Human renal renin. Complete purification and characterization

Genetic variants in the renin-angiotensin-aldosterone system: Impact on cancer risk, prognosis, and therapeutic directions

Although renin-angiotensin-aldosterone system (RAAS) is known to maintain blood pressure and electrolyte balance, it has recently been linked to a number of biological processes such as angiogenesis, tumorigenesis, metastasis, and cellular proliferation, increasing the risk of cancer development and progression. Multiple genetic variants have been found to affect the genes encoding RAAS components, altering gene transcription and protein expression. This review provides an up-to-date insight into the role of RAAS in carcinogenesis, as well as the impact of RAAS genetic variants on the risk of cancer development, progression, and patient survival and outcomes, as well as response to treatment. This paves the way for the application of precision medicine in cancer risk assessment and management by implementing preventative programs in individuals at risk and guiding the therapeutic direction in cancer patients.

Hormone-Dependent Regulation of Renin and Effects on Prorenin Receptor Signaling in the Collecting Duct

The production of renin by the principal cells of the collecting duct has widened our understanding of the regulation of intrarenal angiotensin II (Ang II) generation and blood pressure. In the collecting duct, Ang II increases the synthesis and secretion of renin by mechanisms involving the activation of Ang II type 1 receptor (AT1R) via stimulation of the PKCα, Ca²⁺, and cAMP/PKA/CREB pathways. Additionally, paracrine mediators, including vasopressin (AVP), prostaglandins, bradykinin (BK), and atrial natriuretic peptide (ANP), regulate renin in principal cells. During Ang II-dependent hypertension, despite plasma renin activity suppression, renin and prorenin receptor (RPR) are upregulated in the collecting duct and promote de novo formation of intratubular Ang II. Furthermore, activation of PRR by its natural agonists, prorenin and renin, may contribute to the stimulation of profibrotic factors independent of Ang II. Thus, the interactions of RAS components with paracrine hormones within the collecting duct enable tubular compartmentalization of the RAS to orchestrate complex mechanisms that increase intrarenal Ang II, Na+ reabsorption, and blood pressure.

The Transcription Factor Sox6 Controls Renin Expression during Renal Artery Stenosis

Background

Renal artery stenosis (RAStenosis) or renal artery occlusion is an intractable problem affecting about 6% of people >65 and up to 40% of people with coronary or peripheral vascular disease in the Unites States. The renal renin-angiotensin-aldosterone system plays a key role in RAStenosis, with renin (which is mainly produced in the kidney) being recognized as the driver of the disease. In this study, we will determine a new function for the transcription factor Sox6 in the control of renal renin during RAStenosis.

Methods

We hypothesize that knocking out Sox6 in Ren1d-positive cells will protect mice against renovascular hypertension and kidney injury. To test our hypothesis, we used a new transgenic mouse model, Ren1dcre/Sox6fl/fl (Sox6 KO), in which Sox6 is knocked out in renin-expressing cells. We used a modified two-kidney, one-clip (2K1C) Goldblatt mouse model to induce RAStenosis and renovascular hypertension. BP was measured using the tail-cuff method. Renin, prorenin, Sox6, and NGAL expressions levels were measured with Western blot, in situ hybridization, and immunohistochemistry. Creatinine levels were measured using the colorimetric assay.

Results

Systolic BP was significantly lower in Sox6 KO 2 weeks after RAStenosis compared with Sox6 WT (Ren1dcre/Sox6wt/wt). Renin, prorenin, and NGAL expression levels in the stenosed kidney were lower in Sox6 KO compared with Sox6 WT mice. Furthermore, creatinine clearance was preserved in Sox6 KO compared with Sox6 WT mice.

Conclusions

Our data indicate that Sox6 controls renal renin and prorenin expression and, as such, has a function in renovascular hypertension induced by RAStenosis. These results point to a novel transcriptional regulatory network controlled by Sox6.

