Inhibition of angiotensin converting enzyme and potentiation of bradykinin by retro-inverso analogues of short peptides and sequences related to angiotensin I and bradykinin

Smart biomaterials: Surfaces functionalized with proteolytically stable osteoblast-adhesive peptides

Engineered scaffolds for bone tissue regeneration are designed to promote cell adhesion, growth, proliferation and differentiation. Recently, covalent and selective functionalization of glass and titanium surfaces with an adhesive peptide (HVP) mapped on [351-359] sequence of human Vitronectin allowed to selectively increase osteoblast attachment and adhesion strength in in vitro assays, and to promote osseointegration in in vivo studies. For the first time to our knowledge, in this study we investigated the resistance of adhesion sequences to proteolytic digestion: HVP was completely cleaved after 5 h. In order to overcome the enzymatic degradation of the native peptide under physiological conditions we synthetized three analogues of HVP sequence. A retro-inverted peptide D-2HVP, composed of D amino acids, was completely stable in serum-containing medium. In addition, glass surfaces functionalized with D-2HVP increased human osteoblast adhesion as compared to the native peptide and maintained deposition of calcium. Interestingly, D-2HVP increased expression of IBSP, VTN and SPP1 genes as compared to HVP functionalized surfaces. Total internal reflection fluorescence microscope analysis showed cells with numerous filopodia spread on D-2HVP-functionalized surfaces. Therefore, the D-2HVP sequence is proposed as new osteoblast adhesive peptide with increased bioactivity and high proteolytic resistance.

Insights into cardiovascular effects of proline-rich oligopeptide (Bj-PRO-10c) revealed by structure-activity analyses: dissociation of antihypertensive and bradycardic effects

We have previously reported that the proline-rich decapeptide from Bothrops jararaca (Bj-PRO-10c) causes potent and sustained antihypertensive and bradycardic effects in SHR. These activities are independent of ACE inhibition. In the present study, we used the Ala-scan approach to evaluate the importance of each amino acid within the sequence of Bj-PRO-10c (Pyr(1)-Asn(2)-Trp(3)-Pro(4)-His(5)-Pro(6)-Gln(7)-Ile(8)-Pro(9)-Pro(10)). The antihypertensive and bradycardic effects of the analogues Bj-PRO-10c Ala(3), Bj-PRO-10c Ala(7), Bj-PRO-10c Ala(8) were similar to those of Bj-PRO-10c, whereas the analogues Bj-PRO-10c Ala(2), Bj-PRO-10c Ala(4), Bj-PRO-10c Ala(5), Bj-PRO-10c Ala(9), and Bj-PRO-10c Ala(10) kept the antihypertensive activity and lost bradycardic activity considerably. In contrast, Bj-PRO-10c Ala(1) and Bj-PRO-10c Ala(6) were unable to provoke any cardiovascular activity. In summary, we demonstrated that (1) the Pyr(1) and Pro(6) residues are essential for both, the antihypertensive and bradycardic effects of Bj-PRO-10c; (2) Ala-scan approach allowed dissociating blood pressure reduction and bradycardic effects. Conformational properties of the peptides were examined by means of circular dichroism (CD) spectroscopy. The different Ala-scan analogues caused either an increase or decrease in the type II polyproline helix content compared to Bj-PRO-10c. The complete loss of activity of the Pro(6) → Ala(6) mutant is probably due to the fact that in the parent peptide the His(5)-Pro(6) bond can exist in the cis configuration, which could correspond to the conformation of this bond in the bound state. Current data support the Bj-PRO-10c as a promising leader prototype to develop new agents to treat cardiovascular diseases and its co-morbidities.

