Spinach-derived eye drops harness ambient light to treat dry eye syndrome

Plants depend on sunlight and photosynthesis to survive — and now scientists have adapted the same process for the human eye, potentially opening up new treatment options for dry eye syndrome, a condition that affects more than one billion people worldwide.

Led by a team from the National University of Singapore (NUS), the researchers extracted photosynthetic membrane stacks from spinach leaves and applied them via eye drops to laboratory-grown human eye cells and to the eye cells of mice engineered to have a condition similar to dry eye disease.

The transplant proved effective. When exposed to ambient light, the nanoparticles introduced to mammalian eye cells began producing NADPH — a chemical "battery" that cells use to protect against harmful damage.

NADPH is essential for countering reactive oxygen species (ROS), which drive inflammation and cellular stress in dry eye disease.

LEAF technology explained

The researchers have named their new technology LEAF: light-reaction enriched thylakoid NADPH-foundry. Thylakoids are the key NADPH-generating components of chloroplasts — the structures responsible for carrying out photosynthesis in plant cells.

Spinach was selected for the study due to its high chloroplast yield and the relative ease of extracting its biological machinery, as well as the practical advantage of being both inexpensive and widely available.

Within 30 minutes of light exposure, the researchers demonstrated that NADPH generated by the process reduced ROS activity and returned immune cells in the cornea to a protective, anti-inflammatory state.

"This is an exciting finding as we have, for the first time, demonstrated that plant photosynthetic machinery can be transplanted into mammalian tissue to generate biologically useful molecules, powered entirely by the same light that enables our vision," said biomolecular engineer Xing Kuoran from NUS. "We, too, can have limited photosynthetic abilities."

Effective in tear samples and outperforming existing treatments

The treatment also proved effective in tear samples taken from patients with dry eye disease. In people with the condition, tear fluid itself can become damaging.

LEAF treatment reduced levels of harmful oxidants, cutting hydrogen peroxide by 95 per cent. The restorative effects were observed both inside and outside eye cells.

"With LEAF, we now have a technology that harnesses ambient light to directly restore the molecule that dry eye disease depletes," said biomolecular engineer David Leong Tai Wei from NUS.

"As it is derived from spinach, delivered as a simple eye drop, requires no external device or power source and uses the ambient light that is used for vision, we believe it has a strong potential for clinical translation."

In mice treated twice daily over five days, the LEAF treatment outperformed Restasis — a medication commonly prescribed for dry eye disease that is relatively expensive and can cause side effects, including increased eye irritation.

Clinical trials on the horizon

Whilst the research remains at an early stage, preparations for clinical trials are already under way. The team also intends to examine how the treatment performs over longer periods, as the LEAF particles currently degrade within the eye cells after a few hours, losing effectiveness.

The researchers also see potential applications beyond dry eye disease, suggesting the same approach could be applied to other inflammatory conditions — wherever defence against ROS is required and the relevant tissue can be exposed to visible light.

"It is almost surreal when thinking of a possible future reality where human cells can have some limited but beneficial form of photosynthetic ability not only in the eye but elsewhere, too," said Leong.

The research has been published in the journal Cell.