Transient Receptor Potential Ankyrin 1 Receptor Activation In Vitro and In Vivo by Pro-tussive Agents: GRC 17536 as a Promising Anti-Tussive Therapeutic
et al. (2014) Transient Receptor Potential Ankyrin 1 Receptor Activation In Vitro and In Vivo
by Pro-tussive Agents: GRC 17536 as a Promising Anti-Tussive Therapeutic. PLoS ONE 9(5): e97005. doi:10.1371/journal.pone.0097005
Transient Receptor Potential Ankyrin 1 Receptor Activation In Vitro and In Vivo by Pro-tussive Agents: GRC 17536 as a Promising Anti-Tussive Therapeutic
Indranil Mukhopadhyay 0
Abhay Kulkarni 0
Sarika Aranake 0
Pallavi Karnik 0
Mahesh Shetty 0
Sandeep Thorat 0
Indraneel Ghosh 0
Dinesh Wale 0
Vikram Bhosale 0
Neelima Khairatkar-Joshi 0
Stuart E. Dryer, University of Houston, United States of America
0 Biological Research, Glenmark Research Centre, Glenmark Pharmaceuticals Ltd. , Navi Mumbai, Maharashtra , India
Cough is a protective reflex action that helps clear the respiratory tract which is continuously exposed to airborne environmental irritants. However, chronic cough presents itself as a disease in its own right and despite its global occurrence; the molecular mechanisms responsible for cough are not completely understood. Transient receptor potential ankyrin1 (TRPA1) is robustly expressed in the neuronal as well as non-neuronal cells of the respiratory tract and is a sensor of a wide range of environmental irritants. It is fast getting acceptance as a key biological sensor of a variety of pro-tussive agents often implicated in miscellaneous chronic cough conditions. In the present study, we demonstrate in vitro direct functional activation of TRPA1 receptor by citric acid which is routinely used to evoke cough in preclinical and clinical studies. We also show for the first time that a potent and selective TRPA1 antagonist GRC 17536 inhibits citric acid induced cellular Ca+2 influx in TRPA1 expressing cells and the citric acid induced cough response in guinea pigs. Hence our data provides a mechanistic link between TRPA1 receptor activation in vitro and cough response induced in vivo by citric acid. Furthermore, we also show evidence for TRPA1 activation in vitro by the TLR4, TLR7 and TLR8 ligands which are implicated in bacterial/respiratory virus pathogenesis often resulting in chronic cough. In conclusion, this study highlights the potential utility of TRPA1 antagonist such as GRC 17536 in the treatment of miscellaneous chronic cough conditions arising due to diverse causes but commonly driven via TRPA1.
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Cough is a vagally mediated reflex and a primary defensive
mechanism to protect the airway by forceful expulsion of irritant
agents from the respiratory tract. Although a protective response,
sometimes it becomes excessive and harmful to the airway mucosa
leading to compromised quality of life. Cough is broadly divided
into acute and chronic persistent cough [1]. Cough accompanying
acute illnesses generally resolves in few days to few weeks. In
contrast, chronic cough is recognized as a clinical condition and
defined as one that lingers for more than three to eight weeks,
sometimes lasting for months or even years. Despite its wide
prevalence, treatment options for chronic cough are very limited
and often symptomatic. Currently available and most commonly
used treatments such as dextromethorphan, hydrocodone and
codeine are inadequate due to limited efficacy and CNS side
effects or abuse liability [2,3,4]. Their other undesirable side effects
include respiratory depression and gastrointestinal disturbances.
Activation of sensory nerves innervating anatomical regions
implicated in cough reflex, including the larynx, trachea and large
bronchi, by exogenous inhaled or aspirated substances or by
locally produced endogenous biochemical mediators can produce
cough [5]. Miscellaneous peripheral receptors expressed on the
pulmonary C fibers [6,7] and central mechanisms [8] have been
implicated in cough reflex in animals as well as in humans. There
is strong emerging evidence implicating TRPA1 receptor
activation in driving chronic cough. TRPA1 is an irritant sensing ion
channel expressed in the vast majority of vagal nociceptive
Cfibers of the bronchopulmonary region [9]. A large number of in
vitro and in vivo studies have recently established TRPA1 as a major
chemosensory receptor of the airways [10,11,12,13]. Many
environmental irritants known to cause coughing directly activate
TRPA1 receptor further emphasizing the relevance of TRPA1
expression in these respiratory vagal nerves. For example, acrolein
- found in car exhausts, crotonaldehyde - in cigarette smoke, wood
smoke particulate matter etc. are all reported to activate TRPA1
[14,15,16]. TRPA1 is also implicated in cough hypersensitivity
associated with chronic exposure to environmental irritants, such
as in highly polluted areas, or in occupations where workers are
exposed to a number of dangerous irritants on a daily basis.
TRPA1 on sensory nerves detects not only exogenous
environmental agents that may be inhaled, but is also activated by known
endogenous tussive molecules such as PGE2 and bradykinin
produced during t (...truncated)