Nitric oxide scavengers in the treatment of shock associated with systemic inflammatory response syndrome

Integrating Multi-Type Component Determination and Anti-Oxidant/-Inflammatory Assay to Evaluate the Impact of Pre-Molting Washing on the Quality and Bioactivity of Cicadae Periostracum

Cicadae Periostracum (CP) is a traditional Chinese medicinal herb derived from the slough that is molted from the nymph of the insect Cryptotympana pustulata Fabricius. Washing with water to remove residual silt is a primary processing method of CP that is recommended by the Chinese Pharmacopoeia, but how washing methods affect the quality and bioactivity of CP is unknown. In this study, the quality and bioactivity of non-washed CP (CP-NW), post-molting-washed CP (CP-WAT), and pre-molting-washed CP (CP-WBT) were comparatively investigated. The quality of these CP samples was evaluated in terms of the UPLC-QTOF-MS/MS-based chemical profiling and semi-quantification of 39 N-acetyldopamine oligomers (belonging to six chemical types), the HPLC-UV-based quantification of 17 amino acids, the ICP-MS-based quantification of four heavy metals, and the contents of ash; the bioactivities of the samples were compared regarding their anti-oxidant and anti-inflammatory activities. It was found that, compared with CP-NW, both CP-WBT and CP-WAT had significantly lower contents of ash and heavy metals. Moreover, compared with CP-WAT, CP-WBT contained lower levels of total ash, acid-insoluble ash, and heavy metals and higher contents of N-acetyldopamine oligomers and amino acids. It also had enhanced anti-oxidant and anti-inflammatory activities. A Spearman's correlation analysis found that the contents of N-acetyldopamine oligomers and free amino acids were positively correlated with the anti-oxidant/-inflammatory activities of CP. All these results suggest that pre-molting washing can not only remove the residual silt but can also avoid the loss of the bioactive components and assure higher bioactivities. It is concluded that pre-molting washing could enhance the quality and bioactivity of CP and should be a superior alternative method for the primary processing of qualified CP.

Selective and sensitive fluorescence imaging reveals microenvironment-dependent behavior of NO modulators in the endothelial system

Nitric oxide (NO) is a second messenger playing crucial roles in the signaling of a variety of cellular functions. Due to its pathophysiological significance, various NO modulators have been developed to explore NO pathways and some have been used as therapies. These modulators are often used directly to observe pharmacological effects in cell lines, but their actual effect on intracellular NO level is seldom analyzed. Herein, facilitated by a selective and sensitive fluorescence probe, we observed that some NO modulators displayed unexpected behaviors with both NO scavenger carboxy-PTIO and endothelial nitric oxide synthase (eNOS) inhibitor N(ω)-nitro-l-arginine methyl ester (l-NAME) failing to decrease intracellular free NO level in EA. hy926 cells while NO donor diethylamine-NONOate (DEA·NONOate) and eNOS activator calcimycin (A23187) failing to increase free NO level in human umbilical vein endothelial cell line (HUV-EC-C), although the reagents were confirmed to work normally in the primary human umbilical vein endothelial cells (primary HUVECs) and RAW 264.7 macrophage cells. Further research suggested that these unusual behaviors might be attributed to the cellular microenvironments including both the NO synthase (NOS) level and the endogenous glutathione (GSH) level. Genetically manipulating eNOS level in both cells restores the expected response, while decreasing GSH level restores the ability of DEA·NONOate to increase NO level in HUV-EC-C. These results reveal that the cellular microenvironment has a profound impact on pharmacological effect. Our study suggests GSH as a reservoir for NO in live cells and highlights the value of chemical probes as valuable tools to reveal microenvironment-dependent pharmacological effects.

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An imaging based method for evaluating the efficacy of NO modulators in live cells was developed.

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Some NO modulators were observed yielding unexpected effects on cellular NO levels in some endothelial cell lines.

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Further study unveiled intracellular microenvironments have profound effects on the efficacy of NO modulators in live cells.

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This result highlights the pitfall of the specific cellular microenvironments on drug efficacy.

Role of IRF4 in the Protection of Metformin-Mediated Sepsis Myocarditis

AIMS

Metformin has been shown to play a protective role in diabetes. However, we found that metformin could mediate myocardial protection. Given that protein kinase C eplison (PKCε) and interferon regulatory factor 4 (IRF4) are critical for cardioprotection signaling. And measurement of fluorescence resonance energy transfer (FRET) efficiency can be used to determine whether 2 fluorophores are within a certain distance of each other. So we sought to determine whether metformin promotes PKCε/IRF4 activation by FRET.

