Altered urinary excretion of aquaporin 2 in IgA nephropathy

OBJECTIVE

The intrarenal renin-angiotensin system (RAS) activation plays a pivotal role in immunoglobulin A nephropathy (IgAN) pathogenesis, which is still largely undefined. Recently, vasopressin (AVP) has been advocated to contribute to the genesis and progression of chronic kidney diseases (CKD) directly, and indirectly, via RAS activation. Our aim is to explore the intrarenal activity of AVP, its relationship with RAS activity, as well as its modulation by therapies in IgAN.

DESIGN

In this observational study, we measured plasma copeptin, a surrogate marker of AVP, the urine excretion of aquaporin 2 (AQP2), a protein reflecting renal AVP action, and angiotensinogen (AGT), a parameter of renal RAS activation, and their relationship with renal function in 44 IgAN patients at the time of renal biopsy, without any drug therapy, and after 6-month treatment with ACEi or steroid+ACEi. Twenty-one patients with other CKD and 40 healthy subjects were recruited as controls.

METHODS

ELISAs were used to measure all variables of interest.

RESULTS

At baseline, IgAN patients showed higher urinary levels of AQP2, compared with controls and patients with other CKD. Urinary AQP2 and AGT levels strongly correlated with the presence of arterial hypertension. Steroids+ACEi caused the decrease of all the variables examined. The fall of urinary AQP2 and AGT following drug treatments was associated with the decrease of daily proteinuria.

CONCLUSION

Our findings would support the involvement of AVP-AQP2 axis, interacting with the RAS, in the progression of IgAN and candidate AQP2 as a possible novel marker of the disease.

Rat tissue kallikrein releases a kallidin-like peptide from rat low-molecular-weight kininogen

The kallikrein-kinin system is subdivided into the plasma and tissue-kallikrein-kinin system, with bradykinin (BK) and kallidin (KAL) (Lys(0)-bradykinin) as functional peptides. This occurs in both humans and other mammals. Both peptides are released by plasma and tissue-kallikrein. BK, but not KAL, has been detected in rats until now. One can explain this observation by the structural differences found in the sequence of rat high- and low-molecular kininogen containing an Arg-residue instead of a Lys-residue in front of the N-terminus of the BK sequence. Nevertheless, we were able to measure a kallidin-like peptide (KLP), in rat plasma and urine, using a specific KAL antiserum. In order to confirm our data, we isolated low-molecular-weight kininogen from rat plasma and incubated it with purified rat glandular kallikrein. The generated peptide was retained on a high-pressure liquid chromatography column and displaced by an excess of angiotensin I. The KLP-containing fraction was identified with the KLP radioimmunoassay. A specific ion signal with a mass to charge ratio (m/z) of 1216.73 was detected with matrix-assisted laser desorption/ionization mass spectrometry. As proposed earlier, the structure of this peptide is Arg(1)-KAL, instead of Lys(1)-KAL. The structural similarity between the Lys- and the Arg-residue explains the high crossreactivity (80%) of KLP with the specific KAL antibody. The incubation of KLP with angiotensin-converting enzyme yields two molecules with masses of 913.4 and 729.3 containing the sequence H-Arg-Arg-Pro-Pro-Gly-Phe-Ser-Pro-OH and H-Arg-Arg-Pro-Pro-Gly-Phe-OH. The enzymatic cleavage could be inhibited by captopril. The data suggest that in rats, as in other mammals, the tissue kallikrein-kinin system mediates its physiological effects via a kallidin-like peptide, which is Arg(1)-kallidin (Arg(0)-bradykinin).

Effect of acute hyperglycaemia on sodium handling and excretion of nitric oxide metabolites, bradykinin, and cGMP in Type 1 diabetes mellitus

AIMS

The aim of this study was to evaluate the effect of acutely induced hyperglycaemia on renal sodium handling and to explore the role of the bradykinin-nitric oxide-cGMP signalling pathway.

PATIENTS AND METHODS

We compared 20 Type 1 diabetic (DM1) patients without microalbuminuria with 15 weight-, age-, and sex-matched healthy controls (C). Clearances of para-aminohippuric acid (CPAH), inulin (Cin), lithium, sodium, and urinary nitrite/nitrate (NOx), cGMP and bradykinin excretion rates were measured in two 90-min periods: a glycaemic clamp-induced euglycaemia (5 mmol/l-period I) and hyperglycaemia (12 mmol/l-period II) (Study 1) and during time-controlled euglycaemia (5 mmol/l-period I and 5 mmol/l-period II) to avoid the effects of time and volume load (Study 2).

RESULTS

Cin and CPAH were not significantly different during euglycaemia (period I of Study 1) in DM1 and controls, whereas fractional excretion of sodium was decreased in DM1 (1.84 +/- 0.75 vs. 2.36 +/- 0.67%; P < 0.05) due to an increase in fractional distal tubular reabsorption of sodium (94.01 +/- 1.94 vs. 92.24 +/- 2.47%; P < 0.05). A comparison of changes during Study 1 and Study 2 revealed acute hyperglycaemia did not change renal haemodynamics significantly, while fractional distal tubular reabsorption of sodium increased (DM1: P < 0.05; C: P < 0.01) and fractional excretion of sodium decreased (P < 0.01) in both groups. The urinary excretion rates of NOx were comparable during euglycaemia in DM1 and C. While in C, they significantly increased during Study 1 (period I: 382 +/- 217 vs. period II: 515 +/- 254 nmol/min; P < 0.01) and Study 2 (period I: 202.9 +/- 176.8 vs. period II: 297.2 +/- 267.5 nmol/min; P < 0.05) as a consequence of the water load, no changes were found in DM1. The urinary excretion of bradykinin was lower in DM1 compared with C (0.84 +/- 0.68 vs. 1.20 +/- 0.85 micro g/min; P < 0.01) during euglycaemia; it was not affected by hyperglycaemia. There were no significant differences between DM1 and C and in cGMP urinary excretion rates following hyperglycaemia.

