Serum and sputum neurotrophin levels in chronic persistent cough.
BACKGROUND
Neurotrophins (NTs) are a family of growth factors, including nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and neurotrophin3 (NT-3) that are involved in inflammation. Serum and induced sputum NT levels are increased in asthma and in cough because of idiopathic pulmonary fibrosis, respectively. Neurogenic inflammation is implicated in the pathogenesis of chronic cough in individuals with normal chest radiography, but the role of NTs in this condition is unknown.


OBJECTIVE
To assess if NT levels are elevated in the serum and airways in subjects with chronic persistent cough.


METHODS
Eighty-one subjects with chronic cough persistent for over 1 year; with normal chest radiography and spirometry were included. Thirty healthy subjects were controls. Serum NGF, BDNF and NT-3 were measured by enzyme immunoassay. In a subset, NGF was measured in induced sputum. Sputum cell counts and allergen-specific serum IgE were measured and all patients received specific sequential treatment trials to achieve a final diagnosis for the cough.


RESULTS
There was no significant difference either in the levels of serum or sputum NTs in chronic cough subjects compared with controls or between the most common causes of cough: post-nasal drip syndrome, gastro-oesophageal reflux disease, asthma and bronchiectasis. The median (inter-quartile range) for sputum NGF (pg/mL) was 516 (296-772) in healthy controls and 580 (312-880) in subjects with chronic cough (P=0.284). There was no correlation between NT levels and sputum cell counts. Sputum NGF levels correlated with duration of cough (r=0.34, P=0.002).


CONCLUSIONS
NTs are not elevated in induced sputum or serum of subjects with chronic persistent cough. This implies that NTs do not have a central role in perpetuating airway inflammation in chronic persistent cough.
Chaudhuri
R
R
Departments of Respiratory Medicine, University of Glasgow and Western Infirmary, Glasgow, UK.
McMahon
A D
AD
McSharry
C P
CP
Macleod
K J
KJ
Fraser
I
I
Livingston
E
E
Thomson
N C
NC
D000328:Adult; D000368:Aged; D001249:Asthma / Q000097:blood / Q000378:metabolism; D019208:Brain-Derived Neurotrophic Factor / Q000032:analysis / Q000097:blood; D001987:Bronchiectasis / Q000097:blood / Q000378:metabolism; D002452:Cell Count; D002908:Chronic Disease; D003371:Cough / Q000276:immunology / Q000378:metabolism*; D005260:Female; D005541:Forced Expiratory Volume / Q000502:physiology; D005764:Gastroesophageal Reflux / Q000097:blood / Q000378:metabolism; D006801:Humans; D008297:Male; D008875:Middle Aged; D020932:Nerve Growth Factor / Q000032:analysis / Q000097:blood; D009414:Nerve Growth Factors / Q000032:analysis* / Q000097:blood; D020933:Neurotrophin 3 / Q000032:analysis / Q000097:blood; D009504:Neutrophils / Q000276:immunology; D013183:Sputum / Q000737:chemistry*
D019208:Brain-Derived Neurotrophic Factor; D009414:Nerve Growth Factors; D020933:Neurotrophin 3; D020932:Nerve Growth Factor