Involvement of microRNA modifications in anticancer effects of major polyphenols from green tea, coffee, wine, and curry.

Epidemiological studies have shown that consumption of green tea, coffee, wine, and curry may contribute to a reduced risk of various cancers. However, there are some cancer site-specific differences in their effects; for example, the consumption of tea or wine may reduce bladder cancer risk, whereas coffee consumption may increase the risk. Animal and cell-based experiments have been used to elucidate the anticancer mechanisms of these compounds, with reactive oxygen species (ROS)-based mechanisms emerging as likely candidates. Chlorogenic acid (CGA), curcumin (CUR), epigallocatechin gallate (EGCG), and resveratrol (RSV) can act as antioxidants that activate AMP-activated protein kinase (AMPK) to downregulate ROS, and as prooxidants to generate ROS, leading to the downregulation of NF-κB. Polyphenols can modulate miRNA (miR) expression, with these dietary polyphenols shown to downregulate tumor-promoting miR-21. CUR, EGCG, and RSV can upregulate tumor-suppressing miR-16, 34a, 145, and 200c, but downregulate tumor-promoting miR-25a. CGA, EGCG, and RSV downregulate tumor-suppressing miR-20a, 93, and 106b. The effects of miRs may combine with ROS-mediated pathways, enhancing the anticancer effects of these polyphenols. More precise analysis is needed to determine how the different modulations of miRs by polyphenols relate to the cancer site-specific differences found in epidemiological studies related to the consumption of foods containing these polyphenols.

Health Effects of Soy Isoflavones and Green Tea Catechins on Cancer and Cardiovascular Diseases Based on Urinary Biomarker Levels.

Plant polyphenols have various health effects. Genistein, which is abundant in soybeans, and epigallocatechin-3-gallate, which is abundant in green tea, are major flavonoids, a subclass group of polyphenols. Several epidemiological studies have shown that these flavonoids have beneficial effects against cancer and cardiovascular diseases. However, other studies did not show such effects. Several confounding factors, including recall bias, are related to these inconsistent findings, and the determination of metabolites in the urine may be useful in reducing the number of confounding factors. Equipment, which can be used by research participants to collect samples from a portion of voided urine within 24 h without the help of medical workers, has been developed for epidemiological investigations. Previous studies, in which flavonoid metabolites in these urine samples were measured, revealed that soy intake was correlated with a reduced risk of certain types of cancer and cardiovascular diseases worldwide. Although soybeans and green tea consumption may have protective effects against cancer and cardiovascular diseases, further clinical studies that consider different confounding factors are required to provide evidence for the actual impact of dietary flavonoids on human diseases, including cancer and cardiovascular diseases. One possible mechanism involved is discussed in relation to the downregulation of reactive oxygen species and the upregulation of 5'-adenosine monophosphate-activated protein kinase elicited by these flavonoids.

Nitrogen Balance and Bioavailability of Amino Acids in Spirulina Diet-Fed Wistar Rats.

Spirulina widely known to consumers as a health food is mainly a dried product. Since data for raw spirulina as a protein source are insufficient, the nutritional values of dry and raw spirulina diets in Wistar rats were determined. Digestibility coefficients were significantly lower in the dry (84.1 ± 0.5%) and raw (85.7 ± 0.4%) spirulina diets than that in the casein diet (96.6 ± 0.2%), although biological values of dry (86.3 ± 1.3%) and raw (77.9 ± 2.6%) spirulina diets were significantly higher than that of the casein diet (71.9 ± 2.5%). The protein digestibility-corrected amino acid score of raw spirulina (86.6 ± 0.5%) was significantly higher than that of dry spirulina (85.1 ± 0.5%). Additionally, amino acid profiling of portal/venous blood in spirulina diet-fed rats revealed that Ala, Gly, Val, and Leu/Ile were markedly decreased after systemic circulation. These results suggest that dry and raw spirulina diets may be effective not only as a protein source but also as a supplement to support protein/amino acid bioavailability.

Anti-Cancer Effects of Green Tea Epigallocatchin-3-Gallate and Coffee Chlorogenic Acid.

