Zinc Nutrition and Inflammation in the Aging Retina

Zinc is an essential nutrient for human health. It plays key roles in maintaining protein structure and stability, serves as catalytic factor for many enzymes, and regulates diverse fundamental cellular processes. Zinc is important in affecting signal transduction and, in particular, in the development and integrity of the immune system, where it affects both innate and adaptive immune responses. The eye, especially the retina-choroid complex, has an unusually high concentration of zinc compared to other tissues. The highest amount of zinc is concentrated in the retinal pigment epithelium (RPE) (RPE-choroid, 292 ± 98.5 µg g^-1 dry tissue), followed by the retina (123 ± 62.2 µg g^-1 dry tissue). The interplay between zinc and inflammation has been explored in other parts of the body but, so far, has not been extensively researched in the eye. Several lines of evidence suggest that ocular zinc concentration decreases with age, especially in the context of age-related disease. Thus, a hypothesis that retinal function could be modulated by zinc nutrition is proposed, and subsequently trialled clinically. In this review, the distribution and the potential role of zinc in the retina-choroid complex is outlined, especially in relation to inflammation and immunity, and the clinical studies to date are summarized.

The estrogenic retina: The potential contribution to healthy aging and age-related neurodegenerative diseases of the retina

These last two decades have seen an explosion of clinical and epidemiological research, and basic research devoted to envisage the influence of gender and hormonal fluctuations in the retina/ocular diseases. Particular attention has been paid to age-related disorders because of the overlap of endocrine and neuronal dysfunction with aging. Hormonal withdrawal has been considered among risk factors for diseases such as glaucoma, diabetic retinopathy and age-related macular disease (AMD), as well as, for Alzheimer's disease, Parkinson's disease, or other neurodegenerative disorders. Sex hormones and aging have been also suggested to drive the incidence of ocular surface diseases such as dry eye and cataract. Hormone therapy has been approached in several clinical trials. The discovery that the retina is another CNS tissue synthesizing neurosteroids, among which neuroactive steroids, has favored these studies. However, the puzzling data emerged from clinical, epidemiological and experimental studies have added several dimensions of complexity; the current landscape is inherently limited to the weak information on the influence and interdependence of endocrine, paracrine and autocrine regulation in the retina, but also in the brain. Focusing on the estrogenic retina, we here review our knowledge on local 17β-oestradiol (E2) synthesis from cholesterol-based neurosteroidogenic path and testosterone aromatization, and presence of estrogen receptors (ERα and ERβ). The first cholesterol-limiting step and the final aromatase-limiting step are discussed as possible check-points of retinal functional/dysfunctional E2. Possible E2 neuroprotection is commented as a group of experimental evidence on excitotoxic and oxidative retinal paradigms, and models of retinal neurodegenerative diseases, such as glaucoma, diabetic retinopathy and AMD. These findings may provide a framework to support clinical studies, although further basic research is needed.

Ranibizumab versus bevacizumab for the treatment of idiopathic choroidal neovascularization: 2-Year results

PURPOSE

To compare the efficacy and safety of bevacizumab vs ranibizumab for the treatment of idiopathic choroidal neovascularization (ICNV).

METHODS

This retrospective study included 60 eyes of 60 patients with ICNV who underwent intravitreal injection of bevacizumab (1.25 mg/0.05 mL, n = 30 eyes) or ranibizumab (0.5 mg/0.05 mL, n = 30 eyes). Multiple treatments were based on complete ophthalmologic investigation including slit-lamp biomicroscopy, fundus examination, fundus fluorescein angiography (FFA), optical coherence tomography (OCT), and best-corrected visual acuity (BCVA). The BCVA, central retinal thickness (CRT), intraocular pressure (IOP), FFA results, and complications were compared between the 2 groups during the 2-year follow-up.

RESULTS

Visual acuity was significantly better at 1, 3, 6, 12, and 24 months after treatment (p<0.01), with no significant difference in visual acuity between the bevacizumab and ranibizumab groups. In both groups of patients, the CRT after treatment was significantly less than before. At 12 and 24 months, the CRT in the ranibizumab group was significantly less than in the bevacizumab group (p<0.05). The FFA examination showed that CNV was reduced after intravitreal injection of either drug, with no significant difference in IOP between the 2 groups. No ophthalmologic or systemic complications occurred.

CONCLUSIONS

Bevacizumab and ranibizumab are effective and safe in the treatment of ICNV, with similar effects in improving visual acuity and reducing retinal edema. The long-term efficacy of ranibizumab is superior to bevacizumab in reducing CRT.

