Search for dietary antimutagens and anticarcinogens: methodological aspects and extrapolation problems

Antimutagenic effect of essential oil of sage (Salvia officinalis L.) and its monoterpenes against UV-induced mutations in Escherichia coli and Saccharomyces cerevisiae

Mutagenic and antimutagenic potential of essential oil (EO) of cultivated sage (S. officinalis L.) and its monoterpenes: thujone, 1,8-cineole, camphor and limonene against UVC-induced mutations was studied with Salmonella/microsome, E. coli WP2, E. coli K12 [Simić, D., Vuković-Gacić, B., Knezević-Vukcević, J., 1998. Detection of natural bioantimutagens and their mechanisms of action with bacterial assay-system. Mutat. Res. 402, 51-57] and S. cerevisiae D7 reversion assays. The toxicity of EO differed, depending on the strain used. The most sensitive were permeable strains TA100, TA102, E. coli K12 IB112 and non-permeable WP2. Mutagenic potential of EO and monoterpenes was not detected, with or without S9. EO reduced the number of UV-induced revertants in a concentration-dependent manner, reaching 50-70% of inhibition at the maximum non-toxic concentrations: 3 microl/plate (TA102), 5 microl/plate (WP2), 7.5 microl/plate (IB112), 30 microl/plate (E. coli K12 SY252) and 60 microl/plate (D7). The metabolic activation had no effect on antimutagenic potential of EO. Similar toxicity of monoterpenes was observed in TA100, E. coli SY252 and D7, with the exception of limonene (less toxic to D7). Reduction of UV-induced revertants by non-toxic concentrations of monoterpenes, tested with SY252 and D7, reached 40-50% at 15-20 microl/plate of thujone, 10 microl/plate of cineole and 1-10 microg/plate of camphor. Limonene showed antimutagenic effect only in D7. Our data recommend sage monoterpenes for further chemoprevention studies.

Effects of Diuron [3-(3,4-dichlorophenyl)-1,1-dimethylurea] on the urinary bladder of male Wistar rats

Diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea) is a substituted urea herbicide widely used on agricultural crops such as soy, cotton and sugar cane. In a previous long-term study this herbicide exerted carcinogenic activity on the urinary bladder mucosa of male Wistar rats. In general, the genotoxic and mutagenic potentials of Diuron are considered to be negative. The present study aimed to evaluate the mode of action of Diuron on the urinary bladder mucosa of male Wistar rats. Six-week old male Wistar rats were fed pelleted Nuvilab diet mixed with Diuron at 125, 500 and 2500 ppm. As a positive control, 8.3% sodium saccharin (NaS) was fed in the diet. Preceding the sacrifice of the animals at the 20th week, urinary pH was measured and the genotoxic potential of Diuron was evaluated by the comet assay. Histological urothelial lesions in the urinary bladder and in the renal pelvis mucosa, cell proliferation/apoptosis evaluations, and scanning electron microscopy (SEM) of the urinary bladder mucosa were also performed. No DNA changes were found in urothelial or peripheral blood cells, and urinary pH was comparable to controls in all Diuron groups. In the urinary bladder urothelium, the incidence of simple hyperplasia (SH) by light microscopy was significantly increased (7/10; p<0.005) in the 2500 ppm Diuron group but not at the lower doses. By SEM, three of five animals treated with 2500 ppm Diuron showed urothelial cell necrosis and hyperplasia. In the renal pelvis, the incidence of SH was significantly increased in the Diuron 500 and 2500 ppm and in the NaS 8.3% groups. Cell proliferation was significantly increased in the Diuron 2500 ppm (p<0.05) and NaS 8.3% (p<0.05) groups. The results indicate that a high dietary concentration of Diuron is associated with urothelial necrosis and continuous regenerative cell proliferation that leads to urothelial hyperplasia.

Dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) and 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA), two naturally occurring benzoxazinones contained in sprouts of Gramineae are potent aneugens in human-derived liver cells (HepG2)

