Development, validation and application of an enzyme immunoassay (EIA) of atriopeptin

Detection of Borrelia burgdorferi antigens in tissues and plasma during early infection in a mouse model

Borrelia burgdorferi is the causative agent of Lyme borreliosis, which is the most common tick-borne human disease in Europe and North America. Currently, the diagnosis of Lyme borreliosis is based on serological tests allowing indirect detection of anti-Borrelia antibodies produced by patients. Their main drawback is a lack of sensitivity in the early phase of disease and an incapacity to prove an active infection. Direct diagnostic tests are clearly needed. The objectives of this study were to produce tools allowing sensitive detection of potential circulating Borrelia antigens and to evaluate them in a mouse model. We focused on two potential early bacterial makers, the highly variable OspC protein and the conserved protein FlaB. High-affinity monoclonal antibodies were produced and used to establish various immunoassays and western blot detection. A very good limit of detection for OspC as low as 17 pg/mL of sample was achieved with SPIE-IA. In infected mice, we were able to measure OspC in plasma with a mean value of 10 ng/mL at 7 days post-inoculation. This result suggests that OspC could be a good blood marker for diagnosis of Lyme borreliosis and that the tools developed during this study could be very useful.

Sensitive and specific enzyme immunoassays for antigenic trisaccharide from Bacillus anthracis spores

A straightforward synthesis of an anthrose-containing trisaccharide derived from Bacillus anthracis was achieved. Antibodies raised against this hapten provide a highly sensitive enzyme immunoassay with a detection limit of 8.5 pmol mL(-1). By investigating the specificity of the antibodies obtained using different mono-, di- and trisaccharide synthetic analogues, we demonstrated that the epitope was mainly made up of the methyl group at C-5, the butamido group at C-4 and the hydroxyl at C-3 of the anthrose unit, the other parts of the trisaccharide appearing little involved in the recognition.

Synthesis of an anthrose derivative and production of polyclonal antibodies for the detection of anthrax spores

A straightforward synthesis of a derivative of anthrose, the non-reducing terminal fragment of the antigenic tetrasaccharide from Bacillus anthracis, was achieved starting from d-galactose. This hapten is able to induce a highly specific and sensitive immune response in rabbit when attached to a carrier protein.

Post-translational amino acid racemization in the frog skin peptide deltorphin I in the secretion granules of cutaneous serous glands

The dermal glands of the South American hylid frog Phyllomedusa bicolor synthesize and expel huge amounts of cationic, alpha-helical, 24- to 33-residue antimicrobial peptides, the dermaseptins B. These glands also produce a wide array of peptides that are similar to mammalian hormones and neuropeptides, including a heptapeptide opioid containing a D-amino acid, deltorphin I (Tyr-DAla-Phe-Asp-Val-Val-Gly NH2). Its biological activity is due to the racemization of L-Ala2 to D-Ala. The dermaseptins B and deltorphins are all derived from a single family of precursor polypeptides that have an N-terminal preprosequence that is remarkably well conserved, although the progenitor sequences giving rise to mature opioid or antimicrobial peptides are markedly different. Monoclonal and polyclonal antibodies were used to examine the cellular and ultrastructural distributions of deltorphin I and dermaseptin B in the serous glands by immunofluoresence confocal microscopy and immunogold-electron microscopy. Preprodeltorphin I and preprodermaseptins B are sorted into the regulated pathway of secretion, where they are processed to give the mature products. Deltorphin I, [l-Ala2]-deltorphin I and dermaseptin B are all stored together in secretion granules which accumulate in the cytoplasm of all serous glands. We conclude that the L- to D-amino acid isomerization of the deltorphin I occurs in the secretory granules as a post-translational event. Thus the specificity of isomerization depends on the presence of structural and/or conformational determinants in the peptide N-terminus surrounding the isomerization site.

Biosynthesis of a D-amino acid in peptide linkage by an enzyme from frog skin secretions

d-amino acids are present in some peptides from amphibian skin. These residues are derived from the corresponding L-amino acids present in the respective precursors. From skin secretions of Bombinae, we have isolated an enzyme that catalyzes the isomerization of an L-Ile in position 2 of a model peptide to D-allo-Ile. In the course of this reaction, which proceeds without the addition of a cofactor, radioactivity from tritiated water is incorporated into the second position of the product. The amino acid sequence of this isomerase could be deduced from cloned cDNA and genomic DNA. After expression of this cDNA in oocytes of Xenopus laevis, isomerase activity could be detected. Polypeptides related to the frog skin enzyme are present in several vertebrate species, including humans.

Characterization of a Lactococcus lactis strain that secretes a major epitope of bovine beta-lactoglobulin and evaluation of its immunogenicity in mice

Bovine beta-lactoglobulin (Blg) is one of the major cow's milk allergens. Peptide 41-60 of Blg (Blg41-60) was described as a murine T-cell determinant and a murine, rat, and human immunoglobulin E (IgE) epitope. The aim of this study was the expression of Blg41-60 as a fusion protein in the food-grade bacterium Lactococcus lactis and the characterization of its immunogenicity in mice. We constructed a recombinant strain of L. lactis capable of inducible production and secretion of Blg41-60::Nuc, a fusion protein between Blg41-60 and the mature part of the staphylococcal nuclease (Nuc). The highest production yield of Blg41-60::Nuc (32.5 mg/liter) was reached 4 h after induction. At this time, up to 75% of Blg41-60::Nuc was secreted. When monoclonal antibodies specific for Blg41-60 were used, purified Blg41-60::Nuc and synthetic Blg41-60 exhibited very similar immunoreactivities. Subcutaneous coadministration of purified Blg41-60::Nuc and killed nonrecombinant L. lactis resulted in the induction of specific anti-Blg41-60 IgG2a and IgG1. The IgG1/IgG2a ratio and the lack of specific IgE suggest a Th1-type immune response, i.e., a nonallergic response. Similar administrations of the killed Blg41-60::Nuc-producing L. lactis strain did not elicit a specific immune response, whereas a transitory mucosal IgA-specific immune response was induced in mice after oral administration of the live Blg41-60::Nuc-producing L. lactis strain.

