Drugs to suppress cough

Safety and Pharmacokinetics of HRS-2261, a P2X3 Receptor Antagonist, in Healthy Subjects: A Randomized, Double-Blind, Placebo-Controlled Phase 1 Study

BACKGROUND

P2X3 receptor antagonists hold promising potential as a therapeutic option for patients with refractory or unexplained chronic cough, a condition lacking approved therapies. This study assessed the safety, tolerability, and pharmacokinetics (PK) of HRS-2261, a novel selective P2X3 receptor antagonist, in healthy subjects.

METHODS

This randomized, double-blinded, placebo-controlled phase 1 trial of HRS-2261 consisted of three phases: the single ascending dose (SAD) study phase, the food-effect study phase, and the multiple ascending dose (MAD) study phase. In the SAD phase, healthy subjects were randomly assigned to receive a single oral dose of HRS-2261 (25, 100, 200, 400, 800, and 1200 mg) or placebo. Subjects in the 200 mg group of the SAD phase progressed directly to the food-effect phase following safety evaluation. In the MAD phase, healthy subjects were randomized to receive HRS-2261 (50, 200, and 400 mg) or placebo twice daily for 14 consecutive days. The primary endpoints were safety and tolerability.

RESULTS

A total of 62 and 30 subjects were enrolled in the SAD and MAD phases, respectively, with 12 subjects from the SAD phase transitioning to the food-effect phase. The incidence and severity of adverse events (AEs) were not dose dependent, and most AEs were mild except for one moderate AE (epididymitis, which was not related to treatment) in the 400 mg group. Dysgeusia was reported in nine subjects, including two from the SAD phase, one from the food-effect phase, and six from the MAD phase. The median Tmax and geometric mean t1/2 were 0.9-2.0 h and 4.1-8.5 h in the SAD, and 2.0-2.7 h and 4.6-5.0 h on day 14 in the MAD, respectively. Drug exposures in the SAD and MAD phases were both less than dose proportional. The accumulation of the drug was slight with repeated twice-daily dosing. Food-effect study results showed that food intake did not affect the plasma exposure of HRS-2261.

CONCLUSIONS

HRS-2261 demonstrated good tolerability, with a low incidence of dysgeusia. The PK profile was favorable. This study supports further development of HRS-2261 as a potential P2X3 receptor antagonist for chronic cough.

TRIAL REGISTRATION NUMBER

Clinical trials.gov, identifier: NCT05274516. Trial registration date: March 10, 2022.

How We Do It: Managing Cough in Idiopathic Pulmonary Fibrosis

In many studies, more than one-half of patients with idiopathic pulmonary fibrosis (IPF) endorse cough. In IPF (as in other conditions), when chronic, cough may be frustrating and lead to significant impairments in quality of life. In patients with IPF, comorbid conditions such as gastroesophageal reflux can cause or contribute to cough; when stemming from IPF itself, chronic cough likely arises from multiple mechanisms including mechanical and neurosensory changes. In this article, we review our approach at attempting to identify causes of chronic cough in patients with IPF; these include gastroesophageal reflux disease or upper airway cough syndrome and IPF itself. We cursorily summarize the current evidence for the treatment of chronic cough in IPF, briefly review data on the treatment of unexplained chronic cough and extrapolate it to the treatment of refractory cough in IPF, but we focus our attention on our approaches to evaluation and management, recognizing that some may not be supported by a robust cache of data.

Potential therapeutic approaches of microRNAs for COVID-19: Challenges and opportunities

The coronavirus disease 2019 (COVID-19) emerges as current outbreak cause by Novel Severe Acute Respiratory Syndrome Corona Virus-2 (SARS-CoV-2). This infection affects respiratory system and provides uncontrolled systemic inflammatory response as cytokine storm. The main concern about SARS-CoV-2 pandemic is high viral pathogenicity with no specific drugs. MicroRNAs (miRs) as small non-coding RNAs (21–25 ​nt) regulate gene expression. The SARS-CoV-2 encoded-miRs affect human genes that involved in transcription, translation, apoptosis, immune response and inflammation. Also, they alter self-gene regulation and hijacked host miRs that provide protective environment to maintain its latency. On the other hand, Host miRs play critical role in viral gene expression to restrict infection. Over expression/inhibition of miRs might result in cell cycle irregularity, impaired immune response or cancer. In this manner, exact role of each miR should be specified. Mimic encoded-miRs like antagomirs showed successful result in phases of clinical trial prevent from negative effects of viral encoded-miRs. Products of mimic miRs are inexpensive corresponds to synthesis of primer; they are short and nanoscale in size. Although SARS-CoV-2 genome is undergoing evaluation, detection of exact molecular pathogenesis open up opportunities to for vaccine development. Salivaomics can evaluate SARS-CoV-2 genome, transcriptome, proteome and biomarkers like miRs in oral related and cancer disease. In this review, we studied the challenge and opportunities of miRs in therapeutic approach for SARS-CoV-2 infection, then overviewed the role of miRs in saliva droplet during SARS-CoV-2 infection and related cancer.

