Rat model of reperfused partial liver infarction: characterization with multiparametric magnetic resonance imaging, microangiography, and histomorphology

Determining acute ischemic stroke onset time using machine learning and radiomics features of infarct lesions and whole brain

Accurate determination of the onset time in acute ischemic stroke (AIS) patients helps to formulate more beneficial treatment plans and plays a vital role in the recovery of patients. Considering that the whole brain may contain some critical information, we combined the Radiomics features of infarct lesions and whole brain to improve the prediction accuracy. First, the radiomics features of infarct lesions and whole brain were separately calculated using apparent diffusion coefficient (ADC), diffusion-weighted imaging (DWI) and fluid-attenuated inversion recovery (FLAIR) sequences of AIS patients with clear onset time. Then, the least absolute shrinkage and selection operator (Lasso) was used to select features. Four experimental groups were generated according to combination strategies: Features in infarct lesions (IL), features in whole brain (WB), direct combination of them (IW) and Lasso selection again after direct combination (IWS), which were used to evaluate the predictive performance. The results of ten-fold cross-validation showed that IWS achieved the best AUC of 0.904, which improved by 13.5% compared with IL (0.769), by 18.7% compared with WB (0.717) and 4.2% compared with IW (0.862). In conclusion, combining infarct lesions and whole brain features from multiple sequences can further improve the accuracy of AIS onset time.

Magnetic Resonance Diffusion Tensor Imaging Characterize the Hepatic Ischemia-Reperfusion Injury in an Animal Study

BACKGROUND

Hepatic ischemia-reperfusion (I/R) injury is the main cause of morbidity and mortality after hepatectomy; thus, new methods for reducing I/R injury are required. The aim of this study is to evaluate changes in the average apparent diffusion coefficient (ADCavg) and fractional anisotropy (FA) in rabbits with partial hepatic I/R injury with magnetic resonance diffusion tensor imaging (DTI).

METHODS

The left lobe of the rabbit liver underwent 60 minutes of ischemia followed by 0.5, 2, 6, 12, 24, and 48 hours of reperfusion. T2-weighted images (T2WI), T1-weighted images (T1WI), DTI, and contrast-enhanced T1WI were performed; 6 b values were used for DTI on 6 diffusion directions. The serum levels of transaminases and liver histopathology findings were examined.

RESULTS

In the early stage of I/R (0.5 hour), ADCavg decreased significantly and increased sharply to 2 hours, then increased from 6 hours to 48 hours of reperfusion, except for a transient decrease (24 hours). Meanwhile, FA showed almost the opposite trend, drastically increasing during the first 0.5 hour and then slightly decreasing until 48 hours of reperfusion, except for an obvious decrease in the 2-hours group. The serum levels of liver markers and the pathologic scores were sharply increased in the I/R group after reperfusion and correlated with DTI of hepatic tissue after I/R.

CONCLUSIONS

Diffusion tensor imaging is feasible for imaging I/R-induced liver damage and can discriminate isotropic properties of the liver after I/R injury with objective changes in the ADCavg and FA. Diffusion tensor imaging can be a promising novel approach for use in clinical management after liver surgery.

A Focus on the Role of DSC-PWI Dynamic Radiomics Features in Diagnosis and Outcome Prediction of Ischemic Stroke

Background: The ability to accurately detect ischemic stroke and predict its neurological recovery is of great clinical value. This study intended to evaluate the performance of whole-brain dynamic radiomics features (DRF) for ischemic stroke detection, neurological impairment assessment, and outcome prediction. Methods: The supervised feature selection (Lasso) and unsupervised feature-selection methods (five-feature dimension-reduction algorithms) were used to generate four experimental groups with DRF in different combinations. Ten machine learning models were used to evaluate their performance by ten-fold cross-validation. Results: In experimental group_A, the best AUCs (0.873 for stroke detection, 0.795 for NIHSS assessment, and 0.818 for outcome prediction) were obtained by outstanding DRF selected by Lasso, and the performance of significant DRF was better than the five-feature dimension-reduction algorithms. The selected outstanding dimension-reduction DRF in experimental group_C obtained a better AUC than dimension-reduction DRF in experimental group_A but were inferior to the outstanding DRF in experimental group_A. When combining the outstanding DRF with each dimension-reduction DRF (experimental group_B), the performance can be improved in ischemic stroke detection (best AUC = 0.899) and NIHSS assessment (best AUC = 0.835) but failed in outcome prediction (best AUC = 0.806). The performance can be further improved when combining outstanding DRF with outstanding dimension-reduction DRF (experimental group_D), achieving the highest AUC scores in all three evaluation items (0.925 for stroke detection, 0.853 for NIHSS assessment, and 0.828 for outcome prediction). By the method in this study, comparing the best AUC of Ft-test in experimental group_A and the best_AUC in experimental group_D, the AUC in stroke detection increased by 19.4% (from 0.731 to 0.925), the AUC in NIHSS assessment increased by 20.1% (from 0.652 to 0.853), and the AUC in prognosis prediction increased by 14.9% (from 0.679 to 0.828). This study provided a potential clinical tool for detailed clinical diagnosis and outcome prediction before treatment.

