Assessing individual metabolic responsiveness to a lipid challenge using a targeted metabolomic approach

The development of assessment techniques with immediate clinical applicability is a priority for resolving the growing epidemic in metabolic disease. Many imbalances in diet-dependent metabolism are not detectable in the fasted state. Resolving the high inter-individual variability in response to diet requires the development of techniques that can detect metabolic dysfunction at the level of the individual. The intra- and inter-individual variation in lipid metabolism in response to a standardized test meal was determined. Following an overnight fast on three different days, three healthy subjects consumed a test meal containing 40% of their daily calories. Plasma samples were collected at fasting, and 1, 3, 6, and 8 h after the test meal. Plasma fatty acid (FA) concentrations within separated lipid classes and lipoprotein fractions were measured at each time point. The intra-individual variation within each subject across three days was lower than the inter-individual differences among the three subjects for over 50% of metabolites in the triacylglycerol (TG), FA, and phosphatidylcholine (PC) lipid classes at 6 h, and for 25–50% of metabolites across lipid classes at 0, 1, 3, and 8 h. The consistency of response within individuals was visualized by principal component analysis (PCA) and confirmed by ANOVA. Three representative metabolites that discriminated among the three individuals in the apolipoprotein B (ApoB) fraction, TG16:1n7, TG18:2n6, and PC18:3n3, are discussed in detail. The postprandial responses of individuals were unique within metabolites that were individual discriminators (ID) of metabolic phenotype. This study shows that the targeted metabolomic measurement of individual metabolic phenotype in response to a specially formulated lipid challenge is possible even without lead-in periods, dietary and lifestyle control, or intervention over a 3-month period in healthy free-living individuals.     

Improved quality of 1H NMR spectroscopic data for enhanced metabolic profiling of low molecular weight metabolites in human serum

NMR based metabolic profiling of blood samples in epidemiological studies can be used for molecular phenotyping and biomarker discovery. Often metabolic changes in blood are more subtle and demand a high quality spectrum especially when looking at low molecular weight compounds. In order to improve ¹H NMR spectroscopic data we compared different serum sample preparation methods. Application of phosphate buffer reduces chemical shift variation, enhances resolution of signal multiplicity, facilitates visual inspection of NMR spectra and annotation of signals compared to traditionally used saline. For analysis of low molecular weight compounds we found that standard 1D spectra of ultrafiltrated serum samples show enhanced spectral quality of small metabolites as compared to transverse relaxation edited spectra (also called Carr–Purcell–Meiboom–Gill, CPMG) spectra of unfiltered serum samples due to improved signal-to-noise ratio. Thus, NMR signals attributable to different amino acids and other small metabolites could readily be detected in spectra of ultrafiltrated serum, but remained invisible in the corresponding CPMG spectra. An OPLS model of fasting blood glucose showed an increase of Q² when using spectra from ultrafiltrated serum (Q² = 0.261) compared to using CPMG spectra (Q² = 0.173). Similar results were observed for OPLS models of BMI (Q² = 0.253 and Q² = 0.216, respectively). Furthermore, a reduction in model dimensionality was observed when using ultrafiltrated serum data. In conclusion we recommend sample preparation of serum samples in phosphate buffer instead of saline. Ultrafiltration of serum samples prior to NMR analysis is beneficial especially for low concentrated small metabolites.     

Plasma zinc response to a breakfast meal or fasting in elderly women

The aim of this study was to determine whether the postprandial decline in plasma zinc concentration is altered by aging. Eleven women, between the ages of 65 and 82 yr, participated in two separate experimental protocols: a high carbohydrate breakfast trial and a fasting trial. Plasma zinc concentrations were measured from blood samples obtained at 8∶00am (baseline fasting) and at 30-min intervals until 1∶00pm during each trial. Following the breakfast meal, plasma zinc concentrations declined 14% from 75±1 to 65±2 μg/dL (p<0.05), reaching a nadir 2.7±0.2 h after the meal. This decline was significantly (p<0.0001) greater than the 3.6% fall observed during the fasting trial. Postprandial changes in the plasma zinc concentrations were correlated with postprandial changes in serum glucose (r=−0.43,p<0.001), serum insulin (r=−0.17,p<0.01), and serum phosphorus(r=0.32,p<0.005). These data show that plasma zinc concentrations decline following food intake in elderly women in the same manner as previously described for younger adult women.     

