A new feature of angiotensin-converting enzyme in the brain: hydrolysis of substance P

Inhibition of angiotensin converting enzyme increases PKCβI isoform expression via activation of substance P and bradykinin receptors in cultured astrocytes of mice

BACKGROUND

Angiotensin-converting enzyme inhibitor (ACEi) inhibits the catalysis of angiotensin I to angiotensin II and the degradation of substance P (SP) and bradykinin (BK). While the possible relationship between ACEi and SP in nociceptive mice was recently suggested, the effect of ACEi on signal transduction in astrocytes remains unclear.

OBJECTIVES

This study examined whether ACE inhibition with captopril or enalapril modulates the levels of SP and BK in primary cultured astrocytes and whether this change modulates PKC isoforms (PKCα, PKCβI, and PKCε) expression in cultured astrocytes.

METHODS

Immunocytochemistry and Western blot analysis were performed to examine the changes in the levels of SP and BK and the expression of the PKC isoforms in primary cultured astrocytes, respectively.

RESULTS

The treatment of captopril or enalapril increased the immunoreactivity of SP and BK significantly in glial fibrillary acidic protein-positive cultured astrocytes. These increases were suppressed by a pretreatment with an angiotensin-converting enzyme. In addition, treatment with captopril increased the expression of the PKCβI isoform in cultured astrocytes, while there were no changes in the expression of the PKCα and PKCε isoforms after the captopril treatment. The captopril-induced increased expression of the PKCβI isoform was inhibited by a pretreatment with the neurokinin-1 receptor antagonist, L-733,060, the BK B1 receptor antagonist, R 715, or the BK B2 receptor antagonist, HOE 140.

CONCLUSIONS

These results suggest that ACE inhibition with captopril or enalapril increases the levels of SP and BK in cultured astrocytes and that the activation of SP and BK receptors mediates the captopril-induced increase in the expression of the PKCβI isoform.

Inhibition of angiotensin converting enzyme induces mechanical allodynia through increasing substance P expression in mice

Although emerging evidence shows that angiotensin converting enzyme (ACE) is associated with pain, it is not clear whether inhibition of ACE could affect to nociceptive transmission and which mediators are involved in this process. Here we investigated whether administration of the ACE inhibitors, captopril and enalapril increases the expression of substance P (SP) and whether this increase contributes to the induction of mechanical allodynia in mice. ACE was expressed in the lumbar dorsal root ganglion (DRG) and the superficial dorsal horn (SDH) region of the spinal cord in mice. Either intraperitoneal or intrathecal administration of the ACE inhibitors, captopril and enalapril for 10 days significantly increased the paw withdrawal frequency to innocuous mechanical stimuli and the levels of SP in both the lumbar DRG and the SDH region of the spinal cord dorsal horn. In addition, intraperitoneal administration of the SP receptor (neurokinin-1 receptor) antagonist, L-733,060 suppressed mechanical allodynia that was induced by pretreatment of captopril and enalapril. Intraplantar administration of SP for 3 days induces mechanical allodynia, and this effect was reduced by exogenous ACE administration. These findings demonstrate that inhibition of ACE increases the levels of SP in both the lumbar DRG and spinal cord dorsal horn, ultimately contributing to the induction of mechanical allodynia in mice.

Targeting Neuropathic Pain: Pathobiology, Current Treatment and Peptidomimetics as a New Therapeutic Opportunity

There is a huge need for pharmaceutical agents for the treatment of chronic Neuropathic Pain (NP), a complex condition where patients can suffer from either hyperalgesia or allodynia originating from central or peripheral nerve injuries. To date, the therapeutic guidelines include the use of tricyclic antidepressants, serotonin-noradrenaline reuptake inhibitors and anticonvulsants, beside the use of natural compounds and non-pharmacological options. Unfortunately, these drugs suffer from limited efficacy and serious dose-dependent adverse effects. In the last decades, the heptapeptide SP1-7, the major bioactive metabolite produced by Substance P (SP) cleavage, has been extensively investigated as a potential target for the development of novel peptidomimetic molecules to treat NP. Although the physiological effects of this SP fragment have been studied in detail, the mechanism behind its action is not fully clarified and the target for SP1-7 has not been identified yet. Nevertheless, specific binding sites for the heptapeptide have been found in brain and spinal cord of both mouse and rats. Several Structure-Affinity Relationship (SAR) studies on SP1-7 and some of its synthetic analogues have been carried out aiming to developing more metabolically stable and effective small molecule SP1-7-related amides that could be used as research tools for a better understanding of the SP1-7 system and, in a longer perspective, as potential therapeutic agents for future treatment of NP.

Effect of angiotensin-converting enzyme tag single nucleotide polymorphisms on the outcome of patients with traumatic brain injury

BACKGROUND

Genetic variants appear to influence, at least to some degree, the extent of brain injury and the clinical outcome of patients who have sustained a traumatic brain injury (TBI). Angiotensin-converting enzyme (ACE) is a zinc metallopeptidase that is implicated in the regulation of blood pressure and cerebral circulation. ACE gene polymorphisms were found to regulate serum ACE enzyme activity.

OBJECTIVE

The present study aimed to investigate possible influence of ACE gene region variants on patients' outcome after TBI.

PATIENTS AND METHODS

In total, 363 TBI patients prospectively enrolled in the study were genotyped for five tag single nucleotide polymorphisms (SNPs) across the ACE gene. Using logistic regression analyses, tag SNPs and their constructed haplotypes were tested for associations with 6-month Glasgow Outcome Scale scores, after adjustment for age, sex, Glasgow Coma Scale scores at admission, and the presence of a hemorrhagic event in the initial computed tomography scan.

RESULTS

Significant effects on TBI outcome were found for three neighboring tag SNPs in the codominant (genotypic) model of inheritance [rs4461142: odds ratio (OR) 0.26, 95% confidence interval (CI) 0.12-0.57, P = 0.0001; rs7221780: OR 2.67, 95% CI 1.25-5.72, P = 0.0003; and rs8066276: OR 3.82, 95% CI 1.80-8.13, P = 0.0002; for the heterozygous variants compared with the common alleles]. None of the constructed common tag SNPs haplotypes was associated with TBI outcome.

CONCLUSION

The present study provides evidence of the possible influence of genetic variations in a specific region of the ACE gene on the outcome of TBI patients. This association may have pharmacogenetic implications in identifying those TBI patients who may benefit from ACE inhibition.

Genetic Variants of Angiotensin-Converting Enzyme Are Linked to Autism: A Case-Control Study

Background

Autism is a disease of complex nature with a significant genetic component. The importance of renin-angiotensin system (RAS) elements in cognition and behavior besides the interaction of angiotensin II (Ang II), the main product of angiotensin-converting enzyme (ACE), with neurotransmitters in CNS, especially dopamine, proposes the involvement of RAS in autism. Since the genetic architecture of autism has remained elusive, here we postulated that genetic variations in RAS are associated with autism.

Methods

Considering the relation between the three polymorphisms of ACE (I/D, rs4343 and rs4291) with the level of ACE activity, we have investigated this association with autism, in a case-control study. Genotype and allele frequencies of polymorphisms were determined in DNAs extracted from venous blood of 120 autistic patients and their age and sex-matched healthy controls, using polymerase chain reaction (PCR) and PCR–restriction fragment length polymorphism (PCR–RFLP) methods.

