bluuebunny/crossref_metadata_2025 huggingface dataset:
The Tetrodotoxin‐Resistant Na+ Channel Nav1.8 is Essential for the Expression of Spontaneous Activity in Damaged Sensory Axons of Mice
Authors: Roza Carolina , Laird Jennifer M.A. , Souslova Veronika , Wood John N. , Cervero Fernando
Published: August 2003

The tetrodotoxin‐resistant sodium channel α subunit, Nav1.8, is exclusively expressed in primary sensory neurons and is suggested to play a role in the generation of ectopic action potentials after axonal injury and thereby contribute to neuropathic pain. Here we investigated the involvement of Nav1.8 in ectopic impulse generation in damaged axons by examining spontaneous activity and mechanosensitivity in neuromas formed by section of the saphenous nerve in Nav1.8 null mice and in their wild‐type littermates. We recorded 522 identified units from 24 neuromas in vitro at two time points, 8–11 days (median 10 days) and 19–29 days (median 22 days) post‐operatively. At ≈10 days, neither genotype showed spontaneous activity, but a significantly higher proportion of fibres were mechanosensitive in wild‐type (54 %) compared to Nav1.8 null neuromas (18 %). At ≈22 days, 19 % of fibres recorded in wild‐type neuromas showed spontaneous activity, whereas only one fibre of the 238 (0.4 %) recorded in neuromas taken from null mice showed ongoing activity. In recordings at ≈22 days, a similar proportion of fibres were mechanosensitive in wild‐type and Nav1.8 null neuromas (51 and 46 %, respectively). We conclude that Nav1.8 is essential for the expression of spontaneous activity in damaged sensory axons, and may also contribute to the development of ectopic mechanosensitivity.
Down‐regulation of placental transport of amino acids precedes the development of intrauterine growth restriction in rats fed a low protein diet
Authors: Jansson Nina , Pettersson Jessica , Haafiz Allah , Ericsson Anette , Palmberg Isabelle , Tranberg Mattias , Ganapathy Vadivel , Powell Theresa L. , Jansson Thomas
Published: August 2003

Intrauterine growth restriction (IUGR) represents an important risk factor for perinatal complications and for adult disease. IUGR is associated with a down‐regulation of placental amino acid transporters; however, whether these changes are primary events directly contributing to IUGR or a secondary consequence is unknown. We investigated the time course of changes in placental and fetal growth, placental nutrient transport in vivo and the expression of placental nutrient transporters in pregnant rats subjected to protein malnutrition, a model for IUGR. Pregnant rats were given either a low protein (LP) diet (n= 64) or an isocaloric control diet (n= 66) throughout pregnancy. Maternal insulin, leptin and IGF‐I levels decreased, whereas maternal amino acid concentrations increased moderately in response to the LP diet. Fetal and placental weights in the LP group were unaltered compared to control diet at gestational day (GD) 15, 18 and 19 but significantly reduced at GD 21. Placental system A transport activity was reduced at GD 19 and 21 in response to a low protein diet. Placental protein expression of SNAT2 was decreased at GD 21. In conclusion, placental amino acid transport is down‐regulated prior to the development of IUGR, suggesting that these placental transport changes are a cause, rather than a consequence, of IUGR. Reduced maternal levels of insulin, leptin and IGF‐1 may link maternal protein malnutrition to reduced fetal growth by down‐regulation of key placental amino acid transporters.
Assessment of Current Turbine Engine High Cycle Fatigue Test Methods
Authors: Nichol K. L.
Published: August 2003

Testing of turbine engine components to verify structural durability goals is performed in a variety of ways and at a variety of facilities. Further, methods used differ between engine companies and even among engine programs within the same company. A recent emphasis on reducing high cycle fatigue (HCF) failures of engine components has made it obvious that improvements and standardization of HCF test methods are needed. This paper presents findings from an assessment of current HCF test approaches and identifies weaknesses that form the basis for recommending improvements. Weaknesses identified included data processing, mode identification, and selection of instrumentation locations.
A Reduced-Order Model for Evaluating the Effect of Rotational Speed on the Natural Frequencies and Mode Shapes of Blades
Authors: Marugabandhu P. , Griffin J. H.
Published: August 2003

A reduced-order model has been developed that can be used to accurately and quickly calculate the changes in the natural frequencies and mode shapes of a blade that are caused by centrifugal stiffening. It has been corroborated by comparisons with finite element analyses of a cantilevered tapered plate and with frequencies from a low aspect ratio fan blade.
Effect of Fuel Injection Timing Relative to Ignition Timing on the Natural-Gas Direct-Injection Combustion
Authors: Huang Z. , Shiga S. , Ueda T. , Nakamura H. , Ishima T. , Obokata T. , Tsue M. , Kono M.
Published: August 2003

The effect of fuel injection timing relative to ignition timing on natural gas direct-injection combustion was studied by using a rapid compression machine (RCM). The ignition timing was fixed at 80 ms after the compression start. When the injection timing was relatively early (injection start at 60 ms), the heat release pattern showed a slower burn in the initial stage and a faster burn in the late stage, which is similar to that of flame propagation of a premixed gas. In contrast to this, when the injection timing was relatively late (injection start at 75 ms), the heat release rate showed a faster burn in the initial stage and a slower burn in the late stage, which is similar to that of diesel combustion. The shortest duration was realized at the injection end timing of 80 ms (the same timing as the ignition timing) over a wide range of equivalence ratio. The degree of charge stratification and the intensity of turbulence generated by the fuel jet are considered to cause this behavior. Early injection leads to longer duration of the initial combustion, whereas late injection leads to a longer duration of the late combustion. Early injection showed relatively lower CO concentration in the combustion products while late injection gave relatively lower NOx. It was suggested that early injection leads to combustion with weaker stratification, and late injection leads to combustion with stronger stratification. Combustion efficiency was kept at a high value over a wide range of equivalence ratio.
Statistical Correlation Between the Crankshaft’s Speed Variation and Engine Performance—Part II: Detection of Deficient Cylinders and Mean Indicated Pressure Calculation
Authors: Taraza D.
Published: August 2003

