Eye lens opacity in cortical cataracts associated with actin-related globular degeneration

Role of actin-binding proteins in cataract formation

INTRODUCTION

Actin has been implicated in lens opacification; however, the specific actin-related pathways involved in cataracts remain unelucidated. In this study, actin-related proteome changes and signaling pathways involved in the development of cataracts were evaluated.

METHODS

The anterior capsule and phacoemulsification (phaco) cassette contents were collected during cataract surgery from 11 patients with diabetic cataract (DC), 12 patients with age-related cataract (ARC), and seven patients with post-vitrectomy cataract (PVC). Untargeted, global identification and quantification of proteins was performed through liquid chromatography-mass spectrometry with the data-independent acquisition (DIA).

RESULTS

In phaco cassette samples, proteins with significantly lower expression in ARC than in DC and PVC were involved in various pathways, including actin binding, actin cytoskeleton reorganization, actin filament capping, cortical actin cytoskeleton organization, and small GTPase-mediated signal transduction pathways. In anterior capsules, proteins with significantly lower expression in ARC than in DC and PVC were involved in actin binding and actin cytoskeleton reorganization pathways.

CONCLUSION

Actin cytoskeleton and actin-binding proteins are involved in lens fiber elongation and differentiation. Rho GTPases contribute to actin cytoskeletal reorganization, and their inactivation is linked to abnormal lens fiber migration. These findings link actin binding to lens fiber integrity, lens opacification, and cataracts.

The oxidized thiol proteome in aging and cataractous mouse and human lens revealed by ICAT labeling

Age‐related cataractogenesis is associated with disulfide‐linked high molecular weight (HMW) crystallin aggregates. We recently found that the lens crystallin disulfidome was evolutionarily conserved in human and glutathione‐depleted mouse (LEGSKO) cataracts and that it could be mimicked by oxidation in vitro (Mol. Cell Proteomics, 14, 3211‐23 (2015)). To obtain a comprehensive blueprint of the oxidized key regulatory and cytoskeletal proteins underlying cataractogenesis, we have now used the same approach to determine, in the same specimens, all the disulfide‐forming noncrystallin proteins identified by ICAT proteomics. Seventy‐four, 50, and 54 disulfide‐forming proteins were identified in the human and mouse cataracts and the in vitro oxidation model, respectively, of which 17 were common to all three groups. Enzymes with oxidized cysteine at critical sites include GAPDH (hGAPDH, Cys247), glutathione synthase (hGSS, Cys294), aldehyde dehydrogenase (hALDH1A1, Cys126 and Cys186), sorbitol dehydrogenase (hSORD, Cys140, Cys165, and Cys179), and PARK7 (hPARK7, Cys46 and Cys53). Extensive oxidation was also present in lens‐specific intermediate filament proteins, such as BFSP1 and BFSP12 (hBFSP1 and hBFSP12, Cys167, Cys65, and Cys326), vimentin (mVim, Cys328), and cytokeratins, as well as microfilament and microtubule filament proteins, such as tubulin and actins. While the biological impact of these modifications for lens physiology remains to be determined, many of these oxidation sites have already been associated with either impaired metabolism or cytoskeletal architecture, strongly suggesting that they have a pathogenic role in cataractogenesis. By extrapolation, these findings may be of broader significance for age‐ and disease‐related dysfunctions associated with oxidant stress.

Breakdown of interlocking domains may contribute to formation of membranous globules and lens opacity in ephrin-A5(-/-) mice

