Vegetables, fruit, and cancer prevention: a review

In this review of the scientific literature on the relationship between vegetable and fruit consumption and risk of cancer, results from 206 human epidemiologic studies and 22 animal studies are summarized. The evidence for a protective effect of greater vegetable and fruit consumption is consistent for cancers of the stomach, esophagus, lung, oral cavity and pharynx, endometrium, pancreas, and colon. The types of vegetables or fruit that most often appear to be protective against cancer are raw vegetables, followed by allium vegetables, carrots, green vegetables, cruciferous vegetables, and tomatoes. Substances present in vegetables and fruit that may help protect against cancer, and their mechanisms, are also briefly reviewed; these include dithiolthiones, isothiocyanates, indole-3-carbinol, allium compounds, isoflavones, protease inhibitors, saponins, phytosterols, inositol hexaphosphate, vitamin C, D-limonene, lutein, folic acid, beta carotene, lycopene, selenium, vitamin E, flavonoids, and dietary fiber. Current US vegetable and fruit intake, which averages about 3.4 servings per day, is discussed, as are possible noncancer-related effects of increased vegetable and fruit consumption, including benefits against cardiovascular disease, diabetes, stroke, obesity, diverticulosis, and cataracts. Suggestions for dietitians to use in counseling persons toward increasing vegetable and fruit intake are presented.

Xanthohumol and related prenylflavonoids from hops and beer: to your good health!

Xanthohumol (3'-[3,3-dimethyl allyl]-2',4',4-trihydroxy-6'-methoxychalcone) is the principal prenylated flavonoid of the female inflorescences of the hop plant ('hops'), an ingredient of beer. Human exposure to xanthohumol and related prenylflavonoids, such as 8-prenylnaringenin and isoxanthohumol, is primarily through beer consumption. Xanthohumol has been characterized a 'broad-spectrum' cancer chemopreventive agent in in vitro studies, while 8-prenylnaringenin enjoys fame as the most potent phytoestrogen known to date. These biological activities suggest that prenylflavonoids from hops have potential for application in cancer prevention programs and in prevention or treatment of (post-)menopausal 'hot flashes' and osteoporosis. Xanthohumol and 8-prenylnaringenin are metabolized into many flavonoid derivatives with modified 3,3-dimethyl allyl (prenyl) moieties. Xanthohumol is formed in lupulin glands by a specialized branch of flavonoid biosynthesis that involves prenylation and O-methylation of the polyketide intermediate chalconaringenin. Although a lupulin gland-specific chalcone synthase is known, the aromatic prenyltransferase and O-methyltransferase participating in xanthohumol have not been identified. The prenylflavonoid pathway is a possible target for breeding or biotechnological modification of hops with the aim of increasing xanthohumol levels for beer brewing and 8-prenylnaringenin levels for pharmaceutical production.

Lycopene in tomatoes: chemical and physical properties affected by food processing

Lycopene is the pigment principally responsible for the characteristic deep-red color of ripe tomato fruits and tomato products. It has attracted attention due to its biological and physicochemical properties, especially related to its effects as a natural antioxidant. Although it has no provitamin A activity, lycopene does exhibit a physical quenching rate constant with singlet oxygen almost twice as high as that of beta-carotene. This makes its presence in the diet of considerable interest. Increasing clinical evidence supports the role of lycopene as a micronutrient with important health benefits, because it appears to provide protection against a broad range of epithelial cancers. Tomatoes and related tomato products are the major source of lycopene compounds, and are also considered an important source of carotenoids in the human diet. Undesirable degradation of lycopene not only affects the sensory quality of the final products, but also the health benefit of tomato-based foods for the human body. Lycopene in fresh tomato fruits occurs essentially in the all-trans configuration. The main causes of tomato lycopene degradation during processing are isomerization and oxidation. Isomerization converts all-trans isomers to cis-isomers due to additional energy input and results in an unstable, energy-rich station. Determination of the degree of lycopene isomerization during processing would provide a measure of the potential health benefits of tomato-based foods. Thermal processing (bleaching, retorting, and freezing processes) generally cause some loss of lycopene in tomato-based foods. Heat induces isomerization of the all-trans to cis forms. The cis-isomers increase with temperature and processing time. In general, dehydrated and powdered tomatoes have poor lycopene stability unless carefully processed and promptly placed in a hermetically sealed and inert atmosphere for storage. A significant increase in the cis-isomers with a simultaneous decrease in the all-trans isomers can be observed in the dehydrated tomato samples using the different dehydration methods. Frozen foods and heat-sterilized foods exhibit excellent lycopene stability throughout their normal temperature storage shelf life. Lycopene bioavailability (absorption) can be influenced by many factors. The bioavailability of cis-isomers in food is higher than that of all-trans isomers. Lycopene bioavailability in processed tomato products is higher than in unprocessed fresh tomatoes. The composition and structure of the food also have an impact on the bioavailability of lycopene and may affect the release of lycopene from the tomato tissue matrix. Food processing may improve lycopene bioavailability by breaking down cell walls, which weakens the bonding forces between lycopene and tissue matrix, thus making lycopene more accessible and enhancing the cis-isomerization. More information on lycopene bioavailability, however, is needed. The pharmacokinetic properties of lycopene remain particularly poorly understood. Further research on the bioavalability, pharmacology, biochemistry, and physiology must be done to reveal the mechanism of lycopene in human diet, and the in vivo metabolism of lycopene. Consumer demand for healthy food products provides an opportunity to develop lycopene-rich food as new functional foods, as well as food-grade and pharmaceutical-grade lycopene as new nutraceutical products. An industrial scale, environmentally friendly lycopene extraction and purification procedure with minimal loss of bioactivities is highly desirable for the foods, feed, cosmetic, and pharmaceutical industries. High-quality lycopene products that meet food safety regulations will offer potential benefits to the food industry.

