chem - trace metals

trace metals

• many different analytes found in small amounts

• homeostasis → generally only absorb what you need

  • small changes can have big consequences

• ubiquitous in environment

  • contamination is a problem → use of royal blue tubes

how many groups of trace metals are there?

• 4

  • essential

  • evidence of essential role, but not RDA

  • consistently found in tissues in ultra-trace amounts

  • no known function (toxic)

trace metals groups - essential trace metals !!!! (IMPORTANT)

• recommended dietary allowance (RDA) established

• Iron, Zinc Selenium

trace metals groups - evidence of essential role, but not RDA

• COPPER, manganese, chromium, cobalt, molybdenum, fluorine

trace metals groups - consistently found in tissues in ultra trace amounts

• not shown to be essential or detrimental

• lithium, nickel, tin, silicon

trace metals groups - no known function - toxic trace metals

• aluminum, beryllium, cadmium, arsenic, mercury

iron

• MOST IMPORTANT of the trace metals

• metabolism

  • total amount in adults is 4-5 g (75% ACTIVE; 25% STORED)

  • maintain levels by adjusting absorption via small intestine

  • most commonly measured:

    • total iron (Fe)

    • total iron binding capacity (TIBC)

transferrin

• transports iron IN BLOOD

• has binding sites for TWO Fe3+ (ferric) ions

• normally 1/3 is saturated (33%)

transferrin receptors

• TfR1, TfR2

• transferrin binds to cells at receptors

• allows iron to enter cells

ferritin

• intracellular storage form of iron IN CIRCULATION

• keeps iron in its SOLUBLE and NON-TOXIC (Fe3+) form

hemosiderin

• aggregate of FERRITIN

• used to store EXCESS IRON in bone marrow, liver, or spleen

ferroportin

• opposite side of enterocyte

• exports iron OUT of cells INTO the bloodstream

hepcidin

• important mechanism to control iron “negative regulator”

• decreases intestinal absorption of iron

• inhibits expression of DcytB and DMT1

process of iron absorption

• Fe from diet absorbed by enterocytes in duodenum lining

  • most dietary iron is in oxidized state Fe3+ (ferric, NON-heme) form — LESS SOLUBLE

    • vitamin C enhances non-heme iron absorption

• only Fe2+ (ferrous, HEME iron) can be absorbed by enterocytes — MORE SOLUBLE

• DUODENAL CYTOCHROME B (Dcytb) on enterocytes

  • reduces Fe3+ to Fe2+

• DIVALENT METAL TRANSPORTER (DMT1)

  • facilitates transfer of iron across intestinal epithelial cells from lumen

iron absorption graphic

process of iron absorption and metabolism

• intestinal cells can either store iron as ferritin or move it into rest body using ferroportin (iron exporter)

• transferrin distributes iron throughout the body to all cells which store iron

• oxidation turns it back to ferric form

• ferric form iron is bound in blood by transferrin

  • approximately 1/3 of transferrin binding sites are saturated (33% saturation)

• if Fe stays into enterocyte

  • excreted in feces

iron absorption graphic #2

iron absorption and metabolism steps

1. dietary non-heme iron (Fe3+) must be reduced for transport across apical brush border

2. DMT1 mediated proton-dependent Fe2+ import

3. HCP1 transports dietary heme iron

4. heme oxygenase releases iron from protoporphyrin, allowing it to enter the same pool as non-heme iron

5. some iron is used or stored within the enterocyte in ferritin, and is later lost when the intestinal mucosa is sloughed

6. ferroportin exports some iron, where it is oxidized to Fe3+ for incorporation into serum transferrin

iron specimen

• serum or heparinized plasma

• diurnal variation → 30% higher in AM

• avoid hemolysis — large amount of iron in RBC

• contamination problems

  • use special tubes

  • new glassware or acid washed tubes

total serum iron methods

• must disrupt protein/iron bond

  • does so through use of acid (HCl)

• automated methods use dialysis to separate iron

  • requires reducing agent to reduce Fe3+ to Fe2+

  • ascorbic acid or sodium metabisulfite

• react Fe2+ with chromogen

  • terosite, ferrozine, bathophenanthroline or TPTZ

• serum blanks remove interference

TIBC (total iron binding capacity)

