Vitreous stimulates proliferation of fibroblasts and retinal pigment epithelial cells

A modified protocol for isolation of retinal microglia from the pig

Microglia are the resident immune cells in the retina. To investigate their properties and behaviour, a reliable and yielding procedure to culture them is necessary. We here describe a way of isolation of microglial cells from the porcine retina, as pig eyes are similar to human eyes in size, structure and vasculature, including similarities in proteins and pathways. Retina was isolated from fresh pig eyes, dissociated by a mixture of collagenase, hyaluronidase and DNAse, and passed through a cell strainer. After triple centrifugation with decreasing velocity and re-suspension, cells were seeded into poly-d-lysine coated culture flasks and cultured using DMEM and macrophage-colony stimulating factor (M-CSF). Number of cells increased gradually during the first 10-14 days, till they could be split and used for experiments. Identity of isolated cells as microglia was assessed by immunostaining against the microglia/macrophage markers Iba1, CD11b, CD68, CD45 and TMEM119. Phagocytic function of microglia could be demonstrated by phagocytosis of fluorescence beads and their response to lipopolysaccharide (LPS). As a conclusion, we developed a protocol for isolation and cultivation of pig retinal microglial cells that are suitable for research in the laboratory.

An endoscopic overview of the anterior vitreous base in retinal detachment and anterior proliferative vitreoretinopathy

PURPOSE

Anterior proliferative vitreoretinopathy (PVR) is an important cause of persistent or recurrent retinal detachment (RD). Endoscopy provides 360° panoramic viewing of the vitreous cavity and high-magnification viewing of the anterior vitreous base (AVB). This study describes the 'in vivo' anatomy and pathoanatomy of the AVB using an ocular endoscope in RD and anterior PVR.

METHODS

An intraoperative analysis of over 2000 consecutive eyes undergoing vitrectomy for RD operated with endoscopy-assisted vitrectomy was performed. It was recorded in notes dictated during surgery and in standardized operative reports. Around 1500 surgical videotapes, with the exclusion of diabetic retinopathy and trauma, selected by reviewing the OR reports and notes were retrospectively reviewed.

RESULTS

Seven endoscopic criteria associated with anterior PVR complicating RD are described: 'en bloc' stiff anterior vitreous retraction, ciliary detachment, seeding of the AVB by abundant pigmented and/or white granulations, anterior tissue displacement, stiff 'wrinkling' at the vitreoretinal juncture, persistent shallow ciliary/RD under perfluorocarbon liquids and traction-related retinal surface haemorrhages. Causes responsible for failure of conventional vitrectomy for RD are highlighted. Findings in case of hypotony and cyclitic membranes are described.

CONCLUSIONS

Endoscopy is a significant adjunct to our understanding of the development of anterior loop traction by obviating the two constitutive parts of the AVB, anterior and posterior, their interconnections and their respective connections to the anterior segment and to the retina. It provides a unique evaluation and thorough eradication of the anterior vitreous cortex as a scaffold for anterior PVR. It might be an adjunct to the prevention of anterior PVR.

Mechanisms of inflammation in proliferative vitreoretinopathy: from bench to bedside

Proliferative vitreoretinopathy (PVR) is a vision-threatening disease and a common complication of surgery to correct rhegmatogenous retinal detachment (RRD). Several models of the pathogenesis of this disease have been described with some of these models focusing on the role of inflammatory cells and other models focusing on the role of growth factors and cytokines in the vitreous which come into contact with intraretinal and retinal pigment epithelial cells. New experiments have shed light on the pathogenesis of PVR and offer promising avenues for clinical intervention before PVR develops. One such target is the indirect pathway of activation of platelet-derived growth factor receptor alpha (PDGRα), which plays an important role in PVR. Clinical trials assessing the efficacy of 5-fluorouracil (5-FU) and low-molecular-weight heparin (LMWH), daunorubicin, and 13-cis-retinoic acid, among other therapies, have yielded mixed results. Here we review inflammatory and other mechanisms involved in the pathogenesis of PVR, we highlight important clinical trials, and we discuss how findings at the bench have the potential to be translated to the bedside.

