Development of exposure assessment method based on the analysis of urinary heterocyclic amines as biomarkers by on-line in-tube solid-phase microextraction coupled with liquid chromatography–tandem mass spectrometry

Heterocyclic amines (HCAs) formed in cooked meats and fish are mutagens and carcinogens in rodents and nonprimates. Exposure to HCAs may also be a risk factor for human tumors, but the association between dietary intake and human cancer risk has not been determined. To assess recent exposure to HCAs, we developed a simple and sensitive method for measuring HCAs in urine by automated on-line in-tube solid-phase microextraction (SPME) using a Supel-Q PLOT capillary column as an extraction device, in combination with liquid chromatography–tandem mass spectrometry (LC–MS/MS). Thirteen HCAs were separated within 15 min using a ZORBAX Eclipse XDB-C8 column and detected selectively by multiple reaction monitoring using MS/MS. This method can be applied easily to the analysis of small amounts of urine samples without any other pretreatment except for alkaline hydrolysis of bound forms of HCAs. The quantification limits of HCAs in 0.2 mL of urine samples were about 1.7–4.1 pg/mL (S/N?=?10). Using this method, we evaluated the exposure to HCAs in persons who consumed well-done pan-fried beef and the suitability of using urinary HCAs as exposure biomarkers. We also analyzed the ability of vegetable consumption to prevent carcinogenic risks from exposure to HCAs by measuring free and bound forms of HCAs in urine.

A Generic Multiple Reaction Monitoring Based Approach for Plant Flavonoids Profiling Using a Triple Quadrupole Linear Ion Trap Mass Spectrometry

Flavonoids are one of the largest classes of plant secondary metabolites serving a variety of functions in plants and associating with a number of health benefits for humans. Typically, they are co-identified with many other secondary metabolites using untargeted metabolomics. The limited data quality of untargeted workflow calls for a shift from the breadth-first to the depth-first screening strategy when a specific biosynthetic pathway is focused on. Here we introduce a generic multiple reaction monitoring (MRM)-based approach for flavonoids profiling in plants using a hybrid triple quadrupole linear ion trap (QTrap) mass spectrometer. The approach includes four steps: (1) preliminary profiling of major aglycones by multiple ion monitoring triggered enhanced product ion scan (MIM-EPI); (2) glycones profiling by precursor ion triggered EPI scan (PI-EPI) of major aglycones; (3) comprehensive aglycones profiling by combining MIM-EPI and neutral loss triggered EPI scan (NL-EPI) of major glycone; (4) in-depth flavonoids profiling by MRM-EPI with elaborated MRM transitions. Particularly, incorporation of the NH3 loss and sugar elimination proved to be very informative and confirmative for flavonoids screening. This approach was applied for profiling flavonoids in Astragali radix (Huangqi), a famous herb widely used for medicinal and nutritional purposes in China. In total, 421 flavonoids were tentatively characterized, among which less than 40 have been previously reported in this medicinal plant. This MRM-based approach provides versatility and sensitivity that required for flavonoids profiling in plants and serves as a useful tool for plant metabolomics.

Discovery of safety biomarkers for realgar in rat urine using UFLC-IT-TOF/MS and 1H NMR based metabolomics

As an arsenical, realgar (As₄S₄) is known as a poison and paradoxically as a therapeutic agent. However, a complete understanding of the precise biochemical alterations accompanying the toxicity and therapy effects of realgar is lacking. Using a combined ultrafast liquid chromatography (UFLC) coupled with ion trap time-of-flight mass spectrometry (IT-TOF/MS) and ¹H NMR spectroscopy based metabolomics approach, we were able to delineate significantly altered metabolites in the urine samples of realgar-treated rats. The platform stability of the liquid chromatography LC/MS and NMR techniques was systematically investigated, and the data processing method was carefully optimized. Our results indicate significant perturbations in amino acid metabolism, citric acid cycle, choline metabolism, and porphyrin metabolism. Thirty-six metabolites were proposed as potential safety biomarkers related to disturbances caused by realgar, and glycine and serine are expected to serve as the central contacts in the metabolic pathways related to realgar-induced disturbance. The LC/MS and NMR based metabolomics approach established provided a systematic and holistic view of the biochemical effects of realgar on rats, and might be employed to investigate other drugs or xenobiotics in the future.