Multiparametric functional magnetic resonance imaging for evaluation of hepatic warm ischemia-reperfusion injury in a rabbit model

BACKGROUND

To assess the feasibility of noninvasive and quantitative evaluation of hepatic pathophysiological changes in rabbit hepatic warm ischemia-reperfusion injury (WIRI) models by using intravoxel incoherent motion (IVIM), diffusion tensor imaging (DTI) and blood oxygen level dependent (BOLD) MRI.

METHODS

Twenty rabbits were randomly divided into hepatic WIRI model group and sham-operation group (n = 10 for each group). Hepatic WIRI was induced in rabbit by occluding hepatic inflow for 30 min and reperfusion for 6 h. The control group only underwent laparotomy and liver ligament dissection. IVIM with 11 b values (0 to 800 s/mm²), DTI with 2 b values (0 and 500 s/mm²) on 12 diffusion directions, and BOLD MRI with 9 TE (2.57 to 24.25 ms) were performed at 3 T clinical MR scanner. Rabbits were sacrificed for biochemical and histopathological analysis after MR scanning. All of functional MR, biochemical and histopathological parameters were analyzed by independent sample t test, Mann-Whitney U test, Pearson and Spearman correlation methods.

RESULTS

All of MR parameters showed moderate to excellent interobserver reproducibility. True diffusion (Dslow), pseudodiffusion (Dfast), perfusion fraction (PF), and mean diffusitivity (MD) were lower in WIRI models than in control rabbits (P < 0.01), R2* was higher in WIRI models than in control rabbits (P < 0.001), while fractional anisotropy (FA) showed no statistical difference. There were significant differences in I score and all of biochemical parameters between the two groups (P < 0.01). Functional MR parameters corresponded well with all of biochemical parameters and some of histopathological parameters (P < 0.05). Histopathological analysis showed the structure and morphology of hepatic lobule was normal and clear in control rabbits, while diffuse hepatocyte swelling, central vein and sinusoids congestion, and inflammatory cell infiltration in WIRI models.

CONCLUSIONS

IVIM, DTI, and BOLD MRI are noninvasive and useful techniques for assessing the microenvironment changes of hepatic WIRI in rabbit models.

Quantitative Analysis of Hepatic Microcirculation in Rabbits After Liver Ischemia-Reperfusion Injury Using Contrast-Enhanced Ultrasound

Previous studies have shown that contrast-enhanced ultrasound (CEUS) can be used quantitatively to analyze microcirculation blood perfusion in hepatocellular carcinoma patients. However, limited data have described the application of CEUS in hepatic microcirculation after liver ischemic-reperfusion injury (IRI). The purpose of this study was to explore the use of CEUS quantitatively to assess liver microcirculation after liver IRI. We randomly sorted 45 New Zealand rabbits into 3 groups (15 in each). Group A was a control group in which the rabbits underwent laparotomy alone. In groups B and C, hepatic blood was blocked for 30 min. Simultaneously, rabbits in group C underwent left lateral lobe resection. After 30 min of ischemia, CEUS was conducted after 0 h, 1 h, 6 h and 24 h of reperfusion in the 3 groups. Time-intensity curves (TICs) for CEUS were constructed and quantitative parameters (maximum intensity [IMAX], rise time [RT], time to peak [TTP] and mean transit time [mTT]) were obtained. In addition, serum aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels were computed to estimate liver function before the operation and at 0 h, 1 h, 6 h and 24 h after reperfusion, respectively. Pathologic changes in the liver after reperfusion were also observed. Simultaneously, the correlations between serum transaminase and a variety of quantitative analysis parameters were analyzed. In groups B and C, the IMAX value decreased; whereas RT, TTP, mTT and serum ALT and AST levels increased significantly in comparison with those in group A after 0 h and 1 h of reperfusion. The pathology revealed that erythrocytes were destroyed and microcirculation was disturbed. Then, at 6 h of reperfusion, the IMAX continued to decrease. Additionally, the levels of RT, TTP, mTT and serum ALT and AST increased in comparison with those at 1 h of reperfusion. The pathologic analysis revealed inflammatory cell aggregation and leukocyte infiltration. After 24 h of reperfusion, the IMAX was reduced in comparison with that of the 6-h group. The levels of RT, TTP, mTT and serum ALT and serum AST were increased in comparison with that of the 6-h group. These findings were in accordance with the pathologic analysis. In addition, serum transaminase had a negative correlation with IMAX (p < 0.001) and a positive correlation with RT, TTP and mTT (all p < 0.001). So, in conclusion, the quantitative analysis of CEUS can be used to assess hepatic microcirculation after liver IRI.

A multifunctional contrast dye for morphological research

OBJECTIVES

We sought to devise and test a multifunctional contrast dye agent for X-ray based digital radiography (DR) or computer tomography (CT), magnetic resonance imaging (MRI), and colored staining in ex vivo validation part of animal experiments.

MATERIALS AND METHODS

The custom-formulated contrast dye namely red iodized oil (RIO) was prepared by solubilizing a lipophilic dye Oil Red O in iodized poppy seed oil (Lipiodol or LPD) followed by physicochemical characterizations. To explore and test the utility of RIO, normal rats (n = 10) and rabbits (n = 10) with myocardial infarction (MI) were euthanized by overdose of pentobarbital for infusion of RIO through catheterization. The bodies and/or excised organs including heart, liver, spleen, kidneys, pancreas, and intestines of the rats and rabbits were imaged at clinical mammography, CT and MRI units. These images were qualitatively studied and quantitatively analyzed using Wilcoxon Rank test with a P value < 0.05 being considered of a statistically significant difference. Imaging findings were verified by histomorphology.

