Effects of LF 16-0687 Ms, a bradykinin B(2) receptor antagonist, on brain edema formation and tissue damage in a rat model of temporary focal cerebral ischemia

Bradykinin receptor ligands: therapeutic perspectives

Kinins, which are produced by the action of kallikrein enzymes, are blood-derived local-acting peptides that have broad effects mediated by two related G-protein-coupled receptors termed the bradykinin receptors. The endogenous kallikrein-kinin system controls blood circulation and kidney function, and promotes inflammation and pain in pathological conditions, which has led to interest in developing modulators of bradykinin receptors as potential therapeutics. This review discusses recent progress in our understanding of the genetics, molecular biology and pathophysiology of kinins and their receptors, as well as developments in medicinal chemistry, which have brought us closer to therapeutic applications of kinin receptor ligands in various indications. The potential of kinin receptor antagonists as novel analgesic agents that do not result in tolerance or have a liability for abuse has attracted particular interest.

A Novel Nonpeptide Antagonist of the Kinin B1Receptor: Effects at the Rabbit Receptor

The kinin B1 receptor (B1R) has attracted interest as a potential therapeutic target because this inducible G protein-coupled receptor is involved in sustained inflammation and inflammatory pain production. Compound 11 (2-[(2R)-1-[(3,4-dichlorophenyl) sulfonyl]-3-oxo-1,2,3,4-tetrahydroquinoxalin-2-yl]-N-[2-[4-(4,5-dihydro-1H-imidazol-2-yl)phenyl]ethyl]acetamide) is a high-affinity nonpeptide antagonist for the human B1R, but it is potent at the rabbit B1R as well: its Ki value for the inhibition of [3H]Lys-des-Arg9-BK (bradykinin) binding to a novel myc-labeled rabbit B1R expressed in COS-1 is 22 pM. In contractility tests (organ bath pharmacology), we found that compound 11 is an apparently surmountable antagonist of des-Arg9-BK- or Lys-des-Arg9-BK-induced contraction of the rabbit isolated aorta (pA2 values of 10.6+/-0.14 and 10.4+/-0.12, respectively). It did not influence contractions induced by angiotensin II in the rabbit aorta or by BK or histamine in the jugular vein, but it suppressed the prostaglandin-mediated relaxant effect of des-Arg9-BK on the rabbit isolated mesenteric artery. Compound 11 (1 nM) inhibited both the phosphorylation of the extracellular signal-regulated kinase1/2 mitogen-activated protein kinases induced by Lys-des-Arg9-BK in serum-starved rabbit aortic smooth muscle cells and the agonist-induced translocation of the fusion protein B1R-yellow fluorescent protein expressed in human embryonic kidney (HEK) 293 cells. Compound 11 does not importantly modify the expression of myc-B1R over 24 h in HEK 293 cells (no detectable action as "pharmacological chaperone"). The present results support that compound 11 is a potent and highly selective antagonist suitable for further investigations of the role of the kinin B1R in models of inflammation, pain, and sepsis based on the rabbit.

The powerful neuroprotective action of C1-inhibitor on brain ischemia-reperfusion injury does not require C1q

C1-inhibitor (C1-INH) is a major regulator of the complement classical pathway. Besides this action, it may also inhibit other related inflammatory systems. We have studied the effect of C1-INH in C57BL/6 mice with focal transient brain ischemia induced by 30 minutes of occlusion of the middle cerebral artery. C1-INH induced a dose-dependent reduction of ischemic volume that, with the dose of 15 U/mouse, reached 10.8% of the volume of saline-treated mice. Four days after ischemia the treated mice had significantly lower general and focal neurological deficit scores. Fluoro-Jade staining, a marker for neuronal degeneration, showed that C1-INH-treated mice had a lower number of degenerating cells. Leukocyte infiltration, as assessed by CD45 immunostaining, was also markedly decreased. We then investigated the response to ischemia in C1q(-/-) mice. There was a slight, nonsignificant decrease in infarct volume in C1q(-/-) mice (reduction to 72.3%) compared to wild types. Administration of C1-INH to these mice was still able to reduce the ischemic volume to 31.4%. The study shows that C1-INH has a strong neuroprotective effect on brain ischemia/reperfusion injury and that its action is independent from C1q-mediated activation of classical pathway.

Reduction of the prenatal hypoxic-ischemic brain edema with noscapine

Cytotoxic free radicals and release of several neurotransmitters such as bradykinin contribute to the pathogenesis of hypoxic-ischemic brain damage. We have studied the efficacy of noscapine, an opium alkaloid and a bradykinin antagonist, in reducing post-hypoxic-ischemic damage in developing brain of 7-d-old rat pups. Hypoxic-ischemic injury to the right cerebral hemisphere was produced by legation of the right common carotid artery followed by 3 h of hypoxia with 8% oxygen. Thirty to 45 min before hypoxia the rat pups received noscapine (dose = 0.5-2 mg/kg) or saline. Pups were scarified at 24 h post recovery for the assessment of cerebral damage by histological methods. Our results showed that noscapine was an effective agent in reducing the extent of brain injury after hypoxic-ischemic insult to neonatal rats. Therefore, it is concluded that noscapine may be a useful drug in the managements of patients after stroke.

