Effect of N-arachidonoyl-(2-methyl-4-hydroxyphenyl) amine (VDM11), an anandamide transporter inhibitor, on capsaicin-induced cough in mice

Current understanding of Bordetella-induced cough

Typical pathogenic bacteria of the genus Bordetella cause respiratory diseases, many of which are characterized by severe coughing in host animals. In human infections with these bacteria, such as whooping cough, coughing imposes a heavy burden on patients. The pathophysiology of this severe coughing had long been uncharacterized because convenient animal models that reproduce Bordetella-induced cough have not been available. However, rat and mouse models were recently shown as useful for understanding, at least partially, the causative factors and the mechanism of Bordetella-induced cough. Many types of coughs are induced under various physiological conditions, and the neurophysiological pathways of coughing are considered to vary among animal species, including humans. However, the neurophysiological mechanisms of the coughs in different animal species have not been entirely understood, and, accordingly, the current understanding of Bordetella-induced cough is still incomplete. Nevertheless, recent research findings may open the way for the development of prophylaxis and therapeutic measures against Bordetella-induced cough.

A collection of cannabinoid-related negative findings from autaptic hippocampal neurons

Autaptic hippocampal neurons are an architecturally simple model of neurotransmission that express several forms of cannabinoid signaling. Over the past twenty years this model has proven valuable for studies ranging from enzymatic control of endocannabinoid production and breakdown, to CB1 receptor structure/function, to CB2 signaling, understanding 'spice' (synthetic cannabinoid) pharmacology, and more. However, while studying cannabinoid signaling in these neurons, we have occasionally encountered what one might call 'interesting negatives', valid and informative findings in the context of our experimental design that, given the nature of scientific publishing, may not otherwise find their way into the scientific literature. In autaptic hippocampal neurons we have found that: (1) The fatty acid binding protein (FABP) blocker SBFI-26 does not alter CB1-mediated neuroplasticity. (2) 1-AG signals poorly relative to 2-AG in autaptic neurons. (3) Indomethacin is not a CB1 PAM in autaptic neurons. (4) The CB1-associated protein SGIP1a is not necessary for CB1 desensitization. We are presenting these negative or perplexing findings in the hope that they will prove beneficial to other laboratories and elicit fruitful discussions regarding their relevance and significance.

The Mechanism of Pertussis Cough Revealed by the Mouse-Coughing Model

Pertussis, also known as whooping cough, is a contagious respiratory disease caused by the Gram-negative bacterium Bordetella pertussis. This disease is characterized by severe and uncontrollable coughing, which imposes a significant burden on patients. However, its etiological agent and the mechanism are totally unknown because of a lack of versatile animal models that reproduce the cough. Here, we present a mouse model that reproduces coughing after intranasal inoculation with the bacterium or its components and demonstrate that lipooligosaccharide (LOS), pertussis toxin (PTx), and Vag8 of the bacterium cooperatively function to cause coughing. Bradykinin induced by LOS sensitized a transient receptor potential ion channel, TRPV1, which acts as a sensor to evoke the cough reflex. Vag8 further increased bradykinin levels by inhibiting the C1 esterase inhibitor, the major downregulator of the contact system, which generates bradykinin. PTx inhibits intrinsic negative regulation systems for TRPV1 through the inactivation of G_i GTPases. Our findings provide a basis to answer long-standing questions on the pathophysiology of pertussis cough.

[Recent Findings on the Mechanism of Cough Hypersensitivity as a Cause of Chronic Cough]

An increasing number of patients complain to medical institutions about a cough that persists for more than 8 weeks, namely chronic cough. The cough observed in patients with chronic cough is not responsive to conventional antitussive agents such as dihydrocodeine and dextromethorphan, and this is a major clinical problem. The most common pathology of chronic cough in Japan is dry cough. Two causes of dry cough are increased sensitivity of cough receptors (cough hypersensitivity) and increased contraction of bronchial smooth muscle. Among these, the mechanisms of cough hypersensitivity are diverse, and understanding these mechanisms is important for the diagnosis and treatment of chronic cough. In this paper I will review the regulatory mechanisms of cough hypersensitivity, especially the regulation of Aδ fiber excitability by C fibers. Furthermore, the central mechanisms involved cough reflex are discussed in relation to central acting antitussives.

On the Biomedical Properties of Endocannabinoid Degradation and Reuptake Inhibitors: Pre-clinical and Clinical Evidence

The endocannabinoid system (ECS) is composed of endogenous cannabinoids; components involved in their synthesis, transport, and degradation; and an expansive variety of cannabinoid receptors. Hypofunction or deregulation of the ECS is related to pathological conditions. Consequently, endogenous enhancement of endocannabinoid levels and/or regulation of their metabolism represent promising therapeutic approaches. Several major strategies have been suggested for the modulation of the ECS: (1) blocking endocannabinoids degradation, (2) inhibition of endocannabinoid cellular uptake, and (3) pharmacological modulation of cannabinoid receptors as potential therapeutic targets. Here, we focused in this review on degradation/reuptake inhibitors over cannabinoid receptor modulators in order to provide an updated synopsis of contemporary evidence advancing mechanisms of endocannabinoids as pharmacological tools with therapeutic properties for the treatment of several disorders. For this purpose, we revisited the available literature and reported the latest advances regarding the biomedical properties of fatty acid amide hydrolase and monoacylglycerol lipase inhibitors in pre-clinical and clinical studies. We also highlighted anandamide and 2-arachidonoylglycerol reuptake inhibitors with promising results in pre-clinical studies using in vitro and animal models as an outlook for future research in clinical trials.

