Clinical and metabolomic risk factors associated with rapid renal function decline in sickle cell disease

Targeted metabolomics identified novel metabolites, predominantly phosphatidylcholines and docosahexaenoic acid-containing lipids, predictive of incident chronic kidney disease in middle-to-elderly-aged Chinese adults

BACKGROUND

Evidence is limited regarding the association of circulating metabolites with decline of kidney function, letting alone their value in prediction of development of chronic kidney disease (CKD).

METHODS

This study included 3802 participants aged 64.1 ± 7.4 years from the Dongfeng-Tongji cohort, among whom 3327 were CKD-free at baseline (estimated glomerular filtration rate [eGFR] > 60 ml/min per 1.73 m2). We measured baseline levels of 211 metabolites with liquid chromatography coupled with mass spectrometry, including 25 amino acids, 12 acyl-carnitines, 161 lipids, and 13 other metabolites.

RESULTS

The mean (SD) absolute annual change in eGFR was -0.14 ± 4.11 ml/min per 1.73 m2 per year, and a total of 472 participants who were free of CKD at baseline developed incident CKD during follow-up of 4.6 ± 0.2 years (14.2 %). We identified a total of 22 metabolites associated with annual eGFR change and survived Bonferroni correction for multiple testing, including seven metabolites associated with eGFR increase (six being docosahexaenoic acid [DHA]-containing lipids) and 15 associated with eGFR decline (nine being phosphatidylcholines [PCs]). Among them, eight metabolites obtained non-zero coefficients in least absolute shrinkage and selection operator (LASSO) regression on incident CKD, indicating predictive potential, including one amino acid (arginine), one acyl-carnitine (C2), one lysophosphatidylcholine (LPC 22:6), two PCs (32:1 and 34:3), one triacylglycerol (TAG 56:8 [22:6]) and two other metabolites (inosine, niacinamide), and the composite score of these eight metabolites showed an odds ratio (OR) of 8.79 (95 % confidence interval [CI]: 7.49, 10.32; P < 0.001) per SD increase in association with incident CKD. The addition of the metabolite score increased the c-statistic of the reference model of traditional risk factors (including baseline eGFR) by 0.065 (95 % CI: 0.046 to 0.084; P = 3.39 × 10-11) to 0.765 (0.742 to 0.788) in 1000 repetitions of 10-fold cross-validation, while the application of two advanced machine learning algorithms, random forest (RF), and extreme gradient boosting (XGBoost) models produced similar c-statistics, to 0.753 (0.729 to 0.777) and 0.778 (0.733 to 0.824) with increases of 0.074 (0.055 to 0.093; P = 4.11 × 10-14) and 0.073 (0.032 to 0.114; P = 4.00 × 10-4), respectively.

CONCLUSIONS

In this study, we identified 22 metabolites associated with longitudinal eGFR change, nine of which were PCs and six were DHA-containing lipids. We screened out a panel of eight metabolites which improved prediction for the development of CKD by 9 % beyond traditional risk factors including baseline eGFR. Our findings highlighted involvement of lipid metabolism in kidney function impairment, and provided novel predictors for CKD risk.

Prevalence and associated factors of glomerular hyperfiltration among adult stable sickle cells in Kinshasa, DR Congo

INTRODUCTION

Glomerular hyperfiltration is highly frequent, theoretically dependent on cardiac output, low systemic vascular resistance and hemolysis markers. In sickle cell disease (SCD), hyperfiltration is an extremely common phenomenon and occurred in young and early adult patients. Despite the fact that the glomerular hyperfiltration is known as the early manifestations of sickle cell nephropathy, its burden among adult sickle cell disease in sub-Saharan is poor studied. This study aimed to determine the prevalence and associated factors of hyperfiltration.

