Indian Journal of Ophthalmology

ARTICLES
Year
: 1985  |  Volume : 33  |  Issue : 5  |  Page : 303--308

Protein profile is the progressive experimental cataract (selenite model)


PJ Avarachan, UM Rawal 
 Department of Zoology, Gujarat University, Ahmedabad, India

Correspondence Address:
U M Rawal
Reader in Zoology, University School of Sciences, Gujarat University, Ahmedabad-380 001
India




How to cite this article:
Avarachan P J, Rawal U M. Protein profile is the progressive experimental cataract (selenite model).Indian J Ophthalmol 1985;33:303-308


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Avarachan P J, Rawal U M. Protein profile is the progressive experimental cataract (selenite model). Indian J Ophthalmol [serial online] 1985 [cited 2024 Mar 28 ];33:303-308
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Full Text

In the normal lens, the cellular architec�ture is very regular and its transparency is believed to be the result of spatial order of lens poteinsi. Extensive studies have been done on the proteins of human lens, because of its importance in lens transparency[2],[3],[4],[5]. Biochemical causes of various experimental animal cataracts are being used to investigate the under lying mechanism of cataractogene�sis and its sequential changes in man. The exact mechanism of cataract formation is not fully known.

The cataractogenic potential of selenite was first reported by Ostadalova et al[6]. Bhuyan et al confirmed the inducement of selenite cataract in rabbit, rat and guinea pig[7]. The action of selenium, one of the trace elements considered to be of importance for the biological system, is dose dependent. In animals, the dietry requirement of selenium is from 0.03 to 0.04 ppm; a concen�tration above 20 ppm is lethal to animals[8]. No sequential study of biochemical para�meters in blood, aqueous humour and lens of selenite induced cataracts has been done so far.

The purpose of this study described here was to provide a progressive evaluation of (1) the impact of selenite challenge in vivo upon protein contents in the rat lens, aqueous humour and blood with respect to the sequential changes of cataract from nuclear stage to hyper mature stage and (2) the withdrawal effects on protein contents of nuclear, mature and hyper mature cataracts.

 MATERIAL AND METHODS



Charles Foster Albino female rats and their litters of 10-12 pups were individually housed in aluminium cages and fed on standard rat food and water ad libitum. At 9 days of age, total pups were divided into two groups, experimental and control. The experimental groups were subcutaneously injected with twice weekly dose of 20 1z mol sodium selenite per kg body weight. The age related control groups (non-injected) were kept in the same environmental condi�tions, receiving the same food and water. There were three experimental groups : (1) (20 days old) receiving two injections; (2) (27 days old) receiving four injections and (34 days old) receiving six injections. The stages of cataract inducement were con�firmed by ophthalmoscopic observation. The three experimental groups and their con�trols were given one, two and three months withdrawal for the withdrawal study.

At various intervals, the pups were sacrificed and blood samples withdrawn from jugular vein into heparinized tubes. The aqueous humour samples were collected by the method of Kinsey et a1[9]. Complete eye lenses were dissected out by posterior approach and weights taken on a balance sensitive to 0.01 mg. The protein contents of the samples were estimated by the standard method of Lowry et al[10]. Lenses were homogenized in cold double distilled water and centrifuged for 15 minutes at 5,000 rpm, in refrigerated centrifuge. The supernatent was used for soluble protein assay.

 OBSERVATIONS



The subcutaneous injection of a single dose of 20 � mol sodium selenite/kg body weight produced 100% cataract when administered to rat pups at 9th day post partum. Injection on day 15 caused only the formation of occasional opacities. Increasing the dose of injected selenite to 60 � mol/kg body weight resulted in 100% mortality within 24 hours and reducing the dose to less than 10 � mol/kg body wt. caused no effect on lens in vivo. A well-formed nuclear cataract was displayed by two injections of a dose of 20 p mol/kg body weight [Figure 2]. Maturation of cataract was observed within 3-5 injections. Hyper mature cataract was developed by six successive injections [Figure 4].