The Prediction of miRNAs in SARS-CoV-2 Genomes: hsa-miR Databases Identify 7 Key miRs Linked to Host Responses and Virus Pathogenicity-Related KEGG Pathways Significant for Comorbidities

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) is a member of the betacoronavirus family, which causes COVID-19 disease. SARS-CoV-2 pathogenicity in humans leads to increased mortality rates due to alterations of significant pathways, including some resulting in exacerbated inflammatory responses linked to the “cytokine storm” and extensive lung pathology, as well as being linked to a number of comorbidities. Our current study compared five SARS-CoV-2 sequences from different geographical regions to those from SARS, MERS and two cold viruses, OC43 and 229E, to identify the presence of miR-like sequences. We identified seven key miRs, which highlight considerable differences between the SARS-CoV-2 sequences, compared with the other viruses. The level of conservation between the five SARS-CoV-2 sequences was identical but poor compared with the other sequences, with SARS showing the highest degree of conservation. This decrease in similarity could result in reduced levels of transcriptional control, as well as a change in the physiological effect of the virus and associated host-pathogen responses. MERS and the milder symptom viruses showed greater differences and even significant sequence gaps. This divergence away from the SARS-CoV-2 sequences broadly mirrors the phylogenetic relationships obtained from the whole-genome alignments. Therefore, patterns of mutation, occurring during sequence divergence from the longer established human viruses to the more recent ones, may have led to the emergence of sequence motifs that can be related directly to the pathogenicity of SARS-CoV-2. Importantly, we identified 7 key-microRNAs (miRs 8066, 5197, 3611, 3934-3p, 1307-3p, 3691-3p, 1468-5p) with significant links to KEGG pathways linked to viral pathogenicity and host responses. According to Bioproject data (PRJNA615032), SARS-CoV-2 mediated transcriptomic alterations were similar to the target pathways of the selected 7 miRs identified in our study. This mechanism could have considerable significance in determining the symptom spectrum of future potential pandemics. KEGG pathway analysis revealed a number of critical pathways linked to the seven identified miRs that may provide insight into the interplay between the virus and comorbidities. Based on our reported findings, miRNAs may constitute potential and effective therapeutic approaches in COVID-19 and its pathological consequences.

An update and systematic review on drug therapies for the treatment of refractory chronic cough

INTRODUCTION

Chronic Cough (CC) is common and often associated with significant comorbidity and decreased quality of life. In up to 50% of cases, the cough is refractory despite extensive investigation and treatment trials. It is likely that the key abnormality in refractory CC is dysfunctional, hypersensitive sensory nerves, similar to conditions such as laryngeal hypersensitivity and neuropathic pain.

AREAS COVERED

The aim of this systematic review is to assess drug therapies for refractory CC. The authors review the current management of CC and provide discussion of the similarities between neuropathic pain and refractory CC. They review repurposed and new pharmacological treatments. Several meta-analyses were performed to compare the efficacy of treatments where possible.

EXPERT OPINION

Repurposed pain medications such as gabapentin and pregabalin reduce the frequency of cough and improve quality of life. Along with speech pathology, they are important and alternate treatments for refractory CC. However, more treatments are needed and the P2X3 ion channel receptor antagonists show the most promise. With a better understanding of neuronal activation and sensitisation and their signal processing in the brain, improved animal models of cough, and the use of validated cough measurement tools, more effective treatments will develop.

The possible mode of antitussive and expectorant activity of the ethanol seed extracts of Picralima nitida ((Stapf) Th. & H. Durand)

It has been established that Picralima nitida has antitussive effect. This study therefore aimed at determining the possible mode of antitussive and expectorant activity of an ethanolic seed extract of P. nitida (PNE). The muco-suppressant, mast cell stabilization, and the anxiolytic effects of PNE were ascertained using ammonium chloride-induced phenol red secretion in BALB/c mice; compound 48/80-induced mesenteric mast cell degranulation assay; and the open field and the elevated plus maze models respectively. Antibacterial potential was ascertained by the agar plate diffusion method and its antioxidant potential by the 2,2-diphenyl-1-picrylhydrazyl hydrate (DPPH) free radical scavenging, linoleic acid lipid peroxidation, reducing power, and total antioxidant assays. Data obtained was analyzed using One-way analysis of variance (ANOVA) with Dunnett's Multiple Comparison post hoc test. PNE (100-500 mg/kg) reduced (P ≤ 0.05-0.001) tracheal phenol red secretion. The extract (100-500 μg/ml) also dose-dependently (P ≤ 0.05-0.0001) stabilized mast cells. PNE (100-500 mg/kg) increased open arm activities in the elevated plus maze (P ≤ 0.05) as well as central zone exploration (P ≤ 0.05) in the open field test. PNE (10-50 mg/ml) showed activity against Staphylococcus aureus, Streptococcus pneumonia, Escherichia coli, Klebsiella pneumonia, and Salmonella typhi. By the assays, PNE showed significant antioxidant effect. The ethanolic seed extract of P. nitida has demonstrated very significant mast cell stabilizing, mucus suppressant, and antioxidant activity as well as substantial antibacterial and anxiolytic properties; all of which could contribute to its antitussive and expectorant property.