The goal of this two-part paper is to develop a methodology using the variation of the measured crankshaft speed to calculate the mean indicated pressure (MIP) of a multicylinder engine and to detect cylinders that are lower contributors to the total engine output. The statistical model of a harmonic component of the engine torque developed in the first part of the paper is used to achieve this goal. The analysis of the half-order components of the gas pressure torque permits to identify distinct phase angle domains of the resultant torque vector that are specific for the deficiencies of given cylinders. Based on the rigid-body model of the crankshaft, these phase angle domains are correlated to the phase angle domains of the half-order component of the crankshaft speed. Then, the phase angle of the half-order component of the measured crankshaft speed will identify the deficient cylinder. The amplitude of the first major harmonic component of the measured crankshaft speed is correlated to the corresponding harmonic order of the gas pressure torque and is used to calculate the MIP of the engine. The accuracy limits of this “software dynamometer” are also presented.
Controller Design for a Gas Turbine Using Periodic Output Feedback
Authors: Chakrabarti A. K. , Bandyopadhyay B.
Published: August 2003

The advent of electronic controllers in the field of gas turbine control has allowed the implementation of sophisticated control algorithms. This paper proposes one such method, to design a controller using piecewise constant periodic output feedback, which has multifarious advantages, and because the states are not required for feedback, complete pole-assignability is guaranteed and the method is easily implementable.
Combustion in Gas Fueled Compression: Ignition Engines of the Dual Fuel Type
Authors: Karim G. A.
Published: August 2003

In the dual fuel engine much of the energy release comes from the combustion of the gaseous fuel while only a small amount of diesel liquid fuel provides ignition through timed cylinder injection. Such operation with optimum conversion methods has the potential to provide operational characteristics that are comparable or superior to those of the corresponding diesel or spark ignition engines. These characteristics may be realized only if sufficiently effective measures can be ensured both for the avoidance of knock, usually at high loads, and incomplete gaseous fuel utilization at relatively light loads. An objective of this contribution is to demonstrate that the main effort needed to overcome the problems associated with the operation of gas fueled dual fuel engines is via a better control of the relatively complex processes of combustion. Both experimental and analytical modeling procedures for effecting optimum improvement to the combustion process are described.
Homogeneous Charge Compression Ignition Operation With Natural Gas: Fuel Composition Implications
Authors: Hiltner J. , Agama R. , Mauss F. , Johansson B. , Christensen M.
Published: August 2003

Homogeneous charge compression ignition (HCCI) is a potentially attractive operating mode for stationary natural gas engines. Increasing demand for efficient, clean burning engines for electrical power generation provides an opportunity to utilize HCCI combustion if several inherent difficulties can be overcome. Fuel composition, particularly the higher hydrocarbon content (ethane, propane, and butane) of the fuel is of primary concern. Fuel composition influences HCCI operation both in terms of design, via compression ratio and initial charge temperature, and in terms of engine control. It has been demonstrated that greater concentrations of higher hydrocarbons tend to lower the ignition temperature of the mixture significantly. The purpose of this paper is to demonstrate, through simulation, the effect of fuel composition on combustion in HCCI engines. Engine performance over a range of fuels from pure methane to more typical natural gas blends is investigated. This includes both the impact of various fuels and the sensitivity of engine operation for any given fuel. Results are presented at a fixed equivalence ratio, compression ratio, and engine speed to isolate the effect of fuel composition. Conclusions are drawn as to how the difficulties arising from gas composition variations may affect the future marketability of these engines.
Flashback in Lean Prevaporized Premixed Combustion: Nonswirling Turbulent Pipe Flow Study
Authors: Scha¨fer O. , Koch R. , Wittig S.
Published: August 2003

A fundamental study has been performed on the upstream flame propagation of a turbulent kerosene flame, stabilized in a confined stagnation flow at atmospheric pressure. Besides temperature and equivalence ratio, mixture properties and fluid dynamic parameters have been varied. The flashback phenomenon is discussed in terms of critical mean velocities and additionally based on detailed LDV data at the outlet of the premixing duct. The largest critical velocities uc for flashback are found for the “perfectly” premixed case and equivalence ratios close to stoichiometric, which is in accordance with the theory on laminar flame propagation. In the case of a homogeneous mixture, flashback is determined by the velocity distribution at the outlet of the premixing section. In the undisturbed pipe flow the flame propagates through the wall boundary layer. The data for this case are compared with the theory of side-wall quenching in terms of a critical Peclet number and critical velocity gradients at the wall. Both are deduced from the experimental data. Reducing the velocity on the axis forces the flame to propagate through the center at a velocity predicted by correlations on turbulent flame velocity.
Setting Up of a Probabilistic Neural Network for Sensor Fault Detection Including Operation With Component Faults
Authors: Romesis C. , Mathioudakis K.
Published: August 2003

