TRPV1 and SP: key elements for sepsis outcome?

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.

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

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

Involvement of Neural Transient Receptor Potential Channels in Peripheral Inflammation

Transient receptor potential (TRP) channels are a superfamily of non-selective cation channels that act as polymodal sensors in many tissues throughout mammalian organisms. In the context of ion channels, they are unique for their broad diversity of activation mechanisms and their cation selectivity. TRP channels are involved in a diverse range of physiological processes including chemical sensing, nociception, and mediating cytokine release. They also play an important role in the regulation of inflammation through sensory function and the release of neuropeptides. In this review, we discuss the functional contribution of a subset of TRP channels (TRPV1, TRPV4, TRPM3, TRPM8, and TRPA1) that are involved in the body’s immune responses, particularly in relation to inflammation. We focus on these five TRP channels because, in addition to being expressed in many somatic cell types, these channels are also expressed on peripheral ganglia and nerves that innervate visceral organs and tissues throughout the body. Activation of these neural TRP channels enables crosstalk between neurons, immune cells, and epithelial cells to regulate a wide range of inflammatory actions. TRP channels act either through direct effects on cation levels or through indirect modulation of intracellular pathways to trigger pro- or anti-inflammatory mechanisms, depending on the inflammatory disease context. The expression of TRP channels on both neural and immune cells has made them an attractive drug target in diseases involving inflammation. Future work in this domain will likely yield important new pathways and therapies for the treatment of a broad range of disorders including colitis, dermatitis, sepsis, asthma, and pain.

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.

Monosodium urate crystal interleukin-1β release is dependent on Toll-like receptor 4 and transient receptor potential V1 activation

OBJECTIVE

The present study aimed to elucidate the mechanisms involved in MSU-induced IL-1β release in a rodent animal model of acute gout arthritis.

METHODS

Painful (mechanical and thermal hypersensitivity, ongoing pain and arthritis score) and inflammatory (oedema, plasma extravasation, cell infiltration and IL-1β release) parameters were assessed several hours after intra-articular injection of MSU (100 µg/articulation) in wild-type or knockout mice for Toll-like receptor 4 (TLR4), inducible nitric oxide synthase (iNOS), transient receptor potential (TRP) V1 and the IL-1 receptor (IL-1R). Also, wild-type animals were treated with clodronate, lipopolysaccharide from Rhodobacter sphaeroides (LPS-RS) (TLR4 antagonist), spleen tyrosine kinase (SYK) inhibitor (iSYK), aminoguanidine (AMG, an iNOS inhibitor) or SB366791 (TRPV1 antagonist). Nitrite/nitrate and IL-1β levels were measured on the synovial fluid of wild-type mice, 2 h after intra-articular MSU injections, or medium from macrophages stimulated for MSU (1000 μg) for 2 h.

RESULTS

Intra-articular MSU injection caused robust nociception and severe inflammation from 2 up to 6 h after injection, which were prevented by the pre-treatment with clodronate, LPS-RS, iSYK, AMG and SB366791, or the genetic ablation of TLR4, iNOS, TRPV1 or IL-1R. MSU also increased nitrite/nitrate and IL-1β levels in the synovial fluid, which was prevented by clodronate, LPS-RS, iSYK and AMG, but not by SB366791. Similarly, MSU-stimulated peritoneal macrophages released nitric oxide, which was prevented by LPS-RS, iSYK and AMG, but not by SB366791, and released IL-1β, which was prevented by LPS-RS, iSYK, AMG and SB366791.

CONCLUSION

Our data indicate that MSU may activate TLR4, SYK, iNOS and TRPV1 to induce the release of IL-1β by macrophages, triggering nociception and inflammation during acute gout attack.

Patients with high serum substance P levels previously to liver transplantation for hepatocellular carcinoma have higher risk of one-year liver transplantation mortality

Purpose

Substance P is a tachykinins family member with inflammatory effects. Higher circulating levels of substance P have been found in patients with liver diseases and in patients with higher severity of liver diseases. The objective of this study was to determine whether serum levels of substance P levels, prior to liver transplantation (LT) for hepatocellular carcinoma (HCC) are associated with one-year LT mortality.

