Blood-brain Barrier Model May Have Parkinson’s Application

A new human-derived model of the blood-brain barrier (BBB) — a highly selective and protective membrane whose dysfunction is linked to Parkinson’s disease — enables researchers to monitor in detail cellular events upon stress, inflammation, and therapy administration, a study shows.

This model allowed the assessment of the protective effects of the antioxidant molecule N-acetylcysteine amide (NACA) against nitrosative stress-induced inflammation thought to contribute to Parkinson’s and other neurodegenerative conditions.

The study also showed that BBB breakdown under high levels of inflammation is “actually more complex than we thought,” Thomas Winkler, PhD, said in a press release. Winkler, of the KTH Royal Institute of Technology, in Sweden, is the study’s co-senior author.

The findings suggest that this human-derived “BBB-on-chip” tool may be used to create patient-derived models to better understand the role of BBB leakage in neurologic disorders, as well as to test “different antioxidants — and see if we find anything that has even higher neural protection,” Winkler said.

The study, “Continuous Monitoring Reveals Protective Effects of N-Acetylcysteine Amide on an Isogenic Microphysiological Model of the Neurovascular Unit,” was published in the journal Small.

The BBB is a complex three-dimensional structure composed mainly of tightly packed endothelial cells (those lining the inside of blood vessels) that prevent large molecules, viruses, and bacteria in the blood from reaching the brain and spinal cord.

This protective role also prevents the entry of larger therapeutic molecules, becoming an obstacle for therapies targeting the brain and spinal cord.

Notably, increasing evidence suggests that BBB dysfunction and breakdown contributes to several neurodegenerative diseases, including Parkinson’s, as it allows access to toxic molecules, cells, and microbes in circulation.

However, studies of the BBB in living organisms “are often complex and unreliable (or even impossible, at least in humans) due to the difficulty in accessing the BBB without impairing its function,” the researchers wrote.

In the past couple of years, scientists have been working on the development of human-derived BBB-on-chip that better mimics the cellular structure and flow dynamics of the BBB.

Now, Winkler and his team, along with colleagues at the Karolinska Institute, also in Sweden, developed an improved model that allows monitoring of cellular events at the BBB with an unprecedented temporal resolution (less than two minutes).

The new BBB-on-chip model is composed of blood vessel cells and brain cells generated from inducible pluripotent stem cells (iPSCs) derived from a single donor. iPSCs are generated from fully matured cells, such as those in the skin or blood, that are reprogrammed back to a stem cell-like state, where they can give rise to almost every type of human cell.

These blood vessel cells, along with key structural and binding proteins, form a barrier that separates two compartments simulating the external vascular system and the brain’s perivascular space, where a type of brain cells called astrocytes reside. The perivascular space is the fluid-filled area between the BBB blood vessels and the brain.

The researchers then evaluated the effects of administering linsidomine, a molecule known to promote nitrosative stress, on BBB integrity and astrocyte survival, and whether the antioxidant NACA could prevent nitrosative stress-induced damage.

Nitrosative stress, along with oxidative stress, refers to cellular damage associated with an imbalance between the levels of reactive molecules and cells’ production of antioxidants to neutralize them. Both cellular stresses are thought to contribute to Parkinson’s-associated neuroinflammation and neurodegeneration.

NACA is a BBB-penetrant molecule with antioxidant and anti-inflamatory activity through the regulation of these cellular stress-associated reactive molecules.

Results showed that addition of linsidomine to the perivascular space in the BBB-on-chip model promoted nitrosative stress, resulted in widespread astrocyte death, and disrupted the BBB in about 50% of cases.

In turn, administration of NACA to the external vascular space before linsidomine exposure reduced astrocyte death and completely prevented barrier breakdown.

The study “revealed for the first time the effects of direct [nitrosative stress] application on the BBB, as well as the effects of NACA prophylaxis [preventive treatment], in a microphysiological system,” the researchers wrote.

Isabelle Matthiesen, the study’s first author and a PhD student at KTH, said  the study is not meant to provide definitive proof of how antioxidant and anti-inflammatories affect the brain. But it suggests this BBB model could replace testing brain-targeted medications on animal models before clinical trials.

“We successfully based the barrier on human stem cell-derived cells so this model is relevant to [therapies] being testing for humans, while other models are made with animal cells or are too simple to monitor closely,” Matthiesen said.

Winkler noted that the temporal minute-by-minute detail achieved with this model is important because many cellular processes happen quickly.

“When you first administer a [therapy], it causes a huge change in cells, then levels out,” Winkler said, adding that “in the typical methods of testing [therapies], you wouldn’t see those rapid changes.”

“We can now see that the breakdown of the blood brain barrier happens fast under stress and we could see how that could be prevented with the antioxidant,” Winkler concluded.