Characterization of dynorphin A-converting enzyme in human spinal cord. An endoprotease related to a distinct conversion pathway for the opioid heptadecapeptide?

Sex differences in opioid receptor mediated effects: Role of androgens

An abundance of data indicates there are sex differences in endogenous opioid peptides and opioid receptors, leading to functional differences in sensitivity to opioid receptor mediated behaviors between males and females. Many of these sex differences are mediated by the effects of gonadal hormones on the endogenous opioid system. Whereas much research has examined the role of ovarian hormones on opioid receptor mediated endpoints, comparatively less research has examined the role of androgens. This review describes what is currently known regarding the influence of androgens on opioid receptor mediated endpoints and how androgens may contribute to sex differences in these effects. The review also addresses the clinical implications of androgenic modulation of opioid receptor mediated behaviors and suggests future lines of research for preclinical and clinical investigators. We conclude that further investigation into androgenic modulation of opioid receptor mediated effects may lead to new options for addressing conditions such as chronic pain and substance use disorders.

β-Neoendorphin Enhances Wound Healing by Promoting Cell Migration in Keratinocyte

The skin is the largest and a remarkably plastic organ that serves as a protective barrier against environmental stimuli and injuries throughout life. Skin injuries are serious health problems, and wound healing is a critical process to replace devitalized cellular and tissue structures. Although some endogenous opioids are known to be involved in the modulation of wound healing, it remains to be determined whether the β-neoendorphin (β-NEP), an endogenous opioid, has beneficial effects on wound repair in human keratinocyte. In this study, we found that β-NEP accelerated wound repair through activation of mitogen-activated protein kinase (MAPK)/Erk1/2 signaling pathways in human keratinocytes. Moreover, the wound healing effect of β-NEP is mainly through the acceleration of keratinocyte migration without affecting cell proliferation. Therefore, our studies reveal that β-NEP plays an important role in the regulation of wound repair and suggest a therapeutic strategy to promote wound healing using β-NEP.

Inhibitors of neuropeptide peptidases engaged in pain and drug dependence

Owing to a broad spectrum of functions performed by neuropeptides, this class of signaling molecules attracts an increasing interest. One of the key steps in the regulation of biological activity of neuropeptides is proteolytic conversion or degradation by proteinases that change or terminate biological activity of native peptides. These enzymes, in turn, are regulated by inhibitors, which play integral role in controlling many metabolic pathways. Thus, the search for selective inhibitors and detailed knowledge on the mechanisms of binding of these substances to enzymes, could be of importance for designing new pharmacological approaches. The aim of this review is to summarize the current knowledge on the inhibitors of enzymes that convert selected groups of neuropeptides, such as dynorphins, enkephalins, substance P and NPFF fragments. The importance of these substances in pathophysiological processes involved in pain and drug addiction, have been discussed. This article is part of the special issue on Neuropeptides.

Neuropeptides: metabolism to bioactive fragments and the pharmacology of their receptors

The proteolytic processing of neuropeptides has an important regulatory function and the peptide fragments resulting from the enzymatic degradation often exert essential physiological roles. The proteolytic processing generates, not only biologically inactive fragments, but also bioactive fragments that modulate or even counteract the response of their parent peptides. Frequently, these peptide fragments interact with receptors that are not recognized by the parent peptides. This review discusses tachykinins, opioid peptides, angiotensins, bradykinins, and neuropeptide Y that are present in the central nervous system and their processing to bioactive degradation products. These well-known neuropeptide systems have been selected since they provide illustrative examples that proteolytic degradation of parent peptides can lead to bioactive metabolites with different biological activities as compared to their parent peptides. For example, substance P, dynorphin A, angiotensin I and II, bradykinin, and neuropeptide Y are all degraded to bioactive fragments with pharmacological profiles that differ considerably from those of the parent peptides. The review discusses a selection of the large number of drug-like molecules that act as agonists or antagonists at receptors of neuropeptides. It focuses in particular on the efforts to identify selective drug-like agonists and antagonists mimicking the effects of the endogenous peptide fragments formed. As exemplified in this review, many common neuropeptides are degraded to a variety of smaller fragments but many of the fragments generated have not yet been examined in detail with regard to their potential biological activities. Since these bioactive fragments contain a small number of amino acid residues, they provide an ideal starting point for the development of drug-like substances with ability to mimic the effects of the degradation products. Thus, these substances could provide a rich source of new pharmaceuticals. However, as discussed herein relatively few examples have so far been disclosed of successful attempts to create bioavailable, drug-like agonists or antagonists, starting from the structure of endogenous peptide fragments and applying procedures relying on stepwise manipulations and simplifications of the peptide structures.

Interactions between opioids and anabolic androgenic steroids: implications for the development of addictive behavior

Over the past decades, research on doping agents, such as anabolic androgenic steroids (AAS), has revealed that these compounds are often used in combination with other drugs of abuse. It seems that misuse of AAS probably involves more than a desire to enhance appearance or sports performance and studies have revealed that steroids are commonly connected with alcohol, opioids, tobacco, and psychotropic drugs. We have observed that AAS may interact with the endogenous opioids, excitatory amino acids, and dopaminergic pathways involved in the brain reward system. Furthermore, our studies provide evidence that AAS may induce an imbalance in these signal systems leading to an increased sensitivity toward opioid narcotics and central stimulants. In fact, studies performed in various clinics have shown that individuals taking AAS are likely to get addicted to opioids like heroin. This chapter reviews current knowledge on interactions between AAS and endogenous as well as exogenous opioids based not only on research in our laboratory but also on research carried out by several other clinical and preclinical investigators.

Evaluation of an on-capillary copper complexation methodology for the investigation of in vitro metabolism of dynorphin A 1-17

Dynorphin A 1-17 is an endogenous neuropeptide implicated in a variety of neurological disorders including Alzheimer's and Parkinson's diseases and neuropathic pain. Metabolites of this peptide can exhibit their own unique effects in vivo, and it is possible that one of these metabolites is responsible for the neurotoxicity. In this article, the use of CE for the separation of dynorphin A 1-17 from four of its metabolites is described. Buffer additives were investigated to eliminate peptide adsorption to the capillary wall and to improve resolution between closely related metabolites. On-capillary copper complexation was employed and was shown to improve separation efficiency as compared with the separation of native peptides. The method was then applied to in vitro dynorphin metabolism in human plasma as well as rat brain and rat spinal cord slices.