Protein Kinase G Is Involved in Acute but Not in Long-Term Regulation of Renin Secretion

Pharmacological inhibition of the renin–angiotensin–aldosterone system (RAAS) is, in combination with diuretics, the first-choice treatment for hypertension, although 10–20% of patients do not respond adequately. Next to the RAAS, the nitric oxide/cGMP/protein kinase G (PKG) system is the second fundamental blood pressure regulator. Whether both systems influence each other is not well-studied. It has been shown that nitric oxide (NO) supports renin recruitment via activation of soluble guanylate cyclase (sGC) and subsequent generation of cGMP. Whether this leads to an ensuing activation of PKGs in this context is not known. PKGIα, as well as PKGII, is expressed in renin-producing cells. Hence, we analyzed whether these enzymes play a role regarding renin synthesis, secretion, or recruitment. We generated renin-cell-specific PKGI-knockout mice and either stimulated or inhibited the renin system in these mice by salt diets. To exclude the possibility that one kinase isoform can compensate the lack of the other, we also studied double-knockout animals with a conditional knockout of PKGI in juxtaglomerular cells (JG cells) and a ubiquitous knockout of PKGII. We analyzed blood pressure, renin mRNA and renal renin protein content as well as plasma renin concentration. Furthermore, we stimulated the cGMP system in these mice using BAY 41-8543, an sGC stimulator, and examined renin regulation either after acute administration or after 7 days (application once daily). We did not reveal any striking differences regarding long-term renin regulation in the studied mouse models. Yet, when we studied the acute effect of BAY 41-8543 on renin secretion in isolated perfused kidneys as well as in living animals, we found that the administration of the substance led to a significant increase in plasma renin concentration in control animals. This effect was completely abolished in double-knockout animals. However, after 7 days of once daily application, we did not detect a persistent increase in renin mRNA or protein in any studied genotype. Therefore, we conclude that in mice, cGMP and PKG are involved in the acute regulation of renin release but have no influence on long-term renin adjustment.

Control of renin synthesis and secretion

The aspartyl protease renin is the rate limiting activity of the renin-angiotensin-aldosterone system (RAAS). Renin is synthesized as an enzymatically inactive proenzyme which is constitutively secreted from several tissues. Only renin-expressing cells in the kidney are capable of generating active renin from prorenin, which is stored in prominent vesicles and which is released into the circulation upon demand. The acute release of renin is controlled by cyclic adenosine monophosphate (cAMP) and by calcium signaling pathways, which in turn are activated by a number of systemic and local factors. Longer lasting challenges of renin secretion lead to changes in the number of renin-producing cells, which occur by a metaplastic transformation of renin cell precursors such as preglomerular vascular smooth muscle or extraglomerular mesangial cells. This review aims to briefly address the state of knowledge of these various aspects of renin synthesis and secretion and attempts to relate them to the in vivo situation, in particular in men.

The coexistence of Ser84 in renin and His13 in angiotensinogen brings a pH profile of two separate peaks to the reaction of human renin and sheep angiotensinogen

The pH dependence and kinetics parameters of renin-angiotensinogen reactions were determined using wild-type and S84G mutant human renins and wild-type and H13Y mutant sheep angiotensinogens. It is explained in this report that (i) renin catalyzes acidic and basic reactions of which the optimum pHs are 5.5 and 7.5-8.2 respectively, both of which produce angiotensin I; (ii) Ser84 specific to human renin accelerates the acidic reaction by 75-110% through elevation of V(max), and shifts the optimum pH of the basic reaction from 7.5 to 8.0-8.2; and (iii) His13 specific to sheep angiotensinogen accelerates the acidic and basic reactions by 25-42% through reduction of K(m). It is concluded from these results that the coexistence of Ser84 in renin and His13 in angiotensinogen brings a pH profile of two separate peaks at pHs 5.5 and 8.2 to the reaction of human renin and sheep angiotensinogen.

Renin inhibition

Modification of the renin-angiotensin-aldosterone system by renin inhibitors may be an alternative to angiotensin-converting enzyme inhibitors in the treatment of cardiovascular disease. The development of clinically useful renin inhibitors has been hampered by a variety of pharmacologic problems, most notably the poor oral bioavailability of these peptide-related compounds. Peptidomimetic renin inhibitors that have been stabilized to enzymatic degradation in conjunction with optimizing physical characteristics amenable to intestinal absorption offer the greatest promise to date. Studies in animal models demonstrate that renin inhibitors are capable of reducing both systolic and diastolic blood pressures without causing reflex tachycardia. The response appears to be sustained with chronic administration. The beneficial cardiovascular effects of these compounds have been confirmed in the few studies conducted in patients with hypertension and in those with congestive heart failure. Further development of renin inhibitors is warranted.