CONCLUSION

This study demonstrates that DM1 without renal haemodynamic alterations is associated with impaired renal sodium handling. Moreover, we did not find a relationship between the renal excretion rates of vasoactive mediators and sodium handling due to hyperglycaemia.

Regulatory effects of salt diet on renal renin-angiotensin-aldosterone, and kallikrein-kinin systems

The interaction of the renin-angiotensin-aldosterone system (RAAS) and the kallikrein-kinin system (KKS) was investigated in rats fed on a low, normal, and high-salt diet for 2 weeks. At the beginning of the second week, either a B2-receptor antagonist (icatibant), or an AT1-receptor antagonist (losartan), or an aldosterone receptor antagonist (spironolactone) was applied via osmotic pump delivering a constant amount of drug for 7 days. The urinary bradykinin (BK) levels corresponded with increasing NaCl diet and the activity of urinary kallikrein. However, in agreement with other investigators we found a down-regulation of the renal kallikrein gene expression in response to an increasing NaCl diet. Renal kinins are able to stimulate the renal kallikrein expression as well as the renal excretion of active kallikrein via the B2-receptor. The release of renal kallikrein is also mediated by angiotensin II (AngII). After high-salt diet the blood pressure was significantly increased. Losartan and spironolactone were not effective in reducing this increase, as AngII and aldosterone should be low during high-salt diet. However, low-salt diet also yielded an increase in blood pressure, which, however, could be abolished following losartan infusion. The data suggest that the expression of renal kallikrein mRNA is mainly regulated by dietary salt intake. However, kinins are able to stimulate the kallikrein gene expression, as well as the renal kallikrein release. Angll mediates only a stimulatory effect on the urinary kallikrein release. In contrast to the general belief, our data support the opinion that low-salt diet is able to mediate an increase in blood pressure, as the RAAS is stimulated in response to a marked salt deficiency.

Increased activity of the renal kallikrein-kinin system in autosomal dominant polycystic kidney disease in rats, but not in humans

The kallikrein-kinin system (KKS) was investigated in autosomal dominant polycystic kidney disease (ADPKD)-affected rats (PKD) and compared to unaffected controls (SD) and 5/6 nephrectomized rats (5/6 Nx). In addition, patients with ADPKD compared to patients with nonpolycystic kidney disease and healthy controls have been investigated. Plasma and urine samples for determination of creatinine, protein, kallikrein (KAL) and bradykinin (BK) were taken in male 3- and 9-month-old PKD, SD and 9-month-old 5/6 Nx. The same parameters were determined in young (age: 20-40 years) and old (41-65 years) male patients with ADPKD and compared to age-matched patients with nonpolycystic kidney disease and age-matched healthy controls. Plasma and urine KAL were measured by chromogenic peptide substrate, and kininswere determined by radioimmunoassay. Urine KAL and BK levels were increased i n PKD compared to age-matched SD. No differences with respect to serum KAL were found between PKD and SD. In 5/6 Nx, urinary BK levels showed a trend towards higher compared to old SD (p = 0.06). KAL and BK were not increased in serum and urine of patients with ADPKD, in contrast to rats. Urinary KAL excretion was reduced in patients with ADPKD and advanced renal failure. Our results demonstrate an age-dependent activation of the renal KKS in rats with ADPKD, whereas the KKS is not activated in patients with ADPKD and advanced renal failure. These data indicate that there are fundamental differences in the factors influencing the course of the disease in human and rat ADPKD.

Determination of bradykinin in rat urine by coupled-column high pressure liquid chromatography with precolumn derivatization with a water-soluble fluorogenic reagent

Bradykinin (BK) in rat urine was determined by coupled-column HPLC with precolumn fluorogenic derivatization with a water-soluble reagent, 3-(7-fluoro-2,1,3-benzoxadiazole-4-sulfonamido)benzenesulfonic acid (m-BS-ABD-F). The derivatization of BK with m-BS-ABD-F was completed at 70 degrees C for 100 min and gave only a single peak of BK derivative in addition to the peaks of the blank. The hydrophilicity of the derivatization reagent effectively prevented the adsorption of BK during the sample pretreatment and improved the recovery of BK. Good linearity was shown between the amount of BK spiked in urine (0-10 pmol) and the peak area of the BK derivatives (correlation coefficients >0.999), and the detection limits of the BK derivative were 35 fmol (S/N = 3). The precisions (cv, %) of intra- and interday assay were not more than 5.5% and the accuracies were in the range of 95.3-111% (1 and 5 pmol of BK in urine, n = 3). Although the peak regarded as that of the BK derivative rapidly decreased after incubation at 37 degrees C, addition of urinary kininase inhibitors to the urine samples drastically suppressed the decrease of this peak, confirming that the identified peak was that of the BK derivative. The urinary kinin excretion in male SD rats (9-11 weeks old) determined by the present method was 56.0 +/- 22.1 pg/min/kg (mean +/- SE, n = 5).

Kinins in humans

The kinin peptide system in humans is complex. Whereas plasma kallikrein generates bradykinin peptides, glandular kallikrein generates kallidin peptides. Moreover, a proportion of kinin peptides is hydroxylated on proline(3) of the bradykinin sequence. We established HPLC-based radioimmunoassays for nonhydroxylated and hydroxylated bradykinin and kallidin peptides and their metabolites in blood and urine. Both nonhydroxylated and hydroxylated bradykinin and kallidin peptides were identified in human blood and urine, although the levels in blood were often below the assay detection limit. Whereas kallidin peptides were more abundant than bradykinin peptides in urine, bradykinin peptides were more abundant in blood. Bradykinin and kallidin peptide levels were higher in venous than arterial blood. Angiotensin-converting enzyme inhibition increased blood levels of bradykinin, but not kallidin, peptides. Reactive hyperemia had no effect on antecubital venous levels of bradykinin or kallidin peptide levels. These studies demonstrate differential regulation of the bradykinin and kallidin peptide systems, and indicate that blood levels of bradykinin peptides are more responsive to angiotensin-converting enzyme inhibition than blood levels of kallidin peptides.

