OVERVIEW OF TRACE METALS [email protected] S.pdf

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1. OVERVIEW OF TRACE
METALS/ELEMENTS
DR MRS SANDRA A N A CRABBE
MGCP, MBCHB

2. OBJECTIVES (Learning outcomes)
•How to define a trace element.
•The importance clinically of trace elements, particularly Cu, Zn & Se
•The main proteins binding trace elements and their function.
•How trace elements are controlled (homeostasis) within the body.
•Understand the importance of trace elements in human health.
•Laboratory assessment of trace element status

3. OUTLINE

4. Periodic Table showing level of ‘essentiality’

5. INTRODUCTION
•Mammals like humans are thought to use only 25 of the 116 known
elements 19 of which are considered essential
•With the exception of oxygen, these elements are not found as ‘pure’
elements.
•They are either dissolved in water in an ionic form, such as
sodiumionsand chloride ions, or as parts of largemolecules, such
ashaemoglobin.
•Just 4 of these –carbon(C), oxygen (O),hydrogen(H)
andnitrogen(N) –make up about 96% of the human body.

6. 3 Main groups of essential elements (based
on amounts)

7. INTRODUCTION
•The maintenance of normal health requires provision in the diet of
adequate protein, energy substrates, vitamins and also of various
inorganic salts and trace elements
•Trace metals are inorganic micronutrients that are present in very low
concentrations in body fluids and tissues.
•Those present in body fluids (µg/L) and in tissue (mg/kg) are, widely
referred to as "trace elements"
•Those found at ng/L or ug/kg as the "ultratraceelements”
•Their dietary requirements are in μgto mg/day.

9. INTRODUCTION
•They are required for the proper functioning of many enzymes and
other proteins.
•Their deficiency can lead to specific signs and symptoms.
•Sometimes the deficiency is not dietary but due to transport or
recycling defects.
•In humans, metals are obtained exogenously and require intestinal
absorption and transport to the appropriate intra-cellular
compartment for function

10. INTRODUCTION
•An element is considered essentialwhen the signs and symptoms
induced by a deficient diet are uniquely reversed by an adequate
supply of the particular trace element
•For iron, iodine, cobalt (as cobalamins), selenium, copper, and zinc,
there are clinical examples of reversible deficiency disease. Enough is
known about the biochemical functions of these elements to explain
their importance in human nutrition.
•For others, such as manganese, chromium, molybdenum, and
vanadium, their importance remains to be fully accepted in clinical
practice

11. INTRODUCTION
•Other elements, such as bromine, fluorine, cadmium, lead, strontium,
lithium and tin, have been claimed by at least one investigator to be
essential for one or more animal species, as demonstrated by dietary
deprivation studies
•It is important to note that several of these elements are toxic at
higher concentrations

12. Some trace elements and their function
Element Function
Chromium Component of chromodulin(potentiates insulin)
Cobalt Component of vitamin B
12
Copper Cofactor of cytochrome oxidase
Fluorine Present in bone and teeth
Iodine Component of thyroid hormones
Iron Component of haem pigment
Manganese Cofactor for several enzymes
Molybdenum Cofactor for xanthine oxidase
Selenium Cofactor for glutathione oxidase
Silicon Present in cartilage
Zinc Cofactor for many enzymes

13. Additional classification
Pharmacologically beneficial: These include
•fluoride used for protection against dental caries,
•lithium salts used in the treatment of manic depression,
•strontium ranelate for the treatment of osteoporosis.
Dosages required for a beneficial pharmacologic effect greatly exceed
the amounts of these elements normally found in food.

14. Additional classification
•Nutritionally beneficial or possibly essential: For some trace
elements, continued suboptimal dietary intake (in the presence of
physiologic, nutritional, or other metabolic stress) may eventually
have a detrimental effect for which dietary supplementation may
have a ‘health restorative’ effect. Such effects are most clearly
demonstrated in experimental animals.
•Examples include the effects of boron in the presence of vitamin D
depletion and the need for increased vanadium with an
experimentally induced deficient or excessive supply of dietary iodine

15. Important general information

16. Dose-Effect
Relationship
•Deficiency disease may be seen with
low intake of recognized essential
trace elements.
•Increasing dietary supply, leads to a
plateau region of optimal supply.
•Higher intakes will result in adverse
toxic effects.
•Concentration window separating
beneficial from toxic intake varies for
different elements.
•Therefore the RDA is set at
amounts that are sufficient to
prevent deficiency (a tolerable
upper intake value that will
prevent toxicity)

17. Homeostasis of Trace elements
•Homeostasis: self-regulating process by which biological systems tend
to maintain stability while adjusting to conditions that are optimal for
survival.
•Homeostatic controls are required to regulate the supply of essential
trace elements to cells.
•These involve:
i.Regulation of intestinal absorption,
ii.Specific transport systems in peripheral blood,
iii.Uptake and storage mechanisms in tissue,
iv.Control of excretion.

