James S. Nichols

Nitric oxide donor properties of hydroxyurea in patients with sickle cell disease

Summary. Hydroxyurea therapy reduces the rates of vaso‐occlusive crisis in patients with sickle cell anaemia and recent data suggest that hydroxyurea treatment can generate nitric oxide (NO). Nitric oxide has been proposed as a novel therapy for sickle cell disease via a number of pathways. We therefore sought to determine whether hydroxyurea has NO donor properties in patients with sickle cell anaemia and explore potential mechanisms by which NO production could be therapeutic. Venous blood was collected from 19 fasting sickle cell anaemia patients, on chronic hydroxyurea therapy, at baseline and 2 and 4 h after a single morning dose of hydroxyurea, as well as 10 patients not taking hydroxyurea. The plasma and red cell NO reaction products nitrate, nitrite and nitrosylated‐ haemoglobin were measured using ozone‐based chemiluminescent assays (using vanadium, KI and I3– reductants respectively). Consistent with NO release from hydroxyurea, baseline levels of total nitrosylated haemoglobin increased from 300 nmol/l to 500 nmol/l (P = 0·01). Plasma nitrate and nitrite levels also significantly increased with peak levels observed at 2 h. Glutathionyl–haemoglobin levels were unchanged, while plasma secretory vascular cellular adhesion molecule‐1 levels were reduced in patients taking hydroxyurea (419 ± 40 ng/ml) compared with control patients with sickle cell anaemia (653 ± 55 ng/ml; P = 0·003), and were inversely correlated with fetal haemoglobin levels (r = −0·72; P = 0·002). These results demonstrate that hydroxyurea therapy is associated with the intravascular and intraerythrocytic generation of NO. The role of NO in the induction of fetal haemoglobin and possible synergy between NO donor therapy and classic cytostatic and differentiating medications should be explored.

Sildenafil therapy in patients with sickle cell disease and pulmonary hypertension

Pulmonary hypertension is a frequent complication of sickle cell disease that is associated with haemolysis, impaired nitric oxide bioavailability and high mortality. We sought to evaluate the safety and efficacy of selective pulmonary vasodilators and antiproliferative agents in this at‐risk population. After optimising sickle cell disease therapy to stabilise haemoglobin and fetal haemoglobin levels, we evaluated the safety and efficacy of sildenafil in 12 patients with sickle cell disease and pulmonary hypertension. Sildenafil therapy (mean duration 6 ± 1 months) decreased the estimated pulmonary artery systolic pressure [50 ± 4 to 41 ± 3 mmHg; difference 9 mmHg, 95% confidence interval (CI): 0·3–17, P = 0·043] and increased the 6‐min walk distance (384 ± 30 to 462 ± 28 m; difference 78 m, 95% CI: 40–117, P = 0·0012). Transient headaches occurred in two patients and transient eye‐lid oedema in four patients. No episodes of priapism occurred in the three men in the study; two of them were on chronic exchange transfusions and one had erectile dysfunction. In conclusion: (1) sickle cell disease patients with anaemia and pulmonary hypertension have significant exercise limitation; (2) the 6‐min walk distance may be a valid endpoint in this population; (3) therapy with sildenafil appears safe and improves pulmonary hypertension and exercise capacity. Additional phase I studies in males with sickle cell disease followed by phase II/III placebo controlled trials evaluating the safety and efficacy of sildenafil therapy in sickle cell disease patients with pulmonary hypertension are warranted.

Levels of soluble endothelium-derived adhesion molecules in patients with sickle cell disease are associated with pulmonary hypertension, organ dysfunction, and mortality

Endothelial cell adhesion molecules orchestrate the recruitment and binding of inflammatory cells to vascular endothelium. With endothelial dysfunction and vascular injury, the levels of endothelial bound and soluble adhesion molecules increase. Such expression is modulated by nitric oxide (NO), and in patients with sickle cell disease (SCD), these levels are inversely associated with measures of NO bioavailability. To further evaluate the role of endothelial dysfunction in a population study of SCD, we have measured the levels of soluble endothelium‐derived adhesion molecules in the plasma specimens of 160 adult patients with SCD during steady state. Consistent with a link between endothelial dysfunction and end‐organ disease, we found that higher levels of soluble vascular cell adhesion molecule‐1 (sVCAM‐1) were associated with markers indicating renal dysfunction and hepatic impairment. Analysis of soluble intercellular cell adhesion molecule‐1 (sICAM‐1), sE‐selectin and sP‐selectin levels indicated partially overlapping associations with sVCAM‐1, with an additional association with inflammatory stress and triglyceride levels. Importantly, increased soluble adhesion molecule expression correlated with severity of pulmonary hypertension, a clinical manifestation of endothelial dysfunction. Soluble VCAM‐1, ICAM‐1, and E‐selectin were independently associated with the risk of mortality in this cohort. Our data are consistent with steady state levels of soluble adhesion molecules as markers of pulmonary hypertension and risk of death.

