Adenovirus-mediated suicide gene transduction: feasibility in lens epithelium and in prevention of posterior capsule opacification in rabbits

Inhibition of posterior capsule opacification by adenovirus-mediated delivery of short hairpin RNAs targeting TERT in a rabbit model

PURPOSE

Posterior capsule opacification (PCO) is the most common postoperative complication after cataract surgery and cannot yet be eliminated. Here, we investigated the inhibitory effects of telomerase reverse transcriptase (TERT) gene silencing on PCO in a rabbit model.

METHODS

After rabbit lens epithelial cells (LECs) were treated with adenovirus containing short hairpin RNAs (shRNA) targeting TERT (shTERT group), adenovirus containing scramble nonsense control shRNA (shNC group) or PBS (control group), quantitative real-time polymerase chain reaction and Western blotting were used to measure the expression levels of TERT, and a scratch assay was performed to assess the LEC migration. New Zealand white rabbits underwent sham cataract surgery followed by an injection of adenovirus carrying shTERT into their capsule bag. The intraocular pressure and anterior segment inflammation were evaluated on certain days, and EMT markers (α-SMA and E-cadherin) were evaluated by Western blotting and immunofluorescence. The telomerase activity of the capsule bag was detected by ELISA. At 28 days postoperatively, haematoxylin and eosin staining of the cornea and iris and electron microscopy of the posterior capsule were performed.

RESULTS

Application of shTERT to LECs downregulated the expression levels of TERT mRNA and protein. The scratch assay results showed a decrease in the migration of LECs in the shTERT group. In vivo, shTERT decreased PCO formation after cataract surgery in rabbits and downregulated the expression of EMT markers, as determined by Western blotting and immunofluorescence. In addition, telomerase activity was suppressed in the capsule bag. Despite slight inflammation in the iris, histologic results revealed no toxic effects in the cornea and iris.

CONCLUSION

TERT silencing effectively reduces the migration and proliferation of LECs and the formation of PCO. Our findings suggest that TERT silencing may be a potential preventive strategy for PCO.

Influence of super-hydrophobic silicone rubber substrate on the growth and differentiation of human lens epithelial cells

Materials with low cell adhesion are advantageous for production of replacement intraocular lens (IOL) to prevent posterior capsular opacification (PCO). We evaluated the feasibility of compression molding for manufacture of silicone rubber with super-hydrophobic surface and low cell infiltrative characteristics compared to ordinary hydrophobic silicone rubber. Silicone specimens with complex surface topology (super-hydrophobic) or smooth surfaces (hydrophobic) were manufactured by vacuum deforming and molding. Contact angle, microscopic surface structure, and transparency were evaluated. Super-hydrophobic and smooth samples were compared for effects on proliferation, adhesion, and morphology of human lens epithelial cells (hLECs). Epithelial-mesenchymal transition (EMT) was examined by immunofluorescence expression of fibronectin (Fn), Alpha-smooth muscle actin (α-SMA), and vimentin. The surface contact angle of super-hydrophobic silicone was greater than that of smooth silicone (153.8° vs. 116°). The super-hydrophobic surface exhibited a micron-scale palisade structure under scanning electron microscopy (unit length, width, and height of 80, 25, and 25 μm, respectively). However, cell number per 50 × microscopic field on super-hydrophobic surfaces was markedly reduced 24 and 72 h post-seeding compared to smooth surfaces (p < 0.01). Cells were cuboidal or spherical after 72h on super-hydrophobic surfaces, and exhibited numerous surface microvilli with fluff-base polarity, while cells on smooth surfaces exhibited morphological characteristics of EMT. Expression levels of the α-SMA and vimentin were reduced on super-hydrophobic surfaces compared to smooth surfaces. Super-hydrophobic silicon inhibits proliferation, adhesion, and EMT of hLECs, properties that may prevent fibrosis following cataract surgery.

Prevention of posterior capsular opacification

Posterior capsular opacification (PCO) is a common complication of cataract surgery. The development of PCO is due to a combination of the processes of proliferation, migration, and transdifferentiation of residual lens epithelial cells (LECs) on the lens capsule. In the past decades, various forms of PCO prevention have been examined, including adjustments of techniques and intraocular lens materials, pharmacological treatments, and prevention by interfering with biological processes in LECs. The only method so far that seems effective is the implantation of an intraocular lens with sharp edged optics to mechanically prevent PCO formation. In this review, current knowledge of the prevention of PCO will be described. We illustrate the biological pathways underlying PCO formation and the various approaches to interfere with the biological processes to prevent PCO. In this type of prevention, the use of nanotechnological advances can play a role.

