Therapeutic blood-brain barrier modulation and stroke treatment by a bioengineered FZD4-selective WNT surrogate in mice

Derangements of the blood-brain barrier (BBB) or blood-retinal barrier (BRB) occur in disorders ranging from stroke, cancer, diabetic retinopathy, and Alzheimer's disease. The Norrin/FZD4/TSPAN12 pathway activates WNT/β-catenin signaling, which is essential for BBB and BRB function. However, systemic pharmacologic FZD4 stimulation is hindered by obligate palmitoylation and insolubility of native WNTs and suboptimal properties of the FZD4-selective ligand Norrin. Here, we develop L6-F4-2, a non-lipidated, FZD4-specific surrogate which significantly improves subpicomolar affinity versus native Norrin. In Norrin knockout (NdpKO) mice, L6-F4-2 not only potently reverses neonatal retinal angiogenesis deficits, but also restores BRB and BBB function. In adult C57Bl/6J mice, post-stroke systemic delivery of L6-F4-2 strongly reduces BBB permeability, infarction, and edema, while improving neurologic score and capillary pericyte coverage. Our findings reveal systemic efficacy of a bioengineered FZD4-selective WNT surrogate during ischemic BBB dysfunction, with potential applicability to adult CNS disorders characterized by an aberrant blood-brain barrier.

Cross-reactivity profiles of legumes and tree nuts using the xMAP® multiplex food allergen detection assay

The homology between proteins in legumes and tree nuts makes it common for individuals with food allergies to be allergic to multiple legumes and tree nuts. This propensity for allergenic and antigenic cross-reactivity means that commonly employed commercial immunodiagnostic assays (e.g., dipsticks) for the detection of food allergens may not always accurately detect, identify, and quantitate legumes and tree nuts unless additional orthogonal analytical methods or secondary measures of analysis are employed. The xMAP^® Multiplex Food Allergen Detection Assay (FADA) was used to determine the cross-reactivity patterns and the utility of multi-antibody antigenic profiling to distinguish between legumes and tree nuts. Pure legumes and tree nuts extracted using buffered detergent displayed a high level of cross-reactivity that decreased upon dilution or by using a buffer (UD buffer) designed to increase the stringency of binding conditions and reduce the occurrence of false positives due to plant-derived lectins. Testing for unexpected food allergens or the screening for multiple food allergens often involves not knowing the identity of the allergen present, its concentration, or the degree of modification during processing. As such, the analytical response measured may represent multiple antigens of varying antigenicity (cross-reactivity). This problem of multiple potential analytes is usually unresolved and the focus becomes the primary analyte, the antigen the antibody was raised against, or quantitative interpretation of the content of the analytical sample problematic. The alternative solution offered here to this problem is the use of an antigenic profile as generated by the xMAP FADA using multiple antibodies (bead sets). By comparing the antigenic profile to standards, the allergen may be identified along with an estimate of the concentration present. Cluster analysis of the xMAP FADA data was also performed and agreed with the known phylogeny of the legumes and tree nuts being analyzed. Graphical abstract The use of cluster analysis to compare the multi-antigen profiles of food allergens.

Multiplex detection of food allergens and gluten

To help safeguard the food supply and detect the presence of undeclared food allergens and gluten, most producers and regulatory agencies rely on commercial test kits. Most of these are ELISAs with a few being PCR-based. These methods are very sensitive and analyte specific, requiring different assays to detect each of the different food allergens. Mass spectrometry offers an alternative approach whereby multiple allergens may be detected simultaneously. However, mass spectrometry requires expensive equipment, highly trained analysts, and several years before a quantitative approach can be achieved. Using multianalyte profiling (xMAP®) technology, a commercial multiplex test kit based on the use of established antibodies was developed for the simultaneous detection of up to 14 different food allergens plus gluten. The assay simultaneously detects crustacean seafood, egg, gluten, milk, peanut, soy, and nine tree nuts (almond, Brazil nut, cashew, coconut, hazelnut, macadamia, pine nut, pistachio, and walnut). By simultaneously performing multiple tests (typically two) for each analyte, this magnetic bead-based assay offers built-in confirmatory analyses without the need for additional resources. Twenty-five of the assays were performed on buffer extracted samples, while five were conducted on samples extracted using reduced-denatured conditions. Thus, complete analysis for all 14 allergens and gluten requires only two wells of a 96-well microtiter plate. This makes it possible to include in a single analytical run up to 48 samples. All 30 bead sets in this multiplex assay detected 5 ng/mL of food allergen and gluten with responses greater than background. In addition, 26 of the bead sets displayed signal/noise ratios of five or greater. The bead-based design makes this 30-plex assay expandable to incorporate new antibodies and capture/detector methodologies by ascribing these new detectors to any of the unassigned bead sets that are commercially available.