Ephrin-A5, a ligand of the Eph family of receptor tyrosine kinases, plays a key role in lens fiber cell packing and cell-cell adhesion, with approximately 87% of ephrin-A5(-/-) mice develop nuclear cataracts. Here, we investigated the extensive formation of light-scattering globules associated with breakdown of interlocking protrusions during lens opacification in ephrin-A5(-/-) mice. Lenses from wild-type (WT) and ephrin-A5(-/-) mice between 2 and 21 weeks old were studied with light and electron microscopy, immunofluorescence labeling, freeze-fracture TEM and filipin cytochemistry for membrane cholesterol detection. Lens opacities with various densities were first observed in ephrin-A5(-/-) mice at around 60 days old. Dense cataracts in the mutant lenses were seen primarily in the nuclear region surrounded by transparent cortices from all eyes examined. We confirmed that a majority of nuclear cataracts were dislocated posteriorly and ruptured the thinner posterior lens capsule. SEM analysis indicated that numerous interlocking protrusions and wavy ridge-and-valley membrane surfaces in deep cortical and nuclear fibers did not cause lens opacity in both transparent ephrin-A5(-/-) and WT mice. In contrast, abundant isolated membranous globules of approximately 1000 nm in size were distributed randomly along the intact fiber cells during early stage of all ephrin-A5(-/-) cataracts examined. A further examination using both SEM and TEM revealed that isolated globules were generated from the disintegrated interlocking protrusions originally located along the corners of hexagonal fiber cells. Freeze-fracture TEM further revealed the association of square-array aquaporin junctions with both isolated globules and interlocking membrane domains. This study reports for the first time that disrupted interlocking protrusions are the source of numerous large membranous globules that contribute to light scattering and nuclear cataracts in the ephrin-A5(-/-) mice. Our results further suggest that dissociations of N-cadherin and adherens junctions in the associated interlocking domains may result in the formation of isolated globules and nuclear opacities in the ephrin-A5(-/-) mice.

Anterior lens epithelium in intumescent white cataracts - scanning and transmission electron microscopy study

PURPOSE

Our purpose was to study the structure of the lens epithelial cells (LECs) of intumescent white cataracts (IC) in comparison with nuclear cataracts (NC) in order to investigate possible structural reasons for development of IC.

METHODS

The anterior lens capsule (aLC: basement membrane and associated LECs) were obtained from cataract surgery and prepared for scanning electron microscopy (SEM) and transmission electron microscopy (TEM).

RESULTS

We observed by SEM that in IC, LEC swelling was pronounced with the clefts surrounding the groups of LECs. Another structural feature was spherical formations, that were observed on the apical side of LEC's, towards the fibre cell layer, both by SEM and TEM. Development of these structures, bulging out from the apical cell membrane of the LEC's and disrupting it, could be followed in steps towards the sphere formation. The degeneration of the lens epithelium and the structures of the aLC in IC similar to Morgagnian globules were also observed. None of these structural changes were observed in NC.

CONCLUSIONS

We show by SEM and TEM that, in IC, LECs have pronounced structural features not observed in NC. This supports the hypothesis that the disturbed structure of LECs plays a role in water accumulation in the IC lens. We also suggest that, in IC, LECs produce bulging spheres that represent unique structures of degenerated material, extruded from the LEC.

Effect of methionine sulfoxide reductase B1 (SelR) gene silencing on peroxynitrite-induced F-actin disruption in human lens epithelial cells

F-actin plays a crucial role in fundamental cellular processes, and is extremely susceptible to peroxynitrite attack due to the high abundance of tyrosine in the peptide. Methionine sulfoxide reductase (Msr) B1 is a selenium-dependent enzyme (selenoprotein R) that may act as a reactive oxygen species (ROS) scavenger. However, its function in coping with reactive nitrogen species (RNS)-mediated stress and the physiological significance remain unclear. Thus, the present study was conducted to elucidate the role and mechanism of MsrB1 in protecting human lens epithelial (hLE) cells against peroxynitrite-induced F-actin disruption. While exposure to high concentrations of peroxynitrite and gene silencing of MsrB1 by siRNA alone caused disassembly of F-actin via inactivation of extracellular signal-regulated kinase (ERK) in hLE cells, the latter substantially aggravated the disassembly of F-actin triggered by the former. This aggravation concurred with elevated nitration of F-actin and inactivation of ERK compared with that induced by the peroxynitrite treatment alone. In conclusion, MsrB1 protected hLE cells against the peroxynitrite-induced F-actin disruption, and the protection was mediated by inhibiting the resultant nitration of F-actin and inactivation of ERKs.

