Sickle cell nephropathy - a practical approach

Secretory Phospholipase A2 Levels Are High in Women with Sickle Cell Disease and Menstruation-Induced Vaso-Occlusive Crises

Menstruation-induced vaso-occlusive crisis (MIVOC) is a significant cause of morbidity in women with sickle cell disease (SCD). Secretory phospholipase A2 (sPLA2) is an inflammatory biomarker that is elevated in vaso-occlusive events such as acute chest syndrome (ACS), but its role in MIVOC is not previously studied. This study compared the serum level of sPLA2 among women with MIVOC and those without MIVOC. This is a comparative cross-sectional study. 354 women with SCD were screened for MIVOC using a structured questionnaire. sPLA2 levels were assayed using a standard ELISA while full blood counts were performed on an automated hematology analyzer. Data were analyzed using the SPSS software v26.0. Results were summarized as frequencies, percentages, and mean ± standard deviation. Variables were compared using the Student's t-test and Pearson's correlation. A p-value of <.05 was considered significant. The prevalence of MIVOC was 26.8%. Participants with MIVOC (n = 95) had significantly lower mean hemoglobin concentration (8.00 ± 2.03g/dL vs. 9.95 ± 4.15g/dL, p < .000), significantly higher mean platelets count (518.71 ± 84.58 × 109/L vs 322.21 ± 63.80 × 109/L, p < .000) and higher sPLA2 level (6.58 ± 1.94 IU vs 6.03 ± 0.42 IU, p = .008) compared to those without MIVOC (n = 95). Among participants with MIVOC, sPLA2 levels positively correlated with total white blood cell, absolute neutrophil, and lymphocyte counts. This study demonstrates that MIVOC is common among women with SCD and that the pathophysiology of MIVOC may have an inflammatory basis similar to that of ACS. The potential role of anti-inflammatory and antiplatelet agents in preventing and treating MIVOC may be explored.

Renal outcomes in pediatric patients with sickle cell disease: a single center experience in Saudi Arabia

Background

Sickle cell nephropathy (SCN) is a significant complication of sickle cell disease (SCD) with an asymptomatic onset in childhood and potential progression to chronic kidney disease (CKD). The clinical findings of SCN include hyposthenuria, hematuria, proteinuria, hyperfiltration, and CKD. Data on renal manifestation among patients with SCD in Saudi Arabia is lacking. Therefore, this study aimed to evaluate renal outcomes in patients with SCD who visited a hematology clinic at the National Guard Hospital, Jeddah.

Methods

We conducted a retrospective chart review of renal complications in patients with SCD who are within 0-14 years of age and on regular follow-ups at the pediatric hematology clinic in King Abdulaziz Medical City-Jeddah, Saudi Arabia.

Results

Among the 140 patients with SCD, 99 met the inclusion criteria. The median age at diagnosis was 18 (1-108) months. Two SCD phenotypes were observed, with 82 (83%) patients having sickle cell anemia (HbSS) and 17 (17%) having HbS/B+ thalassemia. Of the total patients, 92 (93%) were administered hydroxyurea (HU), with a median starting age of 48 (9-168) months. The most common renal complication observed during routine urinalysis was hematuria (38%), followed by proteinuria (11%). After stratifying the sample into four age groups (0-3 years old, 4-7 years old, 8-11 years old, and 12-14 years old), the mean glomerular filtration rate (GFR) values were 96.16, 101.36, 112.69, and 120.11 ml/min/1.73 m2 respectively. Renal imaging revealed abnormal findings in 27 (29%) patients. The most common abnormality observed on US was increased echogenicity (43%).

Conclusion

SCN is a significant complication of SCD. In this study, we assessed the renal outcomes in pediatric patients with SCD. After analyzing the clinical findings of SCN, we concluded that the presence of renal complications in pediatric patients presented a progressive pattern.

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.

Estimated glomerular filtration rate in Brazilian adults with sickle cell disease: results from the REDS-III multicenter cohort study

Chronic kidney disease (CKD) has a significant impact on sickle cell disease (SCD) morbidity and mortality. Early identification of individuals at highest risk of developing CKD may allow therapeutic intervention to prevent worse outcomes. This study aimed to evaluate the prevalence and risk factors for reduced estimated glomerular filtration rate (eGFR) among adults with SCD in Brazil. Participants in the REDS-III multicenter SCD cohort with more severe genotypes aged ≥ 18 years with at least two serum creatinine values were analyzed. The eGFR was calculated using the Jamaica Sickle Cell Cohort Study GFR equation. The eGFR categories were defined according to the K/DOQI. Participants with eGFR ≥ 90 were compared to those with those with eGFR < 90. Among the 870 participants, 647 (74.4%) had eGFR ≥ 90, 211 (24.3%) had eGFR 60 to 89, six (0.7%) had eGFR 30 to 59, and six (0.7%) had ESRD. Male sex (OR: 37.3; 95%CI: 22.4-65.1), higher age (OR: 1.04; 95%CI: 1.02-1.06), higher diastolic blood pressure (OR: 1.03; 95%CI: 1.009-1.06), lower Hb (OR: 0.80; 95%CI: 0.68-0.93), and lower reticulocytes (OR: 0.94; 95%CI: 0.89-0.99) levels were independently associated with eGFR < 90. There was a trend towards higher odds of death in participants with eGFR < 90 (OR: 1.8; 95%CI: 0.95-3.32; p = 0.065). In turn, participants with eGFR < 60 had a 12.2 (95%CI: 2.1-96.9) times higher odds for death when compared to those with eGFR ≥ 60. In this study, eGFR < 90 was observed in one-quarter of adults. Older age, male sex, higher diastolic blood pressure, lower hemoglobin, and lower reticulocyte levels were associated with occurrence of eGFR < 90. Estimated GFR < 60 increased the risk of mortality.

Glomerular hyperfiltration: part 2-clinical significance in children

Glomerular hyperfiltration (GHF) is a phenomenon that can occur in various clinical conditions affecting the kidneys such as sickle cell disease, diabetes mellitus, autosomal dominant polycystic kidney disease, and solitary functioning kidney. Yet, the pathophysiological mechanisms vary from one disease to another and are not well understood. More so, it has been demonstrated that GHF may occur at the single-nephron in some clinical conditions while in others at the whole-kidney level. In this review, we explore the pathophysiological mechanisms of GHF in relation to various clinical conditions in the pediatric population. In addition, we discuss the role and mechanism of action of important factors such as gender, low birth weight, and race in the pathogenesis of GHF. Finally, in this current review, we further highlight the consequences of GHF in the progression of kidney disease.

Sickle cell nephropathy: insights into the pediatric population

The life expectancy of individuals with sickle cell disease has increased over the years, majorly due to an overall improvement in diagnosis and medical care. Nevertheless, this improved longevity has resulted in an increased prevalence of chronic complications such as sickle cell nephropathy (SCN), which poses a challenge to the medical care of the patient, shortening the lifespan of patients by 20-30 years. Clinical presentation of SCN is age-dependent, with kidney dysfunction slowly beginning to develop from childhood, progressing to chronic kidney disease and kidney failure during the third and fourth decades of life. This review explores the epidemiology, pathology, pathophysiology, clinical presentation, and management of SCN by focusing on the pediatric population. It also discusses the factors that can modify SCN susceptibility.