Antitussive activity of the Schisandra chinensis fruit polysaccharide (SCFP-1) in guinea pigs models

ETHNOPHARMACOLOGICAL RELEVANCE

Schisandra chinensis (Turcz.) Baill. (S. chinensis), locally known as "Wuweizi", has been used in the treatment of chronic cough as prescription medications of Traditional Chinese Medicine for thousands of years. However, the components of antitussive activity of S. chinensis and the mechanism are poorly understood.

AIM OF THE STUDY

This study aims to investigate the antitussive activity of polysaccharides extracted from S. chinensis.

MATERIALS AND METHODS

S. chinensis fruit polysaccharide-1 (SCFP-1) was extracted by 95% ethanol and distilled water successively, and then the water extraction was isolated with chromatographic columns. The preliminary characterization of SCFP-1 was analyzed by gel permeation chromatography (GPC), gas chromatography-mass spectrometry (GC-MS) and some other recognized chemical methods. Antitussive potential of SCFP-1 was estimated at dose of 250, 500, and 1000mg/kg respectively by peroral administration in a guinea pigs model with cough hypersensitivity induced by cigarette smoke (Chronic cough model) or acute cough guinea model induced by citric acid (Acute cough model). Also, the time-dependent antitussive effect of SCFP-1 were evaluated with acute cough model, and compared with codeine.

RESULTS

The molecular of SCFP-1 was 3.18×10⁴Da, mainly being composed of glucose and arabinose (66.5% and 29.4%, respectively). Peroral administration of SCFP-1 at 250, 500, and 1000mg/kg showed remarkable suppressive effects respectively on cough in both of chronic cough model and acute cough model. Meanwhile, inflammatory cell in BALF and some typical characteristics of nonspecific airway inflammation in animals exposed to CS was significantly attenuated after pretreatment with SCFP-1. The cough suppression of SCFP-1 (500 mg/kg) stablly lasted during the whole 5 h of time-dependent experiment, while no positive effect was observed after 300 min of oral administration of codeine.

CONCLUSIONS

SCFP-1 is one of the antitussive components of S. chinensis.

Effects of ipratropium on exercise-induced cough in winter athletes: a hypothesis-generating study

BACKGROUND

Exercise-induced cough (EIC) is frequently reported by winter athletes, but this symptom is not always associated with exercise-induced bronchoconstriction (EIB). The aims of this study were to determine if EIC can be inhibited or reduced with the inhalation of ipratropium, and if EIC in winter athletes is associated with EIB.

METHODS

On 2 visits, 24 cross-country skiers (10 males and 12 females, mean age 17 ± 3 years) performed an outdoor exercise in the winter (30-minute warm-up, followed by a 3-minute sprint), randomly preceded by the inhalation of ipratropium or a placebo. A spirometry was done at baseline and 20 minutes after inhalation of ipratropium or placebo. Exercise was then performed, followed by the measurement of forced expiratory volume in 1 second and the recording of the number of coughs until 60 minutes after exercise. Before and after exercise, the perception of cough intensity was evaluated using a modified Borg scale.

RESULTS

Twelve of 16 athletes who completed the study (75%) were symptomatic following exercise with placebo (number of coughs ≥ 5), but none developed EIB. For these athletes, the number of coughs after exercise (mean number of coughs ± standard deviation: placebo, 26 ± 14; ipratropium, 25 ± 23; P value, nonsignificant) and the maximal perception score for cough intensity (mean Borg score ± standard deviation: placebo, 1.9 ± 1.2; ipratropium, 2.0 ± 1.1; P value, nonsignificant) were not significantly different between ipratropium and placebo. A decrease in the number of coughs was observed in 6 of the symptomatic athletes and an increase was observed in the other 6, resulting in a nonsignificant mean effect.

CONCLUSIONS

Ipratropium does not appear to significantly influence the number and the perception of cough following exercise. Moreover, these results suggest that EIC is not mainly associated with EIB. However, a subgroup of athletes seems to show a beneficial response to ipratropium, suggesting different cough responses in this population.

