Sickle cell disease vasculopathy: a state of nitric oxide resistance

Systems biology of HBOC-induced vasoconstriction

Vasoconstriction is a major adverse effect of HBOCs. The use of a single drug for attenuating HBOC-induced vasoconstriction has been tried with limited success. Since HBOC causes disruptions at multiple levels of organization in the vascular system, a systems approach is helpful to explore avenues to counteract the effects of HBOC at multiple levels by targeting multiple sites in the system. A multi-target approach is especially appropriate for HBOC-induced vasoconstriction, because HBOC disrupts the cascade of amplification by NO-cGMP signaling and protein phosphorylation, ultimately resulting in vasoconstriction. Targeting multiple steps in the cascade may alter the overall gain of amplification, thereby limiting the propagation of disruptive effects through the cascade. As a result, targeting multiple sites may accomplish a relatively high overall efficacy at submaximal drug doses. Identifying targets and doses for developing a multi-target combination HBOC regimen for oxygen therapeutics requires a detailed understanding of the systems biology and phenotypic heterogeneity of the vascular system at multiple layers of organization, which can be accomplished by successive iterations between experimental studies and mathematical modeling at multiple levels of vascular systems and organ systems. Towards this goal, this article addresses the following topics: a) NO-scavenging by HBOC, b) HBOC autoxidation-induced reactive oxygen species generation and endothelial barrier dysfunction, c) NO- cGMP signaling in vascular smooth muscle cells, d) NO and cGMP-dependent regulation of contractile filaments in vascular smooth muscle cells, e) phenotypic heterogeneity of vascular systems, f) systems biology as an approach to developing a multi-target HBOC regimen.

Stuttering priapism: insights into pathogenesis and management

Priapism is defined as a persistent, painful erection that continues beyond, or is unrelated to, sexual stimulation. It may be categorized as either ischemic (low/absent flow) or nonischemic (high flow). Stuttering priapism is a variant of the ischemic type that is characterized by repetitive, transient, painful, self-limiting episodes of priapism. It is associated with various hematological disorders, including sickle cell disease and pharmacological treatments. The consequences of ineffective treatment of priapism are erectile dysfunction and impaired quality of life due to chronic pain and physical disfigurement. Many of the existing medical therapeutic options for treatment of stuttering priapism are nonmechanistic and associated with significant adverse effects. However, the scientific knowledge of stuttering priapism has transitioned in the past few years, from a condition that is poorly understood to one that has borne a burst of evolving molecular science. In this review, the pathophysiology of priapism is discussed, with particular emphasis on new molecular effectors and mechanisms. Novel treatment methods, as well as potential future agents, based on the emerging molecular evidence are discussed.

Myocardial infarction in sickle cell disease: use of translational imaging to diagnose an under-recognized problem

Sickle cell disease (SCD) is an inherited disorder in which microvascular occlusion causes complications across multiple organ systems. The precise incidence of myocardial ischemia and infarction (MI), potentially under-recognized microvascular disease-related complications, remains unknown. The absence of typical atherosclerotic lesions seen in other patients with MI suggests a microvascular mechanism of myocardial injury. Cardiac magnetic resonance (CMR) can demonstrate microvascular disease, making it an appealing modality to assess symptomatic SCD patients. We demonstrate in several dramatic instances how CMR is uniquely able to depict cardiac microvascular obstruction in patients with SCD and chest pain, without which the possibility of myocardial injury would almost certainly be otherwise neglected. Much remains unknown regarding ischemic heart disease in patients with SCD including prevalence, detection, and management. Further work to define evaluation and management algorithms for chest pain in SCD and to develop risk assessment tools may reduce sudden cardiac death in this population.

Interventions for treating leg ulcers in people with sickle cell disease

BACKGROUND

The frequency of skin ulceration makes it an important contributor to the morbidity burden in people with sickle cell disease. Many treatment options are available to the healthcare professional, although it is uncertain which treatments have been assessed for effectiveness in people with sickle cell disease.

OBJECTIVES

To assess the clinical effectiveness and safety of interventions for treating leg ulcers in people with sickle cell disease.

SEARCH METHODS

We searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Haemoglobinopathies Trials Register.We searched LILACS (1982 to August 2012), the African Index Medicus (up to August 2012), ISI Web of Knowledge (1985 to August 2012), and the Clinical Trials Search Portal of the World Health Organization (August 2012). We checked the reference lists of all the trials identified. We also contacted those groups or individuals who may have completed relevant randomised trials in this area.Date of the last search of the Group's Haemoglobinopathies Trials Register: 25 May 2012.

SELECTION CRITERIA

Randomised controlled trials of interventions for treating leg ulcers in people with sickle cell disease compared to placebo or an alternative treatment.

DATA COLLECTION AND ANALYSIS

Two authors independently selected studies for inclusion. All three authors independently assessed the risk of bias of the included studies and extracted data.

MAIN RESULTS

Six studies met the inclusion criteria (198 participants with 250 ulcers). Each trial investigated a different intervention and within this review we have grouped these as systemic pharmaceutical interventions (L-cartinine, arginine butyrate, isoxsuprine) and topical pharmaceutical interventions (Solcoseryl(®) cream, RGD peptide dressing, topical antibiotics). Three interventions reported on the change in ulcer size (arginine butyrate, RGD peptide, L-cartinine). Of these, RGD peptide matrix significantly reduced ulcer size compared with a control group, mean reduction 6.60cm(2) (95% CI 5.51 to 7.69). Three trials reported on the incidence of complete closure (isoxsuprine, arginine butyrate, RGD peptide matrix). None reported a significant effect. No trial reported on: the time to complete ulcer healing; ulcer-free survival following treatment for sickle cell leg ulcers; quality of life measures; or incidence of amputation. There was no reported information on the safety of these interventions.

AUTHORS' CONCLUSIONS

There is evidence that a topical intervention (RGD peptide matrix) reduced ulcer size in treated participants compared to controls. This evidence of efficacy is limited by the generally high risk of bias associated with these reports.We planned to analyse results according to general groups: pharmaceutical interventions (systemic and topical); and non-pharmaceutical interventions (surgical and non-surgical). However, we were unable to pool findings due to the heterogeneity in outcome definitions, and inconsistency between the unit of randomisation and the unit of analysis. This heterogeneity, along with a paucity of identified trials, prevented us performing any meta-analyses.This Cochrane review provides some evidence for the effectiveness of one topical intervention - RGD peptide matrix. However, this intervention was assessed as having a high risk of bias due to inadequacies in the single trial report. Other included studies were also assessed as having a high risk of bias. We recommend that readers interpret the trial results with caution. The safety profile of the all interventions was inconclusive.

