Complete elimination of the hepatobiliary mr contrast agent Gd-EOB-DTPA in hepatic dysfunction: An experimental study using transport-deficient, mutant rats

Physiologically Based Pharmacokinetic Modeling of Transporter-Mediated Hepatic Disposition of Imaging Biomarker Gadoxetate in Rats

Physiologically based pharmacokinetic (PBPK) models are increasingly used in drug development to simulate changes in both systemic and tissue exposures that arise as a result of changes in enzyme and/or transporter activity. Verification of these model-based simulations of tissue exposure is challenging in the case of transporter-mediated drug–drug interactions (tDDI), in particular as these may lead to differential effects on substrate exposure in plasma and tissues/organs of interest. Gadoxetate, a promising magnetic resonance imaging (MRI) contrast agent, is a substrate of organic-anion-transporting polypeptide 1B1 (OATP1B1) and multidrug resistance-associated protein 2 (MRP2). In this study, we developed a gadoxetate PBPK model and explored the use of liver-imaging data to achieve and refine in vitro–in vivo extrapolation (IVIVE) of gadoxetate hepatic transporter kinetic data. In addition, PBPK modeling was used to investigate gadoxetate hepatic tDDI with rifampicin i.v. 10 mg/kg. In vivo dynamic contrast-enhanced (DCE) MRI data of gadoxetate in rat blood, spleen, and liver were used in this analysis. Gadoxetate in vitro uptake kinetic data were generated in plated rat hepatocytes. Mean (%CV) in vitro hepatocyte uptake unbound Michaelis–Menten constant (K_m,u) of gadoxetate was 106 μM (17%) (n = 4 rats), and active saturable uptake accounted for 94% of total uptake into hepatocytes. PBPK–IVIVE of these data (bottom-up approach) captured reasonably systemic exposure, but underestimated the in vivo gadoxetate DCE–MRI profiles and elimination from the liver. Therefore, in vivo rat DCE–MRI liver data were subsequently used to refine gadoxetate transporter kinetic parameters in the PBPK model (top-down approach). Active uptake into the hepatocytes refined by the liver-imaging data was one order of magnitude higher than the one predicted by the IVIVE approach. Finally, the PBPK model was fitted to the gadoxetate DCE–MRI data (blood, spleen, and liver) obtained with and without coadministered rifampicin. Rifampicin was estimated to inhibit active uptake transport of gadoxetate into the liver by 96%. The current analysis highlighted the importance of gadoxetate liver data for PBPK model refinement, which was not feasible when using the blood data alone, as is common in PBPK modeling applications. The results of our study demonstrate the utility of organ-imaging data in evaluating and refining PBPK transporter IVIVE to support the subsequent model use for quantitative evaluation of hepatic tDDI.

In vivo imaging of insulin-secreting human pancreatic ductal cells using MRI reporter gene technique: A feasibility study

PURPOSE

The purpose of this study was to investigate the feasibility of in vivo imaging of human pancreatic ductal cells by OATP1B3 reporter gene under MRI.

METHODS

A human cell line (PANC-1) derived from the pancreatic ductal epithelium was used in this study. After transduction of OATP1B3, the cellular physiological functions and the ability of intracellular uptake of the MRI contrast medium (Gd-EOB-DTPA) were examined. Induced differentiation of the PANC-1 cells into hormone-secreting cells were performed to simulate pancreatic β-like cells. The hormone-secreting cells were implanted into rats and in vivo MRI was evaluated.

RESULTS

The mRNA and proteins of OATP1B3 were highly expressed. No significant change of cellular physiological functions was found after the expression. After induced differentiation, the hormone secretion capacities of the OATP1B3-expressing PANC-1 cells were confirmed. Intra-cellular uptake of Gd-EOB-DTPA was determined in vitro by inductively coupled plasma mass spectrometry and MRI. In vivo MRI of the OATP1B3-expressing xenograft revealed an increased signal intensity after contrast enhancement.

CONCLUSION

OATP1B3 can be used as a safe and feasible in vivo MRI gene reporter for human pancreatic ductal cells.

Comparison between dynamic gadoxetate-enhanced MRI and 99mTc-mebrofenin hepatobiliary scintigraphy with SPECT for quantitative assessment of liver function

Objectives

To compare Gd-EOB-DTPA dynamic hepatocyte-specific contrast-enhanced MRI (DHCE-MRI) with ^99mTc-mebrofenin hepatobiliary scintigraphy (HBS) as quantitative liver function tests for the preoperative assessment of patients undergoing liver resection.

Methods

Patients undergoing liver surgery and preoperative assessment of future remnant liver (FRL) function using ^99mTc-mebrofenin HBS were included. Patients underwent DHCE-MRI. Total liver uptake function was calculated for both modalities: mebrofenin uptake rate (MUR) and Ki respectively. The FRL was delineated with both SPECT-CT and MRI to calculate the functional share. Blood samples were taken to assess biochemical liver parameters.

Results

A total of 20 patients were included. The HBS-derived MUR and the DHCE-MRI-derived mean Ki correlated strongly for both total and FRL function (Pearson r = 0.70, p = 0.001 and r = 0.89, p < 0.001 respectively). There was a strong agreement between the functional share determined with both modalities (ICC = 0.944, 95% CI 0.863–0.978, n = 20). There was a significant negative correlation between liver aminotransferases and bilirubin for both MUR and Ki.

