European Observatory for Nanomaterials

Nanotechnological methods in eye research have been gaining momentum. None have, as yet, been used for effective treatment of eye disease. More recently, work has considered two families of eye disease, both of which have ageing as a major risk factor. The first is cataract, an opacification of the eye lens, which is considered treatable, although surgery remains the only treatment modality. This is not without risk, is not readily available in the developing world and does not offer any non-surgical alternatives, which in most, if not all cases, is likely to be the preferred option by patients. The other, is the family of diseases of the retinal pigment epithelium and Bruch’s membrane, layers of the retina. Damage to these structures can lead to permanent sight loss and for which there is no current treatment.

Cataract is commonly referred to as a single disease, yet it has many causal factors all of which lead to the lens being incapable of transmitting light to the retina. Causal factors that have been identified include oxidation, glycation, phosphorylation, and deamidation of lens structural proteins, the crystallins as well as detrimental alterations in water channel proteins known as aquaporins [1]. Ultimately, these causal factors result in a change in the protein and water arrangements, essential for maintenance of transparency, resulting in light scatter and/or light absorption, both of which prevent light from reaching the retina (Figure 1).

Treating cataract

Cataract is essentially a disease of protein misfolding and as such is linked to diseases of similar origin such as diabetes and Alzheimer's disease [2,3] with certain cataracts being manifestations of these systemic conditions.

Cerium oxide possesses antioxidant and anti-glycation properties, rendering this compound a potential candidate for an effective non-surgical treatment for cataract, and it has been explored as a nanoparticle, or nanoceria for a variety of eye conditions [4]. However, nanoceria demonstrates poor stability in physiological media. This has been remedied by coating nanoceria in ethylene glycol producing particles of 2-5nm, with high colloidal stability and showing photoluminescence for several wavelengths [5]. These coated nanoparticles were tested on human lens epithelial cells, revealing no adverse changes in the cell morphology or growth rate, while demonstrating significant antioxidant effects. Further investigations showed that these coated nanoceria were able to mimic the actions of catalase: a major antioxidant enzyme [6].  Exposure of a major eye lens protein, a-crystallin, to these coated nanoparticles also yielded inhibition of glucose-induced protein glycation [6], indicating potential for treating not only cataracts caused by oxidative stress but also those caused by glycation, particularly those cataracts that are found in diabetics.

Exposed to concentrations of 400 µg/ml of nanoceria, human lens epithelial cells were able to grow and proliferate up to three days, followed by decreased viability and signs of apoptosis (cell death) [7] (Figure 2). This was the first study to show some indication of safe levels of nanoceria on human lens epithelial cells and requires further testing on whole lenses in vitro and ultimately in vivo.

Treating retinal disease

The retinal pigment epithelium is critical for protecting and maintaining the photoreceptors in the retina. In the human eye, the retinal pigment epithelium cannot regenerate, hence any damage to this cell layer can be seriously debilitating to sight. Conditions of the retinal pigment epithelium include those that are genetic, age-related (one of the most common being age-related macular degeneration), as well as secondary manifestations of systemic diseases. The retinal pigment epithelium is adjacent to Bruch’s membrane, which provides these cells with a supportive matrix. Damage to Bruch’s membrane can also lead to progression of age-related macular degeneration [8].

Thus far, no treatment exists for these sight-threatening conditions, although promising results have been shown for various cellular replacement therapies [9]. The main challenge for any cell transplantation is to identify an effective method that offers sustained cell function and viability without inducing an inflammatory response [10,11]. One proposed solution for this challenge could be the use of artificial scaffolds [12-14]. In this case, advances in electrospinning, a fabrication technique that can produce membranes of nanofibers, could potentially be used to recreate the supportive matrix structure of Bruch’s membrane [15]. 

A recent major advance in electrospinning has been made with the fabrication of nanoscaffolds incorporating polymers: polyacrylonitrile and a polyetheramine called jeffamine. These modifications increase mechanical strength and hydrophilicity of the scaffold as well as improve its structural capacity [16]. The scaffold was tested with a retinal pigment epithelial cell line (ARPE-19) comparing various growth factors, viability, and sustainability to growth of these cells on tissue culture plastic which served as a control [16]. The ARPE-19 cells manifested twice as much secretion of vascular endothelial growth factor on the nanoscaffold than on the control surface [16]. Further investigations comparing cell growth on scaffolds treated with an anti-inflammatory substance, fluocinolone acetonide, with growth on untreated scaffolds, showed that ARPE-19 cells were able to grow, proliferate and survive for up to 150 days on scaffolds treated with fluocinolone acetonide. These cells maintained their morphology as well as their epithelial phenotype and continue to express biomarkers needed for retention of their fundamental physiological features [16] (Figure 3).

This research shows tremendous promise as a substrate for the retinal pigment epithelium and as a potential replacement for Bruch’s membrane, leading to development of subretinal transplantation treatments that will successfully treat serious sight-threatening conditions.

