Efficacy, pharmacokinetics, and safety of icatibant for the treatment of Japanese patients with an acute attack of hereditary angioedema: A phase 3 open-label study

BACKGROUND

Hereditary angioedema (HAE) is a genetic disease characterized by recurrent swelling episodes affecting the skin, gastrointestinal mucosa, and upper respiratory tract.

METHODS

A phase 3, single-arm, open-label study was performed to evaluate a selective bradykinin B₂ receptor antagonist, icatibant, for the treatment of acute attacks in Japanese patients with HAE Type I or II. After the onset of an acute attack, icatibant 30 mg was administered by the patient or a healthcare professional via subcutaneous injection in the abdomen.

RESULTS

Eight patients who had an attack affecting the skin (n = 4), abdomen (n = 3), or larynx (n = 1) were treated with icatibant (3 of the injections were self-administered). The median time to onset of symptom relief was 1.75 h (95% confidence interval, 1.00-2.50), and all patients had symptom relief within 5 h after administration. The time to maximum plasma concentration of icatibant was 1.79 h, and the maximum plasma concentration was 405 ng/ml. Seven patients experienced an injection site reaction, and 3 patients had adverse events (2 patients had a worsening or repeat HAE attack 29.0 and 18.3 h after icatibant administration, respectively, and 1 had headache).

CONCLUSIONS

Although the number of patients is small, the efficacy and tolerability of icatibant for acute attacks were demonstrated in Japanese patients with HAE, regardless of self-administration or administration by healthcare professional.

[EFFICACY, PHARMACOKINETICS, AND SAFETY OF ICATIBANT FOR THE TREATMENT OF JAPANESE PATIENTS WITH AN ACUTE ATTACK OF HEREDITARY ANGIOEDEMA: A PHASE 3 OPEN-LABEL STUDY]

BACKGROUND

Hereditary angioedema (HAE) is characterized by paroxysmal edema of the skin, gastrointestinal mucosa, and upper respiratory tract.

PURPOSE

This study investigated icatibant, a selective bradykinin B2 receptor antagonist, as treatment for Japanese patients with an acute HAE attack.

METHODS

This was an open-label, single-arm, Phase 3 study of Japanese adults with HAE type I or II. Icatibant (30 mg) was administered (by a healthcare professional [HCP] or self-administered) as a subcutaneous injection in the abdomen.

RESULTS

Eight patients (4 cutaneous, 3 abdominal, 1 laryngeal) were treated with icatibant (all single injection; 3 self-administered, 5 HCP-administered). The median time to onset of symptom relief was 1.75 hours (95% confidence interval, 1.00 to 2.50); all patients had onset of relief within 5 hours. The estimated time to maximum icatibant concentration in the circulation was 1.79 hours and the maximum concentration was 405 ng/mL. There were 3 patients who experienced 3 adverse events (2 HAE attacks and 1 headache); 7 patients experienced an injection site reaction.

CONCLUSION

Although our study was limited by the small number of patients, we found that icatibant was an effective and well-tolerated treatment for Japanese patients with acute HAE attacks, regardless of whether it was administered by a HCP or self-administered.

Neuroprotection against apoptosis of SK-N-MC cells using RMP-7- and lactoferrin-grafted liposomes carrying quercetin

A drug delivery system of quercetin (QU)-encapsulated liposomes (LS) grafted with RMP-7, a bradykinin analog, and lactoferrin (Lf) was developed to permeate the blood-brain barrier (BBB) and rescue degenerated neurons, acting as an Alzheimer's disease (AD) pharmacotherapy. This colloidal formulation of QU-encapsulated LS grafted with RMP-7 and Lf (RMP-7-Lf-QU-LS) was used to traverse human brain microvascular endothelial cells (HBMECs) regulated by human astrocytes (HAs) and to treat SK-N-MC cells after an insult with cytotoxic β-amyloid (Aβ) fibrils. We found that surface RMP-7 and Lf enhanced the ability of QU to cross the BBB without inducing strong toxicity and damaging the tight junction. In addition, RMP-7-Lf-QU-LS significantly reduced Aβ-induced neurotoxicity and improved the viability of SK-N-MC cells. Compared with free QU, RMP-7-Lf-QU-LS could also significantly inhibit the expression of phosphorylated c-Jun N terminal kinase, phosphorylated p38, and phosphorylated tau protein at serine 202 by SK-N-MC cells, indicating an important role of RMP-7, Lf, and LS in protecting neurons against apoptosis. RMP-7-Lf-QU-LS is a promising carrier targeting the BBB to prevent Aβ-insulted neurodegeneration and may have potential in managing AD in future clinical applications.

Involvement of bradykinin B2 and muscarinic receptors in the prolonged diuretic and antihypertensive properties of Echinodorus grandiflorus (Cham. & Schltdl.) Micheli

BACKGROUND

Although Echinodorus grandiflorus (Cham. & Schltr.) Michel are used in Brazilian folk medicine as a diuretic drug, to date, no study has evaluated the mechanisms involved in this activity after prolonged administration in rats.

AIM OF THE STUDY

Evaluate the possible mechanisms involved in the prolonged diuretic activity of ethanol soluble fraction obtained from Echinodorus grandiflorus (ES-EG) and to assess its relationship with hypotensive and antihypertensive activity using normotensive rats and those with renovascular hypertension (2K1C).

METHODS

The diuretic effects of ES-EG (30-300 mg/kg; p.o.) were compared with hydrochlorothiazide in a repeated-dose treatment for 7 days. The urinary volume and sodium, potassium, chloride, bicarbonate contents, conductivity, pH and density were estimated in sample collected in 24 h for 7 days. Plasma sodium, potassium, total protein, urea, creatinine, aldosterone, vasopressin, nitrite, acetylcholinesterase concentration and angiotensin converting enzyme (ACE) activity were measured in samples collected at the end of the experimental period (seventh day). Using pharmacological antagonists or inhibitors, the involvement of bradykinin, prostaglandin, acetylcholine and nitric oxide (NO) in ES-EG-induced diuresis was determined. In addition, activities of erythrocytary carbonic anhydrase and renal Na+/K+/ATPase were evaluated in vitro.

RESULTS

ES-EG increased diuresis similarly to hydrochlorothiazide and also presented HCO3-sparing effects and increased serum nitrite levels. Moreover, the intraduodenal administration of ES-EG induces significant hypotensive and antihypertensive effects in 2K1C rats. Previous treatment with HOE-140, indometacin and atropine fully avoided the diuretic effect of ES-EG, and including L-NAME pre-administration, it prevented the hypotensive and hypertensive activity induced by ES-EG. In addition, the association between HOE-140 and atropine or indometacin and L-NAME fully inhibited the hypotensive and antihypertensive effects of ES-EG. The 7-day treatment with ES-EG resulted in increased plasma nitrite levels. All other parameters were not affected by treatment with ES-EG.

CONCLUSIONS

Our results suggest that the mechanisms through which Echinodorus grandiflorus extracts induce prolonged diuresis and reduce blood pressure in normotensive and 2K1C rats are mainly related to activation of muscarinic and bradykinin receptors with direct effects on prostaglandins and nitric oxide pathways.

Preclinical pharmacology, metabolic stability, pharmacokinetics and toxicology of the peptidic kinin B1 receptor antagonist R-954

We previously showed that R-954 (AcOrn[Oic(2),(αMe)Phe(5),dβNal(7),Ile(8)]desArg(9)-bradykinin) is a potent, selective and stable peptide antagonist of the inducible GPCR kinin B1 receptor. This compound shows potential applications for the treatment of several diseases, including cancer and neurological disturbances of diabetes. To enable clinical translation, more information regarding its pharmacological, pharmacokinetics (PK) and toxicological properties at preclinical stage is warranted. This was the principal objective of the present study. Herein, specificity of R-954 was characterized in binding studies on 133 human molecular targets to reveal minor cross-reactivities against the angiotensin AT2 and the bombesin receptors (110- and 330-fold lower affinity than for B1R, respectively). The pharmacokinetic of R-954 was studied in both normal and streptozotocin-diabetic anaesthetized rats providing half-lives of 1.9-2.7h. R-954 does not appear to be metabolized in the rat circulation and in several rat tissue homogenates, as the kidney, lung and liver. It appears to be excreted as parent drug in the bile (21%) and in urine. A preliminary toxicological profile of R-954 was obtained in rats under various administration routes. R-954 appears to be well tolerated. Overall, these results indicate that R-954 exhibits favorable preclinical pharmacological/PK characteristics and encouraging safety profiles, suitable for early studies in humans.

Angiotensin-converting enzyme inhibition increases basal vascular tissue plasminogen activator release in women but not in men

OBJECTIVE

Angiotensin-converting enzyme inhibition (ACEI) increases vascular tissue plasminogen activator (t-PA) release through endogenous bradykinin (BK). We tested the hypothesis that gender influences the effect of ACEI on t-PA release.

