村上 明

Double applications of phorbol eaters trigger excessive reactive oxygen species (ROS) production in mouse skin. previously reported data suggest that the two applications induce distinguishable biochemical events, namely, priming and activation. The former is characterized as a recruitment of inflammatory cells, such as neutrophils, by chemotactic factors to inflammatory regions and edema formation. The latter is responsible for ROS generation. Thus, inhibitory effects of 1'-acetoxychavicol acetate (ACA), previously reported to be a superoxide generation inhibitor is vitro, on 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced oxidative stress and inflammatory responses in mouse skin model were examined using a double application of ACA. We demonstrated that two pretreatments and pretreatment with ACA (810 mmol) in the activation phase suppressed double TPA application-induced H2O2 formation in mouse skin, ACA exhibited no inhibitory effects on edema formation and the enhancement of myeloperoxidase activity during the first TPA treatment, whereas the anti-inflammatory agent genistein administered at the same dose inhibited both biomarkers, No inhibitory potential of ACA for TPA-induced H2O2 formation in the priming phase was confirmed. On the other hand, in the in vitro study, ACA inhibited ROS generation in differentiated HL-60 cells more strongly than did 1'-hydroxychavicol, which showed no inhibition by pretreatment in the activation phase In addition, allopurinol did not inhibit double TPA application-induced H2O2 formation in mouse skin, These findings suggest that the NADPH oxidase system of neutrophils rather than the epithelial xanthine oxidase system is dominant for the O-2(-)-generating potential in double TPA-treated mouse skin. ACA significantly inhibited mouse epidermis thiobarbituric acid-reacting substance formation, known as an overall oxidative damage biomarker, Moreover, histological studies demonstrated that ACA inhibited double TPA treatment-induced morphological changes reflecting inflammatory response, such as edema formation, leukocyte infiltration, hyperplasia, and cell proliferation. Furthermore, pretreatment with ACA but not 1'-hydroxychavicol in the activation phase inhibits double TPA application-induced increases in both number of leukocytes and proliferating cell nuclear antigen index. These results suggested that ROS from leukocytes including O-2(-) plays an important role for continuous and excessive production of chemotactic factors, leading to chronic inflammation and hyperplasia, which are inhibitable by ACA. Thus, we concluded that O-2(-) generation inhibitors are agents that effectively inhibit oxidative stress and inflammatory responses in mouse skin.

Rosmarinic acid (RoA) has been isolated in high yield (0.1%) from the leaves of Perilla frutescens Britton var, acuta f. viridis, one of the most common garnishes in Japan, as a superoxide scavenger in a xanthine/xanthine oxidase system. The scavenging activity of RoA was significantly higher than that of ascorbic acid (AA). The structure-activity relationships using RoA, caffeic acid (CaA), and its related compounds indicated that the presence of an ortho dihydroxyphenyl group is essential for the scavenging effect. In addition, the conjugated double bond in the C3 carbon chain is important for enhancing the effect. The activity of RoA was then shown to be due to the additive effect of both CaA and (3,4-dihydroxyphenyl)lactic acid units, both of which are hydrolyzed products of RoA. RoA significantly inhibited both intracellular superoxide and peroxide formation in differentiated HL-60 cells, suggesting that RoA effectively exhibited antioxidative activity in the biological systems through the scavenging of superoxide.

Rosmarinic acid (RoA) has been isolated in high yield (0.1%) from the leaves of Perilla frutescens Britton var, acuta f. viridis, one of the most common garnishes in Japan, as a superoxide scavenger in a xanthine/xanthine oxidase system. The scavenging activity of RoA was significantly higher than that of ascorbic acid (AA). The structure-activity relationships using RoA, caffeic acid (CaA), and its related compounds indicated that the presence of an ortho dihydroxyphenyl group is essential for the scavenging effect. In addition, the conjugated double bond in the C3 carbon chain is important for enhancing the effect. The activity of RoA was then shown to be due to the additive effect of both CaA and (3,4-dihydroxyphenyl)lactic acid units, both of which are hydrolyzed products of RoA. RoA significantly inhibited both intracellular superoxide and peroxide formation in differentiated HL-60 cells, suggesting that RoA effectively exhibited antioxidative activity in the biological systems through the scavenging of superoxide.

The effects of 1'-acetoxychavicol acetate (ACA) on endogenous rat liver carcinogenesis because of chronic feeding of a choline-deficient, L-amino acid-defined (CDAA) diet were examined. Male Fischer 344 rats, 6 weeks old, received the CDAA diet containing ACA at doses of 0, 0,005, 0.010 and 0.050% for 12 weeks and were then killed. ACA decreased the numbers of putative preneoplastic, glutathione S-transferase placental form (GST-P)-positive, focal lesions developing in the livers of rats fed the CDAA diet but did not alter their sizes. At the same time, ACA reduced the levels of 8-hydroxyguanine, a parameter of oxidative DNA damage, but did not significantly affect generation of 2-thiobarbituric acid-reacting substances, indicators of oxidative extra-DNA damage, or hepatocyte proliferation. Furthermore, ACA did not exert any significant effects on the numbers or sizes of GST-P-positive lesions in the livers of fats when administered between weeks 2 and 8 after initiation with a single i.p. dose of 200 mg/kg body wt of N-nitrosodiethylamine. These results indicate that ACA prevents the CDAA diet-associated induction of putative preneoplastic lesions by reduction of oxidative DNA damage but does not affect their subsequent growth.

