Alcohol and lung injury and immunity

Abstract

Annually, excessive alcohol use accounts for more than $220 billion in economic costs and 80,000 deaths, making excessive alcohol use the third leading lifestyle-related cause of death in the US. Patients with an alcohol-use disorder (AUD) also have an increased susceptibility to respiratory pathogens and lung injury, including a 2-4-fold increased risk of acute respiratory distress syndrome (ARDS). This review investigates some of the potential mechanisms by which alcohol causes lung injury and impairs lung immunity. In intoxicated individuals with burn injuries, activation of the gut-liver axis drives pulmonary inflammation, thereby negatively impacting morbidity and mortality. In the lung, the upper airway is the first checkpoint to fail in microbe clearance during alcohol-induced lung immune dysfunction. Brief and prolonged alcohol exposure drive different post-translational modifications of novel proteins that control cilia function. Proteomic approaches are needed to identify novel alcohol targets and post-translational modifications in airway cilia that are involved in alcohol-dependent signal transduction pathways. When the upper airway fails to clear inhaled pathogens, they enter the alveolar space where they are primarily cleared by alveolar macrophages (AM). With chronic alcohol ingestion, oxidative stress pathways in the AMs are stimulated, thereby impairing AM immune capacity and pathogen clearance. The epidemiology of pneumococcal pneumonia and AUDs is well established, as both increased predisposition and illness severity have been reported. AUD subjects have increased susceptibility to pneumococcal pneumonia infections, which may be due to the pro-inflammatory response of AMs, leading to increased oxidative stress.

Keywords: Airway cilia; Alcohol; Alveolar macrophage; Gut-liver-lung axis; Lung immunity; Lung injury.

Fig. 1. Hypothetical schema summarizing alcohol-induced systemic oxidative stress

During prolonged alcohol use, the ciliated airway epithelium of the upper airway undergoes post-translational modifications that disrupt ciliary signaling and function, allowing inhaled pathogens into the lower airways and alveolar space. The oxidized alveolar microenvironment in the lower airway alters alveolar macrophage activation, impairing phagocytosis and bacterial clearance. Alcohol-induced gut leak and epithelial barrier dysfunction in the gut cause bacterial products to enter the systemic circulation, leading to subsequent liver steatosis, Kupffer cell activation, and interleukin-6 (IL-6) production and release. Circulating bacterial products and chemokines exacerbate the lung inflammatory response to remote injury and pathogen-associated molecular patterns (PAMPs), increasing susceptibility to bacterial pneumococcal infections.