Trabeculectomy with mitomycin C in pseudophakic patients with open-angle glaucoma: outcomes and risk factors for failure

PURPOSE

To evaluate tonometric outcomes of trabeculectomy with mitomycin C in pseudophakic patients with open-angle glaucoma and associated risk factors for failure.

DESIGN

Retrospective cohort study.

METHODS

Seventy-three pseudophakic patients (89 eyes) with primary open-angle, normal-tension, exfoliative, or pigmentary glaucoma were recruited. Success rates were defined according to three criteria: (A) intraocular pressure (IOP) < or = 18 mm Hg and IOP reduction > or = 20%; (B) IOP < or = 15 mm Hg and IOP reduction > or = 25%; and (C) IOP < or = 12 mm Hg and IOP reduction > or = 30%. IOP, visual acuity, complications, and additional interventions were documented after surgery. Cox's proportional hazard regression analysis was used to identify risk factors for failure.

RESULTS

Mean IOP (+/-SD) decreased from a preoperative value of 18.8 +/- 6.6 mm Hg to 10.2 +/- 5.1 mm Hg at one year and to 10.0 +/- 4.2 at two years (P < .001 for both). Average number of preoperative medications decreased from 3.0 +/- 1.1 to 0.5 +/- 1.0 at one year and to 0.5 +/- 0.9 at two years (P < .001 for both). For criteria A, B, and C, success rates (+/-SE) were 87% +/- 4%, 83% +/- 5%, and 76% +/- 5% at 1 year and 67% +/- 4%, 58% +/- 8%, and 50% +/- 7 at two years. Laser suture lysis was performed in 30 eyes, and 11% of those required a second glaucoma procedure.

CONCLUSION

Increasing age, use of a limbus-based conjunctival flap, and performance of laser suture lysis were factors that were associated with a smaller risk of failure. Present findings indicate that trabeculectomy with mitomycin C provides acceptable long-term success rates in pseudophakic patients, with a low incidence of complications.

Prevalence and risk factors for proliferative vitreoretinopathy in eyes with rhegmatogenous retinal detachment but no previous vitreoretinal surgery

PURPOSE

To determine the prevalence of and risk factors for proliferatative vitreoretinopathy (PVR) in eyes with rhegmatogenous retinal detachment but no previous vitreoretinal surgery.

DESIGN

Observational case series.

METHODS

Prospective study.

SETTING

A private vitreoretinal clinic in Caracas, Venezuela.

STUDY POPULATION

119 eyes of 119 patients who presented with rhegmatogenous retinal detachment but no previous vitreoretinal surgery between 1995 and 1998.

OBSERVATION PROCEDURES

Data from detailed preoperative and postoperative examinations of each eye were recorded prospectively and entered into an electronic database.

MAIN OUTCOME MEASURES

Prevalence of PVR of any type and severe PVR, preoperative risk factors for PVR of any type and severe PVR, effect of PVR and retinal detachment duration on initial and final visual acuity, and surgical complexity.

RESULTS

The prevalence of PVR of any type was 52.9% and of severe PVR was 26.9%. The mean retinal detachment duration (+/-SD) was 58.4 (+/-129.1) days, and the mean time from initial examination to surgical treatment (+/-SD) was 24.3 (81.2) days. By univariable analysis, long retinal detachment duration, poor initial visual acuity, and large retinal detachment extent were significantly associated with PVR prevalence and severity. The presence of vitreous hemorrhage was significantly associated with PVR prevalence, and cataract was significantly associated with PVR severity. By multivariable analysis, long retinal detachment duration and large retinal detachment extent were simultaneous risk factors for PVR prevalence, while long retinal detachment, large retinal detachment extent, and poor initial visual acuity were simultaneous risk factors for PVR severity. Eyes with longer retinal detachment duration, PVR of any type, and severe PVR had worse initial and final visual acuities than eyes with shorter retinal detachment duration or those without PVR, respectively. Eyes with PVR had more complex surgery than those without PVR.

