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Plastic leaching illustration

Plasticizer interaction with the heart

Calling an ambulance during an emergency, emailing a journal article before a 5 p.m. deadline and maintaining conditions during the fifth week of a 6-week lab study, without altering the light or temperature, requires electricity and translates into time, money and lives saved. During critical moments, we appreciate the tiny particles and ions in electric currents that power our phones, computers or laboratory equipment. We seldom think about the speed of these connections or potential disruptors when conditions are stable. The same applies to the electric currents, or electrophysiology, of our heart.

Arrhythmias affect millions of Americans but can be controlled with routine screenings and preventive care. In an intensive care setting, helping a patient maintain a steady heart rate, especially if they are at risk for cardiac complications, may support a faster recovery, shorter hospital stay, reduced health care costs and improved health outcomes, such as avoiding complications from heart failure or stroke.

A preclinical study, entitled “Plasticizer Interaction With the Heart,” appears in the July issue of Circulation: Arrhythmia and Electrophysiology and examines the role plastic exposure, akin to exposure in a medical setting, has on heart rhythm disruptions and arrhythmias.

changes in heart rhythm due to plastics

New preclinical research finds acute exposure to MEHP, a common plasticizer used in medical equipment, increases risk for alternans and arrhythmias, disruptions in heart rhythm. The images above show changes in heart rhythm, measured by slowed epicardial conduction velocity, enhanced action potential prolongation and impaired sinus node activity.

The research team, led by researchers at Children’s National Health System, discovered increased risks for irregular heart rhythms after exposing intact, in vitro heart models to 30 minutes of mono-2-ethylhexyl phthalate (MEHP), a metabolite from Di-2-ethylhexyl phthalate (DEHP). DEHP is a chemical commonly used to make plastics pliable in FDA-approved medical devices. This phthalate accounts for 40% of the weight of blood storage bags and up to 80% of the weight of tubes used in an intensive care setting, such as for assisted feeding or breathing, and for catheters used in diagnostics or to conduct minimally invasive cardiac procedures.

The team chose to study the heart’s reaction to 60 µM of MEHP, a level comparable to stored blood levels of MEHP observed in pediatric patients and in neonatal exchange transfusion procedures. They found 30-minute exposure to MEHP slowed atrioventricular conduction and increased the atrioventricular node effective refractory period. MEHP prolonged action potential duration time, enhanced action potential triangulation, increased the ventricular effective refractory period and slowed epicardial conduction velocity, which may be due to the inhibition of Nav 1.5, or sodium current.

“We chose to study the impact of MEHP exposure on cardiac electrophysiology at concentrations that are observed in an intensive care setting, since plastic medical products are known to leach these chemicals into a patient’s bloodstream,” says Nikki Gillum Posnack, Ph.D., a principal investigator with the Sheikh Zayed Institute for Pediatric Surgical Innovation at Children’s National and an assistant professor of pediatrics at the George Washington University School of Medicine and Health Sciences. “In critical conditions, a patient may have a blood transfusion, require extracorporeal membrane oxygenation, undergo cardiopulmonary bypass or require dialysis or intravenous fluid administration. All of these scenarios can lead to plastic chemical exposure. Our research team wants to investigate how these plastic chemicals can impact cardiac health.”

In this review, Dr. Posnack’s team mentions one reason for the observed changes in the preclinical heart models may be due to the structure of phthalates, which resemble hormones and can interfere with a variety of biological processes. Due to their low molecular weight, these chemicals can interact directly with ion channels, nuclear receptors and other cellular targets.

Existing epidemiological research shows associations between exposure to phthalates and adverse health outcomes, including metabolic disturbances, reproductive disorders, inflammatory conditions, neurological disorders and cardiovascular disease. This is the first study to examine the link between cardiac electrophysiology in intact hearts and exposure to MEHP, comparable to levels observed in an ICU.

Dr. Posnack’s team previously found DEHP reduced cellular electrical coupling in cardiomyocyte cell models, which slowed conduction velocity and produced an arrhythmogenic phenotype. A microarray analysis found heart cells treated with DEHP led to mRNA changes in genes responsible for contracting and calcium handling. Another preclinical study showed DEHP altered nervous system regulation of the cardiovascular system. Future studies to expand on this research may include the use of larger preclinical models or human assessments. For the latter, stem cell-derived cardiomyocytes can be used to compare the safety profile of plastic chemicals with potential alternatives.

An accompanying editorial, entitled “Shocking Aspects of Nonconductive Plastics,” authored by cardiology researchers at the University of Wisconsin-Madison, puts this novel research into perspective. Like Dr. Posnack, the team notes that while the clinical impact plasticizers have on heart health still needs to be determined, the work contributes to compelling data among multiple researchers and shows DEHP and MEHP are not inert substances.

