Trace Elements PDF

TRACE ELEMENTS Trace Elements  Trace elements are usually associated with an enzyme (metalloenzyme) or another protein (metalloprotein) as an essential component or cofactor.  Deficiencies typically impair one or more biochemical functions and excess concentrations are associated with at...

TRACE ELEMENTS Trace Elements  Trace elements are usually associated with an enzyme (metalloenzyme) or another protein (metalloprotein) as an essential component or cofactor.  Deficiencies typically impair one or more biochemical functions and excess concentrations are associated with at least some degree of toxicity.  Although trace elements, such as iron, copper, and zinc, are found in mg/L concentrations, ultratrace elements, such as selenium, chromium, and manganese, are found in less than μg/L concentrations. Trace Elements  An element is considered essential if a deficiency impairs a biochemical or functional process and replacement of the element corrects this impairment.  Decreased intake, impaired absorption, increased excretion, and genetic abnormalities are examples of conditions that could result in deficiency of trace elements. Trace Elements  The World Health Organization has established the dietary requirement for nutrients as the smallest amount of the nutrient needed to maintain optimal function and health.  An element that is not considered essential is classified as nonessential  Nonessential trace elements are of interest due to their toxicity Instrumentation and Methods  Atomic Absorption Spectrometer (AAS)- source, atomizer, monochromator, detector  Flame AAS  Graphite furnace AAS  Cold Vapor AAS  Hydride Generation AAS  Inductively Coupled Plasma Atomic Emission Spectroscopy (ICP-AES)- source, monochromator, detector  Inductively Coupled Plasma Mass Spectroscopy (ICP-MS)  Neutron Activation Analysis (NAA) GENERAL CONSIDERATIONS IN SAMPLE COLLECTION, PROCESSING AND LABORATORY DETERMINATIONS OF TRACE ELEMENTS  Specimens for analysis of trace elements must be collected with attention to details such as anticoagulant, collection apparatus, and specimen type (serum, plasma, or blood).  the low concentration in biologic specimens and the ubiquitous presence in the environment, extraordinary measures are required to prevent contamination of the specimen GENERAL CONSIDERATIONS IN SAMPLE COLLECTION, PROCESSING AND LABORATORY DETERMINATIONS OF TRACE ELEMENTS.  using special sampling and collection devices, specially cleaned glassware, and water and reagents of high purity.  The selection of needles, evacuated blood collection tubes, anticoagulants and other additives, water and other reagents, pipettes, and sample cups must be carefully evaluated for use in trace and ultatrace analyses  Instrumentation must have high analytic sensitivity and specificity because of the extremely low concentrations of trace elements found in body fluids and the physiochemical similarity of some elements.  For many years the most commonly used instrument for trace metal analysis he been the atomic absorption spectrometer, often with flameless atomization. Alternative Analytic Technniques  Neutron Activation Analysis (NAA)  Anodic Stripping Voltametry (ASV)  Adsorptive Stripping Voltametry (ADSV)  Ion Chromatography (IC)  Gas Chromatography –Mass Spectrometry (GC-MS)  Laser Ablation ICP-MS TRACE ELEMENTS IN CLINICAL CHEMISTRY ELEMENTS PROVEN PROBABLY NONESSENTIAL ESSENTIAL ESSENTIAL TO DATE TRACE IRON ZINC COPPER ULTRATRACE MANGANESE NICKEL ALUMINUM COBALT VANADIUM ARSENIC SELENIUM TIN CADMIUM MOLYBDENUM FLOURIDE CHROMIUM GOLD IODINE LEAD MERCURY SILICON Arsenic  w/ metallic and nonmetallic properties  Ubiquitous w/ natural sources: volcanoes and weathering of minerals  Anthropogenic sources (production of metals)  A wood preservative, pesticide, ammunition, semiconductor processing Health Effects  Nonessential w/no function in human physiology  Approved arsenic trioxide for acute promyelocytic leukemia Absorption, Transport and Excretion  Route of exposure is by ingestion of food (sea foods) and water and by inhalation of contaminated air.  