had undergone PIT with buffered 5% dextrose (Dextrose group) or 0.5% lidocaine (Lidocaine group) for pain control. The data of patients, namely sex, age, and pain score (numerical rating scale, NRS) were collected before PIT. The data of NRS, side effects, and satisfaction grade (excellent, good, fair, or poor) were collected one week after each of the four PIT, and two weeks after the last PIT.

Results

Overall, 112 subjects were enrolled. The Dextrose group included 89 and Lidocaine group included 23 patients. Because the number of patients in the Lidocaine group was too small to allow statistical analysis, the trend in Lidocaine group was just observed in each disease. There were no significant side effects except for a few bruise cases on the site of injection in all groups. The NRS in most Dextrose groups except CRPS were reduced significantly; however, the Lidocaine group showed a trend of pain reduction only in PHN. The Dextrose group except CRPS showed increased satisfaction two weeks after the final PIT.

Conclusion

From the results, it is suggested that PIT with buffered 5% dextrose may have a good effect for neuropathic pain without any side effect except for patients with CRPS. This may offer a window into a new tool that practitioners can employ in their quest to help patients with neuropathic pain.

Novel marine natural products as effective TRPV1 channel blockers

Chronic pain management poses a formidable challenge to healthcare, exacerbated by current analgesic options' limitations and adverse effects. Transient receptor potential vanilloid 1 (TRPV1), a non-selective cation channel, has emerged as a promising target for novel analgesics. However, safety and tolerability concerns have constrained the development of TRPV1 modulators. In this study, we explored marine-derived natural products as a source of potential TRPV1 modulators using high-throughput dye-uptake assays. We identified chrexanthomycins, a family of hexacyclic xanthones, exhibited potent TRPV1 inhibitory effects, with compounds cC and cF demonstrating the most significant activity. High-resolution patch-clamp assays confirmed the direct action of these compounds on the TRPV1 channel. Furthermore, in vivo assays revealed that cC and cF effectively suppressed capsaicin-induced pain sensation in mice, comparable to the known TRPV1 inhibitor, capsazepine. Structural-activity relationship analysis highlighted the importance of specific functional groups in modulating TRPV1 activity. Our findings underscore the therapeutic potential of chrexanthomycins and pave the way for further investigations into marine-derived TRPV1 modulators for pain management.

Impact of TRPV1 on Pathogenesis and Therapy of Neurodegenerative Diseases

Transient receptor potential vanilloid 1 (TRPV1) is a transmembrane and non-selective cation channel protein, which can be activated by various physical and chemical stimuli. Recent studies have shown the strong pathogenetic associations of TRPV1 with neurodegenerative diseases (NDs), in particular Alzheimer's disease (AD), Parkinson's disease (PD) and multiple sclerosis (MS) via regulating neuroinflammation. Therapeutic effects of TRPV1 agonists and antagonists on the treatment of AD and PD in animal models also are emerging. We here summarize the current understanding of TRPV1's effects and its agonists and antagonists as a therapeutic means in neurodegenerative diseases, and highlight future treatment strategies using natural TRPV1 agonists. Developing new targets and applying natural products are becoming a promising direction in the treatment of chronic disorders, especially neurodegenerative diseases.

Progress in the development of TRPV1 small-molecule antagonists: Novel Strategies for pain management

Transient receptor potential vanilloid 1 (TRPV1) channels are widely distributed in sensory nerve endings, the central nervous system, and other tissues, functioning as ion channel proteins responsive to thermal pain and chemical stimuli. In recent years, the TRPV1 receptor has garnered significant interest as a potential therapeutic approach for various pain-related disorders, particularly TRPV1 antagonists. The present review offers a comprehensive, systematic exploration of both first- and second-generation TRPV1 antagonists in the context of pain management. Antagonists are categorized and explicated according to their structural characteristics. Detailed examination of binding modes, structural features, and pharmacological activities, alongside a critical appraisal of the advantages and limitations inherent to typical compounds within each structural category, are undertaken. Detailed discussions of the binding modes, structural features, pharmacological activities, advantages, and limitations of typical compounds within each structural category offer valuable insights and guidance for the future research and development of safer, more effective, and more targeted TRPV1 antagonists.

Insights from molecular dynamics simulations of TRPV1 channel modulators in pain

TRPV1 is a nonselective cation channel vital for detecting noxious stimuli (heat, acid, capsaicin). Its role in pain makes it a potential drug target for chronic pain management, migraines, and related disorders. This review updates molecular dynamics (MD) simulation studies on the TRPV1 channel, focusing on its gating mechanism, ligand-binding sites, and implications for drug design. The article also explores challenges in developing modulators, SAR optimization, and clinical trial studies. Efforts have been undertaken to concisely present MD simulation findings, with a focus on their relevance to drug discovery.

Ocular Pharmacology and Toxicology of TRPV1 Antagonist SAF312 (Libvatrep)

Purpose

To evaluate the pharmacology and toxicology of SAF312, a transient receptor potential vanilloid 1 (TRPV1) antagonist.

Methods

TRPV1 expression in human ocular tissues was evaluated with immunohistochemistry. Inhibition of calcium influx in Chinese hamster ovary (CHO) cells expressing human TRPV1 (hTRPV1) and selectivity of SAF312 were assessed by a fluorescent imaging plate reader assay. Ocular tissue and plasma pharmacokinetics (PK) were assessed following a single topical ocular dose of SAF312 (0.5%, 1.0%, 1.5%, 2.5%) in rabbits. Safety and tolerability of SAF312 were evaluated in rabbits and dogs. Effects of SAF312 on corneal wound healing after photorefractive keratectomy (PRK) surgery were assessed in rabbits.

Results

TRPV1 expression was noted in human cornea and conjunctiva. SAF312 inhibited calcium influx in CHO-hTRPV1 cells induced by pH 5.5 (2-[N-morpholino] ethanesulfonic acid), N-arachidonoylethanolamine, capsaicin, and N-arachidonoyl dopamine, with IC50 values of 5, 10, 12, and 27 nM, respectively, and inhibition appeared noncompetitive. SAF312 demonstrated high selectivity for TRPV1 (>149-fold) over other TRP channels. PK analysis showed highest concentrations of SAF312 in cornea and conjunctiva. SAF312 was found to be safe and well tolerated in rabbits and dogs up to the highest feasible concentration of 2.5%. No delay in wound healing after PRK was observed.