METHODS

This was an analytical multicentric cross-sectional study involving stable adult sickle cell patients in Kinshasa, recruited between March and October 2023. Parameters of interest encompasses demographic, clinical, biological, echocardiographic and pulse wave measurement data. Hyperfiltration was defined using the CDK-EPI equation based on cystatin C; eGFR >130 for women and >140 ml/min/1.73m2 for men. We used multivariate logistic regression analysis to search determinants of glomerular hyperfiltration.

RESULTS

Two hundred and fourty six (246) patients with SCD were enrolled. The prevalence of hyperfiltration was 20.7%. In multiple logistic regression analysis, hyperfiltration status was independently associated with age (< 25 years) [3.57 (1.78-7.49); p = 0.027)], female sex [4.36 (2.55-5.62); p = 0.031), CRP (< 6 mg/l) [0.77 (0.61-0.97); p = 0.028)], central systolic pressure (< 100 mmHg) and central diastolic pressure (< 60 mmHg) [0.86(0.74-0.98), p = 0.028)], [(0.83 (0.71-0.98); p = 0.032)].

CONCLUSION

One out of five SS adults exhibits hyperfiltration, which is associated with young age and female sex, whereas low CRP and blood pressure were negative risk factors.

Nontargeted Plasma Proteomic Analysis of Renal Disease and Pulmonary Hypertension in Patients with Sickle Cell Disease

Sickle cell disease (SCD) is characterized by red blood cell sickling, vaso-occlusion, hemolytic anemia, damage to multiple organ systems, and, as a result, shortened life expectancy. Sickle cell disease nephropathy (SCDN) and pulmonary hypertension (pHTN) are common and frequently co-occurring complications of SCD; both are associated with markedly accelerated mortality. To identify candidate circulating biomarkers of SCDN and pHTN, we used mass spectrometry to quantify the relative abundance of >1000 proteins in plasma samples from 189 adults with SCD from the Outcome Modifying Genes in SCD (OMG-SCD) cohort (ProteomeXchange identifier PXD048716). Forty-four proteins were differentially abundant in SCDN, most significantly cystatin-C and collagen α-1(XVIII) chain (COIA1), and 55 proteins were dysregulated in patients with SCDN and pHTN, most significantly insulin-like growth factor-binding protein 6 (IBP6). Network analysis identified a module of 133 coregulated proteins significantly associated with SCDN, that was enriched for extracellular matrix proteins, insulin-like growth factor binding proteins, cell adhesion proteins, EGF-like calcium binding proteins, and several cadherin family members. Collectively, these data provide a comprehensive understanding of plasma protein changes in SCDN and pHTN which validate numerous studies of chronic kidney disease and suggest shared profiles of protein disruption in kidney dysfunction and pHTN among SCD patients.

Genome-wide meta-analysis identifies new candidate genes for sickle cell disease nephropathy

Sickle cell disease nephropathy (SCDN), a common SCD complication, is strongly associated with mortality. Polygenic risk scores calculated from recent transethnic meta-analyses of urinary albumin-to-creatinine ratio and estimated glomerular filtration rate (eGFR) trended toward association with proteinuria and eGFR in SCD but the model fit was poor (R2 < 0.01), suggesting that there are likely unique genetic risk factors for SCDN. Therefore, we performed genome-wide association studies (GWAS) for 2 critical manifestations of SCDN, proteinuria and decreased eGFR, in 2 well-characterized adult SCD cohorts, representing, to the best of our knowledge, the largest SCDN sample to date. Meta-analysis identified 6 genome-wide significant associations (false discovery rate, q ≤ 0.05): 3 for proteinuria (CRYL1, VWF, and ADAMTS7) and 3 for eGFR (LRP1B, linc02288, and FPGT-TNNI3K/TNNI3K). These associations are independent of APOL1 risk and represent novel SCDN loci, many with evidence for regulatory function. Moreover, GWAS SNPs in CRYL1, VWF, ADAMTS7, and linc02288 are associated with gene expression in kidney and pathways important to both renal function and SCD biology, supporting the hypothesis that SCDN pathophysiology is distinct from other forms of kidney disease. Together, these findings provide new targets for functional follow-up that could be tested prospectively and potentially used to identify patients with SCD who are at risk, before onset of kidney dysfunction.

