Hemorrhagic shock resuscitation with carbon monoxide saturated blood

Carbon monoxide combined with artificial blood cells acts as an antioxidant for tissues thermally-damaged by dye laser irradiation

Artificial red blood cells [i.e., hemoglobin vesicles (HbVs)] can be used as photosensitizers in pulsed-dye laser (PDL) treatment for port wine stains in animal models. Small HbVs are distributed in the vicinity of the endothelial cells of the blood vessels. In our previous in vivo experiments, both HbVs and red blood cells absorbed photons of the laser and generated heat, contributing to removal of very small blood vessels and large deeper subcutaneous blood vessels with PDL irradiation. Herein, we tested carbon monoxide-bound HbVs (CO-HbVs) that would produce heat energy while releasing CO in vessels after dye laser irradiation in a rabbit auricle model. We conducted this experiment to confirm secondary progression of thermal injury being reduced with the antioxidative property of CO. We histopathologically evaluated the damages to the large vessels and surrounding dermal tissue following PDL irradiation alone or subsequent to the intravenous injection of the qualified HbVs. The soft tissue damages were graded on a five-point scale and compared statistically. Intravenous CO-HbVs significantly reduced damage to the surrounding tissue after subsequent PDL irradiation; however, the degree of damage to the larger vessel wall resulted in a variety of changes, including a slight increase in our histopathological grades. This beneficial effect in dye laser treatment for port wine stains may be the result of the antioxidative property of CO against free radicals in the zone of stasis that may still be theoretically viable in burns. This effect of CO protecting tissues from thermal damage is consistent with previous reports of CO as a reducing agent. If the reducing agent can be delivered directly to the affected area immediately after the burn injury, even in a small amount, the complex inflammatory cascade may be reduced and unnecessary inflammation after laser treatment that lowers the patient's quality of life can be avoided.

Effect of carbon monoxide administration using haemoglobin-vesicles on the hippocampal tissue

Carbon monoxide (CO) is a toxic gas that causes neuropathy. However, CO is endogenously produced in small amounts showing various beneficial effects. We hypothesized that CO-bound haemoglobin-vesicle (HbV) administration would reduce cerebral ischaemia-reperfusion injury without causing neuropathy. Three experiments were conducted. First, rats were exposed to CO inhalation to create a CO-poisoning group, and they were sacrificed on 0, 7, 14, and 21 days after CO exposure. Histopathologically, hippocampal damage was prominent at 14 days. Second, the rats were administered with CO-HbV equivalent to 50 or 25% of circulating blood volume (CO-HbV50 or CO-HbV25 group). Rats were sacrificed 14 days after administration. Third, rats put into haemorrhagic shock by 50% of circulating blood withdrawal were resuscitated using saline, autologous blood, and CO-HbV. They were sacrificed 14 days after resuscitation. Hippocampal damage assessment clarified that almost no necrotic cells were observed in the CO-HbV50 group. Necrotic cells in the CO-HbV25 group were comparable to those found for the control group. In rats resuscitated from haemorrhagic shock, the hippocampal damage in the group using CO-HbV was the mildest. Administration of CO-HbV did not lead to marked hippocampal damage. Furthermore, CO-HbV was effective at preventing cerebral ischaemia-reperfusion injury after haemorrhagic shock.

Examination of central nervous system by functional observation battery after massive intravenous infusion of carbon monoxide-bound and oxygen-bound hemoglobin vesicles in rats

Carbon monoxide (CO) is known as a toxic gas inducing "CO poisoning", which acutely affects the central nervous system (CNS) and which persistently affects brain functions depending on the exposure time and CO concentration. By contrast, in pathological rodent models, intravenous infusion of CO-bound hemoglobin vesicles (CO-HbV) has shown various beneficial effects such as anti-oxidative and anti-inflammatory reactions. This study assessed effects of CO-HbV infusion on CNS using a functional observation battery, sensory reflexes, grip strength, and landing foot splay measurements. The test fluids were CO-HbV and O₂-bound HbV (O₂-HbV) suspended in saline ([Hb] ​= ​10 ​g/dL), and saline alone for comparison. The rats received either 16 or 32 ​mL/kg of fluid intravenously at 1.5 ​mL/min/kg. Observations were made before infusion, and at 5 ​min, 4, 8, 24, 48 and 72 ​h after infusion. Massive doses of 16 and 32 ​mL/kg respectively corresponded to about 29 and 57% of the whole circulating blood volume (56 ​mL/kg). No toxicological effect was observed in any measurement item for any group in comparison to the control saline infusion group. Histopathological examination of hippocampal tissue at 14 days after infusion showed the number of necrotic cells to be minimal. Results obtained from rats in this experiment suggest that the massive intravenous infusion of CO-HbV yields beneficial anti-oxidative and anti-inflammatory effects without showing CO-poisoning-related symptoms of CNS damage.

