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Polymeric Nanoparticles as Carriers for Antimicrobial Peptides: Factors Affecting Peptide and Membrane Interactions
Uppsala University, Disciplinary Domain of Medicine and Pharmacy, Faculty of Pharmacy, Department of Pharmacy. (Farmaceutisk fysikalisk kemi)ORCID iD: 0000-0001-5626-3959
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

As resistance towards conventional antibiotics is becoming more pronounced, cationic antimicrobial peptides (AMPs) have received considerable attention as possible therapeutic alternatives. Thousands of potent AMPs occur in humans, animals, plants and fungi as a natural part of the immune system. However, there are several challenges with AMP therapeutics related to formulation and delivery. Examples include proteolytic sensitivity and serum protein binding, resulting in quick degradation, loss of activity and clearance. Therefore, it is important to find a suitable drug delivery system to meet these protection and delivery challenges. Micro-/nanogels are loosely crosslinked polymer colloids with high water content that can be made to trigger at a wide range of stimuli. They have shown promise as delivery systems for AMPs, as the aqueous environment they create allows the peptides to maintain their natural conformation, while their gel networks offer protection and triggered release. This thesis aims towards expanding the knowledge about degradable and non-degradable pH-responsive micro-/nanogels as carriers for AMPs.

The results in this thesis show that factors relating to the drug delivery system (degradability, charge and crosslinker density), the surrounding media (pH and ionic strength) and the peptide properties (length, charge, PEGylation) all affect the peptide loading to, protection, release from and effect of AMP-loaded gels. Studies of the interaction of AMP-loaded microgels with bacteria-modelling liposomes and lipid bilayers have verified peptide effect after gel incorporation, as further demonstrated by in vitro studies on several bacterial strains. Neutron reflectometry provided detailed mechanistic information on the interaction between AMP-loaded gels and bacteria-modelling lipid bilayers, showing that the antimicrobial unit is the released peptide. All gels showed low, promising hemolysis and some gels could offer protection against proteolytic degradation of AMPs.

In summary, non-degradable and degradable micro-/nanogels are versatile and interesting candidates as AMP carriers. Small changes in the gel composition or the AMP used can dramatically change the peptide loading, release and effect. It is therefore necessary to carefully consider and evaluate the optimal carrier for every AMP and the application at hand.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. , p. 74
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Pharmacy, ISSN 1651-6192 ; 280
Keywords [en]
antimicrobial peptide, microgel, degradable, nanogel, drug delivery, PEGylation, secondary structure, model membrane, lipid bilayer, neutron reflectometry, ellipsometry
National Category
Pharmaceutical Sciences Physical Chemistry
Research subject
Pharmaceutical Physical Chemistry
Identifiers
URN: urn:nbn:se:uu:diva-383639ISBN: 978-91-513-0778-7 (print)OAI: oai:DiVA.org:uu-383639DiVA, id: diva2:1360403
Public defence
2019-11-29, Room A1:107a, BMC, Husargatan 3, Uppsala, 09:15 (English)
Opponent
Supervisors
Available from: 2019-11-07 Created: 2019-10-12 Last updated: 2019-11-27
List of papers
1. Factors Affecting Peptide Interactions with Surface-Bound Microgels
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2016 (English)In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 17, no 2, p. 669-678Article in journal (Refereed) Published
Abstract [en]

