TRPV1 deletion enhances local inflammation and accelerates the onset of systemic inflammatory response syndrome

Role of Kynurenine and Its Derivatives in the Neuroimmune System

In recent years, there has been a growing realization of intricate interactions between the nervous and immune systems, characterized by shared humoral factors and receptors. This interplay forms the basis of the neuroimmune system, the understanding of which will provide insights into the pathogenesis of neurological diseases, in which the involvement of the immune system has been overlooked. Kynurenine and its derivatives derived from tryptophan have long been implicated in the pathogenesis of various neurological diseases. Recent studies have revealed their close association not only with neurological disorders but also with sepsis-related deaths. This review provides an overview of the biochemistry of kynurenine and its derivatives, followed by a discussion of their role via the modulation of the neuroimmune system in various diseases.

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.

Neuroimmune modulation by tryptophan derivatives in neurological and inflammatory disorders

The nervous and immune systems are highly developed, and each performs specialized physiological functions. However, they work together, and their dysfunction is associated with various diseases. Specialized molecules, such as neurotransmitters, cytokines, and more general metabolites, are essential for the appropriate regulation of both systems. Tryptophan, an essential amino acid, is converted into functional molecules such as serotonin and kynurenine, both of which play important roles in the nervous and immune systems. The role of kynurenine metabolites in neurodegenerative and psychiatric diseases has recently received particular attention. Recently, we found that hyperactivity of the kynurenine pathway is a critical risk factor for septic shock. In this review, we first outline neuroimmune interactions and tryptophan derivatives and then summarized the changes in tryptophan metabolism in neurological disorders. Finally, we discuss the potential of tryptophan derivatives as therapeutic targets for neuroimmune disorders.

Lipopolysaccharide pretreatment increases the sensitivity of the TRPV1 channel and promotes an anti-inflammatory phenotype of capsaicin-activated macrophages

BACKGROUND

The transient receptor potential vanilloid 1 (TRPV1) is well-established in neuronal function, yet its role in immune reactions remains enigmatic. The conflicting data on its inflammatory role, suggesting both pro-inflammatory and anti-inflammatory effects upon TRPV1 stimulation in immune cells, adds complexity. To unravel TRPV1 immunomodulatory mechanisms, we investigated how the TRPV1 agonist capsaicin influences lipopolysaccharide (LPS)-induced pro-inflammatory macrophage phenotypes.

RESULTS

Changes in the surface molecules, cytokine production, and signaling cascades linked to the phenotype of M1 or M2 macrophages of the J774 macrophage cell line and bone marrow-derived macrophages, treated with capsaicin before or after the LPS-induced inflammatory reaction were determined. The functional capacity of macrophages was also assessed by infecting the stimulated macrophages with the intracellular parasite Leishmania mexicana.

CONCLUSION

Our findings reveal that TRPV1 activation yields distinct macrophage responses influenced by the inflammatory context. LPS pre-treatment followed by capsaicin activation prompted increased calcium influx, accompanied by a shift toward an anti-inflammatory M2b-like polarization state.

TRPV1: Receptor structure, activation, modulation and role in neuro-immune interactions and pain

In the 1990s, the identification of a non-selective ion channel, especially responsive to capsaicin, revolutionized the studies of somatosensation and pain that were to follow. The TRPV1 channel is expressed mainly in neuronal cells, more specifically, in sensory neurons responsible for the perception of noxious stimuli. However, its presence has also been detected in other non-neuronal cells, such as immune cells, β- pancreatic cells, muscle cells and adipocytes. Activation of the channel occurs in response to a wide range of stimuli, such as noxious heat, low pH, gasses, toxins, endocannabinoids, lipid-derived endovanilloid, and chemical agents, such as capsaicin and resiniferatoxin. This activation results in an influx of cations through the channel pore, especially calcium. Intracellular calcium triggers different responses in sensory neurons. Dephosphorylation of the TRPV1 channel leads to its desensitization, which disrupts its function, while its phosphorylation increases the channel's sensitization and contributes to the channel's rehabilitation after desensitization. Kinases, phosphoinositides, and calmodulin are the main signaling pathways responsible for the channel's regulation. Thus, in this review we provide an overview of TRPV1 discovery, its tissue expression as well as on the mechanisms by which TRPV1 activation (directly or indirectly) induces pain in different disease models.

The Role of TRP Channels in Sepsis and Colitis

To date, several members of the transient receptor potential (TRP) channels which provide a wide array of roles have been found in the gastrointestinal tract (GI). The goal of earlier research was to comprehend the intricate signaling cascades that contribute to TRP channel activation as well as how these receptors' activity affects other systems. Moreover, there is a large volume of published studies describing the role of TRP channels in a number of pathological disorders, including inflammatory bowel disease (IBD) and sepsis. Nevertheless, the generalizability of these results is subject to certain limitations. For instance, the study of IBD relies on various animal models and experimental methods, which are unable to precisely imitate the multifactorial chronic disease. The diverse pathophysiological mechanisms and unique susceptibility of animals may account for the inconsistency of the experimental data collected. The main purpose of this study was to conduct a comprehensive review and analysis of existing studies on transient receptor potential (TRP) channels implicating specific models of colitis and sepsis, with particular emphasis on their involvement in pathological disorders such as IBD and sepsis. Furthermore, the text endeavors to evaluate the generalizability of experimental findings, taking into consideration the limitations posed by animal models and experimental methodologies. Finally, we also provide an updated schematic of the most important and possible molecular signaling pathways associated with TRP channels in IBD and sepsis.

The role of transient receptor potential (TRP) channels in phagocytosis: A comprehensive review

When host cells are exposed to foreign particles, dead cells, or cell hazards, a sophisticated process called phagocytosis begins. During this process, macrophages, dendritic cells, and neutrophils engulf the target by expanding their membranes. Phagocytosis of apoptotic cells is called efferocytosis. This process is of significant importance as billions of cells are eliminated daily without provoking inflammation. Both phagocytosis and efferocytosis depend on Ca2+ signaling. A big family of Ca2+ permeable channels is transient receptor potentials (TRPs) divided into nine subfamilies. We aimed to review their roles in phagocytosis. The present review article shows that various TRP channels such as TRPV1, 2, 3, 4, TRPM2, 4, 7, 8, TRPML1, TRPA1, TRPC1, 3, 5, 6 have roles at various stages of phagocytosis. They are involved in the phagocytosis of amyloid β, α-synuclein, myelin debris, bacteria, and apoptotic cells. In particular, TRPC3 and TRPM7 contribute to efferocytosis. These effects are mediated by changing Ca2+ signaling or targeting intracellular enzymes such as Akt. In addition, they contribute to the chemotaxis of phagocytic cells towards targets. Although a limited number of studies have assessed the role of TRP channels in phagocytosis and efferocytosis, their findings indicate that they have critical roles in these processes. In some cases, their ablation completely abolished the phagocytic function of the cells. As a result, TRP channels are potential targets for developing new therapeutics that modulate phagocytosis.