Inhibition of kinin degradation on the luminal side of renal tubules reduces high blood pressure in deoxycorticosterone acetate salt-treated rats

1. To determine whether the antihypertensive response in deoxycorticosterone acetate (DOCA) salt-treated rats was mediated by kinins on the luminal side of renal tubules or in the circulation, selective urinary kininase inhibitors were administered to normal Brown Norway Kitasato (BN-Ki) rats and kininogen-deficient Brown Norway Katholiek (BN-Ka) rats. 2. Kinins were degraded by neutral endopeptidase (NEP) and carboxypeptidase Y-like kininase (CPY) in urine, but were inactivated mainly by angiotensin-converting enzyme (ACE) in the plasma. 3. Ebelactone B inhibited CPY, while poststatin inhibited CPY and NEP. 4. Daily administration of poststatin (5 mg/kg per day, s.c.) for 3 days reduced blood pressure (BP) in DOCA salt-treated BN-Ki rats, but not in BN-Ka rats. 5. Ebelactone B (5 mg/kg per day, s.c.) also reduced BP in BN-Ki rats, which was accompanied by increased urinary sodium excretion, but had no effect on BP in BN-Ka rats. 6. Lisinopril (5 mg/kg per day, s.c.) had no effect on BP in either rat strain. 7. Arterial kinin levels in BN-Ki rats increased significantly (2.2-4.6 pg/mL) with captopril (10 mg/kg, s.c.). However, arterial kinin levels that induced hypotension following the infusion of bradykinin (1000 ng/kg per min, i.v.) were 110-fold higher than endogenous arterial kinin levels attained following captopril. 8. These results suggest that inhibition of kinin degradation on the luminal side of the renal tubules may effectively attenuate hypertension.

Is bradykinin a mediator of renal neuropeptide Y effects?

We have previously reported that the bradykinin receptor antagonist icatibant attenuates the neuropeptide-Y-induced diuresis and natriuresis in anaesthetized rats (Am J Physiol 275:F502-F509, 1998). Therefore, we have now determined whether bradykinin mimics tubular responses to neuropeptide Y in acutely pentobarbital-anaesthetized rats. Infusion of the neuropeptide Y receptor agonist peptide YY (2 micrograms kg-1 min-1) enhanced diuresis and natriuresis approximately equal to 2- and 4-fold, respectively, but did not increase urinary bradykinin excretion. Intrarenal infusion of bradykinin (100 ng kg-1 min-1) reduced renal blood flow by approximately equal to 12% and this was abolished by concomitant administration of icatibant (200 ng kg-1 min-1). However, intrarenal bradykinin infusion did not affect creatinine clearance, urine flow rate or sodium excretion (basal values: 0.8 ml min-1, 111 microliters/15 min and 7.7 mumol/15 min, respectively). These data do not support our original hypothesis that bradykinin mediates the renal effects of neuropeptide Y.

Effects of neutral endopeptidase inhibition and combined angiotensin converting enzyme and neutral endopeptidase inhibition on angiotensin and bradykinin peptides in rats

The combination of neutral endopeptidase 24.11 (NEP) and angiotensin converting enzyme (ACE) inhibition is a candidate therapy for hypertension and cardiac failure. Given that NEP and ACE metabolize angiotensin (Ang) and bradykinin (BK) peptides, we investigated the effects of NEP inhibition and combined NEP and ACE inhibition on the levels of these peptides. We administered the NEP inhibitor ecadotril (0, 0.1, 1, 10, 100 mg/kg per day), either alone or together with the ACE inhibitor perindopril (0.2 mg/kg per day), to rats by 12 hourly gavage for 7 days. Ecadotril produced diuresis, natriuresis, increased urine cyclic guanosine monophosphate and BK-(1-9) levels, increased Ang II and Ang I levels in plasma, and increased Ang I levels in heart. Perindopril reduced Ang II levels in kidney, and increased BK-(1-9) levels in blood, kidney and aorta. Combined NEP/ACE inhibition produced the summation of these effects of separate NEP and ACE inhibition. In addition, perindopril potentiated the ecadotril-mediated diuresis, natriuresis and decrease in urine BK-(1-7)/BK-(1-9) ratio, which is an index of BK-(1-9) metabolism. Moreover, combined NEP/ACE inhibition increased Ang II levels in plasma and lung. These data indicate that summation of the effects of separate NEP and ACE inhibition provides the basis for the therapeutic efficacy of their combination. Whereas potentiation by perindopril of the diuretic and natriuretic effects of ecadotril may contribute to the therapeutic effects, increased Ang II levels in plasma and lung may compromise the therapeutic effects of combined NEP/ACE inhibition.

Low-salt diet downregulates plasma but not tissue kallikrein-kinin system

The kallikrein-kinin system (KKS) is involved in the regulation of blood pressure and in the sodium and water excretion. In humans, the KKS is divided functionally into a plasma KKS (pKKS) generating the biologically active peptide bradykinin and into the tissue (glandular) KKS (tKKS) generating the active peptide kallidin. The objective of this study was to examine the effect of a low-NaCl diet on the concentration of both pKKS and tKKS in plasma and urine in 10 healthy volunteers. After a 4-day low-NaCl diet, the urinary sodium and chloride excretions had decreased from 234 to 21.2 mmol/24 h and from 198 to 14.6 mmol/24 h, respectively. The plasma levels of ANG I, aldosterone, and angiotensin converting enzyme (ACE) significantly increased from 50.4 to 82.8 pg/ml, from 129 to 315 pg/ml, and from 46.4 to 59.8 U/ml, respectively, demonstrating the physiological adjustment to the low-salt diet. In plasma, the levels of bradykinin and plasma kallikrein had significantly decreased from 13.7 to 7.57 pg/ml and 14.4 to 7.13 U/ml, respectively. However, the levels of high-molecular-weight kininogen (HMW kininogen) remain unchanged (101 vs. 112 microg/ml, not significant). Contrary to plasma kallikrein, the plasma levels of tissue kallikrein increased (0.345 vs. 0.500 U/ml; P < 0.01). The plasma kallidin levels, however, did not change (64.7 vs. 68.6 pg/ml, not significant). This can be explained by a simultaneous decrease in the plasma low-molecular-weight kininogen (LMW kininogen) levels (89.9 vs. 44.4 microg/ml; P < 0.05). As in plasma, we find increased urinary concentrations of renal (tissue) kallikrein (23.3 to 42.8 U/24 h; P < 0.05) that contrast with, and are presumably counterbalanced by, urinary LMW kininogen levels (77.0 vs. 51.8 microg/24 h; P < 0.05). Consequently, in urine low-NaCl diet caused no significant change in either bradykinin or kallidin (9.2 vs. 10.8 microg/24 h, and 10.9 vs. 10.3 microg/24 h). It is concluded that the stimulation of the renin-angiotensin system on a low-NaCl diet is associated with a decrease in pKKS (bradykinin and plasma kallikrein) but not in tissue and renal KKS. Although tissue kallikrein is increased, there is no change in kallidin, as LMW kininogen in plasma and urine is decreased. These data suggest a difference in the regulation of pKKS and tKKS by low-salt diet.

