Healthy African American Control Subjects Research Articles

Empirical model of human blood transverse relaxation at 3 T improves MRI T2 oximetry.

We sought a human blood T2 -oximetery calibration curve over the wide range of hematocrits commonly found in anemic patients applicable with T2 relaxation under spin tagging (TRUST). Blood was drawn from five healthy control subjects. Ninety-three in vitro blood transverse relaxation (T2b ) measurements were performed at 37°C over a broad range of hematocrits (10-55%) and oxygen saturations (14-100%) at 3 Tesla (T). In vivo TRUST was performed on 35 healthy African American control subjects and 11 patients with chronic anemia syndromes. 1/T2 rose linearly with hematocrit (r2 = 0.96), for fully saturated blood. Upon desaturation, 1/T2 rose linearly with the square of the oxygen extraction, (1-Y)2 , and the slope was linearly proportional to hematocrit (r2 = 0.88). The resulting bilinear model between 1/T2 , (1-Y)2 , and hematocrit had a combined r2 of 0.96 and a coefficient of variation of 6.1%. Using the in vivo data, the bilinear model had significantly lower bias and variability than existing calibrations, particularly for low hematocrits. In vivo Bland Altman analysis demonstrated clinically relevant bias that was -6% (absolute saturation) for hematocrits near 30% and rose to + 6% for hematocrits near 45%. This work introduces a robust bilinear calibration model that should be used for MRI oximetry. Magn Reson Med 77:2364-2371, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Expression of Interferon-γ Receptor Genes in Peripheral Blood Mononuclear Cells Is Associated With Rheumatoid Arthritis and Its Radiographic Severity in African Americans.

The factors responsible for radiographic severity in African American patients with rheumatoid arthritis (RA) are poorly understood. We sought to identify genes whose expression in peripheral blood mononuclear cells is associated with radiographic severity in RA. In the first phase of the study, we performed real-time quantitative polymerase chain reaction to analyze the expression of 182 candidate genes in 40 African American RA patients with extremes of radiographic damage (low versus high radiographic scores) and disease duration (≤2 years versus >2 years) and 20 healthy African American control subjects; the genes were selected based on plausible immune pathways. In the second phase, we analyzed the expression of the genes that were shown to be significantly associated with radiographic scores in 576 African American patients with RA and 51 African American control subjects who had not been studied previously, accounting for autoantibody status and disease duration. We observed significant differences in IFNGR1 expression between patients with RA and control subjects (adjusted P [P(adj)] = 6 × 10(-14)) and in IFNGR2 expression between RA patients with erosions and those with no erosions (P(adj) = 0.01 by Wilcoxon's rank sum test). We also observed significant correlations between IFNGR2 expression and radiographic scores (P(adj) = 0.03 for erosions, P(adj) = 0.04 for joint space narrowing, and P(adj) = 0.03 for total radiographic score [zero-inflated negative binomial regression model]) and annualized progression rate (P(adj) = 0.0024 by Spearman's correlation analysis). These findings have important implications with respect to the role of interferon-γ (IFNγ) in the pathogenesis of RA and may lead to identification of a biomarker for radiographic damage. Additional studies are needed to define the cell subsets responsible for the association of IFNγ receptor gene expression with radiographic findings, which downstream mechanisms are involved, and generalizability to other RA populations.

Association of pro-inflammatory high-density lipoprotein cholesterol with clinical and laboratory variables in sickle cell disease

BackgroundAlthough cholesterol levels are known to be decreased in sickle cell disease (SCD), the level of pro-inflammatory high-density lipoprotein cholesterol (proHDL) and its association with clinical complications and laboratory variables has not been evaluated.Design and methodsPlasma levels of total cholesterol, high-density lipoprotein cholesterol (HDL), proHDL, and selected clinical and laboratory variables were ascertained in a cohort of SCD patients and healthy African American control subjects in this single-center, cross-sectional study.ResultsAlthough total cholesterol was significantly lower in SCD patients compared with control subjects, HDL and proHDL levels were similar in both the SCD and control groups. In univariate analyses, proHDL was correlated with echocardiography-derived tricuspid regurgitant jet velocity. ProHDL was higher in SCD patients with suspected pulmonary hypertension (PHT) compared to patients without suspected PHT. ProHDL was positively correlated with lactate dehydrogenase, total bilirubin, direct bilirubin, indirect bilirubin, prothrombin fragment 1+2, D-dimer, and thrombin–antithrombin complexes. In multivariable analyses, only higher lactate dehydrogenase and direct bilirubin levels were associated with higher levels of proHDL.ConclusionsSCD is characterized by hypocholesterolemia. Although proHDL is not increased in SCD patients compared with healthy controls, it is significantly associated with markers of liver disease. In addition, proHDL is associated with tricuspid regurgitant jet velocity and markers of coagulation, although these associations are not significant in multivariable analyses.

