Association of Markers of Haemolysis and Endothelial Dysfunction with Disease Severity and ABO Phenotype in Individuals with Sickle Cell Anaemia in South-West of Nigeria

Abstract

Background: Haemoglobin S (HbS) originates from a single nucleotide substitution in the gene encoding ß-globin. The pathological effect of this abnormality is haemolysis; which culminates in an increased level of free haemoglobin and arginase in plasma. The released free cell haemoglobin (Hbfree) reacts with Nitric Oxide and Arginine, leading to an increased expression of vascular cell adhesion molecule (VCAM). The relationship of ABO blood types as it affects this abnormality have been established in sickle cell anaemia disease population. This study explored the association between disease severity, markers of haemolysis and endothelial dysfunction with ABO phenotype in individuals with sickle cell anaemia (SCA). Materials and Methods: This is a comparative cross-sectional study consisting of seventy-three (73) participants with SCD. Consented sickle cell anaemia individuals of age16 years and above in steady state were recruited for this study, while those with sickle cell anaemia in crisis or recent episode of crisis less than 1 month, recent blood transfusion less than 3 months, SCA individual on Nitrate therapy, hydroxyurea, recent arginine therapy treatments less than 3 months, statins drugs (HMG coA-Reductase inhibitors), sildenafil therapy, allopurinol (xanthine oxidase inhibitor) and contraceptives were excluded from the study. Their clinical characteristics, disease severity, ABO blood phenotype, markers of haemolysis (Free cell haemoglobin-Hbfree, lactate dehydrogenase (LDH), total and conjugated bilirubin, corrected reticulocyte count, and reticulocyte production index) and markers for endothelial dysfunction (vascular cell adhesion molecule (VCAM), von Willebrand Factor (vWF) and nitric oxide (NO) were measured. Free haemoglobin (HbFree), VCAM, vWF and NO levels were determined using enzyme linked immunoassay method. LDH, bilirubin; total and conjugated were determined using COBAS C311 chemistry auto-analyzer (and the unconjugated bilirubin was determined). Full blood count and reticulocyte count were determined using Sysmex 350XN 5-part haematology auto-analyzer. Blood group phenotype was determined using the tiles method. Results: The Majority (71.2%) of the participants had moderate disease as determined by a modified SCD scoring system published by Adegoke et al. (2013). Markers of haemolysis, Hb free and LDH were significantly higher in the non-O blood group participants, consequently NO level was significantly lower while VWF and VCAM were higher in these participants. In terms of clinical severity, Hb Free level was significantly higher in the non-O blood type for those with moderate and severe disease phenotypes but not for mild diseases. While LDH was significantly higher in non-O for severe but not clinically for mild and moderate diseases. Conversely, all the markers of endothelial dysfunction showed statistical significant differences in their levels for moderate and severe disease categories. Among the study participants with O blood group type, LDH and VWF were significant predictors of disease severity. Every unit increase in LDH had a 5% increase in odds of clinically severe disease (AOR =1.05, 95% CI = 1.005-1.095) and for VWF, every unit increase was linked with approximately 44% increase in odds of clinically severe disease (AOR =1.44, 95% CI = 1.06-1.95). None of the markers measured were significant predictors for clinical disease severity for non-O. Conclusion: This study indicates that Sickle cell anaemia patients with O blood group type exhibited a lower degree of haemolysis and endothelial dysfunction as compared to those with non- O blood group. LDH and vWF were reliable markers for predicting disease severity in SCA with blood group O phenotype.