Can we stop the onslaught of non-exudative (or dry) age-related macular degeneration (AMD)? A determined team of researchers from the Gifu Pharmaceutical University’s Department of Biofunctional Evaluation, Gifu, Japan, is on to the task. The group recently published a study1 in the Journal of Pharmacological Sciences on how the use of aflibercept could have a positive effect in the treatment of non-exudative AMD in a paper entitled “Intravitreal aflibercept protects photoreceptors of mice against excessive light exposure.”
Their investigation stemmed from a 2015 study by some of the group’s team members that showed an anti-placental growth factor (PlGF) antibody protected the retina in a light-induced retinal damage model, which is commonly used as a model for dry age-related macular degeneration (or non-exudative AMD).2
To continue the first episode of their investigations in 2015, the team now looked at how aflibercept could inhibit both vascular endothelial growth factors (VEGF) and PlGF.
Currently, aflibercept is used to treat exudative (or wet; neovascular) AMD, as well as retinal vein occlusion (RVO) and diabetic macular edema (DME).
The team first set out to investigate if aflibercept could protect the function and structure of photoreceptors against light exposure in mice, as well as on PlGF-treated human retinal pigment epithelial cells (hRPE).
Using an animal study, carried out in line with ARVO Statement for the Use of Animals in Ophthalmic and Vision Research, the researchers conditioned non-anesthesized mice by exposing them to 24 hours of darkness in a room. Next, they were exposed to three hours of 8000 lx of white fluorescent light and subsequently placed back into darkness for another 24 hours before being returned to the regular daily light cycle.
The mice were injected in the left eye intravitreally with aflibercept, or VEGF, or an anti-VEGF antibody before the light exposure.
After 5 days of light exposure, a recording of the electroretinograms (ERGs) and its analysis were carried out. Subsequently, after anesthesizing and dilating the pupils of the mice, the left eyes of the mice underwent a flash ERG and readings were recorded. Their left eyes were then removed from them and placed into a solution containing 4% paraformaldehyde (PFA). They also measured the thickness of the outer nuclear layer (ONL) which was 240µm intervals from the optic disc to the periphery.
The next part of the test involved injecting hRPE cells which were previously incubated for 14 days and later stained for zonula occludens-1 (ZO1). This is in order to examine the tight junctions of the hRPE cells.
After being prepared, the eyes were then enucleated to evaluate the tight junction of the RPE cells in vivo. The team looked at the images photographed for three quadrants of the eye and manually traced the cell to cell junctions, pitting the thickness of the ONL against the distance from the optic nerve head.
What they found was an intravitreal injection of 20µg/eye of aflibercept before the light exposure significantly reduced the degree of the ONL’s thinning. However, the intravitreal injection of both the VEGF and the anti-VEGF antibody did not affect the thickness of the ONL.
When examining the tight junction protein of the RPE cells, they also discovered that the PlGF exposure caused a disruption of ZO1. However, aflibercept curbed the disruption of the RPE tight junctions caused by the PlGF.
Furthermore, they also found that VEGF receptor signalling may be tied to the disruption of the RPE. More studies will be done to investigate the links between these two, as reports indicate that perhaps a balance of VEGF within the retinal neurons and RPE is essential.
Overall, the team’s previous and present studies seem to suggest that aflibercept, which traps PlGF and has been used widely for the treatment of wet AMD, could also be considered for the treatment of dry AMD.
“Excellent clinical outcomes of anti-angiogenic agents in the treatment of retinovascular disease have been reproducibly demonstrated both in various clinical trials and clinical practice,” added Dr. Igor Kozak, clinical lead at Moorfields Eye Hospital Centre in Abu Dhabi, United Arab Emirates.
Vascular endothelial growth factor (VEGF)-A, VEGF-B, and PlGF are known to be elevated in these diseases, and their suppression leads to obvious, but perhaps not sustainable, clinical response.
Dr. Kozak says that while the ophthalmic community has been educated about molecules of VEGF family for years, PlGF came to doctors’ attention predominantly with the introduction of aflibercept to clinical use. The knowledge about the role of PlGF in retinal vasculopathies and especially diabetic retinopathy and diabetic macular edema has been exponentially growing.3-5
“The concept of blocking PlGF to preserve retinal microanatomy and electroretinography response is novel,” said Dr. Kozak. As demonstrated in the study of Kuse et al1, this was all achieved using aflibercept along with tightening cellular junctions of hRPE cells disrupted by PlGF.
“Apart from its primary role as antiangiogenic agent, aflibercept may have a secondary role as a potential neuroprotective agent. As such, this concept would be appealing not only to retinal exudative diseases but also to non-exudative diseases such as dry age-related macular degeneration,” concluded Dr. Kozak.
Editor’s Note: Dr. Kozak was generous enough to contribute on this story, but he was not a part of the mentioned study.
References:
1 Kuse Y, Takahashi K, Inoue Y, et al. Intravitreal aflibercept protects photoreceptors of mice against excessive light exposure. J Pharmacol Sci. 2018; S1347-8613(18)30130-0 [Epub ahead of print]
2 Izawa H, Inoue Y, Ohno Y, et al. Protective effects of antiplacental growth factor antibody against light-induced retinal damage in mice. Invest Ophthalmol Vis Sci. 2015;56(11):6914e6924.
3 Mesquita J, Castro-de-Sousa JP, Vaz-Pereira S, et al. Vascular endothelial growth factors and placentagrowth factor in retinal vasculopathies: Current research and future perspectives. Cytokine Growth Factor Rev. 2018;39:102-115.
4 Al Kahtani E, Xu Z, Al Rashead S, et al. Vitreous levels of placental growth factor correlate with activity of proliferative diabetic retinopathy and are not influenced by bevacizumab treatment. Eye (Lond). 2017;31(4):529-536. 5 Van Bergen T, Hu TT, Etienne I, et al. Neutralization of placental growth factor as a novel treatment option in diabetic retinopathy. Exp Eye Res 2017;165:136-150.
