Renal nitric oxide synthases in transgenic sickle cell mice

Mouse models of sickle cell disease: Imperfect and yet very informative

The root cause of sickle cell disease (SCD) has been known for nearly a century, however, few therapies to treat the disease are available. Over several decades of work, with advances in gene editing technology and after several iterations of mice with differing genotype/phenotype relationships, researchers have developed humanized SCD mouse models. However, while a large body of preclinical studies has led to huge gains in basic science knowledge about SCD in mice, this knowledge has not led to the development of effective therapies to treat SCD-related complications in humans, thus leading to frustration with the paucity of translational progress in the SCD field. The use of mouse models to study human diseases is based on the genetic and phenotypic similarities between mouse and humans (face validity). The Berkeley and Townes SCD mice express only human globin chains and no mouse hemoglobin. With this genetic composition, these models present many phenotypic similarities, but also significant discrepancies that should be considered when interpreting preclinical studies results. Reviewing genetic and phenotypic similarities and discrepancies and examining studies that have translated to humans and those that have not, offer a better perspective of construct, face, and predictive validities of humanized SCD mouse models.

Glomerular filtration rate abnormalities in sickle cell disease

Sickle cell disease (SCD) is a group of inherited blood disorders affecting the β-globin gene, resulting in the polymerization of hemoglobin and subsequent sickling of the red blood cell. Renal disease, the most common complication in SCD, begins in childhood with glomerular hyperfiltration and then progresses into albuminuria, a fast decline of glomerular filtration, and renal failure in adults. This mini-review focuses on glomerular filtration abnormalities and the mechanisms of hyperfiltration, explores genetic modifiers and methods of estimating glomerular filtration rates, and examines novel biomarkers of glomerular filtration in SCD.

Nitric oxide and sickle cell disease-Is there a painful connection?

Sickle cell disease is the most common hemoglobinopathy and affects millions worldwide. The disease is associated with severe organ dysfunction, acute and chronic pain, and significantly decreased life expectancy. The large body of work demonstrating that hemolysis results in rapid consumption of the endogenous vasodilator nitric oxide, decreased nitric oxide production, and promotion of vaso-occlusion provides the basis for the hypothesis that nitric oxide bioavailability is reduced in sickle cell disease and that this deficit plays a role in sickle cell disease pain. Despite initial promising results, large clinical trials using strategies to increase nitric oxide bioavailability in sickle cell disease patients yielded no significant change in duration or frequency of acute pain crises. Further, recent investigations showed that sickle cell disease patients and mouse models have elevated baseline levels of blood nitrite, a reservoir for nitric oxide formation and a product of nitric oxide metabolism, regardless of pain phenotype. These conflicting results challenge the hypotheses that nitric oxide bioavailability is decreased and that it plays a significant role in the pathogenesis in sickle cell disease acute pain crises. Conversely, a large body of work demonstrates that nitric oxide, as a neurotransmitter, has a complex role in pain neurobiology, contributes to the development of central sensitization, and can mediate hyperalgesia in inflammatory and neuropathic pain. These results support an alternative hypothesis: one proposing that altered nitric oxide signaling may contribute to the development of neuropathic and/or inflammatory pain in sickle cell disease through its role as a neurotransmitter.

Decoding the role of SOD2 in sickle cell disease

Sickle cell disease (SCD) is an inherited hemoglobinopathy caused by a single point mutation in the β-globin gene. As a consequence, deoxygenated hemoglobin polymerizes triggering red blood cell sickling and hemolysis, vaso-occlusion, and ischemia/reperfusion. Allied to these pathologies is the overproduction of reactive oxygen species driven by hemoglobin Fenton chemistry and peroxidase reactions as well as by secondary activation of vascular oxidases, including NAD(P)H oxidase and xanthine oxidase. In addition, hypoxia, produced by sickle red blood cell occlusion, disrupts mitochondrial metabolism and generates excess superoxide through electron leak from the mitochondrial respiratory chain. Superoxide dismutase 2 (SOD2) is a mitochondrial-specific antioxidant enzyme that dismutates superoxide to hydrogen peroxide, which is then converted to water by catalase and glutathione peroxidase. In SCD, the antioxidant defense system is significantly diminished through decreased expression and activity levels of antioxidant enzymes, including superoxide dismutase, catalase, and glutathione peroxidase. From a translational perspective, genetic variants including a missense variant in SOD2 (valine to alanine at position 16) are present in 45% of people with African ancestry and are associated with increased sickle complications. While it is known that there is an imbalance between oxidative species and antioxidant defenses in SCD, much more investigation is warranted. This review summarizes our current understanding of antioxidant defense systems in SCD, particularly focused on SOD2, and provides insight into challenges and opportunities as the field moves forward.

Impact of ET-1 and sex in glomerular hyperfiltration in humanized sickle cell mice

Hyperfiltration, highly prevalent early in sickle cell disease (SCD), is in part driven by an increase in ultrafiltration coefficient (K_f). The increase in K_f may be due to enlarged filtration surface area and/or increased glomerular permeability (P_alb). Previous studies have demonstrated that endothelin-1 (ET-1) contributes to P_alb changes in models of diabetes and SCD. Thus, we performed longitudinal studies of renal function to determine the relationship between ET-1 and glomerular size and P_alb that may contribute to hyperfiltration in humanized sickle cell (HbSS) and control (HbAA) mice at 8-32 weeks of age. HbSS mice were characterized by significant increases in plasma and glomerular ET-1 expression in both sexes although this increase was significantly greater in males. HbSS glomeruli of both males and females presented with a progressive and significant increase in glomerular size, volume, and K_f During the onset of hyperfiltration, plasma and glomerular ET-1 expression were associated with a greater increase in glomerular size and K_f in HbSS mice, regardless of sex. The pattern of P_alb augmentation during the hyperfiltration was also associated with an increase in glomerular ET-1 expression, in both male and female HbSS mice. However, the increase in P_alb was significantly greater in males and delayed in time in females. Additionally, selective endothelin A receptor (ET_A) antagonist prevented hyperfiltration in HbSS, regardless of sex. These results suggest that marked sex disparity in glomerular hyperfiltration may be driven, in part, by ET-1-dependent ultra-structural changes in filtration barrier components contributing to glomerular hyperfiltration in HbSS mice.

