Classification of human scleral spur cells in monolayer culture

Levels of aqueous humor trace elements in patients with open-angle glaucoma

PURPOSE

Trace elements might play a role in the complex multifactorial pathogenesis of open-angle glaucoma. The aim of this study was to analyze concentrations of trace elements in aqueous humor samples of patients with primary open-angle glaucoma (POAG) and pseudoexfoliation glaucoma (PEXG).

PATIENTS AND METHODS

Thirty-three aqueous humor samples were obtained from patients undergoing cataract surgery: 12 patients with POAG (age 65.3±10.50, female 8, male 4), 10 patients with PEXG (age 65.9±11.27, female 6, male 4) and 11 patients without glaucoma (age 69.5±13.70, female 7, male 4) serving as controls. Aqueous humor levels of cadmium, iron, manganese, cobalt, copper and zinc were measured by Flow-Injection-Inductively-Coupled-Plasma-Mass-Spectrometry (FI-ICP-MS).

RESULTS

From the statistical evaluation, we observed that patients with POAG had significantly higher aqueous humor levels of zinc (p=0.006) compared to controls. Increased aqueous humor levels of zinc were also observed in patients with PEXG in relation to control (p=0.0006). For iron we observed a significantly reduction in PEXG compared to control (p=0.002) and a significant difference between POAG and PEXG (p=0.0091). No significant differences were observed in aqueous humor levels of manganese, cobalt, copper, cadmium between glaucoma and control patients. No differences were seen for iron (POAG vs. controls). Analysis of trace element ratios was added.

CONCLUSION

Significant differences in aqueous humor levels of zinc and iron between glaucoma and control patients support the hypothesis that these trace elements are involved in the pathogenesis of open-angle glaucoma.

Life under pressure: The role of ocular cribriform cells in preventing glaucoma

Primary open-angle glaucoma is a multifactorial blinding disease often impacting the two pressure-sensitive regions of the eye: the conventional outflow pathway and the optic nerve head (ONH). The connective tissues that span these two openings in the globe are the trabecular meshwork of the conventional outflow pathway and the lamina cribrosa of the ONH. Resident cribiform cells of these two regions are responsible for actively remodeling and maintaining their connective tissues. In glaucoma, aberrant maintenance of the juxtacanalicular tissues (JCT) of the conventional outflow pathway results in ocular hypertension and pathological remodeling of the lamina cribrosa results in ONH cupping, damaging retinal ganglion cell axons. Interestingly, cells cultured from the lamina cribrosa and the JCT of the trabecular meshwork have similarities regarding gene expression, protein production, plus cellular responses to growth factors and mechanical stimuli. This review compares and contrasts the current knowledge of these two cell types, whose health is critical for protecting the eye from glaucomatous changes. In response to pressure gradients across their respective cribiform tissues, the goal is to better understand and differentiate healthy from pathological behavior of these two cell types.

The many faces of the trabecular meshwork cell

With the combined purpose of facilitating useful vision over a lifetime, a number of ocular cells have evolved specialized features not found elsewhere in the body. The trabecular meshwork (TM) cell at the irido-corneal angle, which is a key regulator of intraocular pressure, is no exception. Examination of cells in culture isolated from the human TM has shown that they are unique in many ways, displaying characteristic features of several different cell types. Thus, these neural crest derived cells display expression patterns and behaviors typical of endothelia, fibroblasts, smooth muscle and macrophages, owing to the multiple roles and two distinct environments where they operate to maintain intraocular pressure homeostasis. In most individuals, TM cells function normally over a lifetime in the face of persistent stressors, including phagocytic, oxidative, mechanical and metabolic stress. Study of TM cells isolated from ocular hypertensive eyes has shown a compromised ability to perform their daily duties. This review highlights the many responsibilities of the TM cell and its challenges, progress in our understanding of TM biology over the past 30 years, as well as discusses unanswered questions about TM dysfunction that results in IOP dysregulation and glaucoma.

Vitamin E reduces TGF-beta2-induced changes in human trabecular meshwork cells

AIM

To determine the effects of vitamin E on transforming growth factor-beta2 (TGF-β2)-induced cellular changes in cultured human trabecular meshwork (TM) cells.

MATERIALS AND METHODS

Human TM cells were pre-treated with different concentrations of vitamin E. Afterwards, cells were exposed to 1.0 ng/ml TGF-β2 for 24 h. Expressions of the heat shock protein αB-crystallin, the extracellular matrix (ECM) component fibronectin and the ECM-degrading enzyme matrix metalloproteinase-2 (MMP-2) were examined by real-time polymerase chain reaction (PCR) analyses. The cytoskeleton was investigated by phalloidin staining.

