Sickle cell disease vasculopathy: a state of nitric oxide resistance

Arginine metabolism and nutrition in growth, health and disease

L-Arginine (Arg) is synthesised from glutamine, glutamate, and proline via the intestinal-renal axis in humans and most other mammals (including pigs, sheep and rats). Arg degradation occurs via multiple pathways that are initiated by arginase, nitric-oxide synthase, Arg:glycine amidinotransferase, and Arg decarboxylase. These pathways produce nitric oxide, polyamines, proline, glutamate, creatine, and agmatine with each having enormous biological importance. Arg is also required for the detoxification of ammonia, which is an extremely toxic substance for the central nervous system. There is compelling evidence that Arg regulates interorgan metabolism of energy substrates and the function of multiple organs. The results of both experimental and clinical studies indicate that Arg is a nutritionally essential amino acid (AA) for spermatogenesis, embryonic survival, fetal and neonatal growth, as well as maintenance of vascular tone and hemodynamics. Moreover, a growing body of evidence clearly indicates that dietary supplementation or intravenous administration of Arg is beneficial in improving reproductive, cardiovascular, pulmonary, renal, gastrointestinal, liver and immune functions, as well as facilitating wound healing, enhancing insulin sensitivity, and maintaining tissue integrity. Additionally, Arg or L-citrulline may provide novel and effective therapies for obesity, diabetes, and the metabolic syndrome. The effect of Arg in treating many developmental and health problems is unique among AAs, and offers great promise for improved health and wellbeing of humans and animals.

Antibiotics for treating osteomyelitis in people with sickle cell disease

BACKGROUND

Osteomyelitis (both acute and chronic) is one of the most common infectious complications in people with sickle cell disease. 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 osteomyelitis.

OBJECTIVES

To determine whether an empirical antibiotic treatment approach (monotherapy or combination therapy) is effective and safe as compared to pathogen-directed antibiotic treatment and whether this effectiveness and safety is dependent on different treatment regimens, age or setting.

SEARCH STRATEGY

We searched The Group's Haemoglobinopathies Trials Register, which comprises references identified from comprehensive electronic database searches and handsearching of relevant journals and abstract books of conference proceedings. We also searched the LILACS database (1982 to 14 January 2009) and www.clinicaltrials.gov (June 2008).Date of most recent search of the Haemoglobinopathies Trials Register: 14 November 2008.

SELECTION CRITERIA

We searched for published or unpublished randomised and quasi-randomised controlled trials.

DATA COLLECTION AND ANALYSIS

Each author intended to independently extract data and assess trial quality by standard Cochrane Collaboration methodologies, but no eligible randomised controlled trials were identified.

MAIN RESULTS

We were unable to find any randomised or quasi-randomised controlled trials on antibiotic treatment approaches for osteomyelitis in people with sickle cell disease.

AUTHORS' CONCLUSIONS

We were unable to identify any relevant trials on the efficacy and safety of the antibiotic treatment approaches for people with sickle cell disease suffering from osteomyelitis. Randomised controlled trials are needed to establish the optimum antibiotic treatment for this condition.

Hepatocellular protection by nitric oxide or nitrite in ischemia and reperfusion injury

Ischemia and reperfusion (I/R)-induced liver injury occurs in several pathophysiological disorders including hemorrhagic shock and burn as well as resectional and transplantation surgery. One of the earliest events associated with reperfusion of ischemic liver is endothelial dysfunction characterized by the decreased production of endothelial cell-derived nitric oxide (NO). This rapid post-ischemic decrease in NO bioavailability appears to be due to decreased synthesis of NO, enhanced inactivation of NO by the overproduction of superoxide or both. This review presents the most current evidence supporting the concept that decreased bioavailability of NO concomitant with enhanced production of reactive oxygen species initiates hepatocellular injury and that endogenous NO or exogenous NO produced from nitrite play important roles in limiting post-ischemic tissue injury.