Conclusions

SAF312 is a potent, selective, and noncompetitive antagonist of hTRPV1 with an acceptable preclinical safety profile for use in future clinical trials.

Translational Relevance

SAF312, which was safe and well tolerated without causing delay in wound healing after PRK in rabbits, may be a potential therapeutic agent for ocular surface pain.

Endocannabinoid-Binding Receptors as Drug Targets

Cannabis plant has been used from ancient times with therapeutic purposes for treating human pathologies, but the identification of the cellular and molecular mechanisms underlying the therapeutic properties of the phytocannabinoids, the active compounds in this plant, occurred in the last years of the past century. In the late 1980s and early 1990s, seminal studies demonstrated the existence of cannabinoid receptors and other elements of the so-called endocannabinoid system. These G protein-coupled receptors (GPCRs) are a key element in the functions assigned to endocannabinoids and appear to serve as promising pharmacological targets. They include CB₁, CB₂, and GPR55, but also non-GPCRs can be activated by endocannabinoids, like ionotropic receptor TRPV₁ and even nuclear receptors of the PPAR family. Their activation, inhibition, or simply modulation have been associated with numerous physiological effects at both central and peripheral levels, which may have therapeutic value in different human pathologies, then providing a solid experimental explanation for both the ancient medicinal uses of Cannabis plant and the recent advances in the development of cannabinoid-based specific therapies. This chapter will review the scientific knowledge generated in the last years around the research on the different endocannabinoid-binding receptors and their signaling mechanisms. Our intention is that this knowledge may help readers to understand the relevance of these receptors in health and disease conditions, as well as it may serve as the theoretical basis for the different experimental protocols to investigate these receptors and their signaling mechanisms that will be described in the following chapters.

N-Methylamide-structured SB366791 derivatives with high TRPV1 antagonistic activity: toward PET radiotracers to visualize TRPV1

Transient receptor potential cation channel subfamily V member 1 (TRPV1)-targeted compounds were synthesized by modifying the structure of SB366791, a pharmaceutically representative TRPV1 antagonist. To avoid amide-iminol tautomerization, structurally supported N-methylated amides (i.e., 3-alkoxy-substitued N-meythylamide derivatives of SB366791) were evaluated using a Ca2+ influx assay, in which cells expressed recombinant TRPV1 in the presence of 1.0 μM capsaicin. The antagonistic activities of N-(3-methoxyphenyl)-N-methyl-4-chlorocinnamamide (2) (RLC-TV1004) and N-{3-(3-fluoropropoxy)phenyl}-N-methyl-4-chlorocinnamamide (4) (RLC-TV1006) were found to be approximately three-fold higher (IC50: 1.3 μM and 1.1 μM, respectively) than that of SB366791 (IC50: 3.7 μM). These results will help reinvigorate the potential of SB366791 in medicinal chemistry applications. The 3-methoxy and 3-fluoroalkoxy substituents were used to obtain radioactive [11C]methoxy- or [18F]fluoroalkoxy-incorporated tracers for in vivo positron emission tomography (PET). Using the 11C- or 18F-labeled derivatives, explorative PET imaging trials were performed in rats.

Role of TRPV1 in respiratory disease and association with traditional Chinese medicine: A literature review

Transient receptor potential vanilloid type 1 (TRPV1), involved in multiple pathophysiological processes including inflammation, is a thermally activated, non-selective cation channel. It has been identified that TRPV1 is highly involved in some common respiratory diseases including allergic rhinitis, asthma, chronic obstructive pulmonary disease, and pulmonary infection by participating in neurogenic and immunogenic inflammation, sensitization, and oxidative stress. In recent years, the hypothesis of transient receptor potential (TRP) has been introduced in studies on the theory of five flavors and four properties of Chinese medicinal. However, the hypothesis is undetermined due to the multi-component and multi-target characteristics of Chinese medicinal. This study describes the relations between TRPV1 and four types of respiratory diseases based on the literature in recent five years. In the meantime, the therapeutic effect of Chinese medicinal by intervening TRPV1 was reviewed, in an attempt to provide certain evidence for future studies on the medicinal property-effect relationship, mechanism of drug action, the syndrome differentiation in traditional Chinese medicine (TCM) for respiratory diseases and to help for new drug development.

Identification of a Partial and Selective TRPV1 Agonist CPIPC for Alleviation of Inflammatory Pain

Transient receptor potential vanilloid 1 (TRPV1) is a non-selective cation channel, predominantly expressed in a subset of peripheral sensory neurons for pain signaling. Topical application of agonist capsaicin for desensitizing TRPV1 currents has been approved for relief of chronic pain. However, the potent TRPV1 capsaicin is not ingestible and even topical capsaicin causes common side effects such as skin irritation, swelling, erythema and pruritus, suggesting that a mild TRPV1 agonist might be helpful for reducing side effects while reliving pain. In this study, we reported on a partial and selective TRPV1 agonist 4-(5-chloropyridin-2-yl)-N-(1H-indazol-6-yl)piperazine-1-carboxamide named CPIPC that was modified based on targeting the residue Arg557, important for conversion between the channel antagonism and agonism. Whole-cell patch clamp recordings indicated a concentration-dependent activation of TRPV1 currents by CPIPC with an EC₅₀ of 1.56 ± 0.13 μM. The maximum efficacy of CPIPC (30 μM) was about 60% of saturated capsaicin (10 μM). Repetitive additions of CPIPC caused TRPV1 current desensitization in both TRPV1-expressing HEK293 cells and dorsal root ganglion (DRG) sensory neurons. Oral administration of CPIPC dose-dependently alleviated inflammatory pain in mice. Further site-directed mutagenesis combined with molecular docking revealed that residue Arg557 is critical for TRPV1 activation by CPIPC. Taken together, we identified a novel partial and selective TRPV1 agonist CPIPC that exhibits antinociceptive activity in mice.

