A critical assessment of some biomarker approaches linked with dietary intake

In this review many examples are given of the complexities involved in using some biomarkers in relation to assessing the effects of dietary exposure, when there is frequently a need to determine changes following long-term low level exposure to dietary components. These range from understanding why the biomarker might be valuable and how best it can be measured, to the pitfalls which can occur in the interpretation of data. Analytical technique is considered in relation to folate and selenium, and flavonoid and carotenoid species are used to illustrate how the metabolism of a compound may alter the validity or adequacy of a marker. Vitamin A is discussed in relation to the difficulties which can arise when there are several biomarkers that may be available to assess exposure to one nutrient. Vitamin B12 is discussed in relation to the dietary choices made by individuals. Possible interactions and the role of measuring total antioxidant capacity is considered in some detail. In contrast to most nutrients, there is a marked lack of biomarkers of either exposure or effect for most non-nutrients. The role of biological effect monitoring is considered for dietary contaminants, fumonisins and polyhalogenated aromatic hydrocarbons. Aflatoxins are discussed to exemplify food contaminants for which the biomarker approach has been extensively studied. Finally some compounds which are deliberately added to foods and some which appear as processing contaminants are each considered briefly in relation to the requirement for a biomarker of exposure to be developed.

Antimutagenic activity of green tea and black tea extracts studied in a dynamic in vitro gastrointestinal model

An in vitro gastrointestinal model, which simulates the conditions in the human digestive tract, was used to determine potential antimutagenic activity of extracts of black tea and green tea. In this paper, results are presented on the availability for absorption of potential antimutagenic compounds present in tea and on the influence of the food matrix on this activity. Between 60 and 180min after the tea was introduced into the model, antimutagenic activity was recovered from the jejunal compartment by means of dialysis: the dialysate appeared to inhibit the mutagenicity of the food mutagen MeIQx in the direct plate assay with Salmonella typhimurium (Ames test). The maximum inhibition was measured at 2h after the start of the experiment and was comparable for black tea and green tea extract. To determine the influence of food matrices on the antimutagenic activity of tea, the model was loaded with black tea together with milk or a homogenized standard breakfast. The maximum inhibition observed with black tea was reduced by 22, 42 and 78% in the presence of whole milk, semi-skimmed milk, and skimmed milk, respectively. Whole milk and skimmed milk abolished the antimutagenic activity of green tea by more than 90%; for semi-skimmed milk the inhibition was more than 60%. When a homogenized breakfast was added into the model together with the black tea extract, the antimutagenic activity was completely eliminated. When tea and MeIQx were added together into the digestion model, MeIQx mutagenicity was efficiently inhibited, with green tea showing a slightly stronger antimutagenic activity than black tea. In this case, the addition of milk had only a small inhibiting effect on the antimutagenicity. Antioxidant capacity and the concentration of catechins were also measured in the jejunal dialysates. The reduction in antimutagenic activity corresponded with reduction in antioxidant capacity and with a decrease of concentration of three catechins, viz. catechin, epigallocatechin gallate and epigallocatechin. The in vitro gastrointestinal model appears to be a useful tool to study the antimutagenicity of food components.

Effects of acute (-)-hydroxycitrate supplementation on substrate metabolism at rest and during exercise in humans

BACKGROUND

(-)-Hydroxycitrate (HCA), a competitive inhibitor of ATP-citrate lyase, should reduce the extramitochondrial acetyl-CoA pool. It has been hypothesized that HCA ingestion can reduce malonyl-CoA concentrations and consequently increase fatty acid oxidation in vivo.

OBJECTIVE

This study investigated the acute effects of HCA supplementation on substrate utilization at rest and during exercise in endurance-trained humans.

DESIGN

Ten cyclists [x+/- SD) age: 24 +/- 2 y, weight: 73 +/- 2 kg, maximal oxygen uptake: 4.95 +/- 0.11 L/min, maximal work output (W:max): 408 +/- 8 W] were studied at rest and during 2 h of exercise at 50% W:max on 2 occasions. Both 45 and 15 min before exercise and 30 and 60 min after the start of exercise, 3.1 mL/kg body wt of an HCA solution (19 g/L) or placebo was ingested. Total fat and carbohydrate oxidation rates were assessed. Blood samples were collected at 15-min intervals at rest and every 30 min during exercise.

RESULTS

Plasma HCA concentrations increased after HCA ingestion up to 0.39 +/- 0.02 mmol/L (82.0 +/- 4.8 mg/L). However, no significant differences in total fat and carbohydrate oxidation rates were observed between trials. Accordingly, plasma glucose, glycerol, and fatty acid concentrations did not differ between trials. Plasma lactate concentrations were significantly lower in the HCA than in the placebo trial after 30 min of exercise but at the end of the exercise period they did not differ between trials.

