Tag Archive for: Nikki Posnack

bisphenol A

Alternative synthetic compound might offer safer solution to children’s health

bisphenol A

Not only is bisphenol A (BPA) added to medical equipment used to treat patients, it can also be found in 60% of neonatal intensive care unit (NICU) supplies, such as bandages and items for feeding, suggesting that occupational and clinical environments have a higher exposure to this synthetic compound.

Researchers at Children’s National Hospital found that a commonly used plastic, known as bisphenol S (BPS), was the least disruptive to cardiac electrophysiology and may serve as a safer chemical alternative for plastic medical devices used to treat vulnerable populations compared to other compounds, according to a new preclinical study published in Toxicological Sciences.

For decades, the medical device industry has used bisphenol chemicals known to antagonize ion channels, impair electrical conduction and trigger arrhythmias that affect the overall cardiovascular health in children. Not only is bisphenol A (BPA) added to medical equipment used to treat patients, it can also be found in 60% of neonatal intensive care unit (NICU) supplies, such as bandages and items for feeding, suggesting that occupational and clinical environments have a higher exposure to this synthetic compound.

Yet, very little is known about the downstream impact of BPA, BPS or bisphenol F (BPF) exposure on cardiac physiology.

To shed light on the safety profile of BPA and its alternatives BPS and BPF in plastic medical devices, Children’s National researchers present the first study that compares the acute effects of these three chemicals on cardiac electrophysiology in a preclinical model.

According to the researchers, children should continue receiving medical care to treat their condition.

“It is important to investigate iatrogenic plastic chemical exposures in young patients, as biomonitoring studies have reported elevated chemical exposures in NICU and pediatric intensive care unit patients,” said Devon Guerrelli, M.S., a Ph.D. candidate at Children’s National. “Our lab is actively working with cardiac surgeons to investigate patient exposure to both BPA and phthalate plasticizer chemicals. Patients and their parents can rest assured that our team’s priority is safety and advancement of the field.”

Future studies are needed to fully understand the chemicals’ safety on cardiac electrical and mechanical function due to notable biological differences between humans and preclinical models. The researchers call for the scientific community to explore the impact of these compounds on other organ systems by comprehensively assessing intracellular targets, genomic and proteomic expression profiles.

While health concerns remain, there is no consensus among the scientific community on the potential use of safer compound alternatives in pediatric plastic medical devices.

“First, a variety of preclinical models have been used by the scientific community to assess BPA toxicity. But, there is considerable variability between these different models, including differences in ion channel expression, which may produce conflicting results and limit extrapolation of the data to humans,” said Nikki Posnack, Ph.D., principal investigator at Children’s National Sheikh Zayed Institute for Pediatric Surgical Innovation and senior author. “Accordingly, in the presented study, we tested the effects of bisphenol chemicals using three different preclinical models. Second, studies assessing the safety profile of new structural analogs to BPA are limited.”

The researchers compared the cardiac safety profile of BPA, BPS and BPF by using a whole-cell voltage clamping recording on cell lines to study voltage-gated channels Nav1.5, Cav 1.2 and hERG, allowing the measurements of the cell’s electrical properties and total current through all the channels on a membrane in non-human subjects and cardiomyocytes human cell lines. Results of the study found that BPA was the most potent inhibitor of sodium, calcium and potassium channel currents compared to the alternatives BPS and BPF. BPA and BPF exposure also slowed atrioventricular conduction and increased atrioventricular nodal refractoriness.

“Based on our findings, acute exposure to high concentrations of BPA could lead to changes in cardiac electrophysiology,” said Tomas Prudencio, M.S., a research technician at Children’s National and lead author. “This includes slowing of electrical conduction from the atria to the ventricles, which would present as a prolongation of the PR interval in an electrocardiogram.”

newborn baby

Study suggests chronic hypoxia delays cardiac maturation in CHD

newborn baby

Every year, nearly 40,000 babies are born with a congenital heart defect (CHD) — the leading cause of birth defect-associated infant illness and death.