BAX gene over-expression via nucleofection to induce apoptosis in human lens epithelial cells

Despite significant advances in cataract surgery techniques, posterior capsule opacification (PCO) remains a common complication. In PCO, remaining epithelial cells cloud the lens capsule and impair postoperative vision. This in vitro study was designed to investigate the potential of a gene-based approach, specifically over-expression of the proapoptotic BAX gene, to prevent PCO. Human lens epithelial cells (HLECs) were transfected by nucleofection with a plasmid encoding a fusion protein of green fluorescent protein and human BAX. The expression levels of BAX and its antiapoptotic counterpart BCL2 were determined by realtime reverse transcription polymerase chain reaction, Western blotting and immunofluorescence. BAX over-expression-induced cell death was analyzed by fluorescence-activated cell sorting using the Annexin V antibody. Fluorescence microscopy and transmission electron microscopy were used to assess changes in morphology and ultrastructure. Differential expression of the downstream apoptosis-related factor, caspase 3, was detected by Western blotting. Nucleofection efficiency was high (nearly 80%). BAX-transfected HLECs showed remarkably enhanced BAX gene expression and BAX:BCL2 ratio, but relatively little change in endogenous BCL2 expression. BAX over-expression also led to significant cytotoxicity, induction of apoptosis-related characteristics and activation of caspase 3. In conclusion, our results indicate that BAX gene over-expression can trigger cell death in HLECs via an apoptotic pathway. Thus, BAX may be a promising candidate for human gene therapy to treat PCO.

Construction of a eukaryotic expression plasmid encoding the human PKAR IIβ gene and its expression in human gastric cancer BGC-823 cells

AIM: To construct a eukaryotic expression plasmid encoding the human protein kinase A regulatory subunit II beta (PKAR IIβ) gene and to examine its expression and localization in BGC-823 gastric cells using green fluorescent protein as a reporter.

METHODS: The coding sequence of the PKAR IIβ gene was amplified from the plasmid pRSETB-PKARIIβ by PCR and subcloned into pEGFP-C1 vector after digestion with Xho I and EcoR I. After the identity of recombinant plasmid was verified by direct sequencing, the plasmid was transfected into BGC-823 cells. The expression of the recombinant plasmid in BGC-823 cells was detected by Western blot. The localization of GFP-PKARIIβ in BGC-823 cells was observed by laser scanning confocal microscopy.

RESULTS: The coding sequence of the PKARIIβ gene was inserted into the pEGFP-C1 vector successfully. Restriction enzymes digestion showed that the length of the insert was 1.2 kb, matching the expected size. The expression of GFP-PKARIIβ fusion protein, which had a molecular weight of 72 000 Da, was detected in BGC-823 cells by Western blot. The GFP-PKARIIβ protein was localized predominantly to the cytoplasm but sparsely to the nucleus of HEK293 and BGC-823 cells.

CONCLUSION: A recombinant plasmid expressing the PKARIIβ gene has been successfully constructed and provides a tool for future investigation of PKARIIβ functions. The GFP-PKARIIβ fusion protein was expressed mainly in the cytoplasm of HEK293 and BGC7901 cells.

Construction of pEGFP-restin recombinant plasmid and its expression in BGC-803 gastric cancer cells

AIM: To construct a vector containing human restin gene and observe its expression in gastric cancer cells BGC-803 with green fluorescence protein as the reporter gene.

METHODS: Restin gene was amplified from mRNA of fetal kidney tissue by RT-PCR. The RT-PCR products and pEGFP-C1 were simultaneously digested, then purified, ligated, and transformed to construct the recombinant vector pEGFP-restin. Then the recombinant pEGFP-restin was transfected into gastric cancer cells BGC-803. The expression of green fluorescence protein was observed by fluorescence microscopy, and Western blot was used to examine the expression of target protein.

RESULTS: Agarose gel elctrophrosis showed a 600-bp band of the RT-PCR product, which matched the expected size. Through digestion, the inserted DNA sequence was confirmed to be the premature gene of restin, which was ligated to pEGFP-C1 and transfected into BGC-803 cells successfully. The strong expression of green fluorescence protein was observed by fluorescence microscopy, and the expression of target protein was identified using Western blot.

CONCLUSION: The recombinant vector pEGFP-restin is successfully constructed, providing important subject for further investigation of restin function.

