9th International Congress on Photobiology and 12th annual meeting of the American Society for Photobiology. Abstracts of papers. Philadelphia, Pennsylvania, 1-6 July 1984.
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Animals↗
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Role of carbonyl cyanide m-chlorophenylhydrazone in enhancing photobiological hydrogen production by marine green alga Platymonas subcordiformis.
We demonstrated that a significant volume of H(2) gas could be photobiologically produced by a marine green alga Platymonas subcordiformis when an uncoupler of photophosphorylation, carbonyl cyanide m-chlorophenylhydrazone (CCCP), was added after 32 h of anaerobic dark incubation, whereas a negligible volume of H(2) gas was produced without CCCP. The role of CCCP in enhancing photobiological H(2) production was delineated. CCCP as an ADRY agent (agent accelerating the deactivation reactions of water-splitting enzyme system Y) rapidly inhibited the photosystem II (PSII) activity of P. subcordiformis cells, resulting in a markedly decline in the coupled oxygen evolution. The mitochondrial oxidative respiration was only slightly inactivated by CCCP, which depleted O(2) in the light. As a result, anaerobiosis during the stage of photobiological H(2) evolution was established, preventing severe O(2) inactivation of the reversible hydrogenase in P. subcordiformis. The uncoupling effect of CCCP accelerates electron transfer from water due to a disruption of the proton motive force and release of DeltapH across the thylakoid membrane and thus enhances the accessibility of electron and H(+) to hydrogenase. The electrons for hydrogen photoevolution are mainly from the photolysis of water (90%). Upon the addition of CCCP, Chl a/b ratio increased, which implies a decrease in the light-harvesting PSII antennae or an increase in PSII/PSI ratio, possibly resulting in higher efficiency of utilization of light energy. The enhancement of H(2) evolution by the addition of CCCP is mostly due to the combination of the above three mechanisms. However, the disruption of the proton gradient across the thylakoid membrane may prevent a sustained photobiological H(2) evolution due to a shortfall of ATP generation essential for the maintenance and repair functions of the cells.
Chlorophyll↗
In situ electrooxidation of photobiological hydrogen in a photobioelectrochemical fuel cell based on Rhodobacter sphaeroides.
In this paper, we present a photobiological fuel cell that utilizes the metabolic activity of living cells of Rhodobacter sphaeroides for the generation of electricity based on the in situ oxidation of photobiological hydrogen. Organic acids and alcohols contained in synthetic media as well as in fermented media of Escherichia coli K 12 served as the proton donor source for the photobiological hydrogen production by R. sphaeroides. We demonstrate thatthe photobiological hydrogen is efficiently oxidized in the microbial medium at electrocatalytic electrodes coated with a platinum-poly(3,4-ethylenedioxythiophene) (Pt-PEDOT) bilayer composite. The experimental results are discussed in terms of current and power output, substrate, and solar conversion efficiency.
Bioelectric Energy Sources↗
Photobiological information obtained from XPA gene-deficient mice.
The XPA gene-deficient mouse, an animal model of xeroderma pigmentosum (XP), develops enhanced photobiologic reactions including acute inflammation, immunosuppression and skin carcinogenesis, because of the defect in the excision repair of ultraviolet-induced DNA lesions. The results strongly suggest that nuclear DNA is an important chromophore to initiate acute and chronic skin damages. The model mouse is a useful experimental animal not only to investigate the mechanisms of photosensitivity in XP, but also to study physiological photobiology in humans, because photobiologic reactions are greatly intensified in this mouse.
Animals↗
Photochemistry and photobiology of actinic erythema: defensive and reparative cutaneous mechanisms.
