Effect of alpha-alpha diaspirin crosslinked hemoglobin (DCLHb) on the potency of sodium nitroprusside and nitroglycerine to decrease blood pressure in rats: a dose-response study

Nitric Oxide in Cardiac Surgery: A Review Article

Perioperative organ injury remains a medical, social and economic problem in cardiac surgery. Patients with postoperative organ dysfunction have increases in morbidity, length of stay, long-term mortality, treatment costs and rehabilitation time. Currently, there are no pharmaceutical technologies or non-pharmacological interventions that can mitigate the continuum of multiple organ dysfunction and improve the outcomes of cardiac surgery. It is essential to identify agents that trigger or mediate an organ-protective phenotype during cardiac surgery. The authors highlight nitric oxide (NO) ability to act as an agent for perioperative protection of organs and tissues, especially in the heart-kidney axis. NO has been delivered in clinical practice at an acceptable cost, and the side effects of its use are known, predictable, reversible and relatively rare. This review presents basic data, physiological research and literature on the clinical application of NO in cardiac surgery. Results support the use of NO as a safe and promising approach in perioperative patient management. Further clinical research is required to define the role of NO as an adjunct therapy that can improve outcomes in cardiac surgery. Clinicians also have to identify cohorts of responders for perioperative NO therapy and the optimal modes for this technology.

Nitroglycerin attenuates vasoconstriction of HBOC-201 during hemorrhagic shock resuscitation

BACKGROUND

Vasoconstriction, an inherent property of Hemoglobin Based Oxygen Carriers (HBOC) potentially due to nitric oxide (NO) scavenging, may increase cardiovascular complications in HBOC resuscitated trauma patients. The purpose of this study was to determine if co-administration of a weak NO donor, intravenous nitroglycerin (NTG), with HBOC-201 during resuscitation from hemorrhagic shock could safely attenuate HBOC-201 vasoconstriction.

METHODS AND RESULTS

Hemorrhagic shock was induced in 44 swine randomized to receive fluid resuscitation with HBOC, HBOC+NTG10 mcg/kg/min, HBOC+NTG20 mcg/kg/min, HBOC+NTG40 mcg/kg/min, Hetastarch (HES), HES+NTG20 mcg/kg/min, NTG20 mcg/kg/min and Lactated Ringers (LR). HBOC resuscitation from hemorrhagic shock increased mean arterial pressure (MAP=94+/-33 mmHg), mean pulmonary artery pressure (MPAP=29+/-11 mmHg) and systemic vascular resistance (SVR=2684+/-871 dyns/cm(5)) in comparison to HES. Co-administration of NTG during HBOC resuscitation attenuated vasoconstriction with HBOC+40 mcg/kg/min demonstrating the most robust reduction in vasoconstriction (MAP=59+/-23 mmHg, MPAP=18+/-7 mmHg, and SVR=1827+/-511 dyns/cm(5)), although the effects were transient. Co-administration of NTG with HBOC did not alter base deficit, lactate, methemoglobin levels, nor cause profound hypotension during resuscitation.

CONCLUSION

Nitroglycerin attenuates vasoconstrictive properties of HBOC when co-administered during resuscitation in this swine model of hemorrhagic shock. Translational survival studies are required to determine if this strategy of attenuation of the vasoconstriction of HBOC-201 reduces cardiovascular complications and improves outcome with HBOC fluid resuscitation for hemorrhagic shock.

Recent developments in the understanding and management of paroxysmal nocturnal haemoglobinuria

Paroxysmal nocturnal haemoglobinuria (PNH) has been recognised as a discrete disease entity since 1882. Approximately a half of patients will eventually die as a result of having PNH. Many of the symptoms of PNH, including recurrent abdominal pain, dysphagia, severe lethargy and erectile dysfunction, result from intravascular haemolysis with absorption of nitric oxide by free haemoglobin from the plasma. These symptoms, as well as the occurrence of thrombosis and aplasia, significantly affect patients' quality of life; thrombosis is the leading cause of premature mortality. The syndrome of haemolytic-anaemia-associated pulmonary hypertension has been further identified in PNH patients. There is currently an air of excitement surrounding therapies for PNH as recent therapeutic developments, particularly the use of the complement inhibitor eculizumab, promise to radically alter the symptomatology and natural history of haemolytic PNH.

What sense lies in antisense inhibition of inducible nitric oxide synthase expression?

The impact of nitric oxide (NO) synthesized after activation by proinflammatory cytokines and/or bacterial products by an inducible NO synthase (iNOS) is still contradictory. Expression of iNOS in inflammatory reactions is often found predominantly in cells of epithelial origin, and in these cases NO may serve as a protective agent limiting pathogen spreading, downregulating local inflammatory reactions by inducing production of Th2-like responses in a classical feedback circle, or limiting tissue damage during stress conditions. However, an abundant amount of data on chronic human disorders with predominant proinflammatory Th1-like reactions points to a destructive role of iNOS activity calling for a specific inhibition. Various methods to inhibit iNOS have been established to elucidate a protective versus a destructive role of NO during various stresses. In this review, we focus on antisense (AS)-mediated gene knock-down as a relatively new method to inhibit NO production and summarize the techniques applied and their successes. At least in theory, it provides a specific, rapid, and potentially high-throughput method for inhibiting gene expression and function. We here discuss the opportunities of iNOS-directed AS-ODN, and extensively deal with limitations and experimental problems.

