bluuebunny/crossref_metadata_2025 huggingface dataset:
Introduction. Calcium signals and developmental patterning
Authors: Whitaker Michael , Smith Jim
Published: January 2008

Calcium ions generate ubiquitous cellular signals. Calcium signals play an important role in development. The most obvious example is fertilization, where calcium signals and calcium waves are triggered by the sperm and are responsible for activating the egg from dormancy and cell cycle arrest. Calcium signals also appear to contribute to cell cycle progression during the rapid cell cycles of early embryos. There is increasing evidence that calcium signals are an essential component of the signalling systems that specify developmental patterning and cell fate. This issue arises from a Discussion Meeting that brought together developmental biologists studying calcium signals with those looking at other patterning signals and events. This short introduction provides some background to the papers in this issue, setting out the emerging view that calcium signals are central to dorsoventral axis formation, gastrulation movements, neural specification and neuronal cell fate.
Dynamic determinations: patterning the cell behaviours that close the amphibian blastopore
Authors: Keller Ray , Shook David
Published: January 2008

We review the dynamic patterns of cell behaviours in the marginal zone of amphibians with a focus on how the progressive nature and the geometry of these behaviours drive blastopore closure. Mediolateral cell intercalation behaviour and epithelial–mesenchymal transition are used in different combinations in several species of amphibian to generate a conserved pattern of circumblastoporal hoop stresses. Although these cell behaviours are quite different and involve different germ layers and tissue organization, they are expressed in similar patterns. They are expressed progressively along presumptive lateral–medial and anterior–posterior axes of the body plan in highly ordered geometries of functional significance in the context of the biomechanics of blastopore closure, thereby accounting for the production of similar patterns of circumblastoporal forces. It is not the nature of the cell behaviour alone, but the context, the biomechanical connectivity and spatial and temporal pattern of its expression that determine specificity of morphogenic output during gastrulation and blastopore closure. Understanding the patterning of these dynamic features of cell behaviour is important and will require analysis of signalling at much greater spatial and temporal resolution than that has been typical in the analysis of patterning tissue differentiation.
From individual Wnt pathways towards a Wnt signalling network
Authors: Kestler Hans A , Kühl Michael
Published: January 2008

Wnt proteins play important roles during vertebrate and invertebrate development. They obviously have the ability to activate different intracellular signalling pathways. Based on the characteristic intracellular mediators used, these are commonly described as the Wnt/β-catenin, the Wnt/calcium and the Wnt/Jun N-terminal kinase pathways (also called planar cell polarity pathway). In the past, these different signalling events were mainly described as individual and independent signalling branches. Here, we discuss the possibility that Wnt proteins activate a complex intracellular signalling network rather than individual pathways and suggest a graph representation of this network. Furthermore, we discuss different ways of how to predict the specific outcome of an activation of this network in a particular cell type, which will require the use of mathematical models. We point out that the use of deterministic approaches via the application of differential equations is suitable to model only small aspects of the whole network and that more qualitative approaches are possibly a suitable starting point for the prediction of the global behaviour of such large protein interaction networks.
The dynamic interplay between a cell fate determinant and a lysozyme homolog drives the asymmetric division cycle of Caulobacter crescentus
Authors: Radhakrishnan Sunish Kumar , Thanbichler Martin , Viollier Patrick H.
Published: January 2008

Caulobacter crescentus divides asymmetrically into a swarmer cell and a stalked cell, a process that is governed by the imbalance in phosphorylated levels of the DivK cell fate determinant in the two cellular compartments. The asymmetric polar localization of the DivJ kinase results in its specific inheritance in the stalked daughter cell where it phosphorylates DivK. The mechanism for the polar positioning of DivJ is poorly understood. SpmX, an uncharacterized lysozyme homolog, is shown here to control DivJ localization and activation. In the absence of SpmX, DivJ is delocalized and dysfunctional, resulting in developmental defects caused by an insufficiency in phospho-DivK. While SpmX stimulates DivK phosphorylation in the stalked cell, unphosphorylated DivK in the swarmer cell activates an intricate transcriptional cascade that leads to the production of the spmX message. This event primes the swarmer cell for the impending transition into a stalked cell, a transition that is sparked by the abrupt accumulation and localization of SpmX to the future stalked cell pole. Localized SpmX then recruits and stimulates DivJ, and the resulting phospho-DivK implements the stalked cell fate. The dynamic interplay between SpmX and DivK is at the heart of the molecular circuitry that sustains the Caulobacter developmental cycle.
Meiotic crossover number and distribution are regulated by a dosage compensation protein that resembles a condensin subunit
Authors: Tsai Chun J. , Mets David G. , Albrecht Michael R. , Nix Paola , Chan Annette , Meyer Barbara J.
Published: January 2008

Biological processes that function chromosome-wide are not well understood. Here, we show that the Caenorhabditis elegans protein DPY-28 controls two such processes, X-chromosome dosage compensation in somatic cells and meiotic crossover number and distribution in germ cells. DPY-28 resembles a subunit of condensin, a conserved complex required for chromosome compaction and segregation. In the soma, DPY-28 associates with the dosage compensation complex on hermaphrodite X chromosomes to repress transcript levels. In the germline, DPY-28 restricts crossovers. In many organisms, one crossover decreases the likelihood of another crossover nearby, an enigmatic process called crossover interference. In C. elegans, interference is complete: Only one crossover occurs per homolog pair. dpy-28 mutations increase crossovers, disrupt crossover interference, and alter crossover distribution. Early recombination intermediates (RAD-51 foci) increase concomitantly, suggesting that DPY-28 acts to limit double-strand breaks (DSBs). Reinforcing this view, dpy-28 mutations partially restore DSBs in mutants lacking HIM-17, a chromatin-associated protein required for DSB formation. Our work further links dosage compensation to condensin and establishes a new role for condensin components in regulating crossover number and distribution. We propose that both processes utilize a related mechanism involving changes in higher-order chromosome structure to achieve chromosome-wide effects.
SCFCdc4 acts antagonistically to the PGC-1α transcriptional coactivator by targeting it for ubiquitin-mediated proteolysis
Authors: Olson Brian L. , Hock M. Benjamin , Ekholm-Reed Susanna , Wohlschlegel James A. , Dev Kumlesh K. , Kralli Anastasia , Reed Steven I.
Published: January 2008

