Physiological Capacity of the Reticuloendothelial System for the Degradation of Hemoglobin Vesicles (Artificial Oxygen Carriers) after Massive Intravenous Doses by Daily Repeated Infusions for 14 Days

Development of liposomal contrast agent with high iodine concentration and minimal effect on renal function

Purpose

The use of contrast media is essential to achieve high accuracy in diagnostic imaging. Iodine contrast media, one of these contrast media, has nephrotoxicity as a side effect. Therefore, the development of iodine contrast media that can reduce nephrotoxicity is expected. Since liposomes are generally adjustable in size (100-300 nm) and are not filtered by the renal glomerulus, we hypothesized that iodine contrast media could be encapsulated in liposomes and administered to avoid the nephrotoxicity of iodine contrast media. The aim of this study is to develop an iomeprol-containing liposome (IPL) agent with high iodine concentration and to investigate the effect of intravenous administration of IPL on renal function in a rat model with chronic kidney injury.

Materials and methods

IPLs were prepared by encapsulating an iomeprol (400mgI/mL) solution in liposomes by a kneading method using a rotation-revolution mixer. Radiodensities of iomeprol and IPL were measured. IPL or iopamidol at normal dose (0.74 g I/kg) or high dose (3.7 g I/kg) was administered to healthy and 5/6-nephrectomized rats (n = 3-6). Serum creatinine (sCr) and histopathological change of tubular epithelial cells were evaluated after injection.

Results

The iodine concentration of IPL was 220.7 mgI/mL, equivalent to 55.2% of the iodine concentration of iomeprol. The CT values of IPL was 4731.6 ± 53.2 HU, 59.04% that of iomeprol. The ratios of change in sCr in 5/6-nephrectomized rats that received high-dose iopamidol were 0.73, which were significantly higher than that in 5/6-nephrectomized rats that received high-dose IPL (-0.03) (p = 0.006). Change in foamy degeneration of tubular epithelial cells was confirmed in 5/6-nephrectomized rats that received high-dose iopamidol than that in the sham control group and healthy rats that received normal dose iopamiron (p = 0.016, p = 0.032, respectively). Foamy degeneration of tubular epitherial cells was rarely observed in the IPL injection group.

Conclusions

We developed new liposomal contrast agents that have high iodine concentration and minimal effect on renal function.

Research of storable and ready-to-use artificial red blood cells (hemoglobin vesicles) for emergency medicine and other clinical applications

Hemoglobin (Hb) is the most abundant protein in blood, with concentration of about 12-15 g/dl. The highly concentrated Hb solution (35 g/dl) is compartmentalized in red blood cells (RBCs). Once Hb is released from RBCs by hemolysis during blood circulation, it induces renal and cardiovascular toxicities. To date, hemoglobin-based oxygen carriers of various types have been developed as blood substitutes to mitigate the Hb toxicities. One method is Hb encapsulation in phospholipid vesicles (liposomes). Although the Hb toxicity can be shielded, it is equally important to ensure the biocompatibility of the liposomal membrane. We have developed Hb-vesicles (HbV). A new encapsulation method using a rotation-revolution mixer which enabled efficient production of HbV with a high yield has considerably facilitated R&D of HbV. Along with our academic consortium, we have studied the preclinical safety and efficacy of HbV extensively as a transfusion alternative, and finally conducted a phase I clinical trial. Moreover, carbonyl-HbV and met-HbV are developed respectively for an anti-inflammatory and anti-oxidative agent and an antidote for poisons. This review paper specifically presents past trials of liposome encapsulated Hb, biocompatible lipid bilayer membranes, and efficient HbV preparation methods, in addition to potential clinical applications of HbV based on results of our in vivo studies.

Resuscitative efficacy of hemoglobin vesicles for severe postpartum hemorrhage in pregnant rabbits

We aimed to investigate the resuscitative efficacy of hemoglobin vesicles (HbVs) as a red blood cell (RBC) substitute for the initial treatment of severe postpartum hemorrhage (PPH). Twenty-five pregnant rabbits underwent cesarean section; uncontrolled hemorrhage was induced by transecting the right uterine artery to establish a severe PPH model. During the first 30 min, all rabbits were administered 6% hydroxyethyl starch (HES) of an equivalent volume to the hemorrhage every 5 min. Thereafter, they received any of the following three isovolemic fluids for resuscitation every 5 min: RBCs with platelet-poor plasma (RBC/PPP) (n = 8), 6% HES (n = 7), or HbVs with 25% human serum albumin (n = 10). After surgical hemostasis at 60 min, survival was monitored until 12 h. No rabbits receiving only HES infusion survived beyond 6 h, whereas all rabbits receiving RBC/PPP transfusion survived. The rabbits receiving HbV infusion showed significantly higher mean arterial pressure and hemoglobin levels than the HES-receiving rabbits, and 8 of 10 rabbits survived for 6 h. The HbV group showed significantly higher survival than the HES group but worse survival than the RBC/PPP group. In conclusion, HbV infusion for severe PPH effectively prevents lethal hemorrhagic shock in a pregnant rabbit model.