Prodynorphin mutations cause the neurodegenerative disorder spinocerebellar ataxia type 23

Spinocerebellar ataxias (SCAs) are dominantly inherited neurodegenerative disorders characterized by progressive cerebellar ataxia and dysarthria. We have identified missense mutations in prodynorphin (PDYN) that cause SCA23 in four Dutch families displaying progressive gait and limb ataxia. PDYN is the precursor protein for the opioid neuropeptides, α-neoendorphin, and dynorphins A and B (Dyn A and B). Dynorphins regulate pain processing and modulate the rewarding effects of addictive substances. Three mutations were located in Dyn A, a peptide with both opioid activities and nonopioid neurodegenerative actions. Two of these mutations resulted in excessive generation of Dyn A in a cellular model system. In addition, two of the mutant Dyn A peptides induced toxicity above that of wild-type Dyn A in cultured striatal neurons. The fourth mutation was located in the nonopioid PDYN domain and was associated with altered expression of components of the opioid and glutamate system, as evident from analysis of SCA23 autopsy tissue. Thus, alterations in Dyn A activities and/or impairment of secretory pathways by mutant PDYN may lead to glutamate neurotoxicity, which underlies Purkinje cell degeneration and ataxia. PDYN mutations are identified in a small subset of ataxia families, indicating that SCA23 is an infrequent SCA type (∼0.5%) in the Netherlands and suggesting further genetic SCA heterogeneity.

Suppressive effects by cysteine protease inhibitors on naloxone-precipitated withdrawal jumping in morphine-dependent mice

The effects of various protease inhibitors on naloxone-precipitated withdrawal jumping were examined in morphine-dependent mice. The doses of morphine were subcutaneously given twice daily for 2 days (day 1, 30 mg/kg; day 2, 60 mg/kg). On day 3, naloxone (8 mg/kg) was intraperitoneally administered 3h after final injection of morphine (60 mg/kg), and the number of jumping was immediately recorded for 20 min. Naloxone-precipitated withdrawal jumping was significantly suppressed by the intracerebroventricular administration of N-ethylmaleimide (0.5 nmol) and Boc-Tyr-Gly-NHO-Bz (0.4 nmol), inhibitors of cysteine proteases involved in dynorphin degradation, 5 min before each morphine treatment during the induction phase, with none given on the test day, as well as by dynorphin A (62.5 pmol) and dynorphin B (250 pmol). However, amastatin, an aminopeptidase inhibitor, phosphoramidon, an endopeptidase 24.11 inhibitor, and captopril, an angiotensin-converting enzyme inhibitor, caused no changes. The present results suggest that cysteine protease inhibitors suppress naloxone-precipitated withdrawal jumping in morphine-dependent mice, presumably through the inhibition of dynorphin degradation.

Nociceptive behavior induced by the endogenous opioid peptides dynorphins in uninjured mice: evidence with intrathecal N-ethylmaleimide inhibiting dynorphin degradation

Dynorphins, the endogenous opioid peptides derived from prodynorphin may participate not only in the inhibition, but also in facilitation of spinal nociceptive transmission. However, the mechanism of pronociceptive dynorphin actions, and the comparative potential of prodynorphin processing products to induce these actions were not fully elucidated. In our studies, we examined pronociceptive effects of prodynorphin fragments dynorphins A and B and big dynorphin consisting of dynorphins A and B, and focused on the mechanisms underlying these effects. Our principal finding was that big dynorphin was the most potent pronociceptive dynorphin; when administered intrathecally into mice at extremely low doses (1-10fmol), big dynorphin produced nociceptive behavior through the activation of the NMDA receptor ion-channel complex by acting on the polyamine recognition site. We next examined whether the endogenous dynorphins participate in the spinal nociceptive transmission using N-ethylmaleimide (NEM) that blocks dynorphin degradation by inhibiting cysteine proteases. Similar to big dynorphin and dynorphin A, NEM produced nociceptive behavior mediated through inhibition of the degradation of endogenous dynorphins, presumably big dynorphin that in turn activates the NMDA receptor ion-channel complex by acting on the polyamine recognition site. Our findings support the notion that endogenous dynorphins are critical neurochemical mediators of spinal nociceptive transmission in uninjured animals. This chapter will review above-described phenomena and their mechanism.

Cysteine protease inhibitors suppress the development of tolerance to morphine antinociception

The effects of various protease inhibitors on the development of antinociceptive tolerance to morphine were examined in mice. Intrathecal (i.t.) administration of morphine (0.01-1 nmol) produced a dose-dependent and significant antinociceptive effect in the 0.5% formalin test. When the doses of morphine (mg/kg, s.c. per injection) were given as pretreatment twice daily for two days [first day (30) and second day (60)], i.t. administration of morphine (0.1 nmol) was inactive due to antinociceptive tolerance on the third day. Tolerance to i.t. morphine was significantly suppressed by the i.t. injection of N-ethylmaleimide or Boc-Tyr-Gly-NHO-Bz, inhibitors of cysteine proteases involved in dynorphin degradation, as well as by dynorphin A, dynorphin B and (-) U-50,488, a selective kappa-opioid receptor agonist. On the other hand, amastatin, an aminopeptidase inhibitor, phosphoramidon, an endopeptidase 24.11 inhibitor, lisinopril, an angiotensin-converting enzyme inhibitor, and phenylmethanesulfonyl fluoride, a serine protease inhibitor, were inactive. These results suggest that cysteine protease inhibitors suppress the development of morphine tolerance presumably through the inhibition of dynorphin degradation.