Reduced blood pressure in sickle cell disease is associated with decreased angiotensin converting enzyme (ACE) activity and is not modulated by ACE inhibition

Background

Sickle cell disease (SCD) incurs vaso-occlusive episodes and organ damage, including nephropathy. Despite displaying characteristics of vascular dysfunction, SCD patients tend to present relatively lower systemic blood pressure (BP), via an unknown mechanism. We investigated associations between BP and renin-angiotensin-system (RAS) components in SCD and determined whether an inhibitor of angiotensin converting enzyme (ACE; often used to slow SCD glomerulopathy) further modulates BP and RAS components in a murine model of SCD.

Methods

BP was compared in human subjects and mice with/without SCD. Plasma angiotensin II, ACE and renin were measured by immunoassay. BP was reevaluated after treating mice with enalapril (25 mg/kg, 5x/week) for 5 weeks; plasma and organs were stored for angiotensin II and ACE activity measurement, and quantitative real-time PCR.

Results

Diastolic BP and systolic BP were significantly lower in patients and mice with SCD, respectively, compared to controls. Reduced BP was associated with increased plasma renin and markers of kidney damage (mice) in SCD, as well as significantly decreased plasma ACE concentrations and ACE enzyme activity. As expected, enalapril administration lowered BP, plasma angiotensin II and organ ACE activity in control mice. In contrast, enalapril did not further reduce BP or organ ACE activity in SCD mice; however, plasma angiotensin II and renin levels were found to be significantly higher in enalapril-treated SCD mice than those of treated control mice.

Conclusion

Relative hypotension was confirmed in a murine model of SCD, in association with decreased ACE concentrations in both human and murine disease. Given that ACE inhibition has an accepted role in decreasing BP, further studies should investigate mechanisms by which ACE depletion, via both Ang II-dependent and alternative pathways, could contribute to reduce BP in SCD and understand how ACE inhibition confers Ang II-independent benefits on kidney function 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.

Mineral bone disorders and kidney disease in hospitalized children with sickle cell anemia

BACKGROUND

Mineral bone disorders (MBD) are common in sickle cell anemia (SCA). Frequent vaso-occlusive crises (VOC) further impact MBD in children with SCA. We evaluated the prevalence of markers of SCA-related MBD (sMBD) in hospitalized children and assessed the relationship between sMBD and individual mineral abnormalities with kidney disease.

METHODS

We prospectively recruited 185 children with SCA hospitalized with a VOC. Serum measures of mineral bone metabolism (calcium, phosphate, parathyroid hormone, 25-hydroxy vitamin D, FGF23, osteopontin) were measured at enrollment. The primary outcome was markers of sMBD defined as a composite of hypocalcemia, hyperphosphatemia, hyperparathyroidism, or deficiency in 25-OH vitamin D. Secondary outcomes included individual abnormalities in mineral metabolism. The Kidney Disease: Improving Global Outcomes (KDIGO) guidelines were used to define SCA-associated acute kidney injury (AKI). AKI was further assessed using urine NGAL as a marker of tubular injury. Acute kidney disease (AKD) was defined as a composite of AKI, an eGFR < 90 ml/min per 1.73 m² using the Cystatin C GFR equation, or evidence of structural injury (positive biomarker test or albuminuria).

RESULTS

The mean age of children was 8.9 years and 41.6% were female. The prevalence of sMBD was 47.6%, with hypocalcemia the most frequent abnormality (29.9%, 55/184) followed by hyperphosphatemia (20.7%, 38/184), hyperparathyroidism (8.7%, 16/185), and vitamin D deficiency (5.4%, 10/185). There was no association between sMBD and sKDIGO-defined AKI using serial changes in creatinine or when incorporating biomarkers to define AKI. However, the presence of AKD was associated with a 2.01-fold increased odds of sMBD (95% CI 1.05 to 3.83) and was driven by a decrease in eGFR (OR, 2.90 95% CI: 1.59 to 5.29). When evaluating individual mineral abnormalities, hypocalcemia was associated with AKD and low eGFR while hyperparathyroidism was associated with low eGFR, AKI and structural injury. Vitamin D deficiency was associated with structural kidney injury. Vitamin D deficiency, hyperparathryoidism, and increases in FGF23 and osteopontin predicted mortality (p < 0.05 for all).

CONCLUSION

MBD is common among children with SCA hospitalized with VOC. Biomarkers of kidney injury and bone health may help risk stratify children at risk of sMBD. Routine evaluation of sMBD in children with SCA may improve long-term bone health.

Angiotensin-converting enzyme (ACE) inhibitors for proteinuria and microalbuminuria in people with sickle cell disease

BACKGROUND

Sickle cell disease is a group of disorders characterized by deformation of erythrocytes. Renal damage is a frequent complication in sickle cell disease as a result of long-standing anemia and disturbed circulation through the renal medullary capillaries. Due to the improvement in life expectancy of people with sickle cell disease, there has been a corresponding significant increase in the incidence of renal complications. Microalbuminuria and proteinuria are noted to be a strong predictor of subsequent renal failure. There is extensive experience and evidence with angiotensin-converting enzyme (ACE) inhibitors over many years in a variety of clinical situations for patients who do not have sickle cell disease, but their effect in people with this disease is unknown. It is common practice to administer ACE inhibitors for sickle nephropathy due to their renoprotective properties; however, little is known about their effectiveness and safety in this setting. This is an update of a Cochrane Review first published in 2013 and 2015.

OBJECTIVES

To determine the effectiveness of ACE inhibitor administration in people with sickle cell disease for decreasing intraglomerular pressure, microalbuminuria and proteinuria and to to assess the safety of ACE inhibitors as pertains to their adverse effects.

SEARCH METHODS

The authors searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Hameoglobinopathies Trials Register comprising references identified from comprehensive electronic database searches and handsearches of relevant journals and abstract books of conference proceedings. Date of the most recent search: 18 October 2021. We also searched clinical trial registries. Date of the most recent search: 22 August 2021.

SELECTION CRITERIA

Randomized or quasi-randomized controlled trials of ACE inhibitors designed to reduce microalbuminuria and proteinuria in people with sickle cell disease compared to either placebo or standard treatment regimen.

DATA COLLECTION AND ANALYSIS

Three authors independently applied the inclusion criteria in order to select studies for inclusion in the review. Two authors assessed the risk of bias of studies and extracted data and the third author verified these assessments.

MAIN RESULTS

Seven studies were identified through the searches. Six studies were excluded. The included study randomized 22 participants (7 males and 15 females) having proteinuria or microalbuminuria with sickle cell disease and treated the participants for six months (median length of follow up of three months) with captopril or placebo. Overall, the certainty of the evidence provided in this review was very low, since most risk of bias domains were judged to have either an unclear or a high risk of bias. Because of this, we are uncertain whether captopril makes any difference, in total urinary albumin excretion (at six months) as compared to the placebo group, although it yielded a mean difference of -49.00 (95% confidence interval (CI) -124.10 to 26.10) or in the absolute change score, although it yielded a mean difference of -63.00 (95% CI -93.78 to -32.22). At six months albumin excretion in the captopril group was noted to decrease from baseline by a mean (standard deviation) of 45 (23) mg/day and the placebo group was noted to increase by 18 (45) mg/day. Serum creatinine and potassium levels were reported constant throughout the study (very low-certainty evidence). The potential for inducing hypotension should be highlighted; the study reported a decrease of 8 mmHg in systolic pressure and 5 mmHg in diastolic and mean blood pressure (very low-certainty evidence).

