Insulin-degrading enzyme regulates extracellular levels of amyloid beta-protein by degradation

Excessive cerebral accumulation of the 42-residue amyloid beta-protein (Abeta) is an early and invariant step in the pathogenesis of Alzheimer's disease. Many studies have examined the cellular production of Abeta from its membrane-bound precursor, including the role of the presenilin proteins therein, but almost nothing is known about how Abeta is degraded and cleared following its secretion. We previously screened neuronal and nonneuronal cell lines for the production of proteases capable of degrading naturally secreted Abeta under biologically relevant conditions and concentrations. The major such protease identified was a metalloprotease released particularly by a microglial cell line, BV-2. We have now purified and characterized the protease and find that it is indistinguishable from insulin-degrading enzyme (IDE), a thiol metalloendopeptidase that degrades small peptides such as insulin, glucagon, and atrial natriuretic peptide. Degradation of both endogenous and synthetic Abeta at picomolar to nanomolar concentrations was completely inhibited by the competitive IDE substrate, insulin, and by two other IDE inhibitors. Immunodepletion of conditioned medium with an IDE antibody removed its Abeta-degrading activity. IDE was present in BV-2 cytosol, as expected, but was also released into the medium by intact, healthy cells. To confirm the extracellular occurrence of IDE in vivo, we identified intact IDE in human cerebrospinal fluid of both normal and Alzheimer subjects. In addition to its ability to degrade Abeta, IDE activity was unexpectedly found be associated with a time-dependent oligomerization of synthetic Abeta at physiological levels in the conditioned media of cultured cells; this process, which may be initiated by IDE-generated proteolytic fragments of Abeta, was prevented by three different IDE inhibitors. We conclude that a principal protease capable of down-regulating the levels of secreted Abeta extracellularly is IDE.

Efficient electrocatalysis of L-cysteine oxidation at carbon ionic liquid electrode

The electrochemistry of L-cysteine (CySH) in neutral aqueous media was investigated using carbon ionic liquid electrode (CILE). Comparative experiments were carried out using glassy carbon electrodes. At CILE, highly reproducible and well-defined cyclic voltammograms were obtained for l-cysteine with a peak potential of 0.49V vs Ag/AgCl, showing that CILE manifests a good electrocatalytic activity toward oxidation of l-cysteine. A linear dynamic range of 2-210microM with an experimental detection limit of 2microM was obtained. The method was successfully applied to the determination of l-cysteine in a sample of soya milk. Cysteine oxidation at CILE does not result in deactivation of the electrode surface. Mechanistic studies showed that, at CILE, the overall CySH oxidation is controlled by the oxidation of the CyS(-) electroactive species.

Cloud point extraction, preconcentration and simultaneous spectrophotometric determination of nickel and cobalt in water samples

Cloud point extraction has been used for the preconcentration and simultaneous spectrophotometric determination of nickel and cobalt after the formation of a complex with 2-amino-cyclopentene-1-dithiocarboxylic acid (ACDA), and latter analysis by spectrophotometer using Triton X-114 as surfactant. The parameters affecting the separation phase and detection process were optimized. Under the optimum experimental conditions (i.e. pH=5, 0.07 mM ACDA, Triton X-114=0.25% (w/v)), calibration graphs were linear in the range of 20-500 and 20-200 microg l(-1) with detection limits of 10 and 7.5 microg l(-1) for Ni and Co, respectively. The method was applied to the determination of Ni and Co in natural and waste water samples with satisfactory results.

Identification of gamma-endorphin-generating enzyme as insulin-degrading enzyme

The EL-4 thymoma cell line contains a peptidase which converts beta-endorphin to beta-endorphin 1-17 (gamma-endorphin), beta-endorphin 1-18, and their corresponding C-terminal fragments. This enzyme was purified approximately 700-fold to a single band on an SDS-polyacrylamide gel (106 kDa) in 16% yield. Estimation of the native molecular weight by molecular sieve chromatography gave a value of approximately 220 kDa, indicating that this enzyme is a dimer. Peptide sequencing demonstrated this activity can be attributed to insulin degrading enzyme, a previously described member of the inverzincin family (Hooper, 1994). Kinetic studies with a number of peptide substrates indicate that the enzyme preferentially cleaves on the amino side of hydrophobic or basic residues. However, the substrate specificity is more complex since not all basic and hydrophobic residues in a peptide are cleaved. The enzyme exhibits a requirement for a P'2 residue. On the basis of kcat/K(m) values, insulin, growth hormone releasing factor, and beta-endorphin are nearly equivalent substrates for the enzyme; however, growth hormone releasing factor and beta-endorphin exhibit a 40-fold higher kcat, but a 10-fold decreased affinity relative to insulin. A role for insulin-degrading enzyme as both a beta-endorphin-processing and -inactivating enzyme is implicated from these studies.

Delayed primary repair of intrathoracic esophageal perforation: is it safe?