Enzymatic characterization of purified recombinant human renin

Renin is a highly specific aspartyl protease of the renin-angiotensin system initially synthesized as preprorenin. Recombinant human prorenin was produced in cell factories from stably transfected DAMP cells, a dog epithelial cell line. The equivalent of 10-15 mg of recombinant human renin was secreted in the supernatant from each cell factory. Following a single affinity chromatography step using a renin inhibitor as the ligand, a 181-fold purification was achieved with 81% recovery of the renin activity. This highly pure recombinant enzyme having a specific activity of 3.44 mg angiotensin I.mg protein-1.h-1 was used for kinetic analysis. The kinetic parameters were determined with the natural substrate angiotensinogen and a tetradecapeptide substrate corresponding to the amino terminus of angiotensinogen, Asp1-Asn14, at their respective optimum pH of 5.5 and 6.8. Although there was a six-fold increase in both Km and kcat values for the peptidic substrate (13.3 microM and 8.1 s-1, respectively), when compared with values for the natural substrate (2.04 microM and 1.41 s-1), the catalytic efficiency (0.69 microM-1.s-1) of the enzyme for both substrates was the same. However, the kcat/Km value with angiotensinogen at the physiological pH 7.4 was 30% lower than that observed at the optimum pH 5.5. The recombinant human renin displayed similar optimum pH and kinetic parameters with angiotensinogen and the tetradecapeptide substrate when compared with human kidney renin.

Pharmacological properties of YM-26365, a low molecular weight, orally active renin inhibitor

This report describes the pharmacological properties of a novel renin inhibitor (YM-26365: (3R)-3-[3-[(1S)-1-cyclohexylmethyl-2-hydroxy-3- [(1-methyl-5-tetrazolyl)thio]propyl]ureido]-1-methyl-5-phenyl- 2,3-dihydro-1H-1,4-benzodiazepin-2-one) with molecular weight 577 and no peptide bonds. YM-26365 inhibited human plasma renin with an IC50 value of 2.9 x 10(-6) M, but did not affect plasma renin from dogs, rabbits, and rats at 10(-4) M. YM-26365 inhibited not only human renin, but also cathepsin D with an IC50 value of 1.7 x 10(-5) M. This compound competitively inhibited the reaction between recombinant human renin and N-acetyl tetradecapeptide with a Ki value of 1.1 x 10(-6) M. In pithed spontaneously hypertensive rats, YM-26365 at 10 mg/kg i.v. significantly antagonized the pressor response to recombinant human renin, but did not affect responses to angiotensin II, angiotensin I, norepinephrine, or arginine vasopressin. Similarly, oral administration of YM-26365 (10 and 30 mg/kg) to pithed spontaneously hypertensive rats caused a shift to the right of the recombinant human renin dose-pressor response curve. Systemic bioavailability as determined on the basis of the ratio of the total area under the plasma concentration-time curve after 3 mg/kg i.v. and 30 mg/kg orally to rats was 9.6%. These results demonstrate that YM-26365 is a weak but orally absorbed, low molecular weight renin inhibitor.

KRI-1314: an orally effective inhibitor of human renin

Biochemical and pharmacological properties of KRI-1314, a newly synthesized, low molecular weight (M.W.: 690) renin inhibitor, were investigated in vitro and in vivo. The novel amino acid norstatine, which is shorter in chain length than the well-known statine, was incorporated into KRI-1314 as a tetrahedral transition-state analogue for the Leu10-Val11 scissile peptide in the renin substrate. KRI-1314 more strongly inhibited plasma renins from primates than those from dogs, rabbits, guinea pigs and rats. KRI-1314 competitively inhibited highly-purified human renin with a Ki value of 9.9 x 10(-10) M. KRI-1314 strongly inhibited the tissue renin-like activities of various organs from Japanese monkeys, with IC50 values on the order of 10(-8) M. KRI-1314 was also very stable in various tissue homogenates from Japanese monkeys. Both intravenous (from 0.25 to 3 mg/kg) and oral (10 and 30 mg/kg) administration of KRI-1314 to anesthetized and conscious sodium-depleted Japanese monkeys, respectively, significantly lowered the blood pressure and plasma renin activity without affecting the heart rate. In Japanese monkeys, KRI-1314 was continuously detected in the plasma up to at least 7 hr after oral administration of 10 and 30 mg/kg. These results demonstrate that KRI-1314 is a highly potent, primate-selective and long-lasting oral renin inhibitor with a blood pressure lowering effect.

