The pharmacological challenge to tame the transient receptor potential vanilloid-1 (TRPV1) nocisensor

Modeling pulsed dye laser treatment of psoriatic plaques by combining numerical methods and image-derived lesion morphologies

OBJECTIVES

Knowledge of the physical effects of pulsed dye laser (PDL) treatment of psoriatic lesions is essential in unraveling the remedial mechanisms of this treatment and hence also in maximizing in its disease-modifying potential. Therefore, the main objective of this study was to provide estimates of these physical effects (for laser wavelengths of 585 and 595 nm), with the aim of identifying pathogenic processes that may be affected by these conditions.

METHODS

We modeled the laser light propagation and subsequent photothermal heating by numerically solving the transient diffusion and heat equations simultaneously. To this end, we used the finite element method in conjunction with an image-derived psoriatic lesion morphology (which was defined by segmenting blood vessels from a confocal microscopy image of a fluorescently labeled section of a 3 mm punch biopsy of a psoriatic lesion). The resulting predictions of the generated temperature field within the lesion were then used to assess the possibility of stalling or arresting some suspected pathogenic processes.

RESULTS

According to our results, it is conceivable that perivascular nerves are thermally denatured, as almost all locations that reach 60°C were found to be within 18 µm (at 585 nm) and 11 µm (at 595 nm) of a blood vessel wall. Furthermore, activation of TRPV1 and TRPV2 channels in perivascular neuronal and immune cells is highly likely, since a critical temperature of 43°C is generated at locations within up to 350 µm of a vessel wall (at both wavelengths) and sustained for up to 700 ms (at 585 nm) and 40 ms (at 595 nm), while a critical temperature of 52°C is reached by locations within 80 µm (at 585 nm) and 30 µm (at 595 nm) of a vessel wall and sustained for up to 100  ms (at 585 nm) and 30 ms (at 595 nm). Finally, we found that the blood vessel coagulation-inducing temperature of 70°C is sustained in the vascular epithelium for up to 19 and 5 ms at 585 and 595 nm, respectively, rendering partial or total loss of vascular functionality a distinct possibility.

CONCLUSIONS

The presented approach constitutes a useful tool to provide realistic estimates of the photothermal effects of PDL treatment of psoriatic plaques (as well as other selective photothermolysis-based treatments), yielding information that is essential in guiding future experimental studies toward unraveling the remedial mechanisms of these treatments.

Cannabinoid Analgesia in Postoperative Pain Management: From Molecular Mechanisms to Clinical Reality

Postoperative pain (POP) is a challenging clinical phenomenon that affects the majority of surgical patients and demands effective management to mitigate adverse outcomes such as persistent pain. The primary goal of POP management is to alleviate suffering and facilitate a seamless return to normal function for the patient. Despite compelling evidence of its drawbacks, opioid analgesia remains the basis of POP treatment. Novel therapeutic approaches rely on multimodal analgesia, integrating different pharmacological strategies to optimize efficacy while minimizing adverse effects. The recognition of the imperative role of the endocannabinoid system in pain regulation has prompted the investigation of cannabinoid compounds as a new therapeutic avenue. Cannabinoids may serve as adjuvants, enhancing the analgesic effects of other drugs and potentially replacing or at least reducing the dependence on other long-term analgesics in pain management. This narrative review succinctly summarizes pertinent information on the molecular mechanisms, clinical therapeutic benefits, and considerations associated with the plausible use of various cannabinoid compounds in treating POP. According to the available evidence, cannabinoid compounds modulate specific molecular mechanisms intimately involved in POP. However, only two of the eleven clinical trials that evaluated the efficacy of different cannabinoid interventions showed positive results.

Turning down the body heat: A novel mechanism for TRPV1 antagonist-induced hyperthermia

While effective analgesics, TRPV1 antagonists can dangerously alter thermoregulation. In this issue of Neuron, Huang et al.1 demonstrate that interaction with the S4-S5 linker of TRPV1 determines whether an antagonist affects core body temperature, with promising implications for analgesic development.

TRPV1 analgesics disturb core body temperature via a biased allosteric mechanism involving conformations distinct from that for nociception

Efforts on developing transient receptor potential vanilloid 1 (TRPV1) drugs for pain management have been hampered by deleterious hypo- or hyperthermia caused by TRPV1 agonists/antagonists. Here, we compared the effects of four antagonists on TRPV1 polymodal gating and core body temperature (CBT) in Trpv1+/+, Trpv1-/-, and Trpv1T634A/T634A. Neither the effect on proton gating nor drug administration route, hair coverage, CBT rhythmic fluctuations, or inflammation had any influence on the differential actions of TRPV1 drugs on CBT. We identified the S4-S5 linker region exposed to the vanilloid pocket of TRPV1 to be critical for hyperthermia associated with certain TRPV1 antagonists. PSFL2874, a TRPV1 antagonist we discovered, is effective against inflammatory pain but devoid of binding to the S4-S5 linker and inducing CBT changes. These findings implicate that biased allosteric mechanisms exist for TRPV1 coupling to nociception and CBT regulation, opening avenues for the development of non-opioid analgesics without affecting CBT.

The challenge of pharmacotherapy for musculoskeletal pain: an overview of unmet needs

Musculoskeletal disorders are characterized by several impairments, including pain, affecting muscles, bones, joints and adjacent connective tissue, resulting in temporary or permanent functional limitations and disability. Musculoskeletal pain is particularly prevalent worldwide and greatly impacts the quality of life, social participation and economic burden. To date, several issues persist about the classification of musculoskeletal pain and its management strategies and resources. The treatment of musculoskeletal pain conditions is complex and often requires a multimodal approach, including pharmacological and non-pharmacological therapy that might be ineffective in many cases, resulting in poor patient satisfaction and controversial expectations about the potential benefits of available interventions. This manuscript provides an overview of unmet needs in managing musculoskeletal pain, particularly focusing on pharmacotherapeutic pitfalls in this context.

The potential mechanisms underlying the modulating effect of perirenal adipose tissue on hypertension: Physical compression, paracrine, and neurogenic regulation

Hypertension, a prevalent global cardiovascular disease, affects approximately 45.4 % of adults worldwide. Despite advances in therapy, hypertension continues to pose a significant health risk due to inadequate management. It has been established that excessive adiposity contributes majorly to hypertension, accounting for 65 to 75 % of primary cases. Fat depots can be categorised into subcutaneous and visceral adipose tissue based on anatomical and physiological characteristics. The metabolic impact and the risk of hypertension are determined more significantly by visceral fat. Perirenal adipose tissue (PRAT), a viscera enveloping the kidney, is known for its superior vascularisation and abundant innervation. Although traditionally deemed as a mechanical support tissue, recent studies have indicated its contributing potential to hypertension. Hypertensive patients tend to have increased PRAT thickness compared to those without, and there is a positive correlation between PRAT thickness and elevated systolic blood pressure. This review encapsulates the anatomical characteristics and biogenesis of PRAT. We provide an overview of the potential mechanisms where PRAT may modulate blood pressure, including physical compression, paracrine effects, and neurogenic regulation. PRAT has become a promising target for hypertension management, and continuous effort is required to further explore the underlying mechanisms.