Antibiotics for treating community acquired pneumonia in people with sickle cell disease

BACKGROUND

As a consequence of their condition, people with sickle cell disease are at high risk of developing an acute infection of the pulmonary parenchyma called community-acquired pneumonia. Many different bacteria can cause this infection and antibiotic treatment is generally needed to resolve it. There is no standardized approach to antibiotic therapy and treatment is likely to vary from country to country. Thus, there is a need to identify the efficacy and safety of different antibiotic treatment approaches for people with sickle cell disease suffering from community-acquired pneumonia.

OBJECTIVES

To determine the efficacy and safety of the antibiotic treatment approaches (monotherapy or combined) for people with sickle cell disease suffering from community-acquired pneumonia.

SEARCH METHODS

We searched The Group's Haemoglobinopathies Trials Register (25 May 2012), which comprises references identified from comprehensive electronic database searches and handsearching of relevant journals and abstract books of conference proceedings. We also searched LILACS (1982 to 27 April 2012), African Index Medicus (1982 to 27 April 2012) and WHO ICT Registry (27 April 2012).

SELECTION CRITERIA

We searched for published or unpublished randomized controlled trials.

DATA COLLECTION AND ANALYSIS

We intended to summarise data by standard Cochrane Collaboration methodologies, but no eligible randomized controlled trials were identified.

MAIN RESULTS

We were unable to find any randomized controlled trials on antibiotic treatment approaches for community-acquired pneumonia in people with sickle cell disease.

AUTHORS' CONCLUSIONS

The updated review was unable to identify randomized controlled trials on efficacy and safety of the antibiotic treatment approaches for people with sickle cell disease suffering from community-acquired pneumonia. Randomized controlled trials are needed to establish the optimum antibiotic treatment for this condition. The trials regarding this issue should be structured and reported according to the CONSORT statement for improving the quality of reporting of efficacy and improved reports of harms in clinical research. Triallists should consider including the following outcomes in new trials: number of days to become afebrile; mortality; onset of pain crisis or complications of SCD following CAP; diagnosis; hospitalisation (admission rate and length of hospital stay); respiratory failure rate; and number of participants receiving a blood transfusion.There are no trials included in the review and we have not identified any relevant trials up to May 2012. We therefore do not plan to update this review until new trials are published.

Correlation of low levels of nitrite and high levels of fetal hemoglobin in patients with sickle cell disease at baseline

Background

Sickle cell disease is a hemoglobinopathy characterized by hemolytic anemia, increased susceptibility to infections and recurrent vaso-occlusive crises that reduces the quality of life of sufferers.

Objective

To evaluate the correlation of the levels of lactate dehydrogenase, malonaldehyde and nitrite to fetal hemoglobin in patients with sickle cell disease not under treatment with hydroxyurea in outpatients at a university hospital in Fortaleza, Ceará, Brazil.

Methods

Forty-four patients diagnosed with sickle cell disease were enrolled at baseline. Diagnosis was confirmed by evaluating the beta globin gene using polymerase chain reaction-restriction fragment length polymorphism. The concentration of fetal hemoglobin was obtained by high-performance liquid chromatography. Serum levels of nitrite, malonaldehyde and lactate dehydrogenase were measured by biochemical methods.

Results

Significantly higher levels of lactate dehydrogenase, nitrite and malonaldehyde were observed in patients with sickle cell disease compared to a control group. The study of the correlation between fetal hemoglobin levels and these variables showed a negative correlation with nitrite levels. No correlation was found between fetal hemoglobin and malonaldehyde or lactate dehydrogenase. When the study population was stratified according to fetal hemoglobin levels, a decrease in the levels of nitrite was observed with higher levels of fetal hemoglobin (p-value = 0.0415).

Conclusion

The results show that, similar to fetal hemoglobin levels, the concentration of nitrite can predict the clinical course of the disease, but should not be used alone as a modulator of prognosis in patients with sickle cell disease.

Transfusion-related acute gut injury: feeding, flora, flow, and barrier defense

TRAGI (transfusion-related acute gut injury) is an acronym we proposed to characterize a severe neonatal gastrointestinal reaction temporally related to a transfusion of packed blood red cells (PRBCs) for anemia in very low birth weights. The following are in support of a causative relationship: (1) the timing of necrotizing enterocolitis after a PRBC transfusion not being random, (2) traditional risk factors for necrotizing enterocolitis are often absent, (3) significant anemia appears to be a universal finding, (4) the age of donor blood is often slightly older than controls, (5) TRAGI is not postnatal age dependent, and (6) TRAGI does not show a centering at 31 weeks' postconceptual age as does nontransfusion-related NEC. Although TRAGI is linked to the timing of PRBC transfusions, we propose a novel hypothesis that the convergence at 31 weeks' postconceptual age for classic NEC approximates the age of presentation of other oxygen delivery and neovascularization syndromes (eg, retinopathy of prematurity), suggesting its etiologic link to a generalized systemic maturational mechanism or another common developmental theme. This report will begin by reviewing the history of the clinical presentation and discovery of TRAGI and will then analyze various pathophysiologic mechanisms that may account for the phenomenon when clinicians render therapies. We will end by a call to action for randomized clinical trials to test various etiologic theories.

Beyond the definitions of the phenotypic complications of sickle cell disease: an update on management

The sickle hemoglobin is an abnormal hemoglobin due to point mutation (GAG → GTG) in exon 1 of the β globin gene resulting in the substitution of glutamic acid by valine at position 6 of the β globin polypeptide chain. Although the molecular lesion is a single-point mutation, the sickle gene is pleiotropic in nature causing multiple phenotypic expressions that constitute the various complications of sickle cell disease in general and sickle cell anemia in particular. The disease itself is chronic in nature but many of its complications are acute such as the recurrent acute painful crises (its hallmark), acute chest syndrome, and priapism. These complications vary considerably among patients, in the same patient with time, among countries and with age and sex. To date, there is no well-established consensus among providers on the management of the complications of sickle cell disease due in part to lack of evidence and in part to differences in the experience of providers. It is the aim of this paper to review available current approaches to manage the major complications of sickle cell disease. We hope that this will establish another preliminary forum among providers that may eventually lead the way to better outcomes.

Sickling cells, cyclic nucleotides, and protein kinases: the pathophysiology of urogenital disorders in sickle cell anemia

Sickle cell anemia is one of the best studied inherited diseases, and despite being caused by a single point mutation in the HBB gene, multiple pleiotropic effects of the abnormal hemoglobin S production range from vaso-occlusive crisis, stroke, and pulmonary hypertension to osteonecrosis and leg ulcers. Urogenital function is not spared, and although priapism is most frequently remembered, other related clinical manifestations have been described, such as nocturia, enuresis, increased frequence of lower urinary tract infections, urinary incontinence, hypogonadism, and testicular infarction. Studies on sickle cell vaso-occlusion and priapism using both in vitro and in vivo models have shed light on the pathogenesis of some of these events. The authors review what is known about the deleterious effects of sickling on the genitourinary tract and how the role of cyclic nucleotides signaling and protein kinases may help understand the pathophysiology underlying these manifestations and develop novel therapies in the setting of urogenital disorders in sickle cell disease.

