Are there neuropeptide-specific peptidases?

Stochastic neuropeptide signals compete to calibrate the rate of satiation

Neuropeptides have important roles in neural plasticity, spiking and behaviour1. Yet, many fundamental questions remain regarding their spatiotemporal transmission, integration and functions in the awake brain. Here we examined how MC4R-expressing neurons in the paraventricular nucleus of the hypothalamus (PVHMC4R) integrate neuropeptide signals to modulate feeding-related fast synaptic transmission and titrate the transition to satiety2-6. We show that hunger-promoting AgRP axons release the neuropeptide NPY to decrease the second messenger cAMP in PVHMC4R neurons, while satiety-promoting POMC axons release the neuropeptide αMSH to increase cAMP. Each release event is all-or-none, stochastic and can impact multiple neurons within an approximately 100-µm-diameter region. After release, NPY and αMSH peptides compete to control cAMP-the amplitude and persistence of NPY signalling is blunted by high αMSH in the fed state, while αMSH signalling is blunted by high NPY in the fasted state. Feeding resolves this competition by simultaneously elevating αMSH release and suppressing NPY release7,8, thereby sustaining elevated cAMP in PVHMC4R neurons throughout a meal. In turn, elevated cAMP facilitates potentiation of feeding-related excitatory inputs with each bite to gradually promote satiation across many minutes. Our findings highlight biochemical modes of peptide signal integration and information accumulation to guide behavioural state transitions.

Presynaptic sensor and silencer of peptidergic transmission reveal neuropeptides as primary transmitters in pontine fear circuit

Neurons produce and release neuropeptides to communicate with one another. Despite their importance in brain function, circuit-based mechanisms of peptidergic transmission are poorly understood, primarily due to the lack of tools for monitoring and manipulating neuropeptide release in vivo. Here, we report the development of two genetically encoded tools for investigating peptidergic transmission in behaving mice: a genetically encoded large dense core vesicle (LDCV) sensor that detects presynaptic neuropeptide release and a genetically encoded silencer that specifically degrades neuropeptides inside LDCVs. Using these tools, we show that neuropeptides, not glutamate, encode the unconditioned stimulus in the parabrachial-to-amygdalar threat pathway during Pavlovian threat learning. We also show that neuropeptides play important roles in encoding positive valence and suppressing conditioned threat response in the amygdala-to-parabrachial endogenous opioidergic circuit. These results show that our sensor and silencer for presynaptic peptidergic transmission are reliable tools to investigate neuropeptidergic systems in awake, behaving animals.

Competition between stochastic neuropeptide signals calibrates the rate of satiation

We investigated how transmission of hunger- and satiety-promoting neuropeptides, NPY and αMSH, is integrated at the level of intracellular signaling to control feeding. Receptors for these peptides use the second messenger cAMP, but the messenger's spatiotemporal dynamics and role in energy balance are controversial. We show that AgRP axon stimulation in the paraventricular hypothalamus evokes probabilistic and spatially restricted NPY release that triggers stochastic cAMP decrements in downstream MC4R-expressing neurons (PVH MC4R ). Meanwhile, POMC axon stimulation triggers stochastic, αMSH-dependent cAMP increments. NPY and αMSH competitively control cAMP, as reflected by hunger-state-dependent differences in the amplitude and persistence of cAMP transients evoked by each peptide. During feeding bouts, elevated αMSH release and suppressed NPY release cooperatively sustain elevated cAMP in PVH MC4R neurons, thereby potentiating feeding-related excitatory inputs and promoting satiation across minutes. Our findings highlight how state-dependent integration of opposing, quantal peptidergic events by a common biochemical target calibrates energy intake.

Novel genetically encoded tools for imaging or silencing neuropeptide release from presynaptic terminals in vivo

Neurons produce and release neuropeptides to communicate with one another. Despite their profound impact on critical brain functions, circuit-based mechanisms of peptidergic transmission are poorly understood, primarily due to the lack of tools for monitoring and manipulating neuropeptide release in vivo. Here, we report the development of two genetically encoded tools for investigating peptidergic transmission in behaving mice: a genetically encoded large dense core vesicle (LDCV) sensor that detects the neuropeptides release presynaptically, and a genetically encoded silencer that specifically degrades neuropeptides inside the LDCV. Monitoring and silencing peptidergic and glutamatergic transmissions from presynaptic terminals using our newly developed tools and existing genetic tools, respectively, reveal that neuropeptides, not glutamate, are the primary transmitter in encoding unconditioned stimulus during Pavlovian threat learning. These results show that our sensor and silencer for peptidergic transmission are reliable tools to investigate neuropeptidergic systems in awake behaving animals.

Thimet Oligopeptidase Biochemical and Biological Significances: Past, Present, and Future Directions

Thimet oligopeptidase (EC 3.4.24.15; EP24.15, THOP1) is a metallopeptidase ubiquitously distributed in mammalian tissues. Beyond its previously well characterized role in major histocompatibility class I (MHC-I) antigen presentation, the recent characterization of the THOP1 C57BL6/N null mice (THOP1^−/−) phenotype suggests new key functions for THOP1 in hyperlipidic diet-induced obesity, insulin resistance and non-alcoholic liver steatosis. Distinctive levels of specific intracellular peptides (InPeps), genes and microRNAs were observed when comparing wild type C57BL6/N to THOP1^−/− fed either standard or hyperlipidic diets. A possible novel mechanism of action was suggested for InPeps processed by THOP1, which could be modulating protein-protein interactions and microRNA processing, thus affecting the phenotype. Together, research into the biochemical and biomedical significance of THOP1 suggests that degradation by the proteasome is a step in the processing of various proteins, not merely for ending their existence. This allows many functional peptides to be generated by proteasomal degradation in order to, for example, control mRNA translation and the formation of protein complexes.

The atypical chemokine receptor ACKR3/CXCR7 is a broad-spectrum scavenger for opioid peptides

Endogenous opioid peptides and prescription opioid drugs modulate pain, anxiety and stress by activating opioid receptors, currently classified into four subtypes. Here we demonstrate that ACKR3/CXCR7, hitherto known as an atypical scavenger receptor for chemokines, is a broad-spectrum scavenger of opioid peptides. Phylogenetically, ACKR3 is intermediate between chemokine and opioid receptors and is present in various brain regions together with classical opioid receptors. Functionally, ACKR3 is a scavenger receptor for a wide variety of opioid peptides, especially enkephalins and dynorphins, reducing their availability for the classical opioid receptors. ACKR3 is not modulated by prescription opioids, but we show that an ACKR3-selective subnanomolar competitor peptide, LIH383, can restrain ACKR3’s negative regulatory function on opioid peptides in rat brain and potentiate their activity towards classical receptors, which may open alternative therapeutic avenues for opioid-related disorders. Altogether, our results reveal that ACKR3 is an atypical opioid receptor with cross-family ligand selectivity.

Opioids modulate pain, anxiety and stress by activating four subtypes of opioid receptors. The authors show that atypical chemokine receptor 3 (ACKR3) is a scavenger for various endogenous opioid peptides regulating their availability without activating downstream signaling.

