ppt on vanilloid receptors
TRANSCRIPT
VANILLOID RECEPTORS
Aakrati Gupta
(2011H108048H)
16-04-2012
CONTENTS
Introduction
TRPV1 Structure
TRPV1 Expression
Implications in various disease states
Agonists
Antagonists
TRANSIENT RECEPTOR POTENTIAL
RECEPTORS(TRP)
TRP superfamily
TRPC TRPM TRPV TRPP TRPML TRPA TRPN
6 types(mammals 2 types(non-
mammals)
TRPV1
TRPV2
TRPV6
Osm-9
NanchungTRPV3
TRPV4
TRPV5High Ca2+ selectivity & low temperature
sensitivity
Heat activated receptors & non
selective for cations(also Ca2+)In drosophila
Activated by
vanilloids(capsaicin)
INTRODUCTION
TRP family
TRP channels were initially discovered in trp mutant strain of the fruit fly Drosophila.
It includes > 30 cation channels, the majority of which are permeable for
divalent and monovalent cations, including Ca2+, Na+, and Mg2+.
They have broad tissue distribution and may participate in divergent functions such as:
visual and auditory functions, speech, pain signal transduction,
regulation of blood circulation, gut motility, mineral absorption and fluid balance, airway
and bladder hypersensitivities, cell survival, growth and death.
TRPV1
It is a non-selective cation channel.
in humans, is encoded by the TRPV1 gene
It has been considered as a ‘pathological’ receptor, it has a
significant role in the pain transduction pathway and pro-
inflammatory role in a variety of disease and injury states.
It is activated by capsaicin, the main pungent principle of hot chilli
peppers.
It is a polymodal TRP channel that can be activated by noxious
heat, pH changes, fatty acid amides, and endogenous lipid ligands.
First cloned from rat dorsal root ganglia(DRG).
STRUCTURE OF TRPV1
It is a single polypeptide, 838 amino acid, 95kD.
It has a large intracellular amino-(N-) and carboxy-(C-) terminal and 6
transmembrane segment.
An additional short hydrophobic stretch between TM5 and TM6.
TRPV-1 subunits assemble as tetramers.
N- terminus (432 a.a) has 3 ankyrin repeats(essential for channel
function).
C- terminus(154 a.a) has a TRP domain which serves as a molecular
determinant.
C- terminus has amino acid residues for PIP2 binding
To the N-terminus PKA and PKC binds.
TRPV1 EXPRESSION
Neuronal cells:
small to medium diameter primary afferent fibres.
sensory neurons
Dorsal root ganglia(DRG)
Trigeminal neurons
o Non –neuronal cells:
Keratinocytes, bladder urothelium, smooth muscle, liver, polymorphonuclear granulocytes, pancreatic B cells, endothelial cells, lymphocytes, macrophages
o Brain :
Dopaminergic neurons of substantia nigra, hippocampal pyramidal neurons, hypothalamus.
A-δ myelinated fibres
unmyelinated C fibres
IN NEURONAL CELLS
IN NON NEURONAL CELLS
Location/Cell type Function
Keratinocytes Release of pro-inflammatory
mediator, sensor for noxious
cutaneous stimulation
Bladder urothelial cells Regulation of bladder reflex
contractions
Smooth muscle Vasoconstriction
Cerebromicrovascular
endothelial cells
Contribution to the regulation
of cerebral blood flow and
BBB permeability
polymorphonuclear
granulocytes,
Lymphocytes, macrophages
Possible pro-inflammatory
role, yet the role of TRPV1 on
cells of the
immune system is currently
elusive
Preadipocytes and adipose
tissue
Regulation of adipogensis
PARADOXICAL EFFECTS OF TRPV1
Nociception and pro-inflammatory effects
Diabetic painful
neuropathy
Cancer pain
Peripheral neuropathic
pain
Chronic persistent
cough
osteoarthritis
Rheumatoid arthritis
Faecalincontinence
Oesophagealreflux
disease
cystitis
DIABETIC NEUROPATHY:
Study done in:
STZ induced diabetic rats.
