Evaluation of gadoxetate disodium as a contrast agent for mouse liver imaging: comparison with gadobenate dimeglumine

MRI-Based Cell Tracking of OATP-Expressing Cell Transplants by Pre-Labeling with Gd-EOB-DTPA

PURPOSE

A critical step in cell-based therapies is determining the exact position of transplanted cells immediately post-transplant. Here, we devised a method to detect cell transplants immediately post-transplant, using a clinical gadolinium-based contrast agent. These cells were detected as hyperintense signals using a clinically familiar T1-weighted MRI protocol.

PROCEDURES

HEK293 cells were stably transduced to express human OATP1B3, a hepatic organic anion transporting polypeptide that transports Gd-EOB-DTPA into cells that express the transporters, the intracellular accumulation of which cells causes signal enhancement on T1-weighted MRI. Cells were pre-labeled prior to injection in media containing Gd-EOB-DTPA for MRI evaluation and indocyanine green for cryofluorescence tomography validation. Labeled cells were injected into chicken hearts, in vitro, after which MRI and cryofluorescence tomography were performed in sequence.

RESULTS

OATP1B3-expressing cells had substantially reduced T1 following labeling with Gd-EOB-DTPA in culture. Following their implantation into chicken heart, these cells were robustly identified in T1-weighted MRI, with image-derived injection volumes of cells commensurate with intended injection volumes. Cryofluorescence tomography showed that the areas of signal enhancement in MRI overlapped with areas of indocyanine green signal, indicating that MRI signal enhancement was due to the transplanted cells.

CONCLUSIONS

OATP1B3-expressing cells can be pre-labeled with Gd-EOB-DTPA prior to injection into tissue, affording the use of clinically familiar T1-weighted MRI to robustly detect cell transplants immediately after transplant. This procedure is easily generalizable and has potential advantages over the use of iron oxide based cell labeling agents and imaging procedures.

MRI-based cell tracking of OATP-expressing cell transplants by pre-labeling with Gd-EOB-DTPA

Purpose

A critical step in cell-based therapies is determining the exact position of transplanted cells immediately post-transplant. Here, we devised a method to detect cell transplants immediately post-transplant, using a clinical gadolinium-based contrast agent. These cells were detected as hyperintense signals using a clinically familiar T1-weighted MRI protocol.

Procedures

HEK293 cells were stably transduced to express human OATP1B3, a hepatic organic anion transporting polypeptide that transports Gd-EOB-DTPA into cells that express the transporters, the intracellular accumulation of which cells causes signal enhancement on T1-weighted MRI. Cells were pre-labeled prior to injection in media containing Gd-EOB-DTPA for MRI evaluation and indocyanine green for cryofluorescence tomography validation. Labeled cells were injected into chicken hearts, in vitro, after which MRI and cryofluorescence tomography were performed in sequence.

Results

OATP1B3-expressing cells had substantially reduced T1 following labeling with Gd-EOB-DTPA in culture. Following their implantation into chicken heart, these cells were robustly identified in T1-weighted MRI, with image-derived injection volumes of cells commensurate with intended injection volumes. Cryofluorescence tomography showed that the areas of signal enhancement in MRI overlapped with areas of indocyanine green signal, indicating that MRI signal enhancement was due to the transplanted cells.

Conclusions

OATP1B3-expressing cells can be pre-labeled with Gd-EOB-DTPA prior to injection into tissue, affording the use of clinically familiar T1-weighted MRI to robustly detect cell transplants immediately after transplant. This procedure is easily generalizable and has potential advantages over the use of iron oxide based cell labeling agents and imaging procedures.

Synthesis and Evaluation of Manganese(II)-Based Ethylenediaminetetraacetic Acid-Ethoxybenzyl Conjugate as a Highly Stable Hepatobiliary Magnetic Resonance Imaging Contrast Agent

In this study, we designed and synthesized a highly stable manganese (Mn²⁺)-based hepatobiliary complex by tethering an ethoxybenzyl (EOB) moiety with an ethylenediaminetetraacetic acid (EDTA) coordination cage as an alternative to the well-established hepatobiliary gadolinium (Gd³⁺) chelates and evaluated its usage as a T₁ hepatobiliary magnetic resonance imaging (MRI) contrast agent (CA). This new complex exhibits higher r₁ relaxivity (2.3 mM^-1 s^-1) than clinically approved Mn²⁺-based hepatobiliary complex Mn-DPDP (1.6 mM^-1 s^-1) at 1.5 T. Mn-EDTA-EOB shows much higher kinetic inertness than that of clinically approved Gd³⁺-based hepatobiliary MRI CAs, such as Gd-DTPA-EOB and Gd-BOPTA. In addition, in vivo biodistribution and MRI enhancement patterns of this new Mn²⁺ chelate are comparable to those of Gd³⁺-based hepatobiliary MRI CAs. The diagnostic efficacy of the new complex was demonstrated by its enhanced tumor detection sensitivity in a liver cancer model using in vivo MRI.

