Scientists confirm correlation between malignant hyperthermia and exertional heat stroke

New research published online in The FASEB Journal may ultimately help athletes and trainers better understand who may be more at risk for heat stroke. In the report, scientists use animals to show that there is a link between the susceptibility to malignant hyperthermia (MH) and exertional heat stroke.

“Global warming and increasing frequency of heat waves, which are particularly dangerous in large urban areas, in future years will represent a reason of concern for human health,” said Feliciano Protasi, Ph.D., a researcher involved in the work at the Department of Neuroscience, Imaging and Clinical Sciences, University G. d’Annunzio, Chieti, Italy. “However, in spite of the increased incidence, severity and life-threatening nature of heat stroke, there are currently no safe and effective drug interventions to protect or reverse this deadly syndrome. We hope that our study will contribute to develop preventive measures and/or acute treatments for heat stroke caused by environmental heat and physical exertion.”

Scientists used three groups of mice to reach their conclusion. The first two groups (RYR1Y522S/WT and CASQ1-null mice) had altered genes that made them susceptible to lethal hyperthermic crises when exposed to anesthetics, while the third group was normal (wild-type mice). When the three sets of mice were exposed to a protocol of exertional stress (incremental running at 34 degrees Celsius and 40 percent humidity) the MH-susceptible mice (but not the normal mice) suffered lethal overheating episodes.

“This work addresses a dangerous, often lethal, physiological maladjustment that animals and humans can undergo,” said Thoru Pederson, Ph.D., Editor-in-Chief of The FASEB Journal. “The door now stands open to finding effective preventative drugs.”

With $8.6 Million Grant From Nih, UCLA-Led Consortium Will Map the Heart’s Nervous System

A consortium directed by UCLA’s Dr. Kalyanam Shivkumar has received a three-year, $8.6 million grant from the National Institutes of Health to map the heart’s nervous system. The group’s goal: To conduct research that leads to new ways to treat cardiovascular disease by targeting nerves in the heart’s nervous system.

More than 800,000 people in the U.S. die each year from cardiovascular diseases such as heart failure, arrhythmia and hypertension. These problems often are linked to the autonomic nervous system, the part of the nervous system that signals the heart to beat and controls breathing, digestion and other body processes that typically happen without conscious effort.

Researchers believe that modulating those electrical signals holds promise as a way to treat heart failure and other common cardiovascular problems.

“Understanding the nervous system’s control of the heart is such a complex problem that it requires a collaborative approach, and we’re pleased that so many experts are coming together for this initiative,” said Shivkumar, the study’s lead investigator and director of the UCLA Cardiac Arrhythmia Center and Electrophysiology Programs.

“Our goal is to precisely map the heart’s anatomy and code the function of the nerves that control the heart from a very basic level all the way to clinical studies in humans.”

UCLA is one of seven institutions participating in the project. Principal investigators at the other universities are Dr. Viviana Gradinaru of Caltech, Dr. Stephen Liberles of Harvard University, Dr. Charless Fowlkes of UC Irvine, Dr. Irving Zucker of the University of Nebraska Medical Center, Dr. Beth Habecker of Oregon Health and Science University and Dr. David Paterson of Oxford University.

The information the consortium produces could point the way to new therapies that target neural structures, and it could suggest ways for scientists to create more effective electrical stimulation therapies based on the methods being used today, said Shivkumar, who is also chief of the UCLA Cardiovascular Interventional programs and a professor of medicine, radiology and bioengineering at the David Geffen School of Medicine at UCLA.

“Understanding how the nervous system controls the heart offers researchers a tremendous opportunity to open up new paths to treat cardiac disease,” said Dr. Kelsey Martin, dean of the David Geffen School of Medicine. “We are thrilled that our UCLA team is leading the charge on this exciting new research.”

The award is from an NIH program called Stimulating Peripheral Activity to Relieve Conditions, or SPARC, which supports research on how the electrical signals of the peripheral nerves that connect the brain and spinal cord to the rest of the body control internal organ function. The UCLA-led consortium is one of 27 multidisciplinary research teams that received SPARC awards in 2016; the grants totaled more than $20 million.