Adenosine deaminase-adenosine pathway in hemolysis-associated pulmonary hypertension

Hemolysis-associated pulmonary hypertension (HA-PH) is a serious clinical complication of various hemolytic disorders, and pulmonary hypertension (PH) is considered the greatest risk factor for death in patients with a hemolytic disorder. It is now well established that hemolysis causes the release of soluble hemoglobin and arginase from injured erythrocytes into plasma. This leads to nitric oxide (NO) deficiency, oxidative stress and a state of endothelial dysfunction that is associated with clinical development of PH. We challenge this concept and propose that in addition to the NO-arginase pathway, the adenosine deaminase-adenosine pathway plays a significant role in HA-PH and that modulation of this pathway may offer protective/therapeutic effects in HA-PH. Our preliminary data suggest that in HA-PH adenosine deaminase (ADA) is released from injured erythrocytes into plasma and that metabolic conversion of adenosine (ADO) to inosine by ADA reduces extracellular ADO levels. Adenosine, mainly via activation of adenosine A(2A) receptors, mediates a number of biological responses that may reduce hemolysis-induced vasculopathy and the risk of PH. Hypoxia is the strongest stimulus for ADO synthesis, and this increased ADO production counteracts some of the tissue/vascular injury caused by hypoxia itself. Unfortunately, under hypoxic conditions (anemia, vasoconstriction, and vaso-occlusion) in HA-PH, this "ADO negative-feed back" is abolished and the vascular protective effects of ADO are severely diminished by ADA released from injured erythrocytes. We hypothesize that in hemolytic anemia the repetitive release of ADA increases the risk for vaso-occlusive events and PH. We also propose that increase in extracellular ADO levels or activation of adenosine A(2A) receptors attenuates HA-PH, and we suggest further preclinical and clinical investigation of ADA inhibitors and ADO agonists in HA-PH.

Interventions for treating painful sickle cell crisis during pregnancy

BACKGROUND

Sickle cell disease is a group of genetic haemoglobin disorders. All over the world, about 300,000 children with these disorders are born each year. Acute sickle cell pain episodes are the most common cause of hospitalisation. Pregnancy in women with sickle cell disease is associated with an increased incidence of maternal and fetal morbidity and mortality. The painful crisis is a severe complication of this illness, and it requires several interventions: packed red cell transfusion, fluid replacement therapy, analgesic drugs, oxygen therapy and steroids; but the approach is not standardised.

OBJECTIVES

To assess the effectiveness and safety of different regimens of packed red cell transfusion, oxygen therapy, fluid replacement therapy, analgesic drugs, and steroids for the treatment of painful sickle cell crisis during pregnancy.

SEARCH STRATEGY

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (December 2007), the Cochrane Cystic Fibrosis and Genetic Disorders Group's Trials Register (October 2007), LILACS database (1982 to December 2007) and the following web sites: ClinicalTrials.gov (http://www.clinicaltrials.gov) (December 5, 2007); Current Controlled Trials (http://controlled-trials.com/) (December 5, 2007), and Sistema de Información Esencial en Terapéutica y Salud (http://www.icf.uab.es/informacion/Papyrus/sietes.asp) (December 1, 2007). We also handsearched the European Haematology Association conference (June 2007), the American Society of Hematology conference (December 2007) and reference lists of all retrieved articles.

SELECTION CRITERIA

We intended to include randomised clinical trials.

DATA COLLECTION AND ANALYSIS

We intended to summarise data by standard Cochrane Collaboration methodologies.

MAIN RESULTS

We could not find any randomised clinical trials on interventions (packed red cell transfusion, oxygen therapy, fluid replacement therapy, analgesic drugs, and steroids) for the treatment of painful sickle cell crisis during pregnancy.

AUTHORS' CONCLUSIONS

This review found no randomised clinical trials on the safety and efficacy of interventions for treating painful sickle cell crisis during pregnancy. The effects of interventions need to be tested in randomised clinical trials.

