Posts tagged blood brain barrier

In a remarkable series of experiments on a fungus that causes cryptococcal meningitis, a deadly infection of the membranes that cover the spinal cord and brain, investigators at UC Davis have isolated a protein that appears to be responsible for the fungus’ ability to cross from the bloodstream into the brain.

The discovery — published online June 3 in mBio, the open-access, peer-reviewed journal of the American Society for Microbiology — has important implications for developing a more effective treatment for Cryptococcus neoformans, the cause of the condition, and other brain infections, as well as for brain cancers that are difficult to treat with conventional medications. 

“This study fills a significant gap in our understanding of how C. neoformans crosses the blood-brain barrier and causes meningitis,” said Angie Gelli, associate professor of pharmacology at UC Davis and principal investigator of the study. “It is our hope that our findings will lead to improved treatment for this fungal disease as well as other diseases of the central nervous system.”

Normally the brain is protected from bacterial, viral and fungal pathogens in the bloodstream by a tightly packed layer of endothelial cells lining capillaries within the central nervous system — the so-called blood-brain barrier. Relatively few organisms — and drugs that could fight brain infections or cancers — can breach this protective barrier.

The fungus studied in this research causes cryptococcal meningoencephalitis, a usually fatal brain infection that annually affects some 1 million people worldwide, most often those with an impaired immune system. People typically first develop an infection in the lungs after inhalation of the fungal spores of C. neoformans in soil or pigeon droppings. The pathogen then spreads to the brain and other organs.

Unique protein identified

In an effort to discover how C. neoformans breaches the blood-brain barrier, the investigators isolated candidate proteins from the cryptococcal cell surface. One was a previously uncharacterized metalloprotease that they named Mpr1. (A protease is an enzyme — a specialized protein — that promotes a chemical reaction; a metalloprotease contains a metal ion — in this case zinc — that is essential for its activity.) The M36 class of metalloproteases to which Mpr1 belongs is unique to fungi and does not occur in mammalian cells.

The investigators next artificially generated a strain of C. neoformans that lacked Mpr1 on the cell surface. Unlike the normal wild-type C. neoformans, the strain without Mpr1 could not cross an artificial model of the human blood-brain barrier.

They next took a strain of common baking yeast — Saccharomyces cerevisiae — that does not cross the blood-brain barrier and does not normally express Mpr1, and modified it to express Mpr1 on its cell surface. This strain then gained the ability to cross the blood-brain barrier model.

Investigators then infected mice with either the C. neoformans that lacked Mpr1 or the wild-type strain by injecting the organisms into their bloodstream. Comparing the brain pathology of mice 48 hours later, they found numerous cryptococci-filled cysts throughout the brain tissue of mice infected with the wild-type strain; these lesions were undetectable in those infected with the strain lacking Mpr1. In another experiment, after 37 days of being infected by the inhalation route, 85 percent of the mice exposed to the wild-type C. neoformans had died, while all of those given the fungus without Mpr1 were alive.

“Our studies are the first clear demonstration of a specific role for a fungal protease in invading the central nervous system,” said Gelli. “The details of exactly how it crosses is an important new area under investigation.”

New targeted therapies possible

According to Gelli, their discovery has significant therapeutic potential via two important mechanisms. Either Mpr1 — or an aspect of the mechanism by which it crosses the blood-brain barrier — could be a target of new drugs for treating meningitis caused by C. neoformans. In a person who develops cryptococcal lung infection, such a treatment would ideally make the fungus less likely to enter the brain and lead to a rapidly fatal meningitis.

Secondly, Mpr1 could be developed as part of a drug-delivery vehicle for brain infections and cancers. An antibiotic or cancer-fighting drug that is unable to cross the blood-brain barrier on its own could be attached to a nanoparticle containing Mpr1, allowing it to hitch a ride and deliver its goods to where it is needed.

“The biggest obstacle to treating many brain cancers and infections is getting good drugs through the blood-brain barrier,” said Gelli. “If we could design an effective delivery system into the brain, the impact would be enormous for treating some of these terrible diseases.”

