Systemic neuroprotectin D1 is a potent inhibitor of laser-induced choroidal neovascularization

Key Points

Fort Lauderdale, FL-The neuroprotectin D1 (NPD1) molecule swiftly reduced leakage from choroidal neovascular lesions as well as lesion diameter in a study conducted in an animal model. These results suggest that NPD1, a mediator derived from docosahexaenoic acid (DHA), an omega-3 fatty acid found in retinal pigment epithelial (RPE) cells, could have therapeutic application in the treatment of neovascular age-related macular degeneration (AMD), according to Nicolas G. Bazan, MD, PhD, who reported the findings at the annual meeting of the Association for Research in Vision and Ophthalmology.

NPD1 represents a different approach to AMD therapy from most other options currently offered to patients, said Dr. Bazan, who is director, Neuroscience Center of Excellence, Health Sciences Center, Louisiana State University School of Medicine. He and colleagues discovered NPD1 while exploring how the retina responds to injury and subsequently showed that NPD1 was a modulator of proinflammatory gene expression and cell survival.

According to a recently published study in Investigative Ophthalmology and Visual Science (2007;48:4866-4881), NPD1 could be part of an endogenous response intended to counteract inflammation that could damage the RPE and the photoreceptor cells of the macula. NPD1 survival signaling is upregulated in response to oxidative and nitrosylative stress. In addition, pigment epithelium-derived factor, a neutrophin made in RPE cells, is an activator of NPD1 in RPE cells exposed to oxidative stress.

Concerning his recent work on inhibition of laser-induced choroidal neovascularization (CNV) in a mouse model, Dr. Bazan and his colleagues used a model in which potential technical artifacts, such as retinal neovascularization and nonspecific local inflammatory activity resulting from the laser injury, were well defined and controlled to minimize a biased assessment of CNV outcomes.

In the experiment, the pupils of anesthetized mouse eyes were dilated, and lesions were made around the optic nerve at 3, 6, 9, and 12 o'clock. Pulses were delivered by a green diode ophthalmic laser (Novus Spectra, Lumenis)-50-µm lesions, 200 mW energy, and 100 ms duration-mounted on a slit lamp (SL-D7, Topcon). The pulses produced a retinal bubble as Bruch's membrane was breached.

Either NPD1 or vehicle consisting of saline and ethanol was delivered intraperitoneally on days 1, 2, 4, 6, and 8. Images of fluorescein isothiocyanate (FITC) leakage were obtained from each lesion on days 7 and 14, 5 minutes after delivery of the FITC. The images were captured, viewed, and ranked as strong, moderate, light, and none by an ophthalmologist. For this study, strong was equivalent to clinically relevant leakage in humans.

The eyes then were collected and fixed; the retinas were removed, leaving a flat-mounted choroid labeled with FITC-conjugated isolectin B4, which is specific for endothelial cells. The diameters of the choroidal lesions then were plotted to determine the degree of neovascularization.

The investigative team chose to determine leakage at days 7 and 14 after induction of the NPD1 or vehicle because there are no changes of an unspecific nature in inflammatory mediators at those times, Dr. Bazan said. The results showed that at day 7, leakage had been reduced to 13% in the eyes given NPD1 compared with 75% in the control eyes. By day 14, the leakage had been further reduced to 5% in the NPD1 eyes, equivalent to a protection level of about 90%. In addition, the number of eyes ranked as having no leakage had increased to 68% in the NPD1 eyes by day 14, compared with 15% in the controls.

The choroidal lesion diameters of the control retinas increased to about 105 µm, whereas lesion sites in the NPD1 retinas decreased from about 50 to 18 µm at day 14.

This rapid reduction in leakage from the lesion sites and in lesion site diameter suggests that systemic NPD1 protects by acting on pathophysiologic events during the development of CNV, Dr. Bazan said. Having determined through their studies of the bioactivity of NPD1 that it is anti-inflammatory, antiapoptotic, antiangiogenic, and it enhances photoreceptor-RPE cell homeostasis, he and his colleagues believe that NPD1 or a synthetic active analogue could have therapeutic value in wet AMD and other retinal neurodegenerative diseases.

A privately held biotechnology company in Bedford, MA, is developing a compound based on NPD1 and expects to initiate a clinical trial soon, Dr. Bazan concluded.