Metabolism of sinigrin (2-propenyl glucosinolate) by the human colonic microflora in a dynamic in vitro large-intestinal model

Abstract

Cruciferous vegetables, such as Brassica, which contain substantial quantities of glucosinolates, have been suggested to possess anticarcinogenic activity. Cutting and chewing of cruciferous vegetables releases the thioglucosidase enzyme myrosinase, which degrades glucosinolates to isothiocyanates and other minor metabolites. Cooking of cruciferous vegetables inactivates the myrosinase enzyme, allowing intact glucosinolates to reach the large intestine, where they can be degraded by the indigenous microflora into isothiocyanates. This local release of isothiocyanates may explain the protective effect of cruciferous vegetables on the colon epithelium. However, little is known about the amounts and identities of glucosinolate metabolites produced by the human microflora. The production of allyl isothiocyanate from sinigrin was investigated in a dynamic in vitro large-intestinal model, after inoculation with a complex microflora of human origin. Sinigrin and allyl isothiocyanate concentrations were analysed in the lumen and dialysis fluid of the model. Peak levels of allyl isothiocyanate were observed between 9 and 12 h after the addition of sinigrin. The model was first set up with a pooled and cultured human microflora, in which 1 and 4% of, respectively, 1 and 15 mM sinigrin, was converted into AITC. However, the conversion rate was remarkably higher if different individual human microflora were used. Between 10% and 30% (mean 19%) of the sinigrin was converted into allyl isothiocyanate. The results of this study suggest that allyl isothiocyanate is converted further into other, yet unknown, metabolites.

Glucosinolates inBrassicavegetables: The influence of the food supply chain on intake, bioavailability and human health

“…They showed that the bioavailability of isothiocyanates from fresh broccoli is approximately three times higher than that from steamed broccoli, in which myrosinase is inactivated. The microbial gut flora is also capable of forming isothiocyanates but the efficiency is lower compared to the action of plant myrosinase [272]. Food products containing active myrosinase, like sprouting Brassica vegetables and shortly cooked Brassica vegetables are preferred.…”

Hydrolysis of Glucosinolates to Isothiocyanates after Ingestion of Raw or Microwaved Cabbage by Human Volunteers

“…The processes of ingestion and digestion of brassica vegetables lead, therefore, to glucosinolate hydrolysis. Myrosinase activity has also been demonstrated in the human gut microflora (3,4). Glucosinolate hydrolysis can lead to a range of breakdown products, depending on the conditions under which hydrolysis occurs and the structure of the parent glucosinolate.…”

Apolipoprotein E genotype affects tissue metallothionein levels: studies in targeted gene replacement mice

“…AITC is derived from its precursor sinigrin (a glucosinolate) following myrosinase-catalysed hydrolysis (Krul et al 2002;Bhattacharya et al 2010). AITC directly interacts with sulfhydryl groups (Zhang et al 2005) and predominantly conjugates with cysteine residues .…”