Elemental analysis in clinical practice

Nicholas J Miller FRCPath,

Laboratory Director, Biolab Medical Unit,

ThermoFisher summer symposium

7th June 2011, QEII Conference Centre

Nutritional Elements

•Macro minerals (7) Na, K, Cl (electrolytes)

Ca, Mg, P (mainly bone)

S (mainly amino acids)

• Trace elements = < 0.01% of the total body mass (9) Fe, Zn, Cu, Mn, I, Se, Mo, Co, Cr,

•Ultra-trace elements (7) As, B, F, Ni, Si, Sn,V

Trace elements are enzyme co-factors

• 1/3 of known enzymes require metals for their function

– Metalloenzymes

• Fe2+, Fe3+, Cu2+, Zn2+, Mn2+, Co2+

– Metal-activated enzymes

• Na+, K+, Mg2+, Ca2+

Toxicity of metals

• Substitution for essential metals in enzymes,

• Interference with intracellular signalingpathways and with Ca2+ metabolism,

• Induction of oxidative stress,

• Interference with DNA transcription,translation and repair.

Essential metals in human metabolism

“Window of essentiality”

Concentration of metal

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Nutritional element profile in plasma

• Calcium, chromium, copper, iron, magnesium, manganese, selenium, sodium, zinc,

•Aluminium, cobalt, molybdenum and nickel,

•Usually red cell magnesium as well.

Magnesium

• Pumped into mammalian cells - but no big gradient,

• So dissimilar function from Na+, K+, Ca2+,

• Plasma levels are maintained at the expense of intracellular stores,

• Mg-dependent enzymes in cytoplasm e.g. ATPases, + control of many reactions such as ATP pumps and cellular contraction.

Zinc

• The most common catalytic metal ion in thecytoplasm, with Zn-dependent enzymesinvolved in a great variety of reactions,

• Zn is required for regulation of DNA ineukaryotes,

• Zn deficiency has multiple effects,

• C. 20% of the world population is estimated tobe Zn-deficient (Brown KH and Wuehler SE , 2000).

Copper• Most of the plasma Cu is on the ferro-oxidase

enzyme caeruloplasmin and increases inconcentration in the acute phase reaction,

• Plasma Cu is low in Wilson’s disease (excesscopper storage causing toxicity),

• Otherwise plasma Cu is low in severedeficiency, as is erythrocyte SOD activity.

Selenium• There are around 30 selenoproteins that may

be found in the plasma,

• These include GSHPx & selenoprotein P,

• Erythrocyte Se reflects rbc GSHPx at the timeof erythropoiesis,

• In practice plasma Se is the best index of Sedeficiency (and ICPMS has revolutionised thisanalysis).

Chromium and Manganese

• ICPMS has greatly improved the measurementof these metals, which are found in plasmaclose to the analytical detection limit,

• Chromium levels fall progressively with age,

• Manganese is being added to the food chain,

• Analyse whole blood for assessment of toxiclevels of Cr and Mn.

Molybdenum• Humans consume 100 to 500 µg Mo/day rincipally

from organ meats, whole-grain cereals, andlegumes,

• Essential in humans , due to its role in threeenzymes:

• Sulphite oxidase• Xanthine oxidase• Aldehyde oxidase

• The occurrence of Mb deficiency is unknown sincethis measurement has only recently becomeavailable.

Toxic elements in blood

• Cadmium,

• Lead,

• Mercury.

Two major mechanisms of heavy metal toxicity

–Binding to –SH and nitro-groups ofbiomolecules,• Cofactor substitution, conformational changes, etc.

–Oxidative damage due to directcatalysis of ROS production and/or toinhibition of ETC in mitochondria.

Uptake of toxic metals• There are multiple pathways of metal uptake

into the cell,

• Toxic metals use routes which have evolved for the uptake of essential metals, esp. via ion channels and carrier proteins, with limited transport across membranes,

• Greater uptake of toxic metals when supply of nutrient metals is limited.

Cadmium• Cd is chemically similar to Zn and a contaminant of Zn

products (e.g. galvanised steel,

• Actively taken up by plants (along with Zn),

• Much Cd in humans is from ingestion of food plants grown in a Cd-rich soil; also from smoke, diesel fumes etc.,

• Toxicity via binding to SH groups and enzyme inhibition (IARC group 1 - known carcinogen),

• Chronic toxicity - kidney is major target organ, also lung damage and osteomalacia (Itai itai disease = ouch ouch),

• Chelation not recommended (potential for renal damage).

Lead• Binds to SH groups and inhibits enzymes (esp. ALA-D,

ferrochelatase),

• Divalent lead competes with calcium in signal transduction and nerve transmission,

• Affects cell membranes, ion transport, reproduction,

• Burtons lines - grey-blue lines of lead sulphide in gums,

• Chelation with EDTA or DMSA (use of penicillamine declining).

Childhood lead poisoning

• Symptoms of lead poisoning in children

• Neurological problems– Learning disabilities

– Lowered intelligence

– Behavioral problems

– In severe cases -seizures, comas, and death

Childhood lead poisoning

Mercury• There is a lack of agreement as to the significance of

blood mercury levels,

• Mercurialentis - brown band around the eye from Hg deposition – seen after chronic industrial exposure,

• Main UK sources of mercury appear to be dental amalgam and ingestion of certain fish,

• We find significant levels of mercury in the blood and hair of some subjects, with an increased mercury excretion in the urine after chelation challenge.

Elemental analysis for clinical use:• Analysis of plasma collected into trace element-

free tubes for deficiencies of nutritional metals,

• Red cell analysis for Mg,

• Whole blood analysis for toxic levels,

• Chelation challenge and urine analysis for toxic metals.