Peroxisome proliferator-activated receptor γ (PPARγ) coactivator-1α (PGC-1α) is a highly regulated transcriptional coactivator that coordinates energy metabolism in mammals. Misregulation of PGC-1α has been implicated in the pathogenesis of several human diseases, including diabetes, obesity, and neurological disorders. We identified SCFCdc4 as an E3 ubiquitin ligase that regulates PGC-1α through ubiquitin-mediated proteolysis. PGC-1α contains two Cdc4 phosphodegrons that bind Cdc4 when phosphorylated by Glycogen Synthase Kinase 3β (GSK3β) and p38 MAPK, leading to SCFCdc4-dependent ubiquitylation and proteasomal degradation of PGC-1α. Furthermore, SCFCdc4 negatively regulates PGC-1α-dependent transcription. We demonstrate that RNAi-mediated reduction of Cdc4 in primary neurons results in an increase of endogenous PGC-1α protein, while ectopic expression of Cdc4 leads to a reduction of endogenous PGC-1α protein. Finally, under conditions of oxidative stress in neurons, Cdc4 levels are decreased, leading to an increase in PGC-1α protein and PGC-1α-dependent transcription. These results suggest that attenuation of SCFCdc4-dependent proteasomal degradation of PGC-1α has a role in mediating the PGC-1α-dependent transcriptional response to oxidative stress.
MODEL FOR THE RATIONALIZATION OF MAGNETIC FIELD EFFECTS IN VIVO. APPLICATION OF THE RADICAL‐PAIR MECHANISM TO BIOLOGICAL SYSTEMS
Authors: SCAIANO J. C. , COZENS FRANCES L. , McLEAN JACK
Published: January 2008

Abstract: A model for magnetic field effects in biological systems is proposed. This model employs the basic concepts of the radical pair mechanism, and predicts that magnetic fields will increase the average radical concentration, lengthen their lifetime and enhance the probability of radical reactions with cellular components. The relevance of these effects in relation to cancer initiation, promotion and progression is discussed.
COMPARISON OF THE SOLID‐MATRIX LUMINESCENCE PROPERTIES AND PHOTOPHYSICAL PARAMETERS OF TWO PRODUCTS FROM BENZO(a)PYRENE‐DNA ADDUCTS
Authors: Chu Yu , Hurtubise Robert J.
Published: January 2008

Abstract: The solid‐matrix luminescence properties and several calculated photophysical parameters of two important products from the benzo(a)pyrene‐DNA adducts were compared. The products were benzo(a)pyrene‐r‐7,t‐8,9,c‐10‐tetrahydrotetrol (I‐1) and 7R,8S,9S‐trihydroxy‐10‐(N2‐deoxyguanosyl‐3′‐phosphate)‐7,8,9,10‐tetrahydroben‐zo(a)pyrene (BPDE‐dG). The solid‐matrix luminescence data were obtained for I‐1 and BPDE‐dG adsorbed on two different solid matrices, namely, 1%α‐cyclodextrin (CD)/NaCl and 25% trehalose/NaCl and at two different temperatures (93 K and 296 K). The 25% trehalose/NaCl gave higher fluorescence and phosphorescence quantum yields from both I‐1 and BPDE‐dG in contrast to the 1%α‐CD/NaCl matrix. The BPDE‐dG showed lower fluorescence quantum yields on the solid matrices compared to I‐1. The lower fluorescence quantum yields for BPDE‐dG were attributed to a photoinduced electron transfer mechanism. In contrast to the room‐temperature solution fluorescence of BPDE‐dG, BPDE‐dG gave rather high fluorescence quantum yields at room temperature when adsorbed on the two solid matrices. From solid‐matrix luminescence quantum yields and solid‐matrix luminescence lifetimes, many photophysical parameters were calculated and compared. Several differences among the rate constants were noted with the two solid matrices for BPDE‐dG and I‐1. For example, BPDE‐dG showed internal conversion at 296 K with 25% trehalose/NaCl, but no internal conversion was observed at 93 K with this solid matrix. Also, for BPDE‐dG the phosphorescence rate constants at 296 K and 93 K were very small with 25% trehalose/NaCl, but the intersystem crossing rate constants from the triplet state to the ground state were very large. The results from this work show how solid‐matrix luminescence can be employed to obtain unique luminescence information from the I‐1 and BPDE‐dG systems.
RESEARCH NOTE: THIOPYRONINE‐AND 8‐METHOXYPSORALEN‐SENSITIZED PHOTODYNAMIC EFFECT ON CELL GROWTH, COLONY FORMING ABILITY AND RNA SYNTHESIS IN Saccharomyces MUTANTS DEFICIENT IN DNA REPAIR
Authors: Roth Robert M. , Takamori Yasuhiko , Lochmann Ernst‐Randolf
Published: January 2008

