Publications by authors named "Wouter H J Vaes"

29 Publications

  • Page 1 of 1

Quantification of azacitidine incorporation into human DNA/RNA by accelerator mass spectrometry as direct measure of target engagement.

J Pharm Biomed Anal 2021 Aug 19;202:114152. Epub 2021 May 19.

Celgene, a Wholly Owned Subsidiary of Bristol Myers Squibb, 556 Morris Ave, Summit, NJ, United States.

We report an accelerator mass spectrometry (AMS) assay to quantify azacitidine (Aza) incorporation into DNA and RNA from human acute myeloid leukemia (AML) cells, mouse bone marrow (BM) and peripheral blood mononuclear cells (PBMCs). Aza, a cytidine nucleoside analogue, is a disease modifying pharmacological agent used for treatment of myelodysplastic syndromes (MDS) and AML. Our assay was able to directly quantify the complex of Aza incorporated into DNA/RNA, via isolation of DNA/RNA from matrix (i.e., cancer cells, BM and PBMC) and subsequent measurement of total radioactivity (i.e., C-Aza) by using AMS. The sensitivity of the method was able to quantify as little as a single Aza molecule incorporated into DNA with approximately 2 × 10 nucleotides from PBMCs. An in vivo mouse model was used for establishing the lower limits of quantification (LLOQs) for Aza incorporated into DNA/RNA in mouse PBMCs (∼ 3.7 × 10) and BM (∼27.8 mg) collected 24 h post-dose after total exposure of 18 nCi/mouse (Aza 1 mg/kg). The LLOQs for PBMC analysis were 2.5 picogram equivalents per microgram (pgEq/μg) DNA and 0.22 pgEq/μg RNA, and for BM analysis were 1.7 pgEq/μg DNA and 0.22 pgEq/μg RNA. A linear relationship (i.e., ∼10-fold) was established of radioactive dose from C-Aza 17 nCi/mouse to 188 nCi/mouse and AMS response (i.e., C/C ratio ranging from 2.45 × 10 to 2.50 × 10), as Aza was incorporated into DNA in mouse BM. The current method enables the direct measurement of Aza incorporation into DNA and RNA from patient PBMCs and BM to provide dosing optimization, and to assess target engagement with as little as ∼5 mL whole blood and ∼3 mL of BM from patients.
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http://dx.doi.org/10.1016/j.jpba.2021.114152DOI Listing
August 2021

Towards human organ perfusion models to elucidate drug pharmacokinetics in health and disease.

Drug Metab Rev 2020 08 18;52(3):438-454. Epub 2020 Jun 18.

The Netherlands Organisation for Applied Scientific Research (TNO), Zeist, The Netherlands.

To predict the absorption, distribution, metabolism and excretion (ADME) profile of candidate drugs a variety of preclinical models can be applied. The ADME and toxicological behavior of newly developed drugs are often investigated prior to assessment in humans, which is associated with long time-lines and high costs. Therefore, good predictions of ADME profiles earlier in the drug development process are very valuable. Good prediction of intestinal absorption and renal and biliary excretion remain especially difficult, as there is an interplay of active transport and metabolism involved. To study these processes, including enterohepatic circulation, tissue models are highly relevant and can be regarded as the bridge between and models. In this review the current and in more detail models for studying pharmacokinetics in health and disease are discussed. Additionally, we propose novel models, i.e., perfused whole-organs, which we envision will generate valuable pharmacokinetic information in the future due to improved translation to the situation. These machine-perfused organ models will be particularly interesting in combination with biomarkers for assessing the functionality of transporter and CYP450 proteins.
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http://dx.doi.org/10.1080/03602532.2020.1772280DOI Listing
August 2020

The Oral Bioavailability and Metabolism of Midazolam in Stable Critically Ill Children: A Pharmacokinetic Microtracing Study.

Clin Pharmacol Ther 2021 01 28;109(1):140-149. Epub 2020 Jun 28.

Intensive Care and Pediatric Surgery, Erasmus Medical Center - Sophia Children's Hospital, Rotterdam, The Netherlands.

Midazolam is metabolized by the developmentally regulated intestinal and hepatic drug-metabolizing enzyme cytochrome P450 (CYP) 3A4/5. It is frequently administered orally to children, yet knowledge is lacking on the oral bioavailability in term neonates up until 1 year of age. Furthermore, the dispositions of the major metabolites 1-OH-midazolam (OHM) and 1-OH-midazolam-glucuronide (OHMG) after oral administration are largely unknown for the entire pediatric age span. We aimed to fill these knowledge gaps with a pediatric [ C]midazolam microtracer population pharmacokinetic study. Forty-six stable, critically ill children (median age 9.8 (range 0.3-276.4) weeks) received a single oral [ C]midazolam microtracer (58 (40-67) Bq/kg) when they received a therapeutic continuous intravenous midazolam infusion and had an arterial line in place enabling blood sampling. For midazolam, in a one-compartment model, bodyweight was a significant predictor for clearance (0.98 L/hour) and volume of distribution (8.7 L) (values for a typical individual of 5 kg). The typical oral bioavailability in the population was 66% (range 25-85%). The exposures of OHM and OHMG were highest for the youngest age groups and significantly decreased with postnatal age. The oral bioavailability of midazolam, largely reflective of intestinal and hepatic CYP3A activity, was on average lower than the reported 49-92% for preterm neonates, and higher than the reported 21% for children> 1 year of age and 30% for adults. As midazolam oral bioavailability varied widely, systemic exposure of other CYP3A-substrate drugs after oral dosing in this population may also be unpredictable, with risk of therapy failure or toxicity.
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http://dx.doi.org/10.1002/cpt.1890DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7818442PMC
January 2021

Proof of Concept: First Pediatric [ C]microtracer Study to Create Metabolite Profiles of Midazolam.

Clin Pharmacol Ther 2020 11 27;108(5):1003-1009. Epub 2020 Jun 27.

Intensive Care and Department of Pediatric Surgery, Erasmus Medical Center - Sophia Children's Hospital, Rotterdam, The Netherlands.

