Deconjugation Kinetics of Glucuronidated Phase II Flavonoid Metabolites by B-glucuronidase from Neutrophils

Flavonoids are inactivated by phase II metabolism and occur in the body as glucuronides. Mammalian ß-glucuronidase released from neutrophils at inflammatory sites may be able to deconjugate and thus activate flavonoid glucuronides. We have studied deconjugation kinetics and pH optimum for four sources of ß-glucuronidase (human neutrophil, human recombinant, myeloid PLB-985 cells, Helix pomatia) with five flavonoid glucuronides (quercetin-3-glucuronide, quercetin-3'-glucuronide, quercetin-4'-glucuronide, quercetin-7-glucuronide, 3'-methylquercetin-3-glucuronide), 4-methylumbelliferyl-ß-D-glucuronide, and para-nitrophenol-glucuronide. All substrate-enzyme combinations tested exhibited first order kinetics. The optimum pH for hydrolysis was between 3.5-5, with appreciable hydrolysis activities up to pH 5.5. At pH 4, the Km ranged 44-fold from 22 µM for quercetin-4'-glucuronide with Helix pomatia ß-glucuronidase, to 981 µM for para-nitrophenol-glucuronide with recombinant ß-glucuronidase. Vmax (range: 0.735-24.012 µmol·min-1·unit-1 [1 unit is defined as the release of 1 µM 4-methylumbelliferyl-ß-D-glucuronide per min]) and the reaction rate constants at low substrate concentrations (k) (range: 0.002-0.062 min-1·(unit/L)-1 were similar for all substrates-enzyme combinations tested. In conclusion, we show that ß-glucuronidase from four different sources, including human neutrophils, is able to deconjugate flavonoid glucuronides and non-flavonoid substrates at fairly similar kinetic rates. At inflammatory sites in vivo the pH, neutrophil and flavonoid glucuronide concentrations seem favorable for deconjugation. However, it remains to be confirmed whether this is actually the case

Determination of the natamycin content of cheese rind and cheese : a collaborative study

A collaborative test on the determination of natamycin in cheese rind was carried out. The described method comprises: 1) sampling, 2) homogination, 3) extraction, 4) clean up, 5) concentration, 6) determination - spectroscopy - HPLC-UV. For practical reasons the steps 3 to 6 only could be incorporated in this test. Eight laboratories participated. Three samples of decreasing levels were distributed

Effect of wound healing period and temperature, irradiation and post irradiation storage temperature on the keeping quality of potatoes

The effect of irradiation doses, wound healing temperature, post harvest irradiation time (wound healing period) and storage temperature on a number of quality parameters such as loss of weight, sprout inhibition and rot incidence, chemical parameters such as sugar and vitamin e content, sensory parameters taste and colour and also wound healing ability were investigated. The potatoes were irradiated with a dose range of 50 to 100 Gy, after a wound healing period varying from 0 to 6 weeks at 15 or 20 °C. The product was stored at 10 and 20 °C and 90% relative humidity

Determination of the natamycin content of cheese rind and cheese : a collaborative study

A collaborative test on the determination of natamycin in cheese rind was carried out. The described method comprises: 1) sampling, 2) homogination, 3) extraction, 4) clean up, 5) concentration, 6) determination - spectroscopy - HPLC-UV. For practical reasons the steps 3 to 6 only could be incorporated in this test. Eight laboratories participated. Three samples of decreasing levels were distributed

Consumption of high doses of chlorogenic acid, present in coffee, or black tea increases plasma total homocysteine concentrations in humans