Role of the renal kallikrein-kinin system in the development of hypertension

Role of renal kallikrein-kinin system has been studied using mutant Brown-Norway Katholiek (BN-Ka) rats, in which both high- and low-molecular weight kininogens were almost absent in plasma and kinin in urine was mainly not detectable. Mutant BN-Ka rats were very sensitive to increased salt intake, resulting in raised systemic blood pressure that is linked to reduced urinary excretion of sodium, when compared with normal BN-Kitasato (BN-Ki) rats. Consequently, sodium accumulated in erythrocytes and cerebrospinal fluid in mutant BN-Ka rats. Subcutaneous infusion of angiotensin II (20 mg/day/rat) also enhanced the concentration of sodium in erythrocytes and in cerebrospinal fluid and increased the systemic pressure by releasing aldosterone. A 4-day infusion of 0.3 M sodium solution (6 ml/kg/h) to the abdominal aorta of conscious and un-restrained mutant BN-Ka rats increased the pressor responses of the arterioles to norepinephrine and angiotensin II (i.a.) by 30- and 10-fold, respectively. Infusion of ebelactone B, (a selective inhibitor of carboxypeptidase Y-like exopeptidase, a kininase in rat urine), to normal BN-Ki rats during induction of hypertension with DOCA and salt, resulted in the reduction of the raised blood pressure, indicating that a site of action of kinins was at the luminal membrane of the renal tubule cells. Our results support the view that the role of renal kallikrein-kinin system is to excrete 'excess sodium' and a reduction in the generation of renal kinins may be a factor in the development of hypertension as a result of the sodium accumulation in the body.

Na-K-ATPase along rat nephron after subtotal nephrectomy: effect of enalapril

Tubular overwork is thought to be a promoter of the tubular hypertrophy and renal failure that occur in response to renal mass reduction. Because Na-K-adenosinetriphosphatase (Na-K-ATPase) is an index of tubular work, we evaluated the effects of subtotal nephrectomy and of enalapril therapy, which delays the evolution of renal lesions, on tubular hypertrophy and Na-K-ATPase activity along the rat nephron. Within 6 wk, 70% reduction of renal mass engendered hypertrophy of the proximal convoluted tubule (PCT), thick ascending limb (TAL), and collecting duct (CD), as well as parallel increments in Na-K-ATPase activity per millimeter tubule length (Na-K-ATPase activity per unit surface area was not modified by subtotal nephrectomy). Chronic enalapril therapy prevented part of the hypertrophy (but not Na-K-ATPase stimulation) of the PCT and the whole stimulation of Na-K-ATPase (but not hypertrophy) in the CD, whereas it had no effect on the TAL. Enalapril effect on Na-K-ATPase in CD might result from reduced bradykinin metabolism, as the reduction in urinary excretion of bradykinin observed in subtotally nephrectomized rats was prevented by enalapril therapy.

Bradykinin excretion is increased in severely hyperglycemic streptozotocin-diabetic rats

The renal kallikrein-kinin system (KKS) was studied in pair-fed streptozotocin (STZ)-induced diabetic rats and compared with age-matched controls. Twelve weeks after STZ injection, rats were normotensive, showed hyperglycemia, proteinuria, polydipsia and reduced glomerular filtration rate (GFR) and body weight. The activities of urinary prekallikrein (PKLK) and kallikrein (KLK) were reduced accompanied by an up to 3-fold increase of bradykinin (BK) excretion compared to controls. The increased BK excretion suggests that the renal KKS in STZ-diabetes is activated and that the reduction in urinary PKLK and KLK activity may be due to an increased consumption of these enzymes or to a negative feedback mechanism. The stimulation of the renal KKS in STZ-diabetes could reflect an attempt of the organism to balance glomerular hypertension.

Effects of B1 and B2 kinin receptor antagonists in diabetic mice

Streptozotocin (STZ) has been extensively used to produce type I diabetes in animals. This experimental disease is characterized by a mild inflammatory reaction in the Langerhans islets. Because kinins have been proposed as prominent inflammatory mediators in the pathogenesis of several diseases, we decided to evaluate the role of kinins and their receptors in the evolution of insulitis. Male C57BL/Ks mdb mice were injected with STZ (40 mg/kg) for 5 consecutive days. The kinin B1 receptor antagonist [Leu8]des-Arg9-bradykinin or the B2 antagonist d-Arg[Hyp3,Thi5,D-Tic7, Oic8]bradykinin (HOE-140) was injected subcutaneously into STZ mice at 300 micrograms/kg body weight twice a day and 500 micrograms/kg per day, respectively. Treatment with antagonists was started 3 days after STZ and lasted for 10 days. Plasma glucose was determined by the glucose oxidase method, and urine samples collected on day 13 were assayed for proteins, nitrites, and kallikreins. Diabetic mice showed hyperglycemia and increased diuresis, marked proteinuria, and increased excretion of nitrites and kallikreins. The treatment with the B2 receptor antagonist did not show any effect on glycemia, but it significantly reduced water and protein excretion, compared with the STZ group. STZ mice treated with the B1 receptor antagonist showed normal glycemia and complete normalization of diuresis and protein, nitrite, and kallikrein excretion. The results obtained in the present investigation support the assumption that the kallikrein-kinin system intervenes in the maintenance of diabetic lesions, and they also indicate that B1 kinin receptors play a significant role in this experimental disease.