Benzoxazinoids (BAs) are toxic constituents of sprouts of Gramineae such as wheat, maize and rye and are part of the plant defence system against pests. In the last years, sprouts have been increasingly consumed as health foods and are also used for the production of dietary supplements. In the present study we investigated the mutagenic activities of the two most abundant BAs, namely 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) and 2,4-dihydroxy-1,4-benzoxazin-3-one (DIBOA) in the Salmonella/microsome assay and additionally, in micronucleus (MN) assay and single cell gel electrophoresis (SCGE) assay in a human-derived liver cell line (HepG2). DIBOA caused significant induction of his(+) revertants in all three strains in the range between 0.02 and 0.50 mg/plate; the highest activity was observed in TA100 (fivefold increase over the background at the highest dose level). The effect in YG1024 (a derivative of TA98 with increased acetyltransferase activity) was only slightly higher than the effect in the parental strain indicating that acetylation plays no crucial role in the activation of this BA. DIMBOA was in general less active and a positive result was only seen in the base substitution strain (TA100). Addition of rat liver homogenate (S9-mix) led to a significant (ca. twofold) increase of the mutagenic activities of both BAs. In SCGE assays with HepG2 cells consistently negative results were obtained with both compounds whereas in MN assays significant dose dependent effects were observed under similar experimental conditions. DIMBOA caused significant effects already at concentrations > or =1 microM; at the highest dose (20 microM) the MN frequency was sevenfold higher than the background level. DIBOA caused weaker effects and was positive at doses > or =2.5 microM, the maximal induction (twofold over background) was observed with 20 microM. Overall, DIMBOA was ca. 30-fold more active as DIBOA. Subsequent experiments with pancentromeric probes showed that >80% of the MN induced at the highest doses gave a centromere positive signal indicating that both BAs are aneugenic. This is an interesting observation as it is assumed that aneuploidy is a key event in cancer induction and at present no other aneugenic plant-derived substances of dietary relevance are known.

Inhibitory effects of beer on mutation in the Ames test and DNA adduct formation in mouse organs induced by 2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP)

An evaluation of the antigenotoxic potential of beer components against carcinogens contained in the human diet, namely heterocyclic amines (HCAs) including 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), was determined. The protective mechanism involved was also investigated. Beer samples were found to inhibit the mutagenicity of HCAs in the Ames test. Beer solution, consisting of a freeze-dried and dissolved sample, given as drink-water significantly reduced the formation of PhIP-DNA adducts in mouse colon and lung compared to control mice fed with PhIP in the absence of beer solution. Furthermore, beer solution added in the diet as a food additive mimic significantly reduced the amount of DNA adducts present in the liver and lung of mice fed with PhIP. In an effort to investigate the mechanism responsible for the observed protective effect, the effect of beer solutions on HCA metabolizing enzymes was investigated. Beer solutions inhibited the activity of CYP1A1 and CYP1A2, as determined from deethylation and demethylation assays using 7-ethoxy- and 7-methoxyresolufin, respectively. Considering the overall suppression of PhIP genotoxicity by beer, this study confirmed that beer components can interfere with the enzyme activity involved in the metabolism of HCAs and subsequently suppress the observed genotoxicity. The results of this study showed that beer components act in a protective capacity against the genotoxic effects of heterocyclic amines in vivo.

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.

Absence of carcinogenic and anticarcinogenic effects of annatto in the rat liver medium-term assay

Annatto (Bixa orellana L.) is a natural food colorant extensively used in many processed foods, especially dairy products. The lower cost of production and the low toxicity, make annatto a very attractive and convenient pigment in substitution to the many synthetic colorants. In the present study we investigate the carcinogenic and anticarcinogenic effects of dietary annatto in Wistar rat liver using the preneoplastic glutathione S-transferase (GST-P) foci and DNA damage biomarkers. Annatto, containing 5% bixin, was administered in the diet at concentrations of 20, 200, and 1000 ppm (0.07; 0.80 and 4.23 bixin/kg body wt/day, respectively), continuously during 2 weeks before, or 8 weeks after DEN treatment (200 mg/kg body wt, i.p.), to evaluate its effect on the liver-carcinogenesis medium-term bioassay. The comet assay was used to investigate the modifying potential of annatto on DEN (20 mg/kg body wt)-induced DNA damage. The results showed that annatto was neither genotoxic nor carcinogenic at the highest concentration tested (1000 ppm). No protective effects were also observed in both GST-P foci development and comet assays. In conclusion, in such experimental conditions, annatto shows no hepatocarcinogenic effect or modifying potential against DEN-induced DNA damage and preneoplastic foci in the rat liver.