Laser Speckle Contrast Imaging Characterizes Delayed Reperfusion After Transient Brachial Artery Occlusion in Patients with Sickle Cell Diseas

AbstractAbstract 1080 Background:The pathophysiology of sickle cell disease (SCD) involves vascular complications such as stroke and pulmonary hypertension. Elevated pulmonary artery pressure estimated by cardiac ultrasound or measured by invasive right heart catheterization is associated with early mortality among patients with SCD. Peripheral vascular dysfunction has also been observed in SCD and may be easier to assess than pulmonary vascular resistance and therefore more suitable for epidemiologic or interventional studies of SCD. Three previous studies found no difference in the maximal blood flow (or percentage increase) stimulated by occlusion and reperfusion of the brachial artery, a conduit vessel, when measured by Doppler ultrasound at periodic intervals. However, a study using continuous laser Doppler measurements of cutaneous microvascular blood flow found that patients with SCD had prolonged time to maximal blood flow and prolonged time to return to baseline compared to healthy controls. In our study, we used two-dimensional laser speckle contrast imaging (LSCI) to assess the cutaneous microvascular blood flow response in adults with SCD after five minutes of brachial artery occlusion. Methods:Nine subjects with sickle cell disease were enrolled and compared against nine healthy African-American control subjects matched for age, sex, ethnicity, and body mass index. Cutaneous blood flow was directly measured using LCSI at baseline, during and after a standard brachial artery occlusion-reperfusion maneuver (inflation of an occlusive pneumatic cuff for five minutes). This stimulates a transient increase in blood flow to levels above baseline during the reperfusion phase. Blood flow data were averaged over a defined region of interest on the medial aspect of the forearm. Microvascular blood flow responsiveness was calculated as the time to maximum (time elapsed from 50% of maximum to maximum blood flow) and the time to return to baseline (time elapsed from maximum to 50% of maximum blood flow). We performed measurements on each individual on two separate days, and compared the microvascular blood flow responses between the groups using two-way ANOVA with repeated measures. Results:We enrolled nine patients with sickle cell disease (age 35 ± 8.8, BMI 23 ± 3.9, 3 men/6 women) and nine healthy controls (age 35 ± 10.7 years, BMI 25 ± 3.2, 3 men/6 women). Baseline microvascular blood flow measured in arbitrary units (AU) was greater in patients with sickle cell disease compared to healthy controls (53.1 ± 9.2 AU vs 37.2 ± 4.4 AU, p < 0.0001) but maximal microvascular blood flow was similar (121.3 ± 29.3 AU vs 124.7 ± 26.6 AU, p = 0.58). Analysis of the time from half-maximum to maximum blood flow revealed that patients with sickle cell disease take longer to reach maximum blood flow (19.1 ± 11.6 s vs 11.8 ± 1.0 s, p = 0.03) and longer to decrease from maximum to half-maximum blood flow during the recovery period (43.5 ± 13.0 s vs 28.6 ± 10.4 s, p = 0.002). Conclusion:Compared to healthy individuals, patients with SCD have greater baseline microvascular blood flow but similar maximal blood flow during reperfusion. However, patients with SCD differ significantly from healthy control subjects in the time required to reach maximal blood flow and the time required to return to baseline, both of which are prolonged in patients with SCD. This may reflect delayed or impaired endothelial responses to shear stress and/or greater viscosity of blood. Time to maximal blood flow might represent a useful physiological biomarker as a proxy for clinical severity of sickle cell anemia, and a potential surrogate marker in early phase clinical trials. This technique merits additional characterization and validation. Disclosures:No relevant conflicts of interest to declare.

