NUTRITION
Supplementation of selenium reduces chemical hepatocarcinogenesis in male Sprague-Dawley rats

https://doi.org/10.1016/j.jtemb.2009.09.003Get rights and content

Abstract

Selenium is an essential micronutrient mineral found mainly in soils and has been shown to prevent certain cancers in humans and animals. However, the dose and effects of selenium on liver cancer are controversial. The aim of this study was to investigate the effects of sodium selenite (4 mg/kg in drinking water) on chemically induced hepatocarcinogenesis in rats. Hepatocarcinogenesis was induced by a single intraperitoneal injection of diethyl nitrosamine (DEN) (200 mg/kg body weight) and 2 weeks later, the carcinogenic effect was promoted by 2-acetylaminofluorene (2-AAF) (0.02%). 44 Sprague-Dawley rats were divided into 6 groups: negative control, positive control (DEN+2-AAF), pre-selenium group (sodium selenite for 4 weeks, then DEN+2-AAF), pre-selenium control group (sodium selenite for 4 weeks, no DEN or 2-AAF), post-selenium group (sodium selenite for 8 weeks after 4 weeks of DEN injection) and post-selenium control group (sodium selenite for 8 weeks, no DEN or 2-AAF). Hematoxylin and eosin plus Gordon and Sweet’s methods were used to stain liver tissues. The results showed that the number and sizes of hepatic nodules in pre- and post-selenium treatment groups significantly decreased (P<0.05) compared with the positive control. Microscopic analysis of pre- and post-selenium groups showed that the majority of nodules were hyperplastic with preserved liver architecture, whereas the positive control was full of neoplastic nodules with a completely disrupted liver architecture. Hence, pre- and post-selenium treatments can reduce the extent of liver cancer on chemically induced hepatocarcinogenesis in rats.

Introduction

Hepatocellular carcinoma (HCC) is common in the developing countries such as China, Korea and Africa [1]. Although, it is low in the developed countries, recent study of But et al. [2] showed that HCC is increasing in the developed countries such as USA, UK and France. Chronic infection with hepatitis B and C are the major risk factors for HCC worldwide. Other factors that contribute to the formation of HCC include exposure to aflatoxin, alcohol abuse, hemochromatosis, fatty liver disease and androgenic steroid use [3].

Selenium is a naturally occurring mineral element found mostly in soils and rocks. It functions as an essential micronutrient at a level of about 0.1 mg/kg in the animal diet, and selenium becomes toxic at levels of 8–10 mg/kg [4]. It is an essential component of glutathione peroxidase and thioredoxin reductase [5]. Experimental, epidemiological and clinical studies have shown that selenium can protect against the development of certain cancers [6], [7], [8]. A variety of clinical studies from different countries have shown that supplementation of selenium for a certain period of time reduces the incidence of certain cancers [6], [9], [10], [11]. In 1986, Combs and Combs [12] estimated that in more than 100 animal studies for which tumor or pre-neoplastic endpoints had been measured, two thirds of these studies showed reductions in the tumor incidence with half showing reductions of 50% or more. They observed that only a few studies have found selenium to be ineffective. In addition, other researchers have reported the chemoprevention effect of selenium against certain cancers in rodents [7], [13], [14]. Numerous epidemiological studies have shown that cancer patients have lowered selenium level, on average, than healthy controls [8], [15], [16], [17]. To date, the use of selenium in preventing or treating cancers is limited and controversial. Thus, the purpose of this study was to investigate the macro and microscopic effects of pre and post-selenium treatments on chemically induced liver cancer in rats.

Section snippets

Chemicals

Sodium selenite, diethyl nitrosamine (DEN) and 2-acetylaminofluorene (2-AAF) were obtained from Sigma Chemical Co., Germany. Hematoxylin, eosin and silver nitrate from BDH, UK. Paraffin waxes, xylene, denatured ethyl alcohol and formaldehyde from MERCK, Germany.

Animals and diet

Male Sprague-Dawley rats (120–190 g) (6–8 weeks) were obtained from the Laboratory Animal Resource Unit, Faculty of Medicine, Universiti Kebangsaan Malaysia, Kuala Lumpur, Malaysia. They were housed in plastic cages (3–4 rats per cage)

Results

During the entire period of the study, no obvious symptoms or changes in hair, nails or skin were seen among all the groups of rats. Water intakes for all groups were 10.5–12.5 mL per 100 g body weight. However, food intakes differed; treated groups (2, 3 and 5) had an average of 5.30–7.10 g per 100 g body weight whereas untreated groups (1, 4 and 6) had an average of 9.20–11.0 g per 100 g body weight. For unknown reasons, 3 rats died before the end of the study, one from Group 3 (week 4), Group 4

Discussion

The results of this study show that dietary administration of sodium selenite (4 mg/kg) has reduced the extent of liver cancer on chemically induced hepatocarcinogenesis in rats. An interesting finding in this study was that dietary selenium concentration (0.2 mg/kg, which is at the recommended range level) had no effect on the numbers and sizes of liver nodules as seen in the positive control. This might indicate that a high dose of selenium is required to inhibit or slow down the formation of

Acknowledgments

This study was supported by grant from the Ministry of Science, Technology and Innovation (MOSTI), Malaysia (no 05-01-02-SF0014).

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