Lack of correlation between intraocular inflammation and after-cataract formation in the rabbit eye

Oxidative stress induces inflammation of lens cells and triggers immune surveillance of ocular tissues

Recent reports have challenged the notion that the lens is immune-privileged. However, these studies have not fully identified the molecular mechanism(s) that promote immune surveillance of the lens. Using a mouse model of targeted glutathione (GSH) deficiency in ocular surface tissues, we have investigated the role of oxidative stress in upregulating cytokine expression and promoting immune surveillance of the eye. RNA-sequencing of lenses from postnatal day (P) 1-aged Gclc^f/f;Le-Cre^Tg/- (KO) and Gclc^f/f;Le-Cre^-/- control (CON) mice revealed upregulation of many cytokines (e.g., CCL4, GDF15, CSF1) and immune response genes in the lenses of KO mice. The eyes of KO mice had a greater number of cells in the aqueous and vitreous humors at P1, P20 and P50 than age-matched CON and Gclc^w/w;Le-Cre^Tg/- (CRE) mice. Histological analyses revealed the presence of innate immune cells (i.e., macrophages, leukocytes) in ocular structures of the KO mice. At P20, the expression of cytokines and ROS content was higher in the lenses of KO mice than in those from age-matched CRE and CON mice, suggesting that oxidative stress may induce cytokine expression. In vitro administration of the oxidant, hydrogen peroxide, and the depletion of GSH (using buthionine sulfoximine (BSO)) in 21EM15 lens epithelial cells induced cytokine expression, an effect that was prevented by co-treatment of the cells with N-acetyl-l-cysteine (NAC), a antioxidant. The in vivo and ex vivo induction of cytokine expression by oxidative stress was associated with the expression of markers of epithelial-to-mesenchymal transition (EMT), α-SMA, in lens cells. Given that EMT of lens epithelial cells causes posterior capsule opacification (PCO), we propose that oxidative stress induces cytokine expression, EMT and the development of PCO in a positive feedback loop. Collectively these data indicate that oxidative stress induces inflammation of lens cells which promotes immune surveillance of ocular structures.

Immune cells in lens injury repair and fibrosis

Immune cells, both tissue resident immune cells and those immune cells recruited in response to wounding or degenerative conditions, are essential to both the maintenance and restoration of homeostasis in most tissues. These cells are typically provided to tissues by their closely associated vasculatures. However, the lens, like many of the tissues in the eye, are considered immune privileged sites because they have no associated vasculature. Such absence of immune cells was thought to protect the lens from inflammatory responses that would bring with them the danger of causing vision impairing opacities. However, it has now been shown, as occurs in other immune privileged sites in the eye, that novel pathways exist by which immune cells come to associate with the lens to protect it, maintain its homeostasis, and function in its regenerative repair. Here we review the discoveries that have revealed there are both innate and adaptive immune system responses to lens, and that, like most other tissues, the lens harbors a population of resident immune cells, which are the sentinels of danger or injury to a tissue. While resident and recruited immune cells are essential elements of lens homeostasis and repair, they also become the agents of disease, particularly as progenitors of pro-fibrogenic myofibroblasts. There still remains much to learn about the function of lens-associated immune cells in protection, repair and disease, the knowledge of which will provide new tools for maintaining the core functions of the lens in the visual system.

Efficacy of COX-2 inhibitors in controlling inflammation and capsular opacification after phacoemulsification cataract removal

OBJECTIVE

To evaluate the efficacy of 0.9% bromfenac (Xibrom™) or a celecoxib-impregnated intraocular lens (celecoxib-IOL) compared with 1% prednisolone acetate (PA) in controlling postoperative inflammation and posterior capsule opacification (PCO).

ANIMAL STUDIED

Fifty-nine dogs undergoing cataract extraction by phacoemulsification.

PROCEDURE

Bilateral patients received bromfenac or celecoxib-IOL plus PA in one eye, and PA in the contralateral eye. Unilateral patients received bromfenac or PA. Complete ophthalmic examination including tonometry, slit-lamp grading of flare and PCO, and digital image acquisition for masked PCO evaluation was performed within 24 h and 1, 4, 12, 24, and 56 weeks following surgery.