Effects of antioxidant supplementation on mRNA expression of glucose-6-phosphate dehydrogenase, β-actin and 18S rRNA in the anterior capsule of the lens in cataract patients

This was a preliminary study of the effects of antioxidant supplementation on the peroxidation status of the lens by investigating mRNA expression of anti-oxidative enzymes in the lens. The mRNA expression levels of glucose-6-phosphate dehydrogenase (G6PDH), β-actin (β-ACT) and 18S rRNA (18S) were measured in this study because they are common reference genes for measuring mRNA levels by means of a real-time reverse transcription polymerase chain reaction (RT-PCR) in various tissues. Thirteen patients with binocular cataracts of the same grade were included in the study after giving informed consent. A piece of the anterior capsule, along with a sample of lenticular epithelial cells (LECs), was collected as a pre-intake sample during cataract surgery. Ocuvite + Lutein(®), an antioxidant supplement, was administered orally beginning the day after surgery. Six weeks later, a piece of the anterior capsule along with a sample of LECs, was collected as a post-intake sample during cataract surgery of the opposite eye. RNA was purified from the homogenized samples, and cDNA was reverse transcribed to measure mRNA levels. The expression levels of G6PDH, 18S and β-ACT were measured using RT-PCR. The expression levels of G6PDH and 18S were significantly higher in the post-intake samples than they were in the pre-intake samples. Significant positive correlations between the expression levels of G6PDH and 18S were observed in both the pre- and post-intake samples. Following gender-specific analyses, the expression levels of G6PDH and 18S in the post-intake samples were found to be significantly higher among the female patients. A significant positive correlation between the expression levels of G6PDH and 18S was observed in the post-intake samples from the male patients. There were no significant changes in the gene expression levels of β-ACT after supplementation among male or female patients. β-ACT has been verified for use as a reference gene for measuring the effects of antioxidant supplementation in the lens by RT-PCR. Antioxidant supplementation was noted to increase G6PDH in the pentose phosphate cycle and 18S rRNA in the ribosome.

Dietary supplements reduce the cataractogenic potential of proton and HZE-particle radiation in mice

Abstract The present study was undertaken to investigate the ability of dietary supplements to reduce the formation and severity of cataracts in mice irradiated with high-energy protons or iron ions, which are important components of the radiation encountered by astronauts during space travel. The mice were exposed to proton or iron-ion radiation and fed with a control diet or diets supplemented with the soybean-derived protease inhibitor, Bowman-Birk inhibitor (BBI), in the form of BBI Concentrate (BBIC) or an antioxidant formulation [containing l-selenomethionine (SeM), N-acetyl cysteine (NAC), ascorbic acid, co-enzyme Q10, alpha-lipoic acid and vitamin E succinate] both before and after the radiation exposure. At approximately 2 years after the radiation exposure, the animals were killed humanely and lenses were harvested and characterized using an established classification system that assigns discrete scores based on the severity of the lens opacifications. The results showed that exposure to 1 GeV/nucleon proton (3 Gy) or iron-ion (50 cGy) radiation significantly increased the cataract prevalence and severity in CBA/J mice to levels above the baseline levels of age-induced cataract formation in this mouse strain. Treatment with BBIC or the antioxidant formulation significantly reduced the prevalence and severity of the lens opacifications in the mice exposed to iron-ion radiation. Treatment with BBIC or the antioxidant formulation also decreased the severity of the lens opacifications in the mice exposed to proton radiation; however, the decrease did not reach statistical significance. These results indicate that BBIC and the antioxidant formulation evaluated in this study could be useful for protecting astronauts against space radiation-induced cataracts during or after long-term manned space missions.

Differential binding of mutant (R116C) and wildtype alphaA crystallin to actin

PURPOSE

Quantitate the interaction of mutant (R116C) and wildtype human alphaA crystallins with actin.

