bluuebunny/crossref_metadata_2025 huggingface dataset:
A Saturated X-ray Laser Beam at 7 Nanometers
Authors: Zhang J. , MacPhee A. G. , Lin J. , Wolfrum E. , Smith R. , Danson C. , Key M. H. , Lewis C. L. S. , Neely D. , Nilsen J. , Pert G. J. , Tallents G. J. , Wark J. S.
Published: July 2002

A saturated nickel-like samarium x-ray laser beam at 7 nanometers has been demonstrated with an output energy of 0.3 millijoule in 50-picosecond pulses, demonstrating that saturated operation of a laser at wavelengths shorter than 10 nanometers can be achieved. The narrow divergence, short wavelength, short pulse duration, high efficiency, and high brightness of this samarium laser make it an ideal candidate for many x-ray laser applications.
High-Altitude Observations of the Polar Wind
Authors: Moore T. E. , Chappell C. R. , Chandler M. O. , Craven P. D. , Giles B. L. , Pollock C. J. , Burch J. L. , Young D. T. , Waite J. H. , Nordholt J. E. , Thomsen M. F. , McComas D. J. , Berthelier J. J. , Williamson W. S. , Robson R. , Mozer F. S.
Published: July 2002

Plasma outflows, escaping from Earth through the high-altitude polar caps into the tail of the magnetosphere, have been observed with a xenon plasma source instrument to reduce the floating potential of the POLAR spacecraft. The largest component of H
+
flow, along the local magnetic field (30 to 60 kilometers per second), is faster than predicted by theory. The flows contain more O
+
than predicted by theories of thermal polar wind but also have elevated ion temperatures. These plasma outflows contribute to the plasmas energized in the elongated nightside tail of the magnetosphere, creating auroras, substorms, and storms. They also constitute an appreciable loss of terrestrial water dissociation products into space.
Spontaneous Oscillation and Self-Pumped Phase Conjugation in a Photorefractive Polymer Optical Amplifier
Authors: Grunnet-Jepsen A. , Thompson C. L. , Moerner W. E.
Published: July 2002

Optical processing with photorefractive polymers depends on achieving high optical gain, which depends exponentially on the product of the interaction length and the gain coefficient. By use of several polymer layers to increase the overall interaction length and a new high-performance photorefractive polymer composite, the overall optical one-pass gain becomes as large as a factor of 5. For a two-layer sample placed in an optical cavity made with two concave mirrors, spontaneous oscillation due to two-beam coupling gain was observed. Because only one pumping beam is required, this configuration also acts as a self-pumped phase-conjugating mirror with a reflectivity of 13 percent for an applied electric field of 75 volts per micrometer, marking a milestone for this growing class of optoelectronic materials.
An NGF-TrkA-Mediated Retrograde Signal to Transcription Factor CREB in Sympathetic Neurons
Authors: Riccio Antonella , Pierchala Brian A. , Ciarallo Christopher L. , Ginty David D.
Published: July 2002

Nerve growth factor (NGF) is a neurotrophic factor secreted by cells that are the targets of innervation of sympathetic and some sensory neurons. However, the mechanism by which the NGF signal is propagated from the axon terminal to the cell body, which can be more than 1 meter away, to influence biochemical events critical for growth and survival of neurons has remained unclear. An NGF-mediated signal transmitted from the terminals and distal axons of cultured rat sympathetic neurons to their nuclei regulated phosphorylation of the transcription factor CREB (cyclic adenosine monophosphate response element
–
binding protein). Internalization of NGF and its receptor tyrosine kinase TrkA, and their transport to the cell body, were required for transmission of this signal. The tyrosine kinase activity of TrkA was required to maintain it in an autophosphorylated state upon its arrival in the cell body and for propagation of the signal to CREB within neuronal nuclei. Thus, an NGF-TrkA complex is a messenger that delivers the NGF signal from axon terminals to cell bodies of sympathetic neurons.
Structural Plasticity in a Remodeled Protein-Protein Interface
Authors: Atwell Shane , Ultsch Mark , De Vos Abraham M. , Wells James A.
Published: July 2002

Remodeling of the interface between human growth hormone (hGH) and the extracellular domain of its receptor was studied by deleting a critical tryptophan residue (at position 104) in the receptor, creating a large cavity, and selecting a pentamutant of hGH by phage display that fills the cavity and largely restores binding affinity. A 2.1 Å resolution x-ray structure of the mutant complex showed that the receptor cavity was filled by selected hydrophobic mutations of hGH. Large structural rearrangements occurred in the interface at sites that were distant from the mutations. Such plasticity may be a means for protein-protein interfaces to adapt to mutations as they coevolve.
Inducing and Viewing the Rotational Motion of a Single Molecule
Authors: Stipe B. C. , Rezaei M. A. , Ho W.
Published: July 2002

Tunneling electrons from the tip of a scanning tunneling microscope were used to induce and monitor the reversible rotation of single molecules of molecular oxygen among three equivalent orientations on the platinum(111) surface. Detailed studies of the rotation rates indicate a crossover from a single-electron process to a multielectron process below a threshold tunneling voltage. Values for the energy barrier to rotation and the vibrational relaxation rate of the molecule were obtained by comparing the experimental data with a theoretical model. The ability to induce the controlled motion of single molecules enhances our understanding of basic chemical processes on surfaces and may lead to useful single-molecule devices.
An Antibody exo Diels-Alderase Inhibitor Complex at 1.95 Angstrom Resolution
Authors: Heine Andreas , Stura Enrico A. , Yli-Kauhaluoma Jari T. , Gao Changshou , Deng Qiaolin , Beno Brett R. , Houk Kendall N. , Janda Kim D. , Wilson Ian A.
Published: July 2002

