The mutant form of human apoA1, known as apoA1 Milano, is formed as a resul
t of arginine 173 to cysteine substitution and inhibits experimental athero
sclerosis in cholesterol-fed animals. This study was designed to determine
if apoA1 Milano would modify arterial thrombogenesis. Sprague Dawley rats w
ere intravenously administered the carrier alone (n = 8) or apoA1 Milano (2
0 mg.kg(-1).d(-1) for 4 to 10 days, n = 17). The abdominal cavity was opene
d, and the abdominal aorta was isolated. Whatman paper impregnated with 35%
FeCl3 was wrapped around the surface of the aorta, and aortic flow was rec
orded continuously. In carrier-treated rats, an occlusive platelet-fibrin-r
ich thrombus was formed in 21.2 +/- 4.1 (meant SD) minutes. Treatment of ra
ts with apoA1 Milano markedly delayed time to thrombus formation (38.8 +/-
11.9 versus 21.2 +/- 4.1 minutes, P < 0.01), inhibited platelet aggregation
(25 +/- 7% versus 50 +/- 11%, P < 0.01), and reduced weight of the thrombu
s (18.5 +/- 1.8 versus 23.7 +/- 2.3 mg/cm, P < 0.01), Total cholesterol and
HDL levels remained similar in both groups of rats, but plasma apoA1 Milan
o levels were elevated in apoA1 Milano-treated rats. In in vitro studies, i
ncubation of platelets with apoA1 Milano reduced ADP-induced platelet aggre
gation by about 50%, but apoA1 Milano had no direct effect on vasoreactivit
y. This study provides further evidence for critical role of platelets in t
hrombosis. Use of apoA1 Milano offers a novel approach to inhibit arterial
thrombosis.