Results

There were strong associations between both DD genotype of ACE I/D and the D allele, with autism (P = 0.006, OR = 2.9, 95% CI = 1.64–5.13 and P = 0.006, OR = 2.18, 95% CI = 1.37–3.48 respectively). Furthermore, a significant association between the G allele of rs4343 and autism was observed (P = 0.006, OR = 1.84, 95%CI = 1.26–2.67). Moreover, haplotype analysis revealed an association between DTG haplotype and autism (P = 0.008).

Conclusion

Our data suggests the involvement of RAS genetic diversity in increasing the risk of autism.

Subjective and Cardiovascular Effects of Intravenous Methamphetamine during Perindopril Maintenance: A Randomized, Double-Blind, Placebo-Controlled Human Laboratory Study

BACKGROUND

Our pilot study suggested that the angiotensin-converting enzyme inhibitor perindopril might reduce some subjective effects produced by i.v. methamphetamine. We characterized the impact of a wider range of perindopril doses on methamphetamine-induced effects in a larger group of non-treatment-seeking, methamphetamine-using volunteers.

METHODS

Before treatment, participants received 30mg methamphetamine. After 5 to 7 days of perindopril treatment (0, 4, 8, or 16mg/d), participants received 15 and 30mg of methamphetamine on alternate days. Before and after treatment, participants rated subjective effects and cardiovascular measures were collected.

RESULTS

Prior to treatment with perindopril, there were no significant differences between treatment groups on maximum or peak subjective ratings or on peak cardiovascular effects. Following perindopril treatment, there were significant main effects of treatment on peak subjective ratings of "anxious" and "stimulated"; compared to placebo treatment, treatment with 8mg perindopril significantly reduced peak ratings of both anxious (P=.0009) and stimulated (P=.0070). There were no significant posttreatment differences between groups on peak cardiovascular effects.

CONCLUSIONS

Moderate doses of perindopril (8mg) significantly reduced peak subjective ratings of anxious and stimulated as well as attenuated many other subjective effects produced by methamphetamine, likely by inhibiting angiotensin II synthesis. Angiotensin II is known to facilitate the effects of norepinephrine, which contributes to methamphetamine's subjective effects. The lack of a classic dose-response function likely results from either nonspecific effects of perindopril or from between-group differences that were not accounted for in the current study (i.e., genetic variations and/or caffeine use). The current findings suggest that while angiotensin-converting enzyme inhibitors can reduce some effects produced by methamphetamine, more consistent treatment effects might be achieved by targeting components of the renin-angiotensin system that are downstream of angiotensin-converting enzyme.

Structural basis of Ac-SDKP hydrolysis by Angiotensin-I converting enzyme

Angiotensin-I converting enzyme (ACE) is a zinc dipeptidylcarboxypeptidase with two active domains and plays a key role in the regulation of blood pressure and electrolyte homeostasis, making it the principal target in the treatment of cardiovascular disease. More recently, the tetrapetide N-acetyl-Ser–Asp–Lys–Pro (Ac-SDKP) has emerged as a potent antifibrotic agent and negative regulator of haematopoietic stem cell differentiation which is processed exclusively by ACE. Here we provide a detailed biochemical and structural basis for the domain preference of Ac-SDKP. The high resolution crystal structures of N-domain ACE in complex with the dipeptide products of Ac-SDKP cleavage were obtained and offered a template to model the mechanism of substrate recognition of the enzyme. A comprehensive kinetic study of Ac-SDKP and domain co-operation was performed and indicated domain interactions affecting processing of the tetrapeptide substrate. Our results further illustrate the molecular basis for N-domain selectivity and should help design novel ACE inhibitors and Ac-SDKP analogues that could be used in the treatment of fibrosis disorders.

Pharmacological Activities and Hydrolysis by Peptidases of [Phospho-Ser(6)]-Bradykinin (pS(6)-BK)

Phosphorylated kininogen and some of its fragments containing serine phosphorylated bradykinin ([pS(6)]-Bk) were identified in human serum and plasma by a phosphoproteomic approach. We report the kininogenase ability of human tissue and plasma kallikreins and tryptase to generate [pS(6)]-Bk or Lys-[pS(6)]-Bk having as substrate the synthetic human kininogen fluorescent fragment Abz-MISLMKRPPGF[pS(386)]PFRSSRI-NH2. The pharmacological assays of [pS(6)]-Bk showed it as a full B2 bradykinin receptor agonist in smooth muscle, it produces a portal liver hypertensive response in rat and mouse paw edema that lasts longer than Bk. The rat hypotensive response to infusions of Bk is greater than that of [pS(6)]Bk, both if injected through femoral vein or aorta. [pS(6)]-Bk was more resistant than Bk to kininase digestion performed with angiotensin converting enzyme, neprilysin, thimet oligopeptidase, aminopeptidase P and carboxypeptidase M. (1)H-NMR experiments indicated that [pS(6)]-Bk has lower flexibility, with the pS(6)-P(7) bond restricted to the trans conformation, and can explain [pS(6)]-Bk resistance to hydrolysis. In conclusion, [pS(6)]-Bk presenting lower activity than Bk, with longer lasting effects and being slowly released by kininogenases from synthetic Abz-MISLMKRPPGF[pS(386)]PFRSSRI-NH2, suggests that phosphorylation of the kininogens can be an efficient kallikrein-kinin system regulator.

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.

Applications of blood-based protein biomarker strategies in the study of psychiatric disorders

Major psychiatric disorders such as schizophrenia, major depressive and bipolar disorders are severe, chronic and debilitating, and are associated with high disease burden and healthcare costs. Currently, diagnoses of these disorders rely on interview-based assessments of subjective self-reported symptoms. Early diagnosis is difficult, misdiagnosis is a frequent occurrence and there are no objective tests that aid in the prediction of individual responses to treatment. Consequently, validated biomarkers are urgently needed to help address these unmet clinical needs. Historically, psychiatric disorders are viewed as brain disorders and consequently only a few researchers have as yet evaluated systemic changes in psychiatric patients. However, promising research has begun to challenge this concept and there is an increasing awareness that disease-related changes can be traced in the peripheral system which may even be involved in the precipitation of disease onset and course. Converging evidence from molecular profiling analysis of blood serum/plasma have revealed robust molecular changes in psychiatric patients, suggesting that these disorders may be detectable in other systems of the body such as the circulating blood. In this review, we discuss the current clinical needs in psychiatry, highlight the importance of biomarkers in the field, and review a representative selection of biomarker studies to highlight opportunities for the implementation of personalized medicine approaches in the field of psychiatry. It is anticipated that the implementation of validated biomarker tests will not only improve the diagnosis and more effective treatment of psychiatric patients, but also improve prognosis and disease outcome.

Proteolysis controls endogenous substance P levels

Substance P (SP) is a prototypical neuropeptide with roles in pain and inflammation. Numerous mechanisms regulate endogenous SP levels, including the differential expression of SP mRNA and the controlled secretion of SP from neurons. Proteolysis has long been suspected to regulate extracellular SP concentrations but data in support of this hypothesis is scarce. Here, we provide evidence that proteolysis controls SP levels in the spinal cord. Using peptidomics to detect and quantify endogenous SP fragments, we identify the primary SP cleavage site as the C-terminal side of the ninth residue of SP. If blocking this pathway increases SP levels, then proteolysis controls SP concentration. We performed a targeted chemical screen using spinal cord lysates as a proxy for the endogenous metabolic environment and identified GM6001 (galardin, ilomastat) as a potent inhibitor of the SP _1–9-producing activity present in the tissue. Administration of GM6001 to mice results in a greater-than-three-fold increase in the spinal cord levels of SP, which validates the hypothesis that proteolysis controls physiological SP levels.

