Influence of Cationic meso-Substituted Porphyrins on the Antimicrobial Photodynamic Efficacy and Cell Membrane Interaction in Escherichia coli

Abstract

Photodynamic inactivation (PDI) is a non-antibiotic option for the treatment of infectious diseases. Although Gram-positive bacteria have been shown to be highly susceptible to PDI, the inactivation of Gram-negative bacteria has been more challenging due to the impermeability properties of the outer membrane. In the present study, a series of photosensitizers which contain one to four positive charges (1–4) were used to evaluate the charge influence on the PDI of a Gram-negative bacteria, Escherichia coli (E. coli), and their interaction with the cell membrane. The dose-response PDI results confirm the relevance of the number of positive charges on the porphyrin molecule in the PDI of E. coli. The difference between the Hill coefficients of cationic porphyrins with 1–3 positive charges and the tetra-cationic porphyrin (4) revealed potential variations in their mechanism of inactivation. Fluorescent live-cell microscopy studies showed that cationic porphyrins with 1–3 positive charges bind to the cell membrane of E. coli, but are not internalized. On the contrary, the tetra-cationic porphyrin (4) permeates through the membrane of the cells. The contrast in the interaction of cationic porphyrins with E. coli confirmed that they followed different mechanisms of inactivation. This work helps to have a better understanding of the structure-activity relationship in the efficiency of the PDI process of cationic porphyrins against Gram-negative bacteria.

Self‐Assembled Binaphthyl‐Bridged Amphiphilic AABB Phthalocyanines: Nanostructures for Efficient Antimicrobial Photodynamic Therapy

“…Compared to other tetracationic pyridinium PS, [15, 35, 37] the inherent oriented amphiphilic character and self‐assembly behavior of PS‐1 and PS‐2 provide them with much stronger photo‐antimicrobial activity, both in terms of concentration of the PS and light dose. Comparing with other nanostructured PS, the Zn II Pc self‐assembled nanodots reported by J. Yoon and co‐workers fully inhibit the growth of E. coli only at 50 μ m [29b] .…”

Cationic Porphyrins as Effective Agents in Photodynamic Inactivation of Opportunistic Plumbing Pathogen Legionella pneumophila

“…The obtained MEC values (Table 3) indicate a somewhat dark toxicity for all tested dyes after incubation with L. pneumophila for 30 min, the highest being observed for the compound with a long alkyl chain, TMPyP3-C 17 H 35 (>1.56 µM), while the other two porphyrins that are hydrophilic show two-fold dark toxicity (>12.5 µM) in comparison to hydrophilic phenothiazine dyes TBO and MB (>25.6 µM). The mechanism of self-promoted uptake, which is due to interactions between the positive charges of cationic PSs and negative charges of LPS, has been used previously to explain similar dark toxicity [25]. Even though the experiment was performed in dark, the determination of the colony forming units (CFU) could not be carried out in complete darkness.…”

“…The impact of positive charges, their number and distribution in a molecule, has been previously investigated, mostly on E. coli and S. aureus [8,12,26,27]. Recently, a tetra-cationic porphyrin similar to TMPyP3 was reported to have higher PDI activity compared to the tri-cationic porphyrin, and was shown to be internalized by E. coli, while the tri-cationic bound to the cellular membrane [25]. On the other hand, tetra-cationic porphyrins are also known to interact strongly with nucleic acids, causing photodamage to plasmid DNA for instance, while tri-cationic porphyrins target lipids in the cell membrane [25].…”

“…Recently, a tetra-cationic porphyrin similar to TMPyP3 was reported to have higher PDI activity compared to the tri-cationic porphyrin, and was shown to be internalized by E. coli, while the tri-cationic bound to the cellular membrane [25]. On the other hand, tetra-cationic porphyrins are also known to interact strongly with nucleic acids, causing photodamage to plasmid DNA for instance, while tri-cationic porphyrins target lipids in the cell membrane [25]. This could also explain the strongest PDI activity of significantly more lipophilic tri-cationic porphyrin TMPyP3-C 17 H 35 , as opposed to hydrophilic tri-cationic porphyrin TMPyP3-CH 3 .…”

Cationic Pyrrolidine/Pyrroline-Substituted Porphyrins as Efficient Photosensitizers against E. coli

“…Moreover, the extensive research concerning the actuation of porphyrins as photosensitizer agents, towards different microbial species, such as fungi and bacteria (Gram-positive and Gram-negative) in planktonic and biofilm forms, viruses and parasites, shows also the necessity of adapting the treatment protocol, namely in terms of PS structure to the microorganism type [ 28 ]. For instance, the best photoinactivation rates of Gram-negative bacteria occur using positively charged PSs, which allows the interaction of the PS with negatively charged sites in liposaccharides belonging to the outer bacterial membrane [ 23 , 30 , 31 , 32 , 33 ].…”