Thimet Oligopeptidase (EC 3.4.24.15) Key Functions Suggested by Knockout Mice Phenotype Characterization

Thimet oligopeptidase (THOP1) is thought to be involved in neuropeptide metabolism, antigen presentation, neurodegeneration, and cancer. Herein, the generation of THOP1 C57BL/6 knockout mice (THOP1^−/−) is described showing that they are viable, have estrus cycle, fertility, and a number of puppies per litter similar to C57BL/6 wild type mice (WT). In specific brain regions, THOP1^-/- exhibit altered mRNA expression of proteasome beta5, serotonin 5HT2a receptor and dopamine D2 receptor, but not of neurolysin (NLN). Peptidomic analysis identifies differences in intracellular peptide ratios between THOP1^-/- and WT mice, which may affect normal cellular functioning. In an experimental model of multiple sclerosis THOP1^-/- mice present worse clinical behavior scores compared to WT mice, corroborating its possible involvement in neurodegenerative diseases. THOP1^-/- mice also exhibit better survival and improved behavior in a sepsis model, but also a greater peripheral pain sensitivity measured in the hot plate test after bradykinin administration in the paw. THOP1^-/- mice show depressive-like behavior, as well as attention and memory retention deficits. Altogether, these results reveal a role of THOP1 on specific behaviors, immune-stimulated neurodegeneration, and infection-induced inflammation.

PnPP-19, a spider toxin peptide, induces peripheral antinociception through opioid and cannabinoid receptors and inhibition of neutral endopeptidase

BACKGROUND AND PURPOSE

The synthetic peptide PnPP-19 has been studied as a new drug candidate to treat erectile dysfunction. However, PnTx2-6, the spider toxin from which the peptide was designed, induces hyperalgesia. Therefore, we intended to investigate the role of PnPP-19 in the nociceptive pathway.

EXPERIMENTAL APPROACH

Nociceptive thresholds were measured by paw pressure test. PnPP-19 was administered intraplantarly alone or with selective cannabinoid or opioid receptor antagonists. The hydrolysis of PnPP-19 by neutral endopeptidase (NEP) (EC 3.4.24.11), an enzyme that cleaves enkephalin, was monitored by HPLC and the cleavage sites were deduced by LC-MS. Inhibition by PnPP-19 and Leu-enkephalin of NEP enzyme activity was determined spectrofluorimetrically.

KEY RESULTS

PnPP-19 (5, 10 and 20 μg per paw) induced peripheral antinociception in rats. Specific antagonists of μ opioid receptors (clocinnamox), δ opioid receptors (naltrindole) and CB1 receptors (AM251) partly inhibited the antinociceptive effect of PnPP-19. Inhibition of fatty acid amide hydrolase by MAFP or of anandamide uptake by VDM11 enhanced PnPP-19-induced antinociception. NEP cleaved PnPP-19 only after a long incubation, and Ki values of 35.6 ± 1.4 and 14.6 ± 0.44 μmol·L(-1) were determined for PnPP-19 and Leu-enkephalin respectively as inhibitors of NEP activity.

CONCLUSIONS AND IMPLICATIONS

Antinociception induced by PnPP-19 appears to involve the inhibition of NEP and activation of CB1, μ and δ opioid receptors. Our data provide a greater understanding of the antinociceptive effects of PnPP-19. This peptide could be useful as a new antinociceptive drug candidate.

Spinal ERK2 activation through δ2-opioid receptors contributes to nociceptive behavior induced by intrathecal injection of leucine-enkephalin

Intrathecal (i.t.) injection of leucine-enkephalin (Leu-ENK), co-administered with peptidase inhibitors, phosphoramidon (an endopeptidase 24.11 inhibitor), and bestatin (a general aminopeptidase inhibitor), produced behaviors consisting of the biting and/or licking of the hindpaw and the tail along with hindlimb scratching directed toward the flank, which peaked at 10-15 min after an injection. This characteristic behavior was not observed in mice treated with i.t. Leu-ENK alone. We also investigated the effect of the extracellular signal-regulated kinase (ERK) in spinal processing of nociception induced by i.t. co-administration of Leu-ENK with phospharamidon and bestatin. Western blot analysis of phospho-ERK (pERK) showed a significant increase of pERK2 in the lumbar spinal cord in response to i.t. Leu-ENK co-injected with peptidase inhibitors. The MAP kinase-ERK inhibitor, U0126 dose-dependently attenuated the nociceptive behavior and spinal ERK activation to i.t. Leu-ENK co-injected with peptidase inhibitors. Furthermore, the nociceptive behavior and spinal ERK activation evoked by i.t. Leu-ENK in combination with peptidase inhibitors were inhibited by co-administration of the non-selective δ-opioid receptor antagonist, naltrindole, the selective δ2-opioid receptor antagonist, naltriben, the non-competitive N-methyl-D-aspartate (NMDA) antagonist, MK-801 or the non-selective nitric oxide synthase inhibitor, L-NAME, the selective nNOS inhibitor, N(ω)-propyl-L-arginine or the selective iNOS inhibitor, W1400, but not by the selective δ1-receptor antagonist, BNTX (7-benzylidenenaltrexone). These results suggest that spontaneous nociceptive behaviors produced by i.t. co-administration of Leu-ENK with peptidase inhibitors may be induced by an activation of the glutamate-NO-ERK pathway through the δ2-opioid receptor in the dorsal spinal cord.

Influence of cholecystokinin on the synaptosomal dopamine uptake in the nucleus accumbens of rats

The influence of the sulfated cholecystokinin octapeptide (CCK-8S) on the synaptosomal high-affinity [(3)H]dopamine (DA) uptake was investigated in the medial and lateral part of nucleus accumbens in rats. CCK-8S induced a concentration-dependent biphasic inhibition of [(3)H]-DA uptake in both subregions. After preincubation of CCK-8S with the synaptosomes the inhibitory effect was completely abolished. Kinetic analysis of the uptake influence suggests an uncompetitive inhibition by CCK-8S; this means that CCK-8S attacks only the DA-uptake carrier complex by inhibitory manner. The possible regulatory relevance of this mechanism is discussed.

Neuropeptidases and the metabolic inactivation of insect neuropeptides

Neuropeptidases play a key role in regulating neuropeptide signalling activity in the central nervous system of animals. They are oligopeptidases that are generally found on the surface of neuronal cells facing the synaptic and peri-synaptic space and therefore are ideally placed for the metabolic inactivation of neuropeptide transmitters/modulators. This review discusses the structure of insect neuropeptides in relation to their susceptibility to hydrolysis by peptidases and the need for specialist enzymes to degrade many neuropeptides. It focuses on five neuropeptidase families (neprilysin, dipeptidyl-peptidase IV, angiotensin-converting enzyme, aminopeptidase and dipeptidyl aminopeptidase III) that have been implicated in the metabolic inactivation of neuropeptides in the central nervous system of insects. Experimental evidence for the involvement of these peptidases in neuropeptide metabolism is reviewed and their properties are compared to similar neuropeptide inactivating peptidases of the mammalian brain. We also discuss how the sequencing of insect genomes has led to the molecular identification of candidate neuropeptidase genes.

Evaluation of a novel aminopeptidase N inhibitor, in vitro, using two assay systems

The activities of the novel aminopeptidase N inhibitor (APNI), beta-Amino-alpha-Hydroxyl-Phenyl butanic acid-Valine (AHPA-Val), were compared with APNI (amastatin). AHPA-Val and amastatin produced competitive inhibition of the hydrolysis of Tyr-Gly in the guinea-pig striatal membrane preparation, with K(i) equal to 14.06 microM and 12.48 microM respectively. Met-enkephalin-induced twitch inhibition of the guinea-pig ileum preparation was enhanced by AHPA-Val and amastatin with pA(1/2) values (the negative logarithm concentration of APNI that decreased the IC(50) of Met-enkephalin by half), of 7.08 and 7.79 respectively. These results suggest that AHPA-Val has good activity as an APNI and that these two assay systems are useful for evaluating the potency of novel APNIs.

