PCTH 400

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PCTH 400 Asthma Dr Darryl Knight Canada Research
Chair in Airway Disease Professor of
Pharmacology James Hogg iCAPTURE centre, St.
Pauls Hospital dknight_at_mrl.ubc.ca
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Why is asthma a hot topic?

• Asthma is still common, increasing, and expensive
  inflammation/remodeling starts in early
  childhood
• Testable hypothesis that CD4 Th2 lymphocytes
  associated with asthma (Th1/Th2 hypothesis)
  Hygiene Hypothesis role of eosinophils, etc
• There is no cure. Treatment relieves symptoms.
• Is a primary focus of pharma because of its
  chronicity.

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Worldwide Variation in Prevalence of Asthma
Symptoms International Study of Asthma and
Allergies in Children (ISAAC) Lancet
19983511225
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Asthma is a Progressive Lung Disease
Adults with severe asthma continue to show
progressive declines in FEV1, especially if their
asthma began in childhood.
Duration of Asthma
Jenkins HA et al J Allergy Clin Immunol 2002
109 3-13
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The two phases of asthma
FEV1 forced expiratory volume in 1 second
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Airway Remodeling is a featureof Pediatric
Asthmatic Airways
Asthmatic Male 11Y
Normal Male 11Y
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Gene-Environment Interactions in the
pathogenesis of Asthma
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Genetic and environmental influences in asthma
People with a genetic predisposition to asthma
Allergens
Inducers
Inappropriate immune response (Th2 cell cytokines)
Airways inflammation (Th2 cells, mast cells,
eosinophils)
Bronchoconstricting stimuli (allergens,
histamine, irritants,etc.)
Triggers
Asthma symptoms (wheeze, cough, chest tightness)
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Risk Factors that Lead to Asthma Development

• Predisposing Factors
• Atopy
• Causal Factors
• Indoor Allergens
• Domestic mites
• Animal Allergens
• Cockroach Allergens
• Fungi
• Outdoor Allergens
• Pollens
• Fungi
• Occupational Sensitizers

• Contributing Factors
• Respiratory infections
• Small size at birth
• Diet
• Air pollution
• Outdoor pollutants
• Indoor pollutants
• Smoking
• Passive Smoking
• Active Smoking

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How many triggers of asthma
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1
3
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Is the epithelium important?

• The cell of first contact for inhaled
  environment.
• Initially thought of as a simple physical
  barrier. Now known to synthesize and secrete a
  battery of cytokines, chemokines and growth
  factors to attract and activate other cells that
  play a role in airway inflammation.
• An especially attractive target in which to
  identify new molecular mechanisms and therapeutic
  targets.
• Amenable to topical therapy

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Is asthmatic epithelium abnormal?

• Evidence in adult asthma
• Asthmatic epithelium shows evidence of structural
  damage and fragility, with increased numbers of
  shed epithelial cells in induced sputum.
• More susceptible to oxidant-induced stress.
• Normal repair processes are also
  compromised,constitutively high expression of
  cell cycle inhibitors
• pro-inflammatory transcription factors such as
  p21kip1,STAT-6, STAT-1, NFkB (Sampath, JCI 2001,
  Knight Holgate, 2003)
• A significant number of the novel asthma
  associated genes identified by positional cloning
  are primarily epithelial (eg, ESE3, DPP10, HLA-G,
  GPRA8, PCDH-1, and filaggrin)

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Evidence of epithelial damage in children
Asthmatic
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Normal
Barbato et al., Am J Respir Crit Care Med 2006
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Mediator profile of epithelial cells from
asthmatic and non-asthmatic children
Kicic et al., Am J Respir Crit Care Med, 2006.
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Gene expression infogram for the 128 most
informative genes found on the U133A array
comparing epithelilal cells from asthmatic (A)
and healthy controls (C ). The two controls 66
and 67, that appear to cluster with the
asthmatics had a history of wheeze but were not
classified as doctor-diagnosed asthma.
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Asthmatic epithelial cells proliferate faster
Kicic et al., Am J Respir Crit Care Med, 2006.
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but are unable to repair wounds
Kicic et al., Am J Respir Crit Care Med, 2006.
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Dysregulated repair leads to airway remodeling
Leading to changes in the airway structure and
function
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Airway remodeling

• Has both reversible (either spontaneously or
  with drugs) and irreversible components
• Reversible components include

-Mucus secretion -Edema formation -cellular
infiltration -vessel dilatation -muscle
contraction
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IRREVERSIBLE (?) COMPONENTS

• -Hypertrophy/hyperplasia
• Airway smooth muscle A 20-150 increase in the
  area of of asm has been demonstrated. However,
  whether theincrease is due to hyperplasia (more
  cells) or hypertrophy (biggercells) is
  controversial.
• submucosal glands Glandular hypertrophy is a
  wellrecognized component of airway wall
  thickening. In addition,goblet cell metaplasia
  is frequently seen.
• -scar formation or fibrosis thickening of the
  sub-epithelial basement membrane is a common
  occurrence. The patho-physiological
  significance is unclear, although correlation
  withmethacholine sensitivity has been reported.