Exposure measurement of aflatoxins and aflatoxin metabolites in human body fluids. A short review

Aflatoxins are highly toxic secondary fungal metabolites mainly produced by Aspergillus flavus and A. parasiticus. Human exposure to aflatoxins may result directly from ingestion of contaminated foods, or indirectly from consumption of foods from animals previously exposed to aflatoxins in feeds. This paper focuses on exposure measurement of aflatoxins and aflatoxin metabolites in various human body fluids. Research on different metabolites present in blood, urine, breast milk, and other human fluids or tissues including their detection techniques is reviewed. The association between dietary intake of aflatoxins and biomarker measurement is also highlighted. Finally, aspects related to the differences between aflatoxin determination in food versus the biomarker approach are discussed.     

GC-FPD measurement of urinary dialkylphosphate metabolites of organophosphorous pesticides as pentafluorobenzyl derivatives in occupationally exposed workers and in a general population in Shanghai (China)

Measurement of organophosphorus (OP) pesticide metabolites in human biological fluids is an important biomarker of pesticides exposure. We measured the urinary excretion of OP pesticide metabolites to evaluate occupational and non-occupational exposure to OP pesticides in the Chinese population in Shanghai (Eastern China). We collected urine samples from 30 exposed workers in a dimethoate emulsion packing division and from 60 healthy adults without any report of occupational exposure. DMP, DMTP, DMDTP, DEP, DEDP and DEDTP were measured by GC-FPD after derivatization with pentafluorobenzyl bromide. The LOQ values (1 mL urine) were 2.0 μg/L for DMP and DETP, 4.0 μg/L for DEP and DEDTP, 8.0 μg/L for DMDTP, and 10.0 μg/L for DMTP. Dimethyl phosphates were detected in the majority of the urine samples, i.e., 90–100% in the exposed group and 80–87% in the control group. The concentration of the urinary diethyl phosphates DEP and DETP was above the LOQ values in 40 and 20% of samples for the exposed group, and in 50 and 30% of the samples for the control group, respectively. DEDTP was not detectable in the urine samples except for a post-shift exposed worker (detection frequency, 6.7%). Median creatinine-adjusted values (μg/g cr.) for DAP in Chinese with pre-shift, post-shift and without occupational exposure to OP were 316, 584 and 170 for DMP, below LOQ, 115 and 114 for DEP, 840, 1730 and 693 for DMTP, and 255, 756 and 135 for DMDTP, respectively. In all subjects, the highest excretion levels were found for DMTP. Several OP pesticide metabolites were frequently detected in urine samples of both populations studied.     

Analysis of human urine for fifteen phthalate metabolites using automated solid-phase extraction

We improved our previous analytical method to measure phthalate metabolites in urine as biomarkers for phthalate exposure by automating the solid-phase extraction (SPE) procedure and expanding the analytical capability to quantify four additional metabolites: phthalic acid, mono-3-carboxypropyl phthalate, mono-isobutyl phthalate (miBP), and monomethyl isophthalate. The method, which involves automated SPE followed by isotope dilution-high performance liquid chromatography (HPLC)-electrospray ionization (ESI)-tandem mass spectrometry (MS), allows for the quantitative measurement of 15 phthalate metabolites in urine with detection limits in the low ng/ml range. SPE automation allowed for the unattended sequential extraction of up to 100 samples at a time, and resulted in an increased sample throughput, lower solvent use, and better reproducibility than the manual SPE. Furthermore, the modified method permitted for the first time, the separation and quantification of mono-n-butyl phthalate (mBP) and its structural isomer miBP. The method was validated on spiked pooled urine samples and on pooled urine samples from persons with no known exposure to phthalates.     