• measures the blood’s ability to bind iron with transferrin

• tests measure the maximum amount of Fe that can be carried

• NOT a direct measurement of something

  • ONLY GIVES APPROXIMATE MEASURE OF TRANSFERRIN

• less expensive than direct measurement

• TIBC = Fe + UIBC (unsaturated iron binding capacity)

other measures of iron status

• transferrin

  • directly measured

  • made by the liver that binds and transports iron (iron carrying bus)

  • related to TIBC

    • slightly lower than TIBC

• ferritin

  • only small amounts in plasma

  • declines early in iron deficiency — before changes in red cells or serum iron concentration

  • chronic diseases can increase (acute phase rxn)

  • test methods

    • ELISA or other immunologic techniques

normal values - iron

• males: 60 - 150 ug/dl

• females: 50 -130 ug/dl

normal values - TIBC

• 270 - 380 ug/dl

normal values - % saturation

• approximately 1/3 saturated w iron

• 20 - 55% range

ferritin

• males: 20 - 250 ng/ml

• female: 10 - 120 ng/ml

clinical correlation - iron deficiency

• iron deficiency

  • one of the most prevalent disorders

  • often seen in young children, women, and elderly

  • chronic blood loss is so often the cause in men (GI bleeds)

• laboratory findings

  • IRON = LOW

  • TIBC = HIGH/INCREASED

  • SERUM FERRITIN = DECREASED

    • more sensitive and reliable

  • hematologic picture

    • microcytic/hypochromic anemia, low MCV, anisocytosis, poikilocytosis, ovalocytes, reactive thrombocytosis

hemochromatosis

• progressive disease that results from iron overload

• body iron accumulates and excess iron deposits in liver, pancreas, heart, joints, and endocrine glands

• free iron is toxic and can damage organs

• must be carried by proteins to prevent damage

hemochromatosis classification

• primary or hereditary hemochromatosis:

  • several genetic defects which affect iron metabolism

• non-genetic or secondary causes:

  • alcoholism (downregulates hepcidin → more absorption)

  • liver damage

  • multiple transfusion

classical hemochromatosis

• symptoms

  • diabetes and skin pigmentation (bronze color)

  • weakness, malaise, fatigue, lethargy, and weight loss

  • hepatosplenomegaly, abnormal liver enzymes

  • arthritis

  • cardiomyopathy

  • hypogonadism and early menopause in women

• lab results

  • ELEVATED hemoglobin and hematocrit

  • fasting transferrin iron saturation = (serum iron/ TIBC) * 100 = >45%

  • serum ferritin > 1000 ng/ml

clinical correlation chart (IMPORTANT !!!!)

clinical correlation - IDA (iron deficiency anemia)

• iron = DECREASED

• TIBC = INCREASED

• % saturation = DECREASED

clinical correlation - chronic disease

• iron = DECREASED

• TIBC = DECREASED

• % saturation = DECREASED

clinical correlation - thalassemia

• iron = INCREASED

• TIBC = DECREASED

• % saturation = INCREASED

clinical correlation - hemochromatosis

• iron = INCREASED

• TIBC = DECREASED

• % saturation = INCREASED

zinc

• second in importance as essential trace element (2nd to Iron)

  • deficiency common throughout life (vegetarians)

• necessary for many enzymatic rxn

• influence activity of more than 300 enzymes

• used in production of plants, skin lotions

• important in wound healing, metabolism of proteins, glucose, cholesterol membrane structure, insulin function, growth factor effects

zinc - health effects, deficiency, and toxicity

• metabolism

  • 20-30% absorbed

  • most transported in blood by albumin

• deficiency

  • growth in reduction, slow skeletal maturation, reduces taste perception, impaired T cell immunity, insufficient wound healing

  • old age, lactation associated w poor zinc nutrition

  • COMMON DEFICIENCY IN ALCOHOLISM (reduces Zn absorption and excretion)

• toxicity

  • GI symptoms, decrease heme synthesis due to induce copper deficiency and hyperglycemia

  • exposure to fumes and dust “zinc fume fever” — pneumonia, severe inflammation, fever, hyperpnea, coughing, pain in legs and chest, and vomiting