Glycosylation of active human renin is necessary for secretion: effect of targeted modifications of Asn-5 and Asn-75

Renin is a mammalian aspartic protease that is rate-limiting in the renin-angiotensin cascade. Preprorenin is the translational product of the human renin gene and is secreted as prorenin, an inactive zymogen, primarily from the juxtaglomerular cells of the kidney. It has previously been shown that the 46-amino-acid pro domain is not necessary for the secretion of fully active or mature renin from mammalian cells. Additionally, previous reports indicated that glycosylation of Asn-5 and Asn-75, the two potential sites of N-glycosylation in renin, is not necessary for the secretion of prorenin from mammalian cells. In the present study, the role of N-glycosylation in the secretion of mature renin was examined. Asn to Ser mutations at one or both of the glycosylation sites of mature renin were made and the expression of these constructs was examined in COS, CHO, and Sf9 insect cells. In the absence of the pro sequence, N-glycoylation at Asn-75 was essential for the secretion of active renin protein from all three cell types. The mutation at Asn-75 caused a more dramatic reduction in renin secretion than the mutation at Asn-5. This is in contrast to results previously reported for prorenin.

The effect of intravenous recombinant human renin on blood pressure in pithed spontaneously hypertensive rats

The effect of highly purified recombinant human renin (rh-renin), expressed in Chinese hamster ovary cells, on mean blood pressure (MBP) was evaluated in pithed spontaneously hypertensive rats (SHR) and Wistar-Kyoto rats (WKY). Intravenous bolus injection of rh-renin produced dose-dependent increases in MBP in pithed SHR and WKY. The pressor response to rh-renin in pithed SHR was about 3 times as potent as that in pithed WKY. Intravenous infusion of rh-renin produced dose-dependent progressive increases in MBP during the first 40 min, reaching plateaus and thereafter MBP was maintained up to 120 min. This hypertensive response to rh-renin was antagonized by renin inhibitors, YM-21095 and KRI-1314, which inhibited the reaction between rh-renin and tetradecapeptide competitively, with Ki values of 5.1 x 10(-10) and 4.3 x 10(-9) M, respectively. In rh-renin-infused pithed SHR, the hypotensive effect of YM-21095 was 37 times as potent as that of KRI-1314. These results suggest that rh-renin can stimulate the rat renin-angiotensin system, thereby producing hypertension. Moreover, the rh-renin-infused rat model could be useful to evaluate the effect of renin inhibitor.

Human prorenin

Human prorenin is the enzymatically inactive biosynthetic precursor of renin. Recent interest has focused on the posttranslational sorting and processing of prorenin to renin since markedly increased levels of circulating prorenin have been associated with both physiological and pathological changes. These observations raise the question of whether prorenin processing may be a regulatory event in renin production in the kidney. In the juxtaglomerular cells of the kidney, prorenin can be sorted to either of two pathways: 1) the regulated pathway, which is mediated by secretory granules, where a thiol protease resembling cathepsin B processes prorenin to renin by cleavage of the amino terminal 43-amino acid prosegment, which allows exposure of the active site of renin, or 2) the constitutive pathway, which is not regulated and does not involve conversion of prorenin to renin. Studies in which segments of prorenin are modified by site-directed mutagenesis suggest that the prosegment and glycosylation are not required for sorting, although they may influence or participate in sorting, or both. Certain areas in the prosegment are important determinants of enzyme activity and ability to cleave the prosegment. Further structural analysis of prorenin will be useful to assess details of its sorting and processing. In addition, a number of extrarenal tissues such as uterine lining, ovarian theca, corpus luteum, pituitary, and adrenal, express the renin gene. These tissues have different capabilities to sort and process prorenin compared with kidney, and some tissues secrete only prorenin. Whether prorenin-to-renin conversion is necessary to activate these local renin-angiotensin systems is a key issue.(ABSTRACT TRUNCATED AT 250 WORDS)

The purification and characterization of recombinant human renin expressed in the human kidney cell line 293

The cDNA encoding human preprorenin has been introduced into the adenovirus-transformed human kidney cell line 293. The recombinant 293 cells expressed and secreted prorenin; trypsin was used to activate the secreted prorenin to renin in vitro. The recombinant protein was purified to homogeneity by a single affinity chromatographic step. Using synthetic tetradecapeptide, the Km was 57.1 +/- 9.3 microM and the kcat was (7.48 +/- 1.57) x 10(3)/hr. Activation with trypsin resulted in a secondary cleavage between Arg53 and Leu54 generating a two chain form held together via a disulfide between Cys51 and Cys58. This secondary cleavage did not affect enzyme activity as determined by the ability of renin to degrade a synthetic tetradecapeptide substrate. Our paper demonstrates the potential for producing large quantities of renin from human kidney cells and also suggests that the use of trypsin, which has been widely used to convert prorenin to renin in vitro, causes a secondary cleavage in the renin peptide chain.