Variation and impact of polygenic hematologic traits in monogenic sickle cell disease

Several of the complications observed in sickle cell disease (SCD) are influenced by variation in hematologic traits (HT), such as fetal hemoglobin (HbF) level and neutrophil count. Previous large-scale genome-wide association studies carried out in largely healthy individuals have identified thousands of variants associated with HT, which have then been used to develop multi-ancestry polygenic trait scores (PTS). Here, we tested whether these PTS associate with HT in SCD patients and if they can improve statistical models associated with SCD-related complications. In 2,056 SCD patients, we found that the PTS predicted less HT variance than in non-SCD individuals of African ancestry. This was particularly striking at the Duffy/DARC locus, where we observed an epistatic interaction between the SCD genotype and the Duffy null variant (rs2814778) that led to a two-fold weaker effect on neutrophil count. PTS for these HT which are measured as part of routine practice were not associated with complications in SCD. In contrast, we found that a simple PTS for HbF that includes only six variants explained a large fraction of the phenotypic variation (20.5-27.1%), associated with acute chest syndrome and stroke risk, and improved the statistical modeling of the vaso-occlusive crisis rate. Using Mendelian randomization, we found that increasing HbF by 4.8% reduces stroke risk by 39% (P=0.0006). Taken together, our results highlight the importance of validating PTS in large diseased populations before proposing their implementation in the context of precision medicine initiatives.

Glomerular filtration rate abnormalities in sickle cell disease

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

Neutrophil gelatinase-associated lipocalin is elevated in children with acute kidney injury and sickle cell anemia, and predicts mortality

Urine neutrophil gelatinase-associated lipocalin (NGAL) is a biomarker of acute kidney injury that has been adapted to a urine dipstick test. However, there is limited data on its use in low-and-middle-income countries where diagnosis of acute kidney injury remains a challenge. To study this, we prospectively enrolled 250 children with sickle cell anemia aged two to 18 years encompassing 185 children hospitalized with a vaso-occlusive pain crisis and a reference group of 65 children attending the sickle cell clinic for routine care follow up. Kidney injury was defined using serial creatinine measures and a modified-Kidney Disease Improving Global Outcome definition for sickle cell anemia. Urine NGAL was measured using the NGAL dipstick and a laboratory reference. The mean age of children enrolled was 8.9 years and 42.8% were female. Among hospitalized children, 36.2% had kidney injury and 3.2% died. Measured urine NGAL levels by the dipstick were strongly correlated with the standard enzyme-linked immunosorbent assay for urine NGAL (hospitalized children, 0.71; routine care reference, 0.88). NGAL levels were elevated in kidney injury and significantly increased across injury stages. Hospitalized children with a high-risk dipstick test (300ng/mL and more) had a 2.47-fold relative risk of kidney injury (95% confidence interval 1.68 to 3.61) and 7.28 increased risk of death (95% confidence interval 1.10 to 26.81) adjusting for age and sex. Thus, urine NGAL levels were found to be significantly elevated in children with sickle cell anemia and acute kidney injury and may predict mortality.

Longitudinal Study of Glomerular Hyperfiltration in Adults with Sickle Cell Anemia: A Multicenter Pooled Analysis

