Antioxidant bioavailability issues

1
Antioxidant bioavailability issues

• Frank J Kelly
• Kings College, London

2
Adequate antioxidant intake is important to
prevent this happening
3
Plasma vitamin C concentrations in 80 healthy
subjects
30

• Mean 79 ? 28 µM
• min 17.9 µM
• max 165.9 µM

20
Number
10
0
160
140
120
100
80
60
40
20
vitamin C (mM)
4
Plasma vitamin E in two subjects
5
Subject A has lower alpha-tocopherol levels
than subject B because

• Lower dietary intake of ?-tocopherol
• Decreased absorption of ?-tocopherol
• Decreased hepatic processing of ?-tocopherol
• Decreased VLDL carrying capacity of ?-tocopherol
• Increased plasma clearance of ?-tocopherol
• Increased utilisation rate for ?-tocopherol

6
Stable isotope technology
CH3
HO
D0
CH3
CH3
CH3
CH3
CH3
O
CH3
CH3
CD3
HO
CH3
CH3
CH3
D6
CH3
CD3
O
CH3
CH3
CD3
D9
HO
CH3
CH3
CH3
CH3
O
CD3
CH3
CD3
7
Analytical approach
Plasma RBC buccal cells
Lipid extraction
Collect ?-toc peak?
HPLC
Blood
BC
add Internal Std
add Internal Std
GC/MS analysis of do,d6 and d9 ?-toc
Extract silylatite
8
Biokinetics of ?-tocopherol uptake
10
8
6
deuterated tocopherol (uM)
plasma
4
2
erythrocytes
0
0
10
20
30
40
50
60
time (hours)
9
What influences blood ?-tocopherol levels?
Roxborough et al. Free Rad Res, 2000
10
What influences blood ?-tocopherol levels?

Intra-individual variation
Roxborough et al. Free Rad Res, 2000
11
Roxborough et al. Free Rad Res, 2000
12
tocopherols
CH3
R1
5
6
HO
CH3
CH3
CH3
tocotrienols
7
CH3
O
R2
8
CH3
CH3
Vitamin E collectively describes 2 groups of
stereo-isomers

13
Question 2. Why does ?-tocopherol dominate in
vivo?
14
Question 1. Why does ?-tocopherol dominate in
vivo?
10
8
6
deuterated tocopherol (uM)
4
?-tocopherol
2
?-tocopherol
0
0
10
20
30
40
50
60
time (hours)
15
Question 1. Why does ?-tocopherol dominate in
vivo?
16
Dietary vitamin E
pancreatic esterase bile acids
intestine
CM
CM catabolism
CM remnant

excretion
plasma
peripheral tissue
lipoproteins
17
?-tocopherol metabolism

• Oxidative metabolism
• Non-oxidative metabolism

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ROO .
tocopheroxyl radical
alkyldioxytocopherone
H2O
tocopherylquinone
Ring opening side chain oxidation
-2e
2e
side chain oxidation
tocopherylhydroquinone
tocopheronic acid
O
O
2,5,7,8-tetramethyl-2(2-carboxy ethyl)-6-hydrochr
oman (chroman acid, CEHC)
O
Tocopheronolactone (quinone lactone, QL)
19
C
H
3
O
Ion 276
O
O
C
H
3
H
O
C
3
C
H
3
9.00
9.50
C
D
3
Ion 279
O
O
O
C
H
3
O
H
C
3
C
H
3
Abundance
9.50
9.00
Ion 282
?-quinone lactone
9.50
9.00
Ion 285
9.50
9.00
Time (mins)
20
C
H
Ion 422
3
H
O
120000
O
H
60000
O
H
C
3
C
H
3
O
C
H
3
0
11.00
11.50
Ion 425
120000
60000
0
11.00
11.50
?-chroman acid
Abundance
Ion 428
120000
60000
0
11.00
C
D
3
Ion 43
H
O
120000
O
H
O
60000
D
C
3
C
H
3
O
C
D
3
0
11.00
11.50
Time (mins)
21
Question 3. How is ?-tocopherol metabolised?
22
Inter-individual variation in vitamin E metabolism
Chroman Acid
Lactone
7
0.5
6
0.4
5
0.3
4
(umol/g creatinine)
3
0.2
2
0.1
1
0
0
23
Does ?-tocopherol uptake/metabolism change in
those taking supplements?
Plasma concentrations of ?-tocopherol ? only
2-3-fold with supplements

• where does the rest go?

24
Supplementation protocol
D6-?-tocopherol
D3-?-tocopherol
Pre-supplementation
28 days supplementation
Post-supplementation
25
Does ?-tocopherol uptake/metabolism changein
those taking supplements?
?-tocopherol content (umol/mmol cholesterol)
26
Does ?-tocopherol uptake/metabolism change in
those taking supplements?
6
4
2
a
0
(µmol/mmol Cholesterol)
Deuterated -tocopherol
-2
0
12
27
51
0
12
27
51
Pre-supplementation
Post-supplementation
Sample time (hours)
a
a
200 mg
-tocopherol
400 mg
-tocopherol
Placebo
27
What is happening to the old ?-tocopherol ?

• Being moved into tissue (for storage) ?
• Being excreted from the body ?

28
RBC ?-tocopherol content
30
25
20
µmol/L
15
10
5
(µmol/L)
0
0
14
28
Days supplementation
29
Where does the excess ?-tocopherol go?
?-CEHC
Days of supplementation
30
Summary Uptake and metabolism of ?-tocopherol
dietary vitamin E
supplements
GI tract
CM remnant
tocopherol metabolites
tocopherols
?-TTP
Discrimination in favour of ?-toc
excretion
excretion
VLDL
Plasma
?
Vitamin C
oxidation
PERHIPHERAL TISSUES