Association of angiotensin-converting enzyme (ACE) gene polymorphism with elevated serum ACE activity and major depression in an Iranian population

Genetic factors contribute substantially to the likelihood of developing major depressive disorder (MDD). The importance of renin-angiotensin system (RAS) elements in cognition and behaviour and their involvement in aetiology and treatment of depression imply that RAS gene polymorphism(s) associated with RAS overactivity might also be associated with depression. In the present study, genotype and allele frequencies of six common polymorphisms of genes encoding for RAS components were determined in DNAs extracted from venous blood of 191 depressed and 104 healthy individuals using polymerase chain reaction (PCR) and polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) and serum angiotensin-converting enzyme (ACE) activity was assayed using a high-performance liquid chromatography (HPLC) method. The results showed, for the first time, that GG genotype of ACE A2350G was significantly associated with MDD among Iranian participants (P=0.001; odds ratio (OR)=6.2; 95% confidence interval (CI)=2.1-18.3). Significant higher serum ACE activity (P=0.0001) as well as higher diastolic blood pressure (P=0.036) were observed in depressed patients compared to the healthy control group. Depressed patients carrying GG genotype of the A2350G polymorphism had a significantly higher serum ACE activity (P=0.02) than individuals with either AA or AG genotype. In conclusion, this study supports the hypothesis of RAS overactivity in depression in that the genotype associated with higher serum ACE activity in an Iranian population was also associated with MDD.

No evidence of an association between two genes, EDN1 and ACE, and childhood-onset mood disorders

Recent evidence supports a pathological link between heart disease and depressive symptoms, suggesting that depression is both etiologic and prognostic to heart disease. Thus, biological molecules which are at the interface between heart and mind are plausible candidate genes for depressive disorders. To investigate this line of enquiry we have investigated two genes, Endothelin 1 (EDN1) and Angiotensin-converting enzyme (ACE) in a family-based sample with childhood-onset mood disorders (COMDs). EDN1 is highly expressed in endothelium where it acts as a potent vasoconstrictor, and is also expressed in the brain where it exhibits neurotransmitter characteristics. ACE acts as a potent vasopressor, and interacts with the hypothalamic-pituitary-adrenocortical (HPA) system, which is often dysregulated in mood disorders. Furthermore, ACE has recently been found to be associated with major depression. Polymorphisms were selected to best capture the genetic variation at the two loci, and to replicate previous associations. The markers were genotyped across EDN1 and ACE in a sample comprised of 382 Hungarian nuclear families ascertained through affected probands diagnosed with a mood disorders before the age of 15. We found no evidence of association between either of these genes and COMD. Consequently, we were unable to support our hypothesis that these two genes, which are involved in both vascular and brain functions are contributing to the susceptibility to mood disorders of children/adolescents.

Intrathecal substance P augments morphine-induced antinociception: possible relevance in the production of substance P N-terminal fragments

The present study sought to examine the mechanism of substance P to modulate the antinociceptive action of intrathecal (i.t.) morphine in paw-licking/biting response evoked by subcutaneous injection of capsaicin into the plantar surface of the hindpaw in mice. The i.t. injection of morphine inhibited capsaicin-induced licking/biting response in a dose-dependent manner. Substance P (25 and 50 pmol) injected i.t. alone did not alter capsaicin-induced nociception, whereas substance P at a higher dose of 100 pmol significantly reduced the capsaicin response. Western blots showed the constitutive expression of endopeptidase-24.11 in the dorsal and ventral parts of lumbar spinal cord of mice. The N-terminal fragment of substance P (1-7), which is known as a major product of substance P by endopeptidase-24.11, was more effective than substance P on capsaicin-induced nociception. Combination treatment with substance P (50 pmol) and morphine at a subthreshold dose enhanced the antinociceptive effect of morphine. The enhanced effect of the combination of substance P with morphine was reduced significantly by co-administration of phosphoramidon, an inhibitor of endopeptidase-24.11. Administration of D-isomer of substance P (1-7), [D-Pro(2), D-Phe(7)]substance P (1-7), an inhibitor of [(3)H] substance P (1-7) binding, or antisera against substance P (1-7) reversed the enhanced antinociceptive effect by co-administration of substance P and morphine. Taken together these data suggest that morphine-induced antinociception may be enhanced through substance P (1-7) formed by the enzymatic degradation of i.t. injected substance P in the spinal cord.

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.

Small peptides mimicking substance P (1-7) and encompassing a C-terminal amide functionality

Some of the biological effects demonstrated after administration of substance P (SP) in vivo can indirectly be attributed to the fragmentation of the undecapeptide to its N-terminal bioactive fragment SP(1-7). This heptapeptide (H-Arg-Pro-Lys-Pro-Gln-Gln-Phe-OH) is a major bioactive metabolite from SP that frequently exerts similar biological effects as the parent peptide but also, in several cases, completely opposite actions. Specific binding sites for the heptapeptide SP(1-7) that are separate from the SP preferred NK receptors have been identified. In this study we demonstrate that (a) the C-terminal part of the SP metabolite SP(1-7) is most important for binding as deduced from an Ala scan and that a replacement of Phe(7) for Ala is deleterious, (b) truncation of the N-terminal amino acid residues of SP(1-7) delivers peptides with retained binding activity, although with somewhat lower binding affinities than SP(1-7) and (c) a C-terminal amide group as a replacement for the terminal carboxy group of SP(1-7) and for all of the truncated ligands synthesized affords approximately 5-10-fold improvements of the binding affinities.

Investigation of the metabolism of substance P at the blood-brain barrier using LC-MS/MS

Substance P (SP) has been associated with pain and depression as well as neurodegenerative diseases. Many of these diverse actions of SP can potentially be attributed to SP metabolites generated at the blood-brain barrier (BBB). In this study, the metabolism of SP was investigated using an in vitro model of the BBB and LC-MS/MS. Substance P metabolism was found to be non-saturable in the concentration range of 100 nM to 10 microM, with approximately 70% of the peptide remaining intact after 5 h. The major metabolites of SP were identified by MS as 3-11 and 5-11. Two previously unreported metabolites, 5-11 and 6-11, were also found in our studies. Several additional minor SP metabolites, including 1-9 and 2-11, were also identified. A profile of the SP metabolites generated by the BBB over time was obtained. The results from the present study provide a better understanding of the role of the blood-brain barrier in the pharmacology of SP.

ACEPolymorphisms

Angiotensin converting enzyme (ACE) plays an essential role in two physiological systems, one leading to the production of angiotensin II and the other to the degradation of bradykinin. The wide distribution and multifunctional properties of these peptides suggest that ACE could be involved in various pathophysiological conditions. The discovery that ACE levels are under genetic control ushered in a new era of investigation; most studies focused on an insertion/deletion (I/D) polymorphism in intron 16 of the ACE gene as a marker for a functional polymorphism. Recently, many single nucleotide polymorphisms were detected in the gene and the search for the locations of functional polymorphisms became a topic of extensive investigation. Nevertheless, association studies on the I/D polymorphism and clinical outcomes continued, mostly with conflicting results. This article reviews the current state of knowledge regarding ACE polymorphisms and suggests that a functional polymorphism is most likely located between intron 18 and the 3' UTR. The potential existence of another functional polymorphism in the 5' UTR, however, cannot be excluded. This review also presents an overview of ACE function in different pathophysiological systems, and summarizes previous reports on ACE and clinical outcomes. Although findings on the I/D polymorphism and disorders like diabetic nephropathy and Alzheimer disease can be considered conclusive, reports on most of the cardiovascular phenotypes are still controversial. Genotypic and phenotypic misclassifications, insufficient power in some studies, and the presence of interaction with other genes or environmental factors are possible explanations for the contradictory findings.