In our previous short-term experiment, Citrus auraptene inhibited the development of azoxymethane (AOM)-induced aberrant crypt foci, which are precursor lesions for colorectal carcinoma. In the present study, the possible inhibitory effect of dietary administration of auraptene was investigated using an animal colon carcinogenesis model with a colon carcinogen AOM. Male F344 rats were given s.c. injections of AOM (15 mg/kg body weight) once a week for 3 weeks to induce colon neoplasms. They also received diets containing 100 or 500 ppm auraptene for 4 weeks in groups of "initation" feeding, starting 1 week before the first dosing of AOM. The diets containing auraptene were also given to rats for 38 weeks in groups of "postinitiation" feeding. At the termination of the study (38 weeks), dietary administration of auraptene caused dose-dependent inhibition in AOM-induced large bowel carcinogenesis. Auraptene feeding during the initiation phase reduced the incidence of colon adenocarcinoma by 49% at 100 ppm (P = 0.099) and 65% at 500 ppm (P = 0.0075). Auraptene administration during the postinitiation phase inhibited the incidence of colon adenocarcinoma by 58% at 100 ppm (P = 0.021) and 65% at 500 ppm (P = 0.0075). Also, the multiplicity of colon carcinoma was significantly reduced by initiation feeding at a dose level of 500 ppm (P < 0.01) and postinitiation feeding at a level of 100 and 500 ppm (P < 0.05 and P < 0.01, respectively). Feeding of auraptene suppressed the expression of cell proliferation biomarkers (ornithine decarboxylase activity and polyamine content) in the colonic mucosa and reduced the production of aldehydic lipid peroxidation [malondialdehyde and 4-hydroxy-2(E)-nonenal]. In addition, auraptene increased the activities of Phase II drug-metabolizing enzymes (glutathione S-transferase and quinone reductase) in the Liver and colon. These findings suggest that the inhibitory effects of auraptene on AOM-induced colon tumorigenesis at the initiation level might be associated, in part, with increased activity of Phase II enzymes, and those at the postinitiation stage might be related to suppression of cell proliferation and lipid peroxidation in the colonic mucosa.

Although nitric oxide (NO) is an important biological mediator, excessive production in inflammation is thought to be a causative factor of cellular injury and cancer in the long term. In the present study the effects of 1'-acetoxychavicoI acetate (ACA), which has anticarcinogenic properties, on NO production in murine macrophage cell line RAW264 cells stimulated with lipopolysaccharide or interferon-gamma were examined. ACA suppressed NO production dose dependently with an IC50 of 160 ng/ml (680 nM), The decrease in NO production was shown to parallel reduced expression of iNOS mRNA and protein. The influence of ACA on transcription factors, such as NF-kappa B, AP-1 and Stat1, which are involved in expression of the iNOS gene was assessed. ACA was found to suppress degradation of I kappa B, an NF-kappa B inhibitory factor, and consequently inhibit NF-kappa B activation. Activation of AP-1 and Stat1 was also blocked by ACA treatment. Thus we demonstrate that ACA exerts potent inhibitory effects on NO production, apparently mediated by modulation of activation of several transcription factors. This could contribute to the anticarcinogenic properties of ACA.

Three known thiocarbamate (TC)- and isothiocyanate (ITC)-related compounds have been isolated from the leaves of Moringa oleifero, a traditional herb in southeast Asia, as inhibitors of tumor promoter teleocidin B-4-induced Epstein-Barr virus (EBV) activation in Raji cells, Interestingly, only niaziminin among 10 TCs including 8 synthetic ones showed considerable inhibition against EBV activation. The structure-activity relationships indicated that the presence of an acetoxy group at the 4'-position of niaziminin is important and indispensable for inhibition. On the other hand, among the ITC-related compounds, naturally occurring 4-[(4'-O-acetyl-alpha-L-rhamnosyloxy)benzyl]ITC and commercially available allyl-and benzyl-ITC and commercially available allyl- and benzyl-ITC significantly inhibited activation, suggesting that the isothiocyano group is a critical structural factor for activity.

