Transient Receptor Potential A1 and Cannabinoid Receptor Activity in Human Normal and Hyperplastic Prostate: Relation to Nerves and Interstitial Cells

Early investigational agents for the treatment of benign prostatic hyperplasia'

INTRODUCTION

Benign prostatic hyperplasia (BPH), as a clinical entity that affects many people, has always been in the forefront of interest among researchers, pharmaceutical companies, and physicians. Patients with BPH exhibit a diverse range of symptoms, while current treatment options can occasionally cause adverse events. All the aforementioned have led to an increased demand for more effective treatment options.

AREAS COVERED

This review summarizes the outcomes of new medications used in a pre-clinical and clinical setting for the management of male lower urinary tract symptoms (LUTS)/BPH and provides information about ongoing trials and future directions in the management of this condition. More specifically, sheds light upon drug categories, such as reductase‑adrenoceptor antagonists, drugs interfering with the nitric oxide (NO)/cyclic guanosine monophosphate (GMP) signaling pathway, onabotulinumtoxinA, vitamin D3 (calcitriol) analogues, selective cannabinoid (CB) receptor agonists, talaporfin sodium, inhibitor of transforming growth factor beta 1 (TGF-β1), drugs targeting the hormonal control of the prostate, phytotherapy, and many more.

EXPERT OPINION

Clinical trials are being conducted on a number of new medications that may emerge as effective therapeutic alternatives in the coming years.

Selective inhibition of neurogenic, but not agonist-induced contractions by phospholipase A2 inhibitors points to presynaptic phospholipase A2 functions in contractile neurotransmission to human prostate smooth muscle

BACKGROUND

Phospholipases A2 (PLA2 ) may be involved in α1 -adrenergic contraction by formation of thromboxane A2 in different smooth muscle types. However, whether this mechanism occurs with α1 -adrenergic contractions of the prostate, is still unknown. While α1 -adrenoceptor antagonists are the first line option for medical treatment of voiding symptoms in benign prostatic hyperplasia (BPH), improvements are limited, probably by nonadrenergic contractions including thromboxane A2 . Here, we examined effects of PLA2 inhibitors on contractions of human prostate tissues.

METHODS

Prostate tissues were obtained from radical prostatectomy. Contractions were induced by electric field stimulation (EFS) and by α1 -adrenergic agonists in an organ bath, after application of the cytosolic PLA2 inhibitors ASB14780 and AACOCF3, the secretory PLA2 inhibitor YM26734, the leukotriene receptor antagonist montelukast, or of solvent to controls.

RESULTS

Frequency-dependent contractions of human prostate tissues induced by EFS were inhibited by 25% at 8 Hz, 38% at 16 Hz and 37% at 32 Hz by ASB14780 (1 µM), and by 32% at 16 Hz and 22% at 32 Hz by AACOCF3 (10 µM). None of both inhibitors affected contractions induced by noradrenaline, phenylephrine or methoxamine. YM26734 (3 µM) and montelukast (0.3 and 1 µM) neither affected EFS-induced contractions, nor contractions by α1 -adrenergic agonists, while all contractions were substantially inhibited by silodosin (100 nM).

CONCLUSIONS

Our findings suggest presynaptic PLA2 functions in prostate smooth muscle contraction, while contractions induced by α1 -adrenergic agonists occur PLA2 -independent. Lacking sensitivity to montelukast excludes an involvement of PLA2 -derived leukotrienes in promotion of contractile neurotransmission.

Expression and distribution of the transient receptor potential cationic channel ankyrin 1 (TRPA1) in the human seminal vesicles

Background and Aims

The transient receptor potential cationic channel ankyrin 1 (TRPA1), a channel protein permeable to most divalent cations, has been suggested to play a role in mechano‐afferent/efferent signaling (including the release of neurotransmitters) in the human urinary tract (bladder, prostate, and urethra). To date, only a few studies have addressed the expression of this receptor in male and female reproductive tissues. The present study aimed to evaluate human seminal vesicles (SVs)  for the expression and localization of TRPA1.

Methods

SV tissue was obtained from 5 males who had undergone pelvic surgery due to malignancies of the prostate or urinary bladder. The expression of messenger ribonucleic acid (mRNA) specifically encoding for the TRPA1 protein was elucidated by means of reverse transcriptase polymerase chain reaction (RT‐PCR). Using immunohistochemical methods, the distribution of TRPA1 was examined in relation to the endothelial and neuronal nitric oxide synthases (eNOS, nNOS) and the neuropeptides calcitonin gene‐related peptide (CGRP) and vasoactive intestinal polypeptide (VIP).