The C-terminal t peptide of acetylcholinesterase forms an α helix that supports homomeric and heteromeric interactions

Acetylcholinesterase subunits of type T (AChET) possess an alternatively spliced C-terminal peptide (t peptide) which endows them with amphiphilic properties, the capacity to form various homo-oligomers and to associate, as a tetramer, with anchoring proteins containing a proline rich attachment domain (PRAD). The t peptide contains seven conserved aromatic residues. By spectroscopic analyses of the synthetic peptides covering part or all of the t peptide of Torpedo AChET, we show that the region containing the aromatic residues adopts an alpha helical structure, which is favored in the presence of lipids and detergent micelles: these residues therefore form a hydrophobic cluster in a sector of the helix. We also analyzed the formation of disulfide bonds between two different AChET subunits, and between AChET subunits and a PRAD-containing protein [the N-terminal fragment of the ColQ protein (QN)] possessing two cysteines upstream or downstream of the PRAD. This shows that, in the complex formed by four T subunits with QN (T4-QN), the t peptides are not folded on themselves as hairpins but instead are all oriented in the same direction, antiparallel to that of the PRAD. The formation of disulfide bonds between various pairs of cysteines, introduced by mutagenesis at various positions in the t peptides, indicates that this complex possesses a surprising flexibility.

A sensitive and specific enzyme immunoassay for the detection of methyl ether derivatives of cyclomaltoheptaose

We have raised antibodies against two methylated derivatives of beta-CD, heptakis(2,6-di-O-methyl)cyclomaltoheptaose (Dimeb) and heptakis(2,3,6-tri-O-methyl)cyclomaltoheptaose (Trimeb). These antibodies were used to develop two specific and sensitive enzyme immunoassays, presenting a detection limit close to 500 and 30 pg/mL for Trimeb and Dimeb, respectively. Cross reactivities of different linear and cyclic maltooligosaccharides were investigated, demonstrating a high specificity against the structural features of the secondary hydroxyls rim. Several commercial Dimeb samples, containing different mixtures of partially methylated beta-cyclodextrin derivatives including RAMEB, which contains only a few amount of pure Dimeb, could be easily evaluated by the Dimeb immunoassay. Both of these assays have been shown to allow accurate measurement in plasma and urine, thus appearing as useful tools for further applications in biological material.

Monoaminergic control of vasopressin and VIP expression in the mouse suprachiasmatic nucleus

We studied the effects of serotonin and noradrenaline on the expression of arginine-vasopressin (AVP) and vasoactive intestinal peptide (VIP) in the suprachiasmatic nucleus (SCN). We used transgenic Tg8 mice knockout for the MAO-A (monoamine oxidase A) gene, which are characterized by increased amounts of serotonin and noradrenaline in brain compared to wild-type mice (C3H). The MAO-A deficiency caused an increase in AVP and VIP expression (determined by immunohistochemistry, enzyme immunoassay, and in situ hybridization) compared to C3H mice. The number of peptidergic neurons was also increased. Inhibiting serotonin or noradrenaline synthesis in Tg8 mice by the administration of parachlorophenylalanine or alpha-methylparatyrosine, respectively, the amounts of AVP, VIP and their mRNAs were decreased, but not the number of peptidergic neurons. This study indicates that serotonin and noradrenaline stimulate AVP and VIP expression, and could participate in the differentiation of the neurochemical phenotype in the mouse SCN.

Development of a direct assay for measuring intracellular AZT triphosphate in humans peripheral blood mononuclear cells

Direct LC/MS/MS methods have recently been developed for measuring triphosphate anabolites of several nucleosidic reverse transcriptase inhibitor (NRTI) in peripheral blood mononuclear cells (PBMCs) from HIV-positive patients. Whereas AZT is one of the most-used NRTIs, no such method has been developed for AZT-TP, its active anabolite, mainly because of the presence of endogenous nucleotides that interfere with such an assay. In this paper, we first describe the development of two enzyme immunoassays (EIA) of AZT-TP in PBMCs: one directly measuring AZT-TP content; the other, measuring the nucleoside AZT after selective extraction of AZT-TP and dephosphorylation. The precision of these two assays was too low to achieve precise determination of AZT-TP in PBMC samples. Direct LC/MS/MS is not specific enough for AZT-TP, since at least two interfering endogenous nucleotides (same m/z ratio and fragment as well as retention time close to that of AZT-TP) are found in the intracellular medium of PBMCs. The off-line combination of immunoaffinity extraction (IAE) and LC/MS/MS proved to be a successful strategy allowing without dephosphorylation appropriate specificity and sensitivity (limit of quantification established as 9.3 fmol/10(6) cells) to determine AZT-TP in PBMCs from 7 mL of blood of HIV-infected patients. Validation of this IAE-LC/MS/MS method demonstrated CV percent for repeatability and intermediate precision lower than 15%. More than 150 samples/week can be analyzed by one analyst, making this method suitable for routine analysis during clinical studies.

