Biomedical subjects

H D Kleinert

Publications and source records attributed to H D Kleinert.

At least 37 records · Page 2Linked to original sources

PubMed1990

Clinical pharmacology of enalkiren, a novel, dipeptide renin inhibitor.

Enalkiren (A-64662), a potent, dipeptide renin inhibitor, mimics the transition state of the human renin substrate, angiotensinogen. Enalkiren has been shown to produce dose-related suppression of plasma renin activity (PRA) and angiotensin II when administered intravenously. Doses of enalkiren of less than 0.1 mg/kg induced little hemodynamic response in normotensive and hypertensive volunteers despite marked suppression of PRA. However, at doses of 0.3 and 1.2 mg/kg, enalkiren produced significant, dose-related decreases in systolic and diastolic blood pressure (BP) in hypertensive patients, and the BP response was enhanced by pretreatment with hydrochlorothiazide. The effects of enalkiren on PRA and BP are prolonged despite its relatively short elimination phase plasma half-life (1.6 h). Persistent pharmacologic activity without evidence of tachyphylaxis was demonstrated during 1 week of treatment in hypertensive patients. The observed dissociation between suppression of PRA and BP response and the recruitment of dose-related BP decrements, despite complete suppression of PRA, are unexplained phenomena. The results of clinical trials with enalkiren are encouraging, and suggest that renin inhibitors may be safe, useful therapeutic agents in the management of hypertension.

Dipeptides↗

PubMed1990

Effect of intrarenal renin inhibition on renal hemodynamics and excretory function.

This study was designed to investigate in sodium-depleted monkeys the renal hemodynamic and excretory effects resulting from blockade of the renin-angiotensin system induced by intrarenal infusion of the primate-selective renin inhibitor A-65317. Intrarenal infusion of A-65317 (n = 6) at a dose of 0.01 micrograms.kg-1.min-1 elicited an increase (P less than 0.05) in renal blood flow (RBF) from 43.5 +/- 2.7 to 49.4 +/- 4.4 ml/min and glomerular filtration rate (GFR) from 6.3 +/- 0.3 to 6.9 +/- 0.4 ml/min, with no significant changes in mean arterial pressure (MAP) or plasma renin activity (PRA). Increases (P less than 0.05) in the urine flow rate (0.18 +/- 0.04 to 0.28 +/- 0.04 ml/min) and the fractional excretion of sodium (0.18 +/- 0.06 to 0.35 +/- 0.13%) were also observed. After a recovery period, the intrarenal infusion dose of A-65317 was increased to 0.1 microgram.kg-1.min-1 and RBF increased (P less than 0.05) from 42.9 +/- 3.9 to 53.0 +/- 3.7 ml/min in conjunction with a significant 85 +/- 4% inhibition of PRA and a 14 +/- 4 mmHg reduction in MAP. GFR and electrolyte excretion remained at control levels. Intrarenal infusion of vehicle (n = 6) had no significant effect on any of the variables studied. In a separate group of monkeys, intravenous (iv) infusion of A-65317 at 0.01 microgram.kg-1.min-1 (n = 5) did not result in significant changes from control.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin II↗

PubMed1990

Prolonged duration of blood pressure response to enalkiren, the novel dipeptide renin inhibitor, in essential hypertension.

