Light-absorbing Compounds Research Articles

Molecular Characterization of Brown Carbon in Biomass Burning Aerosol Particles.

Emissions from biomass burning are a significant source of brown carbon (BrC) in the atmosphere. In this study, we investigate the molecular composition of freshly emitted biomass burning organic aerosol (BBOA) samples collected during test burns of sawgrass, peat, ponderosa pine, and black spruce. We demonstrate that both the BrC absorption and the chemical composition of light-absorbing compounds depend significantly on the type of biomass fuels. Common BrC chromophores in the selected BBOA samples include nitro-aromatics, polycyclic aromatic hydrocarbon derivatives, and polyphenols spanning a wide range of molecular weights, structures, and light absorption properties. A number of biofuel-specific BrC chromophores are observed, indicating that some of them may be used as source-specific markers of BrC. On average, ∼50% of the light absorption in the solvent-extractable fraction of BBOA can be attributed to a limited number of strong BrC chromophores. The absorption coefficients of BBOA are affected by solar photolysis. Specifically, under typical atmospheric conditions, the 300 nm absorbance decays with a half-life of ∼16 h. A "molecular corridor" analysis of the BBOA volatility distribution suggests that many BrC compounds in the fresh BBOA have low saturation mass concentration (<1 μg m-3) and will be retained in the particle phase under atmospherically relevant conditions.

Optical properties and aging of light-absorbing secondary organic aerosol

Abstract. The light-absorbing organic aerosol (OA) commonly referred to as “brown carbon” (BrC) has attracted considerable attention in recent years because of its potential to affect atmospheric radiation balance, especially in the ultraviolet region and thus impact photochemical processes. A growing amount of data has indicated that BrC is prevalent in the atmosphere, which has motivated numerous laboratory and field studies; however, our understanding of the relationship between the chemical composition and optical properties of BrC remains limited. We conducted chamber experiments to investigate the effect of various volatile organic carbon (VOC) precursors, NOx concentrations, photolysis time, and relative humidity (RH) on the light absorption of selected secondary organic aerosols (SOA). Light absorption of chamber-generated SOA samples, especially aromatic SOA, was found to increase with NOx concentration, at moderate RH, and for the shortest photolysis aging times. The highest mass absorption coefficient (MAC) value is observed from toluene SOA products formed under high-NOx conditions at moderate RH, in which nitro-aromatics were previously identified as the major light-absorbing compounds. BrC light absorption is observed to decrease with photolysis time, correlated with a decline of the organic nitrate fraction of SOA. SOA formed from mixtures of aromatics and isoprene absorb less visible (Vis) and ultraviolet (UV) light than SOA formed from aromatic precursors alone on a mass basis. However, the mixed SOA absorption was underestimated when optical properties were predicted using a two-product SOA formation model, as done in many current climate models. Further investigation, including analysis on detailed mechanisms, are required to explain the discrepancy.

A fluorescence lifetime-based binding assay for acetylpolyamine amidohydrolases from Pseudomonas aeruginosa using a [1,3]dioxolo[4,5-f][1,3]benzodioxole (DBD) ligand probe

High-throughput assays for drug screening applications have to fulfill particular specifications. Besides the capability to identify even compounds with low potency, one of the major issues is to minimize the number of false-positive hits in a screening campaign in order to reduce the logistic effort for the subsequent cherry picking and confirmation procedure. In this respect, fluorescence lifetime (FLT) appears as an ideal readout parameter that is supposed to be robust against autofluorescent and light-absorbing compounds, the most common source of systematic false positives. The extraordinary fluorescence features of the recently discovered [1,3]dioxolo[4,5-f][1,3] benzodioxole dyes were exploited to develop an FLT-based binding assay with exceptionally robust readout. The assay setup was comprehensively validated and shown to comply not only with all requirements for a powerful high-throughput screening assay but also to be suitable to determine accurate binding constants for inhibitors against enzymes of the histone deacetylase family. Using the described binding assay, the first inhibitors against three members of this enzyme family from Pseudomonas aeruginosa were identified. The compounds were characterized in terms of potency and selectivity profile. The novel ligand probe should also be applicable to other homologues of the histone deacetylase family that are inhibited by N-hydroxy-N'-phenyloctandiamide.