Most common single‐nucleotide polymorphisms associated with rheumatoid arthritis in persons of European ancestry confer risk of rheumatoid arthritis in African Americans

Large-scale genetic association studies have identified >20 rheumatoid arthritis (RA) risk alleles among individuals of European ancestry. The influence of these risk alleles has not been comprehensively studied in African Americans. We therefore sought to examine whether these validated RA risk alleles are associated with RA risk in an African American population. Twenty-seven candidate single-nucleotide polymorphisms (SNPs) were genotyped in 556 autoantibody-positive African Americans with RA and 791 healthy African American control subjects. Odds ratios (ORs) and 95% confidence intervals (95% CIs) for each SNP were compared with previously published ORs for RA patients of European ancestry. We then calculated a composite genetic risk score (GRS) for each individual based on the sum of all risk alleles. Overlap of the ORs and 95% CIs between the European and African American populations was observed for 24 of the 27 candidate SNPs. Conversely, 3 of the 27 SNPs (CCR6 rs3093023, TAGAP rs394581, and TNFAIP3 rs6920220) demonstrated ORs in the opposite direction from those reported for RA patients of European ancestry. The GRS analysis indicated a small but highly significant probability that African American patients relative to control subjects were enriched for the risk alleles validated in European RA patients (P = 0.00005). The majority of RA risk alleles previously validated for RA patients of European ancestry showed similar ORs in our population of African Americans with RA. Furthermore, the aggregate GRS supports the hypothesis that these SNPs are risk alleles for RA in the African American population. Future large-scale genetic studies are needed to validate these risk alleles and identify novel RA risk alleles in African Americans.

Identification of Thrombospondin-1 and L-Selectin as Potential Plasma Biomarkers of Silent Cerebral Infarct In Children with Sickle Cell Disease Using a Proteomic-Based Approach

AbstractAbstract 259 Objectives:Silent cerebral infarction (SCI) occurs in approximately 27% of children with sickle cell disease (SCD) by age 6 years, and is associated with decreased neurocognitive function and a 14-fold increased risk of progression to overt stroke. While several clinical parameters, such as increased white blood cell (WBC) and platelet counts and decreased hemoglobin (Hb) or hematocrit, have been reported in the literature to be associated with SCI, to date no validated biomarkers exist to predict SCI in patients with SCD. Furthermore, recent unpublished data from the Silent Infarct Transfusion (SIT) Trial has identified systolic blood pressure and total hemoglobin as risk factors. The aim of this study was to identify candidate biomarker plasma proteins that correlate with SCI in patients with SCD. Methods:We used a proteomic discovery approach involving three sequential separation steps to compare the plasma proteomes of 15 children with SCD (7 with SCI and 8 without SCI), aged 5–15 years. Baseline steady-state plasma samples were obtained from the SIT Trial Biologic Repository and matched for age, Hb and WBC. Plasma samples were Hb depleted in the first dimension, separated using immunoaffinity depletion and reverse phase liquid chromatography fractionation, and then trypsin-digested for characterization using label-free quantification on a LTQ-Orbitrap (Thermo) mass spectrometer. The resulting MS/MS data were analyzed using PASS (Integrated Analysis, Bethesda, MD) with X! Tandem searches (www.thegpm.org; version 2008.12.01) of the International Protein Index peptide database (human, 3.19). We measured candidate proteins in a validation cohort of 116 children with SCD (n=65 SCI, 51 non-SCI) and 24 age-matched, healthy African American control subjects using enzyme-linked immunosorbent assays (thrombospondin 1 [TSP1], L-selectin, RandD Systems, Minneapolis, MN) and immunoassays (E- and P-selectin, Mesoscale Discovery, Maryland). All samples were run in duplicate according to the manufacturers' protocols. Statistical differences in biomarker plasma concentrations between groups were compared by the Mann-Whitney U test. Results:TSP1 (5 peptides) and L-selectin (3 peptides) were among 335 proteins that showed differential detection between the SCI and non-SCI groups based on the spectral counts. TSP1 is an extracellular matrix glycoprotein that is involved with platelet aggregation, inhibition of neovascularization and tumorigenesis and has been shown to promote the adherence of sickle erythrocytes to the vascular endothelium. L-selectin is an adhesion molecule that mediates leukocyte interaction with the vascular endothelium. In a validation cohort of 116 children with SCD (n=65 SCI, 51 non-SCI) and 24 age matched, healthy African American control subjects, TSP1 and L-selectin were both significantly increased in SCI vs. non-SCI groups (median 8.5 vs. 6.2 μ g/ml for TSP1, P =0.03; 1.5 vs. 1.4 μ g/ml for L-selectin, P =0.03). As expected, neither TSP nor L-selectin were elevated in the age-matched normal controls (median=4.6 μ g/ml for TSP1, P =0.10, 1.2 μ g/ml for L-selectin, P =0.10). The specificity of the L-selectin results was verified by demonstrating that E-selectin and P-selectin were not increased in the SCI group. TSP1 was correlated with baseline oxygen saturation in both the SCI and non-SCI groups (r=-0.51, and r=-0.35, P<0.001). L-selectin correlated with systolic blood pressure in the SCI group only (r=0.3, P<0.02). Conclusions:TSP1 and L-selectin may represent the first two plasma biomarkers of SCI in children with SCD. Although further studies are needed, these and other potential biomarkers may provide insight into the pathophysiology of SCI, and may fill an important clinical need in identifying children with SCD who are at risk for SCI. [Display omitted] Disclosures:No relevant conflicts of interest to declare.

