Reactivity of Singlet Oxygen with DNA, an Update

Visible light potentiates rapid cell destruction and death by curcumin in vitro

Curcumin, a small molecule derived from the plant Curcuma longa, is a pleiotropic agent with widely varying pharmacological activities attributed to it. In addition to its anti-cancer activity curcumin is also known to be cytotoxic upon photoactivation. Time-lapse DIC and correlative fluorescence microscopy were used to evaluate the effects of curcumin, combined with continuous exposure to visible light, on cellular components of RTG-2 cells. Curcumin combined with visible light resulted in rapid and dramatic destruction of cells. F-actin and microtubule cytoskeletons were drastically altered, both showing fragmentation and overall loss from cells. Nuclei exhibited granulated nucleoplasm, condensed DNA, and physical shrinkage. Mitochondria rapidly fragmented along their length and disappeared from cells. Plasma membrane was breached based on lipophilic dye staining and the entrance of otherwise impermeant small molecules into the cell. Grossly distorted morphology hallmarked by significant swelling and coarse granulation of the cytoplasm was consistently observed. All of these effects were dependent on visible light as the same cellular targets in curcumin-treated cells outside the illuminated area were always unperturbed. The combination of curcumin and continuous exposure to visible light enables rapid and irreversible cellular destruction which can be monitored in real-time. Real-time monitoring of this structural disintegration suggests a new approach to applying curcumin in photodynamic treatments, where the progression of cell and tissue destruction might be simultaneously evaluated through optical means.

Contribution of oxidation reactions to photo-induced damage to cellular DNA

This review article is aimed at providing updated information on the contribution of immediate and delayed oxidative reactions to the photo-induced damage to cellular DNA/skin under exposure to UVB/UVA radiations and visible light. Low-intensity UVC and UVB radiations that operate predominantly through direct excitation of the nucleobases are very poor oxidizing agents giving rise to very low amounts of 8-oxo-7,8-dihydroguanine and DNA strand breaks with respect to the overwhelming bipyrimidine dimeric photoproducts. The importance of these two classes of oxidatively generated damage to DNA significantly increases together with a smaller contribution of oxidized pyrimidine bases upon UVA irradiation. This is rationalized in terms of sensitized photooxidation reactions predominantly mediated by singlet oxygen together with a small contribution of hydroxyl radical that appear to also be implicated in the photodynamic effects of the blue light component of visible light. Chemiexcitation-mediated formation of "dark" cyclobutane pyrimidine dimers in UVA-irradiated melanocytes is a recent major discovery that implicates in the initial stage, a delayed generation of reactive oxygen and nitrogen species giving rise to triplet excited carbonyl intermediate and possibly singlet oxygen. High-intensity UVC nanosecond laser radiation constitutes a suitable source of light to generate pyrimidine and purine radical cations in cellular DNA via efficient biphotonic ionization.

The thioredoxin system determines CHK1 inhibitor sensitivity via redox-mediated regulation of ribonucleotide reductase activity

Checkpoint kinase 1 (CHK1) is critical for cell survival under replication stress (RS). CHK1 inhibitors (CHK1i's) in combination with chemotherapy have shown promising results in preclinical studies but have displayed minimal efficacy with substantial toxicity in clinical trials. To explore combinatorial strategies that can overcome these limitations, we perform an unbiased high-throughput screen in a non-small cell lung cancer (NSCLC) cell line and identify thioredoxin1 (Trx1), a major component of the mammalian antioxidant-system, as a determinant of CHK1i sensitivity. We establish a role for redox recycling of RRM1, the larger subunit of ribonucleotide reductase (RNR), and a depletion of the deoxynucleotide pool in this Trx1-mediated CHK1i sensitivity. Further, the TrxR inhibitor auranofin, an approved anti-rheumatoid arthritis drug, shows a synergistic interaction with CHK1i via interruption of the deoxynucleotide pool. Together, we show a pharmacological combination to treat NSCLC that relies on a redox regulatory link between the Trx system and mammalian RNR activity.