Transient receptor potential vanilloid type 1: cardioprotective effects in diabetic models

Cardiovascular disease, especially heart failure (HF) is the leading cause of death in patients with diabetes. Individuals with diabetes are prone to a special type of cardiomyopathy called diabetic cardiomyopathy (DCM), which cannot be explained by heart diseases such as hypertension or coronary artery disease, and can contribute to HF. Unfortunately, the current treatment strategy for diabetes-related cardiovascular complications is mainly to control blood glucose levels; nonetheless, the improvement of cardiac structure and function is not ideal. The transient receptor potential cation channel subfamily V member 1 (TRPV1), a nonselective cation channel, has been shown to be universally expressed in the cardiovascular system. Increasing evidence has shown that the activation of TRPV1 channel has a potential protective influence on the cardiovascular system. Numerous studies show that activating TRPV1 channels can improve the occurrence and progression of diabetes-related complications, including cardiomyopathy; however, the specific mechanisms and effects are unclear. In this review, we summarize that TRPV1 channel activation plays a protective role in the heart of diabetic models from oxidation/nitrification stress, mitochondrial function, endothelial function, inflammation, and cardiac energy metabolism to inhibit the occurrence and progression of DCM. Therefore, TRPV1 may become a latent target for the prevention and treatment of diabetes-induced cardiovascular complications.

Senso-immunology: the past, present, and future

Pain and mechanical stimulation are thought to be alarm systems that alert the brain to physical abnormalities. When we experience unpleasant feelings in infected or traumatized tissues, our awareness is directed to the afflicted region, prompting activities such as resting or licking the tissue. Despite extensive research into the molecular biology of nociceptors, it was unclear whether their role was limited to the generation and transmission of unpleasant feelings or whether they actively modulate the pathogenesis of infected or traumatized tissues. Recently, it has become clear how the sensory and immune systems interact with one another and share similar receptors and ligands to modify the pathogenesis of various diseases. In this paper, we summarize the mechanisms of crosstalk between the sensory and immune systems and the impact of this new interdisciplinary field, which should be dubbed 'senso-immunology,' on medical science.

Function of TRP channels in monocytes/macrophages

The transient receptor potential channel (TRP channel) family is a kind of non- specific cation channel widely distributed in various tissues and organs of the human body, including the respiratory system, cardiovascular system, immune system, etc. It has been reported that various TRP channels are expressed in mammalian macrophages. TRP channels may be involved in various signaling pathways in the development of various systemic diseases through changes in intracellular concentrations of cations such as calcium and magnesium. These TRP channels may also intermingle with macrophage activation signals to jointly regulate the occurrence and development of diseases. Here, we summarize recent findings on the expression and function of TRP channels in macrophages and discuss their role as modulators of macrophage activation and function. As research on TRP channels in health and disease progresses, it is anticipated that positive or negative modulators of TRP channels for treating specific diseases may be promising therapeutic options for the prevention and/or treatment of disease.

Carcinogenesis and Metastasis: Focus on TRPV1-Positive Neurons and Immune Cells

Both sensory neurons and immune cells, albeit at markedly different levels, express the vanilloid (capsaicin) receptor, Transient Receptor Potential, Vanilloid-1 (TRPV1). Activation of TRPV1 channels in sensory afferent nerve fibers induces local effector functions by releasing neuropeptides (most notably, substance P) which, in turn, trigger neurogenic inflammation. There is good evidence that chronic activation or inactivation of this inflammatory pathway can modify tumor growth and metastasis. TRPV1 expression was also demonstrated in a variety of mammalian immune cells, including lymphocytes, dendritic cells, macrophages and neutrophils. Therefore, the effects of TRPV1 agonists and antagonists may vary depending on the prominent cell type(s) activated and/or inhibited. Therefore, a comprehensive understanding of TRPV1 activity on immune cells and nerve endings in distinct locations is necessary to predict the outcome of therapies targeting TRPV1 channels. Here, we review the neuro-immune modulation of cancer growth and metastasis, with focus on the consequences of TRPV1 activation in nerve fibers and immune cells. Lastly, the potential use of TRPV1 modulators in cancer therapy is discussed.

TRPV1 is involved in abdominal hyperalgesia in a mouse model of lipopolysaccharide-induced peritonitis and influences the immune response via peripheral noradrenergic neurons

AIMS

The transient receptor potential vanilloid subfamily 1 (TRPV1) not only plays a role as a nociceptor but also has some regulatory effects on the immune system. We investigated the effects of TRPV1 on abdominal pain and the immune system in lipopolysaccharide (LPS)-induced peritonitis and the association between TRPV1 and peripheral noradrenergic neurons.

MAIN METHODS

Experiments were performed in 8- to 14-week-old male wild-type (WT) and TRPV1 knockout (KO) mice. The mice were intraperitoneally injected with a non-lethal dose of LPS. Pain assessment and investigation of changes in the immune system were performed. Denervation of sympathetic nerves and the noradrenergic splenic nerve was induced by intraperitoneal administration of 6-hydroxydopamine.

KEY FINDINGS

The levels of serum cytokines were not significantly different in WT mice and TRPV1 KO mice. Abdominal mechanical hyperalgesia was greater in WT mice than in TRPV1 KO mice from 6 h to 3 days. The numbers of macrophages, neutrophils, dendritic cells, and CD4 T cells in the spleens of TRPV1 KO mice were significantly increased compared to those in WT mice 4 days after LPS administration. By noradrenergic denervation, the numbers of those cells in WT mice increased to levels comparable to those in TRPV1 KO mice.

SIGNIFICANCE

In LPS-induced peritonitis, abdominal inflammatory pain was transmitted via TRPV1. In addition, TRPV1 had an anti-inflammatory effect on the spleen in the late phase of peritonitis. This anti-inflammatory effect was thought to be mediated by activation of the sympathetic nervous system and/or noradrenergic splenic nerve induced by TRPV1 activation.

Plant-Derived (Poly)phenols and Their Metabolic Outcomes: The Pursuit of a Role for the Gut Microbiota

Plant-derived (poly)phenolic compounds have been undoubtedly shown to promote endocrine homeostasis through the improvement of diverse metabolic outcomes. Amongst diverse potential mechanisms, the prebiotic modulatory effects exerted by these compounds on the gut microbiota have supported their nutraceutical application in both experimental and clinical approaches. However, the comprehension of the microbiota modulatory patterns observed upon (poly)phenol-based dietary interventions is still in its infancy, which makes the standardization of the metabolic outcomes in response to a given (poly)phenol a herculean task. Thus, this narrative review sought to gather up-to-date information on the relationship among (poly)phenols intake, their modulatory effect on the gut microbiota diversity, and consequent metabolic outcomes as a supportive tool for the future design of experimental approaches and even clinical trials.

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.

N-Oleoyl dopamine induces IL-10 via central nervous system TRPV1 and improves endotoxemia and sepsis outcomes

Background

The transient receptor potential vanilloid 1 (TRPV1) participates in thermosensation and inflammatory pain, but its immunomodulatory mechanisms remain enigmatic. N-Oleoyl dopamine (OLDA), an endovanilloid and endocannabinoid, is a TRPV1 agonist that is produced in the central nervous system and the peripheral nervous system. We studied the anti-inflammatory effects and TRPV1-dependent mechanisms of OLDA in models of inflammation and sepsis.

Methods

Mice were challenged intratracheally or intravenously with LPS, or intratracheally with S. aureus to induce pneumonia and sepsis, and then were treated intravenously with OLDA. Endpoints included plasma cytokines, leukocyte activation marker expression, mouse sepsis scores, lung histopathology, and bacterial counts. The role of TRPV1 in the effects of OLDA was determined using Trpv1^−/− mice, and mice with TRPV1 knockdown pan-neuronally, in peripheral nervous system neurons, or in myeloid cells. Circulating monocytes/macrophages were depleted using clodronate to determine their role in the anti-inflammatory effects of OLDA in endotoxemic mice. Levels of exogenous OLDA, and of endovanilloids and endocannabinoids, at baseline and in endotoxemic mice, were determined by LC–MS/MS.

