Effects of methoxsalen from Poncirus trifoliata on acetylcholinesterase and trimethyltin-induced learning and memory impairment.

Previously, we identified methoxsalen (8-methoxy-2',3',6,7-furocoumarin) as the bioactive compound probably responsible for acetylcholinesterase (AchE) inhibition achieved by feeding crude extract of Poncirus trifoliate. To confirm the activity of methoxsalen, Institute of Cancer Research (ICR) mice were fed a control or a methoxsalen-supplemented diet for 4 weeks, and then learning and memory enhancing effects with respect to trimethyltin (TMT)-induced neurotoxicity were evaluated. The brain tissues of ICR mice were dissected after completion of the behavioral tests for biochemical analysis. Methoxsalen effectively reversed TMT-induced memory impairment on both Y-maze and passive avoidance tests. Brain AchE activity was inhibited by the oral consumption of all concentrations of methoxsalen. Moreover, the level of oxidative stress was significantly ameliorated in the groups on methodsalen containing diets. This is the first in vivo study conducted with methoxsalen in the field of AD research, and it indicates that further investigation of methoxsalen is warranted.

Effects of furanocoumarins from apiaceous vegetables on the catalytic activity of recombinant human cytochrome P-450 1A2.

Inhibition of cytochrome P-450 1A2 (CYP1A2)-mediated activation of procarcinogens may be an important chemopreventive mechanism. Consumption of apiaceous vegetables (rich in furanocoumarins) inhibits CYP1A2 in humans. Because many furanocoumarins are potent inhibitors of several CYPs, we characterized the effects of three furanocoumarins from apiaceous vegetables on human CYP1A2 (hCYP1A2). We assessed hCYP1A2 methoxyresorufin O-demethylase (MROD) activity using microsomes from Saccharomyces cerevisiae expressing hCYP1A2. Isopimpinellin exhibited mechanism-based inactivation (MBI) of hCYP1A2 (K(i) = 1.2 µM, k (inact) = 0.34 min⁻¹, and partition ratio = 8). Imperatorin and trioxsalen were characterized as mixed inhibitors with K(i) values of 0.007 and 0.10 µM, respectively. These results indicate that even if present at low levels in apiaceous vegetables, imperatorin, trioxsalen and isopimpinellin may contribute significantly to CYP1A2 inhibition and potentially decreased procarcinogen activation. Moreover, the in vivo effect of isopimpinellin on CYP1A2 may be longer lasting compared to reversible inhibitors.

Ipomoea batatas attenuates amyloid ß peptide-induced neurotoxicity in ICR mice.

In this study, the protective effects of 17 Korean native plants against amyloid ß peptide (Aß)-induced oxidative stress were screened using the 2',7'-dichlorofluorescin diacetate assay and the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Ipomoea batatas exerted the highest protective effects against oxidative stress and was selected for further investigation. To confirm the protective activity of this extract, the I. batatas extract was fed to ICR mice that had been injected with Aß to induce neuronal deficits. In these experiments, the extract of I. batatas significantly reversed Aß-induced neurotoxicity as assessed by the passive avoidance test, a behavioral experiment. Moreover, I. batatas administration reduced the level of lipid peroxidation and increased catalase activities in biochemical studies using the brain tissue of mice. These results indicate that I. batatas might be beneficial against Alzheimer's disease, especially by limiting oxidative stress in the brain.

Coffee intake and risk of colorectal cancer among Chinese in Singapore: the Singapore Chinese Health Study.

We prospectively investigated whether coffee consumption was associated with decreased risk of colorectal cancer and whether cigarette smoking and stage of disease modify the association in the Singapore Chinese Health Study. During the first 12 years of follow-up, 961 colorectal cancer cases occurred in the cohort of over 60,000 middle-aged or older Chinese men and women living in Singapore. Baseline dietary exposures were assessed through in-person interviews using a validated food frequency questionnaire. The relation between coffee consumption and colorectal cancer risk was assessed by proportional hazards (Cox) regression. No overall association between coffee intake and colorectal cancer was observed. However, in analysis by subsite and stage restricted to ever smokers, the coffee-colon cancer association became statistically significant for advanced disease (P for trend = 0.01). The hazard ratio was 0.56 (95% confidence interval = 0.35-0.90) for advanced colon cancer in drinkers of 2 or more cups per day compared with those who drank no coffee or less than 1 cup per day. Although there is a null association between coffee intake and risk of colorectal cancer overall, coffee may protect against smoking related advanced colon cancer.

Modulation of human serum glutathione S-transferase A1/2 concentration by cruciferous vegetables in a controlled feeding study is influenced by GSTM1 and GSTT1 genotypes.