Three known thiocarbamate (TC)- and isothiocyanate (ITC)-related compounds have been isolated from the leaves of Moringa oleifero, a traditional herb in southeast Asia, as inhibitors of tumor promoter teleocidin B-4-induced Epstein-Barr virus (EBV) activation in Raji cells, Interestingly, only niaziminin among 10 TCs including 8 synthetic ones showed considerable inhibition against EBV activation. The structure-activity relationships indicated that the presence of an acetoxy group at the 4'-position of niaziminin is important and indispensable for inhibition. On the other hand, among the ITC-related compounds, naturally occurring 4-[(4'-O-acetyl-alpha-L-rhamnosyloxy)benzyl]ITC and commercially available allyl-and benzyl-ITC and commercially available allyl- and benzyl-ITC significantly inhibited activation, suggesting that the isothiocyano group is a critical structural factor for activity.

The inhibitory effects of curcumin and two tetrahydrocurcuminoids on tumor promoter-induced oxidative stress in vitro and in vivo were investigated. Curcumin, tetrahydrocurcumin (THC) and dihydroxytetrahydrocurcumin (DHTHC) exhibited significant inhibitory effects on 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced O-2(-) generation in differentiated HL-60 cells. The inhibitory activity of THC was weaker than that of curcumin, This tendency was the inverse of the results of previous studies on in vitro antioxidative activity against lipid peroxidation, The curcuminoids inhibited TPA-induced intracellular peroxide formation in differentiated HL-60 cells. THC exhibited much weaker inhibition of intracellular peroxide formation than curcumin, suggesting that this inhibition might be attributable to the inhibition of O-2(-) generation. The inhibitory effects of curcuminoids on TPA-induced H2O2 formation in female ICR mouse skin were further examined using the double-TPA-application model. Each TPA application induces two distinct biochemical events, 1) recruitment of inflammatory cells to the inflammatory regions and 2) activation of oxidant-producing cells. Double pretreatment of mice with curcuminoids before each TPA treatment significantly suppressed double TPA application-induced H2O2 formation in the mouse skin. Coadministrations of curcumin with either first or second TPA treatment significantly inhibited H2O2 formation. In addition, THC tends to show weaker inhibitory activities than curcumin in bioassays related to tumor promotion, i.e., inhibition of tumor promoter-induced inflammation in mouse skin and Epstein-Barr virus activation. These tendencies were parallel to those in the tumor-suppressive potential of curcumin and THC in mouse skin, as previously reported. Thus, we concluded that curcuminoids significantly suppress TPA-induced oxidative stress via both interference with infiltration of leukocytes into the inflammatory regions and inhibition of their activation.

A total of 48 (60 test samples) species of plants commonly eaten in Japan were randomly collected and their methanol extracts were tested for in vitro nitric oxide (NO) generation inhibitory activities in a murine macrophage cell line, RAW 264.7, stimulated with both lipopolysaccharide (LPS, 100 ng/ml) and interferon-gamma (IFN-gamma, 100 U/ml). Seventeen (28.3%) of the 48 extracts strongly inhibited NO generation at a concentration of 200 mu g/ml by 70% or more with significant cell viability (>50%). The extracts from avocado, tare, red turnip, sereves, komatsuna, basil, mitsuba and Chinese mustard markedly inhibited iNOS activity. These results suggest that a wide variety of edible plants in Japan contain the secondary metabolites carrying cancer preventive activity through reduction of excess amounts of NO. (C) 1998 Elsevier Science Ireland Ltd.

The modifying effects of citrus auraptene given during the initiation and post-initiation phases of oral carcinogenesis initiated with 4-nitroquinoline 1-oxide (4-NQO) were investigated in male F344 rats. At 6 weeks of age, animals were divided into experimental and control groups, and fed the diets containing 100 ppm or 500 ppm auraptene. At 7 weeks of age, all animals except those treated with auraptene alone and control groups were given 4-NQO (20 ppm) in the drinking water for 8 weeks to induce tongue carcinoma. Starting 7 days before the 4-NQO exposure, groups of animals were fed the diets containing auraptene (100 and 500 ppm) for 10 weeks and then switched to the basal diet. Starting 1 week after the cessation of 4-NQO exposure, the groups given 4-NQO and a basal diet were switched to the diets mixed with auraptene (100 and 500 ppm), and maintained on these diets for 22 weeks. The other groups consisted of rats fed auraptene alone (500 ppm) or untreated rats. All rats were necropsied at the termination of the study (week 32). The incidences of tongue lesions (neoplasms and preneoplasms), polyamine levels in the tongue tissue and cell proliferation activity estimated by 5-bromodeoxyuridine (BrdU)-labelling index were compared among the groups. In addition, the activities of gluthathione S-transferase (GST) and quinone reductase (QR) in liver and tongue of rats gavaged various doses of auraptene (0, 200, 400 and 800 mg/kg body wt) for 5 days were assayed. Feeding of auraptene at both doses during the initiation phase caused a significant reduction in the frequency of tongue carcinoma (100 ppm auraptene, 91% reduction, P < 0.001; 500 ppm auraptene, 63% reduction, P < 0.05). When fed auraptene after 4-NQO exposure, the frequency of tongue carcinoma was also decreased (100 ppm auraptene, 100% reduction, P < 0.001; 500 ppm auraptene, 74% reduction, P < 0.01). The incidences of tongue severe dysplasia in these groups were significantly smaller than those in carcinogen controls (P < 0.05). There were no pathological alterations in rats treated with 500 ppm auraptene alone or those in an untreated control group. Dietary administration of auraptene significantly decreased BrdU-labelling index and polyamine concentrations in the oral mucosa (P < 0.05). In addition, auraptene administration significantly increased the activities of GST and QR in the liver and tongue. Although dose-dependent effect was not found, citrus auraptene is effective in inhibiting the development of oral neoplasms induced by 4-NQO. Thus, suppression by the initiation-feeding of auraptene might relate to elevation in the phase II enzymes GST and QR of the liver and tongue, and inhibition occurring during the post-initiation might be related to suppression of increased cell proliferation caused by 4-NQO in the oral mucosa.