Abstract: We compared the photodynamic effects of thiopyronine (TP) and visible light, and 8‐methoxypsoralen (8‐MOP) and ultraviolet A (UV‐A) light, on growth, colony forming ability and RNA synthesis in a repair‐proficient Saccharomyces strain and three mutants deficient in DNA repair mechanisms (DNA repair assays). With 8‐MOP and UV‐A repair‐deficient mutants were significantly more sensitive than the repair‐proficient strain indicating that the system is sensitive for the detection of DNA damage. With TP and visible light, the photodynamic effects were comparable in the mutants and the control, indicating no DNA damage. These results support previous work showing that the main target of TP photosensitization in eukaryotes is not nuclear DNA.
MEMBRANE IONIC CURRENT PHOTOMODIFICATION BY ROSE BENGAL AND MENADIONE: ROLE OF SINGLET OXYGEN
Authors: Arriaga Edgar , Frolov Andrey , Tarr Merrill , Valenzeno Dennis Paul
Published: January 2008

Abstract: Photosensitized modification of ionic leak current and potassium current was studied in frog cardiac atrial cells using whole cell patch clamp techniques. Rose bengal (RB) and menadione (MQ) were used as photosensitizers. Separate photophysical studies of the photosensitizers in deuterium oxide solution demonstrated that MQ did not produce singlet oxygen as evidenced by the lack of luminescence at 1270 nm, whereas RB was an efficient singlet oxygen generator. Both photosensitizers sensitized block of potassium current in atrial cells, and both sensitized an increase of ionic leak current. However, when photosensitizer concentrations and illumination intensities were adjusted to match the rate of block of potassium current by the two photosensitizers, there were dramatic differences in leak current increase, both quantitatively and qualitatively. Menadione sensitized a much slower increase in leak current than did RB. Further, the leak current sensitized by MQ had a more positive reversal potential than that sensitized by RB, suggesting a less potassium‐selective leak current pathway. The results suggest that, while the effects of singlet oxygen and non‐singlet oxygen modification of cell membranes may be similar, there may also be significant differences in the resulting membrane permeabilities. The results also demonstrate that MQ and RB may be useful agents to study the role of singlet oxygen versus non‐singlet oxygen modification of biological systems.
REASSESSMENT OF THE DIFFERENTIAL EFFECTS OF ULTRAVIOLET AND IONIZING RADIATION ON HIV PROMOTER: THE USE OF CELL SURVIVAL AS THE BASIS FOR COMPARISONS
Authors: Beer Janusz Z. , Olvey Kathleen M. , LEE Wah , Zmudzka Barbara Z.
Published: January 2008

Abstract: Effects of different radiation treatments on the human immunodeficiency virus‐1 (HIV) promoter were reassessed for exposures comparable to those encountered in clinical or cosmetic practice, using survival of the host cell as a basis for comparisons. The exposures were performed with two ultraviolet radiation sources commonly used as medical or cosmetic devices (UVASUN 2000 and FS20 lamps), a germicidal (G15T8) lamp and an X‐ray machine. The UVC component of the FS20 lamp was filtered out. The emission spectra of the lamps were determined. The characteristics of these sources allowed us to discriminate among effects of UVA1 (340–400 nm), UVB + UVA2 (280–340 nm) and UVC (254 nm) radiations. Effects of irradiation were ascertained using cultures of HeLa cells stably transfected with the HIV promoter linked to a reporter—chloramphenicol acetyl transferase—gene. The exposures used caused at least two logs of cell killing. In this cytotoxicity range, UVA1 or X radiations had no effect on the HIV promoter, whereas UVB + UVA2 or UVC radiations activated the HIV promoter in a fluence‐dependent manner. Survivals following exposure to UVB + UVA2 or UVC radiation were (1) at the lowest measurable HIV promoter activation, 30 and 20%, respectively, (2) at one‐half maximal activation, 6 and 3%, respectively and (3) at the maximal activation, 0.5 and 0.2%, respectively. The results suggest that, among the radiations studied, UVB is the most important modality from the viewpoint of its potential effects on HIV‐infected individuals, since (1) UVA1 or X radiations have no effects on the HIV promoter, (2) human exposure to UVC radiation is infrequent and (3) human UVB exposure is very common.
THEORETICAL STUDY OF COLOR CONTROL MECHANISM IN RETINAL PROTEINS.: I. ROLE OF THE TRYPTOPHAN RESIDUE, TYROSINE RESIDUE AND WATER MOLECULE
Authors: Beppu Yoshitaka , Kakitani Toshiaki
Published: January 2008

Abstract: We calculated the opsin shift due to the electrostatic interaction between tryptophan or tyrosine residues and the chromophore by the perturbation method for various mutual configurations. The obtained opsin shift maps for these configurations demonstrated that when the above residues reside around the ionone ring side, the positive opsin shift (bathochromic shift) is obtained, and when they reside around the Schiff‐base side, the negative opsin shift (hypsochromic shift) is obtained. These properties hold true, irrespective of the orientation of those residues, indicating that higher order multipoles of the group play a central role. The maximum value of the opsin shift by these groups amounts to several hundred wavenumbers. These results indicate that the location of some of those amino acid residues at proper positions around the chromophore can cause a considerable opsin shift. We also calculated opsin shift maps for the various mutual configurations between a water molecule and the chromophore for comparison.
ACOUSTIC DETECTION OF TRIPLET STATES FORMED BY RADICAL PAIR RECOMBINATION IN QUINONE‐DEPLETED PHOTOSYNTHETIC REACTION CENTERS, BY MAGNETIC FIELD MODULATION (MAGNETOPHOTOACOUSTIC EFFECT)‐A FEASIBILITY STUDY
Authors: Malkin Shmuel , Hoff Arnold J.
Published: January 2008

