Systemic Biodistribution and Intravitreal Pharmacokinetic Properties of Bevacizumab, Ranibizumab, and Aflibercept in a Nonhuman Primate Model.

Purpose: To determine the intravitreal pharmacokinetic properties and to study the systemic biodistribution characteristics of I-124-labeled bevacizumab, ranibizumab, and aflibercept with positron emission tomography-computed tomography (PET/CT) imaging in a nonhuman primate model. Methods: Three groups with four owl monkeys per group underwent intravitreal injection with 1.25 mg/0.05 mL I-124 bevacizumab, 0.5 mg/0.05 mL I-124 ranibizumab, or 2.0 mg/0.05 mL I-124 aflibercept in the right eye of each subject. All subjects were imaged using PET/CT on days 0, 1, 2, 4, 8, 14, 21, 28, and 35. Serum blood draws were performed at hours 1, 2, 4, 8, 12 and days 1, 2, 4, 8, 14, 21, 28, and 35. Radioactivity emission measurements were used to determine the intravitreal half-lives of each agent and to study the differences of radioactivity uptake in nonocular organs. Results: The intravitreal half-lives were 3.60 days for I-124 bevacizumab, 2.73 days for I-124 ranibizumab, and 2.44 days for I-124 aflibercept. Serum levels were highest and most prolonged for bevacizumab as compared to both ranibizumab and aflibercept. All agents were primarily excreted through the renal and mononuclear phagocyte systems. However, bevacizumab was also found in significantly higher levels in the liver, heart, and distal femur bones. Conclusions: Among the three anti-VEGF agents used in clinical practice, bevacizumab demonstrated the longest intravitreal retention time and aflibercept the shortest. Significantly higher and prolonged levels of bevacizumab were found in the serum as well as in the heart, liver, and distal bones. These differences may be considered by clinicians when formulating treatment algorithms for intravitreal therapies with these agents.

Retinal Damage Induced by Internal Limiting Membrane Removal.

The internal limiting membrane (ILM), the basement membrane of the Müller cells, serves as the interface between the vitreous body and the retinal nerve fiber layer. It has a fundamental role in the development, structure, and function of the retina, although it also is a pathologic component in the various vitreoretinal disorders, most notably in macular holes. It was not until understanding of the evolution of idiopathic macular holes and the advent of idiopathic macular hole surgery that the idea of adjuvant ILM peeling in the treatment of tractional maculopathies was explored. Today intentional ILM peeling is a commonly applied surgical technique among vitreoretinal surgeons as it has been found to increase the rate of successful macular hole closure and improve surgical outcomes in other vitreoretinal diseases. Though ILM peeling has refined surgery for tractional maculopathies, like all surgical procedures it is not immune to perioperative risk. The essential role of the ILM to the integrity of the retina and risk of trauma to retinal tissue spurs suspicion with regard to its routine removal. Several authors have investigated the retinal damage induced by ILM peeling and these complications have been manifested across many different diagnostic studies.

Systemic treatments for noninfectious vitreous inflammation.

Vitreous inflammation, or vitritis, may result from many causes, including both infectious and noninfectious, including rheumatologic and autoimmune processes. Vitritis is commonly vision threatening and has serious sequelae. Treatment is frequently challenging, but, today, there are multiple methods of systemic treatment for vitritis. These categories include corticosteroids, antimetabolites, alkylating agents, T-cell inhibitors/calcineurin inhibitors, and biologic agents. These treatment categories were reviewed last year, but, even over the course of just a year, many therapies have made progress, as we have learned more about their indications and efficacy. We discuss here discoveries made over the past year on both existing and new drugs, as well as reviewing mechanisms of action, clinical dosages, specific conditions that are treated, adverse effects, and usual course of treatment for each class of therapy.

Inflammatory mechanisms of idiopathic epiretinal membrane formation.

The pathogenesis of idiopathic epiretinal membranes (iERMs), a common pathology found in retina clinics, still eludes researchers to date. Ultrastructural studies of iERMs in the past have failed to identify the cells of origin due to the striking morphologic changes of cells involved via transdifferentiation. Thus, immunohistochemical techniques that stain for the cytostructural components of cells have confirmed the importance of glial cells and hyalocytes in iERM formation. The cellular constituents of iERMs are thought to consist of glial cells, fibroblasts, hyalocytes, etc. that, in concert with cytokines and growth factors present in the vitreous, lead to iERM formation. Recently, research has focused on the role of the posterior hyaloid in iERM formation and contraction, particularly the process of anomalous PVD as it relates to iERM formation. Recent advances in proteomics techniques have also elucidated the growth factors and cytokines involved in iERM formation, most notably nerve growth factor, glial cell line-derived growth factor, and transforming growth factor ß1.