A metabolomic evaluation of the phytochemical composition of tomato juices being used in human clinical trials
Introduction
Epidemiological research has shown a correlation between increased consumption of tomato products and a decreased risk of certain diseases, including prostate cancer (Giovannucci, 1999, Hadley et al., 2002). This relationship has also been observed in studies with animals fed diets supplemented with tomatoes. However, we still know little about the mechanism behind this observed protective effect. Much research has focused on the tomato carotenoid lycopene as a potential bioactive compound due to its antioxidant capacity and abundance in the tomato. Lycopene is an efficient singlet oxygen quencher and free radical scavenger (Böhm et al., 2002, Di Mascio et al., 1989) and there is evidence suggesting that these properties could translate into a protective effect in vivo. Additionally, lycopene has been shown to accumulate in human tissues, such as the prostate, where it may have some biological effect (Clinton et al., 1996).
Research has traditionally focused on the red tomato, but in a recent human clinical study conducted by our group, lycopene from the juice of a unique tangerine tomato variety was found to be 8.5 times more bioavailable than lycopene from a red tomato juice (Cooperstone et al., 2015). Tangerine tomatoes are orange in color, which is a result of lycopene being biosynthesized in a tetra-cis (7Z, 9Z, 7′Z, 9′Z) geometrical configuration rather the all-trans configuration found in red tomatoes. This conformational change causes a shift in the absorption spectrum of lycopene, resulting in a marked color change. The enhanced bioavailability of lycopene from the tangerine tomato has been attributed in part to the lipid dissolved state of tetra-cis-lycopene in the tomato compared to the crystalline form of all-trans-lycopene.
Given the significant differences in lycopene bioavailability between the red tomato and the tangerine tomato, our group is interested in evaluating whether this translates into a difference in biological activity. We are actively using juices developed from red and tangerine tomatoes as health promoting foods in human clinical interventions with prostate cancer patients. While we know that these two tomato juices differ in their carotenoid profiles, it is unknown how they differ in other potentially bioactive phytochemicals. Tomatoes contain many phenolic compounds, including flavonoids, such as naringenin and kaempferol, and hydroxycinnamic acids, such as ferulic acid and coumaric acid (Moco et al., 2006). These compounds have been shown to possess considerable bioactivity in a variety of test systems (Erlund, 2004, Heim et al., 2002, Meyer et al., 1998) and therefore, it is reasonable to believe that they contribute to the health benefits associated with tomatoes. In fact, some research has demonstrated an enhanced protective effect when feeding whole tomatoes versus lycopene alone (Boileau et al., 2003, Canene-Adams et al., 2007). These data suggest a synergistic effect between the carotenoids and other phytochemicals in tomatoes. In order to understand better any biological effects observed in clinical trials with food products, it is paramount to have a more comprehensive understanding of the chemical differences between the products being evaluated.
The objective of this study is to use a liquid-chromatography mass spectrometry (LC–MS)-based metabolomics approach to identify phytochemical and metabolite differences in both the polar and lipophilic fractions of the red and tangerine tomato juices. Untargeted metabolomic profiling allows for the unbiased detection and differential analysis of thousands of phytochemical species belonging to a number of different compound classes in a single analysis. This approach has been used to characterize phenolic compounds and other secondary metabolites in tomatoes (Gómez-Romero et al., 2010, Moco et al., 2006) and to evaluate the effects of thermal processing on tomato phytochemicals (Capanoglu, Beekwilder, Boyacioglu, Hall, & de Vos, 2008). We hypothesize that a metabolomics approach will allow us to rapidly characterize a broad array of phytochemical differences with potential biological relevance in food-based clinical trials.
Section snippets
Chemicals and standards
All solvents were from Fisher Scientific (Pittsburgh, PA, USA). Methyl tert-butyl ether (MtBE) and acetone were HPLC grade, hexanes was Optima grade, and acetonitrile (ACN) was Optima LC/MS grade. Methanol (MeOH) and water were either HPLC grade (extraction solvents) or Optima LC/MS grade (LC/MS analysis). Ammonium acetate was from J.T. Baker (Phillipsburg, NJ, USA) and formic acid was from Fisher Scientific. Chlorogenic acid standard was purchased from Cayman Chemical (Ann Arbor, MI, USA),
Results and discussion
An untargeted metabolomics approach was taken to broadly evaluate and characterize carotenoid and other phytochemical differences between red and tangerine tomato juices designed for clinical interventions. Metabolomics has been used as a tool for studying food composition in a variety of studies, including those focused on cultivar variation (Dobson et al., 2008, Gómez-Romero et al., 2010), food quality (Johanningsmeier & McFeeters, 2011), and product adulteration (Jandrić et al., 2014,
Conclusions
The objective for using an unbiased or untargeted metabolomics approach was to capture a greater number of phytochemical differences between two tomato products being used in human clinical trials than could be accomplished with conventional targeted approaches. Through our analyses we were able to not only detect differences in carotenoid composition, but we were also able to detect and identify other phytochemical similarities and differences that we would have likely missed had we focused on
Conflict of interest
The authors declare no conflict of interest.
Acknowledgments
We would like to acknowledge David Francis, Ph.D. (Department of Horticulture and Crop Science, The Ohio State University) for providing the tomatoes used in this study and Dan Cuthbertson, Ph.D. (Agilent Technologies) for his assistance with the metabolomics analysis. This study was performed within the Nutrient and Phytochemical Analytics Shared Resource under The Ohio State University Comprehensive Cancer Center (NIH P30 CA016058).
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