Organophosphorus nerve agents (OPNAs) are toxic compounds that are classified as prohibited Schedule 1 chemical weapons. In the body, OPNAs bind to butyrylcholinesterase (BChE) to form nerve agent adducts (OPNA-BChE). OPNA-BChE adducts can provide a reliable, long-term protein biomarker for assessing human exposure. A major challenge facing OPNA-BChE detection is hydrolysis (aging), which can continue to occur after a clinical specimen has been collected. During aging, the o-alkyl phosphoester bond hydrolyzes, and the specific identity of the nerve agent is lost. To better identify OPNA exposure events, a high-throughput method for the detection of five aged OPNA-BChE adducts was developed. This is the first diagnostic panel to allow for the simultaneous quantification of any Chemical Weapons Convention Schedule 1 OPNA by measuring the aged adducts methyl phosphonate, ethyl phosphonate, propyl phosphonate, ethyl phosphoryl, phosphoryl and unadducted BChE. The calibration range for all analytes is 2.00-250. ng/mL, which is consistent with similar methodologies used to detect unaged OPNA-BChE adducts. Each analytical run is 3 min, making the time to first unknown results, including calibration curve and quality controls, less than 1 h. Analysis of commercially purchased individual serum samples demonstrated no potential interferences with detection of aged OPNA-BChE adducts, and quantitative measurements of endogenous levels of BChE were similar to those previously reported in other OPNA-BChE adduct assays.
In this study, a data-dependent, high-resolution tandem mass spectrometry (ddHRMS/MS) method capable of detecting all organophosphorus nerve agent (OPNA) adducts to human butyrylcholinesterase (BChE) was developed. After an exposure event, immunoprecipitation from blood with a BChE-specific antibody and digestion with pepsin produces a nine amino acid peptide containing the OPNA adduct. Signature product ions of this peptic BChE nonapeptide (FGES*AGAAS) offer a route to broadly screen for OPNA exposure. Taking this approach on an HRMS instrument identifies biomarkers, including unknowns, with high mass accuracy. Using a set of pooled human sera exposed to OPNAs as quality control (QC) materials, the developed method successfully identified precursor ions with <1 ppm and tied them to signature product ions with <5 ppm deviation from their chemical formulas. This high mass accuracy data from precursor and product ions, collected over 23 independent immunoprecipitation preparations, established method operating limits. QC data and experiments with 14 synthetic reference peptides indicated that reliable qualitative identification of biomarkers was possible for analytes >15 ng/mL. The developed method was applied to a convenience set of 96 unexposed serum samples and a blinded set of 80 samples treated with OPNAs. OPNA biomarkers were not observed in convenience set samples and no false positive or negative identifications were observed in blinded samples. All biomarkers in the blinded serum set >15 ng/mL were correctly identified. For the first time, this study reports a ddHRMS/MS method capable of complementing existing quantitative methodologies and suitable for identifying exposure to unknown organophosphorus agents.
Tri-ortho-cresyl phosphate (ToCP) is an anti-wear, flame retardant additive used in industrial lubricants, hydraulic fluids and gasoline. The neurotoxic effects of ToCP arise from the liver-activated metabolite 2-(o-cresyl)-4H-1,3,2-benzodioxaphosphoran-2-one (cresyl saligenin phosphate or CBDP), which inhibits esterase enzymes including butyrylcholinesterase (BChE). Following BChE adduction, CBDP undergoes hydrolysis to form the aged adduct ortho-cresyl phosphoserine (oCP-BChE), thus providing a biomarker of CBDP exposure. Previous studies have identified ToCP in aircraft cabin and cockpit air, but assessing human exposure has been hampered by the lack of a laboratory assay to confirm exposure. This work presents the development of an immunomagnetic-UHPLC-MS/MS method for the quantitation of unadducted BChE and the long-term CBDP biomarker, oCP-BChE, in human serum. The method has a reportable range from 2.0 ng/ml to 150 ng/ml, which is consistent with the sensitivity of methods used to detect organophosphorus nerve agent protein adducts. The assay demonstrated high intraday and interday accuracy (>/=85%) and precision (RSD </= 15%) across the calibration range. The method was developed for future analyses of potential human exposure to CBDP. Analysis of human serum inhibited in vitro with CBDP demonstrated that the oCP-BChE adduct was stable for at least 72 h at 4, 22 and 37 degrees C. Compared to a previously reported assay, this method requires 75% less sample volume, reduces analysis time by a factor of 20 and demonstrates a threefold improvement in sensitivity. Published 2015. This article is a U.S. Government work and is in the public domain in the USA.