Sickle cell disease up-regulates vasopressin, aquaporin 2, urea transporter A1, Na-K-Cl cotransporter 2, and epithelial Na channels in the mouse kidney medulla despite compromising urinary concentration ability

Sickle cell disease (SCD)-induced urinary concentration defect has been proposed as caused by impaired ability of the occluded vasa recta due to red blood cell sickling to serve as countercurrent exchangers and renal tubules to absorb water and solutes. However, the exact molecular mechanisms remain largely unknown. The present studies were undertaken to determine the effects of SCD on vasopressin, aquaporin2 (AQP2), urea transporter A1 (UTA1), Na-K-Cl co-transporter 2 (NKCC2), epithelial Na channels (ENaC), aquaporin1 (AQP1), nuclear factor of activated T cells 5 (NFAT5) and Src homology region-2 domain-containing phosphatase-1 (SHP-1), an important regulator of NFAT5, in the Berkeley SCD mouse kidney medulla. Under water repletion, SCD only induced a minor urinary concentration defect associated with increased urinary vasopressin level alone with the well-known effects of vasopressin: protein abundance of AQP2, UTA1 and ENaC-β and apical targeting of AQP2 as compared with non-SCD. SCD did not significantly affect AQP1 protein level. Water restriction had no further significant effect on SCD urinary vasopressin. NFAT5 is also critical to urinary concentration. Instead, water restriction-activated NFAT5 associated with inhibition of SHP-1 in the SCD mice. Yet, water restriction only elevated urinary osmolality by 28% in these mice as opposed to 104% in non-SCD mice despite similar degree increases of protein abundance of AQP2, NKCC2 and AQP2-S256-P. Water-restriction had no significant effect on protein abundance of ENaC or AQP1 in either strain. In conclusion, under water repletion SCD, only induces a minor defect in urinary concentration because of compensation from the up-regulated vasopressin system. However, under water restriction, SCD mice struggle to concentrate urine despite activating NFAT5. SCD-induced urinary concentration defect appears to be resulted from the poor blood flow in vasa recta rather than the renal tubules' ability to absorb water and solutes.

Progressive glomerular and tubular damage in sickle cell trait and sickle cell anemia mouse models

Homozygosity for the hemoglobin (Hb) S mutation (HbSS, sickle cell anemia) results in hemoglobin polymerization under hypoxic conditions leading to vaso-occlusion and hemolysis. Sickle cell anemia affects 1:500 African Americans and is a strong risk factor for kidney disease, although the mechanisms are not well understood. Heterozygous inheritance (HbAS; sickle cell trait) affects 1:10 African Americans and is associated with an increased risk for kidney disease in some reports. Using transgenic sickle mice, we investigated the histopathologic, ultrastructural, and gene expression differences with the HbS mutation. Consistent with progressive glomerular damage, we observed progressively greater urine protein concentrations (P = 0.03), glomerular hypertrophy (P = 0.002), and glomerular cellularity (P = 0.01) in HbAA, HbAS, and HbSS mice, respectively. Ultrastructural studies demonstrated progressive podocyte foot process effacement, glomerular basement membrane thickening with reduplication, and tubular villous atrophy with the HbS mutation. Gene expression studies highlighted the differential expression of several genes involved in prostaglandin metabolism (AKR1C18), heme and iron metabolism (HbA-A2, HMOX1, SCL25A37), electrolyte balance (SLC4A1, AQP6), immunity (RSAD2, C3, UBE2O), fatty acid metabolism (FASN), hypoxia hall-mark genes (GCK, SDC3, VEGFA, ETS1, CP, BCL2), as well as genes implicated in other forms of kidney disease (PODXL, ELMO1, FRMD3, MYH9, APOA1). Pathway analysis highlighted increased gene enrichment in focal adhesion, extracellular matrix-receptor interaction, and axon guidance pathways. In summary, using transgenic sickle mice, we observed that inheritance of the HbS mutation is associated with glomerular and tubular damage and identified several candidate genes and pathways for future investigation in sickle cell trait and sickle cell anemia-related kidney disease.

Synthetic oligosaccharides can replace animal-sourced low-molecular weight heparins

Low-molecular weight heparin (LMWH) is used clinically to treat clotting disorders. As an animal-sourced product, LMWH is a highly heterogeneous mixture, and its anticoagulant activity is not fully reversible by protamine. Furthermore, the reliability of the LMWH supply chain is a concern for regulatory agencies. We demonstrate the synthesis of heparin dodecasaccharides (12-mers) at the gram scale. In vitro experiments demonstrate that the anticoagulant activity of the 12-mers could be reversed using protamine. One of these, labeled as 12-mer-1, reduced the size of blood clots in the mouse model of deep vein thrombosis and attenuated circulating procoagulant markers in the mouse model of sickle cell disease. An ex vivo experiment demonstrates that the anticoagulant activity of 12-mer-1 could be reversed by protamine. 12-mer-1 was also examined in a nonhuman primate model to determine its pharmacodynamic parameters. A 7-day toxicity study in a rat model showed no toxic effects. The data suggest that a synthetic homogeneous oligosaccharide can replace animal-sourced LMWHs.

Association between oxidative stress and vascular reactivity in children with sickle cell anaemia and sickle haemoglobin C disease

Oxidative stress and haemolysis-associated nitric oxide (NO) depletion plays a crucial role in the development of vasculopathy in sickle cell anaemia (SS). However it remains unknown whether oxidative stress and haemolysis levels influence vascular function in patients with sickle haemoglobin C disease (SC). Microvascular response to heat (using Laser Doppler flowmetry on finger), oxidative stress biomarkers, NO metabolites, endothelin-1 and haematological parameters were compared between patients with SS and SC. Vascular function, oxidative and nitrosative markers were also measured in healthy (AA) children. SS and SC had increased plasma advanced oxidation protein products (AOPP), malondialdehyde, plasma antioxidant activities and NO end products, compared to AA. SC had lower catalase activity compared to AA and SS. Haemolytic rate, glutathione peroxidase and nitrotyrosine concentrations were significantly increased in children with SS compared to SC and AA. SS and SC had impaired microvascular reactivity compared to AA. In SS, the plateau phase of the response to local thermal heating was negatively associated with nitrotyrosine and AOPP. No association between vascular function parameters and oxidative stress markers was observed in SC. Mild haemolysis in SC, compared to SS, may limit oxidative and nitrosative stress and could explain the better preserved microvascular function in this group.

Acquired Amino Acid Deficiencies: A Focus on Arginine and Glutamine

Nonessential amino acids are synthesized de novo and therefore not diet dependent. In contrast, essential amino acids must be obtained through nutrition since they cannot be synthesized internally. Several nonessential amino acids may become essential under conditions of stress and catabolic states when the capacity of endogenous amino acid synthesis is exceeded. Arginine and glutamine are 2 such conditionally essential amino acids and are the focus of this review. Low arginine bioavailability plays a pivotal role in the pathogenesis of a growing number of varied diseases, including sickle cell disease, thalassemia, malaria, acute asthma, cystic fibrosis, pulmonary hypertension, cardiovascular disease, certain cancers, and trauma, among others. Catabolism of arginine by arginase enzymes is the most common cause of an acquired arginine deficiency syndrome, frequently contributing to endothelial dysfunction and/or T-cell dysfunction, depending on the clinical scenario and disease state. Glutamine, an arginine precursor, is one of the most abundant amino acids in the body and, like arginine, becomes deficient in several conditions of stress, including critical illness, trauma, infection, cancer, and gastrointestinal disorders. At-risk populations are discussed together with therapeutic options that target these specific acquired amino acid deficiencies.

