Membrane Rigidity and Phosphatidic Acid (PtdOH) Signal: Two Important Events in Acinetobacter guillouiae SFC 500-1A Exposed to Chromium(VI) and Phenol.

The remodeling of membrane lipids is a mechanism that allows microorganisms to survive in unfavorable environments such as industrial effluents, which often contain inorganic and organic pollutants, like chromium and phenol. In the present work, we evaluated the effect of Cr(VI) and phenol on the membrane of Acinetobacter guillouiae SFC 500-1A, a bacterial strain isolated from tannery sediments where such pollutants can be found. The presence of lipid kinases and phospholipases and the changes in their activities under exposure to these pollutants were determined. Cr(VI) and Cr(VI) + phenol caused the membrane to become more rigid for up to 16 h after exposure. This could be due to an increase in cardiolipin (Ptd2 Gro) and a decrease in phosphatidylethanolamine (PtdEtn), which are indicative of more order and rigidity in the membrane. Increased phospholipase A activity (PLA, EC 3.1.1.4) could be responsible for the decrease in PtdEtn levels. Moreover, our results indicate that Cr(VI) and Cr(VI) + phenol trigger the phosphatidic acid (PtdOH) signal. The finding of significantly increased phosphatidylinositol-4-phosphate (PtdIns-4-P) levels means this is likely achieved via PtdIns-PLC/DGK. This report provides the first evidence that A. guillouiae SFC 500-1A is able to sense Cr(VI) and phenol, transduce this signal through changes in the physical state of the membrane, and trigger lipid-signaling events.

Reactive Oxygen Species-mediated Degradation of Antidiabetic Compounds: Cytotoxic Implications of Their Photodegradation Products.

Reactive oxygen species (ROS) have been described in their double physiological function, helping in the maintenance of health as well as contributing to oxidative stress. Diabetes mellitus is a chronical disease nearly related to oxidative stress, whose treatment (in type II variant) consists in the administration of antidiabetic compounds (Andb) such as Gliclazide (Gli) and Glipizide (Glip). In this context, as Andb may be exposed to high ROS concentrations in diabetic patients, we have studied the potential ROS-mediated degradation of Gli and Glip through photosensitized processes, in the presence of Riboflavin (Rf) vitamin. We found that singlet oxygen (O2 (1 ∆g )) participated in the Rf-sensitized photodegradation of both Andb, and also superoxide radical anion in the case of Gli. Two principal products derived from O2 (1 ∆g )-mediated degradation of Gli were identified and their chemical structures characterized, through HPLC mass spectrometry. O2 (1 ∆g )-mediated degradation products and their toxicity was assayed on Vero cell line. These studies demonstrated that neither Gli nor its photoproducts caused cytotoxic effect under the experimental conditions assayed. Our results show strong evidences of ROS-mediated Andb degradation, which may involve the reduction or loss of their therapeutic action, as well as potential cytotoxicity derived from their oxidation products.

Photosensitized degradation in water of the phenolic pesticides bromoxynil and dichlorophen in the presence of riboflavin, as a model of their natural photodecomposition in the environment.

Within the context of environmentally friendly methods for the elimination of surface-water pollutants, the photodegradation of the phenolic pesticides bromoxynil (BXN) and dichlorophen (DCP) under simulated natural conditions has been studied. The work was done in the presence of the visible-light absorber photosensitizer riboflavin (Rf), usually present in trace quantities in natural waters. Under aerobic conditions, an efficient photooxidation of both pesticides was observed. The relatively intricate photochemical mechanism involves pesticide and oxygen consumption and, to a lesser extent, Rf degradation. The kinetic and mechanistic study supports that both H(2)O(2) and singlet molecular oxygen, O(2)((1)Δ(g)), are involved in the process. Kinetic data for the O(2)((1)Δ(g))-mediated oxidation indicate that BXN and DCP are photodegraded with this species faster than the parent compound phenol, very frequently employed as a model for aquatic contaminants, likely due to their lower pK(a) values. This observation allows the design of phenolic pesticides with different photodegradation rates under environmental conditions.

Stability of flavonoids in the presence of riboflavin-photogenerated reactive oxygen species: a kinetic and mechanistic study on quercetin, morin and rutin.

Kinetic and mechanistic aspects on the stability of the flavones (FL) quercetin (Que), morin (Mor) and rutin (Rut), in methanolic solution and in the presence of reactive oxygen species (ROS) generated by visible light-promoted riboflavin (Rf, vitamin B(2)) photoirradiation were studied. The system was chosen as a model for the evaluation of the in vivo protective effect of biological targets by the flavones. The overall picture includes the vitamin as an endogenous natural photosensitizer. A systematic study on the effect of ROS on FL photostability shows that under work conditions Que is oxidized by singlet molecular oxygen (O(2)((1)Delta(g))), superoxide radical anion (O(2)(-)) and hydrogen peroxide; Mor is degraded by O(2)((1)Delta(g)) and O(2)(-) whereas Rut only reacts with O(2)((1)Delta(g)). Que and Rut, with an extremely poor overall rate constant, are mainly physical quenchers of O(2)((1)Delta(g)). Mor, with O(2)((1)Delta(g))-interception ability slightly lower than the recognized synthetic antioxidant trolox (Tx), behaves as a typical sacrificial scavenger provided that ca 80% of the collisions with O(2)((1)Delta(g)) cause its own degradation, whereas this parameter reaches around 50% in the case of Tx.

Comparative study of the photophysical behavior of fisetin in homogeneous media and in anionic and cationic reverse micelles media.

The 3,3', 4',7 tetrahydroxiflavone (fisetin) is a natural therapeutically active and fluorescent polyhydroxyflavone, with important spectroscopic and biological behavior. Fisetin shows dual emission, with a normal band (N) from the S1 --> S0 transition and the one generated in the excited state (phototautomer; PT) from the intramolecular proton transfer (ESIPT) process. The influence of different interfaces on the ESIPT process of fisetin was investigated in reverse micelles media (RMs) made of the anionic sodium 1,4-bis (2-ethylhexyl) sulfosuccinate (AOT) and cationic benzyl n-hexadecyl dimethylammonium chloride (BHDC) surfactants, in benzene. The studies were carried out by absorption, emission spectroscopy, steady-state anisotropy and time-resolved fluorescence measurements. Fisetin behavior was also investigated in homogeneous media with special emphasis in water and benzene, which are the polar core and the organic pseudofase in the RMs, respectively. In addition, the effect of concentration in benzene and the variation of the pH in water were studied. Fluorescence lifetime measurements show that in water the ESIPT process is independent on the concentration, while in benzene it was possible to detect fluorescent aggregate species (Nas) formed in the ground state. The effect of the pH in water allowed us to identify the anionic fisetin (A-) emission. The studies in RMs show that fisetin interacts specifically with the head of the surfactants, which always results in diminishing the emission of the PT. Also the formation of A- is detected particularly at W0 > 0. Appreciable high anisotropy values are obtained in RMs, as compared with those in fluid homogeneous media, which are independent of the water content confirming that fisetin molecules are anchored in the anionic as well as in the cationic interfaces.

Rose Bengal-sensitized photooxidation of the dipeptides L-tryptophyl-L-phenylalanine, L-tryptophyl-L-tyrosine and L-tryptophyl-L-tryptophan: kinetics, mechanism and photoproducts.

The Rose Bengal-sensitized photooxidations of the dipeptides l-tryptophyl-l-phenylalanine (Trp-Phe), l-tryptophyl-l-tyrosine (Trp-Tyr) and l-tryptophyl-l-tryptophan (Trp-Trp) have been studied in pH 7 water solution using static photolysis and time-resolved methods. Kinetic results indicate that the tryptophan (Trp) moiety interacts with singlet molecular oxygen (O(2)((1)Delta(g))) both through chemical reaction and through physical quenching, and that the photooxidations can be compared with those of equimolecular mixtures of the corresponding free amino acids, with minimum, if any, influence of the peptide bond on the chemical reaction. This is not a common behavior in other di- and polypeptides of photooxidizable amino acids. The ratio between chemical (k(r)) and overall (k(t)) rate constants for the interaction O(2)((1)Delta(g))-dipeptide indicates that Trp-Phe and Trp-Trp are good candidates to suffer photodynamic action, with k(r)/k(t) values of 0.72 and 0.60, respectively (0.65 for free Trp). In the case of Trp-Tyr, a lower k(r)/k(t) value (0.18) has been found, likely as a result of the high component of physical deactivation of O(2)((1)Delta(g)) by the tyrosine moiety. The analysis of the photooxidation products shows that the main target for O(2)((1)Delta(g)) attack is the Trp group and suggests a much lower accumulation of kynurenine-type products, as compared with free Trp. This is possibly because of the occurrence of another accepted alternative pathway of oxidation that gives rise to 3a-oxidized hydrogenated pyrrolo[2,3-b]indoles.

Micellar effect on the scavenging of singlet molecular oxygen by hydroxybenzenes.

The antioxidative effectiveness of three hydroxyaromatic derivatives (OHAD), namely phenol, resorcinol and phloroglucinol, as reflected by their scavenging ability of the photochemically generated species singlet molecular oxygen [O(2)((1)Delta(g))], was studied in aqueous solution and micellar media. Kinetic results, obtained through time-resolved phosphorescence detection of O(2)((1)Delta(g)) emission and polarographic methods, at pH 7 and 12 in homogeneous and CTAB micellar media, were compared. Calculated photooxidation quantum efficiencies (phi(r)), ranging from very low values ( approximately 0.01) to relatively high ones (approximately 0.3), depend on the preferential solubilization sites of the hydroxyaromatic derivatives either in the micellar or homogeneous media. OHAD in water pH 7 and in CTAB 0.02 M pH 12 exhibit their highest antioxidative efficiency as O(2)((1)Delta(g)) scavengers. In these conditions, they present the best degree of self protection against O(2)((1)Delta(g))-mediated photooxidation with relatively high values for the overall quenching rate constant and, simultaneously, the lowest phi(r).