Nitric oxide donors in the treatment of cardiovascular and pulmonary diseases

Nitric Oxide-cGMP Pathway Modulation in an Experimental Model of Hypoxic Pulmonary Hypertension

Manipulation of nitric oxide (NO) may enable control of progression and treatment of pulmonary hypertension (PH). Several approaches may modulate the NO-cGMP pathway in vivo. Here, we investigate the effectiveness of 3 modulatory sites: (i) the amount of l-arginine; (ii) the size of plasma NO stores that stimulate soluble guanylate cyclase; (iii) the conversion of cGMP into inactive 5′-GMP, with respect to hypoxia, to test the effectiveness of the treatments with respect to hypoxia-induced PH. Male rats (n = 80; 10/group) maintained in normoxic (21% O₂) or hypoxic chambers (10% O₂) for 14 days were subdivided in 4 sub-groups: placebo, l-arginine (20 mg/ml), the NO donor molsidomine (15 mg/kg in drinking water), and phoshodiesterase-5 inhibitor sildenafil (1.4 mg/kg in 0.3 ml saline, i.p.). Hypoxia depressed homeostasis and increased erythropoiesis, heart and right ventricle hypertrophy, myocardial fibrosis and apoptosis inducing pulmonary remodeling. Stimulating anyone of the 3 mechanisms that enhance the NO-cGMP pathway helped rescuing the functional and morphological changes in the cardiopulmonary system leading to improvement, sometimes normalization, of the pressures. None of the treatments affected the observed parameters in normoxia. Thus, the 3 modulatory sites are essentially similar in enhancing the NO-cGMP pathway, thereby attenuating the hypoxia-related effects that lead to pulmonary hypertension.

Nitric oxide modulators: an emerging class of medicinal agents

Nitric oxide, a unique messenger in biological system, is ubiquitously present virtually in all tissues revealing its versatile nature of being involved in diverse physiological functions such as vascular tone, inhibition of platelet aggregation, cell adhesion, neurotransmission and enzyme and immune regulation. The tremendous advancements made in the past few decades in this area suggests that the nitric oxide modulation either by its exogenous release through nitric oxide donors or inhibition of its synthesis by nitric oxide synthase inhibitors in physiological milieu may provide newer clinical strategies for the treatment of some diseases. In this review, an attempt is made to document and understand the biological chemistry of different classes of nitric oxide modulators that would prove to be a fruitful area in the years to come.

Gaseous nitric oxide bactericidal activity retained during intermittent high-dose short duration exposure

Previously, we have shown that gaseous Nitric oxide (gNO) has great potential as an effective topical anti-infective agent for non-healing wounds due to its non-specific antimicrobial properties. These same antimicrobial attributes may be useful for pulmonary infections. However, gNO would have limited usefulness as an inhaled antimicrobial agent as continuous exposure to the concentration required for a bactericidal effect (160-200 ppm) leads to methemoglobinemia. To overcome this problem, we investigated whether a thirty minute exposure of 160 ppm every four hours would retain the same antimicrobial effect as continuous delivery. In vitro, exposure of clinical multi-drug resistant Staphylococcus aureus and Escherichia coli strains isolated from the lungs of nosocomial pneumonia patients and a lethal antibiotic-resistant strain of Pseudomonas aeruginosa, isolated from a deceased cystic fibrosis patient resulted in over a 5 log(10) reduction in bacterial load after multiple thirty minute treatments (4 cycles) every four hours to 160 ppm gNO. The intermittent regimen required 320 (SD=0)ppm h for 100% lethality whereas the continuous exposure required 800 (SD=160)ppm h. We have also shown that selection for a gNO resistant phenotype did not lead to decrease sensitivity to gNO therapy (p>0.05). In addition, no host cellular toxicity was observed in human THP-1 monocytes and macrophages following intermittent delivery of a high concentration of gNO, and the proliferation and migration of pulmonary epithelial cells was not adversely affected by the administration of intermittent high-dose gNO. These results justify further studies that should focus on whether intermittent delivery of 160 ppm of gNO every four hours can technically be administered while keeping inhaled NO(2) levels less than 2 ppm and methemoglobin saturation less than 2.5 percent.