Every year, nearly 40,000 babies are born with a congenital heart defect (CHD) — the leading cause of birth defect-associated infant illness and death. An event that may contribute to cyanotic CHD is the lack of oxygen, known as hypoxia, before and after birth, impacting gene expression and cardiac function that delay postnatal cardiac maturation, according to a new pre-clinical model led by researchers at Children’s National Hospital.

Single ventricle, transposition of the great arteries, truncus arteriosus and severe forms of tetralogy of Fallot, such cyanotic congenital heart diseases have lower circulating blood oxygen levels. The lack of oxygen in the blood begins prenatally and continues after birth until definitive repair, suggesting a delay on cardiac maturation.

There is little research on the underpinnings that explain the lack of oxygen’s effects on the developing heart, which could help inform adequate therapies in the pediatric population to promote cardiovascular health across the lifetime. The researchers developed the first pre-clinical model that explores the effects of chronic hypoxia in perinatal and postnatal stages on the developing heart under conditions seen in cyanotic CHD.

“To the best of our knowledge, ours is the first study to perform complete gene expression arrays on animals after perinatal hypoxia,” said Jennifer Romanowicz, senior noninvasive imaging fellow at Boston Children’s Hospital and lead author of the study. “Not only did these studies allow us to determine the effects of hypoxia on heart development, but the detailed results of our study will be available to other researchers to independently address other questions about perinatal hypoxia and heart development.”

The study published in the American Journal of Physiology: Heart and Circulatory Physiology suggests that chronic lack of oxygen alters the electrical properties of heart tissue, called the electrophysiological substrate, and the contractile apparatus, a muscle composed of proteins that control cardiac contraction. Multiple genes involved with the contractile apparatus were expressed differently in the non-human subjects.

“What was remarkable was that most abnormalities normalized after the animals recovered in normal oxygen levels,” said Romanowicz. “This is an optimistic sign that early repair of cyanotic congenital heart disease may allow the heart to finish development.”

The researchers placed pregnant non-human subjects in hypoxic chambers starting on embryonic day 16, mimicking the second trimester in humans. The same subjects gave birth in the hypoxic chambers, and the newborns were kept there until postnatal day eight when the heart muscle maturation is nearly complete. To understand how human infants recover with normalized oxygen levels after surgical repair of cyanotic CHD, the researchers moved hypoxic subjects to normal oxygen conditions for recovery and tested again at postnatal day 30.

“Next steps include using a pre-clinical model of cyanotic congenital heart disease that more accurately represents human neonatal physiology,” said Devon Guerrelli, Ph.D. candidate at Children’s National. We plan to work with the cardiac surgery team at Children’s National to investigate changes in the myocardium due to hypoxia in pediatric patients who are undergoing surgical repair.”

Nikki Posnack, Ph.D., principal investigator at Sheikh Zayed Institute for Pediatric Surgical Innovation and Nobuyuki Ishibashi, M.D., director of Cardiac Surgery Research Laboratory at Children’s National, led and guided the team of researchers involved in the study.

pile of plastic bottles

The linkage between chemicals used in plastics and cardiovascular disease

pile of plastic bottles

For people across the globe, plastics are synonymous with modern life and it’s impossible to avoid exposure to them, including clinical environments where a variety of frequently used materials, such as tubing and blood storage bags, are made from plastics.

For people across the globe, plastics are synonymous with modern life and it’s impossible to avoid exposure to them, including clinical environments where a variety of frequently used materials, such as tubing and blood storage bags, are made from plastics. Led by Nikki Posnack, Ph.D, principal investigator at The Sheikh Zayed Institute for Pediatric Surgical Innovation at Children’s National Hospital, a team of Children’s National researchers has been studying the potential effects of chemicals found in plastics, such as BPA and DEHP, as possible contributors to cardiovascular disease.

Along with conducting proprietary studies of the potential effects, Posnack and her team recently reviewed available scientific studies to further identify and illuminate the potential links between exposure to the synthetic additives contained in plastics and cardiovascular mortality. The article was published this month in Nature Reviews Cardiology.

In the article Posnack cites a 10-year longitudinal study with the finding that high exposure to BPA was associated with a 46-49% higher hazard ratio for cardiovascular and all-cause mortality, compared with low exposure to BPA.