Growth and development affect drug-metabolizing enzyme activity thus could alter the metabolic profile of a drug. Traditional studies to create metabolite profiles and study the routes of excretion are unethical in children due to the high radioactive burden. To overcome this challenge, we aimed to show the feasibility of an absorption, distribution, metabolism, and excretion (ADME) study using a [ C]midazolam microtracer as proof of concept in children. Twelve stable, critically ill children received an oral [ C]midazolam microtracer (20 ng/kg; 60 Bq/kg) while receiving intravenous therapeutic midazolam. Blood was sampled up to 24 hours after dosing. A time-averaged plasma pool per patient was prepared reflecting the mean area under the curve plasma level, and subsequently one pool for each age group (0-1 month, 1-6 months, 0.5-2 years, and 2-6 years). For each pool [ C]levels were quantified by accelerator mass spectrometry, and metabolites identified by high resolution mass spectrometry. Urine and feces (n = 4) were collected up to 72 hours. The approach resulted in sufficient sensitivity to quantify individual metabolites in chromatograms. [ C]1-OH-midazolam-glucuronide was most abundant in all but one age group, followed by unchanged [ C]midazolam and [ C]1-OH-midazolam. The small proportion of unspecified metabolites most probably includes [ C]midazolam-glucuronide and [ C]4-OH-midazolam. Excretion was mainly in urine; the total recovery in urine and feces was 77-94%. This first pediatric pilot study makes clear that using a [ C]midazolam microtracer is feasible and safe to generate metabolite profiles and study recovery in children. This approach is promising for first-in-child studies to delineate age-related variation in drug metabolite profiles.
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http://dx.doi.org/10.1002/cpt.1884DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7689753PMC
November 2020

Enteral Acetaminophen Bioavailability in Pediatric Intensive Care Patients Determined With an Oral Microtracer and Pharmacokinetic Modeling to Optimize Dosing.

Crit Care Med 2019 12;47(12):e975-e983

Intensive Care and Department of Pediatric Surgery, Erasmus MC-Sophia Children's Hospital, Rotterdam, The Netherlands.

Objectives: Decreasing morbidity and mortality by rationalizing drug treatment in the critically ill is of paramount importance but challenging as the underlying clinical condition may lead to large variation in drug disposition and response. New microtracer methodology is now available to gain knowledge on drug disposition in the intensive care. On the basis of studies in healthy adults, physicians tend to assume that oral doses of acetaminophen will be completely absorbed and therefore prescribe the same dose per kilogram for oral and IV administration. As the oral bioavailability of acetaminophen in critically ill children is unknown, we designed a microtracer study to shed a light on this issue.

Design: An innovative microtracer study design with population pharmacokinetics.

Setting: A tertiary referral PICU.

Patients: Stable critically ill children, 0-6 years old, and already receiving IV acetaminophen.

Interventions: Concomitant administration of an oral C radiolabeled acetaminophen microtracer (3 ng/kg) with IV acetaminophen treatment (15 mg/kg every 6 hr).

Measurements: Blood was drawn from an indwelling arterial or central venous catheter up to 24 hours after C acetaminophen microtracer administration. Acetaminophen concentrations were measured by liquid chromatography-mass spectrometry and C concentrations by accelerated mass spectrometry.

Main Results: In 47 patients (median age of 6.1 mo; Q1-Q3, 1.8-20 mo) the mean enteral bioavailability was 72% (range, 11-91%). With a standard dose (15 mg/kg 4 times daily), therapeutic steady-state concentrations were 2.5 times more likely to be reached with IV than with oral administration.

Conclusions: Microtracer studies present a new opportunity to gain knowledge on drug disposition in the intensive care. Using this modality in children in the pediatric intensive care, we showed that enteral administration of acetaminophen results in less predictable exposure and higher likelihood of subtherapeutic blood concentration than does IV administration. IV dosing may be preferable to ensure adequate pain relief.
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http://dx.doi.org/10.1097/CCM.0000000000004032DOI Listing
December 2019

Assessment of Dermal Absorption of Aluminum from a Representative Antiperspirant Formulation Using a Al Microtracer Approach.

Clin Transl Sci 2018 11 27;11(6):573-581. Epub 2018 Jul 27.

TNO, Zeist, The Netherlands.

A clinical pharmacokinetic study was performed in 12 healthy women to evaluate systemic exposure to aluminum following topical application of a representative antiperspirant formulation under real-life use conditions. A simple roll-on formulation containing an extremely rare isotope of aluminum ( Al) chlorohydrate (ACH) was prepared to commercial specifications. A Al radio-microtracer was used to distinguish dosed aluminum from natural background, using accelerated mass spectroscopy. The Al citrate was administered intravenously (i.v.) to estimate fraction absorbed (F ) following topical delivery. In blood samples after i.v. administration, Al was readily detected (mean area under the curve (AUC) = 1,273 ± 466 hours×fg/mL). Conversely, all blood samples following topical application were below the lower limit of quantitation (LLOQ; 0.12 fg/mL), except two samples (0.13 and 0.14 fg/mL); a maximal AUC was based on LLOQs. The aluminum was above the LLOQ (61 ag/mL) in 31% of urine samples. From the urinary excretion data, a conservative estimated range for dermal F of 0.002-0.06% was calculated, with a mean estimate of 0.0094%.
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http://dx.doi.org/10.1111/cts.12579DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6226111PMC
November 2018

Successful Use of [C]Paracetamol Microdosing to Elucidate Developmental Changes in Drug Metabolism.

Clin Pharmacokinet 2017 Oct;56(10):1185-1195

Intensive Care and Department of Pediatric Surgery, Erasmus MC-Sophia Children's Hospital, Rotterdam, The Netherlands.

Background: We previously showed the practical and ethical feasibility of using [C]-microdosing for pharmacokinetic studies in children. We now aimed to show that this approach can be used to elucidate developmental changes in drug metabolism, more specifically, glucuronidation and sulfation, using [C]paracetamol (AAP).

Methods: Infants admitted to the intensive care unit received a single oral [C]AAP microdose while receiving intravenous therapeutic AAP every 6 h. [C]AAP pharmacokinetic parameters were estimated. [C]AAP and metabolites were measured with accelerator mass spectrometry. The plasma area under the concentration-time curve from time zero to infinity and urinary recovery ratios were related to age as surrogate markers of metabolism.

Results: Fifty children [median age 6 months (range 3 days-6.9 years)] received a microdose (3.3 [2.0-3.5] ng/kg; 64 [41-71] Bq/kg). Plasma [C]AAP apparent total clearance was 0.4 (0.1-2.6) L/h/kg, apparent volume of distribution was 1.7 (0.9-8.2) L/kg, and the half-life was 2.8 (1-7) h. With increasing age, plasma and urinary AAP-glu/AAP and AAP-glu/AAP-sul ratios significantly increased by four fold, while the AAP-sul/AAP ratio significantly decreased.