18. Homeostasis
•The principal excretory route for trace metals is in faeces, both by
regulation of initial absorption and by re-secretion into the intestinal
tract in bile.
•Urinary excretion is another route for elimination, depending on the
element.
•Loss of trace elements by other routes, such as in hair and/or nails, by
skin cell loss, and in sweat, is generally minor

19. Consequences of inadequate trace element
intake
1.Optimal tissue function with body stores replete
2.Mobilization of stores
3.Initial depletion {compensation if possible(increased absorption from
gut, reduced renal excretion, reduced growth velocity)}
4.Intracellular content reduced
5.Impaired biochemical functions {reduced intracellular enzyme activity
(metabolic effects, antioxidant systems), Gene expression/regulation}
6.Nonspecific functional effects: {Short term (cognitive effects,
fatigue/work capacity, immunologic function), Long term (free radical
damage to DNA/cell membranes
7.Clinical disease
8.Death

20. General considerations in analyses
•Enzymes can be measured as surrogate markers of trace element
status e.g. glutathione peroxidase in serum or erythrocytes for
selenium
•Measurement of concentration in plasma or serum this may not be
reliable for some parameters under some circumstances such as the
seriously ill. The plasma and intracellular concentrations may not
correlate.
•Measurement of tissue concentration (not very common) e.g. Cu in
liver biopsy for Willsons disease
•Urine measurement, not always helpful. Example of use urinary
iodide as indicator of poor dietary iodine intake

21. General considerations in analyses
•Effect of inflammation
•The concentration in plasma of various trace elements can alter
signifcantlywhen a systemic inflammatory response syndrome (SIRS)
results from trauma or infection.
•The changes may be a result of variations in the binding proteins in
plasma such as albumin or retinol-binding protein (RBP), which
decrease as part of SIRS.
•Studies in patients with SIRS as categorized on the basis of increased
C-reactive protein (CRP) concentrations have documented decreases
in some vitamins and changes in the concentrations of many trace
elements.

22. Important factors that need to be considered for the understanding of
how trace elements function, include
•ionic forms,
•relative solubilities,
•possible organo-complex formation

23. Chemistry and metal interactions
•Trace elements interact with available ligands, e.g., nitrogen, sulfur,
and oxygen to form a wide variety of chemical complexes or species.
•Some metals such as Fe, Cu, Mo, and Cr are stable in more than one
valence state and participate in biologically important oxidation-
reduction reactions
•Bioavailability from foods and drinks primarily depends on solubility
and the presence of other dietary components which either promote
or inhibit absorption

24. Biochemistry and homeostasis
•Most aspects of intermediary metabolism require essential trace
elements in the form of metalloenzymes that have a number of
catalytic properties.
•Some metalloproteins are required for the transport and safe storage
of very reactive metal ions such as Fe
3+
or Cu
2+
.
•Examples include metallothionein (Cu, Zn), transferrin, ferritin and
hemosiderin (Iron), and ceruloplasmin (Cu).

25. Factors involved in overt deficiency (1)
•Poor dietary intake
•Intestinal malabsorption
•Increased excretory losses as a result of disease, injury, and infection.
Liver disease, inflammatory bowel disease, and renal disease will affect
trace element absorption and excretion to a variable extent and may
cause an acquired deficiency disease.

26. Factors involved in overt deficiency (2)
•Catabolic responses to injury, infection, and malignant disease can
result in increased essential trace element losses in faecesand in
urine.
•Severe burn injuries cause extensive loss in exudates through the
damaged skin.
•Postsurgical patients, especially those with short bowel syndrome,
require prolonged periods of nasogastric tube feeding or IV feeding,
and if treated with nutrient regimens lacking sufficient inorganic
micronutrients, they will develop symptomatic deficiency disease.

