Bronchoalveolar Lavage Cytokine Profiles Reflect Involvement in Pulmonary Recovery After Pulmonary Hypertension in a Pig Model of Endotoxin‐Induced Acute Lung Injury

Abstract

We previously demonstrated in a pig model of acute lung injury (ALI) with endotoxin (ETX)‐induced pulmonary hypertension (PHN) that different cytokines in the circulation appear to mediate pulmonary vasoactivity vs alveolar gas exchange. Despite improvements in PHN and blood gas exchange, serum cytokine levels remain elevated several hours after ETX exposure. With prolonged elevated levels of cytokines, it would be logical that some would be involved in pulmonary recovery from ETX.We sought to further explore the relationship between cytokines and ALI by evaluating lung cytokine levels after ETX‐induced ALI. We tested the hypothesis that cytokine profiles in bronchoalveolar lavage (BAL) specimens several hours after ETX exposure would reflect a reparative response and be different from the blood cytokine profile seen at the initiation of inflammation.Anesthetized Yorkshire cross piglets (n = 17, 7.5 ± 0.2 kg body weight) were catheterized and baseline hemodynamics and blood gases were assessed. E. coli ETX was administered (up to 35,000 units i.v.) and titrated to achieve ALI criteria of PaO2/FiO2 less than 350 mmHg. Pulmonary to systemic vascular resistance ratios (PVR/SVR) were elevated in pigs receiving ETX (0.49 ± 0.04, n = 12) compared to controls (0.20 ± 0.01, n = 5). Blood was obtained every 2–4 hours for blood gases and cytokine profiles (Milliplex MAP for Luminex, MagPix). After 16 hours, BAL was performed for cytokine profiles. Hemodynamic measurements and cytokine levels remained constant in the control group.Compared to controls, blood TNF‐alpha levels remain elevated for 6–10 hours after ETX exposure (p <0.05), while other cytokine levels returned to baseline levels within 2–6 hours. In contrast, BAL obtained 12–16 hours after ETX exposure, showed IL‐2 (0.97 ± 0.11 vs 0.58 ± 0.11 pg/ml, p<0.057), IL‐4 (1.17 ± 0.13 vs 0.59 ± 0.05 pg/ml, p<0.015), and IL‐8 (418 ± 62 vs 167 ± 40 pg/ml, p<0.026) to remain elevated in ETX versus control pigs, respectively.Multiple regression analysis was performed to determine which BAL markers may be related to changes in pulmonary vasoconstriction versus gas exchange. BAL obtained 12–16 hours after ALI compared against PVR/SVR levels during the ALI period showed that PVR/SVR was negatively related to BAL IL‐1b and positively related to BAL IL‐8 and IL‐1a (r = 0.91, p<0.0013). PaO2/FiO2 during early ALI was negatively related to IL‐8 and IL‐6, and positively correlated with IL‐1b, IL‐12, and TNF‐alpha (r = 0.940, p<0.0001) in BAL specimens. The association of elevated BAL IL‐8 with more severe PHN and hypoxemia is consistent with IL‐8 functioning as a chemotactic factor to cause cell migration to inflamed regions of the lung. The prolonged elevation of BAL cytokines specific to regulation of tissue regeneration may serve as good markers for assessment of lung injury severity long after blood circulating cytokine levels have normalized.Support or Funding InformationThis project was funded by the US Army Medical Command. The views expressed in this abstract are those of the authors and do not reflect the official policy or position of the Department of the Army, Department of Defense, or the U.S. Government.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.