Forms:  Arsenobetaine and arsenocholine – nontoxic  Pentavalent arsenic, trivalent arsenic and methylated arsenic compounds - toxic Toxicity  Exposure can lead to acute and chronic intoxication  Can be grouped into inorganic, methylated, and organic forms  Inorganic species are highly toxic  Methylated are intermediate in toxicity  Organic are nontoxic  Arsenic trioxide (odorless and tasteless) is one of the best known poison in human history  0.01 to 0.05g produce toxic symptoms and lethal dose is 0.12 and 0.3 g Signs and symptoms  Depends on the duration and extent of exposure and the underlying condition  Acute exposure can result to death  Symptoms may include gastrointestinal, bone marrow, cardiovascular, CNS, renal and hepatic, dermatologic system and malignant changes. Laboratory evaluation  IC-MS, GFAAS, HGASS  Urine is preferred over blood as specimen due to its short half-life  For recent exposure (3weeks) – hair, nail Cadmium  Use in manufacture of pigments, batteries, in metal and plastic industries  Fossil fuels and incineration of municipal waste materials are source of cadmium Health effects  No known role in normal human physiology  Toxicity comes from Cd forming protein-Cd adducts  Cadmium denatures cadmium-bound proteins resulting in loss of function.  Newborns are free of Cd  Cd increases w/ age and smoking Absorption, Transport and Excretion  Exposure is by ingestion and inhalation  Absorption of Cd is higher in females than in males due to differences in iron stores.  Excretion is via feces  In blood, Cd is bound to RBCs Toxicity  Renal dysfunction is a common presentation for chronic CD exposure  Nasal epithelial damage and lung damage  Exposure can affect the liver, immune, blood, and nervous system Laboratory Evaluation  Quantified by GFAAS and ICP-MS and ICP-AES  Avoid colored containers during collection as it often contain cadmium. Lead  Heavy metal found in environment  Can be both an acute and chronic toxin  Used in production of storage batteries, ammunition, solder and foils  Tetraethyl lead was used as additive in gasoline  Present in paints  In recent years, there have been massive recalls of toys from China due to elevated lead content Health Effects  No know role in normal human physiology Absorption, Transport and Excretion  Exposure in primarily by respiratory or gastrointestinal and inhalation  absorption vary according to age, nutritional status and certain substances (iron, Ca, Mg, alcohol, fat) may impair absorption  Low dietary Zn, ascorbic acid and citric acid may enhance absorption  Lead is transported to the blood by hemoglobin  Half life in blood is about 2 to 3 weeks  Stored in soft tissues and most is excreted via urine and feces. The rest is excreted in hair, sweat, nails and others. Toxicity  Symptoms are seen at blood levels of 60 ug/dL or higher  IQ declines in children w/ blood levels of 10 ug/dL or higher  CNS symptoms-clumsiness, gait abnormalities, headache, behavioral changes seizures, severe cognitive and behavioral problems  GIT symptoms -abdominal pain, constipation, and colic  Peripheral neuropathies, motor weakness, chronic renal insufficiency and systolic hypertension and anemia Lab Evaluation  Whole venous blood is preferred over plasma and serum  Urine is useful in detecting recent exposure or monitor chelation therapy  Plasma aminolevulinic acid, whole blood zinc protoporphyrin or free erythrocyte protoporyrins is useful as screening for occupational exposure  ICP-MS, ICP-AES, GFAAS Mercury  Also called quicksilver, is a heavy, silvery metal.  Dimethyl mercury is an extremely toxic compound  Oxidation states: Hg(0), Hg(I), Hg(II)  Product of natural out gassing, fungicide, and dental amalgams and used in electrical switches  Some OTC drugs contain traces of mercury compounds: topical antiseptics, stimulant laxatives, diaper rash ointment, eye drops, and nasal sprays. Health Effects  No known function in normal physiology  Hg(I)chloride is use as diuretic, tropical disinfectant and laxative Absorption, transport and Excretion  Inhalation, ingestion, absorption thru skin, injection and dental amalgams  Accumulates in kidney, liver, spleen, brain, glands and reproductive organs  Excreted in feces and urine Toxicity  Is based on reaction w/ sulfhydryl groups, by inactivating proteins by binding to cysteine  Attacks the CNS, immune, digestive systems and lung and kidneys  Headache, tremor, impaired coordination, abdominal cramps, diarrhea, dermatitis.  Some vaccines have contained Thimerosal before. Thimerosal is a mercury-containing compound metabolized into ethylmercury. It was widely speculated that this mercury based preservative triggered autism in children. Chromium  Used in manufacture of stainless steel, wood treatment, welding, tanning and paints  States: trivalent and hexavalent  Cr(VI) is better absorbed and more toxic that Cr(III) and is also a carcinogen implicated in lung cancer  CHROMIUM  Wide industrial use in metal alloys, metal plating dyes and leather tanning,  chromium is common in the environment, occurring both naturally and as industrial waste.  