Bahri Aydin

Heparin Mimetic Peptide Nanofibers Promote Angiogenesis

New blood vessel formation (angiogenesis) is one of the most important processes required for functional tissue formation. Induction of angiogenesis is usually triggered by growth factors released by cells. Glycosaminoglycans (e.g., heparan sulphates) in the extracellular matrix aid in proper functioning of these growth factors. Therefore, exogeneous heparin or growth factors were required for promoting angiogenesis in previous regenerative medicine studies. Here we report for the first time induction of angiogenesis by a synthetic nanofibrous peptide scaffold without the addition of any exogenous growth factors or heparin. We designed and synthesized a self-assembling peptide amphiphile molecule that is functionalized with biologically active groups to mimic heparin. Like heparin, this molecule has the ability to interact with growth factors and effectively enhance their bioactivity. The nanofibers formed by these molecules were shown to form a 3D network mimicking the structural proteins in the extracellular matrix. Because of heparin mimicking capabilities of the peptide nanofibers, angiogenesis was induced without the addition of exogenous growth factors in vitro. Bioactive interactions between the nanofibers and the growth factors enabled robust vascularization in vivo as well. Heparin mimetic peptide nanofibers presented here provide new opportunities for angiogenesis and tissue regeneration by avoiding the use of heparin and exogenous growth factors. The synthetic peptide nanofiber scaffolds enriched with proper chemical functional groups shown in this study can be used to induce various desired physiological responses for tissue regeneration.

Optical Coherence Tomographic Assessment of Diabetic Macular Edema: Comparison with Fluorescein Angiographic and Clinical Findings

Purpose: To compare the optical coherence tomographic (OCT) features with clinical and fluorescein angiographic (FA) findings in patients with diabetic retinopathy. Methods: In a retrospective study ophthalmologic examination together with FA and OCT images were obtained from 195 eyes of 110 patients with different stages of diabetic retinopathy and OCT images were obtained from 40 eyes of 20 control subjects. Fluorescein leakage characteristics were organized into five groups: no leakage (1), focal (2), diffuse (3), combined focal + diffuse leakage (4) and cystoid (5). The Pearson correlation test was used to test the correlation between visual acuity and central foveal thickness and ANOVA was used for the statistical comparison between the groups. Results: The OCT images demonstrated retinal swelling in 66.1% of eyes, cystoid macular edema (CME) in 11.8% of eyes, serous foveal detachment + swelling in 6.2% of eyes, serous foveal detachment + swelling + CME in 3.6% of eyes and normal foveal structure in 12.3% of eyes. The best-corrected visual acuity was significantly correlated with central foveal thickness (r: –0.528, p < 0.01). There was 77% agreement between clinical examination and OCT results. CME was detected with OCT in 15.4% of eyes in our study, 40% of which was not detected with slit-lamp biomicroscopy and 63.3% of which was not evident in FA. None of the serous foveal detachments could be detected during slit-lamp biomicroscopy or FA. Conclusions: OCT-3 provided objective documentation of foveal structural changes in eyes with diabetic retinopathy. Best-corrected visual acuity provided a significant correlation with the retinal thickness at the central fovea. These results indicate that OCT can facilitate deciding on the treatment protocol (surgical or medical) and follow-up of diabetic patients, which is especially important in the early stages of diabetic maculopathy when the structural changes are not yet evident with slit-lamp biomicroscopy or angiographically.

Bioactive self-assembled peptide nanofibers for corneal stroma regeneration.

Defects in the corneal stroma caused by trauma or diseases such as macular corneal dystrophy and keratoconus can be detrimental for vision. Development of therapeutic methods to enhance corneal regeneration is essential for treatment of these defects. This paper describes a bioactive peptide nanofiber scaffold system for corneal tissue regeneration. These nanofibers are formed by self-assembling peptide amphiphile molecules containing laminin and fibronectin inspired sequences. Human corneal keratocyte cells cultured on laminin-mimetic peptide nanofibers retained their characteristic morphology, and their proliferation was enhanced compared with cells cultured on fibronectin-mimetic nanofibers. When these nanofibers were used for damaged rabbit corneas, laminin-mimetic peptide nanofibers increased keratocyte migration and supported stroma regeneration. These results suggest that laminin-mimetic peptide nanofibers provide a promising injectable, synthetic scaffold system for cornea stroma regeneration.

