Shinjiro Muneta

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

An orally active renin inhibitor, ES 6864 (JV-(2R)-3-morpholinocarbonyl-2-(l-naphthylmethyl) propionyl]-(4-thiazoIyl)-L-alanyl-cyclostatine-(2-morpholinoethyl)amide), was synthesized. ES 6864 was found to be a highly potent inhibitor of human renin with a value of 7.3 × 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.

ES-8891, an orally active inhibitor of human renin.

A newly synthesized orally active renin inhibitor, jV-morpholinoacetyl-(l-naphthyl)-L-alanyl-(4-thiazolyl)-L-alanyl (3S,4S)-4-amino-3-hydroxy-5-cyclohexylpentanoyl-/i-hexylamide (ES-8891), was found to be a highly potent competitive inhibitor of human renin with an inhibition constant of 1.1 nM. This inhibitor was also active against monkey renin, although there was less inhibition of renin in pig, rabbit, and rat ES-8891 did not inhibit cathepsin D, pepsin, trypsin, chymotrypsin, angiotensin converting enzyme, and urinary kallikrein at a concentration of 10−5 M. A single oral administration of ES-8891 (10 or 30 mg/kg) to conscious, sodium-depleted marmosets caused a dose-related decrease in plasma renin activity and blood pressure. ES-8891 (30 mg/kg) produced an 80% inhibition of plasma renin activity, which lasted for more than 6 hours. Kidney renin messenger RNA was not significantly changed 6 hours after oral administration of ES-8891 (30 mg/kg). A single oral administration of 240 mg ES-8891 to healthy human volunteers (n=6) produced a significant inhibition of plasma renin activity (75% inhibition at 0.5 and 1 hour, 50% inhibition at 2 hours) with a good correlation of plasma levels of ES-8891. There were no significant changes in blood pressure or heart rate, and no adverse effects were observed. These results suggest that ES-8891 is an orally active human renin inhibitor that may be clinically useful.

THE EFFECT OF THE RENIN INHIBITOR ES-1005 ON THE EXPRESSION OF THE KIDNEY RENIN GENE IN SODIUM-DEPLETED MARMOSETS

The effect of the renin inhibitor ES-1005 or captopril on the expression of the kidney renin gene was investigated in sodium-depleted marmosets. We measured the level of kidney renin messenger RNA (mRNA) after continuous administration of ES-1005 (48 mg/kg per day) or captopril (2 mg/kg per day) intraperitoneally, via an osmotic mini-pump, for one week. The level of kidney renin mRNA was measured by densitometric Northern blot analysis using an alpha-32P-labelled human renin cDNA fragment as the hybridization probe. Captopril treatment markedly increased plasma renin activity and the level of kidney renin mRNA by 4.7-fold and 6.3-fold, respectively. ES-1005 treatment completely inhibited plasma renin activity and significantly decreased the level of kidney renin mRNA (46% of the normal control P less than 0.01). However, plasma immunoreactive renin concentration was significantly increased by the treatment with ES-1005 (P less than 0.05). These results suggest that the treatment with the renin inhibitor ES-1005 for one week has a paradoxical effect on kidney renin gene expression and renin release from the kidney in sodium-depleted marmosets.

Both a Calcium Antagonist and ACE Inhibitor Reverse Hypertrophy in Hypertension But a Calcium Antagonist also Depresses Contractility

