Age-related macular degeneration (AMD) is a leading cause of vision loss in the West.
AMD is primarily characterized by the accumulation of lipid and protein droplets, known as lipofuscin, in the retina, leading to damage of cells and deterioration of central vision.
Currently, no effective treatment for AMD exists, and how healthy eyes prevent lipofuscin accumulation is not well-understood.
Discovery: Quantum Chemistry Reaction with Melanin
A collaborative research team from Yale University and the University of Tübingen in Germany has discovered that an uncommon quantum chemistry reaction involving melanin aids in the removal of lipofuscin.
This discovery could provide key insights for future AMD treatments.
“It’s beginning to look like melanin is nature’s solution to a variety of biology’s challenges,” said Douglas E. Brash, a professor at Yale and a co-author of the study.
The Eye’s Protective Mechanism
In the eye, specialized cells called photoreceptors convert light into signals that are sent to the brain.
The cells contain stacks of membranes filled with rhodopsin, the molecule responsible for capturing light and converting it to an electrical signal.
Once exposed to light, these discs undergo a recycling process, with undigested material becoming lipofuscin. As lipofuscin accumulates, it causes damage to retinal cells, leading to AMD.
The Role of Melanin
Previous research has shown that albino mice, which lack melanin, tend to accumulate lipofuscin earlier than other mice.
In the new study, the research team induced melanin synthesis in albino mice, which led to a reduction in lipofuscin accumulation.
The Quantum Chemistry Reaction
Brash, whose research focuses on how ultraviolet light leads to skin cancer, previously found that a quantum chemistry reaction occurring within melanin can cause DNA damage.
To determine if a similar reaction might facilitate lipofuscin removal, Brash identified compounds that could directly excite electrons.
“We know that melanin becomes less effective as we get older,” Brash said.
“So once the Schraermeyer lab had determined that melanin was required for photoreceptor disc turnover and essential for preventing lipofuscin buildup, we wanted to see if a chemiexcited drug might be a way to circumvent melanin while inducing its effects.”
Experiment: Testing the Compounds
The research team tested the compounds on retinal tissue from albino mice and observed a substantial reduction in lipofuscin within two days.
Implication: A New Potential Therapy
The subsequent chemistry by which the excited electrons reverse lipofuscin remains to be determined. However, Schraermeyer is optimistic about translating this discovery into clinical practice.
“For 30 years I was convinced that melanosomes—the organelles in cells that create melanin—degrade the lipofuscin but couldn’t identify a mechanism,” he said.
“Chemiexcitation is the missing link, and it should let us bypass the problem that AMD begins when the eye’s melanin declines with age. A drug that is chemiexcited directly may be a breakthrough for our patients.”
If you care about eye health, please read studies about one step closer to treatment for the most common blinding eye disease, and scientists find drug treatment for eye disease cataracts.
The study was published in PNAS.
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