Functional and Mechanistic Characterization of Limb Ulcers in Patients With Sickle Cell Disease (DrepanO2)

Sickle Cell Disease is the most frequent genetic disease in the world (representing one birth over 1900, in France). The polymerization of the abnormal hemoglobin (i.e., HbS) when deoxygenated is at the origin of a mechanical distortion of red blood cells (RBC) into a crescent-like shape. Sickled RBCs are very fragile and rigid, which lead patients to have severe anemia and to develop frequent and repeated painful vaso-occlusive crises. Furthermore, the repetition of sickling-unsickling cycles causes irreversible damages to the RBCs, which shorten their half-life. Accumulation of free hemoglobin and heme in the plasma is involved in blood vessels lesions in both the macro- and micro- circulation. The resulting vascular dysfunction could explain why limb ulcers are 10 fold more frequent in patients with sickle cell disease compared to the general population and may happen at a younger age. Limb ulcers induce significant morbidity (delay of healing between 9 and 26 weeks in the french cohort), and are associated to significant pain (needing opioid pain-killer) and increase the risk of infection. Cost of care is also increased. Moreover, ulcers induce missed school and work days. Data on cutaneous microcirculation and ulcers physiopathology in patients with sickle cell disease are scarce. We want to realise a microcirculatory and neurological functional study of patients with with and without ulcers and a characterization of biomarkers present in the blood or in the wound fluid which can participate to ulcers physiopathology. To ensure healing, adapted therapeutics are essential. Several strategies are proposed such as: lifestyle measures (venous compression, lower limb elevation, rest), dressings, hyperbaric oxygenotherapy (also used in diabetic ulcers). The project is devoted to study the mechanisms involved in leg ulcers and the effects of therapeutical/behavioral strategies.

For patients with limb ulcers : at inclusion visit and after healing or at 6 months if ulcer does not heal: Microvascular analysis (laser doppler, TcPO2), Neurological analysis ( sensitivity testing with thermal and mechanical test), Analysis of physical characteristics of red blood cells and inflammatory marks, Analysis of cytokine and metalloproteases in the wound fluid, Assessment of healing according usual treatment

For patients without limb ulcers : at inclusion visit only Microvascular analysis (laser doppler, TcPO2), Neurological analysis (sensitivity testing with thermal and mechanical test), Analysis of physical characteristics of red blood cells and inflammatory marks

Alteration of cutaneous microvascular function and peripheral sensorial neurological function in patients with limb ulcers

Cutaneous microvascular function is assessed with : laser Doppler Including measurement of blood pressure before and after testing, heart rate before and after testing, cutaneous temperature, values of laser Doppler before and after vasodilatation with acetylcholine, deionized water, local heating (42°C) TcPO2 on the first intermetatarsal space and bordering ulcer Peripheral sensorial neurological function is assessed with Von Frey monofilament, hot (50°C)/cold (4°C) test, pic-touch test and pallesthesia.

Modification of hemorheological red blood cells characteristics between patients with and without ulcers

Analysis of hemorheological characteristics in the 2 arms after blood test with blood viscosity and RBC rheological measurements (deformability/aggregation)

Analysis of metalloproteases (MMP-8 and MMP-9) and inflammatory markers (TNF-alpha, Il-6, Il1-beta, VCAM 1, P-selectin) in the wound fluid

Compare microcirculation, pro inflammatory marker in the wound fluid and in the blood and hemorheological characteristics after usual treatment to obtain healing

Compare results (previously described) in the group of patients with ulcers, between initial and second visit

Inclusion Criteria: Sickle Cell Disease (homozygous SS or Sb0) Age ≥ 18 years old Consent patients Social regimen Exclusion Criteria: tutela or curatella Vaso occlusive crisis < 1 month