Targeting NADPH oxidase decreases oxidative stress in the transgenic sickle cell mouse penis

INTRODUCTION

Sickle cell disease (SCD) is a state of chronic vasculopathy characterized by endothelial dysfunction and increased oxidative stress, but the sources and mechanisms responsible for reactive oxygen species (ROS) production in the penis are unknown.

AIMS

We evaluated whether SCD activates NADPH oxidase, induces endothelial nitric oxide synthase (eNOS) uncoupling, and decreases antioxidants in the SCD mouse penis. We further tested the hypothesis that targeting NADPH oxidase decreases oxidative stress in the SCD mouse penis.

METHODS

SCD transgenic (sickle) mice were used as an animal model of SCD. Hemizygous (hemi) mice served as controls. Mice received an NADPH oxidase inhibitor apocynin (10 mM in drinking water) or vehicle. Penes were excised at baseline for molecular studies. Markers of oxidative stress (4-hydroxy-2-nonenal [HNE]), sources of ROS (eNOS uncoupling and NADPH oxidase subunits p67(phox) , p47(phox) , and gp91(phox) ), and enzymatic antioxidants (superoxide dismutase [SOD]1, SOD2, catalase, and glutathione peroxidase-1 [GPx1]) were measured by Western blot in penes.

MAIN OUTCOME MEASURES

Sources of ROS, oxidative stress, and enzymatic antioxidants in the SCD penis.

RESULTS

Relative to hemi mice, SCD increased (P<0.05) protein expression of NADPH oxidase subunits p67(phox) , p47(phox) , and gp91(phox) , 4-HNE-modified proteins, induced eNOS uncoupling, and reduced Gpx1 expression in the penis. Apocynin treatment of sickle mice reversed (P<0.05) the abnormalities in protein expressions of p47(phox) , gp91(phox) (but not p67(phox) ) and 4-HNE, but only slightly (P>0.05) prevented eNOS uncoupling in the penis. Apocynin treatment of hemi mice did not affect any of these parameters.

CONCLUSION

NADPH oxidase and eNOS uncoupling are sources of oxidative stress in the SCD penis; decreased GPx1 further contributes to oxidative stress. Inhibition of NADPH oxidase upregulation decreases oxidative stress, implying a major role for NADPH oxidase as a ROS source and a potential target for improving vascular function in the SCD mouse penis.

Association of oxidative stress markers with atherogenic index of plasma in adult sickle cell nephropathy

This paper evaluates the association of oxidative stress and atherogenic index of plasma in order to assess the cardiovascular risk in Sickle cell nephropathy especially as lipoprotein levels are lower in SCD than non-SCD patients. Antioxidant enzymes, malondialdehyde(MDA), urea, creatinine, and glomerular filtration rate were evaluated in 110 confirmed sickle cell disease patients: 65 males in steady state, aged 21.1 ± 6.0 years, 30 males with macroalbuminuria, aged 24.5 ± 7.0, years and 15 with chronic kidney disease (CKD), aged 31.8 ± 2.0 years. The mean activity levels of glutathione peroxidase (GPx), superoxide dismutase (Cu/ZnSOD), and catalase (CAT) were significantly lower (P < 0.001) in SCD with macroalbuminuria and CKD while MDA was higher (P < 0.001) in SCD with macroalbuminuria and CKD compared with controls. There was negative correlation between GPx (P < 0.001), Cu/ZnSOD (P < 0.02), and Atherogenic index of plasma in SCD with CKD, while MDA shows a positive correlation (P < 0.001) with AIP in SCD with CKD. There was however no correlation between CAT and AIP. Decreased activity levels of antioxidant enzymes and low HDL-cholesterol concentration were confirmed in adult SCD with CKD in Nigerians. The increase oxidative stress and high atherogenic index in CKD may accelerate the process of cardiovascular complications in adult SCD patients. Atherogenic index of plasma was negatively correlated with antioxidant enzymes and positively with MDA.

Vasculature and kidney complications in sickle cell disease

Recent developments in sickle cell disease include the concept of a vasculopathic state and the classification of sickle cell disease into a hemolysis-endothelial dysfunction phenotype or a viscosity-vasoocclusion phenotype. The hemolysis-endothelial dysfunction phenotype largely reflects deficiency of or resistance to nitric oxide. In addition to discussing these areas, we suggest that the hemolysis-endothelial dysfunction phenotype also reflects the instability of sickle hemoglobin, the release of heme, and the induction of heme oxygenase-1. From these perspectives the renal complications of sickle cell disease are discussed and classified.

Pathology of sickle cell disease

Sickle cell disease (SCD) is a hereditary chronic hemolytic anemia with numerous clinical consequences. Intravascular sickling of red blood cells leads to multiorgan dysfunction. Although the pathophysiology of SCD has been well studied, there remains a lack of effective treatment. Refinements in overall care have improved quality of life; however, premature death is still not uncommon. SCD usually presents in childhood and is common in areas where malaria is (or was) common. The association with malaria is apparently of benefit to the individual because these individuals tend to contract a milder form of the disease. This review highlights the spectrum of pathology seen in people with SCD, with an emphasis on the pathogenesis of sudden death.

L-arginine, a nitric oxide precursor, reduces dapsone-induced methemoglobinemia in rats

Dapsone use is frequently associated to hematological side effects such as methemoglobinemia and hemolytic anemia, which are related to N-hydroxylation mediated by the P450 enzyme system. The aim of the present study was to evaluate the influence of L-arginine supplementation, a precursor for the synthesis of nitric oxide, as single or multiple dose regimens on dapsone-induced methemoglobinemia. Male Wistar rats were treated with L-arginine at 5, 15, 30, 60 and 180 mg/kg doses (p.o., gavage) in single or multiple dose regimens 2 hours prior to dapsone administration (40 mg/kg, i.p.). The effect of the nitric oxide synthase inhibitor L-NAME was investigated by treatment with multiple doses of 30 mg/kg (p.o., gavage) 2 hours before dapsone administration. Blood samples were collected 2 hours after dapsone administration. Erythrocytic methemoglobin levels were assayed by spectrophotometry. The results showed that multiple dose supplementations with 5 and 15 mg/kg L-arginine reduced dapsone-induced methemoglobin levels. This effect is mediated by nitric oxide formation, since the reduction in methemoglobin levels by L-arginine is blocked by simultaneous administration with L-NAME, a nitric oxide synthase inhibitor.

