Identification of [hydroxyproline3]-lysyl-bradykinin released from human kininogens by human urinary kallikrein

Picomolar Sensitivity Analysis of Multiple Bradykinin-Related Peptides in the Blood Plasma of Patients With Hereditary Angioedema in Remission: A Pilot Study

Background

Hereditary angioedema (HAE) is a rare autosomal dominant disease; the most well understood forms concern the haplodeficiency of C1 esterase inhibitor (C1INH) and a gain of function mutation of factor XII (FXII). The acute forms of these conditions are mediated by an excessive bradykinin (BK) formation by plasma kallikrein.

Methods

A validated LC-MS/MS platform of picomolar sensitivity developed for the analysis of eleven bradykinin-related peptides was applied to the plasma of HAE-C1INH and HAE-FXII sampled during remission.

Results

In HAE-C1INH plasma, the concentrations of the relatively stable BK1−5 fragment (mean ± S.E.M.: 12.0 ± 4.2 pmol/L), of BK2−9 (0.7 ± 0.2 pmol/L) and of the sums of BK and its tested fragments (18.0 ± 6.4 pmol/L) are significantly greater than those recorded in the plasma of healthy volunteers (1.9 ± 0.6, 0.03 ± 0.03 and 4.3 ± 0.8 pmol/L, respectively), consistent with the previous evidence of permanent plasma kallikrein activity in this disease. Kinin levels in the plasma of HAE-FXII patients did not differ from controls, suggesting that triggering factors for contact system activation are not active during remission.

Conclusion

BK1−5, BK2−9 and the sum of BK and its fragments determined by the sensitive LC-MS/MS technique are proposed as potential biomarkers of HAE-C1INH in remission while this was not applicable to HAE-FXII patients.

The kallikrein-kininogen-kinin system: lessons from the quantification of endogenous kinins

The purpose of the present review is to describe the place of endogenous kinins, mainly bradykinin (BK) and des-Arg(9)-BK in the kallikrein-kininogen-kinin system, to review and compare the different analytical methods reported for the assessment of endogenous kinins, to explain the difficulties and the pitfalls for their quantifications in biologic samples and finally to see how the results obtained by these methods could complement and extend the pharmacological evidence of their pathophysiological role.

Bradykinin receptors and their antagonists

Bradykinin and related kinins act on two receptor types, named B1 and B2. Initially identified in classical bioassays, these receptors have been cloned and characterized in binding assays performed on plasma membranes of cells expressing the native or the transfected human kinin B1 or B2 receptor types. The two classification criteria recommended by Schild, namely the order of potency of agonists and the actual affinity of antagonists have been found to be applicable for receptor classification based not on data only from bioassays but also from other approaches (binding assays, molecular biology techniques). The order of potency for agonists was found with naturally occurring peptides (the kinins, their desArg9-metabolites) and with selective agonists (e.g., [Hyp3]bradykinin, [Aib7]bradykinin): the findings obtained with agonists could be validated with various antagonists. Critical evaluation of the initial compounds, typified by D)-Arg-[Hyp3, D-Phe7]bradykinin, has indicated that they are short-acting, partial agonists, non-selective for the bradykinin B2 receptor because they can be metabolized to desArg9-fragments that act on the kinin B1 receptor. Use of such compounds has given rise to misunderstandings, especially with regard to new receptor types (e.g., type B3), the existence of which was not confirmed by molecular cloning. A second generation of antagonists, represented by D-Arg[Hyp3,Thi5,D-Tic7,Oic8]bradykinin (HOE 140) has been found resistant to degradation, long-acting in vivo, selective and specific for the B2 receptor and potent in all species tested. HOE 140 has been used successfully in basic pharmacology, in animal physiopathologies involving kinins and their receptors and even in clinical studies. A third generation of non-peptide B2 receptor antagonists, whose prototype is FR 173657 ((E)-3-(6-acetamido-3-pyridyl)-N-[N-2-4-dichloro-3-[(2-methyl-8-quinolin yl)oxymethyl]phenyl]-N-methylamino carbonyl-methyl]acrylamide) is now emerging and may represent substantial progress since FR 173657 is a potent orally active, selective and specific antagonist of the human and other species B2 receptors. There is also progress regarding antagonists for the B1 receptor. The initial compounds, especially Lys-[Leu8]desArg9-bradykinin remain among of the most potent, specific and selective B1 antagonists which, however, show partial agonistic effects in some B1 receptor subtypes (e.g., the mouse). Progress has been made with AcLys-[D-betaNal7, Ile8]desArg9-bradykinin (R 715) and Lys-Lys-[Hyp3, Cpg5, D-Tic7,Cpg8]desArg9-bradykinin (B 9958) which are pure B1 antagonists in humans and rabbits; both peptides have shown resistance to degradation by peptidases and have little if any, residual agonistic activity on mouse and rat B1 receptors. No non-peptide antagonists are yet available for the B1 receptor.

Identification of endogenous Des-Arg9-[Hyp3]-bradykinin in human plasma with post-source-decay matrix-assisted laser desorption/ionization mass spectrometry

In the present study, the purification and sequence analysis of a peptide extracted from human plasma is described. After three chromatographic steps in one of the plasma fractions, a molecular mass of 920 Da was determined with matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) analysis. Further analysis with post-source-decay (PSD)-MALDI-MS revealed an amino acid sequence arg-pro(pro-gly+16)-phe-ser-pro-phe. With the data given from the spectrum, it was impossible to clarify the partial sequence (pro-gly+16). A comparison with a data base suggested that the sequence is very similar to des-arg9bradykinin (arg-pro-pro-gly-phe-ser-pro-phe). But many fragment masses, including the mass of the parent ion of the unknown peptide, are 16 Da larger than the corresponding fragment masses of des-arg9-bradykinin. The interpretation of the fragment pattern does not allow determination of the position of the amino acid that is 16 Da larger. With automated Edman sequence analysis of the fraction of interest, three more major component peptides in this fraction were observed, which were not detected with MALDI-MS. Nevertheless, with the help of the Edman sequence data it was possible to identify the unknown amino acid in the PSD-MALDI-MS sequence as hydroxyproline at the third position. In conclusion, the existence of des-arg9[hyp3]-bradykinin (arg-pro-hyp-gly-phe-ser-pro-phe) in human plasma is described. Furthermore, the study demonstrates that PSD-MALDI-MS and automated Edman sequence analysis complement each other if single unknown peptides from mixtures are to be sequenced.

Structure-activity studies of B1 receptor-related peptides. Antagonists

We tested several peptides related to des-Arg9-bradykinin as stimulants or inhibitors of B1 (rabbit aorta, human umbilical vein) and B2 (rabbit jugular vein, guinea pig ileum, human umbilical vein) receptors. We also incubated the compounds with purified angiotensin-converting enzyme from rabbit lung to test their resistance to degradation. We evaluated apparent affinities (in terms of the affinity constant pA2) of compounds and their potential residual agonistic activities (alpha E). Bradykinin and des-Arg9-bradykinin were used as agonists for the B2 and B1 receptors, respectively. Degradation of peptides by the angiotensin-converting enzyme was prevented in the presence of a D-residue in position 7 of des-Arg9-bradykinin. Replacement of Pro7 with D-Tic combined with Leu, Ile, Ala, or D-Tic in position 8 led to weak B1 receptor antagonists, some of which had strong residual agonistic activities on the B2 receptor preparations. The use of D-beta Nal in position 7, combined with Ile in position 8 and AcLys at the N-terminal (eg, AcLys[D-beta Nal7, Ile8]des-Arg9-bradykinin) gave the most active B1 receptor antagonist (pA2 of 8.5 on rabbit aorta and human umbilical vein), which is also partially resistant to enzymatic degradation. Extension of the N-terminal end by Sar-Tyr-epsilon Ahx (used for labeling purposes) and even cold-labeling of Tyr with iodine were compatible with high, selective, and specific antagonism of the B1 receptors. We compared some compounds with some already known B1 receptor antagonists to underline the novelty of new peptidic compounds.

Isolation, identification and functional significance of [Hyp2]Met-callatostatin and des Gly-Pro Met-callatostatin, two further post-translational modifications of the blowfly neuropeptide Met-callatostatin

Two post-translationally modified neuropeptides of the Met-callatostatin (Gly-Pro-Pro-Tyr-Asp-Phe-Gly-Met-NH2) family have been identified from head extracts of the blowfly Calliphora vomitoria. They are the octapeptide, [Hyp2]Met-callatostatin, (Gly-Hyp-Pro-Tyr-Asp-Phe-Gly-Met-NH2) and the truncated hexapeptide, des Gly-Pro Met-callatostatin (Pro-Tyr-Asp-Phe-Gly-Met-NH2). The existence of the [Hyp2]Met-callatostatin variant, in addition to the previously identified [Hyp3]Met-callatostatin peptide, suggests that the motif for prolyl hydroxylation in C. vomitoria is more variable than those known from mammalian and other invertebrate studies where, in those regulatory peptides containing a pair of adjacent prolyl residues so far studied, e.g., bradykinin, and the mosquito peptide Aea HP-I, only one of the pair (the second) is known to undergo hydroxylation. The truncated hexapeptide, des Gly-Pro Met-callatostatin could be produced as a result of the action of a dipeptidyl peptidase II type of enzyme which is known from mammalian studies to be unique in its ability to cleave between the two prolyl residues of an Xaa-Pro-Pro- sequence, where Xaa is any unprotected NH2-terminal amino acid. This enzyme is, however, considered unlikely to be able to cleave the Gly-Hyp-Pro-sequence, which would suggest a functional significance for such a post-translational modification. For this reason, it is of interest that [Hyp2]Met-callatostatin (and earlier, [Hyp3]Met-callatostatin) have been shown to be potent inhibitors of the spontaneous contractions of the hindgut of C. vomitoria (biphasic dose-response curve with IC50 values of 10(-14) M and 10(-7) M).(ABSTRACT TRUNCATED AT 250 WORDS)

Hydroxylated kininogens and kinins

Hydroxyprolyl-3-bradykinin was identified in the digest of purified human high molecular weight (H) kininogen with plasma kallikrein. Hydroxyproline was not detected in the heavy and light chains portions of H kininogen, although they include three possible sites for hydroxylation of proline by proline hydroxylase. The content of hydroxyprolyl-3-bradykinin in H kininogen from individual plasmas varied from 14% to 64% of total kinin. The present results and our previous results indicate that only kinin moity in H kininogen from human and monkey plasmas has been partially hydroxylated post-translationally by proline-4-hydroxylase.

Kinetics of bond cleavages at kallidin release by tissue kallikrein: cleavage of two peptide bonds in a single enzyme-substrate complex?

The kinetics of the release of kallidin, L- and KL-chains from bovine L-kininogen by porcine tissue kallikrein were followed and individual kinetic constants for cleavage of the Met-360 and the Arg-370 bond determined. The results suggest that both these bonds in L-kininogen r are hydrolyzed "simultaneously" without appearance of a free singly-nicked intermediate. Kallidin release in the human analogous system is also compatible with such a mechanism.

[Hyp3]-bradykinin and [Hyp3]-Lys-bradykinin interact with B2-bradykinin receptors and stimulate inositol phosphate production in cultured human fibroblasts

The recently isolated, naturally occurring peptide hormones [Hyp3]-bradykinin and [Hyp3]-Lys-bradykinin were investigated for their agonist activity on solubilized binding sites from human fibroblasts. Both ligands competed with [3H]bradykinin binding in a dose-dependent fashion with potencies similar to bradykinin (BK) and Lys-BK. Biological activity was assessed by determination of inositol phosphate accumulation and cyclic 3',5'-adenosine monophosphate synthesis in intact cultured cells. Stimulation by the hydroxylated peptides resulted in a pronounced accumulation of both parameters with similar effectiveness as BK and Lys-BK. These results indicate that [Hyp3]-BK and [Hyp3]-Lys-BK are agonists at the bradykinin receptor system with properties comparable to their non-hydroxylated analogues. This suggests that hydroxylation of kinins does not alter receptor interaction or signal transduction in cultured human fibroblasts.

Degradation pathway of kinins in tumor ascites and inhibition by kininase inhibitors: analysis by HPLC

We have recently found presence of a high concentration of a novel type of kinin, hydroxyprolyl3-bradykinin (Hyp3-BK) in human tumor ascites in addition to conventional bradykinin (BK). Because of their potential physiological activity, it is of interest to know how these bradykinins can be degraded in ascites. Degradation of two synthetic kinins, BK and Hyp3-BK, added to the ascitic fluid from patients with ovarian carcinoma and hepatoma, were analyzed by reversed phase HPLC. Both kinins were degraded into their desArg9-BK or -Hyp3-BK and desPhe8-Arg-9-BK or -Hyp3-BK products following incubation with the ascitic fluid. The rate of the degradation of BK and Hyp3-BK was the same. The formation of desArg9-BK was completely inhibited by kininase I inhibitor, while the formation of desPhe8-Arg9-BK was not completely inhibited by a kininase II inhibitor. The degradation of both kinins was inhibited completely by EDTA. The results indicate the presence of other metalloprotease(s) which cleaves kinins in the ascitic fluid, in addition to kininase I and kininase II. The carboxypeptidase A and carboxypeptidase B inhibitor, benzyl malic acid, failed to block degradation of both kinins. A rapid cleave of Phe-Arg into Phe and Arg was also found in the ascitic fluid. Thus, the major degradation products of kinins in the ascitic fluid were demonstrated to be either desArg9-BK or Hyp3-BK, desPhe8-Arg9-BK or -Hyp3-BK, phenylalanine and arginine. Lysyl-BK and lysylhydroxyprolyl3-BK were rapidly converted into BK and hydroxyprolyl3-BK by the ascitic fluid.

Release of [hydroxyproline3]-kinins by tissue kallikreins of pig, rat and man

To determine the susceptibility of kininogens containing the recently described [Hyp3]-bradykinin moiety to cleavage by tissue kallikreins, we have studied the release of [Hyp3]-kinins from heat inactivated human plasma by purified tissue kallikreins. Kallikreins from man and pig were employed and compared with purified rat urinary kallikrein which is known to have a different cleavage specificity. Kinins released were separated by a modified reversed phase HPLC method and quantitated by bioassay and radioimmunoassay. Human urinary kallikrein and hog tissue kallikreins released 85-90% of the total kinins as Lys-bradykinin and 10-15% as [Hyp3]-Lys-bradykinin. In contrast, rat urinary kallikrein released 77% as bradykinin, 22% as [Hyp3]-bradykinin and negligible amounts of [Hyp3]-Lys-bradykinin from the identical substrate source indicating that rat tissue kallikreins prefer the Lys-Arg-bond within both unhydroxylated and hydroxylated kininogens. Therefore, hydroxylation of human kininogens apparently does not affect their ability to serve as substrates for tissue kallikreins with different cleavage specificities.

Inhibitory effects of kinins on angiotensin I conversion in the local circulation

The inhibition of angiotensin converting enzyme (ACE) by kinins was studied using bradykinin (BK), lysyl-bradykinin (Lys-BK), [Hydroxyproline3]-bradykinin ([Hyp3]-BK) and [Hydroxyproline3]-lysyl-bradykinin ([Hyp3]-Lys-BK). The latter two are novel kinins recently identified in our laboratory. All the four kinins displayed competitive inhibition on the conversion of angiotensin I to angiotensin II by purified canine lung ACE. Inhibition constants (Ki) for the four kinins were estimated from Dixon's plot as follows-BK: 0.27 microM, Lys-BK: 0.57 microM, [Hyp3]-BK: 0.34 microM, and [Hyp3]-Lys-BK: 0.27 microM. In the rat hindlimb perfusion system, the kinins were demonstrated to partially inhibit angiotensin I conversion to angiotensin II by the vascular ACE. Taken together, these results suggest that angiotensin II formation by ACE in the vascular tissue is possibly inhibited by local kinins, especially after ACE inhibitor administration. This indirect action of kinins, coupled with its direct vasodilatory action, might indicate a cooperative participation in vasodilation.

Identification of [hydroxyproline3]-bradykinin released from human plasma and plasma protein Cohn's fraction IV-4 by trypsin

Aside from bradykinin (BK), a novel kinin, [Hydroxyproline3]-bradykinin ( [Hyp3]-BK), was isolated from the reaction mixture of human plasma and plasma protein Cohn's fraction IV-4 with trypsin. The liberated kinins were isolated based on procedures which we previously described for the isolation of [Hyp3]-lysyl-bradykinin ( [Hyp3]-Lys-BK) formed by kallikrein. The ratio of the amounts of two kinins thus formed from human plasma protein Cohn's fraction IV-4 were [Hyp3]-BK 25 +/- 4% and BK 75 +/- 4%, similarly to that of [Hyp3]-Lys-BK and Lys-BK, formed by kallikrein, but it varied by persons. The isolation of [Hyp3]-BK and [Hyp3]-Lys-BK suggests that a novel kininogen containing hydroxyproline in the third position of the bradykinin sequence in human plasma protein, possibly undergone post-translational modifications.

Hydroxyprolyl3-bradykinin in high molecular mass kininogen. Presence in human and monkey kininogens, but not in kininogens from bovine, rat, rabbit, guinea pig and mouse plasmas

The contents of hydroxyprolyl3-bradykinin in high molecular mass (HMM) kininogens from human and animal plasmas were examined by reversed-phase HPLC following their proteolytic scission by bovine plasma kallikrein. The relative contents of hydroxyprolyl3-bradykinin in kinins from HMM kininogens from pooled plasmas of human and monkey origin were 33 and 73%, respectively. On the other hand, hydroxyprolyl3-bradykinin could not be detected in HMM kininogen preparations from bovine, rat, guinea pig, rabbit and mouse plasmas. Hydroxyproline in hydroxyprolyl3-bradykinin was assigned as trans-4-hydroxyproline by comparison of the retention times on reversed-phase HPLC with isomers of hydroxyproline after derivatization with 7-chloro-4-nitrobenzo-2-oxa-1,3-diazole chloride.