Effects of singlet oxygen on membrane sterols in the yeast Saccharomyces cerevisiae

Effect of Chitosan-Riboflavin Bioconjugate on Green Mold Caused by Penicillium digitatum in Lemon Fruit

Penicillium digitatum is the causal agent of green mold, a primary postharvest disease of citrus fruits. This study evaluated the efficacy of a novel photoactive chitosan-riboflavin bioconjugate (CH-RF) to control green mold in vitro and in lemon fruit. The results showed total inhibition of P. digitatum growth on APDA supplemented with CH-RF at 0.5% (w/v) and a significant reduction of 84.8% at 0.25% (w/v). Lemons treated with CH-RF and kept under controlled conditions (20 °C and 90-95% relative humidity) exhibited a noteworthy reduction in green mold incidence four days post-inoculation. Notably, these effects persisted, with all treatments remaining significantly distinct from the control group until day 14. Furthermore, CH-RF showed high control of green mold in lemons after 20 days of cold storage (5 ± 1 °C). The disease incidence five days after cold storage indicated significant differences from the values observed in the control. Most CH-RF treatments showed enhanced control of green mold when riboflavin was activated by white-light exposure. These findings suggest that this novel fungicide could be a viable alternative to conventional synthetic fungicides, allowing more sustainable management of lemon fruit diseases.

Harnessing Efficient ROS Generation in Carbon Dots Derived from Methyl Red for Antimicrobial Photodynamic Therapy

The emergence of drug-resistant pathogenic microorganisms has become a public health concern, with demand for strategies to suppress their proliferation in healthcare facilities. The present study investigates the physicochemical and antimicrobial properties of carbon dots (CD-MR) derived from the methyl red azo dye. The morphological and structural analyses reveal that such carbon dots present a significant fraction of graphitic nitrogen in their structures, providing a wide emission range. Based on their low cytotoxicity against mammalian cells and tunable photoluminescence, these carbon dots are applied to bioimaging in vitro living cells. The possibility of using CD-MR to generate reactive oxygen species (ROS) is also analyzed, and a high singlet oxygen quantum efficiency is verified. Moreover, the antimicrobial activity of CD-MR is analyzed against pathogenic microorganisms Staphylococcus aureus, Candida albicans, and Cryptococcus neoformans. Kirby-Bauer susceptibility tests show that carbon dots synthesized from methyl red possess antimicrobial activity upon photoexcitation at 532 nm. The growth inhibition of C. neoformans from CD-MR photosensitization is investigated. Our results show that N-doped carbon dots synthesized from methyl red efficiently generate ROS and possess a strong antimicrobial activity against healthcare-relevant pathogens.

Mechanism of Action and Efficiency of Ag3PO4-Based Photocatalysts for the Control of Hazardous Gram-Positive Pathogens

Silver phosphate and its composites have been attracting extensive interest as photocatalysts potentially effective against pathogenic microorganisms. The purpose of the present study was to investigate the mechanism of bactericidal action on cells of opportunistic pathogens. The Ag3PO4/P25 (AGP/P25) and Ag3PO4/HA (HA/AGP) powders were prepared via a co-precipitation method. Thereafter, their antimicrobial properties against Enterococcus faecalis, Staphylococcus epidermidis, and Staphylococcus aureus (clinical and reference strains) were analyzed in the dark and after exposure to visible light (VIS). The mechanism leading to cell death was investigated by the leakage of metabolites and potassium ions, oxidative stress, and ROS production. Morphological changes of the bacterial cells were visualized by transmission electron microscopy (TEM) and scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy (SEM EDS) analysis. It has been shown that Ag3PO4-based composites are highly effective agents that can eradicate 100% of bacterial populations during the 60 min photocatalytic inactivation. Their action is mainly due to the production of hydroxyl radicals and photogenerated holes which lead to oxidative stress in cells. The strong affinity to the bacterial cell wall, as well as the well-known biocidal properties of silver itself, increase undoubtedly the antimicrobial potential of the Ag3PO4-based composites.

Mitochondria ROS and mitophagy in acute kidney injury

Mitophagy is an essential mitochondrial quality control mechanism that eliminates damaged mitochondria and the production of reactive oxygen species (ROS). The relationship between mitochondria oxidative stress, ROS production and mitophagy are intimately interwoven, and these processes are all involved in various pathological conditions of acute kidney injury (AKI). The elimination of damaged mitochondria through mitophagy in mammals is a complicated process which involves several pathways. Furthermore, the interplay between mitophagy and different types of cell death, such as apoptosis, pyroptosis and ferroptosis in kidney injury is unclear. Here we will review recent advances in our understanding of the relationship between ROS and mitophagy, the different mitophagy pathways, the relationship between mitophagy and cell death, and the relevance of these processes in the pathogenesis of AKI.Abbreviations: AKI: acute kidney injury; AMBRA1: autophagy and beclin 1 regulator 1; ATP: adenosine triphosphate; BAK1: BCL2 antagonist/killer 1; BAX: BCL2 associated X, apoptosis regulator; BCL2: BCL2 apoptosis regulator; BECN1: beclin 1; BH3: BCL2 homology domain 3; BNIP3: BCL2 interacting protein 3; BNIP3L/NIX: BCL2 interacting protein 3 like; CASP1: caspase 1; CAT: catalase; CCCP: carbonyl cyanide m-chlorophenylhydrazone; CI-AKI: contrast-induced acute kidney injury; CISD1: CDGSH iron sulfur domain 1; CL: cardiolipin; CNP: 2',3'-cyclic nucleotide 3'-phosphodiesterase; DNM1L/DRP1: dynamin 1 like; E3: enzyme 3; ETC: electron transport chain; FA: folic acid; FUNDC1: FUN14 domain containing 1; G3P: glycerol-3-phosphate; G6PD: glucose-6-phosphate dehydrogenase; GPX: glutathione peroxidase; GSH: glutathione; GSK3B: glycogen synthase kinase 3 beta; GSR: glutathione-disulfide reductase; HIF1A: hypoxia inducible factor 1 subunit alpha; HUWE1: HECT, UBA and WWE domain containing 1; IL1B: interleukin 1 beta; IMM: inner mitochondrial membrane; IPC: ischemic preconditioning; IRI: ischemia-reperfusion injury; LIR: LC3-interacting region; LPS: lipopolysaccharide; MA: malate-aspartate; MPT: mitochondrial permeability transition; MUL1: mitochondrial E3 ubiquitin protein ligase 1; mtROS: mitochondrial ROS; NLR: NOD-like receptor; NLRP3: NLR family pyrin domain containing 3; NOX: NADPH oxidase; OGD-R: oxygen-glucose deprivation-reperfusion; OMM: outer mitochondrial membrane; OPA1: OPA1 mitochondrial dynamin like GTPase; OXPHOS: oxidative phosphorylation; PARL: presenilin associated rhomboid like; PINK1: PTEN induced kinase 1; PLSCR3: phospholipid scramblase 3; PMP: peptidase, mitochondrial processing; PRDX: peroxiredoxin; PRKN: parkin RBR E3 ubiquitin protein ligase; RPTC: rat proximal tubular cells; ROS: reactive oxygen species; SLC7A11/xCT: solute carrier family 7 member 11; SOD: superoxide dismutase; SOR: superoxide reductase; SQSTM1/p62: sequestosome 1; TCA: tricarboxylic acid; TIMM: translocase of inner mitochondrial membrane; TOMM: translocase of outer mitochondrial membrane; TXN: thioredoxin; VDAC: voltage dependent anion channel; VCP: valosin containing protein.