Effects of angiotensin-converting enzyme and neutral endopeptidase inhibitors: influence of bradykinin

These experiments compare the effects of a neutral endopeptidase inhibitor, retrothiorphan, 1-[(1-mercaptomethyl-2-phenyl)ethyl]amino-1-oxopropanoic acid, a converting enzyme inhibitor, enalaprilat, and the combination of the two inhibitors on changes in blood pressure and renal function induced by exogenous and endogenous bradykinin in deoxycorticosterone acetate (DOCA)-salt rats. Enalaprilat potentiated the exogenous bradykinin-induced hypotensive responses while retrothiorphan potentiated the effects on urinary cyclic-GMP (cGMP) and bradykinin. The combination potentiated the exogenous bradykinin-induced hypotensive effects and the bradykinin-induced urinary excretion of cGMP, bradykinin and prostaglandin. The bradykinin B2 receptor antagonist, Hoe 140, had no effect on the enalaprilat- and retrothiorphan-induced changes in blood pressure and renal function. In conclusion, while angiotensin-converting enzyme and neutral endopeptidase are involved in the vascular and renal catabolism of exogenous bradykinin, the effects of the peptidase inhibitors do not appear to depend on the protection of endogenous bradykinin under acute conditions in DOCA-salt rats.

Identification of rat urinary kinin as bradykinin

Bradykinin (BK)-like activity, which was detected by BK-enzyme-immunoassay, was purified from 80 ml of ureter urine of Sprague-Dawley rats by Sephadex G 25 chromatography, FPLC, and reversed phase HPLC. The purified kinin fraction showed the same retention time as authentic BK on HPLC and produced contraction of isolated rat uterus, the contraction being suppressed by a B2-antagonist Hoe140. There was no other kinin detected on the HPLC at the corresponding retention time to kallidin, arginyl-BK or T-kinin. The peptide showed an amino acid sequence identical to that of BK by amino acid sequence analysis.

Strategy of measuring bradykinin and kallidin and their concentration in plasma and urine

Bradykinin (BK) and kallidin (KAL) derivatives containing a Cys residue instead of a Ser residue at positions 6 and 7, respectively [BK(Cys6), KAL(Cys7)], were synthesized. These derivatives were linked to BSA via the Cys residue by a heterobifunctional cross-linker. The coupling product containing a kinin with both free N- and C-terminal ends was used as immunogen. We obtained highly sensitive and specific antisera, simultaneously directed against both free ends. The radioimmunoassay for BK displays a sensitivity of 0.5-60 fmol BK at a dilution of 1:80,000 with 125I-BK(Tyr8) as tracer. Des-Arg9-BK, [BK(1-8)], displayed the highest cross-reactivity in the amount of 24%. Des-Arg1-BK and smaller molecular weight fragments display a cross-reactivity of less than 0.1%. The cross-reactivity of the BK antiserum with KAL is approximately 4%. In presence of 125I-KAL(Tyr9) the radioimmunoassay for KAL displays a sensitivity of 2 to 200 fmol KAL to an antiserum dilution of 1:80,000. The cross-reactivity with BK is 0.02%. KAL(Hyp4), BK(Hyp3), and des-Arg10-KAL [KAL(1-9)] show a cross-reactivity of 6.3, 4.9, and 2.4%. All other natural kinin derivatives show a cross-reactivity of less than 1%. Both assays were used to measure BK and KAL concentrations in blood and urine in humans after extraction and HPLC separation. The BK plasma level 1.97 (SD 0.54) pg/ml. The KAL plasma level is 81.0 (SD 14.3) pg/ml, indicating that KAL instead of BK is a circulating peptide. In urine, the BK level is 16.3 pg/ml.(ABSTRACT TRUNCATED AT 250 WORDS)

Long-term infusion of kallikrein attenuates renal injury in Dahl salt-sensitive rats

We investigated whether long-term infusion of kallikrein would attenuate renal injury in salt-induced hypertension in Dahl salt-sensitive rats. A subdepressor dose of purified rat urinary kallikrein (700 ng/d IV) was infused by osmotic minipump for 4 weeks in male Dahl salt-sensitive rats fed a high salt (2% NaCl) diet. This dose did not affect the time-dependent elevation of blood pressure; however, urinary protein excretion was significantly decreased, and glomerular filtration rate was increased. These beneficial effects were reflected morphologically by an attenuation of glomerulosclerotic lesions and tubular injury seen in the hypertensive Dahl salt-sensitive rats. Kallikrein infusion increased urinary excretion of bradykinin and stimulated excretion of cyclic GMP, suggesting that the kallikrein-kinin-prostaglandin and nitric oxide axes were enhanced by rat urinary kallikrein infusion. The alterations induced by kallikrein infusion were potentiated by the concomitant administration of the angiotensin-converting enzyme inhibitor alacepril. These studies indicated that long-term replacement with rat tissue kallikrein attenuates renal injury in hypertensive Dahl salt-sensitive rats.

Demonstration of derivation of rat urinary bradykinin from plasma low-molecular-weight kininogen: a study using kininogen-deficient rats

The origin of urinary bradykinin was defined by use of plasma kininogen-deficient B/N-Katholiek rats, whose ureter urine contains very low amount of urinary kinin. The kinin level increased after the rats received an infusion of normal plasma. Furthermore, the bradykinin content in the ureter urine of these kininogen-deficient rats increased more by infusion of partially purified rat- low-molecular-weight kininogen than by that of high-molecular-weight kininogen. Urinary kallikrein activity of B/N-Katholiek rats was enzymatically identical with that of normal B/N-Kitasato rats. These results indicate that urinary bradykinin found in the ureter urine of normal rats is derived from plasma low-molecular-weight kininogen by cleavage by urinary kallikrein.

