Melatonin promoted chemotaxins expression in lung epithelial cell stimulated with TNF-alpha

Patients with asthma demonstrate circadian variations in the airway inflammation and lung function. Pinealectomy reduces the total inflammatory cell number in the asthmatic rat lung. We hypothesize that melatonin, a circadian rhythm regulator, may modulate the circadian inflammatory variations in asthma by stimulating the chemotaxins expression in the lung epithelial cell.

Lung epithelial cells (A549) were stimulated with melatonin in the presence or absence of TNF-alpha(100 ng/ml). RANTES (Regulated on Activation Normal T-cells Expressed and Secreted) and eotaxin expression were measured using ELISA and real-time RT-PCR, eosinophil chemotactic activity (ECA) released by A549 was measured by eosinophil chemotaxis assay.

TNF-alpha increased the expression of RANTES (307.84 +/- 33.56 versus 207.64 +/- 31.27 pg/ml of control, p = 0.025) and eotaxin (108.97 +/- 10.87 versus 54.00 +/- 5.29 pg/ml of control, p = 0.041). Melatonin(10(-10) to 10(-6)M) alone didn't change the expression of RNATES (204.97 +/- 32.56 pg/ml) and eotaxin (55.28 +/- 6.71 pg/ml). However, In the presence of TNF-alpha (100 ng/ml), melatonin promoted RANTES (410.88 +/- 52.03, 483.60 +/- 55.37, 559.92 +/- 75.70, 688.42 +/- 95.32, 766.39 +/- 101.53 pg/ml, treated with 10(-10), 10(-9), 10(-8), 10(-7),10(-6)M melatonin, respectively) and eotaxin (151.95 +/- 13.88, 238.79 +/- 16.81, 361.62 +/- 36.91, 393.66 +/- 44.89, 494.34 +/- 100.95 pg/ml, treated with 10(-10), 10(-9), 10(-8), 10(-7), 10(-6)M melatonin, respectively) expression in a dose dependent manner in A549 cells (compared with TNF-alpha alone, P < 0.05). The increased release of RANTES and eotaxin in A549 cells by above treatment were further confirmed by both real-time RT-PCR and the ECA assay.

Taken together, our results suggested that melatonin might synergize with pro-inflammatory cytokines to modulate the asthma airway inflammation through promoting the expression of chemotaxins in lung epithelial cell.