METHODS AND RESULTS

We measured the effect of intra-arterial enalaprilat (0.33 microg/min per 100 mL forearm volume) on forearm blood flow (FBF) and net t-PA release before and during BK (25 to 400 ng/min) and methacholine (3.2 to 12.8 microg/min) in premenopausal women, postmenopausal women not using hormone replacement, young men, and older men. Baseline net t-PA release was similar among groups. Enalaprilat increased basal t-PA release in premenopausal (from 0.9+/-1.0 to 5.1+/-1.7 ng/min per 100 mL, P=0.023) and postmenopausal women (from -3.9+/-2.2 to 3.9+/-1.1 ng/min per 100 mL, P=0.010) but not in young or older men (P=0.028 men versus women). Enalaprilat potentiated the effect of exogenous BK on FBF similarly in all groups. However, during enalaprilat, BK-stimulated t-PA release was greatest in premenopausal women (339.9+/-86.4 ng/min per 100 mL at the 100 ng/min dose, P<0.05 versus any other group), intermediate in postmenopausal women (243.8+/-51.1 ng/min per 100 mL, P<0.05 versus either male group), and least in young (111.9+/-19.2 ng/min/100 mL) and older men (103.4+/-27.6 ng/min/100 mL).

CONCLUSIONS

ACEI enhances basal t-PA release in women, independent of menopausal status, but not in men. During ACEI, both gender and menopausal status affect BK stimulated t-PA release.

Inhibition of Type 1 Diabetic Hyperalgesia in Streptozotocin-Induced Wistar versus Spontaneous Gene-Prone BB/Worchester Rats: Efficacy of a Selective Bradykinin B1Receptor Antagonist

Insulin-dependent type 1 diabetes (T1D) is linked to a series of complications, including painful diabetic neuropathy (PDN). Several neurovascular systems are activated in T1D, including the inducible bradykinin (BK) B1 receptor (BKB1-R) subtype. We assessed and compared the efficacy profile of a selective BKB1-R antagonist on hyperalgesia in 2 models of T1D: streptozotocin (STZ) chemically induced diabetic Wistar rats and spontaneous BioBreeding/Worchester diabetic-prone (BB/Wor-DP) rats. Nociception was measured using the hot plate test to determine thermal hyperalgesia. STZ diabetic rats developed maximal hyperalgesia (35% decrease in their hot plate reaction time) within a week and remained in such condition and degree for up to 4 weeks postinjection. BB/Wor-DP rats also developed hyperalgesia over time that preceded hyperglycemia, starting at the age of 6 weeks (9% decrease in the hot plate reaction time) and stabilizing over the age of 16 to 24 weeks to a maximum (60% decrease in the hot plate reaction time). Single, acute subcutaneous administration of the selective BKB1-R antagonist induced significant time- and dose-dependent attenuation of hyperalgesia in both STZ diabetic and BB/Wor-DP rats. Thus, selective antagonism of the inducible BKB1-R subtype may constitute a novel and potential therapeutic approach for the treatment of PDN.

The relationship between flow-mediated brachial artery vasodilation and coronary vasomotor responses to bradykinin: comparison with those to acetylcholine

Flow-mediated dilation (FMD) of brachial artery provides a noninvasive assessment of coronary endothelial dysfunction. Acetylcholine (ACh) has been used as an agent for estimating coronary endothelial function. In contrast to ACh, there is no evidence for a relationship between FMD and coronary vasodilation to bradykinin (BK). The aim of this study was to compare the flow-mediated vasodilation of brachial artery with coronary vasomotor responses to intracoronary ACh or BK in patients with an angiographically normal left anterior descending coronary artery. Ninety-one patients underwent the cardiac catheterization examination with coronary endothelial function testing and the brachial ultrasound study. BK (0.2, 0.6, 2.0 microg/min) and ACh (3, 10, 30 microg/min) were administered into the left coronary artery in a stepwise manner. Coronary blood flow was evaluated by the Doppler flow velocity measurement. Coronary diameters were measured by the quantitative coronary angiography. The assessment of endothelial function in the brachial artery was made in response to reactive hyperemia with high-resolution ultrasound. Bradykinin induced dose-dependent increases in epicardial coronary diameter and blood flow. There was a significant positive correlation between FMD- and BK-induced vasodilations of epicardial coronary arteries (0.2 microg/min: r = 0.30; 0.6 microg/min: r = 0.42; 2.0 microg/min: r = 0.44, P < 0.01, respectively) and resistance coronary arteries (0.2 microg/min: r = 0.40; 0.6 microg/min: r = 0.56; 2.0 microg/min: r = 0.59, P < 0.0001, respectively). FMD correlated with ACh-induced vasomotions of resistance but not epicardial coronary arteries. No correlation was seen between nitroglycerin-induced brachial artery vasodilation and BK-induced coronary vasodilation. The endothelial dysfunction of peripheral arteries correlated well with that of the coronary arteries especially vasomotor responses to BK.

Expression of kinin B1 receptors in the spinal cord of streptozotocin-diabetic rat

Previous studies have reported cardiovascular and nociceptive responses after intrathecal injection of kinin B1 receptor (B1R) agonists in the model of streptozotocin (STZ)-diabetic rat (diabetic). The aim of this study was to measure the early up-regulation of B1R binding sites and mRNA in the thoracic spinal cord of diabetic and control rats. Data show significant increases of specific B1R binding sites in the dorsal horn of diabetic rats 2 days (+315%), 7 days (+303%) and 21 days (+181%) after STZ treatment. Levels of mRNA were significantly increased (+68%) at 2 and 7 days but not at 21 days. These data bring the first molecular evidence for an early up-regulation of B1R in the spinal cord of diabetic rat.

Fate of bradykinin on the rat liver when administered by the venous or arterial route

BACKGROUND AND AIM

Bradykinin (BK) infused into the portal vein elicits a hypertensive response via the B2 receptor (B2R) and is efficiently hydrolyzed by the liver. Our purpose was to characterize the mechanism of interaction between BK and the liver.

METHOD

BK, HOE-140 (a B2R antagonist), des-R(9)-BK (a B1R agonist) and enzyme inhibitors were used in monovascular or bivascular perfusions and in isolated liver cell assays.

RESULTS

Des-R(9)-BK did not elicit a portal hypertensive response (PHR); BK infused into the hepatic artery elicited a calcium-dependent PHR and a calcium-independent arterial hypertensive response (HAHR), with the latter being almost abolished by naproxen. BK has a predominant distribution in the extracellular space and an average hepatic extraction of 8% in the steady state. Hydrolysis products of infused BK (R(1)-F(5) and R(1)-P(7)) did not elicit PHR. Angiotensin converting enzyme (ACE) is concentrated in the perivenous region and B2R in the periportal region. Microphysiometry showed that BK (and not a B1 agonist) interacts with stellate cells and the endothelial sinusoidal/Kupffer cell fraction. This effect was inhibited by the B2R antagonist.

CONCLUSIONS

Events can be summarized as: the hypertensive action of BK on sinusoidal cells of the periportal region is followed by its hydrolysis by ACE which is primarily present in the perivenous region; there is no functional B1R in the normal liver; BK induces HAHR via eicosanoid release and PHR by a distinct pathway on the B2R. Our data suggest that BK may participate in the modulation of sinusoidal microvasculature tonus both in the portal and the arterial routes.

The binding specificity of OppA determines the selectivity of the oligopeptide ATP-binding cassette transporter

The purification and functional reconstitution of a five-component oligopeptide ATP-binding cassette transporter with a remarkably wide substrate specificity are described. High-affinity peptide uptake was dependent on liganded substrate-binding protein OppA, which interacts with the translocator OppBCDF with higher affinity than unliganded OppA. Transport screening with combinatorial peptide libraries revealed that (i) the Opp transporter is not selective with respect to amino acid side chains of the transported peptides; (ii) any peptide that can bind to OppA is transported via Opp, including very long peptides up to 35 residues long; and (iii) the binding specificity of OppA largely determines the overall transport selectivity.

Icatibant

Icatibant [HOE 140, JE 049] is a potent, specific and selective peptidomimetic bradykinin beta2-receptor antagonist. It has a modified peptide structure, and is the first bradykinin receptor antagonist to act on the guinea-pig trachea without demonstrating agonist effects. Icatibant was originated by Hoechst Marion Roussel (now Sanofi-Aventis). Jerini is seeking a partner for development and marketing of icatibant for the treatment of refractory ascites in liver cirrhosis, angioedema and burns. In August 2004, Aventis merged with Sanofi-Synthelabo to form Sanofi-Aventis.Icatibant has shown an excellent safety profile in phase I studies. In December 2003, Jerini demonstrated positive results in the phase IIa study. Results obtained were statistically significant and clinically relevant. At the BIO 2004 International Annual Convention (BIO-2004) [San Francisco, CA, USA; 6-9 June 2004], Jerini reported plans to initiate phase IIb trials in this indication in the second half of 2004. Positive results from an icatibant formulation comparative study, in patients with acute attacks of hereditary angioedema, were announced in August 2004; IV and SC formulations showed no difference in efficacy and safety. It was announced in September 2004 by Jerini that a pivotal study, known as For Angioedema Subcutaneous Treatment (FAST) 1, had been initiated in the US and Canada. The protocol of a European study, to be known as FAST 2, is to be submitted to the authorities in September 2004. Jerini expects to launch the product in 2006. The US FDA granted icatibant, for the treatment of hereditary angioedema, fast-track designation in July 2004. In January 2003, the European Agency for the Evaluation of Medicinal Products granted icatibant orphan drug status in Europe for the treatment of angioedema. In November 2003, Jerini announced that effective December 2003, icatibant had orphan drug status in the US for the same indication.

