TRACE ELEMENT DYNAMICS IN THE VERTEBRATE EYE

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The concentrations of copper (Cu), iron (Fe) and selenium (Se) in the intraocular fluids (IOFs) and plasma of a number of mammalian species have been determined by electrothermal atomic absorption spectrophotometry (EAAS) using methods developed in an ongoing project. The plasma contains considerably higher concentrations of these elements than the IOFs. In plasma almost all of the Cu is bound to the alpha 2-globulin, ceruloplasmin, Fe is bound to transferrin and Se to glutathione peroxidase. During ocular inflammation in rabbits, the aqueous humor concentration of all these elements increase in parallel to the increase in protein concentration, most likely due to the influx of plasma proteins when the blood-aqueous barrier is disrupted. Although these proteins are effective anti-oxidants and may play an important role in the inflammatory response and other disease states, their possible roles in ocular inflammation and disease have not been studied. For example, ceruloplasmin can oxidize a number of substrates, including serotonin and ascorbic acid; interaction with the latter is histaminolytic. The ferroxidase activity of this protein can protect against iron damage by catalyzing high affinity binding of ferric ions to transferrin. Glutathione peroxidase can inactivate hydrogen peroxide. Although it is assumed that the increase in trace element concentration in the IOFs during inflammation is due to the influx of plasma proteins, this has not been proven. In addition transferrin and ceruloplasmin may release the Cu and Fe, which they carry, upon entering the IOFs. In order to determine whether these elements enter the IOFs bound to their carrier proteins, and their subsequent fate, a method has been developed for separation of proteins by molecular weight using HPLC gel filtration and analysis of the resulting fractions for trace element content using EAAS. The technique will be applied to an analysis of the IOFs from normal and inflamed eyes of rabbits and normal and diseased eyes of various animal species treated in our ophthalmology clinic and surgery classes (species include: dogs, cats, cows, sheep, pigs, horses, ponies, etc.). Furthermore, the activities of the plasma proteins which may be present in the IOFs under these conditions will be measured with a view to determining what role (e.g. beneficial or detrimental) they may play in the ocular response to injury, inflammation and disease.