Coffee diterpenes prevent benzo[a]pyrene genotoxicity in rat and human culture systems

In Search of Panacea-Review of Recent Studies Concerning Nature-Derived Anticancer Agents

Cancers are one of the leading causes of deaths affecting millions of people around the world, therefore they are currently a major public health problem. The treatment of cancer is based on surgical resection, radiotherapy, chemotherapy or immunotherapy, much of which is often insufficient and cause serious, burdensome and undesirable side effects. For many years, assorted secondary metabolites derived from plants have been used as antitumor agents. Recently, researchers have discovered a large number of new natural substances which can effectively interfere with cancer cells’ metabolism. The most famous groups of these compounds are topoisomerase and mitotic inhibitors. The aim of the latest research is to characterize natural compounds found in many common foods, especially by means of their abilities to regulate cell cycle, growth and differentiation, as well as epigenetic modulation. In this paper, we focus on a review of recent discoveries regarding nature-derived anticancer agents.

Development and Uses of Offline and Web-Searchable Metabolism Databases - The Case of Benzo[a]pyrene

BACKGROUND

The present work describes development of offline and web-searchable metabolism databases for drugs, other chemicals, and physiological compounds using human and model species, prompted by the large amount of data published after year 1990. The intent was to provide a rapid and accurate approach to published data to be applied both in science and to assist therapy.

METHODS

Searches for the data were done using the Pub Med database, accessing the Medline database of references and abstracts. In addition, data presented at scientific conferences (e.g., ISSX conferences) are included covering the publishing period beginning with the year 1976.

RESULTS

Application of the data is illustrated by the properties of benzo[a]pyrene (B[a]P) and its metabolites. Analysis show higher activity of P450 1A1 for activation of the (-)- isomer of trans-B[a]P-7,8-diol, while P4501B1 exerts higher activity for the (+)- isomer. P450 1A2 showed equally low activity in the metabolic activation of both isomers.

CONCLUSION

The information collected in the databases is applicable in prediction of metabolic drug-drug and/or drug-chemical interactions in clinical and environmental studies. The data on the metabolism of searched compound (exemplified by benzo[a]pyrene and its metabolites) also indicate toxicological properties of the products of specific reactions. The offline and web-searchable databases had wide range of applications (e.g. computer assisted drug design and development, optimization of clinical therapy, toxicological applications) and adjustment in everyday life styles.

Relationship between Telomere Length, Genetic Traits and Environmental/Occupational Exposures in Bladder Cancer Risk by Structural Equation Modelling

Background: Telomere length (TL) maintenance plays an important role in bladder cancer (BC) and prognosis. However the manifold influence of everyday life exposures and genetic traits on leucocyte TL (LTL), is not fully elucidated. Methods: Within the framework of a hospital-based case (n = 96)/control (n = 94) study (all Caucasian males), we investigated the extent to which LTL and BC risk were modulated by genetic polymorphisms and environmental and occupational exposures. Data on lifetime smoking, alcohol and coffee drinking, dietary habits and occupational exposures, pointing to aromatic amines (AAs) and polycyclic aromatic hydrocarbons (PAHs) were collected. Structural equation modelling (SEM) analysis appraised this complex relationships. Results: The SEM analysis indicates negative direct links (p < 0.05) between LTL with age, DNA adducts, alcohol and NAT2, and positive ones with coffee, MPO and XRCC3; and between BC risk (p < 0.01) with cigarettes, cumulative exposure to AAs and coffee, while are negative with LTL and age. There was evidence of indirect effects (p < 0.05) on BC risk, probably via LTL reduction, by age and NAT2 (positive link), MPO and XRCC3 (negative link).

CONCLUSIONS

Our study supports evidence that LTL attrition is a critical event in BC. The new finding that LTL erosion depends on some preventable everyday life exposures genetically modulated, opens new perspectives in BC prevention.

Coffee Consumption Is Positively Associated with Longer Leukocyte Telomere Length in the Nurses' Health Study

BACKGROUND

Coffee is an important source of antioxidants, and consumption of this beverage is associated with many health conditions and a lower mortality risk. However, no study, to our knowledge, has examined whether varying coffee or caffeine consumption levels are associated with telomere length, a biomarker of aging whose shortening can be accelerated by oxidative stress.

OBJECTIVE

We performed a large comprehensive study on how coffee consumption is associated with telomere length.