Conclusion: Using [C]labeled microdosing, the effect of age on orally administered AAP metabolism was successfully elucidated in both plasma and urine. With minimal burden and risk, microdosing is attractive to study developmental changes in drug disposition in children.
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http://dx.doi.org/10.1007/s40262-017-0508-6DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5591809PMC
October 2017

Proteomic Analysis of the Developmental Trajectory of Human Hepatic Membrane Transporter Proteins in the First Three Months of Life.

Drug Metab Dispos 2016 07 21;44(7):1005-13. Epub 2016 Apr 21.

Intensive Care and Department of Pediatric Surgery, Erasmus MC-Sophia Children's Hospital, Rotterdam, The Netherlands (M.G.M., J.D.W., B.D.G., D.T., S.N.W.); Department of Biostatistics, Erasmus MC, Rotterdam, The Netherlands (J.R.); Division of Pediatric Gastroenterology, Erasmus MC-Sophia Children's Hospital, Rotterdam, The Netherlands (B.A.E.K.); TNO, Zeist, The Netherlands (E.v.d.S., H.M.W., W.H.J.V.); and Department of Pharmacology and Toxicology, Radboud University, Nijmegen, The Netherlands (S.N.d.W.)

Human hepatic membrane-embedded transporter proteins are involved in trafficking endogenous and exogenous substrates. Even though impact of transporters on pharmacokinetics is recognized, little is known on maturation of transporter protein expression levels, especially during early life. We aimed to study the protein expression of 10 transporters in liver tissue from fetuses, infants, and adults. Transporter protein expression levels [ATP-binding cassette transporter (ABC)B1, ABCG2, ABCC2, ABCC3, bile salt efflux pump, glucose transporter 1, monocarboxylate transporter 1, organic anion transporter polypeptide (OATP)1B1, OATP2B1, and organic cation/carnitine transporter 2) were quantified using ultraperformance liquid chromatography tandem mass spectrometry in snap-frozen postmortem fetal, infant, and adult liver samples. Protein expression was quantified in isolated crude membrane fractions. The possible association between postnatal and postmenstrual age versus protein expression was studied. We studied 25 liver samples, as follows: 10 fetal [median gestational age 23.2 wk (range 16.4-37.9)], 12 infantile [gestational age at birth 35.1 wk (27.1-41.0), postnatal age 1 wk (0-11.4)], and 3 adult. The relationship of protein expression with age was explored by comparing age groups. Correlating age within the fetal/infant age group suggested four specific protein expression patterns, as follows: stable, low to high, high to low, and low-high-low. The impact of growth and development on human membrane transporter protein expression is transporter-dependent. The suggested age-related differences in transporter protein expression may aid our understanding of normal growth and development, and also may impact the disposition of substrate drugs in neonates and young infants.
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http://dx.doi.org/10.1124/dmd.115.068577DOI Listing
July 2016

The impact of early human data on clinical development: there is time to win.

Drug Discov Today 2016 06 29;21(6):873-9. Epub 2016 Mar 29.

TNO, PO Box 360, 3700AJ Zeist, The Netherlands.

Modern accelerator mass spectrometry (AMS) methods enable the routine application of this technology in drug development. By the administration of a (14)C-labelled microdose or microtrace, pharmacokinetic (PK) data, such as mass balance, metabolite profiling, and absolute bioavailability (AB) data, can be generated easier, faster, and at lower costs. Here, we emphasize the advances and impact of this technology for pharmaceutical companies. The availability of accurate intravenous (iv) PK and human absorption, distribution, metabolism, and excretion (ADME) information, even before or during Phase I trials, can improve the clinical development plan. Moreover, applying the microtrace approach during early clinical development might impact the number of clinical pharmacology and preclinical safety pharmacology studies required, and shorten the overall drug discovery program.
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http://dx.doi.org/10.1016/j.drudis.2016.03.012DOI Listing
June 2016

To Apply Microdosing or Not? Recommendations to Single Out Compounds with Non-Linear Pharmacokinetics.

Clin Pharmacokinet 2016 Jan;55(1):1-15

TNO, Utrechtseweg 48, 3704 HE, Zeist, The Netherlands.

Microdosing studies allow clinical investigation of pharmacokinetics earlier in drug development, before all high-dose safety concerns have been sorted out. Furthermore, microdosing allows inclusion of target groups that are inadmissible in high-dose phase I trials. A potential concern when considering a microdosing study is that a particular drug candidate may display non-linear pharmacokinetics. Saturation of, for example, membrane transport or metabolism at exposure levels between the microdose and therapeutic dose may limit the predictivity of high-dose pharmacokinetics from microdose observations. Guidance on the likelihood of appreciable non-linear pharmacokinetics based on preclinical information can be helpful in staging the clinical phase and the place of microdosing in it. We present a decision tree that evaluates concerns about non-linearities raised in the preclinical phase and their potential impact on the proportionality between microdose and intended therapeutic dose as predicted from preclinical information. The expected maximum concentrations at relevant sites are estimated by non-compartmental methods. These are compared with dissolution, Michaelis constants for active or enzymatic processes, and binding protein concentrations to assess the potential saturation of the processes below therapeutic doses. The decision tree was applied to ten published cases comparing microdose and therapeutic dose pharmacokinetics, for which concerns about non-linear pharmacokinetics were raised a priori. The decision tree was able to discriminate cases showing substantial non-linearities from cases displaying dose-proportional pharmacokinetics. The recommendations described in this paper may be useful in deciding whether a microdosing study is a sensible option to gain early insight in clinical pharmacokinetics of drug candidates.
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http://dx.doi.org/10.1007/s40262-015-0308-9DOI Listing
January 2016

Human systemic exposure to [¹⁴C]-paraphenylenediamine-containing oxidative hair dyes: Absorption, kinetics, metabolism, excretion and safety assessment.

Food Chem Toxicol 2015 Jul 3;81:71-80. Epub 2015 Apr 3.

L'Oréal Research and Innovation, Worldwide Safety Evaluation, Asnières sur Seine, France.

