Gender differences contribute to variability of serum lipid biomarkers for Alzheimer's disease

Background: Alzheimer's disease (AD) cannot currently be diagnosed by a blood test. One reason may be gender differences. Another may be the statistical methods used. The authors evaluate these possibilities. Objective: The authors applied serum lipidomics to find AD biomarkers in men and women. They hypothesized that AD biomarkers would differ between genders and that machine-learning algorithms would improve diagnostic performance. Methods: Serum lipids were analyzed by mass spectrometry for a training set of AD cases and controls and in a blinded test set. Statistical analyses considered gender differences. Results: Lipids best classifying AD subjects differed significantly between men and women. Robust statistical algorithms did not improve diagnostic performance. Conclusion: Poor performance of AD biomarkers appears to be due primarily to inherent variability in AD patients.

Time-resolved microfluidic flow cytometer for decoding luminescence lifetimes in the microsecond region

Time-resolved luminescence detection using long-lived probes with lifetimes in the microsecond region have shown great potential in ultrasensitive and multiplexed bioanalysis. In flow cytometry, however, the long lifetime poses a significant challenge to measure wherein the detection window is often too short to determine the decay characteristics. Here we report a time-resolved microfluidic flow cytometer (tr-mFCM) incorporating an acoustic-focusing chip, which allows slowing down of the flow while providing the same detection conditions for every target, achieving accurate lifetime measurement free of autofluorescence interference. Through configuration of the flow velocity and detection aperture with respect to the time-gating sequence, a multi-cycle luminescence decay profile is captured for every event under maximum excitation and detection efficiency. A custom fitting algorithm is then developed to resolve europium-stained polymer microspheres as well as leukemia cells against abundant fluorescent particles, achieving counting efficiency approaching 100% and lifetime CVs (coefficient of variation) around 2-6%. We further demonstrate lifetime-multiplexed detection of prostate and bladder cancer cells stained with different europium probes. Our acoustic-focusing tr-mFCM offers a practical technique for rapid screening of biofluidic samples containing multiple cell types, especially in resource-limited environments such as regional and/or underdeveloped areas as well as for point-of-care applications.

Microcompartments for Protection and Isolation of Nanoscale DNA Computing Elements

Physical isolation of molecular computing elements holds the potential for increasing system complexity by enabling the reuse of standardized components and by protecting the components from environmental degradation. However, once elements have been compartmentalized, methods for communicating into these compartments are needed. We report the compartmentalization of steroid-responsive DNA aptamers within giant unilamellar vesicles (GUVs) that are permeable to steroid inputs. Monodisperse GUVs are loaded with aptamers using a microfluidic platform. We demonstrate the target-specific activation of individual aptamers within the GUVs and then load two noninterfering aptamers into the same GUV and demonstrate specific responses to all possible combinations of the two input steroids. Crucially, GUVs prevent the degradation of DNA components by nucleases, providing a potential mechanism for deploying nucleic acid components in vivo. Importantly, our compartments also prevent nonspecific cross-talk between complementary strands, thereby providing a method for parallel execution of cross-reacting molecular logic components. Thus, we provide a mechanism for spatially organizing molecular computing elements, which will increase system modularity by allowing standardized components to be reused.

Resonance control of acoustic focusing systems through an environmental reference table and impedance spectroscopy

Acoustic standing waves can precisely focus flowing particles or cells into tightly positioned streams for interrogation or downstream separations. The efficiency of an acoustic standing wave device is dependent upon operating at a resonance frequency. Small changes in a system's temperature and sample salinity can shift the device's resonance condition, leading to poor focusing. Practical implementation of an acoustic standing wave system requires an automated resonance control system to adjust the standing wave frequency in response to environmental changes. Here we have developed a rigorous approach for quantifying the optimal acoustic focusing frequency at any given environmental condition. We have demonstrated our approach across a wide range of temperature and salinity conditions to provide a robust characterization of how the optimal acoustic focusing resonance frequency shifts across these conditions. To generalize these results, two microfluidic bulk acoustic standing wave systems (a steel capillary and an etched silicon wafer) were examined. Models of these temperature and salinity effects suggest that it is the speed of sound within the liquid sample that dominates the resonance frequency shift. Using these results, a simple reference table can be generated to predict the optimal resonance condition as a function of temperature and salinity. Additionally, we show that there is a local impedance minimum associated with the optimal system resonance. The integration of the environmental results for coarse frequency tuning followed by a local impedance characterization for fine frequency adjustments, yields a highly accurate method of resonance control. Such an approach works across a wide range of environmental conditions, is easy to automate, and could have a significant impact across a wide range of microfluidic acoustic standing wave systems.

Presentation matters: Impact of association of amphiphilic LPS with serum carrier proteins on innate immune signaling

Recognition of Pathogen-associated Molecular Patterns (PAMPs) by Toll-like receptors is central to innate immunity. Many bacterial PAMPs such as lipopolysaccharide (LPS) and lipoteichoic acid have amphiphilic properties. The hydrophobicity of amphiphilic PAMPs contributes to increasing entropy and causes these molecules to self-aggregate or bind host carrier proteins in aqueous physiological environments. The goal of this work was to determine how innate immune signaling is impacted by physical presentation and association of amphiphilic PAMPs with serum carrier proteins, using LPS as an example molecule. Specifically, we measured LPS-induced cytokine profiles in murine macrophages when the antigen was presented associated with the various serum carrier proteins in serum versus a serum-depleted system. Our study demonstrates that the observed cytokine profiles are dramatically different when LPS is presented in buffer, versus in serum when it is associated with proteins, specifically with respect to inhibition of pro-inflammatory cytokines in the latter. These studies suggest that LPS-mediated cytokine expression is dependent on its presentation in physiological systems. The amphiphilicity of bacterial PAMPs and consequent association with lipoproteins is a feature, which should be taken into account in the design of in vitro experiments. Further studies of the interdependencies of different serum carriers can identify pathways for drug delivery and diagnostics.

