Amygdalin regulated vasoactive intestinal peptide receptor to protect alveolar epithelial barrier against lung injury induced by influenza a virus.

BACKGROUND: Bitter apricot kernel is a common traditional Chinese medicine used for lung diseases. Previous studies showed that Xuanbai-Chengqi decoction (XCD) containing bitter apricot kernel protected the alveolar and intestinal barriers in influenza-infected mice. However, the specific contribution of bitter apricot kernel and its active substances in viral pneumonia remain unclear. PURPOSE: This study aimed to identify the main active ingredient in bitter apricot kernel and investigate its mechanism in protecting the alveolar epithelial barrier in viral pneumonia. METHOD: Bitter apricot kernel was evaluated based on the efficacy differences between XCD and XCD without bitter apricot kernel. Amygdalin was identified through in vitro activity tests and verified in vivo. Immunohistochemistry, RT-qPCR, and WB were used to assess barrier protection and anti-inflammatory effects. The molecular mechanisms were explored using SPR/LC/MS and validated experimentally. RESULT: Removing bitter apricot kernel significantly weakened XCD's protective effect in influenza A virus-infected mice. Amygdalin showed anti-inflammatory, anti-hypoxia anti-influenza virus activities, and promoted endothelial cell migration in vitro. Amygdalin at 100 mg/kg effectively mitigated pulmonary injury and attenuated excessive inflammatory responses by regulating IL-6 and IL-10 in IAV-infected murine models. Oseltamivir is more effective than amygdalin in inhibiting the replication of influenza viruses and upregulating the expression level of IL-10. Amygdalin protected the alveolar barrier by restoring alveolar type II cells (AT2) and promoting alveolar regeneration, while upregulating surfactant protein A (SP-A) and aquaporin protein-5 (AQP5). Amygdalin bound selectively to vasoactive intestinal peptide receptor 1 (VIPR1) thereby upregulating cyclic adenosine monophosphate (cAMP) levels and the protein expression levels of Protein kinase A (PKA) and Phosphor-protein kinase A (p-PKA). CONCLUSION: Amygdalin is the key bioactive component of bitter apricot kernel, which exhibits protective effects in an IAV-induced pneumonia mouse model by activating the cAMP/PKA/p-PKA signaling cascade and recapitulating the biological effects of vasoactive intestinal peptide (VIP).