A total of 112 species of edible plants (122 samples) from Thailand were randomly collected, and their methanol-extracts screened for in vitro anti-tumor promoting activity using the inhibition test of tumor promoter-induced Epstein-Ban virus (EBV) activation in Raji cells. It was found that 60% of these extracts inhibited EBV activation by 30% or more at a concentration of 200 mg/ml. It should be noted that the ratio was markedly higher than that (26%) previously observed in common edible plants in Japan. The species in the families Labiatae, Piperaceae, Rutaceae and Zingiberaceae were promising sources of effective anti-tumor promoters. In addition, anti-tumor promoting effects of two active constituents, 1,2-di-O-alpha-linolenoyl-3-O-beta-galactopyranosyl-sn-glycerol (DLGG, Citrus hystrix), and 1'-acetoxychavicol acetate (ACA, Languas galanga), together with their possible mode of action investigated thus far, are described.

A total of 135 methanol extracts from 48 plant families (107 species) of edible Indonesian plants were screened for their in vitro anti-tumor-promoting activities using the tumor promoter 12-O-hexadecanoylphorbol- 13-acetate (HPA)-induced Epstein-Barr virus (EBV) activation test in Raji cells. Examined at a concentration of 200 mg/ml, 71% of the extracts inhibited EBV activation by 30% or more. The rate is comparable to the rate observed in our previous tests of edible Thai (60%) plants and much higher than the rate (26%) observed with Japanese plants. In particular, the plant families Zingiberaceae (13/13 active) and Umbelliferae (7/8 active) are suggested to be desirable sources of effective cancer-preventive agents because of the strikingly high frequency of inhibitory activity. Thus, a high potential of edible Southeast Asian plants for cancer chemoprevention is indicated.

The modifying effect of dietary administration of auraptene isolated from the peel of citrus fruit (Citrus natsudaidai Hayata) on the development of azoxymethane (AOM)induced colonic aberrant crypt foci (ACF) was investigated in rats, Male F344 rats were given s.c. injections of AOM (15 mg/kg body wt) once a week for 3 weeks to induce ACF. They also received diets containing 100 or 500 p.p.m. auraptene for 5 weeks, starting 1 week before the first dose of AOM, At termination of the study (week 5) dietary administration of auraptene caused a significant reduction in the frequency of ACF in a dose-dependent manner (P < 0.05), Feeding of auraptene suppressed expression of cell proliferation biomarkers (5-bromo-2'-deoxyuridine labeling-index, ornithine decarboxylase activity, polyamine content and number of silver stained nucleolar organizer region protein particles) in the colonic mucosa and the occurrence of micronuclei caused by AOM, Also, auraptene increased the activities of phase II enzymes (glutathione S-transferase and quinone reductase) in the liver and colon, These findings might suggest that inhibition of AOM-induced ACF may be associated, in part, with increased activity of phase II enzymes in the liver and colon and suppression of cell proliferation in the colonic mucosa.

In our studies to find natural compounds with chemopreventive efficacy in foods, using azoxymethane (AOM)-induced colonic aberrant crypt foci and colonic mucosal cell proliferation as biomarkers, a xanthine oxidase inhibitor, 1'-acetoxychavicol acetate (ACA), present in the edible plant Languas galanga from Thailand was found to be effective. This study was conducted to test the ability of ACA to inhibit AOM-induced colon tumorigenesis when it was fed to rats during the initiation or post-initiation phase. Male F344 rats were given three weekly s.c. injections of AOM (15 mg/kg body weight) to induce colonic neoplasms. They were fed diet containing 100 or 500 ppm ACA for 4 weeks, starting one week before the first dosing of AOM (the initiation feeding). The other groups were fed the ACA diet for 34 weeks, starting one week after the last AOM injection (the post-initiation feeding). At the termination of the study (week 38), AOM had induced 71% incidence of colonic adenocarcinoma (12/17 rats). The initiation feeding with ACA caused significant reduction in the incidence of colon carcinoma (54% inhibition by 100 ppm ACA feeding and 77% inhibition by 500 ppm ACA feeding, P=0.03 and P=0.001, respectively). The post-initiation feeding with ACA also suppressed the incidence of colonic carcinoma (45% inhibition by 100 ppm ACA feeding and 93% inhibition by 500 ppm ACA feeding, P=0.06 and P=0.00003, respectively). Such inhibition was dose-dependent and was associated with suppression of proliferation biomarkers, such as ornithine decarboxylase activity in the colonic mucosa, and blood and colonic mucosal polyamine contents. ACA also elevated the activities of phase II enzymes, glutathione S-transferase (GST) and quinone reductase (QR), in the liver and colon. These results indicate that ACA could inhibit the development of AOM-induced colon tumorigenesis through its suppression of cell proliferation in the colonic mucosa and its induction of GST and QR. The results confirm our previous finding that ACA feeding effectively suppressed the development of colonic aberrant crypt foci. These findings suggest possible chemopreventive ability of ACA against colon tumorigenesis.