Discovery and Confirmation of Diagnostic Serum Lipid Biomarkers for Alzheimer's Disease Using Direct Infusion Mass Spectrometry

Alzheimer's disease (AD) is a neurodegenerative disorder lacking early biochemical diagnosis and treatment. Lipids have been implicated in neurodegenerative disorders including AD. A shotgun lipidomic approach was undertaken to determine if lipid biomarkers exist that can discriminate AD cases from controls. The discovery study involved sera from 29 different stage AD cases and 32 controls. Lipid extraction was performed using organic solvent and the samples were directly infused into a time-of-flight mass spectrometer. Differences between AD cases and controls were detected with 87 statistically significant lipid candidate markers found. These potential lipid markers were reevaluated in a second confirmatory study involving 27 cases and 30 controls. Of the 87 candidates from the first study, 35 continued to be statistically significant in the second confirmatory set. Tandem MS studies were performed and almost all confirmed markers were characterized and classified. Using a Bayesian lasso probit regression model on the confirmed markers, a multi-marker set with AUC = 0.886 was developed comparing all stages of AD with controls. Additionally, using confirmed biomarkers, multi-marker sets with AUCs >0.90 were developed for each specific AD Clinical Dementia Rating versus controls, including the earliest stage of AD. More conservative and likely more realistic statistical analyses still found multi-marker sets that appeared useful in diagnosing AD. Finally, using ordinal modeling a set of markers was developed that staged AD accurately 70% of the time, p = 0.0079. These results suggest that these serum lipidomic biomarkers may help diagnose and perhaps even stage AD.

Line-Focused Optical Excitation of Parallel Acoustic Focused Sample Streams for High Volumetric and Analytical Rate Flow Cytometry

Flow cytometry provides highly sensitive multiparameter analysis of cells and particles but has been largely limited to the use of a single focused sample stream. This limits the analytical rate to ∼50K particles/s and the volumetric rate to ∼250 μL/min. Despite the analytical prowess of flow cytometry, there are applications where these rates are insufficient, such as rare cell analysis in high cellular backgrounds (e.g., circulating tumor cells and fetal cells in maternal blood), detection of cells/particles in large dilute samples (e.g., water quality, urine analysis), or high-throughput screening applications. Here we report a highly parallel acoustic flow cytometer that uses an acoustic standing wave to focus particles into 16 parallel analysis points across a 2.3 mm wide optical flow cell. A line-focused laser and wide-field collection optics are used to excite and collect the fluorescence emission of these parallel streams onto a high-speed camera for analysis. With this instrument format and fluorescent microsphere standards, we obtain analysis rates of 100K/s and flow rates of 10 mL/min, while maintaining optical performance comparable to that of a commercial flow cytometer. The results with our initial prototype instrument demonstrate that the integration of key parallelizable components, including the line-focused laser, particle focusing using multinode acoustic standing waves, and a spatially arrayed detector, can increase analytical and volumetric throughputs by orders of magnitude in a compact, simple, and cost-effective platform. Such instruments will be of great value to applications in need of high-throughput yet sensitive flow cytometry analysis.

A Microsphere-Supported Lipid Bilayer Platform for DNA Reactions on a Fluid Surface

We report a versatile microsphere-supported lipid bilayer system that can serve as a general-purpose platform for implementing DNA nanotechnologies on a fluid surface. To demonstrate our platform, we implemented both toehold-mediated strand displacement (TMSD) and DNAzyme reactions, which are typically performed in solution and which are the cornerstone of DNA-based molecular logic and dynamic DNA nanotechnology, on the surface. We functionalized microspheres bearing supported lipid bilayers (μSLBs) with membrane-bound nucleic acid components. Using functionalized μSLBs, we developed TMSD and DNAzyme reactions by optimizing reaction conditions to reduce nonspecific interactions between DNA and phospholipids and to enhance bilayer stability. Additionally, the physical and optical properties of the bilayer were tuned via lipid composition and addition of fluorescently tagged lipids to create stable and multiplexable μSLBs that are easily read out by flow cytometry. Multiplexed TMSD reactions on μSLBs enabled the successful operation of a Dengue serotyping assay that correctly identified all 16 patterns of target sequences to demonstrate detection of DNA strands derived from the sequences of all four Dengue serotypes. The limit of detection for this assay was 3 nM. Furthermore, we demonstrated DNAzyme reactions on a fluid lipid surface, which benefit from free diffusion on the surface. This work provides the basis for expansion of both TMSD and DNAzyme based molecular reactions on supported lipid bilayers for use in molecular logic and DNA nanotechnology. As our system is multiplexable and results in fluid surfaces, it may be of use in compartmentalization and improved kinetics of molecular logic reactions and as a useful building block in a variety of DNA nanotechnology systems.

Multiplexed Lipid Bilayers on Silica Microspheres for Analytical Screening Applications

Most druggable targets are membrane components, including membrane proteins and soluble proteins that interact with ligands or receptors embedded in membranes. Current target-based screening and intermolecular interaction assays generally do not include the lipid membrane environment in presenting these targets, possibly altering their native structure and leading to misleading or incorrect results. To address this issue, an ideal assay involving membrane components would (1) mimic the natural membrane environment, (2) be amenable to high-throughput implementation, and (3) be easily multiplexed. In a step toward developing such an ideal target-based analytical assay for membrane components, we present fluorescently indexed multiplexed biomimetic membrane assays amenable to high-throughput flow cytometric detection. We build fluorescently multiplexed biomimetic membrane assays by using varying amounts of a fluorescently labeled lipid, NBD-DOPE [1,2-dioleoyl-sn-glycero-3-phosphoethanolamine-N-(7-nitro-2-1,3-benzoxadiazol-4-yl)], incorporated into a phospholipid membrane bilayer supported on 3 μm silica microspheres. Using flow cytometry, we demonstrate this multiplexed approach by measuring specific affinity of two well-characterized systems, the fluorescently labeled soluble proteins cholera toxin B subunit-Alexa 647 and streptavidin-PE/Cy5, to membranes containing different amounts of ligand targets of these proteins, GM1 and biotin-DOPE, respectively. This work will enable future efforts in developing highly efficient biomimetic assays for interaction analysis and drug screening involving membrane components.

