Pharmacologic data reveal the heterogeneity of angiotensin-converting enzyme according to its source (lung versus heart)

Characterization of New Milk-derived Inhibitors of Angiotensin Converting EnzymeIn VitroandIn Vivo

Inhibition of angiotensin converting enzyme (ACE) has been observed with a variety of different peptides, and peptide fragments with inhibitory capabilities have been identified within many different proteins, including milk proteins. The purpose of this study therefore was to identify new short peptides with inhibitory properties from the primary structure of milk proteins and to characterize them in vitro and in vivo, since no milk derived ACE inhibitors have previously been evaluated for their ability to inhibit ACE in vivo. In vitro, 8 of 9 dipeptides were found to be competitive inhibitors of ACE. The IC50 was significantly lower when an angiotensin I-like substrate was used, than when a bradykinin-like substrate was used. Using three different in vivo models for ACE inhibition, a very moderate effect was observed for three of the new peptides, but only for up to 6 or 12 minutes. Nothing was observed with two reference compounds that are reported to be hypotensive ACE-inhibitors derived from milk proteins. This raises the question whether the mechanism of hypotensive action is straightforward inhibition of ACE in vivo.

Delapril plus indapamide: a review of the combination in the treatment of hypertension

Although many data indicate that the management of hypertension has improved over the last two decades, there is still a large proportion of hypertensive individuals who do not receive adequate management of their blood pressure (BP). Combination therapy with two or more antihypertensive agents from different drug classes is increasingly being recognised as the most effective means of achieving target BP values by pharmacological means, particularly in the large number of patients in whom monotherapy proves to be ineffective. Use of an angiotensin-converting enzyme (ACE) inhibitor combined with a diuretic is a well established antihypertensive combination that is very effective because of the different, yet synergistic, mechanisms of actions of agents from these two drug classes. Delapril is a potent antihypertensive ACE inhibitor, and indapamide is a thiazide-like diuretic with additional antihypertensive properties. The combination of delapril and indapamide provides renoprotective effects, and indapamide is also cardioprotective. Use of these two drugs together is therefore a rational selection for combination therapy, and one that has consistently demonstrated lowering of BP to target values with a level of efficacy that is at least as good as other combinations of ACE inhibitors and diuretics. This combination has also been found to provide favourable effects on haemodynamic parameters, including left ventricular mass index and ejection fraction. Furthermore, combining an ACE inhibitor and a thiazide-type diuretic has been associated with a decreased risk of stroke and is recommended for patients with cerebrovascular disease, a setting in which the combination of delapril and indapamide has therapeutic potential. Because of the additive mechanisms of delapril and indapamide, the dose required for an effective antihypertensive effect is relatively low, and the combination is well tolerated at such doses. In particular, metabolic effects normally associated with diuretics are rare at the therapeutic dose of indapamide used in combination with delapril, making the combination suitable for patients with metabolic disorders in whom diuretic therapy would otherwise not be recommended. Delapril 30 mg and indapamide 2.5mg have been combined in a fixed combination, offering the convenience of a one-tablet-per-day antihypertensive drug regimen for most patients, which, along with good tolerability, helps to address the issue of noncompliance.