Results

OLDA administration caused an early anti-inflammatory response in endotoxemic and septic mice with high serum levels of IL-10 and decreased levels of pro-inflammatory cytokines. OLDA also reduced lung injury and improved mouse sepsis scores. Blood and lung bacterial counts were comparable between OLDA- and carrier-treated mice with S. aureus pneumonia. OLDA’s effects were reversed in mice with pan-neuronal TRPV1 knockdown, but not with TRPV1 knockdown in peripheral nervous system neurons or myeloid cells. Depletion of monocytes/macrophages reversed the IL-10 upregulation by OLDA in endotoxemic mice. Brain and blood levels of endovanilloids and endocannabinoids were increased in endotoxemic mice.

Conclusions

OLDA has strong anti-inflammatory actions in mice with endotoxemia or S. aureus pneumonia. Prior studies focused on the role of peripheral nervous system TRPV1 in modulating inflammation and pneumonia. Our results suggest that TRPV1-expressing central nervous system neurons also regulate inflammatory responses to endotoxemia and infection. Our study reveals a neuro-immune reflex that during acute inflammation is engaged proximally by OLDA acting on neuronal TRPV1, and through a multicellular network that requires circulating monocytes/macrophages, leads to the systemic production of IL-10.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12974-022-02485-z.

TRPV1+ sensory nerves modulate corneal inflammation after epithelial abrasion via RAMP1 and SSTR5 signaling

Timely initiation and termination of inflammatory response after corneal epithelial abrasion is critical for the recovery of vision. The cornea is innervated with rich sensory nerves with highly dense TRPV1 nociceptors. However, the roles of TRPV1⁺ sensory neurons in corneal inflammation after epithelial abrasion are not completely understood. Here, we found that depletion of TRPV1⁺ sensory nerves using resiniferatoxin (RTX) and blockade of TRPV1 using AMG-517 delayed corneal wound closure and enhanced the infiltration of neutrophils and γδ T cells to the wounded cornea after epithelial abrasion. Furthermore, depletion of TRPV1⁺ sensory nerves increased the number and TNF-α production of corneal CCR2⁺ macrophages and decreased the number of corneal CCR2^- macrophages and IL-10 production. In addition, the TRPV1⁺ sensory nerves inhibited the recruitment of neutrophils and γδ T cells to the cornea via RAMP1 and SSTR5 signaling, decreased the responses of CCR2⁺ macrophages via RAMP1 signaling, and increased the responses of CCR2^- macrophages via SSTR5 signaling. Collectively, our results suggest that the TRPV1⁺ sensory nerves suppress inflammation to support corneal wound healing via RAMP1 and SSTR5 signaling, revealing potential approaches for improving defective corneal wound healing in patients with sensory neuropathy.

TRPA1 Role in Inflammatory Disorders: What Is Known So Far?

The transient receptor potential ankyrin 1 (TRPA1), a member of the TRP superfamily of channels, is primarily localized in a subpopulation of primary sensory neurons of the trigeminal, vagal, and dorsal root ganglia, where its activation mediates neurogenic inflammatory responses. TRPA1 expression in resident tissue cells, inflammatory, and immune cells, through the indirect modulation of a large series of intracellular pathways, orchestrates a range of cellular processes, such as cytokine production, cell differentiation, and cytotoxicity. Therefore, the TRPA1 pathway has been proposed as a protective mechanism to detect and respond to harmful agents in various pathological conditions, including several inflammatory diseases. Specific attention has been paid to TRPA1 contribution to the transition of inflammation and immune responses from an early defensive response to a chronic pathological condition. In this view, TRPA1 antagonists may be regarded as beneficial tools for the treatment of inflammatory conditions.

An Overview of the TRP-Oxidative Stress Axis in Metabolic Syndrome: Insights for Novel Therapeutic Approaches

Metabolic syndrome (MS) is a complex pathology characterized by visceral adiposity, insulin resistance, arterial hypertension, and dyslipidaemia. It has become a global epidemic associated with increased consumption of high-calorie, low-fibre food and sedentary habits. Some of its underlying mechanisms have been identified, with hypoadiponectinemia, inflammation and oxidative stress as important factors for MS establishment and progression. Alterations in adipokine levels may favour glucotoxicity and lipotoxicity which, in turn, contribute to inflammation and cellular stress responses within the adipose, pancreatic and liver tissues, in addition to hepatic steatosis. The multiple mechanisms of MS make its clinical management difficult, involving both non-pharmacological and pharmacological interventions. Transient receptor potential (TRP) channels are non-selective calcium channels involved in a plethora of physiological events, including energy balance, inflammation and oxidative stress. Evidence from animal models of disease has contributed to identify their specific contributions to MS and may help to tailor clinical trials for the disease. In this context, the oxidative stress sensors TRPV1, TRPA1 and TRPC5, play major roles in regulating inflammatory responses, thermogenesis and energy expenditure. Here, the interplay between these TRP channels and oxidative stress in MS is discussed in the light of novel therapies to treat this syndrome.

Effects of in-vitro modulation of TRPV1 activity on immune response of mice bearing metastatic breast carcinoma: Enhanced inflammatory response may hinder therapeutic potentials of TRPV1 agonists

AIMS

Activation of transient receptor potential vanilloid 1 (TRPV1) ion channels inhibits inflammation, enhance cytotoxic immune response, and may have therapeutic potential in treatment of cancer characterized by increased systemic inflammation. We here determined how activation of TRPV1 alters immune response of tumor-bearing mice.

MAIN METHODS

Three different metastatic subset of 4 T1 breast carcinoma cells were used to induce tumors in Balb-c mice. Mix leukocyte cultures (MLCs) using spleens and draining lymph nodes were prepared and stimulated with various challenges. Effects TRPV1 agonists including capsaicin, antagonist (AMG9810) and Gambogic Amide (GA), a TrkA agonist that sensitizes TRPV1, on secreted levels of cytokines were determined.

KEY FINDINGS

MLCs of tumor-bearing mice secreted markedly higher levels of IL-6 and lower levels of IFN-γ compared to control mice. We observed differential effects of TRPV1 agonists in control and mice bearing different subset of metastatic cells. TRPV1 increased IFN-γ and IL-17 secretion in control mice while they markedly increased IL-6 secretion and suppressed IFN--γ secretion in tumor-bearing mice. Unexpectedly, AMG9810 acted as an inverse agonist and did not antagonize the effects of TRPV1 agonists.

SIGNIFICANCE

Our results demonstrate constitutive activity of TRPV1 in immune cells, suggesting cross activation. To prevent excessive chronic activation of TRPV1 in immune cells in the presence of metastatic breast carcinoma, lower doses of TRPV1 agonist should be considered. Unexpected findings further document that a drug can have multiple intrinsic activities depending on surrounding factors can act on the same receptor as an agonist, antagonist or inverse agonist.