A novel bradykinin potentiating peptide isolated from Bothrops jararacussu venom using catallytically inactive oligopeptidase EP24.15

Characterization of the peptide content of venoms has a number of potential benefits for basic research, clinical diagnosis, development of new therapeutic agents, and production of antiserum. Here, we use a substrate-capture assay that employs a catalytically inactive mutant of thimet oligopeptidase (EC 3.4.24.15; EP24.15) to identify novel bioactive peptides in Bothrops jararacussu venom. Of the peptides captured with inactive EP24.15 and identified by mass spectrometry, three were previously identified bradykinin-potentiating peptides (BPP), <ENWPHPQIPP (Xc), <EGGWPRPGPEIPP (XIIIa) and <EARPPHPPIPP (XIe) (where <E is a pyroglutamyl residue). In addition, we identified a novel BPP peptide containing additional AP amino acids in the C-terminus (<EARPPHPPIPPAP); this novel peptide was named BPP-AP. Next, dermal and muscle microcirculations were visualized using intravital microscopy to establish the roles of peptides BPP-XIe and BPP-AP in this process. After local administration of peptide BPP-XIe (0.5 microg.microL(-1)), leukocyte rolling flux and adhesion were increased by fivefold in post-capillary venules, without any increments in vasodilatation of arterioles compared to control experiments. In contrast, local administration of BPP-AP (0.5 microg.microL(-1)) potently induced vasodilatation of arterioles (nearly 100% increase compared with the vehicle saline control), with only a small increase in leukocyte rolling flux. Therefore, the novel BPP-AP described herein has pharmacological advantages compared to the BPP-XIe. The present study further suggests that inactive oligopeptidase EP24.15 is a useful tool for the isolation of bioactive peptides from crude biological samples.

Role of central and peripheral aminopeptidase activities in the control of blood pressure: a working hypothesis

Although there is a large body of knowledge on protein synthesis, the available data on protein catabolism, although quite substantial, are still inadequate. This is due to the marked differences in the activity of proteolytic enzymes, compounded by different substrate specificities and multiple environmental factors. Understanding enzyme behavior under physiological and pathological conditions requires the identification of specific proteolytic activities, such as aminopeptidases, as able to degrade certain peptidergic hormones or neuropeptides. Another requirement is the isolation, purification and characterization of the enzymes involved. In addition, systematic studies are needed to determine each enzyme's subcellular location, tissue distribution, and the influence of environmental factors such as diurnal rhythm, age, gender, diet, cholesterol, or steroids. Central and peripheral aminopeptidases may play a role in the control of blood pressure by coordinating the effect of the different peptides of the renin-angiotensin system cascade, acting through the AT(1), AT(2), and AT(4) receptors. Our review of the available data suggests the hypothesis that cholesterol or steroids, particularly testosterone, significantly influence aminopeptidase activities, their substrate availability and consequently their functions. These observations may have relevant clinical implications for a better understanding of the pathophysiology of cardiovascular diseases, and thus for their treatment with aminopeptidase inhibitors.

Angiotensin-converting enzyme as a target for the development of novel insect growth regulators

Insect angiotensin converting enzyme (ACE) is a zinc metallopeptidase capable of inactivating a variety of small to medium size peptide hormones by cleavage of C-terminal dipeptides and dipeptideamides. High levels of ACE activity are found in the hemolymph and in reproductive tissues of insects, where the enzyme is considered to have an important role in the metabolism of bioactive peptides. Therefore, inhibiting ACE activity is expected to interfere with the peptidergic endocrine system and to have detrimental effects on growth, development and reproduction. We will review the studies showing that ACE inhibitors do indeed disrupt growth and reproduction in various insect species. We will also present some new genetic and pharmacological data that strengthens our conclusion that ACE should be considered as a potential target for the development of new insect growth regulators.

Neprilysin carboxydipeptidase specificity studies and improvement in its detection with fluorescence energy transfer peptides

We examined the substrate specificity of the carboxydipeptidase activity of neprilysin (NEP) using fluorescence resonance energy transfer (FRET) peptides containing ortho-aminobenzoyl (Abz) and 2,4-dinitrophenyl (Dnp) as a donor/acceptor pair. Two peptide series with general sequences Abz-RXFK(Dnp)-OH and Abz-XRFK(Dnp)-OH (X denotes the position of the altered amino acid) were synthesized to study P1 (cleavage at the X-F bond) and P2 (cleavage at R-F bond) specificity, respectively. In these peptides a Phe residue was fixed in P1' to fulfill the well-known NEP S1' site requirement for a hydrophobic amino acid. In addition, we explored NEP capability to hydrolyze bradykinin (RPPGFSPFR) and its fluorescent derivative Abz-RPPGFSPFRQ-EDDnp (EDDnp=2,4-dinitrophenyl ethylenediamine). The enzyme acts upon bradykinin mainly as a carboxydipeptidase, preferentially cleaving Pro-Phe over the Gly-Phe bond in a 9:1 ratio, whereas Abz-RPPGFSPFRQ-EDDnp was hydrolyzed at the same bonds but at an inverted proportion of 1:9. The results show very efficient interaction of the substrates' C-terminal free carboxyl group with site S2' of NEP, confirming the enzyme's preference to act as carboxydipeptidase at substrates with a free carboxyl-terminus. Using data gathered from our study, we developed sensitive and selective NEP substrates that permit continuous measurement of the enzyme activity, even in crude tissue extracts.

Identification of ten novel genes involved in human spermatogenesis by microarray analysis of testicular tissue

OBJECTIVE

To identify novel genes that are down-regulated in the testicular tissue of infertile men.

DESIGN

Prospective study.

SETTING

University-based reproductive clinics and genetics laboratory.

PATIENTS

Nine patients with normal spermatogenesis, and 15 patients with maturation arrest (MA) or Sertoli cell-only syndrome (SCOS).

INTERVENTION

Testicular samples of patients with the same histology were pooled for complementary DNA (cDNA) microarray analysis.

MAIN OUTCOME MEASURE

Novel, down-regulated genes.

RESULTS

In total, 300 genes were significantly down-regulated in SCOS or MA samples, and 10 novel sterility-related genes were identified. Of the 10 novel genes, 6 genes (Hs.126780, Hs.553658, Hs.274135, Hs.268122, Hs.531701, and Hs.171130) encode proteins with predictable functional domains, and all these functional domains are believed to correlate with spermatogenesis and/or spermiogenesis. Conversely, the other 4 genes (Hs.351582, Hs.407480, Hs.552781, and Hs.355570) do not encompass known functional domains. Two genes (Hs.407480 and Hs.552781) lack mouse orthologues. Most novel genes showed a testis-specific expression pattern in both mice and humans. Reverse transcription-polymerase chain reaction (RT-PCR) showed three distinct types of developmental stage-dependent expressions of message ribonucleic acid (mRNA) for these novel genes in murine testes.

CONCLUSION

These 10 novel genes provide targets to elucidate novel pathways involved in human spermatogenesis.

Reduced fertility in male mice deficient in the zinc metallopeptidase NL1

Members of the M13 family of zinc metalloendopeptidases have been shown to play critical roles in the metabolism of various neuropeptides and peptide hormones, and they have been identified as important therapeutic targets. Recently, a mouse NL1 protein, a novel member of the family, was identified and shown to be expressed mainly in the testis as a secreted protein. To define its physiological role(s), we used a gene targeting strategy to disrupt the endogenous murine Nl1 gene by homologous recombination and generate Nl1 mutant mice. The Nl1(-/-) mice were viable and developed normally, suggesting that zygotic expression of Nl1 is not required for development. However, Nl1(-/-) males produced smaller litters than their wild-type siblings, indicating specific male fertility problems. Reduced fertility may be explained by two impaired processes, decreased egg fertilization and perturbed early development of fertilized eggs. These two phenotypes did not result from gross anatomical modifications of the testis or from impaired spermatogenesis. Basic sperm parameters were also normal. Thus, our findings suggest that one of the roles of NL1 in mice is related to sperm function and that NL1 modulates the processes of fertilization and early embryonic development in vivo.

