Preventive role of renal kallikrein-kinin system in the early phase of hypertension and development of new antihypertensive drugs

Are all individuals equally sensitive in the blood pressure to high salt intake? (Review article)

It has been reported that only one-third of normotensive subjects and half of hypertensive patients are salt-sensitive. Many causes of salt-sensitivity have been proposed. Our suggestion is that a reduced urinary kallikrein level may be one cause, since mutant kininogen-deficient rats, which cannot generate kinin in the urine, are salt-sensitive. Renal kallikrein is secreted by the connecting tubule cells of the kidney, which are located just distal to the macula densa or the tubuloglomerular feedback system. Excess amounts of sodium taken overflow into the distal tubules and are reabsorbed in the collecting ducts. Kinins generated inhibit sodium reabsorption in the collecting ducts. Both blacks and whites with essential hypertension excrete less urinary kallikrein than do their normotensive counterparts, but the mean value in "normotensive blacks" were not different from that in "hypertensive whites". African-Americans consume less potassium than whites. Potassium and ATP-sensitive potassium channel blockers are releasers of renal kallikrein. In a small-scale study, sodium loading caused more increase in the systolic blood pressure in urinary low-kallikrein group than in urinary high-kallikrein group. Large-scale clinical studies, under strict control of potassium intake, are needed to elucidate the relationship between salt-sensitivity and urinary kallikrein levels.

Potassium-induced increase in renal kallikrein secretion is attenuated in dissected renal connecting tubules of young spontaneously hypertensive rats

It is suggested that attenuation of the renal kallikrein-kinin system (KKS) involved the development of hypertension in young spontaneously hypertensive rats (SHR). In the present study, a comparison was made between young SHR and Wistar Kyoto rats (WKY) to examine the ability to secrete renal kallikrein from the microdissected connecting tubules (CNT) by potassium or an ATP-sensitive potassium channel blocker, 4-morpholinecarboximidine-N-1-adamantyl-N'-cyclohexylhydrochloride (PNU-37883A), both of which are renal kallikrein secretagogues. Maximum effect of potassium on kallikrein secretion was observed 10 min after placing the tubules at concentration of 20 mM. Kallikrein secretion was also increased concentration-dependently by PNU-37883A (0.1, 1, 10, and 100 microM). In the presence of EDTA, NiCl2, verapamil, xestspongin C (an inositol 1,4,5-trisphosphate (IP3) receptor-selective antagonist), or ruthenium red (a ryanodine-sensitive receptor blocker), potassium-induced increase in renal kallikrein secretion was inhibited. Augmentation of renal kallikrein secretion by potassium or PNU-37883A was diminished in SHR compared to WKY. These results indicate that the ability to secrete renal kallikrein by potassium was attenuated in young SHR compared with WKY. Furthermore, it is suggested that the potassium-induced renal kallikrein secretion requires an extracellular Ca2+ entry through Ca2+ channels including L-type Ca2+ channels and Ca2+ release from intracellular Ca2+ stores through IP3 receptor and ryanodine receptor.

Suppressed angiogenesis in kininogen-deficiencies

We investigated whether the kinin-generating system enhanced angiogenesis in chronic and proliferative granuloma and in tumor-surrounding stroma. In rat sponge implants, angiogenesis was gradually developed in normal Brown Norway Kitasato rats (BN-Ki). The development of angiogenesis was significantly suppressed in kininogen-deficient Brown Norway Katholiek rats (BN-Ka). The angiogenesis enhanced by basic fibroblast growth factor was also significantly less marked in BN-Ka than in BN-Ki. Naturally occurring angiogenesis was significantly suppressed by B(1) or B(2) antagonist. mRNA of vascular endothelial growth factor was more highly expressed in the granulation tissues in BN-Ki than in BN-Ka. Daily topical injections of aprotinin, but not of soy bean trypsin inhibitor, suppressed angiogenesis. Daily topical injections of low-molecular weight kininogen enhanced angiogenesis in BN-Ka. Topical injections of serum from BN-Ki, but not from BN-Ka, also facilitated angiogenesis in BN-Ka. FR190997, a nonpeptide mimic of bradykinin, promoted angiogenesis markedly, with concomitant increases in vascular endothelial growth factor mRNA. Angiogenesis in the granulation tissues around the implanted Millipore chambers containing Walker-256 cells was markedly more suppressed in BN-Ka than in BN-Ki. Our results suggest that endogenous kinin generated from the tissue kallikrein-kinin system enhances angiogenesis in chronic and proliferative granuloma and in the stroma surrounding a tumor. Thus, the agents for the kinin-generating system and/or kinin receptor signaling may become useful tools for controlling angiogenesis.

