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

Combination of Lanosterol and Nilvadipine Nanosuspensions Rescues Lens Opacification in Selenite-Induced Cataractic Rats

It has recently been reported that lanosterol (LAN) plays a preventive role against lens opacification through the reversal of crystalline aggregation. However, the effect of LAN is not sufficient to restore lens transparency. In this study, we designed ophthalmic nanosuspensions (LAN-ONSs and NIL-ONSs) based on LAN and nilvadipine (NIL), which can counteract cataract-related factors (e.g., enhanced Ca²⁺ and calpain levels), and investigated whether the combination of LAN-ONSs and NIL-ONSs can restore the nuclear lens opacity in sodium-selenite-induced cataractic rats (cataractic rats). The mean particle sizes of the LAN-ONSs and NIL-ONSs were 108.8 nm and 89.0 nm, respectively. The instillation of the LAN-ONSs or NIL-ONSs successfully delivered the drugs (LAN or NIL) into the lenses of the rats, although the instillation of LAN-ONSs or NIL-ONSs alone did not increase lens transparency in the cataractic rats. On the other hand, the cataract-related factors (enhanced Ca²⁺ and calpain levels) were significantly alleviated by the combination of LAN-ONSs and NIL-ONSs; furthermore, the perinuclear refractile ring in the lens nucleus and enhanced number of swollen fibers were attenuated by the LAN-ONS and NIL-ONS combination. Moreover, the opacity levels in the cataractic rats were reduced after treatment with the combination of LAN-ONSs and NIL-ONSs. It is possible that the combination of LAN and NIL will be useful for the treatment of lens opacification in the future.

Instillation of Ophthalmic Formulation Containing Nilvadipine Nanocrystals Attenuates Lens Opacification in Shumiya Cataract Rats

We developed ophthalmic formulations based on nilvadipine (NIL) nanocrystals (NIL-NP dispersions; mean particle size: 98 nm) by using bead mill treatment and investigated whether the instillation of NIL-NP dispersions delivers NIL to the lens and prevents lens opacification in hereditary cataractous Shumiya cataract rats (SCRs). Serious corneal stimulation was not detected in either human corneal epithelial cells or rats treated with NIL-NP dispersions. The NIL was directly delivered to the lens by the instillation of NIL-NP dispersions, and NIL content in the lenses of rats instilled with NIL-NP dispersions was significantly higher than that in the ophthalmic formulations based on NIL microcrystals (NIL-MP dispersions; mean particle size: 21 µm). Moreover, the supply of NIL prevented increases in Ca²⁺ content and calpain activity in the lenses of SCRs and delayed the onset of cataracts. In addition, the anti-cataract effect in the lens of rats instilled with NIL-NP dispersions was also significantly higher than that in NIL-MP dispersions. NIL-NPs could be used to prevent lens opacification.

Ophthalmic In Situ Gelling System Containing Lanosterol Nanoparticles Delays Collapse of Lens Structure in Shumiya Cataract Rats

We attempted to prepare ophthalmic in situ gel formulations containing lanosterol (Lan) nanoparticles (LA-NPs/ISG) and investigated the characteristics, delivery pathway into the lens, and anti-cataract effects of LA-NPs/ISG using SCR-N (rats with slight lens structure collapse) and SCR-C (rats with a combination of remarkable lens structure collapse and opacification). LA-NPs/ISG was prepared by bead milling of the dispersions containing 0.5% Lan powder, 5% 2-hydroxypropyl-β-cyclodextrin, 0.5% methylcellulose, 0.005% benzalkonium chloride, and 0.5% mannitol. The particle size distribution of Lan was 60–250 nm. The LA-NPs/ISG was gelled at 37 °C, and the LA-NPs/ISG was taken into the cornea by energy-dependent endocytosis and then released to the intraocular side. In addition, the Lan contents in the lenses of both SCR-N and SCR-C were increased by the repetitive instillation of LA-NPs/ISG (twice per day). The space and structure collapse in the lens of SCR-N with aging was attenuated by the instillation of LA-NPs/ISG. Moreover, the repetitive instillation of LA-NPs/ISG attenuated the changes in cataract-related factors (the enhancement of nitric oxide levels, calpain activity, lipid peroxidation levels, Ca²⁺ contents, and the decrease of Ca²⁺-ATPase activity) in the lenses of SCR-C, and the repetitive instillation of LA-NPs/ISG delayed the onset of opacification in the SCR-C. It is possible that the LA-NPs/ISG is useful in maintaining lens homeostasis.

