Aspects of bradykinin radioimmunoassay

Interactions of angiotensin II non-peptide AT(1) antagonist losartan with phospholipid membranes studied by combined use of differential scanning calorimetry and electron spin resonance spectroscopy

We used differential scanning calorimetry (DSC) and electron spin resonance (ESR) spectroscopy to investigate the interactions of Losartan, a potent, orally active Angiotensin II AT(1) receptor antagonist with phospholipid membranes. DSC results showed that Losartan sensitively affected the chain-melting behavior of dimyristoylphosphatidylcholine (DMPC) and dipalmitoylphosphatidylcholine (DPPC) bilayer membranes. ESR spectroscopy showed that phosphatidylcholines spin-labeled at the 5-position of the sn-2 acyl chain (n-PCSL with n=5), incorporated either in DMPC or DPPC bilayers containing Losartan, were restricted in motion both in the gel and in the liquid-crystalline membrane phases, indicating a location of the antagonist close to the interfacial region of the phosphatidylcholine bilayer. At high drug concentrations (mole fraction >/= x=0.60), the decrease in chain mobility registered by 5-PCSL in fluid-phase membranes is smaller than that found at lower concentrations, whereas that registered by 14-PCSL is further increased. This indicates a different mode of interaction with Losartan at high concentrations, possibly arising from a location deeper within the bilayer. Additionally, Losartan reduced the spin-spin broadening of 12-PCSL spin labels in the gel-phase of DMPC and DPPC bilayers. As a conclusion, our study has shown that Losartan interacts with phospholipid membranes by affecting both their thermotropic behavior and molecular mobility.

Monoclonal ligand binding site related anti-idiotypic antibodies elicited with a polyclonal kinin antibody

Splenocytes from mice immunized with homogenous, polyclonal, rabbit kinin antibody (BK21) were fused using polyethylene glycol with the mouse myeloma cell line SP2/o. Eleven monoclonal antibodies, whose binding to BK21 could be inhibited by bradykinin, were obtained from 3 fusions. All of these anti-idiotypic antibodies were of the IgG1k isotype, except for one, which was an IgG2ak. An IgMk, auto-anti-idiotypic antibody, reactive with BK21 was obtained from a fusion of SP2/o cells and splenocytes from a mouse immunized with bradykinin conjugated with carbodiimide to keyhole limpet hemocyanin. Bradykinin could completely inhibit the binding of all of the anti-idiotypic antibodies to BK21 in an enzyme-linked immunosorbent assay. This result is consistent with the anti-idiotypic antibodies being reactive with the ligand binding sites of BK21. It was possible to separate the anti-idiotypic antibodies into 2 groups. The first group, 10 of the 12 antibodies tested, was more sensitive to inhibition by bradykinin than the second group and was not readily inhibited by des-Arg9-bradykinin. The second group was about 7 times more sensitive to inhibition by des-Arg9-bradykinin than by bradykinin. Further experiments will be needed to determine whether or not these monoclonal anti-idiotypic antibodies are "internal image" antibodies.

Involvement of inflammatory leukocytes in hepatic induction of T-kininogen in rat

Hepatic synthesis as well as plasma levels of T-kininogen, a protein precursor of T-kinin (Ile-Ser-bradykinin), increase in rats following the induction of acute inflammation. Studies have been undertaken to elucidate an involvement of inflammatory leukocytes in the acute-phase response of T-kininogen. Peritoneal exudate cells (PEC) were prepared from rats six days after the intraperitoneal injection of Freund's complete adjuvant. By transfer of these leukocytes into the peritoneal cavity of normal rats, plasma kininogen levels of these recipients increased about threefold after one day. Secretion of kininogen from rat hepatocytes in primary culture was enhanced about twofold by coculturing with PEC. A similar effect was also obtained by adding culture supernatant of these leukocytes into hepatocytes, and the increased levels of kininogen in culture medium of hepatocytes was due to the increased levels of T-kininogen. From these results, it was concluded that leukocytes in the inflammatory site, probably macrophages, release some substance(s) which stimulate(s) the hepatic synthesis of T-kininogen.

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.