METHODS AND RESULTS

The study built a mouse septic myocarditis model by intraperitoneal injection of Escherichia coli; thus, it provides valuable experimental data for the diagnosis and treatment of septic myocarditis. And cellular model of cardiomyocyte damage from adult rat cardiacmyocytes or H9c2 cells was induced by lipopolysaccharide employed to examine PKCε by molecular, biochemical, and cellular imaging analysis. Life span of septic myocarditis mouse was significantly prolonged by metformin. Metformin also decreased transforming growth factor β level and increased interleukin-10 productions. The FRET analysis in H9c2 cells suggested that there is prominent FRET signal for PKCε along in mitochondrial by metformin.

CONCLUSION

We demonstrate that metformin promotes rapid association of PKCε with IRF4 at mitochondrial microdomain of cardiac myocytes and PKCε via direct molecular interaction with IRF4. This regulatory mechanism may play an important role in cardioprotection.

Cardiac dysfunction, mitochondrial architecture, energy production, and inflammatory pathways: Interrelated aspects in endotoxemia and sepsis

Septic patients with myocardial dysfunction have a 3-fold increase in mortality compared with patients without cardiovascular impairment, and usually show myocarditis, disruption of the contractile apparatus, increased amounts of interstitial collagen, and damaged mitochondria. The presence of nitric oxide and cytokines in cardiac tissue constitute the molecular markers and the intracellular messengers of inflammatory conditions in the heart due to the onset of sepsis and endotoxemia, derived from the nuclear factor-κB pathway activation and proinflammatory gene transcription. Sepsis occurs with an exacerbated inflammatory response that damages tissue mitochondria and impaired bioenergetic processes. The heart consumes 20-30 times its own weight in adenosine triphosphate every day, and 90% of this molecule is derived from mitochondrial oxidative phosphorylation. Cardiac energy management is comprised in sepsis and endotoxemia; both a deficit in energy production and alterations in the source of energy substrates are believed to be involved in impaired cardiac function. Although several hypotheses try to explain the molecular mechanisms underlying the complex condition of sepsis and endotoxemia, the current view is that these syndromes are the result of an intricate balance between prevailing levels of mitochondrial stress, biogenesis/autophagy signaling and mitochondria quality control processes, rather on a single factor. The aim of this review is to discuss current hypothesis of cardiac dysfunction related to energy metabolism and mitochondrial function in experimental models of sepsis and endotoxemia, and to introduce the importance of lipids (mainly cardiolipin) in the mechanism of cardiac energy mismanagement in these inflammatory conditions.

A simple method for establishing adherent ex vivo explant cultures from human eye pathologies for use in subsequent calcium imaging and inflammatory studies

A novel, simple, and reproducible method for cultivating pathological tissues obtained from human eyes during surgery was developed using viscoelastic material as a tissue adherent to facilitate cell attachment and expansion and calcium imaging of cultured cells challenged by mechanical and acetylcholine (ACh) stimulation as well as inflammatory studies. Anterior lens capsule-lens epithelial cells (aLC-LECs) from cataract surgery and proliferative diabetic retinopathy (PDR) fibrovascular epiretinal membranes (fvERMs) from human eyes were used in the study. We hereby show calcium signaling in aLC-LECs by mechanical and acetylcholine (ACh) stimulation and indicate presence of ACh receptors in these cells. Furthermore, an ex vivo study model was established for measuring the inflammatory response in fvERMs and aLC-LECs upon TNFα treatment.