Abstract: An acoustic method is outlined to detect triplet states formed by radical pair recombination in photosynthetic reaction centers. It is based on magnetic field effect on the probability of triplet state formation by recombination. Using a periodically modulated magnetic field in the presence of constant exciting light, a periodic modulation of the triplet state concentration is set in the sample, which is detected through the corresponding modulated heat emission, transduced to acoustic vibration of the gas phase around the sample. This effect is similar to the photoacoustic effect, except that here the light is not modulated. The feasibility of detecting such an effect was proven experimentally, by obtaining a signal from quinone‐depleted reaction centers of Rhodobacter sphaeroides. The signal had twice the frequency of the magnetic field modulation; it was proportional to the light intensity and significantly stronger at the lower temperatures (in the investigated range 113–278 K). No signal was obtained from quinone‐containing reaction centers, which do not produce triplets. A theoretical outline of the effect and the experimental set‐up are described. The magnitude of the effect was calibrated against ordinary photoacoustic measurements, allowing numerical evaluation of certain parameters of the triplet state (e.g. triplet energy or yield) with the aid of auxiliary information from the literature.
A Review of Sunscreen Safety and Efficacy
Authors: Gasparro Francis P. , Mitchnick Mark , Nash J. Frank
Published: January 2008

The use of sunscreen products has been advocated by many health care practitioners as a means to reduce skin damage produced by ultraviolet radiation (UVR) from sunlight. There is a need to better understand the efficacy and safety of sunscreen products given this ongoing campaign encouraging their use. The approach used to establish sunscreen efficacy, sun protection factor (SPF), is a useful assessment of primarily UVB (290–320 nm) filters. The SPF test, however, does not adequately assess the complete photoprotective profile of sunscreens specifically against long wavelength UVAI (340–400 nm). Moreover, to date, there is no singular, agreed upon method for evaluating UVA efficacy despite the immediate and seemingly urgent consumer need to develop sunscreen products that provide broad‐spectrum UVB and UVA photoprotection. With regard to the safety of UVB and UVA filters, the current list of commonly used organic and inorganic sunscreens has favorable toxico‐logical profiles based on acute, subchronic and chronic animal or human studies. Further, in most studies, sunscreens have been shown to prevent the damaging effects of UVR exposure. Thus, based on this review of currently available data, it is concluded that sunscreen ingredients or products do not pose a human health concern. Further, the regular use of appropriate broad‐spectrum sunscreen products could have a significant and favorable impact on public health as part of an overall strategy to reduce UVR exposure.
Studies on the Mechanism of the Enzymatic Photoisomerization of Retinal
Authors: Pepe I. M. , Cugnoli C.
Published: January 2008

The honeybee retina contains the enzyme photoisomerase that converts all‐trans‐retinal to 11‐cis‐retinal in light within the visible range. The activity of the bee photoisomerase was studied on all‐trans‐retinal under pulses of laser light. The experimental data were fitted with a simple equation that describes the mechanism of the isomerization reaction based on three steps having different time constants.
The Photoreceptor for Phototaxis in the Photosynthetic Flagellate Euglena gracilis
Authors: Häder Donat‐P. , Lebert Michael
Published: January 2008

The unicellular flagellate Euglena gracilis shows positive phototaxis at low fluence rates (≤10 W m 2) and negative phototaxis at high fluence rates (≥100 W m 2). Currently, retinal or flavins/pterins are discussed as chromo‐phores of the photoreceptor. When grown in the presence of 4 mM nicotine, a retinal inhibitor, for several generations, the cells still showed both responses, indicating that retinal is unlikely to be the chromophoric group of the photoreceptor responsible for phototaxis. The native flavin(s) can be substituted by growing the cells in roseo‐flavin dissolved in the medium. The absorption spectrum of roseoflavin extends well beyond the action spectrum for phototaxis (up to 600 nm). Excitation at wavelengths >550 nm does not cause phototactic orientation in control cells but causes both positive and negative phototaxis in roseoflavin‐grown cells, indicating an uptake and assembly of the chromophore in the photoreceptor complex. The white mutant strain 1224‐5/1f, induced by streptomycin treatment, lacks flavins as indicated by fluorescence spectroscopy. The phototaxis‐deficient pheno‐type cannot be complemented by the addition of external riboflavin. Fluorescence spectra of intact paraxonemal bodies (PAB) indicate that both pterins and flavins are involved in photoperception and that the excitation energy is efficiently funneled from the pterins to the flavins. This energy transfer is disrupted by solubilization of the PAB. In intact PAB flavins are not accessible to reducing or oxidizing substances, indicating that they are located inside the structure, while pterins are accessible, so that their localization can be assumed to be on the surface. The results described above are discussed with regard to the potential involvement of flavins and pterins as well as retinal in photoperception.
DNA Photodamage, Repair, Gene Induction and Genotoxicity Following Exposures to 254 nm UV and 8‐Methoxypsoralen Plus UVA in a Eukaryotic Cell System
Authors: Averbeck Dietrich , Averbeck Simone
Published: January 2008