Photoantimicrobials in agriculture

Classical approaches for controlling plant pathogens may be impaired by the development of pathogen resistance to chemical pesticides and by limited availability of effective antimicrobial agents. Recent increases in consumer awareness of and/or legislation regarding environmental and human health, and the urgent need to improve food security, are driving increased demand for safer antimicrobial strategies. Therefore, there is a need for a step change in the approaches used for controlling pre- and post-harvest diseases and foodborne human pathogens. The use of light-activated antimicrobial substances for the so-called antimicrobial photodynamic treatment is known to be effective not only in a clinical context, but also for use in agriculture to control plant-pathogenic fungi and bacteria, and to eliminate foodborne human pathogens from seeds, sprouted seeds, fruits, and vegetables. Here, we take a holistic approach to review and re-evaluate recent findings on: (i) the ecology of naturally-occurring photoantimicrobials, (ii) photodynamic processes including the light-activated antimicrobial activities of some plant metabolites, and (iii) fungus-induced photosensitization of plants. The inhibitory mechanisms of both natural and synthetic light-activated substances, known as photosensitizers, are discussed in the contexts of microbial stress biology and agricultural biotechnology. Their modes-of-antimicrobial action make them neither stressors nor toxins/toxicants (with specific modes of poisonous activity), but a hybrid/combination of both. We highlight the use of photoantimicrobials for the control of plant-pathogenic fungi and quantify their potential contribution to global food security.

Study of the synergistic effect of singlet oxygen with other plasma-generated ROS in fungi inactivation during water disinfection

Cold atmospheric plasma (CAP) possesses the ability of high-efficiency disinfection. It is reported that mixtures of reactive oxygen species (ROS) including ^·OH, ¹O₂, O₂^- and H₂O₂ generated from CAP have better antimicrobial ability than mimicked solution of mixture of single ROS type, but the reason is not clear. In this study, CAP was applied to treat yeasts in water in order to investigate the fungal inactivation efficiency and mechanism. The results showed that plasma treatment for 5 min could result in >2-log reduction of yeast cells, and application of varied ROS scavengers could significantly increase the yeast survival rate, indicating that ^·OH and ¹O₂ played the pivotal role in yeast inactivation. Moreover, the synergistic effect of ¹O₂ with other plasma-generated ROS was revealed. ¹O₂ could diffuse into cells and induce the depolarization of mitochondrial membrane potential (MMP), and different levels of MMP depolarization determined different cell death modes. Mild damage of mitochondria during short-term plasma treatment could lead to apoptosis. For long-term plasma treatment, the cell membrane could be severely damaged by the plasma-generated ^·OH, so a large amount of ¹O₂ could induce more depolarization of MMP, leading to increase of intracellular O₂^- and Fe²⁺ which subsequently caused cell inactivation. ¹O₂ could also induce protein aggregation and increase of RIP1/RIP3 necrosome, leading to necroptosis. With participation of ¹O₂, endogenous ^·OH could also be generated via Fenton and Haber-Weiss reactions during plasma treatment, which potentiated necroptosis. Adding l-His could mitigate membrane damage, inhibit the drop of MMP and the formation of necrosome, and thus prevent the happening of necroptosis. These findings may deepen the understanding of plasma sterilization mechanisms and provide guidance for microbial killing in the environment.

Protoporphyrin IX-Chitosan Oligosaccharide Conjugate with Potent Antifungal Photodynamic Activity

A new chemical conjugate between protoporphyrin IX (PPIX) and chitosan oligosaccharides (CH) was prepared and evaluated in vitro as an antifungal agent against Penicillium digitatum. Chemical characterization and photophysical/photochemical studies were conducted. The antifungal effect of the CH-PPIX conjugate was compared to its components (PPIX and CH) and a physical mixture of both, under dark and illuminated conditions. The CH-PPIX conjugate was photostable and inhibited fungal growth with 100% efficiency at a dose of 0.005% w/v under visible light irradiation, while no antifungal activity was observed in the dark. Under the same conditions, CH and PPIX did not display any fungicidal activity, demonstrating the improved properties of the conjugate. Insights into the mechanism of fungal inactivation revealed an efficient spore uptake and photoinduced membrane damage through singlet oxygen generation. This new bioconjugate, which is based on natural components, represents a promising agent for fungicidal formulations based on antimicrobial photodynamic therapy.

