Lack of inhibition of human renin by human des-angiotensin I renin substrate

Effect of SQ29,852, a new angiotensin converting enzyme (ACE) inhibitor with a phosphonic acid group, on the activity of angiotensin converting enzyme from human kidney

1. An in vitro experiment was carried out to compare the inhibitory effect of SQ29,852 on human renal angiotensin converting enzyme (ACE) with those of captopril, enalapril and enalaprilat. 2. SQ29,852 strongly inhibited human renal ACE; its IC50 value was 1.5 x 10(-8) M. In terms of the IC50, SQ29,852's efficacy was about 1/10 of that of captopril and 1/28 of that of enalaprilat, but it was about 14 times more potent than enalapril. 3. SQ29,852 showed no inhibitory effects on cathepsin D, urinary kallikrein, renal renin, pepsin, trypsin and chymotrypsin. Its ACE-specificity was higher than that of captopril. 4. ACE inhibition by SQ29,852 was shown to be competitive, as revealed by Lineweaver-Burk plots. The affinity of SQ29,852 to ACE was shown to be high by a Ki value of 1.2 x 10(-8) M.

A highly potent and long-acting oral inhibitor of human renin

An orally active renin inhibitor, ES 6864 (N-[(2R)-3-morpholinocarbonyl-2-(1-naphthylmethyl)propionyl]-(4- thiazolyl)-L-alanyl-cyclostatine-(2-morpholinoethyl)amide), was synthesized. ES 6864 was found to be a highly potent inhibitor of human renin with a Ki value of 7.3 x 10(-9) M. The compound competitively inhibited human renin. The inhibitor was also potent against monkey renin but was less effective against renins from pig, goat, dog, rabbit, and rat. ES 6864 did not inhibit cathepsin D, pepsin, trypsin, chymotrypsin, angiotensin converting enzyme, and urinary kallikrein at a concentration of 10(-5) M. ES 6864 was resistant to proteolytic actions of the enzymes in rat tissue homogenates (liver, kidney, pancreas, and small intestine). Oral administration of ES 6864 at 30 mg/kg to conscious, sodium-depleted marmosets produced a significant blood pressure reduction and almost complete inhibition of plasma renin activity, which persisted for 5 hours. Oral administration of ES 6864 also produced dose-related decreases of blood pressure in hog renin-infused rats, but the duration of action was much shorter than that in conscious marmosets. The parent compound in the blood following oral administration of ES 6864 to marmosets was confirmed directly by measuring the plasma concentration of ES 6864. These results enhance the possibility of developing renin inhibitors that can be used clinically.

Comparison of angiotensinogen and tetradecapeptide as substrates for human renin. Substrate dependence of the mode of inhibition of renin by a statine-containing hexapeptide

The kinetic properties of two different substrates for human renin, a synthetic tetradecapeptide and the natural substrate human angiotensinogen, have been compared. While the Vmax was similar for the two substrates, the Km values differed by a factor of 10, i.e., 11.7 +/- 0.7 microM (tetradecapeptide) and 1.0 +/- 0.1 microM (angiotensinogen). The mode of inhibition of renin by a statine (Sta)-containing hexapeptide, BW897C, that is a close structural analog of residues 8-13 of human angiotensinogen (Phe-His-Sta-Val-Ile-His-OMe), was determined for the two substrates. Competitive inhibition was observed when tetradecapeptide was the substrate (Ki = 2.0 +/- 0.2 microM), but a more complex mixed inhibition mode (Ki = 1.7 +/- 0.1 microM, Ki' = 3.0 +/- 0.23 microM) was found with angiotensinogen as substrate. This mixed inhibition probably results from the formation of an enzyme-inhibitor-substrate or enzyme-inhibitor-product complex and reflects the more extensive interactions that the protein angiotensinogen, as opposed to the small tetradecapeptide substrate, can make with renin. We conclude that the mixed inhibition observed when angiotensinogen is used as renin substrate could be important in the clinical application of renin inhibitors because it is less readily reversed by increased concentrations of substrate than is simple competitive inhibition.

Statine-containing dipeptide and tripeptide inhibitors of human renin

Dipeptide and tripeptide derivatives containing a statine residue were synthesized as inhibitors of human renin. ES-305, bis[(1-naphthyl)methyl]acetyl(BNMA)-histidyl-statine 2(S)-methylbutylamide was found to be a highly potent inhibitor of human renin with a Ki value of 1.7 X 10(-9) M. Dipeptide derivatives with the BNMA group at the N-terminal (BNMA-Val-Sta-isoleucinol [ES-313], BNMA-Leu-Sta-isoleucinol [ES-316], and BNMA-Nle-Sta-isoleucinol [ES-317]) had potencies against human renin that were similar to the potency of ES-305. All these dipeptide derivatives competitively inhibited human renin. The inhibitors were also potent against monkey renin but were less effective against renins from pig, goat, dog, rabbit, and rat. ES-305 had little effect on cathepsin D and pepsin at the concentration of 10(-5) M. The other derivatives showed detectable inhibition of cathepsin D (IC50, 10(-6) - 10(-7) M) and pepsin (10(-5) - 10(-6) M). All the compounds had little or no effect on trypsin, chymotrypsin, angiotensin converting enzyme, and urinary kallikrein at the concentration of 10(-5) M. Our results indicate that ES-305 is a highly potent and specific inhibitor of human renin. This compound is superior to other, previously described statine-containing renin inhibitors with respect to molecular size and enzyme specificity.