Sunlight is part of our everyday life and most people accept it as beneficial to our health. With the advance of our knowledge in cutaneous photochemistry, photobiology and photomedicine over the past four decades, the terrestrial solar radiation has become a concern of dermatologists and is considered to be a major damaging environmental factor for our skin. Most photobiological effects (e.g., sunburn, suntanning, local and systemic immunosuppression, photoaging or dermatoheliosis, skin cancer and precancer, etc.) are attributed to ultraviolet radiation (UVR) and more particularly to UVB radiation (290-320 nm). UVA radiation (320-400 nm) also plays an important role in the induction of erythema by the photosensitized generation of reactive oxygen species (singlet oxygen (1O2), superoxide (O2.-) and hydroxyl radicals (.OH)) that damage DNA and cellular membranes, and promote carcinogenesis and the changes associated with photoaging. Therefore, research efforts have been directed at a better photochemical and photobiological understanding of the so-called sunburn reaction, actinic or solar erythema. To survive the insults of actinic damage, the skin appears to have different intrinsic defensive mechanisms, among which antioxidants (enzymatic and non-enzymatic systems) play a pivotal role. In this paper, we will review the basic aspects of the action of UVR on the skin: a) photochemical reactions resulting from photon absorption by endogenous chromophores; b) the lipid peroxidation phenomenon, and c) intrinsic defensive cutaneous mechanisms (antioxidant systems). The last section will cover the inflammatory response including mediator release after cutaneous UVR exposure and adhesion molecule expression.
Antioxidants↗
Phototoxicity associated with diclofenac: a photophysical, photochemical, and photobiological study on the drug and its photoproducts.
Diclofenac (1) is a photosensitizing nonsteroidal antiinflammatory drug. Its photodecomposition gives rise to chlorocarbazole 2a. This product undergoes photodehalogenation to 3a in a subsequent step. When the photobiological activities of 1, 2a, and 3a are compared by means of the photohemolysis test, it is clearly observed that chlorocarbazole 2a causes cell lysis with a markedly higher efficiency than the parent drug or the secondary photoproduct 3a. Laser flash photolysis studies suggest that photodehalogenation of 2a occurs from its excited triplet state via quenching by ground-state 2a and formation of an excimer. As a consequence, an aryl radical plus an N-centered carbazolyl radical are formed. These radical intermediates appear to be responsible for the observed photobiological effects of diclofenac, via hydrogen abstraction from the target biomolecules, which initiates a type-I photodynamic effect. The efficient peroxidation of model lipids, such as linoleic acid, photosensitized by 2a are in favor of this proposal. Thus, the photosensitizing properties of diclofenac appear to be associated with the photochemical and photobiological activity of its major photoproduct.
Animals↗
Photobiology and photomedicine: the future is bright.
Important events since 1966 that have helped to advance photobiology in general and photomedicine in particular are reviewed. More formal courses on photobiology are needed so that future photobiologists and photodermatologists will not have to be self-taught about the properties and action of light. The effectiveness of current phototherapies and their future improvement are discussed. Some of the areas of photobiology what will impact on photomedicine in the years to come are ultraviolet (UV) radiation effects on the immune system, the light activation of enzymes as a potential new type of photothoerapy, the development of new photosensitizers for phototherapy, the effects of near-UV radiation on cellular membranes, and, of course, the role of DNA damage and repair in mutagenesis and carcinogenesis. The future is bright for photomedicine.
Carcinogens↗
Cutaneous photobiology: past, present and future.
The history and origin of the science of photobiology are reviewed. Interest in the biologic effects of light gradually increased, beginning with the discovery of ultraviolet and infrared radiation early in the 19th century. The basis of experimental photobiology was laid by the studies of Raab and Tappeiner on photodynamic action and the early uses of phototherapy by Finsen and Dorno. The discovery of the association of porphyrins with some light-related skin diseases and of the capability of chemical agents such as coal tar and bergamot to induce phototoxic contact dermatitis resulted in a flurry of clinical investigations leading to better understanding of the processes of phototoxicity and photoallergy. The early epidemiologic studies of Unna and Dubreuilh relating solar radiation exposure to the formation of actinic keratoses and non-melanoma skin cancer were experimentally confirmed in animals by Findlay, Roffo, and Blum. In the most recent quarter century (1950-1975), cellular and molecular photobiology has been refined. The studies on photochemistry of nucleic acid and of damage and repair mechanisms in DNA have set the stage for understanding the basic processes of biologic effects of light and promise the development of useful applications of specifically directed phototherapy and prevention of such light-induced diseases as skin cancer.