The reference sequence for each human chromosome provides the framework for understanding genome function, variation and evolution. Here we report the finished sequence and biological annotation of human chromosome 1. Chromosome 1 is gene-dense, with 3,141 genes and 991 pseudogenes, and many coding sequences overlap. Rearrangements and mutations of chromosome 1 are prevalent in cancer and many other diseases. Patterns of sequence variation reveal signals of recent selection in specific genes that may contribute to human fitness, and also in regions where no function is evident. Fine-scale recombination occurs in hotspots of varying intensity along the sequence, and is enriched near genes. These and other studies of human biology and disease encoded within chromosome 1 are made possible with the highly accurate annotated sequence, as part of the completed set of chromosome sequences that comprise the reference human genome.
African trypanosomes cause human sleeping sickness and livestock trypanosomiasis in sub-Saharan Africa. We present the sequence and analysis of the 11 megabase-sized chromosomes of Trypanosoma brucei. The 26-megabase genome contains 9068 predicted genes, including approximately 900 pseudogenes and approximately 1700 T. brucei-specific genes. Large subtelomeric arrays contain an archive of 806 variant surface glycoprotein (VSG) genes used by the parasite to evade the mammalian immune system. Most VSG genes are pseudogenes, which may be used to generate expressed mosaic genes by ectopic recombination. Comparisons of the cytoskeleton and endocytic trafficking systems with those of humans and other eukaryotic organisms reveal major differences. A comparison of metabolic pathways encoded by the genomes of T. brucei, T. cruzi, and Leishmania major reveals the least overall metabolic capability in T. brucei and the greatest in L. major. Horizontal transfer of genes of bacterial origin has contributed to some of the metabolic differences in these parasites, and a number of novel potential drug targets have been identified.
The social amoebae are exceptional in their ability to alternate between unicellular and multicellular forms. Here we describe the genome of the best-studied member of this group, Dictyostelium discoideum. The gene-dense chromosomes of this organism encode approximately 12,500 predicted proteins, a high proportion of which have long, repetitive amino acid tracts. There are many genes for polyketide synthases and ABC transporters, suggesting an extensive secondary metabolism for producing and exporting small molecules. The genome is rich in complex repeats, one class of which is clustered and may serve as centromeres. Partial copies of the extrachromosomal ribosomal DNA (rDNA) element are found at the ends of each chromosome, suggesting a novel telomere structure and the use of a common mechanism to maintain both the rDNA and chromosomal termini. A proteome-based phylogeny shows that the amoebozoa diverged from the animal-fungal lineage after the plant-animal split, but Dictyostelium seems to have retained more of the diversity of the ancestral genome than have plants, animals or fungi.
The human X chromosome has a unique biology that was shaped by its evolution as the sex chromosome shared by males and females. We have determined 99.3% of the euchromatic sequence of the X chromosome. Our analysis illustrates the autosomal origin of the mammalian sex chromosomes, the stepwise process that led to the progressive loss of recombination between X and Y, and the extent of subsequent degradation of the Y chromosome. LINE1 repeat elements cover one-third of the X chromosome, with a distribution that is consistent with their proposed role as way stations in the process of X-chromosome inactivation. We found 1,098 genes in the sequence, of which 99 encode proteins expressed in testis and in various tumour types. A disproportionately high number of mendelian diseases are documented for the X chromosome. Of this number, 168 have been explained by mutations in 113 X-linked genes, which in many cases were characterized with the aid of the DNA sequence.
The finished sequence of human chromosome 10 comprises a total of 131,666,441 base pairs. It represents 99.4% of the euchromatic DNA and includes one megabase of heterochromatic sequence within the pericentromeric region of the short and long arm of the chromosome. Sequence annotation revealed 1,357 genes, of which 816 are protein coding, and 430 are pseudogenes. We observed widespread occurrence of overlapping coding genes (either strand) and identified 67 antisense transcripts. Our analysis suggests that both inter- and intrachromosomal segmental duplications have impacted on the gene count on chromosome 10. Multispecies comparative analysis indicated that we can readily annotate the protein-coding genes with current resources. We estimate that over 95% of all coding exons were identified in this study. Assessment of single base changes between the human chromosome 10 and chimpanzee sequence revealed nonsense mutations in only 21 coding genes with respect to the human sequence.
