Tirofiban (Aggrastat®) protects platelets and decreases platelet-granulocyte binding in an extracorporeal circulation model

Objectives: Extracorporeal circulation (ECC) induces platelet activation and inflammation with potentially life-threatening organ dysfunction. Short-acting GP IIb/IIIa inhibitors like tirofiban and eptifibatide protect platelets during ECC without increasing bleeding complications and may reduce inflammation. This study investigates anti-thrombotic and anti-inflammatory effects of different platelet-inhibitors.

Material and Methods: Control (untreated) and treated (using either 150 ng/mL tirofiban, 2.5µg/mL eptifibatide, 0.7µg/mL milrinone, 15µg/mL dipyridamol, or 300 KIU/mL aprotinin) heparinized blood of healthy volunteers (n=6) was recirculated in a well-established ECC-model (Chandler-loop). Platelet-counts, percentage of P-selectin-expressing (activated) platelets, platelet aggregates, and CD15-positive aggregates (indicating proinflammatory platelet-granulocyte binding) were determined before (baseline) and after 30 minutes recirculation in unstimulated and ADP-stimulated samples using flow cytometry. Statistical analysis was performed using multifactor ANOVA after transforming the data (logarithms for counts and logodds for percentages). Least square means were backtransformed to obtain appropriate means and their 95% confidence intervals. Multiple post-hoc comparisons were performed by Tukey's HSD test with a global alpha of 5%.

Results: Significant inhibition was observed for:

• ECC-induced platelet aggregation by tirofiban (unstimulated: 2.2-fold/stimulated: 2.46-fold), eptifibatide (unstimulated: 1.96-fold/stimulated: 2.66-fold), and milrinone (unstimulated: 1.88-fold/stimulated: 1.37-fold);

• ECC-induced P-selectin expression by tirofiban (unstimulated: 3.88-fold/stimulated: 2.55-fold), and eptifibatide (unstimulated: 5.83-fold/stimulated: 3.31-fold);

• ECC-induced platelet-loss by tirofiban (1.27-fold), and eptifibatide (1.25-fold);

• ECC-induced platelet-granulocyte binding by tirofiban (unstimulated: 2.25-fold/stimulated: 1.6-fold), but not by eptifibatide.

Conclusions: Amongst the investigated drugs only GP IIb/IIIa inhibitors decreased activation, aggregation, and loss of platelets during ECC but acted differently on platelet-granulocyte interaction. Especially tirofiban should be considered both for platelet protection and inhibition of platelet-mediated inflammation during ECC.

Results given as means (95% confidence intervals)
	baseline	untreated (30 minutes)	tirofiban (30 minutes)	eptifibatide (30 minutes)	milrinone (30 minutes)	dipyridamol (30 minutes)	aprotinin (30 minutes)
aggregates (unstimulated)	14.4 (9.7–20.9)	26.7 (18.8–36.4)	12.1 (8.1–17.8)	13.6 (9.1–19.8)	14.2 (9.5–20.6)	17.7 (12.0–25.2)	20.4 (14.0–28.7)
aggregates (stimulated)	21.3 (14.7–29.8)	32.5 (23.4–43.0)	13.2 (8.8–19.3)	12.2 (8.1–18.0)	23.6 (16.4–32.6)	27.4 (19.4–37.3)	31.3 (22.5–41.7)
P-selectin (unstimulated)	1.7 (0.8–3.6)	10.5 (5.3–19.8)	2.7 (1.3–5.4)	1.8 (0.9–3.7)	5.2 (2.6–10.4)	4.7 (2.3–9.4)	6.6 (3.3–12.9)
P-selectin (stimulated)	13.9 (7.1–25.2)	25.5 (14.0–41.8)	10.0 (5.0–18.9)	7.7 (3.8–15.0)	23.7 (12.9–39.4)	19.4 (10.3–33.6)	27.7 (15.4–44.6)
CD15 (unstimulated)	8.3 (5.2–12.9)	16.0 (10.4–23.9)	7.1 (4.4–11.2)	10.0 (6.3–15.5)	11.5 (7.3–17.7)	11.5 (7.3–17.6)	17.4 (11.3–25.8)
CD15 (stimulated)	9.3 (5.8–14.4)	15.9 (10.3–23.7)	9.9 (6.3–15.4)	11.5 (7.3–17.7)	13.7 (8.8–20.7)	10.7 (6.8–16.5)	12.7 (8.1–19.3)
platelet count	243.6 (202.3–293.3)	184.2 (153.0–221.8)	234.1 (194.4–281.8)	231.4 (192.2–278.6)	205.8 (170.9–247.8)	194.9 (161.9–234.6)	189.5 (157.4–228.1)