Selective 1H-NMR relaxation investigations of membrane-bound drugs in vitro. 2. Angiotensin II

Binding interactions between human angiotensin II and dipalmitoylphosphatidylcholine bilayer vesicles have been detected by measuring the selective proton spin-lattice relaxation rates of aromatic protons within the peptide. Involvement of the imidazole moiety of the His-6 residue has been demonstrated by the pH dependence of the NMR observables. A lower limit of the binding constant has been evaluated at 78.12 mol-1 dm3 for the interaction involving nonionic intermolecular forces between aromatic residues and the lipid matrix.

Isolation and properties of two rat plasma T-kininogens

Two species of T-kininogen which release T-kinin (Ile-Ser-bradykinin) have been purified from plasma of rats treated with Freund's complete adjuvant. The molecular weight was estimated to be 69,000 for either T-kininogen I and II by SDS-polyacrylamide gel electrophoresis. Trypsin released one mole of T-kinin from one mole of either T-kininogen, but glandular kallikrein, including rat urinary and rat submandibular gland kallikreins and human urinary kallikrein, did not release any kinin from T-kininogens. Cathepsin D, which was purified from rat liver, released T-kinin from T-kininogens at pH 4.0. These results indicate that rat plasma contains two types of T-kininogen which differ from high molecular weight and low molecular weight kininogens.

Release of T-kinin and bradykinin in carrageenin induced inflammation in the rat

Plasma and inflammatory fluid kininogen levels, and blood and inflammatory fluid free kinin levels were determined in rats 24 h after the injection of carrageenin into an air pouch. Plasma T-kininogen levels increased 7-fold. In the inflammatory fluid levels reached 8 micrograms/ml. Blood levels of free kinin showed a 5-fold increase. The kinins were identified on HPLC as T-kinin (Ile-Ser-bradykinin) and bradykinin, 63 and 37%, respectively. These results indicate for the first time that free T-kinin as well as bradykinin is released during an inflammatory response in rat and confirms our previous finding that T-kininogen may be a major acute-phase protein in inflammation.

Monoclonal antibodies to bradykinin inhibit smooth muscle contractile action of bradykinin

Four hybridoma cell lines have been established that secrete monoclonal antibodies to nonapeptide bradykinin. Bradykinin coupled to ovalbumin, using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide as coupling agent, was used to immunize BALB/c mice. Spleen cells from the immunized animals were fused to P3-X63-AG8-653 mouse myeloma cells. The resultant hybrid cells were screened by enzyme-linked immunoassay for production of antibodies to bradykinin. Hybrids from four positive wells were subcloned by limiting dilution and expanded as ascites tumor into pristane-primed mice. All the four hybrids secreted monoclonal antibodies of IgG1 (k) isotype. Unlabeled peptides bradykinin, lysyl-bradykinin (kallidin) and methionyl-lysyl-bradykinin competed with the radiolabeled [Tyr1]kallidin for monoclonal antibody binding sites. These antibodies recognized preferentially either NH2- or COOH-terminals of the nonapeptide bradykinin and can distinguish between des-Arg1-bradykinin and des-Arg9-bradykinin. Bradykinin fragments smaller than eight residues were not recognized by these antibodies. Monoclonal antibodies BK-D6A5, BK-B6C9 and BK-A3D9 neutralized the smooth muscle contractile activity of bradykinin. An enzyme-linked immunoassay developed using these monoclonal antibodies showed the effective range of bradykinin determination between 5 and 150 ng.

B2 bradykinin receptor-like binding in rat renomedullary interstitial cells

A particulate fraction from cultured rat renomedullary interstitial cells (RRIC) was prepared for bradykinin (BK) binding studies. Incubation of three radiolabeled BK analogs, [125I-Tyr1]kallidin, [125I-Tyr5]-BK, and [125I-Tyr8]-BK, with the particulate fraction resulted in degradation of these peptides. Assay conditions which prevented hydrolysis of these radiolabeled kinins were determined. Under these conditions, direct binding studies were performed with [125I-Tyr1]kallidin (TlK) as the radioligand. BK binding affinity, apparent Kassoc. = 1.3 X 10(9) M-1, and specificity, determined with 51 BK analogs, were consistent with those expected of a B2 BK receptor.

T-kininogen--the major plasma kininogen in rat adjuvant arthritis

Total kininogen in plasma of Freund's adjuvant treated rats increased 20-fold 7 days following the injection. Analysis of the kininogens demonstrated that increases in T-kininogen was the major reason for the rise in kininogen. High molecular weight and low molecular weight kininogens showed little or no change. The increase in T-kininogen paralleled the inflammatory condition. Anti-inflammatory agents which reduced paw swelling also reduced plasma T-kininogen levels. Unidentified peaks on HPLC of kinin following plasma treatment by trypsin were shown to be oligopeptides containing T-kinin (Ile-serbradykinin). The relationship of T-kininogen to the inflammatory response is discussed.