The impact of decreased bead count to determine concentrations of amyloid beta1-42, total-tau, and phosphorylated-tau181 in human cerebrospinal fluid using xMAP technology

Alzheimer's disease is the leading cause of human dementia. The lack of diagnostic tests and limited therapeutic options has driven the search for endogenous biomarkers. The INNO-BIA AlzBio3 assay is a multiplex flow-based immunoassay measuring Aβ42, tau, and p-tau in cerebrospinal fluid (CSF). This study assesses assays performance under varying bead count (BC) parameters. Original method validation parameters at 100 BC were acceptable. Reanalyses performed at 3, 10, 25, and 50 BCs were compared to 100 BC data by ANOVA, Bland-Altman analysis, evaluation of concordance correlation coefficients, and frequency distribution of coefficient of variation (CV) ranges. Method validation characteristics were acceptable with 100 BCs. Equivalency for 25 and 50 versus 100 BCs was demonstrated, but not for 3 and 10 BCs. A general trend of decreasing agreement between decreasing BCs and the 100 BC reference resulted in decreases in concordance coefficients ρ(c) . The frequency of CV values greater than 20% increased with decreasing BCs, and CV values of 5% or less decreased with decreased BCs. Statistical analyses demonstrate that BCs of 3 and 10 are not equivalent with the reference and should not be used as a basis for determination of Aβ42, tau, and p-tau concentration in human CSF.

The Alzheimer's Association external quality control program for cerebrospinal fluid biomarkers

BACKGROUND

The cerebrospinal fluid (CSF) biomarkers amyloid β (Aβ)-42, total-tau (T-tau), and phosphorylated-tau (P-tau) demonstrate good diagnostic accuracy for Alzheimer's disease (AD). However, there are large variations in biomarker measurements between studies, and between and within laboratories. The Alzheimer's Association has initiated a global quality control program to estimate and monitor variability of measurements, quantify batch-to-batch assay variations, and identify sources of variability. In this article, we present the results from the first two rounds of the program.

METHODS

The program is open for laboratories using commercially available kits for Aβ, T-tau, or P-tau. CSF samples (aliquots of pooled CSF) are sent for analysis several times a year from the Clinical Neurochemistry Laboratory at the Mölndal campus of the University of Gothenburg, Sweden. Each round consists of three quality control samples.

RESULTS

Forty laboratories participated. Twenty-six used INNOTEST enzyme-linked immunosorbent assay kits, 14 used Luminex xMAP with the INNO-BIA AlzBio3 kit (both measure Aβ-(1-42), P-tau(181P), and T-tau), and 5 used Meso Scale Discovery with the Aβ triplex (AβN-42, AβN-40, and AβN-38) or T-tau kits. The total coefficients of variation between the laboratories were 13% to 36%. Five laboratories analyzed the samples six times on different occasions. Within-laboratory precisions differed considerably between biomarkers within individual laboratories.

CONCLUSIONS

Measurements of CSF AD biomarkers show large between-laboratory variability, likely caused by factors related to analytical procedures and the analytical kits. Standardization of laboratory procedures and efforts by kit vendors to increase kit performance might lower variability, and will likely increase the usefulness of CSF AD biomarkers.

Best practices during bioanalytical method validation for the characterization of assay reagents and the evaluation of analyte stability in assay standards, quality controls, and study samples

Characterization of the stability of analytes in biological samples collected during clinical studies together with that of critical assay reagents, including analyte stock solutions, is recognized as an important component of bioanalytical assay validation. Deficiencies in these areas often come to light during regulatory inspections. Best practices, based on current regulatory guidance, for the assessment of these issues as they pertain to ligand binding and chromatographic assays are covered in this review. Additionally, consensus recommendations reached during the recent AAPS/FDA Workshop on bioanalytical assay validation are highlighted.