Tea and coffee are consumed worldwide and epidemiological and clinical studies have shown their health beneficial effects, including anti-cancer effects. Epigallocatechin gallate (EGCG) and chlorogenic acid (CGA) are the major components of green tea polyphenols and coffee polyphenols, respectively, and believed to be responsible for most of these effects. Although a large number of cell-based and animal experiments have provided convincing evidence to support the anti-cancer effects of green tea, coffee, EGCG, and CGA, human studies are still controversial and some studies have suggested even an increased risk for certain types of cancers such as esophageal and gynecological cancers with green tea consumption and bladder and lung cancers with coffee consumption. The reason for these inconsistent results may have been arisen from various confounding factors. Cell-based and animal studies have proposed several mechanisms whereby EGCG and CGA exert their anti-cancer effects. These components appear to share the common mechanisms, among which one related to reactive oxygen species is perhaps the most attractive. Meanwhile, EGCG and CGA have also different target molecules which might explain the site-specific differences of anti-cancer effects found in human studies. Further studies will be necessary to clarify what is the mechanism to cause such differences between green tea and coffee.

Identification of soybean peptide leginsulin variants in different cultivars and their insulin-like activities.

We have recently reported that green soybean cultivar, echigomidori, and not the yellow cultivar, fukuyutaka, is a rich source of hormone-like peptide leginsulin consisting of 37 amino acids (Leg_1_37, PDB 1JU8A) and its C-terminal glycine deletant, Leg_1_36. Green soybean is mature, but the color of the seedcoat and cotyledon remains green. Therefore, in this study, we examined the leginsulin content in different varieties of 11 colored soybeans (including green, yellow, red, brown and black) and edamame (immature soybean). Profile analysis of soybean constituents by LC-MS showed that Leg_1 (36 + 37) detected as a prominent peak in 3 green and 1 yellow soybean cultivar was the strongest contributor in principal component analysis, indicating Leg_1 is the most characteristic feature for distinguishing soybean cultivars. However, smaller amounts of leginsulin-like peptides, defined as Leg_2 and Leg_3, were detected in other samples. The cDNA sequences and LC-MS/MS analyses revealed that Leg_2 was a homologue of Leg_1 with three amino acid substitutions derived from SNPs, while Leg_3 was a Leg_1/Leg_2 paralog. Expression levels of Leg_1 were markedly higher than Leg_2 and Leg_3. Additionally, in glucose uptake assay, purified TRX-His-tag fused recombinant Leg_1_37 prepared by bacterial expression showed stronger insulin-like activities than other variants including Leg_2, Leg_3, and their Gly deletants in myotube-like differentiated L6 and C2C12 cells. These results suggest that dietary consumption of soybean seed, especially including a higher amount of Leg_1_37, could be useful for lowering of blood glucose.

Phenethyl isothiocyanate activates leptin signaling and decreases food intake.

Obesity, a principal risk factor for the development of diabetes mellitus, heart disease, and hypertension, is a growing and serious health problem all over the world. Leptin is a weight-reducing hormone produced by adipose tissue, which decreases food intake via hypothalamic leptin receptors (Ob-Rb) and the Janus kinase 2/signal transducer and activator of transcription 3 (JAK2/STAT3) signaling pathway. Protein tyrosine phosphatase 1B (PTP1B) negatively regulates leptin signaling by dephosphorylating JAK2, and the increased activity of PTP1B is implicated in the pathogenesis of obesity. Hence, inhibition of PTP1B may help prevent and reduce obesity. In this study, we revealed that phenethyl isothiocyanate (PEITC), a naturally occurring isothiocyanate in certain cruciferous vegetables, potently inhibits recombinant PTP1B by binding to the reactive cysteinyl thiol. Moreover, we found that PEITC causes the ligand-independent phosphorylation of Ob-Rb, JAK2, and STAT3 by inhibiting cellular PTP1B in differentiated human SH-SY5Y neuronal cells. PEITC treatment also induced nuclear accumulation of phosphorylated STAT3, resulting in enhanced anorexigenic POMC expression and suppressed orexigenic NPY/AGRP expression. We demonstrated that oral administration of PEITC to mice significantly reduces food intake, and stimulates hypothalamic leptin signaling. Our results suggest that PEITC might help prevent and improve obesity.

Beneficial Effects of Green Tea Catechins on Neurodegenerative Diseases.