A highly specific Diels-Alder protein catalyst was made by manipulating the antibody repertoire of the immune system. The catalytic antibody 13G5 catalyzes a disfavored exo Diels-Alder transformation in a reaction for which there is no natural enzyme counterpart and that yields a single regioisomer in high enantiomeric excess. The crystal structure of the antibody Fab in complex with a ferrocenyl inhibitor containing the essential haptenic core that elicited 13G5 was determined at 1.95 angstrom resolution. Three key antibody residues appear to be responsible for the observed catalysis and product control. Tyrosine-L36 acts as a Lewis acid activating the dienophile for nucleophilic attack, and asparagine-L91 and aspartic acid–H50 form hydrogen bonds to the carboxylate side chain that substitutes for the carbamate diene substrate. This hydrogen-bonding scheme leads to rate acceleration and also pronounced stereoselectivity. Docking experiments with the four possible ortho transition states of the reaction explain the specific exo effect and suggest that the (3
R
,4
R
)-
exo
stereoisomer is the preferred product.
Strategies and Potential Molecular Targets for Obesity Treatment
Authors: Campfield L. Arthur , Smith Françoise J. , Burn Paul
Published: July 2002

Obesity is an increasingly prevalent and important health problem. Although treatment is available, the long-term maintenance of medically significant weight loss (5 to 10 percent of initial body weight) is rare. Since 1995 there has been an explosion of research focused on the regulation of energy balance and fat mass. Characterization of obesity-associated gene products has revealed new biochemical pathways and molecular targets for pharmacological intervention that will likely lead to new treatments. Ideally, these treatments will be viewed as adjuncts to behavioral and lifestyle changes aimed at maintenance of weight loss and improved health.
Dissociative Recombination of HD
+
in Selected Vibrational Quantum States
Authors: Amitay Z. , Baer A. , Dahan M. , Knoll L. , Lange M. , Levin J. , Schneider I. F. , Schwalm D. , Suzor-Weiner A. , Vager Z. , Wester R. , Wolf A. , Zajfman D.
Published: July 2002

Rate coefficients for dissociative recombination of HD
+
in selected vibrational states have been measured by a combination of two molecular fragment imaging methods by using the heavy-ion storage ring technique. Recombination fragment imaging yields state-to-state reaction rates. These rates are converted to rate coefficients by using vibrational level populations of the stored ion beam, derived from nuclear coordinate distributions measured on extracted ions. The results show strongly increasing rate coefficients for high vibrational excitation, where additional dissociation routes open up, in agreement with a theoretical calculation. Very low rate coefficients are found for certain, isolated vibrational states.
The Magnetic Stability of Spin-Dependent Tunneling Devices
Authors: Gider S. , Runge B.-U. , Marley A. C. , Parkin S. S. P.
Published: July 2002

The tunneling resistance between two ferromagnetic metal layers that are separated by a thin insulator depends on the relative orientation of the magnetization
M
of each layer. In a memory device, independent switching of the magnetically soft layer is achieved by making the other layer either exchange-biased or magnetically hard. The repeated reversal of
M
of the soft layer by field cycling can demagnetize the other magnetically hard layer and thus erase the tunnel junction's memory. The
M
of exchange-biased structures was stable at least to 10
7
cycles, whereas in hard structures,
M
generally decayed logarithmically with the number of field cycles. The decay was very sensitive to the thickness of the hard layer and the composition of the soft layer. However, no decay was observed when the moment reversal was accomplished by coherent rotation, establishing that demagnetization results from the formation and motion of domain walls in the soft layer during field cycling.
Cristobalite in Volcanic Ash of the Soufriere Hills Volcano, Montserrat, British West Indies
Authors: Baxter P. J. , Bonadonna C. , Dupree R. , Hards V. L. , Kohn S. C. , Murphy M. D. , Nichols A. , Nicholson R. A. , Norton G. , Searl A. , Sparks R. S. J. , Vickers B. P.
Published: July 2002

Crystalline silica (mostly cristobalite) was produced by vapor-phase crystallization and devitrification in the andesite lava dome of the Soufriere Hills volcano, Montserrat. The sub–10-micrometer fraction of ash generated by pyroclastic flows formed by lava dome collapse contains 10 to 24 weight percent crystalline silica, an enrichment of 2 to 5 relative to the magma caused by selective crushing of the groundmass. The sub–10-micrometer fraction of ash generated by explosive eruptions has much lower contents (3 to 6 percent) of crystalline silica. High levels of cristobalite in respirable ash raise concerns about adverse health effects of long-term human exposure to ash from lava dome eruptions.
A Search for Companions to Nearby Brown Dwarfs: The Binary DENIS-P J1228.2-1547
Authors: Martı́n E. L. , Brandner W. , Basri G.
Published: July 2002

Hubble Space Telescope imaging observations of two nearby brown dwarfs, DENIS-P J1228.2-1547 and Kelu 1, made with the near-infrared camera and multiobject spectrometer (NICMOS), show that the DENIS object is resolved into two components of nearly equal brightness with a projected separation of 0.275 arc second (5 astronomical units for a distance of 18 parsecs). This binary system will be able to provide the first dynamical measurement of the masses of two brown dwarfs in only a few years. Upper limits to the mass of any unseen companion in Kelu 1 yield a planet of 7 Jupiter masses aged 0.5 × 10
9
years, which would have been detected at a separation larger than about 4 astronomical units. This example demonstrates that giant planets could be detected by direct imaging if they exist in Jupiter-like orbits around nearby young brown dwarfs.
All-Polymer Optoelectronic Devices
Authors: Ho Peter K. H. , Stephen D. , Thomas  , Friend Richard H. , Tessler Nir
Published: July 2002

