Sputum zinc concentration and clinical outcome in older asthmatics.
OBJECTIVE
Mouse models of asthma show that zinc deficiency is associated with airway inflammation (AI), which is attenuated by zinc supplements. Whether zinc has a similar role in the human airway remains controversial, with studies demonstrating both high and low plasma zinc concentrations [Zn] in asthmatic patients compared with control subjects. This variability may reflect the inability of plasma measurements to accurately assess airway zinc levels. Examination of induced sputum is an established technique for measuring AI and mediators of inflammation. Recent advances allow measurement of the rapidly exchangeable (labile) and total zinc pools in sputum. The aims of this study were to measure labile and total [Zn] in sputum and plasma of subjects with or without asthma, and second to correlate [Zn] with symptoms, asthma severity, lung function (FEV(1)) and airway hyper-responsiveness.


METHODS
A total of 163 subjects (114 with asthma) completed a single visit for sputum induction and a blood test. Labile and total [Zn] were measured by Zinquin fluorescence and atomic absorption spectrophotometry.


RESULTS
The mean (SD) age of subjects with and without asthma was 55 (14) and 57 (14) years, respectively. Baseline FEV(1) was significantly lower in subjects with asthma (94.2 (16)%) than in those without asthma (103 (16.6)%). Sputum total and labile [Zn] were lower in subjects with asthma compared with control subjects, with median (interquartile range) values of 31.8 (117) versus 50 (188.5), P = 0.02 and 0 (48) versus 26 (84.5) µg/L, P = 0.05, respectively. Increased frequency of wheeze, as well as asthma severity and reduced FEV(1), was associated with significantly lower labile sputum [Zn].


CONCLUSIONS
These findings suggest that sputum [Zn] reflect clinical outcomes and underlying AI, suggesting a potential role for zinc as a biomarker in asthma.
Department of Medicine, University of Adelaide, The Queen Elizabeth Hospital, Woodville, South Australia, Australia. jayaram.lata@gmail.com
Lata
L
Jayaram
Sanjeev
S
Chunilal
Sandy
S
Pickering
Richard E
RE
Ruffin
Peter D
PD
Zalewski
D000328:Adult; D000368:Aged; D000818:Animals; D001249:Asthma / Q000175:diagnosis* / Q000503:physiopathology*; D015415:Biomarkers / Q000032:analysis; D003430:Cross-Sectional Studies; D005260:Female; D006801:Humans; D007958:Leukocyte Count; D008297:Male; D051379:Mice; D008875:Middle Aged; D015363:Quinolones / Q000032:analysis; D012129:Respiratory Function Tests; D012135:Respiratory Sounds / Q000503:physiopathology; D012463:Saliva / Q000737:chemistry; D012720:Severity of Illness Index; D013054:Spectrophotometry, Atomic; D013183:Sputum / Q000737:chemistry*; D014105:Tosyl Compounds / Q000032:analysis; D015032:Zinc / Q000032:analysis
D015415:Biomarkers; D015363:Quinolones; D014105:Tosyl Compounds; D015032:Zinc; C084731:zinquin