The Role of Magnesium in the Pathogenesis and Treatment of Glaucoma

Glaucoma is characterized by chronic optic neuropathy resulting in progressive vision loss. Not only is glaucoma considered as a condition of elevated intraocular pressure (IOP), but also other risk factors may play a role in the pathogenesis of glaucomatous optic nerve damage. Vascular dysregulation in ocular blood flow and oxidative stress are currently suggested as important risk factors for glaucomatous retinal ganglion cell loss. New treatment modalities that improve ocular blood flow and reduce oxidative stress have been investigated in many studies. Magnesium (Mg) is thought to be one of the molecules that has a treatment potential in glaucoma. Mg has been shown to improve blood flow by modifying endothelial function via endothelin-1 (ET-1) and endothelial nitric oxide (NO) pathways. Mg also exhibits neuroprotective role by blocking N-methyl-D-aspartate (NMDA) receptor-related calcium influx and by inhibiting the release of glutamate, and hence protects the cell against oxidative stress and apoptosis. Both improvement in ocular blood flow and prevention of ganglion cell loss would make magnesium a good candidate for glaucoma management. Further studies on the effect of Mg may open a new therapeutic era in glaucoma.

Magnezyum: Kalsiyum kanal antagonisti olarak göz sağlığı üzerindeki etkileri

Magnesium is the physiologic calcium channel blocker, involving in many different metabolic processes by maintaining cell membrane function, modulating smooth muscle contraction and influencing enzymatic activities. Mag nesium has been shown to increase blood flow to tissues by modifying endothelial function via endothelin-1 (ET-1) and nitric Oxide (NO) pathways. Magnesium also exhibits neuroprotective role by blocking N-methyl-D-aspartate (NMDA) receptor related calcium influx and by inhibiting the release of glutamate, hence protects the cell against oxidative stress and apoptosis. Both increase in blood flow and its neuroprotective effect make magnesium a good candidate for glaucoma studies. Magnesium has been shown to decrease oxidative stress and apoptosis in retinal tissue and to have retinal ganglion cell sparing effect. A series of studies has been conducted about magnesium could decrease insulin resistance in diabetic patients, ease glycemia control and prevent diabetic retinopathy. Magnesium is found to be critically important in maintaining normal ionic homeostasis of lens. Magnesium deficiency has been shown to cause increased lenticular oxidative stress and ionic imbalance in the lens so trigger cataractogenesis. J Clin Exp Invest 2013; 4 (2): 244-251

Retinal endoilluminator toxicity of xenon and light-emitting diode (LED) light source: rabbit model

Abstract Objective: This study evaluates retinal toxicity due to endoillumination with the light-emitting diode (LED) light source in comparison to endoillumination with xenon light source. Material and methods: Twenty-five eyes of 14 New Zealand pigmented rabbits were used in the study. The LED light (Omesis Medical Systems, Turkey) group was composed of 7 right eyes, while the other 7 right eyes constituted the xenon group (420 nm filter, 357mW/cm2) (Bright Star; DORC, Zuidland, Netherlands). Eleven untreated left eyes composed the control group. Twenty gauge pars plana incision 1.5 mm behind the limbus was performed in the right eyes. Twenty gauge bullet type fiberoptic endoilluminator was inserted into the eye from the incision without any pars plana vitrectomy. Fiberoptic endoilluminator was placed in such a way that it was directed toward visual streak of the rabbit retina with a 5 mm distance to retinal surface. Endoillumination was then applied for 20 min with a maximum light intensity for LED and xenon light. In left control eyes, no surgical procedure and no endoillumination were performed. One week after the endoillumination procedure, both eyes of the rabbits were enucleated following electroretinography. Sections stained with hematoxylin and eosin to evaluate morphologic changes. Retina tissues were assessed by active caspase-3 staining. Results: There was no difference in the shape of the waveforms recorded in the eyes endoilluminated with LED light and xenon light sources compared to control eyes both before and after endoillumination application (p > 0.05). Microscopic evaluation of the retinas with hematoxylin and eosin staining demonstrated that all study groups have normal histologic properties similar to control group. No apoptosis positive cells were found within all sections in all groups. Conclusions: When the LED light source is used with maximum power and limited duration for endoillumination in rabbit eyes it does not produce phototoxic effects that may be detectable by electrophysiology and histology similar to xenon light.