Conclusions

Assessment of liver function with DHCE-MRI is comparable with that of ^99mTc-mebrofenin HBS and has the potential to be combined with diagnostic MRI imaging. This can therefore provide a one-stop-shop modality for the preoperative assessment of patients undergoing liver surgery.

Key Points

• Quantitative assessment of liver function using hepatobiliary scintigraphy is performed in the preoperative assessment of patients undergoing liver surgery in order to prevent posthepatectomy liver failure.

• Gd-EOB-DTPA dynamic hepatocyte-specific contrast-enhanced MRI (DHCE-MRI) is an emerging method to quantify liver function and can serve as a potential alternative to hepatobiliary scintigraphy.

• Assessment of liver function with dynamic gadoxetate-enhanced MRI is comparable with that of hepatobiliary scintigraphy and has the potential to be combined with diagnostic MRI imaging.

Electronic supplementary material

The online version of this article (10.1007/s00330-019-06029-7) contains supplementary material, which is available to authorized users.

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.

Organic anion-transporting polypeptide 1B3 as a dual reporter gene for fluorescence and magnetic resonance imaging

Reporter proteins have broad applications in visualizing molecular events at the cellular, tissue and whole-body levels. Transmembrane transporters recognizing specific molecular domains are of particular interest because they enable the migration of signal-source molecules from the extracellular space to the cytoplasm for subsequent application in multimodality imaging. Organic anion-transporting polypeptides (OATPs) have demonstrated their MRI reporter efficacy. We further expanded their use as a dual-modality reporter in MRI and noninvasive in vivo imaging system (IVIS). We overexpressed OATP1B3 in the HT-1080 sarcoma cell line. Both Gd-EOB-DTPA, an MRI contrast agent, and indocyanine green (ICG), a near-infrared fluorescent dye that provides better deep-tissue detection because of its long wavelength, could be delivered to the intracellular space and imaged in a tumor-bearing nude mouse model. Our in vivo dual-imaging reporter system achieved high sensitivity in MRI and observation periods lasting as long as 96 h in IVIS. Because of the superior temporal and spatial resolutions and the clinical availability of both ICG and Gd-EOB-DTPA, this dual-imaging OATP1B3 system will find biomedical use in tumor biology, stem cell trafficking, and tissue engineering.—Wu, M.-R., Liu, H.-M., Lu, C.-W., Shen, W.-H., Lin, I.-J., Liao, L.-W., Huang, Y.-Y., Shieh, M.-J., Hsiao, J.-K. Organic anion-transporting polypeptide 1B3 as a dual reporter gene for fluorescence and magnetic resonance imaging.

Influence of Indocyanine Green on Hepatic Gd-EOB-DTPA Uptake: A Proof-of-Concept Study in Mice

OBJECTIVES

The aim of this study was to explore the influence of indocyanine green (ICG) on hepatic uptake of gadolinium ethoxybenzyldiethylenetriaminepenta-acetic acid (Gd-EOB-DTPA).

MATERIALS AND METHODS

Groups of 6 female C57BL6 mice were injected with 5 mg/kg ICG, 20 mg/kg ICG, or phosphate-buffered saline (control group) 10 minutes before the injection of Gd-EOB-DTPA; identical 3-dimensional gradient echo T1-weighted images were subsequently obtained to create time-intensity curves and to measure the peak contrast ratios (CRs) of liver parenchyma. We studied both hypothermic and normothermic mice. Peak CRs for all experimental conditions were evaluated, and among-group differences were assessed using 2-way factorial analysis of variance with Bonferroni post hoc testing.

RESULTS

In hypothermic mice, the time-intensity curves of the 3 groups gradually increased from 5 to 30 minutes and almost plateaued after 30 minutes. The peak CR decreased as the amount of injected ICG increased (control group, 5 mg/kg ICG, 20 mg/kg ICG: 1.66 ± 0.09, 1.37 ± 0.18, 1.25 ± 0.24, respectively). In normothermic animals, the time-intensity curves of the control and ICG 5 mg/kg groups peaked 10 to 15 minutes after injection, the peak CRs were very similar (control group, 5 mg/kg ICG: 2.01 ± 0.16, 1.95 ± 0.14, respectively), and the intensities thereof then gradually fell until 60 minutes. Compared with these groups, the ICG 20 mg/kg group exhibited lower peak CR (1.48 ± 0.14) and a weaker decrease in intensity to 60 minutes. Both the amount of ICG injected (P < 0.001) and the experimental temperature (P < 0.001) significantly affected the measurements.

CONCLUSIONS

Indocyanine green inhibits the hepatic uptake of Gd-EOB-DTPA and affects the signal intensity upon Gd-EOB-DTPA-enhanced magnetic resonance imaging. Such inhibition was more obvious in hypothermic mice.

MRI as Primary End Point for Pharmacologic Experiments of Liver Regeneration in a Murine Model of Partial Hepatectomy

RATIONALE AND OBJECTIVES

The study aimed to validate magnetic resonance imaging (MRI)-based liver volumetry as a quantitative measure of hepatic regeneration in mice subjected to partial hepatectomy, in view of routine in vivo pharmacologic studies characterizing compounds aiming to accelerate liver regeneration.