CONCLUSIONS

PVR occurred very frequently in this population and was associated with more complex surgery and worse visual outcomes than among eyes without PVR. We have identified preventable risk factors associated with PVR that suggest a specific and significant need for better access to ophthalmologic care and patient education in this group of patients.

Posterior vitreous findings in cases of spontaneous retinal reattachment

PURPOSE

To describe the posterior vitreous findings in two patients with retinal detachment who experienced spontaneous retinal reattachment.

DESIGN

Two observational case reports.

TESTING

Biomicroscopic and high-resolution echographic evaluation of the vitreoretinal relationships.

MAIN OUTCOME MEASURES

Retinal reattachment and echographic vitreoretinal relationships.

RESULTS

Two patients, one with a rhegmatogenous retinal detachment and one with a tractional retinal detachment, were noted to have a partial posterior vitreous detachment with vitreoretinal adherence at the time of presentation. Spontaneous retinal reattachment occurred in both cases, with echography showing complete vitreous separation from the retina.

CONCLUSIONS

Complete posterior vitreous detachment may release tractional components in retinal detachment and contribute to spontaneous retinal reattachment.

Local effects of previous conjunctival incisional surgery and the subsequent outcome of filtration surgery

PURPOSE

Previous ocular surgery involving conjunctival incision is a risk factor for failure of filtration surgery. To determine whether using adjunctive antimetabolite therapy may have a rational basis, a study was performed to determine whether the conjunctival cellular profile was altered by such surgery.

METHODS

After a mean follow-up of 5.9 years, filtration surgery outcomes for 35 patients who had undergone conjunctival incisional surgery were retrospectively compared with 29 control and 18 matched patients who had not undergone such surgery. At the time of filtration surgery, a conjunctival biopsy specimen was obtained from all 82 patients, and these were quantitatively analyzed by light microscopy in a prospective manner.

RESULTS

Trabeculectomy success for the control group (93%) was significantly higher than for the previous surgery group (38%) (P < .001). Compared with control tissue, conjunctiva from the patients who had undergone previous surgery contained more fibroblasts (P < .001, P < .05), macrophages (P < .01, P < .001), and lymphocytes (P = .001, P < .01) in both superficial and deep substantia propria (respective P values). Furthermore, trabeculectomy failure was associated with an increase in number of conjunctival fibroblasts in intraoperative specimens.

CONCLUSIONS

Previous ocular surgery involving the conjunctiva increases the number of conjunctival fibroblasts and inflammatory cells. This may account for the increased risk of trabeculectomy failure. Perhaps on this basis, the use of adjunctive medication may be justified in patients who have undergone previous ocular surgery involving conjunctival incision.

Retrovirus-mediated suicide gene transduction in the vitreous cavity of the eye: feasibility in prevention of proliferative vitreoretinopathy

In proliferative vitreoretinopathy (PVR), retinal pigment epithelial cells, fibroblasts, or other proliferating cells form contractile membranes in the vitreous cavity of the eye, resulting in traction retinal detachment. Retroviral vector-mediated transfer is a suitable method to transduce the herpes simplex virus thymidine kinase (HSV-tk) gene into proliferating cells in PVR, allowing for the selective killing of these cells. To determine the potential of gene transduction in the environment of the vitreous cavity, we evaluated the effect of vitreous humor on retroviral vector-mediated gene transduction of rabbit dermal fibroblasts in vitro and studied in vivo transduction in rabbit experimental PVR with retroviral vector G1BgSvNa. In addition, we studied the bystander effect in vitro and in vivo in a rabbit model of PVR, with low percentages of HSV-tk-positive cells. Finally, we evaluated the efficacy of intravitreal administration of HSV-tk retroviral vector G1TkSvNa followed by ganciclovir (GCV) in the prevention of experimental PVR. Vitreous humor reduced gene transfer efficiency in vitro in a dose-dependent manner. LacZ expression was found in cells of preretinal or intravitreal membranes of animals of both in vivo and in vitro transduction groups; however, in vivo transduction resulted in a decreased number of transduced cells, with a relative transduction efficiency of approximately 2%. Transduction of HSV-tk was associated with a powerful bystander effect both in vitro and in vivo with significant effects even when HSV-tk-positive cells represented only 1% of the population. In vivo transduction with G1TkSvNa followed by GCV significantly inhibited the development of PVR (p < 0.05). These results suggest that retroviral vector-mediated transfer of HSV-tk into the proliferating cells in PVR may be feasible and may provide a novel therapeutic strategy for this disease.