Anandamide transporter-mediated regulation of the micturition reflex in urethane-anesthetized rats

PURPOSE

The aim of this study was to investigate the effects of an anandamide transporter inhibitor that can increase endogenous anandamide concentration on the micturition reflex in urethane-anesthetized rats.

METHODS

Continuous cystometrograms were performed in female Sprague-Dawley rats under urethane anesthesia. After stable micturition cycles were established, VDM11 (1, 3 and 10 mg/kg), an anandamide membrane transporter inhibitor, was administered intravenously to evaluate changes in bladder activity. In experiments examining the effects of cannabinoid (CB) receptor antagonists, VDM11 (10 mg/kg) was injected intravenously when the first bladder contraction was observed after intravenous administration of AM251, a CB1 receptor antagonist (3 mg/kg), or AM630, a CB2 receptor antagonist (3 mg/kg).

RESULTS

Intravenous administration of VDM11 increased intercontraction intervals and threshold pressure at doses of 3 mg/kg or higher in dose-dependent fashion. When AM251 was administered one voiding cycle before VDM11 administration, the increases in intercontraction intervals and threshold pressure induced by VDM11 administration alone were not seen. In contrast, when AM630 was administered before VDM11 administration, increases in intercontraction intervals and threshold pressure were observed, as they were after VDM11 alone.

CONCLUSION

These results suggest that anandamide, an endogenous CB ligand, can modulate the micturition reflex and that anandamide transporters play an important role in this modulation. In urethane-anesthetized rats, inhibition of the uptake of anandamide can inhibit the micturition reflex and these inhibitory effects of VDM11 are at least in part mediated by the CB1 receptor.

Antitussive drugs--past, present, and future

Cough remains a serious unmet clinical problem, both as a symptom of a range of other conditions such as asthma, chronic obstructive pulmonary disease, gastroesophageal reflux, and as a problem in its own right in patients with chronic cough of unknown origin. This article reviews our current understanding of the pathogenesis of cough and the hypertussive state characterizing a number of diseases as well as reviewing the evidence for the different classes of antitussive drug currently in clinical use. For completeness, the review also discusses a number of major drug classes often clinically used to treat cough but that are not generally classified as antitussive drugs. We also reviewed a number of drug classes in various stages of development as antitussive drugs. Perhaps surprising for drugs used to treat such a common symptom, there is a paucity of well-controlled clinical studies documenting evidence for the use of many of the drug classes in use today, particularly those available over the counter. Nonetheless, there has been a considerable increase in our understanding of the cough reflex over the last decade that has led to a number of promising new targets for antitussive drugs being identified and thus giving some hope of new drugs being available in the not too distant future for the treatment of this often debilitating symptom.

A portable automatic cough analyser in the ambulatory assessment of cough

BACKGROUND

Cough is one of the main symptoms of advanced lung disease. However, the efficacy of currently available treatment remains unsatisfactory. Research into the new antitussives requires an objective assessment of cough.

METHODS

The aim of the study was to test the feasibility of a new automatic portable cough analyser and assess the correlation between subjective and objective evaluations of cough in 13 patients with chronic cough. The patients' individual histories, a cough symptom score and a numeric cough scale (1-10) were used as a subjective evaluation of cough and a computerized audio-timed recorder was used to measure the frequency of coughing.

RESULTS

The pre-clinical validation has shown that an automated cough analyser is an accurate and reliable tool for the ambulatory assessment of chronic cough. In the clinical part of the experiment for the daytime, subjective cough scoring correlated with the number of all cough incidents recorded by the cough analyser (r = 0.63; p = 0.022) and the number of cough incidents per hour (r = 0.60; p = 0.03). However, there was no relation between cough score and the time spent coughing per hour (r = 0.48; p = 0.1). As assessed for the night-time period, no correlation was found between subjective cough scoring and the number of incidents per hour (r = 0.29; p = 0.34) or time spent coughing (r = 0.26; p = 0.4).

CONCLUSION

An automated cough analyser seems to be a feasible tool for the ambulatory monitoring of cough. There is a moderate correlation between subjective and objective assessments of cough during the daytime, whereas the discrepancy in the evaluation of night-time coughing might suggest that subjective analysis is unreliable.