CONCLUSION

HCA, even when provided in large quantities, does not increase total fat oxidation in vivo in endurance-trained humans.

Mediterranean diet of Crete: foods and nutrient content

OBJECTIVES

To describe the traditional diet of Crete and evaluate the nutrient composition of 3 types of diet common in Crete by means of chemical analyses of composite food samples. To compare results with dietary analyses from a nutrient database developed at the University of Crete, Greece.

DESIGN

Three composite diet samples were obtained based on 7-day weighed food records representing the traditional Cretan Mediterranean diet (diet A), typical diet of present-day Greek adolescents (diet B), and fasting diet of the Eastern Orthodox church (diet C). Analyses were performed chemically and using a nutrient database.

RESULTS

Chemical analyses provided a definitive measure, for the first time, of the nutrient composition of the complete Greek diet as it was in the early 1960s. In comparing chemical analyses with nutrient database analyses, differences greater than 15% of the analyzed value were found in all 3 diets for cholesterol and some vitamins. The differences between analyzed and calculated values in total fat and saturated fat content were less than 15% in all diets.

APPLICATIONS/CONCLUSIONS

The present study provides 2 practical examples of the Mediterranean diet, which although widely publicized has rarely been analyzed chemically. Diet A has been shown to be related to the lowest rates for coronary heart disease and cancer mortality compared with the diets of the other populations of the Seven Countries study. As such, it could be recommended for health promotion and prevention of disease. Diet C contains even lower amounts of saturated fatty acids and would be excellent for patients with hypercholesterolemia. The high antioxidants in diet C probably maintain very low levels of low-density lipoprotein cholesterol. Dietary analyses of the Greek diet could be based on an operational database such as ours if further chemical analyses are performed on specific foods. These would result in improved precision of the database and possible extension into national food composition tables and a national dietary database.

Ingestion of protein hydrolysate and amino acid-carbohydrate mixtures increases postexercise plasma insulin responses in men

To optimize the postexercise insulin response and to increase plasma amino acid availability, we studied postexercise insulin levels after the ingestion of carbohydrate and wheat protein hydrolysate with and without free leucine and phenylalanine. After an overnight fast, eight male cyclists visited our laboratory on five occasions, during which a control drink and two different beverage compositions in two different doses were tested. After they performed a glycogen-depletion protocol, subjects received a beverage (3.5 mL. kg(-1)) every 30 min to ensure an intake of 1.2 g. kg(-1). h(-1) carbohydrate and 0, 0.2 or 0.4 g. kg(-1). h(-1) protein hydrolysate (and amino acid) mixture. After the insulin response was expressed as the area under the curve, only the ingestion of the beverages containing wheat protein hydrolysate, leucine and phenylalanine resulted in a marked increase in insulin response (+52 and + 107% for the 0.2 and 0.4 g. kg(-1). h(-1) mixtures, respectively; P: < 0. 05) compared with the carbohydrate-only trial). A dose-related effect existed because doubling the dose (0.2-0.4 g. kg(-1). h(-1)) led to an additional rise in insulin response (P: < 0.05). Plasma leucine, phenylalanine and tyrosine concentrations showed strong correlations with the insulin response (P: < 0.0001). This study provides a practical tool to markedly elevate insulin levels and plasma amino acid availability through dietary manipulation, which may be of great value in clinical nutrition, (recovery) sports drinks and metabolic research.

Application of a dynamic in vitro gastrointestinal tract model to study the availability of food mutagens, using heterocyclic aromatic amines as model compounds

The TNO gastro-Intestinal tract Model (TIM) is a dynamic computer-controlled in vitro system that mimics the human physiological conditions in the stomach and small intestine. In the current TIM physiological parameters such as pH, temperature, peristaltic movements, secretion of digestion enzymes, bile and pancreatic juices, and absorption of digested products-by removal through dialysis-was simulated. Heterocyclic aromatic amines (HAA; viz. IQ, MeIQ, MeIQx and PhIP) were used as model compounds for food mutagens, and the passage through TIM was investigated for each of these compounds separately. Subsequently, the influence of a matrix and different rates of passage on the availability for absorption and distribution were studied in experiments with prepared meat, supplemented with MeIQx. Samples taken at various time points from the jejunal and ileal dialysates and from the lumen at the end of the small intestine (ileal delivery) were tested for the presence of mutagenic activity in the Ames test with Salmonella typhimurium strain TA98 as indicator, in the presence of mammalian metabolic activation (rat S9 mix). The results show that, comparable with the human in vivo situation, all four HAA are quickly removed (approx. 50% in 2 hr; approx. 95% in 6 hr) and mainly recovered from the lumen into the jejunal and ileal dialysates (94% of recovery). Only 5+/-1.5% is recovered in the chyme at the end of the small intestine. When MeIQx was added to meat, its availability for absorption was slower, although the influence of the gastrointestinal passage time on the availability of MeIQx was more pronounced than this matrix effect. More MeIQx was found in the jejunal dialysate (23%; P<0.01) and less in the ileal delivery (8%; P<0.01) when simulating the gastrointestinal passage of solid meals was compared to simulating that of liquid meals. The present experiments demonstrate that TIM can be applied to study in vitro the availability of heterocyclic aromatic amines in the gastrointestinal tract. More generally, these studies indicate that TIM shows promise as a useful tool for various research purposes dealing with the availability for absorption of mutagenic as well as antimutagenic components in food.