LC-MS/MS-based multibiomarker approaches for the assessment of human exposure to mycotoxins

Mycotoxins are toxic fungal secondary metabolites that frequently contaminate food and feed worldwide, and hence represent a major hazard for food and feed safety. To estimate human exposure arising from contaminated food, so-called biomarker approaches have been developed as a complementary biomonitoring tool besides traditional food analysis. The first methods based on radioimmunoassays and enzyme-linked immunosorbent assays as well as on liquid chromatography were developed in the late 1980s and early 1990s for the carcinogenic aflatoxins and in the last two decades further tailor-made methods for some major mycotoxins have been published. Since 2010, there has been a clear trend towards the development and application of multianalyte methods based on liquid chromatography–electrospray ionization tandem mass spectrometry for assessment of mycotoxin exposure made possible by the increased sensitivity and selectivity of modern mass spectrometry instrumentation and sophisticated sample cleanup approaches. With use of these advanced methods, traces of mycotoxins and relevant breakdown and conjugation products can be quantified simultaneously in human urine as so-called biomarkers and can be used to precisely describe the real exposure, toxicokinetics, and bioavailability of the toxins present. In this article, a short overview and comparison of published multibiomarker methods focusing on the determination of mycotoxins and relevant excretion products in human urine is presented. Special attention is paid to the main challenges when analyzing these toxic food contaminants in urine, i.e., very low analyte concentrations, appropriate sample preparation, matrix effects, and a lack of authentic, NMR-confirmed calibrants and reference materials. Finally, the progress in human exposure assessment studies facilitated by these analytical methods is described and an outlook on probable developments and possibilities is presented.

Simultaneous determination of water-soluble vitamins in SRM 1849 Infant/Adult Nutritional Formula powder by liquid chromatography–isotope dilution mass spectrometry

Assessing dietary intake of vitamins from all sources, including foods, dietary supplements, and fortified foods, would be aided considerably by having analytical methodologies that are capable of simultaneous determination of several vitamins. Vitamins naturally present in foods may occur in different chemical forms, with levels ranging over several orders of magnitude. Vitamins in dietary supplements and fortified foods, however, are typically added in a single chemical form, and matrix issues are usually not as complex. These sources should thus be relatively amenable to approaches that aim for simultaneous determination of multiple vitamins. Our recent work has focused on development of liquid chromatography (LC)–UV/fluorescence and LC–tandem mass spectrometry methods for the simultaneous determination of water-soluble vitamins (thiamine, niacin, pyridoxine, pantothenic acid, folic acid, biotin, and riboflavin) in dietary supplement tablets and fortified foods, such as formula powders and breakfast cereals. As part of the validation of our methods and collaboration in characterization of a new NIST SRM 1849 Infant/Adult Nutritional Formula powder, we report data on SRM 1849 using isotope dilution mass spectrometric methods. Use of available NIST Standard Reference Materials® as test matrices in our method development and validation gives a benchmark for future application of these methods. We compare three chromatographic approaches and provide data on stability of vitamin standard solutions for LC-based multiple vitamin determinations.

Metabolite profiling and beyond: approaches for the rapid processing and annotation of human blood serum mass spectrometry data

In this paper, we describe data processing and metabolite identification approaches which lead to a rapid and semi-automated interpretation of metabolomics experiments. Data from metabolite fingerprinting using LC-ESI-Q-TOF/MS were processed with several open-source software packages, including XCMS and CAMERA to detect features and group features into compound spectra. Next, we describe the automatic scheduling of tandem mass spectrometry (MS) acquisitions to acquire a large number of MS/MS spectra, and the subsequent processing and computer-assisted annotation towards identification using the R packages MetShot, Rdisop, and the MetFusion application. We also implement a simple retention time prediction model using predicted lipophilicity logD, which predicts retention times within 42 s (6 min gradient) for most compounds in our setup. We putatively identified 44 common metabolites including several amino acids and phospholipids at metabolomics standards initiative (MSI) levels two and three and confirmed the majority of them by comparison with authentic standards at MSI level one. To aid both data integration within and data sharing between laboratories, we integrated data from two labs and mapped retention times between the chromatographic systems. Despite the different MS instrumentation and different chromatographic gradient programs, the mapped retention times agree within 26 s (20 min gradient) for 90 % of the mapped features.

