The effect of feeding piglets with the diet containing green tea extracts or coumarin on in vitro metabolism of aflatoxin B1 by their tissues

Ferulic acid alleviates AFB1-induced duodenal barrier damage in rats via up-regulating tight junction proteins, down-regulating ROCK, competing CYP450 enzyme and activating GST

Previous studies reported that Aflatoxin B1 (AFB1) causes cell damage through its metabolite aflatoxin B1-8, 9-epoxide (AFBO), which is catalyzed by CYP450 enzymes. AFBO can be detoxified by glutathione S transferase (GST). Ferulic acid (FA) is known for its antioxidant capacity and intestinal protective function. However, the mechanism of AFB1 causing duodenal injury and the role of FA in AFB1-induced intestinal damage remains unclear. In this study, rats were exposed to AFB1 and treated with FA for 30 days. The results showed that I) FA alleviated the histopathological changes of duodenum and the ultrastructural changes of tight junctions between duodenal epithelial cells induced by AFB1. II) FA reduced the content of AFB1-ALB adduct in blood. III) The low expression of tight junction proteins (Claudin-1 and ZO-1) and the high expression of ROCK1 and ROCK2 induced by AFB1 were significantly reversed by FA. IV) The high expression of CYP2A6 and CYP3A4 were significantly down-regulated by FA, and the activity of GST was promoted by FA. V) The binding affinity of FA to CYP2A6 is very similar to the binding affinity of AFB1 to CYP2A6, which meaning that there is a competitive relationship between FA and AFB1 when conjugating to CYP2A6. These results suggested that FA proved effective in alleviating AFB1-induced duodenal barrier damage via up-regulating tight junction proteins, down-regulating ROCK, competing CYP450 enzyme, and activating GST in duodenal epithelial cells of rats.

Differential Effects of Green Tea Powders on the Protection of Brown Tsaiya and Kaiya Ducklings against Trichothecene T-2 Toxin Toxicity

Simple Summary

The objective of this study is to examine the effects of T-2 toxin (T-2) and green tea powders (GTP) on growth performance, hematology, and pathology parameters in Brown Tsaiya ducklings (BTDs) and Kaiya ducklings (KDs). T-2 toxin shows a strong and differential toxicity in growth suppression, as well as abnormalities in the hematological and pathological parameters of BTDs and KDs. We found that GTP could potentially prevent T-2-induced poor growth performance and improve some hematological parameters. Moreover, BTDs were more sensitive than KDs in terms of responses to T-2 toxicity and GTP detoxification.

Abstract

A 3-week feeding trial in a 3 × 2 × 2 factorial design was conducted with three concentrations (0, 0.5, and 5 mg/kg) of T-2 toxin (T-2) and two levels (0% and 0.5%) of green tea powder (GTP) supplements used in the diets of female brown Tsaiya ducklings (BTDs) and Kaiya ducklings (KDs), respectively. Breed had a significant effect on the growth performances and the relative weights of organs and carcass. In general, the growth performances of KDs were better than BTDs. The relative weights of organs and carcass of BTDs were typically heavier than those of KDs; however, the breast of KDs was heavier than those of BTDs. Both ducklings received 5 mg/kg of T-2 blended in the diet showed lower feed intake and body weight gain (BWG) in the second and the third week. The diet containing 5 mg/kg of T-2 and 0.5% GTP improved the BWG compared to those fed the diet supplemented with 5 mg/kg of T-2 without GTP in BTDs. Ducklings fed the diet containing 5 mg/kg of T-2 induced hypocalcemia and hypomagnesemia, as well as decreased concentrations of creatine phosphokinase and alkaline phosphatase. The concentrations of blood urea nitrogen (BUN) and glutamate oxaloacetate transaminase (GOT) were increased in KDs and BTDs fed the diet containing 5 mg/kg of T-2 without GTP, respectively. However, duckling diets containing 5 mg/kg of T-2 with 0.5% GTP lowered concentrations of BUN and GOT in the blood plasma of KDs and BTDs, respectively. The diet containing 5 mg/kg of T-2 increased the relative kidney weight but decreased the relative breast weight of ducklings. Enlarged gizzards and reduced relative leg weights were observed in BTDs fed the diets containing 5 mg/kg of T-2. In summary, BTDs are more sensitive than KDs in responding to T-2 toxicity and GTP detoxification. Green tea powder has detoxification ability and could potentially mitigate T-2 toxicity on BWG, BUN, and GOT in ducklings.