AUTHORS' CONCLUSIONS

Overall, we judged the certainty of the evidence to be very low. The included study selectively reported its results, was not powered to detect a group difference, should it exist, and otherwise did not offer enough information to allow us to judge the bias inherent in the study. Indirectness (in relation to the limited age and type of population included) and imprecision (wide confidence intervals around the effect estimate) were observed. More long-term studies involving multiple centers and larger cohorts using a randomized-controlled design are warranted, especially among the pediatric age group. Detailed reporting of each outcome measure is necessary to allow a clear cut interpretation in a systematic review. One of the difficulties encountered in this review was the lack of detailed data reported in the included study. Overall, we judged the certainty of this evidence to be very low.

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.

All-Cause Mortality and Incidence of Major Adverse Cardiac Events in Sickle Cell Nephropathy: A Comparative Study

Background

Sickle cell disease (SCD) is an autosomal recessive disease resulting in hemolytic anemia and recurrent vaso-occlusive events. Consequently, it can result in a broad range of functional and structural renal and cardiac alterations. Chronic kidney disease (CKD), in SCD, is associated with proteinuria, microalbuminuria, and hemoglobinuria. Cardiac complications in SCD include pulmonary hypertension, left ventricular diastolic heart disease, dysrhythmia, and sudden death. In patients with advancing age, cardio-renal dysfunction can have substantial effects on morbidity and mortality. Our primary aim was to compare the incidence of major adverse cardiac events (MACE) and all-cause mortality in sickle cell nephropathy (SCN).

Methods

In this retrospective study, we used International Classification of Diseases (ICD)-10 codes to identify admissions in 2019 with a diagnosis of MACE with a prior diagnosis of SCD and/or SCN. Our search of the HCA Healthcare Enterprise Data Warehouse for adult patients >18 years yielded 6,693 patients with SCD, of which 658 patients (9.8%) had SCN. Primary endpoints were incidence of MACE and all-cause mortality. Patients with MACE encompassed those with nonfatal stroke, nonfatal myocardial infarction, and congestive heart failure (CHF) exacerbations. A secondary endpoint was length of stay (LOS). Logistic regression analysis was used for MACE and all-cause mortality. LOS was analyzed using multiple linear regression analysis. Results were considered statistically significant for analyses showing p <0.05. All outcomes were adjusted for demographic variables and comorbidities.

Results

Logistic regression, after adjustment for comorbidities, demonstrated that SCN patients had significantly higher odds of all-cause mortality (odds ratio [OR] 2.343, p = 0.035, 95% confidence interval [CI] 1.063-5.166) compared to patients without SCN. Compared to those without SCN, those with SCN did not have a higher odds of MACE (OR 1.281, p = 0.265, 95% CI 0.828-1.982). Linear regression for LOS did not reveal a significant association with SCN (p = 0.169, 95% CI 0.157-0.899).

Conclusion

Based on the analysis of 6,693 patients with SCD, SCN was associated with significantly higher odds of all-cause mortality. SCN was not associated with significantly higher odds of MACE or prolonged LOS.

Outcomes following kidney transplantation in patients with sickle cell disease: The impact of automated exchange blood transfusion

There are over 12,000 people with sickle cell disease (SCD) in the UK, and 4-12% of patients who develop Sickle Cell Nephropathy (SCN) progress to End Stage Renal Disease (ESRD). Renal transplantation offers the best outcomes for these patients with but their access to transplantation is often limited. Regular automated exchange blood transfusions (EBT) reduce the complications of SCD and may improve outcomes. However, concerns over alloimmunisation limit its widespread implementation. In this retrospective multicenter study, data were collected on 34 SCD patients who received a kidney transplant across 6 London Hospitals between 1997 and 2017. 20/34 patients were on an EBT program, pre or post renal transplantation. Overall patient and graft survival were inferior to contemporaneous UK data in the ESRD population as a whole, a finding which is well-recognised. However, patient survival (CI 95%, p = 0.0032), graft survival and graft function were superior at all time-points in those who received EBT versus those who did not. 4/20 patients (20%) on EBT developed de novo donor specific antibodies (DSAs). 3/14 patients (21%) not on EBT developed de novo DSAs. The incidence of rejection in those on EBT was 5/18 (28%), as compared with 7/13 (54%) not on EBT. In conclusion, our data, while limited by an inevitably small sample size and differences in the date of transplantation, do suggest that long-term automated EBT post renal transplant is effective and safe, with improvement in graft and patient outcomes and no increase in antibody formation or graft rejection.

Elimination of the fibrinogen integrin αMβ2-binding motif improves renal pathology in mice with sickle cell anemia

Sickle cell anemia (SCA) is caused by a point mutation in the β-globin gene that leads to devastating downstream consequences including chronic hemolytic anemia, episodic vascular occlusion, and cumulative organ damage resulting in death. SCA patients show coagulation activation and inflammation even in the absence of vascular occlusion. The coagulation factor fibrinogen is not only central to hemostasis but also plays important roles in pathologic inflammatory processes, in part by engaging neutrophils/macrophages through the α_Mβ₂ integrin receptor. To determine whether fibrin(ogen)-mediated inflammation is a driver of SCA-associated pathologies, hematopoietic stem cells from Berkeley sickle mice were transplanted into homozygous Fibγ^390-396A mice that express normal levels of a mutant form of fibrin(ogen) that does not engage α_Mβ₂ Fibγ^390-396A mice with SCA displayed an impressive reduction of reactive oxygen species (ROS) in white blood cells (WBCs), decreased circulating inflammatory cytokines/chemokines, and significantly improved SCA-associated glomerular pathology highlighted by reduced glomerulosclerosis, inflammatory cell infiltration, ischemic lesions, mesangial thickening, mesangial hypercellularity, and glomerular enlargement. In addition, Fibγ^390-396A mice with SCA had improved glomerular protective responses and podocyte/mesangial transcriptional signatures that resulted in reduced albuminuria. Interestingly, the fibrinogen γ^390-396A mutation had a negligible effect on cardiac, lung, and liver functions and pathologies in the context of SCA over a year-long observation period. Taken together, our data support that fibrinogen significantly contributes to WBC-driven inflammation and ROS production, which is a key driver of SCA-associated glomerulopathy, and may represent a novel therapeutic target against irreversible kidney damage in SCA.

Prevalence and correlates of microalbuminuria in Yemeni children with sickle cell disease

Microalbuminuria (MA) has been recognized as a sensitive marker of early glomerular injury and a predictor of kidney dysfunction in patients with sickle cell disease (SCD). Limited data are available about MA in SCD children in the Arab countries and none from Yemen. The aim of this study is to determine the prevalence and correlates of MA among 101 children aged 1-16 years, with SCD at their steady state. Children were recruited during their routine health-care visits to the pediatric outpatient clinic in Al-Sadaqa general teaching hospital, Aden, Yemen, between September 2014 and February 2015. A random spot urine sample for each child was screened for MA using Micral-Test strips method. Data on clinical history, anthropometry, blood pressure (BP), and laboratory investigations were obtained. The overall prevalence of MA in this sample was 30.7%, with male predominance (80.6%) (P <0.05). The mean age of children with MA was 7.5 ± 3.2 years, and 10% of them were under five years of age. MA was correlated to both hemoglobin and hematocrit levels, which found to have protective effect against MA (Odds ratio = 0.17 and 0.59, respectively, P <0.05). No correlations were found between MA with age, height, weight, body mass index, recurrent clinical events (painful crises, blood transfusions, and hospitalizations), or fetal hemoglobin levels. BP measurements for all individuals were within the normal ranges, but systolic and diastolic BP were significantly higher in those with MA than without. This study demonstrated a high prevalence of MA in Yemeni children with SCD, and affecting young children as early as 2.5 years of age. Screening for MA as one of the early renal injury markers in children with SCD may help in the prevention of permanent loss of renal function and subsequent renal insufficiency in adulthood.