The diagnostic ability of probabilistic neural networks (PNN) for detecting sensor faults on gas turbines is examined. The structure and the features of a PNN, for sensor fault detection, are presented. It is shown that with the proposed formulation, a powerful tool for sensor fault identification is produced. A particular feature of the PNN produced is the ability to detect sensor faults even in the presence of engine component malfunction, as well as on deteriorated engines. In such situations, the size of bias that can be identified increases. The way to establish the limits of sensor bias that can be detected is presented along with results from application to test cases with realistic noise magnitudes. The diagnostic procedure proposed here is also supported by an engine performance model. The data used for setting up and testing the PNN are generated by such a model.
On-Line Fuel Deoxygenation for Coke Suppression
Authors: Spadaccini L. J. , Huang H.
Published: August 2003

Fuel deoxygenation is being developed as a means for suppressing autoxidative coke formation in aircraft fuel systems, thereby increasing the exploitable cooling capacity of the fuel, enabling major increases in engine operating temperature and cycle efficiency. Reduced maintenance is an added benefit. A prototype membrane filter module for on-line removal of dissolved oxygen, which would otherwise react to form coke precursors, was constructed and successfully demonstrated. The fuel flows over the membrane, while oxygen diffuses through it at a rate that is proportional to the difference in oxygen partial pressures across the surface. Tests were conducted over a range of fuel flow rates (residence times) and temperatures. The filter was operated with air-saturated jet fuel for several hours at a steady-state condition, verifying the capability to remove essentially all of the dissolved oxygen (to <1 ppm) and proving the viability of the concept. A convincing demonstration of coke suppression was performed when air-saturated (normal) and deoxygenated jet fuels were tested in a standard ASTM heated tube apparatus at wall temperatures as high as 850°F. With deoxygenated fuel, there was a dramatic reduction (more than an order of magnitude) in coke deposition relative to air-saturated Jet A, which will allow the maximum fuel temperature to be increased by more than 200°F, doubling the available heat sink. Moreover, deoxygenated Jet A was shown to perform as well as JP-7, the Air Force’s highest thermal stability fuel. An analytical model for oxygen permeation through the membrane was formulated, and used in conjunction with the test data to estimate the filter size required for a practical (i.e., low-volume/high flow rate) deoxygenator.
High Power Density Silicon Combustion Systems for Micro Gas Turbine Engines
Authors: Spadaccini C. M. , Mehra A. , Lee J. , Zhang X. , Lukachko S. , Waitz I. A.
Published: August 2003

As part of an effort to develop a microscale gas turbine engine for power generation and micropropulsion applications, this paper presents the design, fabrication, experimental testing, and modeling of the combustion system. Two radial inflow combustor designs were examined; a single-zone arrangement and a primary and dilution-zone configuration. Both combustors were micromachined from silicon using deep reactive ion etching (DRIE) and aligned fusion wafer bonding. Hydrogen-air and hydrocarbon-air combustion were stabilized in both devices, each with chamber volumes of 191mm3. Exit gas temperatures as high as 1800 K and power densities in excess of 1100MW/m3 were achieved. For the same equivalence ratio and overall efficiency, the dual-zone combustor reached power densities nearly double that of the single-zone design. Because diagnostics in microscale devices are often highly intrusive, numerical simulations were used to gain insight into the fluid and combustion physics. Unlike large-scale combustors, the performance of the microcombustors was found to be more severely limited by heat transfer and chemical kinetics constraints. Important design trades are identified and recommendations for microcombustor design are presented.
Two-Dimensional Flow and NOx Emissions in Deflagrative Internal Combustion Wave Rotor Configurations
Authors: Pekkan K. , Nalim M. R.
Published: August 2003

A wave rotor is proposed for use as a constant volume combustor. A novel design feature is investigated as a remedy for hot gas leakage, premature ignition, and pollutant emissions that are possible in this class of unsteady machines. The base geometry involves fuel injection partitions that allow stratification of fuel/oxidizer mixtures in the wave rotor channel radially, enabling pilot ignition of overall lean mixture for low NOx combustion. In this study, available turbulent combustion models are applied to simulate approximately constant volume combustion of propane and resulting transient compressible flow. Thermal NO production histories are predicted by simulations of the STAR-CD code. Passage inlet/outlet/wall boundary conditions are time-dependent, enabling the representation of a typical deflagrative internal combustor wave rotor cycle. Some practical design improvements are anticipated from the computational results. For a large number of derivative design configurations, fuel burn rate, two-dimensional flow and emission levels are evaluated. The sensitivity of channel combustion to initial turbulence levels is evaluated.
Measurement-Induced Relative-Position Localization Through Entanglement
Authors: Rau A. V. , Dunningham J. A. , Burnett K.
Published: August 2003

We consider the localization of a pair of particles in relative-position space. We show how a sequence of scattering interactions progressively entangles two particles, giving rise to a robust state of well-defined separation and thus providing a natural description of relative position. We use two thought experiments to describe the localization process. The first is an interferometer with recoiling mirrors. The second, and more general, case considers photons scattering from a pair of particles and the resulting emergence of a Young's interference pattern. The underlying framework of the localization process suggests a prominent role for entanglement and relative observables at the boundary between quantum and classical mechanics.
Helicobacter pylori
Vacuolating Cytotoxin Inhibits T Lymphocyte Activation
Authors: Gebert Bettina , Fischer Wolfgang , Weiss Evelyn , Hoffmann Reinhard , Haas Rainer
Published: August 2003

