Download Biomarkers of Nutritional Adequacy II

Nutritional
Assessment of
Minerals
How much is too much
How much is not enough
How can we tell the difference
NUTRITIONAL CONCERNS
Evaluating Individual Need
Evaluating Individual Status
Setting Standards for optima
Population Approach
Balance Studies
Experimental
Biomarkers
Functional tests
Traditional Experimental Approaches to
Determine Optimal Levels
Balance Studies
Purified Diets with varying Mineral Content
Standards of Excellence
Balance
Matching what goes in with what goes out
Absorption
A
Excretion
Kout
Kin
B
K1
D
K-1
C
Absorption-Excretion
Retention
Retention
Kin
=
Kout
Balance
Kin
>
Kout
Positive Balance (growth)
Kin
<
Kout
Negative Balance (wasting)
K1
=
K-1
Balance
K1
>
K-1
Positive Balance
K1
<
K-1
Negative Balance
Problems With Balance as a Criterion of Amount
1. End Point is in doubt
2. Excretion is episodic not continuous
3. Multiple connecting pools of the same mineral
4. System adaptation
Experimental and Clinical Approaches
1. Experimental generally applicable to animal studies
a. Semi Purified diet approach
b. Make quantity of mineral in diet limiting
c. Measure rate of growth, changes in a biomarker
d. Assess quantity needed to suppress symptoms
e. Assess quantity needed to reverse symptoms
2. Clinical approaches generally applicable to humans
a. Correlate symptoms with diet record of patient
b. Determine level needed to suppress or reverse pathologies
Standards of Excellence
Correlate amount needed with a high quality food source
Example: Human or Bovine Milk to determine mineral levels for optimal health
Problems:
1. Milk is poor in iron and copper
2. Milk contains whey protein that blocks calcium absorption
Population Based Studies*
Correlate level with risk
Assign values based on a healthy population
Assign ranges for adequate, subadequate, and toxic levels
*Population based studies are risk assessments that rely on
statistics and Gausian Distribution
Traditional Approaches to Determining the Mineral
Status of an Individual
1. Body stores of the mineral
2. Overt response to increased mineral intake
3. Physical signs of a deficiency
a. Stunted growth
b. Overt abnormalities
4. Internal signs of a deficiency - biomarkers
a. Tissue or blood levels
b. Mineral binding proteins levels
5. Functional Assays
a. Enzyme assays
Biomarkers of Nutritional Adequacy
intestine
Dynamic
storage
Plasma
Rapid turnover
Slow turnover
Functional
pool
Excretion
Selenium
A good mineral to assess
Plasma Selenium (8-10 g/L)
1. Glutathione peroxidase (GPX3)
2. Selenoprotein P (plasma), W (white muscle disease)
H
CH3-S-CH2CH2C-COOH
L-Methionine
H
CH3-Se-CH2CH2C-COOH
+ NH3
+ NH3
Selenomethionine
(major dietary source)
Most selenium absorbed goes into muscle and is not under
homeostatic control
But, plasma selenium rises on selenium intake
OTHER BIOMARKERS OF Se
Whole blood, hair and nail (applies to chronological intake)
Example: People in China where Keshan’s disease is prevalent
were assessed for selenium status by hair and nail measurements of
selenium
Plasma Glutathione peroxidase (GPX3) activity.
Advantages
1. Can readily spot values in the deficient range
2. Concern for contamination is minimal
3. Can be done by a rapid automated procedure
Disadvantages
1. Values plateau when intake exceeds optimum
2. Enzyme unstable to storage
3. Laboratory to laboratory variations
4. GPX3 activity is affected by other nutrient deficiencies
Conclusions
The practical minimum requirement for Se is that which prevents Keshan’s
disease
Recommended intakes of Se have been calculated from the requirement for
optimal glutathione peroxidase (GPX3) activity and biologically necessary Se
compounds
Because GPX3 activity plateaus with increasing Se, its difficult to ascribe a
particular level of Se adequacy based on this index
Suboptimal or marginal Se intake may be monitored by GPX3 mRNA, but
this requires further study
2+
Ca
Its all about bone
Biomarkers
Bone Resorption
urinary deoxypyridinoline (DPD)
collagen-type 1 N-telopeptide (NTX)
Other markers of calcium-related bone Formation
serum osteocalcin (OC)
bone-specific alkaline phosphatase (Bone ALP)
Osteocalcin
HA
( a small 49 residue Ca2+-binding protein
that binds tightly to hydroxyapatite)
COOH
CH2
Ca2+
COOH
HOOC
CH
Vitamin K
CH2
CH2
CH
CH
N
C
N
H
O
H
C
O
GLA (carboxy glutamic acid)
Osteocalcin makes up about 10-20% of the non-collagenous protein in
bone. Synthesized by osteoblasts it functions in calcium homeostasis,
binding tightly to hydroxyapatite mineral surfaces. Serum levels of
osteocalcin have been correlated with bone mineral density.