Poststatin, a novel inhibitor of bradykinin-degrading enzymes in rat urine

Incubation of bradykinin with rat urine resulted in the successive degradation of bradykinin to bradykinin-(1-8), bradykinin-(1-7) and bradykinin-(1-6). In contrast, in rat plasma, bradykinin was degraded via either bradykinin-(1-8) or bradykinin-(1-7) to bradykinin-(1-5). Phosphoramidon (1 mM) partially inhibited the degradation of bradykinin by rat urine, as well as the conversion of bradykinin-(1-7) to bradykinin-(1-6). D,L-2-Mercaptomethyl-3-guanidinoethylthiopropanoic acid (1 mM) and captopril (1 mM) did not have a significant effect on any of the degradation steps in rat urine. In contrast, all of the degradation steps in urine, namely, from bradykinin to bradykinin-(1-8), from bradykinin-(1-8) to bradykinin-(1-7) and from bradykinin-(1-7) to bradykinin-(1-6), were markedly inhibited by poststatin (1 mM), even though this compound was reported originally to be a novel inhibitor of post-proline cleaving enzyme. Poststatin (1 mM) did not inhibit the degradation of bradykinin in rat plasma. These results indicate that poststatin is an effective inhibitor of kinin-degrading enzyme in rat urine.

[Components of kallikrein-kinin system in the urine of patients with glomerulonephritis]

Activities of main components of the kallikrein-kinin system: tissue (renal) and blood plasma kallikreins, kininases I and II, bradykinin-activating activity as well as free kinins, were estimated in urine of patients with latent and nephrotic forms of glomerulonephritis as compared with those parameters in urine of healthy persons. Content of tissue kallikrein was decreased in urine of patients with nephrotic form of glomerulonephritis as distinct from the disease latent form and healthy persons. At the same time, urine of these patients with nephrotic form contained elevated amount of blood plasma kallikrein and other proteinases of blood plasma origin. Bradykinin-inactivating activity as well as activities of kininase I and II were increased in urine of patients with the disease latent form 2-, 7- and 2.5-fold, respectively, and in urine of patients with nephrotic form--40-, 45- and 40-fold, respectively as compared with normal state. Daily excretion of free kinins with urine of healthy persons constituted 6.6 +/- 0.9 micrograms-eqv of bradykinin (BK), in patients with latent and nephrotic forms of glomerulonephritis--1.7 +/- 0.3 and 2.8 +/- microgram-eqv BK, respectively. Three kinins were found in all the examined persons when urine was collected in acid medium: BK, lysyl-BK and Met-Lys-BK; content of BK was minimal in urine of healthy persons and maximal--in urine of patients with nephrotic form of the disease. Clinical importance of the patterns studied and their role in correction of treatment course of patients with nephrotic form of glomerulonephritis are discussed.

Luciferin derivatives in bioluminescence-enhanced enzyme immunoassays

Ultrasensitive bioluminescence immunoassays for the determination of peptides and proteins (illustrated with human urinary kallikrein, bradykinin and the determination of human urinary kallikrein antibody titres) have been developed. The usable ranges of the standard curves are from 5 pg to 5000 pg per litre. The relative intra-assay coefficients of variation of the tests were between 2% and 6%, and the inter-assay coefficients of variation between 4% and 12%.

Differentiation of kinin fractions in ureter urine and bladder urine of normal and kininogen-deficient rats

Like human kininogens-deficiency, the ureter urine of Brown Norway (B/N) Katholiek rat, a congenitally deficient strain in plasma high molecular weight (HMW)- and low molecular weight (LMW)-kininogen, showed no detectable kinin in the peptide fraction of gel chromatography, whereas normal ureter urine (B/N-Kitasato rat) expressed kinin in the peptide fraction, when assayed by bradykinin enzyme immunoassay (EIA). However there was immunoreactive substance in the higher molecular weight fraction in both strains of rat. The nature of this substance is not known, but it may give rise to a wrong estimate for kinin if rat urine is allowed to immunoassay directly, and peptide fraction of urine is not resolved into its components by gel chromatography. Kinin degrading activity in rat urine is so potent that kinin could be mostly degraded when stored in the bladder, since kinin was found in the peptide fraction of fresh ureter urine but not in that of bladder urine of the normal strain.

Isolation and identification of hydroxyproline analogues of bradykinin in human urine

Hydroxyproline (Hyp) analogues of bradykinin and lysyl-bradykinin, in which the third residue of bradykinin, proline, is replaced by hydroxyproline, were isolated from human urine. Their amino acid sequences were confirmed by both amino acid and sequence analyses, and also by comparison of their chromatographic behavior with that of synthetic peptides. The possibility that Lys-Ala3-bradykinin, isolated by Mindroiu et al. [(1986) J. Biol. Chem. 261, 7407-7411] from human urine, was actually Lys-Hyp3-bradykinin is discussed.

Influence of sodium balance on urinary excretion of immunoreactive kinins in rats

Antibodies against bradykinin (BK) and its metabolites, namely des-Arg9-BK and des-Phe8,Arg9-BK were raised in rabbits, and specific radioimmunoassays (RIA) for these peptides were developed. Specificity studies showed that each RIA was specific for its antigen, since the cross-reactivities of various kinin-related peptides were less than 1.5%. The lowest concentration of peptide that could be measured in these assays was approximately 60 pg/ml. The antibodies were used to measure concentrations of BK and its metabolites in urine and kidneys of rats maintained on different sodium balance for 5 wk. The results showed that normal rats excrete low quantities of BK (63.78 +/- 2.98 ng/day, 88 determinations). The urinary excretion of des-Arg9-BK averaged 77.69 +/- 5.53 ng/day, whereas the amount of des-Phe8,Arg9-BK is equal to 7.13 +/- 0.42 ng/day. Sodium loading brings about a small decrease in the concentration of BK (45.57 +/- 2.36 ng/day, 76 determinations), whereas sodium depletion significantly increased the excretion of BK (94.23 +/- 5.50, 102 determinations, P less than 0.01) accompanied by no modification of the excretion of metabolites. Regression analysis of the results showed a positive correlation between urinary volume and BK in control and sodium-loaded animals and urinary BK and sodium in the sodium-loaded group. In kidney homogenates, sodium depletion increased not only the concentration of BK (10-fold) but also that of des-Arg9-BK and des-Phe8,Arg9-BK by a factor of four and two, respectively, when compared with normal and sodium-loaded animals. These results support the hypothesis that the renal kallikrein-kinin system may be regulated by corticosteroids.