Translational research of hemoglobin vesicles as a transfusion alternative

Clinical situations arise in which blood for transfusion becomes scarce or unavailable. Considerable demand for a transfusion alternative persists because of various difficulties posed by blood donation and transfusion systems. Hemoglobin-vesicles (HbV) are artificial oxygen carriers being developed for use as a transfusion alternative. Just as biomembranes of red blood cells (RBCs) do, phospholipid vesicles (liposomes) for Hb encapsulation can protect the human body from toxic effects of molecular Hb. The main HbV component, Hb, is obtained from discarded human donated blood. Therefore, HbV can be categorized as a biologic agent targeting oxygen for peripheral tissues. The purification procedure strictly eliminates the possibility of viral contamination. It also removes all concomitant unstable enzymes present in RBC for utmost safety from infection. The deoxygenated HbVs, which are storable for over years at ambient temperature, can function as an alternative to blood transfusion for resuscitation from hemorrhagic shock and O₂ therapeutics. Moreover, a recent study clarified beneficial effects for anti-oxidation and anti-inflammation by carbon monoxide (CO)-bound HbVs. Autoxidation of HbV (HbO₂ → metHb + O₂-.) is unavoidable after intravenous administration. Co-injection of methylene blue can extract the intraerythrocytic glycolytic electron energy effectively and reduce metHb. Other phenothiazine dyes can also function as electron mediators to improve the functional life span of HbV. This review paper summarizes recent progress of the research and development of HbV, aimed at clinical applications.

The accelerated blood clearance phenomenon of PEGylated nanoemulsion upon cross administration with nanoemulsions modified with polyglycerin

For investigating the accelerated blood clearance (ABC) phenomenon of polyglycerin modified nanoemulsions upon cross administration with polyethylene glycol (PEG) covered nanoemulsion, we used the 1,2-distea-royl-sn-glycero-3-phosphoethanolamine-n-polyglycerine-610 and the 1,2-distearoyl-n-glycero-3-phosphoethanolamine-n-[me-thoxy(polyethylene glycol)-2000] as modify materials, the dialkylcarbocyanines as fluorescence indicator. Exhausted macrophages rat model was established and new material containing polycarboxyl structure was synthesized. The microplate reader and the in vivo optical imaging system were applied to measure the concentration of nanoemulsions in tissues. The results show that the first dose of polyglycerin modified nanoemulsion can induce the ABC phenomenon of the second dose of PEGylated nanoemulsion. With the increase in the amount of the surface polyglycerin, the extent of the ABC phenomenon decreases. Liver accumulation has positive relationship with the ABC phenomenon. Furthermore, kupffer cells in liver can get more immune information from polyhydroxy structure than polycarboxyl group in the modify compound. The results of our work imply that the polycarboxyl structure has advantages to eliminate the ABC phenomenon.

The Use of Hemoglobin Vesicles for Delivering Medicinal Gas for the Treatment of Intractable Disorders

Bioactive gaseous molecules, such as oxygen (O₂) and carbon monoxide (CO), are essential elements for most living organisms to maintain their homeostasis and biological activities. An accumulating body of evidence suggests that such molecules can be used in clinics as a medical gas in the treatment of various intractable disorders. Recent developments in hemoglobin-encapsulated liposomes, namely hemoglobin vesicles (HbV), possess great potential for retaining O₂ and CO and could lead to strategies for the development of novel pharmacological agents as medical gas donors. HbV with either O₂ or CO bound to it has been demonstrated to have therapeutic potential for treating certain intractable disorders and has the possibility to serve as diagnostic and augmenting product by virtue of unique physicochemical characteristics of HbV. The present review provides an overview of the present status of the use of O₂- or CO-binding HbV in experimental animal models of intractable disorders and discusses prospective clinical applications of HbV as a medical gas donor.

Overview of Potential Clinical Applications of Hemoglobin Vesicles (HbV) as Artificial Red Cells, Evidenced by Preclinical Studies of the Academic Research Consortium

Hemoglobin (Hb) is the most abundant protein in whole blood. This fact implies that the oxygen binding and releasing function of Hb is the most vital for sustaining life. All Hb is compartmentalized in red blood cells (RBCs) with corpuscular Hb concentration of about 35 g/dL, covered with a thin biomembrane. In spite of its abundance, Hb sometimes shows toxicity once it is leaked from RBCs. The shielding effect of the RBC membrane is physiologically important. Based on this structural importance, we have studied artificial red cells (Hb vesicles, HbV) as artificial oxygen carriers, which encapsulate a purified and concentrated Hb solution in phospholipid vesicles, mimicking the cellular structure of RBCs. Our academic research consortium has clarified the safety and efficacy of this HbV, aiming at clinical applications. Because of some superior characteristics to those of RBCs, HbV has the potential for use not only as a transfusion alternative but also for oxygen and carbon monoxide therapeutics, perfusate for transplant organs, and photosensitizer. In this review paper, such potential applications are summarized.

Carbon monoxide-bound hemoglobin vesicles ameliorate multiorgan injuries induced by severe acute pancreatitis in mice by their anti-inflammatory and antioxidant properties

Carbon monoxide (CO) has attracted attention as a possible therapeutic agent for affecting anti-inflammatory and antioxidant activities. Previously, CO-bound hemoglobin vesicle (CO-HbV) was developed as a nanotechnology-based CO donor, and its safety profile and therapeutic potential as a clinically applicable carrier of CO were examined in vitro and in vivo. In the present study, the therapeutic efficacy of CO-HbV against severe acute pancreatitis was examined with secondary distal organ-injured model mice that were fed with a choline-deficient ethionine-supplemented diet. A CO-HbV treatment significantly reduced the mortality of the acute pancreatitis model mice compared to saline and HbV. Biochemical and histological evaluations clearly showed that CO-HbV suppressed acute pancreatitis by inhibiting the production of systemic proinflammatory cytokines, neutrophil infiltration, and oxidative injuries in pancreatic tissue. Interestingly, CO-HbV also diminished the subsequent damage to distal organs including liver, kidneys, and lungs. This could be due to the suppression of neutrophil infiltration into tissues and the subsequently enhanced oxidative injuries. In contrast, O₂-bound HbV, the inactive form of CO-HbV, was ineffective against both pancreatitis and distal organ injuries, confirming that CO was directly responsible for the protective effects of CO-HbV in acute pancreatitis. These findings suggest that CO-HbV has anti-inflammatory and antioxidant characteristics of CO and consequently exerts a superior protective effect against acute pancreatitis-induced multiorgan damage.