Chromosome 13 is the largest acrocentric human chromosome. It carries genes involved in cancer including the breast cancer type 2 (BRCA2) and retinoblastoma (RB1) genes, is frequently rearranged in B-cell chronic lymphocytic leukaemia, and contains the DAOA locus associated with bipolar disorder and schizophrenia. We describe completion and analysis of 95.5 megabases (Mb) of sequence from chromosome 13, which contains 633 genes and 296 pseudogenes. We estimate that more than 95.4% of the protein-coding genes of this chromosome have been identified, on the basis of comparison with other vertebrate genome sequences. Additionally, 105 putative non-coding RNA genes were found. Chromosome 13 has one of the lowest gene densities (6.5 genes per Mb) among human chromosomes, and contains a central region of 38 Mb where the gene density drops to only 3.1 genes per Mb.
Chromosome 9 is highly structurally polymorphic. It contains the largest autosomal block of heterochromatin, which is heteromorphic in 6-8% of humans, whereas pericentric inversions occur in more than 1% of the population. The finished euchromatic sequence of chromosome 9 comprises 109,044,351 base pairs and represents >99.6% of the region. Analysis of the sequence reveals many intra- and interchromosomal duplications, including segmental duplications adjacent to both the centromere and the large heterochromatic block. We have annotated 1,149 genes, including genes implicated in male-to-female sex reversal, cancer and neurodegenerative disease, and 426 pseudogenes. The chromosome contains the largest interferon gene cluster in the human genome. There is also a region of exceptionally high gene and G + C content including genes paralogous to those in the major histocompatibility complex. We have also detected recently duplicated genes that exhibit different rates of sequence divergence, presumably reflecting natural selection.
Human chromosome 7 has historically received prominent attention in the human genetics community, primarily related to the search for the cystic fibrosis gene and the frequent cytogenetic changes associated with various forms of cancer. Here we present more than 153 million base pairs representing 99.4% of the euchromatic sequence of chromosome 7, the first metacentric chromosome completed so far. The sequence has excellent concordance with previously established physical and genetic maps, and it exhibits an unusual amount of segmentally duplicated sequence (8.2%), with marked differences between the two arms. Our initial analyses have identified 1,150 protein-coding genes, 605 of which have been confirmed by complementary DNA sequences, and an additional 941 pseudogenes. Of genes confirmed by transcript sequences, some are polymorphic for mutations that disrupt the reading frame.
Since the sequencing of the first two chromosomes of the malaria parasite, Plasmodium falciparum, there has been a concerted effort to sequence and assemble the entire genome of this organism. Here we report the sequence of chromosomes 1, 3-9 and 13 of P. falciparum clone 3D7--these chromosomes account for approximately 55% of the total genome. We describe the methods used to map, sequence and annotate these chromosomes. By comparing our assemblies with the optical map, we indicate the completeness of the resulting sequence. During annotation, we assign Gene Ontology terms to the predicted gene products, and observe clustering of some malaria-specific terms to specific chromosomes. We identify a highly conserved sequence element found in the intergenic region of internal var genes that is not associated with their telomeric counterparts.
The finished sequence of human chromosome 20 comprises 59,187,298 base pairs (bp) and represents 99.4% of the euchromatic DNA. A single contig of 26 megabases (Mb) spans the entire short arm, and five contigs separated by gaps totalling 320 kb span the long arm of this metacentric chromosome. An additional 234,339 bp of sequence has been determined within the pericentromeric region of the long arm. We annotated 727 genes and 168 pseudogenes in the sequence. About 64% of these genes have a 5' and a 3' untranslated region and a complete open reading frame. Comparative analysis of the sequence of chromosome 20 to whole-genome shotgun-sequence data of two other vertebrates, the mouse Mus musculus and the puffer fish Tetraodon nigroviridis, provides an independent measure of the efficiency of gene annotation, and indicates that this analysis may account for more than 95% of all coding exons and almost all genes.
The genome of the model plant Arabidopsis thaliana has been sequenced by an international collaboration, The Arabidopsis Genome Initiative. Here we report the complete sequence of chromosome 5. This chromosome is 26 megabases long; it is the second largest Arabidopsis chromosome and represents 21% of the sequenced regions of the genome. The sequence of chromosomes 2 and 4 have been reported previously and that of chromosomes 1 and 3, together with an analysis of the complete genome sequence, are reported in this issue. Analysis of the sequence of chromosome 5 yields further insights into centromere structure and the sequence determinants of heterochromatin condensation. The 5,874 genes encoded on chromosome 5 reveal several new functions in plants, and the patterns of gene organization provide insights into the mechanisms and extent of genome evolution in plants.