Helicobacter pylori
(
Hp
) vacuolating cytotoxin VacA induces cellular vacuolation in epithelial cells. We found that VacA could efficiently block proliferation of T cells by inducing a G
1
/S cell cycle arrest. It interfered with the T cell receptor/interleukin-2 (IL-2) signaling pathway at the level of the Ca
2
+
-calmodulin–dependent phosphatase calcineurin. Nuclear translocation of nuclear factor of activated T cells (NFAT), a transcription factor acting as a global regulator of immune response genes, was abrogated, resulting in down-regulation of IL-2 transcription. VacA partially mimicked the activity of the immunosuppressive drug FK506 by possibly inducing a local immune suppression, explaining the extraordinary chronicity of
Hp
infections.
Spectroscopic Identification of Carbonate Minerals in the Martian Dust
Authors: Bandfield Joshua L. , Glotch Timothy D. , Christensen Philip R.
Published: August 2003

Thermal infrared spectra of the martian surface indicate the presence of small concentrations (∼2 to 5 weight %) of carbonates, specifically dominated by magnesite (MgCO
3
). The carbonates are widely distributed in the martian dust, and there is no indication of a concentrated source. The presence of small concentrations of carbonate minerals in the surface dust and in martian meteorites can sequester several bars of atmospheric carbon dioxide and may have been an important sink for a thicker carbon dioxide atmosphere in the martian past.
Disruption of Ergosterol Biosynthesis Confers Resistance to Amphotericin B inCandida lusitaniae
Authors: Young Laura Y. , Hull Christina M. , Heitman Joseph
Published: August 2003

Candida lusitaniaeis an emerging human pathogen that, unlike other fungal pathogens, frequently develops resistance to the commonly used antifungal agent amphotericin B. Amphotericin B is a member of the polyene class of antifungal drugs, which impair fungal cell membrane integrity. Here we analyzed mechanisms contributing to amphotericin B resistance inC. lusitaniae. Sensitivity to polyenes in the related fungiSaccharomyces cerevisiaeandCandida albicansrequires the ergosterol biosynthetic geneERG6. In an effort to understand the mechanisms contributing to amphotericin B resistance inC. lusitaniae, we isolated theERG6gene and created aC. lusitaniae erg6Δstrain. This mutant strain exhibited a growth defect, was resistant to amphotericin B, and was hypersensitive to other sterol inhibitors. Based on the similarities between the phenotypes of theerg6Δmutant and clinical isolates ofC. lusitaniaeresistant to amphotericin B, we analyzedERG6expression levels and ergosterol content in multiple clinical isolates.C. lusitaniaeamphotericin B-resistant isolates were found to have increased levels ofERG6transcript as well as reduced ergosterol content. These changes suggest that another gene in the ergosterol biosynthetic pathway could be mutated or misregulated. Further transcript analysis showed that expression of theERG3gene, which encodes C-5 sterol desaturase, was reduced in two amphotericin B-resistant isolates. Our findings reveal that mutation or altered expression of ergosterol biosynthetic genes can result in resistance to amphotericin B inC. lusitaniae.
Recapitulation in
Saccharomyces cerevisiae
of Cytochrome
b
Mutations Conferring Resistance to Atovaquone in
Pneumocystis jiroveci
Authors: Hill Philip , Kessl Jacques , Fisher Nicholas , Meshnick Steven , Trumpower Bernard L. , Meunier Brigitte
Published: August 2003

Pneumocystis jiroveci
(human-derived
P. carinii
) is an opportunistic pathogenic fungus which causes pneumonia and is life-threatening in immunocompromised individuals. Spontaneously acquired resistance to atovaquone, a hydroxynaphthoquinone that is used to treat
P. jiroveci
infections, was linked to mutations in the mitochondrially encoded cytochrome
b
gene. Because
P. jiroveci
cannot be easily cultivated, we have developed
Saccharomyces cerevisiae
as an alternative system to study atovaquone resistance mutations. In this work, we introduced seven mutations linked with atovaquone resistance in
P. jiroveci
into the
S. cerevisiae
cytochrome
b
gene. The effects of the mutations on the respiratory function and on the sensitivity to the inhibitor were then characterized. Six of the reported mutations lowered the sensitivity of the
S. cerevisiae bc
1
complex to atovaquone, while one mutation had no effect on the drug resistance. These results were confirmed by monitoring the in vivo resistance of
S. cerevisiae
mutants which carried both the cytochrome
b
mutations and a deletion of the ABC transporter genes, allowing the drug to bypass the weakened efflux pump system.
S. cerevisiae
thus provides an easy-to-use system to characterize in vivo and in vitro cytochrome
b
mutations reported in pathogens and to assess their role in drug resistance.
Molecular Analysis of incHI1 Antimicrobial Resistance Plasmids from
Salmonella
Serovar Typhi Strains Associated with Typhoid Fever
Authors: Wain John , Diem Nga L. T. , Kidgell Claire , James Keith , Fortune Sarah , Song Diep To , Ali Tahir , Ó Gaora Peadar , Parry Christopher , Parkhill Julian , Farrar Jeremy , White Nicholas J. , Dougan Gordon
Published: August 2003