Composites of nanoparticles and conjugated polymers that exhibit composition-tunable optical constants have been developed for use in semiconducting photonic structures. For example, the 550-nanometer wavelength in-plane refractive index of poly(p-phenylenevinylene)–silica composites can be tailored over the range of 1.6 to 2.7, allowing efficient distributed Bragg reflectors and waveguides to be fabricated. Low levels of chemical doping improve electrical conductivity through these structures without detriment to their photonic properties. Exemplifying these concepts, all-polymer microcavities and microcavity light-emitting diodes were demonstrated. Appropriate confinement of photons and electron-hole pairs in these organic semiconductor-based structures can be achieved.
Regulation of JNK by Src During
Drosophila
Development
Authors: Tateno Minoru , Nishida Yasuyoshi , Adachi-Yamada Takashi
Published: July 2002

In
Drosophila
, the Jun amino-terminal kinase (JNK) homolog Basket (Bsk) is required for epidermal closure. Mutants for
Src42A
, a
Drosophila
c-
src
protooncogene homolog, are described. Src42A functions in epidermal closure during both embryogenesis and metamorphosis. The severity of the epidermal closure defect in the
Src42A
mutant depended on the amount of Bsk activity, and the amount of Bsk activity depended on the amount of Src42A. Thus, activation of the Bsk pathway is required downstream of Src42A in epidermal closure. This work confirms mammalian studies that demonstrated a physiological link between Src and JNK.
Mitochondrial FtsZ in a Chromophyte Alga
Authors: Beech Peter L. , Nheu Thao , Schultz Thomas , Herbert Shane , Lithgow Trevor , Gilson Paul R. , McFadden Geoffrey I.
Published: July 2002

A homolog of the bacterial cell division gene
ftsZ
was isolated from the alga
Mallomonas splendens.
The nuclear-encoded protein (MsFtsZ-mt) was closely related to FtsZs of the α-proteobacteria, possessed a mitochondrial targeting signal, and localized in a pattern consistent with a role in mitochondrial division. Although FtsZs are known to act in the division of chloroplasts, MsFtsZ-mt appears to be a mitochondrial FtsZ and may represent a mitochondrial division protein.
Requirement of the Spindle Checkpoint for Proper Chromosome Segregation in Budding Yeast Meiosis
Authors: Shonn Marion A. , McCarroll Robert , Murray Andrew W.
Published: July 2002

The spindle checkpoint was characterized in meiosis of budding yeast. In the absence of the checkpoint, the frequency of meiosis I missegregation increased with increasing chromosome length, reaching 19% for the longest chromosome. Meiosis I nondisjunction in spindle checkpoint mutants could be prevented by delaying the onset of anaphase. In a recombination-defective mutant (
spo11Δ
), the checkpoint delays the biochemical events of anaphase I, suggesting that chromosomes that are attached to microtubules but are not under tension can activate the spindle checkpoint. Spindle checkpoint mutants reduce the accuracy of chromosome segregation in meiosis I much more than that in meiosis II, suggesting that checkpoint defects may contribute to Down syndrome.
Graphical Evolution of the Arnold Web: From Order to Chaos
Authors: Froeschlé Claude , Guzzo Massimiliano , Lega Elena
Published: July 2002

We represent graphically the evolution of the set of resonances of a quasi-integrable dynamical system, the so-called Arnold web, whose structure is crucial for the stability properties of the system. The basis of our representation is the use of an original numerical method, whose definition is directly related to the dynamics of orbits, and the careful choice of a model system. We also show the transition from the Nekhoroshev stability regime to the Chirikov diffusive one, which is a generic nontrivial phenomenon occurring in many physical processes, such as slow chaotic transport in the asteroid belt and beam-beam interaction.
Detecting and Measuring Cotranslational Protein Degradation in Vivo
Authors: Turner Glenn C. , Varshavsky Alexander
Published: July 2002

Nascent polypeptides emerging from the ribosome and not yet folded may at least transiently present degradation signals similar to those recognized by the ubiquitin system in misfolded proteins. The ubiquitin sandwich technique was used to detect and measure cotranslational protein degradation in living cells. More than 50 percent of nascent protein molecules bearing an amino-terminal degradation signal can be degraded cotranslationally, never reaching their mature size before their destruction by processive proteolysis. Thus, the folding of nascent proteins, including abnormal ones, may be in kinetic competition with pathways that target these proteins for degradation cotranslationally.
African Hot Spot Volcanism: Small-Scale Convection in the Upper Mantle Beneath Cratons
Authors: King Scott D. , Ritsema Jeroen
Published: July 2002

Numerical models demonstrate that small-scale convection develops in the upper mantle beneath the transition of thick cratonic lithosphere and thin oceanic lithosphere. These models explain the location and geochemical characteristics of intraplate volcanos on the African and South American plates. They also explain the presence of relatively high seismic shear wave velocities (cold downwellings) in the mantle transition zone beneath the western margin of African cratons and the eastern margin of South American cratons. Small-scale, edge-driven convection is an alternative to plumes for explaining intraplate African and South American hot spot volcanism, and small-scale convection is consistent with mantle downwellings beneath the African and South American lithosphere.
The Genetic Legacy of Paleolithic
Homo sapiens sapiens
in Extant Europeans: A Y Chromosome Perspective
Authors: Semino Ornella , Passarino Giuseppe , Oefner † Peter J. , Lin Alice A. , Arbuzova Svetlana , Beckman Lars E. , Benedictis Giovanna De , Francalacci Paolo , Kouvatsi Anastasia , Limborska Svetlana , Marcikiæ Mladen , Mika Anna , Mika Barbara , Primorac Dragan , Santachiara-Benerecetti A. Silvana , Cavalli-Sforza L. Luca , Underhill Peter A.
Published: July 2002

