Pharmacological properties of FPL 63547, a novel inhibitor of angiotensin-converting enzyme

Antihypertensive activity of Rosa rugosa Thunb. flowers: angiotensin I converting enzyme inhibitor

ETHNOPHARMACOLOGICAL RELEVANCE

Rosa rugosa Thunb.'s flowers have been used for medicinal and food purposes for hundreds years in China. They have been used in Traditional Chinese Medicine (TCM) to effectively help in expansion of blood vessels and improvement of microcirculation. Current high prevalence of hypertension, and the associated side effects of synthetic Angiotensin I converting enzyme inhibitors usually prescribed for this condition, led us to the investigation of possible inhibitory activity of the Rosa rugosa Thunb. flower extracts on Angiotensin I converting enzyme (ACE).

MATERIALS AND METHODS

Two different extraction preparation: (1) powdered materials were extracted with water (RW) and then with water (RWW), ethyl acetate (RWE) and 95% ethanol (RWE95); (2) powdered materials were extracted with 95% ethanol (RE95) and then with water (RE95W), ethyl acetate (RE95E) and 95% ethanol (RE95E95). The inhibition activity was determined using in vitro the inhibitory effect on Angiotensin I converting enzyme (ACE), and using the acute response and chronic response on blood pressure which measured in spontaneously hypertensive rats (SHRs).

RESULTS

Both RE95E95 and RWW had highest ACE inhibitor activities. The higher inhibitor activity of RE95E95 was also evaluated in SHRs by oral administration for antihypertensive effect. In acute experiment, the decrease in systolic blood pressure (SBP) and the increase in heart rate (HR) was observed at 2h after administration at high (40 g/kg) and low (20 g/kg) dose; such reductions in SBP were maintained for 12h. Low dose had reduced SBP significantly more than high dose. In multiple oral administration chronic experiment, a SBP reduction of 17.5 mmHg was observed after 6d administration at low dose, and such reductions were maintained for the next 8 days.

CONCLUSIONS

The experimental results demonstrated the antihypertensive effect of Rosa rugosa Thunb. flowers, which was attributed to inhibition of Angiotensin I converting enzyme.

Inhibition study of angiotensin converting enzyme by capillary electrophoresis after enzymatic reaction at capillary inlet

Capillary electrophoresis was used to study the inhibition of angiotensin-converting enzyme (ACE) by different inhibitors. Reaction occurred at the capillary inlet during a predetermined waiting period, followed by the electrophoretic separation of the reaction compounds. ACE activity was determined by the quantification of the reaction product, hippuric acid, at 230 nm. The technique was used to study the potency of five different inhibitors (captopril, lisinopril, perindoprilat, quinaprilat and benazeprilat). During a kinetic study, the Ki value of captopril was estimated to be 55.4 +/- 8.8 nM, a value consistent with previously reported values.

Peptidomimetics derived from natural products

Although much has been written in recent years about rational drug design, no drug has been designed de novo, that is, without using a natural substrate or inhibitor or screening lead as a starting point. Instead, as we have seen, medicinal chemists continue to depend upon serendipitous discovery of novel biological activities and novel chemical entities for structures on which to begin work. What rational drug design really means at present is rational drug discovery and rational optimization. These result from the application of modern structural and mechanistic biochemistry, and good synthetic chemistry, to obtain structures with the desired spectrum of biological activities. Traditionally, lead compounds were discovered in plant and animal extracts, and more recently in microorganisms and chemical libraries. These traditional approaches continue, but are augmented by advances in molecular biology, which now provide pure proteins in quantity for screening and structure determination, as well as for characterization by modern biophysical methods. Remarkably, x-ray and NMR methods can now provide the most important information needed to design new drugs, that is, the conformations of ligands bound to target proteins. Approaches to identifying possible ligands based only on the knowledge of the enzyme active site are being developed. Some of these, such as CAVEAT, have been recently reviewed. In spite of these impressive gains, de novo design of new drugs will not be achieved until we learn how to logically build specific inhibitors of a target enzyme knowing only the protein sequence of the enzyme or the amino acid sequence of the messenger substances. We have a long way to go, because by this very rigorous definition, even the successful design of a new nonpeptide drug beginning with enzyme-ligand NMR or x-ray structure constitutes rational optimization. However, as this article has illustrated, we have made great progress. Some of the current and futuristic approaches to drug design are shown in Fig. 8. Development of useful enzyme inhibitors, designed by knowing the enzyme catalytic mechanism or discovered by screening for natural inhibitors, is a very successful rational method. Discovery of receptor antagonists by screening protocols is also productive.(ABSTRACT TRUNCATED AT 400 WORDS)

Preferential biliary elimination of FPL 63547, a novel inhibitor of angiotensin-converting enzyme, in the rat

1. The route of elimination of FPL 63547, a novel inhibitor of angiotensin-converting enzyme (ACE), has been investigated in the anaesthetized rat. Comparisons have been made with other ACE inhibitors. 2. Bile and urine samples were collected over a 5 hour period following a single i.v. dose of ACE inhibitor (2 mumol kg-1). Samples were bioassayed for ACE inhibitory activity using affinity-purified rabbit lung ACE and the amounts of the active form of inhibitor present in each sample were calculated by comparison with a standard curve. 3. FPL 63547 was rapidly and extensively excreted as the diacid in the bile but appeared in the urine in negligible amounts. The bile:urine ratio was 21.4:1 indicating a marked preference for the biliary route. A similar elimination profile was observed when the compound was dosed in its active form (FPL 63547 diacid), 87.9% of which was found in the bile over the 5 h collection period, with a bile: urine ratio of 14.6:1. 4. The marked preference of FPL 63547 for biliary elimination was not shared by the other ACE inhibitors tested in this study. Lisinopril demonstrated the opposite pattern, being excreted almost exclusively by the kidney (bile:urine ratio 0.06:1). Enalapril was eliminated in approximately equal amounts in bile and urine (ratio 0.7:1) while spirapril diacid showed a slight preference for the bile (ratio 2.6:1). 5. The physical chemical properties of FPL 63547 diacid may be responsible for its unusual preference for biliary elimination. In particular, the amphipathic character and strong acid functionality of the compound are thought to favour transport into the bile. 6. Elimination by the biliary route will be preferred in patients whose renal function is impaired as a result of disease or age. In such patients the elimination of renally-excreted ACE inhibitors is known to be compromised, resulting in compound accumulation and the need for closer monitoring. Therefore, the elimination profile of FPL 63547, if confirmed in man, may prove to be clinically advantageous.