The Importance of the Blood-Brain Barrier for Brain Health. Dr. Domenico Pratico, MD, FCPP

Did you know that the brain is a very “thirsty” organ?

Approximately the brain's blood vessels span for about 400 miles, and every single nerve cell (there are about 80 billion) has its own capillary vessel!

Within this intricate system, the brain has developed a highly specialized structure that we call the Blood-Brain-Barrier (BBB).

The BBB is composed of a tightly locked layer of different cells (i.e., endothelial cells, pericytes, etc.) which form a highly selective semi-permeable membrane that separates the circulating blood from the brain tissue and cerebrospinal fluid.

The brain has 400 miles of vessels

What does the BBB do?

As the name suggests, it is a “barrier” that acts like a gatekeeper to the brain. In general, it’s a structure that keeps harmful things out and hold “good” things in. It also controls how various chemical molecules (including compounds we need such aa drugs or even make ourselves like hormones) enter and exit the brain.

The BBB has two main functions:

Protection:

Protects the brain from toxins, pathogens (bacteria and viruses), and other harmful substances.

Homeostasis:

Keeps a stable chemical environment in the brain, crucial for proper function.

The Blood Brain Barrier

What can get through the BBB?

In some cases, it depends on the size of the “particle”. Some things can get through the BBB if small enough such as oxygen and carbon dioxide. Others can get through because they are lipid soluble and can penetrate the cell membranes   By contrast, larger or water-soluble molecules cannot pass the BBB on their own. The only way for these compounds to get through is by using an active system of transportation (aka transporter or a channel) to help them across.

Here are some examples of drugs that can get through the BBB:

• Alcohol

• Anesthetics

• Anxiolytics (antianxiety medications).

• Sedative hypnotics (such as barbiturates, benzodiazepines and similar drugs).

What cannot pass through the BBB?

In general bacteria, viruses, and many toxic substances cannot get through the BBB. However, and unfortunately, the barrier can also block drugs designed to treat disorders of the brain. For this reason, we are exploring ways to temporarily and safely open the BBB to deliver medications to the brain for treating diseases.

What are some common conditions that affect the BBB?

Although normally the BBB is highly secure, in some cases it can be weakened and less effective, which will allow harmful substances to reach the brain. Various factors can disrupt the BBB integrity.

They can be divided into 2 groups: acute and chronic. Here are a few examples.

Acute conditions

• Brain infections (encephalitis and meningitis)

• Concussion and traumatic brain injury

• Stroke

Chronic conditions

• Alzheimer’s disease

• High blood pressure (hypertension)

• High blood sugar (hyperglycemia)

What are the common signs or symptoms of BBB disruption?

There are no specific symptoms to identify problems with the BBB. Some lab tests may be able to indirectly hint at BBB issues, especially tests on cerebrospinal fluid. Most conditions that involve BBB disruptions become apparent through symptoms of the condition itself. Recent studies have shown that using magnetic resonance imaging-guided focused ultrasound is possible to detect a BBB that is not working properly.

Are there any treatments that target the BBB?

There are no treatments that target directly the BBB. However, therapies that target conditions that damage the BBB indirectly can favor the recovery of a functional BBB. Some examples include medications for high blood pressure, or high blood sugar.

What can anyone do to take care of the health of the BBB?

The best approach is to avoid conditions that could lead to its disruption. Here is a list of some of them:

Eat a balanced diet and maintain a healthy weight. Conditions affecting cardiovascular health, especially stroke, can disrupt the BBB.

Treat infections promptly. Eye and ear infections can spread and cause inflammation that disrupts the BBB.

Wear protective gears. Head injuries can cause disruptions of BBB. Using safety equipment like helmets and seat belts is imperative.

Manage health conditions. Chronic conditions like type 2 diabetes, high blood pressure, high cholesterol can damage the BBB. Managing these conditions, with either medication or other treatments, is an important step in protecting the BBB.

In summary, having a healthy BBB is important to protect our brain from “insults” coming from outside and facilitate the “exit” of unwanted substances from the brain. Both activities will help tremendously in maintaining brain’s health and function to the fullest.

Remember, a healthy BBB is synonymous with a healthy brain!

If you are interested in reading more of my blogs:

Check out the recent blog: A Good Diet for the Brain  ~ Dr. Domenico Pratico', MD, FCPP

Dr. Domenico Pratico' , MD, FCPP

Domenico Praticò, MD, holds the Scott Richards North Star Charitable Foundation Chair for Alzheimer’s Research and serves as a Professor and Founding Director of the Alzheimer’s Center at Temple, as well as a Professor of Neural Sciences at Lewis Katz School of Medicine at Temple University.

For more information on the research conducted by Dr. Domenico Pratico, please visit this link.

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