Tubular Acidification Defect in Adults with Sickle Cell Disease

BACKGROUND AND OBJECTIVES

Metabolic acidosis is a frequent manifestation of sickle cell disease but the mechanisms and determinants of this disorder are unknown. Our aim was to characterize urinary acidification capacity in adults with sickle cell disease and to identify potential factors associated with decreased capacity to acidify urine.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Among 25 adults with sickle cell disease and an eGFR of ≥60 ml/min per 1.73 m² from a single center in France, we performed an acute acidification test after simultaneous administration of furosemide and fludrocortisone. A normal response was defined as a decrease in urinary pH <5.3 and an increase in urinary ammonium excretion ≥33 µEq/min at one or more of the six time points after furosemide and fludrocortisone administration.

RESULTS

Of the participants (median [interquartile range] age of 36 [24-43] years old, 17 women), 12 had a normal and 13 had an abnormal response to the test. Among these 13 participants, nine had normal baseline plasma bicarbonate concentration. Plasma aldosterone was within the normal range for all 13 participants with an abnormal response, making the diagnosis of type 4 tubular acidosis unlikely. The participants with an abnormal response to the test were significantly older, more frequently treated with oral bicarbonate, had a higher plasma uric acid concentration, higher hemolysis activity, lower eGFR, lower baseline plasma bicarbonate concentration, higher urine pH, lower urine ammonium ion excretion, and lower fasting urine osmolality than those with a normal response. Considering both groups, the maximum urinary ammonium ion excretion was positively correlated with fasting urine osmolality (r ²=0.34, P=0.002), suggesting that participants with sickle cell disease and lower urine concentration capacity have lower urine acidification capacity.

CONCLUSIONS

Among adults with sickle cell disease, impaired urinary acidification capacity attributable to distal tubular dysfunction is common and associated with the severity of hyposthenuria.

PODCAST

This article contains a podcast at https://www.asn-online.org/media/podcast/CJASN/2019_12_10_CJN07830719.mp3.

Persistent hematuria among children with sickle cell anemia in steady state

Introduction

Persistent hematuria is a chronic complication of sickle cell anemia (SCA) which can progress to chronic kidney disease. The practice of early detection of persistent hematuria in children with SCA in steady state is important for timely intervention.

Objective

To determine the prevalence of persistent hematuria among children with sickle cell anemia in steady state and compare the result with that of a group of HbAA controls. The outcome will possibly strengthen the health policy on the need for regular screening for persistent hematuria in children with SCA.

Methods

Children with sickle cell anemia, aged 2–18 years in steady state, were recruited consecutively from the sickle cell clinic at the University of Nigeria teaching Hospital Enugu. The controls were similarly recruited from the children’s outpatient clinic. To determine persistent hematuria, dipstick urinalysis and microscopy were performed for both subjects and controls at enrollment and repeated after four weeks.

Results

Out of the 122 children with SCA studied, 5 (4.1%) had persistent hematuria. None (0%) of the 122 age- and gender-matched HbAA controls had persistent hematuria. This difference in prevalence of persistence between HbSS patients and HbAA controls was statistically significant (p = 0.02).

Conclusion

Persistent hematuria still occurs significantly more among children with SCA, even among those in steady state. Routine urinalysis at follow-up visits in children with SCA is strongly recommended, as this will aid early detection and prompt management to prevent progression to chronic kidney disease.

Technetium-99m-dimercaptosuccinic acid renal scintigraphy and single photon emission computed tomography/computed tomography in patients with sickle cell disease

PURPOSE

Sickle cell disease (SCD) is a common hematologic hereditary disorder characterized by vaso-occlusive episodes affecting multiple organs, and substantially alters renal structure and function. We aimed to evaluate the utility of renal scintigraphy and single photon emission computed tomography/computed tomography (SPECT/CT) with technetium-99m-dimercaptosuccinic acid (Tc-DMSA) in adult patients with SCD and no clinical evidence of renal insufficiency.

MATERIALS AND METHODS

Twenty-six patients (16 female) aged 23-58 years with SCD and no clinical evidence of renal insufficiency were prospectively studied. Planar and SPECT/CT images were, respectively, obtained after 3 and 4 hours of the injection of 110-180 MBq of Tc-DMSA. The relative radiopharmaceutical uptake and renal length were, respectively, determined using SPECT and CT images. Planar and SPECT/CT images were visually analyzed to identify focal areas of Tc-DMSA reduced uptake and anatomical deformities of the kidneys.

RESULTS

Focal areas of reduced Tc-DMSA uptake with an image aspect of renal scars or inflammation were present in 21/26 patients (81%). In 11/21 (52%) of these patients, the cortical lesions were clearly identified only on SPECT images. Prominent renal columns were observed in 17/26 (65%) patients. The left kidney tended to be more affected than the right kidney. Most patients had enlarged kidneys.

CONCLUSION

Tc-DMSA scintigraphy and SPECT/CT identify renal lesions possible related to renal infarcts or infections in most adult patients with SCD and no clinical evidence of renal insufficiency. Prominent renal columns and increased renal size tend to occur in most of these patients.

Why, Who, When, and How? Rationale for Considering Allogeneic Stem Cell Transplantation in Children with Sickle Cell Disease

Considering the progress made in the management of sickle cell disease during the past 30 years, along with the excellent results obtained with hematopoietic stem cell transplantation (SCT), it is important to reexamine why, who, when and how to recommend allogeneic SCT in children with sickle cell disease. While sickle cell disease has a low risk of death in children and a high risk for morbidity during aging, SCT carries an early risk of death, graft-vs-host disease and infertility. Nevertheless, SCT offers at least 95% chance of cure with low risk of chronic graft-vs-host disease when a matched-sibling donor is available and the risks of infertility can be reduced by ovarian, sperm or testis cryopreservation. Thus, all available therapies such as hydroxyurea, transfusions and SCT should be presented to the parents, providers, and affected children and discussed with them from infancy. Furthermore, the use of these therapies should be adjusted to the severity of the disease and to local availabilities in order to choose the treatment offering the best benefit/risk ratio.

Sickle cell disease nephropathy: an update on risk factors and potential biomarkers in pediatric patients

One of the major chronic complications of sickle cell disease (SCD) is sickle cell nephropathy. The aim of this review is to discuss the pathophysiology, natural history, clinical manifestations, risk factors, biomarkers and therapeutic approaches for sickle cell nephropathy, focusing on studies with pediatric patients. The earliest manifestation of renal disease is an increase in the glomerular filtration rate. A finding that may also be observed in early childhood is microalbuminuria. Nephrin, KIM-1, VGFs, chemokines and renin-angiotensin system molecules have emerged as potential early markers of renal dysfunction in SCD. In regards to a therapeutic approach, renin-angiotensin system inhibitors and angiotensin receptor blockers seem to be effective for the control of albuminuria in adults with SCD, although new studies in children are needed. The precise moment to begin renoprotection in SCD patients who should be treated remains to be determined.

Prevalence and factors associated with renal dysfunction among children with sickle cell disease attending the sickle cell disease clinic at a tertiary hospital in Northwestern Tanzania

BACKGROUND

Little is known on how the interaction between Sickle Cell Disease (SCD) and renal insults caused by other coexisting conditions in Sub Saharan Africa such as urinary schistosomiasis, malnutrition and HIV affect the prevalence of renal dysfunction in children with SCD.

OBJECTIVES

To determine the prevalence and factors associated with renal dysfunction among children with SCD aged 6 months to 12 years attended at a tertiary hospital in Northwestern Tanzania.