Activation by serotonin and noradrenaline of vasopressin and oxytocin expression in the mouse paraventricular and supraoptic nuclei

Noradrenaline and serotonin are known to control arginine-vasopressin (AVP) and oxytocin (OT) secretion in the systemic circulation. The aim of the current study was to investigate whether these monoamines are also able to influence AVP and OT expression in the paraventricular (PVN) and supraoptic nuclei (SON). To test this hypothesis, we used the Tg8 transgenic mice KO for the monoamine oxidase-A gene, which present high levels of noradrenaline and serotonin in the brain. AVP and OT expression were evaluated at peptide and mRNA levels by immunohistochemistry, enzyme immunoassay, and in situ hybridization. Compared with wild type, the amounts of AVP, OT, AVP mRNA, and OT mRNA were increased in the PVN and SON in Tg8 mice. To distinguish the respective contributions of noradrenaline and serotonin to these modifications, we treated Tg8 mice with a synthesis inhibitor of either catecholamines [alpha-methylparatyrosine (alpha-MPT)] or serotonin [parachlorophenylalanine (pCPA)]. Administration of alpha-MPT to Tg8 mice induced a decline in the amounts of AVP, OT, and their mRNA in the PVN and SON. The pCPA treatment in Tg8 mice was also associated with a decrease in OT expression in the PVN and SON and in AVP expression in the PVN, but not in the SON. These results suggest that noradrenaline may activate AVP and OT expression in the PVN and SON. Likewise, serotonin is proposed to stimulate AVP and OT expression in the PVN and only OT expression in the SON.

Differential modulation of alpha, beta and gamma enolase isoforms in regenerating mouse skeletal muscle

Nothing is known about the expression of the glycolytic enzyme enolase in skeletal muscle alterations such as myofiber degeneration and regeneration. Enolase is a dimeric enzyme which exhibits cell type specific isoforms. The embryonic form, alphaalpha, remains expressed in most adult tissues, whereas a transition towards specific isoforms occurs during ontogenesis in two cell types with high energy requirements: alphagamma and gammagamma in neurons, alphabeta and betabeta in striated muscle cells. During murine myogenesis, beta enolase transcripts are detected early in the forming muscles, and the beta gene is further upregulated at specific stages of muscle development. The alpha and beta subunits exhibit characteristic developmental microheterogeneity patterns. High levels of beta enolase subunits characterize the glycolytic fast-twitch fibers of adult muscles. We have investigated the expression of enolase subunits in a mouse experimental model of muscle regeneration. Following a single intramuscular injection of the necrotic agent cardiotoxin, we observed a rapid decrease in the level of the major muscle enolase subunit beta, accounting for the drop in total enolase activity that correlated with the degeneration of myofibers. Concomitant with the regeneration of new fibers, beta subunit levels began to increase, reaching normal values by 30 days after injury. Changes in the embryonic and ubiquitous subunit, alpha, mimicked those occurring during development by two aspects: modifications in electrophoretic variants and redistribution between soluble and insoluble compartments of muscle extracts. Imunocytochemical analyses of alpha and beta enolase subunits first revealed a homogeneous labeling within myofibers. Striations characteristic of normal adult muscle tissue were visible again by day 14 after injury. A perinuclear alpha and beta immunoreactivity was often observed in regenerating myofibers but its functional significance remains to be elucidated. Double labeling experiments with anti-gamma enolase and FITC-alpha bungarotoxin allowed us to follow the neuromuscular junction remodeling that occurs during muscle regeneration despite the absence of nerve injury.

New insight into abnormal prion protein using monoclonal antibodies

Studies of abnormal prion protein (PrPres) are hindered by the lack of specific monoclonal antibodies (mAbs), and the relationships between PrPres, infectivity, and strain specificity in prion diseases are still subject to debate. We have studied PrPres with new mAbs produced against PrP in mice using various immunization strategies. PrPres was analyzed by Western blot with different prion strains in various hosts. Differences in the electrophoretic pattern of human PrPres revealed by these antibodies provide new insight into PrPres cleavage by proteases and interpretation of strain typing. This study confirms that the N-terminal extremity of PrPres is differentially sensitive to proteases. Conversely, the C-terminal extremity, which resists proteolysis, seems to be abnormally detectable by antibodies in ultrastructural studies. This work confirms the highly complex role of PrPres in prion diseases and provides new tools which will be made available to facilitate progress in qualitative and quantitative studies of PrP.

A solid-phase immobilized epitope immunoassay (SPIE-IA) permitting very sensitive and specific measurement of angiotensin II in plasma

We have developed a new enzyme immunometric assay for angiotensin II (AII) based on SPIE-IA technology (solid-phase immobilized epitope-immunoassay). A monoclonal antibody with optimal properties (mAb3 131) was selected from a series of 19 anti-AII mAbs. The mAb had to be purified from ascitic fluid in a specific manner in order to remove endogenous AII from the antibody-binding sites. We established a sensitive (minimum detectable concentration 0.5 pg/ml) and precise (CV below 15% in the 2-100 pg/ml range) SPIE-IA. Using different AII-related peptides, we observed that this new assay has a specificity profile that compares favourably with the corresponding competitive immunoassay. We have used the assay to measure AII in 42 plasma samples, and demonstrated a good correlation with values obtained using a commercial radioimmunoassay. Assay specificity was supported by HPLC fractionation experiments, confirming the absence of interference induced by endogenous AII-related products.

Pharmacokinetic analysis of 6-monoamino-beta-cyclodextrin after intravenous or oral administration to rats using a specific enzyme immunoassay

We have developed a highly sensitive enzyme immunoassay for 6-monoamino-beta-CD (mono(6-amino-6-deoxy)cyclomaltoheptaose) and its parent compound (beta-CD) with a detection limit in the 100 pg/mL range. The polyclonal antibodies obtained are highly specific for the beta-cyclodextrin core and do not recognize other cyclic cyclodextrins (i.e., alpha- and gamma-CD) or linear analogues. This enzyme immunoassay can be used to quantify 6-monoamino-beta-CD in rat urine and plasma. Using this immunoassay, we have evaluated the main pharmacokinetic parameters of 6-monoamino-beta-CD after iv administration to the rat of a 25 mg/kg dose. Since this method is strictly specific to the native beta-CD form, we have demonstrated that the molecule rapidly disappeared from plasma but is probably distributed in the tissues. The urinary route appears as the predominant way of elimination since almost all the administered drug is recovered in urine. Finally, analysis of the same molecule after oral administration to the rat (25 mg/kg) demonstrates low plasma levels and that about 1% of the administered dose is excreted in urine. These experiments demonstrate the high stability of the beta-CD core irrespective of the method of administration. This immunological method could provide relevant information on the fate of beta-CD and some derivatives for drug delivery using different modes of administration (oral, parenteral, transmucosal, or dermal).