RESULTS

All experimental procedures were carried out successfully with the use of RIO. T1 and T2 relaxation time was 234.2 ± 2.6 ms and 141.9 ± 3.0 ms for RIO, close to that of native LPD. Proton ((1) H) NMR spectroscopy revealed almost identical profiles between RIO and native LPD. The clinical mammography unit, 128-slice CT scanner and 3.0T MRI magnet were well adapted for the animal experiments. Combined use of RIO with DR, MRI, CT and histology enabled microangiography of the organs, 3D visualization of rat pancreas, validation of in vivo cardiac quantification of MI and cause determination of the rabbit death after coronary occlusion. RIO appeared as red droplets and vacuoles in vessels by frozen and paraffin sections. Image analysis showed the superiority of DR images, which provided better overall image quality (4.35 ± 0.49) for all analyzed liver vessel segments. MRI images revealed moderate to good overall image quality ratings (3.45 ± 0.52). Comparing the signal intensities of vessel and liver with different MRI sequences, all P values were <0.01.

CONCLUSIONS

RIO proved to be a multifunctional contrast dye, which could be applied as an imaging biomarker for tissue vascularity or blood perfusion, for visualization of organ anatomy and for ex vivo validation of in vivo animal experiments.

Synthesis and Evaluation of 131I-Skyrin as a Necrosis Avid Agent for Potential Targeted Radionuclide Therapy of Solid Tumors

An innovative anticancer approach targeted to necrotic tissues, which serves as a noncancerous and generic anchor, may present a breakthrough. Necrosis avid agents with a flat conjugate aromatic structure selectively accumulate in necrotic tissues, but they easily form aggregates that undesirably distribute to normal tissues. In this study, skyrin, a dianthraquinone compound with smaller and distorted π-cores and thus decreased aggregates as compared with hypericin (Hyp), was designed to target necrosis for tumor therapy. Aggregation studies of skyrin by UV/vis spectroscopy showed a smaller self-association constant with skyrin than with Hyp. Skyrin was labeled by iodine-131 with a radiochemical purity of 98% and exhibited good stability in rat serum for 72 h. In vitro cell uptake studies showed significant difference in the uptake of ¹³¹I-skyrin by necrotic cells compared to normal cells (P < 0.05). Compared in rats with liver and muscle necrosis, radiobiodistribution, whole-body autoradiography, and SPECT/CT studies revealed higher accumulation of ¹³¹I-skyrin in necrotic liver and muscle (p < 0.05), but lower uptake in normal organs, relative to that of ¹³¹I-Hyp. In mice bearing H22 tumor xenografts treated with combretastatin A4 disodium phosphate, the highest uptake of ¹³¹I-skyrin was found in necrotic tumor. In conclusion, ¹³¹I-skyrin appears a promising agent with reduced accumulation in nontarget organs for targeted radionuclide therapy of solid tumors.

Synthesis and Preclinical Evaluation of Radioiodinated Hypericin Dicarboxylic Acid as a Necrosis Avid Agent in Rat Models of Induced Hepatic, Muscular, and Myocardial Necroses

Myocardial infarction (MI) leads to substantial morbidity and mortality around the world. Accurate assessment of myocardial viability is essential to assist therapies and improve patient outcomes. (131)I-hypericin dicarboxylic acid ((131)I-HDA) was synthesized and evaluated as a potential diagnostic agent for earlier assessment of myocardium viability compared to its preceding counterpart (131)I-hypericin ((131)I-Hyp) with strong hydrophobic property, long plasma half-life, and high uptake in mononuclear phagocyte system (MPS). Herein, HDA was synthesized and characterized, and self-aggregation constant Kα was analyzed by spectrophotometry. Plasma half-life was determined in healthy rats by γ-counting. (131)I-HDA and (131)I-Hyp were prepared with iodogen as oxidant. In vitro necrosis avidity of (131)I-HDA and (131)I-Hyp was evaluated in necrotic cells induced by hyperthermia. Biodistribution was determined in rat models of induced necrosis using γ-counting, autoradiography, and histopathology. Earlier imaging of necrotic myocardium to assess myocardial viability was performed in rat models of reperfused myocardium infarction using single photon emission computed tomography/computed tomography (SPECT/CT). As a result, the self-aggregation constant Kα of HDA was lower than that of Hyp (105602 vs 194644, p < 0.01). (131)I-HDA displayed a shorter blood half-life compared with (131)I-Hyp (9.21 vs 31.20 h, p < 0.01). The necrotic-viable ratio in cells was higher with (131)I-HDA relative to that with (131)I-Hyp (5.48 vs 4.63, p < 0.05). (131)I-HDA showed a higher necrotic-viable myocardium ratio (7.32 vs 3.20, p < 0.01), necrotic myocardium-blood ratio (3.34 vs 1.74, p < 0.05), and necrotic myocardium-lung ratio (3.09 vs 0.61, p < 0.01) compared with (131)I-Hyp. (131)I-HDA achieved imaging of necrotic myocardium at 6 h postinjection (p.i.) with SPECT/CT, earlier than what (131)I-Hyp did. Therefore, (131)I-HDA may serve as a promising necrosis-avid diagnostic agent for earlier imaging of necrotic myocardium compared with (131)I-Hyp. This may support further development of radiopharmaceuticals ((123)I and (99m)Tc) based on HDA for SPECT/CT of necrotic myocardium.