Animals↗
Photobiological activity of suction blister fluid from patients treated with 8-methoxypsoralen.
Suction blister fluid was collected from normal human volunteers before (SBF) and 2 h after (SBF 8-MOP) oral 8-methoxypsoralen (0.6 mg/kg) ingestion without irradiation. In SBF 8-MOP the concentration of 8-MOP was 150 ng/ml, and fluorescent metabolites were also present. The toxicity of SBF 8-MOP was then determined with and without UV-A irradiation in the diploid strain D7 of the yeast Saccharomyces cerevisiae which is suitable for the detection of lethal, mutagenic and recombinogenic events. It was compared with that of SBF, SBF with 8-MOP added in vitro (150 ng/ml) and 8-MOP (150 ng/ml) in water. SBF showed no effect with UV-A doses up to 360 kJ m-2; SBF 8-MOP showed a slight decrease in survival and a dose-dependent increase in nuclear mutations, mitotic gene conversion and crossing over; SBF with 8-MOP added in vitro showed increased photobiological activity compared with SBF 8-MOP. This photobiological activity was increased by a factor of six when using 8-MOP in water. These results indicate a different bioavailability of 8-MOP in water and in interstitial fluid containing proteins. The metabolites of 8-MOP in human skin did not increase the photobiological activity of the drug. We conclude that the 8-MOP present in human skin during PUVA therapy is mutagenic and recombinogenic for eukaryotic cells.
Biological Availability↗
Photobiological properties of hydroxy-substituted flavothiones.
Flavothione (FT) and a series of 18 hydroxy- and methoxy-substituted flavothiones were screened for photobiological activity. The 5-hydroxy-substituted compounds (group 3) and the methoxy-substituted flavothiones were inactive. FT and the remaining hydroxy-substituted compounds, all displayed photobiological activity. Among these, the 3-hydroxy-substituted compounds (group 2) were the most efficient photosensitizers overall in spite of their concurrent fast photodegradation. FT and all other hydroxyflavothiones, not substituted in the 3- or 5-positions (group 1), were inefficient compared with group 2. Detailed photobiological tests were carried out for four flavothiones of groups 1 and 2. The biological tests included fungi, several strains of Escherichia coli, Salmonella typhimurium and mammalian cells. In addition, the ability of these flavothiones to perform lipid peroxidation was evaluated. FT and 6-hydroxyflavothione (group 1) induce DNA damage via H-atom abstraction from the lowest n, pi* triplet state of the thione (oxygen independent). For 3-hydroxy and 3,6-dihydroxyflavothione (group 2), both DNA and the membrane are targets. The mechanism likely involves both energy transfer and electron transfer from the lowest pi, pi* triplet state to oxygen, to form singlet oxygen and the superoxide anion. Some of these compounds could be considered as models for environmentally safe photopesticides.
Bacteria↗
Carbomethoxy-derivatives of psoralen: interactions with DNA and photobiological properties.
The dark and photochemical interactions with DNA in vitro as well as the photobiological properties of two psoralen derivatives having a carbomethoxy-group inserted in 3 or 5' position of the furocoumarin nucleus were studied. 3-Carbomethoxy-4',8-dimethylpsoralen photoreacts with DNA in vitro to a very small extent and, as a consequence, it appears to be photobiologically ineffective. On the contrary, 5'-carbomethoxy-4,8-dimethylpsoralen appears very interesting, showing a photobinding and cross-linking capacity with DNA in vitro higher than that of 8-MOP. A similarly higher photobiological activity was also demonstrated, with respect to this reference compound, in experiments on inhibition of DNA and RNA synthesis in Ehrlich ascites tumor cells, and on the killing of bacteria and of T2 bacteriophage. Finally, this compound inhibited the tumor transmitting capacity of Ehrlich ascites tumor cells.
Animals↗
Photochemical and photobiological properties of 4,5'-dimethylpsoralen, a bifunctional contaminant of synthetic 4,5'-dimethylangelicin.