Study of correlation of nitrite levels with malonaldehyde and the prognosis of patients with sickle cell disease on hydroxyurea, Ceará-Brazil

Hydroxyurea (HU) is the only drug approved for the induction of fetal hemoglobin. Besides this benefit, there are others such as the reduction of leukocyte and generation of nitric oxide (NO). Sickle cell anemia (SCA) is characterized by chronic hemolytic anemia and vaso-occlusive phenomena. The aim of this study was to evaluate the correlation of parameters MDA and NO2 with the prognosis of patients with SCA as outpatients at Hospital Universitário Walter Cantídeo. In all, 65 patients with SCA--51 without the use of HU (group I) and 14 chronically treated with HU (group II)--were recruited. Nitrite and malonaldehyde were determined by biochemical methods. We found that in group II there was a significant difference of serum MDA with clinical variables: two or more transfusions during the year (P<0.0469), the presence of malleolar ulcers (P<0.0400), and the occurrence of vaso-occlusive episodes (P<0.0031), and Group I with the occurrence of three or more vaso-occlusive episodes (P<0.0051). Correlating the malonaldehyde with clinical variables in groups I and II, we observed a statistically significant relationship with two or more transfusions during the year and the presence of malleolar ulcer. Our results demonstrate that MDA levels can be used as parameter for prognosis in SCA.

Raised erythrocyte creatine in patients with pulmonary arterial hypertension--evidence for subclinical hemolysis

BACKGROUND

Pulmonary arterial hypertension (PAH) has been associated with hemolytic conditions such as sickle cell disease but the possible role of hemolysis in the pathogenesis or pathophysiology of other forms of PAH has not been studied. Erythrocyte lifespan is the gold-standard test of hemolysis and may be measured by assaying erythrocyte creatine (EC) levels. EC decreases as the erythrocyte ages, so patients with hemolysis have high EC levels.

METHODS

We measured EC and other parameters of hemolysis in patients with idiopathic and connective tissue associated PAH and normal controls.

RESULTS

In patients with PAH (n = 40), EC levels were higher than in controls n = 30 (patients EC 1.72 mcmol/g HgB 95%CI[1.51, 1.96], controls EC 1.05 mcmol/g HgB [0.93, 1.19], p < 0.0001). High levels of EC correlated with worse 6 min walk (r = -0.42, p < 0.0001) and worse functional class (p = 0.002). Other indirect indices of hemolysis (total lactate dehydrogenase, red cell distribution width) were also increased in patients with PAH relative to controls.

CONCLUSIONS

There is evidence of subclinical hemolysis in patients with PAH, and higher levels of hemolysis are associated with poorer exercise capacity.

Priapism in sickle-cell disease: a hematologist's perspective

INTRODUCTION

Priapism is a familiar problem to hematologists, well known for its association with sickle-cell disease (SCD). It also occurs in a variety of other hematological illnesses, nearly all forms of congenital hemolytic anemia, including other hemoglobinopathies and red blood cell membranopathies and enzymopathies.

AIM

Provide urologists with a comprehensive review of priapism in SCD, with an emphasis on the perspective of a practicing hematologist.

METHODS

Medline searches through July 2010 were conducted using the terms priapism, erectile dysfunction, and sickle cell.

MAIN OUTCOME MEASURES

Expert opinion was based on review of the medical literature related to this subject matter.

RESULTS

In men with SCD, large epidemiological studies have linked the risk of priapism to clinical markers of the severity of intravascular hemolysis. Extracellular hemoglobin and arginase released during hemolysis has been implicated in reducing nitric oxide bioavailability, although the relevance of hemolysis to vascular dysfunction has been challenged by some scientists. Consistent with the role of impairment of the nitric oxide axis, mice genetically deficient in nitric oxide production have also been shown to develop priapic activity. Provocative new data indicate that hemolysis-linked dysregulation of adenosine signaling in the penis contributes to priapism in sickle cell mice. Serious questions have arisen regarding the efficacy of mainstays of textbook dogma for treatment of acute severe priapism, including intravenous fluids, alkalinization, and exchange transfusion, and there is increasing acceptance for early aspiration and irrigation of the corpus cavernosum.

CONCLUSION

For patients with sickle cell with recurrent priapism, there is very limited evidence for a medical prophylaxis role for hydroxyurea, etilefrine, pseudoephedrine, leuprolide, sildenafil, and other agents. Recent publications have highlighted nitric oxide and adenosine signal transduction pathways as worthy of additional research. Research and clinical management of sickle-cell priapism is strengthened by multidisciplinary collaboration between hematologists and urologists.

Oxidant-mediated modification of the cellular thiols is sufficient for arginase activation in cultured cells

Increased arginase activity in the vasculature has been implicated in the regulation of nitric oxide (NO) homeostasis, leading to the development of vascular disease and the promotion of tumor cell growth. Recently, we showed that cysteine, in the presence of iron, promotes arginase activity by driving the Fenton reaction. In the present report, we showed that induction of oxidative stress in erythroleukemic cells with the thiol-specific oxidant, diamide, led to an increase in arginase activity by 42% (P = 0.02; vs. control). By using specific antibodies, it was demonstrated that this increase correlated with an increase in arginase-1 levels in the cells and with corresponding decreases in glutathione and protein thiol levels. Treatment of cells with aurothiomalate (ATM), a protein thiol-complexing agent, diminished the activity of arginase and arginase-1 levels by 19.5 and 35.2%, respectively (vs. control) and significantly decreased both glutathione and protein thiol levels, further implicating the thiol redox system in the cellular activation of arginase. Furthermore, diamide significantly altered the kinetics of arginase, resulting in the doubling of its V(max) (vs. control). Our presented data demonstrate, for the first time that the intracellular arginase activation is may be enhanced in part, via a cellular thiol-mediated mechanism.

Antiradical, chelating and antioxidant activities of hydroxamic acids and hydroxyureas

Reactive oxygen species, along with reactive nitrogen species, may play an important role in the pathogenesis and progress of many diseases, including cancer, diabetes and sickle cell disease. It has been postulated that hydroxyurea, one of the main treatments in sickle cell disease, achieves its activity partly also through its antioxidant properties. A series of hydroxyurea derivatives of L- and D-amino acid amides and cycloalkyl-N-aryl-hydroxamic acids was synthesized and investigated for their radical scavenging activity, chelating properties and antioxidant activity. All the compounds showed exceptional antiradical activities. For example, free radical scavenging activities of investigated hydroxyureas were higher than the activity of standard antioxidant, butylated hydroxyanisole (BHA). Moreover, most of the investigated hydroxamic acids were stronger Fe²⁺ ion chelators than quercetin. In addition, the investigated compounds, especially hydroxamic acids, were proven to be excellent antioxidants. They were as effective as BHA in inhibiting β-carotene-linoleic acid coupled oxidation. It is reasonable to assume that the antioxidant activity of the investigated compounds could contribute to their previously proven biological properties as cytostatic and antiviral agents.

