Hemoglobin-based oxygen-carrying resuscitation fluids.
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Animals↗
Biomedical subjects
A S Rudolph
Publications and source records attributed to A S Rudolph.
Physiological responses, organ distribution, and circulation kinetics in anesthetized rats after hypovolemic exchange transfusion with technetium-99m-labeled liposome-encapsulated hemoglobin.
Physiological responses and circulation properties of liposome-encapsulated hemoglobin (LEH) labeled with technetium-99m (99mTc) were measured in rats after a 10% (170 mg/kg hemoglobin; 430 mg/kg phospholipid) or a 50% (450 mg/kg hemoglobin, 2.3 g/kg phospholipid) hypovolemic exchange transfusion (n = 5 per exchange group). Mean arterial pressure returned to baseline values (105 +/- 8 mmHg) by 90 min post-infusion for both groups. By 20 h, mean arterial pressure remained at baseline values for the 10% group, but dropped to 30 +/- 14 mmHg for the 50% group. For both groups, bradycardia was seen after the exchange period, but heart rate recovered by 30 min for the 10% group and by 90 min for the 50% group. The 99mTc-LEH remained in circulation longer for the 50% group (18.2 h half-life) than for the 10% group (2.4 h half-life). Removal of 99mTc-LEH from the bloodstream was via the liver and spleen. At 20 h, 99mTc-LEH accumulation in these organs was greater for the 10% group (liver, 36.2 +/- 1.7%; spleen, 37.5 +/- 2.5%) than for the 50% group (liver, 17.0 +/- 1.4%; spleen, 17.1 +/- 1.4%). The data show that there is less clearance of 99mTc-LEH from the bloodstream by the reticuloendothelial system after a 50% hypovolemic exchange transfusion, thus supporting the possible use of LEH as an oxygen-carrying resuscitative fluid in situations of severe blood loss.
Anesthetics↗
A comparative study of the accurate measurement of endotoxin in liposome-encapsulated hemoglobin.
We have examined three different methods of endotoxin determination utilizing the Limulus Amebocyte Lysate (LAL) assay to accurately determine endotoxin levels in Liposome Encapsulated Hemoglobin (LEH), 1) the gel-clot method, 2) chromogenic spectroscopic-based LAL, and 3) the turbidimetric method which determines endotoxin levels in solutions based on the time needed to reach a specific degree of turbidity. Both the chromogenic and turbidimetric methods require significant dilution of the LEH preparation before accurate measurement can be made. We have tested the levels of endotoxin in LEH solutions using these methods and measured LEH, liposome, and hemoglobin samples spiked with known amounts of endotoxin. A comparison of the three methods shows that the absolute value of endotoxin measured in LEH by the three methods can vary significantly. However, within any one assay the spiked amount of endotoxin in the sample can be accurately measured. The accuracy of these methods may also be complicated by the binding of endotoxin to LEH. This was evident by mixing free endotoxin with LEH followed by centrifugation to separate the LEH. Biological activity of endotoxin bound to LEH was measured by exposure to RAW264.7 followed by the expression of tumor necrosis factor.
Chromogenic Compounds↗
Complement activation by liposome-encapsulated hemoglobin in vitro: the role of endotoxin contamination.
Incubation of liposome-encapsulated Hb (LEH) with rat serum at 37 degrees C led to accelerated decay of serum hemolytic complement (C) activity (CH50/ml). Empty liposomes (L) caused less decrease of CH50/ml, whereas free Hb had no effect on C activity. The LEH- and L-induced increases in C consumption were unlikely a consequence of endotoxin (LPS) contamination, as spiking of rat serum with LPS caused reduction in C only at levels significantly higher than those detectable in LEH or L. LPS-induced C consumption was not potentiated by free hemoglobin.
Animals↗
Complement activation in rats by liposomes and liposome-encapsulated hemoglobin: evidence for anti-lipid antibodies and alternative pathway activation.
