Shining a light on the hidden damage of mild brain injury

Researchers have created a new brain imaging method that can diagnose mild traumatic brain injuries (mTBI) even when existing imaging techniques like magnetic resonance imaging (MRI) show no structural abnormalities. The technique involves loading gadolinium, a standard contrast agent for MRI, into hydrogel-based micropatches attached to immune cells called macrophages.

mTBIs cause inflammation in the brain, which produces signals that attract macrophages to migrate there. Coupling the contrast agent gadolinium to these cells allows MRI to reveal brain inflammation and increase the number of correctly diagnosed TBI cases, thereby improving patient care. The method is described in a new article in Scientific translational medicine.

“Seventy to ninety percent of reported TBI cases are classified as ‘mild,’ but up to ninety percent of TBI cases go undiagnosed, even though their effects may last years and are known to increase the risk of a multitude of neurological disorders. including depression, dementia and Parkinson’s disease,” said lead author Samir Mitragotri, Ph.D., in whose laboratory the research was carried out. “Our cellular imaging approach exploits the innate ability of immune cells to travel throughout the brain in response to inflammation, allowing us to identify TBIs that would not be missed by standard MRI imaging.”

Mitragotri is a faculty member at the Wyss Institute at Harvard University and the Hiller Professor of Bioengineering and Hansjörg Wyss Professor of Biologically Inspired Engineering at Harvard’s John A. Paulson School of Engineering and Applied Sciences (SEAS).

Using immune cells to identify inflammation

Most of us know someone who has suffered a concussion (another name for head trauma), sometimes even several. But the vast majority of people who suffer a head injury are never properly diagnosed. Without this diagnosis, they may worsen their injuries by returning to normal activities before they are fully recovered, which can lead to further harm. Some studies even suggest that repeated head trauma can lead to chronic traumatic encephalopathy (CTE), a neurodegenerative disease that affects more than 90% of professional American football players.

Because the effects of mTBI are thought to be caused by “invisible” brain inflammation, members of the Mitragotri lab decided to leverage their experience with immune cells to create a better diagnosis.

“Our previous projects have focused on controlling the behavior of immune cells or using them to deliver drugs to a specific tissue. We wanted to exploit another innate ability of immune cells – homing in on sites of inflammation in the body – to transport imaging agents into the brain, where they can provide a visible detection signal for mTBI,” said first author Lily Li-Wen Wang, Ph.D.. Wang is a former researcher at the Mitragotri laboratory of the Wyss Institute and SEAS who is now a scientist at the Historical Biography.

The team planned to use its cellular backpack technology to attach gadolinium molecules to macrophages, a type of white blood cell known to infiltrate the brain in response to inflammation. But right away, they ran into a problem: To work as a contrast agent for MRI scans, gadolinium must interact with water.

The original microparticles in their backpack are compost from a polymer called PLGA, which is hydrophobic (meaning it repels water). So Wang and his co-authors began developing a new backpack made from a hydrogel material that could be manufactured on a large scale in the lab.

After years of hard work, they finally created a new hydrogel backpack that could produce a powerful gadolinium-mediated MRI signal, stably attach to mouse and pig macrophages, and maintain their charge for a prolonged period in vitro. They named their new microparticles M-GLAM, short for “Hitchhiking Gd(III)-Loaded Anisotropic Micropatches for Macrophages.” Now it was time to test them in a more realistic setting, for which they teamed up with researchers and clinicians at Boston Children’s Hospital.

First, they injected mouse M-GLAM macrophages into mice to see if they could visualize them in vivo. They were particularly interested to see if they accumulated in the kidneys, because existing gadolinium-based contrast agents like Gadavist can pose health risks to patients with kidney disease.

Their M-GLAMs did not accumulate in the mice’s kidneys, but persisted in their bodies for more than 24 hours without negative side effects. In contrast, mice injected with Gadavist showed substantial accumulation of the contrast agent in their kidneys within 15 minutes of injection, and the substance was completely eliminated from their bodies within 24 hours.

Next, the team tested porcine M-GLAMs in a porcine model of mTBI. They injected the M-GLAMs into the animals’ bloodstream two days after a sham TBI, then used MRI to assess the concentration of gadolinium in the brain. They focused on a small region called the choroid plexus, known as a major conduit for immune cells to the brain.

Pigs injected with M-GLAM showed a significant increase in the intensity of gadolinium present in the choroid plexus, unlike those injected with Gadavist, despite confirmation of an increased density of inflammatory macrophages in the brains of pigs. two groups. The animals showed no toxicity in any of their major organs after treatment administration.

“Another important aspect of our M-GLAMs is that we are able to achieve better imaging with a much lower gadolinium dose than current contrast agents – 500 to 1,000 times lower in the case of Gadavist,” he said. Wang said. “This could enable the use of MRI in patients who currently cannot tolerate existing contrast agents, including those with kidney problems.”

The authors note that although M-GLAM can indicate the presence of inflammation in the brain via the high concentration of macrophages entering it through the choroid plexus, their technique cannot identify the exact location of injury or responses. inflammatory in brain tissue. However, if combined with new treatment modalities like those developed in another recent paper, M-GLAMS could offer a faster and more effective way to identify and reduce inflammation in TBI patients to to minimize damage and speed up recovery.

The researchers have filed a patent application for their technology and hope to be able to commercialize it in the near future. They are currently exploring collaborations with biotechnology and pharmaceutical companies to accelerate clinical trials.

“This work demonstrates how much potential the human body has to unlock for various functions: monitoring health, diagnosing problems, treating diseases and preventing their recurrence. I am impressed by the ingenuity of this team in exploiting immune cells to improve medical imaging and we hope to see it in the hands of clinicians soon,” said Wyss founding director Donald Ingber, MD, Ph.D. Ingber is also the Judah Folkman Professor of Vascular Biology at Harvard Medical School and at Boston Children’s Hospital, and Hansjörg Wyss Professor of Bioinspired Engineering at SEAS.