IUPHAR review: Navigating the role of preclinical models in pain research

Chronic pain is a complex and challenging medical condition that affects millions of people worldwide. Understanding the underlying mechanisms of chronic pain is a key goal of preclinical pain research so that more effective treatment strategies can be developed. In this review, we explore nociception, pain, and the multifaceted factors that lead to chronic pain by focusing on preclinical models. We provide a detailed look into inflammatory and neuropathic pain models and discuss the most used animal models for studying the mechanisms behind these conditions. Additionally, we emphasize the vital role of these preclinical models in developing new pain-relief drugs, focusing on biologics and the therapeutic potential of NMDA and cannabinoid receptor antagonists. We also discuss the challenges of TRPV1 modulation for pain treatment, the clinical failures of neurokinin (NK)- 1 receptor antagonists, and the partial success story of Ziconotide to provide valuable lessons for preclinical pain models. Finally, we highlight the overall success and limitations of current treatments for chronic pain while providing critical insights into the development of more effective therapies to alleviate the burden of chronic pain.

Novel Prevention Approaches of Breast Cancer Surgery Related Complications: Systematic Review and Network Meta-Analysis

BACKGROUND

Breast cancer surgery related complications are a complex condition influenced by interactions among nerve pathways and the physiological responses to breast surgery. The intensity of this complications displays substantial heterogeneity, dependent on individual patient characteristics, the extent of the surgical procedure performed, and various contributing factors.

METHODS

A comprehensive search of electronic databases was conducted to identify relevant randomized controlled trials (RCTs) investigating interventions for post-mastectomy pain syndrome (PMPS). A network meta-analysis was performed to integrate direct and indirect evidence, enabling comparisons of multiple interventions across different outcome measures.

RESULTS

The systematic search yielded a total of 26 RCTs investigating 4 groups of different interventions for PMPS. The interventions included pharmacological agents, nerve blocks, physical therapy, and anesthesia regimens. Nerve blocks (OR: 0.34; 95% CrI: 0.24-0.46) and anesthesia (OR: 0.39; 95% CrI: 0.26-0.56) demonstrated improvements in functional outcomes and quality of life.

CONCLUSION

This systematic review and network meta-analysis provide a comprehensive evaluation of interventions for PMPS, highlighting their varying efficacy in alleviating pain and improving functional outcomes and quality of life. However, further research with large-scale, well-designed RCTs is warranted to strengthen the evidence base and validate the effectiveness of these interventions in managing PMPS effectively.

pH sensing at the intersection of tissue homeostasis and inflammation

pH is tightly maintained at cellular, tissue, and systemic levels, and altered pH - particularly in the acidic range - is associated with infection, injury, solid tumors, and physiological and pathological inflammation. However, how pH is sensed and regulated and how it influences immune responses remain poorly understood at the tissue level. Applying conceptual frameworks of homeostatic and inflammatory circuitries, we categorize cellular and tissue components engaged in pH regulation, drawing parallels from established cases in physiology. By expressing various intracellular (pHi) and extracellular pH (pHe)-sensing receptors, the immune system may integrate information on tissue and cellular states into the regulation of homeostatic and inflammatory programs. We introduce the novel concept of resistance and adaptation responses to rationalize pH-dependent immunomodulation intertwined with homeostatic equilibrium and inflammatory control. We discuss emerging challenges and opportunities in understanding the immunological roles of pH sensing, which might reveal new strategies to combat inflammation and restore tissue homeostasis.

TRPV1: A promising therapeutic target for skin aging and inflammatory skin diseases

TRPV1 is a non-selective channel receptor widely expressed in skin tissues, including keratinocytes, peripheral sensory nerve fibers and immune cells. It is activated by a variety of exogenous or endogenous inflammatory mediators, triggering neuropeptide release and neurogenic inflammatory response. Previous studies have shown that TRPV1 is closely related to the occurrence and/or development of skin aging and various chronic inflammatory skin diseases, such as psoriasis, atopic dermatitis, rosacea, herpes zoster, allergic contact dermatitis and prurigo nodularis. This review summarizes the structure of the TRPV1 channel and discusses the expression of TRPV1 in the skin as well as its role of TRPV1 in skin aging and inflammatory skin diseases.

Transient Receptor Potential Vanilloid1 (TRPV1) Channel Opens Sesame of T Cell Responses and T Cell-Mediated Inflammatory Diseases

Transient receptor potential vanilloid1 (TRPV1) was primarily expressed in sensory neurons, and could be activated by various physical and chemical factors, resulting in the flow of extracellular Ca2+ into cells. Accumulating data suggest that the TRPV1 is expressed in some immune cells and is a novel regulator of the immune system. In this review, we highlight the structure and biological features of TRPV1 channel. We also summarize recent findings on its role in modulating T cell activation and differentiation as well as its protective effect in T cell-mediated inflammatory diseases and potential mechanisms.

Differential immunostaining patterns of transient receptor potential (TRP) ion channels in the rat nodose ganglion

Vagal afferents regulate numerous physiological functions including arterial blood pressure, heart rate, breathing, and nociception. Cell bodies of vagal afferents reside in the inferior vagal (nodose) ganglia and their stimulation by various means is being considered as a way to regulate cardiorespiratory responses and control pain sensations. Stimulation of the nodose by exposure to infrared light is recently being considered as a precise way to elicit responses. These responses would likely involve the activity of temperature-sensitive membrane-bound channels. While papers have been published to track the expression of these transient receptor potential ion channels (TRPs), further studies are warranted to determine the in situ expression of the endogenous TRP proteins in the nodose ganglia to fully understand their pattern of expression, subcellular locations, and functions in this animal model. TRP ion channels are a superfamily of Na⁺ /Ca²⁺ -channels whose members are temperature- and/or mechano-sensitive and therefore represent a potential set of proteins that will be activated directly or indirectly by infrared light. Here, we report the spatial localization of six TRP channels, TRPV1, TRPV4, TRPM3, TRPM8, TRPA1, and TRPC1, from nodose ganglia taken from juvenile male Sprague-Dawley rats. The channels were detected using immunohistology with fluorescent tags on cryosections and imaged using confocal microscopy. All six TRP channels were detected with different levels of intensity in neuronal cell bodies and some were also detected in axonal fibers and blood vessels. The TRP receptors differed in their prevalence, in their patterns of expression, and in subcellular expression/localization. More specifically, TRPV1, TRPV4, TRPA1, TRPM8, TRPC1, and TRPM3 were found in vagal afferent cell bodies with a wide range of immunostaining intensity from neuron to neuron. Immunostaining for TRPV1, TRPV4, and TRPA1 appeared as fine particles scattered throughout the cytoplasm of the cell body. Intense TRPV1 immunostaining was also evident in a subset of axonal fibers. TRPM8 and TRPC1 were expressed in courser particles suggesting different subcellular compartments than for TRPV1. The localization of TRPM3 differed markedly from the other TRP channels with an immunostaining pattern that was localized to the periphery of a subset of cell bodies, whereas a scattering or no immunostaining was detected within the bulk of the cytoplasm. TRPV4 and TRPC1 were also expressed on the walls of blood vessels. The finding that all six TRP channels (representing four subfamilies) were present in the nodose ganglia provides the basis for studies designed to understand the roles of these channels in sensory transmission within vagal afferent fibers and in the responses elicited by exposure of nodose ganglia to infrared light and other stimuli. Depending on the location and functionality of the TRP channels, they may regulate the flux of Na⁺ /Ca²⁺ -across the membranes of cell bodies and axons of sensory afferents, efferent (motor) fibers coursing through the ganglia, and in vascular smooth muscle.