Mouse Hepatic Tumor Vascular Imaging by Experimental Selective Angiography

PURPOSE

Human hepatocellular carcinoma (HCC) has unique vascular features, which require selective imaging of hepatic arterial perfusion and portal venous perfusion with vascular catheterization for sufficient evaluation. Unlike in humans, vessels in mice are too small to catheterize, and the importance of separately imaging the feeding vessels of tumors is frequently overlooked in hepatic tumor models. The purpose of this study was to perform selective latex angiography in several mouse liver tumor models and assess their suitability.

MATERIALS AND METHODS

In several ectopic (Lewis lung carcinoma, B16/F10 melanoma cell lines) and spontaneous liver tumor (Albumin-Cre/MST1fl/fl/MST2fl/fl, Albumin-Cre/WW45fl/fl, and H-ras12V genetically modified mouse) models, the heart left ventricle and/or main portal vein of mice was punctured, and latex dye was infused to achieve selective latex arteriography and/or portography.

RESULTS

H-ras12V transgenic mice (a HCC and hepatic adenoma model) developed multiple liver nodules that displayed three different perfusion patterns (portal venous or hepatic artery perfusion predominant, mixed perfusion), indicating intra-tumoral vascular heterogeneity. Selective latex angiography revealed that the Lewis lung carcinoma implant model and the Albumin-Cre/WW45fl/fl model reproduced conventional angiography findings of human HCC. Specifically, these mice developed tumors with abundant feeding arteries but no portal venous perfusion.

CONCLUSION

Different hepatic tumor models showed different tumor vessel characteristics that influence the suitability of the model and that should be considered when designing translational experiments. Selective latex angiography applied to certain mouse tumor models (both ectopic and spontaneous) closely simulated typical characteristics of human HCC vascular imaging.

Evaluation of a metalloporphyrin (THPPMnCl) for necrosis-affinity in rat models of necrosis

The combination of an (13I)I-labeled necrosis-targeting agent (NTA) with a vascular disrupting agent is a novel and potentially powerful technique for tumor necrosis treatment (TNT). The purpose of this study was to evaluate a NTA candidate, THPPMnCl, using (131)I isotope for tracing its biodistribution and necrosis affinity. (131)I-THPPMnCl was intravenously injected in rat models with liver, muscle, and tumor necrosis and myocardial infarction (MI), followed by investigations with macroscopic autoradiography, triphenyltetrazolium chloride (TTC) histochemical staining, fluorescence microscopy and H&E stained histology for up to 9 days. (131)I-THPPMnCl displayed a long-term affinity for all types of necrosis and accumulation in the mononuclear phagocytic system especially in the liver. Autoradiograms and TTC staining showed a good targetability of (131)I-THPPMnCl for MI. These findings indicate the potential of THPPMnCl for non-invasive imaging assessment of necrosis, such as in MI. However, (13I)I-THPPMnCl is unlikely suitable for TNT due to its long-term retention in normal tissues.

Radiopharmaceutical evaluation of (131)I-protohypericin as a necrosis avid compound

Hypericin is a necrosis avid agent useful for nuclear imaging and tumor therapy. Protohypericin, with a similar structure to hypericin except poorer planarity, is the precursor of hypericin. In this study, we aimed to investigate the impact of this structural difference on self-assembly, and evaluate the necrosis affinity and metabolism in the rat model of reperfused hepatic infarction. Protohypericin appeared less aggregative in solution compared with hypericin by fluorescence analysis. Biodistribution data of (131)I-protohypericin showed the percentage of injected dose per gram of tissues (%ID/g) increased with time and reached to the maximum of 7.03 at 24 h in necrotic liver by gamma counting. The maximum ratio of target/non-target tissues was 11.7-fold in necrotic liver at 72 h. Pharmacokinetic parameters revealed that the half-life of (131)I-protohypericin was 14.9 h, enabling a long blood circulation and constant retention in necrotic regions. SPECT-CT, autoradiography, and histological staining showed high uptake of (131)I-protohypericin in necrotic tissues. These results suggest that (131)I-protohypericin is a promising necrosis avid compound with a weaker aggregation tendency compared with hypericin and it may have a broad application in imaging and oncotherapy.

Radioiodinated hypericin: its biodistribution, necrosis avidity and therapeutic efficacy are influenced by formulation

PURPOSE

To study whether formulation influences biodistribution, necrosis avidity and tumoricidal effects of the radioiodinated hypericin, a necrosis avid agent for a dual-targeting anticancer radiotherapy.

