In vivo detection of oxidation-specific epitopes in atherosclerotic lesions using biocompatible manganese molecular magnetic imaging probes.
OBJECTIVE
This study sought to evaluate the in vivo magnetic resonance imaging (MRI) efficacy of manganese [Mn(II)] molecular imaging probes targeted to oxidation-specific epitopes (OSE).


BACKGROUND
OSE are critical in the initiation, progression, and destabilization of atherosclerotic plaques. Gadolinium [Gd(III)]-based MRI agents can be associated with systemic toxicity. Mn is an endogenous, biocompatible, paramagnetic metal ion that has poor MR efficacy when chelated, but strong efficacy when released within cells.


METHODS
Multimodal Mn micelles were generated to contain rhodamine for confocal microscopy and conjugated with either the murine monoclonal IgG antibody MDA2 targeted to malondialdehyde (MDA)-lysine epitopes or the human single-chain Fv antibody fragment IK17 targeted to MDA-like epitopes ("targeted micelles"). Micelle formulations were characterized in vitro and in vivo, and their MR efficacy (9.4-T) evaluated in apolipoprotein-deficient (apoE(-/-)) and low-density lipoprotein receptor negative (LDLR(-/-)) mice (0.05 mmol Mn/kg dose) (total of 120 mice for all experiments). In vivo competitive inhibition studies were performed to evaluate target specificity. Untargeted, MDA2-Gd, and IK17-Gd micelles (0.075 mmol Gd/kg) were included as controls.


RESULTS
In vitro studies demonstrated that targeted Mn micelles accumulate in macrophages when pre-exposed to MDA-LDL with ∼10× increase in longitudinal relativity. Following intravenous injection, strong MR signal enhancement was observed 48 to 72 h after administration of targeted Mn micelles, with colocalization within intraplaque macrophages. Co-injection of free MDA2 with the MDA2-Mn micelles resulted in full suppression of MR signal in the arterial wall, confirming target specificity. Similar MR efficacy was noted in apoE(-/-) and LDLR(-/-) mice with aortic atherosclerosis. No significant differences in MR efficacy were noted between targeted Mn and Gd micelles.


CONCLUSIONS
This study demonstrates that biocompatible multimodal Mn-based molecular imaging probes detect OSE within atherosclerotic plaques and may facilitate clinical translation of noninvasive imaging of human atherosclerosis.
Imaging Science Laboratory, Department of Radiology, Mount Sinai School of Medicine, New York, NY 10029, USA. saebo@mountsinai.org
Karen C
KC
Briley-Saebo
Tuyen Hoang
TH
Nguyen
Alexander M
AM
Saeboe
Young-Seok
YS
Cho
Sung Kee
SK
Ryu
Eugenia R
ER
Volkova
Eugenia
E
Volkava
Stephen
S
Dickson
Gregor
G
Leibundgut
Philipp
P
Wiesner
Philipp
P
Weisner
Simone
S
Green
Florence
F
Casanada
Yury I
YI
Miller
Walter
W
Shaw
Joseph L
JL
Witztum
Zahi A
ZA
Fayad
Sotirios
S
Tsimikas
D000818:Animals; D001672:Biocompatible Materials; D004195:Disease Models, Animal; D000939:Epitopes; D008074:Lipoproteins / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D008345:Manganese; D051379:Mice; D018345:Mice, Knockout; D008823:Micelles; D010084:Oxidation-Reduction; D058226:Plaque, Atherosclerotic / Q000175:diagnosis / Q000378:metabolism*; D015203:Reproducibility of Results
D001672:Biocompatible Materials; D000939:Epitopes; D008074:Lipoproteins; D008823:Micelles; D008345:Manganese