Scalable production and complete biophysical characterization of poly(ethylene glycol) surface conjugated liposome encapsulated hemoglobin (PEG-LEH)

Particle encapsulated hemoglobin (Hb)-based oxygen (O2) carriers (HBOCs) have clear advantages over their acellular counterparts because of their larger molecular diameter and lack of vasoactivity upon transfusion. Poly(ethylene glycol) surface conjugated liposome encapsulated Hb (PEG-LEH) nanoparticles are considered a promising class of HBOC for use as a red blood cell (RBC) substitute. However, their widespread usage is limited by manufacturing processes which prevent material scale up. In this study, PEG-LEH nanoparticles were produced via a scalable and robust process using a high-pressure cell disruptor, and their biophysical properties were thoroughly characterized. Hb encapsulation, methemoglobin (metHb) level, O2-PEG-LEH equilibria, PEG-LEH gaseous (oxygen, carbon monoxide, nitric oxide) ligand binding/release kinetics, lipocrit, and long-term storage stability allowed us to examine their potential suitability and efficacy as an RBC replacement. Our results demonstrate that PEG-LEH nanoparticle suspensions manufactured via a high-pressure cell disruptor have Hb concentrations comparable to whole blood (~12 g/dL) and possess other desirable characteristics, which may permit their use as potential lifesaving O2 therapeutics.

Microvascular and Systemic Impact of Resuscitation with PEGylated Carboxyhemoglobin-Based Oxygen Carrier or Hetastarch in a Rat Model of Transient Hemorrhagic Shock

BACKGROUND

Hemorrhage is the leading cause of preventable, traumatic death. Currently, prehospital resuscitation fluids provide preload but not oxygen-carrying capacity-a critical blood function that mitigates microvascular ischemia and tissue hypoxia during hemorrhagic shock. Solutions containing polymerized hemoglobin have been associated with vasoactive and hypertensive events. A novel hemoglobin-based oxygen carrier, modified with PEGylation and CO moieties (PEG-COHb), may overcome these limitations.

OBJECTIVES

To evaluate the systemic and microcirculatory effects of PEG-COHb as compared with the 6% hetastarch in a rat model of hemorrhagic shock.

METHODS

Male Sprague Dawley rats (N = 20) were subjected to severe, controlled, hemorrhagic shock. Animals were randomized to 20% estimated blood-volume resuscitation with either 6% hetastarch or PEG-COHb. Continuous, invasive, cardiovascular measurements, and arterial blood gases were measured. Microcirculatory measurements of interstitial oxygenation (PISFO2) and vasoactivity helped model oxygen delivery in the spinotrapezius muscle using intravital and phosphorescence quenching microscopy.

RESULTS

Hemorrhage reduced mean arterial pressure (MAP), arteriolar diameter, and PISFO2, and increased lactate 10-fold in both groups. Resuscitation with both PEG-COHb and hetastarch improved cardiovascular parameters. However, PEG-COHb treatment resulted in higher MAP (P < 0.001), improved PISFO2 (14 [PEG-COHb] vs. 5 [hetastarch] mmHg; P < 0.0001), lower lactate post-resuscitation (P < 0.01), and extended survival from 90 to 142 min (P < 0.001) as compared with the hetastarch group.

CONCLUSIONS

PEG-COHb improved MAP PISFO2, lactate, and survival time as compared with 6% hetastarch resuscitation. Importantly, hypertension and vasoactivity were not detected in response to PEG-COHb resuscitation supporting further investigation of this resuscitation strategy.

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.

Association of exhaled carbon monoxide with risk of cardio-cerebral-vascular disease in the China Kadoorie Biobank cohort study