Characterization of aqueous formulations of tetra- and pentavalent forms of vanadium in support of test article selection in toxicology studies

Tetravalent (V^IV) and pentavalent (V^V) forms of vanadium were selected for testing by the National Toxicology Program via drinking water exposure due to potential human exposure. To aid in the test article selection, drinking water formulations (125-2000 mg/L) of vanadyl sulfate (V^IV), sodium orthovanadate, and sodium metavanadate (V^V) were characterized by ultraviolet/visible (UV/VIS) spectroscopy, mass spectrometry (MS), or ⁵¹V nuclear magnetic resonance (NMR) spectroscopy. Aqueous formulations of orthovanadate, metavanadate, and vanadyl sulfate in general were basic, neutral, and acidic, respectively. Changes in vanadium speciation were investigated by adjusting formulation pH to acidic, neutral, or basic. There was no visible difference in UV/VIS spectra of pentavalent forms. NMR and MS analyses showed that the predominant oxidovanadate species in both ortho- and metavanadate formulations at basic and acidic pH, respectively, were the monomer and decamer, while, a mixture of oxidovanadates were present at neutral pH. Oxidovanadate species were not observed in vanadyl sulfate formulations at acidic pH but were observed at basic pH suggesting conversion of V^IV to V^V. These data suggest that formulations of both ortho- and metavanadate form similar oxidovanadate species in acidic, neutral and basic pH and exist mainly in the V^V form while vanadyl sulfate exists mainly as V^IV in acidic pH. Therefore, the formulation stability overtime was investigated only for sodium metavanadate and vanadyl sulfate. Drinking water formulations (50 and 2000 mg/L) of metavanadate (~pH 7) and vanadyl sulfate (~pH 3.5) were ≥92 % of target concentration up to 42 days at ~5 °C and ambient temperature demonstrating the utility in toxicology studies.

Development of 11-Plex MOL-PCR Assay for the Rapid Screening of Samples for Shiga Toxin-Producing Escherichia coli

Strains of Shiga toxin-producing Escherichia coli (STEC) are a serious threat to the health, with approximately half of the STEC related food-borne illnesses attributable to contaminated beef. We developed an assay that was able to screen samples for several important STEC associated serogroups (O26, O45, O103, O104, O111, O121, O145, O157) and three major virulence factors (eae, stx₁, stx₂) in a rapid and multiplexed format using the Multiplex oligonucleotide ligation-PCR (MOL-PCR) assay chemistry. This assay detected unique STEC DNA signatures and is meant to be used on samples from various sources related to beef production, providing a multiplex and high-throughput complement to the multiplex PCR assays currently in use. Multiplex oligonucleotide ligation-PCR (MOL-PCR) is a nucleic acid-based assay chemistry that relies on flow cytometry/image cytometry and multiplex microsphere arrays for the detection of nucleic acid-based signatures present in target agents. The STEC MOL-PCR assay provided greater than 90% analytical specificity across all sequence markers designed when tested against panels of DNA samples that represent different STEC serogroups and toxin gene profiles. This paper describes the development of the 11-plex assay and the results of its validation. This highly multiplexed, but more importantly dynamic and adaptable screening assay allows inclusion of additional signatures as they are identified in relation to public health. As the impact of STEC associated illness on public health is explored additional information on classification will be needed on single samples; thus, this assay can serve as the backbone for a complex screening system.

Global "omics" evaluation of human placental responses to preeclamptic conditions

BACKGROUND

Preeclampsia (PE) is a leading cause of maternal death. Its cause is still debated but there is general agreement that the placenta plays a central role. Perhaps the most commonly proposed contributors to PE include placental hypoxia, oxidative stress, and increased proinflammatory cytokines. How the placenta responds to these abnormalities has been considered but not as part of a comprehensive analysis of low-molecular-weight biomolecules and their responses to these accepted PE conditions.

OBJECTIVE

Using a peptidomic approach, we sought to identify a set of molecules exhibiting differential expression in consequence of provocative agents/chemical mediators of PE applied to healthy human placental tissue.

STUDY DESIGN

Known PE conditions were imposed on normal placental tissue from 13 uncomplicated pregnancies and changes in the low-molecular-weight peptidome were evaluated. A t test was used to identify potential markers for each imposed stress. These markers were then submitted to a least absolute shrinkage and selection operator multinomial logistic regression model to identify signatures specific to each stressor. Estimates of model performance on external data were obtained through internal validation.

RESULTS

A total of 146 markers were increased/decreased as a consequence of exposure to proposed mediators of PE. Of these 75 changed with hypoxia; 23 with hypoxia-reoxygenation/oxidative stress and 48 from exposure to tumor necrosis factor-α. These markers were chemically characterized using tandem mass spectrometry. Identification rates were: hypoxia, 34%; hypoxia-reoxygenation, 60%; and tumor necrosis factor-α, 50%. Least absolute shrinkage and selection operator modeling specified 16 markers that effectively distinguished all groups, ie, the 3 abnormal conditions and control. Bootstrap estimates of misclassification rates, multiclass area under the curve, and Brier score were 0.108, 0.944, and 0.160, respectively.

CONCLUSION

Using this approach we found previously unknown molecular changes in response to individual PE conditions that allowed development biomolecular signatures for exposure to each accepted pathogenic condition.