A genetic perspective of human history in Europe was derived from 22 binary markers of the nonrecombining Y chromosome (NRY). Ten lineages account for >95% of the 1007 European Y chromosomes studied. Geographic distribution and age estimates of alleles are compatible with two Paleolithic and one Neolithic migratory episode that have contributed to the modern European gene pool. A significant correlation between the NRY haplotype data and principal components based on 95 protein markers was observed, indicating the effectiveness of NRY binary polymorphisms in the characterization of human population composition and history.
Requirement of the RNA Editing Deaminase ADAR1 Gene for Embryonic Erythropoiesis
Authors: Wang Q. , Khillan J. , Gadue P. , Nishikura K.
Published: July 2002

The members of the ADAR (adenosine deaminase acting on RNA) gene family are involved in site-selective RNA editing that changes adenosine residues of target substrate RNAs to inosine. Analysis of staged chimeric mouse embryos with a high contribution from embryonic stem cells with a functional null allele for ADAR1 revealed a heterozygous embryonic-lethal phenotype. Most ADAR1
+/−
chimeric embryos died before embryonic day 14 with defects in the hematopoietic system. Our results suggest the importance of regulated levels of ADAR1 expression, which is critical for embryonic erythropoiesis in the liver.
Multigenerational Cortical Inheritance of the Rax2 Protein in Orienting Polarity and Division in Yeast
Authors: Chen Tracy , Hiroko Takatoshi , Chaudhuri Amitabha , Inose Fumika , Lord Matthew , Tanaka Shigeko , Chant John , Fujita Atsushi
Published: July 2002

Diploid yeast cells repeatedly polarize and bud from their poles, probably because of highly stable marks of unknown composition. Here, Rax2, a membrane protein, was shown to behave as such a mark. The Rax2 protein itself was inherited immutably at the cell cortex for multiple generations, and Rax2 was shown to have a half-life exceeding several generations. The persistent inheritance of cortical protein markers would provide a means to couple a cell's history to the future development of a precise morphogenetic form.
Control of Fusion Pore Dynamics During Exocytosis by Munc18
Authors: Fisher Richard J. , Pevsner Jonathan , Burgoyne Robert D.
Published: July 2002

Intracellular membrane fusion is mediated by the SNARE (soluble
N
-ethylmaleimide–sensitive factor attachment protein receptor) proteins. All vesicle transport steps also have an essential requirement for a member of the Sec1 protein family, including the neuronal Munc18-1 (also known as nSec1) in regulated exocytosis. Here, in adrenal chromaffin cells, we expressed a Munc18 mutant with reduced affinity for syntaxin, which specifically modified the kinetics of single-granule exocytotic release events, consistent with an acceleration of fusion pore expansion. Thus, Munc18 functions in a late stage in the fusion process, where its dissociation from syntaxin determines the kinetics of postfusion events.
Safety and Pharmacokinetics of Once-Daily Regimens of Soft-Gel Capsule Saquinavir plus Minidose Ritonavir in Human Immunodeficiency Virus-Negative Adults
Authors: Kilby J. Michael , Sfakianos Greg , Gizzi Nick , Siemon-Hryczyk Peggy , Ehrensing Eric , Oo Charles , Buss Neil , Saag Michael S.
Published: July 2002

Human immunodeficiency virus type 1 (HIV-1) protease inhibitors have dramatically improved treatment options for HIV infection, but frequent dosing may impact adherence to highly active antiretroviral treatment regimens (HAART). Previous studies demonstrated that combined therapy with ritonavir and saquinavir allows a decrease in frequency of saquinavir dosing to twice daily. In this study, we evaluated the safety and pharmacokinetics of combining once-daily doses of the soft-gel capsule (SGC) formulation of saquinavir (saquinavir-SGC) and minidose ritonavir. Forty-four healthy HIV-negative volunteers were randomized into groups receiving once-daily doses of saquinavir-SGC (1,200 to 1,800 mg) plus ritonavir (100 to 200 mg) or a control group receiving only saquinavir-SGC (1,200 mg) three times daily. Saquinavir-SGC alone and saquinavir-SGC–ritonavir combinations were generally well tolerated, and there were no safety concerns. Addition of ritonavir (100 mg) to saquinavir-SGC (1,200 to 1,800 mg/day) increased the area under the concentration-time curve (AUC) for saquinavir severalfold, and the intersubject peak concentration in plasma and AUC variability were reduced compared to those achieved with saquinavir-SGC alone (3,600 mg/day), while trough saquinavir levels (24 h post-dose) were substantially higher than the 90% inhibitory concentration calculated from HIV-1 clinical isolates. Neither increasing the saquinavir-SGC dose to higher than 1,600 mg nor increasing ritonavir from 100 to 200 mg appeared to further enhance the AUC. These results suggest that an all once-daily HAART regimen, utilizing saquinavir-SGC plus a more tolerable low dose of ritonavir, may be feasible. Studies of once-daily saquinavir-SGC (1,600 mg) in combination with ritonavir (100 mg) in HIV-infected patients are underway.
Differential Removal of Thymidine Nucleotide Analogues from Blocked DNA Chains by Human Immunodeficiency Virus Reverse Transcriptase in the Presence of Physiological Concentrations of 2′-Deoxynucleoside Triphosphates
Authors: Meyer Peter R. , Matsuura Suzanne E. , Schinazi Raymond F. , So Antero G. , Scott Walter A.
Published: July 2002

Removal of 2′,3′-didehydro-3′-deoxythymidine-5′-monophosphate (d4TMP) from a blocked DNA chain can occur through transfer of the chain-terminating residue to a nucleotide acceptor by human immunodeficiency virus type 1 (HIV-1) reverse transcriptase (RT). ATP-dependent removal of either d4TMP or 3′-azido-3′-deoxythymidine-5′-monophosphate (AZTMP) is increased in AZT resistant HIV-1 RT (containing D67N/K70R/T215F/K219Q mutations). Removal of d4TMP is strongly inhibited by the next complementary deoxynucleoside triphosphate (50% inhibitory concentration [IC50] of ∼0.5 μM), whereas removal of AZTMP is much less sensitive to this inhibition (IC50of >100 μM). This could explain the lack of cross-resistance by AZT-resistant HIV-1 to d4T in phenotypic drug susceptibility assays.
Effect of a Bis-Benzyl Polyamine Analogue on
Pneumocystis carinii
Authors: Merali Salim , Sarić Muhamed , Chin Kevin , Clarkson Allen B.
Published: July 2002