Exhaled carbon monoxide (COex) level has been proposed as a noninvasive and easily-obtainable cardiovascular risk marker, however, with limited prospective evidence, and its association with stroke risk has been rarely explored. Measurements of COex were performed during 2004-2008 baseline examinations in the China Kadoorie Biobank study among 512,891 adults aged 30-79 years from 10 diverse study areas. After excluding participants with baseline cardiopulmonary diseases, stroke and cancer, 178,485 men and 267,202 women remained. Cox regression yielded hazard ratios (HRs) and 95% confidence intervals (CIs) for risk of cardio-cerebral-vascular disease (CCVD) associated with COex levels, with sequential addition of adjustment for proxy variables for CO exposure, including study area indexing ambient CO variations at large, and smoking and solid fuel use, apart from adjusting for traditional cardiovascular risk factors. During 7-year follow-up, we documented 1744 and 1430 major coronary events (myocardial infarction plus fatal ischemic heart disease), 8849 and 10,922 ischemic strokes, and 2492 and 2363 hemorrhagic strokes among men and women, respectively. The HRs with 95% CIs comparing the highest with lowest COex quintile were 2.15 [1.72, 2.69] for major coronary events, 1.65 [1.50, 1.80] for ischemic stroke, and 1.35 [1.13, 1.61] for hemorrhagic stroke among men, while among women higher associated risk was only observed for major coronary events (1.64 [1.35, 2.00]) and ischemic stroke (1.87 [1.73, 2.01]). The elevated risks were consistent when COex level was over 3 ppm. However, these associations were all attenuated until null by sequential addition of stratification by study areas, and adjustments of smoking and solid fuel use. Nevertheless, the association with ischemic stroke was maintained among the subgroup of male smokers even with adjustment for the depth and amount of cigarette smoking (HR [95% CI]: 1.37 [1.06, 1.77]), while a negative association with hemorrhagic stroke also appeared within this subgroup. Higher COex level (over 3 ppm) was associated with elevated risk of ischemic CCVD, but not independently of CO exposure. Our finding suggests that, though not an independent risk factor, COex could potentially provide a cost-effective biomarker for ischemic cardio-cerebral-vascular risk, given that CO exposure is ubiquitous.

Resuscitation After Hemorrhagic Shock in the Microcirculation: Targeting Optimal Oxygen Delivery in the Design of Artificial Blood Substitutes

Microcirculatory preservation is essential for patient recovery from hemorrhagic shock. In hemorrhagic shock, microcirculatory flow and pressure are greatly reduced, creating an oxygen debt that may eventually become irreversible. During shock, tissues become hypoxic, cellular respiration turns to anaerobic metabolism, and the microcirculation rapidly begins to fail. This condition requires immediate fluid resuscitation to promote tissue reperfusion. The choice of fluid for resuscitation is whole blood; however, this may not be readily available and, on a larger scale, may be globally insufficient. Thus, extensive research on viable alternatives to blood has been undertaken in an effort to develop a clinically deployable blood substitute. This has not, as of yet, achieved fruition, in part due to an incomplete understanding of the complexities of the function of blood in the microcirculation. Hemodynamic resuscitation is acknowledged to be contingent on a number of factors other than volume expansion. The circulation of whole blood is carefully regulated to optimize oxygen delivery to the tissues via shear stress modulation through blood viscosity, inherent oxygen-carrying capacity, cell-free layer variation, and myogenic response, among other variables. Although plasma expanders can address a number of these issues, hemoglobin-based oxygen carriers (HBOCs) introduce a method of replenishing the intrinsic oxygen-carrying capacity of blood. There continue to be a number of issues related to HBOCs, but recent advances in the next-generation HBOCs show promise in the preservation of microcirculatory function and limiting toxicities. The development of HBOCs is now focused on viscosity and the degree of microvascular shear stress achieved in order to optimize vasoactive and oxygen delivery responses by leveraging the restoration and maintenance of physiological responses to blood flow in the microcirculation. Blood substitutes with higher viscous properties tend to improve oxygen delivery compared to those with lower viscosities. This review details current concepts in blood substitutes, particularly as they relate to trauma/hemorrhagic shock, with a specific focus on their complex interactions in the microcirculation.

Use of Hemoglobin for Delivering Exogenous Carbon Monoxide in Medicinal Applications

Carbon Monoxide (CO), at low concentrations, can have a variety of positive effects on the body including anti-apoptosis, anti-inflammatory, anti-oxidative and anti-proliferative effects. Although CO has great potential for use as a potent medical bioactive gas, for it to exist in the body in stable form, it must be associated with a carrier. Hemoglobin (Hb) represents a promising material for use as a CO carrier because most of the total CO in the body is stored associated with Hb in red blood cells (RBC). Attempts have been made to develop an Hb-based CO carrying system using RBC and Hb-based artificial oxygen carriers. Some of these have been reported to be safe and to have therapeutic value as a CO donor in preclinical and clinical studies. In the present review, we overview the potential of RBC and Hb-based artificial oxygen carriers as CO carriers based on the currently available literature evidence for their use in pharmaceutical therapy against intractable disorders.

