Modulation of aflatoxin B1-induced glutathione S-transferase placental form positive hepatic foci by pretreatment of rats with phenobarbital and buthionine sulfoximine

Protective Effects of Essential Oils as Natural Antioxidants against Hepatotoxicity Induced by Cyclophosphamide in Mice

Clinical application of cyclophosphamide (CP) as an anticancer drug is often limited due to its toxicity. CP is metabolized mainly in the liver by cytochrome P450 system into acrolein which is the proximate toxic metabolite. Many different natural antioxidants were found to alleviate the toxic effects of various toxic agents via different mechanisms. Therefore, the present study aimed at investigating the role of essential oils extracted from fennel, cumin and clove as natural antioxidants in the alleviation of hepatotoxicity induced by CP through assessment of hepatotoxicity biomarkers (AST, ALT, ALP), histopathology of liver tissues as well as other biochemical parameters involved in the metabolism of CP. The data of the present study showed that treatment of male mice with cyclophosphamide (2.5 mg/Kg BW) as repeated dose for 28 consecutive days was found to induce hepatotoxicity through the elevation in the activities of AST, ALT, and ALP. Combined administration of any of these oils with CP to mice partially normalized the altered hepatic biochemical markers caused by CP, whereas administration of fennel, clove or cumin essential oils alone couldn't change liver function indices. Moreover, CP caused histological changes in livers of mice including swelling and dilation in sinusoidal space, inflammation in portal tract and hepatocytes, as well as, hyperplasia in Kuppfer cells. However, co-administration of any of the essential oils with CP alleviated to some extent the changes caused by CP but not as the normal liver. CP was also found to induce free radical levels (measured as thiobarbituric acid reactive substances) and inhibited the activities of superoxide dismutase, glutathione reductase, and catalase as well as activities and protein expressions of both glutathione S-transferase (GSTπ) and glutathione peroxidase. Essential oils restored changes in activities of antioxidant enzymes (SOD, CAT, GR, GST, and GPx) caused by CP to their normal levels compared to control group. In addition, treatment of mice with CP was found to induce the protein expression of CYP 3A4, 2B1/2, 2C6, 2C23. Moreover, the present study showed that essential oils reduced the expression of CYPs 2E1, 3A4 but could not restore the expression of CYP 2C6 and 2C23 compared to CP-treated mice. Interestingly, pretreatment of mice with essential oil of clove was found to restore activities of DMN-dI, AHH, and ECOD which were induced by CP to their normal control levels. It is concluded that EOs showed a marked hepatoprotective effect against hepatotoxicity induced by CP. In addition, co-administration of CP with any of these oils might be used as a new strategy for cancer treatment to alleviate the hepatotoxicity induced by CP.

Protective effects of coffee against induction of DNA damage and pre-neoplastic foci by aflatoxin B₁

SCOPE

Aim of the study was to investigate the protective properties of coffee towards aflatoxin B₁ (AFB₁) induced formation of pre-neoplastic hepatic foci and the identification of the constituents and molecular mechanisms that account for these effects.

MATERIALS AND METHODS

Rats consumed three different brews and were subsequently treated with AFB₁ (0.75 mg/kg b.w. intraperitoneally). Ten weeks later, the numbers and areas of hepatic foci were determined. Furthermore, the impact of the brews on AFB₁-induced DNA damage was quantified in single cell gel electrophoresis assays and the activities of drug metabolising enzymes and glutathione-related parameters were monitored. Additionally, single cell gel electrophoresis assay experiments were conducted with pure caffeine.

CONCLUSION

All brews reduced the frequencies of the hepatic foci. The most pronounced protection (reduction 82%) was seen with the caffeine containing metal and paper filtered brews. DNA migration was reduced between 65 and 75% with the caffeine containing brews. In additional experiments, clear protective effects were found with caffeine at dose levels that corresponded to those contained in the coffee. This observation indicates that the alkaloid accounts partly for the protective effects of coffee. Furthermore, our findings indicate that induction of UDP-glucuronosyltransferase contributes to the chemopreventive effects of coffee since all brews increased the activity of this detoxifying enzyme.