New strategies for the treatment of pulmonary hypertension in sickle cell disease : the rationale for arginine therapy

Nitric oxide (NO) is inactivated in sickle cell disease (SCD), while bioavailability of arginine, the substrate for NO synthesis, is diminished. Impaired NO bioavailability represents the central feature of endothelial dysfunction, and is a key factor in the pathophysiology of SCD. Inactivation of NO correlates with the hemolytic rate and is associated with erythrocyte release of cell-free hemoglobin and arginase during hemolysis. Accelerated consumption of NO is enhanced further by the inflammatory environment of oxidative stress that exists in SCD. Based upon its critical role in mediating vasodilation and cell growth, decreased NO bioavailability has also been implicated in the pathogenesis of pulmonary arterial hypertension (PHT). Secondary PHT is a common life-threatening complication of SCD that also occurs in most hereditary and chronic hemolytic disorders. Aberrant arginine metabolism contributes to endothelial dysfunction and PHT in SCD, and is strongly associated with prospective patient mortality. The central mechanism responsible for this metabolic disorder is enhanced arginine turnover, occurring secondary to enhanced plasma arginase activity. This is consistent with a growing appreciation of the role of excessive arginase activity in human diseases, including asthma and PHT. Decompartmentalization of hemoglobin into plasma consumes endothelial NO and thus drives a metabolic requirement for arginine, whose bioavailability is further limited by arginase activity. New treatments aimed at maximizing both arginine and NO bioavailability through arginase inhibition, suppression of hemolytic rate, or oral arginine supplementation may represent novel therapeutic strategies.

[Kidney and hemoglobinopathy]

Sickle-cell disease (SCD), one of the most common severe monogenic disorders into the world, is associated with an increased frequency of chronic kidney disease. SCD is caused by a point mutation in the gene encoding β globin gene which leads to the formation of hemoglobin S that polymerises after deoxygenation. HbS polymerisation is associated with erythrocyte rigidity and vaso-occlusive episodes that play a central role into SCD pathogenesis. The spectrum of renal diseases during SCD is broad and includes various renal manifestations which become more apparent with increasing age. Underlying pathophysiological processes involved in sickle cell nephropathy are multifactorial but endothelial dysfunction related to chronic hemolysis is a key factor contributing to renal involvement. Our review focuses on the pathogenesis and on the spectrum of renal manifestations occurring in SCD patients.

Novel marker for the detection of sickle cell nephropathy: soluble FMS-like tyrosine kinase-1 (sFLT-1)

BACKGROUND

Given the burden and poor outcome of end-stage renal disease in sickle cell disease (SCD), early markers of sickle cell nephropathy (SN) are desirable. Disordered angiogenesis underlies many complications of SCD. We aimed to determine the relationship between serum FMS-like tyrosine kinase-1 (sFLT-1) and other biomarkers of renal damage for the early diagnosis of SN.

METHODS

Forty-seven SCD patients and 49 healthy controls were enrolled. Microalbuminuria was determined in patient urine samples. Blood samples were tested for sFLT-1, serum creatinine, and various hemolysis and inflammation markers. Peripheral blood monocyte expression of sFLT-1 was measured using real-time polymerase chain reaction (PCR).

RESULTS

The serum level of sFLT-1 (pg/ml) in SCD patients was higher than controls (median/range/IQR = 142/ 60-1300/61 pg/ml vs. 125/ 110-187/52 pg/ml, respectively) (p = 0.006). Median (range) of sFLT-1 level was higher in SCD patients with microalbuminuria compared to SCD patients with normoalbuminuria, 185 (140-1300) vs. 125 (60-189) mg/g, respectively) (p = 0.004). There was a significant positive correlation between serum sFLT-1 and microalbuminuria, lactate dehydrogenase (LDH), and indirect bilirubin (r = 0.59, 0.39, 0.30, and p = <0.001, 0.007, 0.041, respectively). sFLT-1 sensitivity in early detection of renal affection in SCD was 93.6%, while specificity was 68.6%. Finally, peripheral blood monocytes (PBM) sFLT-1 expression was significantly higher in SCD patients compared to controls (p = 0.05).

CONCLUSIONS

sFLT-1 may contribute to pathogenesis of albuminuria in SCD patients and constitute a novel renal biomarker of SN.

Doppler assessment of renal hemodynamic alterations in homozygous sickle cell disease and sickle Beta-thalassemia

We evaluated the renal vascular indices in children and adolescents with sickle cell disease (SCD) using Doppler ultrasonography. We also assessed the renal hemodynamics alterations in patients with homozygous SCD and sickle beta-thalassemia (sickle β-thalassemia). We studied 75 patients (age range = 3-20 years; M = 9.95 ± 4.15) with SCD: 42 patients suffering from homozygous SCD and 33 patients diagnosed with sickle β-thalassemia. Thirty, age- and sex-matched, normal subjects were also included as a control group. Both patients and control groups had Doppler assessment of pulsatility (PI) and resistivity (RI) indices of main renal, segmental, interlobar, and arcuate arteries. Both PIs and RIs were significantly higher in SCD patients, compared with the control group. Among patients, PIs and RIs in the main renal, segmental, interlobar, and arcuate arteries were significantly higher in patients with homozygous SCD as compared with those with sickle β-thalassemia (p values <0.01, <0.001, <0.001, and <0.001 for PIs and <0.001, <0.001, <0.001, and <0.01 for RIs, respectively). We concluded that renal vascular resistance is raised in children and adolescents with SCD. This is more pronounced in patients with homozygous SCD as compared with those with sickle β-thalassemia.

Does nephrotoxicity exist in pediatric epileptic patients on valproate or carbamazepine therapy?

The aim of this study was to investigate the effects of valproate and carbamazepine, on renal glomerular and tubular functions. The patient group comprised 54 children with new-onset epilepsy treated with valproate (n = 30) and carbamazepine (n = 24). Twenty-six healthy children were in the control group. The serum creatinine and cystatin C levels and urinary excretion of N-acetyl-β-d-glucosaminidase (NAG) levels were measured and the glomerular filtration rate (GFR) was estimated. Serum creatinine and cystatin C concentrations were not different between patients and controls. The glomerular filtration rate of the patient groups were higher than those of the control group. Thus, both drugs probably lead to glomerular hyperfiltration and toxicity for glomerular functions. However, urinary N-acetyl-β-d-glucosaminidase/creatinine levels were significantly higher in patients receiving only valproate (6.1 ± 5). The difference between carbamazepine and control groups was not significant for urinary N-acetyl-β-d-glucosaminidase/creatinine levels. Our data suggest that valproate has adverse effects on renal tubular functions.

Sickle cell disease: renal manifestations and mechanisms

Sickle cell disease (SCD) substantially alters renal structure and function, and causes various renal syndromes and diseases. Such diverse renal outcomes reflect the uniquely complex vascular pathobiology of SCD and the propensity of red blood cells to sickle in the renal medulla because of its hypoxic, acidotic, and hyperosmolar conditions. Renal complications and involvement in sickle cell nephropathy (SCN) include altered haemodynamics, hypertrophy, assorted glomerulopathies, chronic kidney disease, acute kidney injury, impaired urinary concentrating ability, distal nephron dysfunction, haematuria, and increased risks of urinary tract infections and renal medullary carcinoma. SCN largely reflects an underlying vasculopathy characterized by cortical hyperperfusion, medullary hypoperfusion, and an increased, stress-induced vasoconstrictive response. Renal involvement is usually more severe in homozygous disease (sickle cell anaemia, HbSS) than in compound heterozygous types of SCD (for example HbSC and HbSβ(+)-thalassaemia), and is typically mild, albeit prevalent, in the heterozygous state (sickle cell trait, HbAS). Renal involvement contributes substantially to the diminished life expectancy of patients with SCD, accounting for 16-18% of mortality. As improved clinical care promotes survival into adulthood, SCN imposes a growing burden on both individual health and health system costs. This Review addresses the renal manifestations of SCD and focuses on their underlying mechanisms.