Carbon monoxide releasing molecule-A1 improves nonalcoholic steatohepatitis via Nrf2 activation mediated improvement in oxidative stress and mitochondrial function

Nuclear factor-erythroid 2 related factor 2 (Nrf2)-mediated signaling plays a central role in maintaining cellular redox homeostasis of hepatic cells. Carbon monoxide releasing molecule-A1 (CORM-A1) has been reported to stimulate up-regulation and nuclear translocation of Nrf2 in hepatocytes. However, the role of CORM-A1 in improving lipid metabolism, antioxidant signaling and mitochondrial functions in nonalcoholic steatohepatitis (NASH) is unknown. In this study, we report that CORM-A1 prevents hepatic steatosis in high fat high fructose (HFHF) diet fed C57BL/6J mice, used as model of NASH. The beneficial effects of CORM-A1 in HFHF fed mice was associated with improved lipid homeostasis, Nrf2 activation, upregulation of antioxidant responsive (ARE) genes and increased ATP production. As, mitochondria are intracellular source of reactive oxygen species (ROS) and important sites of lipid metabolism, we further investigated the mechanisms of action of CORM-A1-mediated improvement in mitochondrial function in palmitic acid (PA) treated HepG2 cells. Cellular oxidative stress and cell viability were found to be improved in PA + CORM-A1 treated cells via Nrf2 translocation and activation of cytoprotective genes. Furthermore, in PA treated cells, CORM-A1 improved mitochondrial oxidative stress, membrane potential and rescued mitochondrial biogenesis thru upregulation of Drp1, TFAM, PGC-1α and NRF-1 genes. CORM-A1 treatment improved cellular status by lowering glycolytic respiration and maximizing OCR. Improvement in mitochondrial respiration and increment in ATP production in PA + CORM-A1 treated cells further corroborate our findings. In summary, our data demonstrate for the first time that CORM-A1 ameliorates tissue damage in steatotic liver via Nrf2 activation and improved mitochondrial function, thus, suggesting the anti-NASH potential of CORM-A1.

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CORM-A1 facilitates Nrf2 translocation and regulates cellular redox homeostasis in liver.

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CORM-A1 improves antioxidant status and lipid metabolism in liver.

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CORM-A1 induces mitochondrial biogenesis, improves energetics and cellular respiration in HepG2 cells.

Formation of high molecular weight p62 by CORM-3

CORM-3 is a water-soluble carbon monoxide (CO)-releasing molecule developed for possible therapeutic use of CO. CORM-3 belongs to a group of metal carbonyl compounds that contain transition metals and carbonyls as the central scaffold and coordinated ligands, respectively. CORM-3 has been reported to be reactive with many proteins in eukaryotes including mammals. Among them, several extracellular proteins, such as lysozyme, as well as plasma albumin and fibronectin, have been shown to interact directly with CORM-3. p62 is an intracellular adaptor protein required for targeting ubiquitinated (Ub) proteins to lysosomal degradation through autophagy. p62 has been shown to undergo self-oligomerization via covalent crosslinking in response to treatment with verteporfin, a benzoporphyrin derivative used for photodynamic therapy. Here we show that CORM-3 also interacts directly with p62. When applied to mouse embryonic fibroblasts (MEFs) at a high concentration (1 mM), CORM-3 causes the formation of reduction- and detergent-resistant high molecular weight (HMW)-p62. HMW-p62 accumulates more in atg5-/- MEFs than in wild type (WT) MEFs, showing the elimination of HMW-p62 through autophagy. HMW-p62 is also generated in H9c2 rat cardiomyoblastoma as well as A549 human alveolar epithelial cells, suggesting that HMW-p62 formation is not specific to MEFs, but, rather, is a general event in mammalian cells. HMW-p62 formation by CORM-3 can be reproduced using purified p62 in vitro, demonstrating the direct interaction between CORM-3 and p62. These results show that p62 is a CORM-3-interactive intracellular protein.

Hemorrhagic Shock and the Microvasculature

The microvasculature plays a central role in the pathophysiology of hemorrhagic shock and is also involved in arguably all therapeutic attempts to reverse or minimize the adverse consequences of shock. Microvascular studies specific to hemorrhagic shock were reviewed and broadly grouped depending on whether data were obtained on animal or human subjects. Dedicated sections were assigned to microcirculatory changes in specific organs, and major categories of pathophysiological alterations and mechanisms such as oxygen distribution, ischemia, inflammation, glycocalyx changes, vasomotion, endothelial dysfunction, and coagulopathy as well as biomarkers and some therapeutic strategies. Innovative experimental methods were also reviewed for quantitative microcirculatory assessment as it pertains to changes during hemorrhagic shock. The text and figures include representative quantitative microvascular data obtained in various organs and tissues such as skin, muscle, lung, liver, brain, heart, kidney, pancreas, intestines, and mesentery from various species including mice, rats, hamsters, sheep, swine, bats, and humans. Based on reviewed findings, a new integrative conceptual model is presented that includes about 100 systemic and local factors linked to microvessels in hemorrhagic shock. The combination of systemic measures with the understanding of these processes at the microvascular level is fundamental to further develop targeted and personalized interventions that will reduce tissue injury, organ dysfunction, and ultimately mortality due to hemorrhagic shock. Published 2018. Compr Physiol 8:61-101, 2018.