Intake of butylated hydroxyanisole and butylated hydroxytoluene and stomach cancer risk: results from analyses in the Netherlands Cohort Study

Both carcinogenic and anticarcinogenic properties have been reported for the synthetic antioxidants butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT). The association between dietary intake of BHA and BHT and stomach cancer risk was investigated in the Netherlands Cohort Study (NLCS) that started in 1986 among 120,852 men and women aged 55 to 69 years. A semi-quantitative food frequency questionnaire was used to assess food consumption. Information on BHA or BHT content of cooking fats, oils, mayonnaise and other creamy salad dressings and dried soups was obtained by chemical analysis, a Dutch database of food additives (ALBA) and the Dutch Compendium of Foods and Diet Products. After 6.3 years of follow-up, complete data on BHA and BHT intake of 192 incident stomach cancer cases and 2035 subcohort members were available for case-cohort analysis. Mean intake of BHA or BHT among subcohort members was 105 and 351 microg/day, respectively. For consumption of mayonnaise and other creamy salad dressings with BHA or BHT no association with stomach cancer risk was observed. A statistically non-significant decrease in stomach cancer risk was observed with increasing BHA and BHT intake [rate ratio (RR) highest/lowest intake of BHA = 0.57 (95% confidence interval (CI): 0.25-1.30] and BHT = 0.74 (95% CI: 0.38-1.43). In this study, no significant association with stomach cancer risk was found for usual intake of low levels of BHA and BHT.

Plasma insulin responses after ingestion of different amino acid or protein mixtures with carbohydrate

BACKGROUND

Protein induces an increase in insulin concentrations when ingested in combination with carbohydrate. Increases in plasma insulin concentrations have been observed after the infusion of free amino acids. However, the insulinotropic properties of different amino acids or protein (hydrolysates) when co-ingested with carbohydrate have not been investigated.

OBJECTIVE

The aim of this study was to define an amino acid and protein (hydrolysate) mixture with a maximal insulinotropic effect when co-ingested with carbohydrate.

DESIGN

Eight healthy, nonobese male subjects visited our laboratory, after an overnight fast, on 10 occasions on which different beverage compositions were tested for 2 h. During those trials the subjects ingested 0.8 g*kg(-)(1)*h(-)(1) carbohydrate and 0.4 g*kg(-)(1)*h(-)(1) of an amino acid and protein (hydrolysate) mixture.

RESULTS

A strong initial increase in plasma glucose and insulin concentrations was observed in all trials, after which large differences in insulin response between drinks became apparent. After we expressed the insulin response as area under the curve during the second hour, ingestion of the drinks containing free leucine, phenylalanine, and arginine and the drinks with free leucine, phenylalanine, and wheat protein hydrolysate were followed by the largest insulin response (101% and 103% greater, respectively, than with the carbohydrate-only drink; P < 0.05).

CONCLUSIONS

Insulin responses are positively correlated with plasma leucine, phenylalanine, and tyrosine concentrations. A mixture of wheat protein hydrolysate, free leucine, phenylalanine, and carbohydrate can be applied as a nutritional supplement to strongly elevate insulin concentrations.

Fruits and vegetables increase plasma carotenoids and vitamins and decrease homocysteine in humans

