MAT.Angiopoietin-1 Modulates Microvascular Blood Flow During Sepsis In Vivo

Alessio Alfieri1, Nicola Brown1, Richard Kammerer2, Zoe Brookes1. 1Microcirculation Research Group, Faculty of Medicine, Dentistry and Health, University of Sheffield, Sheffield, United Kingdom, 2Faculty of Life Sciences, University of Manchester, Manchester, United Kingdom.

Sepsis causes tissue damage and organ failure due to microvascular dysfunction and reduced blood flow [1]. The angiogenic growth factor Angiopoietin-1 (Ang-1) maintains blood vessel integrity and has anti-inflammatory activity, improving blood pressure and reducing mortality during lipopolysaccharide (LPS) exposure in mice [2]. The Ang-1 variant (MAT.Ang-1) has increased solubility and binding to Tie-2 receptors compared to native Ang-1 [3].This study investigated whether MAT.Ang-1 improves hemodynamic function in vivo by reducing decreases in microvascular blood flow that occur during sepsis. Aluminium dorsal microcirculatory chambers were chronically implanted into the dorsal skinfold of male C3H/HeN mice (7-10 weeks, n=15) to expose the striated muscle microcirculation for intravital microscopy between 20-24 hours after LPS, using fluorescein isothiocyanate labelled bovine serum albumin (66 kDa FITC-BSA, 200μl.100g-1 iv.). Mice received ketamine/xylazine (10/1 mg.kg-1 ip.) sedation in (i) control, (ii) LPS (1 mg.kg-1 ip. at 0 hrs and 19 hrs) and LPS + MAT.Ang-1 (33 μg per animal iv. at 20 hrs) treated animals. Blood flow was graded on a scale of 0-4 (normal flow=4, no flow=0); quantitative analysis was performed by particle image velocimetry (PIV) using LaVision DaVis® 7.2 software. LPS reduced blood flow velocity score (mean±sem) at 22 hrs (controls, 3.3±0.3; LPS, 2.4±0.3; p<0.05) and 24 hrs (controls, 3.1±0.3; LPS, 1.5±0.2; p<0.01). Velocity was increased by co-administration of MAT.Ang-1 at 22 hrs (3.0±0.2) and 24 hrs (2.5±0.2). PIV also demonstrated a slight increase in velocity at 22 hrs with MAT.Ang-1 injection (LPS, 0.020±0.01 mm/image; LPS + MAT.Ang-1, 0.038±0.006 mm/image; p=0.2, NS). Therefore, MAT.Ang-1 may improve blood flow during sepsis, contributing to maintenance of blood pressure and organ perfusion, and further studies will be performed with laser Doppler flowmetry to provide further quantitative evidence. (Funded by the British Heart Foundation).

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[2] Witzenbichler B et al. (2005) Circ. 111: 97-105.
[3] Cho CH et al. (2004) Proc. Nat. Acad. Sci. 101: 5547-5552.