Although chromium can exist in an unusually large number of oxidation states, only the +3 and +6 ions are present in living systems.  The +6 ions is far more toxic than the +3 ions.  Meats and grains are relatively rich resources of chromium, the typical diet may be low in chromium.  From 50-200 μg/day appears to be an adequate intake of chromium.  Chromium must be present at much higher concentrations to have toxic effects.  Once absorbed chromium is transported to the tissue by transferrin which has about an equal affinity for Cr+3 ion and for Fe+3 ions.  Important in glucose metabolism as an essential activator of insulin.  A low MW complex of Cr+3 with nicotinic acid and other organic compounds appears to be the factor that activates insulin. Deficiency  Chromium deficiency is associated with insulin resistance and chromium supplementation has demonstrated improved glucose tolerance, reduced insulin concentrations and decreased total cholesterol in type 2 diabetes.  Deficiency is characterized by glucose intolerance, glycosuria, hypercholesterolemia, decreased longevity, decreased sperm counts and impaired fertility Toxicity  Severe dermatitis and skin ulcers  Reparatory irritation  Targets kidney, liver, skin and immune system Lab Evaluation  GFAAS, NAA or ICP-MS  Plasma, serum and urine Iron  The fourth most abundant element in the earth’s crust  Classified as trace element and readily forms complex w/ ligands and participate in redox chemical reactions DISTRIBUTION OF IRON  Of the 3 to 5 g of iron in the body, approximately 2 to 2.5g of iron is in hemoglobin which is contained in red blood cells either in the blood or as precursors in the bone marrow.  A moderate amount of iron (-130 mg) is in myoglobin, the oxygen- carrying protein of muscle.  A small (8 mg), but extremely important, pool is in tissue where iron is bound to several enzymes that require iron for full activity.  These include peroxidases, cytochromes, and many of the Krebs cycle enzymes.  Iron is also stored as ferritin and hemosiderin, primarily in the bone marrow, spleen, and liver.  This critical pool of iron may be the first to become diminished in iron deficiency states.  Only 3 to 5 mg of iron is found in plasma, almost all of it associated with transferrin, albumin, and free hemoglobin DIETARY REQUIREMENTS OF IRON  An adult male, the average loss of 1mg per day must be replaced by dietary sources.  Pregnant or premenopausal women and children have greater iron requirements, often obtained by dietary supplementation.  IRON ABSORPTION  Absorption of iron from the intestine is the primary means of regulating the amount of iron within the body.  only about 10% of the 1 g/day of dietary iron is absorbed  iron must be in the Fe(II) (ferrous) oxidation state and bound to protein.  Because Fe(III) is the predominant form of iron in foods, it must first be reduced to Fe(II) by agents such as vitamin C before it can be absorbed  In the intestinal mucosal cell, Fe(II) is bound by apoferritin, then oxidized by ceruloplasmin to Fe(III) bound to ferritin.  there, iron is absorbed into the blood by apotransferrin, which becomes transferrin as it binds two Fe(III) ions  transferrin carries and releases Fe to the bone marrow, where it is incorporated into hemoglobin of RBCs.  After about 4 months in circulation, red cells are degraded by the spleen, liver, and macrophages, which return Fe to the circulation, where it is bound and carried by transferrin for reuse.  Iron absorption can be adjusted to meet current needs.  Absorption and transport capacity can be increased in conditions such as iron deficiency, anemia or hypoxia. IRON EXCRETION  Most of the small amount of iron normally lost each day is contained in epithelial and red cells excreted in the urine or lost in the feces. with each menstrual cycle women lose approximately 20-40 mg. iron. BIOCHEMICAL FUNCTIONS OF IRON  iron is an essential component of hemoglobin, allowing it to bind reversibility with oxygen in the lung and release oxygen to the tissue.  Peroxide and catalase are iron containing enzymes CLINICAL DISORDER OF IRON DEFICIENCY  Iron deficiency is one of the most prevalent disorders known with 15% of the worldwide population.  Those with a higher than average risk of iron deficiency anemia include pregnant women, young children and adolescents, and women of reproductive age.  Increased blood loss, decreased dietary iron intake, or decreased release from ferritin may result in iron deficiency.  Reduction in iron stores usually precedes both a reduction in circulating iron and anemia, as demonstrated by a decreased red blood cell count, mean corpuscular hemoglobin concentration, and microcytic RBCs.  