Choroid Plexuses May Play a Role in Migraine

Jim Kling

August 24, 2020

Among migraine sufferers, levels of soluble vascular cell adhesion molecule 1 (sVCAM1) in cerebrospinal fluid (CSF) are higher in those who experience more frequent attacks, according to a new study. The molecule could be a novel biomarker for the study of the mechanisms that underlie migraine. The work also suggests that the barrier between blood and CSF, sometimes described as leaky, is in fact selectively permeable.

The findings complement recent PET and dynamic contrast-enhanced MRI studies that have shown no sign of damage to the blood brain barrier (BBB) in migraine. Instead, there may be heightened transport of some molecules from blood to the CSF, evidenced by greater increases in fibrinogen levels in CSF than albumin. sVCAM1 might influence BBB or blood-CSF barrier permeability, possibly as a protective measure against fibrinogen, according to Michael Harrington, MD, scientific director of neuroscience at the Huntington Medical Research Institutes, Pasadena, Calif., who presented the findings in a poster at the virtual annual meeting of the American Headache Society.

BBB Disruption?

The BBB is a well-known structure that regulates what molecules enter the brain, but the blood-CSF barrier, while lesser known, is also important. It comprises choroid plexus epithelial cells that oversee selective exchange of waste products, ions, and nutrients. Acute inflammation or chronic effects from conditions like stroke, multiple sclerosis, and Alzheimer's disease can alter the function of this barrier.

No other capillary biomarkers were different between controls and patients with migraine – only sVCAM1. "My data supports a highly selective transport change from blood to CSF, which I propose is less likely to come from brain capillaries than choroid plexuses, especially since choroid plexuses produce the bulk of the CSF. It's a work in progress, but based on this likelihood of choroid plexus involvement, I am accumulating more data that support the choroid plexuses as the primary source of change in migraine," said Dr. Harrington in an interview.

"The most important finding of the study is that the blood brain barrier is not compromised in people with migraine," said Rami Burstein, PhD, professor of neuroscience at Harvard Medical School, Boston, who was asked to comment on the findings. "Most unwanted adverse events are caused by drug action inside the brain, and thus, peripherally acting drugs become more favorable as they usually have fewer side effects. Given that the headache aspect of migraine could be intercepted outside the brain, the fact that the BBB is not compromised is a very good news," Dr. Burstein added.

Dr. Harrington's team recruited 74 subjects: 14 nonmigraine controls, 16 who were experiencing migraine illness (ictal), 27 not experiencing migraine illness (interictal), and 17 with chronic migraine. The CSF/serum quotient for albumen was higher in the 60 migraineurs than in the 14 controls (5.6 g/L vs. 4.1 g/L; P = .04), as was the CSF/serum quotient for fibrinogen (161.5 g/L vs. 86.1 g/L; P = .007). CSF levels of plasminogen were also higher in patients with migraine (240.7 ng/mL vs. 186.2 ng/mL; P = .03).

When the researchers compared ictal to interictal subjects, they found no difference in fibrinogen or albumen. That suggested that these values are generally increased in migraine patients compared with controls, rather than spiking during attacks. They also divided subjects by annual frequency, including groups experiencing fewer than 24 migraines per year, 24-180 attacks per year, and more than 180 attacks per year. The quotient for fibrinogen increased in migraineurs in general, compared with controls, but then decreased as the frequency of migraine went up (198.6 g/L, 167.0 g/L, and 121.6 g/L, respectively; P = .004).

CSF levels of sVCAM1 were 4.7 ng/mL in controls, 4.5 in the group with fewer than 24 migraines per year, 5.5 in the 24-180 group, and 7.1 in the group with more than 180 (P = .004).

Implications for Therapy

The research, though at a very early stage, could have implications for therapies. Most drugs that treat migraine remain something of a mystery because researchers don't know for sure where they act. In the brain? Systemically? The question of permeability of various molecules through both barriers could lend insight into what's happening. "That's why there is interest in barrier transport, and we're showing there is a selective change of transport in migraineurs," said Dr. Harrington.

As for more general therapeutic implications, "I can only speculate, but clearly there is baseline altered transport, probably in the choroid plexuses of these people," said Dr. Harrington. He added that in time researchers might test drugs to see if they alter sVCAM1 levels or even develop novel drug candidates to act directly on it.

But he also sounded a note of caution because of the exploratory nature of the study. "These are all really early speculations."

The study was funded by NIH, the Sunstar Foundation, Wyngs Foundation, and the Higgins Family. Dr. Harrington has no relevant disclosures.

SOURCE: Harrington M et al. AHS 2020, Abstract 842752.

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