Stress Granule Dysfunction via Chromophore-Associated Light Inactivation

Stress granules (SGs) are cytoplasmic condensates composed of various proteins and RNAs that protect translation-associated machinery from harmful conditions during stress. However, the method of spatiotemporal inactivation of condensates such as SGs in live cells to study cellular phenotypes is still in the process of being demonstrated. Here, we show that the inactivation of SGs by chromophore-associated light inactivation (CALI) using a genetically encoded red fluorescence protein (SuperNova-Red) as a photosensitizer leads to differences in cell viability during recovery from hyperosmotic stress. CALI delayed the disassembly kinetics of SGs during recovery from hyperosmotic stress. Consequently, CALI could inactivate the SGs, and the cellular fate due to SGs could be analyzed. Furthermore, CALI is an effective spatiotemporal knockdown method for intracellular condensates/aggregates and would contribute to the elucidation of importance of such condensates/aggregates.

The Use of Photoactive Polymeric Nanoparticles and Nanofibers to Generate a Photodynamic-Mediated Antimicrobial Effect, with a Special Emphasis on Chronic Wounds

This review is concerned with chronic wounds, with an emphasis on biofilm and its complicated management process. The basics of antimicrobial photodynamic therapy (PDT) and its underlying mechanisms for microbial eradication are presented. Intrinsically active nanocarriers (polydopamine NPs, chitosan NPs, and polymeric micelles) that can further potentiate the antimicrobial photodynamic effect are discussed. This review also delves into the role of photoactive electrospun nanofibers, either in their eluting or non-eluting mode of action, in microbial eradication and accelerating the healing of wounds. Synergic strategies to augment the PDT-mediated effect of photoactive nanofibers are reviewed.

Effects of Intra-Base Pair Proton Transfer on Dissociation and Singlet Oxygenation of 9-Methyl-8-Oxoguanine-1-Methyl-Cytosine Base-Pair Radical Cations

8-Oxoguanosine is the most common oxidatively generated base damage and pairs with complementary cytidine within duplex DNA. The 8-oxoguanosine-cytidine lesion, if not recognized and removed, not only leads to G-to-T transversion mutations but renders the base pair being more vulnerable to the ionizing radiation and singlet oxygen (1 O2 ) damage. Herein, reaction dynamics of a prototype Watson-Crick base pair [9MOG ⋅ 1MC]⋅+ , consisting of 9-methyl-8-oxoguanine radical cation (9MOG⋅+ ) and 1-methylcystosine (1MC), was examined using mass spectrometry coupled with electrospray ionization. We first detected base-pair dissociation in collisions with the Xe gas, which provided insight into intra-base pair proton transfer of 9MOG⋅+  ⋅ 1MC← → ${{\stackrel{ {\rightarrow} } { {\leftarrow} } } }$ [9MOG - HN1 ]⋅ ⋅ [1MC+HN3' ]+ and subsequent non-statistical base-pair separation. We then measured the reaction of [9MOG ⋅ 1MC]⋅+ with 1 O2 , revealing the two most probable pathways, C5-O2 addition and HN7 -abstraction at 9MOG. Reactions were entangled with the two forms of 9MOG radicals and base-pair structures as well as multi-configurations between open-shell radicals and 1 O2 (that has a mixed singlet/triplet character). These were disentangled by utilizing approximately spin-projected density functional theory, coupled-cluster theory and multi-referential electronic structure modeling. The work delineated base-pair structural context effects and determined relative reactivity toward 1 O2 as [9MOG - H]⋅>9MOG⋅+ >[9MOG - HN1 ]⋅ ⋅ [1MC+HN3' ]+ ≥9MOG⋅+  ⋅ 1MC.

Cellular Damage of Bacteria Attached to Senescent Phytoplankton Cells as a Result of the Transfer of Photochemically Produced Singlet Oxygen: A Review

Several studies set out to explain the presence of high proportions of photooxidation products of cis-vaccenic acid (generally considered to be of bacterial origin) in marine environments. These studies show that these oxidation products result from the transfer of singlet oxygen from senescent phytoplankton cells to the bacteria attached to them in response to irradiation by sunlight. This paper summarizes and reviews the key findings of these studies, i.e., the demonstration of the process at work and the effect of different parameters (intensity of solar irradiance, presence of bacterial carotenoids, and presence of polar matrices such as silica, carbonate, and exopolymeric substances around phytoplankton cells) on this transfer. A large part of this review looks at how this type of alteration of bacteria can affect the preservation of algal material in the marine environment, especially in polar regions where conditions drive increased transfer of singlet oxygen from sympagic algae to bacteria.