MATERIALS AND METHODS

Partial hepatectomy was performed in male B6 mice (n = 47). Images were acquired in 14.5 minutes from anesthetized and spontaneously respiring animals, without any gating and without administration of contrast material. Some of the mice (n = 6) were treated with 1, 4-bis [2-(3, 5-dichloropyridyloxy)] benzene (TCPOBOP), a synthetic agonist of mouse constitutive androstane receptor, or with the corresponding vehicle (n = 6). Postmortem analyses included total liver weight and histologic Ki67 expression.

RESULTS

A highly significant correlation (R = 0.98, P = 1.5 × 10^-14) was obtained between the MRI-derived liver volumes and the postmortem liver weights in hepatectomized, untreated mice. MRI reliably monitored enhanced murine liver regrowth following treatment with TCPOBOP, as confirmed by comparative hepatocyte proliferation (Ki67 expression) and liver weight analysis (R = 0.96, P = 2 × 10^-6).

CONCLUSIONS

MRI-based monitoring of liver regrowth in mice without the requirement of euthanizing animals at several time points has been established. In comparison to terminal procedures, the number of hepatectomized mice needed to derive a liver (re)growth curve was reduced by a factor of 6. The feasibility of using this imaging approach in pharmacologic studies in the context of liver regeneration has been demonstrated.

Hepatic function imaging using dynamic Gd-EOB-DTPA enhanced MRI and pharmacokinetic modeling

PURPOSE

To determine whether pharmacokinetic modeling parameters with different output assumptions of dynamic contrast-enhanced MRI (DCE-MRI) using Gd-EOB-DTPA correlate with serum-based liver function tests, and compare the goodness of fit of the different output assumptions.

METHODS

A 6-min DCE-MRI protocol was performed in 38 patients. Four dual-input two-compartment models with different output assumptions and a published one-compartment model were used to calculate hepatic function parameters. The Akaike information criterion fitting error was used to evaluate the goodness of fit. Imaging-based hepatic function parameters were compared with blood chemistry using correlation with multiple comparison correction.

RESULTS

The dual-input two-compartment model assuming venous flow equals arterial flow plus portal venous flow and no bile duct output better described the liver tissue enhancement with low fitting error and high correlation with blood chemistry. The relative uptake rate Kir derived from this model was found to be significantly correlated with direct bilirubin (r = -0.52, P = 0.015), prealbumin concentration (r = 0.58, P = 0.015), and prothrombin time (r = -0.51, P = 0.026).

CONCLUSION

It is feasible to evaluate hepatic function by proper output assumptions. The relative uptake rate has the potential to serve as a biomarker of function. Magn Reson Med 78:1488-1495, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Physiologically realistic and validated mathematical liver model reveals [corrected] hepatobiliary transfer rates for Gd-EOB-DTPA using human DCE-MRI data

Objectives

Diffuse liver disease (DLD), such as non-alcoholic fatty liver disease (NASH) and cirrhosis, is a rapidly growing problem throughout the Westernized world. Magnetic resonance imaging (MRI), based on uptake of the hepatocyte-specific contrast agent (CA) Gd-EOB-DTPA, is a promising non-invasive approach for diagnosing DLD. However, to fully utilize the potential of such dynamic measurements for clinical or research purposes, more advanced methods for data analysis are required.

Methods

A mathematical model that can be used for such data-analysis was developed. Data was obtained from healthy human subjects using a clinical protocol with high spatial resolution. The model is based on ordinary differential equations and goes beyond local diffusion modeling, taking into account the complete system accessible to the CA.

Results

The presented model can describe the data accurately, which was confirmed using chi-square statistics. Furthermore, the model is minimal and identifiable, meaning that all parameters were determined with small degree of uncertainty. The model was also validated using independent data.

Conclusions

We have developed a novel approach for determining previously undescribed physiological hepatic parameters in humans, associated with CA transport across the liver. The method has a potential for assessing regional liver function in clinical examinations of patients that are suffering of DLD and compromised hepatic function.

Assessment of gadoxetate DCE-MRI as a biomarker of hepatobiliary transporter inhibition

Drug-induced liver injury (DILI) is a clinically important adverse drug reaction, which prevents the development of many otherwise safe and effective new drugs. Currently, there is a lack of sensitive and specific biomarkers that can be used to predict, assess and manage this toxicity. The aim of this work was to evaluate gadoxetate-enhanced MRI as a potential novel biomarker of hepatobiliary transporter inhibition in the rat. Initially, the volume fraction of extracellular space in the liver was determined using gadopentetate to enable an estimation of the gadoxetate concentration in hepatocytes. Using this information, a compartmental model was developed to characterise the pharmacokinetics of hepatic uptake and biliary excretion of gadoxetate. Subsequently, we explored the impact of an investigational hepatobiliary transporter inhibitor on the parameters of the model in vivo in rats. The investigational hepatobiliary transporter inhibitor reduced both the rate of uptake of gadoxetate into the hepatocyte, k1 , and the Michaelis-Menten constant, Vmax , characterising its excretion into bile, whereas KM values for biliary efflux were increased. These effects were dose dependent and correlated with effects on plasma chemistry markers of liver dysfunction, in particular bilirubin and bile acids. These results indicate that gadoxetate-enhanced MRI provides a novel functional biomarker of inhibition of transporter-mediated hepatic uptake and clearance in the rat. Since gadoxetate is used clinically, the technology has the potential to provide a translatable biomarker of drug-induced perturbation of hepatic transporters that may also be useful in humans to explore deleterious functional alterations caused by transporter inhibition.

