A cis-configured 3,5-disubstituted piperidine direct renin inhibitor, (syn,rac)-1, was discovered as a high-throughput screening hit from a target-family tailored library. Optimization of both the prime and the nonprime site residues flanking the central piperidine transition-state surrogate resulted in analogues with improved potency and pharmacokinetic (PK) properties, culminating in the identification of the 4-hydroxy-3,5-substituted piperidine 31. This compound showed high in vitro potency toward human renin with excellent off-target selectivity, 60% oral bioavailability in rat, and dose-dependent blood pressure lowering effects in the double-transgenic rat model.
Dual inhibitors of the two zinc metallopeptidases, neutral endopeptidase (NEP, EC 3.4.24.11) and angiotensin-I-converting enzyme (ACE, EC 2.4.15.1), have been the focus of much clinical interest for the treatment of hypertension and congestive heart failure. We have previously reported that compound 2 (N-[[1-[(2(S)-mercapto-3-methyl-1-oxobutyl) amino]-1-cyclopentyl]-carbonyl]-L-tyrosine) was a potent dual inhibitor in vitro (IC50 (ACE) = 7.0 nM, IC50 (NEP) = 1.5 nM) (Fink et al. J. Med. Chem. 1995, 38, 5023-5030). This compound was found to have oral activity; however, its duration of effect was short. A series of thioacetate carboxylic acid ester analogs of compound 2 was prepared. Modifications were also made to the tyrosine phenol. These compounds were evaluated for their ability to inhibit plasma ACE activity when administered orally to conscious normotensive rats. Most of the compounds prepared were found to be orally active with longer durations of effect than compound 2. Compound 38 (N-[[1-[(2(S)-(acetylthio)-3-methyl-1-oxobutyl) amino]-1-cyclopentyl]carbonyl]-O-methyl-L-tyrosine ethyl ester), administered at 11.7 mg/kg po, was found to be more efficacious than captopril at 10 mg/kg po. This compound was also found to inhibit plasma NEP activity following oral administration to conscious rats and was more efficacious than acetorphan. Compound 38 was found to lower blood pressure in the aorta-ligated rat and the spontaneously hypertensive rat when administered orally. The synthesis and biological activity of these dual inhibitors are discussed.
ABSTRACT This review deals with similarities and differences between the effects of ACE inhibitors and AT 1 ‐receptor blockers in the kidney. Specific receptor blockade has demonstrated that the beneficial effects of AT 1 blockers arise from two mechanisms: the reduction of the AT 1 receptor mediated response and the increase in plasma levels of Ang II through the AT 1 ‐receptor blockade, which leads to increased stimulation of the AT 2 receptor (the so‐called yin‐yang effect). Both ACE inhibition and AT 1 ‐receptor blockade provide significant renal protection in the majority of experimental animal models of kidney diseases. AT 1 receptor blockade may offer additional clinical benefits over ACE inhibitor treatment, particularly in the kidney, where AT 1 ‐receptor blockade does not cause the fall in glomerular filtration rate seen with ACE inhibitor treatment. A number of long‐term clinical studies currently running should show the real value of this new class of compounds in the management of hypertension and associated cardiorenal diseases.
In this report we investigate the molecular mechanisms that contribute to tissue damage following ischemia and ischemia coupled with reperfusion (ischemia/reperfusion) in the rat heart and kidney. We observe the activation of three stress-inducible mitogen-activated protein (MAP) kinases in these tissues: p38 MAP kinase and the 46- and 55-kDa isoforms of Jun N-terminal kinase (JNK46 and JNK55). The heart and kidney show distinct time courses in the activation of p38 MAP kinase during ischemia but no activation of either JNK46 or JNK55. These two tissues also respond differently to ischemia/reperfusion. In the heart we observe activation of JNK55 and p38 MAP kinase, whereas in the kidney all three kinases are active. We also examined the expression pattern of two stress-responsive genes, c-Jun and ATF3. Our results indicate that in the heart both genes are induced by ischemia and ischemia/reperfusion. However, in the kidney c-Jun and ATF3 expression is induced only by ischemia/reperfusion. To correlate these molecular events with tissue damage we examined DNA laddering, a common marker of apoptosis. A significant increase in DNA laddering was evident in both heart and kidney following ischemia/reperfusion and correlated with the pattern of kinase activation, supporting a link between stress kinase activation and apoptotic cell death in these tissues.
We tested the hypothesis that the renin inhibitor aliskiren ameliorates organ damage in rats transgenic for human renin and angiotensinogen genes (double transgenic rat [dTGR]). Six-week-old dTGR were matched by albuminuria (2 mg per day) and divided into 5 groups. Untreated dTGR were compared with aliskiren (3 and 0.3 mg/kg per day)-treated and valsartan (Val; 10 and 1 mg/kg per day)-treated rats. Treatment was from week 6 through week 9. At week 6, all groups had elevated systolic blood pressure (BP). Untreated dTGR showed increased BP (202+/-4 mm Hg), serum creatinine, and albuminuria (34+/-5.7 mg per day) at week 7. At week 9, both doses of aliskiren lowered BP (115+/-6 and 139+/-5 mm Hg) and albuminuria (0.4+/-0.1 and 1.6+/-0.6 mg per day) and normalized serum creatinine. Although high-dose Val lowered BP (148+/-4 mm Hg) and albuminuria (2.1+/-0.7 mg per day), low-dose Val reduced BP (182+/-3 mm Hg) and albuminuria (24+/-3.8 mg per day) to a lesser extent. Mortality was 100% in untreated dTGR and 26% in Val (1 mg/kg per day) treated rats, whereas in all other groups, survival was 100%. dTGR treated with low-dose Val had cardiac hypertrophy (4.4+/-0.1 mg/g), increased left ventricular (LV) wall thickness, and diastolic dysfunction. LV atrial natriuretic peptide and beta-myosin heavy chain mRNA, albuminuria, fibrosis, and cell infiltration were also increased. In contrast, both aliskiren doses and the high-dose Val lowered BP to a similar extent and more effectively than low-dose Val. We conclude that in dTGR, equieffective antihypertensive doses of Val or aliskiren attenuated end-organ damage. Thus, renin inhibition compares favorably to angiotensin receptor blockade in reversing organ damage in dTGR.
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