Zearalenone,deoxynivalenol and aflatoxin B<Subscript>1</Subscript> and their metabolites in pig urine as biomarkers for mycotoxin exposure

Methods to determine zearalenone (ZEA), deoxynivalenol (DON), aflatoxins (AF) and their metabolites in pig urine were developed as biomarkers for pig exposure to the mycotoxins in feed. Urine samples were incubated with β-glucuronidase to cleave conjugates, extracted and cleaned-up with solid phase and immunoaffinity columns, followed by HPLC with UV and fluorescence detection. Good recoveries (83–130%), low variation (2–10%), and low detection limits (0.3–9.9 ng/ml) were obtained. The results of controlled AFB₁ feeding trials found no difference in urine concentrations of AFB₁ or AFM₁ from pigs fed three different levels (127, 227, 327 μg/kg) of AFB₁ in diets. The excretion of AFB₁ and AFM₁ in urine was on average 30% of the oral dose and the ratio AFB₁ to AFM₁ was around 23%. The analysis of 15 Vietnamese pig urine samples indicate a relatively high exposure of ZEA, DON and AF, which were found as toxin or metabolites in 47, 73, and 80% of the urine samples, respectively.     

Metabolomics of prolonged fasting in humans reveals new catabolic markers

Fasting is one of the simplest metabolic challenges that can be performed in humans. We here report for the first time a comprehensive analysis of the human ??fasting metabolome?? obtained from analysis of plasma and urine samples in a small cohort of healthy volunteers, using nuclear magnetic resonance (NMR), gas chromatography- and liquid chromatography-mass spectrometry (GC-MS and LC-MS). Intra- and inter-individual variation of metabolites was on measurement of four overnight fasting samples collected from each volunteer over a four week period. One additional sample per volunteer was collected following a prolonged fasting period of 36?h. Amongst a total of 377 quantified entities in plasma around 44% were shown to change significantly in concentration when volunteers extended fasting from 12 to 36?h. In addition to known markers (plasma free fatty acids, glycerol, ketone bodies) that reflect changes in the body??s fuel management under fasting conditions a wide range of ??new?? entities such as ??-aminobutyrate as well as other amino and keto acids were identified as fasting markers. Based on multiple correlations amongst the metabolites and selected hormones in plasma such as leptin or insulin-like-growth-factor-1 (IGF-1), a robust metabolic network with coherent regulation of a wide range of metabolites could be identified. The metabolomics approach described here demonstrates the plasticity of human metabolism and identifies new and robust markers of the fasting state.     

Measurement of dietary exposure: a challenging problem which may be overcome thanks to metabolomics?

The diet is an important environmental exposure, and its measurement is an essential component of much health-related research. However, conventional tools for measuring dietary exposure have significant limitations being subject to an unknown degree of misreporting and dependent upon food composition tables to allow estimation of intakes of energy, nutrients and non-nutrient food constituents. In addition, such tools may be inappropriate for use with certain groups of people. As an alternative approach, the recent techniques of metabolite profiling or fingerprinting, which allows simultaneous monitoring of multiple and dynamic components of biological fluids, may provide metabolic signals indicative of food intake. Samples can be analysed through numerous analytical platforms, followed by multivariate data analysis. In humans, metabolomics has been applied successfully in pharmacology, toxicology and medical screening, but nutritional metabolomics is still in its infancy. Biomarkers of a small number of specific foods and nutrients have been developed successfully but less targeted and more high-throughput methods, that do not need prior knowledge of which signals might be discriminatory, and which may allow a more global characterisation of dietary intake, remain to be tested. A proof a principle project (the MEDE Study) is currently underway in our laboratories to test the hypothesis that high-throughput, non-targeted metabolite fingerprinting using flow injection electrospray mass spectrometry can be applied to human biofluids (blood and urine) to characterise dietary exposure in humans.     