Anti-Inflammatory Effect of Beta-Caryophyllene Mediated by the Involvement of TRPV1, BDNF and trkB in the Rat Cerebral Cortex after Hypoperfusion/Reperfusion

We have previously shown that bilateral common carotid artery occlusion followed by reperfusion (BCCAO/R) is a model to study early hypoperfusion/reperfusion-induced changes in biomarkers of the tissue physiological response to oxidative stress and inflammation. Thus in this study, we investigate with immunochemical assays if a single dose of beta-caryophyllene (BCP), administered before the BCCAO/R, can modulate the TRPV1, BDNF, and trkB receptor in the brain cortex; the glial markers GFAP and Iba1 were also examined. Frontal and temporal-occipital cortical regions were analyzed in two groups of male rats, sham-operated and submitted to BCCAO/R. Six hours before surgery, one group was gavage fed a dose of BCP (40 mg/per rat in 300 μL of sunflower oil), the other was pre-treated with the vehicle alone. Western blot analysis showed that, in the frontal cortex of vehicle-treated rats, the BCCAO/R caused a TRPV1 decrease, an increment of trkB and GFAP, no change in BDNF and Iba1. The BCP treatment caused a decrease of BDNF and an increase of trkB levels in both sham and BCCAO/R conditions while inducing opposite changes in the case of TRPV1, whose levels became higher in BCCAO/R and lower in sham conditions. Present results highlight the role of BCP in modulating early events of the cerebral inflammation triggered by the BCCAO/R through the regulation of TRPV1 and the BDNF-trkB system.

Side Effects of Opioids Are Ameliorated by Regulating TRPV1 Receptors

Humans have used opioids to suppress moderate to severe pain for thousands of years. However, the long-term use of opioids has several adverse effects, such as opioid tolerance, opioid-induced hyperalgesia, and addiction. In addition, the low efficiency of opioids in controlling neuropathic pain limits their clinical applications. Combining nonopioid analgesics with opioids to target multiple sites along the nociceptive pathway may alleviate the side effects of opioids. This study reviews the feasibility of reducing opioid side effects by regulating the transient receptor potential vanilloid 1 (TRPV1) receptors and summarizes the possible underlying mechanisms. Blocking and activating TRPV1 receptors can improve the therapeutic profile of opioids in different manners. TRPV1 and μ-opioid receptors are bidirectionally regulated by β-arrestin2. Thus, drug combinations or developing dual-acting drugs simultaneously targeting μ-opioid and TRPV1 receptors may mitigate opioid tolerance and opioid-induced hyperalgesia. In addition, TRPV1 receptors, especially expressed in the dorsal striatum and nucleus accumbens, participate in mediating opioid reward, and its regulation can reduce the risk of opioid-induced addiction. Finally, co-administration of TRPV1 antagonists and opioids in the primary action sites of the periphery can significantly relieve neuropathic pain. In general, the regulation of TRPV1 may potentially ameliorate the side effects of opioids and enhance their analgesic efficacy in neuropathic pain.

Post-Mastectomy Pain Syndrome: An Up-to-Date Review of Treatment Outcomes

BACKGROUND

Post-mastectomy pain syndrome (PMPS) is a known debilitating surgical complication. While research on prevention, risk factors, and treatments have been conducted, there remains no cohesive treatment paradigm. The aim of our study is to synthesize the existing evidence on PMPS treatment, which may facilitate the implementation of standardized, effective management strategies.

METHODS

Using Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines, a comprehensive search was developed and translated for MEDLINE, Cochrane Library, EMBASE, CINAHL, PsycINFO, Web of Science, and ClinicalTrials.gov. The databases were searched using a combination of free terms, phrase searching, and database-specific controlled vocabulary related to PMPS. All unique records were by two independent reviewers. Publications on chronic (>3 months duration) pain after breast cancer-related surgery were included. Limited case series, case reports, and editorials were not included.

RESULTS

A total of 3402 articles from the years 1946-2019 resulted from the literature search after deduplication. Twenty-seven articles met final inclusion criteria for analysis, which revealed 10 major treatment modalities: fat grafting, neuroma surgery, lymphedema surgery, nerve blocks and neurolysis, laser, antidepressants, neuromodulators, physical therapy, mindfulness-based cognitive therapy, and capsaicin.

CONCLUSIONS

In this review, we present a comprehensive assessment of the treatments available for PMPS that may help guide breast surgeons and reconstructive surgeons to employ the most effective treatment strategies for these patients. This review supports the importance of multimodal, multidisciplinary care in improving the management of PMPS.

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.

A new screening method for identifying chemosensory receptors responding to agonist

Humans sense taste and smell of various chemical substances through approximately 430 chemosensory receptors. The overall picture of ligand-chemosensory receptor interactions has been partially clarified because of numerous interactions. This study presents a new method that enables a rapid and simple screening of chemosensory receptors. It would be useful for identifying chemosensory receptors activated by taste and odor substances.

Comparison of joint degeneration and pain in male and female mice in DMM model of osteoarthritis

OBJECTIVE

While the prevalence of radiographic and symptomatic osteoarthritis (OA) is higher in women, male mice are more frequently used in animal experiments to explore its pathogenesis or drug efficacy. In this study, we examined whether sexual dimorphism affects pain and joint degeneration in destabilization of the medial meniscus (DMM) mouse model.

METHODS

DMM or sham surgery was performed on the knee of male and female C57BL/6 mice. Joint damage was assessed by safranin O staining and scored using the Osteoarthritis Research Society International (OARSI) scoring system. Von Frey hair, incapacitance, and rotarod tests were conducted to measure joint pain. The analgesic effect of capsazepine (CPZ), a TRPV1 antagonist, was compared between male and female mice.

RESULTS

Histology and OARSI scoring analysis showed that cartilage degeneration developed, and progressed in both male and female DMM groups, however, damage was less severe in females at the late stage of OA. Pain behavior, as measured by mechanical allodynia, was displayed for longer in male DMM mice compared to females. Incapacitance data showed that CPZ significantly reduced DMM-induced pain in male mice but not in female mice. Immunofluorescence microscopy analysis demonstrated that DMM surgery increased the expression of TRPV1 in both female and male dorsal root ganglion (DRG). Injection of CPZ significantly suppressed TRPV1 expression in the DRG of male mice only.

CONCLUSION

Joint damage develops comparably in both female and male mice after DMM although it progresses less in females. There was a subtle sex difference in pain behaviors and analgesic efficacy of a TRPV1 antagonist, which was accompanied by a differential regulation of TPRV1.

Activation of TRPV1 by Capsaicin or Heat Drives Changes in 2-Acyl Glycerols and N-Acyl Ethanolamines in a Time, Dose, and Temperature Dependent Manner

Endocannabinoids (eCBs) and transient receptor potential (TRP) channels are associated with thermoregulation; however, there are many gaps in the understanding of how these signaling systems work together in responding to changes in temperature. TRPV1, a calcium-permeable ion channel, is activated by capsaicin, elevated temperature, the eCB Anandamide, and over 15 additional endogenous lipids. There is also evidence for signaling crosstalk between TRPV1 and the eCB receptor, CB₁. We recently found that activation of TRPV1-HEK cells by capsaicin increases the production of the eCB, 2-arachidonoyl glycerol (2-AG), suggesting a molecular link between these receptors. Here, we tested the hypothesis that TRPV1 activation by capsaicin drives regulation of a wider-range of lipid signaling molecules and is time and dose-dependent. We also tested the hypothesis that changes in temperature that drive changes in calcium mobilization in TRPV1-HEK will likewise drive similar changes in lipid signaling molecule regulation. Lipid analysis was conducted by partial purification of methanolic extracts on C18 solid phase extraction columns followed by HPLC/MS/MS. Capsaicin increased the release of 2-acyl glycerols (2-AG, 2-linoleoyl glycerol, 2-oleoyl glycerol), in a concentration- and time-dependent manner, whereas levels of N-acyl ethanolamines (NAEs), including Anandamide, were significantly decreased. Analogous changes in 2-acyl glycerols and NAEs were measured upon ramping the temperature from 37 to 45°C. In contrast, opposite effects were measured when analyzing lipids after they were maintained at 27°C and then quickly ramped to 37°C, wherein 2-acyl glycerol levels decreased and NAEs increased. These results provide further evidence that the eCB system and TRPV1 have integrated signaling functions that are associated with the molecular response to temperature variation.

