Abstract
Introduction: Impaired red blood cell (RBC) rheology, increased RBC adhesiveness to the vascular wall, enhanced inflammation and blunted vascular reactivity are involved in the pathophysiology of sickle cell anemia (SCA). Painful vaso-occlusive crisis (VOC) is the most frequent complication encountered by SCA patients. While several studies compared several biomarkers of severity between patients at steady state and others during VOC, very few works compared the same patients in the two conditions. It is therefore difficult to know what happens during VOC. The present study was devoted to compare several hematological, biochemical, and rheological parameters, as well as RBC adhesiveness at steady state and during VOC. Altogether, 36 SCA patients were studied.
Methods: This prospective monocentric study was performed at the University Hospital of Pointe-a-Pitre (Guadeloupe, French West Indies), in accordance with the guidelines set by the declaration of Helsinki and was approved by the Regional Ethics Committee (CPP Sud/Ouest Outre Mer III, Bordeaux, France, registration number: 2012-A00701-42). After admission to the emergency department for a VOC episode, patients were informed about the purpose and procedures of the study and gave their written consent. Blood was sampled at the arrival of the patients at the emergency department before they received any medications. A visit to the Sickle Cell Center was then scheduled at least 3 months after the emergency department admission to collect routine blood samples at steady state. Steady state condition was defined as a period free of blood transfusion in the previous three months and without any acute SCA complications in the previous two months. RBC deformability was determined at 3 and 30 Pa by ektacytometry (LORRCA, Mechatronics), RBC aggregation properties (RBC aggregation and RBC disaggregation threshold) by syllectometry (LORRCA), blood viscosity by cone-plate viscosimetry (Brookfield, DVII+ model with CPE 40 spindle) at 225 s-1. Irreversible sickle cells (ISCs) were measured on an Imagestream ISX MkII flow cytometer (Amnis Corp, EMD Millipore). Lu/BCAM, ICAM-4/Lw and the alpha4-beta1 integrin were measured by flow cytometry at the RBC surface (FACSCanto II, BD Biosciences). RBC adhesion to monolayers of transformed human bone marrow endothelial cells (TrHBMECs) was studied in continuous flow conditions in Vena8 Endothelial+ Biochips (Cellix Ltd). Other hematological and biochemical parameters were measured by standard techniques.
Results: Compared to steady state values, white blood cell (9.2 [6.7-10.6] versus 12.3 [10.1-16.2] 109/L, p < 0.001) and C-Reactive Protein (3.7 [3.3-6.0] versus 7.1 [3.3-17.5] mg/L, p < 0.05) levels increased during VOC (table 1). Lactate dehydrogenase level slightly increased during VOC (418 [351-564] versus 437 [370-727] IU/L, p < 0.03) but no change was observed for hemoglobin. RBC deformability slightly decreased during VOC (0.34 [0.26-0.44]) compared to steady state (0.38 [0.31-0.46], p < 0.02). RBC aggregation increased during VOC (55 [46-60 %] compared to steady state (51 [46-54] %, p < 0.05). No difference was detected for blood viscosity, RBC surface proteins, RBC adhesion, and RBC disaggregation threshold between the two conditions. During VOC, the percentage of ISCs was inversely correlated with deformability (p < 0.002 and p < 0.006 at 3 and 30 Pa, respectively), but positively correlated with RBC disaggregation threshold (p < 0.002) and with RBC adhesion to TrHBMECs (p < 0.008) (figure 1). At steady state, it was significantly correlated only with the disaggregation threshold (positive correlation, p < 0.03).
Discussion: The most striking observation of this study is the positive correlation between ISCs (rigid cells) and RBC adhesion properties during overt VOC. This is in contrast with the general observation that the most deformable RBCs are those exhibiting the strongest adhesiveness and possibly involved in VOC initiation. Strengthened RBC aggregates may also disturb the blood flow into the microcirculation, hence participating to VOC progression and sustention. Drugs targeting RBC deformability (ISCs) and RBC aggregates might be helpful during established VOC in SCA.
Disclosures
No relevant conflicts of interest to declare.
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