Observations:
TRPV1 protein levels were down-regulated, while the function of
TRPV1 was increased in the DRG neurones isolated from early
diabetic rats.
Also DRG neurons from diabetic rats exhibit increased levels of
oxidative stress in vitro, an effect that is reduced by incubation of
cells with the TRPV1 antagonist, capsazepine.
Conclusion:
early diabetic neuropathy is associated with enhanced function of
TRPV1 in DRG neurones , which may result in compensatory down-
regulation of TRPV1 receptor expression.
PERIPHERAL NEUROPATHIC PAIN
Study done:
total or partial sciatic nerve transection, or spinal nerve ligation.
Observations:
TRPV1 mRNA levels were downregulated in the somata of damaged
sensory neurones.
TRPV1-immunoreactivity was significantly reduced in the somata of
damaged DRG neuronal profiles, compared to controls.
In case of partial transection or spinal nerve ligation, TRPV1
expression was increased in the undamaged DRG somata compared
to controls.
Conclusion:
The persistence of TRPV1 expression in sites close to nerve
injury,although down-regulated in injured nerves, is possibly due to
depletion of growth factors such as NGF in injured nerves.
CANCER PAIN
chronic bone pain(due to bone cancer)or metastases of non-bone
primary tumours as breast, prostate and lung.
osteoclast-induced bone remodelling is accompanied by the robust
production of extracellular protons, which are known to be potent
activators of primary afferent neurones.
acidic microenvironment produced by osteoclasts contributes to bone
cancer-associated pain via activation of acid-sensitive nociceptors
which innervate the marrow and mineralised bone.
Study done in :
osteolytic sarcoma cell-induced-bone cancer model of mice
1. TRPV1 knockout mice,
2. wild-type control mice,
3. with the administration of a selective TRPV1 antagonist.
Int J Cancer 2004;109:182–8.
Observations:
TRPV1 knockout mice and TRPV1 antagonist-treated mice
demonstrated :
-ve ongoing and movement-evoked pain-related behaviour
-ve bone cancer severity
No effect on tumour growth
Conclusions:
3 mechanisms contribute simultaneously to activation and
sensitisation of TRPV1 receptors expressed by sensory fibres
innervating the tumour-bearing joint .
inflammation, tumour-released products and tumour-induced injury to
primary afferent neurones.
ACUTE AND CHRONIC ARTHRITIS:
neuropeptide-containing nerve fibres are present in the knee joint
synovium and adjacent bone.
levels of neuropeptides are significantly increased in samples of
synovial fluid from patients with rheumatoid arthritis.
1.Study done :
CFA-induced hind paw inflammation
Observation:
Myelinated axons were not affected during inflammation.
Conclusion:
an increase in the number of unmyelinated sensory axons
expressing TRPV1 is one of the mechanisms underlying peripheral
sensitisation in inflammation.
2. Study done :
wild-type mice and TRPV1 knockout mice after intra-articular
injection of CFA.
Observation:
knee swelling and vascular hyperpermeability were significantly
higher in the CFA-treated joints of wild-type mice in comparison to
TRPV1 null mice.
No effect on leukocyte accumulation and cytokine production.
thermal hyperalgesia and joint swelling were decreased in TRPV1
knockout mice compared with wild-type controls after intraarticular
injection of mouse recombinant (TNF-α)
Conclusion:
(TNF-α) requires the presence of TRPV1 receptors to function
AIRWAY HYPERSENSITIVITY: number of neuropeptide CGRP containing nerves in the airway
submucosa of patients with chronic persistent cough was shown to be increased.
Also as the cough reflex is mediated by the activation of A-δ fibres, in addition to C-fibres.(TPRV1 present in these)
Study done in:
capsaicin-induced cough in guinea-pigs
Observations:
TRPV1 antagonist, capsazepine, inhibited the capsaicin-induced cough and the endogenous TRPV1 ligand, anandamide, induced coughing.