The induction and repair of different types of photodamage and photogenotoxicity in eukaryotic cells have been the subject of many studies. Little is known about possible links between these phenomena and the induction of DNA damage‐inducible genes. We explored this relationship using the yeast Saccharomyces cerevisiae, a pertinent eukaryotic model. Previous results showed that the photogenotoxic potential of 8‐methoxypsoralen (8‐MOP) plus UVA is higher than that of UV (254 nm). Moreover, the induction of the ribonucleotide reductase gene RNR2 by UV and 8‐MOP plus UVA in an RNR2‐LACZ fusion strain and the formation of DNA double‐strand breaks (dsb) as repair intermediates after such treatments suggest that the latter process could involve a signal for gene induction. To further substantiate this, we measured the induction of the DNA repair gene RAD51 in RAD51‐LACZ fusion strains using the dsb repair and recombination deficient mutant rad52 and the corresponding wild type, and we determined the formation of dsb by pulsed‐field gel electrophoresis. After treatments, the resealing of dsb formed as repair intermediates was impaired in the rad52 mutant. At equal doses, i.e. the same number of lesions, the induction of the RAD51 gene by UV or 8‐MOP plus UVA was significantly reduced in the rad52 mutant as compared with the wild type. The same was true when equitoxic doses were used. Thus, the RAD52 repair pathway appears to play an important role not only in dsb repair but also in gene induction. Furthermore, the signaling pathways initiated by DNA damage and its processing are somewhat linked to the photogenotoxic response.
Wavelength‐dependent Photoacoustic Calorimetry Study of Melanin
Authors: Forest Susan E. , Simon John D.
Published: January 2008

Photoacoustic calorimetry is used to examine the energy dissipation in melanin under physiological conditions (pH 7.2) following irradiation by UV and visible (VIS) light. Four different excitation wavelengths were examined: 264 nm, representative of UVC radiation, 351 nm and 400 nm (UVA‐I radiation) and 527 nm, representative of VIS radiation. Following absorption at 527 nm, essentially all of the photon energy is released nonradiatively on a sub‐nanosecond of excitation. Similar results are observed at 400 nm. At 351 nm, most of the energy was released as heat; a small amount of energy was retained (5 ± 5%). When melanin is excited at 264 nm, 29 ± 7% of the photon energy is retained by the molecule for a time period longer than a few hundred nanoseconds. These results show that a long‐lived excited state or reactive intermediate is generated upon UV irradiation, whereas all of the excitation energy is dissipated nonradiatively in the visible portion of the spectrum. These results establish that the photochemistry of melanin is wavelength dependent.
UVB Radiation Induced Increase in Quercetin: Kaempferol Ratio in Wild‐Type and Transgenic Lines of Petunia
Authors: Ryan Ken G. , Markham Kenneth R. , Bloor Stephen J. , Bradley J. Marie , Mitchell Kevin A. , Jordan Brian R.
Published: January 2008

The use of genetically modified plants offers unique opportunities to study the role of specific flavonoids in plant UVB protection. Along with a parental wild‐type Mitchell Petunia, two transgenic lines with altered flavonoids were also examined; Lc with enhanced levels of antho‐cyanins due to the action of a maize flavonoid regulatory gene Leaf color, and AFLS that carries an antisense fla‐vonol synthase construct and is known to have reduced flavonol levels in flowers. All three lines were grown in near ambient sunlight, sunlight lacking UVB (280–320 nm) radiation and sunlight with 25% added UVB. Ultra‐violet‐B radiation induced significant reductions in the rates of leaf expansion and seedling growth in all three lines. The presence of anthocyanins did not appear to afford Lc plants any special protection from UVB. Ul‐traviolet‐B treatment induced increases in total flavonol content in young plants of all three lines, and this effect decreased with increasing leaf age. Notably, increasing UVB levels led to an increase in the ratio of quercetin: kaempferol with all three cultivars. The AFLS transgenic, contrary to expectations based on its genetic construction, had normal levels of flavonols in the leaves and the highest Q:K ratio of the three cultivars. This transgenic was the least susceptible to UVB, which may indicate an enhanced protective role for quercetin. Because both quercetin and kaempferol have similar UVB screening properties, quercetin may exert this role by other means.
Optics of a Bifacial Leaf: 3. Implications for Photosynthetic Performance
Authors: Richter T. , Fukshansky L.
Published: January 2008

On the basis of a preceding study of light and absorption gradients in a bifacial leaf, spatial patterns of photosynthetic rate and photosynthetic saturation have been analyzed for different cases of natural illumination and different distributions of photosynthetic capacity along the depth coordinate. Two quality criteria of the spatially extended leaf photosynthetic performance arose from this analysis. One of them characterizes the range of the acceptable incident quantum fluxes between the lowest economically acceptable one and the highest still not photodamaging one. The second criterion gives the limit for the fractional part of the leaf photosynthetic capacity that can be utilized before the first photoinhibition effect at some depth occurs. It is shown how the range of the acceptable fluxes can be affected by the interplay between light and capacity gradients.
Photomodification of Cardiac Membrane: Chaotic Currents and High Conductance States in Isolated Patches
Authors: Tarr Merrill , Valenzeno Dennis Paul
Published: January 2008

We have demonstrated previously that photomodification permeabilizes cardiac cells as evidenced by activation of a whole‐cell leak current. In this paper we report that photomodification induces in cell‐attached and inside‐out cardiac membrane patches a chaotic current. Unlike current recordings from many protein ion channels that show stepwise amplitude changes associated with open and closed states of the channel, the chaotic current consists of variable amplitude spike‐like transitions. The amplitudes of these spikes can vary from tenths to tens of picoamperes at a constant transmembrane potential. We provide evidence that the chaotic current is transmembrane rather than trans‐seal and has a voltage dependency expected for current flow through nonspecific conductance pathways. Photomodification can also induce high conductance states (greater than 500 pS) in cell‐attached and inside‐out patches. We present evidence that the high conductance state is also not related to seal breakdown. Our results suggest that both the chaotic current activity in and high conductance state of photo‐modified cardiac membrane patches result from the opening of many small conductance, nonspecific pathways through the membrane.
Stationary Headband for Clinical Time‐of‐Flight Optical Imaging at the Bedside
Authors: Hintz Susan R. , Benaron David A. , van Houten John P. , Duckworth Joshua L. , Liu Frank W. H. , Spilman Stanley D. , Stevenson David K. , Cheong Wai‐Fung
Published: January 2008