Protective Effect of Korean Red Ginseng against Aflatoxin B1-Induced Hepatotoxicity in Rat

Korean red ginseng (KRG), the steamed root of Panax ginseng Meyer, has a variety of biological properties, including anti-inflammatory, antioxidant and anticancer effects. Aflatoxin B1 (AFB1) produced by the Aspergillus spp. causes acute hepatotoxicity by lipid peroxidation and oxidative DNA damage, and induces liver carcinoma in humans and laboratory animals. This study was performed to examine the protective effects of KRG against hepatotoxicity induced by AFB1 using liver-specific serum marker analysis, histopathology, and terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling. In addition, to elucidate the possible mechanism of hepatoprotective effects, superoxide dismutase, catalase, glutathione peroxidase, and malondialdehyde were analyzed. Rats were treated with 250 mg/kg of KRG (KRG group) or saline (AFB1 group) for 4 weeks and then received 150 μg/kg of AFB1 intraperitoneally for 3 days. Rats were sacrificed at 12 h, 24 h, 48 h, 72 h, or 1 wk after AFB1 treatment. In the KRG pre-treatment group, serum alanine aminotransferase, aspartate aminotransferase, and malondialdehyde levels were low, but superoxide dismutase, catalase, and glutathione peroxidase activities were high as compared to the AFB1 alone group. Histopathologically, AFB1 treatment induced necrosis and apoptosis in hepatocytes, and led to inflammatory cells infiltration in the liver. KRG pre-treatment ameliorated these changes. These results indicate that KRG may have protective effects against hepatotoxicity induced by AFB1 that involve the antioxidant properties of KRG.

N-Nitrosodimethylamine changes the expression of glutathione S-transferase in the liver of male mice: The role of antioxidants

The present study investigated the protective effect of gossypol, selenium, zinc, or glutathione (GSH) against dimethylnitrosamine (DMN)-induced hepatotoxicity in the livers of male mice. The expression and the activity of glutathione S-transferase (GST), levels of GSH, and free radicals (malondialdehyde (MDA)), as well as the activity of glutathione reductase were determined after the treatment of mice for seven consecutive days with low or high doses of gossypol, selenium, zinc, or GSH. In experimental groups, DMN was administered as a single dose for 2 h after the repeated dose treatments of mice for seven consecutive days with each antioxidant. DMN reduced the expression and inhibited the activity of GST. However, repeated treatments of mice with low-dose gossypol or high dose of either selenium or GSH followed by a single dose of DMN induced the expression and the activity of GST. In contrast, low-dose treatments of mice with zinc, selenium, or GSH followed by a single dose of DMN reduced the expression and the activity of GST compared to either control or DMN-treated groups. In addition, high-dose treatment with either gossypol or selenium markedly induced the levels of GSH compared to either control or DMN-treated groups. Interestingly, pretreatment of mice with high dose of either gossypol or selenium for seven consecutive days followed by a single dose of DMN decreased the levels of MDA, whereas DMN induced such levels. It is concluded that high dose of either gossypol or selenium is a stronger protector than zinc and GSH in ameliorating the toxic effects of DMN.

A preliminary operational classification system for nonmutagenic modes of action for carcinogenesis

This article proposes a system of categories for nonmutagenic modes of action for carcinogenesis. The classification is of modes of action rather than individual carcinogens, because the same compound can affect carcinogenesis in more than one way. Basically, we categorize modes of action as: (1) co-initiation (facilitating the original mutagenic changes in stem and progenitor cells that start the cancer process) (e.g. induction of activating enzymes for other carcinogens); (2) promotion (enhancing the relative growth vs differentiation/death of initiated clones (e.g. inhibition of growth-suppressing cell-cell communication); (3) progression (enhancing the growth, malignancy, or spread of already developed tumors) (e.g. suppression of immune surveillance, hormonally mediated growth stimulation for tumors with appropriate receptors by estrogens); and (4) multiphase (e.g., "epigenetic" silencing of tumor suppressor genes). A priori, agents that act at relatively early stages in the process are expected to manifest greater relative susceptibility in early life, whereas agents that act via later stage modes will tend to show greater susceptibility for exposures later in life.