CYP1A2, 2A13, and 3A4 network and interaction with aflatoxin B1

Aspergillus fungi are known to produce aflatoxins, among which aflatoxin B1 (AFB1) is the most potent carcinogen that is metabolised by cytochrome P450 (CYP450). In the liver, AFB1 is metabolised into exo-8,9-epoxide by the CYP1A2 enzymes. The resulting epoxide can react with guanine to cause DNA damage. Natural inhibitors are being identified. However, the modes of action are poorly understood. In the current study, we have investigated the mode of action of AFB1 with CYP1A2, CYP3A4 and CYP2A13 using molecular dynamic simulation (MD simulation) approaches. The interaction network and paths among CYP1A2, CYP3A4, and CYP2A13 have been investigated using the STRING database and PathLinker plugin of Cytoscape. CYP3A4 is the most active protein involved in interactions with AFB1 during its metabolism. Residues 362ARG, 445SER, 450LEU and 451PHE of CYP1A2 are important, interacting with AFB1 and converting it to toxic exo-AFB1-8,9-epoxide (AFBEX). The pathway shows that microsomal epoxide hydrolase (EPHX1) may acts as initiator in the signalling pathway where CYP1A2, CYP3A4 and CYP2A13 interact in a sequential order. The interaction network shows there to be a strong association in expression among CYP1A2, CYP3A4 and CYP2A13 along with other metabolising enzymes. The complex of AFB1 and CYP1A2 was found to be stable during the MD simulation. This study provides a better understanding of the mode of action between AFB1 and CYP1A2, CYP3A4 and CYP2A13 which relates to the effective management of AFB1 toxicity. EPHX1 in the protein network may be an ideal target when designing inhibitors to prevent the toxin’s activation. Peptide inhibitors may be designed to block the substrate site residues of CYP1A2 in order to prevent the conversion from AFB1 into AFBEX. This would either neutralise or reduce its toxicity.

Descriptive Histopathological and Ultrastructural Study of Hepatocellular Alterations Induced by Aflatoxin B1 in Rats

Simple Summary

Aflatoxins can affect hepatocytes, which results in a series of histological and ultrastructural changes to the cells. We investigated the hepatocellular alterations induced by aflatoxin B1 in rats. Interestingly, we observed several histopathological and ultrastructural alterations in hepatocytes, including necrotic changes and massive vacuolar degeneration. Ultrastructural examinations of treated groups revealed damage to the sinusoidal endothelium, as well as aggregations of hyperactive Kupffer cells in the space of Disse and damaged telocytes. Our findings provide novel insights into the induction of a series of irreversible adverse effects on hepatocytes by aflatoxin B1. Based on our results, we suggest future investigations for the exploration of mechanistic pathways related to these induced hepatocellular alterations.

Abstract

Liver sinusoids are lined by fenestrated endothelial cells surrounded by perisinusoidal cells, Kupffer cells, and pit cells, as well as large granular lymphocytes. The functional ability of the liver cells can be substantially modified by exposure to toxins. In the current work, we assessed the histopathological and ultrastructural effects of a time-course exposure to aflatoxin B1 (AFB1) on the hepatic structures of rats. A total of 30 adult female Wistar rats were randomly divided into three groups: a control group, a group orally administered 250 µg/kg body weight/day of AFB1 for 5 days/week over 4 weeks, and a group that received the same AFB1 treatment but over 8 weeks. Histopathological and ultrastructural examinations of hepatocytes revealed massive vacuolar degeneration and signs of necrosis. Furthermore, the rat liver of the treated group exhibited damage to the sinusoidal endothelium, invasion of the space of Disse with hyperactive Kupffer cells, and some immune cells, as well as Ito cells overloaded with lipids. In addition, damaged telocytes were observed. Taken together, our results indicate that AFB1 induces irreversible adverse effects on the livers of rats.