Further studies of myometrial bradykinin receptor-like binding

[125I-Tyr1]Kallidin (T1K), a bradykinin (BK) analog with biological potency comparable to BK, was used as a probe for BK receptor-like binding from bovine uterine myometrium. BK binding exhibited a high affinity, Kdissoc = 1.65 X 10(-10) M. The specificity of T1K binding was examined with forty-four BK analogs. Comparison of the binding inhibitory potencies with the relative biological potencies of these analogs on isolated rat uterus resulted in a good correlation, r = 0.87. BK binding activity was solubilized with CHAPS, 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonate, a zwitterionic detergent. The solubilized binding activity exhibited a BK binding affinity, Kdissoc = 2.25 X 10(-10) M, and a specificity for three 125I-labeled kinins similar to those of the particulate BK receptor-like binding activity.

Iodination of [Tyr8]-bradykinin-comparison of chloramine-T and lactoperoxidase techniques

Antigen-antibody kinetics were studied using a hapten which was iodinated by two unique procedures. Using bradykinin, a vasopressor hormone as a model peptide, radioactive iodination (125I) of its 8-tyrosyl analogue was carried out both enzymatically and chemically using modified procedures. Two distinct chemical species were obtained which were characterized on a chromatographic, chemical as well as charge basis as a mono-iodinated form of [Tyr8]-bradykinin using the lactoperoxidase procedure and a di-iodinated entity using chloramine-T technique. The addition of a second iodine atom to the antigen lowers its immunoreactivity for its antibody and thus alters the kinetics of this reaction. Further experiments on the stability (temperature, time of storage, and chemical environment) of these iodinated peptides are described.

Megascoliakinin, a bradykinin-like compound in the venom of Megascolia flavifrons Fab. (Hymenoptera: Scoliidae)

The pharmacological and immunological properties of the venom of Megascolia flavifrons are compared with those of bradykinin and a number of bradykinin analogues. It is postulated that this venom contains a peptide, megascoliakinin, with a bradykinin-like sequence of amino acids, elongated at the C-terminal end with an unknown structure.

Interactions of kinins with angiotensin I converting enzyme (kininase II)

Angiotensin I converting enzyme (ACE) was purified to homogeneity from porcine kidney in order to determine whether iodobradykinins bind to the enzyme and, if so, whether pGlu-Trp-Pro-Arg-Pro-Gin-Ile-Pro-Pro, SQ20881, a competitive ACE inhibitor, changes the conformation of the enzyme in such a way that it binds kinins with an affinity and specificity expected of a bradykinin (BK) receptor, i.e. where the BK potentiating action of SQ20881 involves an increase in the number of BK receptors due to a conformational change in ACE. 125I-Labeled derivatives of [Tyr1]-kallidin and [Tyr-8]-bradykinin bound to the EDTA-inhibited enzyme, and binding was inhibited by nonradioactive BK. [125I-Tyr5]-BK was not bound by the enzyme. Specificity of [125I-Tyr5]-kallidin (T1K) binding was tested with forty-eight BK analogs, and the concentrations of analogs that inhibited 50% of T1K binding were determined. BK at 1.6 +/- 0.3 X 10(-8) M inhibited 505 of T1K binding. In addition, the concentrations of analogs that decreased by 50% the rate of [3H]-Hip-Gly-Gly ([3H]-HGG) hydrolysis by ACE were assessed. BK at 1.2 +/- 0.2 X 10(-6) M decreased the rate of [3H]-HGG hydrolysis by 50%. A comparison between these concentrations of analogs for inhibition of T1K binding and [3H]-HGG hydrolysis yielded a high correlation coefficient (r = 0.85). The specificity of ACE binding was clearly different from that expected of a BK receptor. Compounds structurally unrelated to BK, such as 5Q20881, pGlu-Lys-Trp-Ala-Pro-OH (BPP5a) and angiotensin I, inhibited T1K binding and [3H]-HGG hydrolysis by ACE.