Disposition of glucosinolates and sulforaphane in humans after ingestion of steamed and fresh broccoli

The cancer-chemopreventive effects of broccoli may be attributed, in part, to isothiocyanates (ITCs), hydrolysis products of glucosinolates. Glucosinolates are hydrolyzed to their respective ITCs by the enzyme myrosinase, which is inactivated by heat. In this study, the metabolic fate of glucosinolates after ingestion of steamed and fresh broccoli was compared in 12 male subjects in a crossover design. During each 48-hour baseline period, no foods containing glucosinolates or ITCs were allowed. The subjects then consumed 200 g of fresh or steamed broccoli; all other dietary sources of ITCs were excluded. Blood and urine samples were collected during the 24-hour period after broccoli consumption. Total ITC equivalents in broccoli and total ITC equivalents in plasma and urine were assayed by high-performance liquid chromatography as the cyclocondensation product of 1,2-benzenedithiol. The content of ITCs in fresh and steamed broccoli after myrosinase treatment was found to be virtually identical (1.1 vs. 1.0 micromol/g wet wt). The average 24-hour urinary excretion of ITC equivalents amounted to 32.3 +/- 12.7% and 10.2 +/- 5.9% of the amounts ingested for fresh and steamed broccoli, respectively. Approximately 40% of total ITC equivalents in urine, 25.8 +/- 13.9 and 6.9 +/- 2.5 micromol for fresh and steamed broccoli, respectively, occurred as the N-acetyl-L-cysteine conjugate of sulforaphane (SFN-NAC). Total ITC metabolites in plasma peaked between 0 and 8 hours, whereas urinary excretion of total ITC equivalents and SFN-NAC occurred primarily between 2 and 12 hours. Results of this study indicate that the bioavailability of ITCs from fresh broccoli is approximately three times greater than that from cooked broccoli, in which myrosinase is inactivated. Considering the cancer-chemopreventive potential of ITCs, cooking broccoli may markedly reduce its beneficial effects on health.

An update on the health effects of tomato lycopene

Lycopene is a non-provitamin A carotenoid that is responsible for the red to pink colors seen in tomatoes, pink grapefruit, and other foods. Processed tomato products are the primary dietary lycopene source in the United States. Unlike many other natural compounds, lycopene is generally stable to processing when present in the plant tissue matrix. Recently, lycopene has also been studied in relation to its potential health effects. Although promising data from epidemiological, as well as cell culture and animal, studies suggest that lycopene and the consumption of lycopene containing foods may affect cancer or cardiovascular disease risk, more clinical trial data is needed to support this hypothesis. In addition, future studies are required to understand the mechanism(s) whereby lycopene or its metabolites are proven to possess biological activity in humans.

Biological and therapeutic properties of bee pollen: a review

Natural products, including bee products, are particularly appreciated by consumers and are used for therapeutic purposes as alternative drugs. However, it is not known whether treatments with bee products are safe and how to minimise the health risks of such products. Among others, bee pollen is a natural honeybee product promoted as a valuable source of nourishing substances and energy. The health-enhancing value of bee pollen is expected due to the wide range of secondary plant metabolites (tocopherol, niacin, thiamine, biotin and folic acid, polyphenols, carotenoid pigments, phytosterols), besides enzymes and co-enzymes, contained in bee pollen. The promising reports on the antioxidant, anti-inflammatory, anticariogenic antibacterial, antifungicidal, hepatoprotective, anti-atherosclerotic, immune enhancing potential require long-term and large cohort clinical studies. The main difficulty in the application of bee pollen in modern phytomedicine is related to the wide species-specific variation in its composition. Therefore, the variations may differently contribute to bee-pollen properties and biological activity and thus in therapeutic effects. In principle, we can unequivocally recommend bee pollen as a valuable dietary supplement. Although the bee-pollen components have potential bioactive and therapeutic properties, extensive research is required before bee pollen can be used in therapy. © 2016 Society of Chemical Industry.