Fusarium toxin residues in physiological samples of piglets

Physiological samples of 100 piglets fed diets containing 0.01, 0.06, 0.15, 0.22 and 0.42 mg ZON and 0.2, 0.8, 1.0, 1.9 and 3.9 mg DON per kg over a period of 35±1.5 days were investigated for concentrations of deoxynivalenol (DON) and zearalenone (ZON) and their metabolites. DON was detected in serum, bile and urine in increasing concentrations corresponding to the diet contamination. The metabolite de-epoxy-DON was detected only in urine. The DON contamination of the diet was closely reflected by the serum concentrations of the piglets. ZON and its metabolite α-zearalenol were detected in bile fluid, liver and urine, while β-zearalenol was only detected in bile fluid. In serum neither ZON nor its metabolites were found. The total concentration of ZON plus its metabolites in the bile fluid corresponded well with the dietary contamination. For all analyses it has to be noted that toxin residues were detectable even in individual samples of piglets fed the control diet containing 0.01 mg ZON/kg and 0.2 mg DON/kg. Presented at the 25^th Mykotoxin Workshop in Giessen, Germany, May 19–21, 2003     

Seasonal variation in amount of unabsorbed dietary carbohydrate from the intestine after breakfast in Japanese subjects

We previously showed that daytime dim-light exposure has a negative effect on the efficiency of dietary carbohydrate absorption in the evening, whereas evening-time dim-light exposure has a beneficial effect. These results suggest that seasonal changes in the environmental light may affect gastrointestinal activity, and that there might, therefore, be seasonal variation in the efficiency of dietary carbohydrate absorption from the intestine. In order to prove this hypothesis, we measured the amount of dietary carbohydrate unabsorbed from the intestine after a breakfast in healthy female Japanese subjects during the four seasons of the year. We estimated the amount of unabsorbed dietary carbohydrate by the breath hydrogen test, which measures the amount of hydrogen in exhaled air. A 6 g solution of lactosucrose, an indigestible trisaccharide, was used for comparison. Two groups of subjects, 12 subjects in Osaka and 14 subjects in Nagano, were studied in the winter (January to February), spring (April to May), summer (July to August), and autumn (October to November) of 2004. We found the following results: (1) In no season were there any significant differences between the two subgroups in the orocecal transit time of the breakfast and the lactosucrose solution. Nor were there any significant differences in the amount of unabsorbed dietary carbohydrate from the breakfast. (2) Using the pooled data of the total of 26 subjects, there was no significant seasonal variation in the orocecal transit time of the breakfast or the lactosucrose solution. (3) There was a significant seasonal variation in the amount of unabsorbed dietary carbohydrate from the breakfast. (4) The amount of unabsorbed dietary carbohydrate from the breakfast was largest in winter and smallest in autumn. Results in spring and in summer were similar and intermediate between those in winter and autumn. Post hoc multiple comparison tests showed that the amount of unabsorbed dietary carbohydrate in winter was significantly larger than in autumn. (5) In winter, the average ratio of the amount of unabsorbed dietary carbohydrate to the total amount of carbohydrate in the breakfast was about 12%; in autumn it was about 6%. These results clearly show that there is seasonal variation in the efficiency of intestinal dietary carbohydrate absorption among young female Japanese subjects.     