Capsaicin regulates lipid metabolism through modulation of bile acid/gut microbiota metabolism in high-fat-fed SD rats

Capsaicin (CAP) is one of the active ingredients found in chili peppers and has been shown to reduce fat. This study aimed to explore the mechanisms of CAP activity by investigating intestinal microorganisms and bile acids (BAs). This study utilized 16S RNA sequencing to detect gut microbiota in cecal contents, and BAs in Sprague Dawley (SD) rats were also investigated. The results showed that 1) CAP increased the levels of chenodeoxycholic acid (CDCA), deoxycholic acid (DCA), β-muricholic acid (β-MCA), and tauro-β-muricholic acid sodium salt (T-β-MCA), which can regulate farnesoid X receptor (FXR) to inhibit Fgf15, increased CYP7A1 expression to lower triglycerides (TG) and total cholesterol (TC); 2) CAP decreased the abundance of Firmicutes and promoted the presence of specific fermentative bacterial populations, like Akkermansia; meanwhile, less optimal dose can reduce Desulfovibrio; 3) CAP decreased inflammatory factors IL-6 and IL-1β, and increased transient receptor potential channel of vanilloid subtype 1 (TRPV1) to regulate lipid metabolism, fasting plasma glucose and insulin resistance. In conclusion, CAP can reduce fat accumulation by regulating BAs, microorganisms, and short-chain fatty acids.

Transient Receptor Potential Channels and Auditory Functions

Significance: Transient receptor potential (TRP) channels are cation-gated channels that serve as detectors of various sensory modalities, such as pain, heat, cold, and taste. These channels are expressed in the inner ear, suggesting that they could also contribute to the perception of sound. This review provides more details on the different types of TRP channels that have been identified in the cochlea to date, focusing on their cochlear distribution, regulation, and potential contributions to auditory functions. Recent Advances: To date, the effect of TRP channels on normal cochlear physiology in mammals is still unclear. These channels contribute, to a limited extent, to normal cochlear physiology such as the hair cell mechanoelectrical transduction channel and strial functions. More detailed information on a number of these channels in the cochlea awaits future studies. Several laboratories focusing on TRPV1 channels have shown that they are responsive to cochlear stressors, such as ototoxic drugs and noise, and regulate cytoprotective and/or cell death pathways. TRPV1 expression in the cochlea is under control of oxidative stress (produced primarily by NOX3 NADPH oxidase) as well as STAT1 and STAT3 transcription factors, which differentially modulate inflammatory and apoptotic signals in the cochlea. Inhibition of oxidative stress or inflammation reduces the expression of TRPV1 channels and protects against cochlear damage and hearing loss. Critical Issues: TRPV1 channels are activated by both capsaicin and cisplatin, which produce differential effects on the inner ear. How these differential actions are produced is yet to be determined. It is clear that TRPV1 is an essential component of cisplatin ototoxicity as knockdown of these channels protects against hearing loss. In contrast, activation of TRPV1 by capsaicin protected against subsequent hearing loss induced by cisplatin. The cellular targets that are influenced by these two drugs to account for their differential profiles need to be fully elucidated. Furthermore, the potential involvement of different TRP channels present in the cochlea in regulating cisplatin ototoxicity needs to be determined. Future Directions: TRPV1 has been shown to mediate the entry of aminoglycosides into the hair cells. Thus, novel otoprotective strategies could involve designing drugs to inhibit entry of aminoglycosides and possibly other ototoxins into cochlear hair cells. TRP channels, including TRPV1, are expressed on circulating and resident immune cells. These receptors modulate immune cell functions. However, whether they are activated by cochlear stressors to initiate cochlear inflammation and ototoxicity needs to be determined. A better understanding of the function and regulation of these TRP channels in the cochlea could enable development of novel treatments for treating hearing loss. Antioxid. Redox Signal. 36, 1158-1170.

Venom Peptide Toxins Targeting the Outer Pore Region of Transient Receptor Potential Vanilloid 1 in Pain: Implications for Analgesic Drug Development

The transient receptor potential vanilloid 1 (TRPV1) ion channel plays an important role in the peripheral nociceptive pathway. TRPV1 is a polymodal receptor that can be activated by multiple types of ligands and painful stimuli, such as noxious heat and protons, and contributes to various acute and chronic pain conditions. Therefore, TRPV1 is emerging as a novel therapeutic target for the treatment of various pain conditions. Notably, various peptides isolated from venomous animals potently and selectively control the activation and inhibition of TRPV1 by binding to its outer pore region. This review will focus on the mechanisms by which venom-derived peptides interact with this portion of TRPV1 to control receptor functions and how these mechanisms can drive the development of new types of analgesics.

Are TRPA1 and TRPV1 channel-mediated signalling cascades involved in UVB radiation-induced sunburn?

Burn injuries are underappreciated injuries associated with substantial morbidity and mortality. Overexposure to ultraviolet (UV) radiation has dramatic clinical effects in humans and is a significant public health concern. Although the mechanisms underlying UVB exposure are not fully understood, many studies have made substantial progress in the pathophysiology of sunburn in terms of its molecular aspects in the last few years. It is well established that the transient receptor potential ankyrin 1 (TRPA1), and vanilloid 1 (TRPV1) channels modulate the inflammatory, oxidative, and proliferative processes underlying UVB radiation exposure. However, it is still unknown which mechanisms underlying TRPV1/A1 channel activation are elicited in sunburn induced by UVB radiation. Therefore, in this review, we give an overview of the TRPV1/A1 channel-mediated signalling cascades that may be involved in the pathophysiology of sunburn induced by UVB radiation. These data will undoubtedly help to explain the various features of sunburn and contribute to the development of novel therapeutic approaches to better treat it.

Chinese Medicine Meets Conventional Medicine in Targeting COVID-19 Pathophysiology, Complications and Comorbidities

OBJECTIVE

To investigate how the National Health Commission of China (NHCC)-recommended Chinese medicines (CMs) modulate the major maladjustments of coronavirus disease 2019 (COVID-19), particularly the clinically observed complications and comorbidities.