Cancer-protective factors in fruits and vegetables: biochemical and biological background

Cancer-protective factors are present in several fruits, vegetables and commonly used spices and herbs. They can be divided into several different groups, based on their chemical structure, e.g. polyphenols, thiols, carotenoids and retinoids, carbohydrates, trace metals, terpenes, tocopherols and degradation products of glucosinolates (i.e. isothiocyanates, indoles and dithiothiols) and others. Among each of these groups of compounds are substances, which may exert their cancer-protective action by more than one biochemical mechanism. The biochemical processes of carcinogenesis are still not known in detail and probably varies with the cancer disease in question. Accordingly, the description of the biochemical backgrounds for the actions of cancer-protective factors must be based on a simplified model of the process of carcinogenesis. The model used in this presentation is a generalised initiation-promotion-conversion model, in which initiators are thought to be directly or indirectly genotoxic, promoters are visualised as substances capable of inferring a growth advantage on initiated cells and converters are believed to be genotoxic, e.g. mutagens, clastogens, recombinogens or the like. Experimental evidence for the mechanisms of action of cancer-protective agents in fruits and vegetables that protect against initiation include the scavenging effects of polyphenols on activated mutagens and carcinogens, the quenching of singlet oxygen and radicals by carotenoids, the antioxidant effects of many compounds including ascorbic acid and polyphenols, the inhibition of activating enzymes by some flavonols and tannins, the induction of oxidation- and of conjugation (protective) enzymes by indoles, isothiocyanates and dithiothiones, the shielding of sensitive structures by some polyphenols and the stimulation of DNA-repair exerted by sulphur-containing compounds. Mechanisms at the biochemical level in anti-promotion include the antioxidant effects of carotenoids and the membrane stabilizing effects reported with polyphenols, the inhibition of proteases caused by compounds from soybeans, the stimulation of immune responses seen with carotenoids and ascorbic acid and the inhibition of ornithine decarboxylase by polyphenols and carotenoids. A few inhibitors of conversion have been identified experimentally, and it can be argued on a theoretical basis, that many inhibitors of initiation should also be efficient against conversion. The mechanisms of anticarcinogenic substances in fruits and vegetables are discussed in the light of cancer prevention and inhibition.

Quantification of genistein and genistin in soybeans and soybean products

It has been suggested that the isoflavone, genistein,, may have some role as a chemopreventive agent against cancer in humans. Levels of genistein and its beta-glucoside conjugate, genistin, ingested in soybeans and related bean products by the Japanese were quantified by HPLC, to estimate daily intake of these compounds. Amounts of genistein and genistin in soybeans, soy nuts and soy powder were in the range of 4.6 to 18.2 and 200.6 to 968.1 micrograms/g food, respectively. The values for soy milk and tofu (bean curd) were 1.9 to 13.9 and 94.8 to 137.7 micrograms/g food, respectively. Levels of isoflavones in fermented soybean products, miso (bean paste) and natto (fermented soybeans), were 38.5 to 229.1 micrograms/g food for genistein and 71.7 to 492.8 micrograms/g food for genistin. Thus, the level of genistein in the fermented soybean products was higher than in soy beans and soybean products such as soy milk and tofu. From these observations, it is suggested that the beta-glycosyl bond of genistin is cleaved to produce genistein by microbes during fermentation to yield miso and natto. Soy sauce was also found to contain both isoflavones, but at levels lower than in miso and natto. On the basis of these data for average annual consumption of soybeans and related products, daily intake of genistein and genistin by the Japanese is calculated to be 1.5-4.1 and 6.3-8.3 mg/person, respectively. These levels are much higher than those for Americans or Western Europeans, whose mortality rates for breast, colon and prostate cancers are greater than the Japanese.

