Delaware's Biomedical Research Catalyst
Research Theme – Cardiovascular
Mentor: Dr. Babatunde Ogunnaike, UD – Chemical Engineering
Research Title: Biomaterials for Cardiac Tissue Engineering
Abstract: The engineering of cardiovascular (CV) grafts that mimic the properties of native tissue remains a formidable research and clinical challenge and a principal area for translational research emphasis. In particular, controlling the organization of cells in engineered tissues is a critical issue, and there is a important and well-recognized need to identify physical and molecular pathways that can be manipulated to direct the formation of desirable constructs.
Unfortunately, little is known about (i) the types of physical substrates that might be most effective in guiding multi-cellular assembly, (ii) the cellular mechanisms that drive the formation of integrated structures ex vivo, and (iii) the effects of organizational strategies on the component cells of engineered tissues. With this application, we seek initial funds for a new interdisciplinary research program to address these areas within the context of developing critically-needed implants to treat congenital and acquired CV disease.
Mammalian CV systems are essentially closed, fluid-filled networks of conduits that contain varying degrees of muscle to control luminal volume and restrict or generate flow. Implantable biosynthetic conduits that reproduce essential CV functions would be valuable for the treatment of adult disease but are also uniquely suited for the repair of pediatric defects. Indeed, CV tissue engineering will offer opportunities for the growth and remodeling of implants while minimizing thrombogenesis and intimal hyperplasia and providing for appropriate physiologic responsiveness and graft self-renewal over the lifetime of the implant recipient. Our long-term goal is the development of composite vessels (see Figure 1) with bio-synthetic components that act initially as scaffolds to provide mechanical support while recruiting the appropriate cellular/biological components but that later degrade leaving a completely biologic vessel. The development of such implants will require advances in multiple areas including, 3D fabrication technologies, molecular and physical mechanisms to control cell distribution and function, and evaluating interactions between scaffold materials, cells, and the host physiology. Once fully developed, envisioned applications would involve (i) production of synthetic composite tubes comprising nonoriented and oriented nanofibrous scaffolding, (ii) seeding with autologous cells to populate the layers and establish a biosynthetic device that responds to the in vivo mechanical and humoral environment, and (iii) implantation into a host where conversion to a completely biological conduit would proceed by interaction with the host physiology. Thus, there are substantial areas of research needed in the field and clear opportunities for interdisciplinary research programs.
Accordingly, we have assembled a research team composed of investigators with expertise in polymer and biopolymer design, polymer characterization, CV cell biology and physiology, human CV pathophysiology, and system biology so that the properties of engineered CV grafts can ultimately be engineered from the molecular through the macroscopic, optimized, tested and prepared for eventual transfer into the clinical setting. The proposed research is interdisciplinary and cross institutional involving investigators from the Alfred I duPont Hospital for Children, the DuPont Experimental Station, and the University of Delaware. Together, the team will develop an interdisciplinary research program in CV engineering using funds from INBRE to seed key areas of research and sponsor two graduate students, who will be under the direct supervision of Drs. Akins and Rabolt. Undergraduates will be encouraged to participate in the research program by working in the lab for course credit or in preparation for senior honors theses in their home department, and a course focusing on cardiovascular dynamics and the associated engineering challenges will be developed for advanced undergraduates and graduate students. The investigators will continue to submit conventional and MPI-based R01 applications to further the development of the scientific goals of the program and to continue the development of graduate and undergraduate training initiatives in CV tissue engineering beyond the time-frame of the INBRE mechanism.
The present application centers on two focused aims that address areas critical to the development of the interdisciplinary program. Both aims center on the muscular component (i.e. medial layer) of biosynthetic conduits. The first aim investigates the preparation of a complex composite conduit evaluated with a simple cell system – human smooth muscle cell line, and the second aim investigates the effects of a relatively simple biomaterial on the complex cell:cell interactions found in primary cardiac cells. This design takes full advantage of the expertise of the research team, leverages available INBRE Core Resources, and fits within the budgetary requirements of the INBRE mechanism.
Mentor: Dr. Ulhas Naik, UD – Biological Sciences
Research Title: Endothelial Progenitor Cell Function in Chronic Kidney Disease
Abstract: The endothelium lines the lumen of blood vessels and is a key regulator of vascular homeostasis. A loss of this homeostasis, or endothelial dysfunction, is recognized as a key process in the development and progression of chronic kidney disease (CKD). Endothelial dysfunction is a primary event in the development of atherosclerosis and it is now recognized that cardiovascular disease (CVD) and its complications are the most important cause of morbidity and mortality in CKD.
Therefore, an understanding of the mechanisms responsible for endothelial dysfunction in CKD is important for improving renal and cardiovascular outcomes. Endothelial progenitor cells are stem cells that are mobilized into the circulation from the bone marrow and can help maintain endothelial function by contributing to the replacement of damaged endothelial cells.