Conventional brain‐imaging modalities may be limited by high cost, difficulty of bedside use, noncontinuous operation, invasiveness or an inability to obtain measurements of tissue function, such as oxygenation during stroke. Our goal was to develop a bedside clinical device able to generate continuous, noninvasive, tomographic images of the brain using low‐power nonionizing optical radiation. We modified an existing stage‐based time‐of‐flight optical tomography system to allow imaging of patients under clinical conditions. First, a stationary headband consisting of thin, flexible optical fibers was constructed. The headband was then calibrated and tested, including an assessment of fiber lengths, the existing system software was modified to collect headband data and to perform simultaneous collection of data and image reconstruction, and the existing hardware was modified to scan optically using this headband. The headband was tested on resin models and allowed for the generation of tomographic images in vitro; the headband was tested on critically ill infants and allowed for optical tomographic images of the neonatal brain to be obtained in vivo.
Clinical Evaluation of the Cutaneous Phototoxicity of 5,10,15,20‐Tetra (m‐hydroxyphenyl)chlorin
Authors: Wagnieres Georges , Hadjur Christophe , Grosjean Pierre , Braichotte Daniel , Savary Jean‐François , Monnier Philippe , van den Bergh Hubert
Published: January 2008

The cutaneous phototoxic reaction induced by intravenous injection of 5,‐10,‐15,‐20‐tetra(m‐hydroxyphenyl)chlorin (mTHPC) has been clinically evaluated in patients undergoing photodynamic therapy. These tests were performed on the backs of 23 patients with a solar simulator at various times after drug administration ranging from 5 h to 57 days. The mTHPC doses ranged from 0.1 to 0.3 mg/kg, and the illuminations lasted from 30 s up to 8 min. These tests have shown that the duration of the skin photosensitization induced after a typical therapeutic dose of mTHPC (0.15 mg/kg) is less important than with Photofrin®(2 mg/kg). The level of mTHPC in the skin was also assessed in vivo and at times corresponding to the irradiations using an optical fiber‐based spectrofiuorometer. This study indicates that the light‐induced fluorescence spectroscopy of mTHPC enables prediction of the degree of photosensitivity of the skin.
Possible Mechanisms of Vascular Relaxation Induced by Pulsed‐UV Laser
Authors: Morimoto Yuji , Arai Tsunenori , Matsuo Hirotaka , Kikuchi Makoto
Published: January 2008

This study was designed to examine the mechanism of vasorelaxation induced by pulsed‐UV laser. Luminal diameters of rat femoral arteries were measured prior to and following krypton‐fluoride excimer laser irradiation of 248 nm in wavelength. The diameter was enlarged to 1.3 times the preirradiated size at 1 or 10 Hz irradiation when the fluence was over 2.0 mj/pulse/mm2, while the diameter reached 1.8 times at 100 Hz with a fluence of 0.8 mj/pulse/mm2. Vasorelaxation by the 100 Hz irradiation was inhibited when the artery was pretreated with methylene blue but was enhanced with superoxide dis‐mutase. Pathological analysis revealed an ablation crater and vacuole formation in the vessel at 1 or 10 Hz irradiation, but these changes were not remarkable in the 100 Hz‐exposed sample. These findings suggest that vasorelaxation induced by the pulsed UV irradiation at 1 or 10 Hz results from structural alteration of vascular smooth muscle by the ablation crater or vacuolization. On the other hand, a possible mechanism of vasorelaxation at the 100 Hz irradiation is partially related to nitric oxide.
Caspofungin Prolongs Survival of Transiently Neutropenic Rats with Advanced-Stage Invasive Pulmonary Aspergillosis
Authors: van de Sande Wendy W. J. , van Vianen Wim , ten Kate Marian T. , Vissers Jolanda , Laurijsens John , Tavakol Mehri , Rijnders Bart J. A. , Mathot Ron A. A. , Bakker-Woudenberg Irma A. J. M.
Published: January 2008

A high-dose-step-down strategy for caspofungin treatment was evaluated in an experimental model of advanced-stage invasive pulmonary aspergillosis. The therapeutic efficacy of caspofungin in relation to the severity of invasive pulmonary infection caused by
Aspergillus fumigatus
in transiently neutropenic rats was investigated by using rat survival and the decrease in the fungal burden as the parameters of efficacy. When treatment was started at either 16 h or 24 h after fungal inoculation, caspofungin administered intraperitoneally at 4 mg/kg of body weight/day for 10 days was highly effective (100% and 93% rat survival, respectively). However, only 27% rat survival was obtained when treatment was started at 72 h, when the rats had advanced-stage infection. Increasing the dose from 4 to 10 mg/kg/day could compensate for the decrease in efficacy and resulted in 67% rat survival. The high dose of 10 mg/kg/day for 10 days did not appear to be necessary since a high-dose-step-down dosing schedule with 10 mg/kg/day for 3 days followed by 4 mg/kg/day for 7 days was equally effective. At 10 days after the end of treatment with 10 mg/kg/day caspofungin, the level of neither
A. fumigatus
DNA nor
A. fumigatus
galactomannan in the infected left lung was significantly decreased. In contrast,
A. fumigatus
galactomannan concentrations in serum were significantly decreased. The levels of creatinine, blood urea nitrogen, alanine aminotransferase, and asparate aminotransferase were not elevated during treatment. Caspofungin is effective for the treatment of invasive pulmonary aspergillosis in transiently neutropenic rats and is even effective in rats with advanced-stage infection. In this model, the administration of high-dose-step-down treatment was as effective as treatment with high doses for the whole treatment period.
Epigallocatechin Gallate Inactivates Clinical Isolates of Herpes Simplex Virus
Authors: Isaacs Charles E. , Wen Guang Y. , Xu Weimin , Jia Jun Hua , Rohan Lisa , Corbo Christopher , Di Maggio Vincenzo , Jenkins Edmund C. , Hillier Sharon
Published: January 2008

