Losartan for the nephropathy of sickle cell anemia: A phase-2, multicenter trial

End Organ Affection in Sickle Cell Disease

Sickle cell disease is an orphan disease affecting ethnic minorities and characterized by profound systemic manifestations. Although around 100,000 individuals with SCD are living in the US, the exact number of individuals is unknown, and it is considered an orphan disease. This single-gene disorder leads to red blood cell sickling and the deoxygenation of hemoglobin, resulting in hemolysis. SCD is associated with acute complications such as vaso-occlusive crisis, infections, and chronic target organ complications such as pulmonary disease and renal failure. While genetic therapy holds promise to alter the fundamental disease process, the major challenge in the field remains the target end organ damage and ways to mitigate or reverse it. Here, we provide an overview of the clinical manifestations and pathogenesis with a focus on end-organ damage and current therapeutic options, including recent FDA-approved stem cell and gene editing therapies.

Natural history and variability in albuminuria in pediatric and murine sickle cell anemia

It is critical to characterize the natural history of albuminuria in patients with sickle cell anemia (SCA); however, these data are currently lacking and affecting evidence-based guidelines. We performed a natural history study of the development of pediatric albuminuria. We identified participants with hemoglobin SS/SB0 thalassemia ≥5 years with albumin to creatinine ratio (ACR) measurements performed at a steady-state clinic visit. Participants were characterized as either persistent, intermittent, or never albuminuria. We determined the prevalence of persistent albuminuria, use of ACR ≥100 mg/g as a predictor, and variation in ACR measurements. We mirrored this study to determine the variation in albuminuria measurements in the SCA murine model. Among 355 participants with HbSS/SB0 thalassemia with 1728 ACR measurements, we identified 17% with persistent and 13% with intermittent albuminuria. Thirteen percent of participants with persistent albuminuria developed an abnormal ACR before 10 years of age. A single ACR measurement ≥100 mg/g was associated with 55.5 times (95% confidence interval, 12.3-527) higher odds of having persistent albuminuria. Among participants with ACR ≥100 mg/g, we identified significant variability in the results of repeated measurements. The median ACR at the initial and next measurements were 175.8 mg/g (interquartile range [IQR], 135-242) and 117.3 mg/g (IQR, 64-292). The human variability in ACR was mirrored by ∼20% variability in albuminuria in murine model. This evidence suggests adopting standards for repeating ACR measurements, consider screening for ACR before 10 years of age, and using an ACR >100 mg/g as a risk factor for progression. Pediatric and murine renoprotective clinical trials need to consider the high variability in repeated ACR measurements.

Sickle Cell Disease and CKD: An Update

BACKGROUND

Sickle cell disease is an inherited red blood cell disorder that affects approximately 100,000 people in the USA and 25 million people worldwide. Vaso-occlusion and chronic hemolysis lead to dysfunction of vital organ systems, with the kidneys being among the most commonly affected organs.

SUMMARY

Early renal manifestations include medullary ischemia with the loss of urine-concentrating ability and hyperfiltration. This can be followed by progressive damage characterized by persistent albuminuria and a decline in the estimated glomerular filtration rate. The risk of sickle nephropathy is greater in those with the APOL1 G1 and G2 kidney risk variants and variants in HMOX1 and lower in those that coinherit α-thalassemia. Therapies to treat sickle cell disease-related kidney damage focus on sickle cell disease-modifying therapies (e.g., hydroxyurea) or those adopted from the nonsickle cell disease kidney literature (e.g., renin-angiotensin-aldosterone system inhibitors), although data on their clinical efficacy are limited to small studies with short follow-up periods. Kidney transplantation for end-stage kidney disease improves survival compared to hemodialysis but is underutilized in this patient population.

KEY MESSAGES

Kidney disease is a major contributor to early mortality, and more research is needed to understand the pathophysiology and develop targeted therapies to improve kidney health in sickle cell disease.

Interventions for chronic kidney disease in people with sickle cell disease

BACKGROUND

Sickle cell disease (SCD), one of the commonest severe monogenic disorders, is caused by the inheritance of two abnormal haemoglobin (beta-globin) genes. SCD can cause severe pain, significant end-organ damage, pulmonary complications, and premature death. Kidney disease is a frequent and potentially severe complication in people with SCD. Chronic kidney disease (CKD) is defined as abnormalities of kidney structure or function present for more than three months. Sickle cell nephropathy refers to the spectrum of kidney complications in SCD. Glomerular damage is a cause of microalbuminuria and can develop at an early age in children with SCD, with increased prevalence in adulthood. In people with sickle cell nephropathy, outcomes are poor as a result of the progression to proteinuria and chronic kidney insufficiency. Up to 12% of people who develop sickle cell nephropathy will develop end-stage renal disease. This is an update of a review first published in 2017.

OBJECTIVES

To assess the effectiveness of any intervention for preventing or reducing kidney complications or chronic kidney disease in people with sickle cell disease. Possible interventions include red blood cell transfusions, hydroxyurea, and angiotensin-converting enzyme inhibitors (ACEIs), either alone or in combination.

SEARCH METHODS

We searched for relevant trials in the Cochrane Cystic Fibrosis and Genetic Disorders Group Trials Register, CENTRAL, MEDLINE, Embase, seven other databases, and two other trials registers.

SELECTION CRITERIA

Randomised controlled trials (RCTs) comparing interventions to prevent or reduce kidney complications or CKD in people with SCD. We applied no restrictions related to outcomes examined, language, or publication status.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial eligibility, extracted data, assessed the risk of bias, and assessed the certainty of the evidence (GRADE).