Is opiate action in cough due to sedation?

OBJECTIVES

Opiates have been used for cough suppression for centuries. It is unclear whether this antitussive action is due to their known sedative effects. We aimed to assess correlation between cough suppression and opiate usage.

METHODS

We performed a post hoc analysis of two published trials with three opioids. In study one, patients with chronic cough were treated with 4 weeks of modified release morphine sulphate (5 mg twice daily) or placebo in a double-blinded placebo-controlled fashion. Cough suppression was assessed subjectively by the Leicester Cough Questionnaire and objectively by citric acid aerosol (CAA) induced cough challenge. In study 2, normal volunteers were given single doses of placebo, codeine 30 mg or dextromethorphan 50 mg and cough suppression assessed using the CAA-induced cough challenge. Sedation was contemporaneously assessed by direct questioning.

RESULTS

There were 14 episodes of patient-reported sedation; 2 with modified release morphine sulphate, 9 with codeine and 3 with dextromethorphan. There was no correlation between change in the Leicester Cough Questionnaire or the CAA-induced cough challenge and reported sedation.

CONCLUSION

This observational study suggests that sedation is unlikely to underlie the antitussive properties of these opioids. Eliciting the mechanism of these medications in cough may be a target for future tailored drug development.

Identification of both GABAA receptors and voltage-activated Na(+) channels as molecular targets of anticonvulsant α-asarone

Alpha (α)-asarone, a major effective component isolated from the Chinese medicinal herb Acorus tatarinowii, is clinically used as medication for treating epilepsy, cough, bronchitis, and asthma. In the present study, we demonstrated that α-asarone targets central nervous system GABAA receptor as well as voltage-gated Na(+) channels. Using whole-cell patch-clamp recording, α-asarone inhibited spontaneous firing of output neurons, mitral cells (MCs), in mouse olfactory bulb brain slice preparation and hyperpolarized the membrane potential of MCs. The inhibitory effect of α-asarone persisted in the presence of ionotropic glutamate receptor blockers but was eliminated after adding a GABAA receptor blocker, suggesting that GABAA receptors mediated the inhibition of MCs by α-asarone. This hypothesis was supported by the finding that α-asarone evoked an outward current, but did not influence inhibitory postsynaptic currents (IPSCs). In addition to inhibiting spontaneous firing, α-asarone also inhibited the Nav1.2 channel, a dominant rat brain Na(+) channel subtype. The effects of α-asarone on a defined Nav1.2 were characterized using transfected cells that stably expressed the Nav1.2 channel isoform. α-Asarone displayed strong tonic inhibition of Nav1.2 currents in a concentration- and membrane potential-dependent fashion. α-Asarone reduced channel availability in steady-state inactivation protocols by enhancing or stabilizing Na(+) channel inactivation. Both Na(+) channel blockade and activation of GABAA receptors provide a possible mechanism for the known anti-epileptic effects of α-asarone. It also suggests that α-asarone could benefit patients with cough possibly through inhibiting a Na(+) channel subtype to inhibit peripheral and/or central sensitization of cough reflexes.

CRAC ion channels and airway defense reflexes in experimental allergic inflammation

Calcium release-activated calcium channels (CRAC) play unambiguous role in secretory functions of mast cells, T cells, and eosinophils. Less knowledge exists about the role of CRAC, widely distributed in airway smooth muscle (ASM) cells, in airway contractility. The presented study seeks to determine the possible participation of CRAC in ASM-based inflammatory airway disorders in guinea pigs. The acute and long-term administration (14 days) of the CRAC antagonist 3-fluoropyridine-4-carboxylic acid was used to examine the ASM contractility and associated reflexes in the guinea pig model of allergic airway inflammation by the following methods: (i) evaluation of specific airway resistance in vivo; (ii) evaluation of the contractile response of isolated ASM strips in vitro; and (iii) citric acid-induced cough reflex; (iv) measurement of exhaled NO levels (E(NO)). Allergic airway inflammation was induced by repetitive exposure of guinea pigs to ovalbumin (10(-6) M). The CRAC antagonist administered in a single dose to guinea pigs with confirmed allergic inflammation significantly reduced the cough response and the airway resistance, which corresponded with the findings in vitro. Long-term application of the CRAC antagonist had more strongly expressed effects. The results confirm the role of CRAC in the pathophysiology of experimental animal asthma and have a potential meaning for anti-asthma therapy.