Systemic exposure was measured in humans after hair dyeing with oxidative hair dyes containing 2.0% (A) or 1.0% (B) [(14)C]-p-phenylenediamine (PPD). Hair was dyed, rinsed, dried, clipped and shaved; blood and urine samples were collected for 48 hours after application. [(14)C] was measured in all materials, rinsing water, hair, plasma, urine and skin strips. Plasma and urine were also analysed by HLPC/MS/MS for PPD and its metabolites (B). Total mean recovery of radioactivity was 94.30% (A) or 96.21% (B). Mean plasma Cmax values were 132.6 or 97.4 ng [(14)C]-PPDeq/mL, mean AUC(0-∞) values 1415 or 966 ng [(14)C]-PPDeq/mL*hr in studies A or B, respectively. Urinary excretion of [(14)C] mainly occurred within 24 hrs after hair colouring with a total excretion of 0.72 or 0.88% of applied radioactivity in studies A or B, respectively. Only N,N'-diacetylated-PPD was detected in plasma and the urine. A TK-based human safety assessment estimated margins of safety of 23.3- or 65-fold relative to respective plasma AUC or Cmax values in rats at the NOAEL of a toxicity study. Overall, hair dyes containing PPD are unlikely to pose a health risk since they are used intermittently and systemic exposure is limited to the detoxified metabolite N,N'-diacetyl-PPD.
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http://dx.doi.org/10.1016/j.fct.2015.04.003DOI Listing
July 2015

Observational infant exploratory [(14)C]-paracetamol pharmacokinetic microdose/therapeutic dose study with accelerator mass spectrometry bioanalysis.

Br J Clin Pharmacol 2015 Jul 1;80(1):157-67. Epub 2015 Jun 1.

Department of Women's and Children's Health, Institute of Translational Medicine, University of Liverpool, University of Liverpool, Liverpool, L69 3BX, United Kingdom.

Aims: The aims of the study were to compare [(14)C]-paracetamol ([(14)C]-PARA) paediatric pharmacokinetics (PK) after administration mixed in a therapeutic dose or an isolated microdose and to develop further and validate accelerator mass spectrometry (AMS) bioanalysis in the 0-2 year old age group.

Methods: [(14)C]-PARA concentrations in 10-15 µl plasma samples were measured after enteral or i.v. administration of a single [(14)C]-PARA microdose or mixed in with therapeutic dose in infants receiving PARA as part of their therapeutic regimen.

Results: Thirty-four infants were included in the PARA PK analysis for this study: oral microdose (n = 4), i.v. microdose (n = 6), oral therapeutic (n = 6) and i.v. therapeutic (n = 18). The respective mean clearance (CL) values (SDs in parentheses) for these dosed groups were 1.46 (1.00) l h(-1), 1.76 (1.07) l h(-1), 2.93 (2.08) l h(-1) and 2.72 (3.10) l h(-1), t(1/2) values 2.65 h, 2.55 h, 8.36 h and 7.16 h and dose normalized AUC(0-t) (mg l(-1) h) values were 0.90 (0.43), 0.84 (0.57), 0.7 (0.79) and 0.54 (0.26).

Conclusions: All necessary ethical, scientific, clinical and regulatory procedures were put in place to conduct PK studies using enteral and systemic microdosing in two European centres. The pharmacokinetics of a therapeutic dose (mg kg(-1)) and a microdose (ng kg(-1)) in babies between 35 to 127 weeks post-menstrual age. [(14)C]-PARA pharmacokinetic parameters were within a two-fold range after a therapeutic dose or a microdose. Exploratory studies using doses significantly less than therapeutic doses may offer ethical and safety advantages with increased bionalytical sensitivity in selected exploratory paediatric pharmacokinetic studies.
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http://dx.doi.org/10.1111/bcp.12597DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4500335PMC
July 2015

Pediatric microdose study of [(14)C]paracetamol to study drug metabolism using accelerated mass spectrometry: proof of concept.

Clin Pharmacokinet 2014 Nov;53(11):1045-51

Intensive Care and Department of Pediatric Surgery, Erasmus MC-Sophia Children's Hospital, Room Sp-3458, Wytemaweg 80, P.O. Box 2060, 3000 CB, Rotterdam, The Netherlands.

Background: Pediatric drug development is hampered by practical, ethical, and scientific challenges. Microdosing is a promising new method to obtain pharmacokinetic data in children with minimal burden and minimal risk. The use of a labeled oral microdose offers the added benefit to study intestinal and hepatic drug disposition in children already receiving an intravenous therapeutic drug dose for clinical reasons.

Objective: The objective of this study was to present pilot data of an oral [(14)C]paracetamol [acetaminophen (AAP)] microdosing study as proof of concept to study developmental pharmacokinetics in children.

Methods: In an open-label microdose pharmacokinetic pilot study, infants (0-6 years of age) received a single oral [(14)C]AAP microdose (3.3 ng/kg, 60 Bq/kg) in addition to intravenous therapeutic doses of AAP (15 mg/kg intravenous every 6 h). Blood samples were taken from an indwelling catheter. AAP blood concentrations were measured by liquid chromatography-tandem mass spectrometry (LC-MS/MS) and [(14)C]AAP and metabolites ([(14)C]AAP-Glu and [(14)C]AAP-4Sul) were measured by accelerator mass spectrometry.

Results: Ten infants (aged 0.1-83.1 months) were included; one was excluded as he vomited shortly after administration. In nine patients, [(14)C]AAP and metabolites in blood samples were detectable at expected concentrations: median (range) maximum concentration (C max) [(14)C]AAP 1.68 (0.75-4.76) ng/L, [(14)C]AAP-Glu 0.88 (0.34-1.55) ng/L, and [(14)C]AAP-4Sul 0.81 (0.29-2.10) ng/L. Dose-normalized oral [(14)C]AAP C max approached median intravenous average concentrations (C av): 8.41 mg/L (3.75-23.78 mg/L) and 8.87 mg/L (3.45-12.9 mg/L), respectively.

Conclusions: We demonstrate the feasibility of using a [(14)C]labeled microdose to study AAP pharmacokinetics, including metabolite disposition, in young children.
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http://dx.doi.org/10.1007/s40262-014-0176-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4213380PMC
November 2014

Dietary medium chain fatty acid supplementation leads to reduced VLDL lipolysis and uptake rates in comparison to linoleic acid supplementation.

PLoS One 2014 21;9(7):e100376. Epub 2014 Jul 21.

TNO, Zeist, the Netherlands.