Nitric Oxide for Inhalation in the Acute Treatment of Sickle Cell Pain Crisis: A Randomized Controlled Trial

CONTEXT Inhaled nitric oxide has shown evidence of efficacy in mouse models of sickle cell disease (SCD), case series of patients with acute chest syndrome, and 2 small placebo-controlled trials for treatment of vaso-occlusive pain crisis (VOC). OBJECTIVE To determine whether inhaled nitric oxide gas reduces the duration of painful crisis in patients with SCD who present to the emergency department or hospital for care. DESIGN, SETTING, AND PARTICIPANTS Prospective, multicenter, double-blind, randomized, placebo-controlled clinical trial for up to 72 hours of inhaled nitric oxide gas vs inhaled nitrogen placebo in 150 participants presenting with VOC of SCD at 11 centers between October 5, 2004, and December 22, 2008. Intervention Inhaled nitric oxide gas vs inhaled nitrogen placebo. MAIN OUTCOME MEASURES The primary end point was the time to resolution of painful crisis, defined by (1) freedom from parenteral opioid use for 5 hours; (2) pain relief as assessed by visual analog pain scale scores of 6 cm or lower (on 0-10 scale); (3) ability to walk; and (4) patients and familys decision, with physician consensus, that the remaining pain could be managed at home. RESULTS There was no significant change in the primary end point between the nitric oxide and placebo groups, with a median time to resolution of crisis of 73.0 hours (95% confidence interval [CI], 46.0-91.0) and 65.5 hours (95% CI, 48.1-84.0), respectively (P = .87). There were no significant differences in secondary outcome measures, including length of hospitalization, visual analog pain scale scores, cumulative opioid usage, and rate of acute chest syndrome. Inhaled nitric oxide was well tolerated, with no increase in serious adverse events. Increases in venous methemoglobin concentration confirmed adherence and randomization but did not exceed 5% in any study participant. Significant increases in plasma nitrate occurred in the treatment group, but there were no observed increases in plasma or whole blood nitrite. CONCLUSION Among patients with SCD hospitalized with VOC, the use of inhaled nitric oxide compared with placebo did not improve time to crisis resolution. TRIAL REGISTRATION clinicaltrials.gov Identifier: NCT00094887.

Inhaled nitric oxide augments nitric oxide transport on sickle cell hemoglobin without affecting oxygen affinity

Nitric oxide (NO) inhalation has been reported to increase the oxygen affinity of sickle cell erythrocytes. Also, proposed allosteric mechanisms for hemoglobin, based on S-nitrosation of beta-chain cysteine 93, raise the possibility of altering the pathophysiology of sickle cell disease by inhibiting polymerization or by increasing NO delivery to the tissue. We studied the effects of a 2-hour treatment, using varying concentrations of inhaled NO. Oxygen affinity, as measured by P(50), did not respond to inhaled NO, either in controls or in individuals with sickle cell disease. At baseline, the arterial and venous levels of nitrosylated hemoglobin were not significantly different, but NO inhalation led to a dose-dependent increase in mean nitrosylated hemoglobin, and at the highest dosage, a significant arterial-venous difference emerged. The levels of nitrosylated hemoglobin are too low to affect overall hemoglobin oxygen affinity, but augmented NO transport to the microvasculature seems a promising strategy for improving microvascular perfusion.

Severe painful vaso-occlusive crises and mortality in a contemporary adult sickle cell anemia cohort study.