The role of polyphenols in poultry nutrition

In the last two decades, poultry and animal industries became increasingly interested in using plant-based feed supplements, herbs and their derivatives to retain or enhance their health and productivity. These health benefits for the host mainly attributed to the secondary plant metabolites, namely polyphenols. Polyphenols are renowned for their antioxidant, immunomodulatory, anti-mutagenic and anti-inflammatory properties. However, despite these advantages of polyphenols, they have been characterized by poor absorption in the gut and low concentration in target cells that compromise their role as effective antioxidants. The low bioavailability of polyphenols necessitates the need for further investigations to harness their full potential in poultry farms. This review is existing evidence about the bioavailability of polyphenols and their antioxidant, immunomodulatory, antimicrobial, detoxification properties and their impacts on poultry performance.

Dietary Supplementation with sodium bentonite and coumarin alleviates the toxicity of aflatoxin B1 in rabbits

Eighty-four male New Zealand White rabbits with average body weight 778 ± 65 g were blocked into four groups to evaluate the ability of sodium bentonite and coumarin in alleviating the toxicity of aflatoxin B1. The first group was fed on a diet without any treatment (CON), while the remaining three diets were added with aflatoxin B1 at 0.25 ppm diet. Diet fed to the third and fourth group of rabbits were further supplemented with sodium bentonite at 5 g/kg (SOB) and coumarin at 5 g/kg (COU) of the diet, respectively. Feeding aflatoxin-contaminated diet (AFL) caused necrosis of liver tissue and reduced the weight gain, average daily gain, feed conversion ratio, nutrient digestibility coefficients, and nitrogen balance of rabbits. This, in turn, was reflected as a reduction in carcass characteristics. The serum collected from rabbits fed aflatoxin-contaminated diet showed decreased levels of total protein, albumin, globulin, glucose, total cholesterol, and triglycerides, and increased concentrations of urea, creatinine, and liver enzymes. Further, aflatoxin diet increased the cecal pH, and decreased the ammonia nitrogen, total volatile fatty acids, and individual fatty acids proportion of cecal fluid. Supplementing sodium bentonite and coumarin at 5 g/kg diet reduced the negative effects of aflatoxin B1 on growth performance, digestibility of nutrients, biochemical parameters, carcass characteristics, and cecal fermentation profile. Furthermore, the coumarin-supplemented group showed better body weight gains and carcass weights compared to the rabbits fed with diets containing sodium bentonite. In conclusion, both sodium bentonite and coumarin supplementation was beneficial in ameliorating the toxicity of aflatoxin B1. Further, the increased body weight gains and better-feed conversion in coumarin-supplemented rabbits project the coumarin as a better anti-aflatoxigenic supplement.

The effects of astaxanthin on liver histopathology and expression of superoxide dismutase in rat aflatoxicosis