Dysregulation of dynorphins in Alzheimer disease

The opioid peptides dynorphins may be involved in pathogenesis of Alzheimer disease (AD) by inducing neurodegeneration or cognitive impairment. To test this hypothesis, the dynorphin system was analyzed in postmortem samples from AD and control subjects, and subjects with Parkinson or cerebro-vascular diseases for comparison. Dynorphin A, dynorphin B and related neuropeptide nociceptin were determined in the Brodmann area 7 by radioimmunoassay. The precursor protein prodynorphin, processing convertase PC2 and the neuroendocrine pro7B2 and 7B2 proteins required for PC2 maturation were analyzed by Western blot. AD subjects displayed robustly elevated levels of dynorphin A and no differences in dynorphin B and nociceptin compared to controls. Subjects with Parkinson or cerebro-vascular diseases did not differ from controls with respect to any of the three peptides. PC2 levels were also increased, whereas, those of prodynorphin and pro7B2/7B2 were not changed in AD. Dynorphin A levels correlated with the neuritic plaque density. These results along with the known non-opioid ability of dynorphin A to induce neurodegeneration suggest a role for this neuropeptide in AD neuropathology.

Enzymatic conversion of dynorphin A in the rat brain is affected by administration of nandrolone decanoate

The misuse of anabolic androgenic steroids (AAS) seems to produce profound effects on the central nervous system, leading to aggressive behavior and increased sensitivity to other drugs of abuse. The present study addresses the effect on the enzymatic transformation, here called dynorphin converting enzyme-like activity. The formation of the mu/delta opioid peptide receptor-preferring Leu-enkephalin-Arg(6) from the kappa opioid peptide receptor-preferring dynorphin A was measured in rats treated with nandrolone decanoate. Significant variations in enzymatic transformation were observed in several brain regions. An altered receptor activation profile in these regions may be one contributory factor behind AAS-induced personality changes.

Dynorphin peptides differentially regulate the human kappa opioid receptor

Dynorphins, endogenous peptides for the kappa opioid receptor, play important roles in many physiological and pathological functions. Here, we examined how prolonged treatment with three major prodynorphin peptides, dynorphin A (1-17) (Dyn A), dynorphin B (1-13) (Dyn B) and alpha-neoendorphin (alpha-Neo), regulated the human kappa opioid receptor (hKOR) stably expressed in Chinese hamster ovary (CHO) cells. Results from receptor binding and [(35)S]GTPgammaS binding assays showed that these peptides were potent full agonists of the hKOR with comparable receptor reserve and intrinsic efficacy to stimulate G proteins. A 4-h incubation with alpha-Neo at a concentration of approximately 600xEC(50) value (from [(35)S]GTPgammaS binding) resulted in receptor down-regulation to a much lower extent than the incubation with Dyn A and Dyn B at comparable concentrations ( approximately 10% vs. approximately 65%). Extending incubation period and increasing concentrations did not significantly affect the difference. The plateau level of alpha-Neo-mediated receptor internalization (30 min) was significantly less than those of Dyn A and Dyn B. Omission of the serum from the incubation medium or addition of peptidase inhibitors into the serum-containing medium enhanced alpha-Neo-, but not Dyn A- or Dyn B-, mediated receptor down-regulation and internalization; however, the degrees of alpha-Neo-induced adaptations were still significantly less than those of Dyn A and Dyn B. Thus, these endogenous peptides differentially regulate KOR after activating the receptor with similar receptor occupancy and intrinsic efficacy. Both stability in the presence of serum and intrinsic capacity to promote receptor adaptation play roles in the observed discrepancy among the dynorphin peptides.

Identification of bikunin as an endogenous inhibitor of dynorphin convertase in human cerebrospinal fluid

Dynorphin-converting enzymes constitute a group of peptidases capable of converting dynorphins to enkephalins. Through the action of these enzymes, the dynorphin-related peptides bind to delta-opioid instead of kappa-opioid receptors, leading to a change in the biological function of the neuropeptides. In this article, we describe the identification of the protein bikunin as an endogenous, competitive inhibitor of a dynorphin-converting enzyme in human cerebrospinal fluid. This protein is present together with its target enzyme in the same body fluids. The K(M) value of the convertase was found to be 9 microm, and the K(i) value of the inhibitor was 1.7 nm. The finding indicates that bikunin may play a significant role as a regulatory mechanism of neuropeptides, where one bioactive peptide is converted to a shorter sequence, which in turn, can affect the action of its longer form.

Differential effects of N-peptidyl-O-acyl hydroxylamines on dynorphin-induced antinociception in the mouse capsaicin test

In the capsaicin test, intrathecal (i.t.) dynorphins are antinociceptive. Cysteine protease inhibitors such as p-hydroxymercuribenzoate (PHMB) given i.t. augment and prolong their activity. The effect of two novel cysteine protease inhibitors, N-peptidyl-O-acyl hydroxylamines, on the antinociception induced by i.t. administered dynorphin A or dynorphin B has been investigated. When administered i.t. 5 min before the injection of capsaicin (800 ng) into the plantar surface of the hindpaw, dynorphin A (62.5-1000 pmol) or dynorphin B (0.5-4 nmol) produced a dose-dependent and significant antinociceptive effect. The effect of dynorphin A (1 nmol) and dynorphin B (4 nmol) disappeared completely within 180 and 60 min, respectively. PHMB (2 nmol) and Boc-Tyr-Gly-NHO-Bz (BYG-Bz) (2 nmol) co-administered with dynorphin A or dynorphin B significantly prolonged antinociception induced by both. On the other hand, Z-Phe-Phe-NHO-Bz (ZFF-Bz) (1 and 2 nmol) only prolonged antinociception induced by dynorphin A. The results suggest that Z-Phe-Phe-NHO-Bz is an inhibitor of cysteine proteases preferring cleavage of dynorphin A, with less specificity towards dynorphin B in the mouse spinal cord.