Development of a radioimmunoassay for [DES-ARG9]-bradykinin

Antisera to [des-Arg9]-bradykinin were elicited in rabbits immunized with the peptide conjugated to thyroglobulin and/or ovalbumin. Sera were screened for the presence of antibody with three radioactive antigens, mono-125I-labeled derivatives of [Tyr1, des-Arg]-kallidin, [Tyr, des-Arg]-bradykinin, and [Tyr, des-Arg]-bradykinin that were prepared by treating mono-125I-labeled [Tyr]-kallidin, [Tyr]-bradykinin, and [Tyr]-bradykinin with carboxypeptidase B. Of the six animals immunized, five produced antibodies to [des-Arg]-bradykinin as evidenced by the ability of their sera to bind at least 33% of the added radioactivity at a final dilution of 1:500. Sensitivity and specificity studies were performed with each labeled antigen and a dilution of antiserum that bound 30-50% of the radioactivity. The best labeled antigen-antibody combination, with respect to titer, sensitivity, and specificity was obtained with [mono-125I-Tyr, des Arg]-bradykinin and serum from a rabbit immunized with [des-Arg]-bradykinin conjugated to ovalbumin with toluene diisocyanate. The lowest concentration of [des-Arg]-bradykinin inhibiting 50% of this radioactive antigen binding was 0.23 ng/ml and the lowest concentration which could be distinguished from no [des-Arg]-bradykinin added was 67 pg/ml. This antiserum cross-reacts with bradykinin and lysyl-bradykinin about 9% but not with methionyl-lysyl-bradykinin.

Double-antibody solid-phase radioimmunoassay for blood bradykinin

A solid phase radioimmunoassay for the determination of blood bradykinin has been developed. Highly specific antibodies against bradykinin were raised in rabbits after coupling the peptide to thyroglobulin. Iodination of [Tyr8]-bradykinin was carried out with a chloramine-T procedure resulting in a tracer with high specific activity. Bradykinin was isolated in the following way: blood was sampled directly into acetone, and lipids were removed by extraction with petroleum either (40-60 degrees C). The final purification was made on QAE-Sephadex A-25 at pH 7.4. The mean recovery of added [125I-Tyr8]-bradykinin was 28% with a sample volume of 6 ml whole blood. The sensitivity of the radioimmunoassay was 1.25 pg/tube or 3 pg/ml blood. The reproducibility of the method is satisfactory with a between-assay coefficient of variation below 16%. Levels found in venous blood were below 3 pg bradykinin/ml in normal persons.

Bradykinin, plasma protein fraction, and hypotension

A directive from the Food and Drug Administration indicates that the use of plasma protein fraction (PPF) is contraindicated during cardiopulmonary bypass because of possible hypotension. Bradykinin has been implicated as the cause of this hypotension. Bradykinin levels were measured by radioimmunoassay in PPF and in 5% albumin and were found to be consistently elevated in the former and occasionally in the latter. The addition of PPF to pump primes resulted in significantly elevated levels of bradykinin, which rapidly cleared, indicating that extrapulmonary sites of bradykinin inactivation were efficient. The potential hypotensive effect of PPF was observed by determining the change in mean perfusion pressure in two groups of patients: one group with a 3,000 ml crystalloid prime and the other with a prime of 2,000 ml of crystalloid and 1,000 ml of PPF. There was no significant difference in the perfusion pressure between the two groups at any point, and the hypotensive effects seen in both groups were readily treated, suggesting that the directive against the use of PPF during cardiopulmonary bypass may be unnecessarily restrictive.

Angiotensin and bradykinin interactions with phospholipids

Reversible interactions were demonstrated between some phospholipids and some polypeptides related to angiotensin and bradykinin. The extent of the interaction was dependent on the structures of the lipid and peptide. The naturally occurring compounds that interacted most avidly were cardiolipin and (des-Asp1)-angiotensins. The apparent dissociation constant of this complex in chloroform was 10(-5) M. The complex contained more than one cardiolipin molecule/molecule of peptide. Kinins interacted most strongly with lecithin. The phospholipids altered the chromatographic behavior of radioiodinated derivatives of the polypeptides, and solubilized radioactive and unlabeled polypeptides in chloroform. In aqueous media, cardiolipin suspensions preferentially bound (des-Asp1)-angiotensin II, and inhibited its binding by antibody. The interactions were sensitive to pH and cations in the aqueous phase, and were reversed by some reagents added to the organic phase. These interactions have direct implications for binding reactions of peptides in vitro, and may bear upon the actions of the hormones in vivo.