Transfusion of Red Blood Cells to Patients with Sepsis

Sepsis is one of the major causes of death worldwide, and is the host response to infection which renders our organs malfunctioning. Insufficient tissue perfusion and oxygen delivery have been implicated in the pathogenesis of sepsis-related organ dysfunction, making transfusion of packed red blood cells (pRBCs) a reasonable treatment modality. However, clinical trials have generated controversial results. Even the notion that transfused pRBCs increase the oxygen-carrying capacity of blood has been challenged. Meanwhile, during sepsis, the ability of our tissues to utilize oxygen may also be reduced, and the increased blood concentrations of lactate may be the results of strong inflammation and excessive catecholamine release, rather than impaired cell respiration. Leukodepleted pRBCs more consistently demonstrated improvement in microcirculation, and the increase in blood viscosity brought about by pRBC transfusion helps maintain functional capillary density. A restrictive strategy of pRBC transfusion is recommended in treating septic patients.

The protective effects of carboxyhemoglobin during the resuscitation from hemorrhagic shock in rats

Aim

This study was aimed to explore the effects of carboxyhemoglobin on reperfusion injury in hemorrhagic shock, as well as its action time and related mechanisms.

Results

CO-RBC group showed milder oxidative injury than O2-RBC group. CO reperfusion did not show advantages in functions of kidney and lung during resuscitation. The level of Bax was decreased in CO-RBC group, especially in early CO-RBC group. Moreover, the autophay-related gene Beclin-1 was down-regulated in CO-RBC and early CO-RBC groups. The inflammation was severer in CO-RBC resuscitation group.

Materials and Methods

The hemorrhagic shock model rats were randomly divided into: the hemorrhagic shock group (n = 6); the O2-red blood cells (O₂-RBC) group (n = 6), perfused with O₂-RBC 1 h after ischemia; CO-RBC group (n = 12), perfused with CO-RBC 1 h after ischemia; and early CO-RBC group (n = 12), perfused with CO-RBC 30 min after ischemia. The reperfusion injuries were evaluated through anti-reactive oxygen species (ROS), inflammatory action, organ function, cell apoptosis and autophagy.

Conclusions

Carboxyhemoglobin not only relieves the oxidative injury and inhibites apoptosis and autophagy, but also aggravates inflammatory reactions during reperfusion. The action time of carboxyhemoglobin may be an influencing factor for reperfusion outcomes.

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.

Localized delivery of carbon monoxide

The heme oxygenase (HO)/carbon monoxide (CO) system is a physiological feedback loop orchestrating various cell-protective effects in response to cellular stress. The therapeutic use of CO is impeded by safety challenges as a result of high CO-Hemoglobin formation following non-targeted, systemic administration jeopardizing successful CO therapies as of this biological barrier. Another caveat is the use of CO-Releasing Molecules containing toxicologically critical transition metals. An emerging number of local delivery approaches addressing these issues have recently been introduced and provide exciting new starting points for translating the fascinating preclinical potential of CO into a clinical setting. This review will discuss these approaches and link to future delivery strategies aiming at establishing CO as a safe and effective medication of tomorrow.

Characteristics of exogenous carbon monoxide deliveries

Carbon monoxide (CO) has long been considered an environmental pollutant and a poison. Exogenous exposure to amounts of CO beyond the physiologic level of the body can result in a protective or adaptive response. However, as a gasotransmitter, endogenous CO is important for multiple physiologic functions. To date, at least seven distinct methods of delivering CO have been utilized in animal and clinical studies. In this mini-review, we summarize the exogenous CO delivery methods and compare their advantages and disadvantages.

Replacing the Transfusion of 1-2 Units of Blood with Plasma Expanders that Increase Oxygen Delivery Capacity: Evidence from Experimental Studies

