Microbubble persistence in the microcirculation during ischemia/reperfusion and inflammation is caused by integrin- and complement-mediated adherence to activated leukocytes.
BACKGROUND
Albumin microbubbles that are used for contrast echocardiography persist within the myocardial microcirculation after ischemia/reperfusion (I-R). The mechanism responsible for this phenomenon is unknown.


RESULTS
Intravital microscopy of the microcirculation of exteriorized cremaster muscle was performed in 12 wild-type mice during intravenous injections of fluorescein-labeled microbubbles composed of albumin, anionic lipids, or cationic lipids. Injections were performed at baseline and after 30 to 90 minutes of I-R in 8 mice and 2 hours after intrascrotal tumor necrosis factor-alpha (TNF-alpha) in 4 mice. Microbubble adherence at baseline was uncommon (<2/50 high-power fields). After I-R, adherence increased (P<0.05) to 9+/-5 and 5+/-4 per 50 high-power fields for albumin and anionic lipid microbubbles, respectively, due to their attachment to leukocytes adherent to the venular endothelium. TNF-alpha produced even greater microbubble binding, regardless of the microbubble shell composition. The degree of microbubble attachment correlated (r=0.84 to 0.91) with the number of adhered leukocytes. Flow cytometry revealed that microbubbles preferentially attached to activated leukocytes. Albumin microbubble attachment was inhibited by blocking the leukocyte beta(2)-integrin Mac-1, whereas lipid microbubble binding was inhibited when incubations were performed in complement-depleted or heat-inactivated serum rather than control serum.


CONCLUSIONS
Microvascular attachment of albumin and lipid microbubbles in the setting of I-R and TNF-alpha-induced inflammation is due to their beta(2)-integrin- and complement-mediated binding to activated leukocytes adherent to the venular wall. Thus, microbubble persistence on contrast ultrasonography may be useful for the detection and monitoring of leukocyte adhesion in inflammatory diseases.
Lindner
J R
JR
Cardiovascular Division, University of Virginia School of Medicine, Charlottesville, VA 22908, USA. jlinder@virginia.edu
Coggins
M P
MP
Kaul
S
S
Klibanov
A L
AL
Brandenburger
G H
GH
Ley
K
K
D000418:Albumins / Q000378:metabolism*; D000818:Animals; D003287:Contrast Media / Q000009:adverse effects; D003326:Coronary Circulation; D004452:Echocardiography / Q000009:adverse effects; D007249:Inflammation; D016023:Integrins / Q000378:metabolism*; D007962:Leukocytes / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D015425:Myocardial Reperfusion / Q000009:adverse effects
D000418:Albumins; D003287:Contrast Media; D016023:Integrins