The facilitating effect of blue light on the antifungal agent susceptibilities of passaged conidia from the ocular-derived Fusarium solani species complex

The eye is a light-receiving organ and has anatomical advantages to accept phototherapy. Fungi colonizing on the eyes, which cause ocular mycoses, are affected by daily blue light and could easily accept additional light irritation. Ocular mycoses are recalcitrant and blindness-causing eye diseases, and antifungal agent treatments are insufficient. Our team previously found that blue light could inhibit Fusarium solani hyphal growth but promote conidiation. Here, we investigated the antifungal susceptibilities and biological characteristics of the passaged conidia. Twelve Fusarium solani strains (11 ocular-derived strains and 1 standard laboratory strain) were inoculated under blue light (0.5 mW/cm2) and darkness conditions, respectively, to obtain the passaged conidia of blue light group (n = 12) and darkness group (n = 12). Two groups were tested to determine the growth abilities and in vitro antifungal susceptibilities to five antifungal drugs (voriconazole (VRC), amphotericin B (AMB), terbinafine (TRB), caspofungin (CAS), and 5-flucytosine (5FC)), which were examined by microscopy for morphological observation and spectrophotometry for turbidity analysis. The results showed that blue light group passaged conidia were more sensitive to antifungal drugs (AMB, VRC, TRB, and CAS) compared to darkness group. The MIC50 of VRC significantly decreased after blue light treatment (P < 0.05). The fungal inhibition rate significantly increased for VRC, AMB, and TRB in the low concentration range (P < 0.05 or P < 0.01). Blue light did not affect germination or hyphal extension of passaged conidia. These results suggested that blue light could facilitate fungal inhibition effect of AMB, VRC, TRB, and CAS and may improve the therapeutic efficiency in VRC and AMB clinical applications. Blue light phototherapy may provide a new adjuvant approach for the treatment of ocular mycosis.

Photochemistry and photophysics of cholesta-5,7,9(11)-trien-3β-ol: a fluorescent analogue of cholesterol

Cholesta-5,7,9(11)-trien-3β-ol (9,11-dehydroprovitamin D₃, CTL) is used as a fluorescent probe to track the presence and migration of cholesterol in vivo. CTL is known to be photochemically active, but little consideration has been given to the formation efficiency and possible toxicity of its photoproducts. In degassed tetrahydrofuran (THF) solution, we isolated the photoproduct of CTL and of its 25-hydroxy derivative (HOCTL), and X-ray crystal structures were obtained for HOCTL and the photorearrangement product. The X-ray crystal structure and its ¹H NMR spectrum confirm the product structure as a pentacyclic HOCTL isomer. In the presence of air in THF, endoperoxide formation via [2+4] addition of ¹O₂* across the B ring of CTL or HOCTL becomes the dominant photoreaction. The UV spectrum and decay kinetics of the triplet state of HOCTL, the precursor of ¹O₂*, are determined by transient absorption spectroscopy. We confirm the proposed structure of the endoperoxide by X-ray crystallography. Kinetics analysis of quantum yields provides rate constants for photophysical and photochemical events.

Ultra-high irradiance (UHI) blue light: highlighting the potential of a novel LED-based device for short antifungal treatments of food contact surfaces

Microbial food spoilage is an important cause of health and economic issues and can occur via resilient contamination of food surfaces. Novel technologies, such as the use of visible light, have seen the light of day to overcome the drawbacks associated with surface disinfection treatments. However, most studies report that photo-inactivation of microorganisms with visible light requires long time treatments. In the present study, a novel light electroluminescent diode (LED)-based device was designed to generate irradiation at an ultra-high power density (901.1 mW/cm²). The efficacy of this technology was investigated with the inactivation of the yeast S. cerevisiae. Short-time treatments (below 10 min) at 405 nm induced a ~4.5 log reduction rate of the cultivable yeast population. The rate of inactivation was positively correlated to the overall energy received by the sample and, at a similar energy, to the power density dispatched by the lamp. A successful disinfection of several food contact surfaces (stainless steel, glass, polypropylene, polyethylene) was achieved as S. cerevisiae was completely inactivated within 5 min of treatments. The disinfection of stainless steel was particularly effective with a complete inactivation of the yeast after 2 min of treatment. This ultra-high irradiance technology could represent a novel cost- and time-effective candidate for microbial inactivation of food surfaces. These treatments could see applications beyond the food industry, in segments such as healthcare or public transport. KEY POINTS : • A novel LED-based device was designed to emit ultra-high irradiance blue light • Short time treatments induced high rate of inhibition of S. cerevisiae • Multiple food contact surfaces were entirely disinfected with 5-min treatments.

In Silico Prediction of Steroids and Triterpenoids as Potential Regulators of Lipid Metabolism

This review focuses on a rare group of steroids and triterpenoids that share common properties as regulators of lipid metabolism. This group of compounds is divided by the type of chemical structure, and they represent: aromatic steroids, steroid phosphate esters, highly oxygenated steroids such as steroid endoperoxides and hydroperoxides, α,β-epoxy steroids, and secosteroids. In addition, subgroups of carbon-bridged steroids, neo steroids, miscellaneous steroids, as well as synthetic steroids containing heteroatoms S (epithio steroids), Se (selena steroids), Te (tellura steroids), and At (astatosteroids) were presented. Natural steroids and triterpenoids have been found and identified from various sources such as marine sponges, soft corals, starfish, and other marine invertebrates. In addition, this group of rare lipids is found in fungi, fungal endophytes, and plants. The pharmacological profile of the presented steroids and triterpenoids was determined using the well-known computer program PASS, which is currently available online for all interested scientists and pharmacologists and is currently used by research teams from more than 130 countries of the world. Our attention has been focused on the biological activities of steroids and triterpenoids associated with the regulation of cholesterol metabolism and related processes such as anti-hyperlipoproteinemic activity, as well as the treatment of atherosclerosis, lipoprotein disorders, or inhibitors of cholesterol synthesis. In addition, individual steroids and triterpenoids were identified that demonstrated rare or unique biological activities such as treating neurodegenerative diseases, Alzheimer's, and Parkinson's diseases with a high degree of certainty over 95 percent. For individual steroids or triterpenoids or a group of compounds, 3D drawings of their predicted biological activities are presented.

