Anthocyanins and their physiologically relevant metabolites alter the expression of IL-6 and VCAM-1 in CD40L and oxidized LDL challenged vascular endothelial cells

SCOPE

In vitro and in vivo studies suggest that dietary anthocyanins modulate cardiovascular disease risk; however, given anthocyanins extensive metabolism, it is likely that their degradation products and conjugated metabolites are responsible for this reported bioactivity.

METHODS AND RESULTS

Human vascular endothelial cells were stimulated with either oxidized LDL (oxLDL) or cluster of differentiation 40 ligand (CD40L) and cotreated with cyanidin-3-glucoside and 11 of its recently identified metabolites, at 0.1, 1, and 10 μM concentrations. Protein and gene expression of IL-6 and VCAM-1 was quantified by ELISA and RT-qPCR. In oxLDL-stimulated cells the parent anthocyanin had no effect on IL-6 production, whereas numerous anthocyanin metabolites significantly reduced IL-6 protein levels; phase II conjugates of protocatechuic acid produced the greatest effects (>75% reduction, p ≤ 0.05). In CD40L-stimulated cells the anthocyanin and its phase II metabolites reduced IL-6 protein production, where protocatechuic acid-4-sulfate induced the greatest reduction (>96% reduction, p ≤ 0.03). Similarly, the anthocyanin and its metabolites reduced VCAM-1 protein production, with ferulic acid producing the greatest effect (>65% reduction, p ≤ 0.04).

CONCLUSION

These novel data provide evidence to suggest that anthocyanin metabolites are bioactive at physiologically relevant concentrations and have the potential to modulate cardiovascular disease progression by altering the expression of inflammatory mediators.

The pharmacokinetics of anthocyanins and their metabolites in humans

BACKGROUND AND PURPOSE

Anthocyanins are phytochemicals with reported vasoactive bioactivity. However, given their instability at neutral pH, they are presumed to undergo significant degradation and subsequent biotransformation. The aim of the present study was to establish the pharmacokinetics of the metabolites of cyanidin-3-glucoside (C3G), a widely consumed dietary phytochemical with potential cardioprotective properties.

EXPERIMENTAL APPROACH

A 500 mg oral bolus dose of 6,8,10,3′,5′-¹³C₅-C3G was fed to eight healthy male participants, followed by a 48 h collection (0, 0.5, 1, 2, 4, 6, 24, 48 h) of blood, urine and faecal samples. Samples were analysed by HPLC-ESI-MS/MS with elimination kinetics established using non-compartmental pharmacokinetic modelling.

KEY RESULTS

Seventeen ¹³C-labelled compounds were identified in the serum, including ¹³C₅-C3G, its degradation products, protocatechuic acid (PCA) and phloroglucinaldehyde (PGA), 13 metabolites of PCA and 1 metabolite derived from PGA. The maximal concentrations of the phenolic metabolites (C_max) ranged from 10 to 2000 nM, between 2 and 30 h (t_max) post-consumption, with half-lives of elimination observed between 0.5 and 96 h. The major phenolic metabolites identified were hippuric acid and ferulic acid, which peaked in the serum at approximately 16 and 8 h respectively.

CONCLUSIONS AND IMPLICATIONS

Anthocyanins are metabolized to a structurally diverse range of metabolites that exhibit dynamic kinetic profiles. Understanding the elimination kinetics of these metabolites is key to the design of future studies examining their utility in dietary interventions or as therapeutics for disease risk reduction.

Methods for isolating, identifying, and quantifying anthocyanin metabolites in clinical samples

The metabolic fate of anthocyanins until recently was relatively unknown, primarily as a result of their instability at physiological pH and a lack of published methods for isolating and identifying their metabolites from biological samples. The aim of the present work was to establish methods for the extraction and quantification of anthocyanin metabolites present in urine, serum, and fecal samples. 35 commercial and 10 synthetic analytes, including both known and predicted human and microbial metabolites of anthocyanins, were obtained as reference standards. HPLC and MS/MS conditions were optimized for organic modifier, ionic modifier, mobile phase gradient, flow rate, column type, MS source, and compound dependent parameters. The impact of sorbent, solvent, acid, preservative, elution, and evaporation on solid phase extraction (SPE) efficiency was also explored. The HPLC-MS/MS method validation demonstrated acceptable linearity (R(2), 0.997 ± 0.002) and sensitivity (limits of detection (LODs): urine, 100 ± 375 nM; serum, 104 ± 358 nM; feces 138 ± 344 nM), and the final SPE methods provided recoveries of 88.3 ± 17.8% for urine, 86.5 ± 11.1% for serum, and 80.6 ± 20.9% for feces. The final methods were applied to clinical samples derived from an anthocyanin intervention study, where 36 of the 45 modeled metabolites were detected within urine, plasma, or fecal samples. The described methods provide suitable versatility for the identification and quantification of an extensive series of anthocyanin metabolites for use in future clinical studies exploring absorption, distribution, metabolism, and elimination.

