Effect of calpain on hereditary cataractous rat, ICR/f

Gene profiles and mutations in the development of cataracts in the ICR rat model of hereditary cataracts

Cataracts are opacifications of the lens that cause loss of visual acuity and ultimately of eyesight. Age-related cataract develops in most elderly people, but the mechanisms of cataract onset are incompletely understood. The Ihara Cataract Rat (ICR) is an animal model of hereditary cataracts showing cortical opacity that commonly develops prematurely. We identified putative mechanisms of cataract onset in the ICR rat model by measuring gene expression changes before and after cortical cataract development and conducting point mutation analysis. Genes differentially expressed between 4-week-old animals without cortical cataracts and 8-10-week-old animals with cortical cataracts were selected from microarray analysis. Three connections were identified by STRING analysis: (i) Epithelial-Mesenchymal Transition (EMT), including Col1a2, and Pik3r1. (ii) Lens homeostasis, including Aqp5, and Cpm. (iii) Lipid metabolism, including Scd1, Srebf1, and Pnpla3. Subsequently, mutation points were selected by comparing ICR rats with 12 different rats that do not develop cataracts. The apolipoprotein Apoc3 was mutated in ICR rats. Analyses of gene expression changes and point and mutations suggested that abnormalities in EMT or lipid metabolism could contribute to cataract development in ICR rats.

Structure-Based Virtual Screening and Biological Evaluation of a Calpain Inhibitor for Prevention of Selenite-Induced Cataractogenesis in an in Vitro System

Calpains belong to the family of calcium-dependent, structurally related intracellular cysteine proteases that exhibit significant functions in evolution of different types of cataracts in human as well as animal models. Application of calpain inhibitors generated through a virtual screening workflow may provide new avenues for the prevention of cataractogenesis. Hence, in the current study, compounds were first screened for potent calpain inhibitory activity by employing a structure-based approach, and the screening results were then validated through biological experiments in rat lenses. A hit compound, HTS08688, was obtained by structure-based virtual screening. A micromolar concentration of HTS08688 was found to prevent in vitro cataractogenesis in isolated Wistar rat lenses, while maintaining the antioxidant and calcium concentrations at near normal levels. Inhibition of superoxide anion generation, as observed through cytochemical localization studies, and maintenance of structural integrity, as demonstrated by histological analysis of lenticular tissue, also suggested that HTS08688 can ameliorate the cataractous condition induced by selenite in an in vitro rodent model. A cell proliferation assay was performed; the IC 50 value of the screened calpain inhibitor, HTS08688, against human lenticular epithelial cells-b3 was found to be 177 μM/mL. This combined theoretical and experimental approach has demonstrated a potent lead compound, HTS08688, that exhibits putative anticataractogenic activity by virtue of its potential to inhibit calpain.

Pharmacokinetic and pharmacodynamic evaluation of the anti-cataract effect of eye drops containing disulfiram and low-substituted methylcellulose using ICR/f rats as a hereditary cataract model

We attempted to develop anti-cataract eye drops using disulfiram (DSF) and low-substituted methylcellulose (MC), and evaluated their anti-cataract effect in terms of the lens opacification vs. age-profile curves using a one-exponential equation. The eye drops were prepared using 0.5% DSF and 2% MC (DSF eye drops), and ICR/f rats, a recessive-type hereditary cataractous strain, were used as the experimental model. Gelation of DSF eye drops containing MC was first observed at about 35°C, close to body temperature. In in vivo transcorneal penetration experiments using rabbit corneas, only diethyldithiocarbamate (DDC) was detected in the aqueous humor, while DSF was not detected. The DDC penetration level of DSF eye drops containing MC was approximately 1.3-fold higher than that of DSF eye drops. The opacification rate constant (k) of ICR/f rat instilled with DSF eye drops with or without MC was lower, and the initial time of opacification (τ) was longer than those of ICR/f rats instilled with saline. Furthermore, the k of ICR/f rats instilled with DSF eye drops with MC was lower than that of ICR/f rats instilled with DSF eye drops without MC. In conclusion, the analysis of kinetic parameters including k and τ using a one-exponential equation provided useful information for clarifying the anti-cataract effect of eye drops. ICR/f rats instilled with DSF eye drops using a low-substituted MC-based drug delivery system demonstrated a delay in cataract development, probably resulting from an increase in the retention of DSF eye drops on the cornea.

