Review of experimental models for inducing hepatic cirrhosis by bile duct ligation and carbon tetrachloride injection

PURPOSE: To present a review about a comparative study of bile duct ligation versus carbon tetrachloride Injection for inducing experimental liver cirrhosis. METHODS: This research was made through Medline/PubMed and SciELO web sites looking for papers on the content “induction of liver cirrhosis in rats”. We have found 107 articles but only 30 were selected from 2004 to 2011. RESULTS: The most common methods used for inducing liver cirrhosis in the rat were administration of carbon tetrachloride (CCl4) and bile duct ligation (BDL). CCl4 has induced cirrhosis from 36 hours to 18 weeks after injection and BDL from seven days to four weeks after surgery. CONCLUSION: For a safer inducing cirrhosis method BDL is better than CCl4 because of the absence of toxicity for researches and shorter time for achieving it.


Introduction
Liver cirrhosis (LC) is considered a public health, according to World Health Organization, about 800 thousand people die from LC every year.Only in United States LC is responsible for around 27 thousand deaths per year, representing a mortality rate of 9.2 per 100,000, placing it as the 12 th overall cause of death [1][2][3] .
Nowadays major research centers focus on studying LC, its mechanisms and its behavior, complications and possible treatments.For that reason it has been developed, efficient experimental models of induction of LC in rats.The two most common methods used for experimental LC are the administration of carbon tetrachloride (CCl4) and the bile duct ligation (BDL) 7- 9 .Our aim is to present a comparative study of bile duct ligation versus carbon tetrachloride injection for inducing experimental liver cirrhosis

Methods
This research was made through Medline/PubMed and SciELO web sites looking for papers on the content "induction of liver cirrhosis in rats".We found 107 articles but only 30

Results
The main methods of induction of LC in rats are the administration of carbon tetrachloride and bile duct ligation.
Below are shown induction of cirrhosis by CCl4, dosage of the drug, time for inducing cirrhosis, main test assessment with the method and their results (Table 1) and for bile duct ligation (Table 2).

Discussion
The main methods of induction of LC in rats are the administration of carbon tetrachloride (CCl4) 4 and bile duct ligation (BDL) 11 .CCl4 is one of the most used methods nowadays however it is considered an extremely toxic method 5  (2) Production of free radicals; and (3) Leakage of degradative enzymes from the dying and injured cells.Activated resident Kupffer cells and the neutrophils recruited at the site of parenchymal liver injury are considered as the primary culprits in damaging surrounding healthy cells as the result of nonspecific action.However, evidence suggests that the contribution of the inflammatory cells does not or is not sufficient to mediate progression of injury.
The second theory regarding progression of injury is production of free radicals and oxidative stress, and subsequent lipid peroxidation that propagates injury.Though the antioxidants prevent/delay the tissue damage partially, progression of injury still occurs.The inhibition of lipid peroxidation by antioxidants only decreases the initial injury of CCl4, blocking lipid peroxidation fails to prevent progression of injury and subsequent lethality 45 .By 8 weeks, a micronodular cirrhosis takes place 31 .It has been used mainly by intraperitoneal injection 12 or oral administration 20 , the dosage 0,2 to 5ml/kg and LC is achieved between 36 hours to 18 weeks 15,20,11,24 .
BDL is a safer method comparing to the CCl4.When the BDL is done, it provides an acute obstructive jaundice in two weeks, and progression to cirrhosis in 4 or 6 weeks 9,10 .BDL stimulates the proliferation of biliary epithelial cells and oval cells (which are hepatocyte progenitors), resulting in proliferating bile ductules with an accompanying portal inflammation and fibrosis 43 .
Cholangiocyte proliferation started after BDL at the edge of the portal tract.During the first week from BDL the hepatic microcirculation did not show any alterations with respect to the normal liver 46 .Using this method LC is achieved between seven days to four weeks 17,26 .

Conclusions
Based in our broadly review we concluded that LC can be induced by CCl4 and BDL, however the manipulation of CCl4 can be dangerous for the researcher with risk of inducing liver tumor.BDL is a safer method than CCl4 and cirrhosis could be induced in rats in average mean time of two weeks.
from 2004 to 2011 were selected.The inclusion criteria were: only rats; bile duct ligation and injection of carbon tetrachloride.Histopathologic examination for confirming cirrhosis; Time of inducing cirrhosis.The exclusion criteria were: large animals cirrhosis; others rodent animals; drug inducing cirrhosis such as dimethylnitrosamine; thiocetamide; butylhydroperoxide.Others drugs association methods: buprenorphine with reduction of portal inflow over a stent inserted in the right renal artery; Others methods: unrestricted flow using an aortic-portal segment; orthotopic liver transplantation with unrestricted portal arterialisation.Thioacetamide associated with partial hepatectomy.
. Several important basic mechanisms of tissue damages induced by CCl4 have emerged, involving metabolic activation, reactive free radical metabolites, lipid peroxidation, covalent binding and disturbance of calcium homeostasis.The CCl4 administration results in hepatocyte damage, necrosis, inflammation, and fibrosis, which spreads to link the vascular structures that feed into and drain the hepatic sinusoid (the portal tract and central vein radicle, respectively) 3,39 .It activates the hepatic stellate cell (HSC) inducing hepatocyte apoptosis and zone III necrosis 40 .Continuous administration of CCl4 can provide moderate cell necrosis and fatty infiltration in four weeks.The CCl4 is excreted from the body within the first 24 hour by conjugation reaction mediated by phase.In the literature, three mechanisms have been proposed as the possible explanations for progression of injury: (1) Contribution of inflammatory cells;