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IRREVERSIBLE (?) COMPONENTS
-phenotypic changes in cells The presence and
increased number of (myo)-fibroblasts immediately
underneath the basement membrane correlates with
the basement membranethickening and airway
hyperreactivity. Frequently damaged epithelial
cells may undergo metaplasia and in some cases
de-differentiate into mucus secreting
cells. -angiogenesis blood vessels have been
reported to be increased in size and number in
autopsy specimens from patients dying of asthma.
This would have implications for tissue edema.
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Targets and mechanisms
AcuteInflammation
Airway Remodelling
Chronic Inflammation
Cell recruitment Epithelial damage Early
structural changes
Bronchoconstriction Oedema Secretions Cough
Cellular proliferation Extra-cellular matrix
increase
http//www.mc.uky.edu/ahec/skyahec/RTAMR.htm
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Short acting ?2 agonists

• Rx for Acute Asthma
• The most effective drugs for bronchodilation
• Rx short term relief as needed for acute
  episodes of bronchospasm or prevention of
  exercise-induced bronchospasm.
• Half lives of 6 hrs or less
• Albuterol (Proventil, Ventolin )
• Terbutaline (Brethine, Bricanyl )
• Mechanism stimulate AdCyl ??cAMP ??CaI

McNairn, 2005, University of Edinborough
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Beta Adrenergic AgentsShort Acting Long
acting

• salbutamol (albuterol)
• terbutaline
• adrenaline (epinephrine)
• (isoprenaline)
• Minutes - 4 hours

• formoterol
• salmeterol
• Last up to 12 hours

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Useful Beta Adrenergic Effects

• Relax bronchial smooth muscle
• Inhibit mediator release from mast cells,
  eosinophils, macrophages
• Increase mucous secretion (submucosal gl)
• Increase mucociliary transport
• Inhibit bronchial oedema
• Inhibit cholinergic transmisssion
• Decrease airway hyperresponsiveness

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Unwanted Beta Adrenergic Effects

• Tachycardia
• Skeletal muscle tremor
• Hypokalemia (K shift into muscle tissue)
• Hyperglycaemia (glycogenolysis)
• Hypoxia (pulmonary vasodilation causing increased
  ventilation/perfusion mismatch)

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B-agonist therapy for the treatment of Asthma
racemic albuterol is indispensable in the
management of bronchoconstriction during the
immediate asthmatic reaction, however they are
less effective in the late phase response
?2-agonists contain a chiral carbon, which during
synthesis typically produces a racemic mixture of
stereoisomers. Thus racemic albuterol is a 11
mixture of the active (R)-isomer and its distomer
(S)-albuterol.
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B-agonist therapy for the treatment of Asthma
It is well known that (R)-albuterol is the
eutomer which has bronchorelaxant activity and
(S)-albuterol was originally thought to be
pharmacologically inert.
However (S)-abuterol has since been shown to
induce exaggerated airways airways reactivity and
exacerbate asthmatic symptoms. To date the
biological effects of (S)-albuterol have been
assessed by in vivo studies in clinical trials
and in vitro on airway smooth muscle and
inflammatory cells
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IL-6 release from Normal and Asthmatic
epithelial cells is suppressed by R-albuterol
Asthma Non-Asthma
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IL-8 release from Normal and Asthmatic epithelial
cells is not suppressed by R-albuterol
Similar results seen for TNFa and GMCSF
IL-10 was undetectable
PGE2, RANTES Data forthcoming
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Glucocorticoids (GCS) - Primary
anti-inflammatory Therapy for asthma and related
disorders.
transrepression. negative modulation of gene
transcription by GCS via non genomic
mechanisms. Transrepression is due at least in
part to direct, physical interactions between
monomeric GR and transcription factors
Trans repression
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Airway Epithelial Cell Shedding andApoptosis in
Severe Persistent Asthma

• Human subject with severe, persistent asthma
  (step IV)
• On prednisone, 20 mg/d, plus inhaled
  corticosteroids, leukotriene modifiers, inhaled
  b-agonists

H E 400x
TUNEL immunoperoxidase, 1000x
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Albuterol does not rescue morphological changes
in asthmatic epithelial cells induced by steroid
Albuterol
Control
Control
Dex 10
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Combination of steroid and albuterol does not
induce morphological changes in non-asthmatic
epithelial cells
Albuterol
Control
Control
Dex 10
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Staining of in vivo and in vitro Airways of
Normal and Asthmatic Patients
CK 5 Normal
Asthmatic
In vivo
In vitro
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Airway epithelial Junctional complexes
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Staining of in vivo and in vitro Airways of
Normal and Asthmatic Patients
ZO-1 Normal
Asthmatic
In vivo
In vitro
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E-cadherin expression
Asthmatic
Healthy Normal







40X

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• live in bedding, carpets etc.
• feed off human skin scales
• void faecal pellets (10-50 mm) that contain
  large amounts of digestive enzymesThese faecal
  pellets are dry and can be readily inhaled

with faecal pellets containing allergens, such
as Der P1
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Effects of albuterol isomers on E-cadherin
expression is variable
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Effects of albuterol isomers on ZO-1 expression
is variable

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Simplified view of allergic inflammation in the
airways
(cr)
GG 11th Ed
aI anti-IgE cr cromolyn
l leukotriene inhib. t theophylline ? beta2
agonists cs corticosteroids m antimuscarinics