Novel natural peptide substrates for endopeptidase 24.15, neurolysin, and angiotensin-converting enzyme

Endopeptidase 24.15 (EC; ep24.15), neurolysin (EC; ep24.16), and angiotensin-converting enzyme (EC; ACE) are metallopeptidases involved in neuropeptide metabolism in vertebrates. Using catalytically inactive forms of ep24.15 and ep24.16, we have identified new peptide substrates for these enzymes. The enzymatic activity of ep24.15 and ep24.16 was inactivated by site-directed mutagenesis of amino acid residues within their conserved HEXXH motifs, without disturbing their secondary structure or peptide binding ability, as shown by circular dichroism and binding assays. Fifteen of the peptides isolated were sequenced by electrospray ionization tandem mass spectrometry and shared homology with fragments of intracellular proteins such as hemoglobin. Three of these peptides (PVNFKFLSH, VVYPWTQRY, and LVVYPWTQRY) were synthesized and shown to interact with ep24.15, ep24.16, and ACE, with K(i) values ranging from 1.86 to 27.76 microm. The hemoglobin alpha-chain fragment PVNFKFLSH, which we have named hemopressin, produced dose-dependent hypotension in anesthetized rats, starting at 0.001 microg/kg. The hypotensive effect of the peptide was potentiated by enalapril only at the lowest peptide dose. These results suggest a role for hemopressin as a vasoactive substance in vivo. The identification of these putative intracellular substrates for ep24.15 and ep24.16 is an important step toward the elucidation of the role of these enzymes within cells.

Effect of quercetin on plasma extravasation in rat CNS and dura mater by ACE and NEP inhibition

The effects of quercetin on substance P-induced plasma protein extravasation (PE) in the rat dura mater, cerebellum, olfactory bulb and cortex and also its modulation by endopeptidases, angiotensin-converting enzyme (ACE) and neutral endopeptidase (NEP) were studied. PE was assessed by photometric measurement of extravasated Evans blue. Substance P (SP) and NEP or ACE inhibitors increased the PE in dura mater. Pretreatment with captopril or phosphoramidon potentiated PE induced by SP in the dura mater and cerebellum, respectively. Quercetin increased the PE in the dura mater, cerebellum and cortex. Further results suggested that the PE induced by SP in the dura mater was enhanced by pretreatment with quercetin, similar to that observed with selective peptidase inhibitors. Quercetin-stimulated extravasation in all tissues was abolished by NK-1 receptor blockade. These results suggest that quercetin increases PE in the dura mater and CNS tissues by inhibiting NEP and/or ACE, showing that the effect induced in the dura mater, cerebellum and cortex occurs through endogenous SP accumulation.

Inactivation of a tachykinin-related peptide: identification of four neuropeptide-degrading enzymes in neuronal membranes of insects from four different orders

Tachykinin-related peptides (TRP) are widely distributed in the CNS of insects, where they are likely to function as transmitters/modulators. Metabolic inactivation by membrane ecto-peptidases is one mechanism by which peptide signalling is terminated in the CNS. Using locustatachykinin-1 (LomTK-1, GPSGFYGVRamide) as a substrate and several selective peptidase inhibitors, we have compared the types of membrane associated peptidases present in the CNS of four insects, Locusta migratoria, Leucophaea maderae, Drosophila melanogaster and Lacanobia oleracea. A neprilysin (NEP)-like activity cleaving the G-F peptide bond was the major LomTK-1-degrading peptidase detected in locust brain membranes. NEP activity was also found in Leucophaea brain membranes, but the major peptidase was an angiotensin converting enzyme (ACE), cleaving the G-V peptide bond. Drosophila adult head and larval neuronal membranes cleaved the G-F and G-V peptide bonds. Phosphoramidon inhibited both these cleavages, but with markedly different potencies, indicating the presence in the fly brain of two NEP-like enzymes with different substrate and inhibitor specificity. In Drosophila, membrane ACE did not make a significant contribution to the cleavage of the G-V bond. In contrast, ACE was an important membrane peptidase in Lacanobia brain, whereas very little neuronal NEP could be detected. A dipeptidyl peptidase IV (DPP IV) that removed the GP dipeptide from the N-terminus of LomTK-1 was also found in Lacanobia neuronal membranes. This peptidase was a minor contributor to LomTK-1 metabolism by neuronal membranes from all four insect species. In Lacanobia, LomTK-1 was also a substrate for a deamidase that converted LomTK-1 to the free acid form. However, the deamidase was not an integral membrane protein and could be a lysosomal contaminant. It appears that insects from different orders can have different complements of neuropeptide-degrading enzymes. NEP, ACE and the deamidase are likely to be more efficient than the common DPP IV activity at terminating neuropeptide signalling since they cleave close to the C-terminus of the tachykinin, a region essential for maintaining biological activity.

Antinociceptive effect produced by intracerebroventricularly administered dynorphin A is potentiated by p-hydroxymercuribenzoate or phosphoramidon in the mouse formalin test

The antinociceptive effects of intracerebroventricularly (i.c.v.) administered dynorphin A, an endogenous agonist for kappa-opioid receptors, in combination with various protease inhibitors were examined using the mouse formalin test in order to clarify the nature of the proteases involved in the degradation of dynorphin A in the mouse brain. When administered i.c.v. 15 min before the injection of 2% formalin solution into the dorsal surface of a hindpaw, 1-4 nmol dynorphin A produced a dose-dependent reduction of the nociceptive behavioral response consisting of licking and biting of the injected paw during both the first (0-5 min) and second (10-30 min) phases. When co-administered with p-hydroxymercuribenzoate (PHMB), a cysteine protease inhibitor, dynorphin A at the subthreshold dose of 0.5 nmol significantly produced an antinociceptive effect during the second phase. This effect was significantly antagonized by nor-binaltorphimine, a selective kappa-opioid receptor antagonist, but not by naltrindole, a selective delta-opioid receptor antagonist. At the same dose of 0.5 nmol, dynorphin A in combination with phosphoramidon, an endopeptidase 24.11 inhibitor, produced a significant antinociceptive effect during both phases. The antinociceptive effect was significantly antagonized by naltrindole, but not by nor-binaltorphimine. Phenylmethanesulfonyl fluoride (PMSF), a serine protease inhibitor, bestatin, a general aminopeptidase inhibitor, and captopril, an angiotensin-converting enzyme inhibitor, were all inactive. The degradation of dynorphin A by mouse brain extracts in vitro was significantly inhibited only by the cysteine protease inhibitors PHMB and N-ethylmaleimide, but not by PMSF, phosphoramidon, bestatin or captopril. The present results indicate that cysteine proteases as well as endopeptidase 24.11 are involved in two steps in the degradation of dynorphin A in the mouse brain, and that phosphoramidon inhibits the degradation of intermediary delta-opioid receptor active fragments enkephalins which are formed from dynorphin A.

Molecular characterization of a puromycin-insensitive leucyl-specific aminopeptidase, PILS-AP

The family M1 of Zn-dependent aminopeptidases comprises members of closely related enzymes which are known to be involved in a variety of physiologically important processes. On the basis of two highly conserved peptide motifs, we have identified a new member of this family by PCR amplification and cDNA-library screening. The longest ORF encodes a protein of 930 residues. It contains the HEXXH(X)18E Zn-binding motif and displays high homology to the other M1 family members except for its N-terminus for which a signal sequence of 20 residues can be predicted. This interpretation was supported by expressing fusion proteins formed with green fluorescent protein which localized to intracellular vesicles in COS-7 and BHK cells. Northern-blot analysis revealed ubiquitous expression of a major 3. 1-kb transcript. For enzymatic studies, the complete protein was expressed in Sf 9 insect cells. When aminoacyl beta-naphthylamides were used as substrates, efficient hydrolysis was only observed for Leu (and to a lesser extent Met). The activity was inhibited by chelators of bivalent cations and by other known aminopeptidase inhibitors, but surprisingly puromycin was without effect. This newly identified puromycin-insensitive leucyl-specific aminopeptidase is a signal-sequence-bearing member of family M1 and may be another example of the small subset of substrate-specific peptidases.