Where are the new cough treatments: a debriefing of recent clinical proof-of-concept trials with the NOP agonist SCH 486757

Cough continues to be one of the top reasons why patients seek medical attention from health care providers. The prescription antitussive market is dominated by opioids, such as codeine that produces inconsistent efficacy and is often accompanied by significant side effect liabilities. Consequently, cough represents an unmet medical need and an underserved market. Yet, against the backdrop of increasing cough research, the development of novel treatments has been exceptionally challenging with dextromethorphan being the last US drug approved for cough almost a half century ago. We support the position that an unambiguous and actionable 'road map' that clearly delineates the pathway forward for new cough suppressants from basic research to and beyond clinical proof-of-concept studies will be an important aspect for future success of this pharmacological class of drug. Pivotal to the establishment of such a road map will be the review of lessons learned from antitussive agents that have been recently progressed to proof-of-concept trials. In the present commentary, we briefly discuss observations and challenges pertaining to SCH 486757, a selective orally active NOP agonist that has recently advanced to human antitussive testing.

Functional characterization of a novel benzylisoquinoline O-methyltransferase suggests its involvement in papaverine biosynthesis in opium poppy (Papaver somniferum L)

The benzylisoquinoline alkaloids are a highly diverse group of about 2500 compounds which accumulate in a species-specific manner. Despite the numerous compounds which could be identified, the biosynthetic pathways and the participating enzymes or cDNAs could be characterized only for a few selected members, whereas the biosynthesis of the majority of the compounds is still largely unknown. In an attempt to characterize additional biosynthetic steps at the molecular level, integration of alkaloid and transcript profiling across Papaver species was performed. This analysis showed high expression of an expressed sequence tag (EST) of unknown function only in Papaver somniferum varieties. After full-length cloning of the open reading frame and sequence analysis, this EST could be classified as a member of the class II type O-methyltransferase protein family. It was related to O-methyltransferases from benzylisoquinoline biosynthesis, and the amino acid sequence showed 68% identical residues to norcoclaurine 6-O-methyltransferase. However, rather than methylating norcoclaurine, the recombinant protein methylated norreticuline at position seven with a K(m) of 44 mum using S-adenosyl-l-methionine as a cofactor. Of all substrates tested, only norreticuline was converted. Even minor changes in the benzylisoquinoline backbone were not tolerated by the enzyme. Accordingly, the enzyme was named norreticuline 7-O-methyltransferase (N7OMT). This enzyme represents a novel O-methyltransferase in benzylisoquinoline metabolism. Expression analysis showed slightly increased expression of N7OMT in P. somniferum varieties containing papaverine, suggesting its involvement in the partially unknown biosynthesis of this pharmaceutically important compound.

Addictive evaluation of cholic acid-verticinone ester, a potential cough therapeutic agent with agonist action of opioid receptor

AIM

The purpose of this work was to search for potential drugs with potent antitussive and expectorant activities as well as a low toxicity, but without addictive properties. Cholic acid-verticinone ester (CA-Ver) was synthesized based on the clearly elucidated antitussive and expectorant activities of verticinone in bulbs of Fritillaria and different bile acids in Snake Bile. In our previous study, CA-Ver showed a much more potent activity than codeine phosphate. This study was carried out to investigate the central antitussive mechanism and the addictive evaluation of CA-Ver.

METHODS

Testing on a capsaicin-induced cough model of mice pretreated with naloxone, a non-selective opioid receptor antagonist, was performed for the observation of CA-Ver's central antitussive mechanism. We then took naloxone-induced withdrawal tests of mice for the judgment of CA-Ver's addiction. Lastly, we determined the opioid dependence of CA-Ver in the guinea pig ileum.

RESULTS

The test on the capsaicin-induced cough model showed that naloxone could block the antitussive effect of CA-Ver, suggesting the antitussive mechanism of CA-Ver was related to the central opioid receptors. The naloxone-urged withdrawal tests of the mice showed that CA-Ver was not addictive, and the test of the opioid dependence in the guinea pig ileum showed that CA-Ver had no withdrawal response.

CONCLUSION

These findings suggested that CA-Ver deserved attention for its potent antitussive effects related to the central opioid receptors, but without addiction, and had a good development perspective.

Possible mechanisms of dose-dependent cough suppressive effect of Althaea officinalis rhamnogalacturonan in guinea pigs test system

The rhamnogalacturonan, isolated from the roots of medicinal plant Althaea officinalis L., showed various biological effects on the citric acid-induced cough reflex and reactivity of airways smooth muscle in vitro and in vivo conditions. It possessed dose-dependent cough suppression effect comparable with opioid agonist codeine. However, reactivity of the airways smooth muscle, measured in vitro as well as in vivo conditions was not significantly affected by rhamnogalacturonan and thus bronchodilatory activity did not participate in the cough suppression effect of polysaccharide tested. Moreover, the cough suppression effect of the polymer was not significantly modified by pretreatment of K(+)(ATP) ion channels with selective antagonist and therefore activation of this type of ion channels is not involved in the mechanism of rhamnogalacturonan cough suppressive ability. On the contrary, pretreatment of animals with selective 5-HT(2) receptors antagonist significantly decreased rhamnogalacturonan antitussive efficacy. From this point of view it seems that the cough suppression effect of the polymer is associated with the serotonergic 5-HT(2) receptor's function.