Glyoxal Induced Atmospheric Photosensitized Chemistry Leading to Organic Aerosol Growth

In recent years, it has been proposed that gas phase glyoxal could significantly contribute to ambient organic aerosol (OA) mass through multiphase chemistry. Of particular interest is the reaction between glyoxal and ammonium cations producing light-absorbing compounds such as imidazole derivatives. It was recently shown that imidazole-2-carboxaldehyde (IC) can act as a photosensitizer, initiating aerosol growth in the presence of gaseous volatile organic compounds. Given the potential importance of this new photosensitized growth pathway for ambient OA, the related reaction mechanism was investigated at a molecular level. Bulk and flow tube experiments were performed to identify major products of the reaction of limonene with the triplet state of IC by direct (±)ESI-HRMS and UPLC/(±)HESI-HRMS analysis. Detection of recombination products of IC with limonene or with itself, in bulk and flow tube experiments, showed that IC is able to initiate a radical chemistry in the aerosol phase under realistic irradiation conditions. Furthermore, highly oxygenated limonene reaction products were detected, clearly explaining the observed OA growth. The chemistry of peroxy radicals derived from limonene upon addition of oxygen explains the formation of such low-volatile compounds without any traditional gas phase oxidant.

Organic matrix effects on the formation of light-absorbing compounds from α-dicarbonyls in aqueous salt solution

Aqueous-phase reactions of organic compounds are of general importance in environmental systems. Reactions of α-dicarbonyl compounds in the aqueous phase of atmospheric aerosols can impact their climate-relevant physical properties including hygroscopicity and absorption of light. Less-reactive water-soluble organic compounds may contribute an organic matrix component to the aqueous environment, potentially impacting the reaction kinetics. In this work we demonstrate the effects of organic matrices on the self-reactions of glyoxal (Gly) and methylglyoxal (mGly) in aqueous solutions containing ammonium sulfate. At an organic-to-sulfate mass ratio of 2 : 1, carbohydrate-like matrices resembling oxidized organic aerosol material reduce the rate of formation of light-absorbing products by up to an order of magnitude. The greatest decreases in the reaction rates were observed for organic matrices with smaller, more linear molecular structures. Initial UV-Vis spectra, product studies, relative rate data, acidity changes, and viscosity measurements suggest that shifts in carbonyl equilibria, due in part to (hemi)acetal formation with the matrix, reduce the rate of formation of light-absorbing imidazole and oligomer species.

Brown carbon formation from ketoaldehydes of biogenic monoterpenes

Sources and chemical composition of brown carbon are poorly understood, and even less is known about the mechanisms of its atmospheric transformations. This work presents molecular-level investigations of the reactive compound ketolimononaldehyde (KLA, C9H14O3), a second-generation ozonolysis product of limonene (C10H16), as a potent brown carbon precursor in secondary organic aerosol (SOA) through its reactions with reduced nitrogen compounds, such as ammonium ion (NH4+), ammonia, and amino acids. The reactions of synthesized and purified KLA with NH4+ and glycine resulted in the formation of chromophores nearly identical in spectral properties and formation rates to those found in similarly-aged limonene/O3 SOA. Similar chemical reaction processes of limononaldehyde (LA, C10H16O2) and pinonaldehyde (PA, C10H16O2), the first-generation ozonolysis products of limonene and alpha-pinene, respectively, were also studied, but the resulting products did not exhibit the light absorption properties of brown carbon, suggesting that the unique molecular structure of KLA produces visible-light-absorbing compounds. The KLA/NH4+ and KLA/GLY reactions produce water-soluble, hydrolysis-resilient chromophores with high mass absorption coefficients (MAC = 2000-4000 cm2 g(-1)) at lambda - 500 nm, precisely at the maximum of the solar emission spectrum. Liquid chromatography was used to isolate the light-absorbing fraction, and UV-Vis, FTIR, NMR and high-resolution mass spectrometry (HR-MS) techniques were used to investigate the structures and chemical properties of the light-absorbing compounds. The KLA browning reaction generates a diverse mixture of light-absorbing compounds, with the majority of the observable products containing 1-4 units of KLA and 0-2 nitrogen atoms. Based on the HR-MS product distribution, conjugated aldol condensates, secondary imines (Schiff bases), and N-heterocycles like pyrroles may contribute in varying degree to the light-absorbing properties of the KLA brown carbon. The results of this study demonstrate the high degree of selectivity of organic compound structures on the light-absorbing properties of SOA.