Membrane Insertion for the Detection of Lipopolysaccharides: Exploring the Dynamics of Amphiphile-in-Lipid Assays

Shiga toxin-producing Escherichia coli is an important cause of foodborne illness, with cases attributable to beef, fresh produce and other sources. Many serotypes of the pathogen cause disease, and differentiating one serotype from another requires specific identification of the O antigen located on the lipopolysaccharide (LPS) molecule. The amphiphilic structure of LPS poses a challenge when using classical detection methods, which do not take into account its lipoglycan biochemistry. Typically, detection of LPS requires heat or chemical treatment of samples and relies on bioactivity assays for the conserved lipid A portion of the molecule. Our goal was to develop assays to facilitate the direct and discriminative detection of the entire LPS molecule and its O antigen in complex matrices using minimal sample processing. To perform serogroup identification of LPS, we used a method called membrane insertion on a waveguide biosensor, and tested three serogroups of LPS. The membrane insertion technique allows for the hydrophobic association of LPS with a lipid bilayer, where the exposed O antigen can be targeted for specific detection. Samples of beef lysate were spiked with LPS to perform O antigen specific detection of LPS from E. coli O157. To validate assay performance, we evaluated the biophysical interactions of LPS with lipid bilayers both in- and outside of a flow cell using fluorescence microscopy and fluorescently doped lipids. Our results indicate that membrane insertion allows for the qualitative and reliable identification of amphiphilic LPS in complex samples like beef homogenates. We also demonstrated that LPS-induced hole formation does not occur under the conditions of the membrane insertion assays. Together, these findings describe for the first time the serogroup-specific detection of amphiphilic LPS in complex samples using a membrane insertion assay, and highlight the importance of LPS molecular conformations in detection architectures.

Serum biomarkers predictive of pre-eclampsia

AIM

We sought serum biomarkers predictive of pre-eclampsia (PE).

MATERIALS & METHODS

Sera obtained at 12-14 weeks of pregnancy from 24 cases who later developed PE and 24 controls with uncomplicated pregnancies were processed and analyzed using a serum proteomic approach.

RESULTS

Many statistically significant serum PE biomarker candidates (n > 60) were found comparing cases and controls. In addition, logistic regression analysis modeled biomarker data resulted in 14 different multimarker combinations having high detection sensitivity and specificity (AUC >0.9).

CONCLUSIONS

Developed panels of serum biomarkers appeared effective in identifying pregnant women at 12-14 weeks gestation at risk of PE later in their pregnancy.

Detection and confirmation of serum lipid biomarkers for preeclampsia using direct infusion mass spectrometry

Despite substantial research, the early diagnosis of preeclampsia remains elusive. Lipids are now recognized to be involved in regulation and pathophysiology of some disease. Shotgun lipidomic studies were undertaken to determine whether serum lipid biomarkers exist that predict preeclampsia later in the same in pregnancy. A discovery study was performed using sera collected at 12-14 weeks pregnancy from 27 controls with uncomplicated pregnancies and 29 cases that later developed preeclampsia. Lipids were extracted and analyzed by direct infusion into a TOF mass spectrometer. MS signals, demonstrating apparent differences were selected, their abundances determined, and statistical differences tested. Statistically significant lipid markers were reevaluated in a second confirmatory study having 43 controls and 37 preeclampsia cases. Multi-marker combinations were developed using those lipid biomarkers confirmed in the second study. The initial study detected 45 potential preeclampsia markers. Of these, 23 markers continued to be statistically significant in the second confirmatory set. Most of these markers, representing several lipid classes, were chemically characterized, typically providing lipid class and potential molecular components using MS(2) Several multi-marker panels with areas under the curve >0.85 and high predictive values were developed. Developed panels of serum lipidomic biomarkers appear to be able to identify most women at risk for preeclampsia in a given pregnancy at 12-14 weeks gestation.

A unified sensor architecture for isothermal detection of double-stranded DNA, oligonucleotides, and small molecules

Pathogen detection is an important problem in many areas of medicine and agriculture, which can involve genomic or transcriptomic signatures or small-molecule metabolites. We report a unified, DNA-based sensor architecture capable of isothermal detection of double-stranded DNA targets, single-stranded oligonucleotides, and small molecules. Each sensor contains independent target detection and reporter modules, enabling rapid design. We detected gene variants on plasmids by using a straightforward isothermal denaturation protocol. The sensors were highly specific, even with a randomized DNA background. We achieved a limit of detection of ∼15 pM for single-stranded targets and ∼5 nM for targets on denatured plasmids. By incorporating a blocked aptamer sequence, we also detected small molecules using the same sensor architecture. This work provides a starting point for multiplexed detection of multi-strain pathogens, and disease states caused by genetic variants (e.g., sickle cell anemia).

Two-dimensional spatial manipulation of microparticles in continuous flows in acoustofluidic systems

We report a modeling and experimental study of techniques to acoustically focus particles flowing through a microfluidic channel. Our theoretical model differs from prior works in that we solve an approximate 2-D wave transmission model that accounts for wave propagation in both the solid and fluid phases. Our simulations indicate that particles can be effectively focused at driving frequencies as high as 10% off of the resonant condition. This conclusion is supported by experiments on the acoustic focusing of particles in nearly square microchannels, which are studied for different flow rates, driving frequencies and placements of the lead zirconate titanate transducer, either underneath the microchannel or underneath a parallel trough. The relative acoustic potential energy and the resultant velocity fields for particles with positive acoustic contrast coefficients are estimated in the 2-D limit. Confocal microscopy was used to observe the spatial distribution of the flowing microparticles in three dimensions. Through these studies, we show that a single driving frequency from a single piezoelectric actuator can induce the 2-D concentration of particles in a microchannel with a nearly square cross section, and we correlate these behaviors with theoretical predictions. We also show that it is possible to control the extent of focusing of the microparticles, and that it is possible to decouple the focusing of microparticles in the vertical direction from the lateral direction in rectangular channels with anisotropic cross sections. This study provides guidelines to design and operate microchip-based acoustofluidic devices for precise control over the spatial arrangement of microparticles for applications such as flow cytometry and cellular sorting.

