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.     

Photodynamic Damage to Yeast Subcellular Organelles Induced by Elevated Levels of Endogenous Protoporphyrin IX

The 2,2"-dipyridyl-induced accumulation of protoporphyrin IX in Saccharomyces cerevisiae cells was shown to be accompanied by the photoinhibition of cell respiration and the enhancement of the photoinduced permeability of plasma membranes to the fluorescent dye primuline. The visible-light illumination (at 400–600 nm) of the mitochondria and plasma membranes isolated from yeast cells with a high level of endogenous protoporphyrin IX intensified lipid peroxidation in these subcellular organelles. Comparative studies showed that the rad 52 mutant cells, which are deficient in the postreplicative recombinational DNA repair system, are considerably more sensitive to the inactivating action of visible light than are the wild-type cells and the rad 3 mutant cells, which are deficient in the excision DNA repair system. The contribution of photodynamic damage to the yeast subcellular organelles to the lethal photodynamic effect 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.     

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.     

Synthesis and pharmacological evaluation of a second generation of pyridothiadiazine 1,1-dioxides acting as AMPA potentiators

Taking into account structure-activity relationships obtained with our previous series, new diversely substituted 1,2,4-pyridothiadiazine 1,1-dioxides were designed to obtain novel AMPA potentiators. The aim of this work was focused on the improvement of lipophilicity, which is well known as a critical parameter to obtain in vivo active central nervous system agents. For this purpose, two positions on the pyridine ring were privileged to insert selected groups. Among the synthesized compounds emerged 7-chloro-4-ethyl-3,4-dihydro-2H-pyrido[2,3-e]-[1,2,4]-thiadiazine 1,1-dioxide (12d), which was evaluated in two memory tests in Wistar rats and showed cognition enhancing effects after intraperitoneal injection at doses as low as 0.3mg/kg.     

New photo-induced effects of reactivation and protection of yeast cells under lethal UVB radiation

Brief exposure of yeasts to low-intensity monochromatic light (400–730 nm) has revealed the effects of photoreactivation and photoprotection of the cells inactivated by medium wave UVB radiation (290–320 nm). The red spectral region with a maximum at 680 nm has been found to be the most active in the initiation of photoreactivation and photoprotection. It has been noted that, according to the regularities investigated, these processes differ fundamentally from the known processes of enzymatic photoreactivation and photoprotection, which have a spectral response limited by, respectively, blue (<450 nm) and near (<380 nm) UV light. The data obtained make possible to consider the observed effects of photoreactivation and photo-protection as the manifestation of functioning of some light-dependent defense system capable of increasing the resistance of cells to UVB radiation.     

Bacterial behavior in human blood reveals complement evaders with some persister-like features

Bacterial bloodstream infections (BSI) are a major health concern and can cause up to 40% mortality. Pseudomonas aeruginosa BSI is often of nosocomial origin and is associated with a particularly poor prognosis. The mechanism of bacterial persistence in blood is still largely unknown. Here, we analyzed the behavior of a cohort of clinical and laboratory Pseudomonas aeruginosa strains in human blood. In this specific environment, complement was the main defensive mechanism, acting either by direct bacterial lysis or by opsonophagocytosis, which required recognition by immune cells. We found highly variable survival rates for different strains in blood, whatever their origin, serotype, or the nature of their secreted toxins (ExoS, ExoU or ExlA) and despite their detection by immune cells. We identified and characterized a complement-tolerant subpopulation of bacterial cells that we named “evaders”. Evaders shared some features with bacterial persisters, which tolerate antibiotic treatment. Notably, in bi-phasic killing curves, the evaders represented 0.1–0.001% of the initial bacterial load and displayed transient tolerance. However, the evaders are not dormant and require active metabolism to persist in blood. We detected the evaders for five other major human pathogens: Acinetobacter baumannii, Burkholderia multivorans, enteroaggregative Escherichia coli, Klebsiella pneumoniae, and Yersinia enterocolitica. Thus, the evaders could allow the pathogen to persist within the bloodstream, and may be the cause of fatal bacteremia or dissemination, in particular in the absence of effective antibiotic treatments.