Detonation nanodiamonds as enhancers of E. coli photodynamic inactivation by phthalocyanines in a high molarity buffer solution.

Antimicrobial therapy, especially inactivation of multi-antibiotic-resistant strains, requires creating new approaches for drug action and targeted delivery in different environmental conditions. In this work, detonation nanodiamonds (DNDs) were used to deliver polycationic zinc phthalocyanines to E. coli cells. It is shown that in aqueous solutions, zinc phthalocyanines with cholinyl peripheral substituents form complexes with negatively charged DND based on electrostatic interactions. About 40-70 phthalocyanine molecules can bind to a single DND particle, depending on the number of charged groups of the dye molecule. During the complex formation, quenching of phthalocyanine fluorescence and a decrease in its ability to generate reactive oxygen species were observed. In the presence of bacterial cells, phthalocyanine left the complex and induced a photodynamic effect, the magnitude of which depended on the phthalocyanine charge, the molarity of the buffer solution, and the stoichiometry of the phthalocyanine-DND complex. It was found that at physiological values of the ionic strength of the solution, the photodynamic effect of phthalocyanine with a charge of 8+ in combination with a DND is higher than that of the initial phthalocyanine. Thus, nanodiamonds are a promising platform for the delivery of photosensitizers in antimicrobial therapy.

Low incidence of human coronavirus among hospitalized children in Novosibirsk city, Russia during pre-pandemic period (2013-2020).

We investigated the incidence of 15 respiratory viruses among 2991 children with acute respiratory infections in Novosibirsk city, Russia, prior to the COVID-19 pandemic (2013-2020). Viral infections were detected in 72.5% cases. The incidence of human coronavirus was 2% (Alphacoronaviruses, 63%; Betacoronaviruses, 37%).

[Antibacterial effect of the antiseptic picloxydine dihydrochloride on conjunctival isolates of gram-negative bacteria]. / Antibakterial'noe deistvie antiseptika pikloksidina digidrokhlorida na kon"yunktival'nye izolyaty gramotritsatel'nykh bakterii.

The preoperative and postoperative use of antiseptics can be an alternative to antibiotics in repeated courses of anti-VEGF therapy for reducing the risk of developing antibiotic resistance in eye microflora. Among gram-negative bacteria, the most frequently isolated pathogen that causes eye infections is Pseudomonas aeruginosa, which is characterized by reduced sensitivity to antibiotics and disinfectants. PURPOSE: To study the effect of the antiseptic picloxydine dihydrochloride on the gram-negative bacteria Escherichia coli, Pseudomonas luteola and P. aeruginosa isolated from the conjunctiva. MATERIAL AND METHODS: The identification of bacterial isolates and study of their sensitivity to antibiotics were carried out using the automated bacteriological analyzer BD Phoenix 100. To determine the bactericidal concentration, the method of serial dilutions of the antiseptic in a liquid nutrient medium was used. The binding of cationic molecules of picloxydine dihydrochloride to bacterial cells was detected by neutralizing the bacterial surface with increasing amounts of antiseptic, and measuring the zeta potential on the Zetasizer Nano ZS analyzer. The ultrastructure of bacterial cells was studied using the two-beam scanning ion-electron microscope Quanta 200 3D. RESULTS: The most resistant was P. aeruginosa. The interaction mechanism of picloxydine dihydrochloride with bacterial cells includes electrostatic binding of positively charged antiseptic molecules to negatively charged cell walls. Picloxydine dihydrochloride has a destructive effect on the bacterial cell wall and plasma membrane, which leads to cell lysis and release of intracellular components. CONCLUSION: Picloxydine dihydrochloride exhibits bactericidal activity against gram-negative conjunctival isolates and is promising for preventive use during repeated courses of intravitreal injections.

Hybrid Complexes of Photosensitizers with Luminescent Nanoparticles: Design of the Structure.

Increasing the efficiency of the photodynamic action of the dyes used in photodynamic therapy is crucial in the field of modern biomedicine. There are two main approaches used to increase the efficiency of photosensitizers. The first one is targeted delivery to the object of photodynamic action, while the second one is increasing the absorption capacity of the molecule. Both approaches can be implemented by producing dye-nanoparticle conjugates. In this review, we focus on the features of the latter approach, when nanoparticles act as a light-harvesting agent and nonradiatively transfer the electronic excitation energy to a photosensitizer molecule. We will consider the hybrid photosensitizer-quantum dot complexes with energy transfer occurring according to the inductive-resonance mechanism as an example. The principle consisting in optimizing the design of hybrid complexes is proposed after an analysis of the published data; the parameters affecting the efficiency of energy transfer and the generation of reactive oxygen species in such systems are described.

