Experimental Eye Research 89 (2009) 728–734
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Selenium functionalized intraocular lenses inhibit posterior capsule opacification in an ex vivo canine lens capsular bag assay Simon A. Pot a, *, Heather L. Chandler c, Carmen M.H. Colitz c, Ellison Bentley a, Richard R. Dubielzig b, Thomas S. Mosley d, Ted W. Reid d, e, Christopher J. Murphy a, ** a
Department of Surgical Sciences, School of Veterinary Medicine, University of Wisconsin–Madison, 2015 Linden Drive, Madison, WI 53706, USA Department of Pathobiological Sciences, School of Veterinary Medicine, University of Wisconsin–Madison, 2015 Linden Drive, Madison, WI 53706, USA Department of Veterinary Clinical Sciences, College of Veterinary Medicine, The Ohio State University, 601 Vernon L. Tharp Street, Columbus, OH 43210, USA d Selenium Ltd., 2508 Ashley Worth Blvd., Suite 200, Austin, TX 78738, USA e Department of Ophthalmology and Visual Sciences, Texas Tech University, Health Science Center, 3601 4th Street, Lubbock, TX 79430, USA b c
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Article history: Received 21 April 2009 Accepted in revised form 26 June 2009 Available online 5 July 2009
The purpose of this study was to determine the inhibitory effect of selenocystamine coated intraocular lenses (IOLs) on the formation of posterior capsule opacification (PCO) in an ex vivo canine lens capsular bag assay. Selenocystamine was covalently bound to the surface of poly(2-hydroxyethyl methacrylate) (poly(HEMA)) discs. Three groups of canine lens capsules (6 coated IOLs (SeIOLs), 7 non-coated control IOLs and 8 empty capsules) were cultured for 10 days. During the culture period PCO was scored based on visual inspection of the capsules using phase contrast microscopy. On day 10 all the capsules were prepared for light microscopic examination and lens epithelial cells (LECs) were quantified. Proliferating cell nuclear antigen (PCNA), a-smooth muscle actin (a-SMA) and cleaved caspase-3 were examined by immunohistochemistry. Additionally, cell viability assays were performed on LECs cultured in tissue culture medium pre-incubated with either a SeIOL or control IOL. The viability assays demonstrated that no detectable cytotoxic leachables were associated with the functionalized IOLs. The central posterior capsule was free of cells underneath all SeIOLs, although large numbers of LECs populated the capsular periphery. Apoptotic cells were observed underneath the periphery of some SeIOLs. Both the PCO scores and LEC counts of SeIOL containing capsules were significantly lower than those of control group capsules (p < 0.01 and p ¼ 0.0004, respectively). The use of selenium functionalized IOLs resulted in a significant reduction of PCO in this ex vivo model. Binding of selenocystamine to a foldable IOL may provide an effective method to prevent population of the central posterior capsule with LECs. Ó 2009 Elsevier Ltd. All rights reserved.
Keywords: selenium apoptosis cell culture lens capsule posterior capsule opacification intraocular lens
1. Introduction Cataract is one of the most prevalent causes of blindness in both humans and dogs, with cataract extraction being the most common intraocular surgical procedure performed by physician and veterinary ophthalmologists. The formation of posterior capsule
* Corresponding author. Tel.: þ1 608 213 7303; fax: þ1 608 263 9713. ** Corresponding author. Present address: Department of Surgical and Radiological Sciences, School of Veterinary Medicine, University of California at Davis, 1423 Tupper Hall, Davis, CA 95616-8745, USA. Tel.: þ1 530 754 0216, fax: þ1 530 752 6042. E-mail addresses:
[email protected] (S.A. Pot),
[email protected] (H.L. Chandler),
[email protected] (C.M.H. Colitz),
[email protected] (E. Bentley),
[email protected] (R.R. Dubielzig),
[email protected] (T.S. Mosley),
[email protected] (T.W. Reid),
[email protected] (C.J. Murphy). 0014-4835/$ – see front matter Ó 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.exer.2009.06.016