Frequency of pain crises in sickle cell anemia and its relationship with the sympatho-vagal balance, blood viscosity and inflammation

BACKGROUND

Recent evidence suggests that autonomic nervous system activity could be involved in the pathophysiology of sickle cell disease, but it is unclear whether differences in autonomic nervous system activity are detectable during steady state in patients with mild and severe disease. The aim of the present study was to compare the autonomic nervous system activity, blood rheology, and inflammation in patients with sickle cell anemia according to the frequency of acute pain crisis.

DESIGN AND METHODS

Twenty-four healthy volunteers, 20 patients with sickle cell anemia with milder disease, and 15 patients with sickle cell anemia with more severe disease were recruited. Milder disease was defined as having no pain crisis within the previous year. More severe disease was defined as having had within the previous year three or more pain crises which were documented by a physician and required treatment with narcotics. The autonomic nervous system activity was determined by spectral analysis of nocturnal heart rate variability. Blood viscosity determination and measurements of several inflammatory markers (interleukin-6, soluble vascular cell adhesion molecule-1, soluble CD40 ligand and sL-selectin) were made on blood samples collected in steady-state conditions.

RESULTS

Results showed that: 1) patients who had suffered more frequent pain crises had lower parasympathetic activity and greater sympatho-vagal imbalance than both controls and patients with milder disease. However, when adjusted for age, no significant difference was detected between the two sickle cell anemia patient groups; 2) patients who had suffered more frequent pain crises had higher blood viscosity than patients with milder disease, and this was not dependent on age.

CONCLUSIONS

Results from the present study indicate that both the autonomic nervous system activity and blood viscosity are impaired in patients with sickle cell anemia exhibiting high frequency of pain crisis in comparison with those who did not experience a crisis within the previous year.

Haptoglobin genotypes in sickle-cell disease

We compared the frequencies of the haptoglobin (Hp) genotypes of 775 Brazilian patients with sickle-cell disease divided into the following age groups: 3 months-5 years, 6-10 years, 11-15 years, 16-20 years, and over 20 years. The last group (>20 years) was also compared with a healthy control group and was further divided into subgroups including only subjects aged 21-30 years (V.a and Control.a) and over 30 years (V.b and Control.b). There was no significant difference in the frequencies of the Hp genotypes between the different patient groups or between the patients and controls. However, the Hp2-2 genotype was always less frequent than the Hp1-1 genotype in the patient groups, whereas the opposite was observed in healthy controls. The frequency of Hp2-2 was 25.0% in patients in the 21-30 years age group and fell to 19.5% in those over 30 years. In the controls, the corresponding frequency was around 28%. Although our results do not allow us to conclude that Hp genotypes on their own confer greater or lesser selective advantage on sickle-cell disease patients in the population studied, this polymorphism may, when combined with other genetic and environmental factors, contribute to the clinical diversity observed in this disease.

Pathophysiology of sickle cell disease is mirrored by the red blood cell metabolome

Emerging metabolomic tools can now be used to establish metabolic signatures of specialized circulating hematopoietic cells in physiologic or pathologic conditions and in human hematologic diseases. To determine metabolomes of normal and sickle cell erythrocytes, we used an extraction method of erythrocytes metabolites coupled with a liquid chromatography-mass spectrometry–based metabolite profiling method. Comparison of these 2 metabolomes identified major changes in metabolites produced by (1) endogenous glycolysis characterized by accumulation of many glycolytic intermediates; (2) endogenous glutathione and ascorbate metabolisms characterized by accumulation of ascorbate metabolism intermediates, such as diketogulonic acid and decreased levels of both glutathione and glutathione disulfide; (3) membrane turnover, such as carnitine, or membrane transport characteristics, such as amino acids; and (4) exogenous arginine and NO metabolisms, such as spermine, spermidine, or citrulline. Finally, metabolomic analysis of young and old normal red blood cells indicates metabolites whose levels are directly related to sickle cell disease. These results show the relevance of metabolic profiling for the follow-up of sickle cell patients or other red blood cell diseases and pinpoint the importance of metabolomics to further depict the pathophysiology of human hematologic diseases.

Pulmonary hypertension, tricuspid regurgitant velocity screening, and the nitric oxide pathway

Chronic pulmonary complications, including pulmonary hypertension (PH), are common in sickle cell disease (SCD), especially in adults with sickle cell anemia (SCA). The underlying pathophysiology is complex and variable, involving multiple biological systems. Recent emphasis has been placed on the pleotropic biological factor nitric oxide (NO). An elevated tricuspid regurgitant velocity (TRV) appears to have limitations in specificity in SCA, but may indicate the presence of PH, a diagnosis confirmed by right heart catheterization. TRV has been used in recent clinical trials to identify or define subjects with PH for enrollment into PH-specific interventions; these include sildenafil, which enhances NO-induced vasorelaxation. Results from a controlled trial show no benefit and an unexpected increase in adverse events, emphasizing the biological complexities of SCA. Management remains principally supportive, includes recognition and treatment of comorbidities, and may incorporate individualized PH-specific strategies (despite recent trials) based on appropriate diagnostic testing. Ultimately, therapy is likely to be multimodal and tailored to the processes identified to be the most contributory in a given individual. Based on the relative prevalence of the conditions, routine screening for asthma in children with SCD and by Doppler echocardiography to measure TRV as an initial screen for PH in adults with SCA may be warranted. Data are limited regarding the clinical utility of screening in other forms of SCD and the pediatric population. This article offers an individual perspective on practical and challenging clinical considerations.

Divergent roles of superoxide and nitric oxide in liver ischemia and reperfusion injury

Liver ischemia and reperfusion-induced injury is a major clinical complication associated with hemorrhagic or endotoxin shock and thermal injury as well as liver transplantation and resectional surgery. Data obtained from several different studies suggest that an important initiating event in the pathophysiology of ischemia and reperfusion-induced tissue injury is enhanced production of superoxide concomitant with a decrease in the bioavailability of endothelial cell-derived nitric oxide. This review will summarize the evidence supporting the hypothesis that the redox imbalance induced by alterations in superoxide and nitric oxide generation creates a more oxidative environment within the different cells of the liver that enhances the nuclear transcription factor-κB-dependent expression of a variety of different cytokines and mediators that may promote as well as limit ischemia and reperfusion-induced hepatocellular injury. In addition, the evidence implicating endothelial cell nitric oxide synthase-dependent and -independent generation of nitric oxide as important regulatory pathways that act to limit ischemia and reperfusion-induced liver injury and inflammation is also presented.