Intravenous injection of hemoglobin-containing liposomes (LEH) caused a significant reduction in plasma hemolytic complement activity in rats on a time scale of minutes. Liposomes without hemoglobin also caused complement consumption, but less than LEH, while free hemoglobin was without effect. Consistent with complement activation, the LEH-induced drop in plasma hemolytic complement activity was closely paralleled by an increase in plasma thromboxane B2 level. Studies to determine the mechanism of complement activation demonstrated the presence of natural antibodies in rat serum against all lipid components of LEH, thus, the potential for classical pathway activation. Yet, in vitro incubation of LEH with rat serum showed that: 1) EGTA/Mg++, which inhibits complement activation through the classical pathway, did not inhibit complement consumption by LEH, and 2) the use of serum preheated at 50 degrees C, which inhibits C activation through the alternative pathway by selectively depleting factor B, effectively reversed the complement-consuming effect of LEH. Consequently, LEH-induced complement activation in rat serum seems to involve primarily the alternative pathway.
Animals↗
Spatially controlled adhesion, spreading, and differentiation of endothelial cells on self-assembled molecular monolayers.
Chemically modified glass substrates were used to demonstrate differential adhesion, growth, and differentiation of endothelial cells. Endothelial cells were examined for adhesion and growth on glass, glass treated with N-(2-aminoethyl)-3-aminopropyl trimethoxysilane (EDA), or EDA with a subsequent treatment with physically adsorbed extracellular matrix components human fibronectin and heparin sulfate. EDA and EDA/human fibronectin showed similar abilities to support adhesion, spreading, and proliferation of endothelial cells. In contrast, heparin sulfate inhibited endothelial cell adhesion to EDA. Differentiation of endothelial cells resulting in precapillary cord formation was triggered by addition of basic fibroblast growth factor (bFGF). On EDA and EDA/human fibronectin bFGF causes confluent endothelial cell monolayers to differentiate and form cords, which resulted in a large-scale spatial redistribution of cells on the surface. Formation of organized neovascular assemblies was demonstrated on coplanar molecular patterns of EDA and a nonadhesive perfluorinated alkylsilane (tridecafluoro-1,1,2,2-tetrahydrooctyl)-1-dimethylchloros ilane (13F). Endothelial cells preferentially adhered to the EDA lines and after 24-48 hr, microfilaments aligned with the long axes of the patterned EDA region. Finally, endothelial cells that became confluent within the confines of the EDA region (bound by the nonadhesive, 13F domains) were observed to differentiate into neovascular cords in long-term culture (7-10 days) with bFGF.
Actin Cytoskeleton↗
Biomaterial biotechnology using self-assembled lipid microstructures.
Lipids are a class of molecules which self-assemble into a variety of phase-dependent morphologies. We have employed self-assembled lipid microstructures in the development of a number of biomedical material applications. The blood substitute, liposome encapsulated hemoglobin, is being investigated for the in vivo delivery of hemoglobin without many of the inherent toxicities associated with the delivery of free hemoglobin. This investigation is currently focused on demonstrations of efficacy in stressed animal models and on the safety of administering this material in models of sepsis. The synthetic modification of phospholipids to include photopolymerizable moieties such as diacetylenes has resulted in the spontaneous self-assembly of a hollow microcylinder which we are investigating for the controlled release of growth factors in soft tissue regeneration. Self-assembled monolayers are also being explored for the ability to surface modify biomaterials for improved cell adhesion. Photolithographic techniques have been combined with monolayer deposition to fabricate coplanar patterns of cell adhesion and inhibiting moieties. This results in the ability to spatially control the adhesion of cells to biomaterial surfaces. These cell patterns can form the basis for understanding two- and three-dimensional cellular events on the biomaterial surface and for the fabrication of improved cell-based biocompatible surfaces. The spontaneous self-assembly of lipids to form structures of biotechnological interest presents a unique opportunity to exploit this class of molecules for biomaterial applications.