Binding of a Bolton-Hunter substituted homostatine analog to affinity-immobilized human renin

The binding of a Bolton-Hunter reagent substituted homostatine analog, SDZ 213-776, to human renin was investigated at pH 6.5 and 7.4. At both pH values, SDZ 213-776 bound to human renin in a reversible and saturable manner. The binding characteristics conformed to a one-site binding model. The dissociation constant Kd, obtained at equilibrium, was four-fold lower at pH 6.5 that at pH 7.4 (0.94 nM vs 3.7 nM). Under non-equilibrium conditions, only the association kinetic constant k+1 was affected by pH. The results of the binding assay at pH 6.5 correlated well with those obtained in enzymatic assay at the same pH.

Renin inhibitors

Since the early 1980s, an intensive effort has been focused on the development of orally effective and long-acting inhibitors of renin. During this time, in vitro potency has increased greatly, with several transition-state inhibitor designs yielding inhibitors with subnanomolar IC50 values. In the meantime, both the molecular weight and peptide character of the inhibitors has decreased as important binding elements have been focused into smaller and more stable structures. The resulting inhibitors have shown promising activities in several in vivo models and (in two cases) in man. Nevertheless, renin inhibitors reported to date have limited oral bioavailability and short duration of action, and improvements in both will be necessary for them to compete effectively with ACE inhibitors. Renin inhibitors which have entered clinical studies have at least one naturally occurring amino acid and three or more amide bonds. It is reasonable to expect that continued development will produce wholly nonpeptide inhibitors with still lower MW, and it may be these "second-generation" inhibitors which will succeed as therapeutic agents. Development of orally effective and long-acting inhibitors of renin will enable their long-term antihypertensive efficacy and possible advantages over ACE inhibitor to be investigated.

Substrate specificity of recombinant human renal renin: effect of histidine in the P2 subsite on pH dependence

Steady-state kinetic analysis of human renin demonstrates the histidine proximal to the substrate scissile peptide bond contributes to the unique specificity and pH dependence of this aspartyl protease. Recombinant human renal renin purified from mammalian cell culture appears to be indistinguishable from renin isolated from human kidney with respect to specific activity (1000 Goldblatt units/mg). Recombinant renin contains carbohydrate covalently attached to asparagines at positions 5 and 75 (renin numbering) and disulfide linkages at Cys-51/Cys-58, Cys-217/Cys-221, and Cys-259/Cys-296. Renin pH dependence was evaluated between pH 4.0 and 8.0 by using a synthetic substrate identical with the amino terminus of porcine angiotensinogen (Asp-Arg-Val-Tyr-Ile-His-Pro-Phe-His-Leu*Leu-Val-Tyr-Ser, where the asterisk indicates the scissile peptide bond and the proximal histidine is in italics) and an analogous tetradecapeptide where the proximal histidine was substituted with glutamine. Comparison of the pH profiles shows the catalytic efficiency (V/Km) and maximal velocity (V) of renin are greater above pH 6.5 with the substrate containing histidine proximal to the scissile peptide bond, but below pH 5.0 these parameters are greater with the glutamine substrate analogue. Solvent isotope effects show that proton transfer contributes to the rate-limiting step in catalysis with both substrates and that the proximal histidine does not serve as a base in the catalytic mechanism. Molecular modeling indicates the substrate histidine could hydrogen bond to Asp-226 of the enzyme (renin numbering), thus perturbing the ionization of the catalytic aspartyl groups (Asp-38 and Asp-226).(ABSTRACT TRUNCATED AT 250 WORDS)

Fate of recombinant human renin administered exogenously to anesthetized monkeys

Highly purified recombinant human renin (rh-renin), synthesized by Chinese hamster ovary cells, was labeled with iodine-125 and was given intravenously to pentobarbital-anesthetized common marmosets (Callithrix jacchus) to study the fate of the circulating renin. Specific anti-rh-renin antiserum was used to identify the 125I-rh-renin. Plasma disappearance of the exogenously administered 125I-rh-renin in marmosets (n = 6) showed two exponential components, with a half-life of 12.1 +/- 1.9 minutes for the rapid component and 120.3 +/- 16.4 minutes for the slow component. The metabolic clearance rate was 1.17 +/- 0.26 ml/min/kg. Thirty minutes after the injection of 125I-rh-renin, 43.1 +/- 0.9 and 3.5 +/- 0.5% of the injected dose had distributed to the liver and the kidneys, respectively. With time, the accumulated 125I-rh-renin in the liver and kidneys decreased. The accumulation of 125I-rh-renin was less than 1% of the dose injected in other organs such as lungs, heart, spleen, adrenal glands, testes, and ovaries. Analysis of liver and kidney extracts by high performance liquid chromatography at 30 and 120 minutes indicated that immunoreactive 125I-rh-renin decreased with time and was accompanied by an increase in nonimmunoreactive degradation products of a low molecular weight. The incubation of 125I-rh-renin with monkey or human plasma at 37 degrees C did not degrade the labeled renin. Therefore, rh-renin was rapidly cleared from the circulation by the liver and the kidney.