Heart disease, leukemia linked to dysfunction in nucleus

We put things into a container to keep them organized and safe. In cells, the nucleus has a similar role: keeping DNA protected and intact within an enveloping membrane. But a new study by Salk Institute scientists, detailed in the November 2 issue of Genes & Development, reveals that this cellular container acts on its contents to influence gene expression.

“Our research shows that, far from being a passive enclosure as many biologists have thought, the nuclear membrane is an active regulatory structure,” says Salk Professor Martin Hetzer, who is also holder of the Jesse and Caryl Philips Foundation chair. “Not only does it interact with portions of the genome to drive gene expression, but it can also contribute to disease processes when components are faulty.”

Using a suite of molecular biology technologies, the Salk team discovered that two proteins, which sit in the nuclear envelope, together with the membrane-spanning complexes they form, actively associate with stretches of DNA to trigger expression of key genes. Better understanding these higher-level functions could provide insight into diseases that appear to be related to dysfunctional nuclear membrane components, such as leukemia, heart disease and aging disorders.

Historically, the nuclear membrane’s main purpose was thought to be keeping the contents of the nucleus physically separated from the rest of the cell. Complexes of at least thirty different proteins, called nucleoporins, form gateways (pores) in the membrane, controlling what goes in or out. But as the Hetzer lab’s work on nucleoporins shows, these nuclear pore complexes (NPCs), beyond being mere gateways into the nucleus, have surprising regulatory effects on the DNA inside.

“Discovering that key regulatory regions of the genome are actually positioned at nuclear pores was very unexpected,” says Arkaitz Ibarra, a Salk staff scientist and first author of the paper. “And even more importantly, nuclear pore proteins are critical for the function of those genomic sites.”

Curious about all the regions of DNA with which nucleoporins potentially interact, the team turned to a human bone cancer cell line. The scientists used a molecular biology technique called DamID to pinpoint where two nucleoporins, Nup153 and Nup93, came into contact with the genome. Then they used several other sequencing techniques to understand which genes were being affected in those regions, and how.

The Salk team discovered that Nup153 and Nup93 interacted with stretches of the genome called super-enhancers, which are known to help determine cell identity. Since every cell in our body has the same DNA, what makes a muscle cell different from a liver cell or a nerve cell is which particular genes are turned on, or expressed, within that cell. In the Salk study, the presence of Nup153 and Nup93 was found to regulate expression of super-enhancer driven genes and experiments that silenced either protein resulted in abnormal gene expression from these regions. Further experiments in a lung cancer cell line validated the bone cancer line results: Nucleoporins in the NPC were found to interact with multiple super-enhancer regions to drive gene expression, while experiments that altered the NPC proteins made related gene expression faulty, even though the proteins still performed their primary role as gatekeepers in the cell membrane.

“It was incredible to find that we could perturb the proteins without affecting their gateway role, but still have nearby gene expression go awry,” says Ibarra.

The results bolster other work indicating that problems with the nuclear membrane play a role in heart disease, leukemia and progeria, a rare premature aging syndrome.

“People have thought the nuclear membrane is just a protective barrier, which is maybe the reason why it evolved in the first place. But there are many more regulatory levels that we don’t understand. And it’s such an important area because so far, every membrane protein that has been studied and found to be mutated or mis-localized, seems to cause a human disease,” says Hetzer.

Lights, Camera, Action: New Catheter Lets Doctors See Inside Arteries For First Time

Removing plaque from clogged arteries is a common procedure that can save and improve lives. This treatment approach was recently made even safer and more effective with a new, high-tech catheter that allows cardiologists to see inside the arteries for the first time, cutting out only the diseased tissue. Interventional cardiologists at Sulpizio Cardiovascular Center at UC San Diego Health are the first in the region to use this technology.

The new image-guided device, Avinger’s Pantheris™ Lumivascular atherectomy system, allows doctors to see and remove plaque simultaneously during an atherectomy – a minimally invasive procedure that involves cutting plaque away from the artery and clearing it out to restore blood flow.

The new technology treats patients suffering from the painful symptoms of peripheral artery disease (PAD), a condition caused by a build-up of plaque that blocks blood flow in the arteries of the legs and feet, preventing oxygen-rich blood from reaching the extremities. Patients with PAD frequently develop life threatening complications, including heart attack, stroke, and in some severe cases, patients may even face amputation.