Recent advances in SALDI-MS techniques and their chemical and bioanalytical applications

Although laser desorption mass spectrometry was introduced in the 1960s, the potential of laser mass spectrometry was not realised until the introduction of matrix-assisted laser desorption/ionisation (MALDI) in the 1980s. The technique relies on light-absorbing compounds called matrices that are co-crystallised with the analyte to achieve high ionisation and desorption efficiencies. MALDI offers a lot of advantages and is an indispensable tool in macromolecule analysis. However, the presence of the matrix also produces a high chemical background in the region below m/z 700 in the mass spectrum. Surface-assisted laser desorption/ionisation (SALDI) substitutes the chemical matrix of MALDI for an active surface, which means that matrix interference can be eliminated. SALDI mass spectrometry has evolved in recent years into a technique with great potential to provide insight into many of the challenges faced in modern research, including the growing interest in "omics" and the demands of pharmaceutical science. A great variety of materials have been reported to work in SALDI. Examples include a number of nanomaterials and surfaces. The unique properties of nanomaterials greatly facilitate analyte desorption and ionisation. This article reviews recent advances made in relation to carbon- and semiconductor-based SALDI strategies. Examples of their environmental, chemical and biomedical applications are discussed with the aim of highlighting progression in the field and the robustness of the technique, as well as to evaluate the strengths and weaknesses of individual approaches. In addition, this article describes the physical and chemical processes involved in SALDI and explains how the unique physical and electronic properties of nanostructured surfaces allow them to substitute for the matrix in energy transfer processes.

Photoactivation of 9-hydroxypheophorbide α triggers apoptosis through the reactive oxygen species-mediated mitochondrial pathway and endoplasmic reticulum stress in AMC-HN-3 laryngeal cancer cells

Photodynamic therapy (PDT) is a promising treatment modality for a variety of cancers. It utilizes light-absorbing compounds combined with direct illumination to generate reactive oxygen species in photosensitizer-targeted tumor cells resulting in the final photodamage of tumors. Recently, we demonstrated that a combination modality of 9-hydroxypheophorbide alpha (9-HPbD)-based PDT and carboplatin exerts enhanced cytotoxic and apoptotic effects on AMC-HN-3 laryngeal cancer cells. The present study aimed to investigate the potential apoptotic pathways initiated by 9-HPbD-PDT-mediated reactive oxygen species (ROS) in AMC-HN-3 cells. Cytotoxicity and apoptosis induced by 9-HPbD-PDT were exhibited in a ROS-dependent manner. Mitochondria and the endoplasmic reticulum (ER) were observed as preferential sites of 9-HPbD accumulation in AMC-HN-3 cells. ROS induced by 9-HPbD-PDT directly led to downregulated expression of Bcl-2, loss of mitochondrial membrane potential, release of cytochrome c from mitochondria, elevation of intracellular calcium due to ER stress, as well as induction of CHOP and activation of caspase-3, -8, -9 and -12. Our results demonstrated that ROS induced by 9-HPbD-PDT play a causative role in triggering mitochondrial events, ER stress and probable involvement of the extrinsic apoptotic pathway in AMC-HN-3 cells.

