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Metabolism and Bioavailability of Indole 3 Carbinol Powder
- Sep 04, 2019 -


Some observational studies have reported significant associations between high intakes of cruciferous vegetables and lower risk of several types of cancer. Cruciferous vegetables differ from other classes of vegetables in that they are rich sources of sulfur-containing compounds known as glucosinolates (for detailed information, see the article on Cruciferous Vegetables). The potential health benefits of consuming cruciferous vegetables are attributed to compounds derived from the enzymatic hydrolysis (breakdown) of glucosinolates. Among these compounds is indole-3-carbinol (I3C), a compound derived from the degradation of an indole glucosinolate commonly known as glucobrassicin (Figure 1).



Metabolism and Bioavailability

A number of commonly consumed cruciferous vegetables, including broccoli, Brussels sprouts, and cabbage, are good sources of glucobrassicin — the glucosinolate precursor of I3C (see Food sources).

Myrosinase (β-thioglucosidase), an enzyme that catalyzes the hydrolysis of glucosinolates, is physically separated from glucosinolates in intact plant cells. When raw cruciferous vegetables are chopped or chewed, plant cells are damaged such that glucobrassicin is exposed to myrosinase. The hydrolysis of glucobrassicin initially produces a glucose molecule and the unstable aglycone, thiohydroximate-O-sulfonate. The spontaneous release of a sulfate ion results in the formation of another unstable intermediate form, 3-indolylmethylisothiocyanate. This compound easily splits into thiocyanate ion and I3C (Figure 1). In the acidic environment of the stomach, I3C molecules can combine with each other to form a complex mixture of polycyclic aromatic compounds, known collectively as acid condensation products (Figure 2). Some of the most prominent acid condensation products include 3,3'-diindolylmethane (DIM), 5,11-dihydroindolo-[3,2-b]carbazole (ICZ), and a cyclic triindole (CT) (Figure 2). The biological activities of individual acid condensation products may differ from those of I3C (see Biological Activities).

When cruciferous vegetables are cooked, plant myrosinase is inactivated thus the hydrolysis of glucosinolates is prevented. Intact glucosinolates then transit to the colon and are metabolized by human intestinal bacteria. The generation of I3C from glucobrassicin may still occur to a lesser degree in the large intestine, due to the myrosinase activity of colonic bacteria. Thus, when cruciferous vegetables are cooked, I3C can still form in the colon, but I3C-derived acid condensation products are less likely to form in the more alkaline environment of the intestine.

No I3C could be detected in plasma following oral administration of single doses of I3C, ranging from 200 to 1,200 mg, to healthy women at high risk for breast cancer. However, DIM was detected and peaked in plasma around two hours after I3C ingestion, at concentrations from <100 nanograms per milliliter (ng/mL) with oral doses of 400 to 600 mg of I3C up to 500 ng/mL-600 ng/mL with oral doses of 1,000 to 1,200 mg of I3C. All DIM disappeared from the blood within 24 hours.

Formulation strategies, such as the encapsulation of I3C and DIM into nanoparticles or liposomes, are being developed with the aim of increasing the bioavailability and evaluating the safety and efficacy of these compounds in humans.



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