Phytonutrients - Isothiocyanates

Question 1

Isothiocyanates

Answer 1

Isothiocyanates (ITCs) are biologically active breakdown products of the sulphur-rich compounds, glucosinolates:
* Each glucosinolate forms a different ITC when hydrolysed e.g.
o Glucoraphanin forms sulforaphane.
o Sinigrin forms allyl isothiocyanate.
glucosinolates= natural components of many pungent plants

Question 2

Food sources:

Answer 2

Food sources:
* Cruciferous vegetables (e.g. broccoli, cabbage, kale, Brussel sprouts).
* Horseradish.
* Mustard.

Question 3

Bioavailability:

Answer 3

Myrosinase is the enzyme that catalyses the hydrolysis of glucosinolates to form ITCs.
* It is stored in another compartment of the cell and is only released when the cell wall is damaged e.g. by chopping, slicing, chewing.
* Heat / cooking inactivates myrosinase, though gut bacteria are able to hydrolyse glucosinolates to some extent.
* Cooking, particularly boiling or stir-frying also decreases glucosinolate content. Steaming is a better cooking method.
* Boiling cruciferous vegetables for 9–15 minutes has shown to reduce glucosinolate content by 18-59%.

Question 4

Total glucosinolate content of selected foods (food table):

Answer 4

Food: Serving: Total glucosinolates (mg):
Brussels sprouts: ½ cup 104
Garden cress: ½ cup 98
Mustard greens: ½ cup chopped 79
Kale: 1 cup chopped 67
Turnip: ½ cup cubes 60
Cabbage savoy: ½ cup chopped 35
Watercress: 1 cup chopped 32
Cabbage red: ½ cup chopped 29
Broccoli: ½cup chopped 27
Cauliflower: ½ cup chopped 22

Question 5

Functions:

Answer 5

• Antioxidant/ anti-inflammatory
• Liver detoxification
• Anti-cancer

Question 6

Antioxidant/
anti-inflammatory:

Answer 6

Functions:
* Switches on genes coding for cellular antioxidant defence mechanisms.
* Increase tissue glutathione levels.
* Inhibit pro-inflammatory signaling molecules and cytokines.
Therapeutic uses:
* Reduce the risk of chronic diseases including: diabetes, heart disease, cancer, neurodegenerative disease, autoimmune conditions.

Question 7

Liver detoxification:

Answer 7

Functions:
* Potent inducer of phase II detoxification enzymes; down regulates phase I enzymes.
Therapeutic uses:
* Reduce the risk of chronic diseases including: diabetes, heart disease, cancer, neurodegenerative disease, autoimmune conditions.

Question 8

Anti-cancer:

Answer 8

Therapeutic uses:
* Chronic inflammation and ↑ oxidation, along with poor detoxification pathways are key factors in cancer development.
* ITCs have been shown to:
o Protect DNA from carcinogenic damage and reduce cell proliferation by regulating apoptosis.
o Inhibit angiogenesis and tumour metastasis.
o Enhance glutathione S-transferase —phase II enzymes involved in the detoxification of carcinogens.
o ↓ the secretion of inflammatory signalling molecules and decrease binding of the pro-inflammatory NF-kB.
NF-kB= nuclear factor kappa B

Question 9

Dosage:

Answer 9

• Glucosinolates are present in relatively high concentrations in commonly consumed portions of cruciferous vegetables.
• For example ½ cup of raw broccoli can provide more than 25 mg of total glucosinolates (Retention of glucosinolates is good if vegetables are lightly steamed (up to two minutes)).
• Consumption of at least five weekly servings (80 g per serve) of cruciferous vegetables has been associated with significant reductions in cancer risk.
• There are no specific recommendations for supplement dosages.

Question 10

Safety:

Answer 10

• Dietary sources are generally regarded as safe.
• Safety of purified isothiocyanates / supplements during pregnancy and lactation have not been established.
• Some glucosinolates degrade to goitrin and thiocyanate, compounds referred to as goitrogens. They decrease the thyroids uptake of iodine. In those with low thyroid function ensure good intake of iodine and limit brassica vegetables to 1‒2 serves / day.

Question 11

Interactions:

Answer 11

• ITCs are not known to interact with any pharmaceutical drugs.