Role of nucleotide binding oligomerization domain-like receptor protein 3 inflammasome in stress-induced gastric injury

BACKGROUND AND AIM

The inflammasomes promote pro-caspase-1 cleavage, leading to processing of pro-interleukin (IL)-1β into its mature form. We investigated the role of the IL-1β and nucleotide binding oligomerization domain-like receptor protein 3 (NLRP3) inflammasome in gastric injury in mice receiving water-immersion restraint stress (WIRS), focusing on the cyclooxygenase (COX)-2/prostaglandin (PG) E₂ axis.

METHODS

To induce gastric injury, the mice were placed in a restraint cage and immersed in the water bath to the level of the xiphoid process. Protein levels of mature caspase-1 and IL-1β were assessed by western blotting.

RESULTS

Water-immersion restraint stress induced gastric injury with increase in IL-1β expression by activation of NLRP3 inflammasome. Exogenous IL-1β attenuated the injury, whereas anti-IL-1β neutralizing antibody and IL-1β receptor antibody aggravated it. NLRP3^-/- and caspase-1^-/- mice enhanced the injury with reducing of mature IL-1β, and this aggravation was reduced by exogenous IL-1β supplementation. Toll-like receptor 4^-/- mice were hyporesponsive to WIRS in terms of mature IL-1β production. Rabeprazole attenuated the injury with preventing inflammasome activation. WIRS injured the stomach with promotion of COX-2 mRNA and PGE₂ production, and exogenous IL-1β enhanced these molecules, while IL-1β immunoneutralization exerted opposite effect. PGE₂ supplementation abolished the hypersensitivity in NLRP3^-/- and caspase-1^-/- mice through negative regulation of inflammatory cytokines.

CONCLUSION

These results suggest that NLRP3 inflammasome-derived IL-1β plays a protective role in stress-induced gastric injury via activation of the COX-2/PGE₂ axis. Toll-like receptor 4 signaling and gastric acid may be involved in NLRP3 inflammasome activation.

Anti-Inflammatory and Analgesic Effects of TRPV1 Polypeptide Modulator APHC3 in Models of Osteo- and Rheumatoid Arthritis

Arthritis is a widespread inflammatory disease associated with progressive articular surface degradation, ongoing pain, and hyperalgesia causing the development of functional limitations and disability. TRPV1 channel is one of the high-potential targets for the treatment of inflammatory diseases. Polypeptide APHC3 from sea anemone Heteractis crispa is a mode-selective TRPV1 antagonist that causes mild hypothermia and shows significant anti-inflammatory and analgesic activity in different models of pain. We evaluated the anti-inflammatory properties of APHC3 in models of monosodium iodoacetate (MIA)-induced osteoarthritis and complete Freund’s adjuvant (CFA)-induced rheumatoid monoarthritis in comparison with commonly used non-steroidal anti-inflammatory drugs (NSAIDs) such as diclofenac, ibuprofen, and meloxicam. Subcutaneous administration of APHC3 (0.1 mg/kg) significantly reversed joint swelling, disability, grip strength impairment, and thermal and mechanical hypersensitivity. The effect of APHC3 was equal to or better than that of reference NSAIDs. Protracted treatment with APHC3 decreased IL-1b concentration in synovial fluid, reduced inflammatory changes in joints, and prevented the progression of cartilage degradation. Therefore, polypeptide APHC3 has the potential to be an analgesic and anti-inflammatory substance for the alleviation of arthritis symptoms.

Capsaicin and Gut Microbiota in Health and Disease

Capsaicin is a widespread spice known for its analgesic qualities. Although a comprehensive body of evidence suggests pleiotropic benefits of capsaicin, including anti-inflammatory, antioxidant, anti-proliferative, metabolic, or cardioprotective effects, it is frequently avoided due to reported digestive side-effects. As the gut bacterial profile is strongly linked to diet and capsaicin displays modulatory effects on gut microbiota, a new hypothesis has recently emerged about its possible applicability against widespread pathologies, such as metabolic and inflammatory diseases. The present review explores the capsaicin–microbiota crosstalk and capsaicin effect on dysbiosis, and illustrates the intimate mechanisms that underlie its action in preventing the onset or development of pathologies like obesity, diabetes, or inflammatory bowel diseases. A possible antimicrobial property of capsaicin, mediated by the beneficial alteration of microbiota, is also discussed. However, as data are coming mostly from experimental models, caution is needed in translating these findings to humans.

Fight fire with fire: Neurobiology of capsaicin-induced analgesia for chronic pain

Capsaicin, the pungent ingredient in chili peppers, produces intense burning pain in humans. Capsaicin selectively activates the transient receptor potential vanilloid 1 (TRPV1), which is enriched in nociceptive primary afferents, and underpins the mechanism for capsaicin-induced burning pain. Paradoxically, capsaicin has long been used as an analgesic. The development of topical patches and injectable formulations containing capsaicin has led to application in clinical settings to treat chronic pain conditions, such as neuropathic pain and the potential to treat osteoarthritis. More detailed determination of the neurobiological mechanisms of capsaicin-induced analgesia should provide the logical rationale for capsaicin therapy and help to overcome the treatment's limitations, which include individual differences in treatment outcome and procedural discomfort. Low concentrations of capsaicin induce short-term defunctionalization of nociceptor terminals. This phenomenon is reversible within hours and, hence, likely does not account for the clinical benefit. By contrast, high concentrations of capsaicin lead to long-term defunctionalization mediated by the ablation of TRPV1-expressing afferent terminals, resulting in long-lasting analgesia persisting for several months. Recent studies have shown that capsaicin-induced Ca²⁺/calpain-mediated ablation of axonal terminals is necessary to produce long-lasting analgesia in a mouse model of neuropathic pain. In combination with calpain, axonal mitochondrial dysfunction and microtubule disorganization may also contribute to the longer-term effects of capsaicin. The analgesic effects subside over time in association with the regeneration of the ablated afferent terminals. Further determination of the neurobiological mechanisms of capsaicin-induced analgesia should lead to more efficacious non-opioidergic analgesic options with fewer adverse side effects.

Role of TRPV1 in colonic mucin production and gut microbiota profile

This study focuses on exploring the role of sensory cation channel Transient Receptor Potential channel subfamily Vanilloid 1 (TRPV1) in gut health, specifically mucus production and microflora profile in gut. We employed resiniferatoxin (ultrapotent TRPV1 agonist) induced chemo-denervation model in rats and studied the effects of TRPV1 ablation on colonic mucus secretion patterns. Histological and transcriptional analysis showed substantial decrease in mucus production as well as in expression of genes involved in goblet cell differentiation, mucin production and glycosylation. 16S metagenome analysis revealed changes in abundance of various gut bacteria, including decrease in beneficial bacteria like Lactobacillus spp and Clostridia spp. Also, TRPV1 ablation significantly decreased the levels of short chain fatty acids, i.e. acetate and butyrate. The present study provides first evidence that systemic TRPV1 ablation leads to impairment in mucus production and causes dysbiosis in gut. Further, it suggests to address mucin production and gut microbiota related adverse effects during the development of TRPV1 antagonism/ablation-based therapeutic and preventive strategies.