Placental Growth Factor Is Elevated in Patients with Sickle Cell Disease and Associated with Pulmonary Hypertension, Hemolysis, Inflammation, Iron Overload, and Hepatic Dysfunction.

Abstract 1531Poster Board I-554Placental Growth Factor (PlGF) is a functional cytokine in the vascular endothelial growth factor (VEGF) family that generally promotes angiogenesis, depending on the specific context, and can also promote atherogenesis. Produced in erythroid cells, its level in patients with sickle cell disease (SCD) has been previously related to the rate of erythropoiesis. We evaluated PlGF plasma levels in SCD patients by ELISA, and related it to biomarkers of pulmonary hypertension (PH), an emerging and serious complication of SCD linked to early mortality. We find that PlGF levels are significantly higher in SCD (n=95) than healthy African American control subjects (n=19) (median 16.6 vs. 2.1 pg/mL, p<0.001). PlGF levels were higher in SCD patients with elevated pulmonary pressure (normal pulmonary pressure vs. mildly elevated vs. highly elevated: medians 13.7 vs. 16.7 vs. 19.8 pg/mL, p<0.0001). Supporting a linkage to rate of hemolysis, PlGF correlated with LDH (p=0.001) and inversely with hemoglobin level (p<0.0001). Suggesting a link to inflammation, PlGF correlated significantly with C-reactive protein (p=0.001) and erythrocyte sedimentation rate (p<0.001). PlGF correlated with markers of iron overload, including ferritin, transferrin saturation and inversely with transferrin (all p<0.001). Finally, PlGF correlated with markers of hepatic dysfunction, including low albumin and high direct bilirubin (p<0.001).We found significantly higher PlGF levels in SCD patients taking hydroxyurea compared to those not taking it (median 17.4 vs. 14.0 pg/ml, p<0.01). Confirming that hydroxyurea increases PlGF levels, in a separate cohort of seven patients, PlGF levels rose significantly from their baseline values after initiating hydroxyurea (median approx 22 vs. 27, p<0.05). Our data suggest that elevated PlGF level is associated with PH in patients with SCD, and PlGF is correlated with severity of hemolysis, inflammation, iron overload and hepatic dysfunction. Considering the variable evidence in the literature for either stimulating or inhibiting angiogenesis, it is not clear whether pathologic elevation of PlGF may be mediating pulmonary hypertension, or perhaps conversely providing an adaptive response to vascular damage. It has been suggested by Perelman et al. that PlGF may mediate leukocyte activation that might promote disease severity in SCD. However, hydroxyurea, which tends to ameliorate SCD complications, stimulates PlGF level in an unexpected manner, possibly related to the ability of hydroxyurea to stimulate erythropoietin production, which might in turn induce PlGF. Further research is needed to reconcile the role of PlGF in PH in SCD. DisclosuresTailor:Mesoscale: Employment.