METHODS

We used data from the Nurses' Health Study (NHS), a prospective cohort study of female nurses that began in 1976. We examined the cross-sectional association between coffee consumption and telomere length in 4780 women from the NHS. Coffee consumption information was obtained from validated food-frequency questionnaires, and relative telomere length was measured in peripheral blood leukocytes by the quantitative real-time polymerase chain reaction. Unconditional logistic regression was used to obtain ORs when the telomere length outcome was dichotomized at the median. Linear regression was used for tests of trend with coffee consumption and telomere length as continuous variables.

RESULTS

Higher total coffee consumption was significantly associated with longer telomeres after potential confounding adjustment. Compared with non-coffee drinkers, multivariable ORs for those drinking 2 to <3 and ≥3 cups of coffee/d were, respectively, 1.29 (95% CI: 0.99, 1.68) and 1.36 (95% CI: 1.04, 1.78) (P-trend = 0.02). We found a significant linear association between caffeine consumption from all dietary sources and telomere length (P-trend = 0.02) after adjusting for potential confounders, but not after additionally adjusting for total coffee consumption (P-trend = 0.37).

CONCLUSIONS

We found that higher coffee consumption is associated with longer telomeres among female nurses. Future studies are needed to better understand the influence of coffee consumption on telomeres, which may uncover new knowledge of how coffee consumption affects health and longevity.

Anti-Angiogenic Properties of Cafestol and Kahweol Palmitate Diterpene Esters

Epidemiological studies support the association of coffee-specific diterpenes, with various beneficial health effects. Although anti-antiangiogenic properties of free cafestol and kahweol have been recently described, available data regarding their esterified form, in particular palmitate esters as the main diterpene esters present in coffee, are still rare. Given that angiogenesis plays an important role in many pathological conditions, including cancer growth and metastasis, this study aimed to assess and compare the potential anti-angiogenic effects of cafestol palmitate (CP) and kahweol palmitate (KP) in an in vitro angiogenesis model. According to our findings, both compounds inhibited angiogenesis steps on human microvascular endothelial cells (HMVECs), although a more significant effect was observed for KP. Compared to control, HMVECs viability decreased in a dose-dependent manner upon incubation either with CP or KP. Concentrations of 75 and 100 μM of each compound were cytotoxic. Cell proliferation was also dramatically reduced by both diterpene esters at 50 μM, although KP had a stronger inhibitory effect. However, CP and KP did not induce apoptosis on HMVECs. Both compounds reduced cell migration, but this effect was only statistically significant after KP incubation. Inhibition of VEGFR2 expression and its downstream effector Akt, but not Erk, was also observed in CP- and KP-treated HMVECs. These findings were confirmed using ELISA assay for phosphorylated (active) VEGFR-2. Taken together, these data indicate that both CP and KP can be considered potent compounds against angiogenesis-dependent disorders. Our findings further indicate that KP exerts more potent anti-angiogenic effects than CP, in most of assays. J. Cell. Biochem. 117: 2748-2756, 2016. © 2016 Wiley Periodicals, Inc.

Chemical and biological mechanisms of phytochemical activation of Nrf2 and importance in disease prevention

Plants are an incredibly rich source of compounds that activate the Nrf2 transcription factor, leading to upregulation of a battery of cytoprotective genes. This perspective surveys established and proposed molecular mechanisms of Nrf2 activation by phytochemicals with a special emphasis on a common chemical property of Nrf2 activators: the ability as "soft" electrophiles to modify cellular thiols, either directly or as oxidized biotransformants. In addition, the role of reactive oxygen/nitrogen species as secondary messengers in Nrf2 activation is discussed. While the uniquely reactive C151 of Keap1, an Nrf2 repressor protein, is highlighted as a key target of cytoprotective phytochemicals, also reviewed are other stress-responsive proteins, including kinases, which play non-redundant roles in the activation of Nrf2 by plant-derived agents. Finally, the perspective presents two key factors accounting for the enhanced therapeutic windows of effective phytochemical activators of the Keap1-Nrf2 axis: enhanced selectivity toward sensor cysteines and reversibility of addition to thiolate molecules.