At least a third of the blood supply in the world is used to transfuse 1–2 units of packed red blood cells for each intervention and most clinical trials of blood substitutes have been carried out at this level of oxygen carrying capacity (OCC) restoration. However, the increase of oxygenation achieved is marginal or none at all for molecular hemoglobin (Hb) products, due to their lingering vasoactivity. This has provided the impetus for the development of “oxygen therapeutics” using Hb-based molecules that have high oxygen affinity and target delivery of oxygen to anoxic areas. However it is still unclear how these oxygen carriers counteract or mitigate the functional effects of anemia due to obstruction, vasoconstriction and under-perfusion. Indeed, they are administered as a low dosage/low volume therapeutic Hb (subsequently further diluted in the circulatory pool) and hence induce extremely small OCC changes. Hyperviscous plasma expanders provide an alternative to oxygen therapeutics by increasing the oxygen delivery capacity (ODC); in anemia they induce supra-perfusion and increase tissue perfusion (flow) by as much as 50%. Polyethylene glycol conjugate albumin (PEG-Alb) accomplishes this by enhancing the shear thinning behavior of diluted blood, which increases microvascular endothelial shear stress, causes vasodilation and lowering peripheral vascular resistance thus facilitating cardiac function. Induction of supra-perfusion takes advantage of the fact that ODC is the product of OCC and blood flow and hence can be maintained by increasing either or both. Animal studies suggest that this approach may save a considerable fraction of the blood supply. It has an additional benefit of enhancing tissue clearance of toxic metabolites.

MP4CO, a pegylated hemoglobin saturated with carbon monoxide, is a modulator of HO-1, inflammation, and vaso-occlusion in transgenic sickle mice

Transgenic sickle mice expressing β(S) hemoglobin have activated vascular endothelium in multiple organs that exhibits enhanced expression of NF-ĸB and adhesion molecules and promotes microvascular stasis in sickle, but not normal, mice in response to hypoxia/reoxygenation (H/R), or heme. Induction of heme oxygenase-1 (HO-1) or administration of its products, carbon monoxide (CO) or biliverdin, inhibits microvascular stasis in sickle mice. Infusion of human hemoglobin conjugated with polyethylene glycol and saturated with CO (MP4CO) markedly induced hepatic HO-1 activity and inhibited NF-ĸB activation and H/R-induced microvascular stasis in sickle mice. These effects were mediated by CO; saline or MP4 saturated with O2 (MP4OX) had little to no effect on H/R-induced stasis, though unmodified oxyhemoglobin exacerbated stasis. The HO-1 inhibitor, tin protoporphyrin, blocked MP4CO protection, consistent with HO-1 involvement in the protection afforded by MP4CO. MP4CO also induced nuclear factor-erythroid 2 p45-related factor 2 (Nrf2), an important transcriptional regulator of HO-1 and other antioxidant genes. In a heterozygous (hemoglobin-AS) sickle mouse model, intravenous hemin induced cardiovascular collapse and mortality within 120 minutes, which was significantly reduced by MP4CO, but not MP4OX. These data demonstrate that MP4CO induces cytoprotective Nrf2 and HO-1 and decreases NF-ĸB activation, microvascular stasis, and mortality in transgenic sickle mouse models.

Blood substitutes: evolution from noncarrying to oxygen- and gas-carrying fluids

The development of oxygen (O2)-carrying blood substitutes has evolved from the goal of replicating blood O2 transport properties to that of preserving microvascular and organ function, reducing the inherent or potential toxicity of the material used to carry O2, and treating pathologies initiated by anemia and hypoxia. Furthermore, the emphasis has shifted from blood replacement fluid to "O2 therapeutics" that restore tissue oxygenation to specific tissues regions. This review covers the different alternatives, potential and limitations of hemoglobin-based O2 carriers (HBOCs) and perfluorocarbon-based O2 carriers (PFCOCs), with emphasis on the physiologic conditions disturbed in the situation that they will be used. It describes how concepts learned from plasma expanders without O2-carrying capacity can be applied to maintain O2 delivery and summarizes the microvascular responses due to HBOCs and PFCOCs. This review also presents alternative applications of HBOCs and PFCOCs namely: 1) How HBOC O2 affinity can be engineered to target O2 delivery to hypoxic tissues; and 2) How the high gas solubility of PFCOCs provides new opportunities for carrying, dissolving, and delivering gases with biological activity. It is concluded that the development of current blood substitutes has amplified their applications horizon by devising therapeutic functions for O2 carriers requiring limited O2 delivery capacity restoration. Conversely, full, blood-like O2-carrying capacity reestablishment awaits the control of O2 carrier toxicity.

Hemorrhagic shock: The "physiology approach"

A shift of approach from ‘clinics trying to fit physiology’ to the one of ‘physiology to clinics’, with interpretation of the clinical phenomena from their physiological bases to the tip of the clinical iceberg, and a management exclusively based on modulation of physiology, is finally surging as the safest and most efficacious philosophy in hemorrhagic shock. ATLS^® classification and recommendations on hemorrhagic shock are not helpful because antiphysiological and potentially misleading. Hemorrhagic shock needs to be reclassified in the direction of usefulness and timing of intervention: in particular its assessment and management need to be tailored to physiology.