Standardization of factors that influence human urine metabolomics

In nutritional metabolomics a large inter- and intra-subject variability exists, and thus, it becomes important to limit the variance introduced by external factors. In a composite controlled study with full provision of all food for the standardized intervention, human urinary metabolite profiles were investigated for different factors, such as handling of urine collections, diet standardization, diet culture, cohabitation and gender. In study A, 8 healthy subjects (4 men; 4 women) collected 24-h urine, splitting each void into two specimens stored either at 4°C or at room temperature. In study B, 16 healthy subjects (7 men; 9 women) collected 24-h urine for three days while being on a standardized diet. Samples were analyzed by ¹H NMR and chemometrics. The NMR profiles indicated the presence of metabolites presumably originating from bacterial contamination in 3 out of 16 sample collections stored at room temperature. On the contrary, no changes in the NMR profiles due to contamination occurred in the 24-h urine samples stored at 4°C. The study also showed a trend towards a reduced inter- and intra-individual variation during 3 days of diet standardization. In study A, the urine metabolome showed a clear effect of diet culture and cohabitation, but these effects significantly attenuated after diet standardization (study B). Besides, gender-specific differences were found in both studies. Our results emphasize that best practice for any metabolomic study is a standardized, chilled sample collection procedure, and recommend that diet standardization is performed prior to dietary interventions in order to reduce intra- and inter-subject variability.     

Within-person variability of the ratios of urinary 2-hydroxyestrone to 16alpha-hydroxyestrone in Caucasian women

The ratio of urinary 2-hydroxyestrone (2-OHE1) to 16alpha-hydroxyestrone (16alpha-OHE1) has been suggested as a potential biomarker for breast cancer risk. We evaluated within-person variability of this biomarker in ten healthy Caucasian women aged 23-58 years. Each study participant was asked to provide an overnight fasting morning urine sample once a week for an average of 8 weeks. These urine samples were assayed for 2-OHE1 and 16alpha-OHE1 by using competitive enzyme immunoassay kits purchased from the ImmunaCare Corporation. The coefficients of variation for urinary 2-OHE1/16alpha-OHE1 over the study period ranged from 13.7 to 59.6% (mean, 33.3%) in our study participants. There was a good correlation between the level of the urinary 2-OHE1/16alpha-OHE1 ratio in any single urine sample and the average ratio over the 8-week study period from the same woman, with the mean correlation coefficient of 0.85. These results indicated that the within-person variation of the 2-OHE1 to 16alpha-OHE1 ratio for most women was moderate and the level of this ratio in a single urine sample, in general, reflects reasonably well the level of this biomarker over a 2-month period.     

Analysis of 4-aminobiphenyl in smoker’s and nonsmoker’s urine by tandem mass spectrometry

The aromatic amine 4-aminobiphenyl (4-ABP) is present in tobacco smoke. In humans, it is also a known bladder carcinogen. We describe here a method for the quantification of total 4-ABP in urine using capillary gas chromatography/tandem mass spectrometry, with an effective detection limit in urine samples of approximately 0.87 pg/mL. We also examined the efficiency of chemical or enzymatic hydrolysis of urinary aromatic amine metabolites. Although we found acidic or basic hydrolysis effective, we found enzymatic hydrolysis (β-glucuronidase with either Escherichia coli or Helix pomatia) ineffective. As part of this work, we also confirm the presence of N-acetyl-4-ABP and 4-ABP glucuronide in human urine samples from smokers. These metabolites have been reported in animal studies, but previously they have not been identified in human samples. These metabolites, however, were found to be unstable and thus infeasible for biomonitoring. The final validated urinary total 4-ABP assay was applied to the analysis of samples from smokers and nonsmokers, whose status was confirmed from cotinine EIA measurements. Among 41 confirmed nonsmokers, the geometric mean (95% CI) of 4-ABP concentration was 1.64 pg/mg creatinine (1.30–2.07). Conversely, in 89 smokers, the geometric mean of 4-ABP concentration was significantly greater, at 8.69 pg/mg creatinine (7.43–10.16), p?<?0.001. Our results indicate that following tobacco smoke exposure, total urinary 4-ABP is a reliable biomarker for exposure to this carcinogen.     