RESULTS

Celecoxib-IOL/PA-treated eyes had significantly less flare than PA-treated eyes, which had significantly less flare than bromfenac-treated eyes 24 h postoperatively. There was no significant difference in intraocular pressure (IOP) postoperatively, or at 1, 24, or 56 weeks. Celecoxib-IOL/PA-treated eyes had significantly lower IOP measurements than bromfenac and PA-treated eyes at 4 and 12 weeks. There was no significant difference in PCO level between groups using slit-lamp biomicroscopy at any time point. Masked evaluation of digital images revealed significantly less PCO in celecoxib-IOL/PA- vs. bromfenac-treated eyes at 4 weeks, and in bromfenac- vs. PA-treated eyes at 56 weeks.

CONCLUSIONS

Eyes receiving celecoxib-IOL/PA had better initial control of inflammation. Bromfenac was equally effective compared with PA in controlling inflammation. There was no association between COX-2 inhibitor administration and ocular hypertension. Celecoxib-IOL/PA-treated eyes showed better initial control of PCO (up to 12 weeks), while eyes receiving bromfenac had better long-term control of PCO (56 weeks).

Posterior capsule opacification in eyes with steroid-induced cataracts: Comparison of early results

PURPOSE

To evaluate posterior capsule opacification (PCO) development after cataract surgery in eyes with or without a history of steroid use.

SETTING

Iladevi Cataract & IOL Research Centre, Ahmedabad, India.

DESIGN

Comparative case series.

METHODS

This study comprised consecutive patients with a history of steroid intake (oral, inhaled, injectable, or topical) for at least 4 months who developed posterior subcapsular cataract (PSC) (study group) and patients without a history of steroid intake with uncomplicated PSC (control group). Standardized surgery was performed in both groups. Digital retroillumination photographic documentation was performed 1 month and 1 year postoperatively. The digital images were analyzed for PCO using Evaluation of Posterior Capsule Opacification (EPCO) software; the entire intraocular lens (IOL) optic and the central 3.0 mm optic area were evaluated. The EPCO score and EPCO area were determined.

RESULTS

One year postoperatively, the mean EPCO score was statistically significantly higher in the study group (n = 30) than in the control group (n = 60) (0.33 ± 0.37 [SD] versus 0.15 ± 0.26), as was the mean EPCO area (0.323 ± 0.36 versus 0.15 ± 0.26) (both P<.04). Within the central 3.0 mm optic area, the mean EPCO scores (0.149 ± 0.309 versus 0.003 ± 0.016 P<.04) and mean EPCO area values (0.149 ± 0.309 versus 0.003 ± 0.016) were statistically significantly higher in the study group (P<.04).

CONCLUSION

Steroid-induced PSC was associated with a higher risk for PCO after cataract surgery at the 1-year follow-up.

FINANCIAL DISCLOSURE

No author has a financial or proprietary interest in any material or method mentioned.

Differing effects of dexamethasone and diclofenac on posterior capsule opacification-like changes in a rat lens explant model

Posterior capsular opacification (PCO) arises from lens cells that remain associated with the lens capsule after cataract surgery and subsequently become abnormal, proliferate and migrate into the visual pathway. In this study, a rat lens explant model was used to assess the effects of the prototype steroidal and non-steroidal anti-inflammatory drugs, dexamethasone (DEX) and diclofenac (DIC), on epithelial cells undergoing PCO-like changes. Such drugs are widely used at the time of cataract surgery. TGFbeta2 and FGF-2 were added sequentially and explants were cultured for up to 30 days, with or without addition of DEX or DIC at a clinically relevant concentration. Without DEX or DIC, explants became multilayered and cells tended to retract into PCO-like plaques. Inclusion of DEX, but not DIC, resulted in transient formation of needle-like cells, enhanced cell coverage, and the retention a monolayer of migratory cells surrounding PCO-like plaques. With or without drug addition, most cells became aberrant, as indicated by loss of Pax6 expression and the presence of PCO markers alpha-smooth muscle actin and type I collagen; however, DEX and DIC both strongly enhanced type I collagen accumulation. Furthermore, DEX enhanced cell coverage in explants treated with TGFbeta alone. Thus the behaviour of lens cells was significantly and differentially affected by the presence of DEX and DIC, highlighting the possibility that drugs used to control inflammation after cataract surgery, and the clinician's choice of drugs, may influence PCO development.

Posterior capsule opacification after phacoemulsification in patients with postoperative steroidal and nonsteroidal treatment

PURPOSE

To evaluate the effect of dexamethasone, diclofenac, and a placebo given for 3 weeks after phacoemulsification and intraocular lens (IOL) implantation on the formation of posterior capsule opacification (PCO).

SETTING

St. Erik's Eye Hospital, Stockholm, Sweden.

