Mechanistic Insight into the Photodynamic Effect Mediated by Neutral Red and a New Azine Compound in Staphylococcus aureus Cells

Abstract

The photodynamic activity of Neutral Red and the new monobrominated Neutral Red was studied in suspensions of Staphylococcus aureus. The effect of mannitol and sodium azide in the presence of 25 μm photosensitizer on lethal photosensitization were investigated. The results of the mechanistic evaluation of Neutral Red showed that both mannitol and sodium azide produced a completed protective effect after irradiation without significant differences between them. The evaluation of monobrominated Neutral Red also showed a protective effect of microorganisms with the addition of mannitol. Although sodium azide produced a protective effect of the photoinactivation, it was incomplete and less than that exhibited by mannitol. The results indicate that the starting reagent, Neutral Red, is a producer of radical species, acting through a type I mechanism, whereas the halogenated derivative of Neutral Red produced reactive oxygen species and a contribution of singlet molecular oxygen cannot be discarded in the photoinactivation of Staphylococcus aureus cells. These results, analyzed together with the previously evaluated properties of the dyes, allow us to explain the differences observed in the photoinactivation of Staphylococcus aureus mediated by both azine photosensitizers.

Polymeric micelles as a strategy to enhance the phototoxic efficacy of phenazine photosensitizers

“…Neutral Red (NR), a phenazine dye, is a pure and well‐characterized compound, ROS producer, harmless in darkness, and has a history of photodynamic inactivation of microorganisms. In order to optimize the properties of this PSs, we synthesized monobrominated Neutral Red (NRBr) and evaluated different properties in comparison with its precursor 12–14 . The introduction of heavy atoms into the molecule favored the formation of the excited triplet state of PS, which led to an increase in the 1 O 2 quantum yield (Φ Δ ) 13 .…”

“…In order to optimize the properties of this PSs, we synthesized monobrominated Neutral Red (NRBr) and evaluated different properties in comparison with its precursor. [12][13][14] The introduction of heavy atoms into the molecule favored the formation of the excited triplet state of PS, which led to an increase in the 1 O 2 quantum yield (Φ Δ ). 13 However, the increase in lipophilicity caused the halogenated derivative to present low solubility in aqueous media, which undermines the photochemical and photophysical characteristics of PS.…”

Red Phosphorus/P25 Nanophotosensitizers Coated with Platelet Membrane for Enhancing Cancer Cells Photodynamic Therapy

“…Photodynamic therapy (PDT) was considered as a therapeutic approach that used photoresponsive compounds together with laser irradiation to target malignant cells [1–4] . As an important component of PDT, photosensitizer compounds must comply with three essential requirements: 1) tissue and cellular biocompatibility, 2) specifically targeting of cancer cells, and 3) generate reactive oxygen species (ROS) upon laser irradiation [5–10] .…”

Phenazines and Photoactive Formulations: Promising Photodrugs for Photodynamic Therapy

“…The exciting characteristic of NR as a PS is its water solubility compared with the majority of photosensitive and absorption bands located in the range of 550-700 nm [22]. Concerning with few phenazines studies as photodrugs explored in the literature (Table 2), for instance, the NR phenazines compound, when incorporated into Gold Nanoparticles, contributed to the in vitro tumor cell lines reduction [22], or when in aqueous medium significantly reduced in vitro S. aureus colonies in photoinactivation assays [98,103].…”