Selected transient receptor potential channel genes' expression in peripheral blood mononuclear cells of multiple sclerosis

Transient receptor potential channels have responsibilities in many cellular processes such as cytokine production, cell differentiation, and cytotoxicity by affecting intracellular cation levels or intracellular signal pathways. Multiple sclerosis is a chronic autoimmune central nervous system (CNS) disease caused by environmental and genetic factors. In this study, we aim to investigate TRPV1-TRPV4, TRPM2, TRPM4, TRPM7, TRPC6, and TRPA1 mRNA expression levels, which are associated with the inflammatory process, in the peripheral blood mononuclear cells (PBMCs) of relapsing-remitting multiple sclerosis (RRMS) patients. Thirty-five healthy controls and age-gender matched thirty patients with RRMS were involved in the study. TRPC6, TRPA1, TRPM2, TRPM4, TRPM7, TRPV1, TRPV2, TRPV3, and TRPV4 PBMCs mRNA expression levels were determined by qPCR. In the present study, the TRPC6, TRPM7, TRPV1, TRPV3, and TRPV4 mRNA expressions of RRMS patients in PBMCs decreased at a significant level compared to the healthy control group (p = .000, p = .000, p = .044, p = .000, p = .004, respectively). The decreased expression of TRPC6, TRPM7, TRPV1, TRPV3, and TRPV4 in PBMCs may be associated with the pathogenesis of MS. Further studies are required to understand the mechanism of the relation between these TRP channels and MS and other autoimmune diseases.

Human TRPV1 and TRPA1 are receptors for bacterial quorum sensing molecules

In this study, we investigated the activation of TRPV1 and TRPA1 by N-acyl homoserine lactones, quorum sensing molecules produced by Gram-negative bacteria, and the inhibitory effect of TRPV1 and TRPA1 by autoinducing peptides, quorum sensing molecules produced by Gram-positive bacteria, using human embryonic kidney 293T cell lines stably expressing human TRPV1 and TRPA1, respectively. As a result, we found that some N-acyl homoserine lactones, such as N-octanoyl-L-homoserine lactone (C8-HSL), N-nonanoyl-L-homoserine lactone (C9-HSL) and N-decanoyl-L-homoserine lactone (C10-HSL) activated both TRPV1 and TRPA1. In addition, we clarified that some N-acyl homoserine lactones, for example, N-3-oxo-dodecanoyl-L-homoserine lactone (3-oxo-C12-HSL) only activated TRPV1, and N-acyl homoserine lactones having saturated short acyl chain, such as N-acetyl-L-homoserine lactone (C2-HSL) and N-butyryl-L-homoserine lactone (C4-HSL) only activated TRPA1, respectively. Furthermore, we found that an autoinducing peptide, simple linear peptide CHWPR, inhibited both TRPV1 and TRPA1, and peptide having thiolactone ring DICNAYF, thiolactone ring were formed between C3 to F7, strongly inhibited only the TRPV1. Although the specificity of TRPV1 and TRPA1 for quorum sensing molecules were different, these data suggest that both TRPV1 and TRPA1 would function as receptors for quorum sensing molecule produced by bacteria.

TRPV1: Role in Skin and Skin Diseases and Potential Target for Improving Wound Healing

Skin is innervated by a multitude of sensory nerves that are important to the function of this barrier tissue in homeostasis and injury. The role of innervation and neuromediators has been previously reviewed so here we focus on the role of the transient receptor potential cation channel, subfamily V member 1 (TRPV1) in wound healing, with the intent of targeting it in treatment of non-healing wounds. TRPV1 structure and function as well as the outcomes of TRPV1-targeted therapies utilized in several diseases and tissues are summarized. In skin, keratinocytes, sebocytes, nociceptors, and several immune cells express TRPV1, making it an attractive focus area for treating wounds. Many intrinsic and extrinsic factors confound the function and targeting of TRPV1 and may lead to adverse or off-target effects. Therefore, a better understanding of what is known about the role of TRPV1 in skin and wound healing will inform future therapies to treat impaired and chronic wounds to improve healing.

Distribution of alpha-synuclein in the rat cranial sensory ganglia, and oro-cervical regions

BACKGROUND

Alpha-synuclein (Syn), an unfolded soluble cytosolic protein, is known as a disease-associated protein in the brain. However, little is known about distribution of this protein in the peripheral nervous system. In this study, expression of Syn was investigated in the sensory ganglia of the cranial nerves V, IX and X.

METHODS

To analyze distribution of Syn and its co-expression with calcitonin gene-related peptide (CGRP) or the transient receptor potential cation channel subfamily V member 1 (TRPV1), immunohistochemical techniques were used in the rat cranial sensory ganglia and their peripheral tissues.

RESULTS

Syn-immunoreactive (-ir) neurons were abundant in the sensory ganglia of the petrosal (56.7%), jugular (28.3%) and nodose ganglia (82.5%). These neurons had small to medium-sized cell bodies (petrosal, mean ± S.D. = 667.4 ± 310.8 μ m²; jugular, 625.1 ± 318.4 μ m²; nodose, 708.3 ± 248.3 μ m²), and were distributed throughout the ganglia. However, the trigeminal ganglion was mostly free of Syn-ir neurons. By double and triple immunofluorescence staining, Syn-ir neurons co-expressed CGRP and TRPV1 in the petrosal and jugular ganglia. Syn-immunoreactivity was expressed by nerve fibers in the epithelium and taste bud of oral and cervical viscerae. These nerve fibers were abundant in the naso-pharynx, epiglottis and laryngeal vestibule. Some taste bud cells were also immunoreactive for Syn. In addition, Syn-ir nerve fibers were detected in the vicinity of macrophages, dendritic cells and Langerhans cells.

CONCLUSIONS

Syn was abundant in the visceral sensory neurons but not in somatic sensory neurons. This protein may play a role in nociceptive and chemosensory transduction in the glossopharyngeal and vagal sensory ganglia. It is possible that Syn has a function about the immune mechanism of the upper air way.

Senso-immunology: crosstalk between nociceptive and immune systems

Understanding the molecular mechanisms of nociception has recently grown impressively. Nociception is mediated by mechanical, chemical, or microbial stimuli that evoke unpleasant feelings, alerting the host of the risk of tissue damage. Such diverse arrays of noxious stimuli trigger various escape reactions, usually altering immune homeostasis. Notably, nociceptors can recognize cytokines or pathogens via sensory molecules or innate immune receptors, participating in immune responses. Accumulating evidence suggests that activated nociceptors produce various humoral factors that affect the immune system and act like endocrine/paracrine signals. Thus, understanding the interplay between the nociceptive and immune systems may open new avenues for the development of an interdisciplinary research field, hereinafter referred to as 'senso-immunology'. This review will discuss the physiological relevance of the senso-immune system in the host defense context, focusing on how senso-immune research might yield novel treatments to cure pain and inflammation.