High red blood cell nitric oxide synthase activation is not associated with improved vascular function and red blood cell deformability in sickle cell anaemia

Human red blood cells (RBC) express an active and functional endothelial-like nitric oxide (NO) synthase (RBC-NOS). We report studies on RBC-NOS activity in sickle cell anaemia (SCA), a genetic disease characterized by decreased RBC deformability and vascular dysfunction. Total RBC-NOS content was not significantly different in SCA patients compared to healthy controls; however, using phosphorylated RBC-NOS-Ser(1177) as a marker, RBC-NOS activation was higher in SCA patients as a consequence of the greater activation of Akt (phosphorylated Akt-Ser(473) ). The higher RBC-NOS activation in SCA led to higher levels of S-nitrosylated α- and β-spectrins, and greater RBC nitrite and nitrotyrosine levels compared to healthy controls. Plasma nitrite content was not different between the two groups. Laser Doppler flowmetric experiments demonstrated blunted microcirculatory NO-dependent response under hyperthermia in SCA patients. RBC deformability, measured by ektacytometry, was reduced in SCA in contrast to healthy individuals, and pre-shearing RBC in vitro did not improve deformability despite an increase of RBC-NOS activation. RBC-NOS activation is high in freshly drawn blood from SCA patients, resulting in high amounts of NO produced by RBC. However, this does not result in improved RBC deformability and vascular function: higher RBC-NO is not sufficient to counterbalance the enhanced oxidative stress in SCA.

Hepatic inducible nitric oxide synthase expression increases upon exposure to hypergravity

Stimulation by a number of conditions, including infection, cytokines, mechanical injury, and hypoxia, can upregulate inducible nitric oxide synthase (iNOS) in hepatocytes. We observed that exposure to hypergravity significantly upregulated the transcription of the hepatic iNOS gene. The aim of this study was to confirm our preliminary data, and to further investigate the distribution of the iNOS protein in the livers of mice exposed to hypergravity. ICR mice were exposed to +3 Gz for 1 h. We investigated the time course of change in the iNOS expression. Hepatic iNOS mRNA expression progressively increased in centrifuged mice from 0 to 12 h, and then decreased rapidly by 18 h. iNOS mRNA levels in the livers of centrifuged mice was significantly higher at 3, 6, and 12 h than in uncentrifuged control mice. The pattern of iNOS protein expression paralleled that of the mRNA expression. At 0 and 1 h, weak cytoplasmic iNOS immunoreactivity was found in some hepatocytes surrounding terminal hepatic venules. It was noted that at 6 h there was an increase in the number of perivenular hepatocytes with moderate to strong cytoplasmic immunoreactivity. The number of iNOS-positive hepatocytes was maximally increased at 12 h. The majority of positively stained cells showed a strong intensity of iNOS expression. The expression levels of iNOS mRNA and protein were significantly increased in the livers of mice exposed to hypergravity. These results suggest that exposure to hypergravity significantly upregulates iNOS at both transcriptional and translational levels.

Renal function in children suffering from sickle cell disease: challenge of early detection in highly resource-scarce settings

Background

The prevalence of Sickle cell disease is extremely high in Democratic Republic of Congo. Despite this high prevalence of the disease, data on renal abnormalities in children are rare.

Method

The study proposed to assess blood pressure, glomerular function, urea and uric acid levels in 65 steady state Congolese children with homozygous sickle cell disease and 67 normal controls.

Results

In Hb-SS group, blood pressure level tended to be lower than Hb-AA groups but there was no statistically significant difference (p>0.05) between the two groups. The absolute values for GFR corrected for BSA were significantly higher in Hb-SS group compared to Hb-AA group (130.5±34.1 ml/min/1.73 m² vs 113.7±24.5 ml/min/1.73 m²; p = 0.004). Children with Hb-SS were more likely to hyperfiltrate (30.8% of subjects) than children with Hb-AA (6.1% of subjects). Proteinuria was found in 4 (6.2%) children with Hb-SS. Uric acid level was significantly increased in children with Hb-SS compared to corresponding values in control group (4.4±1.3 mg/dl vs 3.5±1.1 mg/dl; p<0.001). Urea level was significantly decreased compared to corresponding values in Hb-AA group (15.3±8.3 mg/dl vs 22.9±10.1 mg/dl; p<0.001).

Conclusion

Hyperfiltration, low creatinine, lower urea and high uric acid are more common in children with sickle cell disease than in normal controls.

Development of a physiologically-based pharmacokinetic model of the rat central nervous system

Central nervous system (CNS) drug disposition is dictated by a drug's physicochemical properties and its ability to permeate physiological barriers. The blood-brain barrier (BBB), blood-cerebrospinal fluid barrier and centrally located drug transporter proteins influence drug disposition within the central nervous system. Attainment of adequate brain-to-plasma and cerebrospinal fluid-to-plasma partitioning is important in determining the efficacy of centrally acting therapeutics. We have developed a physiologically-based pharmacokinetic model of the rat CNS which incorporates brain interstitial fluid (ISF), choroidal epithelial and total cerebrospinal fluid (CSF) compartments and accurately predicts CNS pharmacokinetics. The model yielded reasonable predictions of unbound brain-to-plasma partition ratio (Kpuu,brain) and CSF:plasma ratio (CSF:Plasmau) using a series of in vitro permeability and unbound fraction parameters. When using in vitro permeability data obtained from L-mdr1a cells to estimate rat in vivo permeability, the model successfully predicted, to within 4-fold, Kpuu,brain and CSF:Plasmau for 81.5% of compounds simulated. The model presented allows for simultaneous simulation and analysis of both brain biophase and CSF to accurately predict CNS pharmacokinetics from preclinical drug parameters routinely available during discovery and development pathways.

Hydroxyurea treatment decreases glomerular hyperfiltration in children with sickle cell anemia

Glomerular hyperfiltration and microalbuminuria/proteinuria are early manifestations of sickle nephropathy. The effects of hydroxyurea therapy on these renal manifestations of sickle cell anemia (SCA) are not well defined. Our objective was to investigate the effects of hydroxyurea on glomerular filtration rate (GFR) measured by (99m)Tc-DTPA clearance, and on microalbuminuria/proteinuria in children with SCA. Hydroxyurea study of long-term effects (HUSTLE) is a prospective study (NCT00305175) with the goal of describing the long-term cellular, molecular, and clinical effects of hydroxyurea therapy in SCA. Glomerular filtration rate, urine microalbumin, and serum cystatin C were measured before initiating hydroxyurea therapy and then repeated after 3 years. Baseline and Year 3 values for HUSTLE subjects were compared using the Wilcoxon Signed Rank test. Associations between continuous variables were evaluated using Spearman correlation coefficient. Twenty-three children with SCA (median age 7.5 years, range, 2.5-14.0 years) received hydroxyurea at maximum tolerated dose (MTD, 24.4 ± 4.5 mg/kg/day, range, 15.3-30.6 mg/kg/day). After 3 years of treatment, GFR measured by (99m)Tc-DTPA decreased significantly from 167 ± 46 mL/min/1.73 m² to 145 ± 27 mL/min/1.73 m² (P = 0.016). This decrease in GFR was significantly associated with increase in fetal hemoglobin (P = 0.042) and decrease in lactate dehydrogenase levels (P = 0.035). Urine microalbumin and cystatin C levels did not change significantly. Hydroxyurea at MTD is associated with a decrease in hyperfiltration in young children with SCA.