Immunohistochemical Distributions of the Tissue Kallikrein-Kinin System in Ischemic and Non-Ischemic Mouse Heart

Kinins have been shown to play a cardioprotective role during myocardial ischemia. However, the localization of each of the components of the kallikrein-kinin system in the heart has not been determined in a cell type-specific manner. Recently, mK1 has been identified as the major tissue kallikrein with the strongest bradykinin-forming activity among the products of the mouse tissue kallikrein gene superfamily. In the study presented here, we investigated the localizations of mK1, kininogen and bradykinin B2 receptors (B2Rs) in ischemic and non-ischemic left ventricles by immunohistochemistry. Kininogen, which contains bradykinin as a surface epitope, was detected by an anti-bradykinin antibody. Changes in the amounts of mK1 and B2R were evaluated by Western blot analysis. Myocardial ischemia was induced by ligation of the left anterior descending coronary artery for 60 min followed by reperfusion for 24 h. mK1 and B2Rs were most abundantly expressed in the vascular endothelium and, to a lesser extent, in fibroblasts. No immunohistochemical signal of these molecules was detected in myocytes. Kininogen was localized in the vascular endothelium and the smooth muscle layer. Myocardial ischemia, although it had no effect on the localization of these molecules, increased the amounts of mK1 and B2R. We have obtained immunohistochemical evidence that all components of the tissue kallikrein-kinin system are present in the mouse heart. The coronary artery is the major site of kallikrein-kinin activity both in ischemic and non-ischemic hearts.

The mutation Ser511Asn leads to N-glycosylation and increases the cleavage of high molecular weight kininogen in rats genetically susceptible to inflammation

Crohn disease is immunologically mediated and characterized by intestinal and systemic chronic inflammation. In a rat model, injection of peptidoglycan-polysaccharide complexes into the intestinal wall induced chronic inflammation in Lewis but neither Fischer nor Buffalo rats, indicating a differential genetic susceptibility. Proteolysis of plasma high molecular weight kininogen (HK) yielding bradykinin and cleaved HK (HKa) was faster in Lewis than in Fischer or Buffalo rat plasma. A single point mutation at nucleotide 1586 was found translating from Ser511 (Buffalo and Fisher) to Asn511 (Lewis). The latter defines an Asn-Xaa-Thr consensus sequence for N-glycosylation. We expressed these domains in Escherichia coli and found no differences in the rate of cleavage by purified kallikrein in the 3 strains in the absence of N-glycosylation. We then expressed these domains in Chinese hamster ovary (CHO) cells, which are capable of glycosylation, and found an increased rate of cleavage of Lewis HK. The Lewis mutation is associated with N-glycosylation as evidenced by a more rapid migration after treatment with N-glycosidase F. When CHO cells were cultured in the presence of tunicamycin, the kallikrein-induced cleavage rate of Lewis HK was not increased. This molecular alteration might be one contributing factor resulting in chronic inflammation in Lewis rats.

Intracarotid administration of short-chain alkylglycerols for increased delivery of methotrexate to the rat brain

1 The intracarotid administration of alkylglycerols has been reported previously by us to be a novel strategy for increased delivery of various chemotherapeutic drugs to the normal brain and brain tumors in rats. 2 Effectiveness and structure-activity relations of the most promising pentyl- and hexylglycerol derivatives have been elucidated in vivo by analyzing the transfer of methotrexate (MTX) across the blood-brain barrier (BBB) in normal rats. The effects were compared with BBB disruption using hypertonic mannitol or intracarotid infusion of bradykinin. Furthermore, toxicity of the alkylglycerols has been studied in long-term experiments. 3 Apart from 1-O-pentyldiglycerol, all alkylglycerols induced a concentration-dependent increase in MTX delivery to the brain varying from 1.1 to more than 300-fold compared to intra-arterial MTX alone. Enhanced barrier permeability rapidly approached baseline values within 5 and 120 min at the latest. Chemical structure, concentration, time schedule of injections and combination of different alkylglycerols were identified as instruments suited to regulate the MTX accumulation within a wide range. Mannitol 1.4 M resulted in very high MTX levels in the brain as observed using the highest concentrations of alkylglycerols. Intracarotid infusion of bradykinin had only a minor effect on the BBB. Using 1-O-pentylglycerol or 2-O-hexyldiglycerol, both cell culture experiments and long-term in vivo analyses including clinical, laboratory and histopathological evaluations revealed no signs of toxicity. 4 In summary, intracarotid short-chain alkylglycerols constitute a very effective and low toxic strategy for transient opening of the BBB to overcome the limited access of cytotoxic drugs to the brain.

Effect of tumour necrosis factor-alpha and interleukin 1beta on endothelium-dependent relaxation in rat mesenteric resistance arteries in vitro

1. Pre-eclampsia is associated with elevated proinflammatory cytokine levels and endothelial dysfunction. This study examined the effect of two cytokines, tumour necrosis factor-alpha (TNF) and interleukin-1beta (IL-1) on endothelium-dependent relaxation in response to acetylcholine (ACH), bradykinin (BK) and histamine (HIS) in rat mesenteric small arteries in vitro. 2. Rat mesenteric arteries were mounted in an isometric myograph. Tone was induced with phenylephrine (PE) or a depolarizing solution containing 80 mM KCl (K(80)). Relaxation was measured in response to ACH, BK, HIS and sodium nitroprusside (SNP), an endothelium-independent relaxant. Inhibition of NO synthase by a combination of N(omega)-monomethyl-L-arginine (L-NMMA) and N(omega)-nitro-L-arginine methyl ester (L-NAME) significantly inhibited relaxation in response to ACH and BK. Addition of an inhibitor of cyclooxygenase, indomethacin, had no additional effect when added to L-NMMA and L-NAME. Inhibition of endothelium-derived hyperpolarizing factor (EDHF) by K(80) partially reduced responses to ACH and BK. Inhibition of HIS-induced relaxation was more marked with K(80). L-NMMA and L-NAME largely abolished the remaining relaxation to ACH, BK and HIS in arteries contracted with K(80). 3. Preincubation with TNF for 30 min caused an inhibition of relaxation in response to ACH and BK in arteries contracted with PE. Responses to HIS and SNP were not affected by TNF under these conditions. TNF also inhibited ACH-induced relaxation in arteries contracted with K(80). IL-1 had no effect on responses to ACH and the combination of TNF and IL-1 was not more effective than TNF alone. 4. The inhibitory effect of TNF on ACH-induced relaxation was abolished by coincubation with superoxide dismutase (SOD) and was not seen if NO synthase was inhibited by L-NMMA and L-NAME. 5. TNF inhibits the NO-dependent component of endothelium-dependent relaxation in response to ACH and BK, but does not inhibit the EDHF-dependent component. This effect may be attributable to the ability of TNF to increase levels of superoxide anions (O(2)(-)) and the ability of O(2)(-) to inactivate NO. This mechanism could contribute to the endothelial dysfunction seen in situations where TNF is elevated, such as pre-eclampsia.

Overexpression of bradykinin type 2 receptors on glioma cells enhances bradykinin-mediated blood-brain tumor barrier permeability increase

Variations in the expression levels of bradykinin (BK) type 2 receptors (B2R) in different brain tumors may explain variable increases in BK-mediated blood-brain tumor barrier (BTB) permeability. This study investigated whether elevation of the B2R expression levels on glioma cells enhances BK-mediated BTB permeability increases. Stable transfectants of C6 rat glioma cells overexpressing B2R were established by transfection with recombinant vectors harboring rat B2R cDNA sequence. Elevated B2R expression levels in transfectants were confirmed by quantitative real-time PCR, Western blots, and [3H]-BK binding studies. BTB permeability was quantified with autoradiography and expressed as a unidirectional transport constant, Ki, for [14C]-alpha-aminoisobutyric acid (AIB: Mr 103), using a rat brain tumor model. Baseline Ki values in tumors overexpressing B2R were not significantly higher than in control tumors. Ki values after BK treatment in tumors overexpressing B2R, however, were significantly higher than in control tumors. Western blots confirmed that B2R expression levels in vivo in tumors overexpressing B2R remained higher than in control tumors. These results suggested that alteration of B2R expression levels on tumor cells could modulate BK-mediated BTB permeability. Therefore, B2R expression levels in human glioma could be used to analyze the treatment results of patients undergoing treatment involving BK-modulated BTB permeability.

Angiotensin-converting enzyme inhibitor-associated angioedema is characterized by a slower degradation of des-arginine(9)-bradykinin

Angioedema (AE) is a rare but potentially life-threatening side effect of therapy with inhibitors of angiotensin-converting enzyme (ACE), the main bradykinin (BK)- inactivating metallopeptidase in humans. The pathogenesis of ACE inhibitor (ACEi)- associated AE (AE+) is presently unknown, although there is increasing evidence of a kinin role. We analyzed the metabolism of endogenous BK (B(2) receptor agonist) and its active metabolite, des-Arg(9)-BK (B(1) receptor agonist), in the presence of an ACEi during in vitro contact activation of plasma from hypertensive patients (n = 39) who presented AE+. Kinetic parameters were compared with those measured in a control group (AE-) of hypertensive patients (n = 39) who never manifested any acute or chronic side effects while treated with an ACEi. The different kinetic parameters were analyzed using a mathematical model (y = k t(alpha) e(-beta t)) previously applied to a normal, healthy population. The slope of BK degradation, but not its formation from high-molecular-weight kininogen, was lower in AE+ patients when compared with the AE- controls. des-Arg(9)-BK accumulation during the kinetic measurements was significantly higher in AE+ plasma. This accumulation of the B(1) agonist in AE+ patients paralleled its half-life of degradation. In conclusion, our results show, for the first time, that an abnormality of endogenous des-Arg(9)-BK degradation exists in the plasma of patients with ACEi-associated AE, suggesting that its pathogenetic mechanism lies in the catabolic site of kinin metabolism.