Altered extracellular striatal in vivo biotransformation of the opioid neuropeptide dynorphin A(1-17) in the unilateral 6-OHDA rat model of Parkinson's disease

The in vivo biotransformation of dynorphin A(1-17) (Dyn A) was studied in the striatum of hemiparkinsonian rats by using microdialysis in combination with nanoflow reversed-phase liquid chromatography/electrospray time-of-flight mass spectrometry. The microdialysis probes were implanted into both hemispheres of unilaterally 6-hydroxydopamine (6-OHDA) lesioned rats. Dyn A (10 pmol microl(-1)) was infused through the probes at 0.4 microl min(-1) for 2 h. Samples were collected every 30 min and analyzed by mass spectrometry. The results showed for the first time that there was a difference in the Dyn A biotransformation when comparing the two corresponding sides of the brain. Dyn A metabolites 1-8, 1-16, 5-17, 10-17, 7-10 and 8-10 were detected in the dopamine-depleted striatum but not in the untreated striatum. Dyn A biotransformed fragments found in both hemispheres were N-terminal fragments 1-4, 1-5, 1-6, 1-11, 1-12 and 1-13, C-terminal fragments 2-17, 3-17, 4-17, 7-17 and 8-17 and internal fragments 2-5, 2-10, 2-11, 2-12, and 8-15. The relative levels of these fragments were lower in the dopamine-depleted striatum. The results imply that the extracellular in vivo processing of the dynorphin system is being disturbed in the 6-OHDA-lesion animal model of Parkinson's disease.

Pronociceptive role of dynorphins in uninjured animals: N -ethylmaleimide-induced nociceptive behavior mediated through inhibition of dynorphin degradation

Intrathecal (i.t.) administration into mice of N-ethylmaleimide (NEM), a cysteine protease inhibitor, produced a characteristic behavioral response, the biting and/or licking of the hindpaw and the tail along with slight hindlimb scratching directed toward the flank. The behavior induced by NEM was inhibited by the intraperitoneal injection of morphine. We have recently reported that dynorphin A and, more potently big dynorphin, consisting of dynorphins A and B, produce the same type of nociceptive response whereas dynorphin B does not [Tan-No K, Esashi A, Nakagawasai O, Niijima F, Tadano T, Sakurada C, Sakurada T, Bakalkin G, Terenius L, Kisara K. Intrathecally administered big dynorphin, a prodynorphin-derived peptide, produces nociceptive behavior through an N-methyl-d-aspartate receptor mechanism. Brain Res 2002;952:7-14]. The NEM-induced nociceptive behavior was inhibited by pretreatment with dynorphin A- or dynorphin B-antiserum and each antiserum also reduced the nociceptive effects of i.t.-injected synthetic big dynorphin. The characteristic NEM-evoked response was not observed in prodynorphin knockout mice. Naloxone, an opioid receptor antagonist, had no effects on the NEM-induced behavior. Ifenprodil, arcaine and agmatine, antagonists at the polyamine recognition site on the N-methyl-D-aspartate (NMDA) receptor ion-channel complex, and MK-801, an NMDA ion-channel blocker inhibited the NEM-induced effects. Ro25-6981, an antagonist of the NMDA receptor subtype containing NR2B subunit was not active. NEM completely inhibited degradation of dynorphin A by soluble and particulate fractions of mouse spinal cord. Collectively, the results demonstrate that endogenous prodynorphin-derived peptides are pronociceptive in uninjured animals, and required for the NEM-induced behavior. The NEM effects may be mediated through inhibition of the degradation of endogenous dynorphins, presumably big dynorphin that in turn activates the NMDA receptor ion-channel complex by acting on the polyamine recognition site.

A novel soluble protein factor with non-opioid dynorphin A-binding activity

A novel soluble non-opioid dynorphin A-binding factor (DABF) was identified and characterized in neuronal cell lines, rat spinal cord, and brain. DABF binds dynorphin A(1-17), dynorphin A(2-17), and the 32 amino acid prodynorphin fragment big dynorphin consisting of dynorphin A and B, but not other opioid and non-opioid peptides, opiates, and benzomorphans. The IC50 for dynorphin A(1-17), dynorphin A(2-17), and big dynorphin is in the 5-10 nM range. Using dynorphin A and big dynorphin fragments a binding epitope was mapped to dynorphin A(6-13). DABF has a molecular mass of about 70 kDa. SH-groups are apparently involved in the binding of dynorphin A since p-hydroxy-mercuribenzoic acid inhibited this process. Upon interaction with DABF dynorphin A was converted into Leu-enkephalin, which remained bound to the protein. These data suggest that DABF functions as an oligopeptidase that forms stable and specific complexes with dynorphin A. The presence of DABF in brain structures and other tissues with low level of prodynorphin expression suggests that DABF as an oligopeptidase may degrade other peptides. Dynorphin A at the sites of its release in the CNS may attenuate this degradation as a competitor when it specifically binds to the enzyme.

Metabolism of dynorphins by peptidases of pulmonary artery endothelial cells

Degradation of several dynorphins by peptidases expressed in cultured porcine pulmonary artery endothelial cells was studied by incubation of the peptide in cell suspensions followed by electrospray ionization and tandem mass spectrometric analyses. Under the in vitro conditions applied, only the metabolism of dynorphin A1-8 occurred in a significant extent. Studies involving specific peptidase inhibitors indicated that mainly bestatin-sensitive aminopeptidases, thiorphan-sensitive endopeptidases, and cFPAAF-pAB-sensitive endopeptidases expressed by the endothelial cells were involved in the process that converted dynorphin A1-8 to dynorphin A2-8, dynorphin A1-6, and leucine enkephalin (dynorphin A1-5), respectively. These peptidases may form a metabolic barrier for the cellular penetration of intact dynorphin A1-8 and/or control effects of the circulating peptide on endothelial opioid receptors of the cells.