Gelli’s group is currently pursuing such a nanoparticle drug-delivery system using Mpr1. They are also further investigating the exact molecular mechanism by which Mpr1 breaches the blood-brain barrier.

(Source: ucdmc.ucdavis.edu)

Until now, scientists have not known exactly how inflammation weakens the Blood-Brain Barrier, allowing toxins and other molecules access to the brain. A new research report appearing in the June 2014 issue of The FASEB Journal solves this mystery by showing that a molecule, called “microRNA-155,” is responsible for cleaving epithelial cells to create microscopic gaps that let material through. Not only does this discovery help explain the molecular underpinnings of diseases like multiple sclerosis, but it also opens an entirely new avenue for developing therapies that can help penetrate the Blood-Brain Barrier to deliver lifesaving drugs.

According to Ignacio A, Romero, Ph.D., “We are beginning to understand the mechanisms by which the barrier between the blood and the brain becomes leaky in inflammatory conditions. Based on these and other findings, drugs that reduce the leakiness of the barrier have the potential to improve symptoms in many neurological conditions.” Romero is one of the researchers involved in the work from the Department of Life, Health and Chemical Sciences of the Biomedical Research Network at The Open University in the United Kingdom.

To make this discovery, Romero and colleagues first measured microRNA-155 (miR-155) levels in cultured human cells and compared them to cells under inflammatory conditions. Researchers then measured levels in the blood vessels of inflamed brain areas of patients with multiple sclerosis (MS) and compared them to non-inflamed areas. In both cases, miR-155 was elevated in inflammation. Then, in mice, normal mice were compared with mice that were genetically altered to lose miR-155. When an inflammatory reaction was induced in these two groups of mice, the mice that could not express miR-155 had a much reduced increase in “leakiness” of the Blood-Brain Barrier than normal mice. Finally, scientists investigated in cultured human cells the mechanism by which miR-155 levels cause leakiness of the barrier and concluded that miR-155 affects the organization of the complex structures that form the tight connections between endothelial cells.

"This study has the potential to be a game-changer in terms of how we treat neurological conditions and how we deliver drugs to the brain," said Gerald Weissmann, M.D., Editor-in-Chief of The FASEB Journal. “Since it was first discovered, the Blood-Brain Barrier has always been a touch elusive. Now, after careful analysis, we are learning exactly how our bodies keep our brains safe and that microRNA-155 is a key player.”

(Source: eurekalert.org)

Copper appears to be one of the main environmental factors that trigger the onset  and enhance the progression of Alzheimer’s disease by preventing the clearance and accelerating the accumulation of toxic proteins in the brain. That is the conclusion of a study appearing today in the journal Proceedings of the National Academy of Sciences. 

“It is clear that, over time, copper’s cumulative effect is to impair the systems by which amyloid beta is removed from the brain,” said Rashid Deane, Ph.D., a research professor in the University of Rochester Medical Center (URMC) Department of Neurosurgery, member of the Center for Translational Neuromedicine, and the lead author of the study. “This impairment is one of the key factors that cause the protein to accumulate in the brain and form the plaques that are the hallmark of Alzheimer’s disease.” 

Copper’s presence in the food supply is ubiquitous. It is found in drinking water carried by copper pipes, nutritional supplements, and in certain foods such as red meats, shellfish, nuts, and many fruits and vegetables. The mineral plays an important and beneficial role in nerve conduction, bone growth, the formation of connective tissue, and hormone secretion. 

However, the new study shows that copper can also accumulate in the brain and cause the blood brain barrier – the system that controls what enters and exits the brain – to break down, resulting in the toxic accumulation of the protein amyloid beta, a by-product of cellular activity.  Using both mice and human brain cells Deane and his colleagues conducted a series of experiments that have pinpointed the molecular mechanisms by which copper accelerates the pathology of Alzheimer’s disease.  

Under normal circumstances, amyloid beta is removed from the brain by a protein called lipoprotein receptor-related protein 1 (LRP1). These proteins – which line the capillaries that supply the brain with blood – bind with the amyloid beta found in the brain tissue and escort them into the blood vessels where they are removed from the brain. 