Results

RT‐PCR revealed signals related to the expected molecular size of 656 bp. Immunohistochemistry demonstrated that TRPA1 is located in nerves running through the smooth muscle portion of the SV. Here, the protein is in part co‐localized with nNOS and CGRP, whereas no co‐localization with VIP was registered. Dot‐like signals specific for TRPA1 were observed in the cytoplasm of epithelial cells lining the lumen of glandular spaces. The epithelial layer also presented staining for eNOS. The smooth musculature appeared free of immunosignals for TRPA1.

Conclusion

The results convincingly show the expression of TRPA1 in nerve endings as well as in epithelial cells of the SV. Based on its location in epithelial cells, TRPA1 might be involved in the mechanism of the NO/cyclic guanosine monophosphate (GMP)‐mediated signaling and also the control of secretory function (mediated by cyclic GMP) in the human SV.

Functional Expression of Transient Receptor Potential and Piezo1 Channels in Cultured Interstitial Cells of Human-Bladder Lamina Propria

The interstitial cells in bladder lamina propria (LP-ICs) are believed to be involved in sensing/afferent signaling in bladder mucosa. Transient receptor potential (TRP) cation channels act as mechano- or chemo-sensors and may underlie some of the sensing function of bladder LP-ICs. We aimed to investigate the molecular and functional expression of TRP channels implicated in bladder sensory function and Piezo1/Piezo2 channels in cultured LP-ICs of the human bladder. Bladder tissues were obtained from patients undergoing cystectomy. LP-ICs were isolated and cultured, and used for real-time reverse transcription-quantitative polymerase chain reaction, immunocytochemistry, and calcium-imaging experiments. At the mRNA level, TRPA1, TRPV2, and Piezo1 were expressed most abundantly. Immunocytochemical staining showed protein expression of TRPA1, TRPV1, TRPV2, TRPV4, TRPM8, as well as Piezo1 and Piezo2. Calcium imaging using channel agonists/antagonists provided evidence for functional expression of TRPA1, TRPV2, TRPV4, Piezo1, but not of TRPV1 or TRPM8. Activation of these channels with their agonist resulted in release of adenosine triphosphate (ATP) from LP-ICs. Inhibition of TRPV2, TRPV4 and Piezo1 blocked the stretch induced intracellular Ca²⁺ increase. Whereas inhibition of TRPA1 blocked H₂O₂ evoked response in LP-ICs. Our results suggest LP-ICs of the bladder can perceive stretch or chemical stimuli via activation of TRPV2, TRPV4, Piezo1 and TRPA1 channels. LP-ICs may work together with urothelial cells for perception and transduction of mechanical or chemical signals in human-bladder mucosa.

Diverse role of endocannabinoid system in mammalian male reproduction

Endocannabinoid system (ECS) is known for its modulatory role in numerous physiological processes in the body. Endocannabinoids (eCBs) are endogenous lipid molecules which function both centrally and peripherally. The ECS is best studied in the central nervous system (CNS), immune system as well as in the metabolic system. The role of ECS in male reproductive system is emerging and the presence of a complete enzymatic machinery to synthesize and metabolize eCBs has been demonstrated in male reproductive tract. Endocannabinoid concentrations and alterations in their levels have been reported to affect the functioning of spermatozoa. A dysfunctional ECS has also been linked to the development of prostate cancer, the leading cause of cancer related mortality among male population. This review is an attempt to provide an insight into the significant role of endocannabinoids in male reproduction and further summarize recent findings that demonstrate the manner in which the endocannabinoid system impacts male sexual behavior and fertility.

Non-electrophilic TRPA1 agonists, menthol, carvacrol and clotrimazole, open epithelial tight junctions via TRPA1 activation

Activation of the transient receptor potential A1 channel (TRPA1) by electrophilic agonists was reported to induce the opening of tight junctions (TJs). Because compounds that increase TJ permeability can be paracellular permeability enhancers, we investigated the effect of non-electrophilic TRPA1 activators, including food ingredients (menthol and carvacrol) and medication (clotrimazole), on epithelial permeability. We show that all three compounds induced increase of the permeability of fluorescein isothiocyanate-conjugated dextran (4 kDa) and decrease of transepithelial electrical resistance, accompanied by Ca2+ influx and cofilin activation in epithelial MDCK II monolayers. These phenotypes were attenuated by pretreatment of a TRPA1 antagonist, suggesting TRPA1-mediated opening of TJs. These results suggest that non-electrophilic TRPA1 activators with established safety can be utilized to regulate epithelial barriers.

