Phillyrin prevents sepsis-induced acute lung injury through inhibiting the NLRP3/caspase-1/GSDMD-dependent pyroptosis signaling pathway

Abstract

Acute lung injury (ALI) is a severe pulmonary disorder of sepsis with high clinical incidence and mortality. Nucleotide-binding oligomerization domain-like receptor family pyrin domain containing 3 (NLRP3)-cysteinyl aspartate specific proteinase 1-gasdermin D (GSDMD)-dependent pyroptosis of alveolar epithelial cells (AECs) has emerged as a crucial contributor to ALI during sepsis. Phillyrin (PHI), a natural lignan isolated from the traditional Chinese herbal medicine Forsythia suspensa, has been shown to have anti-inflammatory, antioxidant and antiviral properties. However, little is known about the protective role and potential mechanism of PHI in sepsis-induced ALI, and it is uncertain whether the protective effect of PHI in sepsis-induced ALI is connected to pyroptosis. This study aims to examine the preventive effects of PHI on sepsis-induced ALI via the inhibition of NLRP3/caspase-1/GSDMD-mediated pyroptosis in AECs. Our findings demonstrate that preadministration of PHI successfully reduces sepsis-induced pulmonary edema, systemic/pulmonary inflammation, and pulmonary histological damage in lung tissues, bronchoalveolar lavage fluid, and the serum of septic mice. Intriguingly, PHI preadministration suppresses sepsis-induced protein expressions of pyroptosis-specific markers, especially their active forms. In vitro assays show that PHI pretreatment also protects type II AECs (MLE-12) from lipopolysaccharide-induced pyroptosis by preventing the activation of the pyroptosis signaling pathway. The results from molecular docking and surface plasmon resonance reveal that PHI has a significant affinity for direct binding to the GSDMD protein, suggesting that GSDMD is a potential pharmacological target for PHI. In conclusion, PHI can prevent sepsis-triggered ALI by effectively suppressing the activation of the canonical pyroptosis signaling pathway and pyroptosis of AECs.

1. Introduction

In the intensive care unit, acute lung injury (ALI) results in severe pulmonary inflammation, pulmonary edema, pulmonary vascular engorgement, diffuse alveolar damage, and refractory hypoxemia [1–3]. Sepsis is the most common risk factor for ALI [4–7]. The fatality rate of sepsis-induced ALI is still as high as 40% [2,8]. Although western medicine that treats sepsis-induced ALI such as broad-spectrum antibiotics, vasoactive medications, and glucocorticoids [3,4,9‒11] may be used to treat clinical symptoms, the complicated and diverse pathophysiology of sepsis-induced ALI makes it difficult to find precise treatments. Furthermore, the toxicity and side effects of existing therapeutic agents do not considerably improve patient prognosis [4,10,12]. Thus, investigating the molecular mechanism of ALI, as well as discovering safe and viable targeted medications for combating ALI, is critical.

The pathological features of sepsis-mediated ALI are lung inflammation, cytokine storms, and damage/dysfunction of the alveolar epithelium-capillary selective barrier [13,14]. Alveolar epithelial cells (AECs) are important defense barriers in lung tissue that can resist the invasion of pathogenic microorganisms while maintaining the integrity of lung tissue in terms of functional and structural dimensions [13]. However, the death of AECs is inexorably connected to the collapse of the alveolar epithelial barrier and the occurrence of ALI [12,14]. Several investigations have revealed that the pathogenesis of ALI in sepsis is accompanied by unique proinflammatory programmed cell death-pyroptosis of AECs [12,13,15,16]. Pyroptosis in human AECs was shown to play a crucial role in lipopolysaccharide (LPS)-induced ALI. Xiang et al. [13], Wang et al. [15], Kang et al. [17] and Zhang et al. [5] studied sepsis, LPS, and H9N2 influenza virus-induced pyroptosis and cytokine storms as prominent mechanisms of ALI.