The research team“dosed” normal mice with copper over a three month period. The exposure consisted of trace amounts of the metal in drinking water and was one-tenth of the water quality standards for copper established by the Environmental Protection Agency. 

“These are very low levels of copper, equivalent to what people would consume in a normal diet.” said Deane.

The researchers found that the copper made its way into the blood system and accumulated in the vessels that feed blood to the brain, specifically in the cellular “walls” of the capillaries. These cells are a critical part of the brain’s defense system and help regulate the passage of molecules to and from brain tissue. In this instance, the capillary cells prevent the copper from entering the brain. However, over time the metal can accumulate in these cells with toxic effect. 

The researchers observed that the copper disrupted the function of LRP1 through a process called oxidation which, in turn, inhibited the removal of amyloid beta from the brain. They observed this phenomenon in both mouse and human brain cells.

The researchers then looked at the impact of copper exposure on mouse models of Alzheimer’s disease. In these mice, the cells that form the blood brain barrier have broken down and become “leaky” – a likely combination of aging and the cumulative effect of toxic assaults – allowing elements such as copper to pass unimpeded into the brain tissue. They observed that the copper stimulated activity in neurons that increased the production of amyloid beta. The copper also interacted with amyloid beta in a manner that caused the proteins to bind together in larger complexes creating logjams of the protein that the brain’s waste disposal system cannot clear. 

This one-two punch, inhibiting the clearance and stimulating the production of amyloid beta, provides strong evidence that copper is a key player in Alzheimer’s disease. In addition, the researchers observed that copper provoked inflammation of brain tissue which may further promote the breakdown of the blood brain barrier and the accumulation of Alzheimer’s-related toxins.  

However, because metal is essential to so many other functions in the body, the researchers say that these results must be interpreted with caution.

“Copper is an essential metal and it is clear that these effects are due to exposure over a long period of time,” said Deane. “The key will be striking the right balance between too little and too much copper consumption. Right now we cannot say what the right level will be, but diet may ultimately play an important role in regulating this process.”

(Source: urmc.rochester.edu)

Stumped for years by a natural filter in the body that allows few substances, including life-saving drugs, to enter the brain through the bloodstream, physicians who treat neurological diseases may soon have a new pathway to the organ via a technique developed by a physicist and an immunologist working together at Florida International University’s Herbert Wertheim College of Medicine.

The FIU researchers developed the technique to deliver and fully release the anti-HIV drug AZTTP into the brain, but their finding has the potential to also help patients who suffer from neurological diseases such as Alzheimer’s, Parkinson’s and epilepsy, as well as cancer.

“Anything where you have trouble getting drugs to the brain and releasing it, this opens so many opportunities,’’ said Madhavan Nair, an FIU professor and chair of the medical school’s immunology department.

In an in vitro laboratory test with HIV-infected cells, Nair and a colleague, Sakhrat Khizroev, a professor of immunology and electrical engineering, attached the antiretroviral drug AZTTP to tiny, magneto-electric nanoparticles. Then, using magnetic energy, they guided the drug across a cell membrane created in the lab to mimic the blood-brain barrier found in the human body.

Once the drug reached its target, researchers triggered its release from the nanoparticle by zapping it with a low-energy electrical current. The drug remained functional and structurally sound after the release, according to the experiment findings.

“We learned to control electrical forces in the brain using magnetics,’’ said Khizroev, who designed, oversaw and supervised the entire project. “We pretty much opened a pathway to the brain.’’

The test findings were published in April in the online peer-reviewed journal, Nature Communications. Researchers believe that using this method will allow physicians to send a higher level of AZTTP — up to 97 percent more — to HIV-infected cells in the brain.

Currently, more than 99 percent of the antiretroviral therapies used to treat HIV, such as AZTTP, are deposited in the liver, lungs and other organs before they reach the brain.

While anti-viral drugs have helped HIV patients live longer by reducing their viral loads, the drugs cannot pass the blood-brain barrier in significant amounts, which allows the virus to lurk unchecked in the brain and can lead to neurological damage, said Dr. Cheryl Holder, a practicing physician and FIU professor who specializes in treating patients with HIV.

“We know that even though the viral load is undetectable in the blood, we don’t know what’s going on in the brain fully,’’ Holder said.