A non-peptide antagonist unusually selective for the human form of the bradykinin B2 receptor

Analgesic and anti-inflammatory applications for non-peptide bradykinin (BK) B2 receptor antagonists have been documented in rats. However, very large species differences in affinity were also noted within this class of drugs, making the preclinical development of relevant drugs difficult. Bradyzide is a potent antagonist at the rat B2 receptor, but a weak one at the human receptor; a series of analogues in which the diphenylmethyl moiety of this drug has been substituted with dibenzosuberane have been reported to gain potency at the human B2 receptor, with some loss of affinity at the rat receptor. The present experiments have been performed in order to verify that the novel series of dibenzosuberane B2 receptor antagonist optimized for affinity in the human species are effective in the isolated human umbilical vein contractility assay. Bradyzide, its analog compound (S)-14c and the dibenzosuberane compounds (S)-14d and 19c surmountably antagonized BK-induced contraction (pA2 values of 5.42, 6.48, 7.42 and 7.53, respectively). In the rabbit jugular vein contractility assay, the pA2 of compound 19c was smaller than 5. Potency at the recombinant rabbit B2 receptor was generally decreasing in the series of four drugs (Ki in a [3H]BK competition assay to recombinant receptors of 0.78, 0.77, 10.2 and 44.4 nM, respectively); these four compounds did not displace [3H]Lys-des-Arg(9)-BK binding from human B1 receptors expressed by smooth muscle cells. The dibenzosuberane compound 19c, verified to functionally antagonize the vascular B2 receptor, is an example of a drug unusually specific for the human form of the receptor.

A preliminary report on the application of noscapine in the treatment of stroke

BACKGROUND

Stroke is the third leading cause of death in most developed countries. Therefore, a need exists for its treatment. Considering the role that is played by bradykinin in pathogenesis of neuronal injury, it has been suggested that bradykinin antagonists may be useful in the treatment of neurological patients. As noscapine can act as an antagonist of bradykinin and can effectively reduce brain injury after hypoxic-ischemic insult in neonatal rats, the present work was carried out to investigate its effectiveness in a clinical setting.

METHODS

Noscapine was administrated orally to ten acute ischemic stroke patients, and the degree of brain injury was evaluated by computed tomography scan and clinical observation. The control group (n=10) did not receive noscapine treatment.

RESULTS

Our study showed that noscapine effectively improved clinical prognosis and reduced the mortality rate down to 20% compared with 80% in the control group. Our patients did not show any specific side effects due to noscapine.

CONCLUSION

It is concluded that oral noscapine can be an effective drug for reducing the mortality rate in stroke; however, further study with a larger number of patients is needed to determine its full potential in stroke.

Bradykinin B2 receptor antagonism: a new direction for acute stroke therapy?

Stroke is responsible for 10% of all deaths worldwide, and there remains an urgent need for the development of clinically effective treatments for acute stroke. Stroke is now considered to be a disease characterized by an ongoing inflammatory process rather than simply acute neurodegeneration. Bradykinin has attracted recent interest as a potential mediator of brain injury following stroke, because it activates several mechanisms responsible for the early manifestations of inflammation, including arteriolar dilatation, increased vascular permeability and oedema formation. These actions of bradykinin occur via activation of B(2) receptors. New evidence suggests that blocking bradykinin B(2) receptors after experimental cerebral ischaemia reduces brain oedema, infarct volume and neuronal necrosis, and improves neurological outcome. Thus, B(2) receptor antagonists may be a promising new class of compounds for clinical use after the onset of cerebral ischaemia.

LF 16-0687 Ms, a bradykinin B2 receptor antagonist, reduces ischemic brain injury in a murine model of transient focal cerebral ischemia

1. Bradykinin promotes neuronal damage and brain edema through the activation of the B(2) receptor. The neuroprotective effect of LF 16-0687 Ms, a B(2) receptor antagonist, has been described when given prior to induction of transient focal cerebral ischemia in rat, but there are no data regarding the consequence of a treatment when given after injury. Therefore, in a murine model of transient middle cerebral artery occlusion (MCAO), we evaluated the effect of LF 16-0687 Ms given prior to and/or after the onset of ischemia on neurological deficit, infarct volume and inflammatory responses including cerebral edema, blood-brain barrier (BBB) disruption and neutrophil accumulation. 2. LF 16-0687 Ms (1, 2 and 4 mg kg(-1)) administered 0.5 h before and, 1.25 and 6 h after MCAO, decreased the infarct volume by a maximum of 33% and significantly improved the neurological recovery. 3. When given at 0.25 and 6.25 h after MCAO, LF 16-0687 Ms (1.5, 3 and 6 mg kg(-1)) decreased the infarct volume by a maximum of 25% and improved the neurological score. 4. Post-treatment with LF 16-0687 Ms (1.5 mg kg(-1)) significantly decreased brain edema (-28%), BBB disruption (-60%) and neutrophil accumulation (-65%) induced by ischemia. Physiological parameters were not modified by LF 16-0687 Ms. 5. These data emphasize the role of bradykinin B(2) receptor in the development of infarct lesion, neurological deficit and inflammatory responses resulting from transient focal cerebral ischemia. Therefore, B(2) receptor antagonist might represent a new therapeutic approach in the pharmacological treatment of stroke.