Survey of the conjugated linoleic acid contents of dairy products

The objective of this research was to determine the content of conjugated linoleic acid, an anticarcinogen, in dairy products. Fifteen cheeses, three fermented dairy products (other than cheeses), and four fluid milk products (two brands for each product) were included in the survey. Total lipids, fatty acids, protein, moisture, and titratable acidity were also measured to determine the relationship between the content of these constituents and conjugated linoleic acid content. The conjugated linoleic acid content of cheeses ranged from 3.59 to 7.96 mg/g of lipid. Blue, Brie, Edam, and Swiss cheeses had significantly higher conjugated linoleic acid content than the other cheeses. Sharp Cheddar cheeses tended to have higher conjugated linoleic acid content than the medium Cheddar cheeses, but the increase was not significant. The conjugated linoleic acid content of the other fermented dairy products ranged from 3.82 to 4.66 mg/g of lipid, and cultured buttermilk had the highest content. The conjugated linoleic acid contents of four fluid milks ranged from 3.38 to 6.39 mg/g of lipid and were not significantly different from one another. Multiple linear regressions of conjugated linoleic acid content and the total fatty acid content indicated a relationship between conjugated linoleic acid content and the content of precursors and intermediates of conjugated linoleic acid formation, including linoleic and oleic acids.

Effect of storage, processing and cooking on glucosinolate content of Brassica vegetables

Epidemiological studies have shown that consumption of Brassica vegetables decrease the risk of cancer. These associations are linked to dietary intake of glucosinolates and their metabolism to cancer preventive isothiocyanates. Bioavailability of glucosinolates and related isothiocyanates are influenced by storage and culinary processing of Brassica vegetables. In this work, the content of the 7 major glucosinolates in broccoli, Brussels sprouts, cauliflower and green cabbage and their stability under different storage and cooking conditions is examined. Glucosinolates and isothiocyanates were quantified by liquid chromatography with tandem mass spectrometric detection (LC-MS/MS). Isothiocyanates were detected with high sensitivity as the corresponding thiourea derivatives. Storage at ambient temperature and in a domestic refrigerator showed no significant difference and a minor loss (9-26%) of glucosinolate levels over 7 days. Vegetables shredded finely showed a marked decline of glucosinolate level with post-shredding dwell time - up to 75% over 6h. Glucosinolate losses were detected partly as isothiocyanates. Cooking by steaming, microwaving and stir-fry did not produce significant loss of glucosinolates whereas boiling showed significant losses by leaching into cooking water. Most of the loss of the glucosinolates (approximately 90%) was detected in the cooking water. Increased bioavailability of dietary isothiocyanates may be achieved by avoiding boiling of vegetables.

Action of chlorogenic acid in vegetables and fruits as an inhibitor of 8-hydroxydeoxyguanosine formation in vitro and in a rat carcinogenesis model

Various plant extracts, such as carrot, burdock (gobou), apricot and prune, showed inhibitory effects in an in vitro assay of lipid peroxide-induced 8-hydroxydeoxyguanosine (8-OH-dG) formation. The major inhibitor purified from various plants extracts was identified as chlorogenic acid (CA), on the basis of UV- and mass-spectra and comparison with a standard sample. To examine whether CA also inhibits 8-OH-dG formation in animal organs, an oxygen radical-forming carcinogen, 4-nitroquinoline-1-oxide, was administered to rats, with or without CA. The 8-OH-dG level in the DNA of the rat tongue, the target organ, was significantly reduced in the CA-treated group.

Anthocyans from fruits and vegetables – Does bright colour signal cancer chemopreventive activity?

Consumption of fruits and berries has been associated with decreased risk of developing cancer. The most abundant flavonoid constituents of fruits and berries are anthocyans (i.e. anthocyanins, glycosides, and their aglycons, anthocyanidins) that cause intense colouration. In this review, we describe epidemiological evidence hinting at the cancer preventive activity of anthocyan-containing foods in humans, results of chemoprevention studies in rodent models with anthocyans or anthocyan-containing fruit/vegetable extracts, and pharmacological properties of anthocyans. Anthocyanidins have been shown to inhibit malignant cell survival and confound many oncogenic signalling events in the 10(-6)-10(-4) M concentration range. Studies of the pharmacokinetics of anthocyanins after their consumption as single agents, anthocyanin mixtures or berry extracts suggest that anthocyanins reach levels of 10(-8)-10(-7) M in human blood. It is unclear whether such concentrations are sufficient to explain anticarcinogenic effects, and whether anthocyanins exert chemopreventive efficacy themselves, or if they need to undergo hydrolysis to their aglyconic counterparts. The currently available literature provides tantalising hints of the potential usefulness of anthocyans or anthocyan mixtures as cancer chemopreventive interventions. Nevertheless further studies are necessary to help adjudge the propitiousness of their clinical development.