Sickle cell disease, vasculopathy, and therapeutics

Sickle cell disease (SCD) is caused by a mutation in both beta globin genes, resulting in chronic hemolysis and multiorgan disease that ultimately leads to premature death. Although hemoglobin S (HbS) polymerization and vaso-occlusion are central to the pathogenesis of SCD, overlapping pathways implicated in SCD-related endothelial dysfunction include hemolysis, defects in nitric oxide metabolism, ischemia-reperfusion injury, oxidative stress, increased cell-to-cell adhesion, and proinflammatory and coagulation mediators. Progression of organ-specific vasculopathy often precedes organ dysfunction and may provide targets for therapeutic intervention. SCD-related vasculopathies include, but are not limited to, moyamoya that often precedes cerebral infarcts or hemorrhage, proliferative retinopathy prior to loss of eyesight, pulmonary vasculopathy associated with pulmonary hypertension, and renal vasculopathy prior to the onset of chronic renal disease. This review evaluates evidence that SCD vasculopathy is a harbinger for organ dysfunction and reviews the potential for targeted antivasculopathy therapies.

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

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

Sickle cell nephropathy: challenging the conventional wisdom

This review explores the current model of sickle cell nephropathy and the limitations of the model. Renal abnormalities are common complications of sickle cell disease (SCD). Beginning in childhood, patients with SCD develop a urinary concentrating defect resulting in polyuria and a predisposition to nocturnal enuresis and dehydration. The current model of sickle cell nephropathy suggests that destruction of the renal medulla induces production of renal vasodilating substances that feedback to the glomerulus causing hyperfiltration. Hyperfiltration leads to glomerulosclerosis and proteinuria, with eventual reduction in kidney function. The crucial steps of vasodilating substance production and hyperfiltration in children with SCD have not been proven. Treatment of sickle cell nephropathy is aimed at the reduction of proteinuria with angiotensin converting enzyme inhibitors or angiotensin receptor blockers. Hydroxyurea and chronic transfusion therapy may also alter the progression of sickle cell nephropathy in children. Further studies are needed to identify an accurate model and effective treatments for sickle cell nephropathy.

Transient receptor potential vanilloid 1 mediates pain in mice with severe sickle cell disease

Pain is the leading cause of emergency department visits, hospitalizations, and daily suffering in individuals with sickle cell disease (SCD). The pathologic mechanisms leading to the perception of pain during acute RBC sickling episodes and development of chronic pain remain poorly understood and ineffectively treated. We provide the first study that explores nociceptor sensitization mechanisms that contribute to pain behavior in mice with severe SCD. Sickle mice exhibit robust behavioral hypersensitivity to mechanical, cold, and heat stimuli. Mechanical hypersensitivity is further exacerbated when hypoxia is used to induce acute sickling. Behavioral mechanical hypersensitivity is mediated in part by enhanced excitability to mechanical stimuli at both primary afferent peripheral terminal and sensory membrane levels. In the present study, inhibition of the capsaicin receptor transient receptor potential vanilloid 1 (TRPV1) with the selective antagonist A-425619 reversed the mechanical sensitization at both primary afferent terminals and isolated somata, and markedly attenuated mechanical behavioral hypersensitivity. In contrast, inhibition of TRPA1 with HC-030031 had no effect on mechanical sensitivity. These results suggest that the TRPV1 receptor contributes to primary afferent mechanical sensitization and a substantial portion of behavioral mechanical hypersensitivity in SCD mice. Therefore, TRPV1-targeted compounds that lack thermoregulatory side effects may provide relief from pain in patients with SCD.

Early and prominent alterations in hemodynamics, signaling, and gene expression following renal ischemia in sickle cell disease

Acute ischemic insults to the kidney are recognized complications of human sickle cell disease (SCD). The present study analyzed in a transgenic SCD murine model the early renal response to acute ischemia. Renal hemodynamics were profoundly impaired following ischemia in sickle mice compared with wild-type mice: glomerular filtration rate, along with renal plasma flow and blood flow rates, were markedly reduced, while renal vascular resistances were increased more than threefold in sickle mice following ischemia. In addition to these changes in renal hemodynamics, there were profound disturbances in renal signaling processes: phosphorylation of members of the MAPK and Akt signaling proteins occurred in the kidney in wild-type mice after ischemia, whereas such phosphorylation did not occur in the kidney in sickle mice after ischemia. ATP content in the postischemic kidney in sickle mice was less than half that observed in wild-type mice. Examination of the expression of candidate genes uncovered changes that may predispose to increased sensitivity of the kidney in sickle mice to ischemia: increased expression of inducible nitric oxide synthase and decreased expression of endothelial nitric oxide synthase, and increased expression of TNF-alpha. Inducibility of anti-inflammatory, cytoprotective genes, such as heme oxygenase-1 and IL-10, was not impaired in sickle mice after ischemia. We conclude that the kidney in SCD is remarkably vulnerable to acute ischemic insults. We speculate that such sensitivity of the kidney to ischemia in SCD may underlie the occurrence of acute kidney injury in patients with SCD and may set the stage for the emergence of chronic kidney disease in SCD.

Nitric oxide and arginine dysregulation: a novel pathway to pulmonary hypertension in hemolytic disorders

Secondary pulmonary hypertension (PH) is emerging as one of the leading causes of mortality and morbidity in patients with hemolytic anemias such as sickle cell disease (SCD) and thalassemia. Impaired nitric oxide (NO) bioavailability represents the central feature of endothelial dysfunction, and is a major factor in the pathophysiology of PH. Inactivation of NO correlates with hemolytic rate and is associated with the erythrocyte release of cell-free hemoglobin, which consumes NO directly, and the simultaneous release of the arginine-metabolizing enzyme arginase, which limits bioavailability of the NO synthase substrate arginine during the process of intravascular hemolysis. Rapid consumption of NO is accelerated by oxygen radicals that exists in both SCD and thalassemia. A dysregulation of arginine metabolism contributes to endothelial dysfunction and PH in SCD, and is strongly associated with prospective patient mortality. The central mechanism responsible for this metabolic disorder is enhanced arginine turnover, occurring secondary to enhanced plasma arginase activity. This is consistent with a growing appreciation of the role of excessive arginase activity in human diseases, including asthma and pulmonary arterial hypertension. New treatments aimed at improving arginine and NO bioavailability through arginase inhibition, suppression of hemolytic rate, oral arginine supplementation, or use of NO donors represent potential therapeutic strategies for this common pulmonary complication of hemolytic disorders.

Sickle cell disease: role of reactive oxygen and nitrogen metabolites

1. Sickle cell disease (SCD) is an inherited disorder of haemoglobin synthesis that is associated with significant morbidity and mortality due to sequelae of episodic vaso-occlusive events: pain crises and multiorgan damage. The microvascular responses to the initiation, progression and resolution of vaso-occlusive events are consistent with an inflammatory phenotype as suggested by activation of multiple cell types, an oxidatively stressed environment and endothelial cell dysfunction. 2. Decreased anti-oxidant defences in SCD patients and mice are accompanied by activation of enzymatic (NADPH oxidase, xanthine oxidase) and non-enzymatic (sickle haemoglobin auto-oxidation) sources of reactive oxygen species. The resultant oxidative stress leads to dysfunction/activation of arteriolar and venular endothelial cells, resulting in impaired vasomotor function and blood cell-endothelial cell adhesion. 3. Changes in substrate and cofactor availability for endothelial cell nitric oxide synthase may underlie reactive oxygen- and nitrogen-induced events that contribute to SCD-induced vasculopathy. 4. The emerging role of reactive oxygen and nitrogen species in the pathogenesis of SCD provides a platform for the development of novel agents to treat this painful and lethal disease.

