Antisense inhibition of the brain kallikrein-kinin system

Involvement of prolylcarboxypeptidase in the effect of rutaecarpine on the regression of mesenteric artery hypertrophy in renovascular hypertensive rats

1. Previous studies indicate that rutaecarpine blocks increases in blood pressure and inhibits vascular hypertrophy in experimentally hypertensive rats. The aim of the present study was to determine whether the effects of rutaecarpine are related to activation of prolylcarboxypeptidase (PRCP). 2. Renovascular hypertensive rats (Goldblatt two-kidney, one-clip (2K1C)) were developed using male Sprague-Dawley rats. Chronic treatment with rutaecarpine (10 or 40 mg/kg per day) or losartan (20 mg/kg per day) for 4 weeks to the hypertensive rats caused a sustained dose-dependent attenuation of increases in blood pressure, increased lumen diameter and decreased media thickness, which was accompanied by a similar reduction in the media cross-sectional area : lumen area ratio in mesenteric arteries compared with untreated hypertensive rats. 3. Angiotensin (Ang) II expression was significantly increased in mesenteric arteries of hypertensive rats compared with sham-operated rats. No significant differences in plasma AngII levels were observed between untreated hypertensive and sham-operated rats. Hypertensive rats treated with high-dose rutaecarpine had significantly decreased Ang II levels in both the plasma and mesenteric arteries. 4. Expression of PRCP protein or kallikrein mRNA was significantly inhibited in the right kidneys and mesenteric arteries of hypertensive rats. However, expression of PRCP protein and kallikrein mRNA was significantly increased after treatment with rutaecarpine or losartan (20 mg/kg per day). 5. The data suggest that the repression of increases in systolic blood pressure and reversal of mesenteric artery remodelling by rutaecarpine may be related to increased expression of PRCP in the circulation and small arteries in 2K1C hypertensive rats.

Mechanisms of Disease: the tissue kallikrein–kinin system in hypertension and vascular remodeling

The pathogenesis of arterial hypertension often involves a rise in systemic vascular resistance (vasoconstriction and vascular remodeling) and impairment of salt excretion in the kidney (inappropriate salt retention despite elevated blood pressure). Experimental and clinical evidence implicate an imbalance between endogenous vasoconstrictor and vasodilator systems in the development and maintenance of hypertension. Kinins (bradykinin and lys-bradykinin) are endogenous vasodilators and natriuretic peptides known best for their ability to antagonize angiotensin-induced vasoconstriction and sodium retention. In humans, angiotensin-converting enzyme inhibitors, a potent class of antihypertensive agents, lower blood pressure at least partially by favoring enhanced kinin accumulation in plasma and target tissues. The beneficial actions of kinins in renal and cardiovascular disease are largely mediated by nitric oxide and prostaglandins, and extend beyond their recognized role in lowering blood pressure to include cardioprotection and nephroprotection. This article is a review of exciting, recently generated genetic, biochemical and clinical data from studies that have examined the importance of the tissue kallikrein-kinin system in protection from hypertension, vascular remodeling and renal fibrosis. Development of novel therapeutic approaches to bolster kinin activity in the vascular wall and in specific compartments in the kidney might be a highly effective strategy for the treatment of hypertension and its complications, including cardiac hypertrophy and renal failure.

Bradykinin receptors as a therapeutic target

Biologically-active kinins, including bradykinin (BK) and Lys(0)-BK (kallidin), are short-lived peptide mediators predominantly generated by the enzymatic action of kallikreins on kininogen precursors. A diverse spectrum of physiological and pathological actions attributed to local kinin production is a consequence of the activation of G-protein-coupled receptors (GPCRs). Currently, two major subtypes of kinin receptor, designated B(1) and B(2), are recognised, although there is much evidence for pharmacological heterogeneity, particularly within the B(2) receptors. Considering these facts and the widespread distribution of kinin receptors in many human tissues, it is no surprise that the therapeutic potential of kinins and kinin receptor antagonists remains the focus of numerous investigations. Studies in animals and animal tissues, instrumental in elucidating the biological roles of kinins, are well-documented in numerous excellent reviews. Unfortunately, and despite the enormous potential illustrated by animal studies, attempts to develop kinin analogues as therapeutic agents to combat human disease have largely proven disappointing. Consequently, this review selectively focuses upon studies that are directly relevant to the targeting of human BK receptors as a therapeutic intervention. In addition to providing a succinct review of well-documented pathological conditions to which kinin receptors contribute, the authors have also included more recent data that illustrate new avenues for the therapeutic application of kinin analogues.