Effects of ethanol administration at a high-dose level on the stimulatory action by bradykinin in vascular permeability

The effects of ethanol (EtOH) administration at a high-dose level on the stimulatory action by bradykinin in vascular permeability were examined in rats, as compared with the effects of histamine and hyaluronidase. Oral administration (7.5 g/kg) and intraperitoneal injection (5 g/kg) of EtOH markedly potentiated the vascular permeability accelerated by bradykinin, but they suppressed in reverse such effects induced by histamine and hyaluronidase. EtOH did not affect the stimulatory action of bradykinin on the vascular permeability when intracutaneous injection was done under the coexistence with bradykinin. The blood pressure was found to descend 30 min later, though there was a transient rise immediately after the oral administration of EtOH (7.5 g/kg). The oral administration of EtOH (7.5 g/kg) caused no change in both enzyme activities of aspartic acid aminotransferase and alanine aminotransferase in blood for 3 h. The intraperitoneal injection of EtOH (5 g/kg) lowered the blood bradykinin level and increased the blood hyaluronidase activity. In vitro, EtOH elicited a concentration-dependent increase in the kallikrein activity, trypsin activity, and bradykinin-decomposed activity in plasma. These results strongly suggest that vascular permeability results from elevation in the bradykinin level, direct action of EtOH on inflamed skin site, and actions of EtOH or its metabolites on bradykinin-regulator, which involves bradykinin receptor and NO and endothelin productions.

Biochemical basis of angioedema associated with recombinant tissue plasminogen activator treatment: an in vitro experimental approach

BACKGROUND

Angioedema has been reported during recombinant tissue plasminogen activator (rtPA) treatment of acute ischemic stroke, often with concomitant use of angiotensin I-converting enzyme inhibitor treatment. Angioedema has been partly attributed to the nonapeptide bradykinin (BK), although its precise role has been poorly documented until now. The purposes of this report are 2-fold. First, we sought to define and characterize the in vitro kinin-forming capacity of rtPA when incubated with human plasma at a concentration within the therapeutic concentration range of rtPA attained in blood in vivo during fibrinolysis. Second, we sought to define the mechanism by which rtPA liberates BK from purified human single-chain high-molecular-weight kininogen, a key constituent of the contact system of plasma and the precursor of BK.

SUMMARY OF REPORT

When incubated with human plasma, in the presence of an angiotensin I-converting enzyme inhibitor, rtPA generates BK, which is further metabolized to des-Arg9-BK. The quantity of kinins generated by rtPA is similar to that observed during the activation of the contact system of plasma with a negatively charged surface, suggesting that it is physiologically relevant. The total amount of des-Arg9-BK liberated during the incubation period depends on the aminopeptidase P activity, its main degrading peptidase. Additionally, incubations using purified proteins of the fibrinolytic and the contact system pathways show that the rtPA kinin-forming capacity is mediated by plasmin.

CONCLUSIONS

We conclude that rtPA used in vitro at a therapeutic concentration has the capacity to generate significant quantities of kinins from human plasma. This kinin-forming activity depends on the activation of the fibrinolytic pathway. These data suggest that angioedema associated with rtPA treatment of ischemic stroke results directly from plasmin-mediated release of BK.

Regulation of blood-brain tumor barrier permeability by calcium-activated potassium channels

The blood-brain tumor barrier (BTB) limits the delivery of therapeutic drugs to brain tumors. We demonstrate in a rat brain tumor (RG2) model an enhanced drug delivery to brain tumor following intracarotid infusion of bradykinin (BK), nitric oxide (NO) donors, or agonists of soluble guanylate cyclase (sGC) and calcium-dependent potassium (K(Ca)) channels. We modulated K(Ca) channels by specific agonists and agents that produce NO and cGMP in situ to obtain sustained enhancement of selective drug delivery to brain tumors. Intracarotid infusion of BK or 1,3-dihydro-1-[2-hydroxy-5-(trifluoromethyl)phenyl]-5-(trifluoromethyl)-2H-benzimidazol-2-one (NS-1619) significantly enhanced BTB permeability (K(i)) to [(14)C]alpha-aminoisobutyric acid in the brain tumor area but not in normal brain tissue. The K(i) increase achieved by BK, NS-1619, NO donors, or the sGC activator 3-(5'-hydroxymethyl-2'furyl)-1-benzylindazole (YC-1) was significantly attenuated when coinfused with a K(Ca) channel antagonist, iberiotoxin. Immunoblot and immunolocalization studies demonstrate overexpression of K(Ca) channels in tumor cells and capillaries compared with normal brain. The potentiometric assays demonstrate the functional activity of K(Ca) channels in rat brain endothelial and glioma cells. Additionally, we show that BK and NS-1619 significantly increased the density of transport vesicles in the cytoplasm of brain tumor capillary endothelia and tumor cells. The cleft indices and cleft area indices in rat tumor capillaries were significantly higher than in normal brain capillaries, and BK infusion did not alter these indices. These data demonstrate that the cellular mechanism for K(Ca) channel-mediated BTB permeability increase is due to accelerated formation of pinocytotic vesicles, which can transport drugs across BTB. We conclude that K(Ca) channels serve as a convergence point in the biochemical regulation of BTB permeability.

Neutron capture therapy of intracerebral melanoma: enhanced survival and cure after blood-brain barrier opening to improve delivery of boronophenylalanine

PURPOSE

Multicentric cerebral metastases of melanoma represent an important clinical problem for which there currently is no satisfactory treatment. We previously developed a model for melanoma metastatic to the brain employing nude rats bearing intracerebral implants of the human MRA27 melanoma. The purpose of the present study was to determine if the efficacy of boron neutron capture therapy (BNCT) could be improved by either Cereport (RMP-7) mediated modulation of blood-brain barrier (BBB) permeability or hyperosmotic mannitol-induced BBB disruption using boronophenylalanine (BPA) as the capture agent.

METHODS AND MATERIALS

Biodistribution studies were carried out at 0.5, 2.5, and 4 h after intracarotid administration of Cereport (1.5 microg/kg) and intracarotid or i.v. administration of BPA (500 mg/kg). Peak tumor boron concentrations (65.4 microg/g) and the best composite tumor:brain (6.1:1) and tumor:blood (6.3:1) ratios were observed at 2.5 h after intracarotid administration. BNCT was initiated at the Brookhaven Medical Research Reactor 13-14 days after intracerebral implantation of 10(6) MRA27 cells.

RESULTS

Untreated control rats had a median survival time (MeST) of 22 days and for irradiated controls, it was 30 days. Rats that received i.v. or intracarotid BPA without Cereport followed by BNCT 2.5 h later had MeSTs of 41 days and 57 days, respectively, with 20% long-term survivors (>180 days) in the latter group. Rats that received intracarotid BPA with Cereport had an MeST of 86 days with 36% long-term survivors, which was very close to that of rats that had hyperosmotic mannitol-induced disruption of the BBB (85 days with 25% long-term survivors). When these two groups were combined, and survival times were compared, using the Wilcoxon rank sum test, to those of rats that received intracarotid BPA without blood-brain barrier disruption, these differences were significant at the level p = 0.01.

CONCLUSIONS

Our data show that optimizing the delivery of BPA by means of intracarotid injection combined with opening the BBB by infusing Cereport or a hyperosmotic solution of mannitol significantly enhanced survival times and produced long-term cures of MRA27 melanoma-bearing rats. These observations are relevant to future clinical studies using BNCT for the treatment of intracerebral melanoma.

Study of bradykinin metabolism in human and rat plasma by liquid chromatography with inductively coupled plasma mass spectrometry and orthogonal acceleration time-of-flight mass spectrometry

Bradykinin is a small peptide that acts mainly as a hormone by activating specific receptors that confer protection against the development of hypertension. The efficacy of bradykinin is influenced by the activities of various kininases present in plasma and blood. In this study, both human and rat plasma were incubated with a labelled form of bradykinin (at 4 and 12.5 microM), that will be referred to as bromobradykinin. The metabolic fate of bromobradykinin was monitored by liquid chromatography coupled to an orthogonal acceleration time-of-flight mass spectrometer (oaTOF). Quantification measurements of the bromine-containing metabolites were performed on-line, via flow splitting, by inductively coupled plasma mass spectrometry (ICPMS). The data obtained highlighted that the mechanism(s) of bradykinin metabolism in human and rat plasma are different, with the metabolism of bradykinin in rat plasma being much more aggressive than that observed in human plasma. In addition to the known bradykinin metabolites, e.g. [1,5], [1,7] from ACE, [1,8] from carboxypeptidase and [2,9] from aminopeptidase activity, we have identified the presence of new bradykinin metabolites in both human and rat plasma. These have been identified as fragment [5], the amino acid phenylalanine, which was present in both the human and rat plasma and the fragments [2,8] and [4,8] in rat plasma. To our knowledge it is the first time that these fragments have been recorded in human and rat plasma. The occurrence of these new fragments provides evidence for the presence of potentially new enzymes and mechanisms of bradykinin metabolism. The method described here provides a powerful technique for monitoring the activity of the many kininases involved in bradykinin metabolism such as ACE (angiotensin I converting enzyme), carboxypeptidase N and aminopeptidase P. In addition, this procedure could be used as a screening assay for selecting and monitoring the actions of inhibitors of the enzymes implicated in bradykinin metabolism directly in plasma or serum.

