Saturday, May 4, 2024
5/4/2024
Surgical repair of congenital heart defects is associated with significant morbidity and mortality. Most pediatric open- heart surgeries involve cardiopulmonary bypass (CPB). A core challenge for these patients is the systemic inflammation and resultant multi-organ dysfunction that occurs in response to CPB. This issue remains an intractable problem despite changes to surgical techniques and corticosteroid administration. Our long-term goals are to understand how the physiological insults present during CPB promote post-CPB inflammation and translate this knowledge into new CPB designs and treatment strategies. The scientific premise for this project is that red blood cells (RBCs) contribute to CPB associated inflammation by activating innate immunity responses. An emerging body of literature suggests that RBCs can actively modulate innate immunity responses. The non-physiologic stimuli present during CPB, particularly elevated shear stress, can induce significant phenotypic changes in the RBCs. For neonatal and pediatric patients, CPB typically involves exposure to exogenous RBCs in the form of “blood priming” of the CPB circuit that may contribute to systemic inflammation after CPB. Current clinical efforts to perform CPB with “clear prime”, filling the circuit with crystalloid fluids, provide a unique opportunity to examine how exposure to exogenous RBCs propagates CPB associated inflammation. Thus, we hypothesize that endogenous and exogenous RBCs injured by supraphysiological shear stress, contribute to the activation of innate immunity responses that drive the post-CPB systemic inflammation and multi-organ dysfunction. Aim 1. Determine the RBC phenotype changes caused by exposure to the supraphysiologic shear stresses present in the CPB circuit. We postulate that supraphysiologic shear stress injures the RBCs, inducing phenotypic changes that cause them to become pro-inflammatory. We will perform computational simulations and in vitro experiments to uncover the shear thresholds (both intensity and duration) and molecular mechanisms involved in the CPB-associated pro- inflammatory RBC injury, which will be validated using samples from pediatric CPB patients. Aim 2. Does CPB promote erythrophagocytosis that exacerbates myeloid cell activation? We postulate that the interactions between RBCs and circulating leukocytes exacerbate the shear- mediated activation of inflammatory phenotypes of the circulating myeloid cells. This aim will will use in vitro experiments, patient samples, and a piglet model of CPB to determine if CPB increases erythrophagocytosis and if erythrophagocytosis activates myeloid cells. Aim 3. Determine if clear priming of CPB circuit reduces CPB associated inflammation. We postulate that the exogenous RBCs used to prime the CPB circuit activate myeloid cells during CPB. In vitro experiments and a pilot clinical study in pediatric patients will determine if using “clear prime” can ameliorate CPB-associated inflammation. Furthermore, we will study if there are differences in clinical outcomes between the clear primed and blood primed patients. This research is novel and significant – the proposed mechanistic and clinical experiments could give rise to a new treatment paradigm for CPB patients, improve outcomes, and reduce healthcare costs by identifying potential molecular targets and supporting the shift towards “clear prime” for CPB to limit the contributions of RBCs to inflammation.
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