Evaluation of a new type of nano-sized carbon monoxide donor on treating mice with experimentally induced colitis

Low concentrations of exogenous carbon monoxide (CO) have been reported to be useful for the treatment of various disorders related to inflammation and oxidative stress. However, a number of obstacles make it difficult to use CO in vivo. Among these are, at high concentrations, it is toxic and the fact that it is difficult to control its delivery in the body. Hemoglobin-encapsulated liposomes, Hemoglobin-vesicles (HbV), have the potential for use as a new type of nano-sized CO donor, referred to as CO-bound HbV (CO-HbV). In this study, we investigated the potential of CO-HbV as a CO donor in terms of toxicity and therapeutic efficacy using an experimental colitis model. Toxicological assessments of CO-HbV showed no severe adverse effects including death, and clinical laboratory tests and histopathological changes remained normal for 28days after the administration of doses up to 1400mgHb/kg. We then evaluated the therapeutic efficacies of CO-HbV on dextran sulfate sodium (DSS)-induced colitis model mice. A single administration of CO-HbV at 3days from beginning of the DSS treatment dramatically improved colitis symptoms, colonic histopathological changes and the duration of survival compared to both saline and HbV administration. In addition, the therapeutic effects of CO-HbV on colitis can be attributed to a decreased level of neutrophil infiltration, the production of pro-inflammatory cytokines and oxidative injuries. Interestingly, it appears that an increase in anti-inflammatory cytokine production contributes, in part, to therapeutic effects of CO-HbV in the treatment of colitis. These safety and efficacy profiles of CO-HbV suggest that it has the potential for use as a drug for treating, not only colitis but also a variety of other disorders associated with inflammation and oxidative stress.

Pharmacokinetic Properties of Single and Repeated Injection of Liposomal Platelet Substitute in a Rat Model of Red Blood Cell Transfusion-Induced Dilutional Thrombocytopenia

A preclinical study of dodecapeptide ((400)HHLGGAKQAGDV(411)) (H12)-(adenosine diphosphate, ADP)-liposomes for use as a synthetic platelet (PLT) substitute under conditions of red blood cell (RBC) transfusion-induced dilutional thrombocytopenia is limited to pharmacological effect. In this study, the pharmacokinetics of H12-(ADP)-liposomes in RBC transfusion-induced dilutional thrombocytopenic rats were evaluated. As evidenced by the use of (14) C, (3) H double-radiolabeled H12-(ADP)-liposomes in which the encapsulated ADP and liposomal membrane were labeled with (14) C and (3) H, respectively, the H12-(ADP)-liposomes remained intact in the blood circulation for up to 3 h after injection, and were mainly distributed to the liver and spleen. The encapsulated ADP was mainly eliminated in the urine, whereas the outer membrane was mainly eliminated in the feces. These successive pharmacokinetic properties of the H12-(ADP)-liposomes in RBC transfusion-induced dilutional thrombocytopenic rats were similar to those in healthy rats, except for the shorter retention time in the circulation. When H12-(ADP)-liposomes were repeatedly injected into RBC transfusion-induced dilutional thrombocytopenic rats at intervals of 5 days at a dose of 10 mg lipids/kg, the second dose of injected H12-(ADP)-liposomes were rapidly cleared from the circulation, namely, via the accelerated blood clearance phenomenon. These novel pharmacokinetic findings provide useful information for the further development of H12-(ADP)-liposomes as a PLT substitute.

Carbon monoxide-bound hemoglobin-vesicles for the treatment of bleomycin-induced pulmonary fibrosis

Carbon monoxide (CO) has potent anti-inflammatory and anti-oxidant effects. We report herein on the preparation of a nanotechnology-based CO donor, CO-bound hemoglobin-vesicles (CO-HbV). We hypothesized that CO-HbV could have a therapeutic effect on idiopathic pulmonary fibrosis (IPF), an incurable lung fibrosis, that is thought to involve inflammation and the production of reactive oxygen species (ROS). Pulmonary fibril formation and respiratory function were quantitatively evaluated by measuring hydroxyproline levels and forced vital capacity, respectively, using a bleomycin-induced pulmonary fibrosis mice model. CO-HbV suppressed the progression of pulmonary fibril formation and improved respiratory function compared to saline and HbV. The suppressive effect of CO-HbV on pulmonary fibrosis can be attributed to a decrease in ROS generation by inflammatory cells, NADPH oxidase 4 and the production of inflammatory cells, cytokines and transforming growth factor-β in the lung. This is the first demonstration of the inhibitory effect of CO-HbV on the progression of pulmonary fibrosis via the anti-oxidative and anti-inflammatory effects of CO in the bleomycin-induced pulmonary fibrosis mice model. CO-HbV has the potential for use in the treatment of, not only IPF, but also a variety of other ROS and inflammation-related disorders.

Biological evaluation of liposome-encapsulated hemoglobin surface-modified with a novel PEGylated nonphospholipid amphiphile

Traumatic injury is often associated with hemorrhagic shock. Liposome-encapsulated hemoglobin (LEH) is being developed as an artificial oxygen carrier to address post-hemorrhage oxygen and volume deficit. Here, we report a new composition of LEH based on the use of polyethylene glycol (PEG2K ) conjugated with nonphospholipid hexadecylcarbamoylmethylhexadecanoate (HDAS) to modify the surface of LEH particles. LEH was manufactured by the high-pressure homogenization method using dipalmitoylphosphatidylcholine (∼38 mol%), cholesterol (∼38 mol%), HDAS (∼20 mol%), and highly purified stroma-free human hemoglobin. HDAS-PEG2K was postinserted into the resultant LEH to generate HDAS-PEG2K -LEH. We investigated the potential immune response to HDAS-PEG2K -LEH in a mice model. At the same time, the preparation was tested in a rat model to study the effect of repeated HDAS-PEG2K -LEH injection over 4 weeks. We found that HDAS-PEG2K modification substantially reduced the circulating levels of anaphylatoxins C3a and C5a, as well as plasma levels of thromboxane B2, in mice. Repeated injections of HDAS-PEG2K -LEH in rats did not appear to alter its clearance profile after 4 weeks of treatment. No antibody response against human hemoglobin or PEG was detected in rat plasma. Histological observations of lung, liver, spleen, and kidney were not significantly different between saline-treated rats and HDAS-PEG2K -LEH-treated rats. Immunohistochemical staining for rat heme oxygenase-1 (HO-1) did not show induced expression of HO-1 in these organs. These results suggest that the new surface modification of LEH is immune-neutral and does not adversely affect histology even after repeated administration.