Selective iNOS inhibition for the treatment of sepsis-induced acute kidney injury

The incidence and mortality of sepsis and the associated development of acute kidney injury (AKI) remain high, despite intense research into potential treatments. Targeting the inflammatory response and/or sepsis-induced alterations in the (micro)circulation are two therapeutic strategies. Another approach could involve modulating the downstream mechanisms that are responsible for organ system dysfunction. Activation of inducible nitric oxide (NO) synthase (iNOS) during sepsis leads to elevated NO levels that influence renal hemodynamics and cause peroxynitrite-related tubular injury through the local generation of reactive nitrogen species. In many organs iNOS is not constitutively expressed; however, it is constitutively expressed in the kidney and, in humans, a relationship between the upregulation of renal iNOS and proximal tubular injury during systemic inflammation has been demonstrated. For these reasons, the selective inhibition of renal iNOS might have important implications for the treatment of sepsis-induced AKI. Various animal studies have demonstrated that selective iNOS inhibition-in contrast to nonselective NOS inhibition-attenuates sepsis-induced renal dysfunction and improves survival, a finding that warrants investigation in clinical trials. In this Review, the selective inhibition of iNOS as a potential novel treatment for sepsis-induced AKI is discussed.

Evolution of Artificial Cells Using Nanobiotechnology of Hemoglobin Based RBC Blood Substitute as an Example

The original artificial red blood cells have evolved into oxygen carriers in the form of polyhemoglobin and conjugated hemoglobin. Clinical conditions requiring only oxygen carriers are responding well to these types of oxygen carriers without the need for a complete artificial red blood cell. For those conditions requiring more than just oxygen carriers, new generations of polyhemoglobin containing antioxidant enzymes are being developed. Though a complete artificial red blood cell comparable to red blood cell is still a dream, development in lipid membrane artificial red blood cells and biodegradable polymeric nano artificial red blood cells are steps towards this possibility. The many years of neglect on basic research in the area of blood substitutes have resulted in the lack of important basic knowledge needed for the rapid development of blood substitutes suitable for clinical use. This is further hampered by the mistaken conception that blood substitute is a single entity. We need to look at blood substitutes as consisting of progressively more complicated entities, e.g. oxygen carriers, oxygen carriers with antioxidant activity, and complete red blood cell substitutes. Each of these entities is not applicable to all clinical conditions, but is suitable for specific applications.

Polyhemoglobin with different percentage of tetrameric hemoglobin and effects on vasoactivity and electrocardiogram

There has been considerable discussions on why some types of haemoglobin-based blood substitutes increase vasoactivity whereas a very few others do not. In this study, we prepare four different types of PolyHb each containing different percentage of tetrameric hemoglobin using glutaraldehyde crosslinking and characterized to ensure that they all have the same oxygen affinity. Thus the preparations are prepared from the same chemical method and have the same oxygen affinity. We infused these in the form of 1/6 volume toploading into anesthetized rats to simulate the use of blood substitutes in surgery. Mean arterial pressure (MAP) increased immediately after injection of PolyHb containing 38% or 78% of tetrameric hemoglobin. However, there was no significant increase in blood pressure with the injection of PolyHb containing 16% or 0.4% tetrameric hemoglobin. In electrocardiogram (ECG) study, we observe that high percentage (78%) of tetrameric hemoglobin causes marked changes in ECG immediately after infusion. Injection of PolyHb containing 16% or 38% of tetrameric hemoglobin resulted in minimal elevation of the ST segment. Infusion of PolyHb containing 0.4% of tetrameric hemoglobin did not result in any changes.

Oxygen-carrying blood substitutes: a microvascular perspective

Development of a viable blood substitute began by focusing on recreating the oxygen-carrying capacity of blood, leading to the recognition that haemoglobin (Hb) is presently unequalled for this function. However, as human Hb is the only realistic source of this protein, the production of a blood substitute that solves transfusional blood availability problems and shortages must introduce a multiplying factor between supply of natural blood and blood substitute, while maintaining equivalency of function/efficacy. In other words, a unit of blood should produce several units of equivalent blood substitute. This expansion is now possible because of new understanding of how blood delivers oxygen in the microcirculation and the consequences of reducing oxygen-carrying capacity in haemorrhage. This information is used to provide improved resuscitation capacity and maintenance of tissue metabolism by tailoring the properties of a blood substitute to the task of maintaining microvascular function, rather than oxygen delivery capacity. Resuscitation in an organism that is haemorrhaging requires maintenance perfusion, a process directly linked to the maintenance of adequate levels of shear stress on the endothelium, induced by either increased blood/plasma viscosity or increased blood flow velocity in the microcirculation. This process must also be intimately coupled with the requirement that no portion of the tissue is anoxic. This disparate set of requirements can be satisfied with high viscosity Hb solutions that have high affinity for oxygen, a combination of properties that causes the microcirculation to remain functional, and a requirement that supersedes restoration of oxygen-carrying capacity in the treatment of haemorrhage.