Dietary medium chain fatty acids (MCFA) and linoleic acid follow different metabolic routes, and linoleic acid activates PPAR receptors. Both these mechanisms may modify lipoprotein and fatty acid metabolism after dietary intervention. Our objective was to investigate how dietary MCFA and linoleic acid supplementation and body fat distribution affect the fasting lipoprotein subclass profile, lipoprotein kinetics, and postprandial fatty acid kinetics. In a randomized double blind cross-over trial, 12 male subjects (age 51±7 years; BMI 28.5±0.8 kg/m2), were divided into 2 groups according to waist-hip ratio. They were supplemented with 60 grams/day MCFA (mainly C8:0, C10:0) or linoleic acid for three weeks, with a wash-out period of six weeks in between. Lipoprotein subclasses were measured using HPLC. Lipoprotein and fatty acid metabolism were studied using a combination of several stable isotope tracers. Lipoprotein and tracer data were analyzed using computational modeling. Lipoprotein subclass concentrations in the VLDL and LDL range were significantly higher after MCFA than after linoleic acid intervention. In addition, LDL subclass concentrations were higher in lower body obese individuals. Differences in VLDL metabolism were found to occur in lipoprotein lipolysis and uptake, not production; MCFAs were elongated intensively, in contrast to linoleic acid. Dietary MCFA supplementation led to a less favorable lipoprotein profile than linoleic acid supplementation. These differences were not due to elevated VLDL production, but rather to lower lipolysis and uptake rates.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0100376PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4105472PMC
April 2015

Automated combustion accelerator mass spectrometry for the analysis of biomedical samples in the low attomole range.

Anal Chem 2014 Aug 25;86(15):7635-41. Epub 2014 Jul 25.

TNO , P.O. Box 360, 3700AJ Zeist, The Netherlands.

The increasing role of accelerator mass spectrometry (AMS) in biomedical research necessitates modernization of the traditional sample handling process. AMS was originally developed and used for carbon dating, therefore focusing on a very high precision but with a comparably low sample throughput. Here, we describe the combination of automated sample combustion with an elemental analyzer (EA) online coupled to an AMS via a dedicated interface. This setup allows direct radiocarbon measurements for over 70 samples daily by AMS. No sample processing is required apart from the pipetting of the sample into a tin foil cup, which is placed in the carousel of the EA. In our system, up to 200 AMS analyses are performed automatically without the need for manual interventions. We present results on the direct total (14)C count measurements in <2 μL human plasma samples. The method shows linearity over a range of 0.65-821 mBq/mL, with a lower limit of quantification of 0.65 mBq/mL (corresponding to 0.67 amol for acetaminophen). At these extremely low levels of activity, it becomes important to quantify plasma specific carbon percentages. This carbon percentage is automatically generated upon combustion of a sample on the EA. Apparent advantages of the present approach include complete omission of sample preparation (reduced hands-on time) and fully automated sample analysis. These improvements clearly stimulate the standard incorporation of microtracer research in the drug development process. In combination with the particularly low sample volumes required and extreme sensitivity, AMS strongly improves its position as a bioanalysis method.
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http://dx.doi.org/10.1021/ac5015035DOI Listing
August 2014

Effect of red wine consumption on biomarkers of oxidative stress.

Alcohol Alcohol 2013 Mar-Apr;48(2):153-9. Epub 2012 Aug 2.

TNO, Utrechtseweg 48, 3704 HE Zeist, The Netherlands.

Aims: To evaluate the effect of acute and chronic consumption of red wine or de-alcoholized red wine with a similar antioxidant capacity on plasma total antioxidant capacity (TEAC), nuclear factor-κB (NF-κB) activity and F2-isoprostanes (8-iso-PGF(2α)) in healthy men.

Methods: Nineteen healthy men with an increased waist circumference (≥94 cm) and a body mass index above 25 kg/m(2) participated in a randomized, controlled crossover design trial. They daily consumed 450 ml of red wine (four drinks; 41.4 g alcohol) or 450 ml of de-alcoholized red wine during dinner for 4 weeks each. On the last day of each treatment period, blood was collected before and 1 h after a standardized dinner with red wine or de-alcoholized red wine and also 24-h urine was collected.

Results: Absolute TEAC levels were higher 1 h after dinner with red wine compared with dinner with de-alcoholized red wine (1.3 versus 1.1 mmol Trolox equivalents/l; P = 0.03). Consumption of dinner together with de-alcoholized red wine acutely stimulated NF-κB activity in peripheral blood mononuclear cells (0.4-0.7 HeLa equivalents/2.5 μg protein; P = 0.006), whereas this increase was completely suppressed when the dinner was combined with red wine. A chronic increase in urinary 8-iso-PGF(2α) after 4 weeks of red wine consumption compared with de-alcoholized red wine consumption (157 pg/mg creatinine and 141 pg/mg creatinine, respectively, P = 0.006) was also observed.

Conclusions: Consumption of a moderate dose of red wine can acutely increase plasma TEAC and suppress NF-κB activation induced by a meal. Controversially, 4 weeks of red wine consumption compared with de-alcoholized red wine consumption increases the oxidative lipid damage marker 8-iso-PGF(2α).
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http://dx.doi.org/10.1093/alcalc/ags086DOI Listing
October 2013

Predicting blood:air partition coefficients using basic physicochemical properties.

Regul Toxicol Pharmacol 2012 Feb 9;62(1):23-8. Epub 2011 Dec 9.

TNO Innovation for Life, Research Group Quality & Safety, The Netherlands.

Quantitative Property Property Relationships (QPPRs) for human and rat blood:air partition coefficients (PBAs) have been derived, based on vapour pressure (Log(VP)), the octanol:water partition coefficient (Log(K(OW))) and molecular weight (MW), using partial least squares multilinear modelling. These parameters are all included in the standard data to be submitted under REACH. The chemical dataset consisted of volatile organic chemicals, principally aliphatic hydrocarbons, benzene derivatives with one aromatic ring, and ethers, with and without halogen atoms. Other chemicals represented were cyclic hydrocarbons and carbonic acid esters. Separate rat and human models were derived, as well as mixed ones. Log(VP) and Log(K(OW)) contributed most to the prediction of Log(PBA) in the three-parameter model, while the contribution of MW was relatively small. Still, the three-parameter model differed significantly from the two-parameter model and performed better. Its performance was comparable to that of models published in public literature, which are based on more complex molecular parameters or on measured olive:oil air and saline/water:air partition coefficients. Since, based on the available data for humans, rats, mice, dogs and rabbits, existence of interspecies differences of PBAs cannot be clearly excluded, the use of separate models for each species is advisable. Concluding, the three-parameter human model Log(PBA)=6.96-1.04 Log(VP)-0.533 Log(K(OW))-0.00495MW and the three-parameter rat model 6.16-0.888 Log(VP)-0.521 Log(K(OW))-0.00201MW provide robust and reliable models for predicting PBA values of volatile organic chemicals using commonly available chemical properties of molecules.
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http://dx.doi.org/10.1016/j.yrtph.2011.11.019DOI Listing
February 2012

Potency of isothiocyanates to induce luciferase reporter gene expression via the electrophile-responsive element from murine glutathione S-transferase Ya.