Background Frequent painful vaso-occlusive crises (VOCs) were associated with mortality in the Cooperative Study of Sickle Cell Disease (CSSCD) over twenty years ago. Modern therapies for sickle cell anemia (SCA) like hydroxyurea are believed to have improved overall patient survival. The current study sought to determine the relevance of the association between more frequent VOCs and death and its relative impact upon overall mortality compared to other known risk factors in a contemporary adult SCA cohort. Methods Two hundred sixty four SCA adults were assigned into two groups based on patient reported outcomes for emergency department (ED) visits or hospitalizations for painful VOC treatment during the 12 months prior to evaluation. Results Higher baseline hematocrit (p = 0.0008), ferritin (p = 0.005), and HDL cholesterol (p = 0.01) were independently associated with 1 or more painful VOCs requiring an ED visit or hospitalization for acute pain. During a median follow-up of 5 years, mortality was higher in the ED visit/hospitalization group (relative risk [RR] 2.68, 95% CI 1.1-6.5, p = 0.03). Higher tricuspid regurgitatant jet velocity (TRV) (RR 2.41, 95% CI 1.5-3.9, p < 0.0001), elevated ferritin (RR 4.00, 95% CI 1.8-9.0, p = 0.001) and lower glomerular filtration rate (RR=2.73, 95% CI 1.6-4.6, p < 0.0001) were also independent risk factors for mortality. Conclusions Severe painful VOCs remain a marker for SCA disease severity and premature mortality in a modern cohort along with other known risk factors for death including high TRV, high ferritin and lower renal function. The number of patient reported pain crises requiring healthcare utilization is an easily obtained outcome that could help to identify high risk patients for disease modifying therapies. Trial Registration ClinicalTrials.gov NCT00011648 http://clinicaltrials.gov/

Iron, inflammation, and early death in adults with sickle cell disease

Rationale: Patients with sickle cell disease (SCD) have markers of chronic inflammation, but the mechanism of inflammation and its relevance to patient survival are unknown. Objective: To assess the relationship between iron, inflammation, and early death in SCD. Methods and Results: Using peripheral blood mononuclear cell transcriptome profile hierarchical clustering, we classified 24 patients and 10 controls in clusters with significantly different expression of genes known to be regulated by iron. Subsequent gene set enrichment analysis showed that many genes associated with the high iron cluster were involved in the toll-like receptor system (TLR4, TLR7, and TLR8) and inflammasome complex pathway (NLRP3, NLRC4, and CASP1). Quantitative PCR confirmed this classification and showed that ferritin light chain, TLR4, and interleukin-6 expression were >100-fold higher in patients than in controls (P<0.001). Further linking intracellular iron and inflammation, 14 SCD patients with a ferroportin Q248H variant that causes intracellular iron accumulation had significantly higher levels of interleukin-6 and C-reactive protein compared with 14 matched SCD patients with the wild-type allele (P<0.05). Finally, in a cohort of 412 patients followed for a median period of 47 months (interquartile range, 24–82), C-reactive protein was strongly and independently associated with early death (hazard ratio, 3.0; 95% confidence interval, 1.7–5.2; P<0.001). Conclusions: Gene expression markers of high intracellular iron in patients with SCD are associated with markers of inflammation and mortality. The results support a model in which intracellular iron promotes inflammatory pathways, such as the TLR system and the inflammasome, identifying important new pathways for additional investigation.

Imaging flow cytometry for automated detection of hypoxia-induced erythrocyte shape change in sickle cell disease.

In preclinical and early phase pharmacologic trials in sickle cell disease, the percentage of sickled erythrocytes after deoxygenation, an ex vivo functional sickling assay, has been used as a measure of a patients disease outcome. We developed a new sickle imaging flow cytometry assay (SIFCA) and investigated its application. To perform the SIFCA, peripheral blood was diluted, deoxygenated (2% oxygen) for 2 hr, fixed, and analyzed using imaging flow cytometry. We developed a software algorithm that correctly classified investigator tagged “sickled” and “normal” erythrocyte morphology with a sensitivity of 100% and a specificity of 99.1%. The percentage of sickled cells as measured by SIFCA correlated strongly with the percentage of sickle cell anemia blood in experimentally admixed samples (R = 0.98, P ≤ 0.001), negatively with fetal hemoglobin (HbF) levels (R = −0.558, P = 0.027), negatively with pH (R = −0.688, P = 0.026), negatively with pretreatment with the antisickling agent, Aes‐103 (5‐hydroxymethyl‐2‐furfural) (R = −0.766, P = 0.002), and positively with the presence of long intracellular fibers as visualized by transmission electron microscopy (R = 0.799, P = 0.002). This study shows proof of principle that the automated, operator‐independent SIFCA is associated with predictable physiologic and clinical parameters and is altered by the putative antisickling agent, Aes‐103. SIFCA is a new method that may be useful in sickle cell drug development. Am. J. Hematol. 89:598–603, 2014.