Oxidative stress status, clinical outcome, and β-globin gene cluster haplotypes in pediatric patients with sickle cell disease

OBJECTIVE

To correlate the clinical and hematological features of β-globin gene haplotypes with the oxidative stress status in pediatric patients with sickle cell disease (SCD).

METHODS

A total of 95 patients with SCD and 40 healthy children were studied. The β-globin cluster, plasma lipid peroxidation (LPO) and plasma nitrite plus nitrate (NOx), and erythrocyte content of glutathione (GSH) and glutathione disulfide (GSSG), and glutathione peroxidase (GPx), reductase (GRd), and superoxide dismutase (SOD) activities were measured.

RESULTS

Plasma LPO (P < 0.001) and NOx (P < 0.05) were significantly higher in patients than in controls. In erythrocytes of patients with SCD, the activities of GRd (P < 0.001) and SOD (P < 0.05) were lower, and the GSSG/GSH ratio (P < 0.001) and GPx activity (P < 0.001) were higher than in controls. High LPO levels and low SOD plus GRd activities were associated with increased severity of clinical manifestations, which correspond mainly to patients with Bantu and Benin haplotypes. LPO levels were reduced in patients with high fetal hemoglobin (HbF) levels, whereas the NOx levels and GRd activity tended to increase in this group.

CONCLUSION

Our results detected an important oxidative stress in patients with SCD and suggest that at least three redox markers, i.e., LPO, GRd, and SOD, were related with their clinical outcomes. Moreover, a relationship between high HbF and low LPO, and high HbF and high GRd activity and NOx levels were found.

Evaluation of the concentration of malondialdehyde and nitrite in patients with sickle cell anemia treated or not with hydroxyurea

ABSTRACT Objective: To determine the serum levels of malondialdehyde and nitrite in patients with sickle cell anemia treated or not with hydroxyurea in outpatient's setting. Methods: Of the 65 patients with sickle cell anemia selected for the study, 51 were not treated with hydroxyurea (Group 1), 14 made chronic use of hydroxyurea (Group 2) and 20 individuals had no hemoglobinopathies (Control Group). Results: The Control Group had a lower and more homogeneous concentration of malondialdehyde levels as compared to the other groups. The results of Groups 1 and 2 showed increased values of malondialdehyde levels when compared to the Control Group. Considering the values of Groups 1 and 2, there were no significant changes in the malondialdehyde levels. There was no significant difference in the serum levels of nitrite between the groups. Group 2 presented a statistically significant correlation between serum malondialdehyde levels and the clinical variables investigated. In turn, Group 1 showed correlation only with occurrence of three or more vaso-occlusive crises. There was no correlation between nitrite levels and the clinical variables. Conclusion: The results revealed that during the pathogenesis of sickle cell anemia, an increase in lipid peroxidation was observed. On the other hand, no changes in oxidative parameters were detected during treatment with hydroxyurea, probably due to the short period of treatment of the patients studied.

The Properties of Red Blood Cells from Patients Heterozygous for HbS and HbC (HbSC Genotype)

Sickle cell disease (SCD) is one of the commonest severe inherited disorders, but specific treatments are lacking and the pathophysiology remains unclear. Affected individuals account for well over 250,000 births yearly, mostly in the Tropics, the USA, and the Caribbean, also in Northern Europe as well. Incidence in the UK amounts to around 12-15,000 individuals and is increasing, with approximately 300 SCD babies born each year as well as with arrival of new immigrants. About two thirds of SCD patients are homozygous HbSS individuals. Patients heterozygous for HbS and HbC (HbSC) constitute about a third of SCD cases, making this the second most common form of SCD, with approximately 80,000 births per year worldwide. Disease in these patients shows differences from that in homozygous HbSS individuals. Their red blood cells (RBCs), containing approximately equal amounts of HbS and HbC, are also likely to show differences in properties which may contribute to disease outcome. Nevertheless, little is known about the behaviour of RBCs from HbSC heterozygotes. This paper reviews what is known about SCD in HbSC individuals and will compare the properties of their RBCs with those from homozygous HbSS patients. Important areas of similarity and potential differences will be emphasised.

Arginase levels and their association with Th17-related cytokines, soluble adhesion molecules (sICAM-1 and sVCAM-1) and hemolysis markers among steady-state sickle cell anemia patients

Sickle cell anemia (SCA) is characterized by a marked endothelial dysfunction, owing to many factors. Arginine metabolism can be related to the inflammatory chronic state presented by patients, playing a key role in their clinical outcome and vascular endothelium. We investigated the serum arginase levels in 50 SCA patients (22 men and 28 women, mean age of 17 +/- 10.5 years) and 28 healthy controls. Serum arginase levels were associated with biochemical hemolysis markers and cytokines involved in Th17 response, as well as levels of soluble intercellular adhesion molecule-1 (sICAM-1) and vascular cell adhesion molecule-1 (sVCAM-1). Arginase concentrations were higher in SCA patients, compared with controls (p = 0.005), and were significantly and positively associated with total bilirubin (p = 0.004), indirect bilirubin (p = 0.04), and aspartate aminotransferase (AST; p = 0.039) in the SCA patient group. Moreover, arginase was significantly and positively associated with transforming growth factor-beta (TGF-beta; p = 0.008) among SCA patients. sICAM-1 was significantly and positively associated to reticulocytes (p = 0.014) and AST (p = 0.04). sVCAM-1 was likewise associated with lactate dehydrogenase (p = 0.03). These data suggest a new insight into arginase metabolism, as we show here a shift in arginine catabolism, where TGF-beta may induces the arginase pathway instead of the nitric oxide pathway and a possible involvement of the vascular activation and the serum arginase in chronic hemolysis among SCA patients. Additional studies should be carried out in order to investigate the mechanisms by which TGF-beta participates in the metabolism of arginase in SCA patients.

