Identification of Novel Iso-Esculeoside B from Tomato Fruits and LC-MS/MS-Based Food Screening for Major Dietary Steroidal Alkaloids Focused on Esculeosides

Transcriptomics and Metabolomics Reveal Tomato Consumption Alters Hepatic Xenobiotic Metabolism and Induces Steroidal Alkaloid Metabolite Accumulation in Mice

SCOPE

Tomato consumption is associated with many health benefits including lowered risk for developing certain cancers. It is hypothesized that tomato phytochemicals are transported to the liver and other tissues where they alter gene expression in ways that lead to favorable health outcomes. However, the effects of tomato consumption on mammalian liver gene expression and chemical profile are not well defined.

METHODS AND RESULTS

The study hypothesizes that tomato consumption would alter mouse liver transcriptomes and metabolomes compared to a control diet. C57BL/6J mice (n = 11-12/group) are fed a macronutrient matched diet containing either 10% red tomato, 10% tangerine tomato, or no tomato powder for 6 weeks after weaning. RNA-Seq followed by gene set enrichment analyses indicates that tomato type and consumption, in general, altered expression of phase I and II xenobiotic metabolism genes. Untargeted metabolomics experiments reveal distinct clustering between control and tomato fed animals. Nineteen molecular formulas (representing 75 chemical features) are identified or tentatively identified as steroidal alkaloids and isomers of their phase I and II metabolites; many of which are reported for the first time in mammals.

CONCLUSION

These data together suggest tomato consumption may impart benefits partly through enhancing detoxification potential.

Content of Two Major Steroidal Glycoalkaloids in Tomato (Solanum lycopersicum cv. Micro-Tom) Mutant Lines at Different Ripening Stages

Esculeoside A and tomatine are two major steroidal alkaloids in tomato fruit (Solanum lycopersicum) that exhibit anti-inflammatory, anticancer, and anti-hyperlipidemia activities. Tomatine contained in immature tomato fruit is converted to esculeoside A as the fruit matures. To develop new tomato varieties based on the content analysis of functional secondary metabolites, 184 mutant lines were generated from the original cultivar (S. lycopersicum cv. Micro-Tom) by radiation breeding. Ultra-performance liquid chromatography coupled with evaporative light scattering detector was used to identify the mutant lines with good traits by analyzing tomatine and esculeoside A content. Compared with the original cultivar, candidates for highly functional cultivars with high esculeoside A content were identified in the mature fruit of the mutant lines. The mutant lines with low and high tomatine content at an immature stage were selected as edible cultivars due to toxicity reduction and as a source of tomatine with various pharmacological activities, respectively. During the process of ripening from green to red tomatoes, the rate of conversion of tomatine to esculeoside A was high in the green tomatoes with a low tomatine content, whereas green tomatoes with a high tomatine content exhibited a low conversion rate. Using methanol extracts prepared from unripe and ripe fruits of the original cultivar and its mutant lines and two major compounds, we examined their cytotoxicity against FaDu human hypopharynx squamous carcinoma cells. Only tomatine exhibited cytotoxicity with an IC₅₀ value of 5.589 μM, whereas the other samples did not exhibit cytotoxicity. Therefore, radiation breeding represents a useful tool for developing new cultivars with high quality, and metabolite analysis is applicable for the rapid and objective selection of potential mutant lines.

Identification and Spatial Distribution of Bioactive Compounds in Seeds Vigna unguiculata (L.) Walp. by Laser Microscopy and Tandem Mass Spectrometry

The research presents a comparative metabolomic study of extracts of Vigna unguiculata seed samples from the collection of the N.I. Vavilov All-Russian Institute of Plant Genetic Resources. Analyzed samples related to different areas of use in agricultural production, belonging to different cultivar groups sesquipedalis (vegetable accessions) and unguiculata (grain accessions). Metabolome analysis was performed by liquid chromatography combined with ion trap mass spectrometry. Substances were localized in seeds using confocal and laser microscopy. As a result, 49 bioactive compounds were identified: flavonols, flavones, flavan-3-ols, anthocyanidin, phenolic acids, amino acids, monocarboxylic acids, aminobenzoic acids, fatty acids, lignans, carotenoid, sapogenins, steroids, etc. Steroidal alkaloids were identified in V. unguiculata seeds for the first time. The seed coat (palisade epidermis and parenchyma) is the richest in phenolic compounds. Comparison of seeds of varieties of different directions of use in terms of the number of bioactive substances identified revealed a significant superiority of vegetable accessions over grain ones in this indicator, 36 compounds were found in samples from cultivar group sesquipedalis, and 24 in unguiculata. The greatest variety of bioactive compounds was found in the vegetable accession k-640 from China.

Steroidal alkaloid biosynthesis is coordinately regulated and differs among tomatoes in the red-fruited clade

The tomato (Solanum spp.) clade of Solanaceae features a unique assortment of cholesterol-derived steroidal alkaloids. However, little quantitative data exists reporting the profile and concentration of these alkaloids across diverse fruit germplasm. To address the lack of knowledge regarding the chemical diversity, concentration, and genetic architecture controlling tomato steroidal alkaloids, we quantitatively profiled and genotyped two tomato populations representing diversity in the red-fruited clade. We grew 107 genetically diverse fresh market, processing, landrace, and wild tomato in multiple environments. Nine steroidal alkaloid groups were quantified using ultra-high performance liquid chromatography tandem mass spectrometry. The diversity panel and a biparental population segregating for high alpha-tomatine were genotyped to identify and validate quantitative trait loci (QTL) associated with steroidal alkaloids. Landraces and wild material exhibited higher alkaloid concentrations and more chemical diversity. Average total content of steroidal alkaloids, often dominated by lycoperoside F/G/esculeoside A, ranged from 1.9 to 23.3 mg 100 g^-1 fresh wt. across accessions. Landrace and wild cherry accessions distinctly clustered based on elevated concentrations of early or late-pathway steroidal alkaloids. Significant correlations were observed among alkaloids from the early and late parts of the biosynthetic pathway in a species-dependent manner. A QTL controlling multiple, early steroidal alkaloid pathway intermediates on chromosome 3 was identified by genome-wide association studies (GWAS) and validated in a backcross population. Overall, tomato steroidal alkaloids are diverse in the red-fruited clade and their biosynthesis is regulated in a coordinated manner.