Descemet Membrane Endothelial Keratoplasty with Irregular-Edged Graft: A Salvage Method for Large Radial Graft Tears

Large radial tears of donor Descemet membrane (DM) during the preparation of Descemet membrane endothelial keratoplasty (DMEK) grafts can make the trephination stage impossible because of small graft diameter. This results in irregular-edged grafts. In this study, we report two pseudophakic bullous keratopathy patients who underwent DMEK surgery with irregular-edged Descemet membrane (DM) grafts. Main outcome measures were preoperative and postoperative 1-, 3-, and 6-month best corrected visual acuity (BCVA), endothelial cell density (ECD) and central corneal thickness (CCT). Intraoperative and early postoperative complications were also evaluated. Both irregular-edged grafts were successfully implanted into the anterior chamber, unfolded, and attached to the posterior corneal stroma. Patients’ BCVA at 6 months was 1.0 (Snellen equivalent: 20/20) and 0.6 (Snellen equivalent: 20/32) respectively. Decrease in ECD at the last visit was 27% and 25%. CCT decreased from 723 μm and 850 μm to 530 μm and 523 μm, respectively. No intraoperative complications occurred except for the large radial Descemet membrane graft tears that developed during donor DM stripping. None of the cases needed a rebubbling procedure postoperatively. We have demonstrated that irregular-edged DM grafts can be successfully implanted for DMEK surgery with good clinical outcomes.

A completely human-derived biomaterial mimicking limbal niche: Platelet-rich fibrin gel

&NA; Platelet‐rich fibrin (PRF) is a natural biomaterial and has excellent biochemical and physical properties with a history of proven biocompatibility in the field of tissue engineering and regenerative medicine. Recent reports of fibrin‐based matrices have offered new opportunities to apply PRF as a supplement for in vitro cell culture. Here, custom‐modified human‐derived PRF (HPRF) was produced via different centrifugation protocols, then, characterized by morphologically and chemically and utilized as a substrate and as a conditioned medium for limbal explant culture for the first time. It was found that the HPRF released significantly higher levels of growth factors which are essential for epithelial cell growth. The enhanced physicochemical properties of the HPRF were also proven in the limbal explant cultures in terms of cell growth, migration, viability, and stemness in comparison with the conventional limbal explant culture on human‐derived amniotic membrane. Consequently, HPRF hydrogels are appealing natural biomaterials for the purpose of mimicking limbal niche and the discovery elucidates this new, xeno‐chemical‐free, completely human‐derived biomaterial can be utilized as a supplement to promote epithelial cell behaviour in vitro. HighlightsInvestigation of xeno‐chemical‐free cell culture systems is a growing area.Mimicking in vivo conditions with biosafe methods is essential for clinical purpose.Choukrouns PRF was first used as substratum and conditioned medium for limbal culture.It promotes epithelial cell growth, migration, viability, and stemness.The applicability of this new concept has to be proven through clinical studies.

Autologous serum eye‐drops and enhanced epithelial healing time after photorefractive keratectomy

The aim of the study is to test whether use of autologous serum eye‐drops can provide earlier epithelial healing following the application of photorefractive keratectomy.

A Comparison of Accommodation Amplitudes of Three Different Acrylic Intraocular Lenses

Aim : To assess the accommodative amplitudes of three different foldable acrylic intraocular lenses (IOLs) by measuring with photorefractor Plusoptix CR03 (Plusoptix GmbH, Nuernberg, Germany). Methods: Fifty five pseudophakic eyes of 46 patients (mean age 65.25±10.63 years) were analyzed one month after uneventful phacoemulsification and IOL implantation surgery. Rayner Centerflex (C-Flex) (n=17), AcyrSof MA60BM (n=17), Sensar AR40e (n=21) IOLs were implanted. An objective, dynamic measurement technique with R mode of Plusoptix CR03 device was used to measure accommodation. Accommodation was measured at near distance (0.33m) and far distance (5m). Results: Accommodation amplitudes (mean ± SD) measured with photorefractor at near distance in Rayner, AcyrSof and Sensar groups were 1.45±0.76 diopter (D), 2.82±1.88 D, 2.44±1.02 D, respectively. Accommodative response of AcyrSof and Sensar IOLs was greater than Rayner IOL significantly (p=0.027 and p=0.004, respectively). At far distance,