The metabolism of aflatoxin B₁ (AFB₁) generates reactive oxygen species (ROS) that destroys hepatocytes. Meanwhile, astaxanthin (AX) is known to have stronger antioxidative activity than other carotenoids. This study aimed to investigate hepatoprotective role of AX from AFB₁-induced toxicity in rat by histopathological study and immunohistochemistry of Cu/Zn-SOD (SOD1) which acts as the first enzyme in antioxidative reaction against cell injury from ROS. Twenty Wistar rats were randomly divided into 4 groups. The control and AFB₁ groups were gavaged by water for 7 days followed by a single DMSO and 1 mg/kg AFB₁, respectively. The AXL+ AFB₁ and AXH+ AFB₁ groups were given of 5 mg/kg and 100 mg/kg AX for 7 days before 1 mg/kg AFB₁ administration. The result showed significantly elevated liver weight per 100 g body weight in AFB₁ group. The histopathological finding revealed vacuolar degeneration, necrosis, megalocytosis and binucleation of hepatocytes with bile duct hyperplasia in AFB₁ group. The severities of pathological changes were sequentially reduced in AXL+AFB₁ and AXH+AFB₁ groups. Most rats in AXH+AFB₁ group owned hypertrophic hepatocytes and atypical proliferation of cholangiocytes which are adaptive responses to severe hepatocyte damage. The SOD1 expression was also significantly higher in AXH+AFB₁ group than solely treated AFB₁ and AXL+AFB₁ groups. In conclusion, AX alleviated AFB₁-induced liver damage in rat by stimulating SOD1 expression and transdifferentiation of cholangiocytes in dose dependent manner.

Assessment of the efficacy of a grape seed waste in counteracting the changes induced by aflatoxin B1 contaminated diet on performance, plasma, liver and intestinal tissues of pigs after weaning

The aim of this study was to investigate the potential of a grape seed byproduct to mitigate the harmful damage produced by aflatoxin B1 (AFB1) at systemic level in plasma and liver as well as at local level in the gastrointestinal tract in weaned piglets. Twenty four crossbred pigs (TOPIG) were randomly assigned to one of four experimental diets: 1)- control diet (normal compound feed for starter piglets without mycotoxin), 2)- AFB1 diet (compound feed contaminated with 320 ppb pure AFB1), 3)- GS diet (compound feed including 8% of grape seed meal), 4)- AFB1+GS diet (compound feed containing 8% of grape seed meal contaminated with 320 ppb AFB1) for 30 days. The results showed that pigs fed AFB1 diet had altered performance (-25.1%), increased the thiobarbituric substances (TBARS) concentration wile reduced total antioxidant capacity and activity of antioxidant enzymes (CAT, SOD and GPx) in plasma and organs. AFB1 produced a dual effect on inflammatory response by increasing the level of pro-inflammatory cytokines in liver and colon and decreasing these cytokines in duodenum. The inclusion of grape seed in the diet of AFB1 intoxicated pigs enhanced the antioxidant enzymes activity, decreased the pro-inflammatory cytokines and TBARS level and ameliorated the growth performance of AFB1-treated animals. These findings suggest that grape waste is a promising feed source in counteracting the harmful effect of aflatoxin B1.

Mycotoxins and oxidative stress: where are we?

Mycotoxins are the most common contaminants of food and feed worldwide and are considered an important risk factor for human and animal health. Oxidative stress occurs in cells when the concentration of reactive oxygen species exceeds the cell’s antioxidant capacity. Oxidative stress causes DNA damage, enhances lipid peroxidation, protein damage and cell death. This review addresses the toxicity of the major mycotoxins, especially aflatoxin B1, deoxynivalenol, nivalenol, T-2 toxin, fumonisin B1, ochratoxin, patulin and zearalenone, in relation to oxidative stress. It summarises the data associated with oxidative stress as a plausible mechanism for mycotoxin-induced toxicity. Given the contamination caused by mycotoxins worldwide, the protective effects of a variety of natural compounds due to their antioxidant capacities have been evaluated. We review data on the ability of vitamins, flavonoids, crocin, curcumin, green tea, lycopene, phytic acid, L-carnitine, melatonin, minerals and mixtures of anti-oxidants to mitigate the toxic effect of mycotoxins associated with oxidative stress.