Monitoring of intracellular levels of 5'-monophosphate-AZT using an enzyme immunoassay

We have developed a competitive enzyme immunoassay suitable for routine monitoring of intracellular levels of 5'-monophosphate-AZT (AZT-MP). This assay is performed in 96-well microtiter plates coated with anti-rabbit immunoglobulin antibodies and is based on the use of rabbit polyclonal antibodies raised against an AZT-MP analog and of an AZT-MP/acetylcholinesterase conjugate as tracer. It is very sensitive, with a detection limit close to 0.1 ng/ml (0.2 pmol/ml), and precise (CV < 20% from 20 to 0.3 ng/ml). Very low cross-reactivities were observed with AZT and the corresponding di- and triphosphate derivatives as well as with other related nucleotides and nucleosides. The validity of the assay was demonstrated by measuring intracellular concentrations of AZT-MP in peripheral blood mononuclear cells (PBMCs) and in monocyte-derived macrophages (MDMs) cultured in the presence of various concentrations of AZT (from 0.01 microM to 10 microM). We observed very high levels of AZT-MP in stimulated (PHA + IL2) PBMCs (> 100 pmol/10(6) cells) while, as expected, much lower concentrations were measured in resting PBMCs or MDMs (0.1 to 2 pmol/10(6) cells). The assay constitutes a very convenient tool permitting easy, precise studies of the first step of the intracellular metabolism of AZT leading to the formation of AZT-TP in cultured cells.

Identification of neuropeptides in the midgut of parasitized insects: FLRFamides as candidate paracrines

Parasitism of Manduca sexta (Lepidoptera: Sphingidae) larvae by the braconid wasp Cotesia congregata (Hymenoptera: Braconidae) leads to accumulation of peptides in host neurons and neurosecretory cells of the central nervous system (CNS) and neurons and endocrine/paracrine cells of the midgut. This accumulation has now facilitated the characterization of two new members of the FLRFamide family from midguts of parasitized larvae. The peptides, given the names F24 and F39, are 24 and 39 amino acids in length with the sequences VRDYPQLLDSGMKRQDVVHSFLRFamide and YAEAAGEQVPEYQALVRDYPQLLDSGMKRQDVVHSFLRFamide. The sequence of F24 is identical to the C-terminal 24 amino acids of F39. The C-terminal 10-mer of each is identical to a previously characterized decapeptide neurohormone (F10). This sequence is preceded by a potential processing site. In nonparasitized insects F39 was present at several-fold the amount of F24. In parasitized insects F24 and F39 accumulate in the middle and posterior regions of the midgut, which are enriched in endocrine/paracrine cells reacting with FLRFamide antisera. In the combined brain and subesophageal ganglion F39 was not detected and the amount of F24 never exceeded 2 fmol per Br/SEG. Of the three peptides, only F10 was found in the hemolymph. Thus, F24 and F39 may be intermediates in the biosynthesis of F10 and may themselves be released locally from endocrine/paracrine cells in the midgut epithelium.

Differential measurement of constitutive (COX-1) and inducible (COX-2) cyclooxygenase expression in human umbilical vein endothelial cells using specific immunometric enzyme immunoassays

We have produced and characterized monoclonal antibodies (mAbs) directed against a specific carboxyterminal sequence of human cyclooxygenase-2 (residues 580-598). A rabbit polyclonal antiserum was also raised against another sequence of 10 amino acids (residues 570-581) not present in human constitutive cyclooxygenase-1. Affinity-purified polyclonal antibodies, coated on microtiter plates, were used as capture antibodies in a two-site immunometric assay, with an mAb-acetylcholinesterase conjugate used as tracer. The detection limit was 500 fmol/ml of peptide C3-COX2 (residues 570-595). The assay was specific for the cyclooxygenase-2 (COX-2) isoform, since no immunoreactivity could be detected in platelet extracts known to be rich in cyclooxygenase-1 (COX-1). In contrast, extracts from cultured human umbilical vein endothelial cells challenged with 20 nM phorbol myristate acetate (PMA) showed an increase in COX-2 immunoreactivity related both to the increase in enzyme activity and the variations observed by Western blot analysis. Under these conditions, analysis of the same cell lysates with another immunometric assay specific for COX-1 revealed insignificant variation of this enzyme. The specificity of detection was further assessed by measuring the immunoreactivity of the fractions obtained after molecular sieve chromatography of control and stimulated cell extracts, and corroborated the marked enhancement of COX-2 by comparison with COX-1. Treatment of PMA-activated cells with H-7 or actinomycin D totally abolished the COX-2 signal and had little effect on COX-1. No significant variation in COX-2 immunoreactivity was observed using the inactive isomer 4 alpha-PMA, even at 100 nM. These assays constitute the first quantitative analysis of constitutive COX-1 and of inducible COX-2 in nucleated cells at the protein level.

A sensitive and specific enzyme immunoassay for cyclomaltoheptaose and some derivatives

Antibodies were raised against cyclomaltoheptaose (beta-cyclodextrin), providing a highly sensitive enzyme immunoassay for beta-cyclodextrin and some derivatives with a detection limit of 120 pg/mL. Investigations of cross-reactivities with a wide variety of linear and cyclic maltooligosaccharides demonstrate that the antibodies are highly specific for cyclomaltoheptaose and a number of derivatives. The epitope is probably located on the secondary hydroxyl groups of the rim side. This enzyme immunoassay is shown to be suitable to detect cyclomaltoheptaose in urine and in plasma.