OEsophageal Ion Transport Mechanisms and Significance Under Pathological Conditions

Ion transporters play an important role in several physiological functions, such as cell volume regulation, pH homeostasis and secretion. In the oesophagus, ion transport proteins are part of the epithelial resistance, a mechanism which protects the oesophagus against reflux-induced damage. A change in the function or expression of ion transporters has significance in the development or neoplastic progression of Barrett’s oesophagus (BO). In this review, we discuss the physiological and pathophysiological roles of ion transporters in the oesophagus, highlighting transport proteins which serve as therapeutic targets or prognostic markers in eosinophilic oesophagitis, BO and esophageal cancer. We believe that this review highlights important relationships which might contribute to a better understanding of the pathomechanisms of esophageal diseases.

Resolvin D1 and D2 Inhibit Transient Receptor Potential Vanilloid 1 and Ankyrin 1 Ion Channel Activation on Sensory Neurons via Lipid Raft Modification

Transient Receptor Potential Vanilloid 1 and Ankyrin 1 (TRPV1, TRPA1) cation channels are expressed in nociceptive primary sensory neurons and regulate nociceptor and inflammatory functions. Resolvins are endogenous lipid mediators. Resolvin D1 (RvD1) is described as a selective inhibitor of TRPA1-related postoperative and inflammatory pain in mice acting on the G protein-coupled receptor DRV1/GPR32. Resolvin D2 (RvD2) is a very potent TRPV1 and TRPA1 inhibitor in DRG neurons, and decreases inflammatory pain in mice acting on the GPR18 receptor, via TRPV1/TRPA1-independent mechanisms. We provided evidence that resolvins inhibited neuropeptide release from the stimulated sensory nerve terminals by TRPV1 and TRPA1 activators capsaicin (CAPS) and allyl-isothiocyanate (AITC), respectively. We showed that RvD1 and RvD2 in nanomolar concentrations significantly decreased TRPV1 and TRPA1 activation on sensory neurons by fluorescent calcium imaging and inhibited the CAPS- and AITC-evoked ⁴⁵Ca-uptake on TRPV1- and TRPA1-expressing CHO cells. Since CHO cells are unlikely to express resolvin receptors, resolvins are suggested to inhibit channel opening through surrounding lipid raft disruption. Here, we proved the ability of resolvins to alter the membrane polarity related to cholesterol composition by fluorescence spectroscopy. It is concluded that targeting lipid raft integrity can open novel peripheral analgesic opportunities by decreasing the activation of nociceptors.

The use of high dose topical capsaicin in the management of peripheral neuropathy: narrative review and local experience

Capsaicin, derived from the chilli pepper plant, is available in high concentration (8%) patches to provide topical therapy for neuropathic pain. Its analgesic effects relate to defunctionalisation and nerve terminal retraction of predominantly C fibres in the dermis and epidermis. Systematic reviews and meta-analysis support its use for the management of post-herpetic neuralgia and HIV neuropathy with some evidence for use in painful peripheral diabetic neuropathy. The article concludes with advice on the practicalities of running a topical 8% capsaicin clinic for peripheral neuropathic pain.

An update on targets for treating osteoarthritis pain: NGF and TRPV1

Purpose of review

a)Osteoarthritis (OA) is the most common form of arthritis, and pain is the primary symptom of the disease, yet analgesic options for treating OA pain remain limited. In this review, we aimed to give an update on the current clinical and preclinical studies targeting two pathways that are being investigated for treating OA pain: the nerve growth factor (NGF) pathway and the transient receptor potential vanilloid-1 (TRPV1) pathway.

Recent findings

b)Antibodies against NGF, small molecule inhibitors of TrkA, TRPV1 agonists, and TRPV1 antagonists are all in different stages of clinical and pre-clinical testing for the treatment of OA pain. NGF antibodies have shown efficacy in the primary endpoints tested compared to placebo, however, rapidly progressive OA has been consistently observed in a subset of patients and the cause remains unclear. TRPV1 agonists have also demonstrated reduced pain with no serious adverse events - the most common adverse events include a burning or warming sensation upon administration.

Summary

c)Targeting the NGF and TRPV1 pathways appear effective for reducing OA pain, but further work is needed to better understand which patients may benefit most from these treatments. The anti-NGF antibody tanezumab and the TRPV1 agonist CNTX-4975 have both received fast-track designation from the FDA for the treatment of OA pain.

Changes in TRPV1-Mediated Physiological Function in Rats Systemically Treated With Capsaicin on the Neonate

Capsaicin is the active component of chili peppers and is a hydrophobic, colorless, odorless, and crystalline to waxy compound. The transient receptor potential vanilloid 1 (TRPV1) is the capsaicin receptor channels that are involved in a variety of functions like transduction and transmission of the physiological stimulus. Subcutaneous injection of capsaicin to a newborn rat leads to involuntary lifelong TRPV1 desensitization. Various physiological changes including sensory and homeostatic actions in the body associated with neonatal capsaicin treatment are induced by direct TRPV1 channel targeting. Interesting changes include unique phenomena such as the reduction in pain perception, abnormal body temperature, increase in infection, infectious or neuropathological itching, and irregular circadian core body temperature rhythm. These symptoms are associated with relatively higher fever or loss of sensory c-fiber related to TRPV1 desensitization. The aforementioned outcomes not only provide a warning about the risk of capsaicin exposure in newborns but also indicate the possible occurrence of relatively rare diseases that are difficult to diagnose. Therefore, Therefore, the present review aims to summarize the unique phenomena caused by systemic capsaicin administration in neonatal rats.

Changes in TRPV1-Mediated Physiological Function in Rats Systemically Treated With Capsaicin on the Neonate

Capsaicin is the active component of chili peppers and is a hydrophobic, colorless, odorless, and crystalline to waxy compound. The transient receptor potential vanilloid 1 (TRPV1) is the capsaicin receptor channels that are involved in a variety of functions like transduction and transmission of the physiological stimulus. Subcutaneous injection of capsaicin to a newborn rat leads to involuntary lifelong TRPV1 desensitization. Various physiological changes including sensory and homeostatic actions in the body associated with neonatal capsaicin treatment are induced by direct TRPV1 channel targeting. Interesting changes include unique phenomena such as the reduction in pain perception, abnormal body temperature, increase in infection, infectious or neuropathological itching, and irregular circadian core body temperature rhythm. These symptoms are associated with relatively higher fever or loss of sensory c-fiber related to TRPV1 desensitization. The aforementioned outcomes not only provide a warning about the risk of capsaicin exposure in newborns but also indicate the possible occurrence of relatively rare diseases that are difficult to diagnose. Therefore, Therefore, the present review aims to summarize the unique phenomena caused by systemic capsaicin administration in neonatal rats.

Lipid Nanoparticle Inclusion Prevents Capsaicin-Induced TRPV1 Defunctionalization

BACKGROUND

Capsaicin (CPS) is a highly selective agonist of the transient receptor potential vanilloid type 1 (TRPV1) with a nanomolar affinity. High doses or prolonged exposure to CPS induces TRPV1 defunctionalization and, although this effect is currently used for the treatment of thermal hyperalgesia in chronic pain conditions, it is responsible of detrimental effects, such as denervation of sensory fibers. The aim of the present study was to formulate CPS loaded lipid nanocarriers (CPS-LN) in order to optimize CPS release, thus preventing TRPV1 internalization and degradation.

METHODS

CPS-LNs were formulated and characterized by in vitro studies. The activation of TRPV1 receptors after CPS-LN administration was evaluated by measuring spontaneous pain that was induced by local injection into the plantar surface of the mouse hind-paw. Moreover, the expression of TRPV1 in the skin was evaluated by western blot analysis in CPS-LN injected mice and then compared to a standard CPS solution (CPS-STD).