MAIN RESULTS

We included three RCTs with 385 participants. We rated the certainty of the evidence as low to very low across different outcomes according to GRADE methodology, downgrading for risk of bias concerns, indirectness, and imprecision. Hydroxyurea versus placebo One RCT published in 2011 compared hydroxyurea to placebo in 193 children aged nine to 18 months. We are unsure if hydroxyurea compared to placebo reduces or prevents progression of kidney disease assessed by change in glomerular filtration rate (mean difference (MD) 0.58 mL/min /1.73 m2, 95% confidence interval (CI) -14.60 to 15.76; 142 participants; very low certainty). Hydroxyurea compared to placebo may improve the ability to concentrate urine (MD 42.23 mOsm/kg, 95% CI 12.14 to 72.32; 178 participants; low certainty), and may make little or no difference to SCD-related serious adverse events, including acute chest syndrome (risk ratio (RR) 0.39, 99% CI 0.13 to 1.16; 193 participants; low certainty), painful crisis (RR 0.68, 99% CI 0.45 to 1.02; 193 participants; low certainty); and hospitalisations (RR 0.83, 99% CI 0.68 to 1.01; 193 participants; low certainty). No deaths occurred in either trial arm and the RCT did not report quality of life. Angiotensin-converting enzyme inhibitors versus placebo One RCT published in 1998 compared an ACEI (captopril) to placebo in 22 adults with normal blood pressure and microalbuminuria. We are unsure if captopril compared to placebo reduces proteinuria (MD -49.00 mg/day, 95% CI -124.10 to 26.10; 22 participants; very low certainty). We are unsure if captopril reduces or prevents kidney disease as measured by creatinine clearance; the trial authors stated that creatinine clearance remained constant over six months in both groups, but provided no comparative data (very low certainty). The RCT did not report serious adverse events, all-cause mortality, or quality of life. Angiotensin-converting enzyme inhibitors versus vitamin C One RCT published in 2020 compared an ACEI (lisinopril) with vitamin C in 170 children aged one to 18 years with normal blood pressure and microalbuminuria. It reported no data we could analyse. We are unsure if lisinopril compared to vitamin C reduces proteinuria in this population: the large drop in microalbuminuria in both arms of the trial after only one month on treatment may have been due to an overestimation of microalbuminuria at baseline rather than a true effect. The RCT did not report serious adverse events, all-cause mortality, or quality of life.

AUTHORS' CONCLUSIONS

We are unsure if hydroxyurea improves glomerular filtration rate or reduces hyperfiltration in children aged nine to 18 months, but it may improve their ability to concentrate urine and may make little or no difference to the incidence of acute chest syndrome, painful crises, and hospitalisations. We are unsure if ACEI compared to placebo has any effect on preventing or reducing kidney complications in adults with normal blood pressure and microalbuminuria. We are unsure if ACEI compared to vitamin C has any effect on preventing or reducing kidney complications in children with normal blood pressure and microalbuminuria. No RCTs assessed red blood cell transfusions or any combined interventions to prevent or reduce kidney complications. Due to lack of evidence, we cannot comment on the management of children aged over 18 months or adults with any known genotype of SCD. We have identified a lack of adequately designed and powered studies, although we found four ongoing trials since the last version of this review. Only one ongoing trial addresses renal function as a primary outcome in the short term, but such interventions have long-term effects. Trials of hydroxyurea, ACEIs or red blood cell transfusion in older children and adults are urgently needed to determine any effect on prevention or reduction of kidney complications in people with SCD.

Blockade of the mineralocorticoid receptor improves markers of human endothelial cell dysfunction and hematological indices in a mouse model of sickle cell disease

Increased endothelin-1 (ET-1) levels in patients with sickle cell disease (SCD) and transgenic mouse models of SCD contribute to disordered hematological, vascular, and inflammatory responses. Mineralocorticoid receptor (MR) activation by aldosterone, a critical component of the Renin-Angiotensin-Aldosterone-System, modulates inflammation and vascular reactivity, partly through increased ET-1 expression. However, the role of MR in SCD remains unclear. We hypothesized that MR blockade in transgenic SCD mice would reduce ET-1 levels, improve hematological parameters, and reduce inflammation. Berkeley SCD (BERK) mice, a model of severe SCD, were randomized to either sickle standard chow or chow containing the MR antagonist (MRA), eplerenone (156 mg/Kg), for 14 days. We found that MRA treatment reduced ET-1 plasma levels (p = .04), improved red cell density gradient profile (D50 ; p < .002), and increased mean corpuscular volume in both erythrocytes (p < .02) and reticulocytes (p < .024). MRA treatment also reduced the activity of the erythroid intermediate-conductance Ca2+ -activated K+ channel - KCa 3.1 (Gardos channel, KCNN4), reduced cardiac levels of mRNAs encoding ET-1, Tumor Necrosis Factor Receptor-1, and protein disulfide isomerase (PDI) (p < .01), and decreased plasma PDI and myeloperoxidase activity. Aldosterone (10-8  M for 24 h in vitro) also increased PDI mRNA levels (p < .01) and activity (p < .003) in EA.hy926 human endothelial cells, in a manner blocked by pre-incubation with the MRA canrenoic acid (1 μM; p < .001). Our results suggest a novel role for MR activation in SCD that may exacerbate SCD pathophysiology and clinical complications.

