Effect of Jinzhen Oral Liquid on cough after lipopolysaccharide-induced infection in rats and mechanism

Abstract

This study aims to explore the effect of Jinzhen Oral Liquid(JOL) on cough after infection in rats and the mechanism. To be specific, a total of 60 male SD rats were classified into 6 groups: normal group(equivalent volume of distilled water, ig), model group(equivalent volume of distilled water, ig), Dextromethorphan Hydrobromide Oral Solution group(3.67 mL·kg~(-1), ig), high-, medium-, and low-dose JOL groups(11.34, 5.67, and 2.84 mL·kg~(-1), respectively, ig). Lipopolysaccharide(LPS, nasal drip), smoking, and capsaicin(nebulization) were employed to induce cough after infection in rats except the normal group. Administration began on the 19 th day and lasted 7 days. Capsaicin(nebulization) was used to stimulate cough 1 h after the last administration and the cough frequency and cough incubation period in rats were recorded. The pathological morphology of lung tissue was observed based on hematoxylin-eosin(HE) staining. Immunohistochemistry(IHC) was used to detect the specific expression of transient receptor potential vanilloid 1(Trpv1), nerve growth factor(NGF), tropomyosin receptor kinase A(TrkA), and phosphorylated-p38 mitogen-activated protein kinase(p-p38 MAPK) in lung tissue, Western blot the protein expression of Trpv1, NGF, TrkA, and p-p38 MAPK in lung tissue, and real-time fluorescent quantitative polymerase chain reaction(real-time PCR) the mRNA expression of Trpv1, NGF, and TrkA. The results showed that model group demonstrated significantly high cough frequency, obvious proliferation and inflammatory cell infiltration in lung tissue, significantly enhanced positive protein expression of Trpv1, NGF, TrkA, and p-p38 MAPK in lung tissue and significant increase in the mRNA expression of Trpv1, NGF, and TrkA compared with the normal group. Compared with the model group, JOL can significantly reduce the cough frequency, alleviate the pathological changes of lung tissue, and decrease the protein expression of Trpv1, NGF, TrkA, and p-p38 MAPK in lung tissue, and high-dose and medium-dose JOL can significantly lower the mRNA expression of Trpv1, NGF, and TrkA. This study revealed that JOL can effectively inhibit Trpv1 pathway-related proteins and improve cough after infection. The mechanism is that it reduces the expression of NGF, TrkA, and p-p38 MAPK in lung tissue, thereby decreasing the expression of Trpv1 and cough sensitivity.