Knowledge of the complete genomic DNA sequence of an organism allows a systematic approach to defining its genetic components. The genomic sequence provides access to the complete structures of all genes, including those without known function, their control elements, and, by inference, the proteins they encode, as well as all other biologically important sequences. Furthermore, the sequence is a rich and permanent source of information for the design of further biological studies of the organism and for the study of evolution through cross-species sequence comparison. The power of this approach has been amply demonstrated by the determination of the sequences of a number of microbial and model organisms. The next step is to obtain the complete sequence of the entire human genome. Here we report the sequence of the euchromatic part of human chromosome 22. The sequence obtained consists of 12 contiguous segments spanning 33.4 megabases, contains at least 545 genes and 134 pseudogenes, and provides the first view of the complex chromosomal landscapes that will be found in the rest of the genome.
The higher plant Arabidopsis thaliana (Arabidopsis) is an important model for identifying plant genes and determining their function. To assist biological investigations and to define chromosome structure, a coordinated effort to sequence the Arabidopsis genome was initiated in late 1996. Here we report one of the first milestones of this project, the sequence of chromosome 4. Analysis of 17.38 megabases of unique sequence, representing about 17% of the genome, reveals 3,744 protein coding genes, 81 transfer RNAs and numerous repeat elements. Heterochromatic regions surrounding the putative centromere, which has not yet been completely sequenced, are characterized by an increased frequency of a variety of repeats, new repeats, reduced recombination, lowered gene density and lowered gene expression. Roughly 60% of the predicted protein-coding genes have been functionally characterized on the basis of their homology to known genes. Many genes encode predicted proteins that are homologous to human and Caenorhabditis elegans proteins.
        
Title: Cumulative reduction in serum cholinesterase following repeated therapeutic plasma exchange Collard CD, Baker BWr, Johnson D, Bressler R, Harati Y Ref: Journal of Clinical Anesthesia, 8:44, 1996 : PubMed
STUDY OBJECTIVE:
To investigate the magnitude of serum cholinesterase reduction following repeated therapeutic plasma exchange in patients with neuromuscular disease.
DESIGN:
Serum cholinesterase activity was measured immediately before and after each plasma exchange in open-label fashion and then analyzed using an analysis of variance model.
SETTING:
Inpatient neurology and allergy and immunology clinics at a university-affiliated hospital.
PATIENTS:
50 consecutive patients with neuromuscular disease.
INTERVENTIONS:
All patients underwent repeated therapeutic plasma exchange, with each subject receiving up to a maximum of six plasma exchanges.
MEASUREMENTS AND MAIN RESULTS:
Serum cholinesterase activity was determined spectrophotometrically. Analysis of variance revealed a significant reduction in serum cholinesterase following each therapeutic plasma exchange (p < 0.0001), a significant and consistent reduction across the six treatments (p < 0.0001), and a significant interaction between (before versus after exchange) and treatment number (p < 0.0001). Mean serum cholinesterase before repeated therapeutic plasma exchange was 4817 U/L, but it decreased to a mean of 929 U/L following six plasma exchanges.
CONCLUSIONS:
There is a significant reduction in serum cholinesterase following repeated therapeutic plasma exchange. It is suggested that drugs metabolized by serum cholinesterase (e.g., succinylcholine, mivacurium) be used with caution in the period immediately following repeated therapeutic plasma exchange.
        
Title: In vitro competitive inhibition of plasma cholinesterase by cocaine: normal and variant genotypes Schwartz HJ, Johnson D Ref: Journal of Toxicology Clinical Toxicology, 34:77, 1996 : PubMed
OBJECTIVE:
To determine the inhibitory constant, Ki, of cocaine for a number of the different genetic variants of human plasma cholinesterase.
DESIGN:
In vitro analysis of plasma cholinesterase activity in the presence of cocaine as a competitive inhibitor.
METHODS:
Six normal (UU) control sera and seven sera with the following plasma cholinesterase genotypes were assayed: AA, UA, AS, UF, US, AF and SS. Plasma cholinesterase activity was determined in the samples by colorimetric measurement of propionylthiocholine metabolism over a range of concentrations. Competitive activities were then determined in the presence of varying concentrations of cocaine. Double reciprocal plots (1/v vs 1/S) were used to calculate Km and Vmax for propionylthiocholine, and Ki for cocaine for each genotype.