“Peripheral artery disease greatly impacts quality of life, with patients experiencing cramping, numbness and discoloration of their extremities,” said Mitul Patel, MD, cardiologist at UC San Diego Health. “This new device is a significant step forward for the treatment of PAD with a more efficient approach for plaque removal and less radiation exposure to the doctor and patient.”

X-ray technology was previously used during similar procedures, but those images are not nearly as clear and do not allow visualization inside the blood vessel. The new catheter, with a fiber optic camera the size of a grain of salt on the tip, is fed through a small incision in the groin that does not require full anesthesia. Once inside, the interventional cardiologist is able to see exactly what needs to be removed without damaging the artery wall, which can cause further narrowing.

PAD affects nearly 20 million adults in the United States and more than 200 million globally. September is PAD Awareness Month, which has a personal meaning to one of Patel’s patients, who recently underwent an atherectomy at UC San Diego Health with the new catheter.

Patel said the patient had severe scar tissue and plaque build-up at a previously treated site in his right leg, limiting blood flow to his calf muscle and his ability to exercise or even walk a short distance.

“He was a good candidate for the new image-guided catheter approach. The device allowed for excellent visualization inside his leg artery as we removed only the diseased tissue,” said Patel.

Now able to walk several miles with this wife without any limitations, the patient’s quality of life has improved, and with some lifestyle changes, he hopes to manage his PAD and prevent another blockage.

Out Of Sync How Genetic Variation Can Disrupt The Heart’S Rhythm

new research from the University of Chicago shows how deficits in a specific pathway of genes can lead to the development of atrial fibrillation, a common irregular heartbeat, which poses a significant health risk.

Researchers describe a complex system of checks and balances, including the intersection of two opposing regulatory methods that work to maintain normal cardiac rhythm, and offer insights that could lead to individualized treatment in humans.

“We hope that this and similar studies contribute to a mechanistic understanding underlying the genetic basis of heart arrhythmias” said study author Ivan Moskowitz, MD, PhD, associate professor in the Department of Pediatrics, Pathology, and Human Genetics at the University of Chicago. “Such studies will allow clinicians to stratify patients based on their likely natural history of disease and potentially their response to specific therapeutics.”

Atrial fibrillation (AF) is the most common cardiac arrhythmia in the world. It affects more than 2.7 million Americans, according to the American Heart Association. AF occurs when the normal rhythm of the heart goes awry, causing a rapid, irregular heartbeat. When blood is not properly ejected from the heart, blood clots can form, leading to high risk of stroke.

Patients with other forms of heart disease, such as congestive heart failure or hypertension, have an increased risk of AF. For decades this observation caused doctors to believe that AF was just a side effect of other heart-related issues. However, some patients with AF have no other cardiac issues and not all patients with congestive heart failure have AF. Having a family member with AF is associated with a greatly increased risk for the arrhythmia, suggesting a genetic component.

One of the regions in the genome implicated in AF is near a gene named Tbx5. Although its role in AF was not understood, Tbx5 is known to control other genes and to be important in both the structure and the rhythm of the heart.

It was long thought that a mouse heart could not develop primary AF, but when first author Rangarajan Nadadur and others in Moskowitz’s team knocked out the Tbx5 gene from adult mice, they found that the mice developed spontaneous AF. Using this model system the researchers investigated what role Tbx5 played by looking for the genes it controlled. About 30 genes have been linked to AF in humans. The researchers found that half of those genes were decreased in the absence of Tbx5 and that Tbx5 directly targeted some of those genes.

Pitx2, a gene controlled by Tbx5, is the most commonly identified gene in genome wide association studies for AF. This finding prompted the researchers to reach out to James Martin’s research group at Baylor College of Medicine, collaborators on a Leducq Foundation grant to study AF, who were studying Pitx2.

“Both Tbx5 or Pitx2 directly control important rhythm genes in the heart, but in opposite directions” said Moskowitz. “Removing either causes a susceptibility to AF.”

“The clinical application of this model is that we may be able to provide more precisely targeted treatments to AF patients depending on whether their cardiac rhythm network is up- or down-regulated,” said Moskowitz. For example, if an important calcium channel is too active and causing AF, blocking it with medication would be helpful. However, if that calcium channel is not active enough and contributing to AF, prescribing a calcium channel blocker may be ineffective or even harmful. “We believe that a better understanding of the mechanisms underlying the genetic risk of the disease will ultimately have a significant impact on treatment.”