Pharmacokinetic study of the structural components of adenosine diphosphate-encapsulated liposomes coated with fibrinogen γ-chain dodecapeptide as a synthetic platelet substitute

Fibrinogen γ-chain (dodecapeptide HHLGGAKQAGDV, H12)-coated, ADP-encapsulated liposomes [H12-(ADP)-liposomes] were developed as a synthetic platelet alternative that specifically accumulates at bleeding sites as the result of interactions with activated platelets via glycoprotein IIb/IIIa and augments platelet aggregation by releasing ADP. The aim of this study is to characterize the pharmacokinetic properties of H12-(ADP)-liposomes and structural components in rats, and to predict the blood retention of H12-(ADP)-liposomes in humans. With use of H12-(ADP)-liposomes in which the encapsulated ADP and liposomal membrane cholesterol were radiolabeled with (14)C and (3)H, respectively, it was found that the time courses for the plasma concentration curves of (14)C and (3)H radioactivity showed that the H12-(ADP)-liposomes remained intact in the blood circulation for up to 24 hours after injection, and were mainly distributed to the liver and spleen. However, the (14)C and (3)H radioactivity of H12-(ADP)-liposomes disappeared from organs within 7 days after injection. The encapsulated ADP was metabolized to allantoin, which is the final metabolite of ADP in rodents, and was mainly eliminated in the urine, whereas the cholesterol was mainly eliminated in feces. In addition, the half-life of the H12-(ADP)-liposomes in humans was predicted to be approximately 96 hours from pharmacokinetic data obtained for mice, rats, and rabbits using an allometric equation. These results suggest that the H12-(ADP)-liposome has potential with proper pharmacokinetic and acceptable biodegradable properties as a synthetic platelet substitute.

Removal of cellular-type hemoglobin-based oxygen carrier (hemoglobin-vesicles) from blood using centrifugation and ultrafiltration

The hemoglobin-vesicle (HbV) is an artificial oxygen carrier encapsulating a concentrated hemoglobin solution in a phospholipid vesicle (liposome). During or after transporting oxygen, macrophages capture HbVs in the reticuloendothelial system (RES) with an approximate circulation half-life of 3 days. Animal studies show transient splenohepatomegaly after large doses, but HbVs were completely degraded, and the components were excreted in a few weeks. If a blood substitute is used for emergency use until red blood cell transfusion becomes available or for temporary use such as a priming fluid for an extracorporeal circuit, then one option would be to remove HbVs from the circulating blood without waiting a few weeks for removal by the RES. Using a mixture of beagle dog whole blood and HbV, we tested the separation of HbV using a centrifugal Fresenius cell separator and an ultrafiltration system. The cell separator system separated the layers of blood cell components from the HbV-containing plasma layer by centrifugal force, and then the HbV was removed from plasma phase by the ultrafiltration system. The HbVs (250-280 nm) are larger than plasma proteins (< 22 nm diameter) but smaller than blood cell components (> 3 µm). The size of HbVs is advantageous to be separated from the original blood components, and the separated blood components can be returned to circulation.

Fluid resuscitation with hemoglobin vesicles prevents Escherichia coli growth via complement activation in a hemorrhagic shock rat model

Hemoglobin vesicles (HbVs) could serve as a substitute for red blood cells (RBCs) in resuscitation from massive hemorrhage. A massive transfusion of RBCs can increase the risk of infection, which is not caused by contaminating micro-organisms in the transfused RBCs but by a breakdown of the host defense system. We previously found that complement activity was increased after resuscitation with HbVs at a putative dose in a rat model of hemorrhagic shock. It is known that complement system plays a key role in host defense in the embryonic stage. Therefore, the objective of this study was to address whether the suppression of bacterial infections in hemorrhagic shock rats was a result of increased complement activity after massive HbV transfusion. For this purpose, Escherichia coli were incubated with plasma samples obtained from a rat model of hemorrhagic shock resuscitated by HbVs or RBCs, and bacterial growth was determined under ex vivo conditions. As a result, E. coli growth was found to be suppressed by increased complement activity, mediated by the production of IgM from spleen. However, this antibacterial activity disappeared when the E. coli were treated with complement-inactivated plasma obtained from splenoctomized rats. In addition, the resuscitation of HbVs from hemorrhagic shock increased the survival rate and viable bacterial counts in blood in cecum ligation and puncture rats, a sepsis model. In conclusion, the resuscitation of HbVs in the rat model of hemorrhagic shock suppresses bacterial growth via complement activation induced by IgM.

