Promotion of Proapoptotic Signals by Lysosomal Photodamage: Mechanistic Aspects and Influence of Autophagy

Prior studies demonstrated that a low level (LD_10–15) of lysosomal photodamage can sensitize cells to the apoptotic death that results from subsequent mitochondrial photodamage. We have proposed that this process occurs via a calpain‐catalyzed cleavage of the autophagy‐associated protein ATG5 to form a proapoptotic fragment. In this report, we provide evidence for the postulated ATG5 cleavage and show that the sequential photodynamic therapy (PDT) protocol can also partly overcome the adverse effect of hypoxia on the initiation of apoptosis. While autophagy can offer cytoprotection after mitochondrial photodamage, this does not appear to apply when lysosomes are the target. This may account for the ability of very low PDT doses directed at lysosomes to evoke ATG5 cleavage. The resulting proapoptotic effect overcomes intrinsic cytoprotection from mitochondrial photodamage along with a further stimulation of phototoxicity.     

Delayed Oxidative Photodamage induced by Photodynamic Therapy

Abstract— Apoptotic DNA fragmentation was observed 60 min after photodynamic therapy of murine leukemia cells in culture, using either of two photosensitizers with predominantly lysosomal targets. When the radical scavengers trolox or α-tocopherol succinate were present during irradiation, the subsequent appearance of apoptotic cells was prevented, as was phototoxicity. Addition of either scavenger during the 60 min after irradiation provided only partial protection from apoptosis and phototoxicity; this protection was abolished if the addition was delayed for 10 min. These results are consistent with a model whereby long-persisting photoproducts continue the initiation of apoptosis for approximately 10 min after irradiation has ceased.     

Retinal Photodamage by Endogenous and Xenobiotic Agents†

The human eye is constantly exposed to sunlight and artificial lighting. Light transmission through the eye is fundamental to its unique biological functions of directing vision and circadian rhythm and therefore light absorbed by the eye must be benign. However, exposure to the very intense ambient radiation can pose a hazard particularly if the recipient is over 40 years of age. There are age‐related changes in the endogenous (natural) chromophores (lipofuscin, A2E and all‐trans‐retinal derivatives) in the human retina that makes it more susceptible to visible light damage. Intense visible light sources that do not filter short blue visible light (400–440 nm) used for phototherapy of circadian imbalance (i.e. seasonal affective disorder) increase the risk for age‐related light damage to the retina. Moreover, many drugs, dietary supplements, nanoparticles and diagnostic dyes (xenobiotics) absorb ocular light and have the potential to induce photodamage to the retina, leading to transient or permanent blinding disorders. This article will review the underlying reasons why visible light in general and short blue visible light in particular dramatically raises the risk of photodamage to the human retina.     

Reversible Effects of Photodamage Directed Toward Mitochondria

When the initial effect of photodynamic therapy (PDT) involves mitochondrial photodamage, an early effect is loss of the mitochondrial membrane potential (ΔΨ_m). Using murine hepatoma 1c1c7 cells and a photosensitizing agent known to target mitochondria, we examined loss of ΔΨ_m, initiation of apoptosis and loss of viability as a function of time and light dose. There was a correlation between loss of viability and the rapid disappearance of ΔΨ_m, as detected by the potential‐sensitive probe Mitotracker Orange (MTO). Loss of ΔΨ_m was, however, reversible even with a substantial loss of viability. Unless there was a supralethal level of photodamage, 1c1c7 cells recovered their mitochondrial membrane potential, even if the cell population was on the pathway to apoptosis and cell death. These results indicate that when mitochondria are the initial PDT target, a qualitative estimate of photokilling can be provided by assessing the initial loss of ΔΨ_m.     

The Effect of Tryptophan on UV-induced DNA Photodamage

Trp–DNA adducts resulting from UV irradiation of pyrimidine bases and nucleotides in the presence of tryptophan (Trp) have been the subject of previous research. However, the relative yield of the adducts compared with the UV screening effect of Trp has not been previously considered. To determine whether Trp–DNA adduct formation or absorption “screening” by Trp is the predominant process when DNA solutions are irradiated with UV light in the presence of Trp, we irradiated Trp-containing DNA oligonucleotide solutions with UVC light and incubated aliquots of those solutions with molecular beacons (MBs) to detect the damage. We observed a rapid decay of fluorescence of the MBs for pure DNA solutions, thereby indicating damage. However, in the presence of Trp, the fluorescence decay is prolonged, with time constants that increase exponentially with Trp concentration. The results are discussed in terms of a beneficial in vivo cellular protection rather than harmful adduct formation and suggest a net sacrificial absorption of UV light by Trp which actually protects the DNA from UV damage.     