Signal propagation in multi-layer DNAzyme cascades using structured chimeric substrates

Signal propagation through enzyme cascades is a critical component of information processing in cellular systems. Although such systems have potential as biomolecular computing tools, rational design of synthetic protein networks remains infeasible. DNA strands with catalytic activity (DNAzymes) are an attractive alternative, enabling rational cascade design through predictable base-pair hybridization principles. Multi-layered DNAzyme signaling and logic cascades are now reported. Signaling between DNAzymes was achieved using a structured chimeric substrate (SCS) that releases a downstream activator after cleavage by an upstream DNAzyme. The SCS can be activated by various upstream DNAzymes, can be coupled to DNA strand-displacement devices, and is highly resistant to interference from background DNA. This work enables the rational design of synthetic DNAzyme regulatory networks, with potential applications in biomolecular computing, biodetection, and autonomous theranostics.

Association of cord blood digitalis-like factor and necrotizing enterocolitis

OBJECTIVE

Endogenous digoxin-like factor (EDLF) has been linked to vasoconstriction, altered membrane transport, and apoptosis. Our objective was to determine whether increased EDLF in the cord sera of preterm infants was associated with an increased incidence of necrotizing enterocolitis (NEC).

STUDY DESIGN

Cord sera from pregnant women enrolled in a randomized trial of MgSO4 for fetal neuroprotection were analyzed for EDLF using a red cell Rb(+) uptake assay in which the inhibition of sodium pump-mediated Rb(+) transport was used as a functional assay of EDLF. Specimens were assayed blinded to neonatal outcome. Cases (NEC, n = 25) and controls (neonates not developing stage 2 or 3 NEC, n = 24) were matched by study center and gestational age. None of the women had preeclampsia. Cases and controls were compared using the Wilcoxon test for continuous and the Fisher exact test for categorical variables. A conditional logistic regression analysis was used to assess the odds of case vs control by EDLF level.

RESULTS

Cases and controls were not significantly different for gestational age, race, maternal steroid use, premature rupture of membranes, or MgSO4 treatment. In logistic models adjusted for treatment group, race, premature rupture of membranes, and gestational age, cord sera EDLF was significantly associated with development of NEC (P = .023).

CONCLUSION

These data demonstrated an association between cord sera EDLF and NEC.

Catalytic molecular logic devices by DNAzyme displacement

Chemical reactions catalyzed by DNAzymes offer a route to programmable modification of biomolecules for therapeutic purposes. To this end, we have developed a new type of catalytic DNA-based logic gates in which DNAzyme catalysis is controlled via toehold-mediated strand displacement reactions. We refer to these as DNAzyme displacement gates. The use of toeholds to guide input binding provides a favorable pathway for input recognition, and the innate catalytic activity of DNAzymes allows amplification of nanomolar input concentrations. We demonstrate detection of arbitrary input sequences by rational introduction of mismatched bases into inhibitor strands. Furthermore, we illustrate the applicability of DNAzyme displacement to compute logic functions involving multiple logic gates. This work will enable sophisticated logical control of a range of biochemical modifications, with applications in pathogen detection and autonomous theranostics.

The intersection of flow cytometry with microfluidics and microfabrication

A modern flow cytometer can analyze and sort particles on a one by one basis at rates of 50,000 particles per second. Flow cytometers can also measure as many as 17 channels of fluorescence, several angles of scattered light, and other non-optical parameters such as particle impedance. More specialized flow cytometers can provide even greater analysis power, such as single molecule detection, imaging, and full spectral collection, at reduced rates. These capabilities have made flow cytometers an invaluable tool for numerous applications including cellular immunophenotyping, CD4+ T-cell counting, multiplex microsphere analysis, high-throughput screening, and rare cell analysis and sorting. Many bio-analytical techniques have been influenced by the advent of microfluidics as a component in analytical tools and flow cytometry is no exception. Here we detail the functions and uses of a modern flow cytometer, review the recent and historical contributions of microfluidics and microfabricated devices to field of flow cytometry, examine current application areas, and suggest opportunities for the synergistic application of microfabrication approaches to modern flow cytometry.

Digoxin antibody fragment, antigen binding (Fab), treatment of preeclampsia in women with endogenous digitalis-like factor: a secondary analysis of the DEEP Trial

OBJECTIVE

Endogenous digitalis-like factors (EDLFs) are elevated in women with preeclampsia, and the use of an anti-digoxin antibody Fab (DIF) in women with preeclampsia who were remote from term reduced maternal blood pressure and preserved renal function. The objective was to determine whether DIF treatment in women with severe preeclampsia in association with positive EDLFs in maternal serum improves maternal-perinatal outcomes.

STUDY DESIGN

This was a planned secondary analysis from a randomized, placebo-controlled, double-blind study of DIF in women with severe preeclampsia with positive EDLF status that was managed expectantly between 23 weeks 5 days and 34 weeks' gestation (19 women received placebo, and 17 women received DIF). Primary outcome variables were a change in creatinine clearance and the use of antihypertensives. Secondary outcomes were maternal and perinatal complications.

RESULTS

Women with positive EDLFs who received DIF had an attenuated decline in creatinine clearance from baseline compared with placebo (-4.5 ± 12.9 vs -53.2 ± 12.6 mL/min; P = .005). In this same group, the use of antihypertensives (the other primary outcome) was lower but not significantly so (41% vs 63%; P = .12). However, women who were treated with DIF had a lower rate of pulmonary edema (1/17 vs 6/19 women; P = .035) and lower rates of neonatal intraventricular hemorrhage (DIF: 0/17 women vs placebo: 5/19 women; P = .015).

