Question: Write a study description for the study titled 'Discovering potential urinary biomarkers of tomato consumption using untargeted metabolomics'.
Answer: Tomatoes are one of the most consumed vegetables in the United States, making them an economically and nutritionally important crop. Previous epidemiological and intervention studies have suggested positive health outcomes associated with tomato consumption. To more conclusively understand the relationship between tomato intake and health benefits, an accurate measurement of tomato consumption is required. Current methods rely on self-report dietary assessments which suffer from recall bias or, plasma lycopene analysis which lacks reliability. Urine sampling allows an objective, non- invasive assessment of dietary intake, resulting in a more robust determination of consumption. Untargeted metabolomics allows for detection of differences in small molecules between groups without preconceived bias, allowing for several classes of compounds to be evaluated as potential biomarkers. The objective of this study was to discover putative urinary biomarkers of tomato consumption using untargeted metabolomics. Healthy subjects (n=11) were evaluated on two separate days: on each day they consumed a controlled diet with either red or tangerine tomato juice with breakfast. Two varieties of tomato juices were included in order to understand how variation in tomato source contributes to intake biomarkers observed. Urine was collected at baseline, 3, 6, 9, 12, and 24 hours. UHPLC-QTOF-MS was used to compare osmolality-normalized urine samples at each time point. Data was collected in both positive and negative modes for comprehensive coverage of metabolites. Raw data was processed using MZmine2. Univariate and multivariate statistical approaches were applied to understand which metabolites were significantly different between urine pre- and-post-tomato consumption. Feature lists were reduced to those that met all three of the following criteria: the compound was significantly different (p<0.05) at every timepoint compared to baseline; the compound had a fold change greater than 2 at every timepoint compared to baseline; the compound had a VIP score greater than 1 for the Partial Least Squares Regression model. We found 99 metabolites in ESI (+) and 46 metabolites in ESI (-) that met these criteria. Online databases were consulted as a first attempt at identifying unknown compounds. Data-independent MS/MS analysis was conducted to generate fragmentation patterns to support feature identification. Authentic standards for naringenin-4-O-glucuronide and naringenin-7-O-glucuronide confirmed their identities in both modes compared to pooled 6 hour urine. Previously reported compounds in urine after tomato consumption, N-caprylhistidinol and N-caprylhistidinol glucuronide were also identified in positive mode with a level 2 confidence, giving more support for future investigation into these compounds as biomarkers. Several compounds from the features of interest reduced lists could be tentatively identified as metabolites that had undergone phase II reactions prior to urinary excretion. Additional studies will need to be done to test the robustness, analytical performance, stability, and reliability of these compounds.