Transient Receptor Potential Vanilloid in the Brain Gliovascular Unit: Prospective Targets in Therapy

The gliovascular unit (GVU) is composed of the brain microvascular endothelial cells forming blood–brain barrier and the neighboring surrounding “mural” cells (e.g., pericytes) and astrocytes. Modulation of the GVU/BBB features could be observed in a variety of vascular, immunologic, neuro-psychiatric diseases, and cancers, which can disrupt the brain homeostasis. Ca²⁺ dynamics have been regarded as a major factor in determining BBB/GVU properties, and previous studies have demonstrated the role of transient receptor potential vanilloid (TRPV) channels in modulating Ca²⁺ and BBB/GVU properties. The physiological role of thermosensitive TRPV channels in the BBB/GVU, as well as their possible therapeutic potential as targets in treating brain diseases via preserving the BBB are reviewed. TRPV2 and TRPV4 are the most abundant isoforms in the human BBB, and TRPV2 was evidenced to play a main role in regulating human BBB integrity. Interspecies differences in TRPV2 and TRPV4 BBB expression complicate further preclinical validation. More studies are still needed to better establish the physiopathological TRPV roles such as in astrocytes, vascular smooth muscle cells, and pericytes. The effect of the chronic TRPV modulation should also deserve further studies to evaluate their benefit and innocuity in vivo.

Phagocytic activity of splenic macrophages is enhanced and accompanied by cytosolic alkalinization in TRPM7 kinase-dead mice

Transient receptor potential melastatin 7 (TRPM7) is a unique protein functioning as a cation channel as well as a serine/threonine kinase and is highly expressed in immune cells such as lymphocytes and macrophages. TRPM7 kinase-dead (KD) mouse model has been used to investigate the role of this protein in immune cells; these animals display moderate splenomegaly and ectopic hemopoiesis. The basal TRPM7 current magnitudes in peritoneal macrophages isolated from KD mice were higher; however, the maximum currents, achieved after cytoplasmic Mg²⁺ washout, were not different. In the present study, we investigated the consequences of TRPM7 kinase inactivation in splenic and peritoneal macrophages. We measured the basal phagocytic activity of splenic macrophages using fluorescent latex beads, pHrodo zymosan bioparticles, and opsonized red blood cells. KD macrophages phagocytized more efficiently and had slightly higher baseline calcium levels compared to WT cells. We found no obvious differences in store-operated Ca²⁺ entry between WT and KD macrophages. By contrast, the resting cytosolic pH in KD macrophages was significantly more alkaline than in WT. Pharmacological blockade of sodium hydrogen exchanger 1 (NHE1) reversed the cytosolic alkalinization and reduced phagocytosis in KD macrophages. Basal TRPM7 channel activity in KD macrophages was also reduced after NHE1 blockade. Cytosolic Mg²⁺ sensitivity of TRPM7 channels measured in peritoneal macrophages was similar in WT and KD mice. The higher basal TRPM7 channel activity in KD macrophages is likely due to alkalinization. Our results identify a novel role for TRPM7 kinase as a suppressor of basal phagocytosis and a regulator of cellular pH.

Neuronal regulation of immunity: why, how and where?

Neuroimmunology is one of the fastest-growing fields in the life sciences, and for good reason; it fills the gap between two principal systems of the organism, the nervous system and the immune system. Although both systems affect each other through bidirectional interactions, we focus here on one direction - the effects of the nervous system on immunity. First, we ask why is it beneficial to allow the nervous system any control over immunity? We evaluate the potential benefits to the immune system that arise by taking advantage of some of the brain's unique features, such as its capacity to integrate and synchronize physiological functions, its predictive capacity and its speed of response. Second, we explore how the brain communicates with the peripheral immune system, with a focus on the endocrine, sympathetic, parasympathetic, sensory and meningeal lymphatic systems. Finally, we examine where in the brain this immune information is processed and regulated. We chart a partial map of brain regions that may be relevant for brain-immune system communication, our goal being to introduce a conceptual framework for formulating new hypotheses to study these interactions.

Neuroimmune communication in infection and pain: Friends or foes?

Clinically, a variety of micro-organisms cause painful infections. Before seen as bystanders in the context of infections, recent studies have demonstrated that, as immune cells, nociceptors can sense pathogen-derived products. Nociceptors and immune cells, therefore, have evolved to communicate with each other to control inflammatory and host responses against pathogens in a complementary way. This interaction is named as neuroimmune communication (or axon-axon immune reflex) and initiates after the release of neuropeptides, such as CGRP and VIP by neurons. By this neurogenic response, nociceptors orchestrate the activity of innate and adaptive immune cells in a context-dependent manner. In this review, we focus on how nociceptors sense pathogen-derived products to shape the host response. We also highlight the new concept involving the resolution of inflammation, which is related to an active and time-dependent biosynthetic shift from pro-inflammatory to pro-resolution mediators, the so-called specialized pro-resolving lipid mediators (SPMs). At very low doses, SPMs act on specific receptors to silence nociceptors, limit pain and neurogenic responses, and resolve infections. Furthermore, stimulation of the vagus nerve induces SPMs production to regulate immune responses in infections. Therefore, harnessing the current understanding of neuro-immune communication and neurogenic responses might provide the bases for reprogramming host responses against infections through well balanced and effective immune response and inflammation resolution.

Somatotopic Organization and Intensity Dependence in Driving Distinct NPY-Expressing Sympathetic Pathways by Electroacupuncture

The neuroanatomical basis behind acupuncture practice is still poorly understood. Here, we used intersectional genetic strategy to ablate NPY+ noradrenergic neurons and/or adrenal chromaffin cells. Using endotoxin-induced systemic inflammation as a model, we found that electroacupuncture stimulation (ES) drives sympathetic pathways in somatotopy- and intensity-dependent manners. Low-intensity ES at hindlimb regions drives the vagal-adrenal axis, producing anti-inflammatory effects that depend on NPY+ adrenal chromaffin cells. High-intensity ES at the abdomen activates NPY+ splenic noradrenergic neurons via the spinal-sympathetic axis; these neurons engage incoherent feedforward regulatory loops via activation of distinct adrenergic receptors (ARs), and their ES-evoked activation produces either anti- or pro-inflammatory effects due to disease-state-dependent changes in AR profiles. The revelation of somatotopic organization and intensity dependency in driving distinct autonomic pathways could form a road map for optimizing stimulation parameters to improve both efficacy and safety in using acupuncture as a therapeutic modality.

Inhibition of transient receptor potential vanilloid 1 (TRPV1) channel regulates chikungunya virus infection in macrophages

Chikungunya virus (CHIKV), a virus that induces pathogenic inflammatory host immune responses, is re-emerging worldwide, and there are currently no established antiviral control measures. Transient receptor potential vanilloid 1 (TRPV1), a non-selective Ca²⁺-permeable ion channel, has been found to regulate various host inflammatory responses including several viral infections. Immune responses to CHIKV infection in host macrophages have been reported recently. However, the possible involvement of TRPV1 during CHIKV infection in host macrophages has not been studied. Here, we investigated the possible role of TRPV1 in CHIKV infection of the macrophage cell line RAW 264.7. It was found that CHIKV infection upregulates TRPV1 expression in macrophages. To confirm this observation, the TRPV1-specific modulators 5'-iodoresiniferatoxin (5'-IRTX, a TRPV1 antagonist) and resiniferatoxin (RTX, a TRPV1 agonist) were used. Our results indicated that TRPV1 inhibition leads to a reduction in CHIKV infection, whereas TRPV1 activation significantly enhances CHIKV infection. Using a plaque assay and a time-of-addition assay, it was observed that functional modulation of TRPV1 affects the early stages of the viral lifecycle in RAW 264.7 cells. Moreover, CHIKV infection was found to induce of pNF-κB (p65) expression and nuclear localization. However, both activation and inhibition of TRPV1 were found to enhance the expression and nuclear localization of pNF-κB (p65) and production of pro-inflammatory TNF and IL-6 during CHIKV infection. In addition, it was demonstrated by Ca²⁺ imaging that TRPV1 regulates Ca²⁺ influx during CHIKV infection. Hence, the current findings highlight a potentially important regulatory role of TRPV1 during CHIKV infection in macrophages. This study might also have broad implications in the context of other viral infections as well.