The present study was undertaken to investigate a mechanism of the inhibitory effect of vitamin E in urethane-induced lung tumorigenesis in mice. We assayed ornithine decarboxylase (ODC) activity and the prostaglandin E-2 (PGE(2)) level in lung at 8 weeks after urethane injection (promotion phase). Excessive vitamin E feeding or indomethacin treatment suppressed the urethane-induced increase in ODC activity, while exogenous PGE(2) overcame the effect of vitamin E on ODC activity. Furthermore, the amount of PGE(2) and the level of ODC activity were well correlated. These results indicate that the vitamin E-induced decrease in PGE(2) level probably contributes to the inhibition of ODC induction and the prevention of tumor development in the lung. (C) 1997 Elsevier Science Inc.

Coumarin-related compounds, auraptene and umbelliferone, have been isolated from the cold-pressed oil of natsumkian (Citrus natsudaidai HAYATA), and tested as inhibitors of tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced Epstein-Barr virus activation in Raji cells. The 50% inhibitory concentration (IC50) of auraptene (18 mu M) was almost equal to that of genistein. Umbelliferone, which lacks a geranyloxyl group present in auraptene, was less active (IC50 = 450 mu M). In a two-stage carcinogenesis experiment with 7,12-dimethylbenz[a]anthracene (topical application at 0.19 mu mol) and TPA (topical application at 1.6 nmol) in ICR mouse skin, topical application of auraptene (at 160 nmol) significantly reduced tumor incidence and the numbers of tumors per mouse by 27% (P < 0.01) and 23% (P < 0.05), respectively. Auraptene at a concentration of 50 mu M markedly suppressed superoxide (O-2(-)) generation induced by 100 nM TPA in differentiated human promyelocytic HL-60 cells. Having no O-2(-) scavenging potential, auraptene may inhibit the multicomponent NADPH oxidase system, Inhibition of intracellular hydroperoxide formation in differentiated HL-60 cells by auraptene was also confirmed by flow-cytometric analysis using 2',7'-dichlorofluorescein diacetate as a fluorescence probe. Quantitative analyses using high-performance liquid chromatography showed the occurrence of auraptene not only in both the peels and sarcocarps of natsumikan, but also in those of hassaku orange (C. hassaku) and grapefruit (C. paradisi), and even in their bottled fresh juice form. These results indicate that auraptene is a chemopreventer of skin tumorigenesis, and implies that suppression of leukocyte activation might be the mechanism through which it inhibits tumor promotion.

The modifying effect of dietary administration of a xanthine oxidase inhibitor 1'-acetoxychavicol acetate (ACA) present in an edible plant Languas galanga in Thailand on the development of azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF) was investigated in rats. Male F344 rats were given s.c. injections of AOM (15 mg/kg body wt) once a week for 3 weeks to induce colonic ACF. They were fed the diets containing 100 or 200 ppm ACA for 5 weeks, starting 1 week before the first dosing of AOM. At the termination of the study (week 5), AOM induced 118 +/- 28 ACF/colon. Dietary administration of ACA caused significant reduction in the frequency of ACF (41% inhibition by 100 ppm ACA feeding and 37% inhibition by 200 ppm ACA feeding, P<0.01). Such inhibition might be associated with suppression of the proliferation biomarkers' expression such as ornithine decarboxylase activity in the colonic mucosa, number of silver-stained nucleolar organizer regions' protein in the colonic mucosal cell nuclei and blood polyamine content. These results indicate that ACA could inhibit the development of AOM-induced ACF through its suppression of cell proliferation in the colonic mucosa and ACA might be a possible chemopreventive agent against colon tumourigenesis.