Discovery of natural TRPA1 activators through pharmacophore-based virtual screening and a biological assay

Transient receptor potential cation channel subfamily A member 1 (TRPA1), a member of the transient receptor potential family, detects a wide range of environmental stimuli, such as low temperature, abnormal pH, and reactive irritants. TRPA1 is of great interest as a target protein in fields related to pharmaceuticals and foods. In this study, a library of natural products was explored to identify TRPA1 activators by pharmacophore screening of known TRPA1 agonists and biological assays for agonist activity. The study identified six natural compounds as novel TRPA1 agonists. The discovery of these compounds may prove useful in elucidating the TRPA1 activation mechanism.

The urothelium, the urinary microbioma and men LUTS: a systematic review

INTRODUCTION

The pathophysiology and management of male patients with lower urinary tract symptoms (LUTS) is still a matter of debate. In the past few years, the urothelium and the urinary microbiota represented important areas of research to improve the understanding and management of these patients. Aim of the present review was to summarize the available data on the urothelium and the microbiota related to male LUTS.

EVIDENCE ACQUISITION

A National Center for Biotechnology Information (NCBI) PubMed search for relevant articles published between January 2000 and December 2019 was performed using the medical subjects heading "urothelium," "microbioma," "microbiota," "urobioma," "urobiota," "benign prostatic hyperplasia," "benign prostatic enlargement," "lower urinary tract symptoms," "lower urinary tract dysfunction," "men," "male," "overactive bladder," "receptors." Exclusion criteria included: animal studies and studies on muscarinic and adrenergic pathways.

EVIDENCE SYNTHESIS

The urothelium has been recently evaluated in humans to evaluate new possible markers and pathways. New possible targets for the treatment of male LUTS include the neural growth factor, the cannabinoid, the vanilloid and the ATP pathways. However, studies in humans are still needed to elucidate the exact role of these pathways in the management of male patients with LUTS. The available evidence on the urinary microbioma in male is poor. Standing to the available, urinary microbioma is evident in healthy urine in males. Moreover, the urinary microbioma varies depending on the method of collection, sexually transmitted disease status, inflammation and urinary symptoms. A possible role of probiotics in the management of LUTS in women has been proposed and may have a role in male patients as well.

CONCLUSIONS

The urothelium and the urinary microbiota are still poorly studied in men with LUTS. Most of the evidence and the hypothesis on the relationship between urothelium/urinary microbiota and LUTS comes from animal/in-vitro evidence while clinical trials are lacking. These pathways seem interesting even in LUTS pathogenesis in men but their possible role as a new therapeutic target is still an open debate.

Emerging drugs to target lower urinary tract symptomatology (LUTS)/benign prostatic hyperplasia (BPH): focus on the prostate

OBJECTIVES

The benign prostatic syndrome, comprising lower urinary tract symptomatology secondary to benign prostatic hyperplasia/enlargement, represents a major health care issue in westernized countries. The pharmacological management involves alpha-adrenoceptor antagonists, intervention into the hormonal control of prostate growth using inhibitors of the enzyme 5-alpha-reductase, and stimulation of the nitric oxide/cyclic GMP pathway by tadalafil, an inhibitor of the phosphodiesterase type 5.

METHODS

This review summarizes the achievements which have been made in the development of drug candidates assumed to offer opportunities as beneficial treatment options in the management of the benign prostatic syndrome.

RESULTS

A review of the literature has revealed that the line of development is focusing on drugs interfering with peripheral neuromuscular/neuronal mechanisms (nitric oxide donor drugs, agonists/antagonists of endogenous peptides, botulinum toxin, NX-1207), the steroidal axis (cetrorelix) or the metabolic turn-over (lonidamine), as well as the combination of drugs already established in the treatment of lower urinary tract symptomatology/benign prostatic hyperplasia (phosphodiesterase 5 inhibitor plus alpha-adrenoceptor antagonist).

CONCLUSION

Many research efforts have provided the basis for the development of new therapeutic modalities for the management of lower urinary tract dysfunctions, some of which might be offered to the patients in the near future.

