Volume 5, Number 2
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Monday, January 17, 2005
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Effects of Amniotic
Membrane on RPE Cell Differentiation Retinal pigment epithelial (RPE) cells cultured on amniotic membrane (AM) may be a useful matrix substrate for retaining the differentiated and epithelial phenotype of RPE for subretinal transplanation, according to a study by the Tokyo Medical and Dental School. Researchers cultured human RPE cells on the basement membrane side of dispase-treated AM. After one week of cellular confluence, they terminated the cultures, collected conditioned medium and extracted total RNA. Next, researchers evaluated the expression pattern of several genes considered to participate in the function of differentiated RPE. Ultrastructural changes were evaluated by transmission electron microscopy. Morphologically, RPE cells cultured on AM exhibited ultrastructural epithelial features, such as microvilli of the apical membrane and intercellular junctions. Gene expression of RPE65, CRALBP, bestrophin and tyrosinase-related protein-2 was upregulated in RPE cells cultured on AM, compared to cells cultured on plastic. In addition, protein production of vascular endothelial growth factor, thrombospondin-1, and pigment epithelium derived factor was markedly increased in cells cultivated on AM. Gene expression of cathepsin D, brain-derived neurotrophic factor and basic fibroblast growth factor, however, did not differ between RPE cells cultured on plastic and those cultured on AM. |
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SOURCE: Ohno-Matsui K, Ichinose S, Nakahama S, et al. The effects of amniotic membrane on retinal pigment epithelial cell differentiation. Mol Vis 2005;11:1-10. |
Trabecular Bypass
Stents Decrease IOP in Cultured Human Anterior Segments Bypassing the trabecular meshwork using a stent lowers intraocular pressure (IOP) in cultured human anterior segments, according to a study by the Mayo Clinic in Rochester, MN. Investigators placed anterior segments from 21 human eyes obtained at autopsy in perfusion culture, and they inserted trabecular bypass stents through the trabecular meshwork, with the lumen of the tube opening into Schlemm"s canal. Eyes received from one to four stents, placed equidistantly. In eyes receiving one or two stents, additional stents were later added, up to four per eye. IOP was lowered after placement of a single stent, from 21.4 +/- 3.8 mmHg to 12.4 +/- 4.2 mmHg. This corresponded to an 84 percent increase in facility of outflow. Eyes receiving more than one stent had final IOP of 11.9 +/- 3.7 mmHg. Nine eyes had sequential addition of stents, and seven of these had a further decrease of IOP (13.6 +/- 4.1 mmHg to 10.0 +/- 4.3 mmHg). Excision of the entire meshwork between stents dropped IOP to 6.3 +/- 3.2 mmHg, indicating some residual meshwork or canal resistance remained even after placement of three stents. The authors believe that this technique holds promise as a new clinical surgery for treating glaucoma. |
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SOURCE: Bahler CK, Smedley GT, Zhou J, Johnson DH. Trabecular bypass stents decrease intraocular pressure in cultured human anterior segments. Am J Ophthalmol 2004;138(6):988-94. |
Stimulation of
Neovascularization by Pigment Epithelium-derived Growth Factor
Ophthalmic researchers at Washington University School of Medicine, St. Louis, examined the effect of pigment epithelium-derived growth factor (PEDF) on laser-induced choroidal neovascularization (CNV). The results of this animal study showed that PEDF demonstrates opposing effects on CNV and endothelial cell function: whereas low doses are inhibitory, high doses can augment the development of the neovasculature. Investigators anesthetized adult C57Bl/6 mice and placed four laser spots in each quadrant of the fundus with a krypton red laser (614 nm, 50 micrometers, 0.05 second, 200 mW). The animals were treated with various doses of PEDF administered with mini-osmotic pumps implanted subcutaneously. Seven days after laser treatment, mice were perfused with 3% fluorescein isothiocyanate (FITC) high-molecular-weight dextran, the eyes enucleated and neovascularization analyzed by confocal microscopy. Data were recorded as the volume of the neovascular complex. The effect of PEDF on endothelial cell migration, vascular tube formation in synthetic basement membrane and VEGF production was also determined. Results showed that mice receiving a lower dose of PEDF (90 microg/mL) had significantly decreased areas of CNV. A high dose of PEDF (360 microg/mL) significantly increased CNV, whereas an intermediate dose (180 microg/mL) of PEDF had no effect. PEDF inhibited endothelial cell migration and vascular tube formation at lower doses (0.5 to 5 microg/mL). High doses of PEDF (25 to 50 microg/mL) stimulated endothelial cell migration, enhanced vascular tube formation in vitro and stimulated VEGF production from endothelial cells. Neutralizing anti-VEGF antibody completely reversed the stimulatory effects of high doses of PEDF on CNV in vivo. The authors believe that these results suggest that the effects of PEDF on neovascularization are more complex than originally believed, and that caution should be exercised when considering PEDF therapies. |
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SOURCE: Apte RS, Barreiro RA, Duh E, et al. Stimulation of neovascularization by the anti-angiogenic factor PEDF. Invest Ophthalmol Vis Sci 2004;45(12):4491-7. |
Intravitreal
Triamcinolone-induced Elevated IOP and Posterior Subcapsular Cataract
Investigators at the Save Sight and Eye Health Institute, University of Sydney, NSW, Australia, recently studied the connection between elevated intraocular pressure (IOP) and accelerated cataract formation in patients treated with intravitreal triamcinolone, and found a strong association. This suggests that the mechanism responsible for the development of steroid-induced posterior subcapsular cataract (PSC) and raised IOP may be similar. The study included patients with phakic eyes who participated in the Intravitreal Triamcinolone Study, a randomized clinical trial of intravitreal triamcinolone for age-related macular degeneration (AMD). The treatment group included 57 eyes; the control group included 54 eyes. One eye per patient was studied. Intervention was 4 mg of intravitreal triamcinolone (treatment group) or 1 ml subconjunctival saline (controls). Main outcome measures included IOP rise of at least 5 mmHg (IOP responders) and progression of posterior subcapsular cataract by two or more grades using photographic standards from the Age Related Eye Disease Study. Progression of PSC by two or more grades in the treatment group was significantly higher among 16 IOP responders (51 percent after two years) than among 37 nonresponders (three percent). No significant progression of PSC occurred in the placebo group or the opposite eye of the treatment group. Progression of cortical cataracts was also significantly higher among responders than nonresponders (15 percent vs. three percent). The progression of nuclear cataracts (13 percent vs. three percent) was not significantly different between IOP responders and nonresponders. The authors concluded that although steroid-related cataracts are unlikely to develop in eyes that do not experience elevated IOP after intravitreal triamcinolone, those eyes that do experience elevated IOP also have a very high risk of rapidly experiencing posterior subcapsular lens opacification. |
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SOURCE: Gillies MC, Kuzniarz M, Craig J, et al. Intravitreal triamcinolone-induced elevated intraocular pressure is associated with the development of posterior subcapsular cataract. Ophthalmol 2005;112(1):139-43. |
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