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Photodynamic inactivation of bacteria using polyethylenimine–chlorin(e6) conjugates: Effect of polymer molecular weight, substitution ratio of chlorin(e6) and pH

Huang, Liyi and Zhiyentayev, Timur and Xuan, Yu and Azhibek, Dulat and Kharkwal, Gitika B. and Hamblin, Michael R. (2011) Photodynamic inactivation of bacteria using polyethylenimine–chlorin(e6) conjugates: Effect of polymer molecular weight, substitution ratio of chlorin(e6) and pH. Lasers in Surgery and Medicine, 43 (4). pp. 313-323. ISSN 0196-8092. https://resolver.caltech.edu/CaltechAUTHORS:20110503-151901647

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Abstract

Background and Objectives: Antimicrobial photodynamic therapy (APDT) is a novel technique to treat local infections. Previously we reported that the attachment of chlorin(e6) to polyethylenimine (PEI) polymers to form PEI-ce6 conjugates is an effective way to improve ce6 PDT activity against bacteria. The aim of this work was to explore how the polymer molecular weight, substitution ratio (SR) of ce6 and pH value affect the PDT efficacy. Study Design/Materials and Methods: We have synthesized PEI-ce6(10) (MW = 60,000, SR = 1) and PEI-ce6(11) (MW = 60,000, SR = 5) and compared these with the previous PEI-ce6(9) (MW = 10,000, SR = 1). We tested the PDT efficacy of these three conjugates against Gram-negative E. coli and Gram-positive bacteria (S. aureus and E. fecalis) at three different pH values (5.0, 7.4, 10.0) that may affect the charge on both the bacterial cells and on the conjugate (that has both basic and acidic groups). Results: PEI-ce6(9) and PEI-ce6(10) were the most effective against these tested bacteria. The PDT effect of all three conjugates depended on pH values. The effective order was pH = 10.0 > pH = 7.4 > pH = 5.0 on E. coli. For S. aureus and E. fecalis the order was pH = 5.0 > pH = 10.0 > pH = 7.4. PEI-ce6(11) PDT activity was worse than PEI-ce6(10) activity which is probably connected to the fact that ce6 molecules are self-quenched within the PEI-ce6(11) molecule. Ce6 quenching within the PEI-ce6 molecules was proved by analyzing fluorescence spectra of PEI-ce6 conjugates at different pH values. There were no differences in bacterial uptake between different pH values in three PEI-ce6 conjugates. Conclusion: We assume high pH (rather than low pH as was hypothesized) disaggregates the conjugates, so the higher pH was more effective than the lower pH against E. coli. But for Gram-positive bacteria, low pH was more effective possibly due to more overall positive charge on the conjugate.


Item Type:Article
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URLURL TypeDescription
http://dx.doi.org/10.1002/lsm.21056DOIUNSPECIFIED
http://onlinelibrary.wiley.com/doi/10.1002/lsm.21056/abstractPublisherUNSPECIFIED
Additional Information:© 2011 Wiley-Liss, Inc. Accepted 15 February 2011; Published online 15 April 2011 in Wiley Online Library. This work was supported by NIH (ROIAI050875 to MRH) and US Air Force MFEL Program (FA9550-04-1-0079). LH received a travel grant from ASLMS for attending the 30th ASLMS Annual Conference and presenting the prelimihary data. This contribution satisfies the condition of the travel grant that a manuscript should be submitted to LSM within one year after the annual conference.
Funders:
Funding AgencyGrant Number
NIHR01A1050875
U.S. Air Force MFEL ProgramFA9550-04-1- 0079
Subject Keywords:antimicrobial photodynamic therapy; polyethylenimine- ehlorine(e6) conjugate; pH value; polymer molecular weight; substitution ratio; static and dynamic quenching
Issue or Number:4
Record Number:CaltechAUTHORS:20110503-151901647
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20110503-151901647
Official Citation:Huang, L., Zhiyentayev, T., Xuan, Y., Azhibek, D., Kharkwal, G. B. and Hamblin, M. R. (2011), Photodynamic inactivation of bacteria using polyethylenimine–chlorin(e6) conjugates: Effect of polymer molecular weight, substitution ratio of chlorin(e6) and pH. Lasers in Surgery and Medicine, 43: 313–323. doi: 10.1002/lsm.21056
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:23536
Collection:CaltechAUTHORS
Deposited By: Jason Perez
Deposited On:04 May 2011 20:04
Last Modified:03 Oct 2019 02:47

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