Examination of the thermotropic behavior of aqueous dispersions of dipalmitoylphosphatidylcholine-cholesterol mixtures by high-sensitivity scanning calorimetry has revealed that the phospholipid gel to liquid-crystalline phase transition consists of two components. One, a relatively sharp transition centered at 39.6-40.7 degrees C, exhibits a transition enthalpy change which decreases linearly with increasing cholesterol content, approaching zero at a cholesterol content of about 25 mol %. The other, a broad, lower intensity transition centered at approximately 41.5 degrees C for cholesterol concentrations of 20 mol %, displays an enthalpy change which is maximal at about 20-25 mol % cholesterol and which decreases as the cholesterol content decreases to zero or increases above 25 mol %. The origin of these two transitions is discussed in terms of a separation of these lipid mixtures into cholesterol-rich and cholesterol-poor domains.

The thermotropic behavior of aqueous dispersions of palmitoylsphingomyelin-cholesterol and lignoceryl-sphingomyelin-cholesterol mixtures has been examined by high-sensitivity differential scanning calorimetry. When less than 25 mol % cholesterol is mixed with either sphingomyelin, the calorimetric endotherm is composed of a sharp and a broad component. The sharp-component enthalpy change decreases as the mole percent cholesterol increases with the extrapolated zero enthalpy point being 25 to 30 mol %. With palmitoylsphingomyelin, the temperature of maximum heat capacity of the sharp component decreases monotonically with increasing cholesterol content, while the lignocerylsphingomyelin sharp-component maximum remains constant until more than 20 mol % sterol is present. The broad-component enthalpy change maximizes at 3--4 kcal/mol between 10 and 20 mol % cholesterol and decreases as the ratio of cholesterol is increased or decreased from this range for both sphingomyelins. The results are compared with those from a previous study on dipalmitoylphosphatidylcholine-cholesterol mixtures and are interpreted as evidence for the coexistence of cholesterol-rich and cholesterol-poor phases.

Recent in vitro studies have shown that di-2-ethylhexyl-phthalate (DEHP) inhibits the deterioration of RBCs during refrigerated storage in containers that use this compound as a plasticizer. The experiments described in this report were designed to assess whether this in vitro protective effect of DEHP would result in a prolonged in vivo survival of RBCs infused into normal human recipients. Whole blood collected from ten normal donors was stored for 35 days in citrate-phosphate- dextrose-adenine (CPDA-1) anticoagulant contained in polyvinylchloride (PVC) bags plasticized with DEHP or a trimellitate compound that is known to have low leachability. Aliquots of RBCs from each container were then labeled with chromium-51 and were reinfused into the original donors. For blood stored in DEHP-plasticized PVC bags, 24% more red cells survived in vivo 24 hours after reinfusion than was observed when the blood had been stored in trimellitate-plasticized bags (P less than .001). Whole blood stored in glass bottles showed a similar improvement in in vivo survival when DEHP was added in weekly increments to mimic the accumulation of this plasticizer seen during storage in plastic containers. Survival of packed red cells stored in the presence of DEHP increased by 14% compared with storage in trimellitate-plasticized bags (P less than .05). In agreement with previous studies, hemolysis and microvesicle formation were also reduced in the presence of DEHP. These results suggest that proposed new storage systems lacking DEHP should be carefully evaluated to determine whether adequate post-transfusion survival of RBCs may be achieved.

The quenching of fluorescence due to energy transfer between a dilute, random array of donor and acceptor chromophores in lipid bilayer was measured and compared to theoretical expressions developed to predict the decrease in emission intensity under these circumstances. The observed intensity was found to be the same function of quencher concentration in both planar, multilamellar dispersions and small, spherical vesicles. The degree of quenching was accurately predicted by a simple relation derived in this paper, as well as a more complex equation previously developed by Tweet, et al. The results suggest that significant quenching may be observed even when the average donor-acceptor separation exceeds the Förster critical distance by severalfold. Application of these results to problems of current interest in membrane research are discussed.