Inorganic ammonium salts and carbonate salts are efficient catalysts for aldol condensation in atmospheric aerosols

In natural environments such as atmospheric aerosols, organic compounds coexist with inorganic salts but, until recently, were not thought to interact chemically. We have recently shown that inorganic ammonium ions, NH(4)(+), act as catalysts for acetal formation from glyoxal, a common atmospheric gas. In this work, we report that inorganic ammonium ions, NH(4)(+), and carbonate ions, CO(3)(2-), are also efficient catalysts for the aldol condensation of carbonyl compounds. In the case of NH(4)(+) this was not previously known, and was patented prior to this article. The kinetic results presented in this work show that, for the concentrations of ammonium and carbonate ions present in tropospheric aerosols, the aldol condensation of acetaldehyde and acetone could be as fast as in concentrated sulfuric acid and might compete with their reactions with OH radicals. These catalytic processes could produce significant amounts of polyconjugated, light-absorbing compounds in aerosols, and thus affect their direct forcing on climate. For organic gases with large Henry's law coefficients, these reactions could also result in a significant uptake and in the formation of secondary organic aerosols (SOA). This work reinforces the recent findings that inorganic salts are not inert towards organic compounds in aerosols and shows, in particular, that common ones, such as ammonium and carbonate salts, might even play important roles in their chemical transformations.

Atmospheric condensed‐phase reactions of glyoxal with methylamine

Glyoxal reacts with methylamine in drying cloud droplet/aerosol surrogates to form high molecular mass oligomers along with smaller amounts of 1,3‐dimethylimidazole and light‐absorbing compounds. The patterns observed by high‐resolution time‐of‐flight aerosol mass spectrometry indicate that oligomers form from repeated imine units. The reactions are 1st order in each reactant: rate‐limiting imine formation is followed by rapid dimer and oligomer formation. While excess methylamine evaporates from the droplet, half the glyoxal does not, due to self‐oligomerization reactions that occur in the absence of methylamine. Glyoxal irreversibly traps volatile amine compounds in the aerosol phase, converting them into oligomers. This is the first reported mechanism for the formation of stable secondary organic aerosol (SOA) material from methylamine, a substance with only one carbon, and could produce as much as 11 Tg SOA yr−1 globally if glyoxal reacts exclusively by this pathway.

Light-absorbing aldol condensation products in acidic aerosols: Spectra, kinetics, and contribution to the absorption index

The radiative properties of aerosols that are transparent to light in the near-UV and visible, such as sulfate aerosols, can be dramatically modified when mixed with absorbing material such as soot. In a previous work we had shown that the aldol condensation of carbonyl compounds produces light-absorbing compounds in sulfuric acid solutions. In this work we report the spectroscopic and kinetic parameters necessary to estimate the effects of these reactions on the absorption index of sulfuric acid aerosols in the atmosphere. The absorption spectra obtained from the reactions of six different carbonyl compounds (acetaldehyde, acetone, propanal, butanal, 2-butanone, and trifluoroacetone) and their mixtures were compared over 190–1100 nm. The results indicated that most carbonyl compounds should be able to undergo aldol condensation. The products are oligomers absorbing light in the 300–500 nm region where few other compounds absorb, making them important for the radiative properties of aerosols. Kinetic experiments in 96–75 wt% H 2SO 4 solutions and between 273 and 314 K gave an activation energy for the rate constant of formation of the aldol products of acetaldehyde of −(70±15) kJ mol −1 in 96 wt% solution and showed that the effect of acid concentration was exponential. A complete expression for this rate constant is proposed where the absolute value in 96 wt% H 2SO 4 and at 298 K is scaled to the Henry's law coefficient for acetaldehyde and the absorption cross-section for the aldol products assumed in this work. The absorption index of stratospheric sulfuric acid aerosols after a 2-year residence time was estimated to 2×10 −4, optically equivalent to a content of 0.5% of soot and potentially significant for the radiative forcing of these aerosols and for satellite observations in channels where the aldol products absorb.

Characterization of a bit-wise volumetric storage medium for a space environment

We report playback performance results of volumetric optical data storage disks that are made from a class of light-absorbing (photo-chromic) compounds. The disks are exposed to a simulated space environment with respect to temperature and radiation. To test for temperature sensitivity, a vacuum oven bakes the disks for certain amount of time at a designated temperature. Radiation exposure includes heavy ions and high energy protons. Disks fail in high temperature and large proton-dose conditions. Heavy ions do not cause significant disk failure. The prevention of disk failure due to harsh space environments is also discussed.

