Inflammatory Biomarker Association with Pulmonary Vasoconstriction Versus Blood Oxygenation in a Pig Model of Endotoxin‐Induced Pulmonary Hypertension

Abstract

Escherichia coli sepsis remains the most mortal cause of early‐onset neonatal sepsis and is characterized by an endotoxin lipopolysaccharide (LPS)‐mediated acute inflammatory response and pulmonary edema. Cytokines are increasingly being evaluated as potential biomarkers for diagnosis of sepsis and monitoring of disease severity but the timing of inflammatory changes in relation to pulmonary hypertension and pulmonary function is unclear.We used a piglet model of endotoxin (ETX)‐induced pulmonary hypertension in the absence of systemic shock to test the hypothesis that pulmonary vasoconstriction versus alveolar gas exchange are mediated by different cytokines. Anesthetized Yorkshire cross piglets (8 kg body weight) were catheterized, and after hemodynamic equilibration, baseline mean arterial pressure, cardiac output, pulmonary arterial pressure, and blood gases were assessed. E. coli endotoxin LPS was administered intravenously (n=10) and carefully titrated (7,500–35,000 units) to achieve pulmonary hypertension without systemic hypotension, and acute lung injury (ALI) criteria of PaO2/FiO2 less than 350 mmHg. Control pigs received normal saline (n=5). Pigs were observed for 18 hours with hemodynamic monitoring and blood was obtained every 2–4 hours for assessment of blood gases and cytokine profiles measured by multiplex magnetic bead assay (Milliplex MAP for Luminex). Hemodynamic measurements, blood oxygenation, and cytokine levels remained constant in the control group. Pulmonary hypertension was seen in the ETX group as evidenced by a mean increase in pulmonary to systemic vascular resistance ratio (PVR/SVR) from 0.16 ± 0.01 to 0.44 ± 0.06 (p<0.05).All 13 inflammatory biomarkers examined (GM‐CSF, INFγ, interleukin (IL)‐1a, IL‐1β, IL‐1ra, IL‐2, IL‐4, IL‐6, IL‐8, IL‐10, IL‐12, IL‐18, and TNF‐α) acutely increased within 2 hours of endotoxin‐induced pulmonary hypertension (ANOVA, p<0.05). Inflammatory marker levels along with PVR/SVR, returned toward baseline levels by 4 hours after ETX exposure and remained no different from controls through 18 hours after ETX. Multiple regression analysis was performed to determine which inflammatory markers in the first 2 hours after ETX may be related to the selective pulmonary vasoactive response to ETX as indicated by the PVR to SVR ratio, versus which markers were associated with reduced pulmonary alveolar gas exchange as reflected by PaO2/FiO2. PVR/SVR was most strongly correlated with IL‐6 and TNF‐α and negatively correlated with IL‐1ra (r=0.92, p<0.01), suggesting that IL‐6 and TNF‐α may be involved in mediating pulmonary vasoconstriction, whereas IL‐1ra antagonizes the vasoactive response to endotoxin. PaO2/FiO2 was positively correlated with IL‐1a, and negatively correlated with INFγ, TNF‐α, IL‐2, and IL‐18 (r=0.93, p<0.01). These findings demonstrate that cytokine changes that accompany endotoxin‐induced pulmonary hypertension occur independent of systemic shock. Further, there appears to be specific differential mediation of the pulmonary vascular response versus pulmonary gas exchange by different cytokines.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 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.