Modulation of sensory nerve function and the cough reflex: understanding disease pathogenesis

To cough is a protective defence mechanism that is vital to remove foreign material and secretions from the airways and which in the normal state serves its function appropriately. Modulation of the cough reflex pathway in disease can lead to inappropriate chronic coughing and an augmented cough response. Chronic cough is a symptom that can present in conjunction with a number of diseases including chronic obstructive pulmonary disease (COPD) and asthma, although often the cause of chronic cough may be unknown. As current treatments for cough have proved to exhibit little efficacy and are largely ineffective, there is a need to develop novel, efficacious and safe antitussive therapies. The underlying mechanisms of the cough reflex are complex and involve a network of events, which are not fully understood. It is accepted that the cough reflex is initiated following activation of airway sensory nerves. Therefore, in the hope of identifying novel antitussives, much research has focused on understanding the neural mechanisms of cough provocation. Experimentally this has been undertaken using chemical or mechanical tussive stimuli in conjunction with animal models of cough and clinical cough assessments. This review will discuss the neural mechanisms involved in the cough, changes that occur under pathophysiological conditions and and how current research may lead to novel therapeutic opportunities for the treatment of cough.

Central mechanisms II: pharmacology of brainstem pathways

Following systemic administration, centrally acting antitussive drugs are generally assumed to act in the brainstem to inhibit cough. However, recent work in humans has raised the possibility of suprapontine sites of action for cough suppressants. For drugs that may act in the brainstem, the specific locations, types of neurones affected, and receptor specificities of the compounds represent important issues regarding their cough-suppressant actions. Two medullary areas that have received the most attention regarding the actions of antitussive drugs are the nucleus of the tractus solitarius (NTS) and the caudal ventrolateral respiratory column. Studies that have implicated these two medullary areas have employed both microinjection and in vitro recording methods to control the location of action of the antitussive drugs. Other brainstem regions contain neurones that participate in the production of cough and could represent potential sites of action of antitussive drugs. These regions include the raphe nuclei, pontine nuclei, and rostral ventrolateral medulla. Specific receptor subtypes have been associated with the suppression of cough at central sites, including 5-HT1A, opioid (mu, kappa, and delta), GABA-B, tachykinin neurokinin-1 (NK-1) and neurokinin-2, non-opioid (NOP-1), cannabinoid, dopaminergic, and sigma receptors. Aside from tachykinin NK-1 receptors in the NTS, relatively little is known regarding the receptor specificity of putative antitussive drugs in particular brainstem regions. Our understanding of the mechanisms of action of antitussive drugs would be significantly advanced by further work in this area.

Cough sensors. II. Transient receptor potential membrane receptors on cough sensors

The transient receptor potential (TRP) family of channels is represented by at least six members in primary sensory neurons. These include the TRP vanilloid subtypes 1 (TRPV1), 2, 3, and 4, the cold and menthol receptor TRPM8, and TRPA1. Much interest has been directed to the study of the TRPV1, because capsaicin has been instrumental in discovering the unique role of a subset of primary sensory neurons in causing nociceptive responses, in activating reflex pathways including cough, and in producing neurogenic inflammation. TRPV1 is now regarded as an integrator of diverse sensory modalities because it undergoes marked plasticity and sensitization through a variety of mechanisms, including activation of G-protein-coupled or tyrosine kinase receptors. Evidence in experimental animals and in patients with airway diseases indicates a marked hypersensitivity to cough induced by TRPV1 agonists. Recent studies with newly developed high-affinity and selective TRPV1 antagonists have revealed that TRPV1 inhibition reduces cough induced by citric acid or antigen challenge.

The endocannabinoid system as an emerging target of pharmacotherapy

The recent identification of cannabinoid receptors and their endogenous lipid ligands has triggered an exponential growth of studies exploring the endocannabinoid system and its regulatory functions in health and disease. Such studies have been greatly facilitated by the introduction of selective cannabinoid receptor antagonists and inhibitors of endocannabinoid metabolism and transport, as well as mice deficient in cannabinoid receptors or the endocannabinoid-degrading enzyme fatty acid amidohydrolase. In the past decade, the endocannabinoid system has been implicated in a growing number of physiological functions, both in the central and peripheral nervous systems and in peripheral organs. More importantly, modulating the activity of the endocannabinoid system turned out to hold therapeutic promise in a wide range of disparate diseases and pathological conditions, ranging from mood and anxiety disorders, movement disorders such as Parkinson's and Huntington's disease, neuropathic pain, multiple sclerosis and spinal cord injury, to cancer, atherosclerosis, myocardial infarction, stroke, hypertension, glaucoma, obesity/metabolic syndrome, and osteoporosis, to name just a few. An impediment to the development of cannabinoid medications has been the socially unacceptable psychoactive properties of plant-derived or synthetic agonists, mediated by CB(1) receptors. However, this problem does not arise when the therapeutic aim is achieved by treatment with a CB(1) receptor antagonist, such as in obesity, and may also be absent when the action of endocannabinoids is enhanced indirectly through blocking their metabolism or transport. The use of selective CB(2) receptor agonists, which lack psychoactive properties, could represent another promising avenue for certain conditions. The abuse potential of plant-derived cannabinoids may also be limited through the use of preparations with controlled composition and the careful selection of dose and route of administration. The growing number of preclinical studies and clinical trials with compounds that modulate the endocannabinoid system will probably result in novel therapeutic approaches in a number of diseases for which current treatments do not fully address the patients' need. Here, we provide a comprehensive overview on the current state of knowledge of the endocannabinoid system as a target of pharmacotherapy.