Separation of advanced from mild hepatic fibrosis by quantification of the hepatobiliary uptake of Gd-EOB-DTPA

OBJECTIVES

To apply dynamic contrast-enhanced (DCE) MRI on patients presenting with elevated liver enzymes without clinical signs of hepatic decompensation in order to quantitatively compare the hepatocyte-specific uptake of Gd-EOB-DTPA with histopathological fibrosis stage.

METHODS

A total of 38 patients were prospectively examined using 1.5-T MRI. Data were acquired from regions of interest in the liver and spleen by using time series of single-breath-hold symmetrically sampled two-point Dixon 3D images (non-enhanced, arterial and venous portal phase; 3, 10, 20 and 30 min) following a bolus injection of Gd-EOB-DTPA (0.025 mmol/kg). The signal intensity (SI) values were reconstructed using a phase-sensitive technique and normalised using multiscale adaptive normalising averaging (MANA). Liver-to-spleen contrast ratios (LSC_N) and the contrast uptake rate (K (Hep)) were calculated. Liver biopsy was performed and classified according to the Batts and Ludwig system.

RESULTS

Area under the receiver-operating characteristic curve (AUROC) values of 0.71, 0.80 and 0.78, respectively, were found for K (Hep), LSC_N10 and LSC_N20 with regard to severe versus mild fibrosis. Significant group differences were found for K (Hep) (borderline), LSC_N10 and LSC_N20.

CONCLUSIONS

Liver fibrosis stage strongly influences the hepatocyte-specific uptake of Gd-EOB-DTPA. Potentially the normalisation technique and K (Hep) will reduce patient and system bias, yielding a robust approach to non-invasive liver function determination.

Effect of change in transporter expression on gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid-enhanced magnetic resonance imaging during hepatocarcinogenesis in rats

BACKGROUND AND AIMS

To analyze the difference in signal intensity on gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid (Gd-EOB-DTPA)-enhanced magnetic resonance imaging (MRI) among various hepatocellular nodules during hepatocarcinogenesis as correlated with the expressions of the transporters of Gd-EOB-DTPA.

METHODS

We received institutional animal review board approval prior to the commencement of all studies. Forty rats were divided into three groups. The rats in the tumor groups received N-nitrosomorpholine solution (n = 16), and rats in the cirrhosis group (thioacetamide [TAA] group) received thioacetamide solution (n = 12). As a control, the remaining 12 rats were fed normal water. Each group was divided into two sub-groups: Group 1 for Gd-EOB-DTPA-enhanced MRI (0.025 mmol Gd/kg, n =7) and Group 2 for reverse transcription-polymerase chain reaction to compare transporter (oatp1 and mrp2) expressions (n = 5 for control and TAA groups, n = 9 for tumor groups).

RESULTS

Signal enhancement of tumors decreased according to the progress of hepatocarcinogenesis. Although the relative enhancement of each tumor group was significantly lower than that of the control group (P < 0.01), and there was no significant difference between TAA, hyperplastic nodules (HPN), and HCC(well) groups. The relative enhancement of the HCC(mod) group was significantly lower than the other groups (P < 0.01). The oatp1 expression of HPN tended to be higher than those of HCC(well) and HCC(mod). The mrp2 expression of TAA was significantly higher than those of HCC(well), HCC(mod), HPN and control (P < 0.01). The mrp2 expression of HPN tended to be higher than those of HCC(well ) and HCC(mod).

CONCLUSION

It was suggested that the signal enhancement on Gd-EOB-DTPA-enhanced MRI would correlate with the transporter expression in various hepatocellular nodules during hepatocarcinogenesis.

Gd-EOB-DTPA enhanced MR imaging: evaluation of biliary and renal excretion in normal and cirrhotic livers

OBJECTIVE

The purpose of this study was to assess the difference in the activity of biliary and renal excretion between normal and cirrhotic livers on contrast-enhanced MR imaging obtained with gadolinium ethoxybenzyl diethylenetriaminepentaacetic acid (Gd-EOB-DTPA).

METHODS

A total of 78 patients with cirrhotic liver (n=44) and with normal liver (n=34) underwent multi-phase Gd-EOB-DTPA enhanced MR imaging (arterial, portal, equilibrium, and three hepatobiliary phases (10, 15 and 20 min HP), respectively), and these contrast-enhanced images were qualitatively and quantitatively evaluated for the differences of the biliary and renal excretion between normal and cirrhotic livers.

RESULTS

The timing of biliary excretion of contrast agents in the cirrhotic liver was significantly slower than that in the normal liver (P<0.001). The degree of contrast enhancement in the common bile duct in the normal liver was significantly better than that in the cirrhotic liver (P=0.003). Contrast agents were demonstrated in the duodenum at 20 min HP in 8/44 (18%) cirrhotic liver while they were seen in 15/34 (44%) normal liver (P=0.013). The enhancement effects of renal medulla and portal vein at 20 min HP in the cirrhotic liver were significantly higher than those of normal liver (P=0.043 and P<0.001, respectively).