A decrease in serum iron and an increase in transferrin/TIBC are classic indices iron deficiency  the serum ferritin concentration has evolved as a more sensitive and reliable for confirming this condition.  CLINICAL DISORDERS OF IRON OVERLOAD  IRON overload is usually caused by an abnormal excess absorption of iron from a normal diet.  Iron overload states are collectively referred to as hereditary hemochromatosis (HH).  Hemosiderosis has been used to specifically designate a condition of iron overload as demonstrated by an increased serum iron and total iron binding capacity (TIBC) or transferrin, but without demonstrable tissue damage.  Heriditary Homochromotosis is caused by a genetic defect cause tissue accumulation of iron affects liver function and often leads to hyperpigmentation of the skin.  Elevated serum iron and transferrin are characteristics of early stages of hemochrinomatosis, the serum ferritin steadily increase with progression of the disease, often to very high levels as the conditions becomes severe some  Some conditions associated with severe hemochromatosis include diabetes mellitus, arthritis, cardiac arrhythmia or failure, cirrhosis, hypothyroidism, impotence, and liver cancer.  Treatment may include therapeutic phlebotomy or administration of chelators, such as deferoxamine. Transferrin can be administered in the case of atransferrinemia Toxicity  Hemochromatosis – iron overload, w or w/o tissue damage.  Associated w/ hereditary hemochromatosis (HH)  Excessive dietary intake  HH causes tissue accumulation of iron affecting liver function and leads to hyperpigmentation of the skin  Treatment includes: phlebotomy and administration of chelators such as deferoxamine LABORATORY EVALUATION OF IRONS STATUS  Disorders of iron metabolism are evaluated primarily by packed cell volume, hemoglobin, red cell count and indices, total iron and TIBC, percent saturation, transferrin, and ferritin  AAS or ICP-MS Total Iron Content (Serum Iron)  Measurement of serum iron concentration refers specifically to the Fe+3 bound to transferrin and not to the iron circulating as free hemoglobin in serum.  The specimen may be collected as serum without anticoagulant or as plasma with heparin.  Oxalate, citrate, or ethylenediaminetetraacetic acid binds Fe ions and all are unacceptable anticoagulants.  Early morning sampling is preferred because of the diurnal variation in iron concentration.  Specimens with visible hemolysis should be rejected.  Spectrophotometric determinations have been adapted to automated analysis.  These procedures generally have the following steps: Fe +3 is released from binding proteins by acidification, reduced to Fe+2 by ascorbate or a similar reducing agent, and complexed with a color reagent such as ferrozine, ferene, or bathophenanthroline. Total Iron-Binding Capacity  Total iron-binding capacity (TIBC) refers to the amount of iron that could be bound by saturating transferrin and other minor iron- binding proteins present in the serum or plasma sample.  Typically, about one-third of the iron binding sites on transferrin are saturated  TIBC is determined by adding sufficient Fe+3 to saturate the binding sites on transferrin, with the excess iron removed by addition of MgCO3 to precipitate any Fe+3 remaining in solution.  After centrifugation to remove the precipitated Fe+3, the supernatant solution containing the soluble iron bound to proteins is analyzed for total iron content.  This is the TIBC, which ranges from around 250 to 425 μg/dL. PERCENT SATURATION  The percent saturation, also called the transferrin saturation, is the ratio of serum iron to TIBC.  The normal range for this is approximately 20% to 50%, but it varies with age and sex Transferrin and Ferritin  Transferrin is measured by immunochemical methods such as nephelometry.  Transferrin or TIBC is increased in iron deficiency and decreased in iron overload and hemochromatosis.  Transferrin (TIBC) may also be decreased in chronic infections and malignancies  Transferrin is primarily monitored as an indicator of nutritional status.  As a negative acute-phase protein, its concentration decreases in inflammatory conditions.  Ferritin is measured in serum by immunochemical methods, such as Immunoradiometric assay (IRMA), enzyme- linked immunosorbent assay (ELISA), and chemiluminescent techniques.  Ferritin is decreased in iron-deficiency anemia and increased in iron overload and hemochromatosis.  Ferritin is often increased in several other conditions, such as chronic infections, malignancy, and viral hepatitis.  