Endothelial progenitor cell function has been shown to be dependent on the ability of EPCs to release nitric oxide. Nitric oxide activity may be impaired in CKD as a result of increased production of the free radical superoxide and elevated levels of asymmetric dimethylarginine, an endogenous inhibitor of nitric oxide synthesis. Studies of endothelial progenitor cells in renal disease have been limited to end stage renal disease (ESRD) and have not investigated the mechanisms of functional impairment. Due to the progressive nature of CKD and the fact that the risk for CVD is elevated early in the progression of CKD, it is important to understand the mechanisms of endothelial dysfunction in CKD to develop early interventions that slow the progression of disease and reduce the risk of CVD. Our global hypothesis is that EPC function is impaired in CKD prior to the development of ESRD contributing to endothelial dysfunction and cardiovascular risk. We have developed in vitro techniques for the study of EPCs and will begin assessing EPC function in human CKD. In this INBRE application we propose to develop the 5/6 ablation-infarction (A/I) rat model of CKD and study in vitro function (migration and incorporation into tube structures) of EPCs isolated from the peripheral blood of these rats.
To gain further insight into EPC function we propose to study the ability of EPCs to participate in vascular repair following carotid artery injury in 5/6 A/I rats. These studies are novel in that they would be the first to study EPC function in an animal model of CKD. Further, we would be in the unique position of being able to translate our findings in the 5/6 A/I animal model of CKD to our ongoing human work. Consistent with the goals of INBRE, these studies will provide preliminary data for an R01 proposal (end of year 2) to continue to elucidate the mechanisms of EPC dysfunction in our animal model.
Therefore, the successful completion of this project would be expected to have a potentially important impact on maintaining renal function and reducing cardiovascular risk in CKD patients. Our research team is made up of faculty in the Department of Health, Nutrition, and Exercise Sciences and the Department of Biology at the University of Delaware. We will utilize the Bioimaging Core Lab at the Delaware Biotechnology Institute and the Center for Translational Cancer Research.
Additionally, this work will provide both graduate and undergraduate students with hands on research training.
Mentor: Dr. William Weintraub, Christiana Care Center for Clinical Outcomes Research
Research Title: Physiological Effects of Dietary Sodium in "Salt Resistant" Humans
Abstract: Recent evidence suggests that sodium may contribute to structural and functional abnormalities, independent of blood pressure (BP). Specifically, data in experimental animals suggest that sodiumloading – independent of changes in BP – promotes cardiac, vascular, and renal damage.
Deleterious physiological changes from excess sodium have been documented in spontaneously hypertensive rats, and – with particular relevance for this proposal – in normotensive Wistar-Kyoto rats. In short, there is a growing appreciation that elevated BP is not the only problem related to excess dietary sodium.
The objective of this INBRE proposal is to build upon these animal studies by exploring these issues in humans; these mechanistic animal studies need to be translated to human studies. We will examine the physiological effects of dietary sodium in a group that we characterize as having salt resistant BP (< 5 mmHg change in mean BP going from a low to high sodium diet). Subjects will complete a 17-day dietary trial (3-day run-in of 100 mmol/day of sodium, 7 days high sodium (350 mmol/day) and 7 days of low sodium (20 mmol/day).
All foods will be prepared for the subjects thought an established collaboration with Christiana Care Health System. Dietary compliance will be assessed by collecting 24 hours of urine on the last day of each condition; salt sensitivity of BP will be individually assessed via 24-hour ambulatory BP on the last day of each condition. Our overall hypothesis is that dietary sodium will adversely affect circadian BP rhythm, arterial function, and venous function. Circadian BP rhythm will be assessed using the night time dip in pressure; arterial function will be assessed via pulse wave velocity and augmentation index; endothelial function will be assessed via brachial flow-mediated dilation; and venous function will be assess via venous occlusion plethysmography.
The strength of this proposal is the sophisticated physiological assessment that will be performed under well-controlled dietary conditions in a group that does not have “salt sensitive” BP. Habitual sodium intake is high in the general population, therefore our focus will be on demonstrating differences in these variables between the high and low sodium conditions.
This proposal brings together a multi-disciplinary team which includes individuals from Physiology, Cardiology, Medical Technology, Nutrition, and Nursing. Two different institutions in the state of Delaware are involved (University of Delaware and Christiana Care Health System). This team represents a true collaborative partnership. This proposal will also provide hands-on research experience for undergraduate and graduate students. The data collected under this funding mechanism will form the basis of an R01 submission.
