DOI

10.17077/etd.qzv1ctod

Document Type

Thesis

Date of Degree

Fall 2016

Access Restrictions

Access restricted until 02/23/2020

Degree Name

MS (Master of Science)

Degree In

Biomedical Engineering

First Advisor

Evan D. Abel

First Committee Member

Evan Dale Abel

Second Committee Member

James A Ankrum

Third Committee Member

Michael A Mackey

Abstract

Lipotoxic cardiomyopathy increases the risk of heart failure in obese patients by adversely altering heart structure and function via toxic lipid specie mediated cellular stress and cell death. Increased fatty acid uptake and esterification in cardiomyocytes increases toxic lipid intermediates. These cardiotoxic lipid species such as diacylglycerol have recently been shown to deacidify lysosomes in cardiomyocytes by activating protein kinase C βII mediated NADPH oxidase 2 generation of superoxide that inhibits proton pumps on lysosomal membranes by S-nitrosylation. Autophagy, a lysosome dependent cellular survival process, is impaired upon cardiomyocyte lipid-overload due to inhibition of pH-dependent proteolytic autophagosome degradation in the lysosome. Subsequent accumulation of autophagic vesicles heightens cardiomyocyte sensitization to additional stresses of ischemia-reperfusion or ER dysfunction, culminating in impaired cardiac metabolic flexibility leading to cell death. Low cardiomyocyte regenerative capacity calls for strategies to preserve cell number in states of increased stress, such as lipid-induced impairment of autophagy. Lysosome-targeted reacidifying devices can provide an effective means to restore autophagic flux.

In this thesis, a therapeutic strategy utilizing poly(DL-lactide-co-glycolide) (PLGA) nanoparticle degradation to reacidify lysosomes and revert cardiotoxic lipid specie induced blockade in autophagic flux in cardiomyocytes is presented. Endocytosed PLGA acidic nanoparticles were designed to rapidly degrade and release acidic monomers in lysosomes to restore pH dependent phosphatase and cathepsin L activity in cardiomyocytes with acute lipotoxicity. Optimized pre-palmitate treatment periods demonstrated that PLGA nanoparticles with polyethylenimine cationic surface coatings provide an effective restoration of autophagic flux in the presence of lipid-overload modeled by acute palmitate treatment in cardiomyocytes.

Public Abstract

With the onset of accessible fatty diets in cultures globally, cardiovascular related deaths have risen to the leading mortality worldwide. Excess fat supply increases fat buildup in heart muscle and produces toxic molecules that cause fundamental changes to heart structure and function. Specifically, generation of reactive oxygen inhibit a ‘self-eating’ cellular survival process known as autophagy by deacidifying lysosomes in heart muscle cells. Blocked autophagy is detrimental to heart structure and function by increasing cell death. Autophagic inflexibility due to increased fat-derived toxic molecules contributes to cardiac fragility and subsequently increases heart failure in instances of additional stress to the heart, such as a heart attack. Devices designed to release acid upon delivery to the lysosome could restart autophagy and reduce the potential for heart failure. The FDA approved acidic biomaterial poly(DL-lactide-co-glycolide) is an attractive building block from which these devices can be made. A proof-of-principle reacidification of lysosomes for restored autophagy and long-term prevention of heart failure in obese patients is demonstrated in this thesis.

Keywords

autophagic flux, lipotoxic cardiomyopathy, lysosomal pH, nanoparticles, poly(DL-lactide-co-glycolide), reacidification

Pages

x, 72 pages

Bibliography

Includes bibliographical references (pages 68-70).

Copyright

Copyright © 2016 Frederick Martin Zasadny

Available for download on Sunday, February 23, 2020

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