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ARTICLES
Year : 1986  |  Volume : 34  |  Issue : 1  |  Page : 45-51

Role of lipid peroxidation and trace metal in cataractogenesis


Industrial Toxicology Research Centre, and Department of Ophthalmology, K.G. Medical College, Lucknow, India

Correspondence Address:
R S Dwivedi
Scientist Industrial Toxicology Research Centre, Post Box-80 Mahatma Gandhi Marg, Lucknow-226 001
India
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Source of Support: None, Conflict of Interest: None


PMID: 3443498

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How to cite this article:
Dwivedi R S, Partap V B. Role of lipid peroxidation and trace metal in cataractogenesis. Indian J Ophthalmol 1986;34:45-51

How to cite this URL:
Dwivedi R S, Partap V B. Role of lipid peroxidation and trace metal in cataractogenesis. Indian J Ophthalmol [serial online] 1986 [cited 2020 Feb 19];34:45-51. Available from: http://www.ijo.in/text.asp?1986/34/1/45/26346

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Table 1

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Cataract has been recognized as world wide public health problem being one of the major causes of human blindness especially in this country. A number of theories like solar radiations[1], nutritional deficiencies[2],[3] hormonal disorders[4],[5] and genetic variations[6] of specific enzymes are pro­posed but none of them have been established as the main cause It has been suggested that the light of avelengths greater than 295 nm are absorbed by the lens and initiate the formation of brownish cataract through the photochemical generations of superoxide radicals (02) and other harmful radicals[7],[8],[9],[10]. These unscavenged radicals could initiate peroxidation of polyunsaturated fatty acids causing photochemical oxidative stress leading to the formation of cataract[11],[12]. Peroxidation products have also been well correlated to the lens damage[13] in view of the facts that retinal photoreceptor cells have a very high rates of oxygen consumption and the outer segments of these cells have experi­mentally high level of polyunsaturated fatty acids[14]. It has therefore. been suggested that oxidative damage is one of the major factors contributing to the lens changes during the cataractogenesis and lenses experi­mentally damaged by photosensitized oxida­tion, exibibit changes similar to these observed in cataractous lenses.

Recently it has been reported that toxic metals like cadmium lead and nickel are accumulated in the lenses from our surround­ing environment[15],[16] where they are found in drinking water, diet contaminated with fertilizers passive smoking etc. These toxic metals are one of the important cofactors of lipidperoxidation process[17],[18],[19]. Studies on human lenses in relation to toxic metals and peroxidation process are very scanty. It was therefore, of particular interest to exa­mine the level of essential and toxic metals of the human lenses and the extent of peroxida­tion process in the development of toxic cataract. Superoxide dismutase (EC 1.15.1.1) an enzyme of antioxidative defence mechanism which protects the system from the delete­rious effects of photochemical oxidation, was also assayed as a function of cataract deve­lopment.

Experimental

Cataractous human lenses, which were removed by intracapsular cryosurgery, were obtained from a Eye Relief Camp, conducted by the department of ophthalmology, K.G. Medical College Lucknow and stored at-20° C until required. The cataractous lenses were classified in Industrial Toxicology Research Centre Lucknow on the basis of colour and opacity into mature and immature lenses as described by Pirie[20] and the degree of immaturity was noted. Opaque lenses of the three patients of the same degree age and sex groups were pooled together and. homogenized in 0,25 M ice cold sucrose solu­tion for enzymatic assay and homogenate was prepared in 0.154 M KCI for the measurment of the peroxidation process. In order to find out a progressive change during cataract development the data of immature lenses (50-70% opacity) were compared to mature lenses (100% opacity).

Biochemical Determinations

Superoxide dismutase (SOD) (EC 1.15.1.1)

The SOD activity was assayed according to the procedure described by Kakkar et at[8]. Assay mixture contained 1.20 ml sodium pyrophosphate buffer (pH 8.3, 0.052 M) 0.1 mi 186 µ m phenazine methosulfate, 0.3 ml 300 µ m nitroblue tetrazolium and 0.2 ml NADH (780 µ m) with an appropriate amount of diluted enzyme preparation and water in a total volume of 3 ml. Reaction was started by the addition of NADH. After incubation at 30°C for 90 sec the reaction was stopped by the addition of I ml of glacial acetic acid. Reaction mixture was stirred vigorously and shaken with 4 ml butanol. The mixture was allowed to stand for 10 min centrifuged and butanol layer was extracted out. Colour intensity of the chromogen developed in the butanoll was measured at 560 nm in spectro­nic-21 spectrophotometer (Bausch & Lomb) against butanol as blank SOD activity was defined in terms of 50% decrease in chroma­zen formation and expressed as Units/min/mg protein.