Molecular cloning and biochemical characterization of a new mouse testis soluble-zinc-metallopeptidase of the neprilysin family

Because of their roles in controlling the activity of several bio-active peptides, members of the neprilysin family of zinc metallopeptidases have been identified as putative targets for the design of therapeutic agents. Presently, six members have been reported, these are: neprilysin, endothelin-converting enzyme (ECE)-1 and ECE-2, the Kell blood group protein, PHEX (product of the phosphate-regulating gene with homologies to endopeptidase on the X chromosome) and X-converting enzyme (XCE). In order to identify new members of this important family of peptidases, we designed a reverse transcriptase-PCR strategy based on conserved amino acid sequences of neprilysin, ECE-1 and PHEX. We now report the cloning from mouse testis of a novel neprilysin-like peptidase that we called NL1. NL1 is a glycoprotein that, among the members of the family, shows the strongest sequence identity with neprilysin. However, in contrast with neprilysin and other members of the family which are type II integral membrane proteins, NL1 was secreted when expressed in cultured mammalian cells, likely due to cleavage by a subtilisin-like convertase at a furin-like site located 22 amino acid residues in the C-terminus of the transmembrane domain. The recombinant enzyme exhibited neprilysin-like peptidase activity and was efficiently inhibited by phosphoramidon and thiorphan, two inhibitors of neprilysin. Northern blot analysis and in situ hybridization showed that NL1 mRNA was found predominantly in testis, specifically in round and elongated spermatids. This distribution of NL1 mRNA suggests that it could be involved in sperm formation or other processes related to fertility.

Characterization of proteolytic activities of pulmonary alveolar epithelium

Pulmonary alveolar type I epithelial cell and its progenitor, type II cell, present major transport and enzyme barriers for systemic delivery of pulmonary administered peptide drugs. The present study investigates the effect of cellular differentiation of type II to type I cells on their proteolytic activities, and evaluates the suitability of a continuous lung cell line, A549, for drug transport and degradation studies. High performance liquid chromatography was used to assess the degradation kinetics of two model peptide substrates, luteinizing hormone releasing hormone (LHRH) and [D-Ala(6)10-fold decrease in proteolytic activities for LHRH, as compared to type II cells. The continuous lung cell line A549 formed leaky monolayers and exhibited similar enzyme activities to the primary type II cells. The responsible enzymes for degradation of LHRH in type II and A549 cells were angiotensin converting enzyme (ACE), EP24.11, and EP24.15. In contrast, no EP24.15 or ACE activity was observed in type I-like pneumocytes and only a weak EP24.11 activity was detected. In all cell types, the degradation rate of [D-Ala(6)]-LHRH was about 3-8 times lower than that of LHRH. This peptide analog was resistant to degradation by EP24.15 and EP24.11, but was susceptible to ACE-mediated cleavage.

Aminopeptidases as potential targets for the control of the Australian sheep blowfly, Lucilia cuprina

A series of experiments were carried out to investigate the role of proteinase enzymes in the growth of larvae of the sheep blowfly, Lucilia cuprina. First, instar larvae were incubated on an artificial growth media in the presence of various concentrations of inhibitors of all the major proteinase classes. Inhibitors of serine proteinases and aminopeptidases were found to cause significant growth inhibition and in some cases death of the larvae within 24 h, suggesting that these enzymes were the major classes involved in protein digestion in the gut of the insect. A second group of experiments analysed the effects of two inhibitors from the same or different proteinase classes in the growth media. Synergistic inhibition of larval growth was observed with the incorporation of inhibitors of serine proteinases and aminopeptidases. The results suggest that these classes of proteinases are both central to protein digestion in this insect, probably in the gut, and that the inhibition of both types of activity leads to an almost complete blockade of digestion. Testing in vivo gave similar results with infections on sheep skin inhibited by either serine proteinase or aminopeptidase enzyme inhibitors and the combination of both stopped the infection process. The role of aminopeptidases in larval metabolism and as potential targets for blowfly control agents is examined.

The role of aminopeptidase N in Met-enkephalin modulated superoxide anion release

We have previously shown that methionine-enkephalin (MENK) alters in dose-dependent fashion the capacity of human neutrophils to produce superoxide anion. The response of neutrophils from different donors was diverse and this effect could be due to variable activity of proteolytic enzymes involved in the degradation of the neuropeptide. In this study, we have demonstrated a highly individual aminopeptidase N (APN) activity of neutrophils from different donors. Preincubation of neutrophils with MENK, but not with the synthetic agonist of the mu (DAGO) or the delta (DPDPE) opioid receptor, down-regulated the APN activity. This was paralleled by a loss in cell surface expression of APN at physiological (10(-10) M) concentrations of MENK. The level of APN activity from different donors correlated with the effect of MENK on superoxide anion release. Neutrophils with low APN activity, if preincubated with MENK, released reduced amounts of superoxide anion. In contrast, neutrophils with high APN activity released increased amounts of superoxide anion after preincubation with MENK. Thus, the highly individual APN activity on the surface of neutrophils from different donors seems to be altered by MENK and to be related to the respiratory burst.

Inhibition of kidney neutral endopeptidase after administration of the neutral endopeptidase inhibitor candoxatril: quantitation by autoradiography

Inhibition of neutral endopeptidase (NEP) in the kidney was studied ex vivo after oral administration of candoxatril (UK79300), an NEP inhibitor, to rats to study the time course and dose response by quantitative in vitro autoradiography by using the NEP inhibitor 125I-SCH47896 as a radioligand. In control rats, high NEP binding was demonstrated in the deep proximal tubule. After oral administration of candoxatril (10 mg/kg), kidney NEP binding was rapidly decreased and recovered gradually over a period of 24 h. The inhibition was maximal at 1 h (13.3 +/- 2.5% of control). Increasing doses of candoxatril administered to rats produced progressive inhibition of NEP binding in the kidney. A dose of 100 mg/kg inhibited kidney NEP binding to 2.6 +/- 0.2% of the control value at 1 h after administration. Candoxatrilat (UK73967), an active metabolite of candoxatril, given intravenously inhibited kidney NEP binding also in a time- and dose-dependent manner. This inhibition of NEP activity at the tissue level may be important in the actions of NEP inhibitors.

Enzymatic degradation of luteinizing hormone releasing hormone (LHRH)/[D-Ala6]-LHRH in lung pneumocytes

PURPOSE

To investigate the cellular proteolytic activities of various lung pneumocytes using luteinizing hormone releasing hormone (LHRH) and [D-Ala6]-LHRH as model peptide substrates.

METHODS

HPLC analysis was used to investigate the degradation kinetics of LHRH/[D-Ala6]-LHRH and to identify their degradation products in isolated lung pneumocytes.

RESULTS

Pulmonary macrophages exhibited the strongest proteolytic activity against LHRH)/[D-Ala6]-LHRH, followed by type II and type I-like pneumocytes. Three major degradation products of LHRH, namely LHRH 4-10, LHRH 6-10, and LHRH 7-10, were identified in macrophages and type II pneumocytes, whereas in type I-like pneumocytes only the LHRH 7-10 was found. Co-incubation of the cells with known enzyme inhibitors including captopril (an ACE inhibitor), thiorphan (an EP24.11 inhibitor), and EDTA (an EP24.15 inhibitor) inhibited the formation of LHRH 4-10, LHRH 7-10, and LHRH 6-10 respectively. In all cell types, the degradation rate of [D-Ala6]-LHRH was about 3-8 times lower than that of LHRH. This peptide analog was resistant to degradation by EP24.15 and EP24.11, but was susceptible to ACE.