METHODS

AlphaA crystallins, expressed in a recombinant system, were purified, followed by passage through an actin affinity column.

RESULTS

Binding of mutant alphaA crystallin was significantly less than binding of wildtype alphaA crystallin.

CONCLUSIONS

The R116C mutation of alphaA crystallin found in human cataracts binds less to the cytoskeletal component actin. Since both alphaA crystallin and actin are necessary for proper development of the lens, decreased binding of the mutant protein to actin may perturb normal differentiation processes of lens cells which are necessary for transparency.

Lens cytoskeleton and transparency: a model

The function of the cytoskeleton in lens was first considered when cytoplasmic microtubules were observed in elongating fibre cells of the chick lens nearly 40 years ago. Since that time, tubulin, actin, vimentin and intermediate filaments have been identified and found to function in mitosis, motility and cellular morphology during lens cell differentiation. A role for the cytoskeleton in accommodation has been proposed and modification of the cytoskeletal proteins has been observed in several cataract models. Recently, a progressive increase in protein aggregation and lens opacification was found to correspond with the loss of cytoskeletal protein in the selenite model for cataract. In the present report a model is proposed for the role of tubulin, actin, vimentin, spectrin and the lens-specific filaments, filensin and CP49, in the establishment and maintenance of transparent lens cell structure.

alpha-crystallin stabilizes actin filaments and prevents cytochalasin-induced depolymerization in a phosphorylation-dependent manner

alpha-crystallin, a major lens protein of approximately 800 kDa with subunits of about 20 kDa has previously been shown to act as a chaperone protecting other proteins from stress-induced damage and to share sequence similarity with small heat-shock proteins, sHsp. It is now demonstrated that this chaperone effect extends to protection of the intracellular matrix component actin. It was found that the powerful depolymerization effect of cytochalasin D could be almost completely blocked by alpha-crystallin, alpha A-crystallin or alpha B-crystallin. However, phosphorylation of alpha-crystallin markedly decreased its protective effect. It is suggested that phosphorylation of alpha-crystallin may contribute to changes in actin structure observed during cellular remodeling that occurs with the terminal differentiation of a lens epithelial cell to a fiber cell and contributes to cellular remodeling in other cell types that contain alpha-crystallin species. This communication presents biochemical evidence clearly demonstrating that alpha-crystallin is involved in actin polymerization-depolymerization dynamics. It is also shown that alpha-crystallin prevented heat-induced aggregation of actin filaments. alpha-crystallin was found to stabilize actin polymers decreasing dilution-induced depolymerization rates up to twofold while slightly decreasing the critical concentration from 0.23 microM to 0.18 microM. Similar results were found with either alpha-crystallin or its purified subunits alpha A-crystallin and alpha B-crystallin. In contrast to the experiments with cytochalasin D, phosphorylation had no effect. There does not appear to be an interaction between alpha-crystallin and actin monomers since the effect of alpha-crystallin in enhancing actin polymerization does not become apparent until some polymerization has occurred. Examination of the stoichiometry of the alpha-crystallin effect indicates that 2-3 alpha-crystallin monomers/actin monomer give maximum actin polymer stabilization.

Vitamin C reduces cytochalasin D cataractogenesis

The effect of cytochalasin D (CD), an actin monomer-stabilizer, has been studied on cataract development in rat lenses. Cataractogenesis was induced by incubating the rat lenses in medium 199 (M199) containing 10(-5) M CD; by the end of 24 h, lenses first developed a visible opacity. The increased lactate dehydrogenase (LDH) activity in the culture medium, leakage of lens cytosolic proteins into the culture medium and observable development of opacity through a dissection microscope were correlated with cell damage associated with cataract formation. Non-denaturing polyacrylamide gel electrophoresis was used to separate three lens LDH isoenzymes. The effect of 1 mM vitamin C (VC) in reducing LDH leakage was also examined. The protective effect of VC on CD-initiated cataractous lenses is significant. This suggest that a portion of the opacity and lens damage may involve oxidative damage to the membrane-cytoskeleton complex which is started by CD, but partially prevented by VC

