Biological activity of nitric oxide in the plasmatic compartment

Abstract

There exist reaction products of nitric oxide (NO) with blood that conserve its bioactivity and transduce an endocrine vasomotor function under certain conditions. Although S-nitrosated albumin has been considered the major species subserving this activity, recent data suggest that additional NO species, such as nitrite, nitrated lipids, N-nitrosamine, and iron-nitrosyl complexes, may contribute. We therefore examined the end products of NO reactions in plasma and blood in vitro and in vivo by using reductive chemiluminescent assays and electron paramagnetic resonance spectroscopy. We found that NO complexes in plasma previously considered to be S-nitrosated albumin were <10 nM after elimination of nitrite and were mercury-stable, consistent with ironnitrosyl or N-nitrosamine complex. During clinical NO gas inhalation protocols or in vitro NO donor treatment of human plasma, S-nitroso-albumin did not form with NO exposure <2 M, but plasma methemoglobin was detectable by paramagnetic resonance spectroscopy. Consistent with this formation of methemoglobin, human plasma was found to consume Ϸ2 M NO at a rate equivalent to that of hemoglobin. This NO consumption was mediated by the reaction of NO with plasma haptoglobin-hemoglobin complexes and limited slower reaction pathways required for S-nitrosation. These data suggest that high-affinity, metalbased reactions in plasma with the haptoglobin-hemoglobin complex modulate plasmatic NO reaction products and limit S-nitrosation at low NO flux. The studies further suggest that alternative NO reaction end products in plasma, such as nitrite, N-nitrosamines, iron-nitrosyls, and nitrated lipids, should be evaluated in blood NO transport along the vasculature. N itric oxide (NO) is a diatomic free radical molecule that plays a principal role in basal blood flow regulation and vascular homeostasis. Although NO is inactivated by dioxygenation reaction with oxyhemoglobin, a perierythrocytic unstirred layer (1, 2), membrane diffusion barrier (3), and cell-free zone in laminar flowing blood (4) reduce NO-hemoglobin reactions Ϸ600-fold, permitting tonic NO-dependent vasodilation and NO reactions with plasmatic proteins and other gas molecules (recently reviewed in ref. 5). The reaction of NO with plasma has been the subject of intense study after initial reports that human plasma contains 7 M S-nitroso-albumin (SNO-albumin), effectively creating a major paradigm that S-nitrosothiols serve as a stable circulating storage form of NO (6). Such a model has been supported by observations of the vasoactivity of infusions of SNO-albumin in animal models, distal vasodilation during infusions of NO solutions into the brachial artery, and the in vitro and in vivo formation of SNO-albumin with micromolar NO exposure to plasma (7-16).However, over the last 10 years the measured levels of plasma S-nitrosothiol and SNO-albumin have varied widely with different analytical methodologies and different species (Table 1 and Supporting Text, which are published as supporting information on the PNAS ...

The potential of Angeli's salt to decrease nitric oxide scavenging by plasma hemoglobin

“…More recently, the importance of intravascular hemolysis on NO bioavailability in diseased states including hemolytic anemias like sickle cell disease and paroxysmal nocturnal hemoglobinuria (PNH), thalassemia intermedia, malaria, thrombotic thrombocytopenic purpura, hemolytic uremic syndrome and cardiopulmonary bypass has been elucidated [17][18][19][68][69][70][71][72][73]. It had been thought that cell-free Hb in the blood was mainly present as metHb, but it is in fact mostly oxyHb [19,74]. Reiter and coworkers found that responsiveness to NO administration was blunted by 80% in patients with sickle cell anemia who had plasma Hb concentrations greater than or equal to 6 μM [19].…”

Assessment of nitric oxide signals by triiodide chemiluminescence

“…Notably, the overall chemistry of triiodide that would specifically identify FeNOs has not been described (40)(41)(42)(43)(44)(45); thus, the chemistry behind the putative effects of added reagents (oxidants, reductants, electrophiles, and nucleophiles) that are used to differentiate FeNO, SNO, and nitrite remains unclear. Moreover, few NO standards have actually been tested, and no basis has been provided for asserting that response of these standards captures the general behavior.…”

“…Moreover, few NO standards have actually been tested, and no basis has been provided for asserting that response of these standards captures the general behavior. Recovery of certain FeNO standards is reported to be as low as zero (40), and the one SNO-Hb standard that has been widely used (an R-structured Hb that contains Ϸ2 NO per tetramer) (40)(41)(42)(43)(44)(45)(46) is neither characteristic of general SNO-Hb reactivity nor of the reactivity of the micropopulation found in RBCs (a valency hybrid, estimated 1 NO per tetramer) (5,47). Furthermore, the claimed effects of added reagents in triiodide assays, including FeCN and NEM (alone and in combination), are not supported, and they, along with the acidic and denaturing conditions of the triiodide assay, can alter the reactivities of SNO and FeNO as well as disrupt the partitioning of NO species within hydrophobic compartments and thus lead to their misidentification.…”

“…In this assay, biological samples are placed in acid plus triiodide to liberate NO. Other reagents [potassium ferricyanide (FeCN), potassium cyanide, N-ethylmaleimide (NEM), sulfanilamide (SAA), and mercurous chloride] are incorporated to selectively eliminate or block formation of one or another NO species (41)(42)(43)(44)(45). For example, pretreatment of biological samples with FeCN (3-200 mM followed by desalting) is reported to selectively remove NO from hemes, and SAA/HCl is reported to selectively eliminate nitrite; NEM and cyanide supposedly stabilize SNOs by blocking reactive thiols and hemes, respectively.…”

Uso de albumina humana em pacientes graves: controvérsias e recomendações

“…Additionally, nitric oxide (NO) may bind to albumin, forming S-nitrous-albumin and regulating its plasma levels. (14) In pathological conditions there is no evidence for this potential NO regulation mechanism, but it acts as a vasodilator in the genesis of septic shock. Albumin's antioxidant effects have previously been demonstrated in the context of acute lung injury.…”