Pneumocystis carinii
is the causative agent of
P. carinii
pneumonia (PCP), an opportunistic infection associated with AIDS and other immunosuppressed conditions. Although polyamine metabolism of this fungus has been shown to be a chemotherapeutic target, this metabolism has not been thoroughly investigated. Reported here is the effect of one polyamine analogue,
N
,
N
′-bis{3-[(phenylmethyl)amino]propyl}-1,7-diaminoheptane (BBS), on
P. carinii
. BBS inhibits the growth of
P. carinii
in culture, but at concentrations higher than those required to inhibit the growth of other pathogens. However, BBS is at least as active in an animal model of PCP as in other models of diseases studied. BBS causes some reduction in
P. carinii
polyamine content and polyamine biosynthetic enzyme activities, but the effect is less than that observed with other pathogens and very much less than the effect of the polyamine biosynthesis inhibitor
dl
-α-difluoromethylornithine. BBS enters
P. carinii
cells via a polyamine transporter, unlike all other cells that have been studied.
P. carinii
cells do not remove the benzyl groups of BBS, as is reported for mammalian cells. The most likely mode of action is displacement of natural polyamines. Overall, the activity of BBS provides further evidence that polyamines and polyamine metabolism are rational targets for the development of drugs to treat PCP. Because the details of BBS-
P. carinii
interaction differ from those of other cells studied, polyamine analogues may provide a highly specific treatment for PCP.
Single-Dose Pharmacokinetics of Amprenavir, a Human Immunodeficiency Virus Type 1 Protease Inhibitor, in Subjects with Normal or Impaired Hepatic Function
Authors: Veronese Laurence , Rautaureau Jacques , Sadler Brian M. , Gillotin Catherine , Petite Jean-Pierre , Pillegand Bernard , Delvaux Michel , Masliah Claude , Fosse Sandrine , Lou Yu , Stein Daniel S.
Published: July 2002

Amprenavir (141W94) is extensively metabolized by P450 cytochromes, specifically, CYP3A4. Because hepatic insufficiency reduces P450-mediated metabolism, the concentrations in plasma of drugs metabolized through this pathway are often increased in subjects with liver disease. Following administration of a single, oral dose of 600 mg of amprenavir, pharmacokinetic parameters were determined for 10 subjects with severe cirrhosis, 10 subjects with moderate cirrhosis, and 10 healthy volunteers. Model-independent methods for determining the area under the plasma concentration-time curve (AUC) from time zero to infinity (AUC
0–∞
) showed an increase in amprenavir AUC
0–∞
of 2.5-fold in the group with moderate cirrhosis and 4.5-fold in the group with severe cirrhosis compared with that in the control group of healthy volunteers (
P
< 0.05). AUC
0–∞
was linearly related to the severity of liver disease, as assessed by the Child-Pugh score. Of the laboratory data used to calculate the Child-Pugh score, only the mean total bilirubin concentration showed a significant relationship with AUC
0–∞
. The relationship between the total bilirubin concentration and the AUC
0–∞
of amprenavir was well characterized by a simple
E
max
model, suggesting that the total bilirubin concentration may be a useful parameter for predicting the amprenavir AUC in subjects with hepatic insufficiency. Finally, the sera of cirrhotic subjects showed significant decreases in the levels of α
1
-acid glycoprotein, the primary plasma binding protein for amprenavir. On the basis of the results of this study, for an exposure equivalent to a clinical dose of 1,200 mg twice daily in subjects without cirrhosis, subjects with Child-Pugh scores of 5 to 8 should receive a twice-daily 450-mg dose of amprenavir, and subjects with Child-Pugh scores of 9 to 15 should receive a twice-daily 300-mg dose of amprenavir.
Pharmacokinetic Interaction between Amprenavir and Clarithromycin in Healthy Male Volunteers
Authors: Brophy Donald F. , Israel Debra S. , Pastor Antonio , Gillotin Catherine , Chittick Greg E. , Symonds William T. , Lou Yu , Sadler Brian M. , Polk Ron E.
Published: July 2002

The P450 enzyme, CYP3A4, extensively metabolizes both amprenavir and clarithromycin. To determine if an interaction exists when these two drugs are coadministered, the pharmacokinetics of amprenavir and clarithromycin were investigated in healthy adult male volunteers. This was a Phase I, open-label, randomized, balanced, multiple-dose, three-period crossover study. Fourteen subjects received the following three regimens: amprenavir, 1,200 mg twice daily over 4 days (seven doses); clarithromycin, 500 mg twice daily over 4 days (seven doses); and the combination of the above regimens over 4 days (seven doses of each drug). Twelve subjects completed all treatments and the follow-up period. The erythromycin breath test (ERMBT) was administered at baseline, 2 h after the final dose of each of the three regimens and at the first follow-up visit. Coadministration of clarithromycin and amprenavir significantly increased the mean amprenavir AUC
ss
,
C
max,ss
, and
C
min,ss
by 18, 15, and 39%, respectively. Amprenavir had no significant effect on the AUC
ss
of clarithromycin, but the median
T
max,ss
for clarithromycin increased by 2.0 h, renal clearance increased by 34%, and the AUC
ss
for 14-(
R
)-hydroxyclarithromycin decreased by 35% when it was given with amprenavir. Amprenavir and clarithromycin reduced the ERMBT result by 85 and 67%, respectively, and by 87% when the two drugs were coadministered. The baseline ERMBT value did not correlate with clearance of amprenavir or clarithromycin. A pharmacokinetic interaction occurs when amprenavir and clarithromycin are coadministered, but the effects are not likely to be clinically important, and coadministration does not require a dosage adjustment for either drug.
Genome-Wide Expression Patterns in
Saccharomyces cerevisiae
: Comparison of Drug Treatments and Genetic Alterations Affecting Biosynthesis of Ergosterol
Authors: Bammert Gary F. , Fostel Jennifer M.
Published: July 2002