Effects of lyophilized black raspberries on azoxymethane-induced colon cancer and 8-hydroxy-2'-deoxyguanosine levels in the Fischer 344 rat

This study examined the effects of lyophilized black raspberries (BRB) on azoxymethane (AOM)-induced aberrant crypt foci (ACF), colon tumors, and urinary 8-hydroxy-2'-deoxyguanosine (8-OHdG) levels in male Fischer 344 rats. AOM was injected (15 mg/kg body wt i.p.) once per week for 2 wk. At 24 h after the final injection, AOM-treated rats began consuming diets containing 0%, 2.5%, 5%, or 10% (wt/wt) BRB. Vehicle controls received 5% BRB or diet only. Rats were sacrificed after 9 and 33 wk of BRB feeding for ACF enumeration and tumor analysis. ACF multiplicity decreased 36%, 24%, and 21% (P < 0.01 for all groups) in the 2.5%, 5%, and 10% BRB groups, respectively, relative to the AOM-only group. Total tumor multiplicity declined 42%, 45%, and 71% (P < 0.05 for all groups). Although not significant, a decrease in tumor burden (28%, 42%, and 75%) was observed in all BRB groups. Adenocarcinoma multiplicity decreased 28%, 35%, and 80% (P < 0.01) in the same treatment groups. Urinary 8-OHdG levels were reduced by 73%, 81%, and 83% (P < 0.01 for all groups). These results indicate that BRB inhibit several measures of AOM-induced colon carcinogenesis and modulate an important marker of oxidative stress in the Fischer 344 rat.

Bioactive organosulfur phytochemicals in Brassica oleracea vegetables--a review

Sulfur-containing phytochemicals of two different kinds are present in all Brassica oleracea (Cruciferae) vegetables (cabbage, broccoli, etc.). They are glucosinolates (previously called thioglucosides) and S-methyl cysteine sulfoxide. These compounds, which are derived in plant tissue by amino acid biosynthesis, show quite different toxicological effects and appear to possess anticarcinogenic properties. Glucosinolates have been extensively studied since the mid-nineteenth century. They are present in plant foods besides Brassica vegetables with especially high levels in a number of seed meals fed to livestock. About 100 different kinds of glucosinolates are known to exist in the plant kingdom, but only about 10 are present in Brassica. The first toxic effects of isothiocyanates and other hydrolytic products from glucosinolates that were identified were goitre and a general inhibition of iodine uptake by the thyroid. Numerous studies have indicated that the hydrolytic products of at least three glucosinolates, 4-methyl-sulfinylbutyl (glucoraphanin), 2-phenylethyl (gluconasturtiin) and 3-indolylmethyl (glucobrassicin), have anticarcinogenic activity. Indole-3-carbinol, a metabolite of glucobrassicin, has shown inhibitory effects in studies of human breast and ovarian cancers. Kale poisoning, or a severe haemolytic anaemia, was discovered in cattle in Europe in the 1930s, but its link with the hydrolytic product of S-methyl cysteine sulfoxide was only shown about 35 years later. S-methyl cysteine sulfoxide and its metabolite methyl methane thiosulfinate were shown to inhibit chemically-induced genotoxicity in mice. Thus, the cancer chemopreventive effects of Brassica vegetables that have been shown in human and animal studies may be due to the presence of both types of sulfur-containing phytochemicals (i.e. certain glucosinolates and S-methyl cysteine sulfoxide).

Antimutagens and anticarcinogens in foods

The role of dietary factors in the prevention of major chronic diseases, cancer in particular, is under intensive investigation by many laboratories around the world. Evidence from epidemiological studies and tests in laboratory animals suggests that food consumed by the general population contains certain ingredients that may have a role in reduction of the incidence of cancer. It has been observed that a number of regular food components, belonging to different chemical groups, do possess cancer preventive and/or beneficial outcomes for some other diseases; these chemicals, therefore, are frequently collectively known as 'chemopreventers'. The mode of action of most chemopreventers is still unknown, although it appears that many of them are antioxidants, and as such, they may scavenge free radicals, formed either during the preparation of food, or by biological processes in the body. As free radicals damage lipids, proteins, cell membranes and DNA, their removal could prevent development of certain chronic diseases, particularly cancer or atherosclerosis. This review summarizes recent developments in the search for beneficial effects of regular food ingredients in prevention of cancer.

Chemoprotective properties of some pungent ingredients present in red pepper and ginger

There has been a substantial body of data, supporting that dietary factors have a profound impact on prevention as well as etiology of human cancer. Capsaicin has been tested by many investigators for its effects on experimental carcinogenesis and mutagenesis. Data in the literature indicate that capsaicin has dual effects on carcinogenic and mutagenic processes. At present, there is no solid evidence that hot red and chili peppers or their principal pungent ingredient capsaicin are carcinogenic in humans although results of early investigations with experimental animals exhibit the moderate tumorigenicity of this compound. In contrast, recent studies reveal substantial antigenotoxic and anticarcinogenic effects of capsaicin, suggesting this compound as another important dietary phytochemical with a potential chemopreventive activity. Some pungent constituents present in ginger and other zingiberaceous plants have potent antioxidant and anti-inflammatory effects, and some of them exhibit anti-tumor promotional activity in experimental carcinogenesis.

