Successful treatment of corticosteroid-refractory hypereosinophilia with Reslizumab

No disponible

Assessing the influence of component processing and donor characteristics on quality of red cell concentrates using quality control data.

BACKGROUND AND OBJECTIVES: Quality control (QC) data collected by blood services are used to monitor production and to ensure compliance with regulatory standards. We demonstrate how analysis of quality control data can be used to highlight the sources of variability within red cell concentrates (RCCs). MATERIALS AND METHODS: We merged Canadian Blood Services QC data with manufacturing and donor records for 28 227 RCC between June 2011 and October 2014. Units were categorized based on processing method, bag manufacturer, donor age and donor sex, then assessed based on product characteristics: haemolysis and haemoglobin levels, unit volume, leucocyte count and haematocrit. RESULTS: Buffy-coat method (top/bottom)-processed units exhibited lower haemolysis than units processed using the whole-blood filtration method (top/top). Units from female donors exhibited lower haemolysis than male donations. Processing method influenced unit volume and the ratio of additive solution to residual plasma. CONCLUSIONS: Stored red blood cell characteristics are influenced by prestorage processing and donor factors. Understanding the relationship between processing, donors and RCC quality will help blood services to ensure the safety of transfused products.

Liver injury is associated with mortality in sickle cell disease.

BACKGROUND: Increased life expectancy in sickle cell disease (SCD) has resulted in greater recognition of the consequences of repeated intravascular vaso-occlusion and chronic haemolysis to multiple organ systems. AIM: To report the long-term consequences of liver dysfunction in SCD. METHODS: A cohort of SCD patients was prospectively evaluated at the National Institutes of Health (NIH) Clinical Center. The association of mortality with liver enzymes, parameters of liver synthetic function and iron overload was evaluated using Cox regression. RESULTS: Exactly, 247 SCD patients were followed up for 30 months of whom 22 (9%) died. After controlling for predictors, increased direct bilirubin (DB), ferritin, alkaline phosphatase and decreased albumin were independently associated with mortality. In a multivariable model, only high DB and ferritin remained significant. Ferritin correlated with hepatic iron content and total blood transfusions but not haemolysis markers. Forty patients underwent liver biopsies and 11 (28%) had fibrosis. Twelve of 26 patients (48%) had portal hypertension by hepatic venous pressure gradient (HVPG) measurements. All patients with advanced liver fibrosis had iron overload; however, most patients (69%) with iron overload were without significant hepatic fibrosis. Ferritin did not correlate with left ventricular dysfunction by echocardiography. DB correlated with bile acid levels suggesting liver pathology. Platelet count and soluble CD14 correlated with HVPG indicating portal hypertension. CONCLUSIONS: Ferritin and direct bilirubin are independently associated with mortality in sickle cell disease. Ferritin likely relates to transfusional iron overload, while direct bilirubin suggests impairment of hepatic function, possibly impairing patients' ability to tolerate systemic insults.

Traffic Light: prognosis-based eligibility for clinical trials of hematopoietic SCT in adults with sickle cell anemia.

Estimating prognosis in sickle cell anemia (SCA) assumes greater importance as intensive treatments, such as hematopoietic SCT (HSCT), are being tested. Here we estimate the mortality risk from the walk-PHaSST (Sildenafil Therapy for Pulmonary Hypertension and Sickle Cell Disease) trial of homozygous SCA patients with suspected pulmonary hypertension (19/468 deaths; 10 centers in the US and UK). Parallel investigations were also undertaken in the Cooperative Study of Sickle Cell Disease (CSCCD) and a contemporary urban sickle cell disease population (Case Western Reserve University-University Hospitals (CWRU-UH), Cleveland, OH, USA). One- and two-value positive predictive values for 2-year mortality (from study entry) are calculated using factors that include demographics, laboratory values and clinical evaluations. We define high-, intermediate-, and low-risk SCA as > 15%, 10-15% and < 10% 2-year mortality. In walk-PHaSST, no single factor qualifies as high-risk SCA, although several combinations of two factors (that is, both age > 35 years and history of chronic transfusion) do. Either elevated white blood cell count (> 13.5 × 10(3) cells/mcL, 7/70 deaths) or elevated Tricuspid Regurgitant Jet Velocity (⩾ 3.0 m/s, 8/67 deaths) was individually associated with intermediate-risk disease, as were many two-factor combinations. N-terminal pro-brain natriuretic peptide > 160 ng/L, lactate dehydrogenase > 600 IU/L, history of chronic transfusion, sepsis or age > 35 years are individually associated with low-risk SCA, as are many two-factor combinations. SCA risk was integrated with estimated donor type-associated risk from HSCT to form 'Traffic Light' eligibility criteria for clinical trials of HSCT. This method is adaptable to evolutions in clinical care.