The effects of sustained renin inhibition by repeated administration of enalkiren (A-64662), the novel dipeptide renin inhibitor, were evaluated in a randomized, double-blind, placebo-controlled, parallel-group study of 32 inpatients (eight per group) with essential hypertension who were maintained on a diet containing 60 meq/day sodium. Three different dosage regimens of enalkiren were studied: 1) 1.2 mg/kg quotid., 2) 0.3 mg/kg q.i.d., and 3) 0.1 mg/kg q.i.d. Each patient received an intravenous infusion every 6 hours for 1 week. Placebo infusions were used to mimic the 4 times/day dosing schedule. Blood pressure was measured periodically via 24-hour automated monitoring equipment. Mean plasma renin activity in the patient groups ranged from 1.58 to 2.68 ng angiotensin I/ml/hr. Plasma renin activity was promptly suppressed in all groups receiving enalkiren. Prolonged duration of plasma renin activity suppression (greater than or equal to 24 hours) was demonstrated after the administration of 1.2 mg/kg enalkiren. The 0.3 mg/kg q.i.d. and 1.2 mg/kg quotid. regimens produced statistically significant reductions (p less than or equal to 0.05) in systolic and diastolic blood pressures with clear evidence of persistent antihypertensive activity for 12 hours or more when compared with the placebo group. Despite relatively large reductions in mean systolic and diastolic blood pressure, mean pulse rates were essentially unchanged. The prolonged reduction in blood pressure with enalkiren without evidence of tachyphylaxis after 1 week of treatment suggests that renin inhibitors may emerge as useful therapeutic agents for the treatment of hypertension.

Adult↗

PubMed1990

Renal hemodynamic and excretory responses to renin inhibition induced by A-64662.

Experiments were conducted in sodium-depleted anesthetized monkeys to determine the effects of the primate-selective renin inhibitor A-64662 on renal function. Five groups of monkeys were examined with each group receiving an i.v. infusion of vehicle or A-64662 at doses (bolus plus continuous infusion) of 0.1 + 0.01, 1.0 + 0.1, 10 + 1.0 or 100 micrograms/kg + 10 micrograms/kg/min (n = 6/dose). Plasma renin activity was inhibited (P less than .05) at all infusion doses ranging from 33 +/- 8% at the lowest dose to 95 +/- 3% at the highest dose. Inhibition of plasma renin activity was accompanied by renal vasodilation as renal blood flow (RBF) increased (P less than .05) in a dose-dependent manner beginning at the dose of 1.0 microgram/kg + 0.1 micrograms/kg/min. RBF increased 36 +/- 7% at the highest dose of A-64662 examined. Associated with the increments in RBF, renal vascular resistance progressively decreased (P less than .05) by 12 +/- 3, 31 +/- 3 and 40 +/- 6%, respectively, with increasing doses of A-64662. Glomerular filtration rate was unchanged at all doses of A-64662. As a result, a significant (P less than .05) fall in the filtration fraction was observed as the dose of A-64662 increased. Mean arterial pressure was unaffected by the two lowest doses of A-64662, but decreased (P less than 0.05) by 13 +/- 1 and 18 +/- 4 mm Hg, respectively, at the two highest doses of A-64662 infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Azido glycols: potent, low molecular weight renin inhibitors containing an unusual post scissile site residue.

Azidomethyl-substituted 1,2- and 1,3-diols were prepared from Boc-cyclohexylalanal and evaluated as transition state analogue renin inhibitors, leading to the development of a small (MW less than 600), nanomolar inhibitor. Remarkable aqueous solubility enhancement followed the incorporation of an N-terminal urea functionality. Evaluation of selected compounds both in vivo and in vitro demonstrated that while transport across the intestine occurred upon id administration, extensive liver extraction resulted in low systemic levels.

Animals↗

PubMed1989

Renin inhibitors: discovery and development. An overview and perspective.

