P1838Thrombocytopenia under ECMO and Shear-induced shedding of platelet receptor Glycoprotein-(GP)Ialpha

Background

Several mechanisms are suspected to thrombocytopenia under Extracorporeal Membrane Oxygenation (ECMO) such as platelet-consumption or sepsis. Shedding of glycoprotein-(GP)Ibα is a recently identified mechanism of platelet clearance. ECMO generates high shear stress forces that could impact GPIbα-shedding. We hypothesized that ECMO continuous-flow devices could directly induce thrombocytopenia through shear-induced GPIbα-shedding.

Aims

Determine if ECMO induce GpIb-shedding in vitro and in vivo and determinates the kinetic evolution of platelet-count and GpIb-shedding after patient's implantation.

Methods

Platelet GPIbα-shedding was first investigated in vitro using a high-shear pump loop model. Plasma with normal platelet count (plasma-NPC) was obtained by dilution of platelet-rich plasma obtained from healthy donors in fresh-frozen-plasma. Samples were collected before and after (5, 30, 60 and 180 min) perfusion at 37°C of plasma-NPC at intermediate and high speed (2.6 and 3.6 L min–1 respectively, n=4 each). Platelet count and GPIbα-shedding were next investigated in 20 ECMO patients before/after implantation (WITECMO trial) and in 20 healthy volunteers. The geometric mean-fluorescence-intensity (gMFI) of platelet GPIbα (PE-staining) and GPIX (FITC-staining) was measured with a Navios flow cytometer (Beckman Coulter, Miami, FL). Results are expressed as GPIbα/GPIX gMFI-ratio.

Results

A significant time-dependent loss of GPIbα/GPIX gMFI-ratio was already apparent after 30 min in vitro and was significantly more pronounced at high-speed compared to intermediate-speed (pANOVA<0.001 and p<0.01 at 180 min respectively). GPIbα/GPIX gMFI-ratio was significantly increased in ECMO patients compared to healthy subjects 1- and 24-hour after implantation (p<0.001). A significantly lower platelet count was observed 1 hour after ECMO implantation (−23% vs baseline, p<0.01) with a further significant decrease at 24-hours (−53% vs baseline, p<0.0001).

Figure 1. A. Significant time-dependent loss of platelet GPIbα/GPIX gMFI-ratio (pANOVA <0.001) assessed by flow-cytometry after 30 min of perfusion at 3.6 L/min with a high-shear continuous-flow device in vitro. B. Representative experiment showing the apparition of a platelet sub-population with loss of GPIbα expression after 30 min of perfusion at 3.6 L/minwith a high-shear continuous-flow device in vitro.

Serological evidence and amino acid sequence of ubiquitin-like protein isolated from coelomic fluid and cells of the earthworm Eisenia fetida andrei

1. A small protein of M(r) 10 kDa has been isolated by reverse-phase chromatography of the basic proteins contained in the coelomic fluid and cell lysate of the earthworm Eisenia fetida andrei. 2. The protein crossreacted in dot-blot with an anti-bovine ubiquitin antiserum. 3. Its N-terminal primary structure was determined by automatic Edman degradation on 26 consecutive amino acids and showed 69% (based on the 26 amino acids) or 82% (based on the first 19 consecutive amino acids) identity with many ubiquitins and similar charge and hydrophobicity profiles and secondary structure conformation.

Antibacterial activity of Eisenia fetida andrei coelomic fluid: transcription and translation regulation of lysozyme and proteins evidenced after bacterial infestation

1. After bacterial infestation lysozyme and antibacterial activities are enhanced, peaking at 4 hr and 3 days, respectively. 2. Both humoral defenses require RNA and protein de novo synthesis in response to pathogenic bacteria injection (actinomycin D and cycloheximide experiments). 3. Antibacterial activity exists naturally at some basic level, involving regular translation of stable RNAs. 4. When antibacterial activity reaches its maximum after bacterial injection, proteins responsible for it undergo a turn-over. 5. Lysozyme and antibacterial proteins cannot account for the whole response to bacterial infestation; some cellular defense mechanisms like phagocytosis are involved at the same time.