“Plastics may be indispensable materials, but their ubiquity does raise concerns about the effects of our continuous exposure to plasticizer additives like di(2-ethylhexyl) phthalate (DEHP) and synthetic chemicals used to create polymers like BPA,” said Posnack. “Although disease causation can be difficult to pinpoint in population and epidemiological studies, experimental work has clearly demonstrated a direct link to plastic chemicals and cardiac dysfunction. It is clear that future collaborative endeavors are necessary to bridge the gap between experimental, epidemiological and clinical investigations to resolve the impact of plastics on cardiovascular health.”

Nikki Gillum Posnack

Nikki Posnack, Ph.D, principal investigator at The Sheikh Zayed Institute for Pediatric Surgical Innovation at Children’s National Hospital.

Posnack added that, given the omnipresence of plastics and their related chemicals, biomonitoring studies have reported detectable levels of DEHP and BPA in 75-90% of the population. Occupational or clinical environments can also result in elevated exposures to these dangerous chemicals. Previous epidemiological studies have reported links between elevated urinary levels of phthalate or bisphenol, common additives in plastic, and an increased risk of coronary and peripheral artery disease, chronic inflammation, myocardial infarction, angina, suppressed heart rate variability and hypertension.

Additionally, available research has shown that incomplete polymerization or degradation of BPA-based plastic products can result in unsafe human exposure to BPA. Despite these links, the article points out, both BPA and DEHP are still manufactured in high volumes and are used to produce a wide variety of consumer and commercial products.

Further exploring implications for pediatrics, a June 2020 article published by Posnack in Birth Defects Research looks at the potential effects of plastic chemicals on the cardiovascular health of fetal, infant and pediatric groups. The article highlighted experimental work that suggests plasticizer chemicals such as bisphenols and phthalates may exert negative influence on pediatric cardiovascular health. The article systematically called out areas of concern supported by research findings. Also addressing current gaps in knowledge, Posnack outlined future research endeavors that would be needed to resolve the relationship between chemical exposures and the impact on pediatric cardiovascular physiology.

In related work, Posnack and her team are expanding their work on plastics used in blood bags to also investigate the role of blood storage duration on health outcomes. A recently published first study demonstrates that “older” blood products (stored 35 or more days) directly impact cardiac electrophysiology, using experimental models. Published October 22, 2020 in the Journal of the American Heart Association, the study concludes that the cardiac effects are likely caused by biochemical alterations in the supernatant from red blood cell units that occur over time, including but not limited to, hyperkalemia (elevated potassium levels).

Nikki Gillum Posnack

Research team develops new and improved method for studying cardiac function

Nikki Gillum Posnack

While researching how plastic affects heart function in sensitive populations, such as children born with congenital heart defects, Children’s National researcher Nikki Posnack, Ph.D., led a team that developed a new and improved, replicable method of performing simultaneous dual optical mapping to examine electrical activity and calcium for the study of cardiac function.

Since arriving at the Sheikh Zayed Institute for Pediatric Surgical Innovation, researcher Nikki Gillum Posnack, Ph.D., a principal investigator with the institute and assistant professor of pediatrics at the George Washington University School of Medicine and Health Sciences, has been focused on examining how exposure to plastic affects heart function in sensitive populations, such as children born with congenital heart defects. She performs optical mapping to conduct this research, but the industry standard approaches of either using dual cameras or sequential single cameras were cost prohibitive and technically challenging while also diminishing the quality of the imaging results.

Fast forward to July 2019 when Dr. Posnack and her team published “Plasticizer Interaction With the Heart” in the journal Arrhythmia and Electrophysiology, which used imaging techniques to reveal the impact of plastic chemicals on the electrical activity of the heart. Dr. Posnack’s laboratory has since expanded this technique and revealed a new replicable method of performing simultaneous dual optical mapping to examine electrical activity and calcium handling in the heart.

Sharing a new method for studying cardiac function

This groundbreaking method is itself the focus of a new BMC Biomedical Engineering journal article titled “Lights, camera, path splitter: a new approach for truly simultaneous dual optical mapping of the heart with a single camera.”