Modulation of cytochrome P450 1A1 by food-derived heterocyclic aromatic amines

A short-term effect of a meal of fried meat is a postprandial induction of hepatic and intestinal cytochrome P450 activity. In order to identify the components responsible for this effect we investigated the potency of food derived genotoxic heterocyclic aromatic amines (HA) to induce CYP1A1 in vitro. In two cell lines, the rat hepatoma cell line H4IIE and the human breast cancer cell line MCF-7, we investigated 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx), 2-amino-3-methyl-9H-pyrido[2,3-b]indole (MeAC), 3-amino-1,4-dimethyl-5H-pyrido[4,3-b]indole (Trp-P-1) and Harman representing the different classes of HA at concentrations from 10(-8) to 10(-4) M. Induction of CYP1A1 was analysed on the mRNA level by semi-quantitative RT-PCR and the protein level (western blot using specific antibodies). The relative order of enzyme induction was Trp-P-1 with 1.4 x 10(-6) M (EC50 compared to TCDD 10(-9) M), MeAalphaC (1.4 x 10(-5)), Harman (2.1 x 10(-4)) and MeIQx (1.0 x 10(-3)). Furthermore, CYP1A1 enzyme activity was analysed as ethoxyresorufin-O-deethylase. While protein and mRNA analyses gave similar results, competitive inhibition impaired the enzyme activity assay. Inhibition of CYP1A1 activity was determined using microsomes of heterologous expressed CYP1A1. This dose-dependent inhibitory activity paralleled the induction potency. These results compare well with earlier data published for hepatic enzyme induction by HA observed in animal experiments. However, since the observed activities are rather weak and the amounts of HA ingested with a meal are low, there may be other factors involved in the observed postprandial enzyme induction in humans. On the other hand, concentrations in the micromolar range that are reached in high dosage animal experiments with HA may well influence cytochrome activity and, thus, influence the experimental outcome of these studies.

Inhibition of liver carcinogenesis in Wistar rats by consumption of an aqueous extract from leaves of Ardisia compressa

This study evaluates the chemopreventive effect of an aqueous extract of dried leaves of Ardisia compressa against liver cancer. A rat liver assay that mimics progressive forms of human disease was used as a carcinogenesis model. Forty-five male Wistar rats (180-200 g body weight) were injected intraperitoneally on day 1 with a single dose (100 mg/kg) of diethylnitrosamine (DEN), and also received via gavage 20 mg/kg acetylaminofluorene (2-AAF), on days 7, 8 and 9. The rats were randomly divided into four groups (n=15). Control groups (Group 1 and Group 2) had free access to water. Group 3 received 0.5% (w/v) of A. compressa tea for 10 days before treatment and during the study as the sole source of fluid until the rats were killed. A fourth group of 15 rats received no carcinogen or promoter but did receive 0.5%, (w/v) of A. compressa tea. All animals had 70% partial hepatectomy at day 10. The incidences of hepatocellular foci, nodules and carcinoma were significantly smaller in Group 3 than in Group 2 (P<0.01). A. compressa tea consumption alone (Group 4) did not induce the development of foci, nodules or carcinomas (P<0.01). The striking observation of this study was that consumption of A. compressa tea resulted in complete inhibition of the chemically-induced hepatocarcinogenesis in Wistar rats.

Investigation of the antimutagenic effects of selected South African medicinal plant extracts

Dichloromethane extracts from different parts of Rhamnus prinoides, Ornithogalum longibracteatum, Gardenia volkensii, Spirostachys africana, Diospyros whyteana, Syzigium cordatum and Prunus africana were investigated for mutagenic and antimutagenic effects in Salmonella/microsome and micronucleus tests. None of the extracts tested in the Ames test were found to induce mutations or to modify the effect of the mutagen 4-nitroquinoline-oxide (4NQO). In the micronucleus test, extracts from twigs/bark of R. prinoides, twigs of D. whyteana, P. africana and S. cordatum significantly lowered the effect of the mutagen mitomycin C (MMC). Extracts from twigs/bark of G. volkensii and S. africana were genotoxic in the micronucleus test, while extracts of O. longibracteatum leaves potentiated the genotoxicity of MMC. This preliminary investigation shows that plant extracts used in traditional medicine may have particular effects with regard to mutagenicity and antimutagenicity indicating careful use in some instances and the need to isolate their active principles for further research.

The 10 basic requirements for a scientific paper reporting antioxidant, antimutagenic or anticarcinogenic potential of test substances in in vitro experiments and animal studies in vivo

There is increasing evidence that chemicals/test substances cannot only have adverse effects, but that there are many substances that can (also) have a beneficial effect on health. As this journal regularly publishes papers in this area and has every intention in continuing to do so in the near future, it has become essential that studies reported in this journal reflect an adequate level of scientific scrutiny. Therefore a set of essential characteristics of studies has been defined. These basic requirements are default properties rather than non-negotiables: deviations are possible and useful, provided they can be justified on scientific grounds. The 10 basic requirements for a scientific paper reporting antioxidant, antimutagenic or anticarcinogenic potential of test substances in in vitro experiments and animal studies in vivo concern the following areas: (1) Hypothesis-driven study design; (2) The nature of the test substance; (3) Valid and invalid test systems; (4) The selection of dose levels and gender; (5) Reversal of the effects induced by oxidants, carcinogens and mutagens; (6) Route of administration; (7) Number and validity of test variables; (8) Repeatability and reproducibility; (9) Statistics; and (10) Quality Assurance.