CONCLUSION

In women with severe preeclampsia who were remote from term who were EDLF positive, the use of DIF was associated with improved maternal and neonatal outcome. These findings suggest the need for a large multicenter trial that would evaluate the benefits of DIF in the treatment of women with severe preeclampsia who are remote from term and with positive EDLF status.

Fluidics

The use of fluidics is implicit in a technology named "flow cytometry," which flows a cell or particle through a sensing volume to obtain serial analysis of particles on a one by one basis. This flow of particles enables flow cytometry to collect information on multiple particle populations, giving it a distinct advantage over bulk analysis approaches. Moreover, flow cytometers can analyze thousands of particles per second in a single flowing stream. Additionally, use of volumetric sample delivery makes it possible for flow cytometers to accurately count cells and particles. Furthermore, the analysis results can be coupled with a fluidic diversion mechanism to sort and collect particles based on desired properties. Finally, when high-throughput sampling technologies are employed to rapidly change the input of the sample stream, a flow cytometer can become an integral tool for high-throughput screening. The above properties have made flow cytometry useful in a wide range of biomedical applications. In this unit we will present an overview of fluidic systems that make flow cytometry possible. This will introduce historical approaches, explanations of the commonly implemented current fluidics, and brief discussions of potential future fluidics where appropriate.

Toxicokinetics of α-thujone following intravenous and gavage administration of α-thujone or α- and β-thujone mixture in male and female F344/N rats and B6C3F1 mice

Plants containing thujone have widespread use and hence have significant human exposure. α-Thujone caused seizures in rodents following gavage administration. We investigated the toxicokinetics of α-thujone in male and female F344/N rats and B6C3F1 mice following intravenous and gavage administration of α-thujone or a mixture of α- and β-thujone (which will be referred to as α,β-thujone). Absorption of α-thujone following gavage administration was rapid without any dose-, species-, sex- or test article-related effect. Absolute bioavailability of α-thujone following administration of α-thujone or α,β-thujone was generally higher in rats than in mice. In rats, females had higher bioavailability than males following administration of either test article although a sex difference was not observed in mice. Cmax and AUC∞ increased greater than proportional to the dose in female rats following administration of α-thujone and in male and female mice following administration of α,β-thujone suggesting possible saturation of elimination kinetics with increasing dose. Dose-adjusted AUC∞ for male and female rats was 5- to 15-fold and 3- to 24-fold higher than mice counterparts following administration of α-thujone and α,β-thujone, respectively (p-value<0.0001 for all comparisons). Following both intravenous and gavage administration, α-thujone was distributed to the brains of rats and mice with females, in general, having higher brain:plasma ratios than males. These data are in support of the observed toxicity of α-thujone and α,β-thujone where females were more sensitive than males of both species to α-thujone-induced neurotoxicity. In general there was no difference in toxicokinetics between test articles when normalized to α-thujone concentration.

High-throughput flow cytometry for drug discovery

High-throughput flow cytometry exploits a novel many-samples/one-file approach to dramatically speed data acquisition, limit aspirated sample volume to as little as 2 μl/well and produce multisample data sets that facilitate automated analysis of samples in groups as well as individually. It has been successfully applied to both cell- and microsphere-based bioassays in 96- and 384-well formats, to screen tens-of-thousands of compounds and identify novel bioactive structures. High-content multiparametric analysis capabilities have been exploited for assay multiplexing, allowing the assessment of biologic selectivity and specificity to be an integral component of primary screens. These and other advances in the last decade have contributed to the application of flow cytometry as a uniquely powerful tool for probing biologic and chemical diversity and complex systems biology.

Elastomeric negative acoustic contrast particles for affinity capture assays

This report describes the development of elastomeric capture microparticles (ECμPs) and their use with acoustophoretic separation to perform microparticle assays via flow cytometry.We have developed simple methods to form ECμPs by cross-linking droplets of common commercially available silicone precursors in suspension followed by surface functionalization with biomolecular recognition reagents. The ECμPs are compressible particles that exhibit negative acoustic contrast in ultrasound when suspended in aqueous media, blood serum, or diluted blood. In this study, these particles have been functionalized with antibodies to bind prostate specific antigen and immunoglobulin (IgG). Specific separation of the ECμPs from blood cells is achieved by flowing them through a microfluidic acoustophoretic device that uses an ultrasonic standing wave to align the blood cells, which exhibit positive acoustic contrast, at a node in the acoustic pressure distribution while aligning the negative acoustic contrast ECμPs at the antinodes. Laminar flow of the separated particles to downstream collection ports allows for collection of the separated negative contrast (ECμPs) and positive contrast particles (cells). Separated ECμPs were analyzed via flow cytometry to demonstrate nanomolar detection for prostate specific antigen in aqueous buffer and picomolar detection for IgG in plasma and diluted blood samples. This approach has potential applications in the development of rapid assays that detect the presence of low concentrations of biomarkers in a number of biological sample types.

Inertial manipulation and transfer of microparticles across laminar fluid streams

A general strategy for controlling particle movement across streams would enable new capabilities in single-cell analysis, solid-phase reaction control, and biophysics research. Transferring cells across streams is difficult to achieve in a well-controlled manner, since it requires precise control of fluid flow along with external force fields or precisely manufactured mechanical structures. Herein a strategy is introduced for particle transfer based on passive inertial lift forces and shifts in the distribution of these forces for channels with shifting aspect ratios. Uniquely, use of the dominant wall-effect lift parallel to the particle rotation direction is explored and utilized to achieve controllable cross-stream motion. In this way, particles are positioned to migrate across laminar streams and enter a new solution without significant disturbance of the interface at rates exceeding 1000 particles per second and sub-millisecond transfer times. The capabilities of rapid inertial solution exchange (RInSE) for preparation of hematological samples and other cellular assays are demonstrated. Lastly, improvements to inline flow cytometry after RInSE of excess fluorescent dye and focusing for downstream analysis are characterized. The described approach is simply applied to manipulating cells and particles and quickly exposing them to or removing them from a reacting solution, with broader applications in control and analysis of low affinity interactions on cells or particles.