Evaluation of an assay for serum 1,5-anhydroglucitol (GlycoMark) and determination of reference intervals on the Hitachi 917 analyzer

BACKGROUND

1,5-Anhydroglucitol (1,5-AG) is a glucose analogue, which is decreased in hyperglycemic individuals. We report the technical performance of an assay (GlycoMark) on a chemistry analyzer, evaluation of analyte stability and determination of reference intervals for 1,5-AG in a non-diabetic US population.

METHODS

NCCLS protocols were followed to evaluate the reagent on a Hitachi 917 chemistry analyzer.

RESULTS

Intra- and interassay imprecision ranged from 1.3% to 3.8% and 0.79% to 3.7%, respectively. The assay was linear to 110 microg/ml. Interference from triglyceride, hemoglobin and bilirubin was <10% to concentrations of 12.6 mmol/l, 12.1 and 911.4 micromol/l, respectively. Correlation coefficients between lot numbers on the Hitachi 917 and between analyses on the Hitachi 917 and the Hitachi 7170 analyzers were >0.99. The lowest limit of detection was 0.49 microg/ml (mean+/-2 S.D.). 1,5-AG was stable at 4 degrees C for 7 days, at 22 degrees C for 5 days, at -80 degrees C for 14 days and for three freeze-thaw cycles at -80 degrees C. The US reference intervals (nonparametric 2.5th-97.5th percentiles) were 10.2-33.8 microg/ml (males) and 5.9-31.8 microg/ml (females).

CONCLUSIONS

The performance of the GlycoMark assay for the measurement of 1,5-AG was acceptable on the Hitachi 917 analyzer.

Circulating 1,5-anhydroglucitol levels in adult patients with diabetes reflect longitudinal changes of glycemia: a U.S. trial of the GlycoMark assay

OBJECTIVE

1,5-Anhydroglucitol (1,5AG) is a major circulating polyol arising primarily from ingestion and excreted competitively with glucose. Japanese studies have demonstrated reduced concentrations of 1,5AG in serum in hyperglycemic patients in comparison with euglycemic subjects and a gradual normalization of 1,5AG values for patients responding to antihyperglycemic therapies. In this first U.S. study, we assessed the ability of 1,5AG measurements to monitor glycemic control in a cohort of 77 patients with diabetes (22 with type 1 diabetes, 55 with type 2 diabetes) who presented with suboptimal glycemic control at baseline (defined as HbA(1c) >or=7%).

RESEARCH DESIGN AND METHODS

Each patient received therapies consisting of combinations of diabetes education, nutritional counseling, and addition or dose adjustment of various insulins or oral antihyperglycemic medications. Therapy was targeted to reduce mean HbA(1c) by >or=1.0% over the monitoring period. 1,5AG, HbA(1c), fructosamine, and random glucose measurements were performed at baseline and at 2, 4, and 8 weeks after the initiation of therapy.

RESULTS

1,5AG, fructosamine, and glucose values progressed significantly toward euglycemia by week 2 of monitoring (Wilcoxon's signed-rank test, P < 0.05), with median changes of 93, -7, and -13% for 1,5AG, fructosamine, and glucose, respectively. In contrast, HbA(1c) values did not respond significantly to therapy until week 4. On an individual patient basis, 89.6% of patients displayed longitudinal changes of 1,5AG from baseline to week 8 in concordance with HbA(1c). 1,5AG was also highly correlated with HbA(1c) and fructosamine (Spearman rho = -0.6459 and -0.6751, respectively; both P < 0.0001).

CONCLUSIONS

We conclude that 1,5AG responds sensitively and rapidly to changes in glycemia and monitors glycemic control in accordance with established markers.