Tissue localization and solubilities of αA-crystallin and its numerous C-terminal truncation products in pre- and postcataractous ICR/f rat lenses

PURPOSE

To investigate the tissue distribution and solubilities of various αA-crystallin truncation products in the cataractous ICR/f rat model.

METHODS

Rat lenses from precataractous (21-day) and postcataractous (100-day) ICR/f rats were sectioned and applied to a matrix-assisted laser desorption/ionization-time-of-flight (MALDI-TOF) target plate. Mass spectrometry images were collected to obtain a macromolecular profile of the abundant lens proteins. Separately, age-matched lenses were extracted into water-soluble (WS) and water-insoluble/urea-soluble (WI-US) fractions and subjected to MALDI-TOF mass spectrometry to correlate the protein solubilities with the imaging data. Protein identities were assigned by using a top-down proteomics approach on a high-resolution mass spectrometer.

RESULTS

Ten novel αA-crystallin truncation products were identified, along with six previously known αA-crystallin truncation products. Nearly all truncations exhibited nuclear localization, with larger truncated products displaying a ringlike localization that progressed outward toward the extranuclear, cortical region. The distributions were similar in both ages with the only significant difference being the amount of tissue area encompassed by a particular species with increasing age. Almost all nuclear products fractionated into the WI-US fraction, whereas the five largest extranuclear species exhibited mixed solubility.

CONCLUSIONS

A successful methodology for the sectioning and imaging of pre- and postcataractous ICR/f rat lenses has been established. Data collected from these analyses indicate that there are multiple αA-crystallin truncation products present in both pre- and postcataractous rats. Furthermore, these species have defined lenticular localizations and unique solubilities that may be a consequence of lens development and protein function within the lens environment.

Comparison of the mechanisms of cataract development involving differences in Ca2+ regulation in lenses among three hereditary cataract model rats

We previously found that the increases in Ca2+ content in the lenses of three hereditary cataract model rats, UPL rat (UPLR), Shumiya cataract rat (SCR) and Ihara cataract rat (ICR), are inhibited by aminoguanidine, a selective inhibitor of inducible nitric oxide synthase, and that the mechanisms of Ca2+ enhancement in these rat models differ. In this study, we compare the mechanisms for dysfunction in Ca2+ regulation in UPLR, SCR and ICR. Decreases in the activity of Ca2+-ATPase were found in the lenses of SCR and ICR concurrent with cataract development. In contrast, the Ca2+-ATPase activity in UPLR with opaque lenses was higher than in those with transparent lenses. On the other hand, ATP levels were markedly decreased in UPLR with opaque lenses. The expression of cytochrome c oxidase (CCO)-1 mRNA and CCO activity in UPLR lenses was found to decrease during cataract development. The nitric oxide (NO) and lipid peroxide levels were also increased in the lenses of UPLR, SCR and ICR with opaque lenses. In UPLR, excessive NO may cause damage to the mitochondrial genome, resulting in a decrease in ATP production and increase in Ca2+-ATPase activity. The decrease in ATP content may cause the decrease in Ca2+-ATPase function resulting in the elevation in lens Ca2+. In SCR and ICR, excessive NO may cause an enhancement of lipid peroxidation resulting in the oxidative inhibition of Ca2+-ATPase. The decrease in Ca2+-ATPase activity may cause the elevation in the level of lens Ca2+, thus leading to lens opacification. Our findings show that the Ca2+ contents in the cataractous lenses of all three model rats are increased, the mechanisms for this Ca2+ enhancement is different in each rat model.