Role of renal endopeptidase 24.11 in kinin metabolism in vitro and in vivo

The relative contributions of three kininases to total urinary kininase activity were determined by measuring the hydrolysis of kinins in the presence and absence of inhibitors of kininase I (2-mercaptomethyl-3-guanidinoethylthiopropanoic acid; MGTA), kininase II (captopril) and neutral endopeptidase 24.11 (NEP or enkephalinase A; phosphoramidon). Surprisingly, NEP was responsible for 68 +/- 2% (N = 18) of the total kininase in the rat while kininase I and II contributed only 9 +/- 0.4% and 23 +/- 1%, respectively. To study the effects of NEP inhibition on renal function, phosphoramidon (110 or 330 micrograms/hr/kg; N = 6) or saline (0.1 microliter/min; N = 6) was infused into rats. Urinary kinins, kininases, renal blood flow (RBF), glomerular filtration rate (GFR), UNaV, UKV and UV were measured during control, experimental and recovery periods. Phosphoramidon at the higher dose decreased total urinary kininase activity from 284 +/- 49 to 58 +/- 5 ng/min/kg (77%, P less than 0.01), and increased kinin excretion from 74 +/- 9 to 128 +/- 21 pg/min/kg (73%, P less than 0.02), UV from 72 +/- 10 to 82 +/- 10 microliters/min/kg (15%, P less than 0.01) and UNaV from 12 +/- 2 to 17 +/- 3 microEq/min/kg (37%, P less than 0.02), while BP, RBF, GFR and UKV did not change. 125I-Tyr0-bradykinin infused into the aorta did not appear in the urine intact during simultaneous phosphoramidon and captopril administration. This is the first demonstration of NEP having a major role in the catabolism of kinins. The increase in UNaV and UV after phosphoramidon administration may be due to the inhibition of intrarenal kinin destruction.

Identification of a new kinin in human urine

The types of kinins excreted in fresh urine of dogs, rats, and humans were compared. Urinary kinins were separated by reverse-phase (C18) high performance liquid chromatography and quantitated by radioimmunoassay using an antibody directed against the COOH-terminal region of the peptide. Kinins were found in the following proportions: 53 +/- 3% bradykinin, 23 +/- 4% Lys-bradykinin, and 13 +/- 7% des-Arg1-bradykinin in dog urine; 67 +/- 6% bradykinin, 6 +/- 3% Lys-bradykinin, and 10 +/- 3% des-Arg1-bradykinin in rat urine; and 12 +/- 4% bradykinin, 30 +/- 3% Lys-bradykinin, 2 +/- 1% des-Arg1-bradykinin, and 41 +/- 3% unknown kinin in human urine. The unknown kinin was purified from a pool of human urine. Amino acid sequencing revealed a structure similar to Lys-bradykinin except that proline in position 4 was replaced by alanine ([Ala3]Lys-bradykinin). Synthetic and endogenous [Ala3]Lys-bradykinins had similar high performance liquid chromotography elution volumes and both had vasodilator activity and contracted the rat uterus. Human urinary kallikrein incubated with semipurified human low molecular weight kininogen released 76% of the total kinins as Lys-bradykinin, 7% as bradykinin, and 17% as [Ala3]Lys-bradykinin. In contrast, rat urinary kallikrein released 86% bradykinin, 18% Lys-bradykinin, and negligible amounts of [Ala3]Lys-bradykinin. The study revealed the presence of a new kinin, [Ala3]Lys-bradykinin, in human urine and it also proves that the types of kinins generated intrarenally are species-dependent.

Measurements of urinary kinins by HPLC-radioimmunoassay

In this paper we describe a method for the individual determination of urinary kinins. Extraction from the urine is performed on an Amberlite CG-50 column and kinins are eluted with formic acid. The samples are further purified and kinins are separated by reversed phase HPLC. Bradykinin and lysylbradykinin are quantified by a sensitive radioimmunoassay capable of detecting 0.1 fmol of either peptide. Procedural losses are monitored by measuring the recovery of [3H]bradykinin and [3H]lysylbradykinin. Simple methods for labeling of bradykinin and lysylbradykinin with tritium are also presented. Recoveries of [3H]bradykinin and [3H]lysylbradykinin from biological material ranged between 77 and 91%. The combination of HPLC with radioimmunoassay makes it possible to determine kinin concentrations of biological samples with a higher sensitivity and greater specificity than previous methods.

A radioimmunoassay method for measurement of urinary kinins

A sensitive and specific radioimmunoassay for measuring urinary kinins was developed. Antibodies against bradykinin were induced in rabbits by injecting bradykinin coupled to bovine albumin. One of the antisera generated was used at a final dilution of 1:18,000 to obtain a 30% total binding of bradykinin-(8-tyrosine)-[125I]-triacetate. Synthetic bradykinin (5-1,000 pg) was used as standard in the curves. The sensitivity of the assay was 5 pg. The recovery of bradykinin added to urinary samples was 86.85 +/- 6%. The intraassay and interassay coefficients of variation were 3.3% (n = 12) and 4.4% (n = 5), respectively. The antiserum showed no cross-reactivity with oxytocin or low molecular weight kininogen and cross-reacted with kallidin (lys-bradykinin), met-kallidin, and angiotensin I, but cross-reaction with angiotensin I (2.5%) was low enough to be disregarded. The mean urinary levels of total kinins in 12 normal subjects were 23.2 +/- (SEM) 2.2 micrograms/day.

