Neutrophil Gelatinase-Associated Lipocalin Levels in Patients with Thalassemia and Sickle Cell Disease: Correlation with Renal Injury

Background and Aims: Neutrophil gelatinase-associated lipocalin (NGAL) is a protein belonging to the lipocalin superfamily initially found in activated neutrophils, in accordance with its role as an innate antibacterial factor. However, it subsequently was shown that many other types of cells, including in the kidney tubule, may produce NGAL in response to various injuries. The increase in NGAL production and release from tubular cells after harmful stimuli of various kinds may have self-defensive intent based on the activation of specific iron-dependent pathways, which in all probability also represent the mechanism through which NGAL promotes kidney growth and differentiation. NGAL levels clearly correlate with severity of renal impairment, probably expressing the degree of active damage underlying the chronic condition. For all these reasons, NGAL may become one of the most promising next-generation biomarkers in clinical nephrology and beyond. We aimed to investigate the clinical significance of NGAL levels and its correlation with renal function in patients with hemoglobinopathies.

Patients and Methods: 117 adult patients with hemoglobinopathies were included in the study divided in 3 groups. Group A: 30 patients with transfusion-dependent thalassemia major (TM); Group B: 29 patients with Non-Transfusion-Dependent Thalassemia (TI) and Group C: 58 patients with HbS/β^thal disease, while 20 apparently healthy individuals served as controls (Group D). In patients and controls along with standard blood and urine chemistry. Measurements of serum Cystatin C and NGAL were performed by means of immunonephelometric and immunoenzymatic techniques, (Siemens Healthcare Diagnostics, Liederbach, Germany and R&D Systems, Minneapolis, MN, USA), respectively. Estimated Glomerular Filtration Rate (eGFR) values were calculated with an unadjusted for body surface Cystatin C based equation: eGFR (mL/min)=77.24(Cys C)^-1.2623.

Results: The main results of the study showed that: a) NGAL levels were significantly higher in all the groups of patients compared to controls: Group A 95.0±45.0µg/L, Group B 139.1±86.1µg/L, Group C 117.8±37.3µg/L vs Group D 50.3±11.3µg/L (p<0.001), b) Cystatin C levels were significantly higher in patients of Group A 0.94±0.34mg/L and Group C 1.04±0.50mg/L compared to controls 0.75±0.09mg/L (p<0.01), while no significant difference was found between Group B 0.72±0.13mg/L and controls (p>0.300), c) NGAL levels and eGFR values (Group A: 96.9±39.8, Group B: 117.0±26.0, Group C: 86.2±27.8 and group D: 109.6±15.0mL/min, respectively) correlated significantly in patients of Group A and Group C (r=-0.739, p<0.001 and r=-0.735, p<0.001, respectively), while NGAL values are independent from eGFR values in patients of Group B.

Conclusions: These findings illustrate the tubular-glomerular activation feedback mirrored by NGAL in patients with transfusion-dependent thalassemia major and HbS/β^thal disease, who suffer from renal injuries, indicating that tubular damage precedes GFR reduction. Upregulation of NGAL in patients with non-transfusion-dependent thalassemia independently of renal injuries may reflect the compensatory, protective role of NGAL in response to diverse cellular stresses, including inflammation and oxidative stress. However, recent reports have implicated NGAL upregulation as a mechanism that contributes to anemia in the setting of chronic low grade inflammation. In experimental models, systemic and medullary NGAL has been demonstrated to induce inhibition of erythropoiesis through induction of apoptosis and arrest of differentiation of erythroid progenitor cells.