Insight into the complex pathophysiology of sickle cell anaemia and possible treatment.

Sickle cell anaemia (SCA) is the consequence of abnormal haemoglobin production due to an inherited point mutation in the ß-globin gene. The resulting haemoglobin tetramer is poorly soluble when deoxygenated, and when this is prolonged, intracellular gelation of sickle haemoglobin occurs, followed by haemoglobin polymerisation. If many cycles of sickling and unsickling occur, the red cell membrane will be disrupted leading to haemolysis and vaso-occlusive events. Recent studies have also shown that leucocyte adhesion molecules and nitric oxide (NO) depletion are involved in endothelial damage. New insights in SCA pathophysiology and vascular biology have shown that cell-derived microparticle (MP) generation is also involved in the vaso-occlusion. Endothelial damage is perpetuated by impaired production or increased consumption of protective modulators such as protein C, protein S and NO. New therapeutic interventions should address these aspects of SCA pathogenesis. To date, the only US-FDA-approved therapy to prevent painful vaso-occulsive episodes is hydroxyurea that reduces haemoglobin polymerisation in sickle cells by increasing the production of foetal haemoglobin and L-glutamine. However, several new drugs have been tested in the last years in randomised clinical trials. We here report an update on the current status of knowledge on SCA.

Sickle cell disease and dental treatment.

Sickle cell disease (SCD) and sickle cell trait (SCT) are found most frequently in individuals of African, Middle Eastern and Indian ethnicity. Population migration has made this disease more common worldwide, including Ireland. We present an overview of this disease, focusing on management and practical implications for dental practitioners.

Observational retrospective study of vascular modulator changes during treatment in essential thrombocythemia.

Essential thrombocythemia (ET) patients are at risk of developing thrombotic events. Qualitative platelet (PLT) abnormalities and activation of endothelial cells (ECs) and PLTs are thought to be involved. Microparticles (MPs) can originate from PLTs (PMPs), ECs (EMPs), or red cells (RMPs). Previous studies have indicated that MPs contribute to ET pathophysiology. Endothelial modulators (eg, nitric oxide [NO], adrenomedullin [ADM], and endothelin-1 [ET-1]) are also involved in the pathophysiology of this condition. We hypothesized that treatments for reducing PLT count might also indirectly affect MP generation and endothelial activity by altering endothelial modulator production. The rationale of this study was that hydroxyurea (HU), a cytostatic drug largely used in ET, induces the production of a potent vasoactive agent NO in ECs. An observational retrospective study was designed to investigate the relationship between MPs, NO, ADM, and ET-1 in ET patients on treatment with HU, anagrelide (ANA), aspirin (ASA), and a group of patients before treatment. A total of 63 patients with ET diagnosis: 18 on HU + ASA, 15 on ANA + ASA, 19 on ASA only, and 11 untreated patients, and 18 healthy controls were included in this study. Blood samples were analyzed for MP (absolute total values) and functional markers (percentage values) by flow cytometry. PLT-derived MPs were studied using CD61, CD62P, CD36, and CD63, whereas endothelial-derived MPs were studied using CD105, CD62E, and CD144. Endothelial modulator markers (NO, ADM, and ET-1) were measured by ELISA. Total MP count was higher in the group treated with ANA + ASA (P < 0.01). MP markers modified in ET patients returned to levels of healthy controls following treatment, in particular, in patients on ANA treatment. NO and ADM values were higher in the HU group (P < 0.001). HU and ANA treatment also affected MP production in a cell origin-specific manner. HU and ANA, although acting via different pathways, have similar final effects. For instance, HU causes vasodilatation by increasing NO and ADM levels, whereas ANA impairs vasoconstriction by reducing ET-1. In conclusion, therapy with HU cytostatic drugs and ANA can reduce PLT count in ET, and also affect endothelial modulatory agents, with HU sustaining vasodilation and prothrombotic MP concentration, whereas ANA decreases vasoconstriction.

Circulating microparticles, protein C, free protein S and endothelial vascular markers in children with sickle cell anaemia.