LABORATORY MARKERS OF IRON STATUS IN SEVERAL DISEASE STATES CONDITION SERUM IRON TRANSFERRIN %SATURATION FERRITIN Normal Intervals (50-160 μg/dL) (200-400 μg/dL) (20-55 μg/dL) (20-250μg/dL) Iron deficiency Decreased Increased Decreased Decreased Iron poisoning/ Increased Decreased Increased Increased overdose Hematochromatosis Incresed Decreased Increased Increased Malnutrition Decreased Decreased Variable Decreased Malignancy Decreased Decreased Decreased Increased Chronic infection Decreased Decreased Decreased Increased Viral hepatitis Increased Increased Normal/ increased Increased Anemia of chronic Decreased Normal/ Decreased Decreased Normal/ increased disease Sideroblastic increased Normal/ Decreased increased Increased anemia Copper  Is soft yet tough metal w/ excellent electrical and heat conducting properties  Forms and alloy w/ Zn (brass), tin (bronze) and nickel for coins. DIETARY REQUIREMENTS OF COPPER  Significant sources of copper include shellfish, liver, nuts and legumes.  Although most diets contain less, an adequate intake of copper appears to be in the range of 1.5-3.0 mg/dl for adults. BIOCHEMICAL FUNCTIONS OF COPPER  Major function of copper is as component of enzymes involved in redox reactions with many involving reactions with oxygen.  These methalloenzymes include ceruplasmin, cytochrome, oxidase superoxide dismutase, dopamine –β- hydroxylase, trysinase, and ascorabate oxidase.  Ceruplasmin as mentioned earlier has ferroxidase activity  Cytochrome c oxidase contain two heme groups and two copper atoms and catalzes the reduction of oxygen to water in the last step of the electron transport chain.  Superoxide dismutase (SOD) which contains both copper and zinc plays active antioxidant to radicals to O₂ and H₂O₂.  tyrosinase is involved in the production of melanin.  Dopamine-β- hydroxylase is important in catecholamine metabolism. COPPER ABSORPTION, TRANSPORT AND EXCREATION  Intestines play an important role in regulation of copper with absorption modulated by need, resulting in a 55-75% rate of absorption.  Both zinc and iron compete with copper for intestinal absorption.  Absorbed copper becomes bound to albumin or complexed to histidine residues as it is transported to the liver where it is stored in the form of cupropotiens.  Ceruplasmin is synthesized in the liver and has ferroxidase activity converting Fe+2 and Fe+3 as it is incorporated into transferrin.  Ceruplasmin is also an acute phase reactant, where increased concentration scavenge oxygen radicals.  Copper is mainly removed by fecal excretion as unabsorbed dietary copper and contained in biliary and intestinal secretions.  Less than 3% of dietary copper is lost in urine and sweat.  ` COPPER DIFICIENCY  Copper deficiency is uncommon, however certain circumstance promote its occurrence, such as malnutrition, malabsorption.  Zinc competes with copper for absorptions from the intestine; therefore increased intake of zinc could cause copper deficiency.  Copper deficiency cause a microcytic, hypochromic anemia associated with low concentrations of ceruplasmin.  An early feature of copper deficiency is neutropenia, which may be related to decreased activity of the copper containing an antioxidant enzyme SOD, shortening the life of erythrocytes and neutrophils.  Severe copper deficiency is associated with neurologic symptoms, decreased pigmentation and other conditions.  In addition both coronary heart disease caused by blood vessel defects are more likely in severe copper deficiency.  Menke’s syndrome is caused by recessive X-linked genetic defect in copper transport and storage.  Mental deterioration, failure to thrive, diminished activities of copper-containing enzymes , connective tissue abnormalities, kinky hair and early death are features of this disease.  If started early enough the condition may be treated with copper histidine.  COPPER EXCESS  Excess occurs mostly be accidental ingestions of copper solutions, use of intrauterine devices containing copper or exposure to copper containing fungicides.  Acute copper toxicity is associated with nausea, vomiting and epigastric pain.  Excess copper as with excess iron can cause free radical production and damage.  Wilson’s disease or hepatolenticular degenerations is associated with copper accumulation in the liver brain, Kidney and cornea.  In Wilson’s disease copper is transported normally from the intestine to the liver but cannot be transported out of the liver into the bile. Patients develop copper overload in the brain and liver, results in a low serum copper concentration.  A low serum copper concentration (