Dynorphin A(1-17) biotransformation in striatum of freely moving rats using microdialysis and matrix-assisted laser desorption/ionization mass spectrometry

The biotransformation of the opioid peptide dynorphin A(1-17) was investigated in striatum of freely moving Fischer rats, by direct infusion of this peptide, followed by recovery of the resulting biotransformation products via microdialysis and identification using matrix-assisted laser desorption/ionization mass spectrometry. The observed peptides are consistent with enzymatic cleavage at the Arg7-Ile8 position of dynorphin A(1-17), followed by terminal degradation of the resulting dynorphin A(1-7) and dynorphin A(8-17) peptides. Unexpectedly, novel post-translational modifications were found on C-terminal fragments of dynorphin A(1-17). Using tandem mass spectrometry, a covalent modification of mass 172 Da, the nature of which is not understood, was found on the tryptophan residue of C-terminal fragments (Trp14). Additional modifications, of mass 42 and 113 Da, were also found on the N-terminus (Ile8 or Pro10) of these same C-terminal fragments. The role of these modifications of C-terminal fragments has not yet been characterized.

Roles of endogenous opioid peptides in modulation of nocifensive response to formalin

Roles of endogenous opioid peptides and their receptors in modulation of the nocifensive responses to formalin in mice were studied. Mice were pretreated i.c.v. or intrathecally (i.t.) with selective opioid receptor antagonists or intrathecally with antisera against endogenous opioid peptides and the nocifensive licking responses to intraplantar injection of formalin (0.5%, 25 microl) were then observed. Pretreatment with the epsilon-opioid receptor antagonist beta-endorphin(1-27) or the selective mu-opioid receptor antagonist D-Phe-Cys-Tyr-Orn-Thr-Pen-Thr-NH(2) (CTOP) given i.c.v. dose dependently enhanced the second, but not the first phase of the nocifensive response. However, i.c.v. pretreatment with the selective delta-receptor antagonist naltrindole or kappa-receptor antagonist nor-binaltrophimine did not affect the nocifensive responses. Intrathecal pretreatment with selective delta(1)-opioid antagonist 7-benzylidene naltrexamine significantly enhanced both the first and second phases of nocifension. Intrathecal pretreatment with CTOP also increased the second but not the first phase of the nocifension. However, i.t. pretreatment with the selective delta(2)-receptor antagonist naltriben or nor-binaltrophimine did not affect the second phase of the nocifension. Intrathecal pretreatment with antiserum against Leu-enkephalin, Met-enkephalin, or dynorphin A(1-17), but not beta-endorphin, enhanced only the second phase of nocifensive response to formalin. It is concluded that the blockade of epsilon- and mu-receptors, but not delta- or kappa-receptors, at the supraspinal sites enhanced the second phase of formalin-induced nocifension. In the spinal cord, Leu-enkephalin, and to a lesser extent, Met-enkephalin and dynorphin A(1-17) and mu- and delta(1)-opioid receptors, but not delta(2)- or kappa-opioid receptors, are involved in modulating the feedback inhibition of the second phase of formalin-induced nocifension.

Dynorphin A inhibits nociceptin-converting enzyme from the rat spinal cord

Cysteine proteinase found in the spinal cord of rat, called nociceptin-converting enzyme (NCE), is competitively inhibited by dynorphin A and its fragment des-[Tyr(1)]-DYN A. This proteinase converts orphanin FQ/nociceptin (OFQ/N) to two major fragments: OFQ/N(1-11) and further OFQ/N(1-6) with analgesic properties. Dynorphin A at the concentration of 10 microM increases K(M) from 15.0 to 55.9 microM. The calculated K(i) for this interaction was estimated at 3.7 microM. This observation may suggest an interaction between opioid and nociceptive systems which may be affected by the balance between opioid and antiopioid systems. This balance between particular OFQ/N sequences that are derived from the same precursor and regulated by proteinases may play an important role in pain. Interestingly, dynorphin B does not reveal a similar action on the NCE.

Antisera against endogenous opioids increase the nocifensive response to formalin: demonstration of inhibitory beta-endorphinergic control

The roles of endogenous opioid peptides in the brain in the modulation of nocifensive responses to formalin in ICR mice were studied. Mice were pretreated intracerebroventricularly (i.c.v.) with rabbit antiserum against beta-endorphin, [Leu5]enkephalin, [Met5]enkephalin or dynorphin A-(1-17) 1 h prior to intraplantar injection of formalin (0.5%, 25 microl) and the nocifensive licking responses were then observed. Pretreatment of mice with antiserum against beta-endorphin enhanced the second phase, but not the first phase of the nocifensive responses to formalin. Pretreatment with antiserum against [Leu5]enkephalin also caused a small but statistically significant enhancement of the second phase, but not the first phase of nocifensive responses to formalin. On the other hand, pretreatment with antiserum against [Met5]enkephalin or dynorphin A-(1-17) did not affect the nocifensive response to formalin. Our results indicate that beta-endorphinergic, and to a lesser extent, [Leu5]enkephalinergic systems are activated at the supraspinal sites to attenuate the nocifensive responses to formalin stimulation.

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.

Anterograde axonal transport of Boc-Arg-Val-Arg-Arg-MCA hydrolyzing enzyme in rat sciatic nerves: cleavage occurs between basic residues

Axonal transport of Boc-Arg-Val-Arg-Arg-MCA hydrolyzing enzyme activity was studied in rat sciatic nerves from 12 to 120 h after double ligations. The anterograde axonal transport increased and peaked 72 h after ligation. The optimum pH for Boc-Arg-Val-Arg-Arg-MCA hydrolyzing enzyme activity was 6.5 to 6.9 and did not require Ca(2+) for the activity. Two molecular forms with enzyme activity were identified by size-exclusion chromatography and the molecular masses of the two enzymes were estimated to be 98 and 52 kDa. Two enzyme activities were strongly inhibited by Hg(2+), Cu(2+) and trypsin inhibitors such as TLCK, antipain and leupeptin. It cleaved the substrate, Boc-Arg-Val-Arg-Arg-MCA, between the dibasic sequence Arg-Arg, and needed a support of aminopeptidase B-like enzyme activity for the liberation of 7-amino-4-methylcoumarin. These results suggest that the enzyme is transported in rat sciatic nerves and involved in the post-translational processing of precursor proteins under the anterograde axonal transport. But there is absolutely no evidence for a role in precursor processing and such a putative role is purely speculative.