Enzymes in the ergosterol-biosynthetic pathway are the targets of a number of antifungal agents including azoles, allylamines, and morpholines. In order to understand the response of
Saccharomyces cerevisiae
to perturbations in the ergosterol pathway, genome-wide transcript profiles following exposure to a number of antifungal agents targeting ergosterol biosynthesis (clotrimazole, fluconazole, itraconazole, ketoconazole, voriconazole, terbinafine, and amorolfine) were obtained. These profiles were compared to the transcript profiles of strains containing deletions of one of the late-stage ergosterol genes:
ERG2
,
ERG5
, or
ERG6
. A total of 234 genes were identified as responsive, including the majority of genes from the ergosterol pathway. Expression of several responsive genes, including
ERG25
,
YER067W
, and
YNL300W
, was also monitored by PCR over time following exposure to ketoconazole. The kinetics of transcriptional response support the conditions selected for the microarray experiment. In addition to ergosterol-biosynthetic genes, 36 mitochondrial genes and a number of other genes with roles related to ergosterol function were responsive, as were a number of genes responsive to oxidative stress. Transcriptional changes related to heme biosynthesis were observed in cells treated with chemical agents, suggesting an additional effect of exposure to these compounds. The expression profile in response to a novel imidazole, PNU-144248E, was also determined. The concordance of responsive genes suggests that this compound has the same mode of action as other azoles. Thus, genome-wide transcript profiles can be used to predict the mode of action of a chemical agent as well as to characterize expression changes in response to perturbation of a metabolic pathway.
Relationship between Capsular Type, Penicillin Susceptibility, and Virulence of Human
Streptococcus pneumoniae
Isolates in Mice
Authors: Azoulay-Dupuis E. , Rieux V. , Muffat-Joly M. , Bédos J. P. , Vallée E. , Rivier C. , Isturiz R. , Carbon C. , Moine P.
Published: July 2002

We examined the relationship between penicillin susceptibility, peritoneal virulence in Swiss mice, and capsular type in a selection of 122 clinical
Streptococcus pneumoniae
isolates belonging to 24 serotypes. Regardless of the serotype, all 32 virulent strains were susceptible to penicillin, and all 41 strains with diminished susceptibility or resistance to penicillin were avirulent. The remaining 49 strains were both susceptible to penicillin and avirulent, irrespective of the serotype. On the basis of their capsular type and pathogenic behavior, strains fell into one of four groups. In the group consisting of serotypes 1, 3, and 4 (
n
= 16), strains were predominantly virulent (81.3%), and all were penicillin susceptible. In the serotype 6 group (
n
= 32), the frequency of virulence was significantly lower (34.4 versus 81.3%,
P
= 0.002), and strains were predominantly penicillin susceptible (71.9%). In the group composed of serotypes 9, 14, 19, and 23 (
n
= 50), all strains were avirulent, and 56% had decreased susceptibility (
n
= 12) or resistance to (
n
= 16) penicillin. The fourth group was heterogenous, as it pooled 24 strains of 15 different serotypes; in this group the frequency of virulence was 33.3%, and strains were predominantly penicillin susceptible (83.3%). These data point to a complex relationship between penicillin susceptibility and virulence in mice but do not entirely separate these characteristics from the role of the capsular type. The possibility that the mechanisms conferring penicillin resistance are related to those leading to a loss of virulence is supported by these findings.
Recombinant Green Fluorescent Protein-Expressing Human Cytomegalovirus as a Tool for Screening Antiviral Agents
Authors: Marschall Manfred , Freitag Martina , Weiler Sigrid , Sorg Gabriele , Stamminger Thomas
Published: July 2002

A recombinant human cytomegalovirus (AD169-GFP) expressing green fluorescent protein was generated by homologous recombination. Infection of human fibroblast cultures with AD169-GFP virus produced stable and readily detectable amounts of GFP signals which were quantitated by automated fluorometry. Hereby, high levels of sensitivity and reproducibility could be achieved, compared to those with the conventional plaque reduction assay. Antiviral activities were determined for four reference compounds as well as a set of putative novel cytomegalovirus inhibitors. The results obtained were exactly in line with the known characteristics of reference compounds and furthermore revealed distinct antiviral activities of novel in vitro inhibitors. The fluorometric data could be confirmed by GFP-based flow cytometry and fluorescence microscopy. In addition, laboratory virus variants derived from the recombinant AD169-GFP virus provided further possibilities for study of the characteristics of drug resistance. The GFP-based antiviral assay appeared to be very reliable for measuring virus-inhibitory effects in concentration- and time-dependent fashions and might also be adaptable for high-throughput screenings of cytomegalovirus-specific antiviral agents.
Molecular Analysis of Antibiotic Resistance Gene Clusters in
Vibrio cholerae
O139 and O1 SXT Constins
Authors: Hochhut Bianca , Lotfi Yasmin , Mazel Didier , Faruque Shah M. , Woodgate Roger , Waldor Matthew K.
Published: July 2002

