On the calcium concentration of cataractous and normal human lenses and protein fractions of cataractous lenses

Calcium concentrations of a large number of cataractous human lenses and nine normal human lenses were measured by atomic absorption spectroscopy. The mean concentration of calcium in cataractous lenses is 2–13 times higher than the mean calcium concentration of the normal lenses. In considering individual lenses, however, a large number of cataractous lenses contain either less or equivalent calcium concentrations than are present in normal lenses.The Calcium distributions in both the water-soluble and water-insoluble protein fractions isolated from yellow and brown cataracts were also determined. While some aggregate fractions of yellow lenses are calcium rich, no clearcut differences in the mean calcium concentrations of the remaining protein fractions could be established.     

Corneal thickness and corneal endothelium in normotensive subjects with unilateral exfoliation syndrome

Purpose: To examine the central corneal thickness (CCT) and corneal endothelium in both eyes of patients with unilateral exfoliation syndrome (EXS). To determine the effect of CCT on the measurement of intraocular pressure (IOP). Methods: In this cross-sectional clinical study, comparisons were made of CCT (Humphrey Ultrasonic Pachometer), corneal endothelial cells (Keeler-Konan contact specular microscope) and IOP (Goldmann applanation tonometer) between the exfoliative (E) and fellow non- exfoliative (NE) eyes in 40 normotensive patients with unilateral EXS. The CCT was used to obtain a corrected value for the IOP. Results: The E eyes had significantly higher values for CCT (0.528±0.030 vs 0.523±0.032 mm, P<0.01) and IOP (15.7±3.6 vs 14.4±2.9 mmHg, P<0.001) than the fellow NE eyes. The paired E and NE eyes did not differ in endothelial cell density (2779±540 vs 2870±386 cells/mm²), in the coefficient of variation of cell size (0.25±0.03 vs 0.26±0.03) or in the frequency of hexagonal cells (80.5±6.5 vs 82.0±5.0%). After correcting IOP for CCT, the E eyes still had significantly higher IOP than the NE eyes (15.1±4.4 vs 14.2±3.7 mmHg, P<0.05). Conclusion: Normotensive eyes with early EXS did not have quantitative (cell density) or qualitative (variation in cell size, frequency of hexagonal cells) morphological changes in corneal endothelium, but had higher values for IOP and CCT. After correcting IOP for CCT, the E eyes still had significantly higher IOP than the fellow NE eyes. Received: 16 December 1999 Revised: 20 March 2000 Accepted: 21 March 2000     

Ion analyses of human cataractous lenses

The sodium, potassium, calcium, magnesium and chloride concentrations have been determined in 52 human cataractous lenses. Three main types of association between concentrations and cataract type were found. Group A, mainly nuclear cataracts, had a near normal range of concentrations. Group B, a mixture of cataract types, including mixed cataracts, had a significantly raised sodium and lowered potassium concentration, but particularly a raised calcium concentration. Group C, mainly cortical and mature cataracts, had grossly increased sodium and calcium concentrations, an increased chloride concentration and a very low potassium level. In all groups the magnesium concentration remained relatively constant.The role of calcium is particularly interesting. In pure nuclear cataracts its concentration is relatively normal and below the equilibrium concentration, but when there is cortical involvement very high calcium levels are found. The values, which are above the calculated equilibrium concentration, indicate that binding of calcium occurs. Group B and C cataractous lenses also showed a significant decrease in dry weight.     

Glutathione and glutathione-related enzymes in human cataractous lenses

Glutathione and its related enzymes were measured for normal and cataractous human lenses. Glutathione decreased progressively with the development of cataracts. This decrease was more pronounced in the nucleus than in the capsule-epithelia of cataractous lenses. Glutathione reductase in nuclear extracts was relatively unchanged during cataract progress, while glutathione synthetase was significantly low in the advanced stages of cataracts. gamma-Glutamylcysteine synthetase was not measurable in the nuclei of cataractous lenses.     

