![]() Directly administered isothiocyanates have much higher bioavailability than glucosinolates, reflecting their intrinsic lipophilicity, but more importantly reflecting the need for ingested glucosinolates to first be converted to isothiocyanates prior to absorption and further metabolism. A human homolog of myrosinase has not been described. While all of these metabolites of isothiocyanates have been detected in urine and plasma after ingestion of cruciferous vegetable preparations or isothiocyanates themselves in humans, the mercapturic acids seem to be the most predominant species.Ĭritical to the formation of isothiocyanates is the plant enzyme myrosinase and β-thioglucosidases occurring in the human gastrointestinal microbiome, which convert precursor glucosinolates into bioactive isothiocyanates. The mercapturic acid, isothiocyanate-N-acetyl cysteine (isothiocyanate-NAC) is ultimately formed by the sequential reactions catalyzed by cysteinylglycinase (CGase) and acetyltransferase (AT). This conjugation is followed by the formation of isothiocyanate-Cys-Gly by gamma glutamyltranspeptidase (GTP). The precursor glucosinolates are metabolized into isothiocyanates by the action of plant myrosinase and undergo further metabolism, initially through conjugation with glutathione (GSH) by glutathione S-transferases (GSTs). Metabolism, bioavailability and elimination Therein lies a major challenge for their use in science-driven interventional studies. The types and concentrations of glucosinolates vary significantly between crucifers and are also subject to change based on temperature, age, soil chemistry, solar irradiance, season, genetics, and plant ontogeny. ![]() For example, glucoraphanin (GR) is the glucosinolate precursor of sulforaphane (SFN 1-Isothiocyanato-4-(methylsulfinyl) butane) while gluconasturtiin is the biogenic source of phenylethyl isothiocyanate (PEITC 2-isothiocyanatoethylbenzene). Different glucosinolates produce distinct isothiocyanates. Over 120 different glucosinolates have been identified and it has been conjectured that almost all of them originate from four plant species - Barbarea vulgaris, Arabidopsis thaliana, Eruca sativa and Isatis tinctoria. Hydrolysis of glucosinolates provides an important defense mechanism against pathogen attacks, changes in the climate and other stresses. Nitrogen and sulfur-containing glucosinolates, present in cruciferous vegetables are hydrolyzed, by the action of the plant myrosinase enzyme, into nitriles, indoles, thiocyanates and isothiocyanates upon cutting, cooking, chewing and digestion. Farmers likely started cultivating wild forms of the mustard plant and via artificial selection were able to produce the large variety of genetically similar yet visibly different species that we see today. ![]() The agricultural use of cruciferous vegetables dates back many centuries. A plethora of diverse plants belong to this family - broccoli, watercress, kale, cabbage, collard greens, Brussels sprouts, bok choy, mustard greens and cauliflower to name a few. Isothiocyanates are stress-response chemicals formed from glucosinolates in plants often belonging to the cruciferae family, and more broadly the Brassica genus. The context for the applications of these compounds and plants in evidence-based food and nutritional policy is also evaluated. Results suggest an opportunity to incorporate them, or more likely preparations derived from their source plants, into larger human disease mitigation efforts. Both of these compounds have been used in small human clinical trials, either within food matrices or as single agents, against a variety of diseases ranging from cancer to autism. Herein, clinical trials employing two isothiocyanates, sulforaphane (SFN 1-Isothiocyanato-4-(methylsulfinyl) butane) and phenethyl isothiocyanate (PEITC 2-isothiocyanatoethylbenzene) that are isolated principally from broccoli and watercress, respectively, are summarized and discussed. However, translating their utility to human populations has been both limited and challenging. Isothiocyanates from cruciferous vegetables have been studied extensively in cells and in animals for their disease preventive and therapeutic effects.
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