Effect of disulfiram eye drops on lipid peroxide formation via excessive nitric oxide in lenses of hereditary cataract ICR/f rats

The ICR/f rat is a recessive-type hereditary cataractous strain, and opacity in the lens usually becomes evident at around 75 d of age. We previously found that the instillation of eye drops containing a disulfiram and hydroxypropyl-beta-cyclodextrin inclusion complex (DSF eye drops) delays lens opacification in ICR/f rats. In this study, we attempted to clarify the mechanisms of the delaying effect of DSF eye drops on cataract development in ICR/f rats. The calcium ion (Ca2+) content in the lenses of ICR/f rats increases at 77 d of age, and this elevation is preceded by a decrease in Ca2+-ATPase activity. On the other hand, the levels of nitric oxide (NO) and lipid peroxide (LPO) also increase in the lenses of ICR/f rats at 63 d of age, while the lenses are still transparent. The instillation of DSF eye drops reduces the changes in Ca2+ content, Ca2+-ATPase activity, NO and LPO levels in the lenses of ICR/f rats. The present study demonstrates that excessive NO production induces the increase in LPO, which causes the decrease in Ca2+-ATPase activity, and the increase in Ca2+ content in the lenses of ICR/f rat during cataract development. DSF eye drops have the ability to attenuate the increase in the NO and LPO levels, resulting in a delay in cataract development.

Inhibitive effects of enhanced lipid peroxidation on Ca(2+)-ATPase in lenses of hereditary cataract ICR/f rats

Our previous studies have demonstrated that the instillation of eye drops containing disulfiram, a radical scavenger and nitric oxide synthase inhibitor, delays cataract development in ICR/f rats, and we have suggested that the production of nitric oxide (NO) and lipid peroxide (LPO) in the lens may relate to the delay in cataract development brought about by disulfiram. However, the involvement of NO and LPO in lenses of ICR/f rats during cataract development has not yet been established. In the present study, we determined changes in NO and LPO levels in lenses of ICR/f rats during cataract development. Opacification of ICR/f rat lenses started at 77 days of age, and the lenses of 91-day-old ICR/f rats were almost entirely opaque. The Ca(2+)-ATPase activity in the lenses of ICR/f rats decreased with increasing age, and an elevation in Ca(2+) content was observed in ICR/f rat lenses with the decrease in Ca(2+)-ATPase activity. NO levels in the lenses of ICR/f rats increased from 63 to 85 days of age, reaching a maximum at 77 days of age. In addition, LPO levels in the lenses of ICR/f rats also increased with increasing age. LPO levels in the lenses of 63- to 91-day-old ICR/f rats were found to be significantly higher compared with those in 22-day-old ICR/f rats. These changes of Ca(2+), Ca(2+)-ATPase, NO and LPO were attenuated by instillation of DSF eye drops. These results suggest that excessive NO may cause enhanced lipid peroxidation resulting in the inhibition of Ca(2+)-ATPase. The decrease in Ca(2+)-ATPase activity may cause the elevation in lens Ca(2+), leading to lens opacification in ICR/f rats.

Delay in ICR/f Rat Lens Opacification by the Instillation of Eye Drops Containing Disulfiram and Hydroxypropyl-.BETA.-cyclodextrin Inclusion Complex

In this study, we attempted to enhance disulfiram (DSF) solubility using a 2-hydroxypropyl-beta-cyclodextrin (HPbetaCD) and hydroxypropylmethylcellulose (HPMC). We also investigated the effect of an HPbetaCD solution containing DSF and HPMC (DSF eye drops) on cataract development in ICR/f rat. The solubility of DSF increased with increasing HPbetaCD concentration, and the solubility of DSF in HPbetaCD solution containing 0.1% HPMC was approximately 20% greater than that of DSF in HPbetaCD solution without HPMC. In in vivo transcorneal penetration experiments using rabbits, only diethyldithiocarbamate (DDC) was detected (DSF was not detected) in the aqueous humor. This DSF-DDC conversion in the cornea was inhibited by treatment with a sulfhydryl (SH) inhibitor, p-mercuribenzoate and N-ethylmaleimide, in in vitro transcorneal penetration experiments using rabbit corneas. On the other hand, the instillation of 0.25% and 0.5% DSF eye drops delayed cataract development in ICR/f rats, a recessive-type hereditary cataractous strain. The present study demonstrates that DSF in HPbetaCD solution with HPMC is converted to DDC by the catalysis of proteins containing SH residues in the cornea, and this DDC may cause the delay in cataract development in ICR/f rats.