Development and characterization of glutamyl-protected N-hydroxyguanidines as reno-active nitric oxide donor drugs with therapeutic potential in acute renal failure

Acute renal failure (ARF) has high mortality and no effective treatment. Nitric oxide (NO) delivery represents a credible means of preventing the damaging effects of vasoconstriction, central to ARF, but design of drugs with the necessary renoselectivity is challenging. Here, we developed N-hydroxyguanidine NO donor drugs that were protected against spontaneous NO release by linkage to glutamyl adducts that could be cleaved by γ-glutamyl transpeptidase (γ-GT), found predominantly in renal tissue. Parent NO donor drug activity was optimized in advance of glutamyl adduct prodrug design. A lead compound that was a suitable substrate for γ-GT-mediated deprotection was identified. Metabolism of this prodrug to the active parent compound was confirmed in rat kidney homogenates, and the prodrug was shown to be an active vasodilator in rat isolated perfused kidneys (EC50 ~50 μM). The data confirm that glutamate protection of N-hydroxyguanidines is an approach that might hold promise in ARF.

Human metabolism and elimination of the anthocyanin, cyanidin-3-glucoside: a (13)C-tracer study

BACKGROUND

Evidence suggests that the consumption of anthocyanin-rich foods beneficially affects cardiovascular health; however, the absorption, distribution, metabolism, and elimination (ADME) of anthocyanin-rich foods are relatively unknown.

OBJECTIVE

We investigated the ADME of a (13)C5-labeled anthocyanin in humans.

DESIGN

Eight male participants consumed 500 mg isotopically labeled cyanidin-3-glucoside (6,8,10,3',5'-(13)C5-C3G). Biological samples were collected over 48 h, and (13)C and (13)C-labeled metabolite concentrations were measured by using isotope-ratio mass spectrometry and liquid chromatography-tandem mass spectrometry.

RESULTS

The mean ± SE percentage of (13)C recovered in urine, breath, and feces was 43.9 ± 25.9% (range: 15.1-99.3% across participants). The relative bioavailability was 12.38 ± 1.38% (5.37 ± 0.67% excreted in urine and 6.91 ± 1.59% in breath). Maximum rates of (13)C elimination were achieved 30 min after ingestion (32.53 ± 14.24 μg(13)C/h), whereas (13)C-labeled metabolites peaked (maximum serum concentration: 5.97 ± 2.14 μmol/L) at 10.25 ± 4.14 h. The half-life for (13)C-labeled metabolites ranged between 12.44 ± 4.22 and 51.62 ± 22.55 h. (13)C elimination was greatest between 0 and 1 h for urine (90.30 ± 15.28 μg/h), at 6 h for breath (132.87 ± 32.23 μg/h), and between 6 and 24 h for feces (557.28 ± 247.88 μg/h), whereas the highest concentrations of (13)C-labeled metabolites were identified in urine (10.77 ± 4.52 μmol/L) and fecal samples (43.16 ± 18.00 μmol/L) collected between 6 and 24 h. Metabolites were identified as degradation products, phenolic, hippuric, phenylacetic, and phenylpropenoic acids.

CONCLUSION

Anthocyanins are more bioavailable than previously perceived, and their metabolites are present in the circulation for ≤48 h after ingestion. This trial was registered at clinicaltrials.gov as NCT01106729.

A new class of NO-donor pro-drugs triggered by γ-glutamyl transpeptidase with potential for reno-selective vasodilatation

This communication describes the synthesis of a new class of N-hydroxyguanidine (NHG) pro-drugs which release nitric oxide (NO), triggered by the action of γ-glutamyl transpeptidase (γ-GT), and have potential for the treatment of acute renal injury/failure (ARI/ARF).