An airway epithelial iNOS-DUOX2-thyroid peroxidase metabolome drives Th1/Th2 nitrative stress in human severe asthma.

Severe refractory asthma is associated with enhanced nitrative stress. To determine the mechanisms for high nitrative stress in human severe asthma (SA), 3-nitrotyrosine (3NT) was compared with Th1 and Th2 cytokine expression. In SA, high 3NT levels were associated with high interferon (IFN)-γ and low interleukin (IL)-13 expression, both of which have been reported to increase inducible nitric oxide synthase (iNOS) in human airway epithelial cells (HAECs). We found that IL-13 and IFN-γ synergistically enhanced iNOS, nitrite, and 3NT, corresponding with increased H(2)O(2). Catalase inhibited whereas superoxide dismutase enhanced 3NT formation, supporting a critical role for H(2)O(2), but not peroxynitrite, in 3NT generation. Dual oxidase-2 (DUOX2), central to H(2)O(2) formation, was also synergistically induced by IL-13 and IFN-γ. The catalysis of nitrite and H(2)O(2) to nitrogen dioxide radical (NO(2)(•)) requires an endogenous peroxidase in this epithelial cell system. Thyroid peroxidase (TPO) was identified by microarray analysis ex vivo as a gene distinguishing HAEC of SA from controls. IFN-γ induced TPO in HAEC and small interfering RNA knockdown decreased nitrated tyrosine residues. Ex vivo, DUOX2, TPO, and iNOS were higher in SA and correlated with 3NT. Thus, a novel iNOS-DUOX2-TPO-NO(2)(•) metabolome drives nitrative stress in HAEC and likely in SA.

Mechanisms of hemolysis-associated platelet activation.

BACKGROUND: Intravascular hemolysis occurs after blood transfusion, in hemolytic anemias, and in other conditions, and is associated with hypercoagulable states. Hemolysis has been shown to potently activate platelets in vitro and in vivo, and several mechanisms have been suggested to account for this, including: (i) direct activation by hemoglobin (Hb); (ii) increase in reactive oxygen species (ROS); (iii) scavenging of nitric oxide (NO) by released Hb; and (iv) release of intraerythrocytic ADP. OBJECTIVE: To elucidate the mechanism of hemolysis-mediated platelet activation. METHODS: We used flow cytometry to detect PAC-1 binding to activated platelets for in vitro experiments, and a Siemens' Advia 120 hematology system to assess platelet aggregation by using platelet counts from in vivo experiments in a rodent model. RESULTS: We found that Hb did not directly activate platelets. However, ADP bound to Hb could cause platelet activation. Furthermore, platelet activation caused by shearing of red blood cells (RBCs) was reduced in the presence of apyrase, which metabolizes ADP to AMP. The use of ROS scavengers did not affect platelet activation. We also found that cell-free Hb enhanced platelet activation by abrogating the inhibitory effect of NO on platelet activation. In vivo infusions of ADP and purified (ADP-free) Hb, as well as hemolysate, resulted in platelet aggregation, as shown by decreased platelet counts. CONCLUSION: Two primary mechanisms account for RBC hemolysis-associated platelet activation: ADP release, which activates platelets; and cell-free Hb release, which enhances platelet activation by lowering NO bioavailability.

Nitrite reduces acute lung injury and improves survival in a rat lung transplantation model.

Ischemia/reperfusion injury (IRI) is the most common cause of early mortality following lung transplantation (LTx). We hypothesized that nitrite, an endogenous source of nitric oxide (NO), may protect lung grafts from IRI. Rat lung grafts were stored in preservation solution at 4°C for 6 hours. Both grafts and recipients were treated with nitrite. Nitrite treatment was associated with significantly higher levels of tissue oxygenation, lower levels of cytokines and neutrophil/macrophage infiltration, lower myeloperoxidase activity, reduced oxidative injury and increased cGMP levels in grafts than in the controls. Treatment with either a nitric oxide scavenger or a soluble guanylyl cyclase (sGC) inhibitor diminished the beneficial effects of nitrite and decreased cGMP concentrations. These results suggest that nitric oxide, generated from nitrite, is the molecule responsible for the effects of nitrite via the nitric oxide/sGC/cGMP pathway. Allopurinol, a xanthine oxidoreductase (XOR) inhibitor, abrogated the protective effects of nitrite, suggesting that XOR is a key enzyme in the conversion of nitrite to nitric oxide. In vitro experiments demonstrated that nitrite prevented apoptosis in pulmonary endothelial cells. Nitrite also exhibits longer survival rate in recipients than control. In conclusion, nitrite inhibits lung IRI following cold preservation and had higher survival rate in LTx model.