牛血清白蛋白的光损伤和光氧化机理

运用激光闪光光解瞬态吸收技术, 在266 nm激光激励下, 研究了牛血清白蛋白(BSA)光损伤和被SO4-·单电子氧化的反应机理, 表征了反应过程中生成的自由基. 结果表明, 在266 nm激光照射下, BSA可同时发生光电离和光激发, 生成色氨酸阳离子自由基(Trp/NH+·), 由Trp/NH+·快速脱质子形成的色氨酸中性自由基(Trp/N·)及色氨酸三重激发态(3Trp*), 3Trp*再与酪氨酸(Tyr)发生分子内电子转移生成酪氨酸中性自由基(Tyr/O·). 在SO4-·单电子氧化的反应中, 借助减谱技术, 求得BSA中Tyr和色氨酸(Trp)自由基的表观生成速率常数, 但未发现分子内电子转移现象, 阐明了SO4-·自由基是通过与BSA中的Tyr和Trp发生电子转移反应来氧化BSA的, SO4-·氧化BSA的反应速率常数为1.51×10¹⁰ L·mol^-1·s^-1, 从而为进一步研究血清白蛋白的氧化还原代谢过程提供理论基础.     

Retinal Photodamage Mediated by All‐trans‐retinal†

Accumulation of all‐trans‐retinal (all‐trans‐RAL), reactive vitamin A aldehyde, is one of the key factors in initiating retinal photodamage. This photodamage is characterized by progressive retinal cell death evoked by light exposure in both an acute and chronic fashion. Photoactivated rhodopsin releases all‐trans‐RAL, which is subsequently transported by ATP‐binding cassette transporter 4 and reduced to all‐trans‐retinol by all‐trans‐retinol dehydrogenases located in photoreceptor cells. Any interruptions in the clearing of all‐trans‐RAL in the photoreceptors can cause an accumulation of this reactive aldehyde and its toxic condensation products. This accumulation may result in the manifestation of retinal dystrophy including human retinal degenerative diseases such as Stargardt’s disease and age‐related macular degeneration. Herein, we discuss the mechanisms of all‐trans‐RAL clearance in photoreceptor cells by sequential enzymatic reactions, the visual (retinoid) cycle, and potential molecular pathways of retinal photodamage. We also review recent imaging technologies to monitor retinal health status as well as novel therapeutic strategies preventing all‐trans‐RAL‐associated retinal photodamage.     

The Formation of DNA Photodamage: The Role of Exciton Localization

The electronic structure during the formation of a cyclobutane pyrimidine dimer (CPD) between two thymine bases is investigated using semi‐empirical and first‐principles approaches. The dimerization of two isolated thymine bases is found to have no barrier or a very small barrier in agreement with previous studies suggesting low photostability of DNA. The well‐known high photostability of DNA can only be explained taking other factors into account. We investigate the role of the exciton location in the particular environment. Different model systems, from isolated thymine bases to an oligonucleotide in aqueous solution, are discussed. Analysis of the frontier orbitals allows one to understand the connection between the location of the exciton, the relative orientation of the thymine bases, and the observed reactivity.     

Intravital Imaging Study on Photodamage Produced by Femtosecond Near‐infrared Laser Pulses In Vivo

Ultrashort femtosecond pulsed lasers may provide indispensable benefits for medical bioimaging and diagnosis, particularly for noninvasive biopsy. However, the ability of femtosecond laser irradiation to produce biodamage in the living body is still a concern. To solve this biosafety issue, results of theoretical estimations as well as the in vitro and in situ experiments on femtosecond biodamage should be verified by experimental studies conducted in vivo. Here, we analyzed photodamage produced by femtosecond (19, 42 and 100 fs) near‐infrared (NIR; ~800 nm) laser pulses with an average power of 5 and 15 mW in living undissected Drosophila larvae (in vivo). These experimental data on photodamage in vivo agree with the results of theoretical modeling of other groups. Femtosecond NIR laser pulses may affect the concentration of fluorescent biomolecules localized in mitochondria of the cells of living undissected Drosophila larva. Our findings confirm that the results of the mathematical models of femtosecond laser ionization process in living tissues may have a practical value for development of noninvasive biopsy based on the use of femtosecond pulses.     

Salinomycin Derivatives Kill Breast Cancer Stem Cells by Lysosomal Iron Targeting

Salinomycin ( 1 ) exhibits a large spectrum of biological activities including the capacity to selectively eradicate cancer stem cells (CSC), making it and its derivatives promising candidates for the development of drug leads against CSC. It has been previously shown that salinomycin and its C20-propargylamine derivative (Ironomycin ( 2 )) accumulate in lysosomes and sequester iron in this organelle. Herein, a library of salinomycin derivatives is reported, including products of C20-amination, C1-esterification, C9-oxidation, and C28-dehydration. The biological activity of these compounds is evaluated against transformed human mammary epithelial HMLER CD24^low/CD44^high cells, a well-established model of breast CSC, and HMLER CD24^high/CD44^low cells deprived of CSC properties. Unlike other structural alterations, derivative 4 , which displays a cyclopropylamine at position C20, showed a strikingly low IC₅₀ value of 23 nm against HMLER CD24^low/CD44^high cells. This study provides highly selective molecules to target the CSC niche, a potential interesting advance for drug development to prevent cancer resistance.     