A novel reversed-phase HPLC method for the determination of urinary creatinine by pre-column derivatization with ethyl chloroformate: comparative studies with the standard Jaffé and isotope-dilution mass spectrometric assays

Creatinine is an important biomarker for renal function diagnosis and normalizing variations in urinary drug/metabolites concentration. Quantification of creatinine in biological fluids such as urine and plasma is important for clinical diagnosis as well as in biomonitoring programs and urinary metabolomics/metabonomics research. Current methods for creatinine determination either are nonselective or involve the use of expensive mass spectrometers. In this paper, a novel reversed-phase high-performance liquid chromatographic (HPLC) method for the determination of creatinine of high hydrophilicity by pre-column derivatization with ethyl chloroformate is presented. N-Ethyloxycarbonylation of creatinine significantly enhanced the hydrophobicity of creatinine, facilitating its chromatographic retention as well as quantification by HPLC. Factors governing the derivatization reaction were studied and optimized. The developed method was validated and applied for the determination of creatinine in rat urine samples. Comparative studies with isotope-dilution mass spectrometric method revealed that the two methods do not yield systematic differences in creatinine concentrations, indicating the HPLC method is suitable for the determination of creatinine in urine samples.

Data-handling strategies for metabonomic studies: example of the UHPLC-ESI/ToF urinary signature of tetrahydrocannabinol in humans

Metabonomics has become a very valuable tool and many research fields rely on results coming out from this combination of analytical techniques, chemometric strategies, and biological interpretation. Moreover, the matrices are more and more complex and the implications of the results are often of major importance. In this context, the need for pertinent validation strategies comes naturally. The choice of the appropriate chemometric method remains nevertheless a difficult task due to particularities such as: the number of measured variables, the complexity of the matrix and the purposes of the study. Consequently, this paper presents a detailed metabonomic study on human urine with a special emphasis on the importance of assessing the data's quality. It also describes, step by step, the statistical tools currently used and offers a critical view on some of their limits. In this work, 29 urine samples among which 15 samples obtained from tetrahydrocannabinol (delta-9-tetrahydrocannabinol)-consuming athletes, 5 samples provided by volunteers, and 9 samples obtained from athletes were submitted to untargeted analysis by means of ultra high-pressure liquid chromatography–electrospray ionization–time-of-flight mass spectrometry. Next, the quality of the obtained data was assessed and the results were compared to those found in databases. Then, unsupervised (principal component analysis (PCA)) and supervised (ANOVA/PCA, partial least-square–discriminant analysis (PLS-DA), orthogonal PLS-DA) univariate and multivariate statistical methods were applied.

Metabolomic profiling of mice urine and serum associated with trans-trans 2, 4-decadienal induced lung lesions by liquid chromatography-mass spectrometry

Metabolomics has become an important tool in clinical research and the diagnosis of human disease. Intratracheal instillation of trans-trans 2,4-decadienal (tt-DDE), a major component in cooking oil fumes, has been demonstrated to cause lung lesions in mice at 8 weeks after treatment. The objective of this study was to identify any changes in metabolite profiles associated with the development of tt-DDE-induced lung lesions. Using a metabolomics strategy involving a liquid chromatography–mass spectrometry-based approach in conjunction with principal component analysis and confirmation by liquid chromatography triple quadrupole tandem mass spectrometry, we have demonstrated that the amino acid profiles of the urine and serum of tt-DDE-treated mice are changed. Ten amino acids were significantly reduced in serum of tt-DDE-treated mice at 8 weeks after treatment. Our results suggest that amino acid profiles may be useful as an early indicator of the presence of tt-DDE-induced lung lesions.

Comprehensive Analysis of LC/MS Data Using Pseudocolor Plots

We have developed new applications of the pseudocolor plot for the analysis of LC/MS data. These applications include spectral averaging, analysis of variance, differential comparison of spectra, and qualitative filtering by compound class. These applications have been motivated by the need to better understand LC/MS data generated from analysis of human biofluids. The examples presented use data generated to profile steroid hormones in urine extracts from a Cushing’s disease patient relative to a healthy control, but are general to any discovery-based scanning mass spectrometry technique. In addition to new visualization techniques, we introduce a new metric of variance: the relative maximum difference from the mean. We also introduce the concept of substructure-dependent analysis of steroid hormones using precursor ion scans. These new analytical techniques provide an alternative approach to traditional untargeted metabolomics workflow. We present an approach to discovery using MS that essentially eliminates alignment or preprocessing of spectra. Moreover, we demonstrate the concept that untargeted metabolomics can be achieved using low mass resolution instrumentation.      