Conclusion:
The activation of A-δ fibres and C-fibres in the airways of guinea-pigs induced by decreasing pH involves TRPV1 as protons increase the TRPV1 channel function .An increase in the content of protons in exhaled breath condensate in chronic cough
FAECAL INCONTINENCE:
Faecal urgency is a distressing, debilitating disorder in rectal cancer
and IBD.
Rectal sensation is conveyed by the polymodal C-fibres and A-δ
fibres.
in patients suffering from rectal hypersensitivity, the number of
TRPV1-expressing nerve fibres was increased in muscle,
submucosal and mucosal layers of rectal biopsy samples.
OESOPHAGEAL REFLUX DISEASE
some patients perceive oesophageal acid exposure as painful,
suggesting that visceral hyperalgesia may contribute to their
symptoms.
Study:
capsaicin injection into the oesophageal wall resulted in severe
chest pain and heartburn.
Observations:
TRPV1 immunoreactive fibres were increased in patients with
erosive oesophagitis.
increased acid exposure is associated with an increase in the
density of nerve fibres expressing TRPV1.
Protective effects
Ischaemia and reperfusion
injury
Hypertension
Inflammatory bowel disease
Sepsis
Obesity
TRPV1 in CVS and GIT: TRPV1 rich nerves are densely distributed in the CV and GI system.
activation of TRPV1 either by endogenous ligands or by exogenous agonists exert hypotensive /protective effects against these systems injury through stimulating the synthesis and release of NT such as CGRP and substance P.
1.CVS:
Study done in:
isolated rat heart
Observations:
cardioprotection provided by CGRP- or capsaicin-induced preconditioning was abolished by CGRP-(8–37), the selective CGRP receptor antagonist.
Also preconditioning-induced cardiac protection against ischemia–reperfusion
injury was significantly impaired in TRPV1 knockout hearts.
European Journal of Pharmacology 627(2010) 1–7
Conclusion:
Activation of TRPV1 either by endogenous or exogenous ligand
exert beneficial effects against cardiac injury.
TRPV1 gene deletion results in excessive inflammation,
disproportional left ventricular remodeling, and deteriorated cardiac
function after myocardial ischemia, indicating that TRPV1 may
prevent infarct expansion and cardiac injury by inhibiting
inflammation and abnormal tissue remodelling.
2.GIT:
It is rich in TRPV1 nerves, play pivotal role in the maintenance of
gastrointestinal mucosa integrity against injurious interventions.
also found in non-nervous tissue such as gastric epithelial cells,
gastrin cells etc.
Study done in:
TRPV1 knockout mice, isolated human antral glands.
o Observations:
luminal acidification did not activate mechanosensory neurons in
TRPV1 knockout mice.
activation of TRPV1 by capsaicin was able to stimulate the secretion
of gastrin from antral glands.
Conclusion:
TRPV1 exerts multiple physiological functions as acid secretion ,
intestinal motility and visceral sensation to gastrin secretion.
Mechanism of protection: release of NT (CGRP ) and the activation
of cyclooxygenase-1 enzymes(inducing the production of
prostaglandin E2).
NO
DRUG
IN ANXIETY:
TRPV1 is expressed also in the brain, where it seems to be
involved in antinociception, locomotor control, and regulation
of affective behavior.
Model: rats , EPM
Observations:
ANANDAMIDE
CB1 TRPV1
Decrease in intracellular Ca2+ and attenuation of
synaptic transmission Elevated
calcium levels and potentiated synaptic transmission
Endogenous agonist
of CB1 receptor
Neu
roscie
nce 2
04
(20
12
) 18
6–
192
This suggests a tripartite regulatory system with antagonistic effects
of CB1 and TRPV1, which are tied together by the same endogenous
ligand. Such a system may have important implication for the
modulation of behavioural responses
TRPV1 is also present in glutamatergic synapses, but its role in fear
and anxiety is less well explored than that of CB1.
Study :
systemic injection of the TRPV1 antagonist capsazepine in rats in the
EPM test reduced anxiety-like behavior.
