Background: Ischemia-reperfusion injury (IRI) is an inherent component of solid organ transplantation and axiomatically linked to graft damage. In the kidney, IRI results in a sterile innate inflammatory response with an early damage and activation of vascular endothelial cells (EC). These cells are the first site of graft injury, while neutrophils are the first line of host defense after reperfusion. The degree of initial neutrophil infiltration predicts the severity of the subsequent inflammatory response since neutrophils act as the gate-keeper cell population, orchestrating the influx of subsequent waves of leukocytes into the graft. Therefore, neutrophil transendothelial migration (TEM) represents a promising target to attenuate IRI. One drug known to stabilize EC integrity and to limit neutrophil TEM is Bryostatin-1, an activator of the EC second messenger protein kinase C delta.

Methods: We used an in vitro IRI model with human umbilical vein ECs (HUVECs) and human neutrophils (approved by the ethic committee (STUDY00000261) to study the role of Bryostatin-1 in IRI-induced neutrophil TEM towards the chemoattractant leukotriene B4 (LTB4). HUVECs were exposed to either normoxic (21% O2) or hypoxic (1.5% O2) conditions for 20 hours (h) with and without Bryostatin-1 (1-100nM) followed by 2 h exposure to Calcein-AM dye labeled neutrophils. The degree of TEM was determined by measuring fluorescence intensity and expressed as migration index (dividing numbers of neutrophils migrated to LTB4 by numbers migrated to vehicle). In addition, myeloperoxidase activity (MPO) was measured as a second marker for neutrophil TEM.

Results and Conclusions: Bryostatin-1 dose-dependently inhibited human neutrophil TEM under normoxic and hypoxic conditions. Bryostatin-1 (100nM) blocked TEM towards LTB4 in normoxic conditions, this was intensified when HUVECs were placed in hypoxic conditions. These data were further supported by a mirrored effect when MPO production (a marker of neutrophil activation) was measured. In summary, these promising in vitro results show that our model recapitulates IRI-induced EC damage, and most importantly that Bryostatin-1 can alter neutrophil TEM in an in vitro IRI model.

CITATION INFORMATION: Becker F, Kebschull L, Castor T, Palmes D, Alexander S, Gavins F. Protective Effects of Bryostatin-1 on Neutrophil Migration in an In Vitro Model of Ischemia Reperfusion Injury: Impact for Therapy. Am J Transplant. 2017;17 (suppl 3).

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