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The Biological Importance Of Copper
Copper is an essential trace metal that we absorb from our diet. The concentration of copper in our bodies must be maintained within certain boundaries if we are to enjoy good health; too little copper or too much copper in the body will cause problems and can cause death. Fortunately, the body is able to regulate the concentration of copper through a process called homeostasis. When the body's burden of copper gets too high, copper is excreted; if it falls too low then more is absorbed from dietary sources. This article will briefly look at the role of copper in the body and provide an overview of the copper blood test that can measure a person’s copper status.
Copper plays both a structural and a catalytic role in certain metallo-enzymes. It is implicated in both oxidative and reductive enzymes and acts as an electron transfer intermediate in these systems. Most of the body’s copper burden (>65%) is associated with a molecule called ceruloplasmin, an oxidase (an enzyme which causes oxidation). Copper species are responsible for functions such as cellular respiration and iron metabolism; protection from free radical damage; melanin pigment synthesis and connective tissue biosynthesis. There is also compelling evidence to suggest that copper has a role to play in gene expression.
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Copper-Related Medical Conditions
Premature babies often suffer from copper deficiency, which can be associated with anaemia that does not respond to iron supplementation. Infants fed on cow’s milk may also be copper deficient, as cow's milk contains much less copper than human breast milk. For babies and infants being nourished intravenously (total parenteral nutrition; TPN), it is essential that the TPN fluid is enriched with appropriate trace metals including copper.
Copper deficiencies are associated with a number of diseases and conditions such as Menke’s syndrome; celiac disease; cystic fibrosis and short bowel syndrome. In contrast, Wilson’s disease is a condition in which the body’s copper burden continues to rise building up in the liver, eyes and brain. The classic symptom of Wilson’s disease are Kayser-Fleicher rings appearing in the eyes of the patient due to the build up of copper. If untreated, Wilson’s disease will cause liver failure and death; fortunately, the condition can be managed with chelation agents.
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Determination Of Copper In Blood
To give an overview of the copper blood test, all of the direct measurements of blood copper concentration rely on atomic spectroscopy. Traditionally, copper concentrations were measured from serum after extraction into methyl isobuyl ketone on a flame atomic absorption spectrometer (AAS). This device measures the reduction in a specific wavelength of light due to absorption by ground-state copper atoms as they pass through the flame. This measurement is directly proportional to the concentration of copper in the sample.
AAS can only determine a single element at a time and its use is being gradually reduced in clinical laboratories around the world as more and more labs turn to inductively coupled plasma optical emission spectroscopy (ICP-OES). In this technique, the sample (requiring a different preparation) is presented to an argon gas plasma which ionises virtually all elements reaching it. The light emitted by these ions is collected at specific wavelengths and quantified to provide a direct determination of the copper concentration in the sample presented to the ICP-OES. By the nature of the technique, information can be gathered simultaneously on a number of different elements which are present in the sample, depending upon the specifics of the ICP-OES device used.
As the cost of inductively coupled plasma mass spectrometers devices has fallen, more ICP-MS are being bought by routine clinical laboratories. In these instruments, the ions formed within the plasma are sampled by a mass spectrometer which produces a signal at the mass to charge ratio of the ion. ICP-MS is capable of providing coverage of almost the entire periodic table and is the most sensitive technique available for trace metal analysis. By virtue of the fact that ions are measured at their characteristic charge to mass ratio, the instrument can also be used to determine isotopic ratios in the sample which offers a range of possibilities for metabolic and multi-factorial studies.
On a personal note, my scientific career started in a clinical biochemistry laboratory performing trace metal analysis by atomic spectroscopy, notably with ICP-MS.
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1. Essentiality of Copper in Humans, R. Uauy et al, Am J Clin Nutr 1998;67 925S-9S.