Decreased nitrite levels in erythrocytes of children with β-thalassemia/hemoglobin E

Efficacy and safety of inhaled nitrite in addition to sildenafil in thalassemia patients with pulmonary hypertension: A 12-week randomized, double-blind placebo-controlled clinical trial

Pulmonary hypertension is a significant complication in thalassemia patients. Recent studies showed that inhaled nebulized nitrite could rapidly decrease pulmonary artery pressure. We conducted a multicenter, randomized, double-blind, placebo-controlled trial in thalassemia patients with symptomatic pulmonary hypertension diagnosed by right heart catheterization. Eleven patients were recruited; five were assigned to the nitrite group and six to the placebo group. Patients were treated with the optimal doses of sildenafil for pulmonary hypertension and randomly assigned into the placebo or nitrite groups. Patients in the nitrite group were given inhaled nebulized 30 mg sodium nitrite twice a day for 12 weeks. The clinical outcomes measured at week 12 were the changes in 6-min walk distance (6MWD), mean pulmonary artery pressure (MPAP), and N-terminal pro B-type natriuretic peptide. The MPAP estimated by echocardiography was significantly reduced from 33.6 ± 7.5 mmHg to 25.8 ± 6.0 mmHg (mean difference = 7.76 ± 3.69 mmHg, p = 0.009 by paired t-test). Furthermore, 6MWD was slightly increased from 382.0 ± 54.0 m to 432 ± 53.9 m (mean difference = 50.0 ± 42.8 m, p = 0.059 by paired t-test) in the nitrite group. At week 12, the nitrite group had lower MPAP than the placebo group (25.8 ± 6.0 vs. 45.7 ± 18.5 mmHg, p = 0.048 by unpaired t-test). No significant difference in 6MWD and N-terminal pro B-type natriuretic peptide between the two groups was observed at week 12. There was no hypotension or other significant adverse effects in the nitrite group.

Nitrite in paraffin-stimulated saliva correlates with blood nitrite

Nitrite anion (NO₂^-) is a circulating nitric oxide (NO) metabolite considered an endothelial function marker. Nitrite can be produced from nitrate (NO₃^-) secreted from plasma into saliva. The nitrate reductase of oral bacteria converts salivary nitrate to nitrite, which is swallowed and absorbed into circulation. In this study, we aimed to examine the relevance between these species' salivary and blood levels. We collected three whole saliva samples (unstimulated, paraffin-stimulated, and post-chlorhexidine mouthwash stimulated saliva) and blood from 75 healthy volunteers. We measured the nitrite and nitrate by the chemiluminescence method. The nitrite levels in stimulated saliva and post-mouthwash stimulated saliva exhibited weak correlations with blood nitrite. There was no correlation between nitrite in unstimulated saliva with blood nitrite. The baseline platelet activity, determined as P-selectin expression, negatively correlated with nitrite in plasma and post-mouthwash stimulated saliva. The salivary nitrate in all saliva samples showed correlations with its plasma levels. We conclude that nitrite in stimulated saliva correlates with blood nitrite.

Vascular and hemostatic alterations associated with pulmonary hypertension in β-thalassemia hemoglobin E patients receiving regular transfusion and iron chelation

INTRODUCTION

Pulmonary hypertension (PH) is the commonest cardiac complication in β-thalassemia intermedia, including β-thalassemia/hemoglobin E (β-thal/HbE), and is strongly associated with splenectomy. We aimed to define the prevalence and comprehensively explore mechanisms of PH in β-thal/HbE patients receiving regular transfusion and iron chelation, which were reported to alleviate PH.

MATERIALS AND METHODS

β-Thal/HbE patients receiving regular transfusion and iron chelation over one year were enrolled. Patients at risk for PH were defined by tricuspid-regurgitant-jet-velocity (TRV) ≥ 2.5 m/s. Laboratory and echocardiographic variables were compared with healthy controls.