METHODS

Iodine-123- and 131-labeled hypericin ((123)I-Hyp and (131)I-Hyp) were prepared with Iodogen as oxidant, and formulated in dimethyl sulfoxide (DMSO)/PEG400 (polyethylene glycol 400)/water (25/60/15, v/v/v) or DMSO/saline (20:80, v/v). The formulations with excessive Hyp were optically characterized. Biodistribution, necrosis avidity and tumoricidal effects were studied in rats (n = 42) without and with reperfused liver infarction and implanted rhabdomyosarcomas (R1). To induce tumor necrosis, R1-rats were pre-treated with a vascular disrupting agent. Magnetic resonance imaging, tissue-gamma counting, autoradiography and histology were used.

RESULTS

The two formulations differed significantly in fluorescence and precipitation. (123)I-Hyp/Hyp in DMSO/PEG400/water exhibited high uptake in necrosis but lower concentration in the lung, spleen and liver (p < 0.01). Tumor volumes of 0.9 ± 0.3 cm(3) with high radioactivity (3.1 ± 0.3% ID/g) were detected 6 days post-treatment. By contrast, (131)I-Hyp/Hypin DMSO/saline showed low uptake in necrosis but high retention in the spleen and liver (p < 0.01). Tumor volumes reached 2.6 ± 0.7 cm(3) with low tracer accumulation (0.1 ± 0.04%ID/g).

CONCLUSIONS

The formulation of radioiodinated hypericin/hypericin appears crucial for its physical property, biodistribution, necrosis avidity and tumoricidal effects.

Necrosis affinity evaluation of 131I-hypericin in a rat model of induced necrosis

Cancers are often with spontaneous or therapeutic necrosis that could be utilized as a generic target for developing new treatments. The purpose of this study was to investigate the biodistribution and pharmacokinetics of radioiodinated hypericin (Hyp), a naturally occurring compound, after intravenous (i.v.) injection in a rat model of liver and muscle necrosis (n = 42), and evaluate its necrosis affinity. Hyp was labeled with (131)I with labeling efficiency >99%. After incubating in solution/rat plasma for 8 days, radiochemical purity of (131)I-Hyp remained 98.1 and 97.1%, respectively, indicating good in vitro stability. SPECT-CT images at 24 h after i.v. injection of (131)I-Hyp in rats with induced liver and muscle necrosis showed obvious tracer absorption in necrotic tissues. Biodistribution studies revealed that the percentage of the injected dose per gram of tissue (%ID/g) evolved from 1.9 %ID/g at 6 h, through a maximum 3.0 %ID/g at 12 h, to 1.0 %ID/g at 192 h in necrotic liver. Pharmacokinetics studies revealed that the terminal elimination half-life, total body clearance and area under the curve of (131)I-Hyp were 32.7 h, 9.2 L/h/kg and 1.6 MBq/L*h, respectively. These results demonstrated that (131)I-Hyp features a long blood circulation in animals and persistent retention in necrotic tissues. Therefore, (131)I-labeled Hyp could be a broad-spectrum anti-tumor agent with a cost much cheaper relative to the biological agents such as monoclonal antibodies.

Diverse responses to vascular disrupting agent combretastatin a4 phosphate: a comparative study in rats with hepatic and subcutaneous tumor allografts using MRI biomarkers, microangiography, and histopathology

OBJECTIVE

Differently located tumors of the same origin may exhibit diverse responses to the same therapeutics. To test this hypothesis, we compared the responses of rodent hepatic and subcutaneous engrafts of rhabdomyosarcoma-1 (R1) to a vascular disrupting agent Combretastatin A4 phosphate (CA4P).

METHODS

Twelve WAG/Rij rats, each bearing three R1 implanted in the right and left hepatic lobes and subcutaneously in the thoracic region, received CA4P intravenously at 5 mg/kg (n = 6) or solvent (n = 6). Therapeutic responses were compared interindividually and intraindividually among tumors of different sites till 48 hours after injection using in vivo MRI, postmortem digital microangiography, and histopathology.

RESULTS

MRI revealed that the subcutaneous tumors (STs) significantly increased in volume than hepatic tumors (HTs) 48 hours after CA4P (P < .05). Relative to vehicle controls and treated group at baseline, necrosis ratio, apparent diffusion coefficient, and enhancement ratio changed slightly with the STs but significantly with HTs (P < .05) after CA4P treatment. Vessel density derived from microangiography was significantly lower in STs compared to HTs without CA4P treatment. CA4P treatment resulted in decreased vessel density in HTs, while it did not affect vessel density in STs. MRI and microangiography outcomes were supported by histopathologic findings.

CONCLUSIONS

MRI and microangiography allowed quantitative comparison of therapeutic responses to CA4P in rats with multifocal tumors. The discovered diverse effects of the same drug on tumors of the same origin but different locations emphasize the presence of cancer heterogeneity and the importance of individualization of drug delivery.

Exploring theranostic potentials of radioiodinated hypericin in rodent necrosis models

Objectives: The present animal experiments were conducted to evaluate radioiodinated Hypericin (Hyp) for its regional distribution as well as theranostic potentials.