4,5'-Dimethylpsoralen, a bifunctional furocoumarin, can be formed as an impurity in the synthesis of its angular isomer, that is 4,5'-dimethylangelicin; the latter has recently been proposed as a potential monofunctional agent for photochemotherapy. To have precise information on the possible modifications of the photochemical and photobiological properties of synthetic 4,5'-dimethylangelicin caused by the presence of its linear isomer, we have studied the interactions of the latter with DNA in both the ground and the excited state and its photobiological activity. 4,5'-Dimethylpsoralen photobinds much more effectively to DNA than its angular isomer and is capable to form effectively inter-strand cross-linkages in DNA while dimethylangelicin is unable to form these bifunctional adducts in DNA. Dimethylpsoralen shows a strong skin-phototoxicity while angelicin lacks this activity. Moreover the antiproliferative activity of the psoralen derivative in terms of DNA synthesis inhibition in Ehrlich cells and of inhibition of infectivity of T2 phages, is about four times higher than that of the angular isomer. These data stress the necessity of the absence of the isomeric linear furocoumarin in the synthetic 4,5'-dimethylangelicin because its presence can markedly modify the photobiological and phototherapeutic properties of the angelicin derivative.
Animals↗
Photobiology of bacteria.
The field of photobiology is concerned with the interactions between light and living matter. For Bacteria this interaction serves three recognisable physiological functions: provision of energy, protection against excess radiation and signalling (for motility and gene expression). The chemical structure of the primary light-absorbing components in biology (the chromophores of photoactive proteins) is surprisingly simple: tetrapyrroles, polyenes and derivatised aromats are the most abundant ones. The same is true for the photochemistry that is catalysed by these chromophores: this is limited to light-induced exciton- or electron-transfer and photoisomerization. The apoproteins surrounding the chromophores provide them with the required specificity to function in various aspects of photosynthesis, photorepair, photoprotection and photosignalling. Particularly in photosynthesis several of these processes have been resolved in great detail, for others at best only a physiological description can be given. In this contribution we discuss selected examples from various parts of the field of photobiology of Bacteria. Most examples have been taken from the purple bacteria and the cyanobacteria, with special emphasis on recently characterised signalling photoreceptors in Ectothiorhodospira halophila and in Fremyella diplosiphon.
Bacteria↗
[Reciprocity regulation in photobiology. An overview].
According to the rule of Bunsen and Roscoe, a photochemical reaction is directly proportional to the total energy dose, irrespective of the time over which this dose is delivered. To date few studies have addressed the validity of this rule in experimental and applied photobiology. Most of these data point to the fact that the rule of reciprocity is invalid or of limited validity for many photobiological reactions. For UV-induced cell death, photocarcinogenesis, psoralen photochemistry, and the effects of low level laser radiation it has been shown that at a constant total dose, the intensity of the source is a major factor that determines quality and quantity of the response. In clinical photomedicine systematic investigations on the reciprocity of exposure time and radiation intensity are lacking. Such studies are urgently needed since it can be concluded from experimental evidence, that their results might lead to therapeutic regimens with an improved therapeutic index, i.e. maximized therapeutic efficacy with minimized adverse reactions.
Animals↗
Psoralen photobiology and photochemotherapy: 50 years of science and medicine.
In 1998 it is appropriate to commemorate the 50th anniversary of el Mofty's use of purified 8-methoxypsoralen (8-MOP) in the treatment of vitiligo (el Mofty AM. A preliminary clinical report on the treatment of leukoderma with Ammi majus linn. J R Egypt Med Assn 1948,31:651 65. el Mofty AM, el Sawalhy H, el Mofty M. Clinical study of a new preparation of 8-methoxypsoralen in photochemotherapy. Int J Dermatol 1994;8:588 92). Two young American dermatologists (Aaron Lerner and Thomas Fitzpatrick) were intrigued by the potency of this material. After Lerner determined that artificial long wavelength ultraviolet (320-400 nm, UVA) radiation was the most efficient for activating 8-MOP. the development of artificial sources enabled the efficient delivery of these photons to skin containing 8-MOP. Their initial studies for vitiligo led to further development of this therapy for the treatment of psoriasis (Parrish JA, Fitzpatrick TB, Tannenbaum L, et al. Photochemotherapy of psoriasis with oral methoxsalen and long-wave ultraviolet light. New Engl J Med 1974;291:1207-11. Honigsmann H, Fitzpatrick TB, Pathak MA, et al. Oral photochemotherapy with psoralen and UVA (PUVA): principles and practice. In: Fitzpatrick TB, Eisen AZ, Wolf K, editors. Dermatology in General Medicine. New York: McGraw-Hill, 1987:1728-54). This photochemotherapy came to be called 'PUVA' (psoralen + UVA). The position PUVA holds today as one of the most common procedures performed in dermatology can be traced to their initial curiosity and their subsequent ingenuity. Further developments in more recent years capitalized on their seminal work. The therapy met with unprecedented success from the outset, leaving little perceived need to understand underlying science. However, in recent years there has been a new found interest in the basic aspects of psoralen photobiology and molecular mechanistic events contributing to therapeutic responses as well as to the development of skin cancers in PUVA patients. These will be surveyed in this review commemorating the 50 years of modern psoralen photobiology and photomedicine.