Synthesis and Applications of Porphyrin-Biomacromolecule Conjugates

With potential applications in materials and especially in light-responsive biomedicine that targets cancer tissue selectively, much research has focused on developing covalent conjugation techniques to tether porphyrinoid units to various biomacromolecules. This review details the key synthetic approaches that have been employed in the recent decades to conjugate porphyrinoids with oligonucleotides and peptides/proteins. In addition, we provide succinct discussions on the subsequent applications of such hybrid systems and also give a brief overview of the rapidly progressing field of porphyrin-antibody conjugates. Since nucleic acid and peptide systems vary in structure, connectivity, functional group availability and placement, as well as stability and solubility, tailored synthetic approaches are needed for conjugating to each of these biomacromolecule types. In terms of tethering to ONs, porphyrins are typically attached by employing bioorthogonal chemistry (e.g., using phosphoramidites) that drive solid-phase ON synthesis or by conducting post-synthesis modifications and subsequent reactions (such as amide couplings, hydrazide-carbonyl reactions, and click chemistry). In contrast, peptides and proteins are typically conjugated to porphyrinoids using their native functional groups, especially the thiol and amine side chains. However, bioorthogonal reactions (e.g., Staudinger ligations, and copper or strain promoted alkyne-azide cycloadditions) that utilize de novo introduced functional groups onto peptides/proteins have seen vigorous development, especially for site-specific peptide-porphyrin tethering. While the ON-porphyrin conjugates have largely been explored for programmed nanostructure self-assembly and artificial light-harvesting applications, there are some reports of ON-porphyrin systems targeting clinically translational applications (e.g., antimicrobial biomaterials and site-specific nucleic acid cleavage). Conjugates of porphyrins with proteinaceous moieties, on the other hand, have been predominantly used for therapeutic and diagnostic applications (especially in photodynamic therapy, photodynamic antimicrobial chemotherapy, and photothermal therapy). The advancement of the field of porphyrinoid-bioconjugation chemistry from basic academic research to more clinically targeted applications require continuous fine-tuning in terms of synthetic strategies and hence there will continue to be much exciting work on porphyrinoid-biomacromolecule conjugation.

Antioxidant Properties of Ergosterol and Its Role in Yeast Resistance to Oxidation

Although the functions and structural roles of sterols have been the subject of numerous studies, the reasons for the diversity of sterols in the different eukaryotic kingdoms remain unclear. It is thought that the specificity of sterols is linked to unidentified supplementary functions that could enable organisms to be better adapted to their environment. Ergosterol is accumulated by late branching fungi that encounter oxidative perturbations in their interfacial habitats. Here, we investigated the antioxidant properties of ergosterol using in vivo, in vitro, and in silico approaches. The results showed that ergosterol is involved in yeast resistance to tert-butyl hydroperoxide and protects lipids against oxidation in liposomes. A computational study based on quantum chemistry revealed that this protection could be related to its antioxidant properties operating through an electron transfer followed by a proton transfer mechanism. This study demonstrates the antioxidant role of ergosterol and proposes knowledge elements to explain the specific accumulation of this sterol in late branching fungi. Ergosterol, as a natural antioxidant molecule, could also play a role in the incompletely understood beneficial effects of some mushrooms on health.

Biofilm eradication and antifungal mechanism of action against Candida albicans of cationic dicephalic surfactants with a labile linker

Our research aims to expand the knowledge on relationships between the structure of cationic dicephalic surfactants—N,N-bis[3,3_-(dimethylamine)propyl]alkylamide dihydrochlorides and N,N-bis[3,3_-(trimethylammonio)propyl]alkylamide dibromides (alkyl: n-C9H19, n-C11H23, n-C13H27, n-C15H31)—and their antifungal mechanism of action on Candida albicans. The mentioned groups of amphiphilic substances are characterized by the presence of a weak, hydrochloride cationic center readily undergoing deprotonation, as well as a stable, strong quaternary ammonium group and alkyl chains capable of strong interactions with fungal cells. Strong fungicidal properties and the role in creation and eradication of biofilm of those compounds were discussed in our earlier works, yet their mechanism of action remained unclear. It was shown that investigated surfactants induce strong oxidative stress and cause increase in cell membrane permeability without compromising its continuity, as indicated by increased potassium ion (K⁺) leakage. Thus experiments carried out on the investigated opportunistic pathogen indicate that the mechanism of action of the researched surfactants is different than in the case of the majority of known surfactants. Results presented in this paper significantly broaden the understanding on multifunctional cationic surfactants and their mechanism of action, as well as suggest their possible future applications as surface coating antiadhesives, fungicides and antibiofilm agents in medicine or industry.

Stress and ageing in yeast

There has long been speculation about the role of various stresses in ageing. Some stresses have beneficial effects on ageing-dependent on duration and severity of the stress, others have negative effects and the question arises whether these negative effects are causative of ageing or the result of the ageing process. Cellular responses to many stresses are highly coordinated in a concerted way and hence there is a great deal of cross-talk between different stresses. Here the relevant aspects of the coordination of stress responses and the roles of different stresses on yeast cell ageing are discussed, together with the various functions that are involved. The cellular processes that are involved in alleviating the effects of stress on ageing are considered, together with the possible role of early stress events on subsequent ageing of cells.