Materials and Methods: Rat models of reperfused liver infarction (RLI) and hepatic rhabdomyosarcoma (R1) were surgically induced. R1 models received Combretastatin A4 phosphate (CA4P) intravenously at 10 mg/kg 24 h prior to radioiodinated Hyp. Three groups of 6 rats each containing 3 RLI and 3 R1 models received iv injections of ¹²³I-Hyp at 37, 74, and 185 MBq/kg respectively and followed by 0.1 ml of 1% Evans blue solution were sacrificed at 4, 24 and 48 hour post injection immediately after in vivo examination of MRI and planar gamma scintigraphy. Besides, two groups of 6 R1 models that received either 300 MBq/kg of ¹³¹I-Hyp or vehicle intravenously were examined using MRI to compare tumor growth for 12 days. Autoradiography, gamma counting, and histopathology were performed for postmortem verifications and quantification.

Results: Necrosis as seen in vivo on contrast-enhanced MRI corresponded well with the hot spots on planar scintigraphy. Autoradiography and gamma counting revealed intense accumulation of ¹²³I-Hyp in necrotic liver (3.94 ± 1.60, 5.38 ± 1.04, and 6.03 ± 2.09 %ID/g ± SD) and necrotic tumor (4.27 ± 0.76, 5.57 ± 0.76, and 5.68 ± 1.33 %ID/g ± SD) relative to normal liver (1.76 ± 0.54, 0.41 ± 0.18, and 0.16 ± 0.07 %ID/g ± SD), with a high necrosis-to-liver ratio of 2.3, 14.0, and 37.0 at 4, 24 and 48 h respectively. Tumor volumes in R1 models that received ¹³¹I-Hyp and vehicle changed from 0.45 ± 0.09, and 0.47 ± 0.12 cm³ (p > 0.05) on day 0 to1.32 ± 0.76 and 3.63 ± 0.72 cm³ (p < 0.001) on day 12, with the corresponding necrosis ratios from 73 ± 12 %, and 76 ± 17 % to 47 ± 18% and 17 ± 13 % (p < 0.01), and with the tumor DT of 7.3 ± 1.0 and 4.2 ± 0.7 days, respectively.

Conclusions: Radioiodinated Hyp as a necrosis avid tracer appears promising for non-invasive imaging diagnosis of necrosis-related pathologies. Its prominent targetability to necrosis allows targeted radiotherapy for malignancies on top of a prior necrosis-inducing treatment.

Perfusion computed tomography evaluation of partial hepatic ischemia reperfusion in a rabbit model

RATIONALE AND OBJECTIVES

An animal model of partial hepatic ischemia/reperfusion injury (I/R) has benefits for decision making and clinical management after liver transplantation or massive hepatic resection. The aim of this study was to evaluate the change in perfusion parameters after partial hepatic I/R in rabbits using multislice computed tomography perfusion imaging.

MATERIALS AND METHODS

Thirty rabbits underwent 60 minutes of left hepatic lobar ischemia followed by 0.5, 2, 6, 12, and 24 hours of reperfusion (six rabbits were used for each reperfusion interval). An additional six rabbits served as sham-operated controls. The perfusion indices of hepatic arterial perfusion, hepatic portal perfusion, total liver perfusion, and hepatic perfusion index were measured. Levels of serum aspartate transaminase and alanine transaminase and liver histopathology at different time points were also examined.

RESULTS

Hepatic microvascular flow patterns showed heterogeneity in the 6-hour, 12-hour, and 24-hour groups. Computed tomographic perfusion parameters were significantly different between infarcted liver tissue and viable liver tissue. In poorly enhancing tissues in the 6-hour, 12-hour, and 24-hour groups, hepatic portal perfusion and total liver perfusion were lower compared to the sham group, but hepatic arterial perfusion of poorly enhancing tissues significantly increased in the 6-hour group and then decreased slightly from 12 to 24 hours after reperfusion. The hepatic perfusion index was always higher compared to that of the sham group. Hepatic arterial perfusion, hepatic portal perfusion, total liver perfusion, and hepatic perfusion index in the noninfarcted areas decreased slowly from 6 to 24 hours after reperfusion. The levels of alanine transaminase and aspartate transaminase in the I/R groups significantly increased after reperfusion and were correlated with the computed tomographic perfusion indices of infarcted liver tissue.

CONCLUSIONS

Computed tomographic perfusion can dynamically monitor the pathologic processes of liver I/R and reveal the underlying microvascular disorder, improving clinical management after liver surgery.

A dual-targeting anticancer approach: soil and seed principle

PURPOSE

To test the hypothesis that targeting the microenvironment (soil) may effectively kill cancer cells (seeds) through a small-molecular weight sequential dual-targeting theragnostic strategy, or dual-targeting approach.

MATERIALS AND METHODS

With approval from the institutional animal care and use committee, 24 rats were implanted with 48 liver rhabdomyosarcomas (R1). First, the vascular-disrupting agent combretastatin A4 phosphate (CA4P) was injected at a dose of 10 mg/kg to cause tumor necrosis, which became a secondary target. Then, the necrosis-avid agent hypericin was radiolabeled with iodine 131 to form (131)I-hypericin, which was injected at 300 MBq/kg 24 hours after injection of CA4P. Both molecules have small molecular weight, are naturally or synthetically derivable, are intravenously injectable, and are of unique targetablities. The tumor response in the dual-targeting group was compared with that in vehicle-control and single-targeting (CA4P or (131)I-hypericin) groups with in vivo magnetic resonance imaging and scintigrams and ex vivo gamma counting, autoradiography, and histologic analysis. Tumor volumes, tumor doubling time (TDT), and radiobiodistribution were analyzed with statistical software. P values below .05 were considered to indicate a significant difference.

