Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis
Coffee and its chemopreventive components Kahweol and Cafestol increase the activity of O6-methylguanine-DNA methyltransferase in rat liver—comparison with phase II xenobiotic metabolism
Introduction
Kahweol and Cafestol (K/C) are two diterpenes that are contained in coffee beans and rather high amounts may also be present in coffee as a beverage [1], [2]. Concentrations of up to 90 and 17 mg/l each have been found in unfiltered Turkish and espresso coffee, respectively [1]. Interestingly, a lower rate of colon cancer, one of the most frequent cancers in the western world, has been observed in consumers of coffees with a high K/C content [3], [4]. This finding may be partially explicable by the association of colon cancer with the relevant exposure of humans to the cooked food mutagen 2-amino-1-methyl-6-phenylimidazo[4,5-b]-pyridine (PhIP) and other heterocyclic aromatic amines [5]. Pretreatment of rats with a 1:1 mixture of K/C palmitates caused a considerable inhibition of PhIP-related genotoxicity, i.e. the formation of PhIP-DNA adducts, in the colon and other organs of these animals [6]. K/C was furthermore shown to exert protection against the mutagenicity and tumorigenicity of the mycotoxin aflatoxin B1 (AFB1) in rat liver preparations [7] and of the polyaromatic hydrocarbon 7,12-dimethylbenz[a]anthracene in the buccal pouch of the hamster [8]. Thus, the chemoprotective potential of K/C is suggested to concern a rather wide range of substances.
The antimutagenic and anticarcinogenic properties of K/C have thus far been primarily related to the beneficial modifications of xenobiotic metabolism that K/C has been observed to cause in the rodent. Such effects include reduced activation of mutagens/carcinogens, e.g. by inhibition of cytochrome P450 enzymes [7], [9] (Huber et al., in preparation) and N-acetyltransferase (Huber, Kadlubar et al., in preparation), as well as their enhanced detoxification. Important carcinogen-detoxifying enzyme systems known to be stimulated by K/C are glutathione transferase (GST) [6], [7], [9], [10], [11], [12] and UDP-glucuronosyl transferase (UDPGT) [12]. The coffee components were reported to enhance most of the various enzyme sub-families into which both GST and UDPGT are subdivided such as GST-α, GST-μ, GST-π, and GST-θ in case of GST and UGT1 and UGT2 in case of UDPGT. Also, K/C increased the levels of glutathione (GSH), the co-factor of GST-related detoxification, and γ-glutamylcysteine-synthetase (GCS), the limiting enzyme of GSH synthesis [13], [14].
In view of the significant effect of K/C on xenobiotic metabolism the question arises whether chemoprotection by K/C may also involve effects that are independent of the metabolism of the native mutagen/carcinogen. Likewise, it is unknown whether K/C treatment remains beneficial even after the occurrence of initial DNA damage. Therefore, in the present study, we investigated the influence of K/C on DNA repair as a possible contribution to the chemoprotective potential. We focused on O6-methylguanine-DNA methyltransferase (MGMT) which repairs O6-methylguanine, a DNA lesion that was found to be highly associated with mutagenicity upon exposure to alkylating xenobiotics such as N-nitrosamines, N-nitrosureas, and azoxymethane [15], [16]. MGMT also repairs larger O6-alkylguanine adducts as well as O4-methylthymine. In several studies, transgenic mice overexpressing MGMT were shown to be less susceptible to xenobiotic-induced tumorigenesis as compared to wild-type animals [17], [18], [19], [20], [21], [22], [23]. On the other hand, xenobiotic-induced tumorigenesis was increased in MGMT knock-out mice [24], [25], [26], and specific K-ras mutations in the human colon were more frequent under conditions of silenced or lowered MGMT [27], [28], [29]. Such findings emphasize the possibility that MGMT induction by a nutrional or life-style-related component might contribute to the chemoprevention of cancer.
The present study involved treatments of male F344 rats with several doses of K/C or Cafestol-alone in the feed and with Turkish coffee in the drinking water. In order to compare the degree and dose range of potential effects of K/C on MGMT with those on phase II xenobiotic metabolism, we also measured several GST-related parameters (overall GST-activity, GST-π-activity, GSH content, GCS activity) and UDPGT activity in the rats receiving Turkish coffee and K/C. The effects of any of these treatments on MGMT and of Turkish coffee on the investigated parameters of hepatic phase II metabolism have not been studied thus far.
Section snippets
Chemicals
K/C (1:1, i.e. 47% Cafestol [CAS 469-83-0], 47% Kahweol [CAS 6894-43-5], 5% isomeric derivatives) and Cafestol (purity > 95%) were a kind gift from Robert J. Turesky of Nestlé (Lausanne, Switzerland). Turkish coffee was prepared from a commercially available Arabica product named “Regio-Der Beste” distributed by SPAR Österreichische Warenhandelsgesellschaft (Salzburg, Austria). All other reagents used in the study were of the highest purity available (p.a. or HPLC grade if required) and were
Increase in MGMT level upon treatment with Kahweol and Cafestol and Turkish coffee
As displayed in Fig. 1A, treatment with a high-dose of K/C resulted in a statistically significant 2.6-fold increase in hepatic MGMT as compared to untreated controls. This prompted us to analyze the dose–response relationship of the effect which showed that hepatic MGMT was enhanced by both K/C and Cafestol-alone in a clearly dose-dependent manner (Fig. 1B). The increases were significant with all K/C-doses except the lowest one and with Cafestol doses≥0.05%. While enhancements in the lower
Discussion
Our study demonstrates the capability of the coffee compounds K/C to increase the hepatic activity of MGMT in a dose-dependent manner. The associated dose–response curve was quantitatively similar to those of the K/C effects on overall GST, GSH, and GCS, and the reaction of the same three parameters to Turkish coffee resembled that of MGMT as well. It remains presently unknown whether these similarities involve regulation by a common molecular mechanism. UDPGT displayed the strongest increases
Acknowledgements
This work was in part supported by the Hochschuljubiläumsstiftung der Stadt Wien (University Anniversary Foundation of the City of Vienna) in Austria and by DFG (SFB 519/B4).
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