Glomerular hyperfiltration is common in young sickle cell anemia patients and precedes development of overt kidney disease. In this multicenter pooled cohort, we characterized hyperfiltration and its decline to normal range in adult patients. Glomerular filtration rate (GFR) was estimated using the creatinine-based 2009 CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) equation omitting race adjustment and the 2021 CKD-EPI equation. Using CKD-EPI–2009, 506 patients had baseline estimated GFR (eGFR) ≥90 mL/min per 1.73 m², median age of 24 (interquartile range [IQR], 19-34) years and 5.17 years of follow-up. The prevalence of hyperfiltration (eGFR ≥140 and ≥130 mL/min per 1.73 m² for men and women, respectively) was 38.3%. Using CKD-EPI–2009, baseline hyperfiltration was less likely with older age (odds ratio [OR], 0.78; 95% confidence interval [CI], 0.73-0.83; P < .0001), male sex (OR, 0.32; 95% CI, 0.18-0.58; P = .0002), and higher weight (OR, 0.96; 95% CI, 0.94-0.99; P = .001). Using CKD-EPI–2021, hyperfiltration was similarly less likely with older age (OR, 0.75; 95% CI, 0.70-0.81; P < .0001), male sex (OR, 0.24; 95% CI, 0.13-0.44; P < .0001), and higher weight (OR, 0.97; 95% CI, 0.95-0.99; P = .004). In patients with baseline hyperfiltration, eGFR declined to normal values at a median age of 26.2 years. Using CKD-EPI–2009, this decline was associated with male sex (HR, 2.20; 95% CI, 1.26-3.87; P = .006), systolic blood pressure (hazard ratio [HR], 1.02; 95% CI, 1.01-1.04; P = .01), and hydroxyurea use (HR, 1.74; 95% CI, 1.002-3.03; P = .05). Using CKD-EPI–2021, decline of eGFR to normal was only associated with male sex (HR, 3.39; 95% CI, 2.01-5.69; P < .0001). Decline to normal eGFR range from hyperfiltration occurs earlier in males, those on hydroxyurea, and with higher systolic blood pressure.

Clonal Hematopoiesis and the Risk of Hematologic Malignancies after Curative Therapies for Sickle Cell Disease

Sickle cell disease (SCD) is associated with severe morbidity and early mortality. Two large population studies found an increased risk for leukemia in individuals with SCD. Notably, while the relative risk of leukemia development is high, the absolute risk is low in individuals with SCD who do not receive cell-based therapies. However, the risk of leukemia in SCD is high after graft rejection and with gene therapy. Clonal hematopoiesis (CH) is a well-recognized premalignant condition in the general population and in patients after high-dose myelotoxic therapies. Recent studies suggest that CH may be more common in SCD than in the general population, outside the cell-based therapy setting. Here, we review risk factors for CH and progression to leukemia in SCD. We surmise why patients with SCD are at an increased risk for CH and why leukemia incidence is unexpectedly high after graft rejection and gene therapy for SCD. Currently, we are unable to reliably assess genetic risk factors for leukemia development after curative therapies for SCD. Given our current knowledge, we recommend counseling patients about leukemia risk and discussing the importance of an individualized benefit/risk assessment that incorporates leukemia risk in patients undergoing curative therapies for SCD.

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.

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.

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.

Rapid decline in estimated glomerular filtration rate in sickle cell anemia: results of a multicenter pooled analysis

Not available.

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.

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.

Diversity of variant alleles encoding Kidd, Duffy, and Kell antigens in individuals with sickle cell disease using whole genome sequencing data from the NHLBI TOPMed Program

BACKGROUND

Genetic variants in the SLC14A1, ACKR1, and KEL genes, which encode Kidd, Duffy, and Kell red blood cell antigens, respectively, may result in weakened expression of antigens or a null phenotype. These variants are of particular interest to individuals with sickle cell disease (SCD), who frequently undergo chronic transfusion therapy with antigen-matched units. The goal was to describe the diversity and the frequency of variants in SLC14A1, ACKR1, and KEL genes among individuals with SCD using whole genome sequencing (WGS) data.

STUDY DESIGN AND METHODS

Two large SCD cohorts were studied: the Recipient Epidemiology and Donor Evaluation Study III (REDS-III) (n = 2634) and the Outcome Modifying Gene in SCD (OMG) (n = 640). Most of the studied individuals were of mixed origin. WGS was performed as part of the National Heart, Lung, and Blood Institute's Trans-Omics for Precision Medicine (TOPMed) program.

