Vascular Dysfunction in Thalassemia Major: Role of Endothelial Monocyte-Activating Polypeptide-II and Oxidative Stress in Relation to Cardiac and Renal Complications

Abstract

Background: β-thalassemia major (β-TM) is an inherited blood disorder that requires liflong transfusion with inevitable iron overload leading to oxidant-antioxidant disturbance and endothelial dysfunction. Endothelial monocyte-activating polypeptide-II (EMAP-II) is a multifunctional polypeptide with pro-inflammatory, anti-angiogenic activity and pro-coagulant activity on the surface of endothelial cells. Endothelin-1 (ET-1), a potent endogenous vasoconstrictor, stimulates production of reactive oxygen species. Aim: To assess serum levels of EMAP II as a potential marker of vasculopathy in children and adolescents with β-TM and its possible relation to ET-1 gene polymorphism (G8002A), oxidative stress and vascular complications. Methods: Fifty-nine β-TM patients without symptomatic cardiac or renal disease were compared to 95 healthy controls and studied stressing on splenectomy, transfusion history, chelation therapy, markers of hemolysis and serum ferritin. Urinary albumin excretion (UAE) was assessed in an early morning fasting urine sample as albumin-to-creatinine ratio (UACR) to detect micro- or macro-albuminuria. Oxidant and antioxidant parameters were measured including assessment of malondialdehyde (MDA) as an index for lipid peroxidation as well as the antioxidant enzymes; superoxide dismutase (SOD), glutathione peroxidase (GPx), reduced glutathione (GSH), glutathione reductase and catalase. Serum EMAP-II levels were measured by enzyme-linked immunosorbent assay (ELISA). Endothelin-1 gene polymorphism (G8002A) was determined using polymerase chain reaction (PCR)-restriction fragment length polymorphism method. Screening for pulmonary hypertension and cardiovascular abnormalities was performed by the non-invasive doppler echocardiograpghy. Results: β-TM patients had significantly higher EMAP II, MDA, superoxide dismutase and glutathione peroxidase while reduced glutathione, glutathione reductase, and catalase were significantly lower than healthy controls. The AA genotype and allele A of ET-1 polymorphism (G8002A) were significantly higher among β-TM patients compared with the control group. The number of patients with heart disease, pulmonary hypertension risk or nephropathy was significantly higher in AA genotype. β-TM patients with AA genotype of ET-1 polymorphism (G8002A) had higher levels of LDH, serum ferritin, EMAP II as well as MDA, superoxide diameter and glutathione peroxidase while glutathione reductase and catalase were significantly lower compared with GG & GA genotypes. When patients were classified according to ferritin cut off 2500 μg/L, it was found that the number of patients with heart disease, pulmonary hypertension risk or nephropathy was significantly higher among those with ferritin ≥ 2500 μg/L. Patients with ferritin ≥ 2500 μg/mL had higher percentage of poor compliance to chelation therapy. Markers of hemolysis, oxidant-antioxidant parameters and EMAP II were significantly higher among β-TM patients with ferritin ≥2500 μg/L. EMAP II was significantly higher among patients with heart disease, pulmonary hypertension risk or nephropathy as well as those with poor compliance to therapy and ferritin ≥2500 μg/L. There were significantly correlations between EMAP II and transfusion index, LDH, ferritin and oxidative stress markers. Conclusion: Endothelial dysfunction is common in pediatric patients with β-TM. This is associated with oxidant-antioxidant imbalance. EMAP II could be a potential serum biomarker for vascular complications in β-TM patients. Endothelin-1 gene polymorphism (G8002A) could be a possible genetic marker for prediction of increased susceptibility to cardiopulmonary and renal complications among pediatric patients with β-TM.