Many recent Asian clinical
Vibrio cholerae
E1 Tor O1 and O139 isolates are resistant to the antibiotics sulfamethoxazole (Su), trimethoprim (Tm), chloramphenicol (Cm), and streptomycin (Sm). The corresponding resistance genes are located on large conjugative elements (SXT constins) that are integrated into
prfC
on the
V. cholerae
chromosome. We determined the DNA sequences of the antibiotic resistance genes in the SXT constin in MO10, an O139 isolate. In SXT
MO10
, these genes are clustered within a composite transposon-like structure found near the element's 5′ end. The genes conferring resistance to Cm (
floR
), Su (
sul
II), and Sm (
strA
and
strB
) correspond to previously described genes, whereas the gene conferring resistance to Tm, designated
dfr18
, is novel. In some other O139 isolates the antibiotic resistance gene cluster was found to be deleted from the SXT-related constin. The El Tor O1 SXT constin, SXT
ET
, does not contain the same resistance genes as SXT
MO10
. In this constin, the Tm resistance determinant was located nearly 70 kbp away from the other resistance genes and found in a novel type of integron that constitutes a fourth class of resistance integrons. These studies indicate that there is considerable flux in the antibiotic resistance genes found in the SXT family of constins and point to a model for the evolution of these related mobile elements.
Cyanovirin-N, a Potent Human Immunodeficiency Virus-Inactivating Protein, Blocks both CD4-Dependent and CD4-Independent Binding of Soluble gp120 (sgp120) to Target Cells, Inhibits sCD4-Induced Binding of sgp120 to Cell-Associated CXCR4, and Dissociates Bound sgp120 from Target Cells
Authors: Mori Toshiyuki , Boyd Michael R.
Published: July 2002

Cyanovirin-N (CV-N), an 11-kDa protein originally isolated from the cyanobacterium
Nostoc ellipsosporum
, potently inactivates diverse strains of human immunodeficiency virus type 1 (HIV-1), HIV-2, simian immunodeficiency virus, and feline immunodeficiency virus. It has been well established that the HIV surface envelope glycoprotein gp120 is a molecular target of CV-N. We recently reported that CV-N impaired the binding of virion-associated gp120 to cell-associated CD4 and that CV-N preferentially inhibited binding of the glycosylation-dependent neutralizing monoclonal antibody 2G12 to gp120. However, CV-N did not interfere with the interactions of soluble CD4 (sCD4) with either soluble gp120 (sgp120) or virion-associated gp120. In the present study, we have evaluated the effects of CV-N on the binding of sgp120 to cell-associated CD4 to clarify the experimental basis of the previous binding results, and we further address the detailed mechanism of action of CV-N. Here we present evidence that (i) CV-N impairs both CD4-dependent and CD4-independent binding of sgp120 to the target cells, (ii) CV-N blocks the sCD4-induced binding of sgp120 with cell-associated coreceptor CXCR4, and (iii) CV-N dissociates bound sgp120 from target cells. The results illustrate that the measured effects of CV-N on gp120-CD4 binding interactions depend upon the type of CD4 (soluble or cell associated), but not upon the type of gp120 (soluble or virion associated), employed in the experimental protocol. In addition, this study reinforces that CV-N acts uniquely to prevent essential interactions between the envelope glycoprotein and target cell receptors and further supports the potential broad utility of CV-N as a microbicide to prevent the transmission of HIV and AIDS.
Efficacy of Zanamivir against Avian Influenza A Viruses That Possess Genes Encoding H5N1 Internal Proteins and Are Pathogenic in Mammals
Authors: Leneva Irina A. , Goloubeva Olga , Fenton Robert J. , Tisdale Margaret , Webster Robert G.
Published: July 2002

In 1997, an avian H5N1 influenza virus, A/Hong Kong/156/97 (A/HK/156/97), caused six deaths in Hong Kong, and in 1999, an avian H9N2 influenza virus infected two children in Hong Kong. These viruses and a third avian virus [A/Teal/HK/W312/97 (H6N1)] have six highly related genes encoding internal proteins. Additionally, A/Chicken/HK/G9/97 (H9N2) virus has PB1 and PB2 genes that are highly related to those of A/HK/156/97 (H5N1), A/Teal/HK/W312/97 (H6N1), and A/Quail/HK/G1/97 (H9N2) viruses. Because of their similarities with the H5N1 virus, these H6N1 and H9N2 viruses may have the potential for interspecies transmission. We demonstrate that these H6N1 and H9N2 viruses are pathogenic in mice but that their pathogenicities are less than that of A/HK/156/97 (H5N1). Unadapted virus replicated in lungs, but only A/HK/156/97 (H5N1) was found in the brain. After three passages (P
3
) in mouse lungs, the pathogenicity of the viruses increased, with both A/Teal/HK/W312/97 (H6N1) (P
3
) and A/Quail/HK/G1/97 (H9N2) (P
3
) viruses being found in the brain. The neuraminidase inhibitor zanamivir inhibited viral replication in Madin-Darby canine kidney cells in virus yield assays (50% effective concentration, 8.5 to 14.0 μM) and inhibited viral neuraminidase activity (50% inhibitory concentration, 5 to 10 nM). Twice daily intranasal administration of zanamivir (50 and 100 mg/kg of body weight) completely protected infected mice from death. At a dose of 10 mg/kg, zanamivir completely protected mice from infection with H9N2 viruses and increased the mean survival day and the number of survivors infected with H6N1 and H5N1 viruses. Zanamivir, at all doses tested, significantly reduced the virus titers in the lungs and completely blocked the spread of virus to the brain. Thus, zanamivir is efficacious in treating avian influenza viruses that can be transmitted to mammals.
Atovaquone Nanosuspensions Show Excellent Therapeutic Effect in a New Murine Model of Reactivated Toxoplasmosis
Authors: Schöler Nadja , Krause Karsten , Kayser Oliver , Müller Rainer H. , Borner Klaus , Hahn Helmut , Liesenfeld Oliver
Published: July 2002