Cough sensors. III. Opioid and cannabinoid receptors on vagal sensory nerves

Cough is a persistent symptom of many inflammatory airways' diseases. Cough is mediated by receptors sited on sensory nerves and then through vagal afferent pathways, which terminate in the brainstem respiratory centre. Cough is often described as an unmet clinical need. Opioids are the only prescription-based antitussives currently available in the UK. They possess limited efficacy and exhibit serious unwanted side effects, such as physical dependence, sedation, respiratory depression and gastrointestinal symptoms. There are three classical opioid receptors: the mu, kappa and delta receptors. Peripheral opioid receptors are sited on sensory nerves innervating the airways. A greater understanding of the role of the peripheral and centrally sited opioid receptors is necessary to allow the development of targeted treatments for cough. Because of the limited efficacy and the side-effect profile of the opioids, potential new treatments are sought to alleviate cough. One class of compounds that is currently under examination is the cannabinoids. Like the opioids, cannabinoids have peripheral and centrally sited receptors and also suffer from the blight of unwanted centrally mediated side effects such as sedation, cognitive dysfunction, tachycardia and psychotropic effects. Two cannabinoid receptors have been identified, the CB(1) and CB(2) receptors, and their distribution varies throughout the peripheral and central nervous system. Encouragingly, early studies with these compounds suggest that it may be possible to separate their antitussive activity from their centrally mediated side effects, with CB(2) agonists showing potential as putative new treatments for cough. In this chapter, we describe the opioid and cannabinoid receptors, their distribution and the effects they mediate. Moreover, we highlight their potential advantages and disadvantages in the treatment of cough.

Multifunctional drugs for head injury

Traumatic brain injury (TBI) remains one of the leading causes of mortality and morbidity worldwide in individuals under the age of 45 years, and, despite extensive efforts to develop neuroprotective therapies, there has been no successful outcome in any trial of neuroprotection to date. In addition to recognizing that many TBI clinical trials have not been optimally designed to detect potential efficacy, the failures can be attributed largely to the fact that most of the therapies investigated have been targeted toward an individual injury factor. The contemporary view of TBI is that of a very heterogenous type of injury, one that varies widely in etiology, clinical presentation, severity, and pathophysiology. The mechanisms involved in neuronal cell death after TBI involve an interaction of acute and delayed anatomic, molecular, biochemical, and physiological events that are both complex and multifaceted. Accordingly, neuropharmacotherapies need to be targeted at the multiple injury factors that contribute to the secondary injury cascade, and, in so doing, maximize the likelihood of a successful outcome. This review focuses on a number of such multifunctional compounds that have shown considerable success in experimental studies and that show maximum promise for success in clinical trials.

Clinical cough VI: the need for new therapies for cough: disease-specific and symptom-related antitussives

Cough is a common symptom that can be self-limiting or persistent. Ideally, treatment of the underlying cause(s) of cough with specific treatments should eliminate cough. This approach may not be successful if no cause can be established or if the treatment of the cause fails. Suppression of cough may be disease-specific or symptom-related. There has been a long tradition in acute cough usually due to upper respiratory tract infections to use symptom-related antitussives. In chronic cough, suppression of cough may be achieved by disease-specific therapies, but in many patients it may be necessary to use symptomatic antitussives. The efficacy of some over-the-counter symptomatic antitussives is often no better than that of a placebo. Currently available cough suppressants include the centrally acting opioids such as morphine, codeine, pholcodeine, and dextromethorphan. Early studies reported success in reducing cough in patients with chronic bronchitis or chronic obstructive pulmonary disease (COPD); however, a carefully conducted blinded controlled study showed no effect of codeine on cough of COPD. Success with these cough suppressants may be achieved at high doses that are associated with side effects. A slow-release preparation of morphine has been shown to have some degree of efficacy, but this should be reserved for the most severe chronic cough patient, and for patients with terminal cancer who may also benefit from its analgesic effects. There are case reports of the success of centrally acting drugs such as amitriptyline, paroxetine, gabapentin, and carbamezepine in chronic cough. New agents derived from basic research such as new opioids such as nociceptin or antagonists of transient receptor potential vanniloid-1 may turn out to have antitussive effects. Efficacy of symptomatic cough suppressants must be tested in double-blind randomized trials using validated measures of cough in patients with chronic cough not responding to specific treatments. Patients with chronic cough need effective antitussives that could be used either on demand or on a long-term basis.