Bioappearance and pharmacokinetics of bioactives upon coffee consumption

Habitual consumption of medium amounts of coffee over the whole life-span is hypothesized to reduce the risk to develop diabetes type 2 (DM2) and Alzheimer’s disease (AD). To identify putative bioactive coffee-derived metabolites, first, pooled urine from coffee drinkers and non-coffee drinkers were screened by UPLC-HDMS. After statistical data analysis, trigonelline, dimethylxanthines and monomethylxanthines, and ferulic acid conjugates were identified as the major metabolites found after coffee consumption. For quantitative analysis of these markers in body fluids, targeted methods based on stable-isotope dilution and UPLC-MS/MS were developed and applied to plasma samples from a coffee intervention study (n?=?13 volunteers) who consumed a single cup of caffeinated coffee brew after a 10-day washout period. Chlorogenic acid-derived metabolites were found to be separated into two groups showing different pharmacokinetic properties. The first group comprised, e.g., ferulic acid and feruloyl sulfate and showed early appearance in the plasma (～1 h). The second group contained particularly chlorogenic acid metabolites formed by the intestinal microflora, appearing late and persisting in the plasma (>6 h). Trigonelline appeared early but persisted with calculated half-life times ～5 h. The plasma levels of caffeine metabolites significantly and progressively increased 2–4 h after coffee consumption and did not reach c _max within the time frame of the study. The pharmacokinetic profiles suggest that particularly trigonelline, caffeine, its metabolites, as well as late appearing dihydroferulic acid, feruloylglycine and dihydroferulic acid sulfate formed from chlorogenic acid by the intestinal microflora accumulate in the plasma due to their long half-life times during habitual consumption of several cups of coffee distributed over the day. Since some of these metabolites have been reported to show antioxidant effects in vivo, antioxidant-response-element activating potential, and neuroprotective properties, respectively, some of these key metabolites might account for the inflammation- and DM2/AD risk reducing effects reported for habitual life time consumption of coffee.

Optimization of harvesting, extraction, and analytical protocols for UPLC-ESI-MS-based metabolomic analysis of adherent mammalian cancer cells

In this study, a liquid chromatography mass spectrometry (LC/MS)-based metabolomics protocol was optimized for quenching, harvesting, and extraction of metabolites from the human pancreatic cancer cell line Panc-1. Trypsin/ethylenediaminetetraacetic acid (EDTA) treatment and cell scraping in water were compared for sample harvesting. Four different extraction methods were compared to investigate the efficiency of intracellular metabolite extraction, including pure acetonitrile, methanol, methanol/chloroform/H₂O, and methanol/chloroform/acetonitrile. The separation efficiencies of hydrophilic interaction chromatography (HILIC) and reversed-phase liquid chromatography (RPLC) with UPLC-QTOF-MS were also evaluated. Global metabolomics profiles were compared; the number of total detected features and the recovery and relative extraction efficiencies of target metabolites were assessed. Trypsin/EDTA treatment caused substantial metabolite leakage proving it inadequate for metabolomics studies. Direct scraping after flash quenching with liquid nitrogen was chosen to harvest Panc-1 cells which allowed for samples to be stored before extraction. Methanol/chloroform/H₂O was chosen as the optimal extraction solvent to recover the highest number of intracellular features with the best reproducibility. HILIC had better resolution for intracellular metabolites of Panc-1 cells. This optimized method therefore provides high sensitivity and reproducibility for a variety of cellular metabolites and can be applicable to further LC/MS-based global metabolomics study on Panc-1 cell lines and possibly other cancer cell lines with similar chemical and physical properties.