Emerging Therapies and Advances in Sickle Cell Disease with a Focus on Renal Manifestations

The underlying mechanisms of disease in sickle cell disease (SCD) contribute to a multifaceted nephropathy, commonly manifested as albuminuria. In severe SCD genotypes ( e.g. , Hemoglobin SS [HbSS]), albuminuria and CKD are major predictors of mortality in this population. Therefore, the monitoring and management of renal function is an intrinsic part of comprehensive care in SCD. Management of nephropathy in SCD can be accomplished with SCD-directed therapies and/or CKD-directed therapies. In the past 5 years, novel disease-modifying and palliative therapies have been approved in SCD to target aspects of the disease, such as anemia, inflammation, and vasculopathy. Along with conventional hydroxyurea and chronic transfusion, l -glutamine, crizanlizumab, and voxelotor have all been shown to mitigate some adverse effect of SCD, and their effect on nephropathy is being investigated. CKD-directed therapies such as renin-angiotensin-aldosterone system blockers have long been used in SCD nephropathy; however, more complete long-term studies on benefits are needed. Given the effect of renal disease on survival, further assessment of the mechanisms and efficacy of these SCD-directed or CKD-directed therapeutic agents is essential.

ATR1 Angiotensin II Receptor Reduces Hemoglobin S Polymerization, Phosphatidylserine Exposure, and Increases Deformability of Sickle Cell Disease Erythrocytes

Angiotensin II (Ang II) regulates blood volume and stimulates erythropoiesis through AT1 (ATR1) and AT2 (ATR2) receptors, found in multiple tissues, including erythrocytes. Sickle cell disease (SCD) patients present altered Ang II levels. Hemoglobin S polymerization, deformability and phosphatidylserine translocation are important features of mature erythrocytes, therefore, our hypothesis is Ang II affects these parameters and, if it does, what would be the influence of AT1R and AT2R on these effects. A polymerization assay (PA), deformability, and annexin V binding were performed in SCD erythrocytes samples adding Ang II, ATR1 antagonist (losartan or eprosartan), and ATR2 antagonist (PD123319). Through the PA test, we observed a dose-dependent polymerization inhibition effect when comparing Ang II to control. Losartan did not affect the level or the rate of Ang II inhibition, while PD123319 showed an increased level of protection against polymerization, and eprosartan brought levels back to control. Ang II was able to reduce the translocation of phosphatidylserine from the inner to the outer leaflet, a marker of eryptosis, in the presence of PD123319. Also, ATR1 showed a positive effect increasing deformability. Our data shows that ATR1 is important for maintenance of erythrocyte physiological function in SCD and for prolonging its life.

The nephropathy of sickle cell trait and sickle cell disease

Sickle cell syndromes, including sickle cell disease (SCD) and sickle cell trait, are associated with multiple kidney abnormalities. Young patients with SCD have elevated effective renal plasma flow and glomerular filtration rates, which decrease to normal ranges in young adulthood and subnormal levels with advancing age. The pathophysiology of SCD-related nephropathy is multifactorial - oxidative stress, hyperfiltration and glomerular hypertension are all contributing factors. Albuminuria, which is an early clinical manifestation of glomerular damage, is common in individuals with SCD. Kidney function declines more rapidly in individuals with SCD than in those with sickle cell trait or in healthy individuals. Multiple genetic modifiers, including APOL1, HMOX1, HBA1 and HBA2 variants are also implicated in the development and progression of SCD-related nephropathy. Chronic kidney disease and rapid decline in estimated glomerular filtration rate are associated with increased mortality in adults with SCD. Renin-angiotensin-aldosterone system inhibitors are the standard of care treatment for albuminuria in SCD, despite a lack of controlled studies demonstrating their long-term efficacy. Multiple studies of novel therapeutic agents are ongoing, and patients with SCD and kidney failure should be evaluated for kidney transplantation. Given the high prevalence and severe consequences of kidney disease, additional studies are needed to elucidate the pathophysiology, natural history and treatment of SCD-related nephropathy.

Advances in the diagnosis and treatment of sickle cell disease

Sickle cell disease (SCD), which affects approximately 100,000 individuals in the USA and more than 3 million worldwide, is caused by mutations in the βb globin gene that result in sickle hemoglobin production. Sickle hemoglobin polymerization leads to red blood cell sickling, chronic hemolysis and vaso-occlusion. Acute and chronic pain as well as end-organ damage occur throughout the lifespan of individuals living with SCD resulting in significant disease morbidity and a median life expectancy of 43 years in the USA. In this review, we discuss advances in the diagnosis and management of four major complications: acute and chronic pain, cardiopulmonary disease, central nervous system disease and kidney disease. We also discuss advances in disease-modifying and curative therapeutic options for SCD. The recent availability of L-glutamine, crizanlizumab and voxelotor provides an alternative or supplement to hydroxyurea, which remains the mainstay for disease-modifying therapy. Five-year event-free and overall survival rates remain high for individuals with SCD undergoing allogeneic hematopoietic stem cell transplant using matched sibling donors. However, newer approaches to graft-versus-host (GVHD) prophylaxis and the incorporation of post-transplant cyclophosphamide have improved engraftment rates, reduced GVHD and have allowed for alternative donors for individuals without an HLA-matched sibling. Despite progress in the field, additional longitudinal studies, clinical trials as well as dissemination and implementation studies are needed to optimize outcomes in SCD.