Hemoglobin vesicles, polyethylene glycol (PEG)ylated liposomes developed as a red blood cell substitute, do not induce the accelerated blood clearance phenomenon in mice

The hemoglobin vesicle (HbV) is an artificial oxygen carrier encapsulating a concentrated hemoglobin solution in a liposome of which the surface is covered with polyethylene glycol (PEG). It was recently reported that repeated injections of PEGylated liposomes induce the accelerated blood clearance (ABC) phenomenon, in which serum anti-PEG IgM plays an essential role. To examine this issue, we investigated whether HbV induces the ABC phenomenon in mice at a dose of 0.1 mg Hb/kg, a dose that is generally known to induce the ABC phenomenon, or at 1400 mg Hb/kg, which is proposed for clinical use. At 7 days after the first injection of nonlabeled HbV (0.1 mg Hb/kg), the mice received HbV in which the Hb had been labeled with (125)I. After a second injection, HbV was rapidly cleared from the circulation, and uptake clearances in liver and spleen were significantly increased. In contrast, at a dose of 1400 mg Hb/kg, the pharmacokinetics of HbV was negligibly affected by repeated injection. It is interesting to note that IgM against HbV was produced 7 days postinjection at both of the above doses, and their recognition site was determined to be 1,2-distearoyl-sn-glycero-3-phosphatidylethanolamine-N-PEG in HbV. These results suggest that a clinical dose of HbV does not induce the ABC phenomenon, and that suppression of ABC phenomenon is caused by the saturation of phagocytic processing by the mononuclear phagocyte system. Thus, we conclude that induction of the ABC phenomenon would not be an issue in the dose regimen used in clinical settings.

Hemoglobin-Vesicles as a Transfusion Alternative

Phospholipid vesicles or liposomes encapsulating purified and concentrated human hemoglobin (Hb-vesicle, HbV) have been developed as a transfusion alternative. They are void of blood-type antigens and infectious viruses; they are stable and suitable for long-term storage. The cellular structure of HbV (particle diameter, ca. 250 nm) prevents direct contact of Hb with the blood components and the endothelial lining shielding cells from the side effects of Hb molecules. Microcirculatory observations show that the cellular structure of HbV is important to control reactions with endothelium-derived vasorelaxation factors. Animal studies of extreme hemodilution and resuscitation from hemorrhagic shock attest to the sufficient oxygen transporting capacity of HbV. Studies of biodistribution and metabolism reveal that HbVs are captured eventually in the reticuloendothelial system, and degraded within one week. In a joint collaboration partnership of academia, a biotech venture company and a corporation, we plan to produce HbV with good manufacturing practices, and to start preclinical and, finally, clinical trials within a few years.

Hemoglobin vesicles improve wound healing and tissue survival in critically ischemic skin in mice

Local hypoxia, as due to trauma, surgery, or arterial occlusive disease, may severely jeopardize the survival of the affected tissue and its wound-healing capacity. Initially developed to replace blood transfusions, artificial oxygen carriers have emerged as oxygen therapeutics in such conditions. The aim of this study was to target primary wound healing and survival in critically ischemic skin by the systemic application of left-shifted liposomal hemoglobin vesicles (HbVs). This was tested in bilateral, cranially based dorsal skin flaps in mice treated with a HbV solution with an oxygen affinity that was increased to a P(50) (partial oxygen tension at which the hemoglobin becomes 50% saturated with oxygen) of 9 mmHg. Twenty percent of the total blood volume of the HbV solution was injected immediately and 24 h after surgery. On the first postoperative day, oxygen saturation in the critically ischemic middle flap portions was increased from 23% (untreated control) to 39% in the HbV-treated animals (P < 0.05). Six days postoperatively, flap tissue survival was increased from 33% (control) to 57% (P < 0.01) and primary healing of the ischemic wound margins from 6.6 to 12.7 mm (P < 0.05) after HbV injection. In addition, higher capillary counts and endothelial nitric oxide synthase expression (both P < 0.01) were found in the immunostained flap tissue. We conclude that left-shifted HbVs may ameliorate the survival and primary wound healing in critically ischemic skin, possibly mediated by endothelial nitric oxide synthase-induced neovascularization.

Fluid resuscitation with artificial oxygen carriers in hemorrhaged rats: profiles of hemoglobin-vesicle degradation and hematopoiesis for 14 days

Polyethylene glycol (PEG)-modified hemoglobin (Hb) vesicles (HbVs) are artificial oxygen carriers encapsulating a concentrated Hb solution in phospholipid vesicles. In our previous studies, HbV showed a sufficient resuscitative effect comparable to that of red blood cells in hemorrhagic shock animal models during several hours' observation. However, the profiles of the recovery, including hematopoiesis and elimination of HbV, remain unknown. This study conducted 14-day observations of Wistar rats after hemorrhagic shock and fluid resuscitation with HbV suspended in recombinant human serum albumin. Shock was induced by 50% blood withdrawal from a femoral artery. The rats showed hypotension, metabolic acidosis, and hyperventilation. After 15 min, they received HbV or shed autologous blood through a femoral vein. Both groups showed rapid recovery of hemodynamic and blood gas parameters. No meaningful difference was found between groups. After decannulation and awakening, the rats were housed in cages. The reduced hematocrit of the HbV group returned to the original level in 7 days. Plasma enzyme levels were slightly higher in both groups at 1 day because of systemic reperfusion injury. Splenomegaly was considerable in the HbV group because of the HbV accumulation and extramedullar hematopoiesis, but it subsided within 14 days. Along with the HbV elimination in the spleen and liver, immunohistochemistry with anti-PEG antibody revealed that PEG-conjugated lipid had disappeared within 14 days. In conclusion, HbV showed a sufficient resuscitative effect comparable to that of red blood cell transfusion. Phagocytized HbV disappeared within 14 days. Elevated hematopoiesis contributed to complete hematocrit recovery within 7 days.

Balance between vasoconstriction and enhanced oxygen delivery

BACKGROUND

Hemoglobin (Hb) solutions are potential alternatives to blood transfusion when native oxygen (O(2))-carrying capacity is lacking. Polymerized bovine Hb (PBH) solutions are characterized by its vasoactivity, low O(2) affinity, oncotic effect, prolonged shelf life, and stability. Responses to facilitated O(2) transport, after exchange transfusion with PBH, were studied in the hamster window chamber model during acute extreme anemia to determine how PBH affects microvascular perfusion and tissue oxygenation.