Effects of post-absorptive and postprandial exercise on glucoregulation in metabolic syndrome

Objective: The aim of this study was to investigate the effects of an acute exercise bout in the morning in the post‐absorptive or postprandial state on the glycemic and insulinemic response to three standardized meals throughout the day. It is hypothesized that post‐absorptive exercise enhances fat oxidation rate during exercise and thereafter attenuates the glucose and insulin response to subsequent meals. Research Methods and Procedures: Seven sedentary males with metabolic syndrome (age, 45 ± 11 years; BMI, 34 ± 3 kg/m²) were studied in a crossover design comparing three conditions: no exercise, postprandial and post‐absorptive exercise (at ～60% of the individual V?O_2max for 45 minutes). Substrate use was evaluated by indirect calorimetry during exercise. Venous blood samples were taken at regular (30‐ to 60‐minute) intervals throughout the day, and glucose, insulin, and triglyceride concentrations were determined. Results: During exercise, a higher fat oxidation rate was observed in the post‐absorptive than the postprandial state. The glycemic response to a standardized high‐carbohydrate breakfast was lower when exercising after breakfast than when exercising before breakfast. There was no effect of either exercise mode on glucose and insulin response to lunch and supper. Discussion: Post‐absorptive exercise has the advantage of promoting fat use, whereas postprandial exercise can attenuate the glycemic response to breakfast. Neither exercise mode acutely induces improved glucoregulation later during the day. The impact of meal timing on the effects of regular exercise training on glycemic control in this population remains to be studied.     

Use of the Local False Discovery Rate for Identification of Metabolic Biomarkers in Rat Urine Following Genkwa Flos-Induced Hepatotoxicity

Metabolomics is concerned with characterizing the large number of metabolites present in a biological system using nuclear magnetic resonance (NMR) and HPLC/MS (high-performance liquid chromatography with mass spectrometry). Multivariate analysis is one of the most important tools for metabolic biomarker identification in metabolomic studies. However, analyzing the large-scale data sets acquired during metabolic fingerprinting is a major challenge. As a posterior probability that the features of interest are not affected, the local false discovery rate (LFDR) is a good interpretable measure. However, it is rarely used to when interrogating metabolic data to identify biomarkers. In this study, we employed the LFDR method to analyze HPLC/MS data acquired from a metabolomic study of metabolic changes in rat urine during hepatotoxicity induced by Genkwa flos (GF) treatment. The LFDR approach was successfully used to identify important rat urine metabolites altered by GF-stimulated hepatotoxicity. Compared with principle component analysis (PCA), LFDR is an interpretable measure and discovers more important metabolites in an HPLC/MS-based metabolomic study.     

Seasonal Variation in Amount of Unabsorbed Dietary Carbohydrate from the Intestine after Breakfast in Japanese Subjects

We previously showed that daytime dim‐light exposure has a negative effect on the efficiency of dietary carbohydrate absorption in the evening, whereas evening‐time dim‐light exposure has a beneficial effect. These results suggest that seasonal changes in the environmental light may affect gastrointestinal activity, and that there might, therefore, be seasonal variation in the efficiency of dietary carbohydrate absorption from the intestine. In order to prove this hypothesis, we measured the amount of dietary carbohydrate unabsorbed from the intestine after a breakfast in healthy female Japanese subjects during the four seasons of the year. We estimated the amount of unabsorbed dietary carbohydrate by the breath hydrogen test, which measures the amount of hydrogen in exhaled air. A 6 g solution of lactosucrose, an indigestible trisaccharide, was used for comparison. Two groups of subjects, 12 subjects in Osaka and 14 subjects in Nagano, were studied in the winter (January to February), spring (April to May), summer (July to August), and autumn (October to November) of 2004. We found the following results: (1) In no season were there any significant differences between the two subgroups in the orocecal transit time of the breakfast and the lactosucrose solution. Nor were there any significant differences in the amount of unabsorbed dietary carbohydrate from the breakfast. (2) Using the pooled data of the total of 26 subjects, there was no significant seasonal variation in the orocecal transit time of the breakfast or the lactosucrose solution. (3) There was a significant seasonal variation in the amount of unabsorbed dietary carbohydrate from the breakfast. (4) The amount of unabsorbed dietary carbohydrate from the breakfast was largest in winter and smallest in autumn. Results in spring and in summer were similar and intermediate between those in winter and autumn. Post hoc multiple comparison tests showed that the amount of unabsorbed dietary carbohydrate in winter was significantly larger than in autumn. (5) In winter, the average ratio of the amount of unabsorbed dietary carbohydrate to the total amount of carbohydrate in the breakfast was about 12%; in autumn it was about 6%. These results clearly show that there is seasonal variation in the efficiency of intestinal dietary carbohydrate absorption among young female Japanese subjects.     