Animals↗
The photobiological production of hydrogen: potential efficiency and effectiveness as a renewable fuel.
Photosynthetic microorganisms can produce hydrogen when illuminated, and there has been considerable interest in developing this to a commercially viable process. Its appealing aspects include the fact that the hydrogen would come from water, and that the process might be more energetically efficient than growing, harvesting, and processing crops. We review current knowledge about photobiological hydrogen production, and identify and discuss some of the areas where scientific and technical breakthroughs are essential for commercialization. First we describe the underlying biochemistry of the process, and identify some opportunities for improving photobiological hydrogen production at the molecular level. Then we address the fundamental quantum efficiency of the various processes that have been suggested, technological issues surrounding large-scale growth of hydrogen-producing microorganisms, and the scale and efficiency on which this would have to be practiced to make a significant contribution to current energy use.
Conservation of Energy Resources↗
Photophysical properties and photobiological activity of the furanochromones visnagin and khellin.
The larger photobiological activity of visnagin (VI) versus khellin (KH) toward several living organisms, including fungi, viruses, yeasts and bacteria, induced a detailed investigation of the photophysical properties of these naturally occurring furanochromones, using laser-flash-photolysis, photoacoustic calorimetry and fluorescence (steady-state and time-resolved) techniques in solvents with different polarity and content of water, including micelles and vesicles. The results have shown that the magnitude of all the three rate constants out of S1 (radiative, kf; internal conversion, kic and intersystem crossing, kisc) for VI and KH strongly depend on the solvent, namely on its hydrogen bonding ability and polarity. The changes of kf and kisc are due to the solvent-assisted mixing and/or inversion of the two first singlet excited states (1n, pi and 1 pi, pi), while kic increases with a decrease of the S0-S1 energy gap. As a consequence, the quantum yield of triplet formation (phi T) strongly decreases from values of approximately 0.8 in dioxane to < 0.05 in water for both compounds. The magnitude of solvent polarity/hydrogen bonding ability required, at which the state order is inverted and phi T starts to decrease, is greater for VI than for KH and consequently phi T (VI) >> phi T (KH) over a broad range of water content including that appropriate to the environment of the compounds in a living system. These facts account for the larger photobiological activity of VI with respect to KH, regarding both the fungus Fusarium culmorum L. and the wild strain of Escherichia coli, studied by us.
Chemical Phenomena↗
Radiometric quantities and units used in photobiology and photochemistry: recommendations of the Commission Internationale de L'Eclairage (International Commission on Illumination).
To characterize photobiological and photochemical phenomena, standardized terms and units are required. Without a uniform set of descriptors, much of the scientific value of publications can be lost. Attempting to achieve an international consensus for a common language has always been difficult, but now with truly international scientific publications, it is all the more important. As photobiology and photochemistry both represent the fusion of several scientific disciplines, it is not surprising that the physical terms used to describe exposures and dosimetric concepts can vary from author to author. There are, however, international organizations that were established to minimize the confusion produced by poor or inconsistent technical terminology. This note is to review the standardized terms and provide a background on how such terms are developed, with the hope that all readers will attempt to follow the standardized terminology.
International Agencies↗