Degradation of bradykinin by isolated neutral endopeptidases of brain and pituitary

Neprilysin Inhibitors and Bradykinin

Bradykinin has important physiological actions related to the regulation of blood vessel tone and renal function, and protection from ischemia reperfusion injury. However, bradykinin also contributes to pathological states such as angioedema and inflammation. Bradykinin is metabolized by many different peptidases that play a major role in the control of bradykinin levels. Peptidase inhibitor therapies such as angiotensin converting enzyme (ACE) and neprilysin inhibitors increase bradykinin levels, and the challenge for such therapies is to achieve the beneficial cardiovascular and renal effects without the adverse consequences such as angioedema that may result from increased bradykinin levels. Neprilysin also metabolizes natriuretic peptides. However, despite the potential therapeutic benefit of increased natriuretic peptide and bradykinin levels, neprilysin inhibitor therapy has only modest efficacy in essential hypertension and heart failure. Initial attempts to combine neprilysin inhibition with inhibition of the renin angiotensin system led to the development of omapatrilat, a drug that combines ACE and neprilysin inhibition. However, omapatrilat produced an unacceptably high incidence of angioedema in patients with hypertension (2.17%) in comparison with the ACE inhibitor enalapril (0.68%), although angioedema incidence was less in patients with heart failure with reduced ejection fraction (HFrEF) treated with omapatrilat (0.8%), and not different from that for enalapril therapy (0.5%). More recently, LCZ696, a drug that combines angiotensin receptor blockade and neprilysin inhibition, was approved for the treatment of HFrEF. The approval of LCZ696 therapy for HFrEF represents the first approval of long-term neprilysin inhibitor administration. While angioedema incidence was acceptably low in HFrEF patients receiving LCZ696 therapy (0.45%), it remains to be seen whether LCZ696 therapy for other conditions such as hypertension is also accompanied by an acceptable incidence of angioedema.

A comparison of the properties and enzymatic activities of three angiotensin processing enzymes: angiotensin converting enzyme, prolyl endopeptidase and neutral endopeptidase 24.11

The discovery of angiotensin-(1-7) [Ang-(1-7)] as a bioactive Ang II fragment of the renin-angiotensin system (RAS) alters the current understanding of the enzymatic components that comprise the RAS cascade. Two neutral endopeptidases, prolyl endopeptidase (E.C. 3.4.21.26) and neutral endopeptidase 24.11 (E.C. 3.4.24.11), are capable of forming Ang-(1-7) from Ang I and have been implicated in the in vivo processing of Ang I. This makes them putative Ang processing enzymes and part of the RAS cascade. This review summarizes the physical characteristics and distribution of angiotensin converting enzyme (E.C. 3.4.15.1), a known Ang I processing enzyme, and compares its features to what is known of prolyl endopeptidase and neutral endopeptidase 24.11.

Behavioural effects of two dipeptides L-phenyl alanyl-L-arginine (Phe-L-Arg) and L-phenyl alanyl-D-arginine (Phe-D-Arg) after intracerebroventricular or intrathecal injections in mice

L-phenylalanyl-L-arginine (Phe-L-Arg) and L-phenylalanyl-D-arginine (Phe-D-Arg), dissolved in a physiological saline were injected intrathecally into the lateral brain ventricle, and their behavioural as well as analgesic effects in mice were determined. It was found that a 100 nM dose of either peptide intracerebroventricularly (i.c.v.) injected induced an increase in the locomotor activity and a convulsive effect, whereas the same dose if injected produced a significant analgesic effect. It has been concluded that Phe-L-Arg and Phe-D-Arg have significant but different central effects in mice.

Purification and characterization of human brain prolyl endopeptidase

Prolyl endopeptidase (EC 3.4.21.26) was purified from human brain by a series of column-chromatographic steps using DEAE-cellulose DE-52, hydroxyapatite, phenyl-Sepharose, Sephacryl S-200 and f.p.l.c. (Mono Q). The enzyme was purified by a factor of 943 and was homogeneous in a SDS/polyacrylamide gel as judged by Coomassie Blue staining. The Mr estimated by SDS/PAGE is 79,600, and under native conditions on Sephacryl S-200 it is 85,600. Therefore the enzyme exists as a monomer. With benzyloxycarbonylglycylproline p-nitroanilide as substrate, the optimum pH of the enzyme is 6.8, and with the substrate concentration between 0.059 mM and 0.37 mM the Km is 9.0 x 10(-4) M. The pI of the enzyme is 4.75. The enzyme is classified as a serine proteinase, as it is strongly inhibited by di-isopropyl fluorophosphate. However, other serine proteinase inhibitors do not inhibit the enzyme significantly, suggesting that the active site of prolyl endopeptidase differs from that of classical serine proteinases such as trypsin. Polyclonal antibodies were raised against purified human brain prolyl endopeptidase in rabbits. Western-blot analysis, enzyme-inhibition assays, antibody binding and immunoprecipitation experiments indicated that the polyclonal antibodies are both specific and inhibitory to the enzyme activity.

A multicatalytic high-molecular-weight neutral endopeptidase from human kidney

A multicatalytic endopeptidase (ME) with three distinct activities, chymotrypsin-like, cucumisin-like, and trypsin-like, occurred in all rat tissues examined with highest activities in kidney, testes, liver, and spleen; they were assayed with benzyloxycarbonyl-Gly-Gly-Leu-p-nitroanilide (Z-Gly-Gly-Leu-pNA), benzyloxycarbonyl-Leu-Leu-Glu-2-naphthylamide (Z-Leu-Leu-Glu-2NA), and benzyloxycarbonyl-Gly-Gly-Arg-2-naphthylamide (Z-Gly-Gly-Arg-2NA), respectively. All three activities were recovered from a single protein band on a polyacrylamide gel after electrophoresis of purified human kidney ME. The native enzyme had a Mr of 650,000, and it consisted of about 5,135 amino acid residues. After denaturation and electrophoresis on sodium dodecyl sulfate (SDS)-polyacrylamide gels kidney ME dissociated into several low Mr components ranging from 23,000 to 33,000. Kidney ME had a pH optimum of 7.6-8.1 with Z-Gly-Gly-Leu-pNA, 7.3 with Z-Leu-Leu-Glu-2NA, and 9.8 with Z-Gly-Gly-Arg-2NA. SDS enhanced chymotrypsin- and cucumisin-like activities by two to three times whereas trypsin-like activity was not enhanced. The specificity constant (kappa cat/Km) of human kidney ME for Z-Gly-Gly-Leu-pNA was 6.7 X 10(3) M-1 S-1; Z-Gly-Gly-Leu-2NA was not hydrolyzed. The specificity constant for Z-Leu-Leu-Glu-2NA was similar to, and for Z-Gly-Gly-Arg-2NA was one half of that for Z-Gly-Gly-Leu-pNA. ME cleaves only the Phe5-Ser6 bond of bradykinin (BK); however, all three ME activities were inhibited by BK. Strong inhibition of ME by albumin suggests that ME is involved in cleavage of larger polypeptides. Antipain and leupeptin almost completely inactivated the trypsin-like activity whereas they had no significant effect on the other two activities. ME is not a metal-loenzyme nor is the serine residue essential for its activities; however, thiol groups are involved. Na+ and K+ inhibited all ME activities. Trypsin-like activity was more sensitive to divalent cations than the other two.

Involvement of endopeptidase 24.15 in the inactivation of bradykinin by rat brain slices

The effect of peptidase inhibitors on the degradation of [3H]-bradykinin by rat hypothalamic slices was studied using HPLC to separate and identify the products. The degradation appears to be mainly mediated by an enzyme which cleaves the peptide at the Phe5-Ser6 bond and is inhibited by 1,10-phenanthroline, dynorphin(1-13) and carboxyphenylethyl-Ala-Ala-Phe-p-aminobenzoate. This suggest the involvement of a membrane bound variant of the soluble metalloendopeptidase (EC3.4.24.15) isolated from rat brain which degrades neurotensin, angiotensin and other neuropeptides as well as bradykinin.

Specific, high-affinity bradykinin binding by purified porcine kidney post-proline cleaving enzyme

Post-proline cleaving enzyme (PPCE) was purified from porcine kidney cytosol. The purified enzyme bound [125I-Tyr5]-bradykinin but neither [125I-Tyr1]-kallidin nor [125I-Tyr8]-bradykinin. Scatchard analysis of the data was consistent with a single class of binding sites with a Kassoc = 1.3 +/- 0.1 X 10(8) M-1. The optimal pH for [125I-Tyr5]-bradykinin binding was 6.8. The specificity of binding was evaluated with sixty-seven bradykinin analogs. The catalytic activity of the enzyme was measured with N-benzyloxycarbonyl-Gly-Pro-methylcoumarinyl-7-amide (Z-Gly-Pro-MCA). The optimal pH for hydrolysis of this substrate was broad and centered at 8.3. The apparent Km and Vmax were obtained from Lineweaver and Burk plots and were 4.8 +/- 0.4 X 10(-5) M and 42 +/- 5 mumoles X mg-1 X min-1 respectively. The IC50 values for bradykinin, diisopropylfluorophosphate (DFP), and N-benzyloxycarbonyl-Pro-Prolinal (Z-Pro-Prolinal) to inhibit Z-Gly-Pro-MCA hydrolysis by PPCE were 5.9 +/- 1.4 X 10(-7) M, 8.8 +/- 3.1 X 10(-7) and 7.9 +/- 0.3 X 10(-9) M respectively. Corresponding values for inhibition of [125I-Tyr5]-bradykinin binding by PPCE were 5.1 +/- 2.3 X 10(-9) M, 1.2 +/- 0.3 X 10(-6) M and 1.4 +/- 0.6 X 10(-8) M.

A high-molecular-mass neutral endopeptidase-24.5 from human lung

A high-Mr neutral endopeptidase-24.5 (NE) that cleaved bradykinin at the Phe5-Ser6 bond was purified to apparent homogeneity from human lung by (NH4)2SO4 fractionation, ion-exchange chromatography and gel filtration. The final enzyme preparation produced a single enzymically active protein band after electrophoresis on a 5% polyacrylamide gel. Human lung NE had an Mr of 650,000 under non-denaturing conditions, but after denaturation and electrophoresis on an SDS/polyacrylamide gel NE dissociated into several lower-Mr components (Mr 21,000-32,000) and into two minor components (Mr approx. 66,000). The enzyme activity was routinely assayed with the artificial substrate Z-Gly-Gly-Leu-Nan (where Z- and -Nan represent benzyloxycarbonyl- and p-nitroanilide respectively). NE activity was enhanced slightly by reducing agents, greatly diminished by thiol-group inhibitors and unchanged by serine-proteinase inhibitors. Human lung NE was inhibited by the univalent cations Na+ and K+. No metal ions were essential for activity, but the heavy-metal ions Cu2+, Hg2+ and Zn2+ were potent inhibitors. With the substrate Z-Gly-Gly-Leu-Nan a broad pH optimum from pH 7.0 to pH 7.6 was observed, and a Michaelis constant value of 1.0 mM was obtained. When Z-Gly-Gly-Leu-Nap (where -Nap represents 2-naphthylamide) was substituted for the above substrate, no NE-catalysed hydrolysis occurred, but Z-Leu-Leu-Glu-Nap was readily hydrolysed by NE. In addition, NE hydrolysed Z-Gly-Gly-Arg-Nap rapidly, but at pH 9.8 rather than in the neutral range. Although human lung NE was stimulated by SDS, the extent of stimulation was not appreciable as compared with the extent of SDS stimulation of NE from other sources.

Post-proline endopeptidase in human placenta

Post-proline endopeptidase (EC 3.4.21.26) was found in human placenta, purified 3390-fold from it and briefly characterized. The post-proline endopeptidase could be completely separated from dipeptidyl peptidase IV (EC 3.4.14.5) by hydrophobic phenyl-Sepharose chromatography. The pH optimum of the enzyme was 6.7. The Km values for 7-(Succinyl-Gly-Pro)-4- methylcoumarinamide was 1.0 mM. The molecular weight of this enzyme was estimated to be 140 000 by gel filtration and 67 000 by dodecyl sulfate gel electrophoresis, indicating its dimeric structure. Human placental post-proline endopeptidase was suggested to be a thiol proteinase by inhibition studies.

Effects of kininase II inhibitors on the vasomotor response to bradykinin of feline intracranial and extracranial arteries in vitro and in situ

Bradykinin is known to effect a vasodilatation of feline cerebral arteries in situ and of both human and feline pial arteries in vitro. In order to demonstrate whether kininase II (localized within the vessel wall or in the surrounding tissue or fluid) influences the response to bradykinin, two different inhibitors of this bradykinin degradation enzyme were tested. Perivascular microapplication of potentiator C (10−10–10−4M) or captopril (10−10–10−3M) did not, by itself, change the diameter of feline pial arteries (87–305 μm) in situ. In a similar investigation, the dilating action of bradykinin (10−8–10−5M) was not modified by the simultaneous application of potentiator C or captopril (10−5M). Furthermore, the relaxing effect of bradykinin (10−10–10−4M) on isolated feline middle cerebral arteries (preconstricted with 5-hydroxytryptamine or prostaglandin F2α) was not influenced by the presence of captopril (10−7M). In contrast, when studied on isolated extracranial vessel segments (feline sublingual artery), bradykinin caused a concentration-dependent constriction of the artery. This constriction was completely reversed to dilatation in the presence of captopril (10−7M). Moreover, the characteristic effect of kininase II inhibition was demonstrated in the isolated guinea pig ileum preparation. In this instance, bradykinin induced a concentration-dependent contraction that was enhanced by potentiator C or captopril. We conclude, therefore, that bradykinin exerts variable responses on vascular smooth muscle, depending on the species used, the muscle location and experimental conditions. Finally, the in situ and in vitro findings for pial and middle cerebral arteries demonstrate that kininase II does not modify the dilating effect of bradykinin under our experimental conditions.

A prolyl endopeptidase from murine macrophages, its assay and specific inactivation

The presence of a prolyl endopeptidase in the soluble fraction of murine peritoneal macrophages is reported. The prolyl endopeptidase is apparently highly specific for cleaving peptides after proline residues. A sensitive new fluorogenic assay substrate matching this specificity, benzyloxycarbonyl-Ala-Ala-Pro beta-methoxynaphthylamide, is described. The enzyme is rapidly inactivated by benzyloxycarbonyl-Ala-Ala-Pro diazomethyl ketone, one of a class of reagents specific for cysteine proteinases, and by diisopropyl fluorophosphate, an inhibitor of serine proteinases. Culture of macrophages with the addition of low levels of benzyloxycarbonyl-Ala-Ala-Pro diazomethyl ketone to the media allows the selective inhibition of the cytoplasmic enzyme as measured in lysates at the termination of culture. After exposure to inhibitor, macrophages resynthesize the enzyme over a period of days, a process which is inhibited by cycloheximide. Similar amounts of activity were found in both normal peritoneal macrophages and those elicited by prior injection of thioglycollate media. The enzyme from murine macrophages appears similar to that reported in bronchopulmonary lavage fluid and lung tissue and to those isolated from brain and pituitary tissues.

Determination of specificity of endopeptidases by combined high-performance liquid chromatography and amino acid analysis

The specificity of three neutral endopeptidases toward several biologically active peptides was determined by combined high-performance liquid chromatography and amino acid analysis of the degradation products. Incubation mixtures were chromatographed on a reversed-phase column equilibrated with a mixture of acetonitrile and potassium phosphate buffer (0.05 M; pH 2.0). Reaction products were eluted with a linear gradient of acetonitrile and the absorbance of the effluent monitored at 210 nm. Fractions corresponding to discrete peaks were subjected to quantitative amino acid analysis. The peptide bond undergoing cleavage is readily assigned from the knowledge of the primary structure of the peptide and the amino acid composition of the reaction products.

Characterization of a nonchymotrypsin-like endopeptidase from anterior pituitary that hydrolyzes luteining hormone-releasing hormone at the tyrosyl-glycine and histidyl-tryptophan bonds

A neutral endopeptidase which degrades luteinizing hormone-releasing hormone (LH-RH, <GLu-His-Trp-Ser-Tyr-Gly-Leu-Arg-Pro-GLy-NH2) has been purified 900-fold from extracts of bovine anterior pituitary. This Ca2+-independent enzyme of 83 000 molecular weight (as estimated by gel filtration) cleaves LH-RH (KM = 180 microM) at the Tyr5-Gly6-His2-Trp3 bonds. Its activity is inhibited by the SH-reactive agents N-ethylmaleimide and p-(chloromercuri)benzoate but not by the OH-reactive agent diisopropyl fluorophosphate. Hydrolysis of the fluorogenic chymotrypsin substrate glutarkyl-Gly-Gly-Phe-beta-naphthylamide by this endopeptidase could not be detected. These properties differentiate the endopeptidase from chymotrypsin and from a glutaryl-Gly-Gly-Phe-beta-naphthylamide hydrolyzing activity of high molecular weight, which has been isolated from the same tissue and also hydrolyzes internal bonds of LH-RH.