Visible light-induced photocatalytic degradation of Acid Orange 7 in aqueous TiO2 suspensions

The photocatalytic degradation of a model azo-dye (Acid Orange, AO7) in aerated aqueous TiO2 dispersion has been studied under visible light (λ>400nm) irradiation. The presence and role of oxidative species, such as singlet oxygen (1O2), superoxide (O2−) and hydroperoxy (HO2) radicals was examined with the use of appropriate quenchers of these species. The reaction pathway of dye degradation was also investigated by monitoring the temporal evolution of intermediates and final products on both the photocatalyst surface and in solution, with the use of a variety of techniques, including GC–MS, FTIR and UV-Vis spectroscopies. It has been found that complete decolorization of the solution may be achieved, accompanied by a substantial decrease of the chemical oxygen demand (COD) of the solution. Evidence is presented that the main oxidative species is O2− (or HO2), while singlet oxygen, when formed, is also active. The adsorbed dye molecule is initially cleaved in the vicinity of the azo-bond and the resulting fragments are oxidized toward compounds of progressively lower molecular weight and, eventually, to CO2 and inorganic ions. However, when the solution is bleached, formation of active oxidative species does not take place, oxidation reactions cease and the concentrations of the dye intermediates remain practically stable upon further exposure to visible light irradiation. Formation of photoinduced hydrogen peroxide, which is also generated under the present conditions, also stops when the dye concentration in solution drops to very low levels. This behavior has been explained evoking the photosensitization mechanism of wide band-gap semiconductors, according to which the reaction is triggered by excitation of the dye molecule by visible light photons, followed by charge injection to the conduction band of the semiconductor and subsequent production of active oxygen radicals. Formation of the latter oxidizing species is possible only in the presence of visible light-absorbing compounds and cannot take place after fragmentation of the parent AO7 molecule in the vicinity of the azo-bond and decolorization.

Mechanisms of action of phenanthroperylenequinones in photodynamic therapy (Review)

Despite the age-old belief that most anti-cancer agents kill tumor cells by necrosis, recent findings have demonstrated that photosensitizers could also kill tumor cells by triggering genetically programmed series of events termed apoptosis. Cell death by apoptosis is a very neat way to eliminate unwanted cells: no traces are left and the cell contents are never released or accessible to the immune system. Hence there is no inflammation. This is in contrast to death by necrosis. Under these conditions, normally the cell swells and then, when membrane integrity comes under attack, the cell collapses like a balloon and the contents spill out into the extracellular milieu. This may result in an inflammatory response. Because of the relatively clean nature of the apoptotic process, it is desirable to identify compounds that effectively activate the apoptotic pathway. Photodynamic therapy (PDT), a new mode of treatment, is based on the combined use of light-absorbing compounds and light irradiation. Recent developments in understanding the mechanisms of the PDT effect of photosensitizers indicate that a critical factor in the success of the agent is the ability to induce apoptosis in the malignant cell population. Hypericin and Hypocrellins are perylquinones, which are novel natural photosensitizers characterized by high absorption around 470 nm and high singlet oxygen yield. To study the signaling mechanism in vitro we have investigated uptake kinetics, intracellular localization, mode of cell death and mechanisms involved in the photodynamic action following PDT in human cell lines of poorly differentiated (CNE2) and moderately differentiated (TW0-1) nasopharyngeal carcinoma (NPC) and also poorly differentiated colon (CCL-220.1) and bladder (SD) cells.

Hypericin induced death receptor-mediated apoptosis in photoactivated tumor cells

Nasopharyngeal carcinoma (NPC) is a malignant disease of the head/neck region with a 5-year survival level of approximately 65%. To explore the novel therapeutic strategies in the management of this disease, the potential effects of photodynamic therapy (PDT) in NPC cells were investigated. PDT, a new mode of treatment, is based on the combined use of light-absorbing compounds and light irradiation. Two human NPC cells such as, poorly differentiated (NPC/CNE2) and moderately differentiated (NPC/TW0-1) and other types of tumor cells like colon (CCL-220.1) and bladder (SD) undergo rapid apoptosis when treated with PDT sensitized with hypericin (HY). It has been shown that this compound has a strong photodynamic effect on tumors and viruses. However, the initiating events of PDT sensitized HY-induced apoptosis are not identified completely. In this study, we sought to determine whether Fas/FasL upregulation and involvement of mitochondrial events are an early event in HY-treated PDT induced apoptosis. Loss of mitochondrial transmembrane potential, release of cytochrome c, involvement of caspases 8 and 3 and the status caspase-3 specific substrate PARP, were evaluated in PDT treated tumor cells. Photosensitization of HY enhanced both CD95/CD95L expression and induced CD95-signaling dependent cell death in all tumor cell lines studied. CD95/CD95L expression appeared within 2 h following light irradiation and appeared to be a principal event in PDT induced apoptosis. Furthermore, these results indicate that release of mitochondrial cytochrome c into the cytoplasm within 2-3 h post PDT is a secondary event following the activation of initiator caspase-8 preceding Apaf-1, caspase-9 and caspase-3 activation, cleavage of PARP and DNA fragmentation.