Generation and Regulation of Spontaneous Contractions in the Prostate

Spontaneous myogenic contractions have been shown to be significantly upregulated in prostate tissue collected from men with Benign Prostatic Hyperplasia (BPH), an extremely common disorder of the ageing male. Although originally thought likely to be involved in 'housekeeping' functions, mixing prostatic secretions to prevent stagnation, these spontaneous myogenic contractions provide a novel opportunity to understand and treat BPH. This treatment potential differs from previous models, which focused exclusively on attenuating nerve-mediated neurogenic contractions. Previous studies in the rodent prostate have provided an insight into the mechanisms underlying the regulation of myogenic contractions. 'Prostatic Interstitial Cells' (PICs) within the prostate appear to generate pacemaker potentials, which arise from the summation of number of spontaneous transient depolarisations triggered by the spontaneous release of Ca²⁺ from internal stores and the opening of Ca²⁺-activated Cl^- channels. Pacemaker potentials then conduct into neighbouring smooth muscle cells to generate spontaneous slow waves. These slow waves trigger the firing of 'spike-like' action potentials, Ca²⁺ entry and contraction, which are not attenuated by blockers of neurotransmission. However, these spontaneous prostatic contractions can be modulated by the autonomic nervous system. Here, we discuss the mechanisms underlying rodent and human prostate myogenic contractions and the actions of existing and novel pharmacotherapies for the treatment of BPH. Understanding the generation of human prostatic smooth muscle tone will confirm the mechanism of action of existing drugs, inform the identification and effectiveness of new pharmacotherapies, as well as predict patient outcomes.

Effects of sulfide and polysulfides transmitted by direct or signal transduction-mediated activation of TRPA1 channels

Hydrogen sulfide (H₂S) is a gaseous mediator in various physiological and pathological processes, including neuroimmune modulation, metabolic pathways, cardiovascular system, tumour growth, inflammation and pain. Now the hydrogen polysulfides (H₂S_n) have been recognised as signalling molecules modulating ion channels, transcription factors and protein kinases. Transient receptor potential (TRP) cation channels can be activated by mechanical, thermal or chemical triggers. Here, we review the current literature regarding the biological actions of sulfide and polysulfide compounds mediated by TRP channels with special emphasis on the role of TRPA1, best known as ion channels in nociceptors. However, the non‐neuronal TRPA1 channels should also be considered to play regulatory roles. Although sulfide and polysulfide effects in different pathological circumstances and TRPA1‐mediated processes have been investigated intensively, our review attempts to present the first comprehensive overview of the potential crosstalk between TRPA1 channels and sulfide‐activated signalling pathways.

Linked Articles

This article is part of a themed section on Chemical Biology of Reactive Sulfur Species. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.4/issuetoc

Fermented whey-based product improves the quality of life of males with moderate lower urinary tract symptoms: A randomized double-blind study

PURPOSE

The purpose of this research was to evaluate the effect of a specific fermented whey product on lower urinary tract symptoms, main prostate related indices and oxidative stress/inflammatory markers in urine and seminal plasma in men with moderate dysuric symptoms. An additional purpose was to clarify associations between different parameters with special emphasis on pain.

METHODS

This was a prospective randomized double-blind 4-weeks study on men with moderate lower urinary tract symptoms who underwent the evaluation for quality of life at the baseline and at the end of the study. The symptoms were characterized by International Prostate Symptom Score (I-PSS) and National Institutes of Health Chronic Prostatitis Symptom Index (NIH-PSI), the maximum urinary flow and the main prostate-related indices. In order to obtain more comprehensive information about the effects of fermented whey product on systemic oxidative stress marker 8-EPI and seminal plasma inflammatory markers (interleukin-6 and interleukin-8) were also measured.

RESULTS

After 4 weeks consumption of fermented whey product there was a statistically significant decrease of prostate-specific antigen level in serum and systemic stress marker 8-EPI in urine compared to control group. Maximum urinary flow and NIH-PSI all studied scores and sub-scores had also significant improvement. In addition, seminal plasma interleukin-8 level substantially decreased.

CONCLUSIONS

The consumption of special fermented whey product improved urinary function, reduced lower urinary tract symptoms, systemic oxidative stress marker and seminal plasma inflammatory status. Thus it contributed to an improvement of the quality of life in men with moderate lower urinary tract symptoms.

Expression and distribution of the transient receptor potential cationic channel A1 (TRPA1) in the human clitoris-comparison to male penile erectile tissue

The transient receptor potential cationic channel ankyrin 1 (TRPA1) is a channel protein assumed to act in various human tissues as mechano- and pain sensor and play a role in neurotransmission. The expression of TRPA has already been investigated in the human prostate and urethra, however, only very few studies have addressed the expression and distribution in the male and female genital tract. The present study aimed to investigate by means of immunohistochemistry (double-labeling technique, laser fluorescence microscopy) in the human clitoris and penile erectile tissue the localization of TRPA1 in relation to nNOS, the vasoactive intestinal polypeptide (VIP) and vesicular acetylcholine transporter (VAChT). In the clitoral tissue, TRPA1 was observed in basal epithelial cells and slender nNOS-positive nerve fibers transversing the subepithelial space. To a certain degree, in the clitoral epithelial cells, TRPA1 was found co-localized with vimentin. In human corpus cavernosum, immunoreactivity for TRPA1 was seen in nerves transversing the cavernous sinusoidal space and running alongside small arteries, these nerves also displayed expression of the vesicular acetylcholine transporter protein (VAChT). Varicose nerves containing nNOS or VIP were not immunoreactive for TRPA1. It seems likely that TRPA1 is involved in nitric oxide-mediated afferent sensory transmission in the clitoris while, in penile erectile tissue, a role for TRPA1 in cholinergic signaling might be assumed.