A new alternative transcript encodes a 60 kDa truncated form of integrin beta 3

A cDNA for integrin beta 3 isolated from a human erythroleukaemia (HEL) cell library contained a 340 bp insert at position 1281. This mRNA, termed beta 3c, results from the use of a cryptic AG donor splice site in intron 8 of the beta 3 gene, and is different from a previously described alternative beta 3 mRNA. The predicted open reading frame of beta 3C stops at a TAG stop codon 69 bp downstream from position 1281. It starts with the signal peptide and the 404 N-terminal extracellular residues of beta 3, encompassing the ligand binding sites, followed by 23 C-terminal intron-derived residues, corresponding to a truncated form of beta 3 lacking the cysteine-rich, transmembrane and cytoplasmic domains. Expression of beta 3C mRNA was demonstrated in human platelets, megakaryocytes, endothelial cells and HEL cells by reverse transcriptase/PCR. The beta 3C transcript was also demonstrated in the mouse, suggesting its conservation through evolution. Finally, a 60 kDa polypeptide corresponding to the beta 3C alternative transcript was demonstrated in platelets by Western blotting using a polyclonal antibody raised against a synthetic peptide designed from the beta 3C intronic sequence. Taken together, these results suggest a biological role for beta 3C, the first alternative transcript showing an altered extracellular domain of a beta integrin.

Subpicogram determination of oxytocin by an enzyme immunoassay using acetylcholinesterase as label

The pure tetrameric form of Acetylcholinesterase (EC-3.1.1.7) from the electric eel electrophorus electricus has been covalently coupled to oxytocin. This conjugate has been used as tracer in a heterologous competitive immunoassay. Microtiter plates coated with a mouse monoclonal anti-rabbit immunoglobulin antibody were used to separate bound and free moieties of the tracer. Acetylcholinesterase activity bound to the solid phase was measured by a colorimetric assay. The minimum detectable concentration was 0.075 pg/well (ie 1.5 pg/ml) and precision was less than 8% at concentration above 0.15 pg/well. An extraction step improved sensitivity up to 10 times with good recoveries. To assess the validity of this assay, basal levels of oxytocin were measured during the oestrous cycle of a cow.

Isolation and structure of novel defensive peptides from frog skin

In addition to the highly specific cell-mediated immune system, vertebrates possess an efficient host-defense mechanism against invading microorganisms which involves the synthesis of highly potent antimicrobial peptides with a large spectrum of activity. A 34-residue cationic and amphiphatic peptide, designated dermaseptin I, was recently isolated from the skin of the arboreal frog Phyllomedusa sauvagii and was shown to exhibit microbicidal activity against various pathogenic microorganisms including bacteria, yeast, protozoa and filamentous fungi. In this study, we report the isolation and characterization of four novel antimicrobial peptides from frog skin through the combined use of an anti-dermaseptin enzyme immunoassay and an antifungal bioassay. The 28-34-residue antimicrobial peptides are cationic, containing 3-5 lysine residues that punctuate an alternating hydrophobic and hydrophilic sequence. Based on their primary structure, all four peptides can be fitted to a class L amphipathic alpha helix which places all lysine residues on the polar side of the helix. The four antimicrobial peptides have high sequence similarity with dermaseptin I (53-94% similarity) suggesting that their respective genes are all members of the same family. In addition, pairwise sequence alignment of dermaseptin I and adenoregulin, a 33-residue cationic peptide recently isolated from frog skin and shown to enhance the binding of agonists to the A1 adenosine receptor, reveals 62% similarity (39% amino acid positional identity). Both peptides share a similar but non-identical spectrum of antimicrobial activity, being active against bacteria, yeast and filamentous molds. However, no significant hemolytic activity was found for these peptides which suggests a selectivity for prokaryotic cells. These findings indicate that adenoregulin should be included in the dermaseptin family of peptides. In addition, tryptic digestion of purified pro-dermaseptin I liberated a 15-amino-acid peptide identified as the authentic C-terminus of dermaseptin I. These results are in accordance with the predicted sequences of pro-dermaseptins obtained through molecular cloning, in which the dermaseptin progenitor sequences are located at the extreme C-terminus of the precursors.

Development of an enzyme immunoassay for arginine-vasopressin (AVP)-like insect diuretic hormone

1. The AVP-like insect diuretic hormone is a biologically active antiparallel dimer present, along with its non-active monomeric form (Cys-Leu-Ile-Thr-Asn-Cys-Pro-Arg-GlyNH2), in the African locust. 2. It exhibits diuretic activity by increasing fluid excretion at the level of the Malpighian tubules. 3. To date, both monomer and dimer have been assayed using a radioimmunoassay originally prepared for mammalian AVP. 4. We have developed here an original enzyme immunoassay based on the use of antibodies to insect AVP-like raised in rabbits against synthetic monomers and dimers, using acetylcholinesterase conjugate as an enzymatic tracer. 5. This enzyme immunoassay enables measurement of the dimer to be made with adequate sensitivity (0.3 nmol/l, i.e. 21 pg/well) and reproducibility while sensitivity of the monomer is somewhat lower (14 nmol/l, i.e. 480 pg/well). 6. The assay was validated by assaying native dimer and monomer throughout the different steps of purification (from a crude extract to reversed-phase liquid chromatographic fractions). 7. A good correlation was observed between radioimmunoassays and enzyme immunoassays. 8. The enzyme immunoassay was also used to measure the level of AVP-like peptides in several insect tissues not explored to date.

