Naringenin (Nar) is a flavonoid derived from plant foods. It has been shown to have anti-inflammatory properties. Many studies have shown that overexpression of reactive oxygen species (ROS) and nuclear factor-κB (NF-κB) leads to increased mucin (MUC) 5AC expression in chronic inflammation of the airway. In addition, some studies have reported that naringenin inhibits NF-κB activity in a murine model of asthma. We speculated that naringenin might be associated with mucous hypersecretion, but the molecular mechanisms remain to be defined. Our study has also investigated whether naringenin could inhibit production of ROS and the activity of NF-κB on the inflammatory pulmonary diseases induced by human neutrophil elastase (HNE) and reduce the mRNA and protein levels of MUC5AC as shown by reverse transcriptase-polymerase chain reaction and real-time PCR (RT-PCR). Serum total MUC5AC protein was detected by enzyme-linked immunosorbent assay (ELISA), the protein morphological changes of MUC5AC were also observed by immunofluorescence and confocal laser technology. Hyperactivation of epidermal growth factor receptor (EGFR) signaling is commonly involved in the mucous hypersecretion process and initiates both the activation of extracellular signal-related kinases 1/2 (ERK1/2) and of phosphatidylinositol 3-kinase (PI3K) and Akt kinase. NF-κB is a key factor downstream of PI3K/Akt signaling, which induces overexpression of the MUC5AC gene. Our data revealed that naringenin inhibited the activation of EGFR resulting in the downregulation of the enzyme activities. Naringenin also reduced the protein expressions of p-EGFR, PI3K, p-Akt, p-ERK1/2, and NF-κB as shown by western blotting. Furthermore, naringenin significantly inhibited PI3K/Akt and ERK MAPKinase signaling with a concurrent reduction in production of ROS and NF-κB activities. These results suggest that naringenin may play a protective role by minimizing mucous production during airway inflammation by down-regulating ROS production and inhibiting the NF-κB activity via EGFR-PI3K-Akt/ERK MAPKinase signaling pathway.

These results indicate that chronic exenatide treatment enhances insulin sensitivity and protects against high fat-induced insulin resistance.