Primary structure and lens-specific expression of genes for an intermediate filament protein and a beta-tubulin in cephalopods

Intermediate filament (IF) protein and tubulin cDNAs of cephalopod eye lenses were cloned and sequenced. The rod regions of the deduced IF proteins of the squid and octopus were more similar (68% identical) than were head (33% identical) and tail (40% identical) regions. The rod sequences were closer to squid neuronal IF protein (39% identical) than to any other known IF protein. There was only 31% identity between the rod regions, 21-30% identity between the head regions and 23-32% identity between the tail regions of the present IF proteins of cephalopods and other invertebrates. The rod regions of the cephalopod IF proteins contained the 6 heptads characteristic of nuclear lamins, consistent with an evolutionary relationship between IF proteins and lamins. The present octopus alpha-tubulin was 93% and beta-tubulin was 87% identical to the corresponding tubulins of insects and vertebrates. SDS-PAGE and peptide sequencing indicated that the order of abundance of the cephalopod lens cytoskeletal proteins was IF proteins, actin and tubulins. Northern blot hybridization revealed a 4 kb mRNA for the octopus IF protein and 2.9 and 7.3 kb mRNAs for the squid IF protein; the alpha-tubulin mRNA was about 1.8 kb in the octopus and squid, and the beta-tubulin mRNA was about 2.8 kb in the octopus. The alpha-tubulin mRNA was present in all tissues examined; by contrast, the present beta-tubulin and IF protein mRNAs appeared specialized for lens expression.

Methylisocyanate and actin polymerization: the in vitro effects of carbamylation

Uremia has been implicated in cataractogenesis due to protein carbamylation by cyanate derived from urea. The present study was designed to directly identify the effects of carbamylation on actin polymerization and the possible contribution to cataract formation. The susceptibility of actin to carbamylation is expected because of the 19 lysines distributed along its length. The lysines of actin were selectively carbamylated by methylisocyanate (MIC) at pH 8.0 and 4 degrees C and actin polymerization assayed by high-shear viscometry, fluorescence and transmission electron microscopy. Our results provide evidence that non-enzymatic carbamylation of the lysine residues prevents the polymerization of actin. In addition, this carbamylated actin inhibited the polymerization of nascent, unmodified actin. High-shear viscosity measurements demonstrated decreased initial apparent rates and decreased steady-states (final specific viscosities) of polymerization. Fluorescence measurements showed decreased relative intensities of fluorescence versus control and confirmed the inhibitory effects of carbamylation by MIC on the steady state of F-actin. Transmission electron microscopy (TEM) showed the presence of disorganized filaments when carbamylated actin was added to polymerizing unmodified actin. Our results suggest that carbamylation of actin can cause a loss of ordered filament structure and shape of the lens fiber cell, thus predisposing it to cataract development.

Selenite nuclear cataractogenesis: a scanning electron microscope study

The sequential changes during selenite nuclear cataractogenesis were examined with a scanning electron microscope (SEM) and correlated with slit lamp observations. A posterior opacity, visible with the slit lamp 1-2 days after injection of sodium selenite, was found to consist of masses of vacuoles in the superficial posterior cortex by SEM. 2-3 days post injection, a biomicroscopic refractile ring around the nucleus was represented by SEM abnormalities suggesting membrane damage and possible loss of cytosol in the perinuclear region. All normal structure in this region was lost by 5 days after injection when the central nucleus had become opaque. SEM also showed evidence for damage in areas which were still clear by slit lamp examination. Changes, characteristic of aging, were found near selenite induced damage in peripheral (younger) fibers.

