Evidence suggests that pro-inflammatory
cytokines and
cortisol play a crucial role in the etiology of
chronic obstructive pulmonary disease (
COPD) and depression. Depression occurs commonly among
COPD patients and an earlier diagnosis would be beneficial. This study investigated the associations between depression, sputum
cytokines and salivary
cortisol in
COPD patients. The diurnal rhythms of sputum
IL-1,
IL-6, TNF-α and salivary
cortisol were measured in
COPD patients with depression compared to those only with depression, or
COPD and healthy controls. The area under the diurnal variation curves (AUC) over the 24h time course and relative diurnal variation (VAR) were calculated while correlation and regression analysis were performed. Patients with co-morbid depression and
COPD showed an increasing sputum
IL-1, sputum TNF-α AUC and a decreasing salivary
cortisol VAR (P<0.001). The combination of sputum TNF-α AUC, sputum
IL-1 AUC, sputum
IL-6 AUC and salivary
cortisol VAR performed best as a potential
biomarker in the diagnosis of depression in
COPD patients, with a sensitivity of 94.74% and a specificity of 96.67%. Positive correlations were found between sputum
IL-1 AUC and sputum TNF-α AUC versus depressive symptoms, respectively a negative correlation was found between salivary
cortisol VAR and depression. They were independently associated with depression in logistic regression models. Depression in
COPD is associated with higher 24-h overall levels of sputum
IL-1, TNF-α and flattened diurnal salivary
cortisol. These non-invasive sputum and salivary
biomarkers may serve as a simple clinical tool for the early diagnosis of depression in
COPD patients.