Effect of restin gene transfection on human gastric carcinoma xenograft growth in nude mice

AIM: To investigate the inhibitory effect of restin transfection on the growth of human gastric cancer BGC-803 tumor xenograft in nude mouse model with the localized expression of restin and to explore its effect on angiogenesis.

METHODS: Gastric cancer BGC-803 cell line was transfected with recombinant pEGFP-restin through LipofectamineTM2000 mediation. The effect on BGC-803 growth was observed by enhanced green fluorescent proteins assay. The expression of restin gene was detected using restriction endonuclease analysis and RT-PCR; cell cycle was observed using flow cytometry (FCM). Through in vitro study, growth inhibition of the restin on the cancer was observed in nude mice. Microvessel density (MVD) and expression of vascular endothelial growth factor (VEGF) were assessed by immunohistochemistry.

RESULTS: The results of identification by restriction endonuclease analysis and RT-PCR demonstrated that restin gene was stably expressed in BGC-803 cells transfected with pEGFP-restin and that significant expression of EGFP was observed in these cells with irregularity. Slower growth speed and smaller volume were found in pEGFP-restin thansfecting cell group than in control group (P < 0.01). The inhibition rates of tumor in empty vector and pEGFP-restin thansfecting cell group were 3.60% and 29.02%, respectively. The MVD was lower in pEGFP-restin thansfecting cell group than in control group (4.25 ± 0.29 vs 9.79 ± 0.94, 10.34 ± 1.22, both P < 0.05); the expression of VEGF was down-regulated compared with control group (12.24 ± 3.45 vs 44.52 ± 9.70, 39.76 ± 6.38, both P < 0.05).

CONCLUSION: Restin transfection could inhibit BGC-803 cell growth in nude mice, which may be related to inhibition of angiogenesis in gastric cancer.

Effects of bicistronic lentiviral vector-mediated herpes simplex virus thymidine kinase/ganciclovir system on human lens epithelial cells

Posterior capsule opacification (PCO) is the most common complication after phacoemulsification cataract surgery. Hyperplasia of the lens epithelial cell after phacoemulsification is thought to be an important feature contributing to PCO. In this study,we investigated the feasibility of killing the human lens epithelial cells (HLECs) by lentivirus-mediated herpes simplex virus thymidine kinase (HSV-tk) gene/ganciclovir (GCV) in HLECs and studied the bystander effect. HLECs were infected with lentiviral vectors coexpressing HSV-tk and enhanced green fluorescent protein (EGFP) or expressing EGFP alone and treated with ganciclovir. Infection efficiency was assessed by fluorescence microscopy, fluorescence-activated cell sorting, and reverse transcription PCR. The cytotoxicity of the HSV-tk/GCV suicide gene therapy system was assessed by DNA ladder and electron microscopy. The time effect and bystander effect of HLEC growth inhibition were evaluated with cell proliferation assay. Lentiviral vector-mediated stable integration and efficient expression of HSV-tk in HLECs, with infection efficiency exceeding 95% GCV at concentrations of 15 approximately 25 mug/ml, significantly induced apoptosis or necrosis of infected HLECs. GCV also killed normal cells mixed with HSV-tk infected cells. The bystander effect markedly increased the cytotoxicity of the HSV-tk/GCV system. Our results suggest that bicistronic lentiviral vectors can efficiently integrate several genes into HLECs and may be a gene therapy platform. Lentivirus-mediated suicide gene therapy might be a feasible treatment strategy to prevent capsule opacification.

Updates on the Surgical Management of Paediatric Cataract with Primary Intraocular Lens Implantation

With the advent of modern surgical techniques, paediatric cataract has become much more manageable. Intraocular lens (IOL) implantation is the standard of care for patients over the age of 2 years. The use of IOL in young infants is still controversial. In addition, there are still unresolved issues, such as the minimum age at which IOL can be safely implanted, IOL power selection and IOL power calculation. The current trends in the management of the above challenges are discussed. Although numerous reports on the prevention and management of posterior capsule opacification have been published, there are ongoing intensive debates and research. Long-term postoperative complications like glaucoma and rhegmatogenous retinal detachment are problems that cannot be overemphasised and these issues are also reviewed. Key words: Congenital cataract, Intraocular lens, Posterior capsule opacification

Prevention of posterior capsule opacification by the induction of therapeutic apoptosis of residual lens cells

