Glucosinolates Flashcards
1
Q
What are glucosinolates?
A
- Type of phytochemical
- Large family of sulfur-containing compounds
- Over 100 types identified
2
Q
What are the food sources of glucosinolates?
A
Cruciferous vegetables
Includes Brassica family
- Broccoli
- Cabbage
- Brussel sprouts
- Cauliflower
- Kale
3
Q
Is there a database for glucosinolates? What are the implications?
A
- There is a specific one developed
- Allows for thorough and accurate quantification of glucosinolate intakes
- Good as starting point, but note that it is the breakdown products that produce effects
4
Q
What is the structure of glucosinolates?
A
- Glucose attached to sulfur via thioglycosidic link
- Exists in plant as a glycoside - Sulfate group
- Imparts strong acidic properties
- Often counterbalanced with potassium (cation) - R-group is derived from amino acids and classifies glucosinolate
5
Q
What are the classifications of glucosinolates?
A
- Aliphatic
- Aromatic
- Indole
6
Q
How are glucosinolates metabolized?
A
- In the plant, sequestered within subcellular compartments (chemically stable and biologically inactive)
- To activate, they are broken down by myrosinases (located in plant vacuoles called myrosin cells separate from glucosinolates)
- Brought into contact by: tissue damage (caused by pests), harvesting, food processing, chewing
- Myrosinases cleave thioglycosidic bond to yield the aglycone (unstable and degrades non-enzymatically and spontaneously)
- Releases sulfate and breakdown products
7
Q
What are breakdown products of glucosinolates? What are they responsible for?
A
- Biologically active; may have anti-carcinogenic effect in humans
- Important roles in the plant defence system against insects, fungi, microorganisms
- Responsible for the bitter taste of certain condiments (horseradish, mustard)
- Responsible for the characteristic flavour of numerous vegetables
8
Q
Discuss bioavailability of glucosinolates.
A
- Depends on food preparation methods
- Myrosinase is inactivated by cooking ⟶ less conversion of glucosinolates to breakdown products
- Light cooking will not completely denature all myrosinases
- Gut bacteria can also produce myrosinases
- Studies show urinary isothiocynates following Brassica veggie consumption even after myrosinase was completely destroyed by cooking
- Therefore, CAN obtain breakdown products from cooked veggies
9
Q
Are broccoli supplements efficient in producing isothiocynate from glucosinolates?
A
- No
- Many supplements do not contain myrosinase enzymes
- You must rely on microbial conversion
10
Q
What are isothiocynates and its major types?
A
- Well-researched breakdown product; lots of evidence supporting inhibition of cancer
- May increase body’s enzyme defense system against carcingens
- PEITC (phenetyl isothiocynate)
- BITC (benzyl isothiocynate)
- Sulforaphane
11
Q
What are the 5 cancer-protective mechanisms of isothiocynates?
A
- Modulates Balance of Phase I and II Enzymes
- Balance is a biomarker for cancer risk; we ideally want higher amounts of Phase II enzymes - Indirect Antioxidant Effects
- Increases phase II enzymes - Induces Apoptosis of Cancer Cells
- Blocks Cell Cycle
- Inhibits growth of cancer cells
12
Q
What are phase I enzymes?
A
- “Activation enzymes”
- Eg. cytochrome p450
- Metabolize lipophilic pro-carcinogens to make them water-soluble for phase II enzymes to act on
- In the process can be converted to carcinogenic intermediates
13
Q
What are phase II enzymes?
A
- “Detoxification enzymes”
- Eg. glutathione transferase; GST
- Metabolize phase I-generated epoxides to form water-soluble, inactive conjugates that are excreted in urine
14
Q
What is Indole-3-Carbinol and why is it unique?
A
- Another glucosinolate breakdown product of interest
- Shown to do all cancer-protective mechanisms as isothiocynates
- BUT unique because can modify estrogen metabolism
15
Q
How does Indole-3-Carbinol modify estrogen metabolism?
A
- Changes in urinary /blood estrogen metabolites
- Increased ratio of urinary [excreted] 2-OH estrogen (protective) to 16-OH estrogen metabolites (bad)
- Good biomarker of breast cancer risk