Coffee induces expression of glucuronosyltransferases by the aryl hydrocarbon receptor and Nrf2 in liver and stomach

BACKGROUND & AIMS

Coffee is one of the most widely consumed beverages worldwide. Epidemiologic data indicate that coffee consumption protects against the progression of chronic liver disease and development of hepatocellular carcinoma and diabetes, but the mechanisms are not clear. UDP glucuronosyltransferases (UGT1A) are proteins with indirect antioxidant, cytoprotective, and genoprotective capabilities; we examined UGT1A regulation in response to coffee in cultured cells and mice.

METHODS

HepG2 and CaCo2 cells were incubated with regular, metal- or paper-filtered, decaffeinated, or instant coffee; green or black tea; cocoa; or metabolic products of caffeine. The effects of UGT1A regulation were investigated with reporter gene assays, immunoblot, TaqMan polymerase chain reaction, mutagenesis, and short interfering (si)RNA analyses. We also studied the effects of coffee in humanized transgenic mice that express human UGT1A.

RESULTS

Incubation of cells with coffee induced transcription of UGT1A1 (5.4-fold), UGT1A3 (5.2-fold), UGT1A4 (4.8-fold), UGT1A7 (6.2-fold), UGT1A8 (5.2-fold), UGT1A9 (3.5-fold), and UGT1A10 (6.1-fold). Induction was independent of caffeine, methylxanthines, or the diterpenes cafestol and kahweol. Mutagenesis and short interfering RNA knockdown studies showed that UGT1A is regulated by the aryl hydrocarbon receptor (AhR) and the nuclear factor erythroid-related factor 2 (Nrf2) by cis-acting antioxidant and xenobiotic response elements (ARE/XRE). In transgenic UGT1A mice, administration of coffee resulted in a 10- and 14-fold induction of UGT1A transcription in liver and stomach, respectively.

CONCLUSIONS

UGT1A genes are induced in vitro and in vivo by coffee, independent of caffeine content, cafestol, or kahweol. Coffee up-regulates glucuronidation by AhR signaling and Nrf2 binding to the ARE/XRE. Glucuronidation could mediate the protective and antioxidant effects of coffee.

Impact of paper filtered coffee on oxidative DNA-damage: results of a clinical trial

Coffee is among the most frequently consumed beverages worldwide and epidemiological studies indicate that its consumption is inversely related to the incidence of diseases in which reactive oxygen species (ROS) are involved (liver cirrhosis, certain forms of cancer and neurodegenerative disorders). It has been postulated that antioxidant properties of coffee may account for this phenomenon. To find out if consumption of paper filtered coffee which is the most widely consumed form in Central Europe and the US protects humans against oxidative DNA-damage, a controlled intervention trial with a cross-over design was conducted in which the participants (n=38) consumed 800ml coffee or water daily over 5 days. DNA-damage was measured in peripheral lymphocytes in single cell gel electrophoresis assays. The extent of DNA-migration attributable to formation of oxidised purines (formamidopyrimidine glycosylase sensitive sites) was decreased after coffee intake by 12.3% (p=0.006). Biochemical parameters of the redox status (malondialdehyde, 3-nitrotyrosine and the total antioxidant levels in plasma, glutathione concentrations in blood, intracellular ROS levels and the activities of superoxide dismutase and glutathione peroxidase in lymphocytes) were not markedly altered at the end of the trial, also the urinary 8-isoprostaglandine F2α concentrations were not affected. Overall, the results indicate that coffee consumption prevents endogenous formation of oxidative DNA-damage in human, this observation may be causally related to beneficial health effects of coffee seen in earlier studies.

Decaffeinated coffee and nicotine-free tobacco provide neuroprotection in Drosophila models of Parkinson's disease through an NRF2-dependent mechanism

Epidemiological studies have revealed a significantly reduced risk of Parkinson's disease (PD) among coffee and tobacco users, although it is unclear whether these correlations reflect neuroprotective/symptomatic effects of these agents or preexisting differences in the brains of tobacco and coffee users. Here, we report that coffee and tobacco, but not caffeine or nicotine, are neuroprotective in fly PD models. We further report that decaffeinated coffee and nicotine-free tobacco are as neuroprotective as their caffeine and nicotine-containing counterparts and that the neuroprotective effects of decaffeinated coffee and nicotine-free tobacco are also evident in Drosophila models of Alzheimer's disease and polyglutamine disease. Finally, we report that the neuroprotective effects of decaffeinated coffee and nicotine-free tobacco require the cytoprotective transcription factor Nrf2 and that a known Nrf2 activator in coffee, cafestol, is also able to confer neuroprotection in our fly models of PD. Our findings indicate that coffee and tobacco contain Nrf2-activating compounds that may account for the reduced risk of PD among coffee and tobacco users. These compounds represent attractive candidates for therapeutic intervention in PD and perhaps other neurodegenerative diseases.