Kinin B2 receptor localization and expression in the hypothalamo-pituitary-adrenal axis of spontaneously hypertensive rats

OBJECTIVE

An enhanced hypothalamo-pituitary-adrenocortical (HPA) activity has been demonstrated during onset of high blood pressure in spontaneously hypertensive rats (SHR). Furthermore, compared to normotensive Wistar-Kyoto (WKY) rats, SHR show hypersensitivity to bradykinin (BK)-induced pressor responses which may be caused by an upregulation of B(2) receptor expression in the brain.

METHODS

We performed an immunohistochemical localization and measured gene expression of B(2) receptors in the hypothalamus, pituitary and adrenal glands of SHR at three ages corresponding to the development of hypertension, i.e. prehypertensive phase, onset of hypertension and established hypertension. Using reverse transcriptase polymerase chain reaction (RT-PCR) and Western blot technique, B(2) receptor mRNA and protein levels, respectively, were measured.

RESULTS

A specific immunostaining for B(2) receptors was observed in the hypothalamic nuclei paraventricularis (PVN) and supraopticus (SON). In the pituitary and adrenal glands, a strong immunostaining was observed in neurohypophysis (NH) and adrenal medulla, respectively. At all ages tested, B(2) receptor mRNA and protein levels were higher in the hypothalamus and adrenal glands of SHR compared to age-matched WKY rats. Among SHR, the mRNA level was increased in neurohypophysis with age, and no difference was found in the adenohypophysis (AH) between SHR and WKY rats.

CONCLUSION

The data demonstrate a specific localization and an upregulation of B(2) receptor expression in the hypothalamus and adrenal glands of SHR, providing an anatomical and molecular basis for a possible contributory role to bradykinin-induced hypersensitivity of cardiovascular responses. The increased B(2) receptor expression in the hypothalamus and adrenal glands may also play a role in the abnormalities of the HPA axis in SHR during the development of hypertension.

Central control mechanisms of circulation in the medulla oblongata by nitric oxide

Nitric oxide (NO) is involved in numerous physiological functions. Besides its role as an endothelium-dependent relaxing factor (EDRF), NO inhibits platelet aggregation, contributes to cytotoxicity against bacteria, is active in synaptic transmission within the brain, etc. NO synthase (NOS) is distributed in brain regions related to the regulation of cardiovascular functions. NO has been inferred not only to act directly on vascular vessels, but also to regulate circulation within the brain. In this review paper, we mainly consider the functions of NO in the cardiovascular center of the medulla oblongata. That is, we describe the anatomical distribution of NOS in the brain, effects of intravenous and intracerebroventricular administration of NOS inhibitors on the circulation, effects of microinjection of NO donors and NOS inhibitors into the nucleus tractus solitarius (NTS) and ventrolateral medulla (VLM), the results of electrophysiological studies on these areas, and finally, the data obtained by new molecular biological techniques.

The bradykinin B1 receptor and the central regulation of blood pressure in spontaneously hypertensive rats