Toxicol In Vitro 2009 Jun 20;23(4):617-21. Epub 2009 Feb 20.

Nutrients and Biomarkers Department, TNO Quality of Life, 3700 AJ Zeist, The Netherlands.

Isothiocyanates are electrophiles that are able to induce phase II biotransformation enzyme gene expression via an electrophile-responsive element (EpRE) in the gene regulatory region. To study the potency of different isothiocyanates to induce the expression of EpRE-regulated genes, a Hepa-1c1c7 luciferase reporter cell line was exposed to structurally different isothiocyanates. The reporter cell line, EpRE(mGST-Ya)-LUX, contains the EpRE from the regulatory region of the mouse glutathione S-transferase Ya gene. Isothiocyanates containing a methyl-sulfur side chain, e.g. sulforaphane, showed a lower EC(50) (0.8-3.2 microM) and a comparable induction factor (17-22.4) compared to the structurally different isothiocyanates containing an alkyl or aromatic side chain, e.g. allyl and phenylethyl isothiocyanate (EC(50) 3.9-6.5 microM, induction factor 17.5-23). After 24h of exposure, on average (+/-SD) 23+/-5% of the isothiocyanate was found in the cells and 77% in the cell medium. Isothiocyanates prove to be strong inducers of electrophile-responsive element-mediated gene expression at physiological concentrations. The here described luciferase reporter cell line is a suitable assay to measure the potency of compounds to induce EpRE-regulated gene expression.
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http://dx.doi.org/10.1016/j.tiv.2009.02.005DOI Listing
June 2009

Bioavailability and kinetics of sulforaphane in humans after consumption of cooked versus raw broccoli.

J Agric Food Chem 2008 Nov;56(22):10505-9

TNO Quality of Life, AJ Zeist, The Netherlands.

The aim of this study was to determine the bioavailability and kinetics of the supposed anticarcinogen sulforaphane, the hydrolysis product of glucoraphanin, from raw and cooked broccoli. Eight men consumed 200 g of crushed broccoli, raw or cooked, with a warm meal in a randomized, free-living, open cross-over trial. Higher amounts of sulforaphane were found in the blood and urine when broccoli was eaten raw (bioavailability of 37%) versus cooked (3.4%, p ) 0.002). Absorption of sulforaphane was delayed when cooked broccoli was consumed (peak plasma time ) 6 h) versus raw broccoli (1.6 h, p ) 0.001). Excretion half-lives were comparable, 2.6 and 2.4 h on average, for raw and cooked broccoli, respectively (p ) 0.5). This study gives complete kinetic data and shows that consumption of raw broccoli results in faster absorption, higher bioavailability, and higher peak plasma amounts of sulforaphane, compared to cooked broccoli.
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http://dx.doi.org/10.1021/jf801989eDOI Listing
November 2008

Red blood cell folate vitamer distribution in healthy subjects is determined by the methylenetetrahydrofolate reductase C677T polymorphism and by the total folate status.

J Nutr Biochem 2007 Oct 5;18(10):693-9. Epub 2007 Apr 5.

Department of Internal Medicine and Institute for Cardiovascular Research ICaR-VU, VU University Medical Center, Amsterdam 1007 MB, The Netherlands.

Background: Red blood cells (RBCs) represent a storage pool for folate. In contrast to plasma, RBC folate can appear in different biochemical isoforms. So far, only the methylenetetrahydrofolate reductase (MTHFR) 677 TT genotype has been identified as a determinant of RBC folate vitamer distribution.

Objective: The purpose of this study is to identify clinical and biochemical determinants of RBC folate vitamer distribution in healthy subjects.

Design: In an observational study, 109 subjects, aged 18 to 65 years, were studied. Red blood cell folate vitamers were analyzed using a liquid chromatography-tandem mass spectrometry method. Other variables recorded included vitamin B(2), B(6) and B(12) status, homocysteine, plasma and RBC S-adenosylhomocysteine and S-adenosylmethionine, renal function and the MTHFR C677T polymorphism.

Results: The MTHFR C677T genotype was the dominant determinant of nonmethylfolate accumulation. The median (range) nonmethylfolate/total folate ratio was 0.58% (0-12.2%) in the MTHFR CC group (n=55), 0.99% (0-14.3%) in the CT group (n=39) and 30.3% (5.7-73.3%) in the TT genotype group (n=15), P<.001. The 95th percentile for the nonmethylfolate/total folate ratio was 2.8% for the CC group, 9.1% for the CT group and 73.3% for the TT group. In the CC and CT genotype subjects, the T-allele and total folate status were positively and independently correlated with nonmethylfolate accumulation, but the degree of nonmethylfolate accumulation in these subjects was usually minor compared with those with the TT genotype. None of the other studied variables was associated with nonmethylfolate accumulation.

Conclusions: The MTHFR C677T genotype is the dominant determinant of nonmethylfolate accumulation in RBCs. In addition, high total folate status may contribute to minor to moderate nonmethylfolate accumulation in MTHFR CC and CT subjects.
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http://dx.doi.org/10.1016/j.jnutbio.2006.11.010DOI Listing
October 2007

Decreased coenzyme Q10 concentration in plasma of children with cystic fibrosis.

J Pediatr Gastroenterol Nutr 2006 Nov;43(5):646-50

Department of Pediatric Gastroenterology, Wilhelmina Children's Hospital, UMC Utrecht, The Netherlands.

Objectives: Coenzyme Q10 (CoQ10) is an effective lipophilic antioxidant and protects against lipid peroxidation by scavenging radicals. Patients with cystic fibrosis generally have fat malabsorption; thus, we hypothesized that overall plasma CoQ10 concentration in pediatric patients with cystic fibrosis might be diminished. Because these patients have increased oxidative stress due to chronic pulmonary inflammation, we also assumed that the oxidized form of CoQ10 might be relatively increased.

Patients And Methods: The total plasma CoQ10 levels and the oxidized and reduced form were measured by high-performance liquid chromatography in 30 children with cystic fibrosis (mean FEV1 % predicted = 88.5% +/- 18.7%) and 30 age-matched controls.