“Toxic plasticizers in children’s toys and baby products hit public headlines 20 years ago, but exposure to these compounds is up to 25x higher in patients undergoing complex medical procedures,” write the University of Wisconsin-Madison researchers. “We readily (and unknowingly) administer these compounds, and at times in high quantity, to some of our most vulnerable patients. This work highlights the need for further investigation into short and long-term plasticizer exposure on cardiac electrophysiology.”

The Agency for Toxic Substances and Disease Registry (ATSDR), part of the Centers for Disease Control and Prevention (CDC), released a public health statement about DEHP in 2002, noting more research in humans is needed to issue formal warnings against this phthalate.

ATSDR states there is no conclusive evidence about the adverse health effects of children exposed to DEHP in a medical setting, such as procedures that require the use of flexible tubing to administer intravenous fluids or medication. However, the CDC statement includes limits of DEHP exposure, based on preclinical models, used to guide upper DEHP limits in consumer products, including food packaging, drinking water, and air quality in the workplace.

“It’s important to note that this was a preliminary study performed on an ex vivo model that is largely resilient to arrhythmias”, says Rafael Jaimes III, Ph.D., the first author of the study and a senior scientist at Children’s National. “Due to the nature of the design, it was somewhat alarming that we found such significant effects. I predict that electrophysiological disturbances will be more pronounced in models that more closely resemble humans. These types of models should absolutely be studied.”

“And, importantly, our results may incentivize the development and use of new products that are manufactured without phthalates,” Dr. Posnack adds.

These questions are powering Dr. Posnack and her team through a decade-long, multi-institution research investigation to understand how plastic chemicals and medical device biomaterials can impact cardiac health.

Additional study authors for this paper include Damon McCullough, B.S., Bryan Siegel, M.D., Luther Swift, Ph.D., Daniel McInerney, B.S., and James Hiebert, B.S., with the Sheikh Zayed Institute for Pediatric Surgical Innovation and Children’s National Heart Institute, part of Children’s National Health System in Washington, D.C.; Erick A. Perez-Alday, Ph.D., and Larisa G Tereshchenko, M.D., Ph.D., with the Knight Cardiovascular Institute at Oregon Health and Science University in Portland, Ore.; Javier Saiz, Ph.D., and Beatriz Trenor, Ph.D., with Ci2B-Universitat Politecnica de Valencia in Spain and Jiansong Sheng, Ph.D., from CiPA Lab, LLC, in Rockville, Md.

The study was supported by the National Institutes of Health (R00ES023477 and R01HL139472), Children’s Research Institute and Children’s National Heart Institute. NVIDIA corporation provided graphics processing, with partial support by the Direccion General de Politica Cientifica de la Generalitat Valenciana (PROMETEU2016/088).

Nikki Gillum Posnack

Do plastic chemicals contribute to the sudden death of patients on dialysis?

Nikki Gillum Posnack

Nikki Posnack, Ph.D., assistant professor with the Children’s National Heart Institute, continues to explore how repeat chemical exposure from medical devices influences cardiovascular function.

In a review published in HeartRhythmNikki Posnack, Ph.D., an assistant professor at the Children’s National Heart Institute, and Larisa Tereshchenko, M.D., Ph.D., FHRS, a researcher with the Knight Cardiovascular Institute at Oregon Health and Science University, establish a strong foundation for a running hypothesis: Replacing BPA- and DEHP- leaching plastics for alternative materials used to create medical devices may help patients on dialysis, and others with impaired immune function, live longer.

While Drs. Tereshchenko and Posnack note clinical studies and randomized controlled trials are needed to test this theory, they gather a compelling argument by examining the impact exposure to chemicals from plastics used in dialysis have on a patient’s short- and long-term health outcomes, including sudden cardiac death (SCD).

“As our society modifies our exposure to plastics to mitigate health risks, we should think about overexposure to plastics in a medical setting,” says Posnack. “The purpose of the review in HeartRhythm is to gather data about the impact chemical compounds, leached from plastic devices, have on cardiovascular outcomes for patients spending prolonged periods of time in the hospital.”

In this review, the authors explore chemical risk exposures in a medical setting, starting with factors that influence sudden cardiac death (SCD) among dialysis patients.

Why study dialysis patients?

SCD in dialysis patients accounts for one-third of deaths in this population. This prompts a need to develop prevention strategies, especially among patients with end-stage renal disease (ESRD).

The highest mortality rate observed among dialysis patients is during the first year of hemodialysis, a dialysis process that requires a machine to take the place of the kidneys and remove waste from the bloodstream and replenish it with minerals, such as potassium, sodium and calcium. During this year, mortality during hemodialysis is observed more frequently during the first three months of treatment, especially among older patients.