CONCLUSIONS

ACE, EP24.11, and EP24.15 are the major enzymes responsible for the degradation of LHRH in macrophages and type II pneumocytes. The magnitude of peptidase activities in these cell types are: EP24.15 > EP24.11 approximately ACE. No EP24.15 or ACE activity was observed in type I-like pneumocytes and only a weak EP24.11 activity was detected.

Characterization and cloning of tripeptidyl peptidase II from the fruit fly, Drosophila melanogaster

We describe the characterization, cloning, and genetic analysis of tripeptidyl peptidase II (TPP II) from Drosophila melanogaster. Mammalian TPP II removes N-terminal tripeptides, has wide distribution, and has been identified as the cholecystokinin-degrading peptidase in rat brain. Size exclusion and ion exchange chromatography produced a 70-fold purification of dTPP II activity from Drosophila tissue extracts. The substrate specificity and the inhibitor sensitivity of dTPP II is comparable to that of the human enzyme. In particular, dTPP II is sensitive to butabindide, a specific inhibitor of the rat cholecystokinin-inactivating activity. We isolated a 4309-base pair dTPP II cDNA which predicts a 1354-amino acid protein. The deduced human and Drosophila TPP II proteins display 38% overall identity. The catalytic triad, its spacing, and the sequences that surround it are highly conserved; the C-terminal end of dTPP II contains a 100-amino acid insert not found in the mammalian proteins. Recombinant dTPP II displays the predicted activity following expression in HEK cells. TPP II maps to cytological position 49F4-7; animals deficient for this interval show reduced TPP II activity.

Hydrolysis of the neuropeptide N-acetylaspartylglutamate (NAAG) by cloned human glutamate carboxypeptidase II

Glutamate carboxypeptidase II may modulate excitatory neurotransmission through the catabolism of the neuropeptide N-acetylaspartylglutamate (NAAG) and possibly other endogenous peptide substrates. To investigate the molecular properties of cloned human GCP II (hGCP II), we analyzed the NAAG-hydrolytic activity conveyed by transfection of a full-length hGCP II cDNA into PC3 cells, which do not express GCP II endogenously. Membrane fractions from these cells demonstrated activity with an apparent Km of 73 nM and Vmax of 35 pmol/(mg protein*min). Activity was inhibited by EDTA and stimulated by the addition of CoCl2. Addition of GCP II inhibitors beta-NAAG, quisqualic acid and 2-(phosphonomethyl)pentanedioic acid (PMPA) inhibited hydrolysis of 2.5 nM NAAG with IC50s of 201 nM, 155 nM and 98 pM, respectively. In competition experiments designed to infer aspects of hGCP II substrate selectivity, NAAG was the most potent alpha peptide tested, with an IC50 of 26 nM. Folate derivatives and some other gamma-glutamyl peptides showed comparable affinity to that of NAAG, also displaying IC50s in the low nM range. Taken together with previous evidence demonstrating their presence in GCP II-expressing tissues, these data suggest that both NAAG and folates are good candidate substrates for GCP II in vivo.

Inactivation of Dip-allatostatin 5 by membrane preparations from the cockroach Diploptera punctata

Incubation of Dip-AST 5 (Asp-Arg-Leu-Tyr-Ser-Phe-Gly-Leu-NH2) with membrane preparations of midgut, hindgut, brain, or corpora allata (CA) results in its inactivation in terms of the inhibition of juvenile hormone biosynthesis. Dip-AST 5 is initially cleaved at Gly7-Leu8 to yield the N-terminal heptapeptide (Asp-Arg-Leu-Tyr-Ser-Phe-Gly). At supraphysiological concentration, the half-life of Dip-AST 5 varied from 24 min by membrane preparations of brain to approximately 53 min following incubation with midgut membrane preparations. At more physiological concentrations (nanomolar), Dip-AST 5 was still initially cleaved to yield the inactive N-terminal heptapeptide with a half-life ranging from 23 min with brain membrane preparations to 85 min with membrane preparations of midgut. The fact that Dip-AST 5 is rapidly degraded to an inactive product by membrane preparations or whole tissues (CA) indicates that Dip-AST 5 has a different metabolic fate in tissue preparations than in diluted hemolymph (Garside et al., 1997). These findings demonstrate that the degradation of allatostatins by tissue preparations of D. punctata may play an important role in the termination of their ability to inhibit juvenile hormone biosynthesis by the CA and/or to modulate muscle activity in the hindgut.

Angiotensin-converting enzyme inhibitors can potentiate ozone-induced airway hyperresponsiveness

We investigated the effects of single and chronic oral administration of angiotensin-converting enzyme inhibitors on ozone-induced airway hyperresponsiveness in guinea pigs. Ozone exposure (3 ppm for 2 h) significantly increased airway responsiveness in vehicle-treated animals and in animals with either single or chronic administration (8 days) of drugs. Single administration of imidapril, enalapril and captopril significantly potentiated ozone-induced airway hyperresponsiveness at a dose of 100, 50 and 50 mg/kg, respectively, although these doses did not influence airway responsiveness in normal guinea pigs, i.e., the magnitude of potentiation was captopril > enalapril > imidapril. In the study of chronic administration of the drugs, imidapril (10-100 mg/kg per day) had no influence on airway responsiveness in both normal and ozone-treated animals. In contrast, captopril and enalapril (10-100 mg/kg per day) dose-dependently potentiated ozone-induced airway hyperresponsiveness, with no influence on airway responsiveness in normal animals. That is, the magnitude was enalapril > captopril. These results indicate that angiotensin-converting enzyme inhibitors potentiate airway responsiveness in ozone-treated guinea pigs but not in normal guinea pigs and that imidapril is less potent than enalapril and captopril in potentiating ozone-induced airway hyperresponsiveness in guinea pigs.

Characterisation of neprilysin (EC 3.4.24.11) S2' subsite

Neprilysin is a neutral peptidase that cleaves small peptide substrates on the amino-side of hydrophobic amino acid residues. In the present study, we have used inhibition of non-mutated and mutated enzymes with dipeptide inhibitors and hydrolysis of the substrate [Leu5, Arg6]enkephalin in order to evaluate the contribution of the S2' subsite to substrate and inhibitor binding. Our results suggest that (1) Arg-102 and Asn-542 provide major contributions to the interaction of the enzyme with the P2' residue of the substrate, (2) the S2' subsite is vast and can accommodate bulky side chains, and (3) Arg-102 restricts access to the S2' subsite to some side chains such as arginine.