The modifying effect of dietary administration of a xanthine oxidase inhibitor 1'-acetoxychavicol acetate (ACA) present in an edible plant Languas galanga in Thailand on the development of azoxymethane (AOM)-induced colonic aberrant crypt foci (ACF) was investigated in rats. Male F344 rats were given s.c. injections of AOM (15 mg/kg body wt) once a week for 3 weeks to induce colonic ACF. They were fed the diets containing 100 or 200 ppm ACA for 5 weeks, starting 1 week before the first dosing of AOM. At the termination of the study (week 5), AOM induced 118 +/- 28 ACF/colon. Dietary administration of ACA caused significant reduction in the frequency of ACF (41% inhibition by 100 ppm ACA feeding and 37% inhibition by 200 ppm ACA feeding, P<0.01). Such inhibition might be associated with suppression of the proliferation biomarkers' expression such as ornithine decarboxylase activity in the colonic mucosa, number of silver-stained nucleolar organizer regions' protein in the colonic mucosal cell nuclei and blood polyamine content. These results indicate that ACA could inhibit the development of AOM-induced ACF through its suppression of cell proliferation in the colonic mucosa and ACA might be a possible chemopreventive agent against colon tumourigenesis.

The anti-tumor-promoting activity of 1'-acetoxychavicol acetate (ACA) was examined in a two-stage carcinogenesis experiment in ICR mouse skin using 7,12-dimethylbenz[a]anthracene (0.19 mu mol) and 12-O-tetradecanoylphorbol-13-acetate (TPA; 1.6 nmol). Topical application of ACA (160 nmol) markedly reduced the average number of tumors per mouse and the ratio of tumor-bearing mice: inhibition ratios 90% (p < 0.001) and 42% (p < 0.005), respectively. ACA even at a dose equimolar to TPA(1.6 nmol) significantly reduced the average number of tumors per mouse: inhibitory ratio 44% (p < 0.05). ACA potently inhibited TPA-induced superoxide (O-2(-)) generation in differentiated HL-60 cells (IC50 = 4.3 mu M) and suppressed the lipid hydroperoxide formation by 42% (p < 0.001) in the ethyl linoleate autoxidation test.

Six chlorophyll-related compounds isolated from leaves of Neptunia oleracea (Leguminosae) inhibited the activation of tumor promoter-induced Epstein-Barr virus (EBV). Photo-irradiation of pheophorbide a, the major active constituent, did not enhance this inhibitory activity, and thus ruled out any photosensitizing effect playing the major role.

Six chlorophyll-related compounds isolated from leaves of Neptunia oleracea (Leguminosae) inhibited the activation of tumor promoter-induced Epstein-Barr virus (EBV). Photo-irradiation of pheophorbide a, the major active constituent, did not enhance this inhibitory activity, and thus ruled out any photosensitizing effect playing the major role.

Cancer chemoprevention is currently regarded as a promising avenue for cancer control. In particular, the inhibition of tumor promotion (anti-tumor promotion) in multistage carcinogenesis is expected to be an efficient strategy, because tumor promotion is experimentally accomplished through the long-term, repetitive exposures of rodents to a tumor promoter, and premalignant lesions caused by a tumor promoter regress, at least in their earlier stages. In this review, we first describe the background of cancer chemoprevention studies as well as recent results of clinical trials. Subsequently, some hypothetical biological and cellular pathways in tumor promotion are explored. In addition, the anti-tumor promoting properties of vegetables, fruits, and edible marine algae, together with their active constituents and action mechanisms thus far known, are also described. Anti-tumor promotion with food phytochemicals may be characterized as an efficient and reliable strategy for cancer chemoprevention.

Cancer chemoprevention is currently regarded as a promising avenue for cancer control. In particular, the inhibition of tumor promotion (anti-tumor promotion) in multistage carcinogenesis is expected to be an efficient strategy, because tumor promotion is experimentally accomplished through the long-term, repetitive exposures of rodents to a tumor promoter, and premalignant lesions caused by a tumor promoter regress, at least in their earlier stages. In this review, we first describe the background of cancer chemoprevention studies as well as recent results of clinical trials. Subsequently, some hypothetical biological and cellular pathways in tumor promotion are explored. In addition, the anti-tumor promoting properties of vegetables, fruits, and edible marine algae, together with their active constituents and action mechanisms thus far known, are also described. Anti-tumor promotion with food phytochemicals may be characterized as an efficient and reliable strategy for cancer chemoprevention.

Two glyceroglycolipids were isolated from the leaves of Citrus hystrix (bitter orange), a traditional herb in Thailand. They were identified as 1,2-di-O-alpha-linolenoyl-3-O-beta-galactopyransyl-sn-glycerol (DLGG, I) and a mixture of two compounds, 1-O-alpha-linolenoyl-2-O-palmitoyl-3-O-beta-galactopyranosyl-sn-glycerol (2a) and its counterpart (2b) (LPGG, 2). Both lipids were potent inhibitors of tumor promoter-induced Epstein-Barr virus (EBV) activation. The IC50 values of 1 and 2 were strikingly lower than those of representative cancer preventive agents such as alpha-linolenic acid, beta-carotene, or (-)-epigallocatechin gallate. In a two-stage carcinogenesis experiment on ICR mouse skin with dimethylbenz[alpha]anthracene (DMBA) and 12-O-tetradecanoylphorbol 13-acetate (TPA), compound 1 exhibited anti-tumor-promoting activity even at a dose 10 times lower than that of alpha-linolenic acid. As some synthetic detergents or saponins were entirely inactive in the EBV activation inhibition test, detergency was suggested not to play a major role in the mode of inhibitory action in vivo. The inhibition of the arachidonic acid cascade may be involved in anti-tumor promotion since 1 inhibited TPA-induced edema formation in the anti-inflammation test using ICR mouse ears.