Potential utility of full-spectrum antioxidant therapy, citrulline, and dietary nitrate in the management of sickle cell disease

There is considerable evidence that oxidative stress and a loss of nitric oxide bioactivity are key mediators of the vasculopathies associated with sickle cell disease. A comprehensive nutraceutical strategy for mitigating the contribution of oxidative stress to pathogenesis - dubbed "full-spectrum antioxidant therapy" - may have utility in this syndrome. This strategy entails concurrent administration of phycocyanobilin - a phytochemical richly supplied by spirulina, shown to inhibit NADPH oxidase in a manner analogous to its chemical relatives biliverdin and bilirubin; high-dose folate - recently shown to quench peroxynitrite-derived radicals and restore coupling of NO synthase; N-acetylcysteine - for boosting intracellular glutathione levels; and a phase 2 inducer such as lipoic acid - to further promote glutathione synthesis while increasing expression of antioxidant enzymes. Suboptimal endothelial arginine levels, reflecting increased plasma arginase activity and elevated ADMA, contribute to the loss of NO bioactivity in sickle cell disease; supplementation with the arginine precursor citrulline may ameliorate this defect. Increased intakes of plant-derived nitrate have the potential to diminish the quenching of NO by plasma hemoglobin in sickle cell patients, while boosting systemic NO production independent of NO synthase activity. In addition to the well-documented utility of hydroxyurea - possibly a suboptimal strategy for life-long therapy owing to its mutagenic activity - rational pharmaceutical options for managing sickle cell disease include pentoxifylline and phosphodiesterase 5 inhibitors such as sildenafil.

The Clinical Application of Ozonetherapy

The reader may be eager to examine in which diseases ozonetherapy can be proficiently used and she/he will be amazed by the versatility of this complementary approach (Table 9 1). The fact that the medical applications are numerous exposes the ozonetherapist to medical derision because superficial observers or sarcastic sceptics consider ozonetherapy as the modern panacea. This seems so because ozone, like oxygen, is a molecule able to act simultaneously on several blood components with different functions but, as we shall discuss, ozonetherapy is not a panacea. The ozone messengers ROS and LOPs can act either locally or systemically in practically all cells of an organism. In contrast to the dogma that “ozone is always toxic”, three decades of clinical experience, although mostly acquired in private clinics in millions of patients, have shown that ozone can act as a disinfectant, an oxygen donor, an immunomodulator, a paradoxical inducer of antioxidant enzymes, a metabolic enhancer, an inducer of endothelial nitric oxide synthase and possibly an activator of stem cells with consequent neovascularization and tissue reconstruction.

Relationship of cell-free hemoglobin to impaired endothelial nitric oxide bioavailability and perfusion in severe falciparum malaria

BACKGROUND

Hemolysis causes anemia in falciparum malaria, but its contribution to microvascular pathology in severe malaria (SM) is not well characterized. In other hemolytic diseases, release of cell-free hemoglobin causes nitric oxide (NO) quenching, endothelial activation, and vascular complications. We examined the relationship of plasma hemoglobin and myoglobin to endothelial dysfunction and disease severity in malaria.

METHODS

Cell-free hemoglobin (a potent NO quencher), reactive hyperemia peripheral arterial tonometry (RH-PAT) (a measure of endothelial NO bioavailability), and measures of perfusion and endothelial activation were quantified in adults with moderately severe (n = 78) or severe (n = 49) malaria and control subjects (n = 16) from Papua, Indonesia.

RESULTS

Cell-free hemoglobin concentrations in patients with SM (median, 5.4 micromol/L; interquartile range [IQR], 3.2-7.4 micromol/L) were significantly higher than in those with moderately severe malaria (2.6 micromol/L; IQR, 1.3-4.5 micromol/L) or controls (1.2 micromol/L; IQR, 0.9-2.4 micromol/L; P < .001). Multivariable regression analysis revealed that cell-free hemoglobin remained inversely associated with RH-PAT, and in patients with SM, there was a significant longitudinal association between improvement in RH-PAT index and decreasing levels of cell-free hemoglobin (P = .047). Cell-free hemoglobin levels were also independently associated with lactate, endothelial activation, and proinflammatory cytokinemia.

CONCLUSIONS

Hemolysis in falciparum malaria results in NO quenching by cell-free hemoglobin, and may exacerbate endothelial dysfunction, adhesion receptor expression and impaired tissue perfusion. Treatments that increase NO bioavailability may have potential as adjunctive therapies in SM.

Hemoglobin-based red blood cell substitutes and nitric oxide

Hemoglobin-based oxygen carriers (HBOCs) have been studied for decades as red blood cell substitutes. Profound vasoconstrictor effects have limited the clinical utility of HBOCs and are attributable to avid scavenging of nitric oxide (NO). Inhaling NO can charge the body's stores of NO metabolites without producing hypotension and can prevent systemic hypertension induced when HBOCs are subsequently infused. Concurrent breathing of low NO doses can prevent pulmonary vasoconstriction after HBOC infusion without augmenting plasma methemoglobinemia.

Cerebrovascular reserve capacity is impaired in patients with sickle cell disease

Sickle cell disease (SCD) is associated with a high incidence of ischemic stroke. SCD is characterized by hemolytic anemia, resulting in reduced nitric oxide-bioavailability, and by impaired cerebrovascular hemodynamics. Cerebrovascular CO2 responsiveness is nitric oxide dependent and has been related to an increased stroke risk in microvascular diseases. We questioned whether cerebrovascular CO2 responsiveness is impaired in SCD and related to hemolytic anemia. Transcranial Doppler-determined mean cerebral blood flow velocity (V(mean)), near-infrared spectroscopy-determined cerebral oxygenation, and end-tidal CO2 tension were monitored during normocapnia and hypercapnia in 23 patients and 16 control subjects. Cerebrovascular CO2 responsiveness was quantified as Delta% V(mean) and Deltamicromol/L cerebral oxyhemoglobin, deoxyhemoglobin, and total hemoglobin per mm Hg change in end-tidal CO2 tension. Both ways of measurements revealed lower cerebrovascular CO2 responsiveness in SCD patients versus controls (V(mean), 3.7, 3.1-4.7 vs 5.9, 4.6-6.7 Delta% V(mean) per mm Hg, P < .001; oxyhemoglobin, 0.36, 0.14-0.82 vs 0.78, 0.61-1.22 Deltamicromol/L per mm Hg, P = .025; deoxyhemoglobin, 0.35, 0.14-0.67 vs 0.58, 0.41-0.86 Deltamicromol/L per mm Hg, P = .033; total-hemoglobin, 0.13, 0.02-0.18 vs 0.23, 0.13-0.38 Deltamicromol/L per mm Hg, P = .038). Cerebrovascular CO2 responsiveness was not related to markers of hemolytic anemia. In SCD patients, impaired cerebrovascular CO2 responsiveness reflects reduced cerebrovascular reserve capacity, which may play a role in pathophysiology of stroke.