A gram scale synthesis of a multi-13C-labelled anthocyanin, [6,8,10,3',5'-13C5]cyanidin-3-glucoside, for use in oral tracer studies in humans

The major dietary anthocyanin, cyanidin-3-glucoside, was prepared on a 4 g scale from three units of diethyl [2-(13)C]malonate and one unit of [1,3-(13)C(2)]acetone, such that five isotope locations were distributed throughout the molecule to provide a penta-(13)C(5)-labelled anthocyanin, [6,8,10,3',5'-(13)C(5)]cyanidin-3-glucoside chloride, for use in human stable-isotope tracer studies.

Bioavailability of Sulforaphane from two broccoli sprout beverages: results of a short-term, cross-over clinical trial in Qidong, China

One of several challenges in design of clinical chemoprevention trials is the selection of the dose, formulation, and dose schedule of the intervention agent. Therefore, a cross-over clinical trial was undertaken to compare the bioavailability and tolerability of sulforaphane from two of broccoli sprout-derived beverages: one glucoraphanin-rich (GRR) and the other sulforaphane-rich (SFR). Sulforaphane was generated from glucoraphanin contained in GRR by gut microflora or formed by treatment of GRR with myrosinase from daikon (Raphanus sativus) sprouts to provide SFR. Fifty healthy, eligible participants were requested to refrain from crucifer consumption and randomized into two treatment arms. The study design was as follows: 5-day run-in period, 7-day administration of beverages, 5-day washout period, and 7-day administration of the opposite intervention. Isotope dilution mass spectrometry was used to measure levels of glucoraphanin, sulforaphane, and sulforaphane thiol conjugates in urine samples collected daily throughout the study. Bioavailability, as measured by urinary excretion of sulforaphane and its metabolites (in approximately 12-hour collections after dosing), was substantially greater with the SFR (mean = 70%) than with GRR (mean = 5%) beverages. Interindividual variability in excretion was considerably lower with SFR than with GRR beverage. Elimination rates were considerably slower with GRR, allowing for achievement of steady-state dosing as opposed to bolus dosing with SFR. Optimal dosing formulations in future studies should consider blends of sulforaphane and glucoraphanin as SFR and GRR mixtures to achieve peak concentrations for activation of some targets and prolonged inhibition of others implicated in the protective actions of sulforaphane. Cancer Prev Res; 4(3); 384-95. ©2011 AACR.

Orally administered isoflavones are present as glucuronides in the human prostate

Better knowledge of the bioavailability and metabolism of isoflavones in prostate tissue is needed to further investigate their mechanisms of action in the context of prostate cancer prevention. A total of 12 men with benign prostatic hyperplasia received soy extract supplementation (3 Evestrel capsules, providing a total of 112.5 mg isoflavones aglycone eq/day) for 3 days before prostate surgery. Blood and prostate tissues were sampled and metabolites were identified using electrospray ionization liquid chromatography tandem mass spectrometry (LC-ESI-MS/MS) and chemically synthesized standards of glucuronidated isoflavones. The main metabolites were the same in prostate tissue and in plasma, namely, 2 monoglucuronides of daidzein and 2 monoglucuronides of genistein. Concentrations of total isoflavones measured in prostate reached 1.05 +/- 0.62 nmol/g tissue (range 0.30-2.23) at the time of sampling, 12 h after the last isoflavone supplementation. At that time point, prostate concentrations were lower than plasma concentrations in all volunteers: 0.47 nmol/g vs. 0.66 microM for daidzein and 0.58 nmol/g vs. 0.78 microM for genistein. Isoflavone mechanisms of action should thus be investigated in in vitro cell studies using physiological conditions, intracellular concentrations below 5 nmol/g and no intracellular deconjugation of the monoglucuronide metabolites.

1-(5-Chloro-2,4-dihydroxyphenyl)-2-(4-ethoxyphenyl)ethanone

The structure of the title compound, C₁₆H₁₅ClO₄, contains aryl rings which are inclined by 75.6 (1)° to each other. It displays intra­molecular O—H⋯O hydrogen bonding between the 2-hydr­oxy and carbonyl groups, forming a six-membered ring. Furthermore, the 4-hydr­oxy group, acting as a hydrogen-bond donor, is bound to the O atom of the 2-hydr­oxy group of another mol­ecule.