Cataract formation and prevention

Cataract, a leading cause of blindness worldwide, is a multifactorial eye disease. In developing countries the incidence of cataract among young generations is not uncommon due to malnutrition, excess exposure to ultraviolet radiation and so on. In developed countries, age-related cataract affecting the population over 65 years of age is a major concern. Oxidative stress was suggested to inflict damage to the lens and induce opacification, and a variety of antioxidant nutrients were tested for the prevention or delay of cataract development. Although promising results were obtained in animal studies of various antioxidants, epidemiological studies on human populations do not seem to support their protective effects unequivocally. It is unlikely that age-related cataract in man, similar to the ageing process itself, will be prevented or delayed by therapeutic drugs in the foreseeable future. At present, keeping a health-conscious life style (i.e., no smoking) may be the most effective and least expensive strategy to prevent the onset of age-related cataract.

C-Terminal Truncation of .ALPHA.-Crystallin in Hereditary Cataractous Rat Lens

C-Terminal truncated alpha-crystallins have been found in lenses of hereditary cataractous rat ICR/f, including two truncated alphaB-crystallins and several truncated alphaA-crystallins. These truncated crystallins probably resulted from degradation by m-calpain and Lp82. The alphaB-crystallin with five amino acid residues deleted showed decreased chaperone activity. Compared with alpha-crystallins from the normal rat lenses, overall chaperone activity of alpha-crystallins from the mutant lenses, including the above truncated alphaB-crystallin, was remarkably reduced. The decreased chaperone activity accompanying the increase in C-terminal truncated alpha-crystallins may cause the insolubilization of many proteins in the mutant lenses, which it is likely to lead to the progression of cataract formation.

Phosphoproteome Analysis of Hereditary Cataractous Rat Lens .ALPHA.-Crystallin

We reported previously that C-terminal truncated alpha-crystallins were found in lenses of hereditary cataractous rat ICR/f. In this study, we examined the phosphorylation of the crystalline lens proteins, alphaB-crystallin and alphaA-crystallin, in cataractous and normal rats of different ages and have found an increase in the phosphorylation of serine residues of truncated alpha-crystallin in cataractous lens. Phosphorylation and C-terminal truncation of alpha-crystallins could, both, reduce their chaperone-like activity and lead to cataract formation.

Cellular Events Preceding Acetaminophen Cataractogenesis Studied by Confocal Fluorescence Microscopy

Acetaminophen (APAP) is biotransformed by hepatic cytochrome P450 (CYP) enzymes to the cataractogenic metabolite N-acetyl-p-benzoquinone imine (NAPQI). In the previous studies in which NAPQI was injected into the anterior chamber of mouse eye, we observed mitochondrial dysfunction and disturbances in Ca2+ homeostasis in the lens epithelium, and activation of the nonlysosomal neutral protease calpain. In this work we investigated whether intraperitoneal injection of APAP elicits similar cellular responses in the lens epithelium prior to the onset of lens opacity development. Following APAP injection, reactive oxygen species generation, intracellular free Ca2+ increase and calpain activation in the lens epithelium were determined in situ by fluorescence confocal microscopy. It was found that cellular events in the lens prior to the onset of opacification were essentially identical to those elicited by NAPQI. In addition, lens calpain activities were characterized based on their Ca2+ requirement and several calpain inhibitors were shown to prevent cataract development.