Metabolic fate of nociceptin/orphanin FQ in the rat spinal cord and biological activity of its released fragment

Metabolism of orphanin FQ/nociceptin (OFQ/N) was studied in the spinal cord of rats. The heptadecapeptide was efficiently cleaved by a neutral serine endopeptidase, thus releasing the major metabolite, OFQ/N(1-11), further truncated to the final product, OFQ/N(1-6). Biologic activity of this latter fragment was tested in vivo, after intracerebroventricular and intrathecal injections. Hexapeptide exhibited a bi-phasic effect, causing antinociception up to 10 min after injection, followed by a hyperalgesia. The analgesic effect was blocked by naloxone and hyperalgesia was inhibited by NMDA--and NMDA/glycine site antagonists. The results indicate that shorter nociceptin fragments still possess their biologic activity though possibly acting via receptors other than ORL1.

Regulation of N-arginine dibasic convertase activity by amines: putative role of a novel acidic domain as an amine binding site

Peptide sequence analysis and cDNA cloning indicate that a previously described mouse arginine-specific dibasic cleaving enzyme (dynorphin converting enzyme) [Csuhai et al. (1995) Biochemistry 34, 12411] is the homologue of N-arginine dibasic convertase (NRDc) isolated from rat testis [Chesneau et al. (1994) J. Biol. Chem. 269, 2056]. A mouse NRDc cDNA exhibited 98% amino acid identity with the rat cDNA. However, within a 74 residue acidic stretch, this identity drops to 82%. Likewise, the corresponding acidic stretch of human NRDc is only 73% identical with that of rat NRDc. To reconcile previously observed kinetic differences between rat and mouse NRDc, the hydrolysis of peptide substrates by the rat, human, and mouse enzymes was compared using phosphate and Tris as buffers. Although the three NRDc's behaved similarly, Tris had a pronounced effect on the kinetics of peptide hydrolysis. With BAM-8, alpha-neoendorphin, and dynorphin B as substrates, Tris increased KM up to 40-fold with little change in Vmax, while with dynorphin A or somatostatin 28 as substrate, Tris caused a decrease in KM of up to 100 fold, again with only a modest change in Vmax. Other amines, including the polyamines putrescine, spermidine, and spermine, all affected NRD convertase activity. It is proposed that amines bind to the acidic stretch found in NRDc, and that quantitative differences in the sensitivity to amines between the rat, mouse, and human enzymes can be at least partially accounted for by differences in their acidic stretch. The role of polyamines as physiological modulators of N-arginine dibasic convertase is considered.

Characterization of immunoreactive dynorphin B and beta-endorphin in human plasma

Dynorphins and beta-endorphin in human plasma were characterized and studied quantitatively using radioimmunoassay, high-performance liquid chromatography (HPLC), and mass spectrometry. Most immunoreactive (ir) dynorphin B and beta-endorphin in human plasma coeluted with authentic peptides in analysis. Dynorphin A was not detected. Added to human plasma it was rapidly converted into Leu-enkephalin-Arg6 followed by elimination of the C-terminal arginine after prolonged incubation. The rate of dynorphin A conversion was estimated at 40 pmol/min/microl plasma. This process was inhibited by the thiol protease inhibitor, PHMB and by EDTA. Dynorphin B, alpha-neoendorphin and big dynorphin were virtually not metabolized by plasma proteases under the same conditions. beta-endorphin was processed into beta-endorphin(1-19) and the corresponding C-terminal counterpart beta-endorphin(20-31) at a rate of about 25 pmol/min/microl of plasma. Based on the above data, a reliable strategy was established to measure dynorphin B- and beta-endorphin-ir in human plasma samples. The basal levels in a male control group were 0.99 +/- 0.11 (n = 11) and 16.3 +/- 1.5 (n = 11) fmol/ml plasma, respectively.

A comparison between microwave irradiation and decapitation: basal levels of dynorphin and enkephalin and the effect of chronic morphine treatment on dynorphin peptides

Opioid peptides were analysed in tissue extracts of various brain structures and the pituitary gland from rats sacrificed by microwave irradiation, and compared with peptide levels in tissue extracts from decapitated rats. Dynorphin A, dynorphin B and Leu-enkephalinArg6, derived from prodynorphin, and Met-enkephalinArg6Phe7 from proenkephalin, were measured. Basal immunoreactive levels of dynorphin A and B were consistently higher in extracts from microwave-irradiated rats, whereas in these extracts immunoreactive levels of Leu-enkephalinArg6, an endogenous metabolite of dynorphin peptides, were either lower than, the same as or higher than in decapitated rats. Immunoreactive levels of Met-enkephalinArg6Phe7 were higher in microwave-irradiated rats. Effects of morphine treatment on prodynorphin peptide levels were evaluated and compared with previous findings in decapitated rats. Dynorphin immunoreactive levels were higher in the nucleus accumbens and striatum of morphine-tolerant rats than in corresponding areas in saline-treated rats. These results indicate tissue-specific metabolism of prodynorphin peptides and show that metabolism of opioid peptides occurs during the dissection procedure after decapitation of the rat even though precautions are taken to minimize degradation.

Opiate modulation of dynorphin conversion in primary cultures of rat cerebral cortex

Rat brain cortical cells in primary culture were used to investigate long-term effects of opiates on endopeptidases acting on dynorphin peptides. Enzyme activity in the soluble fraction of the cells converted dynorphin B to Leu-enkephalin-Arg6 and to a lesser extent to Leu-enkephalin. Five day treatment with 10 microM morphine increased the conversion to Leu-enkephalin-Arg6 by 370%. This effect was prevented by the presence of naloxone in the culture medium. The opiate-inducible activity was directed to the Arg-Arg bond in dynorphins with preference for dynorphin B > alpha-neoendorphin > > dynorphin A. The Km for the generation of Leu-enkephalin-Arg6 from dynorphin B was 40 microM. Enzyme activity was inhibited by dynorphin fragments, in the following order of potency: dynorphin A(1-13) > A(2-13) > A(1-17) > A(2-17) and by SH-reagents, suggesting the presence of a cysteine-protease. The opiate-stimulated dynorphin-converting enzyme (DCE)-activity affects the balance between dynorphin peptides (selective for kappa-opioid receptors) and enkephalin peptides (selective for delta-opioid receptors). Since both types of opioid peptides can influence the development of opiate tolerance, the change in the extent of this transformation may be functionally important.