Posterior capsule opacification (PCO) is a common complication of cataract surgery. Using adenovirus(Ad)-mediated gene transfer, we overexpressed the proapoptotic molecules p53, procaspase 3, Bax, and TRAIL to induce therapeutic programmed cell death of residual lens cells to prevent PCO. Overexpressed TRAIL did not induce apoptosis in cultured rabbit lens cells or in human lens cells. Overexpressed p53 induced apoptosis of lens cells in vitro and ex vivo, but was unable to prevent PCO in vivo. Overexpressed procaspase 3 was associated with engagement of many components of the apoptotic pathway, including cleavage of intracellular caspase targets such as PARP and inter-nucleosome DNA fragmentation. Even when only slightly overexpressed, Bax caused apoptosis of transduced rabbit and human lens cells by engaging the mitochondrial pathway, including catalytic activation of the caspases. A single in vivo injection of Ad vectors expressing either Bax or procaspase 3 into the capsular bag at the end of phacoemulsification prevented PCO in rabbits. These experiments show that Ad-mediated Bax or procaspase 3 overexpression is capable of inducing therapeutic programmed cell death in vitro and in vivo in residual lens cells and preventing PCO in a rabbit model of PCO. Manipulation of proapoptotic molecule expression could be a novel gene therapy approach for prevention of PCO.

Lens cell targetting for gene therapy of prevention of posterior capsule opacification

Posterior capsule opacification is the main complication of cataract surgery. Using adenovirus-mediated gene transfer, we recently reported that it was feasible to prevent PCO by overexpressing pro-apoptotic molecules such as pro-caspase 3 or Bax in the residual lens epithelial cells post-cataract surgery. However, this approach is feasible only if gene transfer can be restricted to the residual cells responsible for PCO. Initially, we tested an adenovirus (human serotype 5, HAd5), a lentivirus (HIV) and an oncoretrovirus (MLV) vector for the their in vivo transduction efficiency of rabbit lens cells. We found that HAd5 vectors were the most efficient (>90% of the cells could be transduced). Six potential lens-specific promoters were then cloned into HAd5 vectors and assayed for their ability to target expression to a specific population of cells, using in vitro, ex vivo and in vivo rabbit tissues and human lens capsular bags. We found that the LEP503, MIP and Filensin promoters induced strong lens-specific expression of a reporter gene, in human lens cells. Following this ex vivo assay, we showed in a rabbit PCO model that gene transfer could be spatially restricted to the capsular bag by confining the vector with Matrigel. Our combined approach using a lens-specific promoter and a biocompatible gel should render feasible a novel therapeutic strategy for PCO that targets the remaining lens cells.

[New methods for the prevention of posterior capsule opacification]

Even though tremendous advances have been made especially during the last 10-15 years in terms of surgical techniques and improvement of implant technology, posterior capsule opacification (PCO) still remains a serious long-term complication. New clinical and laboratory studies (especially of autopsy eyes) have improved our understanding of how IOL design and material influence PCO. Sharp edge optic designs of IOLs of various materials have been shown to significantly reduce secondary cataract. The application of pharmacological substances selectively into the capsular bag is now possible due to the development of the PerfectCapsule System for vacuum-sealed capsule irrigation. Major advances in other areas of biotechnology and immunology including gene therapeutic methods offer totally new approaches for the future in the elimination of lens epithelium cells from the capsular bag. This survey gives an update on current and future means and trends to reduce or prevent PCO formation.

Methods of assessment of patients for Nd:YAG laser capsulotomy that correlate with final visual improvement

BACKGROUND

This paper attempts to clarify the usefulness of various simple pre-operative measures in estimating the potential for a visually successful capsulotomy.

METHODS

24 patients attending for capsulotomy had pre-operative measures of glare with BAT tester, visibility of posterior pole and grading of posterior capsular pearls and fibrosis seen at slit lamp. Visual function was measured before and after standardised capsulotomy. Correlations of the various preoperative measures with eventual visual function improvements were calculated.

RESULTS

Pearls at slit lamp and poor posterior pole visualisation were all correlated with improvements in visual acuity and contrast sensitivity after capsulotomy. Amount of fibrosis visible at slit lamp and glare assessment were not correlated with vision improvements after laser.

CONCLUSION

Of the various measures that are taken prior to Nd : YAG capsulotomy, some correlate with eventual visual improvement but for others no clinical utility was found. Practitioners should note these findings as they are especially of use in more questionable or high-risk cases to help determine whether referral for PCO treatment by Nd: YAG capsulotomy is likely to benefit the patient.