PP087. Deep trial secondary analysis: Digoxin immune fab fragment treatment has additional benefits in endogenous digitalis-like factor positive preeclamptic women

INTRODUCTION

A double blinded placebo controlled clinical trial of a commercial digoxin immune Fab fragment (DIF) in preeclamptic (PE) women provided some benefit to treated subjects (1). In that study DIF, relative to placebo, prevented a decline in CrCl and lowered levels of endogenous digitalis-like factor (EDLF) activity as measured by sodium pump inhibition (SPI). However, some PE subjects had undetectable EDLF.

OBJECTIVES

The hypothesis tested was that only PE women with measureable EDLF would respond to DIF treatment and analysis of EDLF positive women might reveal treatment effects masked by inclusion of EDLF negative, and hence non-responding, PE women. Accordingly, analyses of DIF effects in EDLF positive PE women were conducted.

METHODS

Patient characteristics and study design have been published (1). In these subanalyses, subjects were considered to be EDLF positive if their plasma inhibited red cell sodium pump mediated Rb uptake. All analyses were redone for the EDLF positive subgroup by Covance Inc as in the original trial. Continuous data were analyzed by ANCOVA. Categorical data were analyzed by Barnard Exact Test.

RESULTS

45 subjects (23 DIF, 22 placebo) had baseline SPI evaluated. Of these 22% had undetectable SPI. EDLF positive PE women showed greater and more significant reductions of SPI in response to DIF at each time point (12, 24, 48 hr treatment) than in the original analysis. Subjects with undetectable EDLF showed no significant change in response to DIF or placebo. For CrCl, EDLF positive PE women showed greater and more significant preservation of CrCl compared with original analyses. Subjects absent EDLF showed deterioration of CrCl with or without DIF. Among EDLF positive PE women DIF treated women had significantly less maternal pulmonary edema (p=0.035) and significantly less intraventricular hemorrhage in their infants (p=0.015). There was the suggestion of reductions in the incidence of other maternal and neonatal abnormalities.

CONCLUSION

These data indicate that EDLF positive PE women are those that responded to DIF and also raise the possibility of extended benefits of DIF treatment in this group. Results support further research in this area.

Cluster cytometry for high-capacity bioanalysis

Flow cytometry specializes in high-content measurements of cells and particles in suspension. Having long excelled in analytical throughput of single cells and particles, only recently with the advent of HyperCyt sampling technology, flow cytometry's multiexperiment throughput has begun to approach the point of practicality for efficiently analyzing hundreds-of-thousands of samples, the realm of high-throughput screening (HTS). To extend performance and automation compatibility, we built a HyperCyt-linked Cluster Cytometer platform, a network of flow cytometers for analyzing samples displayed in high-density, 1,536-well plate format. To assess the performance, we used cell- and microsphere-based HTS assays that had been well characterized in the previous studies. Experiments addressed important technical issues: challenges of small wells (assay volumes 10 μL or less, reagent mixing, cell and particle suspension), detecting and correcting for differences in performance of individual flow cytometers, and the ability to reanalyze a plate in the event of problems encountered during the primary analysis. Boosting sample throughput an additional fourfold, this platform is uniquely positioned to synergize with expanding suspension array and cell barcoding technologies in which as many as 100 experiments are performed in a single well or sample. As high-performance flow cytometers shrink in cost and size, cluster cytometry promises to become a practical, productive approach for HTS, and other large-scale investigations of biological complexity.

Increasing evidence for and regulation of a human placental endogenous digitalis-like factor

Endogenous digitalis-like factors (EDLFs) appear to be hypertensiogenic and increased in the serum and placenta of women with preeclampsia (PE), a complication of pregnancy. Digibind, an anti-digoxin antibody Fab fragment, reverses in vitro effects of EDLF and in vivo features of PE. We used Digibind in a radioimmunoassay to measure EDLF and compared this to a bio-functional assay of EDLF with good agreement. These methods confirmed that human placenta was a source of EDLF, synthesizing and releasing EDLF into the media of cultured human placental tissue. Ketoconazole, a steroid synthesis inhibitor, and 17-OH progesterone, a possible substrate of steroid synthesis, were shown to inhibit or increase EDLF release respectively, suggesting overlap of synthetic pathways. Abnormalities of PE such as placental hypoxia, increased reactive oxygen species and increased pro-inflammatory cytokines were demonstrated to increase placental EDLF release. These findings strongly support placental production of EDLF with increased release due to features of PE.

Multinode acoustic focusing for parallel flow cytometry

Flow cytometry can simultaneously measure and analyze multiple properties of single cells or particles with high sensitivity and precision. Yet, conventional flow cytometers have fundamental limitations with regards to analyzing particles larger than about 70 μm, analyzing at flow rates greater than a few hundred microliters per minute, and providing analysis rates greater than 50,000 per second. To overcome these limits, we have developed multinode acoustic focusing flow cells that can position particles (as small as a red blood cell and as large as 107 μm in diameter) into as many as 37 parallel flow streams. We demonstrate the potential of such flow cells for the development of high throughput, parallel flow cytometers by precision focusing of flow cytometry alignment microspheres, red blood cells, and the analysis of a CD4+ cellular immunophenotyping assay. This approach will have significant impact toward the creation of high throughput flow cytometers for rare cell detection applications (e.g., circulating tumor cells), applications requiring large particle analysis, and high volume flow cytometry.