Synthesis of multiply 13C-labeled furofuran lignans using 13C-labeled cinnamyl alcohols as building blocks

Plant lignans are currently being widely studied for their potential benefits for human health as their consumption has been correlated with lower risks for developing chronic diseases, such as breast cancer and coronary heart disease. However, studies of some classes of lignans, in particular the furofurans, are hampered by the lack of suitable standards to allow accurate analysis. Herein, we report the syntheses of two racemic (13)C-labeled furofuran lignans [7,8,9-(13)C(3)]medioresinol and [7,8,9-(13)C(3)]sesamin as internal standards for LC-MS analysis. The labeled furofuran lignans were constructed from triply labeled cinnamyl alcohols, using a radical cyclization method.

Analysis of glucosinolates, isothiocyanates, and amine degradation products in vegetable extracts and blood plasma by LC–MS/MS

Dietary glucosinolates are under intensive investigation as precursors of cancer-preventive isothiocyanates. Quantitation of the dose and bioavailability of glucosinolates and isothiocyanates requires a comprehensive analysis of the major dietary glucosinolates, isothiocyanates, and related metabolites. We report a liquid chromatography with tandem mass spectrometric detection (LC-MS/MS) analytical method for the comprehensive analysis of the seven major dietary glucosinolates, related isothiocyanates, and putative amine degradation products. The parent glucosinolates were sinigrin, gluconapin, progoitrin, glucoiberin, glucoraphanin, glucoalyssin, and gluconasturtiin. The LC-MS/MS analysis method for these compounds was developed and validated; a standard addition analysis protocol was used generally to avoid the requirement for stable isotopic standards. Where stable isotopic standards were available, internal standardization with these gave estimates in agreement with those obtained by the standard addition analysis protocol. For glucosinolates, negative ion electrospray LC-MS/MS analysis was performed. Isothiocyanates and amines were prederivatized to the corresponding thiourea and N-acetamides, respectively, and were quantified by positive ion electrospray LC-MS/MS. The limits of detection were 0.5-2 pmol; the recoveries for glucosinolates, isothiocyanates, and amines were 85-90%, 50-85%, and 60-70%, respectively; and the intra- and interbatch coefficients of variation were 1-4% and 3-10%, respectively. These methods provide facile access to comprehensive analytical data on the major dietary glucosinolates and related metabolites to quantify inputs and metabolic formation of these compounds in cancer prevention and related studies.

Metabolism of phytoestrogen conjugates

Phytoestrogens are plant-derived compounds with physiologic estrogenic effects. They are present in the plant as glycosidic conjugates, some of which contain further chemical modifications (acetate, malonate, and 3-hydroxy-3-methylglutarate esters and 2,3-dihydroxysuccinate ether). In the gastrointestinal tract, the conjugates undergo hydrolysis catalyzed by enzymes in the intestinal wall and by gut bacteria. On entering the systemic circulation, the phytoestrogens may undergo extensive metabolism to other compounds through reactions involving demethylation, methylation, hydroxylation, chlorination, iodination, and nitration. In addition, all these compounds can undergo conjugation to form beta-glucuronides and sulfate esters. This chapter describes the methods of analysis of all these compounds, the sources of or methods to manufacture suitable standards, and the procedures for examining the enzymes that catalyze these reactions.

Phytoestrogen concentrations in serum and spot urine as biomarkers for dietary phytoestrogen intake and their relation to breast cancer risk in European prospective investigation of cancer and nutrition-norfolk