Liquid microjunction surface sampling probe electrospray mass spectrometry for detection of drugs and metabolites in thin tissue sections

A self-aspirating, liquid microjunction surface sampling probe/electrospray emitter mass spectrometry system was demonstrated for use in the direct analysis of spotted and dosed drugs and their metabolites in thin tissue sections. Proof-of-principle sampling and analysis directly from tissue without the need for sample preparation was demonstrated first by raster scanning a region on a section of rat liver onto which reserpine was spotted. The mass spectral signal from selected reaction monitoring was used to develop a chemical image of the spotted drug on the tissue. The probe was also used to selectively spot sample areas of sagittal whole-body tissue from a mouse that had been dosed orally (90 mg/kg) with R,S-sulforaphane 3 h prior to sacrifice. Sulforaphane and its glutathione and N-acetyl cysteine conjugates were monitored with selected reaction monitoring and detected in the stomach and various other tissues from the dosed mouse. No signal for these species was observed in the tissue from a control mouse. The same dosed-tissue section was used to illustrate the possibility of obtaining a lane scan across the whole-body section. In total, these results illustrate the potential for rapid screening of the distribution of drugs and metabolites in thin tissue sections with the liquid micro-junction surface sampling probe/electrospray mass spectrometry approach. Published in 2007 by John Wiley & Sons, Ltd.

A green tea polyphenol, epigalocatechin-3-gallate, induces apoptosis of human hepatocellular carcinoma, possibly through inhibition of Bcl-2 family proteins

BACKGROUND/AIMS

A major polyphenol of green tea, epigallocatechin-3-gallate (EGCG), has previously been shown to induce cell-cycle arrest and apoptosis in various cancers. However, little is known about its effects on hepatocellular carcinomas (HCCs).

METHODS

Four HCC cell lines, HLE, HepG2, HuH-7 and PLC/PRF/5, were treated with EGCG or vehicle. Cell viability was assessed by trypan blue staining and WST-8 assay. Cell-cycle, apoptosis and apoptosis-related proteins in HLE cells were evaluated by flow cytometry and Western blotting. The effect of EGCG was also studied in vivo using a xenograft model. The effect of co-treatment with EGCG and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) was also assessed.

RESULTS

EGCG inhibited the growth of all HCC cell lines at concentrations of 50-100 microg/ml. In HLE cells, EGCG induced apoptosis but not cell-cycle arrest and appears to have down-regulated Bcl-2alpha and Bcl-xl by inactivation of NF-kappaB. Oral administration of EGCG showed similar effects in HLE xenograft tumors. Co-treatment with EGCG and TRAIL synergistically induced apoptosis in HLE cells.

CONCLUSIONS

EGCG induced apoptosis in HLE cells, both in vitro and in vivo. Moreover, it enhanced TRAIL-induced apoptosis. Therefore, EGCG treatment may be useful for improving the prognosis of HCCs.

The composition of cigarette smoke: a retrospective, with emphasis on polycyclic components

The difficulties encountered in extrapolating biological activity from cigarette smoke composition provide generally applicable lessons as they are representative of the problems encountered with other complex mixtures. Researchers attempting to assess risk are faced with attempting to interpret data from a number of areas including: tobacco science; smoke/aerosol chemistry specific to tobacco; sophisticated analytical chemistry applications and techniques for trapping, collecting, separating, and quantifying very specific compounds at nanogram to picogram levels; numerous biological testing methodologies; and animal models of tumors and carcinogenesis. Numerous hypotheses have been developed over the past five decades and tested with the technology of the day in attempts to interpret the biological activity of cigarette smoke in relation to the chemistry of this complex mixture. These hypotheses fall into several categories discussed in this review: mechanisms of pyrogenesis of polycyclic aromatic hydrocarbons (PAHs) in tobacco smoke; levels of PAHs in cigarette mainstream smoke (MS) and its tumorigenicity in mouse skin-painting experiments; control of PAH levels in MS; chemical indicators of cigarette smoke condensate (CSC) tumorigenicity; control of levels of MS components partitioned between the vapor phase and particulate phase of MS; tumorigenic threshold limits of CSC and many of its components; tumorigenic aza-arenes in tobacco smoke; MS components reported to be ciliastatic to smokers' respiratory tract cilia; anticarcinogenic tobacco-smoke components. Of 52 hypotheses reviewed in this paper, 15 have excellent data supporting the hypothesis based on today's technology. The remaining 37 hypotheses, although originally plausible, have since become insupportable in light of new and contradictory data generated over the years. Such data were generated sometimes by the original authors of the hypotheses and sometimes by other investigators. The hypotheses presented today are less likely to be supplanted because they are well conceived and have a strong mechanistic basis. The challenge for the future is the generation and interpretation of data relating the chemistry and biological activity associated with the dynamic and complex mixture of tobacco smoke.

