Exhaled Biomarkers - Exhaled Biomarkers Exhaled Asthma...

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Unformatted text preview: Exhaled Biomarkers Exhaled Asthma & COPD AS Paul DM Seminar 30 March 07 Introduction Introduction • Diagnosis and course of COPD/Asthma – Clinical information – Pulmonary function tests – Arterial blood gases – Chest X-rays • No direct measure of lung inflammation is routinely used What are biomarkers? What • Biomarkers are objectively measured and evaluated indicators of normal biological processes, pathogenic processes or pharmacological responses to a therapeutic intervention What can we measure? What • Exhaled gases eg NO • Exhaled breath condensate markers • Exhaled breath temperatures Why is this so exciting? Why • Many diseases are characterized by chronic inflammation and oxidative stress • Asthma, COPD, bronchiectasis, cystic fibrosis and ILD are examples • Inflammation is not directly measured by any routine investigation done at present • Measuring biomarkers may make this possible Asthma Asthma • Bronchial biopsies are the “gold standard” • invasive • cannot be routine • cannot be repeated often • children and those with severe disease • BAL • Invasive • Infection • Impair gas exchange • Symptoms are a poor indicator • Perception • Masking by SABA/LABA • Histamine/methacholine challenges • Confounded by bronchodilator use • Sputum induction • Unpleasant • Inflammation lasts 24 h • Cannot be repeated in less than 24h Exhaled Breath Condensate Exhaled • Epithelial lining fluid contains 200 volatile substances and various nonvolatile substances • Initial focus on volatile substances particularly NO • Studies are now focusing on nonvolatile substances e.g. proteins, lipids, oxidants and nucleotides Possibilities Possibilities • Determining host inflammatory responses to injury in the lung • Possible single noninvasive sampling method for point-of-care real-time analysis Collection of EBC Collection • Exhaled breath is saturated with water vapor which can be condensed with cooling • Aerosol particles from the lower tract are also present • Source: alveoli vs. airway e.g. H2O2 is from airways (flow dependent) EBC EBC • 0.1-4 particles/cm3 • Mean diameter < 0.3μm • Number depends on • Velocity • Surface tension • Turbulent flow A Collection Apparatus Collection Problems Problems • Glass/polystyrene/polypropylene • Ice/Dry ice/ liquid nitrogen • Nose clips open nasopharyngeal velum • 5-10 min to get 1-3 ml of EBC • Contamination • Exhaled air (two way non-rebreathing valve) • Saliva ( trap, mouth rinsing, salivary amylase) EBC: Inflammatory mediators EBC: detected Smoking Smoking • H2O2 a measure of oxidant activity • Levels in smokers 5x higher • Male smokers > Female smokers • Levels in EBC are lower than in alveoli as there is removal by the anti-oxidant system • Higher levels may indicate risk of developing smoking-related disease ASTHMA ASTHMA FENO • NO levels are increased in bronchial asthma (Alving et al 93) • Pro-inflammatory mediator with immunomodulatory effects. Predisposes to the development of AHR in pathological situations • A weak mediator of sm relaxation in physiological situations • Originates in airway epithelium FENO • May rise in a large number of conditions but is most marked in allergic airway disease • Portable inexpensive meters can measure it easily • More relevant direct measure of inflammation which complements PFT Rationale for FENO measurement Rationale • High degree of correlation with eosinophilic airway inflammation • Eosinophilic inflammation responds to steroids • Raised levels predict steroid responsiveness in pts with non-specific symptoms • ICS treatment results in a fall in levels in a dose dependent manner Asthma vs non-asthma Asthma • Helps to discriminate asthma from non- asthma • Viral illnesses can give false positive results (wait 6 wks) • More sensitive than spirometry and therefore will pick up disease where lung fn is still normal Non-specific respiratory symptoms Non Role in assessing undiagnosed respiratory symptoms • Eosinophilic bronchitis, cough variant asthma, post-viral hyperresponsiveness, Post-nasal drip, GE reflux, VCD, COPD • A rise in FENO predicts steroid responsiveness Pre-school children Pre • Diagnosing asthma from non-asthma in wheezy infants using FENO either offline or online. • Evidence for reliability as a screening tool is mixed • May allow better targeting of antiinflammatory therapy Influence of atopy Influence • Levels are raised in atopic individuals even in the absence of symptoms suggesting low levels of airway inflammation • Complements skin testing and correlates well with IgE levels • No evidence to treat asymptomatic individuals Management of chronic asthma Management • Predicting exacerbations • Predicting outcomes of ICS withdrawal • Adjustment of ICS dose H2O2 and TBAR and • Increased levels in asthma • High correlation between the two • Increase in levels associated with a drop in FEV1 • Significant reduction with treatment with ICS which remained stable for 2 weeks after discontinuation H2O2 levels in children levels • Correlate well with symptoms • Decrease with ICS treatment • May be a good measure for monitoring improvement with treatment Nitrotyrosine Nitrotyrosine • A stable end product of peroxynitrite • Mild (steroid naïve) • Moderate (on ICS) • Severe (on oral CS) • Increased levels were found in the first group Isoprostanes Isoprostanes • Compounds formed by non-enzymatic peroxidation of membrane phopholipids during oxidative stress • Levels are elevated in all asthma with higher levels in more severe disease • Correlation with PFT however is not good Leukotrienes Leukotrienes • Airway smooth muscle contraction, microvascular leakage, mucus hypersecretion • Increased levels of LTB4 in asthma which increase with severity • No correlation with FEV1 pH pH • Acute asthma associated with pH decline of two-log • Normalised with corticosteroid therapy • Suggested that serial measures can help titrate therapy • Hampered by poor reproducibility Future Prospects for EBC in asthma Future • Some markers