Photodynamic Inactivation of Bacteria with Porphyrin Derivatives: Effect of Charge, Lipophilicity, ROS Generation, and Cellular Uptake on Their Biological Activity In Vitro.

Adam Sułek,Marcin Kobielusz,Barbara Pucelik,Agata Barzowska,Janusz M Dąbrowski

doi:10.3390/ijms21228716

Adam Sułek, Marcin Kobielusz + Show 3 more

Open Access

https://doi.org/10.3390/ijms21228716

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Abstract

Resistance of microorganisms to antibiotics has led to research on various therapeutic strategies with different mechanisms of action, including photodynamic inactivation (PDI). In this work, we evaluated a cationic, neutral, and anionic meso-tetraphenylporphyrin derivative’s ability to inactivate the Gram-negative and Gram-positive bacteria in a planktonic suspension under blue light irradiation. The spectroscopic, physicochemical, redox properties, as well as reactive oxygen species (ROS) generation capacity by a set of photosensitizers varying in lipophilicity were investigated. The theoretical calculations were performed to explain the distribution of the molecular charges in the evaluated compounds. Moreover, logP partition coefficients, cellular uptake, and phototoxicity of the photosensitizers towards bacteria were determined. The role of a specific microbial efflux pump inhibitor, verapamil hydrochloride, in PDI was also studied. The results showed that E. coli exhibited higher resistance to PDI than S. aureus (3–5 logs) with low light doses (1–10 J/cm2). In turn, the prolongation of irradiation (up to 100 J/cm2) remarkably improved the inactivation of pathogens (up to 7 logs) and revealed the importance of photosensitizer photostability. The PDI potentiation occurs after the addition of KI (more than 3 logs extra killing). Verapamil increased the uptake of photosensitizers (especially in E. coli) due to efflux pump inhibition. This effect suggests that PDI is mediated by ROS, the electrostatic charge interaction, and the efflux of photosensitizers (PSs) regulated by multidrug-resistance (MDR) systems. Thus, MDR inhibition combined with PDI gives opportunities to treat more resistant bacteria.

Highlights

Porphyrins, due to a strong visible absorption attributed to π–π* electronic transitions, play a crucial role in many metabolic and photochemical processes, including electron transfer [1], oxygen transport [2], and oxygenation catalysis [3,4]
Considering that efflux pump inhibitors are promising adjuvant molecules for photodynamic inactivation (PDI), we have evaluated the relation between the pump inhibitor verapamil (Ver) and PDI mediated by the investigated photosensitizers
This paper discusses the physicochemical properties and examines the antibacterial activity of six different porphyrins, namely, TPP, ClTPP, Cl2TPP, TPPS, Cl2TPPS, and TMPyP, which have not been studied in such a comprehensive approach so far

Summary

Introduction

Porphyrins, due to a strong visible absorption attributed to π–π* electronic transitions, play a crucial role in many metabolic and photochemical processes, including electron transfer [1], oxygen transport [2], and oxygenation catalysis [3,4]. The photodynamic action of modified porphyrins is strongly dependent on the optical/photophysical properties, such as intense absorption in UV-Vis-NIR, the high quantum yield of intersystem crossing (ISC), and efficient energy transfer from the triplet excited state (T1) of these dyes to molecular oxygen with the formation of singlet oxygen (type II photochemical reaction) [8,9,10]. The introduction of sulfonic groups allows to increase their solubility in water, without changing their spectroscopic parameters, and the additional substitutes act as steric hindrance, making the compound more stable [21,22]. The presence of antibiotic-resistant bacteria still requires research on other strategies to eradicate bacteria resistant to many drugs [29,30,31,32]

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