Multicenter analytical performance evaluation of the Elecsys® proBNP assay

The purpose of this multicenter study was to evaluate the technical performance of the automated Elecsys proBNP (brain natriuretic peptide) assay, which is indicated as an aid in the diagnosis of individuals suspected of having congestive heart failure. The Elecsys proBNP assay is an electrochemiluminescent immunoassay employing two polyclonal NT-proBNP-specific antibodies in a sandwich test format. The study was performed on the three Elecsys analyzers (E 1010, E 2010, and E 170) at eight different sites world-wide. Within- and total precision were ≤3%, with total precision slightly higher on the Elecsys E 170 instrument with multiple modules. Reproducibility among sites and platforms was <5%. Precision at particularly low NT-proBNP concentrations was assessed down to approximately 25 pg/ml with CVs of 12.6% at 29.2 pg/ml and 9.6% at 38.5 pg/ml for the Elecsys 1010/2010 and E 170, respectively. Linearity was evaluated up to 25,000 pg/ml with a sample-based non-linear response observed with recoveries of <90% for proBNP concentrations <10 000 pg/ml. Slopes ranged between 0.92 and 1.02 and intercepts from –5.3 to 10.4 pg/ml (r≥0.998) among the three types of analyzers. Slopes were 4.95 and 4.53 in comparison to the Biosite Triage and Shionogi BNP assays. There was no assay interference, and no effect of barrier gels, tube composition, or freeze-thaw. NT-proBNP concentrations in EDTA plasma were up to 10% lower than in serum or heparinized plasma and the analyte was stable at 4°C for up to 72 hours (the maximum time tested). There was no circadian rhythm in normal subjects or congestive heart failure patients and there was no effect of drawing position. In summary, the Elecsys proBNP assay exhibits good technical performance and is suitable for use in routine clinical laboratories to aid in the diagnosis of congestive heart failure.

Electrospray ionization/mass spectrometric analyses of human promonocytic U937 cell glycerolipids and evidence that differentiation is associated with membrane lipid composition changes that facilitate phospholipase A2 activation

Upon differentiation, U937 promonocytic cells gain the ability to release a large fraction of arachidonate esterified in phospholipids when stimulated, but the mechanism is unclear. U937 cells express group IV phospholipase A(2) (cPLA(2)), but neither its level nor its phosphorylation state increases upon differentiation. A group VI PLA(2) (iPLA(2)) that is sensitive to a bromoenol lactone inhibitor catalyzes arachidonate hydrolysis from phospholipids in some cells and facilitates arachidonate incorporation into glycerophosphocholine (GPC) lipids in others, but it is not known whether U937 cells express iPLA(2). We confirm that ionophore A23187 induces substantial [(3)H]arachidonate release from differentiated but not control U937 cells, and electrospray ionization mass spectrometric (ESI/MS) analyses indicate that differentiated cells contain a higher proportion of arachidonate-containing GPC species than control cells. U937 cells express iPLA(2) mRNA and activity, but iPLA(2) inhibition impairs neither [(3)H]arachidonate incorporation into nor release from U937 cells. Experiments with phosphatidate phosphohydrolase (PAPH) and phospholipase D (PLD) inhibitors coupled with ESI/MS analyses of PLD-PAPH products indicate that differentiated cells gain the ability to produce diacylglycerol (DAG) via PLD-PAPH. DAG promotes arachidonate release by a mechanism that does not require DAG hydrolysis, is largely independent of protein kinase C, and requires cPLA(2) activity. This may reflect DAG effects on cPLA(2) substrate state.

Distinction among eight opiate drugs in urine by gas chromatography-mass spectrometry

Opiates are commonly abused substances, and forensic urine drug-testing for them requires gas chromatographic-mass spectrometric (GC-MS) confirmation. There are also medical reasons to test urine for opiates, and confirmation procedures other than GC-MS are often used for medical drug-testing. A thin-layer chromatographic (TLC) method distinguishes morphine, acetylmorphine, hydromorphone, oxymorphone, codeine, dihydrocodeine, hydrocodone, and oxycodone in clinical specimens. In certain clinical circumstances, GC-MS confirmation is requested for opiates identified by TLC, but, to our knowledge, no previous report examines all of the above opiates in a single GC-MS procedure. We find that they can be distinguished by GC-MS analyses of trimethylsilyl (TMS) ether derivatives, and identities of 6-keto opiates can be further confirmed by GC-MS analysis of methoxime (MO)-TMS derivatives. Inclusion of deuterium-labeled internal standards permits identification of the opiates in urine at concentrations below the TLC cutoff level of 600 ng/ml, and the GC-MS assay is linear over a concentration range that spans that level. This GC-MS procedure has proved useful as a third-stage identification step in a medical drug-testing sequence involving prior immunoassay and TLC.