Microbial metabolites are associated with a high adherence to a Mediterranean dietary pattern using a 1H-NMR-based untargeted metabolomics approach

The study of biomarkers of dietary patterns including the Mediterranean diet (MedDiet) is scarce and could improve the assessment of these patterns. Moreover, it could provide a better understanding of health benefits of dietary patterns in nutritional epidemiology. We aimed to determine a robust and accurate biomarker associated with a high adherence to a MedDiet pattern that included dietary assessment and its biological effect. In this cross-sectional study, we included 56 and 63 individuals with high (H-MDA) and low (L-MDA) MedDiet adherence categories, respectively, all from the Prevención con Dieta Mediterránea trial. A ¹H-NMR-based untargeted metabolomics approach was applied to urine samples. Multivariate statistical analyses were conducted to determine the metabolite differences between groups. A stepwise logistic regression and receiver operating characteristic curves were used to build and evaluate the prediction model for H-MDA. Thirty-four metabolites were identified as discriminant between H-MDA and L-MDA. The fingerprint associated with H-MDA included higher excretion of proline betaine and phenylacetylglutamine, among others, and decreased amounts of metabolites related to glucose metabolism. Three microbial metabolites — phenylacetylglutamine, p-cresol and 4-hydroxyphenylacetate — were included in the prediction model of H-MDA (95% specificity, 95% sensitivity and 97% area under the curve). The model composed of microbial metabolites was the biomarker that defined high adherence to a Mediterranean dietary pattern. The overall metabolite profiling identified reflects the metabolic modulation produced by H-MDA. The proposed biomarker may be a better tool for assessing and aiding nutritional epidemiology in future associations between H-MDA and the prevention or amelioration of chronic diseases.     

Modeling Human Exposure to Phthalate Esters: A Comparison of Indirect and Biomonitoring Estimation Methods

Humans are potentially exposed to phthalate esters (PEs) through ingestion, inhalation, and dermal contact. Studies quantifying exposure to PEs include “biomarker studies” and “indirect studies.” Biomarker studies use measurements of PE metabolites in urine to back-calculate exposure to the parent diester, while indirect studies use the concentration of the PE in each medium of exposure and the rate of intake of that medium to quantify intake of the PE. In this review, exposure estimates from biomarker and indirect studies are compiled and compared for seven PEs to determine if there are regional differences and if there is a preferred approach. The indirect and biomarker methods generally agree with each other within an order of magnitude and discrepancies are explained by difficulties in accounting for use of consumer products, uncertainty concerning absorption, regional differences, and temporal changes. No single method is preferred for estimating intake of all PEs; it is suggested that biomarker estimates be used for low molecular weight PEs for which it is difficult to quantify all sources of exposure and either indirect or biomarker methods be used for higher molecular weight PEs. The indirect methods are useful in identifying sources of exposure while the biomarker methods quantify exposure.     

Menstrual cycle exhibits no effect on postprandial lipemia.

Menstrual cycle effects on postprandial lipemia were investigated in 13 healthy women. They were monitored (dietary intake, basal body temperature) for a period of one cycle. Statistically significant follicular-luteal differences were neither observed between fasting triglyceride serum levels nor between areas under triglyceride response curves after a standardized oral fat load.