Lipid peroxidation

Formation of lipid peroxides were deter­mined by assaying the presence of thiobarbi­turic acid (TBA) reacting substances accord­ing to the method of Sharma & Krishna Murti[22]. One of lens homogenate prepared was aerobically incubated at 37°C±1° in a metabolic shaker water bath (Scientronic model SSI-2391 120 srrokes per minutes (ampli­tude 1 cm) for 3 hrs. One ml of 10% (wJv) trichloroacetic acid was added at the end of the reaction and after thorough mixing, reac­tion mixture was centrifuged at 800xg for 10 min. One ml samples of clear supernatant were mixed with one ml of 0.67% 2-thiobar­bituric acid end held in a boiling water bath for 10 min. After cooling samples were diluted with one ml of distilled water. The OD changes were recorded at 535 nm and the results expressed as malonyldialdehyde (MDA) using 1 56 x 10 5 as the extinction coefficient.

Trace Metal Analysis

Individual lenses were weighed; cleaned and washed with phosphate buffered saline and transferred to a 25 ml conical flask which was cleaned thoroughly with hot cone HNO 3 ; rinsed and dried. Care was taken at all stages of preparation to reduce the risk of sample contamination. After complete diges­tion of lenses in HNO 3 , samples were dried and diluted with 1% HNO3. Analysis of the trace metals was performed in Perkin Elmer Model 5000 Atomic absorption spectrometer and results were expressed as jcg of metals per g of wet tissue. Protein determination was carried out according to Lowry et al[2],[3].

Chemicals

NADH, nitroblue tetrazolium, phenazine­methosulfate thiobarbituric acid and other biochemicals were obtained from Sigma Chemical co st. Louis M.O. All other reagents were analytical reagent grade and unless stated otherwise were used without further purification.


  Results and discussion Top


The present investigation was done in non diabetic and healthy patients of the Eye Relief Camp. Fasting blood glucose and blood haemoglobin were determined to assess the physical condition of the patients [Table - 1]. There was no significant change observed in the level of blood glucose and haemoglobin content of the patients.

The peroxidation of fats, was determined by measuring the content of malonaldiadehyde (MDA), a product derived from the lipid peroxide during the process, [Figure - 1]. This aldehyde (MDA) is considered a convenient and suitable indicator of the peroxidation process[22]. The content of MDA of the cataractous human lenses are shown in [Table - 2]. The values for MDA in mature cataractous lenses are compared to immature cat aractous lenses as a base line while evalua­ting the data for progressive cataractogenic changes. Immature lenses were taken in acco­unt in place of normal human lenses because of the difficulty arosen to obtain them. The results of the present investigation demons­trate that there is a significant elevation in contents of MDA in case of mature catarac­tous lenses. It has also been noted that the activity of the enzyme superoxide dismutase (SOD) is simultaneously decreased to a noticiable degree in mature cases showing a reduced capacity to scavenge the superoxide and other injurious radicals photochemically generated in intraocular fluids surounding the lens[14]. These radicals eventually initiate the peroxidation of unsaturated fatty acids resulting to the development of an opacity to the normal lens[14]. Earlier studies have reported the presence of 0 2, H 2 O 2 and other injurious radicals in aqueous and vitreous humour which continuously bath the anterior and posterior surfaces of the lens and indi­cated the possibility of lens opacity[14].

