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.

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.

Non-activated plasma-derived PC improves amputation rate of children undergoing sepsis.

Low circulating protein C (PC) levels have been observed in sepsis, especially in patients with Neisseriae Meningitides infections. Poor clinical outcome and high limb amputation rates have been associated in infected patients with low circulating PC levels. Published studies using activated PC replacement therapy patients with sepsis have shown reduced mortality rates, however, its use has been associated with severe bleeding events. Paediatric sepsis studies using non-activated plasma-derived PC (Ceprotin®) are lacking. We present a retrospective study in children with sepsis who were treated with Ceprotin® focusing on amputation rate post treatment. Thirty subjects were identified. Median age at diagnosis was 2 years. Twenty-one (70%) were treated for Nesseria Meningitides and one (3%) for Streptococcus-A ß-haemolyticus, another 8 (26%) patients with malignancies were treated for neutropenic sepsis. Following Ceprotin® administration, a significant increase in leukocyte count (p=0.004), neutrophil count (p=0.001) and PC (pretreatment=13%, posttreatment=88.5%; p=0.0001) was seen. Prothrombin time (pretreatment =30.3 seconds, posttreatment =16.5; p=0.000) and activated partial thromboplastin time (pretreatment =61.8 sec, postreatment =42.6 sec; p=0.000) were significantly reduced, while fibrinogen levels were significantly elevated (pretreatment =1.9 g/dL, posttreatment =4.4 g/dL; p=0.000). The median time between admission to intensive care and Ceprotin® administration was 10 hrs. Limb amputation rate was reduced (16-23% versus 30-50% from previous studies) and there were no haemorrhagic events observed. This study demonstrates the safe administration of non-activated plasma-derived PC concentrate in patients with sepsis who are coagulopathic and it associated with a reduction in amputation rates.

Recombinant factor VIIa in the management of surgery and acute bleeding episodes in children with haemophilia and high responding inhibitors.

The management of acute and surgical bleeding episodes in children with severe factor VIII or IX deficiency who develop high responding inhibitors presents a major therapeutic challenge to clinicians. Recombinant factor VIIa (rVIIa) is an effective, reliable and safe treatment that can be used to treat acute bleeding episodes prior to commencing an immune tolerance programme and to cover surgical procedures until the immune tolerance programme is successful. In a significant minority of patients, immune tolerance therapy is ineffective and an alternative haemostatic agent such as rVIIa is required for life-long treatment. The present study evaluated the use of rVIIa in a paediatric setting. Twelve children, aged 1-16 years, were treated successfully with rVIIa to prevent surgical bleeding in 20 surgical procedures (19 central venous access device insertion or removal, 1 dental extraction). Minor postoperative haematomata developed in 2 out of 20 cases after regular rVIIa therapy had been discontinued and resolved with a short course of rVIIa in both cases. Three children had six life- or limb-threatening bleeding episodes. All bleeding episodes resolved with regular rVIIa treatment although topical fibrin glue was needed in one child with a frenulum tear. One patient required two red cell transfusions for symptomatic anaemia resulting from two separate bleeding episodes. The rVIIa therapy was well tolerated and there was no evidence of treatment-related complications. We conclude that rVIIa is the treatment of choice for the management of surgery and acute life- or limb-threatening bleeding in children with haemophilia and high responding inhibitors.