Dual Contrast Molecular Imaging Allows Noninvasive Characterization of Myocardial Ischemia/Reperfusion Injury After Coronary Vessel Occlusion in Mice by mri running title
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MRI data-quantification Gadolinium-induced late enhancement for detection of necrosis The area of gadolinium uptake, representing the LGE and therefore necrotic myocardium, was marked manually in three representative sections using ImageJ software (NIH; Version 1.46). A quotient of the area with LGE divided by the total size of the left ventricle was calculated for all three sections and the average is given. The same methodology was used to quantify the size of areas with signal extinction after injection of LIBS-MPIO. LIBS-MPIO induced signal extinction for detection of platelets For MRI signal quantification, each slice of the heart was sectioned into 6 segments following a modified AHA protocol using a Matlab-based (MathWorks Inc., Natick/MA, USA) customized View of 25x25mm, and a matrix size of 256x256 resulting in a resolution of 100μ 0μ μm
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ne ne . T To achieve the best signal to noise ratio, we refrained from obtaining cine-like movies with the ne e ce ce ce ss ss s it it it y y of of of r r e epea ea ea t te ted excitation pulses, but focu u se se se d d on the recordi di i ng n n o o f f f l
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f fr ram m m es. MR MR MRI I I da da da ta ta -q -q -q ua uan nt ntif if fic ic a a atio io on n Gadolinium m -i -i i nd nd n uc uc uc ed ed ed l l at a a e e e en en en ha a a nc nc n em em em en en en t t t fo fo o r r r de de d te te te ct ct ct io io i n n n of of of n n n ec ec ec ro ro ro si si s s s by guest on December 22, 2017 http://circ.ahajournals.org/ Downloaded from DOI: 10.1161/CIRCULATIONAHA.113.008157 9 software. Cardiac segmentation was performed by such a segmentation-tool via manually surrounding the left ventricular epi- and endocardial wall, starting at the anterior crossing of right and left ventricle. In the customized software, this starting point initiated a segmentation of the left ventricle into 6 equiangular segments. A quotient of the mean signal intensities from the anterior and anterolateral segment in relation to the signal of both septal segments was calculated for each slice and every time point. Afterwards, these quotients were normalized to the native pre-injection scan. Finally, the mean of the three slices of the anterior and anterolateral segment was calculated. Although volume application during the experimental procuedures resulted in an increase of the right ventricular volume, an impact on septal wall motion or signal behaviour has not been observed in our studies, which allowed us to use the septum as a reference parameter when evaluating the signal change in the ischemic myocardial region. Echocardiography Ejection fraction was measured planimetrically in a mid-papillary plain in a blinded evaluation of loops acquired with a 15G-7, Philips linear epicardial transducer on an iE33 ultrasound system, Philips, Germany. Histology Infarct size Hearts were excised, LAD ligation re-established and non-affected myocardium perfused with Monolite blue. Tissue was sectioned freshly for triphenyltetrazolium chloride (TTC) staining and subsequent blinded analysis of infarct area, in relation to the monolite blue-negative area at risk was performed in five serial sections (mid-papillary to apical).
Myocardial tissue was embedded using OCT (Sakura Finetek, Netherlands), cut into 10 m thick observed in our studies, which allowed us to use the septum as a reference parame e t t ter
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sections, and fixed using acetone. For staining of neutrophil granulocytes, a rat anti-mouse Ly- 6G IgG2a antibody was used (#551459, BD Biosciences, Pharmingen, San Diego, CA), and for control purposes a rat anti-mouse IgG2a isotype control (#559073, BD Biosciences). Secondary staining was performed with a biotinylated rabbit anti-rat IgG (BA-4001, Vector, Burlingame, CA). Alkaline phosphatase and substrate kit (AK-5000 & SK-5200; Vector) as well as levamisol (X3021, DAKO, Hamburg, Germany) were used for detection. For staining of platelets, a rat anti-mouse CD41 antibody was used (GTX 76011, GeneTex, Irvine, CA), and for control purposes an IgG1 isotype control (MCA1211, Serotec, Puchheim, Germany). Secondary staining was performed with a biotinylated rabbit anti-rat IgG (BA-4001, Vector). Alkaline phosphatase and substrate kit (AK-5000 & SK-5100; Vector) as well as levamisol (X3021, DAKO) were used for detection. Finally, samples were embedded using Kaiser’s Glyceringelatine (1092420100, Merck, Darmstadt, Germany) until adequate staining. Platelets and platelet-neutrophil-conjugates were counted in two representative pictures of 20x magnification out of the ischemic area of two different CD41 or CD41/Gr1 stained slices. For counting MPIOs the ischemic area of ten representative CD41 stained slices was carefully examined. For quantification of necrotic tissue, hematoxylin-eosin (H&E)-staining was performed with a standard protocol using a hematoxylin and eosin solution (Merck; Roth, Karlsruhe, Germany) on frozen sections. Size of necrotic myocardium in each animal was measured in three representative H&E-stained sections at x4 magnification, analogously to measuring the size of LE-area. A quotient of the disrupted, and therefore necrotic area, divided by the total size of the left ventricle was calculated for all three sections and averaged. BA-4001, Vector). Alkaline phosphatase and substrate kit (AK-5000 & SK-5100 00 0;
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DOI: 10.1161/CIRCULATIONAHA.113.008157 11
Statistics Statistical analysis was supported by GraphPad Prism (GraphPad Software Inc., Version 4.0). For statistical analysis of two groups, a Mann-Whitney test was performed. For analysis of data with more than two groups, Kruskal-Wallis test was used. Comparison of MRI signal intensities in LIBS and control group after MPIO application, as well as the effect of gadolinium on myocardial signal within each group (all signal values before and after gadolinium injection) was undertaken using a two-way repeated-measures- ANOVA analysis. The accuracy of microscope-supported evaluation of MPIO and platelet counts was defined by error estimation. Correlations were investigated by linear regression tests. Results are given as dot-plot graphs with means. Test results were considered significant at values of P<0.05.