STUDY DESIGN AND METHODS

An anemic state was induced by hemodilution with a plasma expander (70-kDa dextran). After hemodilution, animals were randomly assigned to exchange transfusion groups based on the concentration of PBH used, namely, PBH at 13 g(Hb) per dL (PBH13), PBH diluted to 8 or 4 g(Hb) per dL in albumin solution at matching colloidal osmotic pressure (COP; PBH8 and PBH4), and no PBH only albumin solution at matching COP (PBH0). Measurement of systemic variables, microvascular hemodynamics, capillary perfusion, and intravascular and tissue O(2) levels was performed at 11 percent Hct.

RESULTS

Restitution of O(2)-carrying capacity with PBH13 restored higher arterial pressure and triggered vasoconstriction, low perfusion, and higher peripheral resistance. Groups PBH4 and PBH0 had lower arterial pressures than Group PBH13. Groups PBH4 and PBH8 maintained higher perfusion and functional capillary density than Groups PBH13 and PBH0. In all groups, blood gas variables and acid-base balance were recovered proportional to microvascular perfusion. Arterial O(2) tensions were improved for Groups PBH4 and PBH8 by preventing O(2) precapillary release and increasing O(2) reserve.

CONCLUSION

Further studies to establish acellular Hb optimal dosage, efficacy, safety, and effects on outcome are indicated before these solutions are implemented in routine practice.

Systemic administration of hemoglobin vesicle elevates tumor tissue oxygen tension and modifies tumor response to irradiation

BACKGROUND

We have developed a phospholipid liposome vesicle encapsulating concentrated human hemoglobin (hemoglobin vesicle, HbV) as an artificial oxygen carrier, as an alternative to red cell transfusion. We have verified its oxygen transporting capability in a variety of preclinical models. Recent evidence suggests that artificial oxygen carriers may also be applicable for better oxygenation of ischemic or hypoxic tissues including tumors. To our knowledge, tumor oxygenation using a liposome-type artificial oxygen carrier has not been closely tested. In the present study, we tested whether systemic HbV administration changes tumor tissue oxygen tension, and if it modifies tumor response to irradiation.

MATERIALS AND METHODS

Lewis lung carcinoma was grown subcutaneously in the left hindleg of C57BL/6 mice. Experiments were initiated when the tumors reached approximately 8 mm. All experiments were done under room air. Tumor tissue oxygen tension was measured by phosphorescence quenching up to 45 min after systemic sample administration (saline: n = 5; HbV: n = 5; HbV containing methemoglobin (metHbV): n = 4; HbV with high oxygen affinity (lowP50HbV): n = 8) and compared between samples. To test the effects on irradiation response, samples (saline: n = 7; HbV: n = 7; metHbV: n = 7; lowP50HbV: n = 7) were administered prior to single 20-Gy irradiation, and tumor growth was compared.

RESULTS

Tumor tissue oxygen tension transiently increased approximately 2-fold after HbV administration in comparison to other samples. Tumor growth was marginally delayed after irradiation by prior administration of HbV in comparison to other samples. HbV administration without irradiation did not affect significant tumor growth delay.

CONCLUSIONS

These results correlatively suggest that HbV augmented tumor growth delay following irradiation, at least in part, by affecting tumor tissue oxygen tension.

Haemoglobin-vesicles as artificial oxygen carriers: present situation and future visions

During the long history of development of haemoglobin (Hb)-based O2 carriers (HBOCs), many side effects of Hb molecules have become apparent. They imply the physiological importance of the cellular structure of red blood cells. Hb-vesicles (HbV) are artificial O2 carriers that encapsulate concentrated Hb solution with a thin lipid membrane. We have overcome the intrinsic issues of the suspension of HbV as a molecular assembly, such as stability for storage and in blood circulation, blood compatibility and prompt degradation in the reticuloendothelial system. Animal tests clarified the efficacy of HbV as a transfusion alternative and the possibility for other clinical applications. The results of ongoing HbV research make us confident in advancing further development of HbV, with the expectation of its eventual realization.

Enzymatic elimination of hydrogen peroxide by a methemoglobin/L-Tyrosine system

We studied the peroxidase activity of ferrylhemoglobin radical (Hb(Fe(4+) = O*)) generated by the reaction of metHb (Hb(Fe(3+))) with hydrogen peroxide (H(2)O(2)). To clarify the behaviors of ferrylHb radical, it was isolated from the reaction mixture of metHb and H(2)O(2) by GPC at 4 degrees C. The radical species underwent rapid autoreduction to metHb at 37 degrees C accompanied with denaturation; however, it was stable for several minutes at 4 degrees C. In ESR measurements, the signal of the ferrylHb radical immediately disappeared in the presence of L-Tyrosine (L-Tyr), and simultaneously, the signal of the ferric heme increased. This suggested that the ferrylHb radical immediately converted to metHb by L-Tyr even at 4 degrees C. Furthermore, dimerized L-Tyr was detected in the reaction mixture. This showed that the ferrylHb radical was reduced to metHb by electron donation from L-Tyr. The enzymatic reaction using L-Tyr as the substrate resulted in the elimination of H(2)O(2) in this system.

