Researchers at the University of California have identified a substance in the eye that promotes age-related macular degeneration – an increasingly prevalent disease among older adults.
A study by the University of California, published in the scientific journal Proceedings of the National Academy of Sciences (PNAS), opens the door to potential new therapies for dry age-related macular degeneration.
Macular degeneration is a silent and progressive eye disease that appears to be on the rise, especially among older adults (particularly those aged 75 and over). It gradually damages the central area of the retina, for reasons that are not yet fully understood.
People with early macular degeneration have varying degrees of difficulty reading, recognising faces and carrying out their day-to-day activities, like driving a car.
There are currently no effective cures for this disease, but a few types of treatment do exist for another form of macular degeneration that is less common (10-15% of cases) but more rapid and aggressive, called wet macular degeneration because it is caused by an abnormal increase in blood vessels.
But let’s get back to the dry form, which is undeniably more common. The California-based researchers focused on a substance called heparan sulfate, which is produced naturally by the body but which – and here’s what they discovered – also appears to play a key role in age-related macular degeneration.
How? Scientists have known for some time that a key feature of the disease is the build-up of pinhead-like “debris” called drusen, made up of lipids and proteins. Drusen form in the back of the eye between two layers – the retinal pigment epithelium and Bruch’s membrane. They impede the metabolism of the retina (which is located above these layers), speeding up the degeneration of photoreceptor cells. The presence of drusen gradually results in a dark spot in your field of vision, which may grow progressively larger.
The California-based researchers found that heparan sulfate acts as a powerful “molecular glue” on Bruch’s membrane, thus encouraging the build-up of lipid-containing fragments and the formation of drusen.
As noted by the researchers in the scientific journal PNAS, this substance is found in large amounts in the eyes of patients with dry age-related macular degeneration. But when heparan sulfate is absent or blocked, the fat particles no longer accumulate. Therefore, targeting this “sticky interaction” could be a way to prevent or even reverse the signs of macular degeneration before vision loss occurs, suggest the researchers.
But how can this be achieved? The US scientists tried using heparin, a substance with anticoagulant properties that is closely related – chemically speaking – to heparan sulfate, but with an entirely different structure and function. The similarity allows heparin to “mimic” the behaviour of heparan sulfate, by binding to the lipid-containing debris.
However, unlike heparan sulfate, heparin is then also able to “wash” this debris away, thus removing the drusen, at least in the laboratory. According to the researchers, we can therefore assume that substances like heparin can be used in the future to halt or slow down dry macular degeneration.
But more studies will be necessary. What’s more, modified forms of heparin will need to be used, say the scientists, without the strong anticoagulant effect of classic heparin, which could become dangerous (leading to bleeding) if used in the long term. In short, one challenge leads to another...