Oestrogen effects on urine concentrating response in young women

Oestrogen lowers the plasma osmotic threshold for arginine vasopressin (AVP) release but without commensurate changes in renal concentrating response, suggesting oestrogen (OE2) may lower renal sensitivity to AVP. Ten women (23 +/- 1 years) received a gonadotropin releasing hormone analogue (GnRHa), leuprolide acetate, to suppress OE2 for 35 days, and then added OE2 (two patches each delivering 0.1 mg day-1) on days 32-35. On days 28 and 35 we tested blood and renal water and sodium (Na+) regulation during stepwise 60 min AVP infusions (10, 35, 100, 150 and 200 microu (kg body weight)-1 Pitressin). Plasma OE2 concentration increased from 19 +/- 4 to 152 +/- 3 pg ml(-1) and plasma progesterone concentration was unchanged (1.0 +/- 0.4 and 0.7 +/- 0.1 ng ml(-1)) for GnRHa and OE2 administration, respectively. Standard log plots of plasma AVP concentration ([AVP]P) vs. urine osmolality (OsmU) were fitted to a sigmoidal curve, and EC50 was determined by non-linear regression curve fitting of concentration-response data. OsmU rose exponentially during AVP infusions, but hormone treatments did not affect EC50 (3.3 +/- 0.07 and 3.1 +/- 0.6 pg ml(-1), for GnRHa and OE2, respectively). However, the urine osmolality increase was greater within the physiological range (approximately 2.5-3.4 pg ml(-1) [AVP]P) during OE2 treatment. Throughout most of the AVP infusion, the rate of clearance of AVP from plasma (PCRAVP) was increased during OE2 (45.5 ml (kg body weight)(-1) min(-1)) compared to GnRHa administration (33.1 ml (kg body weight)(-1) min(-1); mean for the 100-200 microu (kg body weight)(-1) infusion rates). The rate of renal free water clearance (CH2O) was similar between hormone treatments. Sodium excretion fell during OE2 administration due to greater distal tubular sodium reabsorption. Despite more rapid PCRAVP, renal concentrating response to graded AVP infusions was unaffected by oestrogen treatment suggesting oestrogen does not affect overall renal sensitivity to AVP. However, OE2 may increase renal fluid retention within a physiological range of AVP.

Affinity of angiotensin I-converting enzyme (ACE) inhibitors for N- and C-binding sites of human ACE is different in heart, lung, arteries, and veins

Angiotensin-converting enzyme (ACE) has two enzymatically active domains: a C-domain in the carboxy terminal region and an N-domain in the amino terminal region. We based the pharmacologic characterization of these sites on the rat testis-lung model. In testis, only a truncate form of ACE is present (C-site), whereas both N- and C-sites are present in lung. In this model, captopril was shown to be N-selective and delaprilat to be C-selective. Ro 31-8472, a cilazapril derivative, and enalaprilat proved to be not site selective. We used these drugs to evaluate the affinity of C and N sites in various human tissues involved in the cardiovascular actions of ACE and used [125I]Ro31-8472 as ligand. The number and affinity of ACE binding sites were 17,680 +/- 2,345 fmol/mg protein (Kd = 0.32 +/- 0.04 nM) in lung, 560 +/- 65 (Kd = 0.36 +/- 0.05 nM) in heart, 237 +/- 51 (Kd = 0.37 +/- 0.06 nM) in coronary artery, 236 +/- 63 (Kd = 0.14 +/- 0.05 nM) in saphenous vein, and 603 +/- 121 (Kd = 0.50 +/- 0.06 nM) in mammary artery. The affinity (pKi) of captopril for the N sites ranged from 9.40 +/- 0.14 (lung) to 8.41 +/- 0.10 (coronary artery). The affinity for the C-site by delaprilat ranged from 9.97 +/- 0.15 (coronary artery) to 9.10 +/- 0.14 (mammary artery). Therefore, the affinity of C- and N-sites of ACE for ACE inhibitor (ACEI) drugs is different according to the organ involved. Because ACE is a glycosylated enzyme and glycosylation is organ dependent, we suggest that organ-specific glycosylation affects the binding characteristics of ACE inhibitors to N- or C-site of human tissular ACE.

Angiotensin-converting enzyme inhibitors in the clinical setting of chronic congestive heart failure

The addition of an angiotensin-converting enzyme (ACE) inhibitor to digitalis and diuretics in chronic congestive heart failure (CHF) prolongs survival and improves the clinical condition of patients. These actions depend on the inhibition of ACE and are, therefore, common to all ACE inhibitors. Thus, the inclusion of an ACE inhibitor in the therapeutic regimen of chronic CHF is mandatory, whenever feasible. The use of ACE inhibitors in chronic CHF should avoid symptomatic hypotension and inordinate decreases in renal function. To this end, ACE inhibitor therapy should progress by gradually increasing doses, and sodium intake and dosages of diuretics and ACE inhibitors should be adjusted in the light of changing circumstances. ACE inhibitors with short elimination half-lives should be preferred in chronic CHF, since they allow quicker dose adjustment than their longer-acting congeners, and given that compliance with once and twice daily dosing would be similar.