TRPA1 as a drug target--promise and challenges

The transient receptor potential ankyrin 1 (TRPA1) channel is a nonselective cation channel belonging to the superfamily of transient receptor potential (TRP) channels. It is predominantly expressed in sensory neurons and serves as an irritant sensor for a plethora of electrophilic compounds. Recent studies suggest that TRPA1 is involved in pain, itch, and respiratory diseases, and TRPA1 antagonists have been actively pursued as therapeutic agents. Here, we review the recent progress, unsettled issues, and challenges in TRPA1 research and drug discovery.

Identification of natural compound carnosol as a novel TRPA1 receptor agonist

The transient receptor potential ankyrin 1 (TRPA1) cation channel is one of the well-known targets for pain therapy. Herbal medicine is a rich source for new drugs and potentially useful therapeutic agents. To discover novel natural TRPA1 agonists, compounds isolated from Chinese herbs were screened using a cell-based calcium mobilization assay. Out of the 158 natural compounds derived from traditional Chinese herbal medicines, carnosol was identified as a novel agonist of TRPA1 with an EC₅₀ value of 12.46 µM. And the agonistic effect of carnosol on TRPA1 could be blocked by A-967079, a selective TRPA1 antagonist. Furthermore, the specificity of carnosol was verified as it showed no significant effects on two other typical targets of TRP family member: TRPM8 and TRPV3. Carnosol exhibited anti-inflammatory and anti-nociceptive properties; the activation of TRPA1 might be responsible for the modulation of inflammatory nociceptive transmission. Collectively, our findings indicate that carnosol is a new anti-nociceptive agent targeting TRPA1 that can be used to explore further biological role in pain therapy.

Cannabinoids and the endocannabinoid system in lower urinary tract function and dysfunction

AIMS

To review knowledge on cannabinoids and the endocannabinoid system in lower urinary tract function and dysfunction.

METHODS

Review of MEDLINE using defined search terms, and manual analysis. Articles published in English were included.

RESULTS AND DISCUSSION

Components of the endocannabinoid system—cannabinoid (CB)receptor types 1 and 2, anandamide, and fatty acid amide hydrolase (FAAH), which degrades anandamide and related fatty-acid amides—have been located to lower urinary tract tissues of mice, rats, monkeys, and humans. Studies have located CB receptors in urothelium and sensory nerves and FAAH in the urothelium. CB receptor- and FAAH-related activities have also been reported in the lumbosacral spinal cord. Data on supraspinal CB functions in relation to micturition are lacking. Cannabinoids are reported to reduce sensory activity of isolated tissues, cause antihyperalgesia in animal studies of bladder inflammation, affect urodynamics parameters reflecting sensory functions in animals models, and appear to have effects on storage symptoms in humans. FAAH inhibitors have affected sensory bladder functions and reduced bladder overactivity in rat models. Cannabinoids may modify nerve-mediated functions of isolated lower urinary tract tissues.

CONCLUSIONS

Evidence suggests components of the endocannabinoid system are involved in regulation of bladder function, possibly at several levels of the micturition pathway. It is unclear if either CB receptor has a dominant role in modification of sensory signals or if differences exist at peripheral and central nervous sites. Amplification of endocannabinoid activity by FAAH inhibitors may be an attractive drug target in specific pathways involved in LUTS.

The TRPA1 channel in migraine mechanism and treatment

Migraine remains an elusive and poorly understood disease. The uncertainty is reflected by the currently unsatisfactory acute and prophylactic treatments for this disease. Genetic and pharmacological information points to the involvement of some transient receptor potential (TRP) channels in pain mechanisms. In particular, the TRP vanilloid 1 (TRPV1) and TRP ankyrin 1 (TRPA1) channels seem to play a major role in different models of pain diseases. Recent findings have underscored the possibility that TRP channels expressed in the nerve terminals of peptidergic nociceptors contribute to the migraine mechanism. Among this channel subset, TRPA1, a sensor of oxidative, nitrative and electrophilic stress, is activated by an unprecedented series of irritant and pain-provoking exogenous and endogenous agents, which release the pro-migraine peptide, calcitonin gene-related peptide, through this neuronal pathway. Some of the recently identified TRPA1 activators have long been known as migraine triggers. Furthermore, specific analgesic and antimigraine medicines have been shown to inhibit or desensitize TRPA1 channels. Thus, TRPA1 is emerging as a major contributing pathway in migraine and as a novel target for the development of drugs for pain and migraine treatment.