In present investigation it has also been demonstrated that there is a noticiable fall in the levels of essential trace metals like Cu, Zn, Mang, Fe etc. Compared to the level of toxic metals cadmium and nickel which are elevated in cataractous lenses [Table - 3]. An increase in toxic metal contents has been shown to accelerate the formation of lipid peroxides which are deleterious in nature[18],[19] An association of toxic metals especially cadmium and lipid peroxidations has already been established by Kinter and Pritchard[17]. Decreased level of essential trace metals, which are an integral part of a number of enzymes of biosystem[24], in cataractous lenses showing a derailment in the oxidative defence and protective mecha­nism of the lens. Cu. Zn and Mn the com­ponents of SOD and Fe are less in mature cases, suggesting a decreased defenee against oxidative insult. Also the decrease in SOD may be indicative that O 2 , has a specific role in lipid peroxidation in lens. This shows that the substantial protective action of SOD, against the cytotoxic effects resulting from the univalent reduction of oxygen is impaired. Superoxide dismutase along with catalase and glutathione peroxidase constitute a protec­tive defence mechanism of the ocular system against a photoperoxidative damage[25]. Activity of glutathione peroxidase (EC. 1.11.1.9) was found to be remarkably decrea­sed as we have retorted in our previous com­munication[26]. Therefore, it appears that concomitant photochemical generation of MDA in extracellular environment[27] in absence of a well attenuated system is partly responsible for the development of opacity to the lens. Impaired metabolism of essential trace metals which control the lens permea­bility (16) and play a very vital role in main­taining red ox potential of the ocular environ­ment, alongwitb an increased level of toxic metals potentiate the cataractogenic process Further, study is in progress to explore out the role of trace metals in the development of toxic cataract.


  Summary Top


Process of lipid peroxidalion and the levels of trace metal-iron, manganese copper zinc, sodium, potassium, calcium, cadmium and nickel were examined in cataractous human lenses to ascertain their roles, if any, in cataractogenesis. Enzyme superoxide dismutase (SOD-EC 1.15.1.1.) was also assayed as a function of cataract develop­ment. Results of the present investigation reveal that an increased peroxidation of unsaturated fatty acids and decreased SOD activity in mature cases could be due to an impairment in metabolism of trace metals. Elevated levels of toxic metals like cadmium in cataractoos lens, may partly, be responsi­ble for potentiation of peroxidation process resulting an oxidative insult and in term lead­ing to the development of toxic cataract.


  Acknowledgements Top


Authors are grateful to Dr. P.K. Ray Director, Industrial Toxicology Research Centre, for his keen interest and valuable discussion; Dr. P.N. Viswanathan, for his helpful suggestion; Dr. R.C. Srivastava, for support, Typographic assistance of Shri S.B. Singh is gratefully acknowledged.

 
  References Top

1.
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2.
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8.
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11.
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12.
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13.
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14.
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15.
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17.
Kinter WD and Pritchard 3D, 1977, Altered permeability of cell membrane. In, Handbook of Physiology Sect-9. Reactions to environmental agent Ed. S.D.G.K. Lee, H.L. Falh: S D. Murphy and S.R Gieger pp. 563. Bethesda, MD, American Physiolcg cal Society.  Back to cited text no. 17
    
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19.
Dwivedi RS, Kaur G, Srivastava RC and Krishnamurti CR, 1984, Lipid peroxidation in tin intoxicated partially hepatectomized rats. Bull Environ. Contamn. Toxicol. 33200.  Back to cited text no. 19
    
20.
Pine A, 1968, Colour and solubility of the proteins of the human cataracts. Invest. Ophthalmol. 7, 6321.  Back to cited text no. 20
    
21.
Kakkar P. Das B and Viswanathan PN, 1983, A modified spectrophotometric assay of superoxide dismutase. Ind. J. Biochem. Biophys. 21, 130.  Back to cited text no. 21
    
22.
Sharma OP and Krishnamurti CR, 1976, Ascorbic acid, naturally occurring mediator of lipid peroxide formation in rat brain. J. Neurochem. 27, 299,  Back to cited text no. 22
    
23.
Lowry OH, Rosebrough NJ, Farr Al and Randall RJ, 1951, Protein measurement with folin phenol reagent. J. Biol. Chem. 193, 265.  Back to cited text no. 23
    
24.
Fridovich I, 1975, Superoxide dismutases. A review Biochem. 44, 147.  Back to cited text no. 24
    
25.
Halliwell B and Gutteridge John MC, 1985, Free radicals in biology and medicine pp. 200. Oxford Science Publication.  Back to cited text no. 25
    
26.
Dwivedi RS and Pratap VB, 1985, A bioche­mical investigation of human cataractous lenses. Exp. Eye. Res. (Communicated).  Back to cited text no. 26
    
27.
Varma SD, Srivastava VK and Richards RD 1982, Photoperoxidation in lens and cataract forma­tion. Preventive role of superoxide dismutase, catalase and vitamin C. Ophthal Res, 14, 167.  Back to cited text no. 27
    


    Figures

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    Tables

  [Table - 1], [Table - 2], [Table - 3]



 

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