Sequestration of extracellular hemoglobin within a haptoglobin complex decreases its hypertensive and oxidative effects in dogs and guinea pigs

Release of hemoglobin (Hb) into the circulation is a central pathophysiologic event that contributes to morbidity and mortality in chronic hemolytic anemias and severe malaria. These toxicities arise from Hb-mediated vasoactivity, possibly due to NO scavenging and localized tissue oxidative processes. Currently, there is no established treatment that targets circulating extracellular Hb. Here, we assessed the role of haptoglobin (Hp), the primary scavenger of Hb in the circulation, in limiting the toxicity of cell-free Hb infusion. Using a canine model, we found that glucocorticoid stimulation of endogenous Hp synthesis prevented Hb-induced hemodynamic responses. Furthermore, guinea pigs administered exogenous Hp displayed decreased Hb-induced hypertension and oxidative toxicity to extravascular environments, such as the proximal tubules of the kidney. The ability of Hp to both attenuate hypertensive responses during Hb exposure and prevent peroxidative toxicity in extravascular compartments was dependent on Hb-Hp complex formation, which likely acts through sequestration of Hb rather than modulation of its NO- and O2-binding characteristics. Our data therefore suggest that therapies involving supplementation of endogenous Hb scavengers may be able to treat complications of acute and chronic hemolysis, as well as counter the adverse effects associated with Hb-based oxygen therapeutics.

Elevated endothelial progenitor cells during painful sickle cell crisis

OBJECTIVE

Circulating endothelial progenitor cells (EPCs) counts were determined in patients with sickle cell disease (SCD) to elucidate their role in SCD-related ischemia-induced angiogenesis and reendothelialization.

MATERIALS AND METHODS

Circulating EPC counts (KDR(+)/CD34(+)/Cd45(dim) cells) and their relation to serum levels of EPC mobilizing growth factors erythropoietin, vascular endothelial growth factor, and interleukin-8 were investigated in SCD patients during asymptomatic state (n=66) and painful crisis (n=36) and compared to healthy controls (n=13).

RESULTS

EPC counts were comparable between controls (0; range, 0-1.1 cells/mL) and patients (0; range, 0-0 cells/mL) in asymptomatic state, but were significantly higher during painful crisis (41.7; range, 0-186 cells/mL; p<0.05). Also in a paired analysis of 12 patients who were included both during asymptomatic state and painful crisis, EPC counts increased significantly during painful crisis (from 0 [range, 0-0] to 26 [range, 0-149 cell/mL; p<0.05). EPC counts were not related to any of the measured growth factors.

CONCLUSION

The higher EPC counts during painful crisis might indicate a role for EPC mobilization in reendothelialization. As a relationship of EPCs with the established mobilizing growth factors, measured in this study was not observed, the mechanism of EPC mobilization in SCD remains to be elucidated.

Establishment of a transgenic sickle-cell mouse model to study the pathophysiology of priapism

INTRODUCTION

Priapism is a poorly understood disease process with little information on the etiology and pathophysiology of this erectile disorder. One group of patients with a high prevalence of priapism is men with sickle-cell disease.

AIM

Establish an in vivo transgenic sickle-cell mouse model to study the pathophysiology of sickle-cell disease-associated priapism.

METHODS

Transgenic sickle-cell disease mice, expressing human sickle hemoglobin, were utilized. Three groups of mice were used: (i) wild type (WT), (ii) sickle-cell heterozygotes (Hemi), and (ii) sickle-cell homozygotes (Sickle). Two age groups of each cohort of mice were utilized: young adult (4-6 months) and aged (18-22 months).

MAIN OUTCOME MEASURES

Histological (trichrome stain to measure ratio of collagen to smooth muscle), penile hydroxyproline content (collagen content), and transmission electron microscopic analysis of WT, Hemi, and Sickle mice penes, as well as in vivo erectile responses [change in intracavernous pressure (ICP)] to cavernous nerve stimulation (CNS), were determined. The frequency of erectile responses (erections/hour) pre- and poststimulation was also measured in each of the experimental groups.

RESULTS

Sickle mice had increased (P < 0.05) collagen to smooth muscle ratio and hydroxyproline content in the penis when compared with WT and Hemi mice penes. Transmission electron microscopy demonstrated thickened smooth muscle cell bundles, disruption of the endothelial lining of the corporal sinusoids, and increased (P < 0.05) caveolae number. Sickle mice had significantly (P < 0.05) higher ICP to CNS and increased (P < 0.05) frequency of erections pre- and post-CNS when compared with WT and Hemi mice erectile responses. Sickle mice did develop ED (change in ICP in response to CNS) with increasing age.

CONCLUSION

The morphometric changes of the penis and exaggerated in vivo erectile responses support the use of this transgenic sickle-cell disease animal model to study the pathophysiological mechanisms involved in sickle-cell disease-associated priapism.

Increased cavernosal relaxations in sickle cell mice priapism are associated with alterations in the NO-cGMP signaling pathway

INTRODUCTION

Priapism is defined as prolonged and persistent penile erection, unassociated with sexual interest or stimulation, and is one of the many serious complications associated with sickle cell disease (SCD).

AIM

The aim of this study was to evaluate the role of the NO-cGMP signaling pathway in priapism in Berkeley murine model of SCD (SS).

METHODS

SS mice and C57BL/6 mice (control) penile tissues were removed and the erectile tissue within the corpus cavernosum (CC) was surgically dissected free. The strips were mounted in 10 mL organ baths containing Krebs solution at 37 degrees C (95% O(2), 5% CO(2), pH 7.4), and vertically suspended between two metal hooks.

MAIN OUTCOME MEASURES

Cumulative concentration-response curves were constructed for acetylcholine (ACh; endothelium-dependent responses), sodium nitroprusside (SNP; endothelium-independent relaxations) and BAY 41-2272 (a potent activator of NO-independent site of soluble guanylate cyclase) in CC precontracted with phenylephrine. Cavernosal responses induced by frequency-dependent electrical field stimulation (EFS) were also carried out to evaluate the nitrergic cavernosal relaxations.

RESULTS

In SS mice, ACh-induced cavernosal relaxations were leftward shifted by 2.6-fold (P < 0.01) that was accompanied by increases in the maximal responses (78 +/- 5% and 60 +/- 3% in SS and C57B6/6J mice, respectively). Similarly, SNP- and BAY 41-2272-induced CC relaxations were leftward shifted by approximately 3.3- and 2.2-fold (P < 0.01) in SS mice, respectively. A significant increase in maximal responses to SNP and BAY 41-2272 in SS mice was also observed (113 +/- 6% and 124 +/- 5%, respectively) compared with C57B6/6J mice (83 +/- 4% and 99 +/- 2%, respectively). The EFS-induced cavernosal relaxations were also significantly higher SS mice.

CONCLUSION

These results showed that SS mice exhibit amplified corpus carvenosum relaxation response mediated by NO-cGMP signaling pathway. Intervention in this signaling pathway may be a potential therapeutic target to treat SCD priapism.