Pathological and biochemical evaluation of coumarin and chlorophyllin against aflatoxicosis in rat

Aflatoxin contamination of animal diet has adverse effects on animal health and productivity. This study was performed to investigate the effect of using coumarin and/or chlorophyllin in rat diet against aflatoxicosis. Fifty-four rats were assigned into 7 groups (6 rats each). G1 was a negative control. G2 received water with coumarin 0.5%. G3 received water with chlorophyllin 0.5%. G4 received water with coumarin 0.5% and chlorophyllin 0.5%. G5-8 fed aflatoxin B₁ 1000ppb in diet. Group 6-8 were administered similar treatments as G2-4. The experiment ended after 8 weeks. Random glucose, total lipid, total cholesterol, total triglycerides, total protein, serum ALT, AST, creatinine, and urea were measured. Histopathology of liver, kidney and pancreas and immunohistochemical staining of placental glutathione-S-transferase (GST-P) in liver were performed. The glucose serum level, cholesterol, AST, and ALT were elevated in G5 compared to G6-8. The liver and kidney lesions in G5 included vacuolation and necrosis which subsided in G6-8. The necrosis and inflammatory cells infiltration in the pancreas of G5 were absent in G6-8. GST-P positive hepatocytes were abundant in G5, few in G6 and absent in G7 and G8. In conclusion, the chlorophyllin and coumarin possessed protective and anti-carcinogenic effect against aflatoxicosis in rats.

Therapeutic properties of green tea against environmental insults

Pesticides, smoke, mycotoxins, polychlorinated biphenyls (PCBs), and arsenic are the most common environmental toxins and toxicants to humans. These toxins and toxicants may impact on human health at the molecular (DNA, RNA, or protein), organelle (mitochondria, lysosome, or membranes), cellular (growth inhibition or cell death), tissue, organ, and systemic levels. Formation of reactive radicals, lipid peroxidation, inflammation, genotoxicity, hepatotoxicity, embryotoxicity, neurological alterations, apoptosis, and carcinogenic events are some of the mechanisms mediating the toxic effects of the environmental toxins and toxicants. Green tea, the nonoxidized and nonfermented form of tea that contains several polyphenols, including green tea catechins, exhibits protective effects against these environmental toxins and toxicants in preclinical studies and to a much-limited extent, in clinical trials. The protective effects are collectively mediated by antioxidant, antiinflammatory, antimutagenic, hepatoprotective and neuroprotective, and anticarcinogenic activities. In addition, green tea modulates signaling pathway including NF-κB and ERK pathways, preserves mitochondrial membrane potential, inhibits caspase-3 activity, down-regulates proapoptotic proteins, and induces the phase II detoxifying pathway. The bioavailability and metabolism of green tea and its protective effects against environmental insults induced by pesticides, smoke, mycotoxins, PCBs, and arsenic are reviewed in this paper. Future studies with emphasis on clinical trials should identify biomarkers of green tea intake, examine the mechanisms of action of green tea polyphenols, and investigate potential interactions of green tea with other toxicant-modulating dietary factors.

Dietary pretreatment with green tea polyphenol, (-)-epigallocatechin-3-gallate reduces the bioavailability and hepatotoxicity of subsequent oral bolus doses of (-)-epigallocatechin-3-gallate

Human case-studies have reported an association between green tea-based dietary supplements and hepatotoxicity. Studies have demonstrated the hepatotoxicity of high-dose oral bolus dosing with the tea polyphenol (-)-epigallocatechin-3-gallate (EGCG) in mice and dogs. We examined the effect of pretreatment with dietary EGCG on the hepatotoxicity and bioavailability of acute oral bolus dosing with EGCG in CF-1 mice. EGCG (750 mg/kg, i.g., once daily for 3 days) increased plasma alanine aminotransferase by 80-fold, decreased both reduced (by 59%) and total (by 33%) hepatic glutathione, and increased hepatic levels of phosphorylated histone 2AX. Pretreatment with dietary EGCG (3.2 mg/g diet) for 2 weeks mitigated hepatotoxicity. Acute oral EGCG also decreased mRNA expression of glutathione reductase. Dietary pretreatment prevented these decreased and increased glutathione peroxidase (Gpx)2, Gpx3, Gpx5, and Gpx7 expression. We found that dietary EGCG reduced the plasma (57% reduction) and hepatic (71% reduction) EGCG exposure following oral bolus dosing compared to mice that were not pre-treated. Overall, it appears that EGCG can modulate its own bioavailability and that dietary treatment may reduce the toxic potential of acute high oral bolus doses of EGCG. These data may partly explain the observed variation in hepatotoxic response to green tea-containing dietary supplements.