Clinical hemoglobinopathies: iron, lungs and new blood

PURPOSE OF REVIEW

Sickle cell disease and beta-thalassemia major are clinically significant hereditary anemias that elicit worldwide attention due to the frequency and severity of these disorders. Historically, most children who inherited these disorders died in the first decade of life. Recently, however, supportive care has extended lifespan through the fifth decade of life and beyond, with survival through early adulthood now indistinguishable from those unaffected by these disorders. As a result, chronic health impairments that significantly reduce the quality of life such as pulmonary hypertension and the consequences of transfusional iron overload have become principal challenges.

RECENT FINDINGS

We focus on important recent advances that are very likely to alter the nature of supportive care of these disorders or make it possible to identify prospectively high-risk patients who might benefit from novel therapies or even curative treatment in the form of hematopoietic cell transplantation. The availability of the latter, traditionally constrained by the requirement of a human leukocyte antigen-identical sibling donor, is very likely to be broadened as results after unrelated donor hematopoietic cell transplantation improve.

SUMMARY

In this review, several areas that are very likely to have a significant impact in the management of patients who inherit these disorders are discussed.

Glomerular Involvement in Adults with Sickle Cell Hemoglobinopathies: Prevalence and Clinical Correlates of Progressive Renal Failure

Patients with sickle cell anemia (SCA) may develop a glomerulopathy with proteinuria and progressive renal insufficiency, leading to ESRD. Albuminuria is a sensitive marker of glomerular damage in this population and precedes the development of renal insufficiency. For determination of the prevalence of glomerular damage in SCA and the clinical correlates of renal insufficiency, 300 adult patients with SCA were studied (hemoglobin SS = 184; and 116 with other sickling hemoglobinopathies: SC, SD, and S-beta thalassemia); albumin excretion rates (AER) and renal function (Cockroft-Gault formula) were determined, and clinical and hematologic evaluations were conducted. In hemoglobin SS disease, increased AER (micro- and macroalbuminuria) occurred in 68% of adult patients, and macroalbuminuria occurred in 26%. In other sickling disorders, increased AER occurs in 32% of adults, and macroalbuminuria occurs in 10%. The development of graded albuminuria was age dependent, so at 40 yr, 40% of patients with SS disease had macroalbuminuria. There were no differences in hematologic parameters (hemoglobin levels, white blood cell count, percentage of reticulocytes, platelet counts, or lactate dehydrogenase levels) between patients with normoalbuminuria and those with micro- or macroalbuminuria. By multivariate analysis, albuminuria correlated with age and serum creatinine in SS disease but not with BP or hemoglobin levels. In other sickling disorders, albuminuria tended to be associated with age but not with hemoglobin or BP levels. The diastolic BP was lower in patients with SCA than in African American control subjects, and the development of renal insufficiency, which was present in 21% of adults with SS disease, was not accompanied by significant hypertension. It is concluded that glomerular damage in adults with SCA is very common, and a majority of patients with SS disease are at risk for the development of progressive renal failure. The development of micro- and macroalbuminuria is not related to the degree of anemia, suggesting that sickle cell glomerulopathy is not solely related to hemodynamic adaptations to chronic anemia. In contrast to other glomerulopathies, the development of systemic hypertension is uncommon in SS disease with renal insufficiency.

Dysregulated arginine metabolism, hemolysis-associated pulmonary hypertension, and mortality in sickle cell disease

CONTEXT

Sickle cell disease is characterized by a state of nitric oxide resistance and limited bioavailability of l-arginine, the substrate for nitric oxide synthesis. We hypothesized that increased arginase activity and dysregulated arginine metabolism contribute to endothelial dysfunction, pulmonary hypertension, and patient outcomes.

OBJECTIVE

To explore the role of arginase in sickle cell disease pathogenesis, pulmonary hypertension, and mortality.

DESIGN

Plasma amino acid levels, plasma and erythrocyte arginase activities, and pulmonary hypertension status as measured by Doppler echocardiogram were prospectively obtained in outpatients with sickle cell disease. Patients were followed up for survival up to 49 months.

SETTING

Urban tertiary care center and community clinics in the United States between February 2001 and March 2005.

PARTICIPANTS

Two hundred twenty-eight patients with sickle cell disease, aged 18 to 74 years, and 36 control participants.

MAIN OUTCOME MEASURES

Plasma amino acid levels, plasma and erythrocyte arginase activities, diagnosis of pulmonary hypertension, and mortality.

RESULTS

Plasma arginase activity was significantly elevated in patients with sickle cell disease, with highest activity found in patients with secondary pulmonary hypertension. Arginase activity correlated with the arginine-ornithine ratio, and lower ratios were associated with greater severity of pulmonary hypertension and with mortality in this population (risk ratio, 2.5; 95% confidence interval [CI], 1.2-5.2; P = .006). Global arginine bioavailability, characterized by the ratio of arginine to ornithine plus citrulline, was also strongly associated with mortality (risk ratio, 3.6; 95% CI, 1.5-8.3; P<.001). Increased plasma arginase activity was correlated with increased intravascular hemolytic rate and, to a lesser extent, with markers of inflammation and soluble adhesion molecule levels.

CONCLUSIONS

These data support a novel mechanism of disease in which hemolysis contributes to reduced nitric oxide bioavailability and endothelial dysfunction via release of erythrocyte arginase, which limits arginine bioavailability, and release of erythrocyte hemoglobin, which scavenges nitric oxide. The ratios of arginine to ornithine and arginine to ornithine plus citrulline are independently associated with pulmonary hypertension and increased mortality in patients with sickle cell disease.

Arginine supplementation improves rotorod performance in sickle transgenic mice

Patients with sickle cell disease (SCD) have been shown to have impaired visual-motor speed and coordination. Sensorimotor deficits in mice can be investigated by motor coordination tests that require whole body movements such as the rotorod. A sickle transgenic mouse model (S+S-Antilles) that expresses human alpha, human beta(S) and human beta(S-Antilles), is homozygous for the mouse beta(major) deletion, and has low plasma arginine was compared to control C57BL/6J mice and S+S-Antilles mice supplemented with 5% arginine on the rotorod. The rotorod consists of a 2.5 cm diameter, grooved rod turning at constant acceleration, requiring postural adjustments on the part of the mice to maintain equilibrium. C57BL mice on Purina mouse chow had an average latency to fall of S+S-Antilles mice on Purina mouse chow had an average of 127+/-56 s S+S-Antilles mice after 5% arginine supplementation had a mean latency of Arginine may improve rotorod performance in sickle transgenic mice by increasing NO synthesis thereby improving vasodilatation and blood flow with reversal of ischemia in brain and/or muscle. In conclusion, impaired rotorod performance in sickle transgenic mice presents an opportunity to apply this simple task to provide an efficient method to screen some types of therapeutic regimens for efficacy in SCD.