RESULTS

Eight days after treatment, the tumor volume of rhabdomyosarcoma in the vehicle-control group was double that in both single-targeting groups (P < .001) and was five times that in the dual-targeting group (P < .0001), without treatment-related animal death. The TDT was significantly longer in the dual-targeting group (P < .0001). Necrosis appeared as hot spots on scintigrams, corresponding to 3.13% of the injected dose of (131)I-hypericin per gram of tissue (interquartile range, 2.92%-3.97%) and a target-to-liver ratio of 20. The dose was estimated to be 100 times the cumulative dose of 50 Gy needed for radiotherapeutic response. Thus, accumulated (131)I-hypericin from CA4P-induced necrosis killed residual cancer cells with ionizing radiation and inhibited tumor regrowth.

CONCLUSION

This dual-targeting approach may be a simple and workable solution for cancer treatment and deserves further exploitation.

Pathological and MR-DWI study of the acute hepatic injury model after stem cell transplantation

AIM: To investigate apparent diffusion coefficient (ADC) values as an indication of reconditioning of acute hepatic injury (AHI) after allogeneic mononuclear bone marrow cell (MBMC) transplantation.

METHODS: Three groups were used in our study: a cell transplantation group (n = 21), transplantation control group (n = 21) and normal control group (n = 10). AHI model rabbits in the cell transplantation group were injected with 5 mL of MBMC suspension at multiple sites in the liver and the transplantation controls were injected with 5 mL D-Hanks solution. At the end of the 1st, 2nd and 4th wk, 7 rabbits were randomly selected from the cell transplantation group and transplantation control group for magnetic resonance diffusion-weighted imaging (MR-DWI) and measurement of the mean ADC values of injured livers. After MR-DWI examination, the rabbits were sacrificed and the livers subjected to pathological examination. Ten healthy rabbits from the normal control group were used for MR-DWI examination and measurement of the mean ADC value of normal liver.

RESULTS: At all time points, the liver pathological scores from the cell transplantation group were significantly lower than those in the transplantation control group (27.14 ± 1.46 vs 69.29 ± 6.16, 22.29 ± 2.29 vs 57.00 ± 1.53, 19.00 ± 2.31 vs 51.86 ± 6.04, P = 0.000). The mean ADC values of the cell transplantation group were significantly higher than the transplantation control group ((1.07 ± 0.07) × 10^-3 mm²/s vs (0.69 ± 0.05) × 10^-3 mm²/s, (1.41 ± 0.04) × 10^-3 mm²/s vs (0.84 ± 0.06) × 10^-3 mm²/s, (1.68 ± 0.04) × 10^-3 mm²/s vs (0.86 ± 0.04) × 10^-3 mm²/s, P = 0.000). The pathological scores of the cell transplantation group and transplantation control group gradually decreased. However, their mean ADC values gradually increased to near that of the normal control. At the end of the 1st wk, the mean ADC values of the cell transplantation group and transplantation control group were significantly lower than those of the normal control group [(1.07 ± 0.07) × 10^-3 mm²/s vs (1.76 ± 0.03) × 10^-3 mm²/s, (0.69 ± 0.05) × 10^-3 mm²/s vs (1.76 ± 0.03) × 10^-3 mm²/s, P = 0.000]. At any 2 time points, the pathological scores and the mean ADC values of the cell transplantation group were significantly different (P = 0.000). At the end of the 1st wk, the pathological scores and the mean ADC values of the transplantation control group were significantly different from those at the end of the 2nd and 4th wk (P = 0.000). However, there was no significant difference between the 2nd and 4th wk (P = 0.073 and 0.473, respectively). The coefficient of correlation between the pathological score and the mean ADC value in the cell transplantation group was -0.883 (P = 0.000) and -0.762 (P = 0.000) in the transplantation control group.

CONCLUSION: Tracking the longitudinally dynamic change in the mean ADC value of the AHI liver may reflect hepatic injury reconditioning after allogeneic MBMC transplantation.

Feng Chen's work on translational and clinical imaging

Dr. Feng Chen is a chief medical doctor and the vice chairman of the Department of Radiology in Zhong Da Hospital at Southeast University, Nanjing, China and a senior researcher in the Department of Radiology at the Catholic University of Leuven, Belgium. His main areas of interest are translational imaging research including stroke, tumor angiogenesis, assessment of therapeutic response in solid tumors, and magnetic resonance contrast media. Dr. Feng Chen has published 44 scientific papers in peer-reviewed international journals. He and his colleagues have developed an imaging platform which includes animal models, animal preparations and multiparametric magnetic resonance imaging (MRI) protocols for translational animal imaging research using clinical machines. His MRI findings on rodent stroke are considered to "serve as a model for future laboratory investigations of treatment of acute stroke and unify the approaches developed for clinical studies". He and his colleagues have introduced a novel liver tumor model in rodents, in which a series of studies concerning the antitumor activity of vascular disrupting agents have been successively conducted and assessed by in vivo MRI, especially by diffusion weighted imaging as an imaging biomarker. His goal is to provide valuable references for clinical practice and to contribute to the translation of animal imaging research into patient applications.