Synergistic effect of black tea and curcumin in improving the hepatotoxicity induced by aflatoxin B1 in rats

Aflatoxin B1 (AFB1) is a toxic compound commonly found as a contaminant in human food. It is carcinogenic due its potential in inducing the oxidative stress and distortion of the most antioxidant enzymes. Since black tea possesses strong antioxidant activity, it protects cells and tissues against oxidative stress. Curcumin (CMN), a naturally occurring agent, has a combination of biological and pharmacological properties that include antioxidant activity. Therefore, the present study was carried out to investigate the possible role of separate and mixed supplementation of black tea extract and CMN in the hepatotoxicity induced by AFB1 in rats. A total of 48: adult male Sprague Dawley rats were randomly divided into eight groups with six rats in each group. Group 1 (normal control) includes rats that received no treatment. Groups 2, 3, and 4 (positive control) include rats that received olive oil, black tea extract, and CMN, respectively. Group 5 includes rats that received AFB1 at a dose of 750 μg/kg body weight (b.w.) dissolved in olive oil. Groups 6, 7, and 8 include rats that received AFB1 along with 2% black tea extract, CMN at a dose of 200 mg/kg b.w., and both black tea extract and CMN at the same previous doses, respectively. After 90 days, biochemical and histopathological examination was carried out for the blood samples and liver tissues. A significant decrease in the antioxidant enzymes and a significant increase in the lipid peroxidation and hydrogen peroxide in the rats treated with AFB1 were observed. Moreover, there were dramatic changes in the liver function biomarkers, lipid profile, and liver architecture. Supplementation of black tea extract or CMN showed an efficient role in repairing the distortion of the biochemical and histological changes induced by AFB1 in liver. This improvement was more pronounced when both CMN and black tea were used together.

The effects of green tea polyphenols on drug metabolism

INTRODUCTION

Tea, made from the dried leaves of the plant Camellia sinensis Theaceae, is a very popular beverage consumed worldwide. Recently, green tea extract-based dietary supplements have also been widely consumed for the acclaimed beneficial health effects, such as weight reduction. Although tea consumption is considered to be innocuous, the potential interactions between tea polyphenols and drugs have been demonstrated in studies in vitro and in vivo.

AREAS COVERED

This article reviews the current literature on the chemistry and biotransformation of tea constituents, mainly catechins from green tea. The article also provides a review of their effects on the absorption, efflux, metabolism and elimination of different drugs.

EXPERT OPINION

Tea catechins may bind to certain drugs to affect their absorption and bioactivities. Tea catechins may inhibit the activities of drug-metabolizing enzymes and drug transporters or affect the expression of these proteins, either upregulation or downregulation. Although these effects have been demonstrated in studies in vitro and in animal models, such effects have only been observed in limited cases in humans at common doses of human tea consumption. The ingestion of tea catechins from dietary supplements, which could be in large bullet doses, may produce more profound effects on drug metabolism, and such effects with drugs need to be further investigated.

Modulation of Wnt/β-catenin signaling pathway by bioactive food components

The Wnt/β-catenin signaling pathway, one of the most conserved intercellular signaling cascade, is a known regulator of cellular functions related to tumor initiation and progression, cell proliferation, differentiation, survival and adhesion. Because aberrant Wnt/β-catenin signaling has been observed in a variety of human cancers including a majority of colorectal cancers, about half of prostate cancers and a third of melanomas, inhibitors of its complex signaling pathways are being investigated for therapy as well as chemoprevention of these cancers. During the last decade, several naturally occurring dietary agents have been shown to target intermediates in the Wnt/β-catenin signaling pathway. In this review, we highlight the current understanding of the Wnt/β-catenin signaling pathway and present an analysis of the key findings from laboratory studies on the effects of a panel of dietary agents against a variety of cancers. Promise of these agents for treating and preventing human cancer is then discussed.