Pharmacological suppression of the renin angiotensin system (RAS) by inhibiting angiotensin-converting enzyme (ACE), both as monotherapy and in conjunction with other conventional agents, has been proven to be an effective therapeutic approach to the treatment of hypertension and congestive heart failure. Renin is the enzyme that catalyzes the first and rate limiting step, preceding the involvement of ACE, in the production of the potent pressor hormone angiotensin II (Ang II). Unlike ACE, which has multiple substrates, renin is selective for a single naturally occurring substrate, angiotensinogen. Interruption of the generation of ANG II by renin inhibitors at the highly specific, initial step of the cascade may have therapeutic advantages over ACE inhibitors and other antihypertensive agents with less precise mechanisms of action, by producing fewer clinical side effects. Exciting advances in the discovery of renin inhibitors have led to the synthesis of potent, dipeptide inhibitors of renin, which have been shown in the laboratory to be efficacious hypotensive agents when administered intravenously. Although there are recently reported compounds that demonstrate some degree of oral activity, efforts to enhance bioavailability are presently underway in order to develop orally active therapeutic agents. The development of renin inhibitors will provide target-specific agents for the treatment of various cardiovascular disorders, and will serve as invaluable tools to study the role of the RAS in regulating blood pressure and fluid volume. An overview of the progress in the discovery and development of renin inhibitors is presented.

Animals↗

PubMed1989

Effects of chronic infusion of renin inhibitor A-64662 in sodium-depleted monkeys.

The potent and primate-selective renin inhibitor A-64662 (n = 8) or vehicle (n = 6) was administered intravenously for 7 days to sodium-depleted cynomolgus monkeys to investigate the chronic effects on arterial pressure, sodium excretion, and the renin-angiotensin-aldosterone system. A 0.1-mg/kg i.v. bolus followed by a continuous 0.01-mg/kg/min infusion of A-64662 lowered mean arterial pressure from 89 +/- 3 (average of 4 control days) to 75 +/- 4 mm Hg (p less than 0.05) after 1 day of administration. This decrement was associated with marked inhibition of plasma renin activity (PRA) from 57.7 +/- 11.1 to 1.3 +/- 0.6 ng angiotensin I (Ang I)/ml/hr (p less than 0.05). Similar hypotensive levels (range 73 +/- 4 to 77 +/- 4 mm Hg) were observed on days 2-7 of A-64662 infusion and PRA remained suppressed, ranging from 0.6 +/- 0.4 to 1.9 +/- 1.0 ng Ang I/ml/hr. Plasma angiotensin II (Ang II) levels were reduced (p less than 0.05) from the control value of 66.7 +/- 20.2 to 12.4 +/- 3.3 and 26.4 +/- 6.5 pg/ml on the second and seventh days, respectively, of A-64662 infusion. In contrast, infusion of vehicle alone had no discernible effect on mean arterial pressure, PRA, or plasma Ang II concentrations. Plasma aldosterone decreased (p less than 0.05) from control on the second and third days of A-64662 infusion, although differences between the treatment groups were not detected throughout the study. Urinary sodium excretion remained at control levels throughout the infusion of A-64662. Cessation of A-64662 administration resulted in a recovery of mean arterial pressure to preinfusion levels within 1 day. This study indicates that continuous infusion of A-64662 results in a sustained hypotension in sodium-depleted monkeys. This effect appears to be related, at least partially, to inhibition of PRA and lower plasma Ang II levels.

Aldosterone↗

PubMed1989

Hemodynamic and humoral effects of the new renin inhibitor enalkiren in normal humans.

The effect of the renin inhibitor enalkiren (Abbott-64662) was evaluated in eight normal volunteer subjects on a standardized sodium diet (100 mmol/day) by measurement of various components of the renin-angiotensin system and drug levels in plasma. On day 1, vehicle and doses of 0.001, 0.003, and 0.01 mg/kg i.v. were administered within 2 minutes at 90-minute intervals. On day 2, vehicle and doses of 0.01, 0.03, and 0.1 mg/kg i.v. were given. With the higher doses, blood pressure tended to decrease slightly with no change in heart rate. Plasma renin activity and plasma angiotensin-(1-8)octapeptide (angiotensin II) fell markedly in a dose-dependent manner. Inhibition of plasma renin activity was maximal 5 minutes after administration of the drug and persisted 90 minutes after the doses of 0.03 and 0.1 mg/kg. Not surprisingly, there was a close correlation between plasma renin activity and plasma angiotensin II levels (r = 0.81, n = 28, p less than 0.001). In contrast, active and total renin measured directly by monoclonal antibodies rose in dose-related fashion in response to renin inhibition. Pharmacokinetic parameters were calculated using the plasma drug concentrations obtained up to 6 hours after the 0.1 mg/kg dose. By means of a two-compartment model, plasma mean half-life of the drug was estimated at 1.60 +/- 0.43 hours.