Effects of electrostatics and peptide size on peptide interactions with surface-bound microgels were investigated with ellipsometry, confocal microscopy, and atomic force microscopy (AFM). Results show that binding of cationic poly-l-lysine (pLys) to anionic, covalently immobilized, poly(ethyl acrylate-co-methacrylic acid) microgels increased with increasing peptide net charge and microgel charge density. Furthermore, peptide release was facilitated by decreasing either microgel or peptide charge density. Analogously, increasing ionic strength facilitated peptide release for short peptides. As a result of peptide binding, the surface-bound microgels displayed pronounced deswelling and increased mechanical rigidity, the latter quantified by quantitative nanomechanical mapping. While short pLys was found to penetrate the entire microgel network and to result in almost complete charge neutralization, larger peptides were partially excluded from the microgel network, forming an outer peptide layer on the microgels. As a result of this difference, microgel flattening was more influenced by the lower Mw peptide than the higher. Peptide-induced deswelling was found to be lower for higher Mw pLys, the latter effect not observed for the corresponding microgels in the dispersed state. While the effects of electrostatics on peptide loading and release were similar to those observed for dispersed microgels, there were thus considerable effects of the underlying surface on peptide-induced microgel deswelling, which need to be considered in the design of surface-bound microgels as carriers of peptide loads, for example, in drug delivery or in functionalized biomaterials.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2016
National Category
Pharmaceutical Sciences
Research subject
Pharmaceutical Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-278894 (URN)10.1021/acs.biomac.5b01616 (DOI)000369875900029 ()26750986 (PubMedID)
Funder
Swedish Research Council
Available from: 2016-02-26 Created: 2016-02-26 Last updated: 2019-10-12Bibliographically approved
2. Membrane interactions of microgels as carriers of antimicrobial peptides
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2018 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 513, p. 141-150Article in journal (Refereed) Published
Abstract [en]

Microgels are interesting as potential delivery systems for antimicrobial peptides. In order to elucidate membrane interactions of such systems, we here investigate effects of microgel charge density on antimicrobial peptide loading and release, as well as consequences of this for membrane interactions and antimicrobial effects, using ellipsometry, circular dichroism spectroscopy, nanoparticle tracking analysis, dynamic light scattering and z-potential measurements. Anionic poly(ethyl acrylate-co-methacrylic acid) microgels were found to incorporate considerable amounts of the cationic antimicrobial peptides LL-37 (LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES) and DPK-060 (GKHKNKGKKNGKHNGWKWWW) and to protect incorporated peptides from degradation by infection-related proteases at high microgel charge density. As a result of their net negative z-potential also at high peptide loading, neither empty nor peptide-loaded microgels adsorb at supported bacteria-mimicking membranes. Instead, membrane disruption is mediated almost exclusively by peptide release. Mirroring this, antimicrobial effects against several clinically relevant bacteria (methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli, and Pseudomonas aeruginosa) were found to be promoted by factors facilitating peptide release, such as decreasing peptide length and decreasing microgel charge density. Microgels were further demonstrated to display low toxicity towards erythrocytes. Taken together, the results demonstrate some interesting opportunities for the use of microgels as delivery systems for antimicrobial peptides, but also highlight several key factors which need to be controlled for their successful use.

Place, publisher, year, edition, pages
ACADEMIC PRESS INC ELSEVIER SCIENCE, 2018
Keywords
Antimicrobial peptide, Drug delivery, Lipid membrane, Microgel
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-351759 (URN)10.1016/j.jcis.2017.11.014 (DOI)000428834900015 ()29145017 (PubMedID)
Funder
EU, FP7, Seventh Framework Programme, 604182
Available from: 2018-05-31 Created: 2018-05-31 Last updated: 2019-10-12Bibliographically approved
3. Membrane Interactions of Antimicrobial Peptide-Loaded Microgels
Open this publication in new window or tab >>Membrane Interactions of Antimicrobial Peptide-Loaded Microgels
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(English)Manuscript (preprint) (Other academic)
Keywords
antimicrobial peptide, bilayer, membrane, microgel, neutron reflectometry
National Category
Pharmaceutical Sciences
Research subject
Pharmaceutical Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-395109 (URN)
Available from: 2019-10-12 Created: 2019-10-12 Last updated: 2019-10-12
4. Microgels as carriers of antimicrobial peptides – effects of peptide PEGylation
Open this publication in new window or tab >>Microgels as carriers of antimicrobial peptides – effects of peptide PEGylation
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2019 (English)In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 565, p. 8-15Article in journal (Refereed) Published
Abstract [en]