Sickle Cell Disease and Kidney

Sickle cell disease causes several kidney manifestations. They include defects in urine concentration, impaired handling of potassium and hydrogen ion, albuminuria, acute kidney injury, and chronic kidney disease to name a few. Glomerular hyperfiltration, tubular hyperfunctioning, endothelial damage from repeated sickling and vaso-occlusive episodes, and iron-induced proinflammatory changes in the glomerular mesangium and tubulointerstitium are some of the mechanisms of kidney damage. Albuminuria is one of the most and common clinical features of kidney disease and progresses with age. Kidney disease in patients with sickle cell is associated with increased mortality. Annual screening for proteinuria starting at age 10 years and limiting the use of nonsteroidal anti-inflammatory agents and the use of angiotensin-converting enzyme inhibitors may help in early detection and delaying the progression of kidney disease. Adequate hydration, angiotensin-converting enzyme inhibitors, and adequate control of sickle cell are the main stay of treatment for albuminuria. The hemoglobin goal for patients with sickle cell nephropathy is lesser (10 g/dL) than that for patients with chronic kidney disease due to other causes given that a higher hemoglobin level increases viscosity and the risk of precipitating vaso-occlusive episodes. A multidisciplinary approach is recommended for managing patients with sickle cell and kidney diseases.

Risk factors for CKD stage II onset in a prospective cohort of homozygous sickle cell adults

Prevalence of renal impairment is increasing with aging in sickle cell anemia (SCA) patients, and is responsible for a high morbidity and mortality. However, sickle cell nephropathy's natural course remains mostly unknown. We conducted a prospective observational cohort study aimed to identify risk factors for CKD stage II in a cohort of SCA patients. Baseline clinical and biological parameters were collected. Renal parameters were updated at each visit. Risk factors were analyzed using the Cox model. Five-hundred and thirty-five SCA patients were included with a median follow-up of 5.33 (IQR:2.10-8.13) years. Median age was 22 (IQR:19-30) years old. Glomerular hyperfiltration was detected in 299 (55.9%) patients, microalbuminuria and macroalbuminuria in 180 (34%) and 67 (12.7%) patients respectively. During follow up, CKD stage II onset was detected in 39 patients (7.3%). Risk factors for CKD stage II after adjustment on baseline eGFR and age were macroalbuminuria HR: 3.89 [95% CI: 1.61;9.43], diastolic blood pressure (DBP) above 70 mm Hg HR: 2.02 [1.02-3.971], LDH (for 100 IU/L increase) HR: 1.28 [1.12;1.48] and tricuspid regurgitation velocity >2.5 m/sec HR: 2.89 [1.20-6.99]. Multivariate analysis also found age as a strong independent risk factor with HR: (per year increase) 1.13 [1.09;1.16] and a 13.3-fold increase above 30 years (p < 0.001). Our results show a high incidence of CKD stage II with aging, with a strong significant risk increase after 30-years-old, and pinpoint baseline DBP, macroalbuminuria and increased LDH as independent risk factors raising the issue of optimal blood pressure targets for SCA patients.

Olinciguat, a stimulator of soluble guanylyl cyclase, attenuates inflammation, vaso-occlusion and nephropathy in mouse models of sickle cell disease

BACKGROUND AND PURPOSE

Reduced bioavailability of NO, a hallmark of sickle cell disease (SCD), contributes to intravascular inflammation, vasoconstriction, vaso-occlusion and organ damage observed in SCD patients. Soluble guanylyl cyclase (sGC) catalyses synthesis of cGMP in response to NO. cGMP-amplifying agents, including NO donors and phosphodiesterase 9 inhibitors, alleviate TNFα-induced inflammation in wild-type C57BL/6 mice and in 'humanised' mouse models of SCD.

EXPERIMENTAL APPROACH

Effects of the sGC stimulator olinciguat on intravascular inflammation and renal injury were studied in acute (C57BL6 and Berkeley mice) and chronic (Townes mice) mouse models of TNFα-induced and systemic inflammation associated with SCD.

KEY RESULTS

Acute treatment with olinciguat attenuated increases in plasma biomarkers of endothelial cell activation and leukocyte-endothelial cell interactions in TNFα-challenged mice. Co-treatment with hydroxyurea, an FDA-approved SCD therapeutic agent, further augmented the anti-inflammatory effect of olinciguat. In the Berkeley mouse model of TNFα-induced vaso-occlusive crisis, a single dose of olinciguat attenuated leukocyte-endothelial cell interactions, improved blood flow and prolonged survival time compared to vehicle-treated mice. In Townes SCD mice, plasma biomarkers of inflammation and endothelial cell activation were lower in olinciguat- than in vehicle-treated mice. In addition, kidney mass, water consumption, 24-h urine excretion, plasma levels of cystatin C and urinary excretion of N-acetyl-β-d-glucosaminidase and neutrophil gelatinase-associated lipocalin were lower in Townes mice treated with olinciguat than in vehicle-treated mice.

CONCLUSION AND IMPLICATIONS

Our results suggest that the sGC stimulator olinciguat attenuates inflammation, vaso-occlusion and kidney injury in mouse models of SCD and systemic inflammation.

