Reproducible production of thioacetamide-induced macronodular cirrhosis in the rat with no mortality

Abstract

Background/Aims: Hepatotoxin-induced rat models of liver cirrhosis are limited by the wide heterogeneity of cirrhosis produced. The present study developed a modified, reliable, and reproducible technique by which hepatic and systemic responses to thioacetamide during induction of cirrhosis were monitored by weekly weight changes.

Methods: Male Wistar rats (200–230 g) were divided into three groups. Group 1 (n=20) received continuous administration of 0.03% (w/v) thioacetamide in the drinking water for 12 weeks. Group 2 (n=20) received the same concentration of 0.03% thioacetamide as an initial concentration that was modified according to weekly weight changes in response to thioacetamide during the induction of cirrhosis. Group 3 (n=6) received normal water and served as controls.

Results: Mortality of Group 1 was 30% and the production of cirrhosis was only 45%. In contrast, there were no deaths in Group 2 and well-developed macronodular cirrhosis was found in 90% of the rats which was associated with significant portal hypertension, as indicated by increased portal venous pressure (13.6±0.4 vs. 9.1±0.3 mmHg, cirrhotic vs. control, respectively, P<0.01, Student's unpaired t-test).

Conclusions: Variations in responses to thioacetamide can be easily monitored by weekly weight changes to reduce mortality to zero and simultaneously increase the production and quality of cirrhosis induced in rats.

Introduction

Animal models of liver cirrhosis are important for research into the underlying mechanisms or treatments associated with this disease. Currently, cirrhosis is mainly induced either by the ligation of common bile duct (CBDL) [1] or by application of hepatotoxins such as carbon tetrachloride (CCl₄) or thioacetamide (TAA) [2]. The CBDL model is traumatic and, in particular, significant hepatic fibrosis in this model may be minimal or absent [3]. In contrast, cirrhosis induced by hepatotoxins, when successful, is stable and irreversible, and the unwanted effects of circulating hepatotoxins can be minimized simply by ceasing drug administration for 1–3 weeks [4], [5].

Previous experience has shown that TAA-induced cirrhosis was associated with a relatively lower mortality of 35% in contrast to 50% with CCl₄-induced cirrhosis (unpublished data). It was also reported that regenerative nodules and liver fibrosis were more prominent in the TAA model than in the CCl₄ model, and that histology of the TAA model was more akin to human cirrhosis [6], [7]. In addition, due to the low vaporization of TAA, continuous administration of 0.03% TAA in the drinking water is a convenient and non-invasive method for induction of cirrhosis in this model [6], [8].

In common with other hepatotoxin-induced models, results of the TAA model have been heterogeneous during the stages and development of cirrhosis and this has limited its application. The observation that a given dose of a hepatotoxin could be fatal to one rat but had little effect upon the liver of another rat has indicated the degree of variation in hepatic sensitivity between individual rats [9]. It appeared that rats could only become cirrhotic if the doses received were sufficiently high to induce hepatic damage but low enough to avoid death from acute liver failure. The exact magnitude of the safety margin for each individual rat between production of sufficient cirrhosis and death is unpredictable, and induction of cirrhosis may be often conducted blind if no information regarding hepatic and systemic responses to the toxin is available.

The usual methods of assessing liver damage are by repeated hepatic biopsy and serial blood sampling for liver function tests. These techniques are traumatic and highly dangerous to rats with severe chemical hepatitis or necrosis due to clotting deficiencies. However, Proctor and Chatamra [10] described a simple approach to monitor the variation in hepatic responses to intragastric CCl₄ by daily weight changes. In the present study, cirrhosis was induced in rats by TAA with an initial concentration of 0.03% (w/v) in the drinking water. The aims of the present study were to determine (i) individual variation in response to the fixed concentration of 0.03% TAA, (ii) the optimal range of weight changes that could be served as a guideline for the successful induction of cirrhosis, and (iii) the suitable initial concentration of TAA for induction of cirrhosis by using a modified method.