One-year observation of Wistar rats after intravenous infusion of hemoglobin-vesicles (artificial oxygen carriers)

Hemoglobin-vesicles (HbV) or liposome-encapsulated Hb are artificial oxygen carriers. Our previous studies of the bolus infusion of HbV into Wistar rats showed that HbV was captured by the reticuloendothelial system from the blood stream and degraded completely with no deteriorative effect for 2 weeks. However, one authority on artificial organs research suggested conducting a one-year observation because he experienced, with one lipid-emulsified perfluorocarbon (PFC), that rats died within one year from a pulmonary abnormality after receiving the PFC emulsion due to the unstable dispersion state (personal communication). We thought this would never happen for HbV because the dispersion state of HbV is stable with PEG-modification. To confirm this, we made one-year observations after HbV infusion as suggested. Five male Wistar rats intravenously received 20 ml/kg HbV suspended in saline ([Hb] = 10 g/dL). They were housed in separated cages and provided with food and water ad libitum. All rats survived one year, and were apparently healthy. Their body weights (821+/-75 g) reflected obesity from their confinement in small cages. No histopathological abnormality was found in the lung. Plasma biochemical analyses showed overall normal organ functions. In our previous report, plasma lipid levels increased transiently at 1 or 2 days; then they reverted to the control level at 7 days. One year later, the rats showed much higher plasma lipid levels, a symptom of hyperlipidemia that is attributable to obesity and aging. It seemed the transient increases at the early days had no impact compared with the levels of hyperlipemia of the old rats.

Effect of hemoglobin vesicle, a cellular-type artificial oxygen carrier, on middle cerebral artery occlusion- and arachidonic acid-induced stroke models in rats

Hemoglobin vesicle (HbV), which is also called liposome-encapsulated hemoglobin, functions as a hemoglobin-based oxygen carrier and is expected to be utilized in emergency situations including hemorrhagic shock and several kinds of ischemic diseases. In the present study, we evaluated the efficacy of HbV for improving stroke-related symptoms induced by middle cerebral artery (MCA) occlusion/reperfusion and an intra-internal carotid arterial injection of arachidonic acid (AA) in rats. When HbV (10 mL/kg, i.v.) was administered to rats immediately after the MCA occlusion, it reduced the cerebral infarct volumes of the cortex and total of the cortex plus sub-cortex significantly as compared with saline as a vehicle. In AA-induced stroke model, HbV (10 mL/kg, i.v.) improved the motor dysfunction score and inhibited the increase in cerebral water content suggesting it could suppress cerebral edema. These results strongly suggest that HbV would provide a novel beneficial option for the treatment of stroke, especially acute ischemic stroke.

Hemoglobin Vesicles Containing Methemoglobin and l-Tyrosine to Suppress Methemoglobin Formation in Vitro and in Vivo

Hemoglobin (Hb) vesicles have been developed as cellular-type Hb-based O(2) carriers in which a purified and concentrated Hb solution is encapsulated with a phospholipid bilayer membrane. Ferrous Hb molecules within an Hb vesicle were converted to ferric metHb by reacting with reactive oxygen species such as hydrogen peroxide (H(2)O(2)) generated in the living body or during the autoxidation of oxyHb in the Hb vesicle, and this leads to the loss of O(2) binding ability. The prevention of metHb formation by H(2)O(2) in the Hb vesicle is required to prolong the in vivo O(2) carrying ability. We found that a mixed solution of metHb and L-tyrosine (L-Tyr) showed an effective H(2)O(2) elimination ability by utilizing the reverse peroxidase activity of metHb with L-Tyr as an electron donor. The time taken for the conversion of half of oxyHb to metHb (T(50)) was 420 min for the Hb vesicles containing 4 g/dL (620 microM) metHb and 8.5 mM L-Tyr ((metHb/L-Tyr) Hb vesicles), whereas the time of conversion for the conventional Hb vesicles was 25 min by stepwise injection of H(2)O(2) (310 microM) in 10 min intervals. Furthermore, in the (metHb/L-Tyr) Hb vesicles, the metHb percentage did not reach 50% even after 48 h under a pO(2) of 40 Torr at 37 degrees C, whereas T(50) of the conventional Hb vesicles was 13 h under the same conditions. Moreover, the T(50) values of the conventional Hb vesicles and the (metHb/L-Tyr) Hb vesicles were 14 and 44 h, respectively, after injection into rats (20 mL/kg), confirming the remarkable inhibitory effect of metHb formation in vivo in the (metHb/L-Tyr) Hb vesicles.

Nanotechnology: intelligent design to treat complex disease

The purpose of this expert review is to discuss the impact of nanotechnology in the treatment of the major health threats including cancer, infections, metabolic diseases, autoimmune diseases, and inflammations. Indeed, during the past 30 years, the explosive growth of nanotechnology has burst into challenging innovations in pharmacology, the main input being the ability to perform temporal and spatial site-specific delivery. This has led to some marketed compounds through the last decade. Although the introduction of nanotechnology obviously permitted to step over numerous milestones toward the development of the "magic bullet" proposed a century ago by the immunologist Paul Ehrlich, there are, however, unresolved delivery problems to be still addressed. These scientific and technological locks are discussed along this review together with an analysis of the current situation concerning the industrial development.

Acute 40 percent exchange-transfusion with hemoglobin-vesicles (HbV) suspended in recombinant human serum albumin solution: degradation of HbV and erythropoiesis in a rat spleen for 2 weeks

BACKGROUND

Hemoglobin-vesicles (HbVs; diameter, 251 +/- 81 nm) are artificial O(2) carriers. Their efficacy for acute exchange transfusion has been characterized in animal models. However subsequent profiles of recovery involving the degradation of HbV in the reticuloendothelial system (RES) and hematopoiesis remain unknown.

STUDY DESIGN AND METHODS

Isovolemic 40 percent exchange transfusion was performed in 60 male Wistar rats with HbV suspended in 5 g per dL recombinant human serum albumin (rHSA; HbV/rHSA, [Hb] = 8.6 g/dL), stored rat RBCs suspended in rHSA (sRBC/rHSA), or rHSA alone. Hematological and plasma biochemical analyses and histopathological examination focusing on the spleen were conducted for the subsequent 14 days.