Role of N-linked oligosaccharides attached to human renin expressed in COS cells

One or both of two putative N-glycosylation sites (at asparagine-5 and -75) of human renin was eliminated by amino acid replacement of the asparagine residue with an alanine residue using site-directed mutagenesis. The three glycosylation-deficient renins (Asn-5, Asn-75, Asn-5 and -75 mutants) were expressed in COS cells and secreted into the conditioned media. The secreted amounts of the three mutants were different from one another, although the mutant and wild-type renins had practically the same specific activity. An Asn-5 and -75 mutant which did not contain any glycosylation sites was unstable in the medium, suggesting that the N-linked oligosaccharides play an important role in stabilization of human renin.

Human placental chorionic renin: production, purification and characterization

Native human renin, produced from the culture of human chorionic trophoblasts, has been purified to homogeneity on a milligram scale using a five-step purification scheme. The chorion cells secrete 50-200 milliGoldblatt Units of trypsin-activatable prorenin per ml into the medium. The pro-enzyme is partially purified by ammonium sulfate fractionation and chromatographies on QAE-Sephadex and cibracon blue-agarose. Following conversion of prorenin to the active enzyme by porcine trypsin, the renin is purified to homogeneity by affinity chromatography and gel filtration. Chorionic prorenin has a molecular weight of 43,000; the active enzyme 40,000. Both proteins exist as a single polypeptide chain as determined by SDS-polyacrylamide gel electrophoresis under reducing conditions. The average specific activity of six different preparations was found to be 1072 Goldblatt Units/mg. The amino acid composition and N-terminal sequence of the active enzyme has been determined and is identical to the human kidney enzyme. Microheterogeneity of chorionic renin was demonstrated by isoelectrofocusing analysis. The physical characterization of chorionic renin is compared with that reported for the human kidney enzyme.

Renin-angiotensin system

Renin, a protease that cleaves the prohormone angiotensinogen thereby releasing angiotensin I, plays a major role in regulating blood pressure and electrolyte balance. Although renin is synthesized mainly in the cortical cells of the kidney, the presence of renin or reninlike activity has been recognized in various extrarenal tissues of humans and animals, including such reproductive organs as LH-containing cells of the anterior pituitary, placentral trophoblasts, and Leydig cells of the male gonad. It has also been learned that the renin in these extrarenal tissues generates angiotensins locally, which may interact with angiotensin II receptors in a paracrine or autocrine manner. However, the precise roles of the renin-angiotensin system in extrarenal tissue are not yet understood. We demonstrated the renin-angiotensin system in human testis by measuring the plasma renin activity (PRA), plasma angiotensin II (PAII), and testosterone in the internal spermatic vein (ISV) simultaneously after treatment with hCG, and elucidated the relationship between the renin-angiotensin system and sex steroids from Leydig cells of the male gonad.

Comparative enzymatic studies of human renin acting on pure natural or synthetic substrates

Some of the essential structural requirements for the enzymatic reaction of pure human renin acting on pure human and rat angiotensinogen and on their synthetic tetradecapeptide substrates were investigated. The five carboxy terminal amino acids of synthetic tetradecapeptides played a significant role in substrate recognition and/or hydrolysis by human renin. Kinetic constants Km, Kcat and kcat/Km of the various human renin assays were different according to the substrate used. The presence of either an asparagine or a threonine residue in the S'4 renin subsite did not affect significantly the kinetic constant values. A tyrosine residue, rather than a histidine residue, in the S'3 renin subsite gave the best synthetic substrate studied. When tyrosine residue was present in the S'2 renin subsite an important decrease in kcat was observed. Human angiotensinogen was hydrolysed by human renin with lower Km and kcat values than those measured with human and porcine synthetic substrates, suggesting that the 3-dimensional structure of human angiotensinogen plays a key role in the hydrolysis. This finding was supported by assays performed with rat angiotensinogen, which was cleared by human renin with the same kcat value as rat tetradecapeptide, but with a 49-fold lower Km. Between human and rat angiotensinogen a kcat/Km value of only 2-fold higher has been found in the renin assay using human substrate.