Clinical cough V: complementary and alternative medicine: therapy of cough

We review the actions of complementary and alternative medicines (CAMs) in the treatment of cough and of the conditions associated with it; in particular asthma and upper respiratory tract infections. These therapies may work (1) peripherally, at the sites in the airways and lungs at which cough is being activated, (2) in the brainstem, where the neural "cough center" is situated, or (3) at the cerebral cortex, where cough can be initiated, suppressed or modified by conscious or unconscious controls. Of the large number of trials of CAMs against cough, most are inadequate in design. It may be difficult to randomize selection. Blinding is often impossible both for the patient and the therapist, and adequate placebo controls may be difficult to devise. The patient can usually identify the "active" treatment by the taste or smell of a medicine, or from the approach and apparatus being used. Pure chemicals can be extracted from many of the herbs used as antitussives, and can be shown to be effective in randomized, blind, and controlled trials, but it does not follow that the herb itself, used in the recommended formula and shown to be antitussive, acts by this agency unless a placebo effect is ruled out. A few herbs are identified where the evidence points to a true antitussive action. Of nonherbal treatments, the few positive results are usually outweighed by the larger number of negative ones. Thus, in general, CAMs for cough are welcomed enthusiastically by the patient but lack sound evidence for their efficacy. Antitussive chemicals can be extracted from many herbs, but it is no more than a reasonable hypothesis that the herb itself acts through this pathway.

Management of chronic cough

Cough that remains unexplained after basic clinical assessment is a common reason for referral to secondary care. Much of the evidence about management of isolated chronic cough is derived from case series; this evidence suggests that isolated chronic cough is usually due to asthma, gastro-oesophageal reflux disease, and upper airway conditions, and that it can be cured in most people by treatment of these conditions. However, there is increasing recognition that satisfactory control of chronic cough is not achieved in a substantial number of patients seen in secondary care. Moreover, there is a concern that perpetuation of the belief that chronic cough is solely due to the effects of comorbid conditions is inhibiting research into the pathophysiology of an abnormally heightened cough reflex, and jeopardising development of improved treatments. We advocate a change in emphasis, which makes a clear distinction between cough due to corticosteroid-responsive eosinophilic airway diseases and corticosteroid-resistant non-eosinophilic cough. We recommend that some factors with weak evidence of an association with cough are best viewed as potential aggravating factors of an intrinsic abnormality of the cough reflex, rather than the cause. We call for more research into the basic mechanisms and pharmacological control of an abnormally heightened cough reflex, and recommend ways to assess the effects of potentially antitussive treatments.

Chronic cough: future directions in chronic cough: mechanisms and antitussives

Cough is an important defensive reflex of the respiratory tract needed to clear and protect the upper airways; however, it may become exaggerated and interfere with quality of life. Although chronic cough may be successfully treated when associated with the common causes such as asthma and eosinophilic bronchitis, gastrooesophageal reflux disease and post-nasal drip syndrome or rhinosinusitis, increasingly, idiopathic cough or cough with no associated cause is recognised. Chronic cough is often associated with an increased response to tussive agents such as capsaicin, used as an index of the cough reflex. Some airway receptors mediate or influence cough through activation of vagal afferent pathways which converge on brain stem respiratory networks and of supramedullary centres. Plastic changes in intrinsic and synaptic excitability at the brain stem, spinal or ganglionic level may be the mechanism by which the cough reflex is enhanced in chronic cough. Subjective and objective measurements of cough in the clinic are now available but a major unmet need in chronic cough is the availability of effective antitussives. Future directions in chronic cough include the pathophysiological mechanisms of the enhanced cough reflex, and the discovery of effective antitussives that can successfully alleviate chronic cough.

Inhibition of citric acid- and capsaicin-induced cough by novel TRPV-1 antagonist, V112220, in guinea-pig

BACKGROUND

Cough reflex can be induced by the pepper extract capsaicin and by low pH in guinea-pig airways. Transient receptor potential vanniloid-1 (TPRV-1) is expressed in the sensory and afferent nerve fibres in airways.

OBJECTIVE

We hypothesized that a novel pyridazinylpiperazine analog TPRV-1 inhibitor can effectively reduce cough reflex stimulated by citric acid and capsaicin.

METHODS

Guinea pigs were injected with specific TPRV-1 inhibitor, V112220, a pyridazinylpiperazine analog of N-(4-tertiarybutylphenyl)-4-(3-chloropyridin-2-yl) tetrahydropyrazine-1(2H)-carbox-amide (BCTC) (3 mg/kg) intra-peritoneally. One hour before cough response assessment. Coughs were recorded using a recorder system that identified cough sound and accompanying expiratory flows, distinct from sneezes. Guinea-pigs exposed to citric acid (0.4 M) and to capsaicin (10-4M) aerosols, in succession separately by 2 hours.

