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A new eye drop enabled photosynthesis to occur in a mouse’s eye.(Image credit: Ralf Bessoth / 500px via Getty Images)Share this article 0Join the conversationFollow usAdd us as a preferred source on GoogleSubscribe to our newsletter
Researchers have created novel eye drops that permit mouse eyes to carry out specific stages of photosynthesis.
The drops, containing photosynthetic components derived from spinach leaves, utilize light-dependent processes to alleviate symptoms associated with dry eye disease, as detailed in a study published on May 15 in the journal Cell. While these drops were administered to mice, the aspiration is that following further investigation, this therapeutic approach might eventually be applicable to humans.
This research represents a “clever utilization” of engineering principles inspired by natural symbiotic interactions, commented Corey Allard, a cell biologist at Harvard Medical School who was not involved in the study.
Plants depend on photosynthesis to generate energy, in the form of glucose, from solar radiation. Photosynthesis takes place within organelles known as chloroplasts, which impart their characteristic green hue to plants. Although no animals naturally photosynthesize independently, certain species have established symbiotic connections with photosynthetic algae, enabling them to harness solar energy. Some sea slug varieties, such as the leaf sheep (Costasiella kuroshimae) and the mangrove leaf slug (Elysia bangtawaensis), even incorporate chloroplasts from the algae they consume.
In the current research, David Tai Leong, a chemical engineer affiliated with the National University of Singapore, along with his associates, explored the potential for mammalian eyes to accommodate similar biological functions. Their objective was to identify a method for treating dry eye disease, a condition affecting the eye’s tear film, which leads to the production of oxidants and inflammation that can compromise vision.
To formulate the eye drops, the team initially isolated stacked structures called thylakoid grana from spinach chloroplasts. Thylakoid grana are the chlorophyll-containing components within chloroplasts where the initial, light-dependent phases of photosynthesis occur. Subsequently, the team encased these thylakoid stacks within minuscule vesicles, creating a system they termed “light-reaction enriched thylakoid NADPH-foundry,” or LEAF.
When integrated into eye drops, LEAF demonstrated a reduction in ocular inflammation in mice experimentally induced with dry eye disease. During the pathway to glucose synthesis, chloroplasts generate a compound named NADPH within the thylakoid grana. NADPH functions as an antioxidant, and in this context, it aided in neutralizing compounds that were intensifying the eye inflammation in the mice.
Following a five-day treatment period, the mice that received the LEAF eye drops exhibited outcomes comparable to those treated with an established, commercially available medication for dry eye disease. They displayed improved tear production and diminished corneal damage when contrasted with mice that were administered only saline eye drops.
“The eye is exceptionally well-suited for this kind of strategy, as light is an inherent element of its normal physiological operation,” stated Dr. Xianfeng Lin, an orthopedic surgeon at Zhejiang University School of Medicine in China, via email to Live Science. While Lin was not involved in this latest investigation, he and his colleagues published a 2022 study in the journal Nature that employed a comparable photosynthetic system to mitigate inflammation associated with arthritis in mouse knees.
“This work expands the functional role of light in the eye from solely sensory perception to potentially contributing to local metabolic support and tissue regeneration,” Lin added.
Despite the presence of chlorophyll in the eye drops, their concentration is exceedingly low, rendering the drops transparent.
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“We are able to leverage a highly refined photosynthetic apparatus, thus negating the need for substantial quantities of the LEAF system,” Leong explained. “Due to its minimal concentration, the green hue is imperceptible, so we won’t end up with emerald-colored eyes like the Incredible Hulk.”
The eye drops are not yet ready for human application; they require comprehensive testing to ensure safety and long-term effectiveness. Nevertheless, the team is actively planning the establishment of a clinical trial that will initially focus on safety assessments, Leong informed Live Science.
Should human approval be granted, the medication would harness the inherent workings of our eyes, requiring only ambient light for activation. A patient would then be “receiving a therapy that is in harmony with our daily routines,” Leong concluded.
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