RESULTS

There were 68 β-thal/HbE, including 31 (45.6%) splenectomized patients, and 38 controls included for analysis. PH was detected in 29 β-thal/HbE (42.6%). β-Thal/HbE with PH had a significant reduction in nitric oxide metabolites (NOx) but elevations in thrombin-antithrombin (TAT) complex, soluble thrombomodulin (sTM), endothelin-1 (ET-1) and flow-mediated dilation (FMD) values compared to those without PH (all, p < 0.05). TRV was significantly correlated with NOx, TAT, sTM, ET-1 and FMD values (r = -0.514, r = 0.281, r = 0.313, r = 0.245 and r = -0.474; all p < 0.05). Erythropoietic activity, serum ferritin, circulating total tissue factor (TF) antigen, microparticle-associated TF activity, microparticle's procoagulant activity and soluble p-selectin levels were not different between PH and non-PH subgroups. Notably, there were no significant associations between splenectomy and PH.

CONCLUSIONS

PH remains prevalent in β-thal/HbE patients receiving long-term transfusion and iron chelation. PH is not associated with splenectomy status but correlated with NO depletion, TF-independent hypercoagulability and endothelial perturbation.

Decreased nitrite reductase activity of deoxyhemoglobin correlates with platelet activation in hemoglobin E/ß-thalassemia subjects

Nitric oxide (NO) can be generated from nitrite by reductase activity of deoxygenated hemoglobin (deoxyHb) apparently to facilitate tissue perfusion under hypoxic condition. Although hemoglobin E (HbE) solutions have been shown to exhibit decreased rate of nitrite reduction to NO, this observation has never been reported in erythrocytes from subjects with hemoglobin E/ß-thalassemia (HbE/ß-thal). In this study, we investigated the nitrite reductase activity of deoxyHb dialysates from 58 non-splenectomized and 23 splenectomized HbE/ß-thal subjects compared to 47 age- and sex-matched normal subjects, and examined its correlation with platelet activity. Iron-nitrosyl-hemoglobin (HbNO) was measured by tri-iodide reductive chemiluminescence as a marker of NO generation. HbNO produced from the reaction of nitrite with deoxyHb dialysate from both non-splenectomized and splenectomized HbE/ß-thal subjects was lower than that of normal (AA) hemoglobin subjects. P-selectin expression, a marker of platelet activation, at baseline and in reactivity to stimulation by adenosine diphosphate (ADP), were higher in HbE/ß-thal subjects than normal subjects. HbNO formation from the reactions of nitrite and deoxyHb inversely correlated with baseline platelet P-selectin expression, HbE levels, and tricuspid regurgitant velocity (TRV). Nitrite plus deoxygenated erythrocytes from HbE/ß-thal subjects had a lower ability to inhibit ADP-induced P-selectin expression on platelets than erythrocytes from normal subjects. We conclude that deoxyHb in erythrocytes from HbE/ß-thal subjects has a decreased ability to reduce nitrite to NO, which is correlated with increased platelet activity in these individuals.

Deferiprone increases endothelial nitric oxide synthase phosphorylation and nitric oxide production

Iron chelation can improve endothelial function. However, effect on endothelial function of deferiprone has not been reported. We hypothesized deferiprone could promote nitric oxide (NO) production in endothelial cells. We studied effects of deferiprone on blood nitrite and blood pressure after single oral dose (25 mg/kg) in healthy subjects and hemoglobin E/β-thalassemia patients. Further, effects of deferiprone on NO production and endothelial NO synthase (eNOS) phosphorylation in primary human pulmonary artery endothelial cells (HPAEC) were investigated in vitro. Blood nitrite levels were higher in patients with deferiprone therapy than those without deferiprone (P = 0.023, n = 16 each). Deferiprone increased nitrite in plasma and whole blood of healthy subjects (P = 0.002 and 0.044) and thalassemia patients (P = 0.003 and 0.046) at time 180 min (n = 20 each). Asymptomatic reduction in diastolic blood pressure (P = 0.005) and increase in heart rate (P = 0.009) were observed in healthy subjects, but not in thalassemia patients. In HPAEC, deferiprone increased cellular nitrite and phospho-eNOS (Ser1177) (P = 0.012 and 0.035, n = 6) without alteration in total eNOS protein and mRNA. We conclude that deferiprone can induce NO production by enhancing eNOS phosphorylation in endothelial cells.