Absorption, distribution, and biliary excretion of cafestol, a potent cholesterol-elevating compound in unfiltered coffees, in mice

Cafestol is a diterpene present in unfiltered coffees. It is the most potent cholesterol-elevating compound present in the human diet. However, the precise mechanisms underlying this effect are still unclear. In contrast, cafestol is also known as a hepatoprotective compound, which is likely to be related to the induction of glutathione biosynthesis and conjugation. In the present study, we investigated whole-body distribution, biliary excretion, and portal bioavailability of cafestol in mice. First, dissection was used to study distribution. Five hours after an oral dose with (3)H-labeled cafestol, most activity was found in small intestine, liver, and bile. These results were confirmed by quantitative whole-body autoradiography in a time course study, which also showed elimination of all radioactivity within 48 h after administration. Next, radiolabeled cafestol was dosed intravenously to bile duct-cannulated mice. Five hours after the dose 20% of the radioactivity was found in bile. Bile contained several metabolites but no parent compound. After intestinal administration of radioactive cafestol to portal vein-cannulated mice, cafestol was shown to be rapidly absorbed into the portal vein as the parent compound, a glucuronide, and an unidentified metabolite. From the presence of a glucuronide in bile that can be deconjugated by a bacterial enzyme and the prolonged absorption of parent compound from the gastrointestinal tract, we hypothesized that cafestol undergoes enterohepatic cycling. Together with our earlier observation that epoxidation of the furan ring occurs in liver, these findings merit further research on the process of accumulation of this coffee ingredient in liver and intestinal tract.

A combination of 3D-QSAR, docking, local-binding energy (LBE) and GRID study of the species differences in the carcinogenicity of benzene derivatives chemicals

A combination of 3D-QSAR, docking, local-binding energy (LBE) and GRID methods was applied as a tool to study and predict the mechanism of action of 100 carcinogenic benzene derivatives. Two 3D-QSAR models were obtained: (i) model of mouse carcinogenicity on the basis of 100 chemicals (model 1) and (ii) model of the differences in mouse and rat carcinogenicity on the basis of 73 compounds (model 2). 3D-QSAR regression maps indicated the important differences in species carcinogenicity, and the molecular positions associated with them. In order to evaluate the role of P450 metabolic process in carcinogenicity, the following approaches were used. The 3D models of CYP2E1 for mouse and rat were built up. A docking study was applied and the important ligand-protein residues interactions and oxidation positions of the molecules were identified. A new approach for quantitative assessment of metabolism pathways was developed, which enabled us to describe the species differences in CYP2E1 metabolism, and how it can be related to differences in the carcinogenic potential for a subset of compounds. The binding energies of the important substituents (local-binding energy-LBE) were calculated, in order to quantitatively demonstrate the contribution of the substituents in metabolic processes. Furthermore, a computational procedure was used for determining energetically favourable binding sites (GRID examination) of the enzymes. The GRID procedure allowed the identification of some important differences, related to species metabolism in CYP2E1. Comparing GRID, 3D-QSAR maps and LBE results, a similarity was identified, indicating a relationship between P450 metabolic processes and the differences in the carcinogenicity.

Induction of Nrf2-mediated cellular defenses and alteration of phase I activities as mechanisms of chemoprotective effects of coffee in the liver

Coffee consumption has been associated with a significant decrease in the risk of developing chronic diseases such as Parkinson disease, diabetes type-2 and several types of cancers (e.g. colon, liver). In the present study, a coffee-dependent induction of enzymes involved in xenobiotic detoxification processes was observed in rat liver and primary hepatocytes. In addition, coffee was found to induce the mRNA and protein expression of enzymes involved in cellular antioxidant defenses. These inductions were correlated with the activation of the Nrf2 transcription factor as shown using an ARE-reporter luciferase assay. The induction of detoxifying enzymes GSTs and AKR is compatible with a protection against both genotoxicity and cytotoxicity of aflatoxin B1 (AFB1). This hypothesis was confirmed in in vitro and ex vivo test systems, where coffee reduced both AFB1-DNA and protein adducts. Interestingly, coffee was also found to inhibit cytochrome CYP1A1/2, indicating that other mechanisms different from a stimulation of detoxification may also play a significant role in the chemoprotective effects of coffee. Further investigations in either human liver cell line and primary hepatocytes indicated that the chemoprotective effects of coffee against AFB1 genotoxicity are likely to be of relevance for humans. These data strongly suggest that coffee may protect against the adverse effects of AFB1. In addition, the coffee-mediated stimulation of the Nrf2-ARE pathway resulting in increased endogenous defense mechanisms against electrophilic but also oxidative insults further support that coffee may be associated with a protection against various types of chemical stresses.