Possible reasons for an increased risk of an earlier death include chemical exposure, which is casually associated with altered cardiac function, as well as genetic risks for irregular heart rhythms and heart failure. In the HeartRhythm review, Drs. Tereshchenko and Posnack analyze factors that influence mortality:

Hemodialysis treatment, dialysis, is associated with plastic chemical exposure

Drs. Tereshchenko and Posnack note that dialysis tubing and catheters are commonly manufactured using polyvinyl chloride (PVC) polymers. The phthalate plastics used to soften PVC can easily leech if exposed to lipid-like substances, like blood. Research shows phthalate chemical concentrations increase during a four-hour dialysis.

Di(2-ethylhexyl) phthalate (DEHP) is a common plastic used to manufacture dialysis tubes, thanks to its structure and economy.

Bisphenol-A (BPA) is another common material used in medical device manufacturing. From the membranes of medical tools to resins, or external coatings and adhesives, BPA leaves behind a chemical residue on PVC medical devices.

In reviewing the research, the authors find dialysis patients are often exposed to high levels of DEHP and BPA. The amount of exposure to these chemicals varies in regards to room temperature, time of contact, other circuit coatings and the flow rate of dialysis. A faster flow rate correlates with reductions in chemical leaching and lower mortality rates.

Plastic chemical exposure is casually associated with altered cardiac function

Drs. Tereshchenko and Posnack note a causal relationship already exists between chemicals absorbed from plastics and cardiovascular outcomes.

Dr. Posnack’s previous research found BPA concentrations impaired electrical conduction in neonatal cardiomyocytes – young, developing heart cells – potentially altering the heart’s normal rhythm and function.

To the best of their knowledge, no clinical research has been conducted on DEHP exposure and SCD. However, proof-of-concept models find in vivo phthalate exposure alters autonomic regulation, which can slow down natural heart-rate rhythm and create a lag in recovery time to stressful stimuli. For humans, this type of stressful stimulation would be equivalent to recovering from a bike ride, car accident, or in this case, ongoing dialysis treatment with impaired immune function.

In other models, BPA exposure has been shown to cause bradycardia, or a delayed heart rate. In excised whole heart models, BPA has also been shown to alter cardiac electrical activity.

Abnormal electrophysiological substrate in end-stage renal disease

Since the heart and kidneys work in tandem to transport blood throughout the body, and manage vital functions, such as our heart rate, blood flow and breathing, the authors cite additional factors that lead to ongoing heart and kidney problems, with a look at end-stage renal disease (ESRD).

General heart-function kidney risks include abnormal electrophysiological (EP) substrate, the underlying electrical activity of the cardiac tissue, and genetic risk factors, including the TBX3 gene, a gene associated with a unique positioning of the heart and SCD.

“We don’t want to cite alarm about having a medical procedure or about relying on external help, such as dialysis, for proper kidney function,” says Posnack. “Especially since dialysis is a life-saving medical intervention for patients with inadequate kidney function.”

Pre-existing abnormal EP substrate interacts with plastic chemical exposure in incident dialysis, which increases risk of SCD in genetically predisposed ESRD patients

To summarize their findings, Drs. Tereshchenko and Posnack list a handful of support areas, starting with observations about reductions in cardiovascular mortality and SCD following kidney transplants. They note hemodialysis catheters are associated with larger DEHP exposure and a higher risk of SCD, compared to arteriovenous fistulas, highways surgically created to connect blood from the artery to the vein.

Drs. Posnack and Tereshchenko also note a correlative observation about higher SCD rates observed six hours after hemodialysis, when peak levels of DEHP and BPA are circulating in the bloodstream.

To compare and control for these factors among dialysis patients, the researchers cite different mortality patterns with hemodialysis and peritoneal dialysis. Patients on hemodialysis experience higher mortality during the first year of treatment, compared to peritoneal dialysis, who have higher mortality rates after the second year of treatment. Hemodialysis relies on a machine to take the place of kidney function, while peritoneal dialysis relies on a catheter, a small tube surgically inserted into the stomach.

“Our goal is to build on our previous research findings by analyzing variables that have yet to be studied before, and to update the field of medicine in the process,” says Dr. Posnack. “This includes investigating the cardiovascular risks of using BPA- and DEHP-materials to construct medical devices. Ultimately, we hope to determine whether plastic materials contribute to cardiovascular risks, and investigate whether patients might benefit from the use of alternative materials for medical devices.

Drs. Tereshchenko and Posnack note that despite the associations between chemical exposure from medical devices and increased cardiovascular risks, there are no restrictions in the United States on the use of phthalates and BPA chemicals used to manufacture medical devices.

Their future research will explore how replacing BPA- and DEHP-leaching plastics influence mortality and morbidity rates of ESRD patients on dialysis, as well as other patients exposed to repeat chemical exposure, such as patients having cardiac surgery.

“We want to make sure we identify and then work to minimize any potential risks of plastic exposure in a medical setting,” adds Dr. Posnack. “Our goal is to put the health and safety of patients first.”

Dr. Posnack’s research is funded by two grants (R01HL139472, R00ES023477) from the National Institutes of Health.