Free amino acids in cataractous lenses

AK Gupta; GS Sarin

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Year : 1976 | Volume : 24 | Issue : 2 | Page : 1-4

Free amino acids in cataractous lenses

AK Gupta, GS Sarin
Maulana Azad Medical College and Associated Hospitals, New Delhi, India

Correspondence Address:
A K Gupta
Professor of Ophthalmology, Maulana Azad Medical College and Associated Irwin and G.B. Pant Hospital, New Delhi-110002
India

Source of Support: None, Conflict of Interest: None

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PMID: 1031387

How to cite this article:
Gupta A K, Sarin G S. Free amino acids in cataractous lenses. Indian J Ophthalmol 1976;24:1-4

How to cite this URL:
Gupta A K, Sarin G S. Free amino acids in cataractous lenses. Indian J Ophthalmol [serial online] 1976 [cited 2021 Apr 18];24:1-4. Available from: https://www.ijo.in/text.asp?1976/24/2/1/31508

Present knowledge of the distribution of free amino acids in lenses is largely derived from studies on experimental animals: rabbit[[6],[9],[11] calf[2],[6] rat[8],[15], cat[15], and monkey,[15]. The concentration of amino acids in the lens has been shown to exceed that in the ocular fluids which bathe it[11]

The lens contains a high concentration of soluble proteins upon which in part its transparency is dependent[17]. Free amino acids present in the lens, can be broadly divided into two categories: proteogenic amino acids (amino acids from which proteins are synthesized) and non-proteogenic amino acids (these amino acids are not protein constituents). Free amino acids play an important role as precursors of lens proteins, hence, the study of lens free amino acids provides a most suitable subject for study. Present study is confined to the proteogenic amino acids.

It is very difficult to procure normal lenses for any biochemical investigations. The nearest approach to the normal seemed likely to be eye bank material. However, it has not yet been established that post mortem changes in the concentration and distribution of amino acids within the eye, from the time of death to analysis, are small. The results from such a study, therefore, will be suspicious.

The present study was undertaken to determine whether or not changes in free amino acids (proteogenic) pattern occurs in different stages of cataract formation.

Material and Methods

Fifty cases with senile cataracts were included in this study. There were 34 males and 16 females (age range 40 to 85 years). There were 11 cases of immature cataracts, 19 cases of mature senile cataracts, 9 cases of hypermature cataracts and 11 cases of nuclear black cataracts.

Free amino acids have been determined by two dimensional paper chromatographic analysis of deproteinized lens extracts. Only intact intracapsular lenses have been used. Lenses were obtained by forceps extraction under local anaesthesia and delivered promptly to the laboratory. Lenses were freed from adherent vitreous humour and homogenised in one ml. of water with cooling in an ice bath. Proteins were precipitated by addition of 10 per cent trichloroacetic acid. Precipitated proteins were packed at 13,500 r.p.m. for ten minutes in a refrigerated centrifuge at 4° centigrade. 500 microliters of the supernatant was analysed.

Results

Although an almost equivalent amount of lens was analysed in each case, the chromatographic pattern varied markedly.

The study was restricted to 16 amino acids, which are mainly proteogenic. These are : alanine, arginine, aspartic acid, glutamic acid, glycine, histidine, isoleucine, leucine, lysine, methionine, phenyl alanine, proline, serine, threonine, tyrosine and valine. The frequency of occurrence of all the 16 amino acids was studied by comparing the data in different categories of cataracts [Figure - 1],[Figure - 2]. We failed to detect tryptophane, cysteine and hydroxyproline in all the cases studied. It was noted that presence of aspartic acid, arginine, glutamic acid, leucine, serine and threonine in the free amino acid pool was almost equally frequent in immature, mature and hypermature lenses. However, in nuclear black cataracts aspartic acid and arginine were much less frequently observed while glutamic acid and leucine were more frequently seen as compared to those seen in other three stages of cataracts.

Alanine, glycine, isoleucine, lysine, phenyl alanine, proline, tyrosine and valine were found less and less frequently with the advancement of cataract. This was true also for alanine, glycine, isoleucine and tyrosine in cases of nuclear black cataracts. Lysine was not detected in any of nuclear black cataract cases. Phenyl alanine and proline were specially more frequently found for some unexplained reasons in cases of nuclear black cataracts. Histidine was seen progressively more frequently in mature, hypermature and nuclear black cataracts. Methionine was seen most frequently in mature cataracts.

Discussion

Free amino acid pool has been shown to be in a fairly stable balance state for months in cases of protein deficient animals inspite of continuous negative systemic nitrogen balance and severe "eight loss and the lens continues to grow at a normal rate[1]. In contrast, in alloxan diabetic rabbits, changes in free amino acid levels were immediately apparent[12]. Decrease in the concentration of the amino acid pool to almost the level in aqueous humour takes place within a few days in severely hypoglycemic rabbits'. The loss of free amino acid has also been found in alloxan diabetic rabbits8 and pancreatectomized rats[16].Decrease in free amino acid levels was first reported for lenses of xylose fed rats[18] and has also been reported for galactose fed rats[13].

Barber[1] in 1968 had proved that in human senile cataracts the elevation of amino acids above normal concentration preceded the stage of very low concentration. Although this course of events is compatible with the concept of autolysis due to lowered intracellular pH[7] or to disruption of lysosomes[16], what was suggested[1] was that elevation of amino acid concentration may be a contributing cause in the development of senile cataracts, rather than a mere symptom of autolysis.

Amino acids have been shown to be actively transported from plasma into the posterior aqueous humour and from there into the lens[3],[4],[5],[9],[10],[11]. These observations suggest the possibility that failure of one or both of the systems responsible for their transport may result in cataracts, and prompted Reddy and Kinsey[12] to investigate accumulation of amino acids in lenses of animals developing cataracts from diabetes as a result of being maintained on a diet rich in galactose.

The results of our study revealed that it is only some of the amino acids which show alteration in their frequency of occurrence in different stages of cataract formation and it goes well with the above observation.

Summary

Fifty cases of cataractous lenses have been studied for free amino acid (proteogenic) pool. The cases included immature senile, mature senile, hypermature and nuclear black cataracts. It was observed that the frequency of occurrence of only some of the amino acids was affected with the progression of cataracts.

References

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