Cationic Antiseptics Facilitate Pore Formation in Model Bacterial Membranes.

Antiseptics are an essential line of defense against bacterial and viral infections in modern medical practice. Many of them are supposed to act on microbial membranes. However, the detailed mechanisms of their action are still elusive. Here, we utilized coarse-grained molecular dynamics simulations to investigate interactions of different types of cationic antiseptics (CAs) with a model bacterial membrane. The simulations revealed qualitatively distinct patterns of dynamic and structural alterations of membrane induced by different types of antiseptics although none of them caused disintegration or solubilization of the bilayer even at the highest explored concentration. At the same time, the adsorption of antiseptics rendered membranes more vulnerable to poration under exposure to the external electric field. We further discuss the possible relation of the enhanced pore formation induced by CAs to their cytotoxic action.

[Conjunctival microflora and its antibiotic sensitivity after serial intravitreal injections]. / Mikroflora kon''iunktivy i ee chuvstvitel'nost' k antibiotikam posle mnogokratnykh intravitreal'nykh in''ektsii.

INTRODUCTION: The approach to post-procedure management of patients undergoing intravitreal injections should be unified and consistent. Frequent use of antibiotic drugs leads to generation of resistant conjunctival strains. PURPOSE: To study the composition of conjunctival microflora and its antibiotic susceptibility in patients who received 20 or more intravitreal injections and concomitant antibiotic therapy, and in a group of patients of the same age without history of intravitreal injections or ophthalmological operations. MATERIAL AND METHODS: A total of 40 inoculations were performed (20 patients in each group, 40 eyes). In case of culture growth, species identification and antibiotic sensitivity of the microorganisms were investigated using automated identification and susceptibility testing system BD Phoenix 100. RESULTS: Culture growth was observed in 70% of the control group patients. All isolated microorganisms were different types of staphylococci - Staphylococcus epidermidis (78.57%), S. caprae (7.14%), S. hominis (7.14%), and S. aureus (7.14%). In the second group, we observed culture growth in 55% of cases. Eleven cultures were Gram-positive bacteria: S. epidermidis (72.73%), S. haemolyticus (18.18%), S. aureus (9.09%). Gram-negative Pseudomonas aeruginosa was detected in 1 patient. In the control group, multi-resistant cultures accounted for 42.86%. In the group of patients with multiple intravitreal injections, 75% of cases showed multiresistance (9 out of 12 isolates). In the group of patients who have undergone 20 or more injections, greatest resistance was observed to penicillin G, doxycycline, gentamicin, erythromycin, clindamycin, moxifloxacin, fusidic acid, chloramphenicol, and trimethoprim/sulfamethoxazole compared to the control group. CONCLUSION: Overuse of antibiotics in the management of patients receiving intravitreal injections leads to selection of resistant strains.

[Antibiotic resistance in patients after serial intravitreal injections]. / Rezistentnost' k antibiotikam u patsientov na fone mnogokratnykh intravitreal'nykh in''ektsii.

Despite the lack of convincing data on the effectiveness of antibiotic therapy in the prevention of Post-Injection Endophthalmitis (PIE), the use of topical antibiotics for intravitreal injections is still a common practice. Frequent, monthly use of antibiotics results in changes of the composition of conjunctival flora and spontaneous mutations of bacteria, and leads to selective survival of resistant and virulent strains that can cause serious damage inside the eye.

A CdSe/ZnS quantum dot-based platform for the delivery of aluminum phthalocyanines to bacterial cells.

Enhancement of optical properties of photosensitizers by additional light-harvesting antennas is promising for the improvement of the photodynamic therapy. However, large number of parameters determine interactions of nanoparticles and photosensitizers in complex and, thus the photodynamic efficacy of the hybrid structure. In order to achieve high efficiency of energetic coupling and photodynamic activity of such complexes it is important to know the location of the photosensitizer molecule on the nanoparticle, because it affects the spectral properties of the photosensitizer and the stability of the hybrid complex in vitro/in vivo. In this work complexes of polycationic aluminum phthalocyanines and CdSe/ZnS quantum dots were obtained. We used quantum dots which outer shell consists of polymer with carboxyl groups and provides water solubility and the negative charge of the nanoparticle. We found that phthalocyanine molecules could penetrate deeply into the polymer shell of quantum dot, leading thereby to significant changes in the spectral and photodynamic properties of phthalocyanines. We also showed that noncovalent interactions between phthalocyanine and quantum dot provide possibility for a release of the phthalocyanine from the hybrid complex and its binding to both Gram-positive and Gram-negative bacterial cells. Also, detailed characterization of the nanoparticle core and shell sizes was carried out.

