Influence of the Hydrophobicity of Pluronic Micelles Encapsulating Curcumin on the Membrane Permeability and Enhancement of Photoinduced Antibacterial Activity

Abstract

Apart from its well-known activity as an antimicrobial agent, Curcumin (CURC) has recently started to arouse interest as a photosensitizer in the photodynamic therapy of bacterial infections. The aim of the present study was to evidence the influence of the encapsulation of Curcumin into polymeric micelles on the efficiency of photoinduced microbial inhibition. The influence of the hydrophobicity of the selected Pluronics (P84, P123, and F127) on the encapsulation, stability, and antimicrobial efficiency of CURC-loaded micelles was investigated. In addition, the size, morphology, and drug-loading capacity of the micellar drug delivery systems have been characterized. The influence of the presence of micellar aggregates and unassociated molecules of various Pluronics on the membrane permeability was investigated on both normal and resistant microbial strains of E. coli, S. aureus, and C. albicans. The antimicrobial efficiency on the common pathogens was assessed for CURC-loaded polymeric micelles in dark conditions and activated by blue laser light (470 nm). Significant results in the reduction of the microorganism's growth were found in cultures of C. albicans, even at very low concentrations of surfactants and Curcumin. Unlike the membrane permeabilization effect of the monomeric solution of Pluronics, reported in the case of tumoral cells, a limited permeabilization effect was found on the studied microorganisms. Encapsulation of the Curcumin in Pluronic P84 and P123 at very low, nontoxic concentrations for photosensitizer and drug-carrier, produced CURC-loaded micelles that prove to be effective in the light-activated inhibition of resistant species of Gram-positive bacteria and fungi.

Keywords: curcumin; membrane permeabilization; microbial photoinactivation; photodynamic therapy; polymeric micelles.

Figure 1

Size distribution (a) and zeta potential (b) for Pluronic P123 micellar dispersion loaded with Curcumin.

Figure 2

Representative TEM images of samples of void (a) and CURC-loaded P123 micelles (b).

Figure 3

FTIR spectra of polymeric micelles with and without encapsulated Curcumin (a) Pluronic P84; (b) Pluronic P123; (c) Pluronic F127.

Figure 4

The CURC release profile from micellar solutions of various Pluronic derivatives. Data expressed as the mean value and standard deviation of three experiments.

Figure 5

UV-VIS (a) and fluorescence (b) spectra of CURC encapsulated in various micellar systems and dissolved in various solvents.

Figure 6

Degradation of CURC encapsulated in Pluronic micelles under visible irradiation (470 nm).

Figure 7

Relative PI fluorescence in E. coli cultures incubated with micellar and unassociated molecules of Pluronic derivatives: Pluronic P84 (a); Pluronic P123 (b); Pluronic F127 (c). The concentration of Curcumin solubilized in DMSO and in polymeric micellar dispersion is 100 µM. Concentrations of Pluronic derivatives were selected according to their CMC values (Table 1) to cover the micellar domain (concentrations equal to CMC and 10-fold higher) and unimer domain (concentrations equal to CMC/100 and CMC/10).

Figure 8

Relative PI fluorescence in S. aureus cultures incubated with micellar and unassociated molecules of Pluronic derivatives: Pluronic P84 (a); Pluronic P123 (b); Pluronic F127 (c). The concentration of Curcumin solubilized in DMSO and in polymeric micellar dispersion is 100 µM. Concentrations of Pluronic derivatives were selected according to their CMC values (Table 1) to cover the micellar domain (concentrations equal to CMC and 10-fold higher) and unimer domain (concetrations equal to CMC/100 and CMC/10).

Figure 9

Relative PI fluorescence in C. albicans cultures incubated with micellar and unassociated molecules of Pluronic derivatives: Pluronic P84 (a); Pluronic P123 (b); Pluronic F127 (c). The concentration of Curcumin solubilized in DMSO and in polymeric micellar dispersion is 100 µM. Concentrations of Pluronic derivatives were selected according to their CMC values (Table 1) to cover the micellar domain (concentrations equal to CMC and 10-fold higher) and unimer domain (concetrations equal to CMC/100 and CMC/10).

Figure 10

Relative NPN fluorescence in E. coli cultures incubated with micellar and unassociated molecules of Pluronic derivatives: Pluronic P84 (a); Pluronic P123 (b); Pluronic F127 (c). The concentration of Curcumin solubilized in DMSO and in polymeric micellar dispersion is 100 µM. Concentrations of Pluronic derivatives were selected according to their CMC values (Table 1) to cover the micellar domain (concentrations equal to CMC and 10-fold higher) and unimer domain (concentrations equal to CMC/100 and CMC/10).

Figure 11

Graphical representation of the log10 values of colony forming units (CFU)/mL representing the viable cells of S. aureus (a), C. albicans (b), and E. coli (c) strains, after incubation in two different conditions: blue light (470 nm) and darkness.

Figure 11

Graphical representation of the log10 values of colony forming units (CFU)/mL representing the viable cells of S. aureus (a), C. albicans (b), and E. coli (c) strains, after incubation in two different conditions: blue light (470 nm) and darkness.