Two glyceroglycolipids were isolated from the leaves of Citrus hystrix (bitter orange), a traditional herb in Thailand. They were identified as 1,2-di-O-alpha-linolenoyl-3-O-beta-galactopyransyl-sn-glycerol (DLGG, I) and a mixture of two compounds, 1-O-alpha-linolenoyl-2-O-palmitoyl-3-O-beta-galactopyranosyl-sn-glycerol (2a) and its counterpart (2b) (LPGG, 2). Both lipids were potent inhibitors of tumor promoter-induced Epstein-Barr virus (EBV) activation. The IC50 values of 1 and 2 were strikingly lower than those of representative cancer preventive agents such as alpha-linolenic acid, beta-carotene, or (-)-epigallocatechin gallate. In a two-stage carcinogenesis experiment on ICR mouse skin with dimethylbenz[alpha]anthracene (DMBA) and 12-O-tetradecanoylphorbol 13-acetate (TPA), compound 1 exhibited anti-tumor-promoting activity even at a dose 10 times lower than that of alpha-linolenic acid. As some synthetic detergents or saponins were entirely inactive in the EBV activation inhibition test, detergency was suggested not to play a major role in the mode of inhibitory action in vivo. The inhibition of the arachidonic acid cascade may be involved in anti-tumor promotion since 1 inhibited TPA-induced edema formation in the anti-inflammation test using ICR mouse ears.

A total of 112 species of edible plants (122 samples) from Thailand were randomly collected, and their methanol extracts were screened for in vitro anti-tumor promoting activity using the inhibition test of Epstein-Barr virus (EBV) activation in Raji cells induced by 12-O-hexadecanoylphorbol-13-acetate (HPA, 40 ng/ml). It was found that 60% of these extracts inhibited EBV activation by 30% or more at a concentration of 200 mg/ml. Significantly, the ratio is markedly higher than that (26%) previously observed in common edible plants in Japan. Thus, physiological potentiality of edible Thai plants has been implied in terms of cancer chemoprevention.

Inhibition of tumor promoter-induced Epstein-Barr virus (EBV) activation was screened using tissue culture and thallus extracts of lichens. Usnea longissima Ace thallns and Cetraria ornata MULL. ARG, tissue culture showed strong inhibitory activity, We identified(+)-usnic acid (1), barbatic acid (2), diffractaic acid (3), 4-0-demethylbarbatic acid (4), and evernic acid (5) as inhibitors of EBV activation from the U, longissima thallus, Of these compounds,(+)-usnic acid exhibited the highest inhibitory activity (IC50 = 1.0 mu M).

Inhibition of tumor promoter-induced Epstein-Barr virus (EBV) activation was screened using tissue culture and thallus extracts of lichens. Usnea longissima Ace thallns and Cetraria ornata MULL. ARG, tissue culture showed strong inhibitory activity, We identified(+)-usnic acid (1), barbatic acid (2), diffractaic acid (3), 4-0-demethylbarbatic acid (4), and evernic acid (5) as inhibitors of EBV activation from the U, longissima thallus, Of these compounds,(+)-usnic acid exhibited the highest inhibitory activity (IC50 = 1.0 mu M).

Possible inhibitory properties against tumor promotion (anti-tumor promoting activity) food items as well as their active constituents have been studied by an in vitro assay detecting inhibition of tumor promoter-induced Epstein-Barr virus (EBV) activation. In screening tests of 121 edible plants, 12% of the methanol extracts exhibited strong activity, and 6 and 10% showed moderate and weak activities, respectively. Oleanolic acid (OA) from a green perilla, mokko lactone (ML) and arctic acid from an edible burdock, and gingerol from a ginger were isolated as inhibitors of EBV activation in Raji cells. OA and ML were proven to be anti-tumor promoters by in vivo tests using a mouse skin model. Similar screening tests of marine algae showed that the algae in the genus Phaeophyta, which contains many edible species such as wakame seaweed and sea tangles, in particular possess significant activities. An in vivo test of an extract of wakame seaweed, an important daily food in Japan, indicated strong anti-tumor promoting activity. Further screening tests of tropical plants used as condiments and occasionally medicines suggested that the Zingiberaceae plants possess highly effective anti-tumor promotion activities. (1'S)-1'-Acetoxychavicol acetate (ACA), isolated from Languas galanga, inhibited EBV activation greater than 10 times more potently than other inhibitors from edible plants. On the basis of this investigation, the combination of food constituents is suggested to be a significant source of anti-tumor promoting activity.