CONCLUSION

Biliary excretion of Gd-EOB-DPTA was impaired in cirrhotic livers in comparison with normal livers while renal excretion of Gd-EOB-DPTA was increased.

Hepatic uptake of the magnetic resonance imaging contrast agent Gd-EOB-DTPA: role of human organic anion transporters

Contrast-enhancing magnetic resonance imaging with the liver-specific agent gadolinium-ethoxybenzyl-diethylenetriamine pentaacetic acid (Gd-EOB-DTPA) has been shown to improve the detection rate of focal lesions. There is evidence from preclinical studies that multidrug organic anion transporters are involved in hepatic uptake of Gd-EOB-DTPA. Therefore, we evaluated affinity of the contrast agent to human organic anion-transporting polypeptides (OATP1B1, OATP1B3, OATP2B1) and to the Na(+)/taurocholate cotransporting polypeptide (NTCP) using stable transfected human embryonic kidney (HEK) 293 cells. In competition assays, Gd-EOB-DTPA inhibited the uptake of bromosulfophthalein (BSP) by OATP1B1 (IC(50) = 0.6 mM) and OATP1B3 (IC(50) = 0.4 mM). In comparison, the IC(50) values for rifampicin were 11.9 (OATP1B1), 1.4 (OATP1B3), and 80.5 muM (OATP2B1), respectively. Uptake of BSP by OATP2B1, uptake of taurocholic acid by NTCP, and viability of all HEK cells were not influenced by Gd-EOB-DTPA in concentrations up to 10 mM. In uptake assays using a new liquid chromatography-tandem mass spectrometry method for quantification, Gd-EOB-DTPA was a substrate for OATP1B1 (K(m) = 0.7 mM, V(max) = 10.5 pmol/mg x min), OATP1B3 (K(m) = 4.1 mM, V(max) = 22.7 pmol/mg x min), and NTCP (K(m) = 0.04 mM, V(max) = 1.4 pmol/mg x min). The uptake by OATP2B1 was not different from the vector control. In conclusion, Gd-EOB-DTPA is a substrate of the liver-specific OATP1B1, OATP1B3, and NTCP.

Quantitative evaluation of liver function with MRI Using Gd-EOB-DTPA

Objective

Gadolinium ethoxybenzyl diethylenetriaminepentaacetic acid (Gd-EOB-DTPA) is a newly developed MR contrast agent. After intravenous injection, Gd-EOB-DTPA is gradually taken up by the hepatocytes and eventually excreted via the biliary pathway without any change to its chemical structure. Because of these characteristics, it can be used as a tracer for quantitative liver function testing. The purpose of this study is to develop a noninvasive method of quantitation of the hepatic function using Gd-EOB-DTPA through the deconvolution analysis.

Materials and Methods

Adult New Zealand white rabbits (n = 10, average body weight = 3.5 kg) were used in the present study. Hepatic injury was induced to by the intragastric administration of carbon tetrachloride (CCl4) three times a week for three weeks. Liver enzyme (aspartate aminotransferase, AST; alanine aminotransferase, ALT) levels and the plasma indocyanine green (ICG) retention rate 15 minutes after an intravenous injection of ICG (ICG R15), was checked before and after the three-week administration of CCl4. At the end of experimental period, an observer "blinded" to the treatment given the rabbits performed the histological examination. MRI studies were performed before and after the three-week administration of CCl4 on a 1.5 T scanner using a human extremity coil. After intravenous bolus injection of Gd-EOB-DTPA (0.3 mL of Gd-EOB-DTPA freshly prepared in 2.7 mL of normal saline) through the ear vein, the 250 axial single level dynamic MR images were obtained using a fast low angle shot (FLASH, TR/TE = 11/4.2 msec, flip angle = 15, acquisition time 1 second, slice thickness = 5 mm, matrix = 128×128, field of view = 120 mm) sequence with 1.5 sec time intervals. The time-intensity curves were obtained at the abdominal aorta and the liver parenchyma that was devoid of blood vessels. Deconvolution analysis of the aortic (input function) and hepatic parenchymal (output function) time-intensity curves was performed with a modified Fourier transform technique to calculate the hepatic extraction fraction (HEF). The presence and type of hepatic injury were determined by the histopathologic examination and statistical analysis of the changes of the hepatic enzyme levels, the ICG R15 and Gd-EOB-DTPA HEF values between the time before and after CCl4 administration with Wicoxon signed rank test. Correlation between the Gd-EOB-DTPA HEF and the change of the ICG R15 were analyzed with Pearson's correlation coefficient.

Results

Histopathologic examination showed findings that were compatible with hepatic fibrosis caused by chronic liver injury. The initial blood biochemical studies before the administration of carbon tetrachloride showed that the mean AST and ALT levels were 39.8±5.2 IU/L and 59.1±11.7 IU/L, respectively. The AST and ALT levels increased to 138.4±50.5 IU and 172.0±71.6 IU/L, respectively, after the three week administration of CCl4. The ALT and AST levels were significantly increased after the three weeks of CCl4 administration (p = 0.018). The ICG R15 values were 4.47±2.08% and 19.43±3.98% before and after three-week administration of CCl4, respectively. The ICG R15 values were significantly increased after hepatic injury (p = 0.018). After normalizing the HEF as 100% in each rabbit before CCl4 administration, the deconvoluted curve after CCl4 administration revealed less hepatocyte extraction efficiency with a mean value of 77.7±3.6. There was a significant correlation between the HEF and changes of the ICG R15 by the Pearson correlation coefficient assessment (correlation coefficient = -0.965, p = 0.000).