In population studies, high intakes of coffee are associated with raised concentrations of plasma homocysteine, a predictor of risk of cardiovascular disease. Chlorogenic acid is a major polyphenol in coffee; coffee drinkers consume up to 1 g chlorogenic acid/d. OBJECTIVE: We studied whether chlorogenic acid affects plasma total homocysteine concentrations in humans. For comparison we also studied the effects of black tea rich in polyphenols and of quercetin-3-rutinoside, a major flavonol in tea and apples. DESIGN: In this crossover study, 20 healthy men and women ingested 2 g (5.5 mmol) chlorogenic acid, 4 g black tea solids containing approximately 4.3 mmol polyphenols and comparable to approximately 2 L strong black tea, 440 mg (0.7 mmol) quercetin-3-rutinoside, or a placebo daily. Each subject received each of the 4 treatments for 7 d, in random order. RESULTS: Total homocysteine in plasma collected 4-5 h after supplement intake was 12ø1.2 micromol/L; 95␌I: 0.6, 1.7) higher after chlorogenic acid and 11ø1.1 micromol/L; 95␌I: 0.6, 1.5) higher after black tea than after placebo. Total homocysteine in fasting plasma collected 20 h after supplement intake was 4ø0.4 micromol/L; 95␌I: 0.0, 0.8) higher after chlorogenic acid and 5ø0.5 micromol/L; 95␌I: 0.0, 0.9) higher after black tea than after placebo. Quercetin-3-rutinoside did not significantly affect homocysteine concentrations. CONCLUSIONS: Chlorogenic acid, a compound in coffee, and black tea raise total homocysteine concentrations in plasma. Chlorogenic acid could be partly responsible for the higher homocysteine concentrations observed in coffee drinkers. Whether these effects on homocysteine influence cardiovascular disease risk remains to be established

SIRT1 stimulation by polyphenols is affected by their stability and metabolism

Silent information regulator two ortholog 1 (SIRT1) is the human ortholog of the yeast sir2 protein; one of the most important regulators of lifespan extension by caloric restriction in several organisms. Dietary polyphenols, abundant in vegetables, fruits, cereals, wine and tea, were reported to stimulate the deacetylase activity of recombinant SIRT1 protein and could therefore be potential regulators of aging associated processes. However, inconsistent data between effects of polyphenols on the recombinant SIRT1 and on in vivo SIRT1, led us to investigate the influence of (1) stability of polyphenols under experimental conditions and (2) metabolism of polyphenols in human HT29 cells, on stimulation of SIRT1. With an improved SIRT1 deacetylation assay we found three new polyphenolic stimulators. Epigallocatechin galate (EGCg, 1.76-fold), epicatechin galate (ECg, 1.85-fold) and myricetin (3.19-fold) stimulated SIRT1 under stabilizing conditions, whereas without stabilization, these polyphenols strongly inhibited SIRT1, probably due to H2O2 formation. Using metabolically active HT29 cells we were able to show that quercetin (a stimulator of recombinant SIRT1) could not stimulate intracellular SIRT1. The major quercetin metabolite in humans, quercetin 3-O-glucuronide, slightly inhibited the recombinant SIRT1 activity which explains the lack of stimulatory action of quercetin in HT29 cells. This study shows that the stimulation of SIRT1 is strongly affected by polyphenol stability and metabolism, therefore extrapolation of in vitro SIRT1 stimulation results to physiological effects should be done with caution

Intakes of 4 dietary lignans and cause-specific and all-cause mortality in the Zutphen Elderly Study

BACKGROUND: Plant lignans are converted to enterolignans that have antioxidant and weak estrogen-like activities, and therefore they may lower cardiovascular disease and cancer risks. OBJECTIVE: We investigated whether the intakes of 4 plant lignans (lariciresinol, pinoresinol, secoisolariciresinol, and matairesinol) were inversely associated with coronary heart disease (CHD), cardiovascular diseases (CVD), cancer, and all-cause mortality. DESIGN: The Zutphen Elderly Study is a prospective cohort study in which 570 men aged 64-84 y were followed for 15 y. We recently developed a database and used it to estimate the dietary intakes of 4 plant lignans. Lignan intake was related to mortality with the use of Cox proportional hazards analysis. RESULTS: The median total lignan intake in 1985 was 977 microg/d. Tea, vegetables, bread, coffee, fruit, and wine were the major sources of lignan. The total lignan intake was not related to mortality. However, the intake of matairesinol was inversely associated with CHD, CVD, and all-cause mortality (P </= 0.05 for all) and cancer (P = 0.06). Multivariate-adjusted rate ratios (95% CI) per 1-SD increase in intake were 0.72 (0.53, 0.98) for CHD, 0.83 (0.69, 1.00) for CVD, 0.86 (0.76, 0.97) for all-cause mortality, and 0.81 (0.65, 1.00) for cancer. CONCLUSIONS: Total lignan intake was not associated with mortality. The intake of matairesinol was inversely associated with mortality due to CHD, CVD, cancer, and all causes. We cannot exclude the possibility that the inverse association between matairesinol intake and mortality is due to an associated factor, such as wine consumption