Role for Chemokines in the Vasculopathy Associated with Sickle Cell Dsease and Pulmonary Hypertension

Sickle cell disease (SCD) is a hemolytic disorder characterized by transient vaso-occlusive crisis (VOC). Moreover, there is a high prevalence of SCD-associated pulmonary arterial hypertension (PAH), indicated by a tricuspid regurgitant jet velocity (TRV) ≥ 2.5 m/sec, leading to increased risk for early mortality. Monocytes have been proposed as pivotal cells in vascular inflammation in animal models of SCD. Preliminary studies in our group have shown a potential role for monocyte chemokines in the vasculopathy of SCD. The objective of this study is to investigate the role of two chemokines: regulated upon activation, normal T cell expressed and secreted (RANTES) and macrophage inflammatory protein-1β (MIP-1β) in SCD and SCD-associated PAH. Plasma samples were collected from patients with SCD at steady state and from healthy African-American control subjects. Plasma levels of RANTES and MIP-1β were measured using an enzyme immunoassay system. Patients with SCD exhibited significantly higher levels of both MIP-1β (median 465.3 vs. 398.5 pg/ml, p<0.0001) and RANTES (median 47774 vs. 17445pg/ml, p<0.0004) than healthy controls. Further characterization of SCD patients with or without PAH demonstrated that whereas MIP-1β exhibited no correlation with PAH, RANTES demonstrated an inverse correlation with PAH (r= −0.25, p<0.03) with significance achieved in patients that exhibited severe PAH (TRV> 2.9, p<0.05). These findings suggest thatboth chemokines, RANTES and MIP-1β, are associated with the vasculopathy of SCD, andwhereas MIP-1β does not appear to be associated with SCD-associated PAH, RANTES levels are inversely correlated to the severity of PAH. RANTES merits further investigation as a potential marker in PAH, and for a possible role in its progression.

High Risk of Vitamin D Deficiency in Children with Sickle Cell Disease

Vitamin D is a particularly concerning nutrient for children with homozygous SS sickle cell disease (SCD-SS) due to their increased skin melanin concentrations, reduced levels of physical activity, and poor vitamin D intake. The goal of this study was to compare the vitamin D status of children with SCD-SS to healthy African-American children living in the same geographic area. Growth, dietary intake, serum 25-hydroxyvitamin D [25(OH)D], and intact parathyroid hormone (iPTH) concentrations were measured in 61 African-American subjects with SCD-SS and 89 healthy African-American control subjects age 5 to 18 years from the Philadelphia, PA, region (latitude 39.95° N). Median serum 25(OH)D concentrations were 15 ng/mL (95% confidence interval [CI]: 13, 17) in subjects with SCD-SS and 21 ng/mL (95% CI: 18, 22) in healthy control subjects ( P<0.0002). Vitamin D deficiency [25(OH)D<11 mg/mL] was found in 33% of subjects with SCD-SS and 9% of healthy control subjects ( P<0.001); 25% of subjects with SCD-SS and 17% of healthy control subjects had elevated iPTH [(>59 ρg/mL), P<0.05]. Ninety-three percent of subjects with SCD-SS and 90% of healthy subjects had vitamin D insufficiency [25(OH)D<30 mg/mL]. The risk of vitamin D deficiency among subjects with SCD-SS was 5.3 (95% CI: 2.5, 8.2) times greater than control subjects, adjusted for season and age. Poor vitamin D status was prevalent in children with SCD-SS and healthy African-American children living in the same geographic area. However, children with SCD-SS were at greater risk for vitamin D deficiency than healthy African-American children.

Low Erythrocytic Glutathione Peroxidase-1 Activity Correlates with Hemolytic Rate in Patients with Sickle Cell Disease and Is Elevated on Hydroxyurea.

