Osmotic tolerance limits of red blood cells from umbilical cord blood.

Effective methods for long-term preservation of cord red blood cells (RBCs) are needed to ensure a readily available supply of RBCs to treat fetal and neonatal anemia. Cryopreservation is a potential long-term storage strategy for maintaining the quality of cord RBCs for the use in intrauterine and neonatal transfusion. However, during cryopreservation, cells are subjected to damaging osmotic stresses during cryoprotectant addition and removal and freezing and thawing that require knowledge of osmotic tolerance limits in order to optimize the preservation process. The objective of this study was to characterize the osmotic tolerance limits of cord RBCs in conditions relevant to cryopreservation, and compare the results to the osmotic tolerance limits of adult RBCs. Osmotic tolerance limits were determined by exposing RBCs to solutions of different concentrations to induce a range of osmotic volume changes. Three treatment groups of adult and cord RBCs were tested: (1) isotonic saline, (2) 40% w/v glycerol, and (3) frozen-thawed RBCs in 40% w/v glycerol. We show that cord RBCs are more sensitive to shrinkage and swelling than adult RBCs, indicating that osmotic tolerance limits should be considered when adding and removing cryoprotectants. In addition, freezing and thawing resulted in both cord and adult RBCs becoming more sensitive to post-thaw swelling requiring that glycerol removal procedures for both cell types ensure that cell volume excursions are maintained below 1.7 times the isotonic osmotically active volume to attain good post-wash cell recovery. Our results will help inform the development of optimized cryopreservation protocol for cord RBCs.

Osmotic parameters of red blood cells from umbilical cord blood.

The transfusion of red blood cells from umbilical cord blood (cord RBCs) is gathering significant interest for the treatment of fetal and neonatal anemia, due to its high content of fetal hemoglobin as well as numerous other potential benefits to fetuses and neonates. However, in order to establish a stable supply of cord RBCs for clinical use, a cryopreservation method must be developed. This, in turn, requires knowledge of the osmotic parameters of cord RBCs. Thus, the objective of this study was to characterize the osmotic parameters of cord RBCs: osmotically inactive fraction (b), hydraulic conductivity (Lp), permeability to cryoprotectant glycerol (Pglycerol), and corresponding Arrhenius activation energies (Ea). For Lp and Pglycerol determination, RBCs were analyzed using a stopped-flow system to monitor osmotically-induced RBC volume changes via intrinsic RBC hemoglobin fluorescence. Lp and Pglycerol were characterized at 4°C, 20°C, and 35°C using Jacobs and Stewart equations with the Ea calculated from the Arrhenius plot. Results indicate that cord RBCs have a larger osmotically inactive fraction compared to adult RBCs. Hydraulic conductivity and osmotic permeability to glycerol of cord RBCs differed compared to those of adult RBCs with the differences dependent on experimental conditions, such as temperature and osmolality. Compared to adult RBCs, cord RBCs had a higher Ea for Lp and a lower Ea for Pglycerol. This information regarding osmotic parameters will be used in future work to develop a protocol for cryopreserving cord RBCs.

A method to measure permeability of red blood cell membrane to water and solutes using intrinsic fluorescence.

BACKGROUND: Designing effective cryopreservation procedures for cells requires knowledge of permeability of cell membrane to water and solutes. To determine cell membrane permeability, one needs to measure the rate of cell volume changes in anisotonic environment. Red blood cells (RBCs) respond very quickly to changes in extracellular solutes concentration, which complicates the use of traditional methods. Preservation of RBCs from umbilical cord blood for neonatal transfusions is currently broadly discussed in the literature, but data on osmotic permeability of cord RBCs is controversial. Therefore, alternative methods to determine osmotic membrane permeability of these cells are warranted. We describe a technique to measure rapid changes in RBC volume through changes in the intensity of RBC autofluorescence. METHODS: To induce osmotically-driven changes in RBC volume, we rapidly mixed human RBCs with anisotonic solutions in a stopped-flow spectroscopy system and the intensity of intrinsic RBC fluorescence was measured. RESULTS: We found that change in RBC volume cause a proportional change in the intensity of RBC autofluorescence. This phenomenon occurs due to the self-quenching of RBC hemoglobin autofluorescence at high intracellular concentrations. CONCLUSIONS: This novel method to determine osmotic permeability of RBCs overcomes the limitations of traditional techniques and has numerous clinical applications.

Quality of red blood cells isolated from umbilical cord blood stored at room temperature.

Red blood cells (RBCs) from cord blood contain fetal hemoglobin that is predominant in newborns and, therefore, may be more appropriate for neonatal transfusions than currently transfused adult RBCs. Post-collection, cord blood can be stored at room temperature for several days before it is processed for stem cells isolation, with little known about how these conditions affect currently discarded RBCs. The present study examined the effect of the duration cord blood spent at room temperature and other cord blood characteristics on cord RBC quality. RBCs were tested immediately after their isolation from cord blood using a broad panel of quality assays. No significant decrease in cord RBC quality was observed during the first 65 hours of storage at room temperature. The ratio of cord blood to anticoagulant was associated with RBC quality and needs to be optimized in future. This knowledge will assist in future development of cord RBC transfusion product.

Intracellular ice formation in confluent monolayers of human dental stem cells and membrane damage.

Dental pulp stem cells (DPSCs) are of interest to researchers and clinicians due to their ability to differentiate into various tissue types and potential uses in cell-mediated therapies and tissue engineering. Currently DPSCs are cryopreserved in suspension using Me(2)SO. However, preservation as two and three dimensional constructs, along with the elimination of toxic Me(2)SO, may be required. It was shown that intracellular ice formation (IIF), lethal to cells in suspensions, may be innocuous in cell monolayers due to ice propagation between cells through gap junctions that results in improved post-thaw recovery. We hypothesized that innocuous IIF protects confluent DPSC monolayers against injury during cryopreservation. The objective was to examine the effects of IIF on post-thaw viability of both confluent monolayers and suspensions of DPSCs. Confluent DPSC monolayers were assessed for the expression of gap junction protein Connexin-43. IIF was induced on the cryostage and in the methanol bath at different subzero temperatures. Membrane integrity and colony-forming ability were assessed post-thaw. Confluent DPSC monolayers expressed Connexin-43. In cell suspensions, 85.9+/-1.7% of cells were damaged after 100% IIF. In cell monolayers, after 100% IIF, only 25.5+/-5.5% and 14.8+/-3.3% of cells were damaged on the cryostage and in the methanol bath respectively. However, DPSC monolayers exposed to 100% IIF showed no colony-forming ability. We conclude that confluent monolayers of DPSCs express the gap junction-forming protein Connexin-43 and upon IIF retain membrane integrity, however lose the ability to proliferate.