Animals↗
Transient changes in the mononuclear phagocyte system following administration of the blood substitute liposome-encapsulated haemoglobin.
We have examined the effects of administration of the blood substitute, liposome-encapsulated haemoglobin (LEH), in the normovolaemic rat. Test groups included LEH, lyophilized EH, the liposome vehicle, unencapsulated haemoglobin and normal saline, which were injected into the tail vein (n = 6; n = 3 for sham and saline groups). Administration of LEH (2.5 g phospholipid, 1.25 g haemoglobin/kg rat) was followed by blood sampling at 2 h, 24 h, 1 wk and 2 wk. Blood samples were analysed for alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, gamma-glutamyltransferase, total and indirect bilirubin, serum creatinine, albumin, total protein, lipase, cholesterol, blood urea nitrogen, haematocrit, haemoglobin and differential white blood cell counts. Observed effects following injection were mild and transient, with baseline values recovered at 1 wk. Alanine aminotransferase increased moderately in the LEH group at 24 h to 601 +/- 143 IU/dl (P < 0.0001), with a return to baseline at 1 wk. Aspartate aminotransferase showed a smaller increase from 46 +/- 5 to 162 +/- 40 at 24 h and also returned to baseline at the 1 wk measurement (P < 0.001). The transient increase in serum transaminases was not observed for the lyophilized LEH group. Tissue sections showed accumulation of liposome groups in resident macrophages of the liver and spleen. Incubation of an adherent population of human peripheral blood monocytes with LEH in culture did not elicit the production of the inflammatory cytokine, tumour necrosis factor. Pre-incubation of monocytes with LEH prior to exposure to endotoxin did, however, result in a reduced expression of this inflammatory cytokine.
Animals↗
Recruitment of tissue resident cells to hydrogel composites: in vivo response to implant materials.
A model of local cellular recruitment was established using hydrogel matrices composed of alginate implanted subcutaneously into mice. Cells which trafficked to the matrix blocks were recovered and characterized for surface phenotype using fluorescently labelled antibodies and flow cytometry (fluorescence activated cell sorting). Temporal information of the differential recruitment of cells was determined. The basic pattern of recruitment in response to the hydrogels was established and mimicked that seen in a local inflammatory response. Neutrophils (PMN) were rapidly recruited (1 d) followed by macrophages and lymphocytes (1-3 d). Cell surface phenotype studies included the determination of CD3+, CD4+ and CD8+ cells, Mac-1+ cells, and immunoglobulin bearing cells. Microscopic analysis revealed numerous activated PMNs and monocyte derived foamy macrophages. Fluorescence immunocytochemistry of frozen sections of the block revealed that macrophages, CD3+ and natural killer cells were all recruited to the interior of the block. Ultrastructural analysis (transmission electron microscopy) showed highly activated macrophages, with abundant rough endoplasmic reticulum and secretory vesicles. Cells which remained on the surface of the matrix block were CD44 positive migratory cells. Electron microscopic evidence showed foamy macrophages with a varying degree of involvement with the hydrogel material. Surface scanning electron microscopy revealed numerous fibroblast-like cells coating the surface of the block. We suggest that these methods may be used to address the inflammatory response elicited with a a variety of implanted materials such as hydrogels, silicones, ceramics and metals. Furthermore, this model has been useful in determining cellular responses to cytokines and growth factors under similar conditions.
Alginates↗
Circulation persistence and biodistribution of lyophilized liposome-encapsulated hemoglobin: an oxygen-carrying resuscitative fluid.