METHODS

By focusing on the potent targets in common with the conventional medicines, we investigated the mechanisms of 11 NHCC-recommended CMs in the modulation of the major COVID-19 pathophysiology (hyperinflammations, viral replication), complications (pain, headache) and comorbidities (hypertension, obesity, diabetes). The constituent herbs of these CMs and their chemical ingredients were from the Traditional Chinese Medicine Information Database. The experimentally-determined targets and the activity values of the chemical ingredients of these CMs were from the Natural Product Activity and Species Source Database. The approved and clinical trial drugs against these targets were searched from the Therapeutic Target Database and DrugBank Database. Pathways of the targets was obtained from Kyoto Encyclopedia of Genes and Genomes and additional literature search.

RESULTS

Overall, 9 CMs modulated 6 targets discovered by the COVID-19 target discovery studies, 8 and 11 CMs modulated 8 and 6 targets of the approved or clinical trial drugs for the treatment of the major COVID-19 complications and comorbidities, respectively.

CONCLUSION

The coordinated actions of each NHCC-recommended CM against a few targets of the major COVID-19 pathophysiology, complications and comorbidities, partly have common mechanisms with the conventional medicines.

Mucin secretory action of capsaicin prevents high fat diet-induced gut barrier dysfunction in C57BL/6 mice colon

The gut barrier - including tight junction proteins (TJPs) and mucus layers, is the first line of defense against physical, chemical or pathogenic incursions. This barrier is compromised in various health disorders. Capsaicin, a dietary agonist of Transient receptor potential vanilloid 1 (TRPV1) channel, is reported to alleviate the complications of obesity. While it is well known to improve energy expenditure and metabolism, and prevent dysbiosis, the more local effects on the host gut - particularly the gut barrier and mucus system remain elusive. To investigate the effect of capsaicin on the gut barrier and mucus production and to understand the involvement of mucus, bacteria, and TRPV1 in these phenomena, we employed a diet-induced obesity model in C57BL/6 mice, and capsaicin (2 mg/kg/day p.o.) or mucin (1 g/kg/day p.o.) as interventions, for 12 weeks. Parameters like weight gain, glucose homeostasis, TJPs expression, mucus staining, intestinal permeability etc were studied. 16 S rDNA sequencing and in vitro Ca²⁺ measurement experiments were performed to explore the role of microbiota in the beneficial effects. Mucin feeding reflected several anti-obesity effects produced by capsaicin, suggesting that mucus modulation might play a crucial role in capsaicin-induced anti-obesity effects. 16 S rDNA sequencing and in vitro Ca²⁺ measurement experiments pointed to TRPV1 modulation by bacteria besides capsaicin. Capsaicin, bacteria and the host mucus system seem to act in a cyclic cascade involving TRPV1, which can be activated by capsaicin and various bacteria. These findings provide new insight into the role of TRPV1 in maintaining a healthy gut environment.

TRPV1 Receptor-Mediated Hypoglycemic Mechanism of Capsaicin in Streptozotocin-Induced Diabetic Rats

Our previous research showed that capsaicin exhibits hypoglycemic effects by activating the transient receptor potential vanilloid 1 (TRPV1) channel in diabetic rats. Interestingly, capsiate was also able to activate the TRPV1 channel, but with a non-significant hypoglycemic effect. This study aimed to investigate the effect of capsaicin on the glycometabolism of streptozotocin (STZ)-induced diabetic rats by blocking the TRPV1 channel. After a 4-week capsaicin treatment (6 mg/kg·bw), the serum insulin level of STZ-induced diabetic rats increased from 15.2 to 22.1 mIU/L, the content of hepatic glycogen and muscle glycogen increased by 81.2 and 20.2%, respectively, and the blood glucose level decreased significantly from 19.3 to 14.7 mmol/L. When the TRPV1 channel was blocked, capsaicin lost the above-mentioned effects, and the hypoglycemic effect was no longer significant. It was concluded that a combined up-regulation of both TRPV1 receptors and pancreatic duodenal homeobox-1 (PDX-1) led to the hypoglycemic effect of capsaicin, which partially explains our previous observation: capsiate activating TRPV1 without showing a significant hypoglycemic effect was due to the lack of a significant up-regulation of PDX-1. Based on the experimental results, we speculated that two signaling pathways [TRPV1-(PDX1)-(GLUT2/GK) and TRPV1-(PDX-1)-(IRS1/2)] exist in the pancreas of STZ-induced diabetic rats.

Transient Receptor Potential Vanilloid 1 (TRPV1) as a plausible novel therapeutic target for treating neurological complications in ZikaVirus

Zika virus was declared a national emergency by WHO (World Health Organization) in 2016 when its widespread outbreaks and life-threatening complications were reported, especially in newborns and adults. Numerous studies reported that neuroinflammation is one of the significant root-causes behind its major neurological complications like microcephaly and Guillain-Barré syndrome (GBS). In this hypothesis, we propose Transient Receptor Potential Vanilloid 1 channel (TRPV1) as a major culprit in triggering positive inflammatory loop, ultimately leading to sustained neuroinflammation, one of the key clinical findings in Zika induced microcephalic and GBS patients. Opening of TRPV1 channel also leads to calcium influx and oxidative stress that ultimately results in cellular apoptosis (like Schwann cell in GBS and developing fetal nerve cells in microcephaly), ultimately leading to these complications. Currently, no specific cure exists for these complications. Most of the antiviral candidates are under clinical trials. Though there is no direct research on TRPV1 as a cause of Zika virus's neurological complications, but similarity in mechanisms is undeniable. Thus, exploring pathobiological involvement of TRPV1 channels and various TRPV1 modulators in these complications can possibly prove to be an effective futuristic therapeutic strategy for treatment and management of these life-threatening complications.

TRP Channels as Sensors of Aldehyde and Oxidative Stress

The transient receptor potential (TRP) cation channel superfamily comprises more than 50 channels that play crucial roles in physiological processes. TRP channels are responsive to several exogenous and endogenous biomolecules, with aldehydes emerging as a TRP channel trigger contributing to a cellular cascade that can lead to disease pathophysiology. The body is not only exposed to exogenous aldehydes via tobacco products or alcoholic beverages, but also to endogenous aldehydes triggered by lipid peroxidation. In response to lipid peroxidation from inflammation or organ injury, polyunsaturated fatty acids undergo lipid peroxidation to aldehydes, such as 4-hydroxynonenal. Reactive aldehydes activate TRP channels via aldehyde-induced protein adducts, leading to the release of pro-inflammatory mediators driving the pathophysiology caused by cellular injury, including inflammatory pain and organ reperfusion injury. Recent studies have outlined how aldehyde dehydrogenase 2 protects against aldehyde toxicity through the clearance of toxic aldehydes, indicating that targeting the endogenous aldehyde metabolism may represent a novel treatment strategy. An addition approach can involve targeting specific TRP channel regions to limit the triggering of a cellular cascade induced by aldehydes. In this review, we provide a comprehensive summary of aldehydes, TRP channels, and their interactions, as well as their role in pathological conditions and the different therapeutical treatment options.