Administration of the anabolic androgenic steroid nandrolone decanoate affects substance P endopeptidase-like activity in the rat brain

The effect of the anabolic androgenic steroid, nandrolone decanoate, on substance P endopeptidase-like activity was examined in adult male Sprague-Dawley rats. Nandrolone decanoate (15 mg/kg day) or oil vehicle (sterile arachidis oleum) were administered by intramuscular injections during 14 days. Substance P endopeptidase, a predominantly cytosolic enzyme, generates the bioactive N-terminal fragment substance P(1-7) from the enzyme substrate substance P. Nandrolone decanoate significantly reduced the substance P endopeptidase-like activity compared to control animals in hypothalamus (43% reduction), caudate putamen (44%), substantia nigra (32%) and the ventral tegmental area (27%). It was previously reported that both hypothalamus and caudate putamen contained significantly higher levels of substance P after nandrolone administration. The higher concentration of substance P in these regions could to an extent be attributed to the reduction in substance P endopeptidase-like activity. This result elucidates the important role of peptidase activity in the regulation of the substance P transmitter system. The present study provides additional support for the hypothesis that alterations in the substance P system in certain brain areas may contribute to some of the personality changes reported in connection with AAS abuse.

Molecular basis of exopeptidase activity in the C-terminal domain of human angiotensin I-converting enzyme: insights into the origins of its exopeptidase activity

Proteolytic processing is a primary means of biological control. Exopeptidases use terminal anchoring interactions to restrict cleavage at peptide substrate N or C termini. In contrast, internal peptide bond targeting by endopeptidases is through context-driven recognition. Angiotensin I-converting enzyme (ACE), a zinc metalloproteinase, has tandem duplicate catalytic domains, N- and C-terminal, each of which is a dual specificity enzyme with exo- and endocarboxypeptidase activities. The mechanisms by which ACE evolved from its endopeptidase ancestors as a dual specificity enzyme have not been defined. Based on kinetic studies of wild-type and mutant forms of the C-terminal catalytic domain of human ACE and of the ACE substrates angiotensin I, substance P, and bradykinin, as well as considerations of the ACE x-ray structure, we provide evidence that the acquisition of its exopeptidase activity is due to novel evolutionary specializations. These involve not only interactions between the S(2)' subsite cognate for the C-terminal substrate P(2)' side chain, acting in concert with carboxylate-docking interactions with Lys(1087) and Tyr(1096), but also electrostatic selection against a cationic C-terminal substrate carboxylate. With a blocked C terminus, substrate side chain interactions are dominant in cleavage site selection. In the evolution of obligate exopeptidases from endopeptidase ancestors, mutations that destroy context-driven peptide bond targeting are likely to have followed the acquisition of terminal docking interactions. Evolutionary intermediates between endopeptidases and obligate exopeptidases could therefore have been dual specificity proteinases like ACE.

Angiotensin converting enzyme (ACE) and neprilysin hydrolyze neuropeptides: a brief history, the beginning and follow-ups to early studies

Our investigations started when synthetic bradykinin became available and we could characterize two enzymes that cleaved it: kininase I or plasma carboxypeptidase N and kininase II, a peptidyl dipeptide hydrolase that we later found to be identical with the angiotensin I converting enzyme (ACE). When we noticed that ACE can cleave peptides without a free C-terminal carboxyl group (e.g., with a C-terminal nitrobenzylamine), we investigated inactivation of substance P, which has a C-terminal Met(11)-NH(2). The studies were extended to the hydrolysis of the neuropeptide, neurotensin and to compare hydrolysis of the same peptides by neprilysin (neutral endopeptidase 24.11, CD10, NEP). Our publication in 1984 dealt with ACE and NEP purified to homogeneity from human kidney. NEP cleaved substance P (SP) at Gln(6)-Phe(7), Phe(7)[see text]-Phe(8), and Gly(9)-Leu(10) and neurotensin (NT) at Pro(10)-Tyr(11) and Tyr(11)-Ile(12). Purified ACE also rapidly inactivated SP as measured in bioassay. HPLC analysis showed that ACE cleaved SP at Phe(8)-Gly(9) and Gly(9)-Leu(10) to release C-terminal tri- and dipeptide (ratio = 4:1). The hydrolysis was Cl(-) dependent and inhibited by captopril. ACE released only dipeptide from SP free acid. ACE hydrolyzed NT at Tyr(11)-Ile(12) to release Ile(12)-Leu(13). Then peptide substrates were used to inhibit ACE hydrolyzing Fa-Phe-Gly-Gly and NEP cleaving Leu(5)-enkephalin. The K(i) values in microM were as follows: for ACE, bradykinin = 0.4, angiotensin I = 4, SP = 25, SP free acid = 2, NT = 14, and Met(5)-enkephalin = 450, and for NEP, bradykinin = 162, angiotensin I = 36, SP = 190, NT = 39, Met(5)-enkephalin = 22. These studies showed that ACE and NEP, two enzymes widely distributed in the body, are involved in the metabolism of SP and NT. Below we briefly survey how NEP and ACE in two decades have gained the reputation as very important factors in health and disease. This is due to the discovery of more endogenous substrates of the enzymes and to the very broad and beneficial therapeutic applications of ACE inhibitors.

Peptidyl dipeptidases (Ance and Acer) of Drosophila melanogaster: major differences in the substrate specificity of two homologs of human angiotensin I-converting enzyme

Drosophila melanogaster angiotensin converting enzyme (Ance) and angiotensin converting enzyme related (Acer) are single domain homologs of mammalian peptidyl dipeptidase A (angiotensin I-converting enzyme) whose physiological substrates have not as yet been identified. We have investigated the in vitro substrate specificities of the two peptidases towards a variety of insect and mammalian peptides. Ance was generally much better than Acer at hydrolyzing peptides of 5-13 amino acids in length. Only two of the peptides, [Leu(5)]enkephalinamide and leucokinin-I were cleaved faster by Acer. Increasing NaCl concentration had opposite affects on the cleavage of [Leu(5)]enkephalin and [Leu(5)]enkephalinamide by Acer, decreasing the activity towards [Leu(5)]enkephalin but increasing the activity towards [Leu(5)]enkephalinamide. Of the insect peptides tested, the tachykinin-related peptide, Lom TK-1, proved to be the best substrate for Ance with a k(cat)/K(m) ratio of 0.122s(-1) microM(-1). However, in comparison, the D. melanogaster tachykinins, DTK-1, DTK-2, DTK-3 and DTK-4 were poor Ance substrates. DTK-5 was the best substrate of this family, but the apparent high K(m) for hydrolysis by Ance suggested that this peptide would not be a natural Ance substrate. This low affinity for DTK-5 is the likely reason why the peptide was not rapidly degraded in D. melanogaster hemolymph, where Ance was shown to be a major peptide-degrading activity.