Subjects of this study consisted of 333 women (aged 45-75 years) drawn from a large United Kingdom prospective study of diet and cancer, the European Prospective Investigation of Cancer and Nutrition-Norfolk study. Using newly developed gas chromatography/mass spectrometry and liquid chromatography/mass spectrometry methods incorporating triply (13)C-labeled standards, seven phytoestrogens (daidzein, genistein, glycitein, O-desmethylangolensin, equol, enterodiol, and enterolactone) were measured in 114 spot urines and 97 available serum samples from women who later developed breast cancer. Results were compared with those from 219 urines and 187 serum samples from healthy controls matched by age and date of recruitment. Dietary levels were low, but even so, mean serum levels of phytoestrogens were up to 600 times greater than postmenopausal estradiol levels. Phytoestrogen concentrations in spot urine (adjusted for urinary creatinine) correlated strongly with that in serum, with Pearson correlation coefficients > 0.8. There were significant relationships (P < 0.02) between both urinary and serum concentrations of isoflavones across increasing tertiles of dietary intakes. Urinary enterodiol and enterolactone and serum enterolactone were significantly correlated with dietary fiber intake (r = 0.13-0.29). Exposure to all isoflavones was associated with increased breast cancer risk, significantly so for equol and daidzein. For a doubling of levels, odds ratios increased by 20-45% [log(2) odds ratio = 1.34 (1.06-1.70; P = 0.013) for urine equol, 1.46 (1.05-2.02; P = 0.024) for serum equol, and 1.22 (1.01-1.48; P = 0.044) for serum daidzein]. These estimates of risk are similar to those established for estrogens and androgens in postmenopausal breast cancer but need confirmation in larger studies.

Neutrophil myeloperoxidase chlorinates and nitrates soy isoflavones and enhances their antioxidant properties

Soy isoflavones and other polyphenolics have a number of potentially important beneficial effects on the pro-oxidant aspects of chronic inflammation. The impact of inflammatory cell-specific metabolism of polyphenolics, which can include halogenation and nitration, on the properties of these compounds has not been examined. Using either human neutrophils or differentiated human leukemia cells (HL-60) stimulated with phorbol ester to elicit a respiratory burst, the hypothesis that local generation of reactive oxygen and nitrogen species may metabolize and modify the biological properties of the soy isoflavones was examined. Coincubation of the stimulated cells with genistein or daidzein had no effect on the respiratory burst. Medium from stimulated cells in the presence of the isoflavones and NO(2)(-) increased the inhibition of copper-induced LDL oxidation. Mass spectrometry analysis of this medium revealed that monochlorinated, dichlorinated, and nitrated isoflavones, formed through a myeloperoxidase-dependent mechanism, were present. The consumption of genistein in the presence of cells was both extensive and rapid with > 95% of the genistein converted to either the chlorinated or nitrated metabolites within 30 min. Chemically synthesized 3'-chlorogenistein and 3'-chlorodaidzein increased the inhibition of LDL oxidation by approximately 4-fold and 2-fold over genistein and daidzein, respectively. These results lead to the hypothesis that inflammatory cell-specific metabolism of polyphenolics can modify the properties of these compounds at the local site of inflammation.

Comparative inhibition by substrate analogues 3-methoxy- and 3-hydroxydesaminokynurenine and an improved 3 step purification of recombinant human kynureninase

Background

Kynureninase is a key enzyme on the kynurenine pathway of tryptophan metabolism. One of the end products of the pathway is the neurotoxin quinolinic acid which appears to be responsible for neuronal cell death in a number of important neurological diseases. This makes kynureninase a possible therapeutic target for diseases such as Huntington's, Alzheimer's and AIDS related dementia, and the development of potent inhibitors an important research aim.

Results

Two new kynurenine analogues, 3-hydroxydesaminokynurenine and 3-methoxydesaminokynurenine, were synthesised as inhibitors of kynureninase and tested on the tryptophan-induced bacterial enzyme from Pseudomonas fluorescens, the recombinant human enzyme and the rat hepatic enzyme. They were found to be mixed inhibitors of all three enzymes displaying both competitive and non competitive inhibition. The 3-hydroxy derivative gave low K_i values of 5, 40 and 100 nM respectively. An improved 3-step purification scheme for recombinant human kynureninase was also developed.

Conclusion

For kynureninase from all three species the 2-amino group was found to be crucial for activity whilst the 3-hydroxyl group played a fundamental role in binding at the active site presumably via hydrogen bonding. The potency of the various inhibitors was found to be species specific. The 3-hydroxylated inhibitor had a greater affinity for the human enzyme, consistent with its specificity for 3-hydroxykynurenine as substrate, whilst the methoxylated version yielded no significant difference between bacterial and human kynureninase. The modified purification described is relatively quick, simple and cost effective.