Observational epidemiologic studies have shown that a high consumption of fruits and vegetables is associated with a decreased risk of chronic diseases. Little is known about the bioavailability of constituents from vegetables and fruits and the effect of these constituents on markers for disease risk. Currently, the recommendation is to increase intake of a mix of fruits and vegetables ("five a day"). We investigated the effect of this recommendation on plasma carotenoids, vitamins and homocysteine concentrations in a 4-wk dietary controlled, parallel intervention study. Male and female volunteers (n = 47) were allocated randomly to either a daily 500-g fruit and vegetable ("high") diet or a 100-g fruit and vegetable ("low") diet. Analyzed total carotenoid, vitamin C and folate concentrations of the daily high diet were 13.3 mg, 173 mg and 228.1 microg, respectively. The daily low diet contained 2.9 mg carotenoids, 65 mg vitamin C and 131.1 microg folate. Differences in final plasma levels between the high and low group were as follows: lutein, 46% [95% confidence interval (CI) 28-64]; beta-cryptoxanthin, 128% (98-159); lycopene, 22% (8-37); alpha-carotene, 121% (94-149); beta-carotene, 45% (28-62); and vitamin C, 64% (51-77) (P < 0.05). The high group had an 11% (-18 to -4) lower final plasma homocysteine and a 15% (0.8-30) higher plasma folate concentration compared with the low group (P < 0.05). This is the first trial to show that a mix of fruits and vegetables, with a moderate folate content, decreases plasma homocysteine concentrations in humans.

Brassica vegetables and cancer prevention. Epidemiology and mechanisms

This paper first gives an overview of the epidemiological data concerning the cancer-preventive effect of brassica vegetables, including cabbages, kale, broccoli, Brussels sprouts, and cauliflower. A protective effect of brassicas against cancer may be plausible due to their relatively high content of glucosinolates. Certain hydrolysis products of glucosinolates have shown anticarcinogenic properties. The results of six cohort studies and 74 case-control studies on the association between brassica consumption and cancer risk are summarized. The cohort studies showed inverse associations between the consumption of brassica's and risk of lung cancer, stomach cancer, all cancers taken together. Of the case-control studies 64% showed an inverse association between consumption of one or more brassica vegetables and risk of cancer at various sites. Although the measured effects might have been distorted by various types of bias, it is concluded that a high consumption of brassica vegetables is associated with a decreased risk of cancer. This association appears to be most consistent for lung, stomach, colon and rectal cancer, and least consistent for prostatic, endometrial and ovarian cancer. It is not yet possible to resolve whether associations are to be attributed to brassica vegetables per se or to vegetables in general. Further epidemiological research should separate the anticarcinogenic effect of brassica vegetables from the effect of vegetables in general. The mechanisms by which brassica vegetables might decrease the risk of cancer are reviewed in the second part of this paper. Brassicas, including all types of cabbages, broccoli, cauliflower, and Brussels sprouts, may be protective against cancer due to their glucosinolate content. Glucosinolates are usually broken down through hydrolysis catalysed by myrosinase, an enzyme that is released from damaged plant cells. Some of the hydrolysis products, viz. indoles, and isothiocyanates, are able to influence phase 1 and phase 2 biotransformation enzyme activities, thereby possibly influencing several processes related to chemical carcinogenesis, e.g. the metabolism, DNA-binding, and mutagenic activity of promutagens. Most evidence concerning anticarcinogenic effects of glucosinolate hydrolysis products and brassica vegetables has come from studies in animals. In addition, studies carried out in humans using high but still realistic human consumption levels of indoles and brassica vegetables have shown putative positive effects on health. The combination of epidemiological and experimental data provide suggestive evidence for a cancer preventive effect of a high intake of brassica vegetables.

In vitro and in vivo inhibition of human flavin-containing monooxygenase form 3 (FMO3) in the presence of dietary indoles

The effect of consumption of glucosinolate-containing Brussels sprouts on flavin-containing monooxygenase functional activity in humans was investigated in 10 healthy, male, non-smoking volunteers. After a 3-week run-in period, 5 volunteers continued on a glucosinolate-free diet for 3 weeks (control group), and 5 others consumed 300 g of cooked Brussels sprouts per day (sprouts group). Human flavin-containing monooxygenase activity was measured by determining the levels of urinary trimethylamine and trimethylamine N-oxide. In the control group similar trimethylamine to trimethylamine N-oxide ratios were observed, while in the sprouts group the trimethylamine to trimethylamine N-oxide ratios were increased 2.6- to 3.2-fold, and thus flavin-containing monooxygenase functional activity was decreased significantly. To investigate the molecular basis for the in vivo inhibition of functional human flavin-containing monooxygenase activity, in vitro studies were carried out examining the effect of acid condensation products of indole-3-carbinol, anticipated to be formed after transit of Brussels sprouts through the gastrointestinal system, on the prominent cDNA-expressed human flavin-containing monooxygenase form 3 enzymes. Two indole-containing materials were observed to be potent inhibitors of human flavin-containing monooxygenases, having Ki values in the low micromolar range. The results suggested that acid condensation products expected to be formed upon transit of Brussels sprouts materials through the gastrointestinal system were potent competitive inhibitors of human flavin-containing monooxygenase form 3 enzymes. The findings indicate that daily intake of Brussels sprouts may lead to a decrease in human flavin-containing monooxygenase activity, and this may have consequences for metabolism of other xenobiotics or dietary constituents.

