Stability of glutathione in induced sputum: impact of freezing.
BACKGROUND
Oxidative stress has repeatedly been linked to the pathogenesis of pulmonary disorders like asthma and chronic obstructive pulmonary disease. Measuring glutathione (GSH) in induced sputum (IS) offers a noninvasive tool to study oxidative stress in airway diseases.


OBJECTIVE
This study assessed the stability of GSH in sputum supernatant under varying conditions.


METHODS
GSH in IS of 14 (7 healthy, 4 chronic obstructive pulmonary disease, 3 allergic rhinitis) nonsmoking subjects was quantified spectrophotometrically. The stability of GSH in supernatant was analyzed over 24 h under different ambient conditions (room temperature and cooling at 4 degrees C). Reproducibility of GSH measurements in immediately processed and frozen supernatant (+72 h) was expressed by intraclass correlation coefficient (R(i)) and coefficient of repeatability (CR).


RESULTS
GSH recovery in supernatant decreased in a time- and temperature-dependent manner. Samples stored at 4 degrees C and room temperature showed a rapid decline of stability after 2 h. Mean GSH concentrations in IS after freezing (-20 degrees C) and thawing after 72 h were not significantly different from GSH values measured immediately after processing of the samples (immediate processing: 17.9 +/- 13.9 microM; 72 h freezing: 16.4 +/- 12.9 microM, p = 0.2). The reproducibility between immediately processed and frozen samples was excellent (R(i) = 0.97; CR = 5.7 microM).


CONCLUSIONS
Storage of sputum supernatant at room temperature or 4 degrees C leads to a rapid decline of GSH recovery compared with baseline values. Immediate freezing of samples is a suitable and valid alternative to rapid processing and allows collection and shipment of samples for subsequent analysis.
Beier
J
J
Pulmonary Department, Internal Medicine, University Hospital Mainz, Mainz, Germany. j.beier@3.med.klinik.uni-mainz.de
Beeh
K M
KM
Kornmann
O
O
Buhl
R
R
D005615:Freezing; D005978:Glutathione / Q000032:analysis*; D006801:Humans; D018384:Oxidative Stress; D011446:Prospective Studies; D012995:Solubility; D013048:Specimen Handling; D013183:Sputum / Q000737:chemistry*; D013696:Temperature
D005978:Glutathione