METHODS

A cross sectional hospital-based study with a short follow up component of 3 months for 153 children with SCD was done to document demographics, clinical characteristics and features of renal dysfunction including urine dipstick albuminuria (>20mg/l) and eGFR (<60ml/ml/min/1.73m2). Other potential renal insults such as HIV infection and Schistosomiasis were also evaluated.

RESULTS

At enrollment, 48/153(31.37%) children had renal dysfunction declining to 31(20.3%) at 3 months follow up. Acute chest syndrome (OR 3.04, 95% CI [1.08-8.96], p = 0.044), severe anemia (OR 0.44, 95% CI [0.26-0.76],p = 0.003), urinary schistosomiasis (OR 7.43, 95% CI [2.10-26.32] p<0.002) and acute malnutrition (OR 4.92, 95% CI [1.29-18.84], p = 0.020). were associated with renal dysfunction.

CONCLUSION

Where prevalent, urinary schistosomiasis and acute malnutrition increase the risk for renal dysfunction in children with SCD. We recommend albuminuria routine screening in children with SCD especially those presenting with acute chest syndrome, severe anemia and features of acute malnutrition for early detection of renal dysfunction among children with 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.

RON kinase inhibition reduces renal endothelial injury in sickle cell disease mice

Sickle cell disease patients are at increased risk of developing a chronic kidney disease. Endothelial dysfunction and inflammation associated with hemolysis lead to vasculopathy and contribute to the development of renal disease. Here we used a Townes sickle cell disease mouse model to examine renal endothelial injury. Renal disease in Townes mice was associated with glomerular hypertrophy, capillary dilation and congestion, and significant endothelial injury. We also detected substantial renal macrophage infiltration, and accumulation of macrophage stimulating protein 1 in glomerular capillary. Treatment of human cultured macrophages with hemin or red blood cell lysates significantly increased expression of macrophage membrane-associated protease that might cleave and activate circulating macrophage stimulating protein 1 precursor. Macrophage stimulating protein 1 binds to and activates RON kinase, a cell surface receptor tyrosine kinase. In cultured human renal glomerular endothelial cells, macrophage stimulating protein 1 induced RON downstream signaling, resulting in increased phosphorylation of ERK and AKT kinases, expression of Von Willebrand factor, increased cell motility, and re-organization of F-actin. Specificity of macrophage stimulating protein 1 function was confirmed by treatment with RON kinase inhibitor BMS-777607 that significantly reduced downstream signaling. Moreover, treatment of sickle cell mice with BMS-777607 significantly reduced glomerular hypertrophy, capillary dilation and congestion, and endothelial injury. Taken together, our findings demonstrated that RON kinase is involved in the induction of renal endothelial injury in sickle cell mice. Inhibition of RON kinase activation may provide a novel approach for prevention of the development of renal disease in sickle cell disease.

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.

Increased prevalence of renal cysts in patients with sickle cell disease

Background

Early detection and interventions have enabled patients with sickle cell disease (SCD) to live well into adulthood. Consequently, the chronicity of SCD allows for the insidious manifestation of multisystem complications, including renal damage. Cystic renal lesions are commonly incidentally discovered on ultrasound and computerised tomography (CT) imaging of the abdomen. Most are benign simple cysts, however, difficulties may be encountered if infection, rupture, haemorrhage or cancerous changes develop. We aimed to determine whether patients with SCD have a higher prevalence of simple renal cysts compared to non-SCD individuals.

Methods

Data for a group of 223 patients with SCD who had undergone an ultrasound and/or CT imaging of the abdomen were extracted for comparison with 180 control patients (haemoglobin genotype unknown), matched for age and ethnicity. Scans were evaluated for 198 SCD patients and 180 controls.

Results

Renal cysts were found in 58% of the SCD group and 20% of the controls (OR 5.4 (CI 2.6–11.0), RR 2.8 (CI 1.9–4.2)). Bilateral renal cysts were found in 28% of the SCD participants in comparison with 5% of the control group. In those who had one or more cysts identified, the average number of cysts was 3.76 for the SCD group and 1.94 for the controls. Men with SCD were more likely to develop cysts than women (66% vs 53%), as were men without SCD (22% vs 17%).

Conclusions

Simple renal cysts occur more frequently, are more abundant and develop at a younger age in patients with SCD than ethnically-matched controls. Further study of the mechanism underlying cyst formation may shed light on both sickle cell nephropathy and other cystic renal diseases.

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

Nephropathy is a common and progressive complication of sickle cell anemia (SCA). In SCA mice, we found that hyperangiotensinemia in the absence of hypertension underlies nephropathy, and its downregulation by losartan, an angiotensin-II-receptor-1 blocker, reduced albuminuria and progression of nephropathy. Therefore, we performed a phase-2 trial of oral losartan, given for 6 months, to explore whether it reduced albuminuria in children and adults with SCA. Participants were allocated to groups defined by class of baseline urinary albumin-to-creatinine ratio (UACR): no albuminuria (NoA), microalbuminuria (MicroA), and macroalbuminuria (MacroA). The primary endpoint was a ≥25% reduction UACR from baseline. There were 32 evaluable participants (mean age 24 years; NoA = 14, MicroA = 12, MacroA = 6). The primary endpoint was met in 83% of the MacroA group (P < 0.0001) and 58% of the MicroA group (P < 0.0001). Median fold-change in UACR was -0.74 for MacroA and -0.46 for MicroA. In MacroA and MicroA, UACR classification improved in 50% but worsened in 11%. Urine osmolality and estimated glomerular filtration rate (eGFR) did not change significantly. Losartan was discontinued in three participants [leg cramps, N = 1; decline in eGFR >25% (142➝104 mL/minute/1.73 m² ), N = 1; rise in serum creatinine >50% (0.2➝0.3 mg/dL), N = 1]. Albuminuria was associated with diastolic dysfunction and impaired functional capacity, although cardiopulmonary status was unchanged after 6 months of losartan therapy. In summary, losartan decreased urinary albumin excretion in most participants with albuminuria. Those with macroalbuminuria had the greatest benefit. This study forms the basis for a phase-3, randomized, placebo-controlled trial of losartan for the nephropathy of SCA.

Sickle cell disease and albuminuria: recent advances in our understanding of sickle cell nephropathy

Albuminuria is considered to be a relevant biomarker for the detection of early glomerular damage in patients with sickle cell disease (SCD). Improvements in our understanding of the pathophysiological processes and molecular mechanisms underlying albuminuria are required, because increasing numbers of patients with SCD are developing chronic kidney disease. The early recognition of sickle cell nephropathy (SCN) and studies of the natural course of this emerging renal disease are therefore crucial, together with identification of the associated clinical and biological risk factors, to make it possible to initiate kidney-protective therapy at early stages of renal impairment. The pathophysiological process underlying SCN remains hypothetical, but chronic haemolysis-related endothelial dysfunction and the relative renal hypoxia triggered by repeated vaso-occlusive crises have been identified as two potential key factors. The optimal preventive and curative management of albuminuria in the context of SCD is yet to be established, but recent studies have suggested that hydroxyurea therapy, the cornerstone of SCD treatment, could play a key role in reducing albuminuria. The place of conventional kidney-protecting measures, such as renin–angiotensin system inhibitors, in the treatment of SCD patients also remains to be determined.

Nephrology key information for internists

Hospitalists and primary care physicians encounter renal disease daily. Although most cases of acute kidney injury (AKI) are secondary to dehydration and resolve by giving fluids, many cases of AKI are due to not uncommon but unfamiliar causes needing nephrology evaluation. Common indications to consult a nephrologist on an emergency basis include hyperkalemia or volume overload in end stage renal disease patients (ESRD). Other causes of immediate consultation are cresenteric glomerulonephritis / rapidly progressive glomerulonephritis in which renal prognosis of the patient depends on timely intervention. The following evidence-based key information could improve patient care and outcomes.

