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 Molndal campus of the University of Gothenburg, Sweden. Each round consists of three quality control samples. Results Forty laboratories participated. Twenty-six used INNOTESTenzyme-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.

Background The cerebrospinal fluid (CSF) biomarkers amyloid beta 1–42, total tau, and phosphorylated tau are used increasingly for Alzheimer’s disease (AD) research and patient management. However, there are large variations in biomarker measurements among and within laboratories. Methods Data from the first nine rounds of the Alzheimer’s Association quality control program was used to define the extent and sources of analytical variability. In each round, three CSF samples prepared at the Clinical Neurochemistry Laboratory (Mölndal, Sweden) were analyzed by single-analyte enzyme-linked immunosorbent assay (ELISA), a multiplexing xMAP assay, or an immunoassay with electrochemoluminescence detection. Results A total of 84 laboratories participated. Coefficients of variation (CVs) between laboratories were around 20% to 30%; within-run CVs, less than 5% to 10%; and longitudinal within-laboratory CVs, 5% to 19%. Interestingly, longitudinal within-laboratory CV differed between biomarkers at individual laboratories, suggesting that a component of it was assay dependent. Variability between kit lots and between laboratories both had a major influence on amyloid beta 1–42 measurements, but for total tau and phosphorylated tau, between-kit lot effects were much less than between-laboratory effects. Despite the measurement variability, the between-laboratory consistency in classification of samples (using prehoc-derived cutoffs for AD) was high (>90% in 15 of 18 samples for ELISA and in 12 of 18 samples for xMAP). Conclusions The overall variability remains too high to allow assignment of universal biomarker cutoff values for a specific intended use. Each laboratory must ensure longitudinal stability in its measurements and use internally qualified cutoff levels. Further standardization of laboratory procedures and improvement of kit performance will likely increase the usefulness of CSF AD biomarkers for researchers and clinicians.

An 85-kDa Group VI phospholipase A 2 enzyme (iPLA 2 ) that does not require Ca 2؉ 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 iPLA 2 isoforms other than the 88-kDa protein. We have cloned cDNA species that encode two distinct iPLA 2 isoforms from human pancreatic islet RNA and a human insulinoma cDNA library. One isoform is an 85-kDa protein (short isoform of human iPLA 2 (SH-iPLA 2 )) and the other an 88-kDa protein (long isoform of human iPLA 2 (LH-iPLA 2 )). Transcripts encoding both isoforms are also observed in human promonocytic U937 cells. Recombinant SH-iPLA 2 and LH-iPLA 2 are both catalytically active in the absence of Ca 2؉ and inhibited by a bromoenol lactone suicide substrate, but LH-iPLA 2 is activated by ATP, whereas SH-iPLA 2 is not. The human iPLA 2 gene has been found to reside on chromosome 22 in region q13.1 and to contain 16 exons represented in the LH-iPLA 2 transcript. Exon 8 is not represented in the SH-iPLA 2 transcript, indicating that it arises by an exon-skipping mechanism of alternative splicing. The amino acid sequence encoded by exon 8 of the human iPLA 2 gene is proline-rich and shares a consensus motif of PX 5 PX 8 HHPX 12 NX 4 Q with the proline-rich middle linker domains of the Smad proteins DAF-3 and Smad4.

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 Ն7%).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 Ն1.0% 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 Ͻ 0.05), with median changes of 93, Ϫ7, and Ϫ13% 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 ϭ Ϫ0.6459 and Ϫ0.6751, respectively; both P Ͻ 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.

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.

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.

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A transcription termination factor (Rho) was purified from the Gram-positive bacterium Micrococcus luteus, and the complete gene sequence was determined. The M. luteus Rho polypeptide has 690 residues, which is 271 residues more than its homolog from Escherichia coli. Most of the additional residues compose a highly charged, hydrophilic segment that is inserted in a nonconserved region between two conserved regions of the RNA-binding domain of the known Rho homolog proteins. This segment extends from residues 49 to 311 and includes a stretch of 238 residues that contain no hydrophobic side chains. Biochemical studies indicate that the M. luteus protein is very similar to E. coli Rho in terms of its RNA-dependent NTPase activity and its sensitivity to the Rho-specific inhibitor bicyclomycin. However, the M. luteus protein has a less stringent RNA cofactor specificity. It also acts to terminate RNA transcription with E. coli RNA polymerase on the cro DNA template, but at much earlier termination stop points than those recognized by E. coli Rho. Thus, the M. luteus protein functions as a true Rho factor, but with a different specificity than that of E. coli Rho. We propose that this altered specificity is consistent with its need to function on transcripts that have a high content of G ؉ C residues.The orderly expression of the genetic information in DNA segments into RNA molecules depends on the function of transcription terminators. In Escherichia coli, one mechanism of transcription termination is mediated in part by an essential protein factor called Rho (1). Rho factor from E. coli has been studied since its discovery nearly 25 years ago (2). The Rho monomer is a 47-kDa protein. However, Rho factor functions as a homohexamer (3) that can bind to a nascent transcript and mediate its release by actions on the transcription complex that are coupled to the hydrolysis of NTPs (1).A recent phylogenetic study by Opperman and Richardson (4) comparing rho genes isolated from organisms from several of the major branches of bacteria suggests that Rho is ubiquitous throughout the bacterial domain. An unexpected result was discovered during the analysis of the rho gene from Micrococcus luteus, a Gram-positive soil bacterium that has an unusually high G ϩ C DNA content (74%) (5). The M. luteus rho homolog was found to have an open reading frame encoding a protein that was homologous to E. coli Rho through a very long portion. However, the homology did not extend all the way through the RNA-binding domain toward the amino terminus of the protein. Because the region of homology starts in a segment that has an in-frame GTG codon preceded by a sequence that is a good match to a Shine-Dalgarno sequence, Opperman and Richardson proposed that translation began at that GTG codon to yield a 41,733-Da protein of 382 amino acids that is 52% identical (71% similar) to E. coli Rho. If this proposal were correct, the M. luteus Rho protein would be unusual in comparison with the other Rho homologs as it would lack a conserved part of its ...