Mass Spectrometry Combinations for Structural Characterization of Sulfated-Steroid Metabolites

Steroid conjugates, which often occur as metabolites, are challenging to characterize. One application is female-mouse urine, where steroid conjugates serve as important ligands for the pheromone-sensing neurons. Although the two with the highest abundance in mouse urine were previously characterized with mass spectrometry (MS) and NMR to be sulfated steroids, many more exist but remain structurally unresolved. Given that their physical and chemical properties are similar, they are likely to have a sulfated steroid ring structure. Because these compounds occur in trace amounts in mouse urine and elsewhere, their characterization by NMR will be difficult. Thus, MS methods become the primary approach for determining structure. Here, we show that a combination of MS tools is effective for determining the structures of sulfated steroids. Using 4-pregnene analogs, we explored high-resolving power MS (HR-MS) to determine chemical formulae; HD exchange MS (HDX-MS) to determine number of active, exchangeable hydrogens (e.g., OH groups); methoxyamine hydrochloride (MOX) derivatization MS, or reactive desorption electrospray ionization with hydroxylamine to determine the number of carbonyl groups; and tandem MS (MSⁿ), high-resolution tandem MS (HRMS/MS), and GC-MS to obtain structural details of the steroid ring. From the fragmentation studies, we deduced three major fragmentation rules for this class of sulfated steroids. We also show that a combined MS approach is effective for determining structure of steroid metabolites, with important implications for targeted metabolomics in general and for the study of mouse social communication in particular.

Assessing hazelnut allergens by protein- and DNA-based approaches: LC-MS/MS,ELISA and real-time PCR

Hazelnut (Corylus avellana L.) is responsible for a significant part of the allergies related to nuts. Still, it is a very much appreciated nut and as consequence is widely used in all types of processed foods, such as chocolates. Correct food labelling is currently the most effective means of preventing the consumption of allergenic ingredients, namely hazelnut, by the sensitised/allergic individuals. Thus, to verify labelling compliance and to ensure allergic patient protection, the development of highly sensitive methodologies is of extreme importance. In this study, three major methodologies, namely enzyme-linked immunosorbent assays (ELISA), liquid chromatography coupled with mass spectrometry and real-time polymerase chain reaction, were evaluated for their performance regarding the detection of hazelnut allergens in model chocolates. The sandwich ELISA and respective antibodies were in-house developed and produced. With sensitivity levels of approximately 1 mg kg^?1 and limits of quantification of 50–100 mg kg^?1, all the performed methods were considered appropriate for the identification of hazelnut in complex foods such as chocolates. To our knowledge, this was the first successful attempt to develop and compare three independent approaches for the detection of allergens in foods.

Rapid and sensitive analysis of phthalate metabolites, bisphenol A, and endogenous steroid hormones in human urine by mixed-mode solid-phase extraction, dansylation, and ultra-performance liquid chromatography coupled with triple quadrupole mass spectrometry

Steroid hormone levels in human urine are convenient and sensitive indicators for the impact of phthalates and/or bisphenol A (BPA) exposure on the human steroid hormone endocrine system. In this study, a rapid and sensitive method for determination of 14 phthalate metabolites, BPA, and ten endogenous steroid hormones in urine was developed and validated on the basis of ultra-performance liquid chromatography coupled with electrospray ionization triple quadrupole mass spectrometry. The optimized mixed-mode solid phase-extraction separated the weakly acidic or neutral BPA and steroid hormones from acidic phthalate metabolites in urine: the former were determined in positive ion mode with a methanol/water mobile phase containing 10 mM ammonium formate; the latter were determined in negative ion mode with a acetonitrile/water mobile phase containing 0.1 % acetic acid, which significantly alleviated matrix effects for the analysis of BPA and steroid hormones. Dansylation of estrogens and BPA realized simultaneous and sensitive analysis of the endogenous steroid hormones and BPA in a single chromatographic run. The limits of detection were less than 0.84 ng/mL for phthalate metabolites and less than 0.22 ng/mL for endogenous steroid hormones and BPA. This proposed method had satisfactory precision and accuracy, and was successfully applied to the analyses of human urine samples. This method could be valuable when investigating the associations among endocrine-disrupting chemicals, endogenous steroid hormones, and relevant adverse outcomes in epidemiological studies.