Longitudinal study of glomerular hyperfiltration and normalization of estimated glomerular filtration in adults with sickle cell disease

Glomerular hyperfiltration is common in sickle cell disease (SCD) and precedes proteinuria and declining kidney function. We evaluated hyperfiltration in SCD patients and its "normalization." Routine visit data were collected retrospectively from adult SCD patients in a single centre from 2004 to 2013. Baseline was defined as first available serum creatinine and hyperfiltration as estimated glomerular filtration rates (eGFR) >130 ml/min/1·73 m² for women and >140 ml/min/1·73 m² for men. Normalization of hyperfiltration was eGFR reduction to 90-130 ml/min/1·73 m² for women or 90-140 ml/min/1·73 m² for men. Among 292 patients, median age was 27 years [interquartile range (IQR):20·0-38·0], and 56·8% had baseline hyperfiltration. Baseline hyperfiltration was inversely associated with age [odds ratio (OR):0·86, 95% confidence interval (CI): 0·82-0·90; P < 0·0001], male sex (OR:0·16, 95% CI: 0·07-0·41; P = 0·0001), haemoglobin (OR:0·76, 95% CI 0·61-0·94; P = 0·01), weight (OR:0·96, 95% CI: 0·93-0·99; P = 0·004), and angiotensin-converting enzyme inhibitor/angiotensin receptor blocker (ACE-I/ARB) use (OR:0·08, 95% CI: 0·01-0·75; P = 0·03), and positively with hydroxycarbamide use (OR:2·99, 95% CI: 1·18-7·56; P = 0·02). Of 89 hyperfiltration patients without baseline proteinuria, 10 (11·2%) developed new-onset proteinuria [median 1·05 years (IQR:0·63-2·09)]. Normalization of hyperfiltration was less likely with higher baseline eGFR [hazard ratio (HR):0·90, 95% CI: 0·86-0·95; P < 0·0001] and more likely in males (HR:6·35, 95% CI:2·71-14·86, <0·0001). Hyperfiltration is common in adult SCD patients, particularly when younger. Decline to normal values is more likely in males, possibly representing kidney function loss rather than improvement in hyperfiltration.

Progression of albuminuria in patients with sickle cell anemia: a multicenter, longitudinal study

Sickle cell nephropathy results in chronic kidney disease (CKD), which is associated with significant morbidity and mortality in sickle cell anemia (SCA). Albuminuria is an early manifestation of sickle nephropathy; however, little is known about progression of albuminuria or its correlation with glomerular filtration rate (GFR) decline or CKD. We studied nephropathy progression in 303 SCA participants in a prospective, multicenter, longitudinal study. We collected steady-state urine and serum samples yearly and assessed albumin/creatinine ratio (ACR), estimated GFR (eGFR), and SCA and nephropathy biomarkers. Participants with albuminuria (ACR ≥30 mg/g) for ≥2 annual measurements were classified as having persistent albuminuria (PA). At baseline (mean age, 21 years; range, 2-64 years), 32% had albuminuria. In longitudinal multivariate analysis, ACR was associated with sex, anemia, older age, and higher bilirubin and kidney injury molecule-1 levels. Albuminuria increased with age by 3.5 mg/g per year (P < .0001). Of 175 participants with ≥3 annual samples, 81% with baseline albuminuria ≥100 mg/g developed PA. Decreased eGFR and adult CKD were associated with PA (P = .002 and P = .02, respectively), but not with baseline albuminuria. Rate of eGFR decline was steeper among adults (but not children) with albuminuria, compared with those without (P = .02). Participants with PA were more likely to have rapid eGFR decline compared with those without (P = .03). In this longitudinal study, albuminuria progressed with age, and adults with albuminuria had worse eGFR decline than those without. Albuminuria ≥100 mg/g predicted PA, which was associated with rapid eGFR decline and CKD development in adults with SCA. This trial was registered at www.clinicaltrials.gov as #NCT02239016.

Sickle Cell Disease

Sickle cell disease is an umbrella term for a group of hemoglobinopathies characterized by the presence of 2 β-globin gene mutations or deletions, at least 1 of which is the point mutation that leads to the production of hemoglobin S. Sickle cell disease is associated with hemolytic anemia, significant chronic end-organ damage, and early death. In high-income countries, at least 95% of children with the disease survive into adulthood, resulting in a growing population of affected adults with significant comorbidities, complex medical issues, and not enough specialists to provide care. Hydroxyurea is the primary therapy, and recent advances in understanding disease pathophysiology have led to new therapies; progress in bone marrow transplant and gene editing has resulted in cure in some patients. The purpose of this review is to provide an overview of the diagnosis, common acute and chronic clinical manifestations, and best practices for management of sickle cell disease.

Proteinuric and nonproteinuric chronic kidney disease among patients with sickle cell anaemia (HbSS) attending a tertiary hospital in north-eastern Nigeria

OBJECTIVE/BACKGROUND

Individuals with sickle cell anaemia (SCA) may manifest various forms of renal abnormalities. Proteinuria is an early marker of renal dysfunction and a strong risk factor for chronic kidney disease (CKD) progression in both patients with SCA and non-SCA population. Currently, the degree of attention given to proteinuric CKD far exceeds that of nonproteinuric CKD, and risk factors that might trigger a progressive decline of the glomerular filtration rate (GFR) in the absence of proteinuria have not been well evaluated in SCA. The aim of this study was to compare the clinical and laboratory parameters among SCA patients with proteinuric and nonproteinuric CKD.

METHODS

This was a cross-sectional study conducted at the University of Maiduguri Teaching Hospital in north-eastern Nigeria between January 2013 and April 2018. Clinical variables including age of diagnosis of SCA, frequency of vaso-occlusive crises, number of hospitalizations per annum and transfusion therapy were collected. Laboratory data including haematological profile and renal function test were obtained from routine blood sampling.