The role of biotransformation in dietary (anti)carcinogenesis

The fact that dietary compounds influence the susceptibility of human beings to cancer, is widely accepted. One of the possible mechanisms that is responsible for these (anti)carcinogenic effects is that dietary constituents may modulate biotransformation enzymes, thereby affecting the (anti)carcinogenic potential of other compounds. This ambiguous theme is the basis for the present paper. The possible effects of enzymatic bioactivation and detoxification of dietary constituents are discussed using two representative examples of phase I and phase II biotransformation enzymes i.e., cytochrome P450 and glutathione S-transferase. Furthermore, the impact of genetic polymorphisms of these two enzyme systems is considered. Although it is very difficult on the basis of the enzyme inducing or inhibiting properties of dietary compounds, especially to characterize them as anticarcinogenic, for certain constituents it is acknowledged that they have anticarcinogenic properties. As such, this provides for an important mechanistic substantiation of the established cancer chemopreventive effect of a diet rich in fruits and vegetables.

Salinomycin-induced polyneuropathy in cats: morphologic and epidemiologic data

In April 1996, an outbreak of toxic polyneuropathy in cats occurred in the Netherlands. All cats had been fed one of two brands of dry cat food from one manufacturer. Chemical analyses of these foods, stomach contents, and liver and kidney of affected cats revealed contamination with the ionophor salinomycin. Epidemiologic and clinical data were collected from 823 cats, or about 1% of the cats at risk. In 21 affected cats, postmortem examination was performed. The affected cats had acute onset of lameness and paralysis of the hindlimbs followed by the forelimbs. Clinical and pathologic examination indicated a distal polyneuropathy involving both the sensory and motor nerves.

Effect of Brussels sprouts on oxidative DNA-damage in man

The effect of consumption of Brussels sprouts on the excretion of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) into human urine was investigated. Ten non-smoking volunteers (five males and five females) were randomly assigned to two groups. Five volunteers started on a diet of 300 g of glucosinolate-free vegetables whereas the other five consumed 300 g of Brussels sprouts per day. After 1 week dietary regimes were reversed. Levels of 8-oxodG in 24-h urine samples were measured by high-performance liquid chromatography. In four of five males a reduction in 8-oxodG was found, whereas in the fifth male the 8-oxodG excretion was high in the control period and was even much higher in the sprouts period. In females no effect of consumption of Brussels sprouts on excretion of 8-oxodG was found. Our previous and present findings support the results of epidemiologic studies that consumption of brassica vegetables may diminish cancer risk.

Safety evaluation of lipase derived from Rhizopus oryzae: summary of toxicological data

A lipase enzyme, obtained from Rhizopus oryzae produced by a fermentation process was subjected to a series of toxicological tests to document the safety for use as a food additive. The enzyme product was examined for acute, subacute and subchronic oral toxicity, and mutagenic potential. An extensive literature search on the production organism has also been conducted. No evidence of (sub)acute oral toxicity or mutagenic potential was found. Administration of the lipase at dosages of 50, 200 and 1000 mg/kg body weight/day for 90 days did not induce noticeable signs of toxicity. A few minor changes in the chemical composition of the blood in the highest dose group were of no toxicological significance. The no-observed-adverse-effect level of the tox-batch in the subchronic toxicity study was 1000 mg/kg body weight/day. It can be concluded that no safety concerns were identified in the studies conducted with this lipase preparation derived from R. oryzae and produced under controlled fermentation conditions.

A review of mechanisms underlying anticarcinogenicity by brassica vegetables

The mechanisms by which brassica vegetables might decrease the risk of cancer are reviewed in this paper. Brassicas, including all types of cabbages, broccoli, cauliflower and Brussels sprouts, may be protective against cancer due to their relatively high glucosinolate content. Glucosinolates are usually broken down through hydrolysis catalyzed by myrosinase, an enzyme that is released from damaged plant cells. Some of the hydrolysis products, viz. indoles and isothiocyanates, are able to influence phase 1 and phase 2 biotransformation enzyme activities, thereby possibly influencing several processes related to chemical carcinogenesis, e.g. the metabolism, DNA-binding and mutagenic activity of promutagens. A reducing effect on tumor formation has been shown in rats and mice. The anticarcinogenic action of isothiocyanates and indoles depends upon many factors, such as the test system, the target tissue, the type of carcinogen challenge and the anticarcinogenic compound, their dosage, as well as the timing of the treatment. Most evidence concerning anticarcinogenic effects of glucosinolate hydrolysis products and brassica vegetables has come from studies in animals. Animal studies are invaluable in identifying and testing potential anticarcinogens. In addition, studies carried out in humans using high but still realistic human consumption levels of indoles and brassica vegetables have shown putative positive effects on health.