RESULTS

V112220 significantly inhibited the number of coughs induced by citric acid (73 +/- 11%, p < 0.01) and capsaicin (70 +/- 9.4%, p < 0.05) compared to vehicle control.

CONCLUSION

A novel pyridazinylpiperazine analog TPRV-1 inhibitor can inhibit the cough reflex, induced by both low pH and capsaicin, suggesting that it could be clinically beneficial in treatment of cough.

The pharmacology of Ro 64-6198, a systemically active, nonpeptide NOP receptor (opiate receptor-like 1, ORL-1) agonist with diverse preclinical therapeutic activity

The NOP receptor (formerly referred to as opiate receptor-like 1, ORL-1, LC132, OP(4), or NOP(1)) is a G protein-coupled receptor that shares high homology to the classic opioid MOP, DOP, and KOP (mu, delta, and kappa, respectively) receptors and was first cloned in 1994 by several groups. The NOP receptor remained an orphan receptor until 1995, when the endogenous neuropeptide agonist, known as nociceptin or orphanin FQ (N/OFQ) was isolated. Five years later, a group at Hoffmann-La Roche reported on the selective, nonpeptide NOP agonist Ro 64-6198, which became the most extensively published nonpeptide NOP agonist and a valuable pharmacological tool in determining the potential of the NOP receptor as a therapeutic target. Ro 64-6198 is systemically active and achieves high brain penetration. It has subnanomolar affinity for the NOP receptor and is at least 100 times more selective for the NOP receptor over the classic opioid receptors. Ro 64-6198 ranges from partial to full agonist, depending on the assay. Preclinical data indicate that Ro 64-6198 may have broad clinical uses, such as in treating stress and anxiety, addiction, neuropathic pain, cough, and anorexia. This review summarizes the pharmacology and preclinical data of Ro 64-6198.

Opiate therapy in chronic cough

RATIONALE

Cough is the most common complaint for which medical attention is sought, and chronic cough can be both physically and mentally debilitating. There is currently no evidence supporting the use of antitussives in chronic treatment-resistant cough.

OBJECTIVES

We tested the hypothesis that morphine sulfate in the dose of 5 mg twice daily would bring about a reduction in cough frequency and severity in patients failing to respond to specific measures.

METHODS

Patients recruited from the Hull Cough Clinic were enrolled into a randomized double-blind placebo-controlled study using 4 weeks of slow-release morphine sulfate and a corresponding period of matched placebo. An open-labeled extension of the core study allowed dose escalation to 10 mg twice daily. Cough was assessed using the Leicester Cough Questionnaire, daily symptom diary, and citric acid cough challenge.

RESULTS

Twenty-seven patients completed the core study. A significant improvement of 3.2 points over baseline was noted on the Leicester Cough Questionnaire (p < 0.01). A rapid and highly significant reduction by 40% in daily cough scores was noted among patients on slow-release morphine sulfate (p < 0.01). Objective testing of the cough reflex using citric acid cough challenge tests did not show any significant changes. Eighteen patients continued into the extension study. Two-thirds of these patients opted to increase the morphine to 10 mg twice daily. At the end of 3 months, there was a similar improvement in cough between the 5- and 10-mg groups.

CONCLUSION

Morphine sulfate is an effective antitussive in intractable chronic cough at the doses of 5 to 10 mg twice daily.

Effective antitussives for the cough patient: an unmet need

Chronic cough is a prevalent symptom in the community but it is likely that only a small fraction of chronic coughers seek medical attention. Chronic cough can be controlled by addressing the 'cause' of the cough, but not all cough is controlled using this approach; an 'idiopathic' cough or cough of unknown aetiology is becoming more well-recognized. In these patients and in those whose cough has not responded to treatment of the cause(s), there is a lack of efficacious antitussive therapies ('non-specific' antitussives). Even in those whose cough is controlled by treatment of the cause, an efficacious antitussive for symptomatic relief would be useful for breakthrough symptoms. It is necessary to address the mechanisms underlying chronic cough, particularly the process of sensitization, both peripherally and centrally, that is the basis of chronic cough; such a process may persist even in the absence of the initiating event that first induced the cough. Currently-available antitussives in both acute and chronic cough are not very effective. Novel targets that may result in effective antitussives have been identified and with the development of clinical tools to measure cough accurately and reliably (e.g. cough counts and cough-specific quality-of-life questionnaires) and the evoked cough response (e.g. citric acid or capsaicin challenges), clinical trials should be performed. The chronic cough population is clinically heterogeneous but is characterized by an enhanced cough reflex; this should be the target population for study. Patients with chronic cough are in desperate need of effective antitussives that can be used either on demand or on a long-term basis.