Serum Cystatin C in sickle cell disease: relation to renal and endothelial dysfunction

Abstract

SUMMARY S ickle cell disease (SCD) is one of the most common severe monogenic disorders in the world. Hemoglobin polymerisation, leading to erythrocyte rigidity and vaso-occlusion, is central to the pathophysiology of this disease, although the importance of chronic anemia, hemolysis, and vasculopathy has been established. SCD patients may experience a variety of clinical complications attributed to anemia, hemolysis, and iron overload. Cystatin C is an extracellular cysteine protease inhibitor that belongs to the cystatin superfamily. Major targets for Cystatin C are the cysteine proteases of the papain family. Cystatin C has being recognized as a useful marker of renal function and a strong predictor for risk of cardiovascular events. Cystatin C serum concentration correlates closely to the glomerular clearance rate and may be superior to serum creatinine. Therefore, we determined the levels of cystatin C in young SCD patients as potential markers for hemolysis associated complications and assessed their relation to markers of hemolysis and iron overload as well as renal and endothelial dysfunction. This study included 53 SCD patients (39 males and 14 females) recruited from the regular attendants of the Pediatric Hematology Clinic, Pediatric Hospital, Ain Shams University. Patients were compared with 35 age- and sex-matched healthy subjects (23 males and 12 females) enrolled as controls. The median age of SCD patients was 8 years (range: 1-17 years) while that of controls was 7.8 (range: 2-17 years). All included patients were subjected to detailed medical history and thorough clinical examination with special emphasis on anthropometric measures, disease duration, evidence of renal, hepatic or cardiac disease, history of sickling crisis or splenectomy, transfusion history and chelation/hydroxyurea therapy. Cystatin C was measured by enzyme linked immunosorbent assay (ELISA) and correlated to carotid intima media thickness (CIMT). All patients were in steady state. In the current work, cyststin C levels and CIMT were significantly higher in SCD patients compared with control group. Analysis of cystatin C in relation to the clinical characteristics of patients with SCD revealed that patients with nephropathy or heart disease had significantly higher levels than those without. Patients who had history of frequent sickling crisis (>3 attacks/ year) had also higher cystatin C levels than those who were in steady state. SCD patients treated with hydroxyurea had lower cystatin C levels than untreated patients. Correlation studies revealed significant positive relations significant positive correlations between cystatin C and each of WBCs count, UACR and CIMT. ROC curve analysis revealed that the cutoff value of cystatin C at 580 ng/mL could differentiate SCD patients with and without nephropathy with 77.8% sensitivity and specificity of 84.6% while the cutoff value 650 ng/mL could differentiate SCD patients with and without heart disease with 100% sensitivity and specificity of 74.4%.