 

References

1. Pierscionek BK. Anti-cataract therapies: is there a need for a new approach based on targeting of aquaporins. Expert Opinion on Therapeutic Targets 25, (2021) 1027-1031

2.Pollreisz A, Schmidt-Erfurth, U. Diabetic cataract – pathogenesis, epidemiology and treatment J. Ophthalmol. (2010) 1– 8

3. Goldstein LE, Muffat JA, Cherny RA, Moir RD, Ericsson MH, Huang X. et al. Cytosolic beta-amyloid deposition and supranuclear cataracts in lenses from people with Alzheimer’s disease. Lancet, 12, (2003) 1258-65

4. Cui W, Wang Y, Luo C, Xu J , Wang K. Han H,  Yao K. Nanoceria for ocular diseases: recent advances and future prospects. Materials Today Nano 18 (2022) 100218

5. Hanafy BI, Cave GWV, Barnett Y, Pierscionek B.  Ethylene glycol coated nanoceria protects against oxidative stress in human lens epithelium. RSC Advances 9 (2019) 16596-16605

6. Hanafy BI, Cave GWV, Barnett Y, Pierscionek BK. Nanoceria prevents glucose-induced protein glycation in eye lens cells. Nanomaterials 11, (2021) 1473

7. Hanafy BI, Cave GWV, Barnett Y, Pierscionek B. Treatment of human lens epithelium with high levels of nanoceria leads to Reactive Oxygen Species mediated apoptosis. Molecules 25 (2020) 441

8. Booij JC, Baas DC, Beisekeeva J, Gorgels TG, Bergen AA. The dynamic nature of Bruch's membrane Prog Retin Eye Res  29 (2010) 1-18.

9. Treharne AJ, Grossel MC, Lotery AJ, Thomson HA. The chemistry of retinal transplantation: the influence of polymer scaffold properties on retinal cell adhesion and control. Br J Ophthalmol. 95 (2011) 768-773.

10. Schwartz SD, Hubschman JP, Heilwell G, Cardenas VF, Pan CK, Ostrick RM, Mickunas E, Gay R, Klimanskaya I, Lanza R. Embryonic stem cell trials for macular degeneration: a preliminary report. Lancet. 379 (2012) 713-720.

11. Schwartz SD, Regillo CD, Lam BL, Eliott D, Rosenfeld PJ, Gregori NZ, Hubschman JP, Davis JL, Heilwell G, Spirn M, Maguire J, Gay R, Bateman J, Ostrick RM, Morris D, Vincent M, Anglade E, Del Priore LV, Lanza R. Human embryonic stem cell-derived retinal pigment epithelium in patients with age-related macular degeneration and Stargardt's macular dystrophy: follow-up of two open-label phase 1/2 studies. Lancet. 385 (2015) 509-516.

12. Gomes SR, Rodrigues G, Martins GG, Roberto MA, Mafra M, Henriques CMR, Silva JC. In vitro and in vivo evaluation of electrospun nanofibers of PCL, chitosan and gelatin: A comparative study. Mater Sci Eng C Mater Biol Appl. 46 (2015) 348-358.

13. White CE, Olabisi RM. Scaffolds for retinal pigment epithelial cell transplantation in age-related macular degeneration. J Tissue Eng. 21 (2017) 8:2041731417720841.

14. Stratakis E. Novel Biomaterials for Tissue Engineering. Int J Mol Sci 19 (2018) 3960.

15. Chen H, Fan X, Xia J, Chen P, Zhou X, Huang J, Yu J, Gu P.  Electrospun chitosan graft-poly (ɛ-caprolactone)/poly (ɛ-caprolactone) nanofibrous scaffolds for retinal tissue engineering. Int J Nanomedicine. 6 (2011) 453.

16. Egbowon BF, Fornari E, Pally JM, Hargreaves AJ, Stevens, McGinnity TM, Pierscionek BK. Retinal pigment epithelial cells can be cultured on fluocinolone acetonide treated nanofibrous scaffold. Materials and Design 232, (2023) 112152.

 

Biography of the author

Professor Barbara Krystyna Pierscionek graduated from Melbourne University in Australia with a PhD on Protein chemistry and Optics of the Eye Lens. She was awarded a prestigious NHMRC research fellow (MRC equivalent) shortly after graduating to start an independent research program on the optics of the eye.

Barbara continues this programme of research in areas of optics and biomechanics of the eye, ageing of the eye and eye disease, non-surgical anti-cataract modalities and nanotechnological applications to the eye. She was the first to investigate nanoceria as a potential anti-cataract treatment and to lead a team on novel nanoscaffolds for retinal implantation. Barbara has received support for her research from Research Councils (NHMRC, EPSRC, BBSRC), EU, Fight for Sight, Royal Society, and industry (Essilor International and Zeiss Meditec), as well as being awarded beam time grants for work in Japan at SPring-8 the world’s largest synchrotron.