Physicochemical characteristics of human high molecular weight angiotensinogen

A high molecular weight angiotensinogen (Mr. 332,000 daltons) was prepared from plasma of pregnant women by gel filtration on Sephacryl S-300. The molecular weight was reduced to 81,000 by treatment with dithiothreitol (DTT), but not by treatment with SDS. DTT-treated high molecular weight (HMW) angiotensinogen was very similar to low molecular weight (LMW) angiotensinogen with respect to molecular weight, pH profile for angiotensin formation by human kidney renin, thermostability, Km value and isoelectric point. The antibody against LMW-angiotensinogen completely cross-reacted with HMW-angiotensinogen. These results suggest that HMW-angiotensinogen is probably a complex of LMW-angiotensinogen and other protein(s) which might be bound by disulfide bond.

Highly potent and specific inhibitors of human renin

Small peptide analogues representing the C-terminal portion of angiotensin I sequence were designed as inhibitors of human renin. Among synthesized compounds, benzyloxycarbonyl (-"Z")-(1-naphthyl)Ala-His-leucinal (ES-188), Z-(1-naphthyl)Ala-His-statine ethyl ester (ES-226), and Z-(1-naphthyl)Ala-His-statine 2-methylbutylamide (ES-254) markedly inhibited human and primate renins (inhibitory concentration, 50% [IC50], near 10(-7) M). These peptide analogues inhibited rabbit renin with one or two orders of magnitude less potency. They were very weak inhibitors of renins from pig, goat, dog, and rat. ES-188 had no discernible effect on cathepsin D, pepsin, or human angiotensin-converting enzyme at the concentration of 10(-4)M. ES-226 had little effect on the three enzymes at the concentration of 10(-5)M; however, ES-254 had a considerable inhibitory effect on cathepsin D (IC50 of 1.4 X 10(-5)M), pepsin (IC50 of 4.2 X 10(-5)M), and human angiotensin-converting enzyme (IC50 of 7.1 X 10(-6)M). Our results indicate that 1-naphthylalanine-containing tripeptide analogues are highly potent human renin inhibitors.

Highly potent and specific inhibitors of human renin

We designed aldehyde derivatives of small peptides representing the C-terminal portion of angiotensin I sequence as an inhibitor of human renin. Among compounds that we synthesized, benzyloxycarbonyl (Z)-Phe-His-Leucinal (compound V), Z-Pro-Phe-His-Leucinal (Compound IV) and Z-[3-(1'-naphthyl)Ala]-His-Leucinal (compound VII) markedly inhibited human renin (IC50, 7.5 X 10(-7), 3.2 X 10(-7) and 8.0 X 10(-8) mol/l, respectively). Compound VII was shown to be noncompetitive (Ki = 2.4 X 10(-7) mol/l). It did not inhibit either cathepsin D or pepsin. Compound V had slight or no inhibitory effect at the concentration of 10(-5) mol/l on six animal renins except for monkey and rabbit renins. Results obtained show that these aldehyde compounds are highly selective and species specific inhibitors for human and monkey renins.

Biochemistry and regulation of angiotensinogen

Angiotensin II and angiotensin III, the active peptides of the renin-angiotensin system, are produced by a cascade of enzymatic reactions, whose initial step is the reaction between renin and its substrate, angiotensinogen. In plasma, the concentration of angiotensinogen is a limiting factor: the Km of the enzymatic reaction is between 1 and 2 microM depending on the species. It is therefore of interest to measure its level in plasma and tissues and to examine the main factors which may influence its synthesis and release. The complete purification of angiotensinogen has made possible the preparation of specific antibodies which cross-react with both angiotensinogen and its residue, des-angio I-angiotensinogen, and are currently used in radioimmunoassays and immunohistochemical studies. A small amount of angiotensinogen is stored in hepatic cells, where it can be detected by immunofluorescence and measured by radioimmunoassay. It is also present in proximal tubular cells of the kidney, probably reabsorbed from glomerular filtrate, but it is absent from juxtaglomerular cells. Several hormones are able to increase liver synthesis of angiotensinogen and its release. Thyroxine, angiotensin II, dexamethasone, ethinyl-estradiol and binephrectomy increase both synthesis and release. Adrenalectomy and converting-enzyme inhibition are accompanied by an increased peripheral consumption of plasma angiotensinogen, and by accumulation of des-angio I-angiotensinogen whose metabolism and role are unknown. The major role of angiotensinogen in renal hemodynamics is demonstrated by its effects on the isolated perfused kidney, an experimental observation which parallels the clinical observation of women on estroprogestative therapy, whose renal blood flow is reduced, even in the absence of a detectable increase in their blood pressure. A better knowledge of renin substrate structure in various species is a necessary requirement for the design of inhibitory analogs of angiotensinogen which will have application for the treatment of hypertension and oedema.