Results: Total plasma CoQ10 levels were significantly lower in the cystic fibrosis group as compared with the control group (0.87 +/- 0.42 micromol/L and 1.35 +/- 0.39 micromol/L, respectively; P < 0.001). When correcting for the lower serum cholesterol level in patients with cystic fibrosis, this difference remained significant: the CoQ10/cholesterol ratio (micromol/mol) was 268.8 +/- 136.7 and 334.0 +/- 102.9 in patients and controls, respectively (P < 0.05). However, the CoQ10 redox status was identical in patients and controls (86.4% +/- 7.1% and 85.4% +/- 7.3%, respectively).

Conclusions: We found that the overall plasma CoQ10 concentration is lower in patients with cystic fibrosis, probably because of fat malabsorption. The CoQ10 redox status was not disturbed, indicating that CoQ10 could still be adequately regenerated in this group of patients with cystic fibrosis with mild-to-moderate pulmonary disease.
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http://dx.doi.org/10.1097/01.mpg.0000233193.77521.66DOI Listing
November 2006

Association between consumption of cruciferous vegetables and condiments and excretion in urine of isothiocyanate mercapturic acids.

J Agric Food Chem 2006 Jul;54(15):5350-8

Business Unit Analytical Research, TNO Quality of Life, P.O. Box 360, 3700 AJ Zeist, The Netherlands.

A high intake of cruciferous vegetables is associated with a reduced risk of cancer and cardiovascular diseases. This protective effect has been linked to isothiocyanates, enzymatic hydrolysis products of glucosinolates. In this study, the metabolic fate of glucosinolates and isothiocyanates after ingestion of 19 different cruciferous vegetables was studied in three male subjects. After the consumption of 13 cruciferous vegetables (glucosinolate content, 0.01-0.94 mmol/kg) and six condiments (isothiocyanate content, 0.06-49.3 mmol/kg), eight different isothiocyanate mercapturic acids were determined in urine samples. Excretion levels after the consumption of raw vegetables and condiments were higher (bioavailability, 8.2-113%) as compared to cooked vegetables (bioavailability, 1.8-43%), but the excretion rate was similar (t1/2=2.1-3.9 h). Isothiocyanates in urine remain longer at a nonzero level after the consumption of glucosinolates from cooked vegetables, as compared to raw vegetables and condiments, and maximal levels in urine were reached about 4 h later. Isothiocyanate mercapturic acids can be used as a biomarker to reflect the active dose of isothiocyanates absorbed.
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http://dx.doi.org/10.1021/jf060723nDOI Listing
July 2006

Evaluation of Simple Treat 3.0 for two hydrophobic and slowly biodegradable chemicals: polycyclic musks HHCB and AHTN.

Water Res 2003 Nov;37(18):4377-84

Institute for Risk Assessment Sciences, Toxicology Division, University of Utrecht, Yalelaan 2, P.O. Box 80.176, 3508 TD, Utrecht, The Netherlands.

In the current study, predictions by Simple Treat 3.0, a fate model for organic chemicals in sewage treatment plants (STPs), are compared with actual measurements in three STPs. Two polycyclic musks, Tonalide (AHTN) and Galaxolide (HHCB), were used for model evaluation. Results show that Simple Treat 3.0 is able to predict the removal efficiency within a factor 4. Predicted concentrations of both chemicals within the different physical compartments of STPs show a high correlation (r(2)=0.80) with experimental values. Although predicted free concentration levels were similar to previously reported experimental data, the trends along the compartments showed an inverse relationship. This bias of the model can be caused by an underestimation of BOD-removal (solids), or an overestimation of bacterial growth, evaporation, or a combination of these three factors. Results show that Simple Treat 3.0 is a valid tool for the risk assessment of slowly biodegradable chemicals, but still some adjustments of the model could be incorporated from a scientific point of view.
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http://dx.doi.org/10.1016/S0043-1354(03)00434-2DOI Listing
November 2003

Removal of two polycyclic musks in sewage treatment plants: freely dissolved and total concentrations.

Environ Sci Technol 2003 Jul;37(14):3111-6

Institute for Risk Assessment Sciences, Toxicology Division, Utrecht University, P.O. Box 80.176, NL-3508 TD Utrecht, The Netherlands.

In the current study, the removal of slowly degradable hydrophobic chemicals in sewage treatment plants (STPs) has been evaluated with emphasis on the combination of free and total concentration data. Free and total concentrations of two polycyclic musks were determined in each compartment of four STPs. The free concentration of the polycyclic musks remains virtually constant throughout all the compartments of the STPs with values between 0.21 and 0.57 microg/L for AHTN and between 0.79 and 2.0 microg/L for HHCB. Total concentrations of these fragrances are highly dependent on the volatile solids in a given compartment resulting in much more variation with values between 0.42 and 92 microg/L for AHTN and between 1.25 and 258 microg/L for HHCB. It is concluded that free concentrations of these hydrophobic chemicals in the compartments of STPs are mostly biodegradation mediated, while total concentrations are mediated by the concentration of solids. The combination of measurements of free and total concentrations can improve estimations regarding removal efficiency and removal pathways.
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http://dx.doi.org/10.1021/es020226xDOI Listing
July 2003

Analysis of isothiocyanate mercapturic acids in urine: a biomarker for cruciferous vegetable intake.

J Agric Food Chem 2003 Jun;51(12):3554-9

Department of Food & Food Supplement Analysis, TNO Nutrition and Food Research, P.O. Box 360, 3700 AJ Zeist, The Netherlands.

Cruciferous vegetables contain glucosinolates, which are degraded to isothiocyanates. These are easily absorbed, conjugated to glutathione, and excreted into the urine as their corresponding mercapturic acids. We have developed and validated a solid phase extraction-high-performance liquid chromatography-electrospray ionization mass spectrometry/mass spectrometry method for the specific analysis of individual isothiocyanate mercapturic acids in urine. The range of reliable analysis was 1.0-310 microM in urine. Urine samples fortified with three different levels of isothiocyanate mercapturic acids were measured on six different days by three independent technicians. The relative standard deviation (RSD) of repeatability was 12, 6, and 3%; the RSD of reproducibility was 19, 14, and 8%, and spike recoveries were 103, 104, and 103%, respectively, for 1.04, 10.5, and 313 microM levels. In 24 h urine collected from two volunteers after they consumed broccoli and cauliflower, clearly sulforaphane mercapturic acid (133 micromol) and allyl isothiocyanate mercapturic acid (4.7 micromol) were found. This procedure demonstrates a reliable and efficient method to study the intake and mode of action of isothiocyanates in animal studies and clinical trials.
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http://dx.doi.org/10.1021/jf0341316DOI Listing
June 2003

Bioconcentration and acute toxicity of polycyclic musks in two benthic organisms (Chironomus riparius and Lumbriculus variegatus).