Quantification of isoflavones and lignans in urine using gas chromatography/mass spectrometry

Phytoestrogens (isoflavones and lignans) are of increasing interest due to their potential to prevent certain types of complex diseases. However, epidemiological evidence is needed on the levels of phytoestrogens and their metabolites in foods and biological fluids in relation to risk of these diseases. We report an assay for phytoestrogens which is sensitive, accurate, and uses low volumes of sample. Suitable for epidemiological studies, the assay consists of a simple sample preparation procedure and has been developed for the analysis of five isoflavones (daidzein, O-desmethylangolensin, equol, genistein, and glycitein) and two lignans (enterodiol and enterolactone), which requires only 200 microl of urine and utilizes one solid-phase extraction stage for sample preparation prior to derivatization for GC/MS analysis. Limits of detection were in the region 1.2 ng/ml (enterodiol) to 5.3ng/ml (enterolactone) and the method performed well in the UK Government's Food Standards Agency-sponsored quality assurance scheme for phytoestrogens. For the first time, average levels of all the above phytoestrogens were measured in samples of urine collected from a free living population sample of women. Results show a large range in both the amount and the type of phytoestrogens excreted.

Comparing the pharmacokinetics of daidzein and genistein with the use of 13C-labeled tracers in premenopausal women

BACKGROUND

Despite significant interest in the risks and benefits of phytoestrogens to human health, few data exist on their pharmacokinetics in humans.

OBJECTIVE

We investigated the pharmacokinetics of the (13)C isotopic forms of daidzein and genistein in healthy humans, specifically addressing intraindividual variability, effect of increasing intake, and influence of prolonged exposure to a soy food diet.

DESIGN

Premenopausal women (n = 16) were administered 0.4 mg [(13)C]daidzein or [(13)C]genistein/kg body wt orally on 3 occasions, including once after eating soy foods for 7 d. On a further occasion the dose was doubled. Plasma and urinary [(13)C]isoflavone concentrations were measured by mass spectrometry.

RESULTS

Serum concentrations of [(13)C]genistein and [(13)C]daidzein peaked after 5.5 and 7.4 h, respectively. The systemic bioavailability and maximum serum concentration of [(13)C]genistein were significantly greater than those of [(13)C]daidzein. The bioavailability of both isoflavones did not increase linearly when the dietary intake was doubled. The mean volume of distribution normalized to bioavailability (V(d)/F), clearance rate, and half-life of [(13)C]daidzein were 336.25 L, 30.09 L/h, and 7.75 h, respectively; the corresponding values for [(13)C]genistein were 258.76 L, 21.85 L/h, and 7.77 h. The average recovery of [(13)C]daidzein and [(13)C]genistein in urine was 30.1% and 9.0% of the dose ingested, respectively.

CONCLUSIONS

The serum pharmacokinetics of [(13)C]daidzein and [(13)C]genistein were reproducible among healthy women, and genistein was more bioavailable than was daidzein. Pharmacokinetics were unaffected by chronic exposure to soy foods. Urinary isoflavone concentrations correlated poorly with maximal serum concentrations, indicating the limitations of urine measurements as a predictor of systemic bioavailability. The bioavailability of both isoflavones was nonlinear at higher intakes, suggesting that uptake is rate-limiting and saturable.

A three-enzyme microelectrode sensor for detecting purine release from central nervous system

As the purines, in particular adenosine, are important signaling agents in the nervous system we have devised a new biosensor for directly measuring their production in real time during physiological activity. Our amperometric adenosine biosensor is made by entrapping 3 enzymes (xanthine oxidase, purine nucleoside phosphorylase and adenosine deaminase) in a composite lactobionamide and amphiphillic polypyrrole matrix around a Pt microelectrode. The resulting sensors are small (25-100 microm diameter), fast responding (10-90% rise time, 2+/-0.23 s), sensitive (100-222 mA M(-1) cm(-2)) and stable (100% activity after 5 days). The sensor was used in vivo to demonstrate the spatial localization of release of adenosine from Xenopus embryo spinal cord during fictive swimming.