27. GENERAL CONSIDERATIONS IN
THE ANALYSES OF TRACE
ELEMENTS

28. Specimen requirements (1)
•Direct determination can be done in various specimen including
whole blood, blood plasma or serum, leucocytes, urine, saliva, CSF,
breast milk and sweat.
•Tissue samples may be obtained by needle biopsy (liver, bone) or
following autopsy.
•Hair and nail samples are useful non-invasive options to assess toxic
metal exposure but for essential elements/
•Problems of external contamination from environmental pollution,
cosmetics, shampoos etcare very real.

29. Specimen requirements (2)
•Plasma protein concentration of the relevant carrier proteins provide
useful additional information (transferrin, albumin, caeruloplasmin
and selenoproteinP) when using blood.
•Direct measurement of intracellular concentration in nucleated cells
(leucocytes and platelets). Challenge is with contamination during the
process of separation of different white cells and platelets in whole
blood
•Problems from prolonged storage of samples and repeated freezing
and thawing not encouraged

30. Other preanalytical factors
•Guidelines giving details of sample collection procedures and procedures
for limiting contamination should be made available
•Age, sex, ethnic origin, time of sample in relation to food intake, time of
day and year, history of medication, tobacco usage etcshould be recorded
when reference intervals are established from healthy controls
•In-patients with infection, post-trauma, post-surgery, systemic
inflammatory response can affect essential trace element concentrations
independent of their nutritional status.
Typical example is in relation to acute phase reactants (APR) which can cause
an increase in permeability of capillary allowing transfer of some plasma
carrier proteins and their trace metals into the interstitiumor induction of
hepatic synthesis of the APRs and therefore elevated with any metals they
carry.

31. Collection equipment (major source of
contamination)
•For blood plasma, plastic tubes with lithium heparin as an
anticoagulant are suitable for most analyses.
•For blood serum, plain glass containers are used (avoid containers
with gel clotting agents)
•For the ultratracemetals (Mn, Cr), special arrangements have to be
made to collect blood via plastic cannulaeor silanizedsteel needles,
and then the sample is placed into acid-washed containers.
•Trace metal vacutainers are available commercially.
•For random urine sample and tissue biopsy samples a plain plastic
container with no added preservatives is preferred

32. •For 24-hour urine collections, it is important that the urine collections
should not be made into disposable fiber or stainless steel containers, and
polyethylene bottles should be used with no chemical additives. On receipt
in the lab sample volume should be noted and aliquots stored at 4-15
0
C
before analysis.
•Zn, Mg, and Mn are at much greater concentration in red cells than in
plasma and, therefore separation of plasma or serum from the cells should
be completed within about six hours.
•Blank tubes should always be checked before any collection system is used.
•If samples are to be referred to a specialist laboratory for analysis it is
useful to include a blank tube together with the specimen(s).

33. Quality assurance considerations
•An effective quality assurance scheme for trace or ultratraceelement analyses
requires incorporation of the following into each batch of analyses:
a)reagent blanks,
b)replicate analyses to assess precision,
c)calibrators of the trace elements of interest in the expected concentration
range of the specimens analyzed, and
d)a control or reference solution with known or certified concentrations of the
trace elements to be determined to assess accuracy and batch-to-batch
precision. The reference material should be of the same matrix type and
contain approximately the same amounts of analyte as the specimens.
•It is also essential that trace element laboratories participate in external quality
assessment programs

34. Analytical methods
•Method must be sensitive, specific, accurate, precise and relatively fast
•Detection limits are very important considering measurements are in ng/g
to ug/g range and in practice, the concentration of the trace/ultratrace
element must be at least 10 times the detection limit of the method
ensuring sufficient accuracy and precision
•Methods include spectrophotometry, atomic absorption
spectrophotometry(AAS), inductively coupled plasma optical emission(ICP-
OES), inductively coupled plasma mass spectrometry(ICP-MS)
•Other less commonly used methods include neutron activation
analysis(NAA), x-ray fluorescence(XRF) and electrochemical methods like
anodic stripping voltammetry(ASV). NAA requires a nuclear irradiation
facility and ASV requires completely mineralized solutions for analysis
(time-consuming process)

35. SOME INDIVIDUAL TRACE
ELEMENTS

36. REFERENCES
•Mehri A. Trace elements in human nutrition (II) –An update. Int J Prev
Med 2020;11:2