Gd-EOB-DTPA-enhanced MRI for quantitative assessment of liver organ damage after partial hepatic ischaemia reperfusion injury: correlation with histology and serum biomarkers of liver cell injury

OBJECTIVE

To evaluate Gd-EOB-DTPA-enhanced MRI for quantitative assessment of liver organ damage after hepatic ischaemia reperfusion injury (IRI) in mice.

METHODS

Partial hepatic IRI was induced in C57Bl/6 mice (n = 31) for 35, 45, 60 and 90 min. Gd-EOB-DTPA-enhanced MRI was performed 1 day after surgery using a 3D-FLASH sequence. A subgroup of n = 9 animals with 60 min IRI underwent follow-up with MRI and histology 7 days after IRI. The total liver volume was determined by manual segmentation of the entire liver. The volume of functional, contrast-enhanced liver parenchyma was quantified by a region growing algorithm (visual threshold) and an automated segmentation (Otsu's method). The percentages of functional, contrast-enhanced and damaged non-enhanced parenchyma were calculated according to these volumes. MRI data was correlated with serum liver enzyme concentrations and histologically quantified organ damage using periodic acid-Schiff (PAS) staining.

RESULTS

The percentage of functional (contrasted) liver parenchyma decreased significantly with increasing ischaemia times (control, 94.4 ± 3.3%; 35 min IRI, 89.3 ± 4.1%; 45 min IRI, 87.9 ± 3.3%; 60 min IRI, 68 ± 10.5%, p < 0.001 vs. control; 90 min IRI, 55.9 ± 11.5%, p < 0.001 vs. control). The percentage of non-contrasted liver parenchyma correlated with histologically quantified liver organ damage (r = 0.637, p < 0.01) and serum liver enzyme elevations (AST r = 0.577, p < 0.01; ALT r = 0.536, p < 0.05). Follow-up MRI visualized recovery of functional liver parenchyma (71.5 ± 8.7% vs. 84 ± 2.1%, p < 0.05), consistent with less histological organ damage on day 7.

CONCLUSION

We demonstrated the feasibility of Gd-EOB-DTPA-enhanced MRI for non-invasive quantification of damaged liver parenchyma following IRI in mice. This novel methodology may refine the characterization of liver disease and could have application in future studies targeting liver organ damage.

KEY POINTS

• Prolonged ischaemia times in partial liver IRI increase liver organ damage. • Gd-EOB-DTPA-enhanced MRI at hepatobiliary phase identifies damaged liver volume after hepatic IRI. • Damaged liver parenchyma quantified with MRI correlates with histological liver damage. • Hepatobiliary phase Gd-EOB-DTPA-enhanced MRI enables non-invasive assessment of recovery from liver injury.

The inhibitory effect of gadoxetate disodium on hepatic transporters: a study using indocyanine green

OBJECTIVES

To assess the inhibitory effect of gadoxetate disodium on the transporter system using indocyanine green (ICG).

MATERIALS AND METHODS

Groups of six female B6 Albino mice were injected with the test agent (0.62 mmol/kg gadoxetate disodium) or phosphate-buffered saline (control) 10 min before injection of ICG. Identical fluorescence images were subsequently obtained to create time-efficiency curves of liver parenchymal uptake. The study was performed on hypothermic and normothermic mice. The logarithms of the absorption rate constants (logKa values) and of the elimination rate constants (logKe values) were calculated for each experimental condition, and between-group differences were compared using Student's t-test.

RESULTS

The logKe values of the test group were lower than those of the control group at both temperatures (-6.52 vs. -5.87 under hypothermic conditions and -4.54 vs. -4.14 under normothermic conditions), and both differences were statistically significant (p = 0.037, 0.015 respectively). In terms of the logKa values, although the difference did not reach statistical significance (p = 0.052), the test group had lower values than the control group under hypothermic conditions (-0.771 vs. -0.376). In normothermic mice, the logKa values for the test and control groups were 0.037 and 0.277 respectively, thus not significantly different (p = 0.404).