小波包去噪信号的分形特征

将分形理论与小波包滤波相结合，用盒维数的大小来评判信号曲线的滤波情况。随着小波包分解尺度的增大，滤波后信号曲线的盒维数逐渐减小，并最后趋于稳定值。因此可以根据盒维数-分解尺度曲线来选择最佳分解尺度。对仿真含噪信号进行了滤波实验，结果表明：即使在信噪比低至0．5时仍能得到较好的结果，并且该法用于毛细管电泳实验数据的处理结果同样令人满意。     

DMT1 Inhibitors Kill Cancer Stem Cells by Blocking Lysosomal Iron Translocation

Cancer stem cells (CSC) constitute a cell subpopulation in solid tumors that is responsible for resistance to conventional chemotherapy, metastasis and cancer relapse. The natural product Salinomycin can selectively target this cell niche by directly interacting with lysosomal iron, taking advantage of upregulated iron homeostasis in CSC. Here, inhibitors of the divalent metal transporter 1 (DMT1) have been identified that selectively target CSC by blocking lysosomal iron translocation. This leads to lysosomal iron accumulation, production of reactive oxygen species and cell death with features of ferroptosis. DMT1 inhibitors selectively target CSC in primary cancer cells and circulating tumor cells, demonstrating the physiological relevance of this strategy. Taken together, this opens up opportunities to tackle unmet needs in anti-cancer therapy.     

Photodamage induced by Zinc(II)-phthalocyanine to microtubules, actin, alpha-actinin and keratin of HeLa cells

We have studied the photosensitizing effects of zinc(II)-phthalocyanine (ZnPc) on the cytoskeleton of HeLa cells using sublethal (10(-7) M, followed by 1 or 3 min of red light to induce 20%, LD20, or 60%, LD60, cell death, respectively) or lethal (5 x 10(-6) M and 15 min of irradiation, LD100) experimental conditions. The immunofluorescent analysis of the cytoskeleton showed a variable photodamage to microtubules (MT), actin microfilaments (AF) and intermediate filaments of keratin (KF), as well as on alpha-actinin, which was dependent on treatment conditions. Both sublethal treatments induced deep alterations on interphase and mitotic MT. The mitotic index increased with time with the maximum at 18 h (12%) or 24 h (14%) after LD20 or LD60, respectively. The alterations on AF and alpha-actinin were much more severe than those observed on KF at any evaluated time. With the exception of the KF, which remained partially organized, the MT and AF network was severely damaged by the lethal treatment. Western blot analysis for alpha-tubulin, G-actin and alpha-actinin from soluble and insoluble fractions confirmed the results observed by immunofluorescence, thus indicating that these cytoskeletal components are involved in cell damage and death by ZnPc photosensitization.     

Promotion of Trimethylsilylation of Phenols by Trifluoroacetic Acid

Abstract

The speed of trimethylsilylation of sterically hindered phenols was increased by promoting the reaction with a small amount of trifluoroacetic acid. Promotion was successful with hexamethyldisilazane, trimethylchlorosilane, bis-(trimethylsilyl)-trifluoroacetamide, bis-(trimethylsilyl)-acetamide, and trimethylsilylimidazole.     

Dendrobium nobile Lindl Polysaccharides Attenuate UVB-induced Photodamage by Regulating Oxidative Stress,Inflammation and MMPs Expression in Mice Model

Acute ultraviolet B (UVB) irradiation predominantly leads to various skin disorders caused by photodamage. The major causes of UVB-induced photodamage include oxidative stress, inflammatory infiltration and collagen degradation. The aim of the study was to elucidate whether DNP had protective effect on the skin of KM mice when exposed to UVB irradiation. The DNP protective properties to skin appearance and histopathological alterations in KM mice were evaluated by hematoxylin–eosin staining, toluidine blue staining, Gomori staining and Masson's trichrome staining and mast cell staining. In this study, DNP pretreatment promoted the activities of antioxidant enzymes, including superoxide dismutase, catalase and glutathione peroxidase, while decreased malondialdehyde level in UVB-irradiated skin, along with downregulation of proteins expression of matrix metalloproteinases and reduction in the level of the proinflammatory cytokines. Based on these findings, we demonstrated that DNP displayed strong ameliorative effects on UVB-induced acute photodamage for the first time, indicating that it would be a promoting ingredient candidate that could be used in antiphotodamage.     

