In vivo Evaluation of Mucociliary Clearance in Mice

Naringenin attenuated airway cilia structural and functional injury induced by cigarette smoke extract via IL-17 and cAMP pathways

BACKGROUND

Cigarette smoke impairs mucociliary clearance via mechanisms such as inflammatory response and oxidative injury, which in turn induces various respiratory diseases. Naringenin, a naturally occurring flavonoid in grapes and grapefruit, has exhibited pharmacological properties such as anti-inflammatory, expectorant, and antioxidant properties. However, it is still unclear whether naringenin protects airway cilia from injury caused by cigarette smoke.

PURPOSE

This study aimed to investigate the effect of naringenin on cigarette smoke extract (CSE)-induced structural and functional abnormalities in airway cilia and highlight the potential regulatory mechanism.

METHODS

Initially, network pharmacology was used to predict the mechanism of action of naringenin in ciliary disease. Next, HE staining, immunofluorescence, TEM, qRT-PCR, western blot, and ELISA were performed to assess the effects of naringenin on airway cilia in tracheal rings and air-liquid interface (ALI) cultures of Sprague Dawley rats after co-exposure to CSE (10% or 20%) and naringenin (0, 25, 50, 100 μM) for 24 h. Finally, transcriptomics and molecular biotechnology methods were conducted to elucidate the mechanism by which naringenin protected cilia from CSE-induced damage in ALI cultures.

RESULTS

The targets of ciliary diseases regulated by naringenin were significantly enriched in inflammation and oxidative stress pathways. Also, the CSE decreased the number of cilia in the tracheal rings and ALI cultures and reduced the ciliary beat frequency (CBF). However, naringenin prevented CSE-induced cilia damage via mechanisms such as the downregulation of cilia-related genes (e.g., RFX3, DNAI1, DNAH5, IFT88) and ciliary marker proteins such as DNAI2, FOXJ1, and β-tubulin IV, the upregulation of inflammatory factors (e.g., IL-6, IL-8, IL-13), ROS and MDA. IL-17 signaling pathway might be involved in the protective effect of naringenin on airway cilia. Additionally, the cAMP signaling pathway might also be related to the enhancement of CBF by naringenin.

CONCLUSION

In this study, we first found that naringenin reduces CSE-induced structural disruption of airway cilia in part via modulation of the IL-17 signaling pathway. Furthermore, we also found that naringenin enhances CBF by activating the cAMP signaling pathway. This is the first report to reveal the beneficial effects of naringenin on airway cilia and the potential underlying mechanisms.

Differential effect of anesthetics on mucociliary clearance in vivo in mice

Respiratory mucociliary clearance (MCC) is a key defense mechanism that functions to entrap and transport inhaled pollutants, particulates, and pathogens away from the lungs. Previous work has identified a number of anesthetics to have cilia depressive effects in vitro. Wild-type C57BL/6 J mice received intra-tracheal installation of ^99mTc-Sulfur colloid, and were imaged using a dual-modality SPECT/CT system at 0 and 6 h to measure baseline MCC (n = 8). Mice were challenged for one hour with inhalational 1.5% isoflurane, or intraperitoneal ketamine (100 mg/kg)/xylazine (20 mg/kg), ketamine (0.5 mg/kg)/dexmedetomidine (50 mg/kg), fentanyl (0.2 mg/kg)/1.5% isoflurane, propofol (120 mg/Kg), or fentanyl/midazolam/dexmedetomidine (0.025 mg/kg/2.5 mg/kg/0.25 mg/kg) prior to MCC assessment. The baseline MCC was 6.4%, and was significantly reduced to 3.7% (p = 0.04) and 3.0% (p = 0.01) by ketamine/xylazine and ketamine/dexmedetomidine challenge respectively. Importantly, combinations of drugs containing fentanyl, and propofol in isolation did not significantly depress MCC. Although no change in cilia length or percent ciliation was expected, we tried to correlate ex-vivo tracheal cilia ciliary beat frequency and cilia-generated flow velocities with MCC and found no correlation. Our results indicate that anesthetics containing ketamine (ketamine/xylazine and ketamine/dexmedetomidine) significantly depress MCC, while combinations containing fentanyl (fentanyl/isoflurane, fentanyl/midazolam/dexmedetomidine) and propofol do not. Our method for assessing MCC is reproducible and has utility for studying the effects of other drug combinations.