The management of intrathoracic esophageal perforation with delayed diagnosis is a subject of controversy. Because of the obvious advantages of primary repair as a simple single-stage operation, this technique was preferentially used to treat 18 of 22 consecutive patients with esophageal perforation. These patients were stratified into three groups according to the time interval between perforation and repair: group A, less than 6 hours, five patients (28%); group B, 6 to 24 hours, six patients (33%); and group C, more than 24 hours, seven patients (39%). Group A patients were older (p < 0.05) and group B had fewer iatrogenic perforations (B, 17%; A, 80%; C, 57%, p < 0.1). Additional tissue was used to buttress the repair site in all three groups (A, 3/5 patients, 60%; B, 4/6 patients, 67%; C, 6/7 patients, 86%; p = not significant). In seven patients (39%), a fundic wrap was used to reinforce the site of primary repair. The outcomes of the three groups were analyzed. Group A had the lowest proportion of postoperative leaks (A, 0/4 patients, 0%; B, 4/6 patients, 67%; C, 5/6 patients, 83%; p < 0.05) and postoperative morbidity (A, 2/5 patients, 40%; B, 6/6 patients, 100%; C, 6/7 patients, 86%; p < 0.1). However the increased incidence of leak and morbidity did not lead to an increase in mortality. One death occurred in each group, with an overall mortality of 17% (A, 1/5 patients, 20%; B, 1/6 patients, 17%; C, 1/7 patients, 14%; p = not significant). We conclude that in the era of advanced intensive care capabilities, primary repair of intrathoracic esophageal perforation can be safely accomplished in most patients regardless of the time interval between perforation and operation. Leakage at the suture site is common unless primary repair is carried out without delay. Postoperative leakage, however, is usually inconsequential and does not necessarily result in an adverse outcome.

Anorectal surgery in the HIV+ patient: update

Anorectal surgery in HIV+ patients historically has been viewed with a great deal of nihilism. Advances in medical therapy and better understanding of unique pathophysiologic processes have afforded the colorectal surgeon the ability to treat better and sometimes cure the anorectal complications of AIDS. We present a series of 75 consecutive surgical procedures (1-year accrual) on HIV+ (40) and CDC AIDS (22) patients. Surgical procedures, perioperative T cell counts, and outcome will be presented; 53 percent of procedures resulted in complete healing of anal wounds; 30 percent resulted in partial healing with symptomatic relief; 17 percent resulted in symptomatic relief or tissue diagnosis without appreciable wound healing. The healing rate was significantly higher in the HIV+ group (69 percent) compared to the AIDS group (26 percent). Perioperative T cell counts did not have predictive value on outcome. No patients suffered significant unexpected morbidity, mortality, or incontinence. Pathophysiologic mechanisms of several disease processes unique to HIV+ patients and data from our ongoing investigation using RNA hybridization are presented.

Deep eutectic-water binary solvent associations investigated by vibrational spectroscopy and chemometrics

Investigation of the behaviour of deep eutectic solvents (DESs) as novel green solvents in the presence of other solvents is of great interest. In this study the behaviour of a common natural DES, namely choline chloride-glycerol deep eutectic solvent (GDES), was studied in the presence of water. A detailed study of the association of the two solvents was performed by integration of two vibrational spectroscopic methods (FTIR and Raman spectroscopy) followed by multivariate analysis. Moreover, a binary mixture of glycerol (Gly) as one of the liquid constituents of GDES and water was explored under the same conditions. A quintuplet and ternary systems were resolved for GDES-water and Gly-water probes, respectively, using multivariate analysis of global data (multi-technique and multi-experiment data arrangements). The results confirmed that in the presence of water the GDES showed different behaviour from its components. Therefore, a DES can be introduced as an independent solvent with its unique properties. Also, different H-bond interaction energies of GDES and its pure components in the presence of water were shown by theoretical calculations based on a density functional theory framework. To investigate the effects of water on the structure of GDES, molecular dynamics (MD) simulations of GDES-water liquid mixtures were performed at 0.9 mole fraction of water.

Degradation of dynorphin-related peptides by the puromycin-sensitive aminopeptidase and aminopeptidase M

The degradation of dynorphin-related peptides by the puromycin-sensitive aminopeptidase and aminopeptidase M was examined using these peptides as alternate substrate inhibitors. Ki determinations showed that both aminopeptidases exhibit a higher affinity for longer dynorphin-related peptides, i.e., Ki for dynorphin A-17 = 23-30 nM with the Ki increasing to 25-50 microM for the enkephalin pentapeptides. Binding appears dependent not only on peptide length, but also on its sequence. With aminopeptidase M, as the peptide size increases from five to 10 amino acids, kcat remains relatively constant; however, as the peptide size increases beyond a decapeptide, kcat decreases significantly. With the puromycin-sensitive aminopeptidase, similar results were obtained except that kcat was greatest for the pentapeptide. Thus, if one considers kcat/Km as the relevant kinetic constant for estimating in vivo peptide hydrolysis, these results are consistent with the involvement of aminopeptidase M and the puromycin-sensitive aminopeptidase in the degradation of extended dynorphin-related peptides.

