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KMID : 0382619810010010187
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Hanyang Journal of Medicine
1981 Volume.1 No. 1 p.187 ~ p.199
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Studies, on Pathogenesis of Cataracts
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Abstract
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It has been reported that cataract continues to be increased in its occurence due to the prolongation of average life span and the increase in the incidence of metabolic diseases including diabetes mellitus. Since cataract is clinically the commonest and most important disease of the lens and reported to be a worldwide major cause of blindness, extensive studies have been carried out to investigate the mechanism by which cataract is formed. Although it has been suggested that opacification of the lens was caused by (1)disturbance in electrolyte metabolism, (2) changes in the nature of lens proteins and (3) changes in the concentration of sulfhydryl (SH) compound, the biochemical nature and pathogenesis of cataract have not yet been clearly understood. In the present study, concentrations of proteins and SH compounds of the lens and the activity of adenosine triphosphatase (ATPase) involved in electrolyte metabolisn. of the lenswere determined to investigate biochemical nature of metabolic alterations in. diabetic cataracts using rats treated with alloxan as an experimental model.
In experimentally induced diabetic rats, the activity of Na+, K+-ATPase in_ the lens started to increase significantly after 10 days of alloxan treatment and a further rise in the enzyme activity was observed after 90 days of alloxan treatment at which time the lens was opacified. These results suggest that the decrease in the activity of Na+,K+-ATPase may be due to the primary effectof diabetes mellitus and be related to the initiation of the lens cloudiness. Onthe other hand, ´the activity of lens Mgt+-ATPase was unchanged up to 90 days of alloxan treatment, indicating that Mgt+-ATPase in the lens has nothing to do with lens opacity. A significant decrease in the activity of Na+,K+-ATPase was observed as early as 10 days after alloxan treatment, whereas the actual swelling of the lens appeared to be taken place after 40 days of alloxan treatment. These results suggest that, in experimentally induced diabetic rats, a profound decrease in the activity of the lens Na+, K+-ATPase may be required for upsetingthe cation balance so as to initiate the lens swelling.
Observations of a significant decrease in the concentration of SH compound of the lens after 40 days of alloxan treatment, a significant decrease in the amount of soluble protein after 60 days of the treatment and a significant increase in. the amount of insoluble protein after 90 days of the treatment indicate that, in experimentally induced diabetic rats, a change in the concentration of SH compound of the lens proceeds prior to the alterations of lens proteins and that sulf-hydryl groups of the soluble protein be oxidized to form mixed disulfide of the insoluble protein which, in turn, initiates the cloudiness of the lens.
While concentrations of three types of lens crystallin proteins were all decreased after 90 days of alloxan treatment, the ratio of each of the crystallin protein to the total soluble protein was variable depending on the type of crystallin protein: the ratio of alpha- crystallin to the total soluble protein was significantly increased; the ratio of gamma-crystallin to the total was significantly decreased; the ratio of beta-crystallin to the total was unchanged. These results suggest that. alpha- and gamma-crystallin proteins might be important intermediates determining the state of lens transparency.
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