Over 100 preclinical studies in several small and large animal species were performed to evaluate the safety and efficacy of diaspirin cross-linked hemoglobin (DCLHb; Baxter Healthcare Corp.) as an oxygen therapeutic. During the preclinical evaluation of DCLHb, myocardial lesions were observed following the administration of DCLHb to certain species. These lesions were characterized as minimal to moderate, focal-to-multifocal myocardial degeneration and/or necrosis that were scored using a severity scale of minimal to marked in relative severity. The lesions were typically observed 24-48 h after single topload infusions of DCLHb into rhesus monkeys or pigs at doses as low as 200 or 700 mg/kg, respectively. Dogs, sheep, and rats did not develop these lesions after single-dose administrations of DCLHb. The left ventricular myocardium, typically near the base of or including the papillary muscles, was the most severely affected region, followed by the intraventricular septum and the right ventricle. The left and right atria were usually not affected. In a study in rhesus monkeys, morphometric analysis revealed that these lesions comprised less than 3% of the total myocardium. Although increases in serum enzyme activities (AST, CK, LDH) were observed after infusion of DCLHb, myocardial-related isoenzymes did not increase. ECG analysis and echocardiography were not altered by these lesions, and there was no observable adverse effect on myocardial function. Polymerization of DCLHb reduced, but did not eliminate, the incidence and severity of the lesions. However, infusion of hemoglobin solutions with reduced reaction rates with nitric oxide (NO) resulted in a significant decrease in lesion incidence and severity, while administration of L-NAME, an NO synthase inhibitor, resulted in the appearance of lesions that were indistinguishable from those induced by hemoglobin, suggesting that reduction in normal NO levels is an important mechanistic factor. Overall, the presence of myocardial lesions represents a histopathologic finding that must be considered during the preclinical testing and development of new HBOCs.

In March 2006, a workshop sponsored by the National Heart, Lung, and Blood Institute was convened to identify the role of basic science research in clarifying issues that are impeding progress in the development of hemoglobin-based oxygen carrying (HBOC) solutions. These discussions resulted in a consensus that, although HBOCs have shown clinical promise, various side effects have inhibited further development and regulatory approval, with cardiovascular events being of particular concern. As a consequence, workshop participants focused on formulating research recommendations to better understand and mitigate these side effects. In addition, several important corollary issues were identified, including better understanding of the impact of HBOC infusion on human physiology; the need for rapid, noninvasive methods for the measurement of tissue oxygenation in human patients to better inform transfusion decisions; further investigation of routes and consequences of hemoglobin metabolism; optimization of clinical protocols for HBOC use; and assessment of the impact of HBOC formulation excipients. Also discussed was the possibility and desirability of developing new HBOCs with improved characteristics, such as prolonged functional intravascular persistence, greater stability, and a decreased propensity to generate reactive oxygen species. One practical limitation in this area is the consistent availability of pure, well-characterized HBOC solutions for the research community. This communication summarizes the opinion of workshop participants on these issues and concludes with a list of specific recommended areas of research that could positively impact the development of blood substitutes.

Di-(2-ethylhexyl) phthalate (DEHP) accumulates in blood brought into contact with materials utilizing this compound as a plasticizer. To determine whether this phthalate diester affects red blood cell integrity, we have compared cell morphology, plasma hemoglobin accumulation, micro-vesicle production, and the concentration of intracellular metabolites and electrolytes of erythrocytes from blood stored at 4 degrees C with and without DEHP. When sufficient emulsified DEHP was mixed with blood to give a final concentration of 300 micrograms/mL, plasma hemoglobin accumulation was reduced by an average of 70%, the percentage of cells exhibiting normal morphology was enhanced by at least 20-fold, and the volume of microvesicles released from red blood cells was reduced by 50% after 35 days of refrigerated storage compared to the values obtained from corresponding samples stored without added phthalate. Similar effects were observed regardless of whether blood was stored in nonplasticized polypropylene or tri-(2-ethylhexyl) trimellitate plasticized polyvinylchloride containers and with DEHP solubilized by a variety of emulsifiers. When 300 micrograms/mL DEHP was added to stored blood containing erythrocytes predominantly in the echinocyte conformation, many of the cells reverted to the normal discoid morphology. The addition of this quantity of DEHP to blood had no significant effect on the course of storage-induced changes in erythrocyte adenosine triphosphate (ATP), 2,3-diphosphoglycerate (2,3-DPG), sodium or potassium concentrations. The data are consistent with the hypothesis that DEHP inhibits the deterioration of the red blood cell membrane that results from the refrigerated storage of whole blood.

To determine the feasibility of heat treating hemoglobin solutions to inactivate viruses, we performed experiments on the thermal stability of this protein and found that the structure and function of deoxyhemoglobin are well preserved during incubation at 60 degrees C for 10 hours at a pH of 7.5. Model viruses and the human immunodeficiency virus were rapidly inactivated under these conditions. The results imply that incubation at 60 degrees C is a practical method for inactivating viruses in hemoglobin solutions.