Novel Chitosan-Riboflavin Conjugate with Visible Light-Enhanced Antifungal Properties against Penicillium digitatum

A novel chemical conjugate between chitosan (CH) and riboflavin (RF) has been synthesized and characterized via Fourier transform infrared, NMR, and other spectroscopic methods. Photophysical and photochemical properties such as absorption spectra, fluorescence emission, fluorescence anisotropy, and singlet oxygen generation were characterized as well. This new biopolymer-based conjugate was designed to have an antifungal effect enhanced through antimicrobial photodynamic therapy. The antifungal effect of this conjugate (CH-RF) was compared with CH and RF against Penicillium digitatum in vitro. The conjugate showed the highest fungal growth inhibition of all systems tested at a dose of 0.5% w/v. This new biopolymer-based compound could be a promising alternative to fungicides used in citrus fruits postharvest.

Potent oxidation of DNA by Ru(ii) tri(polypyridyl) complexes under visible light irradiation via a singlet oxygen-mediated mechanism

The irradiation of Ru(ii) tri(polypridyl) complexes with visible light can induce potent oxidation of DNA mediated by ¹O₂via a type II photosensitization mechanism.

Chemical features of the photosensitizers new methylene blue N and S137 influence their subcellular localization and photoinactivation efficiency in Candida albicans

Antimicrobial photodynamic treatment (APDT) has emerged as an effective therapy against pathogenic fungi with both acquired and intrinsic resistance to commonly used antifungal agents. Success of APDT depends on the availability of effective photosensitizers capable of acting on different fungal structures and species. Among the phenothiazinium dyes tested as photoantifungals, new methylene blue N (NMBN) and the novel pentacyclic compound S137 are the most efficient. In the present study we compared the effects of APDT with NMBN and S137 on the survival of Candida albicans and employed a set of fluorescent probes (propidium iodide, FUN-1, JC-1, DHR-123 and DHE) together with confocal microscopy and flow cytometry to evaluate the effects of these two chemically diverse photosensitizers on cell membrane permeability, metabolism and redox status, and mitochondrial activity. Taken together, our results indicate that, due to chemical features resulting in different lipophilicity, NMBN and S137 localize to distinct subcellular structures and hence inactivate C. albicans cells via different mechanisms. S137 localizes mostly to the cell membrane and, upon light exposure, photo-oxidizes membrane lipids. NMBN readily localizes to mitochondria and exerts its photodynamic effects there, which was observed to be a less effective way to achieve cell death at lower light fluences.

Photoinactivation of Neisseria gonorrhoeae: A Paradigm-Changing Approach for Combating Antibiotic-Resistant Gonococcal Infection

Antimicrobial resistance in Neisseria gonorrhoeae is a major issue of public health, and there is a critical need for the development of new antigonococcal strategies. In this study, we investigated the effectiveness of antimicrobial blue light (aBL; wavelength, 405 nm), an innovative nonpharmacological approach, for the inactivation of N. gonorrhoeae. Our findings indicated that aBL preferentially inactivated N. gonorrhoeae, including antibiotic-resistant strains, over human vaginal epithelial cells in vitro. Furthermore, no aBL-induced genotoxicity to the vaginal epithelial cells was observed at the radiant exposure used to inactivate N. gonorrhoeae. aBL also effectively inactivated N. gonorrhoeae that had attached to and invaded into the vaginal epithelial cells in their cocultures. No gonococcal resistance to aBL developed after 15 successive cycles of inactivation induced by subtherapeutic exposure to aBL. Endogenous aBL-activatable photosensitizing porphyrins in N. gonorrhoeae were identified and quantified using ultraperformance liquid chromatography, with coproporphyrin being the most abundant species in all N. gonorrhoeae strains studied. Singlet oxygen was involved in aBL inactivation of N. gonorrhoeae. Together, these findings show that aBL represents a potential potent treatment for antibiotic-resistant gonococcal infection.

Hydroperoxy steroids and triterpenoids derived from plant and fungi: Origin, structures and biological activities

Hydroperoxides (R-OOH) represent a small family of natural metabolites that have been isolated from higher plants, fungi, and marine organisms. This paper is devoted to the distribution of hydroperoxides in plants, fungi and terrestrial fungal endophytes and their biological activity. Hydroperoxides of plants demonstrate a wide range of biological activities however, antineoplastic and anti-ulcerative are most characteristic with confidence from 91 to 98 percent. For hydroperoxides from fungi, the dominant are antineoplastic and anti-hypercholesterolemic activities with confidence from 89 to 92 percent. Very interesting activity was found for some triterpenoid hydroperoxides, which is characterized as a treatment for the symptoms of dementia. The norlupane hydroperoxide shows activity for the treatment of dementia. It is interesting that the reliability of this activity was very high 97.2%. According to our preliminary data, the norlupane hydroperoxide is apparently the first natural metabolite that showed almost 100 percent activity for the treatment of dementia. However, to confirm these data requires practical and clinical experimental work.

Cell Death Mechanisms Induced by Photo-Oxidation Studied at the Cell Scale in the Yeast Saccharomyces cerevisiae

Blue light (400–430 nm) is known to induce lethal effects in some species of fungi by photo-oxidation caused by the excitation of porphyrins but the mechanisms involved remain poorly understood. In this work, we exposed the yeast Saccharomyces cerevisiae to a high density light flux with two-photon excitation (830 nm equivalent to a one-photon excitation around 415 nm) and used quasi real-time visualization with confocal microscopy to study the initiation and dynamics of photo-oxidation in subcellular structures. Our results show that the oxidation generated by light treatments led to the permeabilization of the plasma membrane accompanied by the sudden expulsion of the cellular content, corresponding to cell death by necrosis. Moreover, excitation in the plasma membrane led to very fast oxidation and membrane permeabilization (<60 s) while excitation at the center of the cell did not induce permeabilization even after a period exceeding 600 s. Finally, our study shows that the relationship between the laser power used for two-photon excitation and the time required to permeabilize the plasma membrane was not linear. Thus, the higher the power used, the lower the energy required to permeabilize the plasma membrane. We conclude that fungal destruction can be generated very quickly using a high density light flux. Better knowledge of the intracellular processes and the conditions necessary to induce necrosis should make it possible in the future to improve the efficiency of antimicrobial strategies photo-oxidation-based.