RESULTS

CPS inclusion in LN induced a lower pain response when compared to CPS-STD; further, it prevented TRPV1 down-regulation in the skin, while CPS-STD induced a significant reduction of TRPV1 expression.

CONCLUSIONS

Drug encapsulation in lipid nanoparticles produced an optimization of CPS release, thus reducing mice pain behavior and avoiding the effects that are caused by TRPV1 defunctionalization related to a prolonged activation of this receptor.

Perineural application of resiniferatoxin on uninjured L3 and L4 nerves completely alleviates thermal and mechanical hypersensitivity following L5 nerve injury in rats

Fifth lumbar (L5) nerve injury in rats causes neuropathic pain manifested with thermal and mechanical hypersensitivity in the ipsilateral hind paw. This study aimed to determine whether the elimination of unmyelinated primary afferents of the adjacent uninjured nerves (L3 and L4) would alleviate peripheral neuropathic pain. Different concentrations of capsaicin or its analog, resiniferatoxin (RTX), were applied perineurally on either the left L4 or L3 and L4 nerves in Wistar rats whose left L5 nerves were ligated and cut. The application of both capsaicin and RTX on the L4 nerve significantly reduced both thermal and mechanical hypersensitivity. However, only the application of RTX on both L3 and L4 nerves completely alleviated all neuropathic manifestations. Interestingly, responses to thermal and mechanical stimuli were preserved, despite RTX application on uninjured L3, L4, and L5 nerves, which supply the plantar skin in rats. Perineural application of RTX caused downregulation of TRPV1, CGRP, and IB4 binding and upregulation of VIP in the corresponding dorsal root ganglia (DRG) and the dorsal horn of the spinal cord. In comparison, VGLUT1 and NPY immunoreactivities were not altered. RTX application did not cause degenerative or ultrastructural changes in the treated nerves and corresponding DRGs. The results demonstrate that RTX induces neuroplasticity, rather than structural changes in primary afferents, that are responsible for alleviating hypersensitivity and chronic pain. Furthermore, this study suggests that treating uninjured adjacent spinal nerves may be used to manage chronic neuropathic pain following peripheral nerve injury.

Hyperthermia induced by transient receptor potential vanilloid-1 (TRPV1) antagonists in human clinical trials: Insights from mathematical modeling and meta-analysis

Antagonists of the transient receptor potential vanilloid-1 (TRPV1) channel alter body temperature (T_b) in laboratory animals and humans: most cause hyperthermia; some produce hypothermia; and yet others have no effect. TRPV1 can be activated by capsaicin (CAP), protons (low pH), and heat. First-generation (polymodal) TRPV1 antagonists potently block all three TRPV1 activation modes. Second-generation (mode-selective) TRPV1 antagonists potently block channel activation by CAP, but exert different effects (e.g., potentiation, no effect, or low-potency inhibition) in the proton mode, heat mode, or both. Based on our earlier studies in rats, only one mode of TRPV1 activation - by protons - is involved in thermoregulatory responses to TRPV1 antagonists. In rats, compounds that potently block, potentiate, or have no effect on proton activation cause hyperthermia, hypothermia, or no effect on T_b, respectively. A T_b response occurs when a TRPV1 antagonist blocks (in case of hyperthermia) or potentiates (hypothermia) the tonic TRPV1 activation by protons somewhere in the trunk, perhaps in muscles, and - via the acido-antithermogenic and acido-antivasoconstrictor reflexes - modulates thermogenesis and skin vasoconstriction. In this work, we used a mathematical model to analyze T_b data from human clinical trials of TRPV1 antagonists. The analysis suggests that, in humans, the hyperthermic effect depends on the antagonist's potency to block TRPV1 activation not only by protons, but also by heat, while the CAP activation mode is uninvolved. Whereas in rats TRPV1 drives thermoeffectors by mediating pH signals from the trunk, but not T_b signals, our analysis suggests that TRPV1 mediates both pH and thermal signals driving thermoregulation in humans. Hence, in humans (but not in rats), TRPV1 is likely to serve as a thermosensor of the thermoregulation system. We also conducted a meta-analysis of T_b data from human trials and found that polymodal TRPV1 antagonists (ABT-102, AZD1386, and V116517) increase T_b, whereas the mode-selective blocker NEO6860 does not. Several strategies of harnessing the thermoregulatory effects of TRPV1 antagonists in humans are discussed.

Effects of Spicy Stimulation and Spicy-Food Consumption on Human Pain Sensitivity: A Healthy Volunteer Study

Spicy-food intake has been shown to affect various human physiological systems and diseases. This study tested the analgesia effect caused by stimulation of a spicy sensation (spicy stimulation) and explored the effect of spicy-food consumption on human basal pain sensitivity. A total of 60 healthy undergraduates were included in the primary study. Placebo and sweet stimulation were used as reference interventions. Pressure and cold-pain thresholds were measured before and after taste stimulation. The frequency of spicy-food intake was also evaluated. An additional 100 subjects were recruited to validate the results. Compared to placebo stimulation, both pressure and cold-pain thresholds increased during spicy stimulation (P < .05). The increased thresholds remained, even when the taste stimulation residue was nearly eliminated (P < .05). The pressure (10.0 [2.1] vs 12.7 [3.0] kg/cm2, P < .001) and cold-pain (4.4 [1.6] vs 6.2 [2.7] seconds, P = .003) thresholds in subjects who consume spicy food ≥3 days/week were significantly lower than in those who consume it <3 days/week. In the validation population, the frequency of spicy-food intake was negatively associated with subjects' pressure (β = -.218, P = .013) and cold-pain (β = -.205, P = .035) thresholds. Spicy stimulation has an analgesia effect on adults that persists even after the taste stimulation stops. Conversely, a long-term spicy diet can reduce the human basal pain threshold. TRIAL REGISTRATION: The study protocol was approved by the Medical Ethics Committee of the Second Affiliated Hospital of Army Medical University, People's Liberation Army (identification No., 2017-023-01), and it was registered on the Chinese Clinical Trial Registry at www.chictr.org.cn (No. ChiCTR1800015053). PERSPECTIVE: This study directly examined the effects of stimulation of a spicy sensation on adult pain sensitivity and was the first to explore the relationship between long-term spicy-food intake and human pain sensitivity. The results provide evidence for future clinical pain intervention and individualized pain treatment.

High-dose phenylephrine increases meningeal blood flow through TRPV1 receptor activation and release of calcitonin gene-related peptide

BACKGROUND

The α₁ -adrenoceptor agonist, phenylephrine, is used at high concentrations as a mydriatic agent and for the treatment of nasal congestion. Among its adverse side-effects transient burning sensations are reported indicating activation of the trigeminal nociceptive system.

METHODS

Neuropeptide release, calcium imaging and meningeal blood flow recordings were applied in rodent models of meningeal nociception to clarify possible receptor mechanisms underlying these pain phenomena.

RESULTS

Phenylephrine above 10 mM dose-dependently released calcitonin gene-related peptide (CGRP) from the dura mater and isolated trigeminal ganglia, whereas hyperosmotic mannitol at 90 mM was ineffective. The phenylephrine-evoked release was blocked by the transient receptor potential vanilloid 1 (TRPV1) antagonist BCTC and did not occur in trigeminal ganglia of TRPV1-deficient mice. Phenylephrine at 30 mM caused calcium transients in cultured trigeminal ganglion neurons responding to the TRPV1 agonist capsaicin and in HEK293T cells expressing human TRPV1. Local application of phenylephrine at micromolar concentrations to the exposed rat dura mater reduced meningeal blood flow, whereas concentrations above 10 mM caused increased meningeal blood flow. The flow increase was abolished by pre-application of the CGRP receptor antagonist CGRP_8-37 or the TRPV1 antagonist BCTC.