RESULTS

A total of 257 patients with SCA (HbSS) were enrolled during the study period of which 42 had proteinuric CKD, and 48 had nonproteinuric CKD. The two groups were matched for the number of hospital admission (p = .063) and blood transfusion per year (p = .450), frequency of painful crisis (p = .210), systolic blood pressure (p = .084) and diastolic blood pressure (p = .400). In the proteinuric CKD group, the mean serum creatinine was higher (332.17 µmol/L, p = .001) and the estimated GFR was lower (31.88 mL/min, p = .046). The serum alkaline phosphatase was higher in the nonproteinuric CKD group (81.81 IU/L, p = .012).

CONCLUSION

Nonproteinuric CKD was more frequent than proteinuric CKD in our study population; however, the proteinuric group presented with more advanced disease.

Rational Drug Design of Peptide-Based Therapies for Sickle Cell Disease

Sickle cell disease (SCD) is a group of inherited disorders affecting red blood cells, which is caused by a single mutation that results in substitution of the amino acid valine for glutamic acid in the sixth position of the β-globin chain of hemoglobin. These mutant hemoglobin molecules, called hemoglobin S, can polymerize upon deoxygenation, causing erythrocytes to adopt a sickled form and to suffer hemolysis and vaso-occlusion. Until recently, only two drug therapies for SCD, which do not even fully address the manifestations of SCD, were approved by the United States (US) Food and Drug Administration. A third treatment was newly approved, while a monoclonal antibody preventing vaso-occlusive crises is also now available. The complex nature of SCD manifestations provides multiple critical points where drug discovery efforts can be and have been directed. These notwithstanding, the need for new therapeutic approaches remains high and one of the recent efforts includes developments aimed at inhibiting the polymerization of hemoglobin S. This review focuses on anti-sickling approaches using peptide-based inhibitors, ranging from individual amino acid dipeptides investigated 30-40 years ago up to more promising 12- and 15-mers under consideration in recent years.

American Society of Hematology 2019 guidelines for sickle cell disease: cardiopulmonary and kidney disease

BACKGROUND

Prevention and management of end-organ disease represent major challenges facing providers of children and adults with sickle cell disease (SCD). Uncertainty and variability in the screening, diagnosis, and management of cardiopulmonary and renal complications in SCD lead to varying outcomes for affected individuals.

OBJECTIVE

These evidence-based guidelines of the American Society of Hematology (ASH) are intended to support patients, clinicians, and other health care professionals in their decisions about screening, diagnosis, and management of cardiopulmonary and renal complications of SCD.

METHODS

ASH formed a multidisciplinary guideline panel that included 2 patient representatives and was balanced to minimize potential bias from conflicts of interest. The Mayo Evidence-Based Practice Research Program supported the guideline development process, including performing systematic evidence reviews up to September 2017. The panel prioritized clinical questions and outcomes according to their importance for clinicians and patients. The panel used the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach, including GRADE evidence-to-decision frameworks, to assess evidence and make recommendations, which were subject to public comment.

RESULTS

The panel agreed on 10 recommendations for screening, diagnosis, and management of cardiopulmonary and renal complications of SCD. Recommendations related to anticoagulation duration for adults with SCD and venous thromboembolism were also developed.

CONCLUSIONS

Most recommendations were conditional due to a paucity of direct, high-quality evidence for outcomes of interest. Future research was identified, including the need for prospective studies to better understand the natural history of cardiopulmonary and renal disease, their relationship to patient-important outcomes, and optimal management.

Kidney biopsy findings in children with sickle cell disease: a Midwest Pediatric Nephrology Consortium study

BACKGROUND

Renal damage is a progressive complication of sickle cell disease (SCD). Microalbuminuria is common in children with SCD, while a smaller number of children have more severe renal manifestations necessitating kidney biopsy. There is limited information on renal biopsy findings in children with SCD and subsequent management and outcome.

METHODS

This is a multicenter retrospective analysis of renal biopsy findings and clinical outcomes in children and adolescents with SCD. We included children and adolescents (age ≤ 20 years) with SCD who had a kidney biopsy performed at a pediatric nephrology unit. The clinical indication for biopsy, biopsy findings, subsequent treatments, and outcomes were analyzed.

RESULTS

Thirty-six SCD patients (ages 4-19 years) were identified from 14 centers with a median follow-up of 2.6 years (0.4-10.4 years). The indications for biopsy were proteinuria (92%) and elevated creatinine (30%). All biopsies had abnormal findings, including mesangial hypercellularity (75%), focal segmental glomerulosclerosis (30%), membranoproliferative glomerulonephritis (16%), and thrombotic microangiopathy (2%). There was increased use of hydroxyurea, angiotensin-converting-enzyme inhibitors, and angiotensin receptor blockers following renal biopsy. At last follow-up, 3 patients were deceased, 2 developed insulin-dependent diabetes mellitus, 6 initiated chronic hemodialysis, 1 received a bone marrow transplant, and 1 received a kidney transplant.

CONCLUSIONS

Renal biopsies, while not commonly performed in children with SCD, were universally abnormal. Outcomes were poor in this cohort of patients despite a variety of post-biopsy interventions. Effective early intervention to prevent chronic kidney disease (CKD) is needed to reduce morbidity and mortality in children with SCD.