Arginine, nitric oxide, carbon monoxide, and endothelial function in severe malaria

PURPOSE OF REVIEW

Parasiticidal therapy of severe falciparum malaria improves outcome, but up to 30% of these patients die despite best therapy. Nitric oxide is protective against severe disease, and both nitric oxide and arginine (the substrate for nitric oxide synthase) are low in clinical malaria. Parasitized red blood cell interactions with endothelium are important in the pathophysiology of malaria. This review describes new information regarding nitric oxide, arginine, carbon monoxide, and endothelial function in malaria.

RECENT FINDINGS

Low arginine, low nitric oxide production, and endothelial dysfunction are common in severe malaria. The degree of hypoargininemia and endothelial dysfunction (measured by reactive hyperemia-peripheral artery tonometry) is proportional to parasite burden and severity of illness. Plasma arginase (an enzyme that catabolizes arginine) is elevated in severe malaria. Administering arginine intravenously reverses hypoargininemia and endothelial dysfunction. The cause(s) of hypoargininemia in malaria is unknown. Carbon monoxide (which shares certain functional properties with nitric oxide) protects against cerebral malaria in mice.

SUMMARY

Replenishment of arginine and restoration of nitric oxide production in clinical malaria should diminish parasitized red blood cells adherence to endothelium and reduce the sequelae of these interactions (e.g. cerebral malaria). Arginine therapy given in addition to conventional antimalaria treatment may prove to be beneficial in severe malaria.

Cysteine-iron promotes arginase activity by driving the Fenton reaction

Impairment of nitric oxide bioavailability secondary to increased arginase activity and overproduction of reactive oxygen species (ROS) is thought to be a major cause of vascular complications in sickle cell disease (SCD). However, the role of ROS in the induction of arginase activity is unknown. This study investigated whether the mechanism of arginase activation involves the ROS produced during oxidative stress. Our study reveals that cysteine-iron dose-dependently stimulated arginase activity with a corresponding increase in (.)OH radical formation. The ()OH radicals produced were significantly inhibited by salicylic acid derivatives and superoxide dismutase. Surprisingly, the inhibition of (.)OH radicals parallels the inhibition of arginase activity, thus suggesting the role of cysteine-iron in the stimulation of arginase via the Fenton reaction. This is the first evidence demonstrating the participation of (.)OH radicals in the stimulation of arginase activity, and thus provides novel avenues for therapeutic modalities in hemoglobinopathies and other inflammation-mediated diseases.

Mechanisms of vasculopathy in sickle cell disease and thalassemia

Many mechanisms contribute to the complex pathophysiology of sickle cell disease (SCD), with dysfunction of the vascular endothelium as a unifying theme. Specifically, hemolysis-associated low arginine and nitric oxide (NO) bioavailability, amplified by NO synthase uncoupling, elevated arginase activity, superoxide production, oxidative stress, accumulation of arginine analogs such as asymmetric dimethylarginine, ischemia-reperfusion injury, inflammation, apolipoprotein A-1 depletion, and a hypercoagulable state are significant mechanisms contributing to endothelial dysfunction. Genetic polymorphisms also influence disease severity. Clearly the variable spectrum of disease is the consequence of multiple events and genetic susceptibility that go beyond the occurrence of a single amino acid substitution in the beta globin chain of hemoglobin. Recent studies begin to demonstrate overlap among these seemingly unrelated processes. Impaired NO bioavailability represents the central feature of endothelial dysfunction, and is a common denominator in the pathogenesis of vasculopathy in SCD. The consequences of decreased NO bioavailability include endothelial cell activation, upregulation of the potent vasoconstrictor endothelin-1, vasoconstriction, platelet activation, increased tissue factor, and activation of coagulation, all of which ultimately translate into the clinical manifestations of SCD. Evidence supporting vasculopathy subphenotypes in SCD, including pulmonary hypertension, priapism, cutaneous leg ulceration, and stroke, will be reviewed and relevance to other hemolytic disorders including the thalassemia syndromes will be considered.