The C-type natriuretic peptide precursor of snake brain contains highly specific inhibitors of the angiotensin-converting enzyme

The bradykinin-potentiating peptides from Bothrops jararaca venom are the most potent natural inhibitors of the angiotensin-converting enzyme. The biochemical and biological features of these peptides were crucial to demonstrate the pivotal role of the angiotensin-converting enzyme in blood pressure regulation. In the present study, seven bradykinin-potentiating peptides were identified within the C-type natriuretic peptide precursor cloned from snake brain. The bradykinin-potentiating peptides deduced from the B. jararaca brain precursor are strong in vitro inhibitors of the angiotensin-converting enzyme (nanomolar range), and also potentiate the bradykinin effects in ex vivo and in vivo experiments. Two of these peptides are novel bradykinin-potentiating peptides, one of which displays high specificity toward the N-domain active site of the somatic angiotensin-converting enzyme. In situ hybridization studies revealed the presence of the bradykinin-potentiating peptides precursor mRNAs in distinct regions of the B. jararaca brain, such as the ventromedial hypothalamus, the paraventricular nuclei, the paraventricular organ, and the subcommissural organ. The biochemical and pharmacological properties of the brain bradykinin-potentiating peptides, their presence within the neuroendocrine regulator C-type natriuretic peptide precursor, and their expression in regions of the snake brain correlated to neuroendocrine functions, strongly suggest that these peptides belong to a novel class of endogenous vasoactive peptides.

Structure-function analysis of the 7B2 CT peptide

Prohormone convertases play important roles in the proteolytic conversion of many protein precursors. The neuroendocrine protein 7B2 and its 31-residue carboxyl-terminal (CT) peptide potently and specifically inhibit prohormone convertase 2 (PC2). We have analyzed the residues contributing to inhibition using N-terminal truncation and alanine scanning. Removal of more than 3 residues from the amino-terminal end of CT1-18 resulted in a more than 190-fold drop in inhibitory activity, showing that most of the residues between 3 and 18 are required for inhibition. In agreement, an Ala scan indicated that only 4 residues could be replaced with Ala without losing mid-nanomolar inhibitory potency; in particular, Gln7, Gln9, and Asp12 could be Ala-substituted to yield peptides with a similar inhibitory potency to the starting peptide. The all-d-retro-inverso, all-l-inverso, and all-d analogues of CT peptide were completely inactive, indicating that amino acid side chains and the CT peptide main chain interact with PC2. CT peptide inhibition could not be competitively blocked by preincubation with truncated CT peptide forms, supporting an absolute requirement for the Lys-Lys pair in initial binding of the CT peptide to the active site.

Internally quenched fluorogenic substrates for angiotensin I-converting enzyme

OBJECTIVE

Development of internally quenched fluorogenic substrates for sensitive and continuous assays of angiotensin I-converting enzyme (ACE).

DESIGN

We synthesized internally quenched fluorogenic bradykinin-related peptides introducing Abz (ortho-aminobenzoic acid) and EDDnp (N-[2,4-dinitrophenyl]-ethylenediamine) at their N- and C-terminal groups, respectively, and these were assayed as ACE substrates. We examined two series of peptides, Abz-GFSPFRX-EDDnp and Abz-GFSPFXQ-EDDnp (X, various amino acids).

METHODS

Hydrolysis of the fluorogenic substrates by ACE was followed by continuous recording of the rising fluorescence (lambda(em) = 420 nm and lambda(ex) = 320 nm). The peptides were obtained by solid-phase synthesis or by classical solution methods.

RESULTS

Despite of the blocked C-terminal sequences, the internally quenched bradykinin-related peptides were hydrolysed by ACE. The best substrates for plasma guinea pig ACE were Abz-GFSPFRA-EDDnp and Abz-GFSPFFQ-EDDnp, in which the fluorescence appeared after the first cleavage that occurred at R-A and F-Q bond, respectively. This ACE activity was sensitive to NaCl concentration and the optimum pH is greater than 8.0. Measurements of ACE activity with Hip-His-Leu and Abz-GFSPFFQ-EDDnp in the serum of 20 healthy patients correlated closely (r = 0.959). Complete inhibition of the hydrolysis of Abz-GFSPFFQ-EDDnp by human serum was observed with captopril and lisinopril.