Transfusion of banked red blood cells and the effects on hemorrheology and microvascular hemodynamics in anemic hematology outpatients

BACKGROUND

The aim of this study was to investigate the effects of red blood cell (RBC) transfusion on the hemorrheologic properties and microcirculatory hemodynamics in anemic hematology outpatients receiving 2 to 4 RBC units of either "fresh" (leukoreduced storage for less than 1 week) or "aged" (leukoreduced storage for 3-4 weeks) RBCs.

STUDY DESIGN AND METHODS

Measurements were performed before and 30 minutes after RBC transfusion in hematology outpatients. Leukoreduced RBC suspensions were stored in saline-adenine-glucose-mannitol (SAGM) additive solution. Whole blood viscosity was measured using Couette low-shear viscometry, RBC deformability and aggregability were measured using laser-assisted optical rotational cell analysis, and microcirculatory density and perfusion were assessed using sidestream dark field imaging.

RESULTS

One group of patients (n = 10) received a median (interquartile range) of 3 (2-3) RBC bags that were stored for 7 (5-7) days (fresh) and the other group of patients (n = 10) received 3 (3-3) RBC bags that were stored for 23 (22-28) days (aged). After transfusion of fresh versus aged RBCs, hematocrit increased to 32 ± 3% versus 31 ± 2% (p < 0.363), whole blood viscosity increased to 4.2 ± 0.4 Pa/sec versus 4.2 ± 0.6 Pa/sec (p < 0.912), RBC deformability index remained unaffected, RBC aggregability index increased to 55 ± 10 versus 55 ± 13 (p = 0.967), microcirculatory flow remained unaffected, and microcirculatory density increased to 19.3 ± 2.5 mm/mm(2) versus 18.7 ± 1.9 mm/mm(2) (p = 0.595), respectively.

CONCLUSION

Storing leukoreduced SAGM-suspended RBCs for 3 to 4 weeks did not affect their ability to improve hemorrheologic properties and microcirculatory hemodynamics in our small group of anemic hematology outpatients. Larger studies are needed to confirm this finding.

Pathological conditions involving extracellular hemoglobin: molecular mechanisms, clinical significance, and novel therapeutic opportunities for α(1)-microglobulin

Hemoglobin (Hb) is the major oxygen (O(2))-carrying system of the blood but has many potentially dangerous side effects due to oxidation and reduction reactions of the heme-bound iron and O(2). Extracellular Hb, resulting from hemolysis or exogenous infusion, is shown to be an important pathogenic factor in a growing number of diseases. This review briefly outlines the oxidative/reductive toxic reactions of Hb and its metabolites. It also describes physiological protection mechanisms that have evolved against extracellular Hb, with a focus on the most recently discovered: the heme- and radical-binding protein α(1)-microglobulin (A1M). This protein is found in all vertebrates, including man, and operates by rapidly clearing cytosols and extravascular fluids of heme groups and free radicals released from Hb. Five groups of pathological conditions with high concentrations of extracellular Hb are described: hemolytic anemias and transfusion reactions, the pregnancy complication pre-eclampsia, cerebral intraventricular hemorrhage of premature infants, chronic inflammatory leg ulcers, and infusion of Hb-based O(2) carriers as blood substitutes. Finally, possible treatments of these conditions are discussed, giving a special attention to the described protective effects of A1M.

Early treatment of transient focal cerebral ischemia with bovine PEGylated carboxy hemoglobin transfusion

The effect of transfusion of PEGylated hemoglobin (PEG-Hb) was evaluated in anesthetized rats subjected to 2 hours of focal cerebral ischemia and 1 day of reperfusion. PEG-Hb was stored in the carboxy state (PEG-COHb) to reduce autooxidation and increase the shelf life. Transfusion of 10 ml/kg of PEG-COHb at 20 minutes of ischemia did not alter arterial blood pressure or increase red cell flux in the ischemic core. Plasma hemoglobin increased to only 0.6 g/dL, yet infarct volume was markedly decreased and neurological deficits were improved. We conclude that early topload transfusion of PEG-COHb protects the brain from ischemic stroke.

Perfusion vs. oxygen delivery in transfusion with "fresh" and "old" red blood cells: the experimental evidence

We review the experimental evidence showing systemic and microvascular effects of blood transfusions instituted to support the organism in extreme hemodilution and hemorrhagic shock, focusing on the use of fresh vs. stored blood as a variable. The question: "What does a blood transfusion remedy?" was analyzed in experimental models addressing systemic and microvascular effects showing that oxygen delivery is not the only function that must be addressed. In extreme hemodilution and hemorrhagic shock blood transfusions simultaneously restore blood viscosity and oxygen carrying capacity, the former being critically needed for re-establishing a functional mechanical environment of the microcirculation, necessary for obtaining adequate capillary blood perfusion. Increased oxygen affinity due to 2,3 DPG depletion is shown to have either no effect or a positive oxygenation effect, when the transfused red blood cells (RBCs) do not cause additional flow impairment due to structural malfunctions including increased rigidity and release of hemoglobin. It is concluded that fresh RBCs are shown to be superior to stored RBCs in transfusion, however increased oxygen affinity may be a positive factor in hemorrhagic shock resuscitation. Although experimental studies seldom reproduce emergency and clinical conditions, nonetheless they serve to explore fundamental physiological mechanisms in the microcirculation that cannot be directly studied in humans.