On the mechanism and biology of cytochrome oxidase inhibition by nitric oxide

The detailed molecular mechanism for the reversible inhibition of mitochondrial respiration by NO has puzzled investigators: The rate constants for the binding of NO and O2 to the reduced binuclear center CuB/a3 of cytochrome oxidase (COX) are similar, and NO is able to dissociate slowly from this center whereas O2 is kinetically trapped, which altogether seems to favor the complex of COX with O2 over the complex of COX with NO. Paradoxically, the inhibition of COX by NO is observed at high ratios of O2 to NO (in the 40-500 range) and is very fast (seconds or faster). In this work, we used simple mathematical models to investigate this paradox and other important biological questions concerning the inhibition of COX by NO. The results showed that all known features of the inhibition of COX by NO can be accounted for by a direct competition between NO and O2 for the reduced binuclear center CuB/a3 of COX. Besides conciliating apparently contradictory data, this work provided an explanation for the so-called excess capacity of COX by showing that the COX activity found in tissues actually is optimized to avoid an excessive inhibition of mitochondrial respiration by NO, allowing a moderate, but not excessive, overlap between the roles of NO in COX inhibition and in cellular signaling. In pathological situations such as COX-deficiency diseases and chronic inflammation, an excessive inhibition of the mitochondrial respiration is predicted.

Mitochondrial nitric oxide metabolism in rat muscle during endotoxemia

In this study, heart and diaphragm mitochondria produced 0.69 and 0.77 nmol nitric oxide (NO)/min mg protein, rates that account for 67 and 24% of maximal cellular NO production, respectively. Endotoxemia and septic shock occur with an exacerbated inflammatory response that damages tissue mitochondria. Skeletal muscle seems to be one of the main target organs in septic shock, showing an increased NO production and early oxidative stress. The kinetic properties of mitochondrial nitric oxide synthase (mtNOS) of heart and diaphragm were determined. For diaphragm, the KM values for O2 and L-Arg were 4.6 and 37 microM and for heart were 3.3 and 36 microM. The optimal pH for mtNOS activity was 6.5 for diaphragm and 7.0 for heart. A marked increase in mtNOS activity was observed in endotoxemic rats, 90% in diaphragm and 30% in heart. Diaphragm and heart mitochondrial O2*- and H2O2 production were 2- to 3-fold increased during endotoxemia and Mn-SOD activity showed a 2-fold increase in treated animals, whereas catalase activity was unchanged. One of the current hypotheses for the molecular mechanisms underlying the complex condition of septic shock is that the enhanced NO production by mtNOS leads to excessive peroxynitrite production and protein nitration in the mitochondrial matrix, causing mitochondrial dysfunction and contractile failure.

Toxicities of hemoglobin solutions: in search of in-vitro and in-vivo model systems

Several hemoglobin-based oxygen carriers (HBOCs) have been developed with a rationale focused on exploiting one or more physicochemical properties (e.g., oxygen affinity, molecular weight, viscosity, and colloid osmotic pressure) resulting from the chemical or recombinant modification of hemoglobin (Hb). Several chemically modified Hbs have reached late stages of clinical evaluation in the United States and Canada. These Hbs, in general, demonstrated mixed preclinical safety and efficacy, and reasonable safety in Phase I trials. However, as clinical development shifted into later stages, an undesirable safety and efficacy profile became clear in patient populations studied, and as a result some products were withdrawn from further clinical pursuit. Several questions still remain unanswered regarding the safety of Hb products for their proposed clinical indication(s). For example, 1) were preclinical studies predictive of clinical outcome? And, 2) were the most appropriate preclinical studies performed to predict clinical outcome? The primary objectives of this analysis are to explore prelinical safety issues associated with HBOCs and provide an overview of the in-vitro and in-vivo models employed. The methods for obtaining data to serve as a basis for discussion are compiled from a literature-based survey of safety and efficacy derived from biochemical, cellular, and whole animal assessment of HBOCs. Results from this overview of a vast body of published data may provide a means for identifying critical preclinical safety issues, which may ultimately lead to identification of potential limitations in the effective clinical use of certain HBOCs.