Do dietary phytochemicals with cytochrome P-450 enzyme-inducing activity increase high-density-lipoprotein concentrations in humans?

Low plasma concentrations of high-density lipoprotein (HDL) are associated with increased risk of coronary heart disease. Several drugs that induce the microsomal cytochrome P-450-dependent enzyme system in liver and intestine, the sites of HDL apolipoprotein (apo) A-I and A-II synthesis, raise plasma HDL concentrations in humans. To test the hypothesis that phytochemicals with cytochrome P-450-inducing activity may also increase plasma HDL concentrations, two controlled dietary trials were undertaken in healthy nonsmoking males aged 20-28 y. One study examined the effect of replacing 300 g glucosinolate-free vegetables with 300 g Brussels sprouts/d for 3 wk. The other study examined the effects of 150 mg eugenol/d in capsule form, using a double-blind, placebo-controlled crossover design. There were no significant increases in plasma apo A-I, apo A-II, HDL cholesterol, or HDL phospholipids. These results suggest that dietary phytochemicals that induce members of the cytochrome P-450 system do not necessarily raise plasma HDL concentrations in humans, but do not exclude the possibility that some phytochemicals may have such an effect.

Effect of a vegan diet on biomarkers of chemoprevention in females

1. In order to study the potential beneficial effects of a vegan diet, a cross-sectional study was performed and several biomarkers of chemoprevention were measured in a population of female 'living food' eaters ('vegans'; n = 20) vs matched omnivorous controls (n = 20). 2. White blood cells obtained from fresh blood samples were subjected to the single-cell gel-electrophoresis assay. There was no statistically significant difference between the vegans and controls in the parameters 'tail length' and 'tail moment'. However, the 'tail moment' was significantly lower in a subset of the vegans (i.e.in those who did not use any vitamin and/or mineral supplements). 3. Fresh blood samples were exposed in vitro to the mutagen mitomycin C just prior to culturing. After culturing the number of binucleated lymphocytes with micronuclei was scored. There was no difference between the controls and vegans in the incidence of baseline micronuclei, nor in the number of mitomycin C-induced micronuclei. However, a significant correlation (r = -0.64, P < 0.01) between the number of mitomycin C-induced micronuclei and the activity of erythrocyte superoxide dismutase was found in the vegans. The number of baseline micronuclei increased with age in both groups. These findings may be of biological relevance. 4. The content of glutathione-S-transferase-alpha in plasma was not different between the vegans (n = 12) and controls (n = 12). 5. The present data indicate a few differences in biomarkers of chemopreventive potential in strict vegans vs matched omnivorous controls. The significance of these changes as biologically relevant indicators of beneficial effects of vegan diets in humans needs to be determined in studies with a larger number of subjects.

Epidemiological studies on brassica vegetables and cancer risk

This paper gives an overview of the epidemiological data concerning the cancer-preventive effect of brassica vegetables, including cabbage, kale, broccoli, Brussels sprouts, and cauliflower. The protective effect of brassicas against cancer may be due to their relatively high content of glucosinolates. Certain hydrolysis products of glucosinolates have shown anticarcinogenic properties. The results of 7 cohort studies and 87 case-control studies on the association between brassica consumption and cancer risk are summarized. The cohort studies showed inverse associations between the consumption of cabbage, cauliflower, and broccoli and risk of lung cancer; between the consumption of brassicas and risk of stomach cancer; between broccoli consumption and risk of all cancers taken together; and between brassica consumption and the occurrence of second primary cancers. Of the case-control studies, 67% showed an inverse association between consumption of total brassica vegetables and risk of cancer at various sites. For cabbage, broccoli, cauliflower, and Brussels sprouts, these percentages were 70, 56, 67, and 29%, respectively. Although the measured effects might have been distorted by various types of bias, it is concluded that a high consumption of brassica vegetables is associated with a decreased risk of cancer. This association appears to be most consistent for lung, stomach, colon, and rectal cancer and least consistent for prostatic, endometrial, and ovarian cancer. It is not yet possible to resolve whether associations are to be attributed to brassica vegetables per se or to vegetables in general. Further epidemiological research should separate the anticarcinogenic effect of brassica vegetables from the effect of vegetables in general.