In vivo metabolism and clearance of substance P and co-expressed tachykinins in rat striatum

Neurons expressing the preprotachykinin A gene, which encodes the sequences of substance P, neurokinin A, neuropeptide gamma and neuropeptide K, exemplify peptide co-existence. Furthermore, there is also evidence that substance P fragments have biological activity. However, the relative contribution of each of these peptides to tachykinin signalling is still poorly understood. An important factor which will determine the characteristics of the signal mediated by co-localised peptides is their clearance from the extracellular space. The striatum, in which tachykinins are present and exert neuromodulatory roles, can be used as a model to investigate this aspect. Therefore, in this study we characterised in vivo in the striatum the metabolism and clearance of substance P and of the other three co-expressed peptides. After intrastriatal administration of 1 pmol, tritiated substance P disappeared too rapidly for metabolites to be detected. However, when 10 nmol substance P and 1 pmol tritiated substance P were co-injected, substance P(1-4) and substance P(1-7), which are biologically active, were detected as major metabolites. Under these conditions, the rate of decay of tritiated substance P was 0.2 nmol/min. The effects of the peptidase inhibitors thiorphan, bestatin and captopril suggested that neutral endopeptidase 24.11 and aminopeptidases were involved in primary substance P cleavages, whereas angiotensin-converting enzyme was involved in secondary cleavages. The monitoring of the decay of unlabelled substance P by high-performance liquid chromatography gave a rate of 0.16 nmol/min. Using high-performance liquid chromatography with capillary electrophoresis, the rates of decay of 10 nmol neurokinin A or neuropeptide gamma were five and seven times faster than that of substance P. In contrast, over the time course of the experiment, no significant decay of neuropeptide K was detected. These results show that substance P disappears rapidly from the extracellular space, and supports the formation in vivo of major N-terminal active substance P metabolites. Our study also highlights significant differences in the clearance of co-expressed tachykinins and suggests that certain species may disappear relatively slowly from the extracellular space, and thus may make a significant temporal and spatial contribution to signalling.

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.

Investigation of the metabolism of substance P at the blood-brain barrier using capillary electrophoresis with laser-induced fluorescence detection

Substance P (SP) metabolism was investigated upon exposure to a monolayer of bovine brain microvessel endothelial cells (BBMECs), a cell culture model of the blood-brain barrier. SP was incubated with the BBMECs and its metabolism was followed as a function of time over a 5-h period. The resulting samples were derivatized with naphthalene-2,3-dicarboxaldehyde (NDA)/cyanide, separated, and detected using cyclodextrin-modified electrokinetic chromatography with laser-induced fluorescence detection (CDMEKC-LIF). Upon exposure to the BBMEC monolayer, SP rapidly degraded to produce the N-terminal (1-9), (1-4) and (1-7) and C-terminal (2-11) and (3-11) fragments. These results were compared with those in an earlier report from our laboratory, where SP metabolism was investigated in vivo by microdialysis sampling in rat striatum.

Investigation of the metabolism of substance P in rat striatum by microdialysis sampling and capillary electrophoresis with laser-induced fluorescence detection

The metabolism of substance P (SP) was investigated in rat striatum using in vivo microdialysis. Substance P was perfused for 5 h at 0.2 microl/min, and its metabolism was followed for over 13 h. The resulting samples were derivatized precolumn with naphthalene-2,3-dicarboxaldehyde (NDA)/cyanide, separated and detected by cyclodextrin-modified electrokinetic chromatography with laser-induced fluorescence detection (CDMEKC-LIF). Substance P rapidly degraded to form the fragments (3-11), (1-9), (1-4) and, to a lesser extent, (1-7). The metabolites reached steady-state levels 2-3 h after addition of SP.

Effects of tachykinins on uterine smooth muscle

1. Sensory nerves supplying the mammalian uterus have been shown to contain substance P (SP) and neurokinin (NK)A. This review presents some of the advances that have led to a greater understanding of the effects of tachykinins on uterine smooth muscle. 2. The cell-surface peptidase neprilysin (EC.3 24.11, endopeptidase 24.11, enkephalinase, CALLA, CD10) has been shown to play a major role in regulating the actions of tachykinins on both rat and human myometrium. Because this peptidase is known to be regulated by steroids and pregnancy, its effects may be of physiological relevance. 3. Tachykinins produce contractions of isolated myometrial preparations from non-pregnant rats and mice. The NK2 receptor mediates these effects in rat uterus, while the NK1 receptor may mediate these effects in the mouse uterus. 4. The effects of tachykinins have been examined on myometrial preparations obtained at Caesarean section from near-term pregnant women. In the presence of the peptidase inhibitors (thiorphan, captopril and bestatin), the mammalian tachykinins SP, NKA and NKB produced concentration-dependent uterine contractions. 5. The order of agonist potency NKA > SP = NKB suggested that NK2 receptors mediate uterine contractions in the human. This was confirmed using the stable analogues [Sar9,Met(O2)11]SP, [Lys5MeLeu9Nle10]NKA(4-10) and [N-MePhe7]NKB, which are NK1, NK2 and NK3 receptor selective, respectively. Only [Lys5MeLeu9Nle10]NKA(4-10) produced concentration-related contractions of human uterine smooth muscle. 6. The experimental findings described in the present review, taken together with results published previously in the literature, indicate that tachykinin peptides may play a physiological or pathophysiological role in regulating uterine smooth muscle activity. However, more extensive research will be required to confirm such a role for these peptides.

Octreotide-induced drinking, vasopressin, and pressure responses: role of central angiotensin and ACh

The involvement of central angiotensinergic and cholinergic mechanisms in the effects of the intracerebroventricularly injected somatostatin analog octreotide (Oct) on drinking, blood pressure, and vasopressin secretion in the rat was investigated. Intracerebroventricular Oct elicited prompt drinking lasting for 10 min. Water consumption depended on the dose of Oct (0.01, 0.1, and 0. 4 microgram). The drinking response to Oct was inhibited by pretreatments with the intracerebroventricularly injected angiotensin-converting enzyme inhibitor captopril, the AT(1)/AT(2) angiotensin receptor antagonist saralasin, the selective AT(1) receptor antagonist losartan, or the muscarinic cholinergic receptor antagonist atropine. The dipsogenic effect of Oct was not altered by prior subcutaneous injection of naloxone. Oct stimulated vasopressin secretion and enhanced blood pressure. These responses were also blocked by pretreatments with captopril or atropine. Previous reports indicate that the central angiotensinergic and cholinergic mechanisms stimulate drinking and vasopressin secretion independently. We suggest that somatostatin acting on sst2 or sst5 receptors modulates central angiotensinergic and cholinergic mechanisms involved in the regulation of fluid balance.

Purification and characterization of a dipeptidyl carboxypeptidase from the polychaete Neanthes virens resembling angiotensin I converting enzyme

Dipeptidyl carboxypeptidase (DCP) is well known as a mammalian angiotensin I converting enzyme (ACE) which plays an important role in blood pressure homeostasis. DCP was purified from the whole body of a polychaete, Neanthes virens. The purified enzyme was homogeneous by SDS-PAGE, with a molecular mass of 71 kDa by SDS-PAGE and 69 kDa by gel filtration, indicating that it is monomeric. The isoelectric point was 4.5 and optimum pH for the activity was 8.0. It showed a specific activity of 466.8 U/mg, which is the highest of known DCPs. The enzyme hydrolyzed angiotensin I to angiotensin II and sequentially released Phe-Arg and Ser-Pro from the C-terminus bradykinin, but does not cleave imido-bonds. Activity was completely inhibited by 1 mM EDTA and 5 mM o-phenanthroline, but it was not affected by serine and aspartic protease inhibitors. The original activity of EDTA-inactivated DCP was restored by addition of cobalt, manganese or low concentrations of zinc. The Km and Vmax values of the enzyme for Bz-Gly-His-Leu were 0.56 mM and 600 mumol/min per mg, respectively. The Ki values for specific mammalian ACE inhibitors, such as captopril and lisinopril, were 1.38 and 2.07 nM, respectively. In conclusion, we have shown the existence of a DCP from the polychaete, N. virens, with similar properties to those of mammalian ACE.