Hemoglobin-based Red Blood Cell Substitutes

Polyhemoglobin is already well into the final stages of clinical trials in humans with one approved for routine clinical use in South Africa. Conjugated hemoglobin is also in ongoing clinical trials. Meanwhile, recombinant Hb has been modified to modulate the effects of nitric oxide. Other systems contain antioxidant enzymes for those clinical applications that may have potential problems related to ischemia-reperfusion injuries. Other developments are based on hemoglobin-lipid vesicles and also the use of nanotechnology and biodegradable copolymers to prepare nanodimension artificial red blood cells containing hemoglobin and complex enzyme systems.

Protection against murine endotoxemia by treatment with Ruta chalepensis L., a plant with anti-inflammatory properties

The anti-inflammatory effect of the extract of Ruta Chalepensis L. (Rutaceae) on the course of lethal endotoxemia in BALB/c mice was studied. When administered by gavage as 1 g/kg per day starting 14 or 7 days prior to injection of 0.75 mg endotoxin (LPS: lipopolysaccharide), the extract markedly reduced lethality (32.5% in both experiments versus approximately 85% of the control mice). A delay in lethality, but not cumulative lethality, was observed when prophylaxis was given 24 and 1 h prior to LPS challenge. The effect was associated with reduced LPS-induced blood levels of nitrite, an indicator of nitric oxide production. In contrast, the blood levels of tumour necrosis factor, interleukin 6 and interleukin 10 did not differ significantly from those of controls given LPS alone. These data show that Ruta Chalepensis L. possesses powerful immunopharmacological properties that make it capable of counteracting the lethal effects of high doses of LPS in vivo.

Ketamine/xylazine attenuates LPS-induced iNOS expression in various rat tissues

Ketamine and xylazine (K/X) are commonly used in combination as an anesthetic agent in experimental animal models. We previously noted that K/X attenuated lipopolysaccharide (LPS)-induced liver injury, gastric stasis, and reduced symptoms of endotoxemia. Because ketamine attenuates expression of several proinflammatory genes, we examined the effects of K/X on inducible nitric oxide synthase (iNOS), which has been implicated in endotoxin-induced tissue injury. We hypothesized that K/X would attenuate LPS-induced expression of iNOS in various organs in the rat. Rats were given either intraperitoneal saline or ketamine (70 mg/kg) and xylazine (6 mg/kg) 1 h before saline or LPS (20 mg/kg). Rats were sacrificed 5 h later and stomach, duodenum, jejunum, ileum, colon, liver, lung, kidney, and spleen were collected for determination of iNOS protein immunoreactivity by Western immunoblot. Data reported in densitometric units (DU) as mean +/- SEM (n >/= 5; ANOVA). LPS significantly increased iNOS protein immunoreactivity in all tissues examined versus saline controls (P </= 0.05, all groups). K/X significantly attenuated LPS-induced iNOS protein immunoreactivity in all of the aforementioned organs (P </= 0.05, all groups). Furthermore, K/X almost completely blunted LPS-induced expression of iNOS in stomach, duodenum, jejunum, and colon. These data indicate that K/X attenuates LPS-induced upregulation of iNOS in a variety of tissues. Furthermore, in rat models studying the in vivo effects of endotoxin, especially those evaluating the gastrointestinal system, careful consideration needs to be given if the anesthetic combination of K/X is used, as it alters LPS-induced expression of iNOS, an important pathophysiologic mediator in endotoxemia.

Future generations of red blood cell substitutes

Polyhaemoglobins (PolyHb) and perfluorochemicals are in advanced phase III clinical trials and conjugated haemoglobins in phase II clinical trial. New recombinant human haemoglobin with no vasoactivity is being developed. A soluble macromolecule of PolyHb-catalase-superoxide dismutase is being studied as an oxygen carrier with antioxidant properties. New artificial red blood cells that are more like RBC are being developed. One is based on haemoglobin lipid vesicles. A more recent one is based on nano-dimension artificial red blood cells containing haemoglobin and RBC enzymes with membrane formed from composite copolymer of polyethylene glycol-polylactic acid. Their circulation time is double that of PolyHb.

