title: In vivo ultrasound visualization of non-occlusive blood clots with thrombin-sensitive contrast agents.
abstract: The use of microbubbles as ultrasound contrast agents is one of the primary methods to diagnose deep venous thrombosis. However, current microbubble imaging strategies require either a clot sufficiently large to produce a circulation filling defect or a clot with sufficient vascularization to allow for targeted accumulation of contrast agents. Previously, we reported the design of a microbubble formulation that modulated its ability to generate ultrasound contrast from interaction with thrombin through incorporation of aptamer-containing DNA crosslinks in the encapsulating shell, enabling the measurement of a local chemical environment by changes in acoustic activity. However, this contrast agent lacked sufficient stability and lifetime in blood to be used as a diagnostic tool. Here we describe a PEG-stabilized, thrombin-activated microbubble (PSTA-MB) with sufficient stability to be used in vivo in circulation with no change in biomarker sensitivity. In the presence of actively clotting blood, PSTA-MBs showed a 5-fold increase in acoustic activity. Specificity for the presence of thrombin and stability under constant shear flow were demonstrated in a home-built in vitro model. Finally, PSTA-MBs were able to detect the presence of an active clot within the vena cava of a rabbit sufficiently small as to not be visible by current non-specific contrast agents. By activating in non-occlusive environments, these contrast agents will be able to detect clots not diagnosable by current contrast agents.
authors.affiliation: Department of Nanoengineering, University of California, San Diego, 9500 Gilman Dr. #0448, La Jolla, CA 92093-0448, USA.
authors.forename: Matthew A
authors.initials: MA
authors.lastname: Nakatsuka
authors.forename: Christopher V
authors.initials: CV
authors.lastname: Barback
authors.forename: Kirsten R
authors.initials: KR
authors.lastname: Fitch
authors.forename: Alexander R
authors.initials: AR
authors.lastname: Farwell
authors.forename: Sadik C
authors.initials: SC
authors.lastname: Esener
authors.forename: Robert F
authors.initials: RF
authors.lastname: Mattrey
authors.forename: Jennifer N
authors.initials: JN
authors.lastname: Cha
authors.forename: Andrew P
authors.initials: AP
authors.lastname: Goodwin
mesh_terms: D000818:Animals; D052157:Aptamers, Nucleotide / Q000737:chemistry / Q000378:metabolism; D001483:Base Sequence; D001777:Blood Coagulation; D003287:Contrast Media / Q000737:chemistry / Q000378:metabolism; D005260:Female; D045423:Microbubbles; D011817:Rabbits; D013917:Thrombin / Q000378:metabolism*; D014463:Ultrasonography; D020246:Venous Thrombosis / Q000000981:diagnostic imaging* / Q000378:metabolism
chemical_list: D052157:Aptamers, Nucleotide; D003287:Contrast Media; C081676:thrombin aptamer; D013917:Thrombin
keywords: Clotting; DNA; In vitro test; In vivo test; Thrombosis
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