In vitro studies of microwave-induced cataract: reciprocity between exposure duration and dose rate for pulsed microwaves

Rat ocular lenses exposed to pulsed microwave irradiation were maintained at constant temperature by circulating phosphate buffered saline in a thermostatically-controlled chamber. Irradiations with pulsed radiation (10 musec, 24 kW pulses) of 918 MHz were done at several different specific absorption rates (SAR) for durations up to 1 hr in order to explore a possible reciprocal relationship. The extent of damage was measured by the maximum depth of granular degeneration in the equatorial region of lenses fixed immediately after irradiation. The parameters of the pulses were increased to 20 musec and 48 kW to explore the variation in the biological effects and threshold with respect to average power, as well as pulse parameters (pulse width, peak power and energy per pulse). A total of 47 lenses were used in 3 X 4 factorial experimental design to explore effects observed at different average powers and durations (6, 20 and 60 min). The results were statistically analyzed by ANOVA and multiple regression analysis with logarithmic transformation. The results are summarized as follows. This data showed clear trends towards increasing depth of granular degeneration with increasing duration of exposure and dose rate. There was considerable evidence to confirm such reciprocity suggesting that total dose is an important parameter. A model postulating reciprocity was shown to explain observed variation in depth of damage as well as one allowing for separate effects of duration and dose rate. Lens fibre cell effects were detected by scanning electron microscopy after 6 min irradiation at the SAR values of 40 and 20 mW g-1. Light microscopic evidence of lens fiber cell damage can be detected at an SAR of 10 mW g-1 after a 1 hr exposure.

Association of alpha-crystallin with actin in cultured lens cells

The nature of the beaded filaments in the lens fiber cell has been debated for some time. One explanation is that beaded filaments represent an association of alpha-crystallin with actin filaments. By using a double labelling technique that allowed us to view actin filaments and alpha-crystallin in the same cell we have demonstrated that some of the alpha-crystallin in lens cells is indeed associated with actin.

Modelling cortical cataractogenesis: VI. Induction by glucose in vitro or in diabetic rats: prevention and reversal by glutathione

Cataractogenesis can be induced by glucose in the rat lens in vitro and in vivo. In vitro, this is done by increasing the amount of glucose in the medium surrounding the isolated lens; within 48 hr considerable globular degeneration is seen subcapsularly, deeper in the equatorial region. In vivo, it is achieved by making the rat diabetic by injecting streptozotocin i.v., which selectively destroys the beta-cells of the pancreas; the blood serum glucose level increases markedly, and thence the aqueous humour level and, in turn, the lens concentration. Globular degeneration occurs as in vitro, but not until 6 weeks is a degree of damage observed comparable to that seen in the lenses incubated in vitro for only 48 hr. Lenticular sorbitol and fructose are also markedly elevated as a result of the high glucose levels. If glutathione (GSH) is present in the medium (0.1 mM) or injected s.c. daily into the diabetic rats, there is no evidence of subcapsular globular degeneration of the cortical fiber cells, even though the lenticular levels of glucose, sorbitol and fructose are the same as when GSH was not given; this is true for either the in vitro or in vivo situation, although individual values in the two situations do differ somewhat from one another. When rats were given GSH beginning several weeks after the diabetic state had been induced, the damage subsequently observed was much less than if the rats had been diabetic without GSH for the same total length of time; it was also much less than damage which should have occurred by the time GSH treatment was instituted. It would thus appear that a certain amount of reversal of the globular degeneration is possible, although damage in the equatorial region (wedge-shaped) seems less amenable to rescue by glutathione. The data indicate that glutathione can prevent or diminish the severity of sugar cataractogenesis, and that there would appear to be more steps in sugar cataractogenesis than simply osmotic damage, although this may be the primary event.

