Fludarabine is a nonmyeloablative immunosuppressant increasingly used as a component of alternative conditioning regimens before allogeneic bone marrow transplantation. It is expected to reduce conditioning-related toxicity and proinflammatory activation of the host tissues. However, in our in vitro study, we provide evidence that 2-fluoroadenine 9-␤-D-arabinofuranoside (F-Ara) as the active metabolized form of fludarabine damages human microvascular endothelial cells (HMECs) and dermal and alveolar epithelial cell lines after 48 hours of culture when it is used in pharmacologically relevant concentrations (range, 10 g/mL-1 g/mL). In addition, flow cytometric analyses revealed a significant up-regulation of intercellular adhesion molecule 1 and major histocompatibility complex (MHC) class I molecules by F-Ara, suggesting a proinflammatory activation of HMECs. Cytotoxicity assays demonstrated that target HMECs pretreated with F-Ara (10 g/ mL) showed increased lysis by allogeneic MHC class I-restricted cytotoxic T lymphocytes from healthy human donors. We conclude that, beside its immunosuppressive activities, F-Ara can be harmful for target tissues of transplantation-related complications and can even stimulate allogeneic immune responses. We identified the pharmaceutical compound defibrotide as protective against F-Arainduced apoptosis and alloactivation, importantly, without affecting the antileukemic effect of F-Ara. This observation argues for a potential clinical usage of defibrotide in pretransplantation conditioning. (Blood. 2002;100:334-340)

Our study shows that inhibition of the reverse mode of the NCE, during reperfusion only, protects cardiomyocytes and whole hearts against reperfusion injury.

The novel inhibitor of the reverse mode of the Na+/Ca2+exchanger (NCE) KB-R7943 (KB) was tested in isolated rat cardiomyocytes exposed to 80 min of simulated ischemia [substrate-free anoxia, extracellular pH (pHo) of 6.4] and 15 min of reoxygenation (pHo 7.4). At pHo 6.4, 20 μmol/l KB was required for complete inhibition of the reverse mode of NCE. Treatment with 20 μmol/l KB only during anoxia did not influence the onset of rigor contracture and intracellular pH (pHi) (monitored with 2′,7′-bis(2-carboxyethyl)-5(6)-carboxyfluorescein) but significantly reduced the cytosolic accumulation of Ca2+ (monitored with fura 2) and Na+ (monitored with sodium-binding benzofuran isophthalate). During reoxygenation, cardiomyocytes developed hypercontracture. This was significantly reduced by anoxic KB treatment. To investigate this protection against reoxygenation-induced injury in the whole heart, we exposed Langendorff-perfused rat hearts to 110 min of anoxia (pHo 6.4) and 50 min of reoxygenation (pHo 7.4). Application of 20 μmol/l KB during anoxia significantly reduced the reoxygenation-induced enzyme release. We conclude that KB offers significant protection of cardiomyocytes against Ca2+ and Na+ overload during anoxia and hypercontracture or enzyme release on reoxygenation.

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