Tea is one of the most consumed beverages in the world. Green tea, black tea, and oolong tea are made from the same plant Camellia sinensis (L.) O. Kuntze. Among them, green tea has been the most extensively studied for beneficial effects on diseases including cancer, obesity, diabetes, and inflammatory and neurodegenerative diseases. Several human observational and intervention studies have found beneficial effects of tea consumption on neurodegenerative impairment, such as cognitive dysfunction and memory loss. These studies supported the basis of tea's preventive effects of Parkinson's disease, but few studies have revealed such effects on Alzheimer's disease. In contrast, several human studies have not reported these favorable effects with regard to tea. This discrepancy may be due to incomplete adjustment of confounding factors, including the method of quantifying consumption, beverage temperature, cigarette smoking, alcohol consumption, and differences in genetic and environmental factors, such as race, sex, age, and lifestyle. Thus, more rigorous human studies are required to understand the neuroprotective effect of tea. A number of laboratory experiments demonstrated the benefits of green tea and green tea catechins (GTCs), such as epigallocatechin gallate (EGCG), and proposed action mechanisms. The targets of GTCs include the abnormal accumulation of fibrous proteins, such as Aß and α-synuclein, inflammation, elevated expression of pro-apoptotic proteins, and oxidative stress, which are associated with neuronal cell dysfunction and death in the cerebral cortex. Computational molecular docking analysis revealed how EGCG can prevent the accumulation of fibrous proteins. These findings suggest that GTCs have the potential to be used in the prevention and treatment of neurodegenerative diseases and could be useful for the development of new drugs.

Anticarcinogenic Effects of Dried Citrus Peel in Colon Carcinogenesis Due to Inhibition of Oxidative Stress.

Colorectal cancer is one of the leading causes of death worldwide. Reactive oxygen species produce oxidative stress and contribute to colorectal carcinogenesis. Because dietary citrus has been shown to reduce oxidative stress, we investigated the effects of citrus peel extract at dilutions of 1/200-1/500 on the activity of oxidative-stress-related transcription factors, including AP-1, NF-κB, NRF2, p53, and STAT3, in human colon cancer cell line HCT116 cells using a luciferase reporter gene assay. NRF2 transcriptional activities were 1.8- to 2.0-fold higher than the untreated control value. In addition, NF-κB, p53, and STAT3 transcriptional activities were 12-26% lower than the untreated control value. Administration of dried citrus peel in the diet of F344 rats at a dose of 1,000 ppm prevented the formation of azoxymethane-induced precancerous aberrant crypt foci (ACF) in the colon. The total number of ACF in rats fed with dried citrus peel was reduced to 75% of the control value. Moreover, the levels of oxidative-stress-related markers, reactive carbonyl species, in the serum of F344 rats were significantly reduced following the administration of dried citrus peel. These data suggest that citrus peel possesses an ability to suppress cellular oxidative stress through induction of NRF2, thereby preventing azoxymethane-induced colon carcinogenesis.

Anti-Cancer Effects of Green Tea by Either Anti- or Pro- Oxidative Mechanisms.

Tea derived from the leaves and buds of Camellia sinensis (Theaceae) is consumed worldwide. Green tea contains various components with specific health-promoting effects, and is believed to exert protective effects against diseases including cancer, diabetes and hepatitis, as well as obesity. Of the various tea components, the polyphenol catechins have been the subject of extensive investigation and among the catechins, (-)-epigallocatechin gallate has the strongest bioactivity in most cases. Our research group has postulated that hepatocyte nuclear factor-4α, sterol regulatory element-binding proteins, and tumor necrosis factor-α are targets of green tea constituents including (-)-epigallocatechin gallate for their anti-diabetes, anti-obesity, and anti-hepatitis effects, respectively. Published papers were reviewed to determine whether the observed changes in these factors can be correlated with anti-cancer effects of green tea. Two major action mechanisms of (-)-epigallocatechin gallate have been proposed; one associated with its anti-oxidative properties and the other with its pro-oxidative activity. When reactive oxygen species are assumed to be involved, our findings that (-)-epigallocatechin gallate down- regulated hepatocyte nuclear factor-4α, sterol regulatory element-binding proteins, and tumor necrosis factor-α may explain the anti-cancer effect of green tea as well. However, further studies are required to elucidate which determinant directs (-)-epigallocatechin gallate action as an anti-oxidant or a pro-oxidant for favorable activity.

Anti-inflammatory effects of green soybean extract irradiated with visible light.