Thrombostatin inhibits cyclic flow variations in stenosed canine coronary arteries

Thrombostatins are a group of compounds based upon a breakdown product of bradykinin, RPPGF. They inhibit alpha-thrombin-induced platelet activation by binding to protease activated receptor 1 and, at a lower affinity, by interacting with thrombin's active site. After a single intravenous infusion of MAP4-RPPGF (11.58 mg/kg), its t1/2alpha was 4.5 min with a clearance of 2.0 ml/min. MAP4-RPPGF administration had a sustained antiplatelet effect, preventing gamma-thrombin-induced (12.5 nM) platelet activation for 4 h. Its antiplatelet effect summated with that of aspirin and/or clopidogrel. MAP4-RPPGF was compared with aspirin and clopidogrel in the Folts model of coronary artery thrombosis. Dogs were randomized to 3 treatment groups: aspirin 1.14 mg/kg i.v., clopidogrel 0.5 mg/kg i.v., or MAP4-RPPGF 0.77 mg/kg i.v. Cyclic flow variations (CFV) were recorded in 5 untreated dogs hourly for 3 successive hours and for 1 h before (all groups >11 CFV/h), and for 2 h after drug infusion in each of the 3 treatment groups. After 1 h drug treatment, all groups of animals had <6 CFV/h; after 2 h treatment, all had <1 CFV/h. All agents significantly reduced CFV from control at each hour, but none was significantly better than any other. Thrombostatin was as effective as aspirin or clopidogrel in inhibiting coronary artery thrombosis in this canine model.

The development of the bradykinin agonist labradimil as a means to increase the permeability of the blood-brain barrier: from concept to clinical evaluation

Labradimil (Cereport; also formerly referred to as RMP-7) is a 9-amino-acid peptide designed for selectivity for the bradykinin B2 receptor and a longer plasma half-life than bradykinin. It has been developed to increase the permeability of the blood-brain barrier (BBB) and is the first compound with selective bradykinin B2 receptor agonist properties to progress from concept design through to tests of efficacy in patients. In vitro studies demonstrate that labradimil has a longer half-life than bradykinin and selectively binds to bradykinin B2 receptors, initiating typical bradykinin-like second messenger systems, including increases in intracellular calcium and phosphatidylinositol turnover. Initial proof of principle studies using electron microscopy demonstrated that intravenous labradimil increases the permeability of the BBB by disengaging the tight junctions of the endothelial cells that comprise the BBB. Autoradiographic studies in rat models further demonstrated that labradimil increases the permeability of the BBB in gliomas. Intravenous or intra-arterial labradimil increases the uptake of many different radiolabelled tracers and chemotherapeutic agents into the tumour in a dose-related fashion. These effects are selective for the tumour and for the brain surrounding the tumour, and are particularly robust in tumour areas that are normally relatively impermeable. The increased chemotherapeutic concentrations are maintained for at least 90 minutes, well beyond the transient effects on the BBB. The increase in permeability with labradimil occurs rapidly but is transient, in that restoration of the BBB occurs very rapidly (2 to 5 minutes) following cessation of infusion. Even with continuous infusion of labradimil, spontaneous restoration of the barrier begins to occur within 10 to 20 minutes. Collectively, these data demonstrate that the B2 receptor system that modulates permeability of the BBB is highly sensitive and autoregulated and that careful attention to the timing of labradimil and the chemotherapeutic agent is important to achieve maximal effects. Survival studies in rodent models of both gliomas and metastatic tumours in the brain demonstrate that the enhanced uptake observed with the combination of labradimil and water-soluble chemotherapeutics enhances survival to a greater extent than achieved with chemotherapy alone. Finally, preliminary clinical trials in patients with gliomas provide confirmatory evidence that labradimil permeabilises the blood-brain tumour barrier and might, therefore, be used to increase delivery of agents such as carboplatin to tumours without the toxicity typically associated with dose escalation.

Anti-ischemic effects of angiotensin- converting enzyme inhibition in hypertension

OBJECTIVES

We investigated whether augmentation of bradykinin (BK) bioavailability with angiotensin-converting enzyme (ACE) inhibition is associated with reduced exercise-induced myocardial ischemia in hypertension.

BACKGROUND

Bradykinin responses are depressed in hypertension, and endothelial dysfunction contributes to myocardial ischemia by promoting abnormal coronary vasomotion during stress.

METHODS

Fourteen hypertensive (HT) and 17 normotensive (NT), mildly symptomatic patients with coronary artery disease (CAD) and ST-segment depression during exercise were studied before and after seven days of oral enalapril (EN), which was titrated from 2.5 to 20 mg daily. Patients underwent two treadmill exercise tests and determination of forearm vasodilator response to BK.

RESULTS

Despite receiving a lower dose of EN (7.8 vs. 14.8 mg, p < 0.001), NT patients had a significant reduction in blood pressure compared to HT patients. Compared to pre-EN, the ischemic threshold, defined as the rate-pressure product at the onset of 1-mm ST depression (p = 0.045), the duration of exercise to 1-mm ST depression (180 +/- 54 s, p = 0.007) and the maximum exercise duration (94 +/- 18 s, p < 0.001) were greater after EN in HT patients, but not in NT subjects (all p > or = 0.3). Patients with a greater drop in blood pressure experienced no improvement in exercise-induced ischemia. Forearm blood flow responses to BK were improved with EN in all patients to a similar extent. Moreover, no correlation was observed between the basal response to BK or the magnitude of its improvement with EN and with either the dose of EN or the improvement in exercise ischemic threshold.

CONCLUSIONS

Exercise-induced myocardial ischemia is ameliorated in HT patients with CAD by ACE inhibition.

Pharmacokinetics of carboplatin administered in combination with the bradykinin agonist Cereport (RMP-7) for the treatment of brain tumours

INTRODUCTION

Cereport (RMP-7) is a novel bradykinin agonist which is being developed as a modulator of the blood-brain barrier (BBB). In order to investigate the pharmacokinetics of carboplatin in combination with Cereport, we performed pharmacological studies in conjunction with early clinical trials.

METHODS

Pharmacokinetic samples were collected from eight patients in a phase I study (Cereport 100-300 ng/ kg) and ten patients in a phase II study (Cereport 300 ng/kg). Pharmacokinetic parameters for carboplatin were compared with respect to the dose of Cereport and with historical controls.

RESULTS

Cereport combined with carboplatin was well-tolerated, with mild haematological toxicities consistent with the target area under the concentration time curve (AUC) of 7 mg/ml x min. Although the clearance of carboplatin was within the range reported for this drug alone, the addition of Cereport resulted in a higher than expected carboplatin AUC. This effect was related to the dose of Cereport in the phase I study (AUC values 104-133% of target, Spearman rank correlation coefficient = 0.71, P < 0.001). The higher than expected AUC value was confirmed in the phase II study (AUC values 106-189% of target).

CONCLUSIONS

Co-administration of Cereport with carboplatin may result in a greater than predicted AUC. The mechanism of this possible interaction remains to be determined, although this did not result in any increased toxicity. Thus, the clinical potential of this combination in the treatment of brain tumours warrants further investigation.

Thrombostatin inhibits induced canine coronary thrombosis

Thrombostatin (RPPGF), an angiotensin converting enzyme metabolite of bradykinin, is an inhibitor of alpha-thrombin's ability to activate platelets. We examined the in vivo pharmacokinetics and pharmacodynamics of thrombostatin in rabbits and its ability to inhibit coronary thrombosis induced by electrolytic injury in dogs. Plasma half-life of thrombostatin had a t1/2alpha of 2.6 min and a t1/2beta of 24 min in rabbits. Ligating the renal arteries did not prolong clearance (t1/2alpha = 2.4 min; t1/2beta = 12 min). Thrombostatin produced a prolonged in vivo antiplatelet effect. At 30 min after a single intravenous administration in rabbits, thrombostatin's plasma concentration was <8.7 microM (5 microg/ml). However, ex vivo 20 and 40 nM gamma-thrombin-induced platelet aggregation of these rabbits' platelets was inhibited 40% for 2.75 and 1 h, respectively. In vitro, flow cytometry studies revealed that thrombostatin specifically bound to human platelets and washed human platelets treated with thrombostatin were less responsive to gamma-thrombin than control platelets. Using electrolytic injury to induce coronary artery thrombosis, dogs treated with thrombostatin, aspirin, or combined thrombostatin and aspirin occluded in 62+/-25 (mean +/- SD), 62+/-36, or 89+/-32 min versus untreated animals which occluded at 39+/-27 min, (p<0.01, p<0.01 and p<0.001, respectively). These studies show that thrombostatin binds to platelets and can delay coronary occlusion in vivo.

[Mechanisms of nutrient and drug transfer through the blood-brain barrier and their pharmacological changes]

The blood-brain barrier is formed by the endothelial cells of the brain capillaries. Its primary characteristic is the impermeability of the capillary wall due to the presence of complex tight junctions and a low endocytic activity. Essential nutrients are delivered to the brain by selective transport mechanisms, such as glucose transporter and a variety of amino acid transporters. Although most drugs enter the brain by passive diffusion through the endothelial cells depending of their lipophilicity, degree of ionization, molecular weight, relative brain tissue and plasma bindings--some of them can use specific endogenous transporters. In these cases, binding competition on the transporter with endogenous products or nutrients can occur and limit the drug transfer. The blood-brain barrier can be a major impediment for the treatment of diseases of the central nervous system, since many drugs are unable to reach this organ at therapeutic concentrations. Various attempts have been made to overcome the limiting access of drugs to the brain: chemical modification of drugs, development of more hydrophobic analogs or linking an active compound to a specific carrier. Transient opening of the blood-brain barrier has been achieved by intracarotid infusion of hypertonic mannitol solutions or of bradykinin analogs in humans. Another way to increase or decrease brain delivery of drugs is to modulate the P-glycoprotein (P-gp) whose substrates are actively pumped out the cell into the capillary lumen. We actually dispose of many P-gp inhibitors or inducers in order to enhance the therapeutic effects of centrally acting drugs or to decrease central adverse effects of peripheric drugs.