Lens actin: purification and localization

Actin was purified from the chick lens using DEAE-52 column chromatography followed by hydroxylapatite chromatography. The antibody produced against the purified actin cross-reacted specifically with lens actin from other species in addition to smooth and skeletal muscle actin and labelled the stress bundles of cultured fibroblasts. Actin was localized, using immunological methods, primarily to the plasma membrane of the epithelial and fiber cells of the chick and human lens. Actin filaments were also identified by HMM S-1 labeling in bovine cortical fiber cells. Using this procedure, the actin filaments were found throughout the fiber cell but were mainly concentrated near the plasma membrane and in cell processes. They formed a population distinct from the beaded filaments. The initial DEAE-52 column chromatography was also useful in the initial purification of lens fiber cell intermediate filament protein and two species of beta-crystallins.

Specificity of glucose transport inhibitors in the frog lens

The unidirectional fluxes (influx and efflux) of glucose across frog lens membranes were investigated using the radio-labelled sugar analogue 3-O-methyl-D-[U-14C]glucose. The effect of various inhibitors of sugar transport on the movement of 3-O-methylglucose was studied and the specificity of the inhibition was estimated by carrying out concomitant measurements of lens sodium content. The movement of 3-O-methylglucose into the lens was rapid, and 50% equilibration occurred within 5 hr. The influx was reduced in the presence of phloretin, phloridzin, ouabain, iodoacetate and cytochalasin B, but only in the case of the latter was there no concomitant change in lens sodium content. Only cytochalasin B can therefore be regarded as a specific inhibitor of glucose transport. The efflux of 3-O-methylglucose was followed after 16 hr incubation with [14C]3-O-methylglucose. The efflux kinetics had a double exponential form and the half-time of the slower phase was 165 mins. The efflux of the slow phase was found to be sensitive to the presence of inhibitors. Phloretin and cytochalasin B produced the most marked reduction in efflux rate, but again only in the latter case was the effect reversible. Bidirectional transport of glucose therefore occurs in the lens and movement in both directions is reduced by cytochalasin B, which appears to be the only inhibitor of transport so far studied that does not disturb lens ion levels.

Modeling cortical cataractogenesis. V. Steroid cataracts induced by solumedrol partially prevented by vitamin E in vitro

Rat lenses incubated in tissue culture medium (M 199) maintain their transparency for a long period of time. The soluble corticosteroid, solumedrol (methyl prednisolone sodium succinate) was added to the medium, at concentrations including the range expected during rejection episodes following organ transplantation (3.8 X 10(-9) M-3.8 X 10(-6) M). At the lowest level used (3.8 X 10(-9) M), five lenses of 12 became opaque following a 48 hr incubation, while at higher concentrations of solumedrol almost all lenses developed opacities. Addition of vitamin E to the medium resulted in partial prevention of the cataract as judged by the smaller proportion of lenses becoming opaque. Examination of the lenses by scanning and transmission electron microscopy (SEM and TEM, respectively), indicated that in untreated lenses the initial location of the cataract is at the anterior pole of the lens where a deepening area of degeneration formed, followed by a uniform subcapsular layer of degeneration spreading over the remainder of the lens. Damage at this location is not typical of most in vitro cortical cataracts. In the presence of vitamin E the extent of damage was less, involving, initially, an equatorial wedge of globular degeneration and spreading anteriorly and posteriorly in a thinner subcapsular layer. This type of damage was more typical of that seen previously for cataracts induced by cytochalasin D, elevated glucose and hygromycin B.

Radiation cataract formation diminished by vitamin E in rat lenses in vitro

Eye lens cataract is a late effect of exposure to ionizing radiation. Depending on the dose and quality of radiation impinging on the lens, the development of a clinically discernible cataract usually takes several months in animal models, when the lens is irradiated in situ. However, we have developed a rapid in vitro assay with the isolated intact rat lens to study the effect of radiation and influence of antioxidants as protective agents. After only 24 hr of post-irradiation incubation at 35.5 degrees C in complete medium 199 + 10% foetal calf serum, damage in the form of globular degeneration subcapsularly and 'holes' in the cortical fibre cells is detectable. Doses as low as 0.10 Gy seem to be capable of causing some damage, and vitamin E (2.4 microns) in the medium confers some protection to the irradiated lens.