|Year : 1985 | Volume
| 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
U M Rawal
Reader in Zoology, University School of Sciences, Gujarat University, Ahmedabad-380 001
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Avarachan P J, Rawal U M. Protein profile is the progressive experimental cataract (selenite model). Indian J Ophthalmol 1985;33:303-8
|How to cite this URL:|
Avarachan P J, Rawal U M. Protein profile is the progressive experimental cataract (selenite model). Indian J Ophthalmol [serial online] 1985 [cited 2020 Jul 5];33:303-8. Available from: http://www.ijo.in/text.asp?1985/33/5/303/30736
In the normal lens, the cellular architecture 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,,,. Biochemical causes of various experimental animal cataracts are being used to investigate the under lying mechanism of cataractogenesis 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. Bhuyan et al confirmed the inducement of selenite cataract in rabbit, rat and guinea pig. 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 concentration above 20 ppm is lethal to animals. No sequential study of biochemical parameters 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 conditions, 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 confirmed by ophthalmoscopic observation. The three experimental groups and their controls 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. 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. 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 µ 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 µ mol/kg body weight resulted in 100% mortality within 24 hours and reducing the dose to less than 10 µ 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 concentration 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 (P<0.05), 28.85% decrease in soluble proteins (P<0.00l) and 96.2% increase of isoluble proteins. In the mature stage of cataract, the changes of values were 12.32% (P<0.001), 49.25% (P<0.001) and 125.5% respectively. Respective changes of values in hyper mature stage were 29.96%, 75.56% and 166.02%. Highly significant decrease in the soluble protein concentration was observed even in the nuclear stage of cataract.
The total protein concentration in aqueous humour and blood was found to be decreased 3.28% (P<0.1) and 1.54% respectively in nuclear cataract; 9.09% (P<0.U01) and 5.53% respectively in mature cataract; and 14.16% (P<0.001) and 9.06% (P<0,001) in hyper mature cataract.
The withdrawal effects on the protein contents in blood, aqueous humour and lens of selenite cataracts are shown in [Table - 2]. In some withdrawal groups, the total and soluble proteins of lens were found to be increased. Significant change of total protein concentration of lens to was observed only in nuclear and cataracts at 2nd and 3rd month withdrawals. The changes of soluble proteins in the nuclear cataract of 2nd and 3rd month withdrawals were found to be significant. Considerable decrease of insoluble proteins in mature and hyper mature cataract was not seen in any of the withdrawal groups.
No significant withdrawal effect on the total protein concentration of aqueous humour was observed in any of the cataract groups.
Highly significant increase of total proteins was noted in all cataractous groups of the 2nd and 3rd month withdrawals.
| Discussions|| |
The results reported here demonstrate that (1) the selenite cataract is age specific and dose dependent, (2) the selenite has got salient effects on the protein levels in blood, aqueous humour and (3) the consecutive changes that occur in cataractous lens may be explained in terms of increased protein degradation or decreased protein synthesis.
It was interesting to note that 100% inducement of cataract occurred only in the post 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 indicates 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. Selenite has been shown to inhibit protein synthesis strongly in vitro. A decline of total protein content in the serum of human, exposed to the selenium factory condition has also been reported . 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,. Selenite has been shown to be incorporated into soft tissues as, seleno-trisulfides (protein-S-Seprotein),. The formation of selenium trisulfide and equimolar quantity of disulfide linkage between SH-groups of biomolecules, was initially proposed by Painter. 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. The normal eye lens contains relatively high concentration of sulfhydryl groups both proteinacious and non proteinacious (Glutathione). 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 conformational changes in the structure and function of lens proteins, forming aggregates, may scatter light and thereby cause opacity,.
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 proportional to the maturation of cataract. Normalisation of protein levels in blood, irrespective 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 ,, selenium overdose could cease in the withdrawal 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 inducement 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 formation in the lenticular proteins. These conformational 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 Research, 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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[Figure - 1], [Figure - 2], [Figure - 3]
[Table - 1], [Table - 2]