• lab evaluation

  • flame AAS, ICP-AES, and ICP-MS

zinc - estimation of levels

• analysis of zinc in a body tissue or fluid

  • zinc content in plasma, serum, RBCs, urine

• plasma or serum zinc

  • may not reflect whole body status

  • correlate with levels of albumin

    • need whole picture: plasma + whole blood + urine must all be tested

  • DIURNAL VARIATION (higher in morning) - declines AFTER MEALS and increases after short term FASTING

  • 10X more zinc in RBCs — DON’T USED HEMOLYZED SAMPLES

  • atomic absorption = most reliable

copper

• widely distributed in nature

• major function - redox rxns

  • critical for the reduction of iron in heme synthesis

• normal copper content: 50-120 mg

  • mostly found in liver, brain, heart and kidneys - not rly in circulation

• 50-80% ingested is absorbed through intestine

• copper transported and stored in LIVER - transported BOUND TO ALBUMIN

• in liver - copper is incorporated into CERULOPLASMIN

  • Cu transport protein

  • 98% excreted through bile; sweat and urine loss 2%

copper health effects, deficiency, and toxicity

• component of several metalloenzymes

• copper deficiency

  • IMPAIRS IRON METABOLISM

  • in premature infants: diseases of small bowel, lymph sarcoma, and scleroderma

  • deficiency: related to malnutrition, malabsorption, chronic diarrhea, hyperalimentation, prolonged feed with low-copper, total-milk diets

• ESTROGENS increase serum copper concentration (stimulates liver to make ceruloplasmin)

• INCREASED in acute phase response due to ceruloplasmin being increased

• lab evaluation

  • measured by flame AAS, ICP-MS

  • Urine or serum used to monitor nutritional adequacy or toxicity

copper signs of deficiency

• neutropenia and hypochromic anemia in early stages

• osteoporosis and various bone abnormalities

• decreased pigmentation of skin and general pallor

• later stages: possible neurological abnormalities - hypotonia, apnea, psychomotor retardation

copper toxicity

• irritant to epithelia and mucous membranes, hepatic and renal damage with hemolysis

• emesis: characteristic blue-green color

copper diseases - Menke’s Disease

• Menke’s “Kinky” or “steely” hair syndrome

• X-linked genetic disorder in copper transport, absorption, and storage

• EXTREME FORM of copper DEFICIENCY

• fatal, progressive brain disease — kinky hair, retardation of growth, mental deterioration coarse feces, disturbance of muscle tone, seizures, and episodes of severe hypothermia

  • symptoms start at 3 months and death usually occurs by 5 years old

• LAB - LOW SERUM COPPER and LOW CERULOPLASMIN levels

  • current day: copper histidine daily injections can help w/ Cu absorption (can possibly prolong life/ better quality of life)

copper diseases - Wilson’s Disease

• AKA Hepatolenticular degeneration

• genetically defect with copper accumulation

  • excess copper does not get eliminated by liver properly

  • copper accumulates in brain, kidney, liver, and corneas

• presents between 6-40 years of age

• clinical findings: neurologic disorders, liver dysfunction, Kayser-Fleischer rings (within the eyes)

• disease can be halted with zinc acetate or chelation therapy

  • helps bind to excess copper and excrete it in urine

  • dietary restrictions help

  • liver transplant may be needed

lead

• widely distributed in earth’s crust - used in batteries, solder, and foils

• once used in gasoline and paints manufactured before the 1970s

• recent years - massive recalls of toys and costume jewelry from China

• no known role in normal human physiology

• exposure — respiratory or gastrointestinal

• 99% taken up by RBCs and interferes with heme synthesis

lead - health effects and toxicity

• in children: >45 ug/dL → acute toxicity; requires clinical intervention

  • CNS: IQ decline, clumsiness, gait abnormalities, behavioral changes, seizures, severe cognitive problems (permanent cognitive damage)

  • GI: abdominal pain, constipation, colic

  • acute neuropahy and anemia

• in adults

  • peripheral neuropathies (nerves damaged in periphery of body), motor weakness, chronic renal insufficiency, systolic HTN, anemia

lead - exposures and lab evaluation

• childhood exposure - paint chips

• adult exposure - occupational exposure (jobs)

• lab specimen: whole blood (EDTA) — NO URINE

  • ICP-MS (preferred)

• treatment: chelation therapy

  • administer chelating agents to bind/remove heavy metals from body (excreted in feces/urine)

  • also used for mercury, iron, arsenic, lead, uranium