Effects of coffee and its chemopreventive components kahweol and cafestol on cytochrome P450 and sulfotransferase in rat liver

Coffee drinking appears to reduce cancer risk in liver and colon. Such chemoprevention may be caused by the diterpenes kahweol and cafestol (K/C) contained in unfiltered beverage. In animals, K/C treatment inhibited the mutagenicity/tumorigenicity of several carcinogens, likely explicable by beneficial modifications of xenobiotic metabolism, particularly by stimulation of carcinogen-detoxifying phase II mechanisms. In the present study, we investigated the influence of K/C on potentially carcinogen-activating hepatic cytochrome P450 (CYP450) and sulfotransferase (SULT). Male F344 rats received 0.2% K/C (1:1) in the diet for 10 days or unfiltered and/or filtered coffee as drinking fluid. Consequently, K/C decreased the metabolism of four resorufin derivatives representing CYP1A1, CYP1A2, CYP2B1, and CYP2B2 activities by approximately 50%. For CYP1A2, inhibition was confirmed at the mRNA level, accompanied by decreased CYP3A9. In contrast to K/C, coffee increased the metabolism of the resorufin derivatives up to 7-fold which was only marginally influenced by filtering. CYP2E1 activity and mRNA remained unchanged by K/C and coffee. K/C but not coffee decreased SULT by approximately 25%. In summary, K/C inhibited CYP450s by tendency but not universally. Inhibition of CYP450 and SULT may contribute to chemoprevention with K/C but involvement in the protection of coffee drinkers is unlikely. The data confirm that the effects of complex mixtures may deviate from those of their putatively active components.

Coffee: good, bad, or just fun? A critical review of coffee's effects on liver enzymes

Coffee consumption is a regular part of daily life throughout the world. Research into the effects of coffee on human health is ongoing, but a recent study suggests that coffee and caffeine consumption can reduce the risk of elevated alanine aminotransferase activity in individuals at high risk for liver disease. This review will analyze the results of that study in light of the current literature.

Coffee consumption induces GSTP in plasma and protects lymphocytes against (+/-)-anti-benzo[a]pyrene-7,8-dihydrodiol-9,10-epoxide induced DNA-damage: results of controlled human intervention trials

A number of animal studies indicate that coffee protects against chemical induction of cancer; also human studies suggest that coffee consumption is inversely related with the incidence of different forms of cancer. The protective effects were attributed to induction of glutathione-S-transferases (GSTs) and aim of the present human study was to find out if coffee causes induction of GSTs and protects against DNA-damage caused by (+/-)-anti-B[a]P-7,8-dihydrodiol-9,10-epoxide (BPDE), the DNA-reactive metabolite of benzo(a)pyrene. Ten participants consumed 1L unfiltered coffee/d over 5 days. Before and after the intervention, saliva and blood were collected and the overall GST activity was measured with 1-chloro-2,4-dinitrobenzene (CDNB). Additionally, GSTP and GSTA were determined in plasma with immunoassays. In blood, only weak (p=0.042) induction of GST (CDNB) was found. Furthermore, pronounced (three-fold) induction of GSTP was observed in blood, whereas GSTA was not altered. No correlations were seen between induction of GST (CDNB) and GSTP activities and the GSTP1 genotypes of the participants. Also clinical parameters (creatinine, alanine, aminotransferase, aspartate aminotransferase, alkaline phosphatase), which are markers for organ damage, were monitored. None of them was altered by coffee, but serum cholesterol levels were slightly (not significantly) enhanced. In a second trial (n=7), GSTP induction by unfiltered and paper filtered coffees, differing in cafestol and kahweol contents, were compared. The participants consumed 1L coffee/d over 3 days. Again significant (three-fold) induction of GSTP was observed. The effects seen with the two coffees were identical, indicating that the diterpenoid concentrations are not responsible for the effects. In a further trial (n=7), the effect of coffee (unfiltered, 1L/d, 5 days) on BPDE induced DNA-migration was studied in comet assays. A 45% reduction effect was observed. Our findings show that coffee induces GSTP in humans and indicate that consumption may lead to protection towards polycyclic aromatic hydrocarbons.