Human pancreatic islets express mRNA species encoding two distinct catalytically active isoforms of group VI phospholipase A2 (iPLA2) that arise from an exon-skipping mechanism of alternative splicing of the transcript from the iPLA2 gene on chromosome 22q13.1

An 85-kDa Group VI phospholipase A2 enzyme (iPLA2) that does not require Ca2+ for catalysis has recently been cloned from three rodent species. A homologous 88-kDa enzyme has been cloned from human B-lymphocyte lines that contains a 54-amino acid insert not present in the rodent enzymes, but human cells have not previously been observed to express catalytically active iPLA2 isoforms other than the 88-kDa protein. We have cloned cDNA species that encode two distinct iPLA2 isoforms from human pancreatic islet RNA and a human insulinoma cDNA library. One isoform is an 85-kDa protein (short isoform of human iPLA2 (SH-iPLA2)) and the other an 88-kDa protein (long isoform of human iPLA2 (LH-iPLA2)). Transcripts encoding both isoforms are also observed in human promonocytic U937 cells. Recombinant SH-iPLA2 and LH-iPLA2 are both catalytically active in the absence of Ca2+ and inhibited by a bromoenol lactone suicide substrate, but LH-iPLA2 is activated by ATP, whereas SH-iPLA2 is not. The human iPLA2 gene has been found to reside on chromosome 22 in region q13.1 and to contain 16 exons represented in the LH-iPLA2 transcript. Exon 8 is not represented in the SH-iPLA2 transcript, indicating that it arises by an exon-skipping mechanism of alternative splicing. The amino acid sequence encoded by exon 8 of the human iPLA2 gene is proline-rich and shares a consensus motif of PX5PX8HHPX12NX4Q with the proline-rich middle linker domains of the Smad proteins DAF-3 and Smad4. Expression of mRNA species encoding two active iPLA2 isoforms with distinguishable catalytic properties in two different types of human cells demonstrated here may have regulatory or functional implications about the roles of products of the iPLA2 gene in cell biologic processes.

Mass spectrometric evidence that agents that cause loss of Ca2+ from intracellular compartments induce hydrolysis of arachidonic acid from pancreatic islet membrane phospholipids by a mechanism that does not require a rise in cytosolic Ca2+ concentration

Stimulation of pancreatic islets with glucose induces phospholipid hydrolysis and accumulation of nonesterified arachidonic acid, which may amplify the glucose-induced Ca2+ entry into islet beta-cells that triggers insulin secretion. Ca2+ loss from beta-cell intracellular compartments has been proposed to induce both Ca2+ entry and events dependent on arachidonate metabolism. We examine here effects of inducing Ca2+ loss from intracellular sequestration sites with ionophore A23187 and thapsigargin on arachidonate hydrolysis from islet phospholipids. A23187 induces a decline in islet arachidonate-containing phospholipids and release of nonesterified arachidonate. A23187-induced arachidonate release is of similar magnitude when islets are stimulated in Ca2+-replete or in Ca2+-free media or when islets loaded with the intracellular Ca2+ chelator BAPTA are stimulated in Ca2+-free medium, a condition in which A23187 induces no rise in beta-cell cytosolic [Ca2+]. Thapsigargin also induces islet arachidonate release under these conditions. A23187- or thapsigargin-induced arachidonate release is prevented by a bromoenol lactone (BEL) inhibitor of a beta-cell phospholipase A2 (iPLA2), which does not require Ca2+ for catalytic activity and which is negatively modulated by and physically interacts with calmodulin by Ca2+-dependent mechanisms. Agents that cause Ca2+ loss from islet intracellular compartments thus induce arachidonate hydrolysis from phospholipids by a BEL-sensitive mechanism that does not require a rise in cytosolic [Ca2+], and a BEL-sensitive enzyme-like iPLA2 or a related membranous activity may participate in sensing Ca2+ compartment content.