Labelling of peptides with 1.4-nm gold particles to demonstrate their binding sites in the rat spinal cord

Recently we presented a method to label the neuropeptide substance P with a 1.4-nm gold particle covalently bound at the N-terminus that can be used for demonstrating its binding sites in histological sections. In this study we examined whether the peptides neuropeptide Y, somatostatin, calcitonin gene-related peptide and bradykinin can be labelled in the same way. Polyacrylamide gel electrophoresis revealed a reduction in mobility for peptide-gold conjugates over gold particles alone consistent with peptide binding. In cryostat sections of the rat lumbar spinal cord, the peptides showed a distinct binding pattern in the grey matter corresponding to data of studies using autoradiographic methods. Therefore, we conclude that this simple and fast method can be used for labelling peptides in general to demonstrate their binding sites in histological sections, provided the peptide binds by its C-terminus.

Des-Arg9-bradykinin metabolism in patients who presented hypersensitivity reactions during hemodialysis: role of serum ACE and aminopeptidase P

Bradykinin (BK) has been proposed as the principal mediator of hypersensitivity reactions (HSR) in patients dialyzed using negatively charged membranes and concomitantly treated with angiotensin-converting enzyme (ACE) inhibitors. We investigated the metabolism of exogenous BK added to the sera of 13 patients dialyzed on an AN69 membrane with a history of HSR (HSR+ patients) and 10 others who did not present such a reaction (HSR- patients) while dialyzed under the same conditions. No significant difference in the t1/2 of BK was found between the patient groups. However, the t1/2 of generated des-Arg9-BK was significantly increased (2.2-fold) in HSR+ patients compared to HSR-subjects. Preincubation of the sera with an ACE inhibitor (enalaprilat) significantly increased the t1/2 of both BK and des-Arg9-BK in both groups. There was no significant difference between the groups with respect to the t1/2 of BK, but there was a significantly greater increase (3.8-fold) in the t1/2 of des-Arg9-BK in HSR+ patients compared to HSR-subjects. The level of serum aminopeptidase P (APP) activity showed a significant decrease in the HSR+ sera when compared to HSR-samples. In HSR- and HSR+ patients, a significant inverse relation (r2 = 0.6271; P < 0.00005) could be calculated between APP activity and des-Arg9-BK t1/2. In conclusion, HSR in hemodialyzed patients who are concomitantly treated with a negatively charged membrane and an ACE inhibitor can be considered as a multifactorial disease in that a decreased APP activity resulting in reduced degradation of des-Arg9-BK may lead to the accumulation of this B1 agonist that could be responsible, at least in part, for the signs and symptoms of HSR.

Bradykinin stimulates type II alveolar cells to release neutrophil and monocyte chemotactic activity and inflammatory cytokines

In the present study, we evaluated the potential of bradykinin (BK) to induce the release of neutrophil and monocyte chemotactic activity (NCA and MCA) and cytokines from an alveolar type II epithelial cell line, A549 cells. BK stimulated A549 cells to release NCA and MCA in a dose- and time-dependent manner (P < 0.001). Checkerboard analysis revealed that both NCA and MCA involved chemotactic and chemokinetic activity. Molecular sieve column chromatography showed three molecular weight masses (near 19 kd, 8 kd, and 400 d) for NCA and several molecular weight peaks (near 66 kd, 25 kd, 19 kd, 16 kd, and 400 d) for MCA. The release of NCA and MCA was inhibited by cycloheximide and lipoxygenase inhibitors (P < 0.01). The NCA and MCA were inhibited by leukotriene B4 (LTB4) receptor antagonist (P < 0.01), and the concentration of LTB4 was high enough for NCA and MCA. Antibodies to interleukin (IL)-8 and granulocyte colony-stimulating factor (G-CSF) attenuated NCA (P < 0.01), and antibodies to monocyte chemotactic protein-1 (MCP-1), G-CSF, and transforming growth factor (TGF)-beta attenuated MCA (P < 0.01). The levels of IL-8, G-CSF, MCP-1, and TGF-beta increased time dependently (P < 0.01). BK also stimulated the release of ILeukin-6 from A549 cells (P < 0.001). The receptors responsible for the release of NCA, MCA, and individual chemokines involved both BKB1 and BKB2 receptors. These data suggest that BK may stimulate alveolar type II pneumocytes to release inflammatory cytokines, which then may modulate the lung inflammation.

Nitric oxide and cyclic GMP attenuate sensitivity of the blood-tumor barrier permeability to bradykinin

Intracarotid infusion of bradykinin and its analogue, RMP-7, selectively increase the permeability of brain tumor capillaries though the nitrix oxide (NO) and cyclic GMP pathway. Maximum blood-tumor barrier (BTB) permeability induced by bradykinin is observed at 15 min after intracarotid infusion and this effect is decreased even if the infusion continues. The mechanism for this decreased effect with long term infusion has not been clearly defined. This study sought to determine the involvement of the NO-cyclic GMP pathway in this event. Regional permeability was investigated in 44 Wistar rats with implanted RG2 gliomas, using quantitative autoradiography to determine the unidirectional transfer constant (Ki) of radiolabeled 14C-dextran. Tumor bearing rats were treated by intracarotid infusion of bradykinin (10 micrograms kg-1 min-1) with or without pretreatment with bradykinin, the NO donor s-nitrosoglutathione (10 nmol kg-1 min-1), or the cyclic GMP analogue, 8Br-cyclic GMP (200 micrograms kg-1 min-1). At 30 min of bradykinin infusion, BTB permeability was significantly lower compared to 15 min of bradykinin infusion (3.79 +/- 0.99 vs. 16.20 +/- 3.43 microliters g-1 min-1, p < 0.001). Pretreatment with an NO donor significantly decreased BTB permeability in bradykinin infused rats (5.09 +/- 2.61 vs. 13.51 +/- 4.19 microliters g-1 min-1, p < 0.001), as did pretreatment with a cyclic GMP analogue (4.48 +/- 0.95 vs. 12.31 +/- 3.90 microliters g-1 min-1, p < 0.001). There was no increased permeability in nontumor brain areas. Increased tumor permeability by bradykinin appears to be regulated by NO and cyclic GMP which are second messengers involved in the bradykinin B2 receptor mediated cascade.

Metabolism of bradykinin by the rat coronary vascular bed

OBJECTIVE

To study the metabolism of bradykinin (BK) after a single passage through the coronary bed in isolated Langendorff rat hearts.

METHODS

BK was infused into the aortic flow line to obtain a final concentration of 10 nM, and the coronary, effluent was collected to quantify BK and des-Arg9-BK by competitive enzyme immunoassay. The nature of immunoreactive material was confirmed by immunograms after HPLC separation. The experiments were performed with hearts perfused at either one of the following coronary flow rates: 1, 5 or 10 ml/min.

RESULTS

BK recovery without inhibitors was 86.3 +/- 2.9, 60.8 +/- 6.3, and 29.6 +/- 6.8% at 10, 5, and 1 ml/min, respectively. The Vmax/Km ratios at these coronary flow rates were 2.19 +/- 0.72, 4.81 +/- 0.64, and 2.59 +/- 0.33 min-1 g-1), respectively. The angiotensin-converting enzyme (ACE) inhibitor, enalaprilat (130 nM), reduced BK degradation at all flow rates. Inhibition of neutral endopeptidase with retrothiorphan (25 nM) had no effect on BK degradation. However, the combined treatment with enalapril and retrothiorphan reduced BK degradation to lower values than enalaprilat alone. The effect of enzyme inhibitors on BK recovery was inversely related to coronary flow: inhibiting BK degradation markedly increased BK recovery at 1 ml/min, but had no effect at 10 ml/min. The kininase I metabolite of BK, des-Arg9-BK, could not be detected under these experimental conditions.

CONCLUSIONS

ACE is the major enzyme responsible for BK degradation during a single passage through the coronary bed. Neutral endopeptidase contributes to BK degradation only when ACE activity is impaired. The effect of enzyme inhibitors on the coronary concentration of BK is highly dependent on coronary flow rate.