Enzymatic inactivation of enkephalin neurotransmitters in the spinal cord of the neonatal rat

The possible involvement of enzymatic degradation in the inactivation of enkephalins in the spinal cord of neonatal rats was investigated electrophysiologically and biochemically. In an isolated spinal cord-saphenous nerve preparation, electrical stimulation of the saphenous nerve evoked a slow depolarization lasting 20-30 s of the ipsilateral L3 ventral root. This slow depolarization was depressed by a mixture of peptidase inhibitors, consisting of actinonin (10 microM), thiorphan (0.6 microM), bestatin (10 microM), arphamenine B (10 microM) and captopril (10 microM). Naloxone (0.5 microM) not only reversed this effect of the mixture of peptidase inhibitors but also potentiated the slow depolarization beyond the pre-control level. In an isolated spinal cord preparation, electrical stimulation of a lumbar dorsal root evoked a slow depolarization of the contralateral ventral root of the same segment. This slow depolarization was depressed by application of [Met5]enkephalin in a dose dependent manner. This effect of [Met5]enkephalin was markedly potentiated by addition of the mixture of peptidase inhibitors. Among the five peptidase inhibitors, actinonin, thiorphan or bestatin alone potentiated the depressant effect of [Met5]enkephalin, whereas arphamenine B and captopril did not. Membrane fractions prepared from neonatal rat spinal cords showed degrading activities for [Met5]- and [Leu5]enkephalins and these activities were inhibited by the mixture of peptidase inhibitors. Among the five peptidase inhibitors, actinonin and thiorphan markedly inhibited the [Met5]enkephalin-degrading activity while bestatin was less effective. Arphamenine B and captopril were ineffective. The present results suggest that enzymatic degradation by peptidases plays a role in the termination of the transmitter action of enkephalins in the neonatal rat spinal cord. The present results, together with our previous results on the enzymatic degradation of tachykinins in a study in which we used the same preparations, suggest that similar but distinct combinations of peptidases are involved in the inactivation of enkephalin and tachykinin neurotransmitters.

Effect of a novel selective and potent phosphinic peptide inhibitor of endopeptidase 3.4.24.16 on neurotensin-induced analgesia and neuronal inactivation

1. We have examined a series of novel phosphinic peptides as putative potent and selective inhibitors of endopeptidase 3.4.24.16. 2. The most selective inhibitor, Pro-Phe-psi(PO2CH2)-Leu-Pro-NH2 displayed a Ki value of 12 nM towards endopeptidase 3.4.24.16 and was 5540 fold less potent on its related peptidase endopeptidase 3.4.24.15. Furthermore, this inhibitor was 12.5 less potent on angiotensin-converting enzyme and was unable to block endopeptidase 3.4.24.11, aminopeptidases B and M, dipeptidylaminopeptidase IV and proline endopeptidase. 3. The effect of Pro-Phe-psi(PO2CH2)-Leu-Pro-NH2, in vitro and in vivo, on neurotensin metabolism in the central nervous system was examined. 4. Pro-Phe-psi(PO2CHH2)-Leu-Pro-NH2 dose-dependently inhibited the formation of neurotensin 1-10 and concomittantly protected neurotensin from degradation by primary cultured neurones from mouse embryos. 5. Intracerebroventricular administration of Pro-Phe-psi(PO2CH2)-Leu-Pro-NH2 significantly potentiated the neurotensin-induced antinociception of mice in the hot plate test. 6. Altogether, our study has established Pro-Phe-psi(PO2CH2)-Leu-Pro-NH2 as a fully selective and highly potent inhibitor of endopeptidase 3.4.24.16 and demonstrates, for the first time, the contribution of this enzyme in the central metabolism of neurotensin.

Tachykinin receptors in the guinea-pig isolated oesophagus: a complex system

1. The tachykinin receptors mediating contraction of isolated longitudinal strips of the guinea-pig oesophageal body were characterized with substance P (SP), neurokinin A (NKA) and neurokinin B (NKB) as well as the analogues, [Sar9,Met(O2)11]SP, [Nle10]NKA(4-10) and [MePhe7]NKB, selective for NK1, NK2 and NK3, receptors, respectively. Experiments were performed both in the absence and presence of a cocktail of peptidase inhibitors, captopril (1 microM), thiorphan (1 microM) and amastatin (20 microM), in order to determine whether membrane bound proteases are important in the metabolism of tachykinins in this preparation. 2. All agonists produced concentration-dependent contractile effects. The presence of the peptidase inhibitors shifted the concentration-response curves of SP, [Nle10]NKA(4-10) and [MePhe7]NKB significantly leftwards and the concentration-response curve of NKB was shifted significantly rightwards. However, the EC50 values were significantly different only for [Nle10]NKA(4-10) and NKB. 3. In the presence of the peptidase inhibitors, the EC50 values of the selective agonists, [MePhe7]NKB (0.6 nM) and [Nle10]NKA(4-10) (66 nM) indicated the presence of both tachykinin NK3 and NK2 receptors. [MePhe7]NKB produced less than 50% of the maximal response obtained with the other agonists. Since [Sar9,Met(O2)11]SP produced a small response in the nanomolar concentration range in about 30% of the preparations tested, it is possible that some NK1 receptors were also present. 4. Assuming competitive antagonism, the NK2-selective antagonist SR 48,968 (30 nM) gave apparent pKH values of 8.13 and 8.65 for [Nle10]NKA(4-10) in the absence and presence of peptidase inhibitors, respectively, supporting the presence of NK2 receptors. 5. The NK3-selective antagonist SR 142,801 (0.1 microM), suppressed responses to low (0.1-10 nM) concentrations of [MePhe7]NKB. These contractile responses to [MePhe7]NKB were also abolished by atropine (0.6 microM) suggesting that this response was mediated via cholinergic nerves. 6. It is concluded that the guinea-pig oesophagus is a complex system which has both NK2 and NK3 receptors and possibly some NK1 receptors as-well.

Degradation of Dip-allatostatins by hemolymph from the cockroach, Diploptera punctata

Incubation of Dip-AST 7 (APSGAQRLYGFGLa) or Dip-AST 9 (GDGRLYAFGLa) (5 microM) with hemolymph for 30 min results in cleavage by a putative endopeptidase, yielding the C-terminal hexapeptide. This metabolic product is subsequently cleaved by an amastatin-sensitive aminopeptidase to yield the the C-terminal pentapeptide, as treatment with the competitive aminoexopeptidase inhibitor, amastatin, results in a significant accumulation of the C-terminal hexapeptide. Interestingly, Dip-AST 5 (DRLYSFGLa) (6 microM), which in common with Dip-AST 7 and 9 possesses Arg-Leu-Tyr, is not rapidly cleaved. However, [3H-Tyr]Dip-AST 5 at physiological concentrations (4 nM), appears to be cleaved by the same enzymes that cleave Dip-AST 7 and 9, albeit at a reduced rate. Incubation of other members of the Dip-allatostatin family with hemolymph also results in cleavage of the peptides, suggesting that there are a variety of endo- and/or exopeptidases present in the hemolymph of D. punctata.

Inhibition of dynorphin-converting enzymes prolongs the antinociceptive effect of intrathecally administered dynorphin in the mouse formalin test

The effects of peptidase inhibitors on the antinociceptive induced by intrathecally (i.t.) administered by dynorphin A and dynorphin B in the mouse formalin test were examined. When administered i.t. 5 min before the injection of 0.5% formalin solution into the dorsal surface of a hindpaw, dynorphin A (0.5-2 nmol) and dynorphin B (2-8 nmol) produced a dose-dependent and significant reduction of the paw-licking response. Dynorphin A (2 nmol) and dynorphin B (8 nmol)-induced antinociception disappeared completely within 90 min and 60 min, respectively. p-Hydroxymercuribenzoate, a cysteine proteinase inhibitor, and phosphoramidon, and endopeptidase 24.11 inhibitor simultaneously administered with dynorphin A or dynorphin B. Significantly prolonged antinociception induced by both dynorphins. However, captopril, and angiotensin-converting enzyme inhibitor, bestatin (a general aminopeptidase inhibitor) and a serine proteinase inhibitor phenylmethanesulfonyl fluoride, were active. Dynorphin converting enzyme(s) transform dynorphin-related peptides to [Leu5]enkephalin and [Leu5]enkephalin-Arg6. Neither [Leu5]enkephalin nor [Leu5]enkephalin-Arg6, even at high dose (10 nmol), produced any antinociceptive effect. However, [Leu5[enkephalin-Arg6, but not [Leu5]enkephalin, produced a significant antinociceptive effect when co-administered with phosphoramidon. Therefore, the prolongation of the antinociception induced by both dynorphins in the presence of phosphoramidon, may be due to inhibition of [Leu5]enkephalin-Arg6 degradation. The present results indicate that dynorphin-converting enzyme(s) may be important enzyme(s) responsible for terminating dynorphin-A- and dynorphin-B-induced antinociception at the spinal cord level in mice.