Effects of green tea catechins on the pro-inflammatory response after haemorrhage/resuscitation in rats

Plant polyphenols, i.e. green tea extract (GTE), possess high antioxidative and anti-inflammatory capacity, thus being protective in various models of acute inflammation. However, their anti-inflammatory effect and a feasible mechanism in haemorrhage/resuscitation (H/R)-induced liver injury remain unknown. We investigated the effects of GTE and the role of NF-κB in the pathogenesis of liver injury induced by H/R, and their effects on intercellular adhesion molecule-1 (ICAM-1) expression and neutrophil infiltration. Female Lewis rats were fed a standard chow diet (control, ctrl) or a diet containing 0·1 % polyphenolic GTE for five consecutive days before H/R. Rats were haemorrhaged to a mean arterial pressure of 30 (sem 2) mmHg for 60 min and resuscitated. Control groups (sham_ctrl and sham_GTE) underwent surgical procedures without H/R. At 2 h after resuscitation, tissues were harvested. Serum alanine aminotransferase (ALT) and IL-6 were measured. Hepatic necrosis, ICAM-1 expression and polymorphonuclear leucocyte (PMNL) infiltration were assessed. Hepatic expression of IκBα (phospho) was measured. H/R induced strong liver damage with increased necrosis and serum ALT levels. Compared with both sham groups, inflammatory markers (serum IL-6 and hepatic PMNL infiltration) were elevated after H/R (P < 0·05). Also, H/R increased IκBα phosphorylation. GTE administration markedly (P < 0·05) decreased serum ALT and IL-6 levels, hepatic necrosis as well as PMNL infiltration and the expression of ICAM-1 and phosphorylated IκBα compared with H/R. In conclusion, we observed that NF-κB activation plays an important role in the pathogenesis of liver injury after H/R through the up-regulation of hepatic ICAM-1 expression and subsequent PMNL infiltration. GTE pre-treatment prevents liver damage in this model of acute inflammation through a NF-κB-dependent mechanism.

Sulforaphane induces glutathione S-transferase isozymes which detoxify aflatoxin B(1)-8,9-epoxide in AML 12 cells

The aflatoxin B(1)-8,9-epoxide (AFBO) is hepatocarcinogenic intermediate of aflatoxin B(1) (AFB(1)) and is detoxified by glutathione S-transferases (GSTs). In this study, we investigated whether sulforaphane (SFN) could increase the rate of conjugation between AFBO and glutathione (GSH) as well as which of the GST isozymes were involved in the conjugation reaction. The conjugation potential was inhibited dose dependently with curcumin, an inhibitor of GSTs. SFN induced the expression of GST A3, GST A4, GST M1, GST P1, and GST T1 in alpha mouse line (AML) 12 cells. The cells treated with SFN (10 microM) for 12 h showed a 35-fold increase in conjugation potential of AFBO with GSH compared with the vehicle-treated cell. The conjugation potential was blocked partially by transfection of cells with siRNAs against each of the GST isozymes. The activity of GST A3 had the strongest effect on the conjugation potential. SFN treatment also increased total GST activity detected with 1-chloro-2,4-dinitrobenzene (CDNB) up to 4.3-fold. The induction fold was much lower than that detected with AFBO. These results suggest that the chemopreventive effect of SFN on the decomposition of AFBO is related to the upregulation of several GST isozymes genes. The increase of GST activity by SFN was extremely specific toward the conjugation reaction of AFBO compared with CDNB. Therefore, this system for detecting GST activity seems to be an excellent method for screening chemopreventive compounds toward AFB(1) toxicity.