Renin activity determination using human plasma as a substrate

A method for human renin activity determination using human plasma as the substrate is described. Angiotensin I is generated by incubating renin with human plasma, which is available along with the commercial radioimmunoassay kit for angiotensin I. The method obviates the need to isolate and purify the substrate, human angiotensinogen, from human plasma. In addition, the assay is highly renin specific, sensitive, and convenient to use for the routine determination of active human renin during its isolation and purification from tissue extracts or from genetically engineered bacterial and nonbacterial expression systems.

The significance of autonomic neuropathy in the elevation of inactive renin in diabetes mellitus

Plasma renin activity (PRA) and inactive renin(IR, activated by trypsin) were measured in the plasma of 15 type II diabetics with autonomic neuropathy (group 3), 15 type II diabetics without (group 2), and 14 nondiabetic control subjects (group 1) in the recumbent position. There were no significant differences between the 3 groups with respect to age, ideal body weight, supine resting mean blood pressure, serum creatinine, daily urinary excretion of sodium, or renin substrate at the time of study. Autonomic neuropathy (AN) was assessed by measurement of the ratio of the longest to the shortest R-R interval during deep breathing (E/I-ratio) and by postural hypotension. PRA was significantly lower in group 3 than in group 1 (p less than 0.05). The IR level was significantly higher in group 3 than in groups 2 and 1 (p less than 0.005 for both comparisons). The ratio of active renin to total renin (TR) (PRA/(IR + PRA)) was significantly lower in group 3 than in groups 2 and 1 (p less than 0.001 for both comparisons). The IR level and PRA/(IR + PRA) were significantly correlated with E/I-ratio (r = -0.498, p less than 0.01 and r = 0.588, p less than 0.001, respectively) and with the severity of postural hypotension (r = 0.383, p less than 0.05 and r = 0.401, p less than 0.05, respectively), but not with the daily urinary excretion of protein or 24 h-creatinine clearance (24 h-Ccr) in the whole diabetics. From these results, we conclude that autonomic neuropathy might be a more important factor than nephropathy in the lower PRA and higher IR level in type II diabetics with AN.

Biochemical evidence for existence of immunoreactive renin in human prolactinoma tissue

High activity of renin was demonstrated in human prolactinoma tissue. This activity was almost completely inhibited by specific antibody raised against human renal renin, indicating that it was not due to the nonspecific action of proteases. The specific activity of renin was 5.04 ng of angiotensin I generated/mg of protein per h, comparable to that of the pituitary tissue prepared from postmortem human subjects. The biochemical properties of the prolactinoma renin were generally similar to those of well-known kidney enzyme, such as molecular mass (Mr = 46,000), optimum pH (6.0), and glycoprotein nature. However, the isoelectric points (pI) of the prolactinoma renin (pI = 4.90, 5.04, 5.24 and 5.41) differed somewhat from those of plasma and kidney renins reported hitherto. These results indicate that true renin can be produced in human prolactinoma tissue.

Human renin inhibiting dipeptide

KRI-1177, a dipeptide containing nor-statine inhibited renin activity in human and Japanese monkey plasma to a markedly greater extent than that in dog, rabbit and rat plasma. The systemic blood pressure of anesthetized monkeys was lowered by intravenous injections of this compound which also reduced plasma renin activity and concentration of angiotensins. KRI-1177 appears to selectively inhibit primate renin activity, thereby producing hypotension.

A case of adrenal tumor producing renin, aldosterone, and sex steroid hormones

A 27-year-old woman with an adrenal tumor that produced renin and aldosterone, associated with hypertension and adrenogenital syndrome, is described. Severe hypertension, cardiomegaly, a low serum potassium level, clinical symptoms of adrenogenital syndrome, and a left upper abdominal tumor also were found. Endocrinological studies showed that plasma and urinary levels of sex steroid hormones such as dehydroepiandrosterone, androsterone, and testosterone were markedly increased. Plasma renin activity, plasma angiotensin II, and plasma aldosterone levels also were increased markedly, although deoxycorticosterone levels remained within the normal range. The possibility of renovascular hypertension was excluded by angiography of the renal artery and by venous sampling of plasma renin activity. Abnormal elevations in plasma aldosterone levels persisted despite normalization of plasma angiotensin II by converting enzyme inhibitor administration. It was suspected that this patient had an adrenal tumor producing renin as well as sex steroids and aldosterone. Microscopy of the resected tumor revealed that the tumor was composed mostly of cells with large nuclei and light cytoplasm. The tumor contained dehydroepiandrosterone, dehydroepiandrosterone sulfate, testosterone, aldosterone, and renin. Immunohistochemical study showed that some of the tumor cells produced renin. Biopsy of the left renal tissue showed evident atrophy of the juxtaglomerular cells and pronounced arteriosclerosis. After resection of the tumor, all blood and urinary levels of the abnormally increased hormones returned to a normal range and an apparent fall of blood pressure was noted. To our knowledge, this is the first report of a renin and aldosterone-producing adrenal tumor associated with hypertension and adrenogenital syndrome.