TRPV1 expressed throughout the arterial circulation regulates vasoconstriction and blood pressure

KEY POINTS

The functional roles of the capsaicin receptor, TRPV1, outside of sensory nerves are unclear. We mapped TRPV1 in the mouse circulation, revealing extensive expression in the smooth muscle of resistance arterioles supplying skeletal muscle, heart and adipose tissue.  Activation of TRPV1 in vascular myocytes constricted arteries, reduced coronary flow in isolated hearts and increased systemic blood pressure. These functional effects were retained after sensory nerve ablation, indicating specific signalling by arterial TRPV1.  TRPV1 mediated the vasoconstrictive and blood pressure responses to the endogenous inflammatory lipid lysophosphatidic acid.  These results show that TRPV1 in arteriolar myocytes modulates regional blood flow and systemic blood pressure, and suggest that TRPV1 may be a target of vasoactive inflammatory mediators.

ABSTRACT

The capsaicin receptor, TRPV1, is a key ion channel involved in inflammatory pain signalling. Although mainly studied in sensory nerves, there are reports of TRPV1 expression in isolated segments of the vasculature, but whether the channel localizes to vascular endothelium or smooth muscle is controversial and the distribution and functional roles of TRPV1 in arteries remain unknown. We mapped functional TRPV1 expression throughout the mouse arterial circulation. Analysis of reporter mouse lines TRPV1^PLAP-nlacZ and TRPV1-Cre:tdTomato combined with Ca²⁺ imaging revealed specific localization of TRPV1 to smooth muscle of terminal arterioles in the heart, adipose tissue and skeletal muscle. Capsaicin evoked inward currents (current density ∼10% of sensory neurons) and raised intracellular Ca²⁺ levels in arterial smooth muscle cells, constricted arterioles ex vivo and in vivo and increased systemic blood pressure in mice and rats. Further, capsaicin markedly and dose-dependently reduced coronary flow. Pharmacological and/or genetic disruption of TRPV1 abolished all these effects of capsaicin as well as vasoconstriction triggered by lysophosphatidic acid, a bioactive lipid generated by platelets and atherogenic plaques. Notably, ablation of sensory nerves did not affect the responses to capsaicin revealing a vascular smooth muscle-restricted signalling mechanism. Moreover, unlike in sensory nerves, TRPV1 function in arteries was resistant to activity-induced desensitization. Thus, TRPV1 activation in vascular myocytes enables a persistent depolarizing current, leading to constriction of coronary, skeletal muscle and adipose arterioles and a sustained increase in systemic blood pressure.

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.

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.

Evidence that the TRPV1 S1-S4 membrane domain contributes to thermosensing

Sensing and responding to temperature is crucial in biology. The TRPV1 ion channel is a well-studied heat-sensing receptor that is also activated by vanilloid compounds, including capsaicin. Despite significant interest, the molecular underpinnings of thermosensing have remained elusive. The TRPV1 S1-S4 membrane domain couples chemical ligand binding to the pore domain during channel gating. Here we show that the S1-S4 domain also significantly contributes to thermosensing and couples to heat-activated gating. Evaluation of the isolated human TRPV1 S1-S4 domain by solution NMR, far-UV CD, and intrinsic fluorescence shows that this domain undergoes a non-denaturing temperature-dependent transition with a high thermosensitivity. Further NMR characterization of the temperature-dependent conformational changes suggests the contribution of the S1-S4 domain to thermosensing shares features with known coupling mechanisms between this domain with ligand and pH activation. Taken together, this study shows that the TRPV1 S1-S4 domain contributes to TRPV1 temperature-dependent activation.

Oxidative and nitrosative stresses in cerebral malaria: can we target them to avoid a bad prognosis?

There is currently a global effort to reduce malaria morbidity and mortality. However, malaria still results in the deaths of thousands of people every year. Malaria is caused by Plasmodium spp., parasites transmitted through the bite of an infected female Anopheles mosquito. Treatment timing plays a decisive role in reducing mortality and sequelae associated with the severe forms of the disease such as cerebral malaria (CM). The available antimalarial therapy is considered effective but parasite resistance to these drugs has been observed in some countries. Antimalarial drugs act by increasing parasite lysis, especially through targeting oxidative stress pathways. Here we discuss the roles of reactive oxygen species and reactive nitrogen intermediates in CM as a result of host-parasite interactions. We also present evidence of the potential contribution of oxidative and nitrosative stress-based antimalarial drugs to disease treatment and control.

Transient Receptor Potential Channels and Inflammatory Bowel Disease

The transient receptor potential (TRP) cation channels are present in abundance across the gastrointestinal (GI) tract, serving as detectors for a variety of stimuli and secondary transducers for G-protein coupled receptors. The activation of TRP channels triggers neurogenic inflammation with related neuropeptides and initiates immune reactions by extra-neuronally regulating immune cells, contributing to the GI homeostasis. However, under pathological conditions, such as inflammatory bowel disease (IBD), TRP channels are involved in intestinal inflammation. An increasing number of human and animal studies have indicated that TRP channels are correlated to the visceral hypersensitivity (VHS) and immune pathogenesis in IBD, leading to an exacerbation or amelioration of the VHS or intestinal inflammation. Thus, TRP channels are a promising target for novel therapeutic methods for IBD. In this review, we comprehensively summarize the functions of TRP channels, especially their potential roles in immunity and IBD. Additionally, we discuss the contradictory findings of prior studies and offer new insights with regard to future research.

TRPV1 in experimental autoimmune prostatitis

BACKGROUND

Chronic prostatitis/chronic pelvic pain syndrome (CP/CPPS) is a disorder that is characterized by persistent pelvic pain in men of any age. Although several studies suggest that the transient receptor potential vanilloid 1 (TRPV1) channel is involved in various pathways of chronic pain, the TRPV1 channel has not been implicated in chronic pelvic pain associated with CP/CPPS.

METHODS

Male C57BL/6J (B6) and TRPV1 knockout (TRPV1 KO) mice (5-7 weeks old) were used to study the development of pelvic allodynia in a murine model of CP/CPPS called experimental autoimmune prostatitis (EAP). The prostate lobes, dorsal root ganglia (DRG), and spinal cord were excised at day 20. The prostate lobes were assessed for inflammation, TRPV1 expression, and mast cell activity. DRG and spinal cord, between the L6-S4 regions, were analyzed to determine the levels of phosphorylated ERK1/2 (p-ERK 1/2). To examine the therapeutic potential of TRPV1, B6 mice with EAP received intraurethral infusion of a TRPV1 antagonist at day 20 (repeated every 2 days) and pelvic pain was evaluated at days 20, 25, 30, and 35.