HIV causes constant inflammation, she said, and the virus can pool in areas of the brain where medicine cannot reach, potentially causing damage.

“It’s important to get the drug to the brain,’’ she said, “to help prevent dementia in older patients, and inflammation.’’

But the ability to target drug delivery and release it on demand in the brain has been impossible without opening the skull, Nair and Khizroev said.

Nair, an immunologist who specializes in HIV research, and Khizroev, an electrical engineer and physicist, began collaborating on the project about 18 months ago after winning a National Institutes of Health grant to study the use of magnetic particles.

One of the keys to success was controlling the release of the drug without adversely affecting the brain.

The researchers found their solution in the magneto-electric nanoparticles, which are uniquely suited to deliver and release drugs in the brain, Khizroev said. These nanoparticles can convert magnetic energy into the electrical energy needed to release the drugs without creating heat, which could potentially harm the brain.

The development of a new, less invasive pathway to the brain would open the door to many new medical uses.

Khizroev said he recently returned from a trip to the University of Southern California, where he briefed physicians at the medical school on the technique and its potential for cancer treatment. And Nair said he received a letter recently on behalf of a 91-year-old man suffering from Parkinson’s, asking when the technique might become available for use in people.

That may take a while. With the first phase of testing successfully completed using in vitro experiments, the second will take place at Emory University in Georgia, where researchers will test the technique on monkeys infected with the HIV virus.

If researchers complete the second phase successfully, clinical trials on humans could follow, Nair said. Approval from the Food and Drug Administration would be required before the technique becomes commercially available, he said.

FIU researchers have applied for a patent and would receive royalties, they said, though the university would benefit the most, in part because a successful research project could open opportunities for more grant funding on other topics.

For Khizroev, who had previously done research on quantum computing and information processing, the project has offered a way to put his scientific knowledge to use in a way that could have a direct affect on people’s health.

“I wanted to apply my knowledge of nanoparticles to something important,’’ he said.

(Source: miamiherald.com)

A research team led by Robert Nagele, PhD, of the New Jersey Institute for Successful Aging (NJISA) at the University of Medicine and Dentistry of New Jersey (UMDNJ)-School of Osteopathic Medicine, has demonstrated that the anti-atherosclerosis drug darapladib can significantly reduce leaks in the blood brain barrier. This finding potentially opens the door to new therapies to prevent the onset or the progression of Alzheimer’s disease. Writing in the Journal of Alzheimer’s Disease (currently in press), the researchers describe findings involving the use of darapladib in animal models that had been induced to develop diabetes mellitus and hypercholesterolemia (DMHC), which are considered to be major risk factors for Alzheimer’s disease.

“Diabetes and hypercholesterolemia are associated with an increased permeability of the blood-brain barrier, and it is becoming increasingly clear that this blood-brain barrier breakdown contributes to neurodegenerative diseases such as Alzheimer’s,” Nagele said. “Darapladib appears to be able to reduce this permeability to levels comparable to those found in normal, non-DMHC controls, and suggests a link between this permeability and the deposition of amyloid peptides in the brain.”

The study involved 28 animal (pig) models that were divided into three groups – DMHC animals treated with a 10 mg/day dose of darapladib; DMHC animals that received no treatment; and non-DMHC controls. Post-mortem analysis of the brains of the darapladib-treated animals showed significant decreases in blood-brain barrier leakage and in the density of amyloid-positive neurons in the cerebral cortices. Interestingly, the amyloid peptides that leaked into the brain tissue were found almost exclusively in the pyramidal neurons of the cerebral cortex, one of the earliest pathologies of the development of Alzheimer’s disease.

“Because our results suggest that these metabolic disorders can trigger neurodegenerative changes through blood-brain barrier compromise, therapies – such as darapladib – that can reduce vascular leaks have great potential for delaying the onset or slowing the progression of diseases like Alzheimer’s,” said the study’s lead author, Nimish Acharya, PhD, of the NJISA and the UMDNJ-Graduate School of Biomedical Sciences. “The clinical, caregiving and financial impact of such an effect cannot be overestimated.”

(Source: newswise.com)