Characterization of subepithelial interstitial cells in normal and pathological human prostate

AIMS

To characterize the subepithelial (SE) stromal cells in normal human prostate and to study phenotypical changes in these SE stromal cells in benign prostate hyperplasia (BPH) and prostate cancer (PCa).

METHODS AND RESULTS

Tissue was obtained from normal, hyperplastic and tumoral areas in prostatectomy specimens. Tissue samples were processed for morphology, immunohistochemistry, immunofluorescence and electron microscopy. An ultrastructural and immunohistochemical phenotype for the SE stromal cells was assessed, and changes occurring in BPH and PCa were looked for. Based on the ultrastructural findings the dominant SE stromal cell types in normal prostate were interstitial Cajal-like cells and spindle-shaped myoid cells with both myoid and fibroblastic features. An immunohistochemical correlate was found with selective expression of mesenchymal and myoid cell markers. In BPH and PCa, a changed stromal cell composition of the SE region was found. Furthermore, direct contacts between spindle-shaped myoid cells and tumour cells were observed in PCa.

CONCLUSIONS

The present study shows for the first time that the SE area in the human prostate houses different stromal cell types with distinct phenotypes. In BPH and PCa specific disease-related changes were observed in the organization and phenotypes of SE interstitial cells.

A tarantula-venom peptide antagonizes the TRPA1 nociceptor ion channel by binding to the S1-S4 gating domain

BACKGROUND

The venoms of predators have been an excellent source of diverse highly specific peptides targeting ion channels. Here we describe the first known peptide antagonist of the nociceptor ion channel transient receptor potential ankyrin 1 (TRPA1).

RESULTS

We constructed a recombinant cDNA library encoding ∼100 diverse GPI-anchored peptide toxins (t-toxins) derived from spider venoms and screened this library by coexpression in Xenopus oocytes with TRPA1. This screen resulted in identification of protoxin-I (ProTx-I), a 35-residue peptide from the venom of the Peruvian green-velvet tarantula, Thrixopelma pruriens, as the first known high-affinity peptide TRPA1 antagonist. ProTx-I was previously identified as an antagonist of voltage-gated sodium (NaV) channels. We constructed a t-toxin library of ProTx-I alanine-scanning mutants and screened this library against NaV1.2 and TRPA1. This revealed distinct partially overlapping surfaces of ProTx-I by which it binds to these two ion channels. Importantly, this mutagenesis yielded two novel ProTx-I variants that are only active against either TRPA1or NaV1.2. By testing its activity against chimeric channels, we identified the extracellular loops of the TRPA1 S1-S4 gating domain as the ProTx-I binding site.

CONCLUSIONS

These studies establish our approach, which we term "toxineering," as a generally applicable method for isolation of novel ion channel modifiers and design of ion channel modifiers with altered specificity. They also suggest that ProTx-I will be a valuable pharmacological reagent for addressing biophysical mechanisms of TRPA1 gating and the physiology of TRPA1 function in nociceptors, as well as for potential clinical application in the context of pain and inflammation.

Acute Uterine Irritation Provokes Colonic Motility via Transient Receptor Potential A1-dependent Spinal NR2B Phosphorylation in Rats

Background:

Patients with inflammatory gynecological/obstetrical problems often complain of irritable bowel syndrome. The authors examined whether acute uterus irritation reflexively provokes colonic motility in rat preparations.

Methods:

A modified colon manometry and striated abdominal muscle electromyogram activity in response to mustard oil (MO) instillation into the uterine horn were continuously recorded in anesthetized rats. The lumbosacral (L6-S1) dorsal horn was dissected to assess the level and the cellular location of phosphorylated NR2B subunit using Western blotting and immunofluorescence analysis, respectively. Finally, the uterine transient receptor potential A1 or spinal NR2B subunit was pharmacologically blocked to elucidate its roles.

Results:

MO (0.1%, 0.2 ml) injected into the lower uterine horn dramatically provoked colonic hypermotility characterized by rhythmic colonic contractions (about 3–4 contractions per 10 min, n = 7) accompanied by synchronized electromyogram firing in the abdominal muscle (about 4–5 folds of control, n = 7). In addition to provoking colonic hypermotility, MO administration also up-regulated phosphorylated (about 2–3 folds of control, n = 7), but not total, NR2B expression in the dorsal horn neurons. Both intrathecal Ro 25–6981 (a selective NR2B subunit antagonist; 10 μM, 10 μl) and intrauterine HC-030031 (a selective transient receptor potential A1 receptor antagonist; 30 mg/kg, 0.2 ml) injected before the MO instillation attenuated the MO-induced colonic hypermotility and spinal NR2B phosphorylation.