Possible anti-tumor promoting properties of a total of 40 methanol extracts from Thai edible plants, including 5 non-edible species, were estimated in vitro by an inhibition test of tumor promoter-induced Epstein-Barr virus (EBV) activation. Fourteen species (35% of the total) were found to be strongly active. In addition, cardamonin (2',4'-dihydroxy-6'-methoxychalcone) was identified as a potently active constituent (IC50 = 3.1 muM) of Boesenbergia pandurata (Zingiberaceae), suggesting it to be an effective anti-tumor promoter.

Possible anti-tumor promoting properties of a total of 40 methanol extracts from Thai edible plants, including 5 non-edible species, were estimated in vitro by an inhibition test of tumor promoter-induced Epstein-Barr virus (EBV) activation. Fourteen species (35% of the total) were found to be strongly active. In addition, cardamonin (2',4'-dihydroxy-6'-methoxychalcone) was identified as a potently active constituent (IC50 = 3.1 muM) of Boesenbergia pandurata (Zingiberaceae), suggesting it to be an effective anti-tumor promoter.

Four bitter compounds, lophiroside A1, A2, B1 and B2, were isolated from the bark of Lophira alata, and their structures were determined by chemical and spectral methods. They are rare types of cyanoglucosides containing a cyanomethylene group in the benzoylated and/or cinnamoylated aglycones. The threshold amount for bitterness of each compound was estimated as 10 mug by a filter paper tasting method.

Three possible flavonoid-type anti-tumour promoters were isolated from the bark of Lophira alata using an in vitro short-term assay, Epstein-Barr virus (EBV) early antigen (EA) induction test. One of the flavonoids was identified as lophirone F. The other two, named azobechalcone A and isolophirachalcone, were a new biflavonoid and a tetraflavonoid, respectively. Azobechalcone A (5-mu-M) and isolophirachalcone (5-mu-M) showed potent inhibitory activities (83% and 65%, respectively) against EBV-EA induction by a tumour promoter, teleocidin B-4 (50 nM). Lophirone F was less active (18% at the same dose) than azobechalcone A and isolophirachalcone.

Three possible flavonoid-type anti-tumour promoters were isolated from the bark of Lophira alata using an in vitro short-term assay, Epstein-Barr virus (EBV) early antigen (EA) induction test. One of the flavonoids was identified as lophirone F. The other two, named azobechalcone A and isolophirachalcone, were a new biflavonoid and a tetraflavonoid, respectively. Azobechalcone A (5-mu-M) and isolophirachalcone (5-mu-M) showed potent inhibitory activities (83% and 65%, respectively) against EBV-EA induction by a tumour promoter, teleocidin B-4 (50 nM). Lophirone F was less active (18% at the same dose) than azobechalcone A and isolophirachalcone.

Two chalcone tetramers were isolated as inhibitors of Epstein-Barr virus (EBV)-activation induced by a tumor promoter, teleocidin B-4, from a medicinal plant in tropical west Africa, Lophira alata (Ochnaceae). One of them was identified as lophirachalcone. The other, named alatachalcone, was new, and the structure was determined by spectral properties. Both compounds also showed potent inhibitory activities against teleocidin B-4-induced inflammation on mouse ear. In an initiation-promotion experiment on mouse skin, alatachalcone (16 nmol) significantly inhibited tumor promotion caused by 12-O-tetradecanoyphorbol-13-acetate (TPA, 1.6 nmol).

Two chalcone tetramers were isolated as inhibitors of Epstein-Barr virus (EBV)-activation induced by a tumor promoter, teleocidin B-4, from a medicinal plant in tropical west Africa, Lophira alata (Ochnaceae). One of them was identified as lophirachalcone. The other, named alatachalcone, was new, and the structure was determined by spectral properties. Both compounds also showed potent inhibitory activities against teleocidin B-4-induced inflammation on mouse ear. In an initiation-promotion experiment on mouse skin, alatachalcone (16 nmol) significantly inhibited tumor promotion caused by 12-O-tetradecanoyphorbol-13-acetate (TPA, 1.6 nmol).

Lophirone A, isolated as a new type of biflavonoid-related inhibitor of Epstein-Barr virus (EBV) activation, was tested for further inhibitory properties against tumor promotion by short-term systems. Lophirone A (200-mu-g) significantly inhibited inflammation of mouse ear (inhibitory effect (IE) = 70%) by 12-O-hexadecanoyl-16-hydroxyphorbol-13-acetate (HHPA, 2-mu-g). It also inhibited both Ca2+- and phospholipid-dependent protein kinase C (PKC) activation by 12-O-tetradecanoylphorbol-13-acetate (TPA, IC50 = 50-mu-M). Application of lophirone A (160 nmol) reduced the number of tumors per mouse (IE = 85 %) in an initiation-promotion experiment using dimethylbenz[a]anthracene (DMBA, 0.19-mu-mol) and TPA (1.6 nmol) on ICR mouse skin. Lophiraic acid, a related polyphenol, was negative in all of the short-term tests. An important chemical factor which may reduce the activities of flavonoid class of inhibitors for tumor promotion was indicated.