Therapeutic strategies for sickle cell disease: towards a multi-agent approach

For over 100 years, clinicians and scientists have been unravelling the consequences of the A to T substitution in the β-globin gene that produces haemoglobin S, which leads to the systemic manifestations of sickle cell disease (SCD), including vaso-occlusion, anaemia, haemolysis, organ injury and pain. However, despite growing understanding of the mechanisms of haemoglobin S polymerization and its effects on red blood cells, only two therapies for SCD - hydroxyurea and L-glutamine - are approved by the US Food and Drug Administration. Moreover, these treatment options do not fully address the manifestations of SCD, which arise from a complex network of interdependent pathophysiological processes. In this article, we review efforts to develop new drugs targeting these processes, including agents that reactivate fetal haemoglobin, anti-sickling agents, anti-adhesion agents, modulators of ischaemia-reperfusion and oxidative stress, agents that counteract free haemoglobin and haem, anti-inflammatory agents, anti-thrombotic agents and anti-platelet agents. We also discuss gene therapy, which holds promise of a cure, although its widespread application is currently limited by technical challenges and the expense of treatment. We thus propose that developing systems-oriented multi-agent strategies on the basis of SCD pathophysiology is needed to improve the quality of life and survival of people with SCD.

Effect of renin-angiotensin-aldosterone system blocking agents on progression of glomerulopathy in sickle cell disease

Although renin-angiotensin-aldosterone system (RAAS) blocking agents decrease albuminuria in short-term studies, there is no evidence confirming their long-term efficacy in sickle cell disease (SCD). In a single-centre, retrospective study, we evaluated the long-term effect of RAAS blocking agents on proteinuria and declining estimated glomerular filtration rates (eGFR). Eighty-six patients on RAAS blocking agents for proteinuria, followed for a median of 2·28 years, were compared with 68 patients with proteinuria followed for 2·24 years who were not receiving such treatment. The log odds of proteinuria decreased over time in patients on RAAS blocking agents (β: -0·23, P = 0·03) and in the non-treatment group (β: -0·54, P < 0·0001), but was not statistically different between both groups (β: 0·31, P = 0·063). The eGFR declined over time in patients on RAAS blocking agents (β: -2·78, P < 0·0001) and in those not on such treatment (β: -4·7, P < 0·0001), and was statistically different between both groups (β: 1·9, P = 0·0002). Baseline eGFR was associated with mortality (Hazard rato: 0·97, P < 0·0001), but RAAS blocking agents had no significant effect on mortality. These data suggest that RAAS blockade may slow the loss of kidney function in SCD.

Nephrin as a biomarker of sickle cell glomerulopathy in Malawi

BACKGROUND

Glomerulopathy is an increasingly identified complication in young patients with sickle cell disease (SCD). Hyperfiltration and albuminuria followed by declining glomerular filtration rates and eventual end-stage renal disease (ESRD) is assumed to be the typical progression of glomerular disease. There are only a few reported biomarkers to identify early-stage renal disease in SCD.

PROCEDURES

We detail the renal profile of 101 children with SCD in Malawi and propose a novel urinary biomarker for the identification of early renal disease.

RESULTS

Among children with sickle cell anemia, 24.8% had a urine albumin-creatinine ratio of 30 mg/g or above. In univariate analysis, only patients with higher urinary nephrin, a urinary marker of glomerular injury, had significantly greater odds of having albuminuria. In multivariable analysis, nephrin remained significantly associated with albuminuria. A nephrin-creatinine ratio (NCR) cut-point of 622 ng/mg, the 50^th percentile, was associated with a 45.8 times greater odds of having albuminuria in children with nephrinuria above this value. Further analysis revealed this urinary NCR cut-point to have 96% sensitivity, 64% specificity, 47% positive predictive value, and 98% negative predictive value for the presence of albuminuria.

CONCLUSIONS

These data suggest that a substantial number of children with SCD in Malawi have renal disease and could be at risk for worsening nephropathy and ESRD as they age. Our data suggest that urinary nephrin could be utilized as an early marker of glomerular disease in SCD.

Renal protection by atorvastatin in a murine model of sickle cell nephropathy

Recent studies have demonstrated pleiotropic effects of statins in various mouse models of kidney disease. In this study, Townes humanized sickle cell mice were treated for 8 weeks with atorvastatin at a dose of 10 mg/kg/day starting at 10 weeks of age. Treatment with atorvastatin significantly reduced albuminuria, and improved both urine concentrating ability and glomerular filtration rate. Atorvastatin also decreased markers of kidney injury and endothelial activation, and ameliorated oxidant stress in renal tissues and peripheral macrophages. Atorvastatin downregulated the expression of mRNA levels of the NADPH oxidases, Cybb (also termed Nox2) and Nox4, which are major sources of oxidant stress in the kidney. These findings highlight the pleiotropic effects of atorvastatin and suggest that it may provide beneficial effects in sickle cell nephropathy.

Prevalence of Microalbuminuria in Adult Patients with Sickle Cell Disease in Eastern Saudi Arabia

Background

Proteinuria is a common feature of sickle cell nephropathy (SCN) that can progress to renal insufficiency and end stage renal disease. Microalbuminuria (MA) is the earliest manifestation of SCN and precedes the development of overt proteinuria. In addition to the renal consequences, MA is linked to cardiovascular complications. Periodic screening and early detection of MA allow early intervention that may reduce the risk of progression to advanced renal failure and cardiovascular diseases.

Objective

The aim of this study was to investigate the prevalence of MA in patients with SCD in the eastern region of Saudi Arabia.