Conclusion

The Gd-EOB-DTPA HEF could be calculated from deconvolution analysis of aortic and hepatic parenchymal time-intensity curves obtained by dynamic MRI. The Gd-EOB-DTPA HEF was well correlated with changes of the ICG R15, which is the most common parameter used in the quantitative estimation of the hepatic function. The Gd-EOB-DTPA HEF is a direct, noninvasive technique for the quantitative evaluation of liver function. It could be a promising alternative for the determination of noninvasive hepatic function in those patients with liver disease.

In vitro and in vivo hepatic transport of the magnetic resonance imaging contrast agent B22956/1: role of MRP proteins

The molecular mechanisms of the hepatic transport of B22956/1, a new gadolinium complex from the class of intravascular contrast agents for MRI, which undergoes extensive biliary elimination, were studied. Biliary and urinary elimination of B22956/1 were measured in normal and in mutant MRP2 lacking rats (TR(-)); cellular trafficking of the compound was assessed in wild and MRP1 or MRP2 transfected MDCKII cells. Eight hours after IV injection of B22956/1, 90+/-8% of the dose was recovered in the bile of normal rats. By contrast, in TR(-) rats, the biliary excretion was significantly lower (14+/-3%) while 55+/-9% of the compound was found in urine. In vitro, the cellular accumulation of B22956/1 was significantly lower in both MRP1 and MRP2 transfected cells as compared to wild type MDCKII cells, and the cellular efflux was prevented by the MRP inhibitor MK571, indicating the involvement of both MRP2 and MRP1 in the transport of B22956/1. Due to the distinct cellular localization of the proteins, MRP2 accounts for the biliary and urinary excretion of the compound, while MRP1 prevents cellular accumulation of the MRI agent. B22956/1 may be useful in clinical conditions where a defective biliary transport is present.

Abc protein transport of MRI contrast agents in canalicular rat liver plasma vesicles and yeast vacuoles

The mechanism of excretion into bile of hepatospecific magnetic resonance imaging (MRI) contrast media employed labeled Gd-reagents EOB.DTPA, BOPTA, B 20790 (iopanoate-linked), and B 21690 (glycocholate-linked) for measurement in rat liver canalicular plasma membrane vesicles and yeast vacuoles. The presence of ATP gave threefold greater transport of B 20790 and B 21690 than of EOB.DTPA and BOPTA. In yeast vacuoles the ATP stimulatory effect was eightfold with B 20790 and fivefold greater for B 21690, whereas in YCF1- or YLLO115w-deleted yeast cells the transport was significantly reduced and absent from double mutants, YCF1 and YLLO15w. The transport was similar in wild-type and deletant cells for B 21690; taurocholate gave 85% inhibition. These data suggest that bilary secretion of structurally related MRI agents depend on molecular structure. The findings are suggestive as of possible value for clinical diagnosis of inherited hyperbilirubinemias and other liver disorders.

Hepatocyte targeting with Gd-EOB-DTPA: potential application for gene therapy

RATIONALE AND OBJECTIVES

To evaluate the suitability of the liver-specific MRI contrast agent Gd-EOB-DTPA as a nonviral vector for gene therapy of hepatocellular carcinoma.

METHODS

Specific uptake of Gd-EOB-DTPA was quantified by relaxometry in rat cultured hepatocytes and the hepatoma cells HepG2 and Huh7. Nonviral vectors for gene transfer were synthesized by coupling Gd-EOB-DTPA to polyethyleneimine or polylysine as DNA condensing agents, and their efficiency was studied using beta-galactosidase (lacZ) as the reporter gene.

RESULTS

Gd-EOB-DTPA was specifically taken up by rat cultured hepatocytes (4.32 vs. 1.08 mmol/L in nonhepatocyte control cells) but not by the hepatoma cells; this uptake was concentration-dependently inhibited by Bromsulphtalein. Polycation linkages were achieved with yields of 0.9 Gd-EOB-DTPA molecule per polyethyleneimine molecule and 10 Gd-EOB-DTPA molecules per polylysine molecule. Incubating the cells with plasmids containing lacZ reporter gene and polyethyleneimine-Gd-EOB-DTPA resulted in a few blue (transfected) cells, whereas no blue cells were observed on incubation with polylysine-Gd-EOB-DTPA.

CONCLUSIONS

Gd-EOB-DTPA is taken up by normal hepatocytes but not by HepG2 and Huh7 cells, probably because of the lack of the organic anion transporter in these hepatoma cells. The Gd-EOB-DTPA polycation conjugates, such as polyethyleneimine-Gd-EOB-DTPA, could serve as transfer vectors of interest for gene targeting imagery at the early stage of hepatocarcinogenesis. However, the transfer efficiency of such conjugates is low and requires improvement.