Coffee consumption and human health--beneficial or detrimental?--Mechanisms for effects of coffee consumption on different risk factors for cardiovascular disease and type 2 diabetes mellitus

Coffee is probably the most frequently ingested beverage worldwide. Especially Scandinavia has a high prevalence of coffee-drinkers, and they traditionally make their coffee by boiling ground coffee beans and water. Because of its consumption in most countries in the world, it is interesting, from both a public and a scientific perspective, to discuss its potential benefits or adverse aspects in relation to especially two main health problems, namely cardiovascular disease and type 2 diabetes mellitus. Epidemiological studies suggest that consumption of boiled coffee is associated with elevated risk for cardiovascular disease. This is mainly due to the two diterpenes identified in the lipid fraction of coffee grounds, cafestol and kahweol. These compounds promote increased plasma concentration of cholesterol in humans. Coffee is also a rich source of many other ingredients that may contribute to its biological activity, like heterocyclic compounds that exhibit strong antioxidant activity. Based on the literature reviewed, it is apparent that moderate daily filtered, coffee intake is not associated with any adverse effects on cardiovascular outcome. On the contrary, the data shows that coffee has a significant antioxidant activity, and may have an inverse association with the risk of type 2 diabetes mellitus.

Coffee diterpenes prevent the genotoxic effects of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and N-nitrosodimethylamine in a human derived liver cell line (HepG2)

Aim of the present experiments was to study the genotoxic effects of coffee diterpenoids, namely cafestol palmitate and a mix of cafestol and kahweol (C+K) in human derived hepatoma (HepG2) cells. Furthermore, we investigated the potential protective properties of these substances towards carcinogens contained in the human diet, namely N-nitrosodimethylamine (NDMA) and 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP). C+K and cafestol palmitate were tested over a broad dose range in micronucleus (MN) assays and no indication for genotoxic effects was seen. In combination experiments with PhIP (300 microM), pronounced inhibition (approximately 1.7-fold) of MN formation was observed with C+K and cafestol palmitate at dose levels > or = 0.9 and 1.7 microg/ml, respectively. Enzyme measurements indicate that the protection is due to inhibition of sulfotransferase, an enzyme involved in the activation of the amine, and/or to induction of UDP-glucuronosyltransferase which detoxifies the DNA-reactive metabolites of PhIP. Furthermore, a significant increase of glutathione-S-transferase was seen, whereas the activities of cytochrome P-450 1A1 and N-acetyltransferase 1 were not significantly altered. Also in combination experiments with C+K and NDMA, strong protective effects (50% reduction of genotoxicity) were seen at low dose levels (> or = 0.3 microg/ml). Since inhibition of MN was also observed when C+K were added after incubation with NDMA, it is likely that the chemoprotective effects are due to induction of DNA repair enzymes. Comparison of data on the effects of C+K on the cholesterol metabolism, which was investigated in earlier in vivo studies, with the present findings suggests that DNA-protective effects take place at exposure levels which are substantially lower than those which cause hypercholesterolemia.

Modification of N‐Acetyltransferases and Glutathione S‐Transferases by Coffee Components: Possible Relevance for Cancer Risk

Enzymes of xenobiotic metabolism are involved in the activation and detoxification of carcinogens and can play a pivotal role in the susceptibility of individuals toward chemically induced cancer. Differences in such susceptibility are often related to genetically predetermined enzyme polymorphisms but may also be caused by enzyme induction or inhibition through environmental factors or in the frame of chemopreventive intervention. In this context, coffee consumption, as an important lifestyle factor, has been under thorough investigation. Whereas the data on a potential procarcinogenic effect in some organs remained inconclusive, epidemiology has clearly revealed coffee drinkers to be at a lower risk of developing cancers of the colon and the liver and possibly of several other organs. The underlying mechanisms of such chemoprotection, modifications of xenobiotic metabolism in particular, were further investigated in rodent and in vitro models, as a result of which several individual chemoprotectants out of the >1000 constituents of coffee were identified as well as some strongly metabolized individual carcinogens against which they specifically protected. This chapter discusses the chemoprotective effects of several coffee components and whole coffee in association with modifications of the usually protective glutathione-S-transferase (GST) and the more ambivalent N-acetyltransferase (NAT). A key role is played by kahweol and cafestol (K/C), two diterpenic constituents of the unfiltered beverage that were found to reduce mutagenesis/tumorigenesis by strongly metabolized compounds, such as 2-amino-1-methyl-6-phenylimidazo-[4,5-b]pyridine, 7,12-dimethylbenz[a]anthracene, and aflatoxin B(1), and to cause various modifications of xenobiotic metabolism that were overwhelmingly beneficial, including induction of GST and inhibition of NAT. Other coffee components such as polyphenols and K/C-free coffee are also capable of increasing GST and partially of inhibiting NAT, although to a somewhat lesser extent.