Central administration of the somatostatin analog octreotide induces captopril-insensitive sleep responses

The effects of intracerebroventricular injections of the long-lasting somatostatin analog octreotide (Oct) were studied on sleep and behavior in rats. Pyrogen-free physiological saline and Oct (0.001, 0.01, 0.1 microgram) or vehicle were administered at light onset, and the electroencephalogram (EEG), motor activity, and cortical brain temperature were recorded during the 12-h light period. Plasma growth hormone (GH) concentrations were measured in samples taken at 30-min intervals after Oct. Oct (0.01 and 0.1 microgram) suppressed non-rapid eye movement sleep (NREMS) for 1-2 h. NREMS intensity (delta EEG activity during NREMS) dose dependently increased in hour 3 postinjection and thereafter (0.1 microgram). Plasma GH concentrations were suppressed after Oct (0.01 and 0.1 microgram), but pulses of GH secretions occurred 90-120 min postinjection in each rat. Oct (0.1 microgram) enhanced behavioral activity, including prompt drinking followed by grooming, scratching, and feeding. Intracerebroventricular injection of the angiotensin-converting enzyme inhibitor captopril (30 microgram, 10 min before Oct), blocked these behavioral responses but not the Oct-induced sleep alterations. The changes in sleep after intracerebroventricular Oct suggest an intracerebral action site and might result from Oct-induced variations in the sleep-promoting activity of GH-releasing hormone.

Major metabolites of substance P degraded by spinal synaptic membranes antagonize the behavioral response to substance P in rats

Substance P (SP) was degraded by synaptic membranes of rat spinal cord. Cleavage products were separated by reversed phase high performance liquid chromatography and identified by amino acid composition analyses. Major products of SP were phenylalanine, SP(1-4), SP(1-6), SP(1-7), SP(10-11), and SP(8-9). Both the degradation of SP and the accumulation of the major cleavage products were strongly inhibited by a metal chelator, o-phenanthroline, and also by specific inhibitors of endopeptidase-24.11, thiorphan, and phosphoramidon. Thus, endopeptidase-24.11 plays a major role in SP degradation in the rat spinal cord. N-Terminal fragments, SP(1-7) and SP(1-4), detected after incubation with spinal synaptic membranes were examined in vivo for antagonism against the scratching, biting, and licking response induced by intrathecal (IT) injection of SP (3.0 nmol) in rats. When IT coadministered with SP, SP(1-7) and SP(1-4) produced a significant inhibition of behavioral response to SP with ED50 of 135.0 pmol and 6.2 nmol, respectively. These results suggest that the degradation of SP in the spinal cord is not only responsible for inactivation of parent peptide, but may also lead to the formation of N-terminal SP-fragments which are shown to display a novel physiological function.

Angiotensin-converting enzyme gene polymorphism and risk of sarcoidosis

The angiotensin-converting enzyme (ACE) has been implicated in the pathophysiology of sarcoidosis. Serum ACE levels in normal and sarcoidosis patients are influenced by an insertion (I)/deletion (D) polymorphism in the ACE gene. To elucidate the role of this ACE gene polymorphism in sarcoidosis, we conducted a case-control study in African Americans and Caucasians. The ACE gene (I/D) polymorphism did not differ between 60 Caucasian cases and 48 control subjects (p = 0.577). In contrast, a comparison of 183 African-American cases and 111 control subjects resulted in a marked difference in genotypic distributions (p = 0.005). In African Americans, the risk for sarcoidosis was 1.30 (95% confidence interval [CI] = 0.72 to 2. 36) for ID heterozygotes, and 3.17 (95% CI = 1.50 to 6.71) for deletion/deletion (DD) homozygotes. The risk associated with the DD homozygotes was even greater in African Americans when cases were restricted to those with a positive family history (odds ratio = 4. 83; 95% CI = 1.86 to 12.59). Further analyses of African-American cases showed that the ACE genotype was not associated with disease severity, extrathoracic involvement, or overall radiographic change 2 to 4 yr after diagnosis. We did find a moderate association between the II genotype and radiographic progression (OR = 2.97; 95% CI = 1.01 to 8.76). Our results suggest the ACE genotype may play a more important role in sarcoidosis susceptibility and progression in African Americans than Caucasians.

An aminoisobutyric acid-containing analogue of the cockroach tachykinin-related peptide, LemTRP-1, with potent bioactivity and resistance to an insect angiotensin-converting enzyme

Nine tachykinin-related peptides (TRPs), designated LemTRP-1-9, were recently isolated from the cockroach, Leucopheae maderae. To obtain a LemTRP resistant to endo- and exoprotease-mediated hydrolysis, we synthesized a peptide with one of the carboxy terminus residues substituted for a sterically hindered aminoisobutyric acid (Aib) and with the amino terminus blocked with a pyroglutamate. The Aib-containing analogue of the nonapeptide LemTRP-1 (Aib-LemTRP-1) thus has the sequence pGlu-Ala-Pro-Ser-Gly-Phe-Leu-Aib-Val-Arg-NH2. This analogue was shown to be resistant to hydrolysis by recombinant angiotensin-converting enzyme (ACE), from Drosophila melanogaster. Endogenous LemTRP-1 on the other hand was rapidly hydrolysed by ACE at the Gly7-Val8 bond, resulting in a single heptapeptide. The Aib-LemTRP-1 has about the same potency as LemTRP-I in inducing contractions of the L. maderae hindgut muscle. It was also tested in intracellular recordings for ability to induce firing of action potentials in dorsal unpaired median (DUM) neurons in the metathoracic ganglion of the locust Locusta migratoria. The Aib-containing analogue was nearly as active as LemTRP-1 and the natural ligand locustatachykinin I. LemTRP-1 and Aib-LemTRP-1 had the same transient time course of action on the cockroach hindgut. This suggests that peptide degradation is not likely to be the cause of the transient action of TRPs.

Hydrolysis of insect neuropeptides by an angiotensin-converting enzyme from the housefly, Musca domestica

The presence in insect tissues of peptides with structural similarities to angiotensin I and to bradykinin, the two best known substrates of mammalian angiotensin-converting enzyme, has not been reported. As part of our study to identify potential substrates for insect angiotensin-converting enzyme, we have investigated the susceptibility of a number of known insect peptide hormones and neurotransmitters to hydrolysis by Musca domestica angiotensin-converting enzyme. Insect peptides belonging to the red pigment-concentrating hormone, leucokinin, locust tachykinin, and depolarizing peptide families were hydrolyzed by housefly angiotensin-converting enzyme, whereas proctolin and crustacean cardioactive peptide were not substrates. Cus-DP II, LK I, LK II, and Lom-TK I were all cleaved at the penultimate C-terminal peptide bond to release a dipeptide amide as a major fragment with Km values of 94 +/- 11, 634 +/- 8, and 296 +/- 35 microM for Cus-DP II, LK I, and Lom-TK I, respectively. The ability of insect angiotensin-converting enzyme to hydrolyze C-terminally amidated peptides in vitro might be of functional significance because the enzyme has been localized to neuropile regions of the insect brain and is present in the hemolymph of houseflies.