Stem Cell Breakthrough Unlocks Mysteries Associated With Inherited And Sometimes Lethal Heart Conditions

Using advanced stem cell technology, scientists from the Icahn School of Medicine at Mount Sinai have created a model of a heart condition called hypertrophic cardiomyopathy (HCM) — an excessive thickening of the heart that is associated with a number of rare and common illnesses, some of which have a strong genetic component. The stem cell lines scientists created in the lab, which are believed to closely resemble human heart tissue, have already yielded insights into unexpected disease mechanisms, including the involvement of cells that have never before been linked to pathogenesis in a human stem-cell model of HCM. The research was published in the journal Stem Cell Reports.

The genetic disorder discussed in the new study is called cardiofaciocutaneous syndrome (CFC), which is caused by a mutation in a gene called BRAF. The condition is rare and affects fewer than 300 people worldwide, according to the National Institutes of Health. It causes abnormalities of the head, face, skin, and major muscles, including the heart.

To learn more about HCM associated with various genetic diseases, Mount Sinai scientists took skin cells from three CFC patients and turned them into highly versatile stem cells, which were then converted into cells responsible for the beating of the heart. This model has relevance for research on several related and more common genetic disorders, including Noonan syndrome, which is characterized by unusual facial features, short stature, heart defects, and skeletal malformations.

“At present, there is no curative option for HCM in patients with these related genetic conditions,” said Bruce D. Gelb, MD, Director of The Mindich Child Health and Development Institute and Professor in the Departments of Pediatrics, Genetics and Genomic Sciences at the Icahn School of Medicine at Mount Sinai. “If our findings are correct, they suggest we might be able to treat HCM by blocking specific cell signals—which is something we know how to do.”

Dr. Gelb says that about 40 percent of patients with CFC suffer from HCM (two of the three study participants had HCM). This suggests a pathogenic connection, though the link has never been fully explored or explained. The primary goal of the current research was to understand the role of a cell-signaling pathway called RAS/MAPK in the cascade of events leading to HCM in patients with CFCs — and by association, with Noonan syndrome, Costello syndrome, and other similar illnesses.

Observing the disease progression in these heart cells, called cardiomyocytes, Dr. Gelb and his team found that some of the changes were caused by interactions with cells that resemble fibroblasts — the same kinds of cells that produce collagen and other proteins. Fibroblasts make up a significant portion of total heart tissue, although it is the cardiomyocytes that are primarily responsible for pumping blood. “These fibroblast-like cells seem to be producing an excess of a protein growth factor called TGF-beta, which, in turn, caused the cardiomyocytes to hypertrophy, or grow larger,” Dr. Gelb said. “We believe this is the first time the phenomenon has been observed using a human induced pluripotent stem cell model of the disease.”

Prior to this observation, Dr. Gelb and his team assumed hypertrophy was “cell autonomous,” meaning intrinsic to the cardiomyocytes themselves. “Based on our cell culture model, we saw that fibroblasts are playing a key role in giving the heart cells the signal that causes them to get big,” Dr. Gelb said. “That was quite unexpected.”

The therapeutic implications may also be profound. “We were able to block TGF-beta in vitro using antibodies that bind to the protein. When we did that, the cardiomyocytes no longer hypertrophy,” Dr. Gelb said. It’s not certain the same effect would be seen in the many clinical cases of HCM that are not influenced by BRAF or the RAS pathway—essentially a chain of cellular proteins that help transmit signals from surface receptors on the cell to DNA in the nucleus –but researchers believe this could be the case.

The bigger surprise, said Dr. Gelb, “is that we may be talking about a signaling circle” in which fibroblasts trigger the release of a growth factor, which causes cardiomyocytes to hypertrophy, which in turn, prompts fibroblasts to release more of the growth factor.” Dr. Gelb didn’t witness this last part of the circle in his stem cell culture, but evidence of fibroblast stimulation has been reported in mouse models that don’t express the RAS mutation. If the circle theory is validated, Dr. Gelb said, there could be new and broad therapeutic interventions for HCM in both RAS and non-RAS contexts. “In theory, at least, a therapy could be useful for both,” he said.