The effects of photodynamic treatment with new methylene blue N on the Candida albicans proteome

Candida albicans is a human pathogenic fungus mainly affecting immunocompromised patients. Resistance to the commonly used fungicides can lead to poor treatment of mucosal infections which, in turn, can result in life-threatening systemic candidiasis. In this scenario, antimicrobial photodynamic treatment (PDT) has emerged as an effective alternative to treat superficial and localized fungal infections. Microbial death in PDT is a consequence of the oxidation of many cellular biomolecules, including proteins. Here, we report a combination of two-dimensional electrophoresis and tandem mass spectrometry to study the protein damage resulting from treating C. albicans with PDT with new methylene blue N and red light. Two-dimensional gels of treated cells showed an increase in acidic spots in a fluence-dependent manner. Amino acid analysis revealed a decrease in the histidine content after PDT, which is one plausible explanation for the observed acidic shift. However, some protein spots remained unchanged. Protein identification by mass spectrometry revealed that both modified and unmodified proteins could be localized to the cytoplasm, ruling out subcellular location as the only explanation for damage selectivity. Therefore, we hypothesize that protein modification by PDT is a consequence of both photosensitizer binding affinity and the degree of exposure of the photooxidizable residues on the protein surface.

Light treatments of nail fungal infections

Nail fungal infections are notoriously persistent and difficult to treat which can lead to severe health impacts, particularly in the immunocompromized. Current antifungal treatments, including systemic and topical drugs, are prolonged and do not effectively provide a complete cure. Severe side effects are also associated with systemic antifungals, such as hepatotoxicity. Light treatments of onychomycosis are an emerging therapy that has localized photodynamic, photothermal or photoablative action. These treatments have shown to be an effective alternative to traditional antifungal remedies with comparable or better cure rates achieved in shorter times and without systemic side effects. This report reviews significant clinical and experimental studies in the field, highlighting mechanisms of action and major effects related to light therapy; in particular, the impact of light on fungal genetics.

Lipid-mediated signals that regulate mitochondrial biology

For decades, lipids were assumed to fulfill roles only in energy storage and membrane structure. Recent studies have discovered critical roles for phospholipids, sphingolipids, and sterols in many cellular pathways, including cell signaling and transcriptional regulation. Frequently, lipids from these various classes work together to achieve defined cellular outcomes. Specific mitochondrial lipids are critical for proper assembly of the electron transport chain complexes and for effective responses to mitochondrial damage, including maintenance of mitochondrial protein homeostasis, regulation of mitophagy, and induction of apoptosis. In this Minireview, we will primarily focus on mitochondrial lipid signaling mediated by lipid-protein interactions.

Sterol Oxidation Mediates Stress-Responsive Vms1 Translocation to Mitochondria

Vms1 translocates to damaged mitochondria in response to stress, whereupon its binding partner, Cdc48, contributes to mitochondrial protein homeostasis. Mitochondrial targeting of Vms1 is mediated by its conserved mitochondrial targeting domain (MTD), which, in unstressed conditions, is inhibited by intramolecular binding to the Vms1 leucine-rich sequence (LRS). Here, we report a 2.7 Å crystal structure of Vms1 that reveals that the LRS lies in a hydrophobic groove in the autoinhibited MTD. We also demonstrate that the oxidized sterol, ergosterol peroxide, is necessary and sufficient for Vms1 localization to mitochondria, through binding the MTD in an interaction that is competitive with binding to the LRS. These data support a model in which stressed mitochondria generate an oxidized sterol receptor that recruits Vms1 to support mitochondrial protein homeostasis.

Antimicrobial photodynamic inactivation inhibits Candida albicans virulence factors and reduces in vivo pathogenicity

The objective of this study was to evaluate whether Candida albicans exhibits altered pathogenicity characteristics following sublethal antimicrobial photodynamic inactivation (APDI) and if such alterations are maintained in the daughter cells. C. albicans was exposed to sublethal APDI by using methylene blue (MB) as a photosensitizer (0.05 mM) combined with a GaAlAs diode laser (λ 660 nm, 75 mW/cm(2), 9 to 27 J/cm(2)). In vitro, we evaluated APDI effects on C. albicans growth, germ tube formation, sensitivity to oxidative and osmotic stress, cell wall integrity, and fluconazole susceptibility. In vivo, we evaluated C. albicans pathogenicity with a mouse model of systemic infection. Animal survival was evaluated daily. Sublethal MB-mediated APDI reduced the growth rate and the ability of C. albicans to form germ tubes compared to untreated cells (P < 0.05). Survival of mice systemically infected with C. albicans pretreated with APDI was significantly increased compared to mice infected with untreated yeast (P < 0.05). APDI increased C. albicans sensitivity to sodium dodecyl sulfate, caffeine, and hydrogen peroxide. The MIC for fluconazole for C. albicans was also reduced following sublethal MB-mediated APDI. However, none of those pathogenic parameters was altered in daughter cells of C. albicans submitted to APDI. These data suggest that APDI may inhibit virulence factors and reduce in vivo pathogenicity of C. albicans. The absence of alterations in daughter cells indicates that APDI effects are transitory. The MIC reduction for fluconazole following APDI suggests that this antifungal could be combined with APDI to treat C. albicans infections.

Population dynamics and habitat sharing of natural populations of Caenorhabditis elegans and C. briggsae

BACKGROUND

The nematode Caenorhabditis elegans is a major model organism in laboratory biology. Very little is known, however, about its ecology, including where it proliferates. In the past, C. elegans was mainly isolated from human-made compost heaps, where it was overwhelmingly found in the non-feeding dauer diapause stage.

