Direct thrombus imaging as a means to control the variability of mouse embolic infarct models: the role of optical molecular imaging.
OBJECTIVE
High experimental variability in mouse embolic stroke models could mask the effects of experimental treatments. We hypothesized that imaging thrombus directly would allow this variability to be controlled.


METHODS
We optically labeled thrombi with a near-infrared fluorescent (NIRF) probe C15 that is covalently linked to fibrin by factor-XIIIa. Labeled thrombus was injected into the left distal internal carotid artery (ICA) of C57/BL6 mice (n=47), near its bifurcation, and laser-Doppler cerebral-blood-flow (CBF) was assessed for 30 minutes. NIRF thrombus imaging was done ex vivo at 24 hours.


RESULTS
CBF variably decreased to 43.9±17.3% at 5 minutes (rCBF; 11.2∼80.4%). NIRF thrombus imaging at 24 hours showed variability in distribution (ICA bifurcation, adjacent and/or remote areas) and burden (2279±1270 pixels; 0∼5940 pixels). Final infarct size was also variable (21.0±10.3%; 4.7∼60.3% of the bihemispheric volume). Despite this heterogeneity, a strong thrombus-infarct correlation was maintained. The left hemispheric target infarct size (% of the hemisphere) correlated with thrombus burden, as a stronger predictor of infarct volume (P<0.001, r=0.50) than rCBF (P=0.02, r=-0.34). The infarct size was best predicted by a combination of thrombus imaging and CBF: left-hemispheric big-thrombi (>1865 pixels)/low-rCBF (≤42%) had an infarct volume of 56.9±10.4% (n=12), big-thrombi/high-rCBF had 45.9±23.5% (n=11), small-thrombi/low-rCBF 35.7±17.3% (n=11) and small-thrombi/ high-rCBF 27.3±16.4% (n=12).


CONCLUSIONS
This is the first study to demonstrate that the highly heterogeneous nature of the mouse embolic stroke model can be characterized and managed by using near-infrared fluorescent thrombus imaging combined with CBF monitoring to stratify animals into useful subgroups.
MINER Laboratory at Department of Neurology, Dongguk University Ilsan Hospital, 814 Siksa-dong, Goyang, Korea. kdongeog@duih.org
Dong-Eog
DE
Kim
Jeong-Yeon
JY
Kim
Matthias
M
Nahrendorf
Su-Kyoung
SK
Lee
Ju Hee
JH
Ryu
Kwangmeyung
K
Kim
Ick Chan
IC
Kwon
Dawid
D
Schellingerhout
D000818:Animals; D001921:Brain / Q000473:pathology*; D020520:Brain Infarction / Q000473:pathology*; D002560:Cerebrovascular Circulation / Q000502:physiology*; D004195:Disease Models, Animal; D020767:Intracranial Thrombosis / Q000473:pathology*; D051379:Mice; D057054:Molecular Imaging / Q000379:methods*