OBJECTIVE: To evaluate the circulation persistence and organ biodistribution of a freeze-dried, oxygen carrying resuscitative fluid: liposome-encapsulated hemoglobin. DESIGN: Randomized, animal studies. SETTING: Accredited animal research facilities. SUBJECTS: Normal female Balb/c mice and male New Zealand rabbits. INTERVENTIONS: Two groups of normal female Balb/c mice were injected in the tail vein with either lyophilized liposome-encapsulated hemoglobin (n = 9) that was reconstituted just before administration, or with unlyophilized liposome-encapsulated hemoglobin (n = 9) as a comparison. Two groups of male New Zealand rabbits were injected in the ear vein with either lyophilized 99mTc-liposome-encapsulated hemoglobin (n = 6) or unlyophilized 99mTc-liposome-encapsulated hemoglobin as a comparison (n = 6). After injection, mice were anesthetized by brief inhalation of halothane followed by blood sampling through the retro-orbital sinus. Rabbits were anesthetized 30 mins before liposome-encapsulated hemoglobin administration with an intramuscular injection of a 5:1 mixture of ketamine (50 mg/kg) and xylazine (10 mg/kg). Rabbits were then dynamically imaged for 90 mins, housed, and at 20 hrs, imaging again followed by autopsy and tissue sampling to validate imaged organ biodistributions. MEASUREMENTS: Circulation persistence in the mouse was measured by removing a blood sample at various time points up to 24 hrs after injection. The blood sample was centrifuged in a hematocrit capillary tube and the disappearance of the sedimented liposome-encapsulated hemoglobin fraction was measured. The change in the sedimented fraction of the liposomes with time was used to generate circulation persistence profiles in mice. The circulation persistence and organ biodistribution of 99mTc-liposome-encapsulated hemoglobin was measured by circling regions of interest on computer-generated gamma camera images. These image intensities were then calculated as a function of total injected dose which was measured from a known volume and activity of 99mTc-liposome-encapsulated hemoglobin. Actual tissue uptake was estimated from images by subtracting blood pool contribution which was measured by injecting 99mTc-labeled rabbit red cells. Imaged organ biodistribution was validated at 20 hrs by measuring activity in weighed portions of tissue after autopsy. MAIN RESULTS: The mean circulation half-life of liposome-encapsulated hemoglobin in mice injected at a dose of 1.0 g phospholipid/kg mouse and 1.95 g hemoglobin/kg was approximately 10.4 +/- 0.5 (SD) hrs. The circulation half-life of lyophilized liposome-encapsulated hemoglobin was 10.7 +/- 0.7 hrs. The circulation profiles demonstrate a rapid removal phase over the first 4 hrs after injection, followed by a secondary slow removal measured up to 24 hrs. The rapid removal phase of liposome-encapsulated hemoglobin and lyophilized liposome-encapsulated hemoglobin in the rabbit (injected at the same dose) indicated that lyophilized liposome-encapsulated hemoglobin persists longer than the unlyophilized form in the first 4 hrs after injection. The organ biodistributions of unlyophilized 99mTc-liposome-encapsulated hemoglobin and lyophilized 99mTc-liposome-encapsulated hemoglobin in the rabbit demonstrate that the reticuloendothelial system is the primary site of removal, with significant uptake of lyophilized 99mTc-liposome-encapsulated hemoglobin by the liver (15.6 +/- 1.0%), bone marrow (12.6 +/- 1.6%), and spleen (9.7 +/- 1.1%). The kidneys showed little accumulation of unlyophilized 99mTc-liposome-encapsulated hemoglobin or lyophilized 99mTc-liposome-encapsulated hemoglobin (1.6 +/- 0.2% and 1.8 +/- 0.1%, respectively), an important result for the efficacy and safety of this hemoglobin-based blood substitute. (ABSTRACT TRUNCATED)
Animals↗
Inclusion of ganglioside GM1 into liposome encapsulated hemoglobin does not extend circulation persistence at clinically relevant doses.