Relationship between posterior capsule opacification and intraocular lens biocompatibility

The type of healing process that occurs in response to cataract surgery and intraocular lens (IOL) implantation is dependent on a complex set of variables. Their interactions determine whether or not optical clarity is restored as a result of this procedure. In this process, wound healing entails cells undergoing either epithelial-mesenchymal transition, resulting in the generation of fibroblastic cells and accumulation of extracellular matrix, or lenticular structure formation. Such desperate cellular behaviors are regulated by the localized release of different cytokines, including transforming growth factor beta and fibroblast growth factors, which can result in post-operative capsular opacification. Other factors affecting the biological and mechanical outcome of IOL implantation are its composition, surface properties and shape.

Quantification of posterior capsule opacification with round and sharp edge intraocular lenses

PURPOSE

To quantitatively evaluate and compare intraocular lenses (IOLs) with a round or sharp optic edge design for posterior capsule opacification (PCO).

STUDY DESIGN

Prospective comparative observational case series. PARTICIPANTS/MATERIALS: Photographs from 174 eyes were analyzed for PCO at the Department of Ophthalmology, Ruprecht-Karls-University of Heidelberg, Heidelberg, Germany.

MAIN OUTCOME MEASURES

Part I: 121 eyes of 121 patients were analyzed for quantification of PCO. IOLs evaluated were Corneal ACR6 (n = 21), Alcon Acrysof (n = 20), Allergan AR40 (n = 27), Pharmacia 811 one-piece polymethyl methacrylate (PMMA) IOL (n = 24), and Pharmacia 911A silicone IOL (n = 29). Mean follow-up was 14.01 +/- 2.81 months; mean patient age was 73.2 +/- 7.3 years. The morphologic PCO formation was evaluated for the entire optic and in the central 3-mm zone. Part II: In 53 eyes of 46 patients aged 73.4 +/- 10.8 years with an Alcon Acrysof IOL, PCO formation and capsulorrhexis/optic overlapping were analyzed 34.2 +/- 4 months after cataract surgery using EPCO Software.

RESULTS

Part I: The PCO values of the entire optic were for Corneal ACR6, 1.93 +/- 0.62; PMMA, 0.64 +/- 0.63; AR40, 0.55 +/- 0.28; Alcon Acrysof, 0.145 +/- 0.27; and 0.161 +/- 0.181 for the Pharmacia 911A IOL (P < 0.01). The PCO values of the central 3-mm zone were for Corneal ACR6, 1.64 +/- 0.96; PMMA, 0.49 +/- 0.39; AR40, 0.22 +/- 0.32; Alcon Acrysof, 0.08 +/- 0.21; and 0.06 +/- 0.11 for the Pharmacia 911A IOL (P < 0.01). Part II: Average overlapping of capsulorrhexis and Acrysof IOL optic was 40.5% +/- 12.4%. There was a significant correlation between PCO values and overlapping (r = -0.69, P < 0.001).

CONCLUSIONS

The sharp-edge IOL types (Alcon Acrysof and Pharmacia 911A silicone IOL) resulted in statistically significantly lower PCO values for analysis of the entire optic area and central 3-mm zone. There was no statistically significant difference in PCO values between the two sharp-edge optic IOLs. An overlapping of capsulorrhexis rim and the anterior IOL optic surface of more than 20% resulted in significantly lower PCO values with the Acrysof IOL.

Systems of analysis of posterior capsule opacification

This paper demonstrates the wide variety of systems for the analysis of posterior capsular opacification (PCO). No single system has been proved to be a gold standard and it is difficult to comment on the advantages of one system over another with the limited current knowledge on the effects of PCO on vision. There are few studies that actually compare the different systems of analysis. Researchers must ensure that the systems they use for PCO analysis are objective and must give maximum consideration to ensuring potential systematic errors are reduced to a minimum. Further research is required into how the various types and locations of PCO affect vision and how well different systems of analysis perform.

Gene therapy for genetic and acquired retinal diseases

We present an overview of the current status of basic science and translational research being applied to gene therapy for eye disease, focusing on diseases of the retina. We discuss the viral and nonviral methods being used to transfer genes to the retina and retinal pigment epithelium, and the advantages and disadvantages of each approach. We review the various genetic and somatic treatment strategies that are being used for genetically determined and acquired diseases of the retina, including gene replacement, gene silencing by ribozymes and antisense oligonucleotides, suicide gene therapy, antiapoptosis, and growth factor therapies. The rationales for the specific therapeutic approaches to each disease are discussed. Schematics of gene transfer methods and therapeutic approaches are presented together with a glossary of gene transfer terminology.