RESULTS

TGF-β2 increased the expressions of αB-crystallin and fibronectin and reduced the levels of MMP-2. TGF-β2 induced the formation of actin stress fibers and cross-linked actin networks. Pre-treatment with different concentrations of vitamin E reversed the TGF-β2-induced cellular changes in cultured human TM cells.

CONCLUSIONS

TGF-β2-mediated changes in human TM cells could be reduced by pre-treatment with vitamin E. Therefore, it may be speculated that increasing the antioxidative capacity may help to lower the incidence of characteristic glaucomatous changes in the TM.

[Cross-linking in an artificial human cornea via induction of tissue transglutaminases]

PURPOSE

In recent years many three-dimensional cornea models have been developed. However, they show poor collagen stability in the stroma. Transglutaminases (Tgases) are calcium-dependent proteins which play an important role in cross-linking of the corneal stroma. The purpose of this study was to find out whether it is possible to induce in vitro cross-linking of the stroma in an artificial hemicornea model with the help of Tgases.

MATERIALS AND METHODS

For the construction of the hemicornea, human SV40 adenovector corneal epithelial cells (HCE) and human SV40 adenovector corneal keratocytes (HCK) were cultivated. Confluent HCK cells were treated for 24 h with transforming growth factor beta (TGFb) 1, 2 and 3 at different concentrations as well as with other growth factors and the treated cells were compared to untreated cultivated cells. The quantification of the expression of the Tgases by HCKs was examined with the use of real time PCR, Western blot imaging and immunochemistry.

RESULTS

All concentrations of TGFbs used resulted in a significant increase of Tgase-mRNA, Tgase protein level and Tgase activity. The Tgases remained unaffected after treatment with other growth factors in comparison to untreated control cells. Treatment of the hemicornea with TGFb2 showed a very strong contraction and haze in comparison to the untreated hemicornea.

CONCLUSION

It has been shown for the first time that TGFb induces a strong expression of Tgases in HCK cells. This effect caused an undesired contraction and haze of the human hemicornea model. Further research is necessary in order to find out whether the induction of Tgases in the HCK cells can be regulated without losing stability of the constructed hemicornea.

Minocycline is cytoprotective in human trabecular meshwork cells and optic nerve head astrocytes by increasing expression of XIAP, survivin, and Bcl-2

INTRODUCTION

Primary open-angle glaucoma (POAG) is one of the leading causes of blindness. Activation of optic nerve head astrocytes (ONHA) and loss of trabecular meshwork cells (TMC) are pathognomonic for this neurodegenerative disease. Oxidative stress and elevated levels of transforming growth factor beta (TGFbeta) play an important role in the pathogenesis of POAG. This study investigates the possible antiapoptotic and cytoprotective effects of minocycline on TMC and ONHA under oxidative stress and increased TGFbeta levels.

METHODS

TMC and ONHA were treated with minocycline 1-150 muM. Possible toxic effects and IC(50) were evaluated after 48 hours. Cell proliferation and viability were examined in order to assess the protective effects of minocycline on TMC and ONHA. Expression of Bcl-2, XIAP, and survivin, as well as their mRNA expression, were assessed by real time polymerase chain reaction (RT-PCR) and Western Blot analysis 48 hours after treatment with minocycline alone and additional incubation with TGFbeta-2 or oxidative stress.

RESULTS

Minocycline 1-75 muM showed no toxic effects on TMC and ONHA. Under conditions of oxidative stress, both TMC and ONHA showed an increase in viability and an ability to proliferate when treated with minocycline 20-40 muM. RT-PCR and Western blotting yielded an overexpression of Bcl-2, XIAP, and survivin when TMC or ONHA were treated with minocycline 20-40 muM under conditions of oxidative stress and when additionally incubated with TGFbeta-2.

CONCLUSION

Minocycline up to 75 muM does not have toxic effects on TMC and ONHA. Treatment with minocycline 20-40 muM led to increased viability and proliferation under oxidative stress and TGFbeta-2, as well as overexpression of Bcl-2, XIAP, and survivin. This protective pathway may help to prevent apoptotic cell death of TMC and ONHA and therefore be a promising approach to avoidance of progression of glaucomatous degeneration.

Intracameral moxifloxacin: in vitro safety on human ocular cells

PURPOSE

The fourth-generation fluoroquinolone, moxifloxacin, covers most gram-positive and gram-negative isolates causing endophthalmitis. It is safe and effective for systemic and topical use, but only limited data are available on prophylactic intracameral administration to prevent endophthalmitis. This study uses a cell culture model to investigate the safety of moxifloxacin for intracameral application.

METHODS

Endothelial toxicity of moxifloxacin was evaluated in cultured human corneas. Possible toxic effects of moxifloxacin (10-750 microg/mL) in corneal endothelial cells (CEC), primary human trabecular meshwork cells (TMC), and primary human retinal pigment epithelial (RPE) cells were evaluated after 24 hours and under conditions of oxidative and inflammatory stress by treatment with tumor necrosis factor alpha, lipopolysaccharides, or interleukin-6. Toxicity was evaluated by tetrazolium dye reduction assay, and cell viability was quantified by a microscopic live-dead assay.

