A Hyperbaric Warm Perfusion System Preserves Tissue Composites Ex vivo and Delays the Onset of Acute Rejection.

BACKGROUND: Ischemia-reperfusion injury (IRI) precipitates acute rejection of vascularized composite allografts (VCA). Hyperbaric preservation of tissues ex vivo, between harvest and revascularization, may reduce IRI and mitigate acute rejection of VCA. METHODS: A porcine heterotopic musculocutaneous gracilis flap model was used. In phase 1, control autografts (n = 5) were infused with University of Wisconsin Solution (UWS) and stored at 4°C for 3 hours. Intervention autografts (n = 5) were placed in a hyperbaric oxygen organ preservation system for 5 hours and infused with hyperoxygenated UWS at 20°C and 3 atm. Grafts were replanted into the animals' necks. In phase 2, similarly treated control (n = 8) and intervention grafts (n = 8) were allotransplanted into the necks of animals separated by a typed and standardized genetic mismatch. No systemic immunosuppression was given. Systemic markers of IRI, and clinical and histopathological assessments of necrosis and rejection were performed. RESULTS: Autotransplanted tissue composites preserved in the hyperbaric chamber showed histopathological evidence of less muscle necrosis at 3 hours (p = 0.05). Despite a longer period of ischemia, no evidence was found of a difference in systemic markers of IRI following revascularization in these groups. Allotransplanted tissues supported ex vivo within the hyperbaric perfusion device experienced acute rejection significantly later than corresponding controls. CONCLUSION: Hyperbaric warm perfusion preserves musculocutaneous tissue composites ex vivo for longer than standard cold preservation in this model. This translates into a delay in acute rejection of allotransplanted tissue composites.

Silica microspheres are superior to polystyrene for microvesicle analysis by flow cytometry.

BACKGROUND: Cell-derived microvesicles (MVs) in biological fluids are studied for their potential role in pathological conditions. Flow cytometry is used to characterize MVs. Polystyrene microspheres are often used in flow cytometry to distinguish MV from cells by setting a 1-µm MV gate in a side-scatter (SSC) vs. forward-scatter (FSC) dot plot. Polystyrene microspheres, however, exhibit higher FSC and SSC than MVs of equal size. Consequently, some platelets are included within the MV gate, which incorrectly increases the reported percentage of platelet-derived MVs. Silica microspheres exhibit FSC that is closer to that of cellular vesicles and, therefore, should permit more accurate discrimination of MV from platelets. OBJECTIVE: Compare silica with polystyrene microspheres to calibrate flow cytometers for definition of MV population and estimation of MV sizes. METHODS: Silica and polystyrene microspheres of various sizes were used in flow cytometry assays to define MV populations and determine platelet and MV sizes in human plasma samples. Sizes determined by flow cytometry were compared to sizes determined by resistive pulse sensing (RPS) method. RESULTS/CONCLUSION: Use of 1.0-µm polystyrene microspheres to define the upper MV gate produced a median platelet contamination of 16.53% (8.24, 20.98) of the MV population; whereas, use of 1.0-µm silica microspheres excluded platelet events completely. Calibration with silica microspheres resulted in significantly better estimation of MV diameter than calibration with polystyrene microspheres. We conclude that silica microspheres are superior to polystyrene microspheres as standards to define MV populations without platelet contamination and to determine MV sizes by flow cytometry for a given cytometer.