Study On The Mechanism Of PP121 In Relieving Asthma Symptoms

Asthma is a heterogeneous disease involving various cells and cellular components,which is mainly characterized by cough,chest tightness,and wheezing caused by airway inflammation,airway remodeling,and airway hyperresponsiveness.These symptoms cause great inconvenience to more than 300 million asthma patients all over the world.Current drugs still have many efficacy and side effects issues,so it is crucial to screen new drugs with high efficacy and safety.Studies have shown that vascular endothelial growth factor（VEGF）could play an important role in developing asthma after binding to its receptor（VEGFR2）.PP121 is an VEGFR2 inhibitor that affects a wide range of tumor cell proliferation by acting on various signaling pathways.At present,few studies targeting VEGF or VEGFR2 in the treatment of asthma.Also,whether PP121 plays a role in the treatment of asthma remains unknown.Our preliminary experiments showed that PP121 had a considerable relaxing effect on the precontracted mice tracheal.In order to further investigate the effect and mechanism of PP121 in relaxing tracheal and relieving asthma,a series of experiments were designed at the tissue level,the cellular level and the living body level,respectively.And the results are as follows:1.The tension transducer was used to detect the tension of isolated mouse tracheal;the patch clamp was used to detect the ion channel current of acutely isolated airway smooth muscle single cells;the lung sections were used to observe the change of bronchial lumen size before and after drug treatment.The results showed that PP121 could inhibit the influx and release of external calcium and down-regulate the concentration of intracellular free Ca²⁺by affecting the opening of L-VDCC,NSCC,NCX and BK_Cachannels,thereby relaxing airway smooth muscle and ultimately expanding the trachea.The toxicity of PP121 was evaluated at the cellular and tissue levels,and the results indicated that PP121 was less toxic.2.Establishment of ovalbumin（OVA）-induced asthmatic mice model（1）PP121 was found to reduce lung swelling in a mouse model of asthma,and histopathologic section analysis of bronchial and lung tissues revealed that PP121 reduced inflammatory infiltration and airway remodeling in asthma.The detection of isolated tracheal tension suggested that PP121 has attenuated airway hyperresponsiveness in mice,and the results of lung function tests revealed that PP121 had reduced the mice’s respiratory system resistance.（2）Real-time PCR experiments showed that PP121 could down-regulate the expressions of inflammatory factors IL-4,IL-5,TNF-α,and mucins MUC5AC and MUC5B in asthma.Meantime,the expression levels of VEGF and VEGFR2 were also down-regulated by PP121.（3）In order to further explore the mechanism of PP121 in alleviating asthma inflammation,the expression levels of VEGFR2,Akt,p38 MAPK proteins and their phosphorylation levels were detected by western blot.The results showed that PP121 reduced the phosphorylation levels of VEGFR2,Akt and p38 MAPK in asthma.In summary,our results indicated that PP121 plays a regulatory role in airway inflammation,airway remodeling and airway hyperreactivity by affecting the activation of VEGF/VEGFR2,PI3K/Akt,and p38 MAPK,as well as inhibiting the expression of inflammatory factors such as IL-4,IL-5,TNF-α.Our results also showed that PP121 has good efficacy and high safety in improving asthma symptoms.It suggests that PP121 might be a potential new drug for asthma treatment.This study will provide new ideas and data reference to the development of new drugs for asthma therapy.