RESULTS

Our data showed that B6 mice with EAP developed pelvic tactile allodynia at days 7, 14, and 20. In contrast, TRPV1 KO mice with EAP do not develop pelvic tactile allodynia at any time point. Although we observed no change in the levels of TRPV1 protein expression in the prostate from B6 mice with EAP, there was evidence of significant inflammation and elevated mast cell activation. Interestingly, the prostate from TRPV1 KO mice with EAP showed a lack of mast cell activation despite evidence of prostate inflammation. Next, we observed a significant increase of p-ERK1/2 in the DRG and spinal cord from B6 mice with EAP; however, p-ERK1/2 expression was unaltered in TRPV1 KO mice with EAP. Finally, we confirmed that intraurethral administration of a TRPV1 antagonist peptide reduced pelvic tactile allodynia in B6 mice with EAP after day 20.

CONCLUSIONS

We demonstrated that in a murine model of CP/CPPS, the TRPV1 channel is key to persistent pelvic tactile allodynia and blocking TRPV1 in the prostate may be a promising strategy to quell chronic pelvic pain.

Molecular Mechanisms of Calcium Signaling During Phagocytosis

Calcium (Ca²⁺) is a ubiquitous second messenger involved in the regulation of numerous cellular functions including vesicular trafficking, cytoskeletal rearrangements and gene transcription. Both global as well as localized Ca²⁺ signals occur during phagocytosis, although their functional impact on the phagocytic process has been debated. After nearly 40 years of research, a consensus may now be reached that although not strictly required, Ca²⁺ signals render phagocytic ingestion and phagosome maturation more efficient, and their manipulation make an attractive avenue for therapeutic interventions. In the last decade many efforts have been made to identify the channels and regulators involved in generating and shaping phagocytic Ca²⁺ signals. While molecules involved in store-operated calcium entry (SOCE) of the STIM and ORAI family have taken center stage, members of the canonical, melastatin, mucolipin and vanilloid transient receptor potential (TRP), as well as purinergic P2X receptor families are now recognized to play significant roles. In this chapter, we review the recent literature on research that has linked specific Ca²⁺-permeable channels and regulators to phagocytic function. We highlight the fact that lipid mediators are emerging as important regulators of channel gating and that phagosomal ionic homeostasis and Ca²⁺ release also play essential parts. We predict that improved methodologies for measuring these factors will be critical for future advances in dissecting the intricate biology of this fascinating immune process.

Inflammation, Cancer and Immunity-Implication of TRPV1 Channel

Process of inflammation and complex interactions between immune and cancer cells within tumor microenvironment are known to drive and shape the outcome of the neoplastic disease. Recent studies increasingly show that ion channels can be used as potential targets to modulate immune response and to treat inflammatory disorders and cancer. The action of both innate and adaptive immune cells is tightly regulated by ionic signals provided by a network of distinct ion channels. TRPV1 channel, known as a capsaicin receptor, was recently documented to be expressed on the cells of the immune system but also aberrantly expressed in the several tumor types. It is activated by heat, protons, proinflammatory cytokines, and associated with pain and inflammation. TRPV1 channel is not only involved in calcium signaling fundamental for many cellular processes but also takes part in cell-environment crosstalk influencing cell behavior. Furthermore, in several studies, activation of TRPV1 by capsaicin was associated with anti-cancer effects. Therefore, TRPV1 provides a potential link between the process of inflammation, cancer and immunity, and offers new treatment possibilities. Nevertheless, in many cases, results regarding TRPV1 are contradictory and need further refinement. In this review we present the summary of the data related to the role of TRPV1 channel in the process of inflammation, cancer and immunity, limitations of the studies, and directions for future research.

TRPV1 Antagonists as Novel Anti-Diabetic Agents: Regulation of Oral Glucose Tolerance and Insulin Secretion Through Reduction of Low-Grade Inflammation?

With a global prevalence among adults over 18 years of age approaching 9%, Type 2 diabetes mellitus (T2DM) has reached pandemic proportions and represents a major unmet medical need. To date, no disease modifying treatment is available for T2DM patients. Accumulating evidence suggest that the sensory nervous system is involved in the progression of T2DM by maintaining low-grade inflammation via the vanilloid (capsaicin) receptor, Transient Receptor Potential Vanilloid-1 (TRPV1). In this study, we tested the hypothesis that TRPV1 is directly involved in glucose homeostasis in rodents. TRPV1 receptor knockout mice (Trpv1^−/−) and their wild-type littermates were kept on high-fat diet for 15 weeks. Moreover, Zucker obese rats were given the small molecule TRPV1 antagonist, N-(4-Tertiarybutylphenyl)-4-(3-cholorphyridin-2-yl)tetrahydropyrazine-1(2H)-carbox-amide (BCTC), per os twice-a-day or vehicle for eight days. Oral glucose tolerance and glucose-stimulated insulin secretion was improved by both genetic inactivation (Trpv1^−/− mice) and pharmacological blockade (BCTC) of TRPV1. In the obese rat, the improved glucose tolerance was accompanied by a reduction in inflammatory markers in the mesenteric fat, suggesting that blockade of low-grade inflammation contributes to the positive effect of TRPV1 antagonism on glucose metabolism. We propose that TRPV1 could be a promising therapeutic target in T2DM by improving glucose intolerance and correcting dysfunctional insulin secretion.

Pain and immunity: implications for host defence

Pain is a hallmark of tissue injury, inflammatory diseases, pathogen invasion and neuropathy. It is mediated by nociceptor sensory neurons that innervate the skin, joints, bones, muscles and mucosal tissues and protects organisms from noxious stimuli. Nociceptors are sensitized by inflammatory mediators produced by the immune system, including cytokines, lipid mediators and growth factors, and can also directly detect pathogens and their secreted products to produce pain during infection. Upon activation, nociceptors release neuropeptides from their terminals that potently shape the function of innate and adaptive immune cells. For some pathogens, neuron-immune interactions enhance host protection from infection, but for other pathogens, neuron-immune signalling pathways can be exploited to facilitate pathogen survival. Here, we discuss the role of nociceptor interactions with the immune system in pain and infection and how understanding these pathways could produce new approaches to treat infectious diseases and chronic pain.

Corneal pain and experimental model development

The cornea is a valuable tissue for studying peripheral sensory nerve structure and regeneration due to its avascularity, transparency, and dense innervation. Somatosensory innervation of the cornea serves to identify changes in environmental stimuli at the ocular surface, thereby promoting barrier function to protect the eye against injury or infection. Due to regulatory demands to screen ocular safety of potential chemical exposure, a need remains to develop functional human tissue models to predict ocular damage and pain using in vitro-based systems to increase throughput and minimize animal use. In this review, we summarize the anatomical and functional roles of corneal innervation in propagation of sensory input, corneal neuropathies associated with pain, and the status of current in vivo and in vitro models. Emphasis is placed on tissue engineering approaches to study the human corneal pain response in vitro with integration of proper cell types, controlled microenvironment, and high-throughput readouts to predict pain induction. Further developments in this field will aid in defining molecular signatures to distinguish acute and chronic pain triggers based on the immune response and epithelial, stromal, and neuronal interactions that occur at the ocular surface that lead to functional outcomes in the brain depending on severity and persistence of the stimulus.