Mentor: Dr. William Weintraub, Christiana Care Center for Clinical Outcomes Research
Research Title: Clinical Outcomes Center Effect of Kidney Function on the Association Between Obesity and Cardiovascular Events
Abstract: The purpose of this proposal is to clarify the clinical impact of a decline of kidney function on the risk of cardiovascular (CV) events in patients overweight or obese. Recent reports have demonstrated that in the general population, being overweight or obese is a known risk factor for CV events and death.
Paradoxically, a large body of evidence has shown that in the population of end-stage renal disease (ESRD) patients, a high body mass index (BMI) seems to provide a longer survival, compared to a BMI<25. However, in the general population studies, individuals are followed up for 15 to 30 years whereas ESRD patients have a much shorter life expectancy.
Moreover, all the studies conducted in the ESRD population have been based on BMI reported at initiation of hemodialysis. It is well known that prior to hemodialysis, patients with low kidney function often experience weight loss because of uremia-induced anorexia or severe exacerbation of comorbidities.
Patients with normal or low BMI at dialysis’ initiation may be in fact patients who are in the process of losing weight because of poor health. Whether obesity is also more likely to be associated with longer survival in patients with a decrease in kidney function prior to the stage of ESRD is unclear.
We propose to examine the association between BMI and kidney function on the risk of CV events in a population of patients followed for their clinical care in several out‐patient clinics in Delaware, all using electronic medical records. This study will be a retrospective longitudinal analysis of patients. We will first determine whether a longitudinal decline in kidney function modifies the association between obesity and CV events (Aim 1).
To do so, we will develop longitudinal models of BMI and BMI + kidney function, and cross-correlate each of these with CV cumulative event rates. Similar cross-correlation patterns would indicate that kidney function does not modify the association between obesity and CV events. Then, we will determine the effects of weight changes prior to the initiation of hemodialysis on CV events rates in patients in hemodialysis (Aim 2). To do so, we will use a Cox proportional hazard regression model to estimate hazard ratios for weight change and other covariates potentially influencing cardiovascular event rates potentially influencing cardiovascular event rates.
Mentor: Dr. William Weintraub, Christiana Care Center for Clinical Outcomes Research
Research Title: Effect of Renin Inhibition on Cardiovascular Autonomic Nerve Function in Diabetes
Abstract: Diabetic neuropathy, a serious and common complication of diabetes, is a heterogeneous disorder affecting different parts of the nervous system. Most common among the neuropathies are diabetic autonomic neuropathy and distal symmetric polyneuropathy (DPN). DPN causes impaired sensation of the lower extremities predisposing individuals to neuropathic foot ulcers, which may lead to infection and lower extremity amputations. The rate of amputation is 10 times higher for patients with diabetes than those without diabetes. Cardiovascular autonomic neuropathy is the most studied and clinically important form of diabetic autonomic neuropathy. Meta-analyses of published data demonstrated that reduced cardiovascular autonomic function, as measured by heart rate variability, is strongly associated with increased risk of silent myocardial ischemia and mortality. If left controlled, persistent overactivity of the autonomic nervous system will result in irreparable cardiac damage, culminating in hypertension, cardiac muscle dysfunction and ultimate failure. Thus, it is vital to find new therapies to stop the development and progression of nerve dysfunction in order to reduce both morbidity and mortality.
Both metabolic and vascular defects have been implicated in the pathogenesis of diabetic neuropathy. Interventions to ameliorate diabetic neuropathy have been evaluated in clinical trials based on theories of pathogenesis.
The renin-angiotensin-aldosterone system (RAAS) plays an integral role in the regulation of the cardiovascular system. Inhibition of the RAAS with angiotensin-converting enzyme (ACE) inhibitors and angiotensin receptor blockers (ARBs) has shown varied results for the treatment of diabetic neuropathy. One explanation could be due to incomplete blockage of the RAAS. Aliskiren, a direct renin inhibitor, is the first in a new class of antihypertensives. Blocking the RAAS at the first point of the pathway may offer an important advantage over other RAAS inhibitors for the treatment of diabetic neuropathy by providing more complete blockage than downstream RAAS inhibitors. It is clear that both the RAAS and autonomic nervous system play integral roles in the development of diabetic neuropathy. The interaction between them, however, has not been studied sufficiently.
In the proposed study, we will assess the effect of direct renin inhibition on nerve dysfunction due to diabetes. To accomplish this goal a double-blind, placebo-controlled randomized trial involving two treatment arms (i.e.,  30 participants enrolled and randomized to 300 mg of Aliskiren;  30 participants enrolled and randomized to placebo) will be performed. In specific aims I and II, we will test the hypothesis that six weeks of targeted-intervention with Aliskiren will lead to changes in activity of the autonomic nervous system (e.g., enhanced parasympathetic function and improved sympathetic/parasympathetic balance with renin blockage) and improved peripheral nerve function. Cardiovascular autonomic function will be measured via assessment modalities of heart rate variability including a new method which evaluates power spectral analysis in combination with respiratory activity. DPN will be assessed via quantitative sensory threshold testing. Study data will be analyzed by repeated measures analysis of variance with 2 independent treatment groups (Aliskiren vs. placebo), and 2 repeated measures, baseline and 6 weeks post-intervention. The study is sufficiently powered (i.e., 80% power) to estimate a mean difference of 0.10 between baseline and follow-up for a measure of parasympathetic function.