Environ Toxicol Chem 2003 May;22(5):1086-92

Institute for Risk Assessment Sciences, IRAS, Toxicology Division, Utrecht University, P.O. Box 80.176, NL-3508 TD Utrecht, The Netherlands.

In the current study, the bioconcentration behavior and acute toxicity of two polycyclic musks, Tonalide 7-acetyl-1,1,3,4,4,6-hexamethyl-1,2,3,4-tetrahydronaphthalene (AHTN) and Galaxolide 1,3,4,6,7,8-hexahydro-4,6,6,7,8,8-hexa-methylcyclopenta[gamma]-2-benzopyran (HHCB), were studied in two benthic organisms. Polycyclic musks are frequently used fragrances, and they have been detected in different compartments of the environment. The aim of this study was to fill some empirical data gaps for AHTN and HHCB for benthic organisms. Results show that differences exist between both organisms. Chironomus riparius exhibited bioconcentration factors (BCFs) for AHTN and HHCB substantially lower than predicted for nontransformed organics. The BCFs for both chemicals increased after coexposure of the organism to the cytochrome P450 inhibitor piperonyl butoxide. Thus, the low BCF values were the result of rapid biotransformation of AHTN and HHCB in the midge larvae. Bioconcentration kinetics indicated that both chemicals induced their own cytochrome P450-mediated metabolism. Acute toxicity of AHTN to midge larvae was reduced compared to predicted baseline toxicity and was similar for HHCB. Bioconcentration of AHTN and HHCB in the worm (Lumbriculus variegatus) is in agreement with predictions based on the octanol-water partition coefficients of these chemicals. Acute toxicity was found to be similar to predicted values for baseline toxicity. Summarizing, for AHTN and HHCB, acute toxicity and bioconcentration behavior in L. variegatus was in accordance with predicted data for nontransformed organics. In C. riparius, bioconcentration as well as toxicity were reduced.
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May 2003

Sorption kinetics and microbial biodegradation activity of hydrophobic chemicals in sewage sludge: model and measurements based on free concentrations.

Environ Sci Technol 2003 Jan;37(1):116-22

Institute for Risk Assessment Sciences, Toxicology Division, Utrecht University, P.O. Box 80.176, NL-3508 TD Utrecht, The Netherlands.

In the current study, a new method is introduced with which the rate-limiting factor of biodegradation processes of hydrophobic chemicals in organic and aqueous systems can be determined. The novelty of this approach lies in the combination of a free concentration-based kinetic model with measurements of both free and total concentrations in time. This model includes microbial biodegradation activity of the chemical in the aqueous phase and chemical sorption kinetics with respect to organic carbon and aqueous phases. The time dependency of free and total concentrations of 7-acetyl-1,1,3,4,4,6-hexamethyltetrahydronaphthalene and 7-acetyl-1,1,3,4,4,6-hexahydro-4,6,6,7,8,8-hexamethylcyclopenta(g)-2-benzopyrane in activated sludge was experimentally determined in vitro. Evaporation losses from the test system were also determined. Least-squares regression to optimize the model parameters resulted in a model that is in accordance with the experimental data. Additionally, the model shows that a comparison between the decrease of free and total chemical concentrations in time, in combination with an independent measurement of the organic carbon/water partition coefficient provides information aboutthe rate-limiting step of the degradation process. This information can be used by sewage treatment plant managers to decide whether the microbial biodegradation activity itself or the desorption from organic carbon to the aqueous phase should be improved.
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http://dx.doi.org/10.1021/es020115yDOI Listing
January 2003

Negligible depletion solid-phase microextraction with radiolabeled analytes to study free concentrations and protein binding: an example with [3H]estradiol.

Anal Chem 2002 Dec;74(23):5993-7

Institute for Risk Assessment Sciences (IRAS), Toxicology Division, Utrecht University, P.O. Box 80176, NL-3508 TD Utrecht, The Netherlands.

A new method is presented that enables sensitive measurement of free concentrations of radiolabeled ligands. Additionally, protein binding of radiochemicals in complex matrixes can be determined with this new technique that combines negligible depletion solid-phase microextraction (nd-SPME) with liquid scintillation counting (LSC) as detection. [3H]Estradiol was taken as an example compound. Possible matrix effects of protein on fiber uptake kinetics were studied. No matrix effect was found, either by fouling of the fiber, or by changed uptake kinetics. The validity of the method was shown in the determination of the affinity constant (Ka) of estradiol for human serum albumin (HSA). The Ka was estimated at 8.9 x 10(4) M(-1), which corresponds well with literature values. This study shows that nd-SPME is suitable to study the free concentration and protein binding of [3H]estradiol. The method described in this paper combines the advantages of nd-SPME with the advantages of radiolabeled analytes, creating a timesaving, simple, and sensitive analytical tool that will be particularly useful in complex matrixes containing many potential interferences for chromatographic methods.
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http://dx.doi.org/10.1021/ac0204552DOI Listing
December 2002

Determination of liposome/water partition coefficients of organic acids and bases by solid-phase microextraction.

Analyst 2002 Jan;127(1):42-8

Swiss Federal Institute for Environmental Science and Technology (EAWAG), Dübendorf.

The extraction of two methylated anilines and three chlorinated phenols by solid-phase microextraction (SPME) fibers coated with polyacrylate was investigated as a function of pH. Only the neutral species of the acids and bases partitioned into the polymer. Extraction kinetics were accelerated for the hydrophobic phenols at pH values around their acidity constant. This is presumably due to a reconstitution of the neutral species in the unstirred aqueous layer adjacent to the polymer surface by the charged species through the fast acid-base equilibrium. Although the charged species is not taken up into the polymer, liposome/water distribution ratios could be measured up to a pH value, where 99% of the compounds were present as charged species. The partition coefficients of the neutral and charged species were extrapolated from the pH profiles of the liposome/water distribution ratios. The resulting values were slightly lower than those measured with equilibrium dialysis. The discrepancies are discussed with respect to differences in the experimental conditions and the possibility of matrix effects during SPME measurements.
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http://dx.doi.org/10.1039/b109355jDOI Listing
January 2002
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