Pulmonary embolism in sickle cell disease: a case-control study.

INTRODUCTION: A pulmonary embolism (PE) is a leading cause of mortality in hospitalized patients, yet the prevalence of PE in sickle cell disease (SCD) and its relation to disease severity or intrinsic hypercoagulability are not established. METHODS: We estimated inpatient PE incidence and prevalence among SCD and non-SCD populations in Pennsylvania, and compared severity of illness and mortality, using Pennsylvania Health Care Cost Containment Council (PHC4) discharge data, 2001-2006. Risk factors for PE were assessed in a case-control study of discharges from the University of Pittsburgh Medical Archival Records System (MARS). RESULTS: The incidence of inpatient PE was higher in the SCD PA population than in the non-SCD Pennsylvania population, 2001-2006. The PE prevalence among SCD discharges ≤ 50 years of age, 0.57%, was similar to that in non-SCD Pennsylvania discharges, 0.60%, and unchanged after adjustment for race. Among SCD discharges, those developing PE were significantly older, with a longer length of stay, greater severity of illness and higher mortality, P < 0.001, than SCD without a PE. Among PE discharges, SCD had a similar severity of illness, P = 0.77, and mortality, P = 0.39, but underwent fewer computerized tomographic scans, P = 0.006, than non-SCD with PE. In the local case-control study, no clinical or laboratory feature was associated with PE. CONCLUSIONS: The incidence of PE is higher and chest computed tomography (CT) utilization is lower in SCD than non-SCD inpatients, suggesting that PE may be under-diagnosed.

Effects of nitrite on modulating ROS generation following ischemia and reperfusion.

It has long been known that the generation of reactive oxygen species (ROS) is a major cause of injury after ischemia/reperfusion. More recently it has emerged that the predominant source of these ROS are the mitochondria, which are specifically damaged during prolonged ischemic episodes. Several strategies have been tested to attenuate mitochondrial damage and reperfusion ROS. Most successful has been ischemic preconditioning, a procedure in which repetitive short periods of ischemia and reperfusion reduce injury from a subsequent prolonged ischemia and reperfusion. Recently, ischemic postconditioning, whereby reperfusion after prolonged ischemia is repetitively interrupted for a short period, has also been shown to equally protect as ischemic preconditioning. Both procedures activate the same down-stream kinase pathways that minimize apoptosis and tissue damage. Endothelial nitric oxide synthase is a target of these kinase pathways and nitric oxide (NO) administration can mimic its protective effect. However, the optimal NO dose is difficult to determine and excess NO levels have been shown to be detrimental. A recently described physiological storage pool of NO, nitrite, has been shown to be a potent mediator of cytoprotection after ischemia/reperfusion that mechanistically reduces mitochondrial ROS generation at reperfusion. Here, we describe the sources, bioactivaton, and mechanisms of action of nitrite and discuss the potential of this simple anion as a therapeutic to protect against ischemia/reperfusion injury.

Pulmonary hypertension in patients with bronchiolitis obliterans syndrome listed for retransplantation.

Bronchiolitis Obliterans Syndrome (BOS) is a major cause of morbidity and mortality post-lung transplantation. Pulmonary hypertension (PH) may complicate the course of patients with advanced lung disease. We sought to characterize the prevalence of PH in patients with BOS. We performed a retrospective analysis of lung transplant recipients with BOS relisted for transplantation with the United Network for Organ Sharing (UNOS). Right heart catheterization (RHC) data were required for analysis. Eighty patients with BOS qualified for the analysis. PH was present in 32.5% of patients with an average mean pulmonary artery pressure (mPAP) of 32.3 mmHg (range: 26-63 mmHg). Of these, 42.3% had an elevated pulmonary capillary wedge pressure. There was no difference in PH prevalence between bilateral (26.5%) and single lung recipients (41.9%), nor did it differ by primary disease. There was no correlation between pulmonary function data and the presence or severity of PH. There was no difference in oxygen requirements or 6-min walk distance between patients with and without PH. This is the first report of PH in patients with BOS. Many of these cases occur in association with diastolic dysfunction. Although no impact on functional status or outcomes was discerned, further studies appear warranted.