CONCLUSIONS

Phenylephrine at high millimolar concentrations activates TRPV1 receptor channels of perivascular afferents and, upon calcium inflow, releases CGRP, which increases meningeal blood flow. Activation of TRPV1 receptors may underlie trigeminal nociception leading to cranial pain such as local burning sensations or headaches caused by administration of high doses of phenylephrine.

SIGNIFICANCE

Phenylephrine is used at high concentrations as a mydriaticum and for treating nasal congestion. As adverse side-effects burning sensations and headaches have been described. Phenylephrine at high concentrations causes calcium transients in trigeminal afferents, CGRP release and increased meningeal blood flow upon activation of TRPV1 receptor channels, which is likely underlying the reported pain phenomena.

The Pivotal Role of TRP Channels in Homeostasis and Diseases throughout the Gastrointestinal Tract

The transient receptor potential (TRP) channels superfamily are a large group of proteins that play crucial roles in cellular processes. For example, these cation channels act as sensors in the detection and transduction of stimuli of temperature, small molecules, voltage, pH, and mechanical constrains. Over the past decades, different members of the TRP channels have been identified in the human gastrointestinal (GI) tract playing multiple modulatory roles. Noteworthy, TRPs support critical functions related to the taste perception, mechanosensation, and pain. They also participate in the modulation of motility and secretions of the human gut. Last but not least, altered expression or activity and mutations in the TRP genes are often related to a wide range of disorders of the gut epithelium, including inflammatory bowel disease, fibrosis, visceral hyperalgesia, irritable bowel syndrome, and colorectal cancer. TRP channels could therefore be promising drug targets for the treatment of GI malignancies. This review aims at providing a comprehensive picture of the most recent advances highlighting the expression and function of TRP channels in the GI tract, and secondly, the description of the potential roles of TRPs in relevant disorders is discussed reporting our standpoint on GI tract–TRP channels interactions.

Calcium signals that determine vascular resistance

Small arteries in the body control vascular resistance, and therefore, blood pressure and blood flow. Endothelial and smooth muscle cells in the arterial walls respond to various stimuli by altering the vascular resistance on a moment to moment basis. Smooth muscle cells can directly influence arterial diameter by contracting or relaxing, whereas endothelial cells that line the inner walls of the arteries modulate the contractile state of surrounding smooth muscle cells. Cytosolic calcium is a key driver of endothelial and smooth muscle cell functions. Cytosolic calcium can be increased either by calcium release from intracellular stores through IP3 or ryanodine receptors, or the influx of extracellular calcium through ion channels at the cell membrane. Depending on the cell type, spatial localization, source of a calcium signal, and the calcium-sensitive target activated, a particular calcium signal can dilate or constrict the arteries. Calcium signals in the vasculature can be classified into several types based on their source, kinetics, and spatial and temporal properties. The calcium signaling mechanisms in smooth muscle and endothelial cells have been extensively studied in the native or freshly isolated cells, therefore, this review is limited to the discussions of studies in native or freshly isolated cells. This article is categorized under: Biological Mechanisms > Cell Signaling Laboratory Methods and Technologies > Imaging Models of Systems Properties and Processes > Mechanistic Models.

Bone Metastasis Pain, from the Bench to the Bedside

Bone is the most frequent site of metastasis of the most common cancers in men and women. Bone metastasis incidence has been steadily increasing over the years, mainly because of higher life expectancy in oncologic patients. Although bone metastases are sometimes asymptomatic, their consequences are most often devastating, impairing both life quality and expectancy, due to the occurrence of the skeletal-related events, including bone fractures, hypercalcemia and spinal cord compression. Up to 75% of patients endure crippling cancer-induced bone pain (CIBP), against which we have very few weapons. This review’s purpose is to discuss the molecular and cellular mechanisms that lead to CIBP, including how cancer cells convert the bone “virtuous cycle” into a cancer-fuelling “vicious cycle”, and how this leads to the release of molecular mediators of pain, including protons, neurotrophins, interleukins, chemokines and ATP. Preclinical tests and assays to evaluate CIBP, including the incapacitance tester (in vivo), and neuron/glial activation in the dorsal root ganglia/spinal cord (ex vivo) will also be presented. Furthermore, current therapeutic options for CIBP are quite limited and nonspecific and they will also be discussed, along with up-and-coming options that may render CIBP easier to treat and let patients forget they are patients.

TRPV1-Like Immunoreactivity in the Human Locus K, a Distinct Subregion of the Cuneate Nucleus

The presence of transient receptor potential vanilloid type-1 receptor (TRPV1)-like immunoreactivity (LI), in the form of nerve fibres and terminals, is shown in a set of discrete gray matter subregions placed in the territory of the human cuneate nucleus. We showed previously that those subregions share neurochemical and structural features with the protopathic nuclei and, after the ancient name of our town, collectively call them Locus Karalis, and briefly Locus K. TRPV1-LI in the Locus K is codistributed, though not perfectly overlapped, with that of the neuropeptides calcitonin gene-related peptide and substance P, the topography of the elements immunoreactive to the three markers, in relation to each other, reflecting that previously described in the caudal spinal trigeminal nucleus. Myelin stainings show that myelinated fibres, abundant in the cuneate, gracile and trigeminal magnocellular nuclei, are scarce in the Locus K as in the trigeminal substantia gelatinosa. Morphometric analysis shows that cell size and density of Locus K neurons are consistent with those of the trigeminal substantia gelatinosa and significantly different from those of the magnocellular trigeminal, solitary and dorsal column nuclei. We propose that Locus K is a special component of the human dorsal column nuclei. Its functional role remains to be determined, but TRPV1 appears to play a part in it.

The detection of capsaicin and dihydrocapsaicin in horse serum following long-term local administration

Background

Capsaicin and dihydrocapsaicin are alkaloids with analgesic effects in humans and animals. When used locally, both of them minimalise pain sensation by defunctionalising nerve endings. According to the Federation Equestrian International Prohibited Substances List, these are substance banned in horse competitions. The aim of the study was to determine the detection time of capsaicin in both plasma and serum after long-term use of a gel recommended for commercial use and applied as intended. The objective of the study was to select the best material for the detection of capsaicin as a doping substance in horses.

Methods

Nine healthy mature horses were administered 0.1% capsaicin topically in the form of a commercial analgesic gel (15 g of the gel per limb) to the front limbs every 24 hours for five days with a polar fleece bandage. Blood serum and plasma were collected prior to gel application and in the 12th, 18th, 24th, 36th, 42nd, 48th, 60th, 84th, 108th, 132nd, 156th hour after the gel application. Qualitative and quantitative analysis was performed using ultra-high performance liquid chromatography coupled with a triple quadrupole mass spectrometry (UHPLC-QqQ-MS/MS).

Results

The concentration of capsaicin in the serum samples did not exceed the lower limit of quantification. Capsaicin was not detected in the plasma samples during the entire study period. Dihydrocapsaicin was not detected in blood serum or plasma.

Conclusion

The presented results suggest that capsaicin is not detected in horse serum in the 24-hour-periodfollowing its last application according to the dosage regimen used by owners and veterinarians for therapy rather than doping, based on a five day gel application and a polar bandage.