N- and C-terminal substance P fragments modulate striatal dopamine outflow through a cholinergic link mediated by muscarinic receptors

The present study investigated whether the modulatory effects of substance P and substance P fragments on striatal dopamine release involve a cholinergic link. Rat striatal slices were incubated with substance P, substance P(1-4), substance P(1-7), substance P(5-11) and substance P(8-11) in the absence or presence of various agents which modify cholinergic transmissions, and endogenous dopamine outflow was measured using high-performance liquid chromatography. The incubation of striatal slices with substance P and its N- and C-terminal fragments (1 nM) induced a significant overflow of endogenous dopamine. Neostigmine (150 nM) potentiated the effects of substance P and its fragments, whereas the incubation with hemicholinium-3 (50 microM) abolished the effects of the peptides on dopamine outflow. The acetylcholinesterase inhibitor and the inhibitor of choline uptake did not have intrinsic effects on dopamine outflow. The muscarinic antagonist atropine (1 microM) reversed completely the effects of substance P and its fragments, whereas the nicotinic antagonists dihydro-beta-erythroidine (0.5 microM) and pempidine (10 microM) were devoid of effects. None of the cholinergic antagonists modified dopamine outflow. The results suggest that substance P and several N- and C-terminal substance P fragments activate cholinergic neurons in striatal slices. The released acetylcholine induces an increased dopamine outflow, mediated by muscarinic receptors. These observations represent additional evidence which supports the functional interactions between substance P, acetylcholine and dopamine in the striatum. Furthermore, they show that substance P fragments may exert neuromodulatory effects through mechanisms similar to those underlying the effects of the parent peptide.

Cloning and characterisation of angiotensin-converting enzyme from the dipteran species, Haematobia irritans exigua, and its expression in the maturing male reproductive system

The angiotensin-converting enzymes (ACE) are involved in the regulation of the specific maturation or degradation of a number of mammalian bioactive peptides. A carboxydipeptidase similar to mammalian ACE has now been identified in the adult stage of the haematophagous fly, Haematobia irritans exigua (buffalo fly), a close relative of the horn fly of North America. The enzyme was purified by lectin-affinity chromatography and ion-exchange chromatography and migrated as a doublet of 70 kDa upon reducing SDS/PAGE. Unlike mammalian ACE, the fly carboxydipeptidase (HieACE) is not membrane bound. The amino acid sequence of an internal peptide from HieACE and a conserved amino acid region present in all mammalian ACE were used to design degenerate oligonucleotide primers suitable for PCR. A DNA fragment amplified from adult buffalo fly cDNA was used to identify a cDNA clone that encoded the enzyme. The cDNA sequence encodes a carboxydipeptidase with 41-42% amino acid identity to the mammalian testicular ACE. The active-site regions of mammalian ACE are conserved in the deduced amino acid sequence of HieACE. Enzymatically, HieACE is very similar to its mammalian counterparts, with comparable Km and V(max) values for the synthetic substrate, benzoylglycylglycylglycine, and similar patterns of inhibition by EDTA, ACE inhibitor peptide and captopril. HieACE also specifically activates angiotensin I to angiotensin II and degrades other mammalian ACE substrates such as bradykinin, substance P and cholecystokinin-8. In the adult fly, HieACE is expressed in the compound ganglion and in the posterior region of the midgut. Similar to the mammalian system, expression of this enzyme is induced in the maturing male reproductive system, which suggests conservation of ACE function in these species.

The endopeptidase activity and the activation by Cl- of angiotensin-converting enzyme is evolutionarily conserved: purification and properties of an an angiotensin-converting enzyme from the housefly, Musca domestica

A soluble 67 kDa angiotensin-converting enzyme (ACE) has been purified by lisinopril-Sepharose affinity column chromatography from adult houseflies, Musca domestica. The dipeptidyl carboxypeptidase activity towards benzoyl-Gly-His-Leu was inhibited by captopril (IC50 50 nM) and fosinoprilat (IC50 251 nM), two inhibitors of mammalian ACE, and was activated by Cl- (optimal Cl- concentration 600 mM). Musca ACE removed C-terminal dipeptides from angiotensin I, bradykinin [Leu5]enkephalin and [Met5]enkephalin and also functioned as an endopeptidase by hydrolysing dipeptideamides from [Leu5]enkephalinamide and [Met5]enkephalinamide, and a dipeptideamide and a tripeptideamide from substance P. Musca ACE was also able to cleave a tripeptide from both the N-terminus and C-terminus of luteinizing hormone-releasing hormone, with C-terminal hydrolysis predominating. Maximal N-terminal tripeptidase activity occurred at 150 mM NaCl, whereas the C-terminal tripeptidase activity continued to rise with increasing concentration of Cl- (0-0.5 M). Musca ACE displays properties of both the N- and C-domains of human ACE, indicating a high degree of conservation during evolution of the substrate specificity of ACE and its response to Cl-.

Evidence for modulatory effects of substance P fragments (1-4) and (8-11) on endogenous dopamine outflow in rat striatal slices

The effects of substance P-(1-4) and substance P-(8-11) on endogenous dopamine outflow in rat striatal slices were investigated. The dose-response curves (0.01 nM to 1 microM) were bell-shaped for both peptides, with significant increases in dopamine outflow at 0.1 and 1 nM. Dopamine overflow elicited by 1 nM substance P-(1-4) or substance P-(8-11) and 25 mM KCl was additive. Although substance P-(8-11) contains a truncated tachykinin sequence, the tachykinin NK1 receptor antagonist WIN 51,708 (17 beta-hydroxy-17 alpha-ethynyl-5 alpha-androstano[3,2-b]pyrimido[1,2- a]benzimidazole (2.5 nM) fully reversed its effect. The interaction between the antagonist and 1 nM substance P-(1-4) was statistically not significant. The data constitute the first evidence that the fragments substance P-(1-4) and substance P-(8-11) could exert central effects and suggest that they may play a role in neuromodulation in the basal ganglia.

Central cardiovascular and behavioral effects of carboxy- and amino-terminal fragments of substance P in conscious rats

The central cardiovascular and behavioral effects of carboxy- (SP 5-11, SP 6-11, SP 7-11, SP 8-11) and amino- (SP 1-7, SP 1-9) terminal substance P (SP) fragments were compared with those of SP 1-11 in conscious rats. In addition, the ability of these SP-fragments to induce desensitization of the central NK1 receptor was investigated. SP 1-11 (50 pmol) injected i.c.v. induced an increase in mean arterial blood pressure (MAP), heart rate (HR) and a typical behavioral response consisting of face washing (FW), hindquarter grooming (HQG) and wet-dog shakes (WDS). The cardiovascular and behavioral responses to equimolar doses of SP 5-11 and SP 6-11 were similar to those of SP 1-11, however, only SP 5-11 induced exactly the same behavioral pattern as SP 1-11. SP 6-11 was more potent in inducing FW and WDS than SP 1-11 or SP 5-11. The carboxy-terminal SP-fragments, SP 7-11 and SP 8-11, and the amino-terminal SP-fragments, SP 1-7, SP 1-9, did not elicit any significant cardiovascular or behavioral responses. Pretreatment with SP 1-11 reduced the cardiovascular and behavioral responses to subsequent injections of SP 1-11. Of all SP-fragments tested, only SP 5-11 was able to attenuate the cardiovascular and behavioral responses to SP 1-11. Our results demonstrate that SP 6-11 represents the shortest carboxy-terminal amino acid sequence, that after i.c.v. injection, elicits the same cardiovascular response as SP 1-11, but fails to desensitize the NK1 receptor. The carboxy-terminal fragment, SP 5-11, is the shortest amino acid sequence which produces the same pattern of central cardiovascular and behavioral responses as SP 1-11 and also retains the ability to desensitize the NK1 receptor like SP 1-11.