persist despite ICS • Leukotriene pathway is not suppressed by • • • steroids Persistent elevation of leukotrienes may be used to initiate therapy with specific inhibitors Lack of correlation with FEV1 does not preclude the use of these markers If rise in markers precedes physiological changes greater utility is likely Exhaled biomarkers Exhaled COPD Inflammation in COPD Inflammation • Chronic inflammation throughout the airways, parenchyma and pulmonary vasculature • Macrophages, T-lymphocytes (CD8+) and neutrophils • Tissue eosinophils (unlike asthma not degranulated) Biomarkers in exhaled air Biomarkers • Exhaled NO: most used and standardised • Exhaled CO • Exhaled Ethane Exhaled Nitric Oxide Exhaled • A gas which regulates vascular and bronchial tone • Alveolar macrophages synthesize it after stimulation by endotoxin and cytokines; part of host defence • Converted to peroxynitrite: a potent epithelial toxin • Promotes proliferation of T lymphocytes Synthesis of NO Synthesis NO levels NO • Healthy subjects: 3-7 ppb • Lower in smokers • No difference between healthy individuals and stable COPD/ lower in those still smoking. • Increased levels in unstable disease owing to neutrophilic inflammation • Increased levels in subsets with an asthmatic component to disease. • Levels decrease with treatment with ICS (probably the effect on some eosinopholic inflammation also present) • Levels correlate with sputum eosinophil levels. • Inverse correlation with FEV1 levels in stable patients • NO is not a good marker for disease severity in COPD • Increased levels • Asthmatic subset • Exacerbations • Smoking reduces levels confounding the picture Exhaled CO Exhaled CO CO • CO is produced in alveoli, nose and paranasal sinuses • Environmental levels affect measurements • Higher in stable COPD • Smoking has the greatest effect 8ppm • URTI also raises levels • Healthy subjects 1-8ppm CO CO • Also increased in asthma • No data exist on correlation with ICS use • Limited utility as a marker because of wide variation with environmental levels and smoking Exhaled alkanes Exhaled • Oxidants can cause injury by lipid peroxidation • ROS and H2O2 released by activated inflammatory cells can induce peroxidation of polyunsaturated membrane fatty acids • This impairs function and inactivates receptors and enzymes, increases permeability and causes airflow limitation Ethane Ethane • Easier to measure • Analyzed by gas chromatography • Expensive and time consuming • Environmental contamination has to be avoided • Age does not affect levels • 0.88 ppb is the normal level • Increased in smokers and those with airway obstruction. Decreased with steroid use Biomarkers in EBC Biomarkers • Biomarkers which are not gases cannot be measured directly • Hydrogen peroxide • Isoprostanes • NO metabolites • TBARS • Salivary contamination is a problem Exhaled Hydrogen peroxide Exhaled • Airway inflammation causes a “ respiratory burst” producing ROS • H2O2 levels reflect oxidative stress in the lung • Measurement is based on reaction with suitable substrates leading to the release of color, light or fluorescence • Normal levels are almost undetectable Hydrogen peroxide Hydrogen • • • • • • • • • Collection and storage is a source of error Exercise increases levels Food and beverages increase levels Levels vary widely with repeated measurements Healthy young non-smokers 0.01-0.09mmol/l Increased in stable COPD/ increased further during an exacerbation Lower levels in current smokers Levels decrease with ICS/NAC Standardization is poor and large intraindividual variability exists. Isoprostanes Isoprostanes • Reduction of bicycloendoperoxide intermediates ( from arachidonic acid reacting with oxygen radicals) • Stable in body fluids • No diurnal variation • Higher levels in smokers • Higher in COPD regardless of smoking status Isoprostanes Isoprostanes • Also high in healthy smokers, asthma and ILD which may confound its use for diagnosing or monitoring COPD Nitric oxide metabolites Nitric • NO is highly reactive and has a short life in vivo • Stable end products include nitrite and nitrate. • • • • Peroxynitrite results from a reaction with superoxide Nitrotyrosine and nitrosothiols result All can be measured in EBC Increased directly after cigarette smoking/in COPD /asthma Steroids reverse the increase in asthma Thiobarbituric acid reactive Thiobarbituric substances (TBARs) • Volatile products of lipid peroxidation • Undetectable in healthy non-smokers • Raised in smokers with no relation to other inflammatory markers • Raised in stable COPD with no difference with smoking status • Also increased in asthma to a higher degree with significant correlation with H2O2 levels • TBAR levels can differentiate stable COPD and healthy individuals and also between those with COPD and asthma • Current smoking status does not change levels in COPD Advantages and Limitations Advantages Advantages Advantages Limitations Limitations Conclusions Conclusions • EBC has potential as a non invasive real time technique • • • • • • in the future Lack of standardisation in collection and analysis for most markers makes comparison of studies and clinical application difficult at present Collected fluid is not anatomic site specific Reference data for healthy individuals needs to be available Smoking status affects different markers in different ways Data on reproducibility and variability is scarce Effect of treatment on different markers needs to be determined before they can be used for follow up Take home message! Take • Biomarkers may be a useful non invasive adjunct in the diagnosis and follow-up of patients with various pulmonary inflammatory conditions at the point of care in real time • Further work is needed to validate standardize and better define the clinical utility of this emerging instrument in pulmonary disease Thank you Thank ...
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This note was uploaded on 12/03/2011 for the course MEDICINE 350 taught by Professor Dr.aslam during the Winter '07 term at Medical College.

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