The first outbreak of multidrug-resistant (MDR) typhoid fever in Vietnam was in 1993, and by 1995 nearly 90% of cases were MDR. Plasmid HCM1, sequenced in full, is an incHI1 plasmid from
Salmonella enterica
serovar Typhi strain CT18, isolated in Vietnam in 1993. Restriction analysis shows that pHCM1 shares a restriction fragment length polymorphism (RFLP) pattern with plasmids isolated from the first outbreak and 10 of 17 MDR plasmids isolated from sporadic cases occurring at the same time in Vietnam. A core region of pHCM1 has significant DNA sequence similarity to plasmid R27, isolated in 1961 from
S. enterica
in the United Kingdom. There are five regions of DNA in pHCM1 which are not present in R27. Two of these are putative acquisition regions; the largest is 34.955 kbp in length and includes sequences of several antibiotic resistance genes and several insertion sequences. The borders of this region are defined by two identical IS
10
left elements, associated with an inversion of DNA or with a truncated Tn
10
element. The second, smaller region is 14.751 kbp and carries a trimethoprim resistance gene
dfr14A
cassette associated with a class 1 integrase. In 1993 to 1994, restriction analysis revealed some variations in the structures of
Salmonella
serovar Typhi MDR plasmids which were mapped to the two putative acquisition regions and three smaller variable regions. In 1996 a single RFLP type, RFLP7, was found to carry the
dfrA7
and
sul
-
1
genes, which were not present on R27 or pHCM1. This plasmid type appears to have a selective advantage over other plasmids with the same resistance phenotype.
Real-Time Monitoring of Bacterial Infection In Vivo: Development of Bioluminescent Staphylococcal Foreign-Body and Deep-Thigh-Wound Mouse Infection Models
Authors: Kuklin Nelly A. , Pancari Gregory D. , Tobery Timothy W. , Cope Leslie , Jackson Jesse , Gill Charles , Overbye Karen , Francis Kevin P. , Yu Jun , Montgomery Donna , Anderson Annaliesa S. , McClements William , Jansen Kathrin U.
Published: August 2003

Staphylococcal infections associated with catheter and prosthetic implants are difficult to eradicate and often lead to chronic infections. Development of novel antibacterial therapies requires simple, reliable, and relevant models for infection. Using bioluminescent
Staphylococcus aureus
, we have adapted the existing foreign-body and deep-wound mouse models of staphylococcal infection to allow real-time monitoring of the bacterial colonization of catheters or tissues. This approach also enables kinetic measurements of bacterial growth and clearance in each infected animal. Persistence of infection was observed throughout the course of the study until termination of the experiment at day 16 in a deep-wound model and day 21 in the foreign-body model, providing sufficient time to test the effects of antibacterial compounds. The usefulness of both animal models was assessed by using linezolid as a test compound and comparing bioluminescent measurements to bacterial counts. In the foreign-body model, a three-dose antibiotic regimen (2, 5, and 24 h after infection) resulted in a decrease in both luminescence and bacterial counts recovered from the implant compared to those of the mock-treated infected mice. In addition, linezolid treatment prevented the formation of subcutaneous abscesses, although it did not completely resolve the infection. In the thigh model, the same treatment regimen resulted in complete resolution of the luminescent signal, which correlated with clearance of the bacteria from the thighs.
Pharmacodynamics of Levofloxacin and Ciprofloxacin in a Murine Pneumonia Model: Peak Concentration/MIC versus Area under the Curve/MIC Ratios
Authors: Scaglione F. , Mouton J. W. , Mattina R. , Fraschini F.
Published: August 2003

During the last decade some studies have shown that the area under the curve (AUC)/MIC ratio is the pharmacodynamic index that best predicts the efficacies of quinolones, while other studies suggest that the predictive value of the peak concentration/MIC (peak/MIC) ratio is superior to the AUC/MIC ratio in explaining clinical and microbiological outcomes. In classical fractionated dose-response studies with animals, it is difficult to differentiate between the AUC/MIC ratio and the peak/MIC ratio because of colinearity. Three different levofloxacin and ciprofloxacin dosing regimens were studied in a neutropenic mouse pneumonia model. The different regimens were used with the aim of increasing the AUC/MIC ratio without changing the peak/MIC ratio and vice versa. The first regimen (RC) consisted of daily doses of 5 up to 160 mg/kg of body weight divided into one, two, or four doses. In the second regimen (R0), mice were given 1.25 mg/kg every hour from 1 to 23 h, while the dose given at 0 h was 2.5, 5, 10, 20, 40, or 80 mg/kg. In the third regimen (R11), mice also received 1.25 mg/kg every hour from 0 to 23 h; but in addition, they also received 2.5, 5, 10, 20, 40, or 80 mg/kg at 11 h. The level of protein binding was also evaluated. The results indicate that the unbound fraction (fu) was concentration dependent for both levofloxacin and ciprofloxacin and ranged from approximately 0.67 to 0.88 for both drugs between concentrations of 0.5 and 80 mg/liter. The relationships between the AUC/MIC ratio and the number of CFU were slightly better than those between the peak/MIC ratio and the number of CFU. There was no clear relationship between the amount of time that the concentration remained above the MIC and effect (R2< 0.1). For both drugs, the peak/MIC ratio that resulted in a 50% effective concentration was lower for the R0 and R11 dosing regimens, indicating the importance of the AUC/MIC ratio. The same was true for the static doses. Survival studies showed that for mice treated with the low doses the rate of survival was comparable to that for the controls, but with the higher doses the rate of survival was better for mice receiving the R0 regimen. We conclude that for quinolones the AUC/MIC ratio best correlates with efficacy against pneumococci and that the effect of the peak/MIC ratio found in some studies could be partly explained by concentration-dependent protein binding.
Effectiveness of Combination Antimicrobial Therapy for
Pseudomonas aeruginosa
Bacteremia
Authors: Chamot Eric , Boffi El Amari Emmanuelle , Rohner Peter , Van Delden Christian
Published: August 2003