Purification and characterization of substance P endopeptidase activities in the rat spinal cord

Two enzymes with substance P degrading activity were purified from the membrane bound fraction of the rat spinal cord. The purified enzymes were characterized with regard to biochemical and kinetic properties. One of the enzymes exhibited close similarity to neutral endopeptidase 24.11 (NEP, EC 3.4.24.11), while the other resembled a substance P converting endopeptidase (SPE), which has previously been identified and purified from human cerebrospinal fluid (CSF). Detergent treated spinal cord homogenates from male Sprague Dawley rats were purified by anion-exchange chromatography (DEAE-sepharose CL-6B), hydrophobic-interaction chromatography (phenyl-sepharose CL-4B) and molecular sieving (Sephadex G-50). Two fractions with enzymes differing in size were recovered and allowed for further purification to apparent homogeneity by ion-exchange chromatography and molecular sieving on a micro-purification system (SMART). The enzyme activities were monitored by following the conversion of synthetic substance P using a radioimmunoassay specific for the heptapeptide product, substance P (1-7). By SDS-polyacrylamide gel electrophoresis of the purified enzymes molecular weights of 43 and 70 kDa were estimated for the SPE-like and NEP-like activity, respectively. A K(m) of 5 microM was determined for the conversion of substance P to its (1-7) fragment by the SPE-like activity. Reversed-phase HPLC together with mass spectrometry permitted identification of all fragments released from substance P by the peptidases. The released fragments were for both enzymes identified as substance P (1-7), substance P (8-11), substance P (1-8), substance P (9-11). The NEP-like enzyme preparation also gave substance P (1-6) as a major product.

Guinea pig preprodynorphin mRNA: primary structure and regional quantitation in the brain

We isolated and sequenced genomic and cDNA clones of the guinea pig preprodynorphin (ppDyn) mRNA. The sequence of ppDyn mRNA was deduced from a combination of genomic and cDNA clones: The primary structure of two coding exons was derived from a genomic clone and 5' and 3' untranslated sequences were obtained using rapid amplification of cDNA ends (RACE). The predicted mRNA of 2,350 nucleotides coincides well with the size of transcripts in Northern blot analyses of RNA from different brain regions. The deduced amino acid sequence of guinea pig ppDyn shares 70%, 68%, and 61% identity to porcine, human, and rat ppDyn, respectively. The 5' untranslated sequences of guinea pig hippocampal and adrenal ppDyn mRNA are identical; both contain sequences of exon I and, like porcine mRNA, lack an exon (exon II) present in human and rat mRNA. Quantitative solution hybridization RNase protection analysis of total RNA from selected guinea pig brain regions was performed. The nucleus accumbens was found to have the greatest abundance of ppDyn mRNA, followed by caudate putamen, hippocampus, hypothalamus, amygdala, frontal cortex, olfactory bulb, and pons/medulla.

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.

Differential biotransformation of dynorphin A (1-17) and dynorphin A (1-13) peptides in human blood, ex vivo

The biotransformation in human blood in vitro of three dynorphin A (Dyn A) peptides was studied by matrix assisted laser desorption mass spectrometry to determine whether the natural peptide, Dyn A(1-17), is biotransformed differently from Dyn A (1-13), the natural sequence shortened form used in numerous neurobiological and pharmacological studies. In addition to studies of Dyn A(1-17), a natural product from prodynorphin and Dyn A(1-13), a natural sequence truncation of Dyn A(1-17), Dyn A(1-10)amide, a synthetic analogue of Dyn A(1-17) presumed to be protected from rapid biotransformation was also studied Synthetic Dyn A peptides were incubated in freshly drawn blood for various periods of time prior to mass spectrometric analysis. Several peptide products were identified from each precursor; the time profiles of appearance and disappearance of the major products were followed. Substantial differences in products and especially in the rate of biotransformation were observed between the processing of Dyn A(1-17) and the two shorter Dyn A peptides, Dyn A(1-13) and Dyn A(1-10)amide. Significant amounts of the natural Dyn A(1-17) survived 4 h of incubation (half-life 3 h). Dyn A (2-17), a major processed product of Dyn A(1-17) in blood, continued to accumulate during the 4-h incubation period. By contrast, both Dyn A(1-13) and Dyn A(1-10) amide were biotransformed very rapidly with half-lives of < 1 min and 10 min, respectively. Most of the products from these two peptide precursors were also further processed rapidly, with the exception of Dyn A(4-12) and Dyn A(4-10)amide, which were detected for over 2 h. Dyn A(1-6) was found as a minor biotransformation product from all three precursor peptides. These findings suggest that an important function of the four C-terminal amino acid residues of the natural form, Dyn A(1-17) [compared to Dyn A(1-13)], is to stabilize or protect the peptide from biotransformation by enzymes, by preserving a natural hairpin structure possibly near the carboxyl-terminus.