This investigation has evaluated the substitution of ganglioside GM1 for dimyristoyl phosphatidylglycerol (DMPG) in the preparation of liposome encapsulated hemoglobin (LEH), with the intention of increasing the circulation persistence of this potential oxygen carrier. Although equivalent yields of each formulation were produced by microfluidization, the hemoglobin encapsulation efficiency was greater for GM1-LEH than DMPG-LEH. Similar particle sizes, phospholipid content, methemoglobin levels, and oxygen-carrying capacity were observed for both formulations. Zeta potential measurements to monitor liposomal surface charge showed GM1-LEH to be more electropositive than DMPG-LEH. Using differential scanning calorimetry, similar enthalpy values and hemoglobin structural transition temperatures were determined for both LEH formulations. Circulation persistence of each LEH formulation was determined following a 0.25 ml (1 g phospholipid/Kg body weight) or 0.5 ml (2 g phospholipid/Kg body weight) injection in mice. During the first 18 hours, GM1-LEH was cleared at a faster rate than DMPG-LEH at both dosages studied. Then the remaining liposomes of each formulation were removed with identical circulation profiles until no liposomes were remaining in circulation at either 50 hours (0.25 ml) or 72 hours (0.5 ml) post-injection. These data reveal that the use of ganglioside GM1 to solely increase the circulation persistence of LEH was of little benefit.
Animals↗
Encapsulated hemoglobin: current issues and future goals.
The promise of encapsulation systems for the sequestration of hemoglobin has been the long-held belief that encapsulation more closely mimics nature's strategy for circulating hemoglobin, and could alleviate hemoglobin based toxicities and increase circulation persistence. Various polymers have been proposed to deliver hemoglobin. One approach toward the encapsulation of hemoglobin has been to employ biodegradable, biocompatible vehicles such as phospholipid vesicles, or liposomes. The majority of encapsulation work with hemoglobin over recent years has focused on liposome encapsulated hemoglobin with demonstrations of efficacy and safety in total and partial isovolemic and hypovolemic exchange models, hemodynamics, circulation persistence and organ biodistribution, processing methods, long term storage through freeze-drying, and serum changes and histopathological consequences following administration in small animals. The data collected thus far indicate that encapsulation of hemoglobin does significantly alter many of the traditionally observed effects following the administration of cell free hemoglobin solutions. Liposome encapsulated hemoglobin circulates for 20-24 hours in small animals and principally distributes to the liver and spleen. The significant accumulation of liposome encapsulated hemoglobin in these organs poses new questions for short and long-term effects on the reticuloendothelial system and macrophage function which are currently being addressed. In addition, transient hemodynamic and serum changes have been observed following the administration of liposome encapsulated hemoglobin. Many of these are similar to the effects observed following administration of liposomes without intravesicular hemoglobin and are dictated by liposome parameters such as surface charge and character, size, and lipid composition. Finally, fundamental large scale production issues such as encapsulation efficiency and particle size distribution must be optimized to facilitate the commercial development of encapsulated hemoglobin. These issues are discussed in the historical context of encapsulated hemoglobin and basic liposome research, current research status, and future challenges for the development of encapsulated hemoglobin as an artificial oxygen carrying fluid.
Animals↗
Circulation profile of technetium-99m labeled liposome encapsulated hemoglobin in a 10% or 50% rat hypovolemic shock model.
The circulation kinetics and organ biodistribution of liposome encapsulated hemoglobin (LEH) was determined non-invasively in hypovolemic rats using a technetium-99m (Tc-99m) liposome labeling procedure. Rats with an indwelling catheter had either 10% or 50% of their blood volume removed and replaced with an equal volume of LEH labeled with Tc-99m (Tc-99m LEH). Mean arterial pressures and heart rates were monitored throughout the experiment. Gamma camera images were acquired during the first 90 minutes following infusion of the Tc-99m LEH and at 20 hours post-infusion. Blood capillaries were drawn at various times to monitor Tc-99m activity and the amount of LEH remaining in circulation. There were significant differences in the kinetics and biodistribution for the two groups. In the 10% group, the LEH was removed quickly from circulation with only 0.9% remaining at 20 hours, while the 50% group had 51.2% at 20 hours. The liver and spleen were the major organs responsible for LEH clearance. The 20 hour biodistribution by tissue sampling showed that the 10% group had 37.6% in the liver and 34.3% in the spleen, while the 50% group had only 18.4% in the liver and 14.6% in the spleen.