Quantification of isoflavones and lignans in serum using isotope dilution liquid chromatography/tandem mass spectrometry

Phytoestrogens (isoflavones and lignans) are receiving increasing attention due to a potential protective effect against a number of complex diseases. However, in order to investigate these associations, it is necessary to accurately quantify the levels of phytoestrogens in foods and biological fluids. We report an assay for three isoflavones (daidzein, genistein, and glycitein), two metabolites of daidzein (O-desmethylangolensin and equol), and two lignans (enterodiol and enterolactone) in human serum using electrospray ionisation liquid chromatography/mass spectrometry (LC/MS) with selective reaction monitoring. A simple, highly automated sample preparation procedure requires only 200 microL of sample and utilises one solid-phase extraction stage. Limits of detection are in the region of 10 pg/mL for all analytes except equol, which had a limit of detection of approximately 100 pg/mL. The method developed is suitable for measuring the concentrations of phytoestrogens in blood samples collected from large epidemiological studies. The results of the analysis of serum samples from 300 men and women living in the UK are reported.

Measurement of intact sulfate and glucuronide phytoestrogen conjugates in human urine using isotope dilution liquid chromatography-tandem mass spectrometry with [13C(3)]isoflavone internal standards

A method has been developed for the analysis of phytoestrogens and their conjugates in human urine using liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). Stable isotopically labeled [13C(3)]daidzein and [13C(3)]genistein were synthesized and used as internal standards for isotope dilution mass spectrometry. Free aglycons and intact glucuronide, sulfate, diglucuronide, disulfate, and mixed sulfoglucuronide conjugates of isoflavones and lignans were observed in naturally incurred urine samples. Sample pretreatment was not necessary, other than addition of internal standards and pH adjustment. Urine was injected directly onto the analytical column. The limits of detection were generally <50ng/ml, precision was generally <10% CV for conjugates. Total hydrolyzed daidzein and genistein were measured against quality assurance urine sample and were accurate to within 12%. The accuracy of conjugate measurement can not be ascertained, as no reference samples are available. The mean sum of daidzein and its conjugates was within 20% of the hydrolyzed value. Concentrations of the free aglycons of up to 22% of genistein and 18% of daidzein were observed. The average pattern was ca. 54% 7-glucuronide, 25% 4(')-glucuronide, 13% monosulfates, 7% free daidzein, 0.9% sulfoglucuronides, 0.4% diglucuronide, and <0.1% disulfate. Selective enzymatic deconjugation with glucuronidase and mixed glucuronidase/sulfatase were used to validate the accuracy of the quantitation of the intact daidzein conjugates. There were no apparent sex differences, or conditioning effects on the conjugation profile of isoflavones after chronic dosing.

Identification of the major glucosinolate (4-mercaptobutyl glucosinolate) in leaves of Eruca sativa L. (salad rocket)

The major and structurally unique glucosinolate (GLS) in leaves of Eruca sativa L. (salad rocket) was identified as 4-mercaptobutyl GLS. Both 4-methylthiobutyl GLS and 4-methylsulfinylbutyl GLS were also present, but at lower concentrations. The 4-mercaptobutyl GLS was observed to oxidise under common GLS extraction conditions, generating a disulfide GLS that may be reduced efficiently by tris(2-carboxyethyl) phosphine hydrochloride (TCEP) to reform the parent molecule. The identities of 4-mercaptobutyl GLS and of the corresponding dimeric GLS were confirmed by LC/MS, MS/MS and NMR. Myrosinase treatment of an enriched GLS fraction or of the purified dimer GLS generated a mixture of unique bi-functional disulfides, including bis-(4-isothiocyanatobutyl) disulfide (previously identified elsewhere). TCEP reduction of the purified dimer, followed by myrosinase treatment, yielded only 4-mercaptobutyl ITC. GLS-derived volatiles generated by autolysis of fresh seedlings and true leaves were 4-mercaptobutyl ITC (from the newly identified GLS), 4-methylthiobutyl ITC (from 4-methylthiobutyl GLS) and 4-methylsulfinylbutyl ITC (from 4-methylsulfinyl-butyl GLS); no unusual bi-functional disulfides were found in fresh leaf autolysate. These results led to the conclusion that, in planta, the new GLS must be present as 4-mercaptobutyl GLS and not as the disulfide found after extraction and sample concentration. This new GLS and its isothiocyanate are likely to contribute to the unique odour and flavour of E. sativa.