Adult↗

PubMed1989

Renin inhibitors: specific modulators of the renin-angiotensin system.

1. Angiotensin II (AII) acts as a potent pressor agent directly, by virtue of its vasoconstrictor activity and indirectly, by the volume expansion resulting from stimulation of aldosterone release from the adrenal cortex, leading to sodium and water retention. Various approaches of interfering with the enzymatic cascade leading to the production of AII have been made in an attempt to define therapeutic agents for the control of hypertension and heart failure. 2. AII receptor antagonists, to date, lack oral activity and have a relatively short duration of action, limiting their clinical usefulness. Inhibitors of angiotensin converting enzyme block AII production, are orally active and have been used successfully in the control of hypertension and in the treatment of congestive heart failure. 3. An ideal approach to the blockade of the renin-angiotensin system (RAS) is the inhibition of renin, an enzyme with only one known substrate (angiotensinogen) which catalyzes the first and rate-limiting step in the RAS. Early attempts to discover a renin inhibitor focused on immunologic inhibitors of renin, fragments of the prorenin sequence and compounds related to pepstatin, a potent pentapeptide inhibitor of pepsin and less potent inhibitor of renin. None of these approaches proved feasible for a variety of reasons including poor absorption, short duration of action and weak activity. 4. Substrate analogs offer the greatest promise for clinically useful renin inhibitors. Most recently, synthesis of compounds mimicking the enzyme transition state, the condition of greatest binding affinity, has resulted in renin inhibitors with potencies in the nanomolar range, which have shown hypotensive activity. These compounds contain at least one peptide bond and have limited oral activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Renin inhibitors. Improvements in the stability and biological activity of small peptides containing novel Leu-Val replacements.

We have designed a novel class of potent (0.3-7 nM) renin inhibitors which contain a dihydroxyethylene replacement for what is formally the Leu10-Val11 amide bond. Good potency (0.6 nM), water solubility (greater than 10 mg/ml at 37 degrees C), stability toward degradation by chymotrypsin (t1/2 = 820 min), and in vivo activity in a primate model (15% drop in mean arterial pressure in association with complete inhibition of plasma renin activity) are properties which have been incorporated into compound 10, an interesting new agent to be used in the study of hypertension.

Animals↗

PubMed1988

Renin inhibitors. Dipeptide analogues of angiotensinogen utilizing a dihydroxyethylene transition-state mimic at the scissile bond to impart greater inhibitory potency.

The synthesis of diol-containing renin inhibitors has revealed that a simple vicinal diol functionality corresponding to the scissile Leu-Val bond in human angiotensinogen is capable of imparting inhibitory activity at a comparable or higher level than either the corresponding aldehyde or hydroxymethyl functionality (compare inhibitors 2a-c or 3a-c). This finding has led to the further optimization of a series of small transition-state analogue inhibitors by the inclusion of a second hydroxyl group in the Leu-Val surrogate to give compounds that inhibited human renin in the 200-700-pM range (e.g. 43, 45, 63, 66). The magnitude of effect of the second hydroxyl group on potency is not only dictated by the absolute stereochemistry of the diol but also by the side chain of the P1 residue. Molecular modeling of the diol-containing inhibitors suggests that one of the hydroxyl groups hydrogen bonds to Asp 32 and Asp 215, while the second hydrogen bonds to Asp 215. These diol inhibitors are extremely selective for human renin over the related enzymes cathepsin D, pepsin, and gastricsin. At high concentrations, compounds containing a leucine or phenylalanine rather than a histidine at the P2 position gave only minor amounts of inhibition of the other enzymes. Inhibitor 43 suppressed plasma renin activity completely and lowered mean blood pressure in monkeys after both intravenous and intraduodenal administration, but the blood pressure drop lasted less than 1 h. Monitoring the blood levels of 43 by enzyme inhibition assay after intraduodenal administration to monkeys or oral administration to rats revealed low absorption and rapid clearance. While intratracheal administration to dogs gave approximately 50% bioavailability, rapid clearance was still a problem. After examination of inhibitor 45 in a sensitive primate model in which monkeys were rendered both hypertensive and hyperreninemic, the effects on lowering systolic but not diastolic pressure were apparent even after 22 h postdosing. Details on the synthesis, in vitro structure-activity relationships, molecular modeling, in vivo activity, and metabolism of these inhibitors are described.