Glutathione S-transferases (GST) detoxify a wide range of carcinogens. Isothiocyanates (ITC), from cruciferous vegetables, are substrates for and inducers of GST. GST variants may alter ITC clearance such that response to crucifers varies by genotype. In a randomized cross-over trial, we tested the hypothesis that changes in serum GSTA1/2 concentration in response to cruciferous vegetable feeding depends on GSTM1/GSTT1 genotype. Thirty-three men and 34 women (age 20-40 years) ate four 14-day controlled diets--basal (vegetable-free), basal supplemented with two different doses of crucifers ("single dose" and "double dose"), and single-dose cruciferous-plus-apiaceous vegetables--fed per kilogram of body weight. Fasting bloods from days 0, 7, 11, and 14 of each diet period were analyzed for serum GSTA1/2 by ELISA. GSTA1/2 increased with single- and double-dose cruciferous compared with basal diet (10% and 13%, respectively; P = 0.02 and 0.004), but cruciferous-plus-apiaceous did not differ from basal (P = 0.59). Overall, GSTA1/2 was higher in GSTM1-null/GSTT1-null than GSTM1+/GSTT1+ individuals (4,198 +/- 338 and 3,372 +/- 183 pg/mL; P = 0.03). The formal interaction of genotype-by-diet was not statistically significant, but the GSTA1/2 increase during the single-dose cruciferous diet was among GSTM1-null/GSTT1-null individuals (by 28%; P = 0.008), largely explained by GSTM1-null/GSTT1-null men (by 41%; P = 0.01). GSTA1/2 increased during the double-dose cruciferous diet in both GSTM1-null/GSTT1-null men (by 35%; P = 0.04) and GSTM1+/GSTT1+ men (by 26%; P = 0.01) but not in women. In summary, cruciferous vegetable supplementation increased GSTA1/2, but the effect was most marked in GSTM1-null/GSTT1-null men.

Apiaceous vegetable constituents inhibit human cytochrome P-450 1A2 (hCYP1A2) activity and hCYP1A2-mediated mutagenicity of aflatoxin B1.

In humans, apiaceous vegetables (carrots, parsnips, celery, parsley, etc.) inhibit cytochrome P-450 1A2, a biotransformation enzyme known to activate several procarcinogens, including aflatoxin B1 (AFB). We evaluated eight phytochemicals from apiaceous vegetables for effects on human cytochrome P-450 1A2 (hCYP1A2) activity using a methoxyresorufin O-demethylase (MROD) assay and a trp-recombination assay. Saccharomyces cerevisiae was used for heterologous CYP1A2 expression and this yeast strain is also diploid and auxotrophic for tryptophan due to mutations in the trp5 alleles. When these two alleles undergo AFB-induced mitotic recombination, gene conversion occurs, allowing yeast to grow in the absence of tryptophan. The apiaceous constituents psoralen, 5-methoxypsoralen (5-MOP), 8-methoxypsoralen (8-MOP), and apigenin were potent inhibitors of hCYP1A2-mediated MROD activity in yeast microsomes, whereas quercetin was a modest hCYP1A2 inhibitor. Naringenin, caffeic acid, and chlorogenic acid did not inhibit hCYP1A2-mediated MROD activity. The 2-h pretreatment of intact yeast cells with psoralen, 5-MOP, and 8-MOP significantly improved cell survival after subsequent 4-h AFB treatment and reduced hCYP1A2-mediated mutagenicity of AFB. Apigenin also significantly decreased mutagenicity. These results suggest that in vivo CYP1A2 inhibition by apiaceous vegetables may be due to the phytochemicals present and imply that apiaceous vegetable intake may be chemopreventive by inhibiting CYP1A2-mediated carcinogen activation.

Cruciferae interact with the UGT1A1*28 polymorphism to determine serum bilirubin levels in humans.

UDP-glucuronosyltransferase (UGT) 1A1 is a conjugating biotransformation enzyme that plays a role in maintaining levels of endogenous compounds (e.g., bilirubin) and handling exogenous compounds, including carcinogens. The UGT1A1*28 polymorphism results in decreased UGT1A1 promoter activity due to 7 thymine-adenine (TA) repeats instead of the commonly found 6 repeats. Studies indicate that foods from the botanical families Cruciferae (e.g., broccoli), Rutaceae (citrus), Liliaceae (e.g., onions), and Leguminosae (legumes) may increase UGT activity. We investigated, in an observational study, whether foods from these botanical groups were associated with increased UGT1A1 activity as indicated by serum bilirubin concentrations and whether the effect varied by UGT1A1*28 genotype, comparing those homozygous for the [TA](7)-repeat allele (7/7) to homozygous wild-types (6/6) and heterozygotes (6/7) combined. Healthy volunteers completed 3-d food records. Blood samples were drawn for genomic DNA collection and bilirubin measures. For total, direct, and indirect bilirubin measures, there was no significant association with any botanical group independently. There was a significant inverse association between all 3 bilirubin measures and interaction of UGT1A1*28 genotype with Cruciferae intake (P < 0.02 for each measure); individuals with the 7/7 genotype had reduced bilirubin concentrations with increased intake of cruciferous vegetables, whereas individuals with the 6/6 or 6/7 genotype did not. With regard to UGT1A1-conjugated carcinogens (e.g., heterocyclic amines, polycyclic aromatic hydrocarbons), individuals with decreased UGT1A1 activity due to the 7/7 genotype may be at greater risk for carcinogenesis, but our results imply that they also may have greater opportunity to decrease that risk through dietary intervention.