Intravascular and interstitial degradation of bradykinin in isolated perfused rat heart

1. Bradykinin (BK) has been shown to exert cardioprotective effects which are potentiated by inhibitors of angiotensin I-converting enzyme (ACE). In order to clarify the significance of ACE within the whole spectrum of myocardial kininases we investigated BK degradation in the isolated rat heart. 2. Tritiated BK (3H-BK) or unlabelled BK was either repeatedly perfused through the heart, or applied as an intracoronary bolus allowing determination of its elution kinetics. BK metabolites were analysed by HPLC. Kininases were identified by ramiprilat, phosphoramidon, diprotin A and 2-mercaptoethanol or apstatin as specific inhibitors of ACE, neutral endopeptidase 24.11 (NEP), dipeptidylaminopeptidase IV and aminopeptidase P (APP), respectively. 3. In sequential perfusion passages, 3H-BK concentrations in the perfusate decreased by 39% during each passage. Ramiprilat reduced the rate of 3H-BK breakdown by 54% and nearly abolished [1-5]-BK generation. The ramiprilat-resistant kininase activity was for the most part inhibited by the selective APP inhibitor apstatin (IC50 0.9 microM). BK cleavage by APP yielded the intermediate product [2-9]-BK, which was rapidly metabolized to [4-9]-BK by dipeptidylaminopeptidase IV. 4. After bolus injection of 3H-BK, 10% of the applied radioactivity were protractedly eluted, indicating the distribution of this fraction into the myocardial interstitium. In samples of such interstitial perfusate fractions, 3H-BK was extensively (by 92%) degraded, essentially by ACE and APP. The ramiprilat- and mercaptoethanol-resistant fraction of interstitial kininase activity amounted to 14%, about half of which could be attributed to NEP. Only the product of NEP, [1-7]-BK, was continuously generated during the presence of 3H-BK in the interstitium. 5. ACE and APP are located at the endothelium and represent the predominant kininases of rat myocardium. Both enzymes form a metabolic barrier for the extravasated fraction of BK. Thus, only interstitial, but not intravascular concentrations of BK are increased by kininase inhibitors to the extent that a significant potentiation of BK effects could be explained. NEP contributes less than 5% to the total kininase activity, but is the only enzyme which is exclusively present in the interstitial space.

Oral activity of peptide bradykinin antagonists following intragastric administration in the rat

This study has investigated the oral activity, following intragastric administration, of three potent and long-acting peptide-based bradykinin antagonists, HOE-140, B9430, and CP-0597, in the anesthetized rat, using bradykinin-induced hypotension. Two of the three bradykinin antagonists, B9430 and HOE-140, but not CP-0597, were found to be active following intragastric administration, producing dose-dependent (1, 3, and 10 mg/kg) and selective inhibition of bradykinin-induced hypotension. At a dose of 10 mg/kg, the inhibition of bradykinin-induced hypotension occurred within 15 min and lasted for at least 2 h, which was the duration of the experiment. HOE-140 and CP-0597, 10 micrograms/kg i.v., produced significant inhibition of bradykinin-induced responses that lasted for 60 min. B9430, 10 micrograms/kg i.v., produced a significantly greater inhibition than HOE-140 and CP-0597, this inhibition being significant for the duration of the experiment (2 h) compared with saline controls. Considering the close chemical structure of CP-0597 compared with HOE-140 and B9430, it is not clear as to why CP-0597 was inactive via the intragastric route. This is the first demonstration of the oral activity of peptide-based bradykinin antagonists following intragastric administration in the rat.

Increased intramuscular concentration of bradykinin increases the static fusimotor drive to muscle spindles in neck muscles of the cat

The aim of the present study was to investigate if increased intramuscular concentrations of bradykinin (BK) in one muscle influence the activity in primary and secondary muscle spindle afferents (MSAs) originating from both ipsi- and contralateral muscles, via fusimotor reflexes. The ipsilateral trapezius (TR) and the splenius (SP) muscles were subjected to sinusoidal stretches and 2-3 MSAs were simultaneously recorded from these muscles. Responses of 29 MSAs (15 SP and 14 TR) were registered in five adult cats anaesthetised with alpha-chloralose. Intramuscular injections of 0.5 ml BK (6-86 micrograms/ml) were administered to both the ipsi- and contralateral SP and TR muscles. Similar doses of BK (5-10 micrograms) have been shown to induce muscle pain when injected into the temporal muscle in man. The responsiveness of the MSAs to the injections of BK was 86% and 87.5% from the contralateral TR and SP muscles, respectively. The effects were predominantly static onto the MSAs. The duration of the effects was on average 3.5-4 min, however some effects lasted for more than 15 min. The effects were always abolished after cutting the nerve to the injected muscle. The large majority of the spindle afferents were unresponsive to i.m. Tyrode injections (23 of 29). For the afferents that were responsive to injection of Tyrode, the effects were always considerably smaller and with shorter duration than those evoked by BK injections. Thus, increased intramuscular concentrations of BK may excite primary and secondary MSAs from ipsi- and contralateral muscles, via fusimotor reflexes evoked most probably by activity in chemosensitive muscle afferents. The results are discussed in relation to a recent hypothesis on pathophysiological mechanisms behind genesis, spread and perpetuation of muscle tension and pain in chronic musculoskeletal pain syndromes.

Cyclophilin-facilitated bradykinin inactivation in the perfused rat lung

Cis and trans isomers of X-proline (X-Pro) bonds can influence some aspects of the kinetics of peptide metabolism. We previously used the peptidyl-prolyl cis-trans isomerase, cyclophilin, to show that angiotensin converting enzyme (ACE) preferentially hydrolyzes the trans isomer of a synthetic tripeptide that contains a C-terminal proline (Dawson et al., Am J Physiol 257:H853-H865, 1989; Merker et al., J Appl Physiol 75: 1519-1524, 1993). Bradykinin (Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg) exists as both cis and trans isomers at all three X-Pro bonds, and although its inactivation in the lung by pulmonary endothelial peptidases is extensive, commonly a small fraction of the peptide survives passage through the lung. To determine whether the presence of cis X-Pro bonds might limit the extent of bradykinin metabolism in the lung, we studied inactivation of bradykinin by the isolated perfused rat lung using the rabbit jugular vein superfused with the pulmonary venous effluent as a bioassay for bradykinin. A large fraction (> 90%) of the bradykinin in a bolus injection was inactivated in a single transit through the pulmonary circulation, but a detectable fraction emerged in the venous effluent. The addition of cyclophilin to the bradykinin in the bolus reduced the bradykinin emerging from the lungs to virtually undetectable levels. When the isomerase inhibitor cyclosporin A was included with bradykinin and cyclophilin in the injectate, this effect of cyclophilin was reversed. These observations suggest that the fraction of bradykinin that normally survives passage through the lungs contains isomers that have at least one X-Pro bond that is refractory to enzymatic inactivation and whose isomerization time constant is significantly longer than the pulmonary capillary transit time.

Involvement of renal kallikrein in the regulation of bicarbonate excretion in rats

1. The experiments reported here were performed to test the hypothesis that renal kallikrein is involved in the regulation of acid-base balance. 2. The bicarbonate concentration and the kallikrein activity in the spontaneously voided urine of conscious rats (experiment 1) were inversely correlated (correlation coefficient (r) = -0.63, P < 0.0001). The correlation was even greater when the urinary bicarbonate concentration was expressed per milligram excreted creatinine (r = -0.74, P < 0.00002). 3. Intravenous injection of the kallikrein inhibitor aprotinin in barbiturate-anaesthetized rats (experiment 2) reduced urinary kallikrein activity (P < 0.05) and increased bicarbonate excretion rate (P < 0.012). 4. Renal arterial infusion of aprotinin in barbiturate-anaesthetized rats (experiment 3) reduced urinary kallikrein activity (120 min, P < 0.01), and increased bicarbonate excretion rate (120 min, P < 0.01). Animals infused with the inhibitor developed a moderate metabolic acidosis (base excess: control, 2.9 +/- 0.7 mM (mean +/- S.E.M.); experimental, -8.1 +/- 0.7 mM; P < 0.05). 5. The bicarbonate concentration of urine fractions obtained after retrograde injection of kallikrein through the ureter into the collecting duct system of barbiturate-anaesthetized rats was lower than that from kidneys administered the vehicle (experiment 4; P < 0.001). A retrograde injection of bradykinin was without effect (experiment 5). 6. We conclude that renal kallikrein is involved in the regulation of urinary bicarbonate excretion. Increased intraluminal activity of the enzyme reduces, and decreased kallikrein activity increases, bicarbonate excretion. The enzyme may be a component of a negative feedback loop controlling the hydrogen ion activity of the extracellular space.

Presystemic bradykinin metabolism in sheep and rat nasal homogenates

Bradykinin (BK) and its fragments BK(1-8), BK(1-7), and BK(1-5) were incubated with sheep nasal homogenates to investigate the extent of peptide metabolism within the nasal mucosa. The products for both bradykinin and BK(1-8) degradation were found to be BK(1-7) and BK(1-5). BK(1-7) was metabolized to BK(1-5) alone. The patterns of degradation suggest that the Pro7-Phe8 bond of bradykinin was hydrolyzed first, then BK(1-7) was further hydrolyzed to form BK(1-5). The metabolism of bradykinin in rat nasal homogenates and plasma was also investigated. BK(1-5) was the only metabolite measurable in the rat nasal homogenates, likely due to the activity of an endopeptidase. The reduction in the bradykinin degradation rate resulting from the inhibition of angiotensin converting enzyme (ACE) or carboxypeptidase N indicates that these enzymes participate in mucosal bradykinin metabolism to some degree. In comparison, the products of bradykinin hydrolysis in rat plasma were found to be BK(1-8), BK(1-7), and BK(1-5). These results indicate that the enzyme populations or/and activities vary significantly between different species and between different tissues within the same species. Although significant aminopeptidase activities were detected in the sheep nasal homogenates, bradykinin was not affected by their presence, since the N-terminal sequence of bradykinin is not susceptible to hydrolysis by most aminopeptidases.