Angiotensinogen↗

PubMed1988

Renin inhibitors. Dipeptide analogues of angiotensinogen utilizing a structurally modified phenylalanine residue to impart proteolytic stability.

A series of renin inhibitors have been prepared and evaluated for their susceptibility to cleavage by the serine protease chymotrypsin. The compounds were designed by consideration of the structural requirements in the active-site region of renin and chymotrypsin. By systematic alteration of the P3 phenylalanine residue, compounds with varying degrees of renin inhibitory potency and chymotrypsin susceptibility were obtained. Selected analogues from this group were examined in vivo for both their hypotensive effects and metabolic patterns.

Angiotensinogen↗

PubMed1988

Effects of the renin inhibitor A-64662 in monkeys and rats with varying baseline plasma renin activity.

The efficacy of the potent, primate selective renin inhibitor A-64662 was studied in monkeys and rats with varying baseline plasma renin activity (PRA) to elucidate the relationship between PRA and the hypotensive response induced by this compound. The effect of a single bolus of vehicle or A-64662 at 0.001, 0.01, 0.1, 1.0, and 10.0 mg/kg i.v. was compared in 30 normal and 30 salt-depleted, anesthetized monkeys (n = 5/dose). Baseline mean arterial pressure (MAP) was similar among all groups, but baseline PRA was elevated in salt-depleted monkeys. A-64662 induced a comparable dose-related fall in MAP, affecting the magnitude and duration of action, accompanied by inhibition of PRA, the duration of which was dose-related in both the normal and salt-depleted groups. However, the minimum effective doses required to reduce MAP by approximately 10% were 0.01 mg/kg for the salt-depleted monkeys and 0.1 mg/kg for the normal monkeys. In a second study, three consecutive boluses of vehicle or A-64662 at 0.1, 1.0, and 10.0 mg/kg were administered to anephric monkeys, human renin-infused anephric monkeys, and normal monkeys (n = 4/group). A dose of 0.1 mg/kg was ineffective, but the 1.0 mg/kg dose lowered MAP by 11 +/- 3% (mean +/- SE) in the anephric monkeys. The infusion of renin into anephric monkeys restored the efficacy of A-64662 at the 0.1 and 1.0 mg/kg doses to responses comparable to those of the normal monkeys. A-64662 at 10.0 mg/kg caused a similar fall in MAP of 50 to 60% in anephric, renin-infused anephric, and normal monkeys in the absence of detectable PRA.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Cardiovascular actions of the primate-selective renin inhibitor, A-62198.