We conducted a preliminary investigation of the effects of visible light irradiation on plant extracts, and we observed a strong suppressive effect on interleukin (IL) 2 expression with the inhibition of c-Jun amino-terminal kinase (JNK) phosphorylation in Jurkat cells by visible light irradiation to ethanol extract from green soybeans (LIEGS). This effect was produced only by extracts from green soybeans (Glycine max) and not other-color soybeans. LIEGS suppressed the lipopolysaccharide-induced IL-6, IL-12 and TNF-α expression levels in human monocyte THP-1 cells in a concentration-dependent manner. LIEGS was applied for 8 weeks to NC/Nga mice. LIEGS suppressed the development of atopic dermatitis (AD)-like skin lesions and reduced the dermatitis scores of the mice. The light irradiation changed the various types of small-molecule compounds in extracts. Visible light irradiation to daidzein with chlorophyll b induced a novel oxidative product of daidzein. This product suppressed IL-2 expression in Jurkat cells.

Health-promoting effects of green tea.

Green tea is manufactured from the leaves of the plant Camellia sinensis Theaceae and has been regarded to possess anti-cancer, anti-obesity, anti-atherosclerotic, anti-diabetic, anti-bacterial, and anti-viral effects. Many of the beneficial effects of green tea are related to the activities of (-)-epigallocatechin gallate (EGCG), a major component of green tea catechins. For about 20 years, we have engaged in studies to reveal the biological activities and action mechanisms of green tea and EGCG. This review summarizes several lines of evidence to indicate the health-promoting properties of green tea mainly based on our own experimental findings.

Effects of a catechin-free fraction derived from green tea on gene expression of enzymes related to lipid metabolism in the mouse liver.

Many biological activities of green tea have been attributed to a major constituent, (minus;)-epigallocatechin gallate (EGCG). We previously reported that EGCG and an EGCG-free fraction derived from green tea modulated the gene expression of gluconeogenic enzymes, glucose-6-phosphatase and phosphoenolpyruvate carboxykinase, in the mouse liver. EGCG is also known to affect the gene expression of enzymes related to lipid metabolism. However, it remains to be examined whether or not a constituent other than EGCG contributes to the change in gene expression of these enzymes. In this study, we prepared an EGCG-free water-soluble fraction (GT-W), and examined its effects on the hepatic gene expression of lipogenic enzymes in mice. The results of quantitative real-time PCR assays indicated that the dietary administration of GT-W for 4 weeks reduced the hepatic gene expression of lipogenic enzymes: fatty acid synthase, hydroxymethylglutaryl coenzyme A reductase, and acetyl-coenzyme A carboxylase alpha. Also, the gene expression of sterol regulatory element-binding transcription factor (Srebf)1 and/or Srebf2 was reduced, suggesting that the reduction of Srebfs contributed to the down-regulation of the lipogenic enzymes, since these transcription factors bind the promoter region to enhance their expression. The plasma levels of triglycerides and cholesterol were reduced with statistical significance in the group given a diet containing GT-W. These results suggest that in addition to EGCG, green tea contains some component(s) which may help to prevent arteriosclerosis and obesity.

Effects of oolong tea on gene expression of gluconeogenic enzymes in the mouse liver and in rat hepatoma H4IIE cells.

Tea has many beneficial effects. We have previously reported that green tea and a catechin-rich green tea beverage modulated the gene expression of the gluconeogenic enzymes glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK) in the normal murine liver. In the present study, we examined the effects of oral administration of oolong tea on the hepatic expression of gluconeogenesis-related genes in the mouse. The intake of oolong tea for 4 weeks reduced the hepatic expression of G6Pase and PEPCK together with that of the transcription factor hepatocyte nuclear factor (HNF) 4α. When rat hepatoma H4IIE cells were incubated in the presence of oolong tea, the expression of these genes was repressed in accordance with the findings in vivo. The reduced protein expression of PEPCK and HNF4α was also demonstrated. We then fractionated oolong tea by sequential extraction with three organic solvents to give three fractions and the residual fraction (Fraction IV). In addition to organic fractions, Fraction IV, which was devoid of low-molecular-weight catechins such as (-)-epigallocatechin gallate (EGCG), had effects similar to those of oolong tea on H4IIE cells. Fraction IV repressed the gene expression of insulin-like growth factor binding protein 1, as insulin did. This activity was different from that of EGCG. The present findings suggest that drinking oolong tea may help to prevent diabetes and that oolong tea contains a component or components with insulin-like activity distinguishable from EGCG. Identification of such component(s) may open the way to developing a new drug for diabetes.

Effects of a catechin-free fraction derived from green tea on gene expression of gluconeogenic enzymes in rat hepatoma H4IIE cells and in the mouse liver.

