In Vitro Photoinactivation of Fusarium oxysporum Conidia with Light-Activated Ammonium Phthalocyanines

Abstract

Antimicrobial photodynamic therapy (aPDT) has been explored as an innovative therapeutic approach because it can be used to inactivate a variety of microbial forms (vegetative forms and spores) without causing significant damage to host tissues, and without the development of resistance to the photosensitization process. This study assesses the photodynamic antifungal/sporicidal activity of tetra- and octasubstituted phthalocyanine (Pc) dyes with ammonium groups. Tetra- and octasubstituted zinc(II) phthalocyanines (1 and 2) were prepared and tested as photosensitizers (PSs) on Fusarium oxysporum conidia. Photoinactivation (PDI) tests were conducted with photosensitizer (PS) concentrations of 20, 40, and 60 µM under white-light exposure at an irradiance of 135 mW·cm–2, applied during 30 and 60 min (light doses of 243 and 486 J·cm−2). High PDI efficiency corresponding to the inactivation process until the detection limit was observed for both PSs. The tetrasubstituted PS was the most effective, requiring the lowest concentration and the shortest irradiation time for the complete inactivation of conidia (40 µM, 30 min, 243 J·cm−2). Complete inactivation was also achieved with PS 2, but a longer irradiation time and a higher concentration (60 µM, 60 min, 486 J·cm−2) were necessary. Because of the low concentrations and moderate energy doses required to inactivate resistant biological forms such as fungal conidia, these phthalocyanines can be considered potent antifungal photodynamic drugs.

Light-Driven Tetra- and Octa-β-substituted Cationic Zinc(II) Phthalocyanines for Eradicating Fusarium oxysporum Conidia

“…With a concentration of 1 µM of PS, and similar irradiation conditions (light dose of 486 J.cm −2 ), a significant inactivation could be observed with all tested PSs, except for PS 1, which represents the first evidence of the lower efficiency of this PS, in comparison with the other molecules. An estimate of the minimum inhibitory concentration (MIC) of thiopyridinium or ammonium phthalocyanines against conidia, pointed to values of 5 to 60 µM [38,39]. Therefore, assays conducted with a concentration of 1 µM may be interpreted as representing sub-lethal conditions, and allow the comparative assessment of the different PSs.…”

“…Regardless of differences in the photosensitization efficiency, which can be related to 1 O 2 generation capacity and the effect of the number of charges on solubility and affinity towards the spore material, all PSs have been shown to be effective against Fusarium oxysporum conidia at concentrations above 10 µM. Other studies of the photoinactivation of Fusarium oxysporum conidia with the use of ammonium phthalocyanines as photosensitizers needed higher concentrations of PS such as 40 and 60 µM at the same light doses [38]. The study found that quaternized derivatives were highly effective as photosensitizers and required only a concentration of 1 µM to significantly inactivate Fusarium oxysporum conidia.…”

“…Investigating the structure-activity relationship plays is essential for developing potent photosensitizers (PSs) capable of inflicting lethal damage on plant pathogens within brief exposure to irradiation without harming host plant tissues. Porphyrin (Por) [33], chlorin (Chl) [36,37], and phthalocyanine (Pc) [38,39] dyes have been extensively employed in the PDI method. Pcs exhibit distinctive UV-visible spectra, typically characterized by a Soret band with a maximum wavelength at 350 nm and intense Q bands within the red/near-infrared range (600-800 nm) [38][39][40].…”

“…Porphyrin (Por) [33], chlorin (Chl) [36,37], and phthalocyanine (Pc) [38,39] dyes have been extensively employed in the PDI method. Pcs exhibit distinctive UV-visible spectra, typically characterized by a Soret band with a maximum wavelength at 350 nm and intense Q bands within the red/near-infrared range (600-800 nm) [38][39][40]. The physicochemical properties and biological activities of Pcs are significantly influenced by their structural features and specific functionalities.…”