Characterization of the aminopeptidase activity of epidermal leukotriene A4 hydrolase against the opioid dynorphin fragment 1-7

Leukotriene A4 hydrolase is a bifunctional cytosolic enzyme, which both hydrolyses leukotriene A4 (LTA4) into leukotriene B4 (LTB4) and exerts aminopeptidase activity against opioid peptides. In the present study we have investigated whether the peptides angiotensin I and II, bradykinin, kallidine, histamine, dynorphin fragment 1-7 and substance P can act as substrates for epidermal and neutrophil LTA4 hydrolase. Among the tested substrates, dynorphin fragment 1-7 was found to be the best substrate for the enzyme. The aminopeptidase activity of epidermal and neutrophil LTA4 hydrolase against dynorphin fragment 1-7 was further characterized. The enzyme was purified from human epidermis and human neutrophils by anion exchange chromatography (Q-Sepharose) and affinity chromatography on a column with the LTA4 hydrolase inhibitor bestatin coupled to AH-Sepharose. The incubation of the dynorphin fragment 1-7 with LTA4 hydrolase resulted in the formation of tyrosine. The presence of the N-terminal amino acid tyrosine is essential for the interaction of opioids with their receptors, and this finding indicates that the LTA4 hydrolase can inactivate dynorphin fragment 1-7. After the two purification steps no other aminopeptidases acting at the N-terminal tyrosine of dynorphin fragment 1-7 was present in the preparation. This was demonstrated by the abolishment of the degradation at the N-terminal end of dynorphin fragment 1-7 when preincubating the enzyme preparation with LTA4 before the incubation with the dynorphin fragment 1-7. The abolishment of the aminopeptidase activity shows that activation of the hydrolase part of the enzyme, with conversion of LTA4 into the potent proinflammatory compound LTB4, results in an inhibition of the aminopeptidase activity of the enzyme. As a result, the catabolism of dynorphin fragment 1-7 and probably of other opioid peptides is inhibited, resulting in sustained biological effects of these opioids. This phenomenon may be important for the maintenance of inflammation in skin conditions, such as psoriasis and atopic dermatitis, in which LTB4 is formed.

Purification and characterization of a dynorphin-processing endopeptidase

Dynorphin B (Dyn B-13, also known as rimorphin) is generated from Dyn B-29 (leumorphin) by the cleavage at a single Arg residue. An enzymatic activity capable of processing at this monobasic site has been previously reported in neurosecretory vesicles of the bovine pituitary and pituitary-derived cell lines. This enzyme termed "the dynorphin-converting enzyme" (DCE) has been purified to apparent homogeneity from the neurointermediate lobe of the bovine pituitary using hydrophobic chromatography on phenyl-Sepharose, preparative isoelectrofocusing in a granulated gel between pH 4 to 6.5, and non-denaturing electrophoresis on 5% polyacrylamide gel. DCE exhibits a pI of about 5.1 and a molecular mass of about 54 kDa under reducing conditions. DCE is a metallopeptidase and exhibits a neutral pH optimum. Specific Inhibitors of soluble metallopeptidases such as enkephalinase (EC 3.4.24.11) or enkephalin generating neutral endopeptidase (EC 3.4.24.15) do not inhibit DCE activity indicating that DCE is distinct from these two enzymes. Cleavage site determination with matrix-assisted laser desorption ionization time of flight (MALDITOF) mass spectrometry shows that DCE cleaves the Dyn B-29 N terminus to the Arg14 generating Dyn B-13 and Dyn B-(14-29). Among other peptides derived from Dyn B-29, DCE cleaves only those peptides that fit the predicted "consensus motif" for monobasic processing. These data are consistent with a broader role for the dynorphin converting enzyme in the biosynthesis of many peptide hormones and neuropeptides by processing at monobasic sites.

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.

Processing of prodynorphin-derived peptides in striatal extracts. Identification by electrospray ionization mass spectrometry linked to size-exclusion chromatography

Proteolytic processing of prodynorphin-derived peptides in rat brain was studied with the help of high performance size exclusion chromatography (SEC) connected to electrospray ionization mass spectrometry. Extracts from rat striatum were incubated with individual synthetic dynorphin peptides. Dynorphin A was the most resistant to proteolytic cleavage, converting slowly to Leu-enkephalin (0.3 pmol/min), whereas dynorphin B was processed to this pentapeptide at a 10(4)-fold higher rate. Minor cleavage was also observed between Arg6-Arg7. Alphaneoendorphin was also rapidly metabolized to Leu-enkephalin (6 nmol/min) and, to a lesser extent, to Leu-enkephalinArg6. This new strategy for studying peptidases can easily be adapted to identification of components present in body fluids.

Capillary liquid chromatography-fast atom bombardment mass spectrometry using a high-resolving cation exchanger, based on a continuous chromatographic matrix. Application to studies on neuropeptide peptidases

Hyphenated mass spectrometric techniques such as LC-MS are advantageous over standard MS methods, because they provide increased sensitivity and minimize signal suppression by other compounds present in the reaction mixture. Recently, we have introduced so-called continuous beds, and applied this technique to prepare a 0.32 mm I.D. cation-exchange capillary column, in order to separate the reaction product substance P(1-7) after proteolytic cleavage of substance P by an endopeptidase recovered from human cerebrospinal fluid. The use of a volatile buffer for elution provides very good flow stability. Ion-exchange microcolumns may be particularly useful for the separation of those peptides that co-elute in reversed-phase chromatography because the separation mechanisms of these two methods are different.

In vitro stability of some reduced peptide bond pseudopeptide analogues of dynorphin A

Eight analogues of DYN A(1-11)-NH2 incorporating the nonhydrolyzable psi [CH2-NH] peptide bond surrogate were tested for their in vitro enzymatic stability in mouse brain homogenates. Results show that the Leu(5)-Arg6 and to a lesser extent the Arg(7)-Ile8 and Ile(8)-Arg9 peptide bonds are the more susceptible to enzymatic cleavage in the native peptide. (Leu5 psi[CH(2)-NH]Arg6)DYN A(1-11)-NH2 exhibits an almost complete resistance to enzymatic cleavage with a half-life greater than 500 min in brain, compared to 42 min for the standard peptide, DYN A(1-11)-NH2.

Proteinergic profiles in cerebrospinal fluid from alcoholic subjects

Minute amounts of cerebrospinal fluid samples from alcoholics were subjected to separation by HPLC-molecular sieving, combined with multispectral UV analysis of the acquired data. A significant difference in the protein/polypeptide pattern within the molecular weight range of 7-10 kDa has been observed between samples, taken directly after detoxification and 2 weeks later. Spectral analysis of the results suggests that the components are of peptidergic nature. On the other hand, albumin content did not differ significantly, suggesting that the blood-brain barrier was not affected. An enzyme marker, dynorphin converting enzyme, remained unchanged in both groups.