Chronic physical activity limits blood rheology alterations in transgenic SAD mice.

Abstract

Hemorheological abnormalities, including increased blood viscosity, are involved in the pathophysiology of sickle cell anemia (SCA) by triggering acute painful vaso-occlusive events. As for cardiac, metabolic or pulmonary diseases, individualized chronic exercise programs have been suggested to improve the health status in SCA 1 but no study until now tested this hypothesis in humans because of the vaso-occlusive risks that SCA patients could encounter during such a protocol. This study examined the effects of a voluntary wheel physical activity program in transgenic mice which express the human hemoglobin SAD transgene (α2 human β2 SAD) containing three sickle mutations: D-punjab (β121Gln), Antilles (β23Ile) and βS(β6Val) (SAD mice) on blood rheology parameters. We particularly focused on, the hematocrit-to-viscosity ratio (HVR), an index of tissue oxygenation which reflects the balance between blood oxygen carrying capacity (i.e., hematocrit), and blood flow resistance (i.e., blood viscosity) 2. We used healthy C57Bl/6J (C57) and transgenic SAD mice, a murine model particularly severe in deoxygenated conditions. Each strain was randomly divided into sedentary (sed) and “physical activity” (PA) groups. At the end of the 8 weeks of protocol, mice were anesthetized and blood was collected by retro-orbital venipuncture into tubes containing ethylene diamine tetra-acetic acid (EDTA) for hemorheological measurements 3. While PA did not significantly change blood viscosity or HVR in C57 mice, it decreased blood viscosity and increased HVR at 18.75 s−1 in SAD mice. A similar trend was observed at 375 s−1 for blood viscosity and, although not significantly different, HVR level was numerically higher in SADPA versus SADsed at this shear rate (Fig. 1B2,C2). Surprisingly, hematocrit was increased in SADPA while it remains unchanged by PA in C57. There is no clear explanation about this difference but despite the higher hematocrit in SADPA versus SADsed mice, the former group exhibited a reduction of blood viscosity compared to their sed counterparts. Although not directly investigated, the decrease in blood viscosity in SADPA is probably attributed to changes in RBC rheological properties such as a decrease in RBC aggregation and/or an improvement of RBC deformability 4. In parallel, the lack of effect of PA on mean corpuscular volume (14.0 ± 0.2 vs. 14.7 ± 0.2 pg) and mean corpuscular hemoglobin concentration (31.3 ± 0.2 vs. 31.8 ± 0.1 g/dl) in SADsed versus SADPA mice suggests that RBC membrane properties have probably been affected by PA. Hematocrit percentage (A), blood viscosity (B1, B2), and HVR (C1, C2) values at 18.75/s and 375/s in C57 and SAD mice (31.1 ± 3.6 weeks old) in sed (C57sed [n = 6] and SADsed [n = 10]) or PA group (C57PA [n = 6] and SADPA [n = 12]). Measurement of blood viscosity was performed with a cone plate viscometer (Brookfield DVII+, with CPE40 spindle) at 37°C and at two shear rates (18.75 and 375 s−1) at native hematocrit. The HVR was calculated as the ratio of the native hematocrit to whole blood viscosity. **(P < 0.01) ***(P < 0.001) Significant difference compared to SAD mice; #(P < 0.05) ##(P < 0.01) Significant PA effect in SAD mice. Values are expressed as mean ± SD. All statistical analyses were conducted using Statistica (Version 8.0, StatSoft, Tulsa, OK). Hematological and hemorheological parameters were compared between SAD and C57 mice using a one-way analysis of variance followed by pairwise comparisons. SADPA mice exhibited also greater WBCs count than SADsed mice (+303%, P < 0.001), whereas such effect of PA was not present in C57. This higher inflammatory state in SADPA mice could be related to the higher mean platelet volume (MPV) level compared to their sed counterparts (+41%, P < 0.01). The size of platelets represented by MPV could up-regulate inflammation 5 and WBCs count 6. Greater inflammation in SADPA mice could be problematic by increasing the risks for vaso-occlusive events to occur. However, another recent study showed improvement of pulmonary endothelial function in trained versus sed SAD mice 7, which could counterbalance the effects of PA on WBCs count and platelet reactivity. Thus, our findings suggest that PA, by increasing HVR and lowering blood viscosity in SAD mice could improve tissue perfusion and decrease vascular resistance, hence limiting the occurrence of vaso-occlusive crisis under stressful situations. Camille Faes, 1 Emmanuelle Charrin,1 Philippe Connes,1,2 Vincent Pialoux,1,2 and Cyril Martin1* 1CRIS EA 647, University Claude Bernard Lyon 1, University of Lyon, France; 2Institut Universitaire de France, Paris, France