The effects of selenium on protein con�centration in lens, aqueous humour and blood in vivo are shown in [Table 1]. In nuclear stage of cataract the changes of protein concentration observed in the lens were 3.1% reduction of total proteins (Ppost partum development of rat, with a dose not less than 20 u mol sodium selenite/kg body weight. The first 15 days post partum period of rat may be highly specific in the impact of selenite on the crystalline lens and its transport system. However, the primary effect of selenite was noted to be on the protein profile of eye lens.

The consecutive biochemical changes that occur in the selenite induced cataractogenesis included the fall of total and soluble proteins of lens; loss of total protein concentration in aqueous humour and blood. This indica�tes that selenite has got potent effect on the vitality of the entire transport system of lens. It was reported that selenium has some affinity to certain plasma proteins[11]. Selenite has been shown to inhibit protein synthesis strongly in vitro[12]. A decline of total protein content in the serum of human, exposed to the selenium factory condition has also been reported [13]. sub Based on the above results and evidences, it may be speculated that the over dose of selenite leads to protein degradation in blood first, which in turn changes the biochemical constitution of aqueous humour and its transportation to the crystalline lens. The fall of total proteins, also, denotes the inhibition of protein synthesis in lens.

Highly significant loss of soluble proteins and elevation of insoluble proteins, right in the nuclear stage, is a salient feature of selenite cataract. This primary effect was found to be increased with the progress of dosage. The inolubilization of lenticular proteins by formation of high molecular weight aggregates, is a common feature of all cataracts. The usual state of selenium in animal tissues is protein bound[14],[15]. Selenite has been shown to be incorporated into soft tissues as, seleno-trisulfides (protein-S-Se�protein)[16],[17]. The formation of selenium trisulfide and equimolar quantity of disulfide linkage between SH-groups of biomolecules, was initially proposed by Painter[18]. The reaction is : 4 RSH+H2SeO3-RSSE+SR+ RSSR+3H2O. Selenite is reported to be an active catalyst in the oxidation of sulfhydryl compounds in vitro[19]. The normal eye lens contains relatively high concentration of sulfhydryl groups both proteinacious and non proteinacious (Glutathione)[20]. Based on the above mentioned affinities of selenium for lens proteins, it may be concluded that the over dose of selenium catalyses the formation of disulfide and seleno-trisulfide cross links in the lenticular proteins. These conforma�tional changes in the structure and function of lens proteins, forming aggregates, may scatter light and thereby cause opacity[21],[22].

In the withdrawal study of selenite induced cataracts, significant increase of total protein and soluble proteins of nuclear cataract lenses were observed in the third month. This change can be due to increased- protein input or increased solubility of insoluble proteins. However, the reversability of cataract is interesting to account here. The potency of reversability in selenite induced cataract was found to be inversely propor�tional to the maturation of cataract. Nor�malisation of protein levels in blood, irres�pective of the cataract stage, is another intresting feature taken into account in this withdrawal study. Since, considerable amount of selenite metabolites are excreted out of the body the retained effect of [23],[24],[25] selenium overdose could cease in the with�drawal periods.

Selenite injection to young rat gives a model for cataractogenesis, incorporating many of the characteristics present in the human senile cataract. Further study of this model can be expected to yield more insights to this phenomenon.

 SUMMARY



Selenite cataract is found to be age specific and dose dependent. Subcutaneous injection of 20 u mol sodium selenite/kg body weight produces 100% cataract induce�ment when administered to rat pups on 9th day post partum. Significant decrease in total and soluble proteins of lens, and total protein of blood and aqueous humour are the important features in this progressive study of selenite induced cataract. These consecutive changes can be explained in terms of increased protein degradation or decreased protein synthesis. The over dose of selenium catalyses the cross-link forma�tion in the lenticular proteins. These con�formational changes in the structure and function of lens-proteins may be the cause of cataract in selenite treated rat. The potency of reversability in selenite induced cataract is inversely proportional to the maturation of cataract.

 ACKNOWLEDGEMENTS



This work has been supported by grants from the Indian Council of Medical Rese�arch, New Delhi (grant No. 3/l /l /27(254)/82 CAR-II). We express our gratitude to Professor V.C. Shah, Head, Department of Zoology. for providing the laboratory facilities.

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