Vitamin D and glucocorticoids differentially modulate chemokine expression in human airway smooth muscle cells

Chemokines play a critical role in the pathogenesis of asthma and facilitate the recruitment of inflammatory cells in the airways. Evidence now suggests that airway smooth muscle (ASM) may serve as a source of chemokines in inflamed airways. Although vitamin D has potent anti-inflammatory properties in vitro in some cell types, its effects on ASM cells remain unclear. Here, we investigated whether 1alpha, 25-dihydroxy vitamin D3 (calcitriol) modulated chemokine production in ASM.

Human ASM cell cultures were derived from tracheal samples taken during surgery. ASM cells were treated with tumour necrosis factor alpha (TNFalpha) and/or interferon gamma (IFNgamma) for 24 h in the presence of calcitriol and/or the glucocorticoid fluticasone added 2 h before. RANTES (regulated upon activation, normal T-cell expressed and secreted), interferon-inducible protein 10 (IP-10) and fractalkine (FKN) levels in cell supernatants were measured by ELISA.

In TNFalpha-treated cells, calcitriol inhibited RANTES and IP-10 secretion in a concentration-dependent manner. FKN levels were negligible. In TNFalpha/IFNgamma-treated cells, whereas fluticasone or calcitriol alone partially inhibited RANTES secretion (by 38 and 20%, respectively), the combination of both drugs additively inhibited RANTES secretion (by 60%). No effect was observed on IP-10 secretion. Whereas fluticasone enhanced FKN secretion (by 50%), calcitriol significantly decreased FKN levels (by 50%). Interestingly, calcitriol blocked the stimulatory effect of fluticasone on FKN secretion, which was inhibited by 60% with the combination of calcitriol and fluticasone.

These findings suggest that vitamin D uniquely modulates human ASM expression of chemokines and may exert some beneficial effects in the treatment of steroid-resistant patients with asthma.