The antioxidant and pro-oxidant activities of green tea polyphenols: a role in cancer prevention

Green tea (Camellia sinensis) is rich in catechins, of which (-)-epigallocatechin-3-gallate (EGCG) is the most abundant. Studies in animal models of carcinogenesis have shown that green tea and EGCG can inhibit tumorigenesis during the initiation, promotion and progression stages. Many potential mechanisms have been proposed including both antioxidant and pro-oxidant effects, but questions remain regarding the relevance of these mechanisms to cancer prevention. In the present review, we will discuss the redox chemistry of the tea catechins and the current literature on the antioxidant and pro-oxidative effects of the green tea polyphenols as they relate to cancer prevention. We report that although the catechins are chemical antioxidants which can quench free radical species and chelate transition metals, there is evidence that some of the effects of these compounds may be related to induction of oxidative stress. Such pro-oxidant effects appear to be responsible for the induction of apoptosis in tumor cells. These pro-oxidant effects may also induce endogenous antioxidant systems in normal tissues that offer protection against carcinogenic insult. This review is meant point out understudied areas and stimulate research on the topic with the hope that insights into the mechanisms of cancer preventive activity of tea polyphenols will result.

Green tea catechin inhibits lipopolysaccharide-induced bone resorption in vivo

BACKGROUND AND OBJECTIVE

Bone resorption is positively regulated by receptor activator of nuclear factor-kappaB ligand (RANKL). Pro-inflammatory cytokines, such as interleukin (IL)-1beta, promote RANKL expression by stromal cells and osteoblasts. Green tea catechin (GTC) has beneficial effects on human health and has been reported to inhibit osteoclast formation in an in vitro co-culture system. However, there has been no investigation of the effect of GTC on periodontal bone resorption in vivo. We therefore investigated whether GTC has an inhibitory effect on lipopolysaccharide (LPS)-induced bone resorption.

MATERIAL AND METHODS

Escherichia coli (E. coli) LPS or LPS with GTC was injected a total of 10 times, once every 48 h, into the gingivae of BALB/c mice. Another group of mice, housed with free access to water containing GTC throughout the experimental period, were also injected with LPS in a similar manner.

RESULTS

The alveolar bone resorption and IL-1beta expression induced by LPS in gingival tissue were significantly decreased by injection or oral administration of GTC. Furthermore, when GTC was added to the medium, decreased responses to LPS were observed in CD14-expressing Chinese hamster ovary (CHO) reporter cells, which express CD25 through LPS-induced nuclear factor-kappaB (NF-kappaB) activation. These findings demonstrated that GTC inhibits nuclear translocation of NF-kappaB activated by LPS. In addition, osteoclasts were generated from mouse bone marrow macrophages cultured in a medium containing RANKL and macrophage colony-stimulating factor with or without GTC. The number of osteoclasts was decreased in dose-dependent manner when GTC was added to the culture medium.

CONCLUSION

These results suggest that GTC suppresses LPS-induced bone resorption by inhibiting IL-1beta production or by directly inhibiting osteoclastogenesis.

Antioxidative and anti-carcinogenic activities of tea polyphenols

Tea (Camellia sinensis, Theaceace), a popular beverage consumed world-wide, has been studied for its preventive effects against cancer as well as cardiovascular, neurodegenerative, and other diseases. Most of the proposed beneficial effects have been attributed to the polyphenolic compounds in tea, but the nature of these activities and the molecular mechanisms of their actions remain unclear. Tea polyphenols are known to be strong antioxidants. Prevention of oxidative stress, modulation of carcinogen metabolism, and prevention of DNA damage have been suggested as possible cancer preventive mechanisms for tea and tea polyphenols. In this chapter, we discuss these topics in the light of biotransformation and bioavailability of tea polyphenols. We also review the preventive effects of tea polyphenols in animal models of carcinogenesis and some of the possible post-initiation mechanisms of action. Finally, we discuss the effects of tea consumption on cancer risk in humans. It is our aim to raise some of the unanswered questions regarding cancer prevention by tea and to stimulate further research in this area.