Hybrid structures of polycationic aluminum phthalocyanines and quantum dots.

Semiconductor nanocrystals (CdSe/ZnS quantum dots, QDs) were used as inorganic focusing antenna, allowing for the enhancement of fluorescence and photosensitizing activity of polycationic aluminum phthalocyanines (PCs). It was found that QDs form stable complexes with PCs in aqueous solutions due to electrostatic interactions. In such hybrid complexes, we observed highly efficient nonradiative energy transfer from QD to PC, leading to a sharp increase in the effective absorption cross section of PC in the absorption bands of the CdSe/ZnS quantum dots. When hybrid complexes are excited within these bands, the intensity of PC fluorescence and the rate of photosensitized singlet oxygen generation increases significantly (up to 500 and 350%, correspondingly) compared to free PC at the same concentration. The observed effect is of interest for modeling primary stages of photosynthesis and increasing photosensitizing activity of dyes used in photodynamic therapy.

Biological photoreceptors of light-dependent regulatory processes.

Progress in understanding primary mechanisms of light reception in photoregulatory processes is achieved through discovering new biological photoreceptors, chiefly the regulatory sensors of blue/UV-A light. Among them are LOV domain-containing proteins and DNA photolyase-like cryptochromes, which constitute two widespread groups of photoreceptors that use flavin cofactors (FMN or FAD) as the photoactive chromophores. Bacterial LOV domain modules are connected in photoreceptor proteins with regulatory domains such as diguanylate cyclases/phosphodiesterases, histidine kinases, and DNA-binding domains that are activated by photoconversions of flavin. Identification of red/far-red light sensors in chemotrophic bacteria (bacteriophytochromes) and crystal structures of their photosensor module with bilin chromophore are significant for decoding the mechanisms of phytochrome receptor photoconversion and early step mechanisms of phytochrome-mediated signaling. The only UV-B regulatory photon sensor, UVR8, recently identified in plants, unlike other photoreceptors functions without a prosthetic chromophore: tryptophans of the unique UVR8 protein structure provide a "UV-B antenna". Our analysis of new data on photosensory properties of the identified photoreceptors in conjunction with their structure opens insight on the influence of the molecular microenvironment on light-induced chromophore reactions, the mechanisms by which the photoactivated chromophores trigger conformational changes in the surrounding protein structure, and structural bases of propagation of these changes to the interacting effector domains/proteins.

Electrostatic binding of substituted metal phthalocyanines to enterobacterial cells: its role in photodynamic inactivation.

The effect of ionic substituents in zinc and aluminum phthalocyanine molecules and of membrane surface charge on the interaction of dyes with artificial membranes and enterobacterial cells, as well as on photosensitization efficiency was studied. It has been shown that increasing the number of positively charged substituents enhances the extent of phthalocyanine binding to Escherichia coli cells. This, along with the high quantum yield of singlet oxygen generation, determines efficient photodynamic inactivation of Gram-negative bacteria by zinc and aluminum octacationic phthalocyanines. The effect of Ca2+ and Mg2+ cations and pH on photodynamic inactivation of enterobacteria in the presence of octacationic zinc phthalocyanine has been studied. It has been shown that effects resulting in lowering negative charge on outer membrane protect bacteria against photoinactivation, which confirms the crucial role in this process of the electrostatic interaction of the photosensitizer with the cell wall. Electrostatic nature of binding is consistent with mainly electrostatic character of dye interactions with artificial membranes of different composition. Lower sensitivity of Proteus mirabilis to photodynamic inactivation, compared to that of E. coli and Salmonella enteritidis, due to low affinity of the cationic dye to the cells of this species, was found.

Effect of middle-wave ultraviolet irradiation and red light on degranulation of peritoneal mast cell in rats.

Middle-wave UV-irradiation inhibits liberator-induced histamine release from mast cells. Red light stimulated liberator-induced degranulation of mast cell. The existence of a membrane-dependent system activated by long-wave (red) light in mammalian cells is discussed.

Light-induced processes of cell protection against photodamage.

The processes of light-induced cell protection against photodamage, including DNA photorepair with involvement of photolyases and photoactivation of enzymatic synthesis of photoprotectors and antioxidants (flavonoids, carotenoids, melanins, serotonin, and hemoxygenase), are discussed. Mechanisms of photoprotective effects against photodynamic oxidation of membrane components and photodamage of DNA are analyzed.

Endogenous porphyrin accumulation and photosensitization in the yeast Saccharomyces cerevisiae in the presence of 2,2'-dipyridyl.