TRPV1 Contributes to Cerebral Malaria Severity and Mortality by Regulating Brain Inflammation

Transient receptor potential vanilloid 1 (TRPV1) is a Ca⁺²-permeable channel expressed on neuronal and nonneuronal cells, known as an oxidative stress sensor. It plays a protective role in bacterial infection, and recent findings indicate that this receptor modulates monocyte populations in mice with malaria; however, its role in cerebral malaria progression and outcome is unclear. By using TRPV1 wild-type (WT) and knockout (KO) mice, the importance of TRPV1 to this cerebral syndrome was investigated. Infection with Plasmodium berghei ANKA decreased TRPV1 expression in the brain. Mice lacking TRPV1 were protected against Plasmodium-induced mortality and morbidity, a response that was associated with less cerebral swelling, modulation of the brain expression of endothelial tight-junction markers (junctional adhesion molecule A and claudin-5), increased oxidative stress (via inhibition of catalase activity and increased levels of H₂O₂, nitrotyrosine, and carbonyl residues), and diminished production of cytokines. Plasmodium load was not significantly affected by TRPV1 ablation. Repeated subcutaneous administration of the selective TRPV1 antagonist SB366791 after malaria induction increased TRPV1 expression in the brain tissue and enhanced mouse survival. These data indicate that TRPV1 channels contribute to the development and outcome of cerebral malaria.

Hydrogen peroxide-based products alter inflammatory and tissue damage-related proteins in the gingival crevicular fluid of healthy volunteers: a randomized trial

Hydrogen peroxide (H₂O₂)-based products are effective in tooth whitening; however, their safety is controversial as they may harm patient tissues/cells. These effects are suggested to be concentration-dependent; nonetheless, to date, there are no reports on H₂O₂-mediated oxidative damage in the gingival tissue, and neither whether this can be detected in gingival crevicular fluid (GCF) samples. We hypothesize that H₂O₂ whitening products may cause collateral oxidative tissue damage following in office application. Therefore, H₂O₂ and nitric oxide (NO) levels were investigated in GCF samples obtained from patients undergoing dental bleaching with H₂O₂ at different concentrations, in a randomized, double-blind, split-mouth clinical trial. A proteomic analysis of these samples was also performed. H₂O₂-based whitening products promoted inflammation which was detected in GCF samples and lasted for longer following 35% H₂O₂ bleaching. This included time-dependent changes in NO levels and in the abundance of proteins associated with NO synthesis, oxidative stress, neutrophil regulation, nucleic acid damage, cell survival and/or tissue regeneration. Overall, H₂O₂-based products used in office promote inflammation irrespective of their concentration. As the inflammation caused by 35% H₂O₂ is longer_, patients may benefit better from using lower concentrations of this bleaching product, as they may result in less tissue damage.

Immune aspects of the bi-directional neuroimmune facilitator TRPV1

A rapidly growing area of interest in biomedical science involves the reciprocal crosstalk between the sensory nervous and immune systems. Both of these systems are highly integrated, detecting potential environmental harms and restoring homeostasis. Many different cytokines, receptors, neuropeptides, and other proteins are involved in this bidirectional communication that are common to both systems. One such family of proteins includes the transient receptor potential vanilloid (TRPV) proteins. Though much progress has been made in understanding TRPV proteins in the nervous system, their functions in the immune system are not well elucidated. Hence, further understanding their role in the peripheral immune system and as regulators of neuroimmunity is critical for evaluating their potential as therapeutic targets for numerous inflammatory disorders, cancers, and other disease states. Here, we focus on the latest advancements in understanding TRPV1 and TRPV2's roles in the immune system, TRPV1 in neuroimmunity, and TRPV1's potential involvement in anti-tumor therapy.

A Cross-Sectional Study of Cannabidiol Users

Introduction: Preclinical and clinical studies suggest that cannabidiol (CBD) found in Cannabis spp. has broad therapeutic value. CBD products can currently be purchased online, over the counter and at Cannabis-specific dispensaries throughout most of the country, despite the fact that CBD is generally deemed a Schedule I controlled substance by the U.S. Drug Enforcement Administration and renounced as a dietary supplement ingredient by the U.S. Food and Drug Administration. Consumer demand for CBD is high and growing, but few studies have examined the reasons for increasing CBD use.

Materials and Methods: A self-selected convenience sample (n = 2409) was recruited via an online survey designed to characterize whom, how, and why individuals are currently using CBD. The anonymous questionnaire was accessed from October 25, 2017 to January 25, 2018. Participants were recruited through social media.

Results: Almost 62% of CBD users reported using CBD to treat a medical condition. The top three medical conditions were pain, anxiety, and depression. Almost 36% of respondents reported that CBD treats their medical condition(s) “very well by itself,” while only 4.3% reported “not very well.” One out of every three users reported a nonserious adverse effect. The odds of using CBD to treat a medical condition were 1.44 (95% confidence interval, 1.16–1.79) times greater among nonregular users of Cannabis than among regular users.

Conclusion: Consumers are using CBD as a specific therapy for multiple diverse medical conditions—particularly pain, anxiety, depression, and sleep disorders. These data provide a compelling rationale for further research to better understand the therapeutic potential of CBD.

Transient Receptor Potential Canonical Channels 4 and 5 Mediate Escherichia coli-Derived Thioredoxin Effects in Lipopolysaccharide-Injected Mice

Thioredoxin plays an essential role in bacterial antioxidant machinery and virulence; however, its regulatory actions in the host are less well understood. Reduced human Trx activates transient receptor potential canonical 5 (TRPC5) in inflammation, but there is no evidence of whether these receptors mediate bacterial thioredoxin effects in the host. Importantly, TRPC5 can form functional complexes with other subunits such as TRPC4. Herein, E. coli-derived thioredoxin induced mortality in lipopolysaccharide- (LPS-) injected mice, accompanied by reduction of leukocyte accumulation, regulation of cytokine release into the peritoneum, and impairment of peritoneal macrophage-mediated phagocytosis. Dual TRPC4/TRPC5 blockade by ML204 increased mortality and hypothermia in thioredoxin-treated LPS mice but preserved macrophage's ability to phagocytose. TRPC5 deletion did not alter body temperature but promoted additional accumulation of peritoneal leukocytes and inflammatory mediator release in thioredoxin-administered LPS mice. Thioredoxin diminished macrophage-mediated phagocytosis in wild-type but not TRPC5 knockout animals. TRPC5 ablation did not affect LPS-induced responses. However, ML204 caused mortality associated with exacerbated hypothermia and decreased peritoneal leukocyte numbers and cytokines in LPS-injected mice. These results suggest that bacterial thioredoxin effects under LPS stimuli are mediated by TRPC4 and TRPC5, shedding light on the additional mechanisms of bacterial virulence and on the pathophysiological roles of these receptors.

Nociceptor sensory neurons suppress neutrophil and γδ T cell responses in bacterial lung infections and lethal pneumonia

Nociceptor sensory neurons suppress innate immunity during bacterial lung infection.

Lung-innervating nociceptor sensory neurons detect noxious or harmful stimuli and consequently protect organisms by mediating coughing, pain, and bronchoconstriction. However, the role of sensory neurons in pulmonary host defense is unclear. Here, we found that TRPV1⁺ nociceptors suppressed protective immunity against lethal Staphylococcus aureus pneumonia. Targeted TRPV1⁺-neuron ablation increased survival, cytokine induction, and lung bacterial clearance. Nociceptors suppressed the recruitment and surveillance of neutrophils, and altered lung γδ T cell numbers, which are necessary for immunity. Vagal ganglia TRPV1⁺ afferents mediated immunosuppression through release of the neuropeptide calcitonin gene–related peptide (CGRP). Targeting neuroimmunological signaling may be an effective approach to treat lung infections and bacterial pneumonia.