Hypoglycemic effect of low-sugar juice derived from Hovenia dulcis on type 1 diabetes mellitus rats

BACKGROUND

Fruit juice is usually rich in monosaccharides and disaccharides. A reverse osmosis separation machine was used to remove monosaccharides and disaccharides from Hovenia dulcis fruit juice, leaving behind most of the bioactive substances in a low-sugar fruit juice (LSFJ), so as to provide a more effective treatment for diabetic patients.

METHOD

This study was carried out with type 1 diabetes mellitus model induced with high dose of streptozotocin (60 mg kg^-1 ), and oral administration of LSFJ for 4 weeks.

RESULTS

LSFJ treatment led to significant gain in body weight and increased serum insulin level, insulin-like growth factor-1 level, blood urea nitrogen level, creatinine level, and hepatic glycogen level. Meanwhile, fasting blood glucose, fructosamine level, and glucose tolerance were also observably enhanced. Additional, LSFJ treatment significantly improved lipid metabolism, islet quality, and islet oxidative stress. The messenger RNA levels of glucose metabolism genes in the pancreas of diabetic rats decreased in the diabetes model group, whereas messenger RNA expression of these genes was significantly increased with LSFJ treatment.

CONCLUSION

These findings indicate that LSFJ can improve symptoms associated with type 1 diabetes mellitus. The research also suggests new strategies for diabetes prevention and treatment. © 2021 Society of Chemical Industry.

Design, synthesis and in vitro and in vivo biological evaluation of flurbiprofen amides as new fatty acid amide hydrolase/cyclooxygenase-2 dual inhibitory potential analgesic agents

Compounds combining dual inhibitory action against FAAH and cyclooxygenase (COX) may be potentially useful analgesics. Here, we describe a novel flurbiprofen analogue, N-(3-bromopyridin-2-yl)-2-(2-fluoro-(1,1'-biphenyl)-4-yl)propanamide (Flu-AM4). The compound is a competitive, reversible inhibitor of FAAH with a K_i value of 13 nM and which inhibits COX activity in a substrate-selective manner. Molecular modelling suggested that Flu-AM4 optimally fits a hydrophobic pocket in the ACB region of FAAH, and binds to COX-2 similarly to flurbiprofen. In vivo studies indicated that at a dose of 10 mg/kg, Flu-AM4 was active in models of prolonged (formalin) and neuropathic (chronic constriction injury) pain and reduced the spinal expression of iNOS, COX-2, and NFκB in the neuropathic model. Thus, the present study identifies Flu-AM4 as a dual-action FAAH/substrate-selective COX inhibitor with anti-inflammatory and analgesic activity in animal pain models. These findings underscore the potential usefulness of such dual-action compounds.

Proof-of-Concept for the Analgesic Effect and Thermoregulatory Safety of Orally Administered Multi-Target Compound SZV 1287 in Mice: A Novel Drug Candidate for Neuropathic Pain

SZV 1287 (3-(4,5-diphenyl-1,3-oxazol-2-yl)propanal oxime) is a novel multi-target candidate under preclinical development for neuropathic pain. It inhibits amine oxidase copper containing 3, transient receptor potential ankyrin 1 and vanilloid 1 (TRPV1) receptors. Mainly under acidic conditions, it is transformed to the cyclooxygenase inhibitor oxaprozin, which is ineffective for neuropathy. Therefore, an enterosolvent capsule is suggested for oral formulation, which we investigated for nociception, basic kinetics, and thermoregulatory safety in mice. The antihyperalgesic effect of SZV 1287 (10, 20, 50, and 200 mg/kg, p.o.) was determined in partial sciatic nerve ligation-induced traumatic neuropathy by aesthesiometry, brain and plasma concentrations by HPLC, and deep body temperature by thermometry. Its effect on proton-induced TRPV1 activation involved in thermoregulation was assessed by microfluorimetry in cultured trigeminal neurons. The three higher SZV 1287 doses significantly, but not dose-dependently, reduced neuropathic hyperalgesia by 50% of its maximal effect. It was quickly absorbed; plasma concentration was stable for 2 h, and it entered into the brain. Although SZV 1287 significantly decreased the proton-induced TRPV1-mediated calcium-influx potentially leading to hyperthermia, it did not alter deep body temperature. Oral SZV 1287 inhibited neuropathic hyperalgesia and, despite TRPV1 antagonistic action and brain penetration, it did not influence thermoregulation, which makes it a promising analgesic candidate.

TRPV1 Activation by Capsaicin Mediates Glucose Oxidation and ATP Production Independent of Insulin Signalling in Mouse Skeletal Muscle Cells

BACKGROUND

Insulin resistance (IR), a key characteristic of type 2 diabetes (T2DM), is manifested by decreased insulin-stimulated glucose transport in target tissues. Emerging research has highlighted transient receptor potential cation channel subfamily V member (TRPV1) activation by capsaicin as a potential therapeutic target for these conditions. However, there are limited data on the effects of capsaicin on cell signalling molecules involved in glucose uptake.

METHODS

C2C12 cells were cultured and differentiated to acquire the myotube phenotype. The activation status of signalling molecules involved in glucose metabolism, including 5' adenosine monophosphate-activated protein kinase (AMPK), calcium/calmodulin-dependent protein kinase 2 (CAMKK2), extracellular signal-regulated protein kinases 1 and 2 (ERK1/2), protein kinase B (AKT), and src homology phosphatase 2 (SHP2), was examined. Finally, activation of CAMKK2 and AMPK, and glucose oxidation and ATP levels were measured in capsaicin-treated cells in the presence or absence of TRPV1 antagonist (SB-452533).