Heme oxygenase 1 protects against hepatic hypoxia and injury from hemorrhage via regulation of cellular respiration

Heme oxygenase 1 (HO-1) is an important regulator of the cellular response to stress and inflammation. These investigations test the hypothesis that HO-1 overexpression protects against hemorrhage-induced hypoxia by regulating cellular respiration and oxygen availability. Male C57BL/6 mice or primary mouse hepatocytes were treated with adenoviral gene transfer of HO-1 (AdHO-1) or beta-galactosidase (AdLacZ). Mice were subjected to hemorrhagic shock and resuscitation or cannulation without hemorrhage. AdHO-1 prevented hemorrhagic shock/resuscitation-induced liver injury. In addition, AdHO-1 prevented hemorrhage-induced liver hypoxia and depletion of adenosine triphosphate. In vitro, HO-1 overexpression resulted in decreased cellular respiration under hypoxic conditions as determined by oxygen consumption and cytochrome c oxidase activity. This resulted in increased intracellular oxygen levels in the setting of low oxygen tensions. In conclusion, HO-1 overexpression protects the liver against hemorrhage-induced injury. This may be secondary to the ability of HO-1 to protect against bioenergetic failure via regulation of cellular respiration.

Microvascular experimental evidence on the relative significance of restoring oxygen carrying capacity vs. blood viscosity in shock resuscitation

The development of volume replacement fluids for resuscitation in hemorrhagic shock comprises oxygen carrying and non carrying fluids. Non oxygen carrying fluids or plasma expanders are used up to the transfusion trigger, and upon reaching this landmark either blood, and possibly in the near future oxygen carrying blood substitutes, are used. An experimental program in hemorrhagic shock using the hamster chamber window model allowed to compare the relative performance of most fluids proposed for shock resuscitation. This model allows investigating simultaneously the microcirculation and systemic reactions, in the awake condition, in a tissue isolated from the environment. Results from this program show that in general plasma expanders such as Ringer's lactate and dextran 70 kDa do not sufficiently restore blood viscosity upon reaching the transfusion trigger, causing microvascular collapse. This is in part restored by a blood transfusion, independently of the oxygen carrying capacity of red blood cells. These results lead to the proposal that effective blood substitutes must be designed to prevent microvascular collapse, manifested in the decrease of functional capillary density. Achievement of this goal, in combination with the increase of oxygen affinity, significantly postpones the need for a blood transfusion, and lowers the total requirement of restoration of intrinsic oxygen carrying capacity.

Increased plasma viscosity prolongs microhemodynamic conditions during small volume resuscitation from hemorrhagic shock

Systemic and microvascular hemodynamic responses to hemorrhagic shock resuscitation with hypertonic saline (HTS, 7.5% NaCl) followed with a small volume of plasma expander were studied in the hamster window chamber model to determine the role of plasma expander viscosity in the acute resuscitation outcome. Moderate hemorrhagic shock was induced by arterial controlled bleeding of 50% of blood volume (BV) and the hypovolemic state was maintained for 1 h. Volume restitution was performed by infusion of HTS, 3.5% of BV followed by 10% of BV plasma expanders. Resuscitation was followed for 90 min. The experimental groups were named based on the plasma expanders infused after the HTS, namely: [Hextend], Hextend (6% Hetastarch 670 kDa in lactated electrolyte solution, 4 cp), [Hextend+V], Hextend with viscosity enhanced by the addition of 0.4% alginate, 8 cp, and [NVR] no volume resuscitation as control group. Measurement of systemic parameters, microvascular hemodynamics and capillary perfusion were performed during hemorrhage, shock and resuscitation. Restitution with Hextend yielded the higher mean arterial pressure (MAP), followed by Hextend+V and NVR. Increasing plasma viscosity did not increase peripheral vascular resistance. Functional capillary density (FCD) was higher for Hextend+V than Hextend and NVR. The level of restoration of acid-base balance correlated with microvascular perfusion and was significantly improved with Hextend+V when compared to Hextend and NVR. These results suggest the importance of restoration of blood rheological properties through enhancing plasma viscosity, influencing the re-establishment of microvascular perfusion during small volume resuscitation from hemorrhagic shock.