Potential application of gaseous nitric oxide as a topical antimicrobial agent

The presence of bacterial colonization in non-healing wounds and burn injuries interferes significantly with the normal process of healing. Recent evidence suggests that nitric oxide (NO) plays an important role in host defense against infection and regulates wound healing and angiogenesis. We investigated the potential application of a medical-grade gaseous form of NO (gNO) as a novel antibacterial agent in wound infection. Using a continuous horizontal-flow delivery system, the antibacterial activity of gNO was tested in vitro against a range of pathogens, including clinical isolates of Staphylococcus aureus, methicillin-resistant S. aureus, Escherichia coli, Group B Streptococcus, Pseudomonas aeruginosa, and Candida albicans. To probe the effect of topical application of gNO on the human skin, the proliferation and extracellular matrix gene expression of human dermal fibroblasts in culture were also analyzed by (3)H-thymidine incorporation assay and Northern blot techniques, respectively. Potent bacteriocidal activity was observed at 200 ppm gNO with an average of 4.1 +/- 1.1 h to completely stop bacterial growth. Interestingly, this dose of gNO did not show any cytotoxic effect in human dermal fibroblasts in culture exposed for up to 48 h. Analysis of gene transcription in fibroblasts revealed a significant increase in MMP-1 mRNA expression as early as 2 h post-exposure to gNO. Although to a lesser degree, a significant reduction in type I procollagen was also observed in the same fibroblasts. The results of this study suggest that exogenous gaseous NO has potent significant antibacterial properties that can be beneficial in reducing bacterial burden in infected wound in burn injuries or non-healing ulcers.

Nitric oxide in respiratory diseases

The formation and modulation of nitric oxide (NO) in the lungs is reviewed. Its beneficial and deleterious roles in airways diseases, including asthma, chronic obstructive pulmonary disease, and cystic fibrosis, and in animal models is discussed. The pharmacological effects of agents that modulate NO production or act as NO donors are described. The clinical pharmacology of these agents is described and the therapeutic potential for their use in airways disease is considered.

Protective effect of a novel NO-donor on ischemia/reperfusion injury in a rat epigastric flap model

An altered metabolism of endothelial cell-derived nitric oxide has been implicated in the microvascular dysfunction associated with ischemia/reperfusion. The objective of this study was to examine whether S-nitroso human serum albumin, a novel nitric oxide-donor, improves flap viability and whether it influences edema formation after prolonged ischemia when administered prior to and in the initial phase of reperfusion. Denervated epigastric island skin flaps were elevated in 30 male Sprague Dawley rats, rendered ischemic for 8 hours, subsequently reperfused and further observed for either 3 hours (acute) or 7 days (chronic). In the sham rats (n = 6), skin flaps were elevated only. Starting 1 hour prior to reperfusion, S-nitroso human serum albumin (n = 12) or human serum albumin (n = 12) as placebo was infused systemically for 2 hours. In the chronic model, flap necrosis as well as viable flap size was evaluated after 7 days of reperfusion in six rats per group, comparing to sham rats. In the acute model, edema formation was evaluated after 3 hours of reperfusion in six rats per group. Administration of S-nitroso human serum albumin significantly decreased flap necrosis from 18.1 +/- 15.6% in the human serum albumin group to 2.1 +/- 1.5% in the S-nitroso human serum albumin group, which was similar to the sham group (2.5 +/- 4.2%). Viable flap size (sham 13.4 +/- 1.6 cm2) was also significantly improved in the S-nitroso human serum albumin group (10.1 +/- 1 cm2) versus the human serum albumin group (7.0 +/- 2.2 cm2). There was no significant difference between the groups regarding postischemic edema formation. These results show that administration of S-nitroso human serum albumin prior to and in the initial phase of reperfusion significantly improves flap viability after 7 days but does not influence early observable edema formation. These findings support the role of nitric oxide as an important mediator in the protection against skin flap ischemia/reperfusion injury.