Liver transplantation is associated with increased met-enkephalin levels in the pig

BACKGROUND

It has been reported that less postoperative morphine is required following liver transplantation than is required following open cholecystectomy. This may be attributable to endogenous factors rather than to altered morphine pharmacokinetics. We measured the plasma concentrations of two endogenous neuropeptides associated with pain modulation, substance P (SP) and met-enkephalin (ME), in pigs undergoing liver transplantation and in control pigs undergoing laparotomy.

METHODS

With the approval of the institutional Animal Care Committee, pigs were anesthetized with ketamine (30 mg/ kg,i.m.), atropine (0.05 mg/kg, i.m.) and acetylpromazine (0.1 mg/kg, i.m.). Anesthesia was maintained with isoflurane in oxygen. Pigs in the transplantation group (n = 10) underwent liver transplantation and control pigs (n = 10) underwent laparotomy. Blood samples for SP and ME measurement were collected pre-incision (Pre-In), pre-emergence (Pre-Em) from anesthesia, 6-12 hours, 18 hours, and 24 hours after surgery. SP and ME levels were determined by radioimmunoassay. Results are expressed as mean +/- SEM (in pg/ml of plasma for both peptides) and were compared by the non-parametric Mann-Whitney U test. Statistical significance was inferred if P < 0.05.

RESULTS

Plasma ME levels were significantly increased in the transplanted pigs at Pre-Em, 6-12 hours and 18 hours after surgery. No statistically significant difference was observed for plasma SP level between the control and transplant pigs.

CONCLUSIONS

Liver transplantation in the pig model is associated with increased concentrations of endogenous ME (but not SP) in plasma for at least 18 hours after surgery as compared to animals undergoing laparotomy.

Studies on the magnitude and the mechanism of cough potentiation by angiotensin-converting enzyme inhibitors in guinea-pigs: involvement of bradykinin in the potentiation

One adverse effect of the angiotensin-converting enzyme (ACE) inhibitors used for treatment of hypertension and congestive heart failure is the production of dry coughs. Imidapril is a new type of ACE inhibitor with a very low incidence of coughs. The magnitude and the mechanism of cough potentiation of imidapril and other ACE inhibitors has been studied in guinea-pigs. In normal guinea-pigs single and repeated dosing of imidapril at 0.1 to 100 mg kg-1 had no effect on capasaicin- or citric acid-induced coughs. Single and repeated dosing of enalapril and captopril at 10 to 30 mg kg-1, respectively, significantly increased the number of capsaicin-induced coughs. Repeated dosing of 1 mg kg-1 enalapril also significantly augmented the capsaicin cough. In bronchitic guinea-pigs imidapril also had no effect on the coughs induced by the two stimulants. Enalapril and captopril significantly increased the number of coughs induced not only by capsaicin but also by citric acid. Lower doses of enalapril were enough to augment the capsaicin-induced coughs, whereas medium to large doses failed to augment the cough irrespective of the protocol of administration. Bradykinin-induced discharges of the vegal afferents from the lower airway were significantly increased by enalaprilat but not by imidaprilat. Capsaicin-induced discharges of the afferents were, on the other hand, significantly depressed by enalaprilat, but not by imidaprilat. Interestingly, enalaprilat depression of the discharges was significantly reversed by Hoe-140, a bradykinin B2 receptor blocker. In guinea-pigs pretreated with a low dose of enalapril, arterial infusion of bradykinin significantly potentiated the coughs induced by capsaicin. The results indicated that imidapril was less potent than enalapril and captopril in potentiating cough responses induced by capsaicin and citric acid in guinea-pigs, and further suggest that bradykinin might be a key substance in the mechanism of the potentiation of coughs associated with ACE inhibitors.

Disposition of 3H-labelled buserelin continuously infused into rats

The disposition of the gonadotropin-releasing hormone (GnRH) agonist buserelin was studied in male rats under conditions of long-term administration. Rats were continuously infused with about 30 pmole [3H]-buserelin/24 h subcutaneously by osmotic minipumps for 4-7 days. After killing the rats, the 3H-activity of the tissues was measured and was found to be highly concentrated (about 10-fold to plasma) only in the pituitary. The daily amounts of 3H-activity excreted in urine and faces were constant over the whole infusion period, suggesting steady state conditions. On a molar basis, of the infused dose of buserelin, 14.8% was found to be excreted into urine as intact peptide, and 16.5, 10.8 and 20.6% as the partial buserelin sequences 1-2, 1-3 and 5-9. It is concluded that the major elimination route of buserelin, constant with time, is glomerular filtration, followed by enzymatic degradation of part of the filtered peptide by kidney tubuli enzymes to the partial sequences 1-2, 1-3 and 5-9, which reflects the proteolytic breakdown of buserelin by kidney membrane peptidases in vitro. Based on the similarities in the pharmacokinetics, in vivo metabolities, and in vitro enzymatic degradabilities among the GnRH agonists that have the native GnRH sequence modified at position 6 with or without additional modification at the C-terminal, the elimination process as shown here for buserelin should also be valid for other GnRH agonists.

Proliferation and differentiation of myelodysplastic CD34+ cells

Myelodysplastic syndromes (MDS) are a heterogeneous group of disorders of hematopoiesis involving hyperproliferative and ineffective hematopoiesis associated with morphologic evidence of marrow cell dysplasia resulting in refractory cytopenia(s), and an increased risk of transformation into acute myeloblastic leukemia (AML). The administration of colony-stimulating factor(s) (CSFs) to patients with MDS increased blood neutrophil concentrations, in most patients, and was also expected to be beneficial and to prevent infections. However, the progression to AML during the treatment with CSFs was suspected in some patients. Therefore, extensive in vitro studies were expected to lead to the establishment of criteria for selection of patients who are likely to benefit from CSF's as well as to establish the overall value of the different types of CSFs therapy. For this purpose, in vitro colony assays provide an excellent tool for investigating the biologic characteristics of MDS progenitor cells. However, conditions of the culture must be such that each progenitor can express its full potential for proliferation and differentiation. Because of the above, MDS progenitor cells cannot be used because they carry an impairment in proliferation and differentiation. To address this problem, one needs to know how many cells are being handled and the maximum numbers of colonies and clusters expected. CD34, a stem cell phenotype, is at present one of the best markers of progenitor cells, and can be used for purposes of purification. Using a defined number of CD34+ cells, it was feasible to make direct investigations on MDS progenitor cells. In this review the properties of MDS progenitor cells are described, in association with proliferation and differentiation, with special emphasis on the phenotypic subpopulations of MDS CD34+ cells.

In vitro metabolism of an insect neuropeptide by neural membrane preparations from Lymantria dispar

Neural membrane fractions, prepared from brain-subesophageal ganglion complexes of the adult lepidopteran Lymantria dispar, contain at least two peptidases capable of metabolizing locust adipokinetic hormone-I in vitro. The initial fragments, pGlu1-Leu2-Asn3 and Phe4-Thr5-Pro6-Asn7-Trp8-Gly9-Thr10, result from the action of an endopeptidase with properties similar to those reported for neutral metalloendopeptidase in Schistocerca gregaria and mammalian endopeptidase 24.11. The heptapeptide is further degraded by an aminopeptidase that exhibits kinetic properties similar to those described for aminopeptidase 3.4.11.2. These enzymes appear to be responsible for the first two steps in AKH catabolism in L. dispar.