Results Attachment of LIBS-MPIOs to activated platelets and microthrombi in vitro Binding of LIBS-MPIO to platelets was confirmed by static and flow chamber adhesion experi- ments. On an activated platelet monolayer, attachment of LIBS-MPIOs was significantly greater when compared to control-MPIOs (Figure 1A, p<0.001). Similar results were obtained for flow chamber experiments with microaggregates/thombi, where the number of LIBS-MPIOs attached was significantly higher than control-MPIOs (Figure 1B, p<0.01, Movies 1 and 2). Platelet-MPIO-infiltration is highest 2 hours after reperfusion For estimation of the optimal time point of maximal platelet accumulation in the ischemic/reper- fused myocardium, and hence for molecular imaging, platelet aggregates with bound LIBS- defined by error estimation. Correlations were investigated by linear regression te te est
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ts t a a re given as dot-plot graphs with means. Test results were considered significant at values of P< < 0. 0. 0. 05 05 05 .
Re esu su s lt lt lt s s s Attachment t o o o f f LI LI I BS BS B -M -M M PI PI I Os Os O t t t o o o ac ac ac ti t t va va va te te e d d d pl pl pl at at a el el e et et e s s s an n n d d d mi mi mi cr cr cr ot ot ot hr r r om om om bi bi bi in in in v v it it i ro ro ro by guest on December 22, 2017 http://circ.ahajournals.org/ Downloaded from DOI: 10.1161/CIRCULATIONAHA.113.008157 12
MPIO were quantified after reperfusion (10min, 2h, 4h, 6h, 8h, 10h, and 12h respectively). As depicted in Figure 1C, the maximum amount of LIBS-MPIO-platelet-aggregates was found 2h after reperfusion, and this was significantly different compared to all other time points (p<0.05). A typical image of a LIBS-MPIO-platelet-aggregate is depicted in the inlay. Platelets are stained in red, MPIOs appear as a round and brown structure, highlighted by arrows.
MRI was performed as described in the Methods section. A representative image of a short axis image from the mid ventricular areas is depicted in Figure 2. For animals with LIBS-MPIO (Figure 2A) and control-MPIO-injection (Figure 2B), a baseline scan before contrast agent application is shown in the first column on the left. After contrast agent application, a continuous signal decrease can be observed in ischemic areas of animals with LIBS-MPIO-injection (red arrows). This signal decrease is the typical susceptibility artifact induced by MPIOs, and therefore depicts areas of contrast agent binding. No such signal effect is visible in animals with control-MPIO-injection. At 37 min, gadolinium was injected in order to image the LGE for detection of myocardial necrosis. The typical gadolinium-induced bright signal can be observed for both animal groups, indicating that myocardial necrosis was evident in these animals.
LGE was quantified in all animals in order to prove comparable amounts of necrosis between animals injected with LIBS-MPIO and control-MPIO, using representative sections of basal, medial and apical myocardial regions in pseudo short-axis images. The LGE-area of the left ventricle (expressed as %) is demonstrated in Figure 3A, which showed no significant differences between the two groups injected either with platelet-targeted or non-targeted MPIOs. application is shown in the first column on the left. After contrast agent applicati ti on on on , , , a co co co nt nt nt in in inuo uo us ignal decrease can be observed in ischemic areas of animals with LIBS-MPIO-injection (red ar r ro ro o ws ws ws ). ) ). T T T hi hi his
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For further characterization of the inflammatory myocardial process, simultaneous staining for platelets (CD41) and neutrophils (Gr1) was performed. A representative section is depicted in Download 1.2 Mb. Do'stlaringiz bilan baham: 
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