Noninvasive biomarkers for the detection of GERD-induced pulmonary injury

Background: The role of gastroesophageal reflux in progressive lung damage is increasingly recognized. We have proposed, based on our work with lung transplant recipients, a novel immune mechanism of pulmonary injury after aspiration of gastric contents, during which higher levels of normally sequestered lung self-antigens (SAgs) collagen V (Col-V) and K-alpha-1 tubulin (Kα1T) in circulating small extracellular vesicles (EVs) induce the production of self-antibodies (SAbs) anti-Col-V and anti-Kα1T. Thus, we aimed to determine whether levels of SAbs or SAgs increased in an animal model of aspiration-induced lung damage in a nontransplant setting. Methods: We created a murine model of repetitive lung aspiration using C57BL/6J mice. Mice were aspirated weekly with 1 mL/kg of hydrochloric acid (n = 9), human gastric contents (n = 9), or combined (1:1) fluid (n = 9) once, three, or six times (n = 3 in each subgroup; control group, n = 9). Blood samples were periodically obtained, and all animals were sacrificed at day 90 for pathological assessment. SAbs were measured using an enzyme-linked immunosorbent assay; SAgs and NF-κB contained in small EVs were assessed by western blot. Results: Aspirated mice weighed significantly less than controls throughout the study and had histological evidence of pulmonary injury at day 90. Overall, aspirated mice developed higher concentrations of anti-Col-V at day 28 (53.9 ± 28.7 vs. 29.9 ± 4.5 ng/mL, p < 0.01), day 35 (42.6 ± 19.8 vs. 28.6 ± 7.2 ng/mL, p = 0.038), and day 90 (59.7 ± 27.7 vs. 34.1 ± 3.2 ng/mL, p = 0.014) than the control group. Circulating small EVs isolated from aspirated mice on day 90 contained higher levels of Col-V (0.7 ± 0.56 vs. 0.18 ± 0.6 m.o.d., p = 0.009) and NF-κB (0.42 ± 0.27 vs. 0.27 ± 0.09 m.o.d., p = 0.095) than those from controls. Conclusions: This experimental study supports the theory that gastroesophageal reflux leads to the development of lung damage and an increase of humoral markers that may serve as noninvasive biomarkers to detect asymptomatic lung injury among patients with gastroesophageal reflux disease.