RESULTS:
The variant forms of the plasma cholinesterase had high cocaine Ki values--all were approximately ten times greater than the Ki for normal plasma cholinesterase.
CONCLUSIONS:
Since the inhibitory constant is an indirect measure of an enzyme's affinity for a competing substrate, a high Ki for cocaine at recreational or therapeutic concentrations would translate into a longer in vivo half-life. Our results support the growing evidence that low plasma cholinesterase activity predisposes to cocaine toxicity.
        
Title: Acetylcholinesterase and butyrylcholinesterase activity in the human term placenta: implications for fetal cocaine exposure Simone C, Derewlany LO, Oskamp M, Johnson D, Knie B, Koren G Ref: Journal of Laboratory & Clinical Medicine, 123:400, 1994 : PubMed
The characterization of the enzymes responsible for drug metabolism in the human placenta is of great importance in determining the possible role the placenta plays in protecting the fetus from potentially fetotoxic drugs. We speculate that the placenta metabolizes cocaine, serving to protect the fetus from the drug's ill effects. Cholinesterase, the principle enzyme that metabolizes cocaine, has been hypothesized to be present yet is not well characterized in the human placenta. The purpose of this study was to quantify human placental acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) activity. Human placentas were obtained from elective cesarean sections, and several lobules were thoroughly perfused with cold buffer to ensure minimal contamination from erythrocyte AChE. Subcellular fractions were then prepared from these lobules by using standard differential centrifugation techniques. Microsomes and cytosol were assayed for AChE and BChE activity by using a spectrophotometric assay. BChE activity was found in the cytosolic fraction of the placental villous tissue, whereas AChE activity was measured in the microsomal fraction. By demonstrating that BChE activity is present in human term placenta we have shown that this organ has the capacity to metabolize cocaine and may therefore serve as a metabolic barrier to fetal exposure to cocaine.
The absorption and disposition kinetics of HI-6 were determined in Beagle dogs given single doses (25 mg kg-1) of the drug by the intravenous, intramuscular, and oral routes. Concentrations of the oxime in plasma and urine were measured by HPLC. A two-compartment open model was used to describe the disposition curve following intravenous drug administration while a one-compartment open model with first-order absorption adequately described the data following intramuscular or oral administration of the dose. Extravascular distribution of HI-6 was limited (Vss 203 ml kg-1) and the drug was eliminated rapidly after intravenous administration (t1/2 46.5 min, MAT 55.4 min). Systemic clearance was 3.68 ml min-1 x kg. A major fraction of the dose (63.7 per cent) was excreted in urine over a 24-h collection period. Following intramuscular drug administration, the absorption half-life (t1/2(a), 5.3 min), MAT (17.1 min), Cmax (70.37 micrograms ml-1) and tmax (15.9 min) indicate that the drug was rapidly absorbed. Systemic availability was 83.43 per cent after oral drug administration, absorption was preceded by a lag time (23.2 min). The t1/2(a) (41.5 min), MAT (81.6 min), Cmax (4.30 micrograms ml-1) and Tmax (90.6 min) indicate somewhat delayed absorption. Systemic availability (11.38 per cent) and the fraction of dose excreted unchanged in the urine (9.3 per cent) show that the drug was poorly absorbed. The apparent half-life (58.0 min) and MRT (137.6 min) following oral administration were significantly longer (p < 0.05) than following intravenous or intramuscular administration suggesting that the rate of absorption from the gastrointestinal tract decreases the elimination rate of the drug. In conclusion, HI-6 has limited distribution within the body, is rapidly eliminated mainly by renal excretion unchanged in the urine, and the bioavailability (i.e. rate and extent of absorption) of the drug varies with the route of administration.
Levels of urinary catecholamines (noradrenaline, adrenaline, dopamine), plasma acetylcholinesterase, serum serotonin and plasma 3-methoxy-4-hydroxyphenylglycol were recorded in 38 adult subjects during the first 21 days after severe head injury. Levels of acetylcholinesterase, serotonin and 3-methoxy-4-hydroxyphenylglycol differed significantly between survivors and those who died. For survivors, initially abnormal biochemical levels recovered toward the norm as time after injury progressed.