The role of mitochondrial nitric oxide synthase in inflammation and septic shock

Nitric oxide and cytokines constitute the molecular markers and the intercellular messengers of inflammation and septic shock. Septic shock occurs with an exacerbated inflammatory response that damages tissue mitochondria. Skeletal muscle appears as one of the main target organs in septic shock, showing an increased nitric oxide (NO) production, an early oxidative stress, and contractile failure. Mitochondria isolated from rat and human skeletal muscle in septic shock show a markedly increased NO generation and a decreased state 3 respiration, more marked with nicotinamide adenine dinucleotide (NAD)-linked substrates than with succinate, without uncoupling or impairment of phosphorylation. One of the current hypothesis for the molecular mechanisms of septic shock is that the enhanced NO production by mitochondrial nitric oxide synthase (mtNOS) leads to excessive peroxynitrite (ONOO(-)) production and protein nitration in the mitochondrial matrix, to mitochondrial dysfunction and to contractile failure. Surface chemiluminescence is a useful assay to assess inflammation and oxidative stress in in situ liver and skeletal muscle. Liver chemiluminescence in inflammatory processes and phagocyte chemiluminescence have been found spectrally different from spontaneous liver chemiluminescence with increased 440-600 nm emission, likely due to NO and ONOO(-) participation in the reactions leading to the formation of excited species.

Present status of modified hemoglobin as blood substitutes and oral therapy for end stage renal failure using artificial cells containing genetically engineered cells

Artificial cell or bioencapsulation has been developed for use in bioartificial organs, drug delivery, blood substitutes, and other areas. Recent rapid advances in modified hemoglobin blood substitutes have resulted in advance stages of Phase III clinical trials. Another area of use is in oral therapy, using artificial cells microencapsulated with genetically engineered cells for use in end stage renal failure and other conditions.

Pyridoxalated hemoglobin polyoxyethylene: a nitric oxide scavenger with antioxidant activity for the treatment of nitric oxide-induced shock

Hemoglobins modified for therapeutic use as either hemoglobin-based oxygen carriers or scavengers of nitric oxide are currently being evaluated in clinical trials. One such product, pyridoxalated hemoglobin polyoxyethylene conjugate (PHP), is a human-derived and chemically modified hemoglobin that has yielded promising results in Phase II clinical trials, and is entering a pivotal Phase III clinical trial for the treatment of shock associated with systemic inflammatory response syndrome (SIRS). Shock associated with SIRS is a NO-induced shock. PHP, a new mechanism-based therapy, has been demonstrated in clinical trials to have the expected hemodynamic activity of raising blood pressure and reducing catecholamine use, consistent with its mechanism of action as a NO scavenger. PHP is conjugated with polyoxyethylene, which results in a surface-decorated molecule with enhanced circulation time and stability as well as in attachment of soluble red blood cell enzymes, including catalase and superoxide dismutase. PHP thus contains an antioxidant profile similar to the intact red blood cell and is therefore resistant to both initial oxidative modification by oxidants such as hydrogen peroxide and subsequent ferrylhemoglobin formation. These studies suggest both that the redox activity of modified hemoglobins can be attenuated and that modified hemoglobins containing endogenous antioxidants, such as PHP, may have reduced pro-oxidant potential. These antioxidant properties, in addition to the NO-scavenging properties, may allow the use of PHP in other indications in which excess NO, superoxide, or hydrogen peroxide is involved, including ischemia-reperfusion injury and hemorrhagic shock.

Biochemical aspects of the reaction of hemoglobin and NO: implications for Hb-based blood substitutes

The role of Hemoglobin (Hb) on nitric oxide (NO) biology has received much attention. Until recently, the reaction between erythrocytic Hb and NO was generally considered in the context of mechanisms that safely detoxify NO. However, recent insights suggest that properties associated with the red blood cell limit NO-Hb interactions under physiological conditions, and provide some resolution to the question of how NO functions in the presence of blood. Furthermore, Hb-dependent mechanisms that preserve, not destroy NO bioactivity in vivo have also been proposed. The emerging picture suggests that the interplay between NO and erythrocytic Hb is important in regulating the functions of both these molecules in vivo. However, Hb-dependent scavenging and loss of NO function is significant when this heme protein is present outside the red blood cell. This can occur during hemolysis or administration of Hb-based blood substitutes. Scavenging of NO is a significant problem that limits the use of Hb-based blood substitutes in the clinic, and development of Hb molecules that do not efficiently react with NO remains an important area of investigation. In this article, the reactions between NO and erythrocytic Hb or cell-free Hb are described and the effects on NO and Hb function in vivo and development of blood substitutes discussed.