RESULTS

Capsaicin activated cell signalling molecules including CAMKK2 and AMPK leading to increased glucose oxidation and ATP generation independent of insulin in the differentiated C2C12 cells. Pharmacological inhibition of TRPV1 diminished the activation of CAMKK2 and AMPK as well as glucose oxidation and ATP production. Moreover, we observed an inhibitory effect of capsaicin in the phosphorylation of ERK1/2 in the mouse myotubes.

CONCLUSION

Our data show that capsaicin-mediated stimulation of TRPV1 in differentiated C2C12 cells leads to activation of CAMKK2 and AMPK, and increased glucose oxidation which is concomitant with an elevation in intracellular ATP level. Further studies of the effect of TRPV1 channel activation by capsaicin on glucose metabolism could provide novel therapeutic utility for the management of IR and T2DM.

TRPV1 Hyperfunction Contributes to Renal Inflammation in Oxalate Nephropathy

Inflammation worsens oxalate nephropathy by exacerbating tubular damage. The transient receptor potential vanilloid 1 (TRPV1) channel is present in kidney and has a polymodal sensing ability. Here, we tested whether TRPV1 plays a role in hyperoxaluria-induced renal inflammation. In TRPV1-expressed proximal tubular cells LLC-PK₁, oxalate could induce cell damage in a time- and dose-dependent manner; this was associated with increased arachidonate 12-lipoxygenase (ALOX12) expression and synthesis of endovanilloid 12(S)-hydroxyeicosatetraenoic acid for TRPV1 activation. Inhibition of ALOX12 or TRPV1 attenuated oxalate-mediated cell damage. We further showed that increases in intracellular Ca²⁺ and protein kinase C α activation are downstream of TRPV1 for NADPH oxidase 4 upregulation and reactive oxygen species formation. These trigger tubular cell inflammation via increased NLR family pyrin domain-containing 3 expression, caspase-1 activation, and interleukin (IL)-1β release, and were alleviated by TRPV1 inhibition. Male hyperoxaluric rats demonstrated urinary supersaturation, tubular damage, and oxidative stress in a time-dependent manner. Chronic TRPV1 inhibition did not affect hyperoxaluria and urinary supersaturation, but markedly reduced tubular damage and calcium oxalate crystal deposition by lowering oxidative stress and inflammatory signaling. Taking all these results together, we conclude that TRPV1 hyperfunction contributes to oxalate-induced renal inflammation. Blunting TRPV1 function attenuates hyperoxaluric nephropathy.

TRPV1 Ion Channel: Structural Features, Activity Modulators, and Therapeutic Potential

Although TRPV1 ion channel has been attracting researchers' attention for many years, its functions in animal organisms, the principles of regulation, and the involvement in pathological processes have not yet been fully clarified. Mutagenesis experiments and structural studies have identified the structural features of the channel and binding sites for its numerous ligands; however, these studies are far from conclusion. This review summarizes recent achievements in the TRPV1 research with special focus on structural and functional studies of the channel and on its ligands, which are extremely diverse in their nature and interaction specificity to TRPV1. Particular attention was given to the effects of numerous endogenous agonists and antagonists that can fine-tune the channel sensitivity to its usual activators, such as capsaicin, heat, acids, or their combination. In addition to the pain sensing not covered in this review, the TRPV1 channel was found to be involved in the regulation of many important physiological and pathological processes and, therefore, can be considered as a promising therapeutic target in the treatment of various diseases, such as pneumonia, ischemia, diabetes, epilepsy, schizophrenia, psoriasis, etc.

The Impact of TRPV1 on Cancer Pathogenesis and Therapy: A Systematic Review

The transient receptor potential cation channel subfamily V member 1 (TRPV1) is a transmembrane protein that can be activated by various physical and chemical stimuli and is associated with pain transduction. In recent years, TRPV1 was discovered to play essential roles in cancer tumorigenesis and development, as TRPV1 expression levels are altered in numerous cancer cell types. Several investigations have discovered direct associations between TRPV1 and cancer cell proliferation, cell death, and metastasis. Furthermore, about two dozen TRPV1 agonists/antagonists are under clinical trial, as TRPV1 is a potential drug target for treating various diseases. Hence, more researchers are focusing on the effects of TRPV1 agonists or antagonists on cancer tumorigenesis and development. However, both agonists and antagonists may reveal anti-cancer effects, and the effect may function via or be independent of TRPV1. In this review, we provide an overview of the impact of TRPV1 on cancer cell proliferation, cell death, and metastasis, as well as on cancer therapy and the tumor microenvironment, and consider the implications of using TRPV1 agonists and antagonists for future research and potential therapeutic approaches.

Translational value of non-human primates in opioid research

Preclinical opioid research using animal models not only provides mechanistic insights into the modulation of opioid analgesia and its associated side effects, but also validates drug candidates for improved treatment options for opioid use disorder. Non-human primates (NHPs) have served as a surrogate species for humans in opioid research for more than five decades. The translational value of NHP models is supported by the documented species differences between rodents and primates regarding their behavioral and physiological responses to opioid-related ligands and that NHP studies have provided more concordant results with human studies. This review highlights the utilization of NHP models in five aspects of opioid research, i.e., analgesia, abuse liability, respiratory depression, physical dependence, and pruritus. Recent NHP studies have found that (1) mixed mu opioid and nociceptin/orphanin FQ peptide receptor partial agonists appear to be safe, non-addictive analgesics and (2) mu opioid receptor- and mixed opioid receptor subtype-based medications remain the only two classes of drugs that are effective in alleviating opioid-induced adverse effects. Given the recent advances in pharmaceutical sciences and discoveries of novel targets, NHP studies are posed to identify the translational gap and validate therapeutic targets for the treatment of opioid use disorder. Pharmacological studies using NHPs along with multiple outcome measures (e.g., behavior, physiologic function, and neuroimaging) will continue to facilitate the research and development of improved medications to curb the opioid epidemic.