[Bradykinin antagonist: current status and perspective]

The kallikrein-kinin system plays an important role in many physiological and pathophysiological conditions such as homeostasis of circulation, inflammation/allergy, pain, shock, etc. Two types of kinin receptor are known, bradykinin (BK) B1 receptor and BK B2 receptor. B2 receptors are constitutively expressed and mediate most physiological actions of kinins, whereas B1 receptors are highly inducible upon inflammatory stimulation or tissue injury, suggesting that they are involved in inflammation and/or nociception. Only three peptide type B2 antagonists, NPC 567, CP-0127 and HOE-140, have been evaluated in clinical studies so far, and some beneficial effects of B2 antagonists have been shown for rhinitis, asthma, systemic inflammatory response syndrome/sepsis and brain injury. However, the results were less convincing than expected. Now several potent and orally active nonpeptide B2-receptor antagonists have been found, which are expected to overcome the weak point of the peptide type antagonists and clarify the therapeutic potential of the B2-receptor antagonist for novel indications as well as those mentioned above. As for B1 receptors, no antagonist has been tested in a clinical trial. The important role of B1 receptors is just being elucidated by use of peptide type antagonists or B1 receptor gene knockout mice. The further development of newer B1 antagonists and clinical evaluation is desired.

The kallikrein-kininogen-kinin system: lessons from the quantification of endogenous kinins

The purpose of the present review is to describe the place of endogenous kinins, mainly bradykinin (BK) and des-Arg(9)-BK in the kallikrein-kininogen-kinin system, to review and compare the different analytical methods reported for the assessment of endogenous kinins, to explain the difficulties and the pitfalls for their quantifications in biologic samples and finally to see how the results obtained by these methods could complement and extend the pharmacological evidence of their pathophysiological role.

In vivo transfer of antisense oligonucleotide against urinary kininase blunts deoxycorticosterone acetate-salt hypertension in rats

We have previously reported that the renal kallikrein-kinin system suppressed the development of deoxycorticosterone acetate (DOCA)-salt hypertension. Kinins were degraded in the kidney mainly by carboxypeptidase Y (CPY)-like kininase. Blockade of renal kinin degradation may reduce hypertension in the developmental stage. We constructed an antisense oligonucleotide against rat CPY homologue (5'-CAT-CTC-TGC-TTC-CTT-GTG-TC-3', AS) and its randomized control oligonucleotide (5'-TCC-TTC-CTG-CTT-GAG-TTC-CT-3', RC), and prepared an HVJ-liposome complex that prolongs and increases the effectiveness of the antisense oligonucleotide. Antisense oligonucleotide was transfected (25 nmole rat(-1), in terms of nucleotide) into the kidney from the renal artery. Blood pressure was measured through a catheter inserted into the abdominal aorta. Mean blood pressure (MBP) in DOCA-salt treated (for 2 weeks) Sprague Dawley strain rats was 130+/-3 mmHg (n=11), and was reduced significantly (P<0.05) more by AS transfection (122+/-4 mmHg, n=6) than by RC treatment (137+/-6 mmHg, n=5) 4 days after the transfection. This reduction in MBP was accompanied by increased urinary sodium excretion (AS, 8.4+/-1.5 mmole day(-1); RC, 4.6+/-0.5 mmole day(-1), P<0.05) and a reduction in urinary CPY-like kininase activity. Ebelactone B (5 mg kg(-1), twice a day, p.o.), an inhibitor for urinary CPY-like kininase, also reduced MBP and induced natriuresis to the same degree as AS. Lisinopril, an inhibitor for angiotensin converting enzyme (ACE) failed to reduce the elevated MBP. These results suggest that CPY-like kininase may have more contribution than ACE to degrade kinin in the kidney, and that knockdown of CPY-like kininase in the kidney may partly prevent rat DOCA-salt hypertension.