Animals↗
Use of technetium-99m-liposomes in tumor imaging.
UNLABELLED: In this study, liposomes labeled with 99mTc have been evaluated as tumor imaging agents. METHODS: Liposomes containing reduced glutathione and carrying either a negative surface charge or no surface charge were labeled with 99mTc using the lipophilic chelator, hexamethylpropyleneamine oxime (HMPAO). The 99mTc-liposomes were intravenously injected into the tail vein of nuce mice which had been implanted intramuscularly in the thigh with nontransfected Chinese hamster ovary cells. Gamma camera images were acquired at 1, 4 and 22 hr and compared with tissue biodistribution studies at 24 hr postinjection. RESULTS: Tumors could be distinguished from normal thigh muscle at 4 hr postinjection for both formulations. Tumor-to-muscle ratios were not significantly different for the two formulations due to the increased normal muscle activity at 24 hr for the neutral liposomes. Liver-to-tumor, liver-to-blood, spleen-to-tumor and spleen-to-blood ratios were significantly lower for the neutral 99mTc-liposomes than for the negative 99mTc-liposomes. Neutral 99mTc-liposomes were cleared slower by the reticuloendothelial system, and therefore remained in the circulation for a longer period of time. CONCLUSION: The results of this study indicate that both formulations could be used as tumor imaging agents, but that neutral 99mTc-liposomes would be more suitable as a drug delivery agent due to their increased total uptake by the tumor and decreased nonspecific uptake by the reticuloendothelial system.
Animals↗
Lyophilized liposome encapsulated hemoglobin: evaluation of hemodynamic, biochemical, and hematologic responses.
OBJECTIVE: To characterize the hemodynamic, biochemical, and hematologic responses to the administration of the oxygen-carrying fluid lyophilized liposome-encapsulated hemoglobin in the conscious, normovolemic rat. DESIGN: Prospective, randomized trial. SETTING: Animal laboratory, Jefferson Medical College. SUBJECTS: Eighty-four male Sprague-Dawley rats. INTERVENTIONS: Catheters were introduced into the right atrium (through the jugular vein) and both femoral arteries of test animals, and a thermistor was placed in the ascending aorta through the left common carotid artery for infusion of lyophilized liposome-encapsulated hemoglobin, blood collection, and blood pressure (BP) and cardiac output determinations. MEASUREMENTS AND MAIN RESULTS: Lyophilized liposome-encapsulated hemoglobin (n = 8) infusion (1 mL/min iv) at 1 or 6 mL/kg (10% of estimated blood volume) had no detectable effect on BP, cardiac output, total peripheral resistance, and heart rate during the 5-hr observation period. The infusion also had no effect on hematocrit, leukocyte count, and serum tumor necrosis factor-alpha concentrations. Survival at 7 days was 100% (n = 20). Lyophilized liposome-encapsulated hemoglobin caused transient (2-hr) thrombocytopenia (-24 +/- 9% vs. a Ringer's lactate control group, p < .01), and marginally increased serum thromboxane B2 concentrations (14.6 +/- 6 pg/100 microL, p < .01). CONCLUSIONS: These data suggest that lyophilized liposome-encapsulated hemoglobin can be safely administered to conscious rats, supporting the development of this substance as a potential blood substitute.
6-Ketoprostaglandin F1 alpha↗
Biodistribution and imaging studies of technetium-99m-labeled liposomes in rats with focal infection.