RESULTS

The reduced hematocrit (Hct) level (26%) for the HbV/rHSA and rHSA groups returned to its original level (43%) in 7 days. Plasma erythropoietin was elevated in all groups: the rHSA group showed the highest value on Day 1 (321 +/- 123 mIU/mL) relating to the anemic conditions (HbV/rHSA, 153 +/- 22; sRBC/rHSA, 63 +/- 7; baseline, 21 +/- 3). Simultaneously, splenomegaly occurred in all the groups as HbV/rHSA > rHSA > sRBC/rHSA. Histopathologically, the accumulated HbV in the spleen was undetectable by Day 14, but hemosiderin was deposited in slight quantities for both the HbV/rHSA and sRBC/rHSA groups. Considerable amounts of erythroblasts were apparent in the spleens of both the rHSA and the HbV/rHSA groups.

CONCLUSION

HbVs were phagocytized and degraded in RES, a physiological compartment for the degradation of RBCs, and the elevated erythropoietic activity resulted in the complete recovery of Hct within 7 days in the rat model.

Oxygen carriers: A selected review

The most common and widely transplanted tissue world wide is blood, which in 2000 resulted in the transfusion of 12.5 million units of blood in the US alone [Goodnough LT, Shander A, Brecher ME. Transfusion medicine: looking to the future. Lancet 2003;361:161-9]. The current use of donated blood products is relatively safe; however, there are inherent problems with allogeneic blood transfusions. The wide spread use of blood in procedures results in problems involving inadequate supply exacerbated in times of war and disasters and by the limited storage life of blood donations (30-42 days). Blood contamination due to patient pre-disposition, poor collection, sterilization, or storage is the second most common cause of death from transfusion in the US [Hillyer CD, Josephson CD, Blajchman MA, Vostal JG, Epstein JS, Goodman JL. Bacterial contamination of blood components: risks, strategies, and regulation: joint ASH and AABB educational session in transfusion medicine. Hematology (Am Soc Hematol Educ Program) 2003:575-89]. Blood is a complex tissue involved in a plethora of homeostatic roles, including immunity, wound healing and the transport of nourishment, electrolytes, hormones, vitamins, heat, oxygen and the removal of metabolic waste products. However, by far the principle role of blood transfusions is the replacement of red cell volume and the maintenance of oxygen levels within the circulation. Creation of investigational new drugs (INDs) which would function as oxygen carriers and prolong shelf life is now a very active arena of scientific research. Several such IND products are now in clinical trials. This article gives an easy to follow concise evaluation of major areas of focus and current testing for each type of blood substitution molecule.

Is hemoglobin in hemoglobin vesicles infused for isovolemic hemodilution necessary to improve oxygenation in critically ischemic hamster skin?

The aim of this study was to test the influence of hemoglobin, encapsulated in phospholipid vesicles as an oxygen carrier, given in the course of isovolemic hemodilution to improve oxygenation in critically ischemic hamster flap tissue. Capillary hemodynamics and macromolecular leakage were investigated with intravital microscopy and analyzed off-line with the CapImage software. Partial tissue oxygen tension was measured with fluorescence quenching electrodes. The occurrence of apoptosis was assessed with the terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay. Vesicles with (HbV) or without (V) encapsulated Hb were suspended in 6% hydroxyethyl starch (HES) used for the 33% blood exchange. In the ischemic tissue, hemodilution led to an increase in functional capillary density by 31% for HES (P < 0.01 vs. other groups), 66% for V-HES, and 62% for HbV-HES (all P < 0.01 vs. control). Capillary diameters behaved inversely proportional to capillary microhemodynamics. The 20% increase in macromolecular leakage found over time in control animals was completely abolished in the vesicles groups (P < 0.01) but not with HES. Oxygen tension was improved from 10.7 to 16.0 mmHg after HbV-HES (P < 0.01 vs. baseline and other groups). Compared with the other groups, apoptosis was significantly reduced after HbV-HES (P < 0.01). We conclude that the encapsulation of Hb was essential to attenuate hypoxia and subsequent cell death in the critically ischemic tissue. However, the effect was partly attributed to the rheological changes exerted by the vesicles.

Oxygen release from low and normal P50 Hb vesicles in transiently occluded arterioles of the hamster window model

A phospholipid vesicle encapsulating Hb [Hb vesicle (HbV)] has been developed as a transfusion alternative. One characteristic of HbV is that the O(2) affinity [Po(2) at which Hb is 50% saturated (P(50))] of Hb can be easily regulated by the amount of the coencapsulated allosteric effector pyridoxal 5'-phosphate. In this study, we prepared two HbVs with different P(50)s (8 and 29 mmHg, termed HbV(8) and HbV(29), respectively) and observed their O(2)-releasing behavior from an occluded arteriole in a hamster skinfold window model. Conscious hamsters received HbV(8) or HbV(29) at a dose rate of 7 ml/kg. In the microscopic view, an arteriole (diameter: 53.0 +/- 6.6 mum) was occluded transcutaneously by a glass pipette on a manipulator, and the reduction of the intra-arteriolar Po(2) 100 mum down from the occlusion was measured by the phosphorescence quenching of preinfused Pd-porphyrin. The baseline arteriolar Po(2) (50-52 mmHg) decreased to about 5 mmHg for all the groups. Occlusion after HbV(8) infusion showed a slightly slower rate of Po(2) reduction compared with that after HbV(29) infusion. The arteriolar O(2) content was calculated at each reducing Po(2) in combination with the O(2) equilibrium curves of HbVs, and it was clarified that HbV(8) showed a significantly slower rate of O(2) release compared with HbV(29) and was a primary source of O(2) (maximum fraction, 0.55) overwhelming red blood cells when the Po(2) was reduced (e.g., <10 mmHg) despite a small dosage of HbV. This result supports the possible utilization of Hb-based O(2) carriers with lower P(50) for oxygenation of ischemic tissues.