Carotenoid esters in vegetables and fruits: a screening with emphasis on beta-cryptoxanthin esters

Carotenoids are found in food plants in free form or as fatty acid esters. Most studies have been carried out after saponification procedures, so the resulting data do not represent the native carotenoid composition of plant tissues. Therefore, nonsaponified extracts of 64 fruits and vegetables have been screened to determine the amount of carotenoid esters in food plants. Because one of the major problems in the quantitation of carotenoids is the availability of pure standard material, the total carotenoid ester content was calculated as lutein dimyristate equivalents. Lutein dimyristate was independently synthesized from lutein and myristoyl chloride. The highest ester concentrations were found in red chili (17.1 mg/100 g) and orange pepper (9.2 mg/100 g); most of the investigated fruits and vegetables showed concentrations up to 1.5 mg/100 g. Special attention was dedicated to beta-cryptoxanthin esters. To enable an accurate detection of the beta-cryptoxanthin ester content, beta-cryptoxanthin was purified from papaya and used for synthesis of beta-cryptoxanthin laurate, myristate, and palmitate, representing the major beta-cryptoxanthin esters in food plants. The study proved tropical and subtropical fruits to be an additional source of beta-cryptoxanthin esters in the human diet. The contents ranged from 8 microg/100 g beta-cryptoxanthin laurate in Tunisian orange to 892 microg/100 g beta-cryptoxanthin laurate in papaya.

Experimental and epidemiological evidence on non-organ specific cancer preventive effect of Korean ginseng and identification of active compounds

Panax ginseng C.A. Meyer has been the most highly recognized medicinal herb in the Orient. The prolonged administration of red ginseng extract significantly inhibits the incidence of hepatoma and also proliferation of pulmonary tumors induced by aflatoxin B(1) and urethane. Statistically significant anticarcinogenic effects were in aged or heat treated extracts of ginseng and red ginseng made by steaming in a 9 weeks medium-term anticarcinogenicity test using benzo[a]pyrene. In case-control studies, odds ratios (OR) of the cancer of lip, oral cavity and pharynx, larynx, lung, esophagus, stomach, liver, pancreas, ovary, and colorectum were significantly reduced. As to the type of ginseng, the ORs for cancer were reduced in user of fresh ginseng extract intakers, white ginseng extract, white ginseng powder, and red ginseng. In a cohort study with 5 years follow-up conducted in a ginseng cultivation area, ginseng users had a decreased relative risk (RR) compared with non-users. The relative risks (RRs) of ginseng users were decreased in gastric cancer and lung cancer. These findings strongly suggest that Panax ginseng C.A. Meyer cultivated in Korea has non-organ specific cancer preventive effects against various cancers. To investigate the active components for cancer prevention, several fractions of fresh and red ginseng and four semi-synthetic ginsenoside Rh(1), Rh(2), Rg(3) and Rg(5), the major saponin components in red ginseng, were prepared among the ginsenosides. By using Yun's model, Rg(3) and Rg(5) showed statistically significant reduction of lung tumor incidence and Rh(2) had a tendency to decrease the incidence. In conclusion, these results strongly suggested that Panax ginseng C.A. Meyer cultivated in Korea is a non-organ specific cancer preventive against human cancers and also indicated that the anticarcinogenicity or human cancer preventive effect of Panax ginseng is due to ginsenoside Rg(3), Rg(5) and Rh(2).

