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ORIGINAL ARTICLE
Year : 2004  |  Volume : 52  |  Issue : 2  |  Page : 145-8

Trace Elements Iron, Copper and Zinc in Vitreous of Patients with Various Vitreoretinal Diseases


Biochemistry Research Department, Sankara Nethralaya, Chennai, India

Correspondence Address:
N Sulochana Konerirajapuram
Biochemistry Research Department, Sankara Nethralaya, Chennai
India
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Source of Support: None, Conflict of Interest: None


PMID: 15283220

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  Abstract 

Purpose: To measure the concentrations of iron, copper and zinc in human vitreous and to interpret their levels with various vitreoretinal diseases like proliferative diabetic retinopathy, retinal detachment, intraocular foreign body, Eales' disease and macular hole.
Methods: Undiluted vitreous fluid collected during pars plana vitrectomy was used to measure trace elements using an atomic absorption spectrophotometer.
Results: The level of vitreous iron increased threefold in Eales' disease (1.85 ± 0.36 pg/ml), 2.5-fold in proliferative diabetic retinopathy (1.534 ± 0.17 pg/ml) and 2.3-fold in eyes with intraocular foreign body (1.341 ± 0.25 pg/ml) when compared with macular hole (0.588 ± 0.16 pg/ml). This was statistically significant (P < 0.05). Zinc was found to be low in Eales' disease (0.57 ± 0.22 pg/ml) when compared with other groups, though the difference was not statistically significant.
Conclusion: The increased level of iron with decreased zinc content in Eales' disease confirms the earlier reported oxidative stress mechanism for the disease. In proliferative diabetic retinopathy and intraocular foreign body the level of iron increases. This is undesirable as iron can augment glycoxidation, which can lead to increased susceptibility to oxidative damage, in turn causing vitreous liquefaction, posterior vitreous detachment and ultimately retinal detachment and vision loss

Keywords: Vitreous, ocular diseases, zinc, copper, iron


How to cite this article:
Konerirajapuram N S, Coral K, Punitham R, Sharma T, Kasinathan N, Sivaramakrishnan R. Trace Elements Iron, Copper and Zinc in Vitreous of Patients with Various Vitreoretinal Diseases. Indian J Ophthalmol 2004;52:145

How to cite this URL:
Konerirajapuram N S, Coral K, Punitham R, Sharma T, Kasinathan N, Sivaramakrishnan R. Trace Elements Iron, Copper and Zinc in Vitreous of Patients with Various Vitreoretinal Diseases. Indian J Ophthalmol [serial online] 2004 [cited 2020 Nov 30];52:145. Available from: https://www.ijo.in/text.asp?2004/52/2/145/14607



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Recent studies on the role of minerals in the pathogene-sis of several diseases are gaining importance. Minerals form a part of the enzyme systems mostly as promoters and regulate many biochemical reactions.[1] While trace amounts of these minerals are needed physiologically, at increased levels they are harmful. Of the various minerals of biochemical importance zinc, copper and iron play a pivotal role in the oxidant/antioxidant mechanism, imbalance of which leads to increased susceptibility to oxidative tissue damage thereby leading to disease pathogenesis as in diabetes mellitus, cancer, neurodegenerative diseases etc.[2]

Zinc is an essential nutrient and the most abundant trace element in the eye. The concentration of zinc is 15 times higher in the retina than in the circulation.[3] Zinc is necessary for the activity of many enzymes like superoxide dismutase, carbonic anhydrase and matrix metallo proteases.[4] It functions as an antioxidant by protecting sulfhydryl groups from oxidation. It competes with copper and iron to reduce the formation of hydroxyl-free radicals by upregulating synthesis of metallothionein, a cysteine-rich protein that can scavenge damaging hydroxyls.[5],[6] Iron and copper can be toxic as they undergo redox reactions, which generate reactive oxygen intermediates (ROI).[7],[8] ROI promotes both glycoxidation and lipoxidation (i.e. oxidation of carbohydrates and lipids), which are known to damage cellular proteins, lipids and DNA.[9],[10] This damage is greater under oxidative stress leading to various pathological conditions.

There is no available information on vitreous levels of iron, copper and zinc in vitreoretinal diseases like Eales' disease, diabetic retinopathy (DR), retinal detachment (RD) and macular hole. While the aetiology of these diseases differs, [11],[12],[13],[14],[15] knowledge of these elements is of immense importance in understanding the aetiopathology of these diseases.

Our study aimed to determine the levels of iron, copper and zinc in vitreous fluids from various vitreoretinal diseases like Eales' disease DR, RD, Intraocular foreign body (IOFB) and macular hole. Vitrectomy is performed as a part of the treatment for these diseases.


  Materials and Methods Top


All experiments pertaining to human subjects were performed according to the tenets of the Helsinki declaration, With approval from the Institutional Research Board and Ethics Committee, informed consent and patient history was obtained from all participants enrolled in the study. Undiluted vitreous samples from 37 patients (32 males, 5 females) in the age group 3-72 were collected by the vitreoretinal surgeon at the time of vitreoretinal surgery using a sterile syringe attached to an automated vitrector during pars plana vitrectomy. The volume of the samples ranged from 0.5 ml to 0.7 ml. The samples were transported to the laboratory and processed immediately. Samples contaminated with blood were not analysed. Based on the clinical diagnosis they were divided into 5 groups [Table - 1].