Background: Glutathione peroxidase-1 (GPX1) is the most significant catalytic antioxidant in the red cell. Congenital deficiency of GPX1 has been reported in association with hemolytic anemia due to oxidant stress. Hemolytic rate has been implicated in the development of sickle vasculopathy.Methods: Red cell pellets were collected from 32 patients with sickle cell disease and 17 healthy African American control subjects, and were stored frozen until assayed. A novel microplate immunoaffinity capture assay was used that measures both immunoreactive GPX1 protein and enzyme activity.Results: Patients with SCD had higher levels of red cell GPX1 activity than controls (2.42 ± 0.12 vs. 1.86 ± 0.15 units/mg red cell protein (mean ± SEM), p=0.006). GPX1 activity correlated with low reticulocyte count (r=−0.50, p=0.004)(Fig. 1A), low indirect bilirubin (r=–0.45, p=0.01) and high fetal hemoglobin expression (r=0.39, p=0.03). GPX1 activity in SCD patients on hydroxyurea was much higher than those not on hydroxyurea (2.75 ± 0.12, n=21 vs. 1.79 ± 0.13, n=11, p<0.001)(Fig. 1B), suggesting that hydroxyurea might induce GPX1 expression. In the patients off hydroxyurea, low GPX1 activity closely correlated with high serum lactate dehydrogenase level, a marker of high hemolytic rate (r=–0.85, p=0.002), suggesting that low GPX1 levels might contribute to rapid hemolytic rate. In a multivariate model, GPX1 was independently associated with reticulocyte count even when adjusted for fetal hemoglobin level.Conclusions: In addition to fetal hemoglobin, hydroxyurea may also induce expression of GPX1, a potent antioxidant that might have a role in decreasing hemolysis associated with the robust oxidant stress of SCD. This finding is consistent with previously published evidence of GPX1 induction by hydroxyurea in cancer cell lines, with increased antioxidant function. Additional studies are needed to confirm this phenomenon in a larger cohort of patients with SCD and to further evaluate the combined effect of fetal hemoglobin co-induction, but this finding suggests a potential mechanism by which hydroxyurea may produce clinical benefit in SCD even in the absence of significant fetal hemoglobin induction. [Display omitted]

Defects in Postabsorptive Plasma Homeostasis of Fatty Acids in Sickle Cell Disease

The chronic hemolytic anemia experienced by sickle cell disease (SCD) patients leads to adverse effects on oxygen transport by the blood and to a decrease in oxygen availability for peripheral tissues. Limited tissue oxygen availability has the potential to modify events of intracellular metabolism and, thus, alter lipid homeostasis. The impact of SCD on plasma fatty acid homeostasis was determined in 8 African American SCD patients and in 6 healthy African American control subjects under postabsorptive conditions and during a 3-hour IV infusion of a nutrient solution containing lipid, glucose, and amino acids. SCD patients had higher fasting levels of plasma nonesterified fatty acids (NEFA), triglycerides, and phospholipids than healthy controls. Similarly, SCD patients had higher fasting levels of fatty acids in plasma triglycerides and phospholipids than healthy controls. Infusion of nutrients resulted in equivalent plasma NEFA profiles, total NEFA, and triglycerides in SCD patients and controls. However, the plasma phospholipid concentrations and fatty acid composition of plasma triglycerides and phospholipids were significantly higher in SCD patients; in particular, plasma pools of oleic acid were consistently increased in SCD. Plasma free oleic acid levels were elevated basally, leading to increased oleic acid content in triglycerides and phospholipids both post absorptively and during nutrient infusion. There is an underlying defect in lipid metabolism associated with SCD best manifested during the fasting state. This abnormality in lipid homeostasis has the potential to alter red blood cell (RBC) membrane fluidity and function in SCD patients.

Arginine Metabolite Profiling in Sickle Cell Disease: Abnormal Levels and Correlations with Pulmonary Hypertension, Desaturation, Hemolysis and Organ Dysfunction.