A patent review of transient receptor potential vanilloid type 1 modulators (2014-present)

Introduction: Transient receptor potential vanilloid 1 (TRPV1) is a nonselective cation channel with high permeability to calcium, which is widely expressed in the central nervous system (CNS) and peripheral nervous system. Since the TRPV1 was molecularly cloned more than 20 years ago, a series of research activities have been carried out on the possibility of new drugs. Areas covered: This review summarizes the patents on TRPV1 regulators (including agonists and antagonists) that were published during 2014-present and predicts the development direction in the future. The patent description is organized according to the applicant company and focuses on the representative compounds and their in vitro and in vivo data. Expert opinion: At present, TRPV1 is considered to be a molecular integrator of a broad range of chemical and physical stimuli. The desensitization of nociceptive neurons caused by TRPV1 agonists and the pharmacological blockade of TRPV1 by powerful small molecular antagonists are different treatments, both of which have analgesic effects. Unfortunately, TRPV1 modulators have suffered from adverse effects related to the role of TRPV1 channel in body temperature regulation and noxious heat sensation. What we need to know is whether these adverse effects are on-target (unavoidable), and whether chemical modification can be used to avoid or reduce these adverse reactions in the process of designing drug molecules, so as to develop a TRPV1 regulator with potent analgesic effect and no obvious adverse effects. Despite the difficulties and roadblocks, TRPV1 modulators remain powerful tools in pain research and represent promising therapeutic agents.

The Mysteries of Capsaicin-Sensitive Afferents

A fundamental subdivision of nociceptive sensory neurons is named after their unique sensitivity to capsaicin, the pungent ingredient in hot chili peppers: these are the capsaicin-sensitive afferents. The initial excitation by capsaicin of these neurons manifested as burning pain sensation is followed by a lasting refractory state, traditionally referred to as "capsaicin desensitization," during which the previously excited neurons are unresponsive not only to capsaicin but a variety of unrelated stimuli including noxious heat. The long sought-after capsaicin receptor, now known as TRPV1 (transient receptor potential cation channel, subfamily V member 1), was cloned more than two decades ago. The substantial reduction of the inflammatory phenotype of Trpv1 knockout mice has spurred extensive efforts in the pharmaceutical industry to develop small molecule TRPV1 antagonists. However, adverse effects, most importantly hyperthermia and burn injuries, have so far prevented any compounds from progressing beyond Phase 2. There is increasing evidence that these limitations can be at least partially overcome by approaches outside of the mainstream pharmaceutical development, providing novel therapeutic options through TRPV1. Although ablation of the whole TRPV1-expressing nerve population by high dose capsaicin, or more selectively by intersectional genetics, has allowed researchers to investigate the functions of capsaicin-sensitive afferents in health and disease, several "mysteries" remain unsolved to date, including the molecular underpinnings of "capsaicin desensitization," and the exact role these nerves play in thermoregulation and heat sensation. This review tries to shed some light on these capsaicin mechanisms.

Di-(2-ethylhexyl) phthalate limits the pleiotropic effects of statins in chronic kidney disease patients undergoing dialysis and endothelial cells

The level of di-(2-ethylhexyl) phthalate (DEHP) is elevated in chronic kidney disease patients undergoing dialysis. However, statins are unable to reduce the cardiovascular events in chronic dialysis patients. In this study, we investigated the effects of DEHP on statin-conferred pleiotropic effects and the underlying molecular mechanism in peritoneal dialysis (PD) patients and endothelial cells (ECs). In PD patients with serum DEHP level ≥0.0687 μg/mL, statin treatment was not associated with lower risk of cardiovascular disease. In ECs, exposure to DEHP abrogated the simvastatin-induced NO bioavailability and EC-related functions. Additionally, DEHP abolished the anti-inflammatory effect of simvastatin on the tumor necrosis factor α-induced upregulation of adhesion molecules and monocyte adhesion to ECs. Mechanistically, DEHP blunted the activation of transient receptor potential vanilloid type 1 (TRPV1), which is required for NO production by simvastatin in ECs. Notably, DEHP increased the activity and expression of protein phosphatase 2B (PP2B), a negative regulator of TRPV1 activity. The effect of DEHP on PP2B activation was mediated by the activation of the NADPH oxidase/reactive oxygen species (NOX-ROS) pathway. Inhibition of PP2B activity by pharmacological antagonists prevented the inhibitory effects of DEHP on simvastatin-induced Ca²⁺ influx, NO bioavailability, and EC migration, proliferation, tube formation, and anti-inflammatory action. Collectively, DEHP activates the NOX-ROS-PP2B pathway, which in turns inhibits TRPV1/Ca²⁺-dependent signaling and abrogates the statin-conferred pleiotropic protection in ECs.

Ca2+-permeable TRPV1 pain receptor knockout rescues memory deficits and reduces amyloid-β and tau in a mouse model of Alzheimer's disease

The transient receptor potential vanilloid 1 (TRPV1) protein is a pain receptor that elicits a hot sensation when an organism eats the capsaicin of red chili peppers. This calcium (Ca2+)-permeable cation channel is mostly expressed in the peripheral nervous system sensory neurons but also in the central nervous system (e.g. hippocampus and cortex). Preclinical studies found that TRPV1 mediates behaviors associated with anxiety and depression. Loss of TRPV1 functionality increases expression of genes related to synaptic plasticity and neurogenesis. Thus, we hypothesized that TRPV1 deficiency may modulate Alzheimer's disease (AD). We generated a triple-transgenic AD mouse model (3xTg-AD+/+) with wild-type (TRPV1+/+), hetero (TRPV1+/-) and knockout (TRPV1-/-) TRPV1 to investigate the role of TRPV1 in AD pathogenesis. We analyzed the animals' memory function, hippocampal Ca2+ levels and amyloid-β (Aβ) and tau pathologies when they were 12 months old. We found that compared with 3xTg-AD-/-/TRPV1+/+ mice, 3xTg-AD+/+/TRPV1+/+ mice had memory impairment and increased levels of hippocampal Ca2+, Aβ and total and phosphorylated tau. However, 3xTg-AD+/+/TRPV1-/- mice had better memory function and lower levels of hippocampal Ca2+, Aβ, tau and p-tau, compared with 3xTg-AD+/+/TRPV1+/+ mice. Examination of 3xTg-AD-derived primary neuronal cultures revealed that the intracellular Ca2+ chelator BAPTA/AM and the TRPV1 antagonist capsazepine decreased the production of Aβ, tau and p-tau. Taken together, these results suggested that TRPV1 deficiency had anti-AD effects and promoted resilience to memory loss. These findings suggest that drugs or food components that modulate TRPV1 could be exploited as therapeutics to prevent or treat AD.