Synthesis of allylthiopyridazine derivatives and inhibition of aflatoxin B1-induced hepatotoxicity in rats

Five kinds of allylthiopyridazine derivatives were synthesized and their chemoprotective activities examined in rats exposed to aflatoxin B1-toxicant. Rats were pretreated with five allylthiopyridazine derivatives at daily oral doses of 50 mg/kg for 10 consecutive days, and during this period with one or three repeated doses of the potent hepatotoxin, aflatoxin B1. The hepatoprotective effects of the allylthiopyridazine derivatives against aflatoxin B1 (1 mg/kg, three times at intervals of 3 days, i.p., or at 3 mg/kg, once at final days, i.p.) administration were showed the significantly normal as compared with control in body and liver weights. Aspartate aminotransferase and alanine aminotransferase levels were markedly elevated after aflatoxin B1 administration, and pretreatment with allylthiopyridazine derivatives, before aflatoxin B1 administration, resulted in decreased levels of these enzymes. In addition, the allylthiopyridazine derivatives, K6 (3-methoxy-), K8 (3-chloro-), K16 (3-ethoxy-) and K17 (3-n-propoxy), induced elevated hepatic GSH levels. Four kinds of allylthiopyridazine derivatives investigated were effective against aflatoxin B1-induced hepatotoxicity.

Chemoprevention of aflatoxin B1-initiated and carbon tetrachloride-promoted hepatocarcinogenesis in the rat by green tea

Chemoprevention of hepatocarcinogenesis by green tea (GT) has been examined in young male Fischer rats fed AIN-76A diet with aflatoxin B1 (AFB1) and CCl4 as the initiator and promoter, respectively. Animals were administered AFB1 (0.25 mg/kg body wt ip) twice a week for 2 weeks, and 2 weeks later, CCl4 was injected (0.8 ml/kg body wt ip) once per week for 11 weeks. Rats given 0.5% GT in their drinking water before and during initiation (0-4 wk) or during promotion (6-16 wk) or throughout the experimental period were sacrificed 24 hours after the last dose of CCl4. Bromodeoxyuridine incorporation as a measure of cell proliferation and glutathione S-transferase placentalform- and gamma-glutamyl transpeptidase-positive hepatic foci were analyzed by histochemical methods. Feeding of GT during initiation or promotion inhibited the number of glutathione S-transferase placental form- and gamma-glutamyl transpeptidase-positive hepatic foci by 30-40% and the area and volume by 50%. GT treatment throughout the period inhibited the number of both types of hepatic foci by 60% and the area and volume by 75-80%. Cell proliferation was inhibited 35% by GT given during promotion, whereas inhibition was 65% when GT was given during initiation or throughout the period. These results indicate that GT feeding inhibits initiation and promotion steps of AFB1 hepatocarcinogenesis and that the inhibition of cell proliferation is responsible for the inhibition of promotion.

Differential effects of acetaminophen pretreatment on hepatic aflatoxin B(1)-DNA binding, cellular proliferation, and aflatoxin B1-induced hepatic foci in rats and hamsters

Effects of acetaminophen (AAP) pretreatment on hepatic aflatoxin B1 (AFB(1))-DNA binding, cellular proliferation, and AFB(1)-induced glutathione S-transferase placental form (GST-P) positive hepatocytes and foci have been examined in young male rats and hamsters. Intraperitoneal (i.p.) dosing of 600mg AAP 3h before AFB(1) i.p. injection showed three-fold more AFB(1)-DNA binding in hamsters and 40% less binding in rats. Cell proliferation analyzed by bromodeoxyuridine incorporation was not significant (0.4-0.6%) 24-96h after AAP (600mg) treatment of rats; however, proliferation was stimulated and was maximum (11%) in hamsters at 72h after AAP treatment. Dosing of rats with AFB(1) alone at 0.5 or 2.5mg level gave an appreciable number of GST-P positive minifoci (two to nine cells) with a few foci larger than 100 microm; pretreatment with AAP (300 or 600mg) 48h before 0.5 or 2.5mg AFB(1) had no effect on the number and focal area of foci. In hamsters, 1 or 2mg AFB(1) alone yielded GST-P positive hepatocytes without any minifoci. Pretreatment with AAP (600mg) 48 or 72h before 1 or 2mg AFB(1) produced increases in both GST-P positive hepatocytes and minifoci. Thus, marked changes are observed after AAP pretreatment in hamsters compared to rats.