Also behavioral analyses of TRPV1 knockout mice(i.e.decreased
anxiety in the EPM , impaired fear expression in response to a tone)
strengthened this notion that TRPV1 affects anxiety diametrically
opposite to CB1.
Conclusion:
Opposite roles of CB1 receptors and TRPV1 channels in synaptic
transmission, fear, and anxiety: whereas activation of CB1 receptors
promotes acute fear adaptation and decreases anxiety, TRPV1
channels exert anxiogenic actions.
TRPV1 AND PARKINSON’S DISORDER
Problem with L-dopa : dyskinesias and psychiatric complications.
Endocannabinoid/endovanilloid system - an important modulator of
basal ganglia functions and its pharmacologic manipulation can be a
therapy to alleviate L-dopa induced dyskinesias.
Study done in:
Male Wistar rats
DA-denervating lesions were performed by unilateral injection of 6-
OHDA.
Two weeks after the lesion, the rats were screened for apomorphine-
induced contralateral rotation to assess the efficacy of the lesion.
Net contralateral turns were calculated by
number of ipsilateral - contralateral rotations.
Only rats displaying more than 300 rotations per 30 min
(corresponding to about 90% depletion of tyrosine hydroxylase
(TH) positive neurons were included in the study.
Exp Neurol. 2007 November ; 208(1): 110–119
daily injection of levodopa + carbidopa for up to 12 days, led to a
gradual development of increasingly severe axial, limb, locomotor
and oro-facial abnormal involuntary movements (AIMs).
Observations:(Catalepsy and AIM score)
Administration of the CB1 agonist WIN 55, attenuated levodopa-
induced axial, limb and oral AIMs dose-dependently via a CB1–
mediated mechanism, it had no effect on locomotive AIMs.
URB597, a potent FAAH inhibitor alone , did not affect AIMs scoring
despite its ability to increase anandamide concentration throughout
the basal ganglia.
As known that anandamide can also bind and activate TRPV1
receptors.
URB597+ TRPV1 antagonist capsazepine- significantly decreased all
AIMs subtypes .
Conclusions :
blockade of TRPV1 receptors unmasks the anti-dyskinetic effects of
FAAH inhibitors.
CB1 and TRPV1 receptors play opposite roles in levodopa-induced
dyskinesias.
TRPV1 AND ALZIEMER’S DISEASE
To investigate both the basal and beta-amyloid peptide impaired cognitive performance of D3R((-/-)) mice, and the role therein of endocannabinoids/endovanilloids.
Study done in :
D3R knock out mice D3R((-/-)) and wild type(WT) mice were divided into 3 groups:
1. Untreated
2. Vehicle
3. beta-amyloid peptide 1-42(BAP).
(TRPV1) antagonist SB366791, were injected intraperitoneally for 11 /7 days.
The retention test was performed 1, 7 and 14 days after the learning trial.
Observations:
D3R((-/-)) mice exhibited a better basal cognitive performance as compared to WT mice , which was reversed by TRPV1 antagonism.
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arm
acol R
es.
20
10
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n;6
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1-6
(TRPV1) antagonist SB366791 did not affect the cognitive
performance of healthy mice, but fully counteracted BAP 1-42-
induced amnesic effects in both D3R((-/-)) and WT mice -when
administered for 11 days
when administered for 7 days, only transiently affected WT mice and
caused more prolonged cognitive ameliorations in D3R((-/-)) mice.
Conclusion :
there is involvement of D3R and TRPV1 in cognitive processes and
the A beta peptides inhibit memory retention in mice through the
involvement of endovanilloids.
Physiological functions
thermoregulation
neurogenesis
Urinary bladder
function
AGONISTS
ANTAGONISTS
EXPRESSION IN RETINA
TRPV1 was detected in astrocytes, blood vessels, microglial cells
and in neurons, indicating that this receptor could be involved in
both visual coding and generating signals to provide retinal
homeostasis.
Int. J. Devl Neuroscience 27 (2009) 709–718