Biomarker and drug-target discovery using proteomics in a new rat model of sepsis-induced acute renal failure.

Sepsis is one of the common causes of acute renal failure (ARF). The objective of this study was to identify new biomarkers and therapeutic targets. We present a new rat model of sepsis-induced ARF based on cecal ligation and puncture (CLP). We used this model to find urinary proteins which may be potential biomarkers and/or drug targets. Aged rats were treated with fluids and antibiotics after CLP. Urinary proteins from septic rats without ARF and urinary proteins from septic rats with ARF were compared by difference in-gel electrophoresis (DIGE). CLP surgery elevated interleukin (IL)-6 and IL-10 serum cytokines and blood nitrite compared with sham-operated rats. However, there was a range of serum creatinine values at 24 h (0.4-2.3 mg/dl) and only 24% developed ARF. Histology confirmed renal injury in these rats. Forty-nine percent of rats did not develop ARF. Rats without ARF also had less liver injury. The mortality rate at 24 h was 27% but was increased by housing the post-surgery rats in metabolic cages. Creatinine clearance and urine output 2-8 h after CLP was significantly reduced in rats which died within 24 h. Using DIGE we identified changes in a number of urinary proteins including albumin, brush-border enzymes (e.g., meprin-1-alpha) and serine protease inhibitors. The meprin-1-alpha inhibitor actinonin prevented ARF in aged mice. In summary, we describe a new rat model of sepsis-induced ARF which has a heterogeneous response similar to humans. This model allowed us to use DIGE to find changes in urinary proteins and this approach identified a potential biomarker and drug target - meprin-1-alpha.

Association between ratings of facial attractivess and patients' motivation for orthognathic surgery.

OBJECTIVES: To compare the judgments of facial esthetics, defects and treatment needs between laypersons and professionals (orthodontists and oral surgeons) as predictors of patient's motivation for orthognathic surgery. DESIGN: Two panels of expert and naïve raters were asked to evaluate photographs of orthognathic surgery patients for facial esthetics, defects and treatment needs. Results were correlated with patients' motivation for surgery. SETTING AND SAMPLE POPULATION: Fifty-seven patients (37 females and 20 males) with a mean age of 26.0 +/- 6.7 years were interviewed prior to orthognathic surgery treatment. Three color photographs of each patient were evaluated by a panel of 14 experts and panel of 18 laypersons. EXPERIMENTAL VARIABLES: Each panel of raters were asked to evaluate the facial morphology, facial attractiveness and recommend surgical treatment (independent variables). The dependent variable was the patient's motivation for orthognathic surgery. Outcome measure--Reliability of raters were analyzed using an unweighted Kappa coefficient and a Cronbach alpha coefficient. Correlations and regression analyses were used to quantify the relationship between variables. RESULTS: Expert raters provided reliable ratings of certain morphological features such as excessive gingival display and classification of mandibular facial form and position. Based on the facial photographs both expert and naïve raters agreed on facial attractiveness of patients. The best predictors of patients' motivation for surgery were the naïve profile attractiveness rating and the patients' expected change in self-consciousness. CONCLUSIONS: Expert raters provide more reliable ratings on certain morphologic features. However, the layperson's profile attractiveness rating and the patients' expected change in self-consciousness were the best predictors for patients' motivation for surgery. These data suggest that patients' motives for treatment are not necessarily related to objectively determined need. Patients' decision to seek treatment was more correlated to laypersons' rating of attractiveness because they see what other laypersons see, and are directly or indirectly affected by others reactions to their appearance. These findings may provide useful information for clinicians in counseling patients who seek orthognathic surgery.

Renal pathology in hemizygous sickle cell mice.