Effect of eugenol on the mutagenicity of benzo[a]pyrene and the formation of benzo[a]pyrene-DNA adducts in the lambda-lacZ-transgenic mouse

To study the possible reduction by eugenol of the mutagenicity and genotoxicity of benzo[a]pyrene (B[a]P) in vivo, the lambda-lacZ-transgenic mouse strain 40.6 (Muta Mouse) was used. Male mice were fed a diet containing 0.4% (w/w) eugenol or a control diet for 58 days. On day 10, half of the mice received an i.p. dose of 100 mg/kg b.w. B[a]P. The lacZ mutants were recovered by packaging of DNA isolated from liver into lambda phage, and expressed in E. coli C lacZ-recA-galE- bacteria. In both control mice and mice fed the eugenol diet, B[a]P treatment resulted in a similar, significant increase in lacZ mutant frequency. Eugenol was not mutagenic by itself. By 32P-postlabelling analysis of the liver DNA using an analysis method with chromatographic conditions for B[a]P-DNA adducts, no effect of eugenol on the formation of B[a]P-DNA adducts in the lambda-lacZ-transgenic mouse was found. By 32P-postlabelling analysis using an alkenylbenzene solvent system the amount of B[a]P-DNA adducts was lower in mice fed the eugenol diet than in mice fed the control diet but the decrease was not statistically significant. However, one spot indicative of an eugenol-associated DNA adduct was detected. The present data provide no evidence for antimutagenic or antigenotoxic potential of eugenol in vivo. Furthermore, they suggest genotoxicity in vivo of eugenol per se.

Effect of short-term dietary administration of eugenol in humans

1. In order to study the antigenotoxic potential of eugenol in humans, ten healthy non-smoking males ingested a daily amount of 150 mg eugenol or the placebo for seven consecutive days. After a washout period of one week, groups ingesting eugenol or the placebo were crossed and received the other treatment for seven consecutive days. 2. On days 8 and 22 blood samples were taken for the assessment of standard clinical biochemical parameters. To study the possible antigenotoxic effect of eugenol, on day 8 and 22 blood samples were collected and exposed in vitro to the established genotoxic agents mitomycin C and vinblastine. After exposure the percentage of cells with chromosome aberrations and micronuclei was determined in cultured white blood cells. On days 8 and 22 paracetamol (500 mg p.o.) was administered as test substance to measure phase-II biotransformation capacity. Glutathione-S-transferase (GST) activities were determined in erythrocytes and blood plasma. 3. No significant differences in the clinical biochemical parameters were detected between the eugenol-period and the placebo-period, indicating that daily administration of 150 mg eugenol for 7 days has no toxic affects. 4. No significant differences on the cytogenetic parameters were found after ingestion of eugenol. Thus, there are no indications for an antigenotoxic potential of eugenol in humans, consuming daily 150 mg eugenol for 7 days. 5. A significant reduction in alpha-class GSTs in plasma (P < 0.05), but not in the other measured biotransformation parameters, was found in volunteers during the eugenol-periods as compared to the placebo-period. This may either reflect GST-inhibition by eugenol or protection against background damage of liver cells by eugenol.

Inhibition of rat, mouse, and human glutathione S-transferase by eugenol and its oxidation products

The irreversible and reversible inhibition of glutathione S-transferases (GSTs) by eugenol was studied in rat, mouse and man. Using liver cytosol of human, rat and mouse, species differences were found in the rate of irreversible inhibition of GSTs by eugenol in the presence of the enzyme tyrosinase. Tyrosinase was used to oxidize eugenol. No inhibition was observed in the absence of tyrosinase. The rate of irreversible inhibition of GSTs was highest in mouse cytosol, and lowest in rat cytosol. In addition, the irreversible inhibition of human and rat GSTs by eugenol was studied using purified isoenzymes of man and rat. The human GST isoenzymes A1-1, M1a-1a and P1-1 and the rat GST isoenzymes 1-1, 2-2, 3-3, 4-4 and 7-7 were irreversibly inhibited by eugenol in the presence of tyrosinase. In this respect human GST P1-1 and rat GST 7-7 were by far the most sensitive enzymes; human GST A2-2 was not inhibited. Indications were found that human GST P1-1 may be inhibited via three mechanisms: in addition to the well documentated nucleophilic addition of quinones and oxidation of cysteine residues, a covalent subunit cross-linking was also observed. The reversible inhibition of human and rat GST by eugenol, eugenol methyl ether, isoeugenol methyl ether, 2-allylphenol and 4-propylphenol was also studied using purified isoenzymes. The reversible inhibition of human and rat GSTs, using 1-chloro-2,4-dinitrobenzene as substrate, was expressed as I25. All compounds caused moderate reversible inhibition (I25 ranged from 0.2 to 5.4 mM for human GSTs and from 0.4 to 4.9 mM for rat GSTs). In rat, eugenol methyl ether was the strongest inhibitor. In human, the overall inhibiting capacities of eugenol, eugenol methyl ether, isoeugenol methyl ether and 4-propyl phenol were more or less similar; 2-allylphenol was the poorest inhibitor.

