Comparison of angiotensin converting enzyme inhibitors and angiotensin II type 1 receptor blockade for the prevention of premalignant changes in the liver
Introduction
Liver is the unique organ for studying chemical carcinogenesis in vivo during the early stages of initiated cells as altered foci. It is a frequent site for the development of chemically induced cancer in rodents (Farber, 1984). Experimental hepatocarcinogenesis can be induced by various chemical carcinogens, like diethylnitrosamine (DENA), 2-acetylaminofluorene (2-AAF), aflatoxin B1, etc.
Angiotensin II (Ang II) is the principal effector molecule of the renin angiotensin system (RAS). The key elements of the RAS, angiotensin converting enzyme (ACE) and angiotensin II receptors, are present in normal liver tissue and there is a major up-regulation of the system in the bile duct ligated liver (Paizis et al., 2002). The documentation of a significant relationship between key elements of the RAS; Ang-II, angiotensin II type 1 receptor (AT1R) and ACE in hepatic fibrosis suggested that Ang-II may be a mediator of fibrosis in the liver. In addition to fibrosis development, Ang II has been shown to induce neovascularization in experimental models both in vitro and in vivo (Pupilli et al., 1999) and it selectively increased the blood flow in the tumor (Hori et al., 2000).
Angiogenesis is now widely recognized as playing a pivotal role in tumor development, including hepatocellular carcinoma (HCC) (Ferrara and Alitalo, 1999). It is now recognized that Ang II exerts a strong pro-angiogenic activity. Accumulating evidences showed that angiogenesis is of great importance for many pathological events, including tumor growth (Yoshiji et al., 2001). Ang II induces angiogenesis in several types of cells, including HCC and activity of serum ACE was a tumor marker of HCC patients (Kardum et al., 1999, Yoshiji et al., 2002). It has been previously reported that clinically used ACE inhibitor; perindopril induced a strong anti-angiogenic activity and inhibited the murine HCC growth in transgenic animal model (Yoshiji et al., 2001). In addition, it has been shown that perindopril attenuated hepatocarcinogenesis induced by feeding choline deficient L-amino acid-defined diet (Yoshiji et al., 2002).
To investigate and compare the potential protective properties of ACE inhibitors; captopril, perindopril and AT1R blocker, losartan on liver carcinogenesis, we used the diethylnitrosamine (DENA) rat carcinogenesis model. DENA is a well known potent hepatocarcinogenic agent present in tobacco smoke, water, cured and fried meals, cheddar cheese, agricultural chemicals, cosmetics and pharmaceutical products (Sullivan et al., 1991, Reh and Fajen, 1996, Brown, 1999. DENA is known to induce damage in many enzymes involved in DNA repair and is normally used to induce liver cancer in experimental animal models (Bhosale et al., 2002). After its use, many studies have showed a series of microscopic lesions called “foci” and “nodules” which have been designated “preneoplastic” or “premalignant” (Pitot and Sirica, 1980). During the process of neoplastic transformation, various histochemical and biochemical marker enzymes and protein antigens are expressed depending upon the stages and magnitude of neoplasia. These markers are frequently considered as surrogate end-point biomarkers in rat liver carcinogenesis model (Tatematsu et al., 1988).
AT1-R mediates most of the biological effects of Ang II. These effects are completely suppressed by AT1-R blocker (ARB). To date and up to our knowledge, there are no published studies investigating the role and the possible mechanism of AT1R blocker; losartan on chemical hepatocarcinogenesis. Therefore, the present work was undertaken to investigate and compare the possible anti-carcinogenic activity of suppression of RAS using captopril; perindopril and blocking of Ang II type 1 receptor using AT1R blocker; losartan.
Section snippets
Chemicals
Diethylnitrosamine (DENA), captoprol, perindopril, losartan and carbon tetrachloride (CCl4) were purchased from Sigma (St. Louis, MO, USA). All remaining chemicals were of the highest grade commercially available.
Animals
Male Swiss albino rats, weighing 200–250 g were used. They were obtained from the Experimental Animal Care Center of King Saud University, Riyadh, K.S.A. Animals were maintained under standard conditions of temperature 24 ± 1 °C and 55 ± 5% relative humidity with regular 12 h light:12 h dark
Statistical analysis
Data are expressed as means ± SEM. Statistical comparison between different groups were done using one way analysis of variance (ANOVA) followed by Tukey–Kramer multiple comparison test, to judge the difference between various groups. Significance was accepted at P < 0.05.
Efficacy of ACE inhibitors and AT1R blocker on the changes in serum hepatic tumor markers induced by experimental hepatic carcinogenesis
Experimental hepatic carcinogenesis initiated by administration of a single dose of DENA (200 mg/kg i.p.) and promoted by CCl4 (2 ml/kg i.g) induced significant 5- and 2.5-fold increments in both serum hepatic tumor markers: α-feto protein (AFP) and carcinoembryonic antigen (CEA) respectively as compared with control group.
Oral treatment of normal rats with captopril (50 mg/kg/day), perindopril (2 mg/kg/day) and losartan (10 mg/kg/day) alone did not show any significant alteration in the measured
Discussion
The present study demonstrates a potential role of ACE inhibitors; captopril, perindopril and AT1R blocker losartan in limiting preneoplastic changes in DENA initiated and CCl4 promoted experimental hepatocarcinogenesis in rats. Prior treatment with the selected doses of the drugs has been found to abate the development of preneoplastic lesions in carcinogen-challenged rat hepatocytes. These results thus indicate the chemo-preventive efficacy of the chosen drugs at the selected doses in
Conflict of interest statement
The authors state that they have no conflict of interest that might influence the design, interpretation or conclusion of this study.
Acknowledgements
This work was supported by King Abdul-Aziz City for Science and Technology (KACST: GSP-18-13) and an Operating grant from Research Center College of Pharmacy, King Saud University (CPRC 229).
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