Investigation of the photodynamic effects of curcumin against Candida albicans.

This study describes the association of curcumin with light emitting diode (LED) for the inactivation of Candida albicans. Suspensions of Candida were treated with nine curcumin concentrations and exposed to LED at different fluences. The protocol that showed the best outcomes for Candida inactivation was selected to evaluate the effect of the preirradiation time (PIT) on photodynamic therapy (PDT) effectiveness, the uptake of curcumin by C. albicans cells and the possible involvement of singlet oxygen in the photodynamic action. Curcumin-mediated PDT was also assessed against biofilms. In addition to the microbiological experiments, similar protocols were tested on a macrophage cell line and the effect was evaluated by Methyltetrazolium assay (MTT) and SEM analysis. The optical properties of curcumin were investigated as a function of illumination fluence. When compared with the control group, a statistically significant reduction in C. albicans viability was observed after PDT (P < 0.05), for both planktonic and biofilm cultures. Photodynamic effect was greatly increased with the presence of curcumin in the surrounding media and the PIT of 20 min improved PDT effectiveness against biofilms. Although PDT was phototoxic to macrophages, the therapy was more effective in inactivating the yeast cell than the defense cell. The spectral changes showed a high photobleaching rate of curcumin.

Effects of metal and the phytyl chain on chlorophyll derivatives: physicochemical evaluation for photodynamic inactivation of microorganisms.

Chlorophyll compounds and their derivatives containing metal or phytyl chain can be used as photosensitizer in photodynamic inactivation of microorganisms (PDI). So, the physicochemical properties and antimicrobial effect of chlorophyll derivatives were investigated: Mg-chlorophyll (Mg-Chl), Zn-chlorophyll (Zn-Chl), Zn-chlorophyllide (Zn-Chlde), Cu-chlorophyll (Cu-Chl), pheophytin (Pheo) and pheophorbide (Pheid). The photobleaching experiments showed photostability according to Cu-Chl > Pheo ∼ Pheid ≫ Zn-Chl ∼ Zn-Chlde > Mg-Chl. This order was discussed in terms of metal and the phytyl chain presences. Pheid and Zn-Chl in aqueous Tween 80 solution exhibited highest singlet oxygen yield compared with the other derivatives. Chlorophyll derivatives (CD) with phytyl chain was limited by the self-aggregation phenomenon at high concentrations, even in micellar systems (Tween 80 and P-123). The antimicrobial effect of CD derivatives was investigated against Staphylococcus aureus, Escherichia coli, Candida albicans and Artemia salina. Pheid showed the best results against all organisms tested, Zn-Chlde was an excellent bactericide in the dark and Cu-Chl had no PDI effect. No correlation with CD uptake by microorganisms and darkness cytotoxicity was found. The physicochemical properties allied to bioassays results indicate that Mg-Chl, Pheo, Zn-Chl and Pheid are good candidates for PDI.

Angiographic effects of indocyanine green photobleaching by the diode laser.

BACKGROUND AND OBJECTIVE: To investigate the cause of hypofluorescent spots detected by indocyanine green (ICG) videoangiography in areas subjected to ICG-enhanced transpupillary thermotherapy in pigmented rabbits. MATERIALS AND METHODS: In 6 eyes, two similar areas were treated with transpupillary thermotherapy. A standard dose of ICG (0.5 mg/kg) was injected intravenously before treatment of the second area. Red-free photographs without further injection of ICG (first ICG videoangiography) were then performed. The first area was re-irradiated using the same parameters. Red-free photographs and a second ICG videoangiography, still without further injection of ICG, were performed. ICG was then re-injected and a third ICG videoangiography was obtained. Finally, fluorescein angiography was performed. RESULTS: The first ICG videoangiography demonstrated hyperfluorescence of the first area and normofluorescence of the second area. The second ICG videoangiography demonstrated hypofluorescence of the first area. The third ICG videoangiography showed hyperfluorescence of both areas. CONCLUSIONS: Hypofluorescence detected after re-irradiation is probably related to ICG photobleaching.

Stroboscopic illumination using light-emitting diodes reduces phototoxicity in fluorescence cell imaging.

Excited fluorophores produce reactive oxygen species that are toxic toward many live cells (phototoxicity) and accelerate bleaching of the fluorophores during the course of extended or repeated measurements (photobleaching). We recently developed an illumination system for fluorescence microscopy using a high power light-emitting diode (LED), which can emit short pulses of light (0.5-2 ms) to excite fluorophores. This system minimizes illumination time, thus reducing phototoxicity and photobleaching artifacts. To demonstrate the usefulness of the new system, we compared images of human sperm loaded with various fluorescent indicators and excited with either a conventional mercury lamp as a continuous excitation light source or the LED as a source of pulsed illumination. We found that sperm motility decreased rapidly and photobleaching was relatively rapid under continuous illumination, whereas under pulsed LED illumination, motility was maintained and photobleaching was much reduced. Therefore, fluorescence microscopy using LED-based pulsed illumination offers significant advantages for long-term live cell imaging, reducing the degree of phototoxicity, and extending the effective lifetime of fluorophores.

Response of Millepora alcicornis (Milleporina: Milleporidae) to two bleaching events at Puerto Morelos reef, Mexican Caribbean.

Two naturally occurring colonies of Millepora alcicornis were monitored during 1997 and 1998, both years in which this species bleached in the Mexican Caribbean. One colony (HL) was naturally exposed to a high light environment and another nearby colony (LL) was exposed to 5.9 times lower light levels due to shadowing by a pier. For 10 days in August 1997, seawater temperatures in the surrounding reef lagoon rose up to 1.5 degrees C above the 6-year August average. The HL colony bleached to white during this period, whereas, the LL colony remained dark-brown colored. The HL colony recovered its normal dark-brown coloration (reversible bleaching) within several weeks, during which time the seawater temperatures returned to average. The following year, for 10 days, seawater temperatures rose up to 3 degrees C above the 7-year August average and both colonies bleached to white and neither colony recovered (irreversible bleaching). Both colonies were rapidly overgrown by algae and hydroids and, as of June 2003, no recovery has taken place. Prior to the 1997 bleaching, experiments using solar radiation showed that the quantum yield of photosystem II charge separation of branches from HL and LL colonies were affected for several hours by exposure to ultraviolet radiation (UVR, 280 to 400 nm), but recovered by the same evening, suggesting that UVR does not have long-term effects on photochemistry in M. alcicornis. In situ effective quantum yield of photosystem II charge separation (deltaF/Fm') measurements before the 1998 bleaching event indicate that both colonies were healthy in terms of the physiological status of their endosymbionts. During and after the 1998 bleaching event, both colonies showed a reduction in deltaF/Fm' and consequently an increase in excitation pressure on photosystem II. The data suggest that temperature is not the only factor that causes bleaching and that solar radiation may play an important role in coral bleaching.