Small Molecule NF-κB Inhibitors as Immune Potentiators for Enhancement of Vaccine Adjuvants

Adjuvants are added to vaccines to enhance the immune response and provide increased protection against disease. In the last decade, hundreds of synthetic immune adjuvants have been created, but many induce undesirable levels of proinflammatory cytokines including TNF-α and IL-6. Here we present small molecule NF-κB inhibitors that can be used in combination with an immune adjuvant to both decrease markers associated with poor tolerability and improve the protective response of vaccination. Additionally, we synthesize a library of honokiol derivatives identifying several promising candidates for use in vaccine formulations.

Ursolic acid protects against cisplatin‑induced ototoxicity by inhibiting oxidative stress and TRPV1‑mediated Ca2+‑signaling

Cisplatin (CDDP) is widely used in clinical settings for the treatment of various cancers. However, ototoxicity is a major side effect of CDDP, and there is an associated risk of irreversible hearing loss. We previously demonstrated that CDDP could induce ototoxicity via activation of the transient receptor potential vanilloid receptor 1 (TRPV1) pathway and subsequent induction of oxidative stress. The present study investigated whether ursolic acid (UA) treatment could protect against CDDP‑induced ototoxicity. UA is a triterpenoid with strong antioxidant activity widely used in China for the treatment of liver diseases. This traditional Chinese medicine is mainly isolated from bearberry, a Chinese herb. The present results showed that CDDP increased auditory brainstem response threshold shifts in frequencies associated with observed damage to the outer hair cells. Moreover, CDDP increased the expression of TRPV1, calpain 2 and caspase‑3 in the cochlea, and the levels of Ca2+ and 4‑hydroxynonenal. UA co‑treatment significantly attenuated CDDP‑induced hearing loss and inhibited TRPV1 pathway activation. In addition, UA enhanced CDDP‑induced growth inhibition in the human ovarian cancer cell line SKOV3, suggesting that UA synergizes with CDDP in vitro. Collectively, the present data suggested that UA could effectively attenuate CDDP‑induced hearing loss by inhibiting the TRPV1/Ca²+/calpain‑oxidative stress pathway without impairing the antitumor effects of CDDP.

TRPV1 Antagonist DWP05195 Induces ER Stress-Dependent Apoptosis through the ROS-p38-CHOP Pathway in Human Ovarian Cancer Cells

In addition to their analgesic activity, transient receptor potential vanilloid 1 (TRPV1) agonists and antagonists demonstrate profound anti-cancer activities in various human cancers. In the present study, we investigated the anti-cancer activity of a novel TRPV1 antagonist, DWP05195, and evaluated its molecular mechanism in human ovarian cancer cells. DWP05195 demonstrated potent growth inhibitory effects in all five ovarian cancer cell lines examined. DWP05195 induced apoptosis through the activation of caspase-3, -8, and -9. DWP05195 induced C/EBP homologous protein (CHOP) expression and endoplasmic reticulum (ER) stress. Sodium phenylbutyrate (4-PBA), an ER-stress inhibitor, and CHOP knockdown significantly suppressed DWP5195-induced cell death. DWP05195-enhanced CHOP expression stimulated intrinsic and extrinsic apoptotic pathways through the regulation of Bcl2-like11 (BIM), death receptor 4 (DR4), and DR5. DWP05195-induced cell death was associated with increased reactive oxygen species (ROS) levels and p38 pathway activation. Pre-treatment with the antioxidant N-acetyl-L-cysteine (NAC) significantly suppressed DWP05195-induced CHOP expression and p38 activation. Inhibition of NADPH oxidase (NOX) through p47phox knockdown abolished DWP05195-induced CHOP expression and cell death. Taken together, the findings indicate that DWP05195 induces ER stress-induced apoptosis via the ROS-p38-CHOP pathway in human ovarian cancer cells.

A single TRPV1 amino acid controls species sensitivity to capsaicin

Chili peppers produce capsaicin (a vanilloid) that activates the transient receptor potential cation channel subfamily V member 1 (TRPV1) on sensory neurons to alter their membrane potential and induce pain. To identify residues responsible for differential TRPV1 capsaicin sensitivity among species, we used intracellular Ca²⁺ imaging to characterize chimeras composed of capsaicin-sensitive rat TRPV1 (rTRPV1) and capsaicin-insensitive chicken TRPV1 (cTRPV1) exposed to a series of capsaicinoids. We found that chimeras containing rat E570-V686 swapped into chicken receptors displayed capsaicin sensitivity, and that simply changing the alanine at position 578 in the S4-S5 helix of the chicken receptor to a glutamic acid was sufficient to endow it with capsaicin sensitivity in the micromolar range. Moreover, introduction of lysine, glutamine or proline at residue A578 also elicited capsaicin sensitivity in cTRPV1. Similarly, replacing corresponding rTRPV1 residue E570 with lysine or glutamine retained capsaicin sensitivity. The hydrophilic capsaicin analog Cap-EA activated a cTRPV1-A578E mutant, suggesting that A578 may participate in vanilloid binding. The hydrophilic vanilloid agonist zingerone did not activate any A578 mutants with capsaicin sensitivity, suggesting that the vanilloid group alone is not sufficient for receptor activation. Our study demonstrates that a subtle modification of TRPV1 in different species globally alters capsaicin responses.

Advances with Long Non-Coding RNAs in Diabetic Peripheral Neuropathy

Long non-coding RNAs (lncRNAs) are a group of non-coding RNAs longer than 200 nucleotides, which are defined as transcripts. The lncRNAs are involved in regulating gene expression at epigenetic, transcriptional, and post-transcriptional levels. Recent studies have found that lncRNA is closely related to many diseases like neurological diseases, endocrine and metabolic disorders. Diabetic peripheral neuropathy (DPN) is one of the most common chronic complications of diabetes mellitus. In this review, we highlight the latest research related to lncRNAs in DPN.