Analysis of minerals

Undiluted vitreous was centrifuged at 3000rpm for 30 minutes and the available volume was made up uniformly to 1ml with Mill Q water for technical reasons. This was digested with 3 ml of concentrated nitric acid perchloric acid mixture (5 :1 ) and heated until all organic material was lost. The residue was made up to 2 ml with 5 parts distilled water. A drop of concentrated nitric acid was added to prevent adsorption of minerals on the wall of the container.[16] The solutions were analysed for copper, iron and zinc by the atomic absorption spectrophotometer (model Perkin Elmer 2380, USA) as described earlier.[17] The instrument was calibrated with standards from Sigma Chemical Company, (St Louis, USA). Results were expressed as mg/ml of vitreous.

Since the sample size was small and groups were unequal, ANOVA was not performed. The results were analysed by the student t test, and statistical significance set at P < 0.05.


  Results Top


[Table - 1] describes the demographic details of subjects enrolled in the study. The levels of trace elements copper, zinc and iron in vitreous samples are given in [Table - 2]. All values are expressed as mean ± standard error. The level of zinc in the vitreous of patients with Eales' disease was lower (0.57 ± 0.22 pg/ml) than in IOFB (1.595 ± 0.24 pg/ml), RD (1.254 ± 0.21 pg/ml) and DR (1.075 ± 0.18 pg/ml). The level of iron was higher in Eales' disease (1.85 ± 0.36 pg/ml), DR (1.534 ± 0.17 pg/ml) and IOFB (1.341 ± 0.25 pg/ml) compared to macular hole (0.588 ± 0.16 pg/ml) and was statistically significant (P< 0.05). The increase of iron in these groups was statistically significant even after excluding the smokers in each group. The level of copper was similar in all groups.


  Discussion Top


The pathology of the vitreoretinal diseases mentioned varies but in all the conditions the retina is affected or damaged leading to severe vision loss. As the vitreous is considered a metabolic repository of the retina, knowledge of the levels of these trace elements in the vitreous may help us understand how these elements are associated with vitreoretinal pathology. Analysis of these three elements was done based on the fact that Fe/Cu amplify free radical mediated oxidative damage[8],[9] while zinc is an antioxidant element.[3] Increased concentrations of iron and copper generate hydroxyl radical from superoxide anion,which in turn damages proteins, lipids and DNA.[9] Fe/Cu also promotes glycoxidation reaction in the presence of glucose and other sugars at alkaline pH forming enediol and dicarbonyls leading to the formation of advanced glycation end products like carboxymethyl lysine (CML), and pentosidine. Accumulation of such products has been reported in diabetes, end-stage renal disease, amyloidosis[18]-[19] and Eales disease.[20] Formation of glycoxidation-mediated advanced glycation end products (AGE) is seen in chronic uremia irrespective of the normoglycemic status but with an increased oxidative stress.[18] The oxidative stress can be combatted with effective antioxidant systems like vitamins A,E,C and the enzymes superoxide dismutase, glutathione peroxidase, catalase, and glutathione.[21] The retina contains large amounts of polyunsaturated fatty acids (PUFA) and is most vulnerable to oxidative stress. Zinc, an integral part of the enzyme superoxide dismutase, protects the retina from oxidative damage along with other antioxidants.[3]

Many studies have been done on the role of oxidative - stress-mediated damage in different ocular disease like diabetic retinopathy, age-related macular degeneration, Eales' disease and uveitis but there are no reports to our knowledge on the levels of iron, copper and zinc in vitreous fluid in these diseases. (Medline search)

In this study, iron increased threefold in the vitreous of patients with Eales' disease compared to macular hole, while the level of zinc decreased compared to other groups. The increase of iron is not desirable as it facilitates glycoxidation and formation of dicarbonyls and thereby AGE.[19] As copper levels are normal in Eales' disease it appears that iron has a greater role in glycoxidation than copper in this disease. It is reported earlier that in Eales' disease, there is tremendous oxidative stress characterised by increased thiobarbituric acid reactive substances with decreased antioxidant enzymes and vitamins in erythrocytes and vitreous.[22],[23] In fact, we found carboxy methyl lysine (CML) AGE in the epiretinal membranes and serum of Eales disease patients.[20] The decreased level of zinc in the vitreous of Eales' disease patients confirms that the vitreous has a decreased antioxidant capacity to counteract the oxidative stress.

In proliferative diabetic retinopathy group there was a 2.5-fold increase of iron in vitreous compared to macular hole. Iron mediates the formation of protein dicarbonyls, and it is reported that there is an increased carbonyl stress in diabetes which leads to increased accumulation of AGE in long and short-lived proteins thereby affecting their normal function.[19]

The IOFB group had a 2.3-fold increase of iron in the vitreous with no significant difference in copper and zinc between groups, suggesting that the nature of the foreign body may have some iron content, and the ocular complications may be mediated through iron. In the RD group there was no significant change in the levels of iron, copper and zinc compared with other groups.

The small sample size is an inherent weakness of this study. These findings should be confirmed with a large sample.

Presently zinc supplementation is gaining importance in the treatment of ARMD and it has been also found that zinc promotes SOD activity in smokers by ousting cadmium.[24],[25] Iron chelators are also suggested as a treatment for diseases like uveitis.[26] Hence determining the levels of these elements in the vitreous will be useful in planning therapeutic approaches. If similar results are obtained, iron chelators with zinc supplementation and fibre rich diet[27] can be given as therapeutic intervention.

This is the first report to our knowledge on the levels of iron, copper and zinc in vitreous specimens in vitreoretinal diseases, namely proliferative diabetic retinopathy, retinal detachment, Eales' disease and macular hole.

Acknowledgement

The atomic absorption spectrophotometer facility at the Radiosotope Laboratory, Madras Veterinary College, Chennai, India was used in the study.



 
  References Top

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    Tables

  [Table - 1], [Table - 2]


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