Red blood cell tolerance to deoxygenation linked to improved splenic filtration in SCA patients

Red blood cell deformability is directly related to spleen filtration for pediatric patients with sickle cell anemia (SCA).

A team, led by Amina Nardo-Marino, Centre for Haemoglobinopathies, Department of Hematology, Copenhagen University Hospital, Rigshospitalet, assessed the relationship between red blood cell deformability, spleen size, and splenic filtration function in pediatric patients with sickle cell anemia in data presented during the American Society of Hematology (ASH) Annual Meeting and Exposition.

The Spleen

Patients with sickle cell anemia often have damaged spleens. In fact, the spleen is many times the 1 of the first organs damaged as the disease progresses.

This provides a particular set of challenges in red blood cell deformability, which causes constant intrasplenic sickling and recurrent splenic ischemia from early childhood on.

There is established research showing that splenic function is lost within the first years of life for the majority of pediatric patients with sickle cell anemia.

Spleen size can vary significantly between different individuals and the determinants of phenotypical variations are not fully understood, making it a challenge to fully forecast outcomes.

The Patients

In the study, the investigators examined 91 pediatric patients aged 0-16 years with a confirmed sickle cell anemia diagnosis from the pediatric hematology clinic at King’s College Hospital in London between December 2018 and January 2019. The patients ranged from aged 7 months to 16 years, with a mean age of 8.4 years.

In addition, 47.3% (n = 43) of the patient population was treated with hydroxycarbamide and data on α-thalassemia genotype were available for 88 participants. Of this group, 7 were homozygous for the 3.7 kb deletion, 33 were heterozygous for the 3.7 kb deletion, and 47 had no detected deletions.

The team excluded participants if they had previously undergone surgical splenectomy or if they had received any blood transfusions within the previous 3 months before study recruitment. Participants were also excluded if they received hydroxycarbamide treatment at the time of recruitment and received therapy for less than 3 months.

There are multiple genetic and external factors that could contribute to spleen size in patients with sickle cell amenia, while elevated levels of hemoglobin F (HbF) and co-inheritance of α-thalassemia have been associated with persistent splenomegaly because of the presence of irreversibly sickle cells.

The investigators obtained measurements of spleen size for all participants using abdominal ultrasound and assessed splenic function by manual pitted red blood cell counts.

Red blood cells were fixed in 2% PBS-buffered paraformaldehyde on the day of the venipuncture. The team also performed differential inference contrast microscopy within 3 months of sampling.

There were a minimum of 500 consecutive red blood cells counted for each sample. The proportion of cells with 1 or more pits were expressed as a percentage of the total number of cells counted.

They also measured red blood cell deformability using the Oxygenscan module of the Laser Optical Rotational Red Cell Analyzer.

Red Blood Cell Deformability

The results show red blood cell deformability expressed as the elongation index at normal oxygen tensions (EImax) and after deoxygenation (EImin) correlated positively with spleen length (EImax: r = 0.41, P <0.001; EImin: r = 0.36; P <0.001). They also found the point of sickling correlated negatively with spleen length (r = -0.36, P <0.001).

After adjusting for percentage HbF and α-thalassemia genotype in multiple linear regression models the results for EImax, EImin and POS remained significant (EImax: P <0.001; EImin: P = 0.005; POS: P = 0.003).

The investigators also found that EImax and EImin both correlated negatively with %PIT (EImax: r = -0.60, P <0.001; EImin: r = -0.34, P <0.001), while POS correlated positive with %PIT (r = 0.50, P <0.001).

Moreover, EImax, EImin and POS remained significant after the investigators adjusted for %HbF in multiple linear regression models (EImax: P <0.001; EImin: P = 0.03; POS: P <0.001).

“We assessed the association between RBC deformability measured using oxygen gradient ektacytometry, spleen size and splenic filtration in 91 children with SCA,” the authors wrote. “Results suggested that children with larger spleens had improved RBC deformability, expressed as a higher EImax and EImin, and increased RBC tolerance to deoxygenation, expressed as a lower POS.”

The investigators went on to say there were portions of the results less clear and should be fleshed out more in the future.

“Results also suggested that improved deformability and increased RBC tolerance to deoxygenation was associated with improved splenic filtration, expressed as a lower %PIT,” the authors wrote. “Although it is difficult to interpret the causal relationship between RBC deformability and splenic injury, our results indicate that decreased deformability contributes to loss of splenic filtration as well as phenotypical variations in spleen size in children with SCA.”

The study, “Decreased Red Blood Cell Deformability Contributes to Loss of Splenic Filtration Function and Variations in Spleen Size in Children with Sickle Cell Anemia,” was published online by ASH 2022.