CONCLUSIONS

Gadoxetate disodium inhibited ICG excretion. Thus, gadoxetate disodium inhibited the ATP-binding cassette sub-family C member 2 transporter.

KEY POINTS

• Gadoxetate disodium inhibited ICG excretion. • Gadoxetate disodium tended to inhibit hepatic ICG uptake. • Drug-drug interactions of gadoxetate disodium need further investigation.

Combining hyperpolarized 13 C MRI with a liver-specific gadolinium contrast agent for selective assessment of hepatocyte metabolism

PURPOSE

Hyperpolarized 13 C MRI is a powerful tool for studying metabolism, but can lack tissue specificity. Gadoxetate is a gadolinium-based MRI contrast agent that is selectively taken into hepatocytes. The goal of this project was to investigate whether gadoxetate can be used to selectively suppress the hyperpolarized signal arising from hepatocytes, which could in future studies be applied to generate specificity for signal from abnormal cell types.

METHODS

Baseline gadoxetate uptake kinetics were measured using T1 -weighted contrast enhanced imaging. Relaxivity of gadoxetate was measured for [1-13 C]pyruvate, [1-13 C]lactate, and [1-13 C]alanine. Four healthy rats were imaged with hyperpolarized [1-13 C]pyruvate using a three-dimensional (3D) MRSI sequence prior to and 15 min following administration of gadoxetate. The lactate:pyruvate ratio and alanine:pyruvate ratios were measured in liver and kidney.

RESULTS

Overall, the hyperpolarized signal decreased approximately 60% as a result of pre-injection of gadoxetate. In liver, the lactate:pyruvate and alanine:pyruvate ratios decreased 42% and 78%, respectively (P < 0.05) following gadoxetate administration. In kidneys, these ratios did not change significantly. Relaxivity of gadoxetate for [1-13 C]alanine was 12.6 times higher than relaxivity of gadoxetate for [1-13 C]pyruvate, explaining the greater selective relaxation effect on alanine.

CONCLUSIONS

The liver-specific gadolinium contrast-agent gadoxetate can selectively suppress normal hepatocyte contributions to hyperpolarized 13 C MRI signals. Magn Reson Med 77:2356-2363, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

MRI in animal models of psychiatric disorders

Here we describe MRI and (1)H MRS protocols for the investigation of animal models (mainly mice and rats) of psychiatric disorders. The introduction provides general findings from brain imaging studies in patients with psychiatric diseases and refers to general rules regarding the use of animal models in research. The methods section includes a selection of basic 9.4 T MRI and MRS protocols applicable for the investigation of animal models of psychiatric disorders (T1W, T2W, FLAIR, (1)H MRS). The notes section discusses in detail a series of factors that can influence the outcome of the experiment: from animal handling, stress-triggering aspects, and experimental design-related factors to technical aspects that affect T (1) and T (2) measurements.

A simple way to acquire T(1)-weighted MR images of rat liver with respiratory triggering

To acquire high-resolution T(1)-weighted images of the liver in rats, for which breath-holding cannot be ensured, respiratory triggering is essential. At the respiratory rate of 30-60 times/min in rats, however, T(1)-weighted images cannot be obtained with simple triggering. As a simple solution to this, we applied multiple repeated acquisitions with one trigger signal. With this technique, sufficient T(1) contrast could be easily achieved in rat liver enhanced by gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid infusion.

Effect of isoflurane anesthesia and hypothermia on the hepatic kinetics of Gd-EOB-DTPA: evaluation using MRI of conscious mice

PURPOSE

To develop a method for body magnetic resonance imaging (MRI) of conscious mice and investigate the effect of isoflurane anesthesia and hypothermia on the hepatic kinetics of gadoxetate disodium (Gd-EOB-DTPA).

MATERIALS AND METHODS

Conscious or anesthetized mice were restrained on a holder and the rectal temperature was measured serially. Serial MRI of the liver was performed after intravenous injection of Gd-EOB-DTPA with or without temperature control. Three mice were studied for each condition.

RESULTS

The temperature dropped rapidly in anesthetized mice beside the MR unit. The decline was less prominent in conscious mice. The temperature decreased less in anesthetized mice and remained constant in conscious mice in the radiofrequency (RF) coil. The washout of Gd-EOB-DTPA was slower in anesthetized hypothermic mice than in conscious normothermic mice. Warmed anesthetized mice showed faster washout, and cooled conscious mice showed delayed washout. Severer hypothermia in anesthetized mice resulted in weaker initial enhancement and slower washout.

