The effects of selenium on the emergence of aflatoxin B1-induced enzyme-altered foci in rat liver

Research Progress on the Toxic Antagonism of Selenium Against Mycotoxins

Animal feed is prone to becoming infected with molds during production and storage, resulting in secondary metabolite mycotoxins, such as aflatoxin B₁ (AFB₁), T-2 toxins, deoxynivalenol (DON), and ochratoxin A (OTA), which are harmful to humans and animals. Selenium is an essential trace element for humans and animals, and it is also an effective antioxidant. Many studies have shown that selenium can reduce the damage caused by mycotoxins in animals. This article reviews the current literature on the antagonistic effects of selenium on AFB₁, T-2, DON, and OTA toxicity.

Dietary antioxidants in the prevention of hepatocarcinogenesis: a review

In this review, the role of dietary antioxidants in the prevention of hepatocarcinogenesis is examined. Both human and animal models are discussed. Vitamin C, vitamin E, and selenium are antioxidants that are essential in the human diet. A number of non-essential chemicals also contain antioxidant activity and are consumed in the human diet, mainly as plants or as supplements, including beta-carotene, ellagic acid, curcumin, lycopene, coenzyme Q(10), epigallocatechin gallate, N-acetyl cysteine, and resveratrol. Although some human and animal studies show protection against carcinogenesis with the consumption of higher amounts of antioxidants, many studies show no effect or an enhancement of carcinogenesis. Because of the conflicting results from these studies, it is difficult to make dietary recommendations as to whether consuming higher amounts of specific antioxidants will decrease the risk of developing hepatocellular carcinoma.

Selenium in chronic liver disease

In order to assess the role of selenium (Se) in chronic liver disease, we have measured serum, urinary and hepatic selenium in a range of liver diseases and correlated them with nutritional status and conventional liver biochemistry. Serum Se levels (microgram/l +/- S.D.) were significantly lower in both alcoholic (63.6 +/- 18.2, p less than 0.0001) and non-alcoholic liver disease (NALD) (60.6 +/- 13.6, p less than 0.0001) compared to healthy controls (87.8 +/- 21.2) and non-malignant 'disease controls' (80.3 +/- 19.1). Hepatic Se levels (microgram/g of dry weight) were also reduced in both ALD (0.568 +/- 0.647, p less than 0.005) and NALD (0.863 +/- 0.308, p less than 0.005) compared to controls (1.227 +/- 0.296), 24-h urinary Se excretion (microgram) in ALD (24.6 +/- 10.7) and NALD (29.0 +/- 14.3) was similar to controls (30.3 +/- 8.7). Serum Se showed a highly significant positive correlation with albumin (p less than 0.001) in both ALD and NALD. Serum levels were also significantly correlated with anthropometric measurements. Dietary assessment of patients with primary biliary cirrhosis and low serum Se levels did not show a reduced dietary intake. Our data show that Se levels are low in liver disease irrespective of aetiology and suggest that these low levels are more likely to be related to overall nutritional status than to dietary intake.

The role of necrosis in hepatocellular proliferation and liver tumors

A sequence of events which appear to be common in the development of cancer in all mammalian species includes atrophy, hyperplasia, and neoplasia. Evidence to date suggests that cell death (necrosis) is an integral, perhaps essential, factor in the initiation and maintenance of the process but the extent to which necrosis is involved, and the nature of that participation is unclear. Choline deficient B6C3F1 mice have been used to accentuate and investigate necrosis and the development of liver neoplasia following exposure to aflatoxin B1. The binding of AFB1 to DNA correlates with the level of acute necrosis and the early appearance of foci of alteration and later, tumor development. Adducts of GSH-DNA varied as do other parameters including products of peroxidation, but the relation of these variables to necrosis and cancer are unclear at present. These parameters are currently under study.

Enzymes of glutathione metabolism as biochemical markers during hepatocarcinogenesis

Enzymes of glutathione metabolism, particularly gamma-glutamyltransferase (GGT) and glutathione S-transferase (GST), play a role in multistage hepatocarcinogenesis. The enhanced expression of these enzymes in preneoplastic altered hepatic foci, nodules, and hepatocellular carcinomas has been demonstrated after treatment with a variety of initiating and promoting agents. Glutathione is necessary for the detoxification of xenobiotics and carcinogens and for cell replication. Induction of GGT in altered hepatocytes may permit these cells to utilize extracellular glutathione to preserve their internal glutathione levels. GST induction allows glutathione utilization for the protection of the altered hepatocyte in an environment of exposure to xenobiotics, such as promoting agents. Thus, the combined effects of GGT and GST, in a toxic environment, may provide for the enhanced proliferation observed in preneoplastic hepatocytes. New clinical and research opportunities may involve the use of GGT and the placental isozyme of GST (PGST) as markers of preneoplasia and neoplasia in humans. Many factors, such as hormones, diet, and exposure to initiating and promoting agents, influence GGT and GST expression. The recent cloning of cDNAs to GGT and PGST offers opportunities for the study of factors involved in the genetic expression of these two enzymes. Coupled with the use of hepatocyte culture and transplantation, the factors involved at the molecular level in the creation of hepatocellular neoplasia may be discovered.