Abbreviations: AKI: Acute kidney injury ESRD: End stage renal disease patients

Sickle cell disease in the older adult

Sickle cell disease (SCD) is an inherited haemoglobin disorder, associated with recurrent painful episodes, ongoing haemolytic anaemia and progressive multi-organ damage. Until the early 1990s, survival beyond the fourth decade for a patient with SCD was considered unusual and prompted case reports. Nowadays, in countries with developed health care systems, more than 90 percent of newborns with SCD survive into adulthood. Nevertheless, their life expectancy is still shortened by more than two decades compared to the general population. With an increasing life expectancy, SCD has now evolved into a debilitating disorder with substantial morbidity resulting from ongoing sickle cell vasculopathy and multi-organ damage. Limited data on health care issues of older adults with SCD poses multiple challenges to patients, their families and health care providers. In this review, we will address and discuss acute and chronic complications of SCD with a special focus on the older adult.

Kidney Disease among Patients with Sickle Cell Disease, Hemoglobin SS and SC

BACKGROUND AND OBJECTIVES

Sickle cell disease (SCD) is an inherited anemia that afflicts millions worldwide. Kidney disease is a major contributor to its morbidity and mortality. We examined contemporary and historical SCD populations to understand how renal disease behaved in hemoglobin SS (HbSS) compared with HbSC.

DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS

Kidney function was examined in the multicentered Treatment of Pulmonary Hypertension and Sickle Cell Disease with Sildenafil Therapy (Walk-PHaSST) Trial (HbSS=463; HbSC=127; years 2007-2009) and historical comparator populations from the Cooperative Study of Sickle Cell Disease (CSSCD; HbSS=708) and the Multicenter Study of Hydroxyurea in Sickle Cell Disease (MSH; HbSS=299).

RESULTS

In adults with SCD, eGFR was lower among older individuals: -1.78 ml/min per 1.73 m(2) per year of age (95% confidence interval [95% CI], -2.06 to -1.50; Walk-PHaSST Trial), -1.75 ml/min per 1.73 m(2) per year of age (95% CI, -2.05 to -1.44; MSH), and -1.69 ml/min per 1.73 m(2) per year of age (95% CI, -2.00 to -1.38; CSSCD) in HbSS compared with -1.09 ml/min per 1.73 m(2) per year of age (95% CI, -1.39 to -0.75) in HbSC (Walk-PHaSST Trial). Macroalbuminuria was seen in 20% of participants with SCD (HbSS or HbSC; P=0.45; Walk-PHaSST Trial), but microalbuminuria was more prevalent in HbSS (44% versus 23% in HbSC; P<0.002). In the Walk-PHaSST Trial, albuminuria was associated with hemolysis (higher lactate dehydrogenase, P<0.001; higher absolute reticulocyte count, P<0.02; and lower Hb, P=0.07) and elevated systolic BP (P<0.001) in HbSS. One half of all participants with HbSS (20 of 39) versus one fifth without (41 of 228) elevated tricuspid regurgitant jet velocity (≥3 m/s; adverse prognostic indicator in SCD) had macroalbuminuria (P<0.001). In the CSSCD, overt proteinuria, detected (less sensitively) by urine dipstick, associated with higher 3-year mortality (odds ratio, 2.48; 95% CI, 1.07 to 5.77). Serum bicarbonate was lower in HbSS (23.8 versus 24.8 mEq/dl in HbSC; P<0.05) and associated with reticulocytopenic anemia and decreased renal function.

CONCLUSIONS

In SCD, albuminuria or proteinuria was highly prevalent, in HbSS more than in HbSC. Proteinuria associated with mortality in HbSS. Older individuals had a lower than expected eGFR, and this was more prominent in HbSS. Current management does not routinely address renal complications in SCD, which could plausibly reduce morbidity and mortality.

Six Months of Hydroxyurea Reduces Albuminuria in Patients with Sickle Cell Disease

The earliest symptom of glomerular injury in patients with sickle cell disease (SCD) is microalbuminuria. The effect of hydroxyurea (HU) on urine albumin-to-creatinine ratio (ACR) is unclear and should be determined, because increasing numbers of patients with SCD take this drug to improve red blood cell function. In this cohort study of 58 SS-homozygous adults with SCD who initiated HU therapy, we evaluated ACR changes and relationships of these changes with demographic, clinical, and biologic parameters at HU initiation (baseline) and 6 months later (follow-up). Between baseline and follow-up, ACR declined significantly for the entire population (3.0-1.7 mg/mmol; P<0.01), but this was primarily driven by the ACR reduction in the microalbuminuria subgroup (8.1-2.3 mg/mmol; P=0.03; n=23). According to bivariate analyses on 39 patients who did not receive a blood transfusion during the study period, the baseline to follow-up ACR decline was strongly associated with decreases in levels of hemolysis markers, percentage of dense red blood cells, and systolic BP. Bivariate analysis also revealed a close association between the ACR decrease and high baseline levels of hemolysis markers and percentage of dense red blood cells. These results show that urine ACR decreased significantly after 6 months of HU and confirm a close relationship between ACR and hemolysis evolution in patients with SCD.

Medullary Microvascular Thrombosis and Injury in Sickle Hemoglobin C Disease

Sickle cell nephropathy is a common complication in patients with sickle cell hemoglobinopathies. In these disorders, polymerization of mutated hemoglobin S results in deformation of red blood cells, which can cause endothelial cell injury in the kidney that may lead to thrombus formation when severe or manifest by multilayering of the basement membranes (glomerular and/or peritubular capillaries) in milder forms of injury. As the injury progresses, the subsequent ischemia, tubular dysfunction, and glomerular scarring can result in CKD or ESRD. Sickle cell nephropathy can occur in patients with homozygous hemoglobin SS or heterozygous hemoglobin S (hemoglobin SC, hemoglobin S/β(0)-thalassemia, and hemoglobin S/β(+)-thalassemia). Clinical manifestations resulting from hemoglobin S polymerization are often milder in patients with heterozygous hemoglobin S. These patients may not present with clinically apparent acute sickle cell crises, but these milder forms can provide a unique view of the kidney injury in sickle cell disease. Here, we report a patient with hemoglobin SC disease who showed peritubular capillary and vasa recta thrombi and capillary basement membrane alterations primarily involving the renal medulla. This patient highlights the vascular occlusion and endothelial cell injury in the medulla that contribute to sickle cell nephropathy.