Aminopeptidase III activity in normal and cataractous lenses

Aminopeptidase III activity was demonstrated in extracts from several different mammalian lenses by the hydrolysis of Arg-MCA at pH 6.0. No more than a two-fold difference was seen in overall specific activity. Sections of bovine lenses were removed from the periphery to the center and assayed. A sharp decline in activity was observed in the inner cortical region, and little or no activity was observed in the lens nucleus. This correlated with an increase in the presence of low molecular weight peptides as determined by SDS polyacrylamide gel electrophoresis. The properties of the aminopeptidase from human lens tissue were the same as those previously reported for the purified enzyme from bovine lens. The aminopeptidase activity of normal and cataractous lenses was compared using 4 different substrates. The cataractous lenses had significantly less total aminopeptidase activity. However, little difference in specific activity was observed based on soluble lens protein content. Similarly, electrophoretic separations of normal and cataractous soluble proteins showed little or no differences in the content of low molecular weight peptides. Therefore, this major human lens aminopeptidase remains functional in the cataractous state.     

Pyridine nucleotides in normal and cataractous human lenses

The levels of NAD⁺, NADH, NADP⁺ and NADPH have been determined in each cortex and nucleus of about 80 normal and cataractous human lenses and in a small number of calf, rabbit and rat lenses. Cataractous lenses had lower levels of all nucleotides than the normal lenses but no progressive decreases were associated with the development of nuclear colour, or with cortical, diabetic, traumatic and steroid cataracts. It was concluded that a lack of reduced pyridine nucleotides was not responsible for a decrease in the ability of the lens to protect itself against oxidative damage.     

Regional water content of clear and cataractous human lenses

The present study evaluates the regional water content of clear and cataractous human lenses. In order to determine the lens water, a freeze-drying technique was used which leaves behind only a very small amount of residual humidity. The effectiveness of freeze-drying was demonstrated in experiments with animal eye lenses (rat, pig, bovine). The results obtained revealed that, like in other mammalian lenses, the human lens cortex exhibits a significantly higher overall water content than the nucleus. This pattern was found in clear lenses as well as in lenses with early 'senile' cataracts. Subcapsulary cataracts present a unique feature as in these lenses the cortical water content is enhanced while the fresh lens weight is significantly reduced. Observations of postmortem human eye lenses indicate that regional differences in water content are greatly abolished 24-48 h after death.     

Freezable and non-freezable water content of cataractous human lenses

Twenty-nine cataractous human lenses between the ages of 36 and 93 were investigated. The total water content of cortex and nucleus were obtained by vacuum dehydration. The freezable water content was measured by differential scanning calorimetry. The non-freezable water content was obtained by difference. To measure the extent that syneresis contributes to cataract formation, an excess function was designed. The excess function represents the changes that occur, for example, in non-freezable water content due to cataractogenesis. It is calculated as the difference between the non-freezable water content of a normal lens and that of a cataractous lens of the same age. On the average, there is 7% less non-freezable water in the cortex of a cataractous lens than in the cortex of a normal lens. The corresponding number for the nucleus is 9%. This represents 29 and 36% changes, respectively, in the cortex and nucleus due to syneresis during cataractogenesis.     

Localization of glutathione-S-transferase in transparent and cataractous human lenses

The localization of glutathione-S-transferase (GST) activity was investigated in 15 cataractous lenses obtained by intracapsular extraction of senile cataract. Additionally, 8 clear lenses, obtained from donor eyes in cases of corneal transplantation or of traumatic lens luxation, were used as controls. The lenses were divided into the central and peripheral portions with a trephine. The activity of GST was quantitated in each portion according to the method described by Habig. GST activity in clear lenses was significantly higher in the peripheral portion than in the central portion and in the former it was significantly higher in clear lenses than in cataractous ones. The ratio of GST activity between central and peripheral portions (C/P) was significantly higher in cataractous lenses than in clear ones. These findings suggested that the scavenging system of the human clear lens is more active in the equatorial portion than in the central portion. Nevertheless the activity of GST in human cataractous lenses decreased more significantly in the peripheral portion than in the central portion. These findings indicated that the human cataract usually develop from equatorial portion of lens.     

Polycyclic aromatic hydrocarbons in clear and cataractous human lenses

In this histochemical study on the ocular lens, the authors test for the presence of various sorts of the (unsaturated) polycyclic aromatic hydrocarbon (PAH) in 66, both clear and cataractous human lenses. A statistically significant greater amount of PAH is found in the cataractous lenses studied (p < 0.01), with two kind of PAH, phenanthrene and 1,2-benzoan-thracene, appearing exclusively in lenses with cataracts. The authors put forward a hypothesis on the cataractogenic effect of PAH on the basis of its interference with lens metabolism and the subsequent production and release of free-radicals.