MOUNT SINAI PIONEERS NEW APPROACH FOR CARDIAC ARRHYTHMIA PATIENTS USING THE EPIACCESS® SYSTEM

The Mount Sinai Hospital is the first site in the New York metropolitan area to pioneer a new approach for the treatment of cardiac arrhythmias using the EpiAccess® system. Developed by medical device company EpiEP, Inc., the EpiAccess system is a specialized instrument that facilitates an epicardial approach for non-surgical procedures on the surface of the heart.

“We are pleased to be among the first facilities in the nation to offer the EpiAccess system,” said Vivek Reddy, MD, Director of Cardiac Arrhythmia Services at The Mount Sinai Hospital and the Mount Sinai Health System. “By providing routine and safe access to the pericardial space, the device offers a new approach to treat arrhythmias from the outside of the heart, enabling enhanced safety in advanced procedures and opening a new frontier for treating our patients.”

Non-surgical epicardial access has traditionally been limited by the two-dimensional image of a needle guided by intermittent fluoroscopy, which makes it difficult to know the precise location of the needle tip when accessing this small space surrounding the heart. The EpiAccess needle’s fiber-optic tip provides real-time pressure frequency data and immediate confirmation to alert physicians about needle tip location during the procedure. It was designed to reduce the risk of complications such as pericardial effusions, procedure time, and exposure to radiation used during these types of procedures.

George Washington University Researchers Receive $1.6 Million to Improve Cardiac Function During Heart Failure

Researchers at the George Washington University (GW) received $1.6 million from the National Heart, Lung, and Blood Institute to study a heart-brain connection that could help the nearly 23 million people suffering from heart failure worldwide. The four-year project will study ways to restore parasympathetic activity to the heart through oxytocin neuron activation, which could improve cardiac function during heart failure.

A distinctive hallmark of heart failure is autonomic imbalance, consisting of increased sympathetic activity and decreased parasympathetic activity. Parasympathetic activity is cardiac protective.

“Parasympathetic activity is what you have when you’re reading a book, or relaxing, and counteracts the sympathetic activity you have when you’re stuck on the metro or have an exam tomorrow,” said David Mendelowitz, Ph.D., vice chair and professor in the Department of Pharmacology and Physiology at the GW School of Medicine and Health Sciences. “Heart failure is a disease that effects both neuro and cardiac function.”

Unfortunately, few effective treatments exist to increase parasympathetic activity to the heart. Based upon exciting preliminary results, this study will examine the activation of neurons in the hypothalamus that release oxytocin, which has shown to increase parasympathetic activity in the heart. While oxytocin is often used to start or increase speed of labor, recent research has uncovered its role in feelings of generosity and bonding. It may also have beneficial effects on the heart.

The project is a collaboration between the GW School of Medicine and Health Sciences and the GW School of Engineering and Applied Science.

“While Dr. Mendelowitz’s research is focused on neuroscience and how the brain works, my work is focused on cardiac function. Heart failure is a disease that affects both, which is why it is imperative for Dr. Mendelowitz and I to use our complimentary expertise to solve this problem,” said Matthew Kay, PE, DSc, associate professor in the Department of Biomedical Engineering at the GW School of Engineering and Applied Science.

Kay and his research team will use high-speed optical assessments of heart function to identify heart-specific benefits of oxytocin nerve activation. Working together, Mendelowitz and Kay have the potential to unravel the complex interaction between the brain and the heart during heart failure.

A Personalized Virtual Heart Predicts the Risk of Sudden Cardiac Death

When electrical waves in the heart run amok in a condition called arrhythmia, sudden death can occur. To save the life of a patient at risk, doctors currently implant a small defibrillator to sense the onset of arrhythmia and jolt the heart back to a normal rhythm. But a thorny question remains: How should doctors decide which patients truly need an invasive, costly electrical implant that is not without health risks of its own?

To address this, an interdisciplinary Johns Hopkins University team has developed a non-invasive 3-D virtual heart assessment tool to help doctors determine whether a particular patient faces the highest risk of a life-threatening arrhythmia and would benefit most from a defibrillator implant. In a proof-of-concept study published May 10 in the online journal Nature Communications, the team reported that its new digital approach yielded more accurate predictions than the imprecise blood pumping measurement now used by most physicians.