Immunoreactive bradykinin and [des-Arg9]-bradykinin in low-renin essential hypertension--before and after treatment with enalapril (MK 421)

Bradykinin (BK) and [des-Arg9]-bradykinin (-9BK) concentrations in blood and urine samples from 18 normotensive subjects and 23 patients with low-renin essential hypertension were determined by radioimmunoassay. BK and -9BK levels in venous blood from normotensive subjects were 67.1 +/- 60.8 pg/ml and 204.1 +/- 44.5 (mean +/- S.D.), respectively, and levels in urine from normotensive subjects were 5.3 +/- 5.3 ng/ml and 1.6 +/- 1.2, respectively. The blood and urinary levels of BK and -9BK in low-renin essential hypertensives were not significantly different from those of normotensives and did not change when the hypertensives were treated with the new orally active angiotensin I-converting enzyme (ACE) inhibitor, enalapril (MK421). It has been proposed that BK levels do not change with ACE inhibition because under these conditions BK might be metabolized to -9BK by kininase I. Since -9BK levels did not increase with MK421 treatment, this possibility can be excluded. The absence of elevations in blood and urine BK and -9BK after administration of MK421 does not support an involvement of kinins in the mechanism of antihypertensive action of MK421 in these patients. On the basis of the data, it is not possible to exclude such an involvement, however, because local changes in kinin concentrations could occur that are not reflected by changes in circulating or urinary kinin levels.

A sensitive radioimmunoassay method for urinary kinins in man

A sensitive and specific radioimmunoassay method for urinary kinins was developed, which uses antiserum against synthetic bradykinin in combination with labeled tyr8-bradykinin. The assay detects as little as 6 pg per tube of bradykinin. The dose-response curves of bradykinin. lysyl-bradykinin (kallidin), and methionyl-lysyl-bradykinin were almost identical. This suggests that the values estimated with bradykinin as the standard exhibit the total urinary kinins which contain these three peptides. The assay was performed without extraction of urinary samples, since a chromatographic study demonstrated that no interfering substances in urine samples remain in our assay system. The urinary levels of total kinins in 10 normal male subjects, three male patients with chronic renal failure, and 12 male patients with essential hypertension was 37.9 +/- 3.9 microgram/day (mean +/- S.E.M.), 9.0 +/- 5.1 microgram/day, and 24.2 +/- 5.2 microgram/day, respectively.

Inhibition of proximal tubular hydrolysis and reabsorption of bradykinin by peptides

[3H] bradykinin ([3H] BKN) was microinfused alone or in the presence of a 390- or 780-fold excess of BKN or angiotensin I (AI) into proximal tubules in Inactin-anesthetized rats. Urinary excretion of 3H-labeled material was measured, and intact peptide and its metabolites were identified and quantified. When [3H] BKN was administered with BKN or AI, urinary recovery of 3H-labeled material was increased in a manner directly proportional to tubular length, suggesting that reabsorption of [3H] BKN is related to extent of tubular contact. BKN and AI were equally effective in inhibiting the reabosroption of [3H] BKN and its metabolites from proximal tubular fluid. In contrast, BKN but not AI effectively inhibited the enzymatic hydrolysis of [3H] BKN in the proximal tubule, The data suggest that the proximal tubular mechanism for reabsorbing BKN and its metabolites is of high capacity but not high specificity and that the mechanisms for enzymatic cleavage and reabsorption of BKN and its metabolites may had different specificites and capacities.

Micropuncture evidence of rapid hydrolysis of bradykinin by rat proximal tubule

3H-labeled bradykinin ([3H]BKN) and 14C-labeled inulin ([14C]In) were simultaneously microinfused into proximal or distal tubules in Inactin-anesthetized rats, and urinary excretion and tubular transit times were measured. In other experiments higher doses of [3H]BKN were microinfused and intact peptide and its metabolites identified and quantified by two-dimensional peptide mapping. The site of infusion was identified by neoprene injection and microdissection. Urinary recovery of 3H label was 24.1% when proximal tubules were infused and 98.0% when distal tubules were infused. For proximal tubules, 85% of 3H activity recovered from urine consisted of metabolites (81%[3H]Pro and 4% [3H]Arg1-Phe5) and 15% was intact BKN. Urinary recoveries of [3H]BKN and metabolites were unrelated to tubular length. With distal tubules all 3H activity appeared as intact BKN. Excretion curves of simultaneously infused [3H]BKN and [14C]In showed no marked differences in configuration for either proximal or distal or distal tubules. We suggested that removal of [3H]BKN by proximal tubular cells occurs by rapid enzymatic cleavage at the luminal surface with reabsorption of most of the products and excretion of the remainder.

Disappearance of bradykinin in the renal circulation of dogs. Effects of kininase inhibition

In chloralose-anesthetized dogs, we investigated the disappearance of bradykinin on passage across the renal circulation. The peptide was infused into a renal artery at various doses (5-200 ng/kg min-1); renal blood flow and the concentration of kinins in renal venous blood were then determined and the percent survival of bradykinin on passage through the kidney calculated. Bradykinin caused a dose-related increase in renal blood flow, urine flow, sodium excretion, and kinin content of renal venous blood. Intravenous administration of BPP9alpha (300 mug/kg), a peptide kininase II inhibitor, potentiated the renal vasodilator, diuretic, and natriuretic actions of bradykinin and augmented the survival of the kinin on passage through the kidney from 12.72 +/- 1.64% in control dogs to 53.92 +/- 7.48% (P less than 0.001). Furthermore, the values of peptide survival were positively correlated with the increases in renal blood flow (r = 0.92, P less than 0.01), urine flow (r = 0.75, P less than 0.01), and sodium excretion (r = 0.68, P less than 0.01) produced by bradykinin. In addition, BPP9alpha by itself increased renal blood flow (16%, P less than 0.01), urine flow (115%, P less than 0.005), and sodium excretion (167%, P less than 0.02). Similarly, the concentration of kinin in renal venous blood and the excretion of urinary kinins rose from 0.11 +/- 0.03 ng/ml and 4.1 +/- 1.1 ng/min to 0.24 +/- 0.05 ng/ml (P less than 0.005) and 38.5 +/- 12.2 ng/min (P less than 0.02). These studies suggest that kinins generated intrarenally play a role in the regulation of renal blood flow and salt-water excretion and that variations in the capacity of the kidney to inactivate kinins may be a determinant of the intrarenal activity of the kallikrein-kinin system.