L-arginine improves endothelial and myocardial function after brain death

Vascular Signaling in Allogenic Solid Organ Transplantation - The Role of Endothelial Cells

Graft rejection remains the major obstacle after vascularized solid organ transplantation. Endothelial cells, which form the interface between the transplanted graft and the host’s immunity, are the first target for host immune cells. During acute cellular rejection endothelial cells are directly attacked by HLA I and II-recognizing NK cells, macrophages, and T cells, and activation of the complement system leads to endothelial cell lysis. The established forms of immunosuppressive therapy provide effective treatment options, but the treatment of chronic rejection of solid organs remains challenging. Chronic rejection is mainly based on production of donor-specific antibodies that induce endothelial cell activation—a condition which phenotypically resembles chronic inflammation. Activated endothelial cells produce chemokines, and expression of adhesion molecules increases. Due to this pro-inflammatory microenvironment, leukocytes are recruited and transmigrate from the bloodstream across the endothelial monolayer into the vessel wall. This mononuclear infiltrate is a hallmark of transplant vasculopathy. Furthermore, expression profiles of different cytokines serve as clinical markers for the patient’s outcome. Besides their effects on immune cells, activated endothelial cells support the migration and proliferation of vascular smooth muscle cells. In turn, muscle cell recruitment leads to neointima formation followed by reduction in organ perfusion and eventually results in tissue injury. Activation of endothelial cells involves antibody ligation to the surface of endothelial cells. Subsequently, intracellular signaling pathways are initiated. These signaling cascades may serve as targets to prevent or treat adverse effects in antibody-activated endothelial cells. Preventive or therapeutic strategies for chronic rejection can be investigated in sophisticated mouse models of transplant vasculopathy, mimicking interactions between immune cells and endothelium.

Short- and long-term effects of brain death on post-transplant graft function in a rodent model

OBJECTIVES

Heart transplantation has become the most effective treatment for end-stage heart failure. Donors after brain death (BD) are currently the only reliable source for cardiac transplants. However, haemodynamic instability and cardiac dysfunction have been demonstrated in brain-dead donors and this could therefore also affect post-transplant graft function. We studied the effects of BD on cardiac function and its short-term (1 h) or long-term (5 h) impacts on graft function.

METHODS

In Lewis rats, BD was induced by inflation of a subdurally placed balloon catheter (n = 7). Sham-operated rats served as controls (n = 9). We continuously assessed cardiac function by left ventricular (LV) pressure-volume analysis. Then, 1 or 5 h after BD or sham operation, hearts were perfused with a cold preservation solution (Custodiol), then explanted, stored at 4°C in Custodiol and heterotopically transplanted. We evaluated graft function 1.5 h after transplantation.

RESULTS

BD was associated with decreased left ventricular contractility (ejection fraction: 37 ± 6 vs 57 ± 5%; maximum rate of rise of LV pressure dP/dtmax: 4770 ± 197 vs 7604 ± 348 mmHg/s; dP/dtmax-end-diastolic volume: 60 ± 7 vs 74 ± 2 mmHg/s; slope Emax of the end-systolic pressure-volume relationship: 2.4 ± 0.1 vs 4.4 ± 0.3 mmHg/µl; preload recruitable stroke work: 47 ± 9 vs 78 ± 3 mmHg; P <0.05) and relaxation (maximum rate of fall of left ventricular pressure dP/dtmin: -6638 ± 722 vs -11 285 ± 539 mmHg/s; time constant of left ventricular pressure decay Tau: 12.6 ± 0.7 vs 10.5 ± 0.4 ms; end-diastolic pressure-volume relationship: 0.22 ± 0.05 vs 0.09 ± 0.03 mmHg/µl, P <0.05) 45 min after its initiation and for the rest of 5 h compared with controls. Moreover, after transplantation, graft systolic and diastolic functions were impaired in the 5-h brain-dead group, while they were identical in the 1-h brain-dead group compared with the corresponding controls.

CONCLUSIONS

We established a well-characterized in vivo rat model to examine the influence of BD on cardiac function using a miniaturized technology for pressure-volume analysis. These results demonstrate that impaired donor cardiac function after short-term BD is reversible after transplantation and long-term BD renders hearts more susceptible to ischaemia/reperfusion injury.

Sodium nitrite protects against kidney injury induced by brain death and improves post-transplant function

Renal injury induced by brain death is characterized by ischemia and inflammation and limiting it is a therapeutic goal that could improve outcomes in kidney transplantation. Brain death resulted in decreased circulating nitrite levels and increased infiltrating inflammatory cell infiltration into the kidney. Since nitrite stimulates nitric oxide signaling in ischemic tissues, we tested whether nitrite therapy was beneficial in a rat model of brain death followed by kidney transplantation. Nitrite, administered over 2 hours of brain death, blunted the increased inflammation without affecting brain death-induced alterations in hemodynamics. Kidneys were transplanted after 2 hours of brain death and renal function followed over 7 days. Allografts collected from nitrite-treated brain dead rats showed significant improvement in function over the first 2 to 4 days post transplantation compared to untreated brain dead animals. Gene microarray analysis after 2 hours of brain death without or with nitrite therapy showed the latter significantly altered the expression of about 400 genes. Ingenuity Pathway analysis indicated multiple signaling pathways were affected by nitrite, including those related to hypoxia, transcription and genes related to humoral immune responses. Thus, nitrite-therapy attenuates brain death-induced renal injury by regulating responses to ischemia and inflammation, ultimately leading to better post-transplant kidney function.