RESULTS

In SLC14A1, variants included four encoding a weak Jka phenotype and five null alleles (JKnull ). JKA*01N.09 was the most common JKnull . One possible JKnull mutation was novel: c.812G>T. In ACKR1, identified variants included two that predicted Fyx (FY*X) and one corresponding to the c.-67T>C GATA mutation. The c.-67T>C mutation was associated with FY*A (FY*01N.01) in four participants. FY*X was identified in 49 individuals. In KEL, identified variants included three null alleles (KEL*02N.17, KEL*02N.26, and KEL*02N.04) and one allele predicting Kmod phenotype, all in heterozygosity.

CONCLUSIONS

We described the diversity and distribution of SLC14A1, ACKR1, and KEL variants in two large SCD cohorts, comprising mostly individuals of mixed ancestry. This information may be useful for planning the transfusion support of patients with SCD.

Potential causal role of l-glutamine in sickle cell disease painful crises: A Mendelian randomization analysis

In a recent clinical trial, the metabolite l-glutamine was shown to reduce painful crises in sickle cell disease (SCD) patients. To support this observation and identify other metabolites implicated in SCD clinical heterogeneity, we profiled 129 metabolites in the plasma of 705 SCD patients. We tested correlations between metabolite levels and six SCD-related complications (painful crises, cholecystectomy, retinopathy, leg ulcer, priapism, aseptic necrosis) or estimated glomerular filtration rate (eGFR), and used Mendelian randomization (MR) to assess causality. We found a potential causal relationship between l-glutamine levels and painful crises (N = 1278, odds ratio (OR) [95% confidence interval] = 0.68 [0.52-0.89], P = 0.0048). In two smaller SCD cohorts (N = 299 and 406), the protective effect of l-glutamine was observed (OR = 0.82 [0.50-1.34]), although the MR result was not significant (P = 0.44). We identified 66 significant correlations between the levels of other metabolites and SCD-related complications or eGFR. We tested these correlations for causality using MR analyses and found no significant causal relationship. The baseline levels of quinolinic acid were associated with prospectively ascertained survival in SCD patients, and this effect was dependent on eGFR. Metabolomics provide a promising approach to prioritize small molecules that may serve as biomarkers or drug targets in SCD.

The relationship between blood metabolites of the tryptophan pathway and kidney function: a bidirectional Mendelian randomization analysis

Blood metabolites of the tryptophan pathway were found to be associated with kidney function and disease in observational studies. In order to evaluate causal relationship and direction, we designed a study using a bidirectional Mendelian randomization approach. The analyses were based on published summary statistics with study sizes ranging from 1,960 to 133,413. After correction for multiple testing, results provided no evidence of an effect of metabolites of the tryptophan pathway on estimated glomerular filtration rate (eGFR). Conversely, lower eGFR was related to higher levels of four metabolites: C-glycosyltryptophan (effect estimate = − 0.16, 95% confidence interval [CI] (− 0.22; − 0.1); p = 9.2e−08), kynurenine (effect estimate = − 0.18, 95% CI (− 0.25; − 0.11); p = 1.1e−06), 3-indoxyl sulfate (effect estimate = − 0.25, 95% CI (− 0.4; − 0.11); p = 6.3e−04) and indole-3-lactate (effect estimate = − 0.26, 95% CI (− 0.38; − 0.13); p = 5.4e−05). Our study supports that lower eGFR causes higher blood metabolite levels of the tryptophan pathway including kynurenine, C-glycosyltryptophan, 3-indoxyl sulfate, and indole-3-lactate. These findings aid the notion that metabolites of the tryptophan pathway are a consequence rather than a cause of reduced eGFR. Further research is needed to specifically examine relationships with respect to chronic kidney disease (CKD) progression among patients with existing CKD.