A-62198 [dimethylacetyl-Phe-His-NHCH(cyclohexylmethyl)CH-(OH)C H(OH)CH2N3] is a potent, selective inhibitor of primate renin. This compound induced a dose-dependent fall in mean arterial blood pressure (MAP) when administered as an i.v. bolus to anesthetized, salt-depleted monkeys. Both the magnitude and the duration of the hypotensive effect were dose related. Its actions were also studied during acute infusions in anesthetized anephric, normal and salt-depleted monkeys. MAP, heart rate and plasma renin activity (PRA) were determined during baseline and 30-min infusions of vehicle alone, followed by A-62198 as boluses of 0.01, 0.1 and 1.0 mg/kg, each maintained by infusing one-tenth of the bolus dose per minute. Vehicle did not alter base-line values. In the normal monkeys, A-62198 induced a dose-related fall in MAP which achieved statistical significance only at the highest dose, while maximally suppressing PRA at all doses (P less than .05, compared to vehicle). The salt-depleted monkeys responded with a dose-related fall in MAP and inhibition of PRA at all doses (P less than .05, compared to vehicle). A-62198 was relatively ineffective in the anephric monkeys which, as expected, had exceedingly low levels of PRA. Heart rate was unaltered regardless of dose or treatment group. Finally, infusion of 1.0 mg/kg bolus + 0.1 mg/kg/min of A-62198 had no effect on MAP or PRA in 2 kidney-1 clip rats, although MAP was reduced subsequent to a superimposed bolus of 0.1 mg/kg of captopril. We conclude that the renin inhibitor, A-62198, is an effective, primate selective hypotensive agent.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1987

Modified peptides which display potent and specific inhibition of human renin.

A new class of angiotensinogen analogues which contain heteroatom-methylene and retro-inverso amide bond replacements was synthesized and evaluated for renin inhibition. Selected compounds in the series were specific for renin over other aspartic proteinases, and the most potent inhibitor demonstrated hypotensive activity in a salt depleted monkey.

Angiotensins↗

PubMed1987

Renin inhibitors. Dipeptide analogues of angiotensinogen incorporating transition-state, nonpeptidic replacements at the scissile bond.

A series of dipeptide analogues of angiotensinogen have been prepared and evaluated for their ability to inhibit the aspartic proteinase renin. The compounds were derived from the renin substrate by replacing the scissile amide bond with a transition-state mimic and by incorporating bioisosteric replacements for the Val-10 amide bond. Analogue 21a exhibited an IC50 of 7.6 nM against purified human renin, showed high specificity for this enzyme, and produced a hypotensive response in anesthetized, salt-depleted cynomolgus monkeys.

Angiotensinogen↗

PubMed1987

Optimization and in vivo evaluations of a series of small, potent, and specific renin inhibitors containing a novel Leu-Val replacement.

Further structure-activity relationships (SAR) for a novel dipeptide series inhibitors are reported. These inhibitors retain the Phe8-His9 portion of angiotensinogen and employ a unique Leu10-Val11 replacement [(LVR), ref 2]. SAR at the Leu10 side chain revealed that the LVR derived from cyclohexylalanine provided a nearly 10-fold boost in potency for the final inhibitor. In addition SAR work was carried out to delineate the relationships between binding potency and (1) the size, shape, and charge of the side chain at the His9 position; (2) the size and topology of the side chain at the Phe8 site; and (3) the size of the Phe8 N-protecting group. One of the more potent inhibitors, 12, was shown to provide a substantial antihypertensive effect in a sodium depleted monkey model when administered intravenously. Metabolism work, in Sprague-Dawley rats, provided insights into the susceptibility of 12 to significant hepatic clearance and provided encouraging evidence for intestinal absorption.

Animals↗

PubMed1986

Peptide analogues of angiotensinogen. Effect of peptide chain length on renin inhibition.

Renin inhibition was evaluated for a series of peptide analogues of angiotensinogen with different chain lengths. Systematic deletion of amino acid residues from the hexapeptide BocPheHisLeuR-ValIleHisOCH3 showed that the presence of residues at the N-terminal Phe and His positions was essential for efficient enzyme-inhibitor binding whereas the C-terminal Ile and His residues were much less important. Synthesis of a tetrapeptide analogue shortened at the C-terminus and containing modified side chains produced a potent inhibitor of renin which demonstrated hypotensive activity in a salt depleted monkey.

Amino Acid Sequence↗