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.
Introduction
An efficient repair system of the liver tissue is required to ensure its proper functioning. The ability of the liver to regenerate itself as a response to loss of hepatic tissue has been known for a long time. This regenerative capacity may be impaired in cases of small-for-size liver grafts, liver resection (eg, tumor surgery), or chronic liver disease and acute liver failure often requiring liver transplant . Thus, there is a need for methods to enhance the intrinsic regeneration potential of the liver, enabling partial transplants, and to propagate hepatocytes ex vivo for use in cell transplant .
Whereas molecular mechanisms of liver cell growth and efficacy of mitogens can be studied in hepatic cell line-based in vitro systems, complex processes such as liver development or regeneration require in vivo models. The partial hepatectomy procedure in small rodents has constituted the most popular liver regeneration model. After surgical removal of three of the five liver lobes, the cells of the remaining two lobes proliferate until the liver regains its original size. Complete recovery takes approximately 8 days in rodents .
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Materials and Methods
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Animals
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Partial Hepatectomy
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TCPOBOP Treatment
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MRI
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MR Image Evaluation
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Liver Regeneration Index
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Liver regeneration index(%)=100×(Vt−VD1)/(Vbas−VD1) Liver regeneration index
(
%
)
=
100
×
(
V
t
−
V
D
1
)
/
(
V
b
a
s
−
V
D
1
)
with V t the liver volume at a given time point t, V D1 the liver volume on day 1 after partial hepatectomy, and V bas the liver volume at baseline prior to surgery. This index removes two possible sources of variance in the study, namely differences in initial liver volume and the volume of liver excised.
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Postmortem Analyses: Liver Weight and Histology
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Liver Function Tests
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Statistical Analyses
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Results
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TABLE 1
Markers of Liver Function in the Blood Serum (Means ± Standard Deviation) on Day 9 After Hepatectomy
Parameter Vehicle TCPOBOP T-Prot (g/L) 55.4 ± 3.8 50.4 ± 2.3 (52.0–61.0) (48.0–54.0) Alb (g/L) 25.8 ± 1.5 22.6 ± 1.1 (24.0–28.0) (21.0–24.0) T-Bil (µmol/L) 8.8 ± 1.6 7.8 ± 4.1 (7.0–11.0) (5.0–15.0) AST (IU/L) 35.2 ± 5.9 47.0 ± 10.6 (29.0–45.0) (37.0–63.0) ALT (IU/L) 20.4 ± 3.0 60.0 ± 37.4 (17.0–24.0) (18.0–103.0)
Alb, albumin; ALT, alanine aminotransferase; AST, aspartate aminotransferase; T-Bil, total bilirubin; T-Prot, total protein.
The range of values obtained for a given parameter is provided in parentheses.
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Discussion and Conclusions
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Acknowledgments
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