Free Amino Acids in Senile Cataractous Lenses: Possible Osmotic Etiology

¹ Wills Eye Hospital and Research Institute, Philadelphia, Pa.

Comparison of free amino acids in freshly excised rabbit lenses and in lenses taken from the contralateral eyes after storage for 24 to 48 hours reveals essentially no postmortem changes. This suggests that human eyebank lenses may be considered as normal with respect to the free amino acid pool. Analysis of senile cataractous lenses, compared to eyebank lenses, reveals a wide range of amino acid concentrations, from much higher to much lower than eyebank lens levels. Amino acid concentrations in cataracts decrease with decreasing lens weight, visual acuity, and per cent protein. Free proteogenic amino acid concentrations decrease from levels well above those in eyebank lenses, while nonproteogenie amino acids decrease only from normal levels. Thus selective accumulation of free proteogenic amino acids seems to be an early event in the etiology of senile cataract. This conclusion suggests the following hypothetical mechanism of senile cataractogenesis. Inhibition of protein synthesis, with continued normal proteolysis, could account for selective increase in proteogenic amino acid levels. Increased normal hydrolysis or pathological autolysis are possible but not essential explanations. Increased intracellular osmotic pressure and resultant imbibition of water may cause the wellknown early intumescence of senile cataract. If damage to cell membranes results, lens protein may be lost by leakage rather than by autolysis. Consequent dilution of cytoplasm and disruption of cellular structure are sufficient explanation of opacification.

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