Delivery systems are likely to be central for the translation of antimicrobial peptides (AMPs) towards therapeutics. Addressing AMP interactions with microgel carriers, we here investigate how poly(ethylene glycol) conjugation ('PEGylation') of AMPs affect their loading and release to/from microgels, combining structural studies using nuclear magnetic resonance (NMR) with ellipsometry, circular dichroism spectroscopy (CD), and light scattering. Such studies demonstrate that poly(ethyl acrylate-co-methacrylic acid) microgels bind considerable amounts of the positively charged AMP KYE28 (KYEITTIHNLFRKLTHRLFRRNFGYTLR) and its PEGylated variants KYE28-PEG48, PEG48-KYE28, and PEG24-KYE28-PEG24. Z-potential measurements indicate that KYE28 resides primarily inside the microgel core, and that localization of the PEGylated peptides is shifted towards the microgel corona. Furthermore, while all peptides are disordered in solution, CD measurements report on helix induction on microgel binding, particularly so for the PEGylated peptides. Addressing such conformational changes in more detail, NMR structural studies showed that peptide-microgel interactions are facilitated by a hydrophobic domain formed by the peptide after microgel binding, and with modulating electrostatic/salt bridge interaction between the positively charged peptide residues and negative microgel charges. As the microgels remain negatively charged also at high peptide load, membrane disruption and antimicrobial effects necessitates peptide release, demonstrated to be promoted by PEGylation and high ionic strength. Importantly, microgel loading, as well as peptide localization, conformation, and release, did not depend significantly on PEG conjugation site, but instead seems to be dictated by the PEG content of the peptide conjugates.

Keywords
Antimicrobial peptide, Drug delivery, Microgel, NMR, PEGylation
National Category
Pharmaceutical Sciences
Identifiers
urn:nbn:se:uu:diva-361401 (URN)10.1016/j.colsurfa.2018.12.049 (DOI)000457062300002 ()
Funder
Swedish Research Council, 2012-1842Swedish Research Council, 2015-06720
Available from: 2018-09-24 Created: 2018-09-24 Last updated: 2019-10-12Bibliographically approved
5. Degradable dendritic nanogels as carriers for antimicrobial peptides
Open this publication in new window or tab >>Degradable dendritic nanogels as carriers for antimicrobial peptides
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2019 (English)In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 554, p. 592-602Article in journal (Refereed) Published
Abstract [en]

In the present study, we investigate degradable anionic dendritic nanogels (DNG) as carriers for antimicrobial peptides (AMPs). In such systems, the dendritic part contains carboxylic acid-based anionic binding sites for cationic AMPs, whereas linear poly(ethylene glycol) (PEG) chains form a shell for promotion of biological stealth. In order to clarify factors influencing membrane interactions of such systems, we here address effects of nanogel charge, cross-linking, and degradation on peptide loading/release, as well as consequences of these factors for lipid membrane interactions and antimicrobial effects. The DNGs were found to bind the AMPs LL-37 (LLGDFFRKSKEKIGKEFKRIVQRIKDFLRNLVPRTES) and DPK-060 (GKHKNKGKKNGKHNGWKWWW). For the smaller DPK-060 peptide, loading was found to increase with increasing nanogel charge density. For the larger LL-37, on the other hand, peptide loading was largely insensitive to nanogel charge density. In line with this, results on the secondary structure, as well as on the absence of stabilization from proteolytic degradation by the nanogels, show that the larger LL-37 is unable to enter into the interior of the nanogels. While 40–60% nanogel degradation occurred over 10 days, promoted at high ionic strength and lower cross-linking density/higher anionic charge content, peptide release at physiological ionic strength was substantially faster, and membrane destabilization not relying on nanogel degradation. Ellipsometry and liposome leakage experiments showed both free peptide and peptide/DNG complexes to cause membrane destabilization, indicated also by antimicrobial activities being comparable for nanogel-bound and free peptide. Finally, the DNGs were demonstrated to display low toxicity towards erythrocytes even at peptide concentrations of 100 µM.

Keywords
Antimicrobial peptide, Degradable, Dendritic, Hyperbranched, drug delivery, Membrane, Nanogel
National Category
Pharmaceutical Sciences Physical Chemistry
Research subject
Pharmaceutical Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-389746 (URN)10.1016/j.jcis.2019.07.028 (DOI)000487346200061 ()31330426 (PubMedID)
Funder
Swedish Research Council, 2016-05157Swedish Research Council, 2017-02341EU, FP7, Seventh Framework Programme, 604182
Available from: 2019-07-23 Created: 2019-07-23 Last updated: 2019-11-01Bibliographically approved

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