Assistant Professor University of Nebraska Medical Center Omaha, Nebraska, United States
Abstract: Congenital heart disease and cardiopulmonary bypass have been implicated in the development of intestinal dysbiosis. Dysbiosis has been shown to exacerbate inflammation in a variety of disease states. Inflammation is a large contributing factor to the morbidity and mortality following cardiac surgery with cardiopulmonary bypass. As we learn more about the importance of the intestinal microbiome, identifying animal models to reduce the dysbiosis and reduce systemic inflammation after cardiopulmonary bypass is important for this patient population.
We set out to determine if an existing piglet model of cardiopulmonary bypass could be used to assess changes to the microbiome, intestinal barrier dysfunction, and intestinal metabolites while evaluating markers for systemic inflammation. We also wanted to evaluate these changes related to data collected in human patients evaluating the same information.
We included 7 control group piglets with mechanical ventilation (MV), and 5 piglets with cardiopulmonary bypass and deep hypothermic circulatory arrest (CPB/DHCA). The MV piglets received 7 hours of ventilatory support before euthanasia. The CPB/DHCA piglets were placed on bypass and then received 75 minutes of DHCA, were rewarmed, and then supported for 4 hours off bypass before euthanasia. Blood and stool were obtained in both groups prior to intervention and then at euthanasia.
While there were no significant differences in overall bacterial abundance between the two groups, measured by operational taxonomic units, we noted reduced phylogenic diversity in the CPB/DHCA group compared to the MV group (p=0.018), figure 1A. There was also significantly different beta diversity between the two groups as well (p=0.017), figure 1B. We noted the presence of intestinal barrier dysfunction with elevations of tight junction proteins claudin-2 (p < 0.0001) and claudin-3 (p < 0.01), along with intestinal specific cytosolic protein fatty acid binding protein 2 (p < 0.01) in plasma samples, seen in comparison with human levels in figure 2. There were significant reductions in all intestinal short chain fatty acids (SCFA) within the CPB/DHCA group, which regulate inflammation and are cardioprotective. Three primary SCFAs compared to human levels of SCFA shown in figure 3. We also identified an increase in IL-1, IL-6, and TNF-a in CPB/DHCA piglets compared to the MV group and show this comparison to human cytokine levels in figure 4.
These results are similar to previously published data on the shift of the microbiome in pediatric patients with congenital heart disease as well as demonstrating evidence of intestinal barrier dysfunction, reduction of short chain fatty acids, along with an increase in systemic inflammatory cytokines. This is the first known animal model of cardiopulmonary bypass to evaluate change to the intestinal microbiome and barrier dysfunction. Identifying this model as feasible to study changes to the microbiome will set the stage for future studies with interventions to the microbiome and evaluation of systemic inflammation through cytokine profiling and immune cell activation.