Molecular mechanisms for the hepatic uptake of magnetic resonance imaging contrast agents

The mechanisms were investigated for the hepatic transport of 4 different gadolinium complexes used as contrast agents for magnetic resonance imaging (MRI). In basolateral rat hepatocyte plasma membrane vesicles, Gd-DTPA uptake was indistinguishable from non-specific binding to vesicles; Gd-BOPTA and Gd-EOB-DTPA entered plasma membrane vesicles following a linear, concentration-dependent mechanism up to 1.5 mM of substrate. By contrast, Gd-B 20790 uptake followed a saturative kinetic with an apparent Km of 92 +/- 15 microM and a Vmax of 143 +/- 42 pmol/mg prot/15 sec, and it occurred into an osmotic-sensitive space. Sulfobromophthalein ant taurocholate, but not unconjugated bilirubin inhibited the uptake rate of Gd-B 20790 but not that of the other three compounds. Injection into Xenopus laevis oocytes of 5 ng of human OATP cRNA resulted, after 3 days, in a >/=2-fold stimulation (p < 0.001) of transport of Gd-B 20790 but not of Gd-BOPTA or Gd-EOB-DTPA. Collectively, these data indicate that the hepatic uptake of the MRI contrast agent Gd-B 20790 is a carrier-mediated mechanism operated by OATP while MRI compounds with other chemical structures enter the hepatocyte by other mechanisms.

Pharmacokinetics of the liver-specific contrast agent Gd-EOB-DTPA in relation to contrast-enhanced liver imaging in humans

This study was performed to evaluate the effect of dose on the pharmacokinetics and efficacy of the gadolinium-based contrast medium gadoxetic acid, disodium, [gadolinium (4S)-4-(4-ethoxybenzyl)-3,6,9-tris(carboxylatomethyl)-3,6, 9-triazaundecandioic acid-disodium salt] (Gd-EOB-DTPA) as a liver-specific hepatobiliary contrast medium for computed tomography. Pharmacokinetics in serum and the pattern of elimination were investigated in 18 healthy volunteers up to 6 days after a 10-minute infusion of 0.2 mmol, 0.35 mmol, and 0.5 mmol of gadolinium per kilogram of body weight. Pharmacokinetic behavior was compared with the compute tomographic attenuation data in the liver parenchyma after the same doses in patients. Urinary and fecal excretion accounted for approximately equal portions of the administered dose. The degree of renal elimination increased with increasing doses, whereas renal clearance and half-life from urine data were not affected by dose. Dose-normalized area under the concentration-time curve was significantly increased with increasing doses indicating saturation in liver uptake for the highest dose. This finding was in agreement with the measured net increase in liver attenuation by computed tomography. Hepatic disposition revealed slight saturation phenomena for the highest dose (0.5 mmol gadolinium/kg). Nevertheless, this dose resulted in sufficient uptake by human liver, allowing for computed tomographic imaging.

Functional hepatobiliary imaging with gadolinium-EOB-DTPA. A comparison of magnetic resonance imaging and 153gadolinium-EOB-DTPA scintigraphy in rats

RATIONALE AND OBJECTIVES

Gadolinium-EOB-DTPA (Gd-EOB-DTPA) is a hepatobiliary magnetic resonance (MR) imaging contrast medium designed to detect focal liver lesions. The objective of this study was to evaluate dynamic Gd-EOB-DTPA-enhanced MR imaging as a new method for assessing liver excretory function and to compare it with a scintigraphic method, the gold standard.

METHODS

Changes in scintigraphic liver activity or MR liver signal intensity were intraindividually monitored over time after intravenous injection of 50 mumol Gd/kg of Gd-EOB-DTPA in controls and rats with common bile duct obstruction or L-ethionine-induced fatty liver (n = 6).

RESULTS

A comparison of liver scintigraphy and MR imaging revealed that elimination half-lives of Gd-EOB-DTPA were significantly longer in rats with common bile duct obstruction (scintigraphy: 100 +/- 27 minutes; MR imaging: 59 +/- 18 minutes) or fatty liver (scintigraphy: 94 +/- 30 minutes; MR imaging: 72 +/- 32 minutes) than in controls (scintigraphy: 20 +/- 2 minutes; MR imaging: 18 +/- 3) (P < 0.05).

CONCLUSIONS

Like liver scintigraphy, functional MR liver imaging using Gd-EOB-DTPA is feasible and can differentiate normal controls from models of biliary and hepatocyte disease.

Effect of manganese dipyridoxal diphosphate on liver magnetic resonance imaging and serum bilirubin in rats with removable biliary obstruction

RATIONALE AND OBJECTIVES

It is known that manganese dipyridoxal diphosphate (Mn-DPDP) causes persisting liver enhancement in cholestatic rats, that free Mn++ plus bilirubin induces intrahepatic cholestasis, and that free Mn++ is released in vivo after Mn-DPDP injection. Hence, there is a concern about potential secondary intrahepatic cholestasis in patients who have biliary obstruction. In this study, we further investigated this issue.

METHODS

Removable total biliary obstruction (RTBO) was induced in 12 rats. Six of them (group A) received Mn-DPDP (25 mumol/kg). The others (group B) served as control animals. The data from serial magnetic resonance imaging and serum bilirubin tests were compared.

RESULTS

Without Mn-DPDP, a minimal increase of the liver intensity was observed in both groups because of cholestasis. In group A, the intensity of the liver was strongly enhanced with Mn-DPDP but normalized within 48 hr after removal of the obstruction. In both groups, total bilirubin levels increased up to 131.67 mumol/l 2 days after RTBO but rapidly decreased within 4 hr and almost normalized within 24 hr after removal of the obstruction, suggesting a lack of Mn-DPDP influence on the bilirubin level.

