Natural anthraquinones probed as Type I and Type II photosensitizers: singlet oxygen and superoxide anion production.

The photosensitizing properties of six anthraquinones (AQs): soranjidiol (1), soranjidiol-1-methyl ether (2), rubiadin (3), rubiadin-1-methyl ether (4), damnacanthal (5) and damnacanthol (6), isolated from leaves and stems of Heterophyllaea pustulata Hook. f. (Rubiaceae) were studied. By means of photobiological and photophysical methods in vitro, the type of photosensitization that these metabolites are capable of producing was determined. Whereas the photosensitized generation of superoxide anion radical (O(2)(-)) (Type I) was evaluated in leukocyte suspensions, singlet molecular oxygen ((1)O(2)) production (Type II) was examined in organic solution. In addition, the quantum yield of (1)O(2) (Phi) in chloroform was measured for those AQs that generate it. It was established that 4 behaves exclusively as a Type I photosensitizer. By contrast, the others AQs act by both types of mechanisms, among which 5 showed the largest Phi of (1)O(2).

Light effect and reactive oxygen species in the action of ciprofloxacin on Staphylococcus aureus.

Oxygen consumption by Staphylococcus aureus ATCC 29213 sensitive to ciprofloxacin was determined with an oxygen selective electrode. Increase in the O(2) consumption was observed with 0.45 micromL(-1) ciprofloxacin while higher concentrations gave rise to a reduction of O(2) consumption. Resistant S. aureus strain did not show increase of O(2) consumption in presence of ciprofloxacin. Nitro Blue Tetrazolium assay showed that production of reactive oxygen species (ROS) increased intracellularly in sensitive bacteria incubated with this antibiotic. The exposition to UV light (360 nm) augmented the intracellular oxidative stress of S. aureus and provoked increment of ROS in extracellular media. Generation of singlet oxygen O(2) ((1)Delta(g)) in S. aureus was measured by means of oxidation of methionine. The absorbance of methionine was monitored at 215 nm and a clear decrease was detected when sensitive S. aureus was stressed with ciprofloxacin. Sodium azide and 2,5-dimethylfuran were used to reinforce the evidence of O(2) ((1)Delta(g)) generation during oxidative stress. Assays with methionine and 2,5-dimethylfuran demonstrated that resistant S. aureus did not increase the production of O(2) ((1)Delta(g)) in the presence of antibiotic. DNA oxidation was investigated in presence of O(2) ((1)Delta(g)) generated by laser excitation of perinaphthenone and subsequent energy transfer. Deactivation of O(2) ((1)Delta(g)) by reaction with DNA of sensitive and resistant bacteria was observed. According to the results obtained, the effect of ciprofloxacin in S. aureus led to an increment of O(2) ((1)Delta(g)) generating oxidative stress in the bacteria.