The article compares and contrasts the current standard for dual camera simultaneous configurations and single camera sequential configurations to Dr. Posnack’s new single camera simultaneous configuration.

Simultaneous dual mapping systems use two probes and dual dyes – one for electrical voltage and the other for calcium. While dual-dye combinations like Di-4-ANEPPS with Indo-1, Di-2-ANEPEQ and calcium green have been developed to separate fluorescence signals by emission, these dye combinations can have spectral overlap, creating the need for non-ideal emission bandpass to negate spectral overlap and/or the inclusion of a calcium probe with an inferior dissociation constant. Additionally, dual-sensor systems require proper alignment to ensure that fluorescence signals are being analyzed from the same tissue region on each individual detector, which could lead to erroneous results. The dual-camera optical setup is expensive, technically challenging and requires a large physical footprint that is often not feasible for basic science and teaching laboratories conducting critical research.

As an alternative, some researchers use a single camera configuration to sequentially image the voltage and calcium probes using excitation light patterning. This approach also has limitations. These single-sensor designs use dual-dye combinations that require two or more excitation light sources, but share a single emission band. Like the dual camera system, this platform design is also technically challenging since the different excitation light wavelengths require light source triggering, camera synchronization and frame interleaving. Due to timing coordination, decreased frame rates, excitation light ramp up/down times and shutter open/close times, single system setups require shorter exposure times compared to dual sensor setups, diminishing the signal-to-noise quality without offering the same temporal fidelity. There is a cost advantage to the single camera system, however, because the additional camera is often one of the most expensive components.

This new single camera, simultaneous dual optical mapping approach is the first multiparametric mapping system that simultaneously acquires calcium and voltage signals from cardiac preparations, using a commercially available optical path splitter, single camera and single excitation light. Using a large field of view sCMOS sensor that is faster and more sensitive, this configuration separates the two emission bands for voltage and calcium probes and simultaneously directs them to either sides of the single, large camera sensor. This protocol employs a commonly used dual-dye combination (RH237 and Rhod2-AM). In contrast, other protocols may require genetically-encoded indicators or fluorescent probes that are not yet commercially available.

The team validated the utility of the approach by performing high-speed simultaneous dual imaging with sufficient signal-to-noise ratio for calcium and voltage signals and specificity of emission signals with negligible cross-talk. Demonstrating the need for simultaneous electrical and calcium sensors, they found that when ventricular tachycardia is induced, there is spatially discordant calcium alternans present in different regions of the heart even when the electrical alternans remain concordant.

Having eliminated the second camera as well as the need for multiple excitation light sources, light pattering and frame interleaving, this system is more cost effective, simpler, and can be easily setup by various types of researchers, not just those with engineering backgrounds.

With a limited research budget and a background in physiology, Dr. Posnack worked collaboratively with her post-doctoral fellow Rafael Jaimes III, an engineer in the Sheikh Zayed Institute for Pediatric Surgical Innovation, to develop a cost-effective system that would enable her to truly study the effects of plastics on the heart.

Multidisciplinary approach

“We’re fortunate to have a multidisciplinary team in the Sheikh Zayed Institute so that I could work with an engineer to develop the technology and system we needed to propel our research,” said Dr. Posnack. “There are so many researchers who have the science background, but not necessarily the technical aptitude, and they get stymied in their research, so we’re proud that this paper will help other researchers replicate the system to study cardiac function.”

The research paper was funded by a grant from the National Institutes of Health as well as support from the Children’s Research Institute, Children’s National Heart Institute and the Sheikh Zayed Institute for Pediatric Surgical Innovation.

The applications for this optical mapping system are significant and Dr. Posnack has been consulted by other research teams looking to implement it in their labs. Additionally, Dr. Posnack has collaborated with several neuroscience teams at Children’s National Hospital, including one that is investigating the effects of hypoxia on brain and heart development, and another that is interested in using image modalities and data processing to analyze calcium as an indicator of neuron firing.

Dr. Posnack continues to use this new dual optical mapping system to further her research as she anticipates the publication of a new article about age-dependent changes in cardiac electrophysiology and calcium handling.