多臂聚乳酸对线型聚乳酸结晶的促进作用

以多端羟基聚酯为引发剂,经丙交酯开环聚合得到多臂聚乳酸（MA-PLA）。 MA-PLA在DSC二次升温过程中,出现明显的冷结晶峰(41.5 J/g)和熔融峰(42.5 J/g),而工业产品聚乳酸PLLA 3051D没有这2个峰,确认该多臂聚乳酸的结晶能力优于3051D。 MA-PLA多臂聚乳酸的左旋乳酸单元含量为97%,高于3051D的91%。 将MA-PLA与PLLA-3051D共混后,在DSC二次升温过程中出现了熔融峰和冷结晶峰。 偏光显微镜观察表明,共混物的成核速率和初期球晶生长速度加快。 等温结晶动力学数据表明,110 ℃等温结晶的半结晶时间由空白样品的53.6 min缩短至共混物的31.7 min,Avrami指数n由空白样品的2.25增加至共混物的2.60,可见多臂聚乳酸对线形聚乳酸结晶性能的改善,主要是加快了成核速率。     

Promotion of base-catalyzed siloxane rearrangements by dimethyl sulfoxide

The effect of small amounts (0.01%–1%) of dimethyl sulfoxide on base-catalyzed polymerization and equilibration of methylsiloxanes has been examined. The addition of 0.5% of the sulfoxide increases the rate of potassium hydroxide-catalyzed polymerization of octamethylcyclotetrasiloxane by factors of 100–1000 and amounts as low as 0.01% have a large effect when low (12 ppm) catalyst concentrations are used. The rate of basecatalyzed equilibration of hexamethyl disiloxane with octamethylcyclotetrasiloxane is similarly enhanced by dimethyl sulfoxide. The equilibration occurs rapidly at 80°C. with 0.01% of potassium hydroxide and 1% of dimethyl sulfoxide, but does not proceed at a measurable rate with potassium hydroxide alone. The combination of 0.01% potassium hydroxide and 1% dimethyl sulfoxide is more effective than 0.1% of tetramethylammonium hydroxide. The large accelerating effect of the sulfoxide is believed to be due to solvation of the cation, which promotes ionization of the metal silanolate, increasing the concentration of silanolate anions.     

Photodamage in a Mitochondrial Membrane Model Modulated by the Topology of Cationic and Anionic Meso‐Tetrakis Porphyrin Free Bases

The photodynamic effects of the cationic TMPyP (meso‐tetrakis [N‐methyl‐4‐pyridyl]porphyrin) and the anionic TPPS4 (meso‐tetrakis[4‐sulfonatophenyl]porphyrin) against PC/CL phosphatidylcholine/cardiolipin (85/15%) membranes were probed to address the influence of phorphyrin binding on lipid damage. Electronic absorption spectroscopy and zeta potential measurements demonstrated that only TMPyP binds to PC/CL large unilamellar vesicles (LUVs). The photodamage after irradiation with visible light was analyzed by dosages of lipid peroxides (LOOH) and thiobarbituric reactive substance and by a contrast phase image of the giant unilamellar vesicles (GUVs). Damage to LUVs and GUVs promoted by TMPyP and TPPS4 were qualitatively and quantitatively different. The cationic porphyrin promoted damage more extensive and faster. The increase in LOOH was higher in the presence of D₂O, and was impaired by sodium azide and sorbic acid. The effect of D₂O was higher for TPPS4 as the photosensitizer. The use of DCFH demonstrated that liposomes prevent the photobleaching of TMPyP. The results are consistent with a more stable TMPyP that generates long‐lived singlet oxygen preferentially partitioned in the bilayer. Conversely, TPPS4 generates singlet oxygen in the bulk whose lifetime is increased in D₂O. Therefore, the affinity of the porphyrin to the membrane modulates the rate, type and degree of lipid damage.     

Promotion by phosphorus compounds of ruthenium-catalyzed methyl formate homologation

Trivalent phosphorus compounds are promoters for methyl formate homologation to ethanol and ethyl formate catalyzed by ruthenium compounds in the presence of iodide at 220°C and 27 MPa of synthesis gas. Under these conditions the phosphines are quaternized, but decomposition of phosphonium salts occurs during the reaction. Promotion is also observed for methyltriphenyl-phosphonium bromide and triphenylphosphine sulfide, but benzyltrimethyl-ammonium bromide, triphenylarsine, and triphenylantimony are not effective. The major ruthenium species present is Ru(CO)₃I₃^- but with triphenylantimony a trimethylantimony complex, Ru(CO)₂(Sb(CH₃)₃)₂I₂, can be isolated in high yield.