A quantitative and comprehensive method to analyze human milk oligosaccharide structures in the urine and feces of infants

Human milk oligosaccharides (HMOs), though non-nutritive to the infant, shape the intestinal microbiota and protect against pathogens during early growth and development. Infant formulas with added galacto-oligosaccharides have been developed to mimic the beneficial effects of HMOs. Premature infants have an immature immune system and a leaky gut and are thus highly susceptible to opportunistic infections. A method employing nanoflow liquid chromatography time-of-flight mass spectrometry (MS) is presented to simultaneously identify and quantify HMOs in the feces and urine of infants, of which 75 HMOs have previously been fully structurally elucidated. Matrix-assisted laser desorption/ionization Fourier transform ion cyclotron resonance MS was employed for high-resolution and rapid compositional profiling. To demonstrate this novel method, samples from mother–infant dyads as well as samples from infants receiving infant formula fortified with dietary galacto-oligosaccharides or probiotic bifidobacteria were analyzed. Ingested oligosaccharides are demonstrated in high abundance in the infant feces and urine. While the method was developed to examine specimens from preterm infants, it is of general utility and can be used to monitor oligosaccharide consumption and utilization in term infants, children, and adults. This method may therefore provide diagnostic and therapeutic opportunities.

Detection of tobacco-related biomarkers in urine samples by surface-enhanced Raman spectroscopy coupled with thin-layer chromatography

The nicotine metabolites, cotinine and trans-3′-hydroxycotinine (3HC) are considered as superior biomarkers for identifying tobacco exposure. More importantly, the ratio of 3HC to cotinine is a good indicator to phenotype individuals for cytochrome P450 2A6 activity and to individualize pharmacotherapy for tobacco addiction. In this paper, a simple, robust and novel method based on surface-enhanced Raman spectroscopy coupled with thin-layer chromatography (TLC) was developed to directly quantify the biomarkers in human urine samples. This is the first time surface-enhanced Raman spectroscopy (SERS) was used to detect cotinine and 3HC in urine samples. The linear dynamic range for the detection of cotinine is from 40 nM to 8 μM while that of 3HC is from 1 μM to 15 μM. The detection limits are 10 nM and 0.2 μM for cotinine and 3HC, respectively. The proposed method was further validated by quantifying the concentration of both cotinine and 3HC in smokers’ urine samples. This TLC-SERS method allows the direct detection of cotinine in the urine samples of both active and passive smokers and the detection of 3HC in smokers.

Trends in liquid-phase microextraction, and its application to environmental and biological samples

Liquid phase microextraction (LPME) is a popular technique for sample pretreatment before the trace determination of target compounds from complex matrices, examples being pesticides in environmental and food samples, or drug residuals in biological samples such as blood or urine. LPME is simple, affordable, easy to operate, and highly sensitive. It is a miniaturized implementation of conventional liquid-liquid extraction in which only a few microliters of solvents are used instead of several hundreds of milliliters. This review focuses on newly developed LPME-based techniques, their application to environmental and biological samples, on their limitations, and on future applications.

Determination of cocaine and methadone in urine samples by thin-film solid-phase microextraction and direct analysis in real time (DART) coupled with tandem mass spectrometry

The use of thin-film solid-phase microextraction (SPME) as the sampling preparation step before direct analysis in real time (DART) was evaluated for the determination of two prohibited doping substances, cocaine and methadone, in urine samples. Results showed that thin-film SPME improves the detectability of these compounds: signal-to-blank ratios of 5 (cocaine) and 13 (methadone) were obtained in the analysis of 0.5 ng/ml in human urine. Thin-film SPME also provides efficient sample cleanup, avoiding contamination of the ion source by salt residues from the urine samples. Extraction time was established in 10 min, thus providing relatively short analysis time and high throughput when combined with a 96-well shaker and coupled with DART technique.

Recent trends in the analysis of amino acids in fruits and derived foodstuffs

The amino acid content of fruit and fruit-derived foods is studied intensely because of the contribution to nutritional value, aroma, taste and health-promoting effects and their possible use as markers of origin and authenticity. In this review, based on 101 references, the most recent trends in the analysis of amino acids are presented: the most important techniques, the different sample treatment procedures (including derivatisation) and the most frequent applications are described and compared. Pertinent publications were retrieved from Scopus and Web of Knowledge database searches lastly performed in February 2012 with the keywords "amino acid", "analysis", "liquid chromatography", "gas chromatography", "electrophoresis", "fruit", and "vegetables"; the time limit was set from the year 2000 onwards. Although amino acids have been analysed in foods for decades, new technical possibilities and advancements have allowed ever-increasing accuracy and targeting of the methods in order to overcome the challenges posed by the complex plant matrices and their high intrinsic variability.