Conclusion:

The comorbidity of gynecological/obstetrical and gastrointestinal problems is not coincidental but rather causal in nature, and clinicians should investigate for gynecological/urological diseases in the setting of bowel problems with no known pathological etiology.

TRPA1 and other TRP channels in migraine

Ever since their identification, interest in the role of transient receptor potential (TRP) channels in health and disease has steadily increased. Robust evidence has underlined the role of TRP channels expressed in a subset of primary sensory neurons of the trigeminal ganglion to promote, by neuronal excitation, nociceptive responses, allodynia and hyperalgesia. In particular, the TRP vanilloid 1 (TRPV1) and the TRP ankyrin 1 (TRPA1) are expressed in nociceptive neurons, which also express the sensory neuropeptides, tachykinins, and calcitonin gene-related peptide (CGRP), which mediate neurogenic inflammatory responses. Of interest, CGRP released from the trigeminovascular network of neurons is currently recognized as a main contributing mechanism of migraine attack. The ability of TRPA1 to sense and to be activated by an unprecedented series of exogenous and endogenous reactive molecules has now been extensively documented. Several of the TRPA1 activators are also known as triggers of migraine attack. Thus, TRP channels, and particularly TRPA1, may be proposed as novel pathways in migraine pathophysiology and as possible new targets for its treatment.

Sildenafil effect on the human bladder involves the L-cysteine/hydrogen sulfide pathway: a novel mechanism of action of phosphodiesterase type 5 inhibitors

BACKGROUND

Phosphodiesterase type 5 inhibitors (PDE5-Is) are effective in the treatment of lower urinary tract symptom (LUTS), although their mechanism of action is still unclear. PDE5-Is cause bladder detrusor relaxation, and this effect is partially independent of nitric oxide. Hydrogen sulfide (H(2)S) is a newly discovered transmitter with myorelaxant properties. It is predominantly formed from L-cysteine by cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CSE).

OBJECTIVE

To evaluate whether the L-cysteine/H(2)S pathway contributes to the relaxing effect of sildenafil on the human detrusor dome.

DESIGN, SETTING, AND PARTICIPANTS

Samples of bladders obtained from men undergoing open prostatectomy for benign prostatic hyperplasia (BPH) were used. The presence of CBS and CSE enzymes was assessed by western blot. H(2)S production was measured by a colorimetric assay in basal and stimulated conditions with L-cysteine and in response to sildenafil (1, 3, 10, and 30 μM), 8-bromo-cyclic guanosine monophosphate (8-bromo-cGMP; 100 μM) or dibutyryl-cyclic adenosine monophosphate (dibutyryl-cAMP; 100 μM). A curve concentration effect of sodium hydrosulfide (NaHS), H(2)S donor (0.1 μM to 10mM), L-cysteine (0.1 μM to 10mM), and sildenafil (0.1-10 μM) was performed on precontracted detrusor dome strips. To investigate H(2)S signaling in a sildenafil effect, CBS and CSE inhibitors were used.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Analysis of variance was used, followed by the Bonferroni post hoc test.

RESULTS AND LIMITATIONS

CBS and CSE are present in the human bladder dome and efficiently convert L-cysteine into H(2)S. Both NaHS and L-cysteine relaxed human strips. Sildenafil caused (1) a relaxation of bladder dome strips and (2) a concentration-dependent increase in H(2)S production. Both effects were significantly reduced by CBS and CSE inhibitors. Similar to sildenafil, both 8-bromo-cGMP and dibutyryl-cAMP caused an increase in H(2)S production.

CONCLUSIONS

The sildenafil relaxant effect on the human bladder involves the H(2)S signaling pathway. This effect may account in part for the efficacy of PDE5-Is in LUTS. A better definition of the pathophysiologic role of the H(2)S pathway in the human bladder may open new therapeutic approaches.

The role of transient receptor potential ankyrin 1 (TRPA1) receptor activation in hydrogen-sulphide-induced CGRP-release and vasodilation

