Spinach is said to be rich in vitamin A and good for preventing aging of the eyes. Now a path has opened for spinach to go directly into the eye and even treat ophthalmic diseases. The idea is to put spinach chloroplasts into the human eye to block disease-causing substances through the principles of photosynthesis.
A team led by David Tai Wei Leong of the National University of Singapore's Department of Chemical and Biomolecular Engineering said on the 15th (local time) in the international journal Cell that it "successfully treated dry eye disease by injecting chloroplast components from spinach into animals' corneal cells and harvesting light energy."
◇ Chloroplasts suppress reactive oxygen species that damage cells
Dry eye disease is an ophthalmic condition in which a lack of tears or rapid evaporation causes inflammation in the corneal black part and the conjunctiva of the sclera. In medical terms, it is called keratoconjunctivitis sicca. When the eye becomes inflamed, reactive oxygen species harmful to cells are produced. Healthy eyes produce antioxidants with NADPH (nicotinamide adenine dinucleotide phosphate) to neutralize reactive oxygen species, but eyes with dry eye disease cannot do so.
The researchers focused on the fact that NADPH is synthesized when plant leaves photosynthesize. If the human eye also photosynthesizes like a plant, it could be seen as treating inflammation on its own. To verify this, they extracted thylakoids that synthesize NADPH from commercially available spinach. Thylakoids are coin-shaped structures inside chloroplasts, and their stacked formations are called grana.
Thylakoids receive light and split water to produce ATP (adenosine triphosphate), an energy molecule, and NADPH, which carries hydrogen and electrons. This is the light reaction. In the next step, the dark reaction, chloroplasts use the two substances synthesized in the light reaction to convert carbon dioxide into glucose. The researchers decided to insert only the part that performs the light reaction into the eye. They extracted thylakoids from spinach and made them into nanoparticles 400 nm (nanometers, one-billionth of a meter) in size.
The researchers administered the particles into the eyes of mice with induced dry eye, like eyedrops. Chloroplasts are green, but the nanoparticles were transparent because they were so small. In the experiment, mice that received only saline in their eyes had corneal thickness reduced by 30%, but mice given the chloroplast components showed increased tear secretion and recovery of corneal thickness within five days of treatment. The team said the effect was better than existing treatments. No side effects appeared over two months.
The same effect was seen in human corneal cells. Within 30 minutes, NADPH levels returned to normal, and reactive oxygen species were suppressed. When thylakoid nanoparticles were added to tears collected from patients with dry eye disease, NADPH levels increased 20-fold, and hydrogen peroxide, which damages cells, fell by more than 95%.
◇ Economic impact in the trillions of won, low production cost
More than 1.5 billion people worldwide suffer from dry eye disease. Beyond discomfort and poor vision, it can lead to depression and anxiety. As a result, medical costs are high and work productivity drops, causing serious economic losses. In the United States alone, the economic burden is estimated to reach $3.84 billion (5.76 trillion won) annually. If a treatment that induces photosynthesis in the eye is commercialized, the economic impact is expected to be enormous.
The researchers said they are also preparing clinical trials in actual patients. Leong said, "We directly restored molecules depleted by dry eye disease using the principles of plant photosynthesis," and noted, "Because the spinach-derived material is administered like eyedrops and uses ordinary lighting, the potential for application in patient treatment is very high." Moreover, chloroplast-component therapeutics are inexpensive to produce. The team said that 300 won worth of a handful of spinach could make enough nanoparticles to administer to more than 50 people twice a day for a month.
It is not impossible for animals to photosynthesize. The sea slug Elysia chlorotica can live for months on photosynthesis alone without eating, thanks to absorbing chloroplasts from photosynthetic microalgae. A University of Tokyo team in 2024 transplanted plant chloroplasts into human cells and ran them for two days. There have also been cases of therapeutic effects using the same approach. In 2022, a Zhejiang University School of Medicine team in China reported in Nature that injecting particles containing chloroplast components into the knee joints of mice with arthritis slowed cartilage destruction.
However, before using it in real patients, the therapeutic mechanism needs to be clarified further. Mary Ann Stepp of George Washington University School of Medicine said in the journal Science that "the confirmed efficacy this time could be seen as a result of promoting energy production rather than suppressing inflammation."
Plants also produce ATP, an energy molecule, through photosynthesis. Scientists think ATP may have helped treat dry eye disease. When dry eye disease develops, neurons that help energy production in corneal cells die. The thylakoids of chloroplasts produce ATP and could compensate for this.
References
Cell (2026), DOI: https://doi.org/10.1016/j.cell.2026.04.034
Proceedings of the Japan Academy, Series B (2024), DOI: https://doi.org/10.2183/pjab.100.035
Nature (2022), DOI: https://doi.org/10.1038/s41586-022-05499-y