Reproducible production of thioacetamide-induced macronodular cirrhosis in the rat with no mortality
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cirrhosis was associated with a relatively lower mortality of 35% in contrast to 50% with CCl4-induced cirrhosis (unpublished data).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.
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Animals
Male Wistar rats (200–230 g) were divided into three groups. Group 1 (n=20) received continuous administration of 0.03% TAA (Sigma, Poole, UK) in the drinking water for 12 weeks. Group 2 (n=20) received the same concentration of 0.03% TAA as an initial concentration that was subsequently modified according to weight changes in response to TAA during the induction of cirrhosis. Thus, TAA concentrations were reduced with excess weight loss and vice versa. Group 3 (n=6) received normal water and
Induction of cirrhosis with minimal weight monitoring (Group 1)
The initial TAA concentration of 0.03% was modified according to the individual variation in hepatic responses to TAA, as monitored by weekly changes in body weight.
For convenience, two extremes of weight changes obtained from two individual rats in Group 1 are shown in Fig. 1. Rat 1 had a minimal response to 0.03% TAA and Rat 2 a maximal response that was fatal. The shadowed area represents the range of weight changes from nine cirrhotic rats confirmed histologically at the end of this
Discussion
In the present study, cirrhosis was induced by oral administration of TAA in the drinking water for 12 weeks. The initial 0.03% TAA was subsequently adjusted by weekly weight changes in response to TAA during the development of cirrhosis. This method was effective in the induction of cirrhosis with 90% of rats showing macronodular cirrhosis on macroscopic and microscopic examination. No deaths occurred during induction of cirrhosis.
The administration of TAA in the drinking water had several
Acknowledgements
We would like to thank the British Council and the KC Wong Education Foundation for their assistance in partially financing this research.
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