Methods

A prospective cross-sectional observational study was conducted at Johns Hopkins Aramco Healthcare (JHAH). Urine samples of SCD patients 18 years old and older were tested for the presence of MA using urinary albumin over creatinine ratio (ACR). Correlation was tested with multiple variables including age, gender, body mass index (BMI), hemoglobin level, blood pressure, blood transfusion history, pain episodes, and use of hydroxyurea.

Results

Urine samples were tested on 72 patients. The mean age of the study cohort was 35 ± 16.9 years. Microalbuminuria was detected in 18 patients (25%). No correlation was found with any of the tested variables.

Conclusion

Microalbuminuria is a common finding in patients with SCD in eastern Saudi Arabia. Patients with SCD should be screened for MA, and those with positive tests should probably be treated with antiproteinuric agents that may slow the progression to advanced stages of renal failure and decrease the risk of cardiovascular diseases.

Sickle cell nephropathy: an update on pathophysiology, diagnosis, and treatment

Sickle cell nephropathy is a major complication of sickle cell disease. It manifests in different forms, including glomerulopathy, proteinuria, hematuria, and tubular defects, and frequently results in end-stage renal disease (ESRD). Different pathophysiologic mechanisms have been proposed to explain the development of nephropathy in SCD, where hemolysis and vascular occlusion are the main contributors in the manifestations of this disease. Markers of renal injury, such as proteinuria and tubular dysfunction, have been associated with outcomes among patients with sickle cell nephropathy and provide means for early detection of nephropathy and screening prior to progression to renal failure. In small-sized clinical trials, hydroxyurea has demonstrated to be effective in slowing the progression to ESRD. Dialysis and renal transplantation represent the last resort for patients with sickle cell nephropathy. Nevertheless, despite the availability of diagnostic and therapeutic strategies, sickle cell nephropathy remains a challenging and under-recognized complication for patients with sickle cell disease.

Chronic organ failure in adult sickle cell disease

Sickle cell disease is now a chronic adult illness characterized by progressive multiorgan failure, particularly involving the brain and kidney. The etiology is multifactorial; it includes hemolysis and nitric oxide deficiency. As patients age, most experience neurologic insult. Twenty-five percent of older adults have had a clinical stroke and at least half of the population have had a silent infarct, cortical atrophy, and neurocognitive impairment. Periodic screening with neuroimaging and neurocognitive testing is recommended. Identification and correction of modifiable risk factors such as nocturnal hypoxemia, obstructive sleep apnea, and physical exercise programs should be implemented. Patients with neurocognitive impairment require cognitive remediation and educational accommodations. Chronic renal disease occurs in 25% of older adults and results in 50% of their deaths. Renal failure often develops insidiously. It can be prevented or minimized by early screening and treatment of modifiable risk factors including hypertension and microalbuminuria. There is an increasing number of therapeutic options, including inhibitors of the renin angiotensin system, angiotensin-II receptor blockers, endothelin-1 receptor antagonist, and haptoglobin therapy. Patients with sickle cell disease have increased mortality rates from renal failure compared with nonsickle cell patients, in part from a lack of access to early multidisciplinary care, including timely initiation of dialysis and renal transplantation.

Losartan therapy decreases albuminuria with stable glomerular filtration and permselectivity in sickle cell anemia

Sickle cell nephropathy begins with hyperfiltration and microalbuminuria and may progress to renal failure. The aim of this study was to determine the effects of losartan on glomerular function and albumin excretion in sickle cell anemia (SCA). Individuals with SCA on hydroxyurea with persistent albuminuria were enrolled in a 1-year study of losartan. Glomerular filtration rate (GFR) measured by iohexol clearance, albumin excretion rate (AER), and fractional clearance of dextran were assessed at baseline, short-term (1-2month), and long-term (≥12month) intervals. Twelve subjects (6 microalbuminuria, 6 macroalbuminuria) completed short-term studies; 8 completed long-term studies. Baseline GFR was 112ml/min/1.73m² (71-147ml/min/1.73m²). AER decreased significantly at the short-term (median decrease -134 mcg/min, p=0.0063). GFR was not significantly-different at short-term or long-term intervals. Dextran clearance improved for diameters smaller than albumin (<36Å) but not larger sizes. Losartan therapy for ≥1year in sickle nephropathy results in lower albumin excretion with stable GFR. Filtration of neutral molecules ≥36Å was not changed by losartan, suggesting that the effect of losartan is a mechanism other than alteration of glomerular filtration size-selectivity.

Clinical Features of β-Thalassemia and Sickle Cell Disease

Sickle cell disease (SCD) and β-thalassemia are among the most common inherited diseases, affecting millions of persons globally. It is estimated that 5-7% of the world's population is a carrier of a significant hemoglobin variant. Without early diagnosis followed by initiation of preventative and therapeutic care, both SCD and β-thalassemia result in significant morbidity and early mortality. Despite great strides in the understanding of the molecular basis and pathophysiology of these conditions, the burden of disease remains high, particularly in limited resource settings. Current therapy relies heavily upon the availability and safety of erythrocyte transfusions to treat acute and chronic complications of these conditions, but frequent transfusions results in significant iron overload, as well as challenges from acquired infections and alloimmunization. Hydroxyurea is a highly effective treatment for SCD but less so for β-thalassemia, and does not represent curative therapy. As technology and use of cellular and gene therapies expand, SCD and thalassemia should be among the highest disease priorities.