Partial characterization of a putative new growth factor present in pathological human vitreous

BACKGROUND

Several growth factors have been implicated in the development of proliferative eye diseases, and some of those are present in human vitreous (HV). The effects of HV on cellular responses which modulate proliferative cell processes were studied. This study describes the partial characterization of a vitreous factor activity which does not correspond to any of the previously reported growth factors in pathological HV.

METHODS

Vitreous humour was obtained from medical vitrectomies, from patients with PDR and PVR. The biological activity of the vitreous factor was determined by its ability to increase cytosolic calcium concentration ([Ca2+]i), increase production of inositol phosphates, and induce cell proliferation in the cell line EGFR T17. In some experiments other cell lines, such as NIH 3T3, 3T3-L1, FRTL5, A431, PC12, Y79, and GH3, were also employed. Measurement of [Ca2+]i in cell suspensions was performed using the fluorescent Ca2+ indicator fura-2. The activity of the factor present in HV was compared with other growth factors by means of: (a) [Ca2+]i mobilization pattern, (b) sequential homologous and heterologous desensitization of receptors, (c) effects of phorbol esters on their action, and (d) inactivation after treatment with different proteolytic enzymes.

RESULTS

The HV-induced cell proliferation and increases in [Ca2+]i concentration were characterized by a peculiar time pattern. The different approaches used ruled out its identity with PDGF, bFGF, EGF, TGF-beta, IGFs, TNF-alpha, NGF, and other compounds such as ATP, angiotensin I, and bradykinin. Vitreous factor actions are mediated by specific receptors apparently regulated by PKC. This factor is able to induce [Ca2+]i mobilization in most of the cell lines studied, indicating that its effects are not tissue specific.

CONCLUSIONS

These results suggest the presence of a growth factor activity in pathological HV which may be due to the presence of an undescribed growth factor in the eye.

Fibroblast growth-promoting activity in proliferative vitreoretinopathy: antagonism by acetylsalicylic acid

Proliferative vitreoretinopathy is a severe reactive process which leads to the formation of cellular membranes on the surface of the retina and in the vitreous. We determined the fibroblast growth-promoting activity of intraocular fluid from patients suffering from proliferative vitreoretinopathy, retinal detachment or cataract and further evaluated the effect of acetylsalicylic acid on growth-stimulated fibroblasts. The results demonstrated a significant enhancement of growth-promoting activity of intraocular fluid in proliferative vitreoretinopathy as compared to that of control samples. We showed that the augmented growth-promoting activity of intraocular fluid in proliferative vitreoretinopathy was significantly antagonized by inhibition of cyclooxygenase with acetylsalicylic acid (ID50 approximately 5 microM). In contrast, no significant effect was seen in corresponding control experiments. The findings suggest that metabolites of the cyclooxygenase pathway are involved in the regulation of enhanced intraocular fluid-induced fibroblast proliferation in proliferative vitreoretinopathy and that acetylsalicylic acid might be useful as an antiproliferative agent in intraocular fibrogenesis.