“Our virtual heart test significantly outperformed several existing clinical metrics in predicting future arrhythmic events,” said Natalia Trayanova, the university’s inaugural Murray B. Sachs Professor of Biomedical Engineering. “This non-invasive and personalized virtual heart-risk assessment could help prevent sudden cardiac deaths and allow patients who are not at risk to avoid unnecessary defibrillator implantations.”

Trayanova, a pioneer in developing personalized imaging-based computer models of the heart, supervised the research and was senior author of the journal article. She holds faculty appointments within Johns Hopkins’ Whiting School of Engineering and its School of Medicine, and she is a core faculty member of the university’s Institute for Computational Medicine. For this study, she joined forces with cardiologist and co-author Katherine C. Wu, associate professor in the Johns Hopkins School of Medicine, whose research has focused on magnetic resonance imaging approaches to improving cardiovascular risk prediction.

For this landmark study, Trayanova’s team formed its predictions by using the distinctive magnetic resonance imaging (MRI) records of patients who had survived a heart attack but were left with damaged cardiac tissue that predisposes the heart to deadly arrhythmias. The research was a blinded study, meaning that the team members did not know until afterward how closely their forecasts matched what happened to the patients in real life. This study involved data from 41 patients who had survived a heart attack and had an ejection fraction—a measure of how much blood is being pumped out of the heart—of less than 35 percent.

To protect against future arrhythmias, physicians typically recommend implantable defibrillators for all patients in this range, and all 41 patients in the study received the implants because of their ejection fraction scores. But research has concluded that this score is a flawed measure for predicting which patients face a high risk of sudden cardiac death.

The Johns Hopkins team invented an alternative to these scores by using pre-implant MRI scans of the recipients’ hearts to build patient-specific digital replicas of the organs. Using computer-modeling techniques developed in Trayanova’s lab, the geometrical replica of each patient’s heart was brought to life by incorporating representations of the electrical processes in the cardiac cells and the communication among cells. In some cases, the virtual heart developed an arrhythmia, and in others it did not. The result, a non-invasive way to gauge the risk of sudden cardiac death due to arrhythmia, was dubbed VARP, short for virtual-heart arrhythmia risk predictor. The method allowed the researchers to factor in the geometry of the patient’s heart, the way electrical waves move through it and the impact of scar tissue left by the earlier heart attack.

Eventually, the VARP results were compared to the defibrillator recipients’ post-implantation records to determine how well the technology predicted which patients would experience the life-threatening arrhythmias that were detected and halted by their implanted devices. Patients who tested positive for arrhythmia risk by VARP were four times more likely to develop arrhythmia than those who tested negative. Furthermore, VARP predicted arrhythmia occurrence in patients four-to-five times better than the ejection fraction and other existing clinical risk predictors, both non-invasive and invasive.

“We demonstrated that VARP is better than any other arrhythmia prediction method that is out there,” Trayanova said. “By accurately predicting which patients are at risk of sudden cardiac death, the VARP approach will provide the doctors with a tool to identify those patients who truly need the costly implantable device, and those for whom the device would not provide any life-saving benefits.”

Wu agreed that these encouraging early results indicate that the more nuanced VARP technique could be a useful alternative to the one-size-fits-all ejection fraction score.

“This is a ground-breaking proof-of-concept study for several reasons,” Wu said, “As cardiologists, we obtain copious amounts of data about patients, particularly high-tech imaging data, but ultimately we use little of that information for individualized care. With the technique used in this study, we were able to create a personalized, highly detailed virtual 3-D heart, based on the patient’s specific anatomy. Then, we were able to test the heart virtually to see how irritable it is under certain situations. We could do all this without requiring the patient to undergo an invasive procedure. This represents a safer, more comprehensive and individualized approach to sudden cardiac death risk assessment.”

Wu pointed out that an implantable defibrillator also has a few risks of its own and that avoiding implantation of this device when it is not truly needed eliminates these risks. Implantable defibrillators, she said, require invasive access to the heart, frequent device checks and intermittent battery changes. Complications, she added, can include infection, device malfunction and, in rare instances, heart or blood vessel damage.

