Repairing damaged eye tissue in AMD: steps towards the Holy Grail^!

Queensland Eye Institute (QEI) researchers recently released a journal article entitled ‘A Bruch’s membrane substitute fabricated from silk fibroin supports the function of retinal pigment epithelial cells in vitro’^.

Although the title may be confusing to the non-scientific reader, the implications of this research demonstrate the world-class nature of the scientific work being undertaken at the Queensland Eye Institute. Vision loss and blindness often result from damaged cells within the eye. All of the research being undertaken at the Queensland Eye Institute is aimed at understanding how this damage occurs and finding ways to either prevent or repair it.

To fully understand the impact of the research, statistics relating to vision loss highlight the immense nature of the problem.  In 2011-2012 nearly 12 million Australians reported having a long-term eye condition#.  In 2010, 90 million people in the Western Pacific Region were visually impaired, including more than 10 million blind*.  

Understanding the underlying causes of vision loss and developing effective treatment programs capable of reversing injury and disease is vital to the community.

The Shadforth et al (2015) article addresses the decline of vision that occurs with age-related macular degeneration (AMD).  AMD is a major cause of blindness in people over 40 and is a devastating condition where patients gradually lose their vision. This insidious disease occurs at a time in most people’s lives when they are reaching the prime of life and starting to enjoy some of the fruits of their labours as families grow and financial pressures finally (in many cases) start to ease.  Suddenly faced with this chronic condition, the emotional and financial costs can be overwhelming.

One of the key components of AMD is the destruction of a membrane (Bruch’s membrane) within the eye.  This membrane is an important structure within the outer retina (at the back of the eye) that allows vital molecules to permeate across it, maintaining a carefully controlled internal environment essential for normal eye health.

Researchers at the Queensland Eye Institute are highly skilled in biomaterials and tissue engineering and have been examining the viability of transplanting cells of the RPE back into the eye, thus protecting photoreceptors and slowing down the progression of AMD.  To achieve this, researchers used silk proteins as a matrix to grow the cells.  Silk is already used in many surgical procedures (just think internal sutures) and is well tolerated within the body. Over time, it became clear that the silk proteins themselves could, with some tweaking, not only be used for transplanting cells but become a perfect substitute for replacing the underlying Bruch’s membrane, effectively reconstructing the major area of damage in the eye.

This paper follows the scientists’ journey as they ensure that the damaged cells grow as effectively on the silk proteins as they do on cell culture plate materials (the material used to culture cells in the laboratory). For this approach to be a success, the silk matrix has to emulate the permeability of the Bruch’s membrane and be able to provide a solid growth environment for the cells so that the transplanted RPE cells behave in the same way as cells in the normal eye.

The results: Yes – RPE cells grown on the silk matrix mimicked the activity of cells grown on traditional material!

This supports the group’s previous findings and paves the way to develop the properties of the silk membrane to ensure that mechanical conditions of the transplanted material (such as permeability, pliability and resilience) are as close to the natural environment of the eye as possible.  Once this has been achieved, the next step is clinical trials and (hopefully) a reduction in the suffering of many thousands of people worldwide.

Although this is very exciting research, there is still a long way to go.  Researchers are currently working on increasing the mechanical strength of the membranes to ensure they are strong enough for surgical handling. However, once successful the procedure is promising, not only for AMD but, potentially, for many other diseases.  With diabetic retinopathy on the increase and an estimated 1.7 million people in Australia predicted to be affected by AMD by 2030@ , this research could substantially assist the health and wellbeing of our nation.

^JOURNAL OF TISSUE ENGINEERING AND REGENERATIVE MEDICINE
J Tissue Eng Regen Med (2015).
Published online in Wiley Online Library (wileyonlinelibrary.com) DOI: 10.1002/term.2089
#http://www.aihw.gov.au/eye-health/
*http://www.wpro.who.int/entity/blindness_prevention/info/towards_universal_eye_health_.pdf
@ http://www.mdfoundation.com.au/resources/1/facts-figures_2012.pdf