It remains controversial whether combination therapy, given empirically or as definitive treatment, for
Pseudomonas aeruginosa
bacteremia is associated with a better outcome than monotherapy. The aim of the present study was to compare the rates of survival among patients who received either combination therapy or monotherapy for
P. aeruginosa
bacteremia. We assembled a historical cohort of 115 episodes of
P. aeruginosa
bacteremia treated with empirical antipseudomonal therapy between 1988 and 1998. On the basis of susceptibility testing of the bacteremic
P. aeruginosa
isolate, we defined categories of empirical treatment, including adequate combination therapy, adequate monotherapy, and inadequate therapy, as well as corresponding categories of definitive therapy. Neither the adequacy of the empirical treatment nor the use of combination therapy predicted survival until receipt of the antibiogram. However, the risk of death from the date of receipt of the antibiogram to day 30 was higher for both adequate empirical monotherapy (adjusted hazard ratio [aHR], 3.7; 95% confidence interval [CI], 1.0 to 14.1) and inadequate empirical therapy (aHR, 5.0; 95% CI, 1.2 to 20.4) than for adequate empirical combination therapy. Compared to adequate definitive combination therapy, the risk of death at 30 days was also higher with inadequate definitive therapy (aHR, 2.6; 95% CI, 1.1 to 6.7) but not with adequate definitive monotherapy (aHR, 0.70; 95% CI, 0.30 to 1.7). In this retrospective analysis the use of adequate combination antimicrobial therapy as empirical treatment until receipt of the antibiogram was associated with a better rate of survival at 30 days than the use of monotherapy. However, adequate combination antimicrobial therapy given as definitive treatment for
P. aeruginosa
bacteremia did not improve the rate of survival compared to that from the provision of adequate definitive monotherapy.
Impact of Azithromycin Administration for Trachoma Control on the Carriage of Antibiotic-Resistant
Streptococcus pneumoniae
Authors: Batt Sarah L. , Charalambous Bambos M. , Solomon Anthony W. , Knirsch Charles , Massae Patrick A. , Safari Salesia , Sam Noel E. , Everett Dean , Mabey David C. W. , Gillespie Stephen H.
Published: August 2003

Community distribution of azithromycin has an important role to play in trachoma control. Previous studies have suggested that this may increase the prevalence of macrolide-resistant
Streptococcus pneumoniae. S. pneumoniae
was isolated from children under 7 years of age in Rombo District, northern Tanzania, before and 2 and 6 months after community-wide administration of azithromycin. Overall carriage rates were 11, 12, and 7%, respectively. Only one macrolide-resistant isolate carrying the
mef
gene was obtained 6 months after azithromycin administration. This contrasted with cotrimoxazole and penicillin resistance, both of which were common (cotrimoxazole resistance, 42, 43, and 47%, and penicillin resistance, 21, 17, and 16% at baseline, 2 months, and 6 months, respectively). There was a significant association between cotrimoxazole and penicillin resistance (
P
< 0.0001, Fisher's exact). These data suggest that in communities where macrolide resistance is rare, azithromycin distribution for trachoma control is unlikely to increase the prevalence of resistant organisms.
Randomized Double-Blind Study Comparing 3- and 6-Day Regimens of Azithromycin with a 10-Day Amoxicillin-Clavulanate Regimen for Treatment of Acute Bacterial Sinusitis
Authors: Henry Dan C. , Riffer Ernie , Sokol William N. , Chaudry Naumann I. , Swanson Robert N.
Published: August 2003

A randomized, double-blind, multicenter study of adults with acute bacterial sinusitis (ABS) compared the efficacy and safety of two azithromycin (AZM) regimens, 500 mg/day once daily for 3 days (AZM-3) or 6 days (AZM-6) to the efficacy and safety of an amoxicillin-clavulanate (AMC) regimen of 500-125 mg three times daily for 10 days. A total of 936 subjects with clinically and radiologically documented ABS were treated (AZM-3, 312; AZM-6, 311; AMC, 313). Clinical success rates were equivalent among per-protocol subjects at the end of therapy (AZM-3, 88.8%; AZM-6, 89.3%; AMC, 84.9%) and at the end of the study (AZM-3, 71.7%; AZM-6, 73.4%; AMC, 71.3%). Subjects treated with AMC reported a higher incidence of treatment-related adverse events (AE) (51.1%) than AZM-3 (31.1%,
P
< 0.001) or AZM-6 (37.6%,
P
< 0.001). More AMC subjects discontinued the study (
n
= 28) than AZM-3 (
n
= 7) and AZM-6 (
n
= 11) subjects. Diarrhea was the most frequent treatment-related AE. AZM-3 and AZM-6 were each equivalent in efficacy and better tolerated than AMC for ABS.
Pharmacokinetics of Linezolid in Subjects with Renal Dysfunction
Authors: Brier Michael E. , Stalker Dennis J. , Aronoff George R. , Batts Donald H. , Ryan Kristi K. , O'Grady Margaret , Hopkins Nancy K. , Jungbluth Gail L.
Published: August 2003

