Complement-Dependent Inflammation and Injury in a Murine Model of Brain Dead Donor Hearts

Abstract

Rationale: Donor brain death (BD) is an unavoidable occurrence in heart transplantation and results in profound physiological derangements that render the heart more susceptible to ischemia/reperfusion injury in the recipient and likely has negative long-term consequences to allograft survival. Objective: We developed a novel mouse model of BD and investigated the role of complement in BD-induced myocardial inflammation and injury. Methods and Results: BD was induced by inflation of a balloon catheter in the cranial cavity. BD in wild-type mice resulted in a significant increase in serum concentrations of the complement activation product complement component ( Key Words: complement Ⅲ brain death Ⅲ heart transplantation Ⅲ inflammation Ⅲ mouse model H eart transplantation has become a highly successful treatment for end-stage heart disease. Advances in immunosuppression have led to dramatic improvements in first-year survival, in large part, because of better modulation of the alloimmune response. However, despite these improvements, primary graft failure, acute rejection, and cardiac allograft vasculopathy are still major limitations to short and long-term survival. The precise mechanisms involved in the development of primary graft failure and chronic rejection are not well understood. Recently, brain death and ischemia/ reperfusion injury (IRI) have been implicated in graft endothelial activation and injury, which, in turn, have been linked to the pathogenesis of graft dysfunction and chronic rejection. 1-3 Clinical studies of renal transplant recipients and, to a lesser extent, domino donation in heart transplant recipients have highlighted the deleterious impact that donor brain death (BD) has on transplant outcome. 4 Recipients receiving allografts from living donors experience fewer rejection episodes, are less susceptible to primary graft failure, and, as a consequence, survive significantly longer than patients receiving organs from cadaveric sources. 2-5 Initially, it was proposed that these significant improvements were a result of reduced ischemic times, but recent evidence points toward the effects of BD as a stimulating factor in priming the donor organ and rendering it proinflammatory. 2,6,7 BD results in the outpouring of catecholamines, which promotes intense vasoconstriction, leading to chaotic swings in blood pressure, hypothermia, coagulopathies, hormone depletion, and electrolyte abnormalities. The effects on blood pressure are 2-fold: an initial hypertensive phase is followed by hypotension, resulting in an increase in oxygen supply to the heart. However, the increase is still insufficient to cover the enhanced demand and results in transient global myocardial ischemia. 8,9 The imbalance in myocardial oxygen demand and supply renders peripheral organs ischemic, which may activate the endothelium by processes similar to that associated with IRI. The mechanism(s) of donor organ activation has yet to be fully elucidated, but much of the available data from animal studies suggest that imbalances...

Inflammation in Myocardial Diseases

“…180 This is in contrast to C3 Ϫ/Ϫ mice after brain death, which demonstrated less injury of the myocardium, less myocardial infiltration of immune cells, eg, neutrophils, reduced adhesion molecule expression on the cardiac endothelial cells, and reduced levels of circulating proinflammatory cytokines, eg, TNF-␣ and IL-1␤. 180 In mouse models of IR injury, both IgM and MBL have been shown as important mediators of myocardial IR-induced inflammation and complement activation (possibly via the classical and MBL-dependent pathways), ultimately leading to myocardial tissue damage. 185 In another study, inhibition of the MBL via antibodies was shown to repress the severity of myocardial IR injury.…”

Graft-specific immune cells communicate inflammatory immune responses after brain death

“…5-10 Experimental rat models have been critical in dissecting mechanisms subsequent to BD, and mouse BD models may offer additional opportunities to dissect mechanisms. 9 Syngeneic transplant models are able to Flow cytometry analysis of granulocytes and CD4/CD8 þ lymphocytes with extracellular CD69 and intracellular interleukin (IL)-1 and IL-6 staining in recipient splenocytes (n ¼ 6). In recipients of untreated grafts from brain-dead (BD) donors significantly increased counts of neutrophils, CD69 þ , IL-1 þ , and IL-6 þ lymphocytes compared to recipients of immune-deficient and anti-thymocyte globulin (ATG)-treated grafts.…”

The implications of brain death in donor lung injury: investigation and blockade of the endothelin axis

“…[219] Atkinson et al recently demonstrated that passenger leukocytes are recruited to donor hearts after BD in a murine model. [41] This finding was also confirmed in lung [221] and renal allografts. [13] Gelman et al also demonstrated that recipient T-cells interact with donor APC's and that this is sufficient to activate an inflammatory response.…”

“…[129,192] Animal models have shown that serum levels of IL-1β and TNF-α may be influenced by the rate of induction of brain death. [41,193] Avlonitis et al reported that explosive brain death induced a rapid increase in IL-1β, with significantly elevated levels detectable within one hour and remaining so throughout the duration of the study. [193] TNF-α levels initially rose and then decreased by five hours, though it remained above baseline.…”

“…[13] Complement interacts with, and reinforces, the inflammatory process of IRI by increasing TNF-α and IL-1. [41] C3a and C5a, potent anaphylatoxins generated by the complement cascade, activate mast cells and neutrophils. [220] While the specific mechanism of complement activation in BD is unknown, it is postulated that ischaemia leads to defects in cell membranes, uncovering neoepitopes via exposure of internal cellular components to the humoral immune system, which leads to interaction with natural IgM and activation of the classical complement pathway.…”