1,4-Bis[2-(3,5-dichloropyridyloxy)]benzene induces substantial hyperplasia in fibrotic mouse liver

Ductular reaction correlates with fibrogenesis but does not contribute to liver regeneration in experimental fibrosis models

Background and aims

Ductular reaction is a standard component of fibrotic liver tissue but its function is largely unknown. It is supposed to interact with the matrix producing myofibroblasts and compensate the declining regenerative capacity of hepatocytes. The relationship between the extent of fibrosis—ductular reaction, proliferative activity of hepatocytes and ductular reaction were studied sequentially in experimental hepatic fibrosis models.

Methods

Liver fibrosis/cirrhosis was induced in wild type and TGFβ overproducing transgenic mice by carbon tetrachloride and thioacetamide administration. The effect of thioacetamide was modulated by treatment with imatinib and erlotinib. The extent of ductular reaction and fibrosis was measured by morphometry following cytokeratin 19 immunofluorescent labeling and Picro Sirius staining respectively. The proliferative activity of hepatocytes and ductular reaction was evaluated by BrdU incorporation. The temporal distribution of the parameters was followed and compared within and between different experimental groups.

Results

There was a strong significant correlation between the extent of fibrosis and ductular reaction in each experimental group. Although imatinib and erlotinib temporarily decreased fibrosis this effect later disappeared. We could not observe negative correlation between the proliferation of hepatocytes and ductular reaction in any of the investigated models.

Conclusions

The stringent connection between ductular reaction and fibrosis, which cannot be influenced by any of our treatment regimens, suggests that there is a close mutual interaction between them instead of a unidirectional causal relationship. Our results confirm a close connection between DR and fibrogenesis. However, since the two parameters changed together we could not establish a causal relationship and were unable to reveal which was the primary event. The lack of inverse correlation between the proliferation of hepatocytes and ductular reaction questions that ductular reaction can compensate for the failing regenerative activity of hepatocytes. No evidences support the persistent antifibrotic property of imatinib or erlotinib.

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.

Caffeine increases Nr1i3 expression and potentiates the effects of its ligand, TCPOBOP, in mice liver

<p>Caffeine is one of the world's most consumed substances. It is present in coffee, green tea and guarana, among others. The xenobiotic-sensing nuclear receptor subfamily 1, group I, member 3 (Nr1i3), also known as the Constitutive Androstane Receptor (Car) is a key regulator of drug metabolism and excretion. No consistent description of caffeine effects on this receptor has been described. Thus, to unravel the effects of caffeine on this receptor, we performed experiments in mice. First, C57Bl/6 mice that were treated daily with caffeine (50 mg/kg) for 15 days presented a slight but significant increase in Nr1i3 and Cyp2b10 gene expression. A second experiment was then performed to verify the effects of caffeine on TCPOBOP (1,4-<italic>bis</italic>-[2-(3,5-dichloropyridyloxy)]benzene, 3,3′,5,5′-tetrachloro-1,4-<italic>bis</italic>(pyridyloxy)benzene), the most potent agonist known for mice Nr1i3. Interestingly, caffeine potentiated TCPOBOP pleiotropic effects in mice liver, such as hepatomegaly, hepatotoxicity, hepatocyte proliferation and loss of cell-to-cell communication through gap junctions. In addition, caffeine plus TCPOBOP treatment increased liver gene expression of Nr1i3 and Cyp2b10 comparing with only caffeine or TCPOBOP treatments. Together, these results indicate that caffeine increases the expression of Nr1i3 in mice liver, although at this point it is not possible to determine if Nr1i3 directly or indirectly mediates this effect.</p>