Intracarotid infusion of RMP-7, a bradykinin analog: a method for selective drug delivery to brain tumors

The bradykinin analog, RMP-7, was investigated for its ability to selectively increase uptake of molecular tracers in RG2 glial tumors. When infused in low doses (0.1 microgram/kg/min) through the intracarotid artery ipsilateral to RG2 gliomas in rats, RMP-7 significantly increased the permeability of tumor capillaries to methotrexate and to four other tracers of varying molecular weights, compared to intracarotid infusion of vehicle alone. Tracers used to examine permeability included radiolabeled alpha-aminoisobutyric acid (M(r) 103 D), sucrose (M(r) 342 D), methotrexate (M(r) 454.5 D), inulin (M(r) 5000 D), and dextran (M(r) 70,000 D). Permeability was expressed as the unidirectional transfer constant, Ki (microliters/gm/min). The permeability (Ki) of tumors in the RMP-7 group compared to the vehicle control group was as follows: alpha-aminoisobutyric acid, 35.3 +/- 9.11 versus 12.7 +/- 4.56 (p < 0.001); sucrose, 16.5 +/- 3.83 versus 9.28 +/- 3.12 (p < 0.05); methotrexate, 26.3 +/- 10.3 versus 8.98 +/- 6.78 (p < 0.005); inulin, 13.5 +/- 3.23 versus 6.55 +/- 4.32 (p < 0.005); dextran, 15.2 +/- 3.42 versus 1.47 +/- 1.24 (p < 0.001). The permeability of RG2 gliomas to high-molecular-weight dextran (70,000 D) was 10.3-fold higher in the RMP-7 group than in the vehicle control group. Intracarotid infusion of RMP-7 did not significantly increase the blood volume in tumor or brain tissue. The permeability of normal brain capillaries was unaffected by intracarotid infusion of 0.1 microgram/kg/min RMP-7 relative to that achieved in tumor. These data support the idea that intracarotid infusion of RMP-7 will be a useful technique for selective delivery of antitumor compounds to brain tumors.

Inhibition of bradykinin-induced vasodilation in human forearm vasculature by icatibant, a potent B2-receptor antagonist

1. The effect of icatibant (D-Arg-[Hyp3, Thi5, D-Tic7, Oic8] bradykinin) a potent B2-kinin receptor antagonist, was studied on bradykinin-induced vasodilation in the human forearm. 2. Eight healthy normotensive men were studied in a rising dose random-placebo controlled study. Placebo and icatibant (20, 50 and 100 micrograms kg-1 i.v.) were administered double-blind. Forearm blood flow was measured by venous occlusion plethysmography during rising dose brachial artery infusions of bradykinin (10-3,000 ng min-1) 60-90 min after placebo or icatibant. 3. Plasma concentrations of icatibant fell exponentially following each of three doses, up to the final measurement. Elimination half-lives calculated from linear regression of the mean data were 25, 27 and 29 min after 20, 50 and 100 micrograms kg-1 doses respectively. 4. Icatibant inhibited the effect of bradykinin (P < 0.001 at each dose of icatibant) in a dose-dependent manner. Bradykinin (100 ng min-1) increased mean blood flow in the infused arm by 238 +/- 31% when infused following placebo, by 112 +/- 21% after icatibant 20 micrograms kg-1, by 71 +/- 14% after icatibant 50 micrograms kg-1 and by 48 +/- 9% after icatibant 100 micrograms kg-1. 5. These results demonstrate that icatibant antagonises B2-receptor mediated vasodilation in human forearm resistance vessels. The findings provide a quantitative basis for future studies of the role of bradykinin in the response to angiotensin converting enzyme inhibitors and in circulatory disease.

Metabolism of bradykinin by peptidases in the lung

We investigated the release of carboxypeptidase M (CPM), neutral endopeptidase 24.11 (enkephalinase, NEP), and angiotensin I converting enzyme (kininase II, ACE) and their contribution to bradykinin metabolism in the rat lung. The P3, membrane-enriched fraction of the homogenized lung was rich in all three peptidases. The activities of CPM and NEP were high in bronchoalveolar lavage fluid but lower in alveolar macrophages indicating that they originate from other cells present on the alveolar surface. In situ perfusion of rat lung with buffer that contained either deoxycholate or melittin or compound 48/80, produced lung edema. CPM, NEP, and ACE activities were recovered both in edema and perfusate fluid. The level of CPM and NEP was higher in edema fluid whereas, in contrast, more ACE activity was released into the perfusate. To evaluate the effect of peptidase inhibitors on changes in vascular permeability induced by bradykinin in the in situ perfused rat lung we measured the increase in lung weight as an index of increased vascular permeability or edema. Combined inhibition of either ACE plus NEP or ACE plus CPM augmented the effect of a subthreshold dose of bradykinin. Inhibitors of ACE, NEP, or CPM given alone and a combination of NEP plus CPM inhibitors did not enhance the bradykinin effect. Our results indicate that CPM, NEP, and ACE although present on different lung cells, synergistically modulate bradykinin effects. The different ratios of distribution of these enzymes in the perfusate and in edema fluid may not be due only to their presence on different pulmonary cells but also to their different anchoring mechanisms to plasma membranes.(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolism and characterisation of kinins and Hoe 140 (kinin antagonist) in the synovial fluid of patients with inflammatory joint diseases

Methods have been optimised for the collection of synovial fluid and the chromatographic separation of individual kinins (bradykinin and kallidin) in the fluid by HPLC. In addition, the stability of the kinin antagonist, Hoe 140, in synovial fluid was compared with that of synthetic bradykinin. Although bradykinin was completely degraded after incubation for only 6 h in pooled synovial fluid obtained from patients with rheumatoid arthritis, Hoe 140 was stable for as long as 2 weeks under the same conditions. These studies will provide quantitative information regarding levels of kinins in inflamed joints and an insight into the therapeutic potential of kinin antagonists.

HOE 140, a new highly potent and long-acting bradykinin antagonist in conscious rats

The inhibitory effects of the new bradykinin antagonist HOE 140 (D-Arg-Arg-Pro-Hyp-Gly-Thi-Ser-D-Tic-Oic-Arg) on depressor responses to exogenous bradykinin were investigated in conscious rats and compared with those of the bradykinin antagonist B4146 (D-Arg-Hyp-Pro-Gly-Thi-Ser-D-Pro-Thi-Arg). HOE 140 showed a 250-700-fold higher potency in vivo and a much longer biological half-life than B4146. Plasma catecholamines were not increased after application of HOE 140, indicating that this compound did not interfere with catecholamine release. HOE 140 proved to be a highly potent, specific and long-acting bradykinin B2-receptor antagonist.

Assessment of histamine, bradykinin, prostaglandins E1 and E2 and carrageenin as vascular permeability agents in the horse

The vascular leakage induced by histamine, bradykinin, serotonin and prostaglandin E1 and E2 was assessed. The test agents were injected intradermally into the shaved thoracic skin of horses and the vascular leakage estimated either semi-quantitatively by recording the diameter of the lesions or by measuring the actual volume of extravasated plasma in microliters using iodine-125-labelled human serum albumin (125I-HSA) as a marker in the blood plasma. Using the latter method, the vascular leakage induced by carrageenin and the effect of coadministered prostaglandins E1 and E2 upon the vascular leakage of both histamine and bradykinin were also investigated. No obvious lesions resulted when serotonin (10(-2) mol/l) was injected but histamine and bradykinin produced circular lesions which increased in diameter for approximately 30 min. The size of the lesions and volume of extravasated plasma was dose dependent. On a molar basis, bradykinin (10(-6) mol/l, 10(-5) mol/l) was more potent than histamine but they were equipotent at 10(-4) mol/l. The size of the lesions induced by carrageenin were independent of their anatomical location on the thorax. Except for the second hour, the hourly volume of vascular leakage increased until the fifth hour when the experiment was concluded. The maximum vascular leakage resulting from the injection of prostaglandin E1 or E2 (1, 10, 100 or 1000 ng) was 7 microliters but when co-administered with bradykinin (10(-6) mol/l), the volume of leaked plasma increased from 29 to 78 microliters. No synergy was observed when either prostaglandin was co-administered with histamine (10(-5) mol/l).

Hageman factor-dependent kinin activation in burns and its theoretical relationship to postburn immunosuppression syndrome and infection

Burn injury and intradermal injection of bradykinin or histamine cause permeability changes visualized as dye-release lesions in the skin of guinea pigs injected intravenously with Evans blue dye. Antihistamine pretreatment ablates the histamine but not the effect of thermal injury or bradykinin. Bradykinin is generated via activation of Hageman factor in a two-step reaction. Steps 1 and 2 can be inhibited by corn trypsin inhibitor and soy bean trypsin inhibitors, respectively. Dye-release lesions were reduced from thermal injury and bradykinin injections when these substances were injected into the skin first. Angiotensin-converting enzyme deactivates bradykinin by degrading it. Angiotensin-converting enzyme inhibitor neutralizes angiotensin-converting enzyme. Dye-release lesions from both thermal injury and bradykinin injection were enhanced because of continued bradykinin build-up when these treatments were preceded by subcutaneous injections of angiotensin-converting enzyme inhibitor. Thus bradykinin is generated in thermal injury via the Hageman factor-dependent pathway. Hageman factor sits at the apex of a series of interrelated cascade systems, all of which impinge on the animal's immune status. Uncontrolled Hagemen factor activation in thermal injury may be the link among all the events collectively known as the "post thermal injury immunosuppression syndrome."