Substance P-(1-7) and substance P-(5-11) locally modulate dopamine release in rat striatum

The effects of substance P, substance P-(1-7) and substance P-(5-11) on endogenous dopamine outflow in rat striatal slices were investigated. The dose-response curves (0.01 nM to 10 microM) were bell-shaped, with significant increases at 0.1 and 1 nM but with no effect at higher concentrations. The tachykinin NK1 receptor agonist, [Sar9,Met(O2)11]substance P, significantly increased dopamine outflow at 10 and 100 nM. The effects of substance P or substance P-(5-11) and 25 mM KCl were additive. A negative interaction was observed with substance P-(1-7) and K+. The increase in dopamine outflow elicited by 1 nM substance P and substance P-(5-11) was reversed by the tachykinin NK1 receptor antagonist WIN 51,708 (17 beta-hydroxy-17 alpha-ethynyl-5 alpha-androstano[3,2-b]pyrimido[1,2- alpha]benzimidazole) (25 and 250 nM), whereas only partial reversal was observed for the effect of substance P-(1-7). These results show that substance P fragments locally modulate striatal dopamine outflow and the mechanisms underlying this modulation may differ between N- and C-terminal fragments.

Localization of angiotensin converting enzyme by in vitro autoradiography in the rabbit brain

The distribution of angiotensin converting enzyme was examined in the rabbit brain by in vitro autoradiography with the specific radiolabelled inhibitor 125I-351A. In the rabbit, the highest concentrations of radioligand binding were found in the choroid plexus, blood vessels, subfornical organ, vascular organ of the lamina terminalis, area postrema and inferior olive. High levels of binding were found throughout the basal ganglia, consistent with the results in all other species studied. In the midbrain the central gray and the superior colliculus displayed high levels of binding. In the medulla oblongata high levels of binding were associated with the nucleus of the solitary tract and dorsal motor nucleus of vagus, consistent with the pattern in other species. There was moderate labelling throughout both the cerebral and cerebellar cortices, which contrasts to the rat but is consistent with the situation in primates. Angiotensin converting enzyme (ACE) is more widely distributed in rabbit brain that in rat, human and Macaca fascicularis, and the results suggest ACE has a very general role in the metabolism of neuropeptides. Inhibitors of converting enzyme are very widely used in the treatment of hypertension and heart disease, and the rabbit should provide a useful model for examining the effects of these drugs in the brain.

CP-71,362: a pentapeptide renin inhibitor selective for the canine enzyme

Most renin inhibitors are primate-specific. In the present paper, we describe the effects of CP-71,362, a pentapeptide which preferentially inhibits canine (and to a lesser extent, rat) plasma renin. Vs. the canine enzyme, its affinity (IC50 = 3.3 x 10(-12) M) is 1000x greater than for rat renin (IC50 = 3.3 x 10(-9) M), and 1000x greater than for human (IC50 = 2.3 x 10(-8) M), cynomolgus monkey (IC50 = 1.6 x 10(-8) M), or guinea pig (IC50 = 5.2 x 10(-8) M) enzyme. In anesthetized, sodium-depleted dogs, intravenous infusion of CP-71,362 (ED50 = 1.1 micrograms/kg/min) resulted in dose-dependent decreases (up to -35 mm Hg) in mean arterial pressure (MAP). The maximum fall in MAP was equivalent to that produced by i.v. captopril (5 mg/kg). Similar falls in MAP were observed in conscious sodium-depleted SHR (ED50 = 5 micrograms/kg/min). Via bolus injection, the action of CP-71,362 was relatively brief in dog, guinea pig, and SHR. We conclude that CP-71,362 is a potent canine/rat renin inhibitor and causes profound MAP lowering in these species.

Behavioral activation of neurokinin-1 agonists in relation to enzymatic degradation in the spinal cord

Intrathecal (i.t.) injection of substance P (SP) induced reciprocal hindlimb scratching directed mainly toward the abdominal regions in mice. This behavior pattern appeared within the first minute after i.t. injection of SP. Similar behavioral effects were produced by i.t. injection of neurokinin (NK)-1 agonists, physalaemin (Phy) and [Sar9,Met(O2)11] SP (Sar-SP). The duration of scratching varied among NK-1 agonists; of the NK-1 agonists used, Phy had the most long-lasting duration of scratching in contrast to SP that had a short duration. The rank order of scratching duration was Phy > Sar-SP > SP. SP was rapidly degraded by the solubilized enzyme extracted from the mouse spinal cord as determined by HPLC. Decay of the scratching response to these NK-1 agonists was parallel with the rate of their degradation by the solubilized enzyme. These results suggest that a relatively long-lasting scratching behavior induced by Phy is mainly attributed to the stability against peptidases in the spinal cord.

Characterization of the thermolysin-like cleavage of biologically active peptides by Xenopus laevis peptide hormone inactivating enzyme

Peptide hormone inactivating endopeptidase (PHIE) is a metalloendopeptidase which was isolated from the skin granular gland secretions of Xenopus laevis [Carvalho, K. M., Joudiou, C., Boussetta, H., Leseney, A. M., & Cohen, P. (1992) Proc. Natl. Acad. Sci. U.S.A. 89, 84-88]. This peptidase exhibits a thermolysin-like character and hydrolyzes bonds on the amino terminus of hydrophobic amino acids, performing cleavage of Xaa-Phe, Xaa-Leu, Xaa-Ile, Xaa-Tyr, and Xaa-Trp doublets. When the enzyme recognized a doublet of hydrophobic amino acids such as Phe6-Phe7 of somatostatin-14, Phe7-Phe8 of substance P, Phe4-Leu5 of [Leu5,Arg6]enkephalin, and Tyr4-Ile5 of angiotensin II, cleavage occurred preferentially between these residues. The use of selectively modified carboxy-terminal octapeptide fragments of atrial natriuretic factor (ANF) indicated that the enzyme tolerates as substrates only peptides bearing a P'1 bulky hydrophobic amino acid residue. Although a P'1 hydrophobic residue was a necessary condition, it was found in a number of peptides that all potential cleavage sites were not recognized by the enzyme. These data suggested that this metalloendoprotease requires for its thermolysin-like activity a preferred conformation of the peptide chain. Kinetic results obtained using a series of related substrates derived from biologically active peptides of the atrial natriuretic factor, tachykinin, and enkephalin families indicated the presence of an extended binding site accommodating at least six amino acid residues, in contrast to thermolysin (EC 3.4.24.4) and neutral endopeptidase (NEP; EC 3.4.24.11), which hydrolyze shorter homologous peptides.(ABSTRACT TRUNCATED AT 250 WORDS)