The Intravitreal Injection of Lanosterol Nanoparticles Rescues Lens Structure Collapse at an Early Stage in Shumiya Cataract Rats

We designed an intravitreal injection formulation containing lanosterol nanoparticles (LAN-NPs) via the bead mill method and evaluated the therapeutic effect of LAN-NPs on lens structure collapse and opacification using two rat cataract models (SCR-N, rats with slight lens structure collapse; SCR-C, rats with the combination of a remarkable lens structure collapse and opacification). The particle size of lanosterol in the LAN-NPs was around 50–400 nm. A single injection of LAN-NPs (0.5%) supplied lanosterol into the lens for 48 h, and no irritation or muddiness was observed following repeated injections of LAN-NPs for 6 weeks (once every 2 days). Moreover, LAN-NPs repaired the slight collapse of the lens structure in SCR-N. Although the remarkable changes in the lens structure of SCR-C were not repaired by LAN-NP, the onset of opacification was delayed. In addition, the increase of cataract-related factors (Ca²⁺ contents, nitric oxide levels, lipid peroxidation and calpain activity levels) in the lenses of SCR-C was attenuated by the repeated injection of LAN-NPs. It is possible that a deficiency of lanosterol promotes the production of oxidative stress. In conclusion, it is difficult to improve serious structural collapse with posterior movement of the lens nucleus with a supplement of lanosterol via LAN-NPs. However, the intravitreal injection of LAN-NPs was found to repair the space and structural collapse in the early stages in the lenses.

Changes in mitochondrial cytochrome c oxidase mRNA levels with cataract severity in lens epithelia of Japanese patients

We previously reported that the collapse of ATP production via mitochondrial damage causes ATPase dysfunction, resulting in the onset or progression of lens opacification in cataracts in model rats. In the present study, it was investigated whether the mRNA expression levels of the three subtypes of mitochondrial cytochrome c oxidase (MTCO)1, 2 and 3 and ATP content change with the type and severity of cataracts in human lens. Samples of lens epithelium were collected from Japanese patients during cataract surgery, and the type and severity of the cataracts (grade) were determined according to the WHO classification [cortical (COR), nuclear (NUC), posterior subcapsular (PSC) opacification]. The MTCO1‑3 mRNA expression levels in patients with grade‑1 COR, NUC and PSC opacification were significantly enhanced compared with those of normal patients. The enhanced MTCO1‑3 mRNA levels subsequently decreased in patients with COR, and the MTCO1‑3 mRNA levels and ATP levels in patients with grade‑3 COR were similar to those in normal patients. However, the mRNA expression levels of MTCO3 in patients with grade 3‑NUC opacification and MTCO1‑3 in patients with grade‑3 PSC opacification, along with the ATP content, were significantly lower than in patients without cataracts. In conclusion, it was revealed that ATP production in lens epithelium is enhanced in early‑stage cataracts (grade‑1) in Japanese patients with COR, NUC and PSC opacification. In addition, in severe cataracts (grade‑3), ATP production and content are strongly decreased in Japanese patients with PSC opacification. ATP depletion in human lens epithelium with PSC opacification may promote lens opacification by ATPase dysfunction.

Anthraquinones and flavonoids of Cassia tora leaves ameliorate sodium selenite induced cataractogenesis in neonatal rats

The present study was undertaken to evaluate the efficacy ofCassia toraleaves, an edible plant traditionally used for eye ailments, in preventing experimental cataractogenesis.

A mutation in the start codon of γ-crystallin D leads to nuclear cataracts in the Dahl SS/Jr-Ctr strain

Cataracts are a major cause of blindness. The most common forms of cataracts are age- and UV-related and develop mostly in the elderly, while congenital cataracts appear at birth or in early childhood. The Dahl salt-sensitive (SS/Jr) rat is an extensively used model of salt-sensitive hypertension that exhibits concomitant renal disease. In the mid-1980s, cataracts appeared in a few animals in the Dahl S colony, presumably the result of a spontaneous mutation. The mutation was fixed and bred to establish the SS/Jr-Ctr substrain. The SS/Jr-Ctr substrain has been used exclusively by a single investigator to study the role of steroids and hypertension. Using a classical positional cloning approach, we localized the cataract gene with high resolution to a less than 1-Mbp region on chromosome 9 using an F1(SS/Jr-Ctr × SHR) × SHR backcross population. The 1-Mbp region contained only 13 genes, including 4 genes from the γ-crystallins (Cryg) gene family, which are known to play a role in cataract formation. All of the γ-crystallins were sequenced and a novel point mutation in the start codon (ATG → GTG) of the Crygd gene was identified. This led to the complete absence of the CRYGD protein in the eyes of the SS/Jr-Ctr strain. In summary, the identification of the genetic cause in this novel cataract model may provide an opportunity to better understand the development of cataracts, particularly in the context of hypertension.