Linezolid is a member of a new, unique class of synthetic antibacterial agents called oxazolidinones that are effective against gram-positive bacteria, including vancomycin-resistant organisms. We tested the hypothesis that the linezolid clearance would not be altered in subjects with renal dysfunction. Twenty-four subjects with renal function that ranged from normal to severe chronic impairment were enrolled, including patients with end-stage renal disease who were maintained on hemodialysis. Hemodialysis subjects were studied while they were both on and off dialysis. Linezolid was administered as a single oral 600-mg dose, and plasma and urine samples were assayed for linezolid and metabolites for 48 h for all subjects and for up to 96 h for those subjects with impaired renal function not on dialysis. The total apparent oral clearance of linezolid did not change with renal function and ranged from 92.5 to 109.6 ml/min for subjects not requiring dialysis. For subjects on dialysis, the total apparent oral clearance increased from 76.6 ml/min on their off-dialysis day to 130.0 ml/min on their on-dialysis day. Approximately one-third of the dose was removed by dialysis. However, those subjects with severe renal insufficiency (creatinine clearance, <40 ml/min) and those with end-stage renal disease maintained on hemodialysis had higher concentrations of both metabolites. We conclude that no adjustment of the linezolid dosage is needed in subjects with renal dysfunction or subjects on hemodialysis.
Pharmacokinetics, Toxicities, and Efficacies of Sodium Stibogluconate Formulations after Intravenous Administration in Animals
Authors: Nieto J. , Alvar J. , Mullen A. B. , Carter K. C. , Rodríguez C. , San Andrés M. I. , San Andrés M. D. , Baillie A. J. , González F.
Published: August 2003

The pharmacokinetics and toxicities of free sodium stibogluconate (SSG) and two vesicular formulations of this drug (a nonionic surfactant vesicular formulation of SSG [SSG-NIV] and SSG-NIV-dextran) were determined after treatment with a single intravenous dose in healthy dogs and were related to their antileishmanial efficacies in mice. Analysis of the curves of the concentrations in plasma after intravenous administration of SSG and SSG-NIV in dogs showed that both formulations produced similar antimony (Sb) pharmacokinetics. In contrast, treatment with SSG-NIV-dextran significantly modified the pharmacokinetics of the drug. The elimination half-life was four times longer (280 min) than that observed after administration of SSG (71 min) (P= 0.01), and the volume of distribution at steady state (VSS) was also increased (VSSfor SSG, 0.21 liters/kg;VSSfor SSG-NIV-dextran, 0.34 liters/kg [P= 0.02]), thus indicating that drug encapsulation favors the distribution of Sb into organs and increases its residence time in tissues. This would explain the superior antileishmanial efficacy of this formulation compared to those of the free drug in mice. No signs of toxicity were found in dogs after SSG and SSG-NIV administration. However, SSG-NIV-dextran treatment was associated with short-term toxicity, demonstrated by the development of chills and diarrhea, which cleared by 24 h postdosing, and hepatic dysfunction at 24 h postdosing (P< 0.05). The levels of all the biochemical parameters had returned to normal at 1 month postdosing. No signs of toxicity were observed in mice treated with all three formulations.
Pharmacokinetics, Safety, and Tolerability of Oral Posaconazole Administered in Single and Multiple Doses in Healthy Adults
Authors: Courtney Rachel , Pai Sudhakar , Laughlin Mark , Lim Josephine , Batra Vijay
Published: August 2003

The pharmacokinetics, safety, and tolerability of posaconazole, an investigational triazole antifungal, were evaluated following the administration of rising single and multiple oral doses. A total of 103 healthy adults were enrolled in two phase I trials. Each study had a double-blind, placebo-controlled, parallel-group design with a rising single-dose (RSD) or rising multiple-dose (RMD) scheme. In the RSD study, subjects received single doses of posaconazole oral tablets (50 to 1,200 mg) or placebo. In the RMD study, subjects received posaconazole oral tablets (50 to 400 mg) or placebo twice daily for 14 days. By using model-independent methods, the area under the plasma concentration-time curve and the maximum concentration in plasma were determined and used to assess dose proportionality. In the RSD study, the levels of posaconazole in plasma increased proportionally between the 50- and 800-mg dose range, with saturation of absorption occurring above 800 mg. Dose proportionality was also observed in the RMD study. In both studies, the apparent volume of distribution was large (range, 343 to 1,341 liters) and the terminal-phase half-life was long (range, 25 to 31 h). Posaconazole was well tolerated at all dose levels, and the adverse events were not dose dependent. No clinically significant changes in clinical laboratory test values or electrocardiograms were observed. Following the administration of single and twice-daily rising doses, the level of posaconazole exposure increased in a dose-proportional manner. The long elimination-phase half-life of posaconazole supports once- or twice-daily dosing in clinical trials; however, additional studies are required to determine if further division of the dose will enhance exposure.
Association of the Endotoxin Antagonist E5564 with High-Density Lipoproteins In Vitro: Dependence on Low-Density and Triglyceride-Rich Lipoprotein Concentrations
Authors: Wasan Kishor M. , Sivak Olena , Cote Richard A. , MacInnes Aaron I. , Boulanger Kathy D. , Lynn Melvyn , Christ William J. , Hawkins Lynn D. , Rossignol Daniel P.
Published: August 2003