Role of TRPV1 receptor in inflammation and impairment of esophageal mucosal integrity in a murine model of nonerosive reflux disease

BACKGROUND

Microscopic inflammation and impairment of the esophageal epithelial barrier are considered relevant for perception of symptoms in patients with nonerosive reflux disease (NERD). In these patients, the receptor transient receptor potential vanilloid 1 (TRPV1) is overexpressed in the esophageal mucosa, but its role is not yet fully understood. We evaluated the role of TRPV1 in esophageal inflammation and mucosal barrier impairment in a murine model of NERD.

METHODS

Nonerosive reflux disease was surgically induced in Swiss mice by pyloric substenosis and ligature of the gastric fundus, and the mice were killed 7 days post surgery. The experimental groups were: I, sham surgery (negative control); II, NERD untreated; III and IV, NERD + SB366791 or capsazepine (TRPV1 antagonists); and V, NERD + resiniferatoxin (for long-term desensitization of TRPV1). The esophagus was collected for western blotting and histopathology and for evaluation of wet weight, myeloperoxidase (MPO), keratinocyte-derived chemokine (KC), transepithelial electrical resistance (TEER), and basal permeability to fluorescein.

KEY RESULTS

Compared to sham, NERD mice had increased esophageal wet weight and MPO and KC levels. The mucosa had no ulcers but exhibited inflammation. NERD mice showed mucosal TRPV1 overexpression, a more pronounced decrease in TEER at pH 0.5 (containing pepsin and taurodeoxycholic acid), and increased basal permeability. Pharmacological modulation of TRPV1 prevented esophageal inflammation development, TEER changes by acidic exposure, and increase in esophageal permeability.

CONCLUSIONS & INFERENCES

The TRPV1 receptor has a critical role in esophageal inflammation and mucosal barrier impairment in NERD mice, suggesting that TRPV1 might be a pharmacological target in patients with NERD.

Long Non-coding RNA BC168687 is Involved in TRPV1-mediated Diabetic Neuropathic Pain in Rats

Long noncoding RNAs (lncRNAs) participate in a diverse range of molecular and biological processes, and dysregulation of lncRNAs has been observed in the pathogenesis of various human diseases. We observed alterations in mechanical withdrawal thresholds (MWT) and thermal withdrawal latencies (TWL) in streptozotocin (STZ)-induced diabetic rats treated with small interfering RNA (siRNA) of lncRNA BC168687. We detected expression of transient receptor potential vanilloid type 1 (TRPV1) in rat dorsal root ganglia (DRG) by a series of molecular experiments. We determined relative levels of tumor necrosis factor (TNF)-α and interleukin (IL)-1β in rat serum by enzyme-linked immunosorbent assay (ELISA). In addition, we examined extracellular regulated protein kinases (ERK) and p38 mitogen-activated protein kinase (MAPK) signaling pathways by Western blot (WB). We showed that the MWT and TWL of diabetic rats increased significantly compared with control. Expression of TRPV1 receptors in DRG substantially decreased. Relative levels of TNF-α and IL-1β in the serum of lncRNA BC168687 siRNA-treated rats were reduced. Phosphorylation (p)-ERK and p-p38 signaling pathways in DRG were also decreased. Taken together, we concluded lncRNA BC168687 siRNA may alleviate TRPV1-mediated diabetic neuropathic pain.

Burn injury: Challenges and advances in burn wound healing, infection, pain and scarring

Severe burn injuries are the most traumatic and physically debilitating injuries affecting nearly every organ system and leading to significant morbidity and mortality. Early burn wound excision and skin grafting are common clinical practices that have significantly improved the outcomes for severe burn injured patients by reducing mortality rate and days of hospital stay. However, slow wound healing, infection, pain, and hypertrophic scarring continue to remain a major challenge in burn research and management. In the present article, we review and discuss issues in the current treatment of burn injuries; the advances and novel strategies developed in the past decade that have improved burn management; and also, pioneer ideas and studies in burn research which aims to enhance burn wound care with a focus on burn wound infection, pain management, treatments for scarring and skin tissue engineering.

Striated Perineal Muscles: Location of Somatic and Autonomic Neurons Projecting to the Male Pig Ischiocavernous Muscle. Neurochemical Features of the Sympathetic Subset

The location, number and size of the central and peripheral neurons innervating the ischiocavernous muscle (ICM) were studied in male pigs by means of Fast Blue (FB) retrograde neuronal tracing. Moreover the immunohistochemical properties of the sympathetic ganglia were investigated combining the double immunolabeling method. After injection of FB into the left ICM, a mean number of 245.3 ± 134.9 labeled neurons were found in the ipsilateral ventral horn of the S1-S3 segments of the spinal cord (SC), 129.7 ± 45.5 in the L6-S3 ipsilateral and S2-S3 contralateral spinal ganglia (SGs), 2279.3 ± 622.1 in the ipsilateral L2-S2 and contralateral L5-S2 sympathetic trunk ganglia (STGs), 541.7 ± 158 in the bilateral caudal mesenteric ganglia (CMGs), and 78.3 ± 35.8 in the microganglia of the pelvic plexus (PGs). The mean area of the ICM projecting neurons was 1217 ± 69.7 μm² in the SC, 2737.5 ± 176.5 μm² in the SGs, 982.8 ± 36.8 μm² in the STGs, 865.9 ± 39.14 μm² in the CMGs and 426.2 ± 24.72 μm² in the PGs. The FB positive neurons of autonomic ganglia contained Dopamine β hydroxylase, vesicular acetylcholine transporter, neuronal nitric oxyde sinthase, calcitonine gene related peptide, leu-enkephaline, neuropeptide Y, substance P, vasoactive intestinal polypeptide, and somatostatine often colocalized with tyrosine hydroxylase. The particular localization of the motor somatic nucleus, the abundant autonomic innervation and the qualitatively different content of ICM projecting sympathetic neurons suggest a complex regulation of this striated muscle involved in involuntary functions, such as the erection, ejaculation, micturition and defecation. Anat Rec, 301:837-848, 2018. © 2017 Wiley Periodicals, Inc.

A synthetic peptide blocking TRPV1 activation inhibits UV-induced skin responses

BACKGROUND

Transient receptor potential type 1 (TRPV1) can be activated by ultraviolet (UV) irradiation, and mediates UV-induced matrix metalloproteinase (MMP)-1 and proinflammatory cytokines in keratinocytes. Various chemicals and compounds targeting TRPV1 activation have been developed, but are not in clinical use mostly due to their safety issues.

OBJECTIVE

We aimed to develop a novel TRPV1-targeting peptide to inhibit UV-induced responses in human skin.

METHODS

We designed and generated a novel TRPV1 inhibitory peptide (TIP) which mimics the specific site in TRPV1 (aa 701-709: Gln-Arg-Ala-Ile-Thr-Ile-Leu-Asp-Thr, QRAITILDT), Thr⁷⁰⁵, and tested its efficacy of blocking UV-induced responses in HaCaT, mouse, and human skin.

RESULTS

TIP effectively inhibited capsaicin-induced calcium influx and TRPV1 activation. Treatment of HaCaT with TIP prevented UV-induced increases of MMP-1 and pro-inflammatory cytokines such as interleukin (IL)-6 and tumor necrosis factor-α. In mouse skin in vivo, TIP inhibited UV-induced skin thickening and prevented UV-induced expression of MMP-13 and MMP-9. Moreover, TIP attenuated UV-induced erythema and the expression of MMP-1, MMP-2, IL-6, and IL-8 in human skin in vivo.

CONCLUSION

The novel synthetic peptide targeting TRPV1 can ameliorate UV-induced skin responses in vitro and in vivo, providing a promising therapeutic approach against UV-induced inflammation and photoaging.