Copper
Acceptable but in need of repair
Currently Accepted Biomarkers
Serum copper
Serum ceruloplasmin
Biomarkers to Consider
Erythrocyte Cu/Zn superoxide dismutase (severe only)
Platelet or lymphocyte cytochrome c oxidase
Biomarkers on the Horizon
PAM (peptidylamide monooxygenase)
Copper chaperone for Superoxide dismutase
Problems with Copper Biomarkers
1. Ceruloplasmin is an acute phase protein elevated by:
Infections
Inflammations
stress
2. Ceruloplasmin levels rise in response to estrogen.
Depression of ceruloplasmin and serum Cu may not be evident
3. Ceruloplasmin synthesis my be suppressed by protein deficiency
4. Serum Cu and ceruloplasmin levels are age dependent
Neonates and children are normally lower than adults
Experimental Data
Feeding postmenopausal women a diet of 0.57 mg Cu/day for 3
months did not depress plasma Cu or ceruloplasmin. Platelet and
leukocyte cytochrome c oxidase activity, however, was suppressed.
But feeding adult men 0.38 mg Cu/day for 6 weeks did depress serum
Cu and ceruloplasmin. (Milne and Nielsen Am. J. Clin. Nutr. 63, 358364, 1996)
Healthy adult volunteers fed 50-60 ug additional Cu/kg/day for 3
months failed to show any rise in superoxide dismutase activity or
serum ceruloplasmin. These concentrations failed to change the
range of Cu homeostasis. (Araya et al. Biometals 16, 199-204,
2003.
Peptidylglycine-alpha
amidating monooxygenase (PAM)
O
Pep
C
H
N
C
H
Active
hormone
O
Cu
PAM
COOH
Pep
C
N
H
H
H
+
HOOC-CHO
glyoxylate
Galanin
Gastrin
(monoaminergic neurons)
(gastric acid)
Vasopressin
(water homeostasis)
Thyrotropin releasing
horomone
(thyroid hormone)
Pancreastatin
Neuropeptide Y
PAM
Cu
(Insulin control)
Gonadotropin releasing
hormone
(sex hormones)
(hunger, obesity)
Calcitonin
(osteoporosis)
Substance P
(emotions)
Experimental data
Mice with a genetic defect in ATP7A, a membrane Cu
transport protein, were observed to have depressed levels of 5 of 6
pituitary peptides identified with PAM activity. All the peptides had the
C-terminal amidated group. (Chei et al, Cell Mol. Biol (Noisy-le-grand)
49, 713-722, 2003)
Liver and erythrocyte copper chaperone for Cu/Zn
superoxide dismutase (CCS) was significantly increased in
rats fed a high Zn diet as compared to low Zn. CCS is a
sensitive measure of Zn-induced Cu deficiency. (Iskandar et
al, Nutr. J. 4, 35, 2005)
2+
Mn
Not a clinical or public health concern
Plasma levels reflect dietary levels: down with restriction, up with
supplements
Molybdenum
Biomarkers for deficiency
1. Decrease urinary sulfate and uric acid
2. Elevated sulfite, hypoxanthine and xanthine
Adenine
Hypoxanthine
Xanthine
Uric Acid
Xanthine oxidase a Mo2+ enzyme
Chromium
A rough History
Biomarkers of Deficiency
Impaired glucose tolerance
Plasma not a good indicator
Urinary excretion controversial
Cumulative Risk
1.0
Risk of
deficit
0.5
Acceptable range of intake
LOAEL
Risk of
excess
NOAEL
% at Risk
EAR
RNI
50%
2.5%
UL
0%
Intake
Safety
Cumulative Risk
1.0
0.5
EAR RNI
Intake
UL