RESULTS

No corneal endothelial toxicity could be detected after 30 days of treatment with 500 microg/mL moxifloxacin. Concentrations up to 150 microg/mL had no influence on CEC, TMC, or RPE cell proliferation or on cell viability when administered for 24 hours. After preincubation with tumor necrosis factor alpha, lipopolysaccharides, or interleukin-6 for 24 hours and subsequent treatment with moxifloxacin at concentrations from 10 to 150 microg/mL for 24 hours, no significant decrease in proliferation or viability was observed. Hydrogen peroxide exposure did not increase cellular toxicity.

CONCLUSIONS

This study showed no significant toxicity for moxifloxacin on CEC, TMC, RPE cells, or human corneal endothelium for concentrations up to 150 microg/mL. The minimum inhibitory concentration of moxifloxacin to inhibit 90% of pathogens commonly encountered in endophthalmitis is known to be in the range of 0.25-2.5 microg/mL. Therefore, prophylactic intracameral use of moxifloxacin at concentrations up to 150 microg/mL may be safely used to prevent endophthalmitis after intraocular surgery.

The effect of TGF-beta2 on human trabecular meshwork extracellular proteolytic system

Our study aimed to investigate whether transforming growth factor-beta2 (TGF-beta2), increased in the aqueous humor of eyes with primary open angle glaucoma (POAG), can affect factors responsible for the activity of matrix metalloproteinases (MMPs) in human trabecular cell cultures. With this goal in mind cultures of human trabecular meshwork (hTM) cells derived from 8 donors were treated with TGF-beta2 for 24, 36 and 48 hr. Influence of TGF-beta2 on expression of MMP-2, MMP-9, membrane type 1-MMP (MT1-MMP) and plasminogen activator inhibitor-1 (PAI-1) was examined using RT-PCR, Northern Blot, Western Blot and zymography. The influence of TGF-beta2 treatment on PAI-1 expression was also investigated using immunohistochemistry. It appeared that treatment with TGF-beta2 significantly increased expression of the proform of MMP-2, whereas the active form was not detectable. MMP-9 and MT1-MMP expression were not influenced by TGF-beta2 treatment. There was, however, a significant increase in PAI-1 expression. To investigate whether transformation of the proform of MMP-2 to the active form was inhibited by PAI-1, the influence of treatment with TGF-beta2 and a PAI-1 neutralizing antibody on MMP-2 was investigated using zymogram method. With this treatment protocol the active form of MMP-2 was clearly visible, indicating that TGF-beta2 enhancement of the PAI-1-expression decreases MMP activity. Inhibition of MMP activity through elevated levels of TGF-beta2 might contribute to the increase in ECM in the trabecular meshwork of glaucomatous eyes.

The regulation of trabecular meshwork and ciliary muscle contractility

Current models of aqueous humor outflow no longer treat trabecular meshwork (TM) as an inert tissue passively distended by the ciliary muscle (CM). Instead, ample evidence supports the theory that trabecular meshwork possess smooth muscle-like properties and is actively involved in the regulation of aqueous humor outflow and intraocular pressure. In this model, trabecular meshwork and ciliary muscle appear as functional antagonists, with ciliary muscle contraction leading to a distension of trabecular meshwork with subsequent reduction in outflow. and with trabecular meshwork contraction leading to the opposite effect. Smooth-muscle relaxing substances would therefore appear to be ideal candidates for glaucoma therapy with the dual goal of reducing intraocular pressure via the trabecular meshwork and of improving vascular perfusion of the optic nerve head. However, for such substances to effectively lower intraocular pressure, the effect on the ciliary muscle would have to he minimal. For this reason, more information is needed on the signalling processes involved in regulating trabecular meshwork and ciliary muscle contractility. This review attempts to outline current knowledge of signal transduction pathways leading to relaxation and contraction of ciliary muscle and trabecular meshwork. Pathways can be classified as involving or not involving changes of membrane voltage and of requiring or not requiring external calcium: possibly, other pathways exist. These different pathways involve different ion channels and isoforms of PKC and are expressed to a differing degree in ciliary muscle and trabecular meshwork, leading to differential responses when exposed to relaxing or contracting pharmacological agents. Some of these agents. like tyrosine kinase inhibitors and inhibitors of PKC. have been shown to relax trabecular meshwork while leaving ciliary muscle comparatively unaffected. This profile makes these substances appear as ideal drugs for simultaneously improving ocular outflow and retinal circulation, parameters that determine the time course of visual deterioration in glaucoma.