Material and Methods

In this observational retrospective unicenter study were included patients with LT for HCC. Serum levels of substance P were measured before LT. The end-point of the study was one-year mortality after LT.

Results

We found that one-year survivor patients (n = 127) showed a lower age in liver donors (p = 0.03) and lower levels of serum substance P levels (p = 0.003) than non-survivor patients (n = 15). Logistic regression analysis showed that serum levels of substance P (levels) were associated with one-year mortality (Odds Ratio = 1.011; 95% CI = 1.004–1.018; p = 0.002) controlling for the age of the LT donor.

Conclusions

We believe that our study is the first study reporting data on circulating levels of substance P previously to LT for HCC, and an association between elevated levels of serum substance P before LT and mortality during the first year of LT.

Sustained Low Serum Substance P Levels in Non-Surviving Septic Patients

Previously, researchers found higher serum substance P (SP) concentrations in survivors of severe sepsis than in non-survivors at the time of severe sepsis diagnosis. The objectives of our current study were to determine whether there is an association between serum SP levels during the first week and sepsis mortality, sepsis severity, serum levels of tumor necrosis factor (TNF)-α and interleukin (IL)-10, and whether serum SP levels during the first week could be used as a biomarker of sepsis mortality. We determined serum concentration of SP, TNF-α, and IL-10 at days 1, 4, and 8. The end-point of the study was mortality at 30 days. We found that non-survivor (n = 104) compared to survivor patients (n = 206) showed lower serum SP levels at days 1, 4, and 8 (p < 0.001). Multiple logistic regression analyses showed an association between 30-day mortality and serum SP levels at days 1, 4, and 8 (p < 0.001) controlling for SOFA score, diabetes mellitus, age, and lactic acid levels. The most interesting findings of our study were that there is an association between serum SP levels during the first week and sepsis mortality, and that serum SP levels during the first week could be used as a biomarker of sepsis mortality.

Extraoral Taste Receptor Discovery: New Light on Ayurvedic Pharmacology

More and more research studies are revealing unexpectedly important roles of taste for health and pathogenesis of various diseases. Only recently it has been shown that taste receptors have many extraoral locations (e.g., stomach, intestines, liver, pancreas, respiratory system, heart, brain, kidney, urinary bladder, pancreas, adipose tissue, testis, and ovary), being part of a large diffuse chemosensory system. The functional implications of these taste receptors widely dispersed in various organs or tissues shed a new light on several concepts used in ayurvedic pharmacology (dravyaguna vijnana), such as taste (rasa), postdigestive effect (vipaka), qualities (guna), and energetic nature (virya). This review summarizes the significance of extraoral taste receptors and transient receptor potential (TRP) channels for ayurvedic pharmacology, as well as the biological activities of various types of phytochemical tastants from an ayurvedic perspective. The relative importance of taste (rasa), postdigestive effect (vipaka), and energetic nature (virya) as ethnopharmacological descriptors within Ayurveda boundaries will also be discussed.

Functional expression of TRPV channels in T cells and their implications in immune regulation

The importance of Ca(2+) signalling and temperature in the context of T cell activation is well known. However, the molecular identities of key players involved in such critical regulations are still unknown. In this work we explored the endogenous expression of transient receptor potential vanilloid (TRPV) channels, a group of thermosensitive and non-selective cation channels, in T cells. Using flow cytometry and confocal microscopy, we demonstrate that members belonging to the TRPV subfamily are expressed endogenously in the human T cell line Jurkat, in primary human T cells and in primary murine splenic T cells. We also demonstrate that TRPV1- and TRPV4-specific agonists, namely resiniferatoxin and 4α-phorbol-12,13-didecanoate, can cause Ca(2+) influx in T cells. Moreover, our results show that expression of these channels can be upregulated in T cells during concanavalin A-driven mitogenic and anti-CD3/CD28 stimulated TCR activation of T cells. By specific blocking of TRPV1 and TRPV4 channels, we found that these TRPV inhibitors may regulate mitogenic and T cell receptor mediated T cell activation and effector cytokine(s) production by suppressing tumour necrosis factor, interleukin-2 and interferon-γ release. These results may have broad implications in the context of cell-mediated immunity, especially T cell responses and their regulations, neuro-immune interactions and molecular understanding of channelopathies.