In addition to eliminating unnecessary device implantations, Trayanova noted that this new risk prediction methodology could also be applied to patients who had prior heart damage, but whose ejection fraction score did not target them for therapy under current clinical recommendations. Thus, Trayanova said, VARP has the potential to save the lives of a much larger number of at-risk patients.

Harvard Scientists Report on Novel Method for Extending the Life of Implantable Devices in situ

Blood-contacting implantable medical devices, such as stents, heart valves, ventricular assist devices, and extracorporeal support systems, as well as vascular grafts and access catheters, are used worldwide to improve patients’ lives. However, these devices are prone to failure due to the body’s responses at the blood-material interface; clots can form and inflammatory reactions can prevent the device from performing as indicated. Currently, when this occurs, the only solution is to replace the device.

In a paper published in the April 13 issue of Nature Communications, investigators from Harvard report on a novel biochemical method that enables the rapid and repeated regeneration of selected molecular constituents in situ after device implantation, which has the potential to substantially extend the lifetime of bioactive films without the need for device removal. Their approach could also be used to load and release a number of material-bound constituents for controlled drug loading and delivery.

Newer implantable devices have thin films with bioactive molecules and/or drugs that help prevent clots and inflammation while also enhancing device integration and local tissue repair, as well as inhibiting microbe colonization. For example, the blood-thinner heparin has been coated on the surfaces of cardiovascular devices to prevent clot formation on or within the devices. However, the newer devices have limitations.

“Not only do they have a finite reservoir of bioactive agents, but the surface components of the thin films also degrade or lose their effectiveness when exposed to the physiological environment over time. Presently the only solution is to replace the entire device,” said lead author Elliot Chaikof, MD, PhD, Chair of Surgery at Beth Israel Deaconess Medical Center (BIDMC). Dr. Chaikof is also Professor of Surgery at Harvard Medical School, an associate faculty member of Harvard’s Wyss Institute of Biologically Inspired Engineering, and a faculty member of the Harvard-Massachusetts Institute of Technology Division of Health Sciences and Technology.

A number of approaches have been attempted to improve the stability and activity of thin-film constituents of implantable devices. But despite some progress, a surface coating that reliably retains its biological activity over extended, clinically relevant time periods has not been developed.

The new approach relies on an enzyme, Staphylococcus aureus Sortase A, which catalyzes the linking of two peptide sequences. By inducing a series of mutations, David Liu, PhD, Professor of Chemistry and Chemical Biology at Harvard University and a Howard Hughes Medical Institute Investigator, developed a laboratory-evolved enzyme, Staphylococcus aureus Sortase A (eSrtA), which has an enhanced catalytic activity of approximately 120-fold over the non-mutated, wild-type enzyme. eSrtA catalyzes not only linking of peptides but also breaking them apart, which it can do repeatedly.

“We found that through a two-step process of removing and replacing bioactive coatings, eSrtA enables rapid, repeated thin-film regeneration in the presence of whole blood in vitro and in vivo,” said Liu. “We also developed a series of new enzymes that recognize a variety of distinct peptide sequences that could be put to work in a similar manner.”

“But, we know that there are many questions that only further research can answer,” said Chaikof. “For instance, eSrtA is a bacterial enzyme, and while there is a precedent for the clinical use of such enzymes – for example, streptokinase, uricase, and asparaginase – studies must be done to determine how immunogenic this enzyme might be.”

Additionally, it is unknown how often a bioactive coating would need to be regenerated, how long it would last, or whether the bioactive constituents could become inaccessible over time due to biologic processes.

“Many thousands of people depend on implantable devices with bioactive constituents for their health and well-being, so finding a strategy that will ensure the long-term efficacy of these devices is of paramount importance,” said Chaikof. “While this research is relatively early stage, it opens the door to a new way of approaching and addressing this clinical challenge.”

In addition to Chaikof and Liu, co-authors are BIDMC researchers, Hyun Ok Ham, PhD, Carolyn Haller, PhD, Erbin Dai, PhD, Wookhyun Kim, PhD, and Zheng Qu, PhD, also of the Georgia Institute of Technology; and Brent Dorr, PhD, of Harvard University.

This research is supported by a grant to Drs. Chaikof and Liu from the National Institutes of Health.