HbE/β-Thalassemia and Oxidative Stress: The Key to Pathophysiological Mechanisms and Novel Therapeutics

SIGNIFICANCE

Oxidative stress and generation of free radicals are fundamental in initiating pathophysiological mechanisms leading to an inflammatory cascade resulting in high rates of morbidity and death from many inherited point mutation-derived hemoglobinopathies. Hemoglobin (Hb)E is the most common point mutation worldwide. The βE-globin gene is found in greatest frequency in Southeast Asia, including Thailand, Malaysia, Indonesia, Vietnam, Cambodia, and Laos. With the wave of worldwide migration, it is entering the gene pool of diverse populations with greater consequences than expected.

CRITICAL ISSUES

While HbE by itself presents as a mild anemia and a single gene for β-thalassemia is not serious, it remains unexplained why HbE/β-thalassemia (HbE/β-thal) is a grave disease with high morbidity and mortality. Patients often exhibit defective physical development, severe chronic anemia, and often die of cardiovascular disease and severe infections. Recent Advances: This article presents an overview of HbE/β-thal disease with an emphasis on new findings pointing to pathophysiological mechanisms derived from and initiated by the dysfunctional property of HbE as a reduced nitrite reductase concomitant with excess α-chains exacerbating unstable HbE, leading to a combination of nitric oxide imbalance, oxidative stress, and proinflammatory events.

FUTURE DIRECTIONS

Additionally, we present new therapeutic strategies that are based on the emerging molecular-level understanding of the pathophysiology of this and other hemoglobinopathies. These strategies are designed to short-circuit the inflammatory cascade leading to devastating chronic morbidity and fatal consequences. Antioxid. Redox Signal. 26, 794-813.

Depleted nitric oxide and prostaglandin E2 levels are correlated with endothelial dysfunction in β-thalassemia/HbE patients

Mechanisms of vascular disorders in β-thalassemia/HbE patients remain poorly understood. In the present study, we aimed to determine the presence of endothelial dysfunction and its association with altered vascular mediators in this population. Forty-three β-thalassemia/HbE patients without clinically documented vascular symptoms and 43 age-sex-matched healthy controls were enrolled. Endothelial function was assessed using flow-mediated dilatation (FMD) before and after administration of nitroglycerine (NTG). β-Thalassemia/HbE patients showed a significant endothelial dysfunction using FMD. The percentage change in the brachial artery diameter before NTG was significantly lower in the thalassemia group compared to the control (5.0 ± 5.9 vs. 9.0 ± 4.0%, p < 0.01) while no significant differences after NTG (18.4 ± 8.3 vs. 17.8 ± 6.3%, p = 0.71). Plasma nitric oxide metabolites (NO _x ) and prostaglandin E₂ (PGE₂) levels were significantly decreased in β-thalassemia/HbE (117.2 ± 27.3 vs. 135.8 ± 11.3 µmol/L, p < 0.01) and (701.9 ± 676.0 vs. 1374.7 ± 716.5 pg/mL, p < 0.01), respectively, while a significant elevation in soluble thrombomodulin levels in β-thalassemia/HbE (3587.7 ± 1310.0 vs. 3093.9 ± 583.8 pg/mL, p = 0.028). NO _x and PGE₂ levels were significantly correlated with FMD (r = 0.27, p = 0.025) and (r = 0.35, p = 0.003), respectively. These findings suggest roles for endothelial mediators and a new mechanism underlying endothelial dysfunction in β-thalassemia/HbE patients.