Effect of eugenol on the genotoxicity of established mutagens in the liver

The influence of in vivo treatment with eugenol on established mutagens was studied to determine whether eugenol has antigenotoxic potential. The effects of eugenol in rats was investigated in the unscheduled DNA synthesis (UDS) assay with established mutagens and the Salmonella typhimurium mutagenicity assay. In addition, the effect of in vivo treatment with eugenol on benzo[a]pyrene (B[a]P)-induced genotoxicity in human hepatoma cell line Hep G2 was investigated in the single-cell gel electrophoresis assay. The mutagenicity of B[a]P in the S. typhimurium mutagenicity assay was lower in liver S-9 fractions from control rats. Incubation of liver S-9 fractions from eugenol-treated rats with dimethylbenzanthracene (DMBA) had no antimutagenic effect. Eugenol did not modify UDS activity in hepatocytes isolated from rats pretreated with eugenol orally after exposure of these cells in vitro to DMBA and aflatoxin B1. Four different treatment schemes of combinations of B[a]P and eugenol were examined in Hep G2 cells: pre-treatment with eugenol; simultaneous treatment with eugenol and B[a]P; a combination of these (pretreatment/simultaneous treatment); and post-treatment with eugenol. An increase in the genotoxicity of B[a]P was found in Hep G2 cells. No effect of eugenol on the genotoxicity of B[a]P was found with the pre- and post-treatments. It is concluded that the effect of eugenol on genotoxicity induced by established mutagens is not univocal; in vivo treatment of rats with eugenol resulted in a reduction of the mutagenicity of B[a]P in the S. typhimurium mutagenicity assay, while in the UDS assay no effect of eugenol was found. In vitro treatment of cultured cells with eugenol resulted in an increase in genotoxicity of B[a]P. These findings indicate that there is only limited support for the antigenotoxic potential of eugenol in vivo.

Antioxidant status in long-term adherents to a strict uncooked vegan diet

Antioxidant status was investigated in 20 Finnish middle-aged female vegans and in one male vegan who were following a strict, uncooked vegan diet ("living food diet"), by means of a dietary survey and biochemical measurements (blood concentrations of vitamins C and E and beta-carotene, and the activities of the zinc/copper-dependent superoxide dismutase and selenium-dependent glutathione peroxidase). Values were compared with those of omnivores matched for sex, age, social status, and residence. Antioxidant supplementation was used by 4 of 20 female vegans and by 11 of 20 control subjects. Based on dietary records, the vegans had significantly higher intakes of beta-carotene, vitamin E, vitamin C, and copper, and a significantly lower intake of selenium than the omnivorous control subjects. The calculated dietary antioxidant intakes by the vegans, expressed as percentages of the US recommended dietary allowances, were as follows: 305% of vitamin C, 247% of vitamin A, 313% of vitamin E, 92% of zinc, 120% of copper, and 49% of selenium. Compared with the omnivores, the vegans had significantly higher blood concentrations of beta-carotene, vitamin C, and vitamin E, as well as higher erythrocyte superoxide dismutase activity. These differences were also seen in pairs who were using no antioxidant supplements. The present data indicate that the "living food diet" provides significantly more dietary antioxidants than does the cooked, omnivorous diet, and that the long-term adherents to this diet have a better antioxidant status than do omnivorous control subjects.

Short-term moderate energy restriction does not affect indicators of oxidative stress and genotoxicity in humans

Restriction of energy intake (ER), without malnutrition of essential nutrients, has repeatedly been demonstrated to increase longevity in rodents. In the antioxidant theory of aging the lack of balance between the generation of free radicals and free radical scavenging was thought to be a main causal agent, in the aging process. From this point of view the antiaging effect induced by ER might be due to the lower rate of free-radical production and related damage induced by a lower metabolic rate. The antiaging effects of ER might also occur in humans. This study explored the effects of a 10-week moderately energy-restricted diet (80% of habitual) in 24 non-obese middle-aged men (16 ER subjects, 8 controls) on resting metabolic rate (RMR) and indicators of the primary antioxidant defense system, oxidative stress and genotoxicity. RMR decreased significantly in both groups, even when adjustments were made for the change in body composition. The increase in blood vitamin C concentration correlated with the increase in urinary 8-hydroxydeoxyguanosine (80HdG) excretion. The change in urinary 80HdG excretion also correlated with the change in RMR per kg fat-free mass. No differences between groups were found for changes in indicators of genotoxicity, erythrocyte catalase, glutathione peroxidase and superoxide dismutase activity and in plasma vitamin E, A or beta-carotene concentrations. We conclude that 10 weeks of moderate ER did not affect indicators of antioxidative capacity, oxidative stress and genotoxicity of humans. Since subjects were not in energy balance at the end of the study, no conclusions can be made with respect to long-term effects.