Cancer models-multiparametric applications of clinical MRI in rodent hepatic tumor model

Small animal imaging has been a major player in an increasing amount of oncological experiments wherein magnetic resonance imaging (MRI) has become a favorite choice of measures for in vivo small animal imaging due to its advantages of excellent resolution and innocuousness. Based on a clinical MRI scanner, we propose a protocol of multiparametric MRI for noninvasive characterization and therapeutic evaluation of a rat model with implanted liver tumors. This protocol contains six sequences, namely, T (1)-weighted image (T1WI), T (2)-weighted image (T2WI), diffusion-weighed imaging (DWI), T (1)-weighted dynamic contrast-enhanced MRI (DCE-MRI), T (2)-weighted dynamic susceptibility contrast-enhanced MRI (DSC-MRI), and contrast-enhanced T1WI (CE-T1WI), for acquiring anatomic, diffusion, and perfusion information of tumor models. In this chapter, the details about this complete MRI protocol and the rodent liver tumor model are described in order to facilitate the readers to perform their own translational animal imaging research.

Whole animal imaging

Translational research plays a vital role in understanding the underlying pathophysiology of human diseases, and hence development of new diagnostic and therapeutic options for their management. After creating an animal disease model, pathophysiologic changes and effects of a therapeutic intervention on them are often evaluated on the animals using immunohistologic or imaging techniques. In contrast to the immunohistologic techniques, the imaging techniques are noninvasive and hence can be used to investigate the whole animal, oftentimes in a single exam which provides opportunities to perform longitudinal studies and dynamic imaging of the same subject, and hence minimizes the experimental variability, requirement for the number of animals, and the time to perform a given experiment. Whole animal imaging can be performed by a number of techniques including x-ray computed tomography, magnetic resonance imaging, ultrasound imaging, positron emission tomography, single photon emission computed tomography, fluorescence imaging, and bioluminescence imaging, among others. Individual imaging techniques provide different kinds of information regarding the structure, metabolism, and physiology of the animal. Each technique has its own strengths and weaknesses, and none serves every purpose of image acquisition from all regions of an animal. In this review, a broad overview of basic principles, available contrast mechanisms, applications, challenges, and future prospects of many imaging techniques employed for whole animal imaging is provided. Our main goal is to briefly describe the current state of art to researchers and advanced students with a strong background in the field of animal research.

Radiolabeling and preliminary biological evaluation of a (99m)Tc(CO)(3) labeled 3,3'-(benzylidene)-bis-(1H-indole-2-carbohydrazide) derivative as a potential SPECT tracer for in vivo visualization of necrosis

N,N'-bis(diethylenetriamine pentaacetic acid)-3,3'-(benzylidene)-bis-(1H-indole-2-carbohydrazide) (bis-DTPA-BI) was radiolabeled with (99m)Tc(CO)(3). The resulting (99m)Tc(CO)(3)-bis-DTPA-BI was characterized (LC-MS) and evaluated as a potential SPECT tracer for imaging of necrosis in Wistar rats with a reperfused partial liver infarction and Wistar rats with ethanol induced muscular necrosis. To study the specificity, uptake of (99m)Tc(CO)(3)-bis-DTPA-BI was also studied in a mouse model of Fas-mediated hepatic apoptosis. The obtained results indicate that (99m)Tc(CO)(3)-bis-DTPA-BI displays selective uptake in necrotic tissue and can be used for in vivo visualization of necrosis by SPECT.

Development and evaluation of a 68Ga labeled pamoic acid derivative for in vivo visualization of necrosis using positron emission tomography

In this study, we labeled N,N'-bis(diethylenetriamine pentaacetic acid)-pamoic acid bis-hydrazide (bis-DTPA-PA) with the generator produced PET radionuclide gallium-68 and evaluated 68Ga-bis-DTPA-PA as a potential tracer for in vivo visualization of necrosis by positron emission tomography (PET). Radiolabeling was achieved with a decay-corrected radiochemical yield of 63%. Biodistribution and in vivo stability studies in normal mice showed that 68Ga-bis-DTPA-PA is cleared faster from normal tissue than the previously reported 99mTc(CO)3 complex with bis-DTPA-PA which on the other hand is more stable in vivo. 68Ga-bis-DTPA-PA showed a 3.5-5 times higher binding to necrotic tissue than to viable tissue as shown by in vitro autoradiography while no statistically significant increased hepatic uptake was found in a biodistribution study in a mouse model of hepatic apoptosis. Specificity and avidity for necrosis was further evaluated in rats with a reperfused partial liver infarction and ethanol induced muscular necrosis. Dynamic microPET images showed a fast and prolonged uptake of 68Ga-bis-DTPA-PA in necrotic tissue with in vivo and ex vivo images correlating well with histochemical stainings. With necrotic to viable tissue activity ratios of 8-15 on ex vivo autoradiography, depending on the necrosis model, 68Ga-bis-DTPA-PA showed a faster and higher uptake in necrotic tissue than the 99mTc(CO)3 analog. These results show that 68Ga-bis-DTPA-PA specifically binds to necrotic tissue and is a promising tracer for in vivo visualization of necrosis using PET.