Electrospray ionization mass spectrometric analyses of phospholipids from rat and human pancreatic islets and subcellular membranes: comparison to other tissues and implications for membrane fusion in insulin exocytosis

Glucose-induced insulin secretion from pancreatic islets involves hydrolysis of arachidonic acid from phospholipids as an intermediary event. Accumulation of nonesterified arachidonate in islet membranes may influence both ion fluxes that trigger insulin secretion and fusion of secretory granule and plasma membranes. Recent findings indicate that plasmenylethanolamine species may also participate in fusion of such membranes, but high-performance liquid chromatographic (HPLC) and gas chromatographic/mass spectrometric (GC/MS) analyses of islet secretory granule phospholipids suggested that they contain little plasmenylethanolamine. Here, electrospray ionization mass spectrometry (ESI/MS) of intact phospholipid molecules is used to demonstrate that the most prominent components of all major glycerophospholipid headgroup classes in islets are arachidonate-containing species. Such species contribute the majority of the ESI/MS negative ion current from rat and human islet glycerophosphoethanolamine (GPE), and the fraction of GPE negative ion current contributed by plasmenylethanolamine species in rat islets is higher than that for rat liver or heart and similar to that for brain. The most prominent sn-2 substituent of plasmenylethanolamine species in brain is docosahexaenoate and in islets is arachidonate. Arachidonate-containing plasmenylethanolamine species are also prominent components of GPE from islet secretory granules and plasma membranes. Fusion of islet secretory granule and plasma membranes is demonstrated to be catalyzed by cytosolic components from insulinoma cells and rat brain with chromatographic similarities to a rabbit brain factor that specifically catalyzes fusion of plasmenylethanolamine-containing membranes.

Endocytosis and degradation of bovine apo- and holo-lactoferrin by isolated rat hepatocytes are mediated by recycling calcium-dependent binding sites

We characterized endocytosis of iron-saturated (holo) and iron-depleted (apo) 125I-labeled bovine lactoferrin (Lf) by isolated rat hepatocytes. Hepatocytes ingested both Lf forms--determined by EGTA/dextran sulfate removal of surface-bound Lf--at maximal endocytic rates of 1.85 and 1.52 fmol cell-1 min-1 for 125I-apo-Lf and 125I-holo-Lf, respectively. First-order endocytic rate constants (37 degrees C) for 125I-apo-Lf and 125I-holo-Lf were 0.276 and 0.292 min-1, respectively. Regardless of Lf's iron content, hyperosmotic media (approximately 500 mmol/kg) inhibited Lf uptake by approximately 90%, indicating endocytosis of both Lf forms was primarily clathrin-dependent. Endocytosis of both Lf forms was not altered significantly in the presence of excess iron chelator desferrioxamine or rat holo-transferrin, or by cycloheximide treatment. Fluorescein isothiocyanate- and cyclohexanedione-modified Lf competed fully with native Lf for binding and endocytosis, indicating that, unlike human Lf, modification of lysine or arginine residues does not block the interaction of bovine Lf with cells. After binding Lf at 4 degrees C, cells at 37 degrees C internalized approximately 90% of Lf bound to Ca(2+)-dependent sites but not Lf bound to Ca(2+)-independent sites. Following uptake, hepatocytes released acid-soluble (degraded) products of 125I-Lf biphasically at 37 degrees C, an initial rapid phase within the first 20 min--more pronounced with 125I-holo-Lf--followed by a sustained linear release of 298 and 355 molecule equiv cell-1 min-1 for 125I-apo-Lf and 125I-holo-Lf, respectively. At 4 degrees C, both digitonin-permeabilized and intact cells bound approximately 1.1 x 10(6) 125I-Lf molecules to Ca(2+)-dependent sites per cell, indicating that hepatocytes do not contain a sizeable intracellular pool of these sites. Moreover, cells retained > 70% of Ca(2+)-dependent sites on the surface during sustained Lf endocytosis. Thus, these Lf binding sites recycle during endocytosis at an estimated 4-5 min/circuit.