Enzyme immunometric assay for endothelin using tandem monoclonal antibodies

Seven distinct mouse monoclonal antibodies (mAbs) directed against human endothelin-1 (ET-1) have been obtained. On the basis of specificity studies performed with competitive immunoassays and of complementary binding studies, these mAbs were classified in two groups. mAbs of group A (Endo-4, -5, -6 and -10) were shown to be directed against the N terminal loop while those of group B (Endo-2, -8 and -18) recognized the C terminal part of the peptide. A pair of monoclonal antibodies with optimal properties for a two-site immunometric assay were selected and the test was performed in 96-well microtiter plates coated with one mAb (Endo-18), while another mAb (Endo-4) covalently labeled with enzyme acetylcholinesterase was used as tracer. Under optimal conditions, the assay appeared to be very sensitive since concentrations as low as 1 pg/ml could be significantly detected. The precision was also very good with a coefficient of variation below 10% from 3 to 250 pg/ml. The assay was specific for mature endothelin presenting no cross-reactivity with the precursor Big ET-1. On the other hand, strong cross-reactivity was observed with other ET-1-related peptides, including ET-2, ET-3, VIC peptide and sarafotoxin 6-b. The assay permitted specific determination of ET-1 in supernatants of cultured endothelial cells and the validity of the test was demonstrated by HPLC fractionation experiments. In addition, the assay also appeared to be suitable for direct determination of ET-1 in plasma. Studies performed with plasma from healthy subjects revealed that circulating levels of ET-1 are below or close to the detection limit of the method (< 8 pg/ml).

Processing of atriopeptin prohormone by nonmyocytic atrial cells

Atriopeptin (AP) is synthesized and stored in the mammalian atria as a 126 amino acid prohormone (AP126). Upon secretion, the prohormone undergoes site specific proteolysis within the atria to yield the carboxyl terminal 28 amino acid hormone (AP28). The atrial cell responsible for AP126 bioactivation has not yet been determined. Primary neonatal rat atrial cell cultures were generated with and without depletion of nonmyocytic cells. The molecular form of AP detected in the conditioned media of mixed cultures was determined to be AP126. Addition of dexamethasone to these cultures resulted in the appearance of a peptide that co-migrated with AP28. In contrast, no AP126 processing was detected in the conditioned media of myocyte enriched cultures when grown in the presence of dexamethasone. Readdition of nonmyocytic atrial cells to myocyte enriched cultures successfully reconstituted the steroid induced AP126 processing. Incubation of recombinant AP126argarg with nonmyocytic atrial cell cultures resulted in the generation of AP28argarg. We conclude that a nonmyocytic atrial cell is responsible for AP126 processing in vitro.

Distribution of a negative regulator of haematopoietic stem cell proliferation (AcSDKP) and thymosin beta 4 in mouse tissues

A competitive enzyme immunoassay using acetylcholinesterase as tracer for thymosin beta 4, has been developed. Using this assay and a previously described EIA for AcSDKP, a negative regulator of pluripotent haematopoietic stem cell proliferation, the levels of these two peptides were determined in mouse tissue extracts. The combination of EIAs with different HPLC procedures validated these methods and clearly demonstrated the ubiquity of these peptides in mouse tissues. Similar results are reported for rabbit thymus which suggest different hypotheses for AcSDKP biosynthesis.

An enzyme immunoassay for rat prolactin: application to the determination of plasma levels

Pure acetylcholinesterase (EC 3.1.1.7) from Electrophorus electricus has been covalently coupled to rat prolactin using the heterobifunctional reagent: N-succinimidyl-4 (N-maleimidomethyl) cyclohexane-1-carboxylate (SMCC). This conjugate was used as a tracer in a competitive enzyme immunoassay using a rabbit antiserum, raised against rat prolactin, as first antibody. The assay was performed in 96-well microtiter plates coated with a mouse monoclonal anti-rabbit immunoglobulin antibody. This second antibody solid phase ensured separation of bound and free moieties of the tracer during the specific immunoreaction. The total reaction volume was 150 microliters. Each component (tracer, antiserum and standard) was added in a volume of 50 microliters. The sensitivity of the assay was good since calculation indicated a detection threshold of 25 pg (0.5 ng/ml) and a B/Bo 50% value of 220 pg (4.4 ng/ml). Intra-assay variation was better than 10% over a wide range (135 to 2500 pg) with an optimum of 4% at 300 pg. The inter-assay coefficient of variation was less than 15% for rat plasma samples in the concentration range of 8 to 1000 ng/ml. The good parallelism observed between the standard curve and sample dilution curves, and recovery experiments, indicated that direct assay is possible. This was confirmed by molecular sieve fractionation of plasma samples. The reliability of the assay was confirmed by good correlation with conventional radioimmunoassay (r = 0.996, slope = 0.978).

Post-translational processing and secretory pathway of human atriopeptin in rat pheochromocytoma cells

Atriopeptin (AP) is expressed in several tissues with each tissue capable of specific differences in processing of the prohormone (pro-AP) to mature low molecular forms of the peptide. Since pro-AP has low biological activity, processing into mature AP is a critical activation event. This observation prompted us to study whether granule storage or regulated secretion of AP is essential for cleavage of mature peptide. We examined the processing of AP in adrenal medulla derived cells, using the rat pheochromocytoma cell line (PC12 cell) stably transfected with a genomic human AP DNA in the presence and absence of nerve growth factor (NGF), and also examined the mechanism of AP secretion and compared the results with those obtained using transfected chinese hamster ovary cells (CHO cells). The amount of prohormone was 5-10 fold higher than that of low molecular form of AP in the transfected PC12 cells. This ratio was essentially unchanged in differentiated PC12 cells after NGF treatment of the cells. Potassium depolarization of the transfected PC12 cells caused a 5-fold increase in AP release into the medium primarily as the intact prohormone. On the other hand, transfected CHO cells only exhibited constitutive AP release which is non-response to depolarization. These results suggest that the AP prohormone is sorted into secretory granules as the prohormone in PC12 cells and undergoes regulated release in response to depolarization indicating granule storage or release is not the critical determinant of AP prohormone cleavage.