RESULTS

C. elegans and C. briggsae were found in large, proliferating populations in rotting plant material (fruits and stems) in several locations in mainland France. Both species were found to co-occur in samples isolated from a given plant species. Population counts spanned a range from one to more than 10,000 Caenorhabditis individuals on a single fruit or stem. Some populations with an intermediate census size (10 to 1,000) contained no dauer larvae at all, whereas larger populations always included some larvae in the pre-dauer or dauer stages. We report on associated micro-organisms, including pathogens. We systematically sampled a spatio-temporally structured set of rotting apples in an apple orchard in Orsay over four years. C. elegans and C. briggsae were abundantly found every year, but their temporal distributions did not coincide. C. briggsae was found alone in summer, whereas both species co-occurred in early fall and C. elegans was found alone in late fall. Competition experiments in the laboratory at different temperatures show that C. briggsae out-competes C. elegans at high temperatures, whereas C. elegans out-competes C. briggsae at lower temperatures.

CONCLUSIONS

C. elegans and C. briggsae proliferate in the same rotting vegetal substrates. In contrast to previous surveys of populations in compost heaps, we found fully proliferating populations with no dauer larvae. The temporal sharing of the habitat by the two species coincides with their temperature preference in the laboratory, with C. briggsae populations growing faster than C. elegans at higher temperatures, and vice at lower temperatures.

Phototoxic action of light emitting diode in the in vitro viability of Trichophyton rubrum

BACKGROUND: Trichophyton rubrum is the most common agent of superficial mycosis of the skin and nails causing long lasting infections and high recurrence rates. Current treatment drawbacks involve topical medications not being able to reach the nail bed at therapeutic concentrations, systemic antifungal drugs failing to eradicate the fungus before the nails are renewed, severe side effects and selection of resistant fungal isolates. Photodynamic therapy (PDT) has been a promising alternative to conventional treatments. OBJECTIVES: This study evaluated the in vitro effectiveness of toluidine blue O (TBO) irradiated by Light emitting diode (LED) in the reduction of T. rubrum viability. METHODS: The fungal inoculums' was prepared and exposed to different TBO concentrations and energy densities of Light emitting diode for evaluate the T. rubrum sensibility to PDT and production effect fungicidal after photodynamic treatment. In addition, the profiles of the area and volume of the irradiated fungal suspensions were also investigated. RESULTS: A small reduction, in vitro, of fungal cells was observed after exposition to 100 µM toluidine blue O irradiated by 18 J/cm² Light emitting diode. Fungicidal effect occurred after 25 µM toluidine blue O irradiation by Light emitting diode with energy density of 72 J/cm². The analysis showed that the area and volume irradiated by the Light emitting diode were 52.2 mm² and 413.70 mm³, respectively. CONCLUSION: The results allowed to conclude that Photodynamic therapy using Light emitting diode under these experimental conditions is a possible alternative approach to inhibit in vitro T. rubrum and may be a promising new treatment for dermatophytosis caused by this fungus.

Vitamin E prevents lipid raft modifications induced by an anti-cancer lysophospholipid and abolishes a Yap1-mediated stress response in yeast

We have previously established that the anti-cancer lysophospholipid edelfosine (1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine, Et-18-OCH(3)) induces cell death in yeast by selective modification of lipid raft composition at the plasma membrane. In this study we determined that alpha-tocopherol protects cells from the edelfosine cytotoxic effect, preventing the internalization of sterols and the plasma membrane proton pump ATPase, Pma1p. Two non-mutually exclusive hypotheses were considered to explain the protective effect of alpha-tocopherol: (i) its classical antioxidant activity is necessary to break progression of lipid peroxidation, despite the fact Saccharomyces cerevisiae does not possess polyunsaturated fatty acids and (ii) due to its complementary cone shape, insertion of alpha-tocopherol could correct membrane curvature stress imposed by edelfosine (inverted cone shape). We then developed tools to distinguish between these two hypotheses and dissect the structural requirements that confer alpha-tocopherol its protective effect. Our results indicated its lipophilic nature and the H donating hydroxyl group from the chromanol ring are both required to counteract the cytotoxic effect of edelfosine, suggesting edelfosine induces oxidation of membrane components. To further support this finding and learn more about the early cellular response to edelfosine we investigated the role that known oxidative stress signaling pathways play in modulating sensitivity to the lipid drug. Our results indicate the transcription factors Yap1 and Skn7 as well as the major peroxiredoxin, Tsa1, mediate a response to edelfosine. Interestingly, the pathway differed from the one triggered by hydrogen peroxide and its activation (measured as Yap1 translocation to the nucleus) was abolished by co-treatment of the cells with alpha-tocopherol.

Photodynamic inactivation of four Candida species induced by photogem(®)

This study evaluated the in vitro susceptibility of C. albicans, C. dubliniensis, C. tropicalis and C. krusei to photodynamic therapy (PDT) induced by Photogem^®and light emitted diode (LED). Suspensions of each Candida strain were treated with three photosensitizer (PS) concentrations (10, 25 and 50 mg/L) and exposed to 18, 25.5 and 37.5 J/cm² LED light fluences (λ ~ 455 nm). Control suspensions were treated only with PS concentrations, only exposed to the LED light fluences or not exposed to LED light or PS. Sixteen experimental conditions were obtained and each condition was repeated three times. From each sample, serial dilutions were obtained and aliquots were plated on Sabouraud Dextrose Agar. After incubation of plates (37 °C for 48 hours), colonies were counted (cfu/mL) and the data were statistically analyzed by ANOVA and the Tukey test (α=0.05). Complete killing of C. albicans was observed after 18 J/cm² in association with 50 mg/L of PS. C. dubliniensis were inactivated after 18 J/cm² using 25 mg/L of PS. The inactivation of C. tropicalis was observed after photosensitization with 25 mg/L and subsequent illumination at 25.5 J/cm². For C. krusei, none of the associations between PS and light resulted in complete killing of this species. PDT proved to be effective for the inactivation of C. albicans, C. dubliniensis and C. tropicalis. In addition, reduction in the viability of C. krusei was achieved with some of the PS and light associations.