Hemodynamic response and oxygen transport in pigs resuscitated with maleimide-polyethylene glycol-modified hemoglobin (MP4)

Cell-free Hb increases systemic and pulmonary pressure and resistance and reduces cardiac output and heart rate in animals and humans, effects that have limited their clinical development as “blood substitutes.” The primary aim of this study was to evaluate the hemodynamic response to infusion of several formulations of a new polyethylene glycol (PEG)-modified human Hb [maleimide PEG Hb (MalPEGHb)] in swine, an animal known to be sensitive to Hb-induced vasoconstriction. Anesthetized animals underwent controlled hemorrhage (50% of blood volume), followed by resuscitation (70% of shed volume) with 10% pentastarch (PS), 4% MalPEG-Hb in lactated Ringer (MP4), 4% MalPEG-Hb in pentastarch (HS4), 2% MalPEG-Hb in pentastarch (HS2), or 4% stroma-free Hb in lactated Ringer solution (SFH). Compared with baseline, restoration of blood volume after resuscitation was similar and not significantly different for the PS (103%), HS2 (99%), HS4 (106%), and MP4 (87%) animals but significantly less for the SFH animals (66%) ( P < 0.05). All solutions that contained MalPEG-Hb restored mean arterial and pulmonary pressure and cardiac output. Systemic vascular resistance was unchanged, and pulmonary arterial pressure and resistance were increased slightly. Both systemic and pulmonary vascular resistance increased significantly in animals that received SFH, despite less adequate blood volume restoration. Oxygen consumption was maintained in all animals that received MalPEG-Hb, but not PS. Base excess improved only with MalPEG-Hb and PS, but not SFH. Red blood cell O2extraction was significantly increased in animals that received Hb, regardless of formulation. These data demonstrate resuscitation with MalPEG-human Hb without increasing systemic vascular resistance and support our previous observations in animals suggesting that the efficacy of low concentrations of PEG-Hb in the plasma results from reduced vasoconstriction.

No scavenging and the hypertensive effect of hemoglobin-based blood substitutes

The major pathway for nitric oxide scavenging in red cells involves the direct reaction of the gas with HbO2 to form nitrate and the ferric form of the protein, metHb. Because both atoms of O2 are incorporated into nitrate, this process is called NO dioxygenation (NOD). The NOD reaction involves an initial, very rapid bimolecular addition of NO to bound O2 to form a transient Fe(III)-peroxynitrite complex, which can be observed spectrally at alkaline pH. This intermediate rapidly isomerizes at pH 7 (t1/2 <== 1 ms) to metHb and NO3-, which is nontoxic and readily transported out of red cells and excreted. The rate of NO consumption by intracellular HbO2 during normal blood flow is limited by diffusion up to and into the red cells and is too slow to interfere significantly with vasoregulation. In contrast, extracellular HbO2 is highly vasoconstrictive, and the resultant hypertension is a significant side effect of most hemoglobin-based blood substitutes. The major cause of this blood pressure effect seems to be the high rate of NO dioxygenation by cell-free HbO2, which can extravasate into the vessel walls and interfere directly with NO signaling between endothelial and smooth muscle cells. This interpretation is supported by a strong linear correlation between the magnitude of the blood pressure effect caused by infusion of cross-linked recombinant hemoglobin tetramers in vivo and the rate of NO dioxygenation by these proteins measured in vitro.

Cross-linked bis-hemoglobins: connections and oxygen binding

Covalently linked pairs of cross-linked hemoglobin tetramers ("bis-tetramers", shown schematically as 6-8) were prepared by reacting hemoglobin A with tetrakis acyl phosphate esters (3-5). The effects of the link between tetramers are observed in the oxygen-binding properties of the bis-tetramers: they bind oxygen cooperatively but with Hill coefficients (n(50)) lower than that of the native protein and with a high average affinity. The bis-tetramers with longer connections between tetramers show a higher n(50), suggesting that steric interactions between the tetramers affect cooperativity. These results correlate to the observed reduced vasoactivity of heterogeneous solutions of oligomeric cross-linked hemoglobin tetramers.

Effect of diaspirin cross-linked haemoglobin (DCLHb) on mean arterial pressure during cardiopulmonary bypass in swine

Diaspirin cross-linked haemoglobin (DCLHb) is a haemoglobin-based oxygen carrier which had been proposed as a resuscitative solution to replace red cell transfusion in many clinical situations. The present study was designed to evaluate the effect of different volumes of DCLHb 10% (1, 5 and 10 mL kg-1) on the cardiovascular system during cardiopulmonary bypass (CPB), and to determine the effect of DCLHb (18 mL kg-1) when added directly to the CPB prime in anaesthetized swine. DCLHb, when used as a priming solution, induced a significant increase (around 20%) in mean arterial pressure (MAP), which persisted during the entire period of CPB (P < 0.05) as compared with controls. Administration of increasing doses of DCLHb during the time course of CPB resulted in a progressive increase in MAP (P < 0.05), suggesting a linear dose-response relationship. Nicardipine, a calcium channel blocker, returned MAP to baseline. Finally, weaning of CPB was easier in animals that received DCLHb, thereby suggesting a potential protective effect of free haemoglobin in this particular clinical situation.