Activation of transient receptor potential ankyrin 1 (TRPA1) and vanilloid 1 (TRPV1) channels on capsaicin-sensitive sensory neurons causes release of inflammatory neuropeptides, including calcitonin gene-related peptide (CGRP). We investigated whether the hydrogen sulphide (H(2)S)-evoked CGRP release from sensory neurons of isolated rat tracheae and H(2)S-induced increases in the microcirculation of the mouse ear were mediated by TRPA1 receptor activation. Allylisothiocyanate (AITC) or the H(2)S donor sodium hydrogen sulphide (NaHS) were used as stimuli and CGRP release of the rat tracheae was measured by radioimmunoassay. AITC or NaHS were applied to the ears of Balb/c, C57BL/6, TRPA1 and TRPV1 receptor gene knockout mice and blood flow was detected by laser Doppler imaging. Both AITC and NaHS increased CGRP release from isolated rat tracheae, and both responses were inhibited by the TRPA1 antagonist, HC-030031, but was not affected by the TRPV1 receptor blocker, BCTC. Application of AITC or NaHS increased the cutaneous blood flow in the mouse ears. Similarly to the effect of AITC, the vasodilatory response to NaHS was reduced by HC-030031 or in TRPA1 deleted mice. In contrast, genetic deletion of TRPV1 did not affect the increase in the ear blood flow evoked by AITC or NaHS. We conclude that H(2)S activates TRPA1 receptors causing CGRP release from sensory nerves of rat tracheae, as well as inducing cutaneous vasodilatation in the mouse ear. TRPV1 receptors were not involved in these processes. Our results highlight that TRPA1 receptor activation should be considered as a potential mechanism of vasoactive effects of H(2)S.

TRPA1 antagonists as potential analgesic drugs

The necessity of safe and effective treatments for chronic pain has intensified the search for new analgesic drugs. In the last few years, members of a closely-related family of ion channels, called transient receptor potential (TRP) have been identified in different cell types and their functions in physiological and pathological conditions have been characterized. The transient receptor potential ankyrin 1 (TRPA1), originally called ANKTM1 (ankyrin-like with transmembrane domains protein 1), is a molecule that has been conserved in different species during evolution; TRPA1 is a cation channel that functions as a cellular sensor, detecting mechanical, chemical and thermal stimuli, being a component of neuronal, epithelial, blood and smooth muscle tissues. In mammals, TRPA1 is largely expressed in primary sensory neurons that mediate somatosensory processes and nociceptive transmission. Recent studies have described the role of TRPA1 in inflammatory and neuropathic pain. However, its participation in cold sensation has not been agreed in different studies. In this review, we focus on data that support the relevance of the activation and blockade of TRPA1 in pain transmission, as well as the mechanisms underlying its activation and modulation by exogenous and endogenous stimuli. We also discuss recent advances in the search for new analgesic medicines targeting the TRPA1 channel.

Novel drug targets for the pharmacotherapy of benign prostatic hyperplasia (BPH)

Benign prostatic hyperplasia (BPH) is the major cause of lower urinary tract symptoms in men aged 50 or older. Symptoms are not normally life threatening, but often drastically affect the quality of life. The number of men seeking treatment for BPH is expected to grow in the next few years as a result of the ageing male population. Estimates of annual pharmaceutical sales of BPH therapies range from $US 3 to 10 billion, yet this market is dominated by two drug classes. Current drugs are only effective in treating mild to moderate symptoms, yet despite this, no emerging contenders appear to be on the horizon. This is remarkable given the increasing number of patients with severe symptoms who are required to undergo invasive and unpleasant surgery. This review provides a brief background on prostate function and the pathophysiology of BPH, followed by a brief description of BPH epidemiology, the burden it places on society, and the current surgical and pharmaceutical therapies. The recent literature on emerging contenders to current therapies and novel drug targets is then reviewed, focusing on drug targets which are able to relax prostatic smooth muscle in a similar way to the α(1) -adrenoceptor antagonists, as this appears to be the most effective mechanism of action. Other mechanisms which may be of benefit are also discussed. It is concluded that recent basic research has revealed a number of novel drug targets such as muscarinic receptor or P2X-purinoceptor antagonists, which have the potential to produce more effective and safer drug treatments.

The endocannabinoid system in prostate cancer

Cannabinoids, their receptors and their metabolizing enzymes are emerging as a new regulatory system, which is involved in multiple physiological functions. Normal prostate tissue expresses several constituents of the endocannabinoid system including the CB(1) receptor, receptors belonging to the transient receptor potential family and fatty acid amide hydrolase, a hydrolyzing enzyme, all of which have been localized in the glandular epithelia. Accumulating evidence indicate that the endocannabinoid system is dysregulated in prostate cancer, suggesting that it has a role in prostate homeostasis. Overexpression of several components of the endocannabinoid system correlate with prostate cancer grade and progression, potentially providing a new therapeutic target for prostate cancer. Moreover, several cannabinoids exert antitumoral properties against prostate cancer, reducing xenograft prostate tumor growth, prostate cancer cell proliferation and cell migration. Although the therapeutic potential of cannabinoids against prostate cancer is very promising, future research using animal models is needed to evaluate the influence of systemic networks in their antitumoral action.