Modification of hepatic drug-metabolizing enzymes in rats treated with alkyl sulfides

Natural compounds which elevate detoxification enzymes and/or reduce activating enzymes could be considered as good candidates to protect against cancer. In this work, we studied the modulation of hepatic drug-metabolizing enzymes in rats treated with dimethyl sulfide (DMS), dimethyl disulfide (DMDS), methylpropyl disulfide (MPDS), dipropyl sulfide (DPS), dipropyl disulfide (DPDS) and diallyl disulfide (DADS) issued from Allium species. Compounds containing methyl groups had little or no effect. Compounds with two propyl groups or two allyl groups provoked a pleiotropic response on drug-metabolizing enzymes. DPS, DPDS and DADS induced ethoxyresorufin O-deethylase, methoxyresorufin O-demethylase and mostly pentoxyresorufin O-depentylase and decreased nitrosodimethylamine N-demethylase and erythromycin N-demethylase. These modifications of enzyme activities were accompanied by an increase of CYP 2B1,2 and a decrease of CYP 2E1, evidenced by immunoblotting. The same treatments stimulated some phase II enzyme activities such as glutathione transferase and UDP-glucuronyl transferases. This pattern of induction and/or inhibition of drug metabolizing enzymes was qualitatively similar to that elicited by the enzyme inducer, phenobarbital. The magnitude of the effects produced by DPDS was smaller than those produced by DADS and DPS. Our results suggest a possible protective effect of alkyl sulfides as well as diallyl disulfide, on the first step of carcinogenesis via the modulation of enzymes involved in carcinogen metabolism.

Potentiation of aflatoxin B1-induced hepatocarcinogenesis in the rat by pretreatment with buthionine sulfoximine

A single i.p. dose of aflatoxin B1 (AFB1) (1.0 and 2.0 mg/kg body wt)-induced hepatocarcinogenesis with phenobarbital as a promoter has been examined in young male Fischer rats. Immunohistochemical method has been employed to detect AFB1-induced glutathione S-transferase placental form (GST-P)-positive hepatic foci observed from 3 week and 10 week to 40-48 week periods. With 2.0 mg AFB1 dosing, the number, area and volume occupied by GST-P-positive hepatic foci increased significantly and progressively from 3 week, 10 week and 48 week periods. In long term studies (40-48 weeks), 1.0 mg and 2.0 mg AFB1 dose levels yielded linear response in area and volume occupied by AFB1-induced hepatic foci. Pretreatment of rats with L-buthionine sulfoximine (BSO), a GSH depleter, at a dose of 4 mmol/kg body wt 4 and 2 h before 1.0 or 2.0 mg AFB1 treatment enhanced the number, area and volume of GST-P-positive hepatic foci, increases being the largest at shorter time periods (3 and 10 weeks) compared to longer time periods (40 and 48 weeks). This report appears to be the first example of an enhanced chemical induced hepatocarcinogenesis in a long term study in any experimental animals species by a GSH depleting agent.

Effect of glutathione levels on aflatoxin B1-DNA binding in livers and kidneys of male rats and hamsters pretreated with buthionine sulfoximine and dimethylmaleate

The effects of pretreatment of buthionine sulfoximine (BSO) alone or in combination with diethylmaleate (DEM) on glutathione (GSH) levels and aflatoxin B1 (AFB1)-DNA binding have been examined in livers and kidneys of young male Fischer rats and Syrian golden hamsters 2 h after an intraperitoneal injection of [3H]AFB1 (0.4 mg/kg body wt.). Animals were treated with BSO (4 mmol/kg body wt.) alone at 4 h and 2 h or with DEM (3 mmol/kg body wt.) at 4 h and BSO at 2 h before AFB1 injection. Hepatic AFB1-DNA binding was about 29.0 and 6.0 pmol/mg DNA in rats and hamsters, respectively. In rats, BSO increased AFB1-DNA binding by about 40% with a drop in GSH by 70%. Treatment with DEM-BSO increased AFB1-DNA binding by about 80% with a concomitant drop in GSH in both species. In hamsters, BSO increased AFB1-DNA binding by only 10% with a 50% drop in GSH. The kidneys of both species have lower GSH levels and AFB1-DNA binding than their respective liver tissues. The effect of BSO alone or in combination with DEM on both GSH levels and AFB1-DNA binding are comparable even though BSO alone is less effective in both species. The role of modulation of GSH levels on AFB1-DNA binding and hence biological effects of AFB1 in these two species is discussed.