We have recently developed a procedure to label liposomes containing reduced glutathione (GSH) with 99mTc using the lipophilic chelator, hexamethylpropyleneamine oxime (HMPAO). In the present study, we evaluated the use of 99mTc-liposomes to detect focal infection sites in rats. Rats were infected in the thigh by intramuscular injection with Staphylococcus aureus followed 24 hr later by an intravenous injection of 99mTc-liposomes, 67Ga-citrate, or 99mTc-human serum albumin (HSA). The animals were imaged under a gamma camera and subsequently killed at 4, 24 or 48 hr for tissue biodistribution studies. In contrast to infected rats receiving 67Ga-citrate or 99mTc-HSA, abscesses were prominently localized within 2 hr in rats after 99mTc-liposome injection, and continued to increase in activity up to 24 hr. Abscess-to-muscle ratios calculated from 24-hr biodistribution data obtained from tissue sampling were 35.3 +/- 7.6 for 99mTc-liposomes, 4.1 +/- 0.7 for 67Ga-citrate and 8.0 +/- 1.0 for 99mTc-HSA. These studies show the potential of using 99mTc-liposomes to localize infection.
Animals↗
A new salutary resuscitative fluid: liposome encapsulated hemoglobin/hypertonic saline solution.
Low-volume resuscitation with hypertonic (7.5%) saline (HTS) is an evolving therapeutic modality for patients with hemorrhagic shock. This solution has been shown to exert protective hemodynamic effects in models of controlled hemorrhagic shock and in several clinical trials. However, HTS has no oxygen-carrying capacity and therefore does not improve oxygen delivery directly. One of the leading strategies in developing an oxygen-carrying resuscitative fluid is the encapsulation of hemoglobin within phospholipid vesicles (LEH). This preparation has the advantage of being blood type and antigen free, easily adaptable to scale-up production, and remarkably stable with a long shelf life. We therefore tested the hypothesis that lyophilized LEH reconstituted with HTS will improve tissue oxygenation and survival in rats exposed to a lethal controlled hemorrhagic shock. Shock was induced by withdrawal of 70% of blood volume and therapy (n = 10-16) with HTS (5 mL/kg), LEH (5 mL/kg), lactated Ringer's solution (vol:vol = 1:3), LEH-HTS (5 mL/kg), or oxygen (100%) was initiated 15 minutes later. The LEH-HTS improved skeletal muscle oxygen tension directly measured using a thin-film chamber oxygen sensor (PO2 87 +/- 13 mm Hg vs. 40-50 mm Hg in other groups, p < 0.05). This was associated with improved blood pressure, reduced acidosis, and increased survival at 24 hours (75% vs. 6%-25% in other groups, p < 0.05). In conclusion, the study demonstrates a remarkably salutary effect of LEH reconstituted with HTS as a blood substitute in the treatment of hemorrhagic shock.
Animals↗
Calorimetric studies of lipid tubule formation from ethanol-water solutions.
We have used differential scanning calorimetry to systematically investigate the thermal formation of hollow cylindrical crystalline microstructures or 'tubules' upon cooling a diacetylenic phosphatidylcholine (1,2-bis(10,12-tricosadiynoyl)-sn-glycero-3-phosphocholine) dispersed in varying volume fractions of ethanol/water. Tubule formation is characterized by a large exothermic event, observed upon cooling the lipid in 60-80% ethanol. The enthalpy of the transition was observed to be highest in this window of tubule formation (128-138 J/g) which is significantly higher than previously reported values for the enthalpy of tubule formation in water (90 -95 J/g). The enthalpy associated with the formation of tubules in 70% ethanol was also found to be strongly dependent on the efficiency of tubule formation and decreased as the number density of tubules decreased. A significant decrease in tubule number density could be brought about by increasing the lipid concentration of the 70% ethanol solution. Tubule number density was maximized at lipid concentrations between 0.5 and 2 mg/ml in 70% ethanol. Examination of the C-H stretch region from infrared spectra of the lipid below the phase transition, indicate that the intramolecular chain order-disorder is similar, regardless of the fraction of ethanol. The higher transition enthalpy for the melting of tubules in 60-80% ethanol (compared to water) implies that the high-temperature phase from which the tubules form in ethanol is more disordered than the lamellar liquid crystalline phase from which tubules form in water.
Calorimetry, Differential Scanning↗