Immunocompromised patients are at risk of developing toxoplasma encephalitis (TE). Standard therapy regimens (including sulfadiazine plus pyrimethamine) are hampered by severe side effects. While atovaquone has potent in vitro activity against
Toxoplasma gondii
, it is poorly absorbed after oral administration and shows poor therapeutic efficacy against TE. To overcome the low absorption of atovaquone, we prepared atovaquone nanosuspensions (ANSs) for intravenous (i.v.) administration. At concentrations higher than 1.0 μg/ml, ANS did not exert cytotoxicity and was as effective as free atovaquone (i.e., atovaquone suspended in medium) against
T. gondii
in freshly isolated peritoneal macrophages. In a new murine model of TE that closely mimics reactivated toxoplasmosis in immunocompromised hosts, using mice with a targeted mutation in the gene encoding the interferon consensus sequence binding protein, i.v.-administered ANS doses of 10.0 mg/kg of body weight protected the animals against development of TE and death. Atovaquone was detectable in the sera, brains, livers, and lungs of mice by high-performance liquid chromatography. Development of TE and mortality in mice treated with 1.0- or 0.1-mg/kg i.v. doses of ANS did not differ from that in mice treated orally with 100 mg of atovaquone/kg. In conclusion, i.v. ANSs may prove to be an effective treatment alternative for patients with TE.
Novel Cefotaximase (CTX-M-16) with Increased Catalytic Efficiency Due to Substitution Asp-240→Gly
Authors: Bonnet R. , Dutour C. , Sampaio J. L. M. , Chanal C. , Sirot D. , Labia R. , De Champs C. , Sirot J.
Published: July 2002

Three clinical strains (
Escherichia coli
Rio-6,
E. coli
Rio-7, and
Enterobacter cloacae
Rio-9) collected in 1996 and 1999 from hospitals in Rio de Janeiro (Brazil) were resistant to broad-spectrum cephalosporins and gave a positive double-disk synergy test. Two
bla
CTX-M
genes encoding β-lactamases of pl 7.9 and 8.2 were implicated in this resistance: the
bla
CTX-M-9
gene observed in
E. coli
Rio-7 and
E. cloacae
Rio-9 and a novel CTX-M-encoding gene, designated
bla
CTX-M-16
, observed in
E. coli
strain Rio-6. The deduced amino acid sequence of CTX-M-16 differed from CTX-M-9 only by the substitution Asp-240→Gly. The CTX-M-16-producing
E. coli
transformant exhibited the same level of resistance to cefotaxime (MIC, 16 μg/ml) but had a higher MIC of ceftazidime (MIC, 8 versus 1 μg/ml) than the CTX-M-9-producing transformant. Enzymatic studies revealed that CTX-M-16 had a 13-fold higher affinity for aztreonam and a 7.5-fold higher k
cat
for ceftazidime than CTX-M-9, thereby showing that the residue in position 240 can modulate the enzymatic properties of CTX-M enzymes. The two
bla
CTX-M-9
genes and the
bla
CTX-M-16
gene were located on different plasmids, suggesting the presence of mobile elements associated with CTX-M-encoding genes. CTX-M-2 and CTX-M-8 enzymes were found in Brazil in 1996, and two other CTX-M β-lactamases, CTX-M-9 and CTX-M-16, were subsequently observed. These reports are evidence of the diversity of CTX-M-type extended-spectrum β-lactamases in Brazil.
Occurrence of Extended-Spectrum β-Lactamases in Members of the Family
Enterobacteriaceae
in Italy: Implications for Resistance to β-Lactams and Other Antimicrobial Drugs
Authors: Spanu T. , Luzzaro F. , Perilli M. , Amicosante G. , Toniolo A. , Fadda G. , The Italian ESBL Study Group
Published: July 2002

An Italian nationwide survey was carried out to assess the prevalences and the antimicrobial susceptibilities of members of the family
Enterobacteriaceae
producing extended-spectrum β-lactamases (ESBLs). Over a 6-month period, 8,015 isolates were obtained from hospitalized patients and screened for resistance to extended-spectrum cephalosporins and monobactams. On the basis of a synergistic effect between clavulanate and selected β-lactams (ceftazidime, aztreonam, cefotaxime, cefepime, and ceftriaxone), 509 isolates were found to be ESBL positive (6.3%). Colony blot hybridization with
bla
TEM
and
bla
SHV
DNA probes allowed one to distinguish four different genotypes: TEM-positive, SHV-positive, TEM- and SHV-positive, and non-TEM, non-SHV ESBL types. MICs for each isolate (E-test) were obtained for widely used β-lactams, combinations of β-lactams with β-lactamase inhibitors, aminoglycosides, and fluoroquinolones. Among ESBL-positive strains,
Klebsiella pneumoniae
,
Proteus mirabilis
, and
Escherichia coli
accounted for 73.6% of isolates. Overall, TEM-type ESBLs were more prevalent than SHV-type enzymes (234 versus 173), whereas the prevalence of strains producing both TEM- and SHV-type ESBLs was similar to that of isolates producing non-TEM, non-SHV enzymes (55 and 38, respectively). In vitro, all but one of the ESBL-producing isolates remained susceptible to imipenem. Susceptibility to other drugs varied: piperacillin-tazobactam, 91%; amoxicillin-clavulanic acid, 85%; cefoxitin, 78%; amikacin, 76%; ampicillin-sulbactam, 61%; ciprofloxacin, 58%; and gentamicin, 56%. Associated resistance to aminoglycosides and ciprofloxacin was observed most frequently among TEM-positive strains. Since therapeutic options for multiresistant
Enterobacteriaceae
are limited, combinations of β-lactams and β-lactamase inhibitors appear to represent an important alternative for treating infections caused by ESBL-producing
Enterobacteriaceae
.