Pulmonary arterial hypertension (PAH) in patients with sickle cell disease (SCD) is linked to intravascular hemolysis, renal dysfunction, systolic hypertension, cholestasis, and early mortality. Although the pathophysiology of PAH in SCD is multifactorial, one important and fundamental factor is impaired nitric oxide bioavailability. Severe intravascular hemolysis releases hemoglobin and arginase into blood plasma, leading to consumption of nitric oxide and its plasma precursor L-arginine, the obligate substrate for the nitric oxide synthases (NOS). In order to explore other potential alterations in the arginine pathway that might affect arginine bioavailability and nitric oxide production, we used high-performance liquid chromatography-tandem mass spectrometry to determine the plasma concentrations for several key metabolites that may affect NOS activity or arginine transport: asymmetric dimethylarginine (ADMA), symmetric dimethylarginine (SDMA), N-monomethyl-L-arginine (MMA), and N-ω-hydroxy-L-arginine (NOHA). Plasma levels of ADMA, SDMA and MMA are significantly higher in all forms of SCD than in healthy African American control subjects (Table 1). NOHA, the intermediate species in nitric oxide synthesis from L-arginine, is significantly lower in sickle-β-thalassemia (Sβ-thal) patients and homozygous SCD (SS). L-arginine levels are significantly lower in all forms of SCD, as previously reported.PAH as assessed by echocardiography screening was correlated to SDMA (r=0.30, p<0.0001) and NOHA (r=0.23, p=0.002). Similar correlations were observed to NT-proBNP, another marker of PAH. Low oxygen saturations were linked to high levels of all four arginine metabolites. ADMA levels were elevated with severe hemolysis, and unexpectedly lower with renal dysfunction. Levels of SDMA and NOHA were significantly related to renal dysfunction (p<0.01), with an additional link of NOHA to systemic hypertension (p<0.001). In addition, Cox proportional hazard analysis showed a relationship of the arginine/SDMA ratio to early mortality (p<0.001).In summary, levels of the endogenous NOS inhibitor ADMA are highly elevated in SCD and linked to hemolysis, and may contribute to hemolysis-associated endothelial dysfunction. The levels of SDMA, a competitive inhibitor of arginine transport and intracellular bioavailability, are also elevated and linked to PAH, desaturation, renal dysfunction and early mortality risk. The low levels of arginine and NOHA in SCD are consistent with low substrate availability for NOS, and may also limit NO production. The role of arginine metabolites in dysregulation of the arginine-nitric oxide axis and pulmonary hypertension in SCD merits further investigation.Table 1Arginine Metabolites in Sickle Cell Disease compared to controls.MetaboliteControl (n=29)SC (n=34)Sβ-thal (n=11)SS (n=130)ADMA0.310.82***0.92*0.99***SDMA0.830.92*1.03**1.03***MMA0.130.15*0.20**0.18***NOHA2.502.232.15*1.80**L-Arginine78.351.5***41.6***45.5***Values indicate median values in μM. *p<0.05; **p<0.01; ***p<0.001, Mann-Whitney test compared to controls.

Protein turnover and energy expenditure increase during exogenous nutrient availability in sickle cell disease

In the present study, energy expenditure (EE) and rates of whole-body protein, glucose, and lipid metabolism were assessed in 8 African American sickle cell disease (SCD) patients and in 6 healthy African American control subjects during the infusion of amino acids, glucose, and lipid. Whole-body protein, glucose, and lipid kinetics were estimated by using L-[1-(13)C]leucine, D-[6,6-(2)H2]glucose, and [(2)H5]glycerol, respectively. After a 2-h tracer equilibration period and a 0.5-h basal period, nutrients were administered intravenously for 3 h with 16% of the energy as protein, 52% as carbohydrate, and 32% as fat. Breath and blood were collected during the last 30 min of nutrient infusion and EE was measured by indirect calorimetry. EE was 14% greater (P < or = 0.05) in SCD patients [145.0 +/- 3.5 kJ x kg fat-free mass (FFM)(-1) x d(-1)] than in control subjects (126.8 +/- 3.8 kJ x kg FFM(-1) x d(-1)). Whole-body protein breakdown (4.4 +/- 0.4 compared with 3.1 +/- 0.1 mg x kg FFM(-1) x min(-1), P < or = 0.05) and protein synthesis (4.6 +/- 0.4 compared with 3.2 +/- 0.1 g x kg FFM(-1) x min(-1), P < or = 0.05) were 42% and 44% greater, respectively, in the SCD patients than in control subjects, but whole-body amino acid oxidation (0.90 +/- 0.05 compared with 1.03 +/- 0.09 mg x kg FFM(-1) x min(-1)) was not significantly different between the 2 groups. Whole-body glucose and lipid kinetics did not differ significantly between the groups. EE increased in SCD patients during exogenous nutrient availability, and the additional energy required for the accelerated rates of whole-body protein breakdown and synthesis made a significant contribution to the increase in EE. These metabolic aberrations may increase the dietary energy and protein requirements of SCD patients.