Transgenic mice have been developed that express exclusively human sickle cell beta hemoglobin and have major pathological features found in humans with sickle cell disease. These mice provide a unique opportunity to investigate the fundamental mechanisms of this disease and to design new strategies to correct the associated genetic defect(s). We found that in breeding males expressing only adult human alpha-globin and sickle beta-globin (homozygous SS mice) with females containing these transgenes plus one copy of the mouse beta-globin gene (hemizygous SS mice) greater than expected numbers of hemizygous offspring were produced than homozygous mice (carrying no mouse beta-globin gene). These hemizygous mice, expressing the human alpha and sickle beta(s) transgenes in combination with mouse beta+/-, were used for our preliminary studies of their renal pathology. No kidney lesions were found in the control (129/Sv) mice, whereas about 50% of the hemizygous SS mice showed mild-to-severe kidney lesions, including glomerulonephritis, cystic atypical hyperplastic tubules, and general nephropathy. Kidneys of some hemizygous mice were normal or showed minimal nephropathy, yet those of the susceptible phenotype developed a mild-to-more-severe form of renal lesions. The tubular epithelium of kidneys of hemizygous mice of the more affected phenotype exhibited increased expression of inducible nitric oxide synthase with an increased 3-nitrotyrosine in close proximity. There was also a stronger immunostaining for vascular cell adhesion molecule-1 in the interstitial capillary cells as well as the tubular epithelial cells of the renal cortex, compared with normal control mice. The occurrence of a high incidence of renal abnormalities in our hemizygous SS mice suggests that these mice may provide a suitable model to study the pathogenesis of nephropathy resulting from altered blood flow and/or insufficient oxygen delivery.

Noninvasive determination of spatially resolved and time-resolved tissue perfusion in humans during nitric oxide inhibition and inhalation by use of a visible-reflectance hyperspectral imaging technique.

BACKGROUND: Vascular disease is commonly associated with reduced local synthesis of nitric oxide (NO) and impaired tissue perfusion. We introduce a novel noninvasive, visible-reflectance, hyperspectral imaging technique for quantifying the percentage of hemoglobin existing as oxyhemoglobin (HbO(2)) as an index of skin tissue perfusion. METHODS AND RESULTS: To simulate vascular endothelial dysfunction, N(G)-monomethyl-L-arginine (L-NMMA) was infused into the brachial arteries of 9 healthy subjects for 5 minutes to inhibit forearm NO synthesis, first with the subject breathing room air and subsequently during NO inhalation at 80 ppm for 1 hour. Blood flow was measured by venous occlusion plethysmography, and the percentage of HbO(2) perfusing skin tissue was imaged noninvasively with a visible-reflectance hyperspectral technique. L-NMMA reduced blood flow by 31.7+/-4.9% and percentage of HbO(2) by 6.5+/-0.1 (P=0.002 and P<0.001 versus baseline, respectively). With subjects inhaling NO, blood flow fell during L-NMMA infusion by only 10.9+/-7.3%, and the percentage of HbO(2) decreased by 3.6+/-0.1 (P=0.007 and P<0.001, respectively, versus room air L-NMMA responses). CONCLUSIONS: Visible-reflectance hyperspectral imaging demonstrates (1) a significant decline in the percentage of HbO(2) in skin tissue when blood flow is reduced after inhibition of forearm NO synthesis and (2) restoration of HbO(2) toward basal values with improved blood flow during inhalation of NO. This imaging method may provide an effective approach for time-resolved noninvasive monitoring of skin hemoglobin oxygen saturation and assessment of responses to therapeutic interventions in patients with vascular disease.

Oxygen radical inhibition of nitric oxide-dependent vascular function in sickle cell disease.

Plasma xanthine oxidase (XO) activity was defined as a source of enhanced vascular superoxide (O(2)( *-)) and hydrogen peroxide (H(2)O(2)) production in both sickle cell disease (SCD) patients and knockout-transgenic SCD mice. There was a significant increase in the plasma XO activity of SCD patients that was similarly reflected in the SCD mouse model. Western blot and enzymatic analysis of liver tissue from SCD mice revealed decreased XO content. Hematoxylin and eosin staining of liver tissue of knockout-transgenic SCD mice indicated extensive hepatocellular injury that was accompanied by increased plasma content of the liver enzyme alanine aminotransferase. Immunocytochemical and enzymatic analysis of XO in thoracic aorta and liver tissue of SCD mice showed increased vessel wall and decreased liver XO, with XO concentrated on and in vascular luminal cells. Steady-state rates of vascular O(2)( *-) production, as indicated by coelenterazine chemiluminescence, were significantly increased, and nitric oxide (( *)NO)-dependent vasorelaxation of aortic ring segments was severely impaired in SCD mice, implying oxidative inactivation of ( *)NO. Pretreatment of aortic vessels with the superoxide dismutase mimetic manganese 5,10,15,20-tetrakis(N-ethylpyridinium-2-yl)porphyrin markedly decreased O(2)( small middle dot-) levels and significantly restored acetylcholine-dependent relaxation, whereas catalase had no effect. These data reveal that episodes of intrahepatic hypoxia-reoxygenation associated with SCD can induce the release of XO into the circulation from the liver. This circulating XO can then bind avidly to vessel luminal cells and impair vascular function by creating an oxidative milieu and catalytically consuming (*)NO via O(2)( small middle dot-)-dependent mechanisms.