CONCLUSION

We found that Mn-DPDP did not cause secondary intrahepatic cholestasis. Retained Mn++ is likely eliminated after restoration of bile flow. These results indicate that Mn-DPDP can be used in patients who have obstructive jaundice as long as it is followed by successful bile drainage.

Biodistribution and excretion of 153Gd-labeled gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid following repeated intravenous administration to rats

RATIONALE AND OBJECTIVES

We investigated the distribution of radioactivity in tissues and organs and its disappearance following repeated intravenous (i.v.) administration of 153Gd-labeled gadolinium ethoxybenzyl diethylenetriamine pentaacetic acid (Gd-EOB-DTPA) to rats.

METHODS

A high total dose of 250 mumol/kg of 153Gd-labeled Gd-EOB-DTPA (a daily injection of 50 mumol/kg is equivalent to 92.5 kBq per animal on 5 consecutive days) was given to conscious rats by fast i.v. injection via a tail vein. The organ distribution and the body elimination into urine and feces were investigated at time points 3, 7, 14, and 21 days following the last injection; five animals were used at each time point. All samples were measured by gamma counting of 153Gd over a 10-min period.

RESULTS

The radioactivity quickly disappeared from the body, mostly through feces. In the liver, no radioactivity could be detected at 3 days postinjection. At 21 days postinjection, only 0.002% of the gadolinium injected was detected, the vast majority (approximately 95%) of which was found in the kidneys.

CONCLUSION

After repeated i.v. administration of a total dose of 250 mumol/kg of 153Gd-labeled Gd-EOB-DTPA, the elimination from the body was found to be 99.998% complete. Only negligible long-term retention of radioactive gadolinium was observed despite the relatively high dose injected. No perceptible evidence for decomplexation of Gd-EOB-DTPA could be found.

Potential role of bile duct collaterals in the recovery of the biliary obstruction: experimental study in rats using microcholangiography, histology, serology and magnetic resonance imaging

Obstructive cholestasis induced in animals at the level of the lobar and common bile ducts is known to be reversible with time. This study was conducted not only to test the hypothesis that formation of bile duct collaterals is responsible for the recovery of biliary obstruction but also to assess the potential of hepatobiliary agent-enhanced magnetic resonance imaging for visualizing cholestasis. A total of 52 rats were divided into three groups with selective biliary obstruction, total biliary obstruction and sham surgery. We studied the evolution of cholestasis by correlating microcholangiographic, histological findings with the results of liver tests and hepatobiliary agent-enhanced magnetic resonance imaging. Lobar cholestasis undetected by liver tests but seen on magnetic resonance imaging as a difference between ligated and unligated lobes, occurred in 15 out of 20 rats subjected to selective biliary obstruction within 48 hr after ligation, and recovered later on as a result of the development of bile duct collaterals. Five rats failed to show local cholestasis as a result of the existence of interlobar accessory bile channels. All 18 total biliary obstruction-treated rats were cholestatic soon after ligation, as confirmed by high serum bilirubin and alkaline phosphatase levels and as documented by poor liver enhancement on magnetic resonance imaging. Cholestasis recovered within 4 wk with normalization of liver enhancement on magnetic resonance imaging as a result of the formation of bile duct collaterals (as demonstrated by microcholangiographic and histological study). Bile duct collateral formation is responsible for the recovery from obstructive cholestasis in rats. A similar mechanism might be present in conditions of bile duct obstruction without cholestasis. Hepatobiliary agent-enhanced magnetic resonance imaging is more sensitive than blood tests in detecting local cholestasis and can be used to monitor noninvasively the evolution of biliary obstruction.

Prolonged positive contrast enhancement with Gd-EOB-DTPA in experimental liver tumors: potential value in tissue characterization

To evaluate the potential of the hepatobiliary magnetic resonance (MR) imaging contrast agent gadolinium EOB-DTPA (ethoxybenzyl diethylenetriaminepentaacetic acid) for the characterization of hepatic tumors, 79 primary and six implanted hepatomas in 38 rats were studied. MR imaging findings after administration of Gd-DTPA (0.3 mmol/kg) and Gd-EOB-DTPA (30 mumol/kg) were correlated with microangiographic and histologic findings. Gd-EOB-DTPA produced a strong liver enhancement, which caused prompt negative contrast enhancement (CE) in all implanted hepatomas and in 77 of 79 primary hepatomas. A positive CE that lasted up to 2 hours was found in two of 79 primary hepatomas, both of which were highly differentiated (grade I) hepatocellular carcinomas (HCCs). The rest were moderately differentiated to undifferentiated HCCs (grades II-IV). Rim enhancement, which corresponded histologically to peritumoral malignant infiltration sequestering normal hepatocytes, was seen around all implanted and some primary hepatomas. Positive tumor CE after administration of Gd-EOB-DTPA in this study is much less frequent but much more specific in comparison with the results of previous studies with manganese-DPDP (N,N'-dipyridoxylethylenediamine-N,N'-diacetate 5,5'-bis[phosphate]). These findings may help further discriminate hepatic tumors.