Probability of TCD-Normalization in the "Drepagreffe" Trial Comparing Transplantation to Chronic Transfusion in Sickle Cell Anemia Children with Abnormal-Transcranial Doppler Is Associated with Lower Ang-2 and BDNF Plasma Levels

Sickle cell anemia (SCA) is a chronic illness that causes an increased risk of stroke and progressive brain and cognitive dysfunction. SCA-related cerebral vasculopathy includes vascular remodeling, abnormal arterial velocities and infarction. We studied the relationship between cytokines, velocities, and blood parameters in SCA-children enrolled in the "Drepagreffe" trial, a French prospective, Mendelian-randomized trial with 2 arms (transfusions/transplantation) defined by random-availability of a HLA-matched sibling. This trial enrolled SCA-children younger than 15, regularly transfused for abnormal-TCD history, with at least one non-SCA sibling, and parents agreeing to HLA-typing and transplantation. Between 12/2010 and 6/2013, 67 SCA-children (7 with stroke history) were enrolled. Thirty-two had a matched-sibling donor (MSD) and were transplanted, while 35 (no donor) were included in the transfusion arm.

Hypoxia/angiogenesis and brain injury-related factor expression at 1-year was one of the trial secondary outcome. Elevated plasma BDNF and PDGF-AA have been shown to be significantly associated with high cerebral velocities (Hyacinth 2012). Chronic transfusion has been shown to reduce vascular endothelial activation and thrombogenicity in SCA-children with abnormal-TCD (Hyacinth 2014) but no study has been performed in transplanted SCA-children. Plasma samples were obtained at enrollment and 1-year post-enrollment and stored frozen. The expression of the following cytokines (VEGF, Ang-1, Ang-2, FGFb, HGF, PDGF-BB, BDNF) was assessed with a multiplex immunoassay (Bio-Techne). Ang-2, and BDNF levels were confirmed with specific enzyme-linked immunosorbent assays (ELISA, Bio-Techne). Blood parameters, velocities, ischemic lesions and stenoses were assessed at enrollment and 1-year post-enrollment.

At 1-year, the percentage of patients with normalized-TCD (velocities<170cm/sec) was significantly higher in transplanted patients than in those maintained on chronic transfusion (27/32 (84%) vs 17/35 (49%), respectively; p=0.001). As shown (Table), leukocytes, neutrophils, platelets, reticulocytes, LDH, bilirubin, ferritin, HbS% were highly significantly lower in transplanted children than in those maintained on chronic transfusion, while hemoglobin and HbA% were highly significantly higher. Ang-2 and HGF were significantly lower in transplanted children than in those on chronic transfusion (p<0.001 and p=0.002, respectively). Velocities recorded in the artery with the highest values were significantly positively correlated with Ang-2 (r=0.385, p=0.015) and BDNF (r=0.444, p=0.005). Logistic regression analysis showed that TCD-normalization was significantly associated with the transplantation arm (OR=5.72 (95%CI:1.79-18.27); p=0.003). High hemoglobin (OR=1.49 per 1g/dL increase; 95%CI: 1.08-2.06; p=0.014) and HbA% (OR=1.05 per1% increase; 95%CI: 1.01-1.10; p=0.014) were significantly positively associated with TCD-normalization, but not independently. Higher levels of Ang-2 (OR=0.51 per 1 pg/mL increase, 95%CI:0.29-0.91; p=0.023) and BDNF (OR=0.69 per 1 pg/mL increase, 95%CI:0.50-0.94; p=0.02) were negatively and independently significantly associated with TCD-normalization. Multivariate analysis, also including the treatment arm, showed that BDNF remained an independent risk factor for a lack of TCD-normalization (OR=0.65, 95%CI:0.45-0.92: p=0.017).

This study confirms the association between high levels of BDNF and high velocities, and suggests that transplantation increases the likelihood of TCD-normalization compared to transfusion, and is associated with reduced Ang-2 expression in plasma, which may reflect improved brain oxygenation.

View largeDownload slide

View largeDownload slide

Close modal