Curative vs targeted therapy for SCD: does it make more sense to address the root cause than target downstream events?

Sickle cell disease (SCD) places a heavy burden on a global and increasing population predominantly resident in resource-poor and developing countries. Progress continues to be made in preventing childhood mortality, and increasing numbers of chronically ill adults with disease are requiring care for disease sequelae. Curative therapies for SCD are therefore attractive to physicians and investigators focused on SCD. Gene therapies are being developed, and several are now in various stages of early-phase human clinical trials. However, we must also pursue avenues through which we can do the most good for the most people alive today. Such efforts include improving our understanding of disease mechanisms and which disease sequelae most strongly affect survival and interfere with quality of life. The pathways leading to disease sequelae are multiple, complex, and highly interactive. Four drugs have now been approved by the US Food and Drug Administration for SCD; however, each has a distinct mechanism and a measurable but limited effect on the many clinical sequelae of SCD. We therefore need to learn how to approach multi-agent therapy for SCD. The order of addition of each agent to treat a specific patient will need to be guided by response to previous therapy, risk factors identified for specific disease outcomes, and clinical studies to determine more comprehensively how the 4 currently approved drugs might interact and produce (or not) additive effects. Moreover, this will have to be accomplished with defined end points in mind, according to which pose the greatest threats to quality of life as well as survival.

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.

Differential role of adenosine signaling cascade in acute and chronic pain

Adenosine is a signaling molecule induced under stress such as energy insufficiency and ischemic/hypoxic conditions. Adenosine controls multiple physiological and pathological cellular and tissue function by activation of four G protein-coupled receptors (GPCR). Functional role of adenosine signaling in acute pain has been widely studied. However, the role of adenosine signaling in chronic pain is poorly understood. At acute levels, adenosine can be beneficial to anti-pain whereas a sustained elevation of adenosine can be detrimental to promote chronic pain. In recent years, extensive progress has been made to define the role of adenosine signaling in chronic pain and to dissect molecular new insight underlying the development of chronic pain. In this review, we summarize the differential role of adenosine signaling cascade in acute and chronic pain with a major focus on recent studies revealing adenosine ADORA2B receptor activation in the pathology of chronic pain. We further provide a therapeutic outlook of how multiple adenosine signaling components can be useful to treat chronic pain.

Rapid decline in estimated glomerular filtration rate is common in adults with sickle cell disease and associated with increased mortality

We evaluated the prevalence of rapid decline in kidney function, its potential risk factors and influence upon mortality in sickle cell disease (SCD) in a retrospective single-center study. Rapid decline of kidney function was defined as estimated glomerular filtration rate (eGFR) loss of >3·0 ml/min/1·73 m² per year. A multivariable logistic regression model for rapid eGFR decline was constructed after evaluating individual covariates. We constructed multivariate Cox-regression models for rapid eGFR decline and mortality. Among 331 SCD patients (median age 29 years [interquartile range, IQR: 20, 41]; 187 [56·5%] female) followed for median 4·01 years (IQR: 1·66, 7·19), rapid eGFR decline was noted in 103 (31·1%). History of stroke (odds ratio [OR]: 2·91, 95% confidence interval [CI]: 1·25-6·77) and use of angiotensin converting enzyme inhibitors/angiotensin receptor blockers (OR: 3·17, 95% CI: 1·28-7·84) were associated with rapid eGFR decline. The rate of eGFR change over time was associated with mortality (hazard ratio [HR]: 0·99, 95% CI: 0·984-0·995, P = 0·0002). In Cox-regression, rapid eGFR decline associated with mortality (HR: 2·07, 95% CI: 1·039-4·138, P = 0·04) adjusting for age, sex and history of stroke. Rapid eGFR decline is common in SCD and associated with increased mortality. Long-term studies are needed to determine whether attenuating loss of kidney function may decrease mortality in SCD.