Intra-graft injection of tacrolimus promotes survival of vascularized composite allotransplantation.

BACKGROUND: Immunosuppressive therapies derived from solid organ transplantation are effective in promoting survival of vascularized composite allotransplantation (VCA), but they cause serious side effects that are difficult to justify for this non-life-saving procedure. Unlike solid organ transplantation, hand and face transplants offer the possibility of site-specific immunosuppression for reducing systemic exposure while increasing intra-graft concentrations of the drug. Therefore, in this study, we tested whether a single intra-graft injection tacrolimus could promote VCA survival. METHODS: Brown Norway-to-Lewis hind limb transplantations were performed, and animals were left untreated (group I), treated with a daily injection of 1-mg/kg tacrolimus for 21 days (group 2) or injected with 7-mg tacrolimus directly into the transplanted limb on day 1 (group III). Graft rejection was monitored, and animals were sacrificed at grade 3 rejection or 200 days after transplantation. RESULTS: Intra-graft injection of tacrolimus significantly prolonged allograft survival as compared to untreated animals or animals treated with systemic tacrolimus. Half of the intra-graft-treated rats rejected their graft on average at day 70.5. Interestingly, the other half remained rejection-free for more than 200 days without signs of kidney or liver toxicity. In these animals, tacrolimus was detected in the VCA skin but not in the blood until day 200. Long-term survival was not linked to induction of donor-specific tolerance but to a higher level of lymphocyte chimerism. CONCLUSIONS: Intra-graft delivery of tacrolimus may promote VCA survival by increasing tissue drug availability and promoting the establishment of transient chimerism and thus long-term graft acceptance.

Use of dextran sulfate in tourniquet-induced skeletal muscle reperfusion injury.

BACKGROUND: Lower extremity ischemia-reperfusion injury (IRI)-prolonged ischemia and the subsequent restoration of circulation-may result from thrombotic occlusion, embolism, trauma, or tourniquet application in surgery. The aim of this study was to assess the effect of low-molecular-weight dextran sulfate (DXS) on skeletal muscle IRI. METHODS: Rats were subjected to 3 h of ischemia and 2 or 24 h of reperfusion. To induce ischemia the femoral artery was clamped and a tourniquet placed under the maintenance of the venous return. DXS was injected systemically 10 min before reperfusion. Muscle and lung tissue samples were analyzed for deposition of immunoglobulin M (IgM), IgG, C1q, C3b/c, fibrin, and expression of vascular endothelial-cadherin and bradykinin receptors b1 and b2. RESULTS: Antibody deposition in reperfused legs was reduced by DXS after 2 h (P < 0.001, IgM and IgG) and 24 h (P < 0.001, IgM), C3b/c deposition was reduced in muscle and lung tissue (P < 0.001), whereas C1q deposition was reduced only in muscle (P < 0.05). DXS reduced fibrin deposits in contralateral legs after 24 h of reperfusion but did not reduce edema in muscle and lung tissue or improve muscle viability. Bradykinin receptor b1 and vascular endothelial-cadherin expression were increased in lung tissue after 24 h of reperfusion in DXS-treated and non-treated rats but bradykinin receptor b2 was not affected by IRI. CONCLUSIONS: In contrast to studies in myocardial infarction, DXS did not reduce IRI in this model. Neither edema formation nor viability was improved, whereas deposition of complement and coagulation components was significantly reduced. Our data suggest that skeletal muscle IRI may not be caused by the complement or coagulation alone, but the kinin system may play an important role.

Porcine extrahepatic vascular endothelial asialoglycoprotein receptor 1 mediates xenogeneic platelet phagocytosis in vitro and in human-to-pig ex vivo xenoperfusion.

BACKGROUND: Asialoglycoprotein receptor-1 (ASGR1) mediates capture and phagocytosis of platelets in pig-to-primate liver xenotransplantation. However, thrombocytopenia is also observed in xenotransplantation or xenoperfusion of other porcine organs than liver. We therefore assessed ASGR1 expression as well as ASGR1-mediated xenogeneic platelet phagocytosis in vitro and ex vivo on porcine aortic, femoral arterial, and liver sinusoidal endothelial cells (PAEC/PFAEC/PLSEC). METHODS: Porcine forelimbs were perfused with whole, heparinized human or autologous pig blood. Platelets were counted at regular intervals. Pig limb muscle and liver, as well as PAEC/PFAEC/PLSEC, were characterized for ASGR1 expression. In vitro, PAEC cultured on microcarrier beads and incubated with non-anticoagulated human blood were used to study binding of human platelets and platelet-white blood cell aggregation. Carboxyfluorescein diacetate succinimidyl ester-labeled human platelets were exposed to PAEC/PFAEC/PLSEC and analyzed for ASGR1-mediated phagocytosis. RESULTS: Human platelet numbers decreased from 102 ± 33 at beginning to 13 ± 6 × 10/µL (P < 0.0001) after 10 minutes of perfusion, whereas no significant decrease of platelets was seen during autologous perfusions (171 ± 26 to 122 ± 95 × 10/µL). The PAEC, PFAEC, and PLSEC all showed similar ASGR1 expression. In vitro, no correlation was found between reduction in platelet count and platelet-white blood cell aggregation. Phagocytosis of human carboxyfluorescein diacetate succinimidyl ester-labeled platelets by PAEC/PFAEC/PLSEC peaked at 15 minutes and was inhibited (P < 0.05 to P < 0.0001) by rabbit anti-ASGR1 antibody and asialofetuin. CONCLUSIONS: The ASGR1 expressed on aortic and limb arterial pig vascular endothelium plays a role in binding and phagocytosis of human platelets. Therefore, ASGR1 may represent a novel therapeutic target to overcome thrombocytopenia associated with vascularized pig-to-primate xenotransplantation.