Growth of rabbit pigmented and nonpigmented ciliary body epithelium

Pigmented (PE) and nonpigmented epithelial (NPE) cells were carefully dissected from the ciliary processes of rabbit eyes and maintained in vitro. Both epithelial cultured cells showed hexagonal morphology by light microscopy; abundant granules containing pigment could be seen in PE cells while no pigment was seen in the NPE cells. S-100 protein exists in both cultured cells and was used as a marker for the in vitro confirmation of these cells. Collagen type III was used as a negative marker to rule out stromal cell contamination in tissue cultures. PE cells attached and proliferated well in 20% fetal bovine serum (FBS) in minimum essential media (MEM). Greater proliferation was attained when PE cells were exposed to 20% vitreous extract in addition to 20% FBS-MEM. Media conditioned by PE cells did not significantly stimulate PE cells. NPE cells showed greatest proliferation in 20% FBS-MEM with either 20% concentration of media conditioned by PE cells or when exposed to 20% concentration of vitreous extract. Rabbit vitreous may contain factor(s) which stimulate the proliferation of both cultured cells, and conditioned media from the PE cells may contain factor(s) which stimulate NPE cell proliferation.

Immunohistochemical localization of epidermal growth factor receptor in a human epiretinal membrane

Cell growth in proliferative vitreoretinopathy (PVR) is activated by naturally occurring mitogenic substances; thus, growth factors seem to play an important role in PVR. Cell activation by growth factors requires the presence of specific cell-bound receptors by which the mitogenic signal is transmitted. Using the indirect immunoperoxidase method, we investigated frozen sections of 15 epiretinal membranes in PVR for the presence of epidermal growth factor receptor (EGFR), which is commonly utilized by epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha). This receptor could be localized only in one epiretinal membrane. The receptor-bearing cells stained positively for vimentin, cytokeratin, and macrophage marker Ki-M7, indicating that they most probably correspond to transformed macrophages. They stained negatively for desmin and glial fibrillary acidic protein. The cells were embedded in a fibronectin-positive intercellular matrix and were in an actively proliferating state as demonstrated by positive staining for the nuclear proliferation marker Ki-67. We propose that EGFR might be expressed only in certain as yet undefined stages of PVR.

Proliferative vitreoretinopathy--is it anything more than wound healing at the wrong place?

Proliferative vitreoretinopathy (PVR) is a reactive process of the ocular tissue after perforating trauma, retinal detachment, and surgical manipulations. Although several studies, most of them experimental, have focused on the detection of specific etiologic factors in the development of PVR, there is compelling evidence that PVR is nothing more than a physiologic tissue repair process with undesirable consequences for the retina. Important features of PVR involving the role of platelets, mononuclear phagocytes, and fibroblasts parallel the chain of events observed in tissue repair elsewhere in the body. Numerous experimental models for PVR, originally designed to find specific stimuli for the generation of intraocular traction membrane formation, have shown that the process of PVR is the common pathway of the eye's reaction to vitreoretinal trauma of any kind. Accordingly, vitreoretinal surgeons could learn a lot from the work of other disciplines, e.g. surgery and dermatology, on wound healing, and the factors known to modify wound healing elsewhere in the body should be taken into consideration. The well-established impairment of tissue repair processes caused by medical treatment with corticosteroids and cytotoxic agents suggests a combined medical approach to PVR as an adjunct to surgical treatment, using refined methods of application and dosage. Steroids and cytotoxic drugs will influence the course of PVR by suppressing macrophage recruitment and the initial inflammatory reaction as well as the proliferative phase of wound healing with traction retinal detachment, respectively.

Wound healing in glaucoma filtering surgery

Successful glaucoma filtering surgery is characterized by the passage of aqueous humor from the anterior chamber to the subconjunctival space, which results in the formation of a filtering bleb. Aqueous in the subconjunctival space may then exit by multiple pathways. Bleb failure most often results from fibroblast proliferation and subconjunctival fibrosis. Factors associated with an increased risk of bleb failure include youth, aphakia, active anterior segment neovascularization, inflammation, previously failed glaucoma filtering surgery, and, possibly, race. Several surgical and pharmacologic techniques have recently been introduced to enhance success in eyes with poor surgical prognoses. To elucidate the scientific rationale of these methods, we summarize the process of wound healing after glaucoma filtering surgery and describe postoperative clinical and histopathologic features, factors which may affect success, and specific methods to improve surgical success.