An Integrated Metabolomics Study of Glucosinolate Metabolism in Different Brassicaceae Genera

Glucosinolates are a group of plant secondary metabolites that can be hydrolyzed into a variety of breakdown products such as isothiocyanates, thiocyanates, and nitriles. These breakdown products can facilitate plant defense and function as attractants to natural enemies of insect pests. As part of the diet, some of these compounds have shown cancer-preventing activities, and the levels of these metabolites in the edible parts of the plants are of interest. In this study, we systematically examined variations in glucosinolates, their precursors, and their breakdown products in 12 commonly consumed vegetables of the Brassicaceae family with gas chromatography—quadrupole time-of-flight mass spectrometer (GC-Q-TOF/MS), liquid chromatography–quadrupole time-of-flight mass spectrometer (LC-Q-TOF/MS), and liquid chromatography—triple quadrupole mass spectrometer (LC-QQQ/MS), using both untargeted and targeted approaches. The findings were integrated with data from literature to provide a comprehensive map of pathways for biosynthesis of glucosinolates and isothiocyanates. The levels of precursor glucosinolates are found to correlate well with their downstream breakdown products. Further, the types and abundances of glucosinolates among different genera are significantly different, and these data allow the classification of plants based on morphological taxonomy. Further validation on three genera, which are grown underground, in damp soil, and above ground, suggests that each genus has its specific biosynthetic pathways and that there are variations in some common glucosinolate biosynthesis pathways. Our methods and results provide a good starting point for further investigations into specific aspects of glucosinolate metabolism in the Brassica vegetables.

A metabolic pathway for glucosinolate activation by the human gut symbiontBacteroides thetaiotaomicron

ABSTRACTDiet is the largest source of plant-derived metabolites that influence human health. The gut microbiota can metabolize these molecules, altering their biological function. However, little is known about the gut bacterial pathways that process plant-derived molecules. Glucosinolates are well-known metabolites in brassica vegetables and metabolic precursors to cancer-preventive isothiocyanates. Here, we identify a genetic and biochemical basis for isothiocyanate formation byBacteroides thetaiotaomicron,a prominent gut commensal species. Using a genome-wide transposon insertion screen, we identified an operon required for glucosinolate metabolism inB. thetaiotaomicron.Expression of BT2159-BT2156 in a non-metabolizing relative,Bacteroides fragilis, resulted in gain of glucosinolate metabolism. We show that isothiocyanate formation requires the action of BT2158 and either BT2156 or BT2157in vitro. Monocolonization of mice with mutantBtΔ2157showed reduced isothiocyanate production in the gastrointestinal tract. These data provide insight into the mechanisms by which a common gut bacterium processes an important dietary nutrient.

Effect of jasmonic acid on glucosinolate metabolism in different organs of broccoli sprouts

Edible sprouts, especially Brassica sprouts, contain high levels of health-promoting compounds. Exogenous elicitors have been used as strategies to improve the nutraceutical quality of Brassica sprouts. In this study, effects of jasmonic acid (JA) treatment on growth, the levels of glucosinolates and isothiocyanates, as well as myrosinase activity in different organs of broccoli sprouts were investigated. JA treatment markedly increased the contents of glucosinolates (GSLs), especially glucoraphanin, glucobrassicin and neoglucobrassicin in broccoli sprouts. However, gluconapin was not affected even decreased by JA treatment. Cotyledon, hypocotyl and root obtained the different results in induction of GSLs. Among these, neoglucobrassicin obtained the highest enhancement in three organs. Myrosinase activity in cotyledon of broccoli increased after JA treatment, while decreased in hypocotyl. Three concentrations of JA all significantly increased sulforaphane and isothiocyanates formation in cotyledon, hypocotyl and root of broccoli sprouts. Application of 100 μM JA led to the highest myrosinase activity, the least gluconapin and the most sulforaphane and isothiocyanates in cotyledon, as well as the most isothiocyanates in root. These results indicated that JA treatment could be an effective way to improve the cancer-prevention benefits of broccoli sprouts via enhancing sulforaphane and total isothiocyanates.