Binding and cell intoxication studies of anthrax lethal toxin

Anthrax lethal toxin (LT) is a major virulence factor of Bacillus anthracis. The vast majority of the anthrax toxin-related literature describes the assembly of LT as a cell-dependent process. However, some reports have provided evidence for the existence of a fully assembled LT, either in vitro or in the bloodstream of anthrax-infected animals. To follow up on this work, we present studies on fully-assembled LT. We first demonstrate facile and cell-free assembly and purification of LT. We then show that fully assembled LT binds an anthrax toxin receptor with almost 100-fold higher affinity than the protective antigen (PA) alone. Quantitative cell intoxication assays were used to determine the LD(50) (lethal dose 50) for LT. The cell-binding studies revealed that LT binds mammalian cells using a different mode from PA. Even when PA-specific receptors were blocked, fully assembled LT was able to bind the cell surface. Our studies support the existing evidence that LT fully assembles in the blood stream and can bind and intoxicate mammalian cells with very high affinity and efficacy. More importantly, the data presented here invoke the possibility that LT may bind cells in a receptor-independent fashion, or recognize receptors that do not interact with PA. Hence, blood borne LT may emerge as a novel therapeutic target for combating anthrax.

Development of phage-based single chain Fv antibody reagents for detection of Yersinia pestis

BACKGROUND

Most Yersinia pestis strains are known to express a capsule-like antigen, fraction 1 (F1)(.) F1 is encoded by the caf1 gene located on the large 100-kb pFra plasmid, which is found in Y. pestis but not in closely related species such as Yersinia enterocolytica and Yersinia pseudotuberculosis. In order to find antibodies specifically binding to Y. pestis we screened a large single chain Fv antibody fragment (scFv) phage display library using purified F1 antigen as a selection target. Different forms of the selected antibodies were used to establish assays for recombinant F1 antigen and Y. pestis detection.

METHODS

Phage antibody panning was performed against F1 in an automated fashion using the Kingfisher magnetic bead system. Selected scFvs were screened for F1-binding specificity by one-step alkaline phosphatase enzyme linked immunosorbant assay (ELISA), and assayed for binding to recombinant antigen and/or Y. pestis by flow cytometry and whole-cell ELISA.

RESULTS

Seven of the eight selected scFvs were shown to specifically bind both recombinant F1 and a panel of F1-positive Yersinia cells. The majority of the soluble scFvs were found to be difficult to purify, unstable and prone to cross-reactivity with F1-negative Yersinia strains, whereas phage displayed scFvs were found to be easy to purify/label and remarkably stable. Furthermore direct fluorescent labeling of phage displaying scFv allowed for an easy one-step flow cytometry assay. Slight cross-reactivity was observed when fixed cells were used in ELISA.

CONCLUSIONS

Our high throughput methods of selection and screening allowed for time and cost effective discovery of seven scFvs specifically binding Y. pestis F1 antigen. We describe implementation of different methods for phage-based immunoassay. Based on the success of these methods and the proven stability of phage, we indicate that the use of phage-displayed, rather than phage-free proteins, might generally overcome the shortcomings of scFv antibodies.

Correlation of cystatin-C with glomerular filtration rate by inulin clearance in pregnancy

OBJECTIVE

To test utility of cystatin-C as a marker of glomerular filtration rate during pregnancy, we performed serial correlations with inulin clearance during pregnancy and postpartum.

METHODS

Twelve subjects received inulin infusions and serum cystatin-C at three time points. Pearson's correlation coefficient was calculated.

RESULTS

Cystatin-C levels ranged 0.66-1.48 mg/L during pregnancy, and 0.72-1.26 mg/L postpartum. Inulin clearance ranged 130-188 mL/min during pregnancy, and 110-167 mL/min postpartum. Cystatin-C did not correlate with inulin clearance at any time point.

CONCLUSION

Serum cystatin-C did not correlate with inulin clearance during pregnancy or postpartum.

Rapid evaluation of the antibacterial activity of arylene-ethynylene compounds

A series of oligo(arylene-ethynylene) (1-3 repeat units) compounds functionalized with quaternary ammonium groups was screened for their antibacterial activity in the dark and with activation by long-wavelength (365 nm) UV irradiation. Several of these compounds have effective bactericidal activity (>99.9% killing) at concentrations between 0.01 and 10 μg/mL. Our approach uses flow cytometry to rapidly screen and evaluate the susceptibility of bacterial populations. The rapidity, high information content, and accuracy of this approach make it an extremely valuable method for the study of antibacterial compounds.

Microsphere-based flow cytometry protease assays for use in protease activity detection and high-throughput screening

This protocol describes microsphere-based protease assays for use in flow cytometry and high-throughput screening. This platform measures a loss of fluorescence from the surface of a microsphere due to the cleavage of an attached fluorescent protease substrate by a suitable protease enzyme. The assay format can be adapted to any site or protein-specific protease of interest and results can be measured in both real time and as endpoint fluorescence assays on a flow cytometer. Endpoint assays are easily adapted to microplate format for flow cytometry high-throughput analysis and inhibitor screening.

Digoxin immune fab treatment for severe preeclampsia

We evaluated the efficacy, safety, and biological mechanisms of digoxin immune Fab (DIF) treatment of severe preeclampsia. Fifty-one severe preeclamptic patients were randomized in double-blind fashion to DIF ( N = 24) or placebo ( N = 27) for 48 hours. Primary outcomes were change in creatinine clearance (CrCl) at 24 to 48 hours and antihypertensive drug use. Serum sodium pump inhibition, a sequela of endogenous digitalis-like factors (EDLF), was also assessed. CrCl in DIF subjects was essentially unchanged from baseline versus a decrease with placebo (-3 +/- 10 and -34 +/- 10 mL/min, respectively, P = 0.02). Antihypertensive use was similar between treatments (46 and 52%, respectively, P = 0.7). Serum sodium pump inhibition was decreased with DIF compared with placebo at 24 hours after treatment initiation (least squares mean difference, 19 percentage points, P = 0.03). DIF appeared to be well tolerated. These results suggest DIF prevents a decline in renal function in severe preeclampsia by neutralizing EDLF. Sodium pump inhibition was significantly improved. Further research is warranted.