Nitric oxide and tubulointerstitial nephritides

As part of the exponential growth in our understanding of nitric oxide (NO) in health and disease over the past 2 decades, the kidney has become appreciated as a major site where NO may play a number of important roles. Although earlier work on the kidney focused more on effects of NO at the level of larger blood vessels and glomeruli, there has been a rapidly growing body of work showing critical roles for NO in tubulointerstitial disease. In this review we discuss some of the recent contributions to this important field.

Differential gene expression in the kidney of sickle cell transgenic mice: upregulated genes

The S+S-Antilles transgenic mouse used in this study has renal defects similar to those seen in sickle cell anemia patients: congested glomeruli, medullary fibrosis, renal enlargement, vasoocclusion, and a urine concentrating defect. We used gene expression microarrays to identify genes highly up-regulated in the kidneys of these mice and validated their expression by real-time PCR. Kidney hypoxia, as demonstrated by the presence of deoxyhemoglobin, was detected by blood oxygen dependent magnetic resonance imaging (BOLD-MRI). Some of the up-regulated genes included cytochrome P450 4a14, glutathione-S-transferase alpha-1, mitochondrial hydroxymethylglutaryl CoA synthase, cytokine inducible SH-2 containing protein, retinol dehydrogenase type III, arginase II, glycolate oxidase, Na/K ATPase, renin-1, and alkaline phosphatase 2. An increase in enzyme activity was also demonstrated for one of the up-regulated genes (arginase II). These genes can be integrated into several different pathophysiological processes: a hypoxia cascade, a replacement cascade, or an ameliorating cascade, one or all of which may explain the phenotype of this disease. We conclude that microarray technology is a powerful tool to identify genes involved in renal disease in sickle cell anemia and that the identification of various metabolic pathways may open new avenues for therapeutic interventions.

Arginine therapy: a new treatment for pulmonary hypertension in sickle cell disease?

Pulmonary hypertension is a life-threatening complication of sickle cell disease. L-Arginine is the nitrogen donor for synthesis of nitric oxide, a potent vasodilator that is deficient during times of sickle cell crisis. This deficiency may play a role in pulmonary hypertension. The enzyme arginase hydrolyzes arginine to ornithine and urea, and thus, it may compete with nitric oxide synthase, leading to decreased nitric oxide production. Nitric oxide therapy by inhalation has improved pulmonary hypertension associated with acute chest syndrome in sickle cell disease, and several studies demonstrate therapeutic benefits of arginine therapy for primary and secondary pulmonary hypertension. We sought to determine the effects of arginine therapy on pulmonary hypertension in patients with sickle cell disease. Arginase activity was also determined. Oral arginine produced a 15.2% mean reduction in estimated pulmonary artery systolic pressure (63.9 +/- 13 to 54.2 +/- 12 mm Hg, p = 0.002) after 5 days of therapy in 10 patients. Arginase activity was elevated almost twofold (p = 0.07) in patients with pulmonary hypertension and may limit arginine bioavailability. With limited treatment options and a high mortality rate for patients with sickle cell disease who develop pulmonary hypertension, arginine is a promising new therapy that warrants further investigation.

Nitric oxide-dependent generation of reactive species in sickle cell disease. Actin tyrosine induces defective cytoskeletal polymerization

The intermittent vascular occlusion occurring in sickle cell disease (SCD) leads to ischemia-reperfusion injury and activation of inflammatory processes including enhanced production of reactive oxygen species and increased expression of inducible nitric-oxide synthase (NOS2). Appreciating that impaired nitric oxide-dependent vascular function and the concomitant formation of oxidizing and nitrating species occur in concert with increased rates of tissue reactive oxygen species production, liver and kidney NOS2 expression, tissue 3-nitrotyrosine (NO(2)Tyr) formation and apoptosis were evaluated in human SCD tissues and a murine model of SCD. Liver and kidney NOS2 expression and NO(2)Tyr immunoreactivity were significantly increased in SCD mice and humans, but not in nondiseased tissues. TdT-mediated nick end-label (TUNEL) staining showed apoptotic cells in regions expressing elevated levels of NOS2 and NO(2)Tyr in all SCD tissues. Gas chromatography mass spectrometry analysis revealed increased plasma protein NO(2)Tyr content and increased levels of hepatic and renal protein NO(2)Tyr derivatives in SCD (21.4 +/- 2.6 and 37.5 +/- 7.8 ng/mg) versus wild type mice (8.2 +/- 2.2 and 10 +/- 1.2 ng/mg), respectively. Western blot analysis and immunoprecipitation of SCD mouse liver and kidney proteins revealed one principal NO(2)Tyr-containing protein of 42 kDa, compared with controls. Enzymatic in-gel digestion and MALDI-TOF mass spectrometry identified this nitrated protein as actin. Electrospray ionization and fragment analysis by tandem mass spectrometry revealed that 3 of 15 actin tyrosine residues are nitrated (Tyr(91), Tyr(198), and Tyr(240)) at positions that significantly modify actin assembly. Confocal microscopy of SCD human and mouse tissues revealed that nitration led to morphologically distinct disorganization of filamentous actin. In aggregate, we have observed that the hemoglobin point mutation of sickle cell disease that mediates hemoglobin polymerization defects is translated, via inflammatory oxidant reactions, into defective cytoskeletal polymerization.

Evidence for the existence of two distinct functions for the inducible NO synthase in the rat kidney: effect of aminoguanidine in rats with 5/6 ablation

The functional role of the NO synthase (NOS) isoforms in the normal or diseased kidney is uncertain. This study examined the renal expression of the endothelial (eNOS), neuronal (nNOS), and inducible (iNOS) isoforms by both immunohistochemistry and Western blot analyses in sham-operated rats (S) and in rats subjected to 5/6 nephrectomy (Nx). Primary antibodies from two different sources were used to detect iNOS. Additional S and Nx rats were chronically treated with aminoguanidine (AG), a selective iNOS inhibitor. All three isoforms were clearly expressed in S kidney. Their renal abundance, evaluated by Western blot analysis, fell in Nx rats. With the use of anti-iNOS antibodies from two distinct sources, the immunohistochemical analysis showed the presence of what appeared to be two distinct iNOS fractions: a "tubular" fraction, present in S and with decreased intensity in Nx; and an "interstitial" fraction, observed only in inflamed areas of Nx rats. AG treatment greatly attenuated renal injury in Nx rats by a direct antiinflammatory effect, likely related to iNOS inhibition, rather than to amelioration of renal hemodynamics or to reduced protein glycation. These observations suggest that: (1) the functional role of the renal iNOS isoform may vary dramatically under different physiologic conditions; (2) caution should be taken in the interpretation of immunohistochemical iNOS data, because antibodies from different sources may detect different iNOS fractions; and (3) AG treatment may become useful in the treatment of human progressive nephropathies, even those not associated with diabetes or aging.