Many biological activities of green tea have been attributed to a major constituent, (-)-epigallocatechin gallate (EGCG). We previously reported that EGCG and a catechin-rich green tea beverage modulated the gene expression of gluconeogenic enzymes, glucose-6-phosphatase (G6Pase) and phosphoenolpyruvate carboxykinase (PEPCK), in the mouse liver. However, it remains to be examined whether or not a constituent other than EGCG contributes to the change in gene expression of these enzymes. In this study, we separated the hot water infusion of green tea leaves (GT) into an ethanol-soluble fraction (GT-E) and an EGCG-free water-soluble fraction (GT-W), and examined their effects using rat hepatoma H4IIE cells. The inclusion of GT, GT-E, and GT-W in the culture medium reduced the gene expression of G6Pase and PEPCK. GT-W caused a decrease in expression of the transcription factor HNF4α. Reduced levels of PEPCK and HNF4α proteins were demonstrated in the cells treated with GT-W. GT-W showed an activity similar to insulin, but different from EGCG. Administration of GT-W to mice for 4 weeks reduced the hepatic expression of G6Pase, PEPCK, and HNF4α. These results suggest that green tea contains some component(s) with insulin-like activity distinguishable from EGCG and that drinking green tea may help to prevent diabetes.

Chemoprevention of azoxymethane/dextran sodium sulfate-induced mouse colon carcinogenesis by freeze-dried yam sanyaku and its constituent diosgenin.

The effects of sanyaku, a traditional Chinese medicine [freeze-dried powder of the yam tuber (Dioscorea)], and its major steroidal saponin constituent, diosgenin, on colon carcinogenesis were investigated. Male ICR mice were subjected to a single intraperitoneal injection of azoxymethane (AOM; 10 mg/kg body weight) followed by administration of 1.5% dextran sodium sulfate (DSS) in drinking water for 7 days to establish carcinogenesis. Commercial diosgenin or sanyaku, which contained diosgenin at 63.8 ± 1.2 mg/kg dry weight, was given in the diet at 20, 100, or 500 mg/kg for 17 weeks. Groups of mice that received diosgenin or sanyaku at all doses yielded significantly less number of colon tumors compared with the AOM/DSS-treated mice. Occurrence of colonic mucosal ulcer and dysplastic crypt induced by AOM/DSS treatment was also significantly decreased by the administration of diosgenin and sanyaku, which was in accordance with the significant reduction of AOM/DSS-mediated increases in expression of inflammatory cytokines such as IL-1ß by diosgenin and sanyaku. Furthermore, elevated levels of serum triglyceride in the AOM/DSS-treated mice tended to be reduced in mice given diosgenin and sanyaku. Microarray and real-time reverse transcriptase PCR analyses revealed that diosgenin administration increased 12-fold the expression of lipoprotein lipase, which may contribute to reduced serum triglyceride levels. Other genes altered by diosgenin included those associated with antioxidative stress responses and apoptosis, such as heme oxygenase-1, superoxide dismutase-3, and caspase-6. Our results imply that the Chinese medicine sanyaku and the tubers of various yams containing diosgenin as food could be ingested to prevent colon carcinogenesis in humans.

Galloylated catechins as potent inhibitors of hypochlorous acid-induced DNA damage.

Hypochlorous acid (HOCl), a strong oxidant derived from myeloperoxidase in neutrophils and macrophages, can chlorinate DNA bases at the site of inflammation. Because little is known about the protective role of natural antioxidants, such as polyphenols, for the myeloperoxidase-derived DNA damage, we screened the inhibitory effects of various phenolic antioxidants on the chlorination of the 2'-deoxycytidine residue by HOCl in vitro and found that green tea catechins, especially (-)-epicatechin gallate (ECg) and (-)-epigallocatechin gallate (EGCg), significantly inhibited the chlorination. These catechins also reduced nucleoside- and taurine-chloramines, which can induce secondary oxidative damage, into their native forms. Mass spectrometric and nuclear magnetic resonance analyses showed that ECg and EGCg can effectively scavenge HOCl and/or chloramine species resulting in the formation of mono- and dichlorinated ECg and EGCg. Using the HL-60 human leukemia cell line, it was found that ECg could efficiently accumulate in the cells. Immunocytometric analyses using antihalogenated 2'-deoxycytidine antibody showed that pretreatment of cells with ECg inhibited the HOCl-induced immunofluorescence. In addition, the chlorinated ECg derivatives were detected in the HOCl-treated HL-60 cells. These results showed that green tea catechins, especially 3-galloylated catechins, may be the plausible candidate for the prevention of inflammation-derived DNA damage and perhaps carcinogenesis.