The effect of glutathione as chain transfer agent in PNIPAAm-based thermo-responsive hydrogels for controlled release of proteins

PURPOSE

To control degradation and protein release using thermo-responsive hydrogels for localized delivery of anti-angiogenic proteins.

METHODS

Thermo-responsive hydrogels derived from N-isopropylacrylamide (NIPAAm) and crosslinked with poly(ethylene glycol)-co-(L-lactic acid) diacrylate (Acry-PLLA-b-PEG-b-PLLA-Acry) were synthesized via free radical polymerization in the presence of glutathione, a chain transfer agent (CTA) added to modulate their degradation and release properties. Immunoglobulin G (IgG) and the recombinant proteins Avastin® and Lucentis® were encapsulated in these hydrogels and their release was studied.

RESULTS

The encapsulation efficiency of IgG was high (75-87%) and decreased with CTA concentration. The transition temperature of these hydrogels was below physiological temperature, which is important for minimally invasive therapies involving these materials. The toxicity from unreacted monomers and free radical initiators was eliminated with a minimum of three buffer extractions. Addition of CTA accelerated degradation and resulted in complete protein release. Glutathione caused the degradation products to become solubilized even at 37°C. Hydrogels prepared without glutathione did not disintegrate nor released protein completely after 3 weeks at 37°C. PEGylation of IgG postponed the burst release effect. Avastin® and Lucentis® released from degraded hydrogels retained their biological activity.

CONCLUSIONS

These systems offer a promising platform for the localized delivery of proteins.

PPARgamma Agonists: Potential as Therapeutics for Neovascular Retinopathies

The angiogenic, neovascular proliferative retinopathies, proliferative diabetic retinopathy (PDR), and age-dependent macular degeneration (AMD) complicated by choroidal neovascularization (CNV), also termed exudative or “wet” AMD, are common causes of blindness. The antidiabetic thiazolidinediones (TZDs), rosiglitazone, and troglitazone are PPARγ agonists with demonstrable antiproliferative, and anti-inflammatory effects, in vivo, were shown to ameliorate PDR and CNV in rodent models, implying the potential efficacy of TZDs for treating proliferative retinopathies in humans. Activation of the angiotensin II type 1 receptor (AT1-R) propagates proinflammatory and proliferative pathogenic determinants underlying PDR and CNV. The antihypertensive dual AT1-R blocker (ARB), telmisartan, recently was shown to activate PPARγ and improve glucose and lipid metabolism and to clinically improve PDR and CNV in rodent models. Therefore, the TZDs and telmisartan, clinically approved antidiabetic and antihypertensive drugs, respectively, may be efficacious for treating and attenuating PDR and CNV humans. Clinical trials are needed to test these possibilities.

Potential application of adult stem cells in retinal repair--challenge for regenerative medicine

Stem cells (SCs) maintain the balance among somatic cell populations in various tissues and are responsible for organ regeneration. The remarkable progress of regenerative medicine in the last few years indicates promise for the use of SCs in ophthalmic disorder treatment. This review describes the current view on hierarchy in the SC compartment and presents the latest attempts to use adult SCs in the regeneration of the retina. Research performed primarily in animal models gives hope for using similar strategies in humans. However, the search for the optimal source of SCs for cell therapy continues. We briefly discuss various potential sources of adult SCs that could be employed in regenerative medicine, particularly focusing on recently identified, very small embryonic-like SCs (VSEL-SCs). These cells are even present in the bone marrow and adult tissues of older patients and could be harvested from cord blood. We believe that VSEL-SCs, after the establishment of ex vivo expansion and differentiation protocols, could be harnessed for retina regeneration.

Safety and efficacy of intravitreal anti-VEGF injections for age-related macular degeneration

PURPOSE OF REVIEW

To report the safety and efficacy of intravitreal injections for age-related macular degeneration (AMD).

RECENT FINDINGS

Injecting antivascular endothelial growth factor drugs into the vitreal cavity brings new hope to many AMD patients. Currently, several antivascular endothelial growth factor drugs such as pegaptanib, ranibizumab, and bevacizumab are used via the intravitreal route for neovascular AMD. However, these injections are not without ocular or systemic complications.

SUMMARY

Review of current literature suggests that intravitreal antivascular endothelial growth factor agents are generally a safe and effective treatment for neovascular AMD for up to 2-3 years. Presently, there is level I evidence to substantiate this conclusion for pegaptanib and ranibizumab, but not bevacizumab.