Photosynthesis within the brain offers route to stroke recovery

02 Jun 2021

Huazhong University project applies near-IR to nanoparticles and algae for oxygen generation.

Strokes caused by blocked blood vessels in the brain result in 5 million deaths each year and leave many more people facing significant healthcare challenges.

Bioimaging is playing a significant role in understanding and assessing the effects of strokes, thanks to the ability of photonics-based methods to provide details of blood flow and cerebral dynamics.

Examples include the research underway at Spain's ICFO center and discussed at SPIE Photonics West in which a combination of near-IR spectroscopy and diffuse correlation spectroscopy can monitor the damaged blood flow in stroke patients, and potentially quantify the severity of the damage.

A project at China's Huazhong University of Science and Technology has now taken a different approach, and used a photonics technique to generate oxygen directly at the site of blocked blood vessels, as a means to assist clearance of the obstruction.

The research, published in Nano Letters, builds on previous investigations into the beneficial effect of supplying oxygen molecules to the site of damaged cardiac tissues and tumors, as encouragement to the healing operation and the rebalancing of a body's natural metabolic processes.

That work has included the use of blue-green algae as the oxygen source for heart attack patients, although one natural hurdle was the difficulty of arranging for visible light to reach the algae at the internal site so that photosynthesis can take place.

The Huazhing project tackled this issue by pairing an algae with nanoparticles and introducing the mixture to the site of a blocked cerebral blood vessel, before then triggering oxygen generation with deeper-penetrating near-IR irradiation.

Researchers used S. elongatus and paired it with neodymium nanoparticles able to convert near-IR excitation into visible emissions suitable for photosynthesis.

"Near-IR with excellent tissue penetrating capability is converted to visible light by upconveresion nanoparticles to activate S. elongatus generating oxygen in vivo," noted the project in its paper. "This acts in enhancing angiogenesis, reducing infarction, and facilitating repair of brain tissues, thus improving neuronal function recovery."

Novel approach to stroke treatment

Initial lab trials using the combined algae and nanoparticles confirmed that irradiation with near-IR light could indeed spur photosynthesis and oxygen generation. Studying the effect on neuron cultures showed that this nano-photosynthesis approach reduced the number of neurons that died after deliberate oxygen and glucose deprivation.

For in vivo tests, a mix of the algae and nanoparticles was injected into the cerebral cortex of mice at a depth of 1 millimeter. After the mix had been in place for differing time periods, blockages were created in the cerebral artery and the nano-photosynthesis effect initiated.

"The therapy reduced the number of dying neurons, improved the animals' motor function and even helped new blood vessels to start growing," commented the project team.

The next steps in the work will be for further animal testing and ultimately a move towards human clinical trials, where the project believes that a nano-photosynthesis approach could offer a valuable path to new stroke therapies.

"The combination of cell-biological, biochemical, and animal-level behavioral data provides compelling evidence that this oxygen-generating biosystem utilizing microorganism and nanotechnology represents a novel approach to stroke treatment," noted the team.