Phenolic content of various beverages determines the extent of inhibition of human serum and low-density lipoprotein oxidation in vitro: identification and mechanism of action of some cinnamic acid derivatives from red wine

1. An antioxidant effect of phenolic substances in red wine to reduce oxidizability of low-density lipoprotein has been proposed as the basis for a relatively lower incidence of coronary disease in populations with high red wine intake. We have now investigated the possible antioxidant effects of various beverages, including red wines, white wines, beers and red grape juices (diluted 1:500), on metal ion-dependent (copper) and -independent (aqueous peroxyl radicals) oxidation of isolated human low-density lipoprotein. We also tested the effects of these beverages on copper-initiated oxidation of lipoproteins in serum. 2. The higher the polyphenolic content of a beverage, the greater was its antioxidative effect measured as change in lag time in the different oxidation systems. Upon stripping the polyphenolics from the drinks, the lag times returned to control levels in isolated low-density lipoprotein; however, the low concentrations of phenolics remaining after stripping had a lesser but still significant effect on oxidation of lipoproteins in serum. The inhibitory effect of these phenolics appeared to be more pronounced for metal ion (copper)-induced oxidation than for those induced by aqueous peroxyl radicals, suggesting that both copper-binding and free radical-trapping activities may be involved. A mixture of the carboxylic acids representative of those present in red wine exhibited no significant effect on lag time of metal ion-dependent and -independent low-density lipoprotein oxidations. Ethanol, at concentrations of 0.1-0.5%, had no effect on either copper-induced or aqueous peroxyl radical oxidations. 3. Extracts of acid-hydrolysed red wine were separated by thin-layer chromatography and the most active antioxidant fractions identified. GC-MS and HPLC analysis of these fractions resulted in the identification of several cinnamic acid derivatives, such as coumaric acid, caffeic acid and protocatechuic acid. Dose-response studies using the pure compounds indicated that caffeic acid was the most active antioxidant with an IC50 < 1 mumol/l for copper-initiated low-density lipoprotein oxidation. Caffeic acid (1 mumol/l) significantly inhibited lipid hydroperoxide formation while sparing alpha-tocopherol consumption. Caffeic acid at the same concentration also inhibits aqueous peroxyl radical-induced oxidation of low-density lipoprotein, sparing alpha-tocopherol. There was no evidence of caffeic acid preventing the binding of copper to low-density lipoprotein. 4. We conclude that phenolics in both alcoholic and non-alcoholic beverages can give dose-dependent protection against oxidation of low-density lipoprotein. Caffeic acid and protocatechuic acid are two compounds likely to contribute to these effects. These findings may be relevant to the putative cardiovascular-protective effects of high phenolic content alcoholic beverages such as red wine; however, the widespread occurrence of antioxidants such as caffeic acid in fruits and vegetables suggests that these protective principles are not limited to red wine.

Chemopreventive characteristics of avocado fruit

Phytochemicals are recognized as playing an important role in cancer prevention by fruits and vegetables. The avocado is a widely grown and consumed fruit that is high in nutrients and low in calories, sodium, and fats. Studies have shown that phytochemicals extracted from the avocado fruit selectively induce cell cycle arrest, inhibit growth, and induce apoptosis in precancerous and cancer cell lines. Our recent studies indicate that phytochemicals extracted with chloroform from avocado fruits target multiple signaling pathways and increase intracellular reactive oxygen leading to apoptosis. This review summarizes the reported phytochemicals in avocado fruit and discusses their molecular mechanisms and targets. These studies suggest that individual and combinations of phytochemicals from the avocado fruit may offer an advantageous dietary strategy in cancer prevention.

Structure-activity relationships of tea compounds against human cancer cells

The content of the biologically active amino acid theanine in 15 commercial black, green, specialty, and herbal tea leaves was determined as the 2,4-dinitrophenyltheanine derivative (DNP-theanine) by a validated HPLC method. To define relative anticarcinogenic potencies of tea compounds and teas, nine green tea catechins, three black tea theaflavins, and theanine as well as aqueous and 80% ethanol/water extracts of the same tea leaves were evaluated for their ability to induce cell death in human cancer and normal cells using a tetrazolium microculture (MTT) assay. Compared to untreated controls, most catechins, theaflavins, theanine, and all tea extracts reduced the numbers of the following human cancer cell lines: breast (MCF-7), colon (HT-29), hepatoma (liver) (HepG2), and prostate (PC-3) as well as normal human liver cells (Chang). The growth of normal human lung (HEL299) cells was not inhibited. The destruction of cancer cells was also observed visually by reverse phase microscopy. Statistical analysis of the data showed that (a) the anticarcinogenic effects of tea compounds and of tea leaf extracts varied widely and were concentration dependent over the ranges from 50 to 400 microg/mL of tea compound and from 50 to 400 microg/g of tea solids; (b) the different cancer cells varied in their susceptibilities to destruction; (c) 80% ethanol/water extracts with higher levels of flavonoids determined by HPLC were in most cases more active than the corresponding water extracts; and (d) flavonoid levels of the teas did not directly correlate with anticarcinogenic activities. The findings extend related observations on the anticarcinogenic potential of tea ingredients and suggest that consumers may benefit more by drinking both green and black teas.