In the absence of a fully effective herpes simplex virus (HSV) vaccine, topical microbicides represent an important strategy for preventing HSV transmission. (−)-Epigallocatechin gallate (EGCG) (molecular weight, 458.4) is the primary catechin in green tea. The present study shows that EGCG has greater anti-HSV activity than other green tea catechins and inactivates multiple clinical isolates of HSV type 1 (HSV-1) and HSV-2. EGCG reduced HSV-2 titers by ≥1,000-fold in 10 to 20 min and reduced HSV-1 titers by the same amount in 30 to 40 min. The anti-HSV activity of EGCG is due to a direct effect on the virion, and incubating Vero and CV1 cells with EGCG for 48 h prior to infection with HSV-1 and HSV-2, respectively, does not reduce HSV production. Electron microscopic (EM) studies showed that purified virions exposed to EGCG were damaged, and EM immunogold labeling of the envelope glycoproteins gB and gD was significantly reduced following EGCG treatment while capsid protein labeling was unchanged. When purified HSV-1 envelope glycoproteins gB and gD were incubated with EGCG and then examined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, lower-molecular-weight gB and gD bands decreased and new higher-molecular-weight bands appeared, indicating the EGCG-dependent production of macromolecular complexes. gB and gD are essential for HSV infectivity, and these results suggest that EGCG could inactivate HSV virions by binding to gB, gD, or another envelope glycoprotein. EGCG is stable in the pH range found in the vagina and appears to be a promising candidate for use in a microbicide to reduce HSV transmission.
Conserved Water Molecules Stabilize the Ω-Loop in Class A β-Lactamases
Authors: Bös Fabian , Pleiss Jürgen
Published: January 2008

A set of 49 high-resolution (≤2.2 Å) structures of the TEM, SHV, and CTX-M class A β-lactamase families was systematically analyzed to investigate the role of conserved water molecules in the stabilization of the Ω-loop. Overall, 13 water molecules were found to be conserved in at least 45 structures, including two water positions which were found to be conserved in all structures. Of the 13 conserved water molecules, 6 are located at the Ω-loop, forming a dense cluster with hydrogen bonds to residues at the Ω-loop as well as to the rest of the protein. This layer of conserved water molecules is packed between the Ω-loop and the rest of the protein and acts as structural glue, which could reduce the flexibility of the Ω-loop. A correlation between conserved water molecules and conserved protein residues could in general not be detected, with the exception of the conserved water molecules at the Ω-loop. Furthermore, the evolutionary relationship between the three families, derived from the number of conserved water molecules, is similar to the relationship derived from phylogenetic analysis.
P-Glycoprotein Limits Oral Availability, Brain Penetration, and Toxicity of an Anionic Drug, the Antibiotic Salinomycin
Authors: Lagas Jurjen S. , Sparidans Rolf W. , van Waterschoot Robert A. B. , Wagenaar Els , Beijnen Jos H. , Schinkel Alfred H.
Published: January 2008

Salinomycin is a polyether organic anion that is extensively used as a coccidiostatic antibiotic in poultry and commonly fed to ruminant animals to improve feed efficiency. However, salinomycin also causes severe toxicity when accidentally fed to animals in high doses. In addition, humans are highly sensitive to salinomycin and severe toxicity has been reported. Multidrug efflux transporters like P-glycoprotein (P-gp), BCRP, and MRP2 are highly expressed in the intestine and can restrict the oral uptake and tissue penetration of xenobiotics. The purpose of this study was to investigate whether the anionic drug salinomycin is a substrate for one or more of these efflux pumps. Salinomycin was actively transported by human MDR1 P-gp expressed in polarized MDCK-II monolayers but not by the known organic anion transporters human MRP2 and murine Bcrp1. Using P-gp-deficient mice, we found a marked increase in plasma salinomycin concentrations after oral administration and decreased plasma clearance after intravenous administration. Furthermore, absence of P-gp resulted in significantly increased brain penetration. P-gp-deficient mice also displayed clearly increased susceptibility to salinomycin toxicity. Thus far, P-gp was thought to affect mainly hydrophobic, positively charged or neutral drugs in vivo. Our data show that P-gp can also be a major determinant of the pharmacokinetic behavior and toxicity of an organic anionic drug. Variation in P-gp activity might thus directly affect the effective exposure to salinomycin and possibly to other anionic drugs and toxin substrates. Individuals with reduced or absent P-gp activity could therefore be more susceptible to salinomycin toxicity.
Comparative Efficacies of Rifaximin and Vancomycin for Treatment of
Clostridium difficile
-Associated Diarrhea and Prevention of Disease Recurrence in Hamsters
Authors: Kokkotou Efi , Moss Alan C. , Michos Athanasios , Espinoza Daniel , Cloud Jeffrey W. , Mustafa Nasima , O'Brien Michael , Pothoulakis Charalabos , Kelly Ciarán P.
Published: January 2008