INTRODUCTION: Circulating microparticles (MP) have been described in sickle cell anaemia (SCA); however, their interaction with endothelial markers remains unclear. We investigated the relationship between MP, protein C (PC), free protein S (PS), nitric oxide (NO), endothelin-1 (ET-1) and adrenomedullin (ADM) in a large cohort of paediatric patients. METHOD: A total of 111 children of African ethnicity with SCA: 51 in steady state; 15 in crises; 30 on hydroxyurea (HU) therapy; 15 on transfusion; 17 controls (HbAA) of similar age/ethnicity. MP were analysed by flow cytometry using: Annexin V (AV), CD61, CD42a, CD62P, CD235a, CD14, CD142 (tissue factor), CD201 (endothelial PC receptor), CD62E, CD36 (TSP-1), CD47 (TSP-1 receptor), CD31 (PECAM), CD144 (VE-cadherin). Protein C, free PS, NO, pro-ADM and C-terminal ET-1 were also measured. RESULTS: Total MP AV was lower in crisis (1.26×10(6) ml(-1); 0.56-2.44×10(6)) and steady state (1.35×10(6) ml(-1); 0.71-3.0×10(6)) compared to transfusion (4.33×10(6) ml(-1); 1.6-9.2×10(6), p<0.01). Protein C levels were significantly lower in crisis (median 0.52 IU ml(-1); interquartile range 0.43-0.62) compared with all other groups: HbAA (0.72 IU ml(-1); 0.66-0.82, p<0.001); HU (0.67 IU ml(-1); 0.58-0.77, p<0.001); steady state (0.63 IU ml(-1); 0.54-0.70, p<0.05) and transfusion (0.60 IU ml(-1); 0.54-0.70, p<0.05). In addition, levels were significantly reduced in steady state (0.63 IU ml(-1); 0.54-0.70) compared with HbAA (0.72 IU ml(-1); 0.66-0.80, p<0.01). PS levels were significantly higher in HbAA (0.85 IU ml(-1); 0.72-0.97) compared with crisis (0.49 IU ml(-1); 0.42-0.64, p<0.001), HU (0.65 IU ml(-1); 0.56-0.74, p<0.01) and transfusion (0.59 IU ml(-1); 0.47-0.71, p<0.01). There was also a significant difference in crisis patients compared with steady state (0.49 IU ml(-1); 0.42-0.64 vs. 0.68 IU ml(-1); 0.58-0.79, p<0.05). There was high correlation (R>0.9, p<0.05) between total numbers of AV-positive MP (MP AV) and platelet MP expressing non-activation platelet markers. There was a lower correlation between MP AV and MP CD62P (R=0.73, p<0.05) (platelet activation marker), and also a lower correlation between percentage of MP expressing CD201 (%MP CD201) and %MP CD14 (R=0.627, p<0.001). %MP CD201 was higher in crisis (11.6%) compared with HbAA (3.2%, p<0.05); %MP CD144 was higher in crisis (7.6%) compared with transfusion (2.1%, p<0.05); %CD14 (0.77%) was higher in crisis compared with transfusion (0.0%, p<0.05) and steady state (0.0%, p<0.01); MP CD14 was detectable in a higher number of samples (92%) in crisis compared with the rest (40%); %MP CD235a was higher in crisis (17.9%) compared with transfusion (8.9%), HU (8.7%) and steady state (9.9%, p<0.05); %CD62E did not differ significantly across the groups and CD142 was undetectable. Pro-ADM levels were raised in chest crisis: 0.38 nmol L(-1) (0.31-0.49) versus steady state: 0.27 nmol L(-1) (0.25-0.32; p<0.01) and control: 0.28 nmol L(-1) (0.27-0.31; p<0.01). CT-proET-1 levels were reduced in patients on HU therapy: 43.6 pmol L(-1) (12.6-49.6) versus control: 55.1 pmol L(-1) (45.2-63.9; p<0.05). NO levels were significantly lower in chest crisis (19.3 mmol L(-1) plasma; 10.7-19.9) compared with HU (22.2 mmol L(-1) plasma; 18.3-28.4; p<0.05), and HbSC (30.6 mmol L(-1) plasma; 20.8-39.5; p<0.05) and approach significance when compared with steady state (22.5mmol L(-1) plasma; 16.9-28.2; p=0.07). CONCLUSION: Protein C and free PS are reduced in crisis with lower numbers of platelet MP and higher percentage of markers of endothelial damage and of red cell origin. During chest crisis, ADM and ET-1 were elevated suggesting a role for therapy inhibiting ET-1 in chest crisis.