Association between serum substance P levels and mortality in patients with severe sepsis

BACKGROUND

Substance P (SP) is a peptide of the tachykinins family involved in the inflammatory response. Circulating SP levels have been assessed in septic patients in 2 previous studies with a small number of subjects (61 and 42 patients, respectively), and there were no significant differences in SP levels at the moment of sepsis diagnosis between surviving and nonsurviving patients. The main goal of this study was to determine a possible relationship between serum SP levels and patient outcome in the largest cohort of severe septic patients analyzed so far.

METHODS

We performed an observational, prospective, multicenter study in 6 Spanish intensive care units. Serum SP levels were measured at the moment of severe sepsis diagnosis in 238 patients. The end point of the study was 30-day mortality.

RESULTS

We found that surviving septic patients (n = 153) showed higher serum SP levels than did nonsurvivors (n = 85). Multiple logistic regression analysis showed that serum SP levels higher than 350 pg/mL were associated with survival at 30 days (odds ratio, 0.43; 95% confidence interval, 0.24-0.77; P = .005) after controlling for serum lactic acid levels and Sepsis-related Organ Failure Assessment score.

CONCLUSIONS

The major new finding of our study was that serum SP levels were associated with mortality in severe septic patients.

TRP channels in the skin

Emerging evidence suggests that transient receptor potential (TRP) ion channels not only act as 'polymodal cellular sensors' on sensory neurons but are also functionally expressed by a multitude of non-neuronal cell types. This is especially true in the skin, one of the largest organs of the body, where they appear to be critically involved in regulating various cutaneous functions both under physiological and pathophysiological conditions. In this review, we focus on introducing the roles of several cutaneous TRP channels in the regulation of the skin barrier, skin cell proliferation and differentiation, and immune functions. Moreover, we also describe the putative involvement of several TRP channels in the development of certain skin diseases and identify future TRP channel-targeted therapeutic opportunities.

The background to this themed issue on neuropeptides

A meeting of the British Pharmacological Society in association with the European Neuropeptide Club and Americal Summer Neuropeptide Conference in June 2012 led to this themed issue on neuropetides. A wide range of neuropeptides are discussed, in various physiological and pathophysiological conditions, with respect to their upstream and downstream pathways. It is clear, at this point in time, that targeting neuropeptides has therapeutic potential in pathologies ranging from migraine to obesity. It is also clear from the reviews in this issue of the British Journal of Pharmacology that there is still so much to learn.

LINKED ARTICLES

This article is part of a themed section on Neuropeptides. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2013.170.issue-7.

Effect of chirality and lipophilicity in the functional activity of evodiamine and its analogues at TRPV1 channels

BACKGROUND AND PURPOSE

Evodiamine, a racemic quinazolinocarboline alkaloid isolated from the traditional Chinese medicine Evodiae fructus, has been reported to act as an agonist of the transient receptor potential vanilloid type-1 (TRPV1) cation channel both in vitro and in vivo. Evodiamine is structurally different from all known TRPV1 activators, and has significant clinical potential as a thermogenic agent. Nevertheless, the molecular bases for its actions are still poorly understood.

EXPERIMENTAL APPROACH

To investigate the structure-activity relationships of evodiamine, the natural racemate was resolved, and a series of 23 synthetic analogues was prepared, using as the end point the intracellular Ca(2+) elevation in HEK-293 cells stably overexpressing either the human or the rat recombinant TRPV1.

KEY RESULTS

S-(+) evodiamine was more efficacious and potent than R-(-) evodiamine, and a new potent lead (Evo30) was identified, more potent than the reference TRPV1 agonist, capsaicin. In general, potency and efficacy correlated with the lipophilicity of the analogues. Like other TRPV1 agonists, several synthetic analogues could efficiently desensitize TRPV1 to activation by capsaicin.

CONCLUSIONS AND IMPLICATIONS

Evodiamine qualifies as structurally unique lead structure to develop new potent TRPV1 agonists/desensitizers.