Clostridium difficile
-associated colitis is an increasing cause of morbidity and mortality in hospitalized patients, with high relapse rates following conventional therapy. We sought to determine the efficacy of rifaximin, a novel nonabsorbed antibiotic, in the hamster model of
C. difficile
-associated diarrhea (CDAD). Hamsters received clindamycin subcutaneously and 24 h later were infected by gavage with one of two
C. difficile
strains: a reference strain (VPI 10463) and a current epidemic strain (BI17). Vancomycin (50 mg/kg of body weight) or rifaximin (100, 50, and 25 mg/kg) were then administered orally for 5 days beginning either on the same day as infection (prevention) or 24 h later (treatment). Therapeutic effects were assessed by weight gain, histology, and survival. We found that rifaximin was as effective as vancomycin in the prevention and treatment of colitis associated with the two
C. difficile
strains that we examined. There was no relapse after treatment with vancomycin or rifaximin in hamsters infected with the BI17 strain. Hamsters infected with the VPI 10463 strain and treated with rifaximin did not develop relapsing infection within a month of follow-up, whereas the majority of vancomycin-treated animals relapsed (0% versus 75%, respectively;
P
< 0.01). In conclusion, rifaximin was found to be an effective prophylactic and therapeutic agent for CDAD in hamsters and was not associated with disease recurrence. These findings, in conjunction with the pharmacokinetic and safety profiles of rifaximin, suggest that it is an attractive candidate for clinical use for CDAD.
In Vitro Activities of 35 Double Combinations of Antifungal Agents against
Scedosporium apiospermum
and
Scedosporium prolificans
Authors: Cuenca-Estrella Manuel , Alastruey-Izquierdo Ana , Alcazar-Fuoli Laura , Bernal-Martinez Leticia , Gomez-Lopez Alicia , Buitrago Maria J. , Mellado Emilia , Rodriguez-Tudela Juan L.
Published: January 2008

Activities of 35 combinations of antifungal agents against
Scedosporium
spp. were analyzed by a checkerboard microdilution design and the summation of fractional concentration index. An average indifferent effect was detected apart from combinations of azole agents and echinocandins against
Scedosporium apiospermum
. Antagonism was absent for all antifungal combinations against both species.
Effects on Gram-Negative and Gram-Positive Bacteria Mediated by 5-Aminolevulinic Acid and 5-Aminolevulinic Acid Derivatives
Authors: Fotinos Nicolas , Convert Maruska , Piffaretti Jean-Claude , Gurny Robert , Lange Norbert
Published: January 2008

Due mainly to the extensive use of antibiotics, the spread of multiresistant bacterial strains is one of the most worrying threats to public health. One strategy that can be used to overcome potential shortcomings might be the inactivation of these microorganisms by 5-aminolevulinic acid (5-ALA) or 5-ALA derivative-mediated photodynamic therapy (PDT). 5-ALA has no photoactive properties, but when it is given exogenously, it acts as a precursor of photosensitive porphyrins predominantly in tissues or organisms that are characterized by a high metabolic turnover, such as tumors, macrophages, and bacteria. However, the weak ability of 5-ALA to cross biological barriers has led to the introduction of more lipophilic derivatives, such as methyl aminolevulinate or hexyl aminolevulinate, which display improved capacities to reach the cytoplasm. Starting from the hypothesis that more lipophilic compounds carrying only a permanent positive charge under physiological conditions may more easily cross the bacterial multilayer barrier, we have tested the efficacies of some 5-ALA
n
-alkyl esters for the inactivation of bacteria. For this purpose, different bacterial strains were incubated with 5-ALA or its corresponding esters of different lipophilicities. Then, the bacteria were irradiated with light and the numbers of CFU post-PDT were counted and compared to those for the controls, which were kept in the dark. Furthermore, the total amount of accumulated porphyrins was quantified by high-pressure liquid chromatography analysis. In our studies, analysis of the bacterial extracts revealed the presence of all the porphyrins involved in heme biosynthesis, from uroporphyrin to protoporphyin IX. The efficacy of bacterial inactivation was a function of the total amount of porphyrins produced, independently of their nature. The 5-ALA methyl and butyl esters were the most effective compounds with respect to the photodynamic inactivation of bacteria. We observed significant differences in terms of the optimal drug concentration, bactericidal activities, and porphyrin production.
Drug-Regulated Expression ofPlasmodium falciparumP-Glycoprotein Homologue 1: a Putative Role for Nuclear Receptors
Authors: Johnson David J. , Owen Andrew , Plant Nick , Bray Patrick G. , Ward Stephen A.
Published: January 2008

Acquired resistance to therapeutic agents is a major clinical concern in the prevention/treatment of malaria. The parasite has developed resistance to specific drugs through two mechanisms: mutations in target proteins such as dihydrofolate reductase and the bc1 complex for antifolates and nathoquinones, respectively, and alterations in predicted parasite transporter molecules such as P-glycoprotein homologue 1 (Pgh1) andPlasmodium falciparumCRT (PfCRT). Alterations in the expression of Pgh1 have been associated with modified susceptibility to a range of unrelated drugs. The molecular mechanism(s) that is responsible for this phenotype is unknown. We have shown previously (A. M. Ndifor, R. E. Howells, P. G. Bray, J. L. Ngu, and S. A. Ward, Antimicrob. Agents Chemother. 37:1318-1323, 2003) that the anticonvulsant phenobarbitone (PB) can induce reduced susceptibility to chloroquine (CQ) inP. falciparum, and in the current study, we provide the first evidence for a molecular mechanism underlying this phenomenon. We demonstrate that pretreatment with PB can elicit decreased susceptibility to CQ in both CQ-resistant and CQ-sensitive parasite lines and that this is associated with the increased expression of the drug transporter Pgh1 but not PfCRT. Furthermore, we have investigated the proximal promoter regions from bothpfmdr1andpfcrtand identified a number of putative binding sites for nuclear receptors with sequence similarities to regions known to be activated by PB in mammals. Whole-genome analysis has revealed a putative nuclear receptor gene, providing the first evidence that nuclear receptor-mediated responses to drug exposure may be a mechanism of gene regulation inP. falciparum.