Nitric oxide transport on sickle cell hemoglobin: where does it bind?

We have recently reported that nitric oxide inhalation in individuals with sickle cell anemia increases the level of NO bound to hemoglobin, with the development of an arterial-venous gradient, suggesting delivery to the tissues. A recent model suggests that nitric oxide, in addition to its well-known reaction with heme groups, reacts with the beta-globin chain cysteine 93 to form S-nitrosohemoglobin (SNO-Hb) and that SNO-Hb would preferentially release nitric oxide in the tissues and thus modulate blood flow. However, we have also recently determined that the primary NO hemoglobin adduct formed during NO breathing in normal (hemoglobin A) individuals is nitrosyl (heme)hemoglobin (HbFeIINO), with only a small amount of SNO-Hb formation. To determine whether the NO is transported as HbFeIINO or SNO-Hb in sickle cell individuals, which would have very different effects on sickle hemoglobin polymerization, we measured these two hemoglobin species in three sickle cell volunteers before and during a dose escalation of inhaled NO (40, 60, and 80 ppm). Similar to our previous observations in normal individuals, the predominant species formed was HbFeIINO, with a significant arterial-venous gradient. Minimal SNO-Hb was formed during NO breathing, a finding inconsistent with significant transport of NO using this pathway, but suggesting that this pathway exists. These results suggest that NO binding to heme groups is physiologically a rapidly reversible process, supporting a revised model of hemoglobin delivery of NO in the peripheral circulation and consistent with the possibility that NO delivery by hemoglobin may be therapeutically useful in sickle cell disease.

Nitric oxide therapy in sickle cell disease.

Recent clinical and experimental data suggest that nitric oxide (NO) may play a role in the pathogenesis and therapy of sickle cell disease. NO, a soluble gas continuously synthesized in endothelial cells by the NO synthase (NOS) enzyme systems, regulates basal vascular tone and endothelial function, and maintains blood oxygenation via hypoxic pulmonary vasoconstriction and reduced shunt physiology. These vital homeostatic processes may be impaired in sickle cell disease and contribute to its pathogenesis. Therapeutic NO inhalation exerts significant direct effects on the pulmonary vasculature to reduce pulmonary pressures and increase oxygenation that may prove beneficial in acute chest syndrome and secondary pulmonary hypertension. Delivery of NO bound to hemoglobin or in plasma may improve blood flow and hemoglobin saturation, and thus reduce ischemia-reperfusion injury. Other NO-related effects on adhesion molecule expression and fetal hemoglobin induction are of interest. While direct evidence for a clinical benefit of NO therapy in sickle cell disease has not been reported, studies are underway to determine if inhaled NO will reduce the substantial morbidity and mortality suffered by these patients.

Regional cerebral hyperperfusion and nitric oxide pathway dysregulation in Fabry disease: reversal by enzyme replacement therapy.

BACKGROUND: Fabry disease is an X-linked lysosomal deficiency of alpha-galactosidase A that results in cellular accumulation of galacto-conjugates such as globotriosylceramide, particularly in blood vessels. It is associated with early-onset stroke and kidney and heart failure. METHODS AND RESULTS: Using [(15)O] H(2)O and PET, we found increased resting regional cerebral blood flow in Fabry disease without evidence of occlusive vasculopathy or cerebral hypoperfusion. Because nitric oxide is known to play an important role in vascular tone and reactivity, we studied plasma nitrate, nitrite, and low-molecular-weight S-nitrosothiol levels by chemiluminescence. Skin biopsy specimens and archived brain tissue were also examined immunohistochemically for nitrotyrosine. Plasma nitrate, nitrite, and low-molecular-weight S-nitrosothiol were in the normal range; however, enhanced nitrotyrosine staining was observed in dermal and cerebral blood vessels. After a double-blind, placebo-controlled trial of alpha-galactosidase A therapy, the resting regional cerebral blood flow in the treated group was significantly reduced, with a notable decrease of nitrotyrosine staining in dermal blood vessels. CONCLUSIONS: These findings suggest a chronic alteration of the nitric oxide pathway in Fabry disease, with critical protein nitration that is reversible with enzyme replacement therapy.