Modulation of tea and tea polyphenols on benzo(a)pyrene-induced DNA damage in Chang liver cells

The protective effects of three tea extracts (green tea, GTE; oolong tea, OTE; and black tea, BTE) and five tea polyphenols (epicatechin, EC; epicatechin gallate, ECG; epigallocatechin, EGC; epigallocatechin gallate, EGCG; and theaflavins, THFs) on benzo[a]pyrene (B[a]P)-induced DNA damage in Chang liver cells were evaluated using the comet assay. B[a]P-induced DNA damage in Chang liver cells was significantly (p < 0.05) inhibited by GTE and OTE at a concentration of 10 microg/ml and by BTE at 25 microg/ml. At a concentration of 100 microg/ml, the % tail DNA was reduced from 33% (B[a]P treated only) to 10, 9, 13%, by GTE, OTE and BTE, respectively. EC and ECG did not cause DNA damage in cells according to the results of the comet assay; however, EGC, EGCG and theaflavins caused DNA damage in cells at a concentration of 100 microM. The results indicated that EC and ECG had protective effects against B[a]P-induced DNA damage in cells at a concentration of 10-100 microM. Although EGC, EGCG and the theaflavins caused DNA damage at a high concentration, but they had protective effects against B[a]P-induced DNA damage in cells at a low concentration of 10-50 microM. The results also showed that the DNA damage in cells induced by EGC, EGCG, and the theaflavins was due to the generation of superoxide during incubation with cells at a higher concentration. Therefore, tea catechins and THFs play an important role in enabling tea extracts to inhibit DNA damage in Chang liver cells.

Potential chemoprotective effects of the coffee components kahweol and cafestol palmitates via modification of hepatic N-acetyltransferase and glutathione S-transferase activities

Coffee drinking has been associated with reduced incidence of colorectal cancer, possibly via chemoprotection/modification of the metabolism of dietary heterocyclic amine carcinogens such as 2-amino-1-methyl-6-phenylimidazo-[4,5-b]pyridine (PhIP) by kahweol and cafestol palmitates (K/C), two components of unfiltered coffee. Using the PhIP-exposed male Fisher F344 rat as a model, K/C have been shown to reduce colonic PhIP-DNA adducts by > 50%. We have used the male F344 rat to investigate the effects of dietary K/C (0.02-0.2% as a 1:1 mixture) on the metabolism of PhIP by N-acetyltransferase- (NAT), sulfotransferase- (SULT), and glutathione-dependent pathways. K/C decreased hepatic NAT-dependent PhIP activation by up to 80% in a dose-dependent manner. Conversely, hepatic glutathione S-transferase (GST) activity/expression increased, e.g., 3-4 fold toward 1-chloro-2,4-dinitrobenzene (total activity), up to 23-fold toward 4-vinylpyridine (rGSTP1), and approximately 7-fold for rGSTA2 protein. These effects had fully developed after 5 days of the test diet and persisted for at least 5 days after withdrawal of K/C. Hepatic glutathione increased two- to threefold and this increase was more short-lived than other changes. K/C did not modify hepatic SULT activity or colon NAT and GST activities. Benzylisothiocyanate and black tea, which have also been shown to reduce the formation of PhIP-DNA adducts in this model, had little effect on hepatic NAT, SULT, GST, or GSH. In primary culture of rat hepatocytes, both kahweol and cafestol palmitates reduced NAT activity by 80%. In summary, the unique potential of K/C to convert rapid acetylators to a slow acetylator phenotype, accompanied by GST induction, might contribute to chemoprevention against cancers associated with heterocyclic amines.