Dysfunction in cytochrome c oxidase caused by excessive nitric oxide in human lens epithelial cells stimulated with interferon-γ and lipopolysaccharide

PURPOSE

We previously found two mechanisms for the dysfunction in Ca(2+) regulation caused by excessive nitric oxide (NO) using the lenses of hereditary cataract model rats: the first is that NO causes a decrease in Adenosine-5'-triphosphate (ATP) level via cytochrome c oxidase (CCO), resulting in a decrease in ATPase function; the second is that NO causes enhanced lipid peroxidation, resulting in the oxidative inhibition of Ca(2+)-ATPase. In this study, we demonstrate the effect of excessive NO on lipid peroxidation and ATP production in human lens using a human lens epithelial cell line, SRA 01/04 (human lens epithelial (HLE) cells).

METHODS

Excessive NO via inducible NO synthase (iNOS) was induced by stimulating cells with a combination of interferon-gamma (1000 IU IFN-γ) and lipopolysaccharide (100 ng/mL LPS). CCO activity was measured using a Mitochondrial Isolation kit and Cytochrome c Oxidase Assay kit, and ATP levels were determined using a Sigma ATP Bioluminescent Assay Kit and a luminometer AB-2200.

RESULTS

Cytochrome c oxidase activity and ATP levels were decreased in HLE cells stimulated with IFN-γ and LPS, and aminoguanidine (AG) and diethyldithiocarbamate (DDC) added 6 h before cell collection significantly attenuated these decreases in cells stimulated with the IFN-γ and LPS for 24-30 h. However, the lower CCO activity and ATP levels in HLE cells stimulated with the IFN-γ and LPS for 30 h were not changed by treatment with AG or DDC for 6-12 h, while the CCO activity and ATP levels in HLE cells treated with AG or DDC for 18 were recovered.

CONCLUSION

Excessive NO causes a decrease in CCO activity and ATP levels, and the recovery time for CCO activity is related to exposure time to NO in HLE cells.

Correlation between hyper-sensitivity to hydrogen peroxide and low defense against Ca(2+) influx in cataractogenic lens of Ihara cataract rats

Our previous studies have demonstrated that lipid peroxidation in the lenses of hereditary cataract model rats (Ihara cataract rat (ICR)/f rats) caused a dysfunction in Ca(2+) regulation. In the present study, we investigated the effect of in vitro hydrogen peroxide (H(2)O(2)) stimulation on lipid peroxide (LPO) and the activities of sarco-/endoplasmic reticulum and plasma membrane Ca(2+)-ATPase (SERCA and PMCA) in the ICR/f rat lenses. An increase in LPO level and decreases in the SERCA and PMCA activities were observed with increasing H(2)O(2) concentration, and pretreatment with diethyldithiocarbamate, a potent radical scavenger, attenuated these changes in normal and ICR/f rat lenses. The glutathione levels, glutathione peroxidase and glutathione reductase activities are significantly lower in ICR/f rat lenses than in normal rat lenses. Furthermore, we presented as two kinetic parameters such as DP (defense point) and K(s) (reactive constant) analyzed from above various biological responses vs. H(2)O(2) concentration-profile curves using a one-exponential equation. The DPs for LPO, SERCA and PMCA in ICR/f rat lenses is lower than in normal rat lenses. In contrast to the results in DP, the K(s) for LPO, SERCA and PMCA in ICR/f rat lenses is higher than in normal rat lenses. In addition, the closed relationship of was observed between DP and K(s) for LPO, SERCA and PMCA. These results show that the resistance to H(2)O(2) in the ICR/f rat lenses is lower than that of normal rats. The DP and K(s) values can provide an useful information for resistances to various stimuli in cells and tissues.

Spermidine delays eye lens opacification in vitro by suppressing transglutaminase-catalyzed crystallin cross-linking

A Ca(2+)-dependent TG activity, identified in the eye lens of several mammalian species, has long been implicated in cataract formation. The precise mechanism of the involvement of this enzyme in this process remains unclear. The purpose of this work was to investigate the modulatory effect of polyamines on TG activity during rabbit eye lens in vitro opacification. We observed, in an in vitro Ca(2+)-induced cataract model, a rapid decrease of the endogenous levels of SPD with the progression of opacification, paralleled by an increase of crystallin cross-linking by bis(γ-glutamyl)SPD. This pattern was reversed adding exogenous SPD to the incubation medium. Indeed, endogenous SPD levels were restored and cross-linking by bis(γ-glutamyl)SPD were drastically reduced. Surprisingly, under this experimental condition, the loss of transparency of lens was delayed. We found that exogenous SPD incubation led to a remarkable increase of mono(γ-glutamyl)SPD, likely responsible of the inhibition of cross-linking of lens crystallins and of the transparency persistence.