CCD camera full range pH sensor array

Changes in colors of an array of optical sensors that responds in full pH range were recorded using a CCD camera. The data of the camera were transferred to the computer through a capture card. Simple software was written to read the specific color of each sensor. In order to associate sensor array responses with pH values, a number of different mathematics and chemometrics methods were investigated and compared. The results show that the use of "Microsoft Excel's Solver" provides results which are in very good agreement with those obtained with chemometric methods such as artificial neural network (ANN) and partial least square (PLS) methods.

A catalytically active Jak2 is required for the angiotensin II-dependent activation of Fyn

Recent work with interleukins has shown a convergence of tyrosine phosphorylation signal transduction cascades at the level of the Janus and Src families of tyrosine kinases. Here we demonstrate that activation of the seven-transmembrane AT(1) receptor by angiotensin II induces a physical association between Jak2 and Fyn, in vivo. This association requires the catalytic activity of Jak2 but not Fyn. Deletion studies indicate that the region of Jak2 that binds Fyn is located between amino acids 1 and 240. Studies of the Fyn SH2 and SH3 domains demonstrate that the SH2 domain plays the primary role in Jak2/Fyn association. Not surprisingly, this domain shows a marked preference for tyrosine-phosphorylated Jak2. Surface plasmon resonance estimated the dissociation equilibrium constant (K(d)) of this association to be 2.36 nM. Last, in vivo studies in vascular smooth muscle cells show that, in response to angiotensin II, Jak2 activation is required for Fyn activation and induction of the c-fos gene. The significance of these data is that Jak2, in addition to serving as a critical angiotensin II activated signal transduction kinase, also functions as a docking protein and participates in the activation of Fyn by providing phosphotyrosine residues that bind the SH2 domain of Fyn.

Sensitive indirect spectrophotometric determination of isoniazid

A simple, rapid, sensitive and accurate indirect spectrophotometric method for the microdetermination of isoniazid (INH) in pure form and pharmaceutical formulations is developed. The procedure is based on the reaction of copper(II) with isoniazid in the presence of neocuproine (NC). In the presence of neocuproine, copper(II) is reduced easily by isoniazid to a Cu(I)-neocuproine complex, which shows an absorption maximum at 454 nm. By measuring the absorbance of the complex at this wavelength, isoniazid can be determined in the range 0.3-3.5 microgml-1. This method was applied to the determination of isoniazid in pharmaceutical formulation and enabled the determination of the isoniazid in microgram quantities (0.3-3.5 microgml-1). The results obtained for the assay of pharmaceutical preparations compared well with those obtained by the official method and demonstrated good accuracy and precision.

Purification and characterization of a secreted arginine-specific dibasic cleaving enzyme from EL-4 cells

A secreted dibasic cleaving peptidase capable of converting dynorphins into Leu-enkephalin-Arg6 was purified from the medium of EL-4 mouse thymoma cells. The enzyme is a novel metalloendopeptidase with a neutral pH optimum (6.9) and a molecular weight of approximately 130 000. The dibasic cleaving enzyme was completely inhibited in the presence of 20-50 mM amine buffers, 0.1 mM EDTA, 0.5 mM 1,10-phenanthroline, 0.5 mM N-ethylmaleimide, and 1mM DTNB. Unlike the Kex2 family of proteases, Ca2+ did not activate the endopeptidase, but high concentrations (1 mM) of metal ions such as Cu2+, Ni2+, Zn2+, and Co2+ completely inhibited the enzyme. Inhibition was not seen with 0.2 mM TLCK, 1 mM DTT, and 1 mM PMSF. The enzyme will cleave Arg-Arg and Arg-Lys bonds, but not Lys-Arg or Lys-Lys bonds in identical environments, and no aminopeptidase or carboxypeptidase activity was seen. The size of the substrate does not seem to be a determining factor, since dynorphin A(1-12) is cleaved at a rate similar to prodynorphin B(228-256) containing 29 amino acids. The identity of the residues on either side of the cleavage site influences the rate of processing, as noted by different rates of cleavage for the same size peptides dynorphin A(1-13) vs dynorphin A(1-9) vs beta-neoendorphin. The presence of proline in the P3' (alpha-neoendorphin), P4' (dynorphin A(1-11)), or P5' (bovine adrenal medulla dodecapeptide) position does not prevent cleavage, but neurotensin and its (1-11) fragment containing both P2 and P2' proline residues are not cleaved.

A dramatic change in the interaction of Cu(II) with bio-peptides promoted by SDS--a model for complex formation on a membrane surface

The extent of complex formation between Cu(II) and many biologically active oligopeptides has been shown to change significantly in the presence of SDS micelles, a recognized model for cell lipid membranes. Protonation constants of peptides can be increased by up to 2 log unit, especially when they contain hydrophobic side chains. Metal complex formation is generally less extensive and the conformations of peptides can be altered dramatically when compared to those in simple aqueous solution.