Enzyme immunoassay of benzyl penicilloyl (BPO) groups using acetylcholinesterase as label. Application to the study of the BPO-binding sites on albumin

Benzyl penicilloyl groups (BPO) derive from penicillin G by cleavage of the beta lactam ring; they covalently bind to proteins to give conjugates which have lost all antibiotic properties but are considered as the major allergenic determinants in penicillin allergy. A solid-phase Enzyme Immuno Assay (EIA) of BPO groups in different biological fluids is described. It is a competitive immunoassay using acetylcholinesterase as label. In all biological fluids, very low non-specific binding values are observed. The sensitivity and the precision of the assay are good since ca. 0.5 ng/ml can be measured with a coefficient of variation less than 10%. Cross reactions between BPO and penicillin or penicillin derivatives are nil or very low. This assay is more sensitive, much more rapid and easier to handle than the other methods available and is thus suitable for routine determinations. In association with reversed-phase high performance liquid chromatography this EIA has allowed an initial investigation of the location of BPO-binding sites on micro quantities of serum albumin (ca. 1 mg) from penicillin treated patients.

Enzyme immunoassay for tachykinin-like immunoreactivity in the guinea pig spinal cord

A solid-phase enzyme immunoassay for quantitation of tachykinin-like immunoreactivity (TK-LI) is presented. Because the antiserum K-12 recognizes various tachykinins, such as neurokinin A (100%), kassinin (103%), eledoisin (51%), neurokinin B (18%), physalaemin (0.7%), and substance P (0.7%), the immunoreactivity detected in this enzyme immunoassay has been termed TK-LI. The assay was performed on 96-well microtiter plates coated with a mouse monoclonal second antibody. After preincubation of soluble neurokinin A or samples and K-12 antiserum for 3 h at room temperature, acetylcholinesterase-labelled neurokinin A was allowed to react overnight at 4 degrees C. Samples were finally incubated with Ellman's reagent for 2 h and the absorbance was measured at 414 nm. The threshold for detection of TK-LI was 2 fmol/well. TK-LI release from guinea pig dorsal spinal cord slices was evoked by capsaicin or high K+ medium. The capsaicin-evoked TK-LI release was increased in the presence of thiorphan, but not in that of captopril.

Synthesis and secretion of an atriopeptin-like protein in rat kidney cell culture

The synthesis and secretion of an atriopeptin(AP)-like prohormone (AP126ir) has been demonstrated in rat neonatal renal cell cultures. AP126ir could be detected in the cellular extract and the medium from cultured kidney cells of neonatal and adult rats using an enzyme immunoassay specific for cardiac AP prohormone. On reverse-phase high-performance liquid chromatography, the AP obtained from the extract and the medium comigrated with cardiac AP prohormone. Incubation of the renal AP in the medium with thrombin resulted in the generation of a single low molecular mass peak which migrated with the cardiac carboxy-terminal 28-amino acid AP. Neonatal kidney cells pulsed with [35S]methionine secreted radiolabeled AP126ir, which was detected by immunoprecipitation and sodium dodecyl sulfate-polyacrylamide gel electrophoresis chromatography. Incubation of neonatal kidney cell cultures with the protein synthesis inhibitor cycloheximide resulted in a significant decrease in both the cellular and media AP. No decrease in cellular and media AP was detected when neonatal atrial cultures were treated with cycloheximide. These data demonstrate the de novo synthesis of an AP prohormone-like protein in neonatal rat kidney cultures. Furthermore, unlike the atria, kidney cells appear to secrete AP solely by constitutive means. In primary adult rat kidney cultures, most of AP126ir was detected in the cortical tubule fraction demonstrating that these cells secrete AP126ir in the adult rat kidney. We hypothesize that the renal AP may be important as an autocrine or paracrine regulator of renal function.

Negative regulator of pluripotent hematopoietic stem cell proliferation in human white blood cells and plasma as analysed by enzyme immunoassay

This paper describes the analysis, by a highly sensitive and specific enzyme immunoassay (EIA), of AcSDKP, a tetrapeptide recently isolated from fetal calf bone marrow and subsequently purified and identified which substantially inhibits entry into cycle of hematopoietic pluripotent stem cells (CFU-S). This molecule has a marked protective effect in mice during anticancer chemotherapy with phase-specific drugs and plays an essential role in maintaining CFU-S out of cycle in normal mice. Using acetylcholinesterase-AcSDKP conjugate as tracer, rabbit specific antiserum and 96-well microtiter plates coated with a mouse monoclonal anti-rabbit IgG antibody, this EIA allows detection of AcSDKP at 15 fmol levels with a coefficient of variation less than 10% in the 50-500 fmol range. When combined with high-performance liquid chromatography, this assay clearly reveals the presence of this peptide in normal human white blood cells whereas in supernatant from cultured lymphocytes and in plasma the immunoreactive material is distinct from standard AcSDKP.

Maximizing the natriuretic effect of endogenous atriopeptin in a rat model of heart failure

The effect of pharmacological manipulation of atriopeptin (AP) activity on sodium excretion and blood pressure was examined in the rat aortovenocaval (A-V) fistula model of cardiac failure. Introduction of an A-V shunt led to a marked and sustained elevation of plasma AP immunoreactivity and urinary cGMP levels. Further elevation of plasma AP levels by infusion of exogenous peptide induced modest increases in urinary sodium and cGMP excretion and a decrease in blood pressure but these responses were significantly attenuated compared to sham-operated animals. In contrast, low-dose infusion of M + B 22948 (a cGMP phosphodiesterase inhibitor) or thiorphan [a neutral endopeptidase (membrane metallo-endopeptidase, EC 3.4.24.11) inhibitor] induced a natriuresis in A-V fistula rats, which exceeded that seen in control animals given these compounds and matched the peak natriuresis produced in sham-operated animals by high doses of AP. In the doses used, these compounds had little effect on blood pressure. The greater renal efficacy of M + B 22948 in A-V fistula rats is consistent with postreceptor facilitation of AP activity. The effect of thiorphan on sodium excretion was accompanied by a pronounced increase in urinary cGMP and AP immunoreactivity excretion (and was attenuated by anti-AP monoclonal antibody) but could not be explained solely in terms of an increase in circulating AP levels. It is proposed that thiorphan allows filtered AP to reach renal tubule sites that are normally inaccessible to the peptide and are thus protected from down-regulation by high circulating AP levels. The implication of these observations for patients in cardiac failure is the potential for using pharmacological agents to maximize the response to endogenous AP without compromising cardiac function.

