Inhibition of phthalocyanine-sensitized photohemolysis of human erythrocytes by quercetin

In silico and in vitro insights into the prediction and analysis of natural photosensitive compounds targeting Acinetobacter baumannii biofilm-associated protein

BACKGROUND

The spread of Acinetobacter baumannii strains has become a global concern due to its extensive antibiotic resistance and biofilm formation. To overcome it, new antimicrobial strategies have been needed. Among them, antimicrobial photodynamic therapy (aPDT) is an efficient approach against various microorganisms. This study was focused on the use of curcumin (Cur) and quercetin (Qct) as natural photosensitive compounds to improve the activity of aPDT against A. baumannii biofilm-associated protein (Bap).

MATERIALS AND METHODS

In this in silico and in vitro study, after determining drug-likeness property, ADME/Toxicity profile, and pharmacological activity of Cur and Qct, virtual screening and molecular docking were assessed to determine the potential binding modes of Cur and Qct to Bap. Then, the anti-biofilm potential of natural photosensitizers-mediated aPDT against A. baumannii was evaluated after the determination of minimum inhibitory concentration (MIC). Subsequently, reverse transcription-quantitative real-time PCR (RT-qPCR) was used to exhibit the anti-virulent effect of aPDT against the gene involved in the biofilm formation of A. baumannii RESULTS: Cur and Qct showed almost similar pharmacokinetic and pharmacodynamics properties. These natural photosensitizers obeyed all the criteria of Lipinski's rule of five principles. According to the molecular docking analysis of protein-ligand complexes, Qct and Cur with a high affinity for Bap showed binding affinity of -6.34 and -6.98 kcal/mol, respectively. According to the findings, aPDT using 4 ×, and 8 × MIC of Cur and Qct could significantly reduce A. baumannii growth in biofilm structures in comparison with the control group (P < 0.05). Also, a significant downregulation by 3.7-, and 5.2-fold in gene expression of bap was observed after treatment with sub-MIC doses of Cur- and Qct-mediated aPDT, respectively (P < 0.05).

CONCLUSIONS

In summary, the in silico analysis showed that Cur and Qct had strong binding affinity with Bap as a stable protein of A. baumannii. Furthermore, in vitro results displayed that targeted aPDT based on these natural photosensitizers can be considered a treatment against A. baumannii infections by reducing the growth of microbial biofilm and reducing the expression of bap as a gene involved in A. baumannii biofilm formation.

Biophysical characterization of genistein-membrane interaction and its correlation with biological effect on cells - The case of EYPC liposomes and human erythrocyte membranes

With application of EPR and (1)H NMR techniques genistein interaction with liposomes formed with egg yolk lecithin and with erythrocyte membranes was assessed. The present study addressed the problem of genistein localization and its effects on lipid membrane fluidity and protein conformation. The range of microscopic techniques was employed to study genistein effects on HeLa cells and human erythrocytes. Moreover, DPPH bioassay, superoxide anion radical test and enzymatic measurements were performed in HeLa cells subjected to genistein. The gathered results from both EPR and NMR techniques indicated strong ordering effect of genistein on the motional freedom of lipids in the head group region and the adjacent hydrophobic zone in liposomal as well as in red blood cell membranes. EPR study of human ghost showed also the changes in the erythrocyte membrane protein conformation. The membrane effects of genistein were correlated with the changes in internal membranes arrangement of HeLa cells as it was noticed using transmission electron microscopic and fluorescent techniques. Scanning electron and light microscopy methods showed that one of the aftermaths of genistein incorporation into membranes was creation of echinocytic form of the red blood cells with reduced diameter. Genistein improved redox status of HeLa cells treated with H2O2 by lowering radicals' level. In conclusion, the capacity of genistein to incorporate, to affect membrane organization and to change its biophysical properties is correlated with the changes inside the cells.

Photodynamic inactivation of Escherichia coli and Streptococcus mitis by cationic zinc(II) phthalocyanines in media with blood derivatives

The photodynamic inactivation (PDI) of Escherichia coli and Streptococcus mitis sensitized by cationic phthalocyanines was studied in different media containing blood derivatives. First, the activity of zinc(II) tetramethyltetrapyridino[3,4-b:3',4'-g:3'',4''-l:3''',4'''-q]porphyrazinium (ZnAPc4+), zinc(II) 2,9,16,23-tetrakis[4-(N-methylpyridyloxy)]phthalocyanine (ZnPPc4+) and zinc(II) 2,9,16,23-tetrakis[2-(N,N,N-trimethylamino)ethoxy]phthalocyanine (ZnEPc4+) were compared to photoinactivate these bacteria in saline solutions. After visible light irradiation, a higher photoinactivation of E. coli cells was found for ZnPPc4+, while ZnEPc4+ was the more effective sensitizer to eradicate S. mitis cells. In the presence of human red blood (HRB) cells, two aspects were analyzed: the photohemolysis induced by these cationic phthalocyanines and the PDI of bacteria in medium containing erythrocytes. The highest photohemolytic damage was produced by ZnPPc4+, which can be avoided using azida ion as photoprotective quencher. In both bacteria, the photoinactivation is possible in presence of HRB cells. Mainly, ZnEPc4+ is effective to photoinactivate S. mitis with a low hemolysis of erythrocytes. However, inactivation of E. coli by ZnPPc4+ decreases in medium with HRB cells, further when azide ion is added to avoid hemolysis. The presence of plasma considerable reduces the photocytotoxic effect, which mainly affects the eradication of E. coli. However, the PDI of S. mitis by ZnEPc4+ is even possible in presence of blood derivatives.

The study of the quercetin action on human erythrocyte membranes

Quercetin is a naturally occurring flavonoid that exerts multiple pharmacological effects. In our previous study, we showed that quercetin greatly affects the lipid membrane. In this report, a study of quercetin on human erythrocyte membrane has been performed to determine the influence of this flavonoid on the fluidity and the conformational changes of membrane proteins. An additional aim of the study was to find how quercetin presence affects the resistance of membrane to haemolytic agents. The results showed that incorporation of quercetin into the erythrocyte membranes caused the changes of the partition coefficient of the Tempo spin label between the water and polar head group phases. In the studies, the W/S ratio has been used as a monitor of changes in protein conformation and in the environment within the membrane. It was observed that quercetin caused an increase in protein-protein interactions in human erythrocyte membranes. Haemolytic action of quercetin in the dark was also investigated. This compound showed protective effect against hypotonic haemolysis. However, in the heat-induced haemolysis quercetin caused acceleration of haemolysis. Dark reaction of erythrocyte with quercetin resulted in a shrinkage of the cells and alteration of their shapes. From the results we have concluded that modification of erythrocyte membrane by quercetin proceeds via reaction with membrane lipids and proteins.

Quercetin promotes functional recovery following acute spinal cord injury

We tested the hypothesis that quercetin, a potent Fe(2+)-chelating flavonoid, would decrease secondary damage following spinal cord trauma. MRI studies using the relaxation of the T1 proton signal caused by Fe(2+) ions and the dose-dependent reversal of this effect by addition of quercetin in aqueous solution were used to guide us to the dosage of quercetin to be used in animal experimentations. Forty-four male Wistar rats were used in two experimental series to test the hypothesis that administration of quercetin improves recovery of motor function after acute traumatic spinal cord injury. Animals were subjected to laminectomy and subjected to an extradural 40-g force clip compression for 5 sec at T7. Quercetin or saline was administered intraperitoneally 1 h after injury and then every 12 hr thereafter. Recovery of motor function was assessed using BBB scores at weekly intervals for 4 weeks. A dose of 2.5 micromoles quercetin/kg body weight did not result in significantly better functional outcome, whereas doses ranging from 5 to 100 micromoles quercetin/kg body weight resulted in a significantly better functional outcome with half or more of the animals walking, although with deficit; in contrast, no animals walked in the group of saline-treated animals. No significant differences in behavioral outcome were seen amongst the doses ranging from 5 to 100 micromol/kg, nor was there a difference if animals were treated for 4 or 10 days. Therapeutic outcome was coincident with more efficient iron clearance, suggesting that one possible mechanism whereby quercetin decreases secondary damage is through iron chelation.

Iron release, oxidative stress and erythrocyte ageing

Iron, to be redox cycling active, has to be released from its macromolecular complexes (ferritin, transferrin, hemoproteins, etc.). Iron is released from hemoglobin or its derivatives in a nonprotein-bound, desferrioxamine-chelatable form (DCI) in a number of conditions in which the erythrocytes are subjected to oxidative stress. Such conditions can be related to toxicological events (haemolytic drugs) or to physiological situations (erythrocyte ageing, reproduced in a model of prolonged aerobic incubation), but can also result from more subtle circumstances in which a state of ischemia-reperfusion is imposed on erythrocytes (e.g., childbirth). The released iron could play a central role in oxidation of membrane proteins and senescent cell antigen (SCA) formation, one of the major pathways for erythrocyte removal. Iron chelators able to enter cells (such as ferrozine, quercetin, and fluor-benzoil-pyridoxal hydrazone) prevent both membrane protein oxidation and SCA formation. The increased release of iron observed in beta-thalassemia patients and newborns (particularly premature babies) suggests that fetal hemoglobin is more prone to release iron than adult hemoglobin. In newborns the release of iron in erythrocytes is correlated with plasma nonprotein-bound iron and may contribute to its appearance.

Inhibition of phthalocyanine-sensitized photohemolysis of human erythrocytes by polyphenolic antioxidants: description of quantitative structure-activity relationships

Polyphenolic antioxidants protected against Al-phthalocyanine tetrasulfonate-sensitized photohemolysis of human erythrocytes. A quantitative structure-activity relationship has been obtained to describe the protective effects of di- and trihydroxybenzenes: log cI(50) (microM)=(1.8620+/-1.5565)+(3.6366+/-2.8245) E(1)(7) (V)-(0. 4034+/-0.0765) log P (r(2)=0.8367), where cI(50) represents the concentrations of compounds for the 2-fold increase in the lag-phase of hemolysis, E(1)(7) represents the compound single-electron oxidation potential, and P represents the octanol/water partition coefficient. The cI(50) for quercetin and taxifolin were close, and cI(50) for morin, kaempferol and hesperetin were lower than might be predicted by this equation. The protection from hemolysis by azide, a quencher of singlet oxygen ((1)O(2)) was accompanied by increase in cI(50) of polyphenols, indicating that azide and polyphenols competed for the same damaging species, (1)O(2). These findings point out to two factors, determining the protective efficiency of polyphenols against (1)O(2), namely, ease of electron donation and lipophilicity.

The flavonols quercetin, rutin and morin in DNA solution: UV-vis dichroic (and mid-infrared) analysis explain the possible association between the biopolymer and a nucleophilic vegetable-dye

Previous studies showed evidence that quercetin can bind DNA by intercalation [R. Solimani et al., J. Agric. Food Chem. 43 (1995) 876-882] and a comparison with the flavanol dihydroquercetin indicated that the interaction is correlated to the planarity and hydrophobicity of the benzopyranic-4-one plane [R. Solimani, Int. J. Biol. Macromol. 18 (1996) 287-295]. In this study flow linear dichroism (LD) spectra of the hydrophobic quercetin were compared with hydrophilic aglycoside morin and 3-glycoside rutin in the same conditions: [DNA] = 3.1 x 10(-2) mol/l phosphate, [dye] = (1.0-4.0) x 10(-4) mol/l. Morin and rutin in an aqueous environment showed the same behaviour as quercetin in buffer-ethanol (70:30, v/v) solution, with their common benzopyranic-4-one part within the biopolymer. The LD(R) values (LD normalised to the relative isotropic absorption) indicated a greater affinity of the quercetin for the DNA. Comparison of the LD(R) of morin and rutin showed a ratio LD(R)morin/LD(R)rutin approximately 1.1-1.2 very close to unity and this suggests the localisation of the 3-rutinoside of rutin outside the intercalation site. Dichroic measurements recorded in extreme conditions of concentration partly clarified the sequences of interaction between quercetin and DNA in solution which shows the prototypical behaviour of the flavonolic group. This consists of an initial weak external association, where an electrostatic component is excluded, and which can evolve to intercalation changing the DNA concentration, whereas the quantity of the flavonol influences relatively the association. The carbonylic region of the benzopyranic-4-one chromophore is probably localised outside the intercalation site. This was suggested by indirect infrared (attenuated total reflection ATR) data of the quercetin-ethanol solution: the presence of free and chelated carbonyl determines a greater density of negative charges in this region of the chromophore, with the consequent lower probability of this portion penetrating the external polyanionic perimeter of the DNA. A simple approach to determine the order of magnitude of the anisotropic band II of the flavonols completely covered by the more intense DNA band at 260 nm, was also proposed. The low number of intercalated chromophores did not determine an alteration of the flexibility and hydrodynamic behaviour of the biopolymer and this can be correlated to a biological consideration: the flavonols probably do not interfere with the genetic functionality of the DNA. In contrast, the potentially close relationship between these nucleophilic dyes and the biopolymer, shown in this study, suggests a protective role on the nucleophilic groups of the DNA, which are a target of free radicals and the reactive electrophilic groups.

Quercetin and DNA in solution: analysis of the dynamics of their interaction with a linear dichroism study

Flow-Linear Dichroism (LD) spectra on quercetin-DNA solutions (buffer-ethanol 30%) showed evidence that the flavonol can intercalate the biopolymer. There is no electrostatic component in the formation of the quercetin-DNA complex. The DNA concentration and the planarity of the chromophore are limiting factors in the interaction. There are no induced LD signals for concentrations of the biopolymer less than 7.8 x 10(-3) M phosphate. The interaction is most probably of a hydrophobic nature between the most hydrophobic segment of the quercetin (benzopyran-4-one) and the intercalation site, which allows the chromophore to penetrate the DNA helix and to arrange its planar structure more or less parallel to the adjacent planes of the nitrogenous bases. A comparison between the planar and hydrophobic flavonol quercetin, and the non-planar and hydrophilic flavanone dihydroquercetin, showed that the interaction of the latter with DNA was strongly limited. The notable biological activity of the quercetin compared to the 'weaker' activity of the dihydroquercetin could also be derived from the different planarity (and probably hydrophobicity) of the two flavonoids. The very low concentration of the quercetin-DNA complex was efficiently shown by the high sensitivity of the LD technique, whereas it could not be resolved by isotropic UV-Vis and induced circular dichroism spectra. The hypothesis of a frame shift mutagenicity activity of quercetin (Science 1977; 197: 577-578) is highly improbable. In fact, the affinity of quercetin for DNA, which emerges from this study, is very low compared with that of a typical intercalator agent (Q. Rev. Biophys. I 1992; 25: 51-170).

The influence of merocyanine 540 and protoporphyrin on physicochemical properties of the erythrocyte membrane

The interaction of the red cell membrane with merocyanine 540 or protoporphyrin led to four phenomena, most probably interrelated. (i) The morphology changed from the normal discoid to an echinocytic form. This morphological change persisted when followed over a period of 24 h. (ii) Simultaneously, cell deformability was decreased, as revealed by viscosity measurements and a cell-filtration technique. (iii) Both drugs caused swelling of the erythrocytes in isotonic medium, due to a very-short-term increased permeability of the membrane, also for larger molecules such as lactose. The pathway of this temporary leak seems to be unrelated to the Na+/K+ -ATPase, the K+/Cl- and the Na+/K+/Cl- cotransport systems, the Ca2+-activated Gardos pathway, the oxidation/deformation-activated leak pathway and the so-called residual transport route. Despite the morphological changes, K+-leakage induced by mechanical stress was not increased. (iv) During osmotic swelling, the critical hemolytic volume was found to be increased in the presence of either merocyanine 540 or protoporphyrin. The increase critical volume protected erythrocytes against osmotic hemolysis.

Inactivation of viruses by chemically and photochemically generated singlet molecular oxygen

Inactivation of viruses in blood plasma can be achieved by photodynamic procedures using methylene blue (MB) or other photoactive dyes. Singlet molecular oxygen (1O2) probably contributes to the virucidal effects of photosensitization. We report the inactivation of herpes simplex virus type 1 (HSV-1) and suid herpes virus type 1 (SHV-1) by chemically generated singlet oxygen, produced by thermal decomposition of the endoperoxide of 3,3'-(1,4-naphthylidene)dipropionate (NDPO2). We demonstrate that viruses can be inactivated by 1O2 generated by chemiexcitation in a reaction in the dark, even in the presence of human plasma. Virus inactivation in phosphate-buffered saline (PBS) was enhanced when water was replaced by deuterium oxide (D2O) and diminished when human plasma or quenchers (imidazole or histidine) were added. The singlet oxygen quenching activities of plasma, imidazole and histidine correlated with their inhibitory effects on virus inactivation. The production of 1O2 was assessed by an indicator reaction: the bleaching of p-nitrosodimethylaniline (RNO) with imidazole as 1O2 acceptor. Virus inactivation and singlet oxygen generation of NDPO2 were compared with those of MB/light-mediated photosensitization. Based on similar amounts of 1O2 generated by either procedure, virus inactivation by MB/light was more effective. Virus inactivation by MB/light was not affected by type I quenchers (e.g. mannitol), but was inhibited by human plasma or singlet oxygen quenchers. Furthermore, in D2O-based PBS, virus inactivation was more effective than that in H2O. These observations confirm that singlet oxygen is involved in virus inactivation by MB/light. Taken together, the results demonstrate that singlet oxygen produced by either procedure is virucidal. The enhanced effect of the photochemical procedure suggests that, in addition to type II, type I reactions and/or the binding affinity of the dye for the virus contribute to virus killing by MB/light.

Catalase inactivation following photosensitization with tetrasulfonated metallophthalocyanines

Catalase (CAT) in solution or incorporated in erythrocytes and K562 leukemic cells is inactivated during photosensitization with tetrasulfonated metallophthalocyanines (MePcS4). The effect of added scavengers and D2O showed that both singlet oxygen and free radical species are involved in this process. Evidence was found that direct interactions of ground or excited-stated photosensitizer with CAT are not responsible for CAT inactivation. Specific techniques to probe early damage to the CAT structure involved optical and EPR spectroscopy, HPLC and polyacrylamide gel electrophoresis analyses. Different primary events of photosensitized protein damage included oxidation of cysteine residues as well as other amino acids, as demonstrated by the formation of carbon-centered free radicals and the loss of absorbance at lambda = 275 nm. In parallel, we detected degradation of the CAT heme groups, accompanied by release of Fe(II) ions in solution. These combined phenomena initiate cross-linkages between CAT subunits and subsequent degradation of the protein with formation of irreversible aggregates in solution. Phthalocyanine-mediated photoinactivation of cell-bound CAT results in loss of protection against accumulating H2O2, providing an additional pathway of phototoxicity.

Role of oxygen in the phototoxicity of phthalocyanines

The presence of molecular oxygen is a determinant in the phototoxicity of phthalocyanines, and photosensitized oxidation is the accepted chemical mechanism for photo-dynamic action. However, it is difficult to establish whether the process is initiated by a type I electron transfer, or by a type II energy transfer reaction to form singlet oxygen. Usually, the involvement of singlet oxygen in photodamage has been indicated by the inhibition of the biological effect by a competitive physical or chemical singlet oxygen quencher, or by a rate increase in D2O, in which singlet oxygen has a longer lifetime than in H2O. Unfortunately, these techniques are not completely specific for singlet oxygen. Moreover, thermodynamic considerations suggest that photoinduced electron abstraction from appropriate biomaterials could compete with singlet oxygen production under in vivo conditions. This likely source of one electron-oxidized primary radicals, which can provide the precursors of the oxidative damage in phthalocyanine photosensitization, suggests the possibility of modulated toxicity by interaction with chemical additives. Examples of such additives recently studied are ascorbate, tocopherol and quercetin, all of which are natural antioxidants.

Phthalocyanine-induced photohemolysis: structure-activity relationship and the effect of fluoride

Phthalocyanine (Pc) containing A1, Ga or Zn as central metal ligand and substituted with a varying number of sulfonic acid residues as well as additional benzene rings were synthesized and their photodynamic activity was assayed using photohemolysis of human erythrocytes as an endpoint. The Pc derivatives varied > 300-fold in their photodynamic activity. Activity correlated with binding of the dye to the cell, with the exception of some of the amphiphilic dyes where cell uptake was an order of magnitude higher than expected from the observed activity. Fluoride was shown to inhibit A1PcSn-induced photohemolysis. This effect occurred also with other A1Pc and GaPc derivatives, but the concentration of F- required to slow photohemolysis by a factor of two (Ki) varied between 4 microM and 10 mM. Fluorescence spectral studies indicated complex formation between F- and the dye, which was stronger for A1Pc than GaPc derivatives. Ultrastructural studies using scanning electron microscopy showed that the photosensitized cells were converted to spherocytes and that F- prevented this to a large extent.