EFFECT OF ELEVATED IRON ON ULTRAVIOLET LIGHT-ABSORBING COMPOUNDS OF CUCUMBER COTYLEDON AND LEAF TISSUES

The effect of iron [Fe(II)] on ultraviolet light-absorbing phenolic compounds of cucumber (Cucumis sativus L., cv Poinsett 76) leaf and cotyledon tissues was investigated. Tissue disks (7 mm) were exposed to increasing FeSO4 · 7H2O concentrations from 25 μ M (7 ppm) to 500 μ M (143 ppm) at pH 4.0–7.0 for 24 h in both light and dark. Acidified, aqueous methanol extracts that contain various phenolic compounds were analyzed by high performance liquid chromatography. Depending upon the treatment pH, Fe(II) altered the levels of the UV light-absorbing compounds measured at both 270 and 340 nm, increasing the levels of some compounds at low Fe(II) concentrations, which were subsequently reduced at higher Fe(II) levels. In most cases, the Fe(II)-induced change in phenolic compound concentration was dependent upon tissue type, light condition, and pH. The dose–response relations and pH dependencies for the Fe(II)-induced changes were complex. These results suggest that the FeSO4 · 7H2O treatments may specifically alter certain metabolic processes and do not simply produce reactive oxygen, which degrade the phenolic compounds.

EFFECT OF ELEVATED COPPER ON THE ULTRAVIOLET LIGHT-ABSORBING COMPOUNDS OF CUCUMBER COTYLEDON AND LEAF TISSUES

The effect of copper [Cu(II)] on the ultraviolet light-absorbing compounds of cucumber (Cucumis sativus L., cv Poinsett 76) leaf and cotyledon tissues was investigated. Tissue disks (7 mm) were exposed to CuSO4 · 5H2O concentrations from 50 μM (12.5 ppm) to 2.5 mM (625 ppm) at either pH 6.0 or 4.5 for up to 48 h in both light and dark. Acidified, aqueous methanol extracts (flavonoid-rich fraction) were analyzed by high performance liquid chromatography. Copper(II) altered the levels of the UV-absorbing compounds (340 nm), increasing the levels of some compounds at low Cu(II) concentrations and decreasing the levels of the UV-absorbing compounds at higher Cu(II) levels. In most cases, the magnitude of the Cu(II)-induced changes in cucumber phenolics was dependent upon tissue type, light condition, pH, and treatment duration. Since plant leaf phenolic compounds extracted under these conditions may have antioxidative activity, the ability to chelate prooxidative minerals and protect against ultraviolet B radiation, the Cu(II)-induced changes in phenolic compounds may modify plant responses to environmental stresses and alter the nutritional values of certain vegetable crops.

Considerations on photochemical genotoxicity: report of the International Workshop on Genotoxicity Test Procedures Working Group.