Purification and biochemical characterization of some of the properties of recombinant human kynureninase

Recombinant human kynureninase (L-kynurenine hydrolase, EC 3.7.1.3) was purified to homogeneity (60-fold) from Spodoptera frugiperda (Sf9) cells infected with baculovirus containing the kynureninase gene. The purification protocol comprised ammonium sulfate precipitation and several chromatographic steps, including DEAE-Sepharose CL-6B, hydroxyapatite, strong anionic and cationic separations. The purity of the enzyme was determined by SDS/PAGE, and the molecular mass verified by MALDI-TOF MS. The monomeric molecular mass of 52.4 kDa determined was > 99.99% of the predicted molecular mass. A UV absorption spectrum of the holoenzyme resulted in a peak at 432 nm. The optimum pH was 8.25 and the enzyme displayed a strong dependence on the ionic strength of the buffer for optimum activity. This cloned enzyme was highly specific for 3-hydroxykynurenine (Km = 3.0 microm +/- 0.10) and was inhibited by L-kynurenine (Ki = 20 microm), d-kynurenine (Ki = 12 microm) and a synthetic substrate analogue D,L-3,7-dihydroxydesaminokynurenine (Ki = 100 nm). The activity/concentration profile for kynureninase from this source was sigmoidal in all instances. There appeared to be partial inhibition by substrate, and excess pyridoxal 5'-phosphate was found to be inhibitory.

Analysis of intact glucosinolates by MALDI-TOF mass spectrometry

Glucosinolates are naturally occurring plant compounds that may be important in the dietary prevention of cancer. This study shows that they can be detected in their intact form by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) with a high degree of sensitivity. The methodology was used to characterize a number of individual glucosinolates either produced by synthetic chemistry or isolated from plants. The method was used for crude plant extracts to rapidly examine the glucosinolate profile of the plant. The results for a range of plant extracts showed good agreement with previous LC-MS analysis of the desulfoglucosinolates from the same samples.

2-Amino-4-[3'-hydroxyphenyl]-4-hydroxybutanoic acid; a potent inhibitor of rat and recombinant human kynureninase

A novel structural analogue of kynurenine, 2-amino-4-[3'-hydroxyphenyl]-4-hydroxybutanoic acid 6, was synthesised as an inhibitor of kynureninase. The compound had a significant inhibitory effect on kynureninase from both rat and human, giving a K(i) of 100 nM. It was thus found that removal of the aryl amino group coupled with a reduction of the carbonyl group at position 7 of the alanine side chain greatly enhanced potency of the inhibitor.

High-performance liquid chromatographic separation of natural and synthetic desulphoglucosinolates and their chemical validation by UV, NMR and chemical ionisation-MS methods

Methods are described for the optimised extraction, desulphation and HPLC separation of desulphoglucosinolates. These methods provide rapid separation, identification and quantitative measurements of glucosinolates extracted from Brassica napus L and related crops, of unusual glucosinolates found in crucifer weed species, and also of synthetic alkylglucosinolates. The desulphoglucosinolates used in these studies were either chemically synthesised (at least one example from each major structural class), or purified from various plant sources. Validation of the identities of the desulphoglucosinolates was by comparison of retention times with standards, and by UV, 1H- and 13C-NMR and chemical ionisation MS analysis. A list of useful species, and the specific tissues, from which high concentrations of standards can be extracted is included.

A comparative study on the inhibition of human and bacterial kynureninase by novel bicyclic kynurenine analogues

A series of novel bicyclic analogues of kynurenine were synthesised as inhibitors of kynureninase. The tryptophan-induced bacterial enzyme from Pseudomonas. fluorescens was compared to the constitutive recombinant human enzyme expressed in a baculovirus/insect cell system, with regard to their inhibition by these compounds. All the compounds studied were found to be simple competitive, reversible inhibitors of kynureninase. It was found that altering the size of the second ring of the inhibitor affected the observed Ki values for both enzymes. The addition of an oxygen atom into the second ring had little effect on binding to the bacterial enzyme but gave a more potent inhibitor of human kynureninase. Of the compounds tested, a naphthyl analogue of desaminokynurenine was found to be the most potent inhibitor for both enzymes with Ki values of 5 and 22 microM for bacterial and human enzyme respectively. This report also describes an alternative system for the expression of recombinant human kynureninase which is more convenient for expression in mammalian cells and produces a relatively greater quantity of enzyme.