Isolation and characterization of native human renin derived from Chinese hamster ovary cells

Transfection of Chinese hamster ovary (CHO) cells with a plasmid containing the cDNA for human preprorenin has provided cell lines that secrete 15 mg of native prorenin per liter of culture medium. Tryptic activation of the prorenin occurs by selective cleavage of the Arg66-Leu67 bond (numbering as in preprorenin). The renin product, purified in a single step and in high yield by affinity chromatography, is fully stable for as long as 8 months when stored in solution at 4 degrees C and pH 6.5. Purity of the renin was judged to be greater than 95% by gel electrophoresis, compositional and N-terminal sequence analyses, and specific enzyme activity. An important aspect of the present work is the development of a direct assay for renin which permits accurate and reproducible evaluation of enzyme units and kinetic parameters. Application of methods described herein, combined with appropriate scale-up fermentation capabilities, provides the means for generating gram quantities of human renin and its zymogen.

Complete purification of human renal renin and sequence of the amino terminus

Renin was completely purified from human kidney cortex using a rapid 3-step procedure which included homogenization and ammonium sulfate precipitation, aminohexyl pepstatin affinity chromatography, and affinity chromatography using a synthetic octapeptide renin inhibitor (H-77) with a reduced peptide bond between Leu5 - Leu6. Three kg of cortex dissected from 10 kg of human cadaver kidney yielded 0.7 mg protein with a specific activity of 1123 GU/mg protein and an overall recovery of 52%. Both gel filtration high pressure liquid chromatography and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS PAGE) revealed a molecular weight of 44,000, although 22,000 and 18,000 molecular weight bands were also identified by SDS PAGE. Amino terminal sequencing demonstrated a leucine residue at the 1 position indicating that prorenin is converted to renin following cleavage at the carboxyl end of two dibasic residues, Lys-2-Arg-1. Sequencing of the first 19 amino acids was in agreement with the sequence deduced from human renin cDNA sequence.

Multiple forms of immunoreactive renin in human pituitary tissue

Immunoreactive renin was demonstrated in pituitary tissues of postmortem human subjects with different diseases. The specific immunoreactive renin activity comprised the majority of the tissue renin-like activity (mean, 83%), indicating the absence of nonspecific actions of proteases such as cathepsin D. We used three pituitary specimens with high levels of the specific renin activity for further biochemical characterization of the enzyme. Small differences were found in the molecular mass (45 K, 42 K and 37 K), binding to concanavalin A-Sepharose, and isoelectric points (pI) (4.72, 4.78, 4.86, 5.06, 5.28 and 5.44). These results seem to be interpreted as evidence for the presence of specific renin in the human pituitary with microheterogeneity.

Renin and angiotensin-converting enzyme in human neuroblastoma tissue

High activity of renin was demonstrated in human neuroblastoma tissue. This activity was inhibited by specific antibody raised against human renal renin, indicating that it was not due to the nonspecific action of proteases. The specific activity of renin was 122.8 ng of angiotensin I generated mg of protein-1 h-1. It shared some biochemical features with well-known kidney renin, such as molecular weight, optimum pH, the presence of trypsin-activatable inactive renin, and glycoprotein nature. Furthermore, angiotensin-converting enzyme (ACE) activity (2.64 nmol mg of protein-1 min-1) was found in the tissue. This activity was inhibited by captopril, a specific ACE inhibitor, or by omission of chloride ion. These results suggest that true renin in addition to ACE exists in human neuroblastoma tissue.

True renin in human pituitary tissue

Readily detectable levels of renin activity were demonstrated in human pituitary tissues. This activity was inhibited by specific antibody raised against human renal renin, indicating that it was not due to the nonspecific action of proteases. It shared some biochemical features with well-known kidney renin, such as molecular weight, optimum pH, and the presence of trypsin-activatable inactive renin. These results suggest that true renin exists in human pituitary tissue.