Renal complications of sickle cell disease: managing for optimal outcomes

A broad spectrum of renal changes is observed in patients with sickle cell anemia, and ideal therapeutic measures for the management of these alterations are still being studied. Affected patients have deficient urinary concentration and potassium excretion. Perhaps owing to a compensatory mechanism, the proximal tubules are in a condition of "hyperfunction", with increased sodium and phosphorus reabsorption and greater creatinine and uric acid secretion. Mild tubular acidosis may be present. No treatment has been reported for these tubular changes, except for care in the maintenance of hydration. The use of anti-inflammatory drugs is being studied in order to inhibit the prostaglandins involved in the process. Increased renal blood flow, glomerular filtration rate, and filtration fraction are frequent findings. Hematuria commonly occurs as a consequence of red blood cell sickling in the renal medulla, papillary necrosis, or even renal medullary carcinoma. Measures such as increased fluid ingestion, urine alkalinization and, if necessary, administration of epsilon-aminocaproic acid and certain invasive procedures have been proposed to treat hematuria. Nephropathy in patients with sickle cell anemia can be manifested by proteinuria and, more rarely, nephrotic syndrome. Drugs such as prednisone and cyclophosphamide are ineffective for the treatment of patients with nephrotic syndrome. Angiotensin converting enzyme inhibitors decrease proteinuria, but their long-term effect in preventing the progression of glomerular disease has not been established. Chronic renal failure, although infrequent, may be one of the manifestations of this disease. Hemodialysis and transplantation are satisfactory therapeutic options for patients with end-stage renal disease.

Utility and limitations of serum creatinine as a measure of renal function in experimental renal ischemia-reperfusion injury

BACKGROUND

Ischemia-reperfusion injury (IRI) is the major cause of delayed graft function in renal allografts. The present study was performed to investigate the validity of serum creatinine (SCr) level as an indicator of postischemic renal dysfunction in mice.

METHODS

Renal IRI or sham surgery was induced in C57BL/6 mice, and SCr level and inulin clearance (Cin) were measured between 24 hr and 7 days after ischemia.

RESULTS

Cin in IRI mice was reduced 75% at 72 hr after ischemia in association with a nearly threefold increase in SCr level. Cin in IRI mice did not recover between 72 hr and 7 days after ischemia, even though SCr level at 7 days was not different between control and IRI mice. In IRI mice, SCr level measured at 24, 48, and 72 hr after ischemia correlated inversely with Cin measured at 72 hr, but not 7 days, after ischemia.

CONCLUSIONS

SCr level in the early postischemic period (24-72 hr) seems to be a valid indicator of early postischemic renal dysfunction, and that renal function remains markedly depressed at 7 days despite suggestion from the SCr value that renal function is improving.

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.

Arginine supplementation of sickle transgenic mice reduces red cell density and Gardos channel activity

Nitric oxide (NO), essential for maintaining vascular tone, is produced from arginine by nitric oxide synthase. Plasma arginine levels are low in sickle cell anemia, and it is reported here that low plasma arginine is also found in our sickle transgenic mouse model that expresses human alpha, human beta(S), and human beta(S-Antilles) and is homozygous for the mouse beta(major) deletion (S+S-Antilles). S+S-Antilles mice were supplemented with a 4-fold increase in arginine that was maintained for several months. Mean corpuscular hemoglobin concentration (MCHC) decreased and the percent high-density red cells was reduced. Deoxy K(+) efflux is characteristic of red cells in sickle cell disease and contributes to the disease process by increasing the MCHC and rendering the cells more susceptible to polymer formation. This flux versus the room air flux was reduced in S+S-Antilles red cells from an average value of 1.6 +/- 0.3 mmol per liter of red cells x minute (FU) in nonsupplemented mice to 0.9 +/- 0.3 FU (n = 4, P < .02, paired t test) in supplemented mice. In room air, V(max) of the Ca(++)-activated K(+) channel (Gardos) was reduced from 4.1 +/- 0.6 FU (off diet) to 2.6 +/- 0.4 FU (n = 7 and 8, P < .04, t test) in arginine-supplemented mice versus clotrimazole. In conclusion, the major mechanism by which arginine supplementation reduces red cell density (MCHC) in S+S-Antilles mice is by inhibiting the Ca(++)-activated K(+) channel.

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.

Endothelial dysfunction in patients with sickle cell disease is related to selective impairment of shear stress-mediated vasodilation

Interactions between the endothelium and erythrocytes may contribute to the vascular complications of sickle cell disease (SCD). Endothelium-derived nitric oxide (NO) plays a major role in the regulation of vasomotor tone in response to wall shear stress (WSS) variations and pharmacologic stimuli. However, little is known about endothelial NO production in patients with steady-state SCD. We investigated endothelial NO production in response to flow or vasoactive agonists in 16 homozygous patients with steady-state SCD and 15 controls. Flow-mediated dilation (FMD), arterial diameter changes in response to 100% oxygen inhalation, blood viscosity, and calculated WSS were determined in all patients and controls. At baseline, WSS was higher in SCD patients than in controls, whereas arterial diameter was similar. In patients with SCD, FMD was impaired (1.73% +/- 0.44% vs 3.97% +/- 0.24% in the controls, P <.001) and vasoconstriction in response to 100% oxygen was abolished. Using venous occlusion plethysmography, forearm blood flow (FBF) was evaluated in response to acetylcholine, nitro-monomethyl-L-arginine (L-NMMA), and sodium nitroprusside (SNP) in subgroups of 9 controls and 7 patients with SCD. Acetylcholine induced a significantly greater FBF increase in the patients (9.7 +/- 2.9 mL/min/100 mL of forearm volume vs 2.5 +/- 1.5 mL/min/100 mL in the controls, P <.001), whereas responses to L-NMMA and SNP were similar. These results suggest that endothelial dysfunction may prevent the arterial diameter of patients with SCD from adapting to chronic or acute shear stress elevations. This may contribute to the pathophysiology of vaso-occlusive crisis in patients with SCD.

Oxidative stress and induction of heme oxygenase-1 in the kidney in sickle cell disease

Chronic nephropathy is a recognized complication of sickle cell disease. Using a transgenic sickle mouse, we examined whether oxidative stress occurs in the sickle kidney, the origins and functional significance of such oxidant stress, and the expression of the oxidant-inducible, potentially protective gene, heme oxygenase-1 (HO-1); we also examined the expression of HO-1 in the kidney and in circulating endothelial cells in sickle patients. We demonstrate that this transgenic sickle mouse exhibits renal enlargement, medullary congestion, and a reduced plasma creatinine concentration. Oxidative stress is present in the kidney as indicated by increased amounts of lipid peroxidation; heme content is markedly increased in the kidney. Exacerbation of oxidative stress by inhibiting glutathione synthesis with buthionine-sulfoximine dramatically increased red blood cell sickling in the sickle kidney: in buthionine-sulfoximine-treated sickle mice, red blood cell sickling extended from the medulla into the cortical capillaries and glomeruli. HO activity is increased in the sickle mouse kidney, and is due to induction of HO-1. In the human sickle kidney, HO-1 is induced in renal tubules, interstitial cells, and in the vasculature. Expression of HO-1 is increased in circulating endothelial cells in patients with sickle cell disease. These results provide the novel demonstration that oxidative stress occurs in the sickle kidney, and that acute exacerbation of oxidative stress in the sickle mouse precipitates acute vaso-occlusive disease. Additionally, the oxidant-inducible, heme-degrading enzyme, HO-1, is induced regionally in the murine and human sickle kidney, and systemically, in circulating endothelial cells in sickle patients.