opacification (PCO) is the most common long-term complication of cataract surgery (Schaumberg et al., 1998). The prevalence of PCO in humans increases from 11.8% at one year and 20.7% at three years to 28.4% at five years after cataract surgery (Schaumberg et al., 1998). PCO in humans can be treated effectively with neodymium:yttriumaluminum-garnet (Nd:YAG) laser capsulotomy, but the costs involved and the morbidity due to surgical complications can be significant (Liu, 1996). It has been reported that between 62% and 100% of canine patients undergoing phacoemulsification with intraocular lens (IOL) implantation develop PCO (Bras et al., 2006; Sigle and Nasisse, 2006). In contrast to humans, Nd:YAG laser capsulotomy is not a successful treatment modality for PCO in canine patients (Nasisse et al., 1990; Gelatt and Gelatt, 2001). PCO is caused by proliferation, migration and epithelial to mesenchymal transition of residual lens epithelial cells (LECs) that are left in the capsular bag after irrigation and aspiration of the
S.A. Pot et al. / Experimental Eye Research 89 (2009) 728–734
lens cortex. Migration of LECs occurs along the entire interior surface of the remaining capsular bag, the anterior hyaloid membrane and along the surface of an implanted IOL (Wormstone, 2002; De Groot et al., 2003). These metaplastic LECs express alpha smooth muscle actin (a-SMA) and produce a variety of types of collagen (Gerardi et al., 1999; Colitz et al., 2000; Chandler et al., 2007). The presence of a-SMA containing metaplastic LECs may lead to wrinkling of the posterior lens capsule, resulting in light scattering, image distortion and impairment of vision (Meacock et al., 2000b; Wormstone et al., 2002). Extracellular matrix components produced by metaplastic LECs can lead to consolidation of lens capsule wrinkles caused by cellular contraction (Kurosaka et al., 1996; Davidson et al., 2000b; Hinz and Gabbiani, 2003; Hinz, 2007). PCO in humans and dogs shows similar histological and immunohistochemical features, which suggests a similar pathogenesis (Colitz et al., 2000). Consequently, the canine lens capsular bag assay provides a useful ex vivo model for PCO formation in humans (Davidson et al., 2000b). Mechanical and pharmaceutical methods to prevent PCO by removing or destroying residual LECs during cataract surgery have been attempted but none have proved satisfactorily practical, effective and safe for routine clinical practice (Davidson et al., 2000a). Most, if not all, of the various methods employed to prevent PCO show a delay, rather than a complete inhibition of PCO formation in vitro and in vivo (Behar-Cohen et al., 1995; Nishi, 1999; Meacock et al., 2000a; Inan et al., 2001; Nishi et al., 2001; Pandey et al., 2002; Wormstone et al., 2002; Maloof et al., 2005; Malecaze et al., 2006; Chandler et al., 2007; Cheng et al., 2007; Findl et al., 2007). Furthermore, some of these techniques can cause collateral damage to surrounding intraocular tissues (Inan et al., 2001; Maloof et al., 2005). Therefore, long term, continuous inhibition of LEC proliferation and migration to the central visual axis needs to be the therapeutic goal. Additionally, the safety of surrounding ocular tissues needs to be guaranteed. Fairly recently, an understanding of selenium as a catalytic generator of superoxide radicals (O 2 ) from the oxidation of thiols has emerged (Chen and Spallholz, 1995). Selenocystamine, a symmetrical diselenide (RSeSeR), is toxic because thiols such as glutathione (GSH), ubiquitously present in the body, reduce it to two selenide anions (RSe-) (Spallholz et al., 2001). The selenide anions, if present in a sufficiently high concentration, catalyze the further oxidation of thiols and produce superoxide radicals (O 2 ) and hydrogen peroxide (H2O2). These and likely other reactive oxygen species can cause apoptosis and appear to account for selenium’s toxicity (Spallholz, 1994; Chen and Spallholz, 1995; Stewart et al., 1999; Spallholz et al., 2001; Kim et al., 2003). Since selenide anions (RSe-) catalyze the superoxide radical production they do not need to be recycled back to RSeSeR to perpetuate the reaction. Cells dying as a result of apoptosis are removed by phagocytosis without further activation of the immune system. In contrast, necrotic cells cause an inflammatory response and collateral damage to nearby structures (Watanabe et al., 2002). Attachment on the surface of a cell or entry into a cell is required for selenium toxicity (Chen and Spallholz, 1995). Widespread selenium toxicity is prevented by the short half life (