The aim of this study was to compare the effects of a calcium antagonist, nicardipine SR, with an angiotensin-converting enzyme (ACE) inhibitor, alacepril, on the regression of left ventricular hypertrophy (LVH) and function. Twenty patients with LVH, aged 42–73 years, were treated with nicardipine SR or alacepril. Ten patients were treated with nicardipine SR (40–80 mg) for 21 months, and the other 10 patients were treated with alacepril (25–100 mg) for 18 months. All patients underwent echocardiography to assess left ventricular structure and function before and after the treatment. After nicardipine SR or alacepril treatment, blood pressure was decreased significantly from 176.0 ± 13.9/97.0 ± 5.3 mmHg to 140.0 ± 14.0/77.4 ± 7.2 mmHg and from 168.2 ± 22.3/99.0 ± 5.5 mmHg to 138.4 ± 12.5/85.2 ± 9.7 mmHg, respectively (both p < 0.01), whereas heart rate did not change (73.8 ± 14.6 beats/min vs. 69.9 ± 13.5 beats/min and 71.6 ± 9.7 vs. 65.8 ± 8.1 beats/min, respectively). The left ventricular mass index decreased significantly from 133.2 ± 11.7 g/m2 to 114.4 ± 15.7 g/m2 with nicardipine SR and from 137.1 ± 14.8 g/m2 to 99.3 ± 23.0 g/m2 with alacepril (both p < 0.01). The fractional shortening, peak shortening rate, and peak lengthening rate all improved significantly after each treatment. The end-systolic wall stress/left ventricular end-systolic volume index, as an index of left ventricular contractility, was decreased significantly after treatment with nicardipine SR but was not changed after treatment with alacepril. In conclusion, both nicardipine SR and alacepril similarly reduced LVH and improved left ventricular systolic and diastolic function. However, alacepril did not alter left ventricular contractility, whereas nicardi-pine SR decreased left ventricular contractility.

Effects of renin inhibitors on the expression of kidney renin gene and tissue renin-like activity.

The effect of renin inhibitor ES-1005 on renin gene expression was investigated in sodiumdepleted marmosets. The kidneys were removed after continuous infusion of ES-1005 (12mg/kg perh) for 2h. The relative amount of kidney renin messenger (m)RNA was measured by densitometric Northern blot analysis using an α-32P-iabelled human renin complementary (c)DNA fragment as a hybridization probe. Plasma renin activity was completely inhibited by ES-1005. The level of kidney renin mRNA decreased significantly to about onethird of the normal control value. We also investigated the inhibitory potency of the renin inhibitor ES-6864 on the renin-like activity in dog tissues (adrenal glands, aorta and brainstem). ES-6864 inhibited the tissue renin-like activity with an IC50 of 10 -7 to 10-8mol/l in vitro. Renin inhibitors not only inhibit the activity of plasma and tissue renin, but also suppress the synthesis of renin in the kidney.

Blood pressure elevation caused by inhibition of brain glutathione reductase

The effect of brain glutathione reductase activity on blood pressure regulation was investigated. The intravenous administration of the glutathione reductase inhibitor, nitrofurantoin (0.1-0.3 mg/rat), to seven normotensive Wistar rats caused dose-dependent rises in blood pressure and the heart rate (delta mean blood pressure 17 +/- 1 mmHg; delta heart rate 89 +/- 7 beats/min for 0.3 mg). Rats treated with 0.3 mg nitrofurantoin showed a 50% decrease in glutathione reductase activity with a twofold increase in the ratio of glutathione disulphide to reduced glutathione in the hypothalamus and brainstem, and a 1.5-fold increase in plasma noradrenaline and plasma renin activity compared with controls. These nitrofurantoin-induced effects were totally abolished by pretreatment with a sympathetic ganglion blocker (4 mg pentolinium tartrate, administered subcutaneously) except for the increased ratio of glutathione disulphide to reduced glutathione and the decreased glutathione reductase activity in the brain. These results suggest that the blood pressure elevation caused by inhibition of brain glutathione reductase activity occurs through activation of the sympathetic nervous system and the renin-angiotensin system.

Biochemistry of Renin

In the last decade renin research progressed rapidly. This was due to the development of protein and peptide chemistry, modern immunology and molecular biology.

Response of plasma renin-angiotensin system to a single captopril administration in patients receiving long-term treatment with captopril.

1. The responses of angiotensin II (AII), AIII, aldosterone and plasma renin activity (PRA) to a single dose of captopril were investigated in hypertensive patients receiving long‐term (more than I year) captopril therapy (CT patients) and compared with those of non‐treated hypertensive patients (NT patients).