The Role of Phosphodiesterase 12 (PDE12) as a Negative Regulator of the Innate Immune Response and the Discovery of Antiviral Inhibitors

Background: PDE12 degrades 2′,5′-oligoadenylate, a second messenger involved in the antiviral action of interferon. Results: Inactivation of the PDE12 gene and novel inhibitors of the enzyme render cells resistant to more than one virus. Conclusion: PDE12 negatively regulates the innate immune response, and inhibitors of PDE12 have antiviral activity. Significance: PDE12 inhibitors have the potential to be broadly acting antiviral medicines. 2′,5′-Oligoadenylate synthetase (OAS) enzymes and RNase-L constitute a major effector arm of interferon (IFN)-mediated antiviral defense. OAS produces a unique oligonucleotide second messenger, 2′,5′-oligoadenylate (2–5A), that binds and activates RNase-L. This pathway is down-regulated by virus- and host-encoded enzymes that degrade 2–5A. Phosphodiesterase 12 (PDE12) was the first cellular 2–5A- degrading enzyme to be purified and described at a molecular level. Inhibition of PDE12 may up-regulate the OAS/RNase-L pathway in response to viral infection resulting in increased resistance to a variety of viral pathogens. We generated a PDE12-null cell line, HeLaΔPDE12, using transcription activator-like effector nuclease-mediated gene inactivation. This cell line has increased 2–5A levels in response to IFN and poly(I-C), a double-stranded RNA mimic compared with the parental cell line. Moreover, HeLaΔPDE12 cells were resistant to viral pathogens, including encephalomyocarditis virus, human rhinovirus, and respiratory syncytial virus. Based on these results, we used DNA-encoded chemical library screening to identify starting points for inhibitor lead optimization. Compounds derived from this effort raise 2–5A levels and exhibit antiviral activity comparable with the effects observed with PDE12 gene inactivation. The crystal structure of PDE12 complexed with an inhibitor was solved providing insights into the structure-activity relationships of inhibitor potency and selectivity.

Topical sodium nitrite for chronic leg ulcers in patients with sickle cell anaemia: a phase 1 dose-finding safety and tolerability trial

BACKGROUND Well-tolerated and effective treatments are needed for chronic leg ulcers in sickle cell anaemia. Topical sodium nitrite, a known nitric oxide donor, enhances blood flow in ulcers and has known bacteriostatic effects. We aimed to assess the safety, tolerability, and pharmacokinetics of topical sodium nitrite in patients with sickle cell disease and chronic leg ulcers. METHODS We enrolled adult patients from an ambulatory clinic at the National Institutes of Health (Bethesda, MD, USA) with sickle cell anaemia with leg ulcers (with a surface area of 2.5-100 cm2) persisting for at least 4 weeks into a safety and tolerability phase 1 dose-escalation trial of topical sodium nitrite. Increasing concentrations of sodium nitrite cream were applied twice weekly for 4 weeks to one ulcer per patient at five dose levels (0.5%, 1%, 1.5%, 1.8%, and 2%). The primary endpoints were safety and tolerability, with secondary endpoints of pharmacokinetics, blood flow, and wound healing. Pain relief was analysed post hoc. Endpoints were analysed over time for the whole study population and according to dose level. This study is registered with ClinicalTrials.gov, number NCT01316796. FINDINGS Between April 4, 2011, and March 19, 2013, we enrolled 18 adult patients with sickle cell anaemia and leg ulcers into our trial. We assigned three patients into each cohort, and each cohort was treated with a different concentration of sodium nitrite cream (cohort 1: 0.5%, cohort 2: 1.0%, cohort 3: 1.5%, and cohort 4: 2.0%). Patients were not enrolled into the next cohort dose until we were able to establish that no dose-limiting toxicities were observed. An additional six patients were enrolled to cohort 3a: 1.8%, after two patients in cohort 4 had asymptomatic drops in diastolic blood pressure. No grade 3-4 adverse events were observed, and there were no serious adverse events or dose-limiting side-effects. Pharmacokinetic analysis showed that systemic absorption of sodium nitrite was very low. Application of topical sodium nitrite was associated with a significant increase in peri-wound cutaneous blood flow measured by laser speckle contrast imaging (p=0.0002), corroborated by increased peri-wound skin temperature by infrared thermography (p=0.0119). We recorded a dose-dependent decrease in leg ulcer size (p=0.0012) and pain (p<0.0001). Ulcers healed completely in three patients who received the highest concentrations of topical sodium nitrite (the 1.8% and 2% cream). In our post-hoc analysis of pain, brief pain inventory scores improved in pain severity (p=0.0048) and pain interference (p=0.0013). INTERPRETATION Our results indicate that topical sodium nitrite 2% cream is suitable for additional clinical trials in adults with sickle cell anaemia to promote healing of leg ulcers. FUNDING National Heart, Lung and Blood Institute Division of Intramural Research (National Institutes of Health).