Squalene versus ergosterol formation using Saccharomyces cerevisiae: combined effect of oxygen supply, inoculum size, and fermentation time on yield and selectivity of the bioprocess

The dynamics of two wild type strains of Saccharomyces cerevisiae (BY4741 and EGY48) that vary in the ability to produce sterols were compared in batch cultures under different aeration conditions. Poor supply of oxygen enhanced selectivity of the bioprocess in favor of squalene formation. Optimization of inoculum size and fermentation time arranged according to a central composite statistical design revealed significant differences between the strains in terms of yield and productivity. Experimental verification showed that an optimized bioprocess under semianaerobic conditions is competitive with regard to those reported in the literature. Maximum squalene yield and productivity were, respectively, 2967.6 +/- 118.7 microg/L of culture medium and 104 +/- 4.2 microg/Lh for BY4741 and 3129 +/- 109.5 microg/L of culture medium and 155.9 +/- 5.5 microg/Lh for EGY48. The prospect of developing high-purity squalene preparations that meet food safety regulation demands is expected to attract the interest of the food industry.

Fluorescence techniques using dehydroergosterol to study cholesterol trafficking

Cholesterol itself has very few structural/chemical features suitable for real-time imaging in living cells. Thus, the advent of dehydroergosterol [ergosta-5,7,9(11),22-tetraen-3beta-ol, DHE] the fluorescent sterol most structurally and functionally similar to cholesterol to date, has proven to be a major asset for real-time probing/elucidating the sterol environment and intracellular sterol trafficking in living organisms. DHE is a naturally occurring, fluorescent sterol analog that faithfully mimics many of the properties of cholesterol. Because these properties are very sensitive to sterol structure and degradation, such studies require the use of extremely pure (>98%) quantities of fluorescent sterol. DHE is readily bound by cholesterol-binding proteins, is incorporated into lipoproteins (from the diet of animals or by exchange in vitro), and for real-time imaging studies is easily incorporated into cultured cells where it co-distributes with endogenous sterol. Incorporation from an ethanolic stock solution to cell culture media is effective, but this process forms an aqueous dispersion of DHE crystals which can result in endocytic cellular uptake and distribution into lysosomes which is problematic in imaging DHE at the plasma membrane of living cells. In contrast, monomeric DHE can be incorporated from unilamellar vesicles by exchange/fusion with the plasma membrane or from DHE-methyl-beta-cyclodextrin (DHE-MbetaCD) complexes by exchange with the plasma membrane. Both of the latter techniques can deliver large quantities of monomeric DHE with significant distribution into the plasma membrane. The properties and behavior of DHE in protein-binding, lipoproteins, model membranes, biological membranes, lipid rafts/caveolae, and real-time imaging in living cells indicate that this naturally occurring fluorescent sterol is a useful mimic for probing the properties of cholesterol in these systems.

Chemical constituents of Stereum subtomentosum and two other birch-associated basidiomycetes: an interspecies comparative study

Metabolites of the wood-rotting fungus Stereum subtomentosum Pouzar (Basidiomycetes, order Russulales, family Stereaceae) occurring on birch (Betula pendula Roth) trees were phytochemically investigated for the first time. Three main metabolite chemotypes present in MeOH extracts of the fruit bodies, viz. steroids, fatty acids, and water-soluble sugars, were fractionated, isolated, and identified by 1D/2D NMR-spectroscopic analyses, NMR data comparisons, and chemical correlations combined with GC/MS experiments. Thirteen compounds including two 5 alpha,8 alpha-epidioxy steroids, alpha,alpha'-trehalose, D-arabinitol, D-mannitol, and saturated/unsaturated fatty acids, were identified. Differences among S. subtomentosum and two other birch-associated fungal species, Trametes versicolor (L.: Fr.) Pilát, and Piptoporus betulinus (Bull.: Fr.) P. Karst (Basidiomycetes, order Polyporales, family Polyporaceae) were evaluated as regards the richness and abundance relationships in metabolite profiling.

Fluorescent sterols as tools in membrane biophysics and cell biology

Cholesterol is an important constituent of cellular membranes playing a fundamental role in many biological processes. This sterol affects membrane permeability, lateral lipid organization, signal transduction and membrane trafficking. Intracellular sterol transport modes and pathways as well as the regulation of sterol metabolism and disposition in various tissues are areas of intense research. Progress is intimately linked to development and use of appropriate analogs, which closely mimic the properties of cholesterol while allowing to be detected by spectroscopic or microscopic methods. This review provides an overview of various fluorescent sterols used in membrane biophysics and cell biology including analogs of cholesterol and cholesteryl esters. Attention is paid to the natural fluorescent sterol dehydroergosterol (DHE). A survey of the many applications of DHE in biological research is presented. Special emphasis is on recent developments in fluorescence microscopy instrumentation to visualize DHE as an intrinsically fluorescent analog of cholesterol in living cells.

Glycosyl bis-porphyrin conjugates: Synthesis and potential application in PDT

Syntheses of new glycosylated neutral and cationic porphyrin dimers linked at the meso-position via a flexible hydrocarbon chain are described. A detailed 1H and 13C NMR study allows their complete structural elucidation. The UV-visible, fluorescence and MALDI mass spectra are also presented. Photocytotoxicities of these compounds against K562 leukaemia cell line are compared to those of Photofrin II.

5,8-Epidioxysterols and related derivatives from a Chinese soft coral Sinularia flexibilis

Chromatographic separation of the methanolic extract of the marine soft coral, Sinularia flexibilis, resulted in the isolation and characterization of four new sterols, 5alpha,8alpha-epidioxygorgosta-6-en-3beta-ol (1), 5alpha,8alpha-epidioxygorgosta-6,9(11)-dien-3beta-ol (2), 22alpha,28-epidioxycholesta-5,23(E)-dien-3beta-ol (3) and its C-22 epimer (4), along with nine known sterols. The structures of the new compounds were determined on the basis of extensive spectroscopic data (IR, MS, 1H and 13C NMR, HMQC, HMBC, and NOESY) analyses.