Augmentation of the natriuretic activity of exogenous and endogenous atriopeptin in rats by inhibition of guanosine 3',5'-cyclic monophosphate degradation

To investigate the relationship between AP, cyclic GMP, and sodium excretion, we studied the effect of a cyclic GMP phosphodiesterase inhibitor (M + B22948) on the natriuretic response to (a) an infusion of AP (103-126) and (b) acute volume expansion in rats. The phosphodiesterase inhibitor markedly potentiated the effect of low-dose AP infusions on urinary sodium and cyclic GMP excretion without potentiating the fall in blood pressure. Acute volume expansion (1% body wt) led to small but significant (P less than 0.01) rises in plasma AP and urinary cyclic GMP levels. Pretreatment with the phosphodiesterase inhibitor enhanced the natriuretic and cyclic GMP response to volume loading, an effect that was attenuated by administration of a monoclonal antibody directed against AP. These data indicate that cyclic GMP mediates the natriuretic activity of AP and AP and cyclic GMP play active roles in the natriuresis of acute volume expansion. Moreover, pharmacological manipulation of cyclic GMP levels may prove a useful therapeutic strategy for facilitating the natriuretic but not the hypotensive effects of AP.

Production of monoclonal antibodies against interleukin-1 alpha and -1 beta. Development of two enzyme immunometric assays (EIA) using acetylcholinesterase and their application to biological media

We describe two series of monoclonal antibodies (mAbs) directed against human interleukin-1 alpha (36 mAbs) and -1 beta (11 mAbs). The binding compatibility of each of mAb was studied using biotin-labelled mAbs in immunometric tests. Among the different pairs of compatible mAbs, we selected one pair for each interleukin-1 (IL-1) with optimal properties for a two-site immunometric assay. In these assays, covalent conjugates of mAb coupled to the tetrameric form of acetylcholinesterase (mAb-AChE) were used as tracers. The tests were performed in 96-well microtiter plates coated with the complementary mAb. Both assays appeared sensitive and specific since minimum detectable concentrations as low as 1 pg/ml were determined for each IL-1 without any significant cross-reactivity (less than 0.01%). The intra-assay precision was also very good with a coefficient of variation of less than 10% over a wide range (between 3 and 500 pg/ml depending on the time devoted to the enzymatic reaction). The high sensitivity and precision of the assays can be ascribed to the high affinities of the mAbs as well as the optimal catalytic properties of AChE. The specificity of the determination performed in culture medium was demonstrated using different validation tests including a comparison with a bioassay and the fractionation of samples by molecular sieve chromatography. Evidence is presented that the assay could be used for the determination of IL-1 levels in biological media such as plasma or serum.

Isolation of dermenkephalin from amphibian skin, a high-affinity delta-selective opioid heptapeptide containing a D-amino acid residue

The predicted amino acid sequence of the biosynthetic precursor of dermorphin, a highly potent and nearly specific mu-opioid peptide from amphibian skin, contains four repeats of the dermorphin progenitor sequence and one single copy of a different heptapeptide sequence. We have developed a specific enzyme immunoassay and used synthetic peptides to detect and purify the new predicted heptapeptide (2.4 micrograms/g dry skin) from the skin of the Phyllomedusa sauvagei frog from which dermorphin was originally isolated. The identity of the novel pro-dermorphin related peptide, Tyr-D-Met-Phe-His-Leu-Met-Asp-NH2, was established by co-chromatography with synthetic peptides on reverse-phase HPLC, immunological analysis, gas-phase sequencing, mass spectrometry and by pharmacological assays. Opioid-binding assays in vitro demonstrated that both the natural and synthetic heptapeptides displayed exceptionally high selectivity and affinity towards the delta-opioid receptors. Because of its origin and its delta-opioid (enkephalin) activity and specificity, this novel D-amino acid containing peptide is named dermenkephalin.

Novel and sensitive noncompetitive enzyme immunoassay for peptides

A novel and sensitive noncompetitive enzyme immunoassay for peptides is described. Peptides were biotinylated using sulfosuccinimidyl-6-(biotinamido)hexanoate and were trapped onto anti-peptide IgG-coated polystyrene balls. After washing the polystyrene balls to eliminate other biotinylated substances, the biotinylated peptides were eluted with HC1 and were reacted with anti-peptide Fab'-peroxidase conjugate. The complex formed was trapped onto streptavidin-coated polystyrene balls. Peroxidase activity bound to the polystyrene balls was assayed by fluorimetry. The detection limit of angiotensin I as a model peptide was 13 fg (10 amol)/tube and 0.8 ng/l of plasma, which was 80 to 480-fold lower than those previously reported by competitive radioimmunoassay and competitive enzyme immunoassay. And other peptides could also be measured more sensitively by the present noncompetitive enzyme immunoassay method than by competitive immunoassays.

Human atrial natriuretic factor (ANF). Characterisation of a monoclonal antibody panel and its use in radioimmunoassay

The production of nine monoclonal antibodies to human atrial natriuretic factor (ANF 1-28) is described. All possible combinations of two antibodies failed to reveal any which could simultaneously bind ANF. Studies with ANF analogues and the antibodies having the three highest affinity values (KD = 5, 25 and 21 pM) indicated that the antibodies are directed to the central portion of the antigen molecule. The highest affinity antibody was able to replace polyclonal antisera in the radioimmunoassay of ANF in extracts of plasma.