Insertion rates and complications of central lines in the UK population: A pilot study.

BACKGROUND: Central venous catheters are inserted ubiquitously in critical care and have roles in drug administration, fluid management and renal replacement therapy. They are also associated with numerous complications. The true number of central venous catheters inserted per year and the proportion of them associated with complications are unknown in the UK. METHODS: We performed a prospective audit at five hospitals, as a feasibility pilot for a larger, nationwide audit. Using a novel secure online data collection platform, developed earlier and adapted for this project, all central venous catheters inserted for patients admitted to the Intensive Care Units were documented at five pilot sites across the UK. RESULTS: A total of 117 data collection forms were submitted. Users found the electronic data collection system easy to use. All data fields were ready for analysis immediately after data input. Out of the 117 central venous catheters, 17 were haemodialysis catheters and five pulmonary artery introducers. Experienced practitioners (at least three years' experience) inserted 85% of the central venous catheters. The site of insertion was the internal jugular vein for 80%, femoral for 12% and subclavian for 8% of central venous catheters. Most central venous catheters were inserted in ICU (49%) or theatres (42%). Ultrasound was used for 109 (93%) of central venous catheter insertions and its use was not associated with fewer complications. In 15 cases venopuncture was attempted more than once (all with ultrasound) and this was associated with significantly increased risk of complications. There were eight immediate complications (6.8%): five related to venopuncture and inability to pass a guidewire, two carotid artery punctures and one associated with significant arrhythmia. CONCLUSION: This study demonstrates the ease and feasibility of collecting detailed descriptive data on central line insertion and its immediate complications in the UK over two weeks. In our proposed nationwide audit, organisation-level data on local policies and standard operating procedures is required to complete the picture on this important aspect of intensive care practice.

Conserved roles for peptidases in the processing of invertebrate neuropeptides.

Invertebrates use a wide range of peptides as transmitters and hormones to regulate complex behaviour, physiology and development. These animals, especially those that are amenable to genetic study and are the subject of genome-sequencing projects, provide powerful model systems for understanding the functions of peptidases in controlling the bioactivity of peptides. Neprilysin, a zinc metallopeptidase and a key enzyme in the metabolism of mammalian peptides, is also implicated in the inactivation of peptides at synapses and of circulating peptide hormones in insects and nematodes. A family of neprilysin-like genes are present in the genomes of both Drosophila melanogaster and Caenorhabditis elegans; in C. elegans it seems that individual family members have evolved to take on different physiological functions, because they are expressed in a tissue-specific manner. Angiotensin I-converting enzymes (peptidyl dipeptidase A, angiotensin-converting enzyme) are another group of zinc metallopeptidases found in some invertebrates that lack angiotensin peptides. In D. melanogaster there are two functional angiotensin-converting enzymes that are essential for normal development. One of these (Acer) is expressed in the embryonic heart, whereas the second enzyme (Ance) is expressed in several tissues at different stages of the life cycle. The accumulation of Ance within secretory vesicles of some peptide-synthesizing cells suggests a role for the enzyme in the intracellular processing of insect peptides. Ance is very efficient at cleaving pairs of basic residues from the C-terminus of partly processed peptides, suggesting a novel role for the enzyme in prohormone processing. Invertebrates will continue to provide insights into the evolutionarily conserved functions of known peptidases and of those additional family members that are expected to be identified in the future from genome-sequencing projects.

Exploring the Caenorhabditis elegans and Drosophila melanogaster genomes to understand neuropeptide and peptidase function.

Comparison of peptidase gene families in the newly released Drosophila melanogaster and Caenorhabditis elegans genomes highlights important differences in peptidase distributions with relevance to the evolution of both form and function in these two organisms and can help to identify the most appropriate model when using comparative studies relevant to the human condition.

Functional conservation of the active sites of human and Drosophila angiotensin I-converting enzyme.

Human somatic angiotensin I-converting enzyme (sACE) has two active sites present in two homologous protein domains, resulting from a tandem gene duplication. It has been proposed that the N- and C-terminal active sites can have specific in vivo roles. In Drosophila melanogaster, Ance and Acercode for two ACE-like single-domain proteins, also predicted to have distinct physiological roles. We have investigated the relationship of Ance and Acer to the N- and C-domains of human sACE by genomic sequence analysis and by using domain-selective inhibitors, including RXP 407, a selective inhibitor of the human N-domain. These phosphinic peptides were potent inhibitors of Acer, but not of Ance. We conclude that the active sites of the N-domain and of Acer share structural features that permit the binding of the unusual RXP407 inhibitor and the hydrolysis of a broader range of peptide structures. In comparison, Ance, like the human C-domain of ACE, displays greater inhibitor selectivity. From the analysis of the published sequence of the Adh region of Drosophila chromosome 2, which carries Ance, Acer, and four additional ACE-like genes, we also suggest that this functional conservation is reflected in an ancestral gene structure identifiable in both protostome and deuterostome lineages and that the duplication seen in vertebrate genomes predates the divergence of these lineages. The conservation of ACE enzymes with distinct active sites in the evolution of both vertebrate and invertebrate species provides further evidence that these two kinds of active sites have different physiological functions.