Gene replacement therapy for sickle cell disease and other blood disorders

Previous studies have demonstrated that sickle cell disease (SCD) can be corrected in mouse models by transduction of hematopoietic stem cells with lentiviral vectors containing anti-sickling globin genes followed by transplantation of these cells into syngeneic recipients. Although self-inactivating (SIN) lentiviral vectors with or without insulator elements should provide a safe and effective treatment in humans, some concerns about insertional mutagenesis persist. An ideal correction would involve replacement of the sickle globin gene (betaS) with a normal copy of the gene (betaA). We recently derived embryonic stem (ES) cells from a novel knockin mouse model of SCD and tested a protocol for correcting the sickle mutation by homologous recombination. Animals derived after gene replacement produced high levels of normal human hemoglobin (HbA), and the pathology associated with SCD was corrected. These experiments provided a foundation for similar studies in which our group collaborated with Rudolf Jaenisch's laboratory to correct SCD by gene replacement in iPS (induced pluripotent stem) cells derived by direct reprogramming of sickle skin fibroblasts. Corrected iPS cells were differentiated into hematopoeitic progenitors that were transplanted into irradiated sickle recipients. The transplanted animals produced high levels of normal human HbA, and the pathology of SCD was corrected. These proof-of-principle studies provide a foundation for the development of gene replacement therapy for human patients with SCD and other blood disorders.

Antibiotics for treating acute chest syndrome in people with sickle cell disease

BACKGROUND

The clinical presentation of acute chest syndrome is similar whether due to infectious or non-infectious causes, thus antibiotics are usually prescribed to treat all episodes. Many different bacteria have been implicated as causative agents of acute chest syndrome. 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 acute chest syndrome.

OBJECTIVES

To determine whether an empirical antibiotic treatment approach (used either alone or in combination): (a) is effective in treating acute chest syndrome compared to placebo or standard treatment; (b) is safe in treating acute chest syndrome compared to placebo or standard treatment; (c) differs dependent on the regimen used in treating acute chest syndrome differ from each other with respect to efficacy and safety; and (d) varies between different age groups, regions or countries with respect to efficacy and safety.

SEARCH STRATEGY

We searched The Group's Haemoglobinopathies Trials Register, which comprises references identified from comprehensive electronic database searches and handsearching of relevant journals and abstract books of conference proceedings. We also searched the LILACS database (1982 to May 2006) and the website: http://www.clinicaltrials.gov (May 2006). Date of most recent search of the Haemoglobinopathies Trials Register: February 2007.

SELECTION CRITERIA

We searched for published or unpublished randomised controlled trials.

DATA COLLECTION AND ANALYSIS

Each author intended to independently extract data and assess trial quality by standard Cochrane Collaboration methodologies, but no eligible randomized controlled trials were identified.

MAIN RESULTS

We were unable to find any randomised controlled trials on antibiotic treatment approaches for acute chest syndrome in people with sickle cell disease.

AUTHORS' CONCLUSIONS

We were unable to identify randomised controlled trials on efficacy and safety of the antibiotic treatment approaches for people with sickle cell disease suffering from acute chest syndrome. Randomised controlled trials are needed to establish the optimum antibiotic treatment for this condition.

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 STRATEGY

We searched The Group's Haemoglobinopathies Trials Register (December 2005), which comprises references identified from comprehensive electronic database searches and handsearching of relevant journals and abstract books of conference proceedings. We also searched The Cochrane Central Register of Controlled Trials (CENTRAL) in The Cochrane Library (Issue 4, 2005), MEDLINE (1966 to December 5th, 2005), EMBASE (1974 to December 7th, 2005), and LILACS (1982 to December 2005). Date of most recent search: December 2005

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

We were 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.