A nonpeptide mimic of bradykinin blunts the development of hypertension in young spontaneously hypertensive rats

We tested whether FR190997, a nonpeptide B(2) agonist, prevented the development of hypertension in young spontaneously hypertensive rats (SHR), which secrete less kallikrein into the urine than do Wistar-Kyoto rats. An intra-arterial (IA) injection of FR190997 (0.3 to 30 nmol/kg) caused dose-dependent hypotension in conscious Sprague-Dawley rats. Although the maximum hypotensive potency of FR190997 equaled that of bradykinin, its action lasted approximately 10 times as long. Hoe140 (100 nmol/kg IA) significantly blocked the hypotensive response induced by FR190997 (10 nmol/kg). Atropine (100 nmol/kg IA) did not affect this response. A selective infusion of FR190997 into the renal artery induced natriuresis and diuresis in anesthetized rabbits. A continuous infusion (2 nmol. 10 mL(-1). h(-1) per rat) of FR190997 into the abdominal aorta of young SHR (6 weeks old, n=6) for 6 days significantly (P<0.05) reduced mean blood pressure to 114+/-6 (day 2) and 110+/-6 (day 5) mm Hg, from 149+/-7 and 162+/-6 mm Hg, respectively, in vehicle-infused rats (n=6). At 8 days after continuous infusion (day 14), mean blood pressure (148+/-5 mm Hg) in FR190997-infused rats remained significantly (P<0. 05) lower than that in vehicle-infused rats (190+/-6 mm Hg), almost the peak value. The mesenteric artery isolated from FR190997-treated rats (day 14) had lower contractile sensitivity to norepinephrine than that from vehicle-treated rats. These results suggested that the continuous infusion of a nonpeptide B(2) agonist may prevent hypertension if performed in the critical phase.

Facilitation of renal kallikrein-kinin system prevents the development of hypertension by inhibition of sodium retention

We have previously reported that the renal kallikrein-kinin system suppressed the development of hypertension, using kininogen deficient Brown Norway Katholiek rats. Kinins were degraded in urine mainly by carboxypeptidase Y-like kininase (CPY). Blockade of renal kinin degradation may prevent the experimental hypertension through the facilitation of the renal kallikrein-kinin system. Daily administration of ebelactone B (EB), which is isolated from Actinomycetes and strongly inhibits CPY, from the first day of deoxycorticosterone acetate (DOCA)-salt treatment for 4 weeks completely blocked hypertension in Sprague-Dawley rats. This treatment reduced sodium levels in erythrocytes and cerebrospinal fluids (CSF) significantly. By contrast, an ACE inhibitor, lisinopril did not prevent hypertension. The development of hypertension in young spontaneously hypertensive rats was also blunted by EB with reductions in sodium levels in erythrocytes and in CSF. The arterial kinin levels in rats undergoing DOCA-salt treatment were 2.2 +/- 0.2 pg/ml, which were increased significantly to 4.6 +/- 0.4 pg/ml with captopril (10 mg/kg, s.c.). The increased kinin levels were less than those to show hypotension. EB did not increase the arterial kinin levels, with significant increase in urinary kinin secretion. These results suggested that facilitation of the renal kallikrein-kinin system by inhibition of kinin degradation on the luminal side of the renal tubules may effectively prevent hypertension.

A secretory mechanism of renal kallikrein by a high potassium ion; a possible involvement of ATP-sensitive potassium channel

A relatively rapid excretion of urinary kallikrein into urine was observed by an intravenous infusion of high potassium in anesthetized rats. Superfusion of sliced cortex isolated from rat kidney with an isotonic solution containing more than 20 mM of KCl significantly stimulated the release of kallikrein. The latter in vitro result supported another mechanism for the release of renal kallikrein from kidney other than biosynthesis of kallikrein by aldosterone released from adrenal cortex after loading of high potassium and the mechanism was elucidated. ATP-sensitive potassium channel blockers, glibenclamide, 4-morpholinecarboximidine-N-1-adamantyl-N'-cyclohexylhydr ochloride (U37883A), and barium chloride, which inhibit an efflux of intracellular potassium to block the channel, showed a significant increase of the kallikrein release from the slice of kidney cortex. Cytochalasin B, which inhibits a polymerization of actin, also showed a stimulation of the release. Enhanced release of kallikrein by a high potassium or ATP-sensitive potassium channel blocker was reduced by the absence of calcium ion and the presence of voltage-dependent calcium channel blocker in the superfused solution. These results indicate the ATP-sensitive potassium channel which couples to voltage-dependent calcium channel and cytoskeletal protein could be involved in a rapid secretory mechanism of renal kallikrein by high potassium.