Expression and functional characterization of a Drosophila neuropeptide precursor with homology to mammalian preprotachykinin A.

Peptides structurally related to mammalian tachykinins have recently been isolated from the brain and intestine of several insect species, where they are believed to function as both neuromodulators and hormones. Further evidence for the signaling role of insect tachykinin-related peptides was provided by the cloning and characterization of cDNAs for two tachykinin receptors from Drosophila melanogaster. However, no endogenous ligand has been isolated for the Drosophila tachykinin receptors to date. Analysis of the Drosophila genome allowed us to identify a putative tachykinin-related peptide prohormone (prepro-DTK) gene. A 1.5-kilobase pair cDNA amplified from a Drosophila head cDNA library contained an 870-base pair open reading frame, which encodes five novel Drosophila tachykinin-related peptides (called DTK peptides) with conserved C-terminal FXGXR-amide motifs common to other insect tachykinin-related peptides. The tachykinin-related peptide prohormone gene (Dtk) is both expressed and post-translationally processed in larval and adult midgut endocrine cells and in the central nervous system, with midgut expression starting at stage 17 of embryogenesis. The predicted Drosophila tachykinin peptides have potent stimulatory effects on the contractions of insect gut. These data provide additional evidence for the conservation of both the structure and function of the tachykinin peptides in the brain and gut during the course of evolution.

Fertilization-promoting peptide in reproductive tissues and semen of the male marmoset (Callithrix jacchus).

Fertilization-promoting peptide (FPP) is present in the prostate gland and semen of some mammals, and has been shown to enhance the fertilizing ability of both epididymal mouse and ejaculated human spermatozoa. The novel peptide may prove of importance for the treatment of some cases of male infertility, and a suitable animal model would be useful to test this hypothesis. To this end, we examined reproductive tissues and semen of the male marmoset for the presence of FPP. Peptides were extracted from seminal plasma, testes, prostate, and bulbourethral glands of intact and castrated male marmosets. The peptides were identified by ion-exchange chromatography followed by radioimmunoassay. The mean concentration of FPP immunoreactivity in semen from intact males was 58.7 nM (SE +/- 9.9 nM, n = 10), and anion-exchange chromatography revealed FPP as the only immunoreactive peptide present. Analysis of tissues revealed that FPP in semen was likely to be derived from the prostate gland, which contained this peptide as the major source of immunoreactivity (10.86 pmol/gland; SE +/- 4.39 pmol/gland, n = 4). Only low concentrations of FPP were detectable in the bulbourethral glands, and the peptide was undetectable in the testis. Surprisingly, FPP was readily detectable in the seminal plasma from one castrated marmoset and was present in the prostate gland from 3 castrates at levels which did not differ significantly from those in intact animals (5.47 pmol/gland, SE +/- 1.64 pmol/gland, n = 3). Plasma testosterone measurements indicated that residual circulatory androgens remained after castration, which may be consistent both with the maintenance of mating behavior and the presence of prostatic FPP. We conclude that FPP is present within the prostate gland and seminal plasma of the marmoset at concentrations consistent with a role in male fertility in this species.

Peptides related to thyrotrophin-releasing hormone are degraded in seminal plasma by an enzyme similar to prolyl endopeptidase.

A TRH-like peptide, fertilization-promoting peptide (FPP), is present in high concentrations in mammalian prostate and semen and enhances the fertilization potential of spermatozoa. In this study, we have examined the properties of the enzyme that degrades TRH and FPP in rabbit seminal plasma. The enzyme responsible had a pH optimum of approximately 7.0, was inhibited by serine (di-isopropyl flurophosphate) and thiol (N-ethylmaleimide) protease inhibitors, bacitracin and concentrations of Zn2+ naturally present in seminal plasma: these functional reagents are all known to be potent inhibitors of prolyl endopeptidase. The major product after incubation of [3H]TRH in seminal plasma for 100 min was acid TRH (deamidated TRH) which is also the product after incubation of TRH with prolyl endopeptidase. Our results are consistent with the enzyme responsible for degradation of TRH and FPP in seminal plasma being similar to prolyl endopeptidase. The enzyme identified in this study is secreted and is therefore likely to be different from prolyl endopeptidase characterized from porcine brain, because the latter enzyme is known to be located in the cytosolic compartment of the cell.