Endothelial dysfunction has been demonstrated in individuals with diabetes and hyperglycemia has been implicated as a cause of dysfunction. Hyperglycemia also increases the production of angiotensin II in the vessel wall and stimulates vascular NAPH oxidase, increasing oxidative stress. RAAS inhibition may improve endothelial function by reduction of vascular oxidative stress. Studies utilizing both ACE-inhibitors and ARBs have been shown to improve endothelial function in patients with diabetes. The effect of Aliskiren on endothelial function in individuals with diabetes has not been examined. Thus, specific aim III will assess changes in flow mediated dilation, an established measure of vascular endothelial function. This will be performed in a subset of the study cohort. It is hypothesized that Aliskiren will show a positive trend indicating both enhanced vascular endothelial and nerve function. The ability to assess for a trend will provide mechanistic insights into how changes in nerve function are associated with improved blood flow and feasibility data for the development of future studies.
Research Title: Targeted Microbubbles for Contrast Enhanced Vascular Ultrasound Imaging
Abstract: Even though ultrasound is the safest and one of the most popular means of imaging, its utility is limited due to poor contrast – 20% of the 17 million echocardiographies performed in the United States in 2000 did not provide definitive diagnosis for coronary heart disease. Gas-filled encapsulated microbubbles have been clinically approved as vascular contrast agents for imaging of left ventricular function and tissue perfusion. Currently they are being investigated for use in molecularly targeted imaging and drug and gene delivery by fitting them with bio-molecules that will preferentially attach to target tissues and biomarkers. Targeted contrast agents will help in diagnosis and effective therapy for various cardiovascular diseases and cancers. Although such ideas have been demonstrated in the lab, lack of a quantitative model is preventing a rational strategy for quick translation to their clinical use. Understanding, manipulating and controlling the mechanical and chemical responses of contrast agents are crucial for development of such a rational design strategy. In-vitro experiments with clinically approved contrast agents are proposed and mathematical techniques to develop models that will accurately describe and characterize the behaviors of free and targeted contrast agents. Modeling in conjunction with in-vitro experiments will be used to optimize target attachment and echo enhancement.
Mentors: Tom Force, MD; Ulhas Naik, PhD
Research Title: Extracellular Matrix Remodeling and Human Heart Failure
Abstract: Congestive heart failure (CHF) is a chronic, progressive disease with significant morbidity and mortality. The central element of the disease process is characterized as progressive geometric changes of ventricular myocardium in conjunction with functional deterioration, which is induced by dysregulation of normal compensatory mechanism against overwhelming injury and/or biomechanical stress.
Insight is lacking regarding the cellular and molecular regulatory mechanisms that protect the heart from rapid disease progression. It is crucial to understand the underlying mechanism of dysregulation that induces affected heart from physiological compensatory adaptation to progressive pathological maladaptation.
We have recently demonstrated that fibulin-2, an extracellular matrix (ECM) protein, modulates transformation growth factor (TGF)-b signaling that promotes ventricular remodeling after myocardial infarction (MI). ECM serves as an essential tissue reservoir in regulating biological activation of multiple growth factors, proteinases, and enzymes in addition to providing structural integrity as a connective tissue scaffold.
We hypothesize that fibulin-2 enhances TGF-b activation by releasing active TGF-b from inactive latent complex that is stored in ECM. The current project is to test whether this hypothesis is also true in advanced human heart failure. We will examine the degree of fibulin-2 expression, TGF-b activation level, and ECM remodeling (ECM synthesis and degradation) in the myocardial tissues from the patients with end-stage heart failure.
Also we will test prospectively whether the degree of ECM remodeling determines the prognosis after volume unloading interventions in advanced heart failure; (a) mitral valve replacement for mitral insufficiency and (b) left ventricular assist device (LVAD). Clinical data, serum markers, and patients’ activity levels will be assessed before and after interventions to correlate molecular, biochemical, and histological findings of myocardium.
The aims of this proposal are to determine whether up-regulation of fibulin-2 is associated with enhanced TGF-b activation and advanced ECM remodeling in the myocardium of end-stage human heart failure, and whether the degree of ECM remodeling rules the prognosis after ventricular unloading surgical interventions. This translational approach will generate clinical data whether inhibition of fibulin-2 will attenuate the progression of human heart failure after ventricular unloading.