1. We evaluated if the brain bradykinin (BK) B1 receptor is involved in the regulation of blood pressure (BP) in conscious rats. 2. Basal mean BP and HR were 115 +/- 2 and 165 +/- 3 mmHg and 345 +/- 10 and 410 +/- 14 beats min in Wistar Kyoto (WKY) and spontaneously hypertensive rats (SHR), respectively. Intracerebroventricular (i.c.v.) injection of 1 nmol B1 receptor agonist Lys-desArg9-BK significantly increased the BP of WKY and SHR by 7+/-1 and 19+/-2 mmHg, respectively. One nmol Sar[D-Phe8]-desArg9-BK, a kininase-resistant B1 agonist, increased the BP of WKY and SHR by 19+/-2 and 17+/-2 mmHg, respectively and reduced HR in both strains. 3. I.c.v. injection of 0.01 nmol B1 antagonists, LysLeu8-desArg9-BK or AcLys[D-betaNal7,Ile8]-desArg9-BK (R715), significantly decreased mean BP in SHR (by 9+/-2 mmHg the former and 14+/-3 mmHg the latter compound), but not in WKY. In SHR, the BP response to R715 was associated to tachycardia. 4. I.c.v. Captopril, a kininase inhibitor, increased the BP of SHR, this response being partially prevented by i.c.v. R715 and reversed into a vasodepressor effect by R715 in combination with the B2 antagonist Icatibant. 5. I.c.v. antisense oligodeoxynucleotides (ODNs) targeted to the B1 receptor mRNA decreased BP in SHR, but not in WKY. HR was not altered in either strain. Distribution of fluorescein-conjugated ODNs was detected in brain areas surrounding cerebral ventricles. 6. Our results indicate that the brain B1 receptor participates in the regulation of BP. Activation of the B1 receptor by kinin metabolites could participate in the pathogenesis of hypertension in SHR.

Brain as a unique antisense environment

During the last few years, antisense oligodeoxyribonucleotides (asODN) have become a commonly used tool for blocking of gene expression in the mammalian central nervous system. Successful gene inhibition has been reported for such diverse targets as those encoding neurotransmitter receptors, neuropeptides, trophic factors, transcription factors, cytokines, transporters, ion channels, and others. This review presents a discussion of recent studies on ODN in the brain, with a focus on specific approaches taken by the researchers in this field and especially on peculiar features of this organ as a milieu for asODN action. It is concluded that from the presented literature survey no coherent view on how to rationally design ODN for brain studies has emerged.

Fluorescent and biotinylated probes for B2 bradykinin receptors: agonists and antagonists

Peptide ligands carrying additional reporter groups are valuable research tools to facilitate biochemical and pharmacological studies of G protein-coupled receptors. B2 bradykinin receptors, widely distributed in mammalian tissues, regulate many physiological systems and are therapeutic targets. Acylation of the amino-terminus of bradykinin (BK) and a B2a-selective antagonist produced ligands derivatized with biotinamidocaproate or 7-Amino-4-methylcoumarin-3-acetate. These fluorescent and biotinylated peptides bound with high affinity to bovine and rodent B2 receptors. Analysis of second messenger production confirmed that fluorescent and biotinylated analogs of BK were B2 receptor agonists whereas derivatives of DArg0[Hyp3,DPhe7,Leu8]BK were BK receptor antagonists. The complimentary properties of these selective receptor probes will be useful in studying B2 receptor localization, expression and desensitization.

Central delivery of human tissue kallikrein gene reduces blood pressure in hypertensive rats

The human tissue kallikrein gene, in the form of naked DNA (CMV-cHK) or an adenoviral vector (Ad.CMV-cHK), was directly delivered by intracerebroventricular injection into spontaneously hypertensive rats. Control rats received the same amount of vector DNA (pcDNA3) or adenoviral vector (Ad.CMV-LacZ) carrying the lacZ gene. A single injection of the human tissue kallikrein gene caused a rapid and prolonged blood pressure-lowering effect that began 1 day post injection and the effect lasted for more than 7 days. The expression of human tissue kallikrein and its mRNA was identified in the cortex, cerebellum, brain stem, hippocampus and hypothalamus. Cellular localization of beta-galactosidase was detected by X-gal staining in the thalamus, hypothalamus and third ventricle in rats injected with Ad.CMV-LacZ. This suggests that the tissue kallikrein-kinin system may function in the central control of blood pressure homeostasis.

Kinin receptors

Rapid developments are expected in the molecular pharmacology of both B1, and B2 types of kinin receptors, since the underlying genetic structures are now known and widely studied. The consequences of kinin receptor duality and physiopathological regulation have not yet been fully appreciated. Medicinal chemistry is also an active front of research in kinin pharmacology, as more effective drugs targeted at kinin receptors are regularly reported. Various complementary molecular approaches (the receptor binding, cloning, immunoreacting, mutagenesis, inactivation, the study of regulation, allelic polymorphisms, and so forth) are expanding our knowledge of the role of kinins in allergy, inflammation, and singularly, renal medicine.