METHODS

In a 2-year prospective randomized double-blind study, a laser flare meter was used to measure aqueous flare intensity preoperatively and 3 days, 2 weeks, and 2 years after phacoemulsification and IOL implantation. Posterior capsule opacification was evaluated 2 years postoperatively using retroillumination images taken with a Scheimpflug camera. The Evaluation of Posterior Capsule Opacification system was used to score the areas of PCO density.

RESULTS

The median rate of PCO 2 years after phacoemulsification was 0.72 (range 0.32 to 1.57) in the dexamethasone group, 0.78 (range 0.19 to 2.14) in the diclofenac group, and 0.70 (range 0.35 to 1.70) in the placebo group. The differences were not statistically significant (P>.05; Kruskal-Wallis analysis of variance, multiple comparisons). The rate of neodymium:YAG laser posterior capsulotomy during the 2 years after surgery was not statistically different between groups (P>.05, chi-square test). There was no correlation (Spearman rank coefficient) between laser flare measurements and PCO formation in any group during the study (P>.05).

CONCLUSION

Topical instillation of diclofenac, dexamethasone, or a placebo in the immediate period after phacoemulsification and IOL implantation did not seem to influence the formation of PCO 2 years after cataract surgery.

Effects of dexamethasone, diclofenac, or placebo on the inflammatory response after cataract surgery

AIM

To compare the inflammatory response after phacoemulsification and intraocular lens (IOL) implantation using postoperative treatment with dexamethasone, diclofenac, or placebo.

METHODS

A prospective, randomised, controlled double masked study including 180 patients enrolled for cataract surgery. The patients were 64-85 years old and had no eye disease other than cataract. After phacoemulsification and IOL implantation the patients were randomised to topical treatment with dexamethasone phosphate 0.1% (group I), diclofenac sodium 0.1% (group II), or placebo (saline 0.9%) (group III). The drops were administered four times daily during the first week and twice daily during the second, third, and fourth weeks. The inflammatory reaction in the anterior chamber was measured with laser flare photometry preoperatively and 1, 3, and 8 days, 2 and 4 weeks, 2 and 6 months, and 1, 2, and 4 years postoperatively. Inflammatory symptoms were registered. Biomicroscopy and visual acuity determinations were performed. The rate of Nd:YAG laser posterior capsulotomies after 2 and 4 years was determined.

RESULTS

After 3 and 8 days (p <0.0001), 2 weeks (p <0.0001), and 1 month (p = 0.0013) median flare was highest in group III. There were no significant differences between group I and II. Inflammatory symptoms and striate keratopathy were more common in group III.

CONCLUSION

Dexamethasone and diclofenac were equally effective in reducing postoperative inflammation after phacoemulsification and IOL implantation in eyes with no other disease than cataract. Both substances were more effective than placebo.

Development of posterior capsule opacification in the rabbit

PURPOSE

The aim of the present study was to characterize the development of after-cataract in the rabbit by measuring its wet weight, protein, DNA and glycosaminoglycan (GAG) contents and using Scheimpflug and slitlamp analysis. Further, aqueous humor (AqH) leukocytes, protein and lens epithelial cell proliferation activity were determined.

METHODS

AqH was collected and capsular bags including after-cataract were dissected free on days 0, 1, 7, 14, 28 and 56 after cataract surgery. The wet weights were determined and the contents of DNA, protein and GAG in the capsular bags including after-cataract were analyzed. AqH was analyzed for leukocytes, protein and proliferative activity. In another set of experiments, rabbit eyes were analyzed by the Scheimpflug technique and slitlamp examination on days 0, 1, 7, 14, 28 and 56 after cataract surgery. The wet weight of the capsular bag with the after-cataract was also determined.

RESULTS

An increase was found in the wet weight (480%) and the contents of protein (221%), DNA (945%) and GAG (336%) of the capsular bags including after-cataract during the experimental period. In the AqH, all 3 variables measured, leukocytes, protein and proliferative activity, reached their highest levels on day 1 after surgery. In the second set of experiments, the wet weight of the capsular bag including after-cataract increased by 391% during the 56-day experimental period. Posterior capsule opacification (PCO), as measured by Scheimpflug analysis, increased from 0.8 to 81.7% and the scores of Elschnig's pearls as well as fibrosis, analyzed by slitlamp, increased from 0.0 to 2.8 and 3.0, respectively.

CONCLUSIONS

This study shows that the same components that are reported to be important in human PCO are also components of PCO in the rabbit. Thus, the rabbit model seems to accurately reflect human PCO development, and because PCO develops much faster in rabbits that would make the rabbit model suitable for studies to elucidate human PCO development.