Nitrophorins and related antihemostatic lipocalins from Rhodnius prolixus and other blood-sucking arthropods

Recent gene sequence and crystal structure determinations of salivary proteins from several blood-sucking arthropods have revealed an unusual evolutionary relationship: many such proteins derive their functions from lipocalin protein folds. Many blood-sucking arthropods have independently evolved the ability to overcome a host organism's means of preventing blood loss (called hemostasis). Most blood feeders have proteins that induce vasodilation, inhibit blood coagulation, and reduce inflammation, but do so by distinctly different mechanisms. Despite this diversity, in many cases the antihemostatic activities in such organisms reside in proteins with lipocalin folds. Thirteen such lipocalins are described in this review, with a particular focus on the heme-containing nitrophorins from Rhodnius prolixus, which transport nitric oxide, sequester histamine, and disrupt blood coagulation. Also described are the antiplatelet compounds RPAI, moubatin, and pallidipin from R. prolixus, Ornithodoros moubata, and Triatoma pallidipennis; the antithrombin protein triabin from T. pallidipennis; and the tick histamine binding proteins from Rhipicephalus appendiculatus.

H2O2 causes endothelial barrier dysfunction without disrupting the arginine-nitric oxide pathway

We have previously demonstrated that nitric oxide (.NO) donors attenuate and that inhibition of endogenous nitric oxide synthase (NOS) enhances hydrogen peroxide (H2O2)-mediated porcine pulmonary artery endothelial cell (PAEC) injury. The current study investigates the hypothesis that oxidant-mediated inhibition of NOS contributes to PAEC injury. PAEC barrier function, measured as the transmonolayer clearance of albumin, was significantly impaired by H2O2 (10-100 microM) in the absence of cytotoxicity. Treatment with H2O2 did not alter NOS activity, measured as the conversion of [3H]arginine to [3H]citrulline in PAEC lysates, either immediately after treatment with 0-250 microM H2O2 for 30 min or for up to 120 min after treatment with 100 microM H2O2. H2O2 had little effect on NOS activity in intact PAECs, measured as 1) the formation of [3H]citrulline in [3H]arginine-loaded PAECs, 2) PAEC guanosine 3',5'-cyclic monophosphate content, and 3) PAEC.NO release to the culture media. These results indicate that the arginine-.NO pathway remains intact after exposure to oxidant conditions sufficient to promote functional derangements of vascular endothelial cells.

Effect of L-arginine on in vitro plasmin-generation and fibrinogenolysis

L-arginine ahs received much attention in numerous aspects of the regulation of vascular tone and haemostasis. L-arginine seems to be capable to bind to plasminogen, too. The aim of the present paper is to investigate the action of L-arginine on in vitro plasmin generation and fibrino(geno)lysis by chromogenic, kinetic plasmin generation assay and electrophoretic analysis. The acceleration of tPA-induced plasmin generation in the presence of low concentration of L-arginine, along with augmentation of in vitro fibrinogenolysis have been documented. L-arginine may have a role in the modification of fibrinogenolysis, and this role should be considered if arginine is used as an element of some novel antithrombotic agents.

The association of reduced endothelium derived relaxing factor-NO production with endothelial damage and increased in vivo platelet activation in patients with diabetes mellitus

The role of reduced endothelial production of EDRF-NO in the pathogenesis of diabetic angiopathy has received much attention, however, most of the rather conflicting data were gained from animal experiments. Limited human experience seems to be available in insulin dependent diabetes, calling attention to decreased EDRF-NO production. Hereby the clinical, as well as laboratory investigation (urinary and serum nitrate/nitrite, lipid peroxidation, glucometabolic parameters, endothelial and in vivo platelet activation markers, etc.) of 35 non-insulin dependent (NIDDM) and 15 insulin dependent diabetics (IDDM) patients are given. Urinary and serum nitrate/nitrite concentrations were proven to be reduced in both patients groups. This change was independent of diabetes duration, presence of macroangiopathy, coronary heart disease and the glucometabolic parameters, however, correlation was registered with lipid peroxidation (total antioxidant status). An inverse correlation of nitrate/nitrite excretion with endothelial markers (von Willebrand factor, soluble thrombomodulin) was documented in NIDDM, this correlation was much stronger in IDDM. Moreover, in IDDM patients reduced nitrate/nitrite excretion was strongly associated with elevated plasmatic beta-thromboglobulin levels. The data presented here support to the hypothesis, that EDRF-NO production is reduced in diabetes and this reduction seems to correlate with endothelial damage. In IDDM the decreased nitrate/nitrite excretion may also lead to increased in vivo platelet activation, which suggests that the reduced amount of EDRF-NO might play a role in the pathogenesis of angiopathy in IDDM.