Recent toxicological observations have caused concern regarding the need to test, for example, pharmaceuticals and cosmetic products for photochemical genotoxicity. The objective of this report is to give assistance on how to adapt existing test methods to investigate the potential of light-absorbing compounds to induce genotoxic effects on photoactivation. In general, the Organization for Economic Co-Operation & Economic Development (OECD) draft guideline on in vitro phototoxicity testing served as a basis for consideration. Concomitant exposure of the cells to the test compound and solar simulated light was considered appropriate as the initial, basic test condition. Optimization of the exposure scheme, e.g., a change of the irradiation spectrum, might be indicated depending on the initial test results. Selection of test compound concentrations should be based on results obtained with the dark version of the respective test system but might have to be modified if phototoxic effects are observed. Selection of the irradiation dose has to be performed individually for each test system based on dose-effect studies. The irradiation should induce per se a small, reproducible toxic or genotoxic effect. The report includes a specification of necessary controls, discusses factors that might have an impact on the irradiation characteristics, and gives a rationale for the omission of an external metabolic activation system. It also addresses the question that physicochemical and pharmacokinetic properties might trigger the need to test a chemical for photochemical genotoxicity. Relevant experimental observations are presented to back up the recommendations. The working group did not reach a consensus as to whether a single, adequately perfomed in vitro test for clastogenicity would be sufficient to exclude a photogenotoxic liability or whether a test battery including a gene mutation assay would be needed for product safety testing regarding photochemical genotoxicity.

Selective depletion of a thymocyte subset in vitro with an immunomodulatory photosensitizer.

Conventional photodynamic therapy (PDT) utilizes light-absorbing compounds that have anti-cancer activity upon visible light irradiation. PDT has also been utilized for the treatment of certain immune conditions. To further understand the action of PDT upon immune cells, DBA/2 mouse thymocytes were treated with the photosensitizer benzoporphyrin derivative monoacid ring A (BPD-MA, verteporfin) and/or an apoptosis-inducing anti-Fas (APO-1, CD95) monoclonal antibody. Nanomolar levels of BPD-MA in combination with nonthermal visible light irradiation rapidly induced apoptosis as gauged by DNA fragmentation assays. Thymocytes were modestly more sensitive to PDT-induced apoptosis than mature splenic T cells. BPD-MA and light or the anti-Fas antibody decreased CD4(+)CD8(+) cell numbers while relatively sparing CD4(-)CD8(-), CD4(+)CD8(-), and CD4(-)CD8(+) thymocytes. In combination, anti-Fas antibody and PDT augmented activity levels of the apoptosis-related protease caspase-3, cleavage of the caspase-3 substrate poly(ADP) polymerase, and the proportion of cells exhibiting DNA fragmentation and further impacted CD4(+)CD8(+) thymocyte survival. Although CD4(+)CD8(+) thymocytes had the greatest sensitivity to photodynamic depletion, BPD-MA was taken up by the other major thymocyte subsets with equal or greater avidity. Since CD4(+)CD8(+) thymocytes are selectively impacted by PDT and anti-Fas antibody can act in concert with PDT to further cytotoxicity, thymocytes may be useful for the identification of factors that govern immune cell susceptibility to this form of phototherapy.

Characterization of the reflective materials and organelles in the bright irides of North American blackbirds (Icterinae).

The reflective materials in the iris stroma of bright-irised American blackbirds (Icterinae, Emberizidae) and the red-eyed vireo (vireo olivaceus) (Vireonidae) were characterized using high-performance liquid chromatography (HPLC) and diode-array detection. Two purines, guanine and hypoxanthine, and two pteridines, leucopterin and xanthopterin, were detected in large amounts in all bright irides. The brown iris of the red-winged blackbird (Agelaius phoeniceus) by comparison contained only small amounts of these and additional unidentified compounds. The absolute and relative amounts of light-absorbing compounds in the iris varied somewhat among species of blackbirds with bright irides, and markedly within one species (brewer's blackbird, Euphagus cyanocephalus) between sexes and age classes that very in eye color. Differences in the types, numbers, and sizes of pigment organelles in the irides appeared to underlie the differences in amounts of light-absorbing compounds. Guanine was the most abundant light-absorbing compound in all bright irides, accounting for about 90% of the total absorption at 250 nm. A wide range of concentrations of guanine, from 96 to 9 micrograms per iris, produced bright irides. The primary pigment organelles of pigment cells in bright irides were reflecting platelets, which typically appeared as open spaces on electron micrographs. In the red-eyed vireo there were in addition red pterinosome-like pigment organelles in the pigment cells on the anterior surface of the iris stroma. Guanine was present even in irides with no overt reflecting platelets.