Using HSV-thymidine kinase for safety in an allogeneic salivary graft cell line

Extreme salivary hypofunction is a result of tissue damage caused by irradiation therapy for cancer in the head and neck region. Unfortunately, there is no currently satisfactory treatment for this condition that affects up to 40,000 people in the United States every year. As a novel approach to managing this problem, we are attempting to develop an orally implantable, fluid-secreting device (an artificial salivary gland). We are using the well-studied HSG salivary cell line as a potential allogeneic graft cell for this device. One drawback of using a cell line is the potential for malignant transformation. If such an untoward response occurred, the device could be removed. However, in the event that any HSG cells escaped, we wished to provide additional patient protection. Accordingly, we have engineered HSG cells with a hybrid adeno-retroviral vector, AdLTR.CMV-tk, to express the herpes simplex virus thymidine kinase (HSV-tk) suicide gene as a novel safety factor. Cells were grown on plastic plates or on poly-L-lactic acid disks and then transduced with different multiplicities of infection (MOIs) of the hybrid vector. Thereafter, various concentrations of ganciclovir (GCV) were added, and cell viability was tested. Transduced HSG cells expressed HSV-tk and were sensitive to GCV treatment. Maximal effects were seen at a MOI of 10 with 50 microM of GCV, achieving 95% cell killing on the poly-L-lactic acid substrate. These results suggest that engineering the expression of a suicide gene in an allogeneic graft cell may provide additional safety for use in an artificial salivary gland device.

Adenovirus-mediated gene transfer in canine eyes: a preclinical study for gene therapy of human uveal melanoma

BACKGROUND

Melanomas of the uveal tract are the most common intraocular malignancies in adults, with an incidence of six cases per million adults per year. Enucleation, which may enhance the dissemination of tumour cells into the systemic circulation, is still required for eyes with large tumours. Gene therapy is proposed as a new therapeutic approach for uveal melanoma management.

METHODS

The potential of adenovirus-mediated gene transfer to normal eyes of two laboratory Beagles and in an iris tumour of a Great Dane were evaluated. Replication-defective adenoviral vectors (Adbetagal) were used to assess the feasibility, efficiency and safety of direct adenoviral delivery to the anterior chamber of normal eyes and to an iris tumour. The expression of angiostatin into the aqueous humour following an adenoviral-mediated delivery of human angiostatin (AdK3) was also investigated.

RESULTS

The ciliary body was the area preferentially transduced after adenoviral injection into the anterior chamber. It was also demonstrated that a direct intratumoral injection of a recombinant adenovirus efficiently transduces a canine uveal melanoma. Western blot analysis performed on the aqueous humour revealed that the expression of the angiostatin recombinant protein in the aqueous humour correlated with the dose of AdK3 administered. Lymphocyte infiltrates at the site of AdK3 injection indicated induction of a strong cellular immune response, and humoral immune responses developed in all three dogs.

CONCLUSIONS

The present study involving adenovirus-mediated gene transfer to dog eyes provides an essential basis for gene therapy treatment of uveal melanoma-bearing patients.

Posterior capsule opacification and anterior capsule opacification

Posterior capsule opacification (PCO) is still the most frequent complication of cataract surgery. A variety of studies has led to a better understanding of the pathogenesis of PCO, and strategies of molecular biology have produced new therapeutic options, such as immunological techniques or gene therapeutic approaches. Surgical strategies and intra-ocular lens-dependent factors also are capable to reduce the rate of PCO. In-the-bag implantation of intra-ocular lenses with a sharp optic edge seems to be effective in inhibiting equatorial lens epithelial cell migration to the center of the posterior capsule. Several PCO documentation systems have been developed that will lead to more exact and better comparable recording of PCO rates. In the year 2000, PCO or secondary cataract is still the most frequent complication after extracapsular cataract surgery. In a 1998 meta-analysis, PCO rates of 11.8% 1 year after extracapsular cataract surgery with intraocular lens implantation, 20.7% after 3 years, and 28.4 % after 5 years have been reported. For the United States, it has been estimated that the overall expenses for treatment of PCO are only exceeded by the costs for cataract treatment itself. In the past decade, a lot of experimental and clinical studies have been performed on this topic. They have led to 1) to a better understanding of the pathogenesis of the development of anterior and posterior capsule opacification; 2) more objective and better comparable systems of documentation and analysis of PCO; and a number of 3) surgical and 4) pharmaceutical strategies to prevent PCO.