Glucosinaltes Flashcards
What are glucosinolates
Type of phytochemical
Large family of sulfur containing compounds found in capparales family (includes BRassica)
- foods: broccoli, Brussels sprouts, cabbage, kale
Chemically stable and inactive (have to be chewed)
Sequestered within subcellular compartments throughout the plant
Glucosinolate structure
Thioglycosidic link “makes it glycoside”
Sulfate group
- acidic properties
- can occur as anions balanced by cation (potassium)
R group
- AA (defines the type)
Glucosinolate classification
According to AA precursor
- Aliphatic
- Aromatic
- Indole
Approx 130 glucosinolates but not all in human diet
Glucosinolates food composition database
Used for estimation of dietary intakes of glucosinolates
Important to advance knowledge of phytochemicals in relation to disease risk
Data allow for more thorough and accurate quantification of Glucosinolate intakes
Glucosinolate metabolism
Broken down by MYROSINASE
- located in plant vacuoles in my rosin cells
Myrosinases and glucosinolates are separate within the plant
They’re brought in contact by
- tissue damage
- harvesting
- food processing
- chewing
(All disruption)
MYROSINASE how it works
MYROSINASE cleaves the thioglycosidic bond to yield the aglycone
- aglycone now unstable and degrades spontaneously
Non enzymatic rearrangement
- several breakdown products
- dependent on glucosinolate side chain (r group)
- dependent on pH
- sulfate is released
Breakdown products of Glucosinolate metabolism
Can have toxicological effects
Important role in plant defence
Responsible for some bitter tastes
Potential anti carcinogenic effect in humans
Isothiocyanates
One of most well researched Glucosinolate breakdown products
Most anti cancer potential
Types:
- PEITC phenethyl isothiocyante
- BITC benzoyl isothiocyanate
- sulforaphane
Glucosinolate bioavailability
Largely affected by food prep methods
- considerable loss can occur during cooking
MYROSINASE inactivated by cooking
- less breakdown products
Colonic bacteria can also produce myrosinase
- we know because of urinary isothiocyantes even after cooked brassica veggies which destroys the MYROSINASE in the food
Therefore we CAN obtain glucosinolate breakdown products from cooked brassica veggies
Steamed vs fresh broccoli study
Amount of isothiocyanate in urine and blood THREE times higher in fresh broccoli vs steamed
There was still some but not a lot of isothiocyanates with cooked broccoli
- likely due to hydrolysis of glucosinolates by intestinal microflora enzymes
Problem applies to broccoli supplements: they don’t contain the MYROSINASE therefore rely on microbial conversion
Broccosprouts fix this problem
- urine SFN and ERN much higher compared to supplements
Isothiocyanates effect on carcinogen metabolism
Chemoprotection
Increases body’s enzyme defence system against carcinogens
Modulates the balance between phase one and two enzymes (great biomarker for cancer)
- in liver and epithelial cells
Phase One and Two enzymes
First line of defence against carcinogens
- want enough phase two to follow phase one
Phase two:
- the detox enzyme (GST)
- metabolize breakdown products and epoxides
- readily excreted in urine
Diet often can increase both P1 and 2 but only want P2 increased
Cancer protective effects of Glucosinolate breakdown products
- Modulation of phase one and two enzymes
- increases phase two enzymes WITHOUT an increase of P2 - Indirect antioxidant effects
- - increases phase two enzymes - Induces apoptosis
- of cancer cells in vitro - Block cell cycle
- inhibits growth of cancer cells - Modifier of estrogen metabolism
- discussed later+ important
Brassica veggies and cancer prevention
Evidence indicates brassica veggies related to reduced cancer risk (lung, stomach, colon, rectum)
Urinary levels of Isothiocyanates also inversely related to various types of cancer
(Need to make sure this breakdown product is produced)
Another Glucosinolate breakdown product of interest
Indole-3-carbinol
- also induces phase two enzymes
- research also shows effects on estrogen metabolism
- changes in urinary estrogen metabolites
- effects related to reduced risk of breast cancer
