Michael Sayegh

BME PhD Defense Presentation

Date: May 19, 2021

Time: 3:00 PM

Zoom Link: https://zoom.us/j/98388084429  

Committee Members:

Rebecca D. Levit, MD (Advisor)

W. Robert Taylor, MD PhD

Andrés J. García, PhD 

Rabindra Tirouvanziam, PhD

Nick Willett, PhD

Title: Purinergic hydrogels for cardiovascular applications

Thesis abstract:

Despite great advances, ischemic cardiovascular disease is still the leading cause of morbidity and mortality, and novel interventions are needed to improve outcomes. The best current treatment for ischemia, rapid reperfusion via percutaneous coronary intervention, causes subsequent injury due to return of bloodborne oxygen and inflammatory agents.

The innate immune system orchestrates a complex, multi-phasic response to ischemia/reperfusion injury. Neutrophils are the earliest cells to infiltrate, and neutrophil extracellular traps (NETs) are spuriously generated, worsening inflammation. Adenosine is a known anti-inflammatory and vasodilatory agent, and a potent inhibitor of NETs in vitro. However,  the short lifespan of adenosine in circulation and its dose-limiting side effects complicate systemic administration.  Endogenous sources of adenosine include the ecto-nucleotidases CD39 and CD73, which catalyze its production from the phosphorylated adenine nucleotides.

In this work, we first tested the role of NETs in myocardial injury in vitro using cardiomyocyte cultures, and in vivo by NET introduction into health hearts. We investigated the mechanism of NET induced cardiac dysfunction by increased leukocyte infiltration and fibrosis. We tested a CD73-functionalized PEG hydrogel for neutrophil inhibition in vitro and adenosine augmentation in the ischemic mouse hindlimb. We saw an increase in hindlimb perfusion in response to the CD73-functionalized hydrogel. Combined CD39 and CD73 functionalization of a higher density hydrogel extended the release time and widened the pool of substrate for the enzyme cargo. Delivery of CD39 and CD73 functionalized hydrogels to the heart preserved cardiac function post-ischemia/reperfusion and decreased markers of immune activation and NETosis.

Our approach for local, sustained and on-demand adenosine augmentation via biomaterial-supported enzymes allows the examination of the role of adenosine in counteracting novel disease processes such as NETosis, unlocks the anti-inflammatory and perfusion benefits of adenosine and widens its application as a therapeutic in ischemic cardiovascular disease.