CONCLUSION

By separately manipulating the presence or absence of anesthesia and hypothermia, we demonstrated that washout of Gd-EOB-DTPA was delayed under hypothermia, regardless of anesthesia. Serial body MRI of conscious mice was feasible and allowed the evaluation of kinetics of a contrast agent, while excluding the possible effects of anesthesia.

Gd-EOB-DTPA enhanced micro-MR imaging of hepatic tumors in H-ras 12V transgenic mice

RATIONALE AND OBJECTIVES

The aims of this study were to evaluate the morphologic characteristics and growth pattern of hepatic tumors in H-ras 12V transgenic (TG) mice using a micro-magnetic resonance (MR) system and to assess the usefulness of gadolinium ethoxybenzyl diethylenetriamine penta-acetic acid (Gd-EOB-DTPA) enhancement for the detection of hepatic tumors in these mice.

MATERIALS AND METHODS

Hepatocellular carcinoma lines were established to allow insertion of the H-ras 12V transgene under the control of the albumin enhancer/promoter. Seven H-ras 12V TG mice and four wild-type mice were included in this study. The mice underwent various MR imaging examinations, including T1-weighted imaging (repetition time, 300 ms; echo time, 11 ms), Gd-EOB-DTPA-enhanced T1-weighted imaging (dose, 0.025 mmol/kg), and T2-weighted imaging (repetition time, 3500 ms; echo time, 36 ms), with a 4.7-T MR scanner, at 4, 6, 8, and 9 months of age. All mice were euthanized after the final MR imaging procedure, except for one TG mouse and two wild-type mice that were euthanized after MR imaging procedures at 4 months of age. For imaging analysis, the tumor characteristics in each MR sequence, including tumor size, number, and signal intensity (SI), were recorded, and the contrast-to-noise ratio and contrast enhancement ratio were calculated to quantify the SI of the tumor. The MR images were correlated with the findings of histopathologic examinations.

RESULTS

No tumors were detected in the four wild-type mice. In the six TG mice, a total of 67 tumors were found in histopathologic specimens obtained at 9 months of age. Of the 67 tumors, 62 were detected on Gd-EOB-DTPA-enhanced T1-weighted images with fat saturation. The majority of hepatic tumors showed high SI on T1-weighted images without fat saturation. The SI diminished on T1-weighted images with fat saturation. The tumor contrast-to-noise ratio for Gd-EOB-DTPA-enhanced T1-weighted imaging was significantly better than that for the other sequences. The tumors were histopathologically confirmed as hepatocellular adenomas (n = 32) and well-differentiated hepatocellular carcinomas (n = 35).

CONCLUSIONS

Micro-MR imaging can reveal the characteristics of hepatic tumors in a live murine model. Gd-EOB-DTPA-enhanced T1-weighted imaging is helpful in the detection of hepatic tumors in H-ras 12V TG mice.

Diet and gastrointestinal signal on T1-weighted magnetic resonance imaging of mice

In magnetic resonance (MR) imaging of small animals, the gastrointestinal contents may give rise to intense signals on T1-weighted images. The aim of this study was to determine the optimal dietary preparation to reduce gastrointestinal signals in mice and to evaluate the usefulness of this approach. Images of the mouse trunk were obtained using a T1-weighted, three-dimensional fast low-angle shot sequence under various dietary conditions and were compared with respect to the gastrointestinal signals and image quality. The dietary preparation studied included giving alternative diets for 24 h, intestinal cleansing, and 6-h fasting. Mice with and without dietary preparation underwent MR lymphography using gadofluorine 8, and the visualization of abdominal lymph nodes was compared. In the absence of dietary preparation, hyperintense areas were conspicuous in the gastrointestinal system, whereas on the images taken from mice fed potato or sweet potato for 24 h before imaging, gastrointestinal hyperintensity was less prominent. This preparation also reduced artifactual signals and resulted in higher-quality images of the kidneys. Intestinal cleansing, which consisted of 24-h fasting and laxative intake, did not reduce the gastrointestinal signals and caused signal changes that were indicative of fatty liver development. Some of the abdominal lymph nodes of the mice that did not receive dietary preparation were visualized on MR lymphography source images but not on maximum intensity projection (MIP) images. In contrast, on the MIP images of mice fed potato, all the lymph nodes delineated on the source images were successfully visualized. In conclusion, feeding mice potato or sweet potato for 24 h before MR imaging reduces the gastrointestinal signals and image degradation due to artifacts. Appropriate dietary preparations facilitate the display of target structures on MIP images and are expected to enhance the capabilities of small animal MR imaging.