The objective of this study was to determine the distribution profile of the novel endotoxin antagonist E5564 in plasma obtained from fasted human subjects with various lipid concentrations. Radiolabeled E5564 at 1 μM was incubated in fasted plasma from seven human subjects with various total cholesterol (TC) and triglyceride (TG) concentrations for 0.5 to 6 h at 37°C. Following these incubations, plasma samples were separated into their lipoprotein and lipoprotein-deficient fractions by ultracentrifugation and were assayed for E5564 radioactivity. TC, TG, and protein concentrations in each fraction were determined by enzymatic assays. Lipoprotein surface charge within control and phosphatidylinositol-treated plasma and E5564’s influence on cholesteryl ester transfer protein (CETP) transfer activity were also determined. We observed that the majority of E5564 was recovered in the high-density lipoprotein (HDL) fraction. We further observed that incubation in plasma with increased levels of TG-rich lipoprotein (TRL) lipid (TC and TG) concentrations resulted in a significant increase in the percentage of E5564 recovered in the TRL fraction. In further experiments, E5564 was preincubated in human TRL. Then, these mixtures were incubated in hypolipidemic human plasma for 0.5 and 6 h at 37°C. Preincubation of E5564 in purified TRL prior to incubation in human plasma resulted in a significant decrease in the percentage of drug recovered in the HDL fraction and an increase in the percentage of drug recovered in the TRL and low-density lipoprotein fractions. These findings suggest that the majority of the drug binds to HDLs. Preincubation of E5564 in TRL prior to incubation in normolipidemic plasma significantly decreased the percentage of drug recovered in the HDL fraction. Modifications to the lipoprotein negative charge did not alter the E5564 concentration in the HDL fraction. In addition, E5564 does not influence CETP-mediated transfer activity. Information from these studies could be used to help identify the possible components of lipoproteins which influence the interaction of E5564 with specific lipoprotein particles.
Antimicrobial Characterization of Human β-Defensin 3 Derivatives
Authors: Hoover David M. , Wu Zhibin , Tucker Kenneth , Lu Wuyuan , Lubkowski Jacek
Published: August 2003

Human β-defensin 3 (hBD3) is a highly basic 45-amino-acid protein that acts both as an antimicrobial agent and as a chemoattractant molecule. Although the nature of its antimicrobial activity is largely electrostatic, the importance of the molecular structure on this activity is poorly understood. Two isoforms of hBD3 were synthesized: the first with native disulfide linkages and the second with nonnative linkages. In a third synthetic peptide, all cysteine residues were replaced with α-aminobutyric acid, creating a completely linear peptide. A series of six small, linear peptides corresponding to regions of hBD3 with net charges ranging from +4 to +8 (at pH 7) and lengths ranging from 9 to 20 amino acids were also synthesized. The linear full-length peptide showed the highest microbicidal activity againstEscherichia coliandStaphylococcus aureus, while all three full-length forms showed equal activity againstCandida albicans. The linear peptide also showed high activity againstEnterococcus faeciumandPseudomonas aeruginosa.Peptides corresponding to the C terminus showed higher activities when tested againstE. coli, with the most active peptides being the most basic. However, only the peptide corresponding to the N terminus of hBD3 showed any activity againstS. aureusandC. albicans. Further, N-terminal deletion mutants of native hBD3 showed diminished activities againstS. aureus. Thus, the antimicrobial properties of hBD3 derivatives are determined by both charge and structure.
Shikonin, a Component of Chinese Herbal Medicine, Inhibits Chemokine Receptor Function and Suppresses Human Immunodeficiency Virus Type 1
Authors: Chen Xin , Yang Lu , Zhang Ning , Turpin Jim A. , Buckheit Robert W. , Osterling Clay , Oppenheim Joost J. , Howard O. M. Zack
Published: August 2003

Shikonin is a major component of zicao (purple gromwell, the dried root of
Lithospermum erythrorhizon
), a Chinese herbal medicine with various biological activities, including inhibition of human immunodeficiency virus (HIV) type 1 (HIV-1). G protein-coupled chemokine receptors are used by HIV-1 as coreceptors to enter the host cells. In this study, we assessed the effects of shikonin on chemokine receptor function and HIV-1 replication. The results showed that, at nanomolar concentrations, shikonin inhibited monocyte chemotaxis and calcium flux in response to a variety of CC chemokines (CCL2 [monocyte chemoattractant protein 1], CCL3 [macrophage inflammatory protein 1α], and CCL5 [regulated upon activation, normal T-cell expressed and secreted protein]), the CXC chemokine (CXCL12 [stromal cell-derived factor 1α]), and classic chemoattractants (formylmethionyl-leucine-phenylalanine and complement fraction C5a). Shikonin down-regulated surface expression of CCR5, a primary HIV-1 coreceptor, on macrophages to a greater degree than the other receptors (CCR1, CCR2, CXCR4, and the formyl peptide receptor) did. CCR5 mRNA expression was also down-regulated by the compound. Additionally, shikonin inhibited the replication of a multidrug-resistant strain and pediatric clinical isolates of HIV in human peripheral blood mononuclear cells, with 50% inhibitory concentrations (IC
50
s) ranging from 96 to 366 nM. Shikonin also effectively inhibited the replication of the HIV Ba-L isolate in monocytes/macrophages, with an IC
50
of 470 nM. Our results suggest that the anti-HIV and anti-inflammatory activities of shikonin may be related to its interference with chemokine receptor expression and function. Therefore, shikonin, as a naturally occurring, low-molecular-weight pan-chemokine receptor inhibitor, constitutes a basis for the development of novel anti-HIV therapeutic agents.