Genetic diminution of circulating prothrombin ameliorates multiorgan pathologies in sickle cell disease mice

Sickle cell disease (SCD) results in vascular occlusions, chronic hemolytic anemia, and cumulative organ damage. A conspicuous feature of SCD is chronic inflammation and coagulation system activation. Thrombin (factor IIa [FIIa]) is both a central protease in hemostasis and a key modifier of inflammatory processes. To explore the hypothesis that reduced prothrombin (factor II [FII]) levels in SCD will limit vaso-occlusion, vasculopathy, and inflammation, we used 2 strategies to suppress FII in SCD mice. Weekly administration of FII antisense oligonucleotide "gapmer" to Berkeley SCD mice to selectively reduce circulating FII levels to ∼10% of normal for 15 weeks significantly diminished early mortality. More comprehensive, long-term comparative studies were done using mice with genetic diminution of circulating FII. Here, cohorts of FII(lox/-) mice (constitutively carrying ∼10% normal FII) and FII(WT) mice were tracked in parallel for a year following the imposition of SCD via hematopoietic stem cell transplantation. This genetically imposed suppression of FII levels resulted in an impressive reduction in inflammation (reduction in leukocytosis, thrombocytosis, and circulating interleukin-6 levels), reduced endothelial cell dysfunction (reduced endothelial activation and circulating soluble vascular cell adhesion molecule), and a significant improvement in SCD-associated end-organ damage (nephropathy, pulmonary hypertension, pulmonary inflammation, liver function, inflammatory infiltration, and microinfarctions). Notably, all of these benefits were achieved with a relatively modest 1.25-fold increase in prothrombin times, and in the absence of hemorrhagic complications. Taken together, these data establish that prothrombin is a powerful modifier of SCD-induced end-organ damage, and present a novel therapeutic target to ameliorate SCD pathologies.

Changes in Conjunctival Hemodynamics Predict Albuminuria in Sickle Cell Nephropathy

BACKGROUND

Albuminuria is an early manifestation of deterioration in renal function in subjects with sickle cell disease (SCD). Hyperfiltration may be an early mechanism for kidney damage in SCD. The purpose of the current study was to determine the association between conjunctival hemodynamics and albuminuria in SCD subjects with preserved glomerular filtration rate.

METHODS

Conjunctival microcirculation imaging was performed to measure conjunctival diameter and axial blood velocity (V) in 35 SCD and 10 healthy control subjects. Albuminuria, defined as albumin excretion ratio (AER), was obtained from the medical charts. Based on the 95% CI of conjunctival V in control subjects (0.40-0.60 mm/s), SCD subjects were allocated to 3 groups: V1 <0.40 mm/s (n = 7), V2 of 0.40-0.60 mm/s (n = 18) and V3 ≥0.60 mm/s (n = 10).

RESULTS

Mean log(AER) measurements in the V1, V2 and V3 groups were 1.08 ± 0.67, 1.39 ± 0.59 and 2.00 ± 0.91 mg/g creatinine, respectively, and followed a positive linear trend from the V1 to V3 groups (p = 0.01). By multivariate linear regression analysis, conjunctival V significantly correlated with albuminuria (p = 0.01) independent of age, blood pressure, α-thalassemia, hematocrit, white blood cell count and lactate dehydrogenase concentration.

CONCLUSIONS

Increased conjunctival V is associated with albuminuria in SCD subjects. Assessment of conjunctival microvascular hemodynamics may improve our understanding of the pathophysiology and clinical management of sickle cell nephropathy.

Angiotensin-converting enzyme (ACE) inhibitors for proteinuria and microalbuminuria in people with sickle cell disease

BACKGROUND

Sickle cell disease is a group of disorders characterized by deformation of erythrocytes. Renal damage is a frequent complication in sickle cell disease as a result of long-standing anemia and disturbed circulation through the renal medullary capillaries. Due to the improvement in life expectancy of people with sickle cell disease, there has been a corresponding significant increase in the incidence of renal complications. Microalbuminuria and proteinuria are noted to be a strong predictor of subsequent renal failure. There is extensive experience and evidence with angiotensin-converting enzyme (ACE) inhibitors over many years in a variety of clinical situations for patients who do not have sickle cell disease, but their effect in people with this disease is unknown. It is common practice to administer ACE inhibitors for sickle nephropathy due to their renoprotective properties; however, little is known about their effectiveness and safety in this setting. This is an update of a Cochrane Review first published in 2013.

OBJECTIVES

To determine the effectiveness of ACE inhibitor administration in people with sickle cell disease for decreasing intraglomerular pressure, microalbuminuria and proteinuria and to to assess the safety of ACE inhibitors as pertains to their adverse effects.

SEARCH METHODS

The authors searched the Cochrane Cystic Fibrosis and Genetic Disorders Group's Hameoglobinopathies Trials Register comprising references identified from comprehensive electronic database searches and handsearches of relevant journals and abstract books of conference proceedings.Date of the most recent search: 03 June 2015.

SELECTION CRITERIA

Randomized or quasi-randomized controlled trials of ACE inhibitors designed to reduce microalbuminuria and proteinuria in people with sickle cell disease compared to either placebo or standard treatment regimen.

DATA COLLECTION AND ANALYSIS

Three authors independently applied the inclusion criteria in order to select studies for inclusion in the review. Two authors assessed the risk of bias of studies and extracted data and the third author verified these assessments.

MAIN RESULTS

Five studies were identified through the searches, only one met our inclusion criteria. The included study randomized 22 participants (seven males and 15 females) having proteinuria or microalbuminuria with sickle cell disease and treated the participants for six months (median length of follow up of three months) with captopril or placebo. The overall quality of the outcomes reported was high, since most aspects that may contribute to bias were regarded to be of low risk, although allocation concealment was not reported. At six months, the study reported no significant difference in urinary albumin excretion between the captopril group and the placebo group, although the mean urinary albumin excretion in the captopril group was lower by a mean difference of -49.00 (95% confidence interval -124.10 to 26.10) compared to that of placebo. However, our analysis on the absolute change score showed significant changes between the two groups by a mean difference of -63.00 (95% confidence interval -93.78 to -32.22). At six months albumin excretion in the captopril group was noted to decrease from baseline by a mean of 45 ± 23 mg/day and the placebo group was noted to increase by 18 ± 45 mg/day. Serum creatinine and potassium levels were reported constant throughout the study. The potential for inducing hypotension should be highlighted; the study reported a decrease of 8 mmHg in systolic pressure and 5 mmHg in diastolic and mean blood pressure.

AUTHORS' CONCLUSIONS

There is not enough evidence to show that the administration of ACE inhibitors is associated with a reduction of microalbuminuria and proteinuria in people with sickle cell disease, although a potential for this was seen. More long-term studies involving multiple centers and larger cohorts using a randomized-controlled design are warranted, especially among the pediatric age group. Detailed reporting of each outcome measure is necessary to allow a clear cut interpretation in a systematic review. One of the difficulties encountered in this review was the lack of detailed data reported in the included study.

Cystatin C, Beta2 Microglobulin, N-Acetyl-beta-D-glucosaminidase, Retinol-Binding Protein, and Endothelin 1 Levels in the Evaluation of Sickle Cell Disease Nephropathy

OBJECTIVES

Renal involvement is common in sickle cell disease (SCD). Early demonstration of renal injury and commencement of appropriate treatment will increase survival and quality of life in these patients. We investigated renal manifestations in our pediatric and adult SCD patients and evaluated the role of cystatin C, Beta2 microglobulin (B2M), retinol-binding protein (RBP), N-acetyl-beta-D-glucosaminidase (NAG), and endothelin-1 (ET-1) to indicate renal damage.

METHODS

The study involved 45 pediatric and 10 adult patients with SCD and 20 healthy children and 10 healthy adults as a control. All the patients were questioned for possible renal manifestations. 24-hour urine samples were collected and glomerular filtration rates (GFRs) were calculated by using creatinine (GFR(creatinine)), Schwartz formula (GFR(Schwartz)), and cystatin C (GFR(cystatin C)). Blood and urine samples were collected and serum cystatin C, urine B2M, RBP, NAG, and ET-1 levels were measured.

RESULTS

Nocturnal enuresis and proteinuria were the most common renal manifestations in SCD patients. When the groups were compared in terms of GFR, GFR(creatinine) and GFR(Schwartz) levels were higher in group 1 and 2 patients than in control 1 and 2 patients (P < .05). Cystatin C, B2M, RBP, NAG, and ET-1 values were normal in both the patient and the control groups. However, B2M/creatinine levels were higher than 160 μg/mg creatinine levels in 10 patients.

CONCLUSIONS

Serum cystatin C, urine NAG, RBP, and ET-1 levels were found to be insufficient for the evaluation of SCD nephropathy. Increased B2M/creatinie levels can be valuable in estimating possible glomerular and tubular damage in SCD.

A biopsychosocial model for the management of patients with sickle-cell disease transitioning to adult medical care

The lifespan of patients with sickle-cell disease (SCD) continues to increase, and most affected individuals in high-resource countries now live into adulthood. This necessitates a successful transition from pediatric to adult health care. Care for transitioning patients with SCD often falls to primary care providers who may not be fully aware of the many challenges and issues faced by patients and the current management strategies for SCD. In this review, we aim to close the knowledge gap between primary care providers and specialists who treat transitioning patients with SCD. We describe the challenges and issues encountered by these patients, and we propose a biopsychosocial multidisciplinary approach to the management of the identified issues. Examples of this approach, such as transition-focused integrated care models and quality improvement collaboratives, with the potential to improve health outcomes in adulthood are also described.

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.

Red cell exchange: special focus on sickle cell disease

The primary function of red blood cells (RBCs) is to deliver oxygen from the lungs to tissues. Tissue hypoxia occurs when the oxygen-carrying capacity of RBCs is compromised due primarily to 3 causes: (1) a reduction in circulating RBC mass, (2) an increase in circulating RBC mass, or (3) abnormal hemoglobin (Hb) that either does not sufficiently release oxygen to tissues (high-oxygen-affinity hemoglobin) or occludes the microvasculature due to deformed RBCs (sickled RBCs). To improve oxygenation in patients with reduced or increased RBC mass, RBC administration (simple transfusion) or RBC removal (RBC depletion) is performed, respectively. However, for patients with abnormal Hb, RBCs containing abnormal Hb are removed and replaced by healthy volunteer donor RBCs by red cell exchange (RCE). RCE can be performed by manual exchange or by automated exchange using a blood cell separator (erythrocytapheresis). In this review, indications for RCE in sickle cell disease using the evidence-based American Society for Apheresis categories(1) are presented and the rationale for RCE in each disorder are discussed. Simple transfusion versus RCE and manual RCE versus automated RCE are compared. Finally, this review briefly presents some of the challenges of performing erythrocytapheresis in small children and discusses various choices for central venous access during RCE.(2.)

Albuminuria correlates with hemolysis and NAG and KIM-1 in patients with sickle cell anemia

BACKGROUND

Although hyperfiltration and albuminuria are common pathological conditions, kidney injury (KI) biomarkers have been seldom studied in individuals with sickle cell anemia (SCA).

METHODS

We undertook a cross-sectional assessment of urine KI biomarkers in children and adults with SCA with and without albuminuria and a normal estimated glomerular filtration rate (eGFR). Albumin, KI molecule 1 (KIM-1), N-acetyl-ß-D-glucosaminidase (NAG), endothelin-1 and transforming growth factor-β1 (TGF-β1) were measured. Assays were normalized by urine creatinine. Urine intracellular hemosiderin and serum lactate dehydrogenase (LDH) were assessed as markers of hemolysis. Albuminuria was associated to the biomarkers by Pearson and Spearman correlation coefficients. Differences between the albuminuria (yes, no) groups were assessed by the t test.

RESULTS

Nineteen patients with albuminuria (mean urine albumin/creatinine 527.14 ± 1070 mg/g, range 38.3--190 mg/g) and 19 patients without albuminuria (mean urine albumin/creatinine 15.93 ± 5.17 mg/g, range 7.9-28.4 mg/g) were studied. The age range for the whole group was 11-48 years, and 47 % were males. Patients with albuminuria were older, had lower hematocrit, were more likely to test positive for urine hemosiderin and had a higher KIM-1 (P = 0.0035) and NAG/ creatinine ratios (P = 0.0062). Urine hemosiderin strongly correlated to a higher LDH level (P < 0.001).

CONCLUSIONS

Despite a normal or increased eGFR, KI biomarkers were detected in the urine of individuals with SCA. NAG, KIM-1 and urine hemosiderin correlated with the presence of albuminuria.

Reduced plasma angiotensin II levels are reversed by hydroxyurea treatment in mice with sickle cell disease

AIMS

Sickle cell disease (SCD) pathogenesis leads to recurrent vaso-occlusive and hemolytic processes, causing numerous clinical complications including renal damage. As vasoconstrictive mechanisms may be enhanced in SCD, due to endothelial dysfunction and vasoactive protein production, we aimed to determine whether the expression of proteins of the renin-angiotensin system (RAS) may be altered in an animal model of SCD.

MAIN METHODS

Plasma angiotensin II (Ang II) was measured in C57BL/6 (WT) mice and mice with SCD by ELISA, while quantitative PCR was used to compare the expressions of the genes encoding the angiotensin-II-receptors 1 and 2 (AT1R and AT2R) and the angiotensin-converting enzymes (ACE1 and ACE2) in the kidneys, hearts, livers and brains of mice. The effects of hydroxyurea (HU; 50-75mg/kg/day, 4weeks) treatment on these parameters were also determined.

KEY FINDINGS

Plasma Ang II was significantly diminished in SCD mice, compared with WT mice, in association with decreased AT1R and ACE1 expressions in SCD mice kidneys. Treatment of SCD mice with HU reduced leukocyte and platelet counts and increased plasma Ang II to levels similar to those of WT mice. HU also increased AT1R and ACE2 gene expression in the kidney and heart.

SIGNIFICANCE

Results indicate an imbalanced RAS in an SCD mouse model; HU therapy may be able to restore some RAS parameters in these mice. Further investigations regarding Ang II production and the RAS in human SCD may be warranted, as such changes may reflect or contribute to renal damage and alterations in blood pressure.

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.

Renal tubular dysfunction in sickle cell disease

BACKGROUND/AIMS

Kidney abnormalities are one of the main chronic complications of sickle cell disease (SCD). The aim of this study is to investigate the occurrence of renal tubular abnormalities among patients with SCD.

METHODS

This is a prospective study with 26 SCD adult patients in Brazil. Urinary acidification and concentration tests were performed using calcium chloride (CaCl2), after a 12h period of water and food deprivation. Fractional excretion of sodium (FENa), transtubular potassium gradient (TTKG) and solute free water reabsorption (TcH2O) were calculated. The SCD group was compared to a group of 15 healthy volunteers (control group).

RESULTS

Patient`s average age and gender were similar to controls. Urinary acidification deficit was found in 10 SCD patients (38.4%), who presented urinary pH >5.3 after CaCl2 test. Urinary osmolality was significantly lower in SCD patients (355 ± 60 vs. 818 ± 202 mOsm/kg, p=0.0001, after 12h period water deprivation). Urinary concentration deficit was found in all SCD patients (100%). FENa was higher among SCD patients (0.75 ± 0.3 vs. 0.55 ± 0.2%, p=0.02). The TTKG was higher in SCD patients (5.5 ± 2.5 vs. 3.0 ± 1.5, p=0.001), and TcH2O was lower (0.22 ± 0.3 vs. 1.1 ± 0.3L/day, p=0.0001).

CONCLUSIONS

SCD is associated with important kidney dysfunction. The main abnormalities found were urinary concentrating and incomplete distal acidification defect. There was also an increase in the potassium transport and decrease in water reabsorption, evidencing the occurrence of distal tubular dysfunction. .