CONCLUSIONS

We describe internally quenched fluorogenic substrates for ACE devoid of free C-terminal carboxyl group. They are convenient tools for ACE studies as they permit continuous fluorimetric measurements of the enzymatic activity, even in human serum.

All four homochiral enantiomers of a nuclear localization sequence derived from c-Myc serve as functional import signals

The information that targets a protein to the nucleus often consists of a short cluster of basic amino acids called a nuclear localization sequence (NLS). Since a wide range of sequences rich in basic amino acid residues function as NLSs, we postulated that an NLS-like sequence composed exclusively of D-amino acids might have biological activity. We synthesized peptides corresponding to the c-Myc NLS composed of either all L or D-amino acids, both in the forward and reverse order. We tested these peptides for nuclear import activity in a digitonin-permeabilized cell assay. All four peptide-bovine serum albumin conjugates localized to the nucleus with similar efficiency, and each conjugate competed for import with an SV40 large T antigen-derived NLS conjugate. Cross-linking experiments with free NLS peptides in HeLa cytosol indicated that each peptide bound to a protein that migrated at the molecular weight of importin alpha. Recombinant importin alpha, importin beta, Ran, and NTF2 alone were sufficient to support the import of both L-form and D-form conjugates in permeabilized cells. This indicates that both D- and L-form NLS peptides use the same import machinery. Although the free D-forms of the NLS were proteolytically resistant in cytosol, the L-forms were rapidly degraded. To our knowledge, this is the first example of an intracellular pathway in which the receptor is insensitive to the chirality of the ligand.

ACE inhibitor potentiation of bradykinin-induced venoconstriction

1. Angiotensin-converting enzyme (ACE) inhibitors exert their cardiovascular effects not only by preventing the formation of angiotensin II (AII), but also by promoting the accumulation of bradykinin in or at the vessel wall. In addition, certain ACE inhibitors have been shown to augment the vasodilator response to bradykinin, presumably by an interaction at the level of the B2 receptor. We have investigated whether this is a specific effect of the ACE inhibitor class of compounds in isolated endothelium-denuded segments of the rabbit jugular vein where bradykinin elicits a constrictor response which is exclusively mediated by activation of the B2 receptor. 2. Moexiprilat and ramiprilat (< or = 3 nM) enhanced the constrictor response to bradykinin three to four fold. Captopril and enalaprilat were less active by approximately one and quinaprilat by two orders of magnitude. Moexiprilat and ramiprilat, on the other hand, had no effect on the constrictor response to AII or the dilator response to acetylcholine. 3. The bradykinin-potentiating effect of the ACE inhibitors was not mimicked by inhibitors of amino-, carboxy-, metallo- or serine peptidases or the synthetic ACE substrate, hippuryl-L-histidyl-L-leucine, at a concentration which almost abolished the residual ACE activity in the vessel wall. In contrast, angiotensin-(1-7) (10 microM), an angiotensin I metabolite, significantly enhanced the constrictor response to bradykinin. 4. Ramiprilat did not alter the binding of [3H]-bradykinin to a membrane fraction prepared from endothelium-denuded rabbit jugular veins or to cultured fibroblasts, and there was no ACE inhibitor-sensitive, bradykinin-induced cleavage of the B2 receptor in cultured endothelial cells. 5. These findings demonstrate that ACE inhibitors selectively potentiate the B2 receptor-mediated vascular effects of bradykinin. Their relative efficacy appears to be independent of their ACE-inhibiting properties and might be related to differences in molecule structure. Moreover, the potentiation of the biological activity of bradykinin by this class of compounds does not seem to be mediated by a shift in affinity of the B2 receptor or a prevention of its desensitization, but may involve an increase in the intrinsic activity of unoccupied B2 receptor molecules.