RESUMEN
<p><b>Background</b>Excess mucus production is an important pathophysiological feature of chronic inflammatory airway diseases. Effective therapies are currently lacking. The aim of the study was to evaluate the effects of curcumin (CUR) on lipopolysaccharide (LPS)-induced mucus secretion and inflammation, and explored the underlying mechanism in vivo and in vitro.</p><p><b>Methods</b>For the in vitro study, human bronchial epithelial (NCI-H292) cells were pretreated with CUR or vehicle for 30 min, and then exposed to LPS for 24 h. Next, nuclear factor erythroid 2-related factor 2 (Nrf2) was knocked down with Nrf2 small interfering RNA (siRNA) to confirm the specific role of Nrf2 in mucin regulation of CUR in NCI-H292 cells. In vivo, C57BL/6 mice were randomly assigned to three groups (n = 7 for each group): control group, LPS group, and LPS + CUR group. Mice in LPS and LPS + CUR group were injected with saline or CUR (50 mg/kg) intraperitoneally 2 h before intratracheal instillation with LPS (100 μg/ml) for 7 days. Cell lysate and lung tissue were obtained to measured Mucin 5AC (MUC5AC) and Nrf2 mRNA and protein expression by a real-time polymerase chain reaction and Western blotting. Bronchoalveolar lavage fluid (BALF) was collected to enumerate total cells and neutrophils. Histopathological changes of the lung were observed. Data were analyzed by one-way analysis of variance. Student's t-test was used when two groups were compared.</p><p><b>Results</b>CUR significantly decreased the expression of MUC5AC mRNA and protein in NCI-H292 cells exposed to LPS. This effect was dose dependent (2.424 ± 0.318 vs. 7.169 ± 1.785, t = 4.534, and 1.060 ± 0.197 vs. 2.340 ± 0.209, t = 7.716; both P < 0.05, respectively) and accompanied by increased mRNA and protein expression of Nrf2 (1.952 ± 0.340 vs. 1.142 ± 0.176, t = -3.661, and 2.010 ± 0.209 vs. 1.089 ± 0.132, t = -6.453; both P < 0.05, respectively). Furthermore, knockdown of Nrf2 with siRNA increased MUC5AC mRNA expression by 47.7%, compared with levels observed in the siRNA-negative group (6.845 ± 1.478 vs. 3.391 ± 0.517, t = -3.821, P < 0.05). Knockdown of Nrf2 with siRNA also markedly increased MUC5AC protein expression in NCI-H292 cells. CUR also significantly decreased LPS-induced mRNA and protein expression of MUC5AC in mouse lung (1.672 ± 0.721 vs. 5.961 ± 2.452, t = 2.906, and 0.480 ± 0.191 vs. 2.290 ± 0.834, t = 3.665, respectively; both P < 0.05). Alcian blue/periodic acid-Schiff staining also showed that CUR suppressed mucin production. Compared with the LPS group, the numbers of inflammatory cells (247 ± 30 vs. 334 ± 24, t = 3.901, P < 0.05) and neutrophils (185 ± 22 vs. 246 ± 20, t = 3.566, P < 0.05) in BALF decreased in the LPS + CUR group, as well as reduced inflammatory cell infiltration in lung tissue.</p><p><b>Conclusion</b>CUR inhibits LPS-induced airway mucus hypersecretion and inflammation through activation of Nrf2 possibly.</p>
RESUMEN
Perilla frutescens was empirically used for controlling airway inflammatory diseases in folk medicine. We investigated whether caffeic acid, myristicin and rosemarinic acid derived from Perilla frutescens significantly affect the gene expression and production of mucin from airway epithelial cells. Confluent NCI-H292 cells were pretreated with caffeic acid, myristicin or rosemarinic acid for 30 min and then stimulated with phorbol 12-myristate 13-acetate (PMA) for 24 h. The MUC5AC mucin gene expression and production were measured by reverse transcription - polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA), respectively. Additionally, we examined whether caffeic acid, myristicin or rosemarinic acid affects MUC5AC mucin production indued by epidermal growth factor (EGF) and tumor necrosis factor-α (TNF-α), the other two stimulators of production of airway mucin. The results were as follows: (1) Caffeic acid, myristicin and rosemarinic acid inhibited the gene expression and production of MUC5AC mucin induced by PMA from NCI-H292 cells, respectively; (2) Among the three compounds derived from Perilla frutescens, only rosemarinic acid inhibited the production of MUC5AC mucin induced by EGF or TNF-α, the other two stimulators of production of airway mucin. These results suggest that rosemarinic acid derived from Perilla frutescens can regulate the production and gene expression of mucin, by directly acting on airway epithelial cells and, at least in part, explains the traditional use of Perilla frutescens as remedies for diverse inflammatory pulmonary diseases.