The chelator 2,2'-dipyridyl (0.2 mM) induces a remarkable increase of protoporphyrin IX concentration as well as of its Zn-containing complex in the yeast Saccharomyces cerevisiae. Endogenous porphyrin accumulation results in five- to six-fold cell sensitization to visible light (400-600 nm). Mitochondria isolated from the cells grown in the presence of 2,2'-dipyridyl accumulate protoporphyrin IX and Zn-protoporphyrin IX, while plasma membranes besides that exhibit porphyrin-type fluorescence at 670-675 nm in chloroform extract. The protoporphyrin IX content increases more than four-fold in mitochondria and two-fold in plasma membranes isolated from chelator-treated cells. The relative contribution of subcellular structure photodestruction to photoinduced cell inactivation is discussed.

Effect of 2,2'-dipyridyl on accumulation of protoporphyrin IX and its derivatives in yeast mitochondria and plasma membranes.

The iron chelator 2,2'-dipyridyl (0.2 mM) more than fourfold increased the concentration of protoporphyrin IX and also of its zinc-containing complex in mitochondria of the yeast Saccharomyces cerevisiae. Protoporphyrin IX and a chlorine derivative of protoporphyrin IX which fluoresces at 670-675 nm were found in isolated plasma membranes of the yeast grown in the presence of 0.2 mM 2,2'-dipyridyl. The accumulation of endogenous porphyrins resulted in intensification of lipid photoperoxidation in mitochondria and plasma membranes and in a dramatically increased sensitivity of the cells to visible light (400-600 nm). The relative contribution of photodestruction of subcellular structures to photoinduced cell inactivation is discussed.

The role of membrane-bound porphyrin-type compound as endogenous sensitizer in photodynamic damage to yeast plasma membranes.

The effect of visible light (400-600 nm) on Candida guilliermondii and Saccharomyces cerevisiae was studied, and irradiation fluences killing the yeast cells without exogenous sensitizers were determined. The lethal effects are strongly oxygen-dependent, suggesting the involvement of photodynamic reactions mediated by endogenous sensitizer(s). Repair-deficient strains of S. cerevisiae show the same photosensitivity as the wild-type strain indicating that visible light does not photosensitize repairable DNA lesions. As was demonstrated using the microfluorometric method with the fluorochrome primulin, photodestruction of plasma membrane permeability barriers is important for yeast cell lethality. Visible light at cell-killing fluences induces lipid peroxidation in plasma membrane ghosts isolated from C. guilliermondii. Data obtained suggest the important role of singlet oxygen photogenerated by endogenous sensitizer(s) in initiating oxidative reactions. A spectrofluorometric analysis of the plasma membrane ghosts revealed one compound fluorescent in the visible spectral region at 683 nm. Its fluorescence excitation and absorption spectra have structures typical for porphyrins. The plasma membrane-bound porphyrin-like compound is different in some fluorescence properties from mitochondrial porphyrins. Estimation of its amount gives a value of 0.1 nmol porphyrin per milligram of protein of the plasma membrane ghosts. This porphyrin-type compound is considered to be the most probable candidate for the role of the sensitizer in photodynamic damage to yeast plasma membrane and cell inactivation by visible light.

Near-UV activation of yeast growth.

Near-UV radiation (337 nm) at fluences of 2-10 kJ m-2 activates, during the lag-phase, subsequent growth of the yeast Candida guilliermondii. Photostimulation occurs only after a temperature-dependent time interval (1-2 h) between short-period irradiation and the onset of cell growth on a nutrient medium. A photoactivated enzymatic synthesis of an intermediate metabolite regulating cell growth is proposed as the cause of the biochemical changes responsible for the photostimulatory effect. On the basis of the observed disappearance of photostimulation after adding para-chlorphenylalanine (a specific inhibitor of serotonin synthesis), serotonin is suggested to act as the active metabolite. The regulatory function of serotonin is confirmed by the stimulatory effect of exogenous serotonin and its dependence on concentration, which resembles the dependence on near-UV fluence.

Near-UV activation of enzymatic conversion of 5-hydroxytryptophan to serotonin.

Near-UV (337 nm) photoactivation of the 5-hydroxytryptophan decarboxylation reaction producing serotonin has been observed. The photoactivation effect was investigated as a function of fluence rate and fluence, and pH. Photoactivation of decarboxylase